Screw Rotor and Screw Fluid Machine

Abstract

The object of the invention is to provide a screw type fluid machine in which leak of gas is kept in constant, in other words, in which a gap between the screw rotors is kept substantially in constant in a discharging chamber during operation. In a screw type fluid machine, screw rotor having a cross-sectional shape ( 805 ) of a tooth profile with respect to an axial direction thereof includes an arc ( 1 ) forming a deddendum portion, and an arc ( 3 ) forming an outer circumferential portion, wherein one ( 5 ) of two curves connecting the outer circumferential portion and the deddendum portion is defined by a trochoid curve created based on a point on an outer circumference of a mating screw rotor and the other of these two curves, which is divided equally into two sections constituted by a section between a pitch circle and the outer circumferential portion and a section between the pitch circle and the deddendum portion, is defined by a predetermined curve for one ( 7 ) of the sections and a fitting curve for the other ( 9 ) of the sections that is created so as to correspond to the predetermined curve for the one of the sections divided equally into two in the mating screw rotor during meshing.

1 . A screw rotor having a cross-sectional shape of a tooth profile with respect to an axial direction thereof comprising:
 an arc forming a deddendum portion;   an arc forming an outer circumferential portion; and   two curves connecting the outer circumferential portion and the deddendum portion, characterized in that one of said two curves connecting the outer circumferential portion and the deddendum portion is defined by a trochoid curve created based on a point on an outer circumference of a mating screw rotor and the other of said two curves, which is divided equally into two sections constituted by a section between a pitch circle and the outer circumferential portion and a section between the pitch circle and the deddendum portion, is defined by a predetermined curve for one of the sections and a fitting curve for the other of the sections that is created so as to correspond to the predetermined curve for the one of the sections divided equally into two in the mating screw rotor during meshing.   
   
   
       2 . A screw rotor having a cross-sectional shape of a tooth profile with respect to an axial direction thereof comprising:
 an arc forming a deddendum portion;   an arc forming an outer circumferential portion; and   two tooth profile curves connecting the outer circumferential portion and the deddendum portion, characterized in that one of the tooth profile curves connecting the outer circumferential portion and the deddendum portion is defined by such a tooth profile curve that a transfer chamber isolated from other spaces is formed without interfering with a meshing portion of the mating screw rotor, and the other of the tooth profile curves, which is divided equally into two sections constituted by a section between a pitch circle and the outer circumferential portion and a section between the pitch circle and the deddendum portion, is defined by a predetermined curve for one of the sections and a fitting curve created so as to correspond to the predetermined curve for the one of the sections divided equally into two in the mating screw rotor during meshing.   
   
   
       3 . A screw rotor according to  claim 1 , characterized in that the predetermined curve portion that is defined for one of the sections equally divided into two is formed by an arc and a straight line. 
   
   
       4 . A screw rotor according to  claim 1 , characterized in that the predetermined curve portion is formed by a sine curve. 
   
   
       5 . A screw type fluid machine comprising:
 a pump housing having a suction port and a discharge port; and   a pair of screw rotors rotatably mounted in the pump housing so as to be rotated while meshing with each other, wherein a plurality of transfer chambers are formed among the pump housing and the pair of the screw rotors so as to be partitioned from one another by meshing portions of the screw rotors and to be transferred from a suction side to a discharge side in accordance with rotation of the screw rotors,   characterized in that   a cross sectional shape of a tooth profile of the screw rotors with respect to an axial direction thereof includes an arc forming a deddendum portion;   an arc forming an outer circumferential portion; and   two curves connecting the outer circumferential portion and the deddendum portion,   wherein one of said two curves connecting the outer circumferential portion and the deddendum portion is defined by a trochoid curve created based on a point on the mating screw rotor and   the other of said two curves, which is divided equally into two sections constituted by a section between a pitch circle and the outer circumferential portion and a section between the pitch circle and the deddendum portion, is defined by a predetermined curve for one of the sections and a fitting curve for the other of the sections that is created so as to correspond to the predetermined curve for the one of the sections divided equally into two in the mating screw rotor during meshing.   
   
   
       6 . A screw type fluid machine comprising:
 a pump housing having a suction port and a discharge port; and   a pair of screw rotors rotatably mounted in the pump housing so as to be rotated while meshing with each other, wherein a plurality of transfer chambers are formed among the pump housing and the pair of the screw rotors so as to be partitioned from one another by meshing portions of the screw rotors and to be transferred from a suction side to a discharge side in accordance with rotation of the screw rotors,   characterized in that   a cross sectional shape of a tooth profile of the screw rotors with respect to an axial direction thereof includes   an arc forming a deddendum portion;   an arc forming an outer circumferential portion; and   two curves connecting the outer circumferential portion and the deddendum portion,   wherein one of the tooth profile curves connecting the outer circumferential portion and the deddendum portion is defined by such a tooth profile curve that a transfer chamber isolated from other spaces is formed without interfering with a meshing portion of the mating screw rotor, and   the other of the tooth profile curves, which is divided equally into two sections constituted by a section between a pitch circle and the outer circumferential portion and a section between the pitch circle and the deddendum portion, is defined by a predetermined curve for one of the sections and a fitting curve created so as to correspond to the predetermined curve for the one of the sections divided equally into two in the mating screw rotor during meshing.   
   
   
       7 . A screw type fluid machine according to  claim 5 , characterized in that the predetermined curve portion that is one of the sections equally divided into two is formed by an arc and a straight line. 
   
   
       8 . A screw type fluid machine according to  claim 5 , characterized in that the predetermined curve portion is formed by a sine curve.