Abstract:
A method for sheathing an armature for electric machines, in which a stack of lamellae that is equipped with grooves for armature windings is mounted on an armature shaft by means of a bore and is provided with at least one groove insulation with the aid of the sheathing process. The sheathing plastic flows through ducts that extend along the bore of the stack and the armature shaft. The plastic is molded in only on a first face of the stack and flows into the grooves and through the ducts. The plastic invades the grooves also from the second face after being discharged from the ducts and converges with the plastic discharged from the first face. The method implements fixing and insulation of the grooves while the groove insulation is provided with a minimum layer thickness for such sheathings at the bottom thereof in order to allow for maximum copper fillings.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2005/054185 filed on Aug. 25, 2005. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is directed to an improved method for sheathing an armature for electrical machines, in which a lamination that has slots for armature windings is slipped with a bore onto an armature shaft and provided by means of the sheathing with at least one slot insulation. The plastic flows through gates which extend along the bore of the lamination packet and along the surface of the armature shaft. 
     2. Description of the Prior Art 
     Armatures of permanent-magnet-excited small electric motors have lamination packets comprising individual laminations, or lamination packets ready for installation, which are fixed in various ways to the respective armature shafts. Besides fixation using plastic deformation (as in German Patent Disclosure DE 19933037 A), bolts (see French Patent Disclosure FR 2644947), by pressing onto knurled armature shafts, and so forth, fixation by end feeding, or sheathing, is also known. In sheathing processes by the hot-gate molding technique, with PAA6.6, minimal slot insulation wall thicknesses of 0.4 to 0.7 mm over a lamination packet length of approximately 30-40 mm are currently possible in large-scale mass production. 
     Furthermore, stamping packets with bores for cooling (as in Japanese Patent Disclosure JP 2000152527) or for injecting a slot insulation in the form of leadthrough gates in the injection-molding plastic are known. 
     The lamination geometry depends on production requirements, such as linking capability, orientation capability, and magnetic flux (see for instance JP 2003164080 or JP 2002165392). 
     SUMMARY AND ADVANTAGES OF THE INVENTION 
     The method of the invention for sheathing an armature for electrical machines has the advantage of a technical implementation of the fixation and slot insulation of the lamination packet of an armature of a small electric motor or electrical machine with optimized efficiency; the slot insulation in the slot base at the same time has a minimum layer thickness for such sheathings, in order to make maximum copper fillings possible. For this purpose, a method for sheathing an armature for electrical machines is provided, in which a lamination packet having slots for armature windings is placed with a bore onto an armature shaft and is provided by the sheathing with at least one slot insulation, and plastic flows through gates which extend along the bore of the lamination packet and along the surface of the armature shaft; the plastic is injected on only one first face end of the lamination packet, flows from this first face end into the slots and through the gates, and, once the plastic has emerged from the gates on the second face end, enters from the second face into the slots and flows together with the plastic arriving from the first face end. 
     Preferably, the plastic originating at the first face end flows faster through the gates than through the slots. As a result, the slots are filled quite uniformly with plastic. 
     The use of the plastic PAA6.6 is especially advantageous, since this plastic is especially suitable for fuel pumps. 
     In an advantageous refinement, the sheathing is performed by waste-free direct feeding. It is also especially advantageous if the sheathing is done by hot-gate molding. 
     Preferably, the size of the injection mold is adjusted relative to the spacing of the face ends of the lamination packet such that given a production-dictated maximum spacing on each face end, a plastic layer with a thickness of at least 0.2 mm is created. As a result, the tolerances in terms of length of the lamination packet can be mastered easily from a production standpoint. An average armature as a result has a markedly thicker slot insulation layer on one end than at other points of the slot insulation. 
     In a preferred refinement, the lamination packet is fixed on the armature shaft by the sheathing. For this purpose, depending on the required locking force of the packet on the armature shaft, the armature shaft may either be smoothed or knurled, or it may have special locking faces, such as flat faces. 
     With the production method according to the invention, in contrast to conventional production methods, armatures with a slot insulation thickness of 0.25 to 0.4 mm, preferably 0.3 mm, are possible. Moreover, this makes a lamination geometry of an electric motor, such as a fuel pump, possible that is suitable for producing a minimally thin slot insulation for the injection molding material used by means of waste-free sheathing using hot-gate molding and fixing the lamination packet on the armature shaft in the process. 
