JPH07293299A - Air-fuel ratio controller for engine - Google Patents

Abstract

PURPOSE:To suppress an air-fuel ratio variation over the whole misfire range from the initial stage of misfire to the middle or the posterior period. CONSTITUTION:A judging means 22 judges the generation of misfire, and after fuel quantity is increased only immediately after the misfire according to the result of the judgement, calculation is carried out by a calculating means 23, having the fuel reduction quantity as air/fuel ratio correction quantity beta in misfire. The fundamental injection quantity Tp corresponding t the engine operation condition is corrected by a calculating means 24 on the basis of the air/fuel ratio correction quantity beta in misfire, and the fuel in this injection quantity is supplied into an intake pipe by a feeding means 25.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine air-fuel ratio control device, and more particularly to control when a misfire occurs.

[0002]

2. Description of the Related Art It is judged from a measurement result of in-cylinder pressure whether or not a misfire is occurring (or whether or not there is a combustion fluctuation), and when a misfire is occurring, an air-fuel ratio is controlled to a rich side ( See, for example, JP-A-60-249644).

This is because the unburned fuel at the time of misfire adheres and stays in the exhaust pipe in a liquid state, and the proportion of fuel in the exhaust gas becomes small immediately after the misfire, resulting in a temporary lean spike. In order to prevent this, the air-fuel ratio is controlled to the rich side.

[0004]

By the way, as described above, the proportion of fuel in the exhaust gas becomes small and a temporary lean spike occurs only in the early stage of the misfire. Part of the fuel adhering to the pipe wall gradually flows into the catalyst in a liquid state, or is heated by the hot exhaust pipe and part of the adhered fuel evaporates and flows into the catalyst, so that the catalyst inlet , This time, the air-fuel ratio is rich, contrary to the beginning of misfire.

However, since such a rich phenomenon is not taken into consideration in the conventional apparatus, the conversion rate of the catalyst becomes worse due to the rich phenomenon occurring in the latter half of the misfire.

In this case, if the fuel adhering to the exhaust pipe wall can be detected, it is possible to correct the air-fuel ratio to the lean side in the latter stage of the misfire, but the adhering to the exhaust pipe wall is possible. Fuel cannot be detected by the O ₂ sensor. This is because the O ₂ sensor responds to the O ₂ concentration in the exhaust gas, so that the O ₂ concentration does not change before and after the misfire when O ₂ is not consumed.

Therefore, according to the present invention, by performing the air-fuel ratio correction such that the air-fuel ratio is corrected to the rich side only immediately after the misfire and then the air-fuel ratio is corrected to the lean side, the misfire from the early stage to the middle stage and the late stage of the misfire is performed. The purpose is to suppress overall air-fuel ratio fluctuations.

[0008]

As shown in FIG. 16, a first aspect of the present invention is directed to a basic injection amount T depending on the engine operating conditions.
A means 21 for calculating p, a means 22 for determining whether or not a misfire has occurred, and a means 23 for calculating a value for increasing the fuel just after the misfire and reducing the fuel thereafter as a misfire-time air-fuel ratio correction amount β based on the result of this judgment. Further, means 24 for correcting the basic injection amount Tp by the misfire air-fuel ratio correction amount β to calculate the fuel injection amount, and means 25 for supplying the injection amount of fuel to the intake pipe are provided.

As shown in FIG. 17, the second aspect of the present invention is a means 21 for calculating the basic injection amount Tp according to the operating conditions of the engine, and a sensor (for example, O ₂ Sensor and air-fuel ratio sensor) 31, means 32 for calculating the air-fuel ratio feedback correction amount α based on the output of this sensor 31, and the basic injection amount Tp is corrected by this correction amount α to calculate the fuel injection amount. Means 3
3 and means 25 for supplying this injection amount of fuel to the intake pipe
A means 22 for determining whether or not a misfire has occurred, a means 23 for increasing the fuel only immediately after the misfire and a value for reducing the fuel thereafter as the misfire air-fuel ratio correction amount β, and an air-fuel ratio feedback correction. In the middle and when the determination means 22 determines that a misfire has occurred, the calculation of the air-fuel ratio feedback correction amount α is prohibited, and the misfire air-fuel ratio correction amount β is used instead of the air-fuel ratio feedback correction amount α. There is provided means 34 for correcting the basic injection amount Tp to calculate the misfire fuel injection amount, and outputting the misfire fuel injection amount to the fuel supply means 25.

According to a third aspect of the present invention, in the first or second aspect of the invention, the misfire air-fuel ratio correction amount β increases stepwise to a predetermined value A for making the air-fuel ratio rich side immediately after the misfire, and its large value. Predetermined value B that makes the air-fuel ratio leaner from the value
Is a value that decreases by a predetermined decrease amount Δβ ₁ and then increases by a predetermined increase amount Δβ ₂ that is smaller than the decrease amount Δβ ₁ and returns to the value immediately before the misfire.

