Abstract:
An electric machine includes an inner fan in an inner cooling circuit and an outer fan for producing an outer coolant flow that is separate from the inner cooling circuit. The inner and outer fans are connected to a common shaft of the electric machine and have opposite delivery directions along an axial direction of the electric machine. The outer fan is arranged in a fan housing which has an inlet opening for the inward flow of a coolant of the outer coolant flow, and includes an air directing device, which guides the coolant in a line section which extends in the radial direction of the electric machine from the inlet opening towards the outer fan.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/EP2013/071029, filed Oct. 9, 2013, which designated the United States and has been published as International Publication No. WO 2014/060255 and which claims the priority of German Patent Application, Serial No. 10 2012 219 122.4, filed Oct. 19, 2012, pursuant to 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an electric machine. Beyond this the present invention relates to a method for cooling an electric machine. 
     To enable electrical machines to be cooled efficiently in operation, corresponding coolant circuits are provided. Electrical machines which are embodied for example in accordance with cooling type IC 611 have an inner coolant circuit with an inner fan and an outer coolant flow with an outer fan, which can be thermally coupled via a heat exchanger. With electrical machines having two fans which are connected to the shaft of the electrical machine, these fans create an axial force on the rotor as a whole. This force, which is created by the fans in the axial direction of the electrical machine, occurs in particular with rapidly rotating electrical machines. The axial force is additionally increased if, instead of two radial fans, one radial fan and one axial fan are used for example. If the magnetic resetting force which is created by the stator or the laminated core of the electrical machine is smaller than the axial force exerted by the fans, the entire rotor moves away from its geometrical center. With electrical machines which have a fixed bearing, the rotor moves by the play in the fixed bearing until it stops and then imposes an additional axial force on the fixed bearing. This problem also occurs with electrical machines which have a floating bearing for example. 
     To address the aforesaid problem, in no-load tests of such electrical machines, rotor holder facilities are used in order to hold the rotor in the geometrical center. A further option consists of imposing a high axial force on the fixed bearings in operation of the electrical machine. Furthermore it is known, with electrical machines which have two fans on a common shaft, to embody the fans so that their directions of conveyance are aligned in opposing directions. Thus for example a vertical electrical machine is known in which the outer fan is disposed rotated by comparison with the inner fan. This enables this electrical machine to be protected from rain or moisture since the coolant is sucked into the fan housing from below. 
     With such electrical machines the problem also exists of high levels of noise developing from the fans. In addition there is the danger that with the outer coolant flow the heated exhaust air will be sucked in again via the inlet opening of the fan housing of the outer fan. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is therefore to provide an electrical machine which can be operated more efficiently and more flexibly. 
     According to one aspect of the present invention, the object is achieved by an electrical machine including an inner fan in an inner coolant circuit, an outer fan for creating an outer coolant flow which is separate from the inner coolant circuit, the inner fan and the outer fan being connected to a common shaft of the electrical machine and having opposing directions of conveyance along an axial direction of the electrical machine, and a fan housing which houses the outer fan and has an inlet opening for an inward flow of a coolant of the outer coolant flow, the fan housing having an air guidance device which guides the coolant in a line section extending in the radial direction of the electrical machine from the inlet opening to the outer fan. 
     According to another aspect of the present invention, the object is achieved by a method for cooling an electric machine wherein the electrical machine has an inner fan and an outer fan which are connected to a common shaft of the electrical machine, the inner fan and the outer fan having opposing directions of conveyance along an axial direction and the outer fan being disposed in a fan housing which has an inlet opening for an inward flow of a coolant of the outer coolant flow by creating an inner coolant with the inner fan and creating an outer coolant flow separated from the inner coolant circuit with the outer fan, wherein the coolant is guided in a line section which extends in the radial direction of the electrical machine from the inlet opening to the outer fan. 
     Advantageous developments of the present invention are the subject matter of the dependent claims. 
     The inventive electrical machine comprises an inner fan in an inner coolant circuit, an outer fan for creating an outer coolant flow separate from the inner coolant circuit, wherein the inner fan and the outer fan are connected to a common shaft of the electrical machine, the inner fan and the outer fan have opposing directions of conveyance along an axial direction of the electrical machine, the outer fan is disposed in a fan housing which comprises an inlet opening for an inward flow of a coolant of the outer coolant flow, wherein the fan housing comprises an air guidance device which guides the coolant in a line section which extends in the radial direction of the electrical machine from the inlet opening to the outer fan. 
