Vehicle stability control: Four-wheel-steer and steer-by-wire

The vehicle stability has become more and more important with the vehicle speed increasing. To improve the vehicle stability, two active steer technologies, four-wheel-steer and steer-by-wire, have been developed. Both of four-wheel-steer and steer-by-wire can improve the vehicle handling performance through the rear wheel angle and the variable steering ratio respectively. Thee linear two-degree-of-freedom vehicle model is used to express the vehicle dynamics. Firstly, a new rear wheel angle formula is computed to reduce the steady sideslip angle to zero. It is proved that the steer system with four-wheel-steer will always be stable regardless of the vehicle parameters. Secondly, according to the steady steering sensitivity gain, the steering ratio formulas of front-wheel-steer and four-wheel-steer are Computed to keep the steady steering sensitivity gain to be the constant. Simulation results show the effectiveness of the proposed methods.