JP3376201B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly to a technique for preventing deterioration of air-fuel ratio control accuracy due to misfire.

[0002]

2. Description of the Related Art Conventionally, the air-fuel ratio of an engine intake air-fuel mixture is detected based on the oxygen concentration in exhaust gas, and the fuel injection amount is corrected so that the detected actual air-fuel ratio approaches a target air-fuel ratio. Along with setting the air-fuel ratio feedback correction value for, to rewrite the air-fuel ratio learning correction value stored in each operating region based on the air-fuel ratio feedback correction value, to the air-fuel ratio feedback correction value and the air-fuel ratio learning correction value An air-fuel ratio control device for correcting the fuel injection amount based on this is known (see Japanese Patent Laid-Open No. 60-240840, etc.).

[0003]

By the way, if a misfire occurs during execution of the air-fuel ratio control, oxygen is discharged from the misfiring cylinder, so that the oxygen concentration in the exhaust gas increases and the air-fuel ratio becomes lean. Is erroneously detected, the air-fuel ratio is controlled to be richer than the target air-fuel ratio by the air-fuel ratio feedback control, and the rich correction state is erroneously learned as the state of the target air-fuel ratio. .

In particular, in the case where the air-fuel ratio detection based on the oxygen concentration is performed over a wide range and the feedback control is performed to the target air-fuel ratio set according to the operating condition, a comparatively rich condition during cold engine in which misfire easily occurs. When the air-fuel ratio control is performed even in the state of the base air-fuel ratio, the air-fuel ratio is greatly enriched by the occurrence of misfire, the rich correction state is erroneously learned, and the actual air-fuel ratio is eliminated even after the misfire disappears. Since there is a large difference between the target air-fuel ratio and the target air-fuel ratio, there is a fear that control will be greatly disturbed and the exhaust characteristics will be greatly deteriorated.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an air-fuel ratio control device capable of avoiding deterioration of air-fuel ratio control accuracy due to misfire.

[0006]

Therefore, the invention according to claim 1 is constructed as shown in FIG. In FIG.
The air-fuel ratio detection means detects the air-fuel ratio of the engine intake air-fuel mixture based on the oxygen concentration in the engine exhaust, and the air-fuel ratio feedback control means brings the air-fuel ratio detected by the air-fuel ratio detection means close to the target air-fuel ratio. Thus, the feedback correction value for correcting the fuel injection amount to the engine is set.

The air-fuel ratio learning correction value storage means rewritably stores the air-fuel ratio learning correction value for each operation region, and the air-fuel ratio learning means is based on the feedback correction value set by the air-fuel ratio feedback control means. Then, the stored value of the air-fuel ratio learning correction value in the air-fuel ratio learning correction value storage means is rewritten. Then, the fuel injection amount correction means, based on the feedback correction value set by the air-fuel ratio feedback control means and the air-fuel ratio learning correction value stored in the air-fuel ratio learning correction value storage means, the fuel injection amount to the engine. To correct.

On the other hand, the misfire detection means detects the misfire in the engine, and the misfire time air-fuel ratio control stop means detects the misfire by the misfire detection means and in a predetermined period after the misfire is no longer detected. The operations of the air-fuel ratio feedback control means and the air-fuel ratio learning means are stopped. Further, the stop period setting means changes the predetermined period according to the deviation amount between the air-fuel ratio detected by the air-fuel ratio detecting means immediately before the misfire detection and the target air-fuel ratio . According to such a configuration, when misfire is detected, and in a predetermined period after the misfire is no longer detected, control for setting a feedback correction value based on the detection result of the air-fuel ratio, and the set feedback. The update of the air-fuel ratio learning correction value based on the correction value is stopped, and the fuel injection amount is prohibited from being corrected based on the comparison between the detection result of the air-fuel ratio and the target air-fuel ratio.

