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, and the torque converter lock-up is released.
SYSTEM DESCRIPTION
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 ECM optimizes the timing of the lock-up system. Under certain conditions, the lock-up operation is applied during deceleration, in 2nd, 3rd and 4th speed. The lock-up shift valve controls the range of lock-up according to lock-up control solenoid valves A and B. and the 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 ECM. From sensor input signals, the ECM detects whether to turn the lock-up ON or OFF and activates lock-up control solenoid valve A and/or B accordingly. The combination of driving signals to lock-up control solenoid valves A and B is shown in the table below.
NO LOCK-UP
Pressurized fluid regulated by the modulator works on both ends of the lock-up shin valve and on the left side of the lock-up control valve. Under this condition, the pressure on both ends of the lock-up shin valve are equal, and the lock-up shim 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 OFF.
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: Duty operation (ON <-> OFF). The ECM switches the solenoid valve A to ON to release the modulator pressure in the left cavity of the lock-up shin valve. The modulator pressure in the right cavity of the lock-up shim valve overcomes the spring force, thus the lock-up shim valve is moved to the left side. The torque converter pressure is separated into two passages to the torque converter: 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 The 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 governor 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 throttle B pressure,torque converter back pressure and torque converter pressure regulated by the check valve. In low speed range, the throttle B pressure working on the right side of the lock-up control valve is low, causing the valve to be moved to the right side. With the lock-up control solenoid valve B to ON and OFF alternately, the modulator pressure is maintained in the left side 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 (F2) to be lowered slightly, resulting in partial lock-up.
NOTE: When used. "left" or "right,' indicate direction on the hydraulic circuit.
HALF LOCK-UP
Lock-up Control Solenoid Valve A: (ON) Lock-up Control Solenoid Valve B: (ON) The modulator pressure is released by the solenoid valve B. causing the modulator pressure in the left cavity of the lock-up control valve to lower. Also, the modulator pressure in the left cavity of the lock-up timing B valve is low. However, the governor pressure is still low at this time, consequently the lock-up timing B valve is kept on the right side by the spring force. With the lock-up control solenoid valve B turned ON, the lock-up control valve is moved somewhat to the left side, causing the back pressure (F2) to lower. This allows a greater amount of the fluid (F1) to work on the lock-up clutch so as to engage the clutch. The 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, the governor pressure is increased. The lock-up timing B valve overcomes the spring force and moves to the left side. Also this valve closes the port leading to the torque converter check valve. Under this condition, the throttle B pressure working on the right side 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); that is, the lock-up control valve is moved to the left side. As this happens, the torque converter back pressure is released fully, causing 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 ECM switches the solenoid valve B to ON and OFF alternately at high speeds 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.