JP6218622B2 - Internal combustion engine - Google Patents

Description

  The present invention relates to a spark ignition type internal combustion engine mounted on a vehicle.

  In an ignition device mounted on a 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 and the ground electrode are A spark discharge is caused between them and ignites.

  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 initiates flame propagation combustion. Can be generated.

JP 2011-64162 A

  The electrode of the spark plug of the internal combustion engine is gradually worn out as the period of use becomes longer. In particular, when the above active ignition method is used, the wear becomes significant. When a high-frequency electric field or microwave electric field is formed in the space between the center electrode and the ground electrode, not only the center electrode or the ground electrode but also the metal near the spark plug in the combustion chamber is severely scraped, and the scraped metal Becomes ionized and drifts in the combustion chamber. As a result, dielectric breakdown occurs due to the above metal ions adhering to the insulator, which is an insulator provided to insulate the center electrode and the ground electrode, not the required discharge for ignition, This may cause an unexpected discharge.

  The present invention has been made by paying attention to the above-mentioned problem for the first time, and an object thereof is to provide an internal combustion engine capable of continuously and stably performing a required discharge for spark ignition.

  In order to achieve such an object, the present invention takes the following measures.

  That is, the internal combustion engine according to the present invention interacts with the electric field generated in the combustion chamber via the antenna facing the combustion chamber of the cylinder and the spark discharge generated between the center electrode and the ground electrode of the spark plug. A spark ignition type internal combustion engine that generates plasma in a combustion chamber and ignites an air-fuel mixture, and a voltage that makes the potential of the center electrode positive or negative compared to the potential of the ground electrode is generated from the ignition coil for spark discharge. An application device for switching is provided, and this application device applies a positive voltage to the center electrode when the intensity of the electric field supplied to the combustion chamber is a predetermined value or more, and a negative voltage to the center electrode when the intensity is less than the predetermined value. A spark discharge is generated by applying a voltage.

  Here, the electric field strength “below a predetermined value” includes not only the case where the electric field strength is weak but also a state where no electric field is generated.

  If this is the case, when metal ions are generated in the combustion chamber, a positive voltage that prevents metal ions from attaching to the center electrode is applied and spark ignition is performed so that metal is unnecessarily attached to the center electrode. Therefore, it is possible to effectively avoid the problem that dielectric breakdown occurs between the center electrode and the ground electrode. Of course, not only spark ignition by applying a negative voltage but also spark ignition by applying a positive voltage is performed, so that the central electrode can be prevented from being concentrated and worn. As a result, since stable spark ignition is maintained even if the spark plug is continuously used, it is possible to effectively prevent the life of the spark plug from being shortened.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that the lifetime of a spark plug becomes short by the performance deterioration of the electrode for ignition exposed in the combustion chamber of the cylinder of an internal combustion engine.

The figure which shows schematic structure of the internal combustion engine in one Embodiment of this invention. The circuit diagram of the ignition device in the embodiment. The figure explaining the structure of the electric field generator in the embodiment. The circuit diagram of the H bridge which is an element of the electric field generator in the embodiment. The flowchart in the same embodiment. The circuit diagram of the ignition device in the modification 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 spark ignition type 4-stroke gasoline engine, and includes a plurality of cylinders 1 (one of which is shown in FIG. 1). In the vicinity of the intake port of each cylinder 1, an injector 11 for injecting fuel is provided. A spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1.

  FIG. 2 shows an electric circuit for spark ignition. 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.

  In this embodiment, as shown in FIG. 2, the ignition coil 14 includes a negative primary coil 14a for applying a negative voltage to the center electrode, and a positive primary for applying a positive voltage to the center electrode. And a coil 14b. The igniter 13 includes a negative igniter 13a for controlling energization to the negative primary coil 14a and a positive igniter 13b for controlling energization to the positive primary coil 14b. That is, in this embodiment, magnetic fluxes in opposite directions are generated by energizing the negative primary coil 14a and the positive primary coil 14b. As a result, the polarity of the voltage generated in the secondary coil 14c is switched.

  The internal combustion engine of the present embodiment is accompanied by electric field generators 6A and 6B that generate an electric field in the combustion chamber of the cylinder 1. The electric field generators 6A and 6B are intended to radiate a high-frequency electric field into the combustion chamber of the cylinder 1 and generate plasma in the combustion chamber.

