M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
M.I.E.T. ENGINEERING COLLEGE (Approved by AICTE and Affiliated to Anna University Chennai) TRICHY – PUDUKKOTTAI ROAD, TIRUCHIRAPPALLI – 620 007
DEPARTMENT OF MECHANICAL ENGINEERING
COURSE MATERIAL
ME6602 - AUTOMOBILE ENGINEERING
III YEAR - VI SEMESTER
M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
M.I.E.T. ENGINEERING COLLEGE (Approved by AICTE and Affiliated to Anna University Chennai) TRICHY – PUDUKKOTTAI ROAD, TIRUCHIRAPPALLI – 620 007 DEPARTMENT OF MECHANICAL ENGINEERING SYLLABUS (THEORY) Sub. Code : ME6602 Branch / Year / Sem : MECH/III/VI Sub.Name : AUTOMOBILE ENGINEERING Staff Name : M.KIRUBAKARAN
ME6602 AUTOMOBILE ENGINEERING L T P C 3 0 0 3 OBJECTIVES: To understand the construction and working principle of various parts of an automobile. To have the practice for assembling and dismantling of engine parts and transmission system
UNIT I VEHICLE STRUCTURE AND ENGINES 9 Types of automobiles, vehicle construction and different layouts, chassis, frame and body, Vehicle aerodynamics (various resistances and moments involved), IC engines –components- functions and materials, variable valve timing (VVT).
UNIT II ENGINE AUXILIARY SYSTEMS 9 Electronically controlled gasoline injection system for SI engines, Electronically controlled diesel injection system (Unit injector system, Rotary distributor type and common rail direct injection system), Electronic ignition system (Transistorized coil ignition system, capacitive discharge ignition system), Turbo chargers (WGT, VGT), Engine emission control by three way catalytic converter system, Emission norms (Euro and BS). UNIT III TRANSMISSION SYSTEMS 9 Clutch-types and construction, gear boxes- manual and automatic, gear shift mechanisms, Over drive, transfer box, fluid flywheel, torque converter, propeller shaft, slip joints, universal joints ,Differential and rear axle, Hotchkiss Drive and Torque Tube Drive.
UNIT IV STEERING, BRAKES AND SUSPENSION SYSTEMS 9 Steering geometry and types of steering gear box-Power Steering, Types of Front Axle, Types of Suspension Systems, Pneumatic and Hydraulic Braking Systems, Antilock Braking System (ABS), electronic brake force distribution (EBD) and Traction Control.
UNIT V ALTERNATIVE ENERGY SOURCES 9 Use of Natural Gas, Liquefied Petroleum Gas, Bio-diesel, Bio-ethanol, Gasohol and Hydrogen in Automobiles- Engine modifications required –Performance, Combustion and Emission Characteristics of SI and CI engines with these alternate fuels - Electric and Hybrid Vehicles, Fuel Cell Note: Practical Training in dismantling and assembling of Engine parts and Transmission Systems should be given to the students. TOTAL : 45 PERIODS
OUTCOMES: Upon completion of this course, the students will be able to identify the different components in automobile engineering. Have clear understanding on different auxiliary and transmission systems usual.
TEXT BOOKS: 1. Kirpal Singh, “Automobile Engineering”, Vol 1 & 2, Seventh Edition, Standard Publishers, New Delhi, 1997. 2. Jain K.K. and Asthana .R.B, “Automobile Engineering” Tata McGraw Hill Publishers, New Delhi, 2002.
M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
M.I.E.T. ENGINEERING COLLEGE (Approved by AICTE and Affiliated to Anna University Chennai) TRICHY – PUDUKKOTTAI ROAD, TIRUCHIRAPPALLI – 620 007 DEPARTMENT OF MECHANICAL ENGINEERING
Sub. Code : ME6602 Branch/Year/Sem : MECH/III/VI Sub Name : AUTOMOBILE ENGINEERING Staff Name : M.KIRUBAKARAN
COURSE OBJECTIVE
1. To Identify the various parts of the automobile and understand their functions and materials 2. To make familiar with the various engine auxiliary systems 3. To discriminate the functioning of different types of transmission systems 4. Elucidate the functioning of steering, Brakes and suspension systems 5. Identify possible alternate energy sources for IC engine
COURSE OUTCOMES
1. Understand the automobile components and its function 2. Understand the auxiliary systems 3. Understand the vehicle structure 4. Understand the environmental implications of automobile emissions 5. Understand the future developments in the automobile industry
6. Understand the recent trends in alternate fuels and automobile safety system
Prepared by Verified By
M.KIRUBAKARAN HOD
AP/MECH
Approved by
PRINCIPAL
M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
M.I.E.T. ENGINEERING COLLEGE (Approved by AICTE and Affiliated to Anna University Chennai)
TRICHY – PUDUKKOTTAI ROAD, TIRUCHIRAPPALLI – 620 007 DEPARTMENT OF MECHANICAL ENGINEERING
UNIT - I VEHICLE STRUCTURE AND ENGINES
Types of automobiles, vehicle construction and different layouts, chassis, frame and body, Vehicle aerodynamics (various resistances and moments involved), IC engines – components- functions and materials, variable valve timing (VVT). Automobile: Automobile means a self propelled vehicle used for transportation purposes on the ground. 1.1. Types of automobiles Automobiles are classified according to 1. Purpose 2. Capacity 3. Fuel used 4. Number of wheels 5. Drive of the vehicles 6. Body Style 7. Based on type of transmission 8. Based on the side of drive
According to the: 1.1.1. Purpose According to the purpose the vehicles are classified as passenger vehicles and goods vehicles. The vehicle which carries passengers are called as passenger vehicles and those carries materials or goods are called as goods vehicles. Some of the examples of these vehicles are given below. 1. Passenger vehicles: Car, Bus, Jeep, Auto-rickshaw. 2. Goods vehicles: Truck. 1.1.2. Capacity According to the capacity the vehicles are classified as light motor vehicles and heavy motor vehicles. The light motor vehicles can able to carry light things and are also less in size and weight. But the heavy motor vehicles can carry very heavy materials and possess large mass and are bigger in size. 1. Light motor vehicles: Motorcycle, Car, Scooter. 2. Heavy motor vehicles: Bus, Tractor, Truck. 1.1.3. Fuel used On the basis of the fuel used the vehicles can be divided into petrol vehicles, diesel vehicles, electric cab, steam carriages and gas vehicles. 1. Petrol vehicles: Car, Motorcycle, Jeep, Scooter.
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2. Diesel vehicles: Truck, Bus, Tractor, Car. 3. Electric cab: Fork lift, Battery truck. 4. Steam carriages: Steam road roller. 5. Gas vehicles: CNG vehicles. 1.1.4. Number of wheels According to the number of wheels the vehicles are classified as two, three, four, six and eight or more wheelers. 1. Two -wheeler: Motorcycles, Scooter, Moped. 2. Three -wheeler: Tempo, Road roller. 3. Four -wheeler: Car, Bus, Jeep, Tractor. 4. Six- wheeler: Truck, Bus, Gun carriage vehicle. 5. Eight- or more wheelers: Car transporting vehicle, Rocket transporter. 1.1.5. Drive of the vehicles According to the type of drive the vehicles are classified as single-wheel, two-wheel, four-wheel and six-wheel drive vehicle. 1. Single-wheel drive vehicle. 2. Two-wheel drive vehicle. 3. Four- wheel drive vehicle. 4. Six-wheel drive vehicle. 1.1.6. Body Style Body of a car decides the space available for passenger and language in the car. There are various type of body used in Indian market. And they are given below: 1. Hatchback: Hatchbacks are vehicles with a separate engine area, and passenger area (or two boxes), the luggage area is enclosed with the passenger area behind the rear seats. Example: Nano, Indica, Jazz, Punto etc. 2. Sedan/Notchback: Sedan are basically vehicles with an engine area, passenger area, and boot area (or three box), all separate. Example: Indigo Manza, Swift Dzire etc.
3. Estate/Station Wagon: Estates or Station wagons are modified saloon vehicles by combining the boot with passenger area & extending it till the roof. The boot area is significantly larger and does not have third row seating. This makes it convenient to carry big objects. Example: Indigo Marina, Octavia Combi etc. 4. Multi Purpose Vehicle (MPV) / Multi Utility Vehicle (MUV): MPV (Multi-Purpose Vehicles) or MUV (Multi Utility Vehicles) can have the engine, passenger area and boot area enclosed together or they can have the engine area separate and the passenger and boot area enclosed. MUV/MPV can also have third row of seating. These vehicles are two wheel drive. Example: Sumo Grande, Tata Tavera, Tata Innova etc.
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
5. Sport Utility Vehicle (SUV): These vehicle have large tyres, higher seating, higher ground clearance. The engine area is separate and the passenger and boot area are enclosed together. These vehicles are either equipped with 4 wheel drive or has as an option of 4 wheel drive. Example: Safari, Scorpio, Gypsy, Fortuner. 6. Pick-Up Truck: These vehicles have large tyres, higher seating capacity, and higher ground clearance. The engine area is separate and the passenger compartment available in single or double cab configurations. Also, luggage loading bay is available behind the passenger compartment. These vehicles are either equipped with 4 wheel drive or has as an option of 4 wheel drive. Example: Xenon, Scorpio Getaway etc. 7. Van: The engine is placed below the passenger area. Vans can also have Third row of seating. They are also taller and generally more spacious. Example: Winger, Ace Magic, Omni etc.
1.1.7. Based on type of transmission: 1. Automatic transmission vehicles – Automobiles that are capable of changing gear ratios automatically as they move – e.g: Automatic Transmission Cars. 2. Conventional transmission vehicles – Automotives whose gear ratios have to be changed manually 3. Semi-automatic transmission vehicles – Vehicles that facilitate manual gear changing with clutch pedal 1.1.8. Based on the side of drive: 1. Left hand drive automobile – Vehicle in which steering wheel is fitted on the left hand side – e.g: Automobiles found in USA, Russia 2. Right hand drive automobile - Vehicle in which steering wheel is fitted on the right hand side – e.g: Automobiles found in India, Australia
1.2. Vehicle construction and different layouts - Chassis, frame and body
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1.2.1. Chassis: Chassis is the base of a vehicle. Introduction of Chassis Frame: Chassis is a French term and was initially used to denote the frame parts or Basic Structure of the vehicle. It is the back bone of the vehicle. A vehicle without body is called Chassis. The components of the vehicle like Power plant, Transmission System, Axles, Wheels and Tyres, Suspension, Controlling Systems like Braking, Steering etc., and also electrical system parts are mounted on the Chassis frame. It is the main mounting for all the components including the body. So it is also called as Carrying Unit. The following main components of the Chassis are 1. Frame: it is made up of long two members called side member riveted together with the help of number of cross members. 2. Engine or Power plant: It provides the source of power 3. Clutch: It connects and disconnects the power from the engine fly Wheel to the transmission system. 4. Gear Box 5. U Joint 6. Propeller Shaft 7. Differential Functions of the chassis frame: 1. To carry load of the passengers or goods carried in the body. 2. To support the load of the body, engine, gear box etc., 3. To withstand the forces caused due to the sudden braking or acceleration 4. To withstand the stresses caused due to the bad road condition. 5. To withstand centrifugal force while cornering Types of frames 1. Conventional frame 2. Integral frame 3. Semi-integral frame 1.2.2. Conventional chassis or frame-full chassis: In this type of chassis the Body is made as a separate unit and then joined with ladder frame. It supports all the systems in a vehicle such as the Engine, Transmission system, Steering system, M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
Suspension system. It has two long side members and 5 to 6 cross members joined together with the help of rivets and bolts. The frame sections are used generally. a. Channel Section - Good resistance to bending b. Tabular Section - Good resistance to Torsion c. Box Section - Good resistance to both bending and Torsion Advantage: . Higher load capacity and strength Disadvantage: . The body tends to vibrate easily and the overall vehicle handling and refinement is lower. It is used in truck, bus and in SUV cars and bigger vehicles. 1.2.3. Non conventional or frameless chassis: In this type of chassis the ladder frame is absent and the body itself act as the frame. It supports all the systems in a vehicle such as the Engine, Transmission system, Steering system, Suspension system.
Advantage: . Less rattles and squeaks are developed. . Handling is better due to the higher body rigidity and weight. Disadvantage: . The load carrying capacity is lower. . It is not safe in accidental condition. Integral Frame: This frame is used now days in most of the cars. There is no frame and all the assembly units are attached to the body. All the functions of the frame carried out by the body itself. Due to elimination of long frame it is cheaper and due to less weight most economical also. Only disadvantage is repairing is difficult. Semi - Integral Frame: In some vehicles half frame is fixed in the front end on which engine gear box and front suspension is mounted. It has the advantage when the vehicle is met with accident the front frame can be taken easily to replace the damaged chassis frame. This type of frame is used in FIAT cars and some of the European and American cars. Various loads acting on the frame 1.Short duration Load - While crossing a broken patch. 2.Momentary duration Load - While taking a curve. 3.Impact Loads - Due to the collision of the vehicle. 4.Inertia Load - While applying brakes. 5.Static Loads - Loads due to chassis parts. 6.Over Loads - Beyond Design capacity. Automobile body The Automobile bodies are divided in two groups M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
1. Passenger Body 2. Commercial body The body of the most vehicles should fulfil the following requirements: 1. The body should be light. 2. It should have minimum number of components. 3. It should provide sufficient space for passengers and luggage. 4. It should withstand vibrations while in motion. 5. It should offer minimum resistance to air. 6. It should be cheap and easy in manufacturing. 7. It should be attractive in shape and color. 8. It should have uniformly distributed load. 9. It should have long fatigue life. 10. It should provide good vision and ventilation.
It consists of the engine, transmission system, brake system, suspension system, steering system, cooling system, wheels etc. There are two types of chassis (chassis layouts): 1.3. Vehicle layouts 1. Front Engine Rear Wheel Drive 2. Front Engine Front Wheel Drive 3. Rear Engine Rear Wheel Drive 4. All wheel Drive/4 wheel drive 1.3.1. Front Engine Rear Wheel Drive
1.3.2.Front Engine Front Wheel Drive
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
1.3.3. Rear Engine Rear Wheel Drive
1.3.4. All wheel Drive/4 wheel drive
1.4. Vehicle aerodynamics (various resistances and moments involved) Most of us don't think of air or wind as a wall. At low speeds and on days when it's not very windy outside, it's hard to notice the way air interacts with our vehicles. But at high speeds, and on exceptionally windy days, air resistance (the forces acted upon a moving object by the air -- also defined as drag) has a tremendous effect on the way a car accelerates, handles and achieves fuel mileage. Aerodynamics is the study of forces and the resulting motion of objects through the air. For several decades, cars have been designed with aerodynamics in mind, and carmakers have come up with a variety of innovations that make cutting through that "wall" of air easier and less of an impact on daily driving. Essentially, having a car designed with airflow in mind means it has less difficulty accelerating and can achieve better fuel economy numbers because the engine doesn't have to work nearly as hard to push the car through the wall of air. Engineers have developed several ways of doing this. For instance, more rounded designs and shapes on the exterior of the vehicle are crafted to channel air in a way so that it flows around the car with the least resistance possible. Some high-performance cars even have parts that move M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering air smoothly across the underside of the car. Many also include a spoiler -- also known as a rear wing -- to keep the air from lifting the car's wheels and making it unstable at high speeds. Although, as you'll read later, most of the spoilers that you see on cars are simply for decoration more than anything else. Basic idea: As an object moves through the atmosphere, it displaces the air that surrounds it. The object is also subjected to gravity and drag. Drag is generated when a solid object moves through a fluid medium such as water or air. Drag increases with velocity -- the faster the object travels, the more drag it experiences. We measure an object's motion using the factors described in Newton's laws. These include mass, velocity, weight, external force, and acceleration.
1.Lift: It is the sum of all the dynamic forces on a body normal to the direction of external flow around the body. 2 FL=(1/2)CLV A ρ 2.Drag: It is the sum of all the dynamic forces in the direction of fluid flow, so it acts opposite to the direction of object. 2 FD=(1/2)CDV A ρ Drag is generated when a solid object moves through a fluid medium such as water or air. Drag increases with velocity -- the faster the object travels, the more drag it experiences. 3.Weight: Its just the weight of the object in motion. It affects the acceleration of the object. 4.Thrust(Acceleration): Force produced in the opposite direction to drag that is higher than drag so the body can move through the fluid(air). 1.5. Engine components, functions and materials Engine is a device that produces power. It is made by various parts bolted together and they work together to achieve power by burning of fuel. These parts are given below:
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1.5.1. Cylinder Block: Cylinder block or Cylinder is main part of an engine. It is a part in which combustion of fuel takes place. All other parts like piston, connecting rod, crankshaft, water jacket etc. are bolted on it. Made of cast iron or aluminum with cast iron cylinder liners.
1.5.2. Piston: Piston is placed in the cylinder and transmits thrust to the connecting rod. It is free to move. It compresses the air fuel mixture and converts the fuel energy into mechanical energy. It transmits the power to the crankshaft. 1.5.3. Cylinder Head: Cylinder head is fitted on the top of cylinder block and the function of the cylinder head is to seal the working end of cylinder and not to permit entry and exit of gases on cover head valves of the engine. The valves, spark plug, camshaft etc are fitted on it. 1.5.4. Connecting Rod: It connect piston to the crank shaft and transmit the motion and thrust of piston to crank shaft. The lower end of connecting rod is connected to the piston and the bigger is connected to the crank shaft.
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
1.5.5. Crank Shaft: It is located in the bottom end of cylinder block. It transmits the reciprocating motion of piston into rotary motion. This rotary motion used to rotate wheels of the vehicle. 1.5.6. Camshaft: It is fitted either in the cylinder head or at the bottom of the cylinder block. It is use to open or close valves at proper timing in multi-cylinder engine. 1.5.7. Oil Sump: It is bolted at the lower end of the cylinder block. All the oil for lubricating the movable parts is placed in it. Made of steel metal, aluminum, or plastic materials.
1.5.8. Valves: It is fitted on the cylinder head. It regulates the flow of air fuel mixture inside the cylinder and exhaust gas outside the cylinder block. When both inlet and exhaust valves are closed no pressure can go inside or outside of cylinder block. 1.5.9. Spark Plug: It is used in Petrol engine (Spark Ignition Engine). It is fitted on the cylinder head. It is used to ignite the air fuel mixture inside the cylinder at the end of each compression stroke.
1.5.10. Injector: It is used in Diesel engine (Compression Ignition Engine). It is fitted on the cylinder head. It is used to inject fuel in spray form inside the cylinder at the end of compression stroke.
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1.5.11. Push Rod: It is used when the camshaft is situated in the bottom of the cylinder head. It regulates the timing of valves open and close through rocker arm and camshaft. 1.5.12. Manifold: It is bolted on the cylinder head one each for intake and exhaust. Its function is to evenly distribute air-fuel mixture for intake & collects the exhaust gases from all cylinders. 1.5.13. Piston Rings: It provides the good sealing fit and less friction resistance between piston and cylinder. It is split at one point so it can be easily installed into the grooves cut in the piston. Rings are usually made of cast iron, can be plated with chrome or molybdenum
1.5.14. Gaskets: It is used to seal the cylinder head and cylinder so no pressure is allowed to escape. It is placed between the cylinder block and cylinder head. Many types of materials: rubber, paper, aluminum, steel, cork and more. 1.5.15. Gudgeon Pin (Piston Pin): It is the parallel spindles fitted through the piston boss and connecting rod small end. It connects the piston to the connecting rod. Hollow polished steel pin. 1.5.16. Engine Bearing: Bearings are used to support the moving parts. The purpose of bearings is to reduce friction. The crankshaft is supported by bearing. In engine two types of bearing are used sliding bearing and rolling bearing. 1.6. Variable valve timing (VVT) In internal combustion engines, variable valve timing (VVT) is the process of altering the timing of a valve lift event, and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combination with variable valve lift systems. There are many ways in which this can be achieved, ranging from mechanical devices to electro- hydraulic and camless systems. Increasingly strict emissions regulations are causing many automotive manufacturers to use VVT systems. Two-stroke engines use a power valve system to get similar results to VVT. The idea is simple - alter the timing and/or size of the intake and exhaust ports at different engine RPMs to
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering ensure that the engine is as efficient as possible throughout its range of operating speeds. Some of the range of variable valve timing methodologies and their working principles are as follows: 1.6.1.Honda VTEC: VTEC (Variable Valve Timing & Lift Electronic Control "vee teck") is a system developed by Honda which was said to improve the volumetric efficiency of a four-stroke internal combustion engine, resulting in higher performance at high RPM, and lower fuel consumption at low RPM. The VTEC system uses two camshaft profiles and hydraulically selects between profiles. A short opening time for low-speed operation to give good torque and acceleration · A larger opening time for higher speeds to give more power. It is distinctly different from standard VVT (variable valve timing) which advances the valve- timing only and does not change the camshaft profile or valve lift in any way. To do this, the camshaft has two sets of cam lobes for each valve and a sliding locking pin on the cam follower that determines which lobe is operating the valve. The locking pin is moved by a hydraulic control valve based on the engine speed and power delivery requirements. The two lobe shapes are referred to as fuel economy cams and high power cams, meaning that Honda engines with this technology are really two engines in one - a performance engine and an economical engine.
