Lock-Up System

LOCK-UP SYSTEM
Lock-up Clutch





1. Operation (Clutch ON)
With the lock-up clutch ON, the fluid in the chamber between the torque converter cover and lock-up piston is discharged, and the converter fluid exerts pressure through the piston against the converter cover. As a result, the converter turbine is locked on the converter cover firmly. The effect is to bypass the converter, thereby placing the vehicle in direct drive.





2. Operation (Clutch OFF)
With the lock-up clutch OFF, the fluid flows in the reverse of "clutch on." As a result, the lock-up piston is moved away from the converter cover; that is, the torque converter lock-up is released.





In [D4] position in 2nd, 3rd and 4th, and [D3] position in 3rd, pressurized fluid is drained from the back of the torque converter through a fluid passage, causing the lock-up piston to be-held against the torque converter cover. As this takes place, the mainshaft rotates at the same speed as the engine crankshaft. Together with hydraulic control, the TCM optimized 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 lock-up control solenoid valves A and B, and the throttle valve B. When lock-up control solenoid valves A and B activate, modulator pressure changes. Lock-up control solenoid valves A and B are mounted on the torque converter housing, and are controlled by the TCM.


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, the shift valve is moved to the right side by the tension of the valve spring alone. The fluid from the ATF 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.


Partial Lock-up



Lock-up Control Solenoid Valve A: ON Lock-up Control Solenoid Valve B: OFF
The TCM switches solenoid valve A ON to release modulator pressure in the left cavity of the lock-up shift valve. Modulator pressure in the right cavity of the lock-up shift valve overcomes the spring force, and the lock-up shift valve is moved to the left side.
Modulator pressure is separated into the two passages:
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.
Back pressure (F2) is regulated by the lock-up control valve whereas the position of the lock-up timing B valve is determined by the throttle B pressure, tension of the valve spring, and pressure regulated by the modulator. Also the position of the lock-up control valve is determined by the back pressure of the lock-up control valve and torque converter pressure regulated by the check valve. With lock-up control solenoid valve B kept OFF, modulator pressure is maintained in the left end of the lock-up control valve; in other words, the lock-up control valve is moved slightly to the left 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.


Half Lock-up



Lock-up Control Solenoid Valve A: ON Lock-up Control Solenoid Valve B: ON
Modulator pressure is released by solenoid valve B, causing modulator pressure in the left cavity of the lock-up control valve to lower.
Also modulator pressure in the left cavity of lock-up timing B valve is low. However, throttle B pressure is still low so lock up timing B valve is kept on the right side by spring force.
With lock-up control solenoid valve B turned ON, the lock-up control valve is moved somewhat to the left side, causing back pressure (F2) to lower. This allows a greater amount of fluid (F1) to work on the lock-up clutch to engage the clutch.
Back pressure (F2) which still exists, prevents the clutch from engaging fully.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.


Full Lock-up



Lock-up Control Solenoid Valve A: ON Lock-up Control Solenoid Valve B:ON
When the vehicle speed further increases, throttle B pressure is increased in accordance with the throttle opening.
The lock-up timing B valve overcomes spring force and moves to the left side. Also, this valve closes the port leading to the torque converter check valve.
Under this condition, throttle B pressure working on the right end of the lock-up control valve becomes greater than that on the left end (modulator pressure in the left end has already been released by the solenoid valve B); the lock-up control valve is moved to the left. As this happens, torque converter back pressure is fully released, causing the lock-up clutch to be fully engaged.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.


Deceleration Lock-up



Lock-up Control Solenoid Valve A: ON Lock-up Control Solenoid Valve B: Duty Operation (ON <-> OFF)
The TCM switches solenoid valve B ON and OFF rapidly under certain conditions. The slight lock-up and half lock-up regions are maintained so as to lock the torque converter properly.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.