JP2912475B2 - Air-fuel ratio control method 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 method for an internal combustion engine mainly applied to automobiles and the like.

[0002]

2. Description of the Related Art Conventionally, as this kind of air-fuel ratio control method,
A main oxygen sensor is provided upstream of the catalyst in the exhaust system,
A secondary oxygen sensor is provided downstream of the catalyst, and a feedback correction coefficient is increased / decreased by a signal from the main oxygen sensor to perform feedback control of the air-fuel ratio of the air-fuel mixture, and the feedback correction is performed by a signal from the secondary oxygen sensor. There is known a method in which a control constant such as an integration constant, a skip value, or a delay time used when increasing or decreasing a coefficient is changed to correct a deviation of a control center. In such a case, since the control center of the air-fuel ratio feedback control can be constantly corrected toward the vicinity of the stoichiometric air-fuel ratio, the air-fuel ratio control at the time of steady operation can be appropriately performed, and HC can be appropriately controlled. , CO, NOx
Respectively can be effectively purified.

In such a system, usually,
When sudden acceleration is performed, the feedback control is stopped, and the air-fuel ratio is controlled to be rich by open control.

[0004]

However, when a medium acceleration is performed without performing the open control as described above, the transient increase of the fuel may be insufficient, and the air-fuel ratio may be insufficient. Temporarily becomes lean. Then, a large amount of oxygen is led to the exhaust system, and the oxygen is stored in the three-way catalyst. As a result, an error occurs between the detection result of the main oxygen sensor and the actual air-fuel ratio in the catalyst. Therefore, until the stored oxygen is consumed, even if the air-fuel ratio feedback control is executed, it is difficult to appropriately control the air-fuel ratio, and the three-way catalyst becomes unduly lean and the NOx emission amount becomes low. More. In this case, since the auxiliary oxygen sensor continues to output the lean detection signal, the control constant will eventually be corrected to the rich side, but the control constant corresponding to the signal of the auxiliary oxygen sensor will eventually be corrected. As shown in FIG. 4, the change is made stepwise by a small amount in consideration of control stability and the like. Therefore, the state in which the three-way catalyst is unduly lean is maintained for a relatively long time, and a large amount of NOx is discharged during that time.

[0005] As a prior art relating to a method for modifying the air-fuel ratio feedback control at the time when the open increase control at the time of acceleration or the like is completed, for example, one disclosed in Japanese Patent Application Laid-Open No. 64-56937 is disclosed. is there. However, when the open control is completed and the feedback control is resumed, the feedback control coefficient is skipped to a required value, so that the control delay is alleviated. It does not change the control constants. For this reason, the above-mentioned inconvenience cannot be effectively solved.

An object of the present invention is to solve the above problems.

[0007]

In order to achieve the above object, the present invention takes the following measures. That is, in the air-fuel ratio control method for an internal combustion engine according to the present invention, a main oxygen sensor is provided on the upstream side of the catalyst in the exhaust system, and a sub-oxygen sensor is provided on the downstream side of the catalyst, and feedback is performed by a signal from the main oxygen sensor. The correction coefficient is increased or decreased to perform feedback control of the air-fuel ratio of the air-fuel mixture, and a signal from the auxiliary oxygen sensor is used to change a control constant used to increase or decrease the feedback correction coefficient, thereby correcting a deviation of the control center. In such a configuration, the average value of the feedback correction coefficient is sequentially calculated, and from the time when the average value shows a rising tendency equal to or more than a certain value until the signal of the auxiliary oxygen sensor switches to the rich detection state, the control constant is calculated. Is offset to the rich side. As the control constant, for example,
The product used to increase or decrease the feedback correction coefficient
List fractional constants, skip values, or delay times
be able to.

