Patent Publication Number: US-6218761-B1

Title: Armature with plane commutator for an electric motor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an armature with a flat or plane commutator for an electric motor, especially for driving a fuel supply unit, in which the armature has a plurality of metal segments separated from each other by grooves distributed around its circumference on a front side thereof, which are connected with armature windings and which are each covered with a commutator cover at least on a front side thereof which is soldered to the respective metal segment. 
     2. Prior Art 
     This type of armature is described in European Patent Document EP 0 491 904. This armature has metal segments separated from each other by grooves distributed around the circumference on the front side. Each segment is covered on its front side with a commutator cover which is soldered with the segment. The commutator covers are separated from each other by slots which correspond to the grooves separating the segments from each other. When the covers are assembled on the armature, it must be guaranteed that the slots separating them must coincide with the grooves separating the segments so that the covers must be very exactly positioned. The slots between the covers must be formed somewhat wider than the grooves separating the segments to compensate for measurement tolerances of the segments. However the slots between the covers should be formed as small as possible because of operational considerations for the electric motor. Furthermore when the covers are soldered with the segments the solder can enter the grooves between the segments or in the slots between the covers and that can lead to a short circuit between neighboring segments or covers. During the soldering the covers are not fixed so that the covers can take incorrect positions relative to the segments. 
     Furthermore the side surfaces of the segments pointing in the circumferential direction are exposed, so that a deposit can be formed on the metal segments during operation of the electric motor in a corrosive media. The corrosion product formed can lead to a short circuit between the neighboring segments. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an armature with a flat commutator for an electric motor of the above-described kind that does not suffer from the above-described disadvantages. 
     These objects, and others which will be made more apparent hereinafter, are attained in an armature with a flat commutator for an electric motor, especially for driving a fuel supply unit, in which the armature has a plurality of metal segments separated from each other by grooves distributed around its circumference on a front side thereof, which are connected with armature windings and which are each covered with a commutator cover at least on a front side thereof which is soldered to the respective metal segment. 
     According to the invention each commutator cover has a recess on its side facing the armature, in which the associated segment is inserted in a direction of the longitudinal axis of the armature and each commutator cover is connected with its associated segment with solder in the recess. 
     The armature according to the invention with the flat commutator has the advantage that each cover is exactly positioned relative to the associated segment by the segment inserting itself in its corresponding recess and its position is exactly maintained during the soldering. The grooves between the segments can be comparatively wide, since they are covered after connecting the covers and only slots remain between the covers which can be comparatively small because of the exact positioning of the covers. Furthermore the recesses in the covers guarantee that no solder can enter between the covers or segments. 
     Especially advantageous embodiments and features are claimed in the dependent claims appended hereinbelow. 
     In a preferred embodiment the commutator covers at least partially cover the edge surfaces of the metal segments pointing in the circumferential direction and/or the edges surfaces of the metal segments pointing radially inward. In this way the segments are protected from corrosion when the motor is used in the presence of corrosive media. 
     In another preferred embodiment the recesses or cavities in the commutator covers each have an indentation or depression. Because of this advantageous feature solder cannot flow out of the recess. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The objects, features and advantages of the invention will now be illustrated in more detail with the aid of the following description of the preferred embodiments, with reference to the accompanying figures in which: 
     FIG. 1 is a longitudinal cross-sectional view through a fuel supply unit including an electric motor; 
     FIG. 2 is a detailed perspective view of an armature of the electric motor; 
     FIG. 3 is a perspective view of a disk-shaped cover according to one embodiment of the invention; and 
     FIG. 4 is a transverse cross-sectional view through the armature. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A unit  10  for supplying fuel from a fuel tank  12  to an internal combustion engine  14  of a motor vehicle is shown in FIG.  1 . The fuel supply unit  10  can be, for example, in the fuel tank  12 . The fuel supply unit  10  has at least one fuel pump  16  and an electric motor  18  to drive the fuel pump. The fuel pump  16  and the electric motor  18  are arranged in a housing  20  next to each other. The fuel pump  16  has a feed element  22 , which for example is formed as an impeller, which is provided with a plurality of blades distributed around its periphery and which rotates in a pump chamber. The electric motor has an armature  26 , with a shaft  27 , by which it is mounted so as to be rotatable around its longitudinal axis  28 . The feed element  22  of the fuel supply pump  16  is connected with the shaft  27  and rotates with it. Several magnetic segments  30  are distributed around the circumference of the armature  26 . 
