Patent Publication Number: US-2022220852-A1

Title: Double Sided Oil Film Thrust Bearing in a Scroll Pump

Description:
TECHNICAL FIELD 
     The present invention relates to scroll vacuum or pressure pumps and a bearing support for an orbiting scroll plate utilized in the scroll pumps. 
     BACKGROUND 
     A conventional scroll pump is a type of pump that includes a stationary plate scroll having one or more spiral stationary scroll blades, an orbiting plate scroll having one or more spiral orbiting scroll blades, and an eccentric driving mechanism to which the orbiting plate scroll is coupled. In the scroll pump, the stationary plate scroll and the orbiting plate scroll are engaged with each other, thereby forming at least one pumping chamber(s) in between. As the pumping chamber(s) moves away from the inlet toward the outlet in association with orbiting of the movable scroll, the volume of the pumping chamber closest to the inlet is gradually increased. Vacuum is generated in the course of increasing the volume of this pumping chamber. 
     The stationary and orbiting scroll blades are nested with a radial clearance and predetermined relative angular positioning such that a series of pockets are simultaneously defined by and between the blades. The orbiting plate scroll (and hence the orbiting scroll blade) is driven by the eccentric driving mechanism to orbit relative to the stationary plate scroll about a longitudinal axis of the pump passing through the axial center of the stationary scroll blade. See “L” labeled on  FIG. 1 . As a result, the volumes of the pockets delimited by the scroll blades of the pump are varied as the orbiting scroll blade moves relative to the stationary scroll blade. The orbiting motion of the orbiting scroll blade also causes the pockets to move within the pump head assembly such that the pockets are selectively placed in open communication with an inlet and outlet of the scroll pump. 
     In a vacuum scroll pump, the motion of the orbiting scroll blade relative to the stationary scroll blade causes a pocket sealed off from the outlet of the pump and in open communication with the inlet of the pump to expand. Accordingly, fluid is drawn into the pocket through the inlet. The inlet of the pump is connected to a system that is to be evacuated, e.g., a system including a processing chamber in which a vacuum is to be created and/or from which gas is to be discharged. Then the pocket is moved to a position at which it is sealed off from the inlet of the pump and is in open communication with the outlet of the pump, and at the same time the pocket is contracted. Thus, the fluid in the pocket is compressed and thereby discharged through the outlet of the pump. 
     Prior art vacuum scroll pumps typically have an inlet portion having a pump inlet, an exhaust portion having a pump outlet, a frame, a stationary plate scroll fixed to the frame, and an orbiting plate scroll whose scroll blade(s) is nested with that of the stationary plate scroll to define a series of pockets constituting a compression stage. An eccentric drive mechanism supported by the frame and operatively connected to the orbiting plate scroll has been used to drive the orbiting plate scroll in an orbit about a longitudinal axis of the pump. This eccentric drive mechanism often includes a crankshaft and spring-loaded angular contact bearings disposed on the crankshaft, a tubular bellows extending around the eccentric drive mechanism and having a first end connected to the orbiting plate and a second end connected to the frame, and counterbalancing features attached to the crankshaft by which radial loads produced on the eccentric drive mechanism are offset. 
     U.S. Pat. No. 9,605,674 (the entire contents of which are incorporated herein by reference) describes one-type of scroll pump with an eccentric drive mechanism and bearings disposed on the crankshaft. 
     SUMMARY 
     To address the foregoing problems, in whole or in part, and/or other problems that may have been observed by persons skilled in the art, the present disclosure provides methods, processes, systems, apparatus, instruments, and/or devices, as described by way of example in implementations set forth below. 
