Adaptive Robust Control of Multi-Axle Vehicle Electro-Hydraulic Power Steering System With Uncertain Tire Steering Resistance Moment

To investigate the unknown (uncertain) tire steering resistance moment and model uncertainties in a multi-axle vehicle electro-hydraulic power steering system (EHPSS), including the steering mechanisms, valve-controlled double hydraulic actuators, and heavy-duty tires, an adaptive robust control algorithm is developed to estimate the tire steering resistance moment online and compensate for the model uncertainties of EHPSS. The proposed control strategy consists of an adaptive control law and a robust controller which are based on a Lyapunov function. The adaptive control law is employed to update estimated values of the (unknown) tire steering resistance moment and parameter uncertainties in the EHPSS, whereas complicated nonlinearities are addressed by the robust controller. All adaptive laws of the EHPSS and controller, which can impede parametric uncertainties and stabilize the EHPSS, are synthesized by backstepping techniques. The comparative simulation results demonstrate that the proposed adaptive robust control scheme can achieve the desired performance for feasible tracking trajectories despite the existence of an uncertain tire steering resistance moment and external disturbance in the EHPSS.