JP2009057839A - Misfire detection system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent overheating of a catalyst by misfire and improve misfire/ignition determining accuracy, in a system for determining the existence of misfire by detecting ion current generated in response to combustion of an air/fuel mixture in a combustion chamber of an internal combustion engine via a spark plug and comparing the detected value with a misfire determining value. <P>SOLUTION: A first misfire determining value Vth1 is set in the vicinity of the minimum value of the ion current during normal combustion, and a second misfire determining value Vth2 smaller than the first misfire determining value Vth1 is set in the vicinity of the maximum value of noise when complete misfire occurs. When the engine operating condition is such that a frequency of occurrence of misfire is low in a region where the temperature of the catalyst rises largely when the misfire occurs, the misfire/ignition determining accuracy is improved by determining that the overheating of the catalyst is not caused by the misfire and selecting the second misfire determining value Vth2. On the other hand, when the frequency of occurrence of misfire is high, the misfire detection ability is enhanced by determining that the catalyst may be overheated by the misfire and selecting the first misfire determining value Vth1. It is thus possible to detect the misfire early so that the catalyst overheating prevention process can be carried out promptly. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention detects an ionic current generated by combustion of an air-fuel mixture in a combustion chamber of an internal combustion engine through a spark plug, and determines the presence or absence of misfiring based on the detected ionic current value. It is an invention related to a device.

  In recent years, focusing on the characteristics that ions (combustion ions) are generated when the air-fuel mixture burns in the cylinder of the internal combustion engine, the ion current generated in the cylinder for each ignition is detected via the electrode of the ignition plug, A technique for detecting ignition / misfire based on the detected value of ion current has been developed. The conventional ignition / misfire determination method uses the property that the ion current increases at the time of ignition and decreases when the misfire occurs, and the integrated value or peak value of the ion current detection signal is compared with a predetermined misfire determination value. If the integral value or peak value of the ion current detection signal is greater than or equal to the misfire determination value, it is determined to be ignited; otherwise, it is determined to be misfire (see Patent Document 1: Japanese Patent No. 2505620). .

Furthermore, the misfire detection device described in Patent Document 2 (Japanese Patent No. 2552754) takes into account that the noise level of the ion current detection signal changes according to the operation state of the internal combustion engine, and thus the operation state of the internal combustion engine. By changing the misfire determination value according to the above, the misfire determination value is changed according to the change in the noise level due to the change in the operating state of the internal combustion engine, thereby improving the misfire detection accuracy.
Japanese Patent No. 2505620 (page 4 etc.) Japanese Patent No. 2552754 (3rd page, etc.)

  By the way, when misfire of the internal combustion engine occurs, unburned fuel is discharged to the exhaust passage. Depending on the operating state, the oxidation reaction of the unburned fuel is promoted by the exhaust heat, and the catalyst in the exhaust passage is overheated. Could be damaged. In order to prevent overheating of the catalyst due to such misfire, it is desirable to increase the misfire detection sensitivity (by increasing the misfire determination value so that it can be easily determined that misfire has occurred). However, depending on the operating state of the internal combustion engine, even if misfire occurs, the oxidation reaction of unburned fuel is not accelerated (for example, when the exhaust temperature is low or the oxygen concentration is low), and the catalyst does not become overheated. Regardless of the operation state of the internal combustion engine, if the detection sensitivity of misfire is always increased, there is a problem in that it is easy to erroneously determine ignition as misfire in an operation state in which catalyst overheating due to misfire does not occur.

  The technique of Patent Document 2 is a technique for changing a misfire determination value in accordance with a change in noise level due to a change in the operating state of the internal combustion engine, and has a misfire detection sensitivity in order to prevent overheating of the catalyst due to misfire. Since it is not intended to be high, overheating of the catalyst due to misfire cannot be effectively prevented.

  The present invention has been made in view of such circumstances. Accordingly, the object of the present invention is to provide an internal combustion engine that can achieve both prevention of catalyst overheating due to misfire and improvement in misfire / ignition determination accuracy. The object is to provide a misfire detection device.