     According to one embodiment, a vacuum scroll pump has an inlet portion having a pump inlet, and an exhaust portion having a pump outlet; a frame; a stationary scroll plate fixed to the frame and comprising a stationary plate comprising one or more stationary scroll blade(s), wherein the stationary scroll blade(s) has the form of a spiral emanating from a central portion of the stationary plate; an orbiting scroll plate comprising an orbiting plate comprising--one or more orbiting scroll blade(s) projecting axially from a front side of the orbiting plate toward the stationary plate, wherein the orbiting scroll blade has the form of a spiral emanating from a central portion of the orbiting plate, and wherein the stationary scroll blade(s) and the orbiting scroll blade(s) are nested such that pockets are delimited by and between the stationary scroll blade and the orbiting scroll blade; a drive mechanism supported by the frame and operatively connected to the orbiting scroll plate so as to cause the orbiting scroll plate to orbit about a longitudinal axis of the vacuum scroll pump and thereby pump a process gas; a double-sided thrust bearing supporting the orbiting scroll plate scroll; and a bellows which isolates the process gas from the drive mechanism. 
     According to another embodiment, a double-sided thrust bearing for supporting an orbiting scroll plate in a vacuum scroll pump includes a first orbiting thrust bearing configured to connect to the orbiting scroll plate, a stationary double-sided thrust bearing on which the first orbiting thrust bearing orbits during motion of the orbiting scroll plate, a second orbiting thrust bearing coupled to the orbiting thrust bearing, and a lubricating film maintained on both sides of the stationary double-sided thrust bearing contacting the first orbiting thrust bearing and the second orbiting thrust bearing. 
     According to another embodiment, a system includes the aforementioned vacuum scroll pump with its double-sided thrust bearing. 
     Other devices, apparatus, systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood by referring to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views. 
         FIG. 1  is a schematic of a scroll pump to which the present invention may be applied; 
         FIG. 2A  is a schematic of a nested stationary scroll blade and orbiting scroll blade; 
         FIG. 2B  is a schematic of tip seals for a stationary scroll blade and an orbiting scroll blade; 
         FIG. 3A  is a cross-sectional view of the scroll pump including a pump head of the scroll pump showing one embodiment of a double-sided thrust bearing configuration of the present invention; 
         FIG. 3B  is cross-sectional view of the scroll pump of  FIG. 3  showing thereon reactive forces and moments; 
         FIG. 4  is a schematic showing exemplary details of an upper orbiting thrust bearing, stationary thrust bearing, and lower orbiting thrust bearing utilized in the present invention; 
         FIG. 5  is a schematic showing detail of a base attachment for a bellows sealing a crank mechanism of the scroll pump; and 
         FIG. 6  is an assembly view of the vacuum scroll pump of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments and examples of embodiments of the invention will be described more fully hereinafter with reference to the accompanying drawings. In the drawings, the sizes and relative sizes of elements may be exaggerated for clarity. Likewise, the shapes of elements may be exaggerated and/or simplified for clarity and elements may be shown schematically for ease of understanding. Also, like numerals and reference characters are used to designate like elements throughout the drawings. 
     Other terminology used herein for the purpose of describing particular examples or embodiments of the invention is to be taken in context. For example, the term “comprises” or “comprising” when used in this specification indicates the presence of stated features or processes but does not preclude the presence of additional features or processes. Terms such as “fixed” may be used to describe a direct connection of two parts/elements to one another in such a way that the parts/elements cannot move relative to one another or an indirect connection of the parts/elements through the intermediary of one or more additional parts. Likewise, the term “coupled” may refer to a direct or indirect coupling of two parts/elements to one another. The term “delimit” is understood to mean provide a boundary. The term “spiral” as used to describe a scroll blade is used in its most general sense and may refer to any of the various forms of scroll blades known in the art as having a number of turns or “wraps.” 
