Vacuum pump

Abstract

A multiple cylinder having a plurality of cylinders arranged concentrically and a rotor shaft rotatably disposed on the center axis of the multiple cylinder are provided in a pump casing. Each of the cylinders that constitute the multiple cylinder has a mounting portion, through which the cylinders are integrally fixed to the rotor shaft.

What is claimed is:  
     
         1 . A vacuum pump comprising: 
 a multiple cylinder having a plurality of cylinders arranged concentrically;    a rotor shaft rotatably disposed on the center axis of said multiple cylinder; and    a screw pump stator having an exhaust passage of a thread-groove pump between said screw pump stator and each of said cylinders;    wherein each of the cylinders constituting said multiple cylinder has a mounting portion, through which said each cylinder is integrally mounted to the rotor shaft.    
     
     
         2 . A vacuum pump according to  claim 1 , wherein said rotor shaft has a collar on the outer peripheral surface; each of the cylinders constituting said multiple cylinder has a mounting portion to said collar; and the mounting portion of said cylinder and the collar of said rotor shaft are integrally joined.  
     
     
         3 . A vacuum pump according to  claim 2 , wherein the mounting portion of said outer cylinder is fixed to the surface of said collar and the mounting portion of said inner cylinder is fixed to the back of said collar.  
     
     
         4 . A vacuum pump according to  claim 2 , wherein the mounting portion of said inner cylinder is disposed on the surface of said collar, on which the mounting portion of said outer cylinder is disposed and both the mounting portions of the inner and outer cylinders are fastened to said collar with bolts passing therethrough.  
     
     
         5 . A vacuum pump according to  claim 2 , wherein said collar has a shoulder; and wherein the mounting portion of the outer cylinder is fastened to the upper step of the shoulder with bolts and the mounting portion of the inner cylinder is fastened to the lower step of the shoulder with other bolts.  
     
     
         6 . A vacuum pump according to  claim 1 , wherein the outer periphery of the end of said rotor shaft is tapered from the end face of the rotor shaft to a mounting position for said outer cylinder and a tapered hole to be fitted to the tapered portion of the rotor shaft is opened in the mounting portion of said outer cylinder and wherein said rotor shaft and said outer cylinder are integrally joined by a counter joining structure in which said tapered hole and said tapered section are fitted to-each other.  
     
     
         7 . A vacuum pump according to  claim 6 , wherein a push ring which is in contact with the periphery of the tapered hole of the mounting portion of said outer cylinder is disposed at the end face of said rotor shaft, said outer cylinder being fastened to said rotor shaft with a bolt screwed into the end of the rotor shaft through a bolt insertion hole of the push ring.  
     
     
         8 . A vacuum pump according to  claim 1 , wherein the outer periphery of the end of said rotor shaft is tapered from the end face of the rotor shaft to a mounting position for said inner cylinder through the mounting position for said outer cylinder and a tapered hole to be fitted to the tapered portion of the rotor shaft is opened in each of the mounting portion of said outer cylinder and the mounting portion of said inner cylinder and wherein said rotor shaft, said outer cylinder, and said inner cylinder are integrally joined by a counter joining structure in which said tapered hole and said tapered section are fitted to each other.  
     
     
         9 . A vacuum pump according to  claim 8 , wherein a screw part is provided at the periphery of the end of said rotor shaft and at a position slightly higher than the mounting position for said inner cylinder and said inner cylinder is fastened to said rotor shaft with a nut on said screw part tightened from above the mounting portion of said inner cylinder.  
     
     
         10 . A vacuum pump according to  claim 1 , wherein a plurality of rotor blades and stator blades are alternately provided on the outer periphery of the outer cylinder of said cylinders, said rotor blades being integrated with the outer peripheral surface of the outer cylinder and said stator blades being fixed to the inner surface of a pump casing.  
     
     
         11 . A vacuum pump according to  claim 1 , wherein: 
 said multiple cylinder includes a pair of inner and outer cylinders arranged concentrically;    said screw pump stator includes a first screw-pump stator arranged at a position facing the outer peripheral surface of said outer cylinder and a second screw-pump stator arranged between said outer cylinder and said inner cylinder;    said exhaust passage of the thread-groove pump includes a first gas-exhaust passage provided between said first screw-pump stator and said outer cylinder, a second gas-exhaust passage provided between said outer cylinder and said second screw-pump stator, and a third gas-exhaust passage provided between said second screw-pump stator and said inner cylinder, said first gas-exhaust passage and said second gas-exhaust passage being communicated under said outer cylinder and said second gas exhaust passage and said third gas exhaust passage being communicated above said second screw-pump stator.