Patent Description:
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>. 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.

<CIT> describes one-type of scroll pump with an eccentric drive mechanism and bearings disposed on the crankshaft.

The documents <CIT> and <CIT> disclose each a scroll machine having thrust bearings for the orbiting scroll consisting of a stationary and an orbiting plate being attached to one another directly or via an intermediate plate.

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 the invention, a vacuum scroll pump as defined in the accompanying claims that 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 stationary thrust bearing supporting the orbiting scroll plate and arranged between a first orbiting thrust bearing and a second orbiting thrust bearing, the first orbiting thrust bearing being attached to the orbiting scroll plate and to the second orbiting thrust bearing, whereby the orbiting scroll plate slides with both sides of the thrust bearing; and a bellows which isolates the process gas from the drive mechanism.

According to the invention, 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 attached 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 as defined by the appended claims, and be protected by the accompanying claims.

The invention can be better understood by referring to the following figures. In the figures, like reference numerals designate corresponding parts throughout the different views.

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>, a vacuum scroll pump <NUM> to which the present invention can be applied may include a cowling <NUM>, and a pump head assembly <NUM> having an inlet opening <NUM> and an exhaust opening <NUM>, a pump motor <NUM>, and a cooling fan <NUM> disposed in the cowling <NUM>. Furthermore, the cowling <NUM> defines an air inlet 100A and an air outlet 100B at opposite ends thereof, respectively. The cowling <NUM> may also include a cover <NUM> that covers the pump head assembly <NUM> and pump motor <NUM>. The cover <NUM> may be of one or more parts.

As seen in <FIG>, the vacuum scroll pump <NUM> also has a pump inlet <NUM> and constituting a vacuum side of the pump where fluid is drawn into the pump, and a pump outlet <NUM> and constituting a compression side where fluid is discharged to atmosphere or under pressure from the pump. The inlet opening <NUM> of the pump head <NUM> connects the inlet <NUM> of the pump to industrial processing unit <NUM>, and the exhaust opening <NUM> leads to the pump outlet <NUM>. Thus, it may be considered that the portion of the pump from the pump inlet <NUM> to the inlet opening <NUM> of the pump head <NUM> is an inlet portion of the pump, and the portion of the pump from the exhaust opening <NUM> to the pump outlet <NUM> is an exhaust portion of the pump.

As shown in <FIG>, the inlet opening <NUM> may be connected to an industrial processing unit <NUM> 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 <NUM> 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 <NUM> 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 <NUM> 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 <NUM> 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 <NUM> 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 <NUM> 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 <NUM> includes a stationary scroll blade and orbiting scroll blade which provide the pumping mechanism. As shown in <FIG>, 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>) 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 <NUM> and the exhaust opening <NUM> and collectively constitute the compression stage <NUM> (<FIG>) 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> shows a stationary scroll plate <NUM> and an orbiting scroll plate <NUM> with one pocket P depicted. <FIG> also shows a stationary scroll blade tip seal 220a at the end of a stationary scroll blade 220b and an orbiting scroll blade tip seal 230a at the end of an orbiting scroll blade 230b. 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 <NUM>) 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>, a pump head of vacuum scroll pump <NUM> includes a frame <NUM>, a stationary scroll plate <NUM>, an orbiting scroll plate <NUM>, and a drive mechanism such as for example main shaft 241a, eccentric shaft (or crank) 241b, and motor <NUM>. The frame <NUM> may be one unitary piece, or the frame <NUM> may comprise several integral parts that are fixed to one another.

The stationary scroll plate <NUM> is detachably mounted to the frame <NUM> (by fasteners, not shown). The stationary scroll plate <NUM> includes a stationary plate having a front side and a back side, and a stationary scroll blade 220b 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 <NUM>, as is known per se. The orbiting scroll plate <NUM> includes an orbiting plate having a front side and a back side, and an orbiting scroll blade 230b projecting axially from the front side of the orbiting plate. Only the tip seals 230a are shown in <FIG>.

The main shaft 241a is coupled to the motor <NUM> so as to be rotated by the motor <NUM> about a longitudinal axis L of the pump <NUM>. A counterweight <NUM> is also coupled to the crankshaft to balance the inertial force from the orbiting plate scroll <NUM>.

