JP2701186B2 - Misfire detection device for multi-cylinder internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a misfire detecting device for detecting a misfire in a multi-cylinder internal combustion engine for an automobile or the like, when a misfire occurs in a certain cylinder. More particularly, the present invention relates to a misfire detection device for a multi-cylinder internal combustion engine, which determines misfire based on fluctuations in rotation speed of a crankshaft.

[0002]

2. Description of the Related Art In an automobile, it is required to detect a misfire of an internal combustion engine as an exhaust gas source in order to cope with environmental problems and the like. In this case, since the internal combustion engine for a vehicle is a multi-cylinder internal combustion engine, it is required to detect which cylinder has misfired. As such a misfire detection device for a multi-cylinder internal combustion engine, for example,
As disclosed in Japanese Unexamined Patent Publication No. 2-112646, there is known an apparatus in which misfire is detected from fluctuations in rotation speed. In the misfire detection device, the instantaneous rotational speed of the crankshaft at a specific position of each cylinder, for example, near the top dead center, is detected, and misfire is determined based on the fluctuation of the rotational speed.

[0003] Generally, the instantaneous rotational speed of a multi-cylinder internal combustion engine has a periodicity such that it falls most near the top dead center of each cylinder and increases during that time. That is, when a certain cylinder reaches the vicinity of the top dead center in the compression stroke and is ignited and enters the explosion stroke, the crankshaft is accelerated by the gas pressure, and the rotation speed increases. Then, the rotation speed gradually decreases due to the resistance of the load. Then, the operation of accelerating again by igniting the next cylinder is repeated. Therefore, the periodicity as described above is exhibited. However, when a certain cylinder misfires, the crankshaft is not accelerated by that cylinder, so that the rotation speed continues to decrease even if the cylinder exceeds the top dead center. Therefore, as shown in the above publication, if the instantaneous rotational speed of the crankshaft near the top dead center of each cylinder is detected and the fluctuation of the rotational speed is observed, it is normal when the fluctuation is small. Yes, when it drops significantly, it can be determined that a misfire has occurred. Then, when a decrease in the rotational speed is detected, it can be understood that the cylinder that was in the vicinity of the top dead center immediately before that was a misfired cylinder.

[0004]

However, in the case of such a misfire detection device, since the rotational speed detection signal of the internal combustion engine at a specific position of each cylinder is used as it is for misfire detection, the rotation caused by factors other than misfire is detected. Even if there is a speed fluctuation, it cannot be determined whether or not it is due to a misfire. That is, the detection signal of the rotation speed of the internal combustion engine includes, for example, a rotation speed fluctuation twice (secondary) of the engine speed in the case of a four-cycle four-cylinder internal combustion engine, or a four-cycle six-cylinder internal combustion engine. 3
A double (third order) rotation speed fluctuation appears. In the case of an internal combustion engine for a vehicle, the rotational speed also fluctuates due to a change in the driving state of the vehicle, for example, acceleration or deceleration or running on a rough road. Further, once a misfire occurs, the oscillation repeats the oscillation that the rotation speed increases and then decreases again due to the phenomenon of swingback. Therefore, the detection signal of the engine rotation speed also includes a rotation speed fluctuation due to a factor other than the misfire. Therefore, if the rotational speed detection signal of the internal combustion engine is directly used for misfire detection as described above, noise is added particularly when the engine is running at a high speed and a low load or traveling on a relatively low speed rough road, There is a problem that the rotational speed fluctuation due to the misfire becomes unclear, the misfire detection performance is poor, and the determination of the misfire cylinder becomes difficult.

The present invention has been made in view of such a problem, and an object of the present invention is to clarify the rotational speed fluctuation due to a misfire, thereby improving misfire detection performance, and improving the misfire cylinder. An object of the present invention is to provide a misfire detection device for a multi-cylinder internal combustion engine that enables accurate determination.

