Abstract:
An ignition coil for an internal combustion engine with a compact height and width includes an actuated magnetic portion of an iron core around which a primary coil is wound having an axis line crossing an ignition plug axis line of the internal combustion engine at a right angle; and a switching unit which is disposed at an end of the actuated magnetic portion vertically to the axis line of the actuated magnetic portion and intercepts a primary current flowing through the primary coil. This ignition coil can be manufactured at a greatly reduced cost, compared to the conventional ignition coil in which only one of the height or width is made compact, by reducing the required size of the press mold for the case and by reducing the initial investment for the equipment.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ignition coil for an internal combustion engine to make a sparkling discharge on a ignition plug of the internal combustion engine such as a vehicle engine. 
     2. Description of Related Art 
     FIG. 6 shows a cross sectional view of a conventional ignition coil of an internal combustion engine disclosed in Japanese Utility Model Registration No. 3039423. 
     In the drawing there are shown an iron core  1  forming closed magnetic circuit, a gap  1   a  formed in the closed magnetic circuit, an actuated magnetic portion  1   b  of the iron core around which an primary coil  2  and secondary coil  3  are wound and the axis line  1   c  of the actuated magnetic portion of the iron core. The primary coil  2  is wound around a primary bobbin  2   a  and aligned. The secondary coil  3  also wound around a secondary bobbin (not shown) and aligned. 
     An switching unit  4  is disposed in parallel with the actuated magnetic portion  1   b  and provided with switching element  4   a  such as bipolar transistor and IGBT or the like. The primary coil  2  and a terminal  5   a  of a connector  5  are connected electrically one another with a conductor  6 . A high voltage tower  7  outputs an electrical high voltage generated at the secondary coil  3 . After the above described elements are disposed in a case  8 , they are hardened stiffly in an oven together being immersed in vacuum by injection of a resin  9  through an opening  8   a  of case  8 . 
     FIG. 7 shows a preferred embodiment of the ignition coil, described in FIG. 6, mounted to the internal combustion engine. 
     The drawing shows ignition coil  10  described in FIG. 6, the internal combustion engine  11 , the ignition plug  11   a,  an axis line  11   b  of the ignition plug corresponding to the direction of screwing the ignition plug into the internal combustion engine and an adapter  10   a  connected to the ignition coil  10  wherein it is provided with conductor  10   b  inside and connects a ignition plug  11   a  with ignition coil  10  disposed inside a plug hole  11   c . The ignition coil  10  is disposed at the top of the ignition plug of each cylinder lid wherein the axis line  1   c  of the actuated magnetic portion of the iron core and an axis line  11   b  of the ignition plug are perpendicular to each other. 
     For example, in the case where, as DOHC engine shown in FIG. 8, the ignition coil  10  is mounted in a narrow gap between the projections of the cam shield  50  used for the suction and exhaust, the switching unit  4  is disposed at the top of the actuated magnetic portion  1   b  being parallel to the axis line  1   c  of the actuated magnetic portion as shown in FIG.  9 . The total width of the ignition coil may be minimized into minimum dimension L W  excluding the dimension of the switching unit  4 . 
     In case of mounting the ignition coil  10  to the internal combustion engine of the vehicle of which the hood  51  is low, as shown in FIG. 10, the total height of the IG coil needs to be decreased. As shown in FIG. 11 the switching unit  4  is disposed at the opposite side against the corresponding surface  1   d  of the iron core, sandwiching the activated magnetic portion  1   b,  being parallel to the axis line  1   c  of the activated magnetic portion. By this way the total hight of the ignition coil may be minimized into minimum dimension L H  excluding the dimension of the switching unit  4 . 
     The motion of the ignition coil will be described according to the FIG.  12 . 
     Synchronizing to the ON OFF motion of the ignition signal generated from an engine control unit  20 , the switching element  4   a  repeats the ON and OFF of the primary current to the primary coil  2 . When the primary current starts to flow, the current is not dashed but increased in the form of chopping waves proportional to the time of the current flow by an inductance of a magnetic circuit and the primary current is intercepted instantly by the OFF motion of the ignition signal. In the primary coil  2  an electromotive force is generated at the interception of the primary current. In the secondary coil  3 , a high voltage is generated proportional to the multiple number of the turns of both the primary coil  2  and the secondary coil  3 , this high voltage is supplied to the ignition plug  11   a  through the high voltage tower  7  and the adapter conductor  10   b.    
     A center electrode supplied the high voltage from the ignition coil and a side electrode connected to the earth are disposed at the top end of the ignition plug  11   a  and begins the discharge electricity when the air mixture of the fuel between the electrodes caused an isolation breakage by the supplied high voltage. This discharge is called the inductive discharge. The energy supplied from the primary coil of the ignition coil is injected in a mixed air in each cylinder of the internal combustion engine and forms the firing source in the discharge channel and grows it and finally sets fire to the fuel. The output voltage and energy of the ignition coil are almost proportional to the interception current value of the primary current, therefor in result it is proportional to the flowing time of the electricity. 
