JP2019065832A - Igniter - Google Patents

Abstract

To provide an igniter capable of preventing an electrolytic dissociation state of mixture gas between a center electrode and a ground electrode from changing due to flow of the mixture gas in a case of igniting the mixture gas.SOLUTION: An igniter comprises an ignition unit configured to ignite mixture gas in a combustion chamber of an internal combustion engine, and an electrolytic dissociation acceleration unit configured to accelerate electrolytic dissociation of the mixture gas. The ignition unit has a center electrode and a ground electrode oppositely arranged in the combustion chamber, and a voltage application section configured to apply voltage to the center electrode. The electrolytic dissociation acceleration unit is configured to accelerate the electrolytic dissociation of the mixture gas in the combustion chamber after a suction stroke of the combustion chamber and until the voltage application section applies voltage for igniting the mixture gas to the center electrode.SELECTED DRAWING: Figure 3

Description

  The disclosure described herein relates to an igniter for igniting a mixture of gases.

  As shown in Patent Document 1, there is known an igniter including an igniter plug, an igniter coil, and a switching element. The spark plug includes a center electrode and a ground electrode disposed via a gap in the combustion chamber of the engine. The ignition coil comprises a primary coil and a secondary coil magnetically coupled to one another.

  One end of the primary coil is connected to the positive electrode of the battery. The other end of the primary coil is grounded via the input / output terminal of the switching element. One end of the secondary coil is connected to the positive electrode of the battery. The other end of the secondary coil is connected to the center electrode.

  A constant voltage path is connected between the other end of the secondary coil and the center electrode. A zener diode is provided in the constant voltage path. The anode of the zener diode is connected to the other end of the secondary coil. The cathode of the zener diode is connected to the ground side.

  An ignition signal is input to the gate of the above switching element. The switching element is turned on when the ignition signal is turned on. As a result, energization from the battery to the primary coil is started. Storage of magnetic energy in the ignition coil is started.

  After that, the switching element is turned off by the ignition signal being turned off. This induces a high voltage in the secondary coil. A high voltage is applied to the gap between the center electrode and the ground electrode of the spark plug.

  As described above, the Zener diode is provided in the constant voltage path. Therefore, as described above, when a high voltage (secondary voltage) is applied to the gap of the spark plug, breakdown occurs in the zener diode. This limits the secondary voltage to the breakdown voltage of the zener diode. During the time when the secondary voltage is limited to the breakdown voltage, the air-fuel mixture in the gap is ionized. When the mixture in the gap becomes suitable for discharge due to this ionization, a discharge spark is generated in the gap.

Patent No. 5754448

  As described above, in the ignition device shown in Patent Document 1, the air-fuel mixture in the gap is ionized in a period in which the secondary voltage is limited to the breakdown voltage. This is because of the action shown below.

  When a secondary voltage is applied to the gap, an electric field is formed in the gap. Free electrons exist in the gap. Therefore, free electrons present in the gap are accelerated by the electric field and collide with gas molecules. As a result, free electrons are emitted from the gas molecules to generate positive ions (α action). The positive ions thus generated collide with the central electrode. This collision causes free electrons to be emitted from the central electrode (γ action). When the density of positive ions in the vicinity of the central electrode is increased, the electric field in the vicinity of the central electrode is intensified. This promotes the alpha action. The ionization of the mixture of gaps is promoted.

  However, if a mixture flow occurs in the gap between the time when the secondary voltage is applied to the gap and the discharge spark occurs, plus ions near the central electrode flow out of the gap. As a result, the electric field near the central electrode is weakened, and the ionization condition (ionization state) of the air-fuel mixture in the gap is changed. As a result, there is a possibility that the timing at which the discharge spark occurs may be shifted. This may change the output of the engine.

  Therefore, the disclosure described in the present specification provides an igniter capable of suppressing the change in the ionization state of the mixed gas between the center electrode and the ground electrode due to the flow of the mixed gas when igniting the mixed gas. The purpose is to

One of the disclosures is an ignition unit (10, 11, 12, 20) for igniting a mixed gas in a combustion chamber (200) of an internal combustion engine;
An ionization promoting unit (10, 11, 12, 20) for promoting ionization of the mixed gas;
The ignition unit has a center electrode (11) and a ground electrode (12) disposed opposite to each other in the combustion chamber, and a voltage application unit (20) for applying a voltage to the center electrode,
The ionization promoting unit promotes ionization of the mixed gas in the combustion chamber after the intake stroke of the combustion chamber until a voltage for igniting the mixed gas is applied to the central electrode by the voltage application unit.

