JP2012167655A - Combustion control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the combustion control device of an internal combustion engine that can perform a reasonable combustion determination.SOLUTION: The internal combustion engine having a plurality of cylinders includes: a detection means (ST11) for specifying an operation state by specifying the number of rotations of a crankshaft and/or the intake air volume in a combustion chamber prior to ignition timing of the combustion chamber of each cylinder; a determination means (ST23) for performing initial determination of the determination threshold of the combustion determination processing for the combustion chamber of the next ignition timing; a correction means (ST25) for correcting the initially determined determination threshold when the misfire determination is performed at timing one step before; a signal acquisition means (ST21) for acquiring a group of sensor signals after the ignition timing; and a determination means (ST26) for performing the combustion determination processing on the combustion chamber by comparing evaluation data to be generated by evaluating the sensor signal obtained by the signal acquisition means in the time base direction with the determination threshold specified by the acquisition means or the correction means.

Description

  The present invention relates to a combustion control apparatus that detects a combustion state including a misfire state with high accuracy based on an ion signal generated in a combustion chamber of an internal combustion engine and realizes an appropriate operation.

  Nowadays, new cars are obliged to have an on-board diagnostics (OBD) function. When an abnormality such as exhaust gas is detected, a warning is issued to the driver and the diagnostic result of the failure is recorded by the ECU. It has become. Further, an engine equipped with a misfire detection function as an OBD correspondence is increasing.

  In addition, research on detecting a misfire state has been made by focusing on the ionic current generated in the combustion chamber of the internal combustion engine, and the present applicant has already filed a patent application for a misfire detection device with high detection accuracy (patent). Literature 1-5).

  For example, in the invention described in the cited document 1, the ion detection signal from the ion current detection circuit is converted into a binary determination pulse, and misfire detection is performed based on the pulse width of the determination pulse. Specifically, the pulse widths of the plurality of obtained determination pulses are averaged, and when the average value is smaller than the determination threshold, it is determined that the misfire state is present.

  In addition, for the ion detection signal that maintains a predetermined level or higher, the integral value (cumulative value) is calculated, and it is determined whether the state is a combustion state or a misfire state by comparing the cumulative value with the determination threshold value. On the other hand, when the number of times determined to be a misfire state exceeds a reference value in a plurality of ignition cycles (for example, 300 times), a warning operation or the like is executed as an OBD.

  However, regardless of which method is used, the determination threshold is fixedly defined based on the driving state. Here, the operating state is specified by, for example, the number of rotations of the crankshaft or the intake pipe pressure, and a determination threshold value corresponding to the specified operating state is generally extracted from the parameter table of the memory and used. It is.

Japanese Patent Application No. 2006-130935 JP 2010-0777804 A JP 2010-059905 A JP 2010-053781 A JP 2010-053780 A

  By the way, regardless of whether the determination is based on the pulse width of the ion detection signal or the integration value of the ion detection signal, it is extremely important to reduce the number of erroneous determinations in order to increase the accuracy of the OBD. .

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a combustion control device for an internal combustion engine that can make a more accurate and rational combustion determination.

  In order to achieve the above object, as a result of repeating various experiments by the inventor, the operation state is specified based on the detection values of various sensors, and a determination threshold corresponding to the operation state is extracted from the parameter table. The present invention has been completed by finding that a more accurate and rational misfire determination can be made by correcting the determination threshold based on the result of the most recent misfire determination instead of making a normal determination.

  That is, the combustion control device for an internal combustion engine according to the present invention is configured to have a plurality of cylinders, and the air-fuel mixture introduced into the combustion chambers of the respective cylinders is subjected to ignition control in turn each time the ignition timing is reached. For the engine, detection means for specifying the operating state by specifying the rotation speed of the crankshaft of the internal combustion engine and / or the amount of intake air to the combustion chamber prior to the ignition timing of each combustion chamber, In the combustion determination process for the combustion chamber whose ignition control is performed at the immediately preceding timing, and the determination means for initially determining the determination threshold value of the combustion determination process for the combustion chamber that reaches the next ignition timing based on the specified operating state When the misfire is determined, the correction means for correcting the initially determined determination threshold value and a group of sensor signals after the ignition timing for the combustion chamber in which the determination threshold value is specified Combustion for the combustion chamber by comparing the obtained signal acquisition means and the evaluation data generated by evaluating the sensor signal acquired by the signal acquisition means in the time axis direction with the determination threshold specified by the acquisition means or the correction means. Determination means for executing a determination process.