     In the process of being converted to the magnetic energy of the iron core, the energy supplied from the primary coil  2  is limited by the magnetic flux saturation of the iron core  1 . The maximum magnetic flux density of the iron core  1  is “magnetic flux density of the magnetic material used for the iron core for instance silicon steel plate etc.”×“an area of the iron core section.” At the present time the required energy for the engine not requiring the large output energy of the ignition coil especially is about 23 mJ and as for the lean burn engine which appears in recent years and the engine which emits a jet inside the cylinder, the required energy is about 45 mJ. As the result of examining it based upon the iron core used for the ignition coil, it is recognized that required section area of the iron core of the actuated magnetic portion is more than 50 mm 2 . This area may realize the energy of more than 23 mJ. 
     Disposing the magnet in the gap with the polarity having an opposite magnetic direction against the actuated magnetic direction of the primary coil and using it from the condition in which the iron core is saturated in the magnetic field having opposite direction against the actuated magnetic direction, the energy accumulated in the magnetic circuit becomes twice as much. This method may realize the energy of about 45 mJ. 
     BRIEF SUMMARY OF THE INVENTION 
     Object of the Invention 
     One of the main elements defining the length of the ignition coil axis direction is the turning length of the primary coil. It corresponds to the dimension L 0  in FIG.  6 . For example in the prior art, the primary coil  2  wound by 150T having the maximum finished outside dimension is about 0.5 mm. In a primary bobbin  2   a  the coil should be a multiple layer like double layers or four layers because the starting position and the ending one of the coil should be coincides with each other. In the prior art the ignition coil has double layer and the length L 0  of the winding wire is 0.55 mm×(150T/2 layer)=37.5 mm. As the length L 1  of the case is about 45 mm, it is recognized that about 90% of it are the dimension of the primary coil. 
     The cylinder span L k  (FIG. 7) of the internal combustion engine of around 1500 cc vehicle is about 90 mm, therefor in the case of mounting the conventional ignition coil shown in FIG. 6 at the condition shown in FIG. 7, considering: 
     Case length L 1 +dimension to mount the iron core L 2 : 16 mm+connector dimension length L 3 : 22 mm+allowance of the dimension for insertion and removal: 10 mm, it is recognized that there is no more space. 
     If we design the ignition coil acceptable for the cylinder span L K  of about 105 mm based upon the consideration of a big cylinder span engine, it is necessary to keep the case length L 1  within 60 mm. 
     The small diameter of the primary coil will bring a short winding wire length L 0 , but the resistance value of the primary coil will increase. In the case of where the voltage of the battery is low at the start of the internal combustion engine, the resistance limits the primary current. Because of the above-described reason enough interception current is not prepared to get the necessary characteristics. Therefor the best diameter of the primary coil exists. 
     In the system of the individual ignition disposing the ignition coil at the top of the ignition plug of each cylinder, the axis direction length of the ignition coil is limited because of the limitation of the cylinder span of the internal combustion engine. In the case of using the ignition coil which includes the switching unit  4  within it, the position should be kept parallel to the axis line  1   c  of the actuated magnetic portion  1   b  of the iron core. 
     In the conventional product the switching unit  4  including the switching element  4   a  inside it and the axis line  1   c  of the actuated magnetic portion  1   b  of the iron core are disposed in parallel each other therefore we had to prepare two kinds of product to dispose the switching unit  4  at the suitable position for both the case of internal combustion engine layout requiring the shortening the total width L W  of the ignition coil as shown in FIG.  8  and the case of internal combustion engine layout requiring the decreasing the total height L H  of the ignition coil shown in FIG.  10 . In near future when the kinds of the product are increased we have to increase the press mold for the case and investment for the equipment corresponding to the many kinds of product. It is the great disadvantage for the production cost. 
     The object of the present invention is the improvement of the above disadvantage. We can apply only one type of the ignition coil for both the case of internal combustion engine layout requiring the shortening the total width of the ignition coil and the case of internal combustion engine layout requiring the decreasing the total height of the ignition coil. Furthermore we submit the product enable to mount it in a severe layout of the internal combustion engine which is limited both for the height and the width. As the result it is the object of the present invention to get the ignition coil for the internal combustion engine which is enable to reduce the cost greatly by reducing the kind of the press mold for the case and investment for the equipment by reducing the kinds of products, and reducing the labor cost for the production process and increase the production quantity for the each equipment. 
     SUMMARY OF THE INVENTION 
