JP2011226490A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enrich an air-fuel ratio just enough as desired so as to decrease an oxygen storage amount of an exhaust gas purifying catalyst to an appropriate amount immediately after resetting an engine from a fuel cut state, and to decrease the emission of an exhaust gas immediately after resetting.SOLUTION: An oxygen storage amount OS2 during a fuel-cut state is obtained from an integrated value of an intake air amount during the fuel-cut state to set a rich shift amount RS in accordance with the oxygen storage amount OS2. When restarting fuel injection, an air-fuel ratio is enriched in accordance with the rich shift amount RS, and the rich shift amount RS is changed to 0 at a rate ΔRS in accordance with the intake air amount Q.

Description

  The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly, to an air-fuel ratio correction technique immediately after resuming fuel injection from a fuel cut state.

Conventionally, in an internal combustion engine, a three-way catalyst is arranged in an exhaust pipe, and the three-way catalyst converts nitrogen oxide (NOx), carbon monoxide (CO), and hydrocarbon (HC) in the exhaust gas for purification. Things have been done.
By the way, when a so-called fuel cut that temporarily stops fuel injection during deceleration operation is performed, air flows into the three-way catalyst as it is, and the amount of oxygen stored in the three-way catalyst due to the oxygen storage capacity becomes excessive, and the fuel cut When the fuel injection is restarted from the state, the purification action of the catalyst (NOx reduction ability) decreases.

For this reason, in Patent Document 1, when the fuel injection is restarted from the fuel cut state, the target air-fuel ratio is set to the rich side, and the target air-fuel ratio is stoichiometric (theoretical) according to the integrated value of the intake air amount after the restart. There is disclosed a fuel injection control device that returns the air / fuel ratio to an air / fuel ratio).
As described above, if the air-fuel ratio is enriched immediately after returning from the fuel cut, the NOx reduction ability can be recovered at an early stage.

Japanese Patent Laid-Open No. 2005-069188

However, since the target when enriching the air-fuel ratio immediately after returning from the fuel cut is constant in the above-mentioned Patent Document 1, the amount of rich shift is increased due to the difference in the increase in the oxygen storage amount in the fuel cut state. There was a problem of overs and shorts.
For example, if the amount of oxygen storage in the fuel cut state is relatively small and it becomes excessively rich, the oxygen storage amount of the three-way catalyst becomes too small due to the enrichment and returns from the fuel cut with acceleration. In such a case, the conversion rate of HC is reduced.

On the other hand, if the oxygen storage amount in the fuel cut state is relatively large and the enrichment is too small, the oxygen storage amount of the three-way catalyst cannot be reduced quickly, resulting in reduction of NOx. The recovery of capacity will be delayed, and the amount of NOx emissions will increase.
The present invention has been made in view of the above problems, and an object of the present invention is to reduce the exhaust emission immediately after the return so that the enrichment immediately after the return from the fuel cut can be performed without excess or deficiency.

Therefore, according to the first aspect of the present invention, the detected value of the intake air amount of the internal combustion engine during the fuel cut is integrated, and the air-fuel ratio when the fuel supply is restarted from the fuel cut state based on the integrated value of the intake air amount. The rich shift amount is set, and when the fuel supply is resumed from the fuel cut state, the air-fuel ratio is enriched based on the rich shift amount.
According to the above invention, during the fuel cut, the intake air amount flows directly into the exhaust purification catalyst, and the oxygen storage amount (oxygen storage amount) in the exhaust purification catalyst increases according to the inflow air amount. The rich shift amount is determined based on the integrated value of the intake air amount, and when the fuel supply is resumed, the air-fuel ratio is enriched according to the rich shift amount, so that the excessive oxygen storage amount can be quickly obtained. Reduce to.

Therefore, it is possible to set a rich shift amount commensurate with the increase in oxygen storage amount due to fuel cut, and it is possible to prevent a decrease in oxygen storage amount due to insufficient rich shift amount and prevent an increase in NOx emissions, and a rich shift amount. As a result, the amount of HC emissions can be prevented from increasing.
In the second aspect of the invention, the rich shift amount set based on the integrated value of the intake air amount is set as an initial value, and the rich shift amount is changed in a direction in which the enrichment becomes smaller at a speed corresponding to the intake air amount at that time. I tried to make it.

According to the above invention, when the fuel supply is resumed from the fuel cut state, the air-fuel ratio is enriched by the rich shift amount corresponding to the intake air amount accumulated during the fuel cut, and thereafter, the air intake ratio is adjusted according to the intake air amount at that time. The rich shift amount is changed in the direction in which the enrichment is reduced at the speed, and finally the enrichment control is terminated.
Therefore, for example, when the fuel supply is restarted with acceleration, the intake air amount increases due to acceleration, so that the change speed of the rich shift amount is changed, and an appropriate rich shift with respect to the change in operating state You can set the amount.

In the invention according to claim 3, the change speed of the rich shift amount is increased as the intake air amount increases.
According to the above invention, the change speed when changing the rich shift amount in the direction of reducing the enrichment is changed faster as the intake air amount is larger.
Therefore, for example, when the amount of intake air increases due to acceleration when enriched, the rich shift changes at a faster speed, and the rich shift overlaps with the increased amount due to acceleration, resulting in over-richness. Can be prevented.

In the invention according to claim 4, the amount of oxygen stored in the exhaust purification catalyst during the fuel cut is estimated based on the integrated value of the intake air amount during the fuel cut, and the rich shift amount is determined based on the oxygen storage amount. Was set.
According to the above invention, it is required to estimate the oxygen storage amount (oxygen storage amount) from the integrated value of the intake air amount during fuel cut and to return the oxygen storage amount (oxygen storage amount) in the exhaust purification catalyst to an appropriate value. The rich shift amount is set based on the estimated oxygen storage amount.

Therefore, the rich shift amount for returning the oxygen storage amount in the exhaust purification catalyst to an appropriate value can be accurately set based on the oxygen storage amount increased by the fuel cut.
In the invention according to claim 5, the oxygen storage amount is estimated with a value in the vicinity of a preset minimum amount as an initial value.
According to the above invention, when the fuel cut is performed, the oxygen storage amount during the fuel cut is estimated as the oxygen storage amount increases from the initial value near the minimum amount according to the integrated value of the intake air amount. .

Therefore, even if it is difficult to ensure the estimation accuracy of the oxygen storage amount based on the exhaust air-fuel ratio, or even when the oxygen storage amount in the fuel supply state cannot be estimated, the change in the oxygen storage amount due to the fuel cut will be reduced. Thus, it is possible to stably estimate, and thus it is possible to stably obtain the effect of enrichment for returning the excessive oxygen storage amount.
In the invention according to claim 6, the estimated value of the oxygen storage amount is limited to a predetermined upper limit value or less.

