Power transmission device

A power transmission device comprising a planetary gear mechanism and a case housing the planetary gear mechanism,

• wherein the planetary gear mechanism comprises:
• a sun gear fixed to a shaft configured to rotate;
• a ring gear located coaxially with the sun gear and fixed to the case;
• a planetary gear meshed with the sun gear and the ring gear;
• and
• a carrier configured to rotatably support the planetary gear, the carrier being located coaxially with the sun gear and supported rotatably with respect to the case,
• wherein the sun gear and the ring gear are each a helical gear,
• a helix angle of teeth of the sun gear and a helix angle of teeth of the ring gear are set so that a thrust force acting on the sun gear and a thrust force acting on the ring gear are in opposite directions,
• the power transmission device further comprises a load transmission path between the sun gear and the ring gear, through which the thrust force acting on the sun gear and the thrust force acting on the ring gear are transmitted, and
• the load transmission path includes at least a portion of the carrier.