JP2001289111A - Misfire detector for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a misfire detector for an engine allowing the continuous detection of misfire without causing the complication of a structure. SOLUTION: A limiting current type A/F sensor 26 is arranged in an exhaust pipe 12 for an engine 1. The A/F sensor 26 outputs a wider and linear air/fuel ratio signal (AF) in proportion to the oxygen concentration of an exhaust gas from the engine 1. A CPU 31 provided in the ECU 30 performs air/fuel ratio F/B control in accordance with the detection result of the A/F sensor 26. The CPU 31 detects misfire in the engine 1 corresponding to the air/fuel ratio AF each time. Namely, in detecting misfire, the air/fuel ratio AF detected by the A/F sensor 26 is compared with a misfire judgement value preset at a lean side of the air/fuel ratio, and if the air/fuel ratio AF is at a leaner side of the misfire judgement value, the occurrence of misfire is judged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art For example, the following methods (1) and (2) have been known as methods for detecting engine misfire. (1) The amount of change in the engine speed is measured, and the measured amount of change in the speed is compared with a misfire determination value stored in advance. A method for determining that a misfire has occurred when a change in the rotation speed greater than the misfire determination value is confirmed. (2) Using a pressure sensor and an O2 sensor (oxygen concentration sensor) disposed in an engine exhaust pipe, a method of judging the presence or absence of a misfire based on a decrease in pressure and an increase in oxygen concentration
-133271). That is, at the time of misfire, the oxygen concentration in the exhaust gas increases, and the flow rate of the high-temperature exhaust gas decreases, thereby reducing the pressure. Therefore, it is determined that a misfire has occurred when a decrease in pressure and an increase in oxygen concentration occur simultaneously.

[0003]

In the misfire detection method of the above (1), when an external vibration is applied to the engine crankshaft, such as when driving on a bad road, the rotation speed is carelessly regardless of the presence or absence of the misfire. Since it fluctuates and there is a risk of misfire detection, the misfire detection must be temporarily suspended. That is, when the vehicle body vibrates due to an external force or the like, it is impossible to perform misfire detection.

In the case of the misfire detection method (2),
The O2 sensor outputs a substantially binary voltage signal depending on whether the exhaust gas is rich or lean with respect to the stoichiometric air-fuel ratio, and the exhaust gas repeatedly changes rich / lean with the stoichiometric air-fuel ratio as a boundary. At least temporarily, the air-fuel ratio lean (increase in oxygen concentration) is detected. For that reason, in addition to the oxygen concentration determination, it is indispensable to determine the exhaust pipe pressure in order to correctly determine the misfire. In such a case, a pressure sensor must be provided in the engine exhaust pipe. However, it is difficult to install a pressure sensor in the exhaust pipe of a current automobile because of its complicated structure and cost. Therefore, it is substantially difficult to perform the misfire detection of the above (2).

On the other hand, a technique disclosed in Japanese Patent Application Laid-Open No. 4-31652 is known as a technique for using the detection result of the O2 sensor for misfire detection. This is a technique for preventing erroneous detection of misfire. As an outline, an O2 sensor provided in an engine exhaust pipe is used, and an output of the O2 sensor and an engine-specific operating cycle learned in advance are used. It is determined whether the misfire determination result is correct. That is, in the publication, the time required for the O2 sensor output to reach a value near the upper limit or the value near the lower limit, and the maintenance time at the values near the upper and lower limits are detected, and a misfire determination is made by comparing the detected value with the learning value. Judgment of the result.

However, in the above-described technique for preventing misfires from being erroneously detected, it is necessary to learn the output of the O2 sensor in accordance with the operation cycle in a normal cycle, and to perform the learning for each engine having a different engine structure such as a bore and a stroke. Therefore, the processing load is increased and the operation is complicated, which is not suitable for practical use. Further, even if the above-described method for preventing misfire misdetection itself is employed as a misfire detection method, it has been impossible to accurately detect misfire.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object the misfire of an engine capable of continuously detecting a misfire without complicating the configuration. It is to provide a detection device.

