E –LECTURE ON AUTOMOBILE ENGINEERING FOR SIXTH SEMESTER STUDENTS
BY
SANJEEV SINGH LECTURER MECHANICAL ENGINEERING
DEPARTMENT OF MECHANICAL ENGNEERING
BABA KHETANATH GOVT POLYTECHNIC NARNAUL
CHAPTER NO.1 Automobile: Development of the Automobile The automobile has a long history. The French engineer Nicolas Joseph Cugnot built the first self- propelled vehicle (Paris, 1789), a heavy, three-wheeled, steam-driven carriage with a boiler that projected in front; its speed was c.3 mph (5 kph). In 1801 the British engineer Richard Trevithick also built a three-wheeled, steam-driven car; the engine drove the rear wheels. Development of the automobile was retarded for decades by over-regulation: speed was limited to 4 mph (6.4 kph) and until 1896 a person was required to walk in front of a self-propelled vehicle, carrying a red flag by day and a red lantern by night. The Stanley brothers of Massachusetts, the most well-known American manufacturers of steam-driven autos, produced their Stanley Steamers from 1897 until after World War I.
The development of the automobile was accelerated by the introduction of the internal-combustion engine. Probably the first vehicle of this type was the three-wheeled car built in 1885 by the engineer Karl Benz in Germany. Another German engineer, Gottlieb Daimler, built an improved internal-combustion engine c.1885. The Panhard car, introduced in France by the Daimler company in 1894, had many features of the modern car. In the United States, internal-combustion cars of the horseless buggy type were manufactured in the 1890s by Charles Duryea and J. Frank Duryea, Elwood Haynes, Henry Ford, Ransom E. Olds, and Alexander Winton. Many of the early engines had only one cylinder, with a chain-and-sprocket drive on wooden carriage wheels. The cars generally were open, accommodated two passengers, and were steered by a lever.
The free growth of the automobile industry in the early 20th cent. was threatened by the American inventor George Selden's patent, issued in 1895. Several early manufacturers licensed by Selden formed an association in 1903 and took over the patent in 1907. Henry Ford, the leader of a group of independent manufacturers who refused to acknowledge the patent, was engaged in litigation with Selden and the association from 1903 until 1911, when the U.S. Circuit Court of Appeals ruled that the patent, although valid, covered only the two-cycle engine; most cars, including Ford's, used a four-cycle engine. The mass production of automobiles that followed, and the later creation of highways linking cities to suburbs and region to region, transformed American landscape and society.
Since 2010 there has been an increased focus on developing a practical automobile in which a computerized driving system either greatly aids or completely replaces the human driver. Although the technology for an automated vehicle has been explored since the 1920s, real work on semiautonomous and autonomous vehicles did not progress until the 1980s and the development of microcomputers, and even then the technology was not commercially practical. In the early 21st cent. an increasing number of automobile manufacturers begin including automatic safety equipment that activates when the vehicle's computerized systems sense conditions such as impending vehicle instability or collision and takes measures, such as automated braking, to avoid crashes and passenger injury. Significant advances also have been made in the development of self-driving vehicles, a number of which have been road-tested successfully in public traffic since 2010. In some cases, autonomous driving capabilities have been incorporated into cars that are commercially available.
1.2 Classification of Automobiles:
1. Based on Purpose : . Passenger vehicles: These vehicles carry passengers. e.g: Buses, Cars, passenger trains. . Goods vehicles: These vehicles carry goods from one place to another place. e.g: Goods lorry, Goods carrier. . Special Purpose: These vehicles include Ambulance, Fire engines, Army Vehicles.
2. Based on Load Capacity: . Light duty vehicle: Small motor vehicles. eg: Car, jeep, Scooter, motorcycle . Heavy duty vehicle: large and bulky motor vehicles. e.g: Bus, Truck, Tractor
3. Based on fuel used: . Petrol engine vehicles : Automobiles powered by a petrol engine. e.g: scooters, cars, motorcycles. . Diesel engine vehicles : Automobiles powered by diesel engine. e.g: Trucks, Buses, Tractors. . Gas vehicles : Vehicles that use gas turbine as a power source. e.g: Turbine powered cars. . Electric vehicles : Automobiles that use electricity as a power source. e.g: Electric cars, electric buses. . Steam Engine vehicles : Automobiles powered by steam engine. e.g: Steamboat, steam locomotive, steam wagon. 4. Based on Drive of the vehicles: . Left-Hand drive : Steering wheel fitted on the left-hand side. . Right-Hand drive : Steering wheel fitted on the right-hand side. . Fluid drive : Vehicles employing torque converter, fluid flywheel or hydramatic transmission.
5. Based on number of wheels and axles: . Two wheeler : motorcycles, scooters . Three-wheelers : Tempo, auto-rickshaws . Four wheeler : car, Jeep, Bus, truck . Six-wheelers : Buses and trucks have six tires out of which four are carried on the rear wheels for additional reaction. . Six axle wheeler : Dodge(10 tire) vehicle
6. Based on type of transmission: . Automatic transmission vehicles: Automobiles that are capable of changing gear ratios automatically as they move. e.g: Automatic Transmission Cars. . Manual transmission vehicles: Automobiles whose gear ratios have to be changed manually. . Semi-automatic transmission vehicles: Vehicles that facilitate manual gear changing with a clutch pedal.
7. Based on Suspension system used: . Convectional – Leaf Spring Independent – Coil spring, Torsion bar, Pneumatic.
1.3Top 10 Largest Automobile Manufacturing Companies
Tata Motors is the Asia’s largest and 17th largest automobile manufacturing company in the world. This company is known for its production of cars, trucks, vans, coaches and so on. Tata Motors record the highest sales and is widely popular across the country in 2017. This company is passionate about anticipating and providing the best commercial and passenger vehicles globally as well as the best customer experiences. Key facts: TATA MOTORS Established 1945 Employee Strength 60,000 Company Turnover $42 Billion Vehicles Sold >9 Million Sales & Service Points >6, 600
Tata Motors can be found on and off-road in over 175 countries around the globe. Cars, buses and trucks of Tata Motors roll out at 20 locations across the world, seven in India and the rest in the UK, South Korea, Thailand, South Africa and Indonesia. 2) Mahindra & Mahindra Ltd:
Mahindra & Mahindra Ltd is a US $19 billion global federation of companies. This company is the world’s largest tractor manufacturing company and also India’s second largest vehicle manufacturing company. Mahindra & Mahindra is India’s top SUV manufacturing company that produce two wheelers, bus, pickup, tempo, trucks, and commercial vehicles. This company commits to invest in technology and grow global presence. Mahindra & Mahindra aims to multiply output both in quantity and quality with a major focus on manufacturing excellence. This company has created several industry-leading and category-defining brands.
3) Maruti Suzuki:
Maruti Suzuki had brought a big revolution in the automobile industry. This is one of the old companies that expertise in the field of production of cars. This company has manufactured cars such as Alto, Omni, Estilo and so on. The total annual production capacity of this company is about 14, 50,000 units. Maruti Suzuki works with a mission to provide a car for every individual, family, need, budget and Way of Life. For this, it offers 15 brands and over 150 variants ranging from Alto 800 to the Life Utility Vehicle Maruti Suzuki Ertiga.
4) Hero MotoCorp Ltd:
Hero MotoCorp Ltd is one of the best companies in India. Hero MotoCorp Ltd. (Formerly Hero Honda Motors Ltd.) is the world's largest manufacturer of two - wheelers, based in India. This company achieved the coveted position of being the largest two-wheeler manufacturing company in India in 2001 and the 'World No.1' two-wheeler company in terms of unit volume sales in a calendar year. Hero MotoCorp two wheelers are manufactured across 4 globally benchmarked manufacturing facilities. 5) Bajaj Auto Limited:
Bajaj Auto Limited is one of the leading business houses and the company’s flagship company, Bajaj Auto, is ranked as the world’s fourth largest three and two wheeler manufacturer. The Bajaj brand is well-known across several countries in Latin America, Africa, Middle East, South and South East Asia. Their flagship company produces Chetak scooters which were the top seller in the Indian market. The company even made the bikes like pulsar and now they are still working on it. 6) Toyota Motor Corporation:
Toyota Motor Corporation is one of the top most automobile manufacturing companies in the world. This company designs, manufacturers and markets various automobile product ranges from SUVs, minivans, luxury & sport utility vehicles, trucks and buses among others. Toyota Motor Corporation has other vehicle manufacturing subsidiaries which include Daihatsu Motor for the production of mini-vehicles and Hino Motors for the production of buses and trucks. Toyota car engines are fixed with either combustion or lately the hybrid engines such as the one in the Prius. 7) Chevrolet:
Chevrolet is an American division of the General Motors. The company has an array of trucks, automobiles and commercial vehicles as the products it offers with its services including oil changing, vehicle insurance, vehicle financing, vehicle sales and vehicle repairs. Chevrolet has the reputation of being a car of all the purses and all the purposes. Its wide range of vehicles includes subcompact automobiles and medium duty commercial trucks among others.
8) MITSUBISHI MOTORS CORPORATION
Mitsubishi Motors Corporation develops design, and manufacture, sale and purchase automobiles and component parts, replacement parts. This company manufactures component parts, replacement parts and accessories of said used automobiles. Mitsubishi helps to bring higher productivity and quality to the factory floor. In addition, extensive service networks around the globe provide direct communication and comprehensive support to customers. 9) Honda Motor Co Ltd. Company
Honda Motor Co Ltd. Company is a world leading automaker and the largest motorcycle producer in the world. Its motorcycle lines feature everything from super bikes to scooters, with the company also being dedicated to the production of personal watercrafts and ATVs. The models of this company include seven luxury vehicle models as well as SUVs and others. Within its lines are also Honda Power products and machinery such as snow blowers, tillers, lawn mowers, outboard motors and portable generators. Engine quality, durability and economic fuel consumption are the main reasons why customers prefer Honda machines. 10) Ford Motor Company:
Ford Motor Company is one of the leading automobile manufacturers in the world that ranks high among the top automobile companies. Some of its most staple brands include Lincoln, Taurus, Focus, Mustang, and Fiesta etc. The company’s automobiles are characterized with luxury under the Lincoln Marque brand, with other brands being good for sports and off-road performances. In the past, Ford manufactured some of the best, trucks, buses and tractors. 1.4LAYOUT OF CHASSIS & TYPES OF DRIVES OF AUTOMOBILES
LAYOUT OF CHASSIS
The main parts of and automobile are mounted on the chassis. The layout of these components on the chassis are different in different types of vehicles, i.e., cars, jeeps, trucks, buses, etc. The main difference in the layout of this chassis is the position of the engine.
