JPH07269407A - Engine misfire detecting device - Google Patents

Abstract

PURPOSE:To surely detect occurrence of a misfire without misjudgement of the misfire at the time of a target air-fuel ratio change or the like. CONSTITUTION:In an engine CE, a corrected target air-fuel ratio wherein response delay of a linear O2 sensor 9 is compensated is computed by a control unit 13, and when a deviation between this corrected target air-fuel ratio and an air-fuel ratio (detected air-fuel ratio) detected by the linear O2 sensor 9 is larger than a specified value, occurrence of a misfire in the engine CE is judged and the misfire occurrence can be thereby surely detected. Since the response delay of the linear O2 sensor 9 is compensated, deflection or deviation is not generated between the corrected target air-fuel ratio and the detected air-fuel ratio even when the target air-fuel ratio is changed and misjudgement of the misfire is not caused to enhance accuracy of misfire judgement.

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 for determining the presence or absence of engine misfire, and for determining the presence or absence of engine misfire and preventing the occurrence of subsequent misfires based on the determination. The present invention relates to an engine misfire detection device.

[0002]

2. Description of the Related Art Generally, in a fuel injection engine for an automobile, basically, an air-fuel ratio (A / F) is set to a predetermined target air-fuel ratio (for example, A / F = 14.7). The fuel injection amount (injection pulse width) of the fuel injection valve is set according to the intake air amount and the engine speed, that is, according to the intake charging efficiency. However, even if the fuel injection amount is set so that the air-fuel ratio becomes the target air-fuel ratio in this way, the actual air-fuel ratio is actually the target air-fuel ratio due to variations in the injection characteristics of the fuel injection valves or changes in the injection characteristics over time. May not match.

[0003] Therefore, in the general fuel injection engine, the linear O ₂ sensor for detecting the O ₂ concentration in the exhaust gas is provided, the O ₂ concentration in the exhaust gas detected by the linear O ₂ sensor is in a normal operating region Air-fuel ratio grasped from
(Hereinafter, for convenience, this is referred to as the air-fuel ratio detected by the linear O ₂ sensor or the detected air-fuel ratio) According to the deviation from the target air-fuel ratio, the fuel injection amount of the fuel injection valve is corrected so as to eliminate the deviation. The fuel ratio feedback control is performed.

By the way, in such a fuel injection engine, in order to improve the fuel efficiency and reduce the NOx emission amount in recent years, the target air-fuel ratio is set to the theoretical air-fuel ratio in a predetermined operating region (lean burn region) where a high output is not required. A so-called lean burn engine, which is set to a value leaner than the fuel ratio (for example, A / F = 24), is widely used. In such a lean-burn engine, the target air-fuel ratio is usually set to the stoichiometric air-fuel ratio or an air-fuel ratio richer than this in order to increase the engine output in the operating region where high output is required, and in the idle region, combustion is performed. The target air-fuel ratio is set to the stoichiometric air-fuel ratio in order to improve stability.

However, when the lean burn is performed in this way, misfire may occur when the air-fuel ratio swings to the lean side because the target air-fuel ratio is set near the misfire limit. Therefore, in such a lean burn engine, a misfire detection means for detecting misfire is provided,
When a misfire is detected, it is preferable to correct the target air-fuel ratio slightly in the rich direction, for example, so as to prevent the subsequent misfire from occurring.

Therefore, in recent years, there has been proposed a lean burn engine equipped with a misfire detecting means for detecting a misfire based on the output fluctuation of the linear O ₂ sensor, that is, the fluctuation of the detected air-fuel ratio (for example, Japanese Patent Laid-Open No. 63-246434). (See Japanese Patent Publication). The lean burn engine disclosed in Japanese Patent Laid-Open No. 63-246434 is designed to detect the precursor of engine speed fluctuation from the output fluctuation of the linear O ₂ sensor, but such speed fluctuation causes misfire. It is considered that the precursor of the rotation speed fluctuation substantially means a misfire because it is considered to be caused by.

[0007]

However, when misfire is detected on the basis of the output fluctuation of the linear O ₂ sensor, that is, the fluctuation of the detected air-fuel ratio, noise is generated in the linear O ₂ sensor, etc. When the fuel ratio fluctuates, there is a problem that it is erroneously determined that a misfire has occurred, although the misfire has not actually occurred.

