JP2007231750A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device performing air-fuel ratio feedback control based on at least a deviation integral value updated by integration of deviations between output values of an air-fuel sensor downstream of a catalyst and a target value corresponding to a target air-fuel ratio and capable of inhibiting erroneous learning of the deviation integral value toward a rich side even when executing learning of the deviation integral value after return from fuel-cut control (FC). <P>SOLUTION: A feedback correction value is calculated through PID processing about [a deviation between the output value of the air-fuel sensor downstream of the catalyst and an output value Voxsref (constant) corresponding to the target air-fuel ratio] and an air-fuel ratio is controlled to agree with the target air-fuel ratio (= theoretical air-fuel ratio). Only in a predetermined period (flag ORE =1) after the time of FC return, an I processing in the PID processing is exerted with use of [the deviation between the output value of the air-fuel ratio sensor and the target value Voxsrefi (< Voxsref) corresponding to an air-fuel ratio more lean than the target air-fuel ratio] in place of [the deviation between the output value of the air-fuel ratio sensor and Voxsref]. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an air-fuel ratio control device for an internal combustion engine that controls an air-fuel ratio of gas flowing into the catalyst based on an output value of an air-fuel ratio sensor provided downstream of the catalyst disposed in the exhaust passage of the internal combustion engine.

  Conventionally, this type of air-fuel ratio control apparatus is widely known. For example, in an air-fuel ratio control device (exhaust gas purification device) described in Patent Document 1, an air-fuel ratio sensor (usually, downstream of a catalyst (three-way catalyst) having an oxygen storage function disposed in an exhaust passage of an internal combustion engine, A concentration cell type oxygen concentration sensor) is provided. The deviation between the output value of the air-fuel ratio sensor and the target value (target air-fuel ratio equivalent target value) corresponding to the target air-fuel ratio (= theoretical air-fuel ratio) is proportionally / integrated / differentiated (PID processing) to obtain a feedback correction value. Calculated. The air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine by correcting the fuel injection amount based on the feedback correction value (hence, the air-fuel ratio of the gas flowing into the catalyst, hereinafter also simply referred to as “air-fuel ratio”). .) Is feedback controlled so as to match the target air-fuel ratio.

  In the feedback correction value, a gain is added to the integral value of the integral term (I term), that is, the deviation integral value that is updated by sequentially integrating the deviation between the output value of the air-fuel ratio sensor and the target value corresponding to the target air-fuel ratio. The multiplied value is included. As a result, the difference between the actual fuel injection amount and the fuel injection amount required to make the air-fuel ratio coincide with the target air-fuel ratio due to variations in the output characteristics of the air flow meter, the injection characteristics of the injector, etc. , Which is referred to as “error of the fuel injection amount”), the error of the fuel injection amount can be compensated by the deviation integral value (accordingly, the value of the integral term) by executing the feedback control described above, As a result, the air-fuel ratio can be matched with the target air-fuel ratio.

  In other words, the deviation integral value can be a value representing the magnitude of the error in the fuel injection amount. In this type of air-fuel ratio control apparatus, the deviation integral value having such characteristics is stored, and the stored deviation integral value (hereinafter also referred to as “learning value of deviation integral value”) is stored at predetermined timings. In many cases, deviation integral values that are updated (learned) are learned.

  Incidentally, in recent years, from the viewpoint of improving fuel efficiency, fuel cut control for interrupting fuel injection is performed while a predetermined condition such as an accelerator opening being zero is established. During fuel cut control, oxygen-containing air itself flows into the catalyst, increasing the amount of oxygen stored in the catalyst. As a result, when returning from the fuel cut control, the oxygen storage amount reaches the maximum amount that can be stored in the catalyst (hereinafter referred to as “maximum oxygen storage amount”), or near the maximum oxygen storage amount, so that the inside of the catalyst is reduced. Often a lean atmosphere.

  Therefore, after returning from the fuel cut control, the air-fuel ratio of the gas flowing out from the catalyst tends to be leaner than the stoichiometric air-fuel ratio, and the output value of the air-fuel ratio sensor also becomes a value indicating leaner than the stoichiometric air-fuel ratio. That is, the deviation between the air-fuel ratio sensor output value and the target air-fuel ratio equivalent target value can be a large value for correcting the air-fuel ratio to the rich side.

  Therefore, after returning from the fuel cut control, the air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio, whereby the oxygen storage amount of the catalyst is reduced. As a result, the above-described lean atmosphere in the catalyst is reduced. The degree gradually decreases (that is, the output value of the air-fuel ratio sensor gradually approaches the target value corresponding to the target air-fuel ratio).

  As described above, the deviation between the air-fuel ratio sensor output value and the target air-fuel ratio target value corrects the air-fuel ratio to the rich side after the return from the fuel cut control until the lean atmosphere in the catalyst is eliminated. Can be a large value. This means that during this time, the deviation integrated value excessively increases as a value for correcting the air-fuel ratio to the rich side.

  Therefore, if the above-described deviation integral value learning is executed during the period from the return from the fuel cut control until the lean atmosphere in the catalyst is eliminated, the deviation integral value learning value causes the air-fuel ratio to be excessively increased to the rich side. A situation occurs in which the value is updated to the value to be corrected. Hereinafter, such a situation is referred to as “mis-learning to the rich side of the deviation integral value”.

  Therefore, in order to prevent such erroneous learning of the deviation integral value to the rich side, the following Patent Document 2 discloses a technique for prohibiting this type of learning in a predetermined period after returning from the fuel cut control. Are listed.

  However, if learning of the deviation integral value is prohibited in a predetermined period each time the fuel cut control is returned, the chance of learning the deviation integral value is reduced. In particular, in recent years, the frequency with which fuel cut control is executed to further improve fuel efficiency has increased. Under such circumstances, if learning of the deviation integral value is prohibited at each return from the fuel cut control, the learning value of the deviation integral value should be converged (that is, accurately represents the magnitude of the fuel injection amount error). There is a problem that a situation that cannot converge to (value) may occur.

From the above, it is desired to provide an air-fuel ratio control device that can suppress erroneous learning of the deviation integral value to the rich side even if learning of the deviation integral value is executed after returning from the fuel cut control. is there.
JP 2004-183585 A JP 2005-105834 A

  Accordingly, an object of the present invention is to perform air-fuel ratio feedback control based at least on the deviation integral value updated by integrating the value corresponding to the deviation between the output value of the air-fuel ratio sensor downstream of the catalyst and the target value corresponding to the target air-fuel ratio. An object of the present invention is to provide an air-fuel ratio control device that can suppress erroneous learning of the deviation integral value to the rich side even if learning of the deviation integral value is executed after returning from fuel cut control.

  An air-fuel ratio control apparatus according to the present invention has a catalyst (three-way catalyst or the like) having an oxygen storage function disposed in an exhaust passage of an internal combustion engine, and is disposed in an exhaust passage downstream of the catalyst and flows out from the catalyst. The present invention is applied to an internal combustion engine including an air-fuel ratio sensor that outputs a value corresponding to the air-fuel ratio of gas. Here, as the air-fuel ratio sensor, a concentration cell type oxygen concentration sensor is generally used.

  The air-fuel ratio control apparatus according to the present invention is based on at least a deviation integral value that is sequentially accumulated and updated by a value corresponding to a deviation between an output value of the air-fuel ratio sensor and a target value corresponding to a target air-fuel ratio. Feedback correction value calculating means for calculating a feedback correction value for controlling the air-fuel ratio of the gas flowing into the catalyst, and the air-fuel ratio of the gas flowing into the catalyst based on the feedback correction value so as to match the target air-fuel ratio Air-fuel ratio control means for performing feedback control, and fuel cut control means for performing fuel cut control for interrupting fuel injection in accordance with the operating state of the internal combustion engine.

  Here, the “value corresponding to the deviation between the output value of the air / fuel ratio sensor and the target value corresponding to the target air / fuel ratio” is, for example, the deviation itself between the output value of the air / fuel ratio sensor and the target value corresponding to the target air / fuel ratio. And the deviation between the air-fuel ratio detected by the air-fuel ratio sensor and the target air-fuel ratio. Further, the feedback correction value may be calculated based only on an integral term calculated by using the deviation integral value (by integration processing (I processing)), or may be calculated based on the integral term and the deviation. It may be calculated based on the proportional term calculated using the corresponding value itself (by proportional / integral processing (PI processing)), or equivalent to the integral term, the proportional term, and the deviation May be calculated based on a differential term calculated using a time differential value of the value to be performed (by proportional / integral / differential processing (PID processing)).

