JP2005163746A - Air-fuel ratio control system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique which can restrain a gap between an actual exhaust air-fuel ratio and a target rich air-fuel ratio when performing air-fuel ratio rich control in an internal combustion engine which performs the air-fuel ratio rich control after fuel-cut control is stopped. <P>SOLUTION: When amending the amount of fuel supplied to the internal combustion engine, the amount of amendment with respect to a difference between a detection value of an exhaust air-fuel ratio sensor and a target air-fuel ratio in each exhaust air-fuel ratio control at the time of performing the air-fuel ratio rich control is made smaller than at the time of performing air-fuel ratio stoichiometric control(S103). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine that controls an exhaust air-fuel ratio in an internal combustion engine that performs fuel cut control.

  Some internal combustion engines perform so-called fuel cut control for stopping fuel supply to the internal combustion engine when the internal combustion engine is in a predetermined operating state for the purpose of improving fuel consumption. However, when the fuel cut control is executed, the exhaust gas not containing the combustion gas flows out to the exhaust passage, so that the amount of oxygen stored in the exhaust purification catalyst provided in the exhaust passage increases. Therefore, the NOx reduction ability of the exhaust purification catalyst when fuel cut control is stopped and fuel supply to the internal combustion engine is restarted may be excessively reduced. Therefore, in an internal combustion engine that performs fuel cut control, after the fuel cut control is stopped, the exhaust air / fuel ratio is temporarily controlled to be a rich air / fuel ratio that is richer than the stoichiometric air / fuel ratio (hereinafter, this control is referred to as air / fuel ratio rich control). (Refer to Patent Document 1, for example).

  As described above, when the air-fuel ratio rich control is executed after the fuel cut control is stopped, the release of oxygen from the exhaust purification catalyst can be promoted, so that the NOx reduction ability of the exhaust purification catalyst can be recovered earlier. I can do it.

On the other hand, when the internal combustion engine is in a normal operating state, the exhaust air-fuel ratio is set close to the stoichiometric air-fuel ratio in order to more suitably purify not only NOx in the exhaust gas but also HC, CO, etc. in the exhaust gas purification catalyst. There is also known a technique for performing control accordingly (hereinafter, this control is referred to as air-fuel ratio stoichiometric control).
JP-A-8-1899797

  When executing the air-fuel ratio rich control or the air-fuel ratio stoichiometric control, the exhaust air-fuel ratio provided in the exhaust passage on the upstream side of the exhaust purification catalyst in order to set the exhaust air-fuel ratio to the target air-fuel ratio in each control The fuel supply amount to the internal combustion engine is corrected based on the detection value of the sensor.

  However, the detection accuracy of the exhaust air-fuel ratio sensor generally decreases when the exhaust air-fuel ratio deviates from the region near the stoichiometric air-fuel ratio. Therefore, when the air-fuel ratio rich control is executed, the detected value of the exhaust air-fuel ratio sensor may be a leaner or richer value than the actual exhaust air-fuel ratio. Therefore, even if the fuel supply amount to the internal combustion engine is corrected so that the detected value of the exhaust air / fuel ratio sensor becomes the target rich air / fuel ratio (hereinafter referred to as the target rich air / fuel ratio), the actual exhaust air / fuel ratio is corrected. May deviate from the target rich air-fuel ratio.

  The present invention has been made in view of the above problems, and in an internal combustion engine that performs air-fuel ratio rich control after stopping fuel cut control, the actual exhaust air-fuel ratio and target rich when the air-fuel ratio rich control is executed. It is an object of the present invention to provide a technique capable of suppressing a deviation from an air-fuel ratio.

The present invention employs the following means in order to solve the above problems.
That is, according to the present invention, the air-fuel ratio stoichiometric control and the air-fuel ratio rich control are executed.
When correcting the fuel supply amount to the internal combustion engine based on the detected value of the exhaust air / fuel ratio sensor in order to set the exhaust air / fuel ratio to the target air / fuel ratio, the amount of change in the exhaust air / fuel ratio when the air / fuel rich control is executed is The fuel supply amount to the internal combustion engine is corrected so as to be smaller than the change amount of the exhaust air-fuel ratio when the fuel ratio stoichiometric control is executed.

