Precision electro-hydraulic actuator positioning system

A power steering apparatus comprising:

• a hydraulic actuator having a pair of power assist cylinder chambers and operable to generate assisting power,
• a hydrostatic actuator for supplying pressurized fluid to said power assist chambers,
• an electric motor for operating said hydrostatic actuator,
• a control valve mechanism operable by a system controller for bypassing between said pair of power assist cylinder chambers of said hydraulic actuator the pressurized fluid supplied by said hydrostatic actuator,
• pressure sensors for detecting differential pressure between pressures in said pair of power assist cylinder chambers, and
• a motor control responsive to the output of said pressure sensors for controlling said electric motor thereby to cause said motor to drive said hydrostatic actuator in accordance with steering wheel position so as to return the differential pressure to a predetermined first value, said hydrostatic actuator comprising a double-acting actuator piston and cylinder unit having a pair of working chambers separated by said actuator piston and respectively communicating with said pair of power assist cylinder chambers, said electric motor being operable bidirectionally axially to drive a leadscrew on which said piston is mounted for travel in response to axial motion of said leadscrew.

An electro-hydraulic power steering system that comprises:

• an elongated rack adapted to be connected at opposite ends to steerable wheels of a motor vehicle, said rack having a series of teeth along a section of its length,
• a rotatable steering gear in mesh with the rack teeth and adapted to be operably connected to a steering wheel of the vehicle by a shaft so as to receive vehicle operator steering input, said rack extending lengthwise within an elongated housing constructed to form an elongated power assist cylinder,
• a piston carried by said rack and separating said power assist cylinder into first and second power assist working chambers filled with hydraulic fluid,
• an electric-hydrostatic actuator including an electric motor responsive to motor control signals for providing an output to a motor shaft, piston means coupled to said shaft, and hydraulic cylinder means mounted on said motor and cooperating with said piston means for providing a pair of pump fluid cylinders respectively coupled to first and second power assist working chambers,
• a solenoid valve connected between said chambers and responsive to valve control signals for feeding fluid between said chambers,
• a pair of pressure sensors coupled to said power assist working chambers for providing respective pressure signals as a function of fluid pressure in said chambers, which in turn are responsive at least in part to steering input through said shaft, and
• control means responsive to said pressure signals for providing said valve control signal and said motor control signal.