JP2015187390A - internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize an amount of energy input into a combustion chamber at a time of ignition of an air-fuel mixture by active ignition.SOLUTION: An internal combustion engine that can implement active ignition for producing plasmas in a combustion chamber of each cylinder by the interaction between spark discharge that occurs between a center electrode and a ground electrode of an ignition plug and an electric field emitted into the combustion chamber via an antenna facing the interior of the combustion chamber and thereby igniting a fuel, adjusts increasing/decreasing the intensity of the electric field and/or the emission time of the electric field emitted into the combustion chamber in the active ignition in the next and the following expansion cycles of the cylinder S3 on the basis of an internal pressure of the combustion chamber in an expansion cycle of the cylinder S1.

Description

  The present invention relates to an internal combustion engine mounted on a vehicle or the like.

  In an ignition device mounted on a general spark ignition type internal combustion engine, a high voltage generated in the ignition coil when the igniter extinguishes is applied to the center electrode of the ignition plug, so that the center electrode of the ignition plug is grounded. A spark discharge is caused between the electrodes and ignited.

  Recently, in order to ensure that the air-fuel mixture in the combustion chamber of the cylinder is ignited and a stable flame can be obtained, the high frequency output from the high frequency oscillator or the microwave output from the magnetron is radiated into the combustion chamber. An “active ignition” method has been attempted (see, for example, the following patent document). According to the active ignition method, a high-frequency electric field or a microwave electric field is formed in the space between the center electrode and the ground electrode, and the plasma generated in this electric field grows to form a large flame nucleus that starts flame propagation combustion. Can be generated.

JP 2011-0664162 A

  The active ignition method is a promising technique for increasing the certainty of ignition of the air-fuel mixture. However, there is a demerit of power consumption due to electric field radiation into the combustion chamber. The amount of intake air that fills a cylinder, the EGR rate that is the proportion of EGR (Exhaust Gas Recirculation) gas in the intake air, and the air-fuel ratio of the air-fuel mixture are not always constant. In addition, there is a habit of each cylinder, that is, a variation between cylinders. Specifically, the plurality of cylinders included in the internal combustion engine include a cylinder in which EGR gas easily flows and a fresh air does not easily flow in, and a cylinder in which EGR gas does not easily flow in and a fresh air easily flows. The EGR rate of the intake air filled in is not necessarily uniform.

  The degree to which the energy of the electric field supplied to the combustion chamber of the cylinder is absorbed by the air-fuel mixture in the combustion chamber varies depending on the EGR rate, air-fuel ratio, etc. of the air-fuel mixture. Therefore, the optimum electric field strength and radiation time for active ignition can vary frequently and can vary from cylinder to cylinder. If the energy amount of the electric field input to the combustion chamber is insufficient, the air-fuel mixture cannot be ignited well, which may cause unstable combustion or misfire.

  Conversely, if the energy amount of the electric field input to the combustion chamber is unnecessarily excessive, power is wasted. In addition, excess energy that is not absorbed by the air-fuel mixture in the combustion chamber may be reflected back to the high-frequency oscillator or magnetron that is the electric field generator, which may cause the high-frequency oscillator or magnetron to break down. Absent.

  An object of the present invention is to optimize the amount of energy input into the combustion chamber when the air-fuel mixture is ignited by the active ignition method.

  In the present invention, the spark discharge generated between the center electrode and the ground electrode of the spark plug interacts with the electric field radiated into the combustion chamber via the antenna facing the combustion chamber of the cylinder to generate plasma in the combustion chamber. An internal combustion engine capable of performing active ignition for igniting fuel, and based on the pressure in the combustion chamber in the expansion stroke of the cylinder, the intensity of the electric field radiated into the combustion chamber in the active ignition in the subsequent expansion stroke of the cylinder And / or the internal combustion engine which adjusts increase / decrease in the radiation time of an electric field was comprised.

  According to the present invention, it is possible to optimize the amount of energy input into the combustion chamber when the air-fuel mixture is ignited by the active ignition method.

