Abstract:
A scroll-type spiral fluid displacement machine having at least one pair of interfitting scroll elements. The scroll vanes of the scroll elements are constructed upon a base line spiral defined by the equation: 
         L=K   0 φ K1   e   −φ/     K2      
     where L is the distance from the spiral&#39;s origin to any point on the spiral curve, φ is the angular displacement of the spiral, K 0  is a constant greater than 1, K 1 , is a constant greater than 1, and K 2  is a constant greater than 10.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This application relates generally to a spiral scroll-type fluid displacement machine and more particularly to an asynchronous non-constant pitch spiral scroll-type fluid displacement machine. 
         [0003]    2. Description of the Related Art 
         [0004]    Generally, a conventional spiral scroll-type fluid displacement machine is formed with a pair of scroll elements (i.e., an orbiting scroll element and a fixed scroll element) each having spiral vanes that are fitted together in a certain predetermined way to intake fluid such as air or water through an intake port. The interfitting spiral vanes create one or more fluid pockets and trap the fluid inside the pocket(s) by moving the orbiting scroll element in a predetermined manner. The fluid pocket moves toward an outlet port while maintaining pressure in the pocket by continuously moving the orbiting scroll element within the interfitted fixed scroll element. The pressurized fluid is discharged though an outlet port. 
         [0005]    U.S. Pat. No. 801,182 (Creux) describes a conventional spiral scroll-type machine. A typical spiral scroll-type machine includes a pair of scroll elements where one scroll element is termed a fixed scroll and the other one is termed an orbiting scroll. Either the fixed or orbiting scroll comprises a spiral vane or a curled up wrap connected to an end plate in such a manner that the spiral vane is perpendicular to the planar surface of the end plate. The projecting spiral vanes or wraps of the fixed and orbiting scrolls interfit to form a plurality of line contacts between them, and thus at least one pair of fluid pockets is formed. The fixed scroll is stationary and does not move. The orbiting scroll does not rotate by revolving around its center. Rather the movement of the orbiting scroll is an orbiting motion. That is, the non-rotating orbiting scroll is moved in an orbit (generally circular in shape) formed around the center of the fixed scroll. With such orbiting motion, the line contacts between the spiral vanes of the fixed and orbiting scrolls move along the curved surfaces of spiral wraps, thereby creating fluid pockets and possibly changing the volume of (and thus the pressure in) the fluid pockets. The volume can be increased or decreased depending on the orbiting direction of the orbiting scroll, or the geometry of the spiral vane structure. Therefore, a spiral scroll type machine can compress or expand fluids for pumping action. 
         [0006]      FIGS. 10A-10D  show simplified cross-sectional views of interfitted spiral vanes of the fixed and orbiting scroll elements in a spiral scroll-type fluid displacement machine for generally illustrating the concept of the moving pair of spiral vanes moving fluid. Referring to  FIG. 10A , a fluid is sucked into one of the outer openings of the interfitted spiral vanes. Only a single intake of fluid into a fluid pocket is shown for ease of illustration and understanding. As the orbiting scroll progresses along its orbital path, the fluid inlet is closed to create a fluid pocket as shown in  FIG. 10B .  FIG. 10C  shows a complete revolution of the orbiting scroll from  FIG. 10A , showing the progression of the fluid pocket toward the center of the interfitted spiral vanes.  FIG. 10D  shows another complete revolution of the orbiting scroll showing the progression of the fluid pocket to the center of the interfitted spiral vanes where the fluid is discharged. 
         [0007]    In the past decade, the rapid development of the computer and the availability of high-precision CNC machines propelled a marvelous progress in this field. This type of fluid displacement machine demonstrates the following advantages: 
         [0000]    1. High efficiency—mainly because the process of suction-compression-discharge occurs continuously and the expansion of remaining fluid into suction pocket does not exist, thereby offering a higher volume efficiency.
 
2. Torque varies in a relatively small range during a full rotation. Vibration is kept at the low level, as is the noise.
 
3. The structure is simple and compact.
 
         [0008]    The scroll-type compressor has gained increasing popularity and taken more and more market share, which used to be occupied by other types of compressors (such as the reciprocating-type compressor and rotary-type compressor, among others), especially for small-size compressors ranging in power from 0.5 to 15 kilowatts. Scroll-type fluid displacement machines are being widely used in some industries such as for air-conditioning and medical equipment. In order to meet the requirements for broader industry applications, it is desired to further optimize the design of these types of machines. 
