A PROJECT REPORT [10ME85L]

ON ANALYSIS AND OPTIMIZATION OF STUB AXLE OF TATA NANO Submitted in partial fulfillment of the requirement for award of degree in Bachelor of Engineering (Mechanical Engineering)

Of

VISVESVARAYA TECHNOLOGICAL UNIVERSITY, BELGAUM

HITESH KUMAR (1NH10ME019) RAHUL (1NH11ME036) SHRAY SHAH (1NH10ME051) VIGNESHWAR. S (1NH11ME060)

Project work carried out at NEW HORIZON COLLEGE OF ENGINEERING, BANGALORE Under the Guidance of Dr. M.S. Ganesha Prasad Head of Department, Department of Mechanical Engineering, NHCE Department of Mechanical Engineering NEW HORIZON COLLEGE OF ENGINEERING (Accredited by NBA, Permanently Affiliated to VTU) A Recipient of Prestigious Rajyotsava State Award 2012 by the Government of Karnataka Ring Road, Kadubisanahalli, Bellandur Post, Near Marathalli, Bangalore -560 103 Tel.: +91-80-6629 7777. Fax: +91-80- 28440770 Web: www.newhorizonindia.edu 2014-2015

NEW HORIZON COLLEGE OF ENGINEERING (Accredited by NBA, Permanently Affiliated to VTU) A Recipient of Prestigious Rajyotsava State Award 2012 by the Government of Karnataka Ring Road, Kadubisanahalli, Bellandur Post, Near Marathalli, Bangalore -560103 Tel.: +91-80-6629 7777. Fax: +91-80- 28440770 Web: www.newhorizonindia.edu

Certificate This is to certify that the project Report ANALYSIS AND OPTIMIZATION OF STUB AXLE OF TATA NANO [10ME85L] Is a bonafide work carried out by

HITESH KUMAR (1NH11ME019) RAHUL (1NH11ME036)

SHRAY SHAH (1NH11ME051) VIGNESHWAR. S (1NH11ME060) In partial fulfillment for the award of degree of Bachelor of Engineering in Mechanical of the Visvesvaraya Technological University, Belgaum during the year 2014 - 2015. It is certified that all corrections/suggestions indicated for Internal Assessment have been incorporated in the Report deposited in the departmental library. The project report has been approved as it is satisfies the academic requirements in respect of Project Work prescribed for the Bachelor of Engineering degree.

Signature of the Guide Signature of the HOD Signature of the Principal Mr. SRINIVAS AYALURI Dr. M S GANESHA PRASHAD Dr. MANJUNATHA Aeronautical Development Professor and HOD, Principal,

Agency Dept. of Mech Engg NHCE, NHCE, Bangalore Bangalore

External Viva. Name of the examiners. Signature with date.

1. ……………………………………….. ……………………………………

2. ……………………………………….. ……………………………………. ANALYSIS AND OPTIMIZATION OF STUB AXLE OF TATA NANO 2014-15

Chapter 1 Introduction This chapter introduces the Tata Nano car details. The chapter details about Tata Nano specification, project area details, objective of project, project schedule and organization of the report.

1.1The Tata Nano The Tata Nano is a city car manufactured by Tata Motors. The Nano was initially launched with the price tag of Rs 100,000, which was increased with time .Designed to lure India‟s middle classes away from two wheelers, it received by publicity. The Nano (2012) is a 38 PS (28 kW, 37 hp) car with a two- cylinder 624 cc rear engine. The car complies with Bharat Stage 4 Indian Emission Standards, which are roughly equivalent to Euro 4 and thus can meet European Emission Standards as well.[1]

Figure 1.1: Tata Nano in Verkehrszentrun des Deutschem Museum

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1.2 Specifications [2] ENGINE Fuel type : Gasoline Type : 4 Stroke, water cooled, multipoint fuel injection system, SOHC, 2V/Cylinder Cubic capacity : 624 cc Made of : Alloy head, cast iron block Installation : Front, transverse, front wheel drive Max power : 38 PS at 5500 +/-250 rpm Max torque : 51Nm at 4000 +/-500 rpm Redline : 6000 rpm Bore/stroke : 73.5 mm x 73.5 mm Compression ratio : 10.3: 1 Valve gear : 2valves per cylinder, SOHC

CHASSIS AND BODY Construction : 4 Door Kerb weight : 600kg (For STD), 615kg (For CX), 635 (For LXM) Wheels Made of : Steel Tyre size : Front: 135/70R12 (Radial Tubeless), Rear: 155/65R12 (Radial Tubeless) Spare : 135/70R12 (Radial Tubeless) Spare wheel : Steel, 135/70/R12

SUSPENSION Front : Independent, Lower wishbone, McPherson Strut type, with anti-roll bar. Rear : Independent, Semi-trailing arm with coil spring and hydraulic shock absorbers.

