Lock-Up System

Lock-up System
In the D position (3rd and 4th), and the D3 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 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 the lock-up according to A/T clutch pressure control solenoid valve B. The torque converter clutch solenoid valve is mounted on the torque converter housing, and A/T clutch pressure control solenoid valve B is mounted on the transmission housing with solenoid valve A as an assembly. They are all controlled by the PCM.

Lock-up Clutch ON {Engaging Lock-up Clutch)





Fluid in the camber between the torque converter cover and the lock-up clutch piston is drained off, and fluid entered from the chamber between the pump and stator exerts pressure through the lock-up clutch piston against the torque converter cover. The lock-up clutch piston engages with the torque converter cover (lock-up clutch ON), and the mainshaft rotates at the same speed as the engine.

Lock-up Clutch OFF (Disengaging Lock-up Clutch)





Fluid entered from the chamber between the torque converter cover and the lock-up clutch piston passes through the torque converter and goes out from the chambers between the turbine and the stator, and between the pump and the stator. As a result, the lock-up clutch piston moves away from the torque converter cover, and the lock-up clutch is released (lock-up clutch OFF).

No Lock-up





The torque converter clutch solenoid valve is turned OFF by the PCM. The lock-up shift valve receives modulator (LCA) pressure (6C) on the left side, and stays in the right side to uncover the port leading torque converter pressure (94) to the left side of the torque converter. Torque converter pressure (94) enters into the left side of the torque converter to disengage the lock-up clutch. The lock-up clutch piston keeps away from the torque converter cover; the lock-up clutch is OFF.

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

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. Modulator (LCA) pressure (6C) in the left side of the lock-up shift valve is released, and the lock-up shift valve is moved to the left side to switch the port leading torque converter pressure (91) to the right side of the torque converter. Torque converter pressure (91) flows to the right side of the torque converter to engage the lock-up clutch. The PCM also controls the A/T clutch pressure control solenoid valve B. and linear sol B pressure (BE) is applied to the lock-up control valve and the lock-up timing valve. The positions of the lock-up control valve and lock-up timing valve depend on torque converter pressure and linear sol B pressure. When linear sol B pressure (BE) is low, torque converter pressure (91) from the lock-up shift valve to the right side of the torque converter is low, because torque converter pressure (91) leaks at the lock-up control valve. The lock-up clutch is engaged partially. Linear solenoid B pressure (BE) increases, the lock-up control valve is moved to the left side to cover the port draining torque converter pressure(91),and torque converter pressure (91) to torque converter is increased. The engagement of the lock-up clutch depends on torque converter pressure (91).

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

Full Lock-up





When the vehicle speed further increases, the PCM controls the A/T clutch pressure control solenoid valve B to increase linear solenoid B pressure (BE). Linear solenoid B pressure (BE) is applied to the lock-up control valve and the lock-up timing valve, and moves them to the left side. Torque converter pressure (94) from the left side of the torque converter is drained at the lock-up control valve, and torque converter pressure (91) engages the lock-up clutch securely.

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