Patent Publication Number: US-11047356-B2

Title: High frequency ignition device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a high frequency ignition device that mainly uses a plasma discharge by alternative current (AC) power. 
     2. Description of the Related Art 
     In recent years, the problem of environmental conservation and fossil fuel depletion has been raised and it becomes an urgent need to deal with these also in automotive industry. As an example for dealing with this, there is a method of dramatically improving the amount of fuel consumption by reducing a pumping loss by the use of exhaust gas recirculation (EGR). 
     However, burnt, gas, which is exhaust air, is nonflammable and has a larger thermal capacity than that of air; and accordingly, if a large amount of burnt, gas is sucked again, by the EGR, a problem exists in that ignition quality and combustion quality deteriorate. 
     As one of solutions of this problem, there is proposed an ignition device shown in, for example, Patent Document 1, in which a high frequency discharge is used to ignite in a wide range, whereby a more stable flame kernel can be formed and combustion quality can be more stabilized. 
     The ignition device disclosed in Patent Document 1 is used, whereby the more stable flame kernel can be formed as compared to a conventional ignition coil and stable combustion can be obtained even when, for example, a great deal of the aforementioned EGR is supplied. Therefore, since a greater deal of the EGR can be supplied and a pumping loss can be reduced as compared to the conventional ignition device by using, for example, the ignition device disclosed in Patent Document 1, there can be obtained an internal combustion engine that can dramatically improve the amount of fuel consumption, 
     Patent Document 1: Japanese Patent Registration No. 5469229 
     The ignition device disclosed in Patent Document 1 conducts a high frequency current supplied from a high frequency power source; and a capacitor and an inductor, which are connected in series with each other and constitute a band pass filter for blocking a high voltage generated in a secondary coil, are arranged in the same package as a primary coil, and the secondary coil. 
     In the ignition device disclosed in Patent Document 1, when dielectric breakdown is caused between main plug gaps of an ignition plug, or when the high frequency power source causes the high frequency current to flow into a spark discharge path generated between the main plug gaps of the ignition plug, an extremely high AC voltage is generated in a path through which the capacitor and the inductor are connected. 
     In the ignition device disclosed in Patent Document 1, in order to prevent, the occurrence of a spark due to the high voltage, the capacitor and the inductor are subjected to insulation treatment by filling of epoxy material or the like, together with the primary coil and the secondary coil. 
     Although the occurrence of the spark or the like between electrodes of the capacitor, between electrodes of the inductor, or to a contiguous low potential portion can be prevented, the AC high voltage causes a corona discharge on the outside of the case filled with the epoxy material or the like and at a place exposed to a gaseous body such as air. 
     A polybutylene terephthalate (PBT)-made case or the like causes problems such as corrosion, deterioration in durability, and the like due to the occurrence of the corona discharge. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to solve the above described problem and, in a device that generates an AC nigh voltage described above, an object of the present invention is to provide a nigh frequency ignition device which prevents the occurrence of a corona discharge at an unnecessary place and can improve reliability and quality of the device. 
     A high frequency ignition device according to the present invention includes: a high frequency power source; a first device having inductance; a second device having capacitance; a discharge GAP composed of a high voltage electrode and a grounding electrode; and a shield device which covers a connection portion between the first device and the second device and is connected to the ground. The high frequency power source supplies AC power to the discharge GAP by using a resonance circuit composed of the first device and the second device and thereby igniting fuel by discharge plasma generated in the discharge GAP. In the high frequency ignition device, at least the first device, the second device, the connection portion, and the shield device are arranged in the same package and are sealed with an insulating substance. 
     According to the nigh frequency ignition device of the present invention, a high energy discharge is efficiently achieved and large discharge plasma is formed by a simple configuration; startability and combustion quality are not impaired even when an ignition plug with a narrow gap is used; and a reduction in weight by highly supercharged downsizing, an improvement in thermal efficiency by improving a compression ratio, and the like can be achieved. 
