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.