     The armature  26  has a plane commutator  32  on its end facing the feed pump  16 . Brushes  36  bear on the front surface  34  of the flat commutator  32  extending perpendicular to the longitudinal axis  28  of the armature  26 . The brushes  36  are arranged in a cap  38  closing the housing  20 . The plane commutator  32  is connected with armature windings W of the armature  26 . During operation of the fuel supply unit  10  the feed element  22  is driven rotatably by the electric motor  18  so that fuel is fed by it, which flows through the electric motor  18  and leaves via an outlet  40  in the cap  38  thus arriving in the internal combustion engine  14 . 
     The armature  26  of the electric motor  18  is shown in FIG. 2 with its plane commutator still not completed and with its front surface magnified. The armature  26  has metal, especially copper, segments  42  distributed over its circumference on its front side. Each segment  42  is connected with a winding of the armature  26  by means of a connector  44  arranged on its radial outer edge. The segments  42  are separated from each other by radially extending grooves  46 , extend radially outward to the casing of the armature  26  and extend radially inward but not completely to the shaft  27 . A throughgoing metal disk is mounted on the armature  26  during manufacture of the armature  26 , which is turned or milled on its front side facing away from the armature to a predetermined depth, in which an inner annular space is turned or milled out to the shaft  27  and the grooves  46  are milled during the manufacture and separation of the metal segments  42 . The width s of the grooves  46  can be from about 2 to 6 mm, for example, according to the size of the armature  26 . 
     A respective cover  48  shown in FIGS. 3 and 4 is placed on each segment  42  as shown in FIGS. 3 and 4 to form the planar commutator  32  according to the invention. The covers  48  cover the associated segments  42  and the brushes  36  bear or contact on the covers. The covers  48  are made of carbon, for example, from graphite or plasticized carbon and are galvanized. Each cover  48  is formed somewhat wider at the outer periphery of the armature  26  and extends in a radial direction further inward than the associated segment  42 . Each cover  48  is approximately of equal width in the radial direction as its associated segment  42 . Each cover  48  has a recess  50  in its front side facing the armature  26 , which corresponds in its form and size at least approximately to the form and size of the associated segment  42 . Each recess  50  is somewhat wider than its associated segment  42  because of tolerance considerations. Each cover  48  has a web or ridge  51  on each side of its recess  50 . The recess  50  is bounded on a radially inner side by a wall  52  and is open on a radially outer side. Each cover  48  is placed on its associated segment  42  so that the segment  42  inserts at least partially into the recess  50  in a direction of the longitudinal axis  28  of the armature  26 . 
     To connect the cover  48  with the segment solder is put in the recesses  50 , the segments  42  are inserted in the recesses  50  and subsequently the covers and/or the segments are heated, so that the solder melts. The depth c of the recess  50  of the cover  48  in the direction of the longitudinal axis  28  of the armature  26  is preferably dimensioned so that the lateral edge surfaces  43  of the segment  42  inserted in the recess are covered by the lateral edge surfaces  53  of the recess  50  pointing in the circumferential direction to as large an extent as possible. The lateral edge surfaces  43  of the segment  42  are covered by the cover  48  and the fuel supplied by the fuel supply unit  10  cannot or at least can only scarcely come into contact with them. A flow of solder from the recesses  50  is prevented by the webs  51  arranged beside the segments  42 . 
