Abstract:
An ignition coil includes a magnetically-permeable core; a primary winding disposed outward of the core; a secondary winding disposed outward of the primary winding, inductively coupled to the primary winding, and terminating at one end thereof in a low-voltage end and terminates at another end thereof in a high-voltage which is electrically connected directly to a terminal through an electrically conductive polymer; and a case defining an interior having an interior surface such that the core, the primary winding, and the secondary winding are received within the interior of the case such that the at least one of the low-voltage end and the high-voltage end, the terminal, and the electrically conductive polymer are disposed within the recess and such that the electrically conductive polymer is in direct contact with the interior surface within the recess.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application is a continuation application of U.S. patent application Ser. No. 14/531,407 filed on Nov. 3, 2014, which claims the benefit of U.S. provisional patent application Ser. No. 61/917,588 filed on Dec. 18, 2013, the disclosures of which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD OF INVENTION 
       [0002]    The present invention relates to an ignition coil for developing a spark-generating current that is applied to one or more spark plugs of an internal combustion engine. 
       BACKGROUND OF INVENTION 
       [0003]    Ignition coils are known for use in connection with an internal combustion engine such as an automobile engine. Ignition coils typically include a core around which is wound a primary winding. A secondary winding is wound around a secondary winding spool to surround the primary winding such that a high voltage is induced on the secondary winding when an electric current applied to the primary winding is stopped. One end of the secondary winding is a low voltage end which is connected to a ground terminal while the other end of the secondary winding is a high-voltage end which is connected to a high voltage terminal which is in electrical communication with a spark plug, thereby delivering a spark-generating current to the spark plug. 
         [0004]    Connecting the low voltage end and the high-voltage end of the secondary winding to their respective terminals may be complex and costly. In order to attach the low-voltage end of the secondary winding to the low-voltage terminal, the low-voltage end is wrapped onto the low-voltage terminal, and then dipped into solder in order to strip the wire and make the electrical connection. In order to attach the high-voltage end of the secondary winding to the high-voltage terminal, the high-voltage end of the secondary winding is wrapped onto the high-voltage terminal, and then dipped into solder in order to strip the wire and make the electrical connection. Due to the high-voltage terminal being at high-voltage in use, they typically need to be bent and formed to minimize electric field concentrations at the tip. In the case of both the low-voltage end and the high-voltage end of the secondary winding, the terminals need to be assembled to the spool and terminated, then formed in some manner. Furthermore, a resistor is typically added between the secondary winding and the spark plug in order to suppress radio frequency interference (RFI). The addition of a resistor adds additional cost to the system. 
         [0005]    Korean Patent No. KR970005493 teaches using a conductive epoxy to provide electric communication between a terminal pin and an external terminal. However, the terminal pin must still be connected to the high-voltage end of the secondary winding in a conventional manner. 
         [0006]    What is needed is an ignition coil which minimizes or eliminates one or more of the shortcomings as set forth above. 
       SUMMARY OF THE INVENTION 
       [0007]    Briefly described, an ignition coil is provided for delivering a spark-generating current to a spark plug. The ignition coil includes a magnetically-permeable core; a primary winding disposed outward of the core; a secondary winding disposed outward of the primary winding and inductively coupled to the primary winding, the secondary winding terminating at one end thereof in a low-voltage end and terminating at another end thereof in a high-voltage end, wherein at least one of the low-voltage end of the secondary winding and the high-voltage end of the secondary winding is electrically connected directly to a terminal through an electrically conductive polymer; and a case defining an interior having an interior surface such that the core, the primary winding, and the secondary winding are received within the interior of the case, the interior surface defining a recess therein such that the at least one of the low-voltage end of the secondary winding and the high-voltage end of the secondary winding, the terminal, and the electrically conductive polymer are disposed within the recess and such that the electrically conductive polymer is in direct contact with the interior surface within the recess. 