[0008]

According to the present invention, the gas concentration sensor detects the concentration of a specific gas component in the exhaust gas over a wide area. The misfire determining means determines the presence or absence of a misfire based on the concentration of the specific gas component detected by the gas concentration sensor. In this case, it is particularly preferable that the gas concentration sensor detects the concentration of unburned gas components in the exhaust gas.

In short, when a misfire occurs in the engine,
The air-fuel mixture that has flowed into the cylinder is discharged unburned. At this time, the presence or absence of a misfire can be determined by detecting the concentration of the specific gas component in the exhaust gas (particularly, the concentration of the unburned gas component). . At this time, since the presence or absence of a misfire is determined from the concentration value of the specific gas component detected in a wide area, a precise misfire determination can be performed. Further, unlike the related art in which misfire is determined based on the change amount of the engine rotation speed, the misfire determination does not have to be interrupted even on a rough road, and the misfire can be continuously detected. Unlike the above-mentioned Japanese Patent Application Laid-Open No. 5-133271, which is another conventional technique, a pressure sensor disposed on the exhaust pipe is not required, so that the configuration is not complicated.

Further, in the invention according to claim 3, the gas concentration sensor is an air-fuel ratio sensor for detecting an air-fuel ratio in a wide range from an oxygen concentration in exhaust gas, and the misfire detecting means includes:
The detection result of the air-fuel ratio sensor is compared with a predetermined misfire determination value preset on the air-fuel ratio lean side. If the sensor detection result is leaner than the misfire determination value, it is determined that a misfire has occurred.

Here, the air-fuel ratio sensor is, for example, a well-known limiting current type A / F sensor, and the air-fuel ratio feedback control is performed based on the detection result. At this time, since the oxygen concentration in the exhaust gas increases when a misfire occurs, the presence or absence of a misfire can be determined by detecting the increase in the oxygen concentration in the exhaust gas with an air-fuel ratio sensor.

In such a case, for example, when the air-fuel ratio is feedback-controlled near the stoichiometric air-fuel ratio and when the feedback control is performed in the lean region, the detected air-fuel ratio in a state where no misfire has occurred is naturally changed. It is preferable that the misfire determination value is changed according to the target value of the air-fuel ratio. For example, if the target air-fuel ratio shifts to the lean side, the misfire determination value is changed to the lean side accordingly. Thus, even if the target air-fuel ratio in the air-fuel ratio feedback control is changed, a misfire determination can be accurately performed each time.

According to the present invention, the gas concentration sensor is an HC sensor for detecting the concentration of an HC component in exhaust gas, and the misfire detecting means includes a detection result of the HC sensor and a predetermined misfire determination value. And the value of H detected by the HC sensor is higher than the HC concentration set as the misfire determination value.
If the C concentration is high, it is determined that a misfire has occurred. At this time, when a misfire occurs, the amount of HC in the exhaust gas increases,
The presence or absence of a misfire can be determined by detecting the increase by the HC sensor.

Further, in a vehicle engine, the fuel amount may be increased at the time of starting or high load operation, and the fuel amount may be controlled at an air-fuel ratio rich. In this case, as described in claim 6, when the amount of fuel supplied to the engine is increased, the misfire determination value can be accurately determined each time by changing the misfire determination value according to the fuel increase.

According to the present invention, in an engine operating state in which the concentration of the specific gas component of the exhaust gas fluctuates greatly regardless of the fuel amount control, misfire detection based on the detection result of the gas concentration sensor is not performed. For example, at the time of fuel cut or failure of the injector, the oxygen concentration, the HC concentration, and the like greatly fluctuate regardless of the original fuel amount control (air-fuel ratio control). Therefore, in such a case, the misfire determination is interrupted to suppress the deterioration of the accuracy of the misfire determination.