  In order to achieve the above object, the invention according to claim 1 includes an ion current detection means for detecting an ion current generated by combustion of the air-fuel mixture in the combustion chamber of the internal combustion engine through the electrode of the spark plug, The first misfire set based on the minimum value of the ion current at the time of normal combustion in the misfire detection device of the internal combustion engine for judging the presence or absence of misfire by comparing the ion current detection value of the ion current detection means with the misfire judgment value Misfire determination value selection for selecting one of the determination value and the second misfire determination value set to a value smaller than the first misfire determination value based on the maximum noise value at the time of misfire as a misfire determination value And a misfire determination value selection means selects a first misfire determination value when a predetermined misfire has occurred in a predetermined operation region of the internal combustion engine, and selects a second misfire determination value when the predetermined misfire has not occurred. Like Those were.

  In this case, the first misfire determination value can be set to a value larger than the second misfire determination value and set near the minimum value of the ion current during normal combustion. The detection value is high (it is easy to determine that there is a misfire). On the other hand, since the second misfire determination value can be set to a value smaller than the first misfire determination value and set near the maximum noise value at the time of misfire, the ignition is compared with the first misfire determination value. It becomes a judgment value that is difficult to misdetermine as misfire.

  Accordingly, as in the present invention, the first misfire determination value is selected when the predetermined misfire occurrence state is set in the predetermined operation region of the internal combustion engine, and the second misfire determination value is selected when the predetermined misfire occurrence state is not set. Then, in a predetermined operation region where the catalyst temperature rise at the time of misfire is large, when a predetermined misfire occurs (for example, when the number of continuous ignitions is small), it is determined that there is a possibility that the catalyst may be overheated due to misfire. By selecting one misfire judgment value, it is possible to increase the misfire detection sensitivity, detect misfire early, and implement catalyst overheat prevention treatment (fuel cut, etc.) early to overheat the catalyst due to misfire. Can be effectively prevented. On the other hand, when it is not in the predetermined misfire occurrence state, it is determined that there is no possibility of overheating of the catalyst due to misfire, and by selecting the second misfire determination value, it is difficult to erroneously determine ignition as misfire. The misfire / ignition judgment accuracy can be made higher than the misfire judgment value. As a result, the misfire / ignition determination accuracy can be improved while effectively preventing overheating of the catalyst due to misfire.

  In this case, as in claim 2, it may be determined whether or not a predetermined misfire has occurred for each cylinder of the internal combustion engine, and a misfire determination value may be selected for each cylinder. In this way, when some cylinders are in a predetermined misfire occurrence state in the predetermined operation region, the first misfire determination value is selected only for the some cylinders to increase the misfire detection sensitivity. The second misfire determination value can be selected for other cylinders that are not in the predetermined misfire occurrence state, and the misfire / ignition determination accuracy can be maintained at a high level. This makes it possible to minimize the cylinders that increase the misfire detection sensitivity (that is, the cylinders that reduce the misfire / ignition determination accuracy) to increase the catalyst overheating prevention effect due to misfire.

  By the way, in the low speed region and low load region of the internal combustion engine, the exhaust gas temperature is low and the exhaust gas flow rate is also small. Therefore, it is not necessary to select the first misfire determination value having high misfire detection sensitivity. In addition, since the ion current during combustion is small in the low rotation region and the low load region, if the first misfire determination value larger than the second misfire determination value is selected, it becomes easy to erroneously determine ignition as misfire.

  In consideration of these circumstances, the process of selecting the misfire determination value in the low rotation region and / or the low load region of the internal combustion engine as in claim 3 may be omitted. In this way, it is possible to always fix the second misfire determination value with high misfire / ignition determination accuracy in the low rotation region and low load region of the internal combustion engine, and to increase the misfire / ignition determination accuracy. be able to.

