Transmission control for a transmission having one drive establishing device for two independent drive functions

Claim 1

A hydraulic control for a throttle controlled engine driven transmission having a fluid operated drive establishing device which is selectively engageable for two distinct drive ratios at different engagement pressures, said control comprising; a source of fluid pressure; control valve means for controlling the engagement of said drive establishing means including a valve bore, a valve spool slidably disposed in said bore, first pressure responsive area means formed by said bore and spool, second pressure responsive area means formed by said bore and spool, passage means interconnecting said second pressure responsive area means and said drive establishing means; and manual valve means for selecting said drive ratios and including a movable member, first control passage means in fluid communication with said first pressure responsive area means for directing fluid pressure from said source to said first pressure responsive area means when one of said drive ratios is selected to move said valve spool to provide fluid communication between said first pressure responsive area means and said passage means to pressurize both pressure responsive areas to engage said drive establishing device with full source pressure, and second control passage means for directing fluid pressure from said source to said passage means when the other of said drive ratios is selected and the pressure in said passage means acting on said second pressure responsive area means to move said valve spool to discontinue fluid communication between said second control passage means and said passage means at a predetermined pressure level, less than source pressure, to engage said drive establishing device at the predetermined pressure level.