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In a differential device distributing rotational force acting on a differential case to a pair of output shafts, the differential case including an input member and a cover portion, assembling precision of the differential device is enhanced by suppressing strain due to welding and press-fitting. Th

In a differential device distributing rotational force acting on a differential case to a pair of output shafts, the differential case including an input member and a cover portion, assembling precision of the differential device is enhanced by suppressing strain due to welding and press-fitting. The input member includes: a welded portion fitting the cover portion in axial direction and joined by welding; a press-fitted portion located inward of the welded portion in radial direction and axial direction and press-fitted to the cover portion; and a connecting surface connecting the welded portion and the press-fitted portion and forming a space between the connecting surface and the cover portion, the space allowing deformation of the press-fitted portion during press-fitting. The connecting surface includes one end portion continuous to the welded portion and extending outward from the welded portion in radial direction.

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1. A differential device comprising: a differential case; anda differential mechanism housed in the differential case and distributively transmitting rotational force of the differential case to a pair of mutually-independent output shafts,wherein the differential case includes an input member inclu

1. A differential device comprising: a differential case; anda differential mechanism housed in the differential case and distributively transmitting rotational force of the differential case to a pair of mutually-independent output shafts,wherein the differential case includes an input member including an input part which receives the rotational force, an end portion of the input member on at least one side in an axial direction thereof being opened, andat least one cover portion covering the opened end portion of the input member on the one side in the axial direction,the input member includes a welded portion to which the cover portion is fitted in the axial direction of the input member and joined by welding,a press-fitted portion located inward of the welded portion in a radial direction and the axial direction of the input member, the cover portion being press-fitted to the press-fitted portion, anda connecting surface connecting the welded portion and the press-fitted portion and forming a space between the connecting surface and the cover portion, the space allowing deformation of the press-fitted portion during the press-fitting, andthe connecting surface includes one end portion continuous to the welded portion, the one end portion extending outward from the welded portion in the radial direction. 2. The differential device according to claim 1, wherein part of the press-fitted portion and the space are disposed overlapping each other as seen in the radial direction from a center of rotation of the input member. 3. The differential device according to claim 2, wherein the cover portion includes a boss portion concentrically surrounding the output shafts, anda side wall portion connected to the boss portion so as to extend outward in the radial direction from the boss portion,a large-diameter portion and a small-diameter portion are formed in an outer peripheral portion of the side wall portion, the large-diameter portion being fitted to and joined by welding to the welded portion, and the small-diameter portion being continuous to an axial inner end of the large-diameter portion via a step surface and press-fitted into the press-fitted portion,an axial outer end of the press-fitted portion is abutted against or comes close to the step surface, andthe connecting surface includes an inclined portion which gradually separates from the step surface as the connecting surface goes outward in the radial direction from the axial outer end or a vicinity of the axial outer end. 4. The differential device according to claim 1, wherein the cover portion includes a boss portion concentrically surrounding the output shafts, anda side wall portion connected to the boss portion so as to extend outward in the radial direction from the boss portion,a large-diameter portion and a small-diameter portion are formed in an outer peripheral portion of the side wall portion, the large-diameter portion being fitted to and joined by welding to the welded portion, and the small-diameter portion being continuous to an axial inner end of the large-diameter portion via a step surface and press-fitted into the press-fitted portion,an axial outer end of the press-fitted portion is abutted against or comes close to the step surface, andthe connecting surface includes an inclined portion which gradually separates from the step surface as the connecting surface goes outward in the radial direction from the axial outer end or a vicinity of the axial outer end. 5. A differential device which distributively transmits rotational force of an input member to a pair of mutually-independent output shafts, the input member retaining a pinion support portion that supports a pinion and being rotatable together with the pinion support portion, the differential device comprising: a pair of side gears each having a tooth portion placed at an outer peripheral portion thereof in mesh with the pinion and connected to the pair of output shafts, respectively; andat least one cover portion attached to the input member and covering an outside of at least one side gear,wherein the input member includes a welded portion to which the cover portion is fitted in an axial direction of the input member and joined by welding,a press-fitted portion located inward of the welded portion in a radial direction and the axial direction of the input member, the cover portion being press-fitted to the press-fitted portion, anda connecting surface connecting the welded portion and the press-fitted portion and forming a space between the connecting surface and the cover portion, the space allowing deformation of the press-fitted portion during the press-fitting, andthe connecting surface includes one end portion continuous to the welded portion, the one end portion extending outward from the welded portion in the radial direction. 