Shift Indicator - A/T: Description and Operation

This system electronically controls the gear shift timing, lock-up timing, the clutch and brake hydraulic pressure, and the engine torque during shifting to achieve optimum shift feeling.

The vehicle driving conditions and engine operating conditions are detected by various sensors.

1. GEAR SHIFT OPERATION
During driving, the engine control module selects the shift for each gear which is most appropriate to the driving conditions based on input signals from the engine coolant temp. sensor to TERMINAL THW of the engine control module, and also a control signal is input to TERMINAL SPD of the engine control module from the speedometer devoted to the electronically controlled transmission. Current is then output to the electronically controlled transmission solenoid. When shifting to 1st speed, current flows from TERMINAL S1 of the engine control module to TERMINAL (A) 3 (2WD) or (B) 3 (4WD) of the electronically controlled transmission solenoid to GROUND, and continuity to the no. 1 solenoid causes the shift.

For 2nd speed, current flows from TERMINAL S1 of the engine control module to TERMINAL (A) 3 (2WD) or (B) 3 (4WD) of the electronically controlled transmission solenoid to GROUND, and from TERMINAL S2 of the engine control module to TERMINAL (A) 1 (2WD) or (B) 6 (4WD) of the electronically controlled transmission solenoid to GROUND, and continuity to solenoids no. 1 and no. 2 causes the shift.

For 3rd speed, there is no continuous to no. 1 solenoid, only to no. 2, causing the shift.

Shifting into 4th speed (Overdrive) takes place when there is no continuity to either no. 1 or no. 2 solenoid.

2. LOCK-UP OPERATION
When the engine control module judges from each signal that lock-up operation conditions have been met, current flows from TERMINAL SL of the engine control module to TERMINAL (A) 2 (2WD) or (B) 5 (4WD) of the electronically controlled transmission solenoid to GROUND, continuity to the lock-up solenoid causes lock-up operation.

3. STOP LIGHT SW CIRCUIT
If the brake pedal is depressed (Stop light SW On) when driving in lock-up condition, a signal is input to TERMINAL B/K of the engine control module the engine control module operates and current to the lock-up solenoid is cut off.

4. OVERDRIVE CIRCUIT
* O/D main SW on
When the O/D main SW is turned ON (SW point is open), a signal is input to TERMINAL OD2 of the engine control module and engine control module operation causes gear shift when the conditions for overdrive are met.

O/D main SW OFF When the O/D main SW is turned OFF (SW point is closed), the current flowing through the O/D OFF indicator light flows through the O/D main SW to GROUND, causing the indicator light to light up. At the same time, a signal is input to TERMINAL OD2 of the engine control module and engine control module operation prevents shift into overdrive.

5. CENTER DIFFERENTIAL CLUTCH CONTROL (4WD)
The center differential clutch control uses a linear solenoid type valve (Solenoid valve SLD) to control the center differential clutch. By controlling the fluid pressure, the limited slip differential effect of the center differential can always be maintained at the optimum for the current driving conditions to increase road-holding ability.

Solenoid valve SLD opens and closes in response to signals from the engine control module. Thus the solenoid modulator valve maintains a constant fluid pressure for operation of the center differential clutch control valve and center differential clutch.

* Normal driving
Solenoid valve SLD opens and closes in response to the throttle opening angle to control the fluid pressure operating on the center differential clutch. When the vehicle takes off in first gear with a large throttle opening angle, the fluid pressure is kept high. So even if the vehicle takes off suddenly or the road surface is slippery, smooth and mailable acceleration is possible.

* Slipping
When a large difference occurs between the front wheel speed and rear wheel speed at low speeds, solenoid valve SLD is fully closed to apply high fluid pressure to the center differential clutch and provide a large limited slip differential effect.

* Wide cornering
When difference arise between the front wheel speed and rear wheel speed due to differences in the turning radius during cornering at low speeds, solenoid valve SLO is fully open to apply a weak limited slip differential effect and permit smooth cornering.

6. ELECTRONICALLY CONTROLLED TRANSMISSION PATTERN SELECT SW
If the electronically controlled transmission pattern select SW is changed from normal to power, the current through the power indicator flows to GROUND, current flows to TERMINAL P of the engine control module, the engine control module operates, and shift up and shift down occurs at higher vehicle speeds than when the SW is in NORMAL position.