| 摘要 |
With a wave gear device, the gears employ homothetic curve tooth profiles AD, BE. Furthermore, a transposition is applied to the external teeth along the tooth trace such that the movement loci M2, M3 of the external teeth in a section perpendicular to the axis, from the aperture end to the inner end, share the movement locus M1 of the aperture end and bottom portion thereof, and a continuous meshing of the teeth in the tooth trace direction is achieved. Furthermore, the tooth bottom rim thickness of the aperture end of the external teeth is optimized using a modified Goodman diagram, and a tooth bottom rim thickness which takes into account the relationship between the tooth profile and the transmitted torque from the aperture end to the inner end is employed for the flexible external gear. |
| 主权项 |
1. A wave gear device, comprising:
a rigid internal gear of annular shape; a flexible external gear disposed coaxially to an inside thereof; and a wave generator fitted to an inside thereof; the flexible external gear being provided with a flexible cylindrical barrel part, a diaphragm radially extending from a rear end of the cylindrical barrel part, and external teeth formed on an outside peripheral surface part at a front end opening side of the cylindrical barrel part; the external teeth of the flexible external gear being flexed into ellipsoidal shape by the wave generator, and meshing with internal teeth of the rigid internal gear at both ends in a major axis direction of an ellipsoidal curve thereof; the external teeth of the flexible external gear flexed into ellipsoidal shape having increasing amounts of flexure, substantially proportional to a distance from the diaphragm, from a diaphragm side towards a front end opening side along a tooth trace direction thereof; the external teeth of the flexible external gear and the internal teeth of the rigid internal gear both being spur gears of module m; a number of teeth of the flexible external gear being set to 2n fewer than a number of teeth of the rigid internal gear, where n is a positive integer; in an axis-perpendicular cross section at any location in the tooth trace direction of the external gear, an amount of flexure in a radial direction by the external teeth at a major axis location in an ellipsoidal rim neutral line, with respect to a rim neutral line prior to flexure of the external teeth into ellipsoidal shape, being 2 κmn, where κ is a flexural coefficient; the flexural coefficient of an opening end cross section being κ=1 when, in the tooth trace direction of the external teeth of the flexible external gear, an axis-perpendicular cross section at an end on the front end opening side is designated as an opening end cross section, and an axis-perpendicular cross section at an end on the diaphragm side as an inner end cross section; an opening end tooth profile shape in the opening end cross section of the external teeth being defined by an external tooth addendum tooth profile section of convex curving shape, an external tooth linear tooth profile section continuous therewith, an external tooth deddendum tooth profile section of concave curving shape continuous therewith, and an external tooth root section continuous therewith; a tooth profile shape of a section of the external teeth extending from the opening end cross section to the inner end cross section being a shifted tooth profile shape in which minus tooth profile shifting is applied to the opening end tooth profile shape, in order to avoid interference with the internal teeth; a tooth profile shape of the internal teeth in an axis-perpendicular cross section being defined by an internal tooth addendum tooth profile section of convex curving shape, an internal tooth linear tooth profile section continuous therewith, an internal tooth deddendum tooth profile section of concave curving shape continuous therewith, and an internal tooth root section continuous therewith; meshing of the external teeth and the internal teeth being approximated by rack meshing, and movement loci of the external teeth of the flexible external gear with respect to the internal teeth of the rigid internal gear in association with rotation of the wave generator being derived in axis-perpendicular cross sections taken in the tooth trace direction of the external teeth; a first homothetic curve BC being derived by homothetic transformation by a ratio λ at a homothetic center at a point B, the homothetic ratio being λ<1, of a curve segment AB extending from a point A of an apical portion in the movement locus M1 obtained in the opening end cross section, to a point B in a next bottom portion; a second homothetic curve CA being derived through homothetic transformation, by a ratio (1−λ)/λ at a homothetic center at an end point C, of a curve B′C obtained by rotating the first homothetic curve BC by 180 degrees about the end point C of the first homothetic curve BC; a straight line L being drawn to intersect the curve CA at a pressure angle α, and a curve segment AD being derived between the end point A of the curve CA and an intersection point D with the straight line L; the external tooth addendum tooth profile section being defined by the curve segment AD; the external tooth linear tooth profile section being defined by a linear segment extending from the intersection point D in the straight line L; the external tooth deddendum tooth profile section being defined by a concave curve connecting the external tooth linear tooth profile section and the external tooth root section which is defined by a predetermined external tooth root curve, so as to ensure a predetermined radial clearance of the external tooth linear tooth profile section with respect to the internal teeth; a straight line L being drawn to intersect the first homothetic curve BC at the pressure angle α, and a curve segment BE being derived between an end point B in the first homothetic curve BC and an intersection point E with the straight line L; the internal tooth addendum tooth profile being defined by the curve segment BE; the internal tooth linear tooth profile section being defined by a linear segment extending from the intersection point E in the straight line L; on a same plane, a straight line being drawn to connect a point A at which a fatigue limit of alternating stress of steel constituting a material of the flexible external gear is plotted on a vertical axis, and a point B at which a central value of yield stress and tensile strength of the steel is plotted on a horizontal axis, to create a modified Goodman diagram; root rim thickness tm of the opening end cross section of the flexible external gear being determined in such a way that the location of the coordinate points obtained by plotting, on the vertical axis, of stress amplitude expressed as the sum of bending stress produced by flexure on the major axis appearing on the surface of the root rim at the opening end of the flexible external gear in association with ellipsoidal deformation thereof and 1/2 of the tensile stress arising at the root rim due to load torque, and plotting, on the horizontal axis, of the average stress of ½ of the tensile stress, lies on the midpoint M of the line segment AC obtained by designating as C the intersection point of the straight line AB and the straight line passing through the origin at 45 degree angle to the horizontal axis in the modified Goodman diagram; and at individual locations from the opening end to the inner end of the external teeth, root rim thickness in each axis-perpendicular cross section being determined in such a way that the location of coordinate points obtained by plotting, on the vertical axis, of stress amplitude expressed as the sum of bending stress produced by flexure and ½ the tensile stress arising at the root rim at the location in question due to transmission load torque, and plotting, on the horizontal axis, of the average stress of ½ of the tensile stress in question, lies to the right side of the midpoint M on the modified Goodman diagram. |
