Abstract:
This invention relates to a twin-plate, rotary compressor and refers particularly, though not exclusively, to a twin-plate, rotary compressor comprising two conical plates for relative rolling motion within a casing, there being a line contact between the two conical plates; the line contact being maintainable during operation of the compressor; a central seal for sealingly engaging correspondingly-shaped recesses of the two conical plates; and an outer seal in mating relationship with the two conical plates; wherein the central seal is mounted on a drive shaft, the drive shaft being operatively connected to an output shaft of a motor; wherein the drive shaft, the central seal and the outer seal are for rotation about a third axis of rotation, the third axis of rotation being coincident with a longitudinal axis of the drive shaft and a center of the central seal.

Description:
REFERENCES TO RELATED APPLICATIONS 
   This application is a U.S. National Phase 35 U.S.C. §371 of PCT International Application No. PCT/SG05/00173 which has an International filing date of Jun. 1, 2005, designating the U.S., which claims priority to U.S. Provisional Application No. 60/576,616 filed on Jun. 4, 2004. The content of these applications are incorporated herein by reference in their entirety. 

   FIELD OF THE INVENTION 
   This invention relates to a twin-plate, rotary compressor and refers particularly, though not exclusively, to a positive displacement compressor which employs the relative rolling motion of two plates to achieve the compression and discharge of a working fluid. 
   BACKGROUND OF THE INVENTION 
   Reciprocating compressors have been used for a considerable time. However, it is well accepted that a reciprocating motion is not efficient, as the momentum of the piston must be reversed every half cycle. 
   Rotary compressors are known. However, as generally their rubbing components possess high relative velocities, frictional loss is high and therefore efficiency is somewhat limited. 
   SUMMARY OF THE INVENTION 
   In accordance with a first preferred aspect there is provided a rotary, twin-plate compressor comprising: 
   (a) two conical plates for relative rolling motion within a casing, there being a line contact between the two conical plates; and 
   (b) the line contact being maintainable between the two conical plates during operation of the compressor. 
   The line contact may be maintained throughout the compressor&#39;s operational cycle. The line contact may be at a position relative to the casing that is either fixed, or rotating relative to the casing. The two conical plates may be truncated cones. 
   In accordance with a second preferred aspect there is provided a rotary twin-plate compressor comprising a first conical plate having a first axis of rotation, a second conical plate having a second axis of rotation, the first axis of rotation being offset at an offset angle relative to the second axis of rotation. 
   There may be further provided a central seal for sealingly engaging correspondingly-shaped recesses of the two conical plates. The central seal may be substantially spherical. The central seal comprises an inlet port at one end, and having at least one fluid passageway to operatively connect the inlet port to a working chamber. The working chamber may be an enclosed space defined by the central seal, the two conical plates, and an outer seal. 
   The outer seal may comprise an inner surface shaped as a segment of a sphere, each of the two conical plates having an outer surface of a shape to mate with the inner surface. The outer seal comprises an outlet port, the outlet port being an opening through the outer seal. 
   The inner seal may be mounted on a drive shaft, the drive shaft being operatively connected to an output shaft of a motor. 
   The compressor may further comprise a fluid block rigidly connected to the central seal and outer seal, and in sealing engagement to the two conical plates for rotation therewith. 
   For the first aspect, the two conical plates may comprise a first plate having a first axis of rotation and a second plate having a second axis of rotation, the first axis of rotation being offset at an offset angle relative to the second axis of rotation. 
   The offset angle may in the range 1 to 89 degrees, preferably less than 45 degrees, more preferably less than 20 degrees, and most preferably 7.5 degrees. 
   The two conical plates may be identical and each may comprise a conical angle, the conical angle determining the offset angle. 
   The drive shaft, fluid block and outer seal may be for rotation about a third axis of rotation, the third axis of rotation being coincident with a longitudinal axis of the drive shaft and a centre of the central seal. 
   The casing may be hermetically sealed and may comprise a hollow main body, and an end plate at each end of the hollow main body. The compressor may further comprise a discharge outlet in one of the end plates, the hollow main body having an interior at discharge pressure. 
