Electro-hydraulic power steering control with motor speed switching and fluid temperature compensation of standby switch-points

摘要

A vehicle power steering system uses an electric motor to drive a pump 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 for the electric motor which derives a command speed signal from a power steering load signal, senses motor speed and controls electric power to the motor in response thereto to vary the speed of the electric motor in the direction of the command speed signal. In a switching region of the power steering fluid pressure signal, the speed control switches between a low speed for standby operation and a higher speed to supply the power steering operation demands. The speed control modifies the switch-point load value in response to the power steering fluid temperature sensor to compensate for temperature dependent losses. Separate switch-points are preferably provided for increasing and decreasing power steering load to provide hysteresis; and both switch-points are preferably compensated.