Abstract:
A scroll type fluid machinery includes first and second fluid volume changing mechanisms. The first fluid volume changing mechanism includes a first stationary scroll and a first orbiting scroll, and the first orbiting scroll is associated with the first stationary scroll so that the first orbiting scroll is able to orbit with respect to the first stationary scroll. The second fluid volume changing mechanism includes a second stationary scroll and a second orbiting scroll, and the second orbiting scroll is associated with the second stationary scroll so that the second orbiting scroll is able to orbit with respect to the second stationary scroll. The scroll type fluid machinery further includes a plurality of orbiting units. Each of the orbiting units includes a rotating member that is able to rotate relative to the first and second stationary scrolls, and a thrust-canceling shaft connected to the first orbiting scroll and to the second orbiting scroll. The thrust-canceling shaft is eccentrically and rotatably supported in the rotating member, and the orbiting units are arranged to form one or more parallelogram linkages for preventing the first and second orbiting scrolls from self-rotation. One or more orbiting units are used to transmit a driving force to or from the first and the second fluid volume changing mechanisms.

Description:
[0001]    This application is a continuation of international application PCT/CA03/01655, designating the United States and filed Nov. 4, 2003, and U.S. application Ser. No. 10/287,042, filed Nov. 4, 2002, the disclosures of which are expressly incorporated by reference herein. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to a scroll type fluid machinery, which can be used as compressors, vacuum pumps, expansionary machines, etc.  
           [0003]    A regular scroll type fluid machinery usually consists of a casing, a stationary scroll fixed on the casing, a driving crankshaft rotatably supported on the casing with bearings, and an orbiting scroll driven by the crankshaft. The orbiting scroll is constrained by an anti-self-rotating mechanism to realize an orbiting movement with respect to the stationary scroll. The volumes formed between the stationary scroll and the orbiting scroll change with the orbiting movement of the orbiting scroll, and the changing volumes compress the fluid in the volumes. The thrust force generated by the fluid pressure exerts on the orbiting scroll, and passes to a thrust bearing.  
           [0004]    In order to reduce the energy consumed by the friction force on the thrust bearing, a double orbiting scroll structure was proposed. These two orbiting scrolls are mounted back-to-back to cancel the thrust force. This structure has been described in U.S. Pat. Nos. 801,812, 3,011,694, and 4,990,071.  
           [0005]    There are two approaches for providing the driving force in the aforementioned patents. One approach is to make the driving shaft shun the stationary scroll and to input the driving force through some driving mechanisms surrounding the periphery of the orbiting scroll. The other approach is to make the crankshaft go through the center of the stationary scroll to drive the back-to-back orbiting scrolls.  
           [0006]    The first approach greatly increases the size of the machine because the driving shaft must be mounted on the outside surrounding the stationary scroll. The second approach reduces the volume compression ratio of the fluid machinery because the driving device occupies the central portion of the orbiting scroll, which is vitally important to the compression ratio.  
           [0007]    Another structure used to cancel the thrust force can be found in U.S. Pat. Nos. 4,515,539 and 6,267,572B1, and Japanese Patent Document 04-121,474. Two mirror-imaged orbiting scrolls are connected to the two ends of a thrust-canceling shaft, which is rotatably fitted into an eccentric through-hole in a motor shaft. To prevent the orbiting scroll from self-rotation, a mechanism is specially provided. Furthermore, the relatively weak stiffness of the orbiting scroll is caused by the fact that the orbiting scroll is supported by only one thrust canceling shaft, thus affecting the efficiency of the compressors.  
         SUMMARY OF THE INVENTION  
         [0008]    An object of the present invention is to improve the performance, efficiency, and reliability of the scroll type fluid machinery. According to one aspect of the present invention, the scroll type fluid machinery comprises two housings, two stationary scrolls, two orbiting scrolls, and three orbiting units. The two housings are connected with each other. Each of the two stationary scrolls is fixed to the housings. The two stationary scrolls have an end plate and a spiral wrap extending from the end plate. Each of the two orbiting scrolls has an end plate and a spiral wrap extending from the end plate. The two orbiting scrolls are assembled with the two stationary scrolls, respectively. The three orbiting units are located between the two orbiting scrolls. Each of the three orbiting units comprises a rotating member rotatably supported on the two housings through two bearings, a thrust-canceling shaft rotatably supported in an eccentric through-hole in the rotating member through two bearings. Each thrust-canceling shaft is fixed between the two orbiting scrolls. The three orbiting units, the two orbiting scrolls, and the two housings compose three parallelogram linkages that form an anti-self-rotating mechanism. When one or more of the rotating members are driven, the orbiting scrolls orbit in the same radius with respect to the stationary scrolls to change the fluid volumes. Most of the thrusting force on the two orbiting scrolls generated by fluid pressure is canceled by the three thrust-canceling shafts, and the rest is withstood by the bearings in the orbiting units. Due to even loading among the three orbiting units, all three rotating members are driven.  
           [0009]    It is also possible to use two orbiting units. In this case, the two rotating members of the two orbiting units can be driven by two motors. Otherwise, a synchronous device, such as synchronous belt or gears, can be used. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a schematic sectional view of a scroll compressor according to a first embodiment of the present invention.  