  The description order of each means constituting the present invention does not necessarily define the operation order. Further, although the determination threshold value correction method is appropriately determined, for example, in order not to continue the erroneous determination that the combustion state is the misfire state in a plurality of cylinders, the next stage determined to be the misfire state. It is preferable to correct the determination threshold value in the direction in which the misfire determination is difficult (sweet direction) in the combustion determination in the cylinders. This is because in the cylinders following the cylinders that were truly misfired, the amount of intake of the air-fuel mixture increased slightly, corresponding to the fact that the number of revolutions of the crankshaft decreased slightly, and an environment that facilitates combustion was prepared. It is taken into consideration.

  In other words, if the preceding misfire determination is correct, the subsequent cylinders normally have the combustion conditions naturally adjusted, so that no problem will occur even if the combustion determination is made based on the sweet determination threshold. On the other hand, when the preceding misfire determination is wrong and it is erroneously determined that it is in the misfire state even though it is in the combustion state, the combustion determination is made based on the sweet determination threshold in the subsequent cylinder. Therefore, it can be expected that a correct determination result can be obtained. In the preceding misfire determination, the combustion state is erroneously determined to be a misfire state. On the other hand, in the subsequent combustion determination based on the corrected determination threshold, the misfire state may be erroneously determined to be the combustion state. However, even in this case, there is a rationality that the cumulative value of the number of times the misfire is determined is the same.

  Contrary to the above-described determination method, in the preceding misfire determination, when it is erroneously determined that it is in the misfire state even though it is in the combustion state, a severe determination threshold (strict direction in the subsequent cylinder) is determined. ), It is highly possible that the combustion state will continue to be misjudged as a misfire state, and the same misjudgment is likely to continue thereafter.

  In any case, in the present invention, the operating state is preferably specified every time the crankshaft reaches a predetermined crank angle. The sensor signal may be generated based on an ionic current generated in the combustion chamber of the internal combustion engine, generated based on a rotational fluctuation of the crankshaft, or generated based on a pressure in the combustion chamber. preferable.

  The sensor signal based on the ionic current generated in the combustion chamber of the internal combustion engine, the sensor signal generated based on the crankshaft rotational fluctuation, and the sensor signal generated based on the combustion chamber pressure are all or partly combined. A configuration that is used is also suitable.

  According to the above-described present invention, the combustion determination in the subsequent cylinder is executed based on the determination result of the preceding cylinder, so that a more accurate and rational misfire determination can be realized.

It is a circuit diagram which shows the combustion control apparatus which concerns on an Example. It is a flowchart explaining the processing content of an Example. It is a schematic diagram explaining the operation | movement content of an Example.

  Hereinafter, the present invention will be described in detail based on examples. FIG. 1 is a circuit diagram of a combustion control device EQU according to an embodiment. Note that the internal combustion engine (engine) of this embodiment is composed of three cylinders (# 1 to # 3) (see FIG. 3), and the ignition plugs PG of each cylinder are controlled in order, but in FIG. Only a single spark plug PG is shown.

  As shown in FIG. 1, this combustion control device EQU receives an output data of an ion current detection circuit ION that outputs an ion signal Vo, an AD conversion unit 14 that digitally converts the ion signal Vo, and output data of the AD conversion unit 14, and burns. The computer circuit 15 that executes the determination process and the ECU (Engine Control Unit) that outputs the ignition pulse IGN and receives the combustion determination result from the computer circuit 15 are mainly configured.

  In this circuit configuration, the ion current detection circuit ION and the AD conversion unit 14 constitute a signal acquisition unit. The AD conversion unit 14 has a sample and hold function, and the computer circuit 15 includes, for example, a DSP (Digital Signal Processor) as a component.

  The ion current detection circuit ION includes an ignition transformer CL including a primary coil L1 and a secondary coil L2, a switching element Q that controls ON / OFF of the current of the primary coil L1 by a transition operation based on the ignition pulse IGN, and a secondary coil L2. The ignition plug PG that receives the induced voltage and performs a discharging operation and the signal detection unit DET are mainly configured.

  Here, an IGBT (Insulated Gate Bipolar Transistor) is used as the switching element Q. The collector terminal of the switching element Q receives the battery voltage VB via the primary coil L1, and the emitter terminal is connected to the ground.

  The signal detection unit DET is configured around an OP amplifier AMP that functions as a current detection circuit, and includes a capacitor C1, a Zener diode ZD, diodes D1 and D2, and resistors R1 to R3. A bias circuit at the time of ion current detection is generated by a parallel circuit of the capacitor C1 and the Zener diode ZD.

  The high voltage terminal of the secondary coil L2 is connected to the spark plug PG, and the low voltage terminal is connected to a parallel circuit of the capacitor C1 and the Zener diode ZD that generate the bias voltage. The parallel circuit of the capacitor C1 and the Zener diode ZD is connected to the ground through the diode D1. As illustrated, the cathode terminal of the diode D1 is connected to the ground.

