JP2007315297A - Combustion state determining device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the determining accuracy of a combustion state, and to improve failure determining accuracy of an ignition system, while satisfying a request for reducing the cost of a spark plug. <P>SOLUTION: In a general spark plug 14, since a terminal part connected to the secondary side of an ignition coil 11 is formed of an iron-based material, a surface of its terminal part is oxidized, and an insulating oxide film is formed, and this insulating oxide film becomes the cause of causing electric continuity failure when detecting an ion current. As this countermeasure, DC ion detecting voltage charged to an ion detecting power capacitor 17 is set to 200 V or more. Thus, even when flying sparks do not exist (or before the flying sparks), the electric continuity between the spark plug 14 and the ignition coil 11 can be secured by breaking insulating performance of the insulating oxide film of a terminal part surface of the spark plug 14 by the DC ion detecting voltage of 200 V or more, and ion current detecting accuracy is improved, in its turn, the determining accuracy of the combustion state is improved, and the failure determining accuracy of the ignition system can be improved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a combustion state determination device for an internal combustion engine that detects an ionic current generated when an air-fuel mixture in a combustion chamber of the internal combustion engine burns using a spark plug to determine a combustion state of the internal combustion engine.

  In recent years, in order to detect the combustion state of an internal combustion engine, for example, as shown in Patent Document 1 (Japanese Patent No. 3176291), an ionic current flowing between electrodes of a spark plug is detected every ignition, and the ionic current signal is Based on this, a technique for detecting misfire, pre-ignition, knocking, etc. has been developed. In this ion current detection circuit, an ion detection power supply capacitor for applying a direct current (DC) ion detection voltage to the center electrode of the spark plug is connected in series to the secondary side of the ignition coil for causing the spark plug to spark discharge. The ignition detection power supply capacitor is charged by the ignition current flowing between the electrodes of the spark plug during ignition, and the charge voltage of the ion detection power supply capacitor is applied to the center electrode of the ignition plug as a DC ion detection voltage after ignition, Ions generated when the air-fuel mixture burns are collected and detected by the electrode of the spark plug.

  In this ion current detection circuit, as shown in FIG. 2, if the ignition system is normal, a pulsed noise current having a short time width is induced immediately after the ignition coil is energized (immediately after the ignition signal is switched from OFF to ON). LC resonance noise is generated by the residual magnetic energy on the secondary side of the ignition coil after the end of energization of the ignition coil (after the ignition signal is switched from ON to OFF), and then the ion current generated by combustion A waveform appears.

  Focusing on this characteristic, as shown in Patent Document 2 (Japanese Patent No. 2843194), LC resonance noise generated immediately after the end of energization of the ignition coil is detected, and the ignition coil is based on the detection level of this LC resonance noise. There is one that determines whether or not there is a failure.

  By the way, in the ion current detection circuit configured to apply a direct current (DC) ion detection voltage to the center electrode of the spark plug by the charge voltage of the ion detection power supply capacitor, the ion current detection output increases in proportion to the DC ion detection voltage. Therefore, the DC ion detection voltage is set to about 50V to 150V so that a necessary ion current detection output level can be obtained.

  Generally, as described in Patent Document 3 (Japanese Patent No. 3605962), the terminal portion (stem portion) of the ignition plug that connects the ignition coil and the ignition plug is generally formed of an iron-based material. The surface of the terminal portion is oxidized to form an insulating oxide film, and this insulating oxide film causes a conduction failure when detecting an ionic current.

  As shown in FIGS. 4 (a) and 4 (b), the insulating oxide film 2 of the terminal portion 1 of the spark plug is not uniform in thickness, and is thick at a thickness of about 5 to 10 μm and thin. Is known to have a film thickness of about 1-2 μm.

  When a high voltage induced on the secondary side of the ignition coil is applied between the electrodes of the spark plug to cause a spark, the thickness of the insulating oxide film 2 is about 5 to 10 μm as shown in FIG. Even if it is thick, the insulation of the insulating oxide film 2 is destroyed by sparks and discharges. Therefore, as shown in FIG. 5, even if the DC ion detection voltage is about 100 V, the terminal portion of the spark plug 1 and the connection spring 3 of the ignition coil can be secured, and an ionic current due to combustion can be detected.

