JP2006083724A - 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 of an internal combustion engine, surely avoiding interference of the air-fuel ratio feedback control based on the upstream side air-fuel ratio sensor output value upstream from a catalyst with the air-fuel ratio feedback control based on the downstream side air-fuel ratio sensor output value downstream from the catalyst. <P>SOLUTION: In this device, a value based on the upstream side air-fuel ratio sensor output value is processed by a band-pass filter A14 (BPF, passing permission frequency:ω1 to ω2) and a high-path filter A12 (HPF, passing permission frequency:ω2 or more), and the filtered values are input to a P controller not conducting integration processing to thereby perform the fuel injection quantity correction by the main feedback control. A value based on the downstream side air-fuel ratio sensor output value is processed by a low-pass filter A7 (LPF, passing permission frequency:ω1 or less) and the obtained value is input to a PI controller not conducting differential processing to thereby perform the fuel injection quantity correction by the sub-feedback control. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an upstream air-fuel ratio disposed in the upstream and downstream exhaust passages of a three-way catalyst (hereinafter also referred to simply as “catalyst”) disposed in an exhaust passage of an internal combustion engine. The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine that feedback-controls an air-fuel ratio of an air-fuel mixture supplied to the engine based on output values of the sensor and a downstream air-fuel ratio sensor.

  Conventionally, this type of air-fuel ratio control apparatus is widely known (see, for example, Patent Document 1). This air-fuel ratio control device (exhaust gas purification device) inputs the difference between the output value of the downstream air-fuel ratio sensor and a predetermined downstream target value to the sub-feedback controller as a sub-feedback input value, and the sub-feedback controller The feedback input value is subjected to proportional / integral / derivative processing (PID processing) to calculate a sub feedback correction amount.

In addition, this apparatus inputs the difference between the value obtained by correcting the output value of the upstream air-fuel ratio sensor with the calculated sub feedback correction amount and a predetermined upstream target value to the main feedback controller as the main feedback input value. The main feedback controller calculates the main feedback correction amount by performing proportional / integral processing (PI processing) on the main feedback input value. This device feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the engine by correcting the fuel injection amount with the calculated main feedback correction amount.
JP 2004-183585 A

  The disclosed apparatus is configured such that the main feedback input value is directly changed according to the value of the sub feedback correction amount that is the output value of the sub feedback controller. In other words, the main feedback controller and the sub feedback controller are arranged in series.

  Therefore, one of the main feedback control constant (proportional gain and integral gain) used for the main feedback controller and the sub feedback control constant (proportional gain, integral gain and derivative gain) used for the sub-feedback controller. The value on the other side has a strong influence on the adaptation.

  In other words, the respective feedback control constants cannot be matched independently for each feedback control loop (closed loop). Therefore, it is difficult to adapt the feedback control constants, and there is a problem that much labor is required when performing the adaptation.

  In order to cope with such a problem, it is considered preferable to arrange the main feedback controller and the sub feedback controller in parallel with respect to correction of the fuel injection amount. In this case, specifically, the sub-feedback controller calculates the sub-feedback correction amount by, for example, PID processing the difference between the downstream air-fuel ratio sensor output value and the predetermined downstream target value, and the main feedback controller The main feedback correction amount is calculated by, for example, PI processing the difference between the side air-fuel ratio sensor output value and the predetermined upstream target value. Then, the air-fuel ratio of the air-fuel mixture supplied to the engine is feedback controlled by directly correcting the fuel injection amount independently by the calculated main feedback correction amount and the sub feedback correction amount.

  As a result, the feedback control constants can be matched independently of each other for each feedback control loop, and the labor for matching the feedback control constants can be reduced.

  By the way, normally, when the air-fuel ratio of the inflowing exhaust gas is a lean air-fuel ratio, the catalyst stores the oxygen depleted from the nitrogen oxide by reducing nitrogen oxide (NOx) in the exhaust gas and flows in the same. When the air-fuel ratio of the exhaust gas is a rich air-fuel ratio, it has a so-called oxygen storage function that oxidizes unburned components such as HC and CO in the exhaust gas with the stored oxygen. With such an oxygen storage function, a relatively high frequency component in the air-fuel ratio fluctuation of the exhaust gas upstream of the catalyst, and a relatively low frequency in the air-fuel ratio fluctuation have a relatively small amplitude (deviation from the theoretical air-fuel ratio). Small low-frequency components tend to be completely absorbed and hardly appear as air-fuel ratio fluctuations in the exhaust gas downstream of the catalyst.

  On the other hand, the low-frequency component having a relatively low frequency and a relatively large amplitude in the air-fuel ratio fluctuation of the exhaust gas upstream of the catalyst is not completely absorbed by the oxygen storage function of the catalyst, and after a while, the air-fuel ratio of the exhaust gas downstream of the catalyst It tends to appear as a fluctuation. As a result, there are cases where the output value of the upstream air-fuel ratio sensor and the output value of the downstream air-fuel ratio sensor become values indicating the air-fuel ratio shifted in opposite directions with respect to the theoretical air-fuel ratio. In this case, the engine air-fuel ratio control (main feedback control) based on the main feedback correction amount and the engine air-fuel ratio control (sub feedback control) based on the sub feedback correction amount interfere with each other. Air-fuel ratio control cannot be performed.

  Such interference between the main feedback control and the sub feedback control can be avoided by setting the control frequency band of the main feedback control and the control frequency band of the sub feedback control regarding the air-fuel ratio fluctuation of the exhaust gas so as not to overlap each other. For this reason, a value after high-pass filtering the difference between the upstream air-fuel ratio sensor output value and the predetermined upstream target value is used as the main feedback input value, and the downstream air-fuel ratio sensor output value It is conceivable to use the value after the low-pass filter processing of the difference value from the downstream target value as the sub-feedback input value.

  From the above, the present applicant has already proposed the following air-fuel ratio control device (exhaust gas purification device) in Japanese Patent Application No. 2004-13225. This apparatus uses a high-pass filter (HPF) and a low-pass filter (LPF) having a common cutoff frequency ω 1 whose frequency-gain characteristics are shown in FIG.

  In this apparatus, a value after low-pass filtering the difference between the downstream air-fuel ratio sensor output value and a predetermined downstream target value is input to the sub-feedback controller as a sub-feedback input value, and the same sub-feedback controller uses the same value. The sub feedback input value is subjected to PID processing to calculate a sub feedback correction amount. As a result, a high frequency component equal to or higher than the cut-off frequency ω1 in the variation of the sub-feedback input value is attenuated, so that the control frequency band of the sub-feedback control can be a band equal to or lower than the cut-off frequency ω1.

  In addition, this device inputs a value after high-pass filtering the difference between the upstream air-fuel ratio sensor output value and a predetermined upstream target value as a main feedback input value to the main feedback controller. Then, the main feedback input value is PI processed to calculate the main feedback correction amount. As a result, the low frequency component below the cutoff frequency ω1 in the fluctuation of the main feedback input value is attenuated, so that the control frequency band of the main feedback control can be a band above the cutoff frequency ω1.

  This device feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the engine by directly directly correcting the fuel injection amount independently of the calculated main feedback correction amount and the sub feedback correction amount.

  As a result, the main feedback controller and the sub-feedback controller are arranged in parallel with respect to the correction of the fuel injection amount, so that it is possible to reduce the labor when adapting each feedback control constant. Further, since the control frequency band of the main feedback control and the control frequency band of the sub feedback control can be set so as not to overlap each other, it is considered that the interference between the main feedback control and the sub feedback control described above can be avoided.

  However, as a result of further research by the present applicant, in the already proposed air-fuel ratio control apparatus, a correction term (specifically, a proportional term) used to calculate a feedback correction amount that is an output value of the feedback controller. Paying attention to the values of (P term), integral term (I term), and differential term (D term), it has been found that interference between the main feedback control and the sub feedback control is not completely avoided.

  More specifically, FIG. 16 schematically shows an example of each gain characteristic of the correction term with respect to the frequency (hereinafter, also referred to as “input frequency”) in the fluctuation of the input value of the feedback controller that performs the PID processing. FIG. In the example shown in FIG. 16, the case where the gains of the P term, the I term, and the D term are all 0 dB at the reference frequency ωref is shown.

  As shown in FIG. 16, the gain of the P term is constant (0 dB) regardless of the frequency. That is, the value of the P term is not amplified or attenuated regardless of the input frequency. On the other hand, the gain of the I term increases as the input frequency decreases. That is, the value of the I term tends to be amplified as the input frequency is small and attenuated as the input frequency is large. The gain of the D term increases as the input frequency increases. That is, the value of the D term tends to be amplified as the input frequency is increased and attenuated as the input frequency is decreased.

  From the above, as shown in FIG. 15, when the main feedback input value after the high-pass filter (HPF) processing is performed by the main feedback controller is PI-processed, the gain characteristic of the P term (HPF + P term) is high-pass. While the gain characteristic of the filter can coincide with the gain characteristic of the I term (HPF + I term), the gain characteristic of the low pass filter can substantially coincide.

  Further, when the sub feedback input value after the low pass filter (LPF) process is performed by the sub feedback controller, the gain characteristic of the P term (LPF + P term) can coincide with the gain characteristic of the low pass filter, while D The gain characteristic of the term (LPF + D term) can substantially match the gain characteristic of the high-pass filter.

