Screw rotor machine rotors and method of making

A female rotor for a screw rotor machine comprising:

• an elongated formed female rotor rotatable about a central longitudinal axis and having a pitch circle centered on such axis;
• a plurality of elongated helical lobes extending longitudinally of said rotor and circumferentially spaced about such pitch circle so as to provide intervening grooves therebetween;
• a major portion of each of said lobes extending generally radially inwardly of such pitch circle;
• the profile of each of said lobes in a plane perpendicular to such axis having a tip portion and respective generally concave leading and trailing flank portions extending intermediate said tip portion and the root portion of the respective adjacent groove;
• the profiles of each of said leading and trailing flank portions consisting of involute curvature extending between said tip portion and a respective intermediate point and traversing said pitch circle, a circular arc portion extending between said respective intermediate points, said circular arc portion consisting of at least two circular arcs of different radii.

A pair of helical rotors for a screw rotor machine comprising:

• a male rotor and a female rotor adapted to be rotatably carried within a casing of said machine on respective parallel axes for intermeshing counterrotation of said male and female rotors on such respective axes,
• said male rotor being rotatable about a central longitudinal axis and having a pitch circle centered on such axis, a plurality of elongated asymmetrical helical lobes extending longitudinally of said rotor and circumferentially spaced about such pitch circle so as to provide intervening grooves therebetween;
• a major portion of each of said lobes extending generally radially outward from such pitch circles, the profile of each of said lobes in a plane perpendicular to such axis having a tip portion and respective, generally convex leading and trailing flank portions extending intermediate said tip portion and the root portion of the respective adjacent groove;
• the profile of said leading flank portion consisting of involute curvature extending between said respective root portion and an intermediate point and traversing such pitch circle, and a circular arc portion extending between said intermediate point and said tip portion, said circular arc portion consisting of at least two circular arcs of different radii;
• and the profile of said trailing flank consisting of involute curvature extending between the other of said respective root portions and said tip portion and traversing said pitch circle, and
• said female rotor being rotatable about a central longitudinal axis and having a pitch circle centered on such axis;
• a plurality of elongated asymmetrical helical lobes extending longitudinally of said rotor and circumferentially spaced about such pitch circle so as to provide intervening grooves therebetween;
• a major portion of each of said lobes extending generally radially inwardly of such pitch circle;
• the profile of each of said lobes in a plane perpendicular to such axis having a tip portion and respective generally concave leading and trailing flank portions extending intermediate said tip portion and the root portion of the respective adjacent groove;
• the profile of each of said leading and trailing flank portions consisting of involute curvature extending between said tip portion and a respective intermediate point and traversing said pitch circle, and a circular arc portion extending between said respective intermediate points, said circular arc portion consisting of at least two circular arcs of different radii, whereby said rotors are adapted to form variable volume working chambers.