JPH07111153B2 - Accident cylinder detection device for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a misfiring cylinder detection device for an internal combustion engine, and more specifically, it calculates a discriminant value that substantially corresponds to the amount of change in the average effective pressure of each cylinder based on the engine rotation cycle, and determines the discriminant value. And a slice level by detecting a misfiring cylinder by detecting the misfiring cylinder. <Prior Art> In an internal combustion engine, a misfire may occur due to a failure of a fuel supply system such as an ignition system or a fuel injection valve, and further, a compression leak may occur. When the misfire occurs, the misfire is supplied to the misfiring cylinder. The fuel is discharged to the exhaust system without being burned, and this unburned gas may burn in a catalyst device provided for exhaust gas purification to burn the catalyst device. This causes a problem that the concentration of harmful components in the exhaust gas is increased. Therefore, it is required to detect the occurrence of misfire and, when the misfire is detected, perform failsafe control such as warning the occurrence of misfire or stopping the fuel supply to the cylinder in which misfire occurs. As a device for detecting a misfire, there is a device for determining a misfiring cylinder based on the engine rotation fluctuation as shown below (1979
ISATA-Paper `` Experiences with a new method for me
asuring the engine roughness "by R. Latsch, E. Mausne
r, V. Bianchi). That is, the discriminant value LUn indicating the degree of engine fluctuation (engine roughness degree) as the change amount of the average effective pressure of each cylinder is calculated for each cylinder, and the misfiring cylinder is detected based on this discriminant value LUn. LUn is derived as follows. Here, M = engine generated torque, W = load torque, ω = crank angular velocity, θ = inertia moment, t = time,
T = instantaneous value of crank rotation cycle, ξ = crank angle, j =
0,1,3, ..., Tj = 2or1 crankshaft rotation period, Tj _-1 = 1
If the previous Tj, If the above equation is integrated for one crankshaft rotation, Here, assuming that W is a constant and Tj≈Tj ₋₁ ≈Tj ₋₂ , Therefore, since the left side of the above equation is approximately equivalent to the change amount ΔPi of the average effective pressure of the internal combustion engine which is closely related to the occurrence of the misfiring cylinder, if the calculation related to the rotation cycle on the right side is performed, the average effective Since the change in pressure can be captured and the misfiring cylinder can be specified by this, the calculation result on the right side is used as the engine fluctuation degree determination value LUn, and based on this determination value LUn, the average effective pressure is decreasing by a predetermined amount or more. It is possible to detect a misfiring cylinder by discriminating whether or not each cylinder. Here, the arithmetic expression of the engine fluctuation degree determination value LUn substantially corresponding to the change amount ΔPi of the average effective pressure Pi is as follows: However, it is simplified as follows so that it can be easily calculated in practice. That is, Δ (ΔTj) = (Tj ₋₁ −Tj ₋₂ )
− (Tj−Tj ₋₁ ), but in the case of a 4-cylinder internal combustion engine, Tj
_-1 = 180 ° cycle before 360 ° (T sampled every TDC
DC period), Tj _-2 = 180 ° period before 720 ° (2 rotations), Tj =
Use the latest 180 ° cycle. Further, since Tj ³ is difficult to calculate, it is replaced with Tj, Tj _-1 or Tj _-2 . Here, the 180 ° cycle before 360 ° (1 rotation) is half, and the 720 ° (2 rotations) before
The 180 ° cycle is old, the latest 180 ° cycle is new, and Tj
^If Tj _-2 (180 ° cycle before 720 ° = old) is used instead of ³ , the arithmetic expression of the engine fluctuation degree determination value LUn can be simplified as follows. When the engine fluctuation degree determination value LUn is set based on the above equation, as shown in FIG. 5 (a four-cycle four-cylinder engine # 1 cylinder misfire occurrence state), the four-cylinder internal combustion engine #
The discriminant value LU1 corresponding to one cylinder is calculated when the latest value of the 180 ° cycle measurement result updated every TDC (180 °) is influenced by the cylinder pressure (combustion stroke) of the # 1 cylinder. ,
new is the latest 180 ° cycle of this # 1 cylinder, half is the 180 ° cycle affected by the cylinder pressure of the # 4 cylinder one rotation before, and old is the cylinder pressure of the # 1 cylinder one cycle before (two rotations before). Affected 18
It is calculated as a 0 ° cycle. Here, the misfiring cylinder discrimination based on the discrimination value LUn is a discrimination value equal to or lower than the slice level SL (predetermined level of the discrimination value LU) determined by operating conditions (for example, engine rotation speed and engine load).
