Abstract:
A brushless direct current motor with a stator and rotor uses permanent magnets facing the stator and which are held in place by springs that urge the magnets toward the periphery of a support structure for the rotor.

Description:
BACKGROUND 
       [0001]    Brushless direct current motors are utilized in motor vehicles for different drives and are known from practical application. According to the prior art, the permanent magnets of the rotor are encapsulated in plastic. It is also known from practical application to fasten the permanent magnets on the support element using a sleeve. 
         [0002]    The disadvantage of the known direct current motors, however, is that an encapsulation or a sleeve results in an increase in the spacing of the permanent magnets from the coils. A large spacing results in high magnetic leakage, however, and, therefore, to low efficiency of the direct current motor. Sliding a sleeve over the permanent magnets also results in a very large amount of effort to assemble the direct current motor. 
       SUMMARY 
       [0003]    The problem addressed by the invention is that of refining a direct current motor of the type mentioned at the outset in such a way that said motor allows for a reliable attachment of the permanent magnets and allows for particularly small spacings between the permanent magnets of the rotor and the coils of the stator. 
         [0004]    This problem is solved according to the invention by way of the permanent magnets directly delimiting an air gap with respect to the rotor and being preloaded against the periphery of the support element. 
         [0005]    Due to this configuration, the permanent magnets can be situated directly in front of the coils of the stator. The particularly narrow size of the air gap is therefore limited almost exclusively by a thermal expansion and by production tolerances of the adjacent components of the stator and the rotor. Due to this configuration, the direct current motor according to the invention has high efficiency. Thanks to the invention, components for holding the permanent magnets no longer need to be situated in front of the permanent magnets. The preload can be selected in such a way that centrifugal force is counteracted. Therefore, the preload ensures a reliable attachment of the permanent magnets even at high rotational speeds. The brushless direct current motor according to the invention is therefore suitable, in particular, for driving an electrically operated compressor of an internal combustion engine of the motor vehicle. In addition, thanks to the invention, the rotor can be installed in a particularly economical manner. 
         [0006]    According to yet another advantageous refinement of the invention, the preloading of the permanent magnets is implemented using a particularly simple design when spring elements connected to the support element grip an edge of the permanent magnets that is situated in parallel to the rotational axis of the rotor and has a widened portion. 
         [0007]    According to yet another advantageous refinement of the invention, an air gap between the permanent magnets of the rotor and the coils of the stator can be kept particularly low when the permanent magnets have recesses for accommodating a subregion of the spring elements, which recesses are situated on each of the edges of said magnets that are situated in parallel to the rotational axis. 
         [0008]    According to yet another advantageous refinement of the invention, the spring elements can be connected particularly easily to the support element when the spring elements grip an edge of the support element that is situated in parallel to the rotational axis of the rotor. 
         [0009]    According to yet another advantageous refinement of the invention, the rotor is provided with a particularly simple design when the support element comprises several channels which are situated in parallel to the rotational axis of the rotor for accommodating one end of the spring elements. 
         [0010]    According to yet another advantageous refinement of the invention, the spring elements can be produced particularly economically when the spring elements are designed to have a C-shaped cross section. 
         [0011]    According to yet another advantageous refinement, the spring elements are reliably held in their position when two spring elements are supported against one another in order to hold permanent magnets which are adjacent to one another. Due to this configuration, the spring elements on the permanent magnet, the support element, and the adjacent spring element are supported at three points overall. The rotor therefore has high stability. This also results in a particularly small installation space for holding the permanent magnets. 
         [0012]    According to yet another advantageous refinement of the invention, the number of components of the brushless direct current motor can be kept particularly low when the number of spring elements is identical to the number of permanent magnets and when each of the spring elements is situated between two permanent magnets which are adjacent to one another. 
