JP5658647B2 - Ignition system - Google Patents

Description

  The present invention relates to an ignition system having a plasma jet ignition plug.

  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 tip surface of the center electrode and the inner peripheral surface of the shaft hole at its tip portion, and the cavity portion is formed in the ground electrode. It communicates with the outside through the through-hole.

  In such a plasma jet ignition plug, generally, 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 to cause a spark discharge in the gap. 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.

  Also, a general plasma jet ignition plug ignition system includes a spark discharge circuit section for applying a voltage to a gap to generate a spark discharge, a capacitor for supplying a large amount of power to the gap, and a charge for charging the same. A plasma discharge circuit unit having a power source (see, for example, Patent Document 1). In addition, diodes are provided between the plasma jet ignition plug and the spark discharge circuit unit, and between the plasma jet ignition plug and the plasma discharge circuit unit, respectively, from one of the spark discharge circuit unit and the plasma discharge circuit unit. Inflow of current to the other is prevented.

JP 2007-287655 A

  However, in the above prior art, it is necessary to provide a spark discharge circuit portion and a plasma discharge circuit portion (that is, to provide two circuit portions) and to use a high breakdown voltage diode as a diode for preventing inflow of current. For this reason, the product may be increased in size and the production cost may be greatly increased.

  Therefore, in order to reduce production costs, it is conceivable to provide only a spark discharge circuit unit and to supply current from the spark discharge circuit unit to the plasma jet ignition plug. However, in the above-described prior art, a current with a peak value of several tens of A flows from the plasma discharge circuit portion to the plasma jet spark plug for several tens of microseconds, and plasma is ejected over the same amount of time as spark discharge. When the current is supplied only from the circuit section, the current (capacitance current) of several tens of A or more flows in several ns, so even if the current is input multiple times, the spark and fuel There is a possibility that sufficient contact time with the gas cannot be secured. As a result, the fuel gas may be ignited and the ignitability may be insufficient.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to have a current input unit for supplying current to the plasma jet spark plug and to have one current input path to the plasma jet spark plug. In the ignition system (that is, having no plasma discharge circuit portion), it is intended to realize excellent ignitability while reducing production costs and the like.

  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 system of the present configuration includes an insulator having an axial hole extending in the axial direction, and an end surface of the axial hole on the distal end side of the axial hole such that the front end surface of the insulator is positioned on the rear end side in the axial direction with respect to the distal end of the insulator. A center electrode to be inserted; a metal shell disposed on the outer periphery of the insulator; a ground electrode fixed to a tip portion of the metal shell and disposed closer to the distal end side in the axial direction than the tip of the insulator; A plasma jet ignition plug comprising a cavity formed by an inner peripheral surface of the shaft hole and a tip surface of the center electrode, and a gap formed between the center electrode and the ground electrode;
An ignition system including a single ignition coil connected to the plasma jet ignition plug and having a current input unit for supplying a current to the gap;
The ground electrode has a through hole that communicates the cavity portion with the outside, and an inner peripheral surface of the through hole is located on an outer peripheral side with respect to an opening of the shaft hole,
The plasma jet ignition plug has one path through which current is input, and only the current based on the output current from the ignition coil is input to the plasma jet ignition plug.
The current input unit is configured to input a plurality of currents to the gap in one combustion stroke in the internal combustion engine to which the plasma jet ignition plug is attached.

  Note that “only the current based on the output current from the ignition coil is input to the plasma jet ignition plug,” only the output current from the ignition coil is directly applied to the plasma jet ignition plug. As well as the case where the output current from the ignition coil is applied indirectly, the output current from the ignition coil is included. Therefore, for example, the case where a current is supplied from the capacitor charged by the output current from the ignition coil to the plasma jet spark plug is included.

  According to the configuration 1, the ignition system includes the current input unit, and the current injection path to the plasma jet ignition plug is one. The plasma jet ignition plug has a current based on the output current from the ignition coil. It is configured so that only the input is made. This eliminates the need for a plasma discharge circuit section for supplying large power and a diode for preventing inflow of current. As a result, the product can be reduced in size and the production cost can be greatly reduced.

  On the other hand, the ignitability may be insufficient when only the current is supplied from the current input unit. However, according to the above configuration 1, the inner peripheral surface of the through hole is located on the outer peripheral side with respect to the opening of the shaft hole. In addition, the current input unit is configured to input a plurality of currents to the gap in one combustion stroke.

  Here, by configuring the inner peripheral surface of the through hole to be positioned on the outer peripheral side with respect to the opening of the shaft hole, a gap formed between the center electrode and the ground electrode (discharge occurs when current is applied). A part of the portion is exposed to the tip end side in the axial direction. Therefore, the fuel gas is more likely to come into contact with the discharge generated in the gap, and the flame kernel can be generated more reliably. In addition, the generated flame kernel does not have a large jet power and may stay at the opening of the shaft hole and its surroundings, but in addition to the current input for generating the flame kernel, further current is supplied to the gap. Can be supplied to the generated flame kernel. As a result, the flame kernel can be ejected vigorously toward the center of the combustion chamber, and excellent ignitability can be realized.

Configuration 2. In the ignition system of this configuration, in the configuration 1, the distance between the opening of the shaft hole and the inner peripheral surface of the through hole along the direction orthogonal to the axis is 0.25 mm or more and 0.75 mm or less. And
An inner diameter of the shaft hole is 0.5 mm or more and 1.5 mm or less.