     Terminology related to rotational and orbital motions used herein refers to the manner in which the drive mechanisms and the orbiting scroll plate move. The term “rotate” or “rotation” or other derivatives thereof refers to the turning of a shaft which is driven by the motor where for example, if the shaft had its longitudinal direction defining the z-axis of an x-y-z system whose origin was on the center of the shaft, then rotation of the shaft would spin the shaft around the longitudinal axis or z-axis with the x- and y-directions constantly changing their pointing directions. When the shaft is rotating, any deviation of the pointing direction of the z-axis or any deviation of the location of the z axis intersection to the x-y plane is referred to herein as a movement away from the longitudinal direction of the shaft. The term “orbit” or “orbital” or derivatives thereof refers to the eccentric movement of for example an orbiting scroll plate where, if the plate defined the x-y plane of an x-y-z system, then the orbital motion of the orbiting scroll plate would produce no change in any of the x-, y-, and z- pointing directions. 
     Referring to  FIG. 1 , a vacuum scroll pump  1  to which the present invention can be applied may include a cowling  100 , and a pump head assembly  200  having an inlet opening  270  and an exhaust opening  280 , a pump motor  300 , and a cooling fan  400  disposed in the cowling  100 . Furthermore, the cowling  100  defines an air inlet  100 A and an air outlet  100 B at opposite ends thereof, respectively. The cowling  100  may also include a cover  110  that covers the pump head assembly  200  and pump motor  300 . The cover  110  may be of one or more parts. 
     As seen in  FIG. 1 , the vacuum scroll pump  1  also has a pump inlet  140  and constituting a vacuum side of the pump where fluid is drawn into the pump, and a pump outlet  150  and constituting a compression side where fluid is discharged to atmosphere or under pressure from the pump. The inlet opening  270  of the pump head  200  connects the inlet  140  of the pump to industrial processing unit  2000 , and the exhaust opening  280  leads to the pump outlet  150 . Thus, it may be considered that the portion of the pump from the pump inlet  140  to the inlet opening  270  of the pump head  200  is an inlet portion of the pump, and the portion of the pump from the exhaust opening  280  to the pump outlet  150  is an exhaust portion of the pump. 
     As shown in  FIG. 1 , the inlet opening  270  may be connected to an industrial processing unit  2000  which may be a system or a device in which a vacuum is to be created and/or from which gas is to be discharged. In one embodiment, the industrial processing unit  2000  may comprise a turbomolecular pump whose exhaust is being evacuated by the scroll pump of the present invention. In another embodiment, the industrial processing unit  2000  is a detector for detecting a tracer gas of a low molecular weight, and the scroll pump of the present invention draws gas comprising a tracer gas into the detector. In still another embodiment, the industrial processing unit  2000  is a mass spectrometer where for example the scroll pump of the present invention can draw gas from the differential pressure stages introducing a sample from atmospheric pressure into the interior of the mass spectrometer. In a further embodiment, the industrial processing unit  2000  is a materials deposition system processing a gas stream of reactive gases used for forming a film of material on a substrate inside. In yet another embodiment, the industrial processing unit  2000  is an oven or a vacuum oven where the scroll pump of the present invention pumps purge gas flowing through the oven. In a different embodiment, the industrial processing unit  2000  is analytical tool such as for example a scanning electron microscope where reduced vibrations are important, and clean roughing pumps for evacuating load locks is important. 
     Vacuum scroll pump  1  includes a stationary scroll blade and orbiting scroll blade which provide the pumping mechanism. As shown in  FIG. 2A , the stationary scroll blade and orbiting scroll blade are nested together with a predetermined relative angular and axial positioning such that pockets P (one of which is labeled in  FIG. 2A ) are delimited by and between the stationary and orbiting scroll blades during operation of the pump. The pockets P are disposed in series as between the inlet opening  270  and the exhaust opening  280  and collectively constitute the compression stage  260  ( FIG. 1 ) of the pump. Further in this respect, the sides of the scroll blades may not actually contact each other to seal the pockets P. Rather, minute clearances between sidewall surfaces of the scroll blades along with tip seals create seals sufficient for forming satisfactory pockets. More particularly,  FIG. 2B  shows a stationary scroll plate  220  and an orbiting scroll plate  230  with one pocket P depicted.  FIG. 2B  also shows a stationary scroll blade tip seal  220   a  at the end of a stationary scroll blade  220   b  and an orbiting scroll blade tip seal  230   a  at the end of an orbiting scroll blade  230   b.  Accordingly, seals can be provided between the tips of the stationary and orbiting scroll blades and the opposing front sides of the orbiting and stationary plates, respectively. For these seals to work, the axial location of the stationary and orbiting scroll plates is to be precise to ensure proper sealing and to avoid excessive friction which results in high power draw. 
