Abstract:
In a compressor for refrigerant having a suction inlet for refrigerant and a pressure outlet for compressed refrigerant, said compressor comprising a compression unit and an electric motor driving said compression unit, said electric motor being a synchronous reluctance motor having a stator and a rotor, said rotor comprising a plurality of stacked disc elements, each disc element having a plurality of flux barriers configured to give the rotor core an anisotropic magnetic structure and formed as apertures in said disc element, it is provided that said flux barriers are arranged in said rotor core to define channels enabling a flow of refrigerant through said rotor core, said rotor is provided with a first support element acting on a first front side of said rotor core and a second support element acting on a second front side of said rotor core, said support elements being provided with cut-out sections and said cut-out sections being designed to uncover at least 70% of the cross section of apertures defined by said flux barriers in the respective disc element forming the respective front side of said rotor core.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This application is a continuation of international application number PCT/EP2014/071927 filed on Oct. 13, 2014. 
         [0002]    This patent application claims the benefit of International application No. PCT/EP2014/071927 of Oct. 13, 2014 the teachings and disclosure of which are hereby incorporated in their entirety by reference thereto. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    The invention relates to a compressor for refrigerant having a suction inlet for refrigerant and a pressure outlet for compressed refrigerant said compressor comprising a compression unit and an electric motor driving said compression unit, said electric motor being a synchronous reluctance motor having a stator and a rotor, said rotor comprising a plurality of stacked disc elements, said disc elements forming a rotor core, each disc element having a plurality of flux barriers configured to give the rotor core an anisotropic magnetic structure and formed as apertures in said disc element. 
         [0004]    Such a compressor is known from WO 2010/131233 A2 according to which the flux barriers provide an open surface in said disc elements for the refrigerant in order to cool said rotor core. 
         [0005]    It is the object of the present invention to provide a design for said rotor which keeps the disc elements of the rotor core tightly connected to each other and which also enables an efficient cooling of said electric motor, in particular said rotor core. 
       SUMMARY OF THE INVENTION 
       [0006]    This object is solved by a compressor as mentioned above wherein said flux barriers are arranged in said rotor core to define channels enabling a flow of refrigerant through said rotor core, said rotor is provided with a first support element acting on a first front side of said rotor core and a second support element acting on a second front side of said rotor core, said support elements being provided with cut-out sections and said cut-out sections being designed to uncover at least 60% of the cross section of said apertures defined by said flux barriers in the respective disc element forming the respective front side of said rotor core. 
         [0007]    The advantage of the present invention is that on one hand the support elements provide effective means for keeping the disc elements of the rotor core in tight relationship with respect to each other and on the other hand the support elements according to the present invention enable efficient cooling of said rotor core due to the fact that the flow of refrigerant through said channels defined by said flux barriers is only affected to a limited extend by said support elements due to the design of the cut-out sections as defined before. 
         [0008]    It is of particular advantage if the support elements are designed such that at least 70% of the cross section of said apertures in the respective front side is uncovered. 
         [0009]    It is even more of an advantage if the cut-out sections in said support elements are designed such that at least 80%, preferably at least 90%, of the cross sections of said apertures in the respective front side is uncovered. 
         [0010]    According to the present invention in particular rotor cores with different numbers of poles, in particular even numbered poles such for example as two, four, six, eight poles, can be realized. 
         [0011]    According to an advantageous design the channels are extending through said rotor core from one of said front sides to the other one of said front sides. 
         [0012]    In particular the channels run in said rotor core in direction parallel to said rotor axis. 
         [0013]    In order to obtain an optimum design of said support elements a preferred design provides that said support elements have arms acting on flux paths of the respective disc elements forming the respective front sides of said rotor core so that with these arms the support elements can easily act on said front sides in order to compress the disc elements of said rotor core arranged between the support elements. 
         [0014]    The flux paths as defined before are not specified with respect to their extension with respect to the rotor axis. 
         [0015]    It is of particular advantage if said arms are acting on flux paths extending in radial direction to said rotor axis because acting on these flux paths allows a specific advantageous overall compactation of said flux elements in said rotor core. 
