Abstract:
Several embodiments of magnet retainers for rotating electrical machines that provide excellent magnet retention even if very thin high strength magnets are employed and without requiring adhesives.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to a magnets mounting structure for a rotary electric machine and particularly to a magnet holding structure wherein the individual permanent magnets are physically retained in position.  
           [0002]    In most rotary electric machines such as generators and motors, a plurality of permanent magnets are positioned in confronting relation to electrical coils. Generally this is done by positioning a slotted ring in engagement with a cylindrical shell. The permanent magnets are loosely positioned in the slots of the ring. An adhesive is then inserted between the walls of the slots and the magnets to retain them in position.  
           [0003]    Conventionally, when ferrite based magnets were used, the magnets generally had a thickness of 5 mm or more, and the holder ring, too, had a thickness corresponding to that of the magnets.  
           [0004]    However ferrite based permanent magnets are being replaced by high energy neodymium (Nd) based magnets. When the neodymium-based magnets are used, the magnets can be reduced significantly in thickness. Thickness are generally 3 mm or less, however the magnetic force is increased from that of ferrite based magnets so that increased output is effected.  
           [0005]    This gives rise to another problem. Since the neodymium-based magnets are so thin, the magnets placed on the slotted ring tend to fall off during assembly. Furthermore the thinness adds to the assembly time. Also, because of the higher magnetic force there is the possibility that the magnets will be drawn off of the slotted ring when positioned in proximity to the coil windings.  
           [0006]    Therefore it is a principal object of this invention to provide an improved magnet holding arrangement for a rotating electrical machine that is particularly adapted to physically retain very thin magnets.  
         SUMMARY OF INVENTION  
         [0007]    The invention is adapted to be embodied in a magnet arrangement for a rotating electrical machine. The machine is comprised of a cylindrical shell and a magnet carrier having a cylindrical portion complimentary to and engaged with a surface of the cylindrical shell. The magnet carrier is formed with a plurality of circumferentially spaced, axially extending projections defining open ended gaps therebetween. A plurality of permanent magnets are provided with each magnet being received and physically retained in a respective one of the gaps 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0008]    [0008]FIG. 1 is a cross sectional view taken through a portion of an internal combustion engine having an electrical generator constructed in accordance with an embodiment of the invention.  
         [0009]    [0009]FIG. 2 is an enlarged view, in part similar to FIG. 1, but shows more detail of the generator and its attachment to the driving shaft of the engine.  
         [0010]    [0010]FIG. 3 is an end elevational view looking in the direction of the arrow  3  in FIG. 2.  
         [0011]    [0011]FIG. 4 is an exploded perspective view of the magnet assembly constructed in accordance with a first embodiment.  
         [0012]    [0012]FIG. 5 is an end view of one of the permanent magnets.  
         [0013]    [0013]FIG. 6 is a side elevational view of one of the permanent magnets.  
         [0014]    [0014]FIG. 7 is an end view of a magnet holder constructed in accordance with another embodiment.  
         [0015]    [0015]FIG. 8 is an side elevational view of the magnet holder in accordance with this other embodiment FIG. 9 is end view of the magnet carrier or rotor of this embodiment a side elevational view of the magnet holder constructed in accordance with this embodiment and is taken in the direction of the arrows  9 - 9  of FIG. 10.  
         [0016]    [0016]FIG. 10 is a cross sectional of the magnet carrier or rotor of this embodiment taken along the line  10 - 10  of FIG. 9.  
         [0017]    [0017]FIG. 11 is end view, in part similar to FIG. 7 of a complete magnet holder constructed in accordance with another embodiment taken in the direction of the arrows  11 - 11  of FIG. 12.  
         [0018]    [0018]FIG. 12 is a cross sectional of the magnet holder of this embodiment looking in the direction of the line  12 - 12  of FIG. 11.  
         [0019]    [0019]FIG. 13 is end view of an inner casing taken in the direction of the arrows  13 - 13  of FIG. 14.  