According to the above invention, the oxygen storage amount estimated based on the integrated value of the intake air amount is limited so as not to exceed the upper limit value.
Therefore, it is possible to avoid that the oxygen storage amount is estimated to a value that is not actually possible, and that the oxygen storage amount is updated to a region where there is no change as a request for the rich shift amount.
According to the seventh aspect of the present invention, the air-fuel ratio manipulated variable in the internal combustion engine is feedback controlled based on the air-fuel ratio detected by the air-fuel ratio detecting means disposed in the exhaust pipe upstream of the exhaust purification catalyst and the target air-fuel ratio. In the configuration, after the fuel supply is restarted from the state after the fuel cut, the feedback control is started on the condition that the enrichment according to the integrated value of the intake air amount during the fuel cut is stopped.

According to the above invention, the integrated value of the intake air amount during the fuel cut is obtained, the air-fuel ratio after the fuel supply is restarted is enriched by the rich shift amount based on the integrated value, and after the enrichment stops, Air-fuel ratio feedback control based on the air-fuel ratio detection result is started.
Therefore, the air-fuel ratio feedback control is started in the middle of the enrichment to reduce the oxygen storage amount of the exhaust purification catalyst, and the air-fuel ratio is greatly hunted by feedback control to eliminate the rich state. Can be prevented.

According to the eighth aspect of the present invention, the air-fuel ratio manipulated variable in the internal combustion engine is feedback controlled based on the air-fuel ratio detected by the air-fuel ratio detecting means arranged in the exhaust pipe upstream of the exhaust purification catalyst and the target air-fuel ratio. In the configuration, the feedback control is performed on condition that the air-fuel ratio detected by the air-fuel ratio detecting means is less than a determination value.
According to the above invention, when the fuel supply is resumed from the fuel cut state and the atmosphere of the air / fuel ratio detection means gradually returns from the super-overlean state to the vicinity of the target air / fuel ratio, the air / fuel ratio has changed to less than a predetermined value. At that time, the air-fuel ratio feedback control is started.

  Accordingly, since the air-fuel ratio feedback control is started before the air-fuel ratio detecting means detects the air-fuel ratio of the combustion mixture, it is possible to prevent the air-fuel ratio from being greatly hunted.

  According to the above invention, the enrichment immediately after the return from the fuel cut can be performed without excess or deficiency, and the exhaust emission immediately after the return can be reduced.

1 is a system diagram showing an internal combustion engine in an embodiment. The flowchart which shows the main routine of the rich spike control after the fuel cut in embodiment. The flowchart which shows the estimation process of the oxygen storage amount in the fuel cut in embodiment. The flowchart which shows the calculation process of the rich spike amount in embodiment. The flowchart which shows the setting process of the fuel increase flag in embodiment. The flowchart which shows the calculation process of the fuel increase coefficient in embodiment. The flowchart which shows the calculation process of the center air fuel ratio (target air fuel ratio) in embodiment. The flowchart which shows the switch setting process of the air fuel ratio control in embodiment. The flowchart which shows the fuel-injection control in embodiment. The time chart which shows the characteristic of each data in the rich spike control of embodiment. The flowchart which shows 2nd Embodiment of the switching setting process of air fuel ratio control. The time chart which shows the switching timing of the air fuel ratio control in the said 2nd Embodiment. The flowchart which shows 3rd Embodiment of the switching setting process of air fuel ratio control. The time chart which shows the switching timing of the air fuel ratio control in the said 3rd Embodiment.

Embodiments of the present invention will be described below.
FIG. 1 is a system diagram of a vehicle internal combustion engine including an air-fuel ratio control apparatus according to the present invention.
In FIG. 1, an electronic control throttle 104 that opens and closes a butterfly throttle valve 103b by a throttle motor 103a is interposed in an intake pipe 102 of an internal combustion engine 101.

Then, air is sucked into the combustion chamber 106 through the electronic control throttle 104 and the intake valve 105.
A fuel injection valve 131 is provided in each intake port 130 upstream of the intake valve 105 of each cylinder. The fuel injection valve 131 may be an in-cylinder direct injection internal combustion engine that directly injects fuel into the combustion chamber 106.

The fuel injection valve 131 injects fuel toward the intake valve 105 when driven to open by an injection pulse signal from the control unit 114.
The fuel sucked into the combustion chamber 106 mixed with air is ignited and burned by spark ignition by the spark plug 151.
Each ignition plug 151 is directly attached with an ignition coil 152 with a built-in power transistor, and an ignition control signal for controlling on / off of the power transistor is output from the control unit 114, thereby igniting each cylinder. The timing is controlled.

The combustion exhaust in the combustion chamber 106 is discharged to an exhaust pipe 112 through an exhaust valve 107, purified by a front catalytic converter 108 and a rear catalytic converter 109, and then released into the atmosphere.
Note that, as described above, the engine is not limited to the engine having two catalytic converters on the upstream and downstream sides, and may be an engine having only one catalytic converter.

The front catalytic converter 108 and the rear catalytic converter 109 are three-way catalytic exhaust purification catalysts and have oxygen storage capability.
The intake valve 105 and the exhaust valve 107 are driven to open and close by cams provided on the intake side camshaft 111 and the exhaust side camshaft 110, respectively.
An electric fuel pump 136 is built in the fuel tank 135, and the fuel in the fuel tank 135 is pumped toward the fuel injection valve 131 by driving the fuel pump 136.

The control unit 114 has a built-in microcomputer, and controls the electronic control throttle 104, the fuel injection valve 131, the power transistor, and the like by computing detection signals from various sensors according to a program stored in advance.
Examples of the various sensors include an accelerator opening sensor 116 that detects a depression amount (accelerator opening) of an accelerator pedal operated by a driver, and an air flow meter 115 that detects an intake air flow rate Q of the engine 101 (intake air amount detection means). A crank angle sensor 117 that detects the rotational position of the crankshaft 120, a throttle sensor 118 that detects the opening TVO of the throttle valve 103b, a water temperature sensor 119 that detects the coolant temperature of the engine 101, and an upstream side of the front catalyst 108. A wide area air-fuel ratio sensor 121 (air-fuel ratio detecting means) that is disposed in the exhaust pipe 112 and detects the air-fuel ratio in a wide area based on the oxygen concentration in the exhaust, and disposed in the exhaust pipe 112 downstream of the rear catalyst 109 in the exhaust gas. Oxygen that detects rich lean (presence or absence of oxygen) with respect to the stoichiometric air-fuel ratio based on oxygen concentration Capacitors 122 and the like are provided.

