JP6344941B2 - Internal combustion engine - Google Patents

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, 2014-029128, A

  In a conventional active ignition system, an antenna that emits an electric field (especially, an ignition plug) Applied to the center electrode). At least a part of the half-wave energy that is not put into the combustion chamber of the cylinder, that is, is cut off by the half-wave rectifier and is not used for the plasma conversion of the air-fuel mixture is discarded as heat in the half-wave rectifier. It was a waste of power.

  As a measure for avoiding such waste of electric power, it is conceivable to apply full-wave rectification to an antenna after alternating-current rectification output from an electric field generation source.

  However, a voltage waveform obtained as a result of full-wave rectification of a rectangular wave or an alternating current waveform close to a rectangular wave is close to a direct current with a constant voltage. To achieve reliable ignition of the air-fuel mixture in the combustion chamber of the cylinder, the plasma remains in one place until the plasma generated by the air-fuel mixture absorbing electromagnetic energy grows into a large flame kernel. For this purpose, a pulsating current whose voltage changes frequently must be applied to the antenna. If a constant direct current is applied to the antenna, a constant electric field is formed in the combustion chamber, so that even if plasma is generated in the combustion chamber, the plasma quickly moves in one direction and then disappears. In other words, the closer the waveform of the voltage applied to the antenna is to a constant direct current, the more difficult it is to keep the plasma in one place.

  The present invention has been made by paying attention to the above-mentioned problem for the first time, and an object of the present invention is to ensure that the air-fuel mixture can be ignited while avoiding waste of electric power due to half-wave rectification.

In the present invention, an internal combustion engine capable of radiating an electric field into a combustion chamber via an antenna facing a combustion chamber of a cylinder, an AC oscillator that outputs an alternating triangular wave voltage or a sawtooth voltage, and the AC oscillator An internal combustion engine comprising a full-wave rectifier that applies a pulsating voltage obtained by full-wave rectification of the resulting AC triangular wave voltage or sawtooth wave voltage to the antenna was constructed.

  A triangular wave or a sawtooth wave becomes a pulsating flow far from a direct current having a constant voltage even when full-wave rectification is performed. By applying this to the antenna, the plasma can be kept in one place for a certain period of time. The energy efficiency can be improved by using full wave without impairing the ignition performance.

  According to the present invention, in an ignition system that radiates an electric field into the combustion chamber via an antenna facing the combustion chamber of the cylinder, it is possible to reliably ignite the air-fuel mixture while avoiding waste of power due to half-wave rectification. It becomes.

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 triangular wave oscillator which is an element of the electric field generator. The figure which shows the waveform obtained by carrying out full-wave rectification of alternating current triangular wave and this. The figure which shows transition of the ionic current at the time of normal combustion in the internal combustion engine of the embodiment. The circuit diagram of the sawtooth wave oscillator which is an element of the electric field generator in one modification of this invention. The figure which shows the waveform obtained by carrying out full-wave rectification of an alternating-current sawtooth wave.

  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 generates a high frequency for the purpose of generating plasma in the combustion chamber. As shown in FIGS. 3 and 4, the electric field generator 6 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 AC oscillator that outputs an AC high frequency using the DC voltage output from the DC-DC converter 61. A high-frequency generator circuit 62, a step-up transformer 63 that boosts the alternating-current high-frequency output from the high-frequency generator circuit 62 to a higher voltage, a full-wave rectifier 64 that full-wave rectifies the alternating-current high-frequency boosted by the boost transformer 63, Is a component.

  The DC-DC converter 61 can change the magnitude of the direct-current drive voltage applied to the high-frequency generation circuit 62 in response to the instruction 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.

In the present embodiment, the high frequency generation circuit 62 is a triangular wave oscillator that outputs an alternating triangular wave. FIG. 4 shows a circuit configuration example of the triangular wave oscillator. The triangular wave oscillator of the illustrated example is a known one that forms a Schmitt circuit and an integration circuit using two operational amplifiers. The frequency of the triangular wave output from this triangular wave oscillator is R ₂ / (4CR ₁ R ₃ ).

