Patent ID: 7744356
Filing Date: 2010-06-29
Classification: F04C

Abstract:
1. A screw vacuum pump comprising a pair of male and female unequal lead screw rotors, wherein said male and female unequal lead screw rotors include equal lead portions having a lead angle equal to an inlet-side lead angle and formed on an inlet side thereof; equal lead portions having a lead angle equal to a discharge-end lead angle and formed on a discharge side thereof; unequal portions having a lead angle continuously decreasing from the inlet-side lead angle to the discharge-end lead angle and formed between the equal lead portions formed on the inlet side and the equal lead portions formed on the discharge side; and engagement between the male and female lead screw rotors is formed at a position different from each of gear engagement pitch circles, said circles being determined by a distance between axes of said male and female rotors and the numbers of teeth of engagement gears of said male and female rotors, each of said unequal lead portions having a length longer than that of each of said equal lead portions along an axis of said pair of male and female rotors.