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TRANSMISSION Type : Synchromesh on all forward gears, sliding mesh for reverse gear Gearbox : 4 forward & 1 reverse Ratios: 1st : 3.45 3rd : 1.26 2nd : 1.95 4th : 0.838 REV : 3.07 Final drive ratio : 4.2

STEERING TYPE Turning circle radius : 4 m Type : Mechanical Rack & Pinion steering gear with steering column. Steering Wheel : 360 mm dia. Ratio :16:1

BRAKES Front :180 mm dia. drum brake Rear : 180 mm dia. drum brake Parking Brakes : Lever type, Cable operated mechanical linkages acting on rear wheels. Safety Features : Front- 3 point seat belt, Rear-Lap belt

EXTERIOR DIMENSIONS Wheel Base : 2230mm Front Overhang : 464mm Rear Overhang : 405mm Overall Length : 3099mm Max. Width : 1495mm - over body, 1620mm - Over ORVM Overall Height : 1613mm Ground Clearance : 180mm Fuel Tank capacity : 15litres

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1.3 Statement of the Problem This project is started with the assumption that Tata Nano car front steering components are overdesigned. For any design higher mass of part is not recommended. The steering components are studied with respect to dimensions. The parts are analyzed to optimize the current design. Different linkages in steering mechanism are studied to understand relative displacement and load carrying capacity. Studies were carried out as an opportunity to optimize the dimensions of the steering components.

1.4 Objective of the Project Thus the objective is to optimize the Tata Nano car steering and front axle components. The critical component of the front axle system is the Stub Axle. The Stub axle is studied for design (dimension) optimization.

1.5 Project work schedule The project is carried out in several steps. Its starts from stating the problem to proposing the optimized design. It has many folds such as understanding the existing design with the dimensional details, the loading conditions and analyzing the proposed design under same loading condition. The detailed activity with estimate duration is shown below.

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1.6 Brief Description of the Project report The entire project report is detailed under five chapters. Each chapter has its own significance. The brief content of each chapter is highlighted as below.

Chapter one introduces Tata Nano car product, technical specifications, overall dimensions, engine details and steering mechanism. The main focus has been given to the objective of the project, statement of the problem which lead to do this project along with the project schedule with different milestones and estimated duration.

Chapter two focuses on project specific details, explains on the steering components, linkages, front axle arrangement and its mechanism. The main critical component Stub axle is introduced and its dimension, working and functionality are explained. The literature survey on Stub Axle is briefly shared along with the outcome of survey. The theoretical discussions are also detailed in this chapter.

Chapter three explains about detailed work done in understanding the existing Stub Axle design, material property, loading conditions, assumptions and boundary conditions. The mesh sensitivity study is also incorporated. The various tools used to perform the analysis are emphasized.

Chapter four details on various loading conditions that the Stub Axle is subjected to and the result under each category is explained. The Stub Axle under Static, Torsional loading for existing and proposed optimized design is explained. The relative study and the analysis results are described and acceptance of new dimensionally optimized Stub Axle is discussed.

Chapter five describes briefly about the objective of the project and the methodology adopted to perform the project. The summary of the results are highlighted and the conclusion are discussed in detail. This chapter also emphasizes on the scope of the current project and future scope of work in terms of further dimensional changes or material change or complete design change or link aging change.

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Chapter 2 Literature Survey The literature survey was carried on Stub Axle and Front Axle steering system. The important points were noted.

A stub axle is an axle that is connected to an assembly that mounts on one side of a trailer. It does not go all the way across the trailer like a typical straight axle does. The stub axle typically is a part of an assembly that includes the spring and shock mounts and is connected so that it can move freely as an integral part of the trailer's suspension.

By using a stub axle assembly on a trailer, it is able to traverse rough roads without disturbing its load. The axle works much like an on a sports car and allows each tire and wheel assembly to move independently. This drastically improves cornering as well as braking characteristics, especially on slippery roads.

Most units are cast into the axle assembly and the entire piece is one single part, although others are independent assemblies that fit into a receptable on the trailer and is a separate component. In either case, the axle typically has a single wheel and tire bolted to it. Occasionally, this axle can be used in a dual-wheel application as well.

The stub axle, in most cases, is easily replaced if broken. Most axles are bolted into a mounting assembly and can be simply removed by loosening a few bolts and sliding the broken stub out of the housing. In the cast units, the entire unit with stub must be replaced. This typically requires the removal of the springs and shocks as well.

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2.1 Stub Axle A short axle that carries one of the front steered wheels of motor vehicle and is capable of limited angular movement about kingpin. The main axle beam is connected to stub axles by means of kingpins. Stub axle is made up of 3 per cent nickel steel and alloy steels containing chromium and molybdenum.[3]

Types of Stub Axle Based on application  Braked Stub Axles: Designed for agricultural applications. A Stub of full axle drum brake attached to the hub, the backing plate which supports the brake shoes attached to the axle. The brakes are operated by cam lever (sometimes refer to as S- Cam) which is mechanical and can be operated by cable, air or hydraulic cylinder.

Figure 2.1: Braked Stub Axle  Double sided Stub Axles: This Stub Axle assembly was designed for a castor wheel, where the axle protrudes on both sides of the hub. Mounting is done by an arm on both side of the wheel (also refer to as a yoke).

Figure 2.2: Double sided Stub Axle

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 Spider Stub Axles: This is a five spike spider type hub. Designed to use demountable 20” and 22.5” truck wheel with 28 degree mounting flange. Spider Stub Axle assembly with only accept dual wheels.

