Multi-Stage Trochoidal Vacuum Pump

Abstract

A vacuum pump includes first, second, third and fourth pump stages. Each pump stage has a trochoidal-shaped cavity and a rotor that rotates within the respective cavity. Each cavity has a volume determined by the depth of the cavity and a generally corresponding thickness of the rotor. The fourth stage has a largest volume and receives gas at an input pressure. The fourth stage outputs the gas to the third stage at a second pressure higher than the input pressure. The cavity of each successive stage (third, second and first) has a smaller volume and outputs the gas at a higher pressure than the previous stage. The last (first) stage outputs the gas to the atmosphere. The rotors in the stages rotate about a common pump shaft. Each rotor has a multiple vertices that follow the inner perimeter surface of the respective cavity without contact and without requiring additional seals.

1 . A pump comprising:
 a first stage comprising a first trochoidal-shaped cavity having a first volume, the first stage having a first input port and a first output port;   a first rotor that rotates eccentrically within the first cavity about a first cam;   a second stage comprising a second trochoidal-shaped cavity having a second volume greater than the first volume, the second stage having a second input port and a second output port;   a second rotor that rotates eccentrically within the second cavity about a second cam;   a common shaft that rotates the first cam and the second cam; and   a first interconnection conduit that couples the second output port to the first input port.   
   
   
       2 . The pump as defined in  claim 1 , wherein the first cavity has substantially the same shape and area as the second cavity and wherein the second cavity has a greater depth than the first cavity. 
   
   
       3 . The pump as defined in  claim 1 , wherein the first rotor and the second rotor have substantially the same area and wherein the second rotor has a greater thickness than the first rotor. 
   
   
       4 . The pump as defined in  claim 1 , wherein each vertex of each of the first rotor and the second rotor has a continuous, uninterrupted contour. 
   
   
       5 . The pump as defined in  claim 1 , wherein each of the first output port and the second output port has a respective check valve that opens to allow gas to exit the respective cavity via the respective output port when the pressure on the side of the check valve proximate the cavity is sufficiently greater than the pressure on the opposite side of the check valve and that closes to prevent gas from entering the respective cavity via the respective output port when the pressure on the side of the check valve proximate the cavity is insufficient to force the check valve open. 
   
   
       6 . The pump as defined in  claim 5 , where the second input port has a check valve that opens to allow gas to enter the second cavity and that closes to prevent gas from exiting the second cavity via the second input port. 
   
   
       7 . The pump as defined in  claim 6 , wherein the input check valve and the output check valves comprise umbrella valves. 
   
   
       8 . The pump as defined in  claim 1 , wherein the second input port is pneumatically coupled to a system to evacuate gas from the system to reduce the pressure in the system. 
   
   
       9 . The pump as defined in  claim 8 , wherein the first output port discharges the gas at a higher pressure than the pressure in the system. 
   
   
       10 . The pump as defined in  claim 1 , wherein:
 the first rotor is positioned between a first cover and a second cover within the first cavity and rotates in a plane parallel to the first cover and the second cover;   the first rotor has a first face proximate to and spaced apart from the first cover and has a second face proximate to and spaced apart from the second cover; and   each of the first face and the second face of the rotor has a plurality of slots formed therein perpendicular to the face, the plurality of slots on each face functioning as a respective labyrinth seal to reduce the flow of gas across each face between each face and the respective cover.   
   
   
       11 . The pump as defined in  claim 1 , further comprising:
 a third stage comprising a third trochoidal-shaped cavity having a third volume greater than the second volume, the third stage having a third input port and a third output port;   a third rotor that rotates eccentrically within the third cavity about a third cam, the third cam rotated by the common shaft; and   a second interconnection conduit that couples the third output port to the second input port.   
   
   
       12 . The pump as defined in  claim 1 , further comprising:
 a third stage comprising a third trochoidal-shaped cavity having a third volume greater than the second volume, the third stage having a third input port and a third output port;   a third rotor that rotates eccentrically within the third cavity about a third cam, the third cam rotated by the common shaft;   a second interconnection conduit that couples the third output port to the second input port;   a fourth stage comprising a fourth trochoidal-shaped cavity having a fourth volume greater than the third volume, the fourth stage having a fourth input port and a fourth output port;   a fourth rotor that rotates eccentrically within the fourth cavity about a fourth cam, the fourth cam rotated by the common shaft;   a third interconnection conduit that couples the fourth output port to the third input port.   
   
   
       13 . The pump as defined in  claim 12 , wherein:
 the fourth input port is coupled to a system from which gas is to be evacuated, and the fourth pump stage draws gas from the system into the fourth cavity to reduce the pressure in the system to a system pressure and outputs the gas to the third stage via the third interconnection conduit at a fourth stage output pressure that is higher than the system pressure;   the third pump stage increases the pressure of the gas from the fourth stage output pressure to a third stage output pressure and outputs the gas to the second stage via the second interconnection conduit;   the second pump stage increases the pressure of the gas from the third stage output pressure to a second stage output pressure and outputs the gas to the first stage via the first interconnection conduit; and   the first pump stage increases the pressure of the gas from the second stage output pressure to atmospheric pressure and outputs the gas via the first output port.   
   