   The central seal, outer seal and fluid block may comprise a drive assembly. Each of the two conical plates may be mounted on a bush, each bush being mounted on a bush support. 
   The compressor may further comprise lubricant passageways in the bush supports and the two conical plates. 
   The first plate may be stationary relative to the casing, and the second plate may have motion relative to the casing. The line contact may rotate relative to the casing. 
   The compressor may further comprise a third plate located between the first and second plates. The third plate may comprise two surfaces, one of which may form a first line contact with the first plate and the other of which may form a second line contact with the second plate. The first and second plates may be stationary and the third plate may be for a rolling motion relative to both the first and second plates. 
   Both of the two surfaces of the third plate may be concave and conical; the conical surfaces of the third plate having a conical angle different to that of the first plate and that of the second plate. The outer seal may be in rolling motion with the third plate. 
   According to a third preferred aspect, the compressor described above is used as a motor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the present invention may be fully understood and readily put into practical effect, there shall now be described by way of non-limitative example only preferred embodiments of the present invention, the description being with reference to the accompanying illustrative drawings. 
     In the drawings: 
       FIG. 1  is a front perspective view in partial cut-away of a first embodiment; 
       FIG. 2  is a front perspective view of the rotating assemblies of  FIG. 1 ; 
       FIG. 3  is a front perspective view of the piston of  FIGS. 1 and 2 ; 
       FIG. 4  is a schematic side representation of the plates function; 
       FIG. 5  is a schematic side view of the piston of  FIG. 3 ; 
       FIG. 6  is an enlarged view of the upper portion of  FIG. 5  illustrating the rolling line contact; 
       FIG. 7  is a vertical cross-sectional view of the piston of  FIG. 3  showing the centre sphere; 
       FIG. 8  is a perspective view of the piston of the  FIG. 3  showing the outer seal; 
       FIG. 9  is a front perspective view of the piston of  FIG. 9  with the fluid block fitted; 
       FIG. 10  is a rear perspective view corresponding to  FIG. 9 , with one plate hidden; 
       FIG. 11  is a schematic side view of the piston of  FIGS. 9 and 10 ; 
       FIG. 12  is a vertical cross-sectional view of the driver assembly; 
       FIG. 13  is a front perspective view of the assembly of  FIG. 12  showing the inlet port; 
       FIG. 14  is a front perspective view of the assembly of  FIG. 12  showing the outlet port; 
       FIG. 15  is a perspective view in partial cut-away showing fluid paths; 
       FIG. 16  is a vertical cross-sectional view of the compressor portion of  FIG. 15 ; 
       FIG. 17  is a perspective view of the assembly of  FIG. 15  with directional arrows; 
       FIG. 18  is a partial view of the assembly of  FIG. 17  from the top at 0° of rotation; 
       FIG. 19  is a partial view of the assembly of  FIG. 17  from side  1  at 0° of rotation; 
       FIG. 20  is a partial view of the assembly of  FIG. 17  from side  2  at 0° of rotation; 
       FIG. 21  is a partial view of the assembly of  FIG. 17  from the top at 90° of rotation; 
       FIG. 22  is a partial view of the assembly of  FIG. 17  from side  1  at 90° of rotation; 
       FIG. 23  is a partial view of the assembly of  FIG. 17  from side  2  at 90° of rotation; 
       FIG. 24  is a partial view of the assembly of  FIG. 17  from the top at 180° of rotation; 
       FIG. 25  is a partial view of the assembly of  FIG. 17  from side  1  at 180° of rotation; 
       FIG. 26  is a partial view of the assembly of  FIG. 17  from side  2  at 180° of rotation; 
       FIG. 27  is a partial view of the assembly of  FIG. 17  from the top of 270° of rotation; 
       FIG. 28  is a partial view of the assembly of  FIG. 17  from side  1  at 270° of rotation; 
       FIG. 29  is a partial view of the assembly of  FIG. 17  from side  2  at 270° of rotation; 
       FIG. 30  is a schematic partial front perspective view of a second embodiment; 
       FIG. 31  is a front perspective view of the centre plate and central seal of the embodiment of  FIG. 30 ; 
       FIG. 32  is a schematic exploded side view of the three plates of  FIG. 30 ; 
       FIG. 33  is a perspective cross-sectional view of the embodiment of  FIG. 30 ; and 
       FIG. 34  is a series of perspective views of the embodiment of  FIGS. 30 to 33  during rotation, with the outer seal hidden. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The rotary twin-plate compressor  10  comprises ten main components:
     1. a first plate  100 ;   2. a second plate  200 ;   3. a central sphere  12 ;   4. an outer seal  20 ;   5. a fluid block  30 ;   6. an inlet port  40 ;   7. an outlet port  50 ;   8. a casing or shell  60 ;   9. a motor  70 ; and   10. a drive shaft  80 .   

