Abstract:
A core assembly for an ignition coil in an internal combustion engine generally includes an inner core comprising an I-shaped lamination and an outer core comprising a pair of opposing C-shaped lamination stacks. A joint is formed by an end of the I-shaped lamination stack and a pair of adjacent ends of the pair of C-shaped lamination stacks. The core assembly is designed in a manner which minimizes the waste material that is scrapped when forming the lamination stacks, as well as allows the inner lamination stack to be slid down along the inner periphery of the outer stack.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to ignition coils, and more particularly relates to construction of the core portion of the ignition coil which carries the magnetic flux.  
       BACKGROUND OF THE INVENTION  
       [0002]     Ignition coils for internal combustion engines generally comprise a core assembly on which a coil assembly is mounted, all of which is contained inside a plastic housing. The coil assembly includes a primary coil concentrically mounted within a secondary coil, and an electric current is flowed through the primary coil creating a large magnetic field. This magnetic field is guided by the core assembly, which is typically constructed of steel lamination stacks. At the proper time in the engine operating cycle, the electric current is abruptly interrupted, and the rapid change in the magnetic field induces a voltage in the secondary coil sufficiently high to create a spark across gapped electrodes of a spark plug attached to the ignition coil.  
         [0003]     In one design of ignition coils, the core assembly is formed of an inner core or I-shaped lamination stack that resides inside the primary and secondary windings. There is also an outer core or O-shaped lamination stack, which completely encircles the primary and secondary windings and provides a flux path around the windings so that the magnetic flux is linked to both of the windings. The combination of the I-shaped lamination stack and the O-shaped lamination stack combine to form a figure eight or B-shaped core assembly.  
         [0004]     One drawback of this ignition coil design is that there is a waste in material during the manufacture of the lamination stack. Individual laminations are typically cut or sheared and stacked in the stamping operation. For an O-shaped lamination, the center of the O-shape is wasted and scrapped, resulting in relatively small percentage of the steel material actually being used in the core assembly.  
         [0005]     Another problem with this ignition coil design is the difficulty of assembly. In particular, the opposing ends of the I-shaped lamination stack are slid inside of the O-shaped lamination stack. However, in order to slide the inner core inside of the outer core, there cannot be a line-to-line fit at the joints formed between the inner and outer cores. This is because a sufficient clearance must be designed in order to allow assembly of the inner and outer cores. At the same time, the I-shaped lamination stack can be difficult to slide down along the inner periphery of the O-shaped lamination stack.  
         [0006]     Accordingly, there exists a need to provide a core assembly which reduces the waste in manufacturing of the stack, and also which allows the inner core to be slid down across the interior surface of the outer core during assembly.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     One embodiment of the present invention provides a core assembly for an ignition coil in an internal combustion engine which allows the core to be formed in a manor which minimizes the waste material that is scrapped when forming the lamination stacks, as well as allows the inner lamination stack to be slid down along the inner periphery of the outer stack. The core assembly generally includes an inner core and an outer core. The inner core comprises an I-shaped lamination stack defining a core axis. The outer core comprises a pair of opposing C-shaped lamination stacks. The inner core has first and second opposing free ends, while each C-shaped lamination stack has a third free end and a fourth free end. A first joint is formed by the first end of the I-shaped lamination stack and a pair of third ends of the pair of C-shaped lamination stacks. A second joint is formed by the second end of the I-shaped lamination stack and a pair of fourth ends of the pair of C-shaped lamination stacks. In the first joint, the third ends abut each other and are generally parallel to the core axis, while the first end abuts the third ends and is generally perpendicular to the core axis. In the second joint, the fourth ends abut each and are generally parallel to the core axis, while the second end abuts the fourth ends and is generally perpendicular to the core axis.  
         [0008]     In another embodiment of the core assembly, the second end of the inner core defines an extension portion. Further, each C-shaped lamination stack includes a reduced width portion at its fourth free end. The reduced width portions cooperate to define a notch size to receive the extension portion. The second joint is formed by the second end of the I-shaped lamination stack and the pair of fourth ends of the pair of C-shaped lamination stacks. The extension portion of the second end is positioned in the notch and butts against the reduced width portions of the fourth ends.  
         [0009]     According to more detailed aspects, the extension portion preferably has a tapered shape, which may take the form of a triangular shape or a curved shape. For example, the extension portion may be semicircular. The extension portion and the notch extend a distance along the core axis about equal to the width of the outer core. However, the extension portion and notch may extend a distance along the core axis that is less than the width of the outer core. Thus, the notch may extend only a portion of the way through the width of the fourth ends, leaving a portion of the fourth end surfaces abutting along a line parallel to the core axis. The first end of the I-shaped lamination stack preferably has a magnet engaging the third ends of the C-shaped lamination stacks.  
