Abstract:
(Subject  
     The primary object of the present invention is to provide a vehicle alternator and its rotor which can firmly fasten the permanent magnets between the claw-shaped magnetic poles in improved productivity.  
     (Means for Solving the Problems)  
     The object is achieved by a rotor for a vehicle alternator comprising: a Randall type iron core having claw-shaped magnetic poles which are alternately arranged and opposed each other and include a centered cylindrical field winding; and a permanent magnet disposed between the claw-shaped magnetic poles for increasing the magnetic field, wherein the permanent magnet is held by radial elastic force.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. (Field of the Invention)  
           [0002]    The present invention relates to a rotor for a vehicle alternator, more particularly to the holding and fastening of permanent magnets arranged between claw-shaped magnetic poles of a Randall type rotor.  
           [0003]    2. (Prior Art)  
           [0004]    It is well known to increase the exciting force of an alternator having a rotor with Randall type claw-shaped magnetic poles by separately disposing permanent magnets between the opposing claw-shaped magnetic poles. Exemplary examples are described in Japanese Application Patent Laid-Open Publication No. Hei 07-298585 and Japanese Application Patent Laid-Open Publication No. Hei 11-98787. The former describes permanent magnets bonded by an adhesive to the permanent magnet catching portions on the internal sides of flange protrusions and to the sides of claw-shaped magnetic poles. The latter describes protect covers of nonmagnetic stainless steel outside the permanent magnets against the quick rotation of the rotor.  
         SUMMARY OF THE INVENTION  
       Problems to be Solved by the Invention  
         [0005]    Conventionally, the permanent magnets need to be fastened after positioned between the claws. The magnets after magnetized are hard to handle so that, for easy mounting and less damage during the mounting, the magnets are generally mounted on the rotor before magnetized. Particularly, when the magnets after magnetized are mounted on the rotor, subsequent machining of the rotor to adjust the rotor outer diameter or to balance the rotation needs to remove machining chips attached on the magnets, which reduces the workability significantly.  
           [0006]    When the magnets before magnetized are mounted on the rotor, the magnets have no adhesion to the magnetic poles, so that a special tool is necessary to position the magnets with a certain space with the field winding, which reduces the productivity. An adhesive only fastens the magnets on the rotor so that any space can easily occur in the join with the claw-shaped magnetic poles, thereby increasing the magnetic flux loss to cause the output reduction.  
           [0007]    The conventional techniques have another problem that the permanent magnets disposed between the claw-shaped magnetic poles make it hard to apply around the axial center of the field winding the adhesive for fastening and isolating the field winding.  
         Means for Solving the Problems  
         [0008]    The present invention provides a vehicle alternator and its rotor which can firmly fasten the permanent magnets between the claw-shaped magnetic poles in improved productivity. The present invention also provides a vehicle alternator and its rotor having permanent magnets between the claw-shaped magnetic poles, which can reliably apply around the axial center of the permanent magnets the adhesive for isolating the field winding.  
           [0009]    The above rotor for a vehicle alternator can be achieved by a Randall type iron core having claw-shaped magnetic poles which are alternately arranged and opposed each other and include a centered cylindrical field winding; and a permanent magnet disposed between the claw-shaped magnetic poles for increasing the magnetic field, wherein the permanent magnet is held by radial elastic force. The above vehicle alternator can be achieved by a stator; and a rotor being rotatively disposed opposing the stator with a gap therebetween and having a permanent magnet held by radial elastic force.  
           [0010]    In the above vehicle alternator and its rotor, the permanent magnet is encircled in a holder and pressed and held by an elastic body disposed between the holder and the field winding for exerting radial elastic force.  
           [0011]    The holder may be made of a metal strip and integrated with the elastic body. The elastic body is in contact with the field winding via an insulating member. The holder may encircle the permanent magnet longitudinally and have a tongue-like piece of an elastic portion on its surface facing the field winding. The tongue-like piece is a cutout of the holder and has an arc shape being convex toward the field winding. The elastic portion is in contact with an insulating material wound on the field winding. The insulating material is a fabric suitable for dropped adhesives. The holder may include a loop strip which encircles the permanent magnet longitudinally, the starting end at one longitudinal end of the strip having a protrusion extending beyond the permanent magnet width, the finishing end of the strip connecting to the starting end, and the protrusion stopping at one end of a field winding bobbin. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 shows an example of an alternator according to the present invention.  
         [0013]    [0013]FIG. 2 shows an example of a rotor according to the present invention.  
         [0014]    [0014]FIG. 3 shows another example of a rotor according to the present invention.  
         [0015]    [0015]FIG. 4 shows a cross sectional view along the line A-A of FIG. 3.  
         [0016]    [0016]FIG. 5 shows an illustration of liquid adhesives dropped on the rotor of FIG. 2.  
         [0017]    [0017]FIG. 6 shows a radial view of an example of a rotor according to the present invention.  