  Further, as in claim 4, whether or not a predetermined misfire occurrence state may be determined based on the number of consecutive ignitions and / or the misfire occurrence rate. Since the number of continuous ignitions and the rate of misfire are changed depending on the state of misfire, the state of misfire can be accurately determined by using the number of times of continuous ignition and the rate of misfire.

Hereinafter, an embodiment embodying the best mode for carrying out the present invention will be described.
First, the circuit configuration of the ignition control system will be described with reference to FIG.
One end of the primary coil 22 of the ignition coil 21 is connected to the battery 23, and the other end of the primary coil 22 is connected to the collector of the power transistor 25 built in the igniter 24. One end of the secondary coil 26 is connected to a spark plug 27, and the other end of the secondary coil 26 is connected to the ground via two Zener diodes 28 and 29.

  The two Zener diodes 28 and 29 are connected in series in opposite directions, a capacitor 30 is connected in parallel to one Zener diode 28, and an ion current detection resistor 31 is connected in parallel to the other Zener diode 29. A potential Vin between the capacitor 30 and the ionic current detection resistor 31 is input to the inverting input terminal (−) of the inverting amplifier circuit 33 via the resistor 32 and is inverted and amplified. The output voltage V of the inverting amplifier circuit 33 is ionized. The current detection signal is input to the engine control circuit 34. The ion current detection circuit 35 includes Zener diodes 28 and 29, a capacitor 30, an ion current detection resistor 31, an inverting amplification circuit 33, and the like. The ion current detection circuit 35 and the engine control circuit 34 are used to detect an ion current detection device (ion ion). Current detection means).

  During engine operation, the power transistor 25 is turned on / off at the rise / fall of the ignition signal transmitted from the engine control circuit 34 to the igniter 24. When the power transistor 25 is turned on, a primary current flows from the battery 23 to the primary coil 22. After that, when the power transistor 25 is turned off, the primary current of the primary coil 22 is cut off and a high voltage is electromagnetically induced in the secondary coil 26. This high voltage causes spark discharge between the electrodes 36 and 37 of the spark plug 27. This spark discharge current flows from the ground electrode 37 of the spark plug 27 to the center electrode 36, is charged to the capacitor 30 via the secondary coil 26, and flows to the ground side via the Zener diodes 28 and 29. After the capacitor 30 is charged, the ion current detection circuit 35 is driven using the charging voltage of the capacitor 30 regulated by the Zener voltage of the Zener diode 28 as a power source, and the ion current is detected as described later.

  On the other hand, the ionic current flows in the opposite direction to the spark discharge current. In other words, after ignition is finished, a voltage is applied between the electrodes 36 and 37 of the spark plug 27 by the charging voltage of the capacitor 30, so that ions generated when the air-fuel mixture burns in the cylinder are connected between the electrodes 36 and 37. Although an ionic current flows, the ionic current flows from the center electrode 36 to the ground electrode 37, and further flows from the ground side through the ion current detection resistor 31 to the capacitor 30. At this time, the input potential Vin of the inverting amplifier circuit 33 changes according to the change of the ionic current flowing through the ionic current detection resistor 31, and the voltage V corresponding to the ionic current is output to the engine control circuit 34 from the output terminal of the inverting amplifier circuit 33. Is output. An ion current is detected from the output voltage V of the inverting amplifier circuit 33.

  The engine control circuit 34 is mainly composed of a microcomputer, and corresponds to an operating state detected by a rotation angle detection sensor 38 (crank angle sensor), a load detection sensor 39 (intake air amount detection sensor, intake pressure detection sensor) and the like. In addition to performing fuel injection control and ignition timing control, the output of the ion current detection circuit 35 is used to detect an ion current (for example, peak value P of the ion current) in a predetermined combustion ion detection section for each cylinder, The detected value is compared with a misfire determination value to determine the presence or absence of misfire.

  Next, how the ion current waveform detected by the ion current detection circuit 35 changes during normal combustion and noise generation will be described with reference to FIG.

