JP2013040582A - Ignition system and method for controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress consumption of a center electrode or the like, to achieve the excellent durability, and to further enhance the ignitability.SOLUTION: An ignition system 31 includes an ignition plug 1 having a center electrode 5 and a ground contact electrode 27, a discharge power source 41 which generates the spark discharge in a spark discharge gap 28 by applying the voltage to the spark discharge gap 28 formed between both electrodes 5, 27, and an AC power source 51 which charges the AC power to the spark generated by the spark discharge, and generates AC plasma in the spark discharge gap 28. Both the durability and the ignitability are improved by intermittently charging the power not equal to or more than the prescribed power generation capable of generating the AC plasma to the spark a plurality of times during the duration of the spark discharge.

Description

  The present invention relates to an ignition system that generates AC plasma to ignite an air-fuel mixture or the like.

  An ignition plug used in a combustion apparatus such as an internal combustion engine includes, for example, a center electrode extending in the axial direction, an insulator provided on the outer periphery of the center electrode, and a cylindrical metal shell assembled on the outside of the insulator; And a ground electrode having a base end joined to a tip of the metal shell. Then, by applying a high voltage to the center electrode, a spark is generated in the gap formed between the center electrode and the ground electrode, and as a result, the air-fuel mixture is ignited.

  In recent years, in order to improve the ignitability, a technique for generating a spark by supplying high-frequency power into the gap instead of a high voltage is known (for example, see Patent Document 1).

JP 2009-8100 A

  However, in the above technique, since the spark is generated only by the high frequency power, the required voltage may not be output only by the high frequency power depending on the state in the combustion chamber. Therefore, a situation in which no spark occurs (so-called misfire) tends to occur despite the high-frequency power being applied.

  Therefore, it is conceivable to achieve excellent ignitability by supplying AC power (high frequency power) to the generated spark and generating AC plasma. However, the inventor of the present application diligently studied the method, and it has been found that the center electrode and the ground electrode are overheated with the input of AC power, and the center electrode and the like may be rapidly consumed.

  The present invention has been made in view of the above circumstances, and an object thereof is to suppress wear of the center electrode and the like, to realize good durability, and to further improve ignitability. An ignition system that can be used and a control method thereof.

  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 this configuration includes a spark plug having a center electrode and a ground electrode,
A voltage source is applied to a gap formed between the center electrode and the ground electrode, and a discharge power source for generating a spark discharge in the gap;
An ignition system comprising an alternating current power source for supplying alternating current power to a spark generated by the spark discharge and generating alternating current plasma in the gap,
A power control unit is provided that intermittently inputs a power of a predetermined generation power or higher that can generate the AC plasma to the spark a plurality of times during the duration of the spark discharge.

  According to the above configuration 1, while the spark discharge is continued (that is, when the insulation resistance of the gap is sufficiently reduced), a plurality of electric powers more than the generated power capable of generating the AC plasma are intermittently applied to the spark. It is thrown in once. Therefore, in the period (low power period) provided between periods (high power period) in which power equal to or higher than the generated power is input, the center electrode and the ground electrode are radiated without being heated. Therefore, overheating of the center electrode and the like can be suppressed, and as a result, rapid consumption of the center electrode and the like can be more reliably prevented. As a result, excellent durability can be realized.

  Furthermore, the generated alternating-current plasma does not disappear with the end of the generation of generated power (the end of the high power period), and exists for a certain period of time after the end of input of the generated power. That is, AC plasma exists even in the low power period after the high power period. Therefore, when electric power is intermittently input multiple times and when electric power is input at the same time without dividing into multiple times, the electric energy (electric energy) input during the spark discharge is the same. If the electric power is intermittently supplied several times, the AC plasma can be provided for a longer time. As a result, the ignition probability of the air-fuel mixture can be increased, and the ignitability can be improved.

  That is, according to the said structure 1, both durability and ignitability can be improved by supplying electric power intermittently several times with respect to a spark, and excellent ignitability is maintained over a long period of time. can do.