         [0016]    In order to reduce the influence of said arms of said support elements on the flow of refrigerant through said channels in said rotor core one advantageous solution provides that an angular width of said arms of said support elements is limited to the angular width of the respective radial flux path so that the arms are not affecting the cross section of said apertures of said channels extending through said rotor core. 
         [0017]    A further advantageous embodiment provides that said support elements have an outer ring acing on outer ring portions of the respective disc element forming said respective front side of said rotor core. 
         [0018]    Such an outer ring enables the support element to act on the disc elements of said rotor core at a large radial distance from said rotor axis in order to keep said disc elements in tight abutment in particular in the areas formed by said outer ring portions of said disc elements. 
         [0019]    Further it is of advantage if said support elements have an inner ring acting on an inner ring portion of the respective disc element forming the respective front side of said rotor core. This solution has the advantage that the support element can act on the disc elements in an area close to said rotor axis and in particular on an area of said disc elements surrounding a shaft extending through said rotor core and carrying said rotor core. 
         [0020]    The inner ring can be further used for a runout tolerance as lay-on surface. 
         [0021]    In order to enable the support elements to act with sufficient force on said rotor core arranged between said support elements said support elements are connected by connecting elements extending through said rotor core. 
         [0022]    The connecting elements could for example be elements surrounding the shaft and being arranged between the shaft and said rotor core. 
         [0023]    It is of particular advantageous it said connecting elements are arranged in connecting channels formed by connection openings in said disc elements so that these connecting channels can be arranged at a certain radial distance from said rotor axis. 
         [0024]    It is further of advantage if connection openings in said support elements are arranged in said arms acting on flux paths of the disc elements. 
         [0025]    Further the use of support elements provides the chance to use counterbalancing elements in order to counter balance the rotor core and these counterbalancing elements can be fixed or releasably fixed to said support elements so that there is no need to provide any fixture of counterbalancing elements on disc elements of said rotor core which would affect the magnetic structure of said rotor core. 
         [0026]    The support elements can further be used to axially and/or radially fix inserted permanent magnets. 
         [0027]    A further preferred solution of the present invention provides a compressor wherein the support elements for the rotor core are provided with flow reducing elements for reducing flow of refrigerant through at least part of said channels. 
         [0028]    Said flow reducing elements can be for example screen elements or other partially refrigerant permeable elements, or even elements non-permeable for refrigerant. 
         [0029]    One preferred solution provides that the flow reducing elements are cover elements covering at least part of said channels. 
         [0030]    In order to be able to adapt the flow of refrigerant through the rotor it is provided that said flow reducing elements are releasably mounted on said support elements. 
         [0031]    With respect to the design of the compressor itself there have been no further details given before. 
         [0032]    One preferable solution provides that the compressor is provided with a motor housing section said motor housing section being provided with a suction inlet. 
         [0033]    This solution has the advantage that the suction inlet enables to supply refrigerant, in particular refrigerant before being supplied to said compression unit, to said motor housing in order to cool said motor. 
         [0034]    In order to enable efficient cooling of said rotor it is of particular advantage if said motor housing section supplies refrigerant to a first front side of the rotor in order to enable the efficient cooling of said rotor. 
         [0035]    The cooling of the said rotor is further improved if refrigerant is guided in axial directions through said channels in said rotor from said first front side of said rotor to a second front side of said rotor so that the rotor is cooled over its entire length. 
         [0036]    Further it is of advantage if refrigerant is discharged from a second front side of said rotor and guided to said compression unit for compression thereof. 
         [0037]    In order to optimize the flow of refrigerant to said rotor one preferred solution provides that the suction inlet supplies refrigerant to said electric motor through a suction opening arranged coaxial to an axis of rotation of said rotor. 
         [0038]    In particular the housing section is designed such that it is guiding said refrigerant supply through said suction opening to the first front side of said rotor. 