When there is LUn (decrease in average effective pressure above the slice level SL), it is determined that there is a misfire, the discriminant value LUn continuously indicates a decrease in average effective pressure (= discriminant value LU is negative), and either Indicates a decrease amount that exceeds SL, it is performed based on the determination logic that the first one is determined to be due to a misfire, and as shown in FIG. 5, when the # 1 cylinder continues to misfire. , As shown in the figure, the discriminant value LUn is
The discriminant values LU1 and LU3 corresponding to # 1 cylinder and # 3 cylinder are negative values, and both are slice level SL.
Although it is as follows, it is determined that the # 1 cylinder is misfiring because the determination value LU1 corresponding to the # 1 cylinder is the first. <Problems to be Solved by the Invention> By the way, when a specific cylinder is misfired every time,
As shown in the figure, the discriminant value LU corresponding to the misfiring cylinder and the next cylinder
Is a negative value, and at this time the slice level must be closer to zero than the minimum value min of the discriminant value LU to determine misfire, whereas when misfiring has not occurred in all cylinders, the minimum discriminant value LU If you do not make the slice level smaller than the value min, misfire will be misjudged, and the discriminant value
As shown in FIG. 6, the LU level varies greatly depending on the engine operating conditions. Therefore, in the misfiring cylinder detection based on the discriminant value LUn, it is necessary to variably set the slice level according to the engine operating conditions (for example, the engine load and the engine rotation speed). The slice level that was optimized for was stored in the map on ROM. Therefore, a lot of man-hours are required to initially determine the slice level, a large ROM capacity is required, and
If the initial setting of the slice level is incorrect, accurate misfiring cylinder detection may not be possible. The present invention has been made in view of the above problems, in performing the misfiring cylinder detection by comparing the determination value LU and the slice level calculated as described above, while reducing the matching man-hour of the slice level , It is an object of the present invention to reduce the ROM capacity for determining the slice level, and to enable misfiring cylinder detection without erroneous determination by appropriately setting the slice level. <Means for Solving the Problems> Therefore, in the present invention, as shown in FIG. 1, a rotation cycle measuring means for measuring the rotation cycle of the internal combustion engine, and an average of each cylinder based on the rotation cycle measured by the rotation cycle measuring means. An engine variation degree determination value calculating means for calculating an engine variation degree determination value, which is a value approximately corresponding to the amount of change in effective pressure, in association with each cylinder, and an engine variation degree determination value and a slice level calculated by this operation means. A misfiring cylinder detection device for an internal combustion engine including: a misfiring cylinder discrimination means for discriminating a misfiring cylinder by comparison with, and a slice level variable setting means for variably setting a slice level according to the magnitude of an engine fluctuation degree discrimination value. I configured it. Here, as shown by the dotted line in FIG. 1, the slice level variable setting means is based on the change rate calculating means for calculating the change rate of the engine variation degree determination value and the change rate calculated by the change rate calculating means. And a slice level setting means based on a change rate for setting the slice level. Further, as shown by the dotted line in FIG. 1, it is preferable to provide a change rate correction means for correcting the change rate of the engine variation degree determination value calculated by the change rate calculation means based on the engine rotation speed. <Operation> According to the misfire cylinder detection device having such a configuration, the engine fluctuation degree determination value calculation means is substantially equivalent to the change amount of the average effective pressure of each cylinder based on the rotation cycle of the internal