Patent Publication Number: US-2020287438-A1

Title: Brush holding assembly for  an excited-rotor electric machine

Description:
The present invention object is a brush holding assembly device for an excited-rotor electric machine. 
     The present invention therefore has particular application in the making of excited-rotor electric machines, preferably for the use of automotive traction. 
     These types of electric machines, in fact, have a rotor and a stator both fed by a current generator. In order to allow the connection between the generator and the rotor, it is usually provided the use of a manifold engagement. 
     Generally, in fact, a sleeve (called slip ring) is fitted on the rotor rotation shaft on which two circumferential conductive tracks are fixed parallel to each other and connected in turn by copper wires to the rotor windings. 
     On the machine casing there is a housing for a brush holding assembly, inside which there are at least two brushes (or abutment elements) which are placed in sliding contact with the tracks in order to transmit the current. 
     Disadvantageously, the presence of a sliding contact determines that, over time, the brushes may wear out, reducing the contact pressure on the tracks and, therefore, creating reliability problems for the machine. 
     The aim of the present invention is to make available a brush rigging for an excited-rotor electric machine capable of overcoming the drawbacks of the aforementioned prior art. 
     More precisely, the aim of the present invention is to make available a brush rigging for a reliable and easy-to-make excited-rotor electric machine. 
     Said aim is achieved by a brush holding assembly for an excited-rotor electric machine having the characteristics of one or more of the subsequent claims and, in particular, comprising a casing provided with at least two ducts flanked to each other and developing along a preferential direction between a first end and a second end, said second end being open and accessible; A pair of brushes housed and capable of sliding each in a respective duct and projecting externally to said second end; a connecting member arranged to connect with an electric current generation unit associated with said casing at said first end of the ducts. 
     According to an aspect of the present invention, the brush holding assembly comprises presser members associated with the brushes and configured to push said brushes in the direction of the second end in order to keep them pressed on the respective tracks of a rotating manifold of a rotor and at least two conductive elements each developing along the preferential direction of a respective duct, interposed between the respective brush and said connecting member and configured to deform along said preferential direction in order to follow the movement of the brush imparted by the presser members. 
     Advantageously, in this way it is possible to compensate the brush wear while maintaining the connection efficiency and without reducing reliability. 
     Preferably, moreover, each of the conductive elements are defined by a wire or rope (in copper) developing between the respective brush and the connecting member. 
     Alternatively (or jointly), each of the conductive elements comprise a spring-shaped elastically deformable section along said preferential direction. 
    
    
     
       These and other features, with the relative advantages, will become more apparent from the subsequent exemplary, therefore not limiting, description of a preferred, therefore not exclusive, embodiment of a brush holding assembly for an excited-rotor electric machine according to what illustrated in the appended figures, wherein: 
         FIG. 1  schematically shows a brush holding assembly according to the present invention; 
         FIG. 2  schematically shows a contact chamber  101  for an excited-rotor electric machine comprising the brush holding assembly of  FIG. 1 ; 
         FIG. 3  show a perspective view of a further embodiment of a brush holding assembly according to the present invention; 
         FIG. 4  shows a longitudinal sectional view of the brush holding assembly of  FIG. 3 . 
     
    
    