The engine is located at the front of the vehicle, followed by a clutch, gear box, propeller shaft, universals joints, differential, rear axle, etc. The radiator is located in front of the engine. Various other parts of the vehicle not shown in the layout are dynamo, horn, steering box, fan, timing gear, carburetor, air filter, gear control, steering wheel, cylinder, petrol tank, rear axle, front axle. The drive from the gear box is conveyed through a short shaft to the front universal joint of the propeller shaft. From the propeller shaft it is conveyed to the rear wheel through a sliding splined type of joint. The bevel gear of the short shaft is driven by rear universal joint. This bevel gear meshes with a larger bevel gear which drives the two rear axle shafts through a differential gear.
1.5TYPES OF DRIVES OF AUTOMOBILES
Some of the important drives of automobiles may be classified as follows:
1. Front engine - Rear wheel drive
2. Rear engine - Rear wheel drive
3. Front engine - Front wheel drive
4. Four wheel drive
1. Front Engine - Rear Wheel Drive In this layout a front mounted engine-clutch-gear box unit drives a beam type rear axle suspended on leaf sprints through a propeller shaft with two universal joints. With the help of coil sprints, the front wheels are independently sprung. As shown in Fig. 1.4 this layout is one of the oldest layout which remained unchanged for many years. some of the advantages provided by this system are :
(a) Balanced weight distribution between the front and the rear wheels.
(b) Easy front wheel steering.
(c) Behind the rear seats, large luggage space is available.
(d) Accessibility to various components like engine, gearbox and rear axle is better in comparison to other layouts. The control linkages-accelerator, choke, clutch and gearbox are short and simple.
(e) Full benefits of the natural air stream created by vehicle’s movement is taken by the forward radiator resulting in reduced power losses from a large fan.
(f) Small length of the propeller shaft permits the angularity of the universal joints to be small and easily provided by simple types.
By mounting the rear wheel drive assembly on the body unit and using universally jointed shafts to independently steer rear wheels as shown in Fig. 1.5, the layout design can be modified and improved. It provides number of benefits like improved handling, comfort and rear wheel grip as well as reduced unspring weight.
2. Rear engine-Rear wheel drive
This arrangement eliminates the necessity for a propeller shaft when the engine is mounted adjacent to the driven wheels. The engine-clutch-gear box-final drive form a single unit in this layout. As shown in Fig. 1.6, to reduce the ‘overhang’ distance between the wheel centres and the front of the engine, the final drive is generally placed between the clutch and the gear box. In comparison to front wheel drive it has a simpler drive shaft layout. Further, the weight of rear engine on the driving wheels provides excellent tranction and grip especially on steep hills as well as when accelerating. Inspire of the low proportion of the vehicle weight transferring to the front wheels, very effective rear wheel braking is possible. Due to the absence of the propeller shaft the obstructed floor space is reduced. The front of the vehicle can, therefore, be designed for good visibility and smooth air flow. the exhaust gases, fumes, engine heat and noises are also carried away from the passengers. It results in compact layout and short car.
The layout also has got certain disadvantages like restricted luggage space due to narrow front compartment which houses the fuel tank also. Natural air cooling is not possible, it requires a powerful fan. The floor is further obstructed due to long linkage required for the engine, clutch and the gear box controls. The rearward concentration of weight causes the vehicle to be more affected by side winds at high speeds. this makes the vehicle unstable resulting in over steering and turning very sharply into a curve. This necessitates the steering correction in the opposite direction.
3. Front engine-front wheel drive.
This layout provides optimum body-luggage space and a flat floor line resulting in a transverse longitudinal engine position. This drive pulling the car along provides good grip and good road holding on curves due to major weight at the front. The chances of skidding especially on slippery surfaces are very much reduced. Good road adhesion is provided by the large proportion of the vehicle weight acting on the driven wheels. when the vehicle is to be ‘steered in’ to the curve, it provides ‘understeer’ characteristics always preferred by drivers.
The combination of steered and driven wheels with short drive shafts provides the main disadvantage. This requires special universal joints and a more complicated assembly. to prevent the rear wheels from skidding under heavy braking, the ‘reduced’ weight at the rear usually necessitates special arrangement.
4. Front wheel steering Rear wheel drive
1. Access to the engine is very easy.
2. Slowing down of the water circulation causing cooling troubles can be avoided and long hose connections can be saved due to situating of the radiator in the main air stream.
3. This arrangement helps minimize the linkage between the clutch, gear box and engine.
4. The angularity of the propeller shaft is kept to minimum and there is no need of joints due to the shaft length.
Rear Engine-Rear Wheel Drive
Advantages
1. Better road adhesion preferably on steep hills and while accelerating with increased weight on the driving wheels.
2. Generally a proportional part of weight of the car is transferred to the front wheels while braking. Therefore, due to the firm road surface contact maintained by rear engined car results in assistance to stopping of the vehicle.
3. In this arrangement, front wheels are only for steering purposes.
4. The necessaity of the propeller shaft is altogether eliminated due to the combination of engine, gear box and final drive. This also requires only one common oil sump.
5. Good visibility and stream lining is provided by proper design of vehicle front.
6. The passengers are kept away from inconveniences like noise, heat and fumes.
Disadvantages
1. At high speed, the increased weight at the rear end makes the vehicle unstable.
2. To control the engine, clutch and gear box, long linkages are required. 3. The width of the car at the front gets reduced for accommodating the movement of the steering wheels resulting in reduction of size of the luggage compartment for given length and with of the car.
4. The wheels get turned too sharply into the curve due to tendency of over-steering. This necessitates the turning of the steering wheels in the opposite direction to make correction by the driver.
5. Efficient cooling becomes very difficult to obtain due to screening of the engine by the vehicle body.
Front Engine - Front Wheel Drive
Advantages
1. As compared to rear wheel driven car, there is a faster and safer travelling due to good road holding on curves.
2. Good road adhesion is obtained due to a large part of the vehicle’s weight being carried on the driving wheels under normal conditions.
3. Under-steer conditions generally preferred by many drivers are promoted by this type of drive. The car comes back to closer radius if the throttle is released. This makes the steering wheel to run more in the direction of turn to make it a better condition.
4. A lower flat floor lines is provided due to dispensing with the propeller shaft resulting in lowering of centre of gravity.
5. The engine, clutch, gear box and final drive are combined similar to the rear engine car. This provides a more comfortable drive due to final drive spring.
Disadvantages
1. Due to the weight of the vehicle moving to the rear, the weight on the driving wheels is reduced on steep gradients as well as while accelerating.
2. The tractive effort which is most needed on steep gradients and during accelerating is reduced.
3. This disadvantage becomes more serious on slippery gradients.
4. Under these conditions certain modifications in modern designs have been made to ensure provision of sufficient traction.
5. Four-wheels drive
To increase maneuverability of the vehicle required to travel on rough unconstructed roads and tracks another arrangement known as four-wheel drive is provided. due to all the four wheels getting driven, whole of the weight of the vehicle is available for traction. But this advantage is not worth the additional cost on good road surfaces. The system is provided in jeeps which are known as 4 X 4 wheel drive vehicles.
6. Left hand and Right and drives In different countries, the automobiles are driven on different sides of the road, In United Kingdom and all the countries, which were once colonies of the British Rule. The vehicles are driven on the left hand side of the road. In all other countries of the world, normally vehicles are driven on the right hand side of the road. For better driving control, the vehicle drivers must be nearer to one another while passing or crossing. Similarly for safety consideration, the drivers must be in the centre of the road while driving. Therefore, two types of vehicles are manufactured.
(a) Left hand drive: The steering is fitted on the left hand side of the automobile and such vehicles are convenient to drive in countries following right hand drive rules, e.g. U.S.A., Russia, European countries.
(b) Right hand drive : The steering is fitted on the right hand side of the automobile and such vehicles are convenient to drive in countries following left hand drive rules, e.g. U.K., India, Pakistan. However, though rare, left hand cars also driven in such countries.
1.6 Introduction to Hybrid Electric Vehicles
Introduction: What is a hybrid? 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. For example, a truck that uses a diesel to drive a generator, which in turn drives several electrical motors for all-wheel drive, is not a hybrid. But if the truck has electrical energy storage to provide a second mode, which is electrical assists, then it is a hybrid Vehicle. These two power sources may be paired in series, meaning that the gas engine charges the batteries of an electric motor that powers the car, or in parallel, with both mechanisms driving the car directly. Hybrid electric vehicle Hybrid electric vehicle (HEV) 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 Electric Vehicle (EV) The Electric Vehicle (EV) has an M/G which allows regenerative braking for an EV; the M/G installed in the HEV enables regenerative braking. For the HEV, the M/G is tucked directly behind the engine. In Honda hybrids, the M/G is connected directly to the engine. The transmission appears next in line. This arrangement has two torque producers; the M/G in motor mode, M-mode, and the gasoline engine. The battery and M/G are connected electrically. HEVs are a combination of electrical and mechanical components. Three main sources of electricity for hybrids are batteries, FCs, and capacitors. Each device has a low cell voltage, and, hence, requires many cells in series to obtain the voltage demanded by an HEV. Difference in the source of Energy can be explained as: a. The FC provides high energy but low power. The battery supplies both modest power and energy. The capacitor supplies very large power but low energy. The components of an electrochemical cell include anode, cathode, and electrolyte . The current flow both internal and external to the cell is used to describe the current loop.
1.7 Necessity of governor if a carburetor can control the engine speed by controlling the flow of fuel to the engine?
First of all carburetor has no control over the engine speeds. It only atomises the fuel to form a combustible mixture with air for an SI engine which is most important part of the induction system. o During the suction stroke a vacuum is created in the cylinder which causes air to flow through the carburetor and the fuel to be sprayed from the fuel jets. And function of a governor is to maintain the speed of the engine within specified limits whenever there is variation of load. o If the load on the shaft increases, the speed of the engine decreases unless the supply of fuel is increased by opening the throttle valve. o On the other hand if the load on the shaft decreases the speed of the engine increases unless the fuel supply is decreased by closing the valve sufficiently to slow the engine to original speed. o o This throttle valve is operated by governor through a mechanism for the purpose. A governor is a primitive feedback control system and regulates the engine speed to be reasonably constant in the presence of varying loads. A carburetor alone will provide a constant speed under a constant load but the speed will change as the load changes unless a human with foot on the gas pedal is compensating for the load changes. 8-bit, 16-bit, 32-bit microprocessor
It is the architecture of the underlying CPU which determines if it is 8 bit, 16 bit or so on A 8 bit CPU means, it will have 8 parallel conducting wires running from its registers (which can store 8 bit of data at any point of time) to the main memory (RAM, which is a block or stack of 8 bit locations). This set of parallel wires is called the ADDRESS BUS, a similar DATA BUS also exists What does it mean to have registers which can store 8 bit of information? It means that the CPU can read, write and execute this 8 bit information in one clock cycle and is capable of transferring the data or result through these wires at the same time. Computers operate on 0s and 1s only, all data is saved that way, and a bit of information in computing sense (microprocessors) means a “cell” which is either empty (0) or full (1).
