JP2013174144A - Combustion state determining device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further improve the combustion determination accuracy with reference to ion current.SOLUTION: In the case a length of a period where an ion current signal during an expansion stroke measured via a circuit for sensing ion current is higher than a determination threshold value is shorter than a lower limit value, the rotation rate of a crankshaft of an internal combustion engine after ignition is referred to. If raise of the rotation rate is sensed in a predetermined period after the ignition, it is determined that insulating foreign matters are adhered on an electrode of an ignition plug or the circuit is abnormal. If raise of the rotation rate is not sensed in the predetermined period after ignition, it is determined that combustion in the cylinder is defective or misfire.

Description

  The present invention relates to a determination device that determines a combustion state in a cylinder of an internal combustion engine.

  As a method for estimating the combustion state of the fuel in the cylinder, one that detects and refers to the ionic current flowing through the electrode of the spark plug during combustion is known (see, for example, Patent Document 1 below). During poor combustion such as over lean, the peak of the ionic current is lower than during normal combustion. Moreover, at the time of misfire, an ion current cannot be detected in the first place. It is possible to determine whether or not the combustion in the cylinder is normal by measuring the transition of the ion current and comparing the measured value with a threshold value for determination.

  In detecting the ionic current, it is usual to apply a high bias voltage due to the charge stored in the capacitor to the center electrode of the spark plug (see, for example, Patent Document 2 below).

  By the way, as the use period of the spark plug becomes longer, deposits such as fuel components, lubricating oil, and additives gradually adhere to and accumulate on the electrodes. In particular, a deposit containing an insulating material such as silicon dioxide (silica) acts like an electric resistance that reduces the amount of ionic current flowing through the electrode of the spark plug, so that the fuel burns properly in the combustion chamber. Even if ions are generated, the measured value of the ionic current does not exceed the determination threshold value, and there is a possibility that it is erroneously determined as a combustion failure or misfire.

Japanese Patent Application Laid-Open No. 06-034490 JP 2006-200432 A

  An object of the present invention is to further improve the accuracy of determination of a combustion state with reference to an ionic current.

  In the present invention, a circuit that detects an ionic current flowing through an electrode of a spark plug during combustion is used to determine a combustion state in a cylinder of an internal combustion engine, and during an expansion stroke measured through the circuit When the length of the period during which the ionic current signal exceeds the determination threshold is less than the lower limit value, the rotational speed of the crankshaft of the internal combustion engine after ignition is referred to, and the rotational speed increases within a predetermined period after ignition. When it is detected that there has been an insulating foreign matter attached to the electrode of the spark plug or an abnormality has occurred in the circuit, it is determined that the rotational speed has increased within a predetermined period after ignition. When not detected, the combustion state determination device for the internal combustion engine is configured to determine that the combustion in the cylinder is defective or misfire.

  According to the present invention, the accuracy of the knocking determination with reference to the ionic current can be further improved.

The figure which shows schematic structure of the internal combustion engine in one Embodiment of this invention. The circuit diagram of the spark ignition device of an internal combustion engine. The figure which shows each transition of the ionic current and combustion pressure in the cylinder of an internal combustion engine. The figure which illustrates the state from which the detected ion current signal became "upper limit sticking". The figure which illustrates the state from which the detected ionic current signal became "lower limit sticking". The flowchart which shows the example of a procedure of the process which the combustion state determination apparatus of this embodiment performs. The flowchart which shows the example of the procedure of the process which the combustion state determination apparatus performs. The flowchart which shows the example of the procedure of the process which the combustion state determination apparatus performs. The figure which illustrates the pattern of the fluctuation | variation of the rotational speed of the internal combustion engine after ignition.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle in the present embodiment.

  The internal combustion engine in the present embodiment is a spark ignition gasoline engine and includes a plurality of cylinders 1 (one of which is shown in FIG. 1). In the vicinity of the intake port of each cylinder 1, an injector 11 for injecting fuel is provided. A spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1.