  However, when there is no spark (or before the spark), as shown in FIG. 4B, DC ion detection of about 100 V is possible if the thickness of the insulating oxide film 2 is as thin as about 1 to 2 μm. Even if voltage is applied, the insulating property of the insulating oxide film 2 is destroyed, and it is possible to ensure the conduction between the terminal portion 1 of the spark plug and the connection spring 3 of the ignition coil. When the thickness is about 10 μm, as shown in FIG. 5, in the case of no spark (or before the spark), the insulation property of the insulating oxide film 2 is not sufficiently destroyed with a DC ion detection voltage of about 100 V. The continuity between the terminal part 1 of the spark plug and the connection spring 3 of the ignition coil may not be ensured, and the ionic current due to combustion may not be detected. For this reason, there is a case where normal combustion is misjudged as misfire or an ignition system failure is misjudged.

As a countermeasure, as shown in Patent Document 3 (Japanese Patent No. 3605962), the surface of the terminal portion 1 of the spark plug is covered with an oxidation-resistant conductive film (a film of gold, silver, etc.) There is one in which conduction between the terminal portion 1 and the connection spring 3 of the ignition coil (hereinafter referred to as “conduction between the ignition plug and the ignition coil”) is ensured.
Japanese Patent No. 3176291 (FIG. 1 etc.) Japanese Patent No. 2843194 (page 3, etc.) Japanese Patent No. 3605962 (page 4 etc.)

  However, as in Patent Document 3, the surface of the terminal portion 1 of the spark plug is covered with an oxidation-resistant conductive film (a film of gold, silver, etc.) to ensure conduction between the spark plug and the ignition coil. As a result, the manufacturing cost of the spark plug increases, and the demand for reducing the cost of the spark plug cannot be satisfied.

  The present invention has been made in view of such circumstances. Accordingly, the object of the present invention is to detect a spark plug at the time of detecting an ion current without covering the surface of the terminal portion of the spark plug with an oxidation-resistant conductive film. Providing an ion current detection device that can ensure conduction between ignition coils and improve combustion state determination accuracy and ignition system failure determination accuracy while satisfying the demand for lower spark plug costs There is to do.

  In order to achieve the above object, the invention according to claim 1 is directed to ion detection for applying a DC ion detection voltage to the center electrode of the spark plug on the secondary side of the ignition coil for causing the spark plug to spark discharge. A power supply capacitor is connected in series, and a charging voltage of the ion detection power supply capacitor is applied as a DC ion detection voltage to the center electrode of the spark plug to detect an ion current, and from the ion current detection means In a combustion state determination device for an internal combustion engine comprising combustion state determination means for determining a combustion state of the internal combustion engine based on an output ion current signal, the ion current signal caused by a secondary voltage change of the ignition coil Direct current for charging the ion detection power supply capacitor with ignition system failure determination means for determining whether or not there is a failure in the ignition system based on whether or not there is a change On detection voltage is obtained by configured to be above 200V.

  The present inventors conducted a test to examine how the relationship between the continuity between the spark plug and the ignition coil and the DC ion detection voltage changes depending on the presence or absence of a spark (before and after). As shown in FIG. Since the spark plug used in this test is a general spark plug in which the surface of the iron-based terminal portion is not covered with an oxidation-resistant conductive film, an insulating oxide film is formed on the surface of the spark plug terminal portion. Is formed. From this test result, even when there is no spark (or before spark), if the DC ion detection voltage is 200 V or higher (more preferably 250 V or higher), the insulation oxidation of the surface of the terminal portion is performed by the DC ion detection voltage of 200 V or higher. It has been found that the electrical insulation between the spark plug and the ignition coil can be secured by destroying the insulation of the coating.

  From this test result, as in the present invention, when the DC ion detection voltage charged to the ion detection power supply capacitor is set to 200 V or more (more preferably 250 V or more), a spark plug having a terminal portion made of an iron-based material is connected to the terminal. Even if it is used as it is without forming an oxidation-resistant conductive film on the surface of the part, the insulation property of the insulating oxide film on the surface of the terminal part is destroyed by a DC ion detection voltage of 200 V or more (more preferably 250 V or more). Thus, conduction between the spark plug and the ignition coil can be ensured. As a result, while satisfying the demand for reducing the cost of the spark plug, it is possible to improve ion current detection accuracy, and thus improve combustion state determination accuracy and ignition system failure determination accuracy.

