Planetary mechanism of automatic transmission (AT)
The planetary gear is the main element of the automatic transmission, which ensures the transmission of torque from the engine to the wheels. It consists of the following components:
*Ring Gear: A gear with internal teeth that is rigidly mounted on the transmission output shaft.
* Epicyclic Gear: A gear that rotates inside the ring gear and has teeth that mesh with the teeth of the ring gear and sun gear.
* Sun Gear: A central gear that is rigidly mounted on the transmission input shaft.
* Gears: Three or four small gears that are located between the ring gear and the sun gear and rotate on axles mounted in the planetary carrier.
* Planetary carrier: The frame that supports the planetary axles.
Working principle:
The planetary mechanism works on the principle of switching gear ratios by locking one or more elements. To change the gear ratio, friction discs and band brakes are used, which are controlled by the hydraulic automatic transmission control unit.
When the transmission is in first gear, the friction disc locks the planetary carrier. This causes the ring gear and planet gears to rotate around the stationary sun gear. The result is a high gear ratio suitable for low-speed, high-torque riding.
In second gear, the friction disc unlocks the planetary carrier and it begins to rotate freely. The ring gear now meshes with the epicyclic gear, causing it to rotate in the same direction as the sun gear. This results in a smaller gear ratio suitable for higher speeds.
In third gear, the band brake locks the epicyclic gear, preventing it from rotating. This causes the ring gear to rotate in the opposite direction to the sun gear, resulting in an even lower gear ratio.
In fourth gear (direct drive), the band brake locks the ring gear, preventing it from rotating. This results in a direct connection between the sun gear and the output shaft, providing a 1:1 gear ratio.
The planetary mechanism of the automatic transmission allows:
* Ensure smooth gear shifting without loss of power.
* Provide a wide range of gear ratios.
* Control the torque and speed of the vehicle.