Further, in general, when a misfire occurs, the detected air-fuel ratio deviates from the target air-fuel ratio, so it is conceivable to determine that a misfire has occurred when the detected air-fuel ratio deviates from the target air-fuel ratio. However, since the linear O ₂ sensor is provided in the exhaust passage downstream of the combustion chamber, the detected air-fuel ratio inevitably has a response delay with respect to the actual air-fuel ratio in the combustion chamber. Therefore, when the target air-fuel ratio changes, the detected air-fuel ratio will deviate from the target air-fuel ratio for some period after that, and as a result, there is a problem that it is erroneously determined that misfire has occurred. .

The present invention has been made to solve the above-mentioned conventional problems, and when noise is generated in the linear O ₂ sensor, or when the target air-fuel ratio is changed,
Alternatively, when noise occurs in the linear O ₂ sensor and the target air-fuel ratio is changed, there is provided a means capable of surely detecting misfire without making an erroneous determination of misfire. To aim. Furthermore, it is another object of the present invention to provide a means capable of effectively preventing the occurrence of such a misfire when a misfire is detected.

[0010]

In order to achieve the above object, as shown in the configuration of FIG. 1, the first invention is a target air-fuel ratio setting for setting a target air-fuel ratio according to the operating state of the engine A. Means B and air-fuel ratio detecting means C for detecting the air-fuel ratio
And the fuel supply means D so that the air-fuel ratio becomes the target air-fuel ratio based on the target air-fuel ratio set by the target air-fuel ratio setting means B and the air-fuel ratio detected by the air-fuel ratio detection means C.
Of the fuel supply control means E for controlling the fuel supply amount and the response delay model which is a model showing the response delay of the air-fuel ratio detection means C, and is set by the target air-fuel ratio setting means B based on the response delay model. A target air-fuel ratio correcting means F for correcting the target air-fuel ratio thus corrected, a target air-fuel ratio corrected by the target air-fuel ratio correcting means F, and an air-fuel ratio detected by the air-fuel ratio detecting means C. The air-fuel ratio deviation detecting means G for detecting the corrected air-fuel ratio deviation, and when the corrected air-fuel ratio deviation detected by the air-fuel ratio deviation detecting means G is a predetermined value or more, it is determined that the engine A has misfired. Provided is a misfire detection device for an engine, which is provided with a misfire determination means H.

A second aspect of the present invention is the engine misfire detection device according to the first aspect, wherein the response delay model set by the target air-fuel ratio correction means F is the fuel from the fuel supply means D to the air-fuel ratio detection means C. There is provided an engine misfire detection device characterized in that it includes a dead time element representing a transportation delay of the engine.

A third aspect of the present invention is the engine misfire detecting device according to the first or second aspect of the present invention, wherein the response delay model set by the target air-fuel ratio correcting means F is located at the position where the air-fuel ratio detecting means C is arranged. An engine misfire detection device is provided which includes a first-order lag element that represents a time delay from the change in the air-fuel ratio to the time when the change in the air-fuel ratio is output from the air-fuel ratio detecting means C.

A fourth aspect of the present invention is an engine misfire detecting device according to any one of the first to third aspects of the present invention, which includes operating state change detecting means I for detecting a change in a predetermined operating state of the engine A, Misfire determination inhibiting means J ₁ for inhibiting the misfire determination of the misfire determination means H when the change in the operating state of the engine is detected by the operation state change detection means I. Engine misfire. A detection device is provided.

A fifth aspect of the invention is the engine misfire detecting device according to the fourth aspect of the invention, wherein the operating state change detecting means I is provided.
Provides a misfire detection device for an engine, which is adapted to detect a change in an operating state by a change in an engine load.

A sixth aspect of the present invention is the engine misfire detection device according to any one of the first to third aspects, wherein when the target air-fuel ratio set by the target air-fuel ratio setting means B suddenly changes, a misfire determination is made. Provided is a misfire determination device for an engine, which is provided with a misfire determination prohibiting means J ₂ for prohibiting the misfire determination of the means H.

A seventh aspect of the present invention is the engine misfire determination device according to any one of the first to third aspects, wherein the target air-fuel ratio set by the target air-fuel ratio setting means B is the theoretical air-fuel ratio. Provided is a misfire determination device for an engine, which is provided with misfire determination prohibiting means J ₃ for prohibiting the misfire determination of the misfire determining means H when the engine is not lean.

An eighth invention is an engine misfire determination device according to any one of the first to seventh inventions, and when the misfire determination means H determines that the engine A is misfired, the target There is provided an engine misfire detection device characterized in that an air-fuel ratio correction means K for correcting the air-fuel ratio in a rich direction is provided.

A ninth aspect of the present invention is the engine misfire detection device according to the eighth aspect, wherein when the air-fuel ratio correcting means K corrects the target air-fuel ratio in the rich direction, the correction is held until the engine A is stopped. An engine misfire detection device is provided.