The figure which shows schematic structure of the internal combustion engine of one Embodiment of this invention. The circuit diagram of the ignition system of the internal combustion engine of the embodiment. The figure explaining the structure of the electric field generator accompanying the ignition system of the internal combustion engine of the embodiment. The circuit diagram of the H bridge which is an element of the electric field generator. The timing diagram which shows transition of the ionic current at the time of normal combustion in the internal combustion engine of the embodiment. The figure which shows transition of the primary current which flows through the primary side coil of an ignition coil in the period from ignition of an igniter to spark ignition. The flowchart which shows the example of the procedure of the process which the control apparatus of the internal combustion engine of the embodiment performs.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle in the present embodiment. The internal combustion engine in the present embodiment is a direct injection type four-stroke gasoline engine that directly injects fuel into the combustion chamber of the cylinder 1, and a plurality of cylinders 1 (one of which is shown in FIG. 1). ). Each cylinder 1 is provided with an injector 11 for injecting fuel at a position facing the combustion chamber. A spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1.

  FIG. 2 shows an electric circuit of the ignition system. The spark plug 12 receives spark voltage generated by the ignition coil 14 and causes spark discharge between the center electrode and the ground electrode. The ignition coil 14 is integrally incorporated in the coil case together with the igniter 13 having the semiconductor switching element 131.

  When the igniter 13 receives an ignition signal i from an ECU (Electronic Control Unit) 0, which is a control device for the internal combustion engine, first, the semiconductor switch 131 of the igniter 13 is ignited and a current flows to the primary side of the ignition coil 14, immediately thereafter. At this spark ignition timing, the semiconductor switch 131 extinguishes and this current is cut off. Then, a self-induction action occurs, and a high voltage is generated on the primary side. Since the primary side and the secondary side share the magnetic circuit and the magnetic flux, a higher induced voltage is generated on the secondary side. This high induction voltage is applied to the center electrode of the spark plug 12, and a spark discharge is generated between the center electrode and the ground electrode.

  The primary coil of the ignition coil 14 is connected to the in-vehicle power supply battery 17 via the semiconductor switch 131. When the semiconductor switch 131 is ignited and a DC voltage supplied from the battery 17 is applied to the primary side coil to start energization, the primary current flowing through the primary side (low voltage system) circuit including the primary side coil increases.

FIG. 6 illustrates the transition of the primary current after the start of energization of the primary side coil. In FIG. 6, the case where the current limiting function does not work is drawn with a broken line, and the case where the current limiting function works is drawn with a one-dot chain line (the solid line will be described later). Assuming that the primary side electric circuit including the battery 17 and the primary side coil is an RL series circuit, the primary current I (t) when the DC voltage E is applied at time t = 0 is
I (t) ≈ {1-e- ^{(R / L) t} } E / R
It becomes. That is, the primary current increases as a transient phenomenon, but the rate of increase gradually decreases. When a sufficiently long time elapses, the primary current saturates to E / R as shown by the broken line in FIG.

  The igniter 13 has a current limiting function that suppresses excessive primary current. This current limiting function is similar to that of off-the-shelf igniters that are popular today. Specifically, the control circuit 132 constantly measures the primary current in the form of the voltage across the resistor 133 via the detection resistor 133. The semiconductor switch 131 is ignited while the magnitude of the primary current (voltage across the resistor 133) is equal to or less than a specified value, while the semiconductor switch 131 is extinguished when the magnitude exceeds the specified value. As a result, the primary current is clipped to the specified value as indicated by the alternate long and short dash line in FIG.

The induced voltage applied to the center electrode of the spark plug 12 at the time of spark ignition becomes higher as the primary current flowing in the primary coil of the ignition coil 14 at the time t ₁ when the semiconductor switch 131 is extinguished is larger. Therefore, the longer the energization time to the primary coil, the higher the induced voltage applied to the center electrode of the spark plug 12. In addition, a large primary current means that the amount of electric power input to the ignition coil 14 is large, and the longer the energization time to the primary coil, the spark between the center electrode of the spark plug 12 and the ground electrode. The time during which discharge continues is also increased.