Fuel economy mode Power mode 1.6. 2. Toyota VVT-i: VVT-i stands for Variable Valve Timing - Intelligent, VVT-i is the second approach to variable valve timing.The problem with Honda's idea is that you really only have two modes - economy and power. The VVT-i system goes a step further and allows a continuously variable engine operating profile, so rather than simply having economy and power modes, there's an infinite number of positions in between that can be selected on-the-fly in fractions of a second. This means that the engine can be kept in its sweet spot for a far broader range of operating conditions and demands. To do this, VVT-i doesn't have two sets of cam lobes; rather it can dynamically adjust the timing of the entire camshaft instead. This means that whilst the actual duration that the valves are open never changes, their timing in relation to all the other engine operations can be adjusted. In a simple engine, the timing belt or chain from the crankshaft loops up and around a camshaft pulley that turns the camshaft. With VVT-i, the timing belt loops around a pulley that contains hydraulic fluid or oil. The camshaft itself has vanes on the end of it that sit inside the fluid, so in this system, the camshaft is not directly linked to the timing belt pulley. By altering the oil pressure through a series of valves, the position of the camshaft vanes can be altered inside the pulley housing.
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The pulley housing is rendered in yellow - that's the pulley which is driven by the toothed timing belt looped around the outside of it. Inside you can see the red vanes of the camshaft (also in red) which are free to rotate a certain amount back and forth. When rotated all the way in one direction, the engine is in economy mode. When rotated all the way in the other direction it's in power mode.
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
UNIT - II ENGINE AUXILIARY SYSTEMS Electronically controlled gasoline injection system for SI engines, electronically controlled diesel injection system (Unit injector system, Rotary distributor type and common rail direct injection system), Electronic ignition system (Transistorized coil ignition system, capacitive discharge ignition system), Turbo chargers (WGT, VGT), Engine emission control by three way catalytic converter system, Emission norms (Euro and BS).
2.1. Electronically controlled gasoline injection system for SI engines The fuel Induction systems for SI engine are classified as: 1. Carburetors. 2. Gasoline Injection Systems. 3. Multi Point Fuel Injection Systems. Design of SI engines is characterized by homogeneous mixture and spark ignition. The homogeneous mixture is formed outside the engine cylinder and the combustion is initiated inside the cylinder at a particular time towards the end of the compression stroke. The process of mixing is done in the carburetor and is extremely important in spark ignition engines. Till today even though the carbureted fuel system is widely used in spark ignition engines, it has the following drawbacks: 1. High amount of pollutants like UBHC, CO and NOx due to improper vaporization of fuel and incomplete combustion. 2. Difficulty in accurate metering of fuel. 3. Non-uniform mixture distribution to each cylinder in multi-cylinder engines. 4. Low volumetric efficiency due to restricted fuel flow.
In order to overcome the drawbacks of the carbureted fuel system and to meet the present stringent emission standards, there is a need for an alternate gasoline fuel supply system for spark ignition engines. Some of the recent automotive engines are equipped with the gasoline injection system, instead of a carbureted system for the following reasons: 1. Improved atomization. Fuel is forced into the intake manifold under pressure that helps break fuel droplets into a fine mist. 2. Better fuel distribution. Equal flow of fuel vapors into each cylinder. 3. Smoother idle. Lean fuel mixture can be used without rough idle because of better fuel distribution and low-speed atomization. 4. Uniform distribution of fuel in multi-cylinder engine. 5. Lower emissions. Lean efficient air-fuel mixture reduces exhaust pollution. 6. Better cold weather drivability. Injection provides better control of mixture enrichment than a carburetor. 7. Increased engine power. Precise metering of fuel to each cylinder and increased air flow can result in more horsepower output. 8. Fewer parts. Simpler, late model, electronic fuel injection system has fewer parts than modern computer-controlled carburetors.
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
2.1.1. Carburetion
Spark-ignition engines normally use volatile liquid fuels. Preparation of fuel-air mixture is done outside the engine cylinder and formation of a homogeneous mixture is normally not completed in the inlet manifold. Fuel droplets, which remain in suspension, continue to evaporate and mix with air even during suction and compression processes. The process of mixture preparation is extremely important for spark-ignition engines. The purpose of carburetion is to provide a combustible mixture of fuel and air in the required quantity and quality for efficient operation of the engine under all conditions.
Definition of Carburetion The process of formation of a combustible fuel-air mixture by mixing the proper amount of fuel with air before admission to engine cylinder is called carburetion and the device which does this job is called a carburetor.
Definition of Carburetor The carburetor is a device used for atomizing and vaporizing the fuel and mixing it with the air in varying proportions to suit the changing operating conditions of vehicle engines.
Basic principles The carburetor works on Bernoulli's principle: the faster air moves, the lower its static pressure, and the higher its dynamic pressure. The throttle (accelerator) linkage does not directly control the flow of liquid fuel. Instead, it actuates carburetor mechanisms which meter the flow of air being pushed into the engine. The speed of this flow, and therefore its pressure, determines the amount of fuel drawn into the airstream.
A carburetor basically consists of an open pipe through which the air passes into the inlet manifold of the engine. The pipe is in the form of a Venturi: it narrows in section and then widens again, causing the airflow to increase in speed in the narrowest part. Below the Venturi is a butterfly valve called the throttle valve — a rotating disc that can be turned end-on to the airflow, so as to hardly restrict the flow at all, or can be rotated so that it (almost) completely blocks the flow of air. This valve controls the flow of air through the carburetor throat and thus the quantity of air/fuel mixture the system will deliver, thereby regulating engine power and M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering speed. The throttle is connected, usually through a cable or a mechanical linkage of rods and joints or rarely by pneumatic link, to the accelerator pedal on a car, a throttle level in an aircraft or the equivalent control on other vehicles or equipment. Fuel is introduced into the air stream through small holes at the narrowest part of the Venturi and at other places where pressure will be lowered when not running on full throttle. Fuel flow is adjusted by means of precisely calibrated orifices, referred to as jets, in the fuel path.
2.1.2. Gasoline injection system
A modern gasoline injection system uses pressure from an electric fuel pump to spray fuel into the engine intake manifold. Like a carburetor, it must provide the engine with the correct air-fuel mixture for specific operating conditions. Unlike a carburetor, however, PRESSURE, not engine vacuum, is used to feed fuel into the engine. This makes the gasoline injection system very efficient. A gasoline injection system has several possible advantages over a carburetor type of fuel system. Types of gasoline injection systems 1. Single- or multi-point injection 2. Indirect or direct injection Single- or multi-point injection The point or location of fuel injection is one way to classify a gasoline injection system. A single-point injection system, also call throttle body injection (TBI), has the injector nozzles in a throttle body assembly on top of the engine. Fuel is sprayed into the top center of the intake manifold.
Multi-point injection A multi-point injection system, also called port injection, has an injector in the port (air- fuel passage) going to each cylinder. Gasoline is sprayed into each intake port and toward each intake valve. Thereby, the term multipoint (more than one location) fuel injection is used.
Indirect or direct injection system An indirect injection system sprays fuel into the engine intake manifold. Most gasoline injection systems are of this type. Direct injection forces fuel into the engine combustion chambers. Diesel injection systems are direct type.
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System component • Fuel tank • Electric fuel pump • Fuel filter • Electronic control unit • Common rail and Pressure sensor • Electronic Injectors • fuel line Fuel tank: It is safe container for flammable liquids and typically part of an engine system in which the fuel is stored and propelled (fuel pump) or released (pressurized gas) into an engine. Electric fuel pump: An electric fuel pump is used on engines with fuel injection to pump fuel from the tank to the injectors. The pump must deliver the fuel under high pressure (typically 30 to 85 psi depending on the application) so the injectors can spray the fuel into the engine. Electric fuel pumps are usually mounted inside the fuel tank, some vehicles may even have two fuel pumps (a transfer pump inside the tank, and a main fuel pump outside). Fuel filter: The fuel filter is the fuel system's primary line of defense against dirt, debris and small particles of rust that flake off the inside of the fuel tank . Many filters for fuel injected engines trap particles as small as 10 to 40 microns in size. Fuel filter normally made into cartridges containing a filter paper.
Electronic control unit: In automotive electronics, electronic control unit (ECU) is a generic term for any embedded system that controls one or more of the electrical systems or subsystems in a motor vehicle. An engine control unit (ECU), also known as power-train control module (PCM), or engine control module (ECM) is a type of electronic control unit that determines the amount of fuel, ignition timing and other parameters an internal combustion engine needs to keep running. It does this by reading values from multidimensional maps which contain values calculated by sensor devices monitoring the engine.
Working of ECU
Control of fuel injection: ECU will determine the quantity of fuel to inject based on a number of parameters. If the throttle pedal is pressed further down, this will open the throttle body and allow more air to be pulled into the engine. The ECU will inject more fuel according to how much air is passing into the engine. If the engine has not warmed up yet, more fuel will be injected. Control of ignition timing: A spark ignition engine requires a spark to initiate combustion in the combustion chamber. An ECU can adjust the exact timing of the spark (called ignition timing) to provide better power and economy. Control of idle speed : Most engine systems have idle speed control built into the ECU. The engine RPM is monitored by the crankshaft position sensor which plays a primary role in the engine timing functions for fuel injection, spark events, and valve timing. Idle speed is controlled by a programmable throttle stop or an idle air bypass control stepper motor. Common rail and Pressure sensor: The term "common rail" refers to the fact that all of the fuel injectors are supplied by a common fuel rail which is nothing more than a pressure
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering accumulator where the fuel is stored at high pressure. This accumulator supplies multiple fuel injectors with high pressure fuel.
Electronic Injectors: The injectors can survive the excessive temperature and pressure of combustion by using the fuel that passes through it as a coolant. The electronic fuel injector is normally closed, and opens to inject pressurized fuel as long as electricity is applied to the injector's solenoid coil. When the injector is turned on, it opens, spraying atomized fuel at the combustion chamber. Depending on engine operating condition, injection quantity will vary.
Gasoline direct injection
In internal combustion engines, gasoline direct injection is a variant of fuel injection employed in modern two- and four- stroke petrol engines. The petrol/gasoline is highly pressurized, and injected via a common rail fuel line directly into the combustion chamber of each cylinder, as opposed to conventional multi-point fuel injection that happens in the intake tract, or cylinder port.
When the driver turns the ignition key on, the power train control module (PCM) energizes a relay that supplies voltage to the fuel pump. The motor inside the pump starts to spin and runs for a few seconds to build pressure in the fuel system. A timer in the PCM limits how long the pump will run until the engine starts.
Fuel is drawn into the pump through an inlet tube and mesh filter sock. The fuel then exits the pump through a one-way check valve and is pushed toward the engine through the fuel line and filter. The fuel filter traps any rust, dirt or other solid contaminants that may have passed through the pump to prevent such particles from clogging the fuel injectors.
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
The fuel then flows to the fuel supply rail on the engine and is routed to the individual fuel injectors. A fuel pressure regulator on the fuel rail maintains fuel pressure, and recirculates excess fuel back to the tank. The fuel pump runs continuously once the engine starts, and continues to run as long as the engine is running and the ignition key is on. If the engine stalls, the (PCM) will detect the loss of the RPM signal and turn the pump off.
2.2. Electronically controlled diesel injection system It describes the way the fuel is injected (pumped under pressure) into some part of the engine where it can combine with the air charge in the cylinders and combustion can take place, releasing energy to propel the vehicle. In fuel-injected spark ignition [SI] engines, fuel is always injected into the air charge well before ignition takes place. This necessary because the liquid or gaseous fuel must be thoroughly mixed together with air into a combustible mixture, able to be ignited by the electrical arc generated by the sparkplug. If the ratio of air to fuel is not reasonably close to 15:1 in the vicinity of the sparkplug, the mixture will not ignite at all and a miss-fire results. Compression ignition [CI] engines always inject the fuel charge directly into a combustion chamber in the engine. Fuel injection and ignition are inextricably tied together in compression ignition [CI] engines. Recall that CI engines only work because they compress the air charge so that it is hot enough to instantly ignite the fuel charge as it is being injected. The combustion of the fuel begins at the instant it begins being injected (well, within a couple of milliseconds, if you want to split hairs) into the combustion chamber full of very hot air (more than 400 ºC, often over 700 ºC). This means the timing of ignition is intimately tied to the fuel injection process. So, the fuel injection system of a CI engine is responsible for regulating both the quantity of fuel to be injected and timing of the beginning of combustion. Many ingenious techniques have been developed to achieve both these tasks with admirable accuracy, long before the advent of sophisticated electronic controls. The EDC is divided into these main groups of components.
1. Electronic sensors for registering operating conditions and changes. A wide array of physical inputs is converted into electrical signal outputs. Actuators or solenoids which convert the control unit's electrical output signal into mechanical control movement. ECM (Electronic Control Module ) or Engine ECU (Electronic Control Unit) with microprocessors which process information from various sensors in accordance with programmed software and outputs required electrical signals into actuators and solenoids.
Types of diesel injection systems a. Unit injector system, b. Rotary distributor type and c. common rail direct injection system,
2.2.1 Unit injector system Design of the unit injector eliminates the need for high-pressure fuel pipes, and with that their associated failures, as well as allowing for much higher injection pressure to occur. The
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering unit injector system allows accurate injection timing, and amount control as in the common rail system . The unit injector is fitted into the engine cylinder head, where the fuel is supplied via integral ducts machined directly into the cylinder head. Each injector has its own pumping element, and in the case of electronic control, a fuel solenoid valve as well. The fuel system is divided into the low pressure (<500 kPa) fuel supply system, and the high-pressure injection system (<2000 bar).
2.2.2 Rotary distributor type The distributor-type pump uses a vane-type transfer pump to fill the single pumping element. This then raises fuel pressure to injection pressure. A distribution system then distributes fuel to each cylinder, in the firing order of the engine. The most common type in light automotive use is the Bosch VE pump. A drive shaft driven from the engine, rotates a plunger, and a cam disc. Cams on the face of the disc have as many lobes as cylinders in the engine. A plunger spring holds the cam disc against rollers that rotate on their shafts. The lobes move the plunger to-and-fro in its barrel, making it rotate, and reciprocate, at the same time. Its rotation operates the fuel inlet port to the pumping chamber, and at the same time distributes pressurized fuel to the correct injector. The reciprocating motion pressurizes the fuel in the pumping chamber. The plunger‘s pumping action forces fuel through a delivery valve, to the injector. This pump is for a 3-cylinder engine, so it has 3 delivery valves. The barrel has 1 intake port and 3 distribution ports. The plunger has a central passage, a connecting passage to the distributing slit, and a cross-drilling to a control sleeve. As the plunger rotates, each intake slit aligns with the intake port, and the distributing slit with the distributing port. As the plunger rotates, the intake slit moves away from the intake port. At the same time, the plunger is acted on by the cams, causing it to move axially along the barrel, pressurizing the fuel in the pumping chamber. The distributing slit now uncovers the distribution port, and the pressurized fuel passes through delivery valve to the injector. Further rotation of the plunger closes off the distribution port, and opens the intake port. At the same time, the plunger spring moves the plunger back along the barrel for the next pumping stroke. For intake, fuel from the feed pump reaches the open intake port in the barrel. The intake slit aligns with the intake port, and fuel fills the pumping chamber and passages in the plunger. For injection, the plunger rotates to close off the intake port, and moves along the barrel, to pressurize fuel in the pumping chamber. The distributing slit aligns with the distribution port, and the pressurized fuel forces the delivery valve off its seat, and reaches the injector. In this phase, a cut-off port in the plunger is covered by the control sleeve. To end fuel delivery, the plunger‘s cut-off port moves out of the control sleeve, and lets pressurized fuel spill back into the pump housing. This relieves pressure in the pumping chamber, the delivery valve closes, and injection ceases. Metering the fuel is controlled by effective stroke of the control sleeve, and that‘s determined by the action of the governor sliding the control sleeve along the plunger. Sliding it one way opens the cut-off port earlier, and reduces effective stroke. Sliding it this way delays its opening, and increases effective stroke.
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
The governor changes the position of the control sleeve to vary the quantity of fuel delivered, according to throttle position and load. When the ignition is switched off, an electrical solenoid closes off the intake port, and stops fuel delivery. 2.2.3 Common rail direct injection system CRDi stands for Common Rail Direct Injection meaning, direct injection of the fuel into the cylinders of a diesel engine via a single, common line, called the common rail which is connected to all the fuel injectors.
Whereas ordinary diesel direct fuel-injection systems have to build up pressure anew for each and every injection cycle, the new common rail (line) engines maintain constant pressure regardless of the injection sequence. This pressure then remains permanently available throughout the fuel line. The engine's electronic timing regulates injection pressure according to engine speed and load. The electronic control unit (ECU) modifies injection pressure precisely and as needed, based on data obtained from sensors on the cam and crankshafts. In other words, compression and injection occur independently of each other. This technique allows fuel to be injected as needed, saving fuel and lowering emissions.
More accurately measured and timed mixture spray in the combustion chamber significantly reducing unburned fuel gives CRDi the potential to meet future emission guidelines such as Euro V. CRDi engines are now being used in almost all Mercedes-Benz, Toyota, Hyundai, Ford and many other diesel automobiles.
Advantages CRDi engines are advantageous in many ways. Cars fitted with this new engine technology are believed to deliver 25% more power and torque than the normal direct injection engine. It also offers superior pick up, lower levels of noise and vibration, higher mileage, lower emissions, lower fuel consumption, and improved performance. In India, diesel is cheaper than petrol and this fact adds to the credibility of the common rail direct injection system.
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
Disadvantages The key disadvantage of the CRDi engine is that it is costly than the conventional engine. The list also includes high degree of engine maintenance and costly spare parts. Also this technology can‘t be employed to ordinary engines.
2.3. Electronic ignition system Battery ignition system Most of the modern spark-ignition engines use battery ignition system. The essential components of battery ignition system are a battery, ignition switch, ballast resistor, ignition coil, breaker points, condenser, capacitor distributor and spark plugs. The breaker points, condenser, distributor rotor and the spark advance mechanisms are usually housed in the ignition distribution. The breaker points are actuated by a shaft driven at half engine speed for a four stroke cycle engine. The distributor rotor is directly connected to the same shaft. The system has a primary circuit of low-voltage current and a secondary circuit for the high-voltage circuit. The primary circuit consists of the battery, ammeter, ignition switch, primary coil winding and breaker points. The primary coil winding usually has approximately 240 turns of relatively heavy copper wire wound around the soft iron core of ignition coil. The secondary circuit contains the secondary coil windings, distributor, spark plug leads and the spark plug. The secondary windings consists of about 21000 turns of small, well insulate copper wire.
When the ignition switch and the breaker points are closed a low-voltage current flows from the battery through the primary circuit and builts up a magnetic field around the soft iron core of the ignition coil. When the breaker points are opened by the action of the cam on the distributor shaft, the primary circuit is broken and the magnetic field begins to collapse, an induced current from the collapsing magnetic field flows in the same direction in the primary circuit as the battery current and charges the condenser which acts as a reservoir for the flowing current due to a rapidly collapsing magnetic field, high voltage is induced in the primary (it might be as high as 250 volts) and even higher in the secondary (10,000 to 20,000 volts). The high voltage in the secondary passes through the distributor rotor to one of the spark plug leads and into the spark plug. As soon as sufficient voltage is built up in the secondary to overcome the resistance of a spark plug, the spark arcs across the gap and the ignition of the combustible charge in the cylinder takes place. The induced current in the primary to overcome the resistance of a spark across the gap and the ignition of the combustible charge in the cylinder takes place. The induced current is the primary, as it was pointed out above flows in the same direction as it did before the breaker points opened up and charges the condenser.
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
The increasing potential of the condenser retards and finally stops the flow of current in the primary circuit and the rapidly ‗backfires‘ or discharges again through the primary, but in the direction opposite to the original flow of current. This rapid discharge of condense produces directional oscillation in the current flow in the primary circuit. This oscillation is weekend with every succeeding reversal in the current flow until the original potentials and the direction of current flow the primary circuit are established. The discharge of condenser by itself does not produce the spark, but only hastens the collapse of the magnetic field around the soft iron core. The condenser, which has a capacitance range from 0.15 to 0.24 mf in the automotive system, not only assists in the collapse f the magnetic field, but also prevents arcing at the breaker points by providing a place for the induced current to flow in the primary circuit. If the condenser is too small or too large, the breaker points will lead to excessive pitting will result the breaker points and the distributor must be carefully synchronized with the crankshaft of the engine to give the proper timing of the spark in each of the cylinders. The breaker is often refereed to as the timer, since the time or point in the cycle that the spark occurs depends upon the time of opening of the breaker points. The spark plug leads are called the ignition harness. Since the lead carry a very high potential, a special insulation is required to prevent a short circuit. Even with the special insulation, these leads are subjected to breakdowns which result in high-tension short circuits and to leakage that lower the voltage available at the work plug. Also, the leads should be shielded to aid in the prevention of radio interference.