[0019]

EXAMPLES Examples of the present invention will be specifically described below.
As shown in FIG. 2, in a fuel injection type automobile engine CE that uses gasoline as a fuel, when the intake valve 1 is opened, the air-fuel mixture is sucked from the intake port 2 into the combustion chamber 3, and the air-fuel mixture is absorbed. After being compressed by the piston 4, it is ignited and burned by the spark plug 5, and when the exhaust valve 6 is opened, combustion gas (exhaust gas) is discharged to the exhaust passage 8 through the exhaust port 7. ing. Here, in the exhaust passage 8, a linear O ₂ sensor 9 that detects the O ₂ concentration in the exhaust gas and a catalytic converter 10 that uses a three-way catalyst that purifies the exhaust gas are provided in this order from the upstream side. There is. The O ₂ concentration detected by the linear O ₂ sensor 9 is input to the control unit 13, and the control unit 13 calculates the air-fuel ratio based on this O ₂ concentration. Since the O ₂ concentration and the air-fuel ratio have a unique correspondence relationship, the air-fuel ratio is hereinafter referred to as “the air-fuel ratio detected by the linear O ₂ sensor 9” or “the detected air-fuel ratio” for convenience. . The linear O ₂ sensor 9 forms a part of the “air-fuel ratio detecting means” described in the claims.

In the engine CE, as will be described later, in a predetermined operating region, that is, in a lean burn region, the target air-fuel ratio is set to the theoretical air-fuel ratio (air-fuel ratio (air-fuel ratio) in order to improve fuel efficiency and emission performance (reduction of NOx). This is a lean burn engine, that is, an engine with an air-fuel ratio that is leaner than A / F = 14.7) (for example, A / F = 24).

Further, the distributor 11 and the ignition control device 12 supply the ignition plug 5 with high-voltage ignition power at a predetermined timing (ignition timing) set by the control unit 13. There is. The distributor 11 detects the crank angle, and the crank angle is detected by the control unit 1.
3, and the control unit 13 calculates the engine speed based on this crank angle.

In order to supply the air for fuel combustion to the combustion chamber 3 of the engine CE, an intake passage 14 whose upstream end is open to the atmosphere is provided, and the intake passage 14 has an intake air amount in order from the upstream side. A hot wire type air flow sensor 15 for detecting (intake amount), a throttle valve 16 which is opened / closed corresponding to the depression amount of an accelerator pedal (not shown), and pulsation (surging) in the intake passage 14 are reduced. And a surge tank 17 for stabilizing the flow of air. The downstream end of the intake passage 14 is connected to the intake port 2. Further, a fuel injection valve 18 for injecting fuel into the intake passage 14 is arranged near the intake port 2 so that the injection port faces the intake port 2. Here, the fuel injection amount (injection pulse width) and the injection timing of the fuel injection valve 18 are controlled by the control unit 13 as described later. The fuel injection valve 18 corresponds to "fuel supply means" described in the claims.

A bypass intake passage 19 for guiding the air in the intake passage 14 upstream of the throttle valve 16 to the surge tank 17 by bypassing the throttle valve 16 is provided. An ISC valve 20 for controlling the intake air amount is installed. This ISC valve 20 is a control unit 1
In accordance with a signal applied from No. 3, it is opened / closed according to load characteristics, for example, ON / OFF of a compressor of an air conditioner. Further, the engine CE is provided with various sensors such as a water temperature sensor 24 for detecting the engine water temperature, a throttle opening sensor 25 for detecting the throttle opening, and an intake air temperature sensor 26 for detecting the intake air temperature.

The control unit 13 includes "target air-fuel ratio setting means", "fuel supply control means", "target air-fuel ratio correction means", "air-fuel ratio deviation detection means", and "misfire determination" described in the claims. "Means", "operating state change detecting means", "misfire determination prohibiting means", "air-fuel ratio correcting means" and a part of "air-fuel ratio detecting means", and is configured by a microcomputer. A control device, the air-fuel ratio (detected air-fuel ratio) detected by the linear O ₂ sensor 9,
Crank angle signal output from distributor 11
(Engine speed), intake air amount detected by the air flow sensor 15, engine water temperature detected by the water temperature sensor 24, throttle opening detected by the throttle opening sensor 25, intake air temperature detected by the intake air temperature sensor 26 Various control of the engine CE is performed by using such as control information. However, engine C
The control method for general control of E is well known, and the description of the general control method is omitted because it is not the gist of the present invention. Fuel injection control including determination (i.e.,
Only the air-fuel ratio control) will be described.