     At the same time, the lamination geometry is optimized with regard to the magnetic flux, since the yoke recesses required for the fixation and as flux aids for the slot insulation sheathing are each located beneath the respective toothed shaft; the tooth geometry is designed with a regard to maximum copper fill factors, and the yoke thickness and tooth neck width are adapted such that magnetic oversaturation occurs at no point of the lamination. For this purpose, the spacing of the gates from the respective adjacent slot bases is so great in comparison to the spacing of adjacent slots that magnetic saturation does not occur at any point of the lamination packet. Preferably, the spacing of the gates from the respective adjacent slot bases is substantially equal to the spacing of adjacent slots, so that magnetic saturation does not occur at any point of the lamination packet. 
     In an advantageous refinement, the sheathing extends past the face ends of the lamination packet along the armature shaft. This is advantageous if a defined edge for an ensuing full sheathing of the armature is to be produced that then makes possible sealing directly on the shaft at that location. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and advantageous refinements will become apparent from the description contained below, taken with the drawings, in which: 
         FIG. 1  shows an electrical machine embodying the invention, in longitudinal section; 
         FIG. 2  shows an unwound armature in longitudinal section; and 
         FIGS. 3   a ,  3   b ,  3   c  and  3   d  show modified armatures in cross section. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In  FIG. 1 , part of an electrical machine  10  is shown in simplified form in longitudinal section. In the present exemplary embodiment, it is a direct current motor with brushes, also known as a commutator motor, and is part of a fuel pump of a motor vehicle. However, still other applications are possible, for instance in a fan, power window system, wiper drive mechanism, seat adjuster, or other applications in a motor vehicle. It may also be a generator, however. The electrical machine  10  preferably has only one direction of rotation and is therefore especially intended for the aforementioned fan drive mechanism. Because of its low noise, the electrical machine  10  is also extremely well suited for a fan power takeoff mechanism. 
     In the electrical machine  10 , for the case where it is a direct current motor with brushes, a commutator is disposed on the armature shaft. If the electrical machine is a generator, this would be a slip ring. 
     The electrical machine  10  includes a housing, in particular a pole tube  12 , and an armature  14  disposed in this tube. The armature  14  has an armature shaft  16  and a lamination packet  18  with an armature winding  20 . The armature winding  20  is connected via wires  22  to hooks of a commutator  24 . The wires  22  of the armature winding  20  are looped around the hooks and hot-pressed together with them. The commutator  24  is acted upon by two carbon brushes, not shown. The brushes are disposed on a brush holder, also not shown, which is made as an injection-molded plastic part. The armature shaft  16  is disposed in two bearings  26  on the face ends, and these bearings in turn are secured in two bearing caps  28 . Finally, magnets  30  are disposed on the inside circumference of the pole tube  12 , around the lamination packet  18 . 
     In  FIGS. 2 and 3   a , the armature  14  is shown in more detail, in an injection mold  33  ( FIG. 2 ) shown schematically. The lamination packet  18  includes an annular yoke  34  with a bore  36 , with which yoke the lamination packet is slipped onto the armature shaft  16 . Slotlike gates  42  extend along the bore  36 , from a first face end  38  to a second face end  40  of the lamination packet  18 . The slotlike gates  42  may, however, alternatively or additionally extend along the outer circumference of the armature shaft  16 . Protruding from the yoke  34  are radial pole teeth  44 , which in pairs each define undercut slots  46 . The slots  46  and the face ends  38 ,  40  are covered with a plastic layer, preferably PAA6.6. The thickness of the slot insulation  48  ( FIG. 3   d ), with which at least the slots  46  are provided, amounts to 0.25 to 0.4 mm, preferably 0.3 mm, and this includes production-dictated tolerances of 0.05 mm. 
     The spacing of the gates  42  from the respective adjacent slot bases is so great, in comparison to the spacing of adjacent slots  46  or to the thickness of the pole teeth  44 , that magnetic saturation does not occur at any point of the lamination packet  18 . Preferably, the spacing of the gates  42  from the respective adjacent slot bases is essentially equal to the spacing of adjacent slots  46 , or equal to the thickness of the pole teeth  44 , so that magnetic saturation occurs preferably at no point of the lamination packet. The diameter of the gates  42  in the lamination cross section depends on the injection molding material employed, and in particular on its flowing capability in the injection state—LCP, for instance, is markedly less viscous than PAA6.6, but is unsuited to applications in fuels, for instance—and on the required locking force on the armature shaft  16 . 
     The sheathing extends along the armature shaft  16  past the face ends  38 ,  40  of the lamination packet  18  The armature shaft  16  may be smooth ( FIG. 3   a ), knurled ( FIG. 3   b ), or provided with at least one flat face ( FIG. 3   c ). 
