DESIGN AND ANALYSIS OF FRONT AXLE OF HEAVY COMMERCIAL VEHICLE
Ketan Vijay Dhande
1, Prashant Ulhe
21,2 Department of Mechanical Engineering,
SSBT’s College of Engineering and Technology, Jalgaon, (India)
ABSTRACT
An axle is a central shaft for a rotating wheel. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to its surroundings, with the wheels rotating around the axle. The axles serve to transmit driving torque to the wheel, as well as to maintain the position of the wheels relative to each other and to the vehicle body. The axles in a system must also bear the weight of the vehicle plus any cargo. The front axle beam is one of the major parts of vehicle suspension system. It houses the steering assembly as well. About 35 to 40 percent of the total vehicle weight is taken up by the front axle. Hence proper design of the front axle beam is extremely crucial. In present research work design of the front axle for Ashok Leyland 1612 Comet heavy commercial vehicle were done. The approach in this project has been divided into two steps. In the first step front axle was design by analytical method. For this, the vehicle specifications, its gross weight and payload capacity in order to find the stresses and deflection in the beam has been used. In the second step front axle were modeled in NX-CAD and meshed in HYPERMESH software module. The meshed model was solved in ANSYS software. The FE results were compared with analytical design.
Keyords- Analytical Design, Modelling, Meshing, Analysis, Comparison of Results
I. INTRODUCTION
The auto industry is one of the key sectors of the Indian economy. The Industry comprises of automobile and the auto components sectors and encompasses commercial vehicles, multi-utility vehicles, passenger cars, two wheelers, three wheelers and related auto components. During last few decades due to global economic scenario optimum vehicle design is major concern. To accomplish the need to design a moderate car, the structural engineer will need to use imaginative concepts. The demands on the automobile designer increased and changed rapidly, first to meet new safety requirements and later to reduce weight in order to satisfy fuel economy requirements. Experience could not be extended to new vehicle sizes, and performance data was not available on the new criteria. Mathematical modeling was therefore a logical avenue to explore. Most recently, the finite element method, a computer dependent numerical technique, has opened up a new approach to vehicle design [1]. During the vehicle operation, road surface irregularity causes cyclic fluctuation of stresses on the axle, which is the main load carrying member. Therefore it is important to make sure whether the axle resists against the fatigue failure for a predicted service life. Axle experiences different loads in different direction, primarily vertical beaming or bending load due to curb weight and payload, torsion. Due to drive torque, cornering load and braking load. In real life scenario all these loads vary with time. Vertical beaming is one of the severe and frequent loads on an axle Due to their higher loading capacity; solid axles are typically used in the heavy commercial vehicles. During the vehicle service life, dynamic forces caused by the road surface roughness produce dynamic stresses and these forces lead to fatigue failure of axle housing, which is the main load
carrying part of the assembly. Front axle can experience a 3G load condition when vehicle goes on the bump [2- 5]. Performing physical test for vertical beaming fatigue load is costly and time consuming. So there is a necessity to build FE models which can virtually simulate these loads and predict the behavior. Even though the FEA produce fairly accurate results, solution accuracy heavily depends on accuracy of input conditions and overall modeling method used to represent the actual physics of problem. Therefore validation of FEA model is of utmost importance. Typically FEA model is validated by correlating FEA results analytical design [3-6]. An axle is a central shaft for a rotating wheel. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to its surroundings, with the wheels rotating around the axle. The axles serve to transmit driving torque to the wheel, as well as to maintain the position of the wheels relative to each other and to the vehicle body. The axles in a system must also bear the weight of the vehicle plus any cargo. The front axle beam is one of the major parts of vehicle suspension system. It houses the steering assembly as well. About 35 to 40 percent of the total vehicle weight is taken up by the front axle. Hence proper design of the front axle beam is extremely crucial [6-9]. In present research work design of the front axle for Ashok Leyland 1612 Comet heavy commercial vehicle were done. The approach in this project has been divided into two steps. In the first step front axle was design by analytical method. For this, the vehicle specifications, its gross weight and payload capacity in order to find the stresses and deflection in the beam has been used. In the second step front axle were modelled in NX-CAD and meshed in HYPERMESH software module. The meshed model was solved in ANSYS software. The FE results were compared with analytical design
.