In the fuel injection control (air-fuel ratio control) according to the present invention, basically, in the high load region where the charging efficiency exceeds a predetermined value, the target air-fuel ratio is set to the theoretical air-fuel ratio (A /F=14.7), and in the low load region where the charging efficiency is less than or equal to the above predetermined value, the target air-fuel ratio is made lean (for example, A / F = 24) in order to improve fuel efficiency and emission performance. The fuel injection amount (injection pulse width) of the fuel injection valve 18 is controlled so that the detected air-fuel ratio becomes the target air-fuel ratio.

Then, the response delay characteristic of the linear O ₂ sensor 9 is represented, and the linear O ₂ sensor 9 from the fuel injection valve 18 is represented.
The target air-fuel ratio is corrected based on a predetermined model (hereinafter referred to as a response delay model) in consideration of the transport delay element (dead time) of the fluid transport path up to and the primary primary detection element of the linear O ₂ sensor 9. Then, based on the deviation between the corrected target air-fuel ratio (hereinafter, referred to as the corrected target air-fuel ratio) and the detected air-fuel ratio (hereinafter, referred to as the corrected air-fuel ratio deviation), it is determined whether the engine CE has misfired. I am trying to judge.
When it is determined that the engine CE has misfired during lean burn when the target air-fuel ratio is lean, the target air-fuel ratio is corrected in the rich direction to prevent the subsequent misfire. There is. The correction of the target air-fuel ratio in the rich direction is held until the engine CE is stopped. This is because if the cause of the misfire continues to occur, the misfire may occur again if the above correction is canceled.

Further, the misfire determination is prohibited during a transition, a non-lean burn, or a sudden change in the target air-fuel ratio (not a normal change). This is because, in such a case, it is considered that the accuracy of the response delay model deteriorates and the accuracy of misfire determination decreases.

A specific control method of fuel injection control (air-fuel ratio control) including misfire determination (misfire detection) by the control unit 13 will be described below with reference to FIG. 2 as needed in accordance with the flowchart shown in FIG. Note that, in FIG. 4, the throttle opening TVO (graph G ₁ ), the charging efficiency ce (graph G ₂ ), and the like when the fuel injection control (air-fuel ratio control) including such misfire determination is performed by the control unit 13 Better charging efficiency ced (graph G ₂ '), filling efficiency deviation absolute value dce (graph G ₃ ), target air-fuel ratio caf (graph G ₄ ), corrected target air-fuel ratio cafd (graph G ₄ '), air-fuel ratio deviation absolute value dcaf
(Graph G ₅ ), transient flag value (graph G ₆ ), misfire determination condition value (graph G ₇ ), detected air-fuel ratio lafs (graph G ₈ ), modified air-fuel ratio deviation daf (graph G ₉ ), misfire flag value ( Graph G ₁₀ ), air-fuel ratio enrichment correction amount cdll (graph G ₁₁ ), target air-fuel ratio caf after enrichment correction (graph G ₁₂ ) and target air-fuel ratio caf before enrichment correction (graph G ₁₂ ′), An example of a change characteristic with respect to time will be shown. A graph G ₂ "in FIG. 4 is a target air-fuel ratio switching lines, the graph G ₃ 'and a graph G
₅ 'is a transition determination line, graph G _9' is a misfire determination line. Note that, in FIG. 4, the graph G ₈ 'is the same temporal change in the corrected target air-fuel ratio as the graph G ₄ '.

When the fuel injection control is started, steps # 1 to # 6 are first executed in order. Step # 1
The intake air amount qa is read (measurement), the engine speed ne is read (measurement) in step # 2, and step # 3
Then, the filling efficiency ce is calculated by the following equation 1. In the following equation, “←” represents the arithmetic processing in the control unit 13 such as substituting (storing) the arithmetic value on the right side into the variable (storage area) on the left side. For example,
In the case of the expression 1, the numerical value (that is, the conversion coefficient) stored in the variable K (the storage area with the variable name K) is changed to the variable qa
Multiply the number stored in
Substitute (store) the value obtained by dividing this by the value stored in the variable ne (that is, the engine speed) in the variable ce.
Will be done.

[Equation 1] ce ← K · qa / ne ………………………………………………………… Equation 1 ce: Filling efficiency K: Conversion factor qa: Intake air amount ne: Engine Number of rotations

In step # 4, the detected air-fuel ratio lafs is read (measured), and in step # 5, the charging efficiency is calculated by the following equation 2.
The ce is subjected to a smoothing process to calculate the smoothed filling efficiency ced, and in step # 6, the filling efficiency deviation absolute value dce is calculated according to the following expression 3.