According to a fourth aspect of the present invention, in the third aspect, the amount of decrease Δβ ₁ and the amount of increase Δβ ₂ are set to be smaller at low temperature than at high temperature.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects of the invention, the misfire determination means 22 is
As shown in FIG. 18, means 41 for detecting the in-cylinder pressure P,
A means 42 for detecting the crank angle, and a means 43 for sampling at least one or more in-cylinder pressures at a pair of positions which are moved back and forth by substantially the same crank angle about the compression top dead center.
And a means 44 for calculating the sum total ΔP of the pair of in-cylinder pressure differences as an average effective pressure equivalent value, and the average effective pressure equivalent value and the reference value ΔPmin are compared, and the average effective pressure equivalent value is equal to or less than the reference value ΔPmin. Means 45 for determining that
Consists of.

In a sixth aspect based on the fifth aspect, the reference value ΔPmin is set larger as the engine load increases.

A seventh aspect of the present invention is the fuel cell system according to any one of the first to sixth aspects of the invention, wherein the ignition timing is advanced and corrected during the fuel amount reduction correction by the misfire time air-fuel ratio correction amount β.

In an eighth aspect based on the seventh aspect, the advance correction amount ΔADV is set larger as the fuel reduction correction value increases.

[0016]

When a misfire occurs, a part of the unburned fuel remains in the liquid state and adheres to the exhaust pipe, where it stays in the exhaust pipe. As a result, the air-fuel ratio is greatly swung to the lean side and NOx is greatly increased during the misfire. In the latter half of the period, the unburned fuel adhering to the exhaust pipe wall gradually flows into the catalyst in a liquid state, so the air-fuel ratio swings to the rich side this time, and HC increases. In accordance with the change in the air-fuel ratio of
A value that increases the fuel only after the misfire and decreases the fuel after that is calculated as the misfire air-fuel ratio correction amount β, and when the basic injection amount Tp is corrected by this misfire air-fuel ratio correction amount β, the air-fuel ratio that occurs at the beginning of the misfire Not only is the large leaning of the air-fuel ratio suppressed, but the richening of the air-fuel ratio in the latter half of the period during misfire is also prevented.

If the misfire time air-fuel ratio correction is performed during the air-fuel ratio feedback correction, the air-fuel ratio feedback correction interferes with the misfire time air-fuel ratio correction, and it becomes impossible to control the air-fuel ratio during the misfire air-fuel ratio correction to the rich side or the lean side. In the second aspect of the invention, the calculation of the air-fuel ratio feedback correction amount α is prohibited during the air-fuel ratio feedback correction and the misfire determination, and the basic injection amount Tp is replaced by the misfire air-fuel ratio correction amount β instead of the air-fuel ratio feedback correction amount α. By correcting and calculating the misfire fuel injection amount, it is possible to avoid interference with the misfire air-fuel ratio correction due to the air-fuel ratio feedback correction.

According to the third aspect of the invention, in the first or second aspect of the invention, the misfire air-fuel ratio correction amount β increases stepwise to a predetermined value A for making the air-fuel ratio rich side immediately after the misfire, and a large value thereof. A predetermined value B to make the air-fuel ratio leaner from
The amount decreases by a predetermined amount of decrease Δβ ₁ and then increases by a predetermined amount of increase Δβ ₂ that is smaller than the amount of decrease Δβ ₁ and returns to the value immediately before the misfire. A misfiring air-fuel ratio correction amount β that is similar to the air-fuel ratio variation over time is easily given.

According to the fourth aspect of the invention, in the third aspect, when the amount of decrease Δβ ₁ and the amount of increase Δβ ₂ are set to be smaller at a low temperature than at a high temperature, the misfire air-fuel ratio is the same before and after warming up. The correction amount β is accurately provided.

According to a fifth aspect of the present invention, in any one of the first aspect to the fourth aspect, at least one pair of in-cylinder pressures at positions that are moved back and forth by substantially the same crank angle with respect to the compression top dead center are provided. If the summation ΔP of the pair of in-cylinder pressure differences is calculated as the average effective pressure equivalent value, the calculation time is shorter and simpler than the calculation of the average effective pressure itself. The determination means 22 is simply configured.

According to a sixth invention, in the fifth invention,
When the reference value ΔPmin is set larger as the engine load increases, the reference value setting accuracy improves regardless of the engine load.

According to a seventh aspect of the present invention, in any one of the first to sixth aspects, when the ignition timing is advanced while the fuel amount is reduced by the misfire time air-fuel ratio correction amount β,
The occurrence of misfire again is suppressed.

