Fluid pressure modulating apparatus for a fluidically actuated frictional engaging apparatus in a vehicle transmission

Claim 1

A fluid pressure supplying apparatus for a fluidically actuated frictional engaging means adapted for use in a vehicle transmission, comprising: a fluid pressure source; first conduit means for fluidically communicating said fluid pressure source with said frictional engaging means; regulator valve means disposed within said first conduit means for regulating the fluid pressure within said first conduit means to a predetermined line pressure; manual valve means interposed in said first conduit means between said regulator valve means and said frictional engagement means for selecting forward or reverse drive; and modulator valve means interposed in said first conduit means between said manual valve means and said frictional engaging means for supplying a high fluid pressure at the outlet of said modulator valve means less than said line pressure to said frictional engaging means until frictional engagement is initiated, for reducing said high pressure at the outlet of said modulator valve means to a pressure lower than said high pressure during frictional engagement, and for increasing the fluid pressure at the outlet of said modulator valve means to said frictional engaging means after said frictional engagement means is fully engaged, said modulator means comprises a first valve body having a longitudinal bore and a plurality of ports communicating therewith including an inlet port and an outlet port connected to said first conduit means and a drain port, a valve slidably diposed within said bore and provided with first and second lands for controlling communication between said inlet port and said outlet port and said drain port, a first accumulator piston slidably disposed within said bore coaxial with said valve for operative engagement with said valve, spring means urging said valve and said first accumulator piston in opposite directions, a second accumulator piston slidably disposed in said bore coaxial with said valve on the side opposite said first piston, additional spring means urging said second piston toward said valve, first restricted conduit means connecting said inlet port with said bore at the side of said first piston away from said valve and second restricted conduit means connecting said inlet port with said bore intermediate said second piston and said valve.