DESIGN AND ANALYSIS OF AN AUTOMOTIVE FRONT WHEEL HUB
B.TECH MECHANICAL ENGINEERING - VI SEMESTER
DESIGN PROJECT
Presented by Bhoopendra Bhoopendra Singh - 07BME064 Kallur Krishnamoorthy Rajesh - 07BME097
SCHOOL OF MECHANICAL & BUILDING B UILDING SCIENCES
VELLORE INSTUTUTE OF TECHNOLOGY VIT UNIVERSITY VELLORE – VELLORE – 632014, 632014, TAMIL NADU
APRIL 2010
CERTIFICATE
This is to certify that the design project entitled “ Design And Analysis Of An Automotive Front Wheel Hub ” submitted by Bhoopendra Singh - 07BME064 Kallur Krishnamoorthy Rajesh - 07BME097 , doing III Year B.Tech Mechanical Engineering to the School of
Mechanical & Building Sciences, VIT University Vellore is a bonafide record of work carried out by them under my supervision.
Their performance during the project phase is __________________
Guide
Programme Manager
(Prof. Dr. Sunil Bhat)
(Prof. P. Kuppan)
Internal Examiner
External Examiner
ACKNOWLEDGEMENT First we would like to thank VIT University and our chancellor, Dr. G. Viswanathan, for providing us the opportunity to do this project. We would like to thank our guide, Dr. Sunil Bhat, whose expert guidance in solving the problem was a prime reason for the successful ideation and completion of the project. He extended his guidance at all times, and helped us learn in the process through scientific questioning and reasoning. His in depth knowledge in machine design, fracture mechanics, strength of materials, and finite element analysis helped us come out of difficult situations. We would also like to thank Mr. Ravi, PDC Lab assistant, in helping us learn and use the software ANSYS® 11.0. Last but not the least, we would like to thank God Almighty, without whom this project would not have seen the light of the day.
ABSTRACT Design and and analysis of a front wheel hub of a single seater all terrain vehicle vehicle was to be done,to ensure optimum performance, and to finalise the dimensions and material specifications for manufacturing the same for the above said vehicle. First, the given volume was obtained within which the t he component component was to be placed. Initial Init ial dimensions were set based on bearings to be used and Wheel rim dimensions. Various materials were studied and shortlisted for the purpose. The loading conditions were analyzed, and an equivalent mathematical model was constructed. Mathematical analysis was done for various materials. Next, a finite element model was setup and analysed for various materials. The actual stress concentrations were found out. Based on the obtained FEA result, a optimized and enhanced design for high strength – low low weight was obtained. Finally, a weighted matrix method was used to select the final material to be used. Through this project, we have arrived at a optimized design of a front wheel hub, that is both strong and light weight, with reduced material for best performance.
i
LIST OF TABLES Table No.
Table Name
Page No.
1.
Moment of Inertia of equivalent equivalent sections of the Hub
11
2.
Material Comparison Table I- Properties
24
3.
Material Comparison Table II - Performance Performance
24
ii
LIST OF FIGURES Fig. No.
Figure Name
Page No.
1
Hub-Rotor
4
2
Hub-With Suspension Suspension
4
3
Vehicle Dimensions
5
4
Front View Suspension Geometry Based On Vehicle Dynamics
5
5
Hub Side View
9
6
Hub Front View
10
7
Vehicle Hitting A Bump
12
8
. Equivalent Equivalent Cantilever System For A Hub
11
9
Analysis For Steel
17
10
Analysis For Steel
17
11
Analysis For Aluminum
18
12
Analysis For Al-Sic Mmc
18
13
Analysis For Al-C , Mmc
19
14
New, Optimized Design
20
15
Modified Steel Hub Analysis
21
16
Modified Aluminium Hub Analysis
21
17
Modified Al-Sic Mmc Analysis
22
18
New, Optimized Hub Isometric View
25
19
Optimized Hub Side View
25
20
Optimized Hub Front View
26
iii
NOMENCLATURE u
-
initial velocity velocity
v
-
final velocity velocity
a
-
acceleration
t
-
time
s
-
distance
h
-
height
d
-
displacement
σ
-
stress
ε
-
strain
E
-
Young’s modulus
G
-
Shear Modulus
I
-
Moment of Inertia
J
-
Polar Moment of Inertia
θ
-
angular displacement displacement
P
-
Power
T
-
Torque
w
-
Angular Velocity
τ
-
Shear stress
iv
CONTENTS Abstract
(i)
List of Tables
(ii)
List of Figures
(iii)
Nomenclature
(iv) PAGE NO
CHAPTER – I
INTRODUCTION
1.1
Problem Specification
01
1.2
Significance of the Project
01
1.3
Objectives
02
1.4
Methodology
03
CHAPTER – II
LITERATURE REVIEW