In other words a bit of information can hold only two states.
However if you have 8 bits (a byte), that means you could create a set of data which gives you a lot to work with: from: 0 0 0 0 0 0 0 0 to: 1 1 1 1 1 1 1 1 which could be translated from binary to decimal: from 0 to 255
16-bit integers, memory addresses, or other data units are those that are 16 bits (2 octets or 2 Bytes) wide. Also, 16-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size. 16-bit microcomputers are computers in which 16-bit microprocessors were the norm.
As n-bit register can store 2n different values. So as a result, 16-bit register can store 216 different values. If we consider the signed range of integer values that can be stored in 16 bits is −32,768 (−1 × 215) through 32,767 (215 − 1). But on the other hand in case of unsigned range is 0 through 65,535 (216 − 1). Since 216 is 65,536, a processor with 16-bit memory addresses can directly access 216 = × 26 × 210 = 64 x 1024 = 64 x 1K = 64 KB (65,536 bytes) of byte-addressable memory. If a system uses segmentation with 16-bit segment offsets, more can be accessed. In computer architecture, 32-bit integers, memory addresses, or other data units are those that are 32 bits (4 octets or 4 Bytes) wide. Also, 32-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size. 32-bit microcomputers are computers in which 32-bit microprocessors are the norm. We know that n-bit microprocessor can handle n-bit word size.
As n-bit register can store 2n different values so, a 32-bit register can store 232 different values. The range of integer values that can be stored in 32 bits depends on the integer representation used. We know there are two most common representations for integer data. And they are Unsigned and Signed representations. The range is 0 through 4,294,967,295 (2 − 1) for representation as an Unsigned binary number, and −2,147,483,648 (−231) through 2,147,483,647 (231 − 1) for representation as two's complement Signed numbers. 1.8Single overhead cam setup and Dual overhead cam setup Single overhead cam setup A SOHC setup typically allows a 2 or 3 valves per cylinder configuration, where usually, one valve allows air to enter and the other allows gases to escape. However, a manufacturer’s engineering prowess can also allow 4 valves per cylinder configuration using SOHC. Such a setup allows for more airflow than 2 valves per cylinder, as there is a larger open area for the air to enter the cylinder and gases to escape when the valves are open. Example: The TVS Apache
Dual overhead cam setup DOHC was introduced to improve the volumetric efficiency of an internal combustion engine, the result of which is more powerful. With this design, camshafts can be installed further apart from each other. This allows the intake valves to be at a larger angle from the exhaust valves, which results in a more direct airflow through the engine with less obstruction. In other words, a DOHC engine can breathe better and thus produce more horsepower out of smaller engine displacement. Also, it is easier to implement efficiency-enhancing technologies like Variable Valve Timing in a DOHC engine.
Figure: Dual overhead cam setup
CHAPTER NO. 2 Transmission system
Clutch A Clutch is a mechanical device that is use for transferring power from one part of an engine to another. A typical example is an automobile . The recriprocating action of the piston inside the engine produces power.The power generated/provided by the engine is transmitted via a clutch to the wheels through gears to the transmitting shaft. The gears are of various diameters and hence they could control the speed of rotation. The clutch works by engaging and disengaging the gear from the transmitting shaft. Gears of large diameter operate at low speed and could transmit more torque compared to that with small diameter which transmit at high speed and lower torque. In this way the automobile could operate both at low sped and at high speed. The connecting shaft are connected to the wheels via constant velocity joints.
Single plate clutch has one clutch plate and works on the principle of friction. These are of two types: Helical spring type and Diaphragm spring type.
In helical spring-type clutches, the helical springs are used uniformly over the cross-sectional area of the pressure plate to exert axial force.
In diaphragm spring type clutch, diaphragm spring is used to exert axial force.
Construction and working of Single Plate Clutch. Basically, the clutch needs three parts. These are the engine flywheel, a friction disc called the clutch plate, and a pressure plate. A flywheel is a heavy disc with suitable width bolted to the end of crankshaft. Friction disc is also called a clutch plate. It has friction lining on both sides of the friction plate.
The pressure plate is a disc; it engages with a clutch plate. When the engine is running, and the flywheel is rotating, the pressure plate also rotates as the pressure plate is attached to the flywheel.
The friction disc is located between these two. The clutch is released when the operator or driver has pushed down the clutch pedal.
This action forces the pressure plate to move away from the friction disc. There is now air gaps between the flywheel and the friction disc, and between the friction disc and the pressure plate. And no power can be transmitted through the clutch.
During the operation, when the driver releases the clutch pedal, power can flow through the clutch.
Springs mounted in between the clutch plate and pressure plate; it forces the pressure plate against the friction disc. This action clamps the friction disk tightly between the flywheel and the pressure plate. Advantages of Single Plate Clutch. The main advantages of this clutch include its simplicity, easy gear changing, better heat dissipation from the single plate, smooth operation, and better load withstanding capacity.
Disadvantages of Single Plate Clutch. The main drawback of this clutch is that its size is large and requires force to disengage the driving shaft from the driven shaft.
Types of Single Plate Clutch. 1. Helical Spring Type Single Plate Clutch. Below figure represents a single plate clutch of helical spring type. For simplicity sake, the clutch pedal and other links causing movement of pressure plate are not shown.
The clutch plate is mounted on the splined shaft and can move along the axis of the shaft. There is no relative movement between plate and shaft as far as rotational movement is concerned.
Both have the same rotational movement due to splines provided on the shaft. The flywheel is mounted on the engine crankshaft and rotates with it.
The pressure plate is bolted to the flywheel through clutch springs. It can slide freely along the axis of the clutch shaft.
The clutch is engaged due to the force exerted by the clutch springs. This force causes contact between the pressure plate, clutch plate, and the flywheel.
The clutch plate is located between the flywheel and pressure plate. The clutch plate is provided with friction material on both sides.
The rotary movement from the flywheel is transferred to the clutch plate and the clutch shaft due to friction. The clutch shaft also acts as the output shaft. When the clutch pedal is pressed the clutch is ‘disengaged.’ The pressure plate moves back against the force of springs, and the clutch plate becomes free between the flywheel and the pressure plate.
Thus, the flywheel continues to rotate as long as the engine runs but the speed of the clutch plate declines and becomes zero. In this situation, motion is not transferred to the clutch shaft.
2. Diaphragm Spring Type Single Plate Clutch. In this type of clutch, the helical springs are replaced by a single diaphragm spring which is a saucer-shaped disc. The disc is provided with profile as shown in the below figure.
The disc adopts flat shape when the clutch is engaged. In the disengaged position, the disc adopts a buckled shape as shown.
Below figure represents a simplified view of the clutch assembly.
The view shows the clutch in the ‘engaged’ position. The diaphragm spring exerts the force on the pressure plate, which causes the contact between the pressure plate, clutch plate, and flywheel.
When force is applied through the clutch pedal, the diaphragm spring is buckled and contact between pressure plate, clutch plate and flywheel is lost. The clutch is ‘disengaged,’ and motion from the flywheel is not transferred to the clutch shaft.
Read Also: Mechanical Properties of Materials, Metals [A Complete Guide] What is Multi Plate Clutch? A clutch having more than one driven plate is called Multi Plate Clutch.
Some times, a single clutch plate can not transfer the required motion. This may be due to less friction force. The friction force can be increased by increasing the area of contact.
This increases the size of the clutch, and due to limited space available; it may be challenging to increase the size.
Therefore to increase the area of contact, the number of clutch plates is increased. The constructional details of the multi plate clutch are represented in the below figure.
To simplify the figure, the mechanism to engage and disengage the clutch has not been shown. Internal splines are provided on the flywheel. The clutch shaft is provided with splines.
The clutch plates are assembled and are firmly pressed, with the help of pressure plate, by coil springs. These coil spring exert axial force, due to which there is contact between the clutch plates, flywheel, and the pressure plate.
The frictional surfaces on both the sides of plates help to transfer the motion from flywheel to the clutch shaft.
This is the ‘engaged’ position of the multi plate clutch.
By operating the clutch pedal, the force is exerted against the force of springs and contact between the flywheel, clutch plates, and pressure plate is lost, and no motion is transferred from flywheel to clutch shaft. This is ‘disengaged’ position for the multi plate clutch.
Presently, in all the automobiles multi plate clutches are being used.
A wet clutch is a variant of the friction clutch. Here oil is sprayed on the plates with the help of nozzle. These are used in a variety of automobiles.
The friction material used on clutch plates should have a higher coefficient of friction, and these are perforated so that oil can pass through these.
These clutches have intake for oil. A sump is provided at the bottom to collect the oil from where it is drained out.
These types of clutches have a longer life than dry clutches due to better dissipation of heat.
Construction and Working of Multi Plate Clutch. A multi-plate clutch is provided with more than one friction plate. In fact, in this clutch, there are two pressure plates and two friction plates, as shown in the below figure.
These pressure plates are linked to the clutch cover by means of studs. This clutch cover is fitted to the flywheel.
One friction plate is placed between the first and second pressure plate, and the other one is between the second pressure plate and the flywheel. The link mechanism is the same as the one used in the single plate clutch. The two friction plates are connected to the clutch shaft using a spline arrangement.
While the flywheel is rotating, the pressure plates rotate and press against the friction plate. This causes the friction plates and thus the clutch shaft to rotate as well.
When the pedal is pressed, the flywheel continues to rotate, but the friction plates are released. This happens because they are not fully pressed by the pressure plates.
Thus, the clutch shaft also stops rotating. Advantages of Multi Plate Clutch. 1. The number of friction surfaces increases the capacity of the clutch to transmit torque, though the size remains fixed. Therefore, considering the same torque transmission, the overall diameter of the multi plate clutch is reduced when compared to a single plate clutch.
2. Due to this advantage, this type of clutch is used in some heavy transport vehicles and racing cars. 3. This multi plate clutch is used in scooters and motorcycles where there is limited space.
Semi-centrifugal Clutch This type of clutch uses lighter pressure plate springs for a given torque carrying capacity, so that the engagement of the clutch in the lower speed range becomes possible. The centrifugal force supplements the necessary extra clamping thrust at higher speeds. Offset bob weights are attached to the release levers at their outer ends, allowing levers to be centrifugally out of balance (Fig.). The centrifugal force causes the pressure plate to force against the driven plate, adding extra clamping load. Although the thrust due to the clamping springs is constant, the movement due to the centrifugal force varies as the square of the speed (Fig). Therefore, the reserve factor for the thrust spring can be reduced to 1.1 compared to 1.4-1.5 for a conventional helical coil spring clutch unit. Consequently, centrifugal clutch can be used for heavy duty applications requiring transmission of greater torque loads.
