JP4936018B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

  In the present invention, the air-fuel ratio of the mixture ratio supplied to the engine based on the output value of the air-fuel ratio sensor disposed in the exhaust passage of the internal combustion engine (hereinafter also simply referred to as “engine air-fuel ratio”) is fed back. The present invention relates to an air-fuel ratio control device for an internal combustion engine to be controlled.

  Conventionally, an internal combustion engine having a catalyst for purifying exhaust gas (an exhaust purification catalyst, a three-way catalyst) in an exhaust passage has been proposed. This catalyst is high when the temperature of the catalyst is equal to or higher than its activation temperature and the air-fuel ratio of the exhaust gas flowing into the catalyst is within a "predetermined air-fuel ratio width including the stoichiometric air-fuel ratio (so-called window range)". Unburned substances and nitrogen oxides in the exhaust gas can be purified with efficiency. Therefore, in an internal combustion engine equipped with such a catalyst, an air-fuel ratio control device that controls the air-fuel ratio of exhaust gas flowing into the catalyst based on the output value of the air-fuel ratio sensor provided in the exhaust passage is widely adopted. .

  This air-fuel ratio control device calculates the air-fuel ratio of the exhaust gas flowing through the portion where the air-fuel ratio sensor is arranged based on the output value of the air-fuel ratio sensor, and the calculated air-fuel ratio is a predetermined target air-fuel ratio (described above) The feedback control for the air-fuel ratio of the engine is executed so as to coincide with the air-fuel ratio within the window range. As a result, the air-fuel ratio of the exhaust gas flowing into the catalyst is controlled to an appropriate value, and as a result, the engine emission is well maintained. Therefore, in order for this control to be executed properly, it is important that the air-fuel ratio sensor functions normally.

However, there are cases where the air-fuel ratio sensor deteriorates (for example, the output of the air-fuel ratio sensor, the response speed, etc. decrease) due to reasons such as adhesion of unburned substances to the air-fuel ratio sensor, loss of sensor elements and aging deterioration. is there. Therefore, one of the conventional air-fuel ratio control devices diagnoses the deterioration of the air-fuel ratio sensor and amplifies the high-frequency component of the output value of the air-fuel ratio sensor when it is diagnosed that the air-fuel ratio sensor is deteriorated. Amplifies at. As a result, the output value of the air-fuel ratio sensor is compensated (see, for example, Patent Document 1). Hereinafter, this compensation is also referred to as “high frequency component amplification compensation”.
JP 2007-278076 A

  However, the inventor has found that the output value of the air-fuel ratio sensor may not be appropriately compensated even if the above-described high frequency component amplification compensation is executed. This point will be described below.

  As described above, when the air-fuel ratio sensor deteriorates, its output, response speed, etc. (hereinafter, these parameters are collectively referred to as “responsiveness”) are reduced. The output value of the deteriorated air-fuel ratio sensor cannot sufficiently follow the fluctuation when the air-fuel ratio of the exhaust gas flowing through the portion where the air-fuel ratio sensor is disposed fluctuates. Specifically, when the air-fuel ratio sensor deteriorates, it becomes difficult to detect a high-frequency component of the fluctuation of the air-fuel ratio of the exhaust gas, and the magnitude of the output value is compared with that when the air-fuel ratio sensor is not deteriorated. Tend to become smaller (that is, the amplitude of the waveform of the output value becomes smaller).

  On the other hand, high-frequency noise may be mixed in the output value of the air-fuel ratio sensor. As described above, the deteriorated air-fuel ratio sensor has an output value that is smaller in amplitude and less in high-frequency components than the output value of the undegraded air-fuel ratio sensor (hereinafter also referred to as “normal output value”). (Hereinafter also referred to as “degraded output value”). Therefore, in general, the influence of the high frequency noise when the high frequency noise is mixed into the degraded output value is larger than the influence of the high frequency noise when the high frequency noise is mixed into the normal output value. When the above-described “high frequency component amplification compensation” is performed on the deteriorated output value mixed with high frequency noise, the high frequency noise mixed in the deteriorated output value is amplified, and the influence of the high frequency noise is further increased.

  As described above, the air-fuel ratio control apparatus calculates the air-fuel ratio of the exhaust gas based on the output value of the air-fuel ratio sensor. When the influence of the high-frequency noise is sufficiently small, the air-fuel ratio (hereinafter referred to as “the air-fuel ratio” calculated based on the actual air-fuel ratio of the exhaust gas (hereinafter also referred to as “actual air-fuel ratio” for convenience) and the output value of the air-fuel ratio sensor. The term “detected air / fuel ratio” is also referred to as “no problem” in executing the air / fuel ratio control. However, when the influence of high-frequency noise is large, the difference between the actual air-fuel ratio and the detected air-fuel ratio becomes large, so that the air-fuel ratio of the engine cannot be controlled appropriately. As a result, there arises a problem that the emission of the engine deteriorates.

  Further, when the air-fuel ratio sensor deteriorates, the response of the air-fuel ratio sensor when the air-fuel ratio varies from the rich side to the lean side (hereinafter also referred to as “lean direction response”) and the air-fuel ratio from the lean side. The response of the air-fuel ratio sensor when it fluctuates to the rich side (hereinafter also referred to as “rich direction responsiveness”) may not decrease to the same extent. Hereinafter, the deterioration in which the lean direction responsiveness and the rich direction responsiveness are reduced to the same extent is also referred to as “symmetrical deterioration”.

  When only one of the lean direction responsiveness or the rich direction responsiveness is reduced, or when the degree of the lean direction responsiveness is different from the degree of the rich direction responsiveness (hereinafter these deteriorations) The output value of the air-fuel ratio sensor behaves differently when the actual air-fuel ratio fluctuates in the lean direction and when it fluctuates in the rich direction (hereinafter referred to as the output value). This behavior is also called “asymmetric response”.) In general, the engine emission when the air-fuel ratio sensor deteriorates asymmetrically is worse than the engine emission when the air-fuel ratio sensor deteriorates symmetrically.

  The “high frequency component amplification compensation” described above is performed on the output value “whole” of the air-fuel ratio sensor. Therefore, even if “high frequency component amplification compensation” is performed on an output value showing an asymmetric response, the asymmetric response is not eliminated. Furthermore, when “high frequency component amplification compensation” is performed on the output value “whole” showing an asymmetric response, the high frequency component of the output value in the direction of high responsiveness is excessively amplified. When the output value of the air-fuel ratio sensor is compensated in this way, the difference between the actual air-fuel ratio and the detected air-fuel ratio becomes large as described above, so that the air-fuel ratio of the engine cannot be controlled appropriately. As a result, there is a problem that the emission of the engine is further deteriorated.

  The present invention has been made to address the above problems. That is, an object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can appropriately maintain the output value of the internal combustion engine even when the air-fuel ratio sensor deteriorates asymmetrically, thereby maintaining the engine emission satisfactorily. There is to do.

More specifically, the first air-fuel ratio control device for an internal combustion engine of the present invention is:
(1) an air-fuel ratio sensor that is disposed in an exhaust passage of the internal combustion engine and outputs an output value corresponding to the air-fuel ratio of exhaust gas flowing through the disposed portion;
(2) The lean direction response time constant, which is the response time constant of the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas increases, and the response time constant of the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas decreases Response time constant acquisition means for acquiring a certain rich direction response time constant;
(3) The reference response time constant is equal to or greater than the deterioration side response time constant based on the deterioration side response time constant which is the larger one of the lean direction response time constant and the rich direction response time constant. Sensor output processing means for obtaining a post-processing output value by performing low-pass filter processing having a time constant corresponding to the reference response time constant on the output value of the air-fuel ratio sensor,
(4) Air-fuel ratio control means for performing air-fuel ratio feedback control for matching the air-fuel ratio of the air-fuel mixture supplied to the engine with the target air-fuel ratio based on the post-processing output value;
Is provided.

  According to the above configuration, the response time constant of the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas increases (changes from the rich side to the lean side) is acquired as the “lean direction response time constant”. Further, the response time constant of the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas decreases (changes from the lean side to the rich side) is acquired as the “rich direction response time constant”.

In the present invention, the “lean direction response time constant” and the “rich direction response time constant” can be determined as follows, for example.
The “lean direction response time constant” is the actual air-fuel ratio “the air-fuel ratio (stoich−α) that is smaller than the stoichiometric air-fuel ratio stoich by a predetermined value α, and a predetermined value from the stoichiometric air-fuel ratio stoich that is the end point from the start point. When the air-fuel ratio is changed in a stepwise manner up to an air-fuel ratio (stoich + α) that is larger by α, the detected air-fuel ratio becomes “a predetermined ratio (for example, the amount of change in air-fuel ratio (+ 2α) from the same start point to the same end point with reference to the same start point (for example, , 63.2%), the “time” until the air / fuel ratio is reached.
“Rich direction response time constant” means that the actual air-fuel ratio is “the air-fuel ratio (stoich + α) that is larger than the stoichiometric air-fuel ratio stoich by the predetermined value α, and the stoichiometric air-fuel ratio stoich that is the end point from the start point by the predetermined value α. When the air / fuel ratio is changed in a step-like manner to a small air / fuel ratio (stoich−α), the detected air / fuel ratio becomes “a predetermined ratio (−2α) of the change amount (−2α) of the air / fuel ratio from the start point to the end point with reference to the start point. For example, it may be “time” until the air / fuel ratio of 63.2%) is reached.

  That is, the response time constant is an “index indicating the responsiveness of the air / fuel ratio sensor”, and the smaller the value, the more “the air / fuel ratio calculated based on the output value of the air / fuel ratio sensor (detected air / fuel ratio)” The actual air-fuel ratio (actual air-fuel ratio) "is quickly followed. That is, the smaller the response time constant is, the higher the response of the air-fuel ratio sensor is.

  In the first air-fuel ratio control device, either the “lean direction response time constant” or the “rich direction response time constant”, whichever is the “larger” response time constant (hereinafter referred to as “deterioration response time constant”). The “reference response time constant” is determined so as to be “above”. That is, the reference response time constant is a response in a direction in which the response in the lean direction and the response in the rich direction of the air-fuel ratio sensor is “low” (hereinafter also referred to as “degradation side response”), or This is a response time constant corresponding to “lower” response than the degradation side response.

  Then, a low-pass filter process having a time constant corresponding to the above-described reference response time constant is performed on the output value of the air-fuel ratio sensor. Further, the air-fuel ratio of the engine is feedback controlled based on the output value thus processed.

  Therefore, the low-pass filter process substantially removes a frequency component larger than the cutoff frequency determined by the reference response time constant from the output value of the air-fuel ratio sensor from the output value of the air-fuel ratio sensor. As a result, the output value of the air-fuel ratio sensor that has been subjected to the low-pass filter processing (hereinafter also referred to as “post-processing output value”) is substantially composed of only the frequency components that are equal to or lower than the cut-off frequency. In other words, since the “output value on the side with high responsiveness” of the air-fuel ratio sensor is matched with the “output value on the side with low responsiveness” by the above processing, the output value after processing becomes symmetrical. .

  As a result, the air-fuel ratio feedback control is executed based on the post-processing output value showing a symmetrical response, so that the air-fuel ratio of the engine is appropriately controlled. Therefore, the emission of the engine can be maintained satisfactorily.

  Here, the above-mentioned “reference response time constant” may be “deterioration response time constant itself” or “a value obtained by adding a predetermined positive value to the degradation response time constant”. Also good. Here, the “positive value to be added” can be an appropriate value in consideration of the operating state of the engine, the exhaust gas purification capability required for the engine, fuel consumption, and the like.

  Further, the “time constant corresponding to the reference response time constant” may be “the reference response time constant itself” or “a value obtained by adding a predetermined positive value to the reference response time constant”. Here, the “positive value to be added” can be an appropriate value in consideration of the operating state of the engine, the exhaust gas purification capability required for the engine, the fuel consumption, and the like, as described above.

Furthermore, in the first air-fuel ratio control device,
The sensor output processing means (3)
The reference response time constant is configured to be determined based on the deterioration side response time constant when the engine is in the first operating state; and
When the engine is in a second operating state different from the first operating state, it corresponds to “a value obtained by correcting the deterioration-side response time constant based on a parameter corresponding to the second operating state”. It is preferable that the constant is adopted as the time constant of the low-pass filter.

