JP2012219766A - Spark-ignition control method for spark-ignition type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve combustion efficiency by improving responsiveness to a request of output change in an internal combustion engine in which plasma is generated and spark ignition is performed.SOLUTION: In a spark-ignition control method for a spark-ignition type internal combustion engine, an air-fuel mixture is ignited by generating plasma by reacting a spark discharge, which is generated by a high voltage applied via an ignition coil connected to an ignition plug, with an electric field which is generated inside a combustion chamber via a central electrode connected to a high frequency voltage generation means. In accordance with the operating state of the spark-ignition type internal combustion engine, a waveform of a high frequency applied by the high frequency voltage generation means is thinned out.

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 the problems at the time of spark ignition as described above, for example, in the one described in Patent Document 1, plasma is generated in the combustion chamber, and the plasma and the spark discharge are reacted, so that the flame kernel is surely obtained. It is trying to generate. And in this patent document 1, according to the fluctuation | variation of the load of an internal combustion engine, especially the transient operation state at the time of shifting from a steady operation state to a steady operation state, plasma is made to respond | correspond to the amount of fuel and intake air supplied. In this configuration, the strength of the electric field for generation is controlled. Specifically, in Patent Document 1, when controlling the strength of an electric field, an electromagnetic wave output from an electromagnetic wave generator for generating the electric field, for example, a microwave output, that is, a voltage amplitude or a voltage application time is controlled. It is.

  However, if the electromagnetic wave voltage is lowered in the case of transient operation of deceleration, the amount of plasma generated decreases, so that ions, electrons, etc., which are products generated by spark discharge, can move while repeatedly colliding with each other. The range becomes narrower. As a result, the combustion centering on the flame kernel generated by the plasma is expanded only in a narrow range, and as a result, the promotion of the combustion is suppressed. Moreover, if the voltage application time is shortened, the reaction time of the above-mentioned product is shortened, and sufficient combustion promotion cannot be expected.

JP 2011-7157 A

  Accordingly, the present invention focuses on the above points and aims to improve combustion efficiency by improving the response to the request for changing the output in an internal combustion engine that generates plasma and performs spark ignition.

  That is, the spark ignition control method for a spark ignition internal combustion engine according to the present invention includes a spark discharge caused by a high voltage applied through an ignition coil connected to a spark plug and a center electrode connected to a high-frequency voltage generating means. A spark ignition control method for a spark ignition type internal combustion engine that generates plasma by reacting with an electric field generated in a combustion chamber via a gas and ignites an air-fuel mixture, depending on the operating condition of the spark ignition type internal combustion engine The high frequency waveform applied by the high frequency voltage generating means is thinned out.

  According to such a configuration, the intensity of the electric field generated in the combustion chamber is reduced by thinning out the high-frequency waveform applied by the high-frequency voltage generating means in accordance with the operating condition of the spark ignition internal combustion engine. Therefore, the generated plasma is weakened, and it is possible to supply the air-fuel mixture with the energy at the time of ignition in accordance with the operating condition, thereby improving the combustion efficiency.

  The present invention has a configuration as described above, and can supply energy to the air-fuel mixture at the time of ignition in accordance with the operating condition, thereby improving the combustion efficiency. Moreover, the energy loss can be made smaller than when the operation and stop of the high-frequency voltage generating means are repeated.

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 which shows the control procedure of the embodiment. The electric circuit diagram of the ignition device in the modification 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 15 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 a connection terminal 17 electrically connected. 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 includes an ignition coil 21 connected to the ignition plug 1, and a diode 22 having a cathode connected to the secondary winding 21a of the ignition coil 21. A high-frequency voltage generator 24 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 the step-up transformer 23 provided in its output stage. And. The high-frequency voltage generator 24 includes a step-up transformer 23, a high-frequency generation circuit 25 connected to the step-up transformer 23, and a bias circuit 26 that biases the high-frequency voltage by at least its peak value. In the figure, reference numeral 40 denotes a ground having the same potential as that of the vehicle body.