     The lamination geometry with the corresponding gates  42  toward the armature shaft  16  is optimized with regard to the magnetic flux in such a way that given a statically applied magnetic field, magnetic saturation is largely avoided even in the region of the yoke. For that purpose, the gates  42  are placed in a radial extension of the center of the pole teeth  44  and are symmetrical with respect to this center. As a result of this arrangement, the region of maximum magnetic saturation in the yoke region, which moves along the outer contour on a half ellipse each from one gate  42  to the two adjacent gates  42 , is minimized, since it is located in the region of maximum width of the lamination geometry near the yoke and leaves the winding space of the slots  46  open in the inner region, far toward the shaft. Moreover, the number of gates  42  is selected to be dependent on the number of teeth, such that a sufficient contact area with the armature shaft  16  remains so that, since this area in general also comprises basic iron materials, this area can participate in guiding the magnetic flux and thus overall to achieve maximum flux and minimal saturation, with maximum winding space remaining for the copper wires. 
     The minimal slot insulation layer, injection-molded without waste, assures a minimal loss of winding space from the necessary complete insulation and thus additionally promotes the optimization with regard to greater efficiencies. For a fuel pump drive mechanism with geometry according to the invention, which mechanism is slot insulation-sheathed with PAA6.6 by a waste-free direct feeding process, the layer thickness in large-scale mass production (more than 1 million parts per year) approximately 200 to at most 300 μm and thus is more than 50 μm less than the thicknesses known today from non-waste-free sheathings. To increase the winding space still further, the tooth neck width of the lamination can furthermore be reduced to such an extent that the flux is as high as in the regions of maximum flux above the injection gate openings in the yoke region. 
     In the sheathing, the armature  14  is provided by the sheathing with at least one slot insulation. The plastic is injected only in the region of one face end  38 . From the face end  38 , the plastic flows into the slots  46  and through the gates  42 . Preferably, beginning at the first face end  38 , the plastic flows faster through the gates  42  than through the slots  46 . Once the plastic emerges on the second face end from the gates  42 , it enters from the second face end  40  into the slots and flows together with the plastic arriving from the first face end  38 . The sheathing is done by waste-free direct feeding. The sheathing is furthermore done by hot-gate molding. The lamination packet  18  is also fixed on the armature shaft  16  by the sheathing. 
     The size of the injection mold is adjusted, with respect to the spacing of the face ends  38 ,  40  of the lamination packet  18 , in such a way that given a tolerance-dictated maximum spacing on each face end  38 ,  40 , a plastic layer of at least 0.2 mm and preferably 0.3 mm is created. 
     As a result of the overall observation and optimization of the fixation of the lamination packet, the optimized-efficiency design of the lamination cross section, the slot insulation, and the use of waste-free direct feeding by hot-gate molding as the production method, optimizing steps are obtained which overall lead to the lamination geometries and slot insulation layer geometries described, which can be implemented in large-scale mass production by suitable direct feeding methods more economically, with high process safety and quality, than in known armature geometries and production processes. 
     The individual provisions according to the invention are operative above all in the totality and from the technical production aspect that the direct sheathing by hot-gate molding has substantial advantages over known alternative processes, such as powder coating methods, slipping on finished plastic caps, or hot-gate injection molding methods that involve waste, paper insulation, and so forth. For exploiting these production-related advantages, such as the elimination of postmachining steps (cutting off leftover injection molding gates, stripping, cleaning, and so forth), avoiding material waste from trimming, reduced contamination (for instance from powder), higher process safety, and so forth, and at the same time optimizing the efficiency for instance of a small electric motor operated in the presence of fuel (or fluids), with a minimal rotor diameter (for instance to keep hydraulic losses, which rise sharply with the rpm, low) and a minimal armature length (for instance to achieve minimal installation heights for fuel pump modules), what was required was the combination according to the invention of geometric optimizations of the lamination cross sections, the use of the shaft material for conducting flux as well, and a minimal slot insulation layer thickness, above all in the voids between the teeth, so as to generate maximum possible winding spaces for the copper wires. The size of the winding space makes it possible for the first time to fully utilize the possible flux and thus to optimally utilize the electrical energy through the wires for the magnetically induced rotation of the armature and to fully utilize the efficiency of the motor, while at the same time optimizing the cost for production technology with regard to the fixation of the lamination packet on the armature shaft, with regard to the slot insulation, with regard to tolerances in the packet length, and with regard to avoiding waste, as well as assuring cleanliness and process safety. 
     The foregoing relates to a preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.