     “An ignition coil for an internal combustion engine according to a first embodiment of the invention includes: an actuated magnetic portion of an iron core which has an axis line crossing an ignition plug axis line of the internal combustion engine at a right angle and around which a primary coil is wound; and a switching unit which is disposed at an end of the actuated magnetic portion vertically to the axis line of the actuated magnetic portion and flows and intercepts a primary current flowing through the primary coil.” 
     “The ignition coil for an internal combustion engine according to this embodiment of the invention further comprises a cross section area of the iron core being 50 mm 2  or larger.” 
     “The ignition coil for an internal combustion engine according to the first embodiment of the invention further comprises a case that has the actuated magnetic portion and the switching unit built-in, in which a length of the case in an axis line direction of the actuated magnetic portion is shorter than 60 mm 2 .” 
     “The ignition coil for an internal combustion engine according to the first embodiment of the invention has an iron core made of a magnetic steel plate having direction characteristics in the axis line direction of the actuated magnetic portion the actuated magnetic portion.” 
     “The ignition coil for an internal combustion engine according to the first embodiment has a switching element in the switching unit that intercepts a current at 7.5A or larger.” 
     “The ignition coil for an internal combustion engine according to the first embodiment of the invention has an iron core which is a closed magnetic circuit iron core having a gap.” 
     “The ignition coil for an internal combustion engine according to the first embodiment of the invention has an iron core made of a closed magnetic circuit iron core having a gap, in which the gap of the closed magnetic circuit iron core is formed outside of the actuated magnetic portion.” 
     “The ignition coil for an internal combustion engine according to the first embodiment of the invention further comprises a side iron core portion which is connected to the actuated magnetic portion at a part of the closed magnetic circuit iron core and is disposed between the actuated magnetic portion and the switching unit. This side iron core portion has a cross section that is almost equal to that of the actuated magnetic portion, in which a cross section shape of the side iron core portion is a rectangular shape having a shorter side extending in the direction of the axis line of the actuated magnetic portion.” 
     “The ignition coil for an internal combustion engine according to a second embodiment of the invention includes: an actuated magnetic portion of an iron core which has an axis line crossing an ignition plug axis line of the internal combustion engine at a right angle and around which a primary coil is wound; and a switching unit which is disposed at an end of the actuated magnetic portion vertically to the axis line of the actuated magnetic portion and flows and intercepts a primary current flowing through the primary coil, in which the iron core is an open magnetic circuit iron core.” 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plain cross sectional view showing an ignition coil for an internal combustion engine according to Embodiment 1 of the present invention; 
     FIG. 2 is a side cross sectional view showing the ignition coil for an internal combustion engine according to Embodiment 1 of the present invention; 
     FIG. 3 is a plain cross sectional view showing an ignition coil for an internal combustion engine according to Embodiment 2 of the present invention ; 
     FIG. 4 is a side cross sectional view showing the ignition coil for an internal combustion engine according to Embodiment 2 of the present invention; 
     FIG. 5 is a graphical representation showing a relation between generating magnetic force and magnetic flux density in a silicon steel plate with characteristics of direction and non-direction; 
     FIG. 6 is a cross sectional view showing an example of a conventional ignition coil for an internal combustion engine; 
     FIG. 7 is a view showing an example of mounting of a conventional ignition coil in the internal combustion engine; 
     FIG. 8 is a view showing an example of mounting of a conventional ignition coil in the internal combustion engine; 
     FIG. 9 is a perspective view showing an example of a conventional ignition coil for an internal combustion engine; 
     FIG. 10 is a view showing another example of mounting of the conventional ignition coil in the internal combustion engine; 
     FIG. 11 is a perspective view showing another example of the conventional ignition coil for an internal combustion engine; and 
     FIG. 12 is a circuit diagram showing the conventional ignition coil for an internal combustion engine. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described below according to the drawings. 
     Embodiment 1 
     FIG. 1 is a cross sectional plain view shown the ignition coil of the internal combustion engine according to the embodiment of the present invention. FIG. 2 is a cross sectional side view of FIG.  1 . 
     FIG. 1 shows an iron core  1  forming closed magnetic circuit, a gap  1   a  formed in the closed magnetic circuit, an actuated magnetic portion  1   b  of the iron core around which an primary coil  2  and secondary coil  3  are wound and the axis line  1   c  of the actuated magnetic portion of the iron core. The material of the iron core  1  is a magnetic steel plate having the axis direction characteristics toward the axis line  1   c  of the actuated magnetic portion. The cross section area of the iron core  1  is more than 50 mm 2 . The output energy of the ignition coil corresponding to the required energy for the engine can be obtained easily. The gap  1   a  is formed outside of the actuated magnetic portion  1   b  of the iron core. The magnet  15  is disposed in the gap  1   a  with the polarity having an opposite magnetic direction against the actuated magnetic direction of the iron core of the primary coil  2 . 
