Structural Analysis of a ATV Wheel Hub

Structural Analysis of a ATV Wheel Hub

Mr. U. Yashvanth

Asst. Prof., Department of Automobile Engineering Hindustan Institute of Technology & Science Chennai, India 603103

Mr. Mohammad Raffi

Department of Automobile Engineering Hindustan Institute of Technology & Science Chennai, India 603103

Mr. Ganapa Raghu Vamsi Reddy Department of Automobile Engineering Hindustan Institute of Technology & Science Chennai, India 603103

Abstract

Through the concept of automotive product design and analysis, designing and optimizing the wheel hub of a commercial ATV without affecting the strength of the wheel hub. The ATV wheel hub is been analyzed to meet the minimum factor of safety and to contribute more towards vehicle ride handling characteristics. The wheel hub is been optimized in order to reduce the scrub radius of the tire which is in contact with the road and to reduce the unsprang weight of the vehicle. This particular is been achieved without affecting strength and durability of the part. The strength and durability of the part is maintained same with usage of lightweight aero graded Aluminium 7075 T6 material rather than Cast Iron or Mild Steel which reduces nearly thirty six percentage of the wheel hub weight. The design is been optimized in such a way that it contributes more towards the ease of manufacturing and supports change in order of manufacturing.

Keywords Wheel Hub, All Terain Vehicle, Aluminium 7075 T6, Design optimization, Structural Analysis

1. INTRODUCTION

   A wheel hub acts as an interference between the wheel and steering knuckle, which is also been called as uprights. The wheel of the vehicle is been fastened to the wheel hub, where the wheel hub have tendency to rotate freely inside the floating axle of the upright or the stub axle of the upright. The wheel hub may have either six or four wheel bolts to fasten wheel with the hub, which completely depends on the different design and manufacturers.

   It is very crucial to design the wheel hub according to the pitch circle diameter of the wheel rim and to accommodate the disc brake rotor. The wheel hub even plays a vital role over the vehicle ride handling characteristics, which also have a major interference over the scrub radius of the tire. The thickness of the wheel hub may even alter the scrub radius of the tire without any change in the kingpin axis of the upright and offset of the wheel rim. In addition, it is very vital to have a wheel hub with strong wheel supporting points, which can take both linear and axial load acting on the wheel of the vehicle during dynamic condition. Hence, a proper analysis of the wheel hub to has carried out which have a tendency to withstand and adapt to all the road conditions and impact loads acting on the tire.

   Fig 1: Front Isometric view Fig 2: Rear Isometric View Of Whee Hub. Of Wheel Hub.

   The wheel hub is to be made to ensure that it have good resistivity to fatigue and shear stress application during the course of application of braking torque and the sudden impact of bump force over it at the same time.

2. MATERIAL SELECTION

   The wheel hub is to be manufacture to take high axial, longitudinal and lateral loads from road surface. This above conditions can only be satisfied if the wheel hub material have high ultimate tensile strength and ultimate yield strength. Commercially the wheel hubs are manufactured using common available materials like Cast Iron, Wrought Iron and Mild Steel. Iron and Steel have required strength and other physical properties. The only concern using this material are the density of the material, which have higher contribution over the weight of the material. Manufacturing wheel hubs through the above-mentioned material increases the unsprang mass of the vehicle that may compromise the ride characteristics and can decrease the fuel efficiency of the vehicle.

   In order to overcome this problem, aero graded Aluminium 7075 T6 material is been used to manufacture the wheel hub. The Al 7075 T6 have lower density compared to Iron and Steel are also lighter in weight. They even carry similar physical properties with uncompromised ultimate tensile and yield strength. Similarly, Aluminium have same machinability percentage to Iron and Steel. The difference in physical and mechanical properties of the material mentioned below in the table.

