Abstract:
A method produces a brush for a commutator motor, in particularly for a motor vehicle fan, for electrically contacting a connected contact lead to a commutator via a spring-loaded contact with a commutator. Accordingly, a brush material, particularly carbon dust, is poured into a cuboid matrix and compressed by a plunger in a contact direction for forming the brush.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This is a continuation application, under 35 U.S.C. §120, of copending international application No. PCT/EP2013/001455, filed May 16, 2013, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German patent application No. DE 10 2012 010 481.2, filed May 26, 2012; the prior applications are herewith incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The invention relates to a brush and a commutator motor having a brush of this type, in particular of a motor vehicle fan. 
         [0003]    Motor vehicles having an internal combustion engine generate a considerable amount of heat during operation. In order to maintain the operating temperature of the internal combustion engine and also for the operation of an air conditioning unit, a fluid cooling medium is generally used that in turn must be cooled. This is generally performed by a cooling network that is influenced by an airflow that exchanges heat with the cooling medium. By way of example, the cooling medium is conveyed in ducts that are integrated into the cooling network. Since in particular in the case of low vehicle speeds, the airflow is normally not sufficient for cooling purposes, by way of example European patent EP 1 621 773 A1 (corresponding to U.S. Pat. No. 7,042,121) discloses an electrical main fan by which the airflow is amplified. 
         [0004]    The main fan is arranged downstream of the cooling network in the direction of flow. The air is sucked through the cooling network with the aid of an impeller wheel of the fan and conveyed to the internal combustion engine. The impeller wheel is connected to a rotor shaft of the electric motor or rather its rotor (armature) by a central rotor shaft coupling. 
         [0005]    A commutator motor is typically used as an electric motor. A number of carbon brushes that lie in corresponding brush holders are arranged around a central commutator and the carbon brushes are in electrical contact with the commutator and for this purpose brush over its commutator segments during the rotating operation of the motor. A connecting wire that runs perpendicular to the contacting direction is fastened to each brush. During operation of the electric motor, the brushes are worn down as a result of friction as they brush over the commutator. The abraded particles that are produced as a result can settle between the individual commutator segments and short circuit the segments. In addition, the friction heat that is produced as a result can cause the brushes and the carbon dust that is produced to ignite. 
       SUMMARY OF THE INVENTION 
       [0006]    The object of the invention is to provide a particularly suitable brush and a particularly suitable commutator motor having a brush, wherein the brush is to be comparatively durable and resistant to abrasion, suitably comparatively simple and cost-effective to assemble in the commutator motor and also in particular comparatively cost-effective to produce. 
         [0007]    A matrix is filled with a brush material in order to produce the brush. The brush material is in particular carbon dust that is mixed with a fixing medium. The term ‘matrix’ is understood to mean a casting mold whose cavity at least in part corresponds to the outer form of the cast part, in other words the brush. The brush material that is located within the matrix is compressed by a pressing tool and by way of example heated. The movement direction of the pressing tool is along a contacting direction. The contacting direction describes the direction in which the brush that is provided is pressed by a resilient element against a commutator of an electric motor and the direction corresponds to the brush lengthwise direction of the brush that is produced. The pressing tool is consequently in contact with the future contact surface between the preferably rectangular-shaped brush and the commutator or the opposite end of the brush. It is preferred that two pressing tools are used in order to produce the brush and one of the pressing tools is in contact with the future contact surface and the other pressing tool is in contact with the opposite end of the brush. 
         [0008]    The remaining delimiting surfaces of the brush are defined by the matrix. These delimiting surfaces are consequently produced in a smooth and tolerance free manner. The delimiting surfaces do not contain any burrs or deformations. It is therefore not necessary to machine finish the delimiting surfaces by a mill or the like in order to ensure a simple assembly of the brush within a brush holder of the electric motor and to ensure a reliable operation of the electric motor. 
         [0009]    The brush holder forms an at least in part form-locking receiving arrangement of the brush and the brush can be displaced within the brush holder in the radial direction of the electric motor towards the commutator. A form-locking connection is one that connects two elements together due to the shape of the elements themselves, as opposed to a force-locking connection, which locks the elements together by force external to the elements. If the delimiting surfaces were uneven, the brushes could become wedged and the functionality of the electric motor that is also described as a commutator motor would no longer be ensured. As a result of the pressing direction of the one or multiple pressing tools, the brush material is aligned and compressed along a preferred direction, namely the contacting direction. The brush that is produced as a result contains an increased stability and friction resistance in this direction. The operation of the electric motor is therefore comparatively more reliable since both the amount of abrasion as well as the probability of the brush breaking off while brushing over the commutator is reduced. 
