Abstract:
The rotor of an electrical motor should be designed simply and able to be efficiently cooled. To this end, the invention relates to an electrical motor having a rotor that has at least one radial cooling slot ( 16 ) and axially running cooling channels. The first cooling channels ( 18 ) run having their central axis at a different radial height opposite the axis of the rotor ( 11 ) than the second cooling channels ( 19 ). A spacer ( 29 ) is arranged in the at least one radial cooling slot ( 16 ) by means of which a first cooling stream ( 28 ) can be conducted from one of the first cooling channels ( 18 ) into one of the second cooling channels ( 19 ). A second partial package (T 2 ) in the flow direction can also be supplied with cool air in this way if it flows through the first partial package (T 1 ) in a cool region, such as near the shaft.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/EP2009/065717, filed Nov. 24, 2009, which designated the United States and has been published as International Publication No. WO 2010/072496 A2 and which claims the priority of German Patent Application, Serial No. 10 2008 064 498.6, filed Dec. 23, 2008, pursuant to 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an electrical machine having a rotor which has at least one radial cooling slot and axially running cooling ducts which issue into the at least one radial cooling slot in said rotor. The present invention also relates to a method for cooling an electrical machine having a rotor by cooling the rotor with a cooling stream which is introduced axially into the rotor. 
     In principle, it is necessary to supply uniformly cool air (or cooling agent) to the rotor of an electrical machine. At the same time, it should be possible to encapsulate the magnet pockets for protecting the magnets against corrosion and movement without a great amount of work. 
     A type of synchronous machine with permanent magnet excitation and only one core element has been built to date. This has the advantage that the stator in the central region cannot be supplied with a sufficient amount of cooling air. In addition, the rotor is only non-uniformly cooled when the stream of cooling agent floods in. In the case of another type of synchronous machine with permanent magnet excitation, the magnets were fixed (for example by adhesive bonding) on individual core elements. Although more uniform cooling was achieved in this case, it is very complicated to protect the magnets against displacement or against corrosion by encapsulation. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is that of being able to remove heat more uniformly from a rotor of an electrical machine despite simple assembly. A further object is to specify a corresponding cooling method for a rotor of an electrical machine. 
     According to the invention, this object is achieved by an electrical machine having a rotor which has at least one radial cooling slot, with the rotor having axially running cooling ducts which issue into the at least one radial cooling slot in said rotor, with first cooling ducts of the axially running cooling ducts running, by way of their central axis, at a different radial level relative to the axis of the rotor than second cooling ducts of the axially running cooling ducts, and with a spacer being arranged in the at least one radial cooling slot, it being possible for a first cooling stream to be conducted from one of the first cooling ducts to one of the second cooling ducts by said spacer. 
     The invention also provides a method for cooling an electrical machine having a rotor by cooling the rotor with a first cooling stream which is introduced axially into the rotor, with the first cooling stream having a central line which is situated at a first radial level relative to the axis of the rotor when said cooling stream is introduced into the rotor in the flow direction, and the first cooling stream being deflected to a second radial level, which differs from the first radial level, by way of its central line within the rotor. 
     According to the invention, the cooling stream is advantageously moved from one radial level to another radial level in the rotor. As seen in a radial section, this could also be called a change in the cooling agent planes in the rotor. This proves advantageous particularly when the rotor is heated differently at different radial levels. A cooling stream which has still absorbed little heat can thus be deflected in a deliberate manner at a radial position, at which heat has to be removed very effectively, within the rotor. 
     The spacer preferably has a plurality of disks which each have passage openings, with the passage openings in the disks being arranged such that they deflect the first cooling stream in the radial direction. The disks of the spacer therefore acquire an additional function in addition to that of providing a radial cooling slot: they radially deflect a cooling stream. 
     In a specific embodiment, only a single radial cooling slot can be arranged in the rotor. This has the advantage that magnets can be inserted into magnet pockets in the two core elements relatively easily. The magnet pockets can also be encapsulated with insulating encapsulation compound in a relatively uncomplicated manner when there are two core elements. 
     In a further embodiment, a second cooling stream can be introduced into one of the axially running cooling ducts and directed radially to the outside by the spacer. At the point at which the second cooling stream is directed to the outside, the first cooling stream, provided it is deflected at the radial position of the second cooling stream, can now perform its cooling tasks in a second core element, that is to say in another axial region of the rotor. 
     In particular, it is expedient for the first cooling ducts to be arranged at a lower radial level in the rotor than the second cooling ducts. In this case, the first cooling stream flows initially in the vicinity of the shaft, where it absorbs only little heat. After a certain axial distance, the first cooling stream, in the “unused” state, can provide a powerful cooling effect when it is deflected into the second cooling ducts. 
     The rotor can be excited by permanent magnets. These lead only to relatively low losses in the rotor, and therefore it is sufficient to divide the rotor into two core elements and to provide only one single cooling air slot in the center of the rotor. As a result, a rotor with permanent magnet excitation can be produced more easily. Otherwise, when the rotor is fitted with short-circuiting bars, a plurality of core elements can also be provided, it also being possible for the cooling stream to be routed through more than two different planes in the rotor. 