The main shaft 241a is supported by the frame <NUM> via one or more bearing members <NUM> so as to be rotatable relative to the frame <NUM>. Bearing members <NUM> can be hydrodynamic fluid-film journal bearing members, or the bearing members <NUM> can be rolling element bearing members or other members permitting rotation of the main shaft 241a while constraining the main shaft 241a 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. <CIT> describes a bearing member arrangement for supporting both the main crank shaft and an eccentric crank at the top. Thus, the orbiting scroll plate <NUM> is driven by crank 241b so as to orbit about the longitudinal axis L of the pump when the main shaft 241a is rotated by the motor <NUM>. At the top of main shaft 241a is an eccentric shaft 241b offset from the longitudinal axis L. Therefore, when the main shaft 241a rotates, eccentric shaft 241b (i.e., a crank) drives the orbiting scroll plate <NUM> through a hydrodynamic or rolling element bearing <NUM> in an orbit around the drive shaft axis, and the orbiting scroll plate <NUM> moves relative to the stationary scroll plate <NUM>. This movement pushes gas between the blades forming a vacuum behind where the gas is pushed out.

As seen in <FIG>, a double-sided stationary thrust bearing <NUM> is fixed to the frame <NUM> via crankshaft bearing support <NUM>. An upper (or first) orbiting thrust bearing <NUM> is attached to the orbiting scroll plate <NUM> and is also attached to a lower (or second) orbiting thrust bearing <NUM>. Therefore, the orbiting thrust bearing <NUM> and the lower orbiting thrust bearing <NUM> 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 <NUM> (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 bellows <NUM>, 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>. 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 <NUM> 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 <NUM> is provided by oil sump <NUM> located below or with the motor section <NUM>, as shown in <FIG>. The present invention can follow for example similar procedures to those described in <CIT>. For example, lubricating oil pumped by an oil pump <NUM> or centrifugal force can be supplied from an oil sump <NUM> at the base of the motor <NUM> 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 <NUM> to orbit against this force generated by gas compression about the central longitudinal axis of the main shaft 241a. As shown schematically in <FIG>, 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 241b. As a result, an overturning moment M (represented by the curved arrow in <FIG>) 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 <NUM>, along with any axial load from the compression of the fluid and the pressure force from ambient pressure inside the bellows <NUM>.

In more detail, the arrow in <FIG> to the left represents the centrifugal force (generated by the orbiting of scroll plate <NUM>) combined with the compression force noted above. Against this combined force, the arrow to the right is the reaction force generated by bearing element <NUM> 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 <NUM> 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 <NUM> opposes this overturning moment. As shown in <FIG>, the left side of the double-sided stationary thrust bearing <NUM> exerts an upward force on the orbiting plate <NUM> (depicted the arrow pointed up), while the right side of double-sided stationary thrust bearing <NUM> exerts a downward force on the orbiting plate <NUM> (depicted the arrow pointed down),.

Additionally, double-sided stationary thrust bearing <NUM> reacts to vacuum or pressure loading forces on the orbiting scroll plate <NUM>. When the orbiting scroll plate <NUM> is pumping to form a vacuum relative to the ambient (i.e., relative to the atmospheric pressure in the bellows <NUM>), then the orbiting scroll plate <NUM> would experience an upward force which would be constrained by the double-sided stationary thrust bearing <NUM>, which is constrained between the upper orbiting thrust bearing <NUM> and the lower orbiting thrust bearing <NUM>. Similarly, when the pump's inlet is at or close to ambient pressure and the orbiting scroll plate <NUM> is pumping to build pressure relative to the ambient (i.e., relative to the atmospheric pressure in the crank), then the orbiting scroll plate <NUM> would experience a downward force which would be constrained by the double-sided stationary thrust bearing <NUM>, which is constrained between the upper orbiting thrust bearing <NUM> and the lower orbiting thrust bearing <NUM>. 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 <NUM> can have a torsional stiffness that prevents the orbiting scroll plate <NUM> from rotating significantly about the central longitudinal axis of the bellows <NUM>, 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 <NUM>, upper orbiting thrust bearing <NUM>, and lower orbiting thrust bearing <NUM>. The stationary thrust bearing <NUM> reacts to loads in the vertical downward direction through the upper orbiting thrust bearing <NUM>. Lower orbiting thrust bearing <NUM> reacts to loads in the vertical upward direction. Furthermore, any overturning moment or tipping force is constrained by the double-sided stationary thrust bearing <NUM> being sandwiched between the upper orbiting thrust bearing <NUM> and lower orbiting thrust bearing <NUM>, as shown in <FIG>.