With the engine running, the trigger wheel rotates inside the distributor. As a tooth of the trigger wheel passes the pickup coil, the magnetic field strengthens around the pickup coil. This action changes the output voltage or current flow through the coil. As a result, an electrical surge is sent to the electronic control unit, as the trigger wheel teeth pass the pickup coil. Magneto ignition system Magneto ignition system is a special type of ignition system with its own electric generator to provide the required necessary energy for the vehicle (automobile) system. It is mounted on the engine and replaces all components of the coil ignition system except the spark plug. A magneto, when rotated by the engine, is capable of producing a very high voltage and doesn‘t need a battery as source of external energy. A schematic diagram of a high tension magneto ignition system is shown in the figure 1 under. The high tension magneto ignition system incorporates the windings to generate the primary voltage as well as to set up the voltage and thus does not require to operate the spark plug.
Magneto ignition system can be either rotating armature type or rotating magneto type. 1. In the first type, the armature consisting of the primary and secondary windings all rotate between the poles of a stationary magnet. M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
2. In the second type, the magnet revolves and windings are kept stationary. 3. The third type of magneto called the polar inductor type in use. In the polar inductor type magneto, both the magnet and the windings remain stationary but the voltage is generated by reversing the flux field with the help of soft iron polar projections, called inductors. The working principle of the magnetic ignition system is same as that of the coil ignition system. With the help of a cam, the primary circuit flux is changed and a high voltage is produced in the secondary circuit. The variation of the breaker current with speed for the coil ignition system and the magnetic ignition system is shown in the graph 1. It can be seen that since the cranking speed at stat is low the current generated by the magneto is quite small. As the engine speed increases the current flow also increases. Thus, with magneto, there is always a starting difficulty and sometimes a separate battery is needed for starting. The magneto ignition system is best suitable at high speeds and is widely used in automobiles like sports and racing cars, aircraft‘s engines etc. In comparison, the battery ignition system is more expensive but highly reliable. Because of the poor starting characteristics of the magneto system invariably the battery ignition system is preferred to the magneto system in automobile engines. However, in two wheelers magneto ignition system is favored due to light weight and less maintenance. The main advantage of the high tension magneto ignition system lies in the fact that the wirings carry a very high voltage and thus there is a strong possibility of causing engine misfire due to leakage. To avoid this the high tension wires must be suitably shielded. The development of the low tension magneto system is an experiment to avoid this trouble. In the low tension, magneto ignition system the secondary winding is changed to limit the secondary voltage to a value of about 400 volts and distributor is replaced by a brush contact. The high voltage is obtained with the help of a step-up transformer. All these changes have the effect of limiting the high voltage current in the small part of the ignition system wiring and thus avoid the possibilities of leakage etc. Electronic ignition system The basic difference between the contact point and the electronic ignition system is in the primary circuit. The primary circuit in a contact point ignition system is open and closed by contact points. In the electronic system, the primary circuit is open and closed by the electronic control unit (ECU). The secondary circuits are practically the same for the two systems. The difference is that the distributor, ignition coil, and wiring are altered to handle the high voltage produced by the electronic ignition system. One advantage of this higher voltage (up to 60,000 volts) is that spark plugs with wider gaps can be used. This results in a longer spark, which can ignite leaner air-fuel mixtures. As a result engines can run on leaner mixtures for better fuel economy and lower emissions. Electronic Ignition System Components The components of an electronic ignition system regardless of the manufacturer all perform the same functions. Each manufacturer has it own preferred terminology and location of the components. The basic components of an electronic ignition system are as follows:
Trigger wheel- The trigger wheel, also known as a reluctor, pole piece, or armature, is connected to the upper end of the distributor shaft. The trigger wheel replaces the distributor cam. Like the distributor cam lobes, the teeth on the trigger wheel equal the number of engine cylinders.
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Pickup coil- The pickup coil, also known as a sensor assembly, sensor coil, or magnetic pickup assembly, produces tiny voltage surges for the ignition systems electronic control unit. The pickup coil is a small set of windings forming a coil.
Electronic Control Unit Amplifier- The ignition system electronic control unit amplifier or control module is an "electronic switch" that turns the ignition coil primary current ON and OFF. The ECU performs the same function as the contact points. The ignition ECU is a network of transistors, capacitors, resistors, and other electronic components sealed in a metal or plastic housing. The ECU can be located (1) in the engine compartment, (2) on the side of the distributor, (3) inside the distributor, or (4) under the vehicle dash. ECU dwell time (number of degrees the circuit conducts current to the ignition coil) is designed into the electronic circuit of the ECU and is NOT adjustable.
Electronic Ignition System Operation
The electronic control unit increases the electrical surges into ON/ OFF cycles for the ignition coil. When the ECU is ON, current passes through the primary windings of the ignition coil, thereby developing a magnetic field. Then, when the trigger wheel and pickup coil turn OFF the ECU, the magnetic field inside the ignition coil collapses and fires a sparkplug.
2.3.1. Transistorized coil ignition system Transistor Ignition System(Breaker-Point Type): The breaker-point type of transistor ignition system was developed to replace the standard or conventional ignition system. To obtain the maximum power and speed that this engine can produce, you must install an ignition system that outperforms the conventional one. Electronic type of ignition systems provide a hotter, more uniform spark at a more precise interval. This promotes more efficient burning of the air/fuel mixture in the combustion chamber, producing less exhaust emissions and resulting in better engine performance and increased mileage. The increased reliability of electronic ignition allows less frequent maintenance by increasing parts life. At high speeds, the breaker points of a conventional ignition system cannot handle the increased current flowing across them without putting too much. Also, the dwell angle of the breaker points is too small for complete saturation of the ignition coil. The transistorized ignition system takes care of both M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering drawbacks. By comparing figures 4-28 and 4-29, you can see how the transistor ignition system differs from the conventional. When the breaker points are connected to the transistor, as shown in figure 4-29, it nearly eliminates arcing across them since the current flow is small (about one-half ampere). However, the current flow in the primary windings of the coil is about 6amperes. This amount is enough to saturate the coil completely at high engine speeds, and results in a higher output to the secondary circuit. Therefore, the transits or ignition system is superior to the conventional system a high engine speeds because there is less arcing across the breaker points and higher and steadier voltage in the secondary circuit.
2.3.2. Capacitive discharge ignition system
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
Transistor Ignition System(Magnetic-Pulse Type): The drawbacks of a conventional ignition system operating at high engine speeds can also be overcome with the magnetic-pulse type of transistor ignition system (fig. 4-30). Notice that a magnetic pulse distributor, which resembles a conventional distributor is used instead of a breaker-point type of distributor. An iron timer core in this distributor replaces the standard breaker cam. The timer core has equally spaced projections (one for each cylinder of the engine) and rotates inside a magnetic pickup assembly. This pickup assembly replaces the breaker plate assembly of the conventional distributor. Since there are no breaker points and there is no condenser, there can be no arcing across them. Capacitors in this system are for noise suppression. This overcomes one of the drawbacks already mentioned. The other drawback is overcome by controlling the amount of current that flows through the primary windings of the ignition coil and to ground. Transistors in the ignition pulse amplifier do the controlling. Another feature of this transistor ignition system is its coil, which has fewer and heavier primary windings and a higher turns ratio of primary to secondary windings than the conventional coil. Controlling the current flow and using a special coil.
2.4. Turbo chargers A turbocharger consists of a turbine and a compressor linked by a shared axle. The turbine inlet receives exhaust gases from the engine exhaust manifold causing the turbine wheel to rotate. This rotation drives the compressor, compressing ambient air and delivering it to the air intake manifold of the engine at higher pressure, resulting in a greater amount of the air and fuel entering the cylinder. Turbochargers were originally known as turbosuperchargers when all forced induction devices were classified as superchargers. Nowadays the term "supercharger" is usually applied only to mechanically driven forced induction devices. The key difference between a turbocharger and a conventional supercharger is that a supercharger is mechanically driven by the engine, often through a belt connected to the crankshaft, whereas a turbocharger is powered by a turbine driven by the engine's exhaust gas. Compared to a mechanically driven supercharger, turbochargers tend to be more efficient, but less responsive.
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Twin charger refers to an engine with both a supercharger and a turbocharger. Turbochargers are a type of forced induction system. They compress the air flowing into the engine. The advantage of compressing the air is that it lets the engine squeeze more air into a cylinder, and more air means that more fuel can be added. Therefore, you get more power from each explosion in each cylinder. A turbocharged engine produces more power overall than the same engine without the charging. This can significantly improve the power-to-weight ratio for the engine. In order to achieve this boost, the turbocharger uses the exhaust flow from the engine to spin a turbine, which in turn spins an air pump. The turbine in the turbocharger spins at speeds of up to 150,000 rotations per minute (rpm) -- that's about 30 times faster than most car engines can go. And since it is hooked up to the exhaust, the temperatures in the turbine are also very high. 2.4.1. WGT -Waste Gate Turbocharger The turbocharger is bolted to the exhaust manifold of the engine. The exhaust from the cylinders spins the turbine, which works like a gas turbine engine. The turbine is connected by a shaft to the compressor, which is located between the air filter and the intake manifold. The compressor pressurizes the air going into the pistons. The exhaust from the cylinders passes through the turbine blades, causing the turbine to spin. The more exhaust that goes through the blades, the faster they spin. On the other end of the shaft that the turbine is attached to, the compressor pumps air into the cylinders. The compressor is a type of centrifugal pump -- it draws air in at the center of its blades and flings it outward as it spins. In order to handle speeds of up to 150,000 rpm, the turbine shaft has to be supported very carefully. Most bearings would explode at speeds like this, so most turbochargers use a fluid bearing. This type of bearing supports the shaft on a thin layer of oil that is constantly pumped around the shaft. This serves two purposes: It cools the shaft and some of the other turbocharger parts, and it allows the shaft to spin without much friction.
2.4.2. VGT-Variable-geometry turbocharger An alternative to the fixed geometry turbine is the variable geometry turbine. Variable- geometry turbochargers (VGTs) are a family of turbochargers, usually designed to allow the effective aspect ratio (A/R) of the turbo to be altered as conditions change. This is done because optimum aspect ratio at low engine speeds is very different from that at high engine speeds. If the aspect ratio is too large, the turbo will fail to create boost at low speeds; if the aspect ratio is too small, the turbo will choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output. By altering the geometry of M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering the turbine housing as the engine accelerates, the turbo's aspect ratio can be maintained at its optimum. Because of this, VGTs have a minimal amount of lag, have a low boost threshold, and are very efficient at higher engine speeds. VGTs do not require a waste gate. VGTs tend to be much more common on diesel engines as the lower exhaust temperatures mean they are less prone to failure. The few early gasoline-engine VGTs required significant pre-charge cooling to extend the turbocharger life to reasonable levels, but advances in material technology have improved their resistance to the high temperatures of gasoline engine exhaust and they have started to appear increasingly in, e.g., gasoline-engined sports.
The benefits of variable geometry turbines over wastegated turbines: No throttling loss of the wastegate valve; Higher air–fuel ratio and higher peak torque at low engine speeds; Improved vehicle accelerations without the need to resort to turbines with high pumping loss at high engine speeds; Potential for lower engine ΔP (the difference between exhaust manifold and intake manifold pressures); control over engine ΔP that can be used to drive EGR flow in diesel engines with High Pressure Loop (HPL) EGR systems; A better ability to cover a wider region of low BSFC in the engine speed–load domain; Ability to provide engine braking; Ability to raise exhaust temperature for after treatment system management.
2.5. Engine emission control by three way catalytic converter system A catalytic converter is an exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine to less toxic pollutants by catalyzing a redox reaction (an oxidation and a reduction reaction). 2-way catalytic converter: A 2-way (or "oxidation", sometimes called an "oxi-cat") catalytic converter has two simultaneous tasks: Oxidation of carbon monoxide to carbon dioxide: 2 CO + O2 → 2 CO2 Oxidation of hydrocarbons (unburnt and partially burned fuel) to carbon dioxide and water: CxH2x+2 + [(3x+1)/2] O2 → x CO2 + (x+1) H2O (a combustion reaction) This type of catalytic converter is widely used on diesel engines to reduce hydrocarbon and carbon monoxide emissions. 2.5.1.Three-way catalytic converters: Three-way catalytic converters (TWC) have the additional advantage of controlling the emission of nitric oxide and nitrogen dioxide. The exhaust gases from an engine contain harmful substances such as oxides of nitrogen (NOx), carbon monoxide (CO) and Hydrocarbons (HC). These substances produce extreme environment
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering hazards. 3-way catalytic converters convert these harmful substances to less harmful nitrogen (N2), carbon-di-oxide (CO2) and water (H2O). A three-way catalytic converter has three simultaneous tasks: 1. Reduction of nitrogen oxides to nitrogen and oxygen: 2 NOx → x O2 + N2 2. Oxidation of carbon monoxide to carbon dioxide: 2 CO + O2 → 2 CO2 3. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2 + [(3x+1)/2] O2 → x CO2 + (x+1) H2O.
2.5.2.Working Principal: A three-way catalytic converter makes use of two catalysts to convert harmful gases to harmless gases. They are:
1. Reduction Catalyst and 2. Oxidation Catalyst The reduction catalyst is made of platinum and rhodium while the oxidation catalyst is made of platinum and palladium. Both the catalysts have a ceramic honeycomb structure.
Exhaust gases with NOx, CO and HC
Reduction NOx Oxidation catalyst removed catalyst
N2, CO2, and H2O
Stage 1 – Reduction Catalyst: The exhaust gases are first sent over the reduction catalyst (which is made of platinum and rhodium). It converts oxides of nitrogen (NOx) to nitrogen (N2) and oxygen (O2). The following reactions take place when the exhaust gases pass over the reduction catalyst. 2NO → N2 + O2 2NO2 → N2 + 2O2 The reduction catalyst simply rips off nitrogen and oxygen from the oxides of nitrogen. As you might know, nitrogen and oxygen are harmless gases while oxides of nitrogen are really harmful to the environment.
Stage 2 – Oxidation Catalyst: M.I.E.T. /Mech. / III/AE
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Exhaust gases that are free of oxides of nitrogen (NOx) are then sent over the oxidation catalyst (made of platinum and palladium). The oxidation catalyst coverts carbon-monoxide (CO) and hydrocarbons (HC) in the gases into carbon-di-oxide (CO2) and water (H2O). The following reactions takes place when the exhaust gases pass over the oxidation catalyst: 2CO + O2→ 2CO2 HC + O2 → CO2 + H2O
The second reaction (above) is a generalized reaction. In it, HC stands for hydrocarbon. HC might be methane, ethane or other hydrocarbon. The gases that finally come out of the catalyst chamber are N2, CO2, and H2O. 3-way catalytic converters are so named because they are capable of eliminating three pollutants – NOx, CO and HC.
2.6. Emission norms 2.6.1. Euro Emission standards European emission standards define the acceptable limits for exhaust emissions of new vehicles sold in EU member states. The emission standards are defined in a series of European Union directives staging the progressive introduction of increasingly stringent standards. Currently, emissions of nitrogen oxides (NOx), total hydrocarbon (THC), non-methane hydrocarbons (NMHC), carbon monoxide (CO) and particulate matter (PM) are regulated for most vehicle types, including cars, lorries, trains, tractors and similar machinery, barges, but excluding seagoing ships and aeroplanes. For each vehicle type, different standards apply. Compliance is determined by running the engine at a standardised test cycle. Non-compliant vehicles cannot be sold in the EU, but new standards do not apply to vehicles already on the roads. No use of specific technologies is mandated to meet the standards, though available technology is considered when setting the standards. New models introduced must meet current or planned standards, but minor lifecycle model revisions may continue to be offered with pre- compliant engines. European emission standards for passenger cars (Category M*), g/km PN
Tier Date CO THC NMHC NOx HC+NOx PM
[#/km] Diesel
Euro 2.72 0.97 0.14 July 1992 - - - - 1† (3.16) (1.13) (0.18) January Euro 2 1.0 - - - 0.7 0.08 - 1996 January Euro 3 0.66 - - 0.50 0.56 0.05 - 2000 January Euro 4 0.50 - - 0.25 0.30 0.025 - 2005 Euro September 0.50 - - 0.180 0.230 0.005 - 5a 2009 Euro September 0.50 - - 0.180 0.230 0.005 6×1011 5b 2011 September Euro 6 0.50 - - 0.080 0.170 0.005 6×1011 2014 Petrol (Gasoline)
Euro July 1992 2.72 - - - 0.97 - -
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1† (3.16) (1.13) January Euro 2 2.2 - - - 0.5 - - 1996 January Euro 3 2.3 0.20 - 0.15 - - - 2000 January Euro 4 1.0 0.10 - 0.08 - - - 2005 September Euro 5 1.0 0.10 0.068 0.060 - 0.005** - 2009 September 6×1011* Euro 6 1.0 0.10 0.068 0.060 - 0.005** 2014 ** * Before Euro 5, passenger vehicles > 2500 kg were type approved as light commercial vehicles N1-I ** Applies only to vehicles with direct injection engines *** 6×1012/km within first three years from Euro 6 effective dates † Values in parentheses are conformity of production (COP) limits
2.6.2. BS Emission standards India has adopted the European emission limits on a slightly modified driving cycle for the light duty vehicles. The overall emission limits and test procedures for the heavy duty vehicles however are the same as those in Europe. In India, the emission limits are being enforced by a time lag of around 5 years as shown in Table.
Standard Reference Date Region India 2000 Euro 1 2000 Nationwide Bharat Stage II Euro 2 2001 NCR(National Capital Region Delhi), Mumbai, Kolkata, Chennai 2003.04 NCR(National Capital Region Delhi), 11 cities Mumbai, Kolkata, Chennai, Bangalore, Hyderabad, Secunderabad, Ahmedabad, Pune, Surat, Kanpur and Agra 2005.04 Nationwide Bharat Stage III Euro 3 2005.04 NCR(National Capital Region Delhi), Mumbai, Kolkata, Chennai, Bangalore, Hyderabad, Secunderabad, Ahmedabad, Pune, Surat, Kanpur and Agra 2010.04 Nationwide Bharat Stage IV Euro 4 2010.04 NCR(National Capital Region Delhi), † Mumbai, Kolkata, Chennai, Bangalore, Hyderabad, Secunderabad, Ahmedabad, Pune, Surat, Kanpur, Solapur and Lucknow and Agra 2015.07 Above plus 29 cities mainly in the states of Haryana, Uttar Pradesh, Rajasthan and Maharashtra 2015.10 North India plus bordering districts of Rajasthan (9 States) 2016.04 Western India plus parts of South and
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East India (10 States and Territories) 2017.04 Nationwide Bharat Stage V Euro 5 2019.04a Nationwide Bharat Stage VI Euro 6 2021.04b Nationwide
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
UNIT - III TRANSMISSION SYSTEMS
Clutch-types and construction, gear boxes- manual and automatic, gear shift mechanisms, Over drive, transfer box, fluid flywheel, torque converter, propeller shaft, slip joints, universal joints, Differential and rear axle, Hotchkiss Drive and Torque Tube Drive.
3.1. Transmission Systems in Automobile The most common transmission systems that have been used for the automotive industry are: Manual transmission, Automatic transmission, Semi-automatic transmission, Continuously-variable transmission (C.V.T.). 3.1.1. Manual Transmission The first transmission invented was the manual transmission system. The driver needs to disengage the clutch to disconnect the power from the engine first, select the target gear, and engage the clutch again to perform the gear change. The transmission system delivers the engine power to wheels.
Components of manual transmission The main components of manual transmission are: Clutch Gear box U- joint Shafts Differential gear box 3.1.2. Automatic Transmission An automatic transmission uses a fluid-coupling torque converter to replace the clutch to avoid engaging/disengaging clutch during gear change. A completed gear set, called planetary gears, is used to perform gear ratio change instead of selecting gear manually. A driver no longer needs to worry about gear selection during driving. It makes driving a car much easier, especially for a disabled or new driver. However, the indirect gear contact of the torque converter causes power loss during power transmission, and the complicated planetary gear structure makes the transmission heavy and easily broken. 3.1.3. Semi-Automatic Transmission A semi-automatic transmission tries to combine the advantages of the manual and automatic transmission systems, but avoid their disadvantages. However, the complicated design of the semi-automatic transmission is still under development, and the price is not cheap. It is only used for some luxury or sports cars currently.