04
2.0
Vehicle Overview
05
2.1
Bearings Used
06
2.2
Formulae Used
06
2.3
Materials Considered
07
CHAPTER – III
DESIGN OF COMPONENT
08
3.0
Conventional Design
08
3.1
Initial CAD Design
09
CHAPTER – IV
4.0
4.1
STRESS ANALYSIS
11
Mathematical Model
11
4.0.1
Tensile Stress
12
4.0.2
Bending Stress
12
4.0.3
Torsional Stress
13
4.0.4
Von-Mises Stress
14
Finite Element Modeling
16
4.1.1
17
Analysis of initial design
4.1.2
Observation and Changes suggested
20
4.1.3
Analysis of New design
21
CHAPTER – V
MATERIAL SELECTION
23
CHAPTER – VI
CONCLUSION
25
6.0
Final Design Specifications
25
6.1
Observations
27
6.2
Scope for Future work
28
REFERENCES
29
CHAPTER : I
Introduction
While designing a single-seater all terrain recreational vehicle, we were put up with the task of designing and optimizing the Front Wheel Hub of our vehicle. The vehicle is to negotiate all kinds of terrain under high performance mode (race purposes). The vehicle runs under a 11 bhp petrol engine, coupled to a gearbox that produces a maximum acceleration of 1g. Also the front wheel is the steered wheel, hence there will be loads in and about all 3 axes(x,y,z). Since the terrain is rough, the design is required to be very strong. Also, since it is for racing purposes, the design is also supposed to be light weight.
1.0 Problem Specification
To design a front wheel hub for an all terrain vehicle on strength and weight basis. The component is to be modelled mathematically and in finite elements , upon which stress analysis is to be done. Based on the t he results, design optimization is to be made for best design. Also materials have to be analyzed and chosen for the same.
1.1 Significance of the Project
This project has significance to the automotive industry. This project is an example of optimization of design through FEA. The design procedure used here can be standardised for automated design processes.
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1.2 Objectives
The objectives of this design project are summarized as follows:
To analyze the design and improve the design of Front wheel Hub of an ATV for high strength and light weight.
To understand the loading conditions, boundary conditions and the environment environment the t he component component is subjected to.
To formulate a mathematical model, through scientific assumptions and come up with a t heoretical heoretical stress-strain stress-stra in model.
Perform Finite element analysis to find out stress concentrations, concentrations, thereby t hereby finding areas to improve design.
Give final design with dimensions and material specifications.
2
1.3 Methodology
The approach to our design problem is elaborated through the flow-chart given below
Understanding the Problem at hand
Finite Element Analysis
Design Optimization
Making a time schedule
Discussion with Guide
Discussion with guide
Literature survey
Stress Analysis
Material Selection
CAD Modelling
Mathematical Modelling
Final Specifications
3
Compiling a Final Report
CHAPTER : II Literature Survey
In automotive wheel systems, the suspension is connected to the wheel using a hub-rotor assembly. The hub-rotor rotates about the t he upright(which is connected to the suspension), upon bearings. There is a base plate with holes for bolts, which is bolted on the wheel rim.
Bearing housing
Baseplate
Fig 1. HUB-ROTOR
Fig 2. HUB-with suspension suspension
As can be seen, the wheel hub is a symmetric component. All the loads from the wheel to the shocks are transferred through the hub. Hence the safe design of wheel hub is very important. The design of hub depends upon the space given to it, which is decided according to the other suspension components like shock position, arm length, suspension geometry, brakes position etc. The positioning of the other suspension assemblies is not discussed in this design project. Only the design of the hub is discussed here.
4
2.0 Vehicle Overview
Dimensions of the vehicle (SAE MINI BAJA ATV)
Track length
Weight : 350kg
70kg 70kg
Track length : 135 cm Wheelbase : 160 cm
Wheelbase 40:60 weight
Engine: Lombardini 340cc 11hp
distribution
Max. torque on wheels: 1200 N-m Max. speed: 45 kmph Maximum Wheel travel :15cm 105kg
105kg
Rim PCD (for holes holes of bolts): 102 cm Fig 3. Vehicle Dimensions Based on various consideration, the suspension geometry was designed. This gave us the available space for the wheel hub.