     The recess  50  has a bottom surface  54  in the direction of the longitudinal axis  28 . The bottom surface  54  can preferably be inclined so that the depth of the recess  50  increases from its radial outer edge to its radial inner edge and thus forms a depression or indentation V within the recess  50 . In FIG. 3 the inclination of the bottom surface  54  is shown by illustrating the angle α. The indentation or depression V in the recess  50  can be formed in another way, for example by a step at the radial outer edge of the recess  50  or by providing the bottom surface  50  with a curved shape to the radial inner wall  52  of the recess  50 . The liquid solder remains in the recess  50  and thus does not flow out because of its own weight due to the indentation or depression in the recess  50  during soldering of the cover  48  with the segment  42 , when the cover  48  is arranged with its recess  50  pointing or opening upward and when the armature  26  is inserted from above with its segments  42  in the recesses  50 . 
     When the assembled covers  48  are soldered with the associated segments  42 , the complete plane or flat commutator  32  is produces as it is shown in FIG.  4 . Slots  56 , which have a respective width a, which is smaller than the width s of the original grooves  46  between the segments  42 , remain between the covers  48 . The webs  52  of the covers  48  are arranged in the grooves  46 . Since the covers  48  can be exactly positioned relative to the segments by the segments  42  engaging in the recesses  50 , the slots  56  can be comparatively small. 
     Since the assembly of the covers  48  individually or separately would be very expensive, the covers  48  are preferably formed as part of a one-piece disk-shaped body  48 , which is shown in FIG.  3 . The disk-shaped body  58  can, for example be made by pressing and has at least one approximately plane surface  60  on its front side facing the armature  26 . The disk-shaped body  58  has the respective recesses  50  for the covers  48  on its front side facing the metal segments. The recesses  50  can be formed already on pressing the body or subsequently they can be provided by milling. Moreover the slots  56 , which are formed by milling or preferably by sawing, are provided in the front side of the disk-shaped body  58  facing the armature. During the sawing two diametrically opposed slots are formed simultaneously. The depth of the recess  50  in the direction of the longitudinal axis  28  of the armature  26  is indicated with c and the depth of the slot  56  is indicated with e. The depth e of the slot  56  is larger than the depth c of the recess  50 . The webs  51  laterally bounding the recess  50  have a width b. The disk-shaped body  58  has a thickness f, an outer diameter h and an inner diameter g. The length of the recess  50  in the radial direction is indicated with d. The outer diameter h and the inner diameter g of the disk-shaped body  58  are adjusted to the diameter of the armature  26 . The width b of the webs  51  can amount to from about 1 to 2 mm for example. The depth c of the recesses can for example be about 1 to 3 mm and the depth e of the slots  56  can, for example, be about 2 to 4 mm. The thickness f of the disk-shaped body  58  can be, for example, about 4 to 6 mm. 
     The disk-shaped body  58  is put on the segments  42  of the armature  26  and is connected by solder with the segments  42 . Subsequently the front side  60  of the disk-shaped body  58  facing away from the armature  26  is cut, especially by turning, until the slots  56  are open up to the front side of the covers  48  facing away from the armature  26 . When the slots  56  are open, thus the covers  48  are separate from each other and the individual covers  48  are formed. 
     The segments  42  of the armature  26  are at least partially covered on their side surfaces pointing in the circumferential direction and on their edges surfaces pointing radially inwardly and only the edges surface of the segments  42  pointing radially outward are exposed. The side surfaces and the edges surfaces pointing radially inwardly of the segments  42  do not come into contact with the fuel supplied by the fuel supply unit  10  so that no corrosion occurs on these surfaces when a corrosive fuel is being supplied. If necessary the individual free edge surfaces of the segments  42  pointing radially outward can be provided with a protective coating. 
     The disclosure in German Patent Application 198 59 006.7 of Dec. 21, 1998 is incorporated here by reference. This German Patent Application describes the invention described hereinabove and claimed in the claims appended hereinbelow and provides the basis for a claim of priority for the instant invention under 35 U.S.C. 119. 
     While the invention has been illustrated and described as embodied in an armature with a plane or flat commutator for an electrical motor, it is not intended to be limited to the details shown, since various modifications and changes may be made without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.