  By the way, as an ignition device for an internal combustion engine or the like, an ignition device for igniting an air-fuel mixture and a microwave emission device for emitting a microwave to a combustion / reaction region and improving a flame propagation speed, etc. Has been proposed (Japanese Patent Laid-Open No. 2007-113570). Moreover, the said patent document describes that the microwave is radiated | emitted intermittently. However, the technique described in the patent document emits microwaves to a predetermined region (space), and is greatly different from the present invention in which AC power is supplied to a spark in terms of configuration and operation. It is different and technical idea is different. In addition, in the present invention, suppression of wear of the center electrode and the like that may occur due to the application of AC power to the spark is a problem to be solved, whereas in the above patent document, microwaves are emitted to the region. There is no description that the center electrode or the like is consumed by doing so, and there is no description that suggests that. Therefore, also from this point, the present invention is different in technical idea from the technique described in the above-mentioned patent document.

  Configuration 2. In the ignition system of this configuration, in the configuration 1, the power control unit sets a maintenance time of a low power period between high power periods in which power equal to or higher than the generated power is input immediately before the low power period. When the input energy in the high power period is E (J), it is E × 0.6 (ms / J) or more.

  According to the configuration 2, the low power period in which the center electrode or the like radiates heat is sufficiently high corresponding to the input energy (that is, the amount of heat received by the center electrode or the like) in the immediately preceding high power period. Secured for a long time. Therefore, overheating of the center electrode and the like can be further effectively suppressed, and the durability can be further improved.

  Configuration 3. In the ignition system of the present configuration, in the configuration 1 or 2, the power control unit is configured to generate power including a low power period between periods in which power equal to or higher than the generated power is input during the duration of the spark discharge. The time from the start of charging to the end of charging is set to 3.0 ms or less.

  According to the configuration 3, the time from the start of power supply including the low power period to the end of power supply during the spark discharge is 3.0 ms or less. Therefore, it is possible to prevent a situation in which the center electrode and the ground electrode are exposed to a high-temperature AC plasma for an excessively long time, and the center electrode and the ground electrode can be more reliably prevented from being oxidized. As a result, the above-described durability improvement effect can be further enhanced.

  Configuration 4. In the ignition system of this configuration, the power control unit according to any one of the above configurations 1 to 3, the AC power supplied from the AC power supply is maintained for each of the periods in which power equal to or greater than the generated power is input. It is characterized by being not less than the period.

  According to the said structure 4, the maintenance time of a high electric power period is made more than the period of alternating current power. Therefore, electric energy can be more reliably input to the spark, and the ignitability can be further reliably improved.

Configuration 5. The control method of the ignition system of this configuration includes a spark plug having a center electrode and a ground electrode,
A voltage source is applied to a gap formed between the center electrode and the ground electrode, and a discharge power source for generating a spark discharge in the gap;
An ignition system control method comprising: an alternating current power source for supplying alternating current power to a spark generated by the spark discharge and generating alternating current plasma in the gap;
During the duration of the spark discharge, a power that is equal to or higher than a predetermined generation power capable of generating the AC plasma is intermittently supplied to the spark a plurality of times.

  According to the said structure 5, the effect similar to the said structure 1 is show | played fundamentally.

  Configuration 6. The control method of the ignition system of the present configuration is the same as the configuration 5 described above, in which the maintenance time of the low power period between the high power periods in which power equal to or greater than the generated power is input is set to the high power just before the low power period. When the input energy in the period is E (J), it is characterized by being not less than E × 0.6 (ms / J).

  According to the said structure 6, the effect similar to the said structure 2 will be show | played fundamentally.

  Configuration 7. The control method of the ignition system of the present configuration is the above configuration 5 or 6, wherein from the start of power supply including a low power period between periods in which power equal to or greater than the generated power is input during the duration of the spark discharge. The time until the end of charging is 3.0 ms or less.

  According to the said structure 7, the effect similar to the said structure 3 will be show | played fundamentally.

  Configuration 8. In any one of the configurations 5 to 7, the control method of the ignition system according to the present configuration is configured so that each sustain time of a period in which power equal to or higher than the generated power is input is equal to or longer than a cycle of AC power supplied from the AC power source. It is characterized by.