Fully Automatic Centrifugal Clutch Fully automatic centrifugal clutches smoothly take up the drive from engine idling with a progressive reduction in slip within a narrow rising speed range until sufficient engine power is developed to propel the vehicle directly. Above this speed full engagement of clutch takes place. For carrying out gear changes during vehicle movement, a conventional clutch release lever arrangement is additionally incorporated, which enables the driver to disengage and engage the clutch independently of the flyweight action. A reaction plate is installed in between the pressure plate the cover pressing in the automatic centrifugal mechanism. Four equally spaced bob-weights (Fig. ) are attached to this reaction plate through pivot pins, about which they rotate as centre of gravity is on one side of the pins. When the engine speed increases, the bob weight tends to fly outward. The rotational movement of the bob weight is partially prevented by short struts offset to the pivot pins so that this movement and effort are relayed to the pressure plate. At the same time, the reaction plate compresses both the reaction and pressure springs due to the reaction to this axial clamping thrust causing it to move backwards towards the cover pressing. The greater the centrifugal force, more the springs are compressed and their reaction thrust becomes larger, which increases the pressure plate clamping load.
Fully automatic centrifugal clutch. For achieving the best pressure plate thrust suiting to engine speed characteristics (Fig), adjustable reactor springs are installed, which counteract the main compression spring reaction. The initial compression length for loading of these springs is set up by the adjusting nut after assembly of the whole unit. The resultant thrust of both sets of springs control the actual take-up engine speed of the clutch. Gear changes are made by moving the release bearing forwards during the disengaged position of the clutch. This causes the reactor plate to move rear wards by means of the knife-edge link and also withdraws the pressure plate through the reactor springs to release the pressure plate clamping load. Cone Clutch having friction surfaces in the form of a cone.
The engine crankshaft consists of a female cone. The male cone is mounted on the splined clutch shaft. Cone clutch has friction surfaces on the conical portion. The male cone can easily slide on the clutch shaft.
Working Principle
When the clutch is engaged (When the clutch pedal is not pressed) the friction surfaces of the male cone are in contact with the female cone due to the force of the spring. The power is transmitted from engine to transmission. When the clutch is disengaged (When the clutch pedal is pressed) the male cone slides against the spring force. Now, the power does not transmit from the engine. A cone clutch serves the same purpose as a disk or plate clutch. However, instead of mating two spinning disks, the cone clutch uses two conical surfaces to transmit torque by friction.[1] The cone clutch transfers a higher torque than plate or disk clutches of the same size due to the wedging action and increased surface area. Cone clutches are generally now only used in low peripheral speed applications, although they were once common in automobiles and other combustion engine transmission
2.2 Gear box
The most basic definition of a gearbox is that it is a contained gear train, or a mechanical unit or component consisting of a series of integrated gears within a housing. In fact, the name itself defines what it is — a box containing gears. In the most basic sense, a gearbox functions like any system of gears; it alters torque and speed between a driving device like a motor and a load.
Sliding mesh gearbox The credit for the development of first modern manual transmission was given to French inventors Louis-Rene Panhard and Emile Levassor. This type of transmission offered multiple gear ratios. The gears were engaged by sliding them on their shafts. Shifting of gears was not an easy task, it can only be done by a skilled person. While shifting gears, the gears which are needed to be meshed with each other should be almost at same speed while meshing with each other.
Now the sliding mesh gearbox is superseded by constant mesh gearbox in which all gaars mesh at all times with its pair and synchro mesh gearbox is a further refinement of constant mesh gearbox.
Parts of Sliding Mesh Gearbox: The main parts of sliding mesh gearbox are: i) Shafts :- There are 3 shafts present in Sliding Mesh Gearbox: a) Clutch Shaft – It is input shaft in the sliding mesh gear box. The clutch shaft carries the engine output to the gearbox with the help of enaging and disengaging clutch which is mounted at the engine end. A gear is mounted over this shaft known as clutch gear which is used to transmit rotational motion to lay shaft.
b) Lay Shaft or Counter Shaft – After the input shaft comes the Lay Shaft. Lay shaft is an intermediate shaft between the Clutch Shaft and Main Shaft. In the lay shaft, the gears are rigidly fixed and rotates with the lay shaft. One of the gear of this shaft is always in contact with the gear of the clutch shaft. So when the clutch shaft rotates, the lay shaft also rotates. Lay shaft rotates in a direction counter to the engine rotation. So, it is also known as Counter Shaft. Other gears of lay shaft meshes with different gears of main shaft to obtain different gear ratios. Also, lay shaft has reverse gear which has idler gear attached to it.
c) Main Shaft: This shaft is used as an output shaft in sliding mesh gearbox. In this shaft the gears are not rigidly fixed. The gears of this shaft have internally splined grooves and the outer surface of this shaft is made splined so that the gears can easily slide over the shaft. The gears of main shaft slides over the shaft to mesh with appropriate gears of lay shaft so that required gear ratio is obtained.
ii) Gears: Usually two types of gears were used in sliding mesh gearbox. They are:- a) Spur gear Spur gears have straight teeth that are produced parallel to the axis of gear. These gears are most economical types of gear but tend to vibrate and become noisy at high speed.
b) Helical gear The teeth of helical gears are not parallel to gear axis. The tteth of this gear type are at angle to the gear axis.These gears are less noisy and have a smoother operation than spur gear. Also these gears have higher tooth strength and a higher load carrying capacity.
iii) Gear Lever :- It is used slide the gears in the main shaft to obtain appropriate gear ratio. It is operated by the driver. Construction of Sliding Mesh Gearbox: . The clutch shaft is connected to the engine output and rotates when the engine rotates. A gear is mounted on the clutch shaft which is connected with a gear of lay shaft. . The lay shaft has several gears, one of which is connected to gear of clutch shaft and others gears connect with different gear of main shaft to obtain different gear ratio. Also, one gear in lay shaft is reverse gear and has and idler gear which is placed between the lay shaft gear and main shaft gear when operated. . The main shaft has several gears and these gears can slide over the main shaft to mesh with different gears of main shaft. Working of Sliding Mesh Gearbox: . At first, the clutch shaft is driven by engine. It carries the engine output and rotates in the same direction as that of engine. The gear connected to the clutch shaft also rotates. . As gear of clutch shaft rotates, the lay shaft gear which is connected to the clutch shaft gear also rotates but in opposite direction. . So the lay shaft rotates due to rotation of lay shaft gear that is rigidly fixed in the lay shaft. Due to rotation of lay shaft other gears of lay shaft also rotates as all the gears in lay shaft are rigidly fixed including the reverse gear. . The gears of main shaft are internally splined and the main shaft is also splined, so the gears of main shaft can slide over it. The gear of main shaft are shifted and meshed with different gears of lay shaft to obtain different gear ratios required to face different road problems. Different gears of Sliding Mesh Gearbox: Different gears of Sliding Mesh Gearbox is obtained in the following ways:-
1 First Gear : First Gear is used at the time when vechile starts its movement in forward direction. First Gear provide maximum torque and minimum speed and this gear is obtained when the smallest gear on the lay shaft meshes with the biggest gear in the main shaft.
2 Second Gear: Second Gear is obtained when second largest gear of second smallest gear of lay shaft meshes with middle size gear of main shaft. Second Gear provides lower torque and higher speed than First Gear.
3. Third Gear: Third gear is last gear or top gear of Sliding Mesh Gearbox. This gear is obtained when biggest gear of lay shaft meshes with smallest gear of main shaft. This gear provides maximum speed and minimum power.
4. Reverse Gear: Reverse Gear is used when the vechile needs to move in the opposite direction. In this gear the rotation of the output shaft or main shaft is reversed by placing an idler gear between the lay shaft gear and the main shaft gear which changes the direction of rotation of output shaft. Advantages of Sliding Mesh Gearbox: 1 Since only one gear is in mess in sliding mesh gearbox so less fluctuating loads on shafts causing less vibration and noise unlike the contant mesh gearbox in which all gears are in constant mesh. 2. Its efficiency is more than constant gearbox as only one gear is in mess unlike the contant mesh gearbox in which all gears are in constant mesh. 2. Its manufacturing is easy as compared to constant mesh gearbox. 3. Its mechanism is simple. Disadvantages of Sliding Mesh Gearbox: 1 Only spur gears can be used as gears are not in constant mesh like constant mesh gearbox in which helical or herringbone gears can be used. 2 More effort is required to engage the gear as the gear has to be slided in sliding mesh gearbox unlike constant mesh gearbox where only dog clutch has to be slided for enagement of different gears. 3 Less life of gear as more wear and tear of gear is caused in sliding mesh gearbox due to friction. 4 It takes more time nad money to replace the gears if the gearbox fails but in constant mesh gearbox only dog clutches are to be replaced at failure which takes less time and money.
Constant mesh gear boxIn constant mesh gear box all the gears are always in mesh and the engagement between the gears which are freely rotating on the transmission main shaft and the transmission main shaft is effected by moving the dog clutches, as explained below. The engine gear box shaft is integral with a pinion. The pinion meshes with a wheel on the layshaft. The layshaft is therefore driven by the engine shaft. Three more wheels are fixed to the layshaft as in the sliding mesh gearbox. These gears rotate with the layshaft. The transmission main shaft is just above the layshaft and in line with the engine shaft. The three gears (first gear, second gear and reverse gear) on the main shaft are perfectly free to turn on the main shaft. These three gears are in constant mesh with the three wheels on the layshaft. One of these three gears meshes with a wheel on the layshaft through an idler wheel which is mounted and freely rotating on a pin fixed to the gearbox casing.
The three main shaft gears are, therefore constantly driven by the engine shaft, but at different speeds. The first gear and the second gear rotate in the same direction as the engine shaft while the reverse gear rotates in the opposite direction to the engine shaft.
If anyone of the gears on/the mainshaft is coupled up to the main shaft, then there will be a driving connection between the main shaft and the engine shaft. The coupling is affected by the dog clutch units. The dog clutch members are carried on splined (or squared) portions of the mainshaft. They are free to slide on those squared portions, but have to revolve with the shaft.
If one of the dog clutch members (l) is slid to the left it will couple the wheel (first gear) to the main shaft giving the first gear. The drive is then through the wheels and this dog clutch member. The other dog clutch is meanwhile in its neutral position. If, with the above dog clutch member in its neutral position, the other dog clutch member (2) is slid to the right, it will couple the wheel (second gear) to the mainshaft and give second gear. If this dog clutch member is slid to the left, it will couple the mainshaft directly to the pinion fixed to the engine shaft. This will give a direct drive, as in the sliding mesh gear box. The reverse gear is engaged by sliding the dog clutch member (which gives the first gear) to the right. Then it will couple the wheel (reverse gear) to the mainshaft. The drive is then through the wheels, the idler and the dog clutch member. In the constant mesh gear box, the gears on the mainshaft must be free to revolve. For this, they are either be bushed or be carried on ball or roller or needle bearings.
