The Study On Active Steering Technology Of Independently Rotating Wheels

With the acceleration of urbanization progress, the urban railway transit is developing rapidly. Because of its beautiful appearance, comfort, energy conservation, environmental protection, and many other advantages, the 100% low floor vehicle has become one of the most important parts in the urban railway transit. It has a good application prospect. The Independently rotating wheel (IRW) is the key to realize the low floor and its application is also more and more widely. How to improve the steering capability of IRW is a hot and difficult problem for a long time. This paper reviewed the research situation of independent wheel steering technology at home and abroad and actively guide is one of the important research direction.The paper study the relationship between wheel and rail, deduce the formula of gravity restoring force and wheel/rail creep force. After analysis the motion of solid wheelset (SW) and IRW, some conclusion could come out. The main reason for the SW in a straight line and the curve has the self-steering capability is its gravity restoring force and the wheel-rail creep force. IRW loses self-steering capability of longitudinal creep moment, so its restoration capability and curving performance is worse than SW. So it needs some external methods to obtain steering capability.The dynamic models of bogie-based railway vehicle with SW and IRW are set up in the multi-body dynamics software SIMPACK. It is able to deal with modles which account for the complex features of railway vehicles. Simulation results demonstrate the SW has a good self-steering capability in the straight line and curve line, and IRW lack the ability to guide wheel bogie.Then study the active steering approach "Actuated Independently Rotating Wheels" (AIRW) and "Driven Independently Rotating Wheels" (DIRW) based on the kinematical equation of IRW. The control models of AIRW and DIRW are established in MATLAB/ Simulink, and SIMAT co-simulation with the vehicle modle with IRW in SIMPACK. The simulation result shows that both AIRW and DIRW can improve the steering capability of IRW. After compensating the curvature of curve and speed of vehicle, the wheelset lateral displacement can attains the the center of track line with AIRW. The wheelset lateral displacement can’t attain the center of track with DIRW, but it is less than the situation that doesn’t compensate the curvature and speed.In order to futher study for the method of AIRW, we choose the BLDCM electromechanical actuator as the actuating element. Then the double closed loop control modle of BLDCM electromechanical actuator is set up in the MATLAB/Simulink. The simulation results show that:the actuator has good stability, its response speed for step signal and trapezoidal wave signal is fast. As the servo loop of AIRW, it has a good track performance and meets the need of AIRW.Finally, a simple research of the delays and failures for control system are given. Simulation results show that:a 8ms delay has little impact to the control system, but if the delay time is more than 8ms, the system is unstability. If the system is failure, IRW will no longer have the steering ability. Some additional approach should be applied to improve the safety and reliability of the system.