Automatic gearbox - Jatco (Torque Converter): Description and operation (page 4 of 4)

Lock-Up Condition

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M44 1624

1 Impeller 2 Turbine 3 Lock-up clutch 4 Lock-up control valve 5 Torque converter pressure 6 Lock-up solenoid

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7 Pilot pressure 8 Fluid cooler 9 Torque converter applied pressure 10 Lubrication 11 Input shaft

The EAT ECU operates the lock-up solenoid, which in turn supplies pilot pressure to the control valve. The control valve moves under the influence of the pilot pressure, blocking the release pressure feed to the lock-up clutch and redirecting it to the other side of the clutch mechanism.

With the release pressure removed, the lock-up clutch moves and engages with the torque converter, moving the lockup mechanism into the locked condition.

Smooth Lock-Up Smooth lock-up occurs as the mechanism moves from the unlock to the locked condition. Torque converter release pressure is lowered gradually preventing a sudden lock-up clutch engagement, reducing lock-up shock.

The lock-up solenoid is a driven duty solenoid operating at 50Hz. The lock-up control valve has a pressure regulation device which reacts to torque converter release pressure and solenoid pilot pressure.

As the solenoid is operated, the pilot pressure is gradually applied to the control valve. This moves the valve, partially exposing the release pressure to a drain port.

The control valve is moved against an opposing spring by the increasing pilot pressure. The release pressure is decayed proportionally in response to the increasing pilot pressure allowing the clutch to smoothly engage with the torque converter.