More specifically, the air-fuel ratio control apparatus for an internal combustion engine according to the first invention is
An exhaust purification catalyst provided in the exhaust passage and having the characteristics of reducing NOx in the exhaust and storing oxygen in the exhaust;
An exhaust air-fuel ratio sensor that is provided in the exhaust passage upstream of the exhaust purification catalyst and detects an exhaust air-fuel ratio;
Air-fuel ratio stoichiometric control means for performing air-fuel ratio stoichiometric control for controlling the exhaust air-fuel ratio to be close to the theoretical air-fuel ratio;
Fuel cut control means for executing fuel cut control for stopping fuel supply to the internal combustion engine when the internal combustion engine is in a predetermined operating state;
When a predetermined condition is satisfied after the fuel cut control by the fuel cut control means is stopped, air-fuel ratio rich control is executed to temporarily control the exhaust air-fuel ratio to be a target rich air-fuel ratio that is richer than the stoichiometric air-fuel ratio. Air-fuel ratio rich control means for
When the air-fuel ratio stoichiometric control is executed by the air-fuel ratio stoichiometric control means and when the air-fuel ratio rich control is executed by the air-fuel ratio rich control means, the fuel supply amount to the internal combustion engine is corrected based on the detected value of the exhaust air-fuel ratio sensor And a fuel supply amount correcting means for
The fuel supply amount correction means corrects the difference between the detected value of the exhaust air-fuel ratio sensor and the target air-fuel ratio value in each exhaust air-fuel ratio control when correcting the fuel supply amount to the internal combustion engine. Is made smaller when the air-fuel ratio rich control is executed than when the air-fuel ratio stoichiometric control is executed.

  In the present invention, an exhaust purification catalyst having a characteristic of reducing NOx in the exhaust and a characteristic of storing oxygen in the exhaust is provided in the exhaust passage of the internal combustion engine. When the fuel cut control is executed, the amount of oxygen stored in the exhaust purification catalyst increases. Therefore, when the fuel cut control is stopped and the fuel supply to the internal combustion engine is restarted, the NOx reduction ability of the exhaust purification catalyst is excessively reduced. There is a case. Therefore, when the predetermined condition is satisfied after the fuel cut control is stopped, the air-fuel ratio rich control is executed in order to promote the release of oxygen from the exhaust purification catalyst. Here, the predetermined condition is a condition under which it is possible to determine that the NOx reduction capability of the exhaust purification catalyst is excessively reduced by the fuel cut control when the predetermined condition is satisfied. As a case where this predetermined condition is satisfied, a case where the execution time of fuel cut control is a predetermined time or more can be exemplified. Further, the target rich air-fuel ratio that is targeted when the air-fuel ratio rich control is executed is an air-fuel ratio that is richer than the stoichiometric air-fuel ratio and is a predetermined air-fuel ratio.

  Further, when the fuel cut control and the air-fuel ratio rich control are not executed, the air-fuel ratio stoichiometric control is performed so that the exhaust purification catalyst can more suitably purify not only NOx in the exhaust gas but also HC, CO, etc. Execute.

  In the present invention, when the air-fuel ratio rich control or the air-fuel ratio stoichiometric control is executed, the exhaust air-fuel ratio is provided in the exhaust passage on the upstream side of the exhaust purification catalyst so that the exhaust air-fuel ratio becomes the target rich air-fuel ratio or the vicinity of the theoretical air-fuel ratio. The fuel supply amount to the internal combustion engine is corrected based on the detected value of the exhaust air / fuel ratio sensor.

  When correcting the amount of fuel supplied to the internal combustion engine, when the air-fuel ratio stoichiometric control is executed, the detection accuracy of the exhaust air-fuel ratio sensor is high, so that the detected value of the exhaust air-fuel ratio sensor becomes a value near the stoichiometric air-fuel ratio. Further, by correcting the amount of fuel supplied to the internal combustion engine, the actual exhaust air-fuel ratio can be made close to the theoretical air-fuel ratio.

  However, when the air-fuel ratio rich control is executed, the exhaust air-fuel ratio becomes the rich air-fuel ratio, so that the detection accuracy of the exhaust air-fuel ratio sensor is lowered and the detected value may deviate from the actual exhaust air-fuel ratio. Therefore, if the fuel supply amount to the internal combustion engine is corrected so that the detected value of the exhaust air / fuel ratio sensor becomes the target rich air / fuel ratio, the actual exhaust air / fuel ratio may change excessively.