     With reference to the appended figures, with number  1  reference is made to a brush holding assembly for an excited-rotor electric machine according to the present invention. 
     Said brush holding assembly  1  comprises a casing  2  provided with at least two ducts  3  mutually flanked to each other and developing along a preferential direction “A” between a first end  3   a  and a second end  3   b.    
     Preferably, the second end  3   b  is open and accessible along the preferential direction “A”. 
     More preferably, also the first end  3   a  is open and connected to an electrical connecting member  4 . 
     Said connecting member  4  is therefore associated with the casing  2  at the first end  3   a  of the ducts  3  and is arranged to connect with an electric current generation unit (not illustrated). 
     In this light, the connecting member  4  preferably comprises at least one conductive element  4   b  (preferably two) configured to transmit the electric current energy generated by the generating unit. 
     The conductive element  4   b  may be, for example, be defined by a plate anchored to an insulating support  4   a.    
     Alternatively ( FIGS. 3 and 4 ), the conductive element is defined by a pair of plate connectors. 
     In the preferred embodiment, in fact, the electrical connecting member  4  comprises an insulating support  4   a  shaped like a plug (or the like) and selectively coupled, preferably with fast connection means, to the first end  3   a  of the duct to occlude it. 
     Inside each duct  3 , a brush  5  is provided suitable for transmitting the current coming from the connecting member  4 , by sliding contact, to a rotor manifold  100 . 
     It should be noted that the term “brush” refers to both filament brushes and, preferably, bar-shaped brushes having a rectangular cross-section and made of materials such as, for example, high density carbon or graphite impregnated with high electrical conductivity metal. 
     Each brush  5  is housed capable of sliding (along the preferential direction “A”) in the respective duct  3  of the casing  2  and is positioned so as to be (even imperceptibly when in contact with the manifold) externally projecting from the second end  3   b  in order to sliding contact the manifold  100 . 
     Preferably, the casing  2  has at least one through opening  11  made at a side wall  3   c  of each duct  3  in order to increase the heat exchange. 
     More preferably, said through openings  11  have longitudinal development along said preferential direction and run along the brushes  5 . 
     In the illustrated embodiment, the casing has two through openings  11  for each duct  3 . 
     According to an aspect of the present invention, the brush holding assembly  1  comprises presser members  6  associated with the brushes  5  and configured to push said brushes  5  towards the second end  3   a  in order to keep them pressed on the respective tracks of the rotating manifold. 
     The presser members  6  are therefore preferably housed in the duct  3 , operatively interposed between the first end  3   a  and the brush  5 . 
     Preferably, the support also comprises guide means suitable for keeping the movement of the brushes inside the duct  3  linear, facilitating the action of the presser members  6 . 
     In the preferred embodiment, the presser members  6  comprise a spring  6   a , preferably helical, developing between the first end  3   a  of the duct and the brush  5 , more preferably preloaded. 
     Still according to the present invention, moreover, the brush holding assembly  1  comprises at least two conductive elements  7  developing along the preferential direction “A” of a respective duct  3  and each one interposed between a respective brush  5  and said connecting member  4 . 
     Such conductive elements  7  are configured to deform along said preferential direction “A” in order to follow the movement of the brush  5  imparted by the presser members  6  (as a result of wear). 
     Advantageously, in this way there is no risk that the brushes  5 , translating inside the duct  3 , damage the connections or interrupt the connection with the connecting member  4 . 
     Preferably, each of the conductive element  7  are defined by a loose wire or rope  7   a  developing between the respective brush  5  and the connecting member  4 . 
     Alternatively (or jointly), the conductive element  7  comprises a elastically deformable section  8  (for example spring-shaped) along said preferential direction “A”. 
     In some embodiments, the conductive elements  7  can be housed in the ducts  3 . 
     Preferably, however, the casing  2  comprises a pair of auxiliary chambers  9 , flanked to each other and in connection with a respective duct  3 . 
     The conductive elements  7  are at least partially housed inside said auxiliary chambers  9  in order to avoid interference with the presser members  6 . 
     More precisely, the conductive elements  7  develop from the respective brush (in the duct  3 ), continue to escape from the duct and enter the auxiliary chamber  9  and then connect to the connecting member  4 . 
     In this regard, the shape of the transition zone between the duct  3  and the auxiliary chamber  9  is suitably shaped and free from sharp edges in order to allow the conductive element  7  (copper wire or rope or the like) to slide without damaging it. 
     Moreover, in some embodiments, in order to optimize the connection reducing the losses, the conductive element  7  is fixed to the connecting member  4  by means of a pressure engagement  10 , more preferably reversible. 
     Preferably, however, the casing  2 , the two brushes  5 , the connecting member  4 , the presser members  6  and the conductive elements  7  are co-moulded. 
     In this regard, a compensation chamber  10 , preferably housed in the auxiliary chamber  9 , is preferably provided, containing the deformable section of the wire or rope  7   a.    
     According to a preferred variant of the present invention, the two conductive elements  7  are defined by two pre-assembled conductive cartridges  12 . 
     Each cartridge  12  develops longitudinally along the preferential direction “A” and comprises a containment volume inside. 
     More precisely, the cartridge  12  is counter-shaped and engaged into the respective duct  3 . 
     In particular, each cartridge  12  has an end  12   a  constrained to the connecting member  4  and contains (inside said volume) the respective brush  5 , the respective presser member  6  and at least one flexible element  13  developing between a wall of said cartridge  12  and the brush  5 . 
     In the preferred embodiment, the end  12   a  of the cartridge has a pin (or protrusion) which can be coupled with a terminal of the connecting member  4 . 
     More preferably, the end  12   a  of the cartridge  12  is constrained to the connecting member  4  via a welding. 
     This allows to facilitate the mounting method of the brush holding assembly  1 . 
     In fact, thanks to the arrangement of the cartridges  12  containing the brush  5  and the respective presser member  6  it is possible to mount the assembly  1  simply by: 
     arranging the casing  2 ; 
     arranging the cartridges  12 ; 
     engaging each cartridge  12  inside the respective duct  3  so that one end  12   a  of the cartridge  12  is abutted to said at least one connecting member  4 ; 
     coupling said end  12   a  with said connecting member  4  by means of welding. 
     Preferably, moreover, the casing  2  is provided with fixing means  2   a  facing outwardly thereof and shaped to allow a reversible coupling of the casing  2  itself with a housing of the manifold  100 . 
     In this regard, preferably the brush holding assembly  1  according to the invention is used inside a contact chamber  101  for a such shaped excited-rotor electric machine. 
     Said chamber  101  comprises an annular housing  102  for a sliding-ring manifold  100  and a sliding-ring manifold  100  as previously described. 
     Preferably, the annular housing  102  comprises a receiving space  103  for the brush holding assembly  1 . 
     Thanks to the fixing means  2   a  (for example by interlocking or screwing), the brush holding unit  1  (in particular the casing  2 ) can be reversibly coupled with the receiving space  101 . 
     Therefore, such brush holding assembly  1  can be selectively switched, by its fixing means  2   a , between a release configuration and a coupling configuration, wherein the brushes  5  result to be faced internally in the annular housing  102  and abutted to the manifold  100 . 
     The invention achieves the intended aims and achieves important advantages. 
     In fact, the arrangement of a brush holding assembly provided with a deformable conductive element, together with the presence of presser members capable of maintaining contact with the manifold, maximizes the efficiency and reliability of the connection.