The main advantages of the constant mesh gear box over the sliding mesh type are as follows: 1. Helical or double helical gear teeth can be used for the gears instead of spur gears. Then gearing is quieter. 2. Synchronizing devices can be used for smooth engagement. 3. Any damage that results from faulty manipulation occurs to the dog clutch teeth and not to the teeth of the gear wheels. 4. Once the dog clutches are engaged, there is no motion between their teeth. But when gear teeth are engaged, the power is transmitted through the sliding action of the teeth of one wheel on those of the other. The teeth have to be suitably shaped to transmit the motion properly. 5. If the teeth on the wheel are damaged, the motion will be imperfect and noise will result. 6. Damage is less likely to occur to the teeth of the dog clutches, since all the teeth engage at once, whereas in sliding a pair of gears into mesh the engagement is between two or three teeth.
SYNCHROMESH GEAR BOX
Synchromesh gear box is an automatic means for matching the speeds of engaging dogs. Synchromesh gear box is a device which facilitates the coupling of two shafts rotating at different speeds. Synchromesh unit is used in most of modern gear boxes. In synchromesh gear box, sliding dog clutches are replaced by synchromesh device. The synchromesh devices are used to simplify the operation of changing gear. Synchromesh device helps unskilled drivers to change gears without the occurrence of clashes and damages.
By synchromesh device, the members which ultimately are to be engaged positively are first brought into frictional contact and then when the friction has equalized their speeds, the positive connection is made.
The basic requirements of synchromesh device are: (1) A braking device such as cone clutch. (2) To permit easy meshing means of releasing pressure on the clutch before engagement of gears.
The engine shaft carries a pinion which meshes with a wheel fixed to the layshaft, while the gear on the mainshaft is free to rotate and is permanently meshed with another wheel fixed to the layshaft. Both the pinion and the wheel on the mainshaft have integral dog tooth portions and conical portions. The synchronizing drum is free to slide on splines on the mainshaft. This drum has conical portions to correspond with the conical portions on the gearbox shaft pinion and on the wheel that rotates freely on the mainshaft. The synchronizing drum carries a sliding sleeve. In the neutral position, the sliding sleeve is held in place by the spring loaded balls which rest in the dents in the sliding sleeve (or ring gear). There are usually six of these balls.
In changing gear, the gear lever is brought to the neutral position in the ordinary way, but is immediately pressed in the direction it has to go to engage the required gear. When a shift starts, the spring loaded balls cause the synchronizing drum and sliding sleeve, as an assembly to move toward the selected gear. The first contact is between the synchronizing cones on the selected gear and the drum. This contact brings the two into synchronization. Both rotate at the same speed. When the speeds of the two have become equal, a slightly greater pressure on the gear lever overcomes the resistance of the balls. Further movement of the shift fork forces the sliding sleeve on toward the selected gear. The internal splines on the sliding sleeve i.e. the dog portion, match the external splines on the selected gear the dog teeth are locked up, or engaged, and thus positive connection is established. The gear shift is completed.
Torque converter
A torque converter is a donut-shaped device that is attached directly between the engine and the transmission. Inside of the torque converter are two series of curved blades that are facing opposite directions. The space inside of the torque converter is full of a fluid, which is used to transfer the power of the engine to the transmission. At first, this does seem a bit odd. How could a liquid be used to drive a car? Basically, the engine drives one of the turbines called the impeller, which pushes the fluid onto the turbine. The torque converter can be as efficient as possible because the blades are precisely engineered to maximize the transmission of energy and reduce turbulence and heat buildup.
A good analogy to describe this phenomenon is two fans sitting face-to-face. When one fan is plugged in (the engine), it will move the second fan (transmission). If the fan blades are the same weight, then they should spin at the same rate.
This is, of course, a rough simplification of the workings of the torque converter. There are a few elements that allow torque converters to be even more efficient, including the stator, which helps redirect the flow of the fluid back into the impeller to improve efficiency. There are also lock-up torque converters, which, at certain RPMs, lock up the torque converter so that it directly rotates with the engine.
WHAT DOES A TORQUE CONVERTER DO?
A torque converter on an automatic essentially takes the place of the clutch on a manual vehicle. To keep the power output of the engine in the optimum range, the torque converter serves to multiply torque at low RPM. Additionally, the design of a torque converter allows for the rotation of the engine and the transmission to differ, since a torque converter uses a fluid coupling to transfer energy to the transmission rather than the mechanical power transmission of a manual clutch. This, in turn, allows for the automatic transmission to work smoothly, all throughout the power band.
HOW DOES A TORQUE CONVERTER WORK?
So, how does a torque converter work then? How can something fluid provide enough power to move a car (let alone at high speeds)? To explain how this works, let’s revisit the fan analogy. Let’s say that the second fan, the one without power, has a heavier blade than the first one. As the powered fan pushes air onto the second fan, it will still rotate, except slower. This specific situation describes the way a torque converter can potentially multiply torque. While the second fan is moving slower, there is more torque behind it.
Let’s then take that analogy and apply it back to the engine. When the transmission upshifts, the torque necessary to keep the gears moving increases. In other words, as the gears go up, the second fan blade gets heavier and heavier. So, once a higher gear is selected, the torque converter will handle this discrepancy with ease. The engine can maintain the same amount of output while the torque converter will rotate slower, providing more torque to help catch the speed of the transmission up to that of the engine. Additionally, the fact that the impeller is not mechanically connected to the transmission, but rather fluidly connected, it won’t ever get locked up and stall.
Overdrive
Introduction An Overdrive is a component of a transmission system which is attached at the end of the gear box in order to provide highest gear output with minimum engine input which in turn makes the drive smooth and more fuel efficient. It is an arrangement of sun and planetary gear which are arranged in such a fashion that when overdrive is enabled, it provides high rotation per minute to the output shaft with reduced engine rotation per minute which in turn provides smooth, noise free and high fuel economy to the vehicle. In some vehicles like KTM Duke 390 it is said that the top or 6th gear is the overdrive gear.
Need of an Overdrive
When we go on a long drive we shift our drive to the top gear which is said to be the direct drive, which means that the final output shaft is rotating at the engine’s rpm which in turn somehow increase the load on the engine’s shaft, so an overdrive can be used with the transmission box which can reduce engine’s load and provides high speed (higher than engine’s rpm) during a long run. Fuel economy is the first priority of the middle class people in countries like India, as overdrive reduces the engine’s load (as discussed above) so it is obvious that with decreased engine’s load we get better fuel economy. In high end cars like Audi A6, Mercedes E-class , luxury and smooth riding experience is the priority which cannot be compromised , so these cars having automatic transmission is equipped with overdrive which make them more luxurious. As the engine’s load is reduced with the use of overdrive which in turn reduces the wear and tear of the engine as well as transmission box, so we can say that using overdrive also reduces the maintenance of the automobile vehicle. If we talk about the performance, overdrive is said to provide 30% more rpm than engine’s rpm.
Working of an Overdrive Overdrive in cars can be enabled or disabled using any of the electrical, magnetic, pneumatic actuation method through button or knob, in first case let’s just consider both the enable and disabled cases to understand its working- Overdrive Disabled – When overdrive is disabled the input shaft passing through the sun gear rotates the sun gear which in turn rotates the constantly meshed planetary gears and then these planetary gears rotates the annulus and direct drive (same as input shaft rpm) is obtained. Overdrive enabled- When driver enabled the overdrive, the sun gear becomes fixed which mean the annulus is now rotated by the planetary gears or in other words now the input from the input shaft is now transferred through the planetary gear to the annulus due to which overdrive is obtained, which means now the output shaft rotates with the higher rpm than input shaft due to the higher reduction ratio of planetary gears and annulus.
Transmission system In a manual transmission (MT) vehicle the driver takes the decision when to shift and also actuates the clutch and the gears. In an electronic clutch transmission (no clutch pedal), the decision to shift is also taken by the driver. The difference is that the clutch actuation can also be done automatically (by a electrohydraulic or electric actuator) and the gear actuation is still managed by the driver. In a automated manual transmission (AMT) or automatic transmission (AT), both the decision to perform a gear shift and the actuation of clutch/gears are done automatically without the intervention of the driver. The clutch and gear assemblies have electrohydraulic or electric actuators controlled by electronic control modules (ECM). The difference between an AMT and AT is at the hardware level. AMTs have constant mesh gears, like a MT, while AT have planetary (epicyclic) gear assemblies. From the software (function) point of view, both AMTs and ATs, can perform automatic or manual (driver decision) gear shifts.
In this article we are going to focus on automated manual transmissions (AMT). At a global scale, the market share of automated manual transmissions is quite small, only 1% of the total vehicles sold are equipped with AMT.
Image: Globat market share of transmission types Credit: Statista Electric – transmissions for electric vehicles (usually single-speed transmissions) AMT – Automated Manual Transmissions DCT – Double Clutch Transmission CVT – Continuously Variable Transmission AT – Automatic Transmission MT – Manual Transmission
Even if the global market share, between 2012 and 2015, was constant, the number of automate manual transmissions manufactured rose each year. This is mainly due to a higher number of vehicles manufactured and increasing AMT market share in India.
On a vehicle with manual transmission, the engagement/disengagement of the clutch and gears are controlled directly by the driver, through the clutch pedal and gear shift lever. On an AMT, there is no more clutch pedal and the gear shift lever is replaced by program selection lever. The actuation of the clutch and gears is done with electrohydraulic of electric actuators, controlled through electronic signals coming from an electronic control module.
: Main components of a manual transmission (MT) clutch pedal 1. clutch actuation fluid reservoir 2. master cylinder 3. high pressure pipe 4. wheel cylider 5. (clutch) pressure plate 6. dual-mass flywheel 7. friction (clutch) disc 8. synchronizer 9. gear actuation mechanism 10. gear shift lever 11. output shaft 12. input shaft
An automated manual transmission (AMT) is basically a manual transmission (MT) with electronic controlled clutch and gear actuators. To convert a manual transmission into an automated manual transmission, the clutch pedal (1) and the gear shift lever (11) are replaced by electrohydraulic or electric actuators. First generations of AMTs were based on the concept of “add-on“, which means that an existing, already designed MT was converted into an AMT by adding external electronic controlled actuator mechanisms. Later generations of AMTs had the actuators embedded into them from the early stages of the design phases.
Image: MT to AMT conversion Credit: LuK (Schaeffler) A conversion from a MT to an AMT requires: . replacement of the clutch actuation mechanism with an electrohydraulic / electrical actuator . replacement of the gear actuation mechanism with an electrohydraulic / electric actuator . integration of an electronic control module . integration of: input shaft speed sensor, clutch position sensor, gear selection and engagement position sensors, shift lever position sensor, fluid pressure and temperature sensor (in case of an electrohydraulic actuation system) . engine control software which allows torque control during gearshift Depending on the vehicle manufacturer, the automated manual transmissions have different commercial names but, in the end, they are the same in terms of functionality:
2.3 propeller shaft
The propeller shaft is a steel tube which is used to deliver the transmission output torque (from gearbox) to the differential before it goes to the wheel. It has to cope up with the difference in line and level of the gear box output shaft and differential input shaft.