  Therefore, in the present invention, when correcting the fuel supply amount to the internal combustion engine, the correction amount for the difference between the detected value of the exhaust air-fuel ratio sensor and the target air-fuel ratio value in each exhaust air-fuel ratio control is calculated as the air-fuel ratio. When rich control is executed, it is made smaller than when air-fuel ratio stoichiometric control is executed. Here, each exhaust air-fuel ratio control is air-fuel ratio stoichiometric control and air-fuel ratio rich control. That is, the difference between the detected value of the exhaust air-fuel ratio sensor when the air-fuel ratio stoichiometric control is executed and the value near the theoretical air-fuel ratio, the detected value of the exhaust air-fuel ratio sensor when the air-fuel ratio rich control is executed, and the target rich air-fuel ratio value Even if the difference is the same amount, the correction amount of the fuel supply amount to the internal combustion engine is different, and the correction amount at the time of executing the air-fuel ratio rich control is made smaller than the correction amount at the time of executing the air-fuel ratio stoichiometric control .

  If the correction amount of the fuel supply amount to the internal combustion engine is made smaller, the change amount of the exhaust air-fuel ratio becomes smaller. Therefore, it is possible to suppress the actual exhaust air / fuel ratio from being changed excessively during execution of the air / fuel ratio rich control. Therefore, according to the present invention, it is possible to suppress a deviation between the actual exhaust air-fuel ratio and the target rich air-fuel ratio when the air-fuel ratio rich control is executed.

The following means may be adopted as the second invention.
That is, the air-fuel ratio control apparatus for an internal combustion engine according to the second invention is:
An exhaust purification catalyst provided in the exhaust passage and having the characteristics of reducing NOx in the exhaust and storing oxygen in the exhaust;
An exhaust air-fuel ratio sensor that is provided in the exhaust passage upstream of the exhaust purification catalyst and detects an exhaust air-fuel ratio;
Air-fuel ratio stoichiometric control means for performing air-fuel ratio stoichiometric control for controlling the exhaust air-fuel ratio to be close to the theoretical air-fuel ratio;
Fuel cut control means for executing fuel cut control for stopping fuel supply to the internal combustion engine when the internal combustion engine is in a predetermined operating state;
When a predetermined condition is satisfied after the fuel cut control by the fuel cut control means is stopped, air-fuel ratio rich control is executed to temporarily control the exhaust air-fuel ratio to be a target rich air-fuel ratio that is richer than the stoichiometric air-fuel ratio. Air-fuel ratio rich control means for
When the air-fuel ratio stoichiometric control is executed by the air-fuel ratio stoichiometric control means and when the air-fuel ratio rich control is executed by the air-fuel ratio rich control means, the fuel supply amount to the internal combustion engine is corrected based on the detected value of the exhaust air-fuel ratio sensor And a fuel supply amount correcting means for
The fuel supply amount correcting means is characterized in that a correction limit amount when correcting the fuel supply amount to the internal combustion engine is made smaller when the air-fuel ratio rich control is executed than when the air-fuel ratio stoichiometric control is executed.

  As described above, when the air-fuel ratio rich control is executed, the detected value of the exhaust air-fuel ratio sensor may deviate from the actual exhaust air-fuel ratio. Therefore, if the amount of fuel supplied to the internal combustion engine is largely corrected when the difference between the detected value of the exhaust air / fuel ratio sensor and the target rich air / fuel ratio is large, the difference between the actual exhaust air / fuel ratio and the target rich air / fuel ratio is rather large. There is a risk of becoming.

Therefore, in the present invention, the correction limit amount when correcting the fuel supply amount to the internal combustion engine is made smaller when the air-fuel ratio rich control is executed than when the air-fuel ratio stoichiometric control is executed. Here, the correction limit amount is a maximum amount that can be corrected when correcting the fuel supply amount to the internal combustion engine. That is, even if the detected value of the exhaust air-fuel ratio sensor does not become the target air-fuel ratio value in each exhaust air-fuel ratio control, the correction amount of the fuel supply amount to the internal combustion engine has reached the correction limit amount Sometimes no further corrections are made.

  If the correction limit amount of the fuel supply amount to the internal combustion engine is made smaller, the maximum change amount of the exhaust air-fuel ratio becomes smaller. Therefore, when the air-fuel ratio rich control is executed, when the difference between the detected value of the exhaust air-fuel ratio sensor and the target rich air-fuel ratio is large, the exhaust air-fuel ratio is changed excessively, and the actual exhaust air-fuel ratio and the target rich air-fuel ratio are changed. It is possible to suppress an increase in the difference. Therefore, according to the present invention, it is possible to suppress a deviation between the actual exhaust air-fuel ratio and the target rich air-fuel ratio when the air-fuel ratio rich control is executed.