II. COMPNENTS
For design purpose the front axle beam of Ashok Leyland 1612 truck was choosen. All standard axles have an I cross section in the middle (spring seat to spring seat) and circular or elliptical cross sections at the ends. The front axle beam will have I cross section in the middle and circular cross sections at the ends. An axle is usually a forged component for which a higher strength to weight ratio is desirable. The I cross section has lower section modulus and hence gives better performance with lower weight. This type of construction produces an axle that is lightweight and yet has great strength. The I-beam axle is shaped so that the center part is several inches below the ends. This permits the body of the vehicle to be mounted lower than it could be if the axle were straight. A vehicle body that is closer to the road has a lower center of gravity and holds the road better. On the top of the axle, the springs are mounted on flat, smooth surfaces or pads. The mounting surfaces are called spring seats and usually have five holes. The four holes on the outer edge of the mounting surface are for the U- bolts which hold the spring and axle together. The center hole provides an anchor point for the center bolt of the spring. The head of the center bolt, seated in the center hole in the mounting surface, ensures proper alignment of the axle with the vehicle frame. A hole is located in each end of the I-beam section. It is bored at a slight angle and provides a mounting point for the steering knuckle or kingpin. A small hole is drilled from front to rear at a right angle to the steering knuckle pinhole. It enters the larger kingpin hole very slightly. The kingpin retaining bolt is located in this hole and holds the kingpin in place in the axle. The steering knuckle is made with a yoke at one end and a spindle at the opposite end. Bronze bushings are pressed into the upper and lower arms of the yoke, through which the kingpin passes. These bushings provide replaceable bearing surfaces. A lubrication fitting and a drilled passage provide a method of forcing grease onto the bearing surfaces of the bronze bushings. The spindle is a highly machined, tapered, round shaft that has mounting surfaces for the inner and outer wheel bearings. The outer end of the spindle is threaded. These threads are used for installing a nut to
secure the wheel bearings in position. A flange is located between the spindle and yoke. It has drilled holes around its outer edge. This flange provides a mounting surface for the brake drum backing plate and brake components. The kingpin acts like the pin of a door hinge as it connects the steering knuckles to the ends of the axle I-beam. The kingpin passes through the upper arm of the knuckle yoke, through the end of the I-beam and a thrust bearing, and then through the lower arm of the knuckle yoke. The kingpin retaining bolt locks the pin in position. The ball-type thrust bearing is installed between the I-beam and lower arm of the knuckle yoke so that the end of the I-beam rests upon the bearing. This provides a ball bearing for the knuckle to pivot on as it supports the vehicle's weight. When the vehicle is not in motion, the only job that the axle has to do is hold the wheels in proper alignment and support part of the weight. When the vehicle goes into motion, the axle receives the twisting stresses of driving and braking. When the vehicle operator applies the brakes, the brake shoes are pressed against the moving wheel drum. When the brakes are applied suddenly, the axle twists against the springs and actually twists out of its normal upright position. In addition to twisting during braking, the front axle also moves up and down as the wheels move over rough surfaces. Steering controls and linkages provide the means of turning the steering knuckles to steer the vehicle. As the vehicle makes a turn while moving, a side thrust is received at the wheels and transferred to the axle and springs. These forces act on the axle from many different directions. You can see, therefore, that the axle has to be quite rugged to keep all parts in proper alignment.