         [0011]    [0011]FIG. 2 is a left view of the machine shown in FIG. 1, excluding the left stationary scroll, the left orbiting scroll, and the left housing.  
         [0012]    [0012]FIG. 3 is a schematic sectional view of an orbiting unit of the machine shown in FIG. 1.  
         [0013]    [0013]FIG. 4 is a schematic sectional view of a scroll expander according to a second embodiment of the present invention.  
         [0014]    [0014]FIG. 5 is a left view of the machine shown in FIG. 4, excluding the left stationary scroll and left orbiting scroll.  
         [0015]    [0015]FIG. 6 is a schematic sectional view of an orbiting unit of the machine shown in FIG. 4.  
         [0016]    [0016]FIG. 7 is a schematic sectional view of a scroll compressor according to a third embodiment of the present invention.  
         [0017]    [0017]FIG. 8 is a left view of the machine shown in FIG. 7, excluding the left stationary scroll and left orbiting scroll.  
         [0018]    [0018]FIG. 9 is a schematic sectional view of an orbiting unit of the machine shown in FIG. 7.  
         [0019]    [0019]FIG. 10 is a schematic sectional view of a scroll compressor according to a fourth embodiment of the present invention.  
         [0020]    [0020]FIG. 11 is a left view of the machine shown in FIG. 10, excluding the left stationary scroll, left orbiting scroll, and left housing.  
         [0021]    [0021]FIG. 12 is a schematic sectional view of an orbiting unit of the machine shown in FIG. 10.  
         [0022]    [0022]FIG. 13 is a schematic sectional view of a scroll compressor according to a fifth embodiment of the present invention.  
         [0023]    [0023]FIG. 14 is a left view of the machine shown in FIG. 13, excluding the left stationary scroll, left orbiting scroll, and left housing.  
         [0024]    [0024]FIG. 15 is a schematic sectional view of an orbiting unit of the machine shown in FIG. 13.  
         [0025]    [0025]FIG. 16 is a schematic sectional view of a scroll compressor according to a sixth embodiment of the present invention.  
         [0026]    [0026]FIG. 17 is a left view of the machine shown in FIG. 16, excluding the left stationary scroll and left orbiting scroll.  
         [0027]    [0027]FIG. 18 is a schematic sectional view of the first orbiting unit of the machine shown in FIG. 16.  
         [0028]    [0028]FIG. 19 is a schematic sectional view of the second/third orbiting unit of the machine shown in FIG. 16.  
         [0029]    [0029]FIG. 20 is a schematic sectional view of a scroll compressor according to a seventh embodiment of the present invention.  
         [0030]    [0030]FIG. 21 is a left view of the machine shown in FIG. 20, excluding the left stationary scroll, left orbiting scroll, and left housing.  
         [0031]    [0031]FIG. 22 is a schematic drawing of an embodiment having four orbiting units.  
         [0032]    [0032]FIG. 23 is a schematic sectional drawing of an orbiting unit, with the periphery of the rotating member having the form of a sprocket. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]    [0033]FIG. 1 is a schematic sectional view of a scroll compressor according to the first embodiment of the present invention. FIG. 2 is a left view of the compressor excluding its left stationary scroll and left orbiting scroll and left housing. FIG. 3 is a schematic sectional view of an orbiting unit of the compressor. As shown in FIGS. 1-3, a left housing  1 A and a right housing  1 B are mounted in a mirror-image relationship through screws  51  to form a housing  1 . A left stationary scroll  2 A is connected to the left housing  1 A through screws  52 A, and a right stationary scroll  2 B is connected to the right housing  1 B through screws  52 B. The two housings  1 A and  1 B, the two stationary scrolls  2 A and  2 B compose the fixed structure of this machine. The two stationary scrolls  2 A and  2 B comprise, respectively, their own end plates  7 A and  7 B and spiral wraps  9 A and  9 B extending from the corresponding end plates  7 A and  7 B. The scroll compressor includes two suction ports  4 A and  4 B that are connected, and two discharge ports  5 A and  5 B that are also connected. Two orbiting scrolls  3 A and  3 B comprise, respectively, their own end plates  8 A and  8 B and spiral wraps  6 A and  6 B extending from the corresponding end plates  8 A and  8 B. Furthermore, the directions of the spiral wraps  6 A and  6 B should be arranged in a mirror-image relationship, and the directions of the spiral wraps  9 A and  9 B should be arranged in a mirror-image relationship. Three orbiting units  40  are mounted between the two orbiting scrolls  3 A and  3 B. Each of the three orbiting units  40  comprises a rotating member  10  rotatably supported on the two housings  1 A and  1 B through two bearings  11 A and  11 B, and a thrust-canceling shaft  20  rotatably supported in the rotating member  10  by two bearings  14 A and  14 B. The rotating member  10  comprises a balancing weight  19 , a pulley  18  located on the periphery of the rotating member  10 , and an eccentric through-hole  17 . The rotating axis ◯ 2  of the thrust-canceling shaft  20  is eccentric from the rotating axis ◯ 1  of the rotating member  10  with a distance of e. The three thrust-canceling shafts  20  are fixed between the two orbiting scrolls  3 A and  3 B. As shown in FIG. 2, the triangle defined by ◯ 1 -◯ 1 -◯ 1  is identical to the triangle defined by ◯ 2 -◯ 2 -◯ 2 . The three orbiting units  40 , the two orbiting scroll  3 A and  3 B, and the two housings  1 A and  1 B compose three parallelogram linkages which form an anti-self-rotating mechanism. Each thrust-canceling shaft  20  comprises a left end  21 A, a right end  21 B, a sleeve  23 , and a bearing pre-loading screw  22 . The length of the sleeve  23  should be set such that the two ends  21 A and  21 B contact the sleeve  23  with proper preload when the bearings  14 A and  14 