Composition and working principle of basic planetary gear mechanism of transmission

Structure and Types of Planetary Gear Mechanisms There are many types of planetary gear mechanisms, among which the simplest planetary gear mechanism is composed of a sun gear, a gear ring, a planetary carrier and several planetary gears, which is called a planetary row. The sun gear, the gear ring and the planet carrier have the same fixed axis, and the planet wheel is supported on the planet gear shaft fixed on the planet carrier, and simultaneously meshes with the sun gear and the gear ring. When the planetary gear mechanism is running, several planetary gears sleeved on the planet carrier can rotate around their respective axes on the one hand, and on the other hand, they can rotate around sun gear with the planet carrier, just like the planetary motion in the sky, which has two motion states of rotation and revolution, hence the name planetary gear. In the planetary row, the sun gear, the ring gear and the planet carrier with fixed shaft are called the three basic elements of the planetary row. Planetary gear mechanisms can be classified in different ways: (1) According to the different meshing ways of gears, planetary gear mechanisms can be divided into internal meshing and external meshing. Internal meshing planetary gear mechanism is widely used in automatic transmission because of its compact structure and high transmission efficiency. (2) According to the different planetary gear rows, the planetary gear mechanism can be divided into single row and multiple rows. The multi-row planetary gear mechanism consists of a plurality of single-row planetary gear mechanisms. Automotive automatic transmission usually adopts multi-row planetary gear mechanism composed of two or three single-row planetary gear mechanisms. (3) According to the number of planetary gear sets between the sun gear and the ring gear, the planetary gear structure can be divided into single planetary gear type and double planetary gear type. Under the same other conditions, compared with the single planetary gear mechanism, the double planetary gear mechanism can obtain reverse transmission. 2. The variable speed principle of planetary gear mechanism. The single-row planetary gear mechanism has two degrees of freedom, so it has no fixed transmission ratio and cannot be directly used for variable speed transmission. In order to form a transmission mechanism with a certain transmission ratio, one of the three basic elements, namely sun gear, gear ring and planet carrier, must be fixed, or its movement must be restricted, or the two basic elements must be connected with each other, so that the planetary row can become a mechanism with only one degree of freedom, and a certain transmission ratio can be obtained. Automobile automatic transmission is an automatic control transmission. It can automatically change the transmission ratio of the transmission system according to the change of engine load and vehicle speed, so that the automobile can obtain good power and fuel economy, effectively reduce engine emission pollution, and significantly improve the safety, ride comfort and maneuverability of the vehicle. According to the change mode of transmission ratio, automatic transmission of automobile can be divided into three types: step type, stepless type and comprehensive type. Stepwise automatic transmission refers to the transmission that realizes automatic control on the basis of mechanical gear transmission, also known as electronically controlled mechanical automatic transmission (AMT). CVT includes electric, hydraulic (hydraulic torque converter) and metal belt CVT. Comprehensive automatic transmission refers to a hydro-mechanical transmission that realizes automatic control, that is, a hydro-mechanical automatic transmission. Hydromechanical automatic transmission is divided into hydraulic automatic transmission and electro-hydraulic automatic transmission, the latter is widely used.