  FIG. 2 shows an electric circuit for spark ignition. The spark plug 12 receives spark voltage generated by the ignition coil 14 and causes spark discharge between the center electrode and the ground electrode. The ignition coil 14 is integrally incorporated in a coil case together with an igniter 13 that is a semiconductor switching element.

  When the igniter 13 receives an ignition signal i from an ECU (Electronic Control Unit) 0 that is a combustion state determination device of the present embodiment, the igniter 13 is first ignited, and a current flows to the primary side of the ignition coil 14. The igniter 13 is extinguished at the ignition timing, and this current is interrupted. Then, a self-induction action occurs, and a high voltage is generated on the primary side. Since the primary side and the secondary side share the magnetic circuit and the magnetic flux, a higher induced voltage is generated on the secondary side. This high induction voltage is applied to the center electrode of the spark plug 12, and a spark discharge occurs between the center electrode and the ground electrode.

  The ECU 0 detects an ionic current generated in the combustion chamber of the cylinder 1 during the explosion combustion of the fuel, and refers to the ionic current to determine the combustion state.

  As shown in FIG. 2, in this embodiment, a circuit for detecting an ionic current is added to the electric circuit for spark ignition. This detection circuit includes a bias power supply unit 15 for effectively detecting an ionic current and an amplification unit 16 that amplifies and outputs a detection voltage corresponding to the amount of the ionic current. The bias power supply unit 15 includes a capacitor 151 that stores a bias voltage, a Zener diode 152 for increasing the voltage of the capacitor 151 to a predetermined voltage, current blocking diodes 153 and 154, and a load that outputs a voltage corresponding to the ion current. A resistor 155. The amplifying unit 16 includes a voltage amplifier 161 typified by an operational amplifier.

  The capacitor 151 is charged during arc discharge between the center electrode and the ground electrode of the spark plug 12, and then an ion current flows through the load resistor 155 by the bias voltage charged in the capacitor 151. The voltage between both ends of the resistor 155 generated by the flow of the ionic current is amplified by the amplifying unit 16 and received by the ECU 0 as the ionic current signal h.

  FIG. 3 illustrates respective transitions of the ionic current (indicated by a solid line in the figure) and the combustion pressure in the cylinder 1 (in-cylinder pressure; indicated by a broken line in the figure) in normal combustion. The ionic current cannot be detected during the discharge for ignition. In the case of normal combustion, the ionic current decreases by a chemical reaction before the compression top dead center after the end of spark ignition, and then increases again by thermal dissociation. In addition, the ionic current reaches a maximum almost simultaneously with the peak of the combustion pressure.

  The intake passage 3 for supplying intake air takes in air from the outside and guides it to the intake port of each cylinder 1. On the intake passage 3, an air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from the upstream.

  The exhaust passage 4 for discharging the exhaust guides the exhaust generated as a result of burning the fuel in the cylinder 1 from the exhaust port of each cylinder 1 to the outside. An exhaust manifold 42 and an exhaust purification three-way catalyst 41 are disposed on the exhaust passage 4.

  The ECU 0 that controls operation of the internal combustion engine is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like.

  The input interface includes a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal (N signal) b output from an engine rotation sensor that detects the rotation angle of the crankshaft and the engine speed, An accelerator opening signal c output from a sensor that detects the amount of depression of the accelerator pedal or the opening of the throttle valve 32 as an accelerator opening (so-called required load), and a brake that is output from a sensor that detects the amount of depression of the brake pedal Stepping amount signal d, intake air temperature / intake pressure signal e output from a temperature / pressure sensor for detecting intake air temperature and intake pressure in intake passage 3 (especially surge tank 33), water temperature sensor for detecting engine cooling water temperature Output from the cam angle sensor at multiple cam angles of the cooling water temperature signal f output from the intake camshaft or exhaust camshaft A cam angle signal (G signal) g is the ion current signal h or the like to be output from the circuit for detecting an ion current caused by the combustion of the mixture in the combustion chamber are inputted.

  From the output interface, an ignition signal i is output to the igniter 13 of the spark plug 12, a fuel injection signal j is output to the injector 11, an opening operation signal k is output to the throttle valve 32, and the like.