     The challenge with a vacuum pump in using oil film bearings is that the oil must be isolated from the working fluid, which typically requires a bellows (such as for example bellows  250 ) surrounding the drive train. The use of a bellows requires a thrust bearing design capable of taking loads in multiple directions instead of the prior art oil film thrust bearing designs used in scroll compressors which take loads in only one direction. 
     In order to achieve the highest pumping speed in a scroll vacuum pump, it is necessary to increase the size and displacement of the scroll components. This puts a high load and in particular an overturning moment on the orbiting scroll plate bearings. Typically, the orbiting scroll plate bearing in a scroll vacuum pump consists of two back to back angular contact rolling element bearings which take both the radial loads, axial loads, and overturning moment loads, which works well only up to a certain size of pump. In larger scroll pumps, bearing failures are a known reliability issue, and larger components present a noise issue. What is needed is a different bearing architecture which does not use rolling element bearings, such as the oil film bearings used in air conditioning compressors. Yet, even prior art air conditioning scrolls have used only a single sided oil film thrust bearing supporting a thrust load in one direction. 
     As will become evident from the following description, the embodiments disclosed herein provide a solution to this problem. 
     Referring now to  FIG. 3A , a pump head of vacuum scroll pump  1  includes a frame  210 , a stationary scroll plate  220 , an orbiting scroll plate  230 , and a drive mechanism such as for example main shaft  241   a,  eccentric shaft (or crank)  241   b,  and motor  300 . The frame  210  may be one unitary piece, or the frame  210  may comprise several integral parts that are fixed to one another. 
     The stationary scroll plate  220  is detachably mounted to the frame  210  (by fasteners, not shown). The stationary scroll plate  220  includes a stationary plate having a front side and a back side, and a stationary scroll blade  220   b  projecting axially from the front side of the stationary plate. The stationary scroll blade is in the form of a spiral having a number of wraps emanating from the axial center of the stationary scroll plate  220 , as is known per se. The orbiting scroll plate  230  includes an orbiting plate having a front side and a back side, and an orbiting scroll blade  230   b  projecting axially from the front side of the orbiting plate. Only the tip seals  230   a  are shown in  FIG. 3A . 
     The main shaft  241   a  is coupled to the motor  300  so as to be rotated by the motor  300  about a longitudinal axis L of the pump  1 . A counterweight  244  is also coupled to the crankshaft to balance the inertial force from the orbiting plate scroll  230 . 
     The main shaft  241   a  is supported by the frame  210  via one or more bearing members  245  so as to be rotatable relative to the frame  210 . Bearing members  245  can be hydrodynamic fluid-film journal bearing members, or the bearing members  245  can be rolling element bearing members or other members permitting rotation of the main shaft  241   a  while constraining the main shaft  241   a  from movement away from the longitudinal axis L. The rolling element bearing members can be roller bearings, ball bearings, angular contact bearings, cylindrical rollers, spherical rollers, needle rollers, or any other bearing device where a rolling element is contained between two bearing races, one of which rotates with respect to the other. US Pat. Appl. Publ. No. 2016/0356273 (the entire contents of which are incorporated herein by reference) describes a bearing member arrangement for supporting both the main crank shaft and an eccentric crank at the top. Thus, the orbiting scroll plate  230  is driven by crank  241   b  so as to orbit about the longitudinal axis L of the pump when the main shaft  241   a  is rotated by the motor  300 . At the top of main shaft  241   a  is an eccentric shaft  241   b  offset from the longitudinal axis L. Therefore, when the main shaft  241   a  rotates, eccentric shaft  241   b  (i.e., a crank) drives the orbiting scroll plate  230  through a hydrodynamic or rolling element bearing  247  in an orbit around the drive shaft axis, and the orbiting scroll plate  230  moves relative to the stationary scroll plate  220 . This movement pushes gas between the blades forming a vacuum behind where the gas is pushed out. 