According to the present invention, the first misfire determination means obtains a rotation speed fluctuation amount based on the rotation speed information of the engine output shaft detected by the rotation sensor, and determines the rotation speed fluctuation amount and a predetermined value. Then, the presence or absence of a misfire is determined by comparison with the misfire determination value. The second misfire determination means determines the presence or absence of a misfire by comparing the detection result of the gas concentration sensor with a predetermined misfire determination value. The switching means detects the presence or absence of vibration of the engine output shaft due to an external force, and if there is vibration, switches the misfire determination means so that the determination result by the second misfire determination means becomes valid.

That is, when the engine output shaft vibrates, for example, when the vehicle is traveling on a bad road, there is a possibility of misdetection of a misfire. Instead, the misfire determination result based on the exhaust gas component (the determination result by the second misfire determination means) is made valid. Thus, misfire detection using the two misfire detection techniques can be realized.

According to the ninth aspect of the present invention, when the second misfire judging means judges that there is a misfire, subsequently, the first misfire judging means carries out a misfire judgment, and the first misfire judging means performs the misfire judgment. Specifies the misfiring cylinder by That is,
Although it is difficult to determine the misfiring cylinder by the misfiring determination based on the exhaust gas component (second misfiring determining means), it is easy to specify the misfiring cylinder by combination with the misfiring determination based on the rotational speed variation (first misfiring determining means). Becomes

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of the present invention as an air-fuel ratio control system for a vehicle gasoline engine will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an air-fuel ratio control system according to the present embodiment. As shown in FIG.
The engine 1 is configured as a 4-cylinder 4-cycle spark ignition engine. The intake air is taken in from an air cleaner (not shown), passes through the intake pipe 3, the throttle valve 4, the surge tank 5, and the intake manifold 6 from the upstream, and the fuel injected from the injector 7 for each cylinder in the intake manifold 6 Mixed. Then, the mixture is supplied to each cylinder as a mixture having a predetermined air-fuel ratio.

Each cylinder of the engine 1 is provided with an ignition plug 9 which ignites the mixture of each cylinder at a predetermined timing. In the apparatus of the present embodiment, a so-called DLI system is employed, and ignition energy from an unillustrated ignition coil is directly supplied to the ignition plug 9 of each cylinder without passing through a distributor. Exhaust gas discharged from each cylinder after combustion is exhaust manifold 1
After passing through the catalytic converter 14 provided in the exhaust pipe 12 through the exhaust pipe 1 and the exhaust pipe 12, it is discharged to the atmosphere.

The intake pipe 3 is provided with an intake pressure sensor 22 for detecting a negative pressure (intake pressure PM) in the intake pipe downstream of the throttle valve 4. The cylinder block of the engine 1 is provided with a water temperature sensor 24 for detecting the temperature of the engine cooling water (cooling water temperature Thw). A rotation speed sensor 25 for detecting the rotation speed of the engine 1 (engine rotation speed Ne) is provided on a crankshaft (not shown).
The rotation speed sensor 25 outputs 24 pulse signals at equal intervals every two rotations of the engine 1, that is, every 720 ° CA.

In the exhaust pipe 12, a catalytic converter 14
An A / F sensor 26 of a limiting current type is disposed on the upstream side (collection portion of the exhaust manifold 11), and an O2 sensor (hereinafter, for convenience,
A rear O2 sensor 27 is provided.

The A / F sensor 26 has a wide range and linear air-fuel ratio signal (AF) in proportion to the oxygen concentration of the exhaust gas discharged from the engine 1 (or the CO concentration in the unburned gas).
Is output. Briefly describing its characteristics, the A / F sensor 26
Has a saturation region in which the limit current is saturated in proportion to the oxygen concentration or the CO concentration in the exhaust gas with the application of a voltage (voltage V on the horizontal axis) to the sensor 26, as shown in FIG. The air-fuel ratio AF can be measured by detecting the current value (limit current) in this saturation region and converting the current value. That is, the increase / decrease of the limit current corresponds to the increase / decrease of the air-fuel ratio (that is, the degree of lean / rich). The limit current increases as the air-fuel ratio becomes leaner, and the limit current decreases as the air-fuel ratio becomes richer. I do. In addition, as a structure of the A / F sensor 26, a cup type, a laminated type, and the like are conventionally known, but any of them may be used.

