JPH0949454A - Combustion condition detecting device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect a misfire even at low load time to generate a small change of combustion pressure by the misfire. SOLUTION: When a cylinder internal pressure integration value W obtained by integrating a cylinder internal pressure in a prescribed integration interval (S1) is the first judgement value W1 (S2) or less (S3), prossibility of a misfire is judged to be provided, to set 1 to a flag 'CAUTION' (S4). In the case that (S6) the cylinder internal pressure integration value W calculated in the next combustion cycle (S5) of the same cylinder is larger than a value (second judgement value) for adding a prescribed a prescribed value α to a mean value wave at normal time, decreasing of the preceding time cylinder internal pressure integration value W is decided to be caused by a misfire (S7).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion state detecting device for an internal combustion engine, and more particularly to a device for detecting a combustion state based on an integrated value of in-cylinder pressure.

[0002]

2. Description of the Related Art Conventionally, while detecting the cylinder internal pressure of an internal combustion engine, the cylinder internal pressure is integrated within a predetermined integration section during an expansion stroke, and based on a comparison between the integration value and a preset judgment value. The presence or absence of misfire (abnormal combustion) has been detected (see Japanese Patent Laid-Open No. 64-15937).

By detecting the occurrence of misfire by using the integrated value of the in-cylinder pressure as described above, when noise is superimposed on the in-cylinder pressure detection signal as compared with the case of detecting the occurrence of misfire by using the instantaneous value of the in-cylinder pressure. However, accurate misfire detection is possible.

[0004]

By the way, as shown in FIG. 5, the integrated value of the in-cylinder pressure decreases when the engine load is low and the difference between the misfire and the normal combustion becomes small. . Therefore, even if the determination value of the in-cylinder pressure integrated value is set based on the engine load, etc., when the engine is under a low load, it is not possible to accurately determine the presence or absence of misfire by the in-cylinder pressure integrated value, and an erroneous determination is made. There was a horror.

The present invention has been made in view of the above problems, and in an apparatus for detecting abnormal combustion based on the integrated value of the in-cylinder pressure, it is possible to accurately determine whether abnormal combustion (misfire) has occurred even when the load is low. The purpose is to be able to diagnose.

[0006]

Therefore, the invention according to claim 1 is constructed as shown in FIG. In FIG.
The in-cylinder pressure detection means detects the in-cylinder pressure of the internal combustion engine. Then, the in-cylinder pressure integrating means integrates the in-cylinder pressure detected by the in-cylinder pressure detecting means in a predetermined integration section including at least the section in the expansion stroke.

Here, the abnormal combustion determination means determines that the in-cylinder pressure integrated value is the second in the combustion cycle in the next cylinder in which the in-cylinder pressure integrated value obtained by the in-cylinder pressure integration means becomes equal to or less than the first determination value. When it becomes larger than the judgment value of, the occurrence of abnormal combustion is judged. According to this configuration, even if the in-cylinder pressure integrated value becomes equal to or lower than the first determination value and the combustion pressure is reduced, the occurrence of abnormal combustion is not immediately determined based on this, but the next In the combustion cycle of 1, the occurrence of abnormal combustion is determined only when the in-cylinder pressure integrated value becomes larger than the second determination value.

When the in-cylinder pressure integrated value drops due to occurrence of abnormal combustion such as misfire, the in-cylinder pressure integrated value tends to jump up under the influence of the previous misfire during normal combustion in the next combustion cycle (Fig. 4). Therefore, even when it is determined that the in-cylinder pressure integrated value has decreased to the extent of misfire, it is determined that no misfire has occurred if the jump in the in-cylinder pressure integrated value does not occur in the next combustion cycle, The configuration is such that the occurrence of abnormal combustion is determined only when there is a jump.

According to the second aspect of the invention, the first judgment value is set based on the engine load and the engine speed. With this configuration, it is possible to set the determination value for determining the decrease in the combustion pressure due to the occurrence of abnormal combustion, corresponding to the change in the in-cylinder pressure integrated value due to the engine load and the engine rotation speed.

According to the third aspect of the present invention, the second judgment value is set as an addition value of an average value of the in-cylinder pressure integrated values judged to be larger than the first judgment value and a predetermined value. It was configured. The jump in the in-cylinder pressure integrated value in the combustion cycle immediately after the occurrence of the misfire indicates that it exceeds the in-cylinder pressure integrated value in the normal combustion. Therefore, the cylinder determined to correspond to the normal combustion is larger than the first determination value. The occurrence of the bounce is determined when the in-cylinder pressure becomes larger than the average value of the integrated value of the internal pressure by a predetermined value or more.

