Design Improvement in Kingpin Stub Axle Assembly Using FEA Yaseen Khan Asst.Manager - R&D, CAE International Tractors Ltd. R&D Center,vill.Chak Gujran Jalandhar Road, Hoshiarpur Punjab - 146001, India yaseen.khan@sonalika.com Vibhay Kumar Sr. Manager- R&D, CAE International Tractors Ltd. R&D Center,vill.Chak Gujran Jalandhar Road, Hoshiarpur Punjab - 146001, India vibhay.kumar@sonalika.com Satpal S Saini Head - R&D, CAE International Tractors Ltd. R&D Center,vill.Chak Gujran Jalandhar Road, Hoshiarpur Punjab - 146001, India satpal@sonalika.com Abbreviations: Itr.-Iteration,FEA-Finite Element Analysis Keywords: Kingpin,Stub axle,thrust bearing,off road vehicle,fea, Static analysis Abstract Kingpin stub-axle plays major role in many direction control of the vehicle. It is also linked with other linkages and supports the vertical weight of the tractor. Therefore, it requires high precision in tolerance, quality and durability. The main objective of the work is to explore performance opportunities in the design and production of kingpin stub-axle. This can be achieved by performing a detailed load analysis. In order to resist the bumps and jerks that usually occur in an off-road track, an integrated approach of design is developed to obtain an optimized geometry which can give the drivers a fun-to-drive experience. This paper deals with kingpin strength improvement, material selection, thrust bearing selection, taper roller bearings, bushing arrangement of kingpin stub-axle assembly and number of parts by using HyperWorks capability. These objective are achieved by static analysis in number of iterations. Introduction Agricultural tractor is one of the main example for off road vehicles category. Off road condition includes uneven agricultural field surfaces and bumpy village roads, on which the tractor has to operate. These ground irregularities leads to unexpected loads coming on the tractor components. In Off-road vehicle the turning radius is required to be small. This helps in maneuverability. Ackermann geometry is another aspect which helps in maneuverability at low speed. Thus 100% ackermann was used in the geometry as the speeds dealt in tractors and other off road vehicles is generally leading to lower unloading of inner tyre and thus the ackermann geometry plays an important role in the turning radius. Kingpin stub-axle assembly is the main load carrying member for front wheels and helps in steering of the vehicle. It is fitted below the front axle. Stub-axle takes the load coming from the front wheels and transfer it to the support. Front axle is like a simply supported beam member with the partial tractor weight acting on the center and ends being subject to ground reactions through the front wheel. 1
Objective of this paper was to study the behavior of kingpin stub-axle assembly in different load cases, finding weak area and strength improvement so that testing may be reduced or eliminated assembly Details: King pin one end is connected with the stub-axle and another end with the front axle beam via kingpin tube & bushes. Axle-hub is fixed over the stub-axle with taper roller bearings. Thrust bearing is fixed between kingpin and kingpin tube Kingpin Kingpin Tube Front Axle Beam Taper Roller Bearing Bush Thrust Bearing Axle Hub Stubaxle Figure 1: Kingpin Stub-axle assembly FE Modelling Considering different test load conditions, like drop test, torture test, 8-shaped track test, one side impact test etc. Three worst possible loads were calculated for the king pin. Vertical load was applied in the upwards direction, frontal load was applied in the backward direction (towards the rear) and transverse Load (Axial load) of was applied in the outward direction. These loads were applied on the hub and the beam was fully constrained from the area where it joins with the pivot pin tube. For the analysis, parts were joined with each other according to the actual assembly of the king pin. Refer Fig.2. Front axle beam, axle-hub,stub-axle, kingpin are modeled using 3D-tetra10 elements while bearings, bushes are modeled with hex elements. Rigid elements are used to represent bolts and connections. 2
Figure 2: Loads & Boundary condition Note:- Since Part is symmetric along Center axis, only half of axle was modeled for analysis. Iteration Details In 1 st iteration (Fig. 3a), there were only two bushes between kingpin & kingpin tube. Since stresses was high on kingpin in 1 st itr., 2 nd iteration (Fig.3b and Fig.3c) was carried out with additional bush. In 3 rd iteration (Fig.3c) thrust bearing assembly was rearranged. 3 rd Bush added Thrust bearing fitment modified in 3 rd iteration. 3
Fig. 3a : Iteration- 1 Fig. 3b : Iteration- 2 Thrust Bearing Fitment In iteration-3 thrust bearing fitment was improved. according to the reference 1, the smaller bore inner ring(shaft Washer) of a thrust bearing should be fastened on a shaft and the outer (housing washer) Should be clamped in housing for the assembly to function properly. Previously in the king pin assembly, this was not so. Changes was done in the assembly to make the thrust bearing function properly Fig. 3c : Iteration- 2 Fig. 3d : Iteration- 3 Results & Discussions Linear static analysis of king pin stub-axle assembly was done to check its strength. Three Load cases were simulated i.e. Vertical load, Frontal load & Transverse load. In iteration 1 st stresses was quite high at kingpin mid area hence 3 rd bush inserted to transfer load properly. In 2 nd iteration thrust bearing was not inserted properly hence local stress was high, its fitment corrected in 3 rd iteration. It was found to be safe in 3 rd iteration. Maximum stress is observed at kingpin mid near middle bush area.( Fig 4) Maximum stress at stub-axle is observed as shown in figure. 6. Note:- These images (Fig.4,5,6) are of vertical load case, frontal & transverse load case images are not attached. 4
Figure 4: von-mises Stress Plot of Kingpin (3 rd Itr.) Figure 5: Global deformation of model (3 rd Itr.) Figure 6: von-mises Stress Plot of Stub-axle (3 rd Itr.) Benefits Summary Kingpin stub-axle failure in testing eliminated and quality improved. Challenges Modeling of thrust bearing to freeze load transfer path, taper roller bearing and bushes and their connection was a challenge. Conclusions With the help of HyperWorks we are able to model the complex behavior of bearings, bushes & all parts effectively in all iteration. After number of iterations, we are able to conclude that in final model, stress level are within material permissible limits and successfully eliminated its costly testing. 5
ACKNOWLEDGMENTS The authors would like to thank International Tractors Limited - R&D & Altair India for their support. REFERENCES [1] Mechanical Power Transmission Components by David W. South. [2] The Steel Handbook by Alok Nayar. [3] Industrial Steel Reference Book by S.N. Bagchi & Kuldip Prakash. [4] SKF Bearing Catalogue. 6