  That is, the control frequency band of the I term in the main feedback control that performs the PI control is the control frequency band of the sub feedback control (the P term and the I term) in which the PID control is performed (that is, the band of the cut-off frequency ω1 or less). Can match (overlap). In addition, the control frequency band of the D term in the sub-feedback control for performing PID control matches the control frequency band (that is, the band of the cut-off frequency ω1 or higher) of the main feedback control (in which the P term is performed) for PI control (overlapping). )

  In other words, the D term that can amplify the high frequency component above the cutoff frequency ω1 is used in the operation of the sub-feedback controller, and the I term that can amplify the low frequency component below the cutoff frequency ω1 is the main. Interference between the main feedback control and the sub-feedback control remains in both the frequency band above the cut-off frequency ω1 and the frequency band below the cut-off frequency ω1 due to being used in the calculation of the feedback controller. . This leads to hindering good engine air-fuel ratio control. Therefore, there is still room for improvement in the proposed air-fuel ratio control apparatus.

  Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to control the air-fuel ratio by feedback control based on the output value of the upstream air-fuel ratio sensor disposed upstream of the catalyst and the downstream of the catalyst. Another object of the present invention is to provide an air-fuel ratio control apparatus for an internal combustion engine that can reliably avoid interference with air-fuel ratio control by feedback control based on an output value of a downstream air-fuel ratio sensor disposed in the engine.

  The air-fuel ratio control apparatus according to the present invention is similar to the proposed air-fuel ratio control apparatus in that the output value of the upstream air-fuel ratio sensor, or the difference between the output value of the upstream air-fuel ratio sensor and the upstream target value. A first main feedback controller that calculates a first main feedback correction amount by inputting a value after high-pass filtering of the corresponding value as a first main feedback input value, and the calculated first main feedback correction Main feedback control means for feedback control of the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine by correcting the fuel injection amount injected by the fuel injection means by the amount, the output value of the downstream air-fuel ratio sensor, and the downstream target The low-pass filter value or the output value of the downstream air-fuel ratio sensor is low-pass filtered according to the degree of difference from the value. A sub-feedback controller that calculates a sub-feedback correction amount by inputting a value corresponding to the degree of difference between the filtered value and the downstream target value as a sub-feedback input value; Independently of the correction of the fuel injection amount, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is feedback controlled by correcting the fuel injection amount injected by the fuel injection means by the calculated sub-feedback correction amount. Sub-feedback control means.

  Here, the “upstream target value” and the “downstream target value” are preferably set to values corresponding to the stoichiometric air-fuel ratio, and these values are set so that the corresponding air-fuel ratios are equal to each other. It is preferable to set.

  The “value according to the degree of difference between the sensor output value and the target value” is, for example, a deviation between the sensor output value and the target value, or a detected air-fuel ratio (actual air-fuel ratio) corresponding to the sensor output value. And the target air-fuel ratio corresponding to the target value, the cylinder intake air amount divided by the detected air-fuel ratio corresponding to the sensor output value, the actual cylinder fuel supply amount and the cylinder intake air amount It is a deviation from the target in-cylinder fuel supply amount that is a value divided by the target air-fuel ratio corresponding to the target value, and is not limited to these.

  Further, the two values to be subjected to the high-pass filter process (that is, a value corresponding to the degree of difference between the output value of the upstream air-fuel ratio sensor and the output value of the upstream air-fuel ratio sensor and the upstream target value). ), And the above two values used as sub-feedback input values (i.e., values obtained by low-pass filtering a value corresponding to the degree of difference between the output value of the downstream air-fuel ratio sensor and the downstream target value), The combination of the value after the low-pass filter processing of the output value of the downstream air-fuel ratio sensor and the value corresponding to the degree of difference between the downstream target value may be any combination.

  Furthermore, it is preferable that the cut-off frequency of the high-pass filter process by the main feedback control unit and the cut-off frequency of the low-pass filter process by the sub-feedback control unit are the same.

  According to this, the (basic) fuel injection amount determined according to the operating state of the internal combustion engine (for example, the rotational speed of the internal combustion engine, the throttle valve opening, etc.) is determined by the main feedback correction amount and the sub feedback correction amount, respectively. Fuel of the (final) fuel injection amount after being independently corrected is injected by the fuel injection means, and as a result, the air-fuel ratio of the air-fuel mixture supplied to the engine is feedback controlled (main feedback control and sub feedback control). The Therefore, as in the proposed air-fuel ratio control device, the effort for adapting the feedback control constants can be reduced by arranging the main feedback controller and the sub feedback controller in parallel with the internal combustion engine.

  The first main feedback input value input to the first main feedback controller is a value obtained by attenuating a low frequency component equal to or lower than the cut-off frequency of the high-pass filter processing, while being input to the sub feedback controller. The feedback input value is a value obtained by attenuating a high frequency component equal to or higher than the cutoff frequency of the low pass filter process. Therefore, like the proposed air-fuel ratio control apparatus, the control frequency band as the entire main feedback control and the control frequency band as the entire sub feedback control can be set so as not to overlap each other.

  In addition, in the air-fuel ratio control apparatus according to the present invention, the first main feedback controller performs any one of proportional processing, differential processing, and proportional / differential processing only with respect to the first main feedback input value. By doing so, the first main feedback correction amount is calculated. In other words, the integration process for the first main feedback input value is not executed in the first main feedback controller.

  Therefore, the integral term (I term) that can amplify the low frequency component already attenuated in the fluctuation of the first main feedback input value is used to calculate the first main feedback correction amount that is the output value of the first main feedback controller. Not used. As a result, interference between the main feedback control and the sub-feedback control can be completely avoided in a frequency band equal to or lower than the cutoff frequency of the low-pass filter processing (thus, the control frequency band as the entire sub-feedback control).

  Similarly, in the air-fuel ratio control apparatus according to the present invention, the sub-feedback controller performs any one of the proportional processing, only the integration processing, and only the proportional / integration processing on the sub-feedback input value. A sub feedback correction amount is calculated. In other words, the sub-feedback controller does not execute differentiation processing on the sub-feedback input value.

  Therefore, the differential term (D term) that can amplify the already attenuated high frequency component in the fluctuation of the sub feedback input value is not used for calculating the sub feedback correction amount that is the output value of the sub feedback controller. As a result, interference between the main feedback control and the sub-feedback control can be completely avoided even in a frequency band equal to or higher than the cut-off frequency of the high-pass filter processing (accordingly, the control frequency band as the entire main feedback control). As described above, according to the air-fuel ratio control apparatus of the present invention, the interference between the main feedback control and the sub feedback control can be completely avoided over the entire frequency band. Fuel ratio control can be achieved.

  In the air-fuel ratio control apparatus according to the present invention, the main feedback control means is configured to adjust the output value of the upstream air-fuel ratio sensor or the difference between the output value of the upstream air-fuel ratio sensor and the upstream target value. A second main feedback controller for calculating a second main feedback correction amount by inputting a value after bandpass filtering of the corresponding value as a second main feedback input value, and calculating the calculated first main feedback The air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is feedback-controlled by correcting the fuel injection amount injected by the fuel injection means based on the correction amount and the calculated second main feedback correction amount. And the second main feedback controller sets the second main feedback input value to To proportional processing only, the differential processing only, and proportional-derivative processing only, it is preferably configured to calculate the second main feedback correction amount by performing either.

  In this case, the cut-off frequency of the high-pass filter processing by the main feedback control means is the same as the cut-off frequency on the high frequency side of the band-pass filter processing by the main feedback control means, and the main feedback control means More preferably, the cut-off frequency on the low frequency side of the band-pass filter processing is the same as the cut-off frequency of the low-pass filter processing by the sub-feedback control means.

  According to this, for example, as described above, the cut-off frequency on the low frequency side of the bandpass filter process matches the cut-off frequency of the low-pass filter process, and the cut-off frequency on the high frequency side of the bandpass filter process is When the gain characteristics of each filter are set so as to match the cutoff frequency of the high-pass filter processing, the interference between the main feedback control and the sub feedback control is completely avoided over the entire frequency band as described above. obtain.

  In addition, in this case, the control frequency band of the main feedback control as a whole is assigned to the band shared by the bandpass filter (accordingly, the band shared by the second main feedback controller) and the band shared by the highpass filter (accordingly, the first main feedback control It can be further divided into (bands shared by the feedback controller).

  As a result, in the control frequency band of the main feedback control as a whole, it is possible to improve the degree of design freedom regarding the gain characteristics of the filter, thereby increasing the frequency higher than the cut-off frequency of the low-pass filter in the air-fuel ratio fluctuation of exhaust gas. The degree of freedom in designing the main feedback control system with respect to frequency components is improved.

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

(First embodiment)
FIG. 1 shows a schematic configuration of a system in which the air-fuel ratio control apparatus according to the first embodiment is applied to a spark ignition type multi-cylinder (four-cylinder) internal combustion engine 10. The internal combustion engine 10 includes a cylinder block unit 20 including a cylinder block, a cylinder block lower case, an oil pan, and the like, a cylinder head unit 30 fixed on the cylinder block unit 20, and a gasoline mixture in the cylinder block unit 20. And an exhaust system 50 for releasing exhaust gas from the cylinder block 20 to the outside.

  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 continuously changes the phase angle of the intake camshaft. The variable intake timing device 33, the actuator 33 a of the variable intake timing device 33, the exhaust port 34 communicating with the combustion chamber 25, the exhaust valve 35 that opens and closes the exhaust port 34, the exhaust camshaft 36 that drives the exhaust valve 35, and the spark plug 37 And an igniter 38 including an ignition coil that generates a high voltage to be applied to the spark plug 37, and an injector (fuel injection means) 39 for injecting fuel into the intake port 31.

  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. From the throttle valve 43 that makes the opening cross-sectional area of the intake passage variable, the throttle valve actuator 43a comprising a DC motor that constitutes the throttle valve driving means, the swirl control valve (hereinafter referred to as "SCV") 44, and the DC motor. The SCV actuator 44a is provided.