When the engine misfires, oxygen is exhausted from the misfiring cylinder, and the oxygen concentration in the exhaust gas increases by that amount, so it is erroneously detected that the air-fuel mixture becomes leaner than the target air-fuel ratio. If the air-fuel ratio feedback control and the air-fuel ratio learning are executed based on the detection result, the air-fuel ratio will be richer than the target air-fuel ratio.

Further, during the misfire period, the fuel (wall flow) adhering to the intake port in a liquid state is sucked, and the air-fuel ratio remains unchanged for a while after the misfire disappears. Since a large change (change to the rich side) is shown, the air-fuel ratio feedback control and the air-fuel ratio learning are stopped not only during misfire but also for a predetermined period after the misfire is no longer detected. Specifically, just before the misfire is detected,
That is, the air just before the air-fuel ratio feedback control is stopped
Misfire is detected according to the deviation of the fuel ratio from the target air-fuel ratio
Air-fuel ratio feedback control and empty
The period for stopping the fuel ratio learning is changed. That is, misfire immediately
Depending on the amount of deviation from the previous target air-fuel ratio, the wall flow rate may vary.
Therefore, the flow rate of the wall sucked during the misfire is different, and the misfire
Since the magnitude of the air-fuel ratio fluctuation after the
Set a period according to the amount of deviation to prevent erroneous control and learning.
While surely avoiding, stop the air-fuel ratio control to the minimum necessary.
It is designed to be able to

[0011]

[0012]

[0013] In the present invention of claim 2, wherein the stop period setting means, the predetermined time period, the misfire misfire detecting means is configured to change in accordance with time which has been detected. With such a configuration, the period during which the air-fuel ratio feedback control and the air-fuel ratio learning are stopped is changed according to the length of the period during which the misfire is detected, even after the misfire is no longer detected.

If the period of misfire is long, the amount of suction of the wall flow increases, and the fluctuation in the rich direction after the misfire disappears becomes large. Therefore, the period is set according to the misfire period. While avoiding erroneous control and erroneous learning, the air-fuel ratio control can be stopped to the minimum necessary. In the invention according to claim 3 , when the operation of the air-fuel ratio feedback control means and the air-fuel ratio learning means is stopped by the misfire time air-fuel ratio control stopping means, the fuel injection amount correcting means uses the feedback correction value as a reference. It is configured to clamp the value and correct the fuel injection amount.

According to this structure, when the air-fuel ratio feedback control is stopped based on the detection of misfire,
By clamping the feedback correction value to the reference value,
The feedback correction value immediately before the stop prevents large erroneous control under different operating conditions.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. In FIG. 2 showing the system configuration, air is taken into the internal combustion engine 1 through an air cleaner 2, an intake duct 3, and an intake manifold 4. In the intake duct 3,
A butterfly-type throttle valve 5 that interlocks with an accelerator pedal (not shown) is interposed, and the throttle valve 5 adjusts the intake air amount of the engine.

Further, each branch of the intake manifold 4 is provided with an electromagnetic fuel injection valve 6 for each cylinder, and a predetermined air-fuel ratio is controlled by electronically controlling the amount of fuel injected from the fuel injection valve 6. A mixture of is formed. The air-fuel mixture sucked into the cylinder through the intake valve 7 is ignited and burned by spark ignition by the spark plug 8 provided for each cylinder, and the combustion exhaust is discharged through the exhaust valve 9 and illustrated by the exhaust manifold 10. Not guided by the catalyst and muffler.

The control unit 11 for controlling the fuel injection amount by the fuel injection valve 6 and the ignition timing of the spark plug 8 is
A microcomputer is included, and the intake air amount signal Q from the heat ray type air flow meter 12, the throttle valve opening signal TVO from the throttle sensor 13, the crank angle signal from the crank angle sensor 14, the cooling water from the water temperature sensor 15 Temperature signal Tw, cylinder pressure signal P from cylinder pressure sensor 16,
An air-fuel ratio signal or the like from the air-fuel ratio sensor 17 is input.