  The above “time constant corresponding to the value obtained by correcting the deterioration-side response time constant based on the parameter corresponding to the second operating state” is based on “the deterioration-side response time constant based on the parameter corresponding to the second operating state. It may be “corrected value itself” or “a value obtained by adding a predetermined positive value to a value obtained by correcting the deterioration side response time constant based on a parameter corresponding to the second operating state”. Here, the “positive value to be added” can be an appropriate value in consideration of the operating state of the engine, the exhaust gas purification capability required for the engine, fuel consumption, and the like.

  The output value of the air-fuel ratio sensor is generally affected by the state of exhaust gas to be measured (for example, exhaust gas flow rate, pressure, temperature, component, etc.). Therefore, the engine operating state (for example, parameters such as load, engine speed, and cylinder intake air amount) that affect the exhaust gas state is the response of the air-fuel ratio sensor (thus, the degradation-side response time constant). ) Can be changed. Therefore, in the above configuration, the “deterioration response time constant obtained in the first operating state” is corrected based on the parameter corresponding to the second operating state of the engine, and the corrected deterioration side response is corrected. A time constant corresponding to the time constant is employed as the time constant of the low-pass filter in the second operating state.

  With the above configuration, the time constant of the low-pass filter can be appropriately determined according to the operating state. That is, even when the deterioration-side response time constant changes between the first operation state and the second operation state, the time constant of the low-pass filter is set to a value equal to or greater than the deterioration-side response time constant in each operation state. be able to. Accordingly, it is possible to avoid applying an excessive or excessive low-pass filter process to the output value of the air-fuel ratio sensor. As a result, the emission of the engine can be maintained better.

  Here, the parameters adopted as “parameters according to the operating state of the engine” are parameters that affect the responsiveness of the air-fuel ratio sensor, and are appropriately determined in consideration of exhaust gas purification performance and fuel consumption required for the engine. Can be determined. For example, the “parameter according to the operating state of the engine” may be one or any combination of two or more of the engine load, the engine speed, and the in-cylinder intake air amount.

In the first air-fuel ratio control device,
The sensor output processing means (3)
The reference response time constant is configured to be determined based on the deterioration side response time constant when the engine is in the first operating state; and
When the engine is in a second operating state different from the first operating state, a time constant corresponding to “a value obtained by correcting the reference response time constant based on a parameter corresponding to the second operating state” Is preferably adopted as the time constant of the low-pass filter.

  As described above, the deterioration-side response time constant can vary depending on the operating state of the engine (for example, parameters such as load, engine speed, and in-cylinder intake air amount). Therefore, in the above configuration, the “reference response time constant” is corrected based on the parameter corresponding to the operating state of the engine, and the time constant corresponding to the “corrected reference response time constant” is the time constant of the low-pass filter. Adopted as

  Also with the above configuration, the time constant of the low-pass filter can be appropriately determined according to the operating state. That is, even when the deterioration-side response time constant changes between the first operation state and the second operation state, the time constant of the low-pass filter is set to a value equal to or greater than the deterioration-side response time constant in each operation state. be able to. Accordingly, it is possible to avoid applying an excessive or excessive low-pass filter process to the output value of the air-fuel ratio sensor. As a result, the emission of the engine can be maintained better.

  Even in this case, the parameter adopted as the “parameter according to the operating state of the engine” is a parameter that affects the responsiveness of the air-fuel ratio sensor, and considers the exhaust gas purification performance and fuel consumption required for the engine. Can be determined as appropriate. For example, the “parameter according to the operating state of the engine” may be one or any combination of two or more of the engine load, the engine speed, and the in-cylinder intake air amount.

The second air-fuel ratio control apparatus of the present invention is
(1) a catalyst disposed in an exhaust passage of the internal combustion engine;
(2) an upstream air-fuel ratio sensor that is disposed in a portion upstream of the catalyst in the exhaust passage and outputs an output value corresponding to an air-fuel ratio of exhaust gas flowing through the disposed portion;
(3) a downstream air-fuel ratio sensor that is disposed in a portion downstream of the catalyst in the exhaust passage and outputs an output value corresponding to an air-fuel ratio of exhaust gas flowing through the disposed portion;
It is applied to the internal combustion engine provided with.

The second air-fuel ratio control device
(4) a value obtained by performing high-pass filter processing on a deviation between a value corresponding to the output value of the upstream air-fuel ratio sensor and an upstream target value corresponding to the theoretical air-fuel ratio, and the upstream air-fuel ratio sensor The air-fuel ratio of the air-fuel mixture supplied to the engine is fed back based on one of the deviations between the value obtained by subjecting the output value to the high-pass filter processing and the upstream target value corresponding to the stoichiometric air-fuel ratio. Main feedback correction amount calculating means for calculating a main feedback correction amount for control using a first feedback control coefficient including at least one gain;
(5) Mixing supplied to the engine based on a value obtained by subjecting a deviation between a value corresponding to the output value of the downstream air-fuel ratio sensor and a downstream target value corresponding to the theoretical air-fuel ratio to low-pass filter processing Sub-feedback correction amount calculating means for calculating a sub-feedback correction amount for feedback control of the air-fuel ratio of the air independently from the calculation of the main feedback correction amount;
(6) air-fuel ratio control means for performing feedback control so that the air-fuel ratio of the air-fuel mixture supplied to the engine matches the stoichiometric air-fuel ratio based on the main feedback correction amount and the sub-feedback correction amount;
(7) A lean direction response time constant, which is a response time constant of the upstream air-fuel ratio sensor when the exhaust gas air-fuel ratio increases, and an upstream air-fuel ratio sensor when the exhaust gas air-fuel ratio decreases. A response time constant acquisition means for acquiring a rich direction response time constant which is a response time constant;
(8) an air-fuel ratio sensor diagnostic means for determining whether or not a diagnostic index value that is an absolute value of a difference between the lean direction response time constant and the rich direction response time constant is greater than a predetermined allowable value;
Is provided.

Furthermore, in the second air-fuel ratio control device,
The main feedback correction amount calculating means (4)
When the air-fuel ratio sensor diagnosing means determines that the diagnostic index value is greater than the allowable value, at least one gain of the gains included in the first feedback control coefficient instead of the first feedback control coefficient The main feedback correction amount is calculated by using a second feedback control coefficient obtained by reducing.

  In the second air-fuel ratio control device, the “main feedback correction amount” is calculated based on the output value from the upstream air-fuel ratio sensor disposed upstream of the catalyst. Further, the “sub feedback correction amount” is calculated based on the output value of the downstream air-fuel ratio sensor disposed on the downstream side of the catalyst. Based on the “main feedback correction amount” and the “sub feedback correction amount”, control is performed so that the air-fuel ratio of the air-fuel mixture supplied to the engine matches the stoichiometric air-fuel ratio.

  Specifically, the “main feedback correction amount” includes “a value obtained by performing high-pass filter processing on a deviation between a value corresponding to the output value of the upstream air-fuel ratio sensor and the theoretical air-fuel ratio” and “upstream air-fuel ratio correction amount”. Calculated using a first feedback control coefficient including at least one gain on the basis of either “the deviation between the value obtained by subjecting the output value of the fuel ratio sensor to the high-pass filter processing and the theoretical air-fuel ratio”. The

  The “sub-feedback correction amount” is based on “a value obtained by performing low-pass filter processing on the deviation between the value corresponding to the output value of the downstream air-fuel ratio sensor and the downstream target value corresponding to the theoretical air-fuel ratio”. It is calculated independently of the above-described calculation of the main feedback correction amount.

  As described above, the second air-fuel ratio control device performs the high-pass filter process on the value based on the output value of the upstream air-fuel ratio sensor and also performs the low-pass filter process on the value based on the output value of the downstream air-fuel ratio sensor. . The reason for this will be described below.

  The catalyst (three-way catalyst) used in the second air-fuel ratio control device carries a catalyst component (a noble metal such as platinum and rhodium) and an oxygen storage material (CeO2 or the like) on a carrier made of ceramic or the like. The oxygen storage material stores oxygen when exhaust gas whose air-fuel ratio is leaner than the stoichiometric air-fuel ratio flows into the catalyst, and when exhaust gas whose air-fuel ratio is richer than the stoichiometric air-fuel ratio flows into the catalyst Further, it has a function (so-called oxygen storage capacity) for releasing oxygen to the catalytic active point. For this reason, the high-frequency component in the air-fuel ratio fluctuation of the exhaust gas “upstream” of the catalyst and the low-frequency component with a small amplitude (shift amount from the theoretical air-fuel ratio) in the fluctuation are absorbed by the oxygen storage capacity of the catalyst. And does not appear as fluctuations in the air-fuel ratio of the exhaust gas “downstream” of the catalyst.

  On the other hand, the low-frequency component having a large amplitude in the fluctuation of the air-fuel ratio of the exhaust gas upstream of the catalyst is difficult to be absorbed depending on the oxygen storage capacity of the catalyst, and thus appears as a fluctuation in the air-fuel ratio of the exhaust gas downstream of the catalyst. . As a result, the output value of the upstream air-fuel ratio sensor and the output value of the downstream air-fuel ratio sensor may be values indicating the air-fuel ratio shifted in opposite directions with respect to the theoretical air-fuel ratio. In this case, the air-fuel ratio control of the engine based on the main feedback control and the air-fuel ratio control of the engine based on the sub-feedback control interfere with each other, and as a result, good air-fuel ratio control cannot be performed.

  Therefore, “predetermined frequency” (hereinafter referred to as “first cutoff frequency”) that is a frequency component that can appear as a variation in the air-fuel ratio of the catalyst “downstream” among the frequency components in the variation in the output value of the upstream air-fuel ratio sensor. If the output value of the upstream air-fuel ratio sensor after substantially removing (the following low-frequency components) is used for the main feedback control, the air-fuel ratio control is prevented from interfering. be able to.

  Further, among the frequency components in the fluctuation of the output value of the downstream side air-fuel ratio sensor, “high frequency components higher than a predetermined frequency (hereinafter also referred to as“ second cutoff frequency ”)” are substantially removed (low-pass). If the output value of the downstream air-fuel ratio sensor after the filter processing is used for sub-feedback control, the “high-frequency component of fluctuation of the air-fuel ratio” and the “high-frequency disturbance component ( For example, even when the above-described high frequency noise) is mixed into the output value of the downstream air-fuel ratio sensor, the output value after removing these components can be used for the sub-feedback control. Thereby, the air-fuel ratio of the engine can be controlled reliably and accurately.

  Based on the above viewpoint, a high-pass filter process is performed on the value based on the output value of the upstream air-fuel ratio sensor, and a low-pass filter process is performed on the value based on the output value of the downstream air-fuel ratio sensor.

  Further, the second air-fuel ratio control device acquires the lean direction response time constant and the rich direction response time constant in the same manner as the first air-fuel ratio control device, and the absolute value (diagnosis index value) of these differences is predetermined. Is larger than the allowable value, the main feedback using the “second feedback control coefficient obtained by reducing at least one of the gains included in the first feedback control coefficient” instead of the first feedback control coefficient. Take control. That is, the second air-fuel ratio control apparatus monitors the asymmetric deterioration of the upstream air-fuel ratio sensor, and performs main feedback control using the “second feedback control coefficient” when the upstream air-fuel ratio sensor deteriorates asymmetrically.

  The magnitude of the gain included in the feedback control coefficient affects the magnitude of the feedback correction amount. Further, by applying the above-described high-pass filter processing to the output value of the upstream air-fuel ratio sensor, the high-frequency component (the high-frequency component of the variation in the air-fuel ratio of the exhaust gas) is used for main feedback control. . Therefore, the second control device employs the “second feedback control coefficient” when the upstream air-fuel ratio sensor is asymmetrically deteriorated, thereby correcting the amount of correction based on the “high frequency component” of the variation in the air-fuel ratio of the exhaust gas. Make it smaller. Thereby, the influence of the “correction amount based on the high frequency component” calculated by the main feedback control on the “correction amount based on the low frequency component” calculated by the sub feedback control can be reduced.