The oxygen sensor 122 generates an electromotive force in the vicinity of the maximum voltage (for example, 1 V) under the rich condition where the oxygen concentration in the exhaust gas is low, and the oxygen sensor 122 near the minimum voltage (for example, 0 V) in the lean condition where the oxygen concentration in the exhaust gas is high. It is a well-known stoichiometric sensor showing an output.
The wide area air-fuel ratio sensor 121 is a known air-fuel ratio sensor that can detect the air-fuel ratio in the rich region and the lean region more widely than the stoichiometric air-fuel ratio.

  The control unit 114 calculates a target intake air amount (target throttle opening) based on detection signals from the various sensors, controls the electronic control throttle 104, calculates a fuel injection amount, and calculates the fuel injection. An injection pulse signal having a pulse width corresponding to the amount is output to the fuel injection valve 131, and ignition timing is calculated to control on / off of the power transistor.

  In the calculation of the fuel injection amount, a basic fuel injection amount is calculated with respect to the cylinder intake air amount at that time in order to generate an air-fuel mixture with a target air-fuel ratio, while based on the detection result of the wide-area air-fuel ratio sensor 121. The final fuel injection amount is calculated by calculating a feedback correction coefficient for bringing the actual air-fuel ratio closer to the target air-fuel ratio and correcting the basic fuel injection amount with the feedback correction coefficient.

  The feedback correction coefficient (air-fuel ratio manipulated variable) is an air-fuel ratio at which the air-fuel ratio detected by the wide-area air-fuel ratio sensor 121 shows a high value for the conversion ratio of oxidation / reduction in the front catalytic converter 108 and the rear catalytic converter 109 at the same time. Calculated so as to approach a certain center air-fuel ratio (target air-fuel ratio), for example, by proportional / integral / derivative control based on the deviation between the air-fuel ratio detected by the wide-range air-fuel ratio sensor 121 and the center air-fuel ratio (target air-fuel ratio) (Feedback control means).

The central air-fuel ratio (target air-fuel ratio) is a value near the theoretical air-fuel ratio.
Further, the actual center air-fuel ratio at which the conversion ratios of oxidation and reduction are simultaneously high in the catalytic converters 108 and 109 is determined based on the detection result of the oxygen sensor 122, and the actual air-fuel ratio sensor 121 detected by the wide-area air-fuel ratio sensor 121 is determined. The center air-fuel ratio (target air-fuel ratio) to be compared with the air-fuel ratio is corrected.

  In the correction control of the central air-fuel ratio (target air-fuel ratio), the intake air amount × (actual air-fuel ratio−center) is calculated from the actual air-fuel ratio detected by the wide-area air-fuel ratio sensor 121, the central air-fuel ratio, and the intake air amount. By calculating the air-fuel ratio every predetermined cycle and integrating the results, the amount of oxygen stored in the front catalytic converter 108 and the rear catalytic converter 109 (oxygen storage amount) is estimated, and the oxygen storage amount and oxygen Based on the output of the sensor 122, the central air-fuel ratio (target air-fuel ratio) is corrected.

  Specifically, when the output of the oxygen sensor 122 is larger than the rich determination voltage and the air-fuel ratio is rich and the oxygen storage amount is larger than the lower limit determination level, the central air-fuel ratio (target air-fuel ratio) is further increased. When the oxygen sensor 122 output is smaller than the lean determination voltage (<rich determination voltage), the air-fuel ratio is lean, and the oxygen storage amount is less than the upper limit determination level (> lower limit determination level). Corrects the central air-fuel ratio (target air-fuel ratio) to a richer side.

  If the wide-range air-fuel ratio sensor 121 has almost no variation or deterioration, when the stoichiometric air-fuel ratio is controlled to the target air-fuel ratio, the oxygen storage amount is within the upper and lower limits, but the air-fuel ratio sensor is empty during acceleration or the like. When the rich state of the fuel ratio continues, the oxygen adsorbed by the catalyst is consumed for the oxidation of the unburned components, so the oxygen storage amount decreases and eventually falls below the lower limit value to 0, and the non-burning state such as fuel cut continues. Then, the oxygen storage amount increases beyond the upper limit and eventually saturates.

On the other hand, when the output characteristic (voltage characteristic) with respect to the air-fuel ratio deviates from a specified value (design value) due to variations in the wide-area air-fuel ratio sensor 121 or deterioration with time, feedback based on the output of the wide-area air-fuel ratio sensor 121 is performed. Even if the control is converged to the stoichiometric air-fuel ratio, the actual air-fuel ratio deviates rich or lean with respect to the stoichiometric air-fuel ratio.
If the rich state due to the deviation of the feedback control point continues, the oxygen storage amount of the catalyst is reduced to 0, and if the lean state continues, the oxygen storage amount of the catalyst is saturated, and the oxygen sensor 122 is rich or lean. Come to detect.

Further, since the oxygen storage amount is calculated based on the difference between the detected air-fuel ratio of the wide-area air-fuel ratio sensor 121 and the central air-fuel ratio, it is calculated when variations in the wide-area air-fuel ratio sensor 121 and deterioration with time occur. The amount of oxygen storage will deviate from the actual amount of oxygen storage.
For example, when the actual air-fuel ratio obtained as a result of feedback control becomes rich because the wide-range air-fuel ratio sensor 121 detects leaner than actual, the adsorbed oxygen of the catalyst is consumed and the actual oxygen storage The amount finally becomes 0 and the oxygen sensor 122 makes a rich determination, but the calculated value of the oxygen storage amount is calculated more than the actual amount by the amount that the output of the wide area air-fuel ratio sensor 121 is shifted to the lean side. Is done.

  That is, when the oxygen sensor 122 is making the rich determination but the oxygen storage amount has not decreased to 0, the wide-range air-fuel ratio sensor 121 has detected leaner than the actual, and the feedback control point Can be determined to be richer than the stoichiometric air-fuel ratio, the central air-fuel ratio (target air-fuel ratio) is corrected to a leaner side in order to return the feedback control point to the stoichiometric air-fuel ratio.