The rear O2 sensor 27 detects an electromotive force signal VO which differs depending on whether the exhaust gas has a rich or lean air-fuel ratio.
X2 is output. That is, although illustration of the sensor output characteristics is omitted, the electromotive force signal VOX2 is a voltage signal that greatly changes at the stoichiometric air-fuel ratio λ = 1, and its value is a voltage value of about 1 V on the rich side, and lean. Side has a voltage value of about 0V. However, the rear O2 sensor 27 is not an indispensable requirement of the present invention.
/ F sensor, or the sensor itself on the downstream side of the catalyst may be omitted.

The ECU (electronic control unit) 30 includes a CP
U31, ROM32, RAM33, backup RAM
An input port 35 for inputting a detection signal of each sensor described above and an output port 36 for outputting a control signal to each actuator or the like are connected via a bus 37 to constitute a logical operation circuit centered on 34 and the like. . The ECU 30
The detection signals (intake pressure PM, cooling water temperature Thw, engine speed Ne, air-fuel ratio signal, etc.) of the various sensors described above are input via the input port 35. Then, control signals such as the fuel injection amount TAU and the ignition timing Ig are calculated based on these values, and the control signals are output to the injector 7 and the ignition plug 9 via the output port 36, respectively.

In particular, the CPU 31 performs air / fuel ratio feedback (F / B) control based on the detection results of the A / F sensor 26 and the rear O2 sensor 27. At that time, CPU
A stoichiometric F / B control 31 uses a stoichiometric air-fuel ratio (stoichiometric) as a target air-fuel ratio, and a lean combustion F / B control uses a target air-fuel ratio in an air-fuel ratio lean region. Further, the CPU 31 detects a misfire in the engine 1 according to the air-fuel ratio at that time.

Next, the procedure of fuel injection control and misfire detection in the present control device will be described with reference to the flowcharts of FIGS. First, the control procedure of the fuel injection executed by the CPU 31 will be described with reference to the flowchart of FIG. Note that the process of FIG. 3 is executed by the CPU 31 for each combustion of each cylinder (each 180 ° CA in the case of a four-cylinder engine).

Now, when the routine of FIG. 3 starts,
First, in step 101, sensor detection results (engine speed Ne, intake pressure PM, cooling water temperature Thw, etc.) indicating the engine operating state are read, and in subsequent step 102, R
Using a basic injection map stored in advance in the OM 32, a basic injection amount Tp according to the engine speed Ne and the intake pressure PM at each time is calculated. In step 103, it is determined whether a known air-fuel ratio F / B condition is satisfied. Here, the air-fuel ratio F / B condition refers to the cooling water temperature Th.
This includes that w is equal to or higher than a predetermined temperature, not being in a high rotation / high load state, and that the A / F sensor 26 is in an active state.

If the F / B condition is not satisfied, step 10
Proceeding to 4, the air-fuel ratio correction coefficient FAF is set to "1.0".
If the F / B condition is satisfied, the process proceeds to step 105,
The target air-fuel ratio AFtg is set. Target air-fuel ratio AFtg
Is, for example, the current engine speed Ne and intake pressure P
M, which is obtained by referring to a predetermined target air-fuel ratio map, and is set as the stoichiometric air-fuel ratio (A / F = 14.
7) or a lean value corresponding to A / F = 21 to 23 is set.

Thereafter, in step 106, the air-fuel ratio correction coefficient FAtg is determined based on the deviation between the actual air-fuel ratio AF (measured value of the A / F sensor 26) at that time and the target air-fuel ratio AFtg.
Set F. For example, an FAF value is set by an F / B control method based on modern control theory or PID control. At this time, when the output voltage VOX2 of the rear O2 sensor 27 is higher than the comparison voltage, the A / F is set so that the average value of FAF becomes smaller.
The set FAF value may be corrected based on the output of the sensor 26. However, a detailed description of the control method is omitted.