  According to this, ionization of the mixed gas in the combustion chamber (200) is promoted before the voltage for ignition is applied to the center electrode (11). Therefore, even if the mixed gas between the center electrode (11) and the ground electrode (12) flows due to the flow of the mixed gas at the time of ignition, it flows between the center electrode (11) and the ground electrode (12) The ionized state of the mixed gas is expected to be the same as the ionized state of the mixed gas that has flowed out. Thus, unlike the configuration that promotes the ionization of the mixed gas between the center electrode and the ground electrode at the time of ignition, the flow of the mixed gas causes the space between the center electrode (11) and the ground electrode (12) to It is suppressed that the ionization state of the mixed gas changes. Therefore, the mixed gas can be ignited without depending on the flow of the mixed gas.

  The reference numerals in the parentheses above merely indicate the correspondence with the configurations described in the embodiments to be described later, and do not limit the technical scope at all.

It is a block diagram for explaining an ignition device. It is a graph for demonstrating the electric current which flows into an ignition device. It is a timing chart for explaining the drive of an ignition device. It is a graph for demonstrating the applied voltage at the time of arc discharge generation | occurrence | production. It is a conceptual diagram for demonstrating the value relevant to arc discharge. It is a conceptual diagram for demonstrating an intake pressure cooling water temperature map. It is a flowchart for demonstrating calculation of an ionization promotion signal. It is a conceptual diagram for demonstrating a rotational speed load map.

  Hereinafter, embodiments will be described based on the drawings.

First Embodiment
The ignition device according to the present embodiment will be described based on FIGS. 1 to 8. The igniter 100 has an igniter plug 10 and an igniter circuit 20. The spark plug 10 is provided in a combustion chamber 200 of an internal combustion engine (engine). Spark discharge (glow discharge) is generated in the spark plug 10 by the ignition circuit 20. Thereby, the mixed gas in the combustion chamber 200 is ignited.

<The behavior of the engine>
Hereinafter, before describing the ignition device 100, the behavior of the engine will be described. This engine is a four-stroke engine. In the engine in the combustion drive state, the intake stroke, the compression stroke, the combustion expansion stroke, and the exhaust stroke shown below are sequentially repeated.

  In the intake stroke, the piston of the engine descends in the cylinder in conjunction with the rotation of the crankshaft. This increases the volume of the combustion chamber 200 partitioned by the cylinder and the piston. At this time, the combustion chamber 200 and the intake port are communicated by the intake valve, and the gas (mainly air) of the intake port is drawn into the combustion chamber 200. In addition, mist-like fuel is injected from the injector into the combustion chamber 200. As a result, a mixture of gas and fuel of the intake port flows into the combustion chamber 200.

  In the compression stroke, the piston passes through the bottom dead center and ascends in the cylinder. Thereby, the capacity of the combustion chamber 200 is reduced. At this time, the communication between the combustion chamber 200 and the intake port is interrupted by the intake valve. Of course, the communication between the combustion chamber 200 and the exhaust port is blocked by the exhaust valve. Thereby, the mixed gas in the combustion chamber 200 is compressed.

  In the combustion expansion stroke, glow discharge is generated in the spark plug 10 when the piston is moving up to the top dead center or when the piston is falling past the top dead center. As a result, the mixed gas ignites and burns and explodes. The mixed gas in the combustion chamber 200 expands, thereby lowering the piston. The kinetic energy of the piston due to this explosion is converted to rotational energy of the crankshaft. The rotational energy of the crankshaft is output as an output of the engine to a drive wheel or the like through a power transmission device.

  In the exhaust stroke, when the piston starts to rise past the bottom dead center, the drive of the exhaust valve causes the combustion chamber 200 to communicate with the exhaust port. Thereby, the exhaust gas in the combustion chamber 200 is exhausted.

  After the exhaust stroke, when the piston starts to descend past the top dead center, the above-described intake stroke is performed again. As described above, the engine in the combustion driving state sequentially performs four strokes of an intake stroke, a compression stroke, a combustion expansion stroke, and an exhaust stroke.

<Configuration of Ignition Device>
Next, the ignition device 100 will be described. As described above, the ignition device 100 includes the spark plug 10 and the ignition circuit 20. The spark plug 10 has a center electrode 11 and a ground electrode 12. As shown in FIG. 1, the center electrode 11 is connected to the ignition circuit 20. The ground electrode 12 is connected to the ground. The spark plug 10 and the ignition circuit 20 correspond to an ignition unit and an ionization promoting unit. The ignition circuit 20 corresponds to a voltage application unit.

  The center electrode 11 and the ground electrode 12 are disposed to face each other in the combustion chamber 200 with a space therebetween. A part of the center electrode 11 protrudes to the ground electrode 12 side. On the other hand, the portion of the ground electrode 12 facing the center electrode 11 has a flat plate shape. The flat plate portion of the ground electrode 12 and the projection portion of the center electrode 11 are spaced apart and opposed to each other. Hereinafter, the air gap between the center electrode 11 and the ground electrode 12 is referred to as a gap. A plurality of grooves for promoting the occurrence of glow discharge may be formed on the surface of the flat portion of the ground electrode 12 on the center electrode 11 side.