[0008]

When the air-fuel ratio during the air-fuel ratio feedback control temporarily becomes lean due to insufficient transient increase or the like and oxygen is stored in the catalyst, first, the feedback correction coefficient The average starts to rise.
According to the present invention, when the average value of the feedback correction coefficient indicates a rising tendency equal to or more than a certain value, the control constant of the air-fuel ratio feedback control is changed to a value on the rich side. As a result, the control center of the air-fuel ratio feedback control is offset to the rich side, and the control is continued while the air-fuel ratio becomes rich. Therefore, consumption of oxygen stored in the catalyst is promoted, and NOx
The period during which the purification rate of the fuel deteriorates is shortened. Then, when the stored oxygen is appropriately consumed and the signal from the auxiliary oxygen sensor is switched from the lean detection signal to the rich detection signal, the offset of the control constant to the rich side is released, and the normal empty state is released. Return to fuel ratio feedback control. Therefore, during the steady operation, the control center is controlled near the stoichiometric air-fuel ratio, and the above-described three-component purification rate can be improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

The internal combustion engine shown in FIG. 1 is for an automobile. An injector 2 is provided in an intake system 1 and a three-way catalyst 4 is provided in an exhaust system 3. The main oxygen sensor 5 is disposed on the
A secondary oxygen sensor 6 is provided on the downstream side.

A fuel injection command signal a, which is output from the control unit 7 by the amount of fuel injected from the injector 2
Is controlled by The control device 7 is a CPU
8, a memory 9, an input interface 10, and an output interface 11. The microcomputer system 12 mainly includes a signal b from the main oxygen sensor 5,
A signal c from the auxiliary oxygen sensor 6, a signal d from the intake pressure sensor 14 for detecting the intake pressure in the surge tank 13, and a speed sensor 15 for detecting the engine speed.
, Etc. from the input terminal.

The fuel is injected from the injector 2 for a required injection time T at every predetermined crank angle. A program for calculating the injection time T is built in the control device 7. . This program calculates the injection time T in the following procedure. First, based on a signal d from the intake pressure sensor 14 and a signal e from the rotation speed sensor 15, the basic injection time T
Determine P. Then, the basic injection time TP is set to a feedback correction coefficient FAF for air-fuel ratio control and other various correction coefficients (the description is omitted because it is not related to the present invention).
To calculate the effective injection time TAU. After that, the final injection time T is calculated by adding a predetermined invalid injection time TAUV to the effective injection time TAU.

The feedback correction coefficient FAF is used to feedback control the air-fuel ratio A / F of the air-fuel mixture to a value close to the stoichiometric air-fuel ratio in principle by changing the fuel injection amount. I try to make it. First, when the signal b from the main oxygen sensor 5 exceeds the determination voltage to detect a rich state, the feedback correction coefficient FAF is gradually reduced in the fuel reduction direction using a predetermined integration constant KIM. To go. Then, when the signal b from the main oxygen sensor 5 falls below the determination voltage to detect a lean state, the feedback correction coefficient F is obtained when the delay time TDL elapses after reaching the determination voltage.
The AF is skipped to the fuel increasing side by a certain skip value RSP, and thereafter, the feedback correction coefficient FA
F is gradually increased in the fuel increasing direction by using a predetermined integration constant KIP. As a result, the signal b from the main oxygen sensor 5
Exceeds the determination voltage and switches to the rich detection state, when a predetermined delay time TDR has elapsed from the switching point, the feedback correction coefficient FAF is skipped by a certain skip value RSM toward the fuel reduction side, Thereafter, the feedback correction coefficient FAF is gradually reduced in the fuel reduction direction using a predetermined integration constant KIM.
By repeatedly performing the above operation, the air-fuel ratio A / F of the air-fuel mixture is made closer to the stoichiometric air-fuel ratio.
In addition, among the control constants described above, the integral constants KIM, KI
Although P and skip values RSP and RSM are set to constant values, the delay times TDL and TDR can be changed by the signal c from the auxiliary oxygen sensor 6. Specifically, while the auxiliary oxygen sensor 6 is outputting the lean detection signal L, the control constant corresponding value FACF is changed to the rich side by the minute amount N every time the predetermined gate time W elapses. ing. The auxiliary oxygen sensor 6 outputs the rich detection signal R
Is output, and while the state is maintained, the control constant corresponding value FACF is changed to the lean side by a small amount M every time a predetermined gate time W elapses. Then, the control center is corrected by reading the delay times TDR and TDL corresponding to the value of the control constant corresponding value FACF from the map and adopting them.

