Patent ID: 7625191

Claim:
A rotary displacement machine comprising: a housing; and at least two twinned rotors of asymmetrical profile, a first rotor and a second rotor being mounted to rotate in the housing about their longitudinal axis, the twinned rotors each comprising a core having at least one helicoidal thread which projects from the core and extends above the core in the manner of a tooth, the helicoidal thread having a first predetermined dimension in a direction radial to the longitudinal axis of the twinned rotors and above the surface of the rotors, wherein the helicoidal thread comprises a first flank of concave shape and a second flank of convex shape which connect at an upper portion of the helicoidal thread, the first flank having the shape of an epicycloidal arc, wherein the first flank has a shape whose position and length of arc are predetermined such that the first flank and the second flank each connect to one of the opposite ends of a connecting segment, which is presented along an entire length of the helicoidal thread and constitutes a flattened helicoidal surface thereby eliminating the presence of a sharp edge, wherein the connecting segment has, in a direction radial to the longitudinal axis of the twinned rotors, a second predetermined dimension, which is a radial component of the connecting segment, of length L such that the ratio of the second dimension over the first dimension ranges between 0.005 and 0.1.