JPH05202801A - Misfire diagnosing device for internal combustion engine - Google Patents

Abstract

PURPOSE:To simply diagnose a misfire of an internal combustion engine so as to seek the cause of the misfire. CONSTITUTION:An air-fuel ratio fixing control means F open-controls the air- fuel ratio, preferential to a control program for a fuel injection control means E, and when a means G for forcively stopping fuel injection stops the fuel injection into a specific engine cylinder during the open-control, a means H for discriminating a misfiring engine cylinder. Further, a means I for detecting a variation in air-fuel ratio output determines whether the misfire is caused by a failure of an fuel injection system or by a failure of an injection system, in accordance with a difference between output of the air fuel ratio detecting means C before and after of the operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for determining a misfire of an internal combustion engine, and more particularly to a misfire diagnosis device for identifying a cause of misfire of a misfiring cylinder.

[0002]

2. Description of the Related Art As a conventional misfire diagnosing device for an internal combustion engine, there is, for example, one disclosed in Japanese Patent Laid-Open No. 62-107252. That is, the air-fuel ratio of the engine is set to a state richer than the stoichiometric air-fuel ratio to reduce the NOx component in the exhaust gas,
During so-called rich control, the air-fuel ratio sensor provided in the engine exhaust system detects whether the lean signal is output in synchronization with the engine rotation. If so, the specific fuel injection valve malfunctions. Therefore, the unburned air-fuel mixture is exhausted as it is, it is determined that this is detected as a lean signal, and the determination result is notified to the driver or the like by an alarm device.

[0003]

However, in such a conventional misfire diagnosis device for an internal combustion engine, the lean signal output in synchronization with the engine rotation is not limited to the fuel injection system, but the misfire due to a defective ignition system. Is also output in
Even if it was found that a misfire had occurred, the service person who repaired the failure had to check all the fuel injection system and ignition system.

That is, in recent years, the engine room has become narrower than before due to the importance of design and improvement of aerodynamic characteristics. Furthermore, in order to improve various performances, ignition coils are provided in the ignition plugs of each cylinder. The number of items to be directly attached is increasing, and it takes a lot of man-hours and time to inspect these misfire-related parts one by one.

The present invention has been made in view of the above-mentioned conventional problems, and a misfiring engine is checked without checking all parts such as a fuel injection system and an ignition system. It is possible to easily diagnose whether the cause of cylinder misfire is a defective fuel injection system or ignition system, reduce inspection man-hours and time, and thereby provide a misfire diagnosis device for an internal combustion engine that leads to cost reduction. To aim.

[0006]

Therefore, according to the present invention, as shown in FIG. 1, an operating state detecting means B for detecting the operating state of the engine A and an air-fuel ratio detecting means provided in the exhaust system of the engine A are provided. C, a fuel injection means D provided for each cylinder of the engine A, and a fuel injection control means E for controlling the fuel injection means D according to a control program stored in advance based on the output signal of the air-fuel ratio detection means C. In an internal combustion engine equipped with, an air-fuel ratio fixed control means F for performing open control of the air-fuel ratio to a target value prior to the control program, and a fuel injection forced stop means G for stopping fuel injection of a specific cylinder during the open control.
And a misfiring cylinder discriminating means H for discriminating misfire during normal operation of a cylinder in which fuel injection is forcibly stopped, based on fluctuations in operating states before and after forced fuel injection stop, and before and after operation of the fuel injection forced stop means G. Of the output change of the air-fuel ratio output change detecting means I for detecting an output change of the air-fuel ratio detecting means C at the time, and the output change of the air-fuel ratio output change detecting means I when the misfiring cylinder is judged by the misfire cylinder judging means H. A misfire cause determining means J for determining whether the misfire is due to a failure of the fuel injection system or the misfire due to a failure of the ignition system based on the degree.