     The electrical machine is especially embodied as a rapidly rotating electrical machine. For example the electrical machine can be embodied as an asynchronous machine with a squirrel-cage rotor. The electrical machine can be embodied according to cooling type IC 611, i.e. the electrical machine can have two separate coolant circuits or coolant flows, which are thermally coupled via a heat exchanger. In particular air can be used as a coolant. As an alternative or in addition the electrical machine can have water cooling. The coolant in the inner coolant circuit is conveyed with an inner fan. The coolant in the outer coolant flow is moved with an outer fan which is disposed in a separate fan housing. The fan housing has an inlet opening, through which the coolant can flow in. From the fan housing the coolant can be guided into a cooler housing of the electrical machine in which the heat exchanger is located. 
     In the fan housing an air guidance device is provided, with which the coolant or the air leaving the inlet opening is guided to the outer fan in the radial direction of the electrical machine. Through the outer fan the coolant is diverted into the axial direction. For this purpose the inlet opening can be disposed on an outer surface of the fan housing. A number of inlet openings, for example two, can also be provided in the fan housing. The inlet openings, when the electrical machine is set up according to specifications, can be located on a side area or on the underside of the fan housing. The outer fan is offset in the axial direction in relation to the line section which is formed by the air guidance device. Through the embodiment of the air guidance device it can be achieved that less of the noise created by the outer fan reaches the outside. 
     In one form of embodiment the air guidance device is formed by an inner wall of the fan housing and an air guidance element. A part of the air guidance device can be formed by a wall of the fan housing. This wall can extend in the radial direction of the electrical machine. In addition the wall can have a corresponding recess through which a shaft is guided. The second part of the air guidance device can be formed by an air guidance plate. The air guidance plate can have a first area which extends, starting from the inlet opening of the fan housing, in the radial direction. In addition the air guidance plate can have a second area which adjoins an outer side of the outer fan. The second area can extend essentially in the axial direction of the electrical machine. Between the first and the second area the air guidance plate can have an intermediate area which has a corresponding curvature. The shaping of the air guidance plate enables the diversion of the coolant flow in the fan housing to be encouraged. This enables the axial force created by the outer fan to be adapted so that it acts against the axial force of the inner fan. Thus the load imposed on the bearings can be reduced. 
     In a further embodiment the fan housing includes a further air guidance device, which is disposed on an outer surface of the fan housing such that a channel running in the axial direction is formed between the outer surface of the fan housing and an inner wall of the further air guidance device. In this case the further air guidance device can preferably be embodied such that the coolant flows through the channel in the axial direction directed in the opposite direction to the direction of conveyance of the outer fan. The further air guidance device can be embodied as an add-on part which is fastened to the outer surface of the fan housing by a screw connection or a welded connection for example. The further air guidance device has an inlet opening through which the coolant or the outside air can flow in. In the further air guidance device the coolant flows, starting from the inlet opening of the further air guidance device, to the inlet opening of the fan housing. As previously described, the coolant then flows from the inlet opening of the fan housing in the radial direction to the outer fan and is diverted there in the axial direction. The geometrical embodiment of the further air guidance device additionally enables noises generated by the outer fan to be prevented from getting out. The further air guidance device enables—especially in relation to the axial extent of the electrical machine—a space-saving apparatus for sound deadening to be provided. 
     In a further form of embodiment the further air guidance device and the fan housing are embodied in one piece. This enables a housing device to be provided for the outer fan with which the noise generated by the electrical machine can be reduced. In addition the one-piece embodiment of the fan housing and of the further air guidance device enables the installation effort to be reduced. 
     Preferably a sound-deadening element is disposed on an inner wall of the further air guidance device and/or on an inner wall of the fan housing. Corresponding sound-deadening elements, which can be formed from a plastic, wire wool or the like, can be easily attached—for example by an adhesive connection—to the further air guidance device and/or the fan housing. This enables the noise generated by the electrical machine to be additionally reduced in a simple manner. 
     In one embodiment a grating element is disposed on the inlet opening of the fan housing and/or on the inlet opening of the further air guidance device. The grating element can be formed by a metal grating or a mesh. This enables the induction of foreign bodies, which can lead to damage to the outer fan, being prevented. 
     Preferably the outer coolant flow leads from the outer fan through a cooler housing of the electrical machine, wherein an outlet opening of the cooler housing is disposed at a distance from the inlet opening of the air guidance device. The inlet opening of the air guidance device or of the further air guidance device should be disposed as far as possible away from the outlet opening of the cooler housing. Preferably the output opening is disposed in an area of the drive side of the electrical machine and the inlet opening of the air guidance device or of the further air guidance device is disposed on the non-drive side of the electrical machine. This enables it to be prevented that heated air which exits from the outlet opening is sucked back into the corresponding inlet opening. This enables effective cooling of the electrical machine to be made possible. 