  The processor of the ECU 0 interprets and executes a program stored in the memory in advance, calculates operation parameters, and controls the operation of the internal combustion engine. The ECU 0 acquires various information a, b, c, d, e, f, g, and h necessary for operation control of the internal combustion engine via the input interface, knows the engine speed, and is filled in the cylinder 1. Estimate the intake volume. Based on the engine speed, the intake air amount, and the like, various operating parameters such as required fuel injection amount, fuel injection timing (including the number of times of fuel injection for one combustion), fuel injection pressure, and ignition timing are determined. As the operation parameter determination method itself, a known method can be adopted. The ECU 0 applies various control signals i, j, k corresponding to the operation parameters via the output interface.

  In addition, the ECU 0 executes a fuel cut that temporarily stops fuel injection from the injector 11 (and ignition by the spark plug 12) according to the driving situation. Normally, when the accelerator pedal depression amount is 0 or less than a threshold value close to 0 and the engine speed is equal to or higher than the fuel cut permission speed, the fuel cut is started assuming that the fuel cut condition is satisfied. The fuel cut permission rotational speed is higher than the target engine rotational speed during idle operation, and the internal combustion engine immediately before entering the fuel cut is not in an idling state.

  After the fuel cut is started, if any fuel cut end condition is satisfied, such as when the accelerator pedal depression amount exceeds the threshold value or the engine speed has decreased to the fuel cut return speed, the fuel cut ends. Then, the fuel injection (and ignition) is restarted. When the engine speed has decreased to the fuel cut return speed, the engine shifts to the idling state when the fuel cut is completed.

  Hereinafter, the determination of the combustion state with reference to the ion current signal h and the diagnosis will be described in detail. Whether the combustion in the cylinder 1 is correct or not is determined with reference to a detection signal h of an ionic current that occurs during the expansion stroke in the combustion chamber of the cylinder 1 and flows through the electrode of the ignition plug 12 of the cylinder 1. That is, as shown in FIG. 3, the ECU 0 measures the length of the period T (crank angle (CA) or time) during which the ion current signal h exceeds the determination threshold in the expansion stroke, and the length If it is longer than a certain lower limit value, it is determined as normal combustion, while if it is shorter than the lower limit value, it is determined as defective combustion or misfire.

  Incidentally, the magnitude of the determination threshold value may vary depending on the operating range of the internal combustion engine, that is, the number of engine revolutions and / or the required load (the intake amount charged into the cylinder 1 and the fuel injection amount). For example, the memory of the ECU 0 stores map data that defines the relationship between the engine speed and / or the required load and the corresponding determination threshold value. The ECU 0 searches the map using the current engine speed and / or required load as a key, and knows the corresponding determination threshold value. Then, the period T is calculated using the determination threshold.

  However, it is not always possible to obtain the waveform of the ion current signal h as shown in FIG. Deposits gradually adhere to and accumulate on the electrodes of the spark plug 12 as the period of use increases. Deposits include smoldering plugs 12, in other words, conductive materials such as carbon, and insulating materials such as silicon dioxide derived from additives added to fuel and lubricants. To do.

  If a large amount of deposit containing a conductive material adheres to the spark plug 12, the center electrode and the ground electrode of the spark plug 12 are short-circuited. In this case, a charge current flows between the electrodes even though ions or plasma caused by combustion is not generated in the combustion chamber of the cylinder 1. As a result, as illustrated in FIG. 4, the current signal h exceeding the determination threshold is continuously detected, and the situation becomes “upper limit”. This “upper limit sticking” also occurs when the spark ignition circuit or the ion current detection circuit shown in FIG. 2 is short-circuited so as to bypass the electrode of the spark plug 12.

  In turn, if a large amount of deposit containing an insulating material adheres to the spark plug 12, the center electrode and the ground electrode of the spark plug 12 are permanently insulated. Then, although ions or plasma resulting from combustion is generated in the combustion chamber of the cylinder 1, no ion current flows between the electrodes. As a result, as illustrated in FIG. 5, the current signal h does not exceed the determination threshold value, or the period T during which the current signal h exceeds the determination threshold value is always “shortened to the lower limit”. This “lower limit sticking” is not only in the case of defective combustion or misfiring in the combustion chamber of the cylinder 1, but also in the case where the circuit is broken at any part of the spark ignition circuit or the ion current detection circuit shown in FIG. This also occurs when the injector 11 or the igniter 13 fails.

