Abstract: A system for controlling a pump in a hydraulic circuit for an automatic transmission, having a viscosity insensitive fixed orifice and a relatively high resistance laminar orifice connected in series relationship between a vent port and a control pressure supplied to a secondary regulated pressure SRP valve. At relatively low temperature, flow through the laminar orifice is negligible; therefore, the steady-state differential pressure across the fixed orifice is negligible. At relatively higher temperatures, flow through the laminar orifice increases. A pressure divider is established and the feedback differential pressure is reduced in proportion to the hydraulic resistance of the two orifices. Flow to friction elements from a primary pump and auxiliary pump and return of fluid to the inlets of the pumps is controlled through a clutch capacity pressure regulator valve acting in cooperation with the SRP valve.

Abstract: A first pump includes inner and outer intermeshing rotors, the outer rotor formed with external gear teeth. A second pump includes inner and outer meshing rotors, the outer rotor of the second pump having teeth continually engaged with the external teeth of the first pump outer rotor. The inner and outer rotors are formed with mutually intermeshing lobes that define between them pumping chambers through which hydraulic fluid is moved from a suction inlet to a pressurized outlet. A third pumping element includes pumping chambers located in the spaces between the intermeshing involute gear teeth on the outer rotors of the first and second pumps. A passage plate defines suction and pressure passages, which carry hydraulic fluid from a reservoir or sump to outlet ports, through which fluid is supplied to the hydraulic system.