Fig 4.Front View suspension geometry based on Vehicle dynamics 5
2.1 Bearings Used
Based on static loads, the bearing was selected with an axial load of 30000N and a radial load of 10000N and life of ten million revolutions.This was done based on bearing selection procedure given in Design data books. The tapered roller bearing , 32005 (25 x 47) suited the purpose with a width of 15mm 2.2 Formulae Used 1. Laws Of Motion
v= u +at
eqn 1.1
s= ut+0.5at^2
v^2 = u^2 + 2as
eqn 1.2
eqn 1.3
centrifugal force, Fc= mv^2/r
eqn 1.4
2. Stress Strain Analysis
a. Stress, Stress, σ= F/A
eqn 2.1
b. σ=Eε (ε – strain, strain, E-elasticity modulus)
eqn 2.2
c. Bending equation , M= EI( d y/dx )
eqn 2.3
d. Torsion, Torsion, T/J = τ/R = Gθ/L
eqn 2.4
eqn 2.5
eqn 2.6
2
2
e. Principal stresses
f. Von-Mises Hencky maximum distortion energy theory
g. If an impact loading is equalised to a weight W falling from a height H, then, deflection due to impact loading in terms of height of fall and static deflection for same weight is, dmax = dst + ( dst2 + 2Hdst)1/2
6
eqn 2.7
2.3 Materials Considered C45 Steel
It is a medium carbon steel with 0.4 -0.5 % carbon, with yield strength o 380 MPa and an impact strength of 41 N-m. It is used generally in shafts, shafts, gears, spindles etc. Al 6061 T6
6061 is a precipitation hardening aluminum alloy, containing magnesium and silicon as its major alloying elements. It has good mechanical mechanical properties and exhibits good weldability. It is one of the most common alloys of aluminum of aluminum for general purpose use. It is comm co mmonly only available in pre-tempered grades such as, 6061-O (solutioni ( solutionized), zed), 6061-T6 (solutionized and artificially aged), 6061-T651 (solutionized, stress-relieved stretched and artificially aged). Al MMC’s
Metal Matrix Composite (MMC): A composite material in which one constituent is a metal
or alloy forming at least one percolating network. The other constituent is embedded in this metal matrix and usually serves as reinforcement. These generally have low density and high strength. They are used in high performance motor vehicles in wheel rotors, rotor s, shafts, axles, axles, engine components etc. The only limiting factor is manufacturing ease and cost. Al-SiC MMC is a particle reinforced MMC, with Al as matrix and SiC as fibre. The yield strength is 338 MPa. Al-C is a Continuous fibre reinforced MMC, with Al as matrix and Carbon as fibre. The yield strength is 620 MPa.
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CHAPTER : III Design Of Component
The design of hub depends upon the space given to it, which is decided according to the other suspension components like shock position, arm length, suspension geometry, brakes position etc. As given in the literature survey, based on the suspension geometry, the space available was obtained. 3.0 Conventional Design
The Conventional design of a front wheel hub consists of a circular disc with bolt-holes, called baseplate . Extruded from this is a hollow stepped section, which houses the bearings. Another disc is extruded upon this which acts as the brake disc and is usually made from a different material than the hub.
8
3.1 Initial CAD design
Based on the suspension packaging, steering linkages,suspension arms (wishbone system), available space and adherence to track length limit,accessibility of brake disc-calliper assembly, the hub dimensions were fixed to be the following
Fig 5. HUB side view The disc with dia. 132 mm is the baseplate, to be mounted on the rim. The 26mm long section is the bearing housing. The 84 mm dia disc is the brake disc mount. As can be seen in the next figure, the base plate has bolt-holes according to the pitch circle diameter of t he rim.
9
Fig 6. HUB front view
10
CHAPTER : IV Stress Analysis
The hub is being acted by forces in and about all 3 axes. The major forces encountered are the centrifugal force during a bump, the impact force during a full speed jump, the torsional load due to acceleration. All the conditions are considered here, a model is made and vonmises failure theory is applied to find out induced stresses. 4.0 Mathematical Model
Assuming the hub to be a cantilever beam
l1
l2
l3
fig 8. Equivalent Cantilever system system for a Hub 4
section
I, moment moment of inertia(mm )
L, length(mm)
1
2204400
8.5
2
355300
26
3
17052800
6
Table 1 : Moment of Inertia of o f equivalent sections sections of the t he Hub
11
4.0.1 Tensile Stress
Assuming a bump height of 15cm and length 20 cm.