  As shown in FIG. 2 (d), immediately after the start of energization of the primary coil 22 of the ignition coil 21 (immediately after the ignition signal is switched from OFF to ON), a pulsed noise current having a short time width is induced and immediately after the ignition (ignition) Immediately after the signal is switched from ON to OFF, LC resonance is generated by the residual magnetic energy on the secondary side of the ignition coil 21, and then a current waveform of ions generated by combustion (hereinafter referred to as "combustion ions") appears during normal combustion. . In this embodiment, the peak value P of combustion ions appearing after LC resonance is detected for each cylinder, and the detected value is compared with the misfire determination value to determine the presence or absence of misfire.

  On the other hand, as shown in FIG. 2 (e), the noise generated by the electric charge charged in the insulator portion of the spark plug 27 includes spike noise that occurs intermittently after the in-cylinder pressure decreases, There is also a continuous corona discharge noise that occurs continuously when the cylinder pressure immediately after ignition is high.

  By the way, when misfire occurs, unburned fuel is discharged into the exhaust passage. Depending on the operating state of the engine, the oxidation reaction of unburned fuel is promoted by exhaust heat, and the catalyst in the exhaust passage becomes overheated. May be damaged. In order to prevent overheating of the catalyst due to such misfire, it is desirable to increase the misfire detection sensitivity (by increasing the misfire determination value so that it can be easily determined that misfire has occurred). However, depending on the operating condition of the engine, even if misfire occurs, the oxidation reaction of unburned fuel is not accelerated (for example, when the exhaust temperature is low or the oxygen concentration is low), and the catalyst does not become overheated. If the misfire detection sensitivity is always increased regardless of the operating state, there is a problem in that it is easy to erroneously determine that ignition is misfired in an operating state in which catalyst overheating due to misfire does not occur.

  As a countermeasure against this, in this embodiment, the peak value P (#i) of the ionic current is compared with the misfire determination value Vth (#i) for each cylinder as shown in FIG. Further, one of the first misfire determination value Vth1 and the second misfire determination value Vth2 is selected as the misfire determination value Vth (#i) based on the engine operating state and the misfire occurrence state for each cylinder. Yes. (#I) is a cylinder number.

  In this case, the first misfire determination value Vth1 is set to a value larger than the second misfire determination value Vth2 and near the minimum value of the ion current during normal combustion. As a result, the first misfire determination value Vth1 becomes a determination value with higher misfire detection sensitivity than the second misfire determination value Vth2 (it is easy to determine that there is misfire), and a determination value that can detect an unstable combustion cycle as misfire. It becomes. By selecting the first misfire determination value Vth1, the misfire detection sensitivity can be increased, and the misfire can be detected at an early stage to perform the catalyst overheat prevention process (fuel cut or the like) at an early stage.

  On the other hand, the second misfire determination value Vth2 is set to a value smaller than the first misfire determination value Vth1 and near the maximum value of noise at the time of complete misfire due to engine failure or the like. As a result, the second misfire determination value Vth2 is less likely to be erroneously determined as ignition misfire, compared to the first misfire determination value Vth1, and becomes a determination value that can accurately detect complete misfire due to engine failure or the like. By selecting the second misfire determination value Vth2, the misfire / ignition determination accuracy can be made higher than the first misfire determination value Vth1.

When setting the misfire determination value Vth (#i) for each cylinder, first, it is determined whether the engine operating state (engine speed and load factor) is in any of the areas A to C (see FIG. 4).
Here, the region A is set to a region where the catalyst temperature rise during a misfire is small (for example, a low rotation region and a low load region). Further, the region B is set to a region where the catalyst temperature rise during a misfire is large (for example, a medium rotation and medium and high load region). Furthermore, the region C is set to a region (for example, a high rotation region) in which the catalyst temperature rise during a misfire is the largest. In the present embodiment, the region B corresponds to a predetermined operation region referred to in the claims.

