1. Roles of components

The gears are shifted by switching the operation of the clutches and brakes. The shift valves switch the fluid passage that causes the hydraulic pressure to be applied on the brakes and clutches. The shift valves are 1- 2, 2- 3, and 3-4.

2. Operation

Example: 1-2 shift valve

When the hydraulic pressure is applied on the top of shift valve, the transaxle is kept in first gear because the shift valve is at the bottom and fluid passages to the clutches and brakes are cut off. However, when the hydraulic pressure that was applied is cut off by the operation of the solenoid valve, the spring force moves the valve up, so the fluid passage to B2 is opened, B2 operates, and the gear is shifted up to 2nd gear.

Solenoid Valve

The solenoid valve is operated by signals from the Engine & ECT ECU to operate the shift valves and control the hydraulic pressure. There are two types of solenoid valves. A shift solenoid valve opens and closes the fluid passage according to signals from the ECU (opening the fluid passage for an on signal and closing it for an off signal). A linear solenoid valve controls the hydraulic pressure in a linear manner according to the electrical current sent from the ECU. Shift solenoid valves are used for controlling gear shift and linear solenoid valves are used for such functions as controlling hydraulic pressure.

HINT:

There is also a type of shift solenoid valve that raises a spool to open the fluid passage when the signal is off and closes the fluid passage when the signal is on. Also, the shift solenoid valve has No.1 and No.2 while the linear solenoid valve has a SLT that is used instead of the throttle valve and a SLU to control the lock up, etc.

Throttle Valve

The throttle valve produces throttle pressure in response to accelerator pedal angle via throttle cable and throttle cam. Throttle pressure is applied on the primary regulator valve and, accordingly, regulates line pressure in accordance with the throttle valve opening. Some models control the throttle pressure with a linear solenoid valve (SLT) instead of a throttle valve. Such models control the throttle pressure by the Engine & ECT ECU sending signals to the linear solenoid valve according to the signals from the throttle position sensor (accelerator opening angle).

The Engine & ECT ECU performs the following controls.

Control of shift timing

Control of lock-up

Control of flex lock-up

Other controls

The ECT vehicle can be driven smoothly and comfortable by the above controls.

Control of Shift Timing

The Engine & ECT ECU has programmed into its memory the optimal shift pattern for each shift lever position and each driving mode. Based on the shift pattern, the ECU turns the solenoid valves on or off in accordance with the vehicle speed signal from the vehicle speed sensor, with the throttle opening angle signal from the throttle position sensor and with various sensor/switch signals. In this manner, the ECU operates each solenoid valve, opening or closing the fluid passages to the clutches and brakes permits shifting up or down of the transaxle.

SERVICE HINT:

When a vehicle is driven, you can judge if the automatic transaxle is faulty or not by how well the shifting points conform to the automatic shift diagram.

The relationship between the vehicle speed and gear varies by the accelerator opening angle even at the same vehicle speed. When driving while normally keeping the accelerator opening constant, the vehicle speed increases and the transaxle shifts up. When the accelerator is released at point A shown in the figure at left and the accelerator opening reaches point B, the transaxle shifts up from 3rd to O/D gear. Conversely, when the accelerator is further depressed at point A and the accelerator opening reaches point C, the transmission shifts down from 3rd to 2nd gear.

HINT:

When the coolant temperature is low, the transaxle does not shift up to O/D gear.

REFERENCE:

The speed at which the transaxle shifts up and the speed at which it shifts down occur with in a certain range, regardless of the gear. This range is called hysteresis. Hysteresis is a characteristic built into every automatic transaxle to prevent the transaxle from shifting up and down too frequently. The shift timing control differs depending on the driving pattern select switch mode. The ECU determines what the current mode is and controls the shift timing.

Example: For the power mode, the gear shift point and lock-up point are set to a higher engine speed than for the normal mode, which allows the driving sportier vehicle as using a higher engine speed.

Each gear condition is explained using the solenoid valves and shift valves.

1. 1st gear

For gear shift from neutral to 1st gear, the fluid passage to C1 is opened by switching the manual valve. Since the No. 1 solenoid valve is on and the No. 2 solenoid valve is off, the fluid passage to C0 is opened. (No.1 solenoid valve is on, and No.2 solenoid valve is off.) The operation of C1 and F2 creates the fluid passage for 1st gear. In the “D” and “2″ ranges, the engine brake is not applied because of the operation of F2. In the “L” range, the passage to B3 is opened and the engine brake is applied.

Hydraulic pressure to the planetary gear unit

C1 from manual valve

C0 from 3-4 shift valve

B3 from 2-3 shift valve

2. 2nd gear

The No. 2 solenoid valve is switched from off to on according to signals from the ECU. (No.1 solenoid valve is on, and No.2 solenoid valve is on.) The hydraulic pressure applied on the top of the 1-2 and 3-4 shift valves is discharged and the 1-2 shift valve is moved up by the force of the spring. Therefore, the fluid passage opens to B2. The operation of C1 and B2 (F1) shifts up to 2nd gear. In the “D” range, the engine brake is not applied because of the operation of F1. In the “2″ range, the fluid passage to B1 is opened and the engine brake is applied.

Hydraulic pressure to the planetary gear unit

C1 from manual valve

C0 from 3-4 shift valve

B2 from 1-2 shift valve

B1 from 1-2 shift valve

3. 3rd gear

The No. 1 solenoid valve is switched from on to off according to signals from the ECU. (No.1 solenoid valve is off, and No.2 solenoid valve is on.) The hydraulic pressure starts to be applied on the top of the 2-3 shift valve, moving down the 2-3 shift valve. Therefore, the fluid passage opens to C2. The operation of C1 and C2 shifts the gear up to 3rd gear.

Hydraulic pressure to the planetary gear unit

C1 from manual valve

C0 from 3-4 shift valve

B2 from 1-2 shift valve

C2 from 2-3 shift valve

4. O/D gear

The No. 2 solenoid valve is switched from on to off according to signals from the ECU. (No.1 solenoid valve is off, and No.2 solenoid valve is off.) The hydraulic pressure starts to be applied on the top of the 1-2 and 3-4 shift valves, moving down the 3-4 shift valve. (The line pressure from the 2-3 shift valve is applied at the bottom of the 1-2 shift valve, so 1-2 shift valve does not move.) Therefore, the fluid passage that had been acting on C0 to B0 is switched and the gear is shifted up to the O/D gear. When the overdrive main switch is OFF, it cannot shift up to the O/D gear. Because the ECU does not send the signal to turn off the No.2 solenoid valve.

Hydraulic pressure to the planetary gear unit

C1 from manual valve

B0 from 3-4 shift valve

B2 from 1-2 shift valve

C2 from 2-3 shift valve

Description

The shift lever corresponds to the gear shift lever of the manual transaxle. The driver can select the driving mode – forward or reverse travel, neutral, and park – by operating this lever. There are the following types of shift levers. The shift lever used depends on the vehicle and grade.

1. Straight type

2. Column type

3. Gate type

4. Straight type with E-shift system

HINT:

The overdrive main switch may also be called the overdrive OFF switch or the transaxle (transmission) control switch. The E-shift type can shift the gear up or down with the transaxle/transmission shift switch.