While transmitting the power, the angle between the axes of the gear box output shaft and the propeller shaft changes continuously. The angle between the propeller shaft axis and the differential input axes also keeps on changes. Hooke’s joint or universal joint are fitted on both ends of the propeller shaft in order to take care of these angle changes. The effective length of the propeller axis also keeps on changing. To take care of it the propeller shaft has splined ends on which the universal joints are fitted which allows the movement of universal joints along the axis of propeller shaft. The propeller shaft is designed for high critical speed. The shafts are subject to torsion and shear stress therefore they should be strong enough to bear the stress.
Axles
Following are the three different types of axles
Rear Axles Front Axle Stub Axle Rear Axle
In between the differential and the driving wheels is the rear axle to transmit power from the differential to the driving wheels. It is clear from the construction of the differential, that the rear axle is not a single piece, but it is in two halves connected by the differential, one part is known as the half shaft.
The inner end of the half shaft is connected to the sun gear of the differential. and the outer end of the driving wheel. In rear-wheel-drive vehicles, the rear wheels are the driving wheels. Whereas, in front-wheel drive vehicles, the front wheels are the driving wheels. Almost all rear axles on modern passenger cars are live axles, that is, they revolve with the wheels.
Dead axles simply remain stationary, do not move with the wheels. A housing completely encloses the rear axles and the differential, protecting them from water, dust and injury, in addition to mounting their inner bearings and providing a container of the lubricant.
Types of Rear axles
Depending upon the methods of supporting the rear axles and mounting the rear wheels, the three types of rear axles are as follows:
1. Semi-floating axle 2. Full-floating axle 3. Three quarter floating axle
Semi-Floating Axle
A semi-floating axle has a bearing located on the axle and inside the axle casing. It has to support all the loads as listed above. Therefore, it needs to be of a larger size, for the same torque output, than any other type. The inner end of the axle is supported by the differential side gear.
It is thus relieved of the job of carrying the weight of the car by the axle housing. The outer end has to support the weight of the car and take end thrust. The inner end of the axle is splined to the differential side gear.
The outer end is flanged so that the wheel can be bolted directly to it. In some design, the hub of the wheel is keyed to the outer end of the axle. The vehicle load is transmitted to the axle through the casing and the bearing, which causes the bending or shearing of the axle. The semi-floating axle is the simplest and cheapest of all other types and widely used on cars.
Full-Floating Axle
A full floating axle has two deep groove ball or taper roller bearings, located between the axle casing and wheel hub. The outer of an axle is made flanged to which the wheel hub is bolted. The axle is not supported by bearing at either end, and its position is maintained by the way that it is supported at both ends.
Thus the axle is relieved of all strain caused by the weight of the vehicle on the end thrust. It transmits only the driving torque. For this reason, it is called full floating. The axle may be removed from the housing without distributing the wheel by removing the nuts.
An additional advantage of this design is the ability to the vehicle even if it has a broken axle. This type of axle is more, expensive and heavier than the other axle. It is usually fitted on commercial vehicles.
Three-Quarter Floating Axle
This type of axle has a bearing placed between the hub and the axle casing. Thus, the weight of the vehicle is transferred to the axle casing, and only the side thrust and driving torque are taken by the axle.
The axle is keyed rigidly to the hub, thus proving the driving connection and maintaining the alignment of the wheel. The inner end of this axle has the same construction as that of the semi- floating axle. Although the three-quarter floating axle is more reliable it is not as simple as the semi- floating axle.
Front Axle
The front axle is used to carry the weight of the front part of the vehicle as well as to facilitate steering and absorb shocks due to road surface variations. It must be right and robust in construction.
The front axle is usually a steel drop forging having 0.4% carbon steel or 1-3% nickel steel. It is made of I-section in the centre portion, while the ends are made either circular or elliptical. With this construction, it takes bending loads due to the load of the vehicle. Also, the torque centre portion is given a downward sweep. The different components of the front axle are the beam, stub axle, swivel pin and track rod.
Read also: Basic Engine Components (Engine parts Names and Pictures)
Types of Front Axles
Usually, there are two main types of the front axle: 1. Live front axle. 2. Dead front axle.
The front axles are usually dead axles because they do not rotate, in contrast to the live axles that they are used in the rear axle to transmit power to the rear wheels. A live front axle, as compared to the dead axle, has the additional function of transmitting the driving power taken from a transfer gearbox to the front wheels having a different swivelling mechanism.
The live front axles although resembling the gear axles have some difference at the axle half shafts end where the wheels are mounted. A dead front axle has enough rigidity and strength to carry the weight of the vehicle from the springs to the front wheels.
The ends of the axle beam are formed suitably to assemble the stub axle. In order to accommodate a swivel pin connecting the sub axle portion of the assembly, the ends of the beam are usually shaped either as a yoke or plain surface with drilled hole.
The figure shows front axle components with the steering linkage. The wheels are fixed on the stub axles which are usually pivoted. From the stub axle, the inclined steering arms are connected to the track rod ends, and a third steering arm is attached to the drag link. Some vehicles have the drag link placed transversely instead of in the fore and at the position in order to allow a more compact vehicle design. It is often used in independent wheel suspension systems. The drag link connects the steering linkage to the drop arm of the steering box.
Stub Axle
The front wheels are mounted on the stub axles, which are connected to the front axle by means of kingpins. The stub axles are the foreging of 3% nickel steel and alloy steels containing chromium and molybdenum.
The stub axle turns on the pink pin which is a light drive fit in the axle beam eye placed and locked by a taper cotter pin. Phosphor bronze bushes are fitted into the forked ends of the axle to provide a bearing surface for the kingpin.
Vertical load are taken by a steel washer or a thrust bearing located either on the top fork of the stub axle or between the lower fork and the underside of the axle beam.
Types of Stub Axle
Following are the four types of the stub axle:
1. Elliot. 2. Reverse Elliot. 3. Lamoine. 4. Reversed Lamoine.
The Elliot stub axle is attached to the front axle by placing in the yoke end with a kingpin and cotter to join the two together.
In Reversed Elliot type stub axle, the arrangement is reversed. In Lamoine type stub axle, instead of yoke type hinge, an L-shaped spindle is used as shown in the figure.
Why You Need a Differential Car wheels spin at different speeds, especially when turning. You can see from the animation that each wheel travels a different distance through the turn, and that the inside wheels travel a shorter distance than the outside wheels. Since speed is equal to the distance traveled divided by the time it takes to go that distance, the wheels that travel a shorter distance travel at a lower speed. Also note that the front wheels travel a different distance than the rear wheels.
For the non-driven wheels on your car -- the front wheels on a rear-wheel drive car, the back wheels on a front-wheel drive car -- this is not an issue. There is no connection between them, so they spin independently. But the driven wheels are linked together so that a single engine and transmission can turn both wheels. If your car did not have a differential, the wheels would have to be locked together, forced to spin at the same speed. This would make turning difficult and hard on your car: For the car to be able to turn, one tire would have to slip. With modern tires and concrete roads, a great deal of force is required to make a tire slip. That force would have to be transmitted through the axle from one wheel to another, putting a heavy strain on the axle components. Propeller shaft:
The propeller shaft is a driving shaft which connects the transmission main shaft to the differential of the real axle. It transmits the power from gear box to rear axle with the help of universal joints. The propeller shaft is also known as drive shaft.
To receive the power from the gear box output shaft and without any change in speed transmit it to the input pinion of the differential for onward transmission to the rear axle and rear wheels. To cope with the difference in line with the level of the gear box output shaft and the differential input pinion shaft. The propeller shaft has to operate at varied lengths and varied angles.
The engine of the automobile is somewhat rigidly attached to the frame by springs. As the vehicle moves on the road there are jerks and bumps due to which the springs expand and contract. This changes the angle of drive between the propeller shaft and the transmission shaft.The propeller shaft has to withstand the torsional stresses of the transmitting torque, and yet it must be light and well balanced so that vibrations will not occur at high speed. So it is usually made of a strong steel tube
Universal joint:
A universal joint allows driving torque to be carried through two shafts that are at an angle with each other. A simple universal joint consists of two Y- shaped yoke, one on the driving shaft and other on the driven shaft. The four arms of spider are assembled in needle bearings in the two yokes. The driving shaft and yoke force the spider to rotate.
The other two trunnions of the spider then cause the driven yoke to rotate. When the two shafts are at an angle with each other, the needle bearings permit the yokes to swing around on the trunnions with each revolution. A simple universal joint does not transmit the motion uniformly when the shafts are operating an angle. Because of this, two universal joints are used in a vehicle, one between the gear box and the propeller shaft and other between the propeller shaft and the differential pinion shaft.
Slip joint is attached to the driven yoke to increase or decrease the length of propeller shaft. It has outside splines on the shaft and matching internal splines in a mating hollow shaft or yoke. When assembled, the splines cause the shafts to rotate together while they can move back and forth. This changes the length of propeller shaft.
Caster is the tilting of the uppermost point of the steering axis either forward or backward when viewed from the side of the vehicle. A backward tilt is positive; a forward tilt is negative. Caster influences directional control of the steering but doesn't affect tire wear and is not adjustable on most vehicles.
Caster is affected by vehicle height, so it is important to keep the body at its designed height. An overloaded vehicle or one with a weak or sagging rear spring will affect caster. When the rear of the vehicle is lower than its designated trim height, the front suspension moves to a more positive caster. If the rear is higher than its designated trim height, the front suspension moves to a less positive caster.
Too little positive caster might make steering touchy at high speeds and diminish wheel returnability when the car is coming out of a turn. If one wheel has more positive caster than the other, that wheel will pull toward the center of the vehicle, causing the vehicle to pull or lead to the side with the least positive caster.
Camber is the tilting of the wheels from the vertical when viewed from the front of the vehicle. When wheels tilt outward at the top, the camber is positive; when wheels tilt inward at the top, the camber is negative. The amount of tilt is measured in degrees from the vertical. Camber settings influence directional control and tire wear.
Too much positive camber will result in premature wear on the outside of the tire and excessive wear on the suspension parts. Too much negative camber will result in premature wear on the inside of the tire as well as excessive wear on the suspension parts. An unequal side-to-side camber of 1° or more will cause the vehicle to pull or lead to the side with the most positive camber.
T oe is a measurement of how much the wheels are turned in or out from a straight-ahead position. When the wheels are turned in, toe is positive; when the wheels are turned out, toe is negative. The actual amount of toe is normally only a fraction of a degree. The purpose of toe is to ensure that the wheels roll parallel.