Figure2.3: Spider Stub Axle  Steering Stub Axle: A short stub or full length axle complete with hub, including a vertical shaft (known as a king pin) which allows hub to pivot. It is used for changing the direction(steering).

Figure2.4: Steering Stub Axle Based on shapes Stub axles can have any four shapes given[3]:  Elliot  Reversed Elliot  Lamoine  Reversed Lamoine The Reversed Elliot is most commonly used Stub Axle.

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2.2 Steering Systems A steering system is designed to enable the driver to control the travelled path of a vehicle. The steering system must give the operator some form of feedback which would allow him/her to feel about the load condition that the tires of the vehicle experiences. [4] Introduction to wheeled vehicle steering systems A vehicle is not much use if it cannot be steered or guided. The act of guiding the vehicle is called steering. Wheeled vehicles are steered by aiming or pointing the wheels in the direction we want the vehicle to go. The driver of a car or truck guides it by turning the steering wheel. The steering system of cars and trucks consists of levers, links, rods, and a gearbox and sometimes a hydraulic system that assists the driver's steering effort. The steering system is of critical importance in the safe operation of the vehicle. There must be no looseness between the steering wheel and the front wheels if the driver is to keep control over the direction the wheels point. The tires must meet the road at the correct angle to get good traction and to prevent unnecessary tire wear. Also, the driver should be able to hold the wheels in the straight-ahead position and change them to the right or left with very little effort. The important functions of steering system are: 1. It supports the weight of the vehicle. 2. It facilities the steering. 3. It absorbs shocked which are transmitted due to road surface irregularities. 4. It absorbs the torque applied on it due to braking of vehicle.

Steering System Gear Mechanisms There are two types of Steering gear mechanisms 1. Fifth wheel steering system 2. Side pivot steering system Side pivot steering system is divided into two:- a) Davis Steering Gear b) Ackerman Steering Gear Fifth wheel steering mechanism: It is single point steering system in which the front axle with the wheels, moves to right or left. The movement of the whole axle and wheel assembly

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ANALYSIS AND OPTIMIZATION OF STUB AXLE OF TATA NANO 2014-15 is affected by means of a steering and a wheel which is placed between frame and the axle. The Fifth wheel act as a turntable. The axle assembly is connected with the frame by means of a pin which serves as a pivot around which the axle assembly moves. The Fifth wheel contains a ring gear mounted at its rim and is moves by means of a steering. The movement of a steering wheel tends the front axle and wheel assembly to move away.

Figure 2.5: Fifth Wheel Steering System

Side pivot steering mechanism: There are two types of steering gear mechanism Davis steering gear mechanism and Ackerman steering mechanism. The main difference between the two steering mechanism is that the Davis steering has sliding pairs, whereas the Ackermann steering has only turning pairs. The sliding pair has more friction than the turning pair, therefore the Davis steering gear will wear out earlier and become inaccurate after certain time. The Ackermann steering gear is not mathematically accurate except in three positions, while the Davis steering gear is mathematically accurate in all the position. However, the Ackermann steering gear is preferred to the Davis steering gear.

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Davis Steering Gear: The Davis steering gear has sliding pair; it has more function than the turning pair, therefore the Davis steering gear wear out earlier and become inaccurate after certain time. The Davis gear mechanism consist of a cross link KL sliding parallel to another link AB and is connected to the Stub Axles of the two front wheel by means of two similar bell crank levers ACK and DBK pivoted at A and B respectively. The cross link KL slides in bearing and carries pins at its end K and L.

Figure 2.6: Davis Steering System The slide blocks are pivots on these pins and move with the turning of bell crank lever, as the steering wheel is when the vehicle is running straight, the gear set to in its mid-position. The short arms AK and DL are inclined at an angle of (90+α) to their Stub Axles AC and BD. The correct steering depends on a suitable selection of cross arm angle α and is given by tanα = b/2xl

Where b = AB = distance between the pivots of front axles l=wheel base. The range of b/l in 0.4 to 0.5. Hence α lies between 11.3 and 14.10

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Ackermann Steering Gear: It has only turning pairs. It is not mathematically accurate except in three positions. The crank arms are made to incline so that if the axles are extended they will meet on the longitudinal axis of the car near rear axle. This system is called Ackermann steering. [5] The Ackermann steering gear mechanism consists of the cross link KL connected to short axles AC and BD of the two front wheels through the short arms AK and DL, forming bell crank levers CAK and DBL. respectively. When the vehicle is running straight, the crosslink KL is parallel to AB, the short arm AK and BL both make angle α to the horizontal axis of the chassis. In order to satisfy the fundamental equation for correct steering, the links AK and KL are suitably proportioned and angle α is suitably selected. For correct steering, cot (ɸ ) – cot(Ө) = b/l The angle (ɸ ) and Ө are shown in Figure. The value of b/l is between 0.4 and 0.5, generally 0.455. The values of cot (ɸ )- cot(Ө) corresponds to the positions when the steering is correct. In fact there are three values of angle(Ө) which give correct steering of the vehicle; first while it is turn to right, second while it is turning to left and third while running straight.

