Optimal vehicle dynamics controller design using a four-degrees-of-freedom model

A yaw moment control system is developed for a front-wheel-drive vehicle utilizing two brushless d.c. electric motors embedded in the rear wheels. An optimal linear quadratic regulator (LQR) controller is employed by using a four-degrees-of-freedom (4DOF) linear vehicle model. The objective is to include important effects of roll and steering into the controller design. A two-degrees-of-freedom (2DOF) optimal LQR model is also used for comparison purposes. For the simulation of system at different conditions, a non-linear eight-degrees-of-freedom vehicle model is used. The performances of the controlled vehicle have been compared with those of the uncontrolled vehicle in order to investigate the effectiveness of the proposed controllers. Simulation results indicate that, in normal situations where the uncontrolled vehicle becomes unstable, the controlled vehicles with both 2DOF and 4DOF controllers show stable responses. In severe conditions, however, even the 2DOF controller fails to stabilize the vehicle, whereas the 4DOF controller is successful in maintaining the stability of vehicle.