         [0039]    According to the present invention no further details have been given with respect to the arrangement of a rotatable shaft carrying said rotor in said electric motor. 
         [0040]    In principle it would be possible to have the shaft received in bearing systems of said compression unit and extending from said compression unit to said rotor so that the rotor is held by a freely extending end portion of the shaft extending from said compression unit into said electric motor. 
         [0041]    In case of a synchronous reluctance motor it is of advantage to have the rotor precisely guided within the stator in order to reduce the space between said rotor and said stator. 
         [0042]    Therefore it is of particular advantage if said rotor is arranged on a shaft and said shaft is supported by bearing systems arranged on opposite sides of said rotor. 
         [0043]    Another advantageous embodiment provides that said shaft is supported by bearing systems arranged on opposite sides of said compressor unit. 
         [0044]    One advantageous concept provides that said shaft is provided by a first and a second bearing system arranged on opposite sides of a said compression unit and also by a third bearing system arranged on an end of said shaft facing away from said compression unit and extending beyond said rotor so that in addition the shaft is received in two bearing systems on opposite sides of said rotor. 
         [0045]    Further features and advantage of the present invention are outlined in the detailed specification as well as the figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0046]      FIG. 1  shows a perspective view of one embodiment of a compressor according to the present invention; 
           [0047]      FIG. 2  shows a sectional view along lines  2 - 2  in  FIG. 1   
           [0048]      FIG. 3  shows an enlarged sectional view according to  FIG. 2  in the area of the electric motor; 
           [0049]      FIG. 4  shows a perspective view of a rotor of the synchronous reluctance motor according to the present invention; 
           [0050]      FIG. 5  shows a top view on a disc element of the rotor according to the present invention; 
           [0051]      FIG. 6  shows a top view on a support element for the rotor according to the present invention; 
           [0052]      FIG. 7  shows an enlarged top view on a front side of said rotor of a second embodiment of the present invention; 
           [0053]      FIG. 8  shows an enlarge view according to  FIG. 6  of a third embodiment of the present invention; 
           [0054]      FIG. 9  shows a sectional view similar to  FIG. 3  of a fourth embodiment of the present invention; 
           [0055]      FIG. 10  shows a top view similar to  FIG. 5  on a disc element with enlarged receiving opening according to the fourth embodiment; 
           [0056]      FIG. 11  shows a top view similar to  FIG. 6  on a support element with enlarged receiving opening according to the fourth embodiment and 
           [0057]      FIG. 12  shows a perspective view similar to  FIG. 4  of a fifth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0058]    A compressor  10  for refrigerant as shown in  FIG. 1  comprises a compressor housing  12  extending in a longitudinal direction  14 , said compressor housing itself comprises a motor housing section  16 , a compression housing section  22  and a high-pressure housing section  24  arranged in sequence in said longitudinal direction  14 . 
         [0059]    Motor housing section  16  is provided on its side opposite to said compression housing section  22  with a cover  26  releasably connected to a housing shell  28  surrounding a receptacle  32  receiving an electric motor  34 . 
         [0060]    Electric motor  34  comprises a stator  36  arranged in said receptacle  32  and fixed to said housing shell  28  as well as a rotor  38  arranged within said stator  36 . 
         [0061]    Said rotor  38  is mounted on a shaft  42  extending not only through said rotor  38  but also through a compression unit  44 . 
         [0062]    Shaft  42  is preferably rotatably mounted about an axis of rotation  46  in a first bearing system  52  arranged between said compression unit  44  and said electric motor  34  in wall  54  arranged between said compression unit  44  and said motor  34  and preferably separating said receptacle  32  for said electric motor  34  from said compression unit  44 . 
         [0063]    Further shaft  42  is held by a second bearing system  56  arranged on a side of said compression unit  44  opposite to said electric motor  34 . 
         [0064]    Preferably the second bearing system  56  is arranged inside high-pressure housing section  24 . 
         [0065]    In addition to the first bearing system  52  and the second bearing system  56  shaft  42  is further rotatably mounted in a third bearing system  58  which is arranged on a side of said electric motor  34  opposite to said compression unit  44 . 