  In addition, when the tendency that the wide area air-fuel ratio sensor 121 detects leaner than actuality becomes larger, the oxygen storage amount may exceed the upper limit determination level. In this case, the central air-fuel ratio (target air-fuel ratio) is The correction amount to the lean side may be increased in order to make the correction to the lean side larger. That is, as the correction amount to the lean side, two correction amounts, large and small, are set in advance with the upper limit determination level of the oxygen storage amount as a boundary, depending on whether it is higher than the lower limit determination level or higher than the upper limit determination level, The correction amount of the central air-fuel ratio (target air-fuel ratio) to the lean side can be switched.

  On the other hand, when the actual air-fuel ratio obtained as a result of the feedback control becomes lean because the wide-range air-fuel ratio sensor 121 detects richer than actual, the amount of oxygen adsorbed by the catalyst increases, so that the actual oxygen storage amount Will eventually saturate, and the oxygen sensor 122 will make a lean determination, but the calculated value of the oxygen storage amount will be more than the actual value because the output of the wide-range air-fuel ratio sensor 121 is shifted to the rich side. Less calculated.

  That is, when the oxygen sensor 122 is making a lean determination but the oxygen storage amount is not saturated, the wide-range air-fuel ratio sensor 121 detects that the air-fuel ratio sensor is richer than actual, and the feedback control point is the theoretical sky. Since it can be determined that the air-fuel ratio is leaner than the fuel ratio, the central air-fuel ratio (target air-fuel ratio) is corrected to be richer in order to return the feedback control point to the stoichiometric air-fuel ratio.

  In addition, when the tendency that the wide area air-fuel ratio sensor 121 detects richer than actuality becomes larger, the oxygen storage amount may fall below the lower limit determination level. In this case, the central air-fuel ratio (target air-fuel ratio) is The amount of correction to the rich side may be increased in order to make correction to the rich side. That is, as the amount of correction to the rich side, two correction amounts large and small are set in advance with the lower limit determination level of the oxygen storage amount as a boundary, and depending on whether the amount is less than the upper limit determination level or less than the lower limit determination level, The amount of correction of the central air-fuel ratio (target air-fuel ratio) to the rich side can be switched.

Further, the control unit 114 performs fuel cut control for stopping fuel injection by the fuel injection valve 131 during the deceleration operation of the internal combustion engine 101.
Specifically, when the accelerator (throttle) is fully closed and the engine rotational speed exceeds the cut start rotational speed, fuel cut is started so that the accelerator (throttle) is opened or the engine rotational speed falls below the recovery rotational speed. Then, the fuel injection is resumed.

In addition to the fuel cut at the time of deceleration, the control unit 114 performs the fuel cut even at a high rotation speed and a high vehicle speed.
Here, when the fuel injection is resumed from the fuel cut state, the control unit 114 temporarily increases the air-fuel ratio in order to reduce the oxygen storage amount to an appropriate value (about half of the maximum amount) at an early stage. Rich spike control is performed.

Hereinafter, the rich spike control, which is a feature of the present invention, will be described in detail.
The flowchart of FIG. 2 shows the main routine of the rich control. The main routine is executed every predetermined minute time.
First, in step S100, an oxygen storage amount (oxygen storage amount) OS1 used for correction control of the central air-fuel ratio (target air-fuel ratio) is calculated.

As described above, the oxygen storage amount OS1 used for the correction control of the central air-fuel ratio (target air-fuel ratio) is calculated by performing the calculation of intake air amount × (actual upstream upstream actual air-fuel ratio−central air-fuel ratio) at predetermined intervals. It is obtained by integrating the results.
In the calculation of the intake air amount × (catalyst upstream actual air / fuel ratio−center air / fuel ratio), when the catalyst upstream actual air / fuel ratio becomes richer than the center air / fuel ratio, (catalyst upstream actual air / fuel ratio−center air / fuel ratio) becomes On the other hand, the oxygen storage amount OS1 is decreased and changed to a negative value. On the other hand, when the actual upstream air-fuel ratio of the catalyst becomes leaner than the central air-fuel ratio, (actual upstream upstream actual air-fuel ratio minus central air-fuel ratio) becomes The oxygen storage amount OS1 is increased and changed to a positive value.

The calculation of the oxygen storage amount OS1 can be continued during the fuel cut. In this case, during the fuel cut, the change amount OS1 of the oxygen storage amount per execution period of this routine is expressed as OS1 = Q * Gain (Q = Intake air amount, Gain = constant).
Further, the oxygen storage amount OS1 can be reset to an initial value (for example, half of the maximum oxygen storage amount) every time the output of the oxygen sensor 122 is inverted. By the reset process, it is possible to prevent a deviation between a calculation value and an actual oxygen storage amount due to a calculation error of the oxygen storage amount (an increase in calculation error due to integration).

Further, when the output of the oxygen sensor 122 is reversed, it can be considered that the theoretical air-fuel ratio is substantially reached, and the oxygen storage amount can be regarded as half of the maximum amount. If it is set to half, reset processing commensurate with the actual oxygen storage amount can be performed, and the accuracy of the calculated value of the oxygen storage amount can be improved.
In the present embodiment, the front catalytic converter 108 and the rear catalytic converter 109 are regarded as one body, and the total amount of oxygen storage in each catalyst is estimated.

In step S200 (accumulation means), the oxygen storage amount OS2 when the fuel cut is performed is estimated, and in step S300, the rich shift amount RS for restarting fuel injection is calculated based on the oxygen storage amount OS2. Calculate (rich shift amount setting means).
In step S400, a flag indicating whether or not to actually perform rich spike control when resuming fuel injection is set. In step S500, a fuel increase coefficient KRS for realizing rich spike control (riching) is set. Is calculated.

In step S600, the center air-fuel ratio (target air-fuel ratio) is set. In step S700, the air-fuel ratio control is switched between open control and feedback control according to the flag. In step S800 (riching means), the fuel is changed. Perform injection control.
Next, the processing contents in the steps S200 to S800 will be described in detail according to the flowcharts of FIGS.

Each routine shown in the flowcharts of FIGS. 3 to 9 is also executed every predetermined minute time.
The flowchart in FIG. 3 shows the process of estimating the oxygen storage amount OS2 in the fuel cut state in step S200.
In step S201, it is determined whether or not the fuel is cut.

If it is not in the fuel cut state, the process proceeds to step S202, and an initial value is set in the oxygen storage amount OS2 at the time of fuel cut.
The initial value is, for example, a fixed value close to the minimum value of the oxygen storage amount OS2.
However, if the estimation of the oxygen storage amount OS1 in step S100 is accurate, the estimated change OS1 can be used as an initial value at the start of the fuel cut, and an increase in the oxygen storage amount OS2 after the fuel cut can be estimated. .

