HYDRAULISK TRYKFORSYNINGSANLAEG TIL ET SAMMENSAT DREVS STYREKREDSLAEB

A fixed displacement pump is connected to deliver operating fluid to a torque converter and to a transmission shift control valve that is operable for selectively coupling working fluid to one or more hydraulically operable shift elements of a transmission. A converter pressure regulator valve maintains the pressure of the working fluid at the converter at a predetermined minimum and this pressure prevails generally throughout the system. When the transmission shift control valve is actuated so as to couple one or more shift elements to the pump which require more than the predetermined minimum pressure for acceptable operation, a pilot flow occurs through the shift control valve to actuate a boost valve which activates a main transmission pressure regulating valve so as to cause the pressure of the fluid passing to the one or more shift elements to rise to a level for effecting acceptable operation thereof.