         [0018]    [0018]FIG. 7 shows an enlarged view of an example of a rotor according to the present invention.  
         [0019]    [0019]FIG. 8 shows an example of a permanent magnet  9  in a holder  8  according to the present invention, where the doubly shaded region refers to the permanent magnet.  
         [0020]    [0020]FIG. 9 shows an example of the holder  8  alone according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
     Description of the Preferred Embodiments  
       [0021]    [0021]FIG. 1 shows a cross sectional view of an example of the present invention. A pulley  1  receives a driving force from the vehicle via a belt (not shown). Then a rotor  2  held by bearings  3 ,  4  rotates inside a stator  5 . The rotor  2  has a holder  8  and a permanent magnet  9  between claws of a pair of claw-shaped magnetic poles  6 ,  7  including a plurality of claws. The rotor  2  has slip rings  12 ,  13  which receive electric power from brushes  10 ,  11  and excite a field winding  14  in the rotor  2 .  
         [0022]    The vehicle alternator receives a coolant from the internal combustion engine through a coolant inlet  15 . The coolant circulates through passages such as a passage  16  in the vehicle alternator to cool heated components such as the stator  5  and rectifier  18  when the vehicle alternator generates electric power. After cooling, the coolant returns to the internal combustion engine through the coolant outlet  17 . The coolant is then cooled in a radiator of the internal combustion engine and recycled. A voltage regulator  19  regulates the generated voltage. A terminal  20  connects to the rectifier  18  (this connection is not shown) and electrically connects the vehicle wiring and the vehicle alternator to supply the rectified output current to the vehicle.  
         [0023]    [0023]FIG. 2 only shows the rotor  2 . The upper part of FIG. 2 shows the assembled rotor and the permanent magnet in the holder before inserted into the claw-shaped magnetic poles. The lower part of FIG. 2 shows the holder and the permanent magnet being inserted and fastened in a predetermined position in the rotor. The field winding  14  winds around a bobbin  21  which can isolate the field winding  14  from the claw-shaped magnetic poles  6 ,  7 . An insulator  22  is provided on the outermost part of the wires of the field winding  14 . The insulator  22  can keep a tongue-like piece  23  of an elastic portion of the holder  8  from directly contacting with the wires of the field winding  14 . The tongue-like piece  23  is provided on a holder  8 &#39;s surface which faces the field winding  14  when the holder  8  is in position. The insulator  22  may be unnecessary if the holder  8  is made of insulating materials, such as plastic and rubber, which will not damage the insulating film on the wires of the field winding  14  or cause the insulation failure, when the holder  8  is inserted into the claw-shaped magnetic poles along the rotation axis of the rotor. In contrast, the insulator  22  is essential if the holder  8  is made of metals such as spring steel and stainless steel.  
         [0024]    When the holder  8  and the permanent magnet  9  shown in the upper part of FIG. 2 are moved in the direction of the arrow and inserted between the claw-shaped magnetic poles  6 ,  7 , the springy portion  23  of the holder  8  will become deformed and have a spring effect on the claw-shaped magnetic poles  6 ,  7  and outermost insulator  22  of the field winding  14 . Thus, the holder  8  can come into close contact with the internal sides of protrusions  24  of the claw-shaped magnetic poles  6 ,  7  and can secure the radial position of the permanent magnet  9 . The protrusions  24  can keep the holder  8  and permanent magnet  9  on the sides of the claws of the claw-shaped magnetic poles  6 ,  7  from jumping out radially from between the claw-shaped magnetic poles  6 ,  7  by the centrifugal force due to the rotation of the rotor  2 .  
         [0025]    [0025]FIG. 3 shows the holder  8  and permanent magnet  9  held in position in the rotor  2 . FIG. 4 shows a cross sectional view along the line A-A of FIG. 3. As shown in FIGS. 3 and 4, when the tongue-like piece  23  of the elastic portion of the holder  8  is deformed, the holder  8  can come into close contact with the internal surfaces  25  of the protrusions  24  provided on the sides of the claw-shaped magnetic poles  6 ,  7 . As mentioned above, the tongue-like piece  23  is provided on the holder  8 &#39;s surface which faces the field winding  14  when the holder  8  is in position. The protrusions  24  can keep the holder  8  and permanent magnet  9  from jumping out radially from a predetermined position by the centrifugal force due to the rotation of the rotor  2 .  
         [0026]    The insulator  22  can be any insulating material if it is only intended to isolate the field winding  14  from the tongue-like piece  23  of the elastic portion of the holder  8  holding the permanent magnet  9 . However, for isolation and adhesion between the wires of the field winding  14 , between the field winding  14  and the bobbin  21 , and between the bobbin  21  and the claw-shaped magnetic poles  6 ,  7 , the insulator  22  must be materials which can infiltrate an adhesive into between the above described components.  
