Abstract:
An electric machine, includes a rotor, a first radial fan wheel and a second radial fan wheel arranged on opposite sides of the rotor in axial direction, a first cooling air chamber and a second cooling air chamber; a first cooling air path extending in axial direction up to a side of the second radial fan wheel which faces away from the first radial fan wheel and from there leading into the second cooling air chamber, a second cooling air path extending in axial direction up to a side of the first radial fan wheel which faces away from the second radial fan wheel and from there leading into the first cooling air chamber, wherein the first radial fan wheel moves cooling air from the first cooling air chamber along the at least one first cooling air path and the second radial fan wheel moves cooling air from the second cooling air chamber along the at least one second cooling air path.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of German Patent Application, Serial No. 10 2015 011 863.3, filed Sep. 10, 2015, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to an electric machine. 
         [0003]    The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention. 
         [0004]    An electric machine can generally be constructed as an electric motor or a generator. The electric machine is for example a three-phase machine, in particular a three-phase asynchronous machine. It has a rotor, which is supported for rotation about a rotation axis, for example within a housing of the electric machine. The rotor preferably interacts with a stationary stator in order to either convert electric energy into a movement of the rotor or vice versa to convert the rotation of the rotor into electric energy. 
         [0005]    The heat produced hereby has to be dissipated from the electric machine in order to prevent overheating and eventually temperature-related damage to the electric machine. For this purpose radial fan wheels, for example the first radial fan wheel and the second radial fan wheel are for example arranged on opposing sides of the rotor. The radial fan wheels are preferably operatively connected with the rotor, in particular rigidly. Correspondingly the radial fan wheels can be driven the by the rotor. The radial fan wheels can also be driven in a different manner. By means of the radial fan wheels a cooling air stream through the electric machine is generated, via which the heat generated in the electric machine can be at least partially dissipated. 
         [0006]    It would be desirable and advantageous to provide an electric machine, which has advantages compared to known electric machines and in particular enables a more efficient cooling by means of the radial fan wheels. 
       SUMMARY OF THE INVENTION 
       [0007]    According to one aspect of the present invention an electric machine, comprising a rotor rotatable about a rotation axis, a first radial fan wheel and a second radial fan wheel arranged on opposite sides of the rotor in axial direction of the electric machine; a first cooling air chamber and a second cooling air chamber; at least one first cooling air path extending in axial direction up to a side of the second radial fan wheel which faces away from the first radial fan wheel and from said side of the second radial fan leading into the second cooling air chamber, at least one second cooling air path extending in axial direction up to a side of the first radial fan wheel which faces away from the second radial fan wheel and from said side of the first radial fan leading into the first cooling air chamber, wherein the first radial fan wheel moves cooling air from the first cooling air chamber along the at least one first cooling air path and the second radial fan wheel moves cooling air from the second cooling air chamber along the at least one second cooling air path. 
         [0008]    The first cooling air path thus fluidly directly adjoins the first cooling air chamber and extends directly up to the second cooling air chamber. Vice versa the second cooling air path directly adjoins the second cooling air chamber and extends up to directly to the first cooling air chamber. In both cases however the first cooling air chamber and the second cooling air chamber are not a component of the first cooling air path and the second cooling air path. Fluidly the first cooling air path ant the second cooling air path are thus located directly between the first cooling air chamber and the second cooling air chamber or vice versa. The first cooling air path and the second cooling air path are hereby completely fluidly separated from each other so that cooling air can neither pass directly, i.e., not via one of the cooling air chambers, form the first cooling air path into the second cooling air path or vice versa. 
         [0009]    In axial direction viewed relative to the rotation axis of the rotor the first cooling air path directly adjoins the first cooling air chamber or even overlaps with the first cooling air chamber. The firs cooling air path extends in axial direction up to the side of the second cooling air chamber that faces away from the first cooling air chamber, i.e., starting from the first cooling air chamber past the second cooling air chamber. Subsequently the cooling air is introduced from this side into the second cooling air chamber. This also applies vice versa to the second cooling air path, which extends in axial direction from the second cooling air chamber or is arranged so as to overlap with the second cooling air chamber. The second cooling air path extends from the second cooling air chamber up to the side of the first cooling air chamber that faces away from the second cooling air chamber. From this side the second cooling air path then leads into the first cooling air chamber. 
