Acura RL (1996-2004 year). Manual — part 420
In position in 2nd, 3rd and 4th, and position in 3rd, pressurized fluid is drained from the back of the torque converter
through a passage, causing the lock-up piston to be held against the torque converter cover. As this takes place, the main-
shaft rotates at the same speed as the engine crankshaft. Together with hydraulic control, the PCM optimizes the timing of
the lock-up system. Under certain conditions, the lock-up clutch is applied during deceleration in 3rd and 4th gear.
The lock-up system controls the range of lock-up according to torque converter clutch (lock-up control) solenoid valves A
and B, and the throttle valve. When torque converter clutch solenoid valves A and B activate, modulator pressure
changes. Torque converter clutch solenoid valves A and B are mounted on the torque converter housing, and are con-
trolled by the PCM.
NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.
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Description
Lock-up System (cont'd)
No Lock-up
The pressurized fluid regulated by the modulator works on both ends of the lock-up shift valve and on the left side of the
lock-up control valve. Under this condition, the pressures working on both ends of the lock-up shift valve are equal, and
the shift valve is moved to the right side by the tension of the valve spring alone. The fluid from the pump will flow
through the left side of the lock-up clutch to the torque converter; that is, the lock-up clutch is in OFF condition.
NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.
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Partial Lock-up
Torque Converter Clutch (Lock-up Control) Solenoid Valve A: ON Torque Converter Clutch (Lock-up Control) Solenoid
Valve B: OFF
The PCM switches the solenoid valve A on to release the modulator pressure in the left cavity of the lock-up shift valve.
The modulator pressure in the right cavity of the lock-up shift valve overcomes the spring force; thus the lock-up shift
valve is moved to the left side.
The line pressure is then separated into the two passages to the torque converter:
Torque Converter Inner Pressure: enters into right side to engage lock-up clutch
Torque Converter Back Pressure: enters into left side to disengage lock-up clutch
The back pressure (F2) is regulated by the lock-up control valve, whereas the position of the lock-up timing valve is deter-
mined by the throttle B pressure, tension of the valve spring, and pressure regulated by the modulator valve. Also the posi-
tion of the lock-up control valve is determined by the back pressure of the lock-up control valve and torque converter pres-
sure regulated by the check valve. With the torque converter clutch solenoid valve B kept off, the modulator pressure is main-
tained in the left side of the lock-up control valve; in other words, the lock-up control valve is moved slightly to the right side.
This slight movement of the lock-up control valve causes the back pressure to be lowered slightly, resulting in partial lock-up.
NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.
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Lock-up System (cont'd)
Half Lock-up
Torque Converter Clutch (Lock-up Control) Solenoid Valve A: ON Torque Converter Clutch (Lock-up Control) Solenoid
Valve B: ON
The modulator pressure is released by the solenoid valve B, causing the modulator pressure in the left side of the lock-up
control valve to lower.
Also the modulator pressure in the left cavity of the lock-up timing valve is low. However, throttle B pressure is still low at
this time; consequently, the lock-up timing valve is kept on the right side by the spring force.
With the torque converter clutch solenoid valve B turned on, the lock-up control valve is moved somewhat to the left side,
causing the back pressure (F2) to lower. This allows a greater amount of the fluid (F1) to work on the lock-up clutch so as
to engage the clutch. The back pressure (F2) which still exists prevents the clutch from engaging fully.
NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.
Description
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