  The step-up transformer 23 synthesizes and boosts two types of high frequencies output from the high-frequency voltage generation circuit 25 described below about 10 to 20 times, and functions to thin out high-frequency waveforms. In other words, the step-up transformer 23 outputs a high frequency with no waveform thinning by synthesizing a high frequency whose phase applied to the primary side first winding 23b and the primary second winding 23c is ½ wavelength different. By stopping the high frequency applied to the primary side second winding 23c, the high frequency in the form of waveform thinning is output.

  For example, the high-frequency generation circuit 25 boosts the voltage of the vehicle battery 27, for example, about 12 V (volts) to 300 to 500 V by the DC-DC converter 28 that is a booster circuit, and the boosted direct current by the H bridge circuit 29. The frequency is changed to an alternating current of about 200 kHz to 600 kHz.

  For example, the high frequency voltage generation circuit 25 boosts the voltage of the vehicle battery 27, for example, about 12 V (volts) to 300 to 500 V by the DC-DC converter 28 that is a booster circuit, and the boosted direct current is supplied to the H bridge circuit 29. Thus, the frequency is changed to an alternating current of about 100 kHz to 300 kHz. The high-frequency voltage generation circuit 25 of this embodiment generates a main high frequency, that is, a high frequency (hereinafter referred to as a main high frequency) to be applied to the primary side first winding 23b of the step-up transformer 23 by the above-described configuration. A high frequency (hereinafter referred to as a sub-high frequency) to be applied to the primary side second winding 23c of the step-up transformer 23 is generated by a delay circuit (incorporated in the H bridge circuit 29) that delays ½ wavelength. Therefore, the main high frequency and the sub high frequency are high frequencies having the same voltage and frequency. Further, the duty ratio of the main high frequency and the sub high frequency is set to 0.25.

  Therefore, the high-frequency voltage generator 24 outputs a high-frequency voltage boosted to about 4 kVp-p to 8 kVp-p by the step-up transformer 23 and having a frequency of 200 kHz to 600 kHz and duty ratios of 0.25 and 0.50. . Switching of the duty ratio, that is, thinning of the waveform is controlled by the electronic control unit 30. Note that the high-frequency voltage to be output 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). This is because when the high-frequency voltage is smaller than the sustain voltage, the strength of the generated electric field is reduced, and the flow of electrons due to the spark discharge and the ions and radicals generated by the spark discharge may not meander, resulting in plasma. This is because the reduction of the acceleration of combustion is taken into consideration.

  The bias circuit 26 includes resistors 26 a and 26 b that divide the output voltage of the DC-DC converter 28. The bias circuit 26 is connected to the reference voltage side of the H bridge circuit 29 and biases the high frequency output from the H bridge circuit 29 by the peak value. Specifically, for example, when a high frequency of about 280 Vp-p is output from the H bridge circuit 29, the bias circuit 26 outputs a negative DC voltage of 140 V. As a result, a negative DC voltage (pulsating voltage) that periodically changes between 0 V and 280 V is input to the step-up transformer 23. As a result, the step-up transformer 23 and thus the high-frequency voltage generator 24 outputs a negative DC voltage, such as a rectangular wave, which periodically changes with a minimum value of 0 V and a maximum value of 2.8 kV.

  The H bridge circuit 29 is a main high frequency, that is, a high frequency applied to the primary side first winding 23b of the step-up transformer 23 (hereinafter referred to as main high frequency) and a delay circuit that delays the main high frequency by ½ wavelength. A high frequency (hereinafter referred to as sub-high frequency) applied to the primary side second winding 23c of the step-up transformer 23 is generated. Therefore, the main high frequency and the sub high frequency are high frequencies having the same voltage and frequency. Further, the duty ratio of the main high frequency and the sub high frequency is set to 0.25.

  Note that the negative DC voltage output from the high-frequency voltage generator 24 is not limited to the above example, and may be, for example, in the range of 2 kV to 8 kV.

  The diode 22 functions as a backflow prevention diode with respect to a 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 22 has its cathode connected to the secondary winding 21a and its cathode connected to one end of the secondary winding 23a of the step-up transformer 23, so that the negative high voltage is a high-frequency voltage. Backflow to the generator 24 is prevented.