In such an internal combustion engine, the control device 7 has a program for implementing the present invention incorporated therein. As shown in FIG. 3, in this program, first, in step 51, a change amount DFAFAV of the average value FAFAV of the feedback correction coefficient FAF is calculated. That is, in this embodiment, the feedback correction coefficient FAF
Mean value FA based on the latest top value t and the latest bottom value s of
The FAV is sequentially calculated and updated. Then, in this step 51, the average value F
The change amount DFAFAV of AFAV is calculated. Next, the process proceeds to a step 52, wherein a new offset corresponding value FACOFN is calculated. This new offset corresponding value F
ACFOFN is set to a value of zero when the change amount DFAFAV at the time of updating the average value FAFAV is zero, and is set to take a larger value as the change amount DFAFAV increases in the increasing direction. Specifically, the new offset corresponding value FACOFN is calculated based on the change amount DFAFA.
The value corresponding to V is determined, for example, by reading from a map in which characteristic data as shown in FIG. 5 is recorded. In the next step 53, it is determined whether or not the old offset corresponding value FACFOFO calculated at the time of executing the previous routine is larger than the new offset corresponding value FACFON. If it is determined, the process proceeds to step 55. In step 54, the old offset corresponding value FACFOFO is adopted as the offset value FACFOF, and in step 6
Proceed to 1. On the other hand, in step 55, the offset value FA
The new offset corresponding value FACFOFN as CFOF
And proceeds to step 61. In step 61, it is determined whether or not the output of the auxiliary oxygen sensor 6 is a rich detection signal R.
The process proceeds to step 63 when the lean detection signal L is present. In step 62, the final control constant corresponding value FACF
C is a control constant corresponding value FAC used for normal control.
The process proceeds to step 64 by adopting F, and in this step 64, the old offset corresponding value FACFOFO is set to zero and the process proceeds to step 66. On the other hand, in step 63, the control constant corresponding value FA
The value obtained by adding the offset value FACFOF to CF is used, and the process proceeds to step 65. In this step 65, the offset value FACFOF is added to the old offset corresponding value FACFOFO.
The same value as OF is set, and the routine proceeds to step 66. At step 66, the delay times TDR and TDL corresponding to the final control constant corresponding value FACFC are read out from a previously stored map and used for the above-described air-fuel ratio feedback control.

Next, the operation of this embodiment will be described. During normal running, the air-fuel ratio A / F of the air-fuel mixture is controlled near the stoichiometric air-fuel ratio by increasing or decreasing the feedback correction coefficient FAF based on the signal b from the main oxygen sensor 5. As a result of this feedback control, if the atmosphere downstream of the three-way catalyst 4 is biased toward the rich side and the rich detection signal R is output from the auxiliary oxygen sensor 6, the predetermined gate time W elapses. Then, the control constant corresponding value FACF is changed to the lean side by the minute amount M. On the other hand, the secondary oxygen sensor 6
Is switched to a state of outputting the lean detection signal L, and while the state is maintained, the control constant corresponding value FACF is changed to the rich side by a small amount N every time a predetermined gate time W elapses. . Therefore, during such a steady running, the new offset corresponding value FACFON and the old offset corresponding value FACFOFO are both zero, so that
The control shown in FIG. 3 is performed in steps 51 → 52 → 53 → 55 →
It proceeds in the order of 61 → 62 → 64 → 66, or steps 51 → 52 → 53 → 55 → 61 → 63 → 65 → 66
, But in any case, the offset value FACFO
Since F is maintained at zero, the delay times TDR and TDL, which are control constants, are not offset, and the same control as in the related art is executed.