  According to the configuration 2, the distance between the opening of the shaft hole and the inner peripheral surface of the through hole along the direction orthogonal to the axis is set to 0.25 mm or more. Accordingly, a wider range of the gap is exposed to the tip end side in the axial direction, and the fuel gas is more likely to come into contact with the discharge. As a result, flame nuclei can be generated more reliably and ignitability can be further improved.

  On the other hand, the generated flame nucleus is restricted to the inner peripheral surface of the through-hole, and the movement to the outer peripheral side is suppressed. However, if the distance is excessively large, the flame nucleus is pivoted. It may be located on the outer peripheral side far from the opening of the hole. Here, when the gas is ejected from the opening of the shaft hole by supplying electric current, the jet power is given to the flame nucleus, and the flame nucleus is located farther outside than the opening of the shaft hole. In such a case, there is a possibility that a sufficient jet power cannot be given to the flame kernel.

  In this regard, according to the configuration 2, the distance between the opening of the shaft hole and the inner peripheral surface of the through hole along the direction orthogonal to the axis is set to 0.75 mm or less. Accordingly, it is possible to more reliably prevent the situation where the flame kernel is excessively positioned on the outer peripheral side, and it is possible to more reliably give the jet power to the flame kernel. As a result, the ignitability improvement effect can be more reliably exhibited.

  Furthermore, according to the said structure 2, the internal diameter in opening of a shaft hole shall be 1.5 mm or less. Therefore, it is possible to prevent the jet power from diffusing to the outer peripheral side, and it is possible to generate a larger jet power along the axial direction. As a result, the ignitability can be further improved.

  In order to obtain a large jet power, it is desirable to reduce the inner diameter as much as possible. However, if the inner diameter is excessively reduced, only a small amount of carbon or the like has entered the shaft hole. There is a possibility that the shaft hole is blocked and troubles occur in the discharge. In particular, when the inner peripheral surface of the through hole is positioned on the outer peripheral side of the opening of the shaft hole as in the configuration 1, carbon or the like is more likely to enter the shaft hole, so that the shaft hole is more blocked. Concerned.

  In this regard, according to the configuration 2, the inner diameter of the shaft hole opening is 0.5 mm or more. Therefore, it is possible to more reliably prevent the shaft hole from being blocked due to the intrusion of carbon or the like, and it is possible to generate the discharge more reliably.

  Configuration 3. In the ignition system of this configuration, in the configuration 1 or 2, the distance from the tip surface of the insulator to the tip of the inner peripheral surface of the through hole along the axis is 0.3 mm or more and 1.5 mm or less. It is characterized by that.

  According to the configuration 3, the distance from the tip surface of the insulator to the tip of the inner peripheral surface of the through hole along the axis is 0.3 mm or more. Therefore, when the flame kernel is ejected, the flame kernel can be ejected linearly toward the center of the combustion chamber without diffusing. As a result, the ignitability can be further improved.

  Moreover, according to the said structure 3, since the said distance is 1.5 mm or less, the flame-extinguishing effect | action by a ground electrode can be reduced. As a result, a decrease in ignitability due to the flame extinguishing action can be more effectively suppressed.

  In addition, when the current for giving the jet power is input to the gap, the current generated after cutting off the discharge generated by the current input for generating the flame kernel is applied as in the configuration 4 described below. Alternatively, the current may be supplied after the discharge is maintained as in the configuration 5 described later. In either case, jet power can be given to the flame kernel, and excellent ignitability can be realized.

  Configuration 4. In the ignition system of this configuration, in any one of the above configurations 1 to 3, the current input unit interrupts a discharge in the gap generated by the current input, and then supplies the next current to the gap. Features.

  According to the said structure 4, the effect similar to the said structure 1 etc. will be show | played.

  When the current is supplied to the gap after the discharge is interrupted as in the configuration 4, a capacity current in which the current rapidly changes flows, and high-density plasma is generated in the cavity portion. Then, when the generated plasma is ejected from the cavity portion, an ejection power is given to the flame kernel.

Configuration 5. In the ignition system of this configuration, in any one of the above configurations 1 to 3 , the current input unit is configured to supply a next current to the gap while maintaining a discharge in the gap generated by the current input. Features.

  According to the said structure 5, the effect similar to the said structure 1 etc. will be show | played.

  In addition, when a current is supplied to the gap while maintaining a discharge as in the above configuration 5, an induced current flows through the discharge path by applying the current, and the flame core is pushed out by the induced current. On the other hand, a jet power is given.

Configuration 6. In the ignition system of this configuration, in any one of the above configurations 1 to 3 and 5, the current input unit maintains a discharge in the gap generated by supplying current to the gap, and It is characterized in that the current is supplied twice or more in one combustion stroke.

  Due to the influence of the air flow in the combustion chamber, if only one flame kernel is generated in one combustion stroke, combustion of the fuel gas occurs only in a part of the combustion chamber, and combustion occurs in other regions of the combustion chamber. There is a risk that it will not be possible (that is, an unburned area will occur).

  In this respect, according to the above-described configuration 6, a flame kernel having an excellent jet power can be generated a plurality of times in one combustion stroke. Therefore, combustion can be generated in a very wide range in the combustion chamber, and the ignitability can be dramatically improved.

  Configuration 7. In the ignition system of this configuration, in any one of the above configurations 1 to 6, the current input unit is configured to give an ejection output to the flame kernel within 500 μs from the current input to the gap for generating the flame kernel. A current is supplied to the gap.

  After a certain amount of time has elapsed since the generation of flame nuclei, the flame nuclei grow (flame propagates), so even if jet power is given to the flame nuclei, there is almost no effect in terms of ignitability. In other words, energy may be wasted as much as the input current.