  According to the said structure 8, the effect similar to the said structure 4 will be show | played fundamentally.

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 wave form diagram which shows the electric power input into a spark. It is a graph which shows typically the temperature of a center electrode etc. at the time of electric power input. (A) is a power waveform diagram showing a power input mode in case A, (b) is a power waveform diagram showing a power input mode in case B, and (c) is a power waveform diagram in case C. It is a wave form diagram of electric power which shows a mode. It is a graph which shows the gap | interval increase amount in cases AC. (A) is a power waveform diagram showing the power input mode in case D, (b) is a power waveform diagram showing the power input mode in case E, and (c) is a power waveform diagram in case F. It is a wave form diagram of electric power which shows a mode. It is a graph which shows the gap | interval increase in case DF at the time of changing the maintenance period of a low electric power period. It is a wave form diagram which shows the input electric power with respect to the spark in another embodiment. It is a wave form diagram which shows the input electric power with respect to the spark in another embodiment. It is a wave form diagram which shows the input electric power with respect to the spark in another embodiment. It is a wave form diagram which shows the input electric power with respect to the spark in another embodiment. It is a wave form diagram which shows the input electric power with respect to the spark in another embodiment. It is a wave form diagram which shows the input electric power with respect to the spark 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 the ignition system 31. As shown in FIG. 1, the ignition system 31 includes a spark plug 1, a discharge power supply 41, an AC power supply 51, a mixing circuit 61, and a control unit 71 as a power control unit. In FIG. 1, only one spark plug 1 is shown, but an actual combustion apparatus is provided with a plurality of cylinders, and the spark plug 1 is provided corresponding to each cylinder. And the electric power from the power supply 41 for discharge and the alternating current power supply 51 is supplied to each spark plug 1 via the distributor which is not shown in figure.

  First, the configuration of the spark plug 1 will be described.

  As shown in FIG. 2, the spark plug 1 includes a cylindrical insulator 2, a cylindrical metal shell 3 that holds the insulator 2, and the like. 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.

  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 most of the leg length portions 13 are accommodated in the metal shell 3, and the rear end side trunk portion 10 is formed of the metal shell. 3 is exposed from the rear end. In addition, a tapered step portion 14 is formed at a 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, a shaft hole 4 is formed through the insulator 2 along the axis CL1, and an electrode 8 is inserted and fixed in the shaft hole 4. The electrode 8 includes a center electrode 5 provided on the front end side of the shaft hole 4, a terminal electrode 6 provided on the rear end side of the shaft hole 4, and a glass seal portion 7 provided between both the electrodes 5 and 6. And.

  The center electrode 5 has a rod shape as a whole, and its tip protrudes from the tip of the insulator 2 toward the tip in the direction of the axis CL1. The center electrode 5 is made of a Ni alloy containing nickel (Ni) as a main component. Note that an inner layer made of copper or copper alloy having excellent thermal conductivity may be provided inside the center electrode 5. In this case, heat extraction of the center electrode 5 is improved, and durability can be improved.

  The terminal electrode 6 is made of a metal such as low carbon steel and has a rod shape as a whole. In addition, a connection portion 6 </ b> A that is bulged outward in the radial direction is provided at the rear end portion of the terminal electrode 6. 6 A of said connection parts protrude from the rear end of the insulator 2, and are electrically connected with the output (transmission path 32C mentioned later) of the mixing circuit 61. FIG.

  In addition, the glass seal portion 7 is formed by sintering a mixture of metal powder, glass powder, and the like, and electrically connects the center electrode 5 and the terminal electrode 6 to the insulator 2. On the other hand, both electrodes 5 and 6 are fixed.