[Equation 2] ced ← α ・ ced ＋ (1-α) ・ ce ………………………………………… Equation 2

[Equation 3] dce ← │ce−ced│ ……………………………………………………………………………………………………………………………………………………………………………… 3 1) ce: Filling efficiency dce: Absolute value of filling efficiency deviation The absolute value of filling efficiency deviation dce is used as an index for determining whether the engine CE is in a transient state. Specifically, if dce is greater than or equal to a predetermined value KDC, it is determined that the engine CE is in a transient state, and in this case, the misfire determination is prohibited in order to improve the accuracy of the misfire determination as described later.

Next, at step # 7, the charging efficiency ce is a value K corresponding to the target air-fuel ratio switching line (graph G ₂ "in FIG. 4).
Whether or not it exceeds C, that is, the engine CE changes the target air-fuel ratio to the theoretical air-fuel ratio (A /
It is determined whether or not there is a relatively high load state in which F = 14.7). In this embodiment, when the charging efficiency ce exceeds the target air-fuel ratio switching line as shown by the graph G ₂ "in FIG. 4, the target air-fuel ratio is set to the theoretical air-fuel ratio (A / F = 14.7), and when it is below the target air-fuel ratio switching line, a high output is not required so much, so the target air-fuel ratio is lean (A / F = 24-cdll) in order to improve fuel efficiency and emission performance (NOx reduction). ).

Thus, if it is determined in step # 7 that ce> KC (YES), in step # 8 the target air-fuel ratio is reached.
When caf is set to 14.7 (theoretical air-fuel ratio), while it is determined that ce ≦ KC (NO), the target air-fuel ratio is set at step # 9.
(24-cdll). Here, cdll is an air-fuel ratio leaning correction amount for preventing misfire described later.

Next, in step # 10, the corrected target air-fuel ratio cafd is calculated by the following equation (4).

[Formula 4] cafd ← a ・ cafd (i-1) ＋ (1-a) ・ caf (iL) ………………………………………………………………………………………………………………………………………………………………………………………………………………………… -1): Previous modified target air-fuel ratio cafd (i-L): Modified target air-fuel ratio L times before L: Dead time a: First-order lag constant Equation 4 is a model formula representing the response delay of the linear O ₂ sensor 9. Therefore, the dead time L in the equation 4 is the air-fuel mixture (air and fuel vapor) from the fuel injection valve 18 to the linear O ₂ sensor 9.
Or, it is a constant for compensating for dead time which is one of the transportation delay characteristics of the exhaust gas transportation path. The first-order delay constant a is a constant for compensating for the detection first-order delay of the linear O ₂ sensor 9.

That is, the corrected target air-fuel ratio calculated by equation (4)
cafd is a detection value that is predicted to be actually detected by the linear O ₂ sensor 9 at that time when the air-fuel mixture having the target air-fuel ratio caf is supplied to the combustion chamber and combusts without being misfiring. This is the predicted value of the air-fuel ratio. Therefore, if no misfire has occurred, the corrected target air-fuel ratio cafd will be substantially equal to the detected air-fuel ratio lafs (as expected). Therefore, in the present embodiment, when the deviation between cafd and lafs defined by lafs-cafd, that is, the corrected air-fuel ratio deviation daf is large,
It is determined that the engine CE is misfiring. Accordingly, since not performing misfire determination based on the output variation of the linear O ₂ sensor 9, even if noise occurs in the linear O ₂ sensor 9, even though the erroneous decision (misfire misfire has not occurred Judging that a misfire has occurred) does not occur. The response delay model may be a response delay model that does not consider the dead time of the transportation route and considers only the primary delay detected by the linear O ₂ sensor 9 (that is, a simple smoothing process). Conversely, a response delay model that considers only the dead time of the transportation route may be used.

Next, at step # 11, the target air-fuel ratio deviation absolute value dcaf is calculated by the following equation (5).

[Equation 5] dcaf ← │caf−cafd│ ……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………. It is used as an index for determining whether or not the target air-fuel ratio deviation absolute value dcaf and the target air-fuel ratio caf have suddenly changed. Specifically, if dcaf is greater than or equal to the predetermined value KDA, the target air-fuel ratio caf
Is determined to have changed suddenly, and in this case, the misfire determination is prohibited in order to improve the accuracy of the misfire determination as described later.