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3.1.4. Continuously Variable Transmission (C.V.T.) The Continuously Variable Transmission (C.V.T.) is a transmission in which the ratio of the rotational speeds of two shafts, as the input shaft and output shaft of a vehicle or other machine, can be varied continuously within a given range, providing an infinite number of possible ratios. The other mechanical transmissions described above only allow a few different gear ratios to be selected, but this type of transmission essentially has an infinite number of ratios available within a finite range. 3.2. Clutch Clutch is used to engage or disengage the engine to the transmission or gear box. When the clutch is in engaged position, the engine power or rotary motion of engine crankshaft is transmitted to gear box and then to wheels. It is located between the transmission and the engine. When the clutch is engaged, the power flows from the engine to the rear wheels in a rear-wheel- drive transmission and the vehicle moves. When the clutch is disengaged, the power is not transmitted from the engine to the rear wheels and vehicle stops even if engine is running. It operates on the principle of friction. When two surfaces are brought in contact and are held against each other due to friction between them, they can be used to transmit power. If one is rotated, then other also rotates. One surface is connected to engine and other to the transmission system of automobile. Thus, clutch is nothing but a combination of two friction surfaces.
3.2.1. Main Parts of a Clutch It consists of (a) Driving member The driving members consists of a flywheel which is mounted on the engine crankshaft The flywheel is bolted to a cover which carries pressure plate, pressure springs and releasing levers. As the flywheel is bolted to the cover assembly, thus, the entire assembly of the flywheel and the cover rotate all the times. The clutch housing and cover provided with openings so that the heat produced during the function dissipates easily (b) Driven member The driven member consists of a disc or plate called clutch plate. The clutch is free to slide on the splines of the clutch shaft. It carries friction materials on both of its surfaces. When the clutch plate is gripped between the flywheel and the pressure plate, it rotates the clutch shaft through splines. (c) Operating member The operating member consists of a pedal or lever which can be pressed to disengaged the driving and driven plate.
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3.2.2. Types of Friction Materials The friction materials of the clutch plate are generally of 3 types: Mill Board Type Molded type Woven type Mill Board type friction materials mainly include asbestos material with different types of impregnates. Molded type friction materials are made from a matrix of asbestos fiber and starch or any other suitable binding materials. They are then heated to a certain temperature for moulding in dies under pressure. They are also made into sheets by rolling, pressing and backs till they are extremely hard and dense. Metallic wires are used sometimes to increase wear properties. Woven types facing materials are made by impregnating a cloth with certain binders or by weaving threads of copper or brass wires covered with long fiber asbestos and cotton. The woven sheets treated with binding solution are baked and rolled. 3.2.3. Operation of Clutch When the clutch pedal is pressed through pedal movement, the clutch release bearing presses on the clutch release lever plate which being connected to clutch release levers, forces these levers forward. This causes the pressure plate to compress pressure springs, thus allowing it to move away from the clutch driven plate. This action releases the pressure on the driven plate and flywheel, the flywheel is now free to turn independently, without turning the transmission. When the clutch pedal is released, reverse action takes place i.e. the driven plate is again forced against the flywheel by the pressure plate- because of the force exerted by pressure springs. The pressure plate will keep on pressing the facings of driven plate until friction created becomes equal to the resistance of the vehicle. Any further increase in pressure will cause the clutch plate and the transmission shaft to turn along with flywheel, thus achieving vehicle movement. 3.3. Types of Clutches and Constructions Some types of clutches used in vehicles are given below: (a) Friction Clutch: It may be (i) Single plate clutch, (ii) Multi-plate clutch, (iii) Cone clutch.
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Multi-plate clutch can be either wet or dry. A wet clutch is operated in an oil batch whereas a dry clutch does not use oil. (b) Centrifugal clutch. (c) Semi-centrifugal clutch. (d) Hydraulic clutch. (g) Electromagnetic clutch. 3.3.1. Single Clutch Plate It is the most common type of clutch plate used in motor vehicles. Basically it consists of only one clutch plate, mounted on the splines of the clutch plate. The flywheel is mounted on engine crankshaft and rotates with it. The pressure plate is bolted to the flywheel through clutch springs, and is free to slide on the clutch shaft when the clutch pedal is operated. When the clutch is engaged the clutch plate is gripped between the flywheel and pressure plate. The friction linings are on both the sides of the clutch plate. Due to the friction between the flywheel, clutch plate and the pressure plate the clutch plate revolves the flywheel. As the clutch plate revolves the clutch shaft also revolves. Clutch shaft is connected to the transmission gear box. Thus the engine power is transmitted to the crankshaft and then to the clutch shaft. When the clutch pedal is pressed, the pressure plate moves back against the force of the springs, and the clutch plate becomes free between the flywheel and the pressure plate. Thus the flywheel remains rotating as long as the engine is running and the clutch shaft speed reduces slowly and finally it stops rotating. As soon as the clutch pedal is pressed, the clutch is said to be engaged, otherwise it remains engaged due to the spring forces.
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3.3.2. Multi-plate Clutch Multi-plate clutch consists of a number of clutch plates instead of only one clutch plate as in case of single plate clutch. As The number of clutch plates are increased, the friction surfaces also increases. The increased number of friction surfaces obliviously increases the capacity of the clutch to transmit torque. The plates are alternately fitted to engine and gear box shaft. They are firmly pressed by strong coil springs and assembled in a drum. Each of the alternate plate slides on the grooves on the flywheel and the other slides on splines on the pressure plate. Thus, each alternate plate has inner and outer splines. The multi-plate clutch works in the same way as a single plate clutch by operating the clutch pedal. The multi-plate clutches are used in heavy commercial vehicles, racing cars and motor cycles for transmitting high torque. The multi-plate clutch may be dry or wet. When the clutch is operated in an oil bath, it is called a wet clutch. When the clutch is operated dry it is called dry clutch. The wet clutch is used in conjunction with or part of the automatic transmission.
3.3.3. Cone Clutch Cone clutch consists of friction surfaces in the form of cone. The engine shaft consists of female cone. The male cone is mounted on the splined clutch shaft. It has friction surfaces on the conical portion. The male cone can slide on the clutch shaft. Hen the clutch is engaged the friction surfaces of the male cone are in contact with that of the female cone due to force of the spring. When the clutch pedal is pressed, the male cone slides against the spring force and the clutch is disengaged. The only advantage of the cone clutch is that the normal force acting on the friction surfaces is greater than the axial force, as compare to the single plate clutch in which the normal force acting on the friction surfaces is equal to the axial force. The disadvantage in cone clutch is that if the angle of the cone is made smaller than 200 the male cone tends to bind in the female cone and it becomes difficult to disengage the clutch. Cone clutches are generally now only used in low peripheral speed applications although they were once common in automobiles and other combustion engine transmissions. They are usually now confined to very specialist transmissions in racing, rallying, or in extreme off-road vehicles, although they are common in power boats. Small cone clutches are used in synchronizer mechanisms in manual transmissions.
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3.3.4. Centrifugal Clutch The centrifugal clutch uses centrifugal forces, instead of spring force for keeping it in engaged position. Also, it does not require clutch pedal for operating the clutch. The clutch is operated automatically depending on engine speed. The vehicle can be stopped in gear without stalling the engine. Similarly the gear can be started in any gear by pressing the accelerator pedal. A centrifugal clutch works through centrifugal force. The input of the clutch is connected to the engine crankshaft while the output drives gear box shaft, chain, or belt. As engine R.P.M. increases, weighted arms in the clutch swing outward and force the clutch to engage. The most common types have friction pads or shoes radially mounted that engage the inside of the rim of housing. On the center shaft there are an assorted amount of extension springs, which connect to a clutch shoe. When the center shaft spins fast enough, the springs extend causing the clutch shoes to engage the friction face. It can be compared to a drum brake in reverse. The weighted arms force these disks together and engage the clutch. When the engine reaches a certain RPM, the clutch activates, working almost like a continuously variable transmission. As the load increases, the R.P.M. drops thereby disengaging the clutch and letting the rpm rise again and reengaging the clutch. If tuned properly, the clutch will tend to keep the engine at or near the torque peak of the engine. These results in a fair bit of waste heat, but over a broad range of speeds it is much more useful than a direct drive in many applications. Weaker spring/heavier shoes will cause the clutch to engage at a lower R.P.M. while a stronger spring/lighter shoes will cause the clutch to engage at a higher R.P.M. 3.3.5. Semi-centrifugal Clutch A semi centrifugal clutch is used to transmit power from high powered engines and racing car engines where clutch disengagements requires appreciable and tiresome drivers effort. The transmission of power in such clutches is partly by clutch springs and rest by centrifugal action of an extra weight provided in system. The clutch springs serve to transmit the torque up to normal speeds, while the centrifugal force assists at speeds higher than normal. Besides clutch, pressure plate and splines shaft it mainly consists of: Compression spring (3 numbers) Weighted levers (3 numbers) At normal speeds when the power transmission is low the spring keeps the clutch engaged, the weighted levers do not have any pressure on the pressure plate. At high speed, when the power transmission is high the weights fly off and levers exert pressure on the plate which keeps the clutch firmly engaged. Thus instead of having more stiff springs for keeping the M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering clutch engaged firmly at high speeds, they are less stiff, so that the driver may not get any strain in operating the clutch. When the speed decreases, the weights fall and the levers do not exert any pressure on the pressure plate. Only the spring pressure is exerted on the pressure plate which is sufficient to keep the clutch engaged.
3.3.6. Electromagnetic Clutch An electromagnetic clutch is a clutch (a mechanism for transmitting rotation) that is engaged and disengaged by an electromagnetic actuator. In this type of clutch, the flywheel consists of winding. The current is supplied to the winding from battery or dynamo. When the current passes through the winding it produces an electromagnetic field which attracts the pressure plate, thereby engaging the clutch. When supply is cutoff, the clutch is disengaged. The gear lever consists of a clutch release switch. When then the driver holds the gear lever to change the gear the witch is operated cutting off the current to the winding which causes the clutch disengaged. At low speeds when the dynamo output is low, the clutch is not firmly engaged. Therefore three springs are also provided on the pressure plate which helps the clutch engaged firmly at low speed also. Cycling is achieved by turning the voltage/current to the electromagnet on and off. Slippage normally occurs only during acceleration. When the clutch is fully engaged, there is no relative slip, assuming the clutch is sized properly, and thus torque transfer is 100% efficient. The electromagnetic clutch is most suitable for remote operation since no linkages are required to control its engagement. It has fast, smooth operation. However, because energy dissipates as heat in the electromagnetic actuator every time the clutch is engaged, there is a risk of overheating. Consequently the maximum operating temperature of the clutch is limited by the temperature rating of the insulation of the electromagnet. This is a major limitation. Another disadvantage is higher initial cost.
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3.4. Gear boxes A gearbox is a mechanical method of transferring energy from one device to another and is used to increase torque while reducing speed. Torque is the power generated through the bending or twisting of a solid material. This term is often used interchangeably with transmission. Located at the junction point of a power shaft, the gearbox is often used to create a right angle change in direction, as is seen in a rotary mower or a helicopter. Each unit is made with a specific purpose in mind, and the gear ratio used is designed to provide the level of force required. This ratio is fixed and cannot be changed once the box is constructed. The only possible modification after the fact is an adjustment that allows the shaft speed to increase, along with a corresponding reduction in torque. In a situation where multiple speeds are needed, a transmission with multiple gears can be used to increase torque while slowing down the output speed. Principle of Gearing Consider a simple 4-gear train. It consists of a driving gear A on input shaft and a driven gear D on the output shaft. In between the two gears there are two intermediate gears B, C. Each of these gears are mounted on separate shaft. 3.4.1. Types of Gear boxes types These are two primary groups of gearboxes such as a. Manual change gear-boxes b. Automatic gear-boxes. 3.4.2. Manual Change Gearboxes In these gearboxes the driver has complete control of the gear changing process and can select a gear ratio appropriate to the driving conditions by means of the manual control lever. Generally, these are four to five gear ratio options, apart from the reverse gear. There are three basic types of gearboxes: • Sliding-mesh • Constant-mesh • Synchro-mesh Of these, the synchro-mesh type is most prevalent today. It is essentially a combination of the other two types. Although sliding-mesh type gear box is obsolete at present, it has been considered in the text for initial study. i. Sliding Mesh Gear Box It is the simplest gear box. The following figure shows 4-speed gear box in neutral position.4 gears are connected to the lay shaft/counter shaft. A reverse idler gear is mounted on another
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering shaft and always remains connected to the reverse gear of countershaft. This ―H‖ shift pattern enables the driver to select four different gear ratios and a reverse gear. Gears in Neutral: When the engine is running and clutch is engaged the clutch shaft gear drives the countershaft gear. The countershaft rotates opposite in direction of the clutch shaft. In neutral position only the clutch shaft gear is connected to the countershaft gear. Other gears are free and hence the transmission main shaft is not turning. The vehicle is stationary. First or low shaft gear: By operating the gear shift lever the larger gear on the main shaft is moved along the shaft to mesh with the first gear of the counter shaft. The main shaft turns in the same direction as that of the clutch shaft. Since the smaller countershaft is engaged with larger shaft gear a gear reduction of approximately 4:1 is obtained i.e. the clutch shaft turns 4 times for each revolution of main shaft.
Second speed gear: By operating the gear shift lever the third gear on the main shaft is moved along the shaft to mesh with the third gear of the counter shaft. The main shaft turns in same direction as clutch shaft. A gear reduction of approximately 3:1is obtained.
Third speed gear: By operating the gear shift lever, the second gear of the main shaft and countershaft are demeshed and then the third gear of the main shaft are forced axially against the
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering clutch shaft gear. External Teeth on the clutch shaft gear mesh with the internal teeth in the third and top gear. The main shaft turns in same direction as clutch shaft. A gear reduction of approximately 2:1is obtained i.e. the clutch shaft turns 2 times for each revolution of main shaft. Fourth speed gear/ Top or High-Speed Gear: By operating the gear shaft lever the third gears of the main and countershaft is demeshed and the gears present on the main shaft along with the shaft is forced axially against the clutch shaft gear. External teeth present on the main shaft engage with the internal teeth present on the main shaft. The main shaft turns along with the clutch shaft and a gear ratio of approximately 1:1 is obtained. Reverse gear: By operating the gear shift lever, the last gear present on the main shaft is engaged with the reverse idler gear. The reverse idler gear is always in mesh with the counters haft gear. Interposing the idler gear between the counter-shaft reverse gear and main shaft gear, the main shaft turns in the direction opposite to the clutch shaft. This reverses the rotation of the wheels so that the wheel backs.
ii. Constant Mesh Gear Box: In this type of gear box, all gears of the main shaft are in constant mesh with the corresponding gears of the countershaft (Lay shaft). Two dog clutches are provided on the main shaft- one between the clutch gear and the second gear, and the other between the first gear and reverse gear. The main shaft is splined and all the gears are free on it. Dog clutch can slide on the shaft and rotates with it. All the gears on the countershaft are rigidly fixed with it. When the left hand dog clutch is made to slide to the left by means of the gear shift lever, it meshes with the clutch gear and the top speed gear is obtained. When the left hand dog clutch meshes with the second gear, the second speed gear is obtained. Similarly by sliding the right hand dog clutch to the left and right, the first speed gear and reverse gear are obtained respectively. In this gear box because all the gears are in constant mesh they are safe from being damaged and an unpleasant grinding sound does not occur while engaging and disengaging them.
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iii.Syncromesh Gear Box: In sliding Mesh Gear box the two meshing gears need to be revolve at equal peripheral speeds to achieve a jerk less engagement and it is true for constant mesh gear box in which the peripheral speeds of sliding dog and the corresponding gear on the output shaft must be equal. Thus there is a difference in gear and dog which necessitates double declutching. The driver has to disengage the clutch twice in quick succession therefore it is referred as double declutching. There are two steps involved in this process: M.I.E.T. /Mech. / III/AE
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The clutch is disengaged i.e. first declutching and the gear system is placed in its neutral position. Now the clutch is reengaged and acceleration pedal is pressed to adjust the engine speed according to driver‘s judgment. The clutch is disengaged (i.e. second declutching) again the appropriate gear is engaged and then the clutch is reengaged It is that gear box in which sliding synchronizing units are provided in place of sliding dog clutches as in case of constant mesh gear box. With the help of synchronizing unit, the speed of both the driving and driven shafts is synchronized before they are clutched together through train of gears. The arrangement of power flow for the various gears remains the same as in constant mesh gear box. The synchronizer is made of frictional materials. When the collar tries to mesh with the gear, the synchronizer will touch the gear first and use friction force to drive the gear to spin at the same speed as the collar. This will ensure that the collar is meshed into the gear very smoothly without grinding. Synchromesh gear devices work on the principle that two gears to be engaged are first bought into frictional contact which equalizes their speed after which they are engaged readily and smoothly.
3.4.3. Automatic Gearboxes This gear box system includes several sub-systems so that the gear ratio is automatically altered. The driver merely selects the direction of movement, and the gear ratio range. In the US, an automatic gearbox is often called an automatic transmission unit as it is synonymous with transmission. Most current automatic gearboxes use an epicyclic gear system, in which the required gear is obtained by holding or driving a part, or parts of the gear train by means of a friction clutch or brake. A hydraulic system controls the brakes and clutches. It incorporates its own sensing system, or uses an electronic sensor to monitor engine and vehicle operating conditions. Most automatic gear box systems use a torque converter between the engine and gearbox, in addition to the 3 or 4 speed epicyclic gearbox. The torque converter is generally a third clutch that replaces the conventional friction clutch. The two functions provided by the converter include (a) automatic disengagement of the engine from the transmission when the engine speed is less than 1000 rpm ; and (b) provision of an infinitely variable torque and speed ratio to bridge the steps between the discrete epicyclic gearbox ratios. In the UK the combination of an automatic gearbox and torque converter is called an automatic transmission system. 3.4.4. Gear shift mechanisms The following types of devices are mostly used in vehicles: Pin Type Synchronizer ring type A synchronizing system is used for smooth meshing. Synchromesh works like a friction clutch. In the following figure two conical surfaces cone-1 is the part of the collar and the cone-2 is the part of the gear wheel. Cone1, 2 are revolving at different speeds. While cone-2 is revolving, cone-1 gradually slides into it. Friction slows or speeds up the gear wheel. Finally both the cones revolve at same speed.
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It revolving at different speeds. The internal cone comes in contact with the outer cone of the gear wheel. Friction slows or speeds up the gear wheel. And when the collar and gear wheel rotate at same speed the spring loaded outer ring of the collar is pushed forward. The dog slide smoothly into mesh without clashing. The collar and gear wheel lock and revolve at same speed. This the principle of synchromesh.
3.5. Over drive Automatic Transmission: An automatic transmission (commonly "AT" or "Auto") is an automobile gearbox that can change gear ratios automatically as the vehicle moves, freeing the driver from having to shift gears manually. Automatic Transmission Modes: In order to select the mode, the driver would have to move a gear shift lever located on the steering column or on the floor next to him/her. In order to select gears/modes the driver must push a button in (called the shift lock button) or pull the handle (only on column mounted shifters) out. In some vehicles position selector buttons for each mode on the cockpit instead, freeing up space on the central console. Vehicles conforming to U.S. Government standards must have the modes ordered P-R-N-D-L (left to right, top to bottom, or clockwise). Prior to this, quadrant-selected automatic transmissions often utilized a P-N-D-L-R layout, or similar. Such a pattern led to a number of deaths and injuries owing to un-intentional gear miss-selection, as well the danger of having a selector (when worn) jump into Reverse from Low gear during engine braking maneuvers. Automatic Transmissions have various modes depending on the model and make of the transmission. Some of the common modes are: Park Mode (P):- This selection mechanically locks the transmission, restricting the car from moving in any direction. A parking pawl prevents the transmission—and therefore the vehicle—from moving, although the vehicle's non-drive wheels may still spin freely. For this reason, it is recommended to use the hand brake (or parking brake) because this actually locks the (in most cases, rear) wheels and prevents them from moving. This also increases the life of the transmission and the park pin mechanism, because parking on an incline with the transmission in park without the parking brake engaged will cause undue stress on the parking pin. An efficiently-adjusted hand brake should also prevent the car from moving if a worn selector accidentally drops into reverse gear during early morning fast-idle engine warm ups. Reverse (R):- This puts the car into the reverse gear, giving the ability for the car to drive backwards. In order for the driver to select reverse they must come to a complete stop, push the shift lock M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering button in (or pull the shift lever forward in the case of a column shifter) and select reverse. Not coming to a complete stop can cause severe damage to the transmission. Many modern automatic gearboxes have a safety mechanism in place, which does to some extent prevent (but doesn't completely avoid) inadvertently putting the car in reverse when the vehicle is moving. This mechanism usually consists of a solenoid-controlled physical barrier on either side of the Reverse position, which is electronically engaged by a switch on the brake pedal. Therefore, the brake pedal needs to be depressed in order to allow the selection of reverse. Some electronic transmissions prevent or delay engagement of reverse gear altogether while the car is moving. Neutral/No gear (N):- This disconnects the transmission from the wheels so the car can move freely under its own weight. This is the only other selection in which the car can be started. Drive (D):- This allows the car to move forward and accelerate through its range of gears. The number of gears a transmission has depends on the model, but they can commonly range from 3, 4 (the most common), 5, 6 (found in VW/Audi Direct Shift Gearbox), 7 (found in Mercedes 7G gearboxes, BMW M5 and VW/Audi Direct Shift Gearbox) and 8 in the newer models of Lexus cars. Some cars when put into D will automatically lock the doors or turn on the Daytime Running Lamps. Overdrive ([D], Od, Or A Boxed D):- This mode is used in some transmissions to allow early Computer Controlled Transmissions to engage the Automatic Overdrive. In these transmissions, Drive (D) locks the Automatic Overdrive off, but is identical otherwise. OD (Overdrive) in these cars is engaged under steady speeds or low acceleration at approximately 35-45 mph (approx. 72 km/h). Under hard acceleration or below 35-45 mph, the transmission will automatically downshift. Vehicles with this option should be driven in this mode unless circumstances require a lower gear. Second (2 or S):- This mode limits the transmission to the first two gears, or more commonly locks the transmission in second gear. This can be used to drive in adverse conditions such as snow and ice, as well as climbing or going down hills in the winter time. Some vehicles will automatically up-shift out of second gear in this mode if a certain rpm range is reached, to prevent engine damage. First (1 or L):- This mode locks the transmission in first gear only. It will not accelerate through any gear range. This, like second, can be used during the winter season, or for towing.