  The air-fuel ratio control apparatus according to the present invention is characterized in that the feedback correction value calculation means includes an output value of the air-fuel ratio sensor and a target air-fuel ratio equivalent target value in a predetermined period after returning from the fuel cut control. Instead of the value corresponding to the deviation of the air-fuel ratio, the deviation integrated value which is the target value corresponding to the air-fuel ratio leaner than the target air-fuel ratio, which is different from the output value of the air-fuel ratio sensor and the target air-fuel ratio equivalent target value This is because the deviation integrated value is updated by successively integrating values corresponding to deviations from the update target value.

  According to this, in a predetermined period after returning from the fuel cut control (after the fuel cut control is finished), the deviation integrated value is the target air value instead of the output value of the air fuel ratio sensor and the target air fuel ratio equivalent target value. A value corresponding to the deviation from the deviation integral value update target value corresponding to a leaner air-fuel ratio than the fuel ratio is sequentially integrated and updated. On the other hand, as described above, the output value of the air-fuel ratio sensor becomes a value indicating leaner than the target air-fuel ratio until the lean atmosphere in the catalyst is eliminated after returning from the fuel cut control.

  Therefore, it is possible to suppress a situation in which the deviation between the output value of the air-fuel ratio sensor and the deviation integrated value update target value becomes a large value for correcting the air-fuel ratio to the rich side in a predetermined period after returning from the fuel cut control. Can be done. That is, during this period, the deviation integral value can be suppressed from excessively increasing as a value for correcting the air-fuel ratio to the rich side.

  As a result, for example, even if the deviation integrated value learning is executed after the return from the fuel cut control (for example, immediately after the return), the “mis-learning to the rich side of the deviation integrated value” can be suppressed. It is possible to suppress an increase in the amount of emission of unburned HC, CO, etc. due to erroneous learning to the rich side of the value.

  In this way, in order to execute learning of the deviation integral value, the air-fuel ratio control apparatus according to the present invention stores the deviation integral value and updates the stored deviation integral value at every predetermined timing. It is necessary to provide a means for learning deviation integral values.

  In the air-fuel ratio control apparatus according to the present invention, the feedback correction value calculation means is configured to calculate the feedback correction value based on the integral term and at least the proportional term, and from the fuel cut control. Also in the predetermined period after returning, the proportional term is calculated using a value corresponding to a deviation between the output value of the air-fuel ratio sensor and the target value corresponding to the target air-fuel ratio. Is preferred.

  Consider a case where the feedback correction value is calculated based on an integral term and at least a proportional term. In this case, in a predetermined period after returning from the fuel cut control, in addition to the integral term, the proportional term is also calculated using a value corresponding to the deviation between the air-fuel ratio sensor output value and the deviation integral value update target value. If configured to do so, it cannot be guaranteed that the feedback correction value itself is calculated to a value for correcting the air-fuel ratio to the rich side. That is, after returning from the fuel cut control, the air-fuel ratio is not controlled to be richer than the stoichiometric air-fuel ratio, and as a result, the above-described lean atmosphere in the catalyst may not be eliminated.

  On the other hand, according to the above configuration, it can be guaranteed that at least the value of the proportional term is calculated as a value for correcting to the rich side. Therefore, it can be guaranteed that the feedback correction value itself is also calculated to a value for correcting the air-fuel ratio to the rich side. As a result, after returning from the fuel cut control, the air-fuel ratio can be reliably controlled to be richer than the stoichiometric air-fuel ratio, and as a result, the above-described lean atmosphere in the catalyst can be reliably eliminated.

  In this case, the feedback correction value calculation means includes oxygen storage amount increase estimation means for estimating an increase in the oxygen storage amount from the fuel cut control start time to the fuel cut control start time, The air-fuel ratio of the internal combustion engine configured to change the deviation integrated value update target value in accordance with a decrease in the estimated increase in the oxygen storage amount over the predetermined period after returning from fuel cut control. Control device.

  Specifically, the feedback correction value calculation means changes the deviation integral value update target value so as to become a value corresponding to a richer air-fuel ratio as the estimated increase in the oxygen storage amount becomes smaller. It is preferable to be configured to do so.

  As described above, when the air-fuel ratio is reliably controlled to be richer than the stoichiometric air-fuel ratio after returning from the fuel-cut control, the oxygen storage amount of the catalyst is controlled from the start of the fuel-cut control. And then decreases after returning from fuel cut control. In other words, the increase (increase) in the oxygen storage amount of the catalyst from the start of fuel cut control (hereinafter also referred to simply as “increase in oxygen storage”) is the fuel cut from the start of fuel cut control. It increases over the course of control and decreases after returning from fuel cut control.

  As the increase in the oxygen storage amount decreases after returning from fuel cut control, the lean atmosphere in the catalyst tends to decrease, and the air-fuel ratio sensor output value tends to be a value corresponding to a richer air-fuel ratio. There is. Therefore, the deviation integrated value update target value is changed to a value corresponding to a richer air-fuel ratio as the increase in the oxygen storage amount becomes smaller over a predetermined period after returning from the fuel cut control. Thus, the deviation between the air-fuel ratio sensor output value and the deviation integral value update target value can be maintained at a small value over the predetermined period.

  The above configuration is based on such knowledge. As a result, it is possible to further suppress the deviation integrated value from increasing as a value for correcting the air-fuel ratio to the rich side in the predetermined period, and as a result, the deviation integrated value after returning from the fuel cut control. Even if this learning is executed, the “mis-learning to the rich side of the deviation integral value” can be more reliably suppressed.

  Further, when the air-fuel ratio is reliably controlled to be richer than the stoichiometric air-fuel ratio after returning from the fuel cut control in this way, the feedback correction value calculation means, as the end of the predetermined period, It is preferable to use the time point when the estimated increase in the oxygen storage amount that decreases after returning from the fuel cut control becomes zero.

  The time when the increase in the oxygen storage amount that decreases after returning from fuel cut control becomes zero coincides with the time when the above-described lean atmosphere in the catalyst is eliminated, or is considered to be very close to the same point. be able to. Therefore, according to the above configuration, the deviation used to update the deviation integral value is changed from the deviation between the air / fuel ratio sensor output value and the deviation integral value update target value to the air / fuel ratio sensor output value and the target air / fuel ratio equivalent target. The timing for returning to the deviation from the value can be set appropriately.

  In this case, the feedback correction value calculation means sets the air-fuel ratio at which the output value of the air-fuel ratio sensor is richer than the target air-fuel ratio before the decrease in the estimated increase in the oxygen storage amount becomes zero. When the predetermined value is reached, the output value of the air-fuel ratio sensor is richer than the target air-fuel ratio at the end of the predetermined period, instead of when the estimated increase in the oxygen storage amount becomes zero. It is more preferable that the time point when the air fuel ratio is reached is used.

  According to this, due to the increase in the oxygen storage amount being estimated to be large, the deviation integral value differs from the air-fuel ratio sensor output value even though the lean atmosphere in the catalyst has already been eliminated. It is possible to prevent occurrence of a situation where updating is performed using a deviation from the integral value update target value.

  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. This air-fuel ratio control device is also a fuel injection amount control device that controls the fuel injection amount of the engine.

  FIG. 1 shows a schematic configuration of a system in which an air-fuel ratio control apparatus according to an embodiment of the present invention is applied to a four-cycle spark ignition type multi-cylinder internal combustion engine 10. FIG. 1 shows only a cross section of a specific cylinder, but the other cylinders have the same configuration.

  The internal combustion engine 10 includes a cylinder block portion 20 including a cylinder block, a cylinder block lower case, an oil pan, and the like, a cylinder head portion 30 fixed on the cylinder block portion 20, and a gasoline mixture to the cylinder block portion 20. An intake system 40 for supplying and an exhaust system 50 for releasing exhaust gas from the cylinder block 20 to the outside are included.

  The cylinder block unit 20 includes a cylinder 21, a piston 22, a connecting rod 23, and a crankshaft 24. The piston 22 reciprocates in the cylinder 21, and the reciprocating motion of the piston 22 is transmitted to the crankshaft 24 through the connecting rod 23, whereby the crankshaft 24 rotates. The heads of the cylinder 21 and the piston 22 form a combustion chamber 25 together with the cylinder head portion 30.