Toe also serves to offset the small deflections of the wheel support system that occur when the vehicle is rolling forward. In other words, with the vehicle standing still and the wheels set with toe-in, the wheels tend to roll parallel on the road when the vehicle is moving. Improper toe adjustment will cause premature tire wear and steering instability. The kingpin offset/scrub radius is the distance from the center of the wheel contact face to the intersection point of the kingpin extension. The line through the center point of the spring strut support bearing and the control arm ball joint corresponds to the kingpin. The scrub radius is influenced by camber, kingpin angle, and wheel offset of the wheel rim. This is set at the factory and is not adjustable.
Setback is the amount by which one front wheel is farther back from the front of the vehicle than the other. It is also the angle formed by a line perpendicular to the axle centerline with respect to the vehicle's centerline. If the left wheel is farther back than the right, setback is negative; if the right wheel is farther back than the left, setback is positive. Setback should usually be zero to less than half a degree, but some vehicles have asymmetrical suspensions by design.
Wheel balancing
Wheel balancing is the process of balancing the weight of a tire and wheel assembly so that it travels evenly at high speeds. Balancing requires putting a mounted wheel and tire on a balancer, which centers the wheel and spins it to determine where the weights should go. Every time a wheel is first mounted onto a vehicle with a new tire, it has to be balanced. The goal is to make sure the weight is evenly distributed throughout each of the wheels and tires on a vehicle. This process evens out heavy and light spots in a wheel, so that it rotates smoothly. If there is even a slight difference in weight in the wheels, it will cause enough momentum to create a vibration in the car.
In fact, wheels and tires are never exactly the same weight all around. The wheel's valve stem hole will usually subtract a small amount of weight from that side of the wheel. Tires will also have slight weight imbalances, whether from a joining point of the cap plies or a slight deviation from perfectly round. At high speeds, even a tiny imbalance in weight can become a large imbalance in outward force, which could cause the wheel and tire assembly to spin in a heavy and uneven motion. This usually turns into a vibration in the car as well that could cause uneven and damaging wear on the tires.
Chapter 3 Steering Systems The function of a steering system is to convert the rotary movement of the steering wheel in driver’s hand into the angular turn of the front wheels on road. Additionally, the steering system should provide mechanical advantage over front wheel steering knuckles, offering driver an easy turning of front wheels with minimum effort in any desired direction. The main causes of stiff steering include (i) insufficient lubrication of the king-pins or steering linkage, (it) tyre pressure too low, (Hi) wheels out of track, i.e. toe-in not correct, and (iv) stiffness in the steering column itself, caused by lack of lubricant or over tightening. The steering system is designed to enable the driver to control and continuously adjust the steered path of the vehicle. Also it provides a positive response to whatever direction the driver
Ackermann steering geometry is a geometric arrangement of linkages in the steering of a car or other vehicle designed to solve the problem of wheels on the inside and outside of a turn needing to trace out circles of different radii It was invented by the German carriage builder Georg Lankensperger in Munich in 1817, then patented by his agent in England, Rudolph Ackermann (1764–1834) in 1818 for horse-drawn carriages
Davis steering gear is an exact steering gear mechanism. It has two sliding pairs and two turning pairs. In this mechanism, the slotted links are attached to the front wheel axle, which turn about two pivotal points. It has the rod and it is constrained to move in the direction of its length by the sliding two members.
Steering gear
The steering gear is a device for converting the rotary motion of the steering wheel into straight line motion of the linkage. The steering gears are enclosed in a box, called the steering gear box. The steering wheel is connected directly to the steering linkage it would require a great effort to move the front wheels. Therefore to assist the driver, a reduction system is used. The different types of steering gears are as follows:
1.Worm and sector steering gear. 2. Worm and roller steering gear. 3. Cam and double lever steering gear. 4. Worm and ball bearing nut steering gear.
5. Cam and roller steering gear.
. 1Recirculating ball steering gear
This is the most common steering gear in Indian tractors. In this the lower end of the steering column has a worm. A box type nut is clamped on this worm which has numerous ball bearings circulating between the worn and the nut. As the steering wheel on top of the steering column is turned, the nut moves up and down. This movement of the nut is sensed by the sector of the pitman which is connected to the nut. The movement of the nut is transferred into the rotational motion of the pitman. Drop arms are mounted on this pitman shafts. The blow-up figure of a recirculating ball
steering box is as shown in FiG
Worm and Roller Type Steering Box
In case of worm and roller steering, the worm at the lower end of the steering column is in the form of a cam. There is a roller which follows the shape of the worm. The roller is a part of the pitman. As the roller follows the cam when the steering column is turned, the motion is transferred to the pitman and to the drop arms. An exploded view of the worm and nut steering is given in Fig
Worm and Sector Type Steering Box
In this type of steering box, the steering worm of the steering column rotates a steering gear sector which is meshed with the worm. The gear sector in turn rotates the pitman on which it is mounted. The pitman is further connected to the steering linkage for steering the wheels. The Fig shows the method in which the worm and sector steering is used to convert the rotation of steering column
into rotation of pitman.
Rack and Pinion Type Steering Box
In a rack and pinion steering gear, a pinion is attached at the end of the steering shaft. When the steering wheel is turned, the pinion gear spins, moving the rack – left or right, depending on which way the steering is turned. The rack forms the part of the tie rod with steering spindle at its ends which push or pull the steering links for steering the wheels. Fig
.
Chapter 4
BRAKING SYSTEM
Braking action is the use a controlled force to stop the running vehicle. When the brakes are applied frictional force developed which retard the vehicle .
WORKING OF BRAKES
A COMMON MISCONCEPTION ABOUT BRAKES IS THAT BRAKES SQUEEZE AGAINST A DRUM OR DISC, AND THE PRESSURE OF THE SQUEEZING ACTION SLOWS THE VEHICLE DOWN. THIS IS IN FACT A PART OF THE REASON FOR SLOWING DOWN A VEHICLE.
ACTUALLY BRAKES USE FRICTION OF BRAKE SHOES AND DRUMS TO CONVERT KINETIC ENERGY DEVELOPED BY THE VEHICLE INTO HEAT ENERGY.
WHEN WE APPLY BRAKES, THE PADS OR SHOES THAT PRESS AGAINST THE BRAKE DRUMS OR ROTOR CONVERT KINETIC ENERGY INTO THERMAL ENERGY VIA FRICTION. TYPES OF BRAKE
The brake can classified according to following considerations
purpose
1).Foot brake 11) Hand brake
2.Location.
1)Wheel brake 11) Transmission brake
3.Construction
1) Drum brake 11) Disc Brake
4. Mode of operation
1)Mechanical brake
11) Hydraulic brake
111)Vacuum brake
Iv)Air brake
v)Electric brake
Mechanically Operated System
The layout of a simple mechanical system is illustrated in Fig. Four adjustable rods or cables connect the brake shoe operating levers to a transversely mounted cross-shaft. The footbrake and handbrake controls are connected to the cross-shaft using links with elongated holes that allow independent operation of each control.
The mechanical system provides the same brake pedal force to each brake only when the mechanism is balanced so that all the shoes with the drums are operated simultaneously. If one brake has a much smaller shoe-drum clearance than the others, the total force on the brake pedal is directed to that brake and the unbalanced braking action causes the vehicle of ‘pull’ violently to the side with that brake. Compensation devices are installed in the system to overcome this problem.
Figure shows a simple arrangement for balancing two brakes. A fully compensated mechanical brake system requires three compensators that is front (to balance the front brakes), rear (for the rear brakes) and centre (to equalize front and rear MECHANICAL OPERATED BRAKES
MECHANICAL OPERATED BRAKES
DRUM BRAKES The drum brake has a metal brake drum that encloses the brake assembly at each wheel. Two curved brake shoes expand outward to slow or stop the drum which rotates with the wheel.
Hydraulic disc and drum brake
In a disc brake, the fluid from the master cylinder is forced into a caliper where it presses against a piston. The piston in turn squeezes two brake pads against the disc (rotor), which is attached to wheel, forcing it to slow down or stop
WORKING OF DRUM BRAKES
1. Drum brakes work on the same principle as the disc brakes.
2. Shoes press against a rotating surface.
3. In this system that surface is called a drum.
4. Drum brake also has an adjuster mechanism, an emergency brak mechanism and lots of springs.
5. The shoes are pulled away from the drum by the springs when the brakes are released. For the drum brakes to function correctly, the brake shoes must remain close to drum without touching it.
If they get too far away from the drum (as the shoes wear down), the piston will require more fluid to travel that distance and the brake pedal will sink closer to the floor when we apply brake. hat is why most drum brakes have an automatic adjuster.
DRUM BRAKE ADJUSTER
For the drum brakes to function correctly, the brake shoes must remain close to drum without touching it.
If they get too far away from the drum (as the shoes wear down), the piston will require more fluid to travel that distance and the brake pedal will sink closer to the floor when we apply brakes. That is why most drum brakes have an automatic
2. HYDRAULIC BRAKES Brake which are operated by means of hydraulic pressure or fluid pressure are known as hydraulic brakes Components of Hydraulic brakes 1.Brake Pedal 2.Master cylinder 3.Fluid reservoir 4.Wheel cylinder
Figure of Hydraulic brake
HYDRAULIC BRAKES
Hydraulics is the use of a liquid under pressure to transfer force or motion, or to increase an applied force.
The pressure on a liquid is called HYRAULIC PRESSURE.
And the brakes which are operated by means of hydraulic pressure are called HYDRAULIC BRAKES.
These brakes are based on the principle of Pascal’s law.
PASCAL’S LAW The pressure exerted anywhere in a mass of confined liquid is transmitted undiminished in all directions throughout the liquid.
applied in hydraulic lifts, hydraulic brakes etc.
Master cylinder of Hydraulic Brake
When we press the brake pedal, it pushes on primary piston through a linkage.
Pressure is built in the cylinder and the lines as the brake pedal is depressed further.
The pressure between the primary and secondary piston forces the secondary piston to compress the fluid in its circuit.
If the brakes are operating properly, the pressure wll be same in both the circuits.
If there is a leak in one of the circuits, that circuit will not be able to maintain pressure.
Master cylinder
It is the main component of hydraulic braking system. It can rightly name as heart of hydraulic brake system. It serve as following purpose in the system.
It build up hydraulic pressure to operate the the brakes.
It serves as a pump to bleed or force air out of the system.
It contain the fluid reservoir which is using for braking
Wheel Cylinder and Master cylinder
Wheel Cylinder
• It is an important part of hydraulic braking system. The construction of wheel cylinder is very simple. It consists of cylinder body, pistons,rubber cups, coil spring and bleeder valve.The cylinder body contains two holes which provide connections for the pipe line and the bleeder valve. The rubber cups avoid the leakage of the fluid out of the wheel cylinder.
