Continuously variable transmission down shift control

Claim 1

A continuously variable transmission including a primary pulley and a secondary pulley having an endless transmission member of trapezoidal cross section extending around the pair of pulleys, each pulley including an axially fixed and an axially movable conical disc sheave arranged for gripping opposite edges of said transmission member, each pulley having a fluid actuated expansion chamber device urging the pulley sheaves into gripping engagement with the edges of said endless transmission member, the primary expansion chamber device connected to said primary pulley having a greater effective piston area than the corresponding area of the secondary expansion chamber device connected to said secondary pulley, and a fluid circuit connected to said expansion chamber devices including a source of fluid pressure and a system pressure regulator valve, said fluid circuit including system conduit means communicating regulated system pressure to the secondary expansion chamber device, and a ratio control pressure regulator valve connected between said system conduit and said primary expansion chamber device, wherein the improvement comprises a ratio relief valve connected in parallel circuit bridging said ratio control regulator valve, said ratio relief valve including a movable shuttle member having a land arranged for limiting flow through an exhaust port, said shuttle having a first face communicating with said primary expansion chamber device and a second face opposed to said first face communicating with said secondary expansion chamber device, said second face having a smaller area than said first face, said shuttle member including an annular face opposed to said first face, and a one-way check valve disposed between said annular face and said first face.