   The only motion governing the operation of the compressor  10  is rotation. The spherical centre of all components is the spherical centre of the central sphere  12 . 
   The compressor  10  primarily consists of the two conical plates  100  and  200  that are preferably identical and truncated cones in shape. The two plates  100 ,  200  are positioned such that their axes of rotation  102  and  202  respectively are aligned at an offset angle  14 . As the two plates  100 ,  200  rotate in the same direction, a rolling line contact  90  exists between them. The offset angle  14  of alignment of the two rotational axes depends on the value of the conical angle, γ ( FIG. 4 ). This is to maintain the line contact between the two plates  100  and  200 . The offset angle  14  is in the range 1° to 89°, preferably less than 45°, more preferably is less than 20°, and most preferably is 7.5°. 
   Due to this offset angle  14 , the line contact  90  is established by the conical surfaces  120 ,  220  of both plates  100 ,  200 . As the respective symmetrical axes  102 ,  202  of the plates  100 ,  200  are their axes of rotation and as the two plates  100 ,  200  rotate in the same direction, the line contact  90  will be maintained during the operation of the compressor  10 , and throughout the operating cycle of the compressor  10 . In this embodiment the line contact  90  is at a fixed position relative to the casing  60 . More specifically, relative to each plate  100 ,  200 , the other plate will be rolling on it, thus making the line contact  90  a rolling contact. 
   If the conical angles γ are the same, the rolling line contact  90  will be solely a rolling motion. If the conical angles γ are different, the rolling line contact  90  will include a sliding motion, with the extent of the sliding motion being proportional to the difference in the conical angles γ. 
   The working volume  16  of compressor  10  is the space between the two plates  100 ,  200 . It is hermetically sealed as the central sphere  12  acts as an inner seal of the working volume  16 . The inner seal  12  formed by the central sphere  12  prevents the working fluid from escaping through the centre of the two plates  100 ,  200 . In order to allow the rotation of the two plates  100 ,  200  and still maintain the sealing, the surfaces  104 ,  204  of the two plates  100 ,  200  that contact the central sphere  12  are concave and spherical. 
   Although the central sphere  12  is a complete sphere, it is not necessary to be so. As long as the spherical surface of central sphere  12  is large enough to effectively provide the inner seal, it serves its purpose.  FIG. 7  illustrates a central sphere  12  that is a segment of a sphere and somewhat ‘drum’ shaped. The central sphere  12  may be relatively small to provide the effective sealing area. Also, the size of the central sphere  12  may also depend on the conical angle γ. 
   The outer-seal  20  provides an external hermetic seal for the working volume  16 , thus making the working volume  16  an enclosed working chamber. The outer seal  20  has an inner surface  22  that is also shaped as a segment of a sphere with the outer surfaces  114 ,  214  respectively of plates  100 ,  200  being similarly shaped to provide a mating contact. The dimensions of the outer seal  20  depend on the conical angle of the plates  100 ,  200 . A larger conical angle will require a taller outer seal to completely seal the working chamber. 
   Each plate  100 ,  200  has at least one outer groove  106 ,  206  respectively for lubricant distribution to the outer seal  20 , as well be understood from the following description. At least one inner groove  108 ,  208  respectively is provided for lubricant distribution to central sphere  12 . 