After setting the FAF value, in step 107,
Using the following equation, the basic injection amount Tp and the air-fuel ratio correction coefficient F
A final fuel injection amount TAU is calculated from AF and other correction coefficients FALL (various correction coefficients such as a water temperature and an air conditioner load). TAU = Tp / FAF / FALL fuel injection amount T
After the calculation of the AU, a control signal corresponding to the TAU value is output to the injector 7, and the present routine is ended once.

Next, the procedure of misfire detection performed by the CPU 31 will be described with reference to the flowchart of FIG.
The processing in FIG. 4 corresponds to “misfire determination means” described in the claims, and is executed every combustion of each cylinder (in the case of a four-cylinder engine, every 180 ° CA).

First, in step 201, it is determined whether or not the prerequisites for misfire detection, such as that fuel is not being cut and that no abnormality such as disconnection or short circuit has occurred in the injector 7, are satisfied. In short, it is determined whether or not the engine is in an engine operating state in which the air-fuel ratio greatly fluctuates regardless of the fuel injection amount control (air-fuel ratio control). If the above prerequisites do not hold, the present process is terminated without performing misfire detection. If the above precondition is satisfied, the process proceeds to step 202.

In step 202, the air-fuel ratio AF (actual air-fuel ratio) obtained by converting the detection result of the A / F sensor 26 is read. In step 203, the value of the air-fuel ratio for misfire determination (misfire determination value AFmf) is set. I do. Here, the misfire determination value AFmf is a threshold value for judging that the air-fuel ratio AF deviates greatly from the original value, and determines that the air-fuel ratio AF is caused by the occurrence of a misfire, based on the target air-fuel ratio AFtg at that time. Is set to leaner than that. For example, when the stoichiometric air-fuel ratio is controlled, AFmf = 18 to 19
If the air-fuel ratio is controlled by lean combustion,
AFmf = approximately 26 to 28. Further, when the fuel injection amount is increased at the time of engine start or high load operation, the misfire determination value AFmf is changed to the rich side by the fuel increase. However, the misfire determination value AFmf can be used as a predetermined fixed value.

Thereafter, in step 204, the air-fuel ratio AF
Is compared with the misfire determination value AFmf. If the air-fuel ratio AF is richer than the misfire determination value AFmf (AF ≦ AFm
f) Assuming that no misfire has occurred, the process is terminated as it is. If the air-fuel ratio AF is leaner than the misfire determination value AFmf (AF> AFmf), it is determined that a misfire has occurred and the routine proceeds to step 205, where the misfire occurrence is stored in the RAM 33. When a misfire occurs, the driver is warned that a problem such as deterioration of the emission or damage of the exhaust gas purifying catalyst may occur, through lighting control of a warning lamp or the like.

In short, when a misfire occurs, the air-fuel mixture that has flowed into the engine cylinder is discharged without being burned. At that time, the oxygen concentration in the exhaust gas increases.
The presence or absence of a misfire can be determined by detecting with the sensor 26.

According to this embodiment described in detail above, the following effects can be obtained. Since the presence or absence of a misfire is determined from the air-fuel ratio AF detected over a wide area, a precise misfire determination can be made. Further, unlike the related art in which misfire is determined based on the change amount of the engine rotation speed, the misfire determination does not have to be interrupted even on a rough road, and the misfire can be continuously detected. Unlike the above-mentioned Japanese Patent Application Laid-Open No. 5-133271, which is another conventional technique, a pressure sensor disposed on the exhaust pipe is not required, so that the configuration is not complicated. Further, at this time, by setting the misfire determination value AFmf to be variable, the misfire detection sensitivity can be arbitrarily changed.

