Automatic transmission (AT)
An automatic transmission is a mechanism that automatically changes vehicle gears depending on speed and load. It consists of several main components:
Planetary gearbox
* Consists of several rows of gears, which are interconnected by planetary gears.
*Each planetary gear can rotate around its own axis and simultaneously roll on the outer ring gear.
* Combinations of locked and unlocked gears create different gear ratios.
Hydraulic transformer
* Connects the motor to the planetary gearbox through the working fluid.
* Allows engine torque to be converted and multiplied at lower speeds.
* Acts as a torsional vibration damper and ensures smooth gear shifting.
Hydraulic block
* Distributes hydraulic fluid to various parts of the transmission.
* Controls the locking and unlocking of gears in the planetary gearbox.
Electronic control unit (ECU)
* Receives signals from vehicle sensors and determines when and how to shift gears.
* Controls the hydraulic unit and other transmission components.
Other components
* Oil pump, which circulates fluid in the transmission.
* Oil cooler that prevents overheating of the fluid.
* Valve block that regulates the flow of fluid to various components.
Operating principle of automatic transmission
When the driver presses the gas pedal, the ECU determines which gear to engage. The hydraulic unit supplies pressurized fluid to lock or unlock the corresponding gears in the planetary gearbox. This results in a change in the gear ratio and a corresponding change in vehicle speed.
The hydraulic transformer ensures smooth shifting by multiplying engine torque at lower speeds and reducing it at higher speeds.
As vehicle speed increases or load changes, the ECU automatically changes gears to maintain optimal performance.
Modern automatic transmissions typically have multiple forward gears, which increases fuel efficiency and improves performance in a variety of driving modes.