  3 and 4 show an example of the electric field generators 6A and 6B. Electric field generators 6A and 6B include a circuit that uses a vehicle-mounted battery as a power source and converts low-voltage direct current to 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, an H-bridge circuit 62 that converts the DC output from the DC-DC converter 61 into high-frequency AC, A boosting transformer 63 that boosts the alternating current output from the H-bridge circuit 62 to a higher voltage is used as a constituent element.

  In the present embodiment, the first electric field generator 6A, which is a negative voltage generator that applies a negative high-frequency electric field to the center electrode of the ignition plug 12 of the cylinder 1, and the positive high-frequency electric field is applied to the center electrode of the ignition plug 12. The second electric field generator 6B, which is a positive voltage generator, coexists, and the negative electric field generated by the first electric field generator 6A or the positive electric field generated by the second electric field generator 6B is generated at the center electrode of the spark plug 12. Any one of the electric fields can be selectively applied.

  First diodes 64A and 64B and second diodes 65A and 65B are provided at the output ends of the electric field generators 6A and 6B. The first diodes 64 </ b> A and 64 </ b> B have cathodes connected to the signal line of the secondary winding of the step-up transformer 63 and anodes connected to the mixer 66 that is a node with the ignition coil 14. The anodes of the second diodes 65A and 65B are connected to the ground line of the secondary winding of the step-up transformer 63, and the cathodes are grounded.

  The polarities (directions) of the first diodes 64A and 64B and the second diodes 65A and 65B are different between the first electric field generator 6A and the second electric field generator 6B. The first diode 64A and the second diode 65A in the first electric field generator 6A play a role of half-wave rectifying the AC voltage generated by the H bridge circuit 62 into a negative voltage. Similarly, the first diode 64B and the second diode 65B in the second electric field generator 6B play a role of half-wave rectifying the AC voltage generated by the H bridge circuit 62 into a positive voltage.

  A switching unit 7 is interposed between the electric field generators 6A and 6B and the mixer 66 connected to the center electrode of the spark plug 12. Switching unit 7 includes switch 7A for switching connection / disconnection between first electric field generation device 6A and mixer 66 and switch 7B for switching connection / disconnection between second electric field generation device 6B and mixer 66. . For each of the switches 7A and 7B, a semiconductor switching element such as a transistor or a MOSFET may be used, or a mechanical switch such as a relay may be used.

  It is preferable that the mixer 66 has a function of blocking a high-voltage pulse current for spark discharge induced on the secondary side of the ignition coil 14 from flowing toward the electric field generators 6A and 6B. However, this function is not necessary if the high-pressure pulse for spark discharge can be blocked from flowing into the electric field generators 6A and 6B by switching the switches 7A and 7B.

  The high-frequency voltage output by the electric field generators 6A and 6B is normally applied to the center electrode of the spark plug 12 almost simultaneously with the start of the spark discharge, immediately before the start of the spark discharge or immediately after the start of the spark discharge. 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, plasma is generated by the occurrence of 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.

  Incidentally, a pulsating voltage generation circuit can be adopted instead of the H bridge circuit 62 which is an AC voltage generation circuit. In this case, the pulsating voltage generation circuit only needs to generate a DC voltage whose voltage changes periodically, and the waveform thereof may be arbitrary. The pulsating voltage includes a pulse voltage that varies from a reference voltage (which may be 0V) to a constant voltage in a constant cycle, a voltage obtained by half-wave rectifying an AC voltage, a voltage obtained by adding a DC bias to the AC voltage, and the like. The high frequency voltage oscillated by the electric field generators 6A and 6B preferably has a frequency of about 200 kHz to 3000 kHz and an amplitude of about 3 kVp-p to 10 kVp-p.

  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.

  An ECU (Electronic Control Unit) 0 that controls the operation of the internal combustion engine of this embodiment 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. Is the sensor (or shift position switch) to know the coolant temperature signal f and the shift lever range? Shift range signal g outputted, a cam angle signal h or the like to be output from the cam angle sensor is input in a plurality of cam angle of the intake camshaft or an exhaust camshaft.

  From the output interface, an ignition signal i for the igniter 13 of the spark plug 12, a fuel injection signal j for the injector 11, an opening operation signal k for the throttle valve 32, and an electric field for the first electric field generator 6A. (I.e., high frequency) application command signal l, electric field application command signal m, etc. are output to second electric field generator 6B.