         [0008]    A method is also provided for assembling an ignition coil for delivering a spark-generating current to a spark plug, the ignition coil comprising a magnetically-permeable core, a primary winding disposed outward of the core, a secondary winding disposed outward of the primary winding and inductively coupled to the primary winding, the secondary winding terminating at one end thereof in a low-voltage end and terminating at another end thereof in a high-voltage end, a terminal, and a case defining an interior having an interior surface such that the core, the primary winding, and the secondary winding are received within the interior of the case, the interior surface defining a recess; the method comprising: positioning one of the low-voltage end of the secondary winding and the high-voltage end of the secondary winding and the terminal within the recess; providing an electrically conductive polymer in direct contact with the interior surface within the recess; and using the electrically conductive polymer to directly electrically connect at least one of the low-voltage end of the secondary winding and the high-voltage end of the secondary winding to the terminal through the electrically conductive polymer. 
         [0009]    The ignition coil and method of assembling the ignition coil eliminates the need for processing steps for preparing the ends of the secondary winding and soldering the ends of the secondary winding to respective terminals. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]    This invention will be further described with reference to the accompanying drawings in which: 
           [0011]      FIG. 1  is a simplified cross-section view of an ignition coil in accordance with the present invention taken through a first plane; 
           [0012]      FIG. 2  is a simplified cross-section view of the ignition coil of  FIG. 1  taken through a second plane that is substantially parallel to the first plane through which  FIG. 1  is sectioned; 
           [0013]      FIG. 3  is an elevation view of a case of the ignition coil of  FIGS. 1 and 2  looking in the direction of arrow B of  FIG. 1 ; 
           [0014]      FIG. 4  is an enlarged portion of  FIG. 1  showing a high-voltage end of a secondary winding; 
           [0015]      FIG. 5  is an enlarged portion of  FIG. 2  showing a low-voltage end of the secondary winding; and 
           [0016]      FIG. 6  is an alternative arrangement for a high-voltage recess of the ignition coil in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0017]    Reference will first be made to  FIGS. 1 and 2  which show simplified cross-section views of an ignition coil  10  where  FIGS. 1 and 2  are sectioned by parallel planes. Ignition coil  10  may be controlled by a control unit  12  or the like. Ignition coil  10  is configured for connection to a spark plug  14  that is in threaded engagement with a spark plug opening (not shown) in an internal combustion engine (also not shown). Ignition coil  10  is configured to deliver a high-voltage spark-generating current to spark plug  14 , as shown. Generally, overall spark timing (dwell control) and the like is provided by control unit  12 . One ignition coil  10  may be provided per spark plug  14 . 
         [0018]    Ignition coil  10  may include a magnetically-permeable core  16 , a magnetically-permeable structure  18 , hereinafter referred to as high-permeance structure  18 , configured to provide a high permeance magnetic return path which has a base section  20  and a pair of legs  22  and  24 , a primary winding spool  26 , a primary winding  28 , a quantity of encapsulant  30  such as an epoxy potting material, a secondary winding spool  32 , a secondary winding  34 , a case  36 , a low-voltage connector body  38  having primary terminals  40   a ,  40   b , a high-voltage tower  42 , and a high-voltage terminal  44 . 
         [0019]    Core  16  extends along a core longitudinal axis A. Core  16  may be made of laminated steel plates, compression molded insulated iron particles, or other appropriate material. Core  16  may be any cross-sectional shape known to those of ordinary skill in the art, for example only, oval or circular. 
         [0020]    Primary winding spool  26  is configured to receive and retain primary winding  28 . Primary winding spool  26  is disposed adjacent to and radially outward of core  16  and is preferably in coaxial relationship therewith. Primary winding spool  26  may comprise any one of a number of conventional spool configurations known to those of ordinary skill in the art. In the illustrated embodiment, primary winding spool  26  is configured to receive one continuous primary winding. Primary winding spool  26  may be formed generally of electrical insulating material having properties suitable for use in a relatively high temperature environment. For example, primary winding spool  26  may comprise plastic material such as PPO/PS (e.g., NORYL® available from General Electric) or polybutylene terephthalate (PBT) thermoplastic polyester. It should be understood that there are a variety of alternative materials that may be used for primary winding spool  26 . 
