Abstract:
An ignition coil apparatus for high-frequency discharge includes: a primary coil that generates and accumulates a flux; a secondary coil that is magnetically coupled to the primary coil so as to generate a predetermined high voltage when energy of the accumulated flux is released and connected at one end to a high-voltage terminal used to supply energy to an external apparatus; a capacitor that is connected to the high-voltage terminal and prevents passing of the high voltage; and an inductor that, together with the capacitor, allows passing of a predetermined frequency component alone. The primary coil, the secondary coil, the capacitor, and the inductor are installed within a same package.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an ignition apparatus chiefly used to run an internal combustion engine, and more particularly, to an ignition coil apparatus for high-frequency discharge employed in an ignition apparatus for a spark-ignited internal combustion engine. 
         [0003]    1. Background Art 
         [0004]    Problems are arising in terms of environmental conservation and depletion of fuel in recent years and it is urgently necessary for the automobile industry to address these problems. As an example of an effort in addressing these problems, there is a method of markedly improving fuel consumption by means of engine downsizing and weight saving with the use of a supercharger. 
         [0005]    It is known that in a highly supercharged state, an internal pressure of an engine combustion chamber rises extremely high even when fuel is not burning and it therefore becomes difficult to generate a spark discharge to start combustion. One of the reasons underlying this difficulty is that a required voltage to trigger a breakdown between a high-voltage electrode and a GND electrode (gap) of a spark plug becomes so high that it exceeds a withstanding voltage value of an insulator portion of the spark plug. 
         [0006]    A study to increase the withstanding voltage of the insulator portion is being conducted to solve this problem. It is, however, difficult to ensure a withstanding voltage sufficiently high for the required voltage in the actual condition. Under these circumstances, there is no other countermeasure than to narrow a gap spacing of the spark plug. 
         [0007]    Narrowing the gap of the spark plug, however, increases influences of an anti-inflammatory action by the electrode portion in turn. Hence, there arises another problem that start-up performance and combustion characteristics become poor. 
         [0008]    This problem may be eliminated by avoiding such influences, more specifically, by providing more energy than thermal energy consumed by the anti-inflammatory action, that is, at the electrode portion with a spark discharge or by allowing combustion to take place at the remotest point from the electrode. For example, an ignition apparatus disclosed in Patent Document 1 is proposed. 
         [0009]    The ignition apparatus disclosed in Patent Document 1 is an apparatus capable of generating a high-energy spark discharge and forming a discharge plasma spreading in a wider range than that by a normal spark discharge by generating a spark discharge across a spark plug gap using an ignition coil in the related art and by flowing a high-frequency current into a path of the spark discharge via a diode and a mixer. 
       CITED LIST  
     Patent Document 
       [0010]    Patent Document 1: JP-A-2011-099410 
         [0011]    The ignition apparatus in the related art disclosed in Patent Document 1 is to decouple and couple a high voltage system and a high current system using a diode. It is, however, known that lead-free high-voltage diodes are difficult to obtain and not acceptable in terms of mass-productivity. Also, efficiency of the high-voltage diodes is poor because a half-wave of AC energy is cut off. 
       SUMMARY OF THE INVENTION 
       [0012]    The invention is devised to solve the problems of the apparatus in the related art as discussed above and has an object to provide an ignition coil apparatus for high-frequency discharge of a simple configuration that is not only capable of obtaining a high-energy discharge efficiently but also capable of forming a large discharge plasma easily. 
         [0013]    An ignition coil apparatus for high-frequency discharge according to an aspect of the invention includes: a primary coil that generates and accumulates a flux when a current is flown; a secondary coil that is magnetically coupled to the primary coil so as to generate a predetermined high voltage when energy of the accumulated flux is released and connected at one end to a high-voltage terminal used to supply energy to an external apparatus; a capacitor that is connected to the high-voltage terminal and prevents passing of the high voltage; and an inductor that is connected to the capacitor and, together with the capacitor, forms a band-pass filter that allows passing of a predetermined frequency component alone. The primary coil, the secondary coil, the capacitor, and the inductor are installed within a same package. 
         [0014]    The ignition coil apparatus for high-frequency discharge configured as above is capable of supplying a high AC discharge current between electrodes of a spark plug in fast cycles. Therefore, the ignition coil apparatus for high-frequency discharge is of a simple configuration and not only capable of obtaining a high-energy discharge efficiently but also capable of forming a large discharge plasma. Hence, even when a spark plug with a narrow gap is used, start-up performance and combustion characteristics are not deteriorated. Consequently, it becomes possible to reduce a weight by highly boosted downsizing and to enhance thermal efficiency by making a compression ratio higher. Accordingly, fuel used to run the internal combustion engine can be reduced markedly and an emission of CO 2  is reduced considerably. A contribution to environmental conservation can be thus made. 