In short, it is possible to adjust the magnitude of the induced voltage applied to the center electrode of the spark plug 12 and the duration of the spark discharge by adjusting the time points t ₀ and t ₀ ′ when the semiconductor switch 131 is ignited. . In FIG. 6, a case where the energization time to the primary side coil is relatively short (energization starts at a later time t ₀ ) is drawn with a solid line, and the energization time to the primary side coil is relatively long (earlier time t _The energization is started from ₀ ').

  Incidentally, the igniter 13 also has a function of forcibly cutting off the energization to the primary side coil when detecting abnormal heat generation such that the temperature of the ignition coil 14 or the igniter 13 itself exceeds the upper limit value.

  In the internal combustion engine of the present embodiment, an electric field generator 6 for generating an electric field in the combustion chamber of the cylinder 1 is attached to the ignition system. The electric field generator 6 is intended to generate plasma in the combustion chamber. Specific examples of the electric field generator 6 include an AC voltage generation circuit that outputs a high-frequency AC voltage, a pulsating voltage generation circuit that outputs a high-frequency pulsating voltage, and the like.

  As shown in FIGS. 3 and 4, the electric field generator 6 that generates a high frequency includes a circuit that uses a vehicle-mounted battery as a power source and converts low-voltage direct current into high-voltage alternating current. Specifically, a DC-DC converter 61 that boosts a DC voltage of about 12 V provided by the battery to 100 V to 500 V, and an H-bridge circuit 62 that is a high-frequency generation circuit that converts the DC output from the DC-DC converter 61 into AC. And a step-up transformer 63 that boosts the alternating-current high-frequency output from the H-bridge circuit 62 to a higher voltage.

  The DC-DC converter 61 can change the magnitude of the direct-current drive voltage applied to the H bridge circuit 62 in response to the command 1 from the ECU 0, and consequently the amplitude of the high-frequency voltage downstream of the step-up transformer 63. Can be changed. The high-frequency voltage downstream of the step-up transformer 63 preferably has a frequency of about 200 kHz to 3000 kHz and an amplitude of about 3 kVp-p to 10 kVp-p.

  A first diode 64 and a second diode 65 are interposed at the output end of the electric field generator 6. The first diode 64 has a cathode connected to the signal line of the secondary winding of the step-up transformer 63 and an anode connected to the mixer 7, which is a node with the ignition coil 14. The second diode 65 has an anode connected to the ground line of the secondary winding of the step-up transformer 63 and a cathode grounded. The first diode 64 and the second diode 65 rectify the high frequency of alternating current by half-wave rectification downstream of the step-up transformer 63 and pulsate the negative high-voltage pulse current flowing from the secondary side of the ignition coil 14 at the ignition timing. Play a role of blocking.

  Incidentally, when a pulsating voltage generation circuit is employed as the electric field generator 6, the pulsating voltage generation circuit may be any circuit that generates a DC voltage whose voltage periodically changes, and its waveform may be arbitrary. . The pulsating voltage mentioned here includes a pulse voltage that varies from a reference voltage (which may be 0 V) to a constant voltage at a constant period, a voltage obtained by adding a DC bias to an AC voltage, and the like.

  The high frequency voltage generated by the electric field generator 6 is applied to the center electrode of the spark plug 12. That is, the center electrode of the spark plug 12 facing the combustion chamber of the cylinder 1 is an antenna that radiates an electric field. Thereby, a high frequency electric field is formed in the space between the center electrode of the spark plug 12 and the ground electrode in the combustion chamber. Then, a plasma is generated by performing a spark discharge in a high-frequency electric field, and this plasma generates a large radical plasma flame nucleus that starts flame propagation combustion.