     A part of the closed magnetic circuit iron core  1   e  connects to the actuated magnetic portion  1   b  and is disposed between the actuated magnetic portion  1   b  and the switching unit  4 , providing with the side iron core of which the cross section is almost equal to that of the actuated magnetic portion. The form of the cross section of the side iron core is a rectangular shape of which the short axis line coincides with the direction of the axis line of the actuated magnetic portion. 
     The primary coil  2  is wound around a primary bobbin  2   a  and aligned. The secondary coil  3  also wound around a secondary bobbin  3   a  and aligned. An switching unit  4  is disposed at the end portion of the actuated magnetic portion  1   b  vertically to the axis line  1   c  of the actuated magnetic portion and provided with a switching element  4   a  therein such as bipolar transistor, IGBT or the like. The element of the switching unit  4   a  intercepts the current at more than 7.5A. The reference numeral  8  denotes the case which receives each part. The axis line length of the above-described actuated magnetic portion of the case  8  is within 60 mm and by this reason it may be applied to any size of the cylinder span engine. 
     The drawing shows the connector  5  and the terminal  5   a  of the connector  5 . The secondary coil  2 , the terminal  5   a  of the connector  5  and the connecting terminal  4   b  of the switching unit  4  are connected electrically by the conductor  6 . 
     FIG. 2 shows the high voltage tower  7  connected to the secondary coil  3  through the terminal  3   b  and the high voltage tower  8   b  forming a part of the case  8  connected to the adapter  10   a.  The adapter  10   a  is made from an isolation rubber and comprising of the conductor  10   b  therein and connected to the ignition plug (not shown). Reference numeral  9  denotes the injection resin which fixes each part in the case and isolates electrically. 
     The operation of Embodiment 1 is same as the conventional one. Therefore the detailed description will be omitted. 
     An action of each part of the ignition coil will be described in this embodiment. FIG. 5 shows the relation between the generating magnetic force and the magnetic flux density in the silicon steel plate having both the characteristics of the direction and non-direction. 
     The iron core of this embodiment uses the material of the magnetic steel plate having the characteristics of the direction coinciding with the axis line  1   c  of the actuated magnetic portion. Therefore the magnetic flux density of the iron core becomes high rapidly comparing with the case of using non-direction magnetic steel plate. 
     Normally Generating magnetic force (A/m)=Turn number of primary coil n×Primary current I 1   
     Therefore when the primary current is constant the less turn number of the primary coil may get the predetermined magnetic flux density. Accordingly the winding length L 0  of the primary coil may be shortened. 
     In this embodiment, the element of the switching unit  4  which intercepts the current at the high current more than 7.5A is used. As mentioned above: 
     Generating magnetic force of primary coil (A/m)=Turn number of primary coil n×Primary current I 1   
     Therefore when we use it at about 6.5A of the conventional ignition coil, the same generating magnetic force may be obtained by 85% of the turn number of the primary coil. The less turn number of the primary coil may get the predetermined magnetic flux density. Accordingly the winding length L 0  of the primary coil may be shortened. 
     The gap  1   a  of the closed magnetic iron core of this embodiment is formed outside of the actuated magnetic portion  1   b.  When the gap disposed inside the actuated magnetic portion the efficiency of the magnetic circuit is decreased because the magnetic flux is leaked from the primary coil by the influence of the leaked magnetic flux in the gap. As the result, it is recognized by the experiment that at least 10% of the output energy is lost. When the gap  1   a  is disposed inside of the actuated magnetic portion, unless more coils are wound, energy cannot be obtained which is equal to that in the case where there is the gap  1   a  outside. In this embodiment, as the gap  1   a  is formed outside of actuated magnetic portion  1   b,  the less turn number of the primary coil may obtain the same energy. Accordingly the winding length L 0  of the coil may be shortened. 
     In this embodiment of the present invention by using the above-described technology the turn number of the primary coil may be reduced and the winding length of the primary coil may be shortened greatly comparing with the conventional ignition coil. And the switching unit  4  is disposed in the axis direction of the emptied space. 
     In the case of mounting the switching unit  4  at the end of the axis line of the actuated magnetic portion, it is suitable for the switching unit  4  to be arranged vertically to the axis line of the actuated magnetic portion through the side iron core portion  1   e  of the closed magnetic circuit iron core. At that time the cross section area of the side iron core  1   e  is defined same as that of the actuated magnetic portion  1   b.  And the form of the cross section of the side iron core is a rectangular shape of which the short axis line coincides with the direction of the axis line of the actuated magnetic portion, the efficiency is kept at the same level because the cross section area of the magnetic circuit is not changed and Furthermore the total length of the ignition coil may be reduced. 
     Table 1 shows the comparing result of two kinds of the prior arts and the product, which was actually made according to the present invention in FIGS. 9 and 11 described above. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Comparing specification/efficiency of the prior arts and the product made 
               