         [0021]    Primary winding  28 , as described above, is wound onto primary winding spool  26 . Primary winding  28  includes first and second ends that are connected to the primary terminals  40   a ,  40   b  in low-voltage connector body  38 . Primary winding  28  is configured to carry a primary current I p  for charging ignition coil  10  upon control of control unit  12 . Primary winding  28  may comprise copper, insulated magnet wire, with a size typically between about 20-23 AWG. 
         [0022]    Secondary winding spool  32  is configured to receive and retain secondary winding  34 . Secondary winding spool  32  is disposed adjacent to and radially outward of the central components comprising core  16 , primary winding spool  26 , and primary winding  28  and, preferably, is in coaxial relationship therewith. Secondary winding spool  32  may comprise any one of a number of conventional spool configurations known to those of ordinary skill in the art. In the illustrated embodiment, secondary winding spool  32  is configured for use with a continuous winding strategy (e.g., progressive winding) where secondary winding  34  is wound uninterrupted around secondary winding spool  32 . However, it should be understood that other known configurations may be employed, such as, for example only, a segmented winding strategy where a plurality of axially spaced ribs on secondary winding spool  32  forms a plurality of channels therebetween. Secondary winding spool  32  may be formed generally of electrical insulating material having properties suitable for use in a relatively high temperature environment. For example, secondary winding spool  32  may comprise plastic material such as PPO/PS (e.g., NORYL available from General Electric) or polybutylene terephthalate (PBT) thermoplastic polyester. It should be understood that there are a variety of alternative materials that may be used for secondary winding spool  32 . Further features of secondary winding spool  32  will be described in greater detail later. 
         [0023]    Secondary winding  34  includes a low-voltage end  46  (shown in  FIG. 2 ) and a high-voltage end  48  (shown in  FIG. 1 ). Low-voltage end  46  may be electrically connected to a low-voltage terminal  50  within case  36  which is connected to ground by way of a ground connection through low-voltage connector body  38 . The electrical connection of low-voltage end  46  to low-voltage terminal  50  will be discussed in greater detail later. High-voltage end  48  is electrically connected to high-voltage terminal  44  as will also be discussed in greater detail later. Secondary winding  34  may be implemented using conventional approaches and material (e.g. copper, insulated magnet wire) known to those of ordinary skill in the art. 
         [0024]    High permeance structure  18  is configured to provide a high permeance magnetic return path for the magnetic flux produced in core  16  during operation of ignition coil  10 . High permeance structure  18  may be formed, for example, from a stack of silicon steel laminations or other adequate magnetic material. As described previously, high permeance structure  18  includes base section  20  and a pair of legs  22  and  24 . Core  16  is positioned between legs  22  and  24  such that core longitudinal axis A passes through legs  22  and  24 . One end of core  16  mates with leg  22  while the other end of core  16  forms a gap with leg  24  where the gap may be in a range of, for example only, about 0.5 mm to about 2 mm. Further features of high permeance structure  18  are described in United States Patent Application Publication No. US 2013/0291844 A1 to Skinner et al., the disclosure of which is incorporated herein by reference in its entirety. 
         [0025]    Reference will continue to be made to  FIGS. 1 and 2  and additional reference will now be made to  FIG. 3  which shows an elevation view of case  36  viewed in the direction of arrow B shown in  FIG. 1 . Case  36  defines a case interior  52  having an interior surface  54 . Core  16 , high permeance structure  18 , primary winding spool  26 , primary winding  28 , secondary winding spool  32 , secondary winding  34 , high-voltage terminal  44 , and low-voltage terminal  50  are located within case interior  52  but are not shown in  FIG. 3 . 