  The exhaust system 50 includes an exhaust manifold 51 that communicates with the exhaust port 34, and an exhaust pipe (exhaust pipe) that is connected to the exhaust manifold 51 (actually, a collection portion of the exhaust manifolds 51 that communicate with each exhaust port 34). ) 52, an upstream three-way catalyst 53 (also referred to as an upstream catalytic converter or a start catalytic converter) disposed (interposed) in the exhaust pipe 52, hereinafter referred to as a “first catalyst 53”. ), And a three-way catalyst 54 on the downstream side of the exhaust pipe 52 downstream of the first catalyst 53 (because it is disposed below the floor of the vehicle, an under-floor catalytic converter) However, it is hereinafter referred to as “second catalyst 54”). The exhaust port 34, the exhaust manifold 51, and the exhaust pipe 52 constitute an exhaust passage.

  On the other hand, this system includes a hot-wire air flow meter 61, a throttle position sensor 62, a cam position sensor 63, a crank position sensor 64, a water temperature sensor 65, an exhaust passage upstream of the first catalyst 53 (in this example, each of the above exhaust manifolds). The air-fuel ratio sensor 66 (hereinafter referred to as “upstream air-fuel ratio sensor 66”) disposed in the collecting portion 51), the exhaust downstream of the first catalyst 53 and upstream of the second catalyst 54. An air-fuel ratio sensor 67 (hereinafter referred to as “downstream air-fuel ratio sensor 67”) disposed in the passage and an accelerator opening sensor 68 are provided.

  The hot-wire air flow meter 61 outputs a voltage Vg corresponding to the mass flow rate per unit time of the intake air flowing through the intake pipe 41. The relationship between the output Vg of the air flow meter 61 and the measured intake air amount (flow rate) Ga is as shown in FIG. The throttle position sensor 62 detects the opening of the throttle valve 43 and outputs a signal representing the throttle valve opening TA. The cam position sensor 63 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 64 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 65 detects the temperature of the cooling water of the internal combustion engine 10 and outputs a signal representing the cooling water temperature THW.

  The upstream air-fuel ratio sensor 66 is a limiting current type oxygen concentration sensor, and outputs a current corresponding to the air-fuel ratio A / F as shown in FIG. 3, and an output value vabyfs which is a voltage corresponding to this current. In particular, when the air-fuel ratio is the stoichiometric air-fuel ratio, the output value vabyfs becomes the value vstoich. As is apparent from FIG. 3, the upstream air-fuel ratio sensor 66 can accurately detect the air-fuel ratio A / F over a wide range.

  The downstream air-fuel ratio sensor 67 is an electromotive force type (concentration cell type) oxygen concentration sensor, and outputs an output value Voxs that is a voltage that suddenly changes in the vicinity of the theoretical air-fuel ratio, as shown in FIG. ing. More specifically, the downstream air-fuel ratio sensor 67 is approximately 0.1 (V) when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and is approximately 0.1 when the air-fuel ratio is richer than the stoichiometric air-fuel ratio. When 9 (V) and the air-fuel ratio is the stoichiometric air-fuel ratio, a voltage of 0.5 (V) is output. The accelerator opening sensor 68 detects an operation amount of the accelerator pedal 81 operated by the driver, and outputs a signal representing the operation amount Accp of the accelerator pedal 81.

  The electric control device 70 includes a CPU 71 connected by a bus, a routine (program) executed by the CPU 71, a table (look-up table, map), a ROM 72 in which constants and the like are stored in advance, and the CPU 71 temporarily stores data as necessary. This is a microcomputer comprising a RAM 73 for storing data, a backup RAM 74 for storing data while the power is turned on and holding the stored data while the power is shut off, an interface 75 including an AD converter, and the like. . The interface 75 is connected to the sensors 61 to 68, supplies signals from the sensors 61 to 68 to the CPU 71, and in response to instructions from the CPU 71, the actuator 33a, the igniter 38, the injector 39, and the throttle of the variable intake timing device 33. Drive signals are sent to the valve actuator 43a and the SCV actuator 44a.

(Outline of air-fuel ratio feedback control)
Next, an outline of feedback control of the air-fuel ratio of the air-fuel mixture supplied to the engine (hereinafter sometimes simply referred to as “engine air-fuel ratio”) performed by the air-fuel ratio control apparatus configured as described above will be described. To do.

  The first catalyst 53 (the same applies to the second catalyst 54) oxidizes HC and CO and reduces NOx when the air-fuel ratio of the gas flowing into the first catalyst 53 is the stoichiometric air-fuel ratio, Purifies these harmful components with high efficiency. Further, the first catalyst 53 has a function of storing / releasing oxygen (oxygen storage function, oxygen storage / release function), and by this oxygen storage / release function, the air-fuel ratio has shifted from the stoichiometric air-fuel ratio to some extent. However, HC, CO, and NOx can be purified. That is, when the air-fuel ratio of the engine becomes lean and the gas flowing into the first catalyst 53 contains a large amount of NOx, the first catalyst 53 deprives the NOx of oxygen molecules and occludes the oxygen molecules and stores the NOx. Reduce, thereby purifying NOx. When the air-fuel ratio of the engine becomes rich and the gas flowing into the first catalyst 53 contains a large amount of HC and CO, the three-way catalyst gives (releases) the oxygen molecules stored therein. Oxidizes, thereby purifying HC and CO.

  Therefore, in order to efficiently purify a large amount of HC and CO into which the first catalyst 53 continuously flows, the first catalyst 53 must store a large amount of oxygen. In order to efficiently purify a large amount of inflowing NOx, the first catalyst 53 must be in a state where it can sufficiently store oxygen. From the above, the purification capacity of the first catalyst 53 depends on the maximum oxygen amount (maximum oxygen storage amount) that the first catalyst 53 can store.

  On the other hand, a three-way catalyst such as the first catalyst 53 deteriorates due to poisoning due to lead, sulfur, or the like contained in the fuel, or heat applied to the catalyst, and accordingly, the maximum oxygen storage amount gradually decreases. Even in the case where the maximum oxygen storage amount is reduced in this way, in order to continuously suppress the emission emission amount, the air-fuel ratio of the gas discharged from the first catalyst 53 (therefore flowing into the first catalyst 53). It is necessary to control the average air-fuel ratio of the gas to be very close to the stoichiometric air-fuel ratio.

  Therefore, the air-fuel ratio control apparatus according to the present embodiment is configured so that the output value of the downstream air-fuel ratio sensor 67 basically matches the value (0.5 (V)) corresponding to the theoretical air-fuel ratio. Feedback control of the air-fuel ratio of the engine according to the output value vabyfs of the sensor 66 (ie, the air-fuel ratio upstream of the first catalyst) and the output value Voxs of the downstream-side air-fuel ratio sensor 67 (ie, air-fuel ratio downstream of the first catalyst). To do.

  More specifically, this air-fuel ratio control device (hereinafter also referred to as “this device”) includes each means of A1 to A16 as shown in FIG. 5 which is a functional block diagram thereof. It is configured to include. Hereinafter, each means will be described with reference to FIG.

<Calculation of basic fuel injection amount>
First, the in-cylinder intake air amount calculation means A1 is a table in which the intake air flow rate Ga measured by the air flow meter 61, the engine speed NE obtained based on the output of the crank position sensor 64, and the ROM 72 are stored. Based on MapMc, in-cylinder intake air amount Mc, which is the intake air amount of the cylinder that reaches the current intake stroke, is obtained.

  The upstream target air-fuel ratio setting means A2 corresponds to the target value (upstream target value) of the upstream air-fuel ratio sensor output based on the engine speed NE that is the operating state of the internal combustion engine 10, the throttle valve opening TA, and the like. An upstream target air-fuel ratio abyfr (k) to be determined is determined. Here, the subscript (k) indicates a value for the current intake stroke (hereinafter, the same applies to other physical quantities). The upstream target air-fuel ratio abyfr (k) is set to the stoichiometric air-fuel ratio except for special cases after the warm-up of the internal combustion engine 10, for example. Further, the upstream target air-fuel ratio abyfr is stored in the RAM 73 while corresponding to the intake stroke of each cylinder.

  The basic fuel injection amount calculation means A3 uses the in-cylinder intake air amount Mc (k) obtained by the in-cylinder intake air amount calculation means A1 as the upstream target air-fuel ratio abyfr () set by the upstream target air-fuel ratio setting means A2. By dividing by k), the basic fuel injection amount Fbase with respect to the current intake stroke for setting the air-fuel ratio of the engine to the upstream target air-fuel ratio abyfr (k) is obtained.

  As described above, the present apparatus obtains the basic fuel injection amount Fbase using the cylinder intake air amount calculation means A1, the upstream target air-fuel ratio setting means A2, and the basic fuel injection amount calculation means A3.

<Calculation of fuel injection amount>
The fuel injection amount calculating means A4 adds a sub feedback correction coefficient KFisub (sub feedback correction amount) described later and a main feedback correction coefficient KFimain (main feedback) described later to the basic fuel injection amount Fbase obtained by the basic fuel injection amount calculating means A3. The (final) fuel injection amount Fi is obtained based on the following equation (1).

Fi = Fbase, KFisub, KFimain (1)

  In this way, the fuel injection amount Fi obtained by correcting the basic fuel injection amount Fbase by the main feedback correction coefficient KFimain and the sub feedback correction coefficient KFisub by the fuel injection amount calculation means A4 in this way. Is injected by the injector 39 into the cylinder that reaches this intake stroke.

