Planetary Gear Sets

Planetary Gear Sets

Planetary Gear Sets are gear systems that rotate around their rotating shafts, like fixed-axis gears; their rotating shafts also rotate with the shafts of other gears with the planet carrier.
The rotation around its shafts is “rotation,” and rotation around the shafts of other gears is  “revolution,” just like the planets in the solar system.
Compared with general gear transmission, planetary gear transmission has many unique advantages. The most significant feature is that power can be divided when transmitting power, and the input shaft and output shaft are on the same horizontal line. Therefore, planetary gear transmission has been widely used in reducers, speed increases, and communications in various mechanical transmission devices.

Primarily because of its characteristics of “high load and large transmission ratio,” it has been widely used in aircraft and vehicles (cumbersome vehicles). Planetary gears also play an important role in engine torque transmission. Because the engine’s speed and torque characteristics are very different from the road driving needs, the above aspects of the planetary gears can be used for conversion to distribute the engine’s power to the drive wheels properly. The automatic transmissions in automobiles also use these characteristics of planetary gears to obtain different transmission ratios by changing the relative motion relationship of each component through clutches and brakes.

Planetary Gear Sets Details

Applications

However, due to the planetary gear’s complex structure and working state, its vibration and noise problems are also prominent. It is easy to cause failure phenomena such as tooth fatigue pitting, tooth root cracks, and even tooth or shaft breakage. Which affects the equipment operation accuracy, transmission efficiency, and service life of the equipment.
The simple (single-row) planetary gear mechanism is the basis of the speed change mechanism. Generally, the speed change mechanism of an automatic transmission is composing of two or more three rows of planetary gear mechanisms. The simple planetary gear mechanism includes a sun gear, several planetary gears, and a gear ring. The planetary gear is supportting with a fixed shaft of the planet carrier, allowing the planetary gear to rotate on the supporting shaft. Planetary and adjacent sun gears and ring gears are always in a constant meshing state, usually using helical gear to improve operational stability.

Specifications

In a simple planetary gear mechanism, the sun gear is located at the center of the planetary gear mechanism. The sun and planet gear often mesh, and the two external gears mesh in opposite rotation directions. Just as the sun is at the center of the solar system, the sun wheel is named for its position. In addition to being able to rotate around the support axis of the planet carrier, the planet gear will also revolve around the central axis of the sun gear under the circumstances of the planet carrier, just like the rotation of the earth and the revolution around the sun. When this happens, it is called a planetary gear mechanism. For example, in the entire planetary gear mechanism, the rotation of the planet gear exists, and the planet carrier is fixed. This method is similar to a parallel shaft transmission called a fixed shaft transmission. The ring gear is an internal gear. It often meshes with the planetary gear—the internal and external gear mesh with the same rotation direction. The quantity of planetary gears depends on the design load of the transmission, and usually, there are three or four; the more the amount, the greater the burden.
A simple planetary gear mechanism is usually called a three-component mechanism, which refers to the sun gear, planet carrier, and ring gear. Suppose these three components determine the relationship between each other. In that case, generally, one of the components needs to be fixed first, then decide who is the active part and select the rotating speed and rotation direction of the active region. Finally, the rotating speed and direction of the passive role are determined.