  Changes in the secondary voltage of the ignition coil occur immediately after the start of energization of the ignition coil and at the end of discharge after the end of energization. At any timing, the ignition voltage changes depending on whether there is a change in the ion current signal due to the change in the secondary voltage. The presence or absence of a system failure can be determined.

  In this case, in the system for detecting smoldering contamination and pre-ignition of the spark plug by comparing the ionic current signal during the energization period of the ignition coil with the smolder determination threshold value and the pre-ignition determination threshold value, Thus, it is preferable to determine the presence or absence of a failure in the ignition system based on the presence or absence of a change in the ion current signal due to the change in the secondary voltage during the energization period of the ignition coil. In this way, there is an advantage that it is possible to determine the presence or absence of a failure of the ignition system during the energization period of the ignition coil, using the same determination threshold as the determination threshold for detecting smoldering contamination and pre-ignition. . At this time, it is only necessary to determine whether there is a failure in the ignition system immediately after the start of energization of the ignition coil, determine smoldering contamination, and then determine pre-ignition.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment embodying the best mode for carrying out the invention will be described with reference to the drawings.
First, the configuration of an ion current detection circuit (ion current detection means) will be described with reference to FIG. One end of the primary winding 12 of the ignition coil 11 is connected to a power supply terminal (+ B) to which battery voltage is supplied, and the other end of the primary winding 12 is connected to a switching element (not shown) for ignition control. It is connected. One end of the secondary winding 13 of the ignition coil 11 is connected to the ignition plug 14, and the other end of the secondary winding 13 is connected to the ground via two Zener diodes 15 and 16.

  The two zener diodes 15 and 16 are connected in series in opposite directions, one ionizer power supply capacitor 17 is connected in parallel to one zener diode 15, and the ion current detection resistor 18 is connected in parallel to the other zener diode 16. Yes. The ion detection power supply capacitor 17 is charged by an ignition current flowing between the electrodes 19 and 20 of the spark plug 14 at the time of ignition, and the charging voltage (DC ion detection voltage) is 200 V or more (more preferably 250 V) as the Zener voltage of the Zener diode 15. This occurs when the air-fuel mixture in the combustion chamber burns by applying a direct current (DC) ion detection voltage between the electrodes 19 and 20 of the spark plug 14 by the charging voltage of the capacitor 17 after ignition. Ions are collected by the electrodes 19 and 20 of the spark plug 19, and an ion current is passed through the ion detection power supply capacitor 17 in a direction opposite to the ignition current.

  The Zener diode 16 connected in parallel with the ion current detection resistor 18 plays a role of regulating the voltage generated in the ion current detection resistor 18 to a predetermined voltage (the Zener voltage of the Zener diode 16) or less.

  In this ion current detection circuit, the ion current flows from the ground side through the ion current detection resistor 18 to the ion detection power supply capacitor 17 and at the same time, the potential (ion current) between the ion current detection resistor 18 and the ion detection power supply capacitor 17. The voltage generated in the detection resistor 18 is detected by the voltage detection circuit 22, and an ion current signal is output from the voltage detection circuit 22 to the engine control circuit 23. Since the voltage generated in the ionic current detection resistor 18 changes according to the ionic current flowing through the ionic current detection resistor 18, the ionic current is detected by detecting this potential by the voltage detection circuit 22.

  During engine operation, a switching element (not shown) is turned on at the rise (ON timing) of the ignition signal output from the engine control circuit 23, and a primary current flows from the battery to the primary winding 12 of the ignition coil 11, Thereafter, the switching element is turned off at the fall of the ignition signal (OFF timing), the primary current of the primary winding 12 is cut off, and thereby a high voltage is electromagnetically induced in the secondary winding 13, and this high voltage Is applied between the electrodes 19 and 20 of the spark plug 14 to generate a spark discharge.