  As a result, the influence of the asymmetric response of the upstream air-fuel ratio sensor can be reduced as much as possible, so that the engine emission can be maintained satisfactorily.

  Here, the “theoretical air-fuel ratio” in the present invention is not limited to a strict stoichiometric air-fuel ratio. As described above, the catalyst can purify unburned matter and nitrogen oxides with high efficiency when the air-fuel ratio of the exhaust gas flowing into the catalyst is within a predetermined air-fuel ratio range. Therefore, in the present invention, the air-fuel ratio within this air-fuel ratio range is expressed as “theoretical air-fuel ratio”.

  The “first cutoff frequency” and the “second cutoff frequency” used for the main feedback control and the sub feedback control can be set to appropriate values in consideration of exhaust gas purification performance, fuel consumption, and the like required for the engine. Further, the first cutoff frequency and the second cutoff frequency may be the same or different.

  The gains included in the “first feedback control coefficient” and the “second feedback control coefficient” can be determined in consideration of exhaust gas purification performance and fuel consumption required for the engine.

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

(First embodiment)
Hereinafter, a control device (hereinafter also referred to as “first control device”) according to a first embodiment of the present invention will be described.

<Outline of device>
FIG. 1 is a schematic cross-sectional view showing an example of an internal combustion engine 10 to which the first control device is applied. FIG. 1 shows a schematic configuration of a system in which the first control device is applied to a four-cycle spark ignition multi-cylinder (four-cylinder) internal combustion engine 10. FIG. 1 shows only a cross section of a specific cylinder, but the other cylinders have the same configuration.

  The internal combustion engine 10 includes a cylinder block portion 20 including a cylinder block, a cylinder block lower case, an oil pan, and the like, a cylinder head portion 30 fixed on the cylinder block portion 20, and a gasoline mixture to the cylinder block portion 20. An intake system 40 for supplying, an exhaust system 50 for releasing exhaust gas from the cylinder block 20 to the outside, and a transmission 90 (automatic transmission) controlled by a transmission control device 80 (a hydraulic circuit including an electromagnetic valve). Machine).

  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 wall surface of the cylinder 21 and the upper surface of the piston 22 form a combustion chamber 25 together with the lower surface of the cylinder head portion 30.

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

  The engine 10 may include an in-cylinder injector (not shown) that directly injects fuel into the combustion chamber 25 in place of or in addition to the injector 39.

  The intake system 40 is provided in an intake pipe 41 including an intake manifold that communicates with the intake port 31 and forms an intake passage together with the intake port 31, an air filter 42 provided at an end of the intake pipe 41, and the intake pipe 41. A throttle valve 43 is provided which makes the opening cross-sectional area of the intake passage variable. The throttle valve 43 is rotationally driven in the intake pipe 41 by a throttle valve actuator 43a made of a DC motor.

  The exhaust system 50 includes an exhaust manifold 51 including a plurality of branches connected at one end to the exhaust port 34 of each cylinder, and the other ends of the branches of each exhaust manifold 51 and all branches are assembled. An exhaust pipe 52 connected to the collecting portion, and a catalyst 53 disposed on the exhaust pipe 52 are provided. The exhaust port 34, the exhaust manifold 51, and the exhaust pipe 52 constitute an exhaust passage.

  The exhaust system 50 may include a downstream catalyst (not shown) on the downstream side of the catalyst 53 of the exhaust pipe 52 in addition to the catalyst 53.

  The catalyst 53 (when the downstream catalyst is disposed, each of the catalyst 53 and the downstream catalyst; the same applies hereinafter) is supported on a support made of ceramic such as zirconia or the like “a catalyst component made of noble metal such as platinum”. And a three-way catalyst device (exhaust gas purification catalyst) carrying "oxygen storage material such as ceria (CeO2)". In each catalyst, when the temperature of the catalyst material is equal to or higher than the activation temperature and the air-fuel ratio of the gas flowing into the catalyst 53 is the stoichiometric air-fuel ratio, unburnt substances (HC, CO, etc.) and nitrogen oxides (NOx) Promotes the redox reaction and purifies the inflowing gas.

  This control device 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 upstream air-fuel ratio sensor 66, a downstream air-fuel ratio sensor 67, an accelerator opening sensor 68, and A vehicle speed sensor (not shown) is provided.

The air flow meter 61 is a mass flow rate of intake air flowing through the intake pipe 41 (the mass of air sucked into the engine 10 per unit time. In the present invention, it is also simply referred to as “flow rate”) Ga. Is output.
The throttle position sensor 62 detects the opening (throttle valve opening) of the throttle valve 43 and outputs a signal representing the throttle valve opening TA.

The cam position sensor 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 is converted into an engine speed NE by an electric control device 70 described later.
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 disposed in the exhaust passage. The upstream air-fuel ratio sensor 66 is disposed at the downstream side of the collection portion of the branches of the exhaust manifold 51 or the collection portion thereof. The upstream air-fuel ratio sensor 66 is a known limiting current type oxygen concentration sensor. As shown in FIG. 2, the upstream air-fuel ratio sensor 66 outputs an output value Vabyfs that is a voltage corresponding to the air-fuel ratio A / F of the “detected gas”. Therefore, in the present embodiment, the upstream air-fuel ratio sensor 66 is the air-fuel ratio of the gas flowing through the portion of the exhaust passage that is provided with the upstream air-fuel ratio sensor 66 (therefore, the empty air-fuel ratio flowing into the catalyst 53). The output value Vabyfs corresponding to the fuel ratio and the air-fuel ratio of the air-fuel mixture supplied to the engine is output.

  This output value Vabyfs matches the value Vstoich when the air-fuel ratio of the detected gas is the stoichiometric air-fuel ratio. The output value Vabyfs increases as the air-fuel ratio of the detected gas increases (lean). The upstream air-fuel ratio sensor 66 is a wide-area air-fuel ratio sensor whose output continuously changes in response to changes in the air-fuel ratio of the gas to be detected.

  The electric control device 70 described later stores the table (map) Mapabyfs shown in FIG. 2 and detects the air-fuel ratio by applying the actual output value Vabyfs to the table Mapabyfs (acquires the detected air-fuel ratio abyfs). To do). Hereinafter, the air-fuel ratio acquired from the output value Vabyfs of the upstream air-fuel ratio sensor 66 and the table Mapabyfs is also referred to as “upstream air-fuel ratio abyfs”.

  The downstream air-fuel ratio sensor 67 is disposed on the downstream side of the catalyst 53 in the exhaust passage. When the downstream catalyst is provided, the downstream air-fuel ratio sensor 67 is preferably provided in the exhaust passage between the catalyst 53 and the downstream catalyst. The downstream air-fuel ratio sensor 67 is a known electromotive force type oxygen concentration sensor (a known concentration cell type oxygen concentration sensor using stabilized zirconia). The downstream air-fuel ratio sensor 67 is the air-fuel ratio of the detected gas (the time of the air-fuel ratio of the air-fuel mixture supplied to the engine) that is the gas flowing through the exhaust passage and the portion where the downstream air-fuel ratio sensor 67 is disposed. Output value Voxs according to the average value).

  As shown in FIG. 3, the output value Voxs becomes the maximum output value max (for example, about 0.9 V) when the air-fuel ratio of the detected gas is richer than the stoichiometric air-fuel ratio, and the air-fuel ratio of the detected gas is When the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the minimum output value min (for example, about 0.1 V) is obtained. When the air-fuel ratio of the gas to be detected is the stoichiometric air-fuel ratio, the voltage Vst approximately halfway between the maximum output value max and the minimum output value min. (Intermediate voltage Vst, for example, about 0.5 V). Further, this output value Voxs suddenly changes from the maximum output value max to the minimum output value min when the air-fuel ratio of the gas to be detected changes from an air-fuel ratio richer than the stoichiometric air-fuel ratio to a lean air-fuel ratio. When the air-fuel ratio of the detection gas changes from an air-fuel ratio leaner than the stoichiometric air-fuel ratio to a rich air-fuel ratio, it suddenly changes from the minimum output value min to the maximum output value max.

Referring to FIG. 1 again, the accelerator opening sensor 68 outputs a signal representing the operation amount Accp of the accelerator pedal AP operated by the driver.
A vehicle speed sensor (not shown) is installed, for example, around the drive wheel, and outputs a signal representing the vehicle speed SPD.

  The electric control device 70 is a microcomputer including a CPU 71, a ROM 72, a RAM 73, a backup RAM 74, an interface 75 including an AD converter, and the like connected to each other via a bus.

  The interface 75 is connected to the sensors 61 to 68, and supplies signals from the sensors 61 to 68 to the CPU 71. Further, the interface 75 sends a drive signal (instruction signal) to each actuator (actuator 33a, igniter 38, injector 39, throttle valve actuator 43a, etc. of the variable intake timing device 33) according to an instruction from the CPU 71. Yes.

<Air-fuel ratio control>
Hereinafter, the air-fuel ratio control in the first control device will be described.
The first control device performs “main feedback control” for matching the upstream air-fuel ratio abyfs obtained based on the output value Vabyfs of the upstream air-fuel ratio sensor 66 with the upstream target air-fuel ratio abyfr, and the downstream air-fuel ratio. Air-fuel ratio feedback control including “sub-feedback control” for matching the output value Voxs of the sensor 67 with the downstream target value Voxsref is executed. Here, the first control device determines deterioration of the responsiveness of the upstream air-fuel ratio sensor 66 at any time, and determines that the upstream air-fuel ratio sensor 66 is “asymmetrically deteriorated”. The main feedback control is executed based on the “processed output value Vabyfslow obtained by performing low-pass filter processing on Vabyfs”.

  Specifically, first, the output value Vabyfs of the upstream air-fuel ratio sensor 66 (if the upstream air-fuel ratio sensor 66 is determined to be asymmetrically degraded, the post-processing output value Vabyfslow) is expressed as “downstream air-fuel ratio sensor. The sub-feedback correction amount Vafsfb calculated so as to reduce the output deviation amount Dvoxs between the output value Voxs of 67 and the downstream target value Voxsref is corrected. Then, the “feedback control output value Vabyfc” obtained by this correction is applied to the above-described table Mapabyfs (see FIG. 2), whereby “feedback control air-fuel ratio (corrected detected air-fuel ratio) abyfsc” is Calculated. Further, the fuel injection amount is controlled such that the feedback control air-fuel ratio abyfsc matches the “upstream target air-fuel ratio abyfr”. In the first control device, air-fuel ratio feedback control is performed in this way. Hereinafter, this air-fuel ratio feedback control will be described in more detail.

1. More specifically, the first control device calculates the feedback control output value Vabyfc according to the following equation (1). In the equation (1), Vabyfs is an output value of the upstream air-fuel ratio sensor 66 and Vafsfb is a sub-feedback correction amount calculated based on the output value Voxs of the downstream air-fuel ratio sensor 67. These values are all values obtained at the present time. A method of calculating the sub feedback correction amount Vafsfb will be described later.
Vabyfc = Vabyfs + Vafsfb (1)

The first control device obtains the feedback control air-fuel ratio abyfsc by applying the feedback control output value Vabyfc to the table Mapabyfs shown in FIG.
abyfsc = Mapabyfs (Vabyfc) (2)

  On the other hand, the first control device obtains an in-cylinder intake air amount Mc (k) that is an amount of air taken into the cylinder at the present time (time k). The in-cylinder intake air amount Mc (k) is obtained for each intake stroke of each cylinder based on the output Ga of the air flow meter 61 and the engine rotational speed NE at that time (for example, with respect to the output Ga of the air flow meter 61) The value obtained by dividing the first-order lag processing by the engine speed NE) is stored in the RAM 73 while corresponding to each intake stroke. The in-cylinder intake air amount Mc (k) may be calculated by a well-known air model (a model constructed according to a physical law simulating the behavior of air in the intake passage).

