Abstract:
A simplified electrical generator for an internal combustion engine in which the hub portion, magnet carrying portion and race for a one way clutch are all integrally formed to provide a more compact, lighter and lower cost assembly.

Description:
BACKGROUND OF INVENTION  
       [0001]     This invention relates to an electrical generator for an internal combustion engine and more particularly to an improved generator construction that has an integral connection between the portion carrying the permanent magnets thereof and an element of a one way clutch that connects the starter gear with the engine shaft.  
         [0002]     In many internal combustion engines an engine shaft, such as, for example, the crankshaft has an extending end that carries an electrical generator such as a magneto, in proximity to a ring or starter gear that is conventionally coupled to the shaft by a one way clutch to permit the shaft to be turned for starting and then permits free-wheeling after the engine is running. Conventionally the generator has an annular member that carries permanent magnets that cooperate with the coils of a stator to generate electrical power. The annular member is affixed to a hub member that has a connection for rotation with the engine shaft by splines or one or more keys. Also affixed to this hub is an element of the one way clutch with the other element thereof affixed for rotation with the annular member.  
         [0003]      FIG. 1  shows a prior art construction of this general type and is in part similar to those shown in U.S. Pat. No. 6,534,880, assigned to the assignee hereof. Referring to this figure, an electric generator, indicated generally at  11 , is associated with the exposed end portion  12  of an engine crankshaft. A rotor, indicated generally at  13 . of the generator  11 , includes a hub  14  fitted to a tapered end of the crankshaft portion  12  and is axially fixed thereto by a nut  14  threaded onto the crankshaft end  12 . The rotor  13  is fixed against rotation relative to the crankshaft end  12  in a suitable manner, as by means of a key  16 . The hub  14  has an integral flange section  14   a  at one axial end.  
         [0004]     The rotor  13  includes a generally cup shaped element, indicated generally at  17 , having a cylindrical magnet holding portion  18  integrally formed at the outer periphery of an end wall  19 . The end wall  19  has an opening  19   a  for passing the hub  14 . A plurality of circumferentially spaced permanent magnets  21  are suitably fixed to the internal surface of the cylindrical portion  18 .  
         [0005]     The rotor  13  and the hub  14  are integrally by means of plural (three, for example) rivets  22  disposed around the opening  19   a  in the end wall  19  of the rotor  13  and the flange section  14   a  of the hub  14 .  
         [0006]     Cooperating with the magnets  21  and positioned within the cup-shaped rotor  13  is a stator  23  for generating AC power upon the rotation of the rotor  13 . The stator  23  is comprised of a laminated stator yoke  24  having an insulating bobbin  25  around which coils  26  are wound to generate an electromotive force upon the rotation of the rotor  13 .  
         [0007]     Positioned on the opposite side of the hub end wall  19  is a flywheel  27  having a starter gear  28  formed on its outer peripheral edge for cooperation with a starter motor (not shown). This flywheel  27  has a hub portion  27   a  that is journalled on the crankshaft portion  12  by an antifriction, needle bearing  30 . The flywheel  27  is coupled to the crankshaft end portion  12  for engine starting by means of a one way clutch, indicated generally at  28 . The one way clutch  28  is comprised of an outer race  29  that is affixed to the hub portion  14   a  by threaded fasteners  31  that have their heads  31   a  accessible through the interior of the rotor cylindrical portion  21  and which pass through openings formed in its integral flange section  14   a.  The threaded portions of the fasteners are received in tapped openings  31  formed in the outer race  29 .  
         [0008]     The inner race of the one way clutch  28  is formed by the outer surface of the cylindrical hub portion  27   a.  Its roller members are received between these races, as is well known in the art.  
         [0009]     There are other electric generators in which the hub and the rotor are formed as one unit and fixed to the outer ring section of the one-way clutch by threaded fasteners.  
         [0010]     However all of these prior art structures utilize several separate members for the flywheel connection to the one way clutch race thus requiring threaded connections of sufficient depth thus increasing not only the size but also the weight. This increases the inertia and makes the associated engine less responsive to desired speed changes. Also considerable assembly operations are required to further add to the cost.  
         [0011]     Therefore it is a principal object of this invention to provide an improved and simplified electrical generator and starter arrangement for an internal combustion engine.  