  In this respect, according to the above-described configuration 7, the current for supplying the jet power is input within 500 μs from the current input for generating the flame kernel. That is, the current is input only when it contributes to improvement in ignitability. Therefore, waste of energy can be eliminated and the above-described effect of improving the ignitability can be more reliably exhibited.

It is a block diagram which shows schematic structure of an ignition system. It is a partially broken front view which shows the structure of a spark plug. It is a timing chart which shows the injection mode of the electric current with respect to a spark plug. It is a timing chart which shows the injection mode of the electric current with respect to a spark plug. It is a partial expanded sectional view which shows the structure of the front-end | tip part of a spark plug. It is a partial expanded sectional view which shows the structure of the sample 1 corresponded to a comparative example. It is a graph which shows the limit air-fuel ratio of the samples 1 and 2 in the case where the power supply system 1 corresponding to the comparative example is used and the case where the power supply system 2 corresponding to the embodiment is used. It is a graph which shows the L / L improvement value at the time of changing distance A and inner diameter D, after setting distance B to 0.2 mm. It is a graph which shows the L / L improvement value at the time of changing distance A and inner diameter D, after setting distance B to 0.3 mm. It is a graph which shows the L / L improvement value at the time of changing distance A and the internal diameter D, after setting distance B to 0.5 mm. It is a graph which shows the L / L improvement value at the time of changing the distance A and the internal diameter D, after setting the distance B to 1.5 mm. It is a graph which shows the L / L improvement value at the time of changing the distance A and the internal diameter D, after setting the distance B to 2.0 mm. It is a graph which shows the relationship between the electric current injection frequency and the L / L improvement value. It is a graph which shows the relationship between the frequency | count of electric current injection, and the increase amount of a L / L improvement value. It is a timing chart which shows the injection mode of the electric current with respect to a spark plug in another embodiment. It is a block diagram which shows schematic structure of the electric current input part in another embodiment. It is a block diagram which shows schematic structure of the electric current input part 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 a current input unit 41. 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. A current input unit 41 is provided for each spark plug 1.

  First, prior to the description of the ignition system 101, 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 includes an insulator 2 as a cylindrical insulator, 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 extending along the axis CL1, and a center electrode 5 is inserted and fixed to the tip 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. Furthermore, the center electrode 5 has a rod shape (cylindrical shape) as a whole, and the tip thereof is disposed on the rear end side in the axis line CL1 direction with respect to the tip surface of the insulator 2. In addition, the tip of the center electrode 5 is formed of tungsten (W), iridium (Ir), platinum (Pt), nickel (Ni), or an alloy containing at least one of these metals as a main component. An electrode tip 5C 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 resistor 7 is disposed between the center electrode 5 and the terminal electrode 6 of the shaft hole 4. Both ends of the resistor 7 are electrically connected to the center electrode 5 and the terminal electrode 6 through conductive glass seal layers 8 and 9, respectively.

  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.

  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 step 14 of the metal shell 3 is locked to the step 22 of the metal shell 3. It is fixed to the metal shell 3 by caulking the opening on the rear end side 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.

  A disc-shaped ground electrode 27 is joined to the front end of the metal shell 3 so as to be positioned on the front side of the insulator 2 in the direction of the axis CL1. The ground electrode 27 is joined to the metal shell 3 by being inserted into the inner periphery of the front end side of the metal shell 3 and welding its outer peripheral portion to the metal shell 3. In the present embodiment, the ground electrode 27 is joined to the metal shell 3 with its rear end side end surface being in contact with the front end surface of the insulator 2. 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, and the inner diameter of the through hole 27H is constant along the axis CL1. Further, a cavity portion 28 that is a cylindrical space that opens toward the front end side in the direction of the axis CL1 is formed by the inner peripheral surface of the shaft hole 4 and the front end surface of the center electrode 5. It communicates with the outside through the through hole 27H. Further, a gap 29 is formed between the tip surface of the center electrode 5 and the inner peripheral surface of the ground electrode 27, and a discharge is generated when a voltage is applied between the electrodes 5 and 27. A part of the gap 29 is disposed in the cavity portion 28.

  Next, the current input unit 41 for supplying current to the gap 29 will be described.

  As shown in FIG. 1, the current input unit 41 is connected to the spark plug 1 via a noise suppression resistor 51, and includes a primary coil 42, a secondary coil 43, and a core 44. An ignition coil 45, a resistor 46, and a first charging / discharging unit 47 and a second charging / discharging unit 48 disposed in parallel between the ignition coil 45 and the resistor 46 are provided. The conventional ignition system for a plasma jet spark plug has a current input path from the spark discharge circuit portion to the spark plug and a current for supplying large power from the plasma discharge circuit portion to the spark plug as described above. There are two current input paths for the spark plug 1, but in this embodiment, there is one current input path for the spark plug 1. The spark plug 1 is configured so that only the current from the ignition coil 45 is input.

  The primary coil 42 is wound around the core 44, one end of which is connected to the output end of each of the first and second charge / discharge units 47 and 48, and the other end of the secondary coil 43. It is grounded while connected to one end. The secondary coil 43 is wound around the core 44, and is grounded with one end connected to the other end of the primary coil 42, and the other end is connected to a spark plug via a resistor 51. 1 terminal electrode 6.

  In addition, the first and second charging / discharging units 47 (48) include a first diode 471 (481), a second diode 472 (482), a third diode 473 (483), and an igniter 474 (484), respectively. And a capacitor 475 (485).