  In the first and second inventions described above, when the fuel injection amount to the internal combustion engine is corrected, it may be corrected at once, or may be corrected in multiple stages.

  Moreover, you may combine the 1st invention mentioned above and the 2nd invention.

  According to the air-fuel ratio control apparatus for an internal combustion engine according to the present invention, in the internal combustion engine that performs the air-fuel ratio rich control after the fuel cut control is stopped, the target rich air-fuel ratio of the actual exhaust air-fuel ratio when the air-fuel ratio rich control is executed. Deviation from the fuel ratio can be suppressed.

  Embodiments of an air-fuel ratio control apparatus for an internal combustion engine according to the present invention will be described below with reference to the drawings.

<Schematic configuration of the internal combustion engine and its intake and exhaust systems and control system>
First, a first embodiment of an air-fuel ratio control apparatus for an internal combustion engine according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its intake / exhaust system and control system according to the present embodiment.

  An intake passage 4 and an exhaust passage 2 are connected to the internal combustion engine 1. An air flow meter 5 and a throttle valve 6 are provided in the intake passage 4. A three-way catalyst 3 is provided in the exhaust passage 2 as an exhaust purification catalyst. The exhaust purification catalyst only needs to have a characteristic of reducing NOx in the exhaust gas and a characteristic of storing oxygen in the exhaust gas. For example, an occlusion reduction type NOx catalyst, a selective reduction type NOx catalyst, etc. It may be.

  The exhaust passage 2 upstream of the three-way catalyst 3 is provided with an exhaust air / fuel ratio sensor 7 that outputs an electric signal corresponding to the air / fuel ratio (exhaust air / fuel ratio) of the exhaust gas flowing through the exhaust passage 2. The exhaust passage 2 downstream of the three-way catalyst 3 has an oxygen concentration sensor 14 that outputs an electric signal corresponding to the oxygen concentration of the exhaust gas flowing through the exhaust passage 2, and an exhaust gas flowing through the exhaust passage 2. And an exhaust temperature sensor 8 that outputs an electrical signal corresponding to the temperature (exhaust temperature).

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 10 for controlling the internal combustion engine 1. The ECU 10 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver. The ECU 10 is electrically connected to various sensors such as the air flow meter 5, the exhaust air / fuel ratio sensor 7, the oxygen concentration sensor 14, and the exhaust temperature sensor 8, and these output signals are input to the ECU 10. Then, the ECU 10 estimates the temperature of the three-way catalyst 3 from the detection value of the exhaust temperature sensor 8. The ECU 10 is electrically connected to the fuel injection valve and the throttle valve 6 of the internal combustion engine 1 and can control them.

  In the present embodiment, the ECU 10 executes fuel cut control for stopping fuel injection in the internal combustion engine 1 when the internal combustion engine 1 is in a predetermined operation state. Here, the case where the internal combustion engine 1 is in a predetermined operation state can be exemplified by the case where the internal combustion engine 1 is in a deceleration operation state. However, since the oxygen storage amount in the three-way catalyst 3 increases when the fuel cut control is executed, the NOx reduction ability of the three-way catalyst 3 when the fuel cut control is stopped and the fuel injection in the internal combustion engine 1 is restarted. May decrease excessively.

  Therefore, when the ECU 10 determines that the NOx reduction capability of the three-way catalyst 3 has decreased excessively due to the storage of oxygen when the fuel cut control is stopped, the fuel injection amount and the throttle valve in the internal combustion engine 1 are determined. The air-fuel ratio rich control is executed by adjusting the opening degree of 6 and the like. By executing the air-fuel ratio rich control, the release of oxygen from the three-way catalyst 3 can be promoted, so that the NOx reduction ability of the three-way catalyst 3 can be recovered earlier.

  Further, in this embodiment, the ECU 10 is in the internal combustion engine 1 when the fuel cut control and the air-fuel ratio rich control are not executed and when the temperature of the three-way catalyst 3 is within the activation temperature range. Air-fuel ratio stoichiometric control is executed by adjusting the fuel injection amount, the opening degree of the throttle valve 6 and the like. By executing the air-fuel ratio stoichiometric control, it is possible to more suitably purify not only NOx in the exhaust gas but also HC, CO, etc. in the three-way catalyst 3.

