WO2021210158A1

WO2021210158A1 - Ignition system

Info

Publication number: WO2021210158A1
Application number: PCT/JP2020/016849
Authority: WO
Inventors: 中川　光; 貴裕井上; 民田　太一郎; 棚谷　公彦
Original assignee: 三菱電機株式会社
Priority date: 2020-04-17
Filing date: 2020-04-17
Publication date: 2021-10-21
Also published as: JPWO2021210158A1; JP6840301B1

Abstract

Provided is a dielectric barrier discharge type ignition system capable of changing the frequency of an AC voltage applied to a spark plug and changing a discharge energy density while amplifying the AC voltage applied to the spark plug via resonance of a resonance circuit. The ignition system comprises a frequency change connection circuit (3) that has a frequency change circuit (32), which changes a resonance frequency fr of the entire circuit, and that connects a DC/AC converter (2) and a spark plug (4). The ignition system outputs an AC voltage of an AC frequency (fsw) to the DC/AC converter (2), changes a resonance frequency (fr) by controlling the frequency change circuit (32), and changes an AC frequency (fr).

Description

Ignition system

This application relates to an ignition system.

As a method for improving the fuel efficiency of an internal combustion engine mounted on a vehicle, a lean combustion method for burning a lean mixture, an exhaust gas recirculation method for recirculating exhaust gas in a combustion chamber, or a high compression ratio in the combustion chamber. The method etc. are being developed. However, both methods have a problem that it is difficult to ignite the fuel, and improvement in ignitability is required.

In response to the demand for improved ignitability of ignition devices, an ignition system has been proposed that generates chemically active species by dielectric barrier discharge, which is a non-equilibrium plasma, and promotes flammability after ignition or directly ignites fuel. (Patent Document 1). In flammability promotion, before the ignition timing, a non-equilibrium plasma having energy that does not ignite is generated, and many chemically active species are generated. In direct ignition, the fuel is directly burned by inputting high energy at the ignition timing.

Patent No. 64826284 Patent No. 4924275 Japanese Unexamined Patent Publication No. 9-172788

As described above, since the discharge energy required for discharge differs depending on the purpose of the ignition device using the dielectric barrier discharge, it is desirable to adjust the discharge energy according to the purpose and timing. The discharge energy of a dielectric barrier discharge is generally the load capacity determined by the structure of a spark plug and the environment between electrodes, the maximum value of the load applied voltage, the discharge maintenance voltage, the frequency of the load applied voltage, and the voltage to the load. Determined by the application time. The load capacity and discharge maintenance voltage are naturally determined by the device structure and operating environment. Therefore, the parameters that can be used to adjust the discharge energy are the maximum value and frequency of the load applied voltage and the voltage application time to the load.

Patent Document 2 proposes adjusting the discharge energy by controlling the voltage value of the output AC voltage or the wave number in an ignition device using a predetermined spark plug. Here, the wave number is determined from the AC voltage frequency and the voltage application time. Although Patent Document 2 does not describe a specific configuration of an electric circuit, it is considered that a transformer with a very large turn ratio and a large number of semiconductor switches are required for an AC power supply with a high voltage output, and a space for a vehicle or the like. It is difficult to install it in a place with large restrictions.

As a power supply system for configuring an AC power supply with a high voltage output in a relatively small size, a system using a resonance circuit as in Patent Document 3 has been proposed. In this power supply system, the frequency of the AC power supply to be supplied is set to the series resonance frequency of the coil and the capacitor of the load or its vicinity, and a large series resonance voltage is generated in the electrode by the resonance of the load. However, since the frequency that the AC power supply can apply to the load is only the pressure near the resonance frequency, when applied to the dielectric barrier ignition device, the discharge energy cannot be adjusted by the frequency unless the configuration of the load resonance circuit is changed. .. As a result, the discharge energy adjustment of the dielectric barrier discharge is adjusted only by the application time of the AC voltage to the spark plug and the maximum value of the applied voltage. Increasing the applied voltage requires an increase in the insulation distance and an improvement in the power supply output, which causes a problem of increasing the volume of the device. Therefore, the increase / decrease in the voltage application time is mainly used for adjusting the discharge energy. In that case, if the application time is long, a large discharge energy is input between the electrodes, and if the application period is short, a small discharge energy is input between the electrodes. Therefore, for example, it is not possible to output discharge energy with a high degree of freedom, such as inputting a large amount of discharge energy in a short time. As a result, direct ignition, which requires a local high energy input, may not be possible.

Therefore, in the present application, a dielectric barrier discharge type capable of changing the frequency of the AC voltage applied to the spark plug and changing the discharge energy density while amplifying the AC voltage applied to the spark plug by the resonance of the resonance circuit. It is intended to provide an ignition system.

The ignition system according to the present application is
A DC / AC converter with a switch that converts DC power supplied from a DC power supply to AC power,
A spark plug having a pair of electrodes and a dielectric arranged between the pair of electrodes and arranged in the combustion chamber of an internal combustion engine.
A frequency change connection circuit that connects between the DC / AC converter and the spark plug and has a frequency change circuit that changes the resonance frequency of the entire circuit from the DC / AC converter to the spark plug.
It is provided with a control circuit that controls the on / off of the switch of the DC / AC converter, causes the DC / AC converter to output an AC voltage of an AC frequency, and supplies the AC voltage to the spark plug.
The control circuit controls the frequency change circuit of the frequency change connection circuit to change the resonance frequency and change the AC frequency.

According to the ignition system according to the present application, a frequency changing circuit for changing the resonance frequency is provided in the connection circuit connecting the DC / AC converter and the spark plug. Then, the control circuit controls the frequency changing circuit to change the resonance frequency and change the AC frequency. Therefore, the resonance frequency and the AC frequency are changed, and the AC voltage applied to the ignition plug is amplified by the resonance of the resonance circuit. At the same time, the AC frequency of the AC voltage applied to the ignition plug can be changed to change the discharge energy density.

It is a schematic circuit diagram of the ignition system which concerns on Embodiment 1. FIG. It is a schematic diagram of the spark plug attached to the internal combustion engine which concerns on Embodiment 1. FIG. FIG. 5 is a schematic cross-sectional view of the barrier spark plug according to the first embodiment. It is a hardware block diagram of the control circuit which concerns on Embodiment 1. FIG. It is a timing chart for demonstrating the processing of the control circuit which concerns on Embodiment 1. FIG. It is a figure for demonstrating the setting of the resonance frequency and the AC frequency which concerns on Embodiment 1. FIG. It is a schematic circuit diagram of the frequency change connection circuit which concerns on Embodiment 2. FIG. It is a figure explaining the on / off pattern of the switch which concerns on Embodiment 2. FIG. It is a figure for demonstrating the setting of the resonance frequency and the AC frequency which concerns on Embodiment 2. FIG. It is a timing chart for demonstrating the processing of the control circuit which concerns on Embodiment 3.

Hereinafter, the ignition system of the present application will be described in detail with reference to the drawings. In each figure, the same reference numerals indicate the same or corresponding parts.

1. 1. Embodiment 1
The ignition system according to the first embodiment will be described with reference to the drawings. FIG. 1 is a schematic circuit diagram of the ignition system of the first embodiment. The ignition system includes a DC / AC converter 2, a spark plug 4, a frequency change connection circuit 3, and a control circuit 6.

1-1. Internal combustion engine 1
As shown in FIG. 2, the internal combustion engine 1 is a reciprocating gasoline engine in which the piston 12 moves up and down in the cylinder 11. The space inside the cylinder 11 and the piston 12 is a combustion chamber 13, and the spark plug 4 is arranged at the top of the cylinder 11. Further, at the top of the cylinder 11, an intake valve 15 for adjusting the amount of intake air taken into the combustion chamber 13 from the intake pipe 14 and an exhaust valve for adjusting the amount of exhaust gas discharged from the combustion chamber 13 to the exhaust pipe 16 17 and are provided. In the present embodiment, an injector 18 for injecting fuel into the combustion chamber 13 is provided at the top of the cylinder 11. The intake pipe 14 may be provided with an injector 18. As will be described later, the internal combustion engine 1 is controlled by the control circuit 6.

The internal combustion engine 1 is a four-stroke engine in which an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke are combined into one combustion cycle. In the intake stroke, the intake valve 15 is opened and the exhaust valve 17 is closed, and the piston 12 is lowered to suck air from the intake pipe 14 into the combustion chamber 13. Fuel is injected from the injector 18 in the intake stroke, and a mixture of fuel and air is formed in the combustion chamber 13. In the compression stroke, the air-fuel mixture in the combustion chamber 13 is compressed by raising the piston 12 with the intake valve 15 and the exhaust valve 17 closed. Combustion of the air-fuel mixture starts due to the barrier discharge of the spark plug 4 near the end of the compression stroke (top dead center of the piston 12). In the combustion stroke, with the intake valve 15 and the exhaust valve 17 closed, the pressure of the gas in the combustion chamber rises due to the combustion of the air-fuel mixture, and the piston 12 is pushed down. In the exhaust stroke, the burnt gas after combustion is discharged from the combustion chamber 13 to the exhaust pipe 16 by raising the piston 12 in a state where the intake valve 15 is closed and the exhaust valve 17 is open.