  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 and intake air amount, etc., the required fuel injection amount, fuel injection timing (including the number of times of fuel injection for one combustion), fuel injection pressure, ignition timing, and an electric field are generated in the combustion chamber. Various operating parameters such as whether or not and the timing of the electric field generation are determined. The ECU 0 applies various control signals i, j, k, l and m corresponding to the operation parameters via the output interface.

  A high frequency electric field radiated into the combustion chamber using the center electrode of the spark plug 12 as an antenna interacts with a spark discharge generated between the center electrode and the ground electrode of the spark plug 12 to generate plasma and ignite the mixture. When active ignition is performed, either the first electric field generator 6A or the second electric field generator 6B is selected and connected to the mixer 66, and the negative electric field output from the connected electric field generators 6A and 6B is output. Alternatively, a positive high-frequency electric field is applied to the center electrode and radiated from the center electrode into the combustion chamber.

  That is, in one combustion of the air-fuel mixture in the cylinder 1 (in other words, in one cycle (a series of intake stroke-compression stroke-expansion stroke-exhaust stroke)), from the center electrode of the spark plug 12, Radiate either a negative high-frequency electric field or a positive high-frequency electric field. In the combustion of the air-fuel mixture once in the cylinder 1, the ECU 0 switches the switch 7A in accordance with the timing of radiating a high-frequency electric field into the combustion chamber (at substantially the same time as the start of the spark discharge, immediately before the start of the spark discharge or immediately after the start of the spark discharge). Disconnect the switch 7B while connecting and connect only the first electric field generator 6A to the mixer 66, or disconnect the switch 7A while connecting the switch 7B and connect only the second electric field generator 6B to the mixer 66 To do. Then, a high frequency is output from the electric field generators 6A and 6B on the side connected to the mixer 66.

  In addition, in the present embodiment, the electric field generators 6A, 6B connected to the mixer 66 in active ignition to suppress the unilateral wear of the center electrode or the ground electrode of the spark plug 12 and prolong the life of the spark plug 12. That is, the high-frequency electric field to be applied to the center electrode is switched as appropriate.

  When active ignition in which a negative high-frequency electric field is applied to the center electrode of the spark plug 12 is executed, electrons are emitted from the center electrode toward the ground electrode. At this time, it is presumed that the constituent material (metal) of the center electrode is scattered together with the electrons, and the center electrode is severely shaved. However, the ground electrode is less worn than the center electrode.

  In turn, when a positive high-frequency electric field is applied to the center electrode of the spark plug 12 to execute active ignition, electrons are emitted from the ground electrode having a relatively low potential toward the center electrode. Also at this time, it is presumed that the constituent material of the ground electrode is scattered together with the electrons, and the ground electrode is severely shaved. However, the center electrode is less worn than the ground electrode.

  On the other hand, when a negative voltage is applied via the negative primary coil 14a in the ignition coil 14 to execute spark ignition, electrons are emitted from the center electrode toward the ground electrode. At this time, it is presumed that the constituent material (metal) of the center electrode is scattered together with the electrons, and the center electrode is severely shaved. However, the ground electrode is less worn than the center electrode.

  Then, electrons are emitted from the ground electrode having a relatively low potential toward the center electrode. Also at this time, it is presumed that the constituent material of the ground electrode is scattered together with the electrons, and the ground electrode is severely shaved. However, the center electrode is less worn than the ground electrode.

  The operation of the igniter 13, that is, the negative igniter 13a and the positive igniter 13b is controlled by the ignition signal i.

  Thus, an application device is provided for applying a voltage that makes the potential of the center electrode positive or negative compared to the potential of the ground electrode according to the present embodiment so as to be switchable from the ignition coil 14 for spark discharge. However, a spark discharge is generated by applying a positive voltage to the center electrode when the intensity of the electric field supplied to the combustion chamber is a predetermined value or more, and applying a negative voltage to the center electrode when the intensity is less than a predetermined value. To do. Here, the application device in this embodiment is the ignition coil 14 and the igniter 13. Here, it is needless to say that the electric field strength “below a predetermined value” includes not only the case where the electric field strength is weak, but also a state where no electric field is generated.

  Hereinafter, control of the combustion chamber according to the present embodiment will be described based on the flowchart of FIG.