  When the engine operating state is region A, the catalyst temperature rise at the time of misfire is small, and there is almost no possibility of catalyst overheating due to misfire. Therefore, it is necessary to select the first misfire determination value Vth1 with high misfire detection sensitivity. There is no. In addition, in the region A (low rotation region or low load region), the ion current during combustion tends to be small. Therefore, if the first misfire determination value Vth1 larger than the second misfire determination value Vth2 is selected, ignition occurs. Is easily misidentified as misfire.

In consideration of such circumstances, when the engine operating state is region A (region where the catalyst temperature rise during misfire is small), as shown in FIG. 3A, the process of selecting the misfire determination value is prohibited. Then, the misfire determination value Vth (#i) of each cylinder is fixed to the second misfire determination value Vth2 to increase the misfire / ignition determination accuracy.
Vth (#i) = Vth2

  Further, when the engine operating state is the region B (region where the catalyst temperature rise at the time of misfiring is large), it is determined whether or not each cylinder has a high misfiring frequency (predetermined misfiring state). It is determined by whether #i) is smaller than a predetermined value K (for example, 10).

As a result, as shown in FIG. 3B, when the engine operating state is the region B (the region where the catalyst temperature rises greatly at the time of misfire) and the continuous ignition count L (#i) is equal to or greater than a predetermined value K, combustion Since the deterioration is slight and the misfire frequency is low, it is determined that there is no possibility of catalyst overheating due to misfire, the second misfire judgment value Vth2 is selected, and the misfire judgment value Vth (#i) of the relevant cylinder is selected. Is set to the second misfire determination value Vth2 to increase the misfire / ignition determination accuracy.
Vth (#i) = Vth2

On the other hand, as shown in FIG. 3C, when the engine operating state is the region B (the region where the catalyst temperature rise during misfire is large) and the number of times of continuous ignition L (#i) is smaller than a predetermined value K, combustion Since the deterioration is severe and the misfire frequency is high, it is judged that there is a possibility of catalyst overheating due to misfire, the first misfire judgment value Vth1 is selected, and the misfire judgment value Vth (#i) of the cylinder concerned is selected. The first misfire determination value Vth1 is set to increase the misfire detection sensitivity.
Vth (#i) = Vth1

  After that, when the engine operation state is the region B and the number of continuous ignitions L (#i) is equal to or greater than the predetermined value K, it is determined that there is no possibility of catalyst overheating due to misfire, and the second misfire determination value Vth2 is set. The selected misfire determination value Vth (#i) is returned to the second misfire determination value Vth2.

  In addition, when the engine operating state is region C, the catalyst temperature rise at the time of misfire is greatest, and the possibility of catalyst overheating due to misfire is high, so the first misfire detection value Vth1 with high misfire detection sensitivity is selected. It is desirable to do. In addition, in region C (high rotation region), the ionic current at the time of combustion tends to increase. Therefore, even if the first misfire determination value Vth1 larger than the second misfire determination value Vth2 is selected, the ignition is misfired. It becomes difficult to make a mistake.

In consideration of such circumstances, when the engine operating state is in the region C (region where the catalyst temperature rise during the misfire is the largest), as shown in FIG. Forbidden, the misfire determination value Vth (#i) of each cylinder is fixed to the first misfire determination value Vth1, and the misfire detection sensitivity is increased.
Vth (#i) = Vth1

  The setting of the misfire determination value and the misfire determination of the present embodiment described above are executed by the engine control circuit 34 according to the routines of FIGS. The processing contents of these routines will be described below.

[Misfire detection routine]
The misfire determination routine shown in FIGS. 5 and 6 is executed at a predetermined cycle for each cylinder during engine operation. When this routine is started, first, in step 101, engine operating conditions such as engine speed and load factor are detected based on output signals from the rotation angle detection sensor 38, the load detection sensor 39, and the like. Thereafter, the process proceeds to step 102, and after the ion current detection value I (#i) detected by the ion current detection circuit 35 is read, the process proceeds to step 103, and the ion current peak value P (#i) in a predetermined combustion ion detection section. ) Is detected.