  In the above, the flow of electrons due to the spark discharge and the ions and radicals generated by the spark discharge are vibrated and meandered by the influence of the electric field, resulting in a long path length and a dramatic increase in the number of collisions with surrounding water and nitrogen molecules. This is due to the increase. Water molecules and nitrogen molecules that have been struck by ions and radicals become OH radicals and N radicals, and the surrounding gas that has been struck by ions and radicals is also ionized, that is, a plasma state. In addition, the region of ignition of the air-fuel mixture increases and the flame kernel also increases. As a result, the two-dimensional ignition by only the spark discharge is amplified to the three-dimensional ignition, and the combustion rapidly propagates into the combustion chamber and expands at a high combustion speed.

  In the case of performing active ignition, the timing at which a high frequency is applied to the center electrode of the spark plug 12 is usually almost simultaneously with the start of spark discharge, immediately before the start of spark discharge, or immediately after the start of spark discharge.

  Of course, the internal combustion engine of the present embodiment can also ignite the air-fuel mixture by conventional spark ignition that is not active ignition, that is, spark discharge that does not involve emission of a high-frequency electric field from the center electrode of the spark plug 12. In situations where it is easy to ignite and burn stably (it is unlikely to cause a combustion failure), it is conceivable to perform conventional spark ignition to suppress power consumption.

  In the present embodiment, the ECU 0 can detect an ionic current generated in the combustion chamber of the cylinder 1 during the combustion of the air-fuel mixture, and determine the combustion state with reference to the ionic current signal h.

  As shown in FIG. 2, in this embodiment, a circuit for detecting an ionic current is added to the electric circuit of the ignition system. This detection circuit includes a bias power supply unit 15 for effectively detecting an ionic current and an amplification unit 16 that amplifies and outputs a detection voltage corresponding to the amount of the ionic current. The bias power supply unit 15 includes a capacitor 151 that stores a bias voltage, a Zener diode 152 for increasing the voltage of the capacitor 151 to a predetermined voltage, current blocking diodes 153 and 154, and a load that outputs a voltage corresponding to the ion current. A resistor 155. The amplifying unit 16 includes a voltage amplifier 161 typified by an operational amplifier.

  The capacitor 151 is charged during arc discharge between the center electrode and the ground electrode of the spark plug 12, and then an ion current flows through the load resistor 155 by the bias voltage charged in the capacitor 151. The voltage between both ends of the resistor 155 generated by the flow of the ionic current is amplified by the amplifying unit 16 and received by the ECU 0 as the ionic current signal h.

  FIG. 5 illustrates respective transitions of the ionic current (indicated by a solid line in the figure) and the combustion pressure in the cylinder 1 (in-cylinder pressure; indicated by a broken line in the figure) in normal combustion. In the case of normal combustion, the ionic current decreases by a chemical reaction before the compression top dead center after the end of spark ignition, and then increases again by thermal dissociation. At almost the same time as the in-cylinder pressure reaches its peak, the ion current also becomes maximum.

  The ECU 0 determines the length of the period T during which the magnitude of the ion current signal h detected after igniting the air-fuel mixture filled in the combustion chamber of the cylinder 1 exceeds the threshold value (in units of crank angle (° CA) or seconds) ). If the length of the counted period T is equal to or greater than the determination value, it is determined that the air-fuel mixture has burned normally during the expansion stroke of the cylinder 1. On the contrary, if the length of the period T falls below the determination value, it is determined that the combustion of the air-fuel mixture in the expansion stroke of the cylinder 1 is poor, that is, combustion instability or misfire has occurred.

  Note that the ionic current cannot be detected during discharge for ignition. Further, what is shown in FIG. 5 is a waveform of the ion current signal h when the air-fuel mixture is burned by the conventional spark ignition. When performing active ignition in which a high-frequency electric field is radiated from the center electrode of the spark plug 12, ion current cannot be detected even during the emission of the high-frequency electric field.

  An intake passage 3 for supplying intake air to the cylinder 1 of the internal combustion engine takes in air from the outside and guides it to the intake port of each cylinder 1. On the intake passage 3, an air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from the upstream.