  The cylinder head portion 30 includes an intake port 31 communicating with the combustion chamber 25, an intake valve 32 that opens and closes the intake port 31, an intake camshaft that drives the intake valve 32, and a phase angle and lift amount of the intake camshaft are continuously provided. Variable intake timing device 33 to be changed, actuator 33a of variable intake timing device 33, exhaust port 34 communicating with combustion chamber 25, exhaust valve 35 for opening and closing exhaust port 34, exhaust camshaft 36 for driving exhaust valve 35, An ignition plug 37, an igniter 38 including an ignition coil that generates a high voltage to be applied to the ignition plug 37, and an injector (fuel injection means) 39 for injecting fuel into the intake port 31 are provided.

  The intake system 40 is provided in an intake pipe 41 including an intake manifold that communicates with the intake port 31 and forms an intake passage together with the intake port 31, an air filter 42 provided at an end of the intake pipe 41, and the intake pipe 41. A throttle valve 43 and a swirl control valve (hereinafter referred to as “SCV”) 44 that change the opening cross-sectional area of the intake passage are provided.

  The throttle valve 43 is rotationally driven in the intake pipe 41 by a throttle valve actuator 43a made of a DC motor. The SCV 44 is rotationally driven by an SCV actuator 44a made of a DC motor.

  The exhaust system 50 includes an exhaust manifold 51 communicating with the exhaust port 34, an exhaust pipe 52 connected to the exhaust manifold 51, an upstream catalyst 53 disposed in the exhaust pipe 52, and an exhaust pipe 52 downstream of the upstream catalyst 53. Is provided with a downstream catalyst 54. The exhaust port 34, the exhaust manifold 51, and the exhaust pipe 52 constitute an exhaust passage.

Each of the upstream catalyst 53 and the downstream catalyst 54 is a three-way catalyst device that supports an active component made of a noble metal such as platinum. Each catalyst has a function of oxidizing unburned gas such as HC and CO and reducing nitrogen oxides (NOx) when the catalyst inflow gas has a substantially stoichiometric air-fuel ratio. Furthermore, each catalyst has an oxygen storage function for storing (storing) oxygen, and even if the air-fuel ratio shifts from the stoichiometric air-fuel ratio by this oxygen storage function, unburned gas and nitrogen oxides can be purified. . This oxygen storage function is provided by ceria (CeO ₂ ) supported on the catalyst.

  On the other hand, this system includes a hot-wire air flow meter 61, an intake air temperature sensor 62, a throttle position sensor 63, a cam position sensor 64, a crank position sensor 65, a water temperature sensor 66, an air-fuel ratio sensor 67, an oxygen concentration sensor 68, and an accelerator opening. A sensor 69 is provided.

  The air flow meter 61 outputs a signal corresponding to the mass flow rate (intake air flow rate) Ga of intake air flowing through the intake pipe 41. The intake air temperature sensor 62 detects the temperature of the intake air and outputs a signal representing the intake air temperature THA. The throttle position sensor 63 detects the opening (throttle valve opening) of the throttle valve 43 and outputs a signal representing the throttle valve opening TA.

  The cam position sensor 64 generates a signal (G2 signal) having one pulse every time the intake camshaft rotates 90 ° (that is, every time the crankshaft 24 rotates 180 °). The crank position sensor 65 outputs a signal having a narrow pulse every time the crankshaft 24 rotates 10 ° and a wide pulse every time the crankshaft 24 rotates 360 °. This signal represents the engine speed NE. The water temperature sensor 66 detects the temperature of the cooling water of the internal combustion engine 10 and outputs a signal representing the cooling water temperature THW.

  The air-fuel ratio sensor 67 is disposed in the exhaust passage and upstream of the upstream catalyst 53. The air-fuel ratio sensor 67 is a so-called “limit current type oxygen concentration sensor” that detects the air-fuel ratio in the exhaust gas flowing into the upstream side catalyst 53 and, as shown in FIG. The signal Vabyf (V) corresponding to the (fuel ratio) is output.

  The oxygen concentration sensor 68 is disposed in the exhaust passage, downstream of the upstream catalyst 53 and upstream of the downstream catalyst 54. The oxygen concentration sensor 68 is a so-called “concentration cell type oxygen sensor”. As shown in FIG. 3, the oxygen concentration sensor 68 has a maximum output value max (V) and a minimum output value min (V) when the air-fuel ratio of the gas flowing out from the upstream catalyst 53 is richer and leaner than the stoichiometric air-fuel ratio. ) And when the air-fuel ratio of the gas flowing out from the upstream catalyst 53 is the stoichiometric air-fuel ratio, a value approximately halfway between the maximum output value max and the minimum output value min (target air-fuel ratio equivalent target value Voxsref (V)) Is output.

  The accelerator opening sensor 69 outputs a signal representing the operation amount Accp of the accelerator pedal 71 operated by the driver.

  The electric control device 80 includes a CPU 81 connected to each other by a bus, a ROM 82 in which programs executed by the CPU 81, tables (maps, functions), constants, and the like are stored in advance, a RAM 83 in which the CPU 81 temporarily stores data as necessary, The microcomputer includes a backup RAM 84 that stores data while the power is turned on and holds the stored data even while the power is shut off, and an interface 85 including an AD converter.

  The interface 85 is connected to the sensors 61 to 69, supplies signals from the sensors 61 to 69 to the CPU 81, and in response to instructions from the CPU 81, the actuator 33a, the igniter 38, the injector 39, and the throttle valve of the variable intake timing device 33. Drive signals are sent to the actuator 43a and the SCV actuator 44a.

(Outline of air-fuel ratio feedback control)
Next, the outline of the air-fuel ratio feedback control by the air-fuel ratio control apparatus (hereinafter also referred to as “this apparatus”) configured as described above will be described. This apparatus is configured so that the air-fuel ratio of the air-fuel mixture supplied to the engine is adjusted so that the air-fuel ratio of the gas flowing out from the upstream catalyst 53 becomes the target air-fuel ratio (= theoretical air-fuel ratio). The air-fuel ratio (hereinafter also simply referred to as “air-fuel ratio”) is controlled.

  Specifically, the present apparatus is configured such that the output value Voxs (V) of the oxygen concentration sensor 68 disposed downstream of the upstream catalyst 53 and the target air / fuel ratio equivalent target value Voxsref (V) ( The feedback correction value (sub feedback correction amount Vafsfb (%)) is obtained by performing PID processing on the deviation from the constant), and based on the sub feedback correction amount Vafsfb (actually, the output value Vabyf (V) of the air-fuel ratio sensor 67) (Based on) air-fuel ratio feedback control. Note that the air-fuel ratio feedback control based on the output value Voxs of the oxygen concentration sensor 68 may be particularly referred to as “sub-feedback control”.

  Further, the present apparatus performs fuel cut control according to the operating state of the engine, and interrupts the air-fuel ratio feedback control during the fuel cut control. Hereinafter, “fuel cut control” may be referred to as “FC”.

  In addition, this apparatus performs the I process of the PID process only during the predetermined period after the return from the FC (the flag ORE = 1), the “output value Voxs of the oxygen concentration sensor 68 and the target sky. Instead of “deviation from the target value Voxsref corresponding to the fuel ratio”, the output value Voxs of the oxygen concentration sensor 68 and the target for updating the deviation integrated value corresponding to the lean air-fuel ratio rather than the stoichiometric air-fuel ratio set / changed as described later Deviation from value Voxsrefi ". The apparatus performs air-fuel ratio feedback control based on the sub-feedback correction amount Vafsfb obtained thereby. The above is the outline of the air-fuel ratio feedback control by this apparatus.

(Actual operation)
Next, referring to FIG. 4 to FIG. 8 and FIG. 9 showing routines (programs) executed by the CPU 81 of the electric control device 80 for the actual operation of the air-fuel ratio control device configured as described above. While explaining.

  FIG. 9 shows the flag ORE, the target air-fuel ratio equivalent target value Voxsref, the deviation integrated value update target value Voxsrefi, and the upstream side catalyst 53 from the FC start time when FC is executed between times t1 and t2. 6 is a time chart showing an example of each change in the increase amount OSA of the oxygen storage amount. When the value of the flag ORE is “1”, it indicates a state in which the increase amount of the oxygen storage amount OSA remains after the FC recovery, and when the value is “0”, the increase amount of the oxygen storage amount after the FC recovery. The state where OSA does not remain is shown. Hereinafter, the description is started assuming that the current time is before time t1 and the value of the flag ORE is “0”.

