Patent ID: 7164978

Claim:
A vehicle electro-hydraulic power steering unit comprising: a steering mechanism steering a steered wheel in a steering direction in response to operation of a steering wheel; an electro-hydraulic pump driven with a motor ) as a drive source; a piston mechanism that is provided with pressure-receiving chambers on two sides of a piston capable of reciprocating, and that assists said steering mechanism in a steering direction in accordance with a displacement of said piston; a hydraulic circuit that provides a connection between said electro-hydraulic pump and each of said pressure-receiving chambers of said piston mechanism via a supply-and-exhaust valve performing a supply and exhaust operation in response to steering of said steering mechanism, and that causes an assist power to be generated in each of the pressure-receiving chambers in response to the steering of said steering mechanism; a vehicle speed sensor; a torque sensor detecting a steering torque of said steering mechanism; a steering angle sensor; and a control unit controlling said motor that drives said electro-hydraulic pump based on an output signal from said vehicle speed sensor, said torque sensor and said steering angle sensor; wherein driving said motor of said electro-hydraulic pump is started when said steering torque exceeds a torque threshold to be set, and said torque threshold to be set is changed depending on operating conditions.