Figure 2.7: Ackermann Steering System

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Types of steering systems  Axle-Beam Steering System This steering system consists of a steering wheel, which imparts motion to the steering-box. This conveys the steering effort through the drop-arm and drag-link directly to one of the two stub-axles pivoting at the ends of the axle-beam. A track- rod joins both the stub-axles together. The steering box provides a gear reduction so that, with only a small effort, a much larger force can be applied to the steering linkage. At the same time, the degree of stub-axle movement will be reduced for a given angular movement of the steering wheel. This is desirable as it prevents the steering being oversensitive to the drivers touch on the wheel.

Figure 2.8: Axle Beam Steering System

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2.3 Suspension System Introduction For many years vehicle dynamics engineers have struggled to achieve a compromise between vehicle handling, ride comfort and stability. The results of this are clear in the vehicles we see today. In general, at one extreme are large sedan and luxury cars with excellent ride qualities but only adequate handling behavior. At the other end of the spectrum are sports cars with very good handling but very firm ride quality. In between is many number of variations dictated by the vehicle manufacturer and target customer needs. Every automotive suspension has two goals: passenger comfort and vehicle control. Comfort is provided by isolating the vehicle‟s passengers from road disturbances like bumps or potholes. Control is achieved by keeping the car body from rolling and pitching excessively, and maintaining good contact between the tire and the road. By and large, today‟s vehicle suspensions use hydraulic dampers (a.k.a.”shock absorbers”) and springs that are charged with the tasks of absorbing bumps, minimizing the car‟s body motions while accelerating, braking and turning and keeping the tires in contact with the road surface. Typically, these goals are somewhat at odds with each other. Luxury cars are great at swallowing bumps and providing a plush ride, but handling usually suffers as the car is prone to pitch and dive under acceleration and braking, as well as body lean (or “sway”) under cornering.

Objectives  To provide good ride and handling performance – –Vertical compliance providing chassis isolation –Ensuring that the wheels follow the road profile –Very little tire load fluctuation  To ensure that steering control is maintained during maneuvering – –Wheels to be maintained in the proper position w.r.t road surface  To ensure that the vehicle responds favorably to control forces produced by the tires during –Longitudinal braking –Accelerating forces

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–Lateral cornering forces and –Braking and accelerating torques –This requires the suspension geometry to be designed to resist squat, dive and roll of the vehicle body.  To provide isolation from high frequency vibration from tire excitation –Requires appropriate isolation in the suspension joints –Prevent transmission of „road noise‟ to the vehicle body. a)Independent Suspension Steering Systems Independent suspension is a broad term for any automobile suspension system that allows each wheel on the same axle to move vertically (i.e. reacting to a bump in the road) independently of each other. This is contrasted with a or deDion axle system in which the wheels are linked – movement on one side effects the wheel on the other side. Note that "independent" refers to the motion or path of movement of the wheels/suspension. It is common for the left and right sides of the suspension to be connected with anti-roll bars or other such mechanisms. The anti-roll bar ties the left and right suspension spring rates together but does not tie their motion together. Most modern vehicles have independent front suspension (IFS). Many vehicles also have an independent rear suspension (IRS). IRS, as the name implies, has the rear wheels independently sprung. A fully independent suspension has an independent suspension on all wheels. Some early independent systems used swing axles, but modern systems use Chapman or MacPherson struts, trailing arms, multilink, or wishbones. Independent suspension typically offers better ride quality and handling characteristics, due to lower unsprung weight and the ability of each wheel to address the road undisturbed by activities of the other wheel on the vehicle. Independent suspension requires additional engineering effort and expense in development versus a beam or live axle arrangement. A very complex IRS solution can also result in higher manufacturing costs

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Figure 2.9:Independent Suspension Steering System

b) MacPherson Strut Suspension System Tata Nano employees a MacPherson Strut with lower A arm(control arm or track control arm) at the front suspension and an independent coil spring- damper set up at the rear suspension. The MacPherson strut is a type of car suspension system which uses the top of a telescopic damper as the upper steering pivot. It is widely used in the front suspension of modern vehicles and is named for Earle S. MacPherson, who developed the design.

History of MacPherson Strut Earle S. MacPherson was appointed the chief engineer of Chevrolet's Light Car project in 1945, to develop new smaller cars for the immediate post-war market. This gave rise to the Chevrolet Cadet. By 1946 three prototypes of the Cadet design had been produced. These incorporated the first MacPherson struts, giving independent suspension both front and rear.[6] The Cadet project was cancelled in 1947 and the disgruntled MacPherson was enticed away to Ford. Patents were filed in both 1947 for GM[7] and 1949 for Ford[8], the 1949 patent citing designs by Guido Fornaca of FIAT in the mid-1920s. The strut suspension of the pre- war Stout Scarab would also have been a likely influence and like Stout's own influences, the

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ANALYSIS AND OPTIMIZATION OF STUB AXLE OF TATA NANO 2014-15 widespread use of long-travel struts in aircraft landing gear was well known by this time. It is possible that MacPherson was inspired by the suspension on the French Cottin-Desgouttes that used the same design, but with leaf springs. Cottin-Desgouttes front suspension was in turn inspired by J. Walter Christie's 1904 design and he was inspired by plants. MacPherson originally created the design for use at all four wheels, but it is more commonly used for the front suspension only, where it provides a steering pivot as well as a suspension mounting for the wheel. Following MacPherson's arrival at Ford, the first production car to feature MacPherson struts was the British-built 1950 Ford Consul and later Zephyr. The first production car is widely thought to be the French 1949 Ford Vedette, but this was already developed before MacPherson with an independent front suspension based on wishbones and an upper coil spring. Only in 1954, after the Vedette factory had been purchased by Simca, did the revised SimcaVedette switch to using front struts.