<Fuel injection amount correction method 1 in exhaust air-fuel ratio control>
In this embodiment, when the air-fuel ratio rich control or the air-fuel ratio stoichiometric control is executed, the internal combustion engine is operated based on the detected value of the exhaust air-fuel ratio sensor 7 in order to set the exhaust air-fuel ratio to the target rich air-fuel ratio or the theoretical air-fuel ratio. The fuel injection amount in the engine 1 is corrected. Note that the target rich air-fuel ratio here is an air-fuel ratio that is richer than the stoichiometric air-fuel ratio and is a predetermined air-fuel ratio. This target rich air-fuel ratio may be determined with a certain range.

  Here, a correction control routine for the fuel injection amount in the internal combustion engine in the air-fuel ratio rich control and the air-fuel ratio stoichiometric control according to the present embodiment will be described with reference to the flowchart shown in FIG. This routine is stored in advance in the ECU 10 and is repeated every predetermined time after the ECU 10 is started.

  In this routine, first, in S101, the ECU 10 determines whether air-fuel ratio stoichiometric control is being executed. If an affirmative determination is made in S101, the ECU 10 proceeds to S104, and if a negative determination is made, the ECU 10 proceeds to S102.

  In S104, the ECU 10 sets the correction amount for the difference between the detected value of the exhaust air-fuel ratio sensor 7 and the value in the vicinity of the theoretical air-fuel ratio when correcting the fuel injection amount in the internal combustion engine 1 to the standard correction amount. The correction of the fuel injection amount is executed and the execution of this routine is finished. Here, the standard correction amount is obtained by correcting the fuel injection amount in the internal combustion engine 1 by the standard correction amount in each exhaust air-fuel ratio control, so that the detected value of the exhaust air-fuel ratio sensor 7 becomes the target air-fuel ratio value ( That is, the exhaust air / fuel ratio changes such that the value is close to the stoichiometric air / fuel ratio when the air / fuel ratio stoichiometric control is executed, and the target rich air / fuel ratio is the value when the air / fuel ratio rich control is executed.

On the other hand, in S102, the ECU 10 determines whether air-fuel ratio rich control is being executed. If a negative determination is made in S102, it is determined that there is no need to correct the fuel injection amount in order to control the exhaust air-fuel ratio, and the ECU 10 ends the execution of this routine. On the other hand, if a positive determination is made in S102, the correction amount for the difference between the detected value of the exhaust air-fuel ratio sensor 7 and the value of the target rich air-fuel ratio when correcting the fuel injection amount in the internal combustion engine 1 is here. The standard correction amount is multiplied by the coefficient α, the fuel injection amount is corrected, and the execution of this routine is terminated. The coefficient α is a value smaller than 1 and a predetermined value. That is, in this routine, the correction amount for the difference between the detected value of the exhaust air-fuel ratio sensor 7 and the target air-fuel ratio value when correcting the fuel injection amount in the internal combustion engine 1 is executed as the air-fuel ratio rich control. Sometimes it is made smaller than when the air-fuel ratio stoichiometric control is executed.

  As described above, when the air-fuel ratio rich control is executed, the detected value of the exhaust air-fuel ratio sensor 7 may deviate from the actual exhaust air-fuel ratio. Therefore, when the fuel injection amount in the internal combustion engine 1 is corrected so that the detected value of the exhaust air / fuel ratio sensor 7 becomes the target air / fuel ratio, that is, the target rich air / fuel ratio, the actual exhaust air / fuel ratio becomes the target rich air / fuel ratio. However, it may change excessively.

  In this embodiment, when the air-fuel ratio rich control is executed, the correction amount of the fuel injection amount in the internal combustion engine 1 is made smaller than the standard correction amount. That is, the fuel injection amount in the internal combustion engine 1 is corrected so that the detected value of the exhaust air-fuel ratio sensor 7 does not reach the target rich air-fuel ratio. As a result, the actual exhaust air-fuel ratio when the fuel injection amount in the internal combustion engine 1 is corrected when the air-fuel ratio rich control is executed is compared with the case where the fuel injection amount in the internal combustion engine 1 is corrected when the air-fuel ratio stoichiometric control is executed. The amount of change is smaller. Therefore, it is possible to suppress the actual exhaust air / fuel ratio from being changed excessively during execution of the air / fuel ratio rich control. Therefore, according to the present embodiment, it is possible to suppress a deviation between the actual exhaust air-fuel ratio and the target rich air-fuel ratio when the air-fuel ratio rich control is executed.