  The CPU 81 performs the routine for calculating the fuel injection amount Fi and instructing the fuel injection shown in FIG. 4 every time the crank angle of an arbitrary cylinder becomes a predetermined crank angle before the intake top dead center (for example, BTDC 90 ° CA). It is designed to be executed repeatedly. Therefore, when the crank angle of a certain cylinder (hereinafter referred to as “fuel injection cylinder”) reaches the predetermined crank angle, the CPU 81 starts the process from step 400 and proceeds to step 405 to determine whether FC is in progress. Determine whether.

  Since the current time is before time t1, FC is not in progress. Accordingly, the CPU 81 makes a “No” determination at step 405 to proceed to step 410, and in the current intake stroke based on the intake air flow rate Ga measured by the air flow meter 61 and the engine rotational speed NE, The amount of air sucked into the cylinder (cylinder intake air amount Mc) is obtained from map f. This map f is stored in the ROM 82 in advance.

  Subsequently, the CPU 81 proceeds to step 415, and the basic fuel for setting the air-fuel ratio to the target air-fuel ratio by dividing the obtained cylinder intake air amount Mc by the target air-fuel ratio abyfr (theoretical air-fuel ratio in this example). Obtain the injection amount Fbase. Next, the CPU 81 proceeds to step 420, and sets the fuel injection amount Fi to a value obtained by adding an air-fuel ratio feedback correction amount DFi, which will be described later, to the obtained basic fuel injection amount Fbase.

  Then, the CPU 81 proceeds to step 425 to give an instruction for injecting fuel of the fuel injection amount Fi to the injector 39 corresponding to the fuel injection cylinder, and proceeds to step 495 to end this routine once. As a result, the fuel of the fuel injection amount Fi that has been feedback-corrected is injected into the cylinder that reaches the intake stroke. Such processing is repeatedly executed until FC is started (until time t1 in FIG. 9 arrives).

  Next, calculation of the air-fuel ratio feedback correction amount DFi will be described. The CPU 81 repeatedly executes the routine shown in FIG. 5 every elapse of a predetermined time. Accordingly, when the predetermined timing is reached, the CPU 81 starts the process from step 500 and proceeds to step 505 to determine whether or not the air-fuel ratio feedback control condition is satisfied. As the air-fuel ratio feedback control condition, for example, FC is not executed, the engine coolant temperature THW detected by the water temperature sensor 66 is equal to or higher than a predetermined temperature, and the intake air amount (load) per one rotation of the engine is predetermined. It is established when the air-fuel ratio sensor 67 and the oxygen concentration sensor 68 are in the active state. Hereinafter, the description will be continued assuming that all the conditions other than FC are satisfied.

  Since the current time is before time t1, FC is not executed. That is, the air-fuel ratio feedback control condition is satisfied. Accordingly, the CPU 81 makes a “Yes” determination at step 505 to proceed to step 510 where the current output value Vabyf (V) of the air-fuel ratio sensor 67, a sub-feedback correction amount Vafsfb (%) described later, The control air-fuel ratio equivalent output value Vabyfs (V) is obtained based on the equation described in (1).

  Subsequently, the CPU 81 proceeds to step 515 to obtain the control air-fuel ratio abyfs at the present time based on the obtained control air-fuel ratio equivalent output value Vabyfs and the map shown in FIG. This air-fuel ratio is the “apparent air-fuel ratio” of the gas upstream of the upstream side catalyst 53.

  Next, the CPU 81 proceeds to step 520 and divides the latest in-cylinder intake air amount Mc (for the current intake stroke) obtained in the previous step 410 by the obtained control air-fuel ratio abyfs. The in-cylinder fuel supply amount Fc for the intake stroke of the engine is obtained. Next, the CPU 81 proceeds to step 525, and obtains the target in-cylinder fuel supply amount Fcr for the current intake stroke by dividing the in-cylinder intake air amount Mc by the target air-fuel ratio abyfr.

  Subsequently, the CPU 81 proceeds to step 530 to set the in-cylinder fuel supply amount deviation DFc to a value obtained by subtracting the in-cylinder fuel supply amount Fc from the target in-cylinder fuel supply amount Fcr. That is, the in-cylinder fuel supply amount deviation DFc is an amount representing the excess or deficiency of fuel for the current intake stroke.

  Next, the CPU 81 proceeds to step 535, and adds the in-cylinder fuel supply amount deviation DFc obtained in step 530 to the integral value SDFc of the in-cylinder fuel supply amount deviation DFc at that time point, thereby reducing the in-cylinder fuel supply amount deviation. Update integrated value SDFc.

  Then, the CPU 81 proceeds to step 540 and describes in-cylinder fuel supply amount deviation DFc obtained in step 530, the integrated value SDFc of in-cylinder fuel supply amount deviation updated in step 535, and in step 540. The air-fuel ratio feedback correction amount DFi is obtained based on the above equation. Here, Gp is a preset proportional gain, and Gi is a preset integral gain. The coefficient KFB is preferably variable depending on the engine speed NE, the in-cylinder intake air amount Mc, and the like, but is set to “1” here. Then, the CPU 81 proceeds to step 595 to end the present routine tentatively.

  As described above, the air-fuel ratio feedback correction amount DFi is obtained by the proportional integration process (PI process), and the air-fuel ratio feedback correction amount DFi is reflected in the fuel injection amount Fi by the above-described step 420 and step 425 in FIG.

  As a result, the excess or deficiency of the fuel supply amount for the current intake stroke is compensated, so the average value of the air-fuel ratio (and hence the air-fuel ratio of the gas flowing into the upstream catalyst 53) is the target air-fuel ratio abyfr (= theoretical air (Fuel ratio). Such processing is repeatedly executed until FC is started (until time t1 in FIG. 9 arrives).

  Next, air-fuel ratio feedback control (that is, sub-feedback control) based on the output Voxs of the oxygen concentration sensor 68 will be described. By this sub feedback control, the sub feedback correction amount Vafsfb (%) described above is calculated. This sub feedback correction amount Vafsfb corresponds to the “feedback correction value”.

  The CPU 81 executes the routine shown in FIG. 6 every elapse of a predetermined time in order to obtain the sub feedback correction amount Vafsfb. Accordingly, when the predetermined timing is reached, the CPU 81 starts the process from step 600, proceeds to step 605, and determines whether or not the same air-fuel ratio feedback control condition as in the previous step 505 is satisfied.

  As described above, since the current time is before time t1 and FC is not executed, the air-fuel ratio feedback control condition is satisfied. Therefore, the CPU 81 makes a “Yes” determination at step 605 and proceeds to step 610 to determine whether or not it is immediately after the air-fuel ratio feedback control is resumed by the return from the FC (immediately after time t2 in FIG. 9). .

  The current time is before the time t1 and not immediately after the air-fuel ratio feedback control is resumed by the return from the FC. Therefore, the CPU 81 makes a “No” determination at step 610 to proceed to step 615 to determine whether or not the value of the flag ORE is “0”.

  At present, the value of the flag ORE is maintained at “0” (see FIG. 9). Accordingly, the CPU 81 makes a “Yes” determination at step 615 to proceed to step 620 to set the deviation integrated value update target value Voxsrefi to a value equal to the target air-fuel ratio equivalent target value Voxsref.

  Subsequently, the CPU 81 proceeds to step 625 to set the deviation DVoxs to a value obtained by subtracting the output value Voxs of the oxygen concentration sensor 68 from the target air-fuel ratio equivalent target value Voxsref (constant). This deviation DVoxs always corresponds to the “value corresponding to the deviation between the output value of the air-fuel ratio sensor and the target value corresponding to the target air-fuel ratio”.

  Next, the CPU 81 proceeds to step 630 to change the deviation integrated value update deviation DVoxsi from the deviation integrated value update target value Voxsrefi (= target air-fuel ratio equivalent target value Voxsref) set in step 620. Set the output value Vox to a reduced value. That is, the deviation DVoxsi (= deviation DVoxs) for updating the deviation integral value at this stage corresponds to the “value corresponding to the deviation between the output value of the air-fuel ratio sensor and the target value corresponding to the target air-fuel ratio”.

