The gearbox can accelerate and decelerate, which is often referred to as a speed change gearbox. The transmission direction can be changed. For example, we can use two sector gears to transmit the force vertically to the other rotating shaft. It can also change the rotational torque. Under the same power condition, the faster the speed of the gear, the smaller the torque on the shaft, and vice versa. The purpose of separating the engine from the load can be achieved by separating the two originally engaged gears. For example, brake clutch, etc. It can also distribute power. For example, we can use one engine to drive multiple slave shafts through the main shaft of the gearbox, thus realizing the function of one engine driving multiple loads.