| 摘要 |
In screw rotors (21, 22) which are each provided with a screw tooth (211, 221) having a spiral addendum surface portion (211a, 221a) and a deddendum surface portion (211c, 221c), and are used as a pair of male and female, between the addendum surface portion (211a, 221a) and deddendum surface portion (211c, 221c) of the screw tooth (211, 221), there is provided the pitch circumference portion (211p, 221p) which forms a predetermined angle range of circular arc having a definite radius rp on an optional transverse cross section, and the radius of the pitch circumference portion (211p, 221p) is set such that, when the opposing rotors are meshed with each other, out of the meshing clearances between the male and female screw teeth (211, 221), the clearance g1 between the pitch circumference portions (211p, 221p) becomes smaller than the clearances g2, g3, g4 between the other portions.
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