     Furthermore, effects exist in that the occurrence of a corona discharge at an unnecessary place is prevented and improvements in reliability and quality of the device can be achieved. 
     The foregoing and other objects, features, and advantageous effects of the present invention will become more apparent from detailed description in the following embodiments and description in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic configuration view of a high frequency ignition device according to Embodiment 1 of the present invention; 
         FIG. 2  is a specific circuit configuration diagram of the high frequency ignition device according to Embodiment 1 of the present invention; 
         FIG. 3  is a schematic configuration view of a high frequency ignition device according to Embodiment 2 of the present invention; and 
         FIG. 4  is a specific circuit configuration diagram of the high frequency ignition device according to Embodiment 2 of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiment 1 
       FIG. 1  is a schematic configuration view of a high frequency ignition device according to Embodiment 1 of the present invention. In  FIG. 1 , a high frequency ignition device according to Embodiment 1 of the present invention includes: a high frequency power source  101  serving as an energy supply device; a first device  102  having inductance; a second device  103  having capacitance; a shield device  105  which covers a connection portion  104  between the first device  102  and the second device  103  and is connected to the ground; and a discharge GAP  106  composed of a high voltage electrode  106   a  to be connected to the second device  103  and a grounding electrode  106   b  to be connected to the ground. Furthermore, the first device  102 , the second device  103 , the connection path  104 , and the shield device  105  are arranged together in a case  107  and are sealed with an insulating substance  108 . 
     The first device  102  and the second device  103  constitute a resonance circuit; and the high frequency power source  101  outputs AC power near a resonance frequency of the resonance circuit and supplies the AC power to the discharge GAP  106  via the resonance circuit. The high frequency ignition device according to Embodiment 1 forms discharge plasma in the discharge GAP  106  by the AC power and ignites fuel by the discharge plasma. 
     When the high frequency power source  101  supplies the AC power near the resonance frequency to the resonance circuit, an AC high voltage is generated in the connection path  104  between the first device  102  and the second device  103 . The high voltage forms a high electric field between the connection path and ground potential. It is known that when the high electric field is formed in the air, an ion or an electron in the air is accelerated to cause a corona discharge. 
     The corona discharge acts on the formation of ozone or a bond between molecules; and accordingly, if the corona discharge is generated on the surface of a PBT-made case or the like, the corona discharge causes a harmful effect such as corrosion of the case and deterioration in durability. Therefore, when the PBT-made case or the like is used, the occurrence of the corona discharge on the surface or the like needs to be prevented. 
     In order to prevent the occurrence of the corona discharge such as this, the high frequency ignition device according to Embodiment 1 of the present invention provides a configuration in which the high electric field is not formed in an air layer by covering the connection path  104 , in which the high voltage is generated, between the first device  102  and the second device  103  with the shield device  105  that becomes ground potential and by sealing the connection path  104  and the shield device  105  with the insulation substance  108 . 
     Next, a specific circuit configuration of the high frequency ignition device according to Embodiment 1 of the present invention will be described in detail by using a configuration drawing of  FIG. 2 . The high frequency ignition device shown in  FIG. 2  is mounted on an engine serving as an internal combustion engine of an ordinary vehicle. 
     In  FIG. 2 , the high frequency ignition device according to Embodiment 1 of the present invention includes: a control device  201 ; a battery  202 ; a DC/DC converter  203 ; an inverter  204 ; a resonance device  205 ; an ignition coil  206 ; and an ignition plug  207 . 
     The resonance device  205  is composed of an inductor  208 , a capacitor  209 , and the shield device  105 . 
     The battery  202 , the DC/DC converter  203 , and the inverter  204  collectively correspond to the high frequency power source  101  of  FIG. 1 ; and, similarly, the inductor  208  corresponds to the first device  102 ; the capacitor  209  corresponds to the second device  103 ; and the ignition plug  207  corresponds to the discharge GAP  106 . 
