Double sided oil film thrust bearing in a scroll pump

A vacuum scroll pump having 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 at least one stationary scroll blade; an orbiting scroll plate comprising an orbiting plate comprising at least one orbiting scroll blade projecting axially from a front side of the orbiting plate toward the stationary plate; 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; and a bellows which isolates the process gas from the drive mechanism.

RELATED APPLICATIONS

This application is the national stage under 35 U.S.C. 371 of International Application No. PCT/US2019/030044, filed Apr. 30, 2019; the entire contents of which are incorporated by reference herein.

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 onFIG.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.

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 is 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 orbiting scroll plate is defined by 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 toFIG.1, a vacuum scroll pump1to which the present invention can be applied may include a cowling100, and a pump head assembly200having an inlet opening270and an exhaust opening280, a pump motor300, and a cooling fan400disposed in the cowling100. Furthermore, the cowling100defines an air inlet100A and an air outlet100B at opposite ends thereof, respectively. The cowling100may also include a cover110that covers the pump head assembly200and pump motor300. The cover110may be of one or more parts.

As seen inFIG.1, the vacuum scroll pump1also has a pump inlet140and constituting a vacuum side of the vacuum scroll pump1where fluid is drawn into the vacuum scroll pump1, and a pump outlet150and constituting a compression side where fluid is discharged to atmosphere or under pressure from the vacuum scroll pump1. The inlet opening270of the pump head200connects the pump inlet140to an industrial processing unit2000, and the exhaust opening280leads to the pump outlet150. Thus, it may be considered that the portion of the vacuum scroll pump1from the pump inlet140to the inlet opening270of the pump head200is an inlet portion of the vacuum scroll pump1, and the portion of the vacuum scroll pump1from the exhaust opening280to the pump outlet150is an exhaust portion of the vacuum scroll pump1.

As shown inFIG.1, the inlet opening270may be connected to the industrial processing unit2000, 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 unit2000may comprise a turbomolecular pump whose exhaust is being evacuated by the vacuum scroll pump1of the present invention. In another embodiment, the industrial processing unit2000is a detector for detecting a tracer gas of a low molecular weight, and the vacuum scroll pump1of the present invention draws gas comprising a tracer gas into the detector. In still another embodiment, the industrial processing unit2000is a mass spectrometer where for example the vacuum scroll pump1of 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 unit2000is 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 unit2000is an oven or a vacuum oven where the vacuum scroll pump1of the present invention pumps purge gas flowing through the oven. In a different embodiment, the industrial processing unit2000is 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.

The vacuum scroll pump1includes a stationary scroll blade220B and orbiting scroll blade230B which provide the pumping mechanism. As shown inFIG.2A, the stationary scroll blade220B and orbiting scroll blade230B are nested together with a predetermined relative angular and axial positioning such that pockets P (one of which is labeled inFIG.2A) are delimited by and between the stationary and orbiting scroll blades220B and230B during operation of the vacuum scroll pump1. The pockets P are disposed in series as between the inlet opening270and the exhaust opening280and collectively constitute the compression stage260(FIG.1) of the vacuum scroll pump1. Further in this respect, the sides of the scroll blades220B and230B may not actually contact each other to seal the pockets P. Rather, minute clearances between sidewall surfaces of the scroll blades220B and230B along with tip seals220A and230A create seals sufficient for forming satisfactory pockets P. More particularly,FIG.2Bshows a stationary scroll plate220and an orbiting scroll plate230with one pocket P depicted.FIG.2Balso shows a stationary scroll blade tip seal220aat the end of a stationary scroll blade220band an orbiting scroll blade tip seal230aat the end of an orbiting scroll blade230b. Accordingly, seals can be provided between the tips of the stationary and orbiting scroll blades220B and230B 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 bellows250, seeFIGS.3A-5) 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 vacuum scroll 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 vacuum scroll 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 scroll compressors 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 toFIG.3A, a pump head of vacuum scroll pump1includes a frame210, a stationary scroll plate220, an orbiting scroll plate230, and a drive mechanism such as for example main shaft241a, eccentric shaft (or crank)241b, and motor300. The frame210may be one unitary piece, or the frame210may comprise several integral parts that are fixed to one another.