   The fluid block  30  is provided to effect change in the working volume  16  in order to enable compression/expansion of the working fluid. The fluid block  30  is located in conical or wedge-shaped cut-outs  122 ,  222  in the plates  100 ,  200  in a sealing manner with the plates  100 ,  200 . The fluid block  30  is also conical in shape and has geometric matching with the surfaces of plates  100 ,  200  with which it is in contact. 
   The inclusion of the fluid block  30  interferes with the working chamber  16  in such a manner that it separates the working chamber  16  into two. The working chamber is now divided into one compression chamber and one suction chamber. 
   As the fluid block  30  is positioned directly in the path of motion of the two plates  100 ,  200 , the fluid block  30  is in motion when the compressor  10  is operating. The fluid block  30  rotates with the two plates  100 ,  200  so that the motion of the fluid block  30  does not interfere with the rotation of the plates  100 ,  200 . The contact between the fluid block  30  and the plates  100 ,  200  is a sealing engagement throughout the entire working cycle. The fluid block  30  rotates about a third axis of rotation  32 . All three axes  102  and  202 ,  32  intersect at the centre of the central sphere  12 . As such, the axis of rotation  32  of the fluid block  30  is also the symmetrical axis of the central sphere  12  and the outer seal  20 . The plates  100 ,  200  will move laterally relative to the fluid block  30  during the rotation of the plates  100 ,  200 . This is easily seen from  FIGS. 18 to 29 . 
   The three components, central seal  12 , fluid block  30  and outer seal  20  are rigidly connected and to rotate about axis  32 . A T-lock and pin (not shown) is used to connect the three components. However, any suitable connection may be used such as, for example, bolts. In consequence, the fluid block  30 , outer seal  20 , central sphere  12 , and plates  100 ,  200 , are in rotation about axes  32 ,  102  and  202  respectively. 
   The fluid block  30 , outer seal  20  and central sphere  12  constitute a driver assembly. Preferably, the central sphere  12  is made as one piece with the driver shaft  80 . Each plate  100 ,  200  has a bush  110 ,  210  respectively, for mounting the plates  100 ,  200  to bush supports  112 ,  212  respectively. Bush supports  112 ,  212  are joined by bolts  34  adjacent their periphery  26 . 
   The operation of the compressor can be achieved by coupling the driver assembly ( 12 ,  20 ,  30 ) to the motor  70 . As the fluid block  30  is in sealing and motion-inducing contact with the two plates  100 ,  200 , the motion of the fluid block  30  ‘pushes’ on both the plates  100 ,  200  causing them to rotate about their own axes of rotation. Due to a very low relative velocity between the components in contact, the sliding friction is minimal. A consequence of the motion is that the inlet port  40  and outlet port  50  are also rotating. 
   The inlet port  40  is operatively connected to and rotates with the central sphere  12  and has its longitudinal axis concentric with axis  32 . Working fluid can be transferred from the inlet port  40  to the working chamber  16  via internal passageways  18  in central sphere  12 . 
   An inlet pipe  42  is rigidly connected to casing front end  64  and is in sealing engagement with inlet port  40 . The stationary inlet pipe  42  allows the transfer of the working fluid from other parts of the fluid circuit to the compressor  10 . 
   The working fluid enters the compressor  10  through the inlet pipe  42  and inlet port  40  then flows through passageways  18  in the central sphere  12  to the working chamber  16 . There may be any required number of passageways  18 . The relative rolling action of the plates  100 ,  200 , and the line contact  90 , pushes the fluid around the working chamber  16  in a circular manner with the fluid block  30  separating the working chamber into the suction and the compression chambers. The suction chamber is immediately after the fluid block  30  and the compression chamber is immediately before the fluid block  30 . Therefore, each chamber comprises approximately half of the rotational cycle of the plates  100 ,  200 . 
   The working fluid is drawn into the compressor  10  by the expansion of the working volume  16 . Also, and the centrifugal force acting on the rotating fluid causes it to be pushed outwards towards the periphery of the working chamber  16 . As the entrance to the working chamber  16  is from the central sphere  12  and is located close to the rotational centre, more working fluid can therefore be drawn into the working chamber  16 . This may be a form of pre-compression during the expansion phase, and may increase the volumetric efficiency of the compressor  10 . To maximize this effect, the outlet port  50  is preferably near the periphery of the compressor  10 . 