  The first diode 471 (481) and the second diode 472 (482) are provided to prevent current from flowing from one of the charge / discharge units 47 and 48 to the other. The first diode 471 (481) The second diode 472 (482) is provided on the input end side of the charging / discharging unit 47 (48), and the second diode 472 (482) is provided on the output end side of the charging / discharging unit 47 (48).

  The third diode 473 (483) has one end connected between the capacitor 475 (485) and the second diode 472 (482) and the other end grounded. The igniter 474 (484) is formed of a predetermined transistor, and one end thereof is connected between the first diode 471 (481) and the capacitor 475 (485), and the other end is grounded.

  The igniter 474 (484) operates in response to an energization signal input from a predetermined ECU (electronic control unit) 61, and switches the igniter 474 (484) on and off to charge the capacitor 475 (485). And the current input to the spark plug 1 by the discharge of the capacitor 475 (485) can be switched.

  First, the operation of the first charging / discharging unit 47 will be described. The energization signal from the ECU 61 to the igniter 474 is switched from on to off, and the igniter 474 is switched from on to off, whereby a current flows to the capacitor 475 through the third diode 473. The capacitor 475 is charged. On the other hand, by switching the energization signal to the igniter 474 from off to on and turning the igniter 474 from off to on, the electric charge stored in the capacitor 475 is discharged, and the primary voltage is applied to the primary coil 42. With the application of the primary voltage, a secondary voltage is generated in the secondary coil 43, and the secondary voltage is applied to the spark plug 1 and the gap 29 is dielectrically broken, so that a current is supplied to the gap 29.

  Further, the second charging / discharging unit 48 operates similarly to the first charging / discharging unit 47. More specifically, the energization signal from the ECU 61 to the igniter 484 is switched from on to off, and the igniter 484 is switched from on to off, whereby a current flows through the third diode 483 to the capacitor 485 and the capacitor 485 is charged. On the other hand, when the energization signal for the igniter 484 is switched from OFF to ON and the igniter 484 is turned ON from OFF, the electric charge stored in the capacitor 485 is discharged, and the primary voltage is applied to the primary coil 42. Then, with the application of the primary voltage, a current is supplied to the gap 29.

  Note that a voltage is applied to the gap 29 to cause a discharge in the gap 29. During discharge, a minute induced current flows through the gap 29 following a rapidly changing capacitance current.

  In addition, in the present embodiment, the ECU 61 maintains the discharge generated in the gap 29 as the current is supplied in one combustion stroke, and then supplies the next current, and is generated in the gap 29. Either one of the next electric current is input after cutting off the discharged electric current, and the electric current input unit 41 is controlled by the ECU 61 so that the electric current input unit selected by the ECU 61 is applied to the spark plug 1 In contrast, a current is supplied.

  Here, when the next current is supplied while maintaining the discharge generated in the gap 29, first, as shown in FIG. 3, the energization signal S1 from the ECU 61 to the igniter 474 is turned off to on. Then, the capacitor 475 is discharged, and a current is supplied to the gap 29 to cause discharge in the gap 29. Then, when the discharge is maintained, the energization signal S1 is turned off, and the energization signal S2 from the ECU 61 to the igniter 485 is turned on. As a result, charging of the capacitor 475 is started, the capacitor 485 is discharged, and the next current is supplied from the second charging / discharging unit 48 to the gap 29. Thereafter, by alternately switching on and off the first and second charging / discharging units 47 and 48, the discharge in the gap 29 is maintained, and an induced current is supplied to the gap 29 a plurality of times. The Rukoto.

  When an induced current is input a plurality of times to the gap 29, first, a flame kernel is generated with the initial current input. Then, by the induced current thereafter, a force directed to the flame core in the direction pushed from the cavity portion 28 (the front end side in the direction of the axis CL1) is applied, and the jet power directed toward the center side of the combustion chamber with respect to the flame nucleus Is given.

  Further, when the next current is supplied after the discharge in the gap 29 is interrupted, as shown in FIG. 4, an energization signal S1 or an energization signal S2 (both energization signals S1 and S2 may be used). By switching from OFF to ON, a current is supplied from the charge / discharge portions 47 and 48 to the gap 29, and discharge occurs in the gap 29. During the discharge, the energization signal that is turned on is turned off to interrupt the discharge, and then the next current is supplied from the charge / discharge portions 47 and 48 to the gap 29. Thereafter, interruption of discharge, application of current, interruption of discharge, application of current, etc. are repeated. When the next current is input after the discharge is cut off in this way, a capacitive current is repeatedly input to the gap 29, and a high current (for example, several μs) is input to the gap 29 in a short time (for example, several μs). For example, dozens of A) will be thrown in multiple times.

  When a plurality of capacitive currents are input to the gap 29, first, flame nuclei are generated with the initial input of current. Then, a high-density plasma is generated a plurality of times in the cavity portion 28 by the subsequent current application, and the generated plasma is continuously ejected from the cavity portion 28, thereby giving an ejection power to the generated flame kernel. Will be.

  Further, in the present embodiment, the gap 29 for generating the flame kernel is generated both in the case of supplying the next current while maintaining the discharge and in the case of supplying the next current after interrupting the discharge. The current is supplied to the gap 29 for giving a jet power to the flame kernel within 500 μs after the current is supplied.

  In the ignition system 101 in which the current is supplied to the gap 29 a plurality of times as described above, the above-described effects (generating a flame kernel and applying a jet power to the flame kernel) are more reliably exhibited. The spark plug 1 in this embodiment has the following structural features.

