| 摘要 |
A roots type fluid machine includes a housing, a pair of parallel rotary shafts and two-lobe rotors. Each rotor includes two lobe portions and two well portions. Each lobe portion has a profile of convex arc with a radius R and each well portion has a profile of concave arc which is an envelope of the convex arc of the lobe portion. The rotor has a configuration defined by a curve which includes the convex arc, the concave arc and further an involute curve with a base radius r between the convex and concave arcs. The base radius r is set in a range L/(2√{square root over (2)<r<0.3(√{square root over (2)L where distance between axes of the rotary shafts is L, and the radius R is set in a range {(√{square root over (2)/16}piL<R<{(27-5√{square root over (2)/56}L.
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