  Thereafter, the routine proceeds to step 104 where it is determined whether or not the current engine operating state (engine speed and load factor) is in the region B. As shown in FIG. 4, the region B is a region where the catalyst temperature rises greatly in the event of a misfire, and is a medium rotation and medium and high load region (the engine rotation speed is within a range from a predetermined value α to a predetermined value β and the load factor is The area is set to a predetermined value γ or more.

  If it is determined in step 104 that the engine operating state is the region B (region where the catalyst temperature rise during a misfire is large), the process proceeds to step 105, and whether or not the misfire frequency is high for each cylinder. Whether or not the number of consecutive ignitions L (#i) is smaller than a predetermined value K (for example, 10).

As a result, when it is determined that the engine operation state is the region B (the region where the catalyst temperature rises greatly at the time of misfiring) is large and the number of consecutive ignitions L (#i) is equal to or greater than the predetermined value K, the combustion deterioration is slight and the misfire is Since the frequency is low, it is determined that the catalyst is not overheated due to misfire, and the process proceeds to step 106, where the second misfire determination value Vth2 is selected, and the misfire determination value Vth (#i) of the cylinder is set to the first. The second misfire determination value Vth2 is set to increase the misfire / ignition determination accuracy.
Vth (#i) = Vth2

On the other hand, if it is determined in step 105 that the engine operating state is in region B (region where the catalyst temperature rise during misfire is large) and the number of consecutive ignitions L (#i) is smaller than a predetermined value K, combustion deterioration Therefore, it is determined that there is a possibility of overheating of the catalyst due to misfire, and the routine proceeds to step 107, where the first misfire determination value Vth1 is selected and the misfire determination value Vth of the cylinder concerned is selected. (#i) is set to the first misfire determination value Vth1 to increase the misfire detection sensitivity.
Vth (#i) = Vth1

  On the other hand, if it is determined in step 104 that the engine operating state is not the region B (region A or region C), the process proceeds to step 108, and the misfire determination value map in FIG. 4 is referred to. Then, the misfire determination value Vth (#i) corresponding to the current engine operating state is set. As shown in FIG. 4, the region A is a region where the catalyst temperature rise at the time of misfire is small, a low rotation region and a low load region (a region where the engine rotation speed is lower than a predetermined value α and the engine rotation speed is a predetermined value β). Within the following range, the load factor is set to a region lower than the predetermined value γ). On the other hand, the region C is a region where the catalyst temperature rise at the time of misfire is the largest, and is set to a high rotation region (a region where the engine rotation speed is higher than the predetermined value β).

The map of misfire determination values in FIG. 4 shows that when the engine operating state is region A (region where the catalyst temperature rise during misfire is small), the process of selecting the misfire determination value is prohibited and the misfire determination value Vth (# i) is fixed to the second misfire judgment value Vth2 to increase the misfire detection sensitivity. When the engine operating state is in the region C (the region where the catalyst temperature rises at the time of misfire is the largest), the misfire judgment value Vth ( #i) is fixed to the first misfire determination value Vth1, and the misfire detection sensitivity is set high.
The processing in these steps 104 to 108 serves as misfire determination value selection means in the claims.

  Thereafter, the routine proceeds to step 109, where it is determined whether or not the ion current peak value P (#i) is larger than the misfire determination value Vth (#i). As a result, if it is determined that the ionic current peak value P (#i) is greater than the misfire determination value Vth (#i), it is determined that ignition has occurred and the routine proceeds to step 110 where the misfire flag of the cylinder is turned off. Then, the routine proceeds to step 111 where the number of consecutive ignitions L (#i) of the cylinder is incremented by “1”.

  On the other hand, when it is determined in step 109 that the ion current peak value (#i) is equal to or less than the misfire determination value Vth (#i), it is determined that misfire has occurred, and the process proceeds to step 112. After the misfire flag of the cylinder is set to ON, the process proceeds to step 113, and the continuous ignition frequency L (#i) of the cylinder is reset to “0”.