         [0015]    The foregoing and other objects features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a view showing a circuit configuration of a spark-ignited ignition apparatus using an ignition coil apparatus for high-frequency discharge according to a first embodiment of the invention; 
           [0017]      FIGS. 2A and 2B  are views showing a specific configuration of the ignition coil apparatus for high-frequency discharge according to the first embodiment of the invention; and 
           [0018]      FIGS. 3A and 3B  are views showing a specific configuration of an ignition coil apparatus for high-frequency discharge according to a second embodiment of the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    Hereinafter, preferred embodiments of an ignition coil apparatus for high-frequency discharge (hereinafter, also referred to simply as the ignition coil apparatus) of the invention will be described with reference to the drawings. Like components are labeled with like reference numerals in the respective drawings. 
       First Embodiment 
       [0020]    An ignition coil apparatus for high-frequency discharge of the invention relates to a spark-ignited ignition apparatus that generates a spark discharge across a main plug gap of a spark plug with a high voltage generated by an ignition coil apparatus and forms a large discharge plasma across the main plug gap by flowing a high-frequency AC current into a path of the spark discharge. 
         [0021]      FIG. 1  is a view showing a circuit configuration of a spark-ignited ignition apparatus using the ignition coil apparatus according to a first embodiment of the invention. Referring to  FIG. 1 , the spark-ignited ignition apparatus using the ignition coil apparatus for high-frequency discharge according to the first embodiment of the invention includes a spark plug  101 , an ignition coil apparatus  102  that applies a predetermined high voltage and supplies a high-frequency AC current to the spark plug  101 , a high-frequency power supply  103  that supplies high-frequency energy to the ignition coil apparatus  102 , and a control apparatus  104  that controls operations of the ignition coil apparatus  102  and the high-frequency power supply  103 . 
         [0022]    The spark plug  101  includes a high-voltage electrode  101   a  as a first electrode and an outer electrode  101   b  as a second electrode opposing the high-voltage electrode  101   a  with the main plug gas, which is a predetermined interval, in between. 
         [0023]    The ignition coil apparatus  102  includes a primary coil  111  and a secondary coil  112  that are magnetically coupled to each other via a core  118 , a switching element  114  that controls energization of the primary coil  111 , a drive device-A  113  that drives the switching element  114 , and a resistance device  115  that suppresses noises of a capacitive discharge system generated when a breakdown is triggered across the main plug gap of the spark plug  101 . 
         [0024]    The ignition coil apparatus  102  also includes a capacitor  116  and an inductor  117  that together form a band-pass filter that allows a high-frequency current supplied from the high-frequency power supply  103  to pass and blocks a high voltage generated in the secondary coil  112  so as not to be applied to the high-frequency power supply  103 . 
         [0025]    As is shown in  FIG. 1 , it is necessary for the band-pass filter to install the inductor  117  on the side of the high-frequency power supply  103  and the capacitor  116  on the side of the spark plug  101 . When these components are installed inversely, an extremely high voltage is generated across the inductor  117  and it becomes difficult to design a withstanding voltage of the inductor  117 . In addition, because a higher voltage is applied also to the capacitor  116 , it also becomes difficult to design a withstanding voltage of the capacitor  116 . Further, both the inductor  117  and the capacitor  116  are increased in size. Consequently, mass-productivity becomes poor. 
         [0026]    A capacitor with a capacity value smaller than 100 pF is selected as the capacitor  116 . The reason underlying this selection is that when a capacitor with a capacity value larger than 100 pF is selected, a high voltage generated across the secondary coil  112  passes through the capacitor  116  and is applied to the inductor  117  and the high-frequency power supply  103 . Because a high-voltage capacitor becomes larger as a capacity value increases, a capacitor with a capacity value of about 50 pF is selected in the first embodiment. 
         [0027]    One end of the secondary coil  112  is connected to the high-voltage electrode  101   a  of the spark plug  101  via the resistance device  115 . One end of the capacitor  116  is directly connected to the high-voltage electrode  101   a  of the spark plug  101 . 
         [0028]    The resistance device  115  is used to suppress noises and may be omitted in a case where an amount of generated noises is small depending on a structure or a wiring condition of the engine. In this case, one end of the secondary coil  112  is directly connected to the high-voltage electrode  101   a  of the spark plug  101  and one end of the capacitor  116  is also directly connected to the high-voltage electrode  101   a  of the spark plug  101 . 
         [0029]    By installing the primary coil  111 , the secondary coil  112 , the capacitor  116 , and the inductor  117  within a same package in the ignition coil apparatus  102 , a contribution can be made to reducing power consumption by a loss reduction, making the system simpler, reducing the cost, and suppressing noises. 