According to the eighth invention, in the seventh invention,
When the advance correction amount ΔADV is set to be larger as the fuel reduction correction value is larger, the advance correction amount is accurately provided regardless of the magnitude of the fuel reduction correction value.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, 1 is an engine body, 2 is an intake passage, 3 is an exhaust passage, 4 is a throttle valve, 5 is a fuel injector, and 6 is a catalyst. Fuel whose pressure is adjusted to a constant pressure is supplied to the fuel injector 5 through a fuel supply system (not shown), which is opened by a drive pulse from the control unit 16 and is proportional to the valve opening pulse width. A quantity of fuel is injected and delivered.

Reference numeral 11 is a hot-wire type air flow meter for detecting the air flow rate, and 12 is for each crank angle reference position (4
A crank angle sensor that outputs a signal (Ref signal) every 180 ° for cylinders and every 120 ° for 6 cylinders and a signal for each unit crank angle. 13 is a boundary between the theoretical air-fuel ratio according to the residual oxygen concentration in the exhaust gas. O ₂ sensor whose output changes suddenly, 15 is a water temperature sensor that detects the cooling water temperature of the engine, and is a control unit 16 to which signals from these are input. Is executed.

The air-fuel ratio control by the control unit 16 composed of a microcomputer is as follows.

The fuel injector 5 is driven in synchronization with the Ref signal. For example, in the sequential injection method, once every two engine revolutions, for each cylinder Ti = 2 × Te + Ts (1) where Te: effective pulse width Ts: injection pulse given by the formula of invalid pulse width according to battery voltage Injector 5 with width Ti
Is activated. In the case of the simultaneous injection method, the engine 1
Once every rotation, all the cylinders at the same time Ti = Te + Ts Injector 5 with injection pulse width Ti given by the equation (2)
Is activated.

FIG. 2 is a flow chart for calculating the effective pulse width Te of the above equation (1), which has a constant period (for example, 10 ms).
ec).

In step 1, the basic pulse width Tp is calculated from the air flow rate Q detected by the air flow meter 11 and the engine speed N detected by the crank angle sensor: Tp = (Q / N) × K (3) where K: Calculate with a constant formula. The air-fuel ratio determined by this Tp is called the base air-fuel ratio.

In step 2, the effective pulse width Te is calculated by using the basic pulse width Tp: Te = Tp × Co × α × β (4) where Co: various correction coefficients α: air-fuel ratio feedback correction coefficient [%] β : Calculate with the formula of misfire air-fuel ratio correction coefficient [%].

The various correction coefficients Co in the equation (4) are values for ensuring smooth operation under various conditions. For example, at the time of starting, warming up, high load, etc., the basic pulse width T is based on the signals from the water temperature sensor 15 and other sensors.
Correct p. At this time, the value of the air-fuel ratio feedback correction coefficient α, which will be described later, is clamped at 100% (steps 21 and 22 in FIG. 4).

FIG. 3 is a flow chart of calculation of the fuel injection pulse width Ti and execution of injection, which is executed in synchronization with the Ref signal.

Step 11 for sequential injection
Then, the fuel injection pulse width Ti of the above equation (1) is calculated, and this is transferred to the output register in step 12. With the ignition order in a four-cylinder engine set to # 1- # 3- # 4- # 2, when the Ref signal is input this time, for example, T is set to the first cylinder.
If the fuel corresponding to i is supplied, the third Ref.
When the ef signal is input, the No. 4 cylinder is supplied, and when the Ref signal is input three times after, the Ti fuel is supplied to the No. 2 cylinder.

The air-fuel ratio feedback correction coefficient α in the equation (4) is a value obtained in synchronization with the Ref signal by proportional-plus-integral control (a kind of feedback control) based on the output of the O ₂ sensor 13, and the value of α is 100%. When it exceeds, the air-fuel ratio is returned to the rich side by the equation (4), and when it falls below 100%, the air-fuel ratio is returned to the lean side.

FIG. 4 is a flow chart for calculating the air-fuel ratio feedback correction coefficient α, which is executed in synchronization with the Ref signal.

The output of the O ₂ sensor is at a high level (about 1 V) on the rich side of the stoichiometric air-fuel ratio and at a low level (approximately 0 V) on the lean side, and therefore exceeds the slice level provided for approximately 0.5 V. Then, the actual air-fuel ratio is on the rich side, and when it is smaller than the slice level, it is on the lean side. Therefore, for example, when the output of the O ₂ sensor is reversed from the rich side to the lean side, the value obtained by adding the proportional amount P _L to the previous feedback correction coefficient α is updated as this time α (steps 24 and 26 in FIG. 4). , 2
9) From the next time, the integral I _L is added until just before the O ₂ sensor output is inverted to the rich side (step 2 in FIG. 4).
4, 26, 30), the injection amount (injection pulse width Ti) increases due to the fuel increase due to α, and the actual air-fuel ratio gradually increases.

