The speed and traction required by the vehicle are different under different driving conditions. For example, at the beginning, the traction is large, which requires a large torque to push the vehicle forward, while at high speed cruising, the speed is fast, which requires a relatively high speed and a small torque.
The torque of the engine affects the traction and the speed affects the speed. However, the variation range of the torque and speed of the engine is limited, which cannot take care of different driving conditions such as starting, climbing and high speed. Therefore, a gearbox is needed to change the rotation ratio (speed ratio) of the car to adapt to different driving conditions.
as a straight steel man in the automobile circle, the engine is full of enthusiasm and keeps moving forward, but it has one problem: it can't go back. Generally, the crankshaft of an automobile engine can only rotate in one direction. If there is no transmission, it can't go back.
using neutral to interrupt the power transmission is the temper of the engine. If there is a traffic jam or a red light, you have to turn off the engine and ignite it constantly. The engine is a rigid power output, and only when it is turned off can it interrupt the power transmission. When starting, idling, shifting gears, coasting or temporarily stopping, the gearbox can interrupt the power transmission without turning off the engine.
in a word, if the engine is the "heart" of the car, then the gearbox is the "brain" to help the engine make scientific decisions, and only by combining the two can it exert its powerful advantages.