Toyota Supra 1990 Manual page 495

AUTOMATIC TRANSMISSION -
Description
AT-3
Outline of ECT
The conventional automatic transmission operates by mechanically converting vehicle speed into governor
pressure, and throttle opening into throttle pressure, and using these hydraulic pressures to control the operation
of the clutches and brakes in the planetary gear unit, thus controlling the timing of up-shift and down-shift
of the transmission. This is called the "hydraulic control method."
In the case of the ECT, on the other hand, sensors electronically sense the speed of the vehicle and the
throttle opening and send these information to the electronic controlled unit (hereafter called ECU) in the
form of electrical signals. The ECU then controls the operation of the clutches and brakes based on these
data, thus controlling the timing of the shift points.
SHIFT CONTROL
• Hydraulic Controlled Transmission
Shifting in the fully hydraulic controlled automatic transmission is carried out by the hydraulic con-
trol unit in the following way:
Throttle Valve
Throttle Cable
Planetary
Gear Unit
~--------,
I Throttle Valve I
I (Throttle I
I
Opening Signal)
I
________ ...J
(Vehicle
Speed Signal)
AT3254
~THROTTLE
VALVE-------,
The throttle valve in the hydraulic control unit
generates hydraulic pressure in proportion to
the amount that the accelerator pedal is de-
pressed; this pressure (called "throttle pres-
sure") acts as a throttle opening "signal" to the
hydraulic control unit.
- GOVERNOR VALVE - - - - - - - - - ,
The governor valve generates hydraulic pressure
in proportion to the speed of the veh icle; th is
pressure (called "governor pressure") acts as a
vehicle speed "signal" to the hydraulic control
unit.
- HYDRAULIC CONTROL UNIT ---.......,
Governor pressure and throttle pressure cause
the shift valves in the hydraulic control unit to
operate; the strengths of these pressures con-
trol the movements of these valves, and these
valves control the fluid passage to the clutches
and brakes in the planetary gear unit, which in
tu rn control the sh ifting of the transm ission.