1-2. Spark plug 4
The spark plug 4 has a pair of electrodes (first electrode 41 and second electrode 42) and a dielectric 43 arranged between the first electrode 41 and the second electrode 42, and has a combustion chamber 13 of the internal combustion engine 1. Is placed in. At least one electrode is covered with the dielectric 43. Whereas conventional spark plugs apply a high voltage between metal electrodes to generate arc discharge, spark plugs 4 have a dielectric material between the first and second electrodes 42. 43 is arranged, and by applying an AC voltage, a dielectric barrier discharge (hereinafter, also referred to as a barrier discharge) is generated between the electrodes. The barrier discharge ignites the air-fuel mixture in the combustion chamber 13 and generates chemically active species (radicals) for promoting combustion.

As an example of the spark plug 4, FIG. 3 shows a cross-sectional view of the spark plug 4 attached to the combustion chamber 13 of the internal combustion engine 1. Similar to the conventional SI plug, the cylindrical plug outer wall 44 is made of metal, and the outer peripheral surface is threaded and attached to the partition wall 19 (cylinder head) of the combustion chamber 13. Therefore, the plug outer wall 44 is grounded via the internal combustion engine 1. A cylindrical second electrode 42 is formed on the combustion chamber 13 side of the plug outer wall 44. A rod-shaped first electrode 41 is arranged at the center of the plug outer wall 44. A dielectric 43 (for example, ceramic) is arranged and insulated in the cylindrical space between the plug outer wall 44 and the first electrode 41. At the lower end portion arranged in the combustion chamber 13, the thickness of the dielectric 43 covering the first electrode 41 is thin, and a gap is provided between the dielectric 43 and the second electrode 42. .. This gap becomes a discharge gap 45 in which a barrier discharge occurs. The shapes of the first electrode 41, the second electrode 42, and the dielectric 43 at the inner end of the combustion chamber 13 of the spark plug 4 are not limited to the example of FIG. 3, and may be various shapes.

At the outer end of the combustion chamber 13, the first electrode 41 is not covered with the dielectric 43 and is connected to one output terminal of the frequency change connection circuit 3. The second electrode 42 is connected to the other output terminal of the frequency change connection circuit 3 via the internal combustion engine 1.

1-3. DC / AC converter 2
The DC / AC converter 2 is a power converter having a switch 21 that converts the DC power supplied from the DC power source 7 into AC power.

The DC power source 7 connected to the DC / AC converter 2 is a storage battery such as a lead battery, and supplies DC power to the connected DC / AC converter 2. The DC power supply 7 may be any device as long as it has a function of outputting a DC voltage. The DC power supply 7 may be provided with a DC / DC converter that boosts or lowers the DC voltage and outputs the voltage. Alternatively, a DC / DC converter may be provided on the input side of the DC / AC converter 2, and the switch of the DC / DC converter may be controlled by the control circuit 6.

The DC / AC converter 2 includes a switch 21 that is on / off controlled by the control circuit 6. The DC / AC converter 2 is a full-bridge circuit including two series circuits in which two switches 21 are connected in series. In the first series circuit, the switch 21a on the positive electrode side connected to the positive electrode side of the DC power supply 7 and the switch 21b on the negative electrode side connected to the negative electrode side of the DC power supply 7 are connected in series. In the second series circuit, the switch 21c on the positive electrode side connected to the positive electrode side of the DC power supply 7 and the switch 21d on the negative electrode side connected to the negative electrode side of the DC power supply 7 are connected in series.

Note that the DC / AC converter 2 may use various conversion circuits such as a half-bridge circuit or a circuit composed of one switch. The midpoint of the two switches 21 of each series circuit is connected to the frequency change connection circuit 3.

For the switch 21 of the DC / AC converter 2, for example, a semiconductor switch such as a MOS-FET (Metal-Oxide-Semiconductor Field-Effect Transistor) or an IGBT (Insulated-Gate Bipolar Transistor) in which diodes are connected in antiparallel is used. Be done. The drive signal output from the control circuit 6 is input to the gate terminal of the switch 21. When the drive signal is high (1), the switch 21 is turned on, and when the drive signal is low (0), the switch 21 is turned off. The switch 21 of the DC / AC converter 2 may be any switch 21 as long as it can conduct and cut off the electric circuit by turning it on and off. It may be composed of the switches of.

1-4. Frequency change connection circuit 3
The frequency change connection circuit 3 connects between the DC / AC converter 2 and the ignition plug 4, and sets the resonance frequency fr of the entire circuit (referred to as a load resonance circuit) from the DC / AC converter 2 to the ignition plug 4. It is a connection circuit having a frequency change circuit 32 to change.

The frequency change connection circuit 3 has two or more inductors, and as the frequency change circuit 32, one or more switches 32 that change the connection relationship of the inductor to the load resonance circuit, and is a switch of the frequency change connection circuit 3. By turning 32 on or off, the inductance of the load resonance circuit changes, and the resonance frequency fr changes.

According to this configuration, the frequency change connection circuit 3 can be composed of two or more inductors and one or more switches 32, and the frequency change connection circuit 3 can be simplified and miniaturized.

In the present embodiment, the frequency change connection circuit 3 has the first inductor 31, the leakage inductance of the primary winding 33a and the secondary winding 33b of the transformer 33, and the second inductor 34 as inductors. .. The first inductor 31 is connected in series on the connection path between the DC / AC converter 2 and the transformer 33. Specifically, one terminal of the first inductor 31 is connected to one output terminal of the DC / AC converter 2 (in this example, the midpoint of the second series circuit), and the other terminal of the first inductor 31. The terminal is connected to one terminal of the primary winding 33a of the transformer 33. The other terminal of the primary winding 33a of the transformer 33 is connected to the other output terminal of the DC / AC converter 2 (in this example, the midpoint of the first series circuit).

The second inductor 34 is connected in series on the connection path between the transformer 33 and the spark plug 4. Specifically, one terminal of the second inductor 34 is connected to one terminal of the secondary winding 33b of the transformer 33, and the other terminal of the second inductor 34 is connected to the first electrode 41 of the spark plug 4. Has been done. The other terminal of the secondary winding 33b of the transformer 33 is connected to the second electrode 42 of the spark plug 4. The second electrode 42 of the spark plug 4 is also connected to the ground.

In the present embodiment, the frequency change connection circuit 3 includes a first switch circuit 321 connected in parallel to the first inductor 31 as the switch 32. The first switch circuit 321 is a bidirectional switch in which two switches 32a and 32b are connected in series. For the two switches 32a and 32b, a MOS-FET, an IGBT in which diodes are connected in antiparallel, and the like are used. The drain terminals of the two switches 32a and 32b are connected to each other. The drive signal output from the control circuit 6 is input to the gate terminals of the two switches 32a and 32b. When the drive signal is high (1), the two switches 32a and 32b are turned on, and when the drive signal is low (0), the two switches 32a and 32b are turned off. The switch 32 of the frequency change connection circuit 3 may be any switch as long as it can conduct and cut off the electric circuit in both directions by turning it on and off. As described above, it may be composed of switches other than semiconductors.

When the first switch circuit 321 (two switches 32a and 32b) is turned on and becomes conductive, both terminals of the first inductor 31 are short-circuited, and the inductance of the first inductor 31 in the load resonance circuit becomes zero. On the other hand, when the first switch circuit 321 (two switches 32a and 32b) is turned off and is in a cutoff state, the inductance of the first inductor 31 in the load resonance circuit becomes the same inductance. Therefore, when the first switch circuit 321 is turned on or off, the connection relationship of the first inductor 31 to the load resonance circuit changes, and the resonance frequency fr of the load resonance circuit changes as described later.

The frequency change connection circuit 3 supplies the AC power output from the DC / AC converter 2 to the spark plug 4 even when all the switches 32 are turned off.

Therefore, even if the switch 32 cannot be turned on and off normally due to noise or failure, AC power can be supplied from the DC / AC converter 2 to the spark plug 4 and a dielectric barrier discharge can be generated.

As the frequency changing circuit, an electric variable inductance inductor, an electric variable capacitance capacitor, or the like is provided, and the inductance or capacitance is changed by the drive signal of the control circuit 6, and the resonance frequency fr of the load resonance circuit fr. May be changed.

The components constituting the load resonance circuit may include not only elements such as inductors and capacitors, but also distributed constant components such as parasitic inductance of wiring and parasitic capacitance generated between them and peripheral metals. ..

The transformer 33 is wound by a primary winding 33a connected to the DC / AC converter 2 side, a secondary winding 33b connected to the spark plug 4 side, a primary winding 33a, and a secondary winding 33b. It has an iron core to be dressed. The step-up ratio of the transformer 33 is determined by the ratio of the number of turns of the secondary winding 33b to the number of turns of the primary winding 33a. The transformer 33 may not be provided if the AC voltage required for discharging can be secured without the transformer 33.

1-5. Control circuit 6
The control circuit 6 controls the DC / AC converter 2 and the frequency change connection circuit 3. In this embodiment, the control circuit 6 also controls the internal combustion engine 1. Each function of the control circuit 6 is realized by a processing circuit provided in the control circuit 6. Specifically, as shown in FIG. 4, the control circuit 6 is a storage device 61 that exchanges data with an arithmetic processing unit 60 (computer) such as a CPU (Central Processing Unit) and an arithmetic processing unit 60 as a processing circuit. An input circuit 62 for inputting an external signal to the arithmetic processing unit 60, an output circuit 63 for outputting a signal from the arithmetic processing unit 60 to the outside, and the like are provided.