  On the other hand, the anode terminal of the diode D1 is connected to the inverting input terminal (−) of the OP amplifier via the current limiting resistor R1. A current detection resistor R2 is connected between the inverting input terminal (−) and the output terminal of the OP amplifier AMP, and a load resistor R3 is connected between the output terminal and the ground. The non-inverting terminal (+) of the OP amplifier is connected to the ground, and the cathode terminal of the diode D2 is connected to the inverting terminal (−). The anode terminal of the diode D2 is connected to the ground.

  In the ion current detection circuit ION having the above-described configuration, when the ignition pulse IGN changes from the H level to the L level, the ignition plug PG is discharged by the high voltage induced in the secondary coil L2. Since this discharge current flows through the path of the spark plug PG → secondary coil L2 → capacitor C1 → diode D1, the capacitor C1 is charged to a voltage value defined by the breakdown voltage of the Zener diode ZD.

  When the air-fuel mixture in the combustion chamber is ignited by the discharge of the ignition plug PG, the combustion reaction proceeds rapidly thereafter, but the ionic current i is the current detection resistance R2 → current limiting resistance R1 → capacitor C1 → secondary coil L2. → Flows along the path of the spark plug PG. Therefore, the output voltage Vo of the ion current detection circuit ION is Vo = R2 * i, which is a value proportional to the ion current i.

  FIG. 2 is a flowchart showing software processing of the embodiment realized in the computer circuit 15. FIG. 2A shows a combustion determination process executed after the ignition operation of each cylinder, and FIG. 2B shows a measurement process executed at the timing of TDC (Top Dead Center).

  As described above, since this embodiment is a three-cylinder engine, as shown in FIG. 3, the timings of crank angles CA = 0 °, CA = 240 °, CA = 480 ° are set to each cylinder (# 1 to # 3). Therefore, in the measurement process shown in FIG. 2B, signals from various sensors are acquired at each TDC timing (ST10), and the engine speed and intake air are based on the elapsed time from the previous TDC. The quantity is specified and stored (ST11). Note that the engine speed and the intake air amount are operation amounts that specify an operation state for determining the cut-out window Win and the determination threshold value TH for a cylinder whose ignition timing comes later, and are real-time for each measurement process. Change.

  When the ignition timing of any cylinder is reached after such measurement processing, the ignition pulse IGN is supplied to the ignition transformer CL and the combustion determination processing of FIG. 2A is started. In the combustion determination process, the operation parameter table TBL1 (FIG. 2 (c)) is searched based on the operation state specified by the measurement process (FIG. 2 (b)), and the start and end of the cut window Win are specified. (ST20).

  Here, in the operation parameter table TBL1, various operation parameters including the cut window Win and the determination threshold value TH are stored corresponding to the operation state. In this embodiment, the operating state is specified based on the engine speed and the intake air amount. However, the operating state may be specified based on conditions that change to these, and other conditions may be specified. Of course, the operating condition may be specified by adding the above condition.

  Next, among the ion signals acquired after the ignition timing for the ignited cylinder, a series of ion signals Di for the set cut window Win section are acquired and stored (ST21). Although not particularly limited, in this embodiment, the sampling frequency fs is set to 30 kHz. Then, the sum (integral value) SUM = ΣABS (Di) of the absolute value ABS (Di) of the ion signal Di that maintains a level equal to or higher than a predetermined value in the series of ion signals Di is calculated and stored ( ST22).

  Subsequently, the operation parameter table TBL1 is searched based on the engine speed and the intake air amount stored in the process of step ST11, and the determination threshold value TH for evaluating the integral value SUM in step ST22 is initially set. (ST23).

  Then, the value of the error flag ER is determined. If the error flag ER is ER = 1, the correction coefficient table TBL2 is searched based on the engine speed and the intake air amount specified in the process of step ST11. Thus, the determination threshold value TH that is initially set in the process of step ST23 is appropriately corrected (ST25). Although not particularly limited, for example, a correction operation for adding the correction coefficient value AM to the initially set determination threshold value TH is executed (TH ← TH × AM).

  Here, the error flag ER means that it has been determined that a misfire state has occurred in the combustion determination in the preceding cylinder. In the schematic diagram of FIG. 3, the first cylinder # 1 is in the combustion state, but the second cylinder # 2 is in the misfire state, and the pressure waveforms of the cylinders # 1 to # 3 are illustrated. Is also shown schematically. Assuming the combustion operation of the third cylinder in such a case, the second cylinder misfires, so the rotational speed slightly decreases transiently, and the air-fuel mixture in the third cylinder due to the intake inertia. The filling rate becomes higher. Therefore, generally, in the combustion chamber of the third cylinder, combustion is easy, and the pressure in the cylinder tends to increase during combustion (# 3 pressure waveform in FIG. 3).