As a result, when the output of the O ₂ sensor is inverted to the rich side, the value obtained by subtracting the proportional amount P _R from the previous α is updated as the current α (steps 24 and 2 in FIG. 4).
5, 27), and from the next time, the integral I _R is subtracted until just before the O ₂ sensor output is inverted to the lean side again (FIG. 4).
24, 25, 28).

When the output of the O ₂ sensor is reversed to the lean side, the above is repeated.

Due to such repetition, the actual air-fuel ratio changes in a cycle of approximately 1 to 2 Hz, and the average air-fuel ratio is maintained within the window (predetermined air-fuel ratio range centered on the theoretical air-fuel ratio). Is done.

The feedback prohibition flag of step 23 and the misfire time air-fuel ratio correction coefficient β of the equation (4) which have not been described will be described later.

In the early stage of misfire, unburned fuel adheres to and remains in the exhaust pipe in a liquid state, so that the proportion of fuel in the exhaust gas becomes small and a lean spike occurs temporarily.
In the latter stage, the fuel adhering to the exhaust pipe wall gradually flows into the catalyst, and the catalyst inlet enters a rich air-fuel ratio state, so that HC increases.

In order to deal with this, the control unit 16 corrects the air-fuel ratio to the rich side just after the misfire and thereafter corrects the air-fuel ratio to the lean side.

In order to correct the air-fuel ratio at the time of such a misfire,
As shown in the equation (4), a misfire air-fuel ratio correction coefficient β is newly introduced, and a feedback correction prohibition flag of step 23 is added in FIG. 4 in order to make adjustment with the conventional air-fuel ratio feedback correction. There is.

FIG. 5 is a flow chart for sampling a pair of in-cylinder pressures located at the same crank angle (for example, 30 ° and 60 °) about the compression top dead center TDC, which is executed at constant crank angle intervals. .

In step 41, 60 ° BTDC (TDC
60 ° BTDC depending on whether it was before 60 °)
If it becomes, pressure sensor 17 such as spark plug washer
The in-cylinder pressure P detected at that time (see FIG. 1) is transferred to a variable P- ₆₀ in step 42. Similarly, 30 ° BTD
C, 30 ° ATDC (30 ° after TDC), 60 °
At the timing of ATDC, the in-cylinder pressure P at that time is changed to the variable P.
_-30 , P ₃₀ , and P ₆₀ (steps 43 to 48).

FIG. 7 is a flow chart for explaining whether or not there is a misfire. This is at a timing after the sampling of the in-cylinder pressure is completed (for example, a predetermined crank angle after 61 ° after the compression top dead center). Run.

In step 51, the basic pulse width (engine load equivalent amount) Tp is read, and in step 52, the misfire determination reference value ΔPmin is obtained from this Tp by referring to the table having the contents of FIG.

In step 53, using the above-mentioned sampling value, the sum of the difference between the pair of in-cylinder pressures at the positions that move forward and backward by the same crank angle about the compression top dead center is taken as the average effective pressure equivalent value ΔP, and ΔP = (P _30- P _-30 ) + (P ₆₀ -P _-60 ) ... (5) is used for the calculation.

The average effective pressure equivalent value ΔP in the equation (5) and the reference value ΔPmin are compared in step 54, and ΔP ≦ ΔPmi
If n, it is determined that a misfire has occurred, and the misfire time air-fuel ratio correction flag is set to "1" at step 55. The misfire air-fuel ratio correction flag is initially set to "0". Δ
If P> ΔPmin, it is determined that there is no misfire, and FIG.
Exit the routine.

When no misfire has occurred, T in FIG.
Since the cylinder pressure is higher after TDC than before DC, P
₃₀ > P _-30 and P ₆₀ > P _-60 , and the effective average pressure equivalent value ΔP in Eq. (5) has a positive value, but when misfire occurs, the characteristic with TDC as the axis of symmetry (see the broken line) _Therefore , P ₃₀ ≉P _-30 and P ₆₀ ≅P _-60 , and the average effective pressure equivalent value ΔP in the equation (5) becomes a value close to 0. Therefore, if the minimum value of the average effective pressure equivalent value ΔP in the equation (5) when no misfire has occurred is set as the reference value ΔPmin, it can be determined that misfire occurs from ΔP ≦ ΔPmin.

FIG. 9 is a flow chart for explaining calculation of the misfire air-fuel ratio correction coefficient β.
(Ref may be synchronized with the Ref signal).

In step 61, the misfire air-fuel ratio correction flag is checked. If the misfire has not occurred, the misfire time air-fuel ratio correction flag is "0", so the misfire time air-fuel ratio correction coefficient β is clamped to 100% in step 62, and the routine of FIG. 9 is terminated.