         [0010]    Prior to the compression process by the pressing tool, a connecting wire is preferably placed in the brush material. In particular, the connecting wire is entirely surrounded by the brush material in the region of the brush that is produced as a result. By way of example, the matrix is filled with the brush material to a specific level, in a subsequent step the connecting wire is placed in the matrix, and in a further step the matrix is filled with the remaining brush material. After the subsequent compression, the connecting wire is held by the brush in a form-locking and a force-locking manner. The connecting wire runs within the brush in a manner that is essentially parallel to the contacting direction, wherein however it is also feasible for the connecting wire to run in a meandering manner with the preferred direction in the contacting direction in order to ensure that the connecting wire is anchored in an improved manner with the brush. 
         [0011]    The connecting wire exits preferably on the end of the brush, the end being opposite the contact surface. In particular, for this purpose the pressing tool or the base of the matrix that is arranged on this side contains a bore through which the connecting wire is fed into the casting mold for the brush. As a result of a production process of this type, it is possible to omit a complex connection of the connecting wire to the brush, by way of example by drilling a receiving arrangement into the brush and subsequently adhering the connecting wire at that location. 
         [0012]    The brush contains a projection piece that is formed perpendicular to the contacting direction or rather to the brush lengthwise direction. By way of example, an equalizing channel is integrated into the matrix for this purpose. The projection piece renders it possible to handle the brush during assembly of the brush and during operation of the electric motor, wherein the contact surface can be provided free from deformations of this type. Provided that the connecting wire is connected to the opposite end, the connecting wire is not impaired by contact with a tool that is operating together with the projection piece. 
         [0013]    The projection piece is expediently embodied in a generally rectangular-shaped manner. Consequently the projection piece is comparatively robust. In addition, it is consequently rendered possible to form the brush with the projection piece in a comparatively consistent manner. In addition, the space requirement is comparatively small, wherein however a reliable contact with the projection piece is possible. 
         [0014]    The projection piece is advantageously arranged on an axial face of the brush that is subsequently also described as an axial surface. The term “axial face or rather axial surface” is understood to mean a face or rather surface of the brush that delimits the brush in the assembled state in the axial direction of the electric motor. By virtue of positioning the projection piece in this manner, consideration is given to the comparatively small amount of installation space required by the brush carrier, also described as the brush plate, on which the brush holders are located. 
         [0015]    A longitudinal groove that runs in the contacting direction is suitably integrated in the axial surface and the groove extends as far as the projection piece. By way of example, a corresponding longitudinal connecting piece is integrated into the matrix. As a consequence, in particular in connection with the equalizing channel that is integrated in the matrix, a comparatively large effective axial height of the projection piece can be achieved, wherein the projection piece only protrudes beyond a part of this axial height from the axial surface of the brush. The longitudinal groove can additionally or alternatively also be used as a guiding surface for the purpose of producing the projection piece. 
         [0016]    Since the projection piece only enlarges the construction height of the brush in the axial direction, it is possible to arrange further components of the electric motor near to the brush on the brush carrier. Alternatively or in combination therewith the projection piece is offset from the contact surface of the brush and is preferably adjacent to the end of the brush that is opposite thereto. In this manner, any to a large extent pronounced abrasive wear of the brush and the accompanying shortening of the brush in the contacting direction do not damage the projection piece. 
         [0017]    It is preferred that the contact surface of the brush on the commutator is curved towards the interior and the curvature corresponds to the rounded outer surface of the cylindrical commutator. In this manner, the region of the contact surface of the brush is enlarged on the commutator and an electrical voltage drop that is produced as a result between the two is reduced. 
         [0018]    A receiving groove is integrated into the brush, in order to at least in part receive the resilient element that presses on the commutator. The resilient element is suitably held in the receiving groove in a form-locking manner so that no further fastening measures are necessary for the purpose of connecting the resilient element to the brush, wherein the region in which the resilient element has an effect on the brush is defined by the receiving groove. 
         [0019]    It is particularly preferred that the resilient element is embodied as a leaf spring. In other words the resilient element is produced from a resilient steel strip that is rolled onto its ends. In the case of a suitable fastening of the ends on the brush carrier, the brush is pressed against the commutator. In this case, the receiving groove is preferably at least in part integrated in such a manner that it extends circumferentially into the brush or is located on the end of the brush that is opposite the contact surface. 