As shown in the following equation (3), the first control device divides the in-cylinder intake air amount Mc (k) by the current upstream target air-fuel ratio abyfr (k), thereby reducing the basic fuel injection amount Fbase. Ask. The upstream target air-fuel ratio abyfr (k) is stored in the RAM 73 while corresponding to each intake stroke.
Fbase = Mc (k) / abyfr (k) (3)

As shown in the following equation (4), the first control device corrects the basic fuel injection amount Fbase by the main feedback correction amount DFi (adds the main feedback correction amount DFi to the basic fuel injection amount Fbase), and finally The fuel injection amount Fi is calculated. Then, the first control device injects the fuel of the final fuel injection amount Fi from the injector 39 of the cylinder that is in the intake stroke. A method of calculating the main feedback correction amount DFi will be described later.
Fi = Fbase + DFi (4)

The main feedback correction amount DFi in the above equation (4) is obtained as follows.
First, as shown in the following equation (5), the first control device determines that the in-cylinder intake air amount Mc (k−N) at the point “N” before the present time is N cycles (ie, N · 720 ° crank angle). ) Is divided by the feedback control air-fuel ratio (corrected detected air-fuel ratio) abyfsc to obtain “in-cylinder supply” which is the amount of fuel actually supplied to the combustion chamber 25 at the time N cycles before the current time. The fuel amount Fc (k−N) ”is obtained.
Fc (k−N) = Mc (k−N) / abyfsc (5)

  Thus, in order to obtain the in-cylinder fuel supply amount Fc (k−N) before the N cycle from the present time, the in-cylinder intake air amount Mc (k−N) before the N cycle from the present time is determined as the air-fuel ratio for feedback control abyfsc. This is because it takes a time corresponding to N cycles until the air-fuel mixture burned in the combustion chamber 25 reaches the upstream air-fuel ratio sensor 66.

Next, as shown in the following equation (6), the first control device calculates the in-cylinder intake air amount Mc (k−N) N cycles before the current time as the upstream target air-fuel ratio abyfr before N cycles from the current time. By dividing by (k−N), “target in-cylinder fuel supply amount Fcr (k−N)” N cycles before the present time is obtained.
Fcr (k−N) = Mc (k−N) / abyfr (k−N) (6)

As shown in the following equation (7), the first control device subtracts the in-cylinder fuel supply amount Fc (k−N) from the target in-cylinder fuel supply amount Fcr (k−N) N cycles before the present time. The value is set as “in-cylinder fuel supply amount deviation DFc”. This in-cylinder fuel supply amount deviation DFc is an amount representing “the excess or deficiency of the fuel supplied into the cylinder at the time point before N cycles”.
DFc = Fcr (k−N) −Fc (k−N) (7)

Thereafter, the first control device obtains the main feedback correction amount DFi based on the following equation (8). In this equation (8), Gp is a preset proportional gain, and Gi is a preset integral gain. The coefficient KFB in the equation (8) is preferably variable depending on the engine speed NE, the in-cylinder intake air amount Mc, and the like. Here, the coefficient KFB is set to “1”. Further, the value SDFc in the equation (8) is an integral value of the in-cylinder fuel supply amount deviation DFc. That is, the first controller calculates the main feedback correction amount DFi by proportional-integral control based on the feedback control air-fuel ratio abyfsc and the upstream target air-fuel ratio abyfr. The main feedback correction amount DFi is added to the basic fuel injection amount Fbase as shown in the above equation (4), thereby calculating the final fuel injection amount Fi.
DFi = (Gp · DFc + Gi · SDFc) · KFB (8)

  Further, the first control device diagnoses (determines) the responsiveness deterioration of the upstream air-fuel ratio sensor 66 at any time and corrects the output value Vabyfs of the upstream air-fuel ratio sensor 66 according to the result of the diagnosis.

  A method for diagnosing (determining) the response deterioration of the upstream air-fuel ratio sensor 66 will be described with reference to the time chart shown in FIG. FIG. 4 shows an example of “change in detected air-fuel ratio abyfs (b) obtained from output value Vabyfs of upstream air-fuel ratio sensor 66” with respect to “change in actual air-fuel ratio of exhaust gas upstream of catalyst 53 (a)”. It is a time chart which shows.

  First, as shown in FIG. 4A, at time t1, the actual air-fuel ratio is increased from “the air-fuel ratio (stoich−α) smaller by α than the stoichiometric air-fuel ratio stoich” by “α more than the stoichiometric air-fuel ratio stoich”. The air-fuel ratio is changed in steps until the air-fuel ratio (sstoich + α) ”. Then, the actual air-fuel ratio is maintained at “stoich + α” from time t1 to time t3 (period Tp). At this time, as shown in FIG. 4B, it takes a certain amount of time for the detected air-fuel ratio abyfs to reach “stoich + α”. Here, “time until the detected air-fuel ratio abyfs reaches a value (stoich−α + β · A) corresponding to a predetermined ratio β (for example, β = 0.632) of the change amount A of the actual air-fuel ratio” ( That is, the time from time t1 to time t2) is acquired as the lean direction response time constant Taflean.

  Next, at time t3, the actual air-fuel ratio is changed stepwise from “stoich + α” to “stoich−α”. Then, the actual air-fuel ratio is maintained at “stoich−α” from time t3 to time t5 (period Tp). At this time, as described above, a certain amount of time is required for the detected air-fuel ratio abyfs to reach “stoich−α”. Here, “until the detected air-fuel ratio abyfs reaches a value (stoich + α−β · A) corresponding to a predetermined ratio β of the actual air-fuel ratio change amount A (for example, β = 0.632 as described above). "Time" (that is, the time from time t3 to time t4) is acquired as the rich direction response time constant Tafrich.

  Then, when the “absolute value of the difference” between the acquired lean direction response time constant Taflean and the rich direction response time constant Tafrich is larger than a predetermined allowable value, it is determined that the upstream air-fuel ratio sensor 66 is asymmetrically deteriorated. Is done.

  Further, when the first control device determines that the upstream air-fuel ratio sensor 66 has deteriorated asymmetrically, the first control device corrects the output value Vabyfs of the upstream air-fuel ratio sensor 66. A method for correcting the output value Vabyfs of the upstream air-fuel ratio sensor 66 will be described below.

When the upstream air-fuel ratio sensor 66 is determined to be asymmetrically deteriorated by the above method, the low-pass filter process is performed on the output value Vabyfs of the upstream air-fuel ratio sensor 66 according to the following equation (9) and the post-processing Output value Vabyfslow is obtained. In equation (9), Vabyfslow (k) is the post-processing output value after the update, Vabyfslow (k−1) is the post-processing output value before the update, Ts is the execution cycle of this processing, and Taf is the lean direction This is the larger response time constant (deterioration response time constant) of the response time constant Taflean and the rich direction response time constant Tafrich.
Vabyfslow (k) = Vabyfslow (k−1)
+ Ts / Taf ・ (Vabyfs (k) −Vabyfslow (k−1)) (9)

  Thereby, a frequency component larger than the cutoff frequency determined by the deterioration side response time constant Taf in the output value Vabyfs of the upstream air-fuel ratio sensor 66 is substantially removed from the output value Vabyfs. As a result, the output value Vabyfs (processed output value) that has been subjected to the low-pass filter processing is substantially composed only of frequency components that are equal to or lower than the cutoff frequency. In other words, since the “corrected output value” of the air-fuel ratio sensor is adjusted to the “output value of the low responsiveness” by the correction, the output value after processing becomes symmetrical. .

  When determining that the upstream air-fuel ratio sensor 66 is asymmetrically degraded, the first control device replaces the output value Vabyfs in the above equation (1) with the post-processing output value Vabyfslow obtained in the above equation (9). . Then, the first control device calculates the feedback control output value Vabyfc according to the above equation (1) based on the post-processing output value Vabyfslow and the sub feedback correction amount Vafsfb. Thereafter, the first control device executes main feedback control as shown in the equations (2) to (8).

2. Sub-feedback control The first control device calculates the above-described sub-feedback correction amount Vafsfb as follows.
That is, as shown in the following equation (10), the first control device obtains the output deviation amount DVoxs by subtracting the current output value Voxs of the downstream air-fuel ratio sensor 67 from the downstream target value Voxsref.
DVoxs = Voxsref−Voxs (10)

The first control device obtains the sub feedback correction amount Vafsfb based on the following equation (11). In equation (11), Kp is a preset proportional gain (proportional constant), and Ki is a preset integral gain (integral constant). SDVoxs is an integral value of the output deviation amount DVoxs.
Vafsfb = Kp · DVoxs + Ki · SDVoxs (11)

  In this way, the first control device calculates the sub feedback correction amount Vafsfb by proportional-integral control based on the output value Voxs of the downstream air-fuel ratio sensor 67 and the downstream target value Voxsref. This sub-feedback correction amount Vafsfb is used to calculate the feedback control output value Vabyfc, as shown in the above-described equation (11).

  As described above, the first control device corrects the output value Vabyfs of the upstream air-fuel ratio sensor 66 or the processed output value Vabyfslow by adding the sub feedback correction amount Vafsfb, and the feedback control obtained by the correction. The feedback control air-fuel ratio abyfsc is acquired based on the output value Vabyfc (= Vabyfs + Vafsfb) (see FIG. 2). Then, the first control device controls the fuel injection amount Fi so that the acquired feedback control air-fuel ratio abyfsc matches the upstream target air-fuel ratio abyfr.

  As a result, the upstream air-fuel ratio abyfs corresponding to the output value Vabyfs of the upstream air-fuel ratio sensor 66 approaches the upstream target air-fuel ratio abyfr, and at the same time, the output value Voxs of the downstream air-fuel ratio sensor 67 becomes the downstream target value Voxsref. Get closer. That is, the first control device is an air-fuel ratio feedback control means for matching the air-fuel ratio of the engine mixture to the upstream target air-fuel ratio abyfr based on the output value Vabyfs of the upstream air-fuel ratio sensor 66 and the sub feedback correction amount Vafsfb. It has.

  The method for setting the upstream target air-fuel ratio abyfr and the downstream target value Voxsref described above will be described later.

<Actual operation>
Hereinafter, the actual operation of the first control device will be described.
The CPU 71 of the first control device repeatedly executes each routine shown in the flowcharts of FIGS. 5 to 8 at predetermined time intervals.

  More specifically, the CPU 71 executes a fuel injection control routine shown in FIG. 5 at a predetermined timing, and calculates the final fuel injection amount Fi and instructs fuel injection. The CPU 71 calls this routine every time the crank angle of a predetermined cylinder reaches a predetermined crank angle before the intake top dead center (for example, BTDC 90 ° CA) (hereinafter also referred to as “fuel injection cylinder”). Is to be executed repeatedly. That is, the CPU 71 starts processing from step 500 in FIG. 5, sequentially performs processing from step 510 to step 540 described later, proceeds to step 595, and once ends this routine.

Step 510: The CPU 71 acquires the in-cylinder intake air amount Mc (k), which is the amount of air taken into the fuel injection cylinder, based on the intake air amount Ga measured by the air flow meter 61 and the engine speed NE.
Step 520: The CPU 71 obtains the basic fuel injection amount Fbase according to the above equation (3).
Step 530: The CPU 71 corrects the basic fuel injection amount Fbase with the main feedback correction amount DFi according to the above equation (4) to obtain the final fuel injection amount Fi.
Step 540: The CPU 71 injects fuel of the final fuel injection amount Fi from the injector 39 provided corresponding to the fuel injection cylinder.

  Thus, the fuel of the final fuel injection amount Fi is injected into the fuel injection cylinder. Hereinafter, a method for calculating the above-described main feedback correction amount DFi will be described.

  The CPU 71 executes a sensor output correction time constant acquisition routine shown in FIG. 6 every time a predetermined time elapses to determine whether or not the upstream air-fuel ratio sensor 66 is asymmetrically deteriorated, and the upstream air-fuel ratio sensor. When it is determined that 66 is asymmetrically degraded, a degradation-side response time constant Taf for correcting the output value Vabyfs is acquired. That is, the CPU 71 starts the process from step 600 in FIG. 6 at a predetermined timing, and proceeds to step 610 to determine whether or not the “sensor deterioration diagnosis execution condition” is satisfied. In the first control device, the sensor deterioration diagnosis execution condition is satisfied when the upstream air-fuel ratio sensor 66 is in the active state.