  The metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and an ignition plug 1 is attached to an attachment hole of a combustion device (for example, an internal combustion engine or a fuel cell reformer) on the outer peripheral surface thereof. For this purpose, a threaded portion (male threaded portion) 15 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 21 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 portion 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 22 is interposed between the step portions 14 and 21 of both the insulator 2 and the metal shell 3. As a result, the gas tightness in the combustion chamber is maintained, and the fuel gas (air mixture) entering the gap between the leg length 13 of the insulator 2 exposed to the combustion chamber and the inner peripheral surface of the metal shell 3 is prevented from leaking outside. It has become.

  Further, in order to make the sealing by caulking more complete, annular ring members 23 and 24 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 23 , 24 is filled with powder of talc (talc) 25. That is, the metal shell 3 holds the insulator 2 via the plate packing 22, the ring members 23 and 24, and the talc 25.

  In addition, a ground electrode 27 formed of an alloy containing Ni as a main component and bent back at a substantially middle portion is joined to the distal end portion 26 of the metal shell 3. The side surface of the ground electrode 27 faces the tip of the electrode 8 (center electrode 5), and a spark discharge gap 28 is formed as a gap between the tip of the electrode 8 and the ground electrode 27. Has been.

  Next, the configuration of the discharge power supply 41 and the like will be described with reference to FIG.

  The discharge power supply 41 supplies a high voltage to the spark plug 1 and causes a spark discharge in the spark discharge gap 28. In the present embodiment, the discharge power supply 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 of the spark plug 1 via the mixing circuit 61. It is connected to the electrode 6.

  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 according to the energization signal input from the control unit 71. When a high voltage is applied to the spark plug 1, a current is passed from the battery VA to the primary coil 42 to form a magnetic field around the core 44, and the energization signal from the control unit 71 is switched from on to off. As a result, energization of the primary coil 42 from the battery VA is stopped. When the energization is stopped, the magnetic field of the core 44 changes, and a negative high voltage (for example, 5 kV to 30 kV) is generated in the secondary coil 43. By applying this high voltage to the spark plug 1, a spark discharge can be generated in the spark discharge gap 28.

  The AC power source 51 supplies AC power having a relatively high frequency (for example, 50 kHz to 100 MHz) to the spark plug 1. An impedance matching circuit (matching unit) 81 is provided between the AC power supply 51 and the mixing circuit 61. The impedance matching circuit 81 is configured so that the output impedance on the AC power supply 51 side matches the input impedance on the mixing circuit 61 and the spark plug 1 (load) side, and is supplied to the spark plug 1 side. Attenuation of AC power is prevented. The AC power transmission path from the AC power source 51 to the spark plug 1 is constituted by a coaxial cable having an inner conductor and an outer conductor disposed on the outer periphery of the inner conductor. As a result, the reflection of power is prevented. Is planned.

  The mixing circuit 61 converts the high voltage transmission path 32A output from the discharge power supply 41 and the AC power transmission path 32B output from the AC power supply 51 into one transmission path 32C connected to the spark plug 1. In summary, a coil 62 and a capacitor 63 are provided. In the coil 62, a relatively low-frequency current output from the discharge power supply 41 is allowed to pass, while a relatively high-frequency current output from the AC power supply 51 is not allowed to pass. Inflow of the current output from the power supply 51 to the discharge power supply 41 side is suppressed. On the other hand, in the capacitor 63, a relatively high frequency current output from the AC power supply 51 can pass, while a relatively low frequency current output from the discharge power supply 41 cannot pass. Thus, inflow of the current output from the discharge power supply 41 to the AC power supply 51 side is suppressed. The secondary coil 43 may be used in place of the coil 62 and the coil 62 may be omitted.

  In the present embodiment, the voltage from the discharge power supply 41 and the AC power from the AC power supply 51 are supplied to the spark discharge gap 28 through the electrode 8, and the spark generated in the spark discharge gap 28 by the voltage from the discharge power supply 41 is applied. In addition, plasma is generated when AC power from the AC power supply 51 is input. That is, the voltage from the discharge power supply 41 and the AC power from the AC power supply 51 are supplied to the spark discharge gap 28 using the electrode 8 as a common transmission path. As a result, for the spark generated in the spark discharge gap 28, The AC power is directly input.

