Model predictive suspension control on off-road vechicles

Abstract

Reducing the rollover propensity of off-road vehicles while maintaining good ride comfort and off-road capabilities is a well-known challenge. With controllable suspension systems, the dynamics of the vehicle can be altered to give better performance than passive suspension systems. The semi-active hydro-pneumatic suspension system under consideration can switch between soft spring and a stiff spring, as well as between low and high damping. In this study, a model predictive controller, based on a linear quadratic regulator and receding horizon theories, was developed to control individual struts of the suspension system. A combined handing and ride comfort metric was developed to determine the input weights of the model predictive controller based on the driving conditions. The metric discerns between a handling or emergency manoeuvre and normal driving on rough roads. It changes the input weight accordingly to bias the controller towards a handling setting or a ride comfort setting. A 16 degree of freedom simulation model was validated for both the lateral and vertical dynamics and found to be a close representation of the real Land Rover Defender 110 used for the experiments. The controller was implemented into the simulation model to test and ensure the controller worked as intended. The simulation model was validated at speeds varying from 50 km/h to 80 km/h for severe double lane change handling manoeuvres. The ride validation was performed over a rough Belgian paving track at speeds of 21 km/h and 47 km/h. The controller was also experimentally validated for the double lane change, Belgian paving and various other handling and ride comfort tests. In the handling test, the controller performed well keeping the suspension in handling mode and reducing the roll angle as compared to the ride comfort mode. Over the rough tracks, the performance of the controller was not good and the suspension controller did occasionally switch to the handling mode. Although the controller did switch over to the handling mode the vehicle’s ride comfort wasn’t detrimentally influenced. Overall key aspects of the controller were identified for improvement to overcome the problem experienced in ride comfort settings and also improve the handling of the vehicle.