         [0010]    Both cooling air paths thus run through or traverse a large part of the electric machine when viewed in axial direction. By means of the described cooling air paths the heat generated in the electric machine can first be distributed so that the temperature in the electric machine, in particular the highest temperature occurring in the electric machine, can be kept below a maximally admissible temperature. Of course it can also be provided to cool the cooling air, in particular the cooling air that flows along the cooling air paths. For this purpose a heat exchanger can be provided in the first cooling air path and/or the second cooling air path. 
         [0011]    According to another advantageous feature of the invention, the first cooling air path has a first axial flow region and the second cooling air path has a second axial flow region that are arranged so as to overlap with each other when viewed in axial direction and are spaced apart from each other in circumferential direction. The term axial flow region means a region of the first cooling air path or the second cooling air path in which the main flow direction along the corresponding cooling air path extends substantially or exactly in axial direction, i.e., the velocity component in axial direction is greater than the velocity component in other directions. 
         [0012]    The axial flow regions of the cooling air paths are arranged so as to overlap in axial direction and hereby preferably extend parallel to each other. However, they are spaced apart from each other in circumferential direction with respect to the rotation axis. For example the axial flow regions of the cooling air paths are arranged uniformly distributed over the circumference of the electric machine. Hereby the axial flow regions can have the same distance to the rotation axis or as an alternative different distances to the rotation axis. The first axial flow region is thus for example arranged closer to the rotation axis than the second axial flow region or vice versa. Both axial flow regions preferably extend parallel to the rotation axis. 
         [0013]    According to another advantageous feature of the invention, the first axial flow region is present in a first axial flow channel formed in a housing of the electric machine and/or that the second axial flow region is present in a second axial flow channel formed in the housing of the electric machine. The first axial flow channel and/or the second axial flow channel are thus formed in the housing. In the first axial flow channel and/or the second axial flow channel the respective axial flow region is present. Particularly preferably the housing of the electric machine engages at least partially, in particular completely around the first axial flow channel or the second axial flow channel in circumferential direction relative to the longitudinal center axis of the axial flow channel. The longitudinal center axis of the first axial flow channel or the second axial flow channel preferably extends parallel to the rotation axis. 
         [0014]    According to another advantageous feature of the invention, a first heat exchanger is provided in the first axial flow region and/or a second heat exchanger is provided in the second axial flow region. The first heat exchanger or the second heat exchanger preferably serves for cooling the cooling air flowing along the respective axial flow region. For example the respective axial flow region or the respective axial flow channel forms a part of the heat exchanger. For example heat exchanger elements are arranged in the first axial flow channel or the second axial flow channel, which protrude into the respective axial flow channel. The heat exchanger elements are for example configured as ribs, wing structures, winglets and/or wedges. 
         [0015]    According to another advantageous feature of the invention, ribs are used which protrude into the axial flow channel from opposite sides of the axial flow channel and are substantially arranged parallel to each other. The ribs have their greatest longitudinal extent for example in the direction of the main flow direction in the axial flow channel. It can also be provided that these ribs respectively only partially traverse the axial flow channel. Preferably however the ribs protrude into the axial flow channel to a degree so as to engage between two ribs that extend from the opposite side. 
         [0016]    Cooling air, which flows along the axial flow region, as well as cooling fluid flow through the first heat exchanger and/or the second heat exchanger, wherein the cooling air is fluidly separated from the cooling fluid. The cooling fluid hereby has preferably a lower temperature than the cooling air so that heat can be transmitted from the cooling air to the cooling fluid and can be dissipated by the cooling fluid. 
