Patent ID: 7866966

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 chambers, 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: (a) determining a maximum ideal twist angle for said lobe as a function, partially, of said number N of lobes on said rotor, said maximum ideal twist angle being the largest possible twist angle for each rotor lobe without opening a leak path from the outlet port to the inlet port, wherein a total maximum seal time is a sum of an inlet seal time and a transfer seal time, and wherein the transfer seal time is equal to zero at the maximum ideal twist angle; (b) 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; and (c) selecting a twist angle corresponding to a desired transfer seal time while keeping the total maximum seal time constant.