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 drained off, and the converter fluid exerts pressure through the piston against the torque converter cover. As a result, the converter turbine is locked to the converter cover. The effect is to bypass the converter, thereby placing the car 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 moves away from the converter cover, and 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 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 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 lock-up control solenoid valves A and B. and throttle valve. 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 modulator pressure flows to both side of the lock-up shift valve. The modulator pressure on both ends of the lock-up shift are equal and the lock-up shift valve is in the left side by the valve spring tension. The torque converter pressure (92) changes the torque converter pressure (94) at the lock-up shift valve. The torque converter pressure (94) flows through the left side of the lock-up clutch to the torque converter. The lock-up clutch is not engaged.
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
As the speed of the vehicle reaches the prescribed value, the lock-up control solenoid valve A is turned ON by the TCM. The lock-up control solenoid valve B remains OFF. The modulator pressure on the right end of the lock-up shift valve is released, but the led end pressure is not released. The lock-up shift valve is moved to the right side by the modulator pressure on the left end of the lock-up shift valve. The movement of this valve switches the port leading the torque converter pressure (92) to the torque converter. The torque converter pressure is separated to the two passages:
a. Torque Converter Inner Pressure: enters into the right side of the torque converter to engage the lock-up clutch
b. Torque Converter Back Pressure: enters into the led side of the torque converter to disengage the lock-up clutch
The back pressure (F2) of the torque converter is regulated by the lock-up control valve, and the position of the lock-up control valve is determined by the back pressure and the pressure from the lock-up timing valve. The position of the lockup timing valve is determined by the modulator pressure, throttle B pressure and the valve spring. The torque converter inner pressure slightly engages the lock-up clutch since the back pressure is not released by the position of the lock-up control valve.
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
As the speed of the vehicle reaches the prescribed value, the lock-up control solenoid valve B is turned ON by the TCM. The lock-up control solenoid valve A remains ON. The modulator pressure on the left side of the lock-up control valve and lock-up shift valve is released. The lock-up control valve is moved somewhat to the left side and the back pressure of the torque converter leaks away from the lock-up control valve. The back pressure under this condition is lower than the partial lock-up condition. The inner pressure works on the lock-up clutch so as to engage the clutch. The back pressure 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 speed of the vehicle further increases, the throttle B pressure is increased in accordance with the throttle opening. The throttle B pressure flows to the right side of the lock-up timing valve. The lock-up timing valve is moved to the left side overcoming the valve spring tension. The torque converter pressure on the left end of the lock-up control valve is released by the movement of the lock-up timing valve and the lock-up control valve is moved to the left side. As this happens, the back pressure of the torque converter is released fully, and the inner pressure of the torque converter works on the lock-up clutch to be engaged fully.
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 the lock-up control solenoid valve B ON and OFF rapidly under certain conditions. The partial lock-up condition and half lock-up condition are maintained so as to operate the lock-up clutch properly.