Advantage of Hydraulic Brake
Equal braking effort to all the four wheels
Less rate of wear (due to absence of joints compared to mechanical brakes)
Force multiplication (or divisions) very easily just by changing the size of one piston and cylinder relative to other. • Disadvantage of Hydraulic Brake Even slight leakage of air into the breaking system makes it useless.
• The brake shoes are liable to get ruined if the brake fluid leaks out.
Vacuum Brakes
VACUUM BRAKES: In a vacuum brake system, depressing the brake pedal opens a valve between the power cylinder, which contains a piston, and the intake manifold to which the power cylinder is connected. When you apply the brakes, air is exhausted from the cylinder head of the piston. At the same time, atmospheric pressure acts on the rear side of the piston to exert a powerful pull on the rod attached to the piston.
When the brake valve is closed, the chamber ahead of the piston is shut off from the intake manifold and is opened to the atmosphere. The pressure is then the same on both sides of the piston; therefore, no pull is exerted upon the pull rod. The brakes are released and the piston returned to its original position in the power cylinder by the brake shoe return springs.
Air Brake System • A pneumatic brake or compressed air brake system is the type of brake system in which the compressed liquid fluid from the hydraulic system is replaced with the compressed air for applying pressure to the master cylinder’s piston which in turn presses the brake pads in order to stop or decelerate the vehicle.
• Pneumatic air brake system is usually used in heavy vehicles like buses and trucks.
Adjustment of brake drum lining • Drum brakes usually need to be adjusted when the brake pedal has to be pressed down a lot before the brakes engage. Adjustments can be done only on brakes that are in good shape. Keep in mind that not all drum brakes are adjustable. To confirm your brakes are in good working order before you adjust them, check your vehicle for symptoms of a bad or failing drum brake.
Step 1: Lift the rear end of the vehicle. • Make sure the vehicle is in park and that the parking brake is set. • Step 2: Remove the tire. With the vehicle lifted safely and secured, it is time to remove the tires. • Step 3: Access the drum brake adjustment star wheel. The drum brake adjuster is located under an access cover in the back of the drum brake.
• Using the screwdriver, gently pry out the rubber grommet that protects this access cover.
Anti-lock braking system (ABS) As the name signifies, the anti-lock braking system is a safety system in cars and other automobiles that keeps their wheels from locking up and helps their drivers to maintain steering control. Also referred to as anti-skid braking system sometimes, it enables the wheels of a vehicle to maintain tractive contact with the ground so that they don’t go into an uncontrolled skid.
• The basic theory behind anti-lock brakes is simple. It prevents the wheels from locking up, thus avoiding uncontrolled skidding. ABS generally offers improved vehicle control and decreases stopping distances on dry and slippery surfaces. ABS has four major components: 1) Speed Sensor
• This sensor monitors the speed of each wheel and determines the necessary acceleration and deceleration of the wheels. It consists of an exciter (a ring with V-shaped teeth) and a wire coil/magnet assembly, which generates the pulses of electricity as the teeth of the exciter pass in front of it.
2) Valves
• The valves regulate the air pressure to the brakes during the ABS action. There is a valve in the brake line of each brake that is controlled by the ABS. In the first position, the brake valve is open and it allows the pressure from the master cylinder to be transferred to the brakes. In the second position, the brake valve remains closed and pressure from the master cylinder to the brakes is constrained. In the third position, the valve releases some of the pressure on the brakes.
• The third step is repeated until the car comes to a halt. The resistance that you feel when braking suddenly at high speeds is actually the brake valves controlling the pressure that is being transferred to the brakes from the master cyl 3) Electronic Control Unit (ECU) • The ECU is an electronic control unit that receives, amplifies and filters the sensor signals for calculating the wheel rotational speed and acceleration. The ECU receives a signal from the sensors in the circuit and controls the brake pressure, according to the data that is analyzed by the unit.
• 4) Hydraulic Control Unit
The Hydraulic Control Unit receives signals from the ECU to apply or release the brakes under the anti-lock conditions. The Hydraulic Control Unit controls the brakes by increasing the hydraulic pressure or bypassing the pedal force to reduce the braking power.
Chapter no.5
Coil spring
A coil spring is a mechanical device which is typically used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces. They are made of an elastic material formed into the shape of a helix which returns to its natural length when unloaded. Coil springs for vehicles are typically made of hardened steel. A machine called an auto-coiler takes spring wire that has been heated so it can easily be shaped. It is then fed onto a lathe that has a metal rod with the desired coil spring
• LEAF SPRINGS
A leaf spring is a component of some vehicles’ suspension systems. Specifically, a leaf spring is composed of several (or occasionally just one) thin strips of metal, called leaves, arranged on top of each other to form a single curved piece. The bending of the leaves and the friction between them as they slide slightly over each other while bending, absorbs the vehicle’s weight as well as any bumps. Most leaf springs are curved
• Air suspension system Air suspension systems essentially replace a vehicle's coil springs with air springs. The air springs are simply tough rubber and plastic bags inflated to a certain pressure and height to mimic the coil springs. But the similarities end there. By adding in an on-board air compressors, sensors and electronic controls, today's air suspension systems provide several advantages over all-metal, conventional springs, including near-instant tuning, and the ability to adapt handling to different situations and vary load capability Construction:
• A telescopic shock absorber derives its name from tubular shape of early telescopes used in ancient times.They are two types viz. mono tube and twin tube type. The twin type shock absorber is as shown in the figure. • Rod G is attached to a two way valve A; while another similar two way valve B is attached at the lower end of cylinder C.
• There is a fluid (oil) in the space between the valve A and B and also in the annular area between cylinder C and tube D.H is a gland in the head J. The eye E is connected to axle and eye F is connected to the chassis frame.
Working:
Consider that the vehicle has come across a bump.
Then the eye E would move up and thereby the fluid will pass from the lower side of valve assembly A to the upper side. But since the volume of the space above A is less by the volume of rod G, the fluid will also exert its pressure on valve assembly B and go to the underside of valve B.
This passage of the fluid through valve opening provides the damping.
A similar process takes place in opposite direction for rebound.
Chapter no.6 Battery
Working of Lead Acid Battery
The storage battery or secondary battery is such a battery where electrical energy can be stored as chemical energy and this chemical energy is then converted to electrical energy as and when required. The conversion of electrical energy into chemical energy by applying external electrical source is known as charging of battery. Whereas conversion of chemical energy into electrical energy for supplying the external load is known as discharging of secondary battery
During charging of battery is passed through it which causes some chemical changes inside the battery. This chemical changes absorb energy during their formation.
When the battery is connected to the external load, the chemical changes take place in reverse direction, during which the absorbed energy is released as electrical energy and supplied to the load.
Materials used for Lead Acid Storage Battery Cells
The main active materials required to construct a lead acid battery are
Lead peroxide (PbO2) The positive plate is made of lead peroxide. This is dark brown, hard and brittle substance.Sponge lead (Pb) The negative plate is made of pure lead in soft sponge condition.
Dilute sulfuric acid (H2SO4) Dilute sulfuric acid used for lead acid battery has a ratio of water : acid = 3:1
Checking of battery
Battery checking/testing should be considered an integral part of any periodic vehicle maintenance routine and should be performed whether or not a starting problem has occurred. Due to the increased electrical demands on the battery, little warning is given before failure. Pre-emptive battery replacement can help eliminate many of the costs and problems associated with a flat or end of life battery
There are many different types of testing equipment available. A digital battery tester is the preferred option as they are safe, easy to use and offer a quick diagnosis of the condition of the battery. Fixed and adjustable load testers, voltmeters, hydrometers and discharge testers can also be used, however correct training is required prior to using any of these testers to prevent personal injury or damage to the vehicle.
Chapter no.7
Dynamo
• Dynamo is an older term used to describe a generator that makes direct current power. DC power sends electrons in only one direction. The problem with a simple generator is that when the rotor rotates it eventually turns completely around, reversing the current. Early inventors didn't know what to do with this alternating current, alternating current is more complex to control and design motors and lights for. Early inventors had to figure a way to only capture the positive energy of the generator, so they invented a commutator. The commutator is a switch that allows current to only flow in one direction.
• The Dynamo consists of 3 major components: the stator, the armature, and the
commutator. •
The Generator
The generator differs from the dynamo in that it produces AC power. Electrons flow in in both directions in AC power. It wasn't until the 1890s that engineers had figured out how to design powerful motors, transformers and other devices which could use AC power in a way that could compete with DC power.
• While the alternator uses commutators, the generator uses a slip ring with brushes to tap the power off of the rotor. Attached to the slip ring are graphite or carbon "brushes" which are spring loaded to push the brush onto the ring. This keeps power consistently flowing. Brushes get worn down over time and need to be replaced.
• An alternator has a number of advantages and differences compared to a dynamo (generator): 1. It produces a useful output even at low revs which a dynamo cannot. An alternator will still deliver between 13v-14v even at idle speeds enough to charge the battery. This is because it can withstand much higher revs than a dynamo and can thus be geared higher so producing useful output at low revs
• . 2. It is mechanically simpler than a dynamo and therefore easier to maintain and should have a longer life, and can also therefore run at higher revs as described in 1. above
• . 3. An alternator DOES have brushes (which will eventually wear out) but they rest against smooth rings called "slip rings" and therefore the electrical "noise" (interference spikes etc) from them is very low. A dynamo, on the other hand, has brushes which rest against a thing called a commutator, which has a number of segments over which the brushes must pass. This creates a lot of electrical noise (various crap on the supply line in layman's terms). • 4. A dynamo produces AC current from its rotation which is mechanically turned into DC current through the use of the commutator mentioned in 3. above. An alternator produces AC too, but the AC is turned into DC by a diode pack rather than by mechanical means. Neither a dynamo nor an alternator produce smooth DC.... both produce half sinusoids which overlap each other like the power curves from pistons in a 6 or 8 cylinder car. Smoothing is done by the battery "filling in " between the peaks. So the diodes in an alternator rectify the AC (ie: convert it to DC) but do NOT smooth it.
• Alternator components & their functions: Regulator
The voltage regulator controls the amount of power distributed from the alternator to the battery in order to control the charging process. Regulators are designed with different functions and work depending on their specification.
• Rectifier
The rectifier is used to convert current from alternating current (AC) to direct current (DC) during the charging process.
• Rotor
The rotor is the spinning mass inside the alternator that rotates via the pulley and drive belt system. The rotor acts as a spinning electromagnet.
• Slip Rings
The Slip rings are used as a means of providing direct current and power to the rotor.
• Slip Ring End Bearing
The bearings are designed to support the rotation of the rotor shaft.
• Stator
The stator consists of several coils of wire wound through an iron ring. The stator sits outside the rotor, when a magnetic field is created the electrical current is made.
• Drive End Bearing
The bearings are designed to support the rotation of the rotor shaft.
• Pulley
The pulley is connected to the rotor shaft and the drive belt system. Rotation created by the engine the drive belt system turns the pulley beginning the charging process.