Vibration damping device and power transmission device

A power transmission device for a motor vehicle, the power transmission device comprising:

• a case
• a driving-side gear shaft rotatably supported in the case, and into which a rotational power is input into the driving-side gear shaft, the driving-side gear shaft having a companion flange extending radially therefrom and rotationally integrally fitted to the driving-side gear shaft such that the companion flange rotates when the rotational power is inputted to the driving-side gear shaft;
• a driven-side gear shaft accommodated in the case, the driven-side gear shaft meshes with the driving-side gear shaft and rotates in a decelerative manner;
• an output shaft rotatably driven by the driven-side gear shaft;
• and
• a vibration damping device having:
• a mass body disposed spaced apart from a center axis of the driving-side gear shaft by a certain distance;
• and
• a support portion that rotatably supports the mass body with respect to the companion flange of the driving-side gear shaft and holds a posture of the mass body with respect to the center axis of the driving-side gear shaft in an unrockable manner so that the mass body does not substantially apply an inertial force to the driving-side gear shaft in a direction of rotation of the driving-side gear shaft and substantially applies an inertial force to the driving-side gear shaft only in a translational direction other than the direction of the rotation of the driving-side gear shaft,
• wherein the support portion is constituted by a bearing provided between the companion flange of the driving-side gear shaft and the mass body;
• the bearing is constituted by a plurality of rolling members each of which is rollably supported on an outer periphery side of the companion flange of the driving-side gear shaft and rollably engaged with the mass body.