Adaptive Sliding Mode Hierarchical Control for Nonlinear Hydraulic Suspension System with Prescribed Performance

This study addresses the control problem of multi-level, multivariable, and bounded constraints for uncertain active suspension system with nonlinear leaf spring and asymmetric hydraulic actuator via a novel adaptive sliding mode hierarchical control method. Considering the body weight uncertainty and time-varying constraints of body displacement, a prescribed-performance-function-based adaptive backstepping sliding mode control method is developed to generate suitable active force to improve ride comfort and ensure the preset transient/steady-state responses under strict structural hard constraints and allowable tire dynamic load. To further track the required target force, an online estimation law of unknown hydraulic parameters and servo current control law that incorporates projection-based adaptive sliding mode control is designed to actively regulate valve displacement so that the whole hydraulic suspension closed-loop system is asymptotically convergent and stable. Moreover, the boundness of all state variables is proof by Lyapunov theorem. Finally, numerical simulation for quarter-vehicle suspension is presented to verify the effectiveness and superiority of the proposed hierarchical control scheme.