The arithmetic processing device 60 is provided with an ASIC (Application Specific Integrated Circuit), an IC (Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), various logic circuits, various signal processing circuits, and the like. You may. Further, as the arithmetic processing unit 60, a plurality of the same type or different types may be provided, and each processing may be shared and executed. The storage device 61 includes a RAM (Random Access Memory) configured to be able to read and write data from the arithmetic processing unit 60, a ROM (Read Only Memory) configured to be able to read data from the arithmetic processing unit 60, and the like. Has been done.

Various sensors 57 of the internal combustion engine (crank angle sensor, cam angle sensor, intake air amount detection sensor, water temperature sensor, intake air temperature sensor, in-cylinder pressure sensor, ion current detection sensor, etc.) are connected to the input circuit 62, and their outputs are output. It is equipped with an A / D converter or the like that inputs a signal to the arithmetic processing device 60. The output circuit 63 includes a switch 21 of the DC / AC converter 2, a switch 32 of the frequency change connection circuit 3, and various electric loads 58 (injector, electric throttle valve, electric EGR valve, intake / exhaust VVT, etc.) of the internal combustion engine. It is connected and is provided with a drive circuit or the like that outputs a control signal from the arithmetic processing device 60.

The input circuit 62 may include an operational amplifier and a buffer for amplifying a signal, and a photocoupler and an isolator for insulating the signal. The output circuit 63 may include a drive circuit for driving a semiconductor switch, an isolator for insulating the signal, and the like, such as an operational amplifier and a buffer for amplifying the signal.

Then, in each function provided in the control circuit 6, the arithmetic processing unit 60 executes software (program) stored in the storage device 61 such as ROM, and controls the storage device 61, the input circuit 62, the output circuit 63, and the like. It is realized by cooperating with other hardware of the circuit 6. The setting data such as the reference value used by the control circuit 6 is stored in a storage device 61 such as a ROM as a part of software (program). Hereinafter, each function of the control circuit 6 will be described in detail.

The processing of the control circuit 6 will be described with reference to the timing chart of FIG. The horizontal axis shows time, and the vertical axis shows each signal, frequency state, voltage, and energy per ignition. When the signal is 1, it means that it is high, and when it is 0, it means that it is low.

<Control of internal combustion engine>
The control circuit 6 controls the internal combustion engine 1. As basic control, the control circuit 6 has a crank angle, a combustion cycle stroke, a rotation speed, an intake air amount, a filling efficiency, an air-fuel ratio, a cooling water temperature, and an intake air based on the output signals of various input sensors. It detects the operating state of various internal combustion engines such as temperature, exhaust gas recirculation rate (EGR rate), combustion state, and presence / absence of combustion misfire. The control circuit 6 calculates the target air-fuel ratio, fuel injection amount, fuel injection timing, target throttle opening, target EGR opening, target intake / exhaust VVT phase angle, etc. based on the operating state of the internal combustion engine, and determines the injector and electric motor. It drives and controls various electric loads 58 of an internal combustion engine such as a throttle valve, an electric EGR valve, and an intake / exhaust VVT.

<Setting the discharge start time>
The discharge start signal S1 in FIG. 5 is a signal indicating the discharge start time. The control circuit 6 determines the discharge start timing (ignition crank angle) of each combustion cycle based on the operating state of the internal combustion engine, and generates the discharge start signal S1. The operating states of the internal combustion engine include, for example, the rotation speed of the internal combustion engine, pressure information in the combustion chamber (for example, filling efficiency or pressure in the cylinder), compression ratio in the combustion chamber (when a variable compression ratio mechanism is provided), and air-fuel ratio. , And at least one or more of the exhaust gas recirculation rate (EGR rate) is used.

In the present embodiment, the discharge start time is the discharge start time for ignition, and after the discharge start time, the dielectric barrier discharge for ignition is performed.

In the present embodiment, the control circuit 6 sets the discharge start signal S1 to high (1) before a predetermined time of the discharge start time, and sets the discharge start signal S1 to low (0) at the discharge start time.

An external control device may control the internal combustion engine. In this case, an external control device may transmit information on the operating state of the internal combustion engine to the control circuit 6 via communication, and the external control device may transmit high and low signals such as the discharge start signal S1. May be generated and output to the control circuit 6.

<On / off control of DC / AC converter 2>
The discharge period signal S2 is a signal indicating a period during which the DC / AC converter 2 is made to output AC power. The control circuit 6 determines the discharge time based on the operating state of the internal combustion engine and the resonance frequency fr and the AC frequency fsw described later. The control circuit 6 sets the period from the discharge start time to the elapse of the discharge time as the discharge period. The control circuit 6 sets the discharge period signal S2 to high (1) during the discharge period, and sets the discharge period signal S2 to low (0) during other periods. The operating states of the internal combustion engine include, for example, the rotation speed of the internal combustion engine, pressure information in the combustion chamber (for example, filling efficiency or pressure in the cylinder), compression ratio in the combustion chamber (when a variable compression ratio mechanism is provided), and air-fuel ratio. , And at least one or more of the exhaust gas recirculation rate (EGR rate) is used. According to this configuration, since the instantaneous power of discharge, which is the discharge energy per unit time, can be known from the resonance frequency fr and the AC frequency fsw, the discharge time is set so that the total amount of discharge energy is suitable for the operating state of the internal combustion engine. Can be decided. Therefore, deterioration of the combustion state due to insufficient discharge energy can be suppressed, unnecessary increase in power consumption due to excessive discharge energy can be suppressed, and the combustion state can be improved and power consumption can be reduced.

Alternatively, the control circuit 6 determines the total amount of discharge energy required based on the operating state of the internal combustion engine, and divides the total amount of required discharge energy by the instantaneous power W of the discharge determined according to the resonance frequency fr and the AC frequency fsw. Then, the discharge time may be determined. For example, when the required amount of discharge energy is 400 mJ and the instantaneous power W of discharge is 200 W, 2 ms obtained by dividing 400 mJ by 200 W is set as the discharge period. According to this configuration, it is possible to supply the total amount of discharge energy suitable for the operating state of the internal combustion engine, suppress the deterioration of the combustion state due to insufficient discharge energy, and suppress the increase in unnecessary power consumption due to excessive discharge energy. It is possible to improve the combustion state and reduce the power consumption.

The control circuit 6 controls the switch 21 of the DC / AC converter 2 on and off by a known PWM (Pulse Width Modulation) control during the discharge period when the discharge period signal S2 is high (1), and DC / AC. The converter 2 is made to output an AC voltage having an AC frequency fsw, and is supplied to the ignition plug 4. On the other hand, the control circuit 6 stops the on / off control of the DC / AC converter 2 when the discharge period signal S2 is low (0), and does not cause the DC / AC converter 2 to output AC power. The control circuit 6 changes the AC frequency fsw of the AC power. The change in the AC frequency fsw will be described later.

For example, in the control circuit 6, during the discharge period, the switch 21a on the positive electrode side of the first series circuit and the switch 21d on the negative electrode side of the second series circuit are turned on, and the switch on the negative electrode side of the first series circuit is turned on. The first pattern that turns off the switch 21c on the positive electrode side of the 21b and the second series circuit, and the switch 21a on the positive electrode side of the first series circuit and the switch 21d on the negative electrode side of the second series circuit are turned off. The switch 21b on the negative electrode side of the first series circuit and the second pattern for turning on the switch 21c on the positive electrode side of the second series circuit are switched at the AC frequency fsw. On the other hand, the control circuit 6 turns off the four switches 21a to 21c of the DC / AC converter 2 when it is not in the discharge period. The control circuit 6 may use another PWM control method, or may change the amplitude of the AC voltage.

<Change in resonance frequency fr due to switch on / off>
The control circuit 6 controls the frequency change circuit 32 of the frequency change connection circuit 3 to change the resonance frequency fr. In the present embodiment, the control circuit 6 changes the resonance frequency fr by turning on or on the first switch circuit 321 (two switches 32a and 32b) as the frequency changing circuit 32. The change in the resonance frequency fr will be described later.

The control circuit 6 outputs a high (1) or low (0) switch drive signal S3 to the first switch circuit 321. When the switch drive signal S3 is high (1), the two switches 32a and 32b of the first switch circuit 321 are turned on, the electric circuit is conducting, and the switch drive signal S3 is low (0). The two switches 32a and 32b of the switch circuit 321 are turned off, and the electric circuit is cut off.

The resonance frequency fr is the resonance frequency of the load resonance circuit including the DC / AC converter 2, the frequency change connection circuit 3, and the ignition plug 4. By turning on or off the switch 32 of the frequency change connection circuit 3, the resonance frequency fr changes. The resonance frequency fr is set in the range of, for example, 10 kHz to 500 kHz. When the exciting inductance of the transformer 33 is very large with respect to the leakage inductance, the resonance frequency fr can be expressed by the equation (1). Here, L is the combined inductance of the load resonance circuit, and Cp is the combined capacitance of the spark plug 4.