         [0066]    Preferably third bearing system  58  is mounted in a bearing carrier  62  connected to cover  26  by support arms  64  so that bearing carrier  62  is fixedly connected to motor housing section  16 . 
         [0067]    Compressor housing  12  is further provided with a suction inlet  72  to which refrigerant is supplied to and a pressure outlet  74  through which compressed refrigerant is leaving compressor housing  12 . 
         [0068]    As can be seen from  FIGS. 1 to 3  suction inlet  72  is arranged on motor housing section  16 , in particular on cover  26  of motor housing section  16  and supplies refrigerant, in particular uncompressed refrigerant or refrigerant under low pressure, which means pressure lower than the pressure at the pressure outlet  74 , to an inlet opening  76  arranged in cover  26 , preferably concentrically to the axis of rotation  46 . 
         [0069]    Inlet opening  76  is further arranged in axial distance from bearing carrier  62  on a side of bearing carrier  62  opposite to said electric motor  34  and support arms  64  are extending from an outer cover section  78  of cover  26  arranged around inlet opening  76  to bearing carrier  62  so that refrigerant entering receptacle  32  for cooling said electric motor  34  can flow through free spaces between support arms  64  and around bearing carrier  62  in order to meet electric motor  34  for cooling. 
         [0070]    In particular a first flow path  82  for refrigerant is directed to hit motor windings  84  of stator  36  in order the cool motor windings  84  directly and in order to flow around stator  36  through cooling channels  86  provided between stator  36  and housing shell  28 . 
         [0071]    Further a second flow path  92  for the refrigerant hits a first front side  94  of rotor  38 , passes through cooling channels  96  in said rotor  38  and exits from rotor  38  through a second front side  98  arranged opposite to first front side  94  on said rotor  38 . 
         [0072]    First flow path  82  and second flow path  92  both when reaching wall  54  pass through suction opening  102  in order to enter compression unit  44 . 
         [0073]    For example compression unit  44  can be designed as a screw compressor comprising two interacting screws  104 . 
         [0074]    However compression unit  44  can also be designed to be a piston compressor or a scroll compressor. 
         [0075]    Electric motor  34  is designed to be a synchronous reluctance motor having a rotor core  112 , as shown in  FIG. 4 , made of a stack of disc elements  114 , with all disc elements  114  being preferably of identical design. 
         [0076]    Each disc element  114  comprises a plurality of substantially identical poles, for example poles P 1  to P 6 , distributed evenly around rotor axis  116  which in electric motor  34  coincides with axis of rotation  46 . 
         [0077]    However rotor cores  112  with different numbers of poles, in particular even numbered poles such as two, four, six, eight poles, can be realized. 
         [0078]    In the design shown in  FIG. 5  each disc element  114  comprises for example six poles P 1  to P 6  whereas each pole P 1  to P 6  covers a sector extending over an angular distance of 60° of disc element  114 . 
         [0079]    A first pole P 1  and a fourth pole P 4  are limited by separating lines S 1  and S 2  drawn as dashed lines in  FIG. 5  the first pole P 1  and the fourth pole P 4  are and arranged on opposite sides of rotor axis  116 . 
         [0080]    A second pole P 2  and a fifth pole P 5  are arranged within separating lines S 2  and S 3  and a third pole P 3  and a sixth pole P 6  are arranged between separating lines S 3  and S 1 . Poles P 2  and P 5  as well as poles P 3  and P 6  are and also arranged on opposite sides of rotor axis  116 . 
         [0081]    Within each pole P 1  to P 6  each disc element  114  is provided with flux guiding portions  122  to  128  having a high magnetic permeability whereas these flux guiding portions  122  to  128  are separated by flux barriers  132 ,  134 ,  136 . 