When setting the misfire determination value AFmf,
By changing the misfire determination value AFmf according to the target air-fuel ratio AFtg, or when increasing the fuel injection amount, by changing the misfire determination value AFmf according to the fuel increase amount,
Misfire determination can be made accurately each time.

In an engine operating state in which the air-fuel ratio greatly fluctuates regardless of the air-fuel ratio control, such as when the fuel is cut or the injector 7 fails, the misfire detection based on the detected air-fuel ratio AF is not performed. Is suppressed.

(Second Embodiment) Next, a second embodiment of the present invention will be described, focusing on differences from the first embodiment. In the first embodiment, A
Although the misfire detection is performed only by the detected air-fuel ratio AF by the / F sensor 26, in the present embodiment, in addition to the detection method,
Misfire detection is performed according to the engine speed fluctuation amount. That is, in the misfire detection by the detected air-fuel ratio AF, it is difficult to specify the misfire cylinder. However, by combining the misfire detection based on the rotational speed fluctuation amount, the misfire cylinder can be easily determined.

5 (a) and 5 (b) show a misfire detection procedure according to the present embodiment. This process is executed by the CPU 31 instead of the above-described process of FIG. Is done.

In FIG. 5A, first, at step 301
Then, it is determined whether or not the crankshaft (output shaft) of the engine 1 is affected by vibration due to external force. As a specific means for determining the vibration, a method of determining a vibration state from a rotation speed pattern for each predetermined crank angle, a method of determining a vibration state from a detection result of an angular velocity sensor or the like can be applied,
For example, when the vehicle is traveling on a rough road, it is determined that there is vibration.

If there is a vibration, proceed to step 302,
Misfire determination based on the detected air-fuel ratio AF is performed. That is,
According to the procedure of FIG. 4 described above, the presence or absence of a misfire is determined based on the AF value at each time. If there is no vibration, the routine proceeds to step 303, where misfire determination is performed based on the amount of rotation fluctuation for each engine cylinder. In short, in the process of this flowchart, two types of misfire detection methods are selectively executed according to the presence or absence of vibration of the crankshaft. However, the procedure of this misfire determination will be described later with reference to FIG.

On the other hand, in FIG. 5B, first, in step 401, a misfire determination based on the detected air-fuel ratio AF is performed (see FIG. 4 described above). In the following step 402,
It is determined by the detected air-fuel ratio AF that misfire has occurred, and it is determined whether or not that fact has been stored. If no misfire has occurred, the present process is temporarily terminated. If a misfire has occurred, the routine proceeds to step 403, where it is determined whether or not the crankshaft of the engine 1 is affected by vibration due to external force. If there is no vibration, the process proceeds to step 404, where misfire determination is performed based on the amount of rotation fluctuation for each engine cylinder. This step 404 is particularly performed for the purpose of specifying which cylinder is the misfiring cylinder.

In the present embodiment, the above-mentioned step 3
Steps 01 and 403 correspond to “switching means”, steps 303 and 404 correspond to “first misfire determining means”, and steps 302 and 401 correspond to “second misfire determining means”. I do.

Here, one procedure of the misfire detection based on the rotation fluctuation amount will be briefly described with reference to the flowchart of FIG. First, in step 501 of FIG. 6, a required time Tmf within a predetermined misfire detection period is calculated for the current combustion cylinder. In practice, a time Tmf required for the crankshaft to rotate by a predetermined angle (for example, 180 ° CA) is calculated. In the subsequent step 502, the angular time (average rotational speed) ωn (n = 1 to 4) of the crankshaft is calculated for each cylinder from the reciprocal thereof using the calculated required time Tmf.

Next, in step 503, using the following formula, the average rotation speed ωn calculated this time and the average rotation speeds ωn-1, ωn-2, ω calculated last time, two times before and three times before.
The rotation fluctuation amount Δωn between the cylinders is calculated based on n-3.