15
20
Fig. 7 vehicle hitting a bump Assuming the speed of vehicle : 45 km/hr i.e 11.11 m/s Assuming the radius of suspension travel = .67 Centrifugal force on the wheel = 30000 N This force is acting perpendicular to the face of the baseplate. The stress developed by eqn 2.1 is = 4 MPa This is the axial load on the hub , σx = 4Mpa
4.0.2 Bending Stress
Using method of superposition, static deflection due to weight weight at front wheel, and assuming material to be steel dtotal = d1 + d2 + d3 dtotal = 1.5 x 10 -4 mm
12
assuming an impact load condition,from Mechanics of Materials(JAMES M. GERE TMH) pg 674 If an impact loading is equalised to a weight W falling from a height H,then, deflection due to impact loading in terms of height of fall and static deflection for same weight is, dmax = dst + ( dst2 + 2Hdst)1/2 IMPACT ENERGY : assuming the vehicle vehicle at max speed falling from height of 3 feet And assuming half the energy to be absorbed by the suspension system, then the impact energy on the hub-rotor assembly is = 12511 J The equivalent height of fall for the front wheel is 9.11 m Applying the deflection eqn above, We get dmax = 1.2 mm Strain = 4.4 x 10
-4
From eqn 2.2, Induced stress, σ y = 88 Mpa for steel with deflection = 1.2 mm Similarly for Aluminium, σ y =86 MPa with deflection of 2mm.
4.0.3 Torsional Load
Maximum torsion is observed at maximum acceleration of the vehicle We know Power =Torque x ang. Velocity P=Tw T= P/ w T= Pr/v KE = 0.5mv
2
13
Power = d/dt(KE) = mav T= mavr/v T= mar 2
amax for the vehicle was calculated to be 10 m/s , that is at a max torque from the engine and gearbox therefore, T= 187 N-m applying torque eqn. θ =Tl/GJ θmax = θ1 + θ2 + θ3 θmax = 8.3 x 10 -5 rad shear strain = 1.9 x 10
-4
induced shear stress, τ =16 Mpa 4.0.4 Von-Mises Stress
σx= 4 MPa σy = 88 MPa τxy = 16 Mpa applyin eqn 2.5 σ1 = 91 Mpa σ2 = -2 MPa after applying eqn 2.6 σvon mises= 92 MPa
14
The presence of holes, steps and fillets lead to stress concentration. The stress concentration factor for such notches individually are known. In our case there is a combination of shear and bending stresses, with a combinations of holes and fillets. Hence, incorporation of theoretical stress concentration factors would lead to approximate and possible wrong conclusions. Hence it was decided to find out the stress concentration factor from Finite Element Analysis(FEA) of the component.
15
4.1 Finite Element M Modelling odelling
Finite element analysis was done in order to find the actual stresses that are experienced by the component under different loading. ANSYS 11.0 was used for the finite element analysis. The component was modelled in the ANSYS 11.0 modelling environment, with the same dimensions as the real one. Selection Of Element
Element selected for the analysis is a 3D beam element.A 3D beam element has 3 DOF per node (x,y and z direction). It has both strain and bending capabilities. Hence this element was chosen. In ANSYS 11.0 11.0 it comes as “Beam element 3D 44” Meshing
Meshing of the entire componen co mponentt was done within the ANSYS 11.0 environment. environment. Tetrahedral free meshing was done, as the component had smooth curves, and cylindrical topology.Hexahedral would not produce a smooth topology. The meshing was automatically refined at the points where there was discontinuity in the form of step, hole etc. The total no of nodes were 41619 Constraints
The bigger baseplate is bolted on to the wheel rim and his hence constrained in 3 DOF. Loads
Loads are applied on the other base plate. The load was calculated as shown above in the calculations section. All the loads were applied on to the model and analysis was done.
16
4.1.1 Analysis Of Initial Design
Fig.9, 10 : Analysis of Steel
17
Fig 11.Analysis For Aluminum
Fig. 12 : Analysis Analysis For Al-Sic Mmc
18
Fig 13 : Analysis For Al-C , Mmc
19
4.1.2 Observations and design changes suggested
In all the above cases, the stress does not exceed 220 MPa,the highest stress coming at the point where the hub is bolted on the wheel.The contour plot very starkly shows that the area between the holes for bolts, are areas of negligible near zero stress. Hence for material reduction (that is weight reduction) such areas can be removed. After optimising the design and removing material at unwanted locations, this is how it looked like.
