Patent ID: 7488164

Claim:
A method of designing a rotor for a Roots-type blower comprising a housing defining first and second transversely overlapping cylindrical chambers, said housing including a first end wall defining an inlet port, and a second end wall, said housing defining an outlet port formed at an intersection of said first and second chambers, and adjacent said second end wall; said blower including first and second meshed, lobed rotors disposed, respectively, in said first and second chambers; each rotor including a plurality N of lobes, each lobe having first and second axially facing end surfaces sealingly cooperating with said first and second end walls, respectively, and a top land sealingly cooperating with said cylindrical cambers, each lobe having its first and second axially facing end surfaces defining a twist angle, and each lobe defining a helix angle; said method of designing a rotor comprising the steps of: determining a maximum ideal twist angle for said lobe as a function, partially, of said number N of lobes on said rotor; and determining a helix angle for each lobe as a function of said twist angle and an axial length between said first and second axially facing end surfaces of said lobe, said determining of said helix angle comprises the determining of a Lead, wherein said Lead is a function of said maximum ideal twist angle and said axial length, said helix angle then being determined in accordance with the equation: Helix Angle ( HA )=(108/π*arctan ( PD /Lead)), wherein PD is the pitch diameter of the lobe.