What are the main 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 ring gear, a planet carrier and several planet gears, which is called a planetary row. The sun gear, the ring gear and the planet carrier have a common fixed axis. The planet gears are supported on the planet gear shafts fixed on the planet carrier and mesh with the sun gear and the ring gear at the same time. When the planetary gear mechanism is running, the planetary gears that are empty on the planet carrier can rotate on their own axis on the one hand, and on the other hand can rotate with the planet carrier around the sun gear, just like planetary motion in the sky , It has two motion states of rotation and revolution, and the planetary gear is named after it. In the planetary row, the sun gear, the ring gear and the planet carrier with a fixed axis are called the three basic elements of the planetary row.
Planetary gear mechanisms can be classified in different ways:
(1) According to the different ways of gear meshing, planetary gear mechanisms can be divided into internal meshing type and external meshing type. The internal meshing planetary gear mechanism has a compact structure and high transmission efficiency, so it is widely used in automatic transmissions.
(2) According to the number of rows of planetary gears, planetary gear mechanisms can be divided into single row and multiple rows. The multi-row planetary gear mechanism is composed of several single-row planetary gear mechanisms. Multi-row planetary gear mechanisms composed of two or three single-row planetary gear mechanisms are usually used in automobile automatic transmissions.
(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. Compared with the single planetary gear mechanism under the same other conditions, the double planetary gear mechanism can get reverse transmission for the ring gear.
The principle of planetary gear mechanism transmission
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, the sun gear, the ring gear and the planet carrier, must be fixed, or its movement subject to certain restrictions, or some two basic elements can be connected to each other. At the same time, the planetary row becomes a mechanism with only one degree of freedom to obtain a certain transmission ratio.