         [0017]    According to another advantageous feature of the invention, the first cooling air path has a first radial outflow region between the first radial fan wheel and the first axial flow region into which a coil of a stator of the electric machine at least partially protrudes and/or the second cooling air path has a second radial outflow region between the second radial fan wheel and the second axial flow region into which the coil of the stator of the electric machine at least partially protrudes. The first radial outflow region insofar forms a flow communication between the first cooling air chamber and the first axial flow region, while the second radial outflow region forms a flow communication between the second cooling air chamber and the second axial flow region. 
         [0018]    According to another advantageous feature of the invention, the first axial flow region and/or the second axial flow region are arranged so that the coil of the stator, in particular an overhang of the stator, at least partially protrudes into first axial flow region and/or the second axial flow region. The cooling air which flows along the respective radial outflow region insofar flows over the stator or flows against the stator. Hereby the coil of the stator is effectively cooled by the cooling air. 
         [0019]    According to another advantageous feature of the invention, the first radial outflow region and/or the second radial outflow region traverse a cooling sheath of the electric machine which is arranged in the housing. The cooling sheath serves for cooling the electric machine or for conducting heat away from the electric machine. Preferably the cooling sheath or the cooling fluid channel formed in the cooling sheath forms a part of the first heat exchanger and/or the second heat exchanger. 
         [0020]    According to another advantageous feature of the invention, the first radial outflow region or the second radial outflow region extends through the cooling sheath for which the cooling sheath has a corresponding recess. Preferably this recess is formed in the cooling sheath spaced apart from the cooling fluid channel. By means of the cooling sheath thus on one hand a guiding of the cooling air along the first radial outflow region and/or the second radial outflow region is realized and on the other hand an efficient cooling of the electrical machine is achieved. For example the respective axial flow region directly adjoins the recess on the first radial outflow region or the second radial outflow region. 
         [0021]    According to another advantageous feature of the invention, the first axial flow channel and/or the second axial flow channel are delimited in radial direction by an outer circumferential surface of the cooling sheath and an inner circumferential surface of the housing. The respective axial flow channel insofar extends between the cooling sheath and the housing. This means that cooling air flowing through the respective axial flow channel can give off heat to the housing as well as to the cooling sheath. From the housing the heat can be transferred directly to an outer environment of the electric machine. In the cooling sheath on the other hand, as explained above, the cooling fluid channel is provided so that heat introduced into the cooling sheath can be dissipated by means of the cooling fluid. 
         [0022]    As a result of the above described configuration of the electric machine, which has the first cooling air path and the second cooling air path, an active cooling by means of the cooling sheath of the cooling fluid is generally not required. In this case the heat is transferred to the housing by the cooling air that flows through the first axial flow channel or the second axial flow channel and from the housing into the external environment for example by convection, in particular natural convection. 
         [0023]    According to another advantageous feature of the invention, the first cooling air path between the first axial flow region and the second cooling air chamber has a first radial inflow region, which is present in a first radial inflow channel formed in the housing of the electric machine and/or that the second cooling air path between the second axial flow region and the first cooling air chamber has a second radial inflow region which is present in a second radial inflow channel formed in the housing of the electric machine. The first radial inflow region or the first radial inflow channel insofar forms a flow communication between the first axial flow region and the second cooling air chamber, while via the second radial inflow region or the second radial inflow channel a flow communication between the axial flow region and the first cooling air chamber is formed. 
         [0024]    The first radial inflow channel or the second radial inflow channel is formed in the housing of the electric machine. It has a longitudinal center axis, which is at least approximately, in particular exactly, perpendicular to the rotation axis or to a straight line that is parallel to the rotation axis. At its side that faces away from the first axial flow region the first radial inflow channel has at least one overflow opening through which the cooling air can enter the second cooling air chamber. Vice versa the second radial inflow channel has at its end that faces away from the second axial flow region at least one overflow opening through which the cooling air can enter the first cooling air chamber. 
         [0025]    According to another advantageous feature of the invention, multiple overflow openings are assigned to the first radial inflow channel and/or the second radial inflow channel, which are spaced apart from each other in circumferential direction. For example the overflow openings have the same distance to the rotation axis in radial direction. The multiple overflow openings ensure a uniform and low-turbulent supply of the cooling air to the respective radial fan wheel. 