         [0026]    Interior surface  54  of case  36  includes a low-voltage recess  56  therein. Low-voltage recess  56  includes a first low-voltage recess compartment  58  and a second low-voltage recess compartment  60  such that first low-voltage recess compartment  58  and second low-voltage recess compartment  60  are connected to each other by a low-voltage recess channel  62 . Low-voltage end  46  of secondary winding  34  is disposed within first low-voltage recess compartment  58  while low-voltage terminal  50  is disposed within second low-voltage recess compartment  60 . An electrically conductive polymer  64  is disposed within first low-voltage recess compartment  58 , second low-voltage recess compartment  60 , and low-voltage recess channel  62  such that electrically conductive polymer  64  directly places low-voltage end  46  of secondary winding  34  in electrical communication with low-voltage terminal  50 . Electrically conductive polymer  64  may be, for example only, an electrically conductive epoxy or silicone and may contain, for example only about 15% to about 20% by volume carbon black. 
         [0027]    Reference will continue to be made to  FIGS. 1-3  and additional reference will now be made to  FIG. 5  which is an enlarged portion of  FIG. 2 . In order to facilitate insertion of low-voltage end  46  of secondary winding  34  into electrically conductive polymer  64  during assembly, as will be described in greater detail below, low-voltage end  46  of secondary winding  34  may be wound around a low-voltage post  66  in order to provide support thereto. Low-voltage post  66  extends outward from secondary winding spool  32  and may be formed as an integral part thereof. Low-voltage post  66  may include a retention feature, illustrated as low-voltage post step  68 , for preventing low-voltage end  46  of secondary winding  34  from sliding on low-voltage post  66  when low-voltage post  66  and low-voltage end  46  of secondary winding  34  are pushed into electrically conductive polymer  64  during assembly as will be described in greater detail later. While the retention feature has been illustrated as low-voltage post step  68 , it should now be understood that other retention features may be used, for example only, a plurality of steps, ribs, barbs, or surface texture which prevents low-voltage end  46  of secondary winding  34  from sliding on low-voltage post  66  when low-voltage post  66  and low-voltage end  46  of secondary winding  34  are pushed into electrically conductive polymer  64 . 
         [0028]    Again with reference to  FIGS. 1-3 , interior surface  54  of case  36  also includes a high-voltage recess  70  therein. High-voltage recess  70  includes a first high-voltage recess compartment  72  and a second high-voltage recess compartment  74  such that first high-voltage recess compartment  72  and second high-voltage recess compartment  74  are connected to each other by a high-voltage recess channel  76 . High-voltage end  48  of secondary winding  34  is disposed within first high-voltage recess compartment  72  while high-voltage terminal  44  is disposed within second high-voltage recess compartment  74 . Electrically conductive polymer  64  is disposed within first high-voltage recess compartment  72 , second high-voltage recess compartment  74 , and high-voltage recess channel  76  such that electrically conductive polymer  64  directly places high-voltage end  48  of secondary winding  34  in electrical communication with high-voltage terminal  44 . As describe previously, electrically conductive polymer  64  may be, for example only, an electrically conductive epoxy or silicone and may contain, for example only about 15% to about 20% by volume carbon black. 
         [0029]    Reference will continue to be made to  FIGS. 1-3  and additional reference will now be made to  FIG. 4  which is an enlarged portion of  FIG. 1 . Electrically conductive polymer  64  within high-voltage recess channel  76  may be used to form a suppression resistance between first high-voltage recess compartment  72  and second high-voltage recess compartment  74  for suppressing radio-frequency interference (RFI) in use of ignition coil  10 . High-voltage recess channel  76  has a length L 76 , a width W 76  and a height H 76  which may each be tailored to hold a predetermined volume of electrically conductive polymer  64  which results in a predetermined resistance between first high-voltage recess compartment  72  and second high-voltage recess compartment  74 . The predetermined resistance may be, for example only, between about 500 ohms and about 2000 ohms. Using electrically conductive polymer  64  within high-voltage recess channel  76  for suppressing RFI reduces cost by eliminating the need for a separate resistor which is commonly used in ignition coils for suppressing RFI. 