Fig 14 : Opimized hub design After removal, again analysis was carried out for the same.
20
4.1.3 Analysis Of New Design
Fig 15 : Modified Steel Hub Analysis Fig 16 : Modified Aluminium Hub Analysis
21
Fig 17 : Modified Modified Al-Sic Mmc Analysis
As can be easily noted noted , the stress induced in the new design is more than the previous design. Yet it is within the Factor of safety, with a max stress value of 250 MPa. One can easily notice in the increase in the area/elements of increased stress. Previously lesser overall area was under stress. Also note the increased stress in the bearing mount region. Hence finally, the new design with reduced material was decided to be used. This was a result of OPTIMIZATION THROUGH SIMULATION.
22
CHAPTER V : MATERIAL SELECTION The final material selection was based on various factors like strength, elasticity, hardness required, cost, machinability, machinability, weight etc. The comparison table in the next sheet was made according to the data collected from data books about the 5 materials materials considered for the component. As can be seen, steel has excellent performance in all spheres except its weight.Since this Hub is for high performance, weight is of concern. But C45 steel has an excellent fracture toughness. Hence it can be used for mass production commercial vehicles for whom cost and safety is of primary concern. Aluminium 6061 – 6061 – T6 T6 has excellent properties, except that it is easily deformed. Yet it maintains all the FOS values.It is remarkably light-weight, cheap, cheap, easily available and easily machined. It seems to be the best candidate for High Performance race/recreational ATV vehicles.Its easy deformation does not render it safe for commercial applications. applications. Al 2011 T6 also offers similar performance, except that its costlier than Al 6061-T6. The Al-C MMC has excellent properties, but is in fact too strong for our application. The cost and manufacturing involved are too high for this purpose. The Al-SiC MMC too has great properties. properties. But is similar to t o that of Al 6061 T6. And for the cost that would incur for this purpose is impractical. Hence the final material selected is Al 6061 T6.
23
CHAPTER : VI Conclusion
Thus , the design and stress analysis of the front wheel hub was carried out in a systematic manner. After performaing FEA, stress concentrations were found out. Accordingly, Accordingly, dimensions and material has been selected, based on weighted method. 6.0 Final Specifications Dimensions:
Fig 18. New, Optimized Hub Isometric View
Fig. 19 New, Optimized Hub Side view
25
Fig 20 : New, Optimized Hub Front View
26
6.1 Observations
The following points were observed in the design process 1. Static loads have very less induced stress on the component 2. Major stress is from impact load, hence material should have high impact strength 3. The induced stress for both aluminium and steel is almost the same 4. The deflection in aluminium is more than steel, but well within the elastic limit 5. Selection of element is very important to get accurate results results 6. Element is a beam element, because the analysis is approximated to a cantile cantilever ver beam 7. FEA shows that stress concentration due to holes, steps etc are around 2.4-2.8, 2.4 -2.8, due to presence of multiple holes and multiple steps 8. Material reduction was done in areas where the stress was negligible 9. After material reduction , maximum stress increased by 15-20 % 10. After material reduction stress concentration and stress area also increased. increased. 11. MMC , though are high performance material, are very costly to be put use in such applications. Work needs to be done by researchers in order to reduce cost of MMC’s. This could greatly improve performance of various machine components 12. Machinabilty is an important factor when planning for scaled production of parts.
27
6.2 Scope for Future Work
The engineering world today is moving towards automation in all spheres. One such field is design automation. This project has a structured approach to solving the design problem. The approach above can be made into an algorithm for automated design of this component for similar sized/type vehicles. This reduces design cycle time. Literature work is already underway, and the authors are hopeful to achieve a novel algorithm for standard machine elements for automated design.
28
References The following books and papers, relating to design and analysis of wheel hubs were studied
Design of machine elements, V.B.Bhandari TMH
Strength of materials by James M. Gere
Design Data PSG
Automotive Vehicle T Technology echnology,, Hanz-Heisler
BOSCH AUTOMOTIVE HANDBOOK
Design criteria and Durability Durabi lity approval of Wheel hubs, Gerhard Fischer and Vatroslav V. Grubisic,SAE tech. paper series-
Design of Formula SAE suspension, Badih A. Jawad and Jason Baumann, SAE tech. paper series
Material Science and Engineering, William D. Callister, Wiley Publications
ASME Materials Handbook, ASME
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