Abstract:
The case for an electric motor brush defines a housing for a brush and comprises a cooling fin. The case comprises a flat metal base plate and a cover plate formed by separate pieces and defining the housing.

Description:
FIELD OF THE INVENTION 
     The invention relates to cases for electric motor brushes to sub-assemblies for electric motors comprising such cases and to electric motors comprising such cases. 
     BACKGROUND OF THE INVENTION 
     There is known, from French patent application number 2 699 749A, a brush case made by bending a metal blank defining a housing for guiding a brush in a sliding manner, and comprising cooling fins extending to the top of the case. The fins are shaped and disposed to have a large contact surface with the case and to offer a large exchange surface by convection with the ambient air. However, this case has the drawback that the bending of the blank for the manufacture of the case is complicated to perform. Moreover, the possibilities for shaping and arranging the fins remain limited and do not enable good cooling performances to be obtained. 
     One object of the invention is to provide a case which is easier to manufacture and which offers more possibilities and at least one cooling fin, arranged with improved cooling performance. 
     SUMMARY OF THE INVENTION 
     In accordance with the, there is provided a case for an electric motor brush defining a housing for a brush and comprising a cooling fin, a flat metal base plate and a cover plate, the base plate and cover plate being formed by separate pieces defining the housing. 
     Thus, the cover plate and the base plate are produced separately, which facilitates the manufacture of the case. Moreover, this separate design offers great freedom as to shape and arrangement of the fin to optimize the cooling performances. 
     Advantageously, the base plate has a dimension in the transversal direction perpendicular to an axial direction of the cover plate which is at least equal to twice a larger dimension of the cover plate in the transverse direction. 
     Thus the base plate itself offers a large heat exchange surface by convection with the ambient air. 
     The fin advantageously extends from the base plate. 
     The fin advantageously extends in a plane parallel to an axial direction of the cover plate. 
     The fin advantageously extends in a plane perpendicular to the base plate. 
     The case advantageously comprising a stop lug fixed to the base plate and extending in a plane that is not parallel to an axial direction of the cover plate. Thus this lug offers a stop to secure an end of a band spring coiled thereon ensuring the return of the brush towards a commutator of the motor. 
     The stop lug advantageously has two plane faces not parallel to an axial direction of the cover plate and forming an obtuse angle between such faces. Thus, the lug ensures good positioning of the coiled end of the band spring. 
     The stop lug is advantageously in a single piece with the base plate. 
     The cover plate advantageously comprises two lateral walls suitable for extending perpendicularly to the base plate and having cut-outs extending from one axial end of the cover plate. 
     Thus, these cut-outs allow the passage of the band spring. 
     Also provided in accordance with the invention is a for an electric motor comprising a case, a brush suitable to be received slidingly in the case and a band spring for the return of the brush, the case comprises a cooling fin, the a flat metal base plate and a cover plate, the base plate and cover plate being formed by separate pieces defining the housing. 
     There may be provided a brush unit comprising a case and a brush, or a plate bearing several brush units of this type. 
     Furthermore according to the invention an electric motor is provided comprising a case which comprises a cooling fin, a flat metal base plate and a cover plate, the base plate and cover plate being formed by separate pieces defining the housing. 
     Other characteristics and advantages of the invention will become further apparent in the following description of a preferred embodiment given by way of a non-restrictive example. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the attached drawings: 
     FIGS. 1,  2  and  3  are a front view, a view and a top view, respectively of a cover plate of a case according to an embodiment of the invention; 
     FIGS. 4 and 5 are respective front and top views of a base plate intended to be associated with the cover plate of FIG. 1; and 
     FIGS. 6 and 7 are respective partial cross-sectional and top views of a brush-holder plate bearing a case comprising the cover plate of FIG.  1  and the base plate of FIG.  4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIGS. 1 to  5 , a case  2  for the electric motor brush according to the invention comprises a cover plate  4  and a base plate part  6 , both made of metal, here made of brass. The cover plate  4  and the base plate part  6  are each a single piece and produced by cutting and bending two respective blanks made of brass. The cover plate  4  will be described first. 
     The cover plate  4  has the general shape of a rectangle parallelepiped. It has an axial direction  8  defining a front axial end  10  and a rear axial end  12  of the cover plate. The cover plate  4  is profiled in this direction. The cover plate comprises an upper wall  14  and two lateral walls, left and right wall  16 ,  18 . The vertical and horizontal directions, shown in FIGS. 1,  2  and  4 , are used only for the purposes of description. 
     It is obvious that any desired orientation may be used for the case  2  in the motor. The upper wall  14 , left wall  16  and right wall  18  each have a general rectangular shape. The two lateral walls  16 ,  18  extend parallel to one another facing one another and perpendicularly to the upper wall  14 . 
     The upper wall  14  has a cut-out  20  extending from the front axial end  10  parallel to the axis  8 , for the passage of a connecting strand of the brush fixed thereto. 