  Here, it is assumed that the sensor deterioration diagnosis execution condition is satisfied at the present time. According to this assumption, the CPU 71 makes a “Yes” determination at step 610 to proceed to step 620, where the “lean direction response time constant Taflean” separately detected (acquired) by a time constant acquisition routine (not shown) and Get “Rich direction response time constant Tafrich”.

  Here, the time constant acquisition routine is such that the engine 10 “change amount ΔTA per unit time of the throttle valve opening TA is equal to or smaller than a predetermined threshold ΔTAth (ΔTA ≦ ΔTAth), and the engine rotational speed NE is a predetermined first engine rotational speed. NE1 to the second engine speed NE2 or less (NE1 ≦ NE ≦ NE2), and the cylinder intake air amount Mc is greater than or equal to the first cylinder intake air amount Mc1 and less than or equal to the second cylinder intake air amount Mc2 (Mc1 ≦ Mc ≦ Mc2). It is executed during steady operation that is “)”. In this example, “the engine rotational speed NE is a predetermined first engine rotational speed NE1 or more and a second engine rotational speed NE2 or less (NE1 ≦ NE ≦ NE2), and the in-cylinder intake air amount Mc is the first in-cylinder intake. An operation state in which the air amount Mc1 or more and the second cylinder intake air amount Mc2 or less (Mc1 ≦ Mc ≦ Mc2) ”is referred to as a“ first operation state ”. In the time constant acquisition routine, as described above, the lean direction response time constant Taflean is based on the fluctuation of the detected air-fuel ratio abyfs when the actual air-fuel ratio of the exhaust gas is changed stepwise as shown in FIG. And the rich direction response time constant Tafrich is acquired. Note that the time constant acquisition routine is a program that is executed only when the engine 10 is operating in the first operating state and has not been executed once after the current start of the engine 10. May be.

  Next, the CPU 71 proceeds to step 630 to determine whether or not “the absolute value of the difference between the lean direction response time constant Taflean and the rich direction response time constant Tafrich” is larger than a predetermined allowable value δ. In the first control apparatus, when the “absolute value of the difference” is larger than the allowable value δ, it is determined that the upstream air-fuel ratio sensor 66 is asymmetrically deteriorated. On the other hand, when the “absolute value of the difference” is equal to or smaller than the allowable value δ, it is determined that the upstream air-fuel ratio sensor 66 has not deteriorated asymmetrically.

  Here, it is assumed that the “absolute value of difference” described above is equal to or less than the allowable value δ (that is, the upstream air-fuel ratio sensor 66 is not asymmetrically deteriorated). According to this assumption, the CPU 71 determines “No” in step 630 and proceeds to step 640 to set the value of the sensor asymmetric deterioration flag XSAD to “0”. Thereafter, the CPU 71 proceeds to step 695 to end the present routine tentatively.

  When the sensor asymmetric deterioration flag XSAD is “1”, it indicates that the upstream air-fuel ratio sensor 66 is asymmetrically deteriorated. On the other hand, when the sensor asymmetric deterioration flag XSAD is “0”, it indicates that the upstream air-fuel ratio sensor 66 has not undergone asymmetric deterioration. The value of the sensor asymmetric deterioration flag XSAD is set to “0” in an initial routine executed when an ignition key switch (not shown) is changed from OFF to ON.

  Further, the CPU 71 executes a main feedback correction amount DFi calculation routine shown in FIG. 7 at a predetermined timing, and calculates a main feedback correction amount DFi used in the processing shown in the routine of FIG. 5 (see step 530). To do. That is, the CPU 71 starts processing from step 700 and proceeds to step 705 to determine whether or not a main feedback control condition (upstream air-fuel ratio feedback control condition) is satisfied. In the first control device, the main feedback control condition is that the warm-up period of the catalyst 53 has ended, the fuel cut operation is not being executed, the cooling water temperature THW of the engine 10 is equal to or higher than the predetermined first temperature, and the engine This is established when the intake air amount (load) per revolution is equal to or less than a predetermined value and the upstream air-fuel ratio sensor 66 is activated.

  Here, it is assumed that the main feedback control condition is satisfied at the present time. According to this assumption, the CPU 71 determines “Yes” in step 705 of FIG. 7 and proceeds to step 710 to determine whether or not the value of the sensor asymmetric deterioration flag XSAD is “1”. As described above, the current value of the sensor asymmetric deterioration flag XSAD is “0”. Accordingly, the CPU 71 makes a “No” determination at step 710 to directly proceed to step 715. Next, the CPU 71 sequentially performs the processing of steps 715 to 745 described later, proceeds to step 795, and once ends this routine.

Step 715: The CPU 71 acquires the feedback control output value Vabyfc according to the above equation (1). In the first control device, the upstream target air-fuel ratio abyfr is set to the stoichiometric air-fuel ratio.
Step 720: The CPU 71 obtains the feedback control air-fuel ratio abyfsc according to the above equation (2).
Step 725: The CPU 71 acquires the in-cylinder fuel supply amount Fc (k−N) according to the above equation (5).
Step 730: The CPU 71 acquires the target in-cylinder fuel supply amount Fcr (k−N) according to the above equation (6).
Step 735: The CPU 71 acquires the in-cylinder fuel supply amount deviation DFc according to the above equation (7).
Step 740: The CPU 71 acquires the main feedback correction amount DFi according to the above equation (8). In the first control device, the coefficient KFB is set to “1”. The integral value SDFc of the in-cylinder fuel supply amount deviation DFc is obtained in the next step 745.
Step 745: The CPU 71 adds the in-cylinder fuel supply amount deviation DFc obtained in the above step 740 to the integral value SDFc of the in-cylinder fuel supply amount deviation DFc at that time, thereby obtaining a new in-cylinder fuel supply amount deviation DFc. Acquire (update) the integral value SDFc.

  Thus, the main feedback correction amount DFi is obtained by proportional integral control (PI control), and this main feedback correction amount DFi is reflected in the final fuel injection amount Fi (see step 530 in FIG. 5).

  On the other hand, if the main feedback control condition is not satisfied at the time of the determination in step 705, the CPU 71 determines “No” in step 705, proceeds to step 750, and sets the value of the main feedback correction amount DFi to zero. Next, the CPU 71 proceeds to step 755 and sets the value of the integral value SDFc of the in-cylinder fuel supply amount deviation to zero. Thereafter, the CPU 71 proceeds to step 795 to end the present routine tentatively. Thus, when the main feedback control condition is not satisfied, the main feedback correction amount DFi is set to zero. Therefore, at this time, the basic fuel injection amount Fbase is not corrected by the main feedback correction amount DFi.

  Further, the CPU 71 executes a sub-feedback correction amount Vafsfb calculation routine shown in FIG. 8 at a predetermined timing, and calculates a sub-feedback correction amount Vafsfb used in the process shown in the routine of FIG. 7 (see step 715). To do. That is, the CPU 71 starts processing from step 800 in FIG. 8 and proceeds to step 810 to determine whether or not the sub feedback control condition is satisfied. In the first control device, the sub feedback control condition is that a main feedback condition (see step 705) shown in FIG. 7 is established, and the engine coolant temperature THW is equal to or higher than a second temperature higher than the first temperature, Further, it is established when the downstream air-fuel ratio sensor 67 is activated.

  Here, it is assumed that the sub-feedback control condition is satisfied at the present time. According to this assumption, the CPU 71 determines “Yes” in step 810 of FIG. 8 and proceeds to step 820. Next, the CPU 71 sequentially performs the processing from step 820 to step 840 to be described later, proceeds to step 895, and once ends this routine.

Step 820: The CPU 71 acquires an output deviation amount DVoxs that is a difference between the downstream target value Voxsref and the output value Voxs of the downstream air-fuel ratio sensor 67 according to the above equation (10). In the first control device, the downstream target value Voxsref is set to a value corresponding to the theoretical air-fuel ratio.
Step 830: The CPU 71 acquires the sub feedback correction amount Vafsfb according to the above equation (11). Note that the proportional gain Kp and the integral gain Ki at this point are set to appropriate values obtained in advance.
Step 840: The CPU 71 obtains a new output deviation amount integrated value SDVoxs by adding the output deviation amount DVoxs obtained in step 830 to the integral value SDVoxs of the output deviation amount at that time.

  Thus, the sub feedback correction amount Vafsfb is obtained by proportional integral control (PI control), and the output value Vabyfs of the upstream air-fuel ratio sensor 66 described above is corrected by this sub feedback correction amount Vafsfb (Step 715 in FIG. 7 is corrected). reference.). Then, a main feedback amount DFi is obtained based on the corrected feedback control output value Vabyfc (see step 740 in FIG. 7), and this main feedback amount DFi is reflected in the final fuel injection amount Fi (FIG. 5). Step 530).

  On the other hand, when the sub-feedback control condition is not satisfied at the time of determination in step 810, the CPU 71 determines “No” in step 810, proceeds to step 850, and sets the value of the sub-feedback correction amount Vafsfb to zero. Next, the CPU 71 proceeds to step 860 and sets the value of the integral value SDVoxs of the output deviation amount to zero. Thereafter, the CPU 71 proceeds to step 895 to end the present routine tentatively. Thus, when the sub feedback control condition is not satisfied, the sub feedback correction amount Vafsfb is set to zero. Accordingly, at this time, the basic fuel injection amount Fbase is not corrected by the sub feedback correction amount Vafsfb.

  Here, it is assumed that the upstream air-fuel ratio sensor 66 has asymmetrically deteriorated due to reasons such as aging. Furthermore, it is assumed that the sensor deterioration diagnosis execution condition is also satisfied at the present time. According to the above assumption (the sensor deterioration diagnosis execution condition is established), when the CPU 71 starts the process from step 600 in FIG. 6, the CPU 71 determines “Yes” in step 610, proceeds to step 620, and performs lean. The direction response time constant Taflean and the rich direction response time constant Tafrich are acquired, and the process proceeds to step 630. Then, according to the above assumption (the upstream air-fuel ratio sensor 66 is asymmetrically degraded), the absolute value of the difference between the lean direction response time constant Taflean and the rich direction response time constant Tafrich is larger than the allowable value δ. . Accordingly, the CPU 71 determines “Yes” at step 630 and proceeds to step 650 to set the value of the sensor asymmetric deterioration flag XSAD to “1”.

  Next, the CPU 71 proceeds to step 660 to determine whether or not the rich direction response time constant Tafrich is larger than the lean direction response time constant Taflean. Here, at present, it is assumed that the rich direction response time constant Tafrich is larger than the lean direction response time constant. According to this assumption, the CPU 71 determines “Yes” in step 660 and proceeds to step 670 to store the rich direction response time constant Tafrich in the deterioration side response time constant Taf. Thereafter, the CPU 71 proceeds to step 695 to end the present routine tentatively.

  On the other hand, when the lean direction response time constant Taflean is larger than the rich direction response time constant Tafrich at the time of the determination in step 660, the CPU 71 makes a “No” determination at step 660 to proceed to step 680. The lean direction response time constant is stored in the constant Taf. Thereafter, the CPU 71 proceeds to step 695 to end the present routine tentatively.

  At this time, when the CPU 71 starts the process from step 700 in FIG. 7, if the main feedback control condition described above is satisfied, the CPU 71 determines “Yes” in step 705 and proceeds to step 710. As described above, the current value of the sensor asymmetric deterioration flag XSAD is “1”. Accordingly, the CPU 71 determines “Yes” in step 710 and proceeds to step 760.

  In step 760, the CPU 71 performs “low-pass filter processing using the degradation-side response time constant Taf as a time constant” for the output value Vabyfs of the upstream air-fuel ratio sensor 66 according to the above equation (9), and outputs the processed result. Gets the value Vabyfslow. Next, the CPU 71 proceeds to step 765 so as to store the post-processing output value Vabyfslow obtained in step 760 as the output value Vabyfs of the upstream air-fuel ratio sensor 66. With this processing, the output value Vabyfs is replaced with the post-processing output value Vabyfslow.

  Next, based on the output value Vabyfs obtained in step 765 (the post-processing output value Vabyfslow obtained by low-pass filtering the output value Vabyfs of the upstream air-fuel ratio sensor 66), the CPU 71 performs steps 715 to The main feedback correction amount DFi is acquired by sequentially performing the processing of 745.