  The electronic control unit 30 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 the spark ignition depends on the operation state of the engine 100. The high frequency voltage generator 26 incorporates a high frequency control program for performing control to thin out the high frequency waveform applied between the center electrode 14 and the ground electrode 15 of the spark plug 1. The control procedure of the high frequency control program is shown in FIG. This high frequency control program is repeatedly executed at predetermined intervals after the engine 100 is started and until it is stopped.

  During spark ignition, when an ignition signal output from the electronic control device 30 is input to the igniter of the ignition coil 21, a negative polarity high voltage is applied from the secondary winding 21a 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. The high frequency output from the high frequency voltage generator 24 is applied to the spark plug 1 immediately before, almost simultaneously with, or immediately after the induction voltage is generated.

  First, in step S1, it is determined whether the required output of the engine 100 is a predetermined value or less. The required output is detected based on at least the accelerator operation amount or the throttle valve opening. The predetermined value is set to a value that can determine a low-load low-rotation region with a low required output, for example.

  If it is determined in step S1 that the required output of the engine 100 exceeds a predetermined value, this determination is repeatedly performed until the required output becomes equal to or less than the predetermined value. During this time, the high frequency voltage generation circuit 25 applies the main high frequency to the primary side first winding 23b of the step-up transformer 23 and the sub high frequency to the primary side second winding 23c. Therefore, the secondary winding 23a of the step-up transformer 23 has a high frequency having a duty ratio of 0.25 but having two waveforms in one cycle, that is, having a waveform every ½ cycle. Therefore, in the operating state of engine 100 where the required output of engine 100 exceeds a predetermined value, spark ignition is executed at a high frequency that is not thinned out in the waveform.

  On the other hand, if the required output of the engine 100 is equal to or less than the predetermined value in step S1, high frequency waveform thinning is performed in step S2. Specifically, the high-frequency voltage generator 24 receives a control signal from the electronic control unit 30 and stops applying the sub-high frequency to the primary side second winding 23c output from the high-frequency voltage generator 25 by the control signal. As a result, only the main high frequency is input to the step-up transformer 23. Therefore, the high-frequency output from the high-frequency voltage generator 24, that is, the high-frequency applied to the spark plug 1, has a sub-high-frequency waveform thinned out compared to the operating state of the engine 100 where the required output exceeds a predetermined value. In other words, the high frequency is the same frequency and voltage as the high frequency when the required output exceeds a predetermined value, and the duty ratio is 0.25.

  In such a configuration, when an ignition signal output from the electronic control device 30 is input to the igniter of the ignition coil 21 during spark ignition, the secondary electrode 21a of the ignition coil 21 causes the center electrode of the ignition plug 1 to be ignited. A negative high voltage is applied to 14 to start spark discharge. 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.

  Almost simultaneously with the start of the induction discharge, a high frequency is applied to the center electrode 14 from the high frequency voltage generator 24. As a result, a negative electric field is generated so as to surround the center electrode 14. The generated electric field reacts with the product of the spark discharge generated between the center electrode 14 and the ground electrode 15 to generate plasma and ignite the mixture.

  That is, upon ignition, when a spark discharge is generated in the spark plug 1 by the ignition coil 21, a negative pulsating current (current) flows between the gaps 18 of the spark plug 1 along with the spark discharge. An electric field is generated, and a spark discharge (mainly inductive discharge) reacts with a negative electric field to generate plasma, thereby rapidly burning the air-fuel mixture in the combustion chamber 6.

  Specifically, the product generated during the spark discharge by the spark plug 1 reacts with a negative electric field to form plasma. 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 positive ions and radicals, which are the product of the spark discharge and the products generated by the spark discharge, are affected by the negative electric field and away from the vicinity of the center electrode 14 of the spark plug 1. This is because the path length becomes longer due to vibration and meandering toward the surface, and the number of collisions with surrounding water molecules and nitrogen molecules increases dramatically. Water and nitrogen molecules that have been struck by positive ions and radicals become OH radicals and N radicals, and the surrounding gas that has been struck by positive ions and radicals is ionized, in other words, plasma. Thus, the region of ignition of the air-fuel mixture dramatically increases, and the flame kernel that starts the flame propagation combustion also increases.

