CONTROLLING LATERAL VEHICLE PULL DURING BRAKING IN A LIGHT COMMERCIAL VEHICLE WITH LEAF SPRING SUSPENSION THROUGH OPTIMIZATION OF STEERING LINKAGE HARDPOINTS

摘要

The primary objective of this paper is to highlight the iterative approach carried out in half car and full vehicle dynamics simulation to identify key hard points adversely affecting lateral vehicle pull under normal and panic braking situation and subsequently demonstrate the same on actual test vehicle. Leaf spring is subjected to linear movement, angular oscillations and spring wind-up during braking. The spring wind-up plays a pre-dominant role in brake steer behavior of vehicle resulting in lateral vehicle pull on applying brakes. A full vehicle ADAMSCar model is used for this optimization study. The steering system of the LCV consists of steering wheel, steering column, variable ratio steering gearbox with recirculating ball mechanism, pitman arm, draglink, steering arm and master tie rod. The aim of this optimization study is to identify key steering linkage hardpoints adversely affecting lateral vehicle pull and to quantify their contribution to iteratively arrive at an optimum steering linkage hardpoints combination which will minimize the brake pull sensitivity of the vehicle. The last step is to verify these improvements through vehicle testing in a braking maneuver. Vehicle level test results display a strong correlation with ADAMS Car analysis. This study helps us in understanding the subtle details of steering linkage design requirements and provides us a design guideline to deliver a better product. There are no specific limitations for implementing this methodology. However, before finalizing hard points care should be taken to maintain other critical parameters such as bump steer, roll steer and steering effort within acceptable limit. Through this paper we have attempted to bring forth new design considerations for a steering linkage geometry which we feel will be useful for future reference of similar steering system architecture. Key contributing steering linkage hardpoints which affect brake steer and leaf spring wind up have been verified thoroughly with the help of objective testing after evaluating analytically. Design recommendations have also been included in this paper for future use.