JP5800508B2 - Spark ignition control method for spark ignition internal combustion engine - Google Patents

Description

  The present invention relates to a spark ignition control method for a spark ignition type internal combustion engine that promotes combustion by generating plasma by reacting an electric field generated in a combustion chamber with a product generated by spark discharge by an ignition plug. is there.

  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.

  By the way, in the cited document 1, plasma is generated by generating a high-frequency electric field regardless of ignition or misfire. The plasma contains radicals such as OH radicals, ozone and ions. When flame nuclei are formed by ignition, that is, when normal combustion starts, radicals and ozone contribute to the expansion of the flame nuclei and promote combustion. On the other hand, when a misfire occurs without generating flame nuclei, surplus radicals and ozone come into contact with the combustion chamber wall and cylinder bore wall because there are no flame nuclei for reaction of radicals and ozone. As a result, the metal constituting the cylinder bore wall and the combustion chamber wall is oxidized, and the durability of the engine is lowered.

JP 2010-101182 A

  Accordingly, the present invention focuses on the above points and aims to promote combustion using an electric field without impairing the durability of the internal combustion engine.

That is, the spark ignition control method for a spark ignition internal combustion engine according to the present invention includes a spark plug and a product and an electric field generated at the time of spark discharge generated by a high voltage applied via an ignition coil connected to the spark plug. A spark ignition control method for a spark ignition type internal combustion engine in which plasma is generated by reacting an electric field generated in a combustion chamber through a spark plug by a generating means to ignite an air-fuel mixture . The ion current generated during combustion before the start of generation is detected, the combustion state is determined based on the detected ion current, and when the combustion state is determined to be normal, the generation of the electric field is started, while the combustion state is When it is determined that the electric field is not normal, the generation of the electric field is not started .

  According to such a configuration, the electric field is not generated except when it is determined that the combustion is normal by the ion current, that is, when the combustion is abnormal. Therefore, at the time of misfire where the combustion is abnormal, it is possible to suppress unnecessary electric load and damage the electric field generating means, and to suppress oxidation of the combustion chamber wall and the like.

  The present invention is configured as described above, and generates an electric field when it is determined that the combustion state is normal. Therefore, damage to the electric field generating means and oxidation in the combustion chamber can be suppressed, and the durability of the internal combustion engine can be suppressed. Can be improved. Further, since an electric field is generated during normal combustion, the product that can be obtained as a result of spark discharge reacts with the electric field to promote combustion and improve fuel efficiency.

Sectional drawing which shows the principal part of the engine to which embodiment of this invention is applied. The electric circuit diagram of the ignition device in the embodiment. The flowchart of the same 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 has an anode connected to an ignition coil 21 connected to the ignition plug 1 of the first cylinder and a secondary winding 21 a of the ignition coil 21. A high frequency for generating an electric field in the combustion chamber 6, particularly in a region centering on the center electrode 14 of the spark plug 1, at a predetermined timing during spark ignition, with a diode 23 and a step-up transformer 25 at the output stage. And a voltage generator 26. The high-frequency voltage generator 26 serving as an electric field generating unit controls the step-up transformer 25, the generator body 27 connected to the step-up transformer 25, and the timing (timing) at which a voltage based on the high frequency is applied to the spark plug 1. Switching means 28. The switching means 28 controls the electronic control device 29 so that the high-frequency voltage is applied to the spark plug 1 when it is determined that the combustion is normal, that is, no misfire has occurred based on the ion current flowing in the combustion chamber 6. Controlled by

  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 high frequency voltage generator 26 is configured to output a high frequency boosted to about 4 kVp-p to 8 kVp-p by the step-up transformer 25. The output high-frequency voltage is set to a voltage that is sufficient to maintain the induced discharge in the spark discharge, in other words, a voltage that does not attenuate the induced discharge (hereinafter referred to as a sustain voltage). That is, if the high-frequency voltage is smaller than the sustain voltage, the strength of the generated electric field will be low, and the flow of electrons due to spark discharge and the possibility of ions and radicals generated by spark discharge will not meander, causing plasma combustion. Promotion may be reduced.

  The diode 23 functions as a rectifier for the alternating current generated by the high-frequency voltage generator 26, and functions as a backflow prevention diode for the high voltage for spark discharge generated by the ignition coil 21. That is, in this embodiment, when ignition is performed in the combustion stroke, a positive high voltage is applied from the secondary winding 21a of the ignition coil 21 to the center electrode 14 of the spark plug 1. Is. Therefore, the diode 23 has its cathode connected to the corresponding secondary winding 21 a, thereby preventing the positive high voltage from flowing back to the high frequency voltage generator 26.

  Further, the spark plug 1 is connected to an ion current measuring device 24 including a bias power source for measuring the ion current and a current measuring circuit for measuring the ion current. The bias power source applies a measurement voltage (bias voltage) for current measurement to the spark plug 1 almost simultaneously with the spark discharge. The ion current that flows between the inner wall of the combustion chamber 6 and the center electrode 14 of the spark plug 1 and between the center electrode 14 and the ground electrode 15 due to the application of the measurement voltage is reduced by the ion current measuring device 24. It is measured by the current measuring circuit and the electronic control unit 29.