     Finally a method is provided in accordance with the invention for cooling an electrical machine, wherein the electrical machine has an inner fan and an outer fan, which are connected to a common shaft of the electrical machine, the inner fan and the outer fan have opposing directions of conveyance along an axial direction of the electrical machine and the outer fan is disposed in a fan housing which has an inlet opening for an inward flow of the coolant of the outer coolant flow by creating an inner coolant circuit with the inner fan, creating an outer coolant flows separated from the inner coolant circuit with the outer fan and guiding the coolant in a line section which extends in the radial direction of the electrical machine from the inlet opening to the outer fan with air guidance device of the fan housing. 
     The advantages and developments described above in conjunction with the inventive electrical machine can be transferred analogously to the inventive method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The present invention will now be explained in greater detail with reference to the enclosed drawings, in which: 
         FIG. 1  shows an electrical machine in a schematic sectional view; 
         FIG. 2  shows an electrical machine in a further form of embodiment; 
         FIG. 3  shows a housing device for an electrical machine; 
         FIG. 4  shows a housing device for an electrical machine in a further form of embodiment; 
         FIG. 5  shows a housing device for an electrical machine in a further form of embodiment; 
         FIG. 6  shows a housing device for an electrical machine in a further form of embodiment; 
         FIG. 7  shows a housing device for an electrical machine in a further form of embodiment; 
         FIG. 8  shows a housing device for an electrical machine in a further form of embodiment; and 
         FIG. 9  shows a perspective view of a housing device for an electrical machine in a further form of embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The exemplary embodiments described in greater detail below represent preferred forms of embodiment of the present invention. 
       FIG. 1  shows a schematic diagram of an electrical machine  10  in a sectional view from the side. The electrical machine  10  can be embodied as an asynchronous machine with a squirrel cage winding. The electrical machine  10  has an inner fan  12  and an outer fan  14 . The inner fan  12  and the outer fan  14  are disposed on a common shaft  16 . In addition the inner fan  12  and the outer fan  14  have opposing directions of conveyance. The inner fan  12  and the outer fan  14  can be embodied as radial or axial fans. The inner fan inner fan  12  serves to cool the stator and the rotor not shown in the diagram, which have corresponding cooling channels for this purpose. The principal course of the inner coolant circuit formed by the inner fan  12  is indicated by the arrows  18 . The inner coolant circuit leads via a heat exchanger which is not shown here which is disposed in a cooler housing  20 . 
     The outer fan  14  is disposed in a fan housing  22  and conveys the coolant or the air of an outer coolant flow, which is separate from the inner coolant circuit. To this end the fan housing  22  has a corresponding inlet opening  24  through which the air flows in laterally from the outside, at right angles to the plane of the drawing of  FIG. 1 , into the inside of the fan housing  22 . From the inlet opening  24  the coolant flows into the cooler housing  20  and via the heat exchanger. In the cooler housing  20  a partition wall not shown here is provided, in order to separate the inner coolant circuit from the outer coolant flow. The coolant exits from an outlet opening  50  of the cooler housing  20 . 
     An air guidance device  26 , with which the coolant is guided in a line section which extends in the radial direction of the electrical machine  10 , i.e. in a direction to the shaft  16 , from the inlet opening  24  to the outer fan  14  is provided in the fan housing  22 . The air guidance device  26  is formed by an inner wall  32  of the fan housing  22  and by an air guidance element  34 . The inner wall  32  extends in the radial direction of the electrical machine  10 , i.e. radially to the shaft  16 . The air guidance element  34  has a first area  36  which extends, starting from the inlet opening  24 , in the radial direction to the shaft  16 . In addition the air guidance element  34  has a second area  38  which extends in the axial direction  30  to an outer side of the outer fan  14 . Between the first area  36  and the second area  38  the air guidance element  34  has an intermediate area  40  which has a corresponding curvature. Here the inlet opening  24  is disposed on the side outer wall of the fan housing  22 . In addition or as an alternative to this an inlet opening  24   a  can be provided on the underside of the fan housing  22 . A grating element  42  is disposed on the inlet opening  24 , through which foreign bodies can be prevented from getting into the outer coolant flow. 
     The electrical machine shown in  FIG. 1  is an embodiment variant in which an air guidance device on the side outer surface of the fan housing has been dispensed with and in which sound deadening does not play any great part. 
       FIG. 2  on the other hand shows an embodiment variant of an electrical machine in which an axial air induction in the form of a further air guidance device  52  is integrated into a fan housing  22 . Through this an improved sound deadening is produced without additional lateral add-on parts. 