  At this time, the ignition current (spark discharge current) flows from the ground electrode 20 of the spark plug 14 to the center electrode 19 and is charged to the ion detection power supply capacitor 17 through the secondary winding 13, and the charge of the ion detection power supply capacitor 17 is completed. Thereafter, the ignition current flows to the ground side through the Zener diodes 15 and 16.

  After the spark discharge is finished, an ion detection voltage is applied between the electrodes 19 and 20 of the spark plug 14 by the charging voltage of the ion detection power supply capacitor 17, and ions generated when the air-fuel mixture burns are converted into the ion current of the spark plug 14. It flows between the electrodes 19 and 20. This ion current flows from the center electrode 19 to the ground electrode 20, and further flows from the ground side through the ion current detection resistor 18 to the ion detection power supply capacitor 17.

  In this embodiment, the terminal portion 1 (see FIG. 4) of the spark plug 14 that connects the secondary winding 13 of the ignition coil 11 and the spark plug 14 is formed of an iron-based material. For this reason, since the surface of the terminal portion 1 is oxidized to form the insulating oxide film 2, when the DC ion detection voltage (charge voltage of the ion detection power supply capacitor 17) is low, this insulating oxide film 2 is spark plug. 14, and the connection spring 3 of the ignition coil 11 (hereinafter, referred to as “conduction between the spark plug 14 and the ignition coil 11”) are obstructed.

  The present inventors conducted a test to examine how the relationship between the continuity between the spark plug 14 and the ignition coil 11 and the DC ion detection voltage changes depending on the presence or absence of the spark (before and after). The results are shown in FIG. Since the spark plug 14 used in this test is a general spark plug in which the surface of the iron-based terminal portion 1 is not covered with an oxidation-resistant conductive film, the spark plug 14 is insulated from the surface of the terminal portion 1 of the spark plug 14. Oxide film 2 is formed. From this test result, even when there is no spark (or before the spark), if the DC ion detection voltage is 200 V or more (more preferably 250 V or more), the insulation of the surface of the terminal portion 1 by the DC ion detection voltage of 200 V or more. It has been found that the electrical conductivity between the spark plug 14 and the ignition coil 11 can be secured by destroying the insulating property of the conductive oxide film 2.

  From this test result, in this example, the Zener voltage of the Zener diode 15 is 200 V or more (more preferably) so that the DC ion detection voltage charged in the ion detection power supply capacitor 17 is 200 V or more (more preferably 250 V or more). 250V or higher).

  Next, how the detection waveform of the ionic current (the output waveform of the voltage detection circuit 22) changes at the time of normal combustion, at the time of misfire (at the time of poor conduction), and at the time of failure of the ignition system will be described with reference to FIG.

  If the ignition system is normal, a pulsed noise current having a short time width is induced immediately after the start of energization of the primary winding 12 of the ignition coil 11 (immediately after the ignition signal is switched from OFF to ON). LC discharge noise is generated by the residual magnetic energy on the secondary side of the ignition coil 11 after the end of energization (after switching the ignition signal from ON to OFF), and then the waveform of the ion current generated by combustion appears. .

  On the other hand, at the time of misfire, a pulse-like noise current immediately after the start of energization of the primary winding 12 and LC resonance noise after ignition appear, but a waveform of ion current due to combustion does not appear.

  In addition, when the DC ion detection voltage is 150 V or less, the continuity between the spark plug 14 and the ignition coil 11 is unstable, so that the pulsed noise current immediately after the start of energization of the primary winding 12 and the LC after ignition Even if resonance noise appears, the waveform of ion current due to combustion may not appear. For this reason, there is a possibility that normal combustion is erroneously determined as misfire.

  Further, when the energization is disabled due to a failure of the ignition system such as disconnection of the primary winding 12 of the ignition coil 11, the ionic current output of the voltage detection circuit 22 is not output at all, not only the ionic current due to combustion, Noise immediately after ignition signal ON switching and LC resonance noise after ignition are not detected.

