Patent Publication Number: US-2005116577-A1

Title: Holder for a carbon brush

Description:
The invention relates to a holder for a carbon brush, particularly one which may be applied to a commutator or a collector ring with a front area, comprising a spring element with a possibly U- or L-shaped fixing section and a support section for housing the carbon brush.  
      A corresponding holder is disclosed e.g. in DE 199 62 705 A1. In order to fix the carbon brush, the support section comprises an opening, through which the carbon brush extends for fastening it through insulation displacement contact. Since the carbon brush extends in sections on the back along the support section, a minimum installation depth is required, which can lead to significant problems especially with small-power motors. This insulation displacement contact results additionally in a notch effect, which can lead to problems during vibrations. Since the rear area of the carbon brushes extending through the support section frequently has a smaller cross-section than the section facing a commutator, on which the carbon brush rests for current transfer purposes, it is necessary from a manufacturing aspect to press the carbon brush material in the longitudinal direction of the carbon brush to be produced.  
      From U.S. Pat. No. 4,638,201 we know of a holder for a carbon brush. The holder consists of an L-shaped spring element, the one leg of which comprises a U-shaped dent, in which a carbon brush can be fixed.  
      In a holder pursuant to DE 199 62 705 A1, the support section comprises an opening through which a carbon brush extends for fastening it through insulation displacement contact. Since the carbon brush extends in sections on the back along the support section, a minimum installation depth is required, which can lead to significant problems especially with small-power motors. This insulation displacement contact results additionally in a notch effect, which can lead to problems during vibrations. Since the rear area of the carbon brushes extending through the support section frequently has a smaller cross-section than the section facing a commutator on which the carbon brush rests for current transfer purposes, it is necessary from a manufacturing aspect to press the carbon brush material in the longitudinal direction of the carbon brush to be produced.  
      An electric motor for small units pursuant to DE 24 13 578 A1 comprises holders for carbon brushes designed as leaf springs, which each comprise a prismatic extension that can be fixed in a cut-out section of the leaf spring through a notch effect.  
      From DE 23 30 689 A1 we know of a carbon brush holder for small electric machines. Here a carbon brush comprises a projection with a small cross-section that has a single-piece design with the carbon brush, extends through an opening of a spring element, and is fixed by means of resilient flaps.  
      The present invention is based on the object of further developing a holder of the afore-mentioned kind, especially one intended for small carbon brushes for motor vehicle manufacture, in such a way that secure fixing of the carbon brush while avoiding a notch effect is possible, wherein the installation space shall be minimized. Moreover it shall be ensured that the contact resistance between the carbon brush and its holder is as low as possible.  
      Pursuant to the invention this object is achieved essentially in that the carbon brush is intimately connected with the support section and/or is connected thereto with a material connection, wherein in particular a connection by means of gluing with a conductive adhesive or welding or in particular soldering occurs. Hereby the carbon brush is especially metal-coated on the support side, such as nickel-, tin- and/or copper-plated.  
      In a further development it is provided that the support section of the holder comprises a support surface that supports the carbon brush on the back, as well as retention or guide sections protruding from the support section and extending along at least two opposing lateral surfaces of the carbon brush. In particular it is provided that the carbon brush is connected along its back to the support surface in a non-positive manner.  
      Pursuant to the invention the carbon brush is supported over a large area on the support section itself so that the carbon brush does not extend beyond the back of the support section. Consequently the installation depth is solely dependent upon the effective length of the carbon brush interacting with a commutator or collector ring. Moreover the carbon brush can be fixed without insulation displacement contact so that in particular in the case of vibrations disadvantageous notch effects are eliminated.  
      Apart from the intimate connection, additional fixation and hence securing of the carbon brush is achieved especially through the retention or guide sections having a clamping effect on at least two lateral surfaces of the carbon brush.  
      In a further development of the invention it is provided that a retention or guide section protruding from the support section of the spring element extends in particular along each lateral surface, wherein the retention or guide section is a freely cut section that is bent out from the plane formed by the support section.  
      Preferably two retention or guide sections, such as lugs, extend along each lateral surface of the carbon brush. Hereby the carbon brush can be fixed in a clamping manner by means of the retention or guide sections.  
      The carbon brush as such can be a block carbon brush or a hammer carbon brush.  
      Since due to the holder designed pursuant to the invention and the associated fixation of the carbon brush in the back area the cross-section of the carbon brush remains constant, it offers the benefit that a preferred direction must not be adhered to for pressing the carbon brush material. Hence it is feasible without difficulty to use carbon brushes that are pressed perpendicular or parallel to the longitudinal axis of the finished carbon brush.  
      Further details, advantages and features of the invention result not only from the claims, the features disclosed therein—alone and/or in combination, but also from the following description of preferred exemplary embodiments disclosed in the drawings.  
      They show: 
    
    
       FIG. 1  in diagrammatic view a top view onto the carbon brush holder,  
       FIG. 2  in diagrammatic view a side view of the carbon brush holder from  FIG. 1 ,  
       FIG. 3  the carbon brush holder from  FIGS. 1 and 2  with a carbon brush extending therefrom,  
       FIG. 4  the holder with carbon brush revealed in  FIG. 3  in a deviating diagrammatic illustration, and  
       FIG. 5 a  representative illustration of a carbon brush arranged in a small-power motor. 
    
    
       FIG. 5  shows a mere principle of a small-power motor  10  with a motor housing  12  and an electric motor with commutator  14  arranged thereon, to which carbon brushes  16 ,  18  are applied for current transfer purposes. The carbon brushes  16  and  18  each extend from a holder  20 , which is only representatively illustrated with the carbon brush  16 , in the form of a leaf spring, the function of which is known and which comprises a fixing leg or fixing section  22  and a support section  24  housing the carbon brush  16 . The fixing section  22  is fixed between the bearings and abutments  26 ,  28  and  30  in the familiar fashion. For this purpose the fixing section  22  comprises a section  32  that is arched U-shaped in its profile, which surrounds the bearing  28 , while the adjoining sections rest against the abutments  26  and  30  across a surface. This creates a clear fixation of the holder  20 , wherein due to the prestress of the support section  24  in relation to the fixing section  22  the carbon brush  16  extending from the support section  24  is subjected to the necessary force in the direction of the commutator  14 .  
      The carbon brush  16  pursuant to the invention is intimately connected to the support section  24 , such as welded or in particular soldered thereto. To this end, the area of the carbon brush  16  that is intimately connected to the support section  24  can be tin-, nickel-, or copper-plated or can be metal-coated in another suitable fashion.  
      The carbon brush  16  rests with its rear surface  34 , which extends opposite the front area  36  that is applied to the commutator  14 , on the side  38  of the support section  24  that faces the commutator, and is intimately connected thereto. The corresponding metal-coated area of the carbon brush  16  is marked with the reference number  17 . Moreover fixation occurs by means of outwardly bent flaps or lugs  42 ,  44  that are freely cut from the support section  24  and/or its surface  38  forming a plane, wherein at least one flap or one lug  40 ,  42 ,  44  extends along a lateral surface  46 ,  48 ,  50  of the carbon brush  16 . This way the carbon brush  16  is held in a guided fashion to the required extent and if necessary it is fixed by clamping without the presence of insulation displacement contact that would lead to a notch effect, as is the case in the prior art.  
      The flaps or lugs  40 ,  42 ,  44  can also alone have the function of a guide to the carbon brush  16  so as to position it clearly in relation to the support section  24  and then connect it to the support section  24  e.g. through soldering or welding.  
       FIGS. 1 through 4  reveal another preferred embodiment of a holder  52 , the basic design of which however corresponds to the holder  20 , with said holder consisting of a support section  54  and a U-shaped bent fixing section  56 , wherein its free end leg  58  comprises a U-shaped bent section  59 , which for the purpose of fixing the carbon brush holder  52  encloses a bearing corresponding to the bearing  28  pursuant to  FIG. 5 . The U-shaped section  59  comprises legs diverging from each other starting from the traverse or base leg, as illustrated in  FIG. 2 .  
      The support section  54  comprises a freely cut surface  60 , on which a carbon brush like the carbon brush  62  illustrated in  FIGS. 3 and 4  rests with its rear surface and is intimately connected thereto, such as soldered (area  17 ). To guide and s if necessary further fix the carbon brush  62 , retention or guide sections  64 ,  66 ,  68 ,  70 ,  72 ,  74  can be freely cut and be bent out from the plane formed by the surface  60 , said sections extending along the lateral outer surfaces  76 ,  78 ,  80 ,  82  when the carbon brush  62  is positioned and possibly holding the carbon brush  62  in a clamping fashion. The clamping fixation however is not an absolutely required feature since the flat retention sections or lugs  64 ,  66 ,  68 ,  70 ,  72 ,  74  in the actual sense must provide axial guidance on their own to the carbon brush  62 , which due to the spring effect of the support section  54  applies the carbon brush  62  to a commutator.  
      As can be seen in particular in  FIGS. 3 and 4 , two retention or guide sections or lugs  68 ,  70  or  72 ,  74  extend along the narrow sides  80 ,  62  [sic] of the carbon brush  62 , and one retention or guide section or holder section  64 ,  66  extends along the wide sides  76 ,  78 , which are wider than those running on the narrow sides  80 ,  62  [sic]. From each longitudinal edge  84 ,  86 ,  88 ,  90  of the carbon brush  62  a holder lug  68 ,  70 ,  72 ,  74  extends, wherein together with the lugs  64 ,  66  extending along the remaining longitudinal lateral surfaces  76 ,  78  of the carbon brush  62  the carbon brush  62  is axially guided such that its rotation is out of the question. Hence additional securing is provided should the intimate connection between the carbon brush  62  or its metal-coated area  17  and the support section  54  be destroyed.  
      The wide sides  76 ,  78  of the carbon brush  62  extend in the exemplary embodiment along the longitudinal axis of the support section  54 .  
      Since the carbon brush  62  rests over a large area on the plane formed by the support section  54 , namely the support surface  60 , flawless application of the carbon brush  62  to a commutator is ensured even when vibrations occur. Since additionally the carbon brush  62  does not extend through the support section  54 , a lesser installation depth is required.  
      In particular when using block carbon brushes it is beneficial that the pressing-ready mixture that is required for the manufacture of the carbon brush can be pressed in the desired direction in relation to the longitudinal axis of the carbon brush, i.e. for example parallel to the longitudinal direction of the finished carbon brush or perpendicular to it.  
      The intimate connection by soldering can be implemented in that the carbon brush is guided with its back through a tin bath in order to then be connected with the holder.  
      It is also possible to establish an intimate or non-positive connection by using an electrically conductive adhesive between the carbon brush and holder.