JPH05149192A - Miss fire detecting device - Google Patents

Abstract

PURPOSE:To perform easy and accurate detection of a miss fire without varying conventional structure by respectively extracting vibration components in two kinds of high and low frequency bands from detecting signals from a plurality of knock sensors and respectively detecting a knock and a miss fire based on the extracted vibration components. CONSTITUTION:Vibration of an engine is detected by a plurality of knock sensors 1 and 3 and from detecting signals therefrom, a knock vibration component is extracted by means of a first filter 6, and a vibration component during the occurrence of a miss-fire is extracted by a second filter 9. The knock sensors 1 and 3 and the filters 6 and 9 are arbitrarily interconnected through a switch circuit 5. Further, from an output from the first filter 6 at one ignition period, a peak value is determined, the peak value is compared with an output level from the first filter 6, and a knock is detected by a knock detecting part 7. From an output from the second filter 9 at a one ignition period, a miss-fire decision value is determined, the decision value is compared with an output level from the second filter 9, and a miss-fire is detected by a miss-fire detecting part 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to misfire detection of an internal combustion engine for automobiles.

[0002]

2. Description of the Related Art In recent years, exhaust gas regulations of automobiles have been regarded as important with respect to environmental pollution, and misfire detection is required as a part thereof. That is, by detecting the misfire, it is possible to prevent the raw gas from being discharged from the vehicle without being ignited.

FIG. 5 shows an example of an internal pressure sensor of a conventional misfire detecting device. In FIG. 5, 151 is an ignition plug attached to the engine cylinder 152, and 153 is an internal pressure sensor attached instead of the gasket of the ignition plug 151.

The internal pressure sensor 153 constructed as described above
The operation will be described below. When the ignition plug 151 to which the internal pressure sensor 153 is attached is fastened to the engine cylinder 152, a compressive load is applied to the internal pressure sensor 153. When the cylinder internal pressure rises in this state, 151 is pushed out and the compressive load of the internal pressure 153 decreases. In this way, the compression load fluctuates according to the cylinder internal pressure, and an output corresponding to the fluctuation is obtained. This is shown in FIG.

FIG. 6 is a characteristic diagram showing the relationship between the crank angle of one engine cycle and the pressure in the cylinder at the time of ignition and misfire. As is apparent from FIG. 6, the compression / explosion stroke of the engine is shown. There is a large pressure difference between the cylinder internal pressure at ignition and the misfire.
Therefore, by comparing this pressure difference, misfire and ignition can be distinguished.

[0006]

However, the above-mentioned conventional misfire detection devices have problems in terms of reliability and cost of the internal pressure sensor, and most of them are at the research level and the experimental level, so that there is a problem in practical use. was there.

The present invention solves the above-mentioned conventional problems and is excellent in that a misfire can be detected without changing the conventional structure by using a vibration sensor such as a knock sensor which has already been put to practical use in a vehicle. It is an object of the present invention to provide a misfire detection device.

[0008]

In order to achieve the above object, the present invention provides a plurality of knock sensors for detecting engine vibration including a vibration component at the time of misfire, and a knock vibration component based on a signal detected by the knock sensor. , A second filter for extracting a vibration component at the time of misfire, a switch circuit for arbitrarily connecting the plurality of knock sensors to the first and second filters, and the first filter for one ignition timing.
A knock value is obtained from the output from the filter, and a knock detection unit is provided that compares the peak value with the output level from the first filter to perform knock determination and outputs, and a misfire determination value from the output from the second filter at one ignition timing. Is calculated and the output level from the second filter is compared to determine the misfire and output.

[0009]

With the above-described structure, the present invention uses the knock sensor near the burning cylinder, which is easy to detect knock vibration, among the plurality of knock sensors already installed for knock detection. The remaining other knock sensors can be used for misfire detection, and the misfire detection can be reliably performed at low cost without making any changes to the structure of the engine or the like.

