Automotive power steering system

Claim 1

In an automotive power steering system including a pump, a servo-valve, a steering assist fluid motor, a reservoir having a reservoir chamber therein, a plurality of fluid ducts interconnecting said reservoir and said pump and said servo-valve and said fluid motor, and a volume of hydraulic oil in said power steering system establishing a fluid level in said reservoir chamber which varies between a minimum cold level when said working fluid is at a minimum operating temperature and a maximum hot level when said working fluid is at a maximum operating temperature and above which in said reservoir chamber is defined a gas chamber portion thereof, the improvement comprising: means defining a fill port on said reservoir opening into said reservoir chamber at a location above said maximum hot level of said hydraulic oil, a cover on said reservoir closing said fill port and defining a gas-tight seal between said reservoir and said cover to isolate said gas chamber portion from the atmosphere surrounding said reservoir, means connected to said reservoir for introducing into said gas chamber portion a quantity of gas under pressure to establish an above-atmospheric pressure in variable volume gas chamber portion, and a gas accumulator having an expansible chamber connected to said gas chamber portion, said expansible chamber expanding in response to decreases in the volume of said gas chamber portion resulting from thermal expansion of said hydraulic oil to thereby minimize the increase in gas pressure in said gas chamber portion.