The combined inductance Loop when the first switch circuit 321 is off is represented by the equation (2). Here, N1 is the number of turns of the primary winding 33a of the transformer 33, N2 is the number of turns of the secondary winding 33b of the transformer 33, L1 is the inductance of the first inductor 31, and Lleak1 is. The leakage inductance of the primary winding 33a of the transformer 33, Lleak2 is the leakage inductance of the secondary winding 33b of the transformer 33, and L2 is the inductance of the second inductor 34.

When the first switch circuit 321 is on, both ends of the first inductor 31 are short-circuited, so that the inductance L1 of the first inductor 31 in the load resonance circuit becomes 0. Therefore, the combined inductance Lon when the first switch circuit 321 is off is represented by the equation (3), and the inductance is smaller than that of Loff.

Therefore, the resonance frequency fr1 (hereinafter referred to as the first resonance frequency fr1) when the first switch circuit 321 is off is the resonance frequency fr2 (hereinafter referred to as the second resonance frequency) when the first switch circuit 321 is on. The frequency is lower than fr2). The equations (1) to (3) may include the wiring inductance and the parasitic capacitance distributed in each part.

<Interlocking change between resonance frequency fr and AC frequency fsw>
The control circuit 6 changes the AC frequency fsw in conjunction with the change in the resonance frequency fr. FIG. 6 shows a conceptual diagram of the interlocking change of the frequency. The horizontal axis represents the frequency, and the vertical axis represents the gain (ratio) of the amplitude of the AC voltage applied to the spark plug 4 with respect to the amplitude of the AC voltage output from the DC / AC converter 2. When the amplification gain is larger than 1, it indicates that the amplification is performed by the load resonance circuit. The curve A in FIG. 6 shows the characteristics of each frequency and the amplification gain of the load resonance circuit when the load resonance circuit is changed to the first resonance frequency fr1, and the curve B shows the characteristics of the load resonance circuit in the second resonance circuit. It is a characteristic of each frequency and the amplification gain of the load resonance circuit when it is changed to the resonance frequency fr2 of.

FIG. 6 fsw1 is a first AC frequency set corresponding to the first resonance frequency fr1, and fsw2 is a second AC frequency fsw set corresponding to the second resonance frequency fr2. be. As shown in FIG. 6, the control circuit 6 changes the AC frequency fsw within the amplification frequency band in which the applied voltage of the spark plug is amplified with respect to the output voltage of the DC / AC converter by resonance. In the example of FIG. 6, the amplification frequency band is a frequency band in which the amplification gain is larger than 1. In the present embodiment, the control circuit 6 also changes the AC frequency fsw to a frequency within the amplification frequency band and equal to or higher than the resonance frequency fr.

Specifically, the first AC frequency fsw1 is set to a frequency within the amplification frequency band of the first resonance frequency fr1 and equal to or higher than the first resonance frequency fr1. The second AC frequency fsw2 is set to a frequency within the amplification frequency band of the second resonance frequency fr2 and equal to or higher than the second resonance frequency fr2. The first AC frequency fsw1 and the second AC frequency fsw2 are stored in advance in the storage device 61 in correspondence with the first resonance frequency fr1 and the second resonance frequency fr2.

According to this configuration, the AC frequency fsw is changed in the amplification frequency band in conjunction with the change of the resonance frequency fr. Therefore, even if the resonance frequency fr changes, the AC voltage is amplified by the load resonance circuit. It can be supplied to the ignition plug 4 and can efficiently generate a barrier discharge.

Contrary to the setting in FIG. 6, when the AC frequency fsw is set to a frequency lower than the resonance frequency fr, the output current of the DC / AC converter 2 advances with respect to the output voltage and becomes the phase. If the switch 21 of the DC / AC converter 2 is turned on and off while the output current of the DC / AC converter 2 is in phase with the output voltage, the diode connected in antiparallel to each switch 21 becomes steep. There is a possibility that the recovery current will flow and sudden heat generation will occur. Therefore, the control circuit 6 can prevent the switch 21 of the DC / AC converter 2 from suddenly generating heat by controlling the AC frequency fsw to be equal to or higher than the resonance frequency fr, and has a large cooling mechanism such as a heat sink. It is possible to prevent the conversion.

When the amplitude Vp of the applied voltage V of the spark plug 4 does not reach the dielectric breakdown voltage between the electrodes and the dielectric barrier discharge does not occur, the control circuit 6 may bring the AC frequency fsw closer to the resonance frequency fr. .. As a result, the amplitude of the applied voltage of the spark plug 4 can be increased to generate a dielectric barrier discharge. At this time, the control circuit 6 may match the AC frequency fsw with the resonance frequency fr, or may change the AC frequency fsw by the change width Δfsw to gradually approach the resonance frequency fr. At this time, the control circuit 6 is set so that the AC frequency fsw matches the amplification frequency band near the resonance frequency fr or the resonance frequency fr, so that there is no delay from the ignition command by the discharge start signal S1. Dielectric barrier discharge can be generated.

<Change in instantaneous power of discharge due to change in frequency>
Since the AC voltage V applied between the electrodes of the ignition plug 4 is amplified by the resonance phenomenon, the amplitude Vp of the actual applied voltage gradually increases after the output of the AC power of the DC / AC converter 2 starts. After the output is completed, it gradually decreases. Here, the amplitude Vp of the applied voltage V of the spark plug 4 is equal to or greater than the amplitude of the output voltage of the DC power supply 7 multiplied by the turns ratio of the transformer, and is, for example, a high voltage of 1 kV or more. The amplitude Vp of the applied voltage V of the spark plug 4 is set to be equal to or higher than the dielectric breakdown voltage between the electrodes of the spark plug 4, that is, equal to or higher than the voltage capable of generating the dielectric barrier discharge.

The instantaneous power W of the discharge of the spark plug 4 is the discharge energy per unit time of the dielectric barrier discharge generated between the electrodes of the spark plug 4. Here, the instantaneous power W of the dielectric barrier discharge can be expressed by the equation (4). Cg is the capacitance of the spark plug 4 dielectric, C0 is the capacitance between the electrodes of the spark plug 4, and V * is the discharge maintenance applied between the electrodes of the spark plug 4 during discharge. It is a voltage, and Vp is an amplitude of the applied voltage V of the spark plug 4.

In the formula (4), since the capacitance Cg of the dielectric of the spark plug 4 depends on the structure and the material, the control circuit 6 cannot adjust this to an arbitrary value. Since the capacitance C0 between the electrodes of the spark plug 4 is determined by the structure, the gas state between the electrodes, and the like, the control circuit 6 cannot adjust this to an arbitrary value. Since the discharge maintenance voltage V * during discharge is determined by the structure and the discharge state, the control circuit 6 cannot be adjusted arbitrarily. Therefore, the control circuit 6 can adjust the instantaneous power W of the discharge by the AC frequency fsw and the amplitude Vp of the applied voltage V of the spark plug 4.

However, the control circuit 6 needs to adjust the amplitude Vp of the applied voltage V of the spark plug 4 within the range of the dielectric strength of the spark plug 4 or less and the discharge start voltage of the dielectric barrier discharge or more, and the discharge energy. The adjustment range of is small. On the other hand, since the changeable range of the AC frequency fsw is large, the adjustment range of the discharge energy by increasing or decreasing the AC frequency fsw is large.

However, if the AC frequency fsw is separated from the resonance frequency fr, the amplification gain of the load resonance circuit is lowered, the amplitude Vp of the applied voltage of the ignition plug 4 is greatly lowered, and the dielectric barrier discharge cannot be generated. Therefore, as described above, the frequency change connection circuit 3 is configured so that the resonance frequency fr can be changed, and the control circuit 6 changes the AC frequency fsw and the resonance frequency fr in conjunction with each other to change the load resonance circuit. The amplification gain of is kept high.

As a result, the instantaneous power W of the discharge can be increased or decreased by increasing or decreasing the AC frequency fsw while maintaining the amplitude Vp of the applied voltage V of the spark plug 4 at an appropriate voltage. For example, when the AC frequency fsw and the resonance frequency fr are interlocked and doubled so that the amplitude Vp of the applied voltage V is maintained at a constant voltage, the instantaneous power W of the discharge, that is, the energy density is doubled. Can be increased to. On the contrary, when the resonance frequency fr and the AC frequency fsw are increased by about 1/2 times in conjunction with each other, the instantaneous power W of the discharge, that is, the energy density can be reduced by about 1/2 times.

The total amount of discharge energy can be adjusted by increasing or decreasing the discharge period, but the instantaneous power of discharge cannot be changed. For example, when it is necessary to generate a large discharge energy in a short period of time, energy adjustment by interlocking changes of the resonance frequency fr and the AC frequency fsw is effective.

W1 in the timing chart of FIG. 5 is the instantaneous power of the discharge when it is changed to the first AC frequency fsw1 and the first resonance frequency fr1, and W2 is the second AC frequency fsw2 and the second resonance frequency. It is the instantaneous power of the discharge when it is changed to fr2.

<Frequency change according to the operating condition of the internal combustion engine>
The control circuit 6 changes the AC frequency fsw and the resonance frequency fr based on the operating state of the internal combustion engine. According to this configuration, the AC frequency fsw and the resonance frequency fr can be appropriately changed so that the discharge energy density is suitable for the operating state of the internal combustion engine, and the combustion state can be improved or the power consumption can be reduced. ..