   1. Mild Steel

      TABLE I: PHYSICAL AND MECHANICAL PROPERTIES OF MILD STEEL

      PHYSICAL PROPERTIES
      QUANTITY	VALUE	UNIT
      Density	7.87	g/cm3
      MECHANICAL PROPERTIES
      QUANTITY	VALUE	UNIT
      Tensile strength, Ultimate	440	MPa
      Tensile Strength, yield	370	MPa
      Youngs Modulus	205	GPa
      Poisson Ratio	0.290

   2. Cast Iron

      TABLE II: PHYSICAL AND MECHANICAL PROPERTIES OF CAST IRON

      PHYSICAL PROPERTIES
      QUANTITY	VALUE	UNIT
      Density	7.87	g/cm3
      MECHANICAL PROPERTIES
      QUANTITY	VALUE	UNIT
      Tensile strength, Ultimate	520-570	MPa
      Tensile Strength, yield	540	MPa
      Youngs Modulus	200	GPa
      Poisson Ratio	0.291

   3. Aluminium 7075 T6 (Aero-Grade)

   PHYSICAL PROPERTIES
   QUANTITY	VALUE	UNIT
   Density	2.81	g/cm3
   MECHANICAL PROPERTIES
   QUANTITY	VALUE	UNIT
   Tensile strength, Ultimate	572	MPa
   Tensile Strength, yield	503	MPa
   Youngs Modulus	7.71	GPa
   Poisson Ratio	0.33

   PHYSICAL PROPERTIES
   QUANTITY	VALUE	UNIT
   Density	2.81	g/cm3
   MECHANICAL PROPERTIES
   QUANTITY	VALUE	UNIT
   Tensile strength, Ultimate	572	MPa
   Tensile Strength, yield	503	MPa
   Youngs Modulus	7.71	GPa
   Poisson Ratio	0.33

   TABLE III: PHYSICAL AND MECHANICAL PROPERTIES OF AL 7075 T6

   during the application of braking force over the disc rotor called as braking torque and the torque exerted on the wheel by the powertrain for the motion of the vehicle called a driving torque.

   A diagrammatical representation of forces acting on the wheel hub is shown in the below figure,

   Fig 2: Free Body Diagram of Direction of Force Application on Wheel Hub

   IV. CALCULATION

   Note: The following wheel hub is been designed for vehicle of maximum gross weight 300kgs and with maximum speed up to 60kmph

   1. Brake Torque

      Considerations:

      Diameter of Disc Rotor: 0.175m Coefficient of Friction: 0.5 Piston Force: 1,970N

      T= Braking Torque in newton meter Nm r= Radius of rotor in meter

      m

      c= Coefficient of friction between rotor and brake pad

      f=Piston force on rotor in newton

      N

      T= 172.37Nm (1)

      TABLE III: CHEMICAL PROPERTIES OF AL 7075 T6

   2. Lateral Force

      Considerations:

      ELEMENT	% WIEGHT
      Copper, Cu	1.2-2
      Manganese, Mn	MAX 0.3
      Silicon, Si	0.4 Max
      Chromium, Cr	0.18 0.28
      Magnesium, Mg	2.1-2.9
      Titanium, Ti	0.2 Max
      Zinc, Zn	5.1-6.1
      Aluminum, Al	87.1-91.4

      ELEMENT	% WIEGHT
      Copper, Cu	1.2-2
      Manganese, Mn	MAX 0.3
      Silicon, Si	0.4 Max
      Chromium, Cr	0.18 0.28
      Magnesium, Mg	2.1-2.9
      Titanium, Ti	0.2 Max
      Zinc, Zn	5.1-6.1
      Aluminum, Al	87.1-91.4

      Sprung Mass at Front: 150kgs Velocity of Vehicle: 10.5m/s2 Turning Radius: 2.5m

3. FORCES ACTING ON WHEEL HUB

   1. Bump Force

   = = 6,615N (2)

   There are four different types of forces acts on wheel hub during dynamic motion, which is been mentioned below in the following.

   • Lateral Forces

   • Bump Forces

   • Braking Torque

   • Driving Torque

   The force acting on the wheel hub during the course of vehicle cornering exerts opposite cornering force on the wheel, which called as lateral force, exerted axially on the wheel. Similarly, the force exerted of the vehicle wheel during the course of jounce (Bump) known as bump force, exerted longitudinally on the wheel. The torque generated

   The value of bump force is been considered from Suspension Analysis Parallel Wheel Travel of Quarter Car Model simulated in ADAMS Car 2017. Where all the weight of the suspension system, steering system, sprung mass and unsprang mass have been gave as input in the simulation, and simulated over a bump of 6 inch height. The graph displaying the force excreted on the wheel hub is been plotted and the same value is considered for wheel hub analysis.

