JP2012112348A - Spark ignition method for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve ignitability and combustion efficiency when performing ignition by using plasma in an internal combustion engine of a spark ignition type.SOLUTION: The spark ignition method for an internal combustion engine ignites an air-fuel mixture by generating plasma through reaction between an electric field generated in a combustion chamber and spark discharge generated by a high voltage applied between a central electrode and a ground electrode of a spark plug via an ignition coil. The electric field subjected to the reaction with the spark discharge is interrupted on and after a compression upper dead center in one cycle.

Description

  The present invention relates to a spark ignition method for an internal combustion engine in which an electric field generated in a combustion chamber reacts with spark ignition by a spark plug to generate plasma to ignite an air-fuel mixture.

  Conventionally, for example, in an internal combustion engine for an automobile, a high voltage is applied between a center electrode and a ground electrode of an ignition plug, and a spark discharge generated in a gap between both electrodes causes an air-fuel mixture in a combustion chamber at each ignition timing. It is igniting. In such ignition by the spark plug, for example, there may be a case where the spark energy is insufficient and it is difficult to form a flame kernel.

  In order to solve such a problem at the time of spark ignition, for example, like the one described in Patent Document 1, plasma is generated in the combustion chamber, and the plasma and the spark discharge are caused to react, so that the flame kernel is surely obtained. What is generated is known. In this patent document 1, a microwave supplied through an ignition plug generates a high-frequency electric field immediately before or at the same time as the spark discharge, and reacts the spark discharge with the plasma to produce a more powerful flame kernel. Is generated.

  In Patent Document 1, a microwave is used to generate a high-frequency electric field, but the configuration of an apparatus that outputs a microwave is relatively complicated. Further, when the microwave leaks from the internal combustion engine, the influence on the human body is not small. Considering these points, the device configuration is not complicated compared to the microwave oscillation device, and it is considered to use a high frequency, which is easier to handle than the microwave and lower in frequency than the microwave, instead of the microwave. It has been.

  By the way, spark discharge is generally performed by applying a negative high voltage to the center electrode. Corresponding to this negative high voltage spark discharge, the electric field for generating plasma is also made negative. As a result, the vicinity of the electrode of the spark plug, and therefore the periphery thereof, is negatively charged. On the other hand, the flame kernel, combustion gas, or combustion atmosphere is positively charged.

  With such a charged state, a phenomenon in which the flame kernel and the combustion atmosphere try to stay near the electrode of the spark plug is observed. This hinders the expansion of the flame kernel, that is, the increase in the volume of the flame kernel. For this reason, it may be difficult to improve the combustion efficiency by improving the ignitability.

JP 2010-101182 A

  Accordingly, the present invention focuses on the above points and aims to improve ignitability and combustion efficiency when spark-ignited internal combustion engine is ignited using plasma.

  That is, the spark ignition method for an internal combustion engine according to the present invention includes a spark discharge generated by a high voltage applied via an ignition coil between a center electrode and a ground electrode of a spark plug, and an electric field generated in the combustion chamber. A spark ignition method for a spark ignition internal combustion engine that reacts to generate plasma to ignite an air-fuel mixture, characterized in that the electric field reacted with the spark discharge after the compression top dead center in one cycle is cut off. To do.

  According to such a configuration, the flame kernel generated using the plasma generated by the reaction between the spark discharge and the electric field is cut off around the spark plug by the electric field being cut off in the stroke after the compression top dead center, that is, the expansion stroke. The possibility of staying in is reduced. As a result, the expansion of the flame kernel can be promoted, and the combustion efficiency can be improved.

  The present invention has a configuration as described above, generates a plasma by reacting a spark discharge and an electric field, ignites an air-fuel mixture in the presence of the plasma, and after generating a flame nucleus, a compression top dead center. By interrupting the electric field thereafter, the expansion of the flame kernel can be promoted, and the combustion efficiency can be improved.