         [0012]     It is a further object of the invention to provide a lighter weight and less expensive electrical generator and starter arrangement for an internal combustion engine.  
         [0013]     It also is a further object of the invention to provide an improved and simplified arrangement for forming a one way clutch for such mechanisms.  
       SUMMARY OF INVENTION  
       [0014]     This invention is adapted to be embodied in an electrical generator for an internal combustion engine having an engine shaft. The generator is comprised of a hub portion adapted to be affixed for rotation with the engine shaft. A rotor portion is integrally formed with the hub portion and having a first, integral cylindrical portion extending in one axial direction therefrom for carrying a plurality of circumferentially spaced permanent magnets for cooperation with a stator. The hub portion further has a second, integral cylindrical portion extending in an axial direction opposite to the one axial direction for forming a race for a one way clutch for rotatably coupling a starter gear to the engine shaft. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]      FIG. 1  is a cross sectional view taken through the rotational axis of a prior art type of generator for an internal combustion engine.  
         [0016]      FIG. 2  is a cross sectional view in part similar to  FIG. 1  and shows a first embodiment of the invention.  
         [0017]      FIG. 3  is an enlarged cross sectional view taken along the same plane as  FIG. 2  but showing only the hub of the machine.  
         [0018]      FIG. 4  is an end elevational view of the hub looking in the direction of the arrows  4 - 4  in  FIG. 3 .  
         [0019]      FIG. 5  is an end elevational view of the hub looking in the direction of the arrows  5 - 5  in  FIG. 3 .  
         [0020]      FIG. 6  is an enlarged view of the area encompassed by the circle  6  in  FIG. 3 .  
         [0021]      FIG. 7  is an enlarged view, in part similar to  FIG. 6  showing another embodiment.  
         [0022]      FIG. 8  is an enlarged view, in part similar to  FIGS. 6 and 7  to explain why the induction hardening can not be performed with a conventional induction hardening coil.  
         [0023]      FIG. 9  is an enlarged view, in part similar to  FIGS. 6-8  and shows the desired induction hardening pattern.  
         [0024]      FIG. 10  is an enlarged view, in part similar to  FIGS. 6-9  and shows another embodiment and the desired induction hardening tool. 
     
    
     DETAILED DESCRIPTION  
       [0025]     Referring now in detail to the drawings, and initially to  FIG. 2 , an electrical generator and associated internal combustion engine are shown in a view similar to  FIG. 1 . Since the main difference between the embodiments of the invention and the prior art lie in the construction of the magnet carrier or integral rotor, indicated in this embodiment generally by the reference numeral  41 , where components or parts of components are of the same or substantially the same as the prior art construction previously described they are identified by the same reference numerals and will be described again only insofar as is necessary to permit those skilled in the art to understand and practice the invention.  
         [0026]     The rotor has an integral hub portion  42  that is fixed to the engine shaft  12  in any conventional manner as by a tapered opening, key  16 , and threaded fastener  15 . this integral hub portion  42  is unitary with a cylindrical magnet carrier portion  43  that carries on its inner cylindrical surface  43   a  the plurality of circumferentially spaced permanent magnets  21 . These permanent magnets  21  cooperate with the stator assembly  23  in the same manner as in the prior art.  
         [0027]     The integral portions  42  and  43  are connected by a stepped end wall having slightly axially offset inner and outer portions  44  and  45 , respectively. Rollers  46  of a one way clutch, indicated generally by the reference numeral  47 , are held between an outer race forming portion  48  extending from the step formed between the portions  44  and  45  in the opposite axial direction from the magnet carrier portion  43 . The rollers  46  are held axially in position by a retainer  49  and are carried by a roller carrier  51 .  
         [0028]     The details of the construction of the integral rotor  41  will now be further discussed by reference to  FIGS. 3-6 . As already discussed, the rotor  41  is generally constructed with the integral hub portion  42 , the magnet carrier portion  43 , and the clutch outer race forming portion  48 . In addition, the outer surface of the magnet carrier portion  43  is formed with a thick-walled portion or projection  52  for detecting the rotational position of the rotor  41  that extends circumferentially over the predetermined angle range (for example 60 degrees). This cooperates with a sensor (not shown) for detecting the rotational positions of the rotor  41  or its rotational speed. Also, a circumferential notch  53  is formed in the radially outer end wall portion  42   b  of the magnet carrier portion  43  for counter-balancing weight balance compensating for the thick-walled portion  52 .  
