| 摘要 |
A screw rotor for use in screw compressors and screw vacuum pumps comprises a pair of rotors including a male rotor and a female rotor. These rotors have helical lobes in an axial direction and mesh with each other to form a compression chamber. Depending upon a lobe configuration of the rotors, suction pressure and discharge pressure, a negative torque for self-rotation as well as a positive torque opposing to rotation due to a compression action is generated on the female rotor in operation. This phenomenon generates when a value obtained by integrating a torque acting on the female rotor over an entire cross section in an axial direction of the rotors becomes negative. When the negative torque is generated, noises due to tooth separating vibration is caused. Then, a lobe profile is defined such that a magnitude of the negative torque is smaller than that of the positive torque in respective cross sections of the female rotor. That is, a relationship between a radius of a point of contact on a leading surface side of the female rotor and a radius of a point of contact on a trailing surface side or curvatures of the rotors are such that the negative torque is not generated on the lobe profile.
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