combustion engine measured by the rotation cycle measurement means. The engine variation degree determination value that is the value to be calculated is calculated. Then, the misfiring cylinder discrimination means discriminates the misfiring cylinder by comparing the engine fluctuation degree discrimination value with a slice level, and the slice level is set to a larger magnitude of the engine fluctuation degree discrimination value by the slice level variable setting means. It is variably set accordingly. That is, the slice level is not stored in advance in association with the engine operating condition, but is set each time according to the magnitude of the engine fluctuation degree determination value calculated based on the rotation cycle. Here, when the slice level variable setting means is configured to include a change rate calculating means and a slice level setting means based on the change rate, the engine fluctuation degree determination value calculated by the change rate calculating means The slice level setting means based on the change rate sets the slice level based on the change rate. That is, the change rate of the discriminant value is calculated as the magnitude of the engine fluctuation degree discriminant value, and the slice level is variably set based on this change rate. Further, the change rate correction means corrects the change rate of the engine variation degree determination value calculated by the change rate calculation means based on the engine rotation speed, and the slice level is changed based on the change rate corrected at this rotation speed. To be set. That is, when the same step difference of the average effective pressure between the cylinders occurs at low rotation and high rotation, respectively, the change rate of the discriminant value becomes larger on the low rotation side. In order to achieve both the accuracy of misfiring cylinder detection, the change rate is corrected by the engine speed and the slice level is set. <Examples> Examples of the present invention will be described below. In FIG. 2 showing an embodiment, a crankshaft (not shown) of a 4-cycle 4-cylinder internal combustion engine 1 is provided with 120 convex portions formed of a magnetic material and having a crank angle of 3 ° (3 ° CA) around it. The formed signal disc plate 2 is pivotally supported, and the magnet open end of the electromagnetic pickup 3 for 3 ° CA detection, which is fixed near the periphery of the signal disc plate 2, is provided with the convex portion as the crankshaft rotates. Is configured to obtain an induced electromotive force pulse by opening and closing,
The signal disk plate 2 and the electromagnetic pickup 3 for detecting 3 ° CA are adapted to obtain detection signals at every 3 ° CA. In addition, on one end surface of the signal disc plate 2,
A pair of protrusions 2a and 2b are provided on the same circumference with the rotary shaft interposed, and an induced electromotive force pulse is obtained every 180 ° CA by an electromagnetic pickup 4 for TDC detection which detects these protrusions 2a and 2b. By combining the projections 2a and 2b of the signal disc plate 2 and the electromagnetic pickup 4, a detection signal of 180 ° CA can be obtained. Where the protrusions
By aligning the detection positions of the electromagnetic pickups 2a and 2b with the top dead center position (TDC), for example, the compression TDC position of each cylinder can be detected by the ignition signal and the TDC position detection. . The induced electromotive force output from each of the electromagnetic pickups 3 and 4 is input to the zero-cross comparators 5 and 6, respectively, and
It is converted into a pulse wave centered on 0 V based on the magnitude with respect to the V level, and is further shaped by the next waveform shaping circuits 7 and 8 into a pulse wave having 0 V as a low level. The output pulse of the waveform shaping circuit 7 that rises (falls) every 3 ° CA (hereinafter abbreviated as 3 ° CA pulse) is a built-in computer that detects misfiring cylinders and controls fuel supply to the engine 1. It is input to the timer 1 of the control unit 9, and the timer 1 counts the number of 3 ° CA pulses. Also, the output pulse of the waveform shaping circuit 8 that rises (falls) every 180 ° CA at the TDC position of each cylinder (hereinafter referred to as TDC
Abbreviated as pulse. ) Is input to the trigger 1 of the control unit 9. The control unit 9 is input to the trigger 1.