         [0026]    In longitudinal section along the rotation axis or viewed in radial direction the overflow opening has a distance to the rotation axis that is smaller than the distance of fan blades of the first radial fan wheel to the rotation axis. Thus the cooling air is conducted to the respective cooling air chamber on a suction side of the respective radial fan wheel. Correspondingly by means of the radial fan wheel or the radial fan wheels an efficient supply of cooling air through the electric machine or the first cooling air path and/or the second cooling air path can be accomplished. 
         [0027]    According to another advantageous feature of the invention, the first radial inflow channel is formed in a first bearing plate of the housing and/or the second radial inflow channel is formed in a second bearing plate of the housing of the electric machine. The housing has for example a housing sheath, which has openings at its two end sides that are closed by means of the bearing plate. The first bearing plate and the second bearing plate are insofar arranged on sides of the housing sheath that are opposite each another in axial direction or are fastened on the housing sheath. The first radial flow channel is assigned to the first bearing plate of the housing and the second radial inflow channel to the second bearing plate of the housing. Preferably the overflow openings of the respective radial inflow channel are also formed in the respective bearing plate. 
         [0028]    According to another advantageous feature of the invention, multiple first cooling air paths can be provided, wherein respectively two of the first axial flow regions of the first cooling air paths are arranged opposite each other and/or that multiple second cooling air paths are provided, wherein respectively two of the second axial flow regions of the second cooling air paths are arranged opposite each other. By means of the multiple first cooling air paths or the multiple second cooling air paths the cooling efficiency for the electric machine can be further improved. Particularly preferably the axial flow regions of the respective cooling air path are arranged diametrically opposite each other with respect to the rotation axis. Particularly preferably the axial flow regions of all cooling air paths are distributed evenly in circumferential direction, so that a particularly uniform cooling of the electric machine is realized. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0029]    Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
           [0030]      FIG. 1  shows a longitudinal sectional view of an electric machine on a first circumferential position, 
           [0031]      FIG. 2  shows a longitudinal sectional view of an electric machine on a second circumferential position, 
           [0032]      FIG. 3  shows a schematic representation of cooling air paths through the electric machine, 
           [0033]      FIG. 4  shows a cross sectional view though a region of the electric machine in a first embodiment, and 
           [0034]      FIG. 5  shows a cross sectional view through a region of the electric machine in a second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0035]    Throughout all the Figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. 
         [0036]      FIG. 1  shows a schematic longitudinal sectional view of an electric machine  1 , which has a rotor  2  and a stator  3 . The rotor  2  is supported in a housing  5  of the electric machine  1  for rotation about a rotation axis  4 , while the stator  3  is arranged stationary in the housing  5 . The housing  5  has for example a housing sheath  6  which at its end faces is provided with, and in particular closed with, a first bearing plate  7  and a second bearing plate  8 . The bearing plates  7  and  8  have bearings  9 , in particular rolling bearings, which serve for supporting a shaft  10  of the rotor  2 . 
         [0037]    On the shaft  10  a laminated rotor core  11  is arranged, and is in particular connected with the shaft  10  in rotative fixed relationship with the shaft. Via the laminated rotor core  11  a short circuit cage  12  is held on the shaft  10 . F urt her a first radial fan wheel  13  and a second radial fan wheel  14  are arranged on the rotor  2 . For example the radial fan wheels  13  and  14  are connected with the rotor  2  or the shaft  10  in rotative fixed relationship. For this purpose the radial fan wheels  13  and  14  are preferably arranged on the squirrel cage  12  and via the squirrel cage fastened on the laminated rotor core  11  and with this the shaft  10 . The r a dial fan wheels  13  and  14  each have fan wheel blades  15  with which the cooling air can be transported in radial direction. 