The control circuit 6 is provided with the rotation speed of the internal combustion engine, pressure information in the combustion chamber (for example, filling efficiency or pressure in the cylinder), and the compression ratio of the combustion chamber (variable compression ratio mechanism) as the operating state of the internal combustion engine. Case), the air-fuel ratio, the exhaust gas recirculation rate (EGR rate), and the presence or absence of misfire, at least one or more is used. According to this configuration, the AC frequency fsw and the resonance frequency fr can be changed accurately and appropriately based on the operating state of the internal combustion engine related to the combustion state.

The control circuit 6 determines whether or not an increase in the instantaneous power of the discharge is necessary based on the operating state of the internal combustion engine, and if it is determined that an increase in the instantaneous power of the discharge is necessary, the instantaneous power of the discharge is determined. The AC frequency fsw and the resonance frequency fr are made higher than when it is determined that the increase is not necessary.

In the present embodiment, the control circuit 6 changes the AC frequency fsw and the resonance frequency fr to the second AC frequency fsw2 and the second resonance frequency fr2 when it is determined that the instantaneous power of the discharge needs to be increased. When it is determined that the increase in the instantaneous power of the discharge is not necessary, the AC frequency fsw and the resonance frequency fr are changed to the first AC frequency fsw1 and the first resonance frequency fr1.

The frequency switching signal S_flag in FIG. 5 is a signal representing a determination result of the necessity of increasing the instantaneous power of discharge. When the control circuit 6 determines that the instantaneous power of the discharge needs to be increased, the frequency switching signal S_flag is set to high (1), and when it is determined that the instantaneous power of the discharge does not need to be increased, the frequency is set. The switching signal S_flag is set to low (0).

According to this configuration, when it is necessary to increase the instantaneous power of discharge, the instantaneous power of discharge can be increased and the ignitability by barrier discharge can be improved. In particular, even when the discharge period cannot be increased, a large amount of discharge energy can be input to the air-fuel mixture, so that the ignitability can be improved. Further, even when the air-fuel mixture is not directly ignited by the dielectric barrier discharge, the amount of chemically active species generated can be increased by increasing the discharge energy, which contributes to the promotion of combustion after ignition. On the other hand, when it is not necessary to increase the instantaneous power of discharge, the instantaneous power of discharge can be reduced to reduce the power consumption.

When the external control device controls the internal combustion engine, the control circuit 6 determines the necessity of increasing the instantaneous power of the discharge based on the signal input from the external device to the control circuit 6. You may.

In particular, when the control circuit 6 detects a misfire of the internal combustion engine, the AC frequency fsw and the resonance frequency fr are set higher than when the misfire is not detected. The presence or absence of misfire is determined based on the fluctuation information of the crank angle, the detection information of the in-cylinder pressure sensor, the detection information of the ion current detection sensor, and the like. According to this configuration, when a misfire is detected, the ignitability of the air-fuel mixture can be improved and the occurrence of misfire can be suppressed by increasing the instantaneous power of the discharge.

When the control circuit 6 detects a misfire of the internal combustion engine, it changes the AC frequency fsw and the resonance frequency fr to the second AC frequency fsw2 and the second resonance frequency fr2, and does not detect the misfire of the internal combustion engine. Changes the AC frequency fsw and the resonance frequency fr to the first AC frequency fsw1 and the first resonance frequency fr1.

Further, the control circuit 6 determines whether or not the condition is difficult to ignite based on the operating state of the internal combustion engine, and when it is determined that the condition is difficult to ignite, the AC frequency fsw and the resonance frequency fr are set. Set it higher than when it is judged that it is not difficult to ignite.

According to this configuration, when it is difficult to ignite, by increasing the instantaneous power of the discharge, the ignitability of the air-fuel mixture can be improved, the combustion state can be improved, and the occurrence of misfire can be suppressed.

For example, the control circuit 6 determines whether or not it is difficult to ignite by comparing each of the operating states of the internal combustion engine with the determination value of each operating state. The control circuit 6 has an EGR rate when the rotation speed is lower than the judgment value of the rotation speed, when the filling efficiency is lower than the judgment value of the filling efficiency, and when the compression ratio is lower than the judgment value of the compression ratio. , If it is higher than the judgment value of the EGR rate, or if the air-fuel ratio is higher than the judgment value of the air-fuel ratio, it is judged that it is difficult to ignite, and in other cases, it is judged that it is not difficult to ignite. do. Each determination value is set at the boundary between an operating state in which the possibility of misfire is high and an operating state in which the possibility of misfire is not high unless the instantaneous power of discharge is increased. It should be noted that a plurality of operating states may be determined in a complex manner. For example, the control circuit 6 determines that ignition is difficult when the rotation speed is lower than the determination value of the rotation speed and the filling efficiency is lower than the determination value of the filling efficiency.

When the control circuit 6 determines that the ignition is difficult, the AC frequency fsw and the resonance frequency fr are changed to the second AC frequency fsw2 and the second resonance frequency fr2, and it is determined that the ignition is not difficult. In this case, the AC frequency fsw and the resonance frequency fr are changed to the first AC frequency fsw1 and the first resonance frequency fr1.

Alternatively, the control circuit 6 determines whether or not the ignition is easy to ignite based on the operating state of the internal combustion engine, and when it is determined that the ignition is easy to ignite, the AC frequency and the resonance frequency are set to the AC frequency and the resonance frequency. It may be lower than when it is judged that the condition is not easy to ignite.

According to this configuration, it is possible to reduce the power consumption within a range in which the combustion state is not deteriorated and misfire does not occur by reducing the instantaneous power of the discharge when the state is easily ignited.

For example, the control circuit 6 determines whether or not it is in an easily ignited state by comparing each of the operating states of the internal combustion engine with the determination value of each operating state. The control circuit 6 has an EGR rate when the rotation speed is within the judgment range of the rotation speed, when the filling efficiency is higher than the judgment value of the filling efficiency, and when the compression ratio is higher than the judgment value of the compression ratio. , If it is lower than the judgment value of the EGR rate, or if the air-fuel ratio is within the judgment range of the air-fuel ratio, it is judged that the state is easy to ignite, and in other cases, it is judged that the state is not easy to ignite. do. Each determination value is set at the boundary between an operating state in which a misfire is unlikely to occur and an operating state in which a misfire is likely to occur even if the instantaneous power of the discharge is reduced. A part of the operating state may be determined.

When the control circuit 6 determines that the ignition is easy to ignite, the control circuit 6 changes the AC frequency fsw and the resonance frequency fr to the first AC frequency fsw1 and the first resonance frequency fr1 and determines that the ignition is not easy to ignite. In this case, the AC frequency fsw and the resonance frequency fr are changed to the second AC frequency fsw2 and the second resonance frequency fr2.

<Control when frequency changes>
The control circuit 6 increases the AC frequency fsw and then increases the resonance frequency fr when increasing the resonance frequency fr and the AC frequency fsw during the output of the AC voltage of the DC / AC converter 2.

According to this configuration, since the AC frequency fsw is increased before the resonance frequency fr, it is possible to prevent a period in which the AC frequency fsw becomes lower than the resonance frequency fr. Therefore, it is possible to prevent the AC frequency fsw from becoming lower than the resonance frequency fr and the output current of the DC / AC converter 2 leading to the output voltage and becoming a phase. As a result, when each switch 21 of the DC / AC converter 2 is turned on and off, it is possible to prevent a recovery current from flowing through a diode connected in antiparallel to each switch 21 to generate heat. Therefore, it is possible to prevent the switch 21 of the DC / AC converter 2 from generating heat, and it is possible to prevent the cooling mechanism such as the heat sink from becoming large in size.

The delay time from increasing the AC frequency fsw to increasing the resonance frequency fr is set to a time during which the AC frequency fsw does not become lower than the resonance frequency fr.

In the present embodiment, the control circuit 6 increases the AC frequency fsw from the first AC frequency fsw1 to the second AC frequency fsw2, and then turns the first switch circuit 321 from off to on to set the resonance frequency fr. The first resonance frequency fr1 is increased to the second resonance frequency fr2.

On the contrary, the control circuit 6 lowers the resonance frequency fr and then lowers the AC frequency fsw when lowering the resonance frequency fr and the AC frequency fsw during the output of the AC voltage of the DC / AC converter 2. ..

According to this configuration, since the resonance frequency fr is lowered before the AC frequency fsw, it is possible to prevent a period in which the AC frequency fsw becomes lower than the resonance frequency fr. Therefore, it is possible to prevent the AC frequency fsw from becoming lower than the resonance frequency fr and the output current of the DC / AC converter 2 leading to the output voltage and becoming a phase. As a result, when each switch 21 of the DC / AC converter 2 is turned on and off, it is possible to prevent a recovery current from flowing through a diode connected in antiparallel to each switch 21 to generate heat. Therefore, it is possible to prevent the switch 21 of the DC / AC converter 2 from generating heat, and it is possible to prevent the cooling mechanism such as the heat sink from becoming large in size.

The delay time from lowering the resonance frequency fr to lowering the AC frequency fsw is set to a time during which the AC frequency fsw does not become lower than the resonance frequency fr.

