Optimal Vehicle Dynamics - Yaw Rate and Side Slip Angle Control Using 4-Wheel Steering

The development of steer-by-wire involves an increased amount of possibilities for control in future cars. For example, the experimental vehicle available has both front and rear wheel steering. This enables a simultaneous multivariable control of both the yaw rate and the side slip angle. The today existing control approach is designed in the time domain and it has a decoupled control structure, where the yaw rate is controlled by the front wheel steering angle, and the side slip angle is controlled by the rear wheel steering angle. With this approach there are some major difficulties, such as constraint handling and lack of robustness to plant uncertainties, to time delays and to actuator or sensor failure. To solve these problems, a multivariable control scheduling system can be used that has already been applied to robotics, satellite attitude control and ship control but is a novelty for the field of automotive control. It is a coupling control approach, based on Individual Channel Design in the frequency domain, ICD, and considers the internal cross-coupling of the plant. It has been shown that meeting the requirements is not trivial, and a tradeoff has to be done between high performance and entirely meeting the specifications. However, the design shows a considerable degree of both robustness and integrity, which has been verified in theory as well as in simulations, but has to be further checked in real experiments