Patent Publication Number: US-6903481-B2

Title: Commutator for electric motors

Description:
PRIOR ART 
   The present invention relates to a commutator for electric motors, which has a cylindrical collector disposed on a motor armature shaft and has electrical-contact means, which during one rotation of the collector touch at least two each of a plurality of commutator laminations that are present on the collector and thus establish an electrical connection between the applicable commutator laminations. 
   One such commutator, in which carbon brushes slide on the laminations of the collector and thus transmit a direct current into the armature windings, is known for instance from German Patent Disclosure DE 197 52 626 A1. Such commutators equipped with carbon brushes are typically used for direct-current motors or universal motors. Such commutators have the disadvantage of being highly vulnerable to wear, so that the service life of an electric motor is reduced considerably unless the carbon brushes are replaced. The replaceability of the carbon brushes necessitates relatively high engineering effort and expense. As an alternative solution for such high-wear mechanical commutators, there are electric machines that are commutated purely electrically. The electronic circuits required for the electric commutation are relatively complicated and thus cost-intensive. 
   It is therefore the object of the invention to disclose a commutator for electric motors of the type defined at the outset that functions purely mechanically yet nevertheless is very low-wear. 
   ADVANTAGES OF THE INVENTION 
   The aforementioned object is attained with the characteristics of claim  1 . The collector of the motor has electrical-contact means which during one rotation of the collector each touch at least two of a plurality of commutator laminations present on the collector and thus establish an electrical connection between the applicable commutator laminations and external current connections. According to the invention, the electrical-contact means comprise at least two electrically conductive cylinders, disposed in line with one another in the axial direction of the collector, whose longitudinal axes are parallel to the longitudinal axis of the collector. The at least two cylinders are placed in such a way relative to the collector and have a diameter such that the collector in its rotation rolls over the inside faces or outside faces of the at least two cylinders, and in the process each of the cylinders present is only ever touched by one lamination of the collector. Because the collector rolls with its laminations on the cylinders, and there is no sliding contact between the two, the parts belonging to the commutator are subject to only extremely slight wear. In a motor equipped with such a commutator, no replacement of parts, as is the case with a commutator that has carbon brushes, is necessary over the entire service life of the commutator. Moreover, in the mechanical commutator of the invention, the likelihood of failure is even less than in an electrically commutated motor, since electrical components of the commutation circuit are subject to a certain likelihood of failure. 
   Advantageous refinements and embodiments of the invention are disclosed in the dependent claims. 
   One advantageous embodiment of the electrically conductive cylinders provides that they are eccentrically supported relative to the longitudinal axis of the collector. 
   In a first embodiment, the electrically conductive cylinders are embodied as roller bearings, each with one inner ring and one outer ring. The roller bearings surround the collector, and the inner rings of the roller bearings over which the collector rolls are rotatably supported, and the outer rings are fixed. In a second embodiment, the electrically conductive cylinders are again embodied as roller bearings, each with one inner ring and one outer ring. In this case, however, the roller bearings are disposed in the interior of the collector, and the outer rings of the roller bearings over which the collector rolls are rotatably supported, while the inner rings are fixed. 
   Means are provided which establish an electrical connection between the fixed inner rings or outer rings of the roller bearings and external current connections. The means for the electrical connection between the fixed outer rings and inner rings of the roller bearings and the external current connections preferably comprise pins that can be screwed from outside through one or more recesses that fix the outer rings and inner rings, so that the ends of the pins abut against the outer rings and inner rings. 
   Because the electrically conductive cylinders are resiliently supported in the radial direction relative to their longitudinal axis, asymmetries resulting from production tolerances of the collector can be compensated for in a simple way. 
   It is advantageous that the pins that abut against the outer rings and inner rings of the electrically conductive cylinders and establish an electrical contact press the cylinders against the collector, so that the pins simultaneously perform both an electrical and a mechanical function. 

   
     DRAWING 
     The invention is described in further detail below in terms of several exemplary embodiments shown in the drawing. Shown are: 
       FIG. 1 , a longitudinal section through a commutator with two cylinders surrounding the collector; 
       FIG. 2 , a front view and 
       FIG. 3 , a back view of the commutator shown in  FIG. 1 ; and 
       FIG. 4 , a front view of a commutator, with two cylinders disposed inside the collector. 