Furthermore, according to the present invention, as shown in FIG. 2, an operating condition detecting means B for detecting the operating condition of the engine A.
And an air-fuel ratio detection means C provided in the exhaust system of the engine A, a fuel injection means D provided for each cylinder of the engine A, and an output signal of the air-fuel ratio detection means C according to a control program stored in advance. In an internal combustion engine equipped with a fuel injection control means E for feedback controlling the fuel injection means D in a part of the operating area, it is determined that the operating state of the engine A is in a predetermined operating area where the feedback control is not performed. Operating region discriminating means K, a misfiring cylinder discriminating device L for discriminating a misfiring cylinder in the predetermined operating region, and a determination for determining a determination value of the output of the air-fuel ratio detecting device C according to the operating state of the engine A. When the misfiring cylinder is discriminated by the value setting means M and the misfiring cylinder discrimination means L, the output value corresponding to the misfiring cylinder of the air-fuel ratio detecting means C is compared with the judgment value to determine that the fuel injection system has failed. Yo Misfire in either, or also characterized in that and a misfire cause determination means N to determine whether a misfire due to the failure of the ignition system.

[0008]

According to this structure, the air-fuel ratio fixed control means F
However, at a stage in which the air-fuel ratio is open-controlled to a target value in priority to the control program of the fuel injection control means E so that the air-fuel ratio does not fluctuate, the fuel-injection forced stop means G causes the specific cylinder of the specific cylinder to be opened during the open control. Stop fuel injection. Here, the misfiring cylinder discrimination means H discriminates misfiring of the fuel injection stopped cylinder based on the change in the engine operating state before and after the fuel injection is stopped. When it is determined that the specific cylinder is misfiring, the output change of the air-fuel ratio detection means C before and during the operation of the fuel injection forced stop means G detected by the air-fuel ratio output change detection means I becomes equal to that of the output change. Based on this, the cause of misfire will be determined.

That is, as a cause of misfire in the related art, a failure in the fuel injection system and a failure in the ignition system can be mentioned as those that are not easily diagnosed. However, when there is a failure in the fuel injection system, fuel supply is not performed due to forced stop of fuel injection. Since the state or a state close to this state is obtained, the detection output value of the air-fuel ratio detecting means C is
There is not much difference between the two. However, in the case of a failure of the ignition system, the engine is misfiring even though the fuel is being injected from the fuel injection valve, so a mixture of fuel and air is discharged to the engine exhaust system. A part burns in the exhaust system. Therefore, the concentration of O ₂ in the exhaust gas is reduced, and the air-fuel ratio detecting means C that has detected this concentration outputs in a richer tendency than in the case where the fuel injection is forcibly stopped. Therefore, the air-fuel ratio detecting means C in this case has an output which is obviously different from the response output in the case where the fuel injection is forcibly stopped. For example, specifically, when the air-fuel ratio detecting means C is an O ₂ sensor, the air-fuel ratio corresponding output corresponding to the misfiring cylinder becomes leaner than the output when the air-fuel ratio fixing control means F fixes the air-fuel ratio. Since the output power when the fuel injection system fails is larger than the output when the ignition system fails, accordingly, the time for maintaining the predetermined output value becomes longer, and the output value for the relatively long time If the air-fuel ratio detection value after the fuel injection is forcibly stopped is used as an index, the diagnosis can be performed accurately. Therefore, the air-fuel ratio detection means C is compared by comparing the time during which the predetermined output value is maintained during the forced stop of fuel injection with that before the forced stop of fuel injection.
Know the change in the output value of. If there is no change in the output of the air-fuel ratio detecting means C before and during the fuel injection forced stop, it is determined that the misfire is in the same state as the fuel injection forced stop, that is, a failure of the fuel injection system. In other words, it is determined that the ignition system has failed.