B are properly preloaded by the bearing preloading screw  22 . The three pulleys  18  are driven by a pulley  31  of a motor  30 . A pre-tensioning pulley  32  is used to increase the wrap angles on the three pulleys  18  and the pulley  31  of the motor  30  and to apply proper pre-tension to a belt  33 . The orbiting scrolls  3 A and  3 B get a much more even driving force from the three rotating member  10 , and this makes the operation of the machine smoother and more reliable. When the orbiting scrolls  3 A and  3 B orbit, the volumes formed by the spiral wraps  9 A,  9 B and  6 A,  6 B of the stationary scrolls  2 A and  2 B and the orbiting scrolls  3 A and  3 B are continuously changed, fluid introduced through the suction ports  4 A and  4 B is continuously compressed, and finally the compressed fluid is discharged through the discharge ports  5 A and  5 B. During the process of compression, the fluid generates thrusting force exerted on the end plates  8 A and  8 B of the orbiting scrolls  3 A and  3 B. Most of the thrusting force is canceled through the three thrust-canceling shafts  20 , and the rest is withstood by the bearings  11 A,  11 B,  14 A, and  14 B in the orbiting units  40 . The frictional consumption of power is reduced because of the cancellation of the axial thrusting force, resulting in a high efficiency.  
         [0034]    [0034]FIG. 4 is a schematic sectional view of a scroll expander according to the second embodiment of the present invention. FIG. 5 is a left view of the scroll expander, excluding its left stationary scroll and left orbiting scroll. FIG. 6 is a schematic sectional view of an orbiting unit of the scroll expander. As shown in FIGS. 4-6, a left housing  1 A and a right housing  1 B are mounted in a mirror-image relationship through screws  51 . A left stationary scroll  2 A is connected to the left housing  1 A through screws  52 A, and a right stationary scroll  2 B is connected to the right housing  1 B through screws  52 B. The two housings  1 A and  1 B, the two stationary scrolls  2 A and  2 B compose the fixed structure of this machine. The two stationary scrolls  2 A and  2 B comprise, respectively, their own end plates  7 A and  7 B and spiral wraps  9 A and  9 B extending from the corresponding end plates  7 A and  7 B. The scroll expander includes two suction ports  4 A and  4 B that are connected, and two discharge ports  5 A and  5 B that also are connected. Two orbiting scrolls  3 A and  3 B comprise, respectively, their own end plates  8 A and  8 B and spiral wraps  6 A and  6 B extending from the corresponding end plates  8 A and  8 B. Furthermore, the directions of the spiral wraps  6 A and  6 B should be arranged in a mirror-image relationship, and the directions of the spiral wraps  9 A and  9 B should be arranged in a mirror-image relationship. Three orbiting units  40  are mounted between the two orbiting scrolls  3 A and  3 B. Each of the three orbiting units  40  comprises a rotating member  10  rotatably supported on the two housings  1 A and  1 B through two bearings  11 A and  11 B, and a thrust-canceling shaft  20  rotatably supported in the rotating member  10  by two bearings  14 A and  14 B. The rotating member  10  comprises a pulley  18  with an eccentric through-hole  17  of diameter d, two balancing weights  13 A and  13 B fitted in the eccentric through-hole  17  through screws  12 A and  12 B, two holes  119 A and  119 B of diameter D being, respectively, in the two balancing weights  13 A and  13 B. The bearings  14 A and  14 B are fitted in the holes  119 A and  119 B, respectively, to support the thrust-canceling shaft  20 . The diameter D may be made larger than the diameter d so that larger spaces can be provided for the bearings  14 A and  14 B. The rotating axis ◯ 2  of the thrust-canceling shaft  20  is eccentric from the rotating axis ◯ 1  of the rotating member  10  with a distance of e. The three thrust-canceling shafts  20  are fixed between the two orbiting scrolls  3 A and  3 B. As shown in FIG. 5, the triangle defined by ◯ 1 -◯ 1 -◯ 1  is identical to the triangle defined by ◯ 2 -◯ 2 -◯ 2 . The three orbiting units  40 , the two orbiting scroll  3 A and  3 B, and the two housings  1 A and  1 B compose three parallelogram linkages which form an anti-self-rotating mechanism. Each thrust-canceling shaft  20  comprises a left end  21 A, a right end  21 B, a sleeve  23 , and a bearing pre-loading screw  22 . The length of the sleeve  23  should be set such that the two ends  21 A and  21 B contact the sleeve  23  with proper preload when the bearings  14 A and  14 B are properly preloaded by the bearing preloading screw  22 . A pulley  31  of a generator  30  is driven by the three pulleys  18  through a belt  33 . A pre-tensioning pulley  32  is used to increase the wrap angles on the three pulleys  18  and the pulley  31  of the generator  30  and to apply proper pre-tension to the belt  33 . The orbiting scrolls  3 A and  3 B provide a more even driving force to the three rotating members  10 , and this makes the operation of the machine smoother and more reliable. When the orbiting scrolls  3 A and  3 B orbit, the volumes formed by the spiral wraps  9 A,  9 B and  6 A,  6 B of the stationary scrolls  2 A and  2 B and the orbiting scrolls  3 A and  3 B are continuously changed, fluid introduced through the suction ports  4 A and  4 B is continuously expanded, and finally the expanded fluid is discharged through the discharge ports  5 A and  5 B. During the process, the fluid generates thrusting force exerted on the end plates  8 A and  8 B of the orbiting scrolls  3 A and  3 B. Most of the thrusting force is canceled through the three thrust-canceling shafts  20 , and the rest is withstood by the bearings  11 A,  11 B,  14 A, and  14 B in the orbiting units  40 . The frictional consumption of power is reduced because of the cancellation of the axial thrusting force, resulting in a high efficiency.  