     Furthermore, a core element (which contains the first cooling ducts) can be offset in the circumferential direction relative to a core element which contains the second cooling ducts. This serves to reduce the torque ripple of the rotor and can be readily realized by a plurality of disks of the spacer since the offset generally has to be only very low. Therefore, the function of the spacer, specifically that of radial redirection, is likewise not adversely affected by the offset. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The present invention will now be explained in greater detail with reference to the attached drawings, in which: 
         FIG. 1  shows a partial cross section through an air-cooled permanent magnet generator; 
         FIG. 2  shows an enlarged detail from  FIG. 1  for more accurately illustrating the change in level of the cooling stream in the rotor; 
         FIG. 3  shows a perspective view of the rotor from  FIG. 1 , and 
         FIG. 4  shows a plan view of a detail of the radial cooling slot in the rotor from  FIG. 3 . 
         FIG. 5  shows the detail of  FIG. 2  illustrating a short-circuiting bar received in the rotor. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The exemplary embodiments described in greater detail below are preferred embodiments of the present invention. 
       FIG. 1  shows a generator  1  having a cooling device  2 . The cooling device  2  has a fan  3  for drawing in cooling air which it blows into a heat exchanger  4 . The air flows from there to the outside through an outlet nozzle  5 . This defines an external cooling circuit. 
     The heat exchanger  4  cools an internal, closed cooling circuit  7  using the external cooling circuit  6 . The internal cooling circuit  7  is driven by a shaft-mounted fan  8  which is mounted on the B-side of the shaft  9  of the generator  1 . The internal cooling circuit flows through the heat exchanger starting from the fan  8  and enters the winding overhang space on the A-side (drive side) of the generator. Here, said internal cooling circuit flows around the winding overhang  10  and the winding circuit  31  and then flows through the rotor  11  and the stator  12 , as will be explained in greater detail below. Finally, the cooling agent (in particular air) flows through the winding overhang space on the B-side (non-drive side) of the generator and again reaches the shaft-mounted fan  8 . 
     The rotor  11  has a laminated core  13 , pressure rings  14  and  15  being mounted on the end faces of said laminated core. The rotor  11  is divided into two in its axial direction by a radial cooling slot  16 . This cooling slot  16  is formed by a spacer with the disks  29  in this case. 
     The rotor  11  also has axially running cooling ducts, of which the axial centers lie on two coaxial cylinders. In the text which follows, the radial distance between the center axis of a cooling duct and the axis of the shaft  9  is referred to as the radial level of the cooling duct. According to the present example, the rotor  11  therefore has a (third) cooling duct  17  and radially therebeneath, that is to say at a lower radial level, a first axial cooling duct  18 . A second cooling duct  19  is located on the right-hand side of the radial cooling slot  16 , which divides the rotor in the middle, at the same radial level as the first cooling duct  17 . A fourth cooling duct  20  is located radially beneath said second cooling duct, again at the same radial level as the second cooling duct  18 . Permanent magnets  21  are arranged in the laminated core  13  in a manner distributed over the circumference in pockets which are provided specifically for this purpose. Said permanent magnets are pushed into the rotor from the two end faces and are also encapsulated from the two end faces. Since the rotor  11  has only a central radial cooling slot  16 , the insertion of the magnets and the encapsulation are accordingly simple to implement. 
     The stator  12  has a laminated core  22  as the winding support, a large number of radially running cooling slots  23  passing through said laminated core. Axially running cooling ribs  24  are integrally formed on the outer casing of the laminated core  22 . The cooling ribs  24  project in a star-like manner from the stator  12  and can be welded to the laminated core. As an alternative, each individual lamination of the laminated core  22  has radially protruding projections, so that the stacking of the individual laminations produces the cooling ribs  24 . 
     Therefore, a stator cooling stream  25  runs along the stator casing solely in the axial direction. The axial cooling ribs  24  of the stator are effectively cooled by this stream which is supplied almost directly by the heat exchanger  4  virtually without heat absorption. This first cooling stream  25  is still used to cool the winding overhang at the B-side end. 
     As in the example illustrated in  FIG. 1 , a first cooling stream  28  is provided according to the invention, this first cooling stream flowing into the first cooling ducts  18  through the pressure plate  14  on the A-side. A spacer is located in the radial cooling slot  16  in the rotor  11 . In the present example, three disks  29  are used as a spacer. The disks  29  differ and have cutouts  30  in positions which are offset in relation to one another. As a result, the first cooling stream  28  in the radial cooling slot  16  in  FIG. 1  is forced upward into the second cooling ducts  19  which are located to the right of the cooling slot  16  at a higher radial level than the first cooling ducts  18 . Finally, the first cooling stream  28  leaves the second cooling ducts  19  through the B-side pressure plate  15 . To this end, openings are provided in the pressure plate  15 , the size of said openings being such that the resistance of the first cooling stream  28  is not too low and also the second cooling stream  26  has an adequate volumetric flow rate. Downstream of the opening in the pressure plate  15 , the first cooling stream  28  joins a second and a third cooling stream  26 ,  25  in the space in the end face of the generator  1  upstream of the shaft-mounted fan  8 . The first cooling stream  28  is therefore routed in the first part of the rotor (left-hand side in the figure) through the cooler region (region close to the shaft) of the rotor. In the process, said first cooling stream absorbs hardly any heat. Said first cooling stream is then guided upward on the right-hand side of the rotor and there serves to effectively cool the rotor part on the right-hand side. The left-hand half of the rotor part is, as explained above, primarily cooled by the second cooling stream  26 . 