In this way, it is possible to easily diagnose the cause of misfire in a misfiring cylinder without inspecting all parts of the fuel injection system and ignition system for the cylinder in which misfiring has occurred. According to the second aspect of the invention, when it is determined by the operating region determination means K that the operating state of the engine A is in the predetermined operating region where the feedback control is not performed, the air-fuel ratio of the air-fuel mixture is in the feedback control. Further, it does not change and becomes substantially constant. In this state, the misfiring cylinder discriminating means L easily discriminates the misfiring cylinder because the air-fuel ratio fluctuation by the air-fuel ratio detecting means C occurs. Here, the determination value setting means M determines the determination value of the output of the air-fuel ratio detection means C according to the operating state of the engine A, and the misfire cause determination means N corresponds to the misfire cylinder of the air-fuel ratio detection means C. The cause of misfire is determined by comparing the output value with the determination value. For example, if the air-fuel ratio detecting means C is of the O ₂ sensor, O ₂ output time in response to misfire caused so that the output value is above the sensor, since changes in output peak value and the like, discriminant value to a value that can determine these If the above is determined, it is possible to easily determine the cause of misfire in the misfiring cylinder without checking all parts of the fuel injection system and the ignition system in comparison with this discriminant value.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. First, the outline of the engine to be diagnosed will be described with reference to FIG. 3. The engine 11 is a V-type 6 cylinder, and its intake passage 12 is linked with an air flow meter 13 for detecting an intake air amount and an accelerator pedal. A throttle valve 14 that controls the intake air amount is provided.

A fuel injection valve 15 is provided for each cylinder in the manifold portion downstream of the intake passage 12 or in the intake port of the cylinder head. The fuel injection valve 15 is an engine control unit ECM having a built-in microcomputer.
The valve is driven to open according to a control program stored in advance by an injection pulse signal from 16 and fuel is injected and supplied to the engine 11 for each cylinder.

Further, the exhaust passage 1 is used as the air-fuel ratio detecting means C.
One O ₂ sensor 18 whose output value linearly changes depending on the oxygen concentration 7 is provided in each of the exhaust pipes of the left and right banks. The output value of the O ₂ sensor 18 is large when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, and is small when it is lean. A spark plug 19 is provided in each cylinder. In addition, the distributor (not shown)
A crank angle sensor 20 that outputs a crank reference angle signal in synchronization with engine rotation, or additionally outputs a crank unit angle signal in synchronization with engine rotation, is incorporated. The engine speed N is obtained by counting the crank unit angle signal output from the crank angle sensor 20 for a certain period of time, or
The cycle of the crank reference angle signal is measured and detected.

That is, the air flow meter 13, O ₂
The engine 18, the crank angle sensor 20, other sensors such as a water temperature sensor, a throttle valve switch, and the like constitute an engine operating state detecting means B. Here, assuming that the intake air amount per unit time measured by the air flow meter 13 is Q _A , the pulse width Ti injected from the fuel injection valve 15 is Ti.
Is represented by the following formula.

Ti (left bank) = K × Q _A / N × α _LH ×
COEF Ti (right bank) = K × Q _A / N × α _RH ×
COEF Here, K is a constant, N is an engine rotation speed, engine speed per unit time, α _LH , α _RH are air-fuel ratio feedback correction coefficients of the left and right banks of the V-type engine, and COEF is various increase coefficients. ..

Next, a specific configuration of the misfire diagnosis device 21 according to the present invention will be described with reference to FIG. The engine control unit ECM16 receives various operating conditions from the various sensors in order to perform various controls of the engine, and controls various actuators such as fuel injection valves based on the various input conditions. Misfire diagnostic device 21
Is at least I / O (input / output device), ROM (read-only memory), RAM (write-free memory), CP
It is provided with a U (central processing unit), and is connected to the connector 23 of the ECM 16 by the communication line 22 at the time of diagnosis to control, calculate and judge the engine. Further, a display means 24 for displaying a work instruction and a judgment result to a service person, a result of working in accordance with an instruction of the misfire diagnosis device 21, and for operating the misfire diagnosis device 21, for example, The input means 25 such as a keyboard is provided. The display means 24 and the input means 25 can also be used by using a touch screen or the like.

In the diagnosis, the misfire diagnosis device 21 uses the ECM.
When connected to the communication line 16 by a communication line, the output values of various sensors used by the ECM 16 for control and the output values of various actuators can be output to the misfire diagnosis device 21 and used. By outputting an operation command from the misfire diagnosis device 21 to various actuators via the ECM 16, and by outputting various output signals prioritizing the output signal from the ECM 16 to the internal combustion engine from the misfire diagnosis device 21 via the ECM 16. , Diagnosis is carried out.