         [0029]     Thus unlike the prior art where the rotor only has a function for holding the magnets  21  functions as the integral hub portion  42  as well as the outer race forming portion  48  of the one-way clutch  47 . Thus, those bolts and/or rivets previously required for connecting the several separate components can be eliminated. Their elimination also permits the diameter of the one-way clutch  28  can be reduced according with the reduction of the outer race forming portion diameter. Accordingly, the weight of the one-way clutch  28  can be reduced, its moment of inertia can be decreased, and the response at starting can be improved. Furthermore, the number of components can be reduced in comparison with conventional one-way clutches, and therefore the number of man-hours needed to assemble the generator can be reduced.  
         [0030]     When the one way clutch  28  is engaged and disengaged, the outer race forming portion  48  receive force directed outward in the radial direction. Thus excessive force may act upon the clutch outer race forming portion  48  of the rotor  41  and the internal surface of the outer race forming portion  48  may wear due to the contact with the possibility that the durability of the rotor  41  decreased. Therefore, the internal surface (end surface) of the outer race forming portion  48  of the one-way clutch in the present embodiment is treated with induction hardening in order to improve its strength.  
         [0031]     This is shown best in the enlarged view of  FIG. 6 . As seen there, an induction-hardened section  54  is formed over the area from a boundary between the flange section  44  of the integral hub portion  42  and an outer race forming portion end surface  43   a  along the internal surface of the outer race forming portion. Accordingly, the clutch outer race forming portion  48  can have the increased hardness than that of other portions and can ensure the durability of the rotor  41  itself even if it slidably contacts with the rollers  46  of the one way clutch  28 .  
         [0032]     Also as best seen in  FIG. 6 , a notch  55  is formed during processing at the boundary part between the end surface of the clutch outer race forming portion  48  at the hardened portion  54  and the boss radially inner end wall portion  44  perpendicular to the hardened portion  54 . The notch  55  also serves to avoid interference with a corner section of the roller holder  51  during the assembly of the clutch.  
         [0033]      FIG. 7  shows another embodiment of the induction-hardening treatment illustrated in  FIG. 6 . In this embodiment, consideration is given to the possible occurrence of a crack due to residual stresses produced around the notch  55  as described above. That is to say, measures are taken here such that the range of the induction hardening is expanded to the radially inner end wall portion  44  of the integral hub portion  42  so as to decrease the residual stresses around the notch  55 . In addition the shape of the notch  55  itself is enlarged so as not to concentrate the stress in this section during the use of the clutch. In addition, thickness of the radially inner end wall portion  44  itself may be increased so as to increase the strength of the area around the notch  55 .  
         [0034]     Practically, however, even when the induction hardening is intended for the end surface of the clutch outer race forming portion  48  in the integral-type rotor as well as the radially inner end wall portion  44  of the integral hub portion  42 , the induction hardening cannot be applied to a continuous area of the end surface of the clutch outer race forming portion and the radially inner end wall portion  44  as shown in  FIG. 7  by merely placing a high frequency coil to the part encompassed by the circle  6  in  FIG. 3 .  
         [0035]     The problem with performing the induction hardening in such a manner using a conventional high frequency induction hardening coil will be explained by reference to  FIG. 8 . The integral-type rotor of the present invention is the type mounted to, for example, the crankshaft of an engine and requires heat resistance and high strength. Therefore, a material such as S48C containing carbon is used as the rotor material as an example. Here, the end surface  43   a  of the clutch outer race forming portion is a receiving surface of a pin for the one-way clutch and requires additional high strength. Therefore, the outer race forming portion  48  is treated with the induction hardening  54  for increasing its strength. However, the induction hardening generally done with a high frequency coil (waveguide) made of a square pipe having a rectangular cross section and formed in a ring shape. This high frequency coil is applied to the hardened section and energized to heat the section.  
         [0036]     However, when such a high frequency coil is placed facing a fillet of the end surface of the clutch outer race forming portion  48  in the rotor to heat the fillet, the notch  55  formed in the fillet by necessity in processing causes insufficient heating of the depths of the notch  55 , resulting in a non-hardened part in the fillet. Therefore, as shown in  FIG. 8 , the hardened section  54  in the end surface  43   a  of the clutch outer race forming portion and a hardened section  56  in the radially inner end wall portion  44  become discontinuous at the notch  55 , and a boundary of the hardened section is produced. Thus, the stress concentration produced in such hardening discontinuous part (hardening boundary) as well as the stress concentration based on the shape of the notch  55  act upon the fillet to cause the possibility that the fillet may crack.  
