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.

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.

The present invention relates to a toothed belt including: a back portion; a tension member embedded in the back portion in a belt longitudinal direction and including a twisted cord including a steel fiber; a plurality of belt teeth formed on an inner peripheral side of the back portion along the belt longitudinal direction; and a cover layer provided between the tension member and a belt tooth bottom formed between the belt teeth, in which the cover layer has a thickness in a range of 0.2 mm to 1.0 mm, and the back portion, the belt teeth, and the cover layer are integrally formed of a thermoplastic elastomer.

A gearbox (1), in particular coaxial gearbox, includes a ring gear having an internal toothing (3); a tooth carrier (5) having guides (7) which are aligned radially in terms of a rotation axis of the gearbox; teeth (9) which, for engaging with the internal toothing (3), are received in the guides (7), wherein the teeth (9) are mounted in the guides (7) displaceable in the direction of their longitudinal axis (11) relative to the tooth carrier (5); and a cam disk (13) which is rotatable about the rotation axis and is operatively connected to the teeth (9); wherein the teeth (9) have in each case a tooth flank (17) which is at least partially curved along a width curve (51) extending over a width (41) of the tooth flank (17).

A rolling gear rack mechanism with tooth profile having hyperbolic tooth line structure based on a parabolic function includes a gear and a rack. An end face tooth profile of the gear and an end face tooth profile of the rack are composed of an end face working tooth profile curve and a tooth root transition curve, and the end face tooth profile of the gear and the end face tooth profile of rack are both symmetrical left and right. The end face working tooth profile curve of the gear and the end face working tooth profile curve of the rack are parabolic, and a tooth surface of the gear and a tooth surface of the rack have a hyperbolic tooth line structure. At least one pair of gear teeth meshing points of the gear and the rack are located at nodes to achieve rolling meshing contact.