[0006]

In order to achieve this object, according to the present invention, there is provided filter means for filtering a crankshaft rotation speed detection signal detected by a rotation speed detection means to extract a specific frequency component, Misfire is determined by comparing the output value of the filter means with a reference value. As the filter means,
A low-pass filter that passes components below a predetermined frequency,
Alternatively, a high-pass filter that passes a component of a predetermined frequency or more is used as needed. It is also possible to provide a differentiating means for differentiating the output signal of the filter means, and to determine the misfire by comparing the output value of the differentiating means with a reference value. That's it
The signal is processed by filtering means and differentiating means.
If this happens, a signal delay or phase advance will occur,
It may be difficult to determine the cylinder. So, determine misfire
The misfire determination means that such a time delay or phase advance
Misfire cylinder determination means for correcting misfire and determining the misfire cylinder
Be killed.

[0007]

Generally, the frequency of rotation speed fluctuation due to misfire of an internal combustion engine is about 10 to 50 Hz. On the other hand, the frequency of the rotation speed fluctuation of the internal combustion engine caused by the change in the operating state of the automobile is lower, and the frequency of the secondary or tertiary rotation speed fluctuation of the engine speed is higher. Therefore, if the engine speed signal output from the speed detecting means is filtered so that the frequency components of, for example, 10 Hz or less and 50 Hz or more are filtered, the speed variation due to factors other than the misfire is removed. As a result, the signal that has passed through the filter means is mainly due to misfire, so that when the output value of the filter means becomes lower than the reference value, misfire can be determined. In such a case, if the signal filtered by the filter means is differentiated by the differentiating means, the rotation speed fluctuation due to misfire becomes more remarkable. Therefore, by using the output signal of the differentiating means, it is possible to detect misfire more accurately.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of a misfire detection device according to the present invention. As is clear from this figure,
This misfire detection device includes a rotation speed detection means 1 for detecting a rotation speed of a crankshaft of a multi-cylinder internal combustion engine, a signal processing means 2 to which an output signal of the rotation speed detection means 1 is derived, and a signal processing means 2 A misfire judging means 3 for judging misfire from the output signal.

The rotation speed detecting means 1 includes a rotating member which rotates in synchronization with the crankshaft, for example, a ring gear 5 mounted on a flywheel 4 which is rotated by the crankshaft.
, A pickup 6 disposed close to the ring gear 5, and an FV converter 7 for converting an output signal of the pickup 6 into a voltage. The pickup 6 has a coil wound around a magnet.
A voltage is induced in the coil by a change in magnetic flux that occurs each time the teeth of the ring gear 5 pass through the pickup 6. Therefore, a pulse is output from the pickup 6. Then, the width of the pulse becomes the instantaneous rotation speed of the crankshaft at that time. The ring gear 5 has 120
There are teeth. Therefore, the instantaneous rotation speed of 120 times per one rotation of the crankshaft is detected by the pickup 6. The output pulse of the pickup 6 is converted into a voltage waveform by the FV converter 7. In this way, the rotation speed detecting means 1 outputs a waveform of the rotation speed fluctuation connecting the instantaneous rotation speeds of the internal combustion engine.

The signal processing means 2 includes a low-pass filter 8 for filtering a signal having a frequency higher than the set frequency and a high-pass filter 9 for filtering a signal having a frequency lower than the set frequency.
This is configured as filter means consisting of: The low-pass filter 8 removes a rotational speed fluctuation of a secondary (in the case of a four-cylinder internal combustion engine) or a tertiary (in the case of a six-cylinder internal combustion engine) frequency of the engine speed. The frequency is set lower than the second or third order frequency. For this purpose, a frequency changing means 10 is provided in the low-pass filter 8 so that the set frequency changes linearly or in multiple stages according to the rotation speed of the internal combustion engine. The high-pass filter 9 removes the rotational speed fluctuation of the internal combustion engine that occurs when the vehicle is accelerating or decelerating or traveling on a rough road. The set frequency is set higher than the frequency of such rotational speed fluctuation. For example, the frequency is set to about 3 Hz so as not to obscure the waveform of the rotation speed fluctuation at the time. Thus, the signal processing means 2 outputs only a signal of a specific frequency component between the set frequency of the low-pass filter 8 and the set frequency of the high-pass filter 9.

