Abstract:
An armature for a rotating electrical machine and more particularly to an insulating cover for the pole teeth around which the windings are formed that has good strength against the winding without risk of damage of the insulator due to increased thickness in the highly stressed areas.

Description:
BACKGROUND OF INVENTION 
     This invention relates to a dynamo-electric machine and more particularly to an improved insulator for the armature thereof. 
     Rotating electrical machines have been proposed for many applications. For example they may be used as a starter motor for an internal combustion engine. In such an application, a DC electric motor is powered from a battery for starting the engine. The starter motor generally comprises a stator comprising a cylindrical yoke with a plurality of magnets circumferentially bonded to an inner surface of the yoke. An armature (rotor) having coils arranged opposite the magnets and supplied with electrical current for driving a rotating shaft of the armature forming a output shaft of the starter motor. The motor output shaft drives a crankshaft of the engine via a reduction gear, an overrunning clutch for starting the engine in a well known manner. 
     The magnets may be ordinary magnets obtained by magnetizing a ferrite type magnetic material. The coils are formed by winding a wire (in general, a thin wire having a diameter of 0.9 mm or less) on each of a plurality of radially arrayed magnetic pole teeth of the armature. These pole teeth have a general T-shape. At this time, the core pole teeth are covered with insulators around which the wire is wound. In order to reduce the size and to increase the power, starter motors employing high-energy neodymium type magnets instead of the ferrite type magnets has been developed. When neodymium type magnets are employed, the thickness of the magnets can be decreased and the output of the motor can be enhanced. When such high-energy neodymium magnets are employed, the coils are formed using a wire having a diameter of about 1 mm or greater so that a current corresponding to the energy of the magnets can flow. 
     This thick wire has a high rigidity, so that it requires a large tensile force to wind the wire around a magnetic pole tooth to form a coil. Thus, a large pressing force corresponding to the tensile force is exerted on coil end surfaces of the magnetic pole tooth. A method and apparatus for forming such windings is disclosed in the application entitled “WINDING METHOD AND DEVICE FOR AN ARMATURE FOR ROTARY ELECTRIC MACHINES”, Ser. No. 10/064,923, filed concurrently herewith by the assignee hereof, based upon Japanese Application Serial Number 2001-271207, Filed Sep. 7, 2001. 
     Although the method and apparatus described in that copending application is very effective in providing the coil winding, still further improvements can be made. For example, a large stress is applied to edges of the coil end surfaces, namely, edges of the magnetic pole tooth, against which the wire is bent and pressed. This problem can be particularly difficult in connection with the insulating material around which the wire is coiled. This may be understood best by reference to FIGS. 1 through 4. As noted below, these figures are, respectively, a top plan view of the one half of insulating material, a cross section taken along the line  2 — 2  of FIG. 1, a bottom plan view of the insulator half and a cross sectional view taken along the line  4 — 4  of FIG.  3 . 
     The insulating material is made up of two halves only one of which is shown and which is indicated generally by the reference numeral  21 . Basically it has a configuration complimentary to the armature core. This is comprised of a central portion  22  that has an opening  23  for passing the shaft of the associated armature. Radially extending teeth  24 , which are complimentary to the armature teeth, extend outwardly and have a generally U-shaped configuration as shown in the cross sectional views of FIGS. 2 and 4. Generally the insulator  21  is quite thin, having a thickness of only about 0.5 mm. 
     This shape is comprised of individual side portions  25  that face the sides of the armature teeth and which are joined by an integral bridging portion  26  that extends generally in an axial direction relative to the axis of rotation of the machine. As a result, curved edge portions  27  result which are actually thinner than the thickness of the portions  25  and  26  and may be damaged due to the high pressure and loading occurring during the winding operation. If this insulator becomes damaged, then breaking may occur during the winding operation to damage the efficiency of the machine. 
     It is, therefore, a principal object to this invention to provide an improved insulator arrangement for the armature of a rotating electrical machine wherein the strength of the insulator is increased with significantly increasing its size or weight. 