         [0027]    Particularly, if a liquid adhesive is dropped on the rotor  2  in the manufacturing process, the holder  8  and permanent magnet  9  between the claw-shaped magnetic poles may prevent applying the adhesive around the axial center of the field winding  14 .  
         [0028]    To solve the above problem, the insulator  22  can be made of materials which can infiltrate the liquid adhesion, such as tapes made of cotton, and can wind around the radial outside of the field winding  14 , as shown in FIG. 5. Thus, when the liquid adhesive is applied outside the rotor in the manufacturing process, the adhesive applied at the axial ends of the insulator  22  can penetrate axially to the axial center of the rotor  2  and can also penetrate into the interlayer space of the field winding  14 . Thus, the rotors can be manufactured reliably in the same manner as the rotors are manufactured without permanent magnets between the claw-shaped magnetic poles.  
         [0029]    As shown in FIGS. 6 and 7, the holder  8  has a protrusion  26  on its axial end face. When the permanent magnet  9  in the holder  8  is inserted between the claw-shaped magnetic poles  6 ,  7  of the rotor  2 , the protrusion  26  can contact with the wall  27  at the axial end of the bobbin  21 . Thus, the permanent magnet  9  can be located axially in the rotor  2  and the axial magnetic center of the rotor  2  can be determined. An isolating space can also be ensured between the holder  8  which is made of a conductive material and the field winding end  29  winding on the protrusion  28  which is for fastening the end of the field winding wound around the bobbin  21 .  
         [0030]    [0030]FIG. 8 shows an example of the permanent magnet in the holder. The holder  8  encircles the permanent magnet  9  longitudinally. Thus, when the permanent magnet  9  encircled in the holder  8  is in position between the claw-shaped magnetic poles  6 ,  7  of the Randall type iron core, the permanent magnet  9  can come into close contact with the magnetic poles  6 ,  7 . The holder  8  is made of nonmagnetic materials so that the magnetic flux may not leak from between the opposed Randall type magnetic poles.  
         [0031]    [0031]FIG. 9 shows an example of the holder alone. The holder  8  has the tongue-like piece  23  of an elastic portion on its surface which faces the field winding  14  when the holder  8  is in position. The holder  8  holds the permanent magnet  9  with a loop strip of which one longitudinal end and another end are connected. The holder  8  has at one longitudinal end face the protrusion  26  which can stop at one end of the bobbin  21 .  
         [0032]    In the above example, separate holders  8  are used for each permanent magnet  9 . After assembling the field winding  14 , a rotor shaft, and the claw-shaped magnetic poles, the permanent magnet  9  in the holder  8  is inserted along the rotation axis of the rotor  2 . For the radial position of the permanent magnet  9 , the flange protrusions  24  on the periphery of the claw-shaped magnetic poles surfaces with which the permanent magnet  9  contacts can keep the magnet  9  from jumping radially out of a predetermined position and from contacting with the stator by the centrifugal force due to the rotation of the rotor  2  applied on the holder  8  and magnet  9 . The holder  8  can have the spring effect on its surface outside the field winding  14 . The spring effect can push out the permanent magnet  9  in the holder  8  as outwardly as possible in the radial direction of the claw-shaped magnetic poles  6 ,  7  and can bring the holder  8  into contact with the internal surface of the flange protrusion  24  of the claw-shaped magnetic poles  6 ,  7 . Thus, the spring effect can push out the permanent magnet  9  as outwardly as possible in the radial direction without contacting with the stator.  
         [0033]    As described above, it is possible to reduce the magnetic flux loss between the claw-shaped magnetic poles  6 ,  7  as much as possible, which is the original object of the permanent magnet  9  between the claw-shaped magnetic poles  6 ,  7 . It is also possible to secure the radial position of each permanent magnet  9 . Therefore, a large amount of rotors with reliable performance can be produced. Additionally, the axial position of the permanent magnet  9  can be secured as follows: the permanent magnet  9  in the holder  8  is inserted between the claw-shaped magnetic poles  6 ,  7  until the protrusion  26  at the axial end face of the holder  8  contacts with the bobbin which can isolate the field winding  14  from the iron core and the claw-shaped magnetic poles  6 ,  7 .  
         [0034]    The insulator  22  outside the field winding  14  can prevent an electrical short between the field winding and the holder which is made of metal. Particularly, the insulator  22  made of materials which can easily infiltrate the adhesive for isolating and fastening the field winding  14  can resolve the manufacturing problem that the holder  8  between the claw-shaped magnetic poles  6 ,  7  prevent applying the adhesive around the axial center of the field winding  14 .  
       Effects of the Invention  
       [0035]    As described above, the present invention can provide a vehicle alternator and its rotor which can firmly fasten the permanent magnets between the claw-shaped magnetic poles in improved productivity. The present invention can also provide a vehicle alternator and its rotor having permanent magnets between the claw-shaped magnetic poles, which can reliably apply around the axial center of the permanent magnets the adhesive for isolating the field winding.