Thereafter, the process proceeds to step 114 in FIG. 6, and the misfire rate of all cylinders at a predetermined number of ignitions (for example, 1000 ignitions) is calculated by the following equation.
Misfire rate = (number of misfires / number of ignitions) x 100 [%]

  Thereafter, the process proceeds to step 115, where it is determined whether or not the misfire rate is greater than a predetermined value C1 (eg, 3%). If the misfire rate is greater than the predetermined value C1, the process proceeds to step 116 where it is determined that there is a misfire failure. To do.

  Thereafter, the process proceeds to step 117, where it is determined whether or not the misfire rate is larger than a predetermined value C2 (C2> C1, C2 = 25%, for example). If the misfire rate is larger than the predetermined value C2, the process proceeds to step 118. Then, a catalyst overheat prevention process (for example, fuel cut or the like) is executed.

  In the present embodiment described above, the first misfire determination value Vth1 is set near the minimum value of the ion current during normal combustion, and the first misfire is set near the maximum noise value during complete misfire due to engine failure or the like. When the second misfire judgment value Vth2 smaller than the judgment value Vth1 is set, and the engine operating state is in the region B (the region where the catalyst temperature rises greatly during misfire) is low, the catalyst is overheated due to misfire. Since it is determined that no occurrence occurs, the smaller second misfire determination value Vth2 is selected as the misfire determination value Vth (#i), so that the misfire / ignition determination accuracy can be increased. On the other hand, if the engine operating state is a region B (region where the catalyst temperature rise during misfire is large) and the misfire frequency is high, it is determined that the catalyst may be overheated due to misfire, and the misfire determination value Vth ( As #i), the larger first misfire judgment value Vth1 is selected, so that the misfire detection sensitivity can be increased, and misfire is detected early to prevent overheating of the catalyst (fuel cut, etc.) Can be implemented early.

  Further, when the engine operating state is region A (region in which the catalyst temperature rise at the time of misfire is small), it is determined that the catalyst is not overheated due to misfire, and the misfire determination value Vth (#i) is set to the smaller second value. Since the misfire determination value Vth2 is fixed, the misfire / ignition determination accuracy can be increased. On the other hand, when the engine operating state is region C (region where the catalyst temperature rise during misfire is greatest), it is determined that there is a high possibility of catalyst overheating due to misfire, and the misfire determination value Vth (#i) is larger Since the first misfire determination value Vth1 is fixed, the misfire detection sensitivity can be increased, and the misfire can be detected early and the catalyst overheat prevention processing (fuel cut, etc.) can be performed early. it can.

  By these processes, it is possible to improve the misfire / ignition determination accuracy while effectively preventing overheating of the catalyst due to misfire.

  Further, in this embodiment, when the engine operating state is the region B (region where the catalyst temperature rise during a misfire is large), it is determined whether or not a predetermined misfire occurrence state (a state where the misfire frequency is high) for each cylinder. Since the misfire determination value is selected for each cylinder, when some of the cylinders are in a predetermined misfire occurrence state, the larger first misfire determination value for only that part of the cylinders The misfire detection sensitivity can be increased by selecting Vth1. For other cylinders that are not in a predetermined misfire occurrence state, the smaller second misfire determination value Vth2 is selected to determine the misfire / ignition determination accuracy. Can be maintained in a high state. This makes it possible to minimize the cylinders that increase the misfire detection sensitivity (that is, the cylinders that reduce the misfire / ignition determination accuracy) to increase the catalyst overheating prevention effect due to misfire.

  However, the present invention is not limited to the configuration in which the misfire determination value is selected for each cylinder, and the same misfire determination value may be selected for all cylinders.