The misfire determining means 3 has a comparator 12 for comparing the output value of the signal processing means 2 with a reference value derived from a reference value setting device 11. When the output value of the signal processing means 2 is smaller than the reference value, the comparator 1
2 outputs a signal. Comparator 12
Is output to the timer 13, and when the output signal lasts for a time shorter than the predetermined time, the timer 13 outputs a misfire signal. A cylinder discrimination signal from the cylinder discrimination signal generator 14 is further added to the misfire signal, and the misfire cylinder determination means 15 corrects the time delay of the signal by the low-pass filter 8 and the high-pass filter 9 before the misfire cylinder is detected. It is to be fixed.

Next, the operation of the thus configured misfire detection device will be described. In the case of a four-cycle four-cylinder internal combustion engine, a top dead center (TDC) signal d of each cylinder as shown in FIG.
And a cylinder discrimination signal combining the cylinder signal c. The ignition of each cylinder is performed in the order of # 4, # 2, # 1, and # 3. At this time, the waveform output from the FV converter 7 of the rotation speed detecting means 1 is a complicated waveform including various frequency components as shown in FIG.
However, when the ignition of each cylinder is performed normally, the waveform has a relatively periodic waveform as shown in the left end portion of FIG.

Now, it is assumed that a misfire has occurred at the point s, that is, at the third cylinder # 3. Then, since the rotation speed of the crankshaft decreases, the output waveform of the rotation speed detecting means 1 drops significantly. And, due to the turning of the car body due to the misfire,
The engine speed increases and then decreases again. Therefore, the output waveform of the rotation speed detecting means 1 has a large swell as shown from the center to the right in FIG.

When the output waveform of the rotation speed detecting means 1 is passed through the signal processing means 2 as a filtering means, high frequency components are removed by a low pass filter 8 and low frequency components are removed by a high pass filter 9. As a result, as shown in FIG. 2 (C), the output waveform from the signal processing means 2 has a remarkable waveform including only a drop due to a misfire and a swell due to its rebound. Then, the output waveform from the signal processing means 2 is sent to the misfire discrimination means 3 and compared with the reference value generated by the reference value setting device 11. The reference value is a level indicated by h in FIG. Therefore, the drop of the waveform due to misfire becomes lower than the reference value. Thus, by comparing the output value of the signal processing means 2 with the reference value, it is determined that a misfire has occurred.

As described above, the output signal of the rotational speed detecting means 1 is passed through the signal processing means 2 as a filter means composed of the low-pass filter 8 and the high-pass filter 9, thereby generating an engine in a high-speed low-load region of the engine. High-frequency noise of the second or third order of the engine speed and low-frequency noise generated due to a change in the operating state of the vehicle in a relatively low-speed region are removed. That is, in this misfire detection device, misfire is detected by a waveform from which fluctuations in the rotational speed of the internal combustion engine due to factors other than misfire are removed as much as possible. Therefore, the detection of the misfire becomes accurate, and the determination of the misfiring cylinder is also ensured.

By the way, the frequency of the rotational speed fluctuation due to the reciprocation of the misfire is lower than the frequency of the rotational speed fluctuation due to the misfire, but is very close to the frequency. for that reason,
It is difficult to remove the influence of the swingback simply by passing the signal through the signal processing means 2. In other words, in order to remove the influence of the rebound, it is necessary to increase the set frequency of the low frequency to be filtered by the high-pass filter 9, but in such a case, the signal of the decrease in the rotational speed due to misfire becomes small, Moreover, the vibration due to the swing back does not become relatively small. Therefore, even if the signal passes through the signal processing means 2, the swell of the signal remains as described above. Then, due to such undulation, the fall of the waveform due to the swing may be equal to or lower than the level h of the reference value compared with the signal. As a result, there is a possibility that a decrease in the rotation speed due to the swingback is erroneously detected as misfire. Therefore, in this embodiment, the output signal of the comparator 12 is sent to the timer 13 and the signal processing means 2
The duration of the state where the output value from is lower than the reference value is measured. As described above, the repetition has a lower frequency than that of the misfire, so that the cycle becomes longer. Therefore, assuming that the time during which the reference level h is exceeded by misfire is t and the time during which the reference level h is exceeded due to reversal is t ′, t <
t ′. In other words, it is possible to determine whether the time is due to a misfire or a swingback depending on the time.

