Transmission device

A transmission device disposed between an input shaft and an output shaft, the transmission device comprising:

• a planetary gear mechanism having a sun gear, a ring gear, a carrier, and a pinion gear;
• a case housing the planetary gear mechanism;
• a coupling part supported so as to be able to relatively shift with respect to the case;
• and
• a moving mechanism configured to be able to move the coupling part among a first position, a second position, and a third position, wherein:
• one of the sun gear, the ring gear, and the carrier is an input-side rotating body that is connected to the input shaft;
• another of the sun gear, the ring gear, and the carrier is an output-side rotating body that is connected to the output shaft;
• the other one of the sun gear, the ring gear, and the carrier is an intermediate rotating body;
• the case is provided with a first engaging part that is able to be engaged with and disengaged from the coupling part;
• one of the input-side rotating body and the output-side rotating body is provided with a second engaging part that is able to be engaged with and disengaged from the coupling part;
• the intermediate rotating body is provided with a third engaging part that is able to be engaged with and disengaged from the coupling part;
• when the coupling part is in the first position, the coupling part engages the first engaging part and the third engaging part with each other;
• when the coupling part is in the second position, the coupling part engages the second engaging part and the third engaging part with each other;
• and
• when the coupling part is in the third position, the coupling part engages the first engaging part, the second engaging part, and the third engaging part with one another.