Power steering system

Claim 1

A power steering system comprising: a gear box; an input shaft inserted into said gear box; a rotary valve structure arranged in said gear box and associated through said input shaft with a steering wheel; a power cylinder; said rotary valve structure including a rotary spool and a sleeve arranged around said rotary spool; said rotary valve structure further comprising first and second valve groups arranged so as to control the flow rate of fluid fed to said power cylinder and third and fourth valve groups arranged so as to control the flow rate of fluid returned from said power cylinder; said first, second, third and fourth valve groups each comprising a plurality of valves which are alternatively opened or closed depending upon rotation of the steering wheel; and a variable throttle valve arranged on the downstream side of said third and fourth valve groups such that said input shaft and said variable throttle valve are perpendicular to each other; said variable throttle valve including a valve body having an inlet port and an outlet port; said valve body of said variable throttle valve being connected directly to said gear box such that said inlet port communicates with a return port for said third and fourth valve groups and said outlet port communicates with a return port for said first and second valve groups.