As shown in FIG. 4 (b), the misfire diagnosis device 21 directly reads various sensor output values and output values to the actuator without connecting with the ECM 16 via a communication line, and also, Can also be applied as a configuration that can directly operate. FIG. 5 shows an output waveform of the O ₂ sensor 18 according to the embodiment of the present invention. This figure shows the O ₂ sensor output waveform when the air-fuel ratio feedback control of the engine is stopped and the air-fuel ratio is fixed to the rich side of the theoretical air-fuel ratio.

As the cylinder discrimination signal (a), the crank angle sensor 20 outputs a crank reference angle signal once every two revolutions of the engine (one combustion cycle of 720 °). During normal, O ₂ sensor output, the rich time of V _R (v),
Output _VL (v) when leaning. Here, output waveforms of the O ₂ sensor 18 when a specific cylinder (here, No. 1 cylinder in the right bank) misfires are shown in (b) and (c).

(B) is NO. 1 cylinder fuel injection system is N
In the case of G (that is, no injection), the remaining NO in the right bank
． 3, NO. Since 5 cylinders are burning normally, NO.
The gas discharged from one cylinder, that is, the air, is the O ₂ sensor 18
Only when passing through the (right bank) part, it reacts with O ₂ in the exhaust gas and generates a lean output (V _L ). However, in reality, since the output of the O ₂ sensor changes with the inclination shown in the figure until it changes from V _R to V _L , it gradually changes to the lower limit V _L.
Before reaching 0, the combustion gas of the next cylinder (NO.3 cylinder) reaches the O ₂ sensor 18 section, which causes the output to rise and change to V _R.

(C) is NO. 1 cylinder ignition system is NG
The output waveform of the O ₂ sensor 18 when the fuel injection system is not ignited (that is, when the fuel injection system is not ignited) is shown. The lean signal is generated only when the gas discharged from one cylinder passes the O ₂ sensor 18 section. However, in the case of the ignition system NG, NO. The gas discharged from one cylinder is a mixture of fuel and air, and a part of it burns in the exhaust pipe, so the amount of O ₂ is reduced and the time during which O ₂ is sensed is fuel injection. It is shorter than when the system is NG. Therefore, as shown in the figure, when a certain predetermined slice value V _MF (v) is set and the O ₂ sensor output is
Assuming that the time that is a value lower than V _MF (lean side) is t _MF , t _MF (when the fuel injection system is NG)> t _MF (when the ignition system is NG)
Therefore, the cause of misfire can be determined by comparing this t _MF .

By the way, the cause of misfire is clogging of the fuel injection system.
In the case of a failure due to the
Injected, and is it almost the same as when fuel injection is stopped?
, The fuel injection from the fuel injection valve of the misfiring cylinder is forcibly stopped.
Even if it is stopped, O corresponding to the misfiring cylinder₂Sensor 18
The output values from the
Before and after stop, t_MFBecomes almost unchanged. In addition, as shown in FIG.
In addition, t when the fuel injection system is NG _MFIs longer than when the ignition system is NG
Since it is time, t before and after forced stop of fuel injection_MFIs detected
Is easy and can be detected accurately. Obey
Accurately detected t_MFBefore and after forced stop of fuel injection
If it is almost unchanged, the cause of misfire is in the fuel injection system
, That is, t_MFRapidly increases when fuel injection is forcibly stopped
In this case, the cause of misfire is not in the fuel injection system, but in the rest of the ignition system.
You can know that there is.

Next, the internal processing function of the misfire diagnosis device 21 according to claim 1 will be described with reference to FIG. In the present embodiment, the diagnosis is performed in the idling state after the engine is warmed up. In step 1 (denoted as S1 in the drawing; the same applies hereinafter), the misfire diagnosis device 21 outputs an instruction to fix the air-fuel ratio feedback correction coefficient α to 125% (rich clamp) and to bring the air-fuel mixture into a rich state.