     The battery  202  is for use in vehicles and is charged to approximately 12 volts DC, The inductor  208  is approximately 100 microhenries and the capacitor  209  is approximately 50 picofarads. Then, the inductor  208  and the capacitor  209  form a series resonance circuit and a resonance frequency thereof is approximately 2 megahertz. 
     The DC/DC converter  203  boosts 12 volts DC of the battery  202  to a voltage of approximately 200 volts DC. 
     Fuel is supplied to a combustion chamber for operating an engine; and the control device  201  gives instruction so as to output a high voltage to the ignition coil  206  via a path D at an appropriate timing at which a piston becomes near a top dead center, for example, at 20 degrees before the top dead center, and applies the high voltage to a high voltage electrode  207   a  of the ignition plug  207 . If the high voltage exceeds a dielectric breakdown voltage, dielectric breakdown occurs between electrodes  207   c  of the ignition plug  207  and a spark discharge path is formed. 
     When a spark discharge is formed between the electrodes  207   c  of the ignition plug  207 , the inverter  204  converts 200 volts DC boosted by the DC/DC converter  203  into 200 volts AC (peak value) near 2 megahertz that is the resonance frequency. 
     Further, the 200 volts AC is boosted to approximately 1 kilovolt AC by a transformer  210  whose winding turns ratio is approximately 5 times, and then supplied to the spark discharge path between the electrodes  207   c  of the ignition plug  207 . 
     If the AC power is supplied to the spark discharge path, the spark discharge is enhanced and a wide range of extremely strong thermal plasma is formed. By this plasma, the fuel can be ignited even in a fuel state where air/fuel ratio is large, in which ignition cannot be performed by only the spark discharge by the ignition coil  206 , or even in a fuel state containing a great deal of EGR. 
     When AC power is supplied from the inverter  204  to the series resonance circuit, an AC high voltage of not less than several kilovolts is generated in a connection path  211  between the inductor  208  and the capacitor  209 . 
     As described above, an extremely high voltage is applied to the inductor  208  or the capacitor  209 . Thus, such a component is arranged in the PBT case or the like and is subjected to insulation treatment by filling of the epoxy material or the like in the conventional device in order to prevent the occurrence of leakage due to the spark. 
     However, the corona discharge occurred on the surface of the PBT case clue to the high voltage cannot be prevented. 
     In the high frequency ignition device according to Embodiment 1 of the present invention, the shield device  105  which is connected to the ground potential and covers the connection path  211  between the inductor  208  and the capacitor  209  is arranged in a PBT case  212  together with the inductor  208  and the capacitor  209  and is sealed with epoxy resin  213 , whereby the high electric field is not formed in the air layer. 
     Although the high electric field is formed between the connection path  211  between the inductor  208  and the capacitor  209  and the shield device  105  connected to the ground, the connection path  211  and the shield device  105  are sealed with the epoxy resin  213 ; and therefore, the ion, the electron, and the like are not sufficiently accelerated and the occurrence of the corona discharge in the case  212  can be prevented. Furthermore, since potential of the shield device  105  lowers to the ground potential, the high voltage is not generated on the surface of the PBT case  212 ; and therefore, the high electric field is not formed on the outside of the case  212  and the occurrence of the corona discharge can be prevented. 
     The connection path  211  between the inductor  208  and the capacitor  209  and the shield device  105  are electrically coupled and thereby having a capacitance component. If its capacitance value becomes large and, more particularly in this Embodiment 1, if a capacitance value of the capacitor  209  becomes larger than 50 picofarads, a rate at which the AC power is supplied to the discharge path decreases, the AC power flows out to the ground directly via the capacitance due to the shield device  105 , and a loss extremely increases. Thus, this capacitance value needs to be smaller than at least the capacitance value of the device corresponding to the second device  103  so as to be small as much as possible. 
     In order to decrease the capacitance value composed of the connection path  211  and the shield device  105 , for example, the distance between the connection path  211  and shield device  105  is widened as much as possible and/or the epoxy resin  213  to be filled is made small in dielectric constant. Then, in order to reduce the surface area of a metal portion of the shield device  105  as much as possible, it is conceivable to provide a net-like structure or a punching metal structure having a plurality of holes etc. 