         [0010]     In another embodiment of the core assembly, an inner core comprises an I-shaped lamination stack and an outer core comprises a pair of opposing C-shaped lamination stacks. The inner core has first and second opposing free ends, the second end being tapered. Each C-shaped lamination stack has a third and fourth free end, each fourth free end being tapered and cooperating with the other fourth free end to define a notch sized to receive the tapered second end. The opposing C-shaped lamination stacks are pulled apart and pushed back together to allow the inner core to be positioned inside the outer core. The third ends define a first opening and the fourth ends define a second opening when the C-shaped lamination stacks are pulled apart a distance less than the width of the I-shaped lamination stack. The first opening is sized to prevent the first end of the I-shaped lamination stack from entering into the first opening, while the second opening is sized to allow the second end of the I-shaped lamination stack to enter the second opening.  
         [0011]     According to more detailed aspects, the tapered fourth ends are pressed against the tapered second end to position the I-shaped lamination stack along the core axis. The second end of the I-shaped lamination stack may have a triangular shape or a semicircular shape. The notch may extend a distance along the core axis that is equal to or less than the width of the outer core.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. In the drawings:  
         [0013]      FIG. 1  is a plan view of a core assembly constructed in accordance with the teachings of the present invention;  
         [0014]      FIG. 2  is a plan view of the stamping arrangement used for forming the lamination stacks forming the core assembly depicted in  FIG. 1 ;  
         [0015]      FIGS. 3 and 4  are plan views of an alternate embodiment of the core assembly depicted in  FIG. 1 , showing the outer core member pulled apart and pressed together, respectively;  
         [0016]      FIG. 5  is a plan view of yet another embodiment of the core assembly depicted in  FIG. 1 ; and  
         [0017]      FIG. 6  is a plan view of still another embodiment of the core assembly depicted in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     Turning now to the figures,  FIG. 1  depicts a plan view of a core assembly  20  constructed in accordance with the teachings of the present invention. The core assembly  20  includes an outer core  22  and an inner core  26 . Each of the inner and outer cores  22 ,  24  are preferably constructed of steel lamination stacks. These steel lamination stacks are constructed by stamping individual laminations out of a sheet of steel, the stampings then being layered to form the lamination stacks. Preferably, the lamination stacks are formed of a silicon steel, although any other material which guides magnetic flux may be used, including solid forms or other non-lamination structures.  
         [0019]     The inner core  24  is thus formed as an I-shaped lamination stack  26  defining a core axis  25 . The lamination stack  26  includes a first end  28  and an opposing second end  32 . The first end  28  defines a first end surface  30  which abuts against the outer core  22 , while the second end  32  defines a second end surface  34  which abuts against the outer core  22 . The first end  28  may also include a magnet  27 , or other material which serves as an air gap between the inner core  24  and the outer core  22 , as is well known in the art.  
         [0020]     The outer core  22  is of a novel construction, namely two opposing C-shaped lamination stacks  36 ,  38 . The C-shaped lamination stacks  36 ,  38  are arranged as is shown in  FIG. 1  (i.e. mirrored) to form an annular shape surrounding the inner core  24 . Each C-shaped lamination stack  36 ,  38  includes a third free end  40 ,  42  and a fourth free end  48 ,  50 . The third free ends  40 ,  42  define end surfaces  44 ,  46  which abut each other along the line parallel to and aligned with the core axis  25 . Similarly, the fourth ends  48 ,  50  each define ends surfaces  52 ,  54  which abut along a line generally parallel to and aligned with the core axis  25 .  
         [0021]     Stated another way, a first joint  56  is formed by the pair of third ends  40 ,  42  of the pair of C-shaped lamination stacks  36 ,  38 , as well as the first end  28  of the I-shaped lamination stack  26 . The first end  28  and its end surface  30  abuts against the third ends  40 ,  42  (and in particular the inner periphery of the outer core  22 ) along a line that is generally perpendicular to the core axis  25 . Similarly, a second joint  58  is formed by the fourth free ends  48 ,  50  of the C-shaped lamination stacks  36 ,  38 , and the second end  32  of the I-shaped lamination stack  26  whose end surface  34  abuts against the fourth ends  48 ,  50  along the line generally perpendicular to the core axis  25 .  
         [0022]     By forming the outer core  22  of two opposing C-shaped lamination stacks  36 ,  38 , the scrap waste during formation of the lamination stacks  36 ,  38  is significantly reduced, as will be discussed with reference to  FIG. 2 . In the figure, a plan view of a steel sheet  60  is provided showing the stamping patterns thereon. As the C-shaped laminations  36 ,  38  are identically shaped, there need not be any left/right or other designations to distinguish between the two. By virtue of their C-shape, four columns  61 ,  62 ,  63 ,  64  may be formed on a single sheet  60  of steel, each row containing four laminations  36 ,  38 . The stamping pattern results in nearly half of all the material being used for the steel lamination stacks  36 ,  38 , which reflects a 40% to 50% improvement over prior stamping patterns.  