         [0035]    [0035]FIG. 7 is a schematic sectional view of a scroll compressor according to the third embodiment of the present invention. FIG. 8 is the left view of the compressor excluding its left stationary scroll and left orbiting scroll. FIG. 9 is a schematic sectional view of an orbiting unit of the compressor. As shown in FIGS. 7-9, the compressor includes a motor  60  for driving each orbiting unit. Each motor  60  includes a shell  61 , which is fixed between two housings  1 A and  1 B, with the stator  62  of the motor  60  fixed in the shell  61 . The left housing  1 A and the right housing  1 B are mounted in a mirror-image relationship through screws  51 . A left stationary scroll  2 A is connected to the left housing  1 A through screws  52 A, and a right stationary scroll  2 B is connected to the right housing  1 B through screws  52 B. The two housings  1 A and  1 B, the two stationary scrolls  2 A and  2 B, and the shells  61  with the stators  62  compose the fixed structure of this machine. The two stationary scrolls  2 A and  2 B comprise, respectively, their own end plates  7 A and  7 B and spiral wraps  9 A and  9 B extending from the corresponding end plates  7 A and  7 B. The compressor includes two suction ports  4 A and  4 B that are connected, and two discharge ports  5 A and  5 B that are connected. Two orbiting scrolls  3 A and  3 B comprise, respectively, their own end plates  8 A and  8 B and spiral wraps  6 A and  6 B extending from the corresponding end plates  8 A and  8 B. Furthermore, the directions of the spiral wraps  6 A and  6 B should be arranged in a mirror-image relationship, and the directions of the spiral wraps  9 A and  9 B should be arranged in a mirror-image relationship. Three orbiting units  40  are mounted between the two orbiting scrolls  3 A and  3 B. Each of the three orbiting units  40  comprises a rotating member  10  rotatably supported on the two housings  1 A and  1 B through two bearings  11 A and  11 B, and a thrust-canceling shaft  20  rotatably supported in the rotating member  10  by two bearings  14 A and  14 B. The rotating member  10  comprises a hollow shaft  64  of the motor  60  with an eccentric through-hole  17 , a motor rotor  63  fixed on the hollow shaft  64 , and two balancing weights  13 A and  13 B fitted in the eccentric through-hole  17  through screws  12 A and  12 B. The bearings  14 A and  14 B are fitted in the balancing weights  13 A and  13 B, respectively, to support the thrust-canceling shaft  20 . The rotating axis ◯ 2  of the thrust-canceling shaft  20  is eccentric from the rotating axis ◯ 1  of the hollow shaft  64  with a distance of e. The three thrust-canceling shafts  20  are fixed between the two orbiting scrolls  3 A and  3 B. As shown in FIG. 8, the triangle defined by ◯ 1 -◯ 1 -◯ 1  is identical to the triangle defined by ◯ 2 -◯ 2 -◯ 2 . The three orbiting units  40 , the two orbiting scrolls  3 A and  3 B, and the two housings  1 A and  1 B compose three parallelogram linkages which form an anti-self-rotating mechanism. Each thrust-canceling shaft  20  comprises a left end  21 A, a right end  21 B, a sleeve  23 , and a bearing pre-loading screw  22 . The length of the sleeve  23  should be set such that the two ends  21 A and  21 B contact the sleeve  23  with proper preload when the bearings  14 A and  14 B are properly preloaded by the bearing pre-loading screw  22 . The orbiting scrolls  3 A and  3 B get a much more even driving force from the three motors  60 , and this makes the operation of the machine smoother and more reliable. When the orbiting scrolls  3 A and  3 B orbit, the volumes formed by the spiral wraps  9 A,  9 B and  6 A,  6 B of the stationary scrolls  2 A and  2 B and the orbiting scrolls  3 A and  3 B are continuously changed, fluid introduced through the suction ports  4 A and  4 B is continuously compressed, and finally the compressed fluid is discharged through the discharge ports  5 A and  5 B. During the process of compression, the fluid generates thrusting force exerted on the end plates  8 A and  8 B of the orbiting scrolls  3 A and  3 B. Most of the thrusting force is canceled through the three thrust-canceling shafts  20 , and the rest is withstood by the bearings  11 A,  11 B,  14 A, and  14 B in the orbiting units  40 . The frictional consumption of power is reduced because of the cancellation of the axial thrusting force, resulting in a high efficiency.  