   Fig 3: Suspension Parallel Wheel Travel Quarter car Model

   Fig 4: Bump Force Graph on Wheel Hub

   The Bump Force Plotted is 5,550N (3)

   1. CAD MODELLING

      The wheel hub was designed in 3D modeling software namely Dassults Solidworks 2018. The wheel hub is been designed for wheel rim pitch circle diameter of 110mm and disc rotor pitch circle diameter of 36mm. The hub is been designed for stub axle type wheel assembly. The total weight of the hub been measured as 140 grams. The hub can accumulate a single angular contact bearing of width 19mm and diameter 42mm.

      Fig 5: CAD Model Front View Fig 6: CAD Model Rear View

   2. ANALYSIS

      The analysis of the above given CADD model is been carried out in ANSYS Workbench 2019. The main aim of the analysis is to find the stress formation on the hub during the action of load in all condition. The major conditions that been considered are Bump Force, Braking Torque and Lateral Force as calculated above. Depending on this loads the stress developed inside the hub measured with the amount of deformation and the maximum stress taking points predicted. Further, the stress taking points analyzed in order to check the factor of safety of the hub. The minimum factor of safety of the hub considered as 1.5. The hub should undergo minimum amount of deformation, which should be under the elastic limit of the hub material. In addition, the fatigue tool used to determine the life of the hub. The mesh considered and hub setup shown below.

      1. Mesh Setup

         Parameters	Values
         Analysis Type	Structural Analysis
         Meshing Method	Beam Method
         Element Type	Hex Dominant
         Element Size	1mm
         Mesh Type	3D
         Number Of Elements	415514
         Solver	Sparse Direct

         Parameters	Values
         Analysis Type	Structural Analysis
         Meshing Method	Beam Method
         Element Type	Hex Dominant
         Element Size	1mm
         Mesh Type	3D
         Number Of Elements	415514
         Solver	Sparse Direct

         Fig 6: Meshing of Hub Fig 7: Mesh Preview on Hub TABLE V: ANALYSIS PARAMETER SETUP

      2. Load Conditions and Analysis

         Fig 8: Analysis Setup Preview with All the Force Acting On the Wheel Hub

         Form the above figure 8, the bump force is represented as B which is acting towards the y-axis of the hub and similarly the lateral force C is acting towards z-axis of the wheel hub. The wheel hub displaced up to 154.2mm towards y-axis as a representation of hub traveling over a bump, and anti-clock wise rotation of 360 given representing the rotation of the hub. Braking torque D given in clock-wise direction, which acts opposite to the direction of the rotation of the wheel hub.

         Fig 9: Stress Analysis Fig 10: Stress Formation Over Bump Force Area (Max Stress: 148Mpa)

         Fig 11: Stress Analysis Fig 12: Stress Taking Area Over Application of Brakes (Max Stress: 1.8Mpa)

         Fig 13: Stress Analysis over Fig 14: Stress Taking Area Application of Lateral Force (Max Stress: 326Mpa)

         Fig 15: Safety Factor of Wheel Hub (Min: 2.33 & Max: 15)

         The safety factor of the wheel hub was derived using Fatigue Tool option when all the forces where applied on the wheel hub. The life span of the hub have been predicted similarly using Fatigue Tool, where the same stress was continuously applied over the period of cycle till the wheel hub fails in functioning, as shown below in figure 15.

         Fig 16: Life Period of Wheel Hub using Fatigue Tool

   3. CONCLUSION

The wheel hub is been designed and analyzed under all off- roading conditions and plotted the safety factor with minimum and maximum deformation. The minimum life cycle of the part was predicted using stress analysis. The hub designed, in order to accumulate the disc brake rotor and the wheel rim. The hub satisfied the optimization in weight with uncompromised strength. Similarly contributes more towards optimum scrub radius, fuel economy and vehicle ride- handling characteristics. The results obtained through the analysis listed below in the table.

TABLE VI: RESULT

REFERENCES

1. Gillespie, Thomas d Fundamentals of vehicle dynamics, Warren dale, pa: society of automotive engineers Inc., year 1999

2. Milliken, William f & Milliken, Douglas l Race car vehicle dynamics, warren dale, pa: society of automotive engineers Inc., year 1995

3. Smith, Carroll Tune to win, Fallbrook, ca: aero publishers Inc., year 1978

4. Finite element analysis of Chevrolet front hub with the help of inventor vol.02, issue-02, (February 2014) ISSN: 2321-1776.