Regulator valve for hydraulic control system including variable displacement pump

Claim 1

In a hydraulic control system for an automotive automatic transmission, an automatic transmission actuated by hydraulic fluid; a variable capacity pump for supplying hydraulic fluid under pressure for actuating the automatic transmission, said pump having a control arrangement including a control chamber which varies the capacity of said pump in response to the pressure prevailing therein; a pressure regulator valve for regulating the output of said pump by draining off some of the fluid discharged by said pump and developing a control pressure, said regulator valve including a bore formed with: a first port which receives the output of said pump, a second port which fluidly communicates with said control chamber, and a drain port, said regulator valve further including a spool which is reciprocatively disposed in said bore and which is formed with first and second lands, said first land defining a first variable orifice between said first and second ports and said second land defining a second variable orifice between said second and drain ports; and a fixed flow restriction within said bore, for restricting fluid communication between said first and second ports and said second and drain ports, said fixed flow restriction being defined between the wall of said bore and a first portion of said spool which extends between said first and second lands, said portion having a diameter which is selected with respect to the diameter of that portion of the bore in which it is disposed so as to define a gap having a maximum width of 1.5 mm.