The gearbox can change the gear ratio, direction of rotation (such as reverse gear) and set neutral. There are many kinds of structures, and there are many kinds of principles: the automobile gearbox is divided into manual and automatic; it is also divided into gear type and electric type; it is also divided into stepped speed change and stepless speed change. The manual transmission produces variable speed torque through different gear combinations; the automatic transmission consists of a hydraulic torque converter, planetary gears and a hydraulic control system that achieves variable speed torque through a combination of hydraulic transmission and gear combination. 1. The stepped transmission has several fixed gear ratios by replacing gear sets of different diameters. A fixed shaft transmission and a planetary gear transmission. 2. The transmission ratio of the continuously variable transmission can be changed in an infinite number of stages within a certain range, and there are two types of electric type and hydraulic type (moving liquid type). The variable speed transmission component of the electric continuously variable transmission is a DC series motor, and the transmission component of the hydrodynamic continuously variable transmission is a torque converter. 3. The integrated transmission refers to a hydraulic mechanical transmission (hand-in-one) consisting of a torque converter and a gear-type stepped transmission.