     As seen in  FIG. 3A , a double-sided stationary thrust bearing  301  is fixed to the frame  210  via crankshaft bearing support  252 . An upper (or first) orbiting thrust bearing  302  is attached to the orbiting scroll plate  230  and is also attached to a lower (or second) orbiting thrust bearing  303 . Therefore, the orbiting thrust bearing  302  and the lower orbiting thrust bearing  303  move together with the orbiting scroll in an orbit around the drive shaft in sliding contact with both sides of the double-sided stationary thrust bearing  301  (dependent on the pump&#39;s inlet pressure conditions) During vacuum inlet pressure conditions the orbiting plate is generally forced upwards by the ambient gas pressure inside a bellows  250 , whereas in atmospheric inlet pressure conditions the orbiting plate is forced downwards by the high gas compression force in the scroll pockets P shown in  FIG. 2 . 
     Thus, there is provided a double-side oil-film thrust bearing with both the top and bottom sides of the double-sided stationary thrust bearing  301  having oil-film sliding surfaces capable of taking loads in either direction. It should be noted that, in typical operation, the oil film is a boundary lubrication and does not necessarily result in a full hydrodynamic oil film separating the sliding pieces of metal. Oil for lubrication of this double-side oil-film thrust bearing and for the bearing members  245  is provided by oil sump  322  located below or with the motor section  300 , as shown in  FIG. 3A . The present invention can follow for example similar procedures to those described in US Pat. Appl. Publ. No. 2014/0154116, the entire contents of which are incorporated herein by reference. For example, lubricating oil pumped by an oil pump  320  or centrifugal force can be supplied from an oil sump  322  at the base of the motor  300  to the above-mentioned bearings. 
     During a normal operation of the pump, a load is applied to the orbiting scroll blade such that the fluid in the pockets P noted above is compressed. The crankshaft causes the orbiting scroll plate  230  to orbit against this force generated by gas compression about the central longitudinal axis of the main shaft  241   a.  As shown schematically in  FIG. 3B , the compression of the fluid generates a force shown by the arrow to the left which is constrained in one embodiment of the invention by a reactive force represented by the arrow to the right exerted by the eccentric shaft  241   b.  As a result, an overturning moment M (represented by the curved arrow in  FIG. 3B ) generated by the compression of the fluid and the centrifugal force caused by the orbiting mass of the orbiting plate is reacted by the double-sided stationary thrust bearing  301 , along with any axial load from the compression of the fluid and the pressure force from ambient pressure inside the bellows  250 . 
     In more detail, the arrow in  FIG. 3B  to the left represents the centrifugal force (generated by the orbiting of scroll plate  230 ) combined with the compression force noted above. Against this combined force, the arrow to the right is the reaction force generated by bearing element  247  to balance or counter this force. The result of these two forces (offset from each other axially) is the counterclockwise moment M which would tend to make orbiting scroll plate  230  rotate counterclockwise about an axis extending into the paper (i.e., an overturning moment). In one embodiment of the invention, the double-sided stationary thrust bearing  301  opposes this overturning moment. As shown in  FIG. 3B , the left side of the double-sided stationary thrust bearing  301  exerts an upward force on the orbiting plate  230  (depicted the arrow pointed up), while the right side of double-sided stationary thrust bearing  301  exerts a downward force on the orbiting plate  230  (depicted the arrow pointed down), 
     Additionally, double-sided stationary thrust bearing  301  reacts to vacuum or pressure loading forces on the orbiting scroll plate  230 . When the orbiting scroll plate  230  is pumping to form a vacuum relative to the ambient (i.e., relative to the atmospheric pressure in the bellows  250 ), then the orbiting scroll plate  230  would experience an upward force which would be constrained by the double-sided stationary thrust bearing  301 , which is constrained between the upper orbiting thrust bearing  302  and the lower orbiting thrust bearing  303 . Similarly, when the pump&#39;s inlet is at or close to ambient pressure and the orbiting scroll plate  230  is pumping to build pressure relative to the ambient (i.e., relative to the atmospheric pressure in the crank), then the orbiting scroll plate  230  would experience a downward force which would be constrained by the double-sided stationary thrust bearing  301 , which is constrained between the upper orbiting thrust bearing  302  and the lower orbiting thrust bearing  303 . Accordingly, the double-sided thrust bearing reacts against forces which would result in too little or too much axial clearance under the tip seal. 
