Patent ID: 7798794

Claim:
A screw pump comprising: a housing; and a first screw rotor and a second screw rotor received in the housing, wherein the first screw rotor and the second screw rotor rotate in a direction in which the first and second screw rotors become engaged with each other, a fluid being drawn into the housing and then discharged to the exterior through rotation of the first screw rotor and the second screw rotor, wherein a cross section of a tooth profile of the first screw rotor and a cross section of a tooth profile of the second screw rotor perpendicular to the respective rotor axes each include a first circular arc portion, a second circular arc portion, a first curved portion, and a second curved portion, the first circular arc portion and the second circular arc portion each having a first end and a second end, a radius of curvature of the second circular arc portion being smaller than a radius of curvature of the first circular arc portion, the first curved portion connecting the first end of the first circular arc portion to the first end of the second circular arc portion, the second curved portion connecting the second end of the first circular arc portion to the second end of the second circular arc portion, wherein the first curved portion of the first screw rotor is a first trochoidal curve created by the first end of the first circular arc portion of the second screw rotor, wherein the second curved portion of the first screw rotor includes an involute curve and a second trochoidal curve that extend continuously from each other, the involute curve extending continuously from the second end of the first circular arc portion of the first screw rotor, the second trochoidal curve being created by the second end of the first circular arc portion of the second screw rotor, wherein the first curved portion of the second screw rotor is a first trochoidal curve created by the first end of the first circular arc portion of the first screw rotor, and wherein the second curved portion of the second screw rotor includes an involute curve and a second trochoidal curve that extend continuously from each other, the involute curve extending continuously from the second end of the first circular arc portion of the second screw rotor, the second trochoidal curve being created by the second end of the first circular arc portion of the first screw rotor.