  Next, the CPU 81 proceeds to step 635 and adds the deviation integral value updating deviation DVoxsi obtained in step 630 to the deviation integral value SDVoxs (integral value of deviation integral value updating deviation DVoxsi) at that time point, thereby integrating the deviation. Update the value SDVoxs. That is, the deviation integrated value SDVoxs at this stage is updated by sequentially integrating “a value corresponding to the deviation between the output value of the air-fuel ratio sensor and the target value corresponding to the target air-fuel ratio”.

  Subsequently, the CPU 81 proceeds to step 640 to obtain a time differential value DDVoxs of the deviation DVoxs based on the deviation DVoxs obtained in step 625, the previous deviation DVoxsb, and the formula described in step 640. As the previous deviation DVoxsb, the value updated in step 650, which will be described later, at the time of the previous execution of this routine is used. Δt is an execution interval time (for example, 8 msec) of this routine.

  Next, the CPU 81 proceeds to step 645, where the deviation DVoxs obtained in step 625, the deviation integrated value SDVoxs updated in step 635, the time differential value DDVoxs of deviation obtained in step 640, and a later-described step. The sub feedback correction amount Vafsfb (%) is obtained based on the learning value Learn of the deviation integral value SDVoxs to be performed and the expression described in step 645. Here, Kp is a preset proportional gain, Ki is a preset integral gain, and Kd is a preset differential gain.

  In the expression in Step 645, the first term “Kp · DVoxs” on the right side is the proportional term, the sum of the second term “Ki · SDVoxs” on the right side and the fourth term “Ki · Learn” on the right side is the integral term, The third term “Kd · DDVoxs” corresponds to the differential term. That is, the sub feedback correction amount Vafsfb is calculated based on the proportional term, the integral term, and the derivative term. The proportional term and the differential term are always calculated using the “value corresponding to the deviation between the output value of the air-fuel ratio sensor and the target value corresponding to the target air-fuel ratio” itself. Further, the integral term at this stage is calculated using the “value corresponding to the deviation between the output value of the air-fuel ratio sensor and the target value corresponding to the target air-fuel ratio”.

  The CPU 81 proceeds to step 650, sets the previous deviation DVoxsb to the deviation DVoxs obtained in step 625, and then proceeds to step 695 to end the present routine tentatively.

  In this way, the sub feedback correction amount Vafsfb (%) is obtained, and this value is used for the calculation of the control air-fuel ratio equivalent output value Vabyfs (V) in step 510 of FIG. Then, the control air-fuel ratio equivalent output value Vabyfs (V) is converted into the control air-fuel ratio abyfs based on the map shown in FIG. In other words, the control air-fuel ratio abyfs corresponds to the sub-feedback correction amount Vafsfb (%) obtained based on the output value Voxs of the oxygen concentration sensor 68 with respect to the air-fuel ratio actually detected by the air-fuel ratio sensor 67. Therefore, the air / fuel ratio is determined so as to be different.

  As a result, the in-cylinder fuel supply amount Fc calculated in step 520 of FIG. 5 changes according to the output value Voxs of the oxygen concentration sensor 68, so that the air-fuel ratio feedback correction amount DFi is changed to oxygen by steps 530 to 540. It is changed according to the output value Voxs of the density sensor 68. As a result, the air-fuel ratio is controlled so that the air-fuel ratio on the downstream side of the upstream catalyst 53 matches the target air-fuel ratio abyfr (= theoretical air-fuel ratio).

  For example, since the average air-fuel ratio of the engine is lean, the output value Voxs of the oxygen concentration sensor 68 is smaller than the target air-fuel ratio equivalent target value Voxsref (constant) (that is, a value shifted to the lean side). If so, the deviation DVoxs obtained in step 625 (and the integral value updating deviation DVoxsi obtained in step 630) becomes a positive value, so that the sub feedback correction amount Vafsfb obtained in step 645 is positive. It becomes the value of. Therefore, the control air-fuel ratio abyfs obtained in step 515 is obtained as a leaner value (a larger value) than the air-fuel ratio actually detected by the air-fuel ratio sensor 67.

  Therefore, the in-cylinder fuel supply amount Fc obtained in step 520 is a small value, and the in-cylinder fuel supply amount deviation DFc obtained in step 530 is a large value. Accordingly, the air-fuel ratio feedback correction amount DFi becomes a large positive value. As a result, the fuel injection amount Fi obtained in step 420 in FIG. 4 is controlled to be larger than the basic fuel injection amount Fbase so that the air-fuel ratio becomes a rich value.

  On the contrary, since the average air-fuel ratio of the engine is rich, the output value Voxs of the oxygen concentration sensor 68 is larger than the target air-fuel ratio equivalent target value Voxsref (constant) (that is, a value shifted to the rich side). Since the deviation DVoxs (and the integral value updating deviation DVoxsi) is a negative value, the sub-feedback correction amount Vafsfb is a negative value. Therefore, the control air-fuel ratio abyfs obtained in step 515 is obtained as a richer value (smaller value) than the air-fuel ratio actually detected by the air-fuel ratio sensor 67.

  Accordingly, since the in-cylinder fuel supply amount Fc has a large value, the in-cylinder fuel supply amount deviation DFc has a negative value. As a result, the air-fuel ratio feedback correction amount DFi becomes a negative value. Thus, the fuel injection amount Fi is controlled to be smaller than the basic fuel injection amount Fbase so that the air-fuel ratio becomes a lean value. Such processing is repeatedly executed until FC is started (until time t1 in FIG. 9 arrives).

  Next, update (learning) of the learning value Learn of the deviation integral value SDVoxs will be described. The CPU 81 executes the routine shown in FIG. 7 every elapse of a predetermined time. Therefore, when the predetermined timing is reached, the CPU 81 proceeds to step 705 to determine whether or not the learning timing of the learning value Learn of the deviation integral value has arrived. When determining “No”, the CPU 81 immediately proceeds to step 795. This routine is temporarily terminated. For example, in this example, the learning timing of the learning value Learn of the deviation integral value comes every time the number of fuel injections reaches a predetermined number regardless of whether or not FC is being performed.

  When the learning timing of the learning value Learn of the deviation integral value has arrived, the CPU 81 makes a “Yes” determination at step 705 to proceed to step 710, where the deviation updated by the learning value update amount DLearn is updated at step 635. Set the latest value of the integral value SDVoxs divided by the value Nref. The value Nref is a value equal to or greater than “1”, and is set to “1”, “2”, “4”, “8”, for example.

  Subsequently, the CPU 81 proceeds to step 715 to update the learning value Learn of the deviation integral value by adding the learning value update amount DLearn obtained in step 710 to the learning value Learn of the deviation integral value at that time. Next, the CPU 81 proceeds to step 720, resets the deviation integral value SDVoxs by subtracting the learning value update amount DLearn from the deviation integral value SDVoxs at that time, and then proceeds to step 795 to end this routine once.

  In this way, every time the learning timing comes, the learning value Learn of the deviation integral value is updated without changing the sum of the deviation integral value SDVoxs and the learning value Learn of the deviation integral value (SDVoxs + Learn). Thus, every time the learning timing arrives, the deviation integral value SDVoxs gradually approaches “0”, while the deviation integral value learning value Learn accurately represents the magnitude of the “fuel injection amount error”. It approaches the value (that is, the learning value Learn of the deviation integral value should converge). It should be noted that the speed at which the learned value Learn of the deviation integral value approaches the value that accurately represents the magnitude of the “fuel injection amount error” decreases as the value Nref increases. Such processing is repeatedly executed regardless of the FC execution timing.

  Next, calculation of the increase OSA (see FIG. 9) of the oxygen storage amount of the upstream catalyst 53 from the FC start time will be described. The CPU 81 executes the routine shown in FIG. 8 every elapse of a predetermined time. Therefore, when the predetermined timing comes, the CPU 81 proceeds to step 805 to determine whether or not FC is in progress.

  As described above, the current time is before time t1 and is not in FC. Accordingly, the CPU 81 makes a “No” determination at step 805 to proceed to step 810 to determine whether or not the value of the flag ORE is “1”.

  At this time, as described above, the value of the flag ORE is maintained at “0”. Therefore, the CPU 81 makes a “No” determination at step 810 to immediately proceed to step 895 to end the present routine tentatively. Such processing is repeatedly executed until FC is started (until time t1 in FIG. 9 arrives).

  As described above, as shown in FIG. 9, the air-fuel ratio feedback control described above is executed before time t1 when the air-fuel ratio feedback control condition is satisfied. During this time, the deviation integration value update target value Voxsrefi is maintained equal to the target air-fuel ratio equivalent target value Voxsref (constant), and the value of the flag ORE is maintained at “0”.