The period of TDC pulse, that is, 180 ° CA (TDC) period is measured, and the 3 ° CA pulse is counted by using the TDC pulse as a trigger to detect the interrupt execution timing of the misfire detection program around 20 ° ATDC, for example. Then, the misfiring cylinder is detected every 180 ° CA cycle. The means for detecting the rotational position of the crankshaft is, in addition to the type of device for obtaining the induced electromotive force pulse, an optical type for detecting the light passing through a slit provided in the signal disk plate to detect the rotational position of the crankshaft. However, the device is not limited to the device of this embodiment. Next, a misfiring cylinder detection program executed at an execution timing immediately after TDC detected by counting 3 ° CA pulses from the TDC pulse will be described with reference to the flowchart of FIG. In this embodiment, the rotation cycle measuring means, the engine fluctuation degree discriminating value calculating means, the misfiring cylinder discriminating means, the slice level variable setting means, the change rate calculating means, the slice level setting means based on the change rate, and the change rate correcting means are used. The function of is provided as software as shown in the flowchart of FIG. First, in step 1 (denoted as S1 in the figure. The same applies to the following), the latest value Tnew of the TDC cycle (180 ° cycle for four cylinders) measured as the input interval of the TDC pulse is calculated four times before Tol.
Values up to d4 are updated and stored. That is, the latest value of the 180 ° cycle, which is obtained as the time from the TDC immediately before the interrupt execution of this program to the previous TDC, is set in Tnew, and it is obtained in the previous execution of this program and set in Tnew. One cycle before (180 ° CA
The previous) cycle data is set to Told1, and similarly, the cycle Told1 of the previous time is set to the cycle Told2 of two times before (one rotation before), and the cycle 2 of the previous time is set.
The previous cycle Told2 is the cycle To three times before (540 ° CA)
Set to ld3, and the cycle 3 times before the previous cycle Told3
Is set to the cycle Told4 four times before (two times before). In the next step 2, the latest cycle Tne obtained in step 1
w The engine fluctuation degree determination value LU is calculated according to the following equation using the cycle Told2 one rotation before (1/2 cycle before) and the cycle Told4 two rotations before (one cycle before). The above formula is synonymous with the following formula for calculating the discriminant value LU, which is a value substantially equivalent to the amount of change in the average effective pressure of each cylinder described above. The change in the average effective pressure of the cylinder that was in the combustion stroke is estimated. (However, new = latest 180 ° cycle, half = 180 before one rotation
° cycle, old = 180 ° cycle before 2 revolutions) When the engine fluctuation degree discriminant value LU is calculated in step 2, in the next step 3, the discriminant value calculated in step 2 is calculated.
It is determined whether LU is a negative value and indicates a decrease in average effective pressure. When the discriminant value LU is a negative value and indicates a decrease change in the average effective pressure, the routine proceeds to step 4, where the latest value of the discriminant value LU which is a negative value and the discriminant value LU which has recently been negative. Causes data to be updated and stored in time series. That is, this time step 2
The discriminant value LU that was negative and calculated by
u

Set to [0] and the negative discriminant value LU calculated at the closest previous time is set.

The data of [0] is set to oldlu [1], and oldlu is used until the last time.
Set the negative discriminant value LU data set in [1] to oldlu
Set to [2], and then oldlu until the last time
Set the negative discriminant value LU data set in [2] to oldlu
Set to [3] so that four pieces of data are stored as the latest negative discriminant value LU. In the next step 5, in order to sample the minimum value from the four negative discriminant value LU data, the counter i for sequentially comparing the four data is reset to zero and the minimum value min is calculated at this time. The determined discriminant value LU is set. Then, in step 6, it is determined whether or not the counter i is less than 4, and when the counter i is less than 4, the process proceeds to step 7. In step 7, oldlu [i] and min
Are compared with each other, and if oldlu [i]> min, the process proceeds to step 8 and the discriminant value L set to oldlu [i]
Update the data of U to the minimum value min. Further, the counter i is incremented by 1 in step 9 regardless of the determination result in step 7. That is, first, the latest discriminant value LU is set to the minimum value min, and the minimum value min and oldlu are set.

