Logic valving for a transmission control

In a transmission control system having a source of fluid pressure, a plurality of solenoid operated shift valve means which control a plurality of hydraulically actuated friction devices to selectively establish a plurality of forward speed ratios ranging from a lowest ratio to a highest ratio including a second highest speed ratio and a third highest speed ratio by controlling the flow of fluid from said source through said solenoid operated shift valve means, said solenoid operated shift valve means including two normally open valve;

• said control including logic valve means comprising:
• solenoid control means selectively actuatable for establishing a control pressure signal in said logic valve means for signaling the selection of a forward drive request;
• a pair of spool valve means each having a signal chamber which is pressurized in response to actuation of said solenoid control means for urging the spool valve means in one of two directions, spring means for urging the respective spool valve means in the other direction, and differential latching chamber means for urging respective spool valve means in said one direction, said latching chamber means of each spool valve means being in fluid communication with said source through respective ones of the normally open solenoid valves when said solenoid control means is actuated and the respective normally open solenoid valve is unactuated for maintaining said respective spool valves urged against said respective spring means when all said solenoid operated shift valve means become unactuated due to electrical power discontinuance and said source continues to supply fluid to force the transmission to the second highest speed ratio from the highest speed ratio, to the third highest speed ratio from any of the third highest speed ratio and the second highest speed ratio immediately above the third highest speed ratio and to a ratio below the third highest ratio from any of the ratios below the third highest ratio when all of the solenoid valves become unactuated because of electrical power discontinuance and the source is continuing to supply fluid.

In a transmission control system having a source of fluid pressure, a plurality of solenoid operated shift valve means which control a plurality of hydraulically actuated friction device to selectively establish six forward speed ratios including a lowest speed ratio in a transmission by controlling the flow of fluid from said source through said solenoid operated shift valve means, said solenoid operated shift valve means including two normally open valves;

• said control including logic valve means comprising:
• forward solenoid control means selectively actuatable for establishing a control pressure signal in said logic valve means for signaling the selection of a forward drive request;
• a pair of spool valve means each having a signal chamber which is pressurized in response to actuation of said solenoid control means for urging the spool valve means in one of two directions, spring means for urging the respective spool valve means in the other direction, and differential area latching chamber means for urging respective spool valve means in said one direction, one of said spool valve having pressure area means connectible with a friction device for establishing the lowest speed ratio and a reverse ratio for holding the spool valve in the spring urged position when said friction device for establishing the lowest forward ratio is pressurized, said latching chamber means of each spool valve means being in fluid communication with said source through respective ones of the normally open solenoid valves when said solenoid control means is actuated and the respective normally open solenoid valve is unactuated for maintaining said respective spool valves urged against said respective spring means when all said solenoid operated shift valve means become unactuated due to electric power discontinuance and said source continues to supply fluid, to force the transmission to the fifth forward speed ratio from the sixth forward speed ratio, to the four forward speed ratio from any of the fourth and fifth forward speed ratios when all of the solenoid valves become unactuated and the source is continuing to supply fluid.