<Sub feedback control>
The downstream target value setting means A5 is similar to the upstream target air-fuel ratio setting means A2 described above, and is based on the engine speed NE, which is the operating state of the internal combustion engine 10, the throttle valve opening TA, and the like. The downstream target value Voxsref, which is the output target value, is determined. The downstream target value Voxsref is set to 0.5 (V), which is a value corresponding to the stoichiometric air-fuel ratio except for special cases, for example, after the warm-up of the internal combustion engine 10 is finished (see FIG. 4). reference.). In this example, the downstream target value Voxsref is set so that the downstream target air-fuel ratio corresponding to the downstream target value Voxsref always matches the upstream target air-fuel ratio abyfr (k).

  Based on the following equation (2), the output deviation amount calculating means A6 calculates the current output value of the downstream air-fuel ratio sensor 67 from the current downstream target value Voxsref set by the downstream target value setting means A5. The output deviation amount DVoxs is obtained by subtracting Voxs. This output deviation amount DVoxs corresponds to a value corresponding to the degree of difference between the output value Voxs of the downstream air-fuel ratio sensor 67 and the downstream target value Voxsref.

DVoxs = Voxsref-Voxs (2)

  The low-pass filter A7 is a first-order filter as shown in the following formula (3) in which the characteristics are expressed using the Laplace operator s. In the following formula (3), τlow is a time constant of the low-pass filter A7. The frequency-gain characteristic of the low-pass filter A7 is as shown in FIG. As shown in FIG. 6, the low-pass filter A7 passes the high-frequency component by attenuating the high-frequency component equal to or higher than the cutoff frequency ω1 (= 1 / τlow) in the fluctuation of the input value (input signal). Is substantially prohibited.

1 / (1 + τlow · s) (3)

  The low-pass filter A7 is a value after the value of the output deviation amount DVoxs obtained by the output deviation amount calculating means A6 is input and the value of the output deviation amount DVoxs is subjected to low-pass filter processing according to the above equation (3). Output the output deviation DVoxslow after passing the low-pass filter. Therefore, the output deviation amount DVoxslow after passing through the low-pass filter is a value after low-pass filter processing is performed according to the degree of difference between the output value Voxs of the downstream air-fuel ratio sensor 67 and the downstream target value Voxsref.

  The PI controller A8 (sub-feedback controller) performs sub-feedback correction based on the following equation (4) by performing proportional / integral processing (PI processing) on the output deviation amount DVoxslow after passing the low-pass filter, which is the output value of the low-pass filter A7. A sub feedback correction coefficient KFisub (> 0) is obtained as a quantity.

KFisub = (Kp / DVoxslow + Ki / SDVoxslow) +1 (4)

  In the above equation (4), Kp is a preset proportional gain (proportional constant), and Ki is a preset integral gain (integral constant). SDVoxslow is a time integral value of the output deviation amount DVoxslow after passing through the low-pass filter.

  In this way, the present apparatus outputs the output deviation after passing through the low-pass filter, which is a value after low-pass filtering the value corresponding to the degree of difference between the output value Voxs of the downstream air-fuel ratio sensor 67 and the downstream target value Voxsref. By inputting the amount DVoxslow (sub feedback input value) to the PI controller A8, a sub feedback correction coefficient KFisub is obtained, and by multiplying the basic fuel injection amount Fbase by the sub feedback correction coefficient KFisub, the main feedback control described later is performed. The sub-feedback control is executed by correcting the basic fuel injection amount Fbase independently of the correction of the basic fuel injection amount Fbase (by the main feedback correction coefficient KFimain).

  For example, if the average air-fuel ratio of the engine is lean and the output value Voxs of the downstream air-fuel ratio sensor 67 indicates a value corresponding to an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio, the output deviation amount calculating means A6 Since the output deviation amount DVoxs obtained by the above equation (and hence the output deviation amount DVoxslow after passing through the low-pass filter) becomes a positive value (see FIG. 4), the sub feedback correction coefficient KFisub obtained by the PI controller A8 is “1”. Greater value. Thus, the (final) fuel injection amount Fi obtained by the fuel injection amount calculation means A4 is controlled to be larger than the basic fuel injection amount Fbase so that the air-fuel ratio of the engine becomes rich.

  Conversely, when the average air-fuel ratio of the engine is rich, the downstream air-fuel ratio sensor output value Voxs shows a value corresponding to the air-fuel ratio that is richer than the stoichiometric air-fuel ratio. Since the output deviation amount DVoxslow after passing through the low-pass filter becomes a negative value, the sub feedback correction coefficient KFisub becomes a value smaller than “1” (and a value larger than “0”). Thus, the fuel injection amount Fi is controlled to be smaller than the basic fuel injection amount Fbase so that the air-fuel ratio of the engine becomes lean.

  Further, since the PI controller A8 executes integration processing (that is, the integral (I) term “Ki · SDVoxslow” is used), the output deviation amount DVoxs may become zero when the engine is in a steady state. Guaranteed. In other words, the steady deviation between the downstream target value Voxsref and the output value Voxs of the downstream air-fuel ratio sensor 67 becomes zero. In the steady state, when the output deviation amount DVoxs becomes zero, the proportional term Kp · DVoxslow becomes “0”, so the sub-feedback correction coefficient KFisub is a value obtained by adding “1” to the value of the integral term Ki · SDVoxslow. It becomes. By multiplying this value by the basic combustion injection amount Fbase, the error of the injector 39 (the difference between the commanded fuel injection amount Fi and the actual fuel injection amount), the error of the air flow meter 61 (intake air) While the flow rate measurement value Ga and the actual intake air flow rate are compensated for, the air-fuel ratio downstream of the first catalyst 53 (and hence the air-fuel ratio of the engine) in the steady state is the downstream side corresponding to the downstream target value Voxsref. It converges to the target air-fuel ratio (that is, the theoretical air-fuel ratio). The fuel injection amount calculation means A4, the downstream target value setting means A5, the output deviation amount calculation means A6, the low pass filter A7, and the PI controller A8 correspond to the sub feedback control means.

<Main feedback control>
As described above, the first catalyst 53 has the oxygen storage function. Accordingly, a relatively high frequency component (for example, the cut-off frequency ω1 or higher of the low-pass filter A7) in the air-fuel ratio fluctuation of the exhaust gas upstream of the first catalyst 53 and a relatively low frequency (for example, the same) The low frequency component having a relatively small amplitude (deviation from the theoretical air-fuel ratio) that is equal to or lower than the cutoff frequency ω 1 is completely absorbed by the oxygen storage function of the first catalyst 53, thereby There is a tendency not to appear as air-fuel ratio fluctuations in the exhaust gas downstream. Therefore, for example, when the internal combustion engine 10 is in a transient operation state and the air-fuel ratio of the exhaust gas greatly fluctuates at a high frequency equal to or higher than the cut-off frequency ω1, the air-fuel ratio fluctuation is related to the output value of the downstream air-fuel ratio sensor 67. Since it does not appear as Voxs, air-fuel ratio control (that is, compensation for sudden change of the air-fuel ratio in the transient operation state) for air-fuel ratio fluctuations of the cutoff frequency ω1 or higher cannot be achieved by sub-feedback control. Therefore, in order to reliably perform compensation for a sudden change in the air-fuel ratio in the transient operation state, it is necessary to perform main feedback control that is air-fuel ratio control based on the output value vabyfs of the upstream air-fuel ratio sensor 66.

  On the other hand, a low frequency component having a relatively low frequency (for example, the cut-off frequency ω1 or less) and a relatively large amplitude in the air-fuel ratio fluctuation of the exhaust gas upstream of the first catalyst 53 is an oxygen occlusion of the first catalyst 53. The function is not completely absorbed and tends to appear as an air-fuel ratio fluctuation of the exhaust gas downstream of the first catalyst 53 with a slight delay. As a result, there may occur a case where the output value vabyfs of the upstream air-fuel ratio sensor 66 and the output value Voxs of the downstream air-fuel ratio sensor 67 become values indicating the air-fuel ratio shifted in the opposite directions with respect to the theoretical air-fuel ratio. . Therefore, in this case, if the main feedback control and the sub feedback control are performed at the same time, the two air-fuel ratio controls interfere with each other, so that good engine air-fuel ratio control cannot be performed.

  From the above, a frequency component that can appear as a variation in the air-fuel ratio downstream of the first catalyst 53 in the variation in the output value vabyfs of the upstream air-fuel ratio sensor 66 (in this example, a low frequency equal to or lower than the cut-off frequency ω1). If main feedback control is performed using the upstream air-fuel ratio sensor output value vabyfs after the component) is cut, it is considered that interference between the main feedback control and the sub feedback control can be avoided. In addition, it is possible to reliably achieve compensation for a sudden change in the air-fuel ratio in the transient operation state.

  Therefore, as shown in FIG. 5 described above, the present apparatus executes main feedback control using each means A9 to A16. Hereinafter, each means will be described with reference to FIG.

  First, the table conversion means A9 is a table that defines the output value vabyfs of the upstream air-fuel ratio sensor 66 and the relationship between the upstream air-fuel ratio sensor output value vabyfs and the air-fuel ratio A / F shown in FIG. Based on the above, the currently detected air-fuel ratio abyfs by the upstream air-fuel ratio sensor 66 is obtained.

  The target air-fuel ratio delay means A10 is N strokes (N intake strokes) before the present time out of the upstream target air-fuel ratio abyfr obtained for each intake stroke by the upstream target air-fuel ratio setting means A2 and stored in the RAM 73. The upstream target air-fuel ratio abyfr for the cylinder that has reached the intake stroke is read from the RAM 73 and set as the upstream target air-fuel ratio abyfr (kN). Here, the value N differs depending on the displacement of the internal combustion engine 10, the distance from the combustion chamber 25 to the upstream air-fuel ratio sensor 66, and the like.

