Roots-type fluid machine

Abstract

A roots-type fluid machine including a set of rotors and a rotor housing is disclosed. The rotor housing accommodates the rotors and has a suction space. The set of rotors mesh with each other and rotate in the rotor housing so that fluid is drawn into the suction space and discharged from the rotor housing. Each of the set of rotors includes a tooth having a twisted portion and a different shape variation portion. The twisted portion has a twist angle that changes linearly or non-linearly about a rotation axis of the corresponding rotor with respect to the variation of the position in the direction of the axis. The different shape variation portion has a twisted angle that changes by a smaller degree than the variation of the twist angle of the twisted portion.

1 . A roots-type fluid machine comprising a set of rotors and a rotor housing, which accommodates the rotors and has a suction space, the set of rotors meshing with each other and rotate in the rotor housing so that fluid is drawn into the suction space and discharged from the rotor housing,
 wherein each of the set of rotors includes a tooth having a twisted portion and a different shape variation portion, the twisted portion having a twist angle that changes linearly or non-linearly about a rotation axis of the corresponding rotor with respect to a variation of the position in the direction of the axis, and the different shape variation portion having a twisted angle that changes by a smaller degree than the variation of the twist angle of the twisted portion.   
   
   
       2 . The fluid machine according to  claim 1 , wherein the twisted potion is helical and the different shape variation portion has a straight line form parallel to the rotation axis. 
   
   
       3 . The fluid machine according to  claim 1 , wherein the twisted potion is helical and the different shape variation portion has a form the twist angle of which changes with respect to the variation of the position in the axial direction of the rotation axis in a manner represented by a nonlinear function. 
   
   
       4 . The fluid machine according to  claim 1 , wherein the different shape variation portion is provided at a position including the center of the rotor in the direction of the rotation axis. 
   
   
       5 . The fluid machine according to  claim 4 , wherein the twisted portion is provided on each side of the different shape variation portion in the direction of the rotation axis, and the lengths of the twisted portions are equal. 
   
   
       6 . The fluid machine according to  claim 1 , wherein the different shape variation portion is provided at a position including midway between the center of the rotor in the direction of the rotation axis and each of the ends of the associated rotor. 
   
   
       7 . The fluid machine according to  claim 1 , wherein each rotor is configured by laminating a plurality of flat plates having the same shape and the same size in the direction of the rotation axis, and the length of the different shape variation portion in the direction of the rotation axis is greater than the thickness of each flat plate. 
   
   
       8 . The fluid machine according to  claim 1 , wherein, in each rotor, the length of the different shape variation portion in the direction of the rotation axis is shorter than the length of the twisted portion in the direction of the rotation axis.