     The second cooling stream  26  through the rotor is supplied by a cooling agent or cooling air which has already cooled the winding overhang  10  and the winding circuit  31  in the A-side winding overhang space. This second cooling stream  26  passes through the A-side pressure disk  14  and enters the third cooling duct  17  in the rotor  11 . The second stream  26  of cooling agent is directed radially to the outside at the radial cooling slot  16  in the center of the rotor. Said second stream of cooling agent is distributed axially throughout the entire air gap  27  between the rotor  11  and the stator  12 . From there, said stream of cooling agent is forced radially to the outside through the cooling slots  23  in the stator since the pressure disks  14  and  15  have a somewhat larger diameter than the laminated core of the rotor including the permanent magnets  21 . The second cooling or air stream  26  is connected to the third cooling stream  25  at the outer face of the stator. The second cooling stream  26  therefore ensures that the rotor part which is illustrated on the left-hand side in  FIG. 1  is cooled and that the inner part of the stator is cooled over its entire axial length. The second cooling stream  26  therefore has a substantially Z-shaped profile. It initially flows axially, then radially and then axially again. Therefore, an adequate amount of heat can be removed from the stator  12  together with the linear stator cooling stream, even if the rotor has only one radial cooling slot  16  and not a large number of such radial slots. 
     The detail of the rotor  11  with the cooling slot  16  from  FIG. 1  is illustrated on an enlarged scale in  FIG. 2 . The rotor is divided axially into two core elements T 1  and T 2  by the cooling slot  16 . The radial cooling slot  16  is formed by the disks  29  which serve as a spacer between the two core elements T 1  and T 2 . It is clear from the enlarged view in  FIG. 2  that the disks  29  have cutouts or openings  30 , and therefore a cooling stream can pass the respective disk  29 . In the present case, the first cooling stream  28  passes the cooling slot  16  or the disks  29  through openings  30  from one of the first cooling ducts  18  into one of the second cooling ducts  19 . The center of a respective opening  30  therefore rises in the direction of the cooling stream from one disk to the next in the radial direction. There is therefore a flow connection between the first cooling duct  18  and the second cooling duct  19 . 
     The disks  29  have further cutouts  32  which make it possible for the second cooling stream  26 , which enters the rotor through the third cooing ducts  17 , to flow radially to the outside. In this case, it is advantageous, under certain circumstances, for the right-hand disk  29 , which faces the second cooling duct  19 , to seal off the second cooling duct  19  from the third cooling duct  17 , so that the second cooling stream  26 , which is generally already significantly heated when it reaches the cooling slot  16 , does not enter the second cooling duct  19 . Instead, the first cooling stream  28  which is routed in the first core element T 1  can now cool the second core element T 2  in the region of the permanent magnets  21 , that is to say in the outer region of the rotor, on account of the radial change in level. In principle, the directions of flow of each cooling stream in each case in the opposite direction are of course also feasible. 
       FIG. 3  additionally shows the rotor according to the invention in a perspective view. Therefore, as has already been explained in connection with  FIG. 1 , the shaft-mounted fan  8  is located on the shaft  9  in addition to the core elements T 1  and T 2  of the rotor  11  on the B-side. The core elements T 1  and T 2  are separated from one another by the radial cooling slot  16 . The second cooling stream  26  is passed to the outside from said radial cooling slot.  FIG. 3  also shows that the core elements T 1  and T 2  are offset in relation to one another in the circumferential direction. This offset V is illustrated on an enlarged scale in  FIG. 4 . The torque ripple of the rotor  11  is reduced by the offset V in the circumferential direction. Nevertheless, the cutouts  32  in the disks  29  ensure an adequate radial cooling slot. 
       FIG. 5  shows a cross section of the rotor  11  which substantially corresponds to the rotor shown in  FIG. 2 , with the difference residing in the illustration of a short-circuiting bar  21 ′ in the rotor  11 . 
     In summary, it has therefore been found that the invention makes it possible to ensure ventilation with two or more core elements of a rotor with permanent magnet excitation. It is also possible to supply virtually unused cooling air to the rotor over its entire length by using different cooling planes or levels. Numerous further advantages are also provided. Firstly, simple encapsulation is possible on account of it being easy to reach the pockets of the permanent magnets. This results in secure fixing of the magnets and high-quality protection against corrosion. Furthermore, the rotor pressure disks  29 , which separate the core elements of the rotor from one another, can be used to ventilate the stator since they have a fan effect. According to the described design, the latching torque may optionally be lowered by offsetting the core elements. An additional advantage is provided by it being possible for the lamination sections of the two core elements to be identical.