  The ECU 0 of the present embodiment also performs a diagnosis of the ignition plug 12, the spark ignition circuit, the ion current detection circuit, the injector 11 or the igniter 13 as well as the determination of the combustion state in each cylinder 1.

  6 to 8 show an example of the procedure of the combustion state determination process executed by the ECU 0 according to the present embodiment according to the program. The procedure shown in FIGS. 6 to 8 is executed individually for each cylinder 1.

  The ECU 0 measures a period T during which the ion current signal h exceeds the determination threshold during the expansion stroke of the target cylinder 1 (step S1). Then, it is determined whether or not the length of the period T is within the normal range (step S2). If the period T is not less than a certain lower limit value and not more than a certain upper limit value, it is determined that the combustion in the expansion stroke of the cylinder 1 is normal.

  When the period T is longer than the upper limit value (step S3), it is in the state of “upper limit sticking” described above. If the “upper limit” for the target cylinder 1 is continuously repeated for a predetermined number of times or more (step S4), a smoldering or other failure of the spark plug 12 is suspected, and the process proceeds to step S9 shown in FIG. Transition.

  When the period T is shorter than the lower limit value, the situation is the “lower limit sticking” state described above. If the target cylinder 1 continues to be “fixed with the lower limit” continuously over a predetermined number of times (step S5), adhesion of silicon dioxide or the like to the spark plug 12 or other failure is suspected, as shown in FIG. The process proceeds to step S23.

  If the “lower limit sticking” does not continue for a predetermined number of times or is a single occurrence, it is temporarily determined that a combustion failure or misfire has occurred in the cylinder 1. Therefore, the ECU 0 increases the number of misfires stored in the memory by 1 (step S6). If the misfire counter exceeds a predetermined value (step S7), it is determined that the misfire is abnormal and a message to that effect is output (step S8).

  The misfiring abnormality means that normal combustion cannot be performed due to deterioration of the spark discharge capability by the spark plug 12, damage to the igniter 13, short-circuiting or disconnection of the electric circuit for spark discharge, defective fuel injection operation of the injector 11, and the like. It is the situation. In step S8, the ECU 0 writes information indicating the misfire abnormality in the memory, and stores and retains the information to help the cause investigation in the subsequent repair work. In addition, the ECU 0 informs the user's vision or hearing that the misfire is abnormal. For example, a warning light installed in the cockpit is turned on, a warning is displayed on the display, or a warning sound is output from a buzzer or a speaker.

  If it is determined in step S4 that "upper limit sticking" has been repeated for a predetermined number of times or more, then it is checked whether "upper limit sticking" has occurred even during fuel cut (step S9). . If “upper limit sticking” occurs even during fuel cut, there is a high probability that an abnormality has occurred in at least one of the spark plug 12 or the ion current detection circuit.

  In a situation where “upper limit” continues, it is difficult to determine the combustion state with reference to the ion current signal h. Therefore, the ECU 0 refers to the rotational speed of the crankshaft during the expansion stroke of the target cylinder 1 to estimate whether combustion in the cylinder 1 is correct. That is, the rotation speed of the crankshaft when the ignition signal i is input to the igniter 13 associated with the ignition plug 12 of the cylinder 1 and the predetermined period (crank angle (CA) or time) from the input of the ignition signal i. Both the rotation speed of the crankshaft is measured, and it is determined whether or not the latter is higher than the former (step S10). The rotation speed of the crankshaft can be obtained by measuring the time required for the crankshaft to rotate at a predetermined crank angle (for example, 30 ° CA).