  As described above, the main feedback correction amount DFi based on the post-processing output value Vabyfslow is obtained by proportional integral control (PI control), and this main feedback correction amount DFi is reflected in the final fuel injection amount Fi (see step 530 in FIG. 5). reference.).

  Furthermore, when the CPU 71 starts the process from step 800 in FIG. 8, if the above-described sub feedback control condition is satisfied, the CPU 71 determines “Yes” in step 810 and proceeds to step 820 and subsequent steps. Next, as described above, the CPU 71 sequentially performs the processing from step 820 to step 840 to acquire the sub feedback correction amount Vafsfb.

  Thus, the sub-feedback correction amount Vafsfb is obtained by proportional integral control (PI control), and the output value Vabyfs of the upstream air-fuel ratio sensor 66 described above (the output value Vabyfs of the upstream air-fuel ratio sensor 66) is determined by this sub-feedback correction amount Vafsfb. The post-processing output value Vabyfslow obtained by performing low-pass filtering is corrected (see step 715 in FIG. 7). Then, a main feedback amount DFi is obtained based on the corrected feedback control output value Vabyfc (see step 740 in FIG. 7), and this main feedback amount DFi is reflected in the final fuel injection amount Fi (FIG. 5). Step 530).

  As described above, in the first control device, when the absolute value of the difference between the lean direction response time constant Taflean and the rich direction response time constant Tafrich of the upstream air-fuel ratio sensor 66 becomes larger than the predetermined allowable value δ. Therefore, it is determined that the upstream air-fuel ratio sensor 66 has asymmetrically deteriorated. When it is determined that the upstream air-fuel ratio sensor 66 has deteriorated asymmetrically, low-pass filter processing is performed on the output value Vabyfs of the upstream air-fuel ratio sensor 66 with the deterioration-side response time constant Taf as a time constant. Then, feedback control for the air-fuel ratio of the engine 10 is executed based on the processed output value Vabyfslow obtained by the low-pass filter processing. On the other hand, when the upstream air-fuel ratio sensor 66 is not asymmetrically degraded, the low-pass filter process is not performed, and the feedback process for the air-fuel ratio of the engine 10 is performed based on the output value Vabyfs of the upstream air-fuel ratio sensor 66.

As described above, the first control device
An air-fuel ratio sensor (upstream air-fuel ratio sensor 66) that outputs an output value Vabyfs corresponding to the air-fuel ratio of exhaust gas that is disposed in the exhaust passage of the internal combustion engine 10 and that flows through the disposed portion;
The lean direction response time constant Taflean, which is the response time constant of the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas increases, and the rich that is the response time constant of the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas decreases Response time constant acquisition means for acquiring a direction response time constant Tafrich (see step 620 in FIG. 6);
The reference response time constant is determined based on the deterioration side response time constant Taf, which is the larger response time constant of the lean direction response time constant Taflean and the rich direction response time constant Tafrich. (In this example, the reference response time constant is determined to be equal to the degradation-side response time constant Taf. See steps 660 to 680 in FIG. 6). Further, the first control device performs low-pass filter processing having a time constant corresponding to the reference response time constant (in this example, the deterioration side response time constant Taf) on the output value Vabyfs of the air-fuel ratio sensor. Sensor output processing means (see step 760 in FIG. 7) for obtaining a post-processing output value Vabyfslow;
Air-fuel ratio feedback control is performed to match the air-fuel ratio of the air-fuel mixture supplied to the engine with the target air-fuel ratio based on the processed output value (see step 765 and steps 715 to 745 in FIG. 7). Air-fuel ratio control means;
Is provided.

  In this way, the first control device evaluates the degree of deterioration of the air-fuel ratio sensor based on the magnitudes of the lean direction response time constant Taflean and the rich direction response time constant Tafrich. When it is determined that the air-fuel ratio sensor has deteriorated asymmetrically, the response time constant in the direction in which the degree of deterioration is large (deterioration response time constant Taf. That is, the lean direction response time constant Taflean and the rich direction response time constant Tafrich The larger one of the response time constants) is subjected to a -pass filter process on the output value Vabyfs. That is, in the first control device, the degradation-side response time constant Taf is adopted as the reference response time constant, and low-pass filter processing using the reference response time constant as the time constant is executed.

  By the low-pass filter processing, a frequency component larger than the frequency corresponding to the deterioration side response time constant Taf (cutoff frequency) in the output value Vabyfs of the air-fuel ratio sensor is substantially removed from the output value of the air-fuel ratio sensor. The Thereby, as described above, it is possible to obtain a post-processing output value that exhibits symmetric response. Then, by executing the air-fuel ratio feedback control based on the post-processing output value Vabyfslow, the air-fuel ratio of the engine can be appropriately controlled. As a result, the engine emission can be maintained well.

  The first control device is configured to set the “deterioration response time constant Taf” as a reference response time constant. However, the control device of the present invention is configured such that the reference response time constant is set to “a value equal to or greater than the deterioration side response time constant (Taf + Δ)” obtained by adding the predetermined value Δ to the deterioration side response time constant Taf. You can also. At this time, the predetermined value Δ added to the deterioration-side response time constant can be set to an appropriate value in consideration of the operating state of the engine, the exhaust gas purification capability required for the engine, fuel consumption, and the like.

  Here, the first control device evaluates the degree of asymmetric deterioration of the upstream air-fuel ratio sensor 66, and when the degree is greater than a predetermined value (see step 630 in FIG. 6), the upstream air-fuel ratio sensor. The output value Vabyfs of 66 is configured to be low-pass filtered (see step 760 in FIG. 7). However, the control device of the present invention does not include a process for evaluating the degree of asymmetric deterioration of the upstream air-fuel ratio sensor 66 (that is, omits step 630 to step 650 in FIG. 6 and step 710 in FIG. 7). It may be configured to always perform low-pass filter processing using the degradation-side response time constant as a time constant. Further, the time constant of the low-pass filter process may be a value equal to or greater than the degradation-side response time constant as described above.

  The first control device obtains the main feedback correction amount DFi by proportional-integral control (PI control). However, the control device of the present invention may be configured to obtain the main feedback correction amount DFi by, for example, proportional integral derivative control (PID control).

  In the present invention, the upstream target air-fuel ratio abyfr and the downstream target value Voxsref are not limited to the values described above, but may be set to appropriate values in consideration of the operating state of the engine, the exhaust gas purification capacity required for the engine, fuel consumption, and the like. it can.

  The “threshold opening degree TAth”, “first engine rotational speed NE1”, “second engine rotational speed NE2”, “first in-cylinder intake air amount Mc1” and “second in-cylinder intake air amount Mc2” are as follows: It can be set to an appropriate value in consideration of exhaust gas purification capacity and fuel consumption required for the engine.

(Second Embodiment)
Hereinafter, a control device (hereinafter also referred to as “second control device”) according to a second embodiment of the present invention will be described. The second control device is different from the first control device only in that the CPU executes the processing shown in the flowchart of FIG. 9 in addition to the processing shown in the flowcharts of FIGS. Therefore, the following description will be made with this difference as the center.

  Similar to the first control device, the second control device repeatedly executes the processes shown in the flowcharts of FIGS. 5 and 6 at predetermined time intervals. That is, the second control device calculates the basic fuel injection amount Fbase based on the current target air-fuel ratio abyfr (k) and in-cylinder intake air amount Mc (k) by the processing shown in FIG. Then, the second control device corrects the basic fuel injection amount Fbase with the main feedback correction amount DFi to obtain the final fuel injection amount Fi. Next, the second control device gives an instruction to a fuel injection mechanism such as an injector so as to inject the fuel of the final fuel injection amount Fi into the fuel injection cylinder. Further, the second control device diagnoses the deterioration of the upstream air-fuel ratio sensor 66 at a predetermined timing by the processing shown in FIG. 6, and when the upstream air-fuel ratio sensor 66 is asymmetrically deteriorated, The deterioration side response time constant Taf for correcting the output value Vabyfs of the fuel ratio sensor 66 is acquired. In the following, it is assumed that the upstream air-fuel ratio sensor 66 has asymmetrically deteriorated (determined as “Yes” in step 630 in FIG. 6), and the value of the sensor asymmetric deterioration flag XSAD is set to “1”. Continue the explanation.

  The second control device executes a response time constant correction routine shown in FIG. 9 at a predetermined timing, and corrects the deterioration side response time constant Taf based on the operating state of the engine 10. That is, the CPU 71 starts processing from step 900 of FIG. 9 and proceeds to step 910 to determine whether or not the value of the sensor asymmetric deterioration flag XSAD is “1”. If the above assumption is followed, since the value of the sensor asymmetric deterioration flag XSAD is “1”, the CPU 71 determines “Yes” in step 910 and proceeds to step 920. In step 920, the CPU 71 adds the in-cylinder intake air amount Mc and the engine at the present time to a correction coefficient table MapKctc (Mc, NE) in which the relationship between the in-cylinder intake air amount Mc and the correction coefficient Kctc with respect to the engine speed NE is predetermined. By applying the rotational speed NE, the correction coefficient Kctc at the present time is acquired.

  The correction coefficient Kctc indicates that the lean direction response time constant Taflean and the rich direction response time constant Tafrich are acquired as “the first operating state (that is, the engine speed NE is equal to or higher than the predetermined first engine speed NE1 and the second engine. Operating condition where the rotational speed is NE2 or less (NE1 ≦ NE ≦ NE2) and the cylinder intake air amount Mc is greater than or equal to the first cylinder intake air amount Mc1 and less than or equal to the second cylinder intake air amount Mc2 (Mc1 ≦ Mc ≦ Mc2). ) "Is set to" 1 ". In this example, the operation state other than the first operation state is also referred to as “second operation state” for convenience.

  Next, the CPU 71 proceeds to step 930 to multiply the deterioration side response time constant Taf acquired by the processing shown in FIG. 6 (see step 660 to step 680) by the correction coefficient Kctc (Kctc × Taf). As a result, the deterioration side response time constant Taf is corrected. Further, the CPU 71 again stores the value obtained as a result of the multiplication in the deterioration side response time constant Taf. Thereafter, the CPU 71 proceeds to step 995 to end the present routine tentatively.

  On the other hand, when the value of the sensor asymmetric deterioration flag XSAD is “0” at the time of determination in step 910 (that is, when the upstream air-fuel ratio sensor 66 is not asymmetrically deteriorated), the CPU 71 determines that “ The determination is “No” and the process proceeds directly to step 995 to end the present routine tentatively. Accordingly, at this time, the deterioration side response time constant Taf is not corrected.

  Further, the CPU 71 executes the routine shown in FIG. 7 at a predetermined timing, as in the first control device. Here, it is assumed that the main feedback condition described above is satisfied at the present time. Further, as described above, the current value of the sensor asymmetric deterioration flag XSAD is “1”. Accordingly, when the CPU 71 starts processing from step 700 in FIG. 7, it determines “Yes” in both step 705 and step 710 and proceeds to step 760.

  In step 760, the CPU 71 performs low-pass filter processing with the time constant as “deterioration response time constant Taf corrected by the processing shown in the routine of FIG. 9” for the output value Vabyfs of the upstream air-fuel ratio sensor 66. And obtain the output value Vabyfslow after processing. Next, the CPU 71 proceeds to step 765 so as to store the post-processing output value Vabyfslow obtained in step 760 as the output value Vabyfs of the upstream air-fuel ratio sensor 66.

  Then, the CPU 71, based on the output value Vabyfs obtained in step 765 (the processed output value Vabyfslow obtained by low-pass filtering the output value Vabyfs of the upstream air-fuel ratio sensor 66), similarly to the first control device. The main feedback correction amount DFi is acquired by sequentially performing the processing from step 715 to step 745. Further, the CPU 71 executes the routine shown in FIG. 8 to acquire the sub feedback correction amount Vafsfb, as in the first control device.