  That is, as shown in FIG. 5, the inner peripheral surface of the through hole 27 </ b> H formed in the ground electrode 27 is disposed on the outer peripheral side with respect to the opening of the shaft hole 4. Thereby, the imaginary surface VS1 formed by extending the opening of the shaft hole 4 along the axis CL1 toward the tip end side in the axis CL1 direction, and the tip of the inner peripheral surface of the through hole 27H on the axis CL1 side along the direction orthogonal to the axis CL1. The extended virtual surface VS2, the inner peripheral surface of the through hole 27H, and the tip surface of the insulator 2 form a flame nucleus generating portion 31 that is a ring-shaped space. The flame nucleus generation unit 31 is a space exposed to the outside, and the fuel gas flows into the flame nucleus generation unit 31 relatively easily. In addition, a part of a gap 29 (a part indicated by a thick line in FIG. 5) formed between the center electrode 5 and the ground electrode 27 is located in the flame nucleus generating part 31. Therefore, the fuel gas can easily come into contact with the discharge generated in the gap 29, and as a result, flame nuclei can be more reliably generated at the opening of the shaft hole 4 and its periphery.

  Further, in the present embodiment, in order to realize more reliable generation of the flame kernel, the distance A between the opening of the shaft hole 4 and the inner peripheral surface of the through hole 27H along the direction orthogonal to the axis CL1 is set. It is 0.25 mm or more. On the other hand, the distance A is set to 0.75 mm or less in order to give a jet power more reliably to the flame kernel.

  Further, in order to prevent the jet power from diffusing outward in the radial direction and obtain a larger jet power along the direction of the axis CL1, the inner diameter D of the opening of the shaft hole 4 is set to 1.5 mm or less. On the other hand, if carbon or the like enters the shaft hole 4 and the shaft hole 4 is completely closed, the insulation resistance value of the gap 29 is excessively increased, which hinders the generation of flame nuclei. There is a fear. Therefore, in order to prevent the shaft hole 4 from being blocked by carbon or the like, the inner diameter D is set to 0.5 mm or more.

  Further, in order to eject the flame core linearly without diffusing, the distance B from the tip surface of the insulator 2 to the tip of the inner peripheral surface of the through hole 27H along the axis CL1 is set to 0.3 mm or more. ing. On the other hand, the distance B is set to 1.5 mm or less in order to prevent a decrease in ignitability due to the flame extinguishing action of the ground electrode 27 (a phenomenon in which the heat of the flame kernel is drawn by the ground electrode 27).

  As described in detail above, according to the present embodiment, the current input unit 41 is provided and the current input path to the spark plug 1 is one, and only the current from the ignition coil 45 is supplied to the spark plug 1. It is configured to be input. This eliminates the need for a plasma discharge circuit section for supplying large power and a diode for preventing inflow of current. Therefore, the ignition system 101 can be miniaturized and the production cost can be greatly reduced.

  Further, since the inner peripheral surface of the through hole 27H is configured to be positioned on the outer peripheral side with respect to the opening of the shaft hole 4, a part of the gap 29 is exposed to the front end side in the axis line CL1 direction. Therefore, the fuel gas is more likely to come into contact with the discharge generated in the gap 29, and flame nuclei can be generated more reliably. In addition to supplying current for generating flame nuclei, a current is further supplied to the gap 29, so that jet power can be applied to the generated flame nuclei. As a result, the flame kernel can be ejected vigorously toward the center of the combustion chamber, and excellent ignitability can be realized.

  Furthermore, since the distance A is set to 0.25 mm or more, a wider range of the gap 29 is exposed to the front end side in the axis CL1 direction, and the fuel gas is more likely to come into contact with the discharge. As a result, flame nuclei can be generated more reliably and ignitability can be further improved.

  In addition, in this embodiment, since the distance A is set to 0.75 mm or less, it is possible to more reliably prevent a situation in which the flame kernel is excessively positioned on the outer peripheral side. For this reason, it is possible to more reliably give the jet power to the flame kernel, and to more reliably exhibit the effect of improving the ignitability.

  In addition, since the inner diameter D at the opening of the shaft hole 4 is 1.5 mm or less, it is possible to generate a larger jet power along the direction of the axis CL1 and further improve the ignitability. On the other hand, since the inner diameter D is 0.5 mm or more, the blocking of the shaft hole 4 due to the intrusion of carbon or the like can be more reliably prevented, and discharge can be more reliably generated.

  In the present embodiment, since the distance B is 0.3 mm or more, when the flame kernel is ejected, the flame kernel is ejected linearly toward the center of the combustion chamber without diffusing. Can do. As a result, the ignitability can be further improved. On the other hand, since the distance B is set to 1.5 mm or less, the flame extinguishing action by the ground electrode 27 can be reduced, and a decrease in ignitability can be more effectively suppressed.

  Furthermore, in the present embodiment, the current for supplying the jet power is input within 500 μs from the current input for generating the flame kernel. That is, the current is input only when it contributes to improvement in ignitability. Therefore, waste of energy can be eliminated and the above-described effect of improving the ignitability can be more reliably exhibited.