  Focusing on this point, in this embodiment, the presence or absence of an ionic current output (noise current) within the current-carrying section of the ignition coil 11 (during the ignition signal ON period) is determined based on the ionic current output exceeding the failure determination threshold value Vth1. Judgment is made based on the time width (T1), and it is determined whether or not the ignition coil 11 cannot be energized (ignition system failure) depending on whether or not the ion current output time width (T1) is equal to or shorter than the predetermined time C1. judge. In this case, since the LC resonance noise after ignition does not occur when the ignition coil 11 cannot be energized, it is determined that the ignition coil 11 cannot be energized by determining the presence or absence of ionic current output due to the LC resonance noise after ignition. It may be determined whether or not the ignition system is faulty).

  Further, in this embodiment, after ignition, for example, a section from 1 ms (after the end of discharge) to ATDC 120 ° C. is set as a misfire detection section, and the ion current signal of this misfire detection section is compared with the misfire determination level Vth2, Normal combustion and misfire are discriminated based on whether or not the time T2 when the ion current signal exceeds the misfire determination level Vth2 is equal to or longer than the predetermined time C2.

  The ignition system failure determination and misfire determination of the present embodiment described above are executed by the engine control circuit 23 according to the diagnosis determination routine of FIG.

  The diagnosis determination routine of FIG. 3 is executed at a predetermined cycle (for example, 20 μs cycle) during engine operation. First, in step 101, the ion current signal I (output signal of the voltage detection circuit 22) is read, and in the next step 102, It is determined whether or not the ignition coil 11 is within the energization section. If the ignition coil 11 is within the energization section, the process proceeds to step 103 where the ion current signal I is within the energization section of the ignition coil 11. A time T1 exceeding the value Vth1 is detected.

  Thereafter, the routine proceeds to step 104, where the time T1 when the ionic current signal I exceeds the coil energization determination threshold value Vth1 is compared with the determination threshold value C1, and if this time T1 exceeds the determination threshold value C1, the ignition is performed. It is determined that the system is normal (energization to the ignition coil 11 is normal), the process proceeds to step 105, and the ignition system failure flag IG is set to “1”.

  On the other hand, if it is determined in step 104 described above that the time T1 when the ion current signal I exceeds the coil energization determination threshold value Vth1 is equal to or less than the determination threshold value C1, the failure of the ignition system (to the ignition coil 11) is determined. In step 106, the ignition system failure flag IG is set to "0".

  Thereafter, the process proceeds to step 107, where a diagnosis process for the ignition system failure is executed, and the determination result of the ignition system failure is stored in a rewritable nonvolatile memory such as a backup RAM of the engine control circuit 23. If an engine failure is detected, a warning is displayed on the warning display on the instrument panel of the driver's seat, or a warning lamp is lit or flashed to warn the driver, such as fuel cut. A fail-safe process is performed to prevent the unburned gas from being discharged into the exhaust system. If it is determined as “No” in step 102 (that is, not within the energization section of the ignition coil 11), the processing of step 107 is executed by skipping the processing of steps 102 to 106. The processes of steps 101 to 107 described above serve as ignition system failure determination means in the claims.

  Thereafter, the process proceeds to step 108 to determine whether or not it is within the misfire detection section. If it is within the misfire detection section, the process proceeds to step 109 and the ion current signal I exceeds the misfire determination level Vth2 within the misfire detection section. Time T2 is detected.

  Thereafter, the routine proceeds to step 110 where the time T2 when the ion current signal I exceeds the misfire determination level Vth2 is compared with the determination threshold C2, and if this time T2 exceeds the determination threshold C2, it is determined that the combustion is normal. In step 111, the misfire determination flag MF is set to “1”. On the other hand, if it is determined in step 110 that the time T2 when the ionic current signal I exceeds the misfire determination level Vth2 is equal to or less than the determination threshold value C2, it is determined that misfire has occurred, and the process proceeds to step 112, where the misfire determination flag MF Is set to “0”.

  Thereafter, the process proceeds to step 113, the misfire diagnosis process is executed, the misfire determination result is stored in the rewritable nonvolatile memory of the engine control circuit 23, and this routine is finished. If “No” is determined in step 108 (that is, not in the misfire detection section), the process of steps 109 to 112 is skipped, the process of step 113 is executed, and this routine is terminated. The processing of the above steps 108 to 113 serves as a combustion state determination means in the claims.

