JP2015187419A - internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid a problem of the repetition of accidental fire resulting from a fuel adhering to electrode parts of an ignition plug in a direct-fuel-injection internal combustion engine.SOLUTION: An internal combustion engine that is a direct-fuel-injection internal combustion engine directly injecting a fuel into a combustion chamber of each cylinder and that can implement active ignition for producing plasmas in the combustion chamber by the interaction between spark discharge generated 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, is configured to implement the active ignition in the same cycle as a cycle in which combustion failure occurs in the combustion chamber of the cylinder if the occurrence is detected.

Description

  The present invention relates to an in-cylinder direct injection internal combustion engine that directly injects fuel into a combustion chamber of a cylinder.

  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

  In an in-cylinder direct injection internal combustion engine, the fuel injected from the injector may adhere to the electrode portion of the spark plug. This adhered fuel becomes a factor that inhibits spark discharge between the center electrode of the spark plug and the ground electrode, and increases the risk of causing misfire. Once misfire has occurred, there has been a concern that misfire may be repeated by the adhering fuel remaining on the electrode after the next cycle.

  An object of the present invention is to avoid the problem of misfire caused by fuel adhering to an electrode portion of a spark plug in a direct injection type internal combustion engine.

  In order to solve the above-described problems, the present invention is an in-cylinder direct injection internal combustion engine that directly injects fuel into a combustion chamber of a cylinder, and a spark discharge generated between a center electrode and a ground electrode of a spark plug. It is possible to perform active ignition that interacts with the electric field radiated in the combustion chamber via the antenna facing the combustion chamber to generate plasma in the combustion chamber and ignite the fuel, and burns in the combustion chamber of the cylinder When it is detected that a failure (a state in which the fuel injected into the combustion chamber is not sufficiently burned and unburned fuel remains in the combustion chamber; combustion instability or misfiring) has occurred, An internal combustion engine that performs active ignition during the same cycle was configured.

  According to the present invention, in a direct injection type internal combustion engine, it is possible to avoid the problem that misfire is repeated due to fuel adhering to the electrode portion of the spark plug.

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.

  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 and includes 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 a coil case together with an igniter 13 that is a semiconductor switching element. When the igniter 13 receives an ignition signal i from an ECU (Electronic Control Unit) 0 which is a control device of the internal combustion engine, the igniter 13 is first ignited and a current flows to the primary side of the ignition coil 14, and at the ignition timing immediately thereafter. The igniter 13 is extinguished to interrupt this current. 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.

  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.

  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 (Exhaust Gas Recirculation) device 2 realizes a so-called high pressure loop EGR, and an EGR passage 21 communicating 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. The EGR cooler 22 provided on the EGR passage 21 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.

  Then, the ECU 0 in the present embodiment refers to the ion current signal h and determines whether or not a combustion failure has occurred in the combustion chamber of the cylinder 1. When a combustion failure is detected, a cleaning process is performed to remove the fuel adhering to the electrode portion of the spark plug 12 by vaporizing or burning it by executing active ignition.

  As shown in FIG. 5, 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 charged in the combustion chamber of the cylinder 1 exceeds the threshold (crank Count the 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. In contrast, 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.

  The ECU 0 that determines that the combustion failure of the air-fuel mixture has occurred performs active ignition (application of a high-frequency electric field and spark discharge) in the cylinder 1 as soon as possible after the detection of the combustion failure. This active ignition is preferably performed during the same cycle as the cycle in which the combustion failure occurs (the series of intake-compression-expansion-exhaust is one cycle), and in particular, the same as the expansion stroke in which the fuel failure has occurred. It is preferable to carry out in the middle or later stage of the expansion stroke.

  In this embodiment, it is an in-cylinder direct injection internal combustion engine that directly injects fuel into the combustion chamber of the cylinder 1, and an antenna that faces the spark discharge generated between the center electrode and the ground electrode of the spark plug 12 and the combustion chamber. It is possible to perform active ignition in which an electric field radiated into the combustion chamber via (the center electrode of the spark plug 12) interacts to generate plasma in the combustion chamber and ignite the fuel. The internal combustion engine is configured to perform active ignition when it is detected that a combustion failure has occurred in the room, thereby removing the fuel adhering to the electrode portion of the spark plug 12.

  According to the present embodiment, the adhering fuel that hinders the spark discharge in the spark plug 12 can be removed in a timely manner, so that the reliability of ignition of the air-fuel mixture in the cycle after the next cycle in which the combustion failure has occurred is increased, and the combustion is performed. Avoid repetitive instability or misfire.

  In addition, unburnt fuel adhering to the electrode of the spark plug 12 can be burned out and converted into engine torque, so that the required load can be satisfied and the drivability can be improved, and the fuel efficiency is improved. It can also contribute to the development.

  During normal operation except when operating at a high EGR rate where the air-fuel mixture combustion stability is low or when the temperature is low, ignition is performed only by spark discharge, and only when a defective combustion is detected, the spark plug 12 is activated by active ignition. A mode in which cleaning is performed can also be taken. In this case, power consumption due to electric field radiation into the combustion chamber can be suppressed.

  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 method for detecting the combustion failure of the air-fuel mixture in the combustion chamber of the cylinder 1 is not limited to the method of referring to the ion current signal h as in the above embodiment. As already described, there is a correlation between the transition of the ion current signal h and the transition of the in-cylinder pressure (combustion chamber pressure of the cylinder 1) or the in-cylinder temperature (combustion chamber temperature). When a pressure sensor for detecting the in-cylinder pressure or a temperature sensor for detecting the in-cylinder temperature is mounted on the cylinder 1, the combustion of the air-fuel mixture is performed based on the in-cylinder pressure or the in-cylinder temperature measured via the sensor. It is possible to determine whether it is normal or defective. Typically, the length of the period in which the in-cylinder pressure or the in-cylinder temperature exceeds the threshold value is compared with a determination value, and if the length of the period falls below the determination value, combustion failure in the combustion chamber of the cylinder 1 is detected. It is determined that it has occurred.

  Another example of the method for detecting poor combustion is one that refers to the rotational fluctuation of the internal combustion engine. Specifically, the time required for the crankshaft, which is the output shaft of the internal combustion engine, to rotate by a predetermined angle (for example, 30 ° CA) is repeatedly measured, and the required time previously measured from the required time measured this time. By subtracting the time, an index value of the amount of change in the required time, that is, the amount of decrease in the rotational speed for each predetermined angle is obtained. Then, the index value is compared with a determination value. If the index value exceeds the determination value, it is determined that a combustion failure has occurred in the combustion chamber of 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.

  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 6 ... Electric field generator 7 ... Mixer

Claims (1)

This is an in-cylinder direct injection internal combustion engine that directly injects fuel into the combustion chamber of the cylinder, and radiates it into the combustion chamber via the spark discharge generated between the center electrode and the ground electrode of the spark plug and the antenna facing the combustion chamber. An active ignition that interacts with the generated electric field to generate plasma in the combustion chamber and ignite the fuel,
An internal combustion engine that performs active ignition during the same cycle as the cycle in which the combustion failure occurs when it is detected that a combustion failure has occurred in the combustion chamber of the cylinder.

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