Fig.2.1 Layout of Front Axle
Photo 2 (A) Top View of Front Axle
Photo 2 (B) Side View of Front Axle
2.1 Vehicle Specifications
2.1 (a) Specifications
Engine H series 6 ETI turbocharged intercooled 6 cylinder diesel Maximum Power 114 ps (84kW) @ 2400 rpm
Maximum Torque 42 mkg @ 1700-1800 rpm
Clutch 356 mm dia
Transmission 5 speed synchromesh gearbox
Rear Axle Single Speed Hypoid Gear
Frame All ladder type bolted construction
Suspension Semi Elliptic laminated multi leaf with centre bolt
Steering Power Steering
Brakes Dual Line Full Air Brakes
Battery 24V (2*12V) 80 Amp-Hr
Tyres Front 10.00*20 - 16PR Nylon
Rear 10.00*20 - 16PD Nylon
Table 2.1 A) Specifications of Truck 16/12
2.1 (b) Major Dimensions
Table 3.1 B) Major Dimensions of Truck 16/12
Wheel Base 4330 mm
Overall Length 7766 mm
Overall Width 2425 mm
Front Track 1915 mm
Rear Track 1816 mm
Min. Ground Clearance 253 mm
Min. Turning Circle Diameter 17500 mm
Loading Body Length 5640 mm
Max. Speed In Top Gear 74.5 kmph
Maximum Gradeability 12%
2.1 (c) Weights
Table 3.1 c) Weight of Truck 16/12
Unladen Laden
Front Axle 2420 6000
Rear Axle 1820 10200
Total 4240 16200
III. ANALYTICAL METHOD
3.1 Sample Calculation
3.1.1 Moment of Inertia of I Cross Section
Fig. 4.1 I Cross Section of Axle Assumption
H=1.2*B,
h= (H/2) ………….……….. (A)
b= (B/2)
We will design the axle beam by taking consideration of yield stress of both material i.e. Ductile Cast Iron and SAE 1020. The value of yield stress of both materials is 370 MPa.
3.1.2 Calculation of weight
For Truck 16/12,Laden Weight = 6000 kg.
Actual weight coming on axle is,
Considering 3g condition (bump load) = 3 * 6000 = 18000 kg Total Weight on axle is given by = 18000 * 9.81 = 176.58 kN
Weight on each spring seat = 176.58 / 2
= 88290 N
3.2 Result Table
Table 3.2 Analytical Results
Sr. No Material Deflection, ymax
(mm)
Stresses, σ (N/mm2)
1 Ductile Cast Iron 15 ( ) 370
2 SAE 1020 18.621( ) 370
IV. FINITE ELEMENT ANALYSIS
After application of boundary condition, the model is solved. The displacement and stress has been plot in ANSYS software module. The model of axle is simulated for two material namely as Ductile Cast Iron and Cast Iron.
4.1for Ductile Cast Iron
Figure 5.6 (a) shows the deflection of axle for Ductile Cast Iron. The maximum deflection occurred in axle is 19.85 mm. The location of maximum deflection is at the middle of the axle.
4.1.1 Deflection in Axle
Figure 5.8.1 (A) Deflection of Axle for Steel Ductile Cast Iron Material
4.1.2 Stresses in Axle
Figure 4.1.1 (B) Von Mises Stresses In Axle for Ductile Cast Iron Materials
4.2 For Material SAE 1020
4.2.1 Deflection in Axle
Figure 5.8.2 (a) shows the deflection of axle for SAE 1020 material. The maximum deflection occurred in axle is 16.62 mm. The location of maximum deflection is at the middle of the axle.
Figure 4.2 (A) Deflection in Beam for SAE 1020 Material
4.2.3 Stresses in Axle
Figure 5.8.2 (b) shows the Von Mises stress distribution in axle for SAE 1020. The maximum value of stress is 404.87 Mpa.
Figure 5.8.2 (B) Von Mises Stress for Cast Iron Material
4.3 Comparison of Results
The table 5.9 shows the comparison between Analytical and FEA results. The deflection obtained from FEA results are in good relation with Analytical results.
Sr.
No.
Materials Parameters Analytical Results
FEA results % Error
1 Ductile CI
Defection (mm) 15 19.85 24.43
Stress (N/mm2) 370 402.802 8.1
2 SAE 1020
Defection (mm) 18.62 16.62 11.11
Stress (N/mm2) 370 404.87 9.42
Table 4.3 Comparison of Results
V. CONCLUSION
From the above results shown in table 4.3 it is clear that the maximum deflection in axle is for SAE 1020 materials but at the same time the maximum stress distribution is low for SAE 1020 than Ductile Cast Iron. So, that SAE 1020 is better material for manufacturing of axle than Ductile Cast Iron. Also this present thesis we have established a satisfactory co relation between hand calculations done analytically and the FEA results. The displacements predicted in the FEA gave the confidence that the boundary conditions for beam are correctly simulated. Correlation between stress results from analytical calculation and from FEA assures that the mesh size and modeling approach used for the component were well defined. Finally we were able to deliver a safe and validate design to suit the requirements of the project.
REFERENCES
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