   

   DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     FIG. 1  shows a longitudinal section through a commutator of an electric motor, which for example is a direct-current motor or a universal motor. The commutator has a collector  1 , which is supported rotatably about a longitudinal axis  2 ; this longitudinal axis coincides with the axis of rotation of the rotor, not shown in the drawing and receiving a plurality of armature windings, of the electric motor. The collector  1  has a plurality of laminations  3  on its outer circumference in a known manner, and these laminations are electrically connected to the armature windings and by way of which a current is delivered to the armature windings. The means with which one or more laminations  3  of the collector  1  are supplied with a current and with which the current is drawn again from one or more other laminations  3  of the collector  1  are described hereinafter. These contact means that deliver and draw current can be seen from the cross section through the commutator shown in  FIG. 1 ; the structure of the contact means is also clearly illustrated in the front view A in FIG.  2  and the back view B of the commutator of FIG.  3 . 
   The contact means comprise two electrically conductive cylinders  4  and  5 , disposed in line with one another in the axial direction of the collector  1 . The electrically conductive cylinder  4  is supported rotatably about a longitudinal axis  6 , and the electrically conductive cylinder  5  is supported rotatably about a longitudinal axis  7 ; the two longitudinal axes  5  and  6  of the two cylinders  4  and  5  are eccentric relative to the longitudinal axis  2  of the collector  1 . The two longitudinal axes  6  and  7  of the two electrically conductive cylinders  4  and  5  are offset by the same spacing from the longitudinal axis  2  of the collector  1 . 
   The electrically conductive cylinder  4  is embodied as a roller bearing, with one inner ring  8  and one outer ring  9 , and between the inner ring  8  and the outer ring  9  there are balls, rollers or needles  10 , which enable mutual rotation of the inner ring  8  and outer ring  9  about the common longitudinal axis  6 . The electrically conductive cylinder  5  is constructed in the same way as the electrically conductive cylinder  4 . It too comprises an inner ring  11 , an outer ring  12 , and balls, rollers or needles  13  supported between them. 
   The two cylinders  4  and  5  in line with one another in the axial direction are retained by a housing  14  concentrically surrounding the collector  1 . The housing  14  preferably comprises an electrically insulating material. The outer rings  9  and  12  of the two electrically conductive cylinders  4  and  5  are fixed in stationary fashion in the housing  14 . The two electrically conductive cylinders  4  and  5  are resiliently supported in the housing  14  in the radial direction relative to their longitudinal axes  5  and  6 . The resilient support of the two cylinders  4  and  5  can be effected for instance by means of a rubber ring  15  and  16 , respectively, that is introduced between the outer ring  9  and  12  of the cylinder  5  and  6 , respectively, and the inner wall of the housing  14 . The resilient rings  15  and  16  can also comprise some other elastic material, instead of rubber. Preferably, between each outer ring  9  and  12  of the respective cylinder  4  and  5  and the rubber ring  15  and  16  surrounding it, a contact ring  17  and  18 , which comprises an electrically conductive material, is also inserted. 
   As described below, the contact rings  17  and  18  resting on the outer rings  9  and  12  of the two cylinders  4  and  5  electrically connect contact pins  19  and  20 , which deliver current and draw it, to the cylinders  4  and  5 . The contact pin  19  is screwed from outside into the housing  4  perpendicular to the longitudinal axis  6  of the electrically conductive cylinder  4 . Its end protruding out of the housing  14  is embodied as a contact lug  21 , so that the line from a current source can be connected there. The end of the contact pin  19  pointing into the interior of the housing  14  has a tapered shoulder  23 , which is passed through the contact ring  17  and abuts against the outer ring  9  of the cylinder  4 . A flow of current is thus possible via the contact pin  19 , the outer ring  9 , the balls, rollers or needles  10 , and the inner ring  8  of the cylinder  4 . The other contact pin  20  is constructed in the same way as the contact pin  19  described just above. On its end protruding out of the housing  14 , the contact pin  20  has a contact lug  22 , and with its end protruding into the housing, it is provided with a tapered shoulder  24  that is passed through the contact ring  18  and abuts against the outer ring  12  of the cylinder  5 . 