Thus, the misfire signal is output from the timer 13 only when the duration of the state where the output value of the comparator 12 is lower than the reference value is shorter than the predetermined time, so that misfire can be reliably determined. Then, the misfiring signal is sent to the misfiring cylinder determination means 15 to determine which cylinder has misfiring. In this case, the misfire determination is performed when the second cylinder # 2 is near the top dead center because of the time delay of the signal by the low-pass filter 8 and the high-pass filter 9. Therefore, the misfiring cylinder determination means 15 corrects the time delay and determines that the misfiring cylinder is # 3.

FIG. 3 illustrates a method for enabling the misfire detection device to more reliably distinguish between misfire and flurry. In this case, two reference levels h ₁ and h ₂ are set in the reference value setting device 11.
Then, the timer 13 detects the time during which the output value from the signal processing means 2 exceeds the reference levels h ₁ and h ₂ . Here, it is assumed that h ₁ > h ₂ . Further, the time that exceeds the reference level h ₁ due to misfire is t ₁ , and the time that the reference level h ₂ is exceeded is t.
_2, and the time that persists beyond the reference level h ₁ t ₁ ', the time that persists beyond the reference level h ₂ t _2' and the reacting roll phenomenon. Then, the reacting roll than the misfire as described above is a low-frequency, since the period is longer, the _{t 1 <t 1 't 1} -t 2 <t 1' -t 2 '. Therefore, t ₁ is shorter than the predetermined time, and t ₁
If it is detected that −t ₂ is shorter than the predetermined time and exceeds the reference level h ₂ , it can be determined that a misfire has occurred.

FIG. 4 shows a second embodiment of the misfire detecting apparatus according to the present invention.
It is a block diagram showing an example. In this embodiment, portions corresponding to those in the embodiment of FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted. In the case of this embodiment, the signal processing means 2 comprises a filter means comprising a low-pass filter for filtering a signal having a frequency higher than the set frequency and a high-pass filter for filtering a signal having a frequency lower than the set frequency; And a differentiating means comprising a differentiator for outputting a differential signal of Moreover, the low-pass filter and the differentiator are provided in two stages. That is, the FV of the rotation speed detecting means 1
The signal output from the converter 7 is first passed through a first low-pass filter 8a, and then sent to a differentiator 16a.
Further, the signal passes through the second low-pass filter 8b and is sent to the next differentiator 16b. The output signal of the differentiator 16b is guided to the high-pass filter 9. The first low-pass filter 8a removes a rotational speed fluctuation of a secondary (in the case of a four-cylinder internal combustion engine) or tertiary (in the case of a six-cylinder internal combustion engine) frequency of the engine speed. The fixed frequency is lower than the secondary or tertiary frequency of the engine speed but higher than the frequency of the rotational speed fluctuation due to misfire. Also,
The set frequency of the second low-pass filter 8b is set to the same frequency. On the other hand, the high-pass filter 9 removes fluctuations in the rotational speed of the internal combustion engine that occur when the vehicle is running and fluctuations in the rotational speed caused by the swaying after the misfire, and the set frequency is slightly higher than the swaying frequency. In this manner, the signal processing means 2 outputs only a signal of a specific frequency component between the set frequency of the first low-pass filter 8a and the set frequency of the high-pass filter 9 after being differentiated twice. I have.

The misfire judging means 3 has a comparator 12 for comparing the output value of the signal processing means 2 with the reference value derived from the reference value setting device 11, as in the embodiment of FIG. When the output value of the signal processing means 2 is smaller than the reference value, the comparator 12 outputs a misfire signal. The misfire signal is compared with a cylinder discrimination signal guided from a cylinder discrimination signal generator 14 by a misfire cylinder determination means 15, and a time delay of a signal by filters 8 a, 8 b, 9 and a phase advance by differentiators 16 a, 16 b are calculated. After the correction, the misfiring cylinder is determined.