   The outlet port  50  is an opening  52  through the outer seal  20  for the compressed working fluid to exit from the compression chamber  16 . 
   A valve (not shown) will be provided at the discharge port  50  to prevent backflow of the compressed working fluid. A deflection plate is commonly used as a valve to be fitted at the outlet port  50  to prevent backflow of the compressed working fluid. This is because the pressure inside the working chamber  16  will be lower than the discharge pressure during the initial phase of compression. 
   By locating the outlet port  50  in such a manner, the compressor  10  is housed in a hermetically enclosed chamber or outer casing  60 . In this way the compressed working fluid is contained. The compressed working fluid will then be further discharged from the compressor  10  via discharge outlet  56  to other parts of the fluid circuit. 
   The outer casing  60  encloses the compressor unit  10  along with its motor  70  and is hermetically sealed and stationary. This prevents leakage of the working fluid from the compressor  10 . As the compressor  10  and the motor  70  are connected, the whole interior of the outer casing  60  is subjected to discharge pressure. The outer casing  60  comprises two ends  62 ,  64  and a main body  66  that may be of any suitable or required shaped such as, for example, cylindrical, as shown. 
   The motor  70  may be any form or motor such as, for example, an electric motor as illustrated. The motor  70  is mounted within outer casing  60  and has an output shaft  72  that is operatively connected to or integral with drive shaft  80 . Output shaft  72  passes through and is supported and held by a bearing  74  mounted on bush support  212 . If desired or required, the motor  70  may be external of the outer casing  60 . 
   The compressed working fluid from the outlet port  50  flows over the motor  70  for cooling purposes, and may flow through the motor stator. The bush support  212  has holes  46  to enable the compressed working fluid to pass therethrough in route to discharge outlet  56 . 
   Lubrication is important as it helps to reduce friction and assists in preventing leakage of the working fluid. 
   The compressor  10  is charged with lubricant  24  to a required level as shown in  FIG. 16 . The lubricant  24  locates in outer casing  60  and can circulate due to the slots  130 ,  230  in bush supports  112 ,  212  respectively. The space between the bush supports  112 ,  212  also has lubricant  24 . 
   The bush supports  112 ,  212  have lubricant passageways  116 ,  216  respectively to allow lubricant to pass to:
         (a) bushes  110 ,  210 ;   (b) drive shaft  80 ;   (c) output shaft  72  and bearing  74 ;   (d) central sphere  12 ; and   (e) through lubricant passageways  118 ,  218  in plates  100 ,  200  respectively to grooves  106 ,  206  to lubricate the contact between outer surfaces  114 ,  214  and the inner surface  22  of outer seal  20 .       

   Preferably, the working fluid and the lubricant  24  are immiscible. Otherwise, an oil separator (not shown) may be required downstream from discharge outlet  56 . 
   Such a system causes all rotational contacts to be exposed to the lubricant, thereby achieving lubrication. The contact areas between the two plates  100 ,  200 , the central sphere  12 , the outer seal  20  and the fluid block  30 , will also be lubricated during operation. 
   Due to the spinning of the main operational components of compressor  10 , the centrifugal force causes some of the lubricant  24  to be drawn towards the contact surfaces. Excessive lubricant may flow out of the compressor  10  and back to the lubricant reservoir  28 , ready to be circulated again. This circulation of lubricant  24  is possible as the entire housing  60  interior is maintained at discharge pressure during the operation of compressor  10 . 
     FIGS. 17 to 29  depict the working cycle of the compressor at 90° intervals. To effectively enable understanding of the compressor&#39;s operation, three views of the compressor  10  at various positions were taken at 90° intervals. The outer seal  20  is removed for clarity. However, for illustration purposes, a floating circle representing the outlet port  50  is included. Note that the compressor  10  is rotating in the anticlockwise direction when viewed from the front. 