On the other hand, when it is determined that the misfire has occurred in FIG. 7 and the misfire air-fuel ratio correction flag is set to "1" in step 55, step 6 in FIG.
Go to 3. In step 63, whether it is the first time to proceed to step 63, and if it is the first time, step 64 to
Proceed to the initial setting of 67.

In step 64, it is determined whether or not the air-fuel ratio feedback control is being performed. If the air-fuel ratio feedback control is being performed, a flag for prohibiting the air-fuel ratio feedback is provided in step 65 to avoid overlapping control with air-fuel ratio correction at the time of misfire. Is set to "1". This prohibition flag is also initialized to "0". By setting the prohibition flag to "1", the air-fuel ratio feedback correction coefficient α is clamped to 100% in FIG. 4 (step 2).
1, 23, 22).

Subsequently, at step 66, the flag f is set to "0".
Initially set to, and in step 67, the misfire air-fuel ratio correction coefficient β
A predetermined value greater than 100% (for example, 120
%) Insert A. By substituting 120% into β, the amount of fuel is increased by the above equation (4).

In the next cycle, steps 61, 63 to 68
Then, the value of the flag f is checked, but since f = 0, the process proceeds to step 69, and the value of β is compared with the predetermined value B.

Here, since the predetermined value B is a value (for example, 95%) indicating the minimum value of the weight reduction, if it is the first time to proceed to step 69, β> B, and the routine proceeds to step 70.

At step 70, β = β−Δβ ₁ (6) where β is reduced by the formula of Δβ ₁ : amount of reduction (for example, 1%).

When the weight reduction of step 70 is repeated in the next cycle, β is 120% to 119%, 118%, ..., 1
It becomes small as 00%, 99%, and so on. When it becomes 95%, β ≦ B is satisfied at step 69, the routine proceeds to step 71, the flag f is set to “1”, and at step 72 this time β = β + Δβ ₂ (7) However, β is increased by the formula of Δβ ₂ : Increase amount (for example, 0.1%).

When the flag f is set to "1" in step 71, the next cycle flows from step 68 to step 73 where β is compared with 100%. Step 7 for the first time
Since β <100% when proceeding to step 3, step 7
Go to 2 and increase β.

In the next cycle, the increase of β in step 72 is repeated. With this increase, β was 99.8%, 99.9
When 100% is reached after passing through%, β ≧ 100% is established, and the process proceeds from step 73 to step 74 and subsequent post-processing.

In step 74, β is clamped to 100%, and in steps 75 and 76, both the feedback inhibition flag and the misfire time air-fuel ratio correction flag are reset to "0", and the routine of FIG. 9 is ended.

If the feedback prohibition flag is reset to "0" and the air-fuel ratio feedback control is in progress, then FIG.
In step S24, the air-fuel ratio feedback control is restarted.

The operation of this embodiment will now be described with reference to FIG. 10. Due to misfire, the air-fuel ratio becomes lean in the early stage of misfire, and during the latter half of the misfire, this time the air-fuel ratio becomes rich side. (See broken line).

This is because in the initial stage of misfire, a part of the unburned fuel remains in a liquid state and adheres and stays in the exhaust pipe, so that the fuel does not contain much, that is, lean exhaust gas flows into the catalyst. On the other hand, during the latter half of the misfire, the unburned fuel adhering to the exhaust pipe wall gradually flows in a liquid state or evaporates due to heating in the high temperature exhaust pipe and flows into the catalyst. This is because the exhaust gas has a fuel ratio.

Therefore, in the early stage of the misfire, HC slightly decreases as shown in the first and second stages from the bottom of FIG. 10, but it causes a large increase in NOx, and during the late stage of the misfire, HC is increasing (see dashed line).

On the other hand, in this example, if it is determined that a misfire has occurred, as shown in the third stage from the bottom in FIG. 10, the misfire time air-fuel ratio correction coefficient β increases stepwise to 120%. It is increased and then decreased by 1% (reduction Δβ ₁ ) to 95%, and then 0.1% again.
(Increase amount Δβ ₂ ) is returned to 100%.

Due to such a change in β, as shown in the uppermost part of FIG. 10, the amount of fuel is increased and corrected in the region of β> 100%, so that a large leaning of the air-fuel ratio occurring at the early stage of misfire is suppressed. The subsequent fuel amount reduction correction in the region of β <100% prevents the air-fuel ratio from becoming rich in the latter period during misfire (see the solid line). In this way, by suppressing fluctuations in the air-fuel ratio at the catalyst inlet from the early stage to the middle stage of the misfire, the conversion rate of the catalyst is maintained at a high level throughout the misfire. As shown in the stage, both HC and NOx can be reduced (see the solid line).

