Abstract: An apparatus for changing the rotational speed of a mechanism includes an input shaft, several planetary gear units, an output rotor, a rotating disc and a casing. The planetary gear units are connected together. The sun gear of the first unit is connected to the input shaft and the carrier of the last unit is connected to output rotor. An internal gear of one of planetary gear units can rotate in the casing but can be stopped by an internal gear stopping device. The input shaft is connected to the rotating disc. The rotating disc can be brought into contact with the output rotor by a disc-contacting device. The disc-contacting device and the internal gear stopping device are driven in a complementary manner. When the internal gear stopping device is excited and the disc-contacting device is unexcited, the output rotor rotates at a low speed level. When the disc-contacting device is excited and the internal gear stopping device is unexcited, the output rotor rotates at a high speed level.

Abstract: A planetary gear includes a middle planetary gear part, a disc part on one side of the planetary gear part having a radius smaller than a radius of the tooth root circle of the planetary gear part and another disc part on another side of the planetary gear part having a radius bigger than a radius of a tooth edge circle of the planetary gear part. An internal gear includes a middle internal gear part, an inner cylindrical part on one side of the internal gear having a radius smaller than a radius of a tooth edge circle of the internal gear part and another inner cylindrical part on another side of the internal gear having a radius bigger than a radius of a tooth root circle of the internal gear part. The planetary smaller disc parts can rollingly engage the smaller inner cylindrical part of the internal gear. The planetary bigger disc parts can rollingly engage the bigger inner cylindrical part of the internal gear. The planetary gear part and two disc parts are unified in a body.

Abstract: A modified planetary gear assembly includes a sun gear, planetary gears, an internally-toothed ring gear and a carrier, and can either transmit or not transmit torque from the sun gear to the carrier. The internally-toothed ring gear has outer peripheries on both sides suitable for being supported by a bearing device and a middle groove on the outer surface having timing teeth shaped around the groove. The peripheries are supported by a bearing device. A stopper device which is movable in a radial direction is mounted at a point around the middle groove. When the stopper device is moved forward to engage with the timing tooth, the internally-toothed ring gear is fixed and torque is transmitted from the sun gear to the carrier. When the stopper device is retracted, the internally-toothed ring gear freely rotates and no torque is transmitted. Thus, there are two states of torque transmission.