6. The differential device according to claim 5, wherein part of the press-fitted portion and the space are disposed overlapping each other as seen in the radial direction from a center of rotation of the input member. 7. The differential device according to claim 6, wherein the cover portion includes a boss portion concentrically surrounding the output shafts, anda side wall portion connected to the boss portion so as to extend outward in the radial direction from the boss portion,a large-diameter portion and a small-diameter portion are formed in an outer peripheral portion of the side wall portion, the large-diameter portion being fitted to and joined by welding to the welded portion, and the small-diameter portion being continuous to an axial inner end of the large-diameter portion via a step surface and press-fitted into the press-fitted portion,an axial outer end of the press-fitted portion is abutted against or comes close to the step surface, andthe connecting surface includes an inclined portion which gradually separates from the step surface as the connecting surface goes outward in the radial direction from the axial outer end or a vicinity of the axial outer end. 8. The differential device according to claim 5, wherein the cover portion includes a boss portion concentrically surrounding the output shafts, anda side wall portion connected to the boss portion so as to extend outward in the radial direction from the boss portion,a large-diameter portion and a small-diameter portion are formed in an outer peripheral portion of the side wall portion, the large-diameter portion being fitted to and joined by welding to the welded portion, and the small-diameter portion being continuous to an axial inner end of the large-diameter portion via a step surface and press-fitted into the press-fitted portion,an axial outer end of the press-fitted portion is abutted against or comes close to the step surface, andthe connecting surface includes an inclined portion which gradually separates from the step surface as the connecting surface goes outward in the radial direction from the axial outer end or a vicinity of the axial outer end. 9. A differential device which distributively transmits rotational force of an input member to a pair of mutually-independent output shafts, the input member supporting a differential gear support portion that supports a differential gear and being rotatable together with the differential gear support portion, the differential device comprising: a pair of output gears each including a tooth portion placed at an outer peripheral portion thereof in mesh with the differential gear and connected to the pair of output shafts, respectively, andat least one cover portion attached to the input member and covering an outside of at least one output gear,wherein the input member includes a welded portion to which the cover portion is fitted in an axial direction of the input member and joined by welding,a press-fitted portion located inward of the welded portion in a radial direction and the axial direction of the input member, the cover portion being press-fitted to the press-fitted portion, anda connecting surface connecting the welded portion and the press-fitted portion and forming a space between the connecting surface and the cover portion, the space allowing deformation of the press-fitted portion during the press-fitting, andthe connecting surface includes one end portion continuous to the welded portion, the one end portion extending outward from the welded portion in the radial direction,wherein d⁢⁢2/PCD≤3.36·(1z⁢⁢1)23·sin⁡(tan-1⁢z⁢⁢1z⁢⁢2) is satisfied, and Z1/Z2>2 is satisfied, where Z1, Z2, d2 and PCD denote the number of teeth of each of the output gears, the number of teeth of the differential gear, a diameter of the differential gear support portion and a pitch cone distance, respectively. 10. The differential device according to claim 9, wherein part of the press-fitted portion and the space are disposed overlapping each other as seen in the radial direction from a center of rotation of the input member. 11. The differential device according to claim 10, wherein the cover portion includes a boss portion concentrically surrounding the output shafts, anda side wall portion connected to the boss portion so as to extend outward in the radial direction from the boss portion,a large-diameter portion and a small-diameter portion are formed in an outer peripheral portion of the side wall portion, the large-diameter portion being fitted to and joined by welding to the welded portion, and the small-diameter portion being continuous to an axial inner end of the large-diameter portion via a step surface and press-fitted into the press-fitted portion,an axial outer end of the press-fitted portion is abutted against or comes close to the step surface, andthe connecting surface includes an inclined portion which gradually separates from the step surface as the connecting surface goes outward in the radial direction from the axial outer end or a vicinity of the axial outer end. 12. The differential device according to claim 11, wherein Z1/Z2≧4 is satisfied. 13. The differential device according to claim 11, wherein Z1/Z2≧5.8 is satisfied. 14. The differential device according to claim 10, wherein Z1/Z2≧4 is satisfied. 15. The differential device according to claim 10, wherein Z1/Z2≧5.8 is satisfied. 16. The differential device according to claim 9, wherein the cover portion includes a boss portion concentrically surrounding the output shafts, anda side wall portion connected to the boss portion so as to extend outward in the radial direction from the boss portion,a large-diameter portion and a small-diameter portion are formed in an outer peripheral portion of the side wall portion, the large-diameter portion being fitted to and joined by welding to the welded portion, and the small-diameter portion being continuous to an axial inner end of the large-diameter portion via a step surface and press-fitted into the press-fitted portion,an axial outer end of the press-fitted portion is abutted against or comes close to the step surface, andthe connecting surface includes an inclined portion which gradually separates from the step surface as the connecting surface goes outward in the radial direction from the axial outer end or a vicinity of the axial outer end. 17. The differential device according to claim 16, wherein Z1/Z2≧4 is satisfied. 18. The differential device according to claim 16, wherein Z1/Z2≧5.8 is satisfied. 19. The differential device according to claim 9, wherein Z1/Z2≧4 is satisfied. 20. The differential device according to claim 9, wherein Z1/Z2≧5.8 is satisfied.