[0010]

1 is a block diagram showing the overall construction of a misfire detection device according to the present invention. In FIG. 1, reference numerals 1 and 3 denote first and second knock sensors for detecting engine vibration including a misfire component. The first knock sensor 1 and the second knock sensor 3 are attached to an engine block. Reference numeral 12 denotes an engine rotation sensor such as a crankshaft sensor or a TDC sensor, which is synchronized with the movement of a piston. The signal detected by the engine rotation sensor 12 is waveform-shaped by a waveform shaping circuit 13 and then sent to a timing calculation unit 14. Is entered. The timing calculation unit 14 calculates the ignition timing based on the output signal from the waveform shaping circuit 13, and the calculated ignition timing signal is the knock determination circuit 74.
It is input to the misfire determination circuit 104 and the switch circuit 5, respectively.

The switch circuit 5 is an analog switch 51,
52, 53 and 54 and an inverter 55. The analog switches 51 and 53 relay the outputs of the first and second knock sensors to the first and second filters, respectively, according to the misfire timing signal. Further, the analog switches 52 and 54 relay the outputs of the first and second knock sensors to the second and first filters, respectively, according to the misfire timing signal inverted by the inverter 55.

The first filter 6 filters the characteristic frequency of knock from the signal from the first or second knock sensor, and the signal passed through the first filter 6 is input to the knock determination section. In addition, the second filter 9 is the first
Alternatively, the characteristic frequency of misfire is filtered from the signal from the second knock sensor, and the signal that has passed through the second filter 9 is input to the misfire detection unit.

The knock detecting section 7 is a comparison level calculating circuit 72 for calculating a reference level from the average value of the knock sensor signals,
The output of the peak value detection circuit 71 and the peak value detection circuit 71 for detecting the peak value of the knock sensor signal in the period (knock gate) at which the knock output from the knock determination circuit 74 is generated are compared with the output of the comparison level calculation circuit 72. It is composed of a comparator 73 for comparison and a knock determination circuit 74 for making a knock determination from the output of the comparator 73.

The misfire detecting section 10 includes an amplifier 101 for amplifying the output of the second filter 9 and a comparison level calculating circuit 102 for calculating a comparison level from an average value of knock sensor signals.
And a comparator 103 that compares the output of the width device 101 with the output of the comparison level calculation circuit 102, and a misfire determination circuit 104 that performs a misfire determination based on the output of the comparator 103.

Next, the operation of the above-described embodiment constructed as described above will be described with reference to FIGS. In FIG. 1, first, engine vibration is detected by the first knock sensor 1 and the second knock sensor 3. At this time, at the same time, the ignition timing signal (A) synchronized with the engine rotation is output from the timing calculation unit 14. Based on the ignition timing signal (A), at the ignition timing of the cylinder near the installation location of the first knock sensor 1, the signal from the first knock sensor 1 is sent to the first filter 6 and the signal from the second knock sensor 3 is sent. It is input to the second filter 9. Conversely, at the ignition timing of the cylinder near the installation location of the first knock sensor 1, the signal from the first knock sensor 1 is sent to the second filter 9 and the signal from the second knock sensor 3 is sent to the first filter 6. Is entered.

The first filter 6 and the second filter 9 each include a buffer for impedance conversion,
The first filter 6 extracts a vibration component in a high frequency band from the detection signal and outputs it to the knock determination unit 7. Second filter 9
Extracts a vibration component in a low frequency band from the detection signal and outputs it to the misfire detection unit 10. Here, FIG. 2 shows a frequency analysis diagram of the knock sensor. As shown in FIG. 2, a low frequency (for example, 1
There is a clear difference in the level of the vibration sensor in the vicinity of 00 Hz), and misfire can be detected by this level difference. Since the characteristic frequency of knocking is 5 to 12 KHz, the knock signal and the misfire signal can be separated as shown in FIG. 3 by the first and second filters. That is, the pass band of the first filter is the frequency band of the knock signal,
The pass band of the filter 9 is the frequency band of the misfire signal representing the misfire component.

The knock detection section 7 compares the value of the peak value detection circuit 71 with the value of the comparison level calculation circuit 72 for knock determination, and the misfire detection section 10 compares the value of the amplifier 101 with the comparison level calculation circuit 102. The misfire determination is performed by comparing the values, and the signal waveforms at A to C1, C2 to F1, F2 and G in FIG. 1 are shown in FIGS. 4 (A) to (G).