         [0020]    The brush carrier of the electric motor suitably contains a bracket that has a region for latching with the projection piece. During assembly of the electric motor, the brush is initially inserted into the brush holder of the brush carrier and the resilient element is placed on or connected to both the brush as well as to the brush carrier. Expediently hereafter, the connecting wire is electrically contacted with electrical components of the electric motor that are arranged on the brush plate, such as a choke coil. As a consequence of the electrical contact, the brush is moved within the brush holder in a direction counter to the pressing direction radially towards the exterior and latches with the bracket. In this case, the bracket engages at the projection piece and hinders a movement of the brush in the pressing direction that is produced by the resilient element. 
         [0021]    In a subsequent procedural step, the commutator that is mounted in a rotatably fixed manner on a shaft is inserted into a central opening of the brush carrier and the shaft is secured in the axial direction, by way of example by bearings. In a subsequent step, the bracket is opened and the brush is released. The brush is then moved against the commutator by the resilient loading. A comparatively simple production process of the commutator motor is rendered possible by the bracket since the brushes can already be assembled in advance on the brush plate. The subsequent assembly of a rotor that contains the commutator is comparatively simple, particularly the latched brush is held spaced apart from the commutator by the bracket. In other words, the brush does not hinder the insertion of the commutator. 
         [0022]    It is preferred that the bracket is connected to and in particular formed on the brush holder. It is preferred that the bracket is located on an axial side of the brush holder. The production of the brush carrier is simplified by its single-part embodiment and the amount of installation space that is required is reduced as a result of the arrangement on the brush holder. In addition, further elements of the electric motor that are arranged on the brush carrier are not impaired by the bracket. Consequently, it is possible to use a previously existing layout of the brush carrier. It is only necessary to adjust the one or multiple brush holders of the brush carrier. 
         [0023]    The bracket expediently extends in the contacting direction of the brush. In particular, the bracket is pivoted about an axis for the purpose of unlatching the projection piece of the brush and the axis is perpendicular to the contacting direction, wherein for example a film hinge is used. As a result of the bracket being of this type of shape, the bracket is located in a region of the electric motor that is not occupied by any further components of the electric motor which is why a bracket of this type can be integrated into an existing electric motor in a comparatively uncomplicated manner. 
         [0024]    The connecting wire is suitably s-shaped in the region of the brush. In this manner, a reliable contact arrangement of the brush with the connecting wire is also ensured in the case of a comparatively extensive amount of abrasive wear of the brush, since as a result of the s-shape, a sufficient equalizing length of the connecting wire is made available that compensates for the abrasive wear. Directly after assembly, the space of the equalizing length of the connecting wire is advantageously defined and possible other components of the electric motor are not hindered or impaired. 
         [0025]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0026]    Although the invention is illustrated and described herein as embodied in a brush for a commutator motor and a commutator motor having the brush, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0027]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0028]      FIG. 1  is a diagrammatic, side view of a main fan having an electric motor; 
           [0029]      FIG. 2  is a diagrammatic perspective view of a brush carrier of the electric motor; 
           [0030]      FIGS. 3-5  are diagrammatic perspective views of a brush having projection pieces according to the invention; 
           [0031]      FIG. 6  is a perspective view of the brush having a longitudinal groove and the projection pieces in accordance with  FIG. 5 ; 
           [0032]      FIG. 7  is a perspective view of a detail of the brush carrier having the brush; and 
           [0033]      FIG. 8  is an illustration schematically showing a production process of the brush. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    Parts that correspond to one another are provided with identical reference numerals in all figures. 
         [0035]    Referring now to the figures of the drawings in detail and first, particularly to  FIG. 1  thereof, there is shown schematically in a simplified manner a side view of a cooling fan  2  of a motor vehicle, in other words a motor vehicle fan. The cooling fan  2  contains a cooling network  4  through which a cooling duct  6  is guided. A cooling fluid is located within the cooling duct  6  and the cooling fluid is kept in circulation by a non-illustrated pump. The cooling fluid is conveyed through an internal combustion machine  8  and is heated by the internal combustion engine, wherein the internal combustion engine  8  is cooled. The heated cooling fluid is then conveyed through the cooling network  4  that is influenced by airflow. The direction of the airflow is along an airflow direction  10  that essentially corresponds to the main direction of travel of the motor vehicle. 