Figure 2.10:MacPherson Strut Type

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Design A MacPherson strut uses a wishbone, or a substantial compression link stabilized by a secondary link, which provides a bottom mounting point for the hub carrier or axle of the wheel. This lower arm system provides both lateral and longitudinal location of the wheel. The upper part of the hub carrier is rigidly fixed to the bottom of the outer part of the strut proper; this slides up and down the inner part of it, which extends upwards directly to a mounting in the body shell of the vehicle. The line from the strut's top mount to the bottom ball joint on the control arm gives the steering axis inclination. The strut's axis may be angled inwards from the steering axis at the bottom, to clear the tyre; this makes the bottom follow an arc when steering. To be really successful, the MacPherson strut required the introduction of unibody (or monocoque) construction, because it needs a substantial vertical space and a strong top mount, which unibodies can provide, while benefiting them by distributing stresses. The strut will usually carry both the coil spring on which the body is suspended and the shock absorber, which is usually in the form of a cartridge mounted within the strut. The strut can also have the steering arm built into the lower outer portion. The whole assembly is very simple and can be preassembled into a unit; also by eliminating the upper control arm, it allows for more width in the engine compartment, which is useful for smaller cars, particularly with transverse-mounted engines such as most front wheel drive vehicles have.

Advantages and disadvantages Although it is a popular choice, due to its simplicity and low manufacturing cost, the design has a few disadvantages in the quality of ride and the handling of the car. Geometric analysis shows it cannot allow vertical movement of the wheel without some degree of either camber angle change, sideways movement, or both. It is not generally considered to give as good handling as a double wishbone or multi-link suspension, because it allows the engineers less freedom to choose camber change and roll center. Another drawback is that it tends to transmit noise and vibration from the road directly into the body shell, giving higher noise levels and a "harsh" feeling to the ride compared with double wishbones, requiring manufacturers to add extra noise reduction or cancellation and isolation mechanisms.

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Chapter 3 Methodology 3.1 Introduction This chapter details about the simulation methodology followed to understand the stub axle design and proposed optimized design. This include the detailed information about the stub axle CAD model generation, mesh sensitivity studies, assumption made, material properties and boundary condition establishment.

Figure: 3.1: Tata Nano Stub Axle dimensions-Front view

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Figure 3.2: Tata Nano Stub Axle dimensions-Side view

Figure 3.3: Tata Nano Stub Axle dimensions-Top view

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3.2 Model generation The dimensions of the Stub Axle of Tata Nano car have been measured. The Stub Axle 3d CAD model has been developed in UGS. The model is shown in Figure given below[9].

Figure 3.4: Stub Axle-Existing design- Unigraphics Model

3.3 Mesh Generation

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The Stub Axle was meshed with tetrahedron element using ANSYS simulation tool as shown in Figure below. The mesh sensitivity was carried out with different element sizes, viz., 1mm, 2mm, 3mm and 4mm. The high stress region (the junction of the shaft with the flange) was mesh with fine element size was all the sensitivity studies. The mess sensitivity studies clearly indicated that the mesh size of 2mm is suitable for analysis. Thus the rest of analysis was carried out with a mesh size of 2mm.

Figure 3.5: Meshed Model showing critical region

Figure 3.6: Mesh Sensitiviy Results

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3.4 Assumptions  Material is isotropic and homogeneous in nature  Permissible yield strength is consider 60% of tensile strength  Load on Stub axle due to steering torque is minimal  Center of gravity of car is considered at the center of the vehicle.

3.5 Boundary Conditions Stub axle is three legged component. The boundary conditions was studied with respect to different joints , supports and load application. The boundary condition were studied under two different cases:-

Case 1: Load applied on leg and shaft has been fixed with all degrees of freedom.

Figure 3.7:Fixed shaft boundary condition

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Case 2 : Load applied on shaft and leg hole has been fixed with all degrees of freedom.

Figure 3.8:Fixed bracket holes boundary condition

The stress distibution is uniform in case 2 compared to case 1. The Case 1 boundary condition were obsereved as a rigid arrangement, hence stress variation is minimum.But in case 2 boundary condition is observed with proper stress variation. Hence Case 2 is considered for futher subsequent studies.

