JP6391266B2 - 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 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. When field emission is performed regardless of the current operating range of the internal combustion engine and the actual conditions in the combustion chamber, even with conventional spark ignition or active ignition, the air-fuel mixture is sufficiently ignited and burned with weak electric field emission. In spite of this, unnecessarily large electric power may be input into the combustion chamber.

  An object of the present invention is to suppress waste of electric power during ignition of an air-fuel mixture 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 the lower the pressure in the combustion chamber of the cylinder near the ignition timing, the lower the pressure in the combustion chamber, the electrode of the spark plug for performing active ignition on the mixture at the ignition timing the voltage for spark discharge to be applied to the configuration of the lower Ru internal combustion engine.

  ADVANTAGE OF THE INVENTION According to this invention, the waste of the electric power at the time of ignition to the air-fuel mixture by the active ignition method can be suppressed.

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.

  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 (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 addition, in the present embodiment, when active ignition is performed on the air-fuel mixture filled in the combustion chamber of the cylinder 1, the spark plug becomes lower as the in-cylinder pressure (combustion chamber pressure) at a timing near the ignition timing becomes lower. The voltage for spark discharge to be applied to the 12 electrodes is lowered, the electric field to be radiated into the combustion chamber is weakened, and / or the time for radiating the electric field into the combustion chamber is shortened.

  If a pressure sensor for detecting the in-cylinder pressure is mounted on the cylinder 1, the in-cylinder pressure of the cylinder 1 that reaches the ignition timing 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 actually measured via the temperature sensor. The in-cylinder pressure at a timing near the ignition timing can be estimated based on the in-cylinder temperature.

  Alternatively, even if a pressure sensor that detects the in-cylinder pressure or a temperature sensor that detects the in-cylinder temperature is not mounted on the cylinder 1, it is possible to predict the in-cylinder pressure at a timing near the ignition timing of the cylinder 1. For example, the engine speed, the intake pressure and the intake air temperature in the surge tank 33, the opening / closing timing of the intake valve (when the internal combustion engine is equipped with a VVT (Variable Valve Timing) mechanism), etc. are predicted in advance. Map data or a function expression that defines the relationship with the in-cylinder pressure during the compression stroke is stored. The ECU 0 searches the map using the engine speed in the intake stroke of the cylinder 1, the intake pressure and intake temperature in the surge tank 33, the intake valve timing, etc. as keys, or substitutes these into the function formula to The predicted value of the in-cylinder pressure at the timing near the ignition timing is obtained.

  The lower the in-cylinder pressure at the timing near the ignition timing of the cylinder 1, the lower the induction voltage for spark discharge, the weaker the high-frequency electric field radiated into the combustion chamber, or the time for radiating the high-frequency electric field into the combustion chamber. The active ignition is executed by shortening or implementing a plurality or all of them simultaneously. In other words, the lower the in-cylinder pressure in the vicinity of the ignition timing of the cylinder 1, the smaller the amount of electric power that is input into the combustion chamber of the cylinder 1 during active ignition. In a situation where the in-cylinder pressure is relatively low, that is, the atmosphere density in the combustion chamber is relatively low, plasma generation by spark discharge and electric field radiation is easy, so the amount of power supplied to the cylinder 1 in the active ignition is reduced. Thus, it is allowed to reduce power consumption.

  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 executing active ignition that generates plasma in the combustion chamber and ignites the fuel, and the lower the pressure in the combustion chamber of the cylinder 1 near the ignition timing, An internal combustion engine that performs active ignition after lowering the voltage for spark discharge to be applied, weakening the electric field to be radiated into the combustion chamber, or shortening the time to radiate the electric field into the combustion chamber was configured.

  According to the present embodiment, when the in-cylinder pressure at the ignition timing is low, that is, the electric power (spark discharge voltage and / or high-frequency electric field strength) to be input into the combustion chamber for ignition of the air-fuel mixture by active ignition may be small. In some cases, the amount of power spent on active ignition can be saved. Therefore, energy saving can be realized and the fuel consumption can be reduced.

  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 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 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,
As the combustion chamber pressure cylinder in the timing of the vicinity of the ignition timing is low, lower Ru internal combustion engine a voltage for spark discharge to be applied to the electrodes of the spark plug Upon executing the active ignition of the mixed gas to the ignition timing.

Images