The principle of operation of an automatic transmission (automatic transmission)
An automatic transmission is a type of transmission that automatically changes gears based on vehicle speed and engine load. It consists of the following main components:
Torque converter
* Connects the engine and transmission.
* Contains a turbine, reactor and pump filled with transmission fluid (TF).
* Transfers torque from the engine to the transmission and eliminates jerking when changing gears.
Planetary gearbox
*Contains sun gear, planetary gears and ring gear.
* Allows the transmission to have multiple gears using different combinations of gear interactions.
Friction packs
* Consists of friction discs pressed against each other by pistons controlled by hydraulic pressure.
* Switch on and off various combinations of gearbox transmissions by changing the gear ratio.
Hydraulic control unit
* Controls the hydraulic pressure that operates the friction packs.
* Receives input signals from various sensors such as speed sensor, engine load sensor and throttle sensor.
* Detects the appropriate gear and shifts gears accordingly.
Electronic control unit (ECU)
* Present in modern automatic transmissions.
* Instead of a hydraulic control unit, it uses electronic components to control the transmission.
* Provides more precise and adaptive gear shifting.
Gear shift process
1. When the driver moves the gear shift lever to a certain position (for example, “D” for driving), the hydraulic control unit redirects the fuel injection into the appropriate channels.
2. The pressurized fluid activates the friction packs, pressing the friction discs together in a specific combination.
3. This gear interaction changes the gear ratio, transferring different amounts of torque to the transmission output shaft.
4. As vehicle speed increases or engine load changes, the sensors transmit signals to the hydraulic control unit.
5. The control unit adjusts the hydraulic pressure to shift to another gear, ensuring smooth and seamless shifting.
Automatic transmission modes
In addition to the standard driving mode (D), many automatic transmissions have additional modes, such as:
* N (Neutral): The transmission is disengaged and the vehicle can roll freely.
*P (Park): The transmission is mechanically locked, preventing the vehicle from moving.
* R (reverse): The transmission shifts gears in reverse direction.
*S (Sport): Modifies shift characteristics for a more responsive driving experience.
* L (low): Keeps the transmission in low gears to provide more torque at low speeds.