         [0030]    In order to facilitate insertion of high-voltage end  48  of secondary winding  34  into electrically conductive polymer  64  during assembly, as will be described in greater detail below, high-voltage end  48  of secondary winding  34  may be wound around a high-voltage post  78  in order to provide support thereto. High-voltage post  78  extends outward from secondary winding spool  32  and may be formed as an integral part thereof. High-voltage post  78  may include a retention feature, illustrated as high-voltage post step  80 , for preventing high-voltage end  48  of secondary winding  34  from sliding on high-voltage post  78  when high-voltage post  78  and high-voltage end  48  of secondary winding  34  are pushed into electrically conductive polymer  64  during assembly as will be described in greater detail later. While the retention feature has been illustrated as high-voltage post step  80 , it should now be understood that other retention features may be used, for example only, a plurality of steps, ribs, barbs, or surface texture which prevents high-voltage end  48  of secondary winding  34  from sliding on high-voltage post  78  when high-voltage post  78  and high-voltage end  48  of secondary winding  34  are pushed into electrically conductive polymer  64 . 
         [0031]    In order to further enhance the suppression of RFI, high-voltage post  78  may be a piece of steel that is press fit to secondary winding spool  32  rather than being integrally formed with secondary winding spool  32 . Consequently, high-voltage end  48  of secondary winding  34  together with high-voltage post  78  forms an inductor which enhances the suppression of RFI. Alternatively, as shown in  FIG. 4 , an inductor  82  may be embedded within electrically conductive polymer  64  within high-voltage recess  70 . Inductor  82  may be, for example only, an iron core with insulated copper wire wound thereabout. 
         [0032]    Encapsulant  30  may be suitable for providing electrical insulation within ignition coil  10 . In a preferred embodiment, encapsulant  30  may comprise an epoxy potting material. Sufficient encapsulant  30  is introduced in ignition coil  10 , in the illustrated embodiment, to substantially fill the case interior  52 . Encapsulant  30  also provides protection from environmental factors which may be encountered during the service life of ignition coil  10 . There are a number of encapsulant materials known in the art. 
         [0033]    Now with reference to  FIG. 6 , an alternative high-voltage recess  70 ′ is shown where a high-voltage terminal  44 ′ is press fit within high-voltage recess  70 ′. In order to minimize the electric field concentration between high-voltage terminal  44 ′ and the portion of case  36  with which high-voltage terminal  44 ′ is press fit, high-voltage recess  70 ′ is arranged to surround the area of press fit between high-voltage terminal  44 ′ and case  36 . Consequently, electrically conductive polymer  64  will radially surround the portion of case  36  with which high-voltage terminal  44 ′ is press fit thereby providing the same voltage radially inward and outward of the portion of case  36  with which high-voltage terminal  44 ′ is press fit. In this way, the same effect taught in U.S. Pat. No. 8,564,392 to Skinner et al., the disclosure of which is incorporated herein by reference in its entirety, using a properly shaped high-voltage terminal may be achieved while using a high-voltage terminal with a more simple geometry. 