A sectional view showing an important section of an engine to which one embodiment of the present invention is applied. The electric circuit diagram of the ignition device in the embodiment. The flowchart which shows the control procedure of the embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows a configuration of one cylinder of a two-cylinder engine 100 that is a spark ignition type internal combustion engine including a spark plug 1. In this engine 100, the opening 3 of the intake port 2 and the opening 5 of the exhaust port 4 are arranged opposite to each other centering on a spark plug 1 that is attached to substantially the center of the ceiling portion of the combustion chamber 6. Open. That is, the engine 100 is attached to the cylinder block 7, and the camshafts 9 and 10 are attached to the intake side and the exhaust side of the cylinder head 8 forming the ceiling portion of the combustion chamber 6, respectively. The intake port 2 of the cylinder head 8 is opened and closed by an intake valve 11 that reciprocates when the camshaft 9 rotates, and the exhaust port 4 is opened and closed by an exhaust valve 12 that reciprocates when the camshaft 10 rotates. Is. An ignition plug 1 is attached to the ceiling portion of the combustion chamber 6, and a fuel injection valve for generating an air-fuel mixture supplied to the combustion chamber 6 is provided in the intake port 2. The engine 100 itself may be a spark ignition type that is known in this field.

  The spark plug 1 of this embodiment includes a housing 13 made of a conductive material, a center electrode 14 that is insulated and attached in the housing 13, and a gap 14 that generates a spark discharge from the center electrode 14 at the lower end of the housing 13. Basically, a ground electrode 16 provided, and an igniter-equipped ignition coil (hereinafter, referred to as an ignition coil) 21 and 22 in which an igniter and an ignition coil are structurally integrated are connected to each other. Prepare. The spark plug 1 may be one that is well known in this field.

  As shown in FIG. 2, the ignition device 20 connected to the ignition plug 1 is connected to a first ignition coil 21 connected to the ignition plug 1 of the first cylinder and an ignition plug 1 of the second cylinder. The second ignition coil 22, the first diode 23 whose anode is connected to the secondary winding 21 a of the first ignition coil 21, and the anode is connected to the secondary winding 22 a of the second ignition coil 22 A second diode 24 and a transformer 25 with a tap, which is a step-up transformer, are provided at the output stage thereof, at a predetermined time during spark ignition, in the combustion chamber 6, particularly in a region centering on the center electrode 14 of the spark plug 1. And a high frequency voltage generator 26 for generating an electric field. The high-frequency voltage generator 26 that is an electric field generating means includes a transformer 25 with a tap, a generator body 27 connected to the transformer 25 with a tap, a timing (timing) at which a voltage based on a high frequency is applied to the spark plug 1, and Switching means 28 for controlling the timing of stopping the application. The switching means 28 is controlled by an electronic control unit 29 that detects the generation position or generation time (hereinafter referred to as peak time) of the highest discharge voltage in the spark plug 1 and the compression top dead center of one cycle in each cylinder. .

  The generator main body 27 of the high-frequency voltage generator 26, for example, boosts the voltage of a vehicle battery, for example, about 12 V (volts) to 300 to 500 V by a DC-DC converter that is a booster circuit, and the boosted direct current is H-bridged. The circuit is configured to change the frequency to an alternating current of about 200 kHz to 600 kHz, and the high frequency voltage generator 26 is configured to output a high frequency boosted to about 4 kVp-p to 8 kVp-p by the tapped transformer 25. The output high-frequency voltage is set to a voltage that is sufficient to sustain the induction discharge in the spark discharge described later, in other words, a voltage that does not attenuate the induction discharge (hereinafter referred to as a sustain voltage). That is, if the high-frequency voltage is smaller than the sustain voltage, the intensity of the generated electric field becomes low, and there is a possibility that the flow of electrons due to the spark discharge and the ions and radicals generated by the spark discharge may not meander, which will be described later. Acceleration of combustion may decrease.

  The tap transformer 25 has a tap formed at a position where the number of turns is divided into two. Therefore, the secondary winding 25a outputs two alternating currents having the same voltage and different phases by 180 degrees. The secondary winding 25a of the tapped transformer 25 constitutes output means. The tap 25b of the secondary winding 25a of the transformer 25 with tap is connected to the ground (ground line) 27, and one end 25c of the secondary winding 25a is connected to the cathode of the first diode 23. The other end 25 d is connected to the cathode of the second diode 24. The configuration of the high-frequency voltage generator 26 other than the tapped transformer 25 is not particularly limited to this embodiment as long as the high-frequency voltage generator 26 outputs alternating current with the above-described frequency.

  The first and second diodes 23 and 24 function as rectifiers for the alternating current generated by the high-frequency voltage generator 26 and are high for spark discharge generated by the first and second ignition coils 21 and 22. For voltage, it functions as a backflow prevention diode. That is, in this embodiment, when ignition is performed in the combustion stroke, a negative high voltage is applied from the secondary winding 21a (22a) of the ignition coil 21 (22) to the center electrode 14 of the spark plug 1A. A voltage is applied. Accordingly, the first and second diodes 23 and 24 are connected to the corresponding secondary windings 21a and 22a, respectively, so that the negative high voltage flows back to the high-frequency voltage generator 26. To prevent.

