Adaptive open-loop rear-wheel-steering

Open-loop rear-wheel-steering (RWS) control can be enhanced by modifying the open-loop gain table that adapts to changes in vehicle dynamics parameters, such as front and rear cornering compliances. These changes can be caused by tire deflation/inflation, tire wear, loading change and suspension aging, etc. The vehicle parameters can be estimated by using a real-time vehicle parameter estimation technique. The open-loop gain table is modified based on three different strategies: yaw-rate gain matching, lateral-velocity gain matching, and lateral-velocity to yaw-rate ratio matching strategies. The three strategies are investigated using linear analysis. The yaw-rate gain matching strategy does recover yaw-rate gain in the presence of vehicle cornering compliance changes. However it has undesired effect on lateral-velocity response. The other two strategies are both very effective in reducing lateral-velocity although the lateral-velocity to yaw-rate ratio matching strategy is preferred due to its simplicity. When the only change in vehicle dynamics parameters is the rear cornering compliance, the three proposed strategies are found to be equivalent. An adaptive open-loop RWS control structure is then proposed and analyzed with simulation studies. The simulation result shows the effectiveness of the adaptive open-loop control.