| 主权项 |
1. A strain wave gearing comprising a rigid internally toothed gear, a flexible externally toothed gear disposed within the rigid internally toothed gear, and a wave generator fitted within the flexible externally toothed gear, the flexible externally toothed gear comprising a flexible cylindrical barrel part and a circular diaphragm extending radially from a trailing end of the cylindrical barrel part, and external teeth formed on a region of a leading end opening part of the cylindrical barrel part being flexed by the wave generator into an ellipsoidal shape from the trailing end part on the diaphragm side to the leading end part on an opening side so that a degree of flexing substantially proportional to a distance from the diaphragm is produced; wherein in the strain wave gearing:
the rigid internally toothed gear is a modified spur gear having a module m; the flexible externally toothed gear is a modified conical gear having a module m; a number of teeth of the flexible externally toothed gear is 2n less than a number of teeth of the rigid internally toothed gear, where n is a positive integer; the flexible externally toothed gear is ellipsoidally deformed by the wave generator, whereby a rim-neutral circle of the external teeth of the flexible externally toothed gear is deformed into an ellipsoidal rim-neutral curve, and a degree of radial flexing with respect to the rim-neutral circle in a position on a major axis of the rim-neutral curve is κ mn, where K is a deflection coefficient greater than 1; an internal tooth base tooth profile of the rigid internally toothed gear and an external tooth base tooth profile of the flexible externally toothed gear are involute tooth profiles having a pressure angle α of less than 20°; there are determined movement loci of the external teeth of the flexible externally toothed gear in relation to the internal teeth of the rigid internally toothed gear, obtained when rack meshing is used to approximate meshing with the rigid internally toothed gear in a transverse cross-section at each tooth-trace direction position of the external teeth of the flexible externally toothed gear; when, taking a transverse cross-section set in a desired position of the external teeth of the flexible externally toothed gear in the tooth trace direction to be a main cross-section, the movement locus obtained in the main cross-section is called a first movement locus, and the movement locus obtained in each transverse cross-section of the external teeth other than the main cross-section is called a second movement locus, and a tangent drawn on a loop-shaped apex of the first movement locus at which an angle formed with the major axis of the rim-neutral curve is the pressure angle α is called a first tangent, and a tangent drawn on a loop-shaped apex of the second movement locus at which an angle formed with the major axis of the rim-neutral curve is the pressure angle α is called a second tangent, a tooth profile of each transverse cross-section of the external teeth other than the main cross-section is a modified tooth profile modified to a base tooth profile comprising the involute tooth profile such that the second tangent coincides with the first tangent when viewed along a tooth trace direction of the external teeth; a revised Goodman line AB connecting a point A on the vertical axis (O, σA) representing an alternating stress limit (σA) of a steel that is a material of the flexible externally toothed gear and a point B on the horizontal axis (σB, O) representing a center value (σB) between a yield stress and a tensile strength of the steel is drawn in planar coordinates to produce a revised Goodman diagram; and a root rim thickness of the external teeth of the flexible externally toothed gear is determined such that a coordinate point P (σn/2, σb+σn/2), in accompaniment with the ellipsoidal deformation of the flexible externally toothed gear, falls within a triangular acceptable range enclosed by the revised Goodman line AB, the horizontal axis, and the vertical axis of the revised Goodman diagram, the vertical axis being the stress amplitude (σb+σn/2), which is the sum of a flexural stress (σb) derived from flexing of the major axis appearing on a surface of the root rim and half the tensile stress (σn) generated by a transmission torque on the root rim, and the horizontal axis being an average stress (σn/2) of half the tensile stress. |