               
                 according to the present invention 
               
             
          
           
               
                   
                   
                 Prior art 
                   
               
               
                 Specification/ 
                 Prior art Example 1 
                 Example 2 
                 Present invention 
               
               
                 Efficiency 
                 (FIG. 8) 
                 (FIG. 11) 
                 (FIG. 6) 
               
               
                   
               
               
                 Disposition of 
                 Parallel to top of 
                 Parallel to 
                 Vertical to end of 
               
               
                 switching unit 
                 actuated magnetic 
                 side of 
                 actuated magnetic 
               
               
                   
                 portion 
                 actuated 
                 portion 
               
               
                   
                   
                 magnetic 
               
               
                   
                   
                 portion 
               
               
                 Cross section area 
                 72 mm 2   
                 ← 
                 ← 
               
               
                 of actuated 
               
               
                 magnetic portion 
               
               
                 Material of iron 
                 Magnetic steel 
                 ← 
                 Magnetic steel 
               
               
                 core 
                 plate with 
                   
                 plate with 
               
               
                   
                 characteristics of 
                   
                 characteristics of 
               
               
                   
                 non-direction 
                   
                 direction 
               
               
                 Turn number of 
                 150 turn 
                 ← 
                 105 turn 
               
               
                 primary coil 
               
               
                 Length of primary 
                 37.5 mm 
                 ← 
                 26.5 mm 
               