In the present embodiment, the control circuit 6 turns the first switch circuit 321 from on to off, lowers the resonance frequency fr from the second resonance frequency fr2 to the first resonance frequency fr1, and then sets the AC frequency fsw. The second AC frequency fsw2 is reduced to the first AC frequency fsw1.

Alternatively, the control circuit 6 stops the output of the AC voltage of the DC / AC converter 2 when changing the AC frequency fsw and the resonance frequency fr, and changes the resonance frequency fr while the output of the AC voltage is stopped. The AC frequency fsw may be changed when the output of the AC voltage is restarted.

According to this configuration, when the output of the AC power of the DC / AC converter 2 is restarted after the output of the AC power is stopped, the resonance frequency fr is already lower than the AC frequency fsw, so that the AC frequency fsw is increased. It is possible to prevent a period of time lower than the resonance frequency fr. Therefore, it is possible to prevent the AC frequency fsw from becoming lower than the resonance frequency fr and the output current of the DC / AC converter 2 leading to the output voltage and becoming a phase. As a result, when each switch 21 of the DC / AC converter 2 is turned on and off, it is possible to prevent a recovery current from flowing through a diode connected in antiparallel to each switch 21 to generate heat. Therefore, it is possible to prevent the switch 21 of the DC / AC converter 2 from generating heat, and it is possible to prevent the cooling mechanism such as the heat sink from becoming large in size.

<Explanation of control behavior>
Next, the control behavior will be described with reference to the timing chart of FIG. In the initial state, the control circuit 6 sets the frequency switching signal S_flag to low (0), sets the switch drive signal S3 to low (0), turns off the first switch circuit 321 and sets the resonance frequency fr. The first resonance frequency is changed to fr1. Further, the control circuit 6 sets the AC frequency fsw to the first AC frequency fsw1.

The control circuit 6 switches the discharge start signal S1 from 0 to 1 at a time t0 before a predetermined time of the discharge start time, and switches the discharge start signal S1 from 1 to 0 at the time t1 of the discharge start time. When the discharge start signal S1 is switched from 1 to 0, the control circuit 6 switches the discharge period signal S2 from 0 to 1. As described above, the control circuit 6 switches the discharge period signal S2 from 1 to 0 at the time t2 when the discharge time determined based on the operating state of the internal combustion engine has elapsed.

As described above, the control circuit 6 controls the switch 21 of the DC / AC converter 2 on and off during the period from time t1 to time t2 when the discharge period signal S2 is 1, and causes the DC / AC converter 2 to operate. The AC voltage of the first AC frequency fsw1 is output and supplied to the ignition plug 4. Since the first AC frequency fsw1 is set in the amplification frequency band near the first resonance frequency fr1, the AC voltage V amplified by the frequency change connection circuit 3 is applied to the spark plug 4. A dielectric barrier discharge is generated in the spark plug 4, and the air-fuel mixture is ignited.

The control circuit 6 stops the on / off control of the switch 21 of the DC / AC converter 2 and stops the output of the AC power during the period when the discharge period signal S2 is 0.

At time t3, the determination timing of the control parameter of the ignition control of the next combustion cycle has come, so that the control circuit 6 switches the discharge start time, discharge period, and frequency of the next combustion cycle based on the operating state of the internal combustion engine. Determine control parameters such as signal S_flag. In this example, the control circuit 6 detects a misfire of the internal combustion engine in the previous combustion, or determines that it is difficult to ignite based on the operating state of the internal combustion engine, so that the instantaneous power of the discharge increases. It is determined that it is necessary, and the frequency switching signal S_flag is set to 1.

Then, at time t4, the control circuit 6 sets the AC frequency fsw and the resonance frequency fr based on the frequency switching signal S_flag. Since the frequency switching signal S_flag is set to 1, the control circuit 6 sets the AC frequency fsw to the second AC frequency fsw2, switches the switch drive signal S3 from 0 to 1, and turns on the first switch circuit 321. The resonance frequency fr is changed to the second resonance frequency fr2.

The control circuit 6 switches the discharge start signal S1 from 0 to 1 at a time t5 before a predetermined time of the discharge start time, and switches the discharge start signal S1 from 1 to 0 at the time t6 of the discharge start time. When the discharge start signal S1 is switched from 1 to 0, the control circuit 6 switches the discharge period signal S2 from 0 to 1. The control circuit 6 switches the discharge period signal S2 from 1 to 0 at the time t7 when the discharge time has elapsed.

As described above, the control circuit 6 controls the switch 21 of the DC / AC converter 2 on and off during the period from time t6 to time t7 when the discharge period signal S2 is 1, and causes the DC / AC converter 2 to operate. The AC voltage of the second AC frequency fsw2 is output and supplied to the ignition plug 4. Since the second AC frequency fsw2 is set in the amplification frequency band near the second resonance frequency fr2, the AC voltage V amplified by the frequency change connection circuit 3 is applied to the spark plug 4. A dielectric barrier discharge is generated in the spark plug 4, and the air-fuel mixture is ignited. Since the resonance frequency fr is increased, the instantaneous power of the discharge is increased, and the ignitability of the air-fuel mixture can be improved in a state where ignition is difficult.

At time t8, the determination timing of the control parameter of the ignition control of the next combustion cycle has come, so that the control circuit 6 switches the discharge start time, discharge period, and frequency of the next combustion cycle based on the operating state of the internal combustion engine. Determine control parameters such as signal S_flag. In this example, the control circuit 6 did not detect the misfire of the internal combustion engine in the previous combustion, and determined that it was not in a state where it was difficult to ignite based on the operating state of the internal combustion engine. It is determined that it is not necessary, and the frequency switching signal S_flag is set to 0.

Then, at time t9, the control circuit 6 sets the AC frequency fsw and the resonance frequency fr based on the frequency switching signal S_flag. Since the frequency switching signal S_flag is set to 0 in the control circuit 6, the AC frequency fsw is set to the first AC frequency fsw1, the switch drive signal S3 is switched from 1 to 0, and the first switch circuit 321 is turned off. The resonance frequency fr is changed to the first resonance frequency fr1.

The control circuit 6 switches the discharge start signal S1 from 0 to 1 at a time t10 before a predetermined time of the discharge start time, and switches the discharge start signal S1 from 1 to 0 at the time t11 of the discharge start time. When the discharge start signal S1 is switched from 1 to 0, the control circuit 6 switches the discharge period signal S2 from 0 to 1. The control circuit 6 switches the discharge period signal S2 from 1 to 0 at the time t12 when the discharge time has elapsed.

As described above, the control circuit 6 controls the switch 21 of the DC / AC converter 2 on and off during the period from time t11 to time t12 when the discharge period signal S2 is 1, and causes the DC / AC converter 2 to perform on / off control. The AC voltage of the first AC frequency fsw1 is output and supplied to the ignition plug 4. Since the first AC frequency fsw1 is set in the amplification frequency band near the first resonance frequency fr1, the AC voltage amplified by the frequency change connection circuit 3 is applied to the spark plug 4. A dielectric barrier discharge is generated in the spark plug 4, and the air-fuel mixture is ignited. Since it is not in a state where it is difficult to ignite, the resonance frequency fr is lowered and the instantaneous power of discharge is lowered. Therefore, the discharge energy can be reduced and the power consumption can be reduced.

In the example of FIG. 5, the control circuit 6 changed the AC frequency fsw and the resonance frequency fr for each combustion cycle, but it does not have to change for each combustion cycle. For example, the control circuit 6 may change the AC frequency fsw and the resonance frequency fr during the discharge period. Further, although the control circuit 6 does not change the resonance frequency fr during the discharge period, the AC frequency fsw may be changed within the amplification frequency band of the resonance frequency fr.

Further, the frequency change connection circuit 3 does not have to be provided with the transformer 33. In this case, since the second electrode 42 of the spark plug 4 connected to the ground and the other output terminal of the DC / AC converter 2 are connected, the full bridge circuit cannot be used for the DC / AC converter 2. .. Therefore, a half-bridge circuit or the like is used for the DC / AC converter 2. However, when an isolated DC / DC converter is used on the input side of the DC power supply 7 or the DC / AC converter 2, the DC / AC converter 2 has a potential floating from the ground, so that the DC / AC converter 2 A full bridge circuit is used for 2.

2. Embodiment 2
Next, the ignition system according to the second embodiment will be described with reference to the drawings. The description of the same components as in the first embodiment will be omitted. The basic configuration and processing of the ignition system according to the present embodiment are the same as those of the first embodiment. In the first embodiment, the frequency change connection circuit 3 changes the resonance frequency fr in two steps, but in the present embodiment, the frequency change connection circuit 3 changes the resonance frequency fr in three or more steps. It is different from the first embodiment.

FIG. 7 is a schematic circuit diagram of the frequency change connection circuit 3 according to the present embodiment. Similar to the first embodiment, the frequency change connection circuit 3 includes a first inductor 31, a transformer 33, and a second inductor 34. In the present embodiment, the frequency change connection circuit 3 includes a second switch circuit 322 and an impedance element 35 connected in parallel to the first inductor 31 in addition to the first switch circuit 321 connected in parallel to the first inductor 31. I have. The second switch circuit 322 and the impedance element 35 are connected in series. The impedance element 35 has an inductance or a capacitance. Hereinafter, a case where the impedance element 35 has an inductance L1 equivalent to that of the first inductor 31 will be described. The second switch circuit 322 may be a bidirectional switch or a mechanical switch in which two semiconductor switches are connected in series, similarly to the first switch circuit 321. The second switch circuit 322 is turned on or off by the control circuit 6 in the same manner as the first switch circuit 321.