3.6. Transfer box A transfer case is a part of a four-wheel-drive system found in four-wheel-drive and all- wheel-drive vehicles. The transfer case is connected to the transmission and also to the front and rear axles by means of drive shafts.
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Construction: The input shaft is connected to the gear box and carries on it a member having axial teeth. Two input shaft gears are free to rotate on the shaft. Each of these gears have bosses on the side which have axial teeth of the same pitch as the central member on the input shaft. Depending upon the movement of the transfer box gear lever, the central member and thereby the input shaft may be connected either to the small gear or to the big gear. There are two output shafts, one going to the front axle and the second going to the rear axle. The front output shaft is smaller in diameter and is supported inside the rear output shaft which is directly connected to the output gear. The front output shaft has fitted on it a shifter mechanism and also has splines over a small length of it, which when engage with the corresponding internal splines on the rear output shaft, connect the two shafts rotationally with each other. Working: When the shifter mechanism A is in the centre so that no gear is connected to the input shaft, the drive is in neutral as shown in Fig.i. Fig.ii shows when the shifter mechanism A connects the input shaft with the big input gear, but the shifter mechanism B disconnects the front output of shaft from the rear output shaft. In this position, two-wheel drive with the high gear is obtained. In the same way Fig.iii depicts the situation with four wheel drive in low. 3.7. Fluid flywheel A liquid coupling is used to transmit engine turning effort (torque) to a clutch and transmission. The coupling is always a major part of the engine flywheel assembly. As such it is sometime called a fluid flywheel. 3.7.1. Construction of flywheel The fluid flywheel details can be seen in the picture. It consists of two half dough nut shaped shells equipped with interior fins. The fins radiate from the hub, and thereby form radial passages. The areas of these passages, perpendicular to their centre line, are kept constant by a suitable design. Since the circumferential width of the opening close to the hub is less than that at the periphery, the radial size of the opening, close to the hub is made greater than that at the periphery.
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
3.7.2. Working of fluid flywheel The driving unit, called impeller, is linked to the engine crankshaft. When the engine throttle is opened, the oil in the impeller starts moving. Due to the force of the rotating, trapped oil impinges on the fins of the driven unit called runner and causes it to move. In this way, the moving liquid transmits the engine power to the clutch driving plat or to any other unit to which the runner is attached. This happens without any metal contact. In the actual units, the runner speed becomes almost equal to that of the impeller only under the best operating conditions, when the efficiency of liquid coupling is highest. But usually the runner speed is less than that of the impeller. The (speed) lag of the runner behind the impeller is known as slip. This (speed) slip varies with many factors such as engine speed, vehicle speed and engine and vehicle load. Flywheel Torque The slip is greatest with the vehicle at rest (ie runner stationary), and the engine throttle being opened to cause the impeller to start circulating the oil. Under these conditions, the oil moves in two general directions at the same time. It rotates at right angles to the shafts, i.e., undergoes rotary flow. The oil also circulates between the impeller and runner, i.e., undergoes vortex flow. When the rotary flow attains sufficient force and volume, it causes the movement of the runner. The vortex flow is at right angles to the rotary flow. The vortex flow is produced by the oil trapped in the fins of the impeller. The oil flies out against the curved interior, because of centrifugal force. The centrifugal force directs the oil across to the runner, thereby returning it to the impeller in the region of the hub. The vortex flow is maximum when the slip is 100 percent (runner stationary), and decreases as the runner speed approaches that of the impeller. This results from the centrifugal force produced by the oil in the runner, which moves out and opposes the vortex flow. At cruising speeds, there is little or no vortex flow because the centrifugal forces produced in the impeller and runner are almost equal. As such, the efficiency of coupling increases rapidly from zero at rest to nearly 99 percent at higher speeds. Advantages of fluid flywheel An ordinary friction clutch would be damaged by prolonged slipping, with increased fuel consumption. But by prolonged slipping, the fluid flywheel will not suffer any mechanical damage. Although it may become so hot as to burn one‘s hand if one touched it. When a liquid coupling is used with a conventional clutch and transmission, it enables the driver to use the clutch and gears with less skill and fatigue than with an all mechanical linkage. Unskillful clutch engagement or selection of the improper gear will not produce any chattering and bucking. Any sudden load is cushioned and absorbed by the coupling so that dynamic stresses on the gear teeth of the transmission and rear (drive) axle are greatly reduced.
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
Liquid coupling at low speeds are not as efficient as mechanical clutch. As such it reduces engine braking when slowing down the vehicle speed, particularly during coming down a hilly track. Further, it requires higher speeds to start a vehicle by pushing or towing it. 3.8. Torque converter The predominant form of automatic transmission is hydraulically operated, using a fluid coupling/ torque converter and a set of planetary gear-sets to provide a range of torque multiplication. 3.8.1.Parts and Operation A hydraulic automatic transmission consists of the following parts: Torque Converter/Fluid Coupling Planetary Gear Set Clutch packs & Bands Valve Body Hydraulic or Lubricating Oil
Torque Converter/Fluid Coupling: -Unlike a manual transmission system, automatic transmission does not use a clutch to disconnect power from the engine temporarily when shifting gears. Instead, a device called a torque converter was invented to prevent power from being temporarily disconnected from the engine and also to pre-vent the vehicle from stalling when the transmission is in gear. A fluid coupling/torque converter consists of a sealed chamber containing two toroidal- shaped, vaned components, the pump and turbine, immersed in fluid (usually oil). The pump or driving torus (the latter a General Motors automotive term) is rotated by the prime mover, which is typically an internal combustion engine or electric motor. The pump's motion imparts a relatively complex centripetal motion to the fluid. Simplified, this is a centrifugal force that throws the oil outwards against the coupling's housing, whose shape forces the flow in the direction of the turbine or driven torus (the latter also a General Motors term). Here, Corolis force reaction transfers the angular fluid momentum outward and across, applying torque to the turbine, thus causing it to rotate in the same direction as the pump. The fluid leaving the center of the turbine returns to the pump, where the cycle endlessly repeats. The pump typically is connected to the flywheel of the engine—in fact, the coupling's enclosure may be part of the flywheel proper, and thus is turned by the engine's crankshaft. The turbine is connected to the input shaft of the transmission. As engine speed increases while the transmission is in gear, torque is transferred from the engine to the input shaft by the motion of
M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering the fluid, propelling the vehicle. In this regard, the behavior of the fluid coupling strongly resembles that of a mechanical clutch driving a manual transmission. A torque converter differs from a fluid coupling in that it provides a variable amount of torque multiplication at low engine speeds, increasing "breakaway" acceleration. This is accomplished with a third member in the "coupling assembly" known as the stator, and by altering the shapes of the vanes inside the coupling in such a way as to curve the fluid's path into the stator. The stator captures the kinetic energy of the transmission fluid in effect using the left- over force of it to enhance torque multiplication. 3.9. Propeller shaft The drive shaft, or propeller shaft, connects the transmission output shaft to the differential pinion shaft. Since all roads are not perfectly smooth, and the transmission is fixed, the drive shaft has to be flexible to absorb the shock of bumps in the road. Universal, or "U- joints" allow the drive shaft to flex (and stop it from breaking) when the drive angle changes. Drive shafts are usually hollow in order to weigh less, but of a large diameter so that they are strong. High quality steel, and sometimes aluminum are used in the manufacture of the drive shaft. The shaft must be quite straight and balanced to avoid vibrating. Since it usually turns at engine speeds, a lot of damage can be caused if the shaft is unbalanced, or bent. Damage can also be caused if the U-joints are worn out. There are two types of drive shafts, the Hotchkiss drive and the Torque Tube Drive. The Hotchkiss drive is made up of a drive shaft connected to the transmission output shaft and the differential pinion gear shaft. U-joints are used in the front and rear. The Hotchkiss drive transfers the torque of the output shaft to the differential. No wheel drive thrust is sent to the drive shaft. Sometimes this drive comes in two pieces to reduce vibration and make it easier to install (in this case, three U-joints are needed).The two-piece types need ball bearings in a dustproof housing as center support for the shafts. Rubber is added into this arrangement for noise and vibration reduction. The torque tube drive shaft is used if the drive shaft has to carry the wheel drive thrust. It is a hollow steel tube that extends from the transmission to the rear axle housing. One end is fastened to the axle housing by bolts. The transmission end is fastened with a torque ball. The drive shaft fits into the torque tube. A U-joint is located in the torque ball, and the axle housing end is splined to the pinion gear shaft. Drive thrust is sent through the torque tube to the torque ball, to transmission, to engine and finally, to the frame through the engine mounts. That is, the car is pushed forward by the torque tube pressing on the engine.
3.10. Slip joints
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
3.11. Universal joints A universal joint, U-joint, Cardan joint, Hardy-Spicer joint, or Hooke's joint is a linkage that transmits rotation between two non parallel shafts whose axes are coplanar but not coinciding., and is commonly used in shafts that transmit rotary motion. It is used in automobiles where it is used to transmit power from the gear box of the engine to the rear axle. The driving shaft rotates at a uniform angular speed, where as the driven shaft rotates at a continuously varying angular speed. A complete revolution of either shaft will cause the other to rotate through a complete revolution at the same time. Each shaft has fork at its end. The four ends of the two fork are connected by a centre piece, the arms of which rest in bearings, provided in fork ends. The centre piece can be of any shape of a cross, square or sphere having four pins or arms. The four arms are at right angle to each other. When the two shafts are at an angle other than 180° (straight), the driven shaft does not rotate with constant angular speed in relation to the drive shaft; the more the angle goes toward 90° the jerkier the movement gets (clearly, when the angle β = 90° the shafts would even lock). However, the overall average speed of the driven shaft remains the same as that of driving shaft, and so speed ratio of the driven to the driving shaft on average is 1:1 over multiple rotations. The angular speed ω2 of the driven shaft, as a function of the angular speed of the driving shaft ω1 and the angle of the driving shaft φ1, is found using: ω2 = ω1 cosα / (1-sin2α.cos2θ) For a given and set angle between the two shafts it can be seen that there is a cyclical variation in the input to output velocity ratio. Maximum values occur when sin θ = 1, i.e. when θ = 900 and 2700. The denominator is greatest when θ = 0or 1800 and this condition gives the minimum ratio of the velocities.
3.12. Differential
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
Differential is the main component of the power train. It is bolted on the rear axle and connects the propeller shaft to the rear wheels. While a vehicle taking a turn, its outer wheel run faster than the inner wheel. If we connects the propeller shaft by rear axle without using of differential gear, than the torque transmitted both the rear wheels is equal in any condition. So the both rear wheels will run at same speed while taking a turn which occur a problem in driving a vehicle. To eliminate this problem a device is used which is known as differential gear. Differential is the mechanism of gears by means of which outer wheel runs faster than the inner wheel while taking a turn or moving over upheaval road. It is a part of the driving axle housing assembly, which includes the differential, rear axles, wheels and bearings. It consists of a system of gear arranged in such a way that connects the propeller shaft with the rear axle and transmit the different torque to rear wheels if necessary. 3.12.1.Purpose The differential gear box has following functions: Avoid skidding of the rear wheels on a road turning. Reduces the speed of inner wheels and increases the speed of outer wheels, while drawing a curve. Keeps equal speeds of all the wheels while moving on a straight road. Eliminates a single rigid rear axle, and provides a coupling between two rear axles.
3.12.2. Construction of differential Differential is an arrangement of gears which work together and allow the vehicle to take a turn smoothly. In the differential, bevel pinion gear is fixed to the propeller shaft which rotates the crown wheel. The crown wheel has another unit called the differential unit. It consists of two bevel gears (sun gear) and two bevel gears (planet gear). The bevel gears are in contact with the half shaft of the rear axle. When the crown wheel is rotating, it rotates the differential unit. The bevel (sun) gears of the differential rotate the two shafts. 3.12.3. Working of differential When the car is on a straight road, the ring gear, differential case, differential pinion gears, and two differential side gears all turn as a unit. The two differential pinion gears do not rotate on the pinion shaft. This is because they exert equal force on the two differential side gears. As a result the side gears turn at the same speed as the ring gear, which causes both drive wheels to turn at M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering the same speed also. However, when the car begins to round a curve, the differential pinion gears rotate on the pinion shaft. This permits the outer wheel to turn faster than the inner wheel. 3.13. Rear axle Rear axle is the last member of power train. In most of automobiles, real axle is the driving axle. It lies between the driving wheels and the differential gear and transmit power from the differential to the driving wheels. It consists of two half shaft connected to the differential gear, one for one wheel. The inner end of the each half shaft connected to the sun gear of the differential and the outer end to the wheel. The rear axle and differential gear are completely encloses in a housing which protecting them from water, dust and injury. 3.13.1.Function of rear axle The rear axle mainly performs following two functions. 1. It carries the weight of the vehicle. 2. It rotates and transmits the power from the engine to the wheels. 3.13.2. Classification of rear axle Rear axle classified by two methods. 1. According to the design of axle: (A.) Banjo axle: This type of axle is a single shaft and final drive assembly is carried in a separate casing which is bolted to the axle housing. The banjo construction is often used for smaller and lighter vehicle. (B.) Split axle: In this type of axle split shaft are used with the central housing contain the differential gear and it is fitted with a tube on each side to carry the half axles and bearing. 2. According to the method of supporting: (A.) Half floating rear axle: In this axle the bearing which support the axle, are inside the casing. The axle of the wheel is at the center of the axle casing. The whole weight of the vehicle is first transmitted to the suspension spring then to the axle casing, rear axle, wheel and ground. (B.) Three quarter floating rear axle: In this axle bearing are on the outer side of casing between the wheel and the axle casing. The wheels are fitted at the end of the axle by means of a key, bolt or nut. The weight of the vehicle is supported partly by the axle casing and partly by the axle. The main advantage of this type of axle over the half floating axle is that the major part of the load is taken by the axle casing and not by axle. Axle only takes care of the rotating and transmits the power.
(C.) Full floating rear axle: In this type of axle bearing are on the outer side of casing between the wheel and the axle casing. The axle is not supported by the bearing at entire end and its
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering position is maintained by the way that it is supported at both ends. The wheels are fitted at the end of the axle by means of a key, bolt or nut. Thus the entire weight of the vehicle is supported by the wheel and axle casing. The axle is relieved of all strain caused by the weight of the vehicle on end thrust. It transmits only driving torque.
3.14. Hotchkiss Drive The Hotchkiss drive is a system of power transmission. It was the dominant form of power transmission for front-engine, rear-wheel drive layout cars in the 20th century. The name comes from the French automobile firm of Hotchkiss, although it is clear that other makers (such as Peerless) used similar systems before Hotchkiss. During the early part of the 20th century the two major competing systems of power transmission were the shaft-drive and chain-drive configurations. The Hotchkiss drive is a shaft- drive system (another type of direct-drive transmission system is the torque tube, which was also popular until the 1950s). All shaft-drive systems consist of a driveshaft (also called a "propeller shaft" or Cardan shaft) extending from the transmission in front to the differential in the rear. The differentiating characteristic of the Hotchkiss drive is the fact that it uses universal joints at both ends of the driveshaft, which is not enclosed. The use of two universal joints, properly phased and with parallel alignment of the drive and driven shafts, allows the use of simple cross- type universals. (In a torque-tube arrangement only a single universal is used at the end of the transmission tail shaft, and this universal should be a constant velocity joint.) In the Hotchkiss drive, slip-splines or a plunge-type (ball and trunnion u-joint) eliminate thrust transmitted back up the driveshaft from the axle, allowing simple rear-axle positioning using parallel leaf springs. (In the torque-tube type this thrust is taken by the torque tube to the transmission and thence to the transmission and motor mounts to the frame. While the torque- tube type requires additional locating elements, such as a Panhard rod, this allows the use of coil springs.) Some Hotchkiss drive shafts are made in two pieces with another universal joint in the center for greater flexibility, typically in trucks and specialty vehicles built on truck frames. Some installations use rubber mounts to isolate noise and vibration. The 1984–1987 RWD Toyota Corolla (i.e., Corolla SR5 and GT-S) coupe is another example of a car that uses a 2-part Hotchkiss driveshaft with a rubber-mounted center bearing. This design was the main form of power transmission for most cars from the 1920s through the 1970s. Presently (circa 2012), it remains common in pick-up trucks, and sport utility vehicles.
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
3.15. Torque Tube Drive A torque tube system is a driveshaft technology, often used in automobiles with a front engine and rear drive. It is not as widespread as the Hotchkiss drive, but is still occasionally used to this day. Drive shafts are sometimes also used for other vehicles and machinery. The "torque" that is referred to in the name is not that of the driveshaft, along the axis of the car, but that applied by the wheels. The design problem that the torque tube solves is how to get the traction forces generated by the wheels to the car frame. The "torque tube" transmits this force by directly coupling the axle differential to the transmission and therefore propels the car forward by pushing on the engine/transmission and then through the engine mounts to the car frame. In contrast, the Hotchkiss drive has the traction forces transmitted to the car frame by using other suspension components such as leaf springs or trailing arms. A ball and socket type of joint called a "torque ball" is used at one end of the torque tube to allow relative motion between the axle and transmission due to suspension travel. Since the torque tube does not constrain the axle in the lateral (side-to-side) direction a pan hard rod is often used for this purpose. The combination of the pan hard rod and the torque tube allows the easy implementation of soft coil springs in the rear to give good ride quality. In addition to transmitting the traction forces, the torque tube is hollow and contains the rotating driveshaft. Inside the hollow torque ball is the universal joint of the driveshaft that allows relative motion between the two ends of the driveshaft. In most applications the drive shaft uses a single universal joint which has the disadvantage that it causes speed fluctuations in the driveshaft when the shaft is not straight. The Hotchkiss drive uses two universal joints which has the effect of cancelling the speed fluctuations and gives a constant speed even when the shaft is no longer straight.
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
UNIT - IV STEERING, BRAKES AND SUSPENSION SYSTEMS
Steering geometry and types of steering gear box-Power Steering, Types of Front Axle, Types of Suspension Systems, Pneumatic and Hydraulic Braking Systems, Antilock Braking System (ABS), electronic brake force distribution (EBD) and Traction Control.
