A reduction apparatus comprising:
- a cylindrical case having a pair of case parts which are detachably assembled with each other to define a receiving space;
- a fixed ring gear sandwiched between and coupled to the pair of case parts and having teeth which are formed on a circumferential inner surface thereof;
- an output member rotatably received in the receiving space of the case and having an output ring gear and an output shaft, the output ring gear being formed on a circumferential inner surface of the output member in a manner such that the output ring gear has an inner diameter which is the same as that of the fixed ring gear and a gear ratio and a module which are respectively different from those of the fixed ring gear, the output shaft being integrally formed on an outer surface of the output member to project out of the case;
- a carrier having a first carrier member and a second carrier member, the first carrier member possessing a circular plate-shaped configuration and having a guide projection and an input shaft-guiding groove, the guide projection being formed at a center portion of an outer surface of the first carrier member to be rotatably supported on an inner surface of the output member, the input shaft-guiding groove being defined at a center portion of an inner surface of the first carrier member, the second carrier member being arranged to be opposite to the first carrier member with a predetermined separation and to define an accommodating space between the first and second carrier members, the second carrier member having an input shaft-inserting hole which is defined at a center portion thereof;
- an input shaft having shaft portion which is rotatably supported at one end thereof in the input shaft-guiding groove of the first carrier member and projects at the other end thereof out of the case through the input shaft-inserting hole of the second carrier member, the input shaft further having a first sun gear and a second sun gear which are formed on a circumferential outer surface of the shaft portion in a manner such that the first and second sun gears are located between the first and second carrier members and a gap is defined therebetween;
- a plurality of first planetary gears rotatably fitted around a plurality of first connecting members, respectively, which are secured to the first and second carrier members in a manner such that the first connecting members are spaced apart one from another by a predetermined angle along a circumferential direction, the first planetary gears being meshed with the first sun gear of the input shaft;
- and
- a plurality of second planetary gears rotatably fitted around a plurality of second connecting members, respectively, which are secured to the first and second carrier members in a manner such that each second connecting member is positioned between two first planetary gears in the circumferential direction, the second planetary gears being meshed with the second sun gear of the input shaft.