Vehicle power transmission device

1. A vehicle power transmission device comprising: a cylindrical input shaft; a planetary gear type speed reducer disposed concentrically to the input shaft to reduce and output rotation input to the input shaft; and a differential gear device disposed adjacently to the input shaft in a shaft center direction, the differential gear device being rotationally driven by the speed reducer to transmit a drive force to a pair of axles disposed on the shaft center while allowing a rotational difference between the axles,

the speed reducer including a sun gear that is fit with a shaft end portion of the input shaft in a relatively non-rotatable manner,

the sun gear being prevented from relatively moving toward the differential gear device by an annular snap ring fit and attached to an annular snap ring groove formed on an outer circumferential surface of the shaft end portion of the input shaft on the differential gear device side of the sun gear,

the differential gear device including a differential case having a cylindrical end portion formed on the sun gear side or a member fixed thereto that is extended to the outer circumferential side of the snap ring, the differential case having a radial distance of an annular gap formed between the cylindrical end portion or the member fixed thereto and the snap ring set smaller than a groove depth of the snap ring groove,

the member fixed to the cylindrical end portion being a cored bar of an oil seal fixed and attached to the inner circumferential surface of the cylindrical end portion for forming an oil-tight seal between the inner circumferential surface of the cylindrical end portion and the outer circumferential surface of the shaft end portion of the input shaft.

2. The vehicle power transmission device of claim 1 , wherein the input shaft is rotationally driven by an electric motor disposed on the shaft center.

3. The vehicle power transmission device of claim 1 , comprising an oil seal that forms an oil-tight seal between an inner circumferential surface of the cylindrical end portion of the differential case and the outer circumferential surface of the shaft end portion of the input shaft, wherein

the radial distance is set such that the snap ring abuts on the cylindrical end portion or the member fixed thereto such that a deformation amount of the oil seal does not exceed a predetermined allowable deformation range even when the differential case and the input shaft are relatively moved in a radial direction.

4. The vehicle power transmission device of claim 3 , wherein the input shaft is rotationally driven by an electric motor disposed on the shaft center.

5. The vehicle power transmission device of claim 3 , wherein the cylindrical end portion has a gap reducing portion that reduces a volume of an annular gap formed between the inner circumferential surface of the cylindrical end portion and the outer circumferential surface of the shaft end portion of the input shaft to decrease an amount of lubricant oil retained in the gap.

6. The vehicle power transmission device of claim 5 , wherein the input shaft is rotationally driven by an electric motor disposed on the shaft center.

7. The vehicle power transmission device of claim 1 , wherein the cylindrical end portion has a gap reducing portion that reduces a volume of an annular gap formed between the inner circumferential surface of the cylindrical end portion and the outer circumferential surface of the shaft end portion of the input shaft to decrease an amount of lubricant oil retained in the gap.

8. The vehicle power transmission device of claim 7 , wherein the input shaft is rotationally driven by an electric motor disposed on the shaft center.