In step 2, the misfire diagnosis device 21 outputs a command to stop the idle speed feedback control. Therefore, at this stage, the normal idle speed feedback control is stopped, and instead, the idle operation is performed in which the air-fuel ratio is clamped to the rich side of the stoichiometric air-fuel ratio. That is, step 1 and step 2 perform the function of the air-fuel ratio fixed control means F.

In step 3, the engine rotational speed N1 during idle operation during rich clamp is detected by a signal from the crank angle sensor 20. In step 4, the time t _MF1 which is a value (lean side) lower than V _MF of the O ₂ sensor output waveform in the cylinder specified in the next step 5, is detected. In step 5, the misfire diagnosis device 21 outputs NO. An instruction to specify one cylinder and stop the fuel injection of the cylinder is output. That is, step 5 performs the function of the fuel injection forced stop means G.

In step 6, the engine rotation speed N2 when the fuel injection is forcibly stopped is detected by the signal from the crank angle sensor 20. The engine speeds N1 and N2 in Steps 3 and 6 are values obtained by weighting and averaging the engine speeds calculated by the ECM 16 every 10 to 20 ms in the misfire diagnosis device 21 for 5 seconds. , The weighted average is started 5 seconds after the fuel injection is stopped in step 5.

In step 7, NO. Time t _MF2 that is a value lower than V _{MF of} the O ₂ sensor output waveform corresponding to one cylinder
To detect. That is, steps 4 and 7 function as the air-fuel ratio output change detecting means I. Note that the O ₂ sensor output waveforms in steps 4 and 7 are 2
With respect to the O ₂ sensor output waveform sampled every ms, t _MF1 and t _MF2 are calculated by the values compared with V _MF (v),
The weighted average value for 5 seconds is taken.

In step 8, NO. The fuel injection control for one cylinder is started again. In step 9, NO. The change in engine speed before and after forced stop of fuel injection in one cylinder is N1-N
If 2> 25 rpm, NO. Due to the stop of fuel injection in one cylinder, the change in engine speed is sufficiently large.
O. It is judged that one cylinder is in a state different from the state in which the fuel injection is stopped, that is, there is no misfire, and the process proceeds to step 10 so that the misfire is judged for the next cylinder. 2 to NO. Carry out sequentially in 6 cylinders. Then, if all cylinders are carried out and the judgment results of step 9 are all N1-N2> 25 rpm, it is judged that there is no misfiring cylinder. On the other hand, in step 9, N1-N2 <25r
If pm is NO. Even though the fuel injection of one cylinder was stopped and a forced misfire was created, the engine speed did not change, so NO. It is determined that one cylinder has misfired before the forced fuel injection is stopped, and the process proceeds to step 11. Therefore, steps 3, 5, 6, 9 and 10 perform the function of the misfiring cylinder discrimination means H.

In step 11, in step 9,
No. Since it was determined that one cylinder had misfired, the t _{2 MF1} and t _MF2 of the O ₂ sensor output waveforms detected in step 4 and step 7 of that cylinder were compared, and if there was a change, the misfire of that cylinder O ₂ sensor output mode when fuel injection is stopped (t _MF1 ≠ t _{MF2 ≈t MF} (when fuel injection system is NG))
Therefore, it is determined that another cause of misfire, that is, the ignition system NG of the cylinder, and if there is no change, it is approximated to the O ₂ sensor output mode when fuel injection is stopped (t _{MF1 ≈t MF2 ≈t MF} (fuel injection When the system is NG)), the fuel injection system of the cylinder is determined to be NG. That is, step 11 performs the function of the misfire cause determination means J. And NO. 2 to NO. The same is done for 6 cylinders.

In the above embodiment, in order to determine the misfire of the cylinder, the change of the engine speed before and after the stop of the fuel injection of the specific cylinder was observed. However, the torque fluctuation or the output fluctuation may be observed. Once the misfiring cylinder is specified, it is sufficient to determine the cause of misfiring. Therefore, in the embodiment shown in FIG. 6, steps 3, 6, and 9 are omitted, and the specific misfiring cylinder determination is step 5; Obviously, it may be done in the previous stage.

