With automatic transaxle/transmission vehicles, the driver does not need to judge when shifting up and down. The gears are shifted automatically according to the vehicle speed and the amount that the accelerator pedal is depressed. A unit in which automatic gear shifting is controlled by an ECU (Electronic Control Unit) is called an ECT (Electronically- Controlled Transaxle/transmission) and a unit that does not use an ECU is called a full hydraulically-controlled automatic transaxle.
Currently, almost all vehicles use ECTs. In some models, the gear shifting pattern can be selected according to the driver’s preference and road conditions. This provides improved fuel economy and driving performance.
Types of Automatic Transaxle
Automatic transaxles can be basically divided into two types, those used in FF (Front-engine, Front wheel-drive) vehicles and those used in FR (Frontengine, Rear-wheel-drive) vehicles. Transaxles for FF vehicles have an internal final drive unit, but those for FR vehicles have a final drive unit (differential) mounted externally. The type of automatic transaxle used with FR vehicles is
called a transmission.
In the transversely-mounted automatic transaxle, the transmission and the final drive unit are housed integrally in the same case. The final drive unit consists of a pair of reduction gears (the drive and driven gears), and differential gears.
ECT (Electronically Controlled Transaxle)
An ECT (Electronically Controlled Transaxle) consists of following components:
1. Torque converter
Transmitting and multiplying the torque generated by the engine.
2. Planetary gear unit
Shifting such as deceleration,reverse, acceleration, and neutral.
3. Hydraulic control unit
Controlling the hydraulic pressure so that the torque converter and planetary gear unit operate smoothly.
4. Engine & ECT ECU
Controlling the solenoid valves and the hydraulic control unit to provide the optimum driving condition. It uses hydraulic pressure to automatically shift gears in accordance with ECU
control signals. The ECU controls the solenoid valves according to the condition of the engine and vehicle detected by the sensors, thus controlling the hydraulic pressure.
Full Hydraulically-controlled Automatic Transaxle
The construction of the full hydraulicallycontrolled automatic transaxle is basically the same as the ECT. However, this transaxle mechanically controls shifting by detecting the vehicle speed hydraulically from the governor valve and detecting the accelerator opening from the throttle valve via the amount of movement of the throttle cable.