   From the two front views shown in  FIGS. 2 and 3  in the direction A and the direction B of the commutator, it can be seen that the diameter of the inner rings  8  and  11  of the two cylinders  4  and  5  are to be selected relative to the diameter of the collector  1  such that the inner ring  8  and  11  of the cylinder  4  and  5 , respectively, each touches only one lamination of the collector  1 . Specifically, the inner rings  8  and  11  of the two cylinders  4  and  5  each touch diametrically opposed laminations of the collector  1 . Via one of the two cylinders  4  or  5 , a lamination  3  of the collector  1  is supplied with a current, and via the other of the two cylinders  4  or  5 , a current is drawn from another lamination of the collector  1 . With the contact pins  19  and  20  described above, the electrically conductive cylinders  4  and  5  can be pressed onto the laminations  3  of the collector  1 , counter to the spring forces generated by the rubber rings  15  and  16 , by means of being screwed more or less deeply into the housing  14 . If the collector connected to the rotor of the motor is rotating about its longitudinal axis  2 , then the laminations  3  roll over the current-carrying inner rings  8  and  11  of the two eccentrically disposed cylinders  4  and  5 . Because the inner rings  8  and  11  can be made to rotate about the longitudinal axes  6  and  7  relative to the outer rings  9  and  12  of the two cylinders  4  and  5 , the aforementioned rolling motion of the laminations  3  of the collector  1  on the inner rings  8  and  11  comes about, and as a result a considerably lower-wear rolling contact is formed, compared to a sliding contact (as in the case of a carbon brush contact). 
   While in the exemplary embodiment described above, only two laminations each of the collector  1  are contacted by the respective cylinders  4  and  5 —one lamination for current input and the other lamination for current output—it is also possible for more than only two electrically conductive cylinders in line with one another to be provided, if more laminations of the collector are provided for delivering and drawing current. 
   In the exemplary embodiment of a commutator shown in  FIGS. 1 ,  2  and  3 , the collector  1  rolls on the inner rings  8  and  11  of the two cylinders  4  and  5 ; that is, the two cylinders  4  and  5  have a greater diameter than the collector  1 , so that the two cylinders  4  and  5  surround the collector  1 . As can be seen from  FIG. 4 , in a reversal of the above example, the collector  25  can surround the electrically conductive cylinders  26  and  27 .  FIG. 4  shows a front view of a collector  25  with two electrically conductive cylinders  26  and  27 , disposed in its interior, whose longitudinal axes  28  and  29  extend parallel to the longitudinal axis  30  of the collector  25  and are eccentrically offset from it. For the sake of simplicity, neither the housing of the commutator nor the supporting and electrical-contact means for the two electrically conductive cylinders  26  and  27  have been shown in FIG.  4 . Just as in the previous exemplary embodiment above, the electrically conductive cylinder  26  comprises an inner ring  31 , and outer ring  32 , and balls, rollers or needles  33  supported between them, and the electrically conductive cylinder  27  comprises an inner ring  34 , an outer ring  35 , and balls, rollers or needles  36  supported between them. The respective inner rings  31  and  34  of the two electrically conductive cylinders  26  and  27  are fixed, while the outer rings  32  and  35  are rotatable relative to the inner rings  31  and  34  about the axes  28  and  29  of the electrically conductive cylinders  26  and  27 . In this exemplary embodiment of the commutator, the laminations  37  of the collector  25  roll over the outer rings  32  and  35  of the two electrically conductive cylinders  26  and  27 . The current input and output into and out of the two electrically conductive cylinders  26  and  27  is once again, although not shown in  FIG. 4 , done by means of contact pins, which are brought into connection with the fixed inner rings  31  and  34  of the electrically conductive cylinders  26  and  27 . 
   By changing the current flow direction into or out of the two cylinders  4  and  5 , or  26  and  27 , a switchover can be made between counterclockwise and clockwise rotation of the motor. In addition, the motor with the electrically conductive cylinders  4 ,  5  or the electrically conductive cylinders  26 ,  27  can be braked in a very simple way, specifically in that the outer rings  9 ,  12  and inner rings  31 ,  34  respectively rolling on the laminations  3  and  37  of the collector  1  and  25  are braked or are rotated in different directions.