Electronic power assist control steering system

Claim 1

A power steering gear system for controlling the dirigible wheels of a vehicle comprising: a constant flow fluid pressure pump; a gear mechanism having a torque input member adapted to receive driver steering torque and a torque output member adapted to be connected to the dirigible wheels and a fluid motor having a pressure movable member for augmenting steering torque; a steering valve assembly having primary and secondary valve portions with registering valve lands that define variable fluid flow areas, and primary valve lands controlling pressure distribution to opposite side of said pressure movable member to provide a pressure steering assist; a high pressure passage connecting the flow inlet side of said primary valve portion with the high pressure side of said pump and a low pressure passage connecting the flow outlet side of said primary valve portion with the low pressure side of said pump; a steering pressure control valve means for establishing a controlled bypass flow from said high pressure passage to said low pressure passage; a steering pressure control solenoid valve means communicating with said high pressure passage and said low pressure passage for establishing a pressure signal, and a pressure signal passage connecting said steering pressure control solenoid valve and said steering pressure control valve whereby the latter responds to said pressure signal to control the bypass flow between said high pressure passage and said low pressure passage; a steering torque sensor pressure passage extending from said high pressure passage to the inlet side of said secondary valve portion; a steering torque sensor flow control valve means disposed in and forming a part of said steering torque pressure passage for establishing a constant flow to said secondary valve portion; an electronic processor unit including a data input portion, an output driver portion and a memory portion, said driver portion being connected to said solenoid valve, said memory portion having stored therein desired functional relationships between steering torque and steering pressure for various vehicle speeds; and a steering torque pressure sensor and a vehicle speed sensor connected to the data input portion of said processor unit, said pressure sensor being connected to said steering torque sensor pressure passage.