  As described above, the upstream target air-fuel ratio abyfr (kN) N strokes before the current stroke is used until the air-fuel mixture burned in the combustion chamber 25 reaches the upstream air-fuel ratio sensor 66. This is because time L corresponding to N stroke is required.

  The upstream air-fuel ratio deviation calculating means A11 is set by the target air-fuel ratio delay means A10 from the currently detected air-fuel ratio abyfs by the upstream air-fuel ratio sensor 66 obtained by the table conversion means A9 based on the following equation (5). The upstream air-fuel ratio deviation Dabyf is obtained by subtracting the upstream target air-fuel ratio abyfr (kN) N strokes before the current time. The upstream air-fuel ratio deviation Dabyf is an amount representing the difference between the actual air-fuel ratio and the target air-fuel ratio at the time point N strokes before, and the output value vabyfs of the upstream air-fuel ratio sensor 66, the upstream target value, It corresponds to a value corresponding to the degree of difference.

Dabyf ＝ abyfs−abyfr (k-N) (5)

  The high-pass filter A12 is a first-order filter as shown in the following formula (6) in which the characteristics are expressed using the Laplace operator s. In the following formula (6), τhi is a time constant of the high-pass filter A12. The frequency-gain characteristic of the high-pass filter A12 is as shown in FIG. As shown in FIG. 6, the high-pass filter A12 substantially inhibits the passage of the low frequency component by attenuating the low frequency component below the cutoff frequency ω2 (= 1 / τhi).

1-1 / (1 + τhi · s) (6)

  The high-pass filter A12 receives the value of the upstream air-fuel ratio deviation Dabyf obtained by the upstream air-fuel ratio deviation calculating means A11, and calculates the value of the upstream air-fuel ratio deviation Dabyf according to the above equation (6). An upstream air-fuel ratio deviation Dabyfhi after passing the high-pass filter, which is a value after processing, is output. Therefore, the upstream air-fuel ratio deviation Dabyfhi after passing through the high-pass filter is a value after high-pass filter processing is performed according to the degree of difference between the output value vabyfs of the upstream air-fuel ratio sensor 66 and the upstream target value.

  The P controller A13 (first main feedback controller) performs proportional processing (P processing) on the upstream side air-fuel ratio deviation Dabyfhi after passing through the high-pass filter, which is the output value of the high-pass filter A12, based on the following equation (7). 1 Determine the main feedback correction amount DFihi. In the following equation (7), Khi is a preset proportional gain (proportional constant).

DFihi ＝ Khi ・ Dabyfhi ・ ・ ・ (7)

  The bandpass filter A14 is a first-order filter as shown in the following formula (8) in which the characteristics are expressed using the Laplace operator s. The frequency-gain characteristic of the bandpass filter A14 is as shown in FIG. As shown in FIG. 6, the bandpass filter A14 attenuates a low frequency component equal to or lower than the cutoff frequency ω1 (= 1 / τlow) on the low frequency side, which is equal to the cutoff frequency of the lowpass filter A7, and the highpass filter. A high frequency component equal to or higher than the cutoff frequency ω2 (= 1 / τhi) on the high frequency side equal to the cutoff frequency of A12 is attenuated. Thereby, the bandpass filter A14 substantially prohibits the passage of the low frequency component and substantially prohibits the passage of the high frequency component. In other words, the bandpass filter A14 substantially allows only a frequency component having a frequency not lower than the cut-off frequency ω1 on the low frequency side and not higher than the cut-off frequency ω2 on the high frequency side to pass.

1 / (1 + τhi · s) + (1-1 / (1 + τlow · s)) (8)

  The bandpass filter A14 inputs the value of the upstream air-fuel ratio deviation Dabyf obtained by the upstream air-fuel ratio deviation calculating means A11, and band the value of the upstream air-fuel ratio deviation Dabyf according to the above equation (8). An upstream air-fuel ratio deviation Dabyfba after passing the bandpass filter, which is a value after the pass filter processing, is output. Therefore, the upstream air-fuel ratio deviation Dabyfba after passing the band-pass filter is a value after band-pass filtering is performed on a value corresponding to the degree of difference between the output value vabyfs of the upstream air-fuel ratio sensor 66 and the upstream target value. .

  The P controller A15 (second main feedback controller) performs proportional processing (P processing) on the upstream side air-fuel ratio deviation Dabyfba after passing through the bandpass filter, which is an output value of the bandpass filter A14, based on the following equation (9). To obtain the second main feedback correction amount DFiba. In the following equation (9), Kba is a preset proportional gain (proportional constant).

DFiba ＝ Kba ・ Dabyfba ・ ・ ・ (9)

  The main feedback correction coefficient calculation means A16 uses the first main feedback correction amount DFihi and the second main feedback correction amount DFiba to calculate the main feedback correction coefficient KFimain (> 0) based on the following equation (10). Ask. The main feedback correction coefficient KFimain is used when the fuel injection amount Fi is obtained by the fuel injection amount calculation means A4 as described above.

KFimain = DFihi + DFiba + 1 (10)

  In this way, the present apparatus connects the main feedback control circuit and the sub feedback control circuit in parallel for correcting the basic fuel injection amount Fbase. In addition, the present apparatus is a high-pass filter that is a value obtained by performing high-pass filtering on a value corresponding to the degree of difference between the output value vabyfs of the upstream air-fuel ratio sensor 66 and the upstream target value corresponding to the upstream target air-fuel ratio abyfr. An upstream air-fuel ratio deviation Dabyfhi (first main feedback input value) after passing through the filter is input to the P controller A13 to obtain the first main feedback correction amount DFihi, and a value corresponding to the above difference is bandpass filtered. The second main feedback correction amount DFiba is obtained by inputting the upstream air-fuel ratio deviation Dabyfba (second main feedback input value) after passing through the band-pass filter, which is the value after the adjustment, to the P controller A15.

  Then, the present apparatus obtains a main feedback correction coefficient KFimain using the first main feedback correction amount DFihi and the second main feedback correction amount DFiba, and multiplies the basic fuel injection amount Fbase by the main feedback correction coefficient KFimain. Thus, the main fuel injection amount Fbase is corrected independently of the correction of the basic fuel injection amount Fbase by the sub feedback control, and the main feedback control is executed.

  For example, when the air-fuel ratio of the engine suddenly changes and becomes lean, the detected air-fuel ratio abyfs obtained by the table conversion means A9 is leaner than the upstream target air-fuel ratio abyfr set by the upstream target air-fuel ratio setting means A2. Calculated as a value (larger value). For this reason, the upstream air-fuel ratio deviation Dabyf obtained by the upstream air-fuel ratio deviation calculating means A11 has a positive value. Here, the signal indicating the upstream air-fuel ratio deviation Dabyf due to a sudden change in the air-fuel ratio of the engine includes a high frequency component equal to or higher than the cut-off frequency ω1. Such high-frequency components can pass through the high-pass filter A12 or the band-pass filter A14. Accordingly, the upstream air-fuel ratio deviation Dabyfhi after passing the high-pass filter (accordingly, the first main feedback correction amount DFihi) or the upstream air-fuel ratio deviation Dabyfba after passing the band-pass filter (accordingly, the second main feedback correction amount DFiba) is also positive. Value. As a result, the main feedback correction coefficient KFimain calculated by the main feedback correction coefficient calculation means A16 becomes a value larger than “1”. As a result, the fuel injection amount Fi obtained by the fuel injection amount calculation means A4 is controlled to be larger than the basic fuel injection amount Fbase so that the air-fuel ratio of the engine becomes rich.

  On the contrary, when the air-fuel ratio of the engine suddenly changes and becomes rich, the detected air-fuel ratio abyfs is obtained as a richer value (a smaller value) than the upstream target air-fuel ratio abyfr. For this reason, the upstream air-fuel ratio deviation Dabyf is a negative value. Also in this case, the signal indicating the upstream side air-fuel ratio deviation Dabyf includes a high frequency component equal to or higher than the cutoff frequency ω1 that can pass through the high pass filter A12 or the band pass filter A14. Therefore, the upstream air-fuel ratio deviation Dabyfhi after passing the high-pass filter (accordingly, the first main feedback correction amount DFihi) or the upstream air-fuel ratio deviation Dabyfba after passing the band-pass filter (accordingly, the second main feedback correction amount DFiba) is also negative. Value. As a result, the main feedback correction coefficient KFimain becomes a value smaller than “1” (and a value larger than “0”). Thus, the fuel injection amount Fi is controlled to be smaller than the basic fuel injection amount Fbase so that the air-fuel ratio of the engine becomes lean.

  The fuel injection amount calculating means A4, the table converting means A9, the target air-fuel ratio delaying means A10, the upstream air-fuel ratio deviation calculating means A11, the high-pass filter A12, the P controller A13, the bandpass filter A14, the P controller A15, and the main feedback. The correction coefficient calculation means A16 corresponds to the main feedback control means.

  In this way, the substantial (steady) air-fuel ratio control for the air-fuel ratio fluctuation below the cut-off frequency ω1 that can appear as the air-fuel ratio fluctuation downstream of the first catalyst 53 can be reliably performed by the sub-feedback control. In other words, the control frequency band as a whole of the sub-feedback control is a band equal to or lower than the cutoff frequency ω1.

  Further, the low frequency component having the cut-off frequency ω1 or lower cannot pass through the high-pass filter A12 and the bandpass filter A14. Therefore, the air-fuel ratio fluctuation having the cut-off frequency ω1 or lower does not appear as the value of the main feedback correction coefficient KFimain. . In other words, the control frequency band of the main feedback control as a whole is a band equal to or higher than the cutoff frequency ω1. Therefore, since the control frequency band as the whole main feedback control and the control frequency band as the whole sub feedback control do not overlap, it is considered that the occurrence of the interference between the main feedback control and the sub feedback control described above can be avoided.

