Overdrive Range - Fourth Gear (Converter Clutch Applied)

Overdrive Range - Fourth Gear - Converter Clutch Applied:

OVERDRIVE RANGE - FOURTH GEAR Converter Clutch Applied

At higher vehicle speeds, the Hydra-matic 4L60-E transmission uses an Overdrive gear ratio (Fourth gear) to increase fuel economy and maximize engine performance. When vehicle operating conditions are appropriate, the PCM energizes the 1-2 shift solenoid to shift the transmission into Fourth gear.

1-2 Shift Solenoid: Energized (turned ON) by the PCM, the normally open solenoid closes and blocks signal "A" fluid from exhausting through the solenoid. This creates pressure in the signal "A" fluid circuit.

2-3 Shift Solenoid: De-energized (OFF) as in Third gear, it exhausts actuator feed limit (AFL) fluid through the solenoid.

1-2 Shift Valve: D432 fluid pressure from the 2-3 shift valve and spring force hold the valve in the upshifted position against signal "A" fluid pressure.

2-4 BAND APPLIES

3-4 Shift Valve: Signal "A" fluid pressure moves the valve into the upshifted position against spring force. In this position, the valve routes 3-4 signal fluid into the 4th signal fluid circuit.

3-4 Relay Valve and 4-3 Sequence Valve: 4th signal fluid pressure moves both valves into the upshifted (Fourth gear) position against spring force acting on the 4-3 sequence valve. This causes the following changes:
^ Orificed (#7) 2nd fluid is routed through the 3-4 relay valve and into the servo feed fluid circuit.
^ Servo feed fluid is routed through the 4-3 sequence valve and into the 4th fluid circuit.
^ 3-4 accumulator fluid routed from the 2-3 shuttle valve is blocked by both valves.

2-4 Servo Assembly: 4th fluid is routed through the center of the servo pin and acts on the apply side of the 4th apply piston. 4th fluid pressure moves the 4th apply piston against the apply pin spring force acting on the release side of the 4th apply piston. This action moves the apply pin and applies the 2-4 band to obtain Fourth gear.

2-4 BAND APPLY ACCUMULATION

2-3 Shift Valve Train: The valve train remains in the up- shifted position with AFL fluid pressure acting on the 2-3 shuttle valve. In addition to its operation in Third gear, the 2-3 shift valve directs servo feed fluid into the 3-4 accumulator fluid circuit.

3-4 Accumulator Assembly: 3-4 accumulator fluid pressure moves the 3-4 accumulator piston against spring force and orificed accumulator fluid pressure. This action absorbs initial 4th clutch apply fluid pressure to cushion the 2-4 band apply. Remember that both the 3-4 accumulator and 4th fluid circuits are fed by servo feed fluid. As 3-4 accumulator fluid fills the accumulator, any air in the system will exhaust through orifice #19. The piston movement forces some orificed accumulator fluid out of the 3-4 accumulator assembly.

3-4 Accumulator Checkball (#1): The accumulator fluid forced from the accumulator unseats the #1 checkball and enters the accumulator fluid circuit. This fluid is routed to the accumulator valve. This is shown by the arrow directions in the oil circuit.

Accumulator Valve: Accumulator fluid forced from the 3-4 accumulator is orificed to the end of the accumulator valve. This fluid pressure, in addition to spring force and torque signal fluid pressure, regulates the exhaust of excess accumulator fluid pressure through the middle of the valve. This regulation helps control the 2-4 band apply feel.

3-2 Control Solenoid and 3-2 Control Valve: Similar to Third gear, the PCM operates the solenoid at approximately a 90% duty cycle, AFL fluid fills the 3-2 signal fluid circuit and 3-2 signal fluid pressure holds the 3-2 control valve against spring force.

TORQUE CONVERTER CLUTCH APPLIES

Torque Converter Clutch (TCC) Solenoid: When operating conditions are appropriate, the PCM energizes the normally open TCC solenoid. This closes the solenoid, blocks converter clutch signal fluid from exhausting and creates pressure in the converter clutch signal fluid circuit.

Converter Clutch Apply Valve: Converter clutch signal fluid pressure moves the valve against spring force and into the apply position. In this position, release fluid is open to an exhaust port and converter feed fluid fills the apply fluid circuit. Converter feed fluid also feeds the cooler fluid circuit through orifice #3.

Torque Converter: Release fluid from behind the pressure plate exhausts through the end of the turbine shaft. Apply fluid pressure is routed between the converter hub and stator shaft where it enters the torque converter. This fluid applies the converter clutch against the converter cover and keeps the converter filled with fluid.

TCC Apply Checkball (#9): Release fluid exhausting from the converter seats the #9 checkball, located in the end of the turbine shaft, and is orificed around the ball. Orificing the exhausting release fluid controls the converter clutch apply rate.