  The electronic control device 29 incorporates an operation control program for controlling the operation state of the engine 100 based on signals output from various sensors attached to the engine 100, and for spark ignition, the spark plug 1A (1B). A plasma is generated by reacting a spark discharge generated by a high voltage applied via the ignition coil 21 (22) between the center electrode 14 and the ground electrode 15 with an electric field generated in the combustion chamber 6. When the air-fuel mixture is ignited, a spark ignition control program for controlling the high-frequency voltage generator 26 is incorporated so as to cut off the electric field that has reacted with the spark discharge after the compression top dead center in one cycle. This spark ignition control program is executed every ignition timing. FIG. 3 shows the control procedure.

  First, upon spark ignition, when an ignition signal output from the electronic control device 29 is input to the igniter of the ignition coil 21 (22), the secondary side winding 21a (22a) of the ignition coil 21 (22) A negative high voltage is applied to the center electrode 14 of 1A (1B), and spark discharge starts. When the spark discharge starts, a capacitive spark is first generated by the capacitive discharge, and then an induced spark is generated by the induction discharge. Then, the switching means 28 is closed and the high frequency voltage is applied to the spark plug 1A (1B) at the time when the induction discharge starts. The applied high frequency voltage is set to be higher than the voltage required to maintain the induction discharge.

  In this case, a secondary voltage that is an output voltage of the ignition coil 21 (22) is measured, and when the secondary voltage obtained by the measurement is equal to or lower than a predetermined voltage, a high-frequency voltage is applied, in other words, an electric field. Prohibit generation. That is, after the secondary voltage obtained by measurement exceeds a predetermined voltage set to about 60% to 70% of the maximum value of the discharge voltage (hereinafter referred to as peak voltage) in average capacity discharge. The formation of the electric field is started only when the voltage is lower than the determination voltage for determining the timing for generating the electric field.

  The determination voltage is used to determine that the secondary voltage has dropped after the secondary voltage has exceeded the predetermined voltage and developed the peak voltage, and is set to a value lower than the predetermined voltage. Therefore, this timing may be during capacitive discharge that does not lead to induction discharge, but since the secondary voltage is equal to or lower than the determination voltage, even if a high-frequency voltage is superimposed on the voltage of capacitive discharge, the voltage does not become excessive. Therefore, it is not necessary to delay the timing for turning on the switching means 28 until the spark discharge becomes an induction discharge.

  Thus, after applying the high frequency voltage to the spark plug 1A (1B), the applied high frequency voltage is stopped, that is, the control for blocking the generation of the electric field is performed according to the flowchart shown in FIG.

  First, in step S1, it is determined whether or not it is a compression top dead center in one cycle composed of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. This determination is to determine the compression top dead center based on a crank angle signal output from a crank angle sensor attached to control the operation of the engine 100. When it is determined that the compression top dead center has not been reached after the ignition timing, the compression top dead center is determined again based on the crank angle signal.

  In step S2, since the progress of the operation of the engine 100 is one cycle of compression top dead center, the control for opening the switching means 28 is executed to stop the application of the high frequency voltage. Thereby, the generation of the electric field is cut off.

  In the above configuration, in this embodiment, the high frequency from the high frequency voltage generator 26 is half-wave rectified by the first and second diodes 23 and 24 to become a negative pulsating current (voltage) on the central electrode 14. The applied pulsating current (current) flows between the center electrode 14 and the ground electrode 15 between the center electrode 14 and the ground electrode 15 from the latter half of the capacitive discharge at the time of spark discharge to immediately before the induction discharge or to the start of the induction discharge. An electric field is generated. The generated electric field reacts with the spark discharge generated between the center electrode 14 and the ground electrode 15 to generate plasma and ignite the air-fuel mixture.

  In other words, upon ignition, if spark discharge is generated in the spark plug 1A (1B) by the ignition coil 21 (22) at the timing before the compression top dead center, that is, at the advanced ignition timing, the spark discharge is accompanied. Thus, an electric field is generated by applying a high-frequency voltage between the spark plugs 1A (1B) at the above-described timing to cause a pulsating current (current) to flow. Thus, the air-fuel mixture in the combustion chamber 6 is rapidly burned by reacting spark discharge (mainly induced discharge) with an electric field to generate plasma.