The hot-wire type air flow meter 12 directly detects the intake air amount of the engine 1 as a mass flow rate based on the resistance change of the temperature-sensitive resistance due to the intake air amount.
The throttle sensor 13 is an opening TV of the throttle valve 5.
O is detected by a potentiometer. The crank angle sensor 14 outputs a unit angle signal for each unit crank angle and a reference angle signal for each predetermined piston position. Here, the engine rotation speed Ne can be calculated by measuring the number of generations of the unit angle signal within a predetermined time or the generation cycle of the reference angle signal.

The water temperature sensor 15 detects the cooling water temperature Tw in the water jacket of the engine 1 as a temperature representing the engine temperature. In-cylinder pressure sensor 16
Is a ring-shaped piezoelectric element mounted as a washer of the spark plug 8 as disclosed in Japanese Utility Model Laid-Open No. 63-17432, and detects the combustion pressure as a relative pressure with respect to the tightening load of the spark plug. The cylinder pressure P (combustion pressure) for each cylinder by mounting each spark plug 8 of each cylinder.
Can be detected. The cylinder pressure sensor
In addition to the type mounted as the washer of the spark plug 8 as described above, the type 16 may be of a type in which the sensor portion is directly exposed to the combustion chamber and the in-cylinder pressure is detected as an absolute pressure.

The air-fuel ratio sensor 17 (air-fuel ratio detecting means)
Is a known sensor that changes its output value in response to the oxygen concentration in the exhaust gas, which is closely related to the air-fuel ratio of the engine intake air-fuel mixture, and is a sensor that can detect the air-fuel ratio in a wide range (Japanese Patent Laid-Open No. Hei 10-1999) 6-82417, etc.). The control unit 11 determines the basic ignition timing (basic ignition advance value) based on engine operating conditions such as engine load and engine speed,
The ignition timing by the spark plug 8 is controlled.

The control of the injection amount of the fuel injection valve 6 by the control unit 11 is performed as follows. The basic fuel injection amount T based on the intake air amount Q detected by the hot wire air flow meter 12 and the engine rotation speed Ne calculated from the detection signal from the crank angle sensor 14.
While calculating p (= K × Q / Ne: K is a constant), the air-fuel ratio feedback correction value LMD, the air-fuel ratio learning correction value KBLR
The final fuel injection amount Ti (Ti = Tp ×) is obtained by correcting the basic fuel injection amount Tp with various correction factors CO, voltage correction amount Ts, etc. according to operating conditions such as C and cooling water temperature Tw.
LMD × KBLRC × CO + Ts) is obtained (fuel injection amount correction means). Then, a drive pulse signal having a pulse width corresponding to the fuel injection amount Ti is output to the fuel injection valve 6 at a predetermined timing. Fuel adjusted to a predetermined pressure by a pressure regulator (not shown) is supplied to the fuel injection valve 6, and an amount of fuel proportional to the pulse width of the drive pulse signal is injected.

The air-fuel ratio feedback correction value LMD,
The air-fuel ratio learning correction value KBLRC is set as shown in the flowchart of FIG. The functions of the air-fuel ratio feedback control means and the air-fuel ratio learning means are provided by software in the control unit 11 as shown in the flowchart of FIG. 3, and the control unit 11 functions as the air-fuel ratio learning correction value storage means. It is assumed that 11 has a rewritable memory with a backup function.

In the flow chart of FIG. 3, first, in step 1 (denoted as S1 in the drawing; the same applies hereinafter), a plurality of fuel injection amounts are represented based on the basic fuel injection amount Tp representing the engine load and the engine rotation speed Ne. A target air-fuel ratio corresponding to the current engine load and engine speed is obtained by referring to a map in which the target air-fuel ratio is stored in advance for each of the operating regions divided into.
In step 2, the output of the air-fuel ratio sensor 17 is read.

In step 3, the target air-fuel ratio obtained in step 1 is compared with the actual air-fuel ratio detected by the air-fuel ratio sensor 17. Then, when the actual air-fuel ratio is leaner than the target, the routine proceeds to step 4, where the air-fuel ratio feedback correction value LMD is controlled to increase,
The air-fuel ratio is rich-corrected so that it approaches the target air-fuel ratio.

