A plastic helical gear has a three-dimensional tooth surface modification section on a tooth surface of each of involute-shaped teeth. The three-dimensional tooth surface modification section is a combined surface of a tooth top modification surface and an arc crowning surface. The tooth top modification surface is gradually reduced in tooth thickness from a position between a tooth top and a tooth root toward the tooth top. The arc crowning surface is gradually reduced in tooth thickness from a position between one end in the tooth width direction and the other end in the tooth width direction toward both ends in the tooth width direction. A line extending from an intersection point P0 between the starting position of the tooth top modification surface and the apex position of the arc crowning surface to the tooth root is aligned with a line on the tooth surface of the involute-shaped tooth.

A gearbox assembly includes a first gear and a second gear. The first gear includes a plurality of first gear teeth. The second gear includes a plurality of second gear teeth. The plurality of first gear teeth and the plurality of second gear teeth mesh with each other as the first gear and the second gear rotate. A profile shape of at least one first gear tooth of the first gear is characterized by a total profile modification between 66 micrometers and 120 micrometers.

A pressure angle of the worm is set to be greater than a pressure angle of the worm wheel so that a maximum number of meshing teeth becomes smaller than or equal to n (where n is a natural number) with respect to the speed reduction mechanism in which a number of meshing teeth is always n+1 or changed between n+1 and n by rotation under a condition in which the pressure angles of the worm and the worm wheel are the same with respect to each other.

The dedendum tooth profiles of the internal teeth and external teeth of a strain wave gearing are prescribed by a first homothetic curve BC and a second homothetic curve AC obtained from a curve segment from a point A, at which the angle formed by the tangent to a movement locus Mc when meshing is approximated by rack meshing and the major axis is A, to a low point B. The dedendum tooth profile of the internal teeth is prescribed by a curve formed on the internal teeth in the course of the addendum tooth profile of the external teeth moving from an apex of the movement locus to point A. The dedendum tooth profile of the external teeth is prescribed by a curve formed on the external teeth when the addendum tooth profile of the internal teeth moves from the apex to arrive at point A.

Method for generating a tooth space profile (5) between two teeth (4) of a wheel (1) engaging with a roller (3) pinion (2) in a reference plane perpendicular to a central axis (X1) whose intersection with the reference plane defines a centre (C), comprising the step of defining a nominal tooth space with symmetrical first and second profiles so that the space is suitable for receiving a roller which comes into contact, without clearance, with the facing active portions of the first and second profiles at the level of a primitive diameter. The method of the invention comprises the steps of deforming the bottom portion (12) of the first profile so that the bottom point is brought nearer to the centre by an amount equal to a given radial clearance, and moving the first profile angularly through a given angular half-clearance around the centre to shift it away from the radial axis.

Provided is an external meshing cylindrical gear pair with a constant meshing characteristics constructed tooth pair. The external meshing cylindrical gear pair with a constructed tooth pair includes a cylindrical gear I with a constructed tooth pair and a cylindrical gear II with a constructed tooth pair based on conjugate curves. In the present disclosure, normal tooth profile curves of the cylindrical gear I with a constructed tooth pair and the cylindrical gear II with a constructed tooth pair are continuous combined curves with the same curve shape, which facilitates machining by the same cutter. A common normal at an inflection point or a tangent point of the continuous combined curve passes through a pitch point of the gear pair, and a position of the inflection point or the tangent point can be adjusted according to an actual demand. A contact ratio is designed as an integer.

A differential for use in a vehicle drive train having a pair of rotary members including a gear case that is operatively supported in driven relationship with respect to the drive train and a pair of side gears mounted for rotation with a respective one of the rotary members in the gear case. The differential also includes a spider mounted for rotation with the gear case and at least one pair of pinion gears mounted for rotation with the spider and in meshing relationship with the side gears. The side gears have concave teeth flanks and the pinion gears have convex teeth flanks to increase power density through the differential.

Gearbox (1) having a tooth carrier (40) for receiving teeth (7) of a gear ring that are disposed about a rotation axis (5) of the gearbox, wherein the teeth (7) are disposed in the tooth carrier (11) so as to be displaceable and guided in the radial direction, a cam disk (20) which is rotatable about the rotation axis (5) and for driving the teeth (7) in the radial direction has a cam curvature that is variable over the circumference, wherein bearing segments (24) which are mounted so as to slide on the cam disk (20) are disposed between the teeth (7) and the cam disk (20), and wherein the bearing segments (24) have a contact region which has a concave curvature and is disposed so as to be centric on a running surface that faces the cam disk (20), wherein the concave curvature is larger than the smallest cam curvature of the cam disk, and smaller than the largest cam curvature of the cam disk.

A gearbox comprising an internal-external gear pair having a small tooth-difference, the internal-external gear pair comprising: an internal gear arranged about an internal gear axis and having a first number of internal gear teeth; and an external gear having an external gear axis arranged to orbit the internal gear axis and having a second number of external gear teeth, the external gear being arranged to engage with the internal gear teeth; wherein the small tooth-difference is less than a fifth of the number of internal gear teeth; and wherein the internal gear teeth and the external gear teeth have an involute shape with no profile shift, or with a profile shift below a value at which the working pressure angles of the internal-external gear pair would exceed, by more than 20%, a nominal pressure angle of the internal-external gear pair if no profile shift were applied.

A gearbox assembly includes a first gear and a second gear. The first gear includes a plurality of first gear teeth. The second gear includes a plurality of second gear teeth. The plurality of first gear teeth and the plurality of second gear teeth mesh with each other as the first gear and the second gear rotate. A profile shape of at least one first gear tooth of the first gear is characterized by a total profile modification between 66 micrometers and 120 micrometers.