         [0020]    [0020]FIG. 14 is a cross sectional of the inner casing looking in the direction of the line  14 - 14  of FIG. 13. 
     
    
     DETAILED DESCRIPTION  
       [0021]    Referring now in detail to the drawings and initially to FIG. 1, a portion of a motor vehicle engine is illustrated in part and partially in cross section, indicated generally at  21 . Such an application is utilized as this is a typical environment in which the invention may be utilized. Of course, those skilled in the art will readily recognize other applications for the invention.  
         [0022]    The engine  21  includes an electric starter motor  22  that is fixed to the engine body  23 . An output gear  24  of the starter motor  22  is drives a reduction gear  25  via an intermediate gear  26 . The reduction gear  25  drives a starter gear  27 . The started gear  27  is coupled via a one way clutch  28  to a drive ring  29 . The drive ring  29 , in turn, is coupled to the rotor  31  of an electrical generator, indicated generally at  32 , and which embodies the invention.  
         [0023]    The rotor  31  cooperates with a stator  33  that is fixed to the engine frame  23 . The stator has poles around which coils are wound, as is well known in the art. These coils cooperate with permanent magnets  34  fixed in a manner according to the invention as will be described later initially by reference to FIGS. 2 and 3. The magnets  34  are held in a magnet holder indicated in this figure as  35 .  
         [0024]    The rotor  31  is connected to a hub  36  fixed secured to the end of a speed increasing shaft  37  with a bolt  38  and a key (not shown). The speed increasing shaft  37  is rotatably mounted on the engine body  23  through a bolt  39  and a bearing (not shown). The speed increasing shaft  37  is provided with a speed increasing gear  41 . The speed increasing gear  41  is connected to a crankshaft (not shown).  
         [0025]    The turning action of the starter motor  22  is reduced in speed and transmitted to the starter gear  27 , which in turn rotates the hub  36  via the one-way clutch  28 . Accordingly, the rotational action of the crankshaft starts via the speed increasing shaft  37  to cause the engine to start. When the crankshaft rotates at higher speed than the starter motor  22  the clutch  28  will overrun.  
         [0026]    A more detailed description of the electrical generator  32  will now be made by reference to FIGS. 2 and 3. The generator  32  is constructed so that that the rotor assembly  31  is mounted around the stator assembly  33 . This stator assembly  33  includes a plurality of (in this example, eighteen) coils  42  wound around cores  43 .  
         [0027]    The rotor assembly  31 , as described above, is arranged such that the magnets  34  are held by the holder ring  35  mounted to the inner side of a rotor outer cylinder body portion  44 , the magnets  54  are internally pressed against the rotor outer cylinder body portion  44  in a manner to be described later, by reference to the remaining figures. The rotor outer cylinder  44  is secured to the hub  36  with bolts or rivets  45 . The connecting hub  36  has a conical, tapered-shaped mounting hole  46  for mounting on the shaft  37 . The reference numeral  48  designates a 3-phase cable for the coil windings  42 .  
         [0028]    The construction of embodiments of the magnet carrier  35  and its relation to the remainder of the rotor assembly will now be described by reference to the remaining figures and initially by specific reference to FIG. 4. The rotor  31  is comprised of the rotor outer cylinder body  44  with the magnet holder ring  35  fitted to the inner side thereof. The magnet pressing member afore referred to comprises an inner casing  51  further fitted to the inner side of the holder ring  35 . A plurality of magnets  54  are held by the holder ring  35 .  
         [0029]    The rotor outer cylinder  44  is entirely opened at one end and is closed at the other end by an integral end plate  52  at the other end thereof. Around the perimeter of the upper end of the side wall is formed an outer edge  53  with a step  54  on the inner side thereof.  
