JPH0658299B2 - Misfire detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a misfire detection device, and more particularly to a misfire detection device for determining engine misfire from a rate of change of pressure in a combustion chamber.

<Prior art> It is known that engine misfires are likely to occur at light engine loads due to a decrease in compression pressure in the combustion chamber, a lean mixture, or poor ignition of the spark plug. It causes harmful effects such as unpleasant vibration and reduced engine output.

Therefore, various devices have been proposed as means for detecting such a misfire state, for example, Jikken Sho 59-2808.
An example is disclosed in Japanese Patent Publication No.

The misfire detection device disclosed in this publication pays attention to the backflow phenomenon of the exhaust gas generated in the exhaust passage at the time of misfire, and provides two orthogonal pipes in the exhaust passage. The change in pressure is detected to determine misfire.

However, since this device detects a misfire based on the exhaust gas, there is a time delay and the pressure in the exhaust passage fluctuates due to pulsation, which makes it difficult to accurately determine the misfire.

Therefore, the applicant of the present application has proposed a misfire detecting device for solving such a drawback in Japanese Patent Application No. 60-148000.

The misfire detection device according to this application directly measures the pressure in the combustion chamber of the engine with a pressure sensor to determine the misfire state, but this device also has the following problems.

<< Problems to be Solved by the Invention >> The misfire detection device of the present applicant has a compression top dead center in a normal ignition state in the pressure in the combustion chamber from the start of the compression stroke of the engine to the end of the combustion stroke. While the peak value due to compression appears, another peak value due to combustion appears at the time when this top dead center is passed, whereas the peak value due to combustion does not appear in the misfire state, and the pressure inside the combustion chamber is almost normal distribution curve. This was done by paying attention to the fact that the pressure changes in a similar manner, and if the pressure in the combustion chamber at the position deviated by the same crank angle before and after the compression top dead center is equal, it is judged that there is a misfire. .

However, in this misfire detection device, it is necessary to set a position deviated by the same crank angle before and after the peak value, but there is a problem that the setting is difficult unless accurate crank angle information is obtained.

The present invention has been made in view of the above problems, and an object thereof is to provide a misfire detection device capable of surely detecting a misfire with a simple configuration.

<< Means for Solving the Problems >> In order to achieve the above object, the present invention provides a pressure sensor for detecting the pressure in a combustion chamber, and a noise filter for discriminating a necessary signal from an output signal of the pressure sensor. A differentiating means for receiving the output signal from the noise filter and detecting the rate of change of the pressure, and a maximum value occurrence number detecting means for detecting the maximum value occurrence number of the pressure based on the change rate of the output value of the differentiating means. And misfire detection means for sending a misfire detection signal when the number of detections by the maximum value occurrence frequency detection means is less than two during one compression / explosion stroke period when the engine is lightly loaded, and misfire detection is provided. It is characterized in that the device is configured.

Here, the maximum value occurrence number detecting means may employ a counter that measures the number of times the change rate changes from positive to negative and detects the number as the maximum value occurrence number.

<Operation> The misfire detection device with the above configuration converts the pressure in the combustion chamber during the compression / explosion stroke of the engine into a change rate, detects the maximum number of times of the above pressure based on this change rate, and detects this maximum value. Since the presence or absence of a misfire is determined based on whether or not the value is generated twice, the misfire state can be detected easily and reliably without performing a troublesome standard setting.

<Example> Hereinafter, a preferred example of the present invention will be described in detail with reference to the accompanying drawings.

1 to 3 show an embodiment of the misfire detection device according to the present invention.

The misfire detection device shown in the same figure illustrates an example in which the present invention is applied to a fuel injection type engine. In the combustion chamber 12 of the engine 10, a piston 18 is arranged in a cylinder chamber 16 provided in a cylinder block 14. And is formed by the cylinder head 20 coupled above the cylinder block 14.

Intake / exhaust ports 22 and 24 communicating with the combustion chamber 12 are formed in the cylinder head 20, and intake / exhaust ports are provided between the combustion chamber 12 and these ports 22 and 24 to cut off / open the communication state. Valves 26 and 28 are provided respectively.

Intake / exhaust passages 30 and 32 are connected to the intake / exhaust ports 22 and 24, respectively, and a throttle valve 34 and an intake passage 30 for opening and closing the intake passage 30 from the upstream side in order.
A first pressure sensor 36 for detecting the internal pressure and a combustion injection nozzle 38 are installed.

A spark plug 40 for exploding the compressed fuel is provided in the combustion chamber 12, and a second pressure sensor 42 for detecting the pressure in the combustion chamber 12 is attached.

A gear plate 46 is fixedly attached to the crankshaft 44 which is rotated by the vertical reciprocating motion of the piston 18.
A driven gear plate 48 is meshed with the gear plate 46.

