Differential gear mechanism and method for designing the same

A differential gear mechanism comprising a pair of crown gears and a plurality of pinion gears in mesh with the pair of crown gears, wherein

• a tooth tip surface of each gear tooth of the crown gears includes an inclined portion inclined such that the tooth tip surface approaches a tooth bottom as the tooth tip surface extends from a region adjacent to an axis of the pair of crown gears toward a region adjacent to an outer periphery of the pair of crown gears,
• each pinion tooth bottom surface located between adjacent pinion teeth of the pinion gears includes an inclined portion inclined such that the pinion tooth bottom surface approaches a pinion tooth tip as the pinion tooth bottom surface extends from a region adjacent to the axis of the pair of crown gears toward a region adjacent to the outer periphery of the pair of crown gears, and
• when a plurality of contact lines between the gear tooth and the pinion tooth is defined on either a tooth surface of the gear tooth of the crown gear or a tooth surface of the pinion tooth of the pinion gear at a predetermined angle around an axis of the pinion gear, and the plurality of contact lines and a center line of the tooth tip surface of the gear tooth are projected onto a plane, including the axis of the pair of crown gears, around the axis of the pinion gear, the center line of the tooth tip surface projected onto the plane includes an inclined line passing through a range between two of the contact lines which are selected from the plurality of contact lines projected onto the plane and by which a contact ratio is 1.0 or higher.

A differential gear mechanism comprising a pair of crown gears and a plurality of pinion gears in mesh with the pair of crown gears, wherein

• a tooth tip surface of each gear tooth of the crown gears includes an inclined portion inclined such that the tooth tip surface approaches a tooth bottom as the tooth tip surface extends from a region adjacent to an axis of the pair of crown gears toward a region adjacent to an outer periphery of the pair of crown gears,
• each pinion tooth bottom surface located between adjacent pinion teeth of the pinion gears includes an inclined portion inclined such that the pinion tooth bottom surface approaches a pinion tooth tip as the pinion tooth bottom surface extends from a region adjacent to the axis of the pair of crown gears toward a region adjacent to the outer periphery of the pair of crown gears, and
• when a plurality of contact lines between the gear tooth and the pinion tooth is defined on either a tooth surface of the gear tooth of the crown gear or a tooth surface of the pinion tooth of the pinion gear at a predetermined angle around an axis of the pinion gear, and the plurality of contact lines and a center line of the pinion tooth bottom surface of the pinion gear are projected onto a plane, including the axis of the pair of crown gears, around the axis of the pinion gear, the center line of the pinion tooth bottom surface projected onto the plane includes an inclined line passing through a range between two of the contact lines which are selected from the plurality of contact lines projected onto the plane and by which a contact ratio is 1.0 or higher.

A method for designing a differential gear mechanism including a pair of crown gears and a plurality of pinion gears in mesh with the pair of crown gears, the differential gear mechanism designing method comprising:

• defining, on either a tooth surface of a gear tooth of the crown gear or a tooth surface of a pinion tooth of the pinion gear, a plurality of contact lines between the gear tooth and the pinion tooth at a predetermined angle around an axis of the pinion gear;
• projecting the plurality of contact lines onto a plane, including an axis of the pair of crown gears, around the axis of the pinion gear;
• and
• determining a center line of a tooth tip surface of the gear tooth on the plane such that the center line includes an inclined line passing through a range between two of the contact lines which are selected from the plurality of contact lines projected onto the plane and by which a contact ratio is 1.0 or higher.