4.1. Steering geometry Steering geometry is the term manufacturers use to describe steering and wheel alignment. The six fundamental angles or specifications that are required for a proper wheel alignment are as follows: Caster Camber Toe Steering Axis Inclination Toe-Out On Turns Tracking 4.1.1. Castor Definition :- The angle between the king pin centre line (or steering axis) and the vertical, in the plane of the wheel is called the castor angle. If the king pin centre line meets the ground at a point in form of wheel is called positive castor while it is behind the wheel centre line it is called negative castor. Effect:- In rear-wheel drive vehicle, the steering axis pulls the front tyres, whereas the tire drag on account of the vehicle weight is on the vertical line at the centre of the footprint. Since in positive castor steering axis would meet the ground ahead of the centre of tire print, the later would always follow the former. Thus positive castor on the car wheels provides directional stability. Castor has another effect also, when the vehicle having positive castor takes a turn, the outer side of the vehicle is lowered while the inner one is raised i.e. positive castor help the centrifugal force is rolling out the vehicle. Negative castor tends to ‗roll-in‘ the vehicle i.e. the effect of centrifugal force is counteracted. The basic purposes for caster are as follows: To aid directional control of the vehicle To cause the wheels to return to the straight-ahead position To offset road crown pull (steering wheel pull caused by the slope of the road surface)
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
Caster is measured in DEGREES starting at the true vertical (plumb line). Manufacturers give specifications for caster as a specific number of degrees positive or negative. Typically, specifications list more positive caster for vehicles with power steering and more negative caster for vehicles with manual steering (to ease steering effort). Depending upon the vehicle manufacturer and type of suspension, caster may be adjusted by using wedges or shims, eccentric cams, or adjustable struts. Negative caster tilts the top of the steering knuckle toward the front of the vehicle. With negative caster, the wheels will be easier to turn. However, the wheels tend to swivel and follow imperfections in the road surface. Positive caster tilts the top of the steering knuckle towards the rear of the vehicle. Positive caster helps keep the wheels of the vehicle traveling in astraight line. When you turn the wheels, it lifts the vehicle. Since this takes extra turning effort. the wheels resist turning and try to return to the straight-ahead position. 4.1.2. Camber Definition: – Camber is the tilt of the car wheels from the vertical. Camber is positive if the tilt is outward at the top. Camber is also called ‗wheel rake‘. Effect: – It is always desirable that tyres should roll on the ground vertically so that the wear is uniform. If while running, the tyres are uninclined from the vertical either inward or outward, they wear more on one side than the other. Amount: – Camber should not generally exceed 2°. However, the exact amount of camber is specified taking into account the king pin inclination. Camber is the inward and outward tilt of the wheel and tire assembly when viewed from the front of the vehicle. It controls whether the tire tread touches the road surface evenly. Camber is a tire-wearing angle measured in degrees. The purposes for camber are as follows: To aid steering by placing vehicle weight on the inner end of the spindle To prevent tire wear on the outer or inner tread To load the larger inner wheel bearing Positive and negative camber (fig. 8-49) is measured from the true vertical (plumb line). If the wheel is aligned with the plumb line, camber is zero. With positive camber, the tops of the wheels tilt outward when viewed from the front, With negative camber, the tops of the wheels tilt inward when viewed from the front. Most vehicle manufacturers suggest a slight positive camber setting from a 1/ 4 to a 1/ 2 degree. Suspension wear and above normal curb weight caused by several passengers or heavy loads tend to increase negative camber. Positive camber counteracts this.
4.1.3. Toe-In Or Toe-Out Definition :- Toe-in is the amount by which the wheels are set closer together at the front than at the rear when the vehicle is stationary. On the other hand, the wheel may be set closer at the rear than at the form in which case the difference of the distances between the front wheels at the from and at the rear is called toe-out. M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
Effect:- There is usually an inherent tendency for the wheels to toe-out because of purposeful deviation from centre point steering and also due to errors in steering angles of the inner and outer wheels on moderate bends. To offset this tendency a small amount of toe-in is initially provided so that the wheels move perfectly straight ahead under normal running conditions. However in case of some front wheel drive cars, initial toe-out has been provided to counter the tendency to toe-in present therein. The toe-in or toe-out as provided is sometimes called wheel alignment. Amount:- Toe-in initially provided generally does not exceed 3mm. Toe : Toe is determined by the difference in distance between the front and rear of the left and right side wheels. Toe controls whether the wheels roll in the direction of travel. Of all the alignment factors, toe is the most critical. If the wheels do NOT have the correct toe setting, the tires will scuff or skid sideways. Toe is measured in fractions of an inch or millimeters. TOE-IN is produced when the front wheels are closer together in the front than at the rear, when measured at the hub height. Toe-in causes the wheels to point inward at the front. TOE-OUT results when the front of the wheels are farther apart than the rear. Toe-out causes the front of the wheels to point away from each other. The type of drive (rear or front wheel) determines the toe settings. Rear-wheel drive vehicles are usually set to have TOE-IN at the front wheels. This design is due to as a result of the front wheels moving outward while driving, resulting in toe-out. By adjusting the wheels for a slight toe-in (1/ 16 to 1/ 4 in.), the wheels and tires will roll straight ahead when driving.
Front-wheel drive vehicles require different adjustment for toe. This is due to the front wheels driving the vehicle and are pushed forward by engine torque. This makes the wheel toe- in or point inward while driving. To compensate for this. front-wheel drive vehicles have the front wheels adjusted for a slight toe-out (1/ 16 inch). This adjustment will give the front end a zero toe setting. as the vehicle travels down the road. 4.1.4. King Pin Inclination (Steering Axis Inclination):- Definition: – Inclination of the king pin from vertical is called the king pin inclination or king pin rake. In modem cars where the king pin has been replaced by the ball joints, this term has also been renamed as ‗Steering Axis Inclination‘ and is defined as the inclination of the ball joint-axis from the vertical. Steering axis is an imaginary line drawn through the lower and the upper steering pivot points. Effect: – King pin inclination (or steering axis inclination) helps the straight ahead recovery, thus providing directional stability. When the vehicle takes a turn, the inclination of king pin causes the vehicle body to move up, in relation to the wheel. So as soon as the steering wheel is left after the turn is completed, the weight of the vehicle tends to return the wheels to the straight position. Amount: – About 7 to 8 degrees. However the exact amount is decided considering the wheel rake value. M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
4.1.5. Combined Angle and Scrub Radius Definition: – Combined angle or included angle is the formed in the vertical plane between the wheel centre line and the king pin centre line (or steering axis). Combined angle is equal to camber plus king pin inclination (or steering axis inclination). Effect: – The effect of combined angle variation on scrub radius and hence on the forces acting to turn the wheel in case of a rear-wheel drive. It is seen that unless scrub radius is zero a torque acts to turn the wheel away from the straight ahead position. Amount: – Combined angle may be 9-10 degrees and the scrub radius should be up to about 12mm. 4.1.6. Other Important Steering Geometries Terminologies Slip Angle: The angle between direction of the motion of the vehicle and the centre plane of the tyre is known as Slip Angle. It ranges from 8º to 10º. Under steer: When the front slip angle is greater than that of rear, the vehicle tends to steer in the direction of side force. Then it is known as under steer. This provides greater driving stability, especially when there is a side wind. Over Steer: When the rear slip angle is greater than that of front slip angle, the vehicle tends to move away from the direction of centre path. This is known as over steer. This is advantageous when the vehicle moving on the road having many bends curves. Steering Gear Ratio or Reduction Ratio: It has been defined as the ―number of turns on the steering wheel required to produce on turn of steering gear cross shaft to which the pitman arm is attached. Generally it varies between 14′.1 and 24′.1. Turning Radius: It is the radius of the circle on which the outside front wheels moves when the front wheels are turned to their extreme outer position. This radius is 5m to 7.5m for buses and trucks. Wheel Alignment: It returns to the positioning of the front wheels and steering mechanism that gives the vehicle directional stability; reduce the tyre wear to a minimum. 4.2. Steering Gear Boxes The steering gears convert the rotary motion of the steering wheel into the to-and-fro motion of the link rod of the steering linkages. Moreover it also provides necessary leverage so that the driver is able to steer the vehicle without fatigue.
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
4.3. Types of Steering Gear Boxes There are various types of steering gear boxes are available in automobile. Worm and Wheel steering gear box, Cam and double roller steering gear box, Worm and nut steering gear box, Recalculating ball type steering gear box, Rack and pinion steering gear box, 4.4. Power steering In automobiles, power steering (also known as power assisted steering (PAS) or steering assist system) helps drivers steer by augmenting steering effort of the steering wheel.
Hydraulic or electric actuators add controlled energy to the steering mechanism, so the driver needs to provide only modest effort regardless of conditions. Power steering helps considerably when a vehicle is stopped or moving slowly. Also, power steering provides some feedback of forces acting on the front wheels to give an ongoing sense of how the wheels are interacting with the road; this is typically called "rοad feel". Representative power steering systems for cars augment steering effort via an actuator, a hydraulic cylinder, which is part of a servo system. These systems have a direct mechanical connection between the steering wheel and the linkage that steers the wheels. This means that power-steering system failure (to augment effort) still permits the vehicle to be steered using manual effort alone. Other power steering systems (such as those in the largest off-road construction vehicles) have no direct mechanical connection to the steering linkage; they require power. Systems of
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering this kind, with no mechanical connection, are sometimes called "drive by wire" or "steer by wire", by analogy with aviation's "fly-by-wire". In this context, "wire" refers to electrical cables that carry power and data, not thin-wire-rope mechanical control cables. In other power steering systems, electric motors provide the assistance instead of hydraulic systems. As with hydraulic types, power to the actuator (motor, in this case) is controlled by the rest of the power-steering system. Some construction vehicles have a two-part frame with a rugged hinge in the middle; this hinge allows the front and rear axles to become non-parallel to steer the vehicle. Opposing hydraulic cylinders move the halves of the frame relative to each other to steer. Power steering helps the driver of a vehicle to steer by directing some of the power to assist in swiveling the steered road wheels about their steering axes. As vehicles have become heavier and switched to front wheel drive, particularly using negative offset geometry, along with increases in tire width and diameter, the effort needed to turn the wheels about their steering axis has increased, often to the point where major physical exertion would be needed were it not for power assistance. To alleviate this auto makers have developed power steering systems: or more correctly power-assisted steering—on road going vehicles there has to be a mechanical linkage as a failsafe. 4.4. 1. Types of Power steering There are two types of power steering systems; Hydraulic power steering systems and Electric/electronic power steering systems. Hydraulic power steering (HPS): A hydraulic-electric hybrid system is also possible. A hydraulic power steering (HPS) uses hydraulic pressure supplied by an engine-driven pump to assist the motion of turning the steering wheel.
Electric power steering (EPS): Electric power steering (EPS) is more efficient than the hydraulic power steering, since the electric power steering motor only needs to provide assistance when the steering wheel is turned, whereas the hydraulic pump must run constantly. In EPS, the amount of assistance is easily tunable to the vehicle type, road speed, and even driver preference. An added benefit is the elimination of environmental hazard posed by leakage and disposal of hydraulic power steering fluid. In addition, electrical assistance is not lost when the engine fails or stalls, whereas hydraulic assistance stops working if the engine stops, making the steering doubly heavy as the driver must now turn not only the very heavy steering—without any help—but also the power-assistance system itself. 4.4.2. Sensitive Steering
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An outgrowth of power steering is speed sensitive steering, where the steering is heavily assisted at low speed and lightly assisted at high speed. The auto makers perceive that motorists might need to make large steering inputs while manoeuvring for parking, but not while travelling at high speed. The first vehicle with this feature was the Citroën SM with layout, although rather than altering the amount of assistance as in modern power steering systems, it altered the pressure on a centring cam which made the steering wheel try to "spring" back to the straight- ahead position. Modern speed-sensitive power steering systems reduce the mechanical or electrical assistance as the vehicle speed increases, giving a more direct feel. This feature is gradually becoming more common. 4.5. Front axle A set of subassemblies or a separate chassis assembly on self-propelled wheeled vehicles (automobiles, tractors) that connects the front part of the frame or load-carrying body to the front wheels. The design of a front axle depends on the type of suspension. With conventional spring suspension, the front axle is a rigid unsprung beam to which the wheel hubs are attached by means of steering knuckles and kingpins. With independent suspension the front axle is replaced by a load-carrying transverse frame member to which hinged rocker arms are attached. On four-wheel-drive vehicles the front axle is powered as well as the rear axle. In this type of construction the load-carrying beam of the front axle is rigidly joined to the transmission housing. Short semiaxles are connected to the wheels by means of special constant-velocity joints. On rough terrain, the front axle can be connected through a transfer case with a separate shift lever.
Functions of Front Axle It supports the weight of front part of the vehicle. It facilitates steering It absorbs shocks which are transmitted due to road surface irregularities. It absorbs torque applied on it due to braking of vehicle. 4.5.1. Types of Front axle 1. Dead front axle : Dead axles are those axles, which do not rotate. These axles have sufficient rigidity and strength to take the weight. The ends of front axle are suitably designed to accommodate stub axles. In which there is no connection with the engine and having no differential mechanism. The front dead axles are four types : (i) Elliot axle, (ii) Reverse type, (iii) Lemoine, (iv) Reversed lamoine type. 2. Line Front axle: Line axles are used to transmit power from gear box to front wheels. Line front axles although, front wheels. This axles although resemble rear axles but they are different at the ends where wheels are mounted. Maruti-800 has line front axle.
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Stub Axle: Stub axles are connected to the front axle by king pins. Front wheels are mounted on stub axle’s arrangement for steering is connected to stub axles. Stub axle turns on kind pins. King pins is fitted in the front axle beam eye and is located and locked there by a taper cotter pin 4.6. Suspension system Suspension system is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. It is basically cushioned for passengers protects the luggage or any cargo and also itself from damage and wear. Sir William Brush is the father of suspension system in automobiles. The main roles of suspension system are as follows: It supports the weight of vehicle. Provides smoother ride for the driver and passengers i.e. acts as cushion. Protects your vehicle from damage and wear. It also plays a critical role in maintaining self driving conditions. It also keeps the wheels pressed firmly to the ground for traction. It isolates the body from road shocks and vibrations which would otherwise be transferred to the passengers and load. 4.6.1. Principles of Suspension system When a tire hits an obstruction, there is a reaction force. The size of this reaction force depends on the unsprung mass at each wheel assembly.In general, the larger the ratio of sprung weight to unsprung weight, the less the body and vehicle occupants are affected by bumps, dips, and other surface imperfections such as small bridges. A large sprung weight to unsprung weight ratio can also impact vehicle control. No road is perfectly flat i.e. without irregularities. Even a freshly paved highways have subtle imperfections that can be interact with vehicle‘s wheels. These are the imperfections that apply forces on wheels. According to Newton ‘s law of motion all forces have both magnitude and direction. A bump in the road causes the wheel to move up and down perpendicular to the road surface. The magnitude of course ,depends on whether the wheel is striking a giant bump or a tiny speck. Thus, either the wheel experiences a vertical acceleration as it passes over an imperfection. The suspension of a car is actually part of the chassis, which comprises all of the important systems located beneath the car's body. These system include : Frame Suspension system Steering system Tires or Wheels
4.6.2. Components of Suspension system; There are three fundamental components of any suspension system. M.I.E.T. /Mech. / III/AE
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Springs Coil spring Leaf springs Air springs Dampers Shock Absorbers Struts:- Anti-sway Bars Anti sway bars. 4.6.3. Types of Suspension system Suspension systems are divided into three categories Dependent Semi Independent and Independent suspension system. Independent suspension system: Easy way to put them will be movement of one tyre doesn't affect the other one. These are also of many types like McPherson strut- used in mid level cars, double wishbone suspensions - now mostly used in 4-wheelers, leaf springs- used in heavy vehicles. The variety of independent systems is greater and includes: Swing axle, Sliding pillar, MacPherson strut/Chapman strut, Upper and lower A-arm (double wishbone), Multi-link suspension, Semi-trailing arm suspension, Swinging arm, Leaf springs Transverse. Semi Independent suspension system: In a semi-independent suspensions, the wheels of an axle are able to move relative to one another as in an independent suspension but the position of one wheel has an effect on the position and attitude of the other wheel. This effect is achieved via the twisting or deflecting of suspension parts under load. The most common type of semi- independent suspension is the twist beam. Dependent suspension system: If one tyre moves, other shows movement corresponding to that. These are not in much use nowadays but being cheaper compared to independent, they can be used. Examples of location linkages include: Satchell link, Panhard rod, Watt's linkage, WOBLink, Mumford linkage.
4.6.4. Advantages of Suspension systems Comfort to passengers Good handling Shields the vehicle from damage Increases life of vehicle M.I.E.T. /Mech. / III/AE
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Keeps the tires pressed firmly to ground.
4.7. Braking System A brake is a mechanical device which inhibits motion, slowing or stopping a moving object or preventing its motion. The rest of this article is dedicated to various types of vehicular brakes. Most commonly brakes use friction between two surfaces pressed together to convert the kinetic energy of the moving object into heat, though other methods of energy conversion may be employed. For example regenerative braking converts much of the energy to electrical energy, which may be stored for later use. Other methods convert kinetic energy into potential energy in such stored forms as pressurized air or pressurized oil. Eddy current brakes use magnetic fields to convert kinetic energy into electric current in the brake disc, fin, or rail, which is converted into heat. Still other braking methods even transform kinetic energy into different forms, for example by transferring the energy to a rotating flywheel. Brakes are generally applied to rotating axles or wheels, but may also take other forms such as the surface of a moving fluid (flaps deployed into water or air). Some vehicles use a combination of braking mechanisms, such as drag racing cars with both wheel brakes and a parachute, or airplanes with both wheel brakes and drag flaps raised into the air during landing. Friction (pad/shoe) brakes are often rotating devices with a stationary pad and a rotating wear surface. Common configurations include shoes that contract to rub on the outside of a rotating drum, such as a band brake; a rotating drum with shoes that expand to rub the inside of a drum, commonly called a "drum brake", although other drum configurations are possible; and pads that pinch a rotating disc, commonly called a "disc brake". 4.7.1 Types of Braking system By applications 1. Foot Brake, 2. Hand brake. By Method of power 1. Mechanical brake, 2. Hydraulic brake. 3. Vacuum brake, 4. Electrical brake and 5. Air brake. By method of operations 1. Manual brake, 2. Servo brake. 3. Power operation. By construction 1. Drum type brake 2. Disc type brake. 4.8. Anti-lock braking system (ABS) Anti-lock braking system (ABS) is an automobile safety system that allows the wheels on a motor vehicle to maintain tractive contact with the road surface according to driver inputs while braking, preventing the wheels from locking up (ceasing rotation) and avoiding uncontrolled skidding. It is an automated system that uses the principles of threshold braking and
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering cadence braking which were practiced by skillful drivers with previous generation braking systems. It does this at a much faster rate and with better control than a driver could manage. ABS generally offers improved vehicle control and decreases stopping distances on dry and slippery surfaces for many drivers; however, on loose surfaces like gravel or snow-covered pavement, ABS can significantly increase braking distance, although still improving vehicle control. Since initial widespread use in production cars, anti-lock braking systems have evolved considerably. Recent versions not only prevent wheel lock under braking, but also electronically control the front-to-rear brake bias. This function, depending on its specific capabilities and implementation, is known as electronic brake force distribution (EBD), traction control system, emergency brake assist, or electronic stability control(ESC). 4.8.1. Operation of ABS The anti-lock brake controller is also known as the CAB (Controller Anti-lock Brake). Typically ABS includes a central electronic control unit (ECU), four wheel speed sensors, and at least two hydraulic valves within the brake hydraulics. The ECU constantly monitors the rotational speed of each wheel; if it detects a wheel rotating significantly slower than the others, a condition indicative of impending wheel lock, it actuates the valves to reduce hydraulic pressure to the brake at the affected wheel, thus reducing the braking force on that wheel; the wheel then turns faster. Conversely, if the ECU detects a wheel turning significantly faster than the others, brake hydraulic pressure to the wheel is increased so the braking force is reapplied, slowing down the wheel. This process is repeated continuously and can be detected by the driver via brake pedal pulsation. Some anti-lock systems can apply or release braking pressure 15 times per second Because of this, the wheels of cars equipped with ABS are practically impossible to lock even during panic braking in extreme conditions. The ECU is programmed to disregard differences in wheel rotative speed below a critical threshold, because when the car is turning, the two wheels towards the center of the curve turn slower than the outer two. For this same reason, a differential is used in virtually all roadgoing vehicles. If a fault develops in any part of the ABS, a warning light will usually be illuminated on the vehicle instrument panel, and the ABS will be disabled until the fault is rectified. Modern ABS applies individual brake pressure to all four wheels through a control system of hub-mounted sensors and a dedicated micro-controller. ABS is offered or comes standard on most road vehicles produced today and is the foundation for electronic stability control systems, which are rapidly increasing in popularity due to the vast reduction in price of vehicle electronics over the years. Modern electronic stability control systems are an evolution of the ABS concept. Here, a minimum of two additional sensors are added to help the system work: these are a steering wheel angle sensor, and a gyroscopic sensor. The theory of operation is simple: when the gyroscopic sensor detects that the direction taken by the car does not coincide with what the steering wheel sensor reports, the ESC software will brake the necessary individual wheel(s) (up to three with the most sophisticated systems), so that the vehicle goes the way the driver intends. The steering wheel sensor also helps in the operation of Cornering Brake Control (CBC), since this will tell the ABS that wheels on the inside of the curve should brake more than wheels on the outside, and by how much.
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ABS equipment may also be used to implement a traction control system (TCS) on acceleration of the vehicle. If, when accelerating, the tire loses traction, the ABS controller can detect the situation and take suitable action so that traction is regained. More sophisticated versions of this can also control throttle levels and brakes simultaneously. 4.8.2. Components of ABS There are four main components of ABS: Speed sensors, Valves, Pump, and Controller.