  Note that the smoldering contamination and pre-ignition of the ignition plug 14 may be detected by comparing the ion current signal I with the smolder determination threshold value and the pre-ignition determination threshold value within the energization interval of the ignition coil 11. In this way, when performing the ignition system failure determination, the smoldering determination, and the preignition determination within the energization section of the ignition coil 11, these three types of determinations can be performed using the same determination threshold value Vth1. There are advantages you can do. At this time, it is only necessary to determine whether there is a failure in the ignition system immediately after the start of energization of the ignition coil 14, determine smoldering contamination, and then determine pre-ignition.

  According to the present embodiment described above, the DC ion detection voltage for charging the ion detection power supply capacitor 17 is 200 V or more in consideration of the conduction characteristics between the spark plug 14 and the ignition coil 11 with respect to the DC ion detection voltage shown in FIG. (More preferably 250 V or more), the spark plug 14 in which the terminal portion 1 is formed of an iron-based material is used as it is without forming an oxidation-resistant conductive film on the surface of the terminal portion 1. However, the insulation between the insulating oxide film 2 on the surface of the terminal portion 1 can be destroyed by a DC ion detection voltage of 200 V or higher (more preferably 250 V or higher) to ensure conduction between the spark plug 14 and the ignition coil 11. It is possible to improve the ion current detection accuracy while meeting the demand for cost reduction of the spark plug 14, and hence the combustion state determination accuracy, failure of the ignition system It is possible to realize a constant accuracy.

  Further, the present invention may use a spark plug in which the surface of the terminal portion 1 is marked with a plug type identification mark with a paint, and in this case as well, a DC ion of 200 V or more (more preferably 250 V or more) is used. The insulating property of the marking coating film can be destroyed by the detection voltage, and conduction between the spark plug and the ignition coil can be ensured. In this case, it is desirable that the thickness of the marking coating film be 10 μm or less.

  In addition, the present invention can be implemented with various modifications within a range not departing from the gist, such as appropriately changing the configuration of the ion current detection circuit.

It is an electric circuit diagram which shows the structure of the ion current detection circuit in one Example of this invention. It is a time chart explaining how the detection waveform of the ionic current (the output waveform of the voltage detection circuit 22) changes at the time of normal combustion, at the time of misfire (at the time of poor conduction), and at the time of failure of the ignition system. It is a flowchart explaining the flow of a process of a diagnosis determination routine. (A) is a figure explaining the conduction | electrical_connection recovery mode after a spark, (b) is a figure explaining the conduction | electrical_connection recovery mode without a spark. It is a figure explaining the result of the test which considers how the relationship between the electrical continuity between a spark plug and an ignition coil and DC ion detection voltage changes with the presence or absence (before and after) of a spark.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Terminal part, 2 ... Insulating oxide film, 3 ... Connection spring, 11 ... Ignition coil, 12 ... Primary winding, 13 ... Secondary winding, 14 ... Spark plug, 15, 16 ... Zener diode, 17 ... Ion Detection power supply capacitor, 18 ... ion current detection resistor, 19 ... center electrode, 20 ... ground electrode, 22 ... voltage detection circuit, 23 ... engine control circuit (ignition system failure determination means, combustion state determination means)

Claims (2)

An ion detection power supply capacitor connected in series to the secondary side of an ignition coil for causing a spark discharge to the spark plug, and applying a DC ion detection voltage to the center electrode of the spark plug;
An ion current detection means for detecting an ion current by applying a charging voltage of the ion detection power supply capacitor as a DC ion detection voltage to a center electrode of the spark plug;
A combustion state determination device for an internal combustion engine, comprising: a combustion state determination unit that determines a combustion state of the internal combustion engine based on an ion current signal output from the ion current detection unit;
Ignition system failure determination means for determining the presence or absence of an ignition system failure based on the presence or absence of a change in the ion current signal due to a change in the secondary voltage of the ignition coil,
A combustion state determination device for an internal combustion engine, characterized in that a DC ion detection voltage for charging the ion detection power supply capacitor is 200 V or more.   The ignition system failure determination means determines whether or not there is a failure in the ignition system based on whether or not the ion current signal has changed due to a change in secondary voltage during the energization period of the ignition coil. The combustion state determination apparatus of the internal combustion engine as described.

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