Hydraulic control system for automatic transmissions

Claim 1

A hydraulic control system for an automatic transmission having an inhibitor valve, said inhibitor valve comprising a change-over valve having a first set position and a second set position and functioning to supply and discharge a hydraulic pressure to and from a hydraulic servomehcanism for a friction engaging element through its movement between said first and second set positions; a means for urging said change-over valve to said first set position; and a plunger having a first set position and a second set position and functioning to bring said change-over valve into said second set position when the plunger is urged to said second set position; said inhibitor valve functioning to perform the supply and discharge of the hydraulic pressure to and from the hydraulic servomechanism in accordance with a first hydraulic signal and a second hydraulic signal through a first hydraulic signal generating means which produces said first hydraulic signal for urging said change-over valve to said second set position and urging said plunger to said first set position; a second hydraulic generating means for producing said second hydraulic signal for urging said plunger to said second position; and a means for delaying a discharge of said second hydraulic signal; said first hydraulic signal generating means comprising an electronic controller receiving vehicular running conditions such as a vehicle speed and a throttle opening, said electronic controller evaluating the vehicular running conditions and generating a signal corresponding to the evaluation, a solenoid valve energized and deenergized in accordance with the output signal of said electronic controller, and an orifice formed in a first hydraulic signal generating oil passage in which said solenoid valve is provided.