Hydraulic control system

Claim 1

In a control system for actuating a pair of dependent hydraulic clutches, said clutches comprising a first clutch piston, means defining a first pressure chamber behind said first clutch piston, a second clutch piston, means defining a second pressure chamber behind said second clutch piston, and means connecting said first and second clutch pistons whereby both clutch pistons move in response to pressurization of either of said first and second pressure chambers; a source of pressurized hydraulic fluid; a shift valve operable to selectively connect said source with said first and second pressure chambers, an accumulator valve assembly operable to control the flow of pressurized hydraulic fluid from said shift valve to said first and second pressure chambers; and conduit means connecting said source to said shift valve, said shift valve to said accumulator valve and said accumulator valve to said first and second chambers; the improvement wherein said accumulator valve assembly comprises a valve body; a first accumulator piston received within said valve body for controlling fluid flow to said first pressure chamber; a second accumulator piston received within said valve body for controlling fluid flow to said second pressure chamber, said first and second accumulator pistons being disposed in back-to-back relationship within a cylindrical bore formed in said valve body; means defining first and second inlet ports formed through said valve body into said cylindrical bore; means defining first and second outlet ports formed through said valve body into said cylindrical bore; means formed on said first accumulator piston for connecting said first inlet and outlet ports when said first accumulator piston is in a first position, for blocking flow between said first inlet and outlet ports when said first accumulator piston is in a second position, and for reconnecting said first and second inlet and outlet ports when said first accumulator piston is in a third position; means formed on said second accumulator piston for connecting said second inlet and outlet ports when said said accumulator piston is in a second position, for blocking flow between said second inlet and outlet ports when said second accumulator piston is in a second position, and for reconnecting said second inlet and outlet ports when said second accumulator piston is in a third position; and a first spring received between said first and second accumulator pistons to bias said pistons apart in said bore; said system including first and second inlet conduit means connecting said shift valve with said first and second inlet ports respectively, first outlet conduit means connecting said first outlet port with said first clutch pressure chamber, and second outlet conduit means connecting said second outlet port with said second clutch pressure chamber.