On the other hand, when the fuel cut is performed, the process proceeds to step S203.
In step S203, the intake air amount Q sucked into the internal combustion engine 101 during the execution cycle of this routine is multiplied by the gain Gain stored in advance to obtain the increase amount of the oxygen storage amount per execution cycle of this routine. Then, this is added to the previous value of the oxygen storage amount OS2 at the time of fuel cut (integration means), and the addition result is set to the oxygen storage amount OS2.

Accordingly, when the fuel cut is started from the fuel injection state, it is assumed that the oxygen storage amount OS2 increases from the initial value by an amount proportional to the integrated value of the intake air amount, and the oxygen storage amount OS2 at that time is obtained. It will be.
The gain Gain is based on the oxygen adsorption capacity of the catalyst with respect to the amount of intake air, and is set in advance based on experimental results.

In step S204, it is determined whether or not the oxygen storage amount OS updated in step S203 exceeds the maximum value (upper limit value) stored in advance. If the oxygen storage amount OS exceeds the maximum value, the process proceeds to step S205. The storage amount OS2 is reset to the maximum value.
The maximum value does not necessarily need to be the maximum value of the oxygen amount that can be actually stored, and can be set as appropriate in response to a request for rich shift. The maximum oxygen storage amount of the front catalytic converter 108 and the maximum oxygen amount of the rear catalytic converter 109 can be set. The total value of the storage amount can be set as the maximum value, and for example, the total value of the maximum oxygen storage amount of the front catalytic converter 108 and the amount of about half the maximum oxygen storage amount of the rear catalytic converter 109 is It can be the maximum value.

In the internal combustion engine 101 having only the front catalytic converter 108, the maximum oxygen storage amount of the front catalytic converter 108 or about half of the maximum amount can be set as the maximum value.
Further, the deterioration state of the catalytic converters 108 and 109 (deterioration of oxygen storage capacity) is determined from, for example, the detection results of the wide area air-fuel ratio sensor 121 and the oxygen sensor 122, and the maximum value at that time is determined from the deterioration state of the catalytic converters 108 and 109 The storage amount can be estimated, and the maximum storage amount can be set as the maximum value.

Thus, if it is determined how much the oxygen storage amount OS2 has increased by the fuel cut, the target of the rich shift can be appropriately set in the rich spike control for reducing the excessive oxygen storage amount to an appropriate value. It is possible to prevent the exhaust emission from being deteriorated due to excessive or insufficient rich shift.
The flowchart in FIG. 4 shows details of the calculation of the rich shift amount in step S300.

In step S301, it is determined whether or not a fuel cut is in progress.
If the fuel is being cut, the process proceeds to step S302, and the rich shift amount RS is set from the oxygen storage amount OS2 at the time of the fuel cut (rich shift amount setting means).
Here, the larger the oxygen storage amount OS2 at the time of fuel cut, the larger the absolute value of the rich shift amount RS is set to make it richer (lower the air-fuel ratio).

In the present embodiment, the rich shift amount RS is set as a correction amount added to the target air-fuel ratio (center air-fuel ratio). If the rich shift amount RS is 0, the rich control is not substantially performed, and the rich shift is not performed. The amount RS is made richer as the amount RS is smaller than 0 (the larger the absolute value of minus is).
If it is determined in step S301 that the fuel cut is not in progress, the process proceeds to step S303, whether or not the previous value of the rich shift amount RS is smaller than 0, in other words, whether or not it is immediately after the restart of fuel injection from the fuel cut. Determine whether.

  If the previous value of the rich shift amount RS is smaller than 0, the rich shift amount RS has not yet converged to 0. In this case, the process proceeds to step S304, and the intake air amount Q at that time By adding a correction value ΔRS (> 0) set in accordance with the previous value of the rich shift amount RS, the rich shift amount RS is gradually brought close to 0 (the degree of enrichment is gradually reduced), and the target sky The fuel ratio is gradually brought closer to the original center air-fuel ratio.

The correction value ΔRS is set to a larger value as the intake air amount is larger, and the rich shift amount RS is increased and changed at a higher speed as the intake air amount is larger, and approaches 0 (see FIG. 10). ).
As described above, in the fuel cut state, the oxygen storage amount OS2 at the time of fuel cut is sequentially updated according to the integrated value of the intake air flow rate Q, and the rich shift amount RS is sequentially updated according to the oxygen storage amount OS2.

  When the fuel injection is resumed, the rich shift amount RS set at the end of the fuel cut state, in other words, the rich shift amount commensurate with the amount of oxygen finally stored in the catalytic converters 108 and 109 by the fuel cut. Rich spike control is started with RS as an initial value, and then the rich shift amount RS is brought close to 0 at a speed corresponding to the intake air amount Q at that time, so that the rich shift is gradually reduced and the original center air-fuel ratio is reduced. Return to.

As described above, in the rich spike control immediately after the injection is restarted from the fuel cut, the rich shift amount RS is determined according to the amount of oxygen stored during the fuel cut. As the rich shift amount for eliminating the excessive state at an early stage, a value that is not excessive or insufficient can be set.
Therefore, the reduction capability can be recovered by quickly eliminating the excessive oxygen state, the increase in the NOx emission amount immediately after the restart of fuel injection can be avoided, and the HC emission amount can be increased by excessive enrichment. Can be prevented.

Further, the rich shift amount RS is gradually brought close to 0 at a speed corresponding to the intake air amount Q, and the air-fuel ratio feedback control is resumed after the rich shift amount RS changes to 0 as described later. The air-fuel ratio changes smoothly and the air-fuel ratio fluctuates little, so that exhaust emission deterioration due to air-fuel ratio fluctuation can also be avoided.
In addition, for example, when the intake air amount increases due to acceleration when enriched, the rich shift amount RS approaches 0 at a faster speed. Therefore, the rich shift overlaps with the increased amount due to acceleration. This can also prevent HC emissions.

Since the rich shift amount RS is not set by using the output of the oxygen sensor 122, the rich shift control of the present application is also applied to an internal combustion engine that does not include an oxygen sensor or a wide area air-fuel ratio sensor downstream of the rear catalytic converter 109. it can.
If it is determined in step S303 that the previous value of the rich shift amount RS is greater than or equal to 0, the process proceeds to step S305, where the rich shift amount RS is reset to 0 and reversely corrected by the rich shift amount RS. And the rich spike control is stopped.