  As shown in FIG. 1, the ignition circuit 20 has a first path L1 connecting the positive electrode of the battery 40 mounted on the vehicle and the ground, and a second path L2 connecting the first path L1 and the center electrode 11 Have. The ignition circuit 20 has an ignition coil 21, an igniter 22, and a diode 23 provided in the first path L1 and the second path L2. Furthermore, the ignition circuit 20 has an engine ECU 24. The igniter 22 corresponds to a switch element. The engine ECU 24 corresponds to a control unit.

  The ignition coil 21 has a magnetically coupled primary coil 21a and a secondary coil 21b. Magnetic coupling is shown by hatching in FIGS. 1 and 2. The igniter 22 described above is an N-channel MOSFET. The igniter 22 is controlled to open and close by the engine ECU 24.

  The engine ECU 24 is electrically connected to various sensors mounted on the vehicle and the various ECUs. These various sensors are collectively shown as an on-vehicle sensor 300 in FIG. The various ECUs are collectively shown as an on-board ECU 400.

  Various sensor signals detected by the in-vehicle sensor 300 are input to the engine ECU 24. The engine ECU 24 exchanges signals with each other through the in-vehicle ECU 400 and the in-vehicle network. The engine ECU 24 determines generation and output of control signals to be output to the igniter 22 based on various sensor signals input from the in-vehicle sensor 300 and various vehicle information input from the in-vehicle ECU 400.

<Circuit configuration of ignition device>
As shown in FIG. 1, in the first path L1, the primary coil 21a and the igniter 22 are connected in series in order from the positive electrode of the battery 40 to the ground. One end of the primary coil 21 a is connected to the positive electrode of the battery 40. The other end of the primary coil 21 a is connected to the drain electrode of the igniter 22. The source electrode of the igniter 22 is connected to the ground. The gate electrode of the igniter 22 is connected to the engine ECU 24. The closed state and the open state of the igniter 22 are controlled by a control signal output from the engine ECU 24 to the igniter 22. The ground corresponds to the reference potential.

  The second path L2 connects the center electrode 11 to the midpoint between the battery 40 and the primary coil 21a in the first path L1. In the second path L2, the diode 23 and the secondary coil 21b are connected in series in order from the connection point with the first path L1 toward the center electrode 11. The cathode electrode of the diode 23 is connected to the connection point between the first path L1 and the second path L2. The anode electrode of the diode 23 is connected to one end of the secondary coil 21b. The other end of the secondary coil 21 b is connected to the center electrode 11.

<Behavior of the igniter>
Next, the behavior of the ignition device 100 will be described based on FIG. In addition, in FIG. 2, in order to avoid that a description becomes complicated, description of the code | symbol is abbreviate | omitted.

  An alternating voltage or a direct current voltage is applied to the center electrode 11 of the ignition device 100 by the opening / closing control of the igniter 22 by the control signal output from the engine ECU 24. Hereinafter, a control signal for applying an alternating voltage to the center electrode 11 is referred to as an ionization promoting signal. A control signal for applying a DC voltage to the center electrode 11 is referred to as an ignition signal.

  The ionization promoting signal is a pulse signal including a plurality of pulses generated by switching the voltage level between high level and low level at a predetermined cycle. The frequency of this ionization promoting signal is an integral multiple of the resonant frequency of the secondary coil 21b. In the present embodiment, 1 time of the resonance frequency of the secondary coil 21 b is adopted as the frequency of the ionization promoting signal. This frequency is, for example, about 15 kHz. The duty ratio of the ionization promoting signal will be described in detail later.

  When the ionization promotion signal is at high level, the igniter 22 is closed. Therefore, as shown in the (a) column of FIG. 2, a current flows from the battery 40 to the ground through the primary coil 21 a and the igniter 22 in the first path L1. When the ionization promotion signal switches from high level to low level, the igniter 22 goes from the closed state to the open state. As a result, as shown in the column (b) of FIG. 2, the current does not flow to the primary coil 21a. However, the switching from the closed state to the open state of the igniter 22 is repeated at, for example, 15 kHz as described above. Therefore, the amount of current flowing through the primary coil 21a changes continuously in time. Therefore, the strength of the magnetic field generated from the primary coil 21a also changes continuously in time. Thus, a magnetic field whose strength changes continuously in time passes through the secondary coil 21b. As a result, an induced electromotive force is constantly generated in the secondary coil 21b.

  The generation direction of the induced electromotive force generated in the secondary coil 21b changes temporally continuously according to the increase and decrease of the current flowing through the primary coil 21a. That is, the induced electromotive force changes in an alternating manner. Therefore, the voltage (applied voltage) applied to the center electrode 11 connected to the other end of the secondary coil 21b also changes in an alternating manner.