In one embodiment of the invention, this construction with the stationary thrust bearing <NUM>, and the upper orbiting thrust bearing <NUM>, and the lower orbiting thrust bearing <NUM> 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 <NUM>, the upper orbiting thrust bearing <NUM>, and the lower orbiting thrust bearing <NUM>. 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>, bellows <NUM> is attached and sealed to the lower orbiting thrust bearing <NUM> by a bellows attachment <NUM>. Alignment pins <NUM> is used to clock (angularly set) the position of bellows <NUM> to the lower orbiting thrust bearing <NUM>, which is likewise precisely clocked to the upper thrust bearing, <NUM>, which is also precisely clocked to the orbiting scroll plate <NUM>. The bellows attachment <NUM> and the alignment pins <NUM> serve to prevent the orbiting scroll plate <NUM> from rotating significantly about the central longitudinal axis of the bellows <NUM>. In addition, the bellows <NUM> also extends around the drive mechanism (namely, around the main shaft 241a and the double-sided stationary bearing thrust bearing <NUM>). In this way with a static seal <NUM> between upper orbiting thrust bearing <NUM> and lower orbiting thrust bearing <NUM>, the bellows <NUM> seals the double-sided stationary bearing thrust bearing <NUM> and the double-sided oil film bearing surfaces thereof from the process gas. (Other static seals <NUM> are shown in <FIG> which serve to keep oil in the drive mechanism out of the compression stages of the scroll pump. ) <FIG> also shows fastener <NUM> which attaches the upper orbiting thrust bearing <NUM> to the lower orbiting thrust bearing <NUM>. <FIG> further shows fastener <NUM> which attaches the upper orbiting thrust bearing <NUM> to the orbiting scroll plate <NUM> (not shown here).

<FIG> is an outside view of the vacuum scroll pump described above.

Claim 1:
A vacuum scroll pump (<NUM>), comprising:
an inlet portion having a pump inlet (<NUM>), and an exhaust portion having a pump outlet (<NUM>);
a frame (<NUM>);
a stationary scroll plate (<NUM>) fixed to the frame (<NUM>) and comprising a stationary plate comprising at least one stationary scroll blade (220b), wherein the at least one stationary scroll blade has the form of a spiral emanating from a central portion of the stationary plate;
an orbiting scroll plate (<NUM>) comprising an orbiting plate comprising at least one orbiting scroll blade (230b) projecting axially from a front side of the orbiting plate toward the stationary plate, wherein the at least one orbiting scroll blade (230b) has the form of a spiral emanating from a central portion of the orbiting scroll plate, and wherein the at least one stationary scroll blade (220b) and the at least one orbiting scroll blade (230b) are nested such that pockets are delimited by and between the at least one stationary scroll blade (220b) and the at least one orbiting scroll blade (230b);
a drive mechanism (241a, 241b, <NUM>) supported by the frame (<NUM>) and operatively connected to the orbiting scroll plate (<NUM>) so as to cause the orbiting scroll plate (<NUM>) to orbit about a longitudinal axis of the vacuum scroll pump (<NUM>) and thereby pump a process gas;
bellows (<NUM>) which isolates the process gas from the driving mechanism;
characterized by
a double-sided stationary thrust bearing (<NUM>) supporting the orbiting scroll plate and arranged between a first orbiting thrust bearing (<NUM>) and a second orbiting thrust bearing (<NUM>), the first orbiting thrust bearing (<NUM>) being attached to the orbiting scroll plate (<NUM>) and to the second orbiting thrust bearing (<NUM>), whereby the orbiting scroll plate slides with both sides of the thrust bearing.