  The exhaust passage 4 for exhausting the exhaust from the cylinder 1 guides the exhaust generated as a result of burning the fuel in the cylinder 1 from the exhaust port of each cylinder 1 to the outside. An exhaust manifold 42 and an exhaust purification three-way catalyst 41 are disposed on the exhaust passage 4.

  The external EGR device 2 realizes a so-called high-pressure loop EGR. The EGR device 21 communicates the upstream side of the catalyst 41 in the exhaust passage 4 and the downstream side of the throttle valve 32 in the intake passage 3, and the EGR passage 21. The EGR cooler 22 provided in the EGR passage and the EGR valve 23 that opens and closes the EGR passage 21 and controls the flow rate of the EGR gas flowing through the EGR passage 21 are used as elements. The inlet of the EGR passage 21 is connected to the exhaust manifold 42 in the exhaust passage 4 or a predetermined location downstream thereof. The outlet of the EGR passage 21 is connected to a predetermined location downstream of the throttle valve 32 in the intake passage 3, specifically to a surge tank 33.

  The ECU 0 that controls operation of the internal combustion engine is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like.

  The input interface includes a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal b output from an engine rotation sensor that detects the rotation angle and engine speed of the crankshaft, and depression of an accelerator pedal. An accelerator opening signal c output from a sensor that detects the amount or the opening of the throttle valve 32 as an accelerator opening (so-called required load), and a brake pedaling amount signal d output from a sensor that detects the amount of depression of the brake pedal The intake air temperature / intake pressure signal e output from the temperature / pressure sensor for detecting the intake air temperature and the intake pressure in the intake passage 3 (particularly the surge tank 33), and the water temperature sensor for detecting the cooling water temperature of the internal combustion engine are output. Output from the cam angle sensor at a plurality of cam angles of the cooling water temperature signal f and the intake camshaft or exhaust camshaft. A cam angle signal g, the ion current signal h or the like to be output from the circuit for detecting an ion current caused by the combustion of the mixture in the combustion chamber are inputted.

  From the output interface, the ignition signal i for the igniter 13 of the spark plug 12, the fuel injection signal j for the injector 11, the opening operation signal k for the throttle valve 32, and the DC for the DC-DC converter 61. A voltage command signal l for commanding the magnitude of the drive voltage output from the DC converter 61, an opening operation signal m, etc. are output to the EGR valve 23.

  The processor of the ECU 0 interprets and executes a program stored in the memory in advance, calculates operation parameters, and controls the operation of the internal combustion engine. The ECU 0 acquires various information a, b, c, d, e, f, g, and h necessary for operation control of the internal combustion engine via the input interface, knows the engine speed, and is filled in the cylinder 1. Estimate the intake volume. Based on the engine speed, intake air amount, etc., the required fuel injection amount, fuel injection timing (including the number of fuel injections per combustion), fuel injection pressure, ignition timing, and high-frequency electric field applied to the combustion chamber Various operating parameters such as whether or not to perform, the strength of the electric field, and the required EGR rate (or EGR amount) are determined. The ECU 0 applies various control signals i, j, k, l and m corresponding to the operation parameters via the output interface.

  In addition, in this embodiment, when the active ignition is performed on the air-fuel mixture filled in the combustion chamber of the cylinder 1, the previous cycle (intake-compression-expansion-exhaust series of the cylinder 1 is integrated). Based on the performance of the in-cylinder pressure (combustion chamber pressure of the cylinder 1) in the expansion stroke of the cycle), the intensity and / or electric field of the electric field radiated into the combustion chamber at the time of active ignition of the current cycle of the cylinder 1 Increase and decrease adjustment of the radiation time.

  The amount of intake air charged into the cylinder 1, the EGR rate of the intake air, and the air-fuel ratio of the air-fuel mixture are not always constant. In addition, the habit of each cylinder 1 and the variation between the cylinders 1 also exist. That is, the amount of intake air filled in each cylinder 1, the EGR rate of intake air, and the air-fuel ratio are not all equal in the cylinder 1. For example, the plurality of cylinders 1 included in the internal combustion engine include a cylinder 1 in which EGR gas easily flows in and fresh air does not easily flow in, and a cylinder 1 in which EGR gas does not easily flow in and fresh air easily flows. The EGR rate of the intake air filled in is not necessarily equal. The injectors 11 installed in each cylinder 1 also have individual differences and aging changes in the fuel injection performance, and the air-fuel ratio of the air-fuel mixture in each cylinder 1 is not necessarily equal.

