Research on the hybrid redundancy leveling strategy for emergency rescue vehicles

To address the wheel-lifting issue caused by the four-point highest-contact leveling strategy (FPHCLS), this study proposes a hybrid redundant leveling control strategy (HRLCS). First, a model of an emergency rescue vehicle was established and assembled in Matlab/Simulink/Simscape according to specific motion relationships, along with the construction of a hydraulic active suspension system. The vehicle model was then treated as a parallel mechanism, and the FPHCLS was applied to obtain the target displacement commands for the hydraulic actuators. A fuzzy PID controller was designed to ensure that three hydraulic actuators accurately tracked their target displacements, enabling the vehicle body to quickly level to the horizontal plane. Furthermore, inspired by compliant control in robotics, a force-displacement hybrid control was implemented for the right-front hydraulic actuator to maintain the desired pressure in the rodless chamber, ensuring continuous tire-ground contact during posture adjustment. Simulation results demonstrate that, when the vehicle traverses a single-side bridge obstacle and runs on a random road, the proposed HRLCS effectively reduces body pitch and roll motions. Compared with the passive suspension, the root mean square (RMS) values of the pitch and roll angles are reduced by 73% and 78%, respectively, when crossing the single-side bridge, while maintaining tire-ground contact at all times. On random roads, the RMS values of the pitch and roll angles are reduced by 61.2% and 43.4%, respectively.