[0] is compared, and a smaller value is updated and set to the minimum value min from the comparison result.
[1], oldlu [2], oldlu [2] and the minimum value min are changed in comparison symmetry, and the smallest value is sampled from the four discriminant value LU data (all are negative values). . In this way, when the minimum value min is sampled from the past four pieces of data of the discriminant value LU calculated as a negative value, in the next step 10, the discriminant value LU calculated in step 2 this time and the When the program was last run (before 180 ° CA)
Similarly, the absolute value of the deviation from the discriminant value LU _OLD calculated in step 2 (change rate of the discriminant value LU) is calculated, and the calculated value is Dlu.
Set to. When a misfire occurs, the deviation of the discriminant value LU between cylinders becomes large, as shown in FIG.
When the Dlu is smaller than a predetermined value and there is almost no change in the discriminant value LU, it can be considered that it is not the average effective pressure change due to misfire occurrence but the average effective pressure change due to combustion variation between cylinders, and the like. When the Dlu is larger than the predetermined value, it can be considered that the average effective pressure is largely changed between the cylinders due to the occurrence of misfire. In the next step 11, the discriminant value LU calculated in step 2 this time is set to the previous value LU _OLD for the calculation in step 10 when the program is executed next time. In the next step 12, the discriminant value LU obtained in step 10
Dlu, which is the step difference between cylinders, is corrected by the engine speed. That is, when the Dlu is larger than a predetermined value, it is presumed that the average effective pressure change between the cylinders occurs due to the occurrence of misfire, but the tendency differs depending on the engine rotation speed, and as shown in FIG. Since the discriminant value LU difference between the cylinders tends to increase as the rotation speed decreases, so that the Dlu can be treated equally regardless of the rotation, the rotation speed is such that the Dlu is increased and corrected at the high rotation speed. It is based on the correction. Here, the square value of the number of revolutions rpm is multiplied by the Dlu, and it is arranged to divide by a predetermined value for digit alignment, and if a correction is made according to the engine rotational speed in this way,
The ROM capacity can be saved because it is not necessary to provide a map of the coefficient X for each rotation speed. Then, in the next step 13, Dlu, which is the step difference between cylinders of the discrimination value LU corrected based on the rotation speed in step 12 above.
The minimum value min is corrected based on
The coefficient X for setting L is obtained by searching the map. Here, when the Dlu is larger than a predetermined value, the coefficient X is set to a value smaller than 1 according to the increase of the Dlu, and conversely, when the Dlu is smaller than a predetermined value, the coefficient X is set to be larger. It is done. As a result, when the Dlu is less than or equal to a predetermined value and there is no large discriminant value LU step and misfire is not recognized, by setting the slice level SL to a value smaller than the minimum value min, the decision value LU is the slice level. It is determined that the misfire is not performed by being determined to be SL or more, and when the Dlu is greater than or equal to a predetermined value and there is a large discriminant value LU step and misfire is recognized, the slice level SL is more than the minimum value min. As a large value (a value close to zero), the discriminant value LU is discriminated to be equal to or lower than the slice level SL, and misfire discrimination is performed. When the coefficient X for determining the slice level SL is set by multiplying the minimum value min in step 13, in the next step 14, the past four negative determination values sampled in the processing in steps 5 to 9 are set. The minimum value min obtained from LU data is multiplied by the coefficient X to determine the slice level SL. Slice level SL set here and discriminant value
By comparing LU with step 15 described later,
A misfiring cylinder is determined as a cylinder whose average effective pressure Pi is decreasing. As described above, the change rate Dlu of the discriminant value LU and the minimum value min
If the slice level SL is set based on the following, even if the conditions of the rotational speed and the engine load are constant, the slice level SL is set according to the magnitude of the determination value LU at that time, as shown in FIG. When the level SL fluctuates and no misfire has occurred, the slice level SL is set to a value sufficiently smaller than the judgment value LU to avoid misjudgment of misfire, and when the misfire occurs, the slice level SL is changed according to the level of the judgment value LU. Minimum value mi
Accurate misfiring cylinder detection can be performed by changing the value to a value larger than n. Further, since the variable setting of the slice level SL is automatically performed only by matching the coefficient X, the man-hours for matching the slice level SL can be reduced and the ROM capacity can be saved. In step 15, the slice level SL set in step 14 is compared with the discriminant value LU calculated in step 2,