Next, a second embodiment of the air-fuel ratio control apparatus for an internal combustion engine according to the present invention will be described.
The schematic configuration of the internal combustion engine and its intake / exhaust system and control system according to the present embodiment is the same as the schematic configuration of the internal combustion engine according to the first embodiment and its intake / exhaust system and control system, and therefore the description thereof is omitted. .

<Fuel injection amount correction method 2 in exhaust air-fuel ratio control>
Here, a correction control routine for the fuel injection amount in the internal combustion engine in the air-fuel ratio rich control and the air-fuel ratio stoichiometric control according to the present embodiment will be described with reference to the flowchart shown in FIG. In the correction control routine for the fuel injection amount in the internal combustion engine according to the present embodiment, the steps other than S203 and S204 are the same as the correction control routine for the fuel injection amount in the internal combustion engine according to the first embodiment described above. The same steps are denoted by the same reference numerals, and the description thereof is omitted. Similar to the above, this routine is stored in advance in the ECU 10 and is repeated every predetermined time after the ECU 10 is activated.

  In this routine, if an affirmative determination is made in S101, the ECU 10 proceeds to S204. In S204, the ECU 10 sets the correction limit amount for correcting the fuel injection amount in the internal combustion engine 1 to the standard correction limit amount, corrects the fuel injection amount, and ends the execution of this routine. Here, the correction limit amount is a maximum amount that can be corrected when the fuel injection amount in the internal combustion engine 1 is corrected. Further, the standard correction limit amount can be made close to the stoichiometric air-fuel ratio in the air-fuel ratio stoichiometric control if the fuel injection amount in the internal combustion engine 1 is corrected by an amount equal to or less than the standard correction limit amount. It is an amount that can be determined as follows, and is a value determined in advance through experiments or the like.

  In this routine, if an affirmative determination is made in S102, the ECU 10 proceeds to S203. In S203, the ECU 10 sets the correction limit amount when correcting the fuel injection amount in the internal combustion engine 1 to a value obtained by multiplying the standard correction limit amount at the time of air-fuel ratio stoichiometric control by a coefficient β, and correcting the fuel injection amount. To end the execution of this routine. Like the coefficient α, the coefficient β is a value smaller than 1 and a predetermined value. That is, in this routine, the correction limit amount when correcting the fuel injection amount in the internal combustion engine 1 is made smaller when the air-fuel ratio rich control is executed than when the air-fuel ratio stoichiometric control is executed.

  As described above, when the air-fuel ratio rich control is executed, the detected value of the exhaust air-fuel ratio sensor may deviate from the actual exhaust air-fuel ratio. Therefore, as in the case of executing the air-fuel ratio stoichiometric control, the fuel injection in the internal combustion engine 1 is performed when the correction limit amount is set as the standard correction limit amount and the difference between the detected value of the exhaust air-fuel ratio sensor 7 and the target rich air-fuel ratio is large. If the amount is significantly corrected, the difference between the actual exhaust air-fuel ratio and the target rich air-fuel ratio may be increased.

  In this embodiment, when the air-fuel ratio rich control is executed, the correction limit amount for correcting the fuel injection amount in the internal combustion engine 1 is made smaller than the standard correction limit amount. Therefore, the maximum change amount of the exhaust air-fuel ratio when the air-fuel ratio rich control is executed is smaller than the maximum change amount of the exhaust air-fuel ratio when the air-fuel ratio stoichiometric control is executed. Therefore, when the air-fuel ratio rich control is executed, when the difference between the detected value of the exhaust air-fuel ratio sensor 7 and the target rich air-fuel ratio is large, the exhaust air-fuel ratio is changed excessively, and the actual exhaust air-fuel ratio and the target rich air-fuel ratio are changed. It can be suppressed that the difference is increased. Therefore, according to the present invention, it is possible to suppress a deviation between the actual exhaust air-fuel ratio and the target rich air-fuel ratio when the air-fuel ratio rich control is executed.

  In the air-fuel ratio rich control and the air-fuel ratio stoichiometric control of the first and second embodiments described above, when correcting the fuel injection amount in the internal combustion engine 1, it may be corrected at once, or in multiple stages. It may be corrected separately.