  Thus, the sub-feedback correction amount Vafsfb is obtained by proportional integral control (PI control), and the output value Vabyfs of the upstream air-fuel ratio sensor 66 described above (the output value Vabyfs of the upstream air-fuel ratio sensor 66) is determined by this sub-feedback correction amount Vafsfb. The post-processing output value Vabyfslow obtained by performing low-pass filtering is corrected (see step 715 in FIG. 7). Then, a main feedback amount DFi is obtained based on the corrected feedback control output value Vabyfc (see step 740 in FIG. 7), and this main feedback amount DFi is reflected in the final fuel injection amount Fi (FIG. 5). Step 530).

  As described above, in the second control device, when the upstream air-fuel ratio sensor 66 is asymmetrically deteriorated, the deterioration-side response time constant Taf is corrected based on the operating state of the engine (in-cylinder intake air amount and engine rotational speed). Is done. Then, the output value Vabyfs of the upstream air-fuel ratio sensor 66 is subjected to low-pass filter processing using the corrected deterioration side response time constant Taf as a time constant. Thereafter, as with the first control device, feedback control for the air-fuel ratio of the engine 10 is executed based on the processed output value Vabyfslow obtained by the low-pass filter processing.

As described above, in the second control device,
The sensor output processing means in the first controller is
The reference response time constant is configured to be determined based on the deterioration side response time constant Taf when the engine 10 is in the first operating state (see Steps 660 to 680 in FIG. 6), and ,
When the engine 10 is in a second operating state different from the first operating state, a value obtained by correcting the “deterioration response time constant Taf” based on a parameter corresponding to the second operating state (FIG. 9 is used as the time constant of the low-pass filter (see step 760 in FIG. 7).

  As described above, the operating state of the engine 10 affects the responsiveness of the upstream air-fuel ratio sensor 66. For this reason, the time constant of the low-pass filter determined in a specific operation state (in this example, the first operation state) is not an optimal value in another operation state (in this example, the second operation state). There is a fear. Therefore, the second control device corrects the deterioration-side response time constant Taf of the upstream air-fuel ratio sensor 66 based on the operating state of the engine. Then, the second control device corrects the output value Vabyfs of the upstream air-fuel ratio sensor 66 based on the response time constant Taf obtained by this correction. With this configuration, even when the operating state of the engine 10 has changed, the time constant of the low-pass filter can be set to be equal to or greater than the deterioration-side response time constant in each operating state.

  Accordingly, the time constant used for the low-pass filter process can be determined more appropriately, and it is possible to avoid applying an excessive or excessive low-pass filter process to the output value Vabyfs of the upstream air-fuel ratio sensor 66. As a result, the emission of the engine can be maintained better.

  Here, the second control device corrects the “deterioration-side response time constant Taf” according to the operating state of the engine 10, and based on the corrected deterioration-side response time constant Taf, the reference response time constant (accordingly, the low-pass filter). The time constant is determined. However, the second control device is configured to first determine a reference response time constant based on the deterioration-side response time constant Taf, and correct the determined “reference response time constant” according to the operating state of the engine 10. May be.

That is, the sensor output processing means in the first control device is
The reference response time constant is configured to be determined based on the deterioration side response time constant when the engine is in the first operating state; and
When the engine is in a second operating state different from the first operating state, the “reference response time constant” is corrected based on a parameter corresponding to the second operating state, and the corrected value is obtained. A corresponding time constant may be adopted as the time constant of the low-pass filter.

  In the second control device, the “time constant corresponding to the corrected value” may be “the value itself corrected based on the parameter corresponding to the second operating state” or “the parameter corresponding to the second operating state” It may be a value obtained by adding a predetermined positive value to the value corrected based on the above.

  The second control device employs the in-cylinder intake air amount Mc and the engine rotational speed NE as parameters according to the operating state of the engine 10 (see step 920 and step 930 in FIG. 9). However, in the present invention, the accelerator pedal opening degree Accp, the engine load factor KL, etc. are adopted as parameters according to the operating state of the engine 10 instead of or in addition to the in-cylinder intake air amount Mc and the engine rotational speed NE. Also good. Moreover, you may employ | adopt as a parameter according to the driving | running state one or more of these parameters.

(Third embodiment)
Hereinafter, a third embodiment of the present invention (hereinafter also referred to as “third control device”) will be described.

<Outline of device>
The third control device can be applied to an internal combustion engine similar to the internal combustion engine to which the first control device is applied. Therefore, a detailed description of the configuration of the internal combustion engine to which the third control device is applied is omitted.

<Air-fuel ratio control>
Hereinafter, the air-fuel ratio control in the third control device will be described.
As shown in the functional block diagram of FIG. 10, the third control device is configured to include each means of A1 to A12. Details of the functional block diagram of FIG. 10 are disclosed in Japanese Patent Application Laid-Open No. 2004-257377. Hereinafter, these means will be described with reference to FIG.

1. Calculation of Basic Fuel Injection Amount First, the cylinder intake air amount calculation means A1 calculates the cylinder intake air amount Mc (k), which is the amount of air that is taken into the cylinder at the present time (time k). The in-cylinder intake air amount Mc (k) is obtained for each intake stroke of each cylinder based on the output Ga of the air flow meter 61 and the engine rotational speed NE at that time (for example, with respect to the output Ga of the air flow meter 61) The value obtained by dividing the first-order lag processing by the engine speed NE) is stored in the RAM 73 while corresponding to each intake stroke. The in-cylinder intake air amount Mc (k) may be calculated by a well-known air model (a model constructed according to a physical law simulating the behavior of air in the intake passage). Here, the subscript (k) indicates a value for the current intake stroke (hereinafter, the same applies to other parameters).

  The upstream target air-fuel ratio setting means A2 is an upstream target air-fuel ratio abyfr (k) corresponding to a predetermined upstream target value based on the engine speed NE, which is the operating state of the engine 10, the throttle valve opening TA, and the like. To decide. 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 engine 10 is completed, 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.

As shown in the following equation (12), the basic fuel injection amount calculation means A3 divides the in-cylinder intake air amount Mc (k) by the upstream target air-fuel ratio abyfr (k), thereby obtaining the basic fuel injection amount Fbase. Ask for. The basic fuel supply amount Fbase is stored in the RAM 73 while corresponding to the intake stroke of each cylinder.
Fbase = Mc (k) / abyfr (k) (12)

  As described above, the basic fuel injection amount Fbase is obtained by the cylinder intake air amount calculation unit A1, the upstream target air-fuel ratio setting unit A2, and the basic fuel injection amount calculation unit A3.

2. Calculation of fuel injection amount As shown in the following equation (13), the fuel injection amount calculation means A4 for sub feedback control uses a sub feedback control coefficient (sub feedback correction) calculated by a PID controller A16, which will be described later, as a basic fuel injection amount Fbase. The fuel injection amount Fbasesb for sub feedback control is obtained by multiplying the amount) KFi.
Fbaseb = KFi · Fbase (13)

The fuel injection amount calculation means A5 calculates the final fuel injection amount Fi by adding a main feedback correction amount DFi, which will be described later, to the sub feedback control fuel injection amount Fbasesb as shown in the following equation (14).
Fi = Fbasesb + DFi (14)

  As described above, the third control device uses the sub feedback control fuel injection amount calculation means A4 and the fuel injection amount calculation means A5 to change the basic fuel injection amount Fbase based on the main feedback correction amount DFi and the sub feedback control coefficient KFi. to correct. Then, fuel of the fuel injection amount Fi obtained by this correction is injected from the injector 39 into the cylinder that reaches the current intake stroke.

3. Calculation of the main feedback correction amount The table conversion means A6, based on the output value Vabyfs of the upstream air-fuel ratio sensor 66 and the table (map) Mapabyfs shown in FIG. The detected air-fuel ratio abyfs is obtained.
abyfs = Mapabyfs (Vabyfs) (15)

  The in-cylinder intake air amount delay means A7 reaches the intake stroke N cycles before the present time out of the in-cylinder intake air amount Mc obtained by the in-cylinder intake air amount calculation means A1 for each intake stroke and stored in the RAM 73. The in-cylinder intake air amount Mc of the selected cylinder is read from the RAM 73 and set as the in-cylinder intake air amount Mc (k−N).

The in-cylinder fuel supply amount calculation means A8 divides the in-cylinder intake air amount Mc (k−N) N cycles before the current time by the detected air-fuel ratio abyfs as shown in the following equation (16). To determine the actual in-cylinder fuel supply amount Fc (k−N) N cycles before.
Fc (k−N) = Mc (k−N) / abyfs (16)

  Thus, in order to obtain the actual in-cylinder fuel supply amount Fc (k−N) N cycles before the present time, the in-cylinder intake air intake amount Mc (k−N) N cycles before the present time is detected at the present time. The reason for dividing by the fuel ratio abyfs is that it takes time corresponding to N cycles until the air-fuel mixture fueled in the combustion chamber 25 reaches the upstream air-fuel ratio sensor 66.

Next, as shown in the following equation (17), the target in-cylinder fuel supply amount delay means A9 sets the in-cylinder intake air amount Mc (k−N) N cycles before the current time to the upstream before N cycles from the current time. By dividing by the target air-fuel ratio abyfr (k−N), the “target in-cylinder fuel supply amount Fcr (k−N)” N cycles before the present time is obtained.
Fcr (k−N) = Mc (k−N) / abyfr (k−N) (17)

The in-cylinder fuel supply amount deviation calculating means A10 subtracts the in-cylinder fuel supply amount Fc (k−N) from the target in-cylinder fuel supply amount Fcr (k−N) N cycles before the current time according to the following equation (18). Is set as “in-cylinder fuel supply amount deviation DFc”. This in-cylinder fuel supply amount deviation DFc is an amount representing “the excess or deficiency of the fuel supplied into the cylinder at the time point before N cycles”.
DFc = Fcr (k−N) −Fc (k−N) (18)

The in-cylinder fuel supply amount deviation DFc is input to the high-pass filter A11. The high pass filter A11 has the characteristics shown in the following equation (19). The third controller performs high-pass filter processing shown in the following equation (19) on the in-cylinder fuel supply amount deviation DFc, and outputs the in-cylinder fuel supply amount deviation DFchi after passing through the high-pass filter. In the following equation (19), s is a Laplace operator, and τ is a time constant. The high-pass filter A11 substantially removes a low frequency component having a cutoff frequency (1 / τ) or less from the input signal.
1-1 / (1 + τ · s) (19)

The PI controller A12 performs proportional-integral processing (PI processing) on the in-cylinder fuel supply amount deviation DFchi that has passed through the high-pass filter, which is output from the high-pass filter A11, so that the fuel supply amount before N cycles according to the following equation (20) ( The main feedback correction amount DFi for compensating for the excess or deficiency of the high frequency component equal to or higher than the cut-off frequency in (1) is obtained. In the following equation (20), GP is a proportional gain (proportional constant), GI is an integral gain (integral constant), and SDFchi is a time integral value of the in-cylinder fuel supply amount deviation DFchi after passing through the high-pass filter. The coefficient KFB in the equation (20) is preferably variable depending on the engine speed NE, the in-cylinder intake air amount Mc, and the like.
DFi = (Gp · DFchi + Gi · SDFchi) · KFB (20)

  Here, the third control device diagnoses (determines) the deterioration of the responsiveness of the upstream air-fuel ratio sensor 66 in the same manner as the first control device, and determines that the upstream air-fuel ratio sensor 66 has not deteriorated asymmetrically. Then, the preset first proportional gain Gp and first differential gain Gi are employed as the proportional gain and integral gain in the above equation (20) (hereinafter, the first proportional gain Gp and the first differential gain Gi are collectively referred to as “general gain”). (Also referred to as “first feedback control coefficient”). On the other hand, when it is determined that the upstream air-fuel ratio sensor 66 is asymmetrically deteriorated, the third control device obtains “second” obtained by reducing at least one of the gains included in the first feedback control coefficient. "Feedback control coefficient" is adopted.

  As described above, the third control device obtains the main feedback correction amount DFi based on the upstream target air-fuel ratio abyfr and the output value Vabyfs of the upstream air-fuel ratio sensor 66. As shown in the equation (14), the main feedback correction amount DFi is added to the sub feedback control fuel injection amount Fbasesb obtained by the sub feedback control. Thereby, the air-fuel ratio of the engine 10 is corrected by the main feedback correction amount DFi. A method of calculating the sub feedback control fuel injection amount Fbasesb will be described later.