  Next, a case where time t1 has arrived will be described. At time t1, FC is started as shown in FIG. Therefore, the CPU 81 that repeatedly executes the routine of FIG. 4 determines “Yes” when the routine proceeds to step 405, and immediately proceeds to step 495 to end this routine once.

  Such a process is repeatedly executed until FC ends (until time t2 in FIG. 9 arrives). Thereby, fuel injection is interrupted between the times t1 and t2.

  Further, at time t1, since the FC is started, the air-fuel ratio feedback control condition is not satisfied. Therefore, the CPU 81 that repeatedly executes the routine of FIG. 5 determines “No” when it proceeds to step 505, proceeds to step 545, and sets the value of the air-fuel ratio feedback correction amount DFi to “0”. Then, the process proceeds to step 595 to end this routine once.

  Thus, when the air-fuel ratio feedback control condition is not satisfied, such as during FC, the air-fuel ratio feedback correction amount DFi is set to “0” and the air-fuel ratio (basic fuel injection amount Fbase) is not corrected. Such a process is repeatedly executed until FC ends (until time t2 in FIG. 9 arrives).

  Similarly, at time t1, the CPU 81 that repeatedly executes the routine of FIG. 6 determines “No” when it proceeds to step 605, proceeds immediately to step 695, and once ends this routine. Thus, when the air-fuel ratio feedback control condition is not established, the sub feedback correction amount Vafsfb is not calculated. Such a process is repeatedly executed until FC ends (until time t2 in FIG. 9 arrives).

  At time t1, the CPU 81 that repeatedly executes the routine of FIG. 8 determines “Yes” when it proceeds to step 805, proceeds to step 815, and determines whether or not it is immediately after the start of FC. Determine.

  The current time is immediately after time t1 and immediately after the start of FC. Therefore, the CPU 81 makes a “Yes” determination at step 815 to proceed to step 820, in which the oxygen storage amount increase OSA of the upstream side catalyst 53 from the FC start time (hereinafter simply referred to as “oxygen storage amount increase OSA”). Is initialized to “0” (see FIG. 9).

  Subsequently, the CPU 81 proceeds to step 825 to obtain the oxygen storage amount change amount DOSA according to the current intake air flow rate Ga measured by the air flow meter 61 and the formula described in step 825. Here, the value “0.23” is the mass ratio of oxygen contained in the air. Δt is the execution interval time of this routine (for example, 8 msec).

  It can be considered that the flow rate of the gas flowing into the upstream catalyst 53 is substantially equal to the intake air flow rate Ga. In addition, in FC, the gas flowing into the upstream side catalyst 53 is air itself. That is, in the equation described in step 825, the value “Ga · Δt” represents the amount (mass) of air that has flowed into the upstream catalyst 53 during the execution interval time Δt of this routine. Therefore, the value “0.23 · Ga · Δt” (that is, the oxygen storage amount change amount DOSA in step 825) is the amount (mass) of oxygen flowing into the upstream catalyst 53 during the execution interval time Δt of this routine, that is, This represents the increase amount (> 0) of the OSA increase amount during the execution interval time Δt of this routine.

  Next, the CPU 81 proceeds to step 830 and adds the oxygen storage amount increase amount OSA by adding the oxygen storage amount change amount DOSA (> 0) obtained in step 825 to the oxygen storage amount increase amount OSA at that time. Update (increase).

  Next, the CPU 81 proceeds to step 835 to determine whether or not the increase amount OSA of the oxygen storage amount updated in step 830 exceeds the maximum oxygen storage amount Cmax of the upstream catalyst 53, and determines “Yes”. Subsequently, in step 840, the increase amount OSA of the oxygen storage amount is limited to the maximum oxygen storage amount Cmax, and then the process proceeds to step 895. On the other hand, if “No” is determined, the process proceeds to step 895 immediately.

  The maximum oxygen storage amount Cmax of the upstream catalyst 53 is a so-called method (for example, the so-called switching of the air / fuel ratio from one of the rich / lean air / fuel ratios to the other at the timing when the output value Voxs of the oxygen concentration sensor 68 is inverted) Acquired / updated at predetermined timings by active air-fuel ratio control or the like).

  Such processing is repeatedly executed from time t1 when FC is started to time t2 when FC is finished. As a result, as shown in FIG. 9, the increase amount OSA of the oxygen storage amount gradually increases at a speed corresponding to the intake air flow rate Ga during the time t1 to t2.

  As described above, as shown in FIG. 9, during the time t1 to t2 during FC, fuel injection is interrupted and the above-described air-fuel ratio feedback control is also interrupted. During this time, the increase amount OSA of the oxygen storage amount (accordingly, the oxygen storage amount of the upstream catalyst 53) increases. As a result, the degree of the lean atmosphere in the upstream catalyst 53 gradually increases, and the output value Voxs of the oxygen concentration sensor 68 becomes a value indicating lean (<target air-fuel ratio equivalent target value Voxsref). The value of the flag ORE is still maintained at “0”.

  Next, a case where time t2 has arrived will be described. At time t2, FC ends as shown in FIG. Therefore, after time t2, the CPU 81 that repeatedly executes the routine of FIG. 4 determines “No” again when it proceeds to step 405.

  In addition, since FC is not executed at time t2, the air-fuel ratio feedback control condition is satisfied again after time t2. Therefore, the CPU 81 that repeatedly executes the routines of FIGS. 5 and 6 determines “Yes” again when it proceeds to steps 505 and 605. As described above, when returning from the FC, the air-fuel ratio feedback control is immediately resumed.

  Furthermore, when the time t2 comes, the CPU 81 that repeatedly executes the routine of FIG. 6 determines “Yes” in Step 605, determines “Yes” when the process proceeds to Step 610, and proceeds to Step 655. The value of the flag ORE is changed from “0” to “1” (see FIG. 9).

  Accordingly, the CPU 81 makes a “No” determination at subsequent step 615 to proceed to step 660 instead of the above step 620 to replace the deviation integrated value update target value Voxsrefi with the target air-fuel ratio equivalent target value Voxsref. This is determined based on the amount of increase OSA of the occlusion amount and the table MapVoxsrefi shown in FIG. As the increase amount OSA of the oxygen storage amount, a value updated by the routine process of FIG. 8 (currently, the process of step 830, and thereafter, the process of step 855 described later) is used.

  Note that the table shown in FIG. 10 starts FC in a state where the learning value Learn of the deviation integral value has converged to the value to be converged (that is, in a state where the air-fuel ratio matches the target air-fuel ratio abyfr). Along with this, after the end of the FC, a plot of the transition of the relationship between the increase amount OSA of the oxygen storage amount that decreases due to the sub-feedback correction and the output value Voxs of the oxygen concentration sensor 68 as will be described later. It is made based on the results of experiments.

  As a result, as shown in FIG. 9, after time t2, the deviation integrated value update target value Voxsrefi corresponds to a leaner air-fuel ratio than the target air-fuel ratio abyfr different from the target air-fuel ratio equivalent target value Voxsref (constant). To be set (<target air-fuel ratio equivalent target value Voxsref).

  As a result, in step 630, the deviation integrated value update deviation DVoxsi is changed from the deviation integrated value update target value Voxsrefi (<target air-fuel ratio equivalent target value Voxsref) set in step 660 to the output value Voxs of the oxygen concentration sensor 68. Is set to a value obtained by subtracting. Thus, the deviation integrated value update deviation DVoxsi after time t2 corresponds to the “value corresponding to the deviation between the output value of the air-fuel ratio sensor and the deviation integrated value update target value”.

  As a result, the deviation integrated value SDVoxs after time t2 is updated in step 635 by sequentially integrating “a value corresponding to the deviation between the output value of the air-fuel ratio sensor and the deviation integrated value update target value”. That is, after the time t2, the integral term calculated in step 645 is calculated using the “value corresponding to the deviation between the output value of the air-fuel ratio sensor and the deviation integrated value update target value”. become.

  In addition, as described above, at time t2, the output value Voxs of the oxygen concentration sensor 68 is a value indicating lean (<target air-fuel ratio equivalent target value Voxsref). Therefore, after time t2, the deviation DVoxs calculated in step 625 can be guaranteed to be a large positive value. On the other hand, considering the relationship of “deviation integral value update target value Voxsrefi <target air-fuel ratio equivalent target value Voxsref”, the deviation integral value update deviation DVoxsi calculated in step 630 after time t2 is changed to step 625. The value is smaller than the deviation DVoxs calculated in the above. That is, after time t2, the deviation integrated value updating deviation DVoxsi is unlikely to be a large positive value.