  In addition to the detection value of the exhaust air / fuel ratio sensor 7, the detection value of the oxygen concentration sensor 14 may be used for correcting the fuel injection amount in the air / fuel ratio rich control and the air / fuel ratio stoichiometric control.

  Further, the correction control of the fuel injection amount in the internal combustion engine 1 in the first embodiment and the correction control of the fuel injection amount in the internal combustion engine 1 in the second embodiment may be executed in combination.

The figure which shows schematic structure of the internal combustion engine which concerns on the Example of this invention, its intake-exhaust system, and a control system The flowchart figure which shows the correction control routine of the fuel injection quantity in the internal combustion engine in the air fuel ratio rich control and the air fuel ratio stoichiometric control which concern on Example 1 of this invention. The flowchart figure which shows the correction | amendment control routine of the fuel injection quantity in the internal combustion engine in the air fuel ratio rich control and air fuel ratio stoichiometric control which concern on Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 3 ... Three-way catalyst 6 ... Throttle valve 7 ... Exhaust air-fuel ratio sensor 8 ... Exhaust temperature sensor 10 ... ECU
14. Oxygen concentration sensor

Claims (2)

An exhaust purification catalyst provided in the exhaust passage and having the characteristics of reducing NOx in the exhaust and storing oxygen in the exhaust;
An exhaust air-fuel ratio sensor that is provided in the exhaust passage upstream of the exhaust purification catalyst and detects an exhaust air-fuel ratio;
Air-fuel ratio stoichiometric control means for performing air-fuel ratio stoichiometric control for controlling the exhaust air-fuel ratio to be close to the theoretical air-fuel ratio;
Fuel cut control means for executing fuel cut control for stopping fuel supply to the internal combustion engine when the internal combustion engine is in a predetermined operating state;
When a predetermined condition is satisfied after the fuel cut control by the fuel cut control means is stopped, air-fuel ratio rich control is executed to temporarily control the exhaust air-fuel ratio to be a target rich air-fuel ratio that is richer than the stoichiometric air-fuel ratio. Air-fuel ratio rich control means for
When the air-fuel ratio stoichiometric control is executed by the air-fuel ratio stoichiometric control means and when the air-fuel ratio rich control is executed by the air-fuel ratio rich control means, the fuel supply amount to the internal combustion engine is corrected based on the detected value of the exhaust air-fuel ratio sensor And a fuel supply amount correcting means for
The fuel supply amount correction means corrects the difference between the detected value of the exhaust air-fuel ratio sensor and the target air-fuel ratio value in each exhaust air-fuel ratio control when correcting the fuel supply amount to the internal combustion engine. An air-fuel ratio control apparatus for an internal combustion engine, wherein the air-fuel ratio rich control is made smaller than when the air-fuel ratio stoichiometric control is executed. An exhaust purification catalyst provided in the exhaust passage and having the characteristics of reducing NOx in the exhaust and storing oxygen in the exhaust;
An exhaust air-fuel ratio sensor that is provided in the exhaust passage upstream of the exhaust purification catalyst and detects an exhaust air-fuel ratio;
Air-fuel ratio stoichiometric control means for performing air-fuel ratio stoichiometric control for controlling the exhaust air-fuel ratio to be close to the theoretical air-fuel ratio;
Fuel cut control means for executing fuel cut control for stopping fuel supply to the internal combustion engine when the internal combustion engine is in a predetermined operating state;
When a predetermined condition is satisfied after the fuel cut control by the fuel cut control means is stopped, air-fuel ratio rich control is executed to temporarily control the exhaust air-fuel ratio to be a target rich air-fuel ratio that is richer than the stoichiometric air-fuel ratio. Air-fuel ratio rich control means for
When the air-fuel ratio stoichiometric control is executed by the air-fuel ratio stoichiometric control means and when the air-fuel ratio rich control is executed by the air-fuel ratio rich control means, the fuel supply amount to the internal combustion engine is corrected based on the detected value of the exhaust air-fuel ratio sensor And a fuel supply amount correcting means for
The fuel supply amount correction means is configured to make a correction limit amount when correcting the fuel supply amount to the internal combustion engine smaller when executing the air-fuel ratio rich control than when executing the air-fuel ratio stoichiometric control. Engine air-fuel ratio control device.

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