| 摘要 |
A vehicle power steering system (5) uses an electric motor (12) to drive a pump (14) at a variable speed to provide power steering fluid at a variable flow for power assist to operator steering efforts. The system has a speed control (24) for the electric motor which derives (100) a command speed signal from an input load signal, the speed being switched (126) in a switching region of the power steering fluid pressure signal between a low speed for standby operation and a higher speed to supply the power steering operation demands. The system includes sensor apparatus (44,47) for providing a power steering load signal and a power steering fluid temperature sensor (48). The speed control derives the input load signal in the switching region by modifying the power steering load signal in response to the power steering fluid temperature sensor and a motor speed signal to compensate for temperature and speed dependent losses. The speed control further comprises apparatus (40, 300, 30) for sensing motor speed and controlling electric power to the motor in response thereto to vary the speed of the electric motor in the direction of the command speed signal, and apparatus for providing either the sensed motor speed or the command speed signal as the motor speed signal, although the latter is preferred for faster response. Preferably, the power steering load signal is derived from sensed motor output current, the speed control comprises a digital computer, and the compensation is provided by multiplying (134) the command speed signal by a temperature factor derived (132) from power steering fluid temperature and subtracting (122) the product thereof from the power steering load signal. <IMAGE> |