  The electronic control unit 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, an ionic current generated during combustion is generated. A spark ignition control program for controlling the high-frequency voltage generator 26 is built in so as to detect and determine the combustion state based on the detected ion current and generate an electric field when it is determined that the combustion state is normal. Yes. This spark ignition control program is executed every ignition timing. FIG. 3 shows the control procedure.

  When spark ignition is performed, an ignition signal output from the electronic control device 29 is input to the igniter of the ignition coil 21, and a positive high voltage is applied from the secondary winding 21 a of the ignition coil 21 to the center electrode 14 of the spark plug 1. A voltage is applied and spark discharge begins. 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.

  First, in step S1, a bias voltage is applied from the ion current measuring device 24 to the spark plug 1, and an ion current generated in the combustion chamber 6 immediately after the spark discharge is detected. In the case of normal combustion, the ion current shows a substantially maximum current value when the piston reaches the top dead center at which the combustion pressure becomes maximum. On the other hand, if the combustion state is not normal including misfire, the ionic current does not occur or even if the ionic current is generated, the current value is low, and at a certain point in time, there is a large difference compared to others. It does not exhibit the maximum current value that can occur.

  In step S2, it is determined whether or not the detected ion current value is a predetermined value. The predetermined value is set to a value that can determine whether the combustion is normal or misfiring, and is higher than that based on the average current value of the ionic current when the above-described combustion state is not normal. For example, a 30% value of a plurality of average values of maximum current values in a normal combustion state is set. If the detected ion current is less than the predetermined value, this program ends.

  If it is determined in step S2 that the detected ion current is greater than or equal to a predetermined value, an electric field due to positive pulsating flow is generated in step S3. Specifically, after the ion current is determined, the switching means 28 is turned on, and the output of the generator body 27 is output to the step-up transformer 25. As a result, a high-frequency voltage is output from the high-frequency voltage generator 26, rectified by the diode 23, and applied to the spark plug 1 of each cylinder as a positive pulsating current having a cycle corresponding to the frequency of the high-frequency voltage. .

  In such a configuration, when the electronic control unit 29 detects the ionic current in cooperation with the ionic current measuring device 24 at the ignition timing in each cylinder (step S1) and determines that the combustion is normal ( In step S2, “Yes”), an electric field is generated by the high-frequency positive pulsating flow for the combustion gas after ignition, that is, the product generated by spark ignition (step S3).

  The product contains positive ions and radicals. A plasma is generated by generating a positive electric field for such products. By generating plasma in this way, the center electrode 14 and the ground electrode 15 of the spark plug 1 are positioned in a positive electric field, and a repulsive force can be applied to positive ions existing in the vicinity thereof. it can. As a result, positive ions diffuse from the periphery of the electrode of the spark plug 1 over the entire combustion chamber 6, and thus combustion can be promoted.

  In addition, since the combustion state is determined by the ion current and an electric field is generated thereafter, the positive high voltage for spark ignition and the high frequency positive pulsating current for electric field generation are almost equal. At the same time, it is not applied to the spark plug 1. For this reason, the durability of the spark plug 1 can be maintained.

  On the other hand, if the combustion state is not normal, that is, if, for example, misfire occurs (“No” in step S2), the spark ignition control program is terminated without generating an electric field, so that the high frequency voltage generator 26 is damaged It is possible to suppress at least the inner wall of the combustion chamber 6 from being oxidized by plasma.

  Furthermore, in this embodiment, by using the step-up transformer 25 at the output stage of the high-frequency voltage generator 26, it is possible to output alternating current with substantially the same voltage to each cylinder. For this reason, by setting a high-frequency voltage to be output in advance by the step-up transformer 25, a voltage drop in the diode 23 can be compensated for, and plasma with an appropriate density can be generated.

  In addition, this invention is not limited to the above-mentioned embodiment.

  In the above description, the high voltage applied to the center electrode 14 of the spark plug 1 at the time of spark discharge is a positive voltage, but a negative voltage may be used. In this case, the diode 23 connects the anode to the center electrode 14 of the spark plug 1 in order to match the polarity of the pulsating current (voltage) to this positive voltage.

  Moreover, it may replace with the high frequency voltage generator 26, and may be a voltage generator which outputs the pulsating flow which changes with a period equivalent to a high frequency. In this case, the diode 23 in the above embodiment does not function as a rectifying unit, but only functions to prevent backflow. Therefore, when the electric field is generated, the high voltage pulsating current output from the voltage generator can be lowered by the diode forward voltage drop, and the energy required to generate the electric field can be reduced. In addition, since heat generated by the diode 23 is reduced, heat loss can be reduced.

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

  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 requires spark discharge by an ignition plug for ignition.

DESCRIPTION OF SYMBOLS 1 ... Spark plug 20 ... Ignition device 21 ... Ignition coil 24 ... Ion current measuring device 26 ... High frequency voltage generator 29 ... Electronic control unit 100 ... Engine

Claims (1)

The spark plug is provided with a spark discharge generated by a high voltage applied through an ignition coil connected to the spark plug, and an electric field generated by the electric field generating means through the spark plug. A spark ignition control method for a spark ignition type internal combustion engine that reacts to generate plasma to ignite an air-fuel mixture,
After the spark discharge, the ion current generated during combustion before the start of the generation of the electric field is detected,
Determine the combustion state based on the detected ion current,
A spark ignition control method for a spark ignition type internal combustion engine that starts generating an electric field when it is determined that the combustion state is normal, and does not start generating an electric field when it is determined that the combustion state is not normal .