         [0036]    [0036]FIG. 10 is a schematic sectional view of a scroll compressor according to the fourth embodiment of the present invention. FIG. 11 is the left view of the compressor excluding its left stationary scroll, left orbiting scroll, and left housing. FIG. 12 is a schematic sectional view of an orbiting unit of the compressor. As shown in FIGS. 10-12, a left housing  1 A and a right housing  1 B are mounted in a mirror-image relationship through screws  51 . A left stationary scroll  2 A is connected to the left housing  1 A through screws  52 A, and a right stationary scroll  2 B is connected to the right housing  1 B through screws  52 B. The two housings  1 A and  1 B and the two stationary scrolls  2 A and  2 B compose the fixed structure of this machine. The two stationary scrolls  2 A and  2 B comprise, respectively, their own end plates  7 A and  7 B and spiral wraps  9 A and  9 B extending from the corresponding end plates  7 A and  7 B. The compressor includes two suction ports  4 A and  4 B that are connected, and two discharge ports  5 A and  5 B that are connected. Two orbiting scrolls  3 A and  3 B comprise, respectively, their own end plates  8 A and  8 B and spiral wraps  6 A and  6 B extending from the corresponding end plates  8 A and  8 B. Furthermore, the directions of the spiral wraps  6 A and  6 B should be arranged in a mirror-image relationship, and the directions of the spiral wraps  9 A and  9 B should be arranged in a mirror-image relationship. Two orbiting units  40  are mounted between the two orbiting scrolls  3 A and  3 B. Each of the two orbiting units  40  comprises a rotating member  10  rotatably supported on the two housings  1 A and  1 B through two bearings  11 A and  11 B, and a thrust-canceling shaft  20  rotatably supported in the rotating member  10  by two bearings  14 A and  14 B. The rotating member  10  comprises a balancing weight  19 , a synchronous pulley  18  located on the periphery of the rotating member  10 , and an eccentric through-hole  17 . The two thrust-canceling shafts  20  are fixed between the two orbiting scrolls  3 A and  3 B. Each thrust-canceling shaft  20  comprises a left end  21 A, a right end  21 B, a sleeve  23 , and a bearing pre-loading screw  22 . The length of the sleeve  23  should be set such that the two ends  21 A and  21 B contact the sleeve  23  with proper preload when the bearings  14 A and  14 B are properly preloaded by the bearing pre-loading screw  22 . The synchronous pulleys  18  are driven by a synchronous pulley  31  of a motor  30 . A pre-tensioning pulley  32  is used to increase the wrap angle on the two synchronous pulleys  18  and the pulley  31  of the motor  30  and to apply proper pre-tension to a synchronous belt  33 . The rotating axis ◯ 2  of the thrust-canceling shaft  20  is eccentric from the rotating axis ◯ 1  of the rotating member  10  with a distance of e. As shown in FIG. 11, ◯ 1 -◯ 2 -◯ 2 -◯ 1  forms a parallelogram linkage. The two orbiting units  40  plus the synchronous belt  33  form an anti-self-rotating mechanism. The orbiting scrolls  3 A and  3 B can get a more even driving force from the two orbiting units, and this makes the operation of the machine smoother and more reliable. The volumes formed by the spiral wraps  9 A,  9 B and  6 A,  6 B of the stationary scrolls  2 A and  2 B and the orbiting scrolls  3 A and  3 B change continuously when the orbiting scrolls  3 A and  3 B orbit. Fluid introduced through the suction ports  4 A and  4 B is continuously compressed, and discharged through the discharge ports  5 A and  5 B. During the process of compression, the fluid generates thrusting force exerted on the end plates  8 A and  8 B of the orbiting scrolls  3 A and  3 B. Most of the thrusting force is canceled through the two thrust-canceling shafts  20 , and the rest is withstood by the bearings  11 A,  11 B,  14 A, and  14 B in the orbiting units  40 . The frictional consumption of power is reduced because of the cancellation of the axial thrusting force, resulting in a high efficiency.  