         [0038]    The first radial fan wheel  13  is situated in a first cooling air chamber  16 , the second radial fan wheel  14  in a second cooling air chamber  17 . Viewed in axial direction the cooling air chambers  16  and  17  are each situated between one of the bearing plate  7  and  8  on one side and the laminated rotor core  11  on the other side. In particular the cooling air chambers  16  and  17  are fluidly separated from each other in axial direction by the laminated rotor core  11 . A first cooling air path  18  can be seen which has a first radial outflow region  19  a first axial flow region  20  and a first radial inflow region  21 . The first radial outflow region  19  extends form the first cooling air chamber  16  or the first radial fan wheel  13  in radial direction outwards. 
         [0039]    Hereby the first radial outflow region is arranged so that a coil  22  of the stator  3  or a stator overhang which has the coil  22  protrudes into it. The coil  22  or the corresponding stator overhang is for example arranged or fastened fixedly  9  in the housing  5 . For example the laminated stator core  23  for this purpose engages on a cooling sheath  24  which is arranged in the housing  5 . The first radial outflow region  19  traverses the cooling sheath  24  before transitioning into the first axial flow region  20 . For this purpose the cooling sheath  24  has at least one first recess  25 . The recess  25  is for example formed with open borders in the cooling sheath  24  so that the radial outflow region  19  at this site is delimited on one side by the cooling sheath  24  and on the other side by the bearing plate  8 . 
         [0040]    Directly adjoining the first radial outflow region  19  is the first axial flow region  20 . The latter is situated in a first axial flow cannel  26  which is delimited by an outer circumferential surface  27  of the cooling sheath  24  and an inner circumferential surface  28  of the housing  5  in particular the housing sheath  6 . For example the cooling sheath  24  has for forming the first axial flow channel  26  a recess which is open at its border and rests with regions of its outer circumferential surface  27  that are immediately adjacent the recess against the housing  5  or the housing sheath  6 , in particular the inner circumferential surface  28 . 
         [0041]    Directly fluidly adjoining the first axial flow channel  20  is the first radial inflow region  21  which is present in a first radial inflow channel  29 . The first radial inflow channel  29  is formed in the housing  5 , in particular in the first bearing plate  7 . On its side that faces away from the axial flow region  20  the radial inflow channel  29  has at least one overflow opening  30 , preferably however multiple overflow openings  30 . Via the overflow opening  30  the radial inflow channel  29  is fluidly connected with the second cooling air chamber  17 . The overflow opening  30  has hereby preferably in radial direction a smaller distance to the shaft  10  or the rotation axis  4  than the second radial fan wheel  14  and in particular smaller than the fan blades  15  of the second radial fan wheel  14 . 
         [0042]    For forming the radial inflow channel  29  the first bearing plate  7  is for example formed by two bearing plate parts  31  and  32 . Preferably the radial inflow channel  29  is formed with an open border in the bearing plate part  31 . Also the at least one overflow opening  30  is situated in the bearing plate part  31 . The bearing plate part  32  on the other hand is configured as a flat plate. During mounting of the electric machine  1  the bearing plate part  32  is placed on the bearing plate part  31  so that the radial inflow channel  29  is closed relative to an outer environment of the electric machine  1  so that now the radial inflow channel  29  is formed between the bearing plate parts  31  and  32 . 
         [0043]    Particularly preferably a first heat exchanger  33  is assigned to the first axial flow region  20 . For this purpose the cooling sheath  24  has at least one cooling fluid channel  34  thought which cooling fluid can flow during operation of the electric machine  1 . Along the axial flow region  20  heat can be either transferred from the cooling air to the housing according to the arrows  35  or the housing sheath  6 , or can be dissipated from the housing into the outer environment. In addition or as an alternative the heat can, according to the arrows  36 , be transferred to the cooling fluid present in the cooling fluid channel  34  by means of the heat exchanger  33  and be transported out of the electric machine  1  by the cooling fluid. Already in the radial outflow region  19  however heat can be transferred to the cooling air. This is illustrated by arrows  37  and  38 , wherein on one hand heat is transferred from the rotor  2  and on the other hand from the stator  3  to the cooling air. Such a configuration of the electric machine  1  achieves a particularly efficient cooling. 
