Patent ID: 7717818

Claim:
A power transmission apparatus, comprising: a housing extending parallel to an input shaft and being linked to the input shaft; a differential mechanism contained within the housing, the differential mechanism distributing drive force that is inputted from the input shaft via the housing to a first output shaft and a second output shaft; a clutch mechanism for linking the input shaft with either the first or second output shaft; and a driving device for driving the clutch mechanism, wherein the differential mechanism comprises: a ring gear which is provided coaxially with the housing so as to be freely rotatable within the housing; a sun gear which is provided coaxially with the ring gear so as to be freely rotatable within the ring gear; and a planetary gear which is engaged with the ring gear and the sun gear, wherein the planetary gear and an outer peripheral portion of the ring gear each have gear portions which engage to transmit torque through the differential mechanism, wherein the planetary gear is supported by a carrier provided in the housing in such a manner as to be orbital and rotatable, wherein each output shaft is linked to either the ring gear or the sun gear, wherein the clutch mechanism is a friction clutch formed by a plurality of clutch plates, wherein the driving device comprises a piston that extends through said carrier at a location radially outside of said ring gear, and wherein the outer peripheral portion of the ring gear has a diameter sufficiently smaller than the inner circumferential surface of the housing to accommodate clutch plates placed therebetween, and all of said clutch plates are provided on one of the inner circumferential surface of the housing and the outer circumferential surface of the outer peripheral portion of the ring gear.