         [0082]    According to the present invention the flux barriers  132 ,  134 ,  136  are cut-outs in the respective disc element  114  and each of said flux barriers  132 ,  134 ,  136  comprises a central segment  142  extending along a geometric circular line  144  around rotor axis  116  and two side sections  146 ,  148  extending from opposite sides of said central section  142  at an angle α with respect to a strictly radial direction to rotor axis  116  whereas an angle α 1  between a strict radial direction and the respective side sections  146 ,  148  of the first flux barrier  132  is greater than an angle α 2  between side sections  146 ,  148  of flux barrier  134  and the angle α 3  between side section  146 ,  148  and a radial direction of flux barrier  136  is even smaller than α 2  and α 1 . 
         [0083]    All outer flux guiding portions  122  of poles P 1  to P 6  are connected by an outer ring portion  152  and all inner flux guiding portions  128  of poles P 1  to P 6  are interconnected by inner ring portion  154 . 
         [0084]    Further the inner flux guiding portions  128  of adjacent poles, for example pole P 1  and P 2 , extend towards the respective separating line S 2  and merge into each other along separating line S 2 . 
         [0085]    As a result the inner flux guiding portions  128  of each disc element  114  form radial arm portions  156  extending between outer ring portion  152  and inner ring portion  154  in radial direction to rotor axis  116  and symmetric to separating lines S 1 , S 2  and S 3  separating the various poles P 1  to P 6  from each other. 
         [0086]    In order to receive shaft  42  inner ring portion  154  surrounds a shaft receiving opening  158  arranged coaxial to rotor axis  116 . 
         [0087]    In order to improve stability of each disc element  114  flux guiding portions  122 ,  124 ,  126  and  128  are interconnected by small bridging elements  162  to  166  extending across the flux barriers  132 ,  134  and  136 . 
         [0088]    As shown in  FIG. 5  each radial arm  156  is provided with a fixing opening  168 . 
         [0089]    If all disc elements  114  are stacked with the same orientation with respect to each other all flux barriers  132  to  136  are arranged on top of each other so that the plurality of flux barriers  132  forms a channel  172  extending parallel to rotor axis  116  throughout rotor core  112 . 
         [0090]    Further the plurality of flux barriers  134  forms a channel  174  extending parallel to rotor axis  116  throughout rotor core  112  and the plurality of flux barriers  136  forms a channel  176  also extending throughout rotor core  112  parallel to rotor axis  116  throughout rotor core  112 . 
         [0091]    As can be seen in  FIG. 4  the first disc element  114   1  with its front side  182  facing away from core  112  forms a front side of rotor core  112  and the flux barriers  132 ,  134  and  136  due to the fact that they are cut-outs in the first disc element  114   1  form access openings to channels  172 ,  174 ,  176  extending from front side  182  of rotor core  112  to the opposite front side of rotor core  112  in which the corresponding flux barriers  132 ,  134 ,  136  also provide access to channels  172 ,  174 ,  176 . 
         [0092]    In order to keep the stack of disc elements  114  abutting each other the rotor core  112  is provided with support elements  192 ,  194  abutting on the respective front sides  182  of rotor core  112 . 
         [0093]    Each support element, for example support element  192 , shown in  FIG. 6  comprises an outer ring  202 , an inner ring  204  with receiving opening  205  as well as radial arms  206  extending between outer ring  202  and inner ring  204 . 
         [0094]    Preferably the number of radial arms  206  of support elements  192 ,  194  corresponds to the number of radial arm portions  156  of the respective disc elements  114  and the outer ring  202  the inner ring  204  and the radial arms  206  are designed such that they only abut on the respective outer ring portion  152 , the respective inner ring portion  154  and the respective radial arm portions  156  of the respective first and last disc elements  114   1  to  114   N  forming the respective front sides  182 . 
         [0095]    Support elements  192  and  194  are provided with cut-out sections  208  between the respective outer ring  202 , the inner ring  204  and the radial arms  206  having a size so as to keep all the flux barriers  132 ,  134 ,  136  of the first disc element  114   1  and the last disc element  114   N  uncovered by the support elements  192 ,  194  in order to allow access to channels  172 ,  174  and  176  in the respective front face  182  if the support elements  192  and  194  are mounted. 