  The degree to which the energy of the electric field supplied to the combustion chamber of the cylinder 1 is absorbed by the air-fuel mixture in the combustion chamber varies depending on the EGR rate, air-fuel ratio, etc. of the air-fuel mixture. Therefore, the optimum electric field strength and radiation time for active ignition can vary frequently and can vary from cylinder to cylinder. In active ignition, if the amount of energy of the electric field input to the combustion chamber is insufficient, the air-fuel mixture cannot be ignited well, which may cause unstable combustion or misfire.

  Conversely, if the energy amount of the electric field input to the combustion chamber is unnecessarily excessive, power is wasted. In addition, surplus energy that is not absorbed by the air-fuel mixture in the combustion chamber may be reflected back to the electric field generator 6 and may cause the electric field generator 6 to malfunction.

  Therefore, in this embodiment, the in-cylinder pressure in the expansion stroke of the cylinder 1 is measured or estimated, and the characteristics of the atmosphere in the combustion chamber at that time, that is, the EGR rate, the air-fuel ratio, and the like are estimated based on the level of this in-cylinder pressure. Then, according to the estimated EGR rate and the like, the strength of the high-frequency electric field (the magnitude of the high-frequency voltage applied to the center electrode of the spark plug 12) and the radiation time (in the active ignition during the next and subsequent expansion strokes of the same cylinder 1) and the radiation time ( The length of time during which the high-frequency voltage is applied to the center electrode of the spark plug 12 is determined. This is because, for example, the EGR rate of the air-fuel mixture in the expansion stroke (performed by performing ignition combustion of the air-fuel mixture and measuring or estimating the in-cylinder pressure) and the EGR rate of the air-fuel mixture in the next expansion stroke of the same cylinder 1 Because it is expected to be almost equal.

  The intensity and / or radiation time of the high-frequency electric field radiated into the combustion chamber during active ignition is determined individually for each cylinder 1. FIG. 7 shows a specific procedure in which the ECU 0 determines the strength and / or the radiation time of the high frequency electric field.

  First, the ECU 0 measures or estimates the maximum value of the in-cylinder pressure in the expansion stroke of the current cycle in which the air-fuel mixture is actually burned in the target cylinder 1 (step S1). If a pressure sensor for detecting the in-cylinder pressure is mounted on the cylinder 1, the in-cylinder pressure during the expansion stroke can be measured via the pressure sensor. Further, since there is a correlation between the in-cylinder pressure and the in-cylinder temperature (combustion chamber temperature), if a pressure sensor for detecting the in-cylinder temperature is mounted on the cylinder 1, it is measured via the temperature sensor. The in-cylinder pressure during the expansion stroke can be estimated indirectly based on the in-cylinder temperature (and the intake air amount filled in the cylinder 1).

  Alternatively, even if no pressure sensor or temperature sensor is mounted on the cylinder 1, as already described, since there is a correlation with the in-cylinder pressure of the ion current signal h, the ion current signal h detected during the expansion stroke. It is possible to estimate the magnitude of the in-cylinder pressure during the expansion stroke based on the magnitude of. Generally speaking, the ECU 0 refers to the output signal of the in-cylinder pressure sensor, the output signal of the in-cylinder temperature sensor, or the ion current signal h to know the maximum value of the in-cylinder pressure in the expansion stroke of the current cycle.

  Next, the ECU 0 determines the characteristics of the air-fuel mixture filled in the cylinder 1 in the current cycle including the expansion stroke, in particular, the EGR rate (or the amount of EGR gas) from the maximum value of the in-cylinder pressure during the expansion stroke measured or estimated. ) Is estimated (step S2). Normally, it is considered that the higher the EGR rate of the air-fuel mixture, the lower the combustion pressure that actually occurs during the expansion stroke.