The flowchart of FIG. 5 shows in detail the flag setting process in step S400.
In step S401, it is determined whether or not the fuel is being cut. If the fuel is being injected and the fuel is being injected, the process proceeds to step S402.
In step S402, it is determined whether or not the previous fuel cut state has been reached. If it is determined that the previous fuel cut was performed and the present fuel cut is not being performed, the process proceeds to step S403, where the rich shift amount RS is less than zero. It is determined whether or not a spike control request state is present.

If it is determined in step S403 that the rich shift amount RS is smaller than 0, the process proceeds to step S404 to actually enrich the air-fuel ratio based on the rich shift amount RS, and 1 is set in the fuel increase flag. Set (see FIG. 10).
On the other hand, if it is determined in step S401 that the fuel is being cut, if it is determined in step S402 that the fuel was not being cut last time, or if the rich shift amount RS is determined to be 0 or more in step S403. Advances to step S405.

In step S405, it is determined whether or not 1 is set in the fuel increase flag.
If the fuel increase flag = 0, the routine is terminated as it is to maintain the state of the fuel increase flag = 0.
On the other hand, if the fuel increase flag = 1, the process proceeds to step S406, and it is determined whether or not the rich shift amount RS is zero.

When the fuel increase flag = 1 and the rich shift amount RS is not 0, the routine is terminated as it is to continue the rich control, thereby maintaining the state of the fuel increase flag = 1.
On the other hand, when the fuel increase flag = 1 but the rich shift amount RS is 0, the rich spike amount RS is started from the minus value corresponding to the oxygen storage amount OS2 after the rich spike control is started. As a result, the rich shift amount RS returns to 0 (riching is stopped), and it is determined that the necessity of rich spike control is no longer necessary, and the process proceeds to step S407. The fuel increase flag is reset to 0 (see FIG. 10).

The flowchart of FIG. 6 shows in detail the calculation process of the fuel increase coefficient KRS in step S500.
In step S501, it is determined whether 1 is set in the fuel increase flag.
If the fuel increase flag = 0, there is no need for rich spike control, so the process proceeds to step S503, and the fuel increase coefficient KRS is set to 0, so that the fuel injection amount is set using the fuel increase coefficient KRS. Even if the calculation is performed, an increase (rich shift) is not performed by the fuel increase coefficient KRS.

On the other hand, if the fuel increase flag = 1, the routine proceeds to step S502 to execute rich spike control, and the fuel increase coefficient KRS is set to KRS = center air / fuel ratio / (center air / fuel ratio + rich shift amount RS) −1. Calculate as
As described above, the central air-fuel ratio is an air-fuel ratio in which the conversion ratio of oxidation / reduction is high at the same time in the three-way catalytic front catalytic converter 108 and the rear catalytic converter 109. Is the target air-fuel ratio of the air-fuel ratio feedback control based on the detection result of this, and is a value used for estimating the oxygen storage amount OS1, and as described above, from the correlation between the output of the oxygen sensor 122 and the oxygen storage amount OS1 The value to be corrected.

The rich shift amount RS is a negative value during rich spike control, and as a result, the fuel increase coefficient KRS is calculated as a larger value as the absolute value of the rich spike amount RS is larger (see FIG. 10), and based on the coefficient KRS. Thus, the fuel injection amount is corrected to be increased, thereby being controlled to be richer than the center air-fuel ratio.
The flowchart of FIG. 7 shows the setting process of the center air-fuel ratio (target air-fuel ratio) in step S600 in detail.

In step S601, it is determined whether or not the rich shift amount RS is 0. If the rich shift RS = 0, the process proceeds to step S602, and the oxygen storage amount OS1 and the output of the oxygen sensor 122 are set as described above. Based on this, the center air-fuel ratio (target air-fuel ratio) is corrected.
On the other hand, if the rich shift amount RS is not 0, the process proceeds to step S603, where the rich shift amount RS is added to the center air-fuel ratio, and the center air-fuel ratio (target air-fuel ratio) is richly corrected (see FIG. 10).

Therefore, when the air-fuel ratio feedback control is started before the rich shift amount RS becomes 0, the control is performed with the center air-fuel ratio corrected by the rich shift amount RS as a target.
The flowchart in FIG. 8 shows in detail the switching between open control and feedback control in step S700.

In step S701, it is determined whether the fuel is being cut. If the fuel is not being cut, the process proceeds to step S702.
In step S702, the fuel increase flag is determined. If the fuel increase flag = 1, the process proceeds to step S703, where the air-fuel ratio control is set to open control (feed forward control), and based on the detection result of the wide area air-fuel ratio sensor 121. Air-fuel ratio feedback control is stopped and the air-fuel ratio feedback correction coefficient is clamped.

Also, when it is determined in step S701 that the fuel is being cut, the process proceeds to step S703, in which the air-fuel ratio control is set to open control (feed forward control), and the air-fuel ratio feedback control based on the detection result of the wide area air-fuel ratio sensor 121. Is stopped and the air-fuel ratio feedback correction coefficient is clamped.
On the other hand, if the fuel cut is not in progress and the fuel increase flag = 0 and the enrichment is stopped, as shown in FIG. 10, the air-fuel ratio that brings the detection result of the wide-range air-fuel ratio sensor 121 closer to the central air-fuel ratio is obtained. Feedback control is executed (feedback starting means).

The flowchart of FIG. 9 shows the fuel injection control in step S800 in detail.
In step S801, an increase correction amount obtained by multiplying the basic fuel injection amount by the fuel increase coefficient KRS is added to the fuel injection amount. If the fuel increase coefficient KRS is KRS> 0, the fuel injection amount is The increase is corrected so that a rich spike is executed.
FIG. 10 is a timing chart showing the correlation between the presence or absence of fuel cut, the oxygen storage amount, the air-fuel ratio, the rich shift amount RS, the increase coefficient KRS, and the like in the embodiment.

As shown in FIG. 10, when the fuel cut is started, the state shifts from the feedback control state based on the detection result of the wide-range air-fuel ratio sensor 121 until then to the air-fuel ratio open control state, while in the fuel cut state. The increase amount OS2 of the oxygen storage amount is calculated based on the intake air amount Q at that time.
Then, as the oxygen storage amount OS2 increases, the absolute value of the rich shift amount RS is further increased, and when the fuel cut is terminated and the fuel injection is restarted, the increase coefficient KRS corresponding to the rich shift amount RS at that time Thus, by correcting the fuel injection amount to be increased, the oxygen storage amount that has become excessive during the fuel cut can be quickly returned to an appropriate amount.