  Next, in order to confirm the operational effects achieved by the above-described embodiment, as shown in FIG. 6, by setting the distance A to 0 mm, the spark plug sample 1 in which no flame kernel generation unit was provided (corresponding to a comparative example) And a spark plug sample 2 (corresponding to the embodiment) having a distance A of 0.5 mm and provided with a flame nucleation unit, and generating discharge in the gap with one power source. A power supply system 1 (corresponding to a comparative example) that supplies a large amount of power to the gap with another power supply, or a power supply system 2 that includes a current input unit that supplies a plurality of currents to the gap (in the embodiment) The ignitability evaluation test was performed on each sample. The outline of the ignitability evaluation test is as follows. That is, each sample was mounted on a 4-cylinder engine with a displacement of 2.0 L, and the engine was operated at a rotation speed of 1500 rpm with an ignition timing of MBT (optimum ignition position). Then, while gradually increasing the air-fuel ratio (thinning the fuel), the engine torque fluctuation rate is measured for each air-fuel ratio, and the air-fuel ratio when the engine torque fluctuation rate exceeds 5% is taken as the limit air-fuel ratio. Obtained. In this test, first, with respect to Sample 1, the operating conditions and the like of the engine at which the limit air-fuel ratio becomes 20 are specified in both the power supply system 1 and the power supply system 2. Next, for sample 2, the engine was operated using the power supply system 1 under the same conditions as those specified when the power supply system 1 was used, and the critical air-fuel ratio was measured. Further, with respect to Sample 2, the engine was operated using the power supply system 2 under the same conditions as those specified when the power supply system 2 was used, and the critical air-fuel ratio was measured. In addition, it means that it is excellent in ignitability, so that a limit air fuel ratio is large. FIG. 7 shows the test results of the test. In FIG. 7, the test result of sample 1 is shown in black, and the test result of sample 2 is shown in white.

  In each sample, the distance B was 0.5 mm and the inner diameter D was 1.0 mm. Further, when the power supply system 2 is used, in a single combustion stroke, the discharge generated with the first current input is cut off, and then the next current is input 100 μs after the first current input (one time). In the combustion stroke, a total of two currents were supplied to the gap).

  As shown in FIG. 7, it was found that when using the power supply system 1 that generates a large amount of power after generating a discharge in the gap, the sample 2 is inferior to the sample 1 in ignitability. This is because, when the power supply system 1 is used, plasma is generated in the cavity portion when power is turned on, and the generated plasma is ignited by being ejected from the opening of the cavity portion. In the provided sample 2, it is considered that the plasma is easily diffused at the time of jetting, and the jet length of the plasma is not so large.

  On the other hand, when the power supply system 2 in which the current is supplied a plurality of times is used, it has been clarified that the sample 2 is more ignitable than the sample 1. This is because, when the power supply system 2 is used, the flame nucleus generator is ignited by giving a jet output by applying the current to the flame nucleus generated when the current is first applied. In the provided sample 2, it is considered that the fuel gas easily comes into contact with the discharge, and as a result, the flame kernel is more reliably generated.

  From the results of the above test, when using a power supply system having a current input unit that inputs current to the gap multiple times, it has a flame kernel generation unit (that is, the inner peripheral surface of the through hole is more than the opening of the shaft hole). It can be said that excellent ignitability can be realized by using a spark plug (also located on the outer peripheral side).

  Next, after setting the distance B to 0.2 mm, 0.3 mm, 0.5 mm, 1.5 mm, or 2.0 mm, samples of the spark plug in which the distance A and the inner diameter D are variously changed are prepared. Using the power supply system 2, the above-described ignitability evaluation test was performed on each sample in the same manner of current application as described above (the next current was input 100 μs after the initial current input). In this test, the distance B and the inner diameter D are the same, and the limit air-fuel ratio with respect to the reference when the distance A is variously changed with reference to the limit air-fuel ratio of the sample with the distance A set to 0.0 mm. The improvement value (L / L improvement value) was calculated. For example, for a sample in which the distance B is 0.2 mm and the inner diameter D is 0.5 mm, the critical air-fuel ratio of the sample in which the distance B is 0.2 mm, the inner diameter D is 0.5 mm, and the distance A is 0.0 mm As a reference, the distance B and the inner diameter D were made the same, and the L / L improvement value when the distance A was changed was calculated. FIG. 8 shows a test result of a sample with a distance B of 0.2 mm, FIG. 9 shows a test result of a sample with a distance B of 0.3 mm, and FIG. 10 shows a sample of a sample with a distance B of 0.5 mm. The test results are shown, FIG. 11 shows the test results of a sample with a distance B of 1.5 mm, and FIG. 12 shows the test results of a sample with a distance B of 2.0 mm. 8 to 12, the test results of the sample with the inner diameter D of 0.5 mm are indicated by circles, the test results of the sample with the inner diameter D of 1.0 mm are indicated by triangles, and the inner diameter D is 1. The test result of the sample with 5 mm is indicated by a square mark, and the test result of the sample with an inner diameter D of 2.0 mm is indicated by a cross mark. Moreover, in the said test, when the L / L improvement value became 0.3 or more, it determined with the improvement effect of ignitability appearing notably.

As shown in FIGS. 8 to 12, the sample in which the distance A is 0.25 mm or more and 0.75 mm or less and the inner diameter D is 1.5 mm or less has an L / L improvement value of 0.3 or more, and the ignitability It was found that can be improved effectively. This is considered to be because the following (1) to (3) acted synergistically.
(1) By setting the distance A to be 0.25 mm or more, the fuel gas is more easily brought into contact with the discharge, and the flame kernel is generated more reliably.
(2) By setting the distance A to 0.75 mm or less, it is possible to prevent the situation where the flame kernel is positioned on the outer peripheral side excessively from the opening of the shaft hole, and the jet power is more reliably given to the flame kernel. Was it.
(3) By making the inner diameter D 1.5 mm or less, diffusion of the jet output to the outer peripheral side is prevented, and a larger jet output is obtained along the axial direction.