[0011]

Embodiments of the present invention will be described below. In FIG. 2 showing one embodiment, the internal combustion engine 1 is
Air is taken in through the air cleaner 2, the throttle chamber 3, and the intake manifold 4. Then, the combustion exhaust gas from the engine 1 is discharged into the atmosphere through the exhaust manifold 5, the exhaust duct 6, the three-way catalyst 7, and the muffler 8.

The throttle chamber 3 is provided with a throttle valve 9 which opens and closes in conjunction with an accelerator pedal (not shown), and the throttle valve 9 adjusts the intake air amount of the engine 1. Further, spark plugs (not shown) are mounted so as to face the combustion chambers of the cylinders (# 1 to # 4), and a pair of such spark plugs serves as cylinder pressure detecting means for each cylinder. Internal pressure sensor
10a to 10d are provided.

The in-cylinder pressure sensors 10a-10d are actual
As disclosed in Japanese Laid-Open Patent Publication No. 3-17432, a ring-shaped sensor including a piezoelectric element is mounted as a washer for the spark plug, and the spark plug is lifted by receiving cylinder pressure. The set load changes, and a signal corresponding to the in-cylinder pressure is output. Institution 1
The cam shaft (not shown) is provided with a crank angle sensor 11 that detects a crank angle through the rotation of the cam shaft.

In the four-cylinder engine 1 of the present embodiment, the crank angle sensor 11 includes a reference angle signal REF for each crank angle of 180 ° corresponding to a stroke phase difference between cylinders, and a unit angle signal POS for each unit crank angle. It is a sensor which respectively outputs and. In the reference angle signal REF, at least the detection signal corresponding to one specific cylinder can be distinguished from other detection signals by its pulse width or the like so that the cylinder can be discriminated.

The outputs of the in-cylinder pressure sensors 10a-10d and the crank angle sensor 11 are output to a control unit 12 provided for engine control. The control unit 12 having a built-in microcomputer controls the fuel injection amount and the ignition timing by a fuel injection valve (not shown), and on the basis of the outputs of the in-cylinder pressure sensors 10a to 10d as shown in the flowchart of FIG. Detects abnormal combustion state (misfire).

In this embodiment, the functions of the in-cylinder pressure integrating means and the abnormal combustion determining means are provided by the control unit 12 as software, as shown in the flow chart of FIG. In the flowchart of FIG. 3, in step 1 (denoted as S1 in the drawing; the same applies hereinafter), in a predetermined integration section (for example, compression TDC to ATDC 100 °) including at least the section during the expansion stroke, the cylinder pressure detection value for the crank angle is detected. Is integrated to obtain an in-cylinder pressure integrated value W.

In the next step 2, the map storing the first judgment value W1 with the engine load Tp and the engine speed Ne as parameters is referred to, and the map corresponding to the current engine load Tp and engine speed Ne is displayed. The judgment value W1 of 1 is searched.
The first determination value W1 is the determination value W1 only when a misfire occurs.
Is set in advance as a value such that the in-cylinder pressure integrated value W falls below.

In step 3, it is determined whether or not the in-cylinder pressure integrated value W is less than or equal to the first determination value W1. When the in-cylinder pressure integrated value W is less than or equal to the first determination value W1, the process proceeds to step 4, and the flag "CAUTION
Is set to 1 to end this routine once, and waits for the next combustion cycle of the same cylinder.

The in-cylinder pressure integrated value W is the first determination value W
If it is 1 or less, it is highly possible that the in-cylinder pressure integrated value W has decreased due to misfire, but especially when the engine load is low.
Since the change in the in-cylinder pressure integrated value W due to the presence or absence of misfire is small (see FIG. 4), even if the in-cylinder pressure integrated value W is equal to or less than the first determination value W1, there is a possibility that normal combustion actually occurs. There is also.

Therefore, the history that the in-cylinder pressure integrated value W becomes equal to or less than the first judgment value W1 is stored by setting the flag "CAUTION" to 1, and the misfire is caused in the next combustion cycle in the same cylinder. It is for confirming the occurrence. When it is determined in step 3 that the integrated value W exceeds the first determination value W1, the process proceeds to step 5 and it is determined whether or not 1 is set in the flag "CAUTION". That is, the determination in step 4 is to determine whether or not a drop in the integrated value W that may cause misfire was detected in the previous combustion cycle.