The stationary scroll plate220is detachably mounted to the frame210(by fasteners, not shown). The stationary scroll plate220includes a stationary plate having a front side and a back side, and a stationary scroll blade220b(FIG.2B) projecting axially from the front side of the stationary plate. The stationary scroll blade220bis in the form of a spiral having a number of wraps emanating from the axial center of the stationary scroll plate220, as is known per se (seeFIGS.2A and2B). The orbiting scroll plate230includes an orbiting plate having a front side and a back side, and an orbiting scroll blade230b(FIG.2B) projecting axially from the front side of the orbiting plate. The orbiting scroll blade230bis in the form of a spiral having a number of wraps or turns emanating from the axial center of the orbiting scroll plate230(seeFIGS.2A and2B). Only the tip seals230aare specifically designated inFIG.3A.

The main shaft241ais coupled to the motor300so as to be rotated by the motor300about a longitudinal axis L of the vacuum scroll pump1. A counterweight244is also coupled to the crankshaft (e.g., main shaft241a) to balance the inertial force from the orbiting scroll plate230.

The main shaft241ais supported by the frame210via one or more bearing members245so as to be rotatable relative to the frame210. Bearing members245can be hydrodynamic fluid-film journal bearing members, or the bearing members245can be rolling element bearing members or other members permitting rotation of the main shaft241awhile constraining the main shaft241afrom 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 plate230is driven by crank241bso as to orbit about the longitudinal axis L of the vacuum scroll pump1when the main shaft241ais rotated by the motor300. At the top of main shaft241ais the eccentric shaft241b, which is offset from the longitudinal axis L. Therefore, when the main shaft241arotates, the eccentric shaft241b(i.e., a crank) drives the orbiting scroll plate230through a hydrodynamic or rolling element bearing247in an orbit around the drive shaft axis (i.e. longitudinal axis L), and the orbiting scroll plate230moves relative to the stationary scroll plate220. This movement pushes gas between the scroll blades220band230bforming a vacuum behind where the gas is pushed out.

As seen inFIG.3A, a double-sided stationary thrust bearing301is fixed to the frame210via crankshaft bearing support252. An upper (or first) orbiting thrust bearing302is attached to the orbiting scroll plate230and is also attached to a lower (or second) orbiting thrust bearing303. Therefore, the upper orbiting thrust bearing302and the lower orbiting thrust bearing303move together with the orbiting scroll plate230in an orbit around the drive shaft (main shaft241a) in sliding contact with both sides of the double-sided stationary thrust bearing301(dependent on the pump's inlet pressure conditions) During vacuum inlet pressure conditions the orbiting plate is generally forced upwards by the ambient gas pressure inside a bellows250, whereas in atmospheric inlet pressure conditions the orbiting plate is forced downwards by the high gas compression force in the scroll pockets P shown inFIGS.2A and2B. Thus, there is provided a double-sided oil-film thrust bearing with both the top and bottom sides of the double-sided stationary thrust bearing301having 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-sided oil-film thrust bearing and for the bearing members245is provided by oil sump322located below or with the motor section300, as shown inFIG.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 pump320or centrifugal force can be supplied from an oil sump322at the base of the motor300to the above-mentioned bearings.

During a normal operation of the vacuum scroll pump1, a load is applied to the orbiting scroll blade such that the fluid in the pockets P noted above is compressed. The crankshaft (main shaft241aand eccentric shaft241b), as powered by the motor300, causes the orbiting scroll plate230to orbit against this force generated by gas compression about the central longitudinal axis L of the main shaft241a. As shown schematically inFIG.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 shaft241b. As a result, an overturning moment M (represented by the curved arrow inFIG.3B) generated by the compression of the fluid and the centrifugal force caused by the orbiting mass of the orbiting scroll plate230is reacted by the double-sided stationary thrust bearing301, along with any axial load from the compression of the fluid and the pressure force from ambient pressure inside the bellows250.