         [0009]    Although this design concept of scroll-type fluid displacement machines appeared as early as the beginning of twentieth century, its development was hindered due the difficulty to optimize its design and the requirement for high precision machining. A lot of effort is now being invested to improve the performance and reliability of scroll-type fluid displacement machines. Some are focusing on developing dual scroll compressors to enlarge capacity and achieve higher energy efficiency (as in U.S. Pat. Nos. 5,258,046 and 5,556,269). Some are emphasizing the axial and/or radial compliant mechanism (as in U.S. Pat. Nos. 4,846,639, 6,461,131, and 6,695,600). Some are focusing on a coating treatment on the spiral surface in order to prevent seizure or friction and provide good lubrication between scroll wraps. Some are trying to provide a better rotation preventive device (as in U.S. Pat. No. 6,752,606). Designing scroll vanes to improve the performance of compressor is one of various key areas. Some are focusing on the central portion of spiral surface (as in U.S. Pat. No. 5,513,967). Some are stressing on finding an appropriate scroll curve to increase the volume ratio (as in U.S. Pat. No. 5,458,471), or minimize the machine size (as in U.S. Pat. No. 5,318,424), or for special requirements (as in U.S. Pat. No. 5,547,353). 
         [0010]    However, the conventional scroll-type fluid displacement machines have problems in that the fluid pressure distribution and the fluid pressure variation during operation are not optimized such that the conventional scroll-type fluid displacement machines have the shortcomings less-than-optimal efficiency, and relatively high noise and vibration, all of which contributes to decreased durability of the machines. 
       SUMMARY OF THE INVENTION 
       [0011]    With the aid of sophisticated computer-based real-time measurement systems and advanced computer fluid dynamics analysis, it was found that fluid pressure distribution and variation during the operation of scroll-type fluid displacement machines is key to the design of a new fluid displacement machine structure, and to choose an appropriate curve for scroll wraps. The present fluid displacement machine overcomes the general shortcomings of current machines and manifest inherent advantages such as high efficiency, low noise, low vibration and enhanced durability. With such consideration and using an optimization technique, the present invention uses a single, continuous curve as the base line for constructing scroll vanes. 
         [0012]    The scroll vanes of the present invention are constructed based upon a base line spiral defined by the equation: 
         [0000]        L=K   0 φ K1   e   −φ/     K2      
         [0000]    Wherein L is the distance from the origin to any point on the spiral curve, φ is the angular displacement of the spiral, K o  is a constant greater than 1, K 1  is a constant greater than 1, and K 2  is a constant greater than 10. 
         [0013]    The fluid displacement machine according to a preferred embodiment of the present invention comprises two pairs of scroll elements, where each element is made up of a fixed scroll and an orbiting scroll. These two pairs of scroll elements are separate and mounted in a back-to-back manner. The scroll wraps of the two orbiting scrolls are symmetric with respect to the central axis of a driving shaft. So are the scroll vanes of two fixed scrolls. Two pairs of scrolls are offset by a phase difference of 180 degrees. These two orbiting scrolls share the same orbiting circle. 
         [0014]    The scroll elements can be mounted on two separate crankshafts, of which the eccentric parts are positioned opposite radially. The two crankshafts are then linked with a rigid coupling such that the rotation force can be transmitted to the second crankshaft through the first one. The fluid displacement machine has two inlets and two outlets. The inflowing fluid will be divided and may be compressed or expanded through either pair of scrolls simultaneously. The discharged fluid from each outlet is then merged together to export. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a cross-sectional view of scroll-type fluid displacement machine in accordance with a preferred embodiment of the present invention. 
           [0016]      FIG. 2  is an exploded perspective view showing two orbiting scrolls, two fixed scrolls, two crankshafts and one rigid coupling in the arrangement shown in  FIG. 1 . 
           [0017]      FIG. 3  is a side view of the assembly of two crankshafts and one rigid coupling in accordance with a preferred embodiment of the present invention. 
           [0018]      FIG. 4  is a diagram showing the relative position of eccentric parts of the two crankshafts in accordance with a preferred embodiment of the present invention. 
           [0019]      FIG. 5  is a diagram showing the relative position of spiral wraps of two orbiting scrolls machine in accordance with an embodiment of the present invention. 
           [0020]      FIG. 6  is a diagram showing an example of a spiral curve which defines the shapes of spiral wraps of the scrolls in accordance with the present invention. 
           [0021]      FIG. 7  is a cross-sectional view of spiral wrap of an orbiting scroll used in a single-scroll compressor in accordance with a preferred embodiment of the present invention. 
