Vacuum pumps with improved pumping channel cross sections

Abstract

A vacuum pump includes a housing having an inlet port and an exhaust port, at least one molecular drag stage within the housing, the molecular drag stage including a rotor in the form of a molecular drag disk and a stator that defines a tangential flow channel which opens onto a surface of the disk, the rotor having an axis of rotation, and a motor that rotates the rotor so that gas is pumped from the inlet port to the exhaust port. The channel has a cross-section in a plane that contains the axis of rotation which varies in dimension as a function of distance from the axis of rotation. The channel cross-section is selected to limit the tendency for backflow in viscous or partially viscous flow conditions.

1 . A vacuum pump comprising:
 a housing having an inlet port and an exhaust port;   at least one molecular drag stage located within the housing and disposed between the inlet port and the exhaust port, the molecular drag stage including a rotor comprising a molecular drag disk and a stator, the stator defining a tangential flow channel which opens onto a surface of the disk and a baffle that blocks the channel at a circumferential location, the disk having an axis of rotation defining a radial direction and having a peripheral velocity, the channel having a dimension between the disk and the stator that varies in the radial direction according to local pumping effects of the peripheral velocity of the disk; and   a motor to rotate the rotor of the molecular drag stage about the axis of rotation so that gas is pumped from the inlet port to the exhaust port.   
   
   
       2 . The vacuum pump as defined in  claim 1 , wherein the dimension of the channel between the disk and the stator increases with increasing distance from the axis of rotation. 
   
   
       3 . The vacuum pump as defined in  claim 1 , wherein the dimension of the channel between the disk and the stator increases linearly with increasing distance from the axis of rotation. 
   
   
       4 . The vacuum pump as defined in  claim 1 , wherein the stator includes a circumferential divider that extends into the channel and defines inner and outer subchannels. 
   
   
       5 . The vacuum pump as defined in  claim 4 , wherein the inner and outer subchannels have different axial dimensions. 
   
   
       6 . The vacuum pump as defined in  claim 1 , wherein the dimension of the channel between the disk and the stator various continuously in the radial direction. 
   
   
       7 . The vacuum pump as defined in  claim 1 , wherein an outer periphery of the disk extends into the channel and wherein outer corners of the channel are beveled or rounded. 
   
   
       8 . The vacuum pump as defined in  claim 1 , wherein the channel has beveled or rounded corners. 
   
   
       9 . The vacuum pump as defined in  claim 1 , wherein the stator includes two or more circumferential dividers that divide the channel into subchannels. 
   
   
       10 . The vacuum pump as defined in  claim 1 , wherein an axial dimension of the channel between the disk and the stator is configured to produce in the channel a substantially uniform pressure gradient as a function of distance from the axis of rotation. 
   
   
       11 . The vacuum pump as defined in  claim 1 , further comprising one or more additional vacuum pumping stages to define a multistage vacuum pump. 
   
   
       12 . A vacuum pump comprising:
 a housing having an inlet port and an exhaust port;   at least one molecular drag stage located within the housing and disposed between the inlet port and the exhaust port, the molecular drag stage including a rotor and a stator, the stator defining a tangential flow channel which opens onto a surface of the rotor and a baffle that blocks the channel at a circumferential location, the stator including a circumferential divider that extends into the channel and defines inner and outer subchannels; and   a motor to rotate the rotor of the molecular drag stage so that gas is pumped from the inlet port to the exhaust port.   
   
   
       13 . The vacuum pump as defined in  claim 12 , wherein the inner and outer subchannels have different axial dimensions. 
   
   
       14 . The vacuum pump as defined in  claim 12 , wherein the stator includes two or more circumferential dividers that divide the channel into subchannels. 
   
   
       15 . A vacuum pump comprising:
 a housing having an inlet port and an exhaust port;   at least one molecular drag stage located within the housing and disposed between the inlet port and the exhaust port, the molecular drag stage including a rotor and a stator, the stator defining a tangential flow channel which opens onto a surface of the rotor and a baffle that blocks the channel at a circumferential location, the rotor having an axis of rotation, the channel having a channel cross-section in a plane that contains the axis of rotation which varies in dimension as a function of distance from the axis of rotation, over at least part of the channel cross-section; and   a motor to rotate the rotor of the molecular drag stage about the axis of rotation so that gas is pumped from the inlet port to the exhaust port.   
   
   
       16 . The vacuum pump as defined in  claim 15 , wherein the dimension of the channel cross-section increases with increasing distance from the axis of rotation. 
   
   
       17 . The vacuum pump as defined in  claim 15 , wherein the dimension of the channel cross-section increases linearly with increasing distance from the axis of rotation. 
   
   
       18 . The vacuum pump as defined in  claim 15 , wherein an outer periphery of the disk extends into the channel and wherein outer corners of the channel are beveled or rounded. 
   
   
       19 . The vacuum pump as defined in  claim 15 , wherein the channel cross-section has beveled or rounded inner corners. 
   
   
       20 . The vacuum pump as defined in  claim 15 , wherein the channel cross-section is configured to avoid a region of zero gas flow velocity in the channel.