4). Calculation of Sub Feedback Correction Amount The downstream target value setting means A13 is based on the engine rotational speed NE, which is the operating state of the internal combustion engine 10, the throttle valve opening TA, and the like, similarly to the upstream target air / fuel ratio setting means A2. Then, the downstream target value (predetermined downstream target value) Voxsref corresponding to the downstream target air-fuel ratio is determined. This downstream target value Voxsref is set to 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 completed. In the third control device, 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). The

The output deviation amount calculating means A14 calculates the output deviation amount DVoxs by subtracting the current output value Voxs of the downstream air-fuel ratio sensor 67 from the current downstream target value Voxsref according to the following equation (21).
DVoxs = Voxsref−Voxs (21)

The output deviation amount DVoxs is input to the low pass filter A15. The low-pass filter A15 has the characteristics shown in the following equation (22). The third control device performs low-pass filter processing based on the following equation (22) on the input output deviation amount DVoxs, and outputs an output deviation amount DVoxslow after passing through the low-pass filter. In the following equation (22), s is a Laplace operator, and τ is the same time constant as in the above equation (19). The low-pass filter A15 substantially removes a high-frequency component having a cutoff frequency (1 / τ) or higher from the input signal.
1 / (1 + τ · s) (22)

Next, a differential value DDVoxslow of the output deviation amount DVoxslow after passing through the low-pass filter is obtained according to the following equation (23). In the following equation (23), DVoxslow is the output deviation amount after passing through the low-pass filter, DVoxslow1 is the output deviation amount DVoxslow after passing through the low-pass filter before update, and Δt is the calculation cycle of this routine.
DDVoxslow = (DVoxslow−DVoxslow1) / Δt (23)

The PID controller A16 obtains the sub-feedback control coefficient KFi by subjecting the output deviation amount DVoxslow after passing through the low-pass filter output from the low-pass filter A15 to proportional-integral-derivative processing (PID processing) according to the following equation (24). In the following equation (24), Kp is a preset proportional gain (proportional constant), Ki is a preset integral gain (integral constant), Kd is a preset differential gain (differential constant), and SDVoxslow is a low-pass filter. A time integral value of the output deviation amount DVoxslow after passage, and DDVoxslow is a time differential value of the output deviation amount DVoxslow after passage of the low pass filter.
KFi = (Kp · DVoxslow + Ki · SDVoxslow + Kd · DDVoxslow) + 1 (24)

  As described above, the third control device obtains the sub feedback control coefficient KFi based on the downstream target value Voxsref and the output value Voxs of the downstream air-fuel ratio sensor 67. Then, as shown in the above equation (13), the sub-feedback control coefficient KFi is multiplied by the basic fuel injection amount Fbase. Thereby, the air-fuel ratio of the engine 10 is corrected by the sub feedback control coefficient KFi. The sub feedback control fuel injection amount Fbasesb obtained by this correction is further corrected by the main feedback correction amount DFi as described above.

  As described above, the third control device connects the main feedback control circuit and the sub feedback control circuit in parallel to the internal combustion engine 10 (see FIG. 10). The third control device obtains a sub-feedback control coefficient KFi based on the downstream target value Voxsref and the output value Voxs of the downstream air-fuel ratio sensor 67, and corrects the air-fuel ratio of the engine 10 by this sub-feedback control coefficient KFi. Further, the third control device obtains a main feedback correction amount DFi based on the upstream target air-fuel ratio abyfr and the output value Vabyfs of the upstream air-fuel ratio sensor 66, and corrects the air-fuel ratio of the engine 10 by this main feedback correction amount DFi. To do. That is, the correction of the air-fuel ratio by the main feedback control and the correction of the air-fuel ratio by the sub-feedback control are performed independently.

  The method for setting the upstream target air-fuel ratio abyfr and the downstream target value Voxsref described above will be described later.

<Actual operation>
Hereinafter, the actual operation of the third control device will be described.
The CPU 71 of the third control device repeatedly executes each routine shown in the flowcharts of FIGS. 6 and 10 to 13 at predetermined time intervals.

  More specifically, the CPU 71 executes a fuel injection control routine shown in FIG. 11 at a predetermined timing, and calculates the final fuel injection amount Fi and instructs fuel injection. The CPU 71 calls this routine every time the crank angle of a predetermined cylinder reaches a predetermined crank angle before the intake top dead center (for example, BTDC 90 ° CA) (hereinafter also referred to as “fuel injection cylinder”). Is to be executed repeatedly. That is, the CPU 71 starts processing from step 1100 in FIG. 11, sequentially performs processing from step 1110 to step 1150 to be described later, proceeds to step 1195, and once ends this routine.

Step 1110: The CPU 71 acquires the in-cylinder intake air amount Mc (k), which is the amount of air taken into the fuel injection cylinder, based on the intake air amount Ga measured by the air flow meter 61 and the engine speed NE.
Step 1120: The CPU 71 obtains the basic fuel injection amount Fbase according to the above equation (12).
Step 1130: The CPU 71 corrects the basic fuel injection amount Fbase with the sub-feedback correction amount KFi according to the above equation (13) to obtain the sub-feedback control fuel injection amount Fbasesb.
Step 1140: The CPU 71 corrects the sub feedback control fuel injection amount Fbasesb with the main feedback correction amount DFi according to the above equation (14) to obtain the final fuel injection amount Fi.
Step 1150: The CPU 71 injects fuel of the final fuel injection amount Fi from the injector 39 provided corresponding to the fuel injection cylinder.

  Thus, the fuel of the final fuel injection amount Fi is injected into the fuel injection cylinder. Hereinafter, a method for calculating the above-described main feedback correction amount DFi will be described.

  Similar to the first control device, the third control device diagnoses the deterioration of the upstream air-fuel ratio sensor 66 at a predetermined timing by the processing shown in FIG. In the following, it is assumed that the upstream air-fuel ratio sensor 66 has asymmetrically deteriorated (determined as “Yes” in step 630 in FIG. 6), and the value of the sensor asymmetric deterioration flag XSAD is set to “1”. Continue the explanation.

  The third control device executes a main feedback correction amount DFi calculation routine shown in FIG. 12 at a predetermined timing, and sets the main feedback correction amount DFi used in the processing shown in the routine of FIG. 11 (see step 1140). calculate. That is, the CPU 71 starts processing from step 1200 and proceeds to step 1205 to determine whether or not the main feedback control condition is satisfied. In the third control device, the main feedback control condition is that, as in the first control device, the warm-up period of the catalyst 53 has ended, the fuel cut operation is not being executed, and the cooling water temperature THW of the engine 10 is the predetermined first. This is established when the temperature is equal to or higher than one temperature, the intake air amount (load) per revolution of the engine is equal to or less than a predetermined value, and the upstream air-fuel ratio sensor 66 is activated.

  Here, it is assumed that the main feedback control condition is satisfied at the present time. According to this assumption, the CPU 71 determines “Yes” in step 1205 of FIG. 12 and proceeds to step 1210. Next, the CPU 71 sequentially performs processing of steps 1210 to 1230 described later, and proceeds to step 1235.

Step 1210: The CPU 71 acquires the detected air-fuel ratio abyfs according to the above equation (15).
Step 1215: The CPU 71 acquires the in-cylinder fuel supply amount Fc (k−N) according to the above equation (16). In the third control device, the upstream target air-fuel ratio abyfr is set to the stoichiometric air-fuel ratio.
Step 1220: The CPU 71 acquires the target in-cylinder fuel supply amount Fcr (k−N) according to the above equation (17).
Step 1225: The CPU 71 acquires the in-cylinder fuel supply amount deviation DFc according to the above equation (18).
Step 1230: The CPU 71 performs the high-pass filter process shown in the above equation (19) on the in-cylinder fuel supply amount deviation DFc, and obtains the in-cylinder fuel supply amount deviation DFchi after passing through the high-pass filter.

  In step 1235, the CPU 71 determines whether or not the value of the sensor asymmetric deterioration flag XSAD is “1”. As described above, the current value of the sensor asymmetric deterioration flag XSAD is “0”. Therefore, the CPU 71 makes a “No” determination at step 1235 to directly proceed to step 1240.

  In step 1240, the CPU 71 acquires the main feedback correction amount DFi according to the above equation (20). Here, the third control device calculates the main feedback correction amount DFi based on the first feedback control coefficient (the first proportional gain Gp and the first differential gain Gi). In the third control device, the coefficient KFB is set to “1”.

  Next, the CPU 71 proceeds to step 1245, and adds the post-high-pass filter in-cylinder fuel supply amount deviation DFchi obtained in step 1230 to the integrated value SDFchi of the in-cylinder fuel supply amount deviation DFchi after passing through the high-pass filter at that time. Thus, the integrated value SDFchi of the in-cylinder fuel supply amount deviation after passing through the new high-pass filter is acquired (updated). Thereafter, the CPU 71 proceeds to step 1295 to end the present routine tentatively.

  As described above, the main feedback correction amount DFi is obtained by proportional-integral control (PI control) based on the first feedback control coefficient, and this main feedback correction amount DFi is reflected in the final fuel injection amount Fi (see step 1140 in FIG. 11). reference.).

  On the other hand, if the main feedback control condition is not satisfied at the time of determination in step 1205, the CPU 71 determines “No” in step 1205 and proceeds to step 1255 to set the value of the main feedback correction amount DFi to zero. Next, the CPU 71 proceeds to step 1260 to set the integrated value SDFchi of the in-cylinder fuel supply amount deviation after passing through the high-pass filter to zero. Thereafter, the CPU 71 proceeds to step 1295 to end the present routine tentatively. Thus, when the main feedback control condition is not satisfied, the main feedback correction amount DFi is set to zero. Accordingly, at this time, the correction by the main feedback correction amount DFi of the fuel injection amount Fbasesb for sub feedback control is not performed.

  Further, the CPU 71 executes a sub-feedback correction coefficient KFi calculation routine shown in FIG. 13 at a predetermined timing, and calculates a sub-feedback correction coefficient KFi used in the process shown in the routine of FIG. 11 (see step 1130). To do. That is, the CPU 71 starts processing from step 1300 in FIG. 13 and proceeds to step 1310 to determine whether or not the sub feedback control condition is satisfied. In the third control device, the sub feedback control condition is the same as the first control device, the main feedback condition shown in FIG. 12 (see step 1205) is established, and the engine coolant temperature THW is higher than the first temperature. This is established when the temperature is equal to or higher than the second temperature and the downstream air-fuel ratio sensor 67 is activated.

  Here, it is assumed that the sub-feedback control condition is satisfied at the present time. According to this assumption, the CPU 71 determines “Yes” in step 1310 of FIG. 13 and proceeds to step 1320. Next, the CPU 71 sequentially performs the processing of steps 1320 to 1370, which will be described later, proceeds to step 1395, and once ends this routine.

Step 1320: The CPU 71 acquires an output deviation amount DVoxs that is a difference between the downstream target value Voxsref and the output value Voxs of the downstream air-fuel ratio sensor 67 in accordance with the above equation (21). In the first control device, the downstream target value Voxsref is set to a value corresponding to the theoretical air-fuel ratio.
Step 1330: The CPU 71 performs the low-pass filter process shown in the above equation (22) on the output deviation amount DVoxs to obtain the output deviation amount DVoxslow after passing through the low-pass filter.
Step 1340: The CPU 71 obtains a differential value DDVoxslow of the output deviation amount DVoxslow after passing through the low-pass filter according to the above equation (23).
Step 1350: The CPU 71 acquires the sub feedback control coefficient KFi according to the above equation (24). The proportional gain Kp, integral gain Ki, and differential gain Kd at this time are set to appropriate values obtained in advance.
Step 1360: The CPU 71 adds the output deviation amount DVoxslow after passing through the low-pass filter obtained in the above step 1330 to the integral value SDVoxslow of the output deviation amount DVoxlow after passing through the low-pass filter at the present time, and the new output deviation amount after passing through the low-pass filter Get the integral value SDVoxslow.
Step 