Optimization of Steering Geometry in Four-Wheel Steering Vehicles to Minimize Bump Steer and Exploit Kinematic Steering Using a Multibody Approach

This paper presents a methodology for optimizing the steering system of a multi-purpose agricultural vehicle (MPAV) equipped with four-wheel steering (4WS) and a symmetrically configured double-wishbone suspension on both axles. The MPAVs are often prone to bump steer issues due to their narrow track width and the need for long suspension travel. The objective is to define and dimension the steering geometry while maintaining the existing suspension kinematics and preserving the hard points of the wheel hubs. In the scientific literature, this issue is typically addressed by adjusting the hard points of both the steering mechanism and the suspension kinematics. The proposed optimization framework begins with a sensitivity analysis of key design parameters: the position and length of the steering actuator. Based on this analysis, the problem is formulated as an optimization task with two different objective functions, whose solutions are then compared. The functions aim to minimize bump steer and replicate the kinematic steering geometry for both front wheel steering (FWS) and all-wheel steering (AWS) configurations. The steering system is modeled using a multibody (MB) approach, and a genetic algorithm is employed for optimization. Finally, the optimized solutions are evaluated and compared using a full-scale MB vehicle model.