     If the size of the mesh or the size of the hole of the punching metal of the shield device  105  is excessively large, the electric filed leaks out to the outside and the corona discharge is likely to be generated. The electric field strength at the inception of the corona discharge is substantially approximately 5 megavolts/meter under circumstances of atmospheric pressure air. Atmospheric pressure variation or the like is taken into account for this electric field strength, and the size of the hole to be formed in the metal and the structure of the mesh are adjusted with a margin so that the electric field strength to be leaked outside the case is not more than 4 megavolts/meter. 
     As described above, according to Embodiment 1 of the present invention, the portion at which the AC high voltage is generated and the shield device, which covers the portion at which the AC high voltage is generated and is connected to the ground, are arranged together in the case and are sealed with the insulation substance, so that the high electric field is not formed in the air layer and the high electric field is not formed on the outside of the case; and therefore, the occurrence of the corona discharge at the inside/outside of the case can be prevented and durability and reliability of the device can be improved. 
     Furthermore, since the shield device is the net-like structure, power consumption of the high frequency ignition device can be reduced. 
       FIG. 3  is a schematic configuration view of a high frequency ignition device according to Embodiment 2 of the present invention. In  FIG. 3 , a high frequency ignition device according to Embodiment 2 of the present invention includes: a high frequency power source  101  serving as an energy supply device; a first device  102  having inductance; a high voltage electrode  301   a  to be connected to the first device  102 ; a grounding electrode  301   b  to be connected to the ground; a discharge GAP  301   c  located between the high voltage electrode  301   a  and the grounding electrode  301   b ; and a shield device  303  which covers a connection path  302  between the first device  102  and the high voltage electrode  301   a  and is connected to the ground. 
     The connection path  302  and the shield device  303  are electrically coupled and thereby having a capacitance component. 
     Furthermore, the first device  102 , the connection path  302 , the shield device  303 , and the high voltage electrode  301   a  are sealed together with an insulating substance  304 . 
     An inductance component of the first device  102  and the capacitance component by the connection path  302  and the shield device  303  constitute a resonance circuit; and the high frequency power source  101  outputs AC power near a resonance frequency of the resonance circuit and supplies the AC power to the high voltage electrode  301   a . The high frequency ignition device according to Embodiment 2 of the present invention forms discharge plasma in the discharge GAP  301   c  by the AC power and ignites fuel by the discharge plasma. 
     Next, a specific circuit configuration of the high frequency ignition device according to Embodiment 2 of the present invention will be described in detail by using a configuration drawing of  FIG. 4 . The high frequency ignition device shown in  FIG. 4  is mounted on an engine serving as an internal combustion engine of an ordinary vehicle. 
     In  FIG. 4 , the high frequency ignition device according to Embodiment 2 of the present invention includes: a control device  401 ; a battery  202 ; a DC/DC converter  203 ; an inverter  204 ; a resonance device  402 ; and the grounding electrode  301   b.    
     The resonance device  402  includes: an inductor  403 ; the connection path  302 ; the shield device  303 ; and the high voltage electrode  301   a . Then, these are sealed together and fixed with insulating alumina ceramics  404 . 
     The battery  202 , the DC/DC converter  203 , and the inverter  204  collectively correspond to the high frequency power source  101  of  FIG. 3 ; and, similarly, the inductor  403  corresponds to the first device  102 . 
     The battery  202  is for use in vehicles and is charged to approximately 12 volts DC. The inductor  403  is approximately 1 henry; a capacitance value composed of the connection path  302  and the shield device  303  is approximately 10 picofarads; and these form a series resonance circuit and a resonance frequency thereof is approximately 50 kilohertz. The DC/DC converter  203  boosts 12 volts DC of the battery  202  to a voltage of approximately 200 volts DC. 