  Specifically, spark discharge by the spark plug 1A (1B) becomes plasma in an electric field. As a result, by igniting the air-fuel mixture with the generated plasma, the flame nuclei at the beginning of flame propagation combustion become larger than ignition with only spark discharge, and a large amount of radicals are generated in the predetermined space. Combustion is promoted.

  This is because 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 longer 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 ionized, in other words, a plasma state. The ignition region for the air-fuel mixture dramatically increases, and the flame kernel that starts the flame propagation combustion also increases.

  In this case, when the compression top dead center of one cycle is determined, the application of the high frequency voltage thereafter is stopped, so that the above-described flame kernel is not kept near the center electrode 14 of the spark plug 1A (1B). . Accordingly, the flame kernel is not attracted toward the center electrode 14, and its volume is expanded, and combustion is expanded throughout the cylinder. Thereby, since a combustion state is accelerated | stimulated, combustion efficiency becomes high and a fuel consumption can be improved.

  Prior to this, if the capacitive discharge in the spark discharge is not successful and misfire occurs, the output of the high-frequency voltage to form the electric field is prohibited, and the electric field is generated only when the capacitive discharge is successful. Therefore, ignition can be surely performed. In addition, since the generation of an electric field is prohibited when ignition cannot be performed, the high frequency voltage generator 26 can be prevented from being damaged by the high frequency flowing in the rotating circuit generated in the ignition device 20.

  In addition, in this embodiment, the pulsating voltage for generating the electric field is not superimposed on the voltage at the time of the capacitive discharge by generating the electric field after the generation of the peak voltage in the capacitive discharge. Therefore, it is possible to prevent the capacitive discharge from becoming unstable. In addition, since it is possible to suppress an excessively high voltage from being applied to the spark plug 1 due to the superposition of both voltages, the durability of the spark plug 1 can be maintained. In addition, since an electric field is generated during induction discharge, the growth of flame nuclei by plasma can be promoted to increase the combustion efficiency. In addition, since the high-frequency voltage for generating the electric field is set to be equal to or higher than the sustaining voltage for induction discharge, the reliability of electric field generation can be increased and plasma can be stabilized.

  Furthermore, in this embodiment, by using the transformer 25 with a tap in the output stage of the high-frequency voltage generator 26, an alternating current with substantially the same voltage can be output to each cylinder. For this reason, by setting a high-frequency voltage to be output in advance by the transformer 25 with a tap, a voltage drop in the first and second diodes 23 and 24 can be compensated for, and plasma having an appropriate density is obtained. Can be generated.

  One high-frequency voltage generator 26 is connected to the spark plugs 1A and 1B of each cylinder via diodes 23 and 24, but the pulsating current (current) is caused by the center electrode 14 and the ground electrode of the spark plugs 1A and 1B. Only when the gap resistance value decreases due to spark discharge, it flows into the gap 18 between them. Therefore, when a cylinder that is not in the combustion stroke, for example, ignition is performed in the first cylinder and the second cylinder is in a compression stroke without spark discharge, no pulsating current (current) flows in the second cylinder, and therefore no alternating current is consumed. . For this reason, the power consumption of the high frequency voltage generator 26 is not increased, and an increase in power consumption in the high frequency voltage generator 26 can be suppressed.

  In the above description, the high voltage applied to the center electrode 14 of the spark plugs 1A and 1B during the spark discharge is a negative voltage, but it may be a positive voltage. In this case, in order to adjust the polarity of the pulsating current (voltage) to this positive voltage, the first diode 23 and the second diode 24 have their cathodes connected to the center electrode 14 of the spark plugs 1A and 1B.

  Further, the number of cylinders of the engine is not limited to the above-described embodiment.

  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.

  As an application example of the present invention, there is one that is applied to a spark ignition type internal combustion engine that uses gasoline or liquefied natural gas as fuel and that requires spark discharge by an ignition plug for ignition.

DESCRIPTION OF SYMBOLS 1 ... Spark plug 21 ... Ignition coil 100 ... Engine 29 ... Electronic control unit 26 ... High frequency voltage generator 20 ... Ignition device

Claims (1)

A spark discharge generated by a high voltage applied via the ignition coil between the center electrode and the ground electrode of the spark plug reacts with an electric field generated in the combustion chamber to generate plasma to ignite the mixture. A spark ignition method for an internal combustion engine,
A spark ignition method for an internal combustion engine that cuts off an electric field that has been reacted with spark discharge after compression top dead center in one cycle.

Images