  When the applied voltage is lower than the power supply voltage of the battery 40, a reverse bias is applied to the diode 23. As shown in the column (a) of FIG. 2, in this case also, a small amount of current flows in the diode 23. The amount of current flowing through the diode 23 is about several μA.

  On the contrary, when the applied voltage is higher than the power supply voltage of the battery 40, the diode 23 is applied with a forward bias. As shown in the (b) column of FIG. 2, a current to the battery 40 flows through the diode 23.

  As described above, when the igniter 22 is controlled to open and close in a predetermined cycle by the ionization promotion signal, an alternating voltage is applied to the center electrode 11. Thereby, at least one of corona discharge and glow discharge is generated in the center electrode 11.

  The corona discharge and glow discharge are sustained discharges that occur due to the occurrence of an uneven electric field around the center electrode 11. By the generation of at least one of corona discharge and glow discharge, a plurality of paths (streamers) through which charged particles pass are formed between the center electrode 11 and the ground electrode 12. Thereby, the mixed gas located in the vicinity of the central electrode 11 is ionized. In other words, the mixed gas located in the vicinity of the center electrode 11 is ionized. As a result, the number of free electrons contained in the mixed gas is increased. The amplitude of the alternating voltage corresponds to the voltage level of the first voltage.

  The ignition signal is a pulse signal including a single pulse generated by switching to a low level after the voltage level is maintained at a high level for a predetermined time. The predetermined time to be kept at the high level is determined based on the above-described state of acceleration of ionization, various information described later, and the like. The degree of acceleration of ionization depends on the duty ratio of the ionization promoting signal, the output time, and the like. The engine ECU 24 stores a map for these ionization promotion signals and various information. The engine ECU 24 determines a predetermined time based on the ionization promotion signal and various information and a stored map. Of course, such a map is obtained by performing various experiments in advance. Although various maps appear in the following, they are also obtained in advance by carrying out various experiments in the same manner. The various maps are stored in the engine ECU 24.

  When the ignition signal is high, the igniter 22 is closed. Therefore, as shown in column (c) of FIG. 2, a current flows from the battery 40 to the ground through the primary coil 21 a and the igniter 22 in the first path L1. At this time, a reverse bias corresponding to the power supply voltage of the battery 40 is applied to the diode 23. Therefore, almost no current flows in the diode 23. The current does not flow also to the secondary coil 21b of the second path L2. However, the magnetic field generated from the primary coil 21a continues to pass through the secondary coil 21b. Thereby, magnetic energy continues to be accumulated in the secondary coil 21b.

  When the ignition signal changes from the high level to the low level, the energization through the primary coil 21a in the first path L1 is stopped. For this reason, the magnetic field which has passed through the secondary coil 21b rapidly decreases, and an induced electromotive force is generated in the secondary coil 21b. The induced electromotive force is positive on the diode side and negative on the center electrode 11 side. The voltage applied to the center electrode 11 is lower than the ground potential, and the ground electrode 12 has a higher potential than the center electrode 11. A dielectric breakdown occurs between the center electrode 11 and the ground electrode 12, and an arc discharge is generated from the ground electrode 12 toward the center electrode 11. As a result, as shown in the (d) column of FIG. 2, a current flows from the center electrode 11 to the battery 40 through the secondary coil 21 b and the diode 23 in the second path L2. The arc discharge is more likely to occur as the number of free electrons contained in the mixed gas between the center electrode 11 and the ground electrode 12 increases. The voltage applied to the center electrode 11 by the ignition signal corresponds to a second voltage.

  As described above, at least one of corona discharge and glow discharge is generated in the center electrode 11 due to the generation of an alternating voltage due to the ionization promoting signal. This ionizes the mixed gas and increases the number of free electrons contained in the mixed gas.

  Therefore, before generating an arc discharge by an ignition signal, at least one of a corona discharge and a glow discharge is generated in advance on the center electrode 11 to increase the number of free electrons contained in the mixed gas. Thus, arc discharge can be easily generated between the center electrode 11 and the ground electrode 12.

  As described above, the engine sequentially performs four strokes of an intake stroke, a compression stroke, a combustion expansion stroke, and an exhaust stroke. These various strokes are interlocked with the rotational angle of the crankshaft. The on-vehicle sensor 300 includes a rotation sensor that detects the rotation angle of the crankshaft. Therefore, the rotation angle of the crankshaft is input to engine ECU 24 from in-vehicle sensor 300. The engine ECU 24 determines which stroke the engine is performing based on the rotation angle of the crankshaft. Then, the engine ECU 24 determines the output timing of the ionization promoting signal and the ignition signal.

  Specifically, the engine ECU 24 outputs an ionization promoting signal to the igniter 22 after the intake stroke. Thereafter, at a predetermined time before the start of the combustion expansion stroke in the compression stroke, the engine ECU 24 starts to output the ignition signal by setting the control signal to the high level. As a result, the voltage level of the ignition signal switches from the high level to the low level after a predetermined time has elapsed from the start of the output of the ignition signal. At this time, glow discharge occurs and the combustion expansion stroke starts.

