A mechanical paradox planetary gear mechanism, comprising:
- a sun gear configured to be rotatable together with rotation of an input shaft;
- a plurality of first planetary gears arranged around the sun gear at equal intervals, and configured to rotate about their own axes while revolving around the sun gear in a state in which the first planetary gears mesh with the sun gear;
- a first internal gear arranged around the plurality of first planetary gears, and configured to mesh with the plurality of first planetary gears;
- a second internal gear arranged in the same axis as the first internal gear;
- a plurality of second planetary gears respectively arranged on the same axes as the plurality of first planetary gears, and configured to mesh with the second internal gear;
- a plurality of collars mounted on inner circumferences of the first planetary gears and the second planetary gears arranged on the same axes, and configured to be rotatable integrally with the first planetary gears and the second planetary gears on the same axes;
- a plurality of shafts configured to rotatably support the collars, respectively;
- and
- a carrier configured to support the plurality of shafts so as not to be rotatable relative to each other,
- wherein one of the first internal gear and the second internal gear is a rotatable movable internal gear, and the other of the first internal gear and the second internal gear is a non-rotatable fixed internal gear,
- wherein the first planetary gears and the second planetary gears have the same number of teeth, and include axially-extending gear-side engaging portions formed on inner circumferential surfaces of the first planetary gears and the second planetary gears, respectively,
- wherein the collars include, on outer circumferential surfaces of the collars, first collar-side engaging portions capable of engaging with the gear-side engaging portions of the first planetary gears and second collar-side engaging portions capable of engaging with the gear-side engaging portions of the second planetary gears, and
- wherein the first collar-side engaging portions and the second collar-side engaging portions are position-shifted in a circumferential direction of the collars, according to a phase difference between the first planetary gears and the second planetary gears on the same axes calculated based on at least a difference in the number of teeth between the rotatable movable internal gear and the non-rotatable fixed internal gear.