         [0037]     If, however, the amount of heat is increased in order to harden the depths of the notch  55 , the radially inner end wall portion  44  may be melted and damaged. Although the thickness of the radially inner end wall portion  44  could be increased in order to prevent the melting because the weight of the radially inner end wall portion  44  would be increased resulting in increased rotation inertia of the rotor. Therefore other measures for preventing the melting damage should be employed. It is possible to cool the radially inner end wall portion  44  from the backside as shown by an arrow R. However, if the radially inner end wall portion is cooled the heating effect for the notch  55  is decreased and the induction hardening of the fillet cannot be achieved.  
         [0038]     To avoid the aforenoted problems and to provide a hardening pattern as shown in  FIG. 9 , a special configuration of hardening tool is employed. This results, as seen in  FIG. 9 , the hardened area  56  is provided with a tapered surface  57  in the radially inner end wall portion  44  of the integral hub portion  42  in the rotor, communicating with the notch  55 . By forming such tapered surface  57 , heat from the high frequency coil (not shown) is sufficiently transferred to the depths of the notch  55 , and the depths of the notch  55  is hardened. Accordingly, the hardened section  56  in the radially inner end wall portion  44  is connected to the hardened section  54  in the outer race forming portion  48  the hardened section in the depths of the notch  55 . As described above, induction-hardened sections are continuously formed in the fillet with the notch  55 , and thus the stress concentration can be reduced, and the possibility of cracking is decreased.  
         [0039]      FIG. 10  shows another shape of the hardened section and the type of hardening tool that can be employed to achieve the hardened shapes of  FIGS. 9 and 10  As shown in  FIG. 10 a  stepped surface  58  in the radially inner end wall portion  44  of the integral hub portion  42  in the rotor  41 , communicating with the notch  55 .  
         [0040]     As shown in this embodiment, a specially formed high frequency coil  59  having a narrow tip  61  in the cross section is used for high-frequency heating. By forming such a stepped surface  58  and using the high frequency coil  59  having a narrow tip  61  for heating, heat from the high frequency coil  59  is sufficiently transferred to the depths of the notch  55 , the depths of the notch  55  is hardened and the hardened section  56  in the radially inner end wall portion  44  is connected to the hardened section  54  in the end surface of the clutch outer race forming portion  48  through the hardened section in the depths of the notch  55 . As described above, induction-hardened sections are continuously formed in the fillet with the notch  55 , and thus the stress concentration can be reduced and the possibility of crack production can be decreased.  
         [0041]     As already noted, the high frequency coil  59  having the narrow tip  61  shown in the drawing is effectively used in the high-frequency heating for the example of  FIG. 9  previously described. However, if the high frequency coil  59  having a shape shown in  FIG. 10  is not used and a normal high frequency coil having a rectangular cross section is used, as long as the width of the cross section of the coil is not more than the length of the stepped surface  58 , sufficient high-frequency heating can be applied to the depths of the notch  55 , and therefore, the depths of the notch  55  can be hardened.  
         [0042]     As should be apparent from the foregoing description, an electric generator for an internal combustion engine is constructed such that not only are the hub portion and the rotor integral, but also this integration extends to an element of the one-way clutch. Thus, those components which are separated in the prior art require only one unit. As a result, bolts and/or rivets required for connecting several components can be eliminated and the total number of components can be reduced. In addition, the diameter of the one-way clutch can be reduced and its weight can be reduced with a resulting decrease in the moment of inertia. Also, with the decrease in the number of components, the number of man-hours needed to assemble the unit can be reduced. In addition, by treating the outer race forming portion with induction hardening, strength can be ensured and the amount of abrasion due to the contact with the rollers can be reduced. Furthermore, the part of the integral hub portion adjacent to the internal surface of the outer race forming portion of the one-way clutch is also treated with induction hardening in such a way that stress does not tend to concentrate in the boundary part between the outer race forming portion of the one-way clutch and the integral hub portion. Of course those skilled in the art will readily understand that the described embodiments are only exemplary of forms that the invention may take 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.