     The lateral walls  16 ,  18  each have a bulging portion  20  oriented towards the outside of the cover plate, so that in cross section, a central portion  17  having a rectilinear profile of these walls is distant from the axis  8  of the cover plate. Each lateral wall  16 ,  18  has a cut-out  22  extending from the front axial end  10  of the cover plate and breaking off before the mid-distance between the two axial ends of the cover plate. These cut-outs  22  are suitable to receive a return band spring as will shown further on. The bulging portions  17  allow, in the cover plate  4 , the volumes necessary for positioning the spring. They also improve the cooling of the brush received in the cover plate  4 . 
     The lateral walls  16 ,  18  have a bottom zone  24  defining a lower horizontal side of the cut-out  22 . This bottom zone  24  is shorter along the axis  8  than an upper zone  26  of these walls which is adjacent to the upper wall,  14 . Each lateral wall  16 ,  18  bears two attachment lugs  28  extending perpendicularly to the axis  8  from a lower horizontal side of the wall for the purpose of fixing the cover plate  4  to the base plate  6 , and the case  2  to a brush-holder plate. 
     With reference to FIGS. 4 and 5, the base plate part  6  comprises a flat base plate  32  having a general rectangular shape in plane view. In a central zone the base plate  32  has four rectangular through-orifices  34  suitable for receiving the four lugs  28  respectively of the cover plate  4 . The four orifices  34  are disposed symmetrically on either side of a median axial direction  8  of the base plate part  6 . The base plate part  6  comprises two flat fins  36  extending perpendicularly to the base plate  32  and parallel to the axis  8 , from two opposite sides of the base plate  32  which are parallel to one another. The two fins  36  extend facing one another and parallel to one another. Each fin  36  extends over the entire lengths of the associated side of the base plate  32 . 
     The base plate  6  has two apertures  38  having a general rectangular shape in plane view, having one side respectively adjacent to the fins  36 , the apertures being disposed symmetrically to one another with respect to the axis  8 . Two of the orifices  34  open into the associated apertures  38 . The base plate part  6  comprises two stop lugs  40  in a single piece with the base plate. Each lug  40  comprises a wall  42  extending from a front transversal edge of a respective aperture  38 , while being perpendicular to the axis  8  and to the base plate  32 . The lug  40  further includes wall  44  perpendicular to the base plate  32 , inclined with respect to the axis  8  towards it and having a vertical side in common with the wall  42 . The two walls  42 ,  44  are disposed so that they have two faces defining an obtuse angle α. The two lugs  40  are produced by cutting in the associated apertures  38 , then bending. The cover plate  4  has a plane of symmetry passing through the axis  8 . The same applies to the base plate part  6 . 
     With reference to FIGS. 6 and 7, to produce a brush-holder plate  50 , a brush unit is manufactured in the following manner: A cover plate  4  and a base plate part  6  are produced by cutting and bending. The cover plate  4  is then fixed to the base plate part  6  by introducing the attachment lugs  28  into the orifices  34  of the base plate  32 . The cover plate  4  and the base plate  32 , thus, define a housing in which it is possible for the brush  48  to be slidingly movable. Then a band spring  46  is introduced into the cut-outs  22  so that the two coiled ends of the spring come to abut against the above-mentioned faces of the respective stop lugs  40 . Then a brush  48  is engaged in the cover plate  4  by the front axial end  10  by pushing the median portion of the spring  46  into the cover plate. 
     Then a support plate  50  is provided, here made of bakelite with a flat circular shape and having a circular orifice  52  in its center. The plate is intended to bear several cases  2  such as those described above. Each case  2  is fixed to the support plate so that its axis  8  is radial to an axis  53  of the orifice  52  of the support plate. The front edge of the upper wall  14  of the cover plate  4  extends to the right of the edge of the orifice  52 . The base zone  24  of the lateral walls  16 ,  18  is therefore recessed from the orifice  52 . The attachment lugs  28  penetrate into the through-orifices of the plate intended for this purpose and emerge projecting from a face  54  of the plate opposite the case. The base plate  32  produces a surface-to-surface contact with the plate. 
     The fins  36  extend facing and at a distance from the respective lateral walls  16 ,  18  of the cover plate, parallel thereto. The base plate  32  and the fins  36  act as a heat sink and ensure the cooling of the case  2 , which is heated by the brush  48 , by air convection. The case  2  thus offers a large heat exchange surface with the ambient air. The base plate part  6  has a larger dimension a (or width) in a direction perpendicular to the axis  8  and parallel to the base plate  32 , at the level of the fins  36 . The cover plate  4  has a larger dimension p (or width) in the same direction, i.e. in a direction perpendicular to the axis  8  and parallel to the upper wall  14 . Here, the dimension a is roughly three times the dimension p. 
     In this particular instance, the support or brush-holder plate  50  is intended to form part of an electric motor for a motor vehicle such as a geared wiper motor, a cooling motor or a window-crank motor. 
     Of course, a number of modifications may be made to the invention without departing from the scope of the appended claims. The stop lugs  40  for the coiled ends of the band-spring  46  can be connected to the fins  36  by being produced by cutting and bending them.