   
       14 . The pump as defined in  claim 1 , wherein:
 the first trochoidal-shaped cavity includes a first cavity lobe and a second cavity lobe, the first cavity lobe coupled to the first input port, the second cavity lobe coupled to the first output port; and   an internal interconnection passage having an inlet positioned in the first cavity lobe and having an outlet positioned in the second cavity lobe, the internal interconnection passage transferring gas from the first cavity lobe to the second cavity lobe when a vertex of the first rotor is positioned between the inlet and the outlet.   
   
   
       15 . A pump comprising:
 a first stage comprising:
 a first enclosure having a first inner cavity having a first volume, the first inner cavity defined by a first inner surface with a trochoidal shape; 
 a first circular cam having a first central axis and having a first eccentric axis offset from the first central axis, the first circular cam mounted in the first cavity to rotate about the first eccentric axis; 
 a first rotor mounted to rotate about the first central axis of the first circular cam, the first rotor having a plurality of vertices that move along the first inner surface of the first inner cavity; 
 a first input port to enable gas to enter the first inner cavity; 
 a first output port to enable gas to exit from the first inner cavity; 
   a second stage comprising:
 a second enclosure having a second inner cavity having a second volume, the second volume greater than the first volume, the second inner cavity defined by a second inner surface with a trochoidal shape; 
 a second circular cam having a second central axis and having a second eccentric axis offset from the second central axis, the second circular cam mounted in the second cavity to rotate about the second eccentric axis; 
 a second rotor mounted to rotate about the second central axis of the second circular cam, the second rotor having a plurality of vertices that move along the second inner surface of the second inner cavity; 
 a second input port to enable gas to enter the second inner cavity; 
 a second output port to enable gas to exit from the second inner cavity; 
   a common shaft that rotates the first circular cam around the first eccentric axis and that rotates the second circular cam around the second eccentric axis at an input rate, the first rotor rotating about the first circular cam at first rotation rate that is a first fixed fraction of the input rate, the second rotor rotating about the second circular cam at a second rotation rate that is a second fixed fraction of the input rate; and   an interconnection conduit that couples the second output port to the first input port.   
   
   
       16 . The pump as defined in  claim 15 , wherein the first rotation rate and the second rotation rate are the same. 
   
   
       17 . A four-stage vacuum pump comprising:
 a first stage comprising a first trochoidal-shaped cavity having a first volume and having a first rotor that rotates within the first cavity, the first stage receiving a gas at an input pressure and outputting the gas at a second pressure higher than the input pressure;   a second stage comprising a second trochoidal-shaped cavity having a second volume and having a second rotor that rotates within the second cavity, the second stage receiving the gas from the first stage at the second pressure and outputting the gas at a third pressure higher than the second pressure;   a third stage comprising a third trochoidal-shaped cavity having a third volume and having a third rotor that rotates within the third cavity, the third stage receiving the gas from the second stage at the third pressure and outputting the gas at a fourth pressure higher than the third pressure;   a fourth stage comprising a fourth trochoidal-shaped cavity having a fourth volume and having a fourth rotor that rotates within the fourth cavity, the fourth stage receiving the gas from the third stage at the fourth pressure and outputting the gas at an exhaust higher than the fourth pressure; and   a common shaft that rotates a first eccentric cam, a second eccentric cam, a third eccentric cam and a fourth eccentric cam, the first rotor rotates about the first eccentric cam, the second rotor rotates about the second eccentric cam, the third rotor rotates about the third eccentric cam, and the fourth rotor rotates about the fourth eccentric cam.   
   
   
       18 . The pump as defined in  claim 17 , wherein the first volume is greater than the second volume, the second volume is greater than the third volume, and the third volume is greater than the fourth volume. 
   
   
       19 . The pump as defined in  claim 17 , wherein each stage has at least one intake phase and at least one exhaust phase, and wherein the cams and rotors in the stages are positioned at selected respective angular positions on the common shaft such that the rotor in a stage receiving gas from another stage is in an intake phase when the stage providing the gas is in an exhaust phase. 
   
   
       20 . A method of lowering the pressure at an interface, comprising:
 applying a rotational force to a common rotating shaft that is coupled to a first pump stage and at least a second pump stage, each pump stage having a respective trochoidal-shaped chamber and having a respective rotor positioned in the chamber to rotate about a respective eccentric cam driven by the rotating shaft, the chamber in the first pump stage having a first volume, the chamber in the second pump stage having a second volume greater than the first volume;   drawing gas into the second pump stage at an intake pressure, and expelling gas from the second pump stage into the first pump stage at a second stage output pressure greater than the intake pressure; and   expelling gas from the first pump stage at a first stage output pressure greater than the second stage output pressure.