         [0044]      FIG. 2  shows a longitudinal sectional view of the electric machine  1  at a different circumferential position. Generally reference is made to the description above. In the here shown representation a second cooling air path  39  can be seen, which has a second radial outflow region  40 , a second axial flow region  41  and a second radial inflow region  42 . The second cooling air path  39  extends from the second cooling air chamber  17  up to the first cooling air chamber  16 . First the cooling air is transported from the second cooling air chamber  17  along the second radial outflow region  40 , hereby the cooling air flows over the coil  22 . In analogy to the description above heat can thus be transmitted from the rotor  2  and also from the stator  3  to the cooling air. This is indicated by arrows  43  and  44 . 
         [0045]    In the cooling sheath  24  a recess  45  is provided which can be configured analogous to the recess  25 . Through the recess  45  the cooling air can enter the axial flow region  41 . After flowing through the axial flow region the cooling air is conducted in the radial inflow region  42  in the direction of overflow openings  46  through which the cooling air can enter the first cooling air chamber  16  from a radial inflow channel  47  in which the radial inflow region  42  is located. The radial inflow channel  47  is configured analogous to the radial inflow channel  29  in the second bearing plate  8 . For this purpose the bearing plate is made of for example bearing plate parts  48  and  49 . The description above regarding the bearing plate parts  31  and  32  also applies to the bearing plate parts  48  and  49 . 
         [0046]    A second heat exchanger  51  is assigned to the axial flow region  41  that is situated in an axial flow channel  50 . Accordingly heat can be transferred in the axial flow region  41  according to arrows  52  to the hosing  5  or the housing sheath and form the housing into the outer environment. In addition or as an alternative heat can also be transferred to the cooling fluid present in the cooling fluid channel  34  and be discharged with the cooling fluid. This is indicated by the arrows  53 . Generally  t he first cooling air path  18  and the second cooling air path  39  are configured analogously but mirror symmetrically. Accordingly the respective description regarding one of the cooing air paths  18  or  39  can also be applied to the respective other cooling air path  39  or  18 . It has to be noted that the cooling air paths  18  or  39  or at least their axial flow regions  20  and  41  are arranged offset to each other with respect to the rotation axis  4 . Preferably the axial flow regions  20  and  41  overlap each other in axial direction however partially. 
         [0047]      FIG. 3  shows a schematic representation of the cooling air paths  18  and  39 . It can be seen that a closed circuit is present wherein the cooling air is conducted through the cooling air path  18  substantially in a first direction and through the cooling air path  39  in a second direction that is opposite the first direction. Hereby the cooling air reaches along the first cooling air path  18  from the first cooling air chamber  16  into the second cooling air chamber  17  and along the second cooling air path  39  form the second cooling air chamber  17  back into the first cooling air chamber  16 . 
         [0048]      FIG. 4  shows a cross sectional representation of the electric machine  1  in a first embodiment. The section is hereby place along the sectional marks A indicated in  FIG. 1 . By way of the here shown embodiment it is clear that two first cooling air paths  18  and also tow second cooling air paths  29  are present. From the first one the radial outflow regions  19  and the axial flow regions  20  can be recognized in each case. Of the latter one only the axial flow regions  41  are indicated. Its is clear that in the axial flow regions  20  and  41  or the corresponding axial flow channels  26  and  50  respectively ribs  54 , in particular axial ribs  54  are present. These serve for improving heat transmission from the cooling air to the cooling fluid. The ribs  54  are insofar assigned to the heat exchangers  33  and  51 . 
         [0049]      FIG. 5  shows cross section view of the electric machine  1  in a second embodiment. Reference is made to the description above and only the differences are discussed in the following. It can be seen that only one first cooling air path  18  and one second cooling air path  39  is present. It is provided that the axial flow regions  20  and  41  of the cooling air pathsl 8  and  39  are situated in the same side of an imagined plane, which receives the rotation axis  4 . Correspondingly the two axial flow regions  20  and  41  are located in the same side of the electric machine  1 . Such a configuration of the electric machine  1  enables a compact housing  5 .