Δωn = (ωn−1−ωn) − (ωn−3−ωn−2) Here, (ωn−1−ωn) and (ωn−3−ωn−2) represent cylinders having continuous explosion strokes. Rotational fluctuation amount at (ω
(n-1-ωn) is the latest, (ωn-3-ωn-2) is 360 °
This is the value before CA.

Thereafter, at step 504, a misfire determination value REFn for each cylinder is set. Here, the misfire determination value RE
Fn is the value for the current n-th cylinder for which the rotation fluctuation amount Δωn has been calculated, and the engine operating state (Ne,
PM, etc.) (however, a fixed value is also possible).

Thereafter, in step 505, a misfire determination is made by comparing the rotational fluctuation amount Δωn with the misfire determination value REFn for each cylinder. If Δωn> REFn, it is determined that a misfire has occurred, and the routine proceeds to step 506, where a misfire detection flag XMFn indicating that a misfire has occurred in the corresponding cylinder.
Is set to "1". If Δωn ≦ REFn, it is determined that no misfire has occurred, and the routine proceeds to step 507, where the misfire detection flag XMFn is cleared to “0”. Here, the misfire detection flag XMFn is provided for each cylinder so that it is possible to identify which cylinder has misfired.

In step 508 after the operation of the misfire detection flag XMFn, the execution of the next step
02 to the previous value ωn-1
The previous value ωn-1 to the value ωn-2 before the previous value and the value ωn-2
Is rewritten to the value ωn-3 three times before and the RAM 33
, And then the process is temporarily terminated.

As described above, according to the second embodiment, the presence or absence of vibration of the crankshaft due to external force is detected, and the misfire determination based on the detected air-fuel ratio AF and the misfire determination based on the rotation fluctuation amount are determined.
When there is vibration, the misfire determination method is switched so that the determination result based on the detected air-fuel ratio AF becomes valid, so that the misfire determination using the two methods can be realized. That is, even when the vehicle is traveling on a rough road, misfire is not erroneously detected, and appropriate misfire detection can be continued. In addition, misfire cylinders can be specified by combination with misfire determination based on rotation fluctuation.

The present invention can be embodied in the following forms other than the above. As the gas concentration sensor, an HC sensor that detects the concentration of the HC component in the exhaust gas may be used, and the misfire determination may be made according to the detection result of the HC sensor. That is, the detection result of the HC sensor is compared with a predetermined misfire determination value, and if the HC concentration detected by the HC sensor is higher than the HC concentration set as the misfire determination value, it is determined that a misfire has occurred. At this time, at the time of misfiring, the amount of HC in the exhaust gas increases. Therefore, the presence or absence of misfiring can be determined by detecting the increased amount with the HC sensor. The misfire determination value for comparing and determining the detected HC concentration may be variably set according to the fuel injection amount at each time. For example, the larger the fuel injection amount, the larger the value.

Alternatively, a so-called composite gas sensor that can detect the concentration of oxygen in exhaust gas and the concentration of other gas components (HC, CO, etc.) in a single sensor may be used. In short, the gas concentration sensor embodied in the present invention is a sensor that detects the concentration of a specific gas component in exhaust gas over a wide area, in particular, a sensor that detects the concentration of unburned gas component in exhaust gas, It is preferable to determine the presence or absence of a misfire based on the detection result of the gas concentration sensor.

In the first embodiment, since the A / F sensor 26 is provided at the gathering portion of the exhaust manifold 11, when the misfire is determined by the detected air-fuel ratio AF by the A / F sensor 26, the misfire is determined. Although the cylinder was not determined, the exhaust gas after combustion in each cylinder was detected by the A / F sensor 2
The misfire cylinder may be determined in consideration of the time (lag time) until the detection is performed in step S6. Specifically, based on the distance from the exhaust port of each cylinder to the A / F sensor 26 and the flow rate of the exhaust gas at that time, it is inferred which cylinder the air-fuel ratio AF sequentially detected is due to the exhaust gas. When a misfire occurs, the misfire cylinder is determined.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an outline of an engine control device according to an embodiment of the present invention.