On the other hand, when the actual air-fuel ratio is richer than the target, the routine proceeds to step 5, where the air-fuel ratio feedback correction value LMD is controlled to decrease so that the air-fuel ratio is lean corrected and approaches the target air-fuel ratio. To Furthermore,
When the actual air-fuel ratio substantially matches the target air-fuel ratio, the air-fuel ratio feedback correction value LMD is held.

Further, in step 6, the air-fuel ratio learning correction value KBLRC can be rewritten for each of the operating regions divided into a plurality based on the basic fuel injection amount Tp representing the engine load and the engine rotation speed Ne. The air-fuel ratio learning correction value KBLRC of the corresponding operating region on the map stored in is rewritten based on the air-fuel ratio feedback correction value LMD when the actual air-fuel ratio substantially matches the target air-fuel ratio. To do.

Specifically, the air-fuel ratio feedback correction value LMD and the air-fuel ratio learning correction value KBLRC up to that point are weighted averaged, and the weighted average value is used as a new air-fuel ratio learning correction value KBLRC.
The map data is rewritten as. By the air-fuel ratio learning, the difference in the correction request for each operating region is learned, and the substantially target air-fuel ratio can be obtained without correction by the air-fuel ratio feedback correction value LMD.

Here, the air-fuel ratio feedback control and the air-fuel ratio learning control described above are forcibly stopped according to the presence or absence of misfire in the engine, as shown in the flowchart of FIG. The functions as the misfire detecting means and the misfire air-fuel ratio control stopping means are provided in software by the control unit 11 as shown in the flowchart of FIG.

Steps in the flowchart of FIG.
At 11, misfire determination is performed based on the detection result of the in-cylinder pressure sensor 16. Specifically, comparison of the in-cylinder pressure at a predetermined crank angle position with a predetermined value corresponding to a normal combustion state, comparison of an integrated value of the in-cylinder pressure within a predetermined crank angle range with a predetermined value corresponding to a normal combustion state, and further , Misfire is determined based on the variation of the instantaneous value or the integrated value.

If the cylinder pressure sensor 16 is not provided,
The misfire can be detected based on the change in the engine rotation speed Ne, and the misfire may be detected based on the combustion light or the like, and the method for detecting the misfire is not limited. In step 12, it is determined whether or not the occurrence of misfire is detected by the determination in step 11.

When a misfire is detected,
In step 13, the timer TMMF for measuring the period after the misfire is no longer detected is reset to zero, and in step 15, the air-fuel ratio feedback correction value LMD is a reference value and is substantially corrected. Is clamped to 1.0, which is a value that does not perform, and the air-fuel ratio feedback control is stopped. Further, in step 16, the air-fuel ratio learning, specifically, the update of the map data of the air-fuel ratio learning correction value KBLRC is prohibited.

On the other hand, if it is determined in step 12 that the misfire is not detected, the process proceeds to step 14 and the timer TMMF, which is counted up after the misfire is not detected, is equal to or more than a predetermined value. , It is determined whether or not a predetermined period of time has passed since the misfire was no longer detected. If the timer TMMF is less than the predetermined value and the predetermined period has not elapsed after the misfire is not detected, the process proceeds to steps 15 and 16 to stop the air-fuel ratio feedback control and the air-fuel ratio learning control. State
Continue during misfire detection.

On the other hand, when the timer TMMF is equal to or greater than the predetermined value and the predetermined period or more has elapsed after the misfire is no longer detected, the routine proceeds to step 17, where the normal air-fuel ratio feedback control is executed. , Step
At 18, the air-fuel ratio learning control using the result of the feedback control, that is, the update of the map data of the air-fuel ratio learning correction value KBLRC is executed.

