Lock-Up System

Lock-up System





In D4 position (3rd and 4th), and D2 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 the hydraulic control, the PCM 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 the linear solenoid. 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 outside of the torque converter housing, and the linear solenoid is mounted on the transmission housing. They are controlled by the PCM.
The table shows the lock-up conditions for lock-up control solenoid valves and linear solenoid pressure,

Lock-up Clutch





1. Operation (clutch on)
With the lock-up clutch on, the 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. This bypasses the converter, 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 moves away from the converter cover, and the torque converter lock-up is released.

No Lock-up





- Lock-up Control Solenoid Valve A: OFF
- Lock-up Control Solenoid Valve B: OFF
- Linear Solenoid Pressure: High
The pressurized fluid regulated by the modulator works on both ends of the lock-up shift valve. Under this condition, the pressures working on both ends of the lock-up shift valve are equal, and the lock-up shift valve is moved to the right side by the tension of the valve spring. Fluid from the ATF pump will flow through the left side of the lock-up clutch to the torque converter; the lock-up clutch is OFF.

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

Half Lock-up





- Lock-up Control Solenoid Valve A: ON
- Lock-up Control Solenoid Valve B: Duty Operation OFF <--> ON
- Linear Solenoid Pressure: Low
The PCM 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.
Line pressure is then separated into the two passages to the torque converter; torque converter inner pressure enters into right side to engage the lock-up clutch, and torque converter back pressure enters into left side to disengage the lock-up clutch.
Back pressure (F2) is regulated by the lock-up control valve, whereas the position of the lock-up timing valve is determined by linear solenoid pressure and tension of the valve spring. Also the position of the lock-up control valve is determined by the back pressure of the lock-up control valve, torque converter pressure (regulated by the torque converter check valve), and modulator pressure (determined by the lock-up control solenoid valve B). The PCM switches lock-up control solenoid valve B on and off rapidly (duty operation), under certain conditions, to regulate back pressure (F2) and lock the torque converter.

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

Full Lock-up





- Lock-up Control Solenoid Valve A: ON
- Lock-up Control Solenoid Valve B: ON
- Linear Solenoid Pressure: High
When the vehicle speed further increases, linear solenoid pressure increases to high in accordance with the linear solenoid which is controlled by the PCM.
The lock-up timing valve overcomes the spring force and moves to the left side. Also, this valve closes the fluid port leading to the left side of the lock-up control valve.
Under this condition, modulator pressure in the left side of the lock-up control valve had already been released by the lock-up control solenoid valve B; the lock-up control valve is moved to the left side. As this takes place, torque converter back pressure is released fully, causing the lock-up clutch to be engaged fully.

NOTE: When used, "left" and "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 OFF <--> ON
- Linear Solenoid Pressure: Low
The PCM switches solenoid valve B on and off rapidly under certain conditions. The slight lock-up and half lock-up regions are maintained to lock the torque converter properly.

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