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3.6 Stub Axle – Material Properties To identify the material properties of Stub Axle, the material characterization test like tensile test, Proof Stress ,% elongation and hardeness test result were taken from guide. So material property values were reported as shown in table below. The Stub Axle were identify as a isotropic low alloy steel with chemical composition wich conform to EN 18 of BS: 970- 1755. The tensile strength of Stub Axle is reported as 890 Mpa. The permissible yield strength is consider as 60% of tensile strength. Permissible Yield Strength of Stub Axle = 890*0.6 = 534 MPa

Table 3.1: Material properties of stub axle

Material Condition Density(*1000 Modulus of Poission‟s ratio Alloy 5140 Kg/m^3) Elasicitiy(Gpa) AISI 5140 Steel Annealed 7.85 205 0.29

AISI 5140 Steel Normalized 7.85 205 0.29

AISI 5140 Steel Oil quenched 7.85 205 0.29

The Material test report is given below.

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Figure 3.9:Material Test Report

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3.7 Von Misses Stress

What is Von Misses Stress?

Von Misses stress is widely used by designers to check whether their design will withstand a given load condition.

Use of Von Misses stress

Von Misses stress is considered to be a safe haven for design engineers. Using this information an engineer can say his design will fail, if the maximum value of Von Misses stress induced in the material is more than strength of the material. It works well for most cases, especially when the material is ductile in nature. In the following sections we will have a logical understanding of Von Misses stress and why it is used.[10]

When does a material fail? One of the easiestways to check when a material fails is a simple tension test. Here the material is pulled from both ends. When the material reaches the yield point (for ductile material) the material can be considered as failed. The simple tension test is a unidirectional test; this is shown in the first part of Figure .3.9.

Figure 3.10: A simple tension test and a real life loading condition

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Now consider the situation in second part of Figure .3.9, an actual engineering problem with a complex loading condition. Can we say here also, that the material fails when the maximum normal stress value induced in the material is more than the yield point value? If you use such an assumption, you would be using a failure theory called 'normal stress theory'. Many years of engineering experience has shown that normal stress theory doesn‟t work in most of the cases. The most preferred failure theory used in industry is „Von Misses stresses based. We will explore what Von Misses stress is in the coming section.

Distortion energy theory The concept of Von Misses stress arises from the distortion energy failure theory. Distortion energy failure theory is comparison between 2 kinds of energies, 1) Distortion energy in the actual case 2) Distortion energy in a simple tension case at the time of failure. According to this theory, failure occurs when the distortion energy in actual case is more than the distortion energy in a simple tension case at the time of failure. [11]

Distortion energy

It is the energy required for shape deformation of a material. During pure distortion, the shape of the material changes, but volume does not change. This is illustrated in Figure .3.10.

Figure 3.11: Representation of a pure distortion case

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Distortion energy required per unit volume, for a general 3 dimensional case is given in terms of principal stress values as:

Distortion energy for simple tension case at the time of failure is given as:

Expression for Von Misses stress The above 2 quantities can be connected using distortion energy failure theory, so the condition of failure will be as follows.

The left hand side of the above equation is denoted as Von Misses stress.

So as a failure criterion, the engineer can check whether Von Misses stress induced in the material exceeds yield strength (for ductile material) of the material. So the failure condition can be simplified as .

Industrial Application of Von Misses Stress Distortion energy theory is the most preferred failure theory used in industry. It is clear from above discussions that whenever an engineer resorts to distortion energy theory he can use Von Misses stress as a failure criterion. Let's see one example:

Suppose an engineer has to design a cantilever beam using mild steel as the material, with a load capacity of 10000 N. The materials properties of mild steel are also shown in the

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Figure 3.12. The yield stress value of mild steel is 2.5x108 Pa. He wants to check whether his design will withstand the design load.

Figure 3.12:Load on Cantilever I- section beam The following Figure shows the Von Misses stress distribution obtained by FEA analysis of the beam.

Figure 3.13: Distribution of Von Misses stress in the beam obtained from FEA analysis One can note that Von Misses stress is at maximum towards the fixed end of the beam, and the value is 1.32x108 Pa. This is less than the yield point value of mild steel. So the design is safe. In short an engineer's duty is to keep the maximum value of Von Misses stress induced in the material less than its strength.

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Figure 3.14:The Von Misses yield surface in principal stress coordinates

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Chapter 4 Result Analysis 4.1 Static Analysis Static load calculation: When the car is at static position, stub axle undergoes static loading. The static load on stub axle is calculated as shown below[12]. 1.Tata Nano car weight = 635 kg 2. Approximate passenger weight= 280kg( 4*70) Total load acting on car = 915 kg So on each stub axle the static load will be 915/4 = 228.750 kg So weight on each Stub Axle will be228.750*9.81=2244N

Case 1: Fixed shaft and load on bracket holes Total number of nodes on bracket holes = 683 Load on each node = 2244/683 = 3.29N

Figure 4.1: Static load on bracket holes

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Figure 4.2: Displacement plot of Case 1 Static loading Maximum diaplacement obtained = 0.111725mm Dispalcement at critical region ≈ 0.012mm

Figure 4.3: Von Misses stress for case 1 static analysis Maximum stress obtained = 218.693Mpa Stress at critical region ≈ 48~72Mpa

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Case 2 Uniform distriburted load(UDL) The load was applied as a uniform distributed load. Based on mesh sensitivity the number of nodes consider for static load application is 4425. Therefore load on each node = 2244/4425 = 0.507N