     Fuel is supplied to a combustion chamber for operating an engine; and the inverter  204  converts 200 volts DC boosted by the DC/DC converter  203  into 200 volts AC (peak value) near 50 kilohertz at an appropriate timing at which a piston becomes near a top dead center, for example, at 20 degrees before the top dead center. Further, the 200 volts AC is boosted to approximately 1 kilovolt AC by a transformer  210  whose winding turns ratio is approximately 5 times, and then supplied to the inductor  403 . 
     When the AC power near the resonance frequency is supplied to the resonance device  402 , the supplied AC power is further boosted by a resonance phenomenon to generate an AC high voltage not less than several tens kilovolts at the connection path  302  and the high voltage electrode  301   a.    
     When the AC high voltage is supplied to the high voltage electrode  301   a , a wide range of discharge plasma which is a kind of a corona discharge and is referred to as a dielectric barrier discharge is formed mainly in a direction toward the grounding electrode  301   b  in the vicinity of the discharge GAP  301   c . By the wide range of the discharge plasma, the fuel can be ignited even in a fuel state large in air/fuel ratio in which ignition cannot be performed by only a spark discharge by an ignition coil (not shown in the drawing) or even in a fuel state containing a great deal of EGR. 
     If the corona discharge is generated at an unnecessary place, the barrier discharge cannot be generated in the discharge GAP  301   c  or the barrier discharge becomes extremely weak; and accordingly, the fuel cannot be stably ignited or a loss increases and thereby increasing power consumption of the high frequency ignition device. 
     According to the high frequency ignition device according to Embodiment 2 of the present invention, a portion at which the AC nigh voltage is generated by the resonance phenomenon in the resonance device  402  is covered by the shield device  303  except for the high voltage electrode  301   a ; and therefore, the occurrence of the corona discharge can be prevented at an unnecessary place, except for the vicinity of the discharge GAP  301   c.    
     Furthermore, the capacitance value that is electrical coupling capacitance between the connection path  302  and the shield device  303  is decreased as much as possible in order to lower the power consumption of the high frequency ignition device and to efficiently increase a resonance voltage to be applied to the high voltage electrode  301   a.    
     More specifically, in the series resonance circuit, if a real resistance value of the resonance circuit is decreased or the capacitance value of the resonance circuit is decreased, it is known that the resonance voltage is efficiently increased. Therefore, in order to decrease the capacitance value that is the electrical coupling capacitance between the connection path  302  and the shield device  303 , the distance between the connection path  302  and the shield device  303  is increased and/or a dielectric constant of insulation material to be filled is increased. Then, in order to reduce the size of a metal portion of a shield device  303 , the surface area of the metal is reduced by providing a net-like structure or a punching metal structure having a plurality of holes. 
     If the size of the mesh or the size of the hole of the punching metal of the shield device  303  is excessively large, the electric filed leaks out to the outside and the corona discharge is likely to be generated. The electric field strength at the inception of the corona discharge is substantially approximately 5 megavolts/meter under circumstances of atmospheric pressure air. Atmospheric pressure variation or the like is taken into account for this electric field strength, and the size of the hole to be formed in the metal and the structure of the mesh are adjusted with a margin so that the electric field strength to be leaked outside a case is not more than 4 megavolts/meter. 
     As described above, according to the high frequency ignition device according to Embodiment 2 of the present invention, since the portion at which the AC high voltage is generated is covered by the shield device to be connected to the ground except for the high voltage electrode, the occurrence of the corona discharge at the unnecessary place can be prevented and the barrier discharge can be efficiently and stably generated in the discharge GAP  301   c ; and therefore, the fuel can be stably ignited even in the fuel state large in air/fuel ratio or even in the fuel state containing a great deal of EGR. 
     Furthermore, the occurrence of unnecessary corona discharge can be prevented; and therefore, the power consumption of the high frequency ignition device can be reduced. 
     Incidentally, the present invention can freely combine the respective embodiments and appropriately modify and/or omit the respective embodiments, within the scope of the present invention.