  However, although the second cylinder is in the combustion state, the possibility of misjudgment that it is in the misfire state cannot be denied in the combustion determination processing. Therefore, in this embodiment, when the misfire determination is made in the previous cylinder, the determination accuracy is improved by correcting the determination threshold value for the combustion determination process in the subsequent cylinder.

  As the correction coefficient of the present embodiment, an optimum value obtained experimentally in advance is stored in the correction coefficient table TBL2 for each operating state. Therefore, although it cannot be generally stated, a general tendency of the correction coefficient is a numerical value that does not allow erroneous determination that the combustion state is a misfire state to be continued in a plurality of cylinders. Specifically, in the combustion determination in the next-stage cylinder determined to be in the misfire state, the correction threshold value is a correction coefficient value that corrects the determination threshold in a direction in which the misfire determination is difficult (sweet direction).

  In any case, using the initially set determination threshold value TH or the determination threshold value TH that has undergone correction calculation, the integrated value SUM in step ST22 is compared with the determination threshold value TH (ST25). For example, if SUM> TH, the combustion chamber of the cylinder is determined to be in a combustion state, and if SM ≦ TH, it is determined to be in a misfire state (ST26).

  When it is determined that the combustion state is present, the error flag ER is set to ER = 0, and combustion control during combustion is executed (ST27). On the other hand, if it is determined that there is a misfire state, the error flag ER is set to ER = 1, the cumulative misfire count CT is incremented (CNT ← CNT + 1), and combustion control at the time of misfire is executed (ST28).

  If the cumulative misfire count CT exceeds the reference value at the timing when a predetermined ignition cycle is completed, an OBD (On-Board Diagnostics) process is started. However, in this embodiment, since the combustion determination is executed by dynamically correcting the determination threshold value, the accuracy of the misfire determination is increased, and it is possible to prevent an alarm from being issued without meaning.

  As mentioned above, although the Example of this invention was described in detail, the specific description content does not specifically limit this invention, and an appropriate modification | change is possible. For example, in the above embodiment, the ion signal is exclusively used. However, the ion signal can be used in the same manner when the combustion is determined based on the crankshaft rotation fluctuation or the pressure signal indicating the internal pressure of the cylinder. In this case, it is also preferable to appropriately combine the ion signal, the crankshaft rotational fluctuation, and the pressure signal indicating the cylinder internal pressure.

  In the embodiment, the time elapse of steps ST20 to ST26 has been described, but this order can be changed as appropriate. For example, the process of steps ST23 to ST25 may be preceded by the process of step ST21.

ST11 Detection means ST23 Determination means ST25 Correction means ST21 Signal acquisition means ST26 Determination means

Claims (6)

For an internal combustion engine that is configured to have a plurality of cylinders, and that the air-fuel mixture introduced into the combustion chamber of each cylinder is subjected to ignition control in turn each time the ignition timing is reached,
Prior to the ignition timing of each combustion chamber, detection means for identifying the operating state by identifying the number of revolutions of the crankshaft of the internal combustion engine and / or the amount of intake air into the combustion chamber;
A determination means for initially determining a determination threshold value of the combustion determination process for the combustion chamber that reaches the next ignition timing based on the operation state specified by the detection means;
In the combustion determination process for the combustion chamber whose ignition is controlled at the immediately preceding timing, when misfiring is determined, correcting means for correcting the initially determined determination threshold;
Signal acquisition means for acquiring a group of sensor signals after the ignition timing for the combustion chamber for which the determination threshold is specified;
Determination for executing the combustion determination process for the combustion chamber by comparing the evaluation data generated by evaluating the sensor signal acquired by the signal acquisition unit in the time axis direction with the determination threshold specified by the acquisition unit or the correction unit. Means,
A combustion control apparatus for an internal combustion engine, comprising:   The combustion control device according to claim 1, wherein the operating state is specified every time the crankshaft reaches a predetermined crank angle.   The combustion control device according to claim 1, wherein the sensor signal is generated based on an ionic current generated in a combustion chamber of an internal combustion engine.   The combustion control device according to claim 1, wherein the sensor signal is generated based on a rotational fluctuation of a crankshaft.   The combustion control device according to claim 1, wherein the sensor signal is generated based on a pressure in the combustion chamber.   Sensor signals based on ion currents generated in the combustion chamber of the internal combustion engine, sensor signals generated based on crankshaft rotation fluctuations, and sensor signals generated based on combustion chamber pressure are all or partly combined. The combustion control device according to claim 1 or 2, which is used.

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