Hydraulic control system for automatic transmission

Claim 1

In an automatic transmission: a plurality of fluid operated friction units which are selectively made operative and inoperative to establish, in a forward drive range, a plurality of forward speed ratios including a highest speed ratio and other forward speed ratios, said plurality of fluid operated friction units including a fluid operated clutch which is to be engaged when the transmission downshifts from the highest speed ratio to any one of the other forward speed ratios and when the transmission shifts from a neutral position to the forward drive range; a source of fluid pressure; means, including a fluid conduit communicating with said fluid operated clutch, for supplying the fluid pressure from said source of fluid pressure to said fluid operated clutch through said fluid conduit when any one of the other forward speed ratios is established; a pressure accumulator including a bore, a fluid operated piston movably disposed in said bore to form within said bore a first chamber on one side of said piston and a second chamber on an opposite side of said piston, and a spring disposed in said second chamber biasing said piston in a first direction, said first chamber communicating with said source of fluid pressure, said second chamber communicating with said fluid conduit, said piston being urged to move by said spring when said second chamber is supplied with the fluid pressure from said fluid conduit with said first chamber being supplied with the fluid pressure from said source of fluid pressure when said fluid operated clutch is to be engaged when the transmission downshifts from the highest speed ratio to any one of the other forward speed ratios or when the transmission shifts from the neutral position to the forward drive range in order to retard a rise in fluid pressure supplied to said fluid operated clutch through said fluid conduit.