         [0036]    The airflow is amplified or in the case of the vehicle being stationary the airflow is generated by a fan  12  that is described as a main fan  12  and that is arranged in the airflow direction  10  downstream of the cooling network  4 . This is performed by an electric motor  14  that sets an impeller wheel  16  into a rotational movement. In addition, the airflow is conveyed to the internal combustion engine  8  by the impeller wheel  16  and the internal combustion engine is consequently influenced from the exterior with the airflow. This leads to the internal combustion engine  8  being additionally cooled. The impeller wheel  16  is arranged within a cooling frame  18  by which the airflow is directed. Brushes or a specific contour is or are arranged in the transition region between the frame  18  and the impeller wheel  16  and the specific contour prevents a so-called air leakage between the two components. The electric motor  14  is fastened to the frame  18  by struts  20 . The struts  20  are produced as one piece with the frame  18 , by way of example in a synthetic material injection method. 
         [0037]      FIG. 2  illustrates in a perspective manner the electric motor  14  in which a housing and further components are not illustrated for the purpose of improving visibility. The electric motor  14  contains in a central area a shaft  24  that is mounted in such a manner that it can rotate about an axis of rotation  22 . A commutator  26  having twenty commutator segments  28  that are electrically insulated with respect to one another is fastened to the shaft  24  in a rotatably secure manner. Two brushes  30  that extend in a radial direction are located offset essentially at 90° in relation to the axis of rotation  22 . The brushes  30  are at least in part arranged in a form-locking manner within brush holders  32  of a brush carrier  34  that is produced from synthetic material and the brush holders are embodied as one piece with the brush carrier. Each brush  30  is pressed against the commutator  26  by a leaf spring  36  in a respective contacting direction  38  that runs radially inwards and runs perpendicular to a contact surface  40  between the brush  30  and the commutator  26 . 
         [0038]    The brushes  30  brush over the commutator segments  28  in the case of a rotational movement of the shaft  24  and are consequently contacted by the commutator segments in an electrical manner. A connecting wire  42  is fastened to the contact surface  40  between each brush  30  and the end of the respective brush  30  that lies opposite the commutator  26 . The connecting wires  42  are contacted in an electrical manner in each case by a choke coil  44  in order to reduce disruptive feedback within a supply current and the choke coil is clipped to the brush carrier  34  and is electrically connected to an on board electrical system of the motor vehicle by way of a non-illustrated fuse and a supply line  46 . 
         [0039]      FIG. 3  illustrates a perspective view of one of the brushes  30  and  FIG. 4  and  FIG. 5  illustrate a perspective view of the brush  30  and the associated leaf spring  36 .  FIG. 6  illustrates a variant of the brush  30 . The brush  30  is essentially rectangular-shaped, wherein the corrugated contact surface  40  is embodied in a curved manner. The curvature corresponds to the curve of the commutator  26  so that in the assembled state, the brush  30  lies entirely against the commutator  26  with the contact surface  40  that delimits the brush  30  in the pressing-on direction  38 . A rectangular projection piece  50  is formed on one of the two axial surfaces  48  of the brush  30  and the projection piece lies adjacent to the end of the brush  30  that is connected to the connecting wire  42 . 
         [0040]    As is evident in  FIG. 6 , in accordance with the variant of the brush  30 , a longitudinal groove  51  that runs in a contacting direction  38  is integrated into one of the two axial surfaces  48  of the brush and the groove  51  extends as far as the projection piece  50 . The axial surfaces  48  are the side surfaces of the rectangular-shaped brush  30  that delimit the brush in an axial direction  52  that runs parallel to the axis of rotation  22 . 
         [0041]    A comparatively large effective height of the projection piece  50  can be achieved in the axial direction  52  by the longitudinal groove  51 , wherein the projection piece  50  itself protrudes beyond a part of the axial height and beyond the axial surface  48  of the brush  30 . The longitudinal groove  51  can thus comprise by way of example a groove depth of 0.5 mm and the groove depth leads to its effective projection piece height of 1 mm in a particularly effective manner as far as production technology is concerned in the case of a projection piece  50  that protrudes beyond the axial surface  48  by e.g. likewise 0.5 mm. The longitudinal groove  51  can also be used as a guiding surface. 
         [0042]    A receiving groove  54  is integrated into the end of the brush that lies opposite the contact surface  40 , whereby the end contains an L-shaped cross section along a section surface that is defined by the contacting direction  38  and the axial direction  52 . In the mounted state, the leaf spring  36  is arranged in a positive locking manner within the receiving groove  54 . A connecting wire  42  exits the brush  30  above the receiving groove  54  and is embodied in an essentially s-shaped manner in the directly adjacent region  56 , as is illustrated in  FIG. 4 . 
