Features of planetary gearbox

The transmission method of planetary gearboxes is different from the dynamic motion of traditional gearboxes. Transmission of traditional gearboxes depends on contact surfaces between various sized gears; all loads are concentrated on the point of contact. As a result, gears may wear out earlier and are prone to cracks. On the application of high speed reducing ratio, required transmission forces will demand more gears for engagements. Apart from occupying more space, more wear caused by friction is unavoidable. Gaps between engaged gears are multiplied and lead to reduced transmission efficiency. 

Transmission of planetary gearboxes is of a different scenario, the sun gear, planetary pinion and the ring for internal gear has 6 contact surfaces to even out loads applied. Impact loads are spread over gear surfaces of the internal gear ring at 360 degrees. Therefore friction between gears is reduced and it resolves the problem of gear cracks. Planetary pinion gears move in a floating fashion with tight gaps between the associating gears. Each speed reduction only requires speed gear engagement. The space needed is relatively reduced compared to traditional gearboxes. Operation efficiency can reach up to 97%.

Principle of planetary pinion gear speed reduction

Operations of planetary gears are driven by the sun gear. When the sun gear rotates to a certain speed, and the driven planetary gears move about the internal ring (360 degrees) and return to the original position, the rotating speed of the sun gear becomes the speed reduction ratio. Therefore, the speed reduction ration depends on changes of both gears (diagram A). The more teeth the sun gear has, the more gears the planetary gears need in order to achieve a lower speed reduction ratio (diagram B).

Calculation method of planetary gear speed reduction ratio

Speed reducer normally requires a higher speed ratio selection, while the planetary speed reducer can allow more flexible applications. 2 or more speed reduction applications are achievable by means of associating with various speed gears. The end result is a multiplied higher speed reduction ratio assembly.