It is determined whether or not the discriminant value LU calculated this time is a value smaller than the slice level SL. Here, if it is determined that the determination value LU is less than the slice level SL, the flag flag is determined in step 16. The flag flag is set to 1 in step 27, which will be described later, when the discriminant value LU is determined to be negative, and to zero in step 28 when the discriminant value LU is zero or more. When it is determined in 16 that the flag flag is zero, it means that the discriminant value LU is determined to be less than the slice level SL the first time it becomes negative,
In this case, it is estimated that the cylinder in which the average effective pressure is decreasingly changed by the discriminant value LU this time is misfiring, and the routine proceeds to step 17. In step 17, the cylinder in the combustion stroke that has affected the TDC cycle sampled most recently is specified according to which cylinder the previous TDC is the compression TDC, and that cylinder is determined by this judgment value.
The misfire detection cylinder is based on LU. That is, for example, when the current compression TDC is for the # 2 cylinder, the ignition order is #
If 1 → # 3 → # 4 → # 2, there is combustion in the # 4 cylinder immediately before, and the determination value LU is calculated because the cycle is measured under the influence of the combustion in the # 4 cylinder. Based on the discriminant value LU determined to be less than the slice level SL this time #
The occurrence of misfires in the four cylinders is determined, and the routine proceeds to step 18, where the count value C4 for counting the number of misfires in the # 4 cylinder is incremented by 1. Similarly, the misfire detection circuits C1 to C3 are caused to count up for each cylinder, assuming that a misfire has occurred in the cylinder burned immediately before the cylinder to which the current compressed TDC corresponds (steps 19 to 21). On the other hand, when it is determined in step 16 that the flag flag is set to 1, as shown in FIG. 5, the determination value LU
Is continuously negative, and in this case,
Since it is correct to identify the misfiring cylinder based on the initially negative discriminant value LU, it is determined in step 22 that the cylinder that was burned two times before the most recent combustion cylinder identified as the compressed TDC was misfired. That is, when the compressed TDC this time is the # 4 cylinder, the combustion cylinder immediately before is the # 3 cylinder, and the previous time is the # 1 cylinder, so that the combustion cylinder is the # 4 cylinder in step 22. When the determination is made, it is estimated that the # 1 cylinder has misfired, and the routine proceeds to step 23, where C1 for counting up the number of misfires of the # 1 cylinder is incremented by 1. Combustion cylinders are # 2, # 1,
Similarly for the # 3 cylinder, the misfires of the # 3, # 4, and # 2 cylinders are estimated and the number of misfire detections for each cylinder is counted up (steps 24 to 26). In this way, the misfiring cylinder is specified and the misfire count of that cylinder is counted up, and the discrimination value in step 15
When it is determined that LU is negative but equal to or higher than the slice level SL, 1 is set to the flag flag in step 27. When it is determined in step 3 that the discriminant value LU is greater than or equal to zero, the routine proceeds to step 28, where the flag flag is set to zero. When the flag flag is set in step 27 or step 28, the process proceeds to step 29. In step 29, it is determined whether or not the count value cnt for counting the number of times the program has been executed has reached a predetermined value (for example, 1000). Here, when the count value cnt is not counted up to the predetermined value, the routine proceeds to step 30, where the count value cnt is incremented by 1 to end the program, but when it is at the predetermined value, the count value is counted at step 31. After the cnt is reset to zero, the misfire occurrence display for each cylinder is performed based on the misfire occurrence rate for each cylinder in step 32 to step 39. In step 32, by comparing C1 in which the misfire detection circuit of the # 1 cylinder is set with a predetermined value (for example, 40), the count value cnt is counted up to a predetermined value, the number of times is a predetermined number of times or more. When the misfire of the # 1 cylinder is detected at a certain rate, the routine proceeds to step 33, where the occurrence of the misfire of the # 1 cylinder is displayed and warned, for example, on the dashboard of the vehicle in which the engine 1 is mounted. Similarly, by comparing C2 to C4 in which the number of misfire detections of the # 2 to # 4 cylinders is set with a predetermined value, it is determined whether or not the misfire frequency is high for each cylinder, and the number of misfires greater than or equal to the predetermined value For cylinders in which misfires occur frequently, the misfire occurrence is displayed as described above (steps 34 to 3).