         [0030]    The switching element  114  and the driver device-A  113  may be installed inside the ignition coil apparatus  102  with the purpose to reduce noises and increase efficiency. Alternatively, with the purpose to downsize the engine and lower the gravity center thereof, the switching elements  114  and the driver device-A  113  may be installed on the outside of the ignition coil apparatus  102 , for example, inside the control device  104  or inside the high-frequency power supply  103 , so that the ignition coil apparatus  102  is reduced in size and weight. 
         [0031]    A specific configuration example of the ignition coil apparatus for high-frequency discharge according to the first embodiment of the invention will now be described. 
         [0032]      FIGS. 2A and 2B  are views used to describe a configuration of the ignition coil apparatus  102  according to the first embodiment of the invention. Referring to  FIGS. 2A and 2B , the primary coil  111 , the secondary coil  112 , the core  118 , the capacitor  116 A, the inductor  117 , the resistance device  115 A, a driver device-B  203  are installed inside the ignition coil apparatus  102 . The driver device-B  203  is a device formed of the switching element  114  and the driver device-A  113  of  FIG. 1  installed within a same package. 
         [0033]    A connector portion  201  of  FIG. 2B  is a connector portion of the ignition coil apparatus  102  and has a battery terminal, a GND terminal, a terminal to be connected to the control device  104 , and a terminal to be connected to the high-frequency power supply  103 . 
         [0034]    One side of the primary coil  111  is connected to the battery terminal and the other side is connected to the GND terminal via the switching element  114  in the driver device-B  203 . Also, the switching element  114  in the driver device-B  203  is connected to the driver device-A  113  in the driver device-B  203 . The driver device-A  113  is connected to the terminal to be connected to the control device  104  in the connector portion  201 . 
         [0035]    The primary coil  111  is installed circumferentially about the core  118  and further the secondary coil  112  is wound around the primary coil  111 . Owing to this configuration, the primary coil  111  and the secondary coil  112  are brought into a magnetically coupled state. 
         [0036]    By forming the core  118  to have so-called a closed magnetic path completely closed or having a clearance as small as about 1 mm, a better magnetically coupled state can be obtained. It thus becomes possible to reduce the number of turns of the primary coil  111  and the secondary coil  112 . When configured in this manner, a DC resistance component in the path can be suppressed, and therefore a loss caused by heat generation is reduced and energy can be transmitted efficiently. It thus becomes possible to reduce power consumption of the ignition apparatus. In addition, the closed magnetic path is formed, and by closing the magnetic path, flux energy leaking to the outside can be minimized. Hence, not only does it become possible to transmit energy efficiently, but it also becomes possible to reduce the occurrence of noises and magnetic interference with another apparatus. 
         [0037]    One side of the secondary coil  112  is connected to the battery terminal in the connector portion  201  and the other side is connected to one end of the resistance device  115 A. The resistance device  115 A is inserted into and connected to a terminal  206 . The terminal  206  is connected to a spring  204  and a sleeve  205 A as well as to one end of the capacitor  116 A. 
         [0038]    The spring  204  and the sleeve  205 A are connected to the high-voltage electrode  101   a  of the spark plug  101 . The spring  204  is provided to maintain a connection to the high-voltage electrode  101   a  of the spark plug  101  even in a circumstance where the apparatus moves severely. 
         [0039]    The sleeve  205 A is provided to maintain a connection to the high-voltage electrode  101   a  of the spark plug  101  even in a circumstance where the apparatus moves severely. Also, the sleeve  205 A is furnished with a function of reducing an impedance value (inductance value and DC resistance value) across a path from the resistance device  115 A to the high-voltage electrode  101   a  of the spark plug  101 . Hence, because the inductance value and the DC resistance value across this path can be reduced, it becomes possible to transmit energy efficiently by reducing a loss caused by heat generation. Consequently, it becomes possible to reduce power consumption of the apparatus. 
         [0040]    One side of the inductor  117  is connected to the terminal to be connected to the high-frequency power supply  103  in the connector portion  201  and the other side is connected to the capacitor  116 A. The other side of the capacitor  116 A is connected to the terminal  206 . 
         [0041]    A voltage as high as about 10 kV is generated between the inductor  117  and the capacitor  116 A and attention should be paid so as not to install a low-potential conductor near these components. The ignition coil apparatus  102  may be downsized by installing the inductor  117  on the outside of the ignition coil apparatus  102 . In this case, however, it becomes difficult to secure a withstanding voltage of the connector portion  201  and a special connector is required. Hence, it is highly likely that the costs of the ignition coil apparatus  102  are increased. In view of this inconvenience, the apparatus of the first embodiment is configured in such a manner that both the inductor  117  and the capacitor  116 A are installed inside the ignition coil apparatus  102  and insulating treatment is applied using an epoxy material filled therein. 
