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Planetary gears refer to a gear system where, in addition to rotating around their own axis like fixed-axis gears, their axis of rotation also rotates along with the planet carrier around the axis of other gears.

The rotation around one's own axis is called "rotation", while the rotation around the axis of another gear is called "revolution", just like the planets in the solar system, hence the name.

Structural characteristics:

The central rotating component is the sun gear; the planetary gears revolve around the sun gear while also rotating on their own axes; the planetary gears, adjacent sun gears, and ring gears are always in constant mesh; the structure is compact, with the sun gear, planetary carrier, and ring gear being concentric, which eliminates the need for an intermediate shaft and gears; helical gears are commonly used to improve operational smoothness; typically, there are 3/4 planetary gears, with more gears providing greater load-bearing capacity.

Transmission combination

In gear systems that include planetary gears, the transmission principle differs from that of fixed-axis gears.

Due to the presence of the planet carrier, there can be three axes for power input/output. Additionally, means such as clutches or brakes can be employed to restrict the rotation of one of these axes when necessary, leaving only two axes for transmission.

Therefore, there can be multiple combinations of relationships between intermeshing gears:

(1) The power is input from the sun gear and output from the outer gear ring, with the planet carrier locked by the mechanism;

(2) The power is input from the sun gear and output from the planet carrier, with the outer gear ring locked;

(3) Power is input from the planet carrier and output from the sun gear, with the outer gear ring locked;

(4) Power is input from the planet carrier and output from the outer gear ring, with the sun gear locked;

(5) The power is input from the outer gear ring and output from the planet carrier, with the sun gear locked;

(6) Power is input from the outer gear ring and output from the sun gear, with the planet carrier locked;

(7) Two driving forces are inputted from the sun gear and the outer gear ring respectively, and are synthesized before being outputted from the planet carrier;

(8) Two driving forces are inputted from the planet carrier and the sun gear respectively, and are synthesized before being outputted from the outer gear ring;

(9) Two driving forces are inputted from the planet carrier and the outer gear ring respectively, and are synthesized before being outputted from the sun gear;

(10) Power is input from the sun gear and output in two paths from the outer gear ring and the planet carrier;

(11) Power is input from the planet carrier and output in two paths through the sun gear and the outer gear ring;

(12) Input from the power external gear ring is outputted in two paths, from the sun gear and the planet carrier.

How to calculate the speed ratio - single-row planetary gear mechanism

Fix any one of the three components, and the other two components can output a constant transmission ratio;

No components are fixed, where two components are interconnected and drive another component to output;