Enhancing high-speed steering stability of wheel-legged vehicles by active roll control

Wheel-legged vehicles (WLVs) combine the speed of wheels with the active control of legs to traverse challenging terrain, which presents a new development possibility for enhancing the system's mobility and stability. Most of the existing studies mainly focus on the stability of low-speed trajectory optimization or obstacle-surmounting by hybrid walking-driving. Without considering the stability of high-speed driving. To enhance the vehicle stability at high-speed steering, with the additional roll moment generated by the active roll motion taken into account, a 15-degree-of-freedom nonlinear yaw-roll coupled vehicle model is developed. Specifically, a fusion dynamic stability factor for skid steering is presented as the rollover threshold to determine the three-dimensional stability region of longitudinal speed, yaw rate and roll angle, based on which the vehicle's ideal roll angle is obtained. Subsequently, a hierarchical parallel control scheme is proposed to decouple the yaw and roll motions of the wheel-legged vehicle. The fusion dynamic stability factor is regarded as the switching threshold of the upper-level controller, while the lower-level controller adopts the linear quadratic regulator and the sliding mode control to actively control additional roll moment and direct yaw moment, respectively. Furthermore, the studies for the dynamic model and the proposed controller are conducted through vehicle tests. Corresponding test results validate the advantages of the proposed control scheme over conventional schemes without active roll control, in which vehicle stability is effectively improved, thereby preventing vehicle rollover in the case of high-speed steering.