Hydraulic Control System

Construction
The hydraulic control is composed of an oil pump, rotated by the engine, which supplies hydraulic pressure; a valve body which controls the hydraulic pressure and the opening and closing of the fluid passages; and a governor valve which supplies hydraulic pressure in accordance with vehicle speed.




Operation
Hydraulic pressure supplied by the oil pump is controlled by the regulator valve; the resulting oil pressure controlled by the regulator valve is called the line pressure.

Line pressure produces the hydraulic pressure for throttle pressure and governor pressure. Also, line pressure produces hydraulic pressure for the operation of each brake and clutch in the planetary gear unit.

The throttle valve acts to produce hydraulic pressure, called the throttle pressure, which response to accelerator pedal modulation. Throttle pressure increases as the accelerator pedal is depressed.

The governor valve produces hydraulic pressure, called the governor pressure, in response to vehicle speed. Governor pressure increases as vehicle speed increases.

When shift change occurs, in accordance with the difference between throttle pressure and governor pressure, each shift valve shifts, the fluid passages to the clutches and brakes in the planetary gear unit are opened and the clutches and brakes operate.

The operation of the hydraulic control system, using the 2-3 shift valve of A131L as an example, is shown in images.