Roots pump

Abstract

A roots pump including a pair of multi-lobe rotors is disclosed. The pair of rotors each include a first straight portion and a second straight portion. The first straight portion is provided on one of end portions of the rotary shaft of the rotor in an axial direction to extend straight along the axial direction. The straight portion is provided on the other one of the end portions to extend straight along the axial direction. The phases of the first straight portion and the second straight portion are displaced along the circumferential direction of the associated rotary shaft. Each of the pair of rotors further includes a coupling portion, which couples the first straight portion and the second straight portion. The coupling portions of the pair of rotors are engaged with each other to suppress fluid leakage between the pair of rotors.

1 . A roots pump comprising:
 a housing including an inlet, a suction chamber, a discharge chamber, and an outlet;   a pair of rotary shafts rotatably supported by the housing; and   a pair of multi-lobe rotors, each of which being provided on one of the pair of rotary shafts and accommodated in the housing, an inner surface of the housing and the pair of rotors define a pressure chamber, and as the pair of rotors are rotated, fluid drawn into the suction chamber from the inlet is trapped in the pressure chamber, discharged to the discharge chamber from the pressure chamber, and then discharged through the outlet,   wherein each of the pair of rotors includes a first straight portion, which is provided on one of end portions of the rotary shaft in an axial direction to extend straight along the axial direction, and a second straight portion, which is provided on the other one of the end portions to extend straight along the axial direction, the phases of the first straight portion and the second straight portion are displaced along the circumferential direction of the associated rotary shaft, each of the pair of rotors further includes a coupling portion, which couples the first straight portion and the second straight portion, and the coupling portions of the pair of rotors are engaged with each other to suppress fluid leakage between the pair of rotors.   
   
   
       2 . The pump according to  claim 1 , wherein each coupling portion is located at a center portion of the corresponding rotor along the axial direction of the associated rotary shaft, the length of the first straight portion along the axial direction of the rotary shaft is equal to the length of the second straight portion along the axial direction of the rotary shaft. 
   
   
       3 . The pump according to  claim 1 , wherein each rotor is a three-lobe rotor including three lobes and three recesses, each recess being formed between an adjacent pair of the lobes, the lobes and the recesses of each of the first and second straight portions are provided alternately at equal intervals along the circumferential direction of the rotary shaft, and the phase difference between the first straight portion and the second straight portion along the circumferential direction of the rotary shaft is 30°. 
   
   
       4 . The pump according to  claim 1 , wherein the rotational directions of the pair of rotors are opposite to each other, and the direction of the phase displacement of the second straight portion with respect to the first straight portion is opposite between the pair of rotors. 
   
   
       5 . The pump according to  claim 1 , wherein in each rotor, when the number of the lobes is n, and the number of the straight portions is X, the angle θ of the phase displacement of the second straight portion with respect to the first straight portion is expressed by the following expression:
   θ=(360°/2 n )/ X.     
   
   
       6 . A roots pump comprising:
 a housing including an inlet, a suction chamber, a discharge chamber, and an outlet;   a pair of rotary shafts rotatably supported by the housing, the rotary shafts being rotated in opposite directions to each other; and   a pair of multi-lobe rotors, each of which being provided on one of the pair of rotary shafts and accommodated in the housing, an inner surface of the housing and the pair of rotors define a pressure chamber, and as the pair of rotors are rotated in opposite directions to each other, fluid drawn into the suction chamber from the inlet is trapped in the pressure chamber, discharged to the discharge chamber from the pressure chamber, and then discharged through the outlet,   wherein each of the pair of rotors includes at least a first straight portion and a second straight portion, which extend straight along the axial direction of the associated rotary shaft, the phases of the first straight portion and the second straight portion are displaced along the circumferential direction of the associated rotary shaft, the direction of the phase displacement of the second straight portion with respect to the first straight portion is opposite between the pair of rotors, each of the pair of rotors further includes a coupling portion, which couples the first straight portion and the second straight portion, and the coupling portions of the pair of rotors are engaged with each other to suppress fluid leakage between the pair of rotors.   
   
   
       7 . The pump according to  claim 6 , wherein in each rotor, when the number of the lobes is n, and the number of the straight portions is X, the angle θ of the phase displacement of the second straight portion with respect to the first straight portion is expressed by the following expression:
   θ=(360°/2 n )/ X.