JPH04307336A - Misfire detecting apparatus - Google Patents

Abstract

PURPOSE:To detect not only a knock, but misfire by utilizing a knock sensor mounted to an engine, and extracting a signal characteristic of the misfire from the vibration generated at misfiring. CONSTITUTION:This apparatus is comprised of a piezoelectric knock sensor 1 for detecting the vibration of an engine, a first filter 3 for distinguishing knock frequency components from the signals of the knock sensor 1, a knock detecting part 4 for detecting a knock from the outputs of the first filter 3, a second filter 5 for distinguishing the misfire frequency characteristic of misfire from the signals of the knock sensor 1, and a misfire detecting part 6 for detecting the misfire from outputs of the second filter 5. Accordingly, not only a knock is detected, but misfire can be detected.

Description

[Detailed description of the invention]

0001

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

0002

2. Description of the Related Art In recent years, automobile exhaust gas regulations have become important in terms of environmental pollution, and as part of this, misfire detection has become necessary. In other words, misfire information is sent to the control unit that controls gasoline injection, and gasoline injection to the misfired cylinder is stopped, thereby preventing raw gas from being discharged from the vehicle without being ignited.

A conventional misfire detection device will be explained below. In FIG. 5, 51 is a spark plug attached to the engine cylinder, and tightens an internal pressure sensor 52 instead of a gasket. At this time, a compressive load is constantly acting on the internal pressure sensor 52. When the cylinder internal pressure increases in this state, the spark plug 51 is pushed outward, and the compressive load on the internal pressure sensor 52 decreases. In this way, the compressive load of the internal pressure sensor 52 changes depending on the cylinder internal pressure. As shown in FIG. 6, the cylinder internal pressure during the engine's compression and explosion strokes has a large pressure difference between ignition and misfire. Therefore, by comparing this pressure difference, misfire and ignition can be distinguished.

0004

[Problems to be Solved by the Invention] However, the above-mentioned conventional misfire detection devices are at the research/laboratory level, and have the problem of being difficult to put into practical use due to the reliability and cost of the internal pressure sensor. Ta.

The present invention solves the above-mentioned conventional problems, and provides an excellent misfire detection device that can detect not only knocks but also misfires at the same time using a piezoelectric knock sensor that has been put to practical use in vehicles. The purpose is to

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a knock sensor attached to an engine, a first filter for discriminating a knock frequency component from a signal of the knock sensor, and a first filter for discriminating a knock frequency component from a signal of the knock sensor. A knock detection section that detects a knock from the output of the filter, a second filter that discriminates a misfire frequency component from the signal of the knock sensor, and a misfire detection section that detects a misfire from the signal of the second filter are provided. , which allows misfire detection to be performed at the same time as knock detection.

[0007]

[Operation] Therefore, according to the present invention, by using a knock sensor that has already been put into practical use as an automotive vehicle, at the same time as detecting a knock, a frequency component whose output level is higher than that at the time of ignition at the time of a misfire is extracted, and A misfire can be detected by the signal.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of an embodiment of the present invention. In FIG. 1, 1 is a knock sensor, 2 is a buffer, and 3
is a first filter that passes the knock signal (knock frequency component). 4 is a knock detection section, and a peak value detection circuit 4
1. Comparison reference level calculation circuit 42, knock determination circuit 43
It's getting better. 5 is a second filter that passes the misfire signal (misfire frequency component). Reference numeral 6 denotes a misfire detection section, which includes an amplifier 61, a comparison reference level calculation circuit 62, and a misfire determination circuit 63.
It's getting better. 7 is a microcomputer, 8
is an ignition signal, and 9 is an injection signal.

Next, the operation of the above embodiment will be explained. When the knock sensor signal is frequency-analyzed, as shown in Fig. 2, it is found that during misfire and ignition, there is a low frequency range (100 Hz).
There is a clear difference in the output level of the knock sensor 1 in the vicinity), and this frequency component is extracted by the second filter 5 and separated as a misfire signal. Further, as shown in FIG. 3, since the resonance frequency of the knock sensor is in the range of 5 to 12 KHz, this frequency component is extracted by the first filter 3 and separated as a knock signal. As a result, knock sensor 1
The signal is separated into a knock signal and a misfire signal by the first filter 3 and the second filter.

Next, the knock detection section 4 will be explained. The output (knock signal) of the first filter 3 is transmitted to the knock detection section 4
peak value detection circuit 41 and comparison reference level calculation circuit 42
to go into. The peak value detection circuit 41 detects the peak value of the knock signal in synchronization with the knock gate signal calculated by the knock gate calculation section 71 of the microcomputer 7. A comparison reference level calculation circuit 42 calculates a comparison reference level from the average value of the knock signals. The knock determination circuit 43 compares the output of the peak value detection circuit 41 with the comparison reference level calculation circuit 42.
A knock judgment is made by comparing the outputs of the two. When the knock determination output is output, the ignition timing calculation section 72 calculates the ignition timing and outputs the ignition signal 8.

Next, the misfire detection section 6 will be explained. The output (misfire signal) of the second filter 5 is input to the amplifier 61 of the misfire detection section 6 and the comparison reference level calculation circuit 62. An amplifier 61 amplifies the misfire signal and a comparison reference level calculation circuit 62
calculates the comparison reference level from the average value of the misfire signal. A misfire determination circuit 63 compares the output of the amplifier 61 and the output of the comparison reference level calculation circuit 62 to determine a misfire. If a misfire is detected here, a misfire detection output is output, and the fuel injection amount calculation unit 73 takes measures such as stopping fuel injection to the cylinder in which the misfire is occurring. FIG. 4 shows a timing diagram of the present invention. (A) is the ignition timing, (B
) is the knock sensor signal, (C) is the knock signal (solid line part)
and comparison reference level (dotted line), (D) is knock gate signal, (E) is knock judgment output, (F) is misfire signal (solid line) and comparison reference level (dotted line), (G) is misfire detection. This is the output.

As described above, according to the above embodiment, the misfire signal and the knock signal are separated from the signal of the knock sensor 1, the comparison reference level is calculated from the average value of the misfire signals, and the reference level and the misfire are calculated from the average value of the misfire signals. A misfire can be detected by comparing the signal.

[0013]

As described above, the present invention uses an existing vibration sensor such as a knock sensor and separates its frequency components to easily and accurately detect not only knock but also misfire. Therefore, it is possible to realize an excellent misfire detection device that can perform the following steps.

[Brief explanation of drawings]

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

[Figure 2] Frequency analysis diagram of the knock sensor of the misfire detection device in the same example

[Figure 3] Frequency characteristic diagram of the knock sensor of the misfire detection device in the same embodiment

[Fig. 4] Timing diagram of the misfire detection device in this embodiment

[Fig. 5] Cross-sectional view of a conventional misfire detection device

[Fig. 6] A diagram showing the output of the internal pressure sensor in the conventional misfire detection device.

[Explanation of symbols]

1 Knock sensor 2 Buffer 3 First filter 4 Knock detection part 5 Second filter 6 Misfire detection section 7. Microcomputer 8 Ignition signal 9 Injection signal

Claims (1)

[Claims] 1. A piezoelectric knock sensor that detects engine vibration, a first filter that discriminates a knock frequency component from a signal of the piezoelectric knock sensor, and a knock detection device that detects a knock from the output of the first filter. A misfire detection device comprising: a second filter that discriminates a misfire frequency from a signal of the piezoelectric knock sensor; and a misfire detection section that detects a misfire from the output of the second filter.