           [0022]      FIG. 8  is a cross-sectional view of spiral wraps for an orbiting scroll used in a dual-scroll compressor in accordance with a preferred embodiment of the present invention. 
           [0023]      FIG. 9  is a cross-sectional showing the mating of an orbiting scroll with a fixed scroll which are used in a dual-scroll compressor in accordance with an embodiment of the present invention. 
           [0024]      FIGS. 10A-10D  depict cross-sectional views of mating spiral wraps showing the progression of a fluid pocket as the orbiting scroll is rotated along its orbiting path. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Referring to  FIG. 1 , the first fixed scroll  1  has its spiral wrap that interfits the spiral wrap of the first orbiting scroll  2 . The concentric part of crankshaft  4  passes through the center hole of fixed scroll  1  and is supported by bearing  5  while the eccentric part of crankshaft  4  goes through the center hole of orbiting scroll  2  and is supported by bearing  3 . The second fixed scroll  8  has its spiral wrap that interfits the spiral wrap of the first orbiting scroll  9 . The concentric part of crankshaft  10  passes through the center hole of fixed scroll  8  and is supported by bearing  5  while the eccentric part of crankshaft  10  goes through the center hole of orbiting scroll  9  and is supported by bearing  3 . The rigid coupling  6  connects crankshaft  4  and crankshaft  10 . The fixed scroll  1  and fixed scroll  8  are affixed to the housing  7 . The rotating force is transmitted to the end of crankshaft  10  so that the crankshaft  10  drives the orbiting scroll  9  to produce relative orbiting motion. Meanwhile, the force is transmitted to crankshaft  4  through rigid coupling  6  to produce relative orbiting motion. A rotation preventive device includes part  11 ,  12 ,  13 , and  14 , and prevents rotational movement of the orbiting scrolls  2  and  9 . 
         [0026]    The orbital movement generating mechanism for this preferred embodiment comprises two crankshafts  4  and  10  connected by the rigid coupling  6 . However, the orbital movement generating mechanism could comprise a single crankshaft or any other means for producing non-rotating relative orbital movement between the orbital and fixed scrolls. It is noted that, none of the scrolls necessarily needs to be fixed as long as relative orbital movement between mating scrolls is achieved through some means. 
         [0027]      FIG. 2  is an exploded perspective view showing the two orbiting scrolls  2  and  9 , two fixed scrolls  1  and  8 , two crankshafts  4  and  10  and one rigid coupling  6 . 
         [0028]    As shown in  FIG. 3 , the crankshaft  4  and crankshaft  10  are connected by rigid coupling  6 . The eccentric part  4   a  of crankshaft  4  and the eccentric part  10   a  of crankshaft  10  preferably share the same diameter and length. The eccentric distance of  4   a  is preferably equal to that of  10   a.    
         [0029]      FIG. 4  is a diagram representing the relative positioning of the crankshafts  4  and  10  described in  FIG. 3 . C 0  represents the cross-section of the thickest concentric part of crankshaft  4 . C 1  represents the cross-section of the eccentric part  4   a  of crankshaft  4  while C 2  is the cross section of the eccentric part  10   a  of crankshaft  10 . 
         [0030]    C 3  represents the orbiting circle along which the center of C 1  and the center of C 2  travel. The orbiting scroll  2  is mounted on eccentric part  4   a  and the orbiting scroll  9  is mounted on eccentric part  10   a , so these two orbiting scrolls share the same orbiting circle. When connecting crankshaft  4  and crankshaft  10 , it is preferred that the centers of the eccentric parts  4   a  and  10   a  of both crankshafts  4  and  10  are located radially oppositely with respect to the circle C 3 . Such an arrangement simplifies the balancing of the machine. As shown in  FIG. 4 , the center of C 1 , O 1 , is located at the top of C 3  while the center of C 2 , O 2 , is located at the very bottom of C 3 . When crankshaft  4  is rotating in a counter-clockwise direction, the circle C 1  representing the eccentric part  4   a  orbits along the circle C 3  from the top of C 3  counter-clockwise, and the circle C 2  representing the eccentric part  10   a  orbits along the circle C 3  from the bottom of C 3 . During the rotation cycle, eccentric parts  4   a  and  10   a  always remain at radially opposite positions. 