In this way, the air-fuel ratio feedback control and the air-fuel ratio learning control are stopped during the predetermined period of time during the misfire detection and after the misfire is no longer detected, which reduces the accuracy of the air-fuel ratio control. Is avoided. That is, when a misfire occurs, oxygen is discharged from the misfiring cylinder, and this is erroneously detected by the air-fuel ratio sensor 17 as a lean air-fuel ratio. Then, if the air-fuel ratio is erroneously detected on the lean side,
By the air-fuel ratio feedback control, the air-fuel ratio is controlled to be richer than the target air-fuel ratio, and the rich control state is learned as the target air-fuel ratio control state.

Further, even after the misfire disappears, the air-fuel ratio fluctuates in the rich direction due to the wall flow sucked during the misfire, so if the air-fuel ratio control is restarted immediately when the misfire is no longer detected, the misfire will occur. As in the middle case, erroneous control and erroneous learning will be performed. Therefore, during the misfire detection and for a predetermined period even after the misfire is not detected,
The air-fuel ratio feedback control and the air-fuel ratio learning control are stopped to prevent erroneous control and erroneous learning due to misfire.

Further, when the feedback control due to the misfire is stopped, the air-fuel ratio feedback correction value LMD is clamped to the reference value (= 1.0), so that the air-fuel ratio is corrected by the correction by the air-fuel ratio feedback correction value LMD while the feedback is stopped. It is possible to avoid a large deviation, and stable response can be obtained when the feedback control is restarted. By the way, as described above, the period in which the air-fuel ratio feedback control and the air-fuel ratio learning control are stopped even after the misfire is no longer detected is the amount of deviation between the target air-fuel ratio and the actual air-fuel ratio immediately before the misfire detection, and / or , Depending on how long the misfire was detected .

That is, the wall flow rate varies depending on the amount of deviation from the target air-fuel ratio immediately before the misfire, so that the wall flow rate sucked during the misfire changes, and further the wall flow rate sucked changes depending on the length of the misfire period. . And, since the magnitude of the air-fuel ratio fluctuation in the rich direction after the misfire disappears is affected by the wall flow rate sucked during the misfire, the misfire disappeared according to the deviation amount and / or the misfire period. By setting the later air-fuel ratio control stop period, it is possible to stop the air-fuel ratio control to the minimum necessary while surely avoiding erroneous control and erroneous learning.

The deviation amount of the air-fuel ratio can be obtained as a difference between the target air-fuel ratio and the air-fuel ratio detected by the air-fuel ratio sensor 17, while the air-fuel ratio feedback correction value L
It can also be obtained as the difference between MD and the reference value.

[0040]

As described above, according to the invention described in claim 1, the air-fuel ratio feedback control and the air-fuel ratio learning are performed when the misfire is detected and during a predetermined period after the misfire is no longer detected. Since it is made to stop, it is possible to avoid deterioration of air-fuel ratio control accuracy due to misfire and deterioration of exhaust property, and to continue air-fuel ratio control according to the deviation amount from the target air-fuel ratio immediately before misfire. By changing the period during which the air-fuel ratio control is stopped, the air-fuel ratio control can be stopped to the minimum necessary while surely avoiding erroneous control and erroneous learning.

According to the second aspect of the present invention, the air-fuel ratio feedback control and the air-fuel ratio learning are stopped when the misfire is detected and during a predetermined period after the misfire is no longer detected. It is possible to avoid the deterioration of the air-fuel ratio control accuracy and the deterioration of the exhaust property due to the influence of the above, and to change the period during which the air-fuel ratio control is continuously stopped according to the length of the period during which misfire was detected. Thus, there is an effect that the air-fuel ratio control can be stopped to the minimum necessary while surely avoiding the erroneous control and the erroneous learning.

According to the third aspect of the present invention, when the air-fuel ratio feedback control is stopped on the basis of the detection of misfire, the feedback correction value is clamped to the reference value, so that the feedback correction value during the feedback control is stopped is used. This has the effect of suppressing erroneous control of the fuel ratio that is large.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of an apparatus according to the first aspect of the invention.

FIG. 2 is a system configuration diagram of the engine in the embodiment.

FIG. 3 is a flowchart showing a state of air-fuel ratio control.