Speed sensors: A speed sensor is used to determine the acceleration or deceleration of the wheel. These sensors use a magnet and a coil of wire to generate a signal. The rotation of the wheel or differential induces a magnetic field around the sensor. The fluctuations of this magnetic field generate a voltage in the sensor. Since the voltage induced in the sensor is a result of the rotating wheel, this sensor can become inaccurate at slow speeds. The slower rotation of the wheel can cause inaccurate fluctuations in the magnetic field and thus cause inaccurate readings to the controller. Valves: There is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three positions: In position one, the valve is open; pressure from the master cylinder is passed right through to the brake. In position two, the valve blocks the line, isolating that brake from the master cylinder. This prevents the pressure from rising further should the driver push the brake pedal harder. In position three, the valve releases some of the pressure from the brake. The majority of problems with the valve system occur due to clogged valves. When a valve is clogged it is unable to open, close, or change position. An inoperable valve will prevent the system from modulating the valves and controlling pressure supplied to the brakes. Pump: The pump in the ABS is used to restore the pressure to the hydraulic brakes after the valves have released it. A signal from the controller will release the valve at the detection of wheel slip. After a valve release the pressure supplied from the user, the pump is used to restore a desired amount of pressure to the braking system. The controller will modulate the pumps status in order to provide the desired amount of pressure and reduce slipping. Controller: The controller is an ECU type unit in the car which receives information from each individual wheel speed sensor, in turn if a wheel loses traction the signal is sent to the controller, the controller will then limit the brake force (EBD) and activate the ABS modulator which actuates the braking valves on and off.
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Use : There are many different variations and control algorithms for use in ABS. One of the simpler systems works as follows, The controller monitors the speed sensors at all times. It is looking for decelerations in the wheel that are out of the ordinary. Right before wheel locks up, it will experience a rapid deceleration. If left unchecked, the wheel would stop much more quickly than any car could. It might take a car five seconds to stop from 60 mph (96.6 km/h) under ideal conditions, but a wheel that locks up could stop spinning in less than a second. The ABS controller knows that such a rapid deceleration is impossible, so it reduces the pressure to that brake until it sees acceleration, then it increases the pressure until it sees the deceleration again. It can do this very quickly, before the tire can actually significantly change speed. The result is that the tire slows down at the same rate as the car, with the brakes keeping the tires very near the point at which they will start to lock up. This gives the system maximum braking power. This replaces the need to manually pump the brakes while driving on a slippery or a low traction surface, allowing steering even in the most emergency braking conditions. When the ABS is in operation the driver will feel a pulsing in the brake pedal; this comes from the rapid opening and closing of the valves. This pulsing also tells the driver that the ABS has been triggered. Some ABS systems can cycle up to 16 times per second. 4.9. Hydraulic braking system The disc brake or disk brake is a device for slowing or stopping the rotation of a wheel while it is in motion. A brake disc (or rotor in U.S. English) is usually made of cast iron, but may in some cases be made of composites such as reinforced carbon-carbon or ceramic-matrix composites. This is connected to the wheel and/or the axle. To stop the wheel, friction material in the form of brake pads (mounted on a device called a brake caliper) is forced mechanically, hydraulically, pneumatically or electromagnetically against both sides of the disc. Friction causes the disc and attached wheel to slow or stop. Brakes (both disc and drum) convert motion to heat, but if the brakes get too hot, they will become less effective because they cannot dissipate enough heat. This condition of failure is known as brake fade. 4.9.1. Construction of HBS The most common arrangement of hydraulic brakes for passenger vehicles, motorcycles, scooters, and mopeds, consists of the following: Brake pedal or lever A pushrod (also called an actuating rod) A master cylinder assembly containing a piston assembly Reinforced hydraulic lines Brake caliper assembly usually consisting of one or two hollow aluminum or chrome- plated steel pistons (called caliper pistons), a set of thermally conductive brake pads and a rotor (also called a brake disc) or drum attached to an axle.The system is usually filled with a glycol- ether based brake fluid (other fluids may also be used). At one time, passenger vehicles commonly employed drum brakes on all four wheels. Later, disc brakes were used for the front and drum brakes for the rear. However disc brakes have shown better heat dissipation and greater resistance to 'fading' and are therefore generally safer than drum brakes. So four-wheel disc brakes have become increasingly popular, replacing
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering drums on all but the most basic vehicles. Many two-wheel vehicle designs, however, continue to employ a drum brake for the rear wheel. The following description uses the terminology for and configuration of a simple In a hydraulic brake system, when the brake pedal is pressed, a pushrod exerts force on the piston(s) in the master cylinder, causing fluid from the brake fluid reservoir to flow into a pressure chamber through a compensating port. This results in an increase in the pressure of the entire hydraulic system, forcing fluid through the hydraulic lines toward one or more calipers where it acts upon one or two caliper pistons sealed by one or more seated O-rings (which prevent leakage of the fluid). The brake caliper pistons then apply force to the brake pads, pushing them against the spinning rotor, and the friction between the pads and the rotor causes a braking torque to be generated, slowing the vehicle. Heat generated by this friction is either dissipated through vents and channels in the rotor or is conducted through the pads, which are made of specialized heat- tolerant materials such as kevlar or sintered glass. Subsequent release of the brake pedal/lever allows the spring(s) in my master cylinder assembly to return the master piston(s) back into position. This action first relieves the hydraulic pressure on the caliper, then applies suction to the brake piston in the caliper assembly, moving it back into its housing and allowing the brake pads to release the rotor. The hydraulic braking system is designed as a closed system: unless there is a leak in the system, none of the brake fluid enters or leaves it, nor does the fluid get consumed through use.
4.10. Pneumatic braking system An air brake or, more formally, a compressed air brake system, is a type of friction brake for vehicles in which compressed air pressing on a piston is used to apply the pressure to the brake pad needed to stop the vehicle. Air brakes are used in large heavy vehicles, particularly those having multiple trailers which must be linked into the brake system, such as trucks, buses, trailers, and semi-trailers in addition to their use in railroad trains. George Westinghouse first developed air brakes for use in railway service. He patented a safer air brake on March 5, 1872. Westinghouse made numerous alterations to improve his air pressured brake invention, which led to various forms of the automatic brake. In the early 20th century, after its advantages were proven in railway use, it was adopted by manufacturers of trucks and heavy road vehicles. 4.10.1. Construction of PBS
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Air brake systems are typically used on heavy trucks and buses. The system consists of service brakes, parking brakes, a control pedal, and an air storage tank. For the parking brake, there is a disc or drum brake arrangement which is designed to be held in the 'applied' position by spring pressure. Air pressure must be produced to release these "spring brake" parking brakes. For the service brakes (the ones used while driving for slowing or stopping) to be applied, the brake pedal is pushed, routing the air under pressure (approx 100–120 psi or 690–830 kPa) to the brake chamber, causing the brake to be engaged. Most types of truck air brakes are drum brakes, though there is an increasing trend towards the use of disc brakes in this application. The air compressor draws filtered air from the atmosphere and forces it into high-pressure reservoirs at around 120 psi (830 kPa). Most heavy vehicles have a gauge within the driver's view, indicating the availability of air pressure for safe vehicle operation, often including warning tones or lights. Setting of the parking/emergency brake releases the pressurized air in the lines between the compressed air storage tank and the brakes, thus allowing the spring actuated parking brake to engage. A sudden loss of air pressure would result in full spring brake pressure immediately. A compressed air brake system is divided into a supply system and a control system. The supply system compresses, stores and supplies high-pressure air to the control system as well as to additional air operated auxiliary truck systems (gearbox shift control, clutch pedal air assistance servo, etc.).
Highly simplified air brake diagram on a commercial road vehicle (does not show all air reservoirs and all applicable air valves). The air compressor is driven by the engine either by crankshaft pulley via a beltor directly from the engine timing gears. It is lubricated and cooled by the engine lubrication and cooling systems. Compressed air is first routed through a cooling coil and into an air dryer which removes moisture and oil impurities and also may include a pressure regulator, safety valve and smaller purge reservoir. As an alternative to the air dryer, the supply system can be equipped with an anti-freeze device and oil separator. The compressed air is then stored in a reservoir (also called a wet tank) from which it is then distributed via a four way protection valve into the front and rear brake circuit air reservoir, a parking brake reservoir and an auxiliary air supply distribution point. The system also includes various check, pressure limiting, drain and safety valves.Air brake systems may include a wig wag device which deploys to warn the driver if the system air pressure drops too low. 4.10.2. Control system
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The control system is further divided into two service brake circuits: the parking brake circuit and the trailer brake circuit. This dual brake circuit is further split into front and rear wheel circuits which receive compressed air from their individual reservoirs for added safety in case of an air leak. The service brakes are applied by means of a brake pedal air valve which regulates both circuits. The parking brake is the air operated spring brake type where its applied by spring force in the spring brake cylinder and released by compressed air via hand control valve. The trailer brake consists of a direct two line system: the supply line (marked red) and the separate control or service line (marked blue). The supply line receives air from the prime mover park brake air tank via a park brake relay valve and the control line is regulated via the trailer brake relay valve. The operating signals for the relay are provided by the prime mover brake pedal air valve, trailer service brake hand control (subject to a country's relevant heavy vehicle legislation) and the prime mover park brake hand control. 4.10.3. Advantages of Air Brakes Air brakes are used as an alternative to hydraulic brakes which are used on lighter vehicles such as automobiles. Hydraulic brakes use a liquid (hydraulic fluid) to transfer pressure from the brake pedal to the brake shoe to stop the vehicle. Air brakes have several advantages for large multitrailer vehicles: The supply of air is unlimited, so the brake system can never run out of its operating fluid, as hydraulic brakes can. Minor leaks do not result in brake failures. Air line couplings are easier to attach and detach than hydraulic lines; there is no danger of letting air into hydraulic fluid. So air brake circuits of trailers can be attached and removed easily by operators with little training. Air not only serves as a fluid for transmission of force, but also stores potential energy. So it can serve to control the force applied. Air brake systems include an air tank that stores sufficient energy to stop the vehicle if the compressor fails. Air brakes are effective even with considerable leakage, so an air brake system can be designed with sufficient "fail-safe" capacity to stop the vehicle safely even when leaking.
4.11. Electronic brake force distribution (EBD)
Most of the cars today come fitted with ABS or Anti-lock Braking system. Coupled along with ABS, there is another electronic marvel called the EBD or electronic brake force distribution. Simply put, EBD is a system wherein the amount of braking force on each wheel of
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M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering the car can be varied taking factors such as load bearing on each wheel, condition of the road, speed of the vehicle and so on. The simple idea behind an EBD system is that it need not be necessary to apply the same amount of braking force on each wheel so as to reduce the speed of the car or bring it to a complete stop. An EBD system makes use of three components which make it tick. The speed sensors, brake force modulators and electronic control unit (ECU).
1. Speed Sensor: The speed sensor not only calculates the speed of the car, but the speed of the engine also (RPM). One of the scenarios can be that the speed of the wheel might not be the same as the speed of the car. Such a situation can lead to the wheel(s) skidding. The speed sensors calculate the slip ratio and relay it to ECU. 2. Electronic Control Unit: It is a small chip which collects the data from the speed sensors in each wheel and uses the data to calculate the slip ratio (difference between the speed of the car and the rotation of the tyre). Once the slip ratio is determined, it makes use of the brake force modulators to keep the slip ratio within limits. 3. Brake Force Modulators: It is the job of these modulators to pump brake fluid into the brake lines and activate the brake cylinders. The brake force applied on each wheel can be modulated. All these three components work in tandem and make the EBD work and save your day, every time you brake hard. 4.12. Loss of Traction One undesirable side effect of a differential is that it can reduce overall torque - the rotational force which propels the vehicle. The amount of torque required to propel the vehicle at any given moment depends on the load at that instant - how heavy the vehicle is, how much drag and friction there is, the gradient of the road, the vehicle's momentum and so on. For the purpose of this article, we will refer to this amount of torque as the "threshold torque".
The torque on each wheel is a result of the engine and transmission applying a twisting force against the resistance of the traction at that wheel. Unless the load is exceptionally high, the engine and transmission can usually supply as much torque as necessary, so the limiting factor is usually the traction under each wheel. It is therefore convenient to define traction as the amount of torque that can be generated between the tire and the ground before the wheel starts to slip. If the total traction under all the driven wheels exceeds the threshold torque, the vehicle will be driven forward; if not, then one or more wheels will simply spin. M.I.E.T. /Mech. / III/AE
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To illustrate how a differential can limit overall torque, imagine a simple rear-wheel- drive vehicle, with one rear wheel on asphalt with good grip, and the other on a patch of slippery ice. With the load, gradient, etc., the vehicle requires, say, 2000 N-m of torque to move forward (i.e. the threshold torque). Let us further assume that the non-spinning traction on the ice equates to 400 N-m, and the asphalt to 3000 N-m. If the two wheels were driven without a differential, each wheel would push against the ground as hard as possible. The wheel on ice would quickly reach the limit of traction (400 N- m), but would be unable to spin because the other wheel has good traction. The traction of the asphalt plus the small extra traction from the ice exceeds the threshold requirement, so the vehicle will be propelled forward. With a differential, however, as soon as the "ice wheel" reaches 400 N-m, it will start to spin, and then develop less traction ~300 N-m. The planetary gears inside the differential carrier will start to rotate because the "asphalt wheel" encounters greater resistance. Instead of driving the asphalt wheel with more force, the differential will allow the ice wheel to spin faster, and the asphalt wheel to remain stationary, compensating for the stopped wheel by extra speed of the spinning ice wheel. The torque on both wheels will be the same - limited to the lesser traction of 300 N-m each. Since 600 N-m is less than the required threshold torque of 2000 N-m, the vehicle will not be able to move. An observer simply sees one stationary wheel and one spinning wheel. It will not be obvious that both wheels are generating the same torque (i.e. both wheels are in fact pushing equally, despite the difference in rotational speed). This has led to a widely held misconception that a vehicle with a differential is really only "one-wheel-drive". In fact, a normal differential always provides equal torque to both driven wheels (unless it is a locking, torque-biasing, or limited slip type). 4.12.1. Traction control system (TCS) A traction control system (TCS), in German known as Antriebsschlupfregelung (ASR), is typically (but not necessarily) a secondary function of the anti-lock braking system (ABS) on production motor vehicles, designed to prevent loss of traction of driven road wheels. TCS is activated when throttle input and engine torque are mismatched to road surface conditions. Intervention consists of one or more of the following: Brake force applied to one or more wheels Reduction or suppression of spark sequence to one or more cylinders Reduction of fuel supply to one or more cylinders Closing the throttle, if the vehicle is fitted with drive by wire throttle In turbocharged vehicles, a boost control solenoid is actuated to reduce boost and therefore engine power.
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Typically, traction control systems share the electro hydraulic brake actuator (which does not use the conventional master cylinder and servo) and wheel speed sensors with ABS. Traction control helps limit tire slip in acceleration on slippery surfaces. In the past, drivers had to feather the gas pedal to prevent the drive wheels from spinning wildly on slippery pavement. Many of today's vehicles employ electronic controls to limit power delivery for the driver, eliminating wheel slip and helping the driver accelerate under control. Powerful rear-drive cars from the sixties often had a primitive form of traction control called a limited slip rear differential. Sometimes referred to as Positraction, a limited-slip rear axle will mechanically transfer power to the rear wheel with the most traction, helping to reduce, but not eliminate wheel spin. While limited-slip rear axles are still in use in many front- and rear-drive vehicles today, the device can't completely eliminate wheel slip. Hence, a more sophisticated system was needed.
M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
UNIT - V ALTERNATIVE ENERGY SOURCES
Use of Natural Gas, Liquefied Petroleum Gas, Bio-diesel, Bio-ethanol, Gasohol and Hydrogen in Automobiles- Engine modifications required –Performance, Combustion and Emission Characteristics of SI and CI engines with these alternate fuels - Electric and Hybrid Vehicles, Fuel Cell. Note: Practical Training in dismantling and assembling of Engine parts and Transmission Systems should be given to the students. 5.1. Alternate fuels Alternative fuels include gaseous fuels such as hydrogen, natural gas, and propane; alcohols such as ethanol, methanol, and butanol; vegetable and waste-derived oils; and electricity. These fuels may be used in a dedicated system that burns a single fuel, or in a mixed system with other fuels including traditional gasoline or diesel, such as in hybrid-electric or flexible fuel vehicles. Some vehicles and engines are designed for alternative fuels by the manufacturer. Others are converted to run on an alternative fuel by modifying the engine controls and fueling system from the original configuration. 5.1.1. Natural Gas as a Fuel in Automobile A natural gas vehicle (NGV) is an alternative fuel vehicle for autonomous mobility that uses compressed natural gas (CNG) or liquefied natural gas (LNG). Natural gas vehicles should not be confused with vehicles powered by propane (LPG), which is a fuel with a fundamentally different composition. In a natural gas powered vehicle, energy is released by combustion of essentially Methane gas (CH4) fuel with Oxygen (O2) from the air to CO2 and water vapor (H2O) in an internal combustion engine. Methane is the cleanest burning hydrocarbon and many contaminants present in natural gas are removed at source. Safe, convenient and cost effective gas storage and fuelling is more of a challenge compared to petrol and diesel vehicles since the natural gas is pressurized and/or - in the case of LNG - the tank needs to be kept cold. This makes LNG unsuited for vehicles that are not in frequent use. The lower energy density of gases compared to liquid fuels is mitigated to a great extent by high compression or gas liquification, but requires a trade-off in terms of size/ complexity/ weight of the storage container, range of the vehicle between refuelling stops, and time to refuel. Although similar storage technologies may be used for, and similar compromises would apply to, a Hydrogen vehicle as part of a proposed new Hydrogen economy, Methane as a gaseous fuel is safer than Hydrogen due to its lower flammability, low corrosivity and better leak tightness due to larger molecular weight/ size, resulting in lower price hardware solutions based on proven technology and conversions. A key advantage of using natural gas is the existence, in principle, of most of the infrastructure and the supply chain, which is non-interchangeable with Hydrogen. Methane today mostly comes from non-renewable sources but can be supplied or produced from renewable sources, offering net carbon neutral mobility. In many markets, especially the Americas, natural gas may trade at a discount to other fossil fuel products such as petrol, diesel or coal, or indeed be a less valuable by-product associated with their production that has to be disposed. Many countries also provide tax incentives for natural gas powered M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering vehicles due to the environmental benefits to society. Lower operating costs and government incentives to reduce pollution from heavy vehicles in urban areas have driven the adoption of NGV for commercial and public uses, i.e. trucks and buses. Many factors hold back NGV popularization for individual mobility applications, i.e. private vehicles, including: relatively price and environmentally insensitive but convenience seeking private individuals; good profits and taxes extractable from small batch sales of value- added, branded petrol and diesel fuels via established trade channels and oil refiners; resistance and safety concerns to increasing gas inventories in urban areas; dual-use of utility distribution networks originally built for home gas supply and allocation of network expansion costs; reluctance, effort and costs associated with switching; prestige and nostalgia associated with petroleum vehicles; fear of redundancy and disruption. A particular challenge may be the fact that refiners are currently set up to produce a certain fuels mix from crude oil. Aviation fuel is likely to remain the fuel of choice for aircraft due to their weight sensitivity for the foreseeable future. 5.1.2. Liquefied petroleum gas as a Fuel in Automobile Liquefied petroleum gas or liquid petroleum gas (LPG or LP gas), also referred to as simply propane or butane, is a flammable mixture of hydrocarbon gases used as a fuel in heating appliances, cooking equipment, and vehicles. It is increasingly used as an aerosol propellant and a refrigerant, replacing chlorofluorocarbons in an effort to reduce damage to the ozone layer. When specifically used as a vehicle fuel it is often referred to as auto gas. Varieties of LPG bought and sold include mixes that are primarily propane (C 3H8),primarily butane (C4H10) and, most commonly, mixes including both propane andbutane. In winter, the mixes contain more propane, while in summer, they contain more butane. In the United States, primarily two grades of LPG are sold: commercial propane and HD-5. These specifications are published by the Gas Processors Association (GPA) and the American Society of Testing and Materials (ASTM). Propane/butane blends are also listed in these specifications. Propylene, butylenes and various other hydrocarbons are usually also present in small concentrations. HD-5 limits the amount of propylene that can be placed in LPG to 5%, and is utilized as an autogas specification. A powerful odorant, ethanethiol, is added so that leaks can be detected easily. The international standard is EN 589. In the United States, tetrahydrothiophene (thiophane) or amyl mercaptan are also approved odorants,[5] although neither is currently being utilized. LPG is prepared by refining petroleum or "wet" natural gas, and is almost entirely derived from fossil fuel sources, being manufactured during the refining of petroleum (crude oil), or extracted from petroleum or natural gas streams as they emerge from the ground. It was first produced in 1910 by Dr. Walter Snelling, and the first commercial products appeared in 1912. It currently provides about 3% of all energy consumed, and burns relatively cleanly with no soot and very few sulfur emissions. As it is a gas, it does not pose ground or water pollution hazards, but it can cause air pollution. LPG has a typical specific calorific value of 46.1 MJ/kg compared with 42.5 MJ/kg for fuel oil and 43.5 MJ/kg for premium grade petrol (gasoline). However, its energy density per volume unit of 26 MJ/L is lower than either that of petrol or fuel oil, as its relative density is lower (about 0.5–0.58, compared to 0.71–0.77 for gasoline). As its boiling point is below room temperature, LPG will evaporate quickly at normal temperatures and pressures and is usually supplied in pressurised steel
M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering vessels. They are typically filled to 80–85% of their capacity to allow for thermal expansion of the contained liquid. The ratio between the volumes of the vaporized gas and the liquefied gas varies depending on composition, pressure, and temperature, but is typically around 250:1. The pressure at which LPG becomes liquid, called its vapour pressure, likewise varies depending on composition and temperature; for example, it is approximately 220 kilopascals (32 psi) for pure butane at 20 °C (68 °F), and approximately 2,200 kilopascals (320 psi) for pure propane at 55 °C (131 °F). LPG is heavier than air, unlike natural gas, and thus will flow along floors and tend to settle in low spots, such as basements. There are two main dangers from this. The first is a possible explosion if the mixture of LPG and air is within the explosive limits and there is an ignition source. The second is suffocation due to LPG displacing air, causing a decrease in oxygen concentration. Large amounts of LPG can be stored in bulk cylinders and can be buried underground. 5.1.3. Bio diesel as a Fuel in Automobile Biodiesel and conventional diesel vehicles are one in the same. Although light, medium, and heavy-duty diesel vehicles are not technically "alternative fuel" vehicles, many are capable of running on biodiesel. Biodiesel, which is most often used as a blend with regular diesel fuel, can be used in many diesel vehicles without any engine modification. The most common biodiesel blend is B20, which is 20% biodiesel and 80% conventional diesel. B5 (5% biodiesel, 95% diesel) is also commonly used in fleets. Before using biodiesel, be sure to check your engine warranty to ensure that higher-level blends (all OEMs accept the use of B5 and many accept the use of B20) of this alternative fuel don't void or affect it. High-level biodiesel blends (blends over B20) can have a solvency effect in engines and fuel systems that previously used petroleum diesel which may result in degraded seals and clogged fuel filters. Biodiesel improves fuel lubricity and raises the cetane number of the fuel. Diesel engines depend on the lubricity of the fuel to keep moving parts from wearing prematurely. Federal regulations have gradually reduced allowable fuel sulfur to only 15 parts per million, which has often resulted in lowered aromatics content in diesel fuel. One advantage of biodiesel is that it can impart adequate lubricity to diesel fuels at blend levels as low as 1%. 5.1.4. Bio-ethanol as a Fuel in Automobile Ethanol fuel is ethyl alcohol, the same type of alcohol found in alcoholic beverages, used as fuel. It is most often used as a motor fuel, mainly as a biofuel additive for gasoline. The first production car running entirely on ethanol was the Fiat 147, introduced in 1978 in Brazil by Fiat. Ethanol is commonly made from biomass such as corn or sugarcane. Bioethanol is a form of renewable energy that can be produced from agricultural feedstocks. It can be made from very common crops such as hemp, sugarcane, potato, cassava and corn. There has been considerable debate about how useful bioethanol is in replacing gasoline. Concerns about its production and use relate to increased food prices due to the large amount of arable land required for crops, as well as the energy and pollution balance of the whole cycle of ethanol production, especially from corn. Recent developments with cellulosic ethanol production and commercialization may allay some of these concerns. 5.1.5. Gasohol as a Fuel in Automobile Gasohol is an alternative fuel consisting of a mixture of typically 90 percent gasoline with 10 percent anhydrous ethanol. Gasohol can be used in most modern and light duty vehicles with an internal combustion. The Gasohol blend of 90 percent gasoline and 10 percent
M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering anhydrous ethanol has been approved for use in several countries and can be used with no modification to the vehicle's engine. Gasohol is useful in decreasing the population's dependence on foreign oil, and reduces the carbon monoxide emissions by up to 30 percent. The ethanol typically used in the Gasohol production is derived from fermenting agricultural crops. Fuel containing ethanol normally has an "E" number which explains the mixture. E10 consists of 10 percent ethanol and 90 percent gasoline whereas E85 is a blend of 85 percent ethanol and 15 percent gasoline. E5 and E7 are also common ethanol blends.