  And the control part 71 is comprised by the predetermined | prescribed electronic control apparatus (ECU), the application timing of the voltage with respect to the ignition plug 1 from the power supply 41 for discharge, the supply timing of the alternating current power with respect to the ignition plug 1 from the alternating current power supply 51, Control the supply time.

  That is, as shown in FIG. 3, the control unit 71 controls the discharge power supply 41 to cause a spark discharge in the spark discharge gap 28 and to make an alternating current during the duration of the spark discharge (within the discharge maintaining time). By controlling the power supply 51, electric power that is higher than the generated electric power capable of generating AC plasma is intermittently supplied to the spark a plurality of times (in this embodiment, four times). In addition, the control unit 71 determines a period (hereinafter referred to as “high power period”) between periods in which power equal to or higher than the generated power is input to the spark plug 1 within the discharge maintenance time. In the “low power period”, the AC power supply 51 is controlled to stop the application of AC power to the spark plug 1. The generated power capable of generating AC plasma may vary depending on factors such as the configuration of the spark plug and the pressure in the combustion chamber, but is, for example, 50 W or more.

  The electric power in FIG. 3 indicates the amount of work that the alternating current supplied from the alternating current power source 51 to the spark plug 1 per unit time. In the present embodiment, in each high power period, the work amount (power) that the alternating current supplied from the alternating current power source 51 to the spark plug 1 per unit time does not change with time, and is constant. ing. In addition, the amount of power input to the spark plug 1 is made equal in each high power period, and the maintenance time in each high power period is the same.

  Further, when the input energy in the high power period immediately before the one low power period is E (J), the control unit 71 sets the maintenance period of the one low power period to E × 0.6 (ms / J ) The AC power supply 51 is controlled so as to achieve the above. That is, as shown in FIG. 4, in the high power period, the center electrode 5, the ground electrode 27, and the like are heated with the input of power, but the low power period (that is, the temperature of the center electrode 5 and the like decreases). The period of time) is ensured sufficiently long as E × 0.6 (ms / J) or more, so that overheating of the center electrode 5 and the like is suppressed. On the other hand, the maintenance period of each low power period is set not to be excessively long so that the temperature of the AC plasma can be maintained at a temperature higher than the temperature at which the mixture can be ignited (however, the low power period is maintained). The upper time limit can be changed according to the input energy in the previous high power period). Further, in the present embodiment, the sustain periods of the low power period are configured to be the same.

  In addition, as shown in FIG. 3, the control unit 71 sets the time (total time) from the start of power supply including the low power period to the end of power supply during the duration of the spark discharge to be 3.0 ms or less. The AC power supply 51 is controlled.

  Furthermore, the control unit 71 controls the AC power supply 51 so that the sustain period of each high power period is equal to or longer than the cycle of the AC power supplied from the AC power supply 51.

  As described above in detail, according to the present embodiment, during the duration of the spark discharge (that is, when the insulation resistance of the spark discharge gap 28 is sufficiently reduced), the generated power is more than the generation power that can generate the AC plasma. Electric power is intermittently applied several times to the spark. Therefore, in the low power period provided between the high power periods, the center electrode 5 and the ground electrode 27 are radiated without being heated. Therefore, overheating of the center electrode 5 and the like can be suppressed, and as a result, rapid consumption of the center electrode 5 and the like can be more reliably prevented. As a result, excellent durability can be realized.

  Furthermore, the generated AC plasma does not disappear with the end of the high power period, and exists for a certain period of time after the end of the high power period. That is, AC plasma exists even in the low power period after the high power period. Therefore, when electric power is intermittently input multiple times and when electric power is input at the same time without dividing into multiple times, the electric energy (electric energy) input during the spark discharge is the same. If the electric power is intermittently supplied several times, the AC plasma can be provided for a longer time. As a result, the ignition probability of the air-fuel mixture can be increased, and the ignitability can be improved.

  That is, according to the present embodiment, by intermittently supplying power to the spark a plurality of times, both durability and ignitability can be improved, and excellent ignitability can be maintained over a long period of time. can do.