         [0031]      FIG. 5  depicts the relative overlapping positioning of the spiral wraps of two orbiting scrolls  2  and  9 . The rotating axis of the concentric part of crankshaft  4  goes through point O. As shown in  FIG. 5 , orbiting scrolls  2  and  9  are symmetric around the point O. Therefore, the mass distribution of orbiting scroll  2  and that of orbiting scroll  9  would normally also be symmetric around the point O, if the orbiting scrolls are both uniformly made of the same material. The need for balance weight to balance the orbiting scroll is thus eliminated. 
         [0032]    The scroll-type fluid displacement machine in accordance with present invention preferably comprises two inlets and two outlets. Referring back to  FIG. 1 , there are inlets.  1   a  and  8   a , and there are outlets  1   b  and  8   b . The inflowing fluid is divided and fed into the two inlets  1   a  and  8   a , processed in the two pairs of scrolls, discharged through each outlet  1   b  and  8   b , and merged together to export. 
         [0033]    The non-constant-pitch spiral curve shown in  FIG. 6  is used as the base line to define the spiral vanes of the orbiting scrolls. The defining equation for such a spiral curve is: 
         [0000]        L=K   0 φ K1   e   −φ/     K2      
         [0000]    where 
         [0034]    L: the distance from the origin to any point on the spiral curve; 
         [0035]    φ: the angular displacement of the spiral curve 
         [0036]    K 0 : a real number greater 1, (K 0 &gt;1) 
         [0037]    K 1 : a real number greater 1, (K 1 &gt;1) 
         [0038]    K 2 : a real number greater 10, K 2 &gt;10 
         [0039]    The strategy to select an appropriate spiral curve is: 
         [0040]    1. To obtain a high volume ratio. The ratio of the displacement (V s ) to the final compression volume (V e ) is required to be high enough to meet the requirement according the application of the scroll-type fluid displacement machine. 
         [0041]    2. To use a single, continuous, smoothly changing curve to define the scroll wraps for its entire length. It is required that the change of the volume of the fluid pocket formed between two scrolls be smooth and continuous in order to increase or decrease the fluid pressure smoothly and avoid shock. 
         [0042]    3. When the former two conditions are satisfied, it is desired to have a spiral curve, which defines a faster change of volume of the fluid pocket. In so doing, the full cycle of suction-processing-discharge is shortened. Energy efficiency can be also enhanced. 
         [0043]    The particular curve shown in  FIG. 6  is defined by the equation: 
         [0000]        L= 2φ 1.5   e   −φ/100    
         [0044]    It is important to note that this particular curve is just a member of a family of curves that are described by the equation. In practice, the consideration of performance requirements including power, physical properties of fluid and pressure ratio, will be included in the design of the curve. All these requirements must be met with the highest priority. Then the curve will be optimized to enable the fluid displacement machine to achieve its optimum performance in terms of its fluid dynamics. The result of optimization is the best combination of three parameters: K 0 , K 1  and K 2 . The intended machine will be improved in the following aspects: increased operating efficiency, reduced vibration, reduced noise and increased durability. 
         [0045]    The proposed curve can be used to construct a scroll vane for a single-scroll fluid displacement machine as well as dual-scroll fluid displacement machine. A typical method is employed to construct the scroll vanes for a single-scroll fluid displacement machine.  FIG. 7  shows the constructed cross-section of an orbiting scroll  20 . The scroll vane of the corresponding fixed scroll  22  is symmetric to the vane of the orbiting scroll around the origin. 
         [0046]    The proposed curve can be also adopted in the design of dual-scroll fluid displacement machine. A typical dual-scroll fluid displacement machine has a crankshaft which goes through the fixed scroll  22  and the orbiting scroll  20 . In order to allow the eccentric part of the crankshaft to pass through the central portion of orbiting scroll  20 , the spiral scrolls must start from some angular offset, such as is depicted in  FIGS. 8 and 9  where an angular offset of 141° in the second turn counting from the center.  FIG. 8  depicts the cross-section of spiral wraps of orbiting scroll  20 . The dimensions 4.35 mm, 5.79 mm, and 5.16 are shown in  FIG. 8  as an example of one embodiment for one optimum case; nevertheless, it should be clearly understood that the present invention is not just limited to the dimensions shown in  FIG. 8 . Other optimum dimensions satisfying the equation L=K 0 φ K1 e −φ/     K2    besides those shown in  FIG. 8  are also possible. The mating between the orbiting scroll  20  and the fixed scroll  22  is shown in  FIG. 9 . 
         [0047]    It will be clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While various embodiments including the presently preferred one has been described for purposes of this disclosure, various changes and modifications may be made, which are well within the scope of the present invention. Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the invention disclosed and as defined in the appended claims.