What is the principle of transmission

Transmission principle
Why can the transmission adjust the torque and speed of the engine output? In fact, the principle of gears and levers is embedded here. There are several different gears in the transmission, and by combining different sizes of gears together, the torque and speed of the engine can be adjusted. The low torque can be exchanged for high speed, and the low speed can be exchanged for high torque.
The role of the transmission is mainly in three aspects: First, to change the transmission ratio, expanding the range of torque and speed change of the driving wheels; Second, in the case of unchanged engine steering, to achieve the car backwards driving; Third, the use of neutral gear, can interrupt the engine power transmission, so that the engine can start, idle.
Manual transmission principle
The working principle of manual transmission is to switch the active gear on the intermediate shaft by toggling the gearshift, which is combined with the power output shaft through a combination of gears of different sizes, thus changing the torque and speed of the driving wheels.
The power input shaft of the engine is indirectly connected to the power output shaft through an intermediate shaft. As shown in Figure 3-5-3, the two gears of the intermediate shaft (red) and the two gears on the power output shaft (blue) are rotating together with the engine output. However, without the engagement of synchronizer (purple), the two gears (blue) can only be idled on the power output shaft (i.e., they will not drive the output shaft to turn). In the picture, the synchronizer is in the middle, which is equivalent to the transmission being in neutral.