  First, in the present embodiment, active ignition using the electric field generators 6A and 6B is appropriately performed according to the operating state. At this time, it is in an operating state in which misfire is likely to occur, such as during so-called large-scale EGR operation in which exhaust gas is recirculated and mixed into intake air at a high rate using an EGR circuit (not shown), or during lean operation in which the air-fuel ratio is made lean. Sometimes, the electric field strength is set to a predetermined value or more. In this embodiment, it is monitored whether or not the electric field strength is a predetermined value or higher (step S1). When the electric field strength is lower than the predetermined value, that is, when the active ignition itself is not performed or the generated electric field strength is weak, A negative voltage is applied to the center electrode by performing spark ignition using the negative primary coil 14a (step S2).

  When the electric field strength as described above is equal to or higher than a predetermined value, the ECU 0 starts from the spark ignition in which a negative voltage is applied to the center electrode using the negative igniter 13a and the negative primary coil 14a, and then the positive igniter 13b. And it switches to the spark ignition which applies a positive voltage to the center electrode using the positive side primary coil 14b (step S3).

  At this time, the timing for generating the electric field is set to a certain period before and after avoiding the timing for performing spark ignition. As a result, normal spark ignition can be performed regardless of the electric field generated by any of the electric field generators 6A and 6B. In the present embodiment, spark ignition using the ignition coil 14 is performed in the same manner regardless of the electric field generated from the electric field generators 6A and 6B. Here, if the electric field is generated by the positive pulsating flow generated by the electric field generator 6B, a large amount of metal ions are generated in the combustion chamber as the electric field is generated, but the metal ions in the combustion chamber are negative pulses. This is because it is generated in the same manner as an electric field caused by a flow.

  As described above, in the present embodiment, when it is considered that a large amount of metal ions are generated in the combustion chamber, spark ignition is performed using the primary primary coil 14b in which metal ions do not easily adhere to the center electrode. I have to. This effectively avoids the problem that the metal is unnecessarily adhered to the center electrode and dielectric breakdown occurs between the center electrode and the ground electrode. Of course, the spark ignition using the positive primary coil 14b effectively suppresses the central electrode from being concentrated and worn. As a result, since stable spark ignition is maintained even if the spark plug 12 is continuously used, the life of the spark plug 12 can be suppressed from being shortened.

  Although the embodiment of the present invention has been described above, the specific configuration of each unit is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

<Modification>
For example, in the above-described embodiment, the center electrode of the ignition plug 12 facing the combustion chamber of the cylinder 1 is disclosed as an antenna that radiates an electric field. Of course, the ignition plug 12 is not used as an antenna as shown in FIG. The antenna 17 may be provided separately from the spark plug 12. Hereinafter, with respect to the modification of the present embodiment illustrated in FIG. 6, the same reference numerals are given to those corresponding to the components of the above-described embodiment, and detailed description thereof is omitted.

  As shown in the figure, in this modification, the secondary coil 14c is directly connected to the spark plug 12 without a mixer. The electric field generators 6A and 6B are connected to an antenna 17 which is configured separately from the spark plug 12 and exposed at a required position in the combustion chamber via the switch 7A and the switch 7B. . If it is such, the production | generation of an electric field and a spark ignition can be performed at a required timing irrespective of the plus / minus of the discharge for electric field generation, and the positive / negative of the voltage application for a spark ignition.

  Further, in the above embodiment and the modification, the electric field generator has disclosed a mode using a positive pulsating flow or a negative pulsating flow in the above embodiment, but of course, a mode of generating an electric field using alternating current may be applied. . Further, in addition to the above-described embodiments and modifications, specific aspects of the electrodes and antennas are not limited to those of the above-described embodiments, and various aspects including the existing ones can be applied. .

  In addition, the specific configuration of each part is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

  The present invention can be used as a spark ignition type internal combustion engine mounted on a vehicle.

6A, 6B ... Electric field generator 12 ... Spark plug 13 ... Application device (igniter)
14 ... Application device (ignition coil)
14a ... Negative primary coil 14b ... Positive primary coil

Claims (1)

Plasma is generated in the combustion chamber by mixing the electric field generated in the combustion chamber via the antenna facing the combustion chamber of the cylinder and the spark discharge generated between the center electrode and the ground electrode of the spark plug, and mixing A spark ignition internal combustion engine that ignites.
An application device is provided for applying a voltage that makes the potential of the center electrode positive or negative compared to the potential of the ground electrode so as to be switchable from the ignition coil for spark discharge,
This application device generates a spark discharge by applying a positive voltage to the center electrode when the intensity of the electric field supplied to the combustion chamber is a predetermined value or more, and applying a negative voltage to the center electrode when the intensity is less than a predetermined value. An internal combustion engine characterized by the above.

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