First, in response to the misfire timing signal (A) from the timing output unit 14, the knock circuit signals (B) from the first knock sensor and the second knock sensor are switched by the switch circuit 5 to the first and second filters, respectively. 6 and 9
Will be relayed to. The high frequency (5 to 12 KHz) signal component extracted by the first filter 6 is amplified by the peak value detection circuit 71 and the peak value between the high levels of the knock gate signal (D) from the knock determination circuit 74 is set. It detects and supplies the peak detection signal (C1) to one input of the comparative example 73. At the same time, the output of the first filter 6 is supplied to the comparison level calculation circuit 72, where it is subjected to integration processing or other signal processing to output a comparison level signal (C2) which is a threshold voltage, and the other input of the comparator 73. Supply to. In the comparator 73, when the value of the peak detection signal (C1) exceeds the value of the comparison level signal (C2), the comparison detection signal (E) is generated and supplied to the knock determination circuit 74.
The knock determination circuit 74 latches this comparison detection signal (E) and outputs a knock determination output 8.

On the other hand, the signal component of the low frequency (near 100 Hz) extracted by the second filter 9 is the amplifier 1
The signal is amplified by 01 and supplied to one input of the comparator 103 as a misfire detection signal (F1). At the same time, the output of the second filter 9 is output by the comparison level calculation circuit 102 as a comparison level signal (F2) which is a threshold voltage, and is supplied to the other input of the comparator 103.

In the comparator 103, the misfire detection signal (F
When the value of 1) exceeds the value of the comparison level signal (F2),
A comparison detection signal (G) is generated and supplied to the misfire determination circuit 104. The misfire determination circuit 104 latches this comparison detection signal (G) and outputs a misfire determination output 11.

As described above, according to this embodiment, misfire can be detected easily and accurately from the signal of the knock sensor.

Although two knock sensors are used in the above embodiment, engine vibration is detected by one common sensor or three or more knock sensors, and the frequency is separated by the first and second filters. It is also possible to obtain a knock determination output and a misfire determination output.

[0023]

As is apparent from the above embodiment, the present invention uses an existing vibration sensor such as a knock sensor,
At the same time as knock detection is performed by extracting knock vibration component,
By extracting the frequency component of misfire, measuring its level, and comparing it with the determination threshold value, there is an excellent effect that misfire can be detected easily and accurately for each cylinder.

[Brief description of drawings]

FIG. 1 is a block diagram of a misfire detection device according to an embodiment of the present invention.

FIG. 2 is a vibration sensor frequency analysis diagram for explaining the operation of the misfire detection device according to the present embodiment.

FIG. 3 is a frequency characteristic diagram of a knock sensor and a filter for extracting a misfire and a knock in the present embodiment.

FIG. 4 is a timing diagram for explaining the operation of the misfire detection device according to the present embodiment.

FIG. 5 is a diagram of an internal pressure sensor in a conventional example.

FIG. 6 is a diagram showing outputs of an internal pressure sensor in a conventional example during ignition and misfire.

[Explanation of symbols]

 1 1st knock sensor 3 2nd knock sensor 5 switch circuit 6 1st filter 7 knock detection part 8 knock determination output 9 2nd filter 10 misfire detection part 11 misfire detection output 12 engine rotation sensor 13 waveform shaping circuit 14 timing calculation part

Claims (3)

[Claims] 1. A knock sensor for detecting engine vibration, a first filter for extracting a vibration component in a high frequency band from a detection signal detected by the knock sensor, and an output from the first filter at one ignition timing. A knock detection unit that makes a knock determination, a second filter that extracts a vibration component in a low frequency band from a signal detected by the knock sensor, and a misfire detection that makes a misfire determination from the output from the second filter at one ignition timing. And a misfire detection device. 2. A plurality of knock sensors for detecting engine vibration, and a signal detected by at least one of these knock sensors for the first filter, and a signal detected by the remaining other knock sensors for the second filter. The misfire detection device according to claim 1, further comprising a switch circuit for inputting to the. 3. The switch circuit uses the first filter to detect a signal detected from a knock sensor close to a cylinder at an ignition timing among the knock sensors, and the second filter to detect a signal detected from the other knock sensors. The misfire detection device according to claim 2, wherein the inputs are alternately input in synchronization with the movement of the piston.