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.
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.
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.
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.
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).