   In this embodiment, the rolling line contact  90  is stationary relative to the casing  60 . As shown, the rolling line contact  90  is at the top. However, it can be in any suitable location depending on the orientation of the rotational axes  102 ,  202 . 
     FIGS. 18 to 20  show the beginning of the expansion portion of the cycle as the line contact  90  is just after the fluid block  30 , thus minimizing the expansion chamber of the working volume. On the other side of the fluid block  30  the compression portion of the previous cycle had commenced.  FIGS. 21 to 23  show the commencement of the expansion portion of the cycle where fluid is drawn into the working chamber  16 . Compression of the previous cycle continues and discharge of the working fluid is initiated once the chamber pressure exceeds the discharge pressure. Expansion and compression/discharge continues in  FIGS. 24 to 26 . In  FIGS. 27 to 29  compression of the previous cycle approaches its completion and the compression chamber approaches its minimum. The expansion chamber also approaches its maximum, where the working fluid drawn in will undergo compression in the next cycle. 
   The conical plate  100  may be held stationary relative to the casing  60  with only conical plate  200  moving relative to plate  100  in a rotational rolling motion. This will therefore also be a motion relative to casing  60 . In this way the line contact  90  will be maintained as before, but will rotate relative to plate  100  and thus casing  60  at the same speed as the rolling motion of plate  200 . For such an embodiment, the fluid block  30  will be fixed to plate  100  and motor  70  will drive plate  200  only, all other components being fixed. 
     FIG. 30  shows a further embodiment where the same reference numerals are used with a prefix number  2 . The embodiment is a double-volume compressor  2010 . The primary differences are that the first plate  2100  and the second plate  2200  are both fixed relative to casing  60 , and the addition of a centre plate  2300 . However, the motion principle remains unchanged.  FIG. 30  shows the double-volume compressor without the casing  60  or any drive system. The centre plate  2300  is located between the two plates  2100 ,  2200  and forms a line contact  2090  with each of the plates  2100 ,  2200 . In this instance, plates  2100 ,  2200  are identical. In consequence, there is a working volume  2016  between plate  2100  and plate  2300 , and between plate  2200  and plate  2300 . The centre plate  2300  moves about the common spherical central seal  2012  and thereby changes the two working volumes achieving expansion and compression of the working fluid. 
   In order to be able to form the line contact  2090  with plates  2100 ,  2200 , the centre plate  2300  has two surfaces  2302  one of which is in contact with plate  2100  and the other of which is in contact with plate  2200 . The surfaces  2302  are concave and conical. In order to create a working volume  2016 , the conical angle γ c  of the centre plate  2300  is smaller than the conical angle γ of the fixed plates  2100 ,  2200 . The two working volumes  2016  only exist if γ&gt;γ c . 
   Although there is symmetry of the components relative to the horizontal plane cutting through the centre seal as observed in  FIGS. 30 to 34 , this is not essential provided the difference between the conical angles γ concerning each working volume  2016  is the same:
 
γ c −γ [upper]=γ c −γ [lower]
         where upper and lower denotes the two sets of conical angles for each working volume respectively.       

     FIG. 33  shows an illustration of the complete compressor of this embodiment. Unlike the earlier embodiments, the outer seal  2020  is connected to the moving centre plate  2300  and therefore would also be moving. The motor  70  will drive the outer seal  2020  that in turn causes the centre plate  2300  to execute the desired motion. 
   As the outer seal  2020  is in motion the fixture or grounding of the compressor can only be done via the bottom fixed plate  2100 . A large conical angle γ for the bottom plate  2100  is therefore undesirable as it would mean a reduced surface area on the base of the component for a mounting. 
   Two-stage compression may be used by connecting the two working volumes  2016 . 
   Naturally, the compressor  10  may be used as a motor. In this case the inlet port  40  would be the fuel inlet; outlet port  50  the exhaust; and motor  70  would be the “load”. It may also be used as a conventional pump. 
   Whilst there has been described in the foregoing description preferred embodiments of the present invention, it will be understood by those skilled in the technology concerned that many variations or modifications in details of design or construction may be made without departing from the present invention.