9). After determining the misfire occurrence frequency by comparing each of the misfire count values C1 to C4 with a predetermined value, C1 to C4 are respectively reset to zero in step 40, and the count value cnt is again counted up to the predetermined value. The number of misfire detections for each cylinder during a predetermined period is newly set to each misfire count value C1 to C4. In the present embodiment, when the misfire occurrence frequency for each cylinder is equal to or higher than a predetermined value, the cylinder is displayed and a warning is given. However, a failsafe such as stopping the fuel supply to the cylinder together with the warning is given. The control may be executed. <Effects of the Invention> As described above, according to the present invention, an engine fluctuation degree determination value that substantially corresponds to the amount of change in the average effective pressure of each cylinder is calculated based on the rotation cycle, and this determination value and the slice level are calculated. In performing the misfire cylinder detection by comparison, since the slice level is automatically set by variably setting the slice level according to the size of the discriminant value, it is possible to reduce the matching man-hour of the slice level, There is an effect that the ROM capacity for setting the slice level can be saved, and even if the engine operating condition is constant, the slice level can be changed to an appropriate value depending on the presence or absence of misfire to improve the misfire detection accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a system schematic diagram showing an embodiment of the present invention, FIG. 3 is a flow chart showing the contents of misfiring cylinder detection control in the same embodiment, and FIG. Is a time chart showing the relationship between the discriminant value LU and the slice level SL in the above-mentioned embodiment, FIG. 5 is a time chart for explaining the characteristics of misfiring cylinder detection based on the discriminant value LU in a 4-cylinder engine, FIG. FIG. 6 is a diagram showing a change in a discriminant value LU depending on operating conditions. 1 ... Engine, 2 ... Signal disk plate, 3,4 ...
… Electromagnetic pickup, 5,6 …… Zero cross comparator, 7,8 …… Wave shaping circuit, 9 …… Control unit

Claims (3)

[Claims] 1. A rotation cycle measuring means for measuring a rotation cycle of an internal combustion engine, and an engine fluctuation degree determination value which is a value substantially corresponding to a change amount of an average effective pressure of each cylinder based on the measured rotation cycle. An engine fluctuation degree discriminant value computing means for computing corresponding to each cylinder; a misfiring cylinder discriminating means for discriminating a misfiring cylinder by comparing the computed engine fluctuation degree discriminant value with a slice level; A misfire cylinder detection device for an internal combustion engine, comprising: a slice level variable setting means that variably sets according to the magnitude of an engine fluctuation degree determination value. 2. The slice level variable setting means sets a slice level based on a change rate calculating means for calculating a change rate of the engine fluctuation degree determination value, and the change rate calculated by the change rate calculating means. The misfire cylinder detection device for an internal combustion engine according to claim 1, further comprising: 3. The internal combustion engine according to claim 2, further comprising change ratio correction means for correcting the change ratio of the engine fluctuation degree determination value calculated by the change ratio calculation means based on the engine rotation speed. Misfire cylinder detection device.