         [0037]    [0037]FIG. 13 is a schematic sectional view of a scroll compressor according to the fifth embodiment of the present invention. FIG. 14 is the left view of the compressor, excluding its left stationary scroll, left orbiting scroll, and left housing. FIG. 15 is a schematic sectional view of an orbiting unit of the compressor. As shown in FIGS. 13-15, a left housing  1 A and a right housing  1 B are mounted in a mirror-image relationship through screws  51 . A left stationary scroll  2 A is connected to the left housing  1 A through screws  52 A, and a right stationary scroll  2 B is connected to the right housing  1 B through screws  52 B. The two housings  1 A and  1 B and the two stationary scrolls  2 A and  2 B compose the fixed structure of this machine. The two stationary scrolls  2 A and  2 B comprise, respectively, their own end plates  7 A and  7 B and spiral wraps  9 A and  9 B extending from the corresponding end plates  7 A and  7 B. The compressor includes two suction ports  4 A and  4 B that are connected, and two discharge ports  5 A and  5 B that are connected. Two orbiting scrolls  3 A and  3 B comprise, respectively, their own end plates  8 A and  8 B and spiral wraps  6 A and  6 B extending from the corresponding end plates  8 A and  8 B. Furthermore, the directions of the spiral wraps  6 A and  6 B should be arranged in a mirror-image relationship, and the directions of the spiral wraps  9 A and  9 B should be arranged in a mirror-image relationship. Two orbiting units  40  are mounted between the two orbiting scrolls  3 A and  3 B. Each of the two orbiting units  40  comprises a rotating member  10  rotatably supported on the two housings  1 A and  1 B through two bearings  11 A and  11 B, and a thrust-canceling shaft  20  rotatably supported in the rotating member  10  by two bearings  14 A and  14 B. The rotating member  10  comprises a balancing weight  19 , a gear  18  located on the periphery of the rotating member  10 , and an eccentric through-hole  17 . The two thrust-canceling shafts  20  are fixed between the two orbiting scrolls  3 A and  3 B. Each thrust-canceling shaft  20  comprises a left end  21 A, a right end  21 B, a sleeve  23 , and a bearing pre-loading screw  22 . The length of the sleeve  23  should be set such that the two ends  21 A and  21 B contact the sleeve  23  with proper preload when the bearings  14 A and  14 B are properly preloaded by the bearing pre-loading screw  22 . The two gears  18  are driven by a gear  31  of a motor  30  through an idler gear  32 . The rotating axis ◯ 2  of the thrust-canceling shaft  20  is eccentric from the rotating axis ◯ 1  of the rotating member  10  with a distance of e. As shown in FIG. 14, ◯ 1 -◯ 2 -◯ 2 -◯ 1  forms a parallelogram linkage. The two orbiting units plus the idler gear  32  form an anti-self-rotating mechanism. The orbiting scrolls  3 A and  3 B can get a more even driving force from the two orbiting units  40 , and this makes the operation of the machine smoother and more reliable. The volumes formed by the spiral wraps  9 A,  9 B and  6 A,  6 B of the stationary scrolls  2 A and  2 B and the orbiting scrolls  3 A and  3 B change continuously when the orbiting scrolls  3 A and  3 B orbit. Fluid introduced through the suction ports  4 A and  4 B is continuously compressed, and discharged through the discharge ports  5 A and  5 B. During the process of compression, the fluid generates thrusting force exerted on the end plates  8 A and  8 B of the orbiting scrolls  3 A and  3 B. Most of the thrusting force is canceled through the two thrust-canceling shafts  20 , and the rest is withstood by the bearings  11 A,  11 B,  14 A, and  14 B in the orbiting units  40 . The frictional consumption of power is reduced because of the cancellation of the axial thrusting force, resulting in a high efficiency.  
         [0038]    [0038]FIG. 16 is a schematic sectional view of a scroll compressor according to the sixth embodiment of the present invention. FIG. 17 is a left view of the compressor, excluding the left stationary scroll and left orbiting scroll. FIG. 18 is a schematic sectional view of its first orbiting unit  40 . FIG. 19 is a schematic sectional view of its second/third orbiting unit  140 . As shown in FIGS. 16-19, a shell  61  of a motor  60  and two mounting sleeves  151  are mounted between two housings  1 A and  1 B. A stator  62  is fixed in the shell  61 . The left housing  1 A and the right housing  1 B are fixed through screws  51 . The left housing  1 A is connected to a left stationary scroll  2 A through screw set  52 A, and the right housing  1 B is connected to a right stationary scroll  2 B through screw set  52 B. The two housings  1 A and  1 B, the two stationary scrolls  2 A and  2 B, the shell  61  with the stator  62 , and the two mounting sleeves  151  compose the fixed structure of this machine. The two stationary scrolls  2 A and  2 B comprise, respectively, their own end plates  7 A and  7 B and spiral wraps  9 A and  9 B extending from the corresponding end plates  7 A and  7 B. The compressor includes two suction ports  4 A and  4 B that are connected, and two discharge ports  5 A and  5 B should be connected. Two orbiting scrolls  3 A and  3 B comprise, respectively, their own end plates  8 A and  8 B and spiral wraps  6 A and  6 B extending from the corresponding end plates  8 A and  8 B. Furthermore, the directions of the spiral wraps  6 A and  6 B should be arranged in a mirror-image relationship, and the directions of the spiral wraps  9 A and  9 B should be arranged in a mirror-image relationship. A first orbiting unit  40 , a second and a third orbiting units  140  are mounted between the two orbiting scrolls  3 A and  3 B. The first orbiting unit  40 , as shown in FIG. 18, comprises a first rotating member  10  rotatably supported on the two housings  1 A and  1 B