Shift device of hydraulic control system for automatic transmission

Claim 1

A hydraulic control system for an automatic transmission for a motor vehicle having an internal combustion engine with a throttle valve, the automatic transmission including at least one forward drive gear ratio lower than at least one other forward drive gear ratio, the transmission including a plurality of friction elements including a friction element for contributing to shifting between the one forward drive gear ratio and the one other forward drive gear ratio, the hydraulic control system comprising: a first shift valve having a housing with a wall portion defining a valve bore; a second shift valve having a housing with a wall portion defining a valve bore; line pressure generating means for delivering a line pressure to said first shift valve; first signal pressure generating means for delivering a first signal pressure to said first and second shift valves; second signal pressure generating means for delivering a second signal pressure to said first and second shift valves; said first shift valve including a line pressure inlet port, a line pressure outlet port, a first signal pressure port and a second signal pressure port receiving said second signal pressure, said line pressure inlet and outlet ports and said first signal pressure and second signal pressure ports being disposed in said wall portion of said first shift valve; said line pressure inlet and outlet ports being selectively communicating with each other; said second shift valve including a signal pressure inlet port receiving said second signal pressure, and a signal pressure outlet prior communicating with said first signal pressure port of said first shift valve, said signal pressure inlet and signal pressure outlet ports being disposed in said wall portion of said second shift valve; said signal pressure inlet and outlet ports of said second shift valve selectively communicating with each other; said first shift valve including a valve element movable within said valve bore of said first shift valve between a downshift position and an upshift position; said valve element of said first shift valve including means for effecting communication between said line pressure inlet and outlet ports when said valve element of said first shift valve is in the upshift position to, in turn, effect communication between said line pressure generating means and the friction element to establish the one forward drive gear ratio, said valve element of said first shift valve also including means for blocking communication between said line pressure inlet and outlet ports when said valve element is in the downshift position to, in turn, block communication between said line pressure generating means and the friction element; said valve element of said first shift valve including a first pressure acting area exposed to pressure from said first signal pressure port of said first shift valve when said valve element of said first shift valve is in the downshift position, a second pressure acting area exposed to second signal pressure from said second signal pressure port of said first shift valve when said valve element of said first shift valve is in the downshift position, and a third pressure acting area exposed to pressure from said first signal pressure port of said first shift valve when said valve element of said first shift valve is in the upshift position, said valve element of said first shift valve having an end pressure acting area exposed to said first signal pressure from said first signal pressure generating means when said valve element of said first shift valve is in any one of the downshift and upshift positions, said second shift valve including a valve element movable in said valve bore of said second shift valve between first and second positions; said valve element of said second shift valve including means for effecting communication between said signal pressure inlet and signal pressure outlet ports of said second shift valve when said valve element of said second shift valve is in the first position to, in turn, effect communication between said second signal pressure generating means and said first signal pressure port of said first shift valve, said valve element of said second shift valve further including means for blocking communication between said signal pressure inlet and signal pressure outlet ports of said second shift valve when said valve element of said second shift valve is in the second position to, in turn, block communication between said second signal pressure generating means and said first signal pressure port of said first shift valve; said valve element of said second shift valve further including a first pressure acting area exposed to second signal pressure from said signal pressure inlet port of said second shift valve when said valve element of said second shift valve is in the first position and a second pressure acting area exposed to second signal pressure from said signal pressure inlet port when said valve element of said second shift valve is in the second position, said valve element of said second shift valve having an end pressure acting area exposed to said first signal pressure from said first signal pressure generating means.