ABSTRACT
This article deals with two theoretical analyses for optimum control of a driver/four-wheel-steered-vehicle system and their evaluation by computer simulations and experiments with a driving simulator.
Conventional methods of stability and controlability analysis for a front-wheel-steered-vehicle are not always applicable to the four-wheel-steered-vehicle, because lateral and yaw motions of the latter can be controlled independently to some extent. Therefore, a closed-loop system including the vehicle and a driver is treated in the present analyses.
The first analysis employs characteristic roots of the closed-loop system. Comparison between the root locations and the computer simulation results of the system's response reveals that two couples of conjugate complex roots in the characteristic equation exhibit strong influence on the system's maneuverability. Coefficients of a control function for the rear wheel angle were selected to optimize the system's response, based on the complex root locations.
The second analysis employs the optimum regulator method. The criterion is expressed by a function of lateral displacememt of a previewed point, yaw velocity and rear wheel angle. Feed back coefficients of a control function for the rear wheel angle are determined from the computation resutls of the Ricatti equation.
Computer simulations and experiments have proved that suitable selection of rear wheel control functions for the four-wheel-steered-vehicle can satisfy both response and stability performance of the closed-loop system.