  Further, the maintenance time of each low power period is set to E × 0.6 (ms / J) or more, and the low power period is the input energy (that is, the reception of the center electrode 5 etc.) in the immediately preceding high power period. Corresponding to the amount of heat). Therefore, overheating of the center electrode 5 and the like can be further effectively suppressed, and durability can be further improved.

  In addition, the total time from the start of power supply including the low power period to the end of power supply during the spark discharge is 3.0 ms or less. Therefore, the situation where the center electrode 5 and the ground electrode 27 are exposed to a high-temperature AC plasma for an excessively long time can be prevented, and the oxidation of the center electrode 5 and the ground electrode 27 can be prevented more reliably. Can do. As a result, the above-described durability improvement effect can be further enhanced.

  In addition, the maintenance time of the high power period is longer than the AC power cycle. Therefore, electric energy can be more reliably input to the spark, and the ignitability can be further reliably improved.

  Next, in order to confirm the effect achieved by the above embodiment, as shown in FIG. 5A, during the spark discharge, when AC power (300 W) is turned on once with a turn-on time of 1 ms (case A) ) And, as shown in FIG. 5 (b), during the spark discharge, AC power (300W) is intermittently input twice with an input time of 0.5 ms each, and a low power period between both high power periods When the power is stopped for 0.3 ms (case B), and as shown in FIG. 5C, the alternating current power (300 W) is intermittently set to 0.5 ms during the spark discharge. The ignitability evaluation test was performed twice when the low power (30 W) was applied for 0.3 ms in the low power period between the two high power periods (case C).

  The outline of the ignitability evaluation test is as follows. That is, after the spark plug was attached to a 4-cylinder DOHC engine with a displacement of 2000 cc, the air-fuel ratio (A / F) was set to 24 and power was supplied to the spark plug for 1000 cycles. The number of misfire occurrences during 1000 cycles was measured, and the misfire occurrence rate (misfire rate) was calculated. Here, when the misfire rate becomes 0.0%, the evaluation of “◎” is given as being extremely excellent in ignitability, and when the misfire rate becomes 0.1% or more and 0.9% or less Therefore, it was decided to give a rating of “◯” as being excellent in ignitability. On the other hand, if the misfire rate is 1.0% or more and 1.4% or less, it is rated as “△” as being slightly inferior in ignitability, and the misfire rate is 1.5% or more. Therefore, it was decided to give an evaluation of “x” because of poor ignitability. Table 1 shows the test results of the ignitability evaluation test in cases A to C, respectively. Under the conditions of this test, the generated power capable of generating AC plasma is more than 30 W and less than 300 W, and AC plasma can be generated by supplying 300 W AC power to the spark plug. Further, as described above, in cases A to C, the total input energy was the same.

  As shown in Table 1, it has been clarified that excellent ignitability can be realized in cases B and C in which AC power is intermittently supplied several times. This is considered to be due to the fact that the AC plasma exists for a longer period of time and the ignition probability for the air-fuel mixture has increased.

  Next, a durability evaluation test was performed on the cases A to C. The outline of the durability evaluation test is as follows. That is, after attaching the spark plug to a predetermined chamber, the pressure in the chamber was set to 0.4 MPa, the frequency of the applied voltage was set to 20 Hz (that is, at a rate of 1200 times per minute), and AC plasma was generated. . Then, after 40 hours, the size of the spark discharge gap after the test was measured, and the increase amount (gap increase amount) with respect to the size of the spark discharge gap before the test was calculated. FIG. 6 shows the test results of the test. The output frequency of the AC power supply was 13 MHz. An ignition coil was used as a discharge power source, the output energy of the ignition coil was 60 mJ, and the voltage application time (spark discharge duration) from the ignition coil to the spark plug was 2.5 ms. Furthermore, the tip of the center electrode was made of Ni alloy, and the outer diameter of the tip of the center electrode was 2.5 mm. In addition, the size of the spark discharge gap before the test was 0.8 mm.

  As shown in FIG. 6, it was found that Case A was slightly inferior in durability. This is considered to be due to the fact that the center electrode and the like were heated rapidly by supplying AC power at a time.