FIG. 2 is a diagram showing output characteristics of an A / F sensor.

FIG. 3 is a flowchart showing a fuel injection control routine.

FIG. 4 is a flowchart showing a misfire detection routine based on a detected air-fuel ratio.

FIG. 5 is a flowchart illustrating a misfire detection routine according to a second embodiment.

FIG. 6 is a flowchart showing a procedure of misfire detection based on a rotation fluctuation amount.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine, 12 ... Exhaust pipe, 25 ... Rotation speed sensor, 2
6 A / F sensor, 30 ECU, 31 CPU.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshitaka Uematsu 1-1-1, Showa-cho, Kariya-shi, Aichi Pref. F term (for reference) 3G084 BA09 DA27 EA04 EA07 EA11 EB08 EB25 FA00 FA13 FA18 FA24 FA28 FA30 FA33 FA39 3G301 JA08 JB09 JB10 MA01 MA24 NA01 NA08 NB11 NC02 ND01 ND45 NE01 NE14 NE15 NE23 PA07Z PA17Z PCBZPD PDZZBPD PD06PCB PE05Z PE08Z

Claims (9)

[Claims] A gas concentration sensor provided in an engine exhaust pipe for detecting a concentration of a specific gas component in exhaust gas over a wide area; and determining whether a misfire has occurred based on the concentration of the specific gas component detected by the gas concentration sensor. An engine misfire detecting device, comprising: a misfire judging means for judging. 2. The engine misfire detection device according to claim 1, wherein said gas concentration sensor detects the concentration of unburned gas components in exhaust gas. 3. An air-fuel ratio sensor for detecting an air-fuel ratio in a wide range from an oxygen concentration in exhaust gas, wherein the misfire detecting means sets a detection result of the air-fuel ratio sensor on the air-fuel ratio lean side in advance. 3. The engine misfire detection device according to claim 1, wherein the detected misfire determination value is compared with the predetermined misfire determination value, and if the sensor detection result is leaner than the misfire determination value, it is determined that a misfire has occurred. 4. An air-fuel ratio feedback control system for feedback-controlling an air-fuel ratio to a predetermined target value,
The misfire determination value is changed according to the target value of the air-fuel ratio.
An engine misfire detection device according to claim 1. 5. The gas concentration sensor according to claim 1, wherein the gas concentration sensor is a HC sensor for detecting a concentration of an HC component in the exhaust gas, and the misfire detection means compares the detection result of the HC sensor with a predetermined misfire determination value to determine a misfire. HC set as value
3. The engine misfire detection device according to claim 1, wherein if the HC concentration detected by the HC sensor is higher than the concentration, it is determined that a misfire has occurred. 6. The misfire determination value according to the amount of fuel increase when the amount of fuel supplied to the engine is increased.
The misfire detection device for an engine according to any one of the above. 7. A misfire detection based on a detection result of a gas concentration sensor is not performed in an engine operating state in which the concentration of a specific gas component of exhaust gas greatly fluctuates regardless of fuel amount control. An engine misfire detection device according to the above. 8. A rotation sensor for detecting a rotation speed of an engine output shaft; a gas concentration sensor provided in an engine exhaust pipe for detecting a concentration of a specific gas component in exhaust gas over a wide area; First misfire determining means for determining a rotational speed fluctuation amount based on the rotational speed information of the engine output shaft and comparing the rotational speed fluctuation amount with a predetermined misfire determination value to determine the presence or absence of a misfire; A second misfire judging means for judging the presence or absence of a misfire by comparing the detection result with a predetermined misfire judgment value; and detecting the presence or absence of vibration of the engine output shaft due to an external force. Switching means for switching the misfire determination means so that the determination result by the determination means is valid;
A misfire detection device for an engine, comprising: 9. The engine misfire detecting device according to claim 8, wherein when the second misfire judging means judges that there is a misfire, subsequently, the first misfire judging means performs misfire judgment. An engine misfire detection device that specifies a misfire cylinder by first misfire determination means.