The driven gear plate 48 is provided with an arcuate slit hole 50 having a length corresponding to the compression / combustion stroke of the piston 18, and a light source 52 and an optical sensor 54 are arranged so as to face the slit hole 50. If the engine 10 is in the compression / combustion stroke, the optical sensor 54 is turned on and the signal of "1" is output.

Further, an electromagnetic pickup 56 is arranged on the outer peripheral edge of the driven gear plate 48 at a predetermined interval, and the electromagnetic pickup 56 is connected to an F / V converter 58 for converting the periodic signal thereof into a voltage. .

Ignition timing by the ignition plug 40 and combustion injection nozzle 3
The fuel injection timing and the fuel injection amount are controlled by the control device 60, and the misfire signal A from the misfire detector 62 is input to the control device 60. When the engine 10 misfires, the fuel injection nozzle The control device 60 corrects the fuel injection amount by the control unit 38 and the ignition timing by the spark plug 40.
It is carried out in.

The misfire detector 62 includes a pressure signal B in the intake passage 30 from the first pressure sensor 36, a compression / combustion stroke signal C from the optical sensor 54, and an engine from the F / V converter 58. The rotation speed signal N is input, and the signal from the second pressure sensor 42 installed in the combustion chamber 12 is input after being processed by the following circuit.

That is, first, the pressure value P in the combustion chamber detected by the second pressure sensor 42 is input to the differentiator 66 after the necessary signal is discriminated by the noise filter 64, and the differentiator 66 is supplied.
The rate of change dP / dt of the pressure value P is detected by the waveform shaping device 68, and the positive value (dP / dt) of the rate of change dP / dt is then detected by the waveform shaper 68.
Only ^* is extracted and input to the misfire detector 62.

2A shows an output value obtained by detecting the pressure value P in the combustion chamber from the start of the compression stroke of the engine 10 to the end of the combustion stroke by the second pressure sensor 42 and detecting the detected value through the noise filter 64. The graph of Figure 3 shows the comparison between the time of ignition and the time of misfire. Further, FIG. 6B shows a graph of the rate of change dP / dt of the pressure value P obtained by passing the output value from the noise filter 64 through a differentiator 66, in comparison with each other at ignition and at misfire. is there. Further, FIG. 6C shows a graph of the output signal (dP / dt) ^* from the waveform shaper 68 obtained by waveform-shaping the output signal from the differentiator 66 in comparison at the time of ignition and at the time of misfire. It is a thing.

In the normal ignition state at light load, the peak value due to the compression pressure (maximum value) at the compression top dead center and the peak value due to the explosion of the air-fuel mixture after passing the compression top dead center (maximum value). ) Appears, the opportunity to increase the pressure in the combustion chamber and the opportunity to decrease the pressure in the combustion chamber occur twice.
The value of the rate of change dP / dt obtained by differentiating the output signal from No. 4 changes from positive to negative twice, and from negative to positive once. That is, the rectangular pulse signal (dP / dt) ^* is output twice from the waveform shaper 68 in accordance with the pressure rise timing.

On the other hand, in the misfire state, the peak value (maximum value) does not appear after passing the compression top dead center, so that there is only one opportunity to increase the pressure in the combustion chamber and one opportunity to decrease the pressure in the combustion chamber, and the output from the noise filter 64. Change rate dP obtained by differentiating the signal
The transition of the value of / dt from the positive to the negative is once, and the transition from the negative to the positive is zero. That is, the waveform shaper 68 outputs a rectangular pulse signal (dP / dt) corresponding to the pressure rise time.
^{* Will} be output once.

Therefore, in the present invention, misfiring is determined by measuring these differences during the compression / combustion process.

FIG. 3 shows an example of a misfire determination procedure performed by the misfire detector 62.

When the determination flow starts, first, in step 100, the signal C is taken in and it is determined whether or not the value is "1".
If this is not "1", the engine 10 is not in the combustion / compression stroke, so stand by. If the signal C becomes "1", step 1
Move to 01.

In step 101, the engine speed signal N and the intake passage 3
After taking in the pressure signal B within 0, it is judged in step 102 from these values whether the engine 10 is operating in the light load region.

Information regarding the operating region determined by the relationship between the engine speed and the pressure in the intake passage is stored in a preset storage device of the misfire detector 62, and the map value is " 1 ", and the map value is set to" 0 "in the other areas.

If it is determined in step 102 that the map value is not "1", then misfire is an area in which there is almost no problem, so step 10
At 3, the misfire signal "0" is output and the process returns to the start.

On the other hand, if it is determined in step 102 that the map value is "1", the processing from step 104 onward is executed. After the value of the counter i is set to 0 in step 104, it is judged in step 105 whether the signal C is "0". If it is not "0", the waveform shaper 68 is displayed in step 106.
Of the output signal (dP / dt) ^* of "1" is judged, and if it is "1", step 107 is executed immediately, but if it is "0", it returns to step 105 and is in a standby state. When (dP / dt) ^* becomes “1”, the process proceeds to step 107. In step 107, it is determined again whether the signal C is “0”. If it is “0”, the process proceeds to step 108. To do.