  On the other hand, it was found that excellent durability can be realized in cases B and C. This is presumably because the provision of the low power period between the two high power periods caused the temperature of the center electrode or the like to decrease during the low power period, thereby suppressing overheating of the center electrode or the like.

  Based on the results of the above tests, in order to improve both ignitability and durability, the spark is intermittently turned on multiple times during the duration of the spark discharge. It is preferable to do so.

  Next, as shown in FIG. 7A, when the number of times AC power is applied to the spark is 5 times, the maintenance time of each high power period is 0.1 ms, and the magnitude of the input power during the high power period is 300 W (That is, when the input energy in the high power period is 0.03 J, respectively: Case D) and, as shown in FIG. 7B, the number of times AC power is input to the spark is twice, When the maintenance time is 0.5 ms and the magnitude of the input power in the high power period is 300 W (that is, when the input energy in the high power period is 0.15 J, respectively, Case E) and FIG. As shown in FIG. 5, when the number of times AC power is applied to the spark is 2 times, the maintenance time of each high power period is 0.5 ms, and the magnitude of the input power in the high power period is 500 W (that is, in the high power period) Input If each and 0.25J the Energy: de a case F), made various changes and while the durability of the above evaluation tests maintenance time of low power period X (ms). FIG. 8 is a graph showing the relationship between the value obtained by dividing the input energy (J) in one high power period by the maintenance time X (ms) in the low power period and the gap increase amount. In FIG. 8, the test results in Case D are indicated by circles, the test results in Case E are indicated by triangles, and the test results in Case F are indicated by squares. Moreover, the configurations of the AC power source, the spark plug, and the like were the same as in the durability evaluation test described above.

  As shown in FIG. 8, when the value obtained by dividing the maintenance time X in the low power period by the input energy in the high power period of 1 is 0.6 (ms / J) or more, that is, a high of 1 Assuming that the input energy during the power period is E (J), the durability can be further improved when the maintenance time during the low power period is set to E × 0.6 (ms / J) or more. This is considered to be because the low power period in which the center electrode or the like radiates heat is secured long enough to correspond to the input energy in the immediately preceding high power period.

  From the result of the above test, in order to further improve the durability, when the maintenance time of the low power period is set to E (J) as the input energy in the high power period immediately before the low power period, E × 0 .6 (ms / J) or more is preferable.

  Next, by changing the maintenance time of the high power period, the number of times of power supply, and the maintenance time of the low power period, the time from the start of power supply including the low power period to the end of power supply during the duration of the spark discharge About the cases 1-8 which changed (total time) variously, the above-mentioned durability evaluation test was done. Then, the ground electrode was observed after the test to confirm the presence or absence of oxidation on the surface of the ground electrode. Here, in the case where oxidation was not confirmed on the surface of the ground electrode, an evaluation of “◯” was given as being excellent in oxidation resistance. On the other hand, when oxidation was confirmed on the surface of the ground electrode, an evaluation of “x” was made because the oxidation resistance was slightly inferior. Table 2 shows the test results and the maintenance time of the high power period in each case. In each case, the input power in the high power period was 300 W, the duration of the spark discharge was 3 ms, and the ground electrode was formed of a Ni alloy.

  As shown in Table 2, it was found that excellent oxidation resistance can be realized by setting the total time to 3.0 ms or less. This is considered to be because overheating of the ground electrode was suppressed by shortening the time during which the ground electrode was exposed to AC plasma.

  In addition, since the ground electrode is disposed closer to the center of the combustion chamber than the center electrode, it is likely to be hotter and more likely to be oxidized. Therefore, it can be said that by setting the total time to 3.0 ms or less, oxidation of the center electrode, which is generally at a lower temperature than the ground electrode, can be suppressed.

  From the results of the above test, in order to suppress the oxidation of the center electrode and the ground electrode and obtain further excellent durability, the time (total time) from the start to the end of power including the low power period is 3. It can be said that 0 ms or less is preferable.

