The main functions of automotive gears include the following:

1. Power transmission: The main function of a car's gear system is to transmit the power generated by the engine to the wheels, allowing the car to move forward or backward.

2. Conversion of torque and speed: Through different gear combinations and transmission ratios, car gears can provide the low-speed high torque required by the wheels while the engine outputs high-speed low torque, and vice versa. This is particularly important when accelerating, climbing, or driving at high speeds.

3. Direction control: In manual transmissions, changes in gear combinations can enable the vehicle to move forward and backward. In automatic transmissions, the gear system also participates in the change of direction.

4. Distribution of driving force: In a multi wheel drive system, the gear system is responsible for distributing power reasonably to each wheel, ensuring that the vehicle can maintain good stability and traction under different driving conditions.

5. Deceleration and torque increase: In low-speed gears, the gear system can decelerate and increase torque, providing greater torque to help the car accelerate or overcome slopes.

6. Increase speed and reduce torque: When in high-speed gear, the gear system can increase speed and reduce torque, allowing the car to travel at a higher speed.

7. Smooth transmission: High quality gears can ensure smooth power transmission, reduce vibration and noise, and improve driving comfort.

8. Protective function: The synchronizers and other components in the gear system can reduce the impact between gears during gear shifting, protecting the gears from damage.

Automotive gears ensure good power performance and driving experience under different driving conditions through these functions. The design and manufacturing quality of gear systems directly affect the overall performance and reliability of automobiles.