Further, in the air-fuel ratio fixed control in step 2, it is not always necessary to fix the air-fuel ratio on the rich side of the stoichiometric air-fuel ratio. Even on the lean side, at the time of misfire, the output of the O ₂ sensor output to the lean side further than this may be used.
Although the change of the O ₂ sensor output value in step 11 is determined by using t _MF in the above-mentioned embodiment, the peak value of the lean signal may be compared with the reference value or may be compared with each other. It is also possible to determine the change in the waveform itself on the image.

FIG. 7 shows an output waveform of the O ₂ sensor 18 according to another embodiment of the present invention. This figure shows the output waveform of the right bank of the O ₂ sensor 18 in the operating state where the air-fuel ratio is in the rich state (the state may be lean as in the above embodiment). That is, the air-fuel ratio feedback correction coefficient α _RH
Is 100%, the increase coefficient COEF is after warming up and is in an increase state.

The crank reference angle signal as the cylinder discriminating signal (a) indicates that the engine rotates twice (1 combustion cycle: 720 °).
The output from the crank angle sensor 20 is output once each time.
(B) is No. The output waveform of the O ₂ sensor 18 when one cylinder has misfired (in the figure, the fuel injection system is NG) is shown. No. Gas discharged from one cylinder is O ₂ sensor 18
When passing the section, that is, from the cylinder discrimination signal, θ ₁ (d
After eg), a lean signal is generated.

As shown in (c) and (d), no. 3, 5
Different timings (θ ₃ , θ ₅
After) a lean signal is generated. Therefore, this θ ₃ , θ ₅
It is possible to specify the misfiring cylinder at the time of misfiring by detecting. Here, as the θ determination value for determining the misfiring cylinder, a determination value according to the operating state such as the engine speed and the intake air amount is set in advance.

And the O of the misfiring cylinder₂Sensor output waveform
Reference value V_MFLower time t _MFDetect the driving condition
By comparing the difference with the judgment value T set according to the condition,
Determines whether the misfiring cylinder is a fuel injection system NG or an ignition system NG
You can do it at the same time. Where t_MFThe judgment value T of
It is set for each of the fire cylinders according to the respective operating conditions.

Next, the internal processing function of the misfire diagnosis device 21 according to claim 2 will be described with reference to FIG. In step 21, whether the operating condition of the engine is within a predetermined range,
That is, after the engine is warmed up, it is determined whether the air-fuel ratio feedback control is stopped within a predetermined range of the engine speed and the intake air amount (or load), and whether the increase correction according to the load is being performed. For example, the engine speed N is 2000 rpm <N
<3000 rpm, basic fuel injection amount K × QA / N is 3.
It is determined whether the state is 0 ms or more. That is, step 21 performs the function of the operating area determination means K.

In the above state, the engine is under load, and the vehicle cannot enter the predetermined area unless the vehicle is actually driven. Therefore, the serviceman does not load the engine at the service bay or the like. In the case of implementation, the air-fuel ratio feedback correction coefficient α can be forcibly fixed to 125% and the rich state can be obtained as in the embodiment shown in FIG.

In step 22, the O ₂ sensor output waveform is monitored. Here, sampling monitoring is performed every 2 (ms) for 5 seconds. In step 23, whether or not the time t _MF at which the O ₂ sensor output waveform described in FIG. 7 becomes equal to or less than the reference value V _MF (v) exists in synchronization with the cylinder determination signal,
That is, it is determined whether or not there is a lean signal in synchronization with the engine rotation, and if there is no lean signal, it is determined that there is no misfiring cylinder.

In step 24, since it is determined in step 23 that there is a misfiring cylinder, θ shown in FIG. 7 is calculated. Here, θ is calculated as the angle from the cylinder discrimination signal, but it can also be calculated as time. In step 25,
The calculated θ is set to the preset judgment value (θ ₁ , θ
₍₃ , θ ₅ etc.) to determine the misfiring cylinder. That is, steps 23 to 25 perform the function of the misfiring cylinder determination means L.

