|Publication number||US3884599 A|
|Publication date||May 20, 1975|
|Filing date||Jun 11, 1973|
|Priority date||Jun 11, 1973|
|Also published as||CA1037925A, CA1037925A1|
|Publication number||US 3884599 A, US 3884599A, US-A-3884599, US3884599 A, US3884599A|
|Inventors||Mccullough John E, Young Niels O|
|Original Assignee||Little Inc A|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (6), Referenced by (135), Classifications (16)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent [1 1 Young et al.
[ SCROLL-TYPE POSITIVE FLUID DISPLACEMENT APPARATUS  Inventors: Niels 0. Young, Mason, N.H.; John E. McCullough, Carlisle, Mass.
 Assignee: Arthur D. Little, lnc., Cambridge,
 Filed: June 11, 1973 [211 App]. No.: 368,907
 U.S. Cl. 418/55  Int. Cl. F011: 1/02  Field of Search 4l8/55, 56, 57, I31
 References Cited UNITED STATES PATENTS 1,376,291 4/1921 Rolkerr 4l8/55 l,906,l42 4/1933 Ekelof 4l8/57 2,324,l68 7/l943 Montelius i i 4lS/55 3,560,l l9 2/l9'7l Busch et al. 4l8/55 3,600.1 l4 8/l97l Dvorak et all t. 418/55 3,802,809 4/1974 Vulliez 418/55 Primary Examiner-C. J. Husar Attorney, Agent, or Firm-Bessie A. Lepper [451 May 20, 1975 [57 ABSTRACT A positive fluid displacement apparatus employing scroll members having interfitting spiroidal wraps angularly and radially offset such that as the spiral cen ters experience an orbiting motion, they define one or more moving fluid pockets of variable volume. The zones of lowest and highest pressures are connected to fluid ports. Radial sealing is accomplished with minimum wear by using a driving mechanism which provides a centripetal radial force adapted to oppose a fraction of the centrifugal force acting on the orbiting scroll member. The line contact sealing force between the wraps of the scroll members constitutes the sole radial constraining force. Coupling means which are separate from the driving means, and hence from the radial constraining means, are provided to maintain the desired angular relationship between scroll members. Axial sealing is attained by withdrawing a portion of fluid from the zone of highest pressure and using this high-pressure fluid to generate axial sealing forces. The apparatus may serve as a compressor, expander or pump.
58 Claims, 41 Drawing Figures PATENTEM'M'QYS 3,884,599
SHEET UZUF '13 ORBIT CENTER AXIS OF FIXED SCROLL AXIS OF FlXED SCROLL PATENIED HAY 2 0 I975 SHEEI DROP 13 I I s I 1 i Fig.8
PMENIEI] MAY 2 0 I975 SHEET DSUF13 PATENTED MAY 2 0 I975 SHEET 09 0F 13 PATENITQBB HAY 2431975 SHEET llUF 13 T V/A/// 9 299 2 5 a l| 0563 99 999974 222222 5 k N\\\ u n u 22 9 8 2 2 3 8 2 9 8 Fig.34
PATENTED KAYZOIQTS SHEET IZUF 13 Fig.39
I50 39 I43 I40 357 3" Fig. 38
SCROLL-TYPE POSITIVE FLUID DISPLACEMENT APPARATUS This invention relates to fluid displacement apparatus and more particularly to apparatus for handling fluids to compress. expand or pump them.
The need for gas compressors and expanders and for fluid pumps is well known and there are many different types of such apparatus. In these apparatus a working fluid is drawn into an inlet port and discharged through an outlet port at a higher pressure; and when the fluid is a gas its volume may be reduced before delivery through the outlet port, in which case the apparatus serves as a compressor. If the working fluid is a pressurized gas when it is introduced and its volume is increased, then the apparatus is an expansion engine capable of delivering mechanical energy and also if desired of developing refrigeration. Finally, a fluid may be introduced and withdrawn at different pressures but without any appreciable change in volume, in which case the apparatus serves as a fluid pump.
In the following description of the fluid displacement apparatus of this invention it will be convenient to refer to it, and to the prior art, as a compressor. However, it is to be understood that the apparatus of this invention may also be used as an expansion engine and as a pump and its use as such will be described for the various apparatus embodiments.
It is not necessary to discuss the prior art in detail as it pertains to such dynamic apparatus as centrifugal compressors and pumps, or as it pertains to the more commonly used positive-displacement devices of the vane, gear or other rotary types. However it is of interest to note some of the features which characterize these general types of prior art apparatus as a basis for comparison with the fluid displacement apparatus of this invention.
Those pumps, compressors and blowers which may be termed dynamic apparatus must operate at high speeds to achieve large pressure ratios and they typically have efficiencies of less than 90% in terms of mechanical energy converted to flow and compressional energy. Apparatus of the dynamic type find their widest application in large sizes in such applications as gas turbine compressors, stationary power plant steam expanders, and the like.
The positive displacement pumps or compressors of the vane type have rubbing speeds proportional to the radius of the vanes and the vanes rub at varying angles. Furthermore, the vanes operate within a housing of fixed axial length so that any wear upon their flat surface ends will always act to increase the clearance, and hence, the blow-by or leakage of the apparatus. The positive-displacement pumps and compressors of the rotary type are typically constructed to have the rotating components movable between end plates, an arrangement which demands close tolerances to reduce blow-by while permitting free rotation. Wear between the rotating components and end plates increases blowby, a fact which requires the adjustment of the spacings of the end plates through the use of screws and very precisely constructed gaskets in the form of shims. The gaskets, in turn, may not be able to withstand corrosive fluids or fluids at extreme temperatures, e.g., cryogenic liquids or hot gases. Furthermore, these gaskets require precisely located edges to prevent injury by the moving vanes, a fact which adds to the delicacy of assembling the apparatus.
In most industrial applications, particularly those of large scale, the fluid pumps and compressors now being used are adequate for the uses for which they are employed. However, there remains a need for a simple, highly efficient apparatus, essentially unaffected by wear which can handle a wide range of fluids and operate over a wide range of conditions to serve as a pump, compressor or expansion engine. The apparatus of this invention which meets these requirements is based on the use of scroll members, having wraps which make moving contacts to define moving isolated volumes, called pockets, which carry the fluid to be handled. The contacts which define these pockets formed between scroll members are of two types: line contacts between spiral cylindrical surfaces, and area contacts between plane surfaces. The volume of a sealed pocket changes as it moves. At any one instant of time, there will be at least one sealed pocket. When there are several sealed pockets at one instant of time, they will have different volumes, and in the case of a compressor, they will also have different pressures.
There is known in the art a class of devices generally referred to as scroll" pumps, compressors and engines wherein two interfitting spiroidal or involute spiral elements of like pitch are mounted on separate end plates. These spirals are angularly and radially offset to contact one another along at least one pair of line contacts such as between spiral cylinders. The pair of line contacts will lie approximately upon one radius drawn outwardly from the central region of the scrolls. The fluid volume so formed therefore extends all the way around the central region of the scrolls. In certain special cases the pocket or fluid volume will not extend the full 360 but because of special porting arrangements will subtend a smaller angle about the central region of the scrolls. The pockets define fluid volumes which vary with relative orbiting of the spiral centers while maintaining the same relative spiral angular orientation. As the contact lines shift along the scroll surfaces, the pockets thus formed experience a change in volume. The resulting zones of lowest and highest pressures are connected to fluid ports.
An early patent to Creux (US. Pat. No. 801,182) describes this general type of device. Among subsequent patents which have disclosed scroll compressors, and pumps are US. Pat. Nos. 1,376,29l 2,809,779, 2,841,089, 3,560,119, and 3,600,l l4 and British Pat. No. 486,192.
Although the concept of a scroll-type apparatus has been known for some time and has been recognized as having some distinct advantages, the scroll-type apparatus of the prior art has not been commercially suc cessful, primarily because of sealing, wearing and to some extent porting problems which in turn have placed severe limitations on the efficiencies, operating life, and pressure ratios attainable. Thus in some of the prior art devices the apparatus components have had to be machined to accurate shapes and to be fitted with very small tolerances to maintain axial sealing gaps sufficiently low to achieve any useful pressure ratios. This is difficult to do and resembles the problem of constructing apparatus with a reciprocating piston without the use of sealing rings. In other prior art devices, radial sealing has been achieved through the use of more than one form of radial constraint, each being imposed by separate apparatus components requiring precise interbalancing to attain efficient radial sealing. If during extended operation of such devices this interbalancing is disarranged by one component experiencing more wear, or by any other mechanism, the problem of wear of other components may grow progressively worse until satisfactory radial sealing is no longer possible.
In place of ports, delivery of the compressed fluid in a number of the prior art scroll apparatus has been made through the scroll passages, and compression ratios have previously been limited to approximately the ratio of the radius to the outermost pocket to the radius to the innermost pocket at the moment fluid delivery begins, i.e., the moment the inner pocket opens. Therefore, in the design of prior art scroll-type apparatus another important approach to the obtaining of compression ratios greater than about two has been to construct the scrolls and their end plates to resemble very large flat pancakes. In contrast, the scroll apparatus of this invention possesses features making it possible to reduce the outside diameter of the scroll members while attaining desired compression ratios. Among such features are wraps which are configured at their inner ends to delay delivery of fluid into a receiver, wraps having a transition between a double scroll to a single scroll pattern, and special types of porting.
The resulting solutions to the sealing, wearing and porting problems through these and other approaches have not been satisfactory. Thus in the prior art devices, the inherent advantages of scroll-type apparatus (simplicity, high efficiency, flexibility, reversibility, and the like) have not been attained and have, in fact, been usually outweighed by sealing, wearing and porting proglems. It would therefore be desirable to be able to construct scroll type fluid displacement devices which could realize the inherent advantages of this type of ap paratus and which could be essentially free of sealing, wearing and porting problems heretofore encountered.
It is therefore a primary object of this invention to provide improved practical and useful fluiddisplacement apparatus which may serve as compressors, expanders or pumps. It is another object of this invention to provide apparatus of the character described which are of the so-called scroll type and which achieve efficient axial and radial sealing over extended operat ing periods. It is a further object to provide a fluid displacement apparatus which is simple and relatively inexpensive to construct, which has relatively few moving parts and a limited number of rubbing surfaces, and which experiences less friction and wear than other types of apparatus designed for the same purpose. Still another object is to provide such apparatus wherein wear is essentially self compensating.
Another primary object of this invention is to provide fluid displacement apparatus which, as a compressor or The scroll apparatus of this invention incorporates a unique driving means which permits reducing the radial constraints within the apparatus to only those imposed by the moving line contacts between the surfaces of the wraps forming the fluid pockets. The unique driving means is characterized in part by including means to counteract a fraction of the centrifugal force on the moving scroll member with an inwardly directed radial (centripetal) force. There is thus provided a contacting, i.e., radial sealing, force which minimizes wear and which is independent of the functioning of such other apparatus components as the means to maintain the desired angular relationship between the scroll members and the axial sealing means. Axial sealing is preferably attained through pressurized fluid withdrawn from the zone of highest pressure and a spring biased to exert a force on one of the scroll members to urge it against the other scroll member.
An exemplary embodiment of the apparatus of this invention incorporates a unique scroll driver as the driving means. The scroll driver is fixed through bearings to the main drive shaft while the moving scroll member is free to float axially to respond to fluid pressure acting upon its outer surface to attain axial sealing. The scroll driver effects the orbiting of the movable scroll member by making a rolling line contact between its cylindrical surface and a drive surface associaated with the movable scroll. By maintaining the orbit radius of the scroll driver less than the orbit radius of the movable scroll, the required opposing centripital force is provided in the driving means.
Valved porting where required is provided in the fluid displacement apparatus of this invention to better control the flow of fluid in and out. Valved porting generally need not be required for liquid pumps or for gas compressors and expanders wherein the pressure ratios are small or when a pancake' geometry is acceptable. A wide range of scroll designs may be used to achieve a variety of desired results such as different compression ratios, control of fluid volume at the time of discharge, overall size of the apparatus and the like. The apparatus of this invention is readily reversible from a compressor to an expansion engine and it is capable of handling a wide variety of fluids over a wide temperature range. Many of the embodiments illustrated may also be used as pumps for liquids.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.
For a fuller understanding of the nature and objects of the invention, reference should be had to the follow ing detailed description taken in connection with the accompanying drawings in which FIGS. 1-4 are diagrams of exemplary spiral wraps, one moving in a circular orbit with respect to the other, illustrating the manner in which a device incorporating such spiral members can achieve compression of a gas;
FIG. 5 is a combination of a top plan view and two side elevational views of spiral member illustrating the principal forces to which the scroll is subjected;
FIGS. 6A and 6B are diagrams showing forces in the radial-tangential plane which act upon a spiral member and illustrating the mechanism by which radial sealing forces are developed;
FIG. 7 is a cross section through the scroll driver and the moving and stationary scroll members illustrating the manner in which axial sealing is attained;
FIG. 8 is a side elevation view, partly in cross section, of one embodiment of a compressor constructed in accordance with this invention;
FIG. 9 is a cross section of the compressor of FIG. 8 through the plane 9-9 of FIG. 8;
FIGS. 10 and 11 are top planar and bottom planar views of the fixed spiral member of the compressor of FIG. 8;
FIG. 12 is a top planar view of the moving spiral member of the compressor of FIG. 8;
FIGS. 13, 14 and 15 are top planar, cross sectional and end views of one embodiment of a coupling member designed to prevent the relative angular motion of the scroll members during the orbiting of the movable scroll member;
FIGS. 16 and 17 are top planar and bottom planar views of the frame of the compressor of FIG. 8;
FIG. 18 is a cross section of the main shaft and bearing spacer taken through plane 18-18 of FIG. 8',
FIG. 19 is a cross section of the main shaft and balance weights taken through plane 19l9 of FIG. 8;
FIG. 20 is a partial side elevation view, partly in cross section, of another embodiment of a compressor constructed in accordance with this invention;
FIG. 21 is a cross section of the compressor of FIG. 20 through the plane 21-21 of FIG. 20;
FIGS. 22 and 23 are top planar and cross sectional views of another embodiment of a coupling member such as used in the compressor of FIGS. 20 and 21;
FIG. 24 is a cross section through the scroll members of an embodiment of a compressor constructed in accordance with this invention in which each scroll member has two wraps;
FIG. 25 is a cross section through the scroll members of an embodiment of a compressor constructed in accordance with this invention in which each scroll member has two outer wraps which are transformed into single inner wraps;
FIg. 26 is a cross section through the scroll members of an embodiment of a compressor constructed in accordance with this invention in which the innermost ends of the wraps are configured to use a cross-shaped coupling;
FIG. 27 is a perspective view of a cross-shaped coupling.
FIG. 28 is a perspective view of a portion of the innermost end of a wrap of FIG. 26 showing the channel which engages one arm of the cross-shaped coupling;
FIG. 29 is a cross section through the scroll members of an embodiment of a compressor constructed in accordance with this invention in which the wraps are configured to provide a modified porting arrangement;
FIGS. 30 and 31 are perspective and cross section views of the coupling used in the apparatus embodiment of FIG. 29;
FIG. 32 is a cross section through the scroll members of an embodiment of a compressor constructed in accordance with this invention in which the wraps are circular arcs rather than involute spirals;
FIG. 33 is a cross section through the scroll members of an embodiment of a compressor constructed in accordance with this invention in which the wraps are configured so that the clearance volume at the start of delivery of compressed gas is under control of a central port to attain intermittent porting;
FIG. 34 is a cross section across plane 34-34 of the apparatus of FIG. 33;
FIGS. 35-37 are cross sections through the wraps of the scroll members of FIG. 33 illustrating the operation of the apparatus;
FIG. 38 is a cross sectional view of a compressor constructed in accordance with this invention in which the scroll members rotate on parallel axes;
FIG. 39 is a cross section through the driving scroll of FIG. 38 taken through plane 3939 of FIG. 38; and
FIG. 40 is a side elevational view of a compressor constructed in accordance with this invention including housing, heat transfer means, etc.
Before describing specific embodiments of the apparatus of this invention, the principles of its operation may be discussed briefly in order to understand the way in which positive fluid displacement is achieved. The scroll-type apparatus operates by moving a sealed pocket of fluid taken from one region into another region which may be at a different pressure. If the fluid is moved from a lower to higher pressure region, the apparatus serves as a compressor; if from a higher to lower pressure region it serves as an expander; and if the fluid volumes remain essentially constant, then the apparatus serves as a pump.
The sealed pocket of fluid is bounded by two parallel planes defined by end plates, and by two cylindrial surfaces defined by the involute of a circle or other suitably curved configuration. The scroll members are aligned on parallel axes. A sealed pocket moves along between these parallel planes as the two lines of contact between the cylindrical surfaces move. The lines of contact move because one cylindrical element, e.g., a scroll member, moves over the other. This may be accomplished by maintaining one scroll fixed and orbiting the other scroll or by rotating both of the two scrolls on their parallel axes. In the detailed discussion which follows, it will be assumed for the sake of convenience that the positive fluid displacement apparatus is a compressor and that one scroll member is fixed while the other scroll member orbits in a circular path. The embodiment in which both of the scroll members rotate on parallel axes is shown in FIG. 38.
FIGS. 1-4 may be considered to be end views of a compressor wherein the end plates are removed and only the wraps of the scroll members are shown. In the descriptions which follow, the term scroll member will be used to designate the component which is comprised of both the end plate and the elements which define the contacting surfaces making movable line contacts. The term wrap" will be used to designate the elements making movable line contacts. These wraps have a configuration, e.g., an involute of a circle (involute spiral), arc of a circle, etc., and they have both height and thickness. The thickness may vary over the length of the wrap.
In the diagrams of FIGS. 1-4, a stationary scroll member wrap 10 in the form of an involute spiral having axis 11 and a movable scroll member wrap 12 in the form of another involute spiral of the same pitch as spiral 10 and having axis 13 constitute the components which define the moving sealed fluid pocket 14 which is crosshatched for ease of identification. The involute spirals l0 and 12 may be generated, for example, by wrapping a string around a reference circle having radius R The distance between corresponding points of adjacent wraps of each spiral is equal to the circumference of the generating circle. This distance between corresponding points of adjacent wraps of any scroll member is also the pitch, P. As will be seen in FIG. 1, the two scroll members can be made to touch at a number of points, for example in FIG. 1, the points A, B, C and D. These points are, of course, the line contacts between the cylindrical surfaces previously described. It will be seen that line contacts C and D of FIG. 1 define the cross-hatched pocket 14 being considered. These line contacts lie approximately on a single radius which is drawn through point 11, thus forming pocket 14 which extends for approximately a single turn about the central region of the scrolls. Since the spiral wraps have height (normal to the plane of the drawings) the pocket becomes a fluid volume which is decreased from FIG. 1 to FIG. 4 as the movable scroll member is orbited around a circle 15 of radius (P/2)t, where t is the thickness of the wrap. Since wrap 12 does not rotate as it orbits, the path traced out by the walls of wrap 12 may be, in addition, represented as a circle 16. As illustrated in FIGS. 1-4, wrap has a shape characterized by two congruent involute spirals 17 and 18 and wrap 12 has a shape characterized by two congruent involute spirals 19 and 20. The thicknesses, t, of the spiral walls are shown to be identical, although this is not necessary. As will be shown in the description below of FIGS. 21, 24-26, 29, 32 and 33, the wraps may take a number of different configurations and may vary in the number of turns used.
The end plate (not shown in FIGS. 1-4) to which stationary wrap 10 is fixed has a high-pressure fluid port 21 and as the moving wrap 12 is orbited the fluid pocket 14 shifts counterclockwise and decreases in volume to increase the fluid pressure. In FIG. 3, the fluid volume is opened into port 21 to begin the discharge of high-pressure fluid and this discharge of the highpressure fluid is continued as shown in FIG. 4 until such time as the moving wrap has completed it orbit about circle and is ready to seal off a new volume for compression and delivery as shown in FIG. 1.
If high-pressure fluid is introduced into the fluid port 21, the movable scroll 12 will be driven to orbit in a clockwise direction under the force of the fluid pressure and will deliver mechanical energy in the form of rotary motion as it expands into fluid pockets of increasing volume. In such an arrangement the device is an expansion engine.
Although this principle of the operation of scroll apparatus has long been known as evidenced by the prior art, the attainment of practical scroll equipment in a form which would permit the use of such apparatus on a commercial scale has so far not been realized. The failure of prior art scroll equipment to attain its potential has, at least in part, been due to problems of sealing and wearing. More particularly, the scroll devices of the prior art, as far as is known, have not provided an efficient combination of continuous axial and radial sealing; and they have in many cases sought to impose radial constraints on the scroll members by mechanisms other than the line contacts of the wraps themselves while using such mechanisms also to control angular phase relationships between the scroll members. Failing to provide efficient continued axial and radial sealing can materially decrease the efficiency of the apparatus to the point where it is no longer economical to operate. Imposing radial constraints through means other than through the line contacts of the wraps of the scroll members eventually leads to the wearing of the contacting surfaces and then to leakage. Generally such wear will vary from surface to surface and will not be self-compensating, a fact which only serves to aggrevate the problem of wear with continued operation. Combining mechanisms to achieve a desired angular phase relationship between the scroll members with such means to impose radial constraints can add to the problem of wear so that extended operation becomes impractical.
In the apparatus of this invention the disadvantages associated with scroll apparatus of the prior art are eliminated or minimized by limiting the radial displacement constraints to only those imposed by the line contacts of the wraps themselves, by providing a drive force on the movable scroll which has an inwardly directed radial component which opposes at least a fraction of the centrifugal force acting on the movable scroll, and by providing coupling means to control the angular phase relationship of the two scroll members which function independently of any constraint imposing means. The operation of the scroll apparatus remains independent of any pressure events within the scroll; wear of the line contacts between the wraps of the scroll members is essentially self-compensating and hence efficient continued radial scaling is attained over extended periods of operation. Axial sealing is preferably accomplished by using gas from the highest pressure zone of the apparatus in combination with a suitably biased spring to continuously force the scroll members to make axial contact.
To understand the problem of sealing a scroll-type apparatus and to describe the mechanism by which axial and radial sealing is achieved in the apparatus of this invention, it is helpful to examine the principal axial and radial forces acting upon a scroll member. Referring to FIG. 5, it can be shown that in the axial direction, the total external axial force F, on a scroll pair is the sum of an involute contact sealing force and an internal gas load. Therefore, if an external force is provided which is always greater than the internal axial gas force, axial sealing is accomplished. In the apparatus of this invention, this desired condition is achieved by withdrawing fluid from the highest pressure zone and using it to generate an axial sealing force substantially proportional to the highest pressure within the fluid pockets. Referring to FIG. 5, there must then be a surplus axial force acting upon the scroll which is directed along the arrow F This surplus force performs sealing of the edges of one scroll member against the other, and is opposed by a as force directed against the force F,, shown in FIG. 5.
FIG. 7 illustrates one exemplary embodiment of an apparatus which attains continued axial sealin g through the use of gas withdrawn from the highest pressure zone of the apparatus supplemented by the use of a spring biased to force the scroll members toward axial sealing contact. In the embodiment of FIG. 7, which is a cross section through the scroll members and scroll driver, there is illustrated the use of a scroll driver along with a floating movable scroll member to achieve continuous self-adjusting axial sealing. The wrap 10 forming the line-contacting surfaces of the stationary scroll member, generally indicated at 25, is integral with or affixed to a stationary scroll end plate 26 terminating around its peripheral edge in an annular housing 27 which has an annular sealing surface 28. The wrap 12 forming the line-contacting surfaces of the movable scroll member, generally indicated at 30, is integral with or affixed to a movable scroll end plate 31, the peripheral sealing surface 32 of which is adapted to contact annular sealing surface 28 of stationary scroll member 25 to achieve axial sealing of the internal volume 33 defined between end plates 26 and 31. It will be appreciated that rubbing contact must be completely and continually achieved between sealing surfaces 28 and 32 even as these surfaces experience wear during operation. Furthermore, and more importantly, the axial sealing force is used to force the end plates to make sealing contact with the end surfaces of the wraps of the opposing scroll member such as at 41 and 42 to seal the pockets at these areas of contact. This desired axial sealing is attained through the use of a scroll driver, generally indicated at 35, in conjunction with movable scroll member 30 which is allowed to float under the influence of forces upon it. That is, movable scroll member 30 moves under the influence of the forces upon it until there is sufficient contact to seal the pockets.
Movable scroll member 30 includes, in the embodiment of FIG. 7, a scroll driver annular housing ring 36 defining a cylindrical volume 37 in which scroll driver 35 is located. Internally, annular ring 36 has a wall 38 normal to the plane of end plate 31, an annular shoulder 39, and a pressure sealing surface 40 which is, in effect, the central external surface of the movable scroll member 30. The scroll driver 35 is generally configured as a piston, and in this embodiment, comprises a ring 45 having an internal annular shoulder 46 for seating a bearing 47 and a central closure plate 48, the external wall 49 of which faces the driving surface 40. The ring 45 of the scroll driver has a diameter, D slightly less than the diameter, D,, of internal wall 38, thereby defining with it a clearance 50. The difference in diameters may be expressed as (D,D)/D, and it may range from about 0.001 to about 02. Ring 45 is contoured to define a peripheral groove 51 suitable for positioning an elastomeric sealing ring 52 between the scroll driver and internal wall 38 of scroll driver housing ring 36. A preloading spring 53 is designed to exert an axial force on the movable scroll member at those times when the delivery pressure and hence the gas loading force is zero. Preloading spring 53 is positioned to contact annular shoulder 39 and the periphery of scroll driver end plate 48 thereby defining a shallow axial sealing fluid volume 54 between the scroll driver end plate 48 and driving surface 40 of the movable scroll member. Some means. such as hole 44 in spring 53, must be provided so that the spring does not adventitiously seal off volume 37 from 54, for these volumes must be in fluid communication at all times. A fluid port 55 provides fluid communication between the zone of highest fluid pressure in volume 33 and sealing volume 54. Scroll driver 35 is fixed to driver shaft 56 through bearing 47 and the mechanism by which it drives the movable scroll member 30 will be described below.
Inasmuch as the movable scroll member 30 is not rigidly connected to the scroll driver it will be seen that it is free to move axially, i.e., to float. By bleeding high pressure fluid through port 55 into sealing volume 54, a force F which is essentially equal to the internal gas force is provided as the axial sealing force so long as the area of the force applying surface of the scroll driver is sufficiently large. In effect, the fluid pressure within sealing volume 54 forces the movable scroll member away from the scroll driver and against the fixed scroll member to achieve sealing between surfaces 28 and 32, as well as to effect sealing contact between the wrap edges and scroll member end plates. As these sealing surfaces wear, sealing contact is maintained because of the ability of the movable scroll member to float under the force of the pressure of the fluid in sealing volume 54. In practice, it is desirable to bias the total end force F, by means of spring 53 so that F does not go to zero even should the differential pressure in the system go to zero. Thus spring 53 provides an axial sealing force at start up and some additional axial sealing force during operation.
Whereas axial scaling is required to seal the end surfaces of the wrap edges to the end plate of the opposing scroll member, radial sealing is required to maintain a seal along the line contacts made by the cylindrical surfaces of the wraps of the scroll members as the movable scroll member is orbited (See for example points A, B, C and D of FIGS. 1-4 which illustrate the shifting positions of such line contacts). The principal forces which determine radial sealing of the scroll members are sketched out in simplified manner in FIG. 5 which deals with the forces on the moving scroll having a single wrap 12a affixed to an end plate 31a. As the scroll member is orbited about a path with radius R it experiences a tangential force F, and a normal contacting force which is, of course, the centrifugal force, maFR where m is the scroll member mass and w is its angular velocity. This centrifugal force is in excess of that which is required to attain efficient radial sealing, and the magnitude of such excess centrifugal force determines the extent of wear experienced by the contacting cylindrical surfaces of the wraps. In the apparatus of this invention, the driving means associated with the orbiting of the movable scroll member incorporates means to counteract, or oppose, a fraction of the centrifugal force to provide a contacting force which is of a magnitude sufficient to attain effective radial sealing and at the same time is not conducive to excessive wear. Thus the driving means of the apparatus of this invention includes means to provide a centripetal radial force F to oppose a fraction of the centrifugal force acting upon the orbiting scroll member. This is in direct contrast to prior art teaching which discloses the use of an augmented centrifugal force to attain radial sealing (See for example British Specification No. 486,192.)
In the practice of this invention the actual fraction of centrifugal force which is counteracted by the centripetal radial force applying means will depend upon several factors which may be interrelated. The optimum balance between centrifugal force, which is never reduced to zero, and centripetal force can be determined for any scroll apparatus by consideration of such factors as the specific application for which the scroll apparatus is used, the use or nonuse of lubricants, the material from which the wraps are made, the speed of operation, the desired life of the apparatus, and the like. For example, a compressor running dry will generally require that a greater fraction of the centrifugal force be opposed than one operating with a suitable lubricant; and a compressor having wraps formed of materials conducive to wear will require that a larger fraction of the centrifugal force be opposed than one having wraps formed of materials which are not as subject to wear. In general, higher operational speeds and longer operational lives dictate that a greater fraction of the centrifugal force be opposed by a centripetal force.
In conjunction with the providing of means to oppose a fraction of the centrifugal force on the orbiting scroll member, the apparatus of this invention is characterized by additional features which make it possible so to regulate the contacting force as to continuously main tain the radial sealing force between the scroll members at a level consistent with minimum wear and minimum fluid leakage. One of these features is the limiting of the radial constraints within the scroll apparatus to the moving line contacts between the wraps. Thus these radial constraints, controlled solely through the centripetal force providing means, not only minimize wear but impart a flexibility to the operation of the apparatus such that a great part of any wear that does occur is self-compensating. The limiting of the radial constraints to only the moving line contacts between the wraps is contrary to teaching in the prior art as exemplified by US. Pat. No. 3,600,1l4.
Another important feature of the apparatus of this invention is the use of a coupling means, adapted to maintain a fixed angular relationship between the scroll members, which is separate and distinct from the driving means. By using such a coupling means in combination with the unique driving means of this invention, and by limiting the radial contraints to the moving line contacts between the cylindrical surfaces of the wraps, the apparatus of this invention overcomes, at least to a very large extent, the radial sealing and wear problems of the prior art apparatus.
