Valve system in power steering systems

A valve system in a power steering system comprising:

• a pump body having a valve bore, an inlet port, a by-pass port and an outlet port;
• a spool valve slidably carried in said bore and being movable in response to a pressure differential between said inlet port and said outlet port so as to by-pass an excess flow from said inlet port to said by-pass port;
• a recess formed in said spool valve;
• an orifice located in one end of said pump body through which a working liquid is communicated from said inlet port to said outlet port;
• a control rod slidably carried in said recess and having a metering portion at one end thereof which extends through said orifice so as to form a variable orifice in cooperation with said orifice;
• said metering portion being formed with a small diameter portion normally located at said orifice, a large diameter portion normally located in said outlet port and a tapered portion connected therebetween, said large diameter portion being so formed as to reduce the volume of said working liquid passing through said orifice when said control rod is moved inwardly of said recess;
• a spring inserted in said recess for urging said control rod in a direction towards said orifice;
• said control rod being movable relative to said spool valve so as to maintain the relative position of said control rod to said orifice during the movement of said spool valve when a working pressure in the power steering system exceeds a predetermined value.