         [0030]    The holder ring  35  is made of resin and has a plurality of axially extending projections  55  projecting toward the open end (upper end) side of the side wall at regular intervals. In the slots thus formed between the respective projections  55  are inserted and held eighteen, for example, magnets  34  in a press-fitted state. Accordingly, the slots formed between the respective projections  55  is equal to or slightly smaller than the width of the magnet  34  so that the projection  55  and the magnet  34  are in press contact with each other. Press-contacting ribs, as shown in FIGS. 7 and 8 to be described shortly, may be provided on the sides of the respective projections  55 .  
         [0031]    The projections  55  have a axial length at least half the length of the magnets  34  or longer. Therefore, the magnets  34  can securely be held by the projections  55 .  
         [0032]    The inner casing  51  has an outer radially extending flange  56  at its upper edge and a radially extending inner flange  57  at its lower edge. When the inner casing  51  is inserted into the rotor outer cylinder  44  with the holder ring  35  and the magnets  34  sandwiched therebetween, the inner flange  53  is in contact with the end plate  52  of the rotor outer cylinder  44  and the outer flange  56  is engaged with the step  54  of the upper edge of the rotor outer cylinder  44 .  
         [0033]    Referring now to FIGS. 5 and 6, these are a top and a front view, respectively, of the magnets  34 . The magnets  34  are high-energy, neodymium-based magnets and are radially disposed around the inner periphery side of the rotor outer cylinder  44 . As shown in a FIG. 5 the magnets  34  have an arcuate shape in section around the inner periphery of the rotor outer cylinder  44  and a thickness of 3 mm or less.  
         [0034]    It has been noted that the press fitting of the magnets  34  into the slots formed between the projections  55  can be facilitated by forming ribs on the edges of the projections  55 . This is illustrated in FIGS. 7 and 8 and will now be described by reference thereto. As has been noted, the holder ring  35  has the plurality of projections  55 . These extend axially from the upper edge of a ring part  58  at regular intervals in a tooth-like manner. As described above, the space between the projections  55  has such a width that the magnet  34  will be in press-contact therewith The projections  55  have a length of half the magnet or longer. In this embodiment, longitudinal ribs  59  project from the sides of the respective projections  55 . Thus, the press-contacting force exerted against the magnets  34  is increased.  
         [0035]    The construction of the outer shell  44  will now be described in more detail by reference to FIGS. 9 and 10. As has been noted, The rotor outer cylinder has the cylindrical side wall  44  which is entirely opened at its upper end and has the end plate  52  at its lower end. Around the perimeter of the upper end of the side wall  44  is formed the outer edge  55 , and on the inner side thereof is formed the step  54 .  
         [0036]    In the center of the end plate  52  is provided an opening  60  for passing the shaft  37  (FIG. 1). In the end plate  52  are further provided mounting holes  61  for mounting the rotor outer cylinder  44  on the connecting wheel  36  shown in FIG. 1. Also bolt-through connecting holes  62  are formed for connecting the rotor outer cylinder  44  to the one-way clutch  28 . Also mounting holes  63  for mounting the inner flange  57  of the inner casing  51  to the rotor outer cylinder  44 . When so mounted, the outer flange  56  of the inner casing  51  may be locked in position by inwardly bending the edge  55  toward the step  42 .  
         [0037]    The magnet holder ring  35  is shown enlarged in FIGS. 11 and 12 and the parts already described in detail above are indicated by the same reference numerals. Further description of these figures, therefore is not believed to be necessary.  
         [0038]    [0038]FIGS. 13 and 14 are enlarged views of the inner casing  51  which also has been described in detail. However these views also show that the inner flange  57  are formed mounting holes or notches  57   a  in alignment with the mounting holes  63  (FIGS. 9 and 10) in the end plate  52  of the rotor outer cylinder  44 . The reference numeral  57   b  designates recesses corresponding to accommodate bolts  45  (FIG. 1) inserted into six connecting holes  62  in the end plate  52 .  
         [0039]    Thus from the foregoing description it is believed that the described structures provide excellent magnet retention even if very thin high strength magnets are employed. Of course those skilled in the art will readily understand that the foregoing description is that of preferred embodiments of the invention and that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.