As shown in FIG. 8, the entire parallel connection circuit of the first inductor 31, the first switch circuit 321 and the second switch circuit 322 is turned on or off by combining the first switch circuit 321 and the second switch circuit 322. The inductor can be changed in three stages, and the resonance frequency fr can be changed in three stages.

Specifically, by turning off the first switch circuit 321 and the second switch circuit 322, the inductor of the entire parallel connection circuit becomes the inductance L1 of the first inductor 31, and the resonance frequency fr is the same as that of the first embodiment. The same first resonance frequency fr1 is obtained. By turning on the first switch circuit 321 and turning off or on the second switch circuit 322, the inductor of the entire parallel connection circuit becomes 0, and the resonance frequency fr becomes the same second resonance as in the first embodiment. The frequency becomes fr2. By turning off the first switch circuit 321 and turning on the second switch circuit 322, the inductor of the entire parallel connection circuit becomes L1 / 2, which is a combination of the first inductor 31 and the impedance element 35, and the resonance frequency fr. Is the third resonance frequency fr3. The third resonance frequency fr3 becomes a frequency between the first resonance frequency fr1 and the second resonance frequency fr2 (fr1 <fr3 <fr2).

Similar to the first embodiment, the control circuit 6 changes the AC frequency fsw in conjunction with the change in the resonance frequency fr. FIG. 9 shows a conceptual diagram of the interlocking change of the frequency. The horizontal axis represents the frequency, and the vertical axis represents the gain of the amplitude of the AC voltage applied to the spark plug 4 with respect to the amplitude of the AC voltage output from the DC / AC converter 2. When the gain is larger than 1, it indicates that the gain is amplified by the load resonance circuit. The curve A of FIG. 9 shows the characteristics of each frequency and the amplification gain of the load resonance circuit when the load resonance circuit is changed to the first resonance frequency fr1, and the curve B shows the characteristics of the load resonance circuit of the second resonance circuit. It is a characteristic of each frequency and the amplification gain of the load resonance circuit when it is changed to the resonance frequency fr2 of, and the curve C is each when the load resonance circuit is changed to the third resonance frequency fr3. This is a characteristic of the frequency and the amplification gain of the load resonance circuit.

In FIG. 9, fsw1 is a first AC frequency set corresponding to the first resonance frequency fr1, and fsw2 is a second AC frequency fsw set corresponding to the second resonance frequency fr2. Yes, fsw3 is a third AC frequency fsw that is set corresponding to the third resonance frequency fr3. As shown in FIG. 9, the control circuit 6 changes the AC frequency fsw within the amplification frequency band in the vicinity of each resonance frequency fr. Further, the control circuit 6 changes the AC frequency fsw to a frequency within the amplification frequency band and equal to or higher than the resonance frequency fr.

Specifically, the first AC frequency fsw1 is set to a frequency within the amplification frequency band of the first resonance frequency fr1 and equal to or higher than the first resonance frequency fr1. The second AC frequency fsw2 is set to a frequency within the amplification frequency band of the second resonance frequency fr2 and equal to or higher than the second resonance frequency fr2. The third AC frequency fsw3 is set to a frequency within the amplification frequency band of the third resonance frequency fr3 and equal to or higher than the third resonance frequency fr3. The first AC frequency fsw1, the second AC frequency fsw2, and the third AC frequency fsw3 correspond to the first resonance frequency fr1, the second resonance frequency fr2, and the third resonance frequency fr3. It is stored in advance in the storage device 61.

The instantaneous power W3 of the third discharge when the third AC frequency fsw3 and the third resonance frequency fr3 is the instantaneous power W1 of the first discharge when the first AC frequency fsw1 and the first resonance frequency fr1. Greater than, and less than the instantaneous power W2 of the second discharge at the second AC frequency fsw2 and the second resonance frequency fr2 (W1 <W3 <W2).

In the present embodiment, the control circuit 6 determines the required instantaneous power of the discharge in three stages based on the operating state of the internal combustion engine, and determines the AC frequency fsw and the resonance frequency fr in three stages based on the determination result. Change to. It is possible to finely improve the combustion state and reduce the power consumption.

For example, when the control circuit 6 detects a misfire or determines that it is difficult to ignite based on the operating state of the internal combustion engine, the AC frequency fsw and the resonance frequency fr are set to the second AC frequency fsw2 and the second AC frequency fsw2. When the resonance frequency fr2 is changed to 2 and the control circuit 6 determines that the ignition frequency is easy to ignite based on the operating state of the internal combustion engine, the AC frequency fsw and the resonance frequency fr are changed to the first AC frequency fsw1 and the first AC frequency fsw1. The resonance frequency fr1 is changed to 1, and in other cases, the AC frequency fsw and the resonance frequency fr are changed to the third AC frequency fsw3 and the third resonance frequency fr3.

The frequency change connection circuit 3 may include a switch circuit connected in parallel with other inductance elements, or may change the resonance frequency fr in three or more steps. For example, a switch circuit may be connected in parallel to the primary winding 33a of the transformer 33, the secondary winding 33b of the transformer 33, the second inductor 34, and the spark plug 4.

Alternatively, a switch connected in series with the first inductor 31 may be provided, and the control circuit 6 may be turned on and off as necessary.

3. 3. Embodiment 3
Next, the ignition system according to the third embodiment will be described with reference to the drawings. The description of the same components as in the first embodiment will be omitted. The basic configuration and processing of the ignition system according to the present embodiment are the same as those of the first embodiment. In the first embodiment, the control circuit 6 generates a dielectric barrier discharge for ignition, but in the present embodiment, the control circuit 6 is a dielectric for generating a chemically active species (radical). It differs from the first embodiment in that a barrier discharge is also generated.

Since the air-fuel mixture flows in the combustion chamber, the molecules contained in the air-fuel mixture receive discharge energy when flowing in the vicinity of the spark plug 4. Therefore, the discharge energy given to each molecule of the air-fuel mixture is increased or decreased by increasing or decreasing the instantaneous power of discharge (discharging energy density) of the spark plug 4.

According to Patent Document 1, in addition to generating radicals to promote combustion after ignition, barrier discharge can directly ignite the fuel by locally generating strong radicals and reacting with the fuel.

Therefore, the control circuit 6 determines whether to generate radicals as combustion support to promote combustion after ignition or to directly ignite the fuel according to the operating state of the internal combustion engine, and based on the determination result, the alternating current The frequency fsw and the resonance frequency fr are changed to change the instantaneous power of the discharge.

In the present embodiment, the control circuit 6 has a DC / DC / The AC converter 2 is made to output AC power. Then, the control circuit 6, the AC frequency fsw and the resonance frequency fr in the pre-ignition period, and the AC frequency fsw and the resonance frequency fr in the ignition period are changed.

According to this configuration, it is possible to set the frequency and the instantaneous power of the discharge suitable for generating radicals in the pre-ignition period and the instantaneous power of the frequency and the discharge suitable for igniting in the ignition period.

In particular, in an operating state where the air-fuel ratio is lean, the exhaust gas recirculation rate is high, or the like, the ignitability of the air-fuel mixture is poor. Can be improved.

The control circuit 6 makes the AC frequency fsw and the resonance frequency fr of the ignition period higher than the AC frequency fsw and the resonance frequency fr of the pre-ignition period.

In the present embodiment, the control circuit 6 changes the AC frequency fsw and the resonance frequency fr in the pre-ignition period to the first AC frequency fsw1 and the first resonance frequency fr1, and changes the AC frequency fsw and the resonance frequency in the ignition period. The fr is changed to the second AC frequency fsw2 and the second resonance frequency fr2.

According to this configuration, in the pre-ignition period, a relatively low discharge instantaneous power that generates radicals but does not reach ignition is generated, and in the ignition period, a high discharge instantaneous power that reaches ignition is generated. Can be generated.

An example of the processing of the control circuit 6 according to the present embodiment will be described with reference to the timing chart of FIG. The horizontal axis shows time, and the vertical axis shows each signal, frequency state, voltage, and energy per ignition. When the signal is 1, it means that it is high, and when it is 0, it means that it is low.

The control circuit 6 switches the discharge start signal S1 from 0 to 1 at a time t10 before a predetermined time of the discharge start time, and switches the discharge start signal S1 from 1 to 0 at the time t11 of the discharge start time. When the discharge start signal S1 is switched from 1 to 0, the control circuit 6 switches the discharge period signal S2 from 0 to 1. The control circuit 6 determines the pre-ignition period based on the operating state of the internal combustion engine, and sets the start time of the pre-ignition period to the discharge start time. Then, the control circuit 6 switches the discharge period signal S2 from 1 to 0 at the time t12 of the end time of the pre-ignition period. In the pre-ignition period, the control circuit 6 sets the frequency switching signal S_flag to low (0), sets the switch drive signal S3 to low (0), turns off the first switch circuit 321 and resonates frequency fr. Is changed to the first resonance frequency fr1.