     SUMMARY OF INVENTION 
     This invention is adapted to be embodied in a rotating electrical machine comprised of an armature having a circular core of a magnetic material and a plurality of magnetic pole teeth extending radially from the circular core for cooperation with a plurality of circumferentially spaced permanent magnets. Each of the magnetic pole teeth defines a core of generally rectangular cross section with slots formed between circumferentially adjacent pole teeth. An insulator having channel shaped portions covers at least in part the cores of the magnetic pole teeth. The channel shaped portions are comprised of radially extending slot portions extending along the sides of the pole teeth facing the slots. The slot portions are integrally joined by an axial portion extending across an axial outermost side of the pole teeth. The axial portion of the insulator channel shaped portions have a thickness greater than that of the side portions to avoid thinning at the juncture therebetween. Coil windings are wound around the cores of the magnetic pole teeth with the insulator being interposed therebetween. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a top plan view of one of the insulator halves constructed in accordance with the prior art. 
     FIG. 2 is a cross sectional view taken along the line  2 — 2  of FIG.  1 . 
     FIG. 3 is a bottom plan view of the insulator half shown in FIG.  1 . 
     FIG. 4 is a cross sectional view taken along the lines  4 — 4  of FIGS. 1 and 3. 
     FIG. 5 is a cross sectional view taken generally along the axis of rotation of an electrical starter motor constructed in accordance with the invention. 
     FIG. 6 is a cross sectional view taken along the line  6 — 6  of FIG.  5 . 
     FIG. 7 is a cross sectional view taken along the line  7 — 7  of FIG.  5  and shows the brush carrier arrangement of the motor. 
     FIG. 8 is a top plan view, in part similar to FIG. 1, showing the insulator half constructed in accordance with the embodiment of the invention. 
     FIG. 9 is a cross sectional view taken along the line  9 — 9  of FIG.  8 . 
     FIG. 10 is a bottom plan view, in part similar to FIG. 3, but showing the half illustrated in FIG. 1 from the opposite side. 
     FIGS. 11,  12  and  13  are cross sectional views taken along the lines  11 — 11 ,  12 — 12  and  13 — 13  of FIGS. 8 and 10. 
     FIG. 14 is a cross sectional view, in part similar to FIG. 5, but is enlarged so as to show the construction of the armature and the laminations of its core and the insulator halves in place. 
    
    
     DETAILED DESCRIPTION 
     Referring now in detail to the drawings and initially to FIGS. 5 through 7, a starter motor for an internal combustion engine is indicated generally by the reference numeral  51 . The starter motor  51  is constructed in accordance with an embodiment of the invention and although this specific application is illustrated, it should be readily apparent to those skilled in the art that the invention can be utilized with other types of rotating electrical machines. 
     The starter motor  51  is comprised of an outer housing assembly, indicated generally by the reference numeral  52 , which includes a cylindrical yoke portion, indicated generally by the reference numeral  53 . The yoke portion  53  is comprised of a cylindrical shell  54  on the inner surface of which are bonded a plurality of circumferentially spaced permanent magnets  55 . In the illustrated embodiment, there are four such permanent magnets  55  and they are arranged with alternating plurality in a circumferential direction. Preferably, these permanent magnets  55  are formed from a neodymium type material that provides a high energy permanent magnet. 
     The housing  52  is completed by means of a front end cap  56  and rear end cap  57  that are affixed in any suitable manner to the ends of the yoke shell  54  to define an enclosed space in which a rotor in the form of an armature, indicated generally by the reference numeral  58  is journal led. The rear end cap  57  is formed with a mounting bracket  59  so as to permit attachment to the body of the associated engine. 
     The rotor or armature  58  is comprised of an armature shaft  61 , the forward end of which carries a starter gear  62  for associated with the starter gear on the flywheel of the associated internal combustion engine. The end cap  57  has a projecting end in which an O-ring seal  63  is received so as to provide a good seal around the starter gear. This end of the armature shaft  61  is journaled in the end cap  57  by an anti-friction bearing  64 . An oil seal  65  is disposed immediately to the rear of the bearing  64 . In a like manner, the rear end of the armature shaft  61  is journaled in an anti-friction bearing  66  carried by the end cap  57 . 
     The armature  58  is comprised of a core, indicated generally by the reference numeral  67 , and which has a construction as best shown in FIG.  6 . This is comprised of a laminated core having a plurality of radially extending pole teeth  68  which have enlarged head portions  69 . These pole teeth  68  are circumferentially spaced from each other to define slots  71  therebetween. The enlarged head portions  69  leave a narrow mouth  72  therebetween opening into the slots  71 . 
