Dry-compressing vacuum pump

Abstract

A dry-compressing vacuum pump, in particular a screw pump, has two rotor elements (14) which are arranged in a pump chamber (12) and which are each carried by a rotor shaft (22). Two shaft ends of the rotor shafts (22) project through a side wall (28) of the pump housing (10). On the two shaft ends (28) there is arranged in each case one toothed belt pulley (38). Furthermore, a drive device and an electric motor for driving the rotor shaft (22) are provided. According to the invention, the rotor shafts (22) are driven by means of a toothed belt (40). To be able to use a toothed belt for drive purposes, a rotational flank clearance between the two rotor elements (14) of greater than ±0.75°, in particular greater than ±1°, is provided.

What is claimed is: 
     
         1 . A dry-compressing vacuum pump comprising
 two rotor elements which are arranged in a suction chamber,   two rotor shafts, each supporting a rotor element,   two toothed belt wheels respectively arranged on one shaft end extending from the suction chamber,   a drive means driving the rotor shafts, and   a toothed belt connected with the drive means and the toothed belt wheels,   wherein   a circumferential backlash between the two rotor elements of more than ±0.75° is provided.   
     
     
         2 . The dry-compressing vacuum pump of  claim 1 , wherein the maximum volumetric efficiency of the vacuum pump at an operating point in particular between 1 and 10 mbar is at least 75%. 
     
     
         3 . The dry-compressing vacuum pump of  claim 1 , wherein, for synchronizing rotor shafts rotating in opposite directions, the toothed belt is designed as a double-sided toothed belt. 
     
     
         4 . The dry-compressing vacuum pump of  claim 3 , wherein the toothed belt extends between the two toothed belt wheels. 
     
     
         5 . The dry-compressing vacuum pump of  claim 1 , wherein the tooth gap clearance of the two toothed belt wheels is larger than 0.15 mm. 
     
     
         6 . The dry-compressing vacuum pump of  claim 1 , wherein the rotor shafts are supported by grease-lubricated bearings, one bearing being provided per rotor shaft in a housing wall through which the shaft ends are passed. 
     
     
         7 . The dry-compressing vacuum pump of  claim 1 , wherein the vacuum pump compresses against atmosphere and generates a vacuum of at least 200 mbar absolute. 
     
     
         8 . The dry-compressing vacuum pump of  claim 1 , furthere comprising a belt tensioning means provided on the housing wall.