  Thus, it can be ensured that at least the deviation DVoxs becomes a large positive value after the time t2. For this reason, at least the proportional term of the sub feedback correction amount Vafsfb (and hence the sub feedback correction amount Vafsfb itself) is a positive value, that is, a value for correcting the air-fuel ratio to the rich side. As a result, after time t2, the air-fuel ratio is controlled to a rich air-fuel ratio rather than the target air-fuel ratio abyfr (= theoretical air-fuel ratio).

  Further, after time t2, the CPU 81 that repeatedly executes the routine of FIG. 8 determines “No” when it proceeds to step 805, and proceeds to step 810. In addition, at this stage, the value of the flag ORE is “1” by the processing of the previous step 655.

  Accordingly, the CPU 81 makes a “Yes” determination at step 810 to proceed to step 845 to determine whether or not the output value Voxs of the oxygen concentration sensor 68 is smaller than the target air-fuel ratio equivalent target value Voxsref (constant) (ie, lean). It is determined whether or not the indicated value is reached.

  As described above, at the present time, the output value Voxs of the oxygen concentration sensor 68 is a value indicating lean (<Voxsref). Therefore, the CPU 81 makes a “Yes” determination at step 845 to proceed to step 850, where the oxygen storage amount change amount DOSA is set to the current intake air flow rate Ga measured by the air flow meter 61 and the above step 645. It is calculated according to the calculated sub feedback correction amount Vafsfb and the formula described in step 850. Similar to step 825 above, the value “0.23” is the mass proportion of oxygen contained in the air. Δt is the execution interval time of this routine (for example, 8 msec).

  As described above, after time t2, the sub feedback correction amount Vafsfb (%) is a positive value, and the air-fuel ratio is controlled to be richer than the target air-fuel ratio abyfr (= theoretical air-fuel ratio). Therefore, after time t2, the oxygen storage amount of the upstream catalyst 53 decreases. In addition, as the sub feedback correction amount Vafsfb (%) is larger, the air-fuel ratio becomes richer and the decrease rate of the oxygen storage amount of the upstream catalyst 53 becomes larger.

  Therefore, as described above, considering that the value “0.23 · Ga · Δt” represents the amount of oxygen (mass) flowing into the upstream catalyst 53 during the execution interval time Δt of this routine, the value “0.23 · Ga · Δt” “Δt · Vafsfb” (that is, the oxygen storage amount change amount DOSA in step 850) represents the degree of decrease in the oxygen storage amount of the upstream catalyst 53 due to the sub-feedback correction during the execution interval time Δt of this routine. Value. That is, the oxygen storage amount change amount DOSA in step 850 represents the decrease amount (> 0) of the increase in the oxygen storage amount OSA during the execution interval time Δt of this routine.

  Next, the CPU 81 proceeds to step 855 and subtracts the oxygen storage amount increase amount OSA obtained by subtracting the oxygen storage amount change amount DOSA (> 0) obtained in step 850 from the oxygen storage amount increase amount OSA at that time. Update (decrease).

  Next, the CPU 81 proceeds to step 860 to determine whether or not the increase amount OSA of the oxygen storage amount updated in step 855 is larger than “0”. Since the current time point is immediately after the increase amount OSA of the oxygen storage amount that has increased over time t1 to t2 starts to decrease, the increase amount OSA of the oxygen storage amount is larger than “0”. Accordingly, the CPU 81 makes a “Yes” determination at step 860 to proceed to step 895 to end the present routine tentatively.

  Such processing is repeatedly executed until time t3 when the increase amount OSA of the oxygen storage amount that decreases after time t2 becomes “0”. As a result, as shown in FIG. 9, the increase amount OSA of the oxygen storage amount gradually decreases at a speed according to the intake air flow rate Ga and the sub feedback correction amount Vafsfb between times t2 and t3.

  As a result, as shown in FIG. 9, the deviation integrated value update target value Voxsrefi determined using the table shown in FIG. 10 in step 660 increases as the oxygen storage amount increase OSA decreases. Then, it gradually approaches the target air-fuel ratio equivalent target value Voxsref (that is, it is changed to a value corresponding to a richer air-fuel ratio). Note that the value of the flag ORE is maintained at “1”.

  As described above, as shown in FIG. 9, the sub-feedback by the air-fuel ratio feedback control is performed during the time t3 when the increase amount OSA of the oxygen storage amount becomes “0” from the time t2 when returning from the FC (corresponding to the predetermined period). By the correction, the air-fuel ratio is controlled to a rich air-fuel ratio corresponding to the sub feedback correction amount Vafsfb. As a result, the increase amount OSA of the oxygen storage amount (accordingly, the oxygen storage amount of the upstream catalyst 53) decreases. As a result, the extent of the lean atmosphere in the upstream catalyst 53 gradually decreases, and the output value Voxs of the oxygen concentration sensor 68 gradually approaches the target value Voxsref corresponding to the target air-fuel ratio from the value indicating lean.

  As described above, between times t2 and t3, the deviation integrated value update target value Voxsrefi and the output value Voxs of the oxygen concentration sensor 68 change with the same tendency. In other words, the deviation integrated value updating deviation DVoxsi calculated in step 630 can be maintained at a small value between times t2 and t3.

  This means that the deviation integrated value SDVoxs updated in step 635 can be suppressed from increasing excessively as a value for correcting the air-fuel ratio to the rich side between times t2 and t3. means. In other words, between the times t2 and t3, even if the learning timing of the above step 705 comes and the learning value Learn of the deviation integral value is updated (learned), the above “mis-learning to the rich side of the deviation integral value” "Can be suppressed.

  Next, the case where the time t3 arrives will be described. At time t3, as shown in FIG. 9, the increased amount OSA of the reduced oxygen storage amount becomes “0”. This means that the lean atmosphere in the upstream catalyst 53 has been eliminated. In this case, the CPU 81 that repeatedly executes the routine of FIG. 8 determines “No” when it proceeds to step 860, proceeds to step 865, and changes the value of the flag ORE from “1” to “0”.

  Thereby, the CPU 81 that repeatedly executes the routine of FIG. 6 determines to be “Yes” again when it proceeds to step 615, and executes step 620. In other words, after time t3, the same processing as before time t1 described above is executed. That is, the deviation integrated value update target value Voxsrefi is maintained equal to the target air-fuel ratio equivalent target value Voxsref (constant), and the value of the flag ORE is maintained at “0”. That is, the “predetermined period after returning from the fuel cut control” corresponds to the period of the flag ORE = 1.

  It should be noted that the output value Voxs of the oxygen concentration sensor 68 is a value equal to or greater than the target air-fuel ratio equivalent output value Voxsref before the increase in the amount of oxygen storage OSA that has decreased reaches “0” (that is, in the state where the flag ORE = 1). When it is (ie, a value indicating rich), the CPU 81 executing the routine of FIG. 8 determines “No” when it proceeds to step 845 and proceeds to step 865. That is, also in this case, the flag ORE is changed from “1” to “0”, and after this time, the same processing as before the time t1 described above is executed.

  Thereby, the deviation integrated value SDVoxs becomes the oxygen concentration sensor 68 even though the lean atmosphere in the upstream catalyst 53 has already been eliminated due to the fact that the increase OSA of the oxygen storage amount is estimated to be large. Can be prevented from being updated using the deviation DVoxsi between the output value Voxs of the output and the target value Voxsrefi for updating the integral difference value corresponding to the leaner air / fuel ratio than the target air / fuel ratio abyfr (= theoretical air / fuel ratio) .

  The feedback correction value calculating means corresponds to the routine of FIG. 6, the air-fuel ratio control means corresponds to the routines of FIGS. 4 and 5, and the fuel cut control means corresponds to step 405 of FIG. The oxygen storage amount increase estimation means corresponds to the routine of FIG.

  As described above, according to the air-fuel ratio control apparatus of the embodiment of the present invention, “the output value Voxs of the oxygen concentration sensor 68 downstream of the upstream catalyst 53 and the target air-fuel ratio equivalent output value Voxsref (constant) The sub-feedback correction amount Vafsfb is calculated by performing PID processing on “deviation of”, and the air-fuel ratio is controlled to match the stoichiometric air-fuel ratio based on the sub-feedback correction amount Vafsfb.

