Design An Electric Vehicle Steer-by-Wire System Base On FlexRay Bus

The Electric Vehicle Steering system is critical to realize the driver manipulating intention and control Vehicle handing security, stability and comfort. Using by-wire technology on the vehicle steering system means instead of the traditional mechanism between the steering wheel and the front wheel. The electronic control unit and FlexRay bus technology achieve steering motor and road feeling motor operation and data communication. Than it reaches to provide the driver with the purpose of "road feel" and real time steering of electric vehicles. The new bus technology and by-wire technology provide a new pioneering space for the characteristic electric vehicle toward efficient, clean, sustainable development.The main design work is summarized as follows:(1).Analysis the FleRay2.1protocol specification and design the FleRay bus ECU node.Though research and analysis of domestic and foreign by-wire technology and steering systems, this paper proposes a steer-by-wire system basing on the Flexray bus. The FlexRay bus which is based on the time-triggered is an in-vehicle network communication. It can provide high-speed, high fault tolerance and high reliability for wire system. The control unit is MC9S12XF512microcontroller and transceiver controller TJA1080. It is though the design of software and hardware, to achieve the FlexRay bus fault tolerant communication.(2). Steer-by-wire system dynamics model and realization of the control methodThough the analysis and study of work-principle of the steer-by-wire system, it builds a dynamic model of the steer-by-wire system, including the dynamic model of the steering where assembly structure and steering the implementation assembly structure. I choose to use a permanent magnet brushless DC motor as the road feeling motor and steering implementation motor. Depending on different of motor power and motor application, they use different control chip and different control strategies, and doing PID control simulation as MATLAB/Simulink.(3).Steer-by-wire system fault diagnosis and fault-tolerant control methodIn order to ensure the high reliability of the steer-by-wire system, it is very necessary to set fault diagnosis and fault-tolerant for the steering implementation motor controlling and power supplying. The steering implementation motor is the direct driving force of the steer-by-wire system. The failure of Motor and in-vehicle12V power system will directly lead to the system performance degradation even failure. This paper studies a fault diagnosis extraction method of permanent magnet brushless DC motor controlling. Though in-vehicle12V power doing SOC estimate, based on the estimate results to determine whether parallel redundant backup battery fault-tolerant control.