Power steering gear with relief valve on power piston

Claim 1

A vehicular power steering system utilizing pressurized fluid for actuating a hydraulic piston against varying supply pressure and pressure surges generated in response to road shock so long as the pressure does not exceed a predetermined value comprising: an integral power steering gear including a housing, means defining a power cylinder in said housing having first and second ports located respectively at the opposite ends thereof, an axially bored power piston slidably carried in said cylinder and rack teetH carried on said power piston, a cross shaft journaled on said housing for rotating about an axis which extends transversely to the axis of said power cylinder and a sector gear carried on said cross shaft in meshing engagement with said rack teeth, a worm extending in axial alignment into said bore of said piston, cooperating drive means interconnecting said worm and said power piston for rotating said worm in response to axial movement of said power piston, a steering shaft journaled on said housing in axial alignment with said worm, means interconnecting said worm and said steering shaft for rotating said worm in response to rotation of said steering shaft, steering valve means in said housing operably connected to said steering shaft and movable in response to relative rotation of said steering shaft and said cross shaft in excess of a predetermined relative angle of rotation, and means defining an inlet port and an outlet port in said housing; a power fluid pump having a high pressure side and a low pressure side; a fluid supply header connecting said inlet port to said high pressure side of said power fluid pump; a fluid return header connecting said outlet port to said low pressure side of said power fluid pump; first fluid passage means formed in said housing connecting said inlet port to said steering valve means; second fluid passage means formed in said housing connecting said outlet port to said steering valve means; third fluid passage means connecting said steering valve means to said first power cylinder port; fourth fluid passage means connecting said steering valve means to said second power cylinder port; said fluid supply header and said first fluid passage means constituting high pressure circuits and said fluid return header and said second fluid passage means constituting low pressure circuits, said steering valve means being movable between a normal position at which fluid communication between said first and second fluid passage means and said third and fourth fluid passage means is open and first and second operating positions at one of which said first fluid passage means is connected to said third fluid passage means and said second fluid passage means is connected to said fourth fluid passage means, and at the other of which said first fluid passage means is connected to said fourth fluid passage means and said second fluid passage means is connected to said third fluid passage means, said neutral position of said steering valve means obtaining when said predetermined relative angle of rotation between said steering shaft and said cross shaft is not exceeded, said first operating position obtaining when said steering shaft is rotated in one direction and said predetermined relative angle of rotation between said steering shaft and said cross shaft is exceeded and said second operating position obtaining when said predetermined relative angle of rotation between said steering shaft and said cross shaft is exceeded; means defining fifth fluid passage means through said piston for fluid communication between the opposite ends of said cylinder; said fifth fluid passage means including an arcuate peripheral groove in and extending about a portion of said piston in communication with one end of said cylinder; first bore means extending from said groove to the other end of said cylinder; and pressure relief valve means disposed in and normally closing said fifth fluid passage means and arranged so as to be subjected to the fluid pressure between the ends of said power piston and the respective ends of said power cylinder and operable to open in response to said predetermined value of pressure to permit fluid flow between the ends of said power cylinder to relieve excess pressure, said pressure relief valve means including a first valve disposed in said first bore means and normally closing said first bore means and having an axial bore aligNed with said first bore means for communication therethrough; and a second valve disposed in said first bore means in an opposite flow direction to that of said first valve and normally closing said first bore means.