         [0034]    Now with reference to  FIGS. 1-5 , a method of assembling ignition coil  10  will now be described where core  16 , high permeance structure  18 , primary winding spool  26 , primary winding  28 , secondary winding spool  32 , and secondary winding  34  are provided together as a subassembly such that low-voltage end  46  of secondary winding  34  has been wrapped around low-voltage post  66  of secondary winding spool  32  and high-voltage end  48  of secondary winding  34  has been wrapped around high-voltage post  78  of secondary winding spool  32 . First, high-voltage terminal  44  is disposed within second high-voltage recess compartment  74  of case  36 . Next, electrically conductive polymer  64  is dispensed, in liquid form, within low-voltage recess  56  and high-voltage recess  70 . More specifically, electrically conductive polymer  64  is dispensed within first low-voltage recess compartment  58 , second low-voltage recess compartment  60 , low-voltage recess channel  62 , first high-voltage recess compartment  72 , second high-voltage recess compartment  74 , and high-voltage recess channel  76 . It should be noted that high-voltage terminal  44  prevents electrically conductive polymer  64  from escaping from high-voltage recess  70  into high-voltage tower  42 . Subsequently, while electrically conductive polymer  64  is still in liquid form, the subassembly comprising core  16 , high permeance structure  18 , primary winding spool  26 , primary winding  28 , secondary winding spool  32 , and secondary winding  34  is positioned within case interior  52  of case  36  such that low-voltage post  66  together with low-voltage end  46  of secondary winding  34  are pressed into electrically conductive polymer  64  within first low-voltage recess compartment  58  and such that high-voltage post  78  together with high-voltage end  48  of secondary winding  34  are pressed into electrically conductive polymer  64  within first high-voltage recess compartment  72  in the direction of arrow B shown in  FIG. 1 . Low-voltage post step  68  prevents low-voltage end  46  of secondary winding  34  from sliding on low-voltage post  66  as low-voltage end  46  of secondary winding  34  is pressed into electrically conductive polymer  64 . Similarly, high-voltage post step  80  prevents high-voltage end  48  of secondary winding  34  from sliding on high-voltage post  78  as high-voltage end  48  of secondary winding  34  is pressed into electrically conductive polymer  64 . Also while electrically conductive polymer  64  is still in liquid form, low-voltage terminal  50  is pressed into second low-voltage recess compartment  60 . Next, electrically conductive polymer  64  is cured, for example only, by the application of heat such that electrically conductive polymer  64  is no longer a liquid after being cured. After electrically conductive polymer  64  has been cured, encapsulant  30  is dispensed, in liquid form, within case interior  52  to fill the remaining space within case interior  52 . Next encapsulant  30  is cured, for example only, by the application of heat such that encapsulant  30  is no longer a liquid after being cured. 
         [0035]    Electrically connecting low-voltage end  46  of secondary winding  34  to low-voltage terminal  50  directly through electrically conductive polymer  64  eliminates the need for a costly and complex termination arrangement using solder or other similar metal bonding operations. Similarly, electrically connecting high-voltage end  48  of secondary winding  34  to high-voltage terminal  44  directly through electrically conductive polymer  64  eliminates the need for a costly and complex termination arrangement using solder or other similar metal bonding operations. Electrically connecting high-voltage end  48  of secondary winding  34  to high-voltage terminal  44  directly through electrically conductive polymer  64  also allows for simple and cost effective RFI suppression solutions. Furthermore, ignition coils with different placements of high-voltage tower  42  may be needed to meet different packaging requirements. Electrically connecting high-voltage end  48  of secondary winding  34  to high-voltage terminal  44  directly through electrically conductive polymer  64  allows for ignition coils with different placements of high-voltage tower  42  without the need to modify the subassembly comprising core  16 , high permeance structure  18 , primary winding spool  26 , primary winding  28 , and secondary winding spool  32 . Instead case  36 , can be tailored to shorten or lengthen high-voltage recess channel  76  to accommodate the desired location of high-voltage tower  42 . Modifying case  36  may be simpler and less costly than making the necessary modifications to the subassembly comprising core  16 , high permeance structure  18 , primary winding spool  26 , primary winding  28 , and secondary winding spool  32  in order to achieve the desired location of high-voltage tower  42 . 
         [0036]    While a specific configuration of ignition coil  10  has been described, it should be understood that the present invention is applicable for use in a variety of ignition coil configurations. 
         [0037]    While electrically conductive polymer  64  has been described for use with both low-voltage end  46  and high-voltage end  48  of secondary winding  34 , it should now be understood that one end of secondary winding  34  may be connected to its respective terminal using conventional techniques while the other end may be connected to its respective terminal with electrically conductive polymer  64 . 
         [0038]    While electrically conductive polymer  64  has been described for use with both low-voltage end  46  and high-voltage end  48  of secondary winding  34 , it should now be understood that electrically conductive polymers of differing compositions may be used for each end of secondary winding  34 . 
         [0039]    While this invention has been described in terms of preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.