When the fuel injection is resumed, the rich shift amount RS gradually approaches 0 by the correction based on the correction value ΔRS set according to the intake air amount Q, and the absolute value of the rich shift amount RS is Corresponding to the decrease, the increase by the increase coefficient KRS gradually converges to zero.
When the rich shift amount RS returns to 0, feedback control based on the detection result of the wide area air-fuel ratio sensor 121 is resumed, and the air-fuel ratio detected by the wide area air-fuel ratio sensor 121 approaches the central air-fuel ratio (target air-fuel ratio). As described above, the fuel injection amount is corrected.

The center air-fuel ratio (target air-fuel ratio) used for the air-fuel ratio feedback is corrected based on the rich / lean detection by the oxygen sensor 122 and the oxygen storage amount OS1, thereby detecting the air-fuel ratio detected by variation or deterioration of the wide-area air-fuel ratio sensor 121. The deviation is compensated.
Since the front catalytic converter 108 and the rear catalytic converter 109 having oxygen storage capability exist upstream from the oxygen sensor 122, the oxygen sensor 122 detects a lean state with a delay from the start of fuel cut. In the period immediately after resumption of fuel injection, the lean state is continuously detected.

  In the above embodiment, the air-fuel ratio feedback control is resumed after the fuel increase flag is switched from 1 to 0 (the rich shift amount RS is changed to 0). The air-fuel ratio feedback control can be resumed when the air-fuel ratio on the upstream side of the catalyst detected in step S3 decreases to less than a predetermined air-fuel ratio after the fuel injection is resumed.

The flowchart in FIG. 11 shows a second embodiment of the switching process between the open control and the feedback control in step S700.
In step S711, it is determined whether the fuel is being cut. If the fuel is not being cut, the process proceeds to step S712.
In step S712, the fuel increase flag is determined. If the rich spike control according to the rich shift amount RS is being performed with the fuel increase flag = 1, the process proceeds to step S713.

  In step S713, it is determined whether or not the actual air-fuel ratio on the upstream side of the catalyst detected by the wide-area air-fuel ratio sensor 121 is less than a determination value. If the actual air-fuel ratio is in a lean state equal to or greater than the determination value, step S713 is performed. Proceeding to S714, the air-fuel ratio control is set to open control (feed forward control), the air-fuel ratio feedback control based on the detection result of the wide area air-fuel ratio sensor 121 is stopped, and the air-fuel ratio feedback correction coefficient is clamped.

Also, when it is determined in step S711 that the fuel cut is in progress, the process proceeds to step S714, where the air-fuel ratio control is set to open control (feed forward control), and the air-fuel ratio feedback control based on the detection result of the wide area air-fuel ratio sensor 121. Is stopped and the air-fuel ratio feedback correction coefficient is clamped.
On the other hand, if it is determined in step S712 that the fuel increase flag = 0 and the rich shift amount RS has converged to 0 (after the enrichment is stopped), the process proceeds to step S715, and the detection result of the wide area air-fuel ratio sensor 121 is obtained. The air-fuel ratio feedback control is performed so that the air-fuel ratio approaches the central air-fuel ratio (feedback starting means).

  Further, even during rich spike control (rich shift amount RS <0), it is determined in step S713 that the actual air-fuel ratio on the upstream side of the catalyst detected by the wide-area air-fuel ratio sensor 121 is less than the determination value. In this case (see FIG. 12), the process proceeds to step S715, and air-fuel ratio feedback control is performed to bring the detection result of the wide-range air-fuel ratio sensor 121 closer to the central air-fuel ratio (feedback starting means).

The determination value is a value for determining that the air-fuel ratio of the combustion mixture after the fuel injection is restarted by the wide-range air-fuel ratio sensor 121, and is set to a value that is leaner than the center air-fuel ratio. The
As described above, if the air-fuel ratio feedback control is restarted after the detected air-fuel ratio of the wide-area air-fuel ratio sensor 121 has fallen below the determination value, the atmosphere of the wide-area air-fuel ratio sensor 121 is affected by the fuel cut. It can be avoided that the air-fuel ratio feedback control is started in the remaining state.

Accordingly, the air-fuel ratio does not change greatly due to the restart of the air-fuel ratio feedback control, and the air-fuel ratio feedback control can be restarted early while avoiding the deterioration of exhaust emission due to the change of the air-fuel ratio.
Here, the air-fuel ratio feedback control is started before the rich shift amount RS becomes 0. However, the center air-fuel ratio is corrected by the rich shift amount RS in step S603, thereby responding to the rich shift request. Feedback control is performed toward the center air-fuel ratio (target air-fuel ratio), and enrichment for quickly reducing the oxygen storage amount of the catalytic converters 108 and 109 is continued.

  The timing chart of FIG. 12 differs from the timing chart of FIG. 10 only in the timing at which the air-fuel ratio feedback control is resumed after the fuel injection is restarted from the fuel cut, and the other parts are the same as the timing chart of FIG. The description of FIG. 10 described above is also applied to the timing chart of FIG. 12 except for the timing at which the air-fuel ratio feedback control is resumed.

In the timing chart of FIG. 12, it is determined that the actual air-fuel ratio on the upstream side of the catalyst detected by the wide-range air-fuel ratio sensor 121 is less than the determination value, or it is determined that the rich shift amount RS has converged to zero. And air-fuel ratio feedback control that brings the detection result of the wide-range air-fuel ratio sensor 121 closer to the central air-fuel ratio is executed.
In the switching between the open control and the feedback control shown in the flowchart of FIG. 11, both the fuel increase flag and the actual air fuel ratio on the upstream side of the catalyst detected by the wide area air fuel ratio sensor 121 are determined. The determination of the fuel increase flag can be omitted as in the third embodiment shown in the flowchart.

In the flowchart of FIG. 13, in step S721, it is determined whether or not the fuel is being cut. If the fuel is not being cut, the process proceeds to step S722 where the detected air-fuel ratio of the wide area air-fuel ratio sensor 121 is less than the determination value. Judge whether there is.
If the detected air-fuel ratio of the wide-area air-fuel ratio sensor 121 is less than the determination value, the process proceeds to step S723 (feedback starting means), and air-fuel ratio feedback control is performed to bring the detection result of the wide-area air-fuel ratio sensor 121 closer to the central air-fuel ratio. (See FIG. 14).

On the other hand, if the detected air-fuel ratio of the wide area air-fuel ratio sensor 121 is greater than or equal to the determination value, the process proceeds to step S724, where the air-fuel ratio control is set to open control (feed forward control), and the air-fuel ratio based on the detection result of the wide area air-fuel ratio sensor 121 is reached. The feedback control is stopped and the air-fuel ratio feedback correction coefficient is clamped.
Even when the fuel is being cut, the routine proceeds to step S724, where the air-fuel ratio control is set to open control (feed forward control), the air-fuel ratio feedback control based on the detection result of the wide area air-fuel ratio sensor 121 is stopped, and the air-fuel ratio control is stopped. Clamp feedback correction factor.