Then, step # 12 to step # 14
Then, in order, whether the target air-fuel ratio caf exceeds 14.7, that is, whether the target air-fuel ratio is lean, whether the charging efficiency deviation absolute value dce is less than a predetermined value KDC, and the target air-fuel ratio It is determined whether the absolute deviation value dcaf is less than the predetermined value KDA. In this embodiment, basically, as described above, when the corrected air-fuel ratio deviation daf is large, the engine C
Although it is determined that E is misfired, the misfire occurs when the target air-fuel ratio caf is not lean, that is, during non-lean burn, during transition, or when the target air-fuel ratio changes suddenly (not a normal change). The judgment is prohibited.
The reasons for doing this are as follows.

That is, during non-lean burn, the ignitability / combustibility of the air-fuel mixture is high and the possibility of misfire is extremely low. Therefore, misfire determination is prohibited during non-lean burn. In addition, at the time of transition, the linear O ₂ from the fuel injection valve 18
Since the flow of the air-fuel mixture or exhaust gas becomes unsteady in the fluid transportation path to the sensor 9, the response delay model cannot accurately grasp the behavior of the air-fuel mixture or exhaust gas, and therefore the corrected target air-fuel ratio cafd And the detected air-fuel ratio lafs may deviate from each other, which may cause misfire misjudgment. Therefore, the misfire determination is prohibited during the transition. Even when the target air-fuel ratio suddenly changes, the behavior of the air-fuel mixture or exhaust gas cannot be accurately grasped by the response delay model described above.Therefore, there is a gap between the corrected target air-fuel ratio cafd and the detected air-fuel ratio lafs, and misfire may occur. Judgment may occur. Therefore, the misfire determination is prohibited when the target air-fuel ratio suddenly changes. If the target air-fuel ratio caf changes normally (most of the changes in the target air-fuel ratio are normal changes), the response delay model can grasp the behavior of the air-fuel mixture or exhaust gas sufficiently accurately. Is not prohibited.

Thus, step # 12 to step # 1
In step 4, if it is determined that caf> 14.7, dce <KDC, and dcaf <KDA, then (all Y
ES), in step # 15, the corrected air-fuel ratio deviation daf is calculated by the following equation 6.

[Formula 6] daf ← lafs−cafd ……………………………………………………………………………………………………………………………………………………………… 6 daf: Modified air-fuel ratio deviation lafs: Detected air-fuel ratio cafd: Modified target air Fuel ratio

Next, at step # 16, the corrected air-fuel ratio deviation da
It is determined whether or not f exceeds a predetermined value KAF, that is, whether or not there is a misfire. Where daf> KAF
If it is determined to be (YES), that is, engine C
If it is determined that E has misfired, step #
At 17, the air-fuel ratio enrichment correction amount cdll is increased by the predetermined value KL. As described above, the target air-fuel ratio caf is set to (24-cdll) during lean burn. In this case, therefore, the target air-fuel ratio caf is reduced by KL, and therefore KL is corrected in the rich direction. Since the target air-fuel ratio caf is thus corrected in the rich direction, the occurrence of subsequent misfire is prevented or suppressed. Then, step # 18 is executed. On the other hand, if it is determined in step # 16 that daf ≦ KAF (NO), that is, if it is determined that no misfire has occurred, it is not necessary to correct the target air-fuel ratio caf in the rich direction. Step 17 is skipped and step # 18 is executed.

By the way, in step # 12, caf≤
If it is determined to be 14.7 (NO), there is no risk of misfire, so steps # 13 to # 17 are skipped and step # 18 is executed. Step #
If it is determined in step 13 that dce ≧ KDC (NO),
Since the engine CE is in the transient state, steps # 14 to # 17 are skipped and step # 18 is executed. If it is determined in step # 14 that dcaf ≧ KDA (NO), the target air-fuel ratio caf has changed suddenly (not a normal change).
Step 7 is skipped and step # 18 is executed.

At step # 18, the correction coefficient ctotal is calculated by the following equation 7, and then at step # 19, the following equation 8 is obtained.
Thus, the injection pulse width ta of the fuel injection valve 18 is calculated.

[Equation 7] ctotal ← 14.7 / caf …………………………………………………… Equation 7

[Equation 8] ta ← KF ・ ce ・ ctotal ……………………………………………………………………………………………………………………………………………………………………………………………………………… .. Coefficient ce: filling efficiency Here, the correction coefficient ctotal is a correction coefficient for correcting the injection pulse width ta for lean burn according to the target air-fuel ratio caf when the target air-fuel ratio caf is lean, that is, during lean burn. . Therefore, the correction coefficient ctotal becomes 1 when the target air-fuel ratio caf is set to the theoretical air-fuel ratio (A / F = 14.7), that is, when the lean burn is not performed. KF is a conversion coefficient for converting the filling efficiency ce into the injection pulse width ta.