In the misfire detecting apparatus thus constructed, in the case of a four-cycle four-cylinder internal combustion engine, as in the embodiment of FIG.
As shown in (A), a cylinder discrimination signal combining the TDC signal d of each cylinder and the cylinder signal c is output. When the ignition of each cylinder is performed normally, a waveform signal including various frequency components as shown in the left end portion of FIG. Is output. Now, point s in the figure,
That is, it is assumed that a misfire has occurred in the fourth cylinder # 4. Then
Since the rotation speed of the crankshaft decreases, the waveform output from the rotation speed detecting means 1 drops significantly. Then, due to the resurgence of the misfire, the rotation speed increases and then decreases again. Therefore, the output waveform is shown in FIG.
The waveform has a large swell as shown in FIG.

When the output waveform of the rotational speed detecting means 1 is passed through the signal processing means 2, first, high frequency components are removed by the first low-pass filter 8a. Therefore, the secondary or tertiary rotation speed fluctuation of the engine speed is removed from the detected rotation speed fluctuation signal. In that case, the output signal is delayed from the actual detection signal due to the time delay caused by the low-pass filter 8a. As a result, the output waveform from the first low-pass filter 8a becomes a waveform as shown in FIG. In this way, a waveform is obtained in which the drop due to the misfire and the undulation due to the swing are remarkable. The waveform includes low frequency components such as fluctuations in the rotational speed of the internal combustion engine while the vehicle is traveling on a rough road.

Next, the output signal of the first low-pass filter 8a is differentiated by a differentiator 16a. Then, as the phase of the signal waveform advances, the amplitude increases. In that case, the rate of increase of the amplitude increases as the frequency increases. Therefore, the amplitude of the signal of the decrease in the rotational speed due to the misfire becomes much larger than that due to the reversal. On the other hand, since the cycle of the rotation speed fluctuation due to the swingback is almost constant, the cycle does not change by the differentiation. As a result, the waveform output from the differentiator 16a becomes a waveform as shown in FIG. That is,
It is as if the frequency of the signal of rotation speed reduction due to misfire was increased. After the output signal from the differentiator 16a is passed through the second low-pass filter 8b, the differentiator 1
Differentiated again at 6b. As a result, a signal having a higher frequency than a signal of a decrease in rotation speed due to misfire is removed, and a signal at the time of misfire is further sharpened. Thus,
The waveform of the signal output from the differentiator 16b is as shown in FIG. The scale of FIG. 5D is larger than that of FIG. 5C, and the scale of FIG.

The output signal from the differentiator 16b is then passed through a high-pass filter 9 to remove low-frequency components below the frequency of the repetition. As a result, components such as rotation speed fluctuation due to swingback and rotation speed fluctuation during running of the automobile are removed from the signal. In this case, since the signal of the rotation speed fluctuation due to the misfire is sharpened as described above, the signal does not become dull even by passing through the high-pass filter 9. In this way, the signal processing means 2 outputs a waveform signal in which only a decrease in rotation speed due to misfire is clear.

Then, the output waveform signal from the signal processing means 2 is sent to the misfire discrimination means 3 and compared with the reference value generated by the reference value setting unit 11 in the comparator 12. The reference value is a level as shown by h in FIG. Therefore, the drop of the waveform due to misfire becomes lower than the reference value. At other times, it does not become lower than the reference value. Thus, by comparing the output value of the signal processing means 2 with the reference value, it is determined that a misfire has occurred when the output value is lower than the reference value.
2 outputs a misfire signal. Then, the misfiring signal is sent to the misfiring cylinder determination means 15 to determine which cylinder has misfiring. In that case, the filters 8a, 8b, 9
, And the phase advance of the signal by the differentiators 16a and 16b, the determination of misfire is made at a time different from the time when the misfire actually occurs. Therefore, the misfiring cylinder determination means 15 determines the misfiring cylinder after correcting the time lag.

In this way, in this misfire detection device, misfire is detected by a waveform from which fluctuations in the rotational speed of the internal combustion engine due to factors other than the misfire and fluctuations in the rotational speed due to rebound after the misfire have been removed. Therefore, the detection of the misfire becomes more accurate, and the determination of the misfiring cylinder becomes more reliable. In this embodiment, the number of low-pass filters and differentiators may be three or more. In some cases, they may be provided in only one stage. The frequency of the vibration caused by the rebound after the misfire changes depending on the gear ratio of the transmission. Therefore, it is desirable that the set frequency of the high-pass filter 9 be changed according to the gear shift position of the transmission.