  Further, among the samples in which the distance A is 0.25 mm or more and 0.75 mm or less and the inner diameter D is 1.5 mm or less, those having the distance B of 0.3 mm or more and 1.5 mm or less have an L / L improvement value. It became 0.5 or more, and it turned out that it has extremely excellent ignitability. This is because when the distance B is set to 0.3 mm or more, flame nuclei are easily ejected linearly toward the center of the combustion chamber, and because the distance B is set to 1.5 mm or less, This is thought to be due to the reduction of the anti-inflammatory effect by the electrodes.

  From the results of the above test, it can be said that it is more preferable that the distance A is 0.25 mm or more and 0.75 mm or less and the inner diameter D is 1.5 mm or less in order to further improve the ignitability.

  Moreover, it can be said that it is still more preferable that the distance B is 0.3 mm or more and 1.5 mm or less in terms of further improving the ignitability.

  In order to increase the jet power, it is preferable to reduce the inner diameter D. However, if the inner diameter D is excessively reduced, the shaft hole is blocked only by a small amount of carbon or the like entering the shaft hole. This may cause trouble in energization. In particular, in the case of providing a flame nucleus generating part, carbon or the like is more likely to enter the shaft hole, so that the shaft hole is more likely to be blocked. Therefore, it can be said that the inner diameter D is preferably 0.5 mm or more from the viewpoint of more reliably preventing the shaft hole from being blocked by carbon or the like even in the case of providing the flame nucleus generating portion.

  Next, when a power supply system having a current input unit capable of supplying a plurality of currents to the gap is used, the discharge generated with the current input is interrupted and the next current is supplied to the gap (intermittent discharge). ) And the case where the current generated in the gap is maintained and the next current is supplied to the gap (continuous discharge). The L / L improvement value was calculated using the limit air-fuel ratio in the case of In this test, the number of times of current application was 1 to 7 times, and the current application interval was 100 μs when a plurality of currents were supplied. In this test, a spark plug having a distance A of 0.5 mm, a distance B of 0.5 mm, and an inner diameter D of 1.0 mm was used. FIG. 13 is a graph showing the relationship between the number of times of current application and the L / L improvement value. FIG. 14 shows the L / L improvement value when the number of times of current application is n times with respect to the L / L improvement value when the number of current inputs is n-1 times (n is a natural number). (For example, in FIG. 14, the increase amount of the L / L improvement value when the number of times of current application is 3 in FIG. 14 is the current increase with respect to the L / L improvement value when the number of current injection times is 2.) The amount of increase in the L / L improvement value when the number of times of charging is 3 is shown). In addition, in FIG. 13, the test results when intermittent discharge is performed are indicated by circles, and the test results when continuous discharge is performed are indicated by triangles. Moreover, in FIG. 14, the test result at the time of performing intermittent discharge is shown in black, and the test result at the time of performing continuous discharge is shown in white.

  As shown in FIG. 13, it was confirmed that the ignitability can be improved by applying the current a plurality of times both in the case of intermittent discharge and in the case of continuous discharge.

  On the other hand, as shown in FIG. 14, when the current is input for the seventh time (that is, the current input 600 μs after the initial current input), the increase amount of the L / L improvement value becomes 0, and this current input is ignitable. It has become clear that energy is being wasted without contributing to improvement. This is considered to be due to the fact that flame nuclei grow (flame propagates) with the passage of time, so that even if jet power is applied to the flame nuclei, there is almost no effect.

  On the other hand, the L / L improvement value increases until the sixth current injection (that is, the current input from the first current input to 500 μs later), and the current input contributes to the improvement of the ignitability. Became clear.

  From the results of the above test, in order to more reliably demonstrate the effect of improving the ignitability by supplying current, within 500 μs from the initial current input (that is, current input for generating flame nuclei) Therefore, it can be said that it is preferable to input current.

  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-described embodiment, the current input unit 41 can perform once the injection of the next current into the gap 29 while maintaining the discharge in the gap 29 in one combustion stroke. However, as shown in FIG. 15, the next current may be supplied to the gap 29 while maintaining the discharge in the gap 29, or may be performed twice or more in one combustion stroke. In this case, it is possible to generate a plurality of flame nuclei given excellent jet power in one combustion stroke, for example, in a region where combustion did not occur with only one flame nuclei, other flames. Can be burned by nuclei. As a result, combustion can be caused in a very wide range, and the ignitability can be greatly improved.

  (B) In the above embodiment, only the current from the ignition coil 45 is directly supplied to the spark plug 1. On the other hand, at least a part of the output current from the ignition coil may be so configured that it is indirectly input to the spark plug 1 (even in this case, after all, Only the current based on the output current from the coil is input to the spark plug 1). Therefore, for example, as shown in FIG. 16, the current input unit 71 includes one ignition coil 74, and a voltage application unit 72 (for example, a full transistor type ignition device) for applying a voltage to the ignition plug 1. And a capacitor 73 connected in parallel with the spark plug 1 between the spark plug 1 and the voltage application unit 72. Such a current input unit 71 operates as follows, and can input a plurality of currents to the spark plug 1 (gap 29).

  That is, by turning the energization signal from the ECU 61 to the voltage application unit 72 from on to off, a current is output from the ignition coil 74 to the spark plug 1 side (note that the current is continuously output for a predetermined time). ). As a result, the spark plug 1 and the capacitor 73 are charged, and the potential difference of the gap 29 increases. When the potential difference of the gap 29 exceeds the dielectric breakdown voltage of the gap 29, the charge charged in the spark plug 1 and the charge charged in the capacitor 73 flow into the gap 29 and discharge occurs in the gap 29. After the discharge, the spark plug 1 and the capacitor 73 are charged again by the current from the ignition coil 74, and the charge stored in the spark plug 1 and the capacitor 73 when the potential difference of the gap 29 exceeds the dielectric breakdown voltage of the gap 29 again. As a result, discharge occurs in the gap 29. Thereafter, the charging of the spark plug 1 and the capacitor 73 and the discharge due to the electric charge stored in the spark plug 1 and the capacitor 73 are repeatedly performed while the current is output from the ignition coil 74. As a result, the ignition A current is supplied to the plug 1 (gap 29) a plurality of times.

  (C) In the above embodiment, the current input unit 41 includes the first charging / discharging unit 47 and the second charging / discharging unit 48 connected in parallel. However, as illustrated in FIG. You may comprise so that it may have only one charging / discharging part 47. FIG. Moreover, you may comprise so that an electric current input part may have three or more charging / discharging parts in parallel. When only one charging / discharging unit 47 is provided, it is not necessary to provide the first diode 471 and the second diode 472 for preventing current from flowing between the charging / discharging units.

  (D) In the above embodiment, the inner diameter of the through hole 27H is constant along the axis line CL1, but the inner diameter of the through hole 27H slightly changes along the axis line CL1 (for example, toward the front end side in the axis line CL1 direction). The inner diameter may be gradually reduced or expanded). In this case, the distance A refers to the average distance between the opening of the shaft hole 4 and the inner peripheral surface of the through hole 27H along the direction orthogonal to the axis CL1.

  (E) In the above embodiment, the rear end side end surface of the ground electrode 27 is in contact with the front end surface of the insulator 2, but the rear end side end surface of the ground electrode 27 is separated from the front end surface of the insulator 2. Also good. In this case, in order to prevent the flame core from entering between the ground electrode 27 and the insulator 2, the front end surface of the insulator 2 along the axis CL <b> 1 to the rear end of the inner peripheral surface of the through hole 27 </ b> H. The distance is preferably 0.5 mm or less.

  (F) In the above embodiment, the current input unit 41 is provided for each spark plug 1. However, the current input unit 41 is not provided for each spark plug 1, and the current supplied from the current input unit 41 is supplied to the distributor. It may be inserted into each spark plug 1 via

  (G) In the above embodiment, the resistor 51 is provided outside the spark plug 1, but a resistor corresponding to the resistor 51 may be provided inside the spark plug 1.

  DESCRIPTION OF SYMBOLS 1 ... Spark plug (plasma jet spark plug), 2 ... Insulator (insulator), 3 ... Main metal fitting, 4 ... Shaft hole, 5 ... Center electrode, 27 ... Ground electrode, 27H ... Through-hole, 28 ... Cavity part, DESCRIPTION OF SYMBOLS 29 ... Gap, 41 ... Current injection part, 45 ... Ignition coil, 101 ... Ignition system, CL1 ... Axis, EN ... Internal combustion engine

Claims (7)

An insulator having an axial hole extending in the axial direction; and a center electrode inserted on the distal end side of the axial hole such that its front end surface is located on the rear end side in the axial direction with respect to the distal end of the insulator; A metal shell disposed on the outer periphery of the insulator, a ground electrode fixed to the tip of the metal shell and disposed closer to the tip of the insulator than the tip of the insulator, and an inner peripheral surface of the shaft hole And a plasma jet ignition plug having a gap formed between the center electrode and the ground electrode, and a cavity formed by a tip surface of the center electrode,
An ignition system including a single ignition coil connected to the plasma jet ignition plug and having a current input unit for supplying a current to the gap;
The ground electrode has a through hole that communicates the cavity portion with the outside, and an inner peripheral surface of the through hole is located on an outer peripheral side with respect to an opening of the shaft hole,
The plasma jet ignition plug has one path through which current is input, and only the current based on the output current from the ignition coil is input to the plasma jet ignition plug.
The ignition system according to claim 1, wherein the current input unit supplies a plurality of currents to the gap in one combustion stroke in the internal combustion engine to which the plasma jet ignition plug is attached. The distance between the opening of the shaft hole and the inner peripheral surface of the through hole along the direction orthogonal to the axis is 0.25 mm or more and 0.75 mm or less,
The ignition system according to claim 1, wherein an inner diameter of the shaft hole is 0.5 mm or more and 1.5 mm or less.   3. The ignition according to claim 1, wherein a distance from the tip surface of the insulator to the tip of the inner peripheral surface of the through hole along the axis is 0.3 mm or more and 1.5 mm or less. system.   The ignition according to any one of claims 1 to 3, wherein the current input unit interrupts a discharge in the gap generated by the current input, and then supplies the next current to the gap. system. The ignition according to any one of claims 1 to 3 , wherein the current input unit supplies a next current to the gap after maintaining a discharge in the gap generated by the current being supplied. system. The current input unit maintains the discharge in the gap generated by supplying current to the gap and then supplies the next current to the gap twice or more in one combustion stroke. The ignition system according to any one of claims 1 to 3 and 5, characterized in that:   7. The current input unit performs current input to the gap for giving a jet power to the flame kernel within 500 μs from current input to the gap for generating a flame kernel. The ignition system according to any one of the above.

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