     Furthermore, metallic bellows  250  can have a torsional stiffness that prevents the orbiting scroll plate  230  from rotating significantly about the central longitudinal axis of the bellows  250 , i.e., from rotating significantly in its circumferential direction. 
     Accordingly, the overturning or tipping force is constrained in the present invention by double-sided stationary thrust bearing  301 , upper orbiting thrust bearing  302 , and lower orbiting thrust bearing  303 . The stationary thrust bearing  301  reacts to loads in the vertical downward direction through the upper orbiting thrust bearing  302 . Lower orbiting thrust bearing  303  reacts to loads in the vertical upward direction. Furthermore, any overturning moment or tipping force is constrained by the double-sided stationary thrust bearing  301  being sandwiched between the upper orbiting thrust bearing  302  and lower orbiting thrust bearing  303 , as shown in  FIG. 4 . 
     In one embodiment of the invention, this construction with the stationary thrust bearing  301 , and the upper orbiting thrust bearing  302 , and the lower orbiting thrust bearing  303  forms a double-sided oil film thrust bearing, which is capable of taking loads in both up and down directions as well as reacting to overturning moments. In one embodiment of the invention, a lubricating film is maintained in the common space between the stationary thrust bearing  301 , the upper orbiting thrust bearing  302 , and the lower orbiting thrust bearing  303 . Together, these plate-like bearing surfaces in contact with each other comprise the sliding surfaces of a double-sided lubricated thrust bearing. 
     As shown in  FIG. 5 , bellows  250  is attached and sealed to the lower orbiting thrust bearing  303  by a bellows attachment  305 . Alignment pins  354  is used to clock (angularly set) the position of bellows  250  to the lower orbiting thrust bearing  303 , which is likewise precisely clocked to the upper thrust bearing,  302 , which is also precisely clocked to the orbiting scroll plate  230 . The bellows attachment  305  and the alignment pins  354  serve to prevent the orbiting scroll plate  230  from rotating significantly about the central longitudinal axis of the bellows  250 . In addition, the bellows  250  also extends around the drive mechanism (namely, around the main shaft  241 a and the double-sided stationary bearing thrust bearing  301 ). In this way with a static seal  310  between upper orbiting thrust bearing  302  and lower orbiting thrust bearing  303 , the bellows  250  seals the double-sided stationary bearing thrust bearing  301  and the double-sided oil film bearing surfaces thereof from the process gas. (Other static seals  310  are shown in  FIG. 4  which serve to keep oil in the drive mechanism out of the compression stages of the scroll pump.)  FIG. 5  also shows fastener  350  which attaches the upper orbiting thrust bearing  302  to the lower orbiting thrust bearing  303 .  FIG. 5  further shows fastener  352  which attaches the upper orbiting thrust bearing  302  to the orbiting scroll plate  230  (not shown here). 
       FIG. 6  is an outside view of the vacuum scroll pump described above. 
     It will be understood that various aspects or details of the invention may be changed, without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation—the invention being defined by the claims.