In the above embodiment, the signal processing is performed in an analog manner, but this can be changed to digital processing. By doing so, the configuration of the misfire detection device can be further simplified. For example, in the case of the embodiment shown in FIG. 1, it is necessary to use the frequency changing means 10 to change the set frequency of the low-pass filter 8 according to the engine speed. Automatically changes according to the engine speed, so that such means is not required. FIG.
FIG. 3 is a block diagram showing a different embodiment of the present invention in which a misfire is detected by digitally processing the signal. As is apparent from this figure, in this case, the crank angle sensor 21 is used as rotation speed detecting means for detecting the rotation speed of the crankshaft. The crank angle sensor 21 is attached to a camshaft 22 that rotates at half the speed in synchronization with the crankshaft, and the camshaft 22 is rotated by 15 °, that is, one crankshaft every 30 °. It is supposed to generate a pulse. The crank pulse output from the crank angle sensor 21 is input to a signal processing device 23 including a microcomputer. When viewed functionally, the signal processing device 23 includes a low-pass filter 24 and a high-pass filter 25 as filter means for filtering an input signal and passing only a signal of a specific frequency component;
A differentiating means 26 for differentiating the signal output from 25 and a misfire determining means 27 for determining a misfire based on the output signal of the differentiating means 26 are provided. Then, a signal from the signal processing device 23 is output to a display device 28 such as a display or a printer, and when a misfire occurs, it is displayed.

The low-pass filter 24 and the high-pass filter 25 are digital filters called Butterworth filters for performing digital filtering on input pulses, have predetermined transfer function characteristics, and have variable gains. Then, the low-pass filter 24 is substantially T
Attenuates above the DC frequency and the high-pass filter 25
It has a characteristic of attenuating below the C frequency. Further, the differentiating means 26 calculates a difference between the input value at that time and the value input before. And
The misfire judging means 27 compares the input value with the reference value, and when the input value is larger than the reference value, judges that a misfire has occurred and outputs a misfire signal. The reference value is the engine speed N
e, which is previously obtained as a function of the intake pipe negative pressure Pb, the vehicle speed V, or the gear position of the transmission,
It is stored as a map.

In the signal processing device 23, processing as shown in FIG. 7 is performed. That is, when the process is started, a crank pulse is input in step s1. Each time the crank pulse is input, an output value corresponding to the characteristics of the low-pass filter 24 is calculated in step s2. The operation is as follows: when input data is u (k) and output data is y (k), y (k) = b ₁ u (k) + b ₂ u (k−1) + b ₃ u (k−2) −a ₂ y (k−1) −a ₃ y (k−2). Where b ₁ , b ₂ , b ₃ and a
₂ and a ₃ are constants set in advance to remove high-frequency noise. For example, when the Nyquist frequency, which is a half of the sample frequency, is 600 Hz, the attenuation characteristic of the low-pass filter 24 is determined to be within 3 dB at 200 Hz and to be -19 dB or more at 400 Hz. Next, in step s3, it is determined whether or not the engine is in a predetermined stage at that time, that is, whether or not six crank pulses have been counted in the case of a four-cycle four-cylinder internal combustion engine. When it is not on the predetermined stage, it is held as it is.
When it is determined that the crankshaft is on the predetermined stage, the rotation time Me per predetermined rotation angle of the crankshaft is calculated in step s4. The rotation time Me is obtained by the sum of the six crank pulse intervals Cr input so far, that is, Me = Cr _n + C _n−1 +... + C _n−5 . Thus, in the case of a four-cycle four-cylinder internal combustion engine, every time any one of the cylinders reaches TDC, a pulse of the magnitude of Me representing the time during that time is output. Then, in step s5, it is determined whether or not the engine speed Ne at that time is in a relatively low speed region such as, for example, 3000 rpm or less. At M
An output value corresponding to the characteristic of the high-pass filter 25 that passes the e-pulse is calculated. The calculation is also performed by the same formula as that of the low-pass filter 24, but the coefficient is changed so that low-frequency noise due to running on a rough road and rebound of misfire are removed. The numerical value is such that when the Nyquist frequency is 600 Hz, the attenuation characteristic of the high-pass filter 25 is within 3 dB at 70 Hz and -14 dB or more at 30 Hz. When the engine speed Ne is high, step s6 is skipped and the high-pass filter 25
Is not calculated. Next, in step s7,
It is determined whether or not it is in the misfire determination area. Immediately after the start of the internal combustion engine, at the time of rapid acceleration / deceleration, or at the time of a load change, the noise increases, and the probability of erroneous detection increases, so that the misfire determination is not performed. In such a case, it is determined that it is not in the misfire determination area, and the state is maintained as it is. On the other hand, when it is determined that the misfire determination region, Me variation amount DerutaMe, i.e. ΔMe = Me _n -Me _n-1 is calculated in step s8. The variation ΔMe is a differential value of Me, and corresponds to the rotational angular velocity of the crankshaft. Further, in step s9, the current ΔMe and the preceding four ΔMe
The difference ΔΔMe from the average value of Me is calculated. That is, ΔΔMe = ΔMe _n − (ΔMe _n−1 + ΔMe _n−2 +... + ΔMe _n−4 ) / 4. This ΔΔMe is a differential value of ΔMe, and corresponds to the rotational angular acceleration of the crankshaft. When ΔΔMe is obtained in this way, a map search is performed for a misfire determination reference value in step s10. Then, in step s11, these ΔΔMe are compared with the reference value. If the absolute value of ΔΔMe is larger than the reference value, it is determined in step s12 that a misfire has occurred, and a misfire signal is output.

