Sensitivity of rearward amplication control of a truck/full trailer to tyre cornering stiffness variations

Abstract

Highway safety and vehicle performance are two important considerations in the design of a heavy vehicle combination. In this paper a performance measure called the ‘rearward amplification ratio’ (RWA) is used as a control criterion in the design of a vehicle-handling controller. This approach is different to conventional control techniques. The RWA is defined as the ratio of the peak lateral acceleration at the rearmost trailer's centre of gravity (CG) to that of the lead unit during a lane-change manoeuvre. The vehicle under consideration is a six-axle truck/full trailer, which usually exhibits a high level of RWA leading to roll-over during obstacle avoidance manoeuvres. In this study, several control strategies are examined, namely active yaw control at the truck CG, active yaw control at the dolly CG and active yaw control at the trailer CG. These could be employed individually or in combination. The effect of an active control torque applied to various vehicle units is examined by using an optimal linear quadratic regulator approach combined with a simplified four degrees-of-freedom linear vehicle model. The controller performance index parameters are determined for the vehicle based on acceptable RWA target values. The sensitivity of the controller to tyre cornering stiffness variation is further evaluated. Simulation results indicate that the RWA can be reduced without significant change of the uncontrolled vehicle trajectory when active yaw torque is applied to the dolly. The controller can be more effective in improving the dynamic performance and roll stability of this type of commercial vehicle, if applied to the lead unit (truck) or to the last unit (trailer). However, the path of the vehicle will be strongly influenced and driving difficulties can be experienced. For active yaw control at the dolly CG, the optimal controller is found to be most sensitive to the dolly's tyres' cornering stiffness variations and least sensitive to steering axle from the RWA point of view. It is also found that the controller is most sensitive to steering axle parameter variations for path following.