Clutch Priority Valve

The clutch priority valve prevents two gears from being applied at the same time. Its main function is to provide a back-up system in the event of an electrical failure. If a major electrical failure occurs, the PCM will shut down the electrical system and the clutch priority valve and manual valve will provide reverse, and manual 4th.

During normal operation in 2nd, 3rd, and 4th, the clutch priority and 3rd clutch exhaust valves are held to the plug end of the 3rd exhaust valve by spring and line pressure. This position allows for normal operation of clutches by the actuators.

2nd Gear Stuck On: If the 2nd actuator electrical circuit fails "open," causing 2nd clutch to stay applied, the result will be a 2nd gear start. When a 2nd to 3rd shift is made, the combined pressure of 2nd and 3rd apply will act on the priority valve. The valve will move against the spring and line pressure. 2nd apply pressure will be blocked off, and 2nd clutch will be exhausted. When the transaxle shifts to 4th, the 3rd clutch pressure is exhausted at the 3rd actuator and 2nd will remain exhausted as 4th clutch pressure is applied to the end of the 3rd clutch exhaust valve.

3rd Gear Stuck On: If the 3rd actuator electrical circuit fails "open," causing 3rd clutch to stay applied, the result will be a 3rd gear start. When 2nd gear is attempted, 2nd clutch will be exhausted as 2nd and 3rd apply pressures are applied to the clutch priority valve at the same time.

When vehicle speed reaches the point for a shift to 4th, 4th apply pressure is applied to the 3rd clutch exhaust valve which will cause it to move against line pressure toward the clutch priority valve. 3rd apply pressure is blocked and 3rd clutch is exhausted.

TCC Disable: Any time the priority valve moves toward the plunger and a clutch is exhausted, TCC is disabled. Converter feed (TCC apply) oil is valved to TCC disable causing equal pressure on both sides of the torque converter clutch which results in clutch release.

Hydraulic Back-up: During major electrical system failures the PCM will shut down, opening all actuators electrically (On hydraulically). During system failures back-up is provided by the manual valve supplying 2nd apply oil in D2 and 3rd/4th oil in D3 and D4. When a manual D2 to D3/D4 shift is made the 3rd clutch exhaust and the clutch priority valves are moved toward the plunger by 4th clutch pressure. As the valves are moved 2nd and 3rd apply pressures are blocked and 2nd and 3rd clutches are exhausted.

At the same time that line pressure begins to act against spring pressure, line pressure control from the line actuator is applied to the line pressure control plunger to increase force on the regulator valve in the same direction as the spring. Line pressure is increased as pressure to the pressure control plunger is increased by the line actuator.