Next, at step # 20, fuel is injected from the fuel injection valve 18 with an injection pulse width ta at a predetermined timing. Such fuel injection control (air-fuel ratio control) is performed, and the air-fuel ratio is maintained at the target air-fuel ratio both during lean burn and during non-lean burn. After this,
Return to step # 1.

FIG. 4 shows an example of changes over time of various state quantities when the fuel injection control (air-fuel ratio control) including such misfire determination is performed, but in the example shown in FIG. The misfire determination is performed as shown by G ₁₀ , and every time the misfire determination is performed, the air-fuel ratio enrichment correction amount cdll is increased as shown by the graph G ₁₁ , and as a result, at the time of lean burn as shown by the graph G ₁₂ . The target air-fuel ratio caf is gradually corrected in the rich direction. In this way, every time a misfire occurs, countermeasures are taken to prevent this, and the subsequent misfire is prevented or suppressed.

As described above, according to the present embodiment, when high output is required, non-lean burn operation is performed with the target air-fuel ratio as the theoretical air-fuel ratio, and engine output is increased. On the other hand,
When a very high output is not required, the target air-fuel ratio is made lean and lean burn operation is performed, so that fuel efficiency performance and emission performance are improved. Then, the misfire determination is performed during the lean burn operation, and when it is determined that the misfire has occurred, the target air-fuel ratio is corrected in the rich direction, and the subsequent misfire is prevented or suppressed. Further, the correction in the rich direction is held until the engine CE is stopped, and the occurrence of misfire is effectively prevented or suppressed even when the cause of continuous misfire exists. Further, since the misfire determination is not performed based on the output variation of the linear O ₂ sensor 9, when the target air-fuel ratio changes normally or when noise occurs in the linear O ₂ sensor 9, a misfire determination is erroneously made. It won't happen.

Further, since the misfire determination is prohibited when the engine CE is in a transient state, the misfire determination due to the unsteady behavior of the air-fuel mixture or the exhaust gas is prevented, and the accuracy of the misfire determination is improved. Further, when the target air-fuel ratio suddenly changes (not a normal change), the misfire determination is prohibited, so that the misfire determination due to the sudden change in the target air-fuel ratio is prevented and the accuracy of the misfire determination is improved.

[0046]

According to the first aspect of the invention, the misfire is determined based on the deviation between the detected target air-fuel ratio and the corrected target air-fuel ratio in which the response delay of the air-fuel ratio detecting means is compensated. Even when the air-fuel ratio changes (normal change), misfire misjudgment does not occur, and the accuracy of misfire judgment is improved. Further, since the misfire determination is not performed based on the output change of the air-fuel ratio detecting means, the misfire determination does not occur even when noise occurs in the air-fuel ratio detecting means.

According to the second invention, basically, the same action and effect as those of the first invention can be obtained. Further, since the response delay model includes a dead time element from the fuel supply means to the air-fuel ratio detection means, based on the deviation between the corrected target air-fuel ratio compensated for the dead time of the transportation route and the detected air-fuel ratio. Misfire determination is performed, and erroneous misfire determination when the target air-fuel ratio changes is more effectively prevented.

According to the third invention, basically, the same operation and effect as those of the first or second invention can be obtained. Further, since the response delay model includes the primary delay element of the air-fuel ratio detecting means, the misfire determination can be made based on the deviation between the corrected target air-fuel ratio in which the primary delay of the air-fuel ratio detecting means is compensated and the detected air-fuel ratio. If this is done, the misjudgment of misfire when the target air-fuel ratio changes is more effectively prevented.

According to the fourth invention, basically, the same action and effect as any one of the first to third inventions can be obtained. Further, since the misfire determination is prohibited during a transition in which the accuracy of the response delay model decreases, the misfire determination is prevented and the accuracy of the misfire determination is improved.

According to the fifth invention, basically the same action and effect as the fourth invention can be obtained. Furthermore, since the misfire determination is prohibited when the engine load changes when the accuracy of the response delay model decreases, the accuracy of the misfire determination can be improved.

According to the sixth invention, basically, the same action and effect as any one of the first to third inventions can be obtained. Further, since the misfire determination is prevented when the target air-fuel ratio suddenly changes when the accuracy of the response delay model decreases, the misfire determination is prevented and the accuracy of the misfire determination is improved.

According to the seventh invention, basically the same action and effect as any one of the first to third inventions can be obtained. Further, since the misfire determination is prohibited during the non-lean burn in which misfire is unlikely to occur, unnecessary misfire determination is not performed and the load on the control device is reduced.