  As shown in FIG. 3, the full-wave rectifier 64 is a single-phase bridge-type full-wave rectifier that outputs a pulsating current by full-wave rectifying an AC waveform using, for example, four diodes. FIG. 5 illustrates an alternating triangular waveform (indicated by a thin solid line in the figure) before full-wave rectification and a pulsating waveform (indicated by a thick broken line in the figure) after full-wave rectification. The diode of the full wave rectifier 64 also plays a role of blocking the negative high voltage pulse current flowing from the secondary side of the ignition coil 14 at the ignition timing.

  The high-frequency pulsating 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. 6 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.

  In addition, 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 (crank angle (° CA)). Count in units 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.

  Note that the ionic current cannot be detected during discharge for ignition. Further, what is shown in FIG. 6 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.

  In the present embodiment, an internal combustion engine capable of radiating an electric field into a combustion chamber via an antenna (a center electrode of a spark plug 12) facing the combustion chamber of the cylinder 1 and outputs an AC triangular wave voltage An internal combustion engine comprising 62 and a full-wave rectifier 64 that full-wave rectifies and outputs the alternating triangular wave voltage provided from the AC oscillator 62 to the antenna is configured.

  According to this embodiment, when plasma is generated in the combustion chamber of the cylinder 1, a pulsating voltage far from a constant DC voltage can be applied to the antenna facing the combustion chamber. Therefore, it is easy to keep the plasma in one place until the plasma generated by absorbing the energy of the electromagnetic waves grows into a large flame kernel, and mixing while avoiding the waste of power caused by half-wave rectification It is possible to increase the certainty of ignition to the qi. Improvement of energy efficiency by using full wave contributes to power saving and reduction of fuel consumption. Moreover, the electric field generator 6 of this embodiment can be mounted at low cost.

  An improvement in ignition performance, that is, a decrease in the possibility of causing combustion instability or misfire, leads to suppression of deterioration in emissions caused by discharge of unburned fuel and prevention of catalyst 41 from melting. In addition, it contributes to improving drivability and improving fuel efficiency by ensuring sufficient engine torque to meet the required load.

  Further, in a direct injection type internal combustion engine, unburned fuel can be prevented from becoming liquid and adhering to the electrode portion of the spark plug 12, so that combustion instability or misfire does not occur repeatedly.

  During normal operation except during high EGR rate operation where the air-fuel mixture combustion stability is low or at low temperatures, etc., ignition is performed only by spark discharge, and active ignition is performed only when a defective combustion is detected. A mode in which the fuel component of the fuel is treated can also be taken.

The present invention is not limited to the embodiment described in detail above. For example, the AC oscillator 62 that is an element of the electric field generator 6 is not limited to a triangular wave oscillator that outputs a triangular wave. A sawtooth wave oscillator that outputs an alternating sawtooth wave may be employed as the AC oscillator 62. FIG. 7 shows a circuit configuration example of a sawtooth wave oscillator. The sawtooth oscillator of the illustrated example is a known one that forms a Schmitt circuit and an integration circuit using two operational amplifiers. The frequency of the sawtooth wave output from the sawtooth oscillator is R ₃ / {2C (R ₁ + R ₂ ) R ₄ }. Further, FIG. 8 shows an AC sawtooth waveform (shown by a thin solid line in the figure) before full-wave rectification by the full-wave rectifier 64 and a pulsating waveform after full-wave rectification by the full-wave rectifier 64 (shown by a thick broken line in the figure). ).

  The frequency of the AC voltage output from the AC oscillator 62 or the frequency of the pulsating flow after full-wave rectification applied to the antenna is not limited to the high frequency band and may belong to the microwave band or the like.

  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 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 may be applied to a port injection type internal combustion engine that injects fuel to the 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 6 ... Electric field generator 62 ... AC oscillator (triangular wave oscillator, sawtooth wave oscillator)
64 ... Full wave rectifier 7 ... Mixer

Claims (1)

An internal combustion engine capable of radiating an electric field into a combustion chamber via an antenna facing the combustion chamber of a cylinder,
An AC oscillator that outputs AC triangular wave voltage or sawtooth voltage,
An internal combustion engine comprising: a full-wave rectifier that applies a pulsating voltage obtained by full-wave rectification of an alternating triangular wave voltage or a sawtooth wave voltage provided from the AC oscillator to an antenna.

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