  In the above embodiment, the misfire determination value Vth is fixed to the first misfire determination value Vth1 when the engine operating state is the region C (region where the catalyst temperature rise during the misfire is greatest). When the operation state is a predetermined misfire occurrence state in the region C (a state with a high misfire frequency), the larger first misfire determination value Vth1 is selected as the misfire determination value Vth, and the predetermined misfire occurrence occurs in the region C. If not, the smaller second misfire determination value Vth2 may be selected as the misfire determination value Vth.

  In the above embodiment, whether or not the predetermined misfire occurrence state is determined based on the number of consecutive ignitions, but whether or not the predetermined misfire occurrence state is determined based on the number of continuous misfires and the misfire occurrence rate. It may be determined.

  In the above embodiment, the misfire determination value is selectively switched depending on whether or not a predetermined misfire has occurred in the predetermined operation region, but the output distribution of the ion current detection value in the predetermined operation region is a normal combustion distribution. The misfire determination value may be selectively switched depending on whether or not there is.

  In the above embodiment, the first misfire determination value Vth1 is set in the vicinity of the minimum value of the ionic current at the time of normal combustion. However, the engine torque fluctuation is near the minimum value of the ionic current at the time of combustion in the limit state. The first misfire determination value Vth1 may be set.

  In the above embodiment, the present invention is applied to the misfire determination in which the ion current peak value P is compared with the misfire determination value to determine the presence or absence of misfire, but instead of the ion current peak value P, the ion current integrated value Q The present invention may be applied to misfire determination in which other parameters such as the ion current output time T are compared with the misfire determination value to determine the presence or absence of misfire.

It is a circuit diagram which shows the structure of the ignition control system and ion current detection circuit in one Example of this invention. It is a time chart explaining the relationship with an ignition signal, a cylinder pressure, a combustion ion detection area, a detection current waveform at the time of normal combustion, and a detection current waveform at the time of noise occurrence. It is a figure explaining the setting method of a misfire determination value. It is a figure which shows notionally an example of the map of misfire determination value Vth. It is a flowchart (the 1) explaining the flow of a process of misfire determination routine. It is a flowchart (the 2) explaining the flow of a process of misfire determination routine.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 21 ... Ignition coil, 22 ... Primary coil, 23 ... Battery, 24 ... Igniter, 25 ... Power transistor, 26 ... Secondary coil, 27 ... Spark plug, 31 ... Ion current detection resistor, 33 ... Inversion amplification circuit, 34 ... Engine Control circuit (misfire determination value selection means), 35 ... Ion current detection circuit (ion current detection means), 36 ... Center electrode, 37 ... Ground electrode

Claims (4)

Ion current detection means for detecting ion current generated by combustion of the air-fuel mixture in the combustion chamber of the internal combustion engine through the electrode of the spark plug, and comparing the ion current detection value of the ion current detection means with the misfire determination value In the misfire detection device for an internal combustion engine that determines the presence or absence of misfire,
The first misfire determination value set based on the minimum value of the ion current during normal combustion and the second set to a value smaller than the first misfire determination value based on the maximum noise value during misfire A misfire determination value selecting means for selecting one of the misfire determination values as the misfire determination value,
The misfire determination value selection means selects the first misfire determination value when a predetermined misfire has occurred in a predetermined operation region of the internal combustion engine, and selects the second misfire determination value when not in the predetermined misfire occurrence state. A misfire detection apparatus for an internal combustion engine, characterized in that:   The said misfire determination value selection means determines whether it is the said predetermined misfire occurrence state for each cylinder of an internal combustion engine, and selects the said misfire determination value for each cylinder. Misfire detection device for internal combustion engine.   The misfire detection value of the internal combustion engine according to claim 1 or 2, wherein the misfire determination value selection means does not perform a process of selecting the misfire determination value in a low rotation region and / or a low load region of the internal combustion engine. apparatus.   The internal combustion engine according to any one of claims 1 to 3, wherein the misfire determination value selection means determines whether or not the predetermined misfire occurrence state is based on the number of consecutive ignitions and / or the misfire occurrence rate. Engine misfire detection device.

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