  After the return from FC, “the increase amount OSA of the oxygen storage amount of the upstream catalyst 53 from the FC start time” decreases and returns to “0” (or the output value Voxs of the oxygen concentration sensor 68 is rich) In the PID process, the I process is replaced with the “deviation between the output value Voxs and the target air-fuel ratio equivalent target value Voxsref” only during the period (until the value indicates). Deviation between output value Voxs and deviation integration value update target value Voxsrefi (<Voxsref) (see FIG. 10) determined to increase according to the decrease in the amount of increase OSA of the oxygen storage amount. .

  Thus, while the flag ORE = 1, the deviation integrated value update target value Voxsrefi and the output value Voxs of the oxygen concentration sensor 68 change with the same tendency, so that “the output value Voxs and the deviation integrated value update target value Voxsrefi”. "Deviation from" can be kept small. Therefore, the deviation integral value SDVoxs, which is the integral value of the deviation, can be suppressed from excessively increasing as a value for correcting the air-fuel ratio to the rich side. As a result, even when the learning timing arrives while the flag ORE = 1 and the learning value Learn of the deviation integral value SDVoxs is updated (learned), the above-mentioned “mis-learning to the rich side of the deviation integral value” can be suppressed. .

  Further, at the time of return from FC, the upstream side catalyst 53 is in a lean atmosphere, so at least the above-mentioned “output value Voxs and target air-fuel ratio equivalent target value Voxsref are satisfied during the flag ORE = 1. It can be guaranteed that the “deviation” is a positive value. For this reason, at least the proportional term of the sub feedback correction amount Vafsfb (and hence the sub feedback correction amount Vafsfb itself) is a positive value, that is, a value for correcting the air-fuel ratio to the rich side. As a result, while the flag ORE = 1, the air-fuel ratio can be reliably controlled to be richer than the stoichiometric air-fuel ratio, and as a result, the lean atmosphere in the upstream catalyst 53 can be reliably eliminated.

  The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention. For example, in the above-described embodiment, while the flag ORE = 1, the deviation integrated value update target value Voxsrefi (<target air-fuel ratio equivalent target value Voxsref) is increased in accordance with the decrease in the oxygen storage amount increase OSA. Although determined (see FIG. 10), while the flag ORE = 1, the deviation integrated value update target value Voxsrefi (<target air-fuel ratio equivalent target value Voxsref) may be a constant value.

  Further, while the flag ORE = 1, the deviation integrated value update target value Voxsrefi (<target air-fuel ratio equivalent target value Voxsref) follows the actual output value Voxs of the oxygen concentration sensor 68 (with a minute delay). As described above, the determination may be made based on the actual output value Voxs.

  In the above embodiment, the air-fuel ratio feedback control is resumed immediately after returning from the FC. However, the air-fuel ratio feedback control is started from the time after the response delay time of the air-fuel ratio sensor 67 from the time when returning from the FC. May be configured to resume.

It is the figure which showed the outline of the air fuel ratio control apparatus (fuel injection amount control apparatus) which concerns on embodiment of this invention applied to the internal combustion engine. 3 is a graph showing the relationship between the output of the air-fuel ratio sensor shown in FIG. 1 and the air-fuel ratio. 2 is a graph showing the relationship between the output of the oxygen concentration sensor shown in FIG. 1 and the air-fuel ratio. 2 is a flowchart showing a fuel injection control routine executed by a CPU shown in FIG. 3 is a flowchart showing a routine executed by the CPU shown in FIG. 1 for calculating an air-fuel ratio feedback correction amount. 3 is a flowchart showing a routine executed by the CPU shown in FIG. 1 to calculate a sub feedback correction amount. It is the flowchart which showed the routine which CPU shown in FIG. 1 performs in order to update the learning value of a deviation integral value. FIG. 3 is a flowchart showing a routine executed by the CPU shown in FIG. 1 for calculating an increase in the oxygen storage amount of the upstream catalyst by fuel cut control. FIG. When fuel cut control is executed between times t1 and t2, changes in the increase in the amount of increase in the oxygen storage amount of the flag ORE, the target air-fuel ratio equivalent target value and the deviation integrated value update target value, and the upstream catalyst It is the time chart which showed an example. 3 is a graph showing a table that defines a relationship between an increase in the oxygen storage amount of the upstream catalyst and a deviation integral value update target value, which is referred to by the CPU shown in FIG. 1.

Explanation of symbols

25 ... Combustion chamber, 39 ... Injector, 53 ... Upstream catalyst, 61 ... Air flow meter, 67 ... Air-fuel ratio sensor, 68 ... Oxygen concentration sensor, 80 ... Electric controller, 81 ... CPU

Claims (6)

A catalyst having an oxygen storage function disposed in the exhaust passage of the internal combustion engine;
An air-fuel ratio sensor that is disposed in an exhaust passage downstream of the catalyst and outputs a value corresponding to an air-fuel ratio of gas flowing out from the catalyst;
Applied to an internal combustion engine with
The air-fuel ratio of the gas flowing into the catalyst is controlled based at least on a deviation integral value that is sequentially accumulated and updated by a value corresponding to the deviation between the output value of the air-fuel ratio sensor and the target value corresponding to the target air-fuel ratio. Feedback correction value calculating means for calculating a feedback correction value for performing,
Air-fuel ratio control means for performing feedback control so that the air-fuel ratio of the gas flowing into the catalyst matches the target air-fuel ratio based on the feedback correction value;
Fuel cut control means for performing fuel cut control for interrupting fuel injection according to the operating state of the internal combustion engine;
In an air-fuel ratio control apparatus for an internal combustion engine comprising:
The feedback correction value calculation means includes
In a predetermined period after returning from the fuel cut control, instead of a value corresponding to a deviation between the output value of the air-fuel ratio sensor and the target air-fuel ratio equivalent target value, the output value of the air-fuel ratio sensor, The deviation integral is obtained by sequentially integrating a value corresponding to a deviation integral value update target value, which is a target value corresponding to a leaner air / fuel ratio than the target air / fuel ratio, which is different from the target air / fuel ratio equivalent target value. An air-fuel ratio control apparatus for an internal combustion engine configured to update a value. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1,
The feedback correction value calculation means includes
An integral term calculated using the deviation integral value and a proportional term calculated using at least a value corresponding to a deviation between the output value of the air-fuel ratio sensor and the target air-fuel ratio equivalent target value. Configured to calculate the feedback correction value based on:
The feedback correction value calculation means includes
Also in the predetermined period after returning from the fuel cut control, the proportional term is calculated using the value itself corresponding to the deviation between the output value of the air-fuel ratio sensor and the target air-fuel ratio equivalent target value. An air-fuel ratio control apparatus for an internal combustion engine configured as described above. The air-fuel ratio control apparatus for an internal combustion engine according to claim 2,
The feedback correction value calculation means includes
From the fuel cut control start time, comprising an oxygen storage amount increase estimation means for estimating the increase of the oxygen storage amount from the fuel cut control start time,
The internal combustion engine is configured to change the deviation integrated value update target value according to a decrease in the estimated increase in the oxygen storage amount over the predetermined period after returning from the fuel cut control. Fuel ratio control device. The air-fuel ratio control apparatus for an internal combustion engine according to claim 3,
The feedback correction value calculation means includes
An air-fuel ratio control apparatus for an internal combustion engine configured to change the deviation integrated value update target value to a value corresponding to a richer air-fuel ratio as the increase in the estimated oxygen storage amount becomes smaller. In the air-fuel ratio control device for an internal combustion engine according to claim 3 or 4,
The feedback correction value calculation means includes
As the end of the predetermined period, the air-fuel ratio control of the internal combustion engine configured to use the time point when the estimated increase in the oxygen storage amount that decreases after returning from the fuel cut control becomes zero. apparatus. The air-fuel ratio control apparatus for an internal combustion engine according to claim 5,
The feedback correction value calculation means includes
When the output value of the air-fuel ratio sensor becomes a value indicating an air-fuel ratio richer than the target air-fuel ratio before the decrease in the estimated increase in oxygen storage amount becomes zero, the predetermined period As the final stage, the time when the output value of the air-fuel ratio sensor becomes a value indicating an air-fuel ratio richer than the target air-fuel ratio is used instead of the time when the estimated increase in the oxygen storage amount becomes zero. An air-fuel ratio control apparatus for an internal combustion engine configured to do so.

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