In more detail, the arrow inFIG.3Bto the left represents the centrifugal force (generated by the orbiting of orbiting scroll plate230) combined with the compression force noted above. Against this combined force, the arrow to the right represents the reaction force generated by bearing element247to 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 plate230rotate counterclockwise about an axis extending into the paper (i.e., an overturning moment M). In one embodiment of the invention, the double-sided stationary thrust bearing301opposes this overturning moment M. As shown inFIG.3B, the left side of the double-sided stationary thrust bearing301exerts an upward force on the orbiting scroll plate230(depicted by the arrow pointed up), while the right side of double-sided stationary thrust bearing301exerts a downward force on the orbiting scroll plate230(depicted by the arrow pointed down),

Additionally, double-sided stationary thrust bearing301reacts to vacuum or pressure loading forces on the orbiting scroll plate230. When the orbiting scroll plate230is pumping to form a vacuum relative to the ambient (i.e., relative to the atmospheric pressure in the bellows250), then the orbiting scroll plate230would experience an upward force which would be constrained by the double-sided stationary thrust bearing301, which is constrained between the upper orbiting thrust bearing302and the lower orbiting thrust bearing303. Similarly, when the pump inlet140is at or close to ambient pressure and the orbiting scroll plate230is pumping to build pressure relative to the ambient (i.e., relative to the atmospheric pressure in the bellows250), then the orbiting scroll plate230would experience a downward force which would be constrained by the double-sided stationary thrust bearing301, which is constrained between the upper orbiting thrust bearing302and the lower orbiting thrust bearing303. Accordingly, the double-sided thrust bearing reacts against forces which would result in too little or too much axial clearance under the tip seals220aand220b.

Furthermore, metallic bellows250can have a torsional stiffness that prevents the orbiting scroll plate230from rotating significantly about the central longitudinal axis of the bellows250, 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 bearing301, upper orbiting thrust bearing302, and lower orbiting thrust bearing303. The double-sided stationary thrust bearing301reacts to loads in the vertical downward direction through the upper orbiting thrust bearing302. Lower orbiting thrust bearing303reacts to loads in the vertical upward direction. Furthermore, any overturning moment M or tipping force is constrained by the double-sided stationary thrust bearing301being sandwiched between the upper orbiting thrust bearing302and lower orbiting thrust bearing303, as shown inFIGS.3A-4.

In one embodiment of the invention, this construction with the double-sided stationary thrust bearing301, the upper orbiting thrust bearing302, and the lower orbiting thrust bearing303forms 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 M. In one embodiment of the invention, a lubricating film is maintained in the common space between the stationary thrust bearing301, the upper orbiting thrust bearing302, and the lower orbiting thrust bearing303. Together, these plate-like bearing surfaces in contact with each other comprise the sliding surfaces of a double-sided lubricated thrust bearing.

As shown inFIG.5, bellows250is attached and sealed to the lower orbiting thrust bearing303by a bellows attachment305. Alignment pins354are used to clock (angularly set) the position of bellows250to the lower orbiting thrust bearing303, which is likewise precisely clocked to the upper orbiting thrust bearing302, which is also precisely clocked to the orbiting scroll plate230. The bellows attachment305and the alignment pins354serve to prevent the orbiting scroll plate230from rotating significantly about the central longitudinal axis of the bellows250. In addition, the bellows250also extends around the drive mechanism (namely, around the main shaft241aand the double-sided stationary thrust bearing301). In this way, with a static seal310(FIG.4) between the upper orbiting thrust bearing302and lower orbiting thrust bearing303, the bellows250seals the double-sided stationary thrust bearing301and the double-sided oil film bearing surfaces thereof from the process gas. (Other static seals310are shown inFIG.4which serve to keep oil in the drive mechanism out of the compression stages of the vacuum scroll pump1.)FIG.5also shows a fastener350which attaches the upper orbiting thrust bearing302to the lower orbiting thrust bearing303.FIG.5further shows a fastener352which attaches the upper orbiting thrust bearing302to the orbiting scroll plate230(not shown here).

FIG.6is an outside view of the vacuum scroll pump1described above.