  Further, since the high frequency component equal to or higher than the cut-off frequency ω1 in the air-fuel ratio fluctuation (and therefore the fluctuation in the output value vabyfs of the upstream air-fuel ratio sensor 66) passes through the high-pass filter A12 or the band-pass filter A14, Compensation for a sudden change in the air-fuel ratio can be performed quickly and reliably by the main feedback control.

<Reliable avoidance of interference between main feedback control and sub feedback control>
As described above, the correction term used to calculate the feedback correction amount (in this example, the first and second main feedback correction amounts DFihi and DFiba, and the sub feedback correction coefficient KFisub), which is the output value of the feedback controller. Of these, the value of the P term is not amplified or attenuated regardless of the frequency of the input signal to the feedback controller. On the other hand, the value of the I term tends to be more amplified as the frequency of the input signal is smaller and more attenuated as the frequency of the input signal is larger. Further, the value of the D term tends to be more amplified as the frequency of the input signal is larger and attenuated as the frequency of the input signal is smaller.

  Therefore, as shown in FIG. 6, the value (the upstream air-fuel ratio deviation Dabyfhi after passing through the high-pass filter) after the high-pass filter processing by the high-pass filter A12 (HPF) in the P controller A13 (first main feedback controller) is P-processed. In some cases, the gain characteristic of the P term (HPF + P term) may coincide with the gain characteristic of the high-pass filter A12. In other words, the control frequency band of the P term of the P controller A13 is a band equal to or higher than the cutoff frequency ω2.

  Similarly, when the P controller A15 (second main feedback controller) performs P processing on the value after the band pass filter processing by the band pass filter A14 (BPF) (the upstream air-fuel ratio deviation Dabyfba after passing through the band pass filter), The gain characteristic of the P term (BPF + P term) can coincide with the gain characteristic of the bandpass filter A14. In other words, the control frequency band of the P term of the P controller A15 is a band not less than the cutoff frequency ω1 and not more than the cutoff frequency ω2.

  That is, the control frequency band of all the correction terms (HPF + P term and BPF + P term) related to the main feedback control does not overlap with the band below the cut-off frequency ω1 (therefore, the control frequency band as the entire sub feedback control). . This is because the I term that can amplify the low frequency component below the cut-off frequency ω1 already attenuated by the high pass filter A12 and the band pass filter A14 is the output value of the P controllers A13 and A15. 2 Based on the fact that the main feedback correction amounts DFihi and DFiba are not used for calculation. Thus, in this apparatus, main feedback control, sub-feedback control, and interference are completely avoided in the control frequency band of the entire sub-feedback control.

  In addition, as shown in FIG. 6, when PI processing is performed on the value after the low pass filter processing by the low pass filter A7 (LPF) in the PI controller A8 (sub feedback controller) (output deviation amount DVoxslow after passing through the low pass filter), The gain characteristic of the P term (LPF + P term) can coincide with the gain characteristic of the low-pass filter A7. Further, the gain characteristic of the I term (LPF + I term) has a gain larger than the gain of the low-pass filter A7 at a frequency lower than the cutoff frequency ω1, and a gain smaller than the gain of the low-pass filter A7 at a frequency higher than the cutoff frequency ω1. It becomes the characteristic which has. In other words, both the control frequency bands of the P term and the I term of the PI controller A8 are bands below the cut-off frequency ω1.

  That is, the control frequency band of all correction terms (LPF + P term and LPF + I term) related to the sub-feedback control does not overlap with the band of the cut-off frequency ω1 or higher (therefore, the control frequency band of the main feedback control as a whole). . This is because the D term that can amplify the high frequency component of the cutoff frequency ω1 or higher already attenuated by the low-pass filter A7 is not used for the calculation of the sub feedback correction coefficient KFsub that is the output value of the PI controller A8. Based on that. As described above, in this apparatus, the main feedback control, the sub feedback control, and the interference are completely avoided even in the control frequency band of the entire main feedback control.

  As described above, in the present apparatus, interference between the main feedback control and the sub feedback control is completely avoided over the entire frequency band. The above is the outline of the feedback control of the air-fuel ratio of the engine performed by this apparatus.

(Actual operation)
Next, the actual operation of the air / fuel ratio control apparatus according to the first embodiment will be described.
<Air-fuel ratio feedback control>
The CPU 71 performs a routine for calculating the fuel injection amount Fi shown in the flowchart of FIG. 7 and instructing the fuel injection. The crank angle of each cylinder is a predetermined crank angle before each intake top dead center (for example, BTDC 90 ° CA). Each time it becomes, it is executed repeatedly. Therefore, when the crank angle of an arbitrary cylinder reaches the predetermined crank angle, the CPU 71 starts processing from step 700 and proceeds to step 705, and the intake air flow rate Ga measured by the air flow meter 61 and the engine speed NE, Based on the table MapMc, the in-cylinder intake air amount Mc of the cylinder that reaches the current intake stroke is obtained.

  Next, the CPU 71 proceeds to step 710 and divides the obtained in-cylinder intake air flow rate Mc by the current upstream target air-fuel ratio abyfr (k), so that the engine air-fuel ratio becomes the same as the upstream target air-fuel ratio abyfr. A basic fuel injection amount Fbase for obtaining (k) is obtained.

  Next, the CPU 71 proceeds to step 715 and multiplies the determined basic fuel injection amount Fbase by a sub feedback correction coefficient KFisub and a main feedback correction coefficient KFimain calculated in a routine described later, thereby fuel injection according to the above equation (1). Calculate the quantity Fi.

  Then, the CPU 71 proceeds to step 720, gives an instruction for injecting fuel of the fuel injection amount Fi to the injector 39 of the cylinder that reaches the current intake stroke, and then proceeds to step 795 to end this routine once. . As described above, the fuel of the fuel injection amount Fi corrected by the main feedback control and the sub feedback control is injected into the cylinder that reaches the intake stroke.

(Calculation of main feedback correction factor)
Next, the operation for calculating the main feedback correction coefficient KFimain in the main feedback control will be described. The CPU 71 repeatedly executes the routine shown by the flowchart in FIG. 8 every elapse of a predetermined time. Therefore, when the predetermined timing comes, the CPU 71 starts processing from step 800 and proceeds to step 805 to determine whether or not the main feedback control condition is satisfied. The main feedback control condition is satisfied, for example, when the engine coolant temperature THW is equal to or higher than a first predetermined temperature and the intake air amount (load) per one rotation of the engine is equal to or lower than a predetermined value.

  Now, assuming that the main feedback control condition is satisfied, the CPU 71 determines “Yes” in step 805 and proceeds to step 810 to display the current output value vabyfs of the upstream air-fuel ratio sensor 66. The detected air-fuel ratio abyfs at the present time is obtained by performing conversion based on the table shown in FIG.

  Next, the CPU 71 proceeds to step 815, and subtracts the upstream target air-fuel ratio abyfr (kN) N strokes before the current time from the calculated detected air-fuel ratio abyfs, and according to the above equation (5), N strokes before the current time An upstream air-fuel ratio deviation Dabyf representing the difference between the actual air-fuel ratio and the target air-fuel ratio is obtained.

  Next, the CPU 71 proceeds to step 820, where the upstream air-fuel ratio deviation Dabyf is high-pass filtered by the high-pass filter A12 to obtain the upstream air-fuel ratio deviation Dabyfhi after passing through the high-pass filter. To obtain the first main feedback correction amount DFihi.

  Subsequently, the CPU 71 proceeds to step 830 to perform band-pass filter processing on the upstream air-fuel ratio deviation Dabyf by the band-pass filter A14 to obtain the upstream air-fuel ratio deviation Dabyfba after passing through the band-pass filter. The second main feedback correction amount DFiba is obtained according to equation (9).

  Then, the CPU 71 proceeds to step 840 to obtain a main feedback correction coefficient KFimain based on the obtained first main feedback correction amount DFihi, the second main feedback correction amount DFiba, and the above equation (10), and subsequent steps. Proceed to step 895 to end the present routine tentatively.

  Thus, the main feedback correction coefficient KFimain is obtained, and this main feedback correction coefficient KFimain is reflected in the fuel injection amount Fi in step 715 of FIG. 7 described above, so that the air-fuel ratio control of the engine based on the main feedback control described above is performed. Executed.

  On the other hand, if the main feedback control condition is not satisfied at the time of determination in step 805, the CPU 71 determines “No” in step 805 and proceeds to step 845 to set the value of the main feedback correction coefficient KFimain to “1”. Then, the process proceeds to step 895 to end the present routine tentatively. As described above, when the main feedback control condition is not satisfied, the value of the main feedback correction coefficient KFimain is set to “1”, and the correction of the air-fuel ratio of the engine based on the main feedback control is not performed.

(Calculation of sub feedback correction coefficient)
Next, the operation for calculating the sub feedback correction coefficient KFisub in the sub feedback control will be described. The CPU 71 repeatedly executes the routine shown in the flowchart of FIG. 9 every elapse of a predetermined time. Accordingly, when the predetermined timing is reached, the CPU 71 starts processing from step 900 and proceeds to step 905 to determine whether or not the sub feedback control condition is satisfied. The sub feedback control condition is satisfied, for example, when the engine coolant temperature THW is equal to or higher than a second predetermined temperature higher than the first predetermined temperature, in addition to the main feedback control condition in step 805 described above.

