Lock-Up System

Lock-up System
In D4 position (3rd and 4th), and D position (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 PCM optimizes the timing of the lock-up mechanism. When the torque converter clutch solenoid valve (lock-up control solenoid valve) activates, modulator pressure changes to switch lock-up ON and OFF. The lock-up control valve and the lock-up timing valve control the range of lock-up according to A/T clutch pressure control solenoid valves A and B. The torque converter clutch solenoid valve is mounted on the torque converter housing, and A/T clutch pressure control solenoid valves A and B are mounted on the transmission housing. They are controlled by the PCM.

General Operation





1. Operation (clutch on)
With the lock-up clutch on, fluid in the chamber between the torque converter cover and the 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, placing the vehicle in direct drive.





2. Operation (clutch off)
With the lock-up clutch off, fluid flows in the reverse of CLUTCH ON. As a result, the lock-up piston moves away from the vehicle in direct drive.

No Lock-up





The torque converter clutch solenoid valve is turned OFF by the PCM. The lock-up shift valve receives LC pressure (LA) on the left side, and modulator pressure (6) on the right side. The lock-up shift valve is in the right side to uncover the port leading torque converter pressure (92) to the left side of the torque converter. Torque converter pressure (92) becomes torque converter pressure (94), and enters into the left side of the torque converter (to disengage the lock-up clutch). The lock-up clutch is OFF.

NOTE:
- When used, "left" or "right" indicates direction on the hydraulic circuit.
- Hydraulic circuit shows the '98-99 models; the '00-02 models are similar.

Partial Lock-up





As the speed of the vehicle reaches the prescribed value, the torque converter clutch solenoid valve is turned ON by the PCM to release LC pressure (LA) in the left side of the lock-up shift valve. The lock-up shift valve is moved to the left side to switch the port leading torque converter pressure to the left side and right side of the torque converter. Torque converter pressure (92) flows to the right side of the torque converter to engage the lock-up clutch. The PCM also controls A/T clutch pressure control solenoid valves A and B. and LS A or LS B pressure is applied to the lock-up control valve and the lock-up timing valve. The position of the lock-up control valve depends on torque converter pressure and LS A or LS B pressure. When LS A or LS B pressure (58) is lower, torque converter pressure (91) from the lock-up timing valve is lower. The lock-up clutch is engaged partially. LS A or LS B (58) increases, and the lock-up timing valve is moved to the left side to uncover the port leading torque converter pressure to high. The lock-up clutch is then engaged securely. Under this condition, the lock-up clutch is engaged by pressure from the right side of the torque converter; this condition is partial lock-up.

NOTE:
- When used, "left" or "right" indicates direction on the hydraulic circuit.
- Hydraulic circuit shows the '98-99 models; the '00-02 models are similar.

Full Lock-up





When the vehicle speed further increases, the PCM controls A/T clutch pressure control solenoid valves A and B to increase LS A or LS B pressure (58). The LS A or LS B pressure (58) is applied to the lock-up control valve and the lock-up timing valve, and moves them to the left side. Under this condition, torque converter back pressure is released fully, causing the lock-up clutch to be fully engaged.

NOTE:
- When used, "left" or "right" indicates direction on the hydraulic circuit.
- Hydraulic circuit shows the '98-99 models; the '00-02 models are similar.