  In such spark ignition, when changing from an operating situation in which the required output of the engine 100 exceeds a predetermined value to an operating situation that is the following, by thinning out the waveform of the high frequency applied to the spark plug 1, Plasma is generated by generating a high-frequency electric field with a high frequency corresponding to the operating conditions. That is, the energy required to generate plasma can be reduced without changing the voltage, frequency, and input time to the spark plug 1. Therefore, the responsiveness of changing the high frequency for plasma generation is improved corresponding to the operating state of engine 100, and the combustion efficiency can be improved. Moreover, since the high frequency is not turned on / off on the generator main body 27 side, the energy loss can be made smaller than the energy loss associated with the switching.

  In the configuration of this embodiment, when the negative electric field is generated, it is not necessary to use the diode 22 for high-frequency half-wave rectification. Therefore, the high voltage biased pulsating high voltage is applied to the diode forward voltage drop. Therefore, the energy required for generating a negative electric field can be reduced. In addition, since heat generated by the diode 22 is reduced, heat loss can be reduced.

  The connection position of the diode 22 may be between the secondary winding 23a of the step-up transformer 23 and the ground 40 in addition to the above. That is, as shown in FIG. 4, the diode 122 has its cathode connected to the other end of the secondary winding 23 a of the step-up transformer and its cathode connected to the ground 40. By connecting the diode 122 in this way, it functions as a backflow prevention diode for a high voltage for spark discharge, as in the above embodiment. Moreover, the voltage applied to the diode 122 when the pulsating current flows through the secondary winding 23a of the step-up transformer 23 is low, and the power consumption in the diode 122 can be reduced compared to the above embodiment.

  The present invention is not limited to the above embodiment.

  In the above embodiment, a single predetermined value for determining the driving situation is set, but a plurality of determination values are set so that the waveform thinning increases as the required output of the engine 100 decreases. It may be configured. In this case, a plurality of primary windings of the step-up transformer 23 may be provided, and alternating currents having different phases may be applied to the primary windings.

  The main high frequency and the sub high frequency may be output from different high frequency voltage generation circuits.

  In addition, the thinning of the waveform may be, for example, a setting in which the thinning amount is set to be different between an ignition period in which a flame kernel is formed after ignition and a subsequent flame propagation period. In this case, the thinning amount in the flame propagation period is set to be larger than the thinning amount in the ignition period. By setting the thinning amount in such a waveform, it is possible to reduce an obstacle to flame propagation, that is, an inquiry between positive ions generated by spark discharge and a negative high-frequency electric field.

  The timing at which the waveform is thinned may be the compression top dead center when a change in the required output of the engine 100 is determined.

  In the above-described embodiment, the high-frequency voltage generator that outputs a negative DC voltage biased with a high frequency has been described. However, when the high voltage for spark ignition is positive, the direct-current output from the high-frequency voltage generator is described. The voltage is positive according to the high voltage. In this case, the bias circuit is a DC power source that outputs a positive DC voltage, or a voltage dividing circuit using the above-described resistor.

  The voltage waveform of the pulsating current output from the high-frequency voltage generator is not particularly limited, and may be any one of a sine waveform, a triangular waveform, a square waveform, and a sawtooth waveform.

  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, compressed natural gas, or the like as fuel and that requires spark discharge by an ignition plug for ignition.

DESCRIPTION OF SYMBOLS 1 ... Spark plug 20 ... Ignition device 21 ... Ignition coil 24 ... High frequency voltage generator 25 ... High frequency generator circuit 30 ... Electronic control unit 100 ... Engine

Claims (1)

Plasma is generated by reacting the spark discharge generated by the high voltage applied through the ignition coil connected to the spark plug and the electric field generated in the combustion chamber through the center electrode connected to the high-frequency voltage generating means. A spark ignition control method for a spark ignition internal combustion engine that ignites an air-fuel mixture,
A spark ignition control method for a spark ignition type internal combustion engine, wherein the high frequency waveform applied by the high frequency voltage generating means is thinned out in accordance with the operating state of the spark ignition type internal combustion engine.

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