  In the following, for the sake of simplicity, the control signal is denoted as control signal CS. The ionization promotion signal is denoted as ionization promotion signal IPS. The ignition signal is shown as an ignition signal IS. The voltage applied to the center electrode 11 is referred to as an applied voltage V2. The current flowing through the secondary coil 21b is referred to as a current I2. Further, the predetermined time is indicated as a predetermined time Δt. This is the same in the drawings.

  As shown in FIG. 3, the engine ECU 24 of the present embodiment outputs the ionization promoting signal IPS to the igniter 22 in a period from the start time t1 to the end time t2 of the intake stroke. As a result, the applied voltage V2 changes like an AC voltage. The amplitude of the applied voltage V2 is about 2.0 to 4.0 kV. At this time, the current I2 also changes like an alternating current. However, the current I2 at this time is an order of magnitude smaller than the discharge current at the time of glow discharge occurrence. Therefore, in FIG. 3, the current I2 is described so as to hardly change.

  As described above, in the intake stroke, the volume of the combustion chamber 200 is increased by the lowering of the piston, and the gas of the intake port is sucked into the combustion chamber 200. Therefore, in the suction stroke, the gas is hardly discharged out of the combustion chamber 200, and the mixed gas flows in the combustion chamber 200. Therefore, the mixed gas flows in the gap between the center electrode 11 and the ground electrode 12. At this time, at least one of corona discharge and glow discharge is generated in the center electrode 11 by the output of the ionization promotion signal IPS. Therefore, the mixed gas flowing in the gap is ionized sequentially. As a result, the mixed gas in the combustion chamber 200 is ionized on average, and the number of free electrons increases.

  As described above, in the compression stroke, the communication between the intake port and the exhaust port and the combustion chamber is interrupted. Therefore, it is difficult to discharge the mixed gas with the increased number of free electrons to the outside of the combustion chamber 200 by corona discharge or glow discharge.

  The engine ECU 24 estimates a time t3 in which the piston ascends and reaches top dead center in the compression stroke based on the rotational speed of the crankshaft. Then, the engine ECU 24 calculates a timing that is earlier than the time t3 by a predetermined time Δt. The predetermined time Δt is calculated based on the degree of promotion of ionization (the number of free electrons), various information, and the like as described above.

  At time t4, which is earlier than time t3, by a predetermined time Δt, the engine ECU 24 turns the control signal CS to high level and starts to output the ignition signal IS. As a result, current flows through the primary coil 21a, and magnetic energy is accumulated in the secondary coil 21b.

  When a predetermined time Δt elapses from time t4 to time t3, the engine ECU 24 changes the ignition signal IS from the high level to the low level. As a result, as shown in FIG. 3, the applied voltage V2 sharply drops below the ground potential. When the voltage level of applied voltage V2 becomes low enough to cause dielectric breakdown between center electrode 11 and ground electrode 12, glow discharge occurs between center electrode 11 and ground electrode 12, and a discharge current flows . Thus, when the discharge current flows, the energy stored in the secondary coil 21b is released. The peak discharge current is about several tens of mA. After time t3, the applied voltage V2 and the current I2 decrease.

  In FIG. 4, the applied voltage V2 at the time of glow discharge occurrence when the number of free electrons is increased by corona discharge or glow discharge is shown by a solid line. Further, the applied voltage V2 at the time of occurrence of glow discharge when the number of free electrons is not increased is indicated by a broken line. The required voltage shown in FIG. 4 indicates the voltage level of the applied voltage V2 required to cause the arc discharge. As clearly shown in FIG. 4, when the number of free electrons is increased, the required voltage is smaller than when it is not increased.

<Duty ratio of ionization promotion signal>
As described above, the ignition device 100 generates corona discharge or glow discharge before igniting the mixed gas by arc discharge. The corona discharge and glow discharge are generated by the output of the ionization promoting signal IPS, but when the duty ratio is increased, that is, when the pulse width is increased, the voltage V2 applied to the center electrode 11 is increased. Therefore, an increase in duty ratio may cause arc discharge rather than corona discharge or glow discharge. In order to avoid this, the engine ECU 24 determines the duty ratio of the ionization promotion signal IPS based on various information shown in FIG.

  The arc discharge depends on the state of the mixed gas shown in FIG. 5 and the state of the spark plug. The state of the mixed gas includes the pressure, temperature, humidity, A / F value, and EGR value of the mixed gas. The state of the spark plug includes the temperature of the spark plug, the shape, the length of the gap, the material, and the amount of consumption of the electrode. Information related to these is input from the on-vehicle sensor 300 or the on-vehicle ECU 400 to the engine ECU 24. The engine ECU 24 determines the duty ratio of the ionization promotion signal IPS based on these values.

