Abstract: An electrical solenoid operates a three-way valve having a vent port, a port connected to a source of high pressure hydraulic fluid and a port connection to a pilot valve. A check valve supplied from a source of low pressure hydraulic fluid is connected to the cylinder of a clutch or servo of an automatic transmission when a pilot valve opens this communication upon energizing the solenoid coil. The clutch cylinder is depressurized through the pilot valve to the vent port of the solenoid-operated valve.

Abstract: A normally closed line pressure regulator valve has an orifice that is opened and closed as the coil of the solenoid is energized and deenergized. When the valve is opened, the pump outlet is opened to a vent port. A line pressure relief valve in parallel with the solenoid valve opens at a predetermined pressure when the solenoid valve is closed and establishes a maximum line pressure. Minimum line pressure is determined by the pressure drops across orifices located between the outlet of the pump and the vent port. Line pressure is regulated between the maximum and minimum values by energizing and deenergizing the solenoid coil.

Abstract: A control system for operating the clutch and brake elements of a multiple speed ratio transmission includes a manual valve that opens line pressure to a transfer valve, which in its first state pressurizes a feed line through which any of the clutches and servos may be selectively pressurized. In its second state, the transfer valve pressurizes the clutches whose engagement that produces a predetermined speed ratio. The detector valve moves the transfer valve to the second state if the combination of pressurized clutches and servos is other than the combination that produces a drive ratio in normal operation.