On the other hand, when a moderate acceleration without performing the open control is performed, the average value FAFAV of the feedback correction coefficient FAF, which is sequentially updated, starts to increase. At this time, when the average value FAFAV of the feedback correction coefficient FAF shows a rising tendency of a certain value or more, in other words, when the variation amount DFAFAV of the average value FAFAV exceeds a certain value A, a new offset correspondence Value F
The ACFOFN is set to a positive value as shown in FIG. 5, and the control shown in FIG.
Going from 53 to 55, offset corresponding value FACFOF
Is set to the positive value. At the time of such acceleration, the air-fuel ratio A / F becomes lean, so that the control further proceeds in steps 61 → 63 → 65 → 66. Therefore, a value obtained by adding the offset value FACFOF to the above-described control constant corresponding value FACF is adopted as the final control constant corresponding value FACFC, and the delay times TDR and TDL as control constants are offset to the rich side. . As a result, the control center is deviated to a richer side than usual, and the oxygen stored in the three-way catalyst 4 can be quickly consumed during the fuel cut, so that the sub-center is reduced earlier than the conventional one. The oxygen sensor 6 switches to the rich detection signal R output state. Therefore, the time during which the amount of emission of NOx increases due to the influence of oxygen stored in the three-way catalyst 4 can be reduced as compared with the conventional one. When the auxiliary oxygen sensor 6 switches to the rich detection signal R output state in this manner, the control shown in FIG.
→ 53 → 54 → 61 → 62 → 64 → 66, the offset value FACFOF is returned to zero, the offset of the delay times TDR, TDL to the rich side is stopped, and the control returns to the original control.

If the air-fuel ratio A / F becomes lean due to insufficient acceleration increase and oxygen is stored in the three-way catalyst 4, the delay times TDR and TDL are changed as described above. As a result, the control constant of the air-fuel ratio feedback control is offset to the rich side. Therefore, the oxygen stored in the three-way catalyst 4 can be quickly consumed to return to a normal feedback environment.
Moreover, since the offset of the control constant to the rich side is stopped when the auxiliary oxygen sensor 6 switches to the state of outputting the rich detection signal R, even after the oxygen in the catalyst 4 is appropriately consumed. There is no problem that the air-fuel ratio A / F is maintained on the rich side and the emission of HC and CO increases.

In the embodiment described above, the case where the control center is deviated by changing the delay time has been described. However, other control constants, that is, the above-described integration constant and skip value are changed. Alternatively, the control center may be offset.

[0019]

According to the present invention having the above configuration, even if the air-fuel ratio temporarily becomes lean and oxygen is stored in the catalyst due to insufficient acceleration increase or the like,
The oxygen can be rapidly consumed by the offset control of the control constant. Therefore, the air-fuel ratio feedback control is disturbed by the oxygen stored in the catalyst, and NO
The disadvantage that a large amount of x is discharged can be suppressed. In addition, since the offset control of the control constant to the rich side is appropriately terminated according to the signal of the auxiliary oxygen sensor, the rich control of the air-fuel ratio is prolonged, and the HC and CO are reduced.
There is no problem that the amount of waste gas is increased.

[Brief description of the drawings]

FIG. 1 is a schematic configuration explanatory view showing one embodiment of the present invention.

FIG. 2 is a diagram showing a transition of a feedback correction coefficient in the embodiment.

FIG. 3 is a flowchart showing a control procedure of the embodiment.

FIG. 4 is an operation explanatory view of the embodiment.

FIG. 5 is an explanatory diagram showing map contents of the embodiment.

[Explanation of symbols]

 3: Exhaust system 4: Catalyst 5: Primary oxygen sensor 6: Secondary oxygen sensor b: Signal from primary oxygen sensor c: Signal from secondary oxygen sensor A / F: Air-fuel ratio FAF: Feedback correction coefficient FAFAV: Feedback correction coefficient Average value KIM, KIP… Integration constant TDL, TDR… Delay time RSP, RSM… Skip value

Continuation of the front page (56) References JP-A-2-136532 (JP, A) JP-A-63-57842 (JP, A) JP-A-2-136535 (JP, A) JP-A-2-11843 (JP, A) (A) JP-A-2-187336 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F02D 41/14 310

Claims (1)

(57) [Claims] 1. A main oxygen sensor is provided upstream of a catalyst in an exhaust system, and a secondary oxygen sensor is provided downstream of the catalyst.
With the feedback control of the air-fuel ratio of the mixture by increasing or decreasing the feedback correction coefficient by a signal from the main oxygen sensor, wherein a signal from the sub oxygen sensor, the control used when increasing or decreasing the feedback correction coefficient
By changing the constant to correct the deviation of the control center, the average value of the feedback correction coefficient is sequentially calculated, and the signal of the auxiliary oxygen sensor starts from the point in time when the average value shows a rising tendency of a certain value or more. Until is switched to the rich detection state
An air-fuel ratio control method for an internal combustion engine, wherein the control constant is offset to a rich side.