Sliding Mode Control of Wheel Slip Prevention with Robust Variable Structure System Observer for Railway Vehicles

摘要

There exists strong non-linearity in the brake systems of railway vehicles such as compressibility of pneumatics, on/off action of pressure control valves, and so on. Adhesion forces have also non-linear characteristics. Moreover, the friction coefficients of brake materials vary. Therefore, adhesion forces have been modeled with considering nonlinear characteristics, so that they can show the saturation characteristics with the slip ratio. By the way, Anti-Lock Brake system is a standard equipment to secure the stability of operation and shorten braking distances for automobiles. In the case of railway vehicles, there are wheel-slip prevention devices functionally similar to ABS for the automobiles. The conventional controller for the wheel slip prevention of rail vehicles is based on the simple rules using if-then logic. As an example of wheel slip prevention using a more advanced control theory, SHIOMI et al., (1994) reported the fuzzy control. In their report, the effectiveness of the control was shown; however the stability of the closed loop system still remains as problems to be solved. On the other hand, as for the recent researches of automobiles, Drakunov et al., (1994), and YOKOYAMA et al., (1997) reported the sliding mode control for ABS. In their researches, the controller was designed by using periodic switching function or optimal control based on LQ theory. Even though the effectiveness of the control was proved, the braking performances were not clearly shown by experimental results. Wu et al., (2001) also reported a sliding mode control for ABS, and showed braking deceleration performances, but did not show braking distances. Recently, the robust control design and its analysis have been performed for the brake system of railway vehicles. Those systems use the feedback signal of brake cylinder pressure. However, if the sensor of brake cylinder pressure failed, the stability of the systems is lost, and braking performances are worse. Therefore, the estimation method of brake cylinder pressure is necessary. However, there is no report concerning the robust VSS observer for wheel slip control. This paper describes the braking distances results of the robust VSS observer for robust wheel slip control for railway vehicles via computer simulation. The simulation results proved the effectiveness of the proposed control as compared with the sliding mode controller using pressure sensor and the sliding mode controller using robust VSS observer, and showed the high brake performances under nonlinear characteristics of brake dynamics.