Improvements in vehicle handling through integrated control of chassis systems

In this paper methods of improving vehicle stability and emergency handling using electronically controlled chassis systems are discussed. By analysing a simple nonlinear vehicle model in the yaw plane, it is shown that vehicles can become unstable during portions of handling manoeuvres performed at or close to the limit of adhesion. It is further demonstrated how small changes in the balance of tyre forces between front and rear axles may affect vehicle yaw moment and stability. The methods of effecting vehicle yaw dynamics using controllable brakes, steering, and suspension are discussed. Control authority of each chassis system, in terms of its ability to generate a corrective yaw moment, is evaluated and is shown to depend on the operating point of vehicle and tyres. Consequently, regions of effectiveness of each subsystem are defined, which is a prerequisite for development of integrated chassis control systems. Preliminary test results for a vehicle with integrated closed loop control of brakes and suspension, performing typical handling manoeuvres, are presented. They demonstrate the benefits of integrated control in terms of improved handling response, stability, and reduced driver steering effort.