JP2012219707A - Ignition device and ignition system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make high ignitability and a long service lifetime of a plasma jet ignition plug compatible with each other.SOLUTION: An ignition device 31 is configured to be used in a plasma jet ignition plug 1 and includes: a voltage applying part 41 for applying a voltage to a gap 29 of the ignition plug 1; and a capacitor 51 connected in parallel to the ignition plug 1 between the ignition plug 1 and the voltage applying part 41. Electric charges stored in the capacitor 51 are inputted to the gap 29 by the voltage applying part 41 in order to generate a capacitive discharge in a cavity 28. The capacitance of the capacitor 51 can be changed to two types of capacitance values different in magnitude. The ignition device also includes a capacitance control part 62 configured to switch between a first ignition mode and a second ignition mode, in which a capacitive discharge current is smaller than that of in the first ignition mode, by changing the capacitance of the capacitor 51.

Description

  The present invention relates to an ignition device for a plasma jet ignition plug that generates plasma and ignites an air-fuel mixture or the like.

  Conventionally, in a combustion apparatus such as an internal combustion engine, an ignition plug that ignites an air-fuel mixture by spark discharge is used. In recent years, in order to meet the demand for higher output and lower fuel consumption of combustion devices, as a spark plug that spreads quickly and can be ignited more reliably even with a lean mixture with a higher ignition limit air-fuel ratio, Plasma jet spark plugs have been proposed.

  Generally, a plasma jet ignition plug is disposed on a cylindrical insulator having a shaft hole, a center electrode inserted into the shaft hole with the tip surface being more immersed than the tip surface of the insulator, and an outer periphery of the insulator. And a ring-shaped ground electrode joined to the tip of the metal shell. Further, the plasma jet ignition plug has a space (cavity portion) formed by the front end surface of the center electrode and the inner peripheral surface of the shaft hole, and the cavity portion passes through a through hole formed in the ground electrode. It is designed to communicate with the outside.

  In such a plasma jet ignition plug, the air-fuel mixture is ignited as follows. First, a voltage is applied to the gap formed between the center electrode and the ground electrode, and a spark discharge is generated in the gap to cause dielectric breakdown. After that, by supplying electric power to the gap, the gas in the cavity is turned into plasma, and plasma is generated inside the cavity. Then, the generated plasma is ejected from the opening of the cavity portion, so that the air-fuel mixture is ignited.

  In order to generate plasma in the plasma jet ignition plug, a general plasma jet ignition plug ignition device applies a voltage to the gap to generate a spark discharge, and supplies power to the gap. And a power input unit having a power source for charging the capacitor. In addition, diodes are provided between the plasma jet ignition plug and the voltage application unit, and between the plasma jet ignition plug and the power application unit, respectively. Inflow is prevented (see, for example, Patent Document 1).

  By the way, as a technique for realizing even better ignitability, it is conceivable to increase the current flowing at the time of capacitive discharge in the gap by increasing the capacitance of the capacitor, thereby generating a larger plasma. However, when the input energy is increased, the inrush current at the initial stage of capacitive discharge increases, and the center electrode and the ground electrode are easily consumed. As a result, the voltage (required voltage) necessary for spark discharge may increase rapidly.

  Therefore, by using a variable capacitor, the consumption of the center electrode and the like is suppressed by increasing the capacitance of the capacitor only when high ignitability is required based on the operating conditions of the internal combustion engine. It may be possible to extend the service life. A general variable capacitor changes its own capacitance by operating a knob or the like, and the capacitance changes almost linearly. Therefore, the capacitance can be set to various values according to the operating conditions.

JP 2010-218768 A

  However, since the operating conditions change in a very short time, if the capacitance of the capacitor can be set to different values, the capacitance of the capacitor can be made to follow changes in the operating conditions. As a result, when high ignitability is required, there is a risk that problems such as the inability to sufficiently increase the electrostatic capacity may occur.

  The present invention has been made in view of the above circumstances, and its purpose is to increase the changing speed of the capacitance by allowing the capacitance of the capacitor to be set to two different values. To provide an ignition device and an ignition system capable of following the capacitance of a capacitor with respect to changes in operating conditions, and thus achieving both high ignitability and long life in a plasma jet ignition plug. is there.

  Hereinafter, each configuration suitable for solving the above-described object will be described in terms of items. In addition, the effect specific to the corresponding structure is added as needed.

Configuration 1. The ignition device of this configuration is used for a plasma jet ignition plug having a center electrode, a ground electrode, and a cavity that surrounds at least a part of a gap formed between the electrodes and forms a discharge space. An ignition device to be used,
A voltage application unit for applying a voltage to the gap;
Between the plasma jet ignition plug and the voltage application unit, comprising a capacitor connected in parallel with the plasma jet ignition plug,
The electric charge stored in the capacitor by the voltage application unit is thrown into the gap, causing a capacitive discharge in the cavity,
The capacitance of the capacitor can be changed to two different capacitance values,
A capacitance control unit is provided that can switch between a first ignition mode and a second ignition mode having a smaller capacity discharge current than the first ignition mode by changing the capacitance of the capacitor.

  According to the above configuration 1, the capacitance of the capacitor can be changed to a value that is different in magnitude. The first ignition mode in which the capacity discharge current is relatively large and the second ignition in which the capacity discharge current is relatively small by the capacity control unit. The mode can be switched. Therefore, the first ignition mode is set only when high ignitability is required, and the second ignition mode is set in the normal state, thereby effectively suppressing consumption of the center electrode and the like while realizing excellent ignitability. Can do. In addition, since the capacitance of the capacitor can be set only to two different values, the capacitance change speed can be increased, and the capacitance can be changed quickly according to the operating conditions. Can do. As a result, both high ignitability and long life can be effectively realized in the plasma jet ignition plug.

  Furthermore, according to the configuration 1, the capacitor is provided in parallel with the spark plug, and when a voltage is applied to the gap from the voltage application unit, both the spark plug and the capacitor are charged. Yes. Accordingly, it is not necessary to provide a separate power source for generating plasma or a diode for preventing backflow, and the apparatus can be downsized and the manufacturing cost can be reduced.