When it is determined in step 5 that the flag "CAUTION" is set to 1, the process proceeds to step 6, and in step 3 this time it is determined that the first determination value W1 is exceeded. A value obtained by adding a predetermined value α to the average value Wave of the integrated value W determined that the in-cylinder pressure integrated value W exceeds the first determination value W1 in the cylinder (second determination value).
It is determined whether it is greater than or equal to.

Then, the second judgment value (= Wave +
If the integral value W is larger than α), it is determined that the integral value W that has become equal to or less than the first determination value W1 in the previous combustion cycle is due to the occurrence of misfire, and the process proceeds to step 7. ,
Set the misfire flag to 1. On the other hand, when the integrated value W is less than or equal to the second determination value (= Wave + α), the integrated value W was less than or equal to the first determination value W1 in the previous combustion cycle, but this is due to misfire. Determined not to
In step 8, the misfire flag is set to 0.

In step 9, the flag "CAUTION"
Is reset to zero, and in the next step 10, the average value Wave of the integrated value W in the cylinder determined to exceed the first determination value W1 is updated. When a misfire occurs, as shown in FIG. 5, the in-cylinder pressure integrated value W in the next combustion cycle immediately after the misfire tends to jump above the normal level due to the influence of the previous misfire, so that it is higher than the first determination value W1. Even if the integrated value W is small and it is estimated that there is a possibility of misfire, the misfire determination is not performed immediately, but it is checked whether or not the jump-up phenomenon occurs in the next combustion cycle, and then the misfire determination is performed. Is.

Therefore, even when the load is low and the reliability of the misfire detection based on the first determination value W1 is low, the accuracy of the misfire determination is determined by the jump determination based on the second determination value in the next combustion cycle. Will be secured.

[0025]

As described above, according to the first aspect of the present invention, when the in-cylinder pressure integrated value falls due to the occurrence of abnormal combustion such as misfire, the in-cylinder pressure in normal combustion in the next combustion cycle Utilizing the fact that the integrated value shows a tendency to jump up under the influence of the previous misfire, even if it is determined that the in-cylinder pressure integrated value has decreased to the extent of misfire, the in-cylinder pressure integrated value jumps up in the next combustion cycle. If it did not occur, it was determined that there was no misfire, and since it was configured to determine the occurrence of abnormal combustion only when there was a jump, a low load with a small decrease in the in-cylinder pressure integrated value due to misfire. Even at times, there is an effect that abnormal combustion can be accurately detected.

According to the second aspect of the invention, in response to changes in the in-cylinder pressure integrated value due to the engine load and the engine rotation speed,
There is an effect that the determination value for determining the decrease in the combustion pressure due to the occurrence of abnormal combustion can be set accurately. Claim 3
According to the invention described above, there is an effect that the jump of the in-cylinder pressure integrated value in the combustion cycle immediately after the occurrence of the misfire can be accurately determined based on the level of the in-cylinder pressure integrated value in the normal state.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of the invention according to claim 1.

FIG. 2 is a system schematic diagram showing an embodiment of the present invention.

FIG. 3 is a flowchart showing an embodiment of abnormal combustion detection.

FIG. 4 is a diagram showing a change in an in-cylinder pressure integrated value due to an engine load.

FIG. 5 is a diagram showing a phenomenon in which a cylinder pressure integrated value jumps up when a misfire occurs.

[Explanation of symbols]

 1 Internal combustion engine 10a-10d Cylinder pressure sensor 11 Crank angle sensor 12 Control unit

Claims (3)

[Claims] 1. An in-cylinder pressure detecting means for detecting an in-cylinder pressure of an internal combustion engine, and an in-cylinder pressure integrating means for integrating an in-cylinder pressure detected by the in-cylinder pressure detecting means in a predetermined integration section including at least a section in an expansion stroke. And when the in-cylinder pressure integrated value obtained by the in-cylinder pressure integrating means becomes equal to or smaller than the first determination value, the in-cylinder pressure integrated value becomes larger than the second determination value in the next combustion cycle in the cylinder. An abnormal combustion determination means for determining the occurrence of abnormal combustion, and a combustion state detection device for an internal combustion engine, comprising: 2. The first determination value is set based on an engine load and an engine rotation speed.
A combustion state detection device for an internal combustion engine as described above. 3. The second judgment value is set as an addition value of an average value of an in-cylinder pressure integrated value judged to be larger than the first judgment value and a predetermined value. Item 1
Or the combustion state detection device for an internal combustion engine according to item 2.