  Now, assuming that the sub-feedback control condition is satisfied, the CPU 71 determines “Yes” in step 905 and proceeds to step 910. According to the above equation (2), the current downstream target value The output deviation amount DVoxs is obtained by subtracting the current output value Voxs of the downstream air-fuel ratio sensor 67 from Voxsref.

  Next, the CPU 71 proceeds to step 915 to low-pass filter the output deviation amount DVoxs with a low-pass filter A7 to obtain an output deviation amount DVoxslow after passing through the low-pass filter.

  Next, the CPU 71 proceeds to step 920, obtains the sub feedback correction coefficient KFisub according to the above equation (4), and in step 925, in step 915, the integrated value SDVoxslow of the output deviation amount after passing through the low-pass filter at that time is obtained. The obtained output deviation amount DVoxslow after passing through the low-pass filter is added to obtain a new integrated value SDVoxslow of the output deviation amount after passing through the low-pass filter. Then, the CPU 71 proceeds to step 995 to end the present routine tentatively.

  Thus, the sub feedback control coefficient KFisub is obtained, and the sub feedback correction coefficient KFisub is reflected in the fuel injection amount Fi in step 715 of FIG. 7 described above, so that the air-fuel ratio control of the engine based on the sub feedback control described above is performed. Executed.

  On the other hand, if the sub feedback control condition is not satisfied at the time of determination in step 905, the CPU 71 determines “No” in step 905 and proceeds to step 930 to set the value of the sub feedback correction coefficient KFisub to “1”. In step 935, the integrated value SDVoxslow of the output deviation after passing through the low-pass filter is initialized to “0”, and then the process proceeds to step 995 to end the present routine tentatively. Thus, when the sub-feedback control condition is not satisfied, the sub-feedback correction coefficient KFisub is set to “1”, and the correction of the air-fuel ratio of the engine based on the sub-feedback control is not performed.

  As described above, according to the first embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention, the air-fuel ratio based on the output value vabyfs of the upstream-side air-fuel ratio sensor 66 disposed upstream of the first catalyst 53. In main feedback control, which is fuel ratio control, a value based on the upstream air-fuel ratio sensor output value vabyfs (upstream air-fuel ratio deviation Dabyf) is bandpass filtered by a bandpass filter A14 (BPF, pass permission frequency: ω1 to ω2). The first and second main feedback controllers (P controllers A13, A15) are the values after the high-pass filter processing is performed on the upstream value and the upstream air-fuel ratio deviation Dabyf by the high-pass filter A12 (HPF, passage permission frequency: ω2 or more). ), The main feedback correction coefficient KFimain is obtained by performing proportional processing (P processing).

  On the other hand, in sub-feedback control, which is air-fuel ratio control based on the output value Voxs of the downstream air-fuel ratio sensor 67 disposed downstream of the first catalyst 53, a value based on the downstream air-fuel ratio sensor output value Voxs (output deviation amount). Dvoxs) is subjected to low-pass filter processing by a low-pass filter A7 (LPF, pass-permitted frequency: ω1 or less), and a sub-feedback correction coefficient KFisub is obtained by performing proportional / integration processing (PI processing) by a sub-feedback controller (PI controller A8). Is required.

  Then, the main feedback control and the sub feedback control are executed by correcting the fuel injection amount Fi independently of each other by the main feedback correction coefficient KFimain and the sub feedback correction coefficient KFisub.

  As a result, the integration process (I process) that can amplify the low frequency component below the cutoff frequency ω1 is not executed in the first and second main feedback controllers, so that all correction terms (HPF + P term, And the BPF + P term) does not overlap with the band below the cut-off frequency ω1. Further, since the sub-feedback controller does not execute differential processing (D processing) that can amplify a high frequency component higher than the cutoff frequency ω1, control of all correction terms (LPF + P term and LPF + I term) related to the sub-feedback control. The frequency band does not overlap with the band above the cutoff frequency ω1. Therefore, interference between the main feedback control and the sub feedback control is completely avoided over the entire frequency band.

  The main feedback control circuit (accordingly, the first and second main feedback controllers (P controllers A13, A15)) and the sub feedback control circuit (accordingly, the sub feedback controller (PI controller A8)) of the fuel injection amount Fi The correction is connected in parallel. Therefore, the feedback control constant on the main feedback control side (that is, the proportional gain Khi of the P controller A13 and the proportional gain Kba on the P controller A15) and the feedback control constant on the sub feedback control side (that is, the proportional gain Kp of the PI controller A8). , And the integral gain Ki), the degree of the influence of the value on the other side on the matching of the other side is small. As a result, it is possible to reduce the labor when adapting each feedback control constant.

  Further, the control frequency band as a whole of the main feedback control (that is, the band of the cut-off frequency ω1 or higher) is shared by the band that the bandpass filter A14 shares (accordingly, the band that the P controller A15 shares) and the highpass filter A12. It is further divided into bands (thus, bands shared by the P controller A13). As a result, in the control frequency band of the entire main feedback control, the degree of freedom in design regarding the gain characteristics of the filter can be improved, and thereby, with respect to a high frequency component higher than the cutoff frequency ω1 in the air-fuel ratio fluctuation of the exhaust gas. The degree of freedom in designing the main feedback control system is improved.

(Modification of the first embodiment)
Next, an air-fuel ratio control apparatus according to a modification of the first embodiment will be described. In this modification, as shown in FIG. 10 which is a functional block diagram, instead of the upstream air-fuel ratio deviation Dabyf, the detected air-fuel ratio abyfs of the upstream air-fuel ratio sensor 66 is directly applied to the high-pass filter A12 and the bandpass filter A14. Only in the point which inputs, it differs from the said 1st Embodiment. That is, the main feedback correction coefficient KFimain is calculated based on the value after the detected air-fuel ratio abyfs itself is subjected to high-pass filter processing and band-pass filter processing. Hereinafter, the description will be focused on the difference.

  Based on this difference, the CPU 71 of this modified example executes the routine shown in the flowchart of FIG. 11 for calculating the main feedback correction coefficient KFimain instead of the routine shown in FIG. 8 every elapse of a predetermined time. In FIG. 11, the same steps as those shown in FIG. 8 are denoted by the same reference numerals.

  That is, the routine of FIG. 11 does not include step 815 for obtaining the upstream air-fuel ratio deviation Dabyf, and in steps 1105 to 1120 corresponding to steps 820 to 835, the detected air-fuel ratio abyfs itself is subjected to high-pass filter processing. The first main feedback correction amount DFihi is calculated by multiplying the detected air-fuel ratio abyfhi after passing through the high-pass filter obtained by the proportional gain Khi, and the bandpass obtained by subjecting the detected air-fuel ratio abyfs itself to bandpass filtering 8 is different from the routine of FIG. 8 only in that the second main feedback correction amount DFiba is calculated by multiplying the detected air-fuel ratio abyfba after passing through the filter by the proportional gain Kba. Therefore, a detailed description of the other steps of the routine of FIG. 11 is omitted.

  In the first embodiment, the upstream air-fuel ratio deviation Dabyf inputted to the high-pass filter A12 and the band-pass filter A14 is detected from the detected air-fuel ratio abyfs to the upstream target air-fuel ratio abyfr (kN) (in principle, constant at the stoichiometric air-fuel ratio. ) Is subtracted. Therefore, the signal indicating the upstream air-fuel ratio deviation Dabyf is a signal having a waveform that increases or decreases at the same timing and the same amplitude while the central value of the fluctuation is different from the signal indicating the detected air-fuel ratio abyfs.

  Therefore, the signal indicating the upstream air-fuel ratio deviation Dabyfhi after passing through the high-pass filter and the upstream after passing through the band-pass filter, which is composed of high-frequency components having a cutoff frequency ω1 or higher after passing through the high-pass filter A12 and the band-pass filter A14, respectively. The signal indicating the side air-fuel ratio deviation Dabyfba is a signal indicating the detected air-fuel ratio abyfhi after passing through the high-pass filter, which is composed of high-frequency components having the cutoff frequency ω1 or higher after passing through the high-pass filter A12 and the band-pass filter A14, respectively. And a signal indicating exactly the same value as the signal indicating the detected air-fuel ratio abyfba after passing through the band-pass filter. As a result, even in the modified example of the first embodiment, the same operation and effect as the first embodiment can be obtained.

(Second Embodiment)
Next, an air-fuel ratio control apparatus according to the second embodiment will be described. As shown in FIG. 12, which is a functional block diagram, this second embodiment is not provided with a bandpass filter A14 and a P controller A15 (thus, the main feedback correction coefficient calculation means A16 has a first main feedback correction amount DFihi. In that the value obtained by adding “1” to the main feedback correction coefficient KFimain) is different from the first embodiment.

  Further, in the second embodiment, the control frequency band (ω1 to ω2) shared by the bandpass filter A14 is also included in the control frequency band shared by the highpass filter A12 due to the absence of the bandpass filter A14. Therefore, as shown in FIG. 13, the point that the cutoff frequency of the high-pass filter A12 is changed from ω2 to ω1 is also different from the first embodiment. Thereby, the cut-off frequency of the high-pass filter A12 is equal to the cut-off frequency of the low-pass filter A7. Hereinafter, the description will be focused on the difference.

  Based on this difference, the CPU 71 of the second embodiment replaces the routine shown in FIG. 8 with the routine shown in the flowchart of FIG. 14 for calculating the main feedback correction coefficient KFimain at every elapse of a predetermined time. Execute. In FIG. 14, the same steps as those shown in FIG. 8 are denoted by the same reference numerals.

