Lateral speed and yaw rate decoupling control in four wheel active steering vehicles

This thesis presents new results on the design of decoupling control in four wheel active steering vehicles. Linear controllers are derived from a linearised single track car model for four wheel active steering vehicles: yaw rate and lateral speed are the output to be decoupled while the front and rear steering angles are the control inputs. It is shown that the lateral speed dynamics can be decoupled by feeding back longitudinal speed, yaw rate and lateral acceleration measurements: lateral speed measurements or observers are not required. The yaw rate controlled dynamics are independent from lateral speed and can be described by an inputoutput model. Simulations on nonlinear single track third order model and on a higher order vehicle model provided by the CarSimr are carried out to illustrate the improvements in handling and driver subjective rating on the vehicle dynamics. These results show that the proposed methods involve advantages over previous designs with respect to vehicle handling, performance, robustness with respect to unmodelled dynamics and vehicle parameters.