Patent ID: 6893238

Claim:
A displacement-type ring gear machine (pump or motor) including: a) a casing defining a gear chamber comprising at least one supply port and at least one discharge port for a working fluid; b) an internal gear accommodated in the gear chamber, the internal gear being rotatable about an axis of rotation and comprising an external toothing; and c) a gear comprising a rolling circle axis eccentric to the axis of rotation of the internal gear and an internal toothing about the rolling circle axis having at least one tooth more than the external toothing and meshing with the external toothing so as to form expanding and contracting fluid cells which direct the working fluid from the at least one supply port to the at least one discharge port when one of the gears performs a rotational movement relative to the other, d) at least one of the toothings having tips or roots comprising a profile derived from a cycloid, which is generated by the rolling action of a pitch circle on a fixed circle, e) and the meshing toothings comprising a radial clearance and a tangential clearance, wherein f) the tangential clearance is smaller than the radial clearance, g) and the profile of the tips or roots of the at least one of the toothings is formed by the locus of a point on the circumference of a pitch circle whose radius becomes continuously smaller from the two flank portions to the vertex portion in the case of the tips and becomes continuously larger in the case of the roots.