signal pressure forces the gain valve away from the PC valve, resulting in signal pressure acting directly on the PC valve. In reverse range, the reverse signal pressure is exhausted, which allows the gain valve to contact the pressure control valve. Signal pressure acts on top of the gain valve and the force is transmitted to the pressure control valve. Because the gain valve diameter is larger than the diameter of the second stage pressure control valve, a higher clutch pressure for a given signal pressure is achieved. Accumulators help regulate solenoid signal pressure. The pressure control valve bores in the valve body have cast slots in the area of main pressure and exhaust, which increases the stability of the pressure control valves and allows the clutch pressure to be more accurately controlled.
5–3. A.
HYDRAULIC CONTROL SYSTEM CIRCUITS
Hydraulic Circuit—Neutral (Foldout 4) • In neutral, PCS1 is in its normally closed state (de-energized), PCS2 is in its normally open state (de-energized), SS1, SS2, and SS3 are energized, and pressure control solenoid TCC remains de-energized. • SS1, SS2, and SS3 supply control main pressure to the top of SV1, SV2, and SV3, stroking the valves against spring force. • With SV1 stroked, control main pressure is directed through SV1 to PS1, turning the switch on. With SV2 stroked, the exhaust path is blocked for the control main pressure being supplied through an orifice to PS2, and the pressure raises to control main and PS2 turns on. With SV3 stroked, the exhaust path is blocked for the control main pressure being supplied through an orifice to PS3, and the pressure raises to control main and PS3 turns on. With PS1, PS2, and PS3 ON, feedback is provided to the TCM that SV1, SV2, and SV3 are stroked. • Normally closed PCS1 blocks the exhaust of the PCS1 signal pressure, raising the signal
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Copyright © 2005 General Motors Corp.
pressure. PCS1 signal pressure strokes PCV1, raising the PCS1 pressure which is directed to SV2. In its stroked position, SV2 routes fluid to C5 clutch, applying the clutch. All other clutches are exhausted. • With only one clutch applied, the transmission is in neutral. • If electrical power is interrupted while neutral is selected, SS1, SS2, and SS3 are deenergized and SV1 de-strokes. Due to valve timing, when power is lost, SV1 strokes faster than SV3. When SV1 de-strokes, control main pressure is fed through SV1 to the top of SV3, keeping the valve stroked. Normally closed PCS1 continues to block the exhaust of the solenoid signal pressure (solenoid signal remains control main). The solenoid signal pressure on top of PCV1 produces maximum pressure, which is routed to SV2. SV2 stays stroked due to the “latching” effect of C5 clutch pressure acting on two different diameter lands. In its stroked position, pressure continues to be routed to C5 clutch, keeping the clutch applied. Since only one clutch is applied, the transmission remains in neutral. • If electrical power is interrupted with the transmission in neutral and the Manual Selector Valve is moved to a forward range or reverse, the transmission stays in neutral because SV3 stays de-stroked and main pressure is blocked from reaching the Manual Selector Valve. • If the engine is shutdown and restarted with the electrical power interrupted to the TCM, SV1, SV2, and SV3 remain de-stroked. Normally closed PCS1 blocks the exhaust of the PCS1 signal pressure (signal pressure becomes control main). The solenoid signal pressure on top of PCV1 produces maximum pressure, which is routed to SV2. In its destroked position, SV2 routes fluid to C3 clutch. All other clutches are exhausted, so the transmission remains in neutral. When SV3 is de-stroked, main pressure is routed through SV3 to the Manual Selector Valve. If a forward range is selected, the Manual Selector
1000 and 2000 Product Families Principles of Operation—May 2005