  Needless to say, the in-cylinder pressure during the expansion stroke is determined not only by the EGR rate of the intake air but also by the ignition timing and the operating region of the internal combustion engine at that time [engine speed, load (intake pressure in the surge tank 33, cylinder 1) or the like. Therefore, in order to estimate the EGR rate, it is necessary to consider the ignition timing, the operating region of the internal combustion engine, and the like. In addition, the magnitude of the intake EGR rate depends on the opening of the EGR valve 23 and the opening / closing timing of the intake valve and / or the exhaust valve (when the internal combustion engine is equipped with a VVT (Variable Valve Timing) mechanism). To do. In order to increase the estimation accuracy of the EGR rate, it is preferable to take into account the opening degree of the EGR valve 23 and the valve timing of the intake and exhaust valves. In the memory of the ECU 0, the maximum value of the in-cylinder pressure during the expansion stroke, the ignition timing, the parameter indicating the operation region of the internal combustion engine, the opening degree of the EGR valve 23 (not essential), the valve timing (not essential), etc. Stored is map data or a function formula that defines the relationship with the estimated intake EGR rate. In step S2, the ECU 0 determines the maximum value of the in-cylinder pressure during the expansion stroke in the current cycle of the target cylinder 1, the ignition timing of the current cycle, the operating range in the current cycle, and the opening of the EGR valve 23 in the current cycle. The map is searched using degrees (not essential), valve timing (not essential), and the like as keys, or these are substituted into the function formula to obtain the estimated EGR rate of intake in the current cycle. The estimated EGR rate varies somewhat from cycle to cycle, and may vary from cylinder 1 to cylinder 1.

  Then, the ECU 0 determines the intensity and / or the radiation time of the high-frequency electric field radiated into the combustion chamber in the active ignition executed in the next cycle based on the characteristics of the air-fuel mixture obtained in step S2, that is, the estimated EGR rate. (Step S3). As a result, it becomes possible to input electric power having a magnitude corresponding to the characteristics (EGR rate) of the intake air charged into the cylinder 1 in the next cycle, and to absorb a necessary and sufficient amount of energy in the air-fuel mixture. It is possible to cause ignition and combustion. If the mixture cannot absorb a large amount of high-frequency energy, or if the mixture is ignited and combusted in the first place (the EGR rate is low or the amount of oxygen in the combustion chamber is sufficiently large), it is introduced into the combustion chamber The amount of power to be reduced can be reduced.

  However, the amount that the air-fuel mixture filled in the cylinder 1 in the next cycle can absorb high-frequency energy is not limited to the EGR rate of the intake air in the next cycle, but also the operating range of the internal combustion engine at that time [engine speed, The load (intake pressure in the surge tank 33, intake air amount filled in the cylinder 1 or fuel injection amount)] and the like are also affected. In the memory of the ECU 0, map data or a function expression that prescribes the relationship between the parameters indicating the EGR rate of the intake air and the operating region of the internal combustion engine, and the appropriate high-frequency electric field intensity and / or radiation time is stored. . The map or function formula is obtained experimentally in advance. In step S3, the ECU 0 regards the estimated EGR rate of intake air in the current cycle of the target cylinder 1 as the EGR rate of intake air in the next cycle, and uses the EGR rate and the operation region in the next cycle as a key. Or substituting them into the function formula to know the strength and / or radiation time of the high-frequency electric field during active ignition in the next cycle.

  In the present embodiment, the spark discharge generated between the center electrode of the spark plug 12 and the ground electrode and the electric field radiated into the combustion chamber via the antenna facing the combustion chamber of the cylinder 1 (center electrode of the spark plug 12) Is an internal combustion engine capable of performing active ignition for generating plasma in the combustion chamber and igniting the fuel, and based on the pressure in the combustion chamber in the expansion stroke of the cylinder 1, An internal combustion engine that adjusts the intensity of the electric field radiated into the combustion chamber or the emission time of the electric field in the active ignition at the time is configured.