Figure 4.4: Static load on shaft

Figure 4.5: Deformation under static loading

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Exisiting design:Displacement plot

Figure 4.6: Static load- Exisiting design- Displacement- Front view Maximum dispalcement obtained = 0.20342mm Dispalcement at critical region ≈ 0.0226~0.0678mm

Figure 4.7 Static load- Existing design- Displacement- Rotated view

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` Figure 4.8: Static load-Existing design-Stress distribution-Front view Maximum stress obtained = 278.186Mpa Stress at critical region ≈61.82~92.72Mpa

Figure 4.9:Static load-Existing design-Stress distribution-Critical region

Proposed design:

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Figure 4.10:Proposed design in Unigraɸ cs

Figure 4.11:Orthogonal view of the proposed design

Proposed design:Displacement Plot

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Figure 4.12: Static load-Proposed Design-Displacement-Front view Maximum displacement obtained = 0.206352mm Displacement at critical region ≈ 0.023~0.068mm

Figure 4.13: Static load-Proposed Design-Displacement-Rotated view Proposed design:-Stress Distribution

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Figure 4.14: Static load-Proposed Design-Stress distribution-Front view Maximum stress obtained = 276.961Mpa Stress at critical region ≈ 61.85~92.32Mpa

Figure 4.15: Static load-Proposed Design-Stress distribution-Critical region Table 4.1:Result Summary of Static Analysis

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Conditions EXISTING DESIGN PROPOSED DESIGN Maximum 0.20342mm 0.206352mm Displacement Displacement 0.0226 ~ 0.0678mm 0.0229 ~ 0.0688mm at Critical Section Maximum Von 278.186 Mpa 276.961 Mpa Misses Stress Stress at 61.82 ~ 92.73Mpa 61.85 ~ 92.32 Mpa Critical Section

Maximum Von Misses Stress value is 276.961 Mpa. Factor of safety for static load condition for the proposed design = 534/276.96 = 1.93

4.2 Torsional Analysis :

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In the field of solid mechanics, torsion is the twisting of an object due to an applied torque. Stress in Circular shaft due to Torsion 1.The shearing force dF about the axis of the shaft is equal in magnitude to the torque T, can be written as,

Tata Nano car engine torque = 51000N-mm(Tmax)

Effective Torque = 0.6*Tmax

0.6*51000 = 30600N-mm(Te) Considering maximum Torsional Stress for analysis.

Torsional shear force 3 It is given by(Fs) = Tmax×16/(πd ), where d is dia of shaft = 51000×16/(π×203) = 32.46MPa

Shear strength of stub axle material(Fsm) = 0.58×Tensile yeild strength = 0.58×(0.6×890) Where Tensile strength of stub axle material is 890MPa. But Permissible Yield strength is 60 per cent of tensile strength. = 309.7Nmm-2 Load calculation Engine torque(T) =51000 MPa T= F*r where r = 10 mm , radius of shaft Force on shaft =51000/10=5100N Therefore tangential force in each direction = 5100/4=1275N No. of nodes considered in each direction = 100 Load on each node = 1275/100=12.75N

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Figure 4.16 : Torisonal loading on the shaft –Detailed view Force of 12.75N applied in each direction,as shown in diagram.

Figure 4.17 : Torisonal loading on the shaft-Isometric view The above figure illustrates the clockewise twisting due to the force applied in each direction.

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Figure 4.18 : Torsional loading – Side view

Figure 4.19 :Deformation under Torsional Loading

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Existing Design:Displacement plot

Figure 4.20 :Torsional load-Existing Design-Displacement-Front view Maximum displacement obtained = 0.023284mm Displacement at critical region ≈ 0.052~0.010

Figure 4.21 :Torsional load-Existing Design-Displacement-Critical region

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Existing Design:Stress Von Misses

Figure 4.22 :Torsional load-Existing Design-Von Misses-Front view Maximum stress obtained = 80.22Mpa Stress at critical region ≈ 62.4~80.21Mpa

Figure 4.23 :Torsional load-Existing Design-Von Misses-Critical region

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Shear stress in XY plane

Figure 4.24 :Torsional load-Existing design-shear stress XY-Front view Maximum stress obtained = 37.92Mpa

Figure 4.25 :Torsional load-Existing design-shear stress XY-Critical region

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Shear stress in YZ plane

Figure 4.26 :Torsional load-Existing design-shear stress YZ-Front view Maximum stress obtained = 33.95Mpa

Figure 4.27 :Torsional load-Existing design shear stress YZ-Critical region

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Shear stress in XZ plane

Figure 4.28 :Torsional load-Existing design-shear stress XZ-Front view Maximum stress obtained = 40.94Mpa

Figure 4.29 :Torsional load-Existing design-shear stressXZ-Critical region

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Proposed Design Displacement Plot

Figure 4.30 :Torsional load-Proposed Design-Displacement-Front view Maximum displacement obtained = 0.028048mm Displacement at critical region ≈ 0.006~0.012mm

Figure 4.31 :Torsional load-Proposed design-Displacement-Rotated view

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Proposed Design:Stress Distribution Von-Misses Stress

