Flow controlling apparatus for power steering, operating fluid

A flow control apparatus for supplying pressurized fluid from an engine-driven pump to a power steering device and for returning an excess part of said pressurized fluid directly to said pump, comprising:

• a housing;
• a bore formed in said housing;
• a supply passage formed in said housing to be opened into said bore for supplying said pressurized fluid from said engine-driven pump;
• a bypass passage formed in said housing to be opened into said bore in spaced relationship with said supply passage for returning an excess part of said pressurized fluid directly to said pump;
• a spool valve slidably received in said bore for controlling communication between said supply passage and said bypass passage;
• first spring means disposed in said bore for urging said spool valve in a direction toward said supply passage;
• a union fixedly secured to one end of said bore and having an inner portion extending inwardly of said bore toward said spool valve;
• restricted passage means formed between said supply passage and said spool valve for causing a pressure differential thereacross as the flow of said pressurized fluid in said supply passage increases;
• a throttle member fixedly inserted in said union and formed with first and second restricted passages;
• a control spool slidably received in said union between said throttle member and said inner portion of said union and formed with a first fluid passage for fluidically communicating with said restricted passage means and said throttle member;
• second spring means interposed in said union between said throttle member and said control spool for urging said control spool in a direction away from said throttle member;
• said control spool being formed with a control stem to close said first restricted passage of said throttle member when said control spool is moved into abutment with said throttle member against said second spring means;
• a delivery port formed in said union downstream of said throttle member and fluidically communicated with said power steering device;
• a second fluid passage formed in said housing for fluidically communicating said first spring means-disposed bore with said delivery port so as to move said spool valve in response to a pressure differential across said throttle member;
• and
• a third fluid passage formed on said inner portion of said union for applying said pressurized fluid in said supply passage to said control spool against said second spring means.