In the misfire detection device configured as described above, the crank pulse output from the crank angle sensor 21 is subjected to low-pass filtering in the signal processing device 23, so that a high frequency such as the second order of the engine speed is obtained. Noise is removed. Therefore, the Me pulse calculated from the crank pulse signal does not include high-frequency noise. Then, when the engine speed Ne is relatively low, the Me pulse is subjected to high-pass filtering, so that low-frequency noise generated when the vehicle is running on a rough road or due to a reciprocating misfire is also removed. As a result, the signal used for the misfire determination is close to the TDC frequency including only the rotation speed fluctuation due to the misfire. In this case, if the engine speed Ne is in the high rotation region, the high-pass filtering is not performed. That is, the high-pass filter 25 does not work in the block diagram of FIG. When the internal combustion engine is running at high speeds, erroneous detection due to rough road running or duplicate erroneous detection due to reign of misfire does not pose a problem.On the contrary, the absolute value level of input data is impaired by high-pass filtering, so High-pass filtering is performed only in the low engine speed region. Further, it is desirable that the misfire determination be stopped even when switching between the low rotation range and the high rotation range.

When the ignition of each cylinder is performed normally, the value of Me is kept substantially constant, so that ΔMe is small and ΔMe is also sufficiently small. Therefore, no misfire signal is output. However, when a misfire occurs in a certain cylinder, Me up to the TDC of the next cylinder increases. As a result, ΔMe increases and ΔΔM
The absolute value of e also becomes larger than the reference value. As a result, a misfire signal is output from the signal processing device 23 and is displayed on the display device 28.

As described above, the misfire can be accurately detected also by digitally processing the signal. By doing so, the signal processing can be handled by software, so that the accuracy of the misfire detection device can be improved while simplifying the configuration and reducing the cost. Also in this case, due to the characteristics of the low-pass filter 24 and the high-pass filter 25, a time delay occurs between the time when the misfire actually occurs and the time when the misfire is detected. Therefore, the misfire determination means 27 is provided with a misfire cylinder determination means, and the misfire cylinder is determined in consideration of the time delay.

In this embodiment, a TDC pulse can be used instead of a crank pulse. Also, in the embodiment of FIG. 1 or FIG. 4, a crank angle sensor can be used instead of the ring gear 5.