Figure 4.32 :Torsional load-Proposed Design-Von Misses-Front view Maximum stress obtained = 85.81Mpa Stress at critical region ≈ 66.7~85.81Mpa

Figure 4.33 :Torsional load-Proposed Design-Von Misses-Critical region

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Shear Stress in XY plane

Figure 4.34 :Torsional load-Proposed Design-Shear stress XY-Front view Maximum stress obtained = 43.85Mpa

Figure 4.35 :Torsional load-Proposed Design-Shear sress XY-Critical region

Shear Stress in YZ plane

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Figure 4.36 :Torsional load-Proposed Design-Shear stress YZ-Front view Maximum stress obtained = 31.53Mpa

Figure 4.37 :Torsional load-Proposed Design-Shear stress YZ-Critical region

Shear Stress in XZ plane

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Figure 4.38 :Torsional load-Proposed Design-Shear stress XZ-Front view Maximum stress obtained = 40.37Mpa

Figure 4.39 :Torsional load-Proposed Design-Shear stress XZ-Critical region

Table 4.2 Result summary of Torsional Analysis

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PARAMETERS EXISTING DESIGN PROPOSED DESIGN Maximum Displacement 0.02348 mm 0.02848 mm Stress 1)Von-Misses Stress 80.22 Mpa 85.81 Mpa 2)Shear stress in XY plane 37.92 Mpa 43.85 Mpa 3)Shear stress in YZ plane 33.95 Mpa 31.53 Mpa 4)Shear stress in XZ plane 40.94 Mpa 40.87 Mpa

The result analysis indicates that the shear stress for the proposed design along the plane where the torque is applied (i.e. YZ plane) is comparitively less than the existing design. This indicates the proposed design is more efficient in resisting the twisting moment.

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4.3 MassCalculations

Volume of the cylinder = (π/4)*d2*L mm3 where d is th e diameter in mm

L is the length in mm

Volume of the existing shaft = [(π/4)*202*60] +[(π/4)*162*20]

= 22870.79 mm3

Volume of the Proposed hollow shaft=[(π/4)*(202-82)*60] +[(π/4)*(162-82)*20]

= 18849.55 mm3

Decrease in volume =Existing volume – Proposed volume

= 22870.79-18849.55

=4021.23 mm3

% Decrease in volume = (Existing volume – Proposed volume)/Existing Volume

= [(22870.79-18849.55)/22870.79]*100

=17.58 %

Density of the given material is 7850 kg/m3

So, Mass of the decreased volume = Volume*density

= 4021.23*7850*10-9

= 31.56 grams

Mass of the existing design =1.335 Kgs

Mass of the proposed design =1335-31.56 grams

= 1304 grams

=1.304 kgs

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Chapter 5 Conclusion Brief Summary of work Step1: Problem Statement The objective of the poject is to optimize the Tata Nano car Front Axle components. The critical component of the front axle is the Stub Axle. The Stub Axle is studied for design optimization. The Stub Axle is assumed as over designed and analysed for the dimensional optimization Step 2 : Work Methodology adopted The Stub Axle is subjected to static, torsional loading. The ANSYS simulation methodology followed to understand the current Stub Axle design and proposed dimensionally opitimized design. This includes the detailed work like Stub axle CAD model generation, mesh sensitivity studies,assumption, material properties and boundary condition establishment.

From the FEA analysis, we can conclude that:  The proposed design is a good dimensionally optimized design  The stress values are much less then the allowable stress values  The proposed design has a capability to replace the exisiting design.  The weight of existing design is reduced by 31.56 grams.

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Chapter 6 Future Scope of Work

The future scope of work in optimizing the stub axle is: The stub axle has to be analyzed for next possible smaller solid shaft dimension The stub axle material with more strength and less cost has to be analyzed The stub axle with thickness reduction over all dimensions has to be analyzed

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References 1. TaNo‟s ambitious „Air Car‟ faces starting troubleDaily News and Analysis, 25 November 2009. 2. Tata Nano specifications, Tata Motors. 3. Automobile Engineering, Vol.2, Dr. Kirpal Singh, 2014. 4. Patent: A vehicle, method and steering system for a vehicle EP 1534575 B1. 5. Johnson, Erik (June 2007). "2008 Infiniti G37 Sport Coupe - Suspension, Handling, and Four-Wheel Steering". 6. Ludvigsem, Karl (Jan-Feb 1974). “The Truth About Chevy‟s Cashiered Caded”. 7. US 2624592, Earle S. MacPherson, “ Vehicle Wheel Suspension System”, 6 Jan1953. 8. A US 2660449 A, Earle S. MacPherson, “Wheel Suspension for Motor Vehicles”, 24 Nov1953. 9. "Suspension Basics 4 - Torsion Bar Springs". Initial Dave. Retrieved 2015-01-29. 10. Unigraphics Help Manual. 11. Theory of Mechanics and Mechanism by John J Uicker, JR. Gordon R, Pennock& Joseph E, Shigley 3rd Edition; Chapter 1: Pg No 17 12. Strength of Materials by S.Ramamrutham & R. Narayan; Chapter 18; Pg No 1059

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