       FIG. 2  shows an electrical machine  10  in a further form of embodiment in partly sectional schematic view from the side. Here too the coolant is guided by an air guidance device  26  in the radial direction towards a shaft  16  through to the outer fan  14  and subsequently diverted by the outer fan  14  in the axial direction  30 . The diversion of the coolant flow is encouraged by an air guidance element. The air guidance element  34  in this case separates the coolant sucked in from the coolant diverted by the outer fan  14 . An inlet opening  54  for the coolant flow points here not to one side transversely away from an axis of rotation of the shaft  16  (see  FIG. 1 ), but in the axial direction of the shaft  16  forwards in the non-drive-side direction. The inlet opening  54  is integrated into the fan housing  22 . The coolant is sucked in and flows in the axial direction through a further air guidance device  52  integrated into the fan housing  22  initially in the axial direction  30  to the air guidance device  26 . The described arrangement of the inlet opening  54  of the further air guidance device  52  relative to the outlet opening  50  of the cooler housing  20  effectively enables it to be prevented that the heated coolant which flows out of the outlet opening  50 , is sucked in again through the inlet opening  54 . 
     Electrical machines are described below, on the basis of  FIG. 3  to  FIG. 9 , in which an air guidance device  52  is provided as an add-on part on a side outer surface of the fan housing  22 . This add-on part produces an improved deadening of noises of an outer fan. 
       FIGS. 3 to 8  show schematic diagrams of housing devices  56  for electrical machines  10  in a view from above in each case.  FIG. 9  shows a schematic diagram of a partly sectional, perspective view of an electrical machine  10  with a fan housing  22  and an add-on fastened to the side of the machine as an air guidance device  52 , which together form a housing device  56 . 
     In  FIG. 3  to  FIG. 8  the first side  46  and the second side  48  are embodied differently in some cases. This does not absolutely mean that the two sides  46  and  48  of the respective housing device  56  should be embodied differently. This serves instead to clearly delineate the different forms of embodiment of the housing devices  56 . 
       FIG. 3  shows a housing device  56  in a first form of embodiment.  FIG. 9  shows the housing device  56  in a perspective view. Here, and also in the subsequent exemplary embodiments, the air guidance element  34 , compared to the forms of embodiment shown in  FIGS. 1 and 2 , has a sloping portion in the first area  36 . Disposed on the fan housing  22  is a further air guidance device  52 . The further air guidance device  52  can be fastened with a screw connection or welded connection to the fan housing  22 . The inlet opening  54 , which is protected by a grating element  44 , enables the coolant or the air to flow in from outside into the further air guidance device  52 . The air flows in the axial direction  30  to the inlet opening  24  of the fan housing  22 . From there it is guided by the air guidance device  26  in the radial direction  28  to the outer fan  14 . Subsequently the coolant is diverted by the outer fan  14  into the axial direction  30 . The embodiment of the air guidance device  26  and the further air guidance device  52  enables it to be prevented that noises or sounds reach the outside from the outer fan  14 , since the sound is reflected on the walls of the air guidance device  26  and the further air guidance device  52 . In the present exemplary embodiments the further air guidance device  52  on the second side  48  of the housing device  56  has a rectangular cross-section. On the first side  46  of the housing device  56  the further air guidance device  52  is embodied beveled in an area  60  lying opposite the inlet opening  24 . The beveling allows it to be achieved that the coolant flow is directed better by the further air guidance device  52  into the air guidance device  26  of the fan housing  22 . 
       FIG. 4  shows a housing device  56  in a further form of embodiment. Here the further air guidance device  52  on the first side  46  and on the second side  48 , as described in conjunction with  FIG. 3 , has a bevel in each case in the area  60 . In the exemplary embodiment shown in  FIG. 4  the inlet openings  54  of the further air guidance device  52  run at an angle between the radial direction  28  and the axial direction  30 . This enables the inflow of the coolant into the further air guidance device  52  to be improved. 
       FIG. 5  shows a housing device  56  in a further form of embodiment. Here the form of embodiment in accordance with  FIG. 4  is developed in that sound-deadening elements  58  are disposed in each case on the inner walls of the fan housing  22  and the further air guidance device  52 . 
       FIG. 6  shows a further form of embodiment of the housing device  56  in which the first side  46  is embodied in accordance with the form of embodiment of  FIG. 4 . No second air guidance device  52  is disposed on the second side  48 . The second air guidance device  52  can be dispensed with for example if no sound deadening is required. 
       FIG. 7  shows a housing device  56 , which is embodied geometrically like the housing device  56  in accordance with  FIG. 3 . Here the fan housing  22  and the further air guidance device  52  are embodied in one piece.  FIG. 8  shows the housing device  56  in accordance with  FIG. 7  with additional sound-deadening elements  58 .