  According to the present embodiment, variations in characteristics of the air-fuel mixture (especially, EGR rate) and differences between the cylinders 1 are absorbed, and the ignition and combustion of the air-fuel mixture due to active ignition can be made uniform. Therefore, the thermomechanical conversion efficiency of the internal combustion engine is increased, which can contribute to the improvement of fuel consumption performance.

  In addition, it is possible to reduce the risk of misfire due to insufficient high-frequency energy input into the combustion chamber, waste of power due to excessive high-frequency energy, and damage to the electric field generator 6 due to high-frequency reflection. In addition to eliminating the need for a high-performance and high-cost circuit protection device for protecting the electric field generating device 6 from the reflected wave, high-frequency transmission efficiency toward the center electrode of the spark plug 12 as an antenna is improved (transmission loss The output of the DC-DC converter 61, the high-frequency generator circuit 62, and the step-up transformer 63 (or magnetron) constituting the electric field generator 6 is allowed to be minimized, thereby reducing costs and improving reliability. You can also get the utility.

  The present invention is not limited to the embodiment described in detail above. For example, the electric field generator 6 for applying an electric field to the combustion chamber of the cylinder 1 is not limited to an AC voltage generating circuit that applies a high-frequency AC voltage or a pulsating voltage generator circuit that applies a high-frequency pulsating voltage. A magnetron or the like that outputs a microwave may be employed as the electric field generator 6, and active ignition may be performed by applying a microwave electric field into the combustion chamber of the cylinder 1.

  In the above-described embodiment, the center electrode of the spark plug 12 is an antenna for electric field radiation. However, an antenna separate from the spark plug 12 is provided in the cylinder 1, and a high-frequency electric field or micro wave is provided in the combustion chamber of the cylinder 1 through this antenna. A wave electric field may be emitted.

  The high-frequency (or microwave) electric field radiation intensity and / or radiation time determined in step S3 is stored in the memory of the ECU 0 as a learning value for each cylinder 1 and used for subsequent ignition control. Is also possible. In this case, the determined intensity and / or radiation time of the high-frequency electric field is determined based on the target cylinder 1 and the operation region of the internal combustion engine at that time, the ignition timing, the EGR valve 23 opening, and the valve timing (assuming the existence of the VVT mechanism). And the like are stored in association with each other. Then, when the equivalent operation region, ignition timing, EGR valve opening degree, valve timing, etc. are reproduced in the target cylinder 1, the previously stored learned value of the intensity and / or radiation time of the high-frequency electric field is stored from the memory. Read out and use this to perform active ignition in the cylinder 1.

  The internal combustion engine to which the present invention is applied is not limited to a so-called gasoline direct injection engine. Naturally, it is also conceivable to apply the present invention to a diesel engine, a HCCI (homogeneous-charge compression ignition) engine, or the like.

  Furthermore, the present invention can also be applied to a port injection type internal combustion engine that injects fuel into an intake port.

  Other specific configurations of each part can be variously modified without departing from the spirit of the present invention.

  The present invention can be used as an internal combustion engine mounted on a vehicle or the like.

0 ... Control unit (ECU)
DESCRIPTION OF SYMBOLS 1 ... Cylinder 11 ... Injector 12 ... Spark plug, antenna 13 ... Igniter 14 ... Ignition coil 2 ... Exhaust gas recirculation (EGR) device 6 ... Electric field generator 7 ... Mixer

Claims (1)

The spark discharge generated between the center electrode and the ground electrode of the spark plug interacts with the electric field radiated into the combustion chamber via the antenna facing the combustion chamber of the cylinder to generate plasma in the combustion chamber and ignite the fuel. An internal combustion engine capable of performing active ignition,
An internal combustion engine that adjusts the intensity of an electric field radiated in a combustion chamber or an emission time of the electric field in active ignition during the subsequent expansion stroke of the cylinder based on the pressure in the combustion chamber in the expansion stroke of the cylinder.

Images