Many studies have been made concerning the directional motion where only the steer angle of the front wheel is taken as an input. In the case of this input, it is possible to impose an assumption that the forward velocity of the vehicle is kept constant, and the equations of motion become linear and can be solved rather easily. These solutions are helpful in discussing the fundamental characteristics of the directional motion of the vehicle. However, the recent tendency of increasing the magnitude of the tractive force generated by wheels makes it inappropriate to disregard the effect of tractive force on the directional change of motion of the vehicle. In particular, tractive force has a powerful influence on a front wheel drive vehicle. Therefore, in order to make clear the directional motion where tractive force is an input, the following points are discussed in this paper. 1. A theoretical model of the vehicle with three degrees of freedom and the equations of motion based on it are established. These nonlinear simultaneous equations are approximated in linear form by applying the perturbation method and solved by the Laplace transformation. 2. The experimental method to measure the property of a tire and some of the experimental data are presented. These data are necessary for practical applications of the predictions obtained theoretically. 3. Transient responses of a front wheel drive vehicle and of a rear wheel drive vehicle are measured and compared with theoretical values. 4. A criterion is set up upon which the directional stability and controllability of vehicles are evaluated. 5. The means of improving the problems of the directional stability and controllability of a front wheel drive vehicle are suggested theoretically.
Abstract