In the embodiments of the apparatus of this invention illustrated in FIGS. 7-40 the unique driving means, providing a centripetal force to oppose a fraction of the centrifugal force to give the desired contact force and radial sealing, is exemplified by a combination of means to define a cylindrical drive surface associated with the movable scroll member and a scroll driver which defines a cylindrical driving surface adapted to orbit the movable scroll member through line contact with the drive surface. By choosing the orbit radius, R of the movable scroll member to be greater than the orbit radius, R of the scroll driver, the desired centripetal, inwardly directed radial force opposing a fraction of the centrifugal force is attained.
In the embodiment of this invention using a movable scroll member which provides a cylindrical drive surface in combination with a scroll driver which defines a cylindrical driving surface to provide the desired contacting force, an important feature is that the diameter, D ofthe scroll drive must be different from the diameter, D of the cylindrical drive surface. In FIG. 6A, which is, in essence, a cross section taken through plane 6A-6A of FIG. 7, the diameter, D, of the internal wall 38 which serves as the cylindrical drive surface is larger than the external diameter, D of the ring 45 of scroll driver 35 which serves as the cylindrical driving surface. The difference between D, and D is greatly exaggerated in FIG. 6A better to illustrate the forces involved. Due to the difference in these diameters, the scroll driver, represented in FIG. 6A by the ring 45, makes an essentially rolling line contact at L with the movable scroll member, represented in FIG. 6A by internal wall 38.
The moving scroll is contained in the radialtangential plane by forces applied to the internal wall 38 as shown in FIG. 6A. (For continuity of presentation, the center, C, of the movable scroll driving ring is assumed to contain the origin of the involute of the scroll member as well as the center of gravity of the movable scroll member.) These forces applied to the movable scroll member through wall 38 are seen to be the centrifugal force, mw R,,,., and the tangential force F,. By making the orbit radius, R of the scroll driver less than the orbit radius, R of the movable scroll member there is developed a centripetal force which is an inwardly directed radial force F The magnitude of F, is a function of the contact angle which in turn is a function of the difference in orbit radii R and R as well as of the difierence in diameters D, and D,,. Thus this contact angle 0 between the scroll driver and the movable scroll member can be expressed in terms of diameters and orbit radii as sin 0 2(R,,, nr1)/(Dg d)- (l For a given operational speed and fluid pressure, 6 is designed into the apparatus to provide an adequate, but not excessive, radial sealing force which is always less than the centrifugal force mw R on the orbiting scroll as discussed previously.
It is also within the scope of this invention to construct the movable scroll member, as illustrated somewhat diagrammatically in FIG. 68, to have a cylindrical drive surface 380, such as a shaft in place of the internal wall 38 of the annular ring housing and to use a scroll driver which defines an internal driving wall 450, having a diameter greater than the drive surface 380, in place of the external wall of the scroll driver piston. Thus, in this embodiment D, is greater than D,. However, R remains greater than R and the various forces which make up the contacting or radial sealing forces are comparable to the reverse situation as a comparison of FIG. 6A and FIG. 68 makes evident. In the arrangement of FIG. 6B the contact angle 6 is defined as sin 0 2(R R d)/( d D8) The geometry which regulates the radial sealing force also tends to reduce the effects of manufacturing errors and the wasting away of material through wear. If the full centrifugal force were exerted on the radial sealing lines, excessive scroll wear would result. For example in manufacturing the scroll driver, the orbit center might not precisely coincide with the scroll orbit center; in such case 8 would have a component oscillating at the fundamental frequency to. By making the actual values of the numerator and denominator of equation (la) or (lb) some 10 times larger, for example, than the expected manufacturing error, there results less than 10% peak-to-peak a.c. component of radial sealing force compared to its steady value.
FIGS. 8-19 illustrate in detail a compressor constructed in accordance with this invention directly coupled to an electric motor as a driving means. The driving means illustrated is that discussed in conjunction with FIGS. 5-7. FIGS. 8 and 9 clearly illustrate the absence of any radial constraining means other than the contacting forces developed along the line contacts of the wraps. A number of different embodiments of cou-
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|U.S. Classification||418/55.3, 418/55.2, 418/188, 418/55.5, 418/57|
|International Classification||F01C1/00, F01C1/02, F01C21/00, F04C23/00|
|Cooperative Classification||F05B2250/50, F04C2250/10, F01C1/0215, F04C23/008, F01C21/003|
|European Classification||F01C1/02B2, F01C21/00C|