The Engine & ECT ECU has programmed in its memory a lock-up clutch operation pattern for each driving mode. Based on this lock-up pattern, the ECU turns the solenoid valve on or off in accordance with the vehicle speed signals and the throttle opening signals. The ECU will turn on solenoid valve to operate the lockup system if the following three conditions exist simultaneously.
1. The vehicle is traveling in 2nd or 3rd gear or in overdrive (“D” range).
2. The vehicle speed is at or above the specified speed and the throttle opening angle is at or above the specified value.
3. The ECU has received no mandatory lock-up system cancellation signal.
The ECU controls the lock-up timing in order to reduce shock during shifting. If the transaxle shifts up or down while the lock- up system is in operation, the ECU deactivates the lock-up system. This helps to reduce shifting shock. After shifting up or down is completed, the ECU reactivates the lock-up system. However, the ECU forces to cancel the lock-up under the following conditions.
1. The stop light switch comes on (during braking).
2. The IDL points of the throttle position sensor close.
3. The coolant temperature is below a certain temperature.
4. The vehicle speed drops about 10 km/h or more below the set speed while the cruise control system is operating.
Control of Flex Lock-up
The flex lock-up clutch system expands the lock- up operation range by stabilizing and keeping a slight slippage of the lock-up clutch to improve the fuel economy. The Engine & ECT ECU determines the flex lock-up operation range from the throttle opening angle and vehicle speed, and then the ECU sends a signal to the linear solenoid valve (SLU). In addition, the ECU uses the engine speed and transaxle input speed sensor signal to detect the difference between the torque converter pump impeller (engine) and turbine runner (transaxle) speeds. This makes feedback control to optimize the power transmission distribution of the torque converter (fluid power transmission) and lock-up clutch (mechanical power transmission).