In other words, the misfire air-fuel ratio correction coefficient β
Shows the change in the air-fuel ratio caused by the misfire in the conventional example in which the air-fuel ratio is not corrected at the time of misfire. Figure 10
As shown in the uppermost row of Fig. 1, in the conventional example, the air-fuel ratio temporarily fluctuates largely toward the rich side at the initial stage of the misfire, and fluctuates toward the lean side from the middle stage to the latter stage of the misfire. Also, although the runout on the rich side at the beginning of the misfire is large, it is relatively short, and during the misfire,
The lean runout in the latter half is small but lasts relatively long. The β waveform is obtained by approximating such an air-fuel ratio change waveform with a straight line. Therefore, the maximum value A (120%) and the minimum value B (95%) of β and the weight loss Δβ ₁ (1%) corresponding to the slope of the straight line from A to B and 10 from B
The amount of increase Δβ ₂ (0.1
%) Must be determined by matching. The straight line approximation is an example, and a fixed curve may be used for approximation.

On the other hand, when a misfire occurs during the air-fuel ratio feedback correction, the calculation of the air-fuel ratio feedback correction amount α is prohibited, so that the air-fuel ratio feedback correction does not interfere with the misfire air-fuel ratio correction. .

When a misfire is determined by comparing a value related to the combustion pressure with a reference value, the value related to the combustion pressure is a pair of positions that are moved back and forth by the same crank angle about the compression top dead center. Since the total sum of the in-cylinder pressure differences (that is, the average effective pressure equivalent value) is used, the time required to calculate this total sum is shorter and simpler than the time required to calculate the average effective pressure itself.

Further, a reference value ΔPm used for misfire determination
Since in is set to be larger as the basic pulse width Tp as the engine load increases, the setting accuracy of the reference value ΔPmin improves regardless of the engine load.

11 and 12 show the second embodiment. First
In the embodiment, the amount of decrease Δβ ₁ and the amount of increase Δβ ₂ are constant values, but in this example, the values of the amount of decrease Δβ ₁ and the amount of increase Δβ ₂ are both set to be smaller as the cooling water temperature Tw becomes lower according to the cooling water temperature Tw. With such a setting, for example, as shown in FIG. 13, the slope of the straight line from A to B at a low temperature and the slope of the straight line from B to 100% become gentler than those at a high temperature. Even under the same operating conditions, when the temperature is low, the amount of fuel that adheres to the exhaust pipe wall due to misfire is higher than when it is high temperature, and the behavior of the adhered fuel becomes slower. From Δβ ₁ and Δβ ₂
To reduce the value of.

The value of A can also be increased as the cooling water temperature Tw decreases.

According to this example, even when a misfire occurs before warming up with a low cooling water temperature, it is possible to suppress the air-fuel ratio variation over the entire misfire, as in the case where a misfire occurs after warming up. .

FIG. 14 is a flow chart for explaining the calculation of the ignition advance value ADV of the third embodiment.
0 msec).

In this example, similarly to the first embodiment, the air-fuel ratio at the time of misfire is corrected, and the ignition timing is advanced during the lean control of the air-fuel ratio during the misfire and the latter period. .

In step 81, the engine speed N and the basic pulse width Tp are read, and from these values, step 82
Then, the basic advance value ADV0 is obtained by referring to a predetermined map.

At step 83, the misfire time air-fuel ratio correction flag is checked and, if it is "1", the routine proceeds to step 84 where the misfire time air-fuel ratio correction coefficient β is compared with 100%. β <10
When it is 0%, it is judged that the lean control of the air-fuel ratio is being performed, and step 8
In step 5, the ignition timing correction amount ΔADV is obtained from β by referring to the table having the contents of FIG. 15, and the value obtained by adding the correction amount ΔADV to the basic advance value ADV0 is set as the ignition advance value ADV in step 86. , Advance the ignition timing. Figure 1
As shown in FIG. 5, the ignition timing correction amount ΔADV is a value that increases as the value of β decreases.

On the other hand, even if the misfire air-fuel ratio correction flag is "1" and β≥100% or the misfire air-fuel ratio correction flag is "0", the ignition advance value ADV is set to the basic advance value ADV0.
To complete the reach in FIG.

In this example, the ignition timing is advanced and corrected during lean control of the air-fuel ratio in the latter period during misfire,
It is possible to prevent the occurrence of misfire again. In addition,
It is currently unknown why the ignition timing is advanced during the lean control of the air-fuel ratio to prevent the occurrence of misfire again, but it has been experimentally confirmed.

Further, since the ignition timing correction amount ΔADV is made larger as the value of β becomes smaller (that is, the fuel reduction correction value becomes larger), the ignition timing correction amount irrespective of the magnitude of the fuel reduction correction value. ΔADV is given with high accuracy.