In step 108, the output signal of the waveform shaper 68 (dP / d
t) If ^* is "0", move to the next step 109.
If not "0", return to step 107 (dP / dt) ^*
Is waited until it becomes "0", and the process proceeds to step 109.

In step 109, 1 is added to the counter i and step 1
Returning to step 05, in step 105 to step 109, the determination of the signal C and the (dP / dt) ^* signal is repeated twice each.
This is a step for surely counting the counter by 1 with one (dP / dt) ^* signal during the combustion process. For example, if the width of the (dP / dt) ^* signal varies, a counting error may occur. I'm avoiding it.

Then, when it is determined in steps 105 and 107 that the signal C is "0", that is, when the engine 10 has passed the compression / combustion stroke, it is determined in step 110 whether the value of the counter i is larger than "2". When i is determined to be greater than or equal to "2", the misfire signal "0" is output in step 103 and the process returns to the start.

On the other hand, if it is determined in step 110 that i is smaller than "2", a misfire signal "1" is output in step 111 and the process returns to the start.

In this judgment procedure, one compression /
Steps 105 to 109 in the combustion process 2
Step 110 is repeated and the misfire detector 62
Output signal of "0" becomes "0".

Further, in the misfire state, since the steps 105 to 109 are executed only once in one compression / combustion stroke, the output signal of the misfire detector 62 becomes "1".

Now, in the misfire detection procedure performed as described above,
Based on the rate of change dP / dt of the pressure value P in the combustion chamber 12 during one compression / combustion stroke, the waveform shaper 68 outputs the rate of change dP / dt corresponding to the positive pressure rise time. (DP / dt) of the rectangular pulse to be generated ^* number of signals, that is, the rate of change dP / d
Since the number of times the value of t changes from positive to negative is counted to determine the number of times the maximum value of the pressure value P is generated, malfunction factors such as sensor deterioration and compression ratio fluctuations can be eliminated, and accurate crank angle information can be obtained. It is possible to determine misfire easily and accurately without the need for.

Although the engine speed N and the pressure in the intake passage 30 are used to determine the light load region in the above embodiment, the engine speed N and the throttle opening may be used. Also, the rate of change
The signal of the rate of change dP / dt extracted by the waveform shaper 68 for counting the number of times the value of dP / dt shifts from positive to negative may be a signal of a negative component. Furthermore, the misfire detector 62
In the above embodiment, the case where a microcomputer operating by a program flow is used has been described, but of course it may be configured by an individual circuit such as a counter.

Further, as described above, in the normal ignition state under light load, the rate of change dP / dt of the pressure in the combustion chamber has one transition from negative to positive during one compression / combustion stroke period. On the other hand, in the misfire state, the transition from the negative to the positive does not occur. Therefore, by detecting the presence or absence of the transition from the negative to the positive, the pressure in the combustion chamber is set to twice during the compression / combustion stroke period. It is also possible to judge whether or not the maximum value of is generated and thereby judge misfire.

<Effects of the Invention> As described in detail in the above embodiments, according to the misfire detection device according to the present invention, the maximum number of occurrences of the pressure is generated based on the rate of change of the pressure in the combustion chamber during the compression / combustion stroke. It is detected and the presence or absence of misfire is judged based on whether or not this maximum value is generated twice. Therefore, it is necessary to change the judgment standard according to the operating condition of the engine by surely detecting misfire by simple data processing. Absent.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of the device of the present invention, FIG. 2 is an explanatory diagram of a misfire detection principle of the device, and FIG. 3 is a flowchart diagram showing an operation procedure of the device. 12 ... Combustion chamber, 42 ... Second pressure sensor, 62 ...
Misfire detector 64: noise filter, 66: differentiator, 68: waveform shaper

Claims (2)

[Claims] 1. A pressure sensor for detecting the pressure in a combustion chamber,
A noise filter that receives an output signal of the pressure sensor and discriminates a necessary signal, a differential unit that receives an output signal from the noise filter and detects a rate of change of the pressure, and a rate of change of an output value of the differential unit. Based on the maximum value occurrence number detecting means for detecting the maximum value occurrence number of the pressure based on this, the number of detection times by the maximum value occurrence number detecting means is 1 when the engine is under a light load.
A misfire detecting device provided with a misfire determining means for sending out a misfire detection signal when the number of times is less than two during one compression / explosion stroke period. 2. The maximum value occurrence number detecting means is a counter which measures the number of times the change rate changes from positive to negative and detects the number as the maximum value occurrence number. Misfire detection device described in.