         [0013]    According to yet another advantageous refinement of the invention, the brushless direct current motor is particularly suitable for high rotational speeds when each of the spring elements is held in a middle section thereof in the channel in the support element and supports, by way of the outer sections, permanent magnets which are adjacent to one another in each case. Due to this configuration, the preload on the permanent magnets is particularly uniform around the periphery of the support element. This prevents strong loads on the edges of the permanent magnets. 
         [0014]    According to yet another advantageous refinement of the invention, the production of the permanent magnets and of the support element is particularly economical when the permanent magnets and the support element have planar contact surfaces. 
         [0015]    According to yet another advantageous refinement of the invention, an additional positional fixation of the spring elements and, therefore, of the permanent magnets can be easily achieved when the spring elements and a subregion of the support element that holds the spring elements are encapsulated in plastic. 
         [0016]    The invention provides for numerous embodiments. In order to further illustrate the basic principle of the invention, two embodiments are represented in the drawing and are described in the following. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0017]      FIG. 1  schematically shows a cross section through a brushless direct current motor; 
           [0018]      FIG. 2  shows, in greatly enlarged fashion, a subregion of a rotor of the direct current motor from  FIG. 1 ; 
           [0019]      FIG. 3  shows one further embodiment of the rotor; and 
           [0020]      FIG. 4  shows a cross section through one further embodiment of the rotor. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]      FIG. 1  schematically shows a cross section through a brushless direct current motor comprising a fixed stator  1  and a rotor  3  which is mounted so as to be rotatable about a rotational axis  2  situated perpendicularly to the plane of the drawing. The stator  1  comprises several coils  4 ,  4 ′. The rotor  3  comprises several permanent magnets  6 ,  6 ′ which are situated on a support element  5 . The support element  5  is designed as a laminated core. An air gap  7  is situated between the permanent magnets  6 ,  6 ′ and the coils  4 ,  4 ′. The permanent magnets  6 ,  6 ′ therefore directly delimit the air gap  7 . The permanent magnets  6 ,  6 ′ and the support element  5  have planar contact surfaces  8 . The rotor  3  comprises spring elements  9 ,  9 ′ for preloading the permanent magnets  6 ,  6 ′ against the support element  5 . 
         [0022]      FIG. 2  shows, in greatly enlarged fashion, an abutting region of two permanent magnets  6 ,  6 ′ and of the support element  5  of the rotor  3 . The spring elements  9 ,  9 ′ are each C-shaped and grip an edge  10 ,  10 ′, respectively, of the permanent magnets  6 ,  6 ′. The support element  5  comprises a channel  11 , into which the spring elements  9 ,  9 ′ grip. The channel  11  and the edges  10 ,  10 ′ of the permanent magnets  6 ,  6 ′ are situated perpendicularly to the plane of the drawing and, therefore, in parallel to the rotational axis  2  of the rotor  3 . The edges  10 ,  10 ′ have a recess  12 ,  12 ′, respectively, for accommodating a subregion of the spring elements  9 ,  9 ′.  FIG. 2  also shows that spring elements  9 ,  9 ′, which are adjacent to one another, are supported against one another. 
         [0023]      FIG. 3  shows one further embodiment of the rotor  3  in the abutting region of two permanent magnets  6 ,  6 ′, which differs from the embodiment according to  FIG. 2  only in that the spring elements  9 ,  9 ′ have an encapsulation  13  made of plastic in the abutting region. The encapsulation  13  fixes the spring elements  9 ,  9 ′ in their position shown. 
         [0024]      FIG. 4  shows a rotor  14  for the brushless direct current motor represented in  FIG. 1 , which differs from the rotor shown in  FIG. 1  in that the number of permanent magnets  15 ,  15 ′ is identical to the number of spring elements  16 . The spring elements  16  are held in a middle section  17  in cavities  18  of a support element  19  and grip edges  20 ,  20 ′ of the permanent magnets  15 ,  15 ′. The middle section  17  of the spring element  16  has the shape of a loop for ensuring an interlocking hold in the channel  18 .