Patent ID: 7827882
Filing Date: 2010-11-09
Classification: F16H,Y10T

Abstract:
1. A differential gear unit which divides an input driving force into a first output and a second output and permits a difference between a rotational speed of the first output and a rotational speed of the second output, comprising: a casing that defines an internal space and an opening communicated with the internal space and that is rotatable in a given rotational direction and in a rotational direction opposite to the given rotational direction, the casing including an input portion in which the driving force is input, the casing being configured such that fatigue life of the casing when the driving force is repeatedly input in the input portion in the given rotational direction is greater than fatigue life of the casing when the driving force is repeatedly input in the input portion in the rotational direction opposite to the given rotational direction, rotation in the given direction being a rotation around a longitudinal rotational axis of the differential gear casing; a dividing mechanism that is provided in the internal space, and includes a pinion and that divides the driving force into the first output and the second output; and a support member that is provided so as to contact the casing and so as to support the dividing mechanism and that includes a pinion shaft that supports the pinion such that the pinion can rotate on its axis and which makes the pinion revolve around a center of the casing, wherein the fatigue life of the casing is adjusted by making a shape of the opening asymmetrical with respect to the longitudinal rotational axis of the casing, wherein the opening is in a basically elliptical shape having a round shape at each of corner portions, the round shapes of adjacent corner portions are different from each other, and a radius of the round shape of each corner portion continuously changes, wherein the curvature radii of each of the corner portions is different than a curvature of radii of a respectively adjacent corner portion, wherein a portion at which the fatigue life of the casing is increased is a first corner portion at which the tensile stress is generated when forward driving force is input, wherein the first corner portion has increased strength relative to other corner portions of the opening of the casing, wherein a curvature radius of the round shape of the first corner portion of the opening, where a tensile stress is generated when the driving force is input in the given rotational direction, is larger than a curvature radius of the round shape of a second corner portion of the opening, where a compression stress is generated when the driving force is input in the given rotational direction, wherein the fatigue life of the casing is also adjusted by heat treatment, and wherein the first corner portion of the opening of the casing is a heat treated corner portion.