Gasohol has certain advantages: Emissions from using Gasohol are less than that of vehicles using gasoline. Emissions are not only harmful to the environment but can cause serious problems and even death in humans. By minimizing the emissions expelled into the atmosphere, we not only ensure a greener environment, but also a physically healthier population eliminating illness. Such as, asthma and heart disease, caused by vehicle emissions. Using Gasohol assists in the reduction of oil imported from other countries. Not only does this lessen our carbon footprint but, with Gasohol production of up to 85 percent ethanol, less oil needs to be imported to manufacture gasoline. Crop prices are raised with the production of Gasohol. Ethanol is an alcohol derived from crops such as cane, grains and sorghum. This increases the demand and ultimately the price of these crops. Gasohol is typically cheaper than petroleum as it is cheaper to manufacture. With most of the world's automobiles running on Gasohol, it is only a matter of time before vehicles capable of running on pure ethanol will be designed. Although not the perfect solution, Gasohol is a step in the right direction to finding alternative fuels for our automobiles. The positive aspects of Gasohol outweigh the negatives and, with more countries making Gasohol available at their gas stations, everybody is making an effort in ensuring less dangerous gasses are expelled into the atmosphere. 5.1.6. Hydrogen in Automobiles Fuel cell vehicles use hydrogen gas to power an electric motor. Unlike conventional vehicles which run on gasoline or diesel, fuel cell cars and trucks combine hydrogen and oxygen to produce electricity, which runs a motor. Since they‘re powered entirely by electricity, fuel cell vehicles are considered electric vehicles (―EVs‖)—but unlike other EVs, their range and refueling processes are comparable to conventional cars and trucks. Converting hydrogen gas into electricity produces only water and heat as a byproduct, meaning fuel cell vehicles don‘t create tailpipe pollution when they‘re driven. Producing the hydrogen itself can lead to pollution, including greenhouse gas emissions, but even when the fuel comes from one of the dirtiest sources of hydrogen, natural gas, today‘s early fuel cell cars and trucks can cut emissions by over 30 percent when compared with their gasoline-powered counterparts. Future renewable fuel standards—such as the requirements currently in place in California—could make hydrogen even cleaner. Because fuel cell vehicles are only beginning to enter the U.S. market, interested drivers should ensure they live near hydrogen refueling stations. Hydrogen fuel cell features
M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
Hydrogen fuel cell vehicles combine the range and refueling of conventional cars with the recreational and environmental benefits of driving on electricity. Refueling a fuel cell vehicle is comparable to refueling a conventional car or truck; pressurized hydrogen is sold at hydrogen refueling stations, taking less than 10 minutes to fill current models. Some leases may cover the cost of refueling entirely. Once filled, the driving ranges of a fuel cell vehicle vary, but are similar to the ranges of gasoline or diesel-only vehicles (200-300 miles). Compared with battery-electric vehicles—which recharge their batteries by plugging in—the combination of fast, centralized refueling and longer driving ranges make fuel cells particularly appropriate for larger vehicles with long-distance requirements, or for drivers who lack plug-in access at home. Like other EVs, fuel cell cars and trucks can employ idle-off, which shuts down the fuel cell at stop signs or in traffic. In certain driving modes, regenerative braking is used to capture lost energy and charge the battery. Differences between fuel cell cars and other EVs Battery electric vehicles run off an electric motor and battery. This offers them increased efficiency and, like fuel cell vehicles, allows them to drive emissions-free when the electricity comes from renewable sources. Unlike fuel cell cars and trucks, battery electric vehicles can use existing infrastructure to recharge, but must be plugged in for extended periods of time. Learn more about how battery electrics work Plug-in hybrid electric vehicles are similar to battery electric vehicles but also have a conventional gasolines or diesel engine. This allows them to drive short distances on electricity- only, switching to liquid fuel for longer trips. Although not as clean as battery electric or fuel cell vehicles, plug-in hybrids produce significantly less pollution than their conventional counterparts. Learn more about how plug-in vehicles work > Conventional hybrids also have conventional engines and an electric motor and battery, but can‘t be plugged-in. Though cleaner than conventional cars and trucks, non-plug-in hybrids derive all their power from gasoline and diesel, and aren‘t considered electric vehicles. Learn more about how hybrids work 5.2. Engine modifications required and Performance, Combustion and Emission Characteristics of SI and CI engines with these alternate fuels 5.2.1. Natural Gas The modification design of petrol engine for alternative fuelling using Compressed Natural Gas (CNG). It provides an analytical background in the modification design process. A petrol engine Honda CR-V 2.0 auto which has a compression ratio of 9.8 was selected as case study. In order for this petrol engine to run on CNG, its compression had to be increased. An optimal compression ratio of 11.97 was computed using the standard temperature-specific volume relationship for an isentropic compression process. This computation of compression ratio is based on an inlet air temperature of 30oC (representative of tropical ambient condition) and pre-combustion temperature of 540oC (corresponding to the auto-ignition temperature of CNG). Using this value of compression ratio, a dimensional modification Quantity =1.803mm was obtained using simple geometric relationships. This value of 1.803mm is needed to increase the length of the connecting rod, the compression height of the piston or reducing the sealing plate‘s thickness. After the modification process, a CNG engine of air standard efficiency 62.7% (this represents a 4.67% increase over the petrol engine), capable of a maximum powerof 83.6kW at 6500rpm, was obtained. 5.2.2. Liquefied petroleum gas LPG is typically a mixture of several gases in varying proportions. Major constituent gases are propane (C3H8) and butane (C4H10), with minor quantities of propane (C3H6), various butanes (C4H8), iso-butane, and small amounts of ethane (C2H6). The composition of M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering commercial LPG is quite variable. About 55% of the LPG processed from natural gas purification. The other 45% comes from crude oil refining. LPG is derived from petroleum; LPG does less to relieve the country‘s dependency on foreign oil than some other alternative fuels. The gaseous nature of the fuel/air mixture in an LPG vehicle‘s combustion chambers eliminates the cold-start problems associated with liquid fuels. LPG defuses in air fuel mixing at lower inlet temperature than is possible with either gasoline or diesel. This leads to easier starting, more reliable idling, smoother acceleration and more complete and efficient burning with less unburned hydrocarbons present in the exhaust. In contrast to gasoline engines, which produce high emission levels while running cold, LPG engine emissions remain similar whether the engine is cold or hot. Also, because LPG enters an engine‘s combustion chambers as a vapor, it does not strip oil from cylinder walls or dilute the oil when the engine is cold. This helps to have a longer service life and reduced maintenance costs of engine. Also helping in this regard is the fuel‘s high hydrogen-to-carbon ratio (C3H8), which enables propane-powered vehicles to have less carbon build-up than gasoline and diesel- powered vehicles. LPG delivers roughly the same power, acceleration, and cruising speed characteristics as gasoline. Its high octane rating means engine‘s power output and fuel efficiency can be increased beyond what would be possible with a gasoline engine without causing Destructive Knocking. Such fine-tuning can help compensate for the fuel‘s lower energy density. The higher ignition temperature of gas compared with petroleum based fuel leads to reduced auto ignition delays,less hazardous than any other petroleum based fuel and expected to produce less CO, NOx emissions and may cause less ozone formation than gasoline and diesel engines. LPG engines similar to petrol engines, and deliver nearly similar performance and good in combustion characteristics than Gasoline. In the short term, LPG as a alternative fuels reviewed could displace 10 per cent of current usage of oil, or bring significant reductions in CO, CO2 emissions and help to reduce harmful greenhouse gas emissions. In the next five to ten years, LPG will be more widely available and gaining market share across vehicle ranges. 5.2.3. Bio diesel An extended experimental study is conducted to evaluate and compare the use of various Diesel fuel supplements at blend ratios of 10/90 and 20/80, in a standard, fully instrumented, four stroke, direct injection (DI), Ricardo/Cussons ‗Hydra‘ Diesel engine located at the authors‘ laboratory. More specifically, a high variety of vegetable oils or bio-diesels of various origins are tested as supplements, i.e. cottonseed oil, soybean oil, sunflower oil and their corresponding methyl esters, as well as rapeseed oil methyl ester, palm oil methyl ester, corn oil and olive kernel oil. The series of tests are conducted using each of the above fuel blends, with the engine working at a speed of 2000 rpm and at a medium and high load. In each test, volumetric fuel consumption, exhaust smokiness and exhaust regulated gas emissions such as nitrogen oxides (NOx), carbon monoxide (CO) and total unburned hydrocarbons (HC) are measured. From the first measurement, specific fuel consumption and brake thermal efficiency are computed. The differences in the measured performance and exhaust emission parameters from the baseline operation of the engine, i.e. when working with neat Diesel fuel, are determined and compared. This comparison is extended between the use of the vegetable oil blends and the bio-diesel blends. Theoretical aspects of Diesel engine combustion, combined with the widely differing physical and chemical properties of these Diesel fuel supplements against the normal Diesel fuel, are used to aid the correct interpretation of the observed engine behavior.
M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
5.2.4 Ethanol–Gasoline The purpose of this study is to experimentally investigate the engine performance and pollutant emission of a commercial SI engine using ethanol–gasoline blended fuels with various blended rates (0%, 5%, 10%, 20%, 30%). Fuel properties of ethanol–gasoline blended fuels were first examined by the standard ASTM methods. Results showed that with increasing the ethanol content, the heating value of the blended fuels is decreased, while the octane number of the blended fuels increases. It was also found that with increasing the ethanol content, the Reid vapor pressure of the blended fuels initially increases to a maximum at 10% ethanol addition, and then decreases. Results of the engine test indicated that using ethanol–gasoline blended fuels, torque output and fuel consumption of the engine slightly increase; CO and HC emissions decrease dramatically as a result of the leaning effect caused by the ethanol addition; and
CO2 emission increases because of the improved combustion. Finally, it was noted that NOx emission depends on the engine operating condition rather than the ethanol content. 5.2.5. Hydrogen Hydrogen seems to be a viable solution for future transportation. In order for hydrogen vehicles to become commercially feasible, challenging tasks in hydrogen production, distribution and storage have to be addressed properly. The wide flammability limits, low ignition energy and high flame speeds can result in undesirable combustion anomalies, including surface ignition and backfiring as well as auto ignition. However, the works so far reported in the literature show encouraging results from the performance and emission points of view. It is observed that thermal efficiency Hydrogen seems to be a viable solution for future transportation. In order for hydrogen vehicles to become commercially feasible, challenging tasks in hydrogen production, distribution and storage have to be addressed properly. The wide flammability limits, low ignition energy and high flame speeds can result in undesirable combustion anomalies, including surface ignition and backfiring as well as auto ignition. However, the works so far reported in the literature show encouraging results from the performance and emission points of view. It is observed that thermal efficiency. The high auto ignition temperature, finite ignition delay and the high flame velocity of hydrogen show that knocking is less likely for hydrogen relative to gasoline. NOx emissions are found to increase with increase in hydrogen fractions in the mixture mainly in case of an SI engine. NOx emissions depend upon conditions like temperature and oxygen concentration present in the cylinder. Hydrogen is being considered as a primary automotive fuel and as a replacement for conventional fuels. Some of the desirable properties, like high flame velocity, high calorific value motivate to use hydrogen fuel in a dual fuel mode in diesel engine. In this experiment the hydrogen was inducted in the inlet manifold with intake air. The experiments were conducted on a four stroke, single cylinder, water cooled, direct injection (DI), diesel engine at a speed of 1500 rpm. Hydrogen was stored in a high pressure cylinder and supplied to inlet manifold through water and air based flame arrestor. The pressure regulator was used to reduce the cylinder pressure from 140 bar to 2 bar. The hydrogen was inducted with various volume flow rates namely 4lpm, 6lpm and 8lpm respectively by digital volume flow meter. The engine performance, emission and combustion parameters were analyzed at various flow rates of hydrogen and compared with diesel fuel operation. The brake thermal efficiency (BTE) increased and brake specific fuel consumption (BSFC) decreased for hydrogen flow rate of 8lpm as compared to diesel and lower volume flow rate of hydrogen. The hydrocarbon (HC) and
M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering carbon monoxide (CO) decreased and the oxides of nitrogen (NOx) increased for higher volume flow rate of hydrogen compared to diesel and lower volume flow rate of hydrogen. The heat release rate and cylinder pressure increased for higher volume flow rate of hydrogen compared to diesel and lower volume flow rate of hydrogen. 5.3. Electric and Hybrid Vehicles A hybrid vehicle combines any two power (energy) sources. Possible combinations include diesel/electric, gasoline/fly wheel, and fuel cell (FC)/battery. Typically, one energy source is storage, and the other is conversion of a fuel to energy. The combination of two power sources may support two separate propulsion systems. Thus to be a True hybrid, the vehicle must have at least two modes of propulsion. Consistent with the definition of hybrid above, the hybrid electric vehicle combines a gasoline engine with an electric motor. An alternate arrangement is a diesel engine and an electric motor
A hybrid electric vehicle (HEV) is a type of hybrid vehicle and electric vehicle which combines a conventional internal combustion engine (ICE) propulsion system with an electric propulsion system. The presence of the electric power train is intended to achieve either better fuel economy than a conventional vehicle or better performance. There are a variety of HEV types, and the degree to which they function as EVs varies as well. The most common form of HEV is the hybrid electric car, although hybrid electric trucks (pickups and tractors) and buses also exist. Modern HEVs make use of efficiency-improving technologies such as regenerative braking, which converts the vehicle's kinetic energy into electric energy to charge the battery, rather than wasting it as heat energy as conventional brakes do. Some varieties of HEVs use their internal combustion engine to generate electricity by spinning an electrical generator (this combination is known as a motor-generator), to either recharge their batteries or to directly power the electric drive motors. Many HEVs reduce idle emissions by shutting down the ICE at idle and restarting it when needed; this is known as a start-stop system. A hybrid-electric produces less emissions from its ICE than a comparably sized gasoline car, since an HEV's gasoline engine is usually smaller than a comparably sized pure gasoline-burning vehicle (natural gas and propane fuels produce lower emissions) and if not used to directly drive the car, can be geared to run at maximum efficiency, further improving fuel economy. 5.3.1. Advantages of HEVs Oil consumption is less than that of conventional vehicles. M.I.E.T. /Mech. / III/AE
M.I.E.T. ENGINEERING COLLEGE/ DEPT. of Mechanical Engineering
Carbon-based emission is lower, which makes HEVs more eco-friendly. This also helps conserve non-renewable resources like petroleum products. Maintenance costs are lower than those of conventional vehicles. With the electric motor taking charge of the engine during long travels, more mileage can be achieved with HEVs compared to other types of vehicles. 5.4. Fuel Cell A Fuel Cell is an electrochemical device that combines hydrogen and oxygen to produce electricity, with water and heat as its by-product. Since conversion of the fuel to energy takes place via an electrochemical process, not combustion. It is a clean, quiet and highly efficient process- two to three times more efficient than fuel burning. It operates similarly to a battery, but it does not run down nor does it require recharging As long as fuel is supplied, a Fuel Cell will produce both energy and heat A Fuel Cell consists of two catalyst coated electrodes surrounding an electrolyte. One electrode is an anode and the other is a cathode The process begins when Hydrogen molecules enter the anode The catalyst coating separates hydrogen‘s negatively charged electrons from the positively charged protons The electrolyte allows the protons to pass through to the cathode, but not the electrons. There the oxygen and the protons combine with the electrons after they have passed through the external circuit. When the oxygen and the protons combine with the electrons it produces water and heat. Individual fuel cells can then be placed in a series to form a fuel cell stack. The stack can be used in a system to power a vehicle or to provide stationary power to a building.
5.4.1. Advantages of the technology: By converting chemical potential energy directly into electrical energy, fuel cells avoid the ―thermal bottleneck‖ (a consequence of the 2nd law of thermodynamics) and are thus inherently more efficient than combustion engines, which must first convert chemical potential energy into heat, and then mechanical work. Direct emissions from a fuel cell vehicle are just water and a little heat. This is a huge improvement over the internal combustion engine‘s litany of greenhouse gases. Fuel cells have no moving parts. They are thus much more reliable than traditional engines. Hydrogen can be produced in an environmentally friendly manner, while oil extraction and refining is very damaging.
M.I.E.T. /Mech. / III/AE