Eletric pump

Abstract

A Roots pump has a driving shaft press fitted into a driving rotor, and a driven shaft press fitted into a driven shaft. A driving timing gear is located between an electric motor and the driving rotor. The driving rotor has a driving assist shaft that projects in a direction opposite to the driving timing gear. The specific gravity of the material of the driving assist shaft is less than the specific gravity of the material of the driving rotary shaft. A driven rotor has a driven assist shaft that projects in a direction opposite to a driven timing gear. The specific gravity of the material of the driven assist shaft is less than the specific gravity of the material of the driven rotary shaft.

1 . An electric pump, comprising: 
 an electric motor;    a first rotary shaft driven by the electric motor;    a first rotor that is coupled to and rotates integrally with the first rotary shaft, the first rotor being formed of a material the specific gravity of which is less than the specific gravity of the material of the first rotary shaft;    a first timing gear provided to the first rotary shaft, the first timing gear being located between the electric motor and the first rotor with respect to an axial direction of the first rotary shaft, wherein the first rotor has a first gear facing surface, a first opposite surface, and a first assist shaft, the first gear facing surface being an end face that faces the first timing gear with respect to the axial direction, the first opposite surface being an end face that is opposite to the first gear facing surface, and the first assist shaft projecting from the first opposite surface, wherein the first gear facing surface has a first recess, wherein the first rotary shaft is press fitted into the first recess so that the first rotor is coupled to the first rotary shaft, wherein the first assist shaft is arranged to be coaxial with the first rotary shaft, and wherein the specific gravity of the material of the first assist shaft is less than the specific gravity of the material of the first rotary shaft;    a first bearing rotatably supporting the first assist shaft;    a second rotary shaft;    a second rotor that is coupled to and rotates integrally with the second rotary shaft, the second rotor being formed of a material the specific gravity of which is less than the specific gravity of the material of the second rotary shaft;    a second timing gear provided to the second rotary shaft, wherein the first timing gear and the second timing gear cause the second rotary shaft to rotate synchronously with the first rotary shaft, the second timing gear being located between the electric motor and the second rotor with respect to an axial direction of the second rotary shaft, wherein the second rotor has a second gear facing surface, a second opposite surface, and a second assist shaft, the second gear facing surface being an end face that faces the second timing gear with respect to the axial direction, the second opposite surface being an end face that is opposite to the second gear facing surface, and the second assist shaft projecting from the second opposite surface, wherein the second gear facing surface has a second recess, wherein the second rotary shaft is press fitted into the second recess so that the second rotor is coupled to the second rotary shaft, wherein the second assist shaft is arranged to be coaxial with the second rotary shaft, and wherein the specific gravity of the material of the second assist shaft is less than the specific gravity of the material of the second rotary shaft; and    a second bearing rotatably supporting the second assist shaft.    
   
   
       2 . The electric pump according to  claim 1 , 
 wherein the axial dimension of the first recess is less than half the axial dimension of the first rotor, and    wherein the axial dimension of the second recess is less than half the axial dimension of the second rotor.    
   
   
       3 . The electric pump according to  claim 1 , 
 wherein the first assist shaft is made of a material that is the same as the material of the first rotor, and    wherein the second assist shaft is made of a material that is the same as the material of the second rotor.    
   
   
       4 . The electric pump according to  claim 3 , 
 wherein the first assist shaft is integrally molded with the first rotor, and    wherein the second assist shaft is integrally molded with the second rotor.    
   
   
       5 . The electric pump according to  claim 1 , 
 wherein the length of a portion of the first rotary shaft that is press fitted into the first recess is set such that the value obtained by multiplying transmission torque transmitted from the first rotary shaft to the first rotor by a safety factor is equal to a fastening force between the first recess and the first rotary shaft,    wherein the length of a portion of the second rotary shaft that is press fitted into the second recess is set such that the value obtained by multiplying transmission torque transmitted from the second rotary shaft to the second rotor by the safety factor is equal to a fastening force between the second recess and the second rotary shaft.