  FIG. 9 illustrates the transition of the rotational speed of the crankshaft within a predetermined period from the input of the ignition signal i. When the spark plug 12 of the target cylinder 1 sparks and ignites the air-fuel mixture in the combustion chamber of the cylinder 1 and combusts appropriately (shown by the solid line in the figure), the rotational speed should increase after ignition. It is. On the other hand, if the air-fuel mixture in the combustion chamber of the cylinder 1 does not burn properly (indicated by a broken line in the figure), the rotational speed will not increase after ignition, but rather will decrease.

  When the rotational speed increases after ignition, it is presumed that normal combustion has occurred in the cylinder 1, and therefore, the ignition timing retardation correction as a countermeasure against misfire is avoided (step S11). On the contrary, if the rotational speed does not increase after ignition, it is presumed that the cylinder 1 has failed or misfired, so the number of misfires stored in the memory is incremented by 1 (step S12). When the misfire counter exceeds a predetermined value (step S13), it is determined that the misfire is abnormal and a message to that effect is output (step S14). Step S14 is equivalent to step S8.

  Further, regardless of whether the combustion in the cylinder 1 is correct or not, it is confirmed whether or not there is a history of operation for cleaning the spark plug 12 (step S15), and there is a history of operation for cleaning. If not, an operation for cleaning is attempted (step S16). The operation for cleaning the spark plug 12 is a measure for increasing the temperature in the combustion chamber of the cylinder 1 so as to burn and remove carbon or the like adhering to the electrode of the spark plug 12. This includes correction for increasing the fuel injection amount and correction for increasing the engine speed.

  If the operation for cleaning the spark plug 12 has already been performed in the past, the ECU 0 determines that the ion current signal h is abnormal to “stick to the upper limit”, and outputs that fact (step) S17).

  The above-described ion current detection abnormality is caused by the fact that carbon or the like cannot be removed from the spark plug 12 even by the operation for cleaning, or other reasons, that is, a short circuit of the circuit that bypasses the electrode of the spark plug 12. This means that the “upper limit” of the ion current signal h cannot be resolved. In step S17, the ECU 0 writes information indicating that the ionic current detection is abnormal in the memory, and stores and retains the information to help investigate the cause in the subsequent repair work. In addition, the ECU 0 notifies the user of visual or auditory sense that the ionic current detection is abnormal. For example, a warning light installed in the cockpit is turned on, a warning is displayed on the display, or a warning sound is output from a buzzer or a speaker.

  If it is determined in step S9 that “upper limit sticking” has not occurred during the fuel cut, there is a possibility that no serious abnormality has occurred in the spark plug 12 or the ion current detection circuit. However, in a situation where “upper limit” continues, it is still difficult to determine the combustion state with reference to the ion current signal h. Therefore, the ECU 0 rotates the crankshaft when the ignition signal i is input to the igniter 13 associated with the ignition plug 12 of the target cylinder 1, and the rotation speed of the crankshaft within a predetermined period from the input of the ignition signal i. And determine whether or not the latter is higher than the former (step S18).

  When the rotational speed increases after ignition, it is presumed that normal combustion has occurred in the cylinder 1, and therefore, the ignition timing retardation correction as a countermeasure against misfire is avoided (step S19).

  If the rotational speed does not increase after ignition, it is presumed that the cylinder 1 has burnt badly or misfired, so the number of misfires stored in the memory is incremented by 1 (step S20). When the misfire counter exceeds a predetermined value (step S21), it is determined that the misfire is abnormal and the fact is output (step S22). Step S22 is equivalent to step S8.

  If it is determined in step S5 that “sticking to the lower limit” continues for a predetermined number of times or more, then when the ignition signal i is input to the igniter 13 associated with the ignition plug 12 of the target cylinder 1 Both the rotation speed of the crankshaft and the rotation speed of the crankshaft within a predetermined period from the input of the ignition signal i are measured, and it is determined whether or not the latter is higher than the former (step S23).

  When the rotational speed increases after ignition, it is presumed that normal combustion has occurred in the cylinder 1, and therefore, the ignition timing retardation correction is not performed as a countermeasure against misfire (step S24).

  However, the assumption that normal combustion has occurred in the cylinder 1 is completely contradictory to the fact that the ionic current signal h is in the “lower limit stuck” state, and whichever of the ignition plug 12 or the ionic current detection circuit is used. There is a high probability that an abnormality has occurred in at least one of them. Therefore, the ECU 0 determines that the ion current signal h is an abnormality that “sticks to the lower limit”, and outputs that fact (step S25).