In the embodiment, it is determined whether or not a misfire has occurred based on the in-cylinder pressure. However, as disclosed in Japanese Patent Laid-Open No. 5-256184, the misfire determination is performed based on the rotation fluctuation. I don't care. However, it goes without saying that the accuracy of misfire determination is higher and the response is better based on the in-cylinder pressure.

[0084]

According to the first aspect of the present invention, the means for calculating the basic injection amount according to the operating conditions of the engine, the means for judging whether or not a misfire has occurred, and the fuel increase amount just after the misfire based on the result of this judgment are used. Is a means for calculating a value for reducing the fuel as a misfire air-fuel ratio correction amount, a means for correcting the basic injection amount by the misfire air-fuel ratio correction amount, and calculating a fuel injection amount, and a fuel of this injection amount in the intake pipe. Since it is provided with a means for supplying to the air-fuel ratio, it not only suppresses a large leaning of the air-fuel ratio that occurs at the beginning of the misfire, but also prevents the enrichment of the air-fuel ratio during the misfire and the latter half of the misfire. The conversion rate of the catalyst can be maintained at a high level throughout, and deterioration of HC and NOx at the time of misfire can be prevented.

A second aspect of the present invention is a means for calculating the basic injection amount according to the operating conditions of the engine, a sensor for outputting according to the oxygen concentration in the exhaust gas, and an air-fuel ratio feedback correction based on the output of this sensor. Means for calculating the amount,
A means for calculating the fuel injection amount by correcting the basic injection amount with this correction amount, a means for supplying this injection amount of fuel to the intake pipe, a means for determining whether or not a misfire has occurred, and a result of this determination A means for increasing the fuel amount just after the misfire and thereafter decreasing the fuel amount as a misfire air-fuel ratio correction amount;
The calculation of the air-fuel ratio feedback correction amount is prohibited during the air-fuel ratio feedback correction and the misfire determination, and the basic injection amount is corrected by the misfire air-fuel ratio correction amount instead of the air-fuel ratio feedback correction amount, and the misfire fuel injection is performed. Since a means for calculating the amount and outputting this misfire fuel injection amount to the fuel supply means is provided, when misfire occurs during air-fuel ratio feedback correction, interference with misfire air-fuel ratio correction by air-fuel ratio feedback correction Can be avoided.

In a third aspect based on the first or second aspect, the misfiring air-fuel ratio correction amount is stepwise increased to a predetermined value for making the air-fuel ratio rich side immediately after the misfire,
It is a value that decreases from the larger value to a predetermined value that makes the air-fuel ratio leaner by a predetermined amount, and then increases by a predetermined amount that is smaller than that amount and returns to the value immediately before the misfire. A misfire air-fuel ratio correction amount that is similar to the air-fuel ratio fluctuation from the early stage to the middle stage and the latter stage of the misfire can be easily given.

In the fourth aspect of the invention, in the third aspect of the invention, the amount of decrease and the amount of increase are set to be smaller at low temperatures than at high temperatures. Therefore, the pre-warming air-fuel ratio correction amount is the same as that after warming up. Can be given accurately.

In a fifth aspect based on any one of the first to fourth aspects, the misfire determination means includes means for detecting in-cylinder pressure, means for detecting a crank angle, and
A means for sampling at least one pair of in-cylinder pressures at positions that are about the same crank angle back and forth about the compression top dead center, and a means for calculating the sum of the pair of in-cylinder pressure differences as an average effective pressure equivalent value. The means for comparing the average effective pressure equivalent value and the reference value and determining that the average effective pressure equivalent value is equal to or less than the reference value has caused a misfire, the misfire determination means can be simply configured.

In a sixth aspect based on the fifth aspect, the reference value is set larger as the engine load increases, so that the reference value setting accuracy can be improved regardless of the engine load.

In a seventh invention according to any one of the first to sixth inventions, since the ignition timing is advanced and corrected while the fuel amount is being reduced by the misfire-time air-fuel ratio correction amount, the misfire is corrected again. Can be suppressed.

In an eighth aspect based on the seventh aspect, the advance angle correction amount is set to be larger as the fuel reduction correction value is larger. Therefore, regardless of the magnitude of the fuel reduction correction value,
It is possible to accurately give the amount of advance angle correction.

[Brief description of drawings]

FIG. 1 is a system diagram of an embodiment.

FIG. 2 is a flowchart for explaining calculation of an effective pulse width Te.

FIG. 3 is a flowchart for explaining calculation of a fuel injection pulse width Ti and execution of injection.

FIG. 4 is a flowchart for explaining calculation of an air-fuel ratio feedback correction coefficient α.

FIG. 5 is a flowchart for explaining sampling of in-cylinder pressure.

FIG. 6 is a change waveform diagram of the in-cylinder pressure in each compression and expansion stroke.

FIG. 7 is a flowchart for explaining misfire determination.

