Gear shift diagram in an automatic transmission (automatic transmission)
Input shaft
*Connected with engine crankshaft
* Drives planetary mechanisms
* Rectangular flange with slots for locking couplings
Planetary gears
* Sets of sun gears, planetary gears and overrunning clutches
*Transfer power from the input shaft to the output shaft
Couplings
*Actuated by hydraulic pressure and controlled by Electronic Control Unit (ECU)
* Lock planetary gears, providing different gears
Output shaft
* Connected to driveshaft (or wheels in case of front wheel drive vehicles)
*Powers the car
Gear shift steps:
1. Neutral (N): All clutches are open and the output shaft does not rotate.
2. Park (P): The locking lever engages the teeth on the output shaft to prevent the vehicle from moving.
3. Reverse (R): One clutch is locked, reversing the direction of rotation of the output shaft.
4. First gear (1): Two clutches are locked, providing a gear ratio of more than 1:1.
5. Second gear (2): One clutch is locked, providing a gear ratio less than 1:1, but greater than first gear.
6. Third gear (3): All clutches are open, the planetary gear transfers power directly from the input shaft to the output shaft (direct transmission).
7. Fourth gear (4): One clutch is locked (depending on the type of automatic transmission), providing a gear ratio even less than third gear. Some automatic transmissions have an additional fifth or sixth gear to improve fuel economy.
Torque converter lock:
* Under certain conditions (such as driving at a constant speed), the torque converter lock-up acts as a direct transmission, reducing slip losses and increasing efficiency.