Patent ID: 7163387

Claim:
A conjugate pair of intermeshing rotors comprising: a female rotor and a male rotor each including helical lobes having helical crests and intervening grooves, wherein the female rotor and the male rotor each rotate about a parallel axis within a working space of a screw rotor machine, and each of the female rotor and the male rotor includes a tip circle, a pitch circle, and a root circle, wherein a major portion of each of the helical lobes of the female rotor is located inside the pitch circle of the female rotor, and a major portion of each of the helical lobes of the male rotor is located outside the pitch circle of the male rotor, wherein the helical lobes of one of the male rotor and the female rotor follows the intervening grooves of the other of the male rotor and the female rotor to form a continuous sealing line between the male rotor and the female rotor, wherein each of the helical lobes have a leading flank portion and a trailing flank portion, wherein the leading flank portion of the helical lobes of the female rotor have a profile formed from at least one ellipse and the leading flank portion of the helical lobes of the male rotor have a profile formed from at least one ellipse, and wherein the trailing flank portion of the helical lobes of at least one of the female rotor and the male rotor has a profile formed from at least one ellipse.