FIG. 8 is a characteristic diagram of a reference value ΔPmin.

FIG. 9 is a flowchart for explaining calculation of a misfire air-fuel ratio correction coefficient β.

FIG. 10 is a waveform chart for explaining the operation of the embodiment.

FIG. 11 is a characteristic diagram of a reduction amount Δβ _{1 according to} the second embodiment.

FIG. 12 is a characteristic diagram of the increased amount Δβ ₂ of the second embodiment.

FIG. 13 is a waveform diagram for explaining the operation of the second embodiment.

FIG. 14 is a flowchart for explaining calculation of an ignition advance value ADV according to a third embodiment.

FIG. 15 is a characteristic diagram of an ignition timing correction amount ΔADV.

FIG. 16 is a diagram corresponding to the claim of the first invention.

FIG. 17 is a diagram corresponding to the claim of the second invention.

FIG. 18 is a diagram corresponding to the claim of the fifth invention.

[Explanation of symbols]

11 Air Flow Meter 12 Crank Angle Sensor 13 O ₂ Sensor (Oxygen Concentration Sensor) 16 Control Unit 21 Basic Injection Amount Calculation Means 22 Misfire Determining Means 23 Misfire Time Air-Fuel Ratio Correction Amount Calculation Means 24 Fuel Injection Amount Calculation Means 25 Fuel Supply Means 31 Oxygen Concentration sensor 32 Air-fuel ratio feedback correction amount calculation means 33 Fuel injection amount calculation means 34 Misfire fuel injection amount calculation means 41 Cylinder pressure detection means 42 Crank angle detection means 43 Cylinder pressure sampling means 44 Average effective pressure equivalent value calculation means 45 Comparison means

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Claims (8)

[Claims] 1. A means for calculating a basic injection amount according to engine operating conditions, a means for determining whether or not a misfire has occurred, and a value for increasing the fuel just after the misfire and thereafter reducing the fuel based on the result of this judgment. Is calculated as the misfire air-fuel ratio correction amount, means for calculating the fuel injection amount by correcting the basic injection amount with this misfire air-fuel ratio correction amount, and means for supplying this injection amount of fuel to the intake pipe. An air-fuel ratio control device for an engine, which is provided. 2. A means for calculating the basic injection amount according to the operating conditions of the engine, a sensor for outputting according to the oxygen concentration in the exhaust gas, and an air-fuel ratio feedback correction amount for calculating based on the output of this sensor. Means, means for calculating the fuel injection amount by correcting the basic injection amount with this correction amount, means for supplying fuel of this injection amount to the intake pipe, means for determining whether or not misfire has occurred, From the judgment result, means for calculating the value for increasing the fuel only immediately after the misfire and then decreasing the fuel as the misfire air-fuel ratio correction amount, and during the air-fuel ratio feedback correction and when it is judged that the misfire has occurred The calculation of the air-fuel ratio feedback correction amount is prohibited, and the basic injection amount is corrected by the misfire air-fuel ratio correction amount instead of the air-fuel ratio feedback correction amount, and the misfire fuel injection is performed. An air-fuel ratio control device for an engine, comprising: means for calculating an injection amount and outputting the fuel injection amount at the time of misfire to the fuel supply means. 3. The misfire air-fuel ratio correction amount increases stepwise to a predetermined value that makes the air-fuel ratio rich side immediately after misfire, and from that large value to a predetermined value that makes the air-fuel ratio lean side. 3. The air-fuel ratio control device for an engine according to claim 1, wherein the air-fuel ratio control device has a value that decreases by a decrease amount and then increases by a predetermined increase amount that is smaller than the decrease amount and returns to a value immediately before a misfire. . 4. The air-fuel ratio control device for an engine according to claim 3, wherein the amount of decrease and the amount of increase are set to be smaller at low temperature than at high temperature. 5. The misfire determining means at least detects a cylinder internal pressure, a crank angle detecting means, and a pair of cylinder internal pressures at positions which are moved back and forth by substantially the same crank angle about a compression top dead center. One or more sampling means, a means for calculating the sum of the pair of in-cylinder pressure differences as an average effective pressure equivalent value, the average effective pressure equivalent value and a reference value are compared, and the average effective pressure equivalent value is less than or equal to the reference value. 5. The engine air-fuel ratio control device according to claim 1, further comprising means for determining that a misfire has occurred. 6. The air-fuel ratio control device for an engine according to claim 5, wherein the reference value is set to be larger as the engine load increases. 7. The air-fuel ratio control device for an engine according to claim 1, wherein the ignition timing is advanced during the fuel amount reduction correction by the misfire air-fuel ratio correction amount. 8. The advance correction amount is set to be larger as the fuel reduction correction value is larger.
The air-fuel ratio control device for the engine according to.