This paper explains a method of four-wheel steering control by using Sliding Mode Control (SMC). The purpose is to improve the control safety of four-wheeled vehicle by using invariable SMC for disturbance that satisfies the matching condition. Parameter variation and influence of the side wind are thought as disturbance related to driving the car. Steer control that corresponds to the influence of the side wind and parameter variation by using SMC is done, and it is examined to be able to do the achievement of the high stability and the decrease of the error margin with the target path. Then, we propose the adjustment method of the value of a nonlinear gain of the control input that considers the phase-lag to the steer of a lateral acceleration. The improvement of the control of disturbance is achieved by the proposal method.
Sliding Mode Control (SMC) is nonlinear robust control to attempt stabilizing by restraining the state to switching hyperplane. There is a feature of having excellent robustness for disturbance and the uncertainty which fulfill matching condition. In addition, it is known because high control performance is obtained for a nonlinear system and the parameter variation.However, in a principle of SMC, it becomes a factor that the oscillatory phenomenon called chattering is produces because the existence of dead time may influence a high-speed switch of the control input to restrain the state to the switching hyperplane. Moreover, chattering is generated in discrete time system because the sampling time is limited.When SMC is applied to the actual system, the state of the system causes the oscillations such as the high-frequency vibrations and spill-over near the switching hyperplane when chattering is caused, and may lead to the deterioration of the controller.In order to solve this problem, authors proposed a time varying swithcing line of two dimensions designed by the state as a method for newly decreasing chattering (Fig. 1).There is the following feature in this method.
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