through two bearings  11 A and  11 B, and a thrust-canceling shaft  20  rotatably supported in the first rotating member  10  by two bearings  14 A and  14 B. The first rotating member  10  comprises a first hollow shaft  64  with an eccentric through-hole  17 , a motor rotor  63  fixed on the first hollow shaft  64 , a left balancing weight  13 A with a first pulley  18  fitted in the eccentric through-hole  17  through screws  12 A, a right balancing weight  13 B fitted in the eccentric through-hole  17  through screws  12 B. The bearing  14 A fitted in the left balancing weight  13 A and the bearing  14 B fitted in the right balancing weight  13 B support the thrust-canceling shaft  20 . The rotating axis ◯ 2  of the thrust-canceling shaft  20  has an eccentric distance e from the rotating axis ◯ 1  of the first rotating member  10 . The thrust-canceling shaft  20  comprises a left end  21 A, a right end  21 B, a sleeve  23 , and a bearing pre-loading screw  22 . The length of the sleeve  23  should make the two ends  21 A and  21 B contact the sleeve  23  with proper preload when the bearings  14 A and  14 B are properly preloaded by the bearing pre-loading screw  22 . The second/third orbiting unit  140 , as shown in FIG. 19, comprises a second/third rotating member  110  rotatably supported on the two housings  1 A and  1 B through bearings  111 A and  111 B, and a thrust-canceling shaft  120  rotatably supported in the second/third rotating member  110  by bearings  114 A and  114 B. The second/third rotating member  110  comprises a second/third hollow shaft  164  with an eccentric through-hole  117 , a left balancing weight  113 A with a second/third pulley  118  fitted in the eccentric through-hole  117  through screws  112 A, a right balancing weight  113 B fitted in the eccentric through-hole  117  through screws  112 B. The bearing  114 A fitted in the left balancing weight  113 A and the bearing  114 B fitted in the right balancing weight  113 B support the thrust-canceling shaft  120 . The rotating axis ◯ 4  of the thrust-canceling shaft  120  has an eccentric distance e from the rotating axis ◯ 3  of the second/third rotating member  110 . Each thrust-canceling shaft  120  comprises a left end  121 A, a right end  121 B, a sleeve  123 , and a pre-loading screw  122 . The length of the sleeve  123  should make the two ends  121 A and  121 B contact sleeve  123  with proper pre-load. As shown in FIG. 17, the triangle defined by ◯ 1 -◯ 3 -◯ 3  is identical to the triangle defined by ◯ 2 -◯ 4 -◯ 4 . The first orbiting unit  40  and the second and the third orbiting units  140 , the two orbiting scrolls  3 A and  3 B, and the two housings  1 A and  1 B compose three parallelogram linkages which form an anti-self-rotating mechanism. The volumes formed by the spiral wraps  9 A,  9 B and  6 A,  6 B of the stationary scrolls  2 A and  2 B and the orbiting scrolls  3 A and  3 B change continuously when the orbiting scrolls  3 A and  3 B orbit. Fluid introduced through the suction ports  4 A and  4 B is continuously compressed, and discharged through the discharge ports  5 A and  5 B. During the process of compression, the fluid generates thrusting force exerted on the end plates  8 A and  8 B of orbiting scrolls  3 A and  3 B. Most of the thrusting force is canceled through the thrust-canceling shafts  20  and  120 , and the rest is withstood by the bearings  11 A,  11 B,  14 A, and  14 B in the first orbiting unit  40  and the bearings  111 A,  111 B,  114 A, and  114 B in the second and third orbiting units  140 . The frictional consumption of power is reduced because of the cancellation of the axial thrusting force, resulting in a high efficiency.  
         [0039]    In some embodiments of the present invention, all orbiting units are used to transmit driving force and to form parallelogram linkage mechanisms. In general, not all orbiting units are necessarily involved in the transmission of driving force. In fact, it is possible to use other methods to transmit driving force without any of the orbiting units involved.  
         [0040]    [0040]FIG. 20 is a schematic sectional view of a scroll compressor according to the seventh embodiment of the present invention. FIG. 21 is a left view of the compressor, excluding the left stationary scroll, left orbiting scroll, and left housing. As shown in FIGS. 20 and 21, a shell  61  of a motor  60  is mounted between two housings  1 A and  1 B. A stator  62  is fixed in the shell  61 . The left housing  1 A and the right housing  1 B are fixed through screws  51 . The left housing  1 A is connected to a left stationary scroll  2 A through screw set  52 A, and the right housing  1 B is connected to a right stationary scroll  2 B through screw set  52 B. The two housings  1 A and  1 B, the two stationary scrolls  2 A and  2 B, the shell  61  with the stator  62  compose the fixed structure of this machine. The two stationary scrolls  2 A and  2 B comprise, respectively, their own end plates  7 A and  7 B and spiral wraps  9 A and  9 B extending from the corresponding end plates  7 A and  7 B. The compressor includes two suction ports  4 A and  4 B that are connected, and two discharge ports  5 A and  5 B that are connected. Two orbiting scrolls  3 A and  3 B comprise, respectively, their own end plates  8 A and  8 B and spiral wraps  6 A and  6 B extending from the corresponding end plates  8 A and  8 B. Furthermore, the directions of the spiral wraps  6 A and  6 B should be arranged in a mirror-image relationship, and the directions of the spiral wraps  9 A and  9 B should be arranged in a mirror-image relationship. Three orbiting units  40  are mounted between the two orbiting scrolls  3 A and  3 B. Each of the three orbiting units  40  comprises a rotating member  10  rotatably supported on the two housings  1 A and  1 B through two bearings  11 A and  11 B, and