Furthermore, the determination content of step S713 in the flowchart of FIG. 11 can be replaced with a determination as to whether or not a predetermined time has elapsed since the restart of fuel injection.
The predetermined time is a predetermined time at which the actual air-fuel ratio on the upstream side of the catalyst detected by the wide-range air-fuel ratio sensor 121 is estimated to decrease to less than the determination value after resuming fuel injection. This is the time until the atmosphere of the wide area air-fuel ratio sensor 121 is switched from the super lean state during fuel cut to the combustion exhaust atmosphere after the start of fuel injection.

  According to the above configuration, even before the rich shift amount RS becomes zero, the air-fuel ratio feedback control is started when the time after the fuel injection is restarted from the fuel cut reaches a predetermined time. As described above, since the passage of the predetermined time indicates that the atmosphere of the wide-range air-fuel ratio sensor 121 is switched from the super lean state during fuel cut to the combustion exhaust atmosphere after the start of fuel injection, the feedback control starts. Therefore, it is possible to prevent hunting with a large air-fuel ratio.

  The timing chart of FIG. 14 differs from the timing chart of FIG. 10 only in the timing at which the air-fuel ratio feedback control is resumed after the fuel injection is restarted from the fuel cut, and the other parts are the same as the timing chart of FIG. The description of FIG. 10 described above is also applied to the timing chart of FIG. 14 except for the timing of resuming the air-fuel ratio feedback control.

In the timing chart of FIG. 14, when it is determined that the actual air-fuel ratio on the upstream side of the catalyst detected by the wide-area air-fuel ratio sensor 121 is less than the determination value, the detection result of the wide-area air-fuel ratio sensor 121 is brought closer to the central air-fuel ratio. It shows that air-fuel ratio feedback control is executed.
Here, technical ideas other than the claims that can be grasped from the above embodiment will be described together with the effects thereof.
(A) The enrichment means corrects a target air-fuel ratio based on the rich shift amount, and causes the flowchart control means to perform flowchart control based on the corrected target air-fuel ratio. The air-fuel ratio control apparatus for an internal combustion engine according to claim 8.

According to the above invention, the air-fuel ratio feedback control is started before the enrichment request disappears. However, the target air-fuel ratio in the feedback control is corrected with the rich shift amount, so that the target air-fuel ratio corresponding to the rich shift request is corrected. Feedback control is performed toward the fuel ratio, and enrichment for rapidly reducing the oxygen storage amount of the exhaust purification catalyst is continued.
(B) an air-fuel ratio detection means disposed in an exhaust pipe upstream of the exhaust purification catalyst;
Feedback control means for feedback-controlling the air-fuel ratio manipulated variable in the internal combustion engine based on the air-fuel ratio detected by the air-fuel ratio detection means and the target air-fuel ratio;
Feedback starting means for starting feedback control by the feedback control means on condition that a predetermined time has elapsed after resuming fuel supply from the fuel cut state;
The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein

According to the above-described invention, the air-fuel ratio detection means is started by starting the feedback control after the time until the atmosphere of the air-fuel ratio detection means is switched from the super lean state during the fuel cut to the combustion exhaust atmosphere after the fuel supply is resumed. It can be avoided that the air-fuel ratio feedback control is started in the state where the influence of the fuel cut remains in the atmosphere of the means.
Accordingly, the air-fuel ratio does not change greatly due to the restart of the air-fuel ratio feedback control, and the air-fuel ratio feedback control can be restarted early while avoiding the deterioration of exhaust emission due to the change of the air-fuel ratio.

  DESCRIPTION OF SYMBOLS 101 ... Engine, 104 ... Electronically controlled throttle, 108 ... Front catalytic converter, 109 ... Rear catalytic converter, 114 ... Control unit, 115 ... Air flow meter, 121 ... Wide area air-fuel ratio sensor, 122 ... Oxygen sensor, 131 ... Fuel injection valve

Claims (8)

An air-fuel ratio control apparatus for an internal combustion engine provided with an exhaust purification catalyst in an exhaust pipe,
Integrating means for integrating the detected value of the intake air amount of the internal combustion engine during fuel cut;
Rich shift amount setting means for setting the rich shift amount of the air-fuel ratio when restarting fuel supply from the fuel cut state based on the intake air amount integrated by the integrating means;
Enrichment means for enriching the air-fuel ratio based on the rich shift amount when fuel supply is resumed from the fuel cut state;
An air-fuel ratio control apparatus for an internal combustion engine, comprising:   The enrichment means changes the rich shift amount at a speed corresponding to the intake air amount at that time in a direction in which the enrichment becomes smaller, with the rich shift amount set by the rich shift amount setting means as an initial value. 2. An air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein   The air-fuel ratio control apparatus for an internal combustion engine according to claim 2, wherein the enrichment means increases the speed as the intake air amount increases.   The rich shift amount setting means estimates the amount of oxygen stored in the exhaust purification catalyst during fuel cut based on the integrated value of the intake air amount, and sets the rich shift amount based on the oxygen storage amount The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein:   5. The air-fuel ratio control apparatus for an internal combustion engine according to claim 4, wherein the rich shift amount setting means estimates the oxygen storage amount using a value near a preset minimum amount as an initial value.   6. The air-fuel ratio control apparatus for an internal combustion engine according to claim 4, wherein the rich shift amount setting means limits the estimated value of the oxygen storage amount to a predetermined upper limit value or less. An air-fuel ratio detecting means disposed in an exhaust pipe upstream of the exhaust purification catalyst;
Feedback control means for feedback-controlling the air-fuel ratio manipulated variable in the internal combustion engine based on the air-fuel ratio detected by the air-fuel ratio detection means and the target air-fuel ratio;
A feedback start means for starting feedback control by the feedback control means on the condition that the enrichment by the enrichment means is stopped after resuming the fuel supply from the fuel cut state;
The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein An air-fuel ratio detecting means disposed in an exhaust pipe upstream of the exhaust purification catalyst;
Feedback control means for feedback-controlling the air-fuel ratio manipulated variable in the internal combustion engine based on the air-fuel ratio detected by the air-fuel ratio detection means and the target air-fuel ratio;
Feedback start means for performing feedback control by the feedback control means on condition that the air-fuel ratio detected by the air-fuel ratio detection means is less than a determination value;
The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein

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