  In addition, if a diode is provided, resonance of power supplied due to the presence of the diode is suppressed and energy input to the gap is reduced. However, if a diode is not provided, resonance of power is suppressed. The situation will not occur. As a result, the input energy to the spark plug can be increased, and the ignitability can be further improved.

  Configuration 2. The ignition device of this configuration is characterized in that, in the above configuration 1, the capacitance of the capacitor is 35 pF or less in the second ignition mode.

  According to the above configuration 2, the capacitance of the capacitor in the second ignition mode is sufficiently reduced to 35 pF or less. Therefore, the inrush current at the time of capacitive discharge can be sufficiently reduced, and consumption of the center electrode and the like can be more reliably suppressed. As a result, the life of the spark plug can be further extended.

  Configuration 3. The ignition device of this configuration is characterized in that, in the above configuration 1 or 2, the capacitance of the capacitor is 50 pF or more in the first ignition mode.

  According to the configuration 3, the capacitance of the capacitor in the first ignition mode is 50 pF or more. Therefore, the plasma generation amount can be increased sufficiently, and the ignitability can be dramatically improved in the first ignition mode that requires high ignitability.

Configuration 4. The ignition device of this configuration is configured in any one of the above configurations 1 to 3, wherein the voltage application unit is configured to be able to change output energy to the plasma jet ignition plug,
The output energy from the voltage application unit in the first ignition mode is greater than the output energy from the voltage application unit in the second ignition mode.

  When the capacitance of the capacitor is relatively large, if the output energy from the voltage application unit is small, sufficient charge cannot be stored in the spark plug, and the potential difference between the center electrode and the ground electrode causes spark discharge. Therefore, there is a possibility that the voltage (required voltage) necessary for the above will not be exceeded. In this case, since no spark discharge is generated, power cannot be supplied from the capacitor to the gap, and plasma cannot be generated.

  In view of this point, according to Configuration 4, in the first ignition mode in which the capacitance of the capacitor is relatively large, the output energy from the voltage application unit is larger than the output energy in the second ignition mode. Is done. Therefore, even in the first ignition mode in which the capacitance of the capacitor is relatively large, a sufficient charge can be stored in the spark plug, and spark discharge can be more reliably generated. Further, in the second ignition mode, the discharge energy can be kept low, so that consumption of the center electrode and the like can be effectively suppressed.

Configuration 5. The ignition device of this configuration is any one of the above configurations 1 to 4, wherein the capacitor is
At least in the first ignition mode, a first electrode and a second electrode arranged with an insulating dielectric interposed therebetween;
At least one of the first electrode and the second electrode is movable, the movable electrode is disposed at a predetermined first position in the first ignition mode, and predetermined in the second ignition mode. An electromagnetic switch disposed at the second position of
The capacitance control unit operates the electromagnetic switch to change the capacitance of the capacitor by switching the arrangement position of the movable electrode to the first position or the second position. .

  According to the configuration 5, by using the electromagnetic switch, the electrode arrangement position can be instantaneously switched to the first position or the second position, and the capacitance between the first electrode and the second electrode (that is, the capacitor) Can be changed very quickly. Therefore, the capacitance of the capacitor can be changed more quickly with respect to changes in operating conditions and the like. As a result, high ignitability and long life in the spark plug can be realized more effectively.

Configuration 6. In the ignition device according to this configuration, in the configuration 5, when the movable electrode is disposed at the first position, the first electrode and the second electrode are in contact with the dielectric with the dielectric interposed therebetween. And
When the movable electrode is disposed at the second position, at least one of the first electrode and the second electrode is separated from the dielectric.

  According to the configuration 6, in the first ignition mode, the first electrode and the second electrode are in contact with the dielectric, while in the second ignition mode, a gap is formed between at least one of the electrodes and the dielectric. The Therefore, the capacitance of the capacitor can be changed greatly between the two ignition modes without significantly increasing the electrode moving distance. As a result, the effects of the configuration 1 and the like can be more reliably exhibited while reducing the size of the capacitor and the ignition device.

Configuration 7. In the ignition device of this configuration, in the configuration 5 or 6, the first electrode and the second electrode face each other with the dielectric interposed therebetween,
The opposing surfaces of the first electrode and the dielectric and the opposing surfaces of the second electrode and the dielectric are flat surfaces.

  According to Configuration 7, since the first electrode and the second electrode are in surface contact with the dielectric without any gap in the first ignition mode, the opposing areas of the first electrode and the second electrode are not increased so much, The capacitance of the capacitor in the one ignition mode can be made sufficiently large. Therefore, the effects of the above-described configurations can be more reliably exhibited while reducing the size of the ignition device (capacitor).

Configuration 8. In the ignition device according to this configuration, in the configuration 5 or 6, one of the first electrode and the second electrode has a cylindrical shape, and the one electrode is aligned in the radial direction by the electromagnetic switch. Configured to be separable,
The cylindrical dielectric is disposed on the inner periphery of the one electrode,
The other electrode of the first electrode and the second electrode is disposed on the inner periphery of the dielectric,
When the one electrode is disposed at the first position, the one electrode contacts the dielectric;
When the one electrode is disposed at the second position, at least a part of the one electrode is separated from the dielectric.

  According to the configuration 8, the capacitor can be formed in a long and narrow column shape. Therefore, the ignition device can be easily arranged in a cylindrical plug hole provided in the internal combustion engine or the like.

  If the ignition device is arranged in the plug hole, the plug hole functions as a noise shield, and it is possible to prevent a situation in which the operation of the capacitor becomes abnormal due to the influence of noise.

Configuration 9 The ignition device of the present configuration is the above-described configuration 5, wherein one of the first electrode and the second electrode has a cylindrical shape,
The cylindrical dielectric is disposed on the inner periphery of the one electrode,
The other electrode of the first electrode and the second electrode is disposed on the inner periphery of the dielectric,
The electromagnetic switch enables at least one of the first electrode and the second electrode to move along the axial direction of the dielectric,
The opposing area of the first electrode and the second electrode when the movable electrode is arranged at the first position is equal to the first area when the movable electrode is arranged at the second position. The area is larger than the facing area of one electrode and the second electrode.

  According to the configuration 9, the capacitor can be formed in a columnar shape, and the moving direction of the electrode is the axial direction, so that the capacitor can be made thinner. Therefore, the ignition device can be arranged more easily in the plug hole.

  Configuration 10 The ignition device of this configuration is any one of the above configurations 5 to 9, and insulates a gap between at least one of the first electrode and the second electrode and the dielectric at least in the second ignition mode. It is characterized by being filled with oil.

  According to the configuration 10, since the gap between at least one of the first electrode and the second electrode and the dielectric is filled with the insulating oil in at least the second ignition mode, current leakage between the two electrodes is prevented. It can be effectively suppressed. As a result, the voltage resistance of the capacitor can be improved.

  Configuration 11 The ignition device of this configuration is characterized in that, in any one of the above configurations 1 to 10, the capacitor is covered with an insulating case made of insulating rubber or insulating resin.

  According to the configuration 11, current leakage between the capacitor and a metal object (for example, a plug hole) disposed around the capacitor can be prevented more reliably, and the voltage resistance of the capacitor can be further improved. be able to.

Configuration 12 An ignition system of this configuration includes the ignition device according to any one of claims 1 to 11,
And a plasma jet ignition plug to which electric power is supplied from the ignition device.

  According to the configuration 12, the same effects as the configuration 1 and the like are achieved.

It is a block diagram which shows schematic structure of an ignition system. It is a partially broken front view which shows schematic structure of a spark plug. (A) is a cross-sectional schematic diagram of the capacitor in the first ignition mode, and (b) is a schematic cross-sectional diagram of the capacitor in the second ignition mode. (A) is a graph showing transition of gap voltage, discharge current, etc. when the output energy of the voltage application unit is small and the capacitance of the capacitor is large, and (b) is a graph showing the output energy of the voltage application unit. It is a graph which shows transition of the voltage etc. of the gap | interval in the case where the electrostatic capacitance of a capacitor | condenser is large. (A) is a graph which shows transition of the voltage of a gap | interval, etc. when the output energy of a voltage application part is large and the electrostatic capacitance of a capacitor | condenser is large, (b) is a capacitor | condenser with small output energy of a voltage application part. It is a graph which shows transition of the voltage etc. of the gap | interval in case the electrostatic capacitance of is small. (A), (b) is a cross-sectional schematic diagram which shows another example of a capacitor | condenser. It is a graph which shows the test result of the durability evaluation test in sample X equivalent to a comparative example, and sample Y equivalent to an example. It is a graph which shows the test result of the durability evaluation test in the sample which changed the electrostatic capacitance of the capacitor | condenser in 2nd ignition mode variously. It is a graph which shows the test result of the ignitability evaluation test in the sample which changed the electrostatic capacitance of the capacitor | condenser in 1st ignition mode variously. It is a graph which shows the test result of the withstand voltage evaluation test in samples A-E. (A), (b) is a cross-sectional schematic diagram which shows the structure of the capacitor | condenser in another embodiment. (A), (b) is a cross-sectional schematic diagram which shows structures, such as a capacitor | condenser, in another embodiment.

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of an ignition system 101 having a plasma jet ignition plug (hereinafter referred to as “ignition plug”) 1 and an ignition device 31. In FIG. 1, only one spark plug 1 is shown, but the internal combustion engine EN is provided with a plurality of cylinders, and the spark plugs 1 are provided corresponding to the respective cylinders. An ignition device 31 is provided for each spark plug 1.

  First, a schematic configuration of the spark plug 1 will be described. FIG. 2 is a partially cutaway front view showing the spark plug 1. In FIG. 2, the direction of the axis CL1 of the spark plug 1 is the vertical direction in the drawing, the lower side is the front end side of the spark plug 1, and the upper side is the rear end side.

  The spark plug 1 is composed of a cylindrical insulator 2, a cylindrical metal shell 3 that holds the insulator 2, and the like.

  As is well known, the insulator 2 is formed by firing alumina or the like, and in its outer portion, a rear end side body portion 10 formed on the rear end side, and a front end than the rear end side body portion 10. A large-diameter portion 11 that protrudes radially outward on the side, a middle body portion 12 that is smaller in diameter than the large-diameter portion 11, and a tip portion that is more distal than the middle body portion 12. The leg length part 13 formed in diameter smaller than this on the side is provided. In addition, of the insulator 2, the large diameter portion 11, the middle trunk portion 12, and the leg long portion 13 are accommodated inside the metal shell 3. A tapered step portion 14 is formed at the connecting portion between the middle body portion 12 and the long leg portion 13, and the insulator 2 is locked to the metal shell 3 at the step portion 14.

  Further, the insulator 2 is formed with a shaft hole 4 penetrating along the axis CL1, and a center electrode 5 is inserted and fixed to the tip end side of the shaft hole 4. The center electrode 5 includes an inner layer 5A made of copper, a copper alloy or the like having excellent thermal conductivity, and an outer layer made of a Ni alloy containing nickel (Ni) as a main component (for example, Inconel (trade name) 600 or 601). 5B is provided. Further, the center electrode 5 has a rod shape (cylindrical shape) as a whole, and the tip thereof is disposed on the rear end side of the tip surface of the insulator 2. In addition, tungsten (W), iridium (Ir), platinum (in order to improve wear resistance, at a portion of the center electrode 5 extending from the tip to the rear end side in the axis CL1 direction at least 0.3 mm. An electrode tip 5C formed of Pt), nickel (Ni), or an alloy containing at least one of these metals as a main component is provided.

  A terminal electrode 6 is inserted and fixed on the rear end side of the shaft hole 4 in a state of protruding from the rear end of the insulator 2.

  Further, a cylindrical glass seal portion 9 is disposed between the center electrode 5 and the terminal electrode 6. The glass seal portion 9 electrically connects the center electrode 5 and the terminal electrode 6, and the center electrode 5 and the terminal electrode 6 are fixed to the insulator 2.

  In addition, the metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and a spark plug 1 is attached to the outer peripheral surface of the metal shell 3 (for example, an internal combustion engine or a fuel cell reformer). A threaded portion (male threaded portion) 15 for attachment to the hole is formed. In addition, a seat portion 16 is formed on the outer peripheral surface on the rear end side of the screw portion 15, and a ring-shaped gasket 18 is fitted on the screw neck 17 on the rear end of the screw portion 15. Further, on the rear end side of the metal shell 3, a tool engaging portion 19 having a hexagonal cross section for engaging a tool such as a wrench when the metal shell 3 is attached to the combustion device is provided. 1 is provided with a caulking portion 20 for holding the insulator 2. In addition, an annular engagement portion 21 is formed on the outer periphery of the distal end portion of the metal shell 3 so as to protrude toward the distal end side in the axis CL1 direction. A ground electrode 27 is joined. The center electrode 5 and the metal shell 3 that are opposed to each other with the insulator 2 interposed therebetween are configured so as to be able to store electric charges like a capacitor, and the spark plug 1 includes the center electrode 5 and the metal shell 3. And the capacitance corresponding to the material of the insulator 2 and the like.

  A tapered step portion 22 for locking the insulator 2 is provided on the inner peripheral surface of the metal shell 3. The insulator 2 is inserted from the rear end side to the front end side of the metal shell 3, and the rear end of the metal shell 3 is engaged with the step 14 of the metal shell 3. It is fixed to the metal shell 3 by caulking the opening on the side inward in the radial direction, that is, by forming the caulking portion 20. An annular plate packing 23 is interposed between the step portions 14 and 22 of both the insulator 2 and the metal shell 3. As a result, the airtightness in the combustion chamber is maintained, and the fuel gas that enters the gap between the long leg portion 13 of the insulator 2 and the inner peripheral surface of the metal shell 3 is prevented from leaking outside.

  Further, in order to make the sealing by caulking more complete, annular ring members 24 and 25 are interposed between the metal shell 3 and the insulator 2 on the rear end side of the metal shell 3, and the ring member 24. , 25 is filled with powder of talc (talc) 26. That is, the metal shell 3 holds the insulator 2 via the plate packing 23, the ring members 24 and 25, and the talc 26.

  Further, a ground electrode 27 having a disk shape is joined to the front end portion of the metal shell 3, which is positioned on the front side of the insulator 2 in the direction of the axis CL <b> 1. The ground electrode 27 is joined to the metal shell 3 by welding its outer peripheral portion to the engagement portion 21 while being engaged with the engagement portion 21 of the metal shell 3. In the present embodiment, the ground electrode 27 is made of W, Ir, Pt, Ni, or an alloy containing at least one of these metals as a main component.

  In addition, the ground electrode 27 has a through hole 27H penetrating in the thickness direction at the center thereof. A cavity 28, which is a cylindrical space formed by the inner peripheral surface of the shaft hole 4 and the tip surface of the center electrode 5 and opens toward the tip side, communicates with the outside via the through hole 27H. Has been.

  In the spark plug 1 described above, by applying power to the gap 29 formed between the center electrode 5 and the ground electrode 27, plasma is generated in the cavity portion 28 and plasma is ejected from the through hole 27H. It has become. Next, the configuration of the ignition device 31 that supplies power to the gap 29 of the ignition plug 1 will be described.

  As shown in FIG. 1, the ignition device 31 includes a voltage application unit 41 for applying a voltage to the gap 29, and a capacitor 51 that can be charged by the voltage application unit 41.

  The voltage application unit 41 includes a primary coil 42, a secondary coil 43, a core 44, and an igniter 45.

  The primary coil 42 is wound around the core 44. One end of the primary coil 42 is connected to the battery VA for power supply, and the other end is connected to the igniter 45. The secondary coil 43 is wound around the core 44, one end of which is connected between the primary coil 42 and the battery VA, and the other end is connected to the terminal electrode 6 of the spark plug 1. Yes.

  In addition, the igniter 45 is formed by a predetermined transistor, and switches between supply and stop of power supply from the battery VA to the primary coil 42 in accordance with an energization signal input from a predetermined electronic control unit (ECU) 61. . When applying a high voltage to the spark plug 1, first, the energization signal from the ECU 61 is turned on, and a current is passed from the battery VA to the primary coil 42 while the energization signal is on. The flowing current (primary current) increases in proportion to the energization time (the on time of the energization signal). When the primary current flows, a magnetic field is formed around the core 44. In this state, the current from the battery VA to the primary coil 42 is stopped by switching the energization signal from the ECU 61 from on to off. When the current stops, the magnetic field of the core 44 changes, and a negative secondary voltage (several to several tens of kV) is generated in the secondary coil 43 by self-dielectric action. When this secondary voltage is applied to the spark plug 1 (terminal electrode 6), a spark discharge is generated in the gap 29.

  Note that the magnitude of the generated secondary voltage changes with a positive correlation with the magnitude of the primary current. In the present embodiment, the ECU 61 is configured to be able to change the ON time of the energization signal, and as a result, the magnitude of the primary current and thus the output energy to the spark plug 1 can be changed.

  The capacitor 51 is charged with power supplied from the voltage application unit 41 (secondary coil 43) and supplies the charged power to the gap 29 of the spark plug 1. One end of the capacitor 51 is connected between the spark plug 1 and the voltage application unit 41, and the other end is grounded (that is, connected in parallel with the spark plug 1).

  Further, as shown in FIGS. 3A and 3B, the capacitor 51 includes a capacitor component 52, an electrode hold 53, and an electromagnetic switch 54.

  The capacitor component 52 includes a first electrode 521, a second electrode 522, and a dielectric 523 disposed between both the electrodes 521 and 522.

  The first electrode 521 has a flat plate shape and faces the second electrode 522 with a part of the dielectric 523 interposed therebetween. The second electrode 522 has a flat plate portion 522A facing one side of the first electrode 521 at one end portion of the second electrode 522, and extends in a direction perpendicular to the flat plate portion 522A to the other end portion of the second electrode 522. And a supported portion 522B supported by 53. The first electrode 521 is grounded, and the second electrode 522 is connected between the spark plug 1 and the voltage application unit 41 so that the output voltage from the voltage application unit 41 is applied.

  The dielectric 523 is formed of a predetermined insulating material, and at least a portion sandwiched between the electrodes 521 and 522 is a flat plate. Accordingly, in the present embodiment, the opposing surfaces of the first electrode 521 and the dielectric 523 and the opposing surfaces of the second electrode 522 and the dielectric 523 are flat.

  The electrode hold 53 is formed of a predetermined insulating material and can be moved relative to the first electrode 521 and the dielectric 523 along a direction orthogonal to the flat portion of the first electrode 521 and the dielectric 523. It is configured. In addition, an elastic member (spring member) 56 that can expand and contract along the relative movement direction is provided between the electrode hold 53 and the dielectric 523, and the electrode hold 53 is attached to the dielectric 523 side. It is in a state of power. Further, a permanent magnet 57 is fixed to the electrode hold 53.

  The electromagnetic switch 54 is formed by winding a conductive metal wire around a metal core (for example, an iron core) and faces the permanent magnet 57 on the opposite side of the dielectric 523 with the electrode hold 53 interposed therebetween. It is arranged at the position to do. Further, the metal wire of the electromagnetic switch 54 is connected to the ECU 61, and on / off of energization to the electromagnetic switch 54 (its metal wire) can be switched by a capacity control unit 62 (see FIG. 1) provided in the ECU 61. It is configured.

  Here, when the energization of the electromagnetic switch 54 is turned off, as shown in FIG. 3A, the electrode hold 53 moves to the dielectric 523 side by the urging force of the elastic member 56, and as a result, the second electrode 522. Is arranged at a predetermined first position P1. When the second electrode 522 is disposed at the first position P1, the second electrode 522 contacts the dielectric 523, and both the first electrode 521 and the second electrode 522 contact the dielectric 523 with the dielectric 523 interposed therebetween. Will be. As a result, the distance between the electrodes 521 and 522 is relatively small, and no gap is interposed between the second electrode 522 and the dielectric 523, so that the electrostatic capacity of the capacitor 51 (capacitor component 52). The capacity is relatively large.

  On the other hand, when energization of the electromagnetic switch 54 is turned on, a magnetic force is generated in the electromagnetic switch 54 and the permanent magnet 57 is attracted to the electromagnetic switch 54. As a result, the electrode hold 53 moves to the side away from the dielectric 523, and as a result, the second electrode 522 is disposed at the predetermined second position P2. When the second electrode 522 is disposed at the second position P2, the distance between the electrodes 521 and 522 is relatively large, and the dielectric constant between the second electrode 522 and the dielectric 523 is higher than that of the dielectric 523. A low air layer will be interposed. As a result, the capacitance of the capacitor 51 (capacitor component 52) is relatively small. That is, the capacitor 51 can change its own capacitance to two different values.

  Note that the capacity control unit 62 detects various states of the internal combustion engine (not shown) (for example, a combustion pressure sensor, an air-fuel ratio sensor, a temperature sensor, etc.) and a voltage (insulation) required to generate a spark discharge in the gap 29. Based on information such as the breakdown voltage), the ignition mode of the spark plug 1 is switched to one of the first ignition mode and the second ignition mode by switching on / off the energization of the electromagnetic switch 54. In other words, in the first ignition mode (when it is necessary to improve the ignitability compared to normal times), the energization of the electromagnetic switch 54 is turned off and the capacitance of the capacitor 51 is increased. As a result, the electric charge stored in the capacitor 51 is input to the gap 29, and when a capacitive discharge occurs in the cavity 28, the current flowing through the gap 29 (capacitive discharge current) is relatively large. On the other hand, in the second ignition mode (normal time), energization of the electromagnetic switch 54 is turned on, and the capacitance of the capacitor 51 is made relatively small. As a result, when the electric charge stored in the capacitor 51 is thrown into the gap 29, the capacity discharge current is made relatively small.

  Further, by adjusting the constituent material of the dielectric 523 (the relative dielectric constant of the dielectric 523), the facing area of both electrodes 521 and 522, the moving distance of the second electrode 522, etc., the static of the capacitor 51 in the second ignition mode The electric capacity is set to 35 pF or less, and the capacitance of the capacitor 51 in the first ignition mode is set to 50 pF or more. In the present embodiment, the capacitance of the capacitor 51 in the second ignition mode is equal to or greater than the capacitance of the spark plug 1, and the capacitance of the capacitor 51 in the first ignition mode is the consumption suppression of the center electrode 5 and the like. In order to achieve this, it is set to 500 pF or less.

  In addition, as described above, the ECU 61 is configured to be able to change the ON time of the energization signal. In the present embodiment, the ECU 61 determines the ON time of the energization signal in the first ignition mode as the energization in the second mode. The signal is configured to increase more than the on-time of the signal. In other words, the ECU 61 is configured to make the output energy from the voltage application unit 41 in the first ignition mode larger than the output energy from the voltage application unit 41 in the second ignition mode.

  Here, the output energy from the voltage application unit 41 is changed for the following reason. That is, if the output energy from the voltage application unit 41 is relatively small when the capacitance of the capacitor 51 is relatively large, there is a possibility that sufficient charge cannot be stored in the capacitor 51 and the spark plug 1. If charging becomes insufficient, the voltage (potential difference) in the gap 29 falls below the dielectric breakdown voltage (required voltage) in the gap 29, and spark discharge occurs in the gap 29 as shown in FIG. (At this time, the voltage waveform of the gap 29 indicates the capability waveform of the voltage application unit 41), and as a result, power cannot be supplied from the capacitor 51 to the gap 29. On the other hand, if the configuration is such that the output energy from the voltage application unit 41 is constantly increased, even if the capacitance of the capacitor 51 is relatively large, sufficient charge is provided to both the spark plug 1 and the capacitor 51. Can be stored. For this reason, as shown in FIG. 4B, a spark discharge can be generated in the gap 29. As a result, the spark 29 can be used as a trigger to supply power from the capacitor 51 to the gap 29 to generate plasma. it can. However, in this case, since the discharge energy increases due to, for example, prolonged induction discharge that occurs after capacitive discharge, the center electrode 5 and the like are rapidly consumed, and the spark discharge cannot be performed at an early stage. (In order to promote gasification of plasma and increase plasma generation efficiency, it is important to increase the capacity discharge current. Even if the induction discharge current is increased, the ignitability can be improved. Is scarce).

  In view of this point, in this embodiment, in the first ignition mode in which the capacitance of the capacitor 51 is relatively large, as shown in FIG. By doing so, the output energy from the voltage application part 41 is increased. As a result, charging of the spark plug 1 and the capacitor 51 can be performed more reliably, and as a result, spark discharge and plasma generation can be more reliably generated. On the other hand, in the second ignition mode in which the electrostatic capacity of the capacitor 51 is relatively small, as shown in FIG. The output energy of is relatively small. Thereby, it is possible to prevent the central electrode 5 and the like from being rapidly consumed.

  In the present embodiment, the output energy from the voltage application unit 41 in the second ignition mode is sufficiently larger than the amount of power that can be stored in the capacitor 51 and the spark plug 1 in the second ignition mode (for example, the amount of power In the second ignition mode, spark discharge and plasma generation are more reliably generated.

  Returning to FIG. 3, the capacitor 51 is covered with an insulating case 55 made of insulating rubber or insulating resin (for example, silicone rubber, fluororubber, fluororesin, etc. having excellent heat resistance) in order to improve the withstand voltage. ing. In order to further improve the withstand voltage, as shown in FIGS. 6A and 6B, the capacitor component 52 is covered with an inner case 58 made of an insulating resin or the like, and the inner case 58 is covered. May be filled with insulating oil 59. In this case, in the first ignition mode (FIG. 6A), the insulating oil 59 is hardly interposed between the second electrode 522 and the dielectric 523, while the second ignition is performed. In the mode [FIG. 6B], the gap between the second electrode 522 and the dielectric 523 is preferably filled with the insulating oil 59.

  As described above in detail, according to the present embodiment, the capacitance of the capacitor 51 can be changed to a value different in magnitude, and the capacitance control unit 62 causes the first ignition mode having a relatively large capacitance discharge current and the capacitance. The second ignition mode with a relatively small discharge current can be switched. Accordingly, the first ignition mode is set only when high ignitability is required, and the second ignition mode is set in the normal state, thereby effectively suppressing the consumption of the center electrode 5 and the like while realizing excellent ignitability. be able to. Further, the capacitance of the capacitor can be set only to two different values, and is changed by instantaneously moving the second electrode 522 by the electromagnetic switch 54. Accordingly, the changing speed of the capacitance of the capacitor 51 can be dramatically increased, and the capacitance can be quickly changed in accordance with the operating conditions. As a result, it is possible to effectively realize both high ignitability and long life in the spark plug 1.

  Furthermore, according to this embodiment, it is not necessary to provide a separate power source for plasma generation or the like, or a diode for preventing backflow, and the apparatus can be reduced in size and manufacturing cost can be reduced. Further, by configuring without providing a diode, it is possible to increase the input energy to the spark plug 1 and to further improve the ignitability.

  In addition, since the capacitance of the capacitor 51 in the second ignition mode is set to 35 pF or less, the inrush current at the time of capacitive discharge can be sufficiently reduced. Thereby, consumption of the center electrode 5 etc. can be suppressed more reliably, and the life of the spark plug 1 can be further extended.

  Furthermore, the capacitance of the capacitor 51 in the first ignition mode is 50 pF or more, and the ignitability can be dramatically improved in the first ignition mode where high ignitability is required.

  Further, in the first ignition mode in which the capacitance of the capacitor 51 is relatively large, the output energy from the voltage application unit 41 is greater than the output energy in the second ignition mode. Therefore, even in the first ignition mode in which the capacitance of the capacitor 51 is relatively large, a sufficient charge can be stored in the spark plug 1, and a spark discharge can be generated more reliably. Further, in the second ignition mode, since the discharge energy can be suppressed low, it is possible to effectively suppress the consumption of the center electrode 5 and the like.

  In addition, in the first ignition mode, both the electrodes 521 and 522 are in contact with the dielectric 523, while in the second ignition mode, a gap is formed at least between the second electrode 522 and the dielectric 523. Therefore, the capacitance of the capacitor 51 can be changed greatly between the two ignition modes without significantly increasing the moving distance of the second electrode 522. In addition, since both the electrodes 521 and 522 are in surface contact with the dielectric 523 without any gap in the first ignition mode, the static area of the capacitor 51 in the first ignition mode is not increased so much as the facing area of both the electrodes 521 and 522 is not so large. The electric capacity can be increased sufficiently.

  Furthermore, by providing the insulating case 55 and the insulating oil 59, current leakage between the electrodes 521 and 522 can be suppressed, and the withstand voltage of the capacitor 51 can be improved.

  Next, in order to confirm the operational effects achieved by the above embodiment, a sample X (corresponding to a comparative example) of an ignition system having a capacitor with a constant capacitance (100 pF) and capacitances of 20 pF and 100 pF. A sample Y of an ignition system including a capacitor that can be set to any one of them, the capacitance of the capacitor being 100 pF in the first ignition mode, and the capacitance of the capacitor being 20 pF in the second ignition mode (corresponding to the embodiment) And each sample was subjected to a durability evaluation test. The outline of the durability evaluation test is as follows. That is, after attaching a sample spark plug to a predetermined chamber, the pressure in the chamber is 0.4 MPa, the atmosphere in the chamber is a standard gas atmosphere, the output energy in the voltage application unit is 50 mJ, and the frequency of the output voltage is 100 Hz. (Ie, at a rate of 6000 cycles per minute). Then, the time (endurance time) until the size of the gap between the center electrode and the ground electrode reached 1.3 mm from the initial value (1.1 mm) was measured. FIG. 7 shows the test results of the test.

  As shown in FIG. 7, it was revealed that the sample Y corresponding to the example has extremely excellent durability, with a durability time exceeding 800 hours. This is considered to be because the discharge energy can be reduced by suppressing the capacitance of the capacitor in the second ignition mode (normal time) low.

As a result of the above test, in order to extend the life of the spark plug, the capacitance of the capacitor can be changed, and the first ignition mode and the second ignition mode having a smaller capacity discharge current than the first ignition mode are provided. Next, it can be said that the switchable configuration is preferable. Next, samples of the ignition system in which the capacitance C2 (pF) of the capacitor in the second ignition mode is variously changed are manufactured, and the durability evaluation test described above is performed on each sample. It was. FIG. 8 shows the test results of the test.

  As shown in FIG. 8, it was revealed that the sample in which the capacitance C2 of the capacitor in the second ignition mode was 35 pF or less was excellent in durability.

  From the results of the above test, it can be said that the capacitance of the capacitor in the second ignition mode is preferably set to 35 pF or less in order to more reliably realize the life of the spark plug.

  Next, ignition system samples in which the capacitance C1 (pF) of the capacitor in the first ignition mode was variously changed were produced, and an ignitability evaluation test was performed on each sample. The outline of the ignitability evaluation test is as follows. That is, after attaching the spark plug of each sample to a predetermined chamber, the pressure in the chamber is 0.4 MPa, the atmosphere in the chamber is a standard gas atmosphere, the output energy in the voltage application unit is 50 mJ, and the spark plug is discharged. It was. Then, the air-fuel ratio in the chamber was gradually decreased, and the rate at which misfire occurred at each air-fuel ratio (misfire probability) was measured. It can be said that the lower the misfire probability under the condition that the air-fuel ratio is large and the ignition is difficult, the better the ignitability. FIG. 9 shows the test results of the test. In FIG. 9, the test result of the sample with the capacitance C1 of 35 pF is indicated by a circle, and an approximate curve of the test result is indicated by a broken line. Moreover, the test result of the sample with the capacitance C1 of 50 pF is indicated by a triangle, and an approximate curve of the test result is indicated by a one-dot chain line. Furthermore, the test result of the sample with the capacitance C1 of 100 pF is indicated by a square, and an approximate curve of the test result is indicated by a solid line.

  As shown in FIG. 9, the sample with the capacitance C1 of 50 pF or more has a misfire probability of 5% or less and has excellent ignitability even when the air-fuel ratio is increased to about 20. confirmed.

  From the results of the above test, it can be said that the capacitance of the capacitor in the first ignition mode is preferably set to 50 pF or more in order to improve the ignitability more reliably.

  Next, samples of A to E of five types of ignition systems in which the presence or absence of an insulating case and insulating oil and the constituent materials of the insulating case were changed were prepared, and a withstand voltage evaluation test was performed on each of the samples A to E. The outline of the withstand voltage evaluation test is as follows. That is, the ground electrode was removed and no spark discharge was generated in the gap, and the spark plug was attached to a test chamber simulating an engine head having a plug hole. Then, the output voltage from the voltage application unit is gradually increased, and the output voltage (leakage) when current leakage occurs between the first electrode and the second electrode or between the first and second electrodes and the plug hole. Voltage). FIG. 10 shows the test results of the test. Note that sample A is configured without providing an insulating case and insulating oil, and sample B is not provided with an insulating case, but in the second ignition mode, there is a gap between one electrode and the dielectric. The sample C is configured to be filled with insulating oil, and the sample C is provided with an insulating case made of insulating rubber around the capacitor without providing insulating oil. Sample D is provided with an insulating case made of an insulating resin around the capacitor without providing insulating oil. Sample E is provided with an insulating case made of insulating rubber around the capacitor. In the two ignition mode, the gap between one electrode and the dielectric is filled with insulating oil.

  As shown in FIG. 10, it has become clear that the withstand voltage of the capacitor can be improved by providing insulating oil or an insulating case.

  As a result of the above test, in order to improve the withstand voltage, at least in the second ignition mode, the gap between at least one of the first electrode and the second electrode and the dielectric is filled with insulating oil. It is preferable that the capacitor be covered with an insulating case made of insulating rubber or insulating resin, and it is more preferable to provide both insulating oil and insulating case.

  In addition, it is not limited to the description content of the said embodiment, For example, you may implement as follows. Of course, other application examples and modification examples not illustrated below are also possible.

  (A) In the above embodiment, the capacitor 51 is configured such that the flat plate portions of the first electrode 521 and the second electrode 522 face each other with the flat plate portion of the dielectric 523 interposed therebetween. Is not limited to this.

  Therefore, for example, as shown in FIGS. 11 (a) and 11 (b), it is composed of a pair of half-split electrodes 721A and 721B that are assembled into a cylindrical shape. A first electrode 721 that can be separated and moved along the direction; a cylindrical dielectric 723 disposed on the inner periphery of the first electrode 721; and a second electrode 722 disposed on the inner periphery of the dielectric 723. The capacitor 71 may be configured as described above. In this case, since the capacitor 71 has an elongated shape, it is possible to easily dispose the ignition device in the plug hole of the internal combustion engine. In such a capacitor 71, as shown in FIG. 11A, when the first electrode 721 is disposed at the first position P1 (that is, in the first ignition mode), the first electrode 721 is used. When the first electrode 721 is disposed at the second position P2 as shown in FIG. 11 (b) (ie, the second ignition) Mode), at least a part of the first electrode 721 (in this example, the entire area of the inner peripheral surface of the first electrode 721) is separated from the dielectric 723, so that the electrostatic capacity of the first electrode 721 varies in size. The value can be changed. In this example, an elastic member 76A is disposed between the half electrodes 721A and 721B on one end side (front side in FIG. 11) along the longitudinal direction of the capacitor 71, and the other along the longitudinal direction of the capacitor 71. On the end side (the back side in FIG. 11), the elastic member 76B is disposed between the half electrodes 721A and 721B. Further, an urging force is applied to the half electrodes 721A and 721B by the elastic members 76A and 76B so that both the half electrodes 721A and 721B approach each other.

  Furthermore, as shown in FIGS. 12A and 12B, a cylindrical first electrode 821, a cylindrical dielectric 823 disposed on the inner periphery of the first electrode 821, A second electrode 822 disposed around the circumference, a first electrode 821, an electrode hold 83 including a permanent magnet 87 and supporting the second electrode 822, and an electromagnetic switch 84, the first electrode 821 (dielectric material) 823) may be arranged in series along the axial direction of 823). In this case, the capacitor 81 can be formed in a further elongated shape, and the ignition device can be more easily disposed in the plug hole PH. In the capacitor 81, the second electrode 822 is movable along the axial direction of the first electrode 821 (dielectric 823) by the electromagnetic switch 84, and the second electrode 822 is disposed at the first position P1. When the second electrode 822 is disposed at the second position P2 (that is, in the second ignition mode). By making it larger than the opposing area of both the electrodes 821, 822, the capacitance of its own can be changed to two different values. In this alternative example, an elastic member 86 is disposed between the first electrode 821 (which may be the dielectric 823) and the electrode hold 83 on one end side of the first electrode 821, and the second electrode 822 is formed by the elastic member 86. On the other hand, a biasing force directed to the other end side (the lower side in FIG. 11) of the first electrode 821 is applied.

  (B) In the above-described embodiment, the ignition device 31 is provided with one capacitor 51. However, the ignition device 31 may include two or more capacitors connected in parallel. In this case, it is only necessary that the total capacitance of each capacitor can be changed to two different values.

  (C) In the embodiment described above, the ECU 61 is configured to include the capacity control unit 62, but a capacity control unit including a microcomputer, an ASIC, or the like may be provided separately from the ECU 61.

  (D) In the above embodiment, the capacitance of the capacitor can be changed by moving the first electrode or the second electrode. However, the capacitance of the capacitor can be changed by moving the dielectric using an electromagnetic switch or the like. The capacity may be changeable.

  (E) In the above embodiment, the voltage application unit 41 is provided for each spark plug 1, but the power from the voltage application unit 41 is supplied to the distributor without providing the voltage application unit 41 for each spark plug 1. It may be supplied to each spark plug 1 and the capacitor 51 via the above.

  (F) The configuration of the spark plug 1 in the above embodiment is merely an example, and the spark plug 1 to which the present invention is applicable is not particularly limited.

1 ... Plasma jet ignition plug (ignition plug)
DESCRIPTION OF SYMBOLS 5 ... Center electrode 27 ... Ground electrode 28 ... Cavity part 29 ... Gap 31 ... Ignition device 41 ... Voltage application part 51 ... Capacitor 521 ... First electrode 522 ... Second electrode 523 ... Dielectric 54 ... Electromagnetic switch 55 ... Insulating case 59 ... Insulating oil 62 ... Capacity controller 101 ... Ignition system P1 ... First position P2 ... Second position

Claims (12)

An ignition device used for a plasma jet ignition plug having a center electrode, a ground electrode, and a cavity that surrounds at least a part of a gap formed between the electrodes and forms a discharge space,
A voltage application unit for applying a voltage to the gap;
Between the plasma jet ignition plug and the voltage application unit, comprising a capacitor connected in parallel with the plasma jet ignition plug,
The electric charge stored in the capacitor by the voltage application unit is thrown into the gap, causing a capacitive discharge in the cavity,
The capacitance of the capacitor can be changed to two different capacitance values,
Ignition comprising a capacity control unit capable of switching between a first ignition mode and a second ignition mode having a capacity discharge current smaller than that of the first ignition mode by changing the capacitance of the capacitor. apparatus.   2. The ignition device according to claim 1, wherein in the second ignition mode, the capacitance of the capacitor is 35 pF or less.   The ignition device according to claim 1 or 2, wherein in the first ignition mode, the capacitance of the capacitor is 50 pF or more. The voltage application unit is configured to be capable of changing output energy to the plasma jet ignition plug,
4. The output energy from the voltage application unit in the first ignition mode is made larger than the output energy from the voltage application unit in the second ignition mode. 5. Ignition device according to. The capacitor is
At least in the first ignition mode, a first electrode and a second electrode arranged with an insulating dielectric interposed therebetween;
At least one of the first electrode and the second electrode is movable, the movable electrode is disposed at a predetermined first position in the first ignition mode, and predetermined in the second ignition mode. An electromagnetic switch disposed at the second position of
The capacitance control unit operates the electromagnetic switch to change the capacitance of the capacitor by switching the arrangement position of the movable electrode to the first position or the second position. The ignition device according to any one of claims 1 to 4. When the movable electrode is disposed at the first position, the first electrode and the second electrode are in contact with the dielectric across the dielectric,
The at least one of the first electrode and the second electrode is separated from the dielectric when the movable electrode is disposed at the second position. Ignition device according to. The first electrode and the second electrode face each other with the dielectric interposed therebetween,
The ignition device according to claim 5 or 6, wherein the opposing surfaces of the first electrode and the dielectric and the opposing surfaces of the second electrode and the dielectric are flat surfaces. One of the first electrode and the second electrode has a cylindrical shape, and the one electrode is configured to be movable along the radial direction by the electromagnetic switch.
The cylindrical dielectric is disposed on the inner periphery of the one electrode,
The other electrode of the first electrode and the second electrode is disposed on the inner periphery of the dielectric,
When the one electrode is disposed at the first position, the one electrode contacts the dielectric;
The ignition device according to claim 5 or 6, wherein when the one electrode is disposed at the second position, at least a part of the one electrode is separated from the dielectric. One of the first electrode and the second electrode has a cylindrical shape,
The cylindrical dielectric is disposed on the inner periphery of the one electrode,
The other electrode of the first electrode and the second electrode is disposed on the inner periphery of the dielectric,
The electromagnetic switch enables at least one of the first electrode and the second electrode to move along the axial direction of the dielectric,
The opposing area of the first electrode and the second electrode when the movable electrode is arranged at the first position is equal to the first area when the movable electrode is arranged at the second position. The ignition device according to claim 5, wherein the ignition device is larger than an opposing area of one electrode and the second electrode.   The insulating oil is filled in a gap between at least one of the first electrode and the second electrode and the dielectric in at least the second ignition mode. The ignition device according to item 1.   The ignition device according to any one of claims 1 to 10, wherein the capacitor is covered with an insulating case made of insulating rubber or insulating resin. The ignition device according to any one of claims 1 to 11,
An ignition system comprising: a plasma jet ignition plug to which electric power is supplied from the ignition device.

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