[0034]

As is apparent from the above description, according to the present invention, the output signal from the detecting means for detecting the rotational speed of the crankshaft is filtered to extract only the signal component of a specific frequency. So, the engine speed 2
Rotational speed fluctuations due to factors other than misfires, such as rotational speed fluctuations having the second or third order frequency, rotational speed fluctuations due to changes in the driving state of the vehicle, and rotational speed fluctuations due to swingback after a misfire are removed. , And the fluctuation of the rotation speed at the time of misfire can be clarified. Therefore, the misfire detection performance can be improved. Further, the misfiring cylinder can be accurately determined.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a misfire detection device for a multi-cylinder internal combustion engine according to the present invention.

FIG. 2 is a waveform diagram showing signal waveforms output at various parts of the misfire detection device.

FIG. 3 is a waveform chart showing another example of a misfire determination method.

FIG. 4 is a block diagram showing another embodiment of the misfire detection device for a multi-cylinder internal combustion engine according to the present invention.

FIG. 5 is a waveform chart showing signal waveforms output from various parts of the misfire detection device of FIG. 4;

FIG. 6 is a block diagram showing still another embodiment of the misfire detection device for a multi-cylinder internal combustion engine according to the present invention.

FIG. 7 is a flowchart illustrating a procedure of signal processing performed in the misfire detection device of FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rotation speed detection means 2 Signal processing means 3 Misfire discrimination means 5 Ring gear (rotating member) 8, 8a, 8b Low pass filter (Filter means) 9 High pass filter (Filter means) 11 Reference value setting unit 12 Comparator 14 Cylinder discrimination signal generation Unit 15 Misfire cylinder determining means 16a, 16b Differentiator (differentiating means) 21 Crank angle sensor (rotating speed detecting means) 22 Cam shaft (rotating member) 23 Signal processing device 24 Low-pass filter (filter means) 25 High-pass filter (filter means) 26 Differentiating means 27 Misfire determining means

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shigeru Maruyama 1-4-1, Chuo, Wako, Saitama Prefecture Inside Honda R & D Co., Ltd. (72) Koichi Nishimura 1-4-1, Chuo, Wako, Saitama Prefecture Inside Honda R & D Co., Ltd. (72) Inventor Akira Kato 1-4-1, Chuo, Wako-shi, Saitama Prefecture Inside Honda R & D Co., Ltd. (56) References JP-A-2-291476 (JP, A) JP-A Sho-61 -11440 (JP, A) JP-A-59-113269 (JP, A) JP-A-4-194346 (JP, A) JP-A-5-149182 (JP, A) )

Claims (4)

(57) [Claims] 1. A rotation speed detection means for detecting a rotation speed of a crankshaft at that time based on rotation of a rotation member which rotates in synchronization with a crankshaft of a multi-cylinder internal combustion engine, and an output of the rotation speed detection means. Filter means for filtering out a specific frequency component of the signal by filtering the signal; and misfire judging means for judging misfire of the internal combustion engine by comparing an output value of the filter means with a reference value , wherein the misfire judging means The time depending on the characteristics of the filter means.
A misfire cylinder determination method that determines the misfire cylinder taking into account the delay
A misfire detection device for a multi-cylinder internal combustion engine, comprising a stage . 2. The misfire according to claim 1, wherein said filter means comprises a low-pass filter that passes a component of a rotation speed signal output from said rotation speed detection means that is lower than a predetermined frequency. Detection device. 3. The misfire according to claim 1, wherein said filter means is constituted by a high-pass filter which passes a component having a frequency equal to or higher than a predetermined frequency of a rotation speed signal output from said rotation speed detection means. Detection device. 4. A rotation speed detection means for detecting a rotation speed of a crankshaft at that time based on rotation of a rotation member which rotates in synchronization with a crankshaft of a multi-cylinder internal combustion engine, and an output of the rotation speed detection means. Filter means for filtering a signal to extract a specific frequency component thereof; differentiating means for differentiating an output signal of the filter means; comparing an output value of the differentiating means with a reference value to determine misfire of the internal combustion engine comprising a misfire determination means for, the, the misfire determining means, when due to the characteristics of the filter means
Taking into account the delay and the phase advance due to the characteristics of the differentiating means,
Misfiring cylinder determination means to make a decision of the misfiring cylinder Te has been eclipsed set
A misfire detection device for a multi-cylinder internal combustion engine.