               
                 coil 
               
               
                 Interception 
                 6.5 A 
                 ← 
                 7.5 A 
               
               
                 current 
               
               
                 Gap magnet 
                 Disposition of 
                 ← 
                 Disposition of 
               
               
                   
                 actuated magnetic 
                   
                 actuated magnetic 
               
               
                   
                 portion(IN) 
                   
                 portion(OUT) 
               
               
                 Output energy 
                 55 mJ 
                 ← 
                 ← 
               
               
                 Height of periphery 
                 38 mm 
                 28 mm 
                 ← 
               
               
                 dimension L H   
               
               
                 Width of periphery 
                 35 mm 
                 45 mm 
                 35 mm 
               
               
                 dimension L W   
               
               
                 Length of periphery 
                 81 mm 
                 ← 
                 ← 
               
               
                 dimension L L   
               
               
                 Body weight of 
                 170 g 
                 ← 
                 160 g 
               
               
                 ignition coil 
               
               
                   
               
             
          
         
       
     
     In Table 1, as the prior art  1 , as the switching unit  4  is disposed in parallel at the top of the actuated magnetic portion, the width L W  of the periphery of the ignition coil is narrow but the height L H  of that is high. In the example 2 of the prior art, as the switching unit  4  is disposed in parallel at the side of the actuated magnetic portion, the width L H  of the periphery of the ignition coil is low but the width L W  of that is large. As for the ignition coil of this embodiment, both the height L H  and width L W  of the periphery dimension are equal to each smaller dimension of the conventional ignition coil and the length L L  is also equal to that of conventional one. 
     The ignition coil of this embodiment may be mounted to any internal combustion engine to which the conventional ignition coil is mounted. Furthermore it is clear that we can submit the ignition coil which is able to be mounted to the severe layout of the internal combustion engine which is limited both for the height and the width. This ignition coil is able to reduce the cost greatly by reducing the kind of products for a case or the like and investment for the equipment, and reducing the labor cost for the production process and increase the production quantity for the each equipment. 
     In this embodiment, it is not necessary to adopt all technologies to shorten the axis length of the actuated magnetic portion (the winding length of the primary coil) as shown above. It is reasonable that the suitable technologies should be applied according to the required specification to realize this embodiment. 
     Embodiment 2 
     In Embodiment 1 described above, the ignition coil applied to the closed magnetic circuit iron core was explained. However it may be applied to the open magnetic iron core too. FIG. 3 is a plain cross section view in the case where the open magnetic core is applied. FIG. 4 is a side cross section view of FIG.  3 . As the relation between each referential numeral and number is as same as that of FIGS. 1 and 2, the explanation will be omitted. 
     The difference between FIGS. 1 and 2 and FIGS. 3 and 4 will be explained below. Referential numeral  1  denotes the open magnetic iron core and the referential numeral  15  denotes the magnet which disposed at the left end of the iron core  1  having a polarity of the opposite direction against the actuated magnetic direction of the iron core caused by the primary coil  2 . In this embodiment, the motion of the ignition coil is as same as that of the conventional one. Therefore the detailed explanation will be omitted. 
     Next in this embodiment, the motion of the ignition coil will be explained below. 
     If the ignition coil in the open magnetic circuit has the equal turn number of primary coil to that in the open magnetic circuit, the primary current dash dashes rapidly and the output efficiency becomes low. In order to get the same output efficiency as that in case of the closed magnetic circuit, the turn number of the primary coil shall be multiplied by 1.5 to 2. 
     Recently in order to get a spurting of an air-fuel mixture , the multi spark ignition under the low output energy is being examined. For that application, the ignition coil of this embodiment will be effective. 
     The ignition coil according to this embodiment may be still minimized so that the shape of the ignition coil will be able to be smaller than that of preferred Embodiment 1. Therefore the ignition coil of this embodiment may be mounted to any internal combustion engine to which the conventional ignition coil is mounted. Furthermore it is clear that we can submit the ignition coil which is able to be mounted to the severe layout of the internal combustion engine which is limited both for the height and the width. This ignition coil is able to reduce the cost greatly by reducing the kind of products for the case and investment for the equipment, and reducing the labor cost for the production process and increase the production quantity for the each equipment.