  The above ionic current detection abnormality is caused by the fact that silicon dioxide or the like adheres to the electrode of the spark plug 12 and the ionic current does not flow to the electrode, or other causes, that is, the disconnection of the circuit for detecting the ionic current. This means that the ion current that should have flowed to the electrode of the plug 12 cannot be detected, and the “lower limit sticking” of the ion current signal h cannot be eliminated. In step S25, the ECU 0 writes information indicating the abnormality of the ionic current detection in the memory, and stores and holds the information to help the cause investigation in the subsequent repair work. This information is different from the information in step S17. In addition, the ECU 0 notifies the user of visual or auditory sense that the ionic current detection is abnormal. For example, a warning light installed in the cockpit is turned on, a warning is displayed on the display, or a warning sound is output from a buzzer or a speaker.

  If the rotational speed does not increase after ignition, it is presumed that the cylinder 1 has burnt badly or misfired, so the number of misfires stored in the memory is incremented by 1 (step S26). If the misfire counter exceeds a predetermined value (step S27), it is determined that the misfire is abnormal and a message to that effect is output (step S28). Step S28 is equivalent to step S8.

  In the present embodiment, a circuit that detects an ionic current flowing through the electrode of the spark plug 12 during combustion is used to determine the combustion state in the cylinder 1 of the internal combustion engine, and is measured via the circuit. When the length of the period T during which the ionic current signal h during the expansion stroke exceeds the determination threshold is less than the lower limit value, the rotational speed of the crankshaft of the internal combustion engine after ignition is referred to, and the rotational speed is When it is detected that the temperature has risen within a predetermined period, it is determined that an insulating foreign matter is attached to the electrode of the spark plug 12 or an abnormality has occurred in the circuit (step S25), while the rotational speed is ignited. When it is not detected that the engine has risen within a predetermined period thereafter, it is determined that the combustion in the cylinder 1 is defective or misfiring (step S26). 0 to constitute a.

  According to the present embodiment, even if the proper waveform of the ionic current signal h cannot be detected due to secular changes such as deposits adhering to and accumulating on the spark plug 12, fuel combustion is normally performed in the cylinder 1. It is possible to more accurately determine whether or not it has been received.

  Furthermore, when the waveform of the detected ion current signal h is in the “fixed lower limit” state, this is due to defective combustion or misfiring (including disconnection of a circuit for spark ignition and failure of the igniter 13), or an ignition plug It is possible to determine whether or not the detection level of the ion current signal h has decreased due to silicon dioxide adhering to 12 or the like. Since the cause of the abnormality can be identified and identified, it is not necessary to perform unnecessary or inappropriate maintenance, which contributes to a reduction in operation cost.

  The present invention is not limited to the embodiment described in detail above. Various modifications can be made to the specific configuration of each part, processing procedure, and the like without departing from the spirit of the present invention.

  The present invention can be applied to control of an internal combustion engine mounted on a vehicle or the like.

0 ... Combustion state determination device (ECU)
DESCRIPTION OF SYMBOLS 1 ... Cylinder 12 ... Spark plug h ... Ion current signal T ... Period when the ion current signal is over the determination threshold value

Claims (1)

Using a circuit that detects an ionic current flowing through the electrode of the spark plug during combustion, the combustion state in the cylinder of the internal combustion engine is determined,
When the length of the period during which the ionic current signal during the expansion stroke measured via the circuit exceeds the determination threshold is less than the lower limit value, refer to the rotational speed of the crankshaft of the internal combustion engine after ignition,
When it is detected that the rotational speed has increased within a predetermined period after ignition, it is determined that an insulating foreign matter is attached to the electrode of the spark plug or an abnormality has occurred in the circuit,
A combustion state determination device for an internal combustion engine, characterized in that, when it is not detected that the rotational speed has risen within a predetermined period after ignition, the combustion in the cylinder is determined to be defective or misfiring.

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