Overdrive Range - 4-3 Downshift

Overdrive Range - 4-3 Downshift:

OVERDRIVE RANGE 4-3 DOWNSHIFT

When the transaxle is operating in Fourth gear, a 4-3 downshift will occur if there is a significant change (increase) in the throttle position or if the load on the engine is increased. When the 4-3 downshift occurs, the torque converter clutch will release prior to the shift occurring which results in the following changes in the hydraulic system:

LINE PRESSURE INCREASES

Pressure Control Solenoid: The change in throttle position (increase in percentage of travel) signals the PCM to increase the OFF cycle time of the solenoid. When this occurs, higher filtered actuator feed pressure passes through the transaxle pressure control solenoid into the torque signal fluid passage.

Pressure Regulator Valve: Torque signal fluid acting on the end of the valve causes the valve to move against orificed line pressure at the other end of the valve. This movement of the valve increases line pressure in the hydraulic circuits.

Actuator Feed Limit Valve: Increased line pressure passes through the valve and enters the actuator feed circuit. Actuator feed fluid is routed through the force motor feed filter and then into the filtered actuator feed circuit. Filtered actuator feed is then sent to the pressure control solenoid.

TORQUE CONVERTER CLUTCH RELEASES

Converter Clutch Control Solenoid: As the throttle position changes, the throttle position sensor provides input to the PCM indicating throttle angle. The PCM then lowers the ON / OFF cycle time then de-energizes the solenoid thereby letting the filtered 3rd clutch fluid exhaust through the solenoid. With filtered 3rd clutch fluid exhausting, the converter clutch control valve moves into the released position.

Converter Clutch Control Valve: When moved by spring force to the released position, it directs Torque Converter Clutch (TCC) feed limit fluid into the converter release circuit. Converter release fluid is then routed to the torque converter pressure plate and disengages the torque converter clutch. Converter apply fluid from the torque converter clutch pressure plate is then routed back through its circuit to the converter clutch control valve. Converter apply fluid passes through the valve and enters the cooler circuit.

4TH BAND RELEASES

Solenoid "A": De-energizes, allowing solenoid "A" fluid pressure (acting on the end of the 3-4 shift valve) to exhaust through the solenoid. With low fluid pressure in the solenoid "A" fluid circuit, the 3-4 shift valve is forced to move from spring force acting on the opposite end of the valve.

4th Servo Assembly: Spring force actuates the 4th servo piston and returns it to its band released position. This movement forces 4th band fluid from the other side of the piston back through its circuit to the 1-2 shift valve.

1-2 Shift Valve: Held in the upshifted position by spring force and solenoid "B" pressure 4th band fluid is routed back through the valve and into the 4th band feed circuit. 4th band feed is then routed to the 3-4 shift valve.

3-4 Shift Valve: Held in the downshifted position by spring force, 4th band fluid from the 1-2 shift valve is routed through the valve into the orificed D21Y fluid passage. Orificed D21Y fluid is then routed to the 2-3 shift valve where it exhausts.