  That is, when the arc discharge is more likely to occur as the value related to the arc discharge is higher, for example, the engine ECU 24 lowers the duty ratio of the ionization promotion signal IPS contrary to the increase of the value. Conversely, if an arc discharge is more likely to occur, for example, if the value associated with the arc discharge is lower, the engine ECU 24 increases the duty ratio of the ionization promotion signal IPS as opposed to the reduction of that value. Hereinafter, the increase and decrease of the duty ratio of the ionization promotion signal IPS by the engine ECU 24 with respect to each parameter will be listed.

  Arc discharge is more likely to occur as the density of the mixed gas is lower. In contrast, the lower the pressure of the gas mixture, the lower the density of the gas mixture. Also, the higher the temperature of the mixed gas, the thinner the density of the mixed gas. Therefore, the engine ECU 24 lowers the duty ratio as the pressure of the mixed gas is lower. The engine ECU 24 reduces the duty ratio as the temperature of the mixed gas increases. The pressure and temperature of the mixed gas can be estimated from the amount of intake air sucked into the combustion chamber 200, the intake pressure thereof, the temperature of the engine coolant, the temperature of the fuel, and the like.

  Arc discharge is more likely to occur as the humidity of the mixed gas is lower. Therefore, the engine ECU 24 lowers the duty ratio as the humidity of the mixed gas is lower.

  Although not shown in FIG. 5, the arc discharge is more likely to occur as the fuel species contained in the mixed gas is less likely to be vaporized. Therefore, the engine ECU 24 lowers the duty ratio to the extent that the fuel type is difficult to vaporize. The fuel type is stored in advance in the engine ECU 24.

  The above A / F value is an air fuel ratio obtained by dividing the air mass by the fuel mass. As the A / F value is richer, arcing is more likely to occur. Therefore, the engine ECU 24 lowers the duty ratio to such a rich A / F value.

  The above EGR value indicates the amount by which the exhaust gas discharged to the exhaust port in the exhaust stroke is drawn into the combustion chamber 200 in the intake stroke. EGR is an abbreviation for Exhaust Gas Recirculation. As the EGR value increases, the proportion of air drawn into the combustion chamber 200 decreases. This makes arcing less likely to occur. Therefore, the engine ECU 24 increases the duty ratio as the EGR value increases.

  The arc discharge is more likely to occur as the temperature (electrode temperature) of the center electrode 11 and the ground electrode 12 of the spark plug 10 is higher. Therefore, the engine ECU 24 lowers the duty ratio as the temperature of the spark plug 10 increases. The temperature of the spark plug 10 is obtained based on the intake pressure, the engine coolant temperature, and the intake pressure cooling water temperature map shown in FIG. The engine ECU 24 stores this intake pressure cooling water temperature map in advance.

  The arc discharge is more likely to occur as the opposing portions of the center electrode 11 and the ground electrode 12 of the spark plug 10 face each other. The shapes (electrode shapes) of the center electrode 11 and the ground electrode 12 of the spark plug 10 are stored in advance in the engine ECU 24. Therefore, the engine ECU 24 lowers the duty ratio as the sharpness of the spark plug 10 increases.

  The arc discharge is more likely to occur as the separation distance (gap length) between the center electrode 11 and the ground electrode 12 of the spark plug 10 is shorter. The length of such a gap is stored in advance in the engine ECU 24. Therefore, the engine ECU 24 reduces the duty ratio as the gap length decreases.

  As described above, the arc discharge tends to occur as the sharpness of the spark plug 10 increases and as the gap length decreases. However, the shape and gap length of the spark plug 10 change depending on the amount of wear (the amount of electrode wear) of the center electrode 11 and the ground electrode 12 of the spark plug 10. The use of many years makes the spark plug 10 less sharp and the gap length becomes longer. Therefore, the engine ECU 24 increases the duty ratio so that the exhaustion of the spark plug 10 becomes severe.

  The consumption of the spark plug 10 can be estimated by the number of arc discharges of the spark plug 10 and the forming material. The number of arc discharges can be recorded by the engine rotational speed and the engine load information. The forming material can be stored in advance in the engine ECU 24.

<Generation of ionization promotion signal>
Next, the calculation flow of the ionization promotion signal IPS by the engine ECU 24 will be described based on FIGS. 7 and 8.

  First, in step S10, the engine ECU 24 reads the engine rotational speed and the engine load information from the in-vehicle sensor 300 and the in-vehicle ECU 400. After this, the engine ECU 24 proceeds to step S20.