         [0023]     With reference to  FIGS. 3 and 4 , another embodiment of the core assembly  20   a  has been depicted in plan view. Like parts have been given like reference numerals in order to aid in the understanding of the invention. In this embodiment, the inner core  24   a  and its I-shaped lamination stack  26   a  has been formed with an alternatively shaped second end  32   a . In particular, the second end  32   a  has been formed with an extension portion  33   a  which defines an extension end surface  3   a . As shown in  FIGS. 3 and 4 , the extension portion  33   a  has a narrowing shape that is triangular in nature. The extension portion  33   a  extends an axial distance that is approximately equal to a width W of the outer core  22   a.    
         [0024]     The opposing C-shaped lamination stacks  36   a ,  38   a  also include fourth ends  48   a ,  50   a  which have been alternatively shaped, and in particular are narrowing in nature. Stated another way, the fourth ends  48   a ,  50   a  include a reduced width portion which define end surfaces  52   a ,  54   a  for engaging the second end  32   a  of the inner core  24   a . In particular, the end surfaces  52   a ,  54   a  are sloped at an angle that corresponds with the slope of the extension end surface  34   a  to receive the same. Thus, a second joint  58   a  is formed by the second end  33   a  of the I-shaped lamination stack  26   a  and the fourth ends  48   a ,  50   a  of the C-shaped lamination stacks  36   a ,  38   a.    
         [0025]     As best seen in  FIG. 3 , the C-shaped lamination stacks  36   a ,  38   a  may be pulled slightly apart to define a first opening  70  between the first ends  40 ,  42 , and a second opening  72  between the second ends  48   a ,  50   a . By including the tapered extension portion  33   a  on the second end  32   a  of the inner core  24   a , the extension portion  33   a  may enter into the second opening  72  allowing the inner core  24   a  to move downwardly along the core axis  25 . However, the first end  28  of the inner core  24   a  is not sized to pass through the first opening  70  formed between the first ends  40 ,  42 . In this way, when the opposing C-shaped lamination stacks  36   a ,  38   a  are pressed inwardly towards each other, as shown in  FIG. 4 , the sloped end surfaces  52   a ,  54   a  of the fourth ends  48   a ,  50   a  press against the surface  34   a  of the extension portion  33   a  to axially position the inner core  24   a  along the core axis  25 . Specifically, this allows the inner core  24   a  to have its first end  28  pressed firmly against the first ends  40 ,  42  for forming the first joint  56 . Similarly, the reduced width portions at the fourth ends  48   a ,  50   a  cooperate to define a notch  66  which is sized to receive the extension portion  33   a  located at the second end  32   a  of the I-shaped lamination stack  26   a.    
         [0026]     Accordingly, it will be recognized by those skilled in the art that a slightly pulling apart of the C-shaped lamination stacks  36   a ,  38   a  of the outer core  22   a  permits some axial adjustability of the inner core  24   a , allowing the inner core  24   a  to be slid downwardly inside of the outer core  22   a  without any interference from the inner periphery of the outer core  22   a.    
         [0027]     As will be recognized by those skilled in the art, numerous modifications of the extension portion  33   a  on the second end  32   a  of the inner core  26   a ,  24   a  will be readily envisioned, including corresponding shapes for the notch  66  formed by the fourth ends  48   a ,  50   a  of the outer core  22   a . For example, as shown in  FIG. 5 , the second end  32   b  of the I-shaped lamination stack  26   b  can include a tapered extension portion  33   b  which includes a less severe taper than in the prior embodiment depicted in  FIGS. 3 and 4 . Stated another way, the extension portion  33   b  extends an axial distance that is less than a width W of the outer core  22   b.    
         [0028]     Similarly, the fourth ends  48   b ,  50   b  of the opposing C-shaped lamination stacks  36   b ,  38   b  include reduced width portions defining end surfaces  52   b ,  54   b  which corresponds with the extension end surface  34   b . It will also be recognized that the end surfaces  52   b ,  54   b  will directly contact each other along the outer portion of the width of the outer core  22   b  and abut each other along the line extending parallel to the core axis  25 . When the opposing C-shaped lamination stacks  36   b ,  38   b  are pulled apart as shown in  FIG. 5 , the second opening  72   b  is sized and oriented to permit entry of the I-shaped lamination stack  26   b , and in particular the extension portion  33   b  for axial positioning of the inner core  24   b.    
         [0029]     A final example is depicted in  FIG. 6 , where the second end  32   c  of the I-shaped lamination stack  26   c  includes an extension portion  33   c  which is curved, and in particular has a semicircular shape. Likewise, the fourth ends  48   c ,  50   c  of the opposing C-shaped lamination stacks  36   c ,  38   c  include reduced width portions which define fourth end surfaces  52   c ,  54   c . The fourth end surfaces  52   c ,  54   c  are sized and shaped to correspond with the extension end surface  34   c  found at the second end  32   c  of the inner core  24   c . Again, the second opening  72   c  formed between fourth ends  48   c ,  50   c  is sized to permit entry of the inner core  24   c  and allow the inner core  24   c  to be slid inside the outer core  22   c , and then be axially positioned along the core axis  25  such that the first end  28  and magnet  27  are firmly pressed against the third ends  40 ,  42  of the outer core  22   c.    
         [0030]     The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Numerous modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.