Patent ID: 8187136

Claim:
A differential gear assembly comprising: ring gear ( 9 ) to which a driving force is inputted from a driving source so as to be rotated; a differential case ( 2 ) configured to be rotated together with the ring gear ( 9 ); a pinion shaft ( 3 ) installed on the differential case ( 2 ), the pinion shaft ( 3 ) being configured to be rotated together with the differential case ( 2 ); pinion gears ( 21 , 22 ) pivotally mounted on the pinion shaft ( 3 ); and side gears ( 23 , 24 ) configured to be meshed with the pinion gears ( 21 , 22 ); wherein: the differential case ( 2 ) includes: (i) a first differential case ( 2 a ) on a first side of the differential case and comprising a pinion shaft installation part ( 10 ) on which the pinion shaft ( 3 ) is installed, the ring gear ( 9 ) and an area ranging from the pinion-shaft installation part ( 10 ) on which the pinion shaft ( 3 ) is installed to the ring gear ( 9 ); and (ii) a second differential case ( 2 b ) on a second side of the differential case opposite to the first side and not comprising the area ranging from the pinion-shaft installation part ( 10 ) on which the pinion shaft ( 3 ) is installed to the ring gear ( 9 ); wherein the first differential case ( 2 a ) is integrally molded from only a low-carbon steel containing less than 0.45% of carbon, by forging or by forging and cutting; wherein the second differential case ( 2 b ) is integrally molded from only a low-carbon steel containing less than 0.45% of carbon, by forging or by forging and cutting; and wherein the first differential case ( 2 a ) and the second differential case ( 2 b ) are bonded to each other by welding to form a weld outside of the area ranging from the pinion-shaft installation part and the ring gear, said area being seamless.