In step 26, a judgment value T (ms) is preset for each misfiring cylinder according to each operating state, and t _MF is compared with this judgment value T (ms) to obtain T (m
If it is shorter than s), it is determined to be the ignition system NG, and if it is longer, it is determined to be the fuel injection system NG. That is, step 26 performs the functions of both the judgment value setting means M and the misfire cause judgment means N. In the present embodiment, the presence or absence of misfire and the cause of the misfire can be diagnosed in a very short time and easily, and it occurs only in the region of a predetermined operating state, and an intermittent problem that does not always occur. You can also deal with it.

[0041]

As described above, according to the present invention,
By judging the output level of the air-fuel ratio detection means, when the service person inspects the vehicle where the misfire has occurred,
It is possible to easily diagnose the cause of misfire in a specific cylinder without inspecting all the causes of misfire in the fuel injection system and ignition system of each cylinder, reducing the inspection man-hours and inspection time, which leads to cost reduction. At the same time, it also leads to a reduction in the inspection waiting time for the user.

Further, the cause of misfire can be determined by detecting the output waveform of the air-fuel ratio detecting means even within the predetermined operating condition range.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of another embodiment of the present invention.

FIG. 3 is a system diagram showing the configuration of the present invention.

FIG. 4 is a block diagram showing a specific configuration of the present invention.

FIG. 5 is an O ₂ sensor output waveform diagram for explaining the diagnostic principle of the present invention.

FIG. 6 is a flowchart for performing a misfire diagnosis.

FIG. 7 is an O ₂ sensor output waveform diagram for explaining the diagnostic principle of the present invention.

FIG. 8 is a flowchart for performing misfire diagnosis.

[Explanation of symbols]

11 Engine 15 Fuel Injection Valve 16 ECM 18 O ₂ Sensor 20 Crank Angle Sensor 21 Misfire Diagnostic Device 24 Display Means 25 Input Means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazunaga Futagawa, Takara-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd.

Claims (2)

[Claims] 1. An operating state detecting means for detecting an operating state of an engine, an air-fuel ratio detecting means provided in an exhaust system of the engine, a fuel injection means provided for each cylinder of the engine, and an output of the air-fuel ratio detecting means. An internal combustion engine comprising: a fuel injection control unit that controls a fuel injection unit according to a control program stored in advance based on a signal; and an air-fuel ratio fixed control that opens the air-fuel ratio to a target value in priority to the control program. Control means, fuel injection forced stop means for stopping fuel injection of a specific cylinder during the open control, and misfire during normal operation of the cylinder for which fuel injection has been forcibly stopped during operation before and after the forced stop of fuel injection. A misfire cylinder discrimination means for discriminating based on fluctuations; an air-fuel ratio output change detection means for detecting an output change of the air-fuel ratio detection means before and during operation of the fuel injection forced stop means; When the misfiring cylinder is discriminated by the misfiring cylinder discrimination means,
And a misfire cause determining means for determining whether there is a misfire due to a failure in the fuel injection system or a misfire due to a failure in the ignition system based on the degree of output change of the air-fuel ratio output change detecting means. Misfire diagnosis device for internal combustion engine. 2. An operating state detecting means for detecting an operating state of the engine, an air-fuel ratio detecting means provided in an exhaust system of the engine, a fuel injection means provided for each cylinder of the engine, and an output of the air-fuel ratio detecting means. In an internal combustion engine equipped with a fuel injection control means for feedback-controlling the fuel injection means in a part of the operating region according to a control program stored in advance based on the signal, the operating state of the engine is a predetermined value not performing the feedback control. Operating range determination means for determining that the engine is in the operating range, a misfired cylinder determination means for determining a misfired cylinder in the predetermined operating range, and a determination of the output of the air-fuel ratio detection means according to the operating state of the engine. When a misfiring cylinder is discriminated by the misfiring cylinder discriminating means, a judgment value setting means for setting a value,
By comparing the output value corresponding to the misfiring cylinder of the air-fuel ratio detecting means with the judgment value, it is possible to judge whether the misfiring is due to a malfunction of the fuel injection system or the misfiring of the ignition system. A misfire diagnosing device for an internal combustion engine, comprising: