Patent Publication Number: US-2018040997-A1

Title: Brush-holder

Description:
The present invention relates to an improved brush-holder of an electric motor for a motor vehicle starter, as well as to the corresponding electric motor and starter. The invention has a particularly advantageous, but not exclusive, application with motor vehicle starters, in particular those which are installed in vehicles equipped with the function of automatic stopping and restarting of the thermal engine (so-called stop and start function). 
     In a known manner, a brush-holder is fitted around the shaft of the rotor of a starter, such as to make brushes made of electrically conductive material cooperate with an electrical collector integral with the shaft of the rotor. This makes it possible to supply the rotor electrically by switching of the electric current in the conductors of the rotor. 
     For this purpose, the brush-holder comprises a support plate which supports a series of cages, each of which is used as a receptacle for a brush. Each brush comprises a face which is designed to rub against the conductive plates of the connector which are connected to the winding of the rotor. A resilient means, such as a spring, exerts a force in the direction of the collector on each brush received in a cage, in order to ensure the contact between the brush and the plates of the collector. 
     The brushes have alternating polarities. Thus, the brushes with positive polarity are connected electrically, via their respective braid, to an inter-brush connector to which there is also connected electrically the supply wire obtained from the contactor of the starter. In addition, the brushes which are designed for the current return are connected electrically to the earth of the machine by means of their respective braid. 
     In certain brush-holder configurations, it is known to use a spring of a spiral type comprising a wound part fitted on a lug, as well as an arm which extends from an end of the wound part, which arm is designed to be supported on an end face of the brush opposite the face in contact with the plates of the connector. 
     This type of spiral spring makes it possible to increase the size of the brush for a given brush-holder diameter, since the latter is situated between two brushes, and not between the brush and the head of the motor, as is the case for brush holders which use a helical spring. In addition, the fact of increasing the length of the brush makes it possible for the brush to have a longer service life. 
     As described in document FR2996369, the cages are made from a thin metal plate, such as to form substantially an omega, the end branches of which are secured on the plate via a securing device. The problem with a configuration of this type is that the dust which is generated by the brushes can generate short-circuits in the starter. 
     The objective of the invention is in particular to eliminate this disadvantage efficiently, by proposing a brush-holder for an electric motor, in particular for a motor vehicle starter, comprising guide cages which are designed to receive brushes, and a support plate on which the said guide cages are positioned. According to the invention, the said guide cages are made of an insulating material, and the said brush-holder comprises lugs which are secured on the support plate, around each of which a spiral spring is designed to be fitted, in order to exert a force on the brush, such as to place the said brush against a collector. 
     As a result of the production of the cages from an insulating material, which for example can be integral with the support plate, the invention thus makes it possible to solve the aforementioned problems of short-circuits generated by the powder from the brushes. 
     According to one embodiment, each lug is situated between two adjacent guide cages. The fact that the brush is situated between two guide cages makes it possible to increase the size of the brush for a given head diameter. 
     According to one embodiment, the said lugs are made of a metal material. A characteristic of this type makes it possible to ensure efficient retention of the wound part of the spring, since the metal lug can withstand without difficulties the reaction forces applied by the associated spring, unlike a plastic lug. 
     According to one embodiment, the said lugs are obtained from a metal washer. A configuration of this type makes it possible to rigidify the assembly obtained. 
     According to one embodiment, the support plate is over-moulded around the lugs, the said support plate preferably being made of plastic. This makes it possible to render the lugs integral with the support plate. 
     According to one embodiment, the support plate is over-moulded around lugs, and preferably only around the base of the said lugs. 
     According to one embodiment, the said support plate is over-moulded around the said lugs and the said metal washer, the said support plate preferably being made of a plastic material. 
     According to one embodiment, the said metal washer comprises a number of parts corresponding to the number of guide cages, which are separated from one another such as to isolate the said brushes from one another. This therefore prevents risks of short-circuits in the starter. 
     According to one embodiment, the said lugs are secured on the said support plate. 
     According to one embodiment, the said lugs are added, independently from one another, onto the said support plate. 
     According to one embodiment, the said lugs are provided with a base which extends along the support plate, and makes it possible to secure the lug on the said support plate. 
     According to one embodiment, the said lugs are provided with an opening which makes it possible to retain the said lugs during the over-moulding. This makes it possible to guarantee precise positioning of the lugs during the over-moulding operation, by means of indexing tooling comprising fingers which can cooperate with these openings. 
     According to one embodiment, the said brush-holder comprises curved portions which each project from the support plate, parallel to the lugs, and being designed for guiding of wound parts of the said spiral springs. 
     According to one embodiment, the said support plate comprises elements for guiding of an interconnector, in order to connect brushes with the same polarity, on the side of a face opposite that which supports the said guide cages. 
     According to one embodiment, the said guide cages are integral with the said support plate. 
     The invention also relates to an electric motor, comprising a brush-holder as previously defined. 
     The invention also relates to the starter of a motor vehicle comprising an electric motor as previously defined. 
    
    
     
       The invention will be better understood by reading the following description, and examining the figures which accompany it. These figures are provided purely by way of illustration, but in no way limit the invention. 
         FIGS. 1 and 2  are respectively views in perspective and from above, illustrating a first embodiment of a brush-holder of an electric motor according to the present invention; 
         FIG. 3  is a view in perspective of the brush-holder in  FIGS. 1 and 2 , without the brushes or the spiral springs; 
         FIG. 4  is a view in perspective of the metal washer used in the brush-holder in the preceding figures, around which the support plate is designed to be over-moulded; 
         FIG. 5  is a view in perspective illustrating a second embodiment of a brush-holder according to the present invention; 
         FIG. 6  is a view in perspective of an insert used in the brush-holder in  FIG. 5 , in order to form the lugs which support the spiral springs; 
         FIG. 7  is a view in perspective of the brush-holder in  FIG. 5 , without the brushes or the spiral springs; 
         FIG. 8  is a view showing the lower face of the brush-holder in  FIG. 7 ; 
         FIG. 9  is a view in transverse cross-section of the brush-holder in  FIG. 5 , at an insert. 
     
    
    
     Elements which are identical, similar or analogous retain the same reference from one figure to another. 
       FIGS. 1, 2, and 5  show a brush-holder  10  according to the invention, which is designed to be used with an electric motor of a motor vehicle starter. 
     This brush-holder  10  with an axis X comprises a support plate  12  with a substantially annular form around the axis X, and a series of guide cages  13 , which are each used as a receptacle for a brush  15 . 
     The support plate  12  and the cages  13  which it supports are secured on a cover (not represented) which forms a rear bearing for the rotor shaft of the electrical machine. In addition, the central part of the plate  12  comprises an opening  16 . The assembly formed by the support plate  12 , the brush cages  13  and the brushes  15 , is fitted around the shaft of the rotor of the starter. 
     Each brush  15  is fitted such as to slide inside a cage  13 , which is open such as to open onto the opening  16 , in order to allow the brushes  15  to be put into electrical contact with plates supported by a collector of a rotor of an electrical machine. 
     The brushes  15  have alternating polarities. Thus, the brushes  15  with positive polarity are connected electrically, via their respective braid  19 , to a supply wire obtained from the contactor of the starter. In order to connect the braids  19  of two diametrically opposite positive brushes  15  electrically, use is preferably made of an inter-brush connector (not represented). In addition, a bushing  22 , which can be seen clearly in  FIG. 5 , is designed to cooperate with the casing of the starter, in order to ensure the sealing of the brush-holder  10 . In addition the brushes  15  with negative polarity, which are designed for the current return, are connected electrically to the earth of the machine by means of their respective braid  19 . 
     The flexible braids  19  are advantageously made of copper or copper alloy. The braids  19  can act as a fuse in the event of excess current caused by malfunctioning of the starter. 
     In addition, a spiral spring  24 , which is associated with each guide cage  13 , thrusts the corresponding brush  15  radially towards contact plates of the collector. For this purpose, each spring  24  comprises a wound part  26  formed by a plurality of turns, which part is fitted around a lug  29 , as well as an arm  32  which extends from an end of the wound part  26 . The arm  32  has an area of support against a portion of the face of the brush  15 , opposite the face which is in contact with the plates of the collector. Each lug  29  is situated between two adjacent guide cages  13 . The lug  29  has a longitudinal direction of extension L 1 , which extends axially relative to the axis X. 
     In addition, each cage  13  has a receptacle for the brush  15 , which receptacle is delimited by two lateral walls  36 ,  37  opposite one another, which are connected to one another by an upper connection wall  38 . The lateral walls  36 ,  37  each comprise an opening  43 , which, according to the positioning of the spring  24 , will permit the passage of the arm  32  of the spring  24 , and/or of the braid  19  of the corresponding brush  15 . 
     In the embodiment in  FIGS. 1 to 4 , the lugs  29  are obtained from a metal washer  45  with an axis Y, which is combined with the axis X when the washer  45  is integrated with the brush-holder  10 . 
     More specifically, the metal washer  45 , which is shown in detail in  FIG. 4 , has a globally annular form which extends on a plane with orientation which is radial relative to the axis Y. The inner and outer diameters of the washer  45  correspond respectively to the inner and outer diameters of the support plate  12 . The lugs  29  are obtained by cutting parts in the washer  45 , in this case parts with a rectangular form, which parts are then folded back, such as to extend substantially perpendicularly to the plane of the metal washer  45 . 
     The support plate  12 , which is made of plastic material, is over-moulded around the metal washer  45  and the lugs  29 . Thus, the washer  45  and the base of the lugs  29 , corresponding to the junction between the lugs  29  and the washer  45 , are covered by a layer of material which forms the support plate  12 . The metal washer  45  thus makes it possible to rigidify the assembly. 
     In this embodiment, only the base of the lugs  29  is over-moulded. As a variant, not represented in the figures, the entire surface of the lugs  29  can be over-moulded. 
     In addition, the cages  13 , and more specifically the lateral walls  36 ,  37 , are integral with the support plate  12 . The cages  13  can be produced by moulding at the same time as the support plate  12 , thus forming a single piece. The assembly obtained, formed by the support plate  12 , the metal washer  45 , and the cages  13 , is thus an assembly in a single piece. The support plate  12  and the cages  13  are made of a plastic material, thus ensuring good electrical insulation. As a variant, the support plate  12  and the cages could however be made of any other mouldable insulating material. 
     Preferably, the brush-holder  10  additionally comprises curved portions  48 , which are designed for guiding of the wound parts  26  of the spiral springs  24 . These curved portions  48  are annular portions which extend axially relative to the axis X, with an inner diameter corresponding to the outer diameter of the wound part  26  of the springs  24 . These curved portions  48  are also produced integrally with the support plate  12 , and can also be obtained during the moulding of the assembly. 
     In addition, in order to increase the rigidity of the cages  13 , the front edges of the latter situated on the collector side can be connected to one another by a cylindrical portion  49  with axial orientation which is integral with the cages  13  and the support plate  12 . 
     The metal washer  45  is cut in a number of parts corresponding to the number of guide cages  13 , such as to insulate the brushes  15  against one another. This therefore prevents risks of short-circuits. Thus, by means of the removal of strips of material  451  extending between two adjacent cages  13 , which can be seen clearly in  FIGS. 2 and 4 , the washer  45  is cut in four parts, each associated with a corresponding guide cage  13 . The cutting operation is carried out after the operation of over-moulding, during which handling of an entire washer  45  is easy. The braids  19  of the brushes  15  with negative polarity can pass via the space which is left free by the removal of the strips of material  451 , in order to be connected to the earth of the starter. The strips of material  451  have a width which is reduced in comparison with the average width of the washer  45 , in order to facilitate their cutting. 
     In the embodiment in  FIGS. 5 to 9 , added-on lugs  29  are used, constituted by metal inserts. As can be seen clearly in  FIG. 6 , each lug  29  comprises a base  291  and an elongate part  292  obtained from the base  291 , around which a spring  24  is designed to be fitted. The direction of longitudinal extension L 1  of the part  292  extends substantially perpendicularly to the base  291 . As represented, the elongate part  292  can be widened in its part which is lower than the level of the junction with the base  291 . The base  291  of the lugs  29  corresponds to the base of the said lugs of the preceding embodiment. 
     Thus, as is illustrated in  FIGS. 5 to 9 , the lugs  29  are added, independently from one another, onto the support plate  12 . 
     The support plate  12  made of a plastic material is over-moulded around the base  291  of the lugs  29 . Thus, the bases are  291  are covered by a layer of material forming the support plate  12 , such that the lugs  29  are rendered integral with the support plate  12  (cf.  FIG. 9 ). 
     Preferably, in order to guarantee precise positioning of the lugs  29  during the over-moulding operation, the lugs  29  are each provided with a transverse opening  293  provided in their base  291 . These openings  293  are designed each to cooperate with a finger of corresponding indexing tooling. The positioning of the lugs  29  is carried out such that, in the final product, each lug  29  is situated in the vicinity of a corresponding guide cage  13 , and the direction of extension L 1  extends parallel to the axis X of the brush-holder  10 . 
     As a variant, not represented, the lugs  29  of the preceding embodiment illustrated in  FIGS. 3 and 4  can each be provided with an opening  293 . For example, this opening can be formed in the base of the lug. 
     In addition, the cages  13 , and more specifically the lateral walls  36 ,  37 , can be reproduced identically to the embodiment previously described. The assembly obtained, formed in particular by the support plate  12 , the cages  13  and the lugs  29 , is thus an assembly in a single piece, as can be seen clearly in  FIG. 7 . 
     Preferably, the brush-holder  10  also comprises curved portions  48 , which can be reproduced identically to the embodiment previously described. 
     In addition, as can be seen in  FIGS. 5, 7, and 8 , the front edges of the cages  13  can be connected to one another identically to the embodiment previously described, i.e. by the cylindrical portion  49 , in order to rigidify the moulded assembly obtained. 
     As illustrated in  FIG. 8 , the support plate  12  can also comprise elements  52  for guiding of an interconnector on the side of the face opposite that which supports the guide cages  13 . Some of these guide elements  52  are constituted in this case by hooks in the form of an “L”, such as to delimit with the face of the support plate  12  a space which is designed to receive a branch of the interconnector. The guide elements  52  can preferably make it possible to retain the interconnector. In the embodiment in  FIGS. 1 to 4 , the support plate  12  can also comprise guide elements  52  which are situated on the side of the face opposite the cages  13 . 
     As a variant, the support plate  12  is not over-moulded around added-on lugs  29 . In this case, after carrying out the moulding of the assembly comprising the support plate  12 , the cages s 13  and the guide portions  48 , the added-on lugs  29  are secured on the support plate  12 . For this purpose, the lugs  29  can for example be secured by riveting, snapping on, or screwing, onto the support plate  12 . 
     It should be noted that, in all cases, the fact of using metal lugs  29  makes it possible to ensure efficient retention of the wound part  26  of the spring  24 , in that the metal lugs  29  can withstand the forces applied by the spring  24  fitted around each lug  29 . 
     Irrespective of the configuration produced, the risk of short-circuits associated with the dust generated by the brushes  15  is limited, because of the use of the insulating material for production of the cages  13  and the support plate  12 . 
     As a variant, the brush-holder  10  comprises more than four brushes  15 , each brush  15  being able for example to be associated with another brush  15  positioned on the opposite side of the plate  12 . 
     The brush-holder  10  is in this case a brush-holder of an electric motor of a motor vehicle starter. As a variant, the brush-holder  10  could also belong to an alternator or to an alternator-starter. 
     It will be appreciated that the foregoing description has been provided solely by way of example, and does not limit the field of the invention, a departure from which would not be constituted by replacement of the different elements by any other equivalents.