a thrust-canceling shaft  20  rotatably supported in the eccentric through-hole  17  of the rotating member  10  by two bearings  14 A and  14 B. The rotating member  10  is formed together with a balancing weight  13 . The rotating axis ◯ 2  of the thrust-canceling shaft  20  has an eccentric distance e from the rotating axis ◯ 1  of the rotating member  10 . The thrust-canceling shaft  20  comprises a left end  21 A, a right end  21 B, a sleeve  23 , and a bearing pre-loading screw  22 . The length of the sleeve  23  should make the two ends  21 A and  21 B contact the sleeve  23  with proper preload when the bearings  14 A and  14 B are properly preloaded by the bearing pre-loading screw  22 . As shown in FIG. 21, the triangle defined by ◯ 1 -◯ 1 -◯ 1  is identical to the triangle defined by ◯ 2 -◯ 2 -◯ 2 . The three orbiting units  40 , the two orbiting scroll  3 A and  3 B, and the two housings  1 A and  1 B compose three parallelogram linkages that form an anti-self-rotating mechanism. A motor shaft  64  of the motor  60  is rotatably supported on the two housings  1 A and  1 B through two bearings  68 A and  68 B. A left crank portion  67 A formed at one end of the motor shaft  64  for rotatably supporting the left orbiting scroll  3 A though a bearing  66 A, and a right crank portion  67 B formed at the other end of the motor shaft  64  for rotatably supporting the right orbiting scroll  3 B. A rotor  63  of the motor  60  fitted on the motor shaft  64 . The rotating axis ◯ 4  of the two crank portions  67 A and  67 B has an eccentric distance e from the rotating axis ◯ 3  of the motor shaft  64 . The volumes formed by the spiral wraps  9 A,  9 B and  6 A,  6 B of the stationary scrolls  2 A and  2 B and the orbiting scrolls  3 A and  3 B change continuously when the orbiting scrolls  3 A and  3 B orbit. Fluid introduced through the suction ports  4 A and  4 B is continuously compressed, and discharged through the discharge ports  5 A and  5 B. During the process of compression, the fluid generates thrusting force exerted on the end plates  8 A and  8 B of the orbiting scrolls  3 A and  3 B. Most of the thrusting force is canceled through the three thrust-canceling shafts  20 , and the rest is withstood by the bearings  11 A,  11 B,  14 A, and  14 B in the orbiting units  40 . The frictional consumption of power is reduced because of the cancellation of the axial thrusting force, resulting in a high efficiency.  
         [0041]    In the embodiments described hereinbefore, the eccentric distances e of all the orbiting units or the crankshaft in an embodiment are substantially equal, and can be represented by:  
         e   =       p   2     -   t       ,                         
 
         [0042]    where p corresponds to the pitch of the scroll wraps and t is the wall thickness of each wrap.  
         [0043]    Although in the foregoing embodiments, the present invention has been described using scroll compressors and scroll expanders as examples of scroll type fluid machinery, the present invention is not necessarily limited to the scroll compressor and scroll expander, but may also be widely applied to other scroll type fluid machinery, such as vacuum pumps, refrigerant compressors, etc.  
         [0044]    Although in the foregoing embodiments, the scroll type fluid machinery comprises two fluid volume changing mechanisms arranged in a mirror-image relationship, the present invention is not necessarily limited to the described arrangement. For example, the two fluid volume changing mechanisms can be different from each other in dimensions.  
         [0045]    Although in the foregoing embodiments, the scroll type fluid machinery comprises two fluid volume changing mechanisms having the same function, the present invention is not necessarily limited to the described usages. For example, one of the two fluid volume changing mechanisms can be used as a compression mechanism while the other used as an expansion mechanism.  
         [0046]    Although in the foregoing embodiments, the two suction ports are arranged to be connected and the two discharge ports are also arranged to be connected, it should be noted that the present invention is not necessarily limited to the described arrangement. For example, the discharge port of the first fluid volume changing mechanism is connected to the suction port of the second fluid volume changing mechanism.  
         [0047]    Although in the foregoing embodiments, two or three orbiting units are arranged in a machine, the present invention is not necessarily limited to the number of the orbiting units. Four or more orbiting units can be arranged in a machine. For example, an embodiment containing four orbiting units  40  is shown in FIG. 22.  
         [0048]    Although in the foregoing embodiments, two housings are provided to a machine, the present invention is not necessarily limited to the described number of housings or the structure details shown in the drawings. For example, the two housings can be combined to form one body. Those skilled in this art will recognize modifications of structure and the like which do not depart from the true scope of the invention.  
         [0049]    Although a description for some common mechanical devices, such as tip seal, shaft seal, alignment pin, cooling fin structure, etc, is omitted in the foregoing embodiments, the present invention is not limited from their application.  
         [0050]    Although in the foregoing embodiments, the peripheries of the rotating members are described to have the forms of pulleys, gears, etc, the present invention is not necessarily limited to the described forms.  
         [0051]    The peripheries of the rotating members can have the forms of sprockets, cylinders, etc. For example, as show in FIG. 23, the periphery  18  of the rotating member  10  has the form of sprocket.