         [0043]      FIG. 7  illustrates the brush  30  during the process of assembling the commutator motor  14 . The brush  30  is held back by a bracket  58  that is in contact with the projection piece  50  with respect to the force that is exerted by the leaf spring in the contacting direction  38  and consequently is spaced apart from the central opening of the brush carrier  34  within which the commutator  26  lies in the assembled state. The bracket  58  that extends in the contacting direction  38  is formed on one end on the brush holder  32  and the free end that is formed is coupled to the projection piece  50  of the brush  30 . After the commutator  26  is assembled, the brush  30  and the bracket  58  are unlatched whereby the brush  30  is pressed in the axial direction  38  under the free ends of the bracket  58 . The brush  30  is released by the bracket bending away from the brush  30 . In the case of the bracket  58  being brought into its original position, the projection piece  50  is located below the free end or in the contacting direction  38 , offset in relation to the free end of the bracket  58  which is why the projection piece and bracket do not latch again. On the contrary, the brush  30  is pressed unhindered against the commutator  26  by the leaf spring  36  and any abrasive wear that occurs as a result is compensated for during operation of the electric motor  14 . Consequently, the connecting wire  42  and the commutator  26  are contacted in an electrical manner by way of the brush  30 . In the case of replacing or re-adjusting the commutator  26 , the brush  30  is pressed radially outwards in the opposite direction to the contacting direction  38  until the projection piece  50  and the bracket  58  latch again. After the projection piece and bracket have latched, the commutator  26  can be removed or accordingly adjusted unhindered. 
         [0044]      FIG. 8  illustrates schematically and in a simplified manner the process of producing the brush  30 . A mold  64  that is formed by a matrix  60  and a lower pressing tool  62  is filled up to half with a brush material  66 , carbon dust. The form of the lower pressing tool  62  defines the form of the contact surface  40  and the form of the matrix  60  amongst others defines the form of the axial surfaces  48 . The connecting wire  42  is guided into the mold through a central bore  68  within an upper pressing tool  70  and the mold is closed with the upper pressing tool  70 . The upper pressing tool  70  is located on the side of the mold  64  that lies opposite the lower pressing tool  62 . The mold  66  also widens at this location in order to form the projection piece  50 . In a subsequent step, the remaining free part of the mold  64  is filled with the brush material  66  and the part of the connecting wire  42  that is located within the mold is entirely encompassed by the brush material. 
         [0045]    In a subsequent procedural step, the two pressing tools  62 ,  70  are pressed against one another, as a result of which the carbon dust is compressed. The direction of movement of the pressing tools  62 ,  70  is along the contacting direction  38 . Pressure is consequently applied to the brush material  66  by the later the contact surface  40  and the end that is opposite the contact surface  40 . In addition, the matrix  60  is heated and the brush material  66  is consequently baked onto the brush  30  which fastens the connecting wire  42  to the brush  30 . The brush material  66  is conveyed in this preferred direction in a crystalline state as a result of the pressing direction along the contacting direction  38  which increases the resistance capability of the brush  30  with respect to abrasive wear of the commutator  26  during operation of the electric motor  14 . Furthermore, all the side surfaces that extend parallel to the contacting direction  38 , amongst others the axial surfaces  48 , are free from burrs and are smooth as a result of the form of the matrix  60 . As a result of the production method, any inaccuracy and deviations of the brush  30  from the mold  64  can only occur in the region of the contact surface  40  and the opposite end of the brush  30 . Consequently, the brush  30  that is produced is comparatively a precise fit to the brush holder  32  and it is possible to omit a step of machine finishing the side surfaces of the brush  30  that extend parallel to the contacting direction  38 . 
         [0046]    The invention is not limited to the above described exemplary embodiment. On the contrary, other variants of the invention can also be derived therefrom by the person skilled in the art without departing from the subject matter of the invention. In particular in addition, all the individual features that are described in relation to the exemplary embodiment can also be combined with one another in other ways without departing from the subject matter of the invention. 
         [0047]    The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:
     2  Cooling Fan     4  Cooling Network     6  Cooling Duct     8  Machine     10  Airflow Direction     12  Fan     14  Electric Motor     16  Impeller Wheel     18  Cooling Frame     20  Support     22  Axis of Rotation     24  Shaft     26  Commutator     28  Commutator Segment     30  Brush     32  Brush Holder     34  Brush Carrier     36  Leaf Spring     38  Contacting direction     40  Contact surface     42  Connecting Wire     44  Choke Coil     46  Supply Line     48  Axial Surface     50  Projection Piece     51  Longitudinal Groove     52  Axial Direction     54  Receiving Groove     56  Region     58  Bracket     60  Matrix     62  Lower Pressing tool     64  Mold     66  Brush Material     68  Bore     70  Upper Pressing tool