According to the eighth invention, basically, the same operation and effect as any one of the first to seventh inventions can be obtained. Furthermore, when it is determined that the engine has misfired, the target air-fuel ratio is corrected in the rich direction, so that the occurrence of misfire after the misfire determination is prevented or suppressed.

According to the ninth invention, basically, the same operation and effect as those of the eighth invention can be obtained. Further, since the correction of the target air-fuel ratio in the rich direction is maintained until the engine is stopped, the occurrence of misfire is prevented or suppressed even when there is a continuous cause of misfire.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of first to eighth inventions corresponding to claims 1 to 8.

FIG. 2 is a system configuration diagram of an engine including a misfire detection device according to the present invention.

FIG. 3 is a flowchart showing a control method of fuel injection control (air-fuel ratio control) including misfire determination by a control unit.

FIG. 4 is a throttle opening during fuel injection control,
It is a figure which shows the time-dependent change of a charging efficiency, a target air-fuel ratio, a detected air-fuel ratio, a misfire flag, and other operating states.

[Explanation of symbols]

CE ... Engine 3 ... Combustion chamber 5 ... Spark plug 8 ... Exhaust passage 9 ... Linear O ₂ sensor 13 ... Control unit 18 ... Fuel injection valve

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location F02D 41/04 305 B 41/14 310 A 41/22 305 A

Claims (9)

[Claims] 1. A target air-fuel ratio setting means for setting a target air-fuel ratio according to an engine operating state, an air-fuel ratio detecting means for detecting an air-fuel ratio, and a target air-fuel ratio set by the target air-fuel ratio setting means,
Based on the air-fuel ratio detected by the air-fuel ratio detection means, the fuel supply control means for controlling the fuel supply amount of the fuel supply means so that the air-fuel ratio becomes the target air-fuel ratio, and the model showing the response delay of the air-fuel ratio detection means. A certain response delay model is set, target air-fuel ratio correction means for correcting the target air-fuel ratio set by the target air-fuel ratio setting means based on the response delay model, and target air-fuel ratio correction means for correcting the target air-fuel ratio An air-fuel ratio deviation detecting means for detecting a corrected air-fuel ratio deviation which is a deviation between the fuel ratio and the air-fuel ratio detected by the air-fuel ratio detecting means, and a corrected air-fuel ratio deviation detected by the air-fuel ratio deviation detecting means is predetermined. An engine misfire detection device, which is provided with misfire determination means for determining that the engine is misfired when the value is greater than or equal to the value. 2. The engine misfire detection device according to claim 1, wherein the response delay model set by the target air-fuel ratio correction means represents a delay in transportation of fuel from the fuel supply means to the air-fuel ratio detection means. An engine misfire detection device characterized by including a time element. 3. The engine misfire detection device according to claim 1 or 2, wherein the response delay model set by the target air-fuel ratio correction means has an air-fuel ratio at a position where the air-fuel ratio detection means is arranged. An engine misfire detection device including a first-order lag element representing a time delay from the change to the output of the change in the air-fuel ratio from the air-fuel ratio detection means. 4. The engine misfire detection device according to any one of claims 1 to 3, further comprising an operating state change detecting means for detecting a change in a predetermined operating state of the engine, and the operating state change. An engine misfire detection device, comprising: misfire determination prohibiting means for prohibiting the misfire determination of the misfire determining means when a change in the engine operating state is detected by the detecting means. 5. The engine misfire detection means according to claim 4, wherein the operating state change detecting means is adapted to detect a change in operating state due to a change in engine load. Misfire detection device. 6. The engine misfire detection device according to any one of claims 1 to 3, wherein when the target air-fuel ratio set by the target air-fuel ratio setting means suddenly changes, misfire of the misfire determination means. A misfire determination device for an engine, which is provided with a misfire determination prohibition unit that prohibits determination. 7. The engine misfire determination device according to any one of claims 1 to 3, wherein the target air-fuel ratio set by the target air-fuel ratio setting means is:
An engine misfire determination device characterized by comprising misfire determination prohibiting means for inhibiting misfire determination of the misfire determining means when the lean air fuel ratio is not lean. 8. The engine misfire determination device according to any one of claims 1 to 7, wherein the target air-fuel ratio is rich when the engine is misfired by the misfire determination means. An engine misfire detection device characterized in that an air-fuel ratio correction means for correcting the direction is provided. 9. The engine misfire detection device according to claim 8, wherein when the air-fuel ratio correction means corrects the target air-fuel ratio in the rich direction, the correction is held until the engine is stopped. An engine misfire detection device characterized in that