  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 power in each high power period (the amount of work that the alternating current input to the spark plug 1 does per unit time) is constant, and the input power amount in each high power period is It is set to be equal. On the other hand, you may comprise so that electric power may change with time, without making electric power constant in each high electric power period. Therefore, for example, as shown in FIGS. 9 and 10, the power may be gradually reduced in the high power period. In addition, as shown in FIGS. 11 and 12, the input power amount may be changed in each high power period without equalizing the input power amount to the spark plug 1 in each high power period. Furthermore, as shown in FIG. 13, the maintenance time of the high power period may be different. Further, it is not necessary to end the power supply while the spark discharge is continued.

  (B) In the above embodiment, the supply of power to the spark plug 1 is stopped during the low power period. However, as shown in FIG. 14, AC plasma can be generated for the spark plug 1 during the low power period. It is good also as supplying electric power less than generated electric power.

  (C) In the above embodiment, the control unit 71 is configured by an ECU. However, the control unit 71 may be configured by, for example, a microcomputer without configuring the control unit 71 by the ECU. Alternatively, the discharge power source 41 may be controlled by an ECU or the like, and the AC power source 51 may be controlled by a power control unit including a microcomputer or the like.

  (D) The configuration of the spark plug 1 in the above embodiment is an exemplification, and the configuration of the spark plug to which the technical idea of the present invention can be applied is not limited thereto.

DESCRIPTION OF SYMBOLS 1 ... Spark plug 5 ... Center electrode 27 ... Ground electrode 28 ... Spark discharge gap (gap)
DESCRIPTION OF SYMBOLS 31 ... Ignition system 41 ... Power supply for discharge 51 ... AC power supply 71 ... Control part (electric power control part)

Claims (8)

A spark plug having a center electrode and a ground electrode;
A voltage source is applied to a gap formed between the center electrode and the ground electrode, and a discharge power source for generating a spark discharge in the gap;
An ignition system comprising an alternating current power source for supplying alternating current power to a spark generated by the spark discharge and generating alternating current plasma in the gap,
An ignition system, comprising: a power control unit that intermittently inputs a plurality of electric powers greater than or equal to a predetermined generation power capable of generating the AC plasma to the spark during the spark discharge.   The power control unit determines a maintenance time of a low power period between high power periods in which power equal to or greater than the generated power is input, and indicates an input energy in the high power period immediately before the low power period as E (J ), The ignition system according to claim 1, wherein E × 0.6 (ms / J) or more.   The power control unit is configured so that a time from the start of power supply to the end of power supply including a low power period between periods in which power equal to or greater than the generated power is input during the spark discharge is 3.0 ms or less. The ignition system according to claim 1 or 2, characterized in that:   The said power control part makes each maintenance time of the period when the electric power more than the said generation | occurrence | production electric power is supplied more than the period of the alternating current power supplied from the said alternating current power supply, The any one of Claim 1 thru | or 3 characterized by the above-mentioned. The ignition system according to claim 1. A spark plug having a center electrode and a ground electrode;
A voltage source is applied to a gap formed between the center electrode and the ground electrode, and a discharge power source for generating a spark discharge in the gap;
An ignition system control method comprising: an alternating current power source for supplying alternating current power to a spark generated by the spark discharge and generating alternating current plasma in the gap;
A control method for an ignition system, wherein a power equal to or higher than a predetermined generation power capable of generating the AC plasma is intermittently supplied to the spark a plurality of times during the duration of the spark discharge.   When the maintenance time of the low power period between the high power periods in which power equal to or greater than the generated power is input is defined as E (J), the input energy in the high power period immediately before the low power period is E (J) 6. The ignition system control method according to claim 5, wherein x is 0.6 (ms / J) or more.   The time from the start of power supply to the end of power supply including a low power period between periods in which power equal to or greater than the generated power is input during the duration of the spark discharge is set to 3.0 ms or less. The ignition system control method according to claim 5 or 6.   8. The maintenance period according to claim 5, wherein a maintenance time of a period during which power equal to or greater than the generated power is input is equal to or longer than a period of AC power supplied from the AC power supply. Ignition system control method.

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