  That is, the routine of FIG. 14 adds “1” to the first main feedback correction amount DFihi in step 1405 corresponding to step 840 in that there are no steps 830 and 835 for obtaining the second main feedback correction amount DFiba. This is different from the routine of FIG. 8 only in that the main feedback correction coefficient KFimain is calculated. Therefore, a detailed description of the other steps of the routine of FIG. 14 is omitted.

  As described above, in the second embodiment described above, the entire band above the cut-off frequency ω1, which is the control frequency band of the entire main feedback control, is shared by one filter (high-pass filter A12). Therefore, interference between the main feedback control and the sub feedback control can be completely avoided with a simple configuration compared to the first embodiment over the entire frequency band.

  The present invention is not limited to the above embodiments, and various modifications can be adopted within the scope of the present invention. For example, in the first and second embodiments, the detected air-fuel ratio abyfs of the upstream air-fuel ratio sensor 66 is set as “a value corresponding to the degree of difference between the output value of the upstream air-fuel ratio sensor and the upstream target value”. Between the upstream air-fuel ratio sensor output value vabyfs and the sensor output value corresponding to the upstream target air-fuel ratio abyfr (upstream target value), or The actual in-cylinder fuel supply amount that is the value obtained by dividing the in-cylinder intake air amount Mc by the detected air-fuel ratio abyfs, and the target in-cylinder fuel supply amount that is the value obtained by dividing the in-cylinder intake air amount Mc by the target air-fuel ratio abyfr The difference between and may be used.

  In each of the above-described embodiments and modifications, the output value Voxs of the downstream air-fuel ratio sensor 67 is set as “a value corresponding to the degree of difference between the output value of the downstream air-fuel ratio sensor and the downstream target value”. Although the difference from the downstream target value Voxsref is used, the difference between the detected air-fuel ratio of the downstream air-fuel ratio sensor 67 and the downstream target air-fuel ratio corresponding to the downstream target value Voxsref may be used.

  In each of the above-described embodiments and modifications, the main feedback control is executed by multiplying the basic fuel injection amount Fbase by the main feedback correction coefficient KFimain (> 0), which corresponds to the main feedback correction coefficient KFimain. The main feedback control may be executed by adding a main feedback correction amount that can take positive and negative values to the basic fuel injection amount Fbase.

  Similarly, in each of the above-described embodiments and modifications, the sub feedback control is executed by multiplying the basic fuel injection amount Fbase by the sub feedback correction coefficient KFisub (> 0), but the sub feedback correction coefficient KFisub is added to the sub feedback correction coefficient KFisub. The sub-feedback control may be executed by adding a sub-feedback correction amount that can take a corresponding positive / negative value to the basic fuel injection amount Fbase.

  In each of the above-described embodiments and modifications, the sub feedback correction coefficient KFisub is based on the value DVoxslow after low-pass filtering the difference DVoxs between the output value Voxs of the downstream air-fuel ratio sensor 67 and the downstream target value Voxsref. The sub-feedback correction coefficient KFisub is calculated based on the difference between the value after the low-pass filter processing of the output value Voxs of the downstream air-fuel ratio sensor 67 and the downstream target value Voxsref. It may be configured.

  Further, in each of the above-described embodiments and modifications, a primary filter is used as a filter (high-pass filter A12, band-pass filter A14, low-pass filter A7), but each band shared by each filter is further increased. If it is necessary to clearly separate them, second-order or higher-order filters may be used as these filters.

  In each of the above-described embodiments and modifications, the P controller A13 that performs only proportional processing (P processing) is employed as the first main feedback controller, but the D controller that performs only differentiation processing (D processing), Alternatively, a PD controller that performs only proportional / differential processing (PD processing) may be employed.

  Similarly, in each of the above-described embodiments and modifications, the PI controller A8 that performs only proportional / integral processing (PI processing) is employed as the sub-feedback controller, but the P controller that performs only proportional processing (P processing). Alternatively, an I controller that performs only integration processing (I processing) may be employed.

  Moreover, in the said 1st Embodiment and the modification, P controller A15 which performs only a proportional process (P process) is employ | adopted as a 2nd main feedback controller, D controller which performs only a differential process (D process) Alternatively, a PD controller that performs only proportional / differential processing (PD processing) may be employed.

1 is a schematic diagram of an internal combustion engine to which an air-fuel ratio control apparatus according to a first embodiment of the present invention is applied. It is the graph which showed the relationship between the output voltage of the air flow meter shown in FIG. 1, and the measured intake air flow rate. 2 is a graph showing the relationship between the output voltage of the upstream air-fuel ratio sensor shown in FIG. 1 and the air-fuel ratio. 3 is a graph showing the relationship between the output voltage of the downstream air-fuel ratio sensor shown in FIG. 1 and the air-fuel ratio. FIG. 2 is a functional block diagram when the air-fuel ratio control device shown in FIG. 1 executes air-fuel ratio feedback control. FIG. 6 is a diagram showing frequency-gain characteristics for each correction term used in the feedback controller shown in FIG. 5. 2 is a flowchart showing a routine for fuel injection amount calculation executed by a CPU shown in FIG. 1. 2 is a flowchart showing a routine for calculating a main feedback correction coefficient executed by a CPU shown in FIG. 1. 3 is a flowchart showing a routine for calculating a sub-feedback correction coefficient executed by a CPU shown in FIG. 1. It is a functional block diagram when the air-fuel ratio control device according to the modification of the first embodiment of the present invention executes air-fuel ratio feedback control. It is the flowchart which showed the routine for calculating the main feedback correction coefficient which CPU of the air fuel ratio control device which relates to the modification of 1st execution form of this invention executes. It is a functional block diagram when the air-fuel ratio control device according to the second embodiment of the present invention executes air-fuel ratio feedback control. It is the figure which each showed the frequency-gain characteristic about each correction | amendment term used in the feedback controller shown in FIG. It is the flowchart which showed the routine for calculating the main feedback correction coefficient which CPU of the air fuel ratio control device which relates to 2nd execution form of this invention executes. It is the figure which each showed the frequency-gain characteristic about each correction | amendment term used in the feedback controller which the conventional air fuel ratio control apparatus uses. It is the Bode diagram which showed roughly an example of each frequency-gain characteristic about each correction term to the frequency of the input signal to the feedback controller which performs PID processing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 25 ... Combustion chamber, 39 ... Injector, 52 ... Exhaust pipe (exhaust pipe), 53 ... Three way catalyst (1st catalyst), 66 ... Upstream air-fuel ratio sensor, 67 ... Downstream air-fuel ratio sensor, 70 ... electric control device, 71 ... CPU

Claims (4)

A catalyst disposed in an exhaust passage of the internal combustion engine;
An upstream air-fuel ratio sensor disposed in the exhaust passage upstream of the catalyst;
A downstream air-fuel ratio sensor disposed in the exhaust passage downstream of the catalyst;
Fuel injection means for injecting an amount of fuel according to the operating state of the internal combustion engine;
An air-fuel ratio control device for an internal combustion engine applied to an internal combustion engine comprising:
The output value of the upstream air-fuel ratio sensor or the value after high-pass filtering the value corresponding to the degree of difference between the output value of the upstream air-fuel ratio sensor and the upstream target value is the first main feedback input value. And a first main feedback controller that calculates the first main feedback correction amount by inputting as the above, and correcting the fuel injection amount that is injected by the fuel injection means by the calculated first main feedback correction amount. Main feedback control means for feedback control of the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine;
A value after low-pass filtering a value corresponding to the degree of difference between the output value of the downstream air-fuel ratio sensor and the downstream target value, or a value after low-pass filtering the output value of the downstream air-fuel ratio sensor And a sub-feedback controller that calculates a sub-feedback correction amount by inputting a value corresponding to the degree of difference between the target value and the downstream target value as a sub-feedback input value, and correction of the fuel injection amount by the main feedback control means; Sub feedback control means for performing feedback control of the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine by correcting the fuel injection amount injected by the fuel injection means independently of the calculated sub feedback correction amount;
With
The first main feedback controller calculates the first main feedback correction amount by performing only proportional processing, only differentiation processing, and only proportional / differentiation processing on the first main feedback input value. And is configured to
The sub feedback controller is configured to calculate the sub feedback correction amount by performing only one of proportional processing, only integration processing, and only proportional / integration processing on the sub feedback input value. An air-fuel ratio control apparatus for an internal combustion engine. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1,
The main feedback control means includes
The second main feedback input is a value after band-pass filtering the output value of the upstream air-fuel ratio sensor or the value corresponding to the degree of difference between the output value of the upstream air-fuel ratio sensor and the upstream target value. A second main feedback controller for inputting a value and calculating a second main feedback correction amount; and the fuel injection means based on the calculated first main feedback correction amount and the calculated second main feedback correction amount. Is configured to feedback control the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine by correcting the fuel injection amount injected by
The second main feedback controller calculates the second main feedback correction amount by performing only proportional processing, only differentiation processing, and only proportional / differentiation processing on the second main feedback input value. An air-fuel ratio control apparatus for an internal combustion engine configured to do so. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1,
An air-fuel ratio control apparatus for an internal combustion engine, wherein a cutoff frequency of the high-pass filter processing by the main feedback control means and a cutoff frequency of the low-pass filter processing by the sub-feedback control means are the same. The air-fuel ratio control apparatus for an internal combustion engine according to claim 2,
The cut-off frequency of the high-pass filter processing by the main feedback control means and the cut-off frequency on the high frequency side of the band-pass filter processing by the main feedback control means are the same,
An air-fuel ratio control apparatus for an internal combustion engine, wherein a cut-off frequency on a low frequency side of the band-pass filter processing by the main feedback control means and a cut-off frequency of the low-pass filter processing by the sub-feedback control means are the same.

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