         [0096]    In particular the radial arms  206  have an angular width which is smaller the angular width of radial arm portions  156  such that radial arms  206  are arranged within the outer contour of the radial arm portions  156  of the first disc element  114   1  and the last disc element  114   N . 
         [0097]    Therefore the support elements  192 ,  194  with their cut-out sections  208  provide full access to channels  172 ,  174  and  176  extending parallel to rotor axis  116  through the entire rotor core  12 , which channels  172 ,  174 ,  176  are used as cooling channels  96  extending through rotor  38  as mentioned before. 
         [0098]    In order to keep the disc elements  114  compacted together support elements  192  and  194  are connected by connecting elements  212 , preferably connecting rods, which extend through connecting channels  214  in said rotor core  112  formed by the plurality of connecting openings  168  of said disc elements  114  and respective openings  212 . 
         [0099]    Connecting elements  212  enable pretensioning of support elements  192  and  194  in directions towards each other so that the stack of disc elements  114  forming rotor core  112  and arranged between said support elements  192  and  194  is tied together by said support elements  192 ,  194 . 
         [0100]    For counterbalancing rotor  38  support elements  192 ,  194  are provide with fixing means  222  for fixing counterbalancing elements  224 . 
         [0101]    For example fixing means  222  are designed to be recesses in which counterbalancing elements  224  can be mounted. 
         [0102]    A second embodiment of the present invention as shown in  FIG. 7  differs from the first embodiment by the fact that the respective disc elements  114 ′ on their outer ring portions  152 ′ are provided with an outer recess  232  which increases the flow of refrigerant between rotor and stator. 
         [0103]    In particular the outer recess  232  is arranged in the center of the respective pole P, as shown in  FIG. 6  in the center of pole P 1 , and therefore in the middle between the respective separating lines, in case of pole P 1  separating lines S 1  and S 2 , limiting the respective poles P. 
         [0104]    A third embodiment, shown in  FIG. 8 , differs from the aforementioned embodiments by having a radially outer channel of rotor core  112 ″ is filled with permanent magnetic material  242  which improves the efficiency of rotor  112 ″. 
         [0105]    In particular permanent magnetic material  242  enables to increase the gap between rotor  38  and stator  36 . 
         [0106]    With respect to all other features which are not mentioned in connection with the second and third embodiment, the second and third embodiment are identical with the first embodiment so that with respect to the non-explained features reference is made to the explanations given in connection with the first embodiment. 
         [0107]    According to a fourth embodiment shown in  FIG. 9  rotor  38  is provided with a recess  252  receiving a fixing element  254  for axially fixing rotor  38  on shaft  42 . 
         [0108]    Recess  252  is obtained by providing a member disc elements  114 ′ of rotor core  112  which are arranged adjacent support element  192  with a receiving opening  258  enlarged with respect to receiving opening  158  of the other disc elements  114 . 
         [0109]    In addition as shown in  FIG. 11  support element  192 ′ is also provided with an enlarged receiving opening  265 . 
         [0110]    A fifth embodiment shown in  FIG. 12  differs from the aforementioned embodiments by having flow reducing elements  272 , made of any permeable, partially permeable or non-permeable material, in particular cover elements, are fixed to at least one of the support elements  192 ,  194  in order to reduce or block the flow through some or all of the channels  172 ,  174 ,  176  between adjacent arms  206 . 
         [0111]    Preferably flow reducing elements  272  are arranged on opposite sides of rotor axis  116  and in particular symmetric thereto. 
         [0112]    In particular flow reducing elements  272  are adapted to be releasably fixed to support elements  192 ,  194  in order to be able to adapt the flow of refrigerant through rotor core  112  to the amount of cooling necessary for the respective compressor in the respective environment. 
         [0113]    With respect to all other features which are not mentioned in connection with the fourth and fifth embodiment, the fourth and fifth embodiment are identical with the first embodiment so that with respect to the non-explained features reference is made to the explanations given in connection with the first embodiment.