  When the process proceeds to step S20, the engine ECU 24 acquires various information (parameters) for correcting the above-described duty ratio from the in-vehicle sensor 300 and the in-vehicle ECU 400. Specifically, the engine ECU 24 acquires the intake air amount, intake pressure, engine coolant temperature, fuel temperature, mixed gas humidity, A / F value, EGR value, etc. from the in-vehicle sensor 300 and the in-vehicle ECU 400. Do. Then, the engine ECU 24 estimates the pressure and temperature of the mixed gas, and the temperature and consumption of the spark plug 10. After this, the engine ECU 24 proceeds to step S30.

  As described above, in step S10, the engine ECU 24 reads the engine rotational speed and the engine load information from the in-vehicle sensor 300 and the in-vehicle ECU 400. In step S20, the engine ECU 24 acquires the intake air amount, the intake pressure, and the like from the in-vehicle sensor 300 and the in-vehicle ECU 400. For example, there is a correlation between engine load information and the amount of intake air. As described above, the information acquired in step S10 and the information acquired in step S20 include information having a correlation. However, this does not indicate that the information acquired in step S10 is newly acquired in step S20. As described later, the information acquired in step S10 relates to the calculation of the basic duty ratio, and the information acquired in step S10 and step S20 relates to the correction coefficient k. In order to clearly divide and explain the values necessary for the calculation of the basic duty ratio and the calculation of the correction coefficient k, only the steps S10 and S20 are described separately.

  When the process proceeds to step S30, the engine ECU 24 determines the basis of the ionization acceleration signal IPS based on the engine rotational speed and engine load information acquired in step S10 and the rotational speed load map shown in FIG. 8 stored in advance in the engine ECU 24. Calculate the duty ratio. As described above, in the present embodiment, the frequency of the ionization promoting signal IPS is determined to be one times the resonance frequency of the secondary coil 21b. Therefore, in this step S30, the basic signal which is the basis of the ionization promoting signal IPS is calculated. This basic signal corresponds to a basic pulse signal. After this, the engine ECU 24 proceeds to step S40.

  When the process proceeds to step S40, the engine ECU 24 calculates a correction coefficient k for correcting the basic duty ratio, based on the various information acquired and estimated in steps S10 and S20. After this, the engine ECU 24 proceeds to step S50.

  At step S50, the engine ECU 24 calculates the duty ratio of the ionization promotion signal IPS based on the basic duty ratio calculated at step S30 and the correction coefficient k. Thus, the engine ECU 24 calculates the ionization promotion signal IPS.

  The correction coefficient k may be a correction value to be multiplied by the basic duty ratio, or may be a correction value to be added to or subtracted from the basic duty ratio. Alternatively, the correction coefficient k may be determined based on all of the various parameters for correcting the duty ratio described above, or by selecting the correction coefficient for each of the various parameters and then selecting one of them. The correction coefficient k may be determined. As described above, when one of the plurality of correction coefficients is selected, the correction coefficient that reduces the basic duty ratio most is selected among the plurality of correction coefficients in order to avoid the occurrence of arcing.

  In the present embodiment, as described above, one time the resonance frequency of the secondary coil 21b is employed as the frequency of the ionization promoting signal IPS. The frequency may be appropriately corrected in the above-described calculation flow. In this case, the increase and decrease of the frequency and the increase and decrease of the duty ratio with respect to the value related to the arc discharge shown in FIG. 5 are the same. That is, when the duty ratio is lowered, the frequency is also lowered. In addition, it is also possible to adopt a configuration in which only the frequency is corrected without correcting the duty ratio.

<Function effect>
Next, the operation and effect of the ignition device 100 according to the present embodiment will be described. As described above, the engine ECU 24 of the ignition device 100 outputs the ionization promotion signal IPS in the intake stroke. Thereby, an alternating voltage is applied to the center electrode 11, and at least one of corona discharge and glow discharge is generated in the center electrode 11. As a result, ionization of the mixed gas in the combustion chamber 200 is promoted. The number of free electrons contained in the mixed gas in the combustion chamber 200 is increased. After this, the engine ECU 24 outputs an ignition signal IS. As a result, a DC voltage is applied to the center electrode 11 and glow discharge occurs in the center electrode 11. As a result, the mixed gas is ignited.

  According to this, in the intake stroke, ionization of all the mixed gas in the combustion chamber 200 is promoted, not only the mixed gas located in the gap between the center electrode 11 and the ground electrode 12 and in the vicinity thereof . Therefore, even if the mixed gas flows in or near the gap due to the flow of the mixed gas in the compression process, for example, after the intake stroke, the ionized state of the mixed gas newly introduced into the gap is the ionization of the discharged mixed gas. It is expected to be identical to the state. Thus, unlike the configuration that promotes the ionization of the mixture gas in the gap at the time of ignition by the output of the ignition signal, the ionization state of the mixture gas in the gap changes even if the mixture gas in the gap or in the vicinity flows. Is suppressed. Therefore, the mixed gas can be ignited without depending on the flow of the mixed gas. As a result, deviation of the start timing of the combustion expansion stroke is suppressed. Fluctuation of engine output is suppressed.

  As described above, in the intake stroke, the gas is hardly discharged out of the combustion chamber 200, and the mixed gas flows in the combustion chamber 200. Therefore, the mixed gas flows in the gap between the center electrode 11 and the ground electrode 12, and the mixed gas flowing in the gap is sequentially ionized by corona discharge or glow discharge. Therefore, the mixed gas in the combustion chamber 200 is ionized on average.

  Corona discharge and glow discharge are generated at the center electrode 11 generating glow discharge. According to this, for example, an increase in the number of parts is suppressed as compared with a configuration in which an electrode generating corona discharge and glow discharge is separately provided from the center electrode and the ground electrode.

  At least one of the duty ratio and the frequency of the ionization promoting signal IPS that generates at least one of the corona discharge and the glow discharge is determined based on a value related to the glow discharge so that the glow discharge does not occur. This suppresses the occurrence of glow discharge in the spark plug 10 before the start of the combustion expansion stroke.

  Although the preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and can be variously modified and implemented without departing from the spirit of the present disclosure. It is.

(First modification)
In the present embodiment, the engine ECU 24 outputs the ionization promoting signal IPS during the start and end of the intake stroke to promote ionization of the mixed gas. However, the output period of the ionization promotion signal IPS is not limited to the above example. The ionization promotion signal IPS may start to be output during the intake stroke or in the compression stroke. Further, the ionization promotion signal IPS may stop its output in the middle of the intake stroke or in the compression stroke. The output period of the ionization promotion signal IPS may be from the start of the intake stroke to a predetermined time Δt before the start of the combustion expansion stroke.

(Second modification)
The igniter 100 can be applied to a high compression ratio engine, a high supercharged engine, a supercharged downsizing engine, a naturally aspirated engine, and the like. The ignition device 100 can also be applied to a cylinder injection type engine, an intake port injection type engine, a dual injection type engine, and the like.

(Other modifications)
In the present embodiment, an example in which the mixed gas is promoted to be ionized by applying an alternating voltage to the center electrode 11 is shown. However, the ionization of the mixed gas may be promoted by, for example, irradiation of ultraviolet light or X-rays and laser output.

DESCRIPTION OF SYMBOLS 10 ... Ignition plug, 11 ... Center electrode, 12 ... Ground electrode, 20 ... Ignition circuit, 21 ... Ignition coil, 21a ... Primary coil, 21b ... Secondary coil, 22 ... Igniter, 23 ... Diode, 24 ... Engine ECU, 40: battery, 100: ignition device, 200: combustion chamber, 300: in-vehicle sensor, 400: in-vehicle ECU

Claims (6)

An ignition unit (10, 11, 12, 20) for igniting mixed gas in a combustion chamber (200) of an internal combustion engine;
An ionization promoting unit (10, 11, 12, 20) for promoting ionization of the mixed gas;
The ignition unit includes a center electrode (11) and a ground electrode (12) disposed opposite to each other in the combustion chamber, and a voltage application unit (20) for applying a voltage to the center electrode.
The ionization promoting unit ionizes the mixed gas in the combustion chamber after an intake stroke of the combustion chamber until a voltage for igniting the mixed gas is applied to the central electrode by the voltage application unit. Ignition device that promotes the The ionization promoting unit shares the center electrode, the ground electrode, and the voltage application unit with the ignition unit,
The voltage application unit generates at least one of corona discharge and glow discharge by applying a first voltage to the center electrode to promote ionization of the mixed gas, and the voltage level is higher than the first voltage. The ignition device according to claim 1, wherein arc discharge is generated to ignite the mixed gas by applying a second voltage as a voltage for igniting the mixed gas to the center electrode.   The igniter according to claim 2, wherein the first voltage is an alternating voltage, and the second voltage is a direct voltage. The voltage application unit includes: a switch element (22) provided between a power supply (40) and a reference potential; a primary coil (21a) provided between the switch element and the power supply; A secondary coil (21b) magnetically coupled to the next coil to be connected to the center electrode, and a control unit (24) that performs opening / closing control of the switch element,
The control unit
A basic pulse signal is calculated based on the rotational speed of the internal combustion engine and load information;
A correction value for correcting at least one of the duty ratio and the frequency of the basic pulse signal is calculated based on the information on the mixed gas and the information on the center electrode and the ground electrode,
The ignition device according to claim 3, wherein the first voltage is applied to the center electrode by controlling the switching element based on the basic pulse signal and the correction value.   5. The igniter according to claim 4, wherein the information of the mixed gas includes at least one of pressure, temperature, humidity, air-fuel ratio, and amount by which exhaust gas is returned to the combustion chamber.   The ignition device according to claim 4 or 5, wherein the information of the center electrode and the ground electrode includes at least one of a distance between the center electrode and the ground electrode, a shape, a consumed amount, and a temperature. .

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