Strain wave gearing provided with three-dimensional tooth profile

A strain wave gearing comprising:

• a rigid internally toothed gear;
• a flexible externally toothed gear disposed coaxially inside the internally toothed gear;
• and a wave generator fitted inside the externally toothed gear,
• wherein the externally toothed gear is provided with a flexible cylindrical barrel part, a diaphragm that extends radially from a rear end of the cylindrical barrel part, and external teeth formed on an outer peripheral surface portion on an open-end side of the cylindrical barrel part, the open-end side being a front-end side of the cylindrical barrel part;
• the cylindrical barrel part of the externally toothed gear is flexed in an ellipsoidal shape by the wave generator, and the external teeth meshing with internal teeth of the internally toothed gear at both long-axis-direction end portions of the ellipsoidal shape;
• and
• when the external teeth of the externally toothed gear in an ellipsoidally flexed state are sectioned along a plane that includes a center axis and a long axis of the ellipsoidal shape, an amount of radially outward flexing increases in proportion to a distance from the diaphragm, along a tooth trace direction, from an external-teeth inner end on a diaphragm side toward an external-teeth outer end on an open-end side,
• characterized in that,
• when a cross-section sectioned at an orthogonal plane orthogonal to the tooth trace direction at a prescribed tooth-trace-direction position of the external teeth is set as a reference cross-section, a tooth-trace-direction end of the internal teeth on a side that corresponds to the external-teeth outer end is set as an internal-teeth outer end, and the other end of the internal teeth is set as an internal-teeth inner end:
• a tooth profile contour shape of the external teeth in the reference cross-section is a basic external-teeth tooth profile;
• a tooth profile contour shape of the internal teeth at a position of a cross-section of the internal teeth that corresponds to the reference cross-section is a basic internal-teeth tooth profile capable of meshing with the basic external-teeth tooth profile;
• an internal-teeth tooth profile contour shape at individual tooth-trace-direction positions of the internal teeth is a tooth profile obtained by the basic internal-teeth tooth profile being proportionally reduced only in a tooth thickness direction thereof by a factor that is set in accordance with an amount of flexing of the external teeth at the individual tooth-trace-direction positions;
• the external teeth, when viewed along the tooth trace direction, have a tapered tooth profile of fixed tooth depth in which a root circle gradually increases in size from the external-teeth outer end toward the external-teeth inner end;
• and
• a tooth profile contour of the external teeth at individual tooth-trace-direction positions is a tooth profile obtained by the basic external-teeth tooth profile being proportionally increased only in a tooth thickness direction thereof by a factor that is set in accordance with the amount of flexing at the individual tooth-trace-direction positions.