         [0042]    Also, by installing the inductor  117  so as to hardly magnetically interfere with the primary coil  111  and the secondary coil  112 , it becomes possible to stabilize the apparatus performance and upgrade the quality. More specifically, the inductor  117  is installed in such a manner that fluxes generated from the conductor  117  and the primary and secondary coils  111  and  112  are not oriented parallel to each other. For example, as is shown in  FIG. 2A , the inductor  117  is installed so that the fluxes are oriented perpendicularly to each other. 
         [0043]    By using a hollow core or a core of an open magnetic path type as the inductor  117 , the ignition coil apparatus  102  can be downsized. The reason underlying this downsizing is as follows. That is, because a high-frequency AC current of about several amperes flows through the inductor  117 , magnetic saturation readily occurs in a core of a closed magnetic path type. When an allowance is made to prevent magnetic saturation, a huge core becomes necessary. Naturally, the ignition coil apparatus  102  enclosing such a huge core is increased in size. 
         [0044]    As has been described, the ignition coil apparatus for high-frequency discharge according to the first embodiment of the invention is of a simple and compact configuration and not only capable of obtaining a high-energy discharge efficiently but also capable of forming a large discharge plasma. Hence, even when a spark plug with a narrow gap is used, start-up performance and combustion characteristics are not deteriorated. Consequently, it becomes possible to reduce a weight by highly boosted downsizing and to enhance thermal efficiency by making a compression ratio higher. 
         [0045]    Accordingly, fuel used to run the internal combustion engine can be reduced markedly and an emission of CO 2  is reduced considerably. A contribution to environmental conservation can be thus made. 
       Second Embodiment 
       [0046]    An ignition coil apparatus for high-frequency discharge according to a second embodiment of the invention will now be described. In the first embodiment above, the resistance device  115 A and the capacitor  116 A are installed on the outside of a plug hole. On the contrary, in the second embodiment, these resistance device and capacitor are installed inside the plug hole so that radiation noises can be suppressed further. 
         [0047]      FIGS. 3A and 3B  are views showing a configuration of an ignition coil apparatus  102  for high-frequency discharge according to the second embodiment of the invention. 
         [0048]    Referring to  FIGS. 3A and 3B , because the circuit configuration and the components installed inside the ignition coil apparatus  102  are the same as those in the first embodiment above, the description will not be repeated and only a difference will be described in detail. 
         [0049]    In the second embodiment, as is shown in  FIG. 3A , a resistance device  115 B and a capacitor  116 B are installed inside a plug hole  301 . 
         [0050]    The capacitor  116 B is of a cylindrical shape as is shown in  FIG. 3B . One end of an electrode is an inner surface  302 A of the cylinder and the other end is an outer surface  302 B of the cylinder. 
         [0051]    One end of the resistance device  115 B is connected to the secondary coil  112  and the other end is inserted into a terminal  206  and electrically connected to the terminal  206 . The terminal  206  is inserted into the cylinder forming the capacitor  116 B and electrically and physically comes into contact with the electrode  302 A on the inner surface. In addition, the terminal  206  is installed so as to also come into contact with a spring  204  and a sleeve  205 B. 
         [0052]    The electrode  302 B on the outer surface of the cylinder, which is an electrode at the other end of the capacitor  116 B, is connected to the inductor  117  and therefore connected further to the high-frequency power supply  103 . 
         [0053]    The configuration as above can shorten a path through which to flow a current of a capacitive discharge system as a noise source to a shortest length. Also, by keeping the path inside the plug hole  301 , it becomes possible to prevent leakage of noises to the outside of the engine. 
         [0054]    As has been described, the ignition coil apparatus for high-frequency discharge according to the second embodiment of the invention is of a simple and compact configuration and not only capable of obtaining a high-energy discharge efficiently but also forming a large discharge plasma while reducing radiation noises. Hence, even when a spark plug with a narrow gap is used, start-up performance and combustion characteristics are not deteriorated. Consequently, it becomes possible to reduce a weight by highly boosted downsizing and to enhance thermal efficiency by making a compression ratio higher. 
         [0055]    Accordingly, fuel used to run the internal combustion engine can be reduced markedly and an emission of CO 2  is reduced considerably. A contribution to environmental conservation can be thus made. 
         [0056]    The ignition coil apparatus for high-frequency discharge of the invention is mounted on an automobile, a motorcycle, an outboard engine, and other special machines using an internal combustion engine and ignites fuel in a reliable manner to run the internal combustion engine efficiently. Hence, the ignition coil apparatus for high-frequency discharge of the invention is useful in solving a fuel depletion problem and in conserving the environment. 
         [0057]    Various modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this is not limited to the illustrative embodiments set forth herein.