FIG. 4 is a flowchart showing stop of air-fuel ratio control at the time of misfire.

[Explanation of symbols]

1 Internal combustion engine 4 intake manifold 5 Throttle valve 6 Fuel injection valve 8 spark plug 10 Exhaust manifold 11 Control unit 12 Hot wire air flow meter 13 Throttle sensor 14 Crank angle sensor 15 Water temperature sensor 16 In-cylinder pressure sensor 17 Air-fuel ratio sensor

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-4-5450 (JP, A) JP-A-2-33440 (JP, A) JP-A-58-28756 (JP, A) JP-A-60- 240840 (JP, A) JP-A-7-293299 (JP, A) JP-A-6-173745 (JP, A) JP-A-8-14092 (JP, A) JP-A-1-151744 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F02D 41/00-45/00 F02P 1/00-17/00

Claims (3)

(57) [Claims] 1. An air-fuel ratio detecting means for detecting an air-fuel ratio of an engine intake air-fuel mixture based on an oxygen concentration in engine exhaust, and an air-fuel ratio detected by the air-fuel ratio detecting means so as to approach a target air-fuel ratio. Air-fuel ratio feedback control means for setting a feedback correction value for correcting the fuel injection amount to the engine, air-fuel ratio learning correction value storage means for rewritably storing the air-fuel ratio learning correction value for each operating region, and the air-fuel ratio Air-fuel ratio learning means for rewriting the stored value of the air-fuel ratio learning correction value in the air-fuel ratio learning correction value storage means based on the feedback correction value set by the feedback control means, and feedback correction set by the air-fuel ratio feedback control means. The fuel injection amount to the engine is corrected based on the value and the air-fuel ratio learning correction value stored in the air-fuel ratio learning correction value storage means. Fuel injection amount correction means, misfire detection means for detecting misfire in the engine, and when the misfire is detected by the misfire detection means and during a predetermined period after the misfire is no longer detected, the air-fuel ratio feedback control is performed. Means and the air-fuel ratio learning stop means for stopping the operation of the air-fuel ratio control means, and the predetermined period, depending on the amount of deviation between the air-fuel ratio and the target air-fuel ratio detected by the air-fuel ratio detection means immediately before the misfire detection. that the stop period setting means for changing, is structured to include a Te air-fuel ratio control apparatus for an internal combustion engine characterized by. 2. An air-fuel ratio detecting means for detecting the air-fuel ratio of the engine intake air-fuel mixture based on the oxygen concentration in the engine exhaust, and an air-fuel ratio detected by the air-fuel ratio detecting means so as to approach the target air-fuel ratio. Air-fuel ratio feedback control means for setting a feedback correction value for correcting the fuel injection amount to the engine, air-fuel ratio learning correction value storage means for rewritably storing the air-fuel ratio learning correction value for each operating region, and the air-fuel ratio Air-fuel ratio learning means for rewriting the stored value of the air-fuel ratio learning correction value in the air-fuel ratio learning correction value storage means based on the feedback correction value set by the feedback control means, and feedback correction set by the air-fuel ratio feedback control means. The fuel injection amount to the engine is corrected based on the value and the air-fuel ratio learning correction value stored in the air-fuel ratio learning correction value storage means. Fuel injection amount correction means, misfire detection means for detecting misfire in the engine, and when the misfire is detected by the misfire detection means and during a predetermined period after the misfire is no longer detected, the air-fuel ratio feedback control is performed. Means and a misfire time air-fuel ratio control stop means for stopping the operation of the air-fuel ratio learning means, and a stop period setting means for changing the predetermined period according to a period during which misfire was detected by the misfire detecting means, An air-fuel ratio control device for an internal combustion engine, comprising: 3. The fuel injection amount correction means clamps a feedback correction value to a reference value when the operation of the air-fuel ratio feedback control means and the air-fuel ratio learning means is stopped by the misfire air-fuel ratio control stopping means. The air-fuel ratio control device for an internal combustion engine according to claim 1 or 2, wherein the fuel injection amount is corrected.