     Although not shown in details in FIGS. 5 through 7, individual coil windings are formed around the pole teeth  68  preferably in the manner described in the aforenoted co-pending application Ser. No. 10/064,923, based upon Japanese Application No. 2001-271207. The ends of these windings are connected, in a manner as described in the aforenoted co-pending application, to a commutator, indicated generally by the reference numeral  73  and specifically to the contact strips  74  thereof. 
     As best seen in FIG. 7, brushes  75  are carried by brush carriers  76  mounted on a commutator plate or brush holder  77 . These brushes  75  are urged into engagement with the commutator strips  74  by springs  78 . 
     The electrical current for energizing the windings is delivered through a terminal box  79  carried on the rear end cap  57 . The electrical current is supplied to the brushes  75  from terminals  81 . This electrical arrangement is of a type well known in the art and, for that reason; a detailed description of it is not believed to be necessary. Again, since the generally construction of the starter motor  51  is of the type well known in the art, its details of construction except for the insulator assemblies around which the coil windings are formed may be of any type known in the art. These insulators assemblies will now be described in detail by reference to FIGS. 8 through 14. 
     The insulator assemblies are indicated generally by the reference numeral  82 . It is to be understood that the insulator assemblies  82  comprise a pair of assemblies, each of which is received around a respective side of the armature core  67 , the laminations of which clearly are shown in FIG.  14  and indicated by the reference numeral  83 . 
     Each insulator  82  according to this invention comprises a center hub part  84  having a through hole  85  for passing the respective end portion of the rotor shaft  61 . Extending integrally outwardly from the center hub part  84  are a plurality of channel shaped, armature tooth covering parts, indicated generally at  86 . Each of these channel shaped, armature tooth covering parts  86  is comprised of a coil end part covering portion  87 , each of which is for covering a coil end surface of each of the magnetic pole teeth  68 , and side portions  88  covering both side faces of each of the magnetic pole teeth and which face the slots  71  (see FIG.  6 ). 
     Each of the coil end part covering parts  87  of the insulator  82  has a thickness which is larger than that of the side portions  88  and a convex upper surface  89  (see FIGS.  11 - 13 ). Each of the coil end part covering parts  87  convex upper surface  89  slants downwardly from a protruding wall  91  formed on an outer peripheral end thereof. 
     Namely, as shown in FIG.  9  and FIGS.  11 - 13 (A), the taper of the convex upper surface  89  slants such that the height thereof is gradually decreased from the side of the end (outer peripheral end) toward the side of the root of the magnetic pole tooth. Each of the channel shaped, armature tooth covering parts  86  has a protruding wall  91  protruding upward at the outer peripheral ends of the coil end part covering parts  87  for covering the core tooth end enlargements  69 . 
     Each of the coil end part covering parts  87  of the insulator  82  has a large thickness, and thus has increased strength against the tensile force exerted by the coil winding of the wire. Especially, the insulator  82  can have strength against stress concentration on edges of the magnetic pole tooth  68 , so that the insulator  82  is prevented from breaking in winding a wire on the magnetic pole tooth  68 . Also, each of the coil end part covering parts  87  has a convex upper surface (semi-circular cross section in the illustrated example), so that the wire is guided by the edges of the convex upper surface when abutted thereon and wound around the magnetic pole tooth  68  smoothly. 
     Additionally, the convex surface of each of the coil end part covering parts  87  of the insulator  82  relaxes the stress concentration on the edges thereof at the time when the wire abuts thereon, and thus can protect the edges. Also, the taper allows the wound wire to be slid down thereon toward the side of the bottom of the slot by a winding tension applied thereto. This enables the wire to be wound smoothly in an aligned manner and makes the wire less likely to slip off the magnetic pole tooth, so that the wire can be stably maintained. The protruded wall  91  prevents the wire from slipping off the magnetic pole tooth  68 . 
     As should be apparent from the foregoing, each of the coil end part covering parts of the insulator has a large thickness where a tensile force in the wire is applied, and thus has increased strength against a large tensile force. Also, each of the coil end part covering parts having a curved cross-sectional shape distributes stress concentration on the edges thereof and thus can prevent the insulator from being broken even when a large tensile force is applied thereto. This allows the wire to be smoothly wound, so that the wire can be tightly wound in an aligned manner on a magnetic pole tooth and stably maintained there around. Of course, the foregoing description is that of preferred embodiments of the invention and various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.