As described above, the control circuit 6 controls the switch 21 of the DC / AC converter 2 on and off during the pre-ignition period from time t11 to time t12 when the discharge period signal S2 is 1, and controls the DC / AC converter 2. 2 is made to output the AC voltage of the first AC frequency fsw1 and is supplied to the ignition plug 4. Since the first AC frequency fsw1 is set in the amplification frequency band near the first resonance frequency fr1, the AC voltage amplified by the frequency change connection circuit 3 is applied to the spark plug 4. A dielectric barrier discharge of relatively low instantaneous discharge power is generated in the spark plug 4, and radicals are generated in air or a mixture of air and fuel.

At time t13 after time t12, the control circuit 6 changes the frequency switching signal S_flag from 0 to 1 due to the barrier discharge during the ignition period. At time t14 after time t13, the control circuit 6 sets the frequency switching signal S_flag to 1, so the AC frequency fsw is set to the second AC frequency fsw2, and the switch drive signal S3 is changed from 0 to 1. Switching, the first switch circuit 321 is turned on, and the resonance frequency fr is changed to the second resonance frequency fr2.

Then, at time t15, the control circuit 6 has reached the start time of the ignition period, so the discharge period signal S2 is switched from 0 to 1. At time t16, the control circuit 6 has reached the end time of the ignition period, so the discharge period signal S2 is switched from 1 to 0. The control circuit 6 determines the ignition period based on the operating state of the internal combustion engine. The ignition period may be extended when a misfire is detected.

The control circuit 6 controls the switch 21 of the DC / AC converter 2 to be turned on and off during the ignition period from time t15 to time t16 when the discharge period signal S2 is 1, and causes the DC / AC converter 2 to have a second alternating current. An AC voltage having a frequency of fsw2 is output and supplied to the ignition plug 4. Since the second AC frequency fsw2 is set in the amplification frequency band near the second resonance frequency fr2, the AC voltage amplified by the frequency change connection circuit 3 is applied to the spark plug 4. A dielectric barrier discharge of relatively high instantaneous discharge power is generated in the spark plug 4, and the air-fuel mixture is ignited.

The control circuit 6 repeatedly executes the process from the time t10 to the time t16 for each combustion cycle.

In the example of FIG. 10, the output of the AC voltage of the DC / AC converter 2 is stopped during the period from time t12 to time t15 between the pre-ignition period and the ignition period. That is, the control circuit 6 stops the output of the AC voltage of the DC / AC converter 2 when changing the AC frequency fsw and the resonance frequency fr, and changes the resonance frequency fr while the output of the AC voltage is stopped. When the output of the AC voltage is restarted, the AC frequency fsw is changed.

According to this configuration, as described in the first embodiment, it is possible to prevent the output current of the DC / AC converter 2 from being in phase with respect to the output voltage. As a result, when each switch 21 of the DC / AC converter 2 is turned on and off, it is possible to prevent a recovery current from flowing through a diode connected in antiparallel to each switch 21 to generate heat. Therefore, it is possible to prevent the switch 21 of the DC / AC converter 2 from generating heat, and it is possible to prevent the cooling mechanism such as the heat sink from becoming large in size.

The AC voltage output stop period should be set to the period until the current flowing in the load resonance circuit before the stop is attenuated to 1/10 or less. By restarting the output of the AC voltage after the current is sufficiently attenuated, the recovery current can be reliably reduced and the heat generation can be reliably reduced.

Alternatively, it is not necessary to provide an output stop period for stopping the output of the AC voltage of the DC / AC converter 2 between the pre-ignition period and the ignition period. In this case, as described in the first embodiment, the control circuit 6 sets the AC frequency fsw when increasing the resonance frequency fr and the AC frequency fsw during the output of the AC voltage of the DC / AC converter 2. After increasing, the resonance frequency fr may be increased.

For example, the control circuit 6 changes the AC frequency fsw from the first AC frequency fsw1 to the second AC frequency fsw2 immediately before the ignition timing, and changes the resonance frequency fr from the first resonance frequency fr1 to the second at the ignition timing. The resonance frequency is changed to fr2.

Although the present application describes various exemplary embodiments and examples, the various features, embodiments, and functions described in one or more embodiments are applications of a particular embodiment. It is not limited to, but can be applied to embodiments alone or in various combinations. Therefore, innumerable variations not illustrated are envisioned within the scope of the techniques disclosed herein. For example, it is assumed that at least one component is modified, added or omitted, and further, at least one component is extracted and combined with the components of other embodiments.

1 internal combustion engine, 2 DC / AC converter, 3 frequency change connection circuit, 4 ignition plug, 6 control circuit, 7 DC power supply, 13 combustion chamber, 21 DC / AC converter switch, 31 1st inductor, 32 frequency change Circuit (switch), 33 transformer, 41 1st electrode, 42 2nd electrode, 43 dielectric, 321 1st switch circuit, 322 2nd switch circuit, fr resonance frequency, fr1 1st resonance frequency, fr2 2nd resonance Frequency, fr3 third resonance frequency, fsw AC frequency, fsw1 first AC frequency, fsw2 second AC frequency, fsw3 third AC frequency

Claims

A DC / AC converter with a switch that converts DC power supplied from a DC power supply to AC power,
A spark plug having a pair of electrodes and a dielectric arranged between the pair of electrodes and arranged in the combustion chamber of an internal combustion engine.
A frequency change connection circuit that connects between the DC / AC converter and the spark plug and has a frequency change circuit that changes the resonance frequency of the entire circuit from the DC / AC converter to the spark plug.
It is provided with a control circuit that controls the on / off of the switch of the DC / AC converter, causes the DC / AC converter to output an AC voltage of an AC frequency, and supplies the AC voltage to the spark plug.
The control circuit is an ignition system that controls the frequency change circuit of the frequency change connection circuit to change the resonance frequency and change the AC frequency.
The frequency change connection circuit includes two or more inductors and, as the frequency change circuit, one or more switches that change the connection relationship of the inductor with respect to the entire circuit, and is a switch of the frequency change connection circuit. The ignition system according to claim 1, wherein the inductance of the entire circuit changes depending on whether the circuit is turned on or off, and the resonance frequency changes.
The control circuit changes the AC frequency in conjunction with the change in the resonance frequency, and the AC frequency is amplified by resonance to amplify the applied voltage of the ignition plug with respect to the output voltage of the DC / AC converter. The ignition system according to claim 1 or 2, wherein the ignition system is changed within the amplified frequency band.
The ignition system according to claim 3, wherein the control circuit changes the AC frequency to a frequency within the amplification frequency band and equal to or higher than the resonance frequency.
The ignition system according to any one of claims 1 to 4, wherein the control circuit changes the AC frequency and the resonance frequency based on the operating state of the internal combustion engine.
In the control circuit, as the operating state of the internal combustion engine, the rotation speed of the internal combustion engine, the pressure information in the combustion chamber, the compression ratio of the combustion chamber, the air-fuel ratio, the exhaust gas recirculation rate, and the presence or absence of misfire. The ignition system according to claim 5, wherein at least one of the above is used.
The ignition according to any one of claims 1 to 6, wherein the control circuit raises the AC frequency and the resonance frequency when the misfire of the internal combustion engine is detected, as compared with the case where the misfire is not detected. system.
The control circuit determines whether or not the state is difficult to ignite based on the operating state of the internal combustion engine, and when it is determined that the state is difficult to ignite, the AC frequency and the resonance frequency are ignited. The ignition system according to any one of claims 1 to 7, wherein the ignition system is made higher than when it is determined that the condition is not difficult.
The control circuit determines whether or not it is in an easily ignitable state based on the operating state of the internal combustion engine, and when it is determined that it is in an easily ignitable state, it ignites the AC frequency and the resonance frequency. The ignition system according to any one of claims 1 to 8, which is lower than when it is determined that the condition is not easy.
The control circuit increases the AC frequency and then increases the resonance frequency when increasing the resonance frequency and the AC frequency during the output of the AC voltage of the DC / AC converter. The ignition system according to any one of 9 to 9.
Claim 1 in which the control circuit lowers the resonance frequency and then lowers the AC frequency when lowering the resonance frequency and the AC frequency during the output of the AC voltage of the DC / AC converter. 10. The ignition system according to any one of 10.
The control circuit stops the output of the AC voltage of the DC / AC converter when changing the AC frequency and the resonance frequency, and changes the resonance frequency while the output of the AC voltage is stopped, and changes the AC voltage. The ignition system according to any one of claims 1 to 9, wherein the AC frequency is changed when the output of the device is restarted.
The frequency change connection circuit according to any one of claims 1 to 12, wherein the AC power output from the DC / AC converter is supplied to the spark plug even when all the switches are turned off. Ignition system.
The control circuit supplies AC power to the DC / AC converter during the pre-ignition period and the ignition period during the ignition period from the start of the inflow of air into the combustion chamber to the start of ignition. The ignition system according to any one of claims 1 to 13, which is output and changes the AC frequency and the resonance frequency in the pre-ignition period and the AC frequency and the resonance frequency in the ignition period.
The ignition system according to claim 14, wherein the control circuit makes the AC frequency and the resonance frequency of the ignition period higher than the AC frequency and the resonance frequency of the pre-ignition period.