STRAIN WAVE GEAR SPEED REDUCER, METHOD FOR MANUFACTURING STRAIN WAVE GEAR SPEED REDUCER AND ACTUATOR FOR LINK MECHANISM FOR INTERNAL COMBUSTION ENGINE

Provided is a strain wave gear speed reducer which can improve both load torque performance and productivity, a method for manufacturing a strain wave gear speed reducer, and an actuator for link mechanism for internal combustion engine. A strain wave gear speed reducer includes; a flexible external gear having a plurality of external teeth each of which has a straight tooth profile; a rigid internal gear disposed on an outer periphery of the flexible external gear, the number of internal teeth of the rigid internal gear being greater than the number of the external teeth, the internal tooth having a straight tooth profile, and a tooth top of the internal tooth having a shape which matches or overlaps with a movement envelope of the external tooth as viewed from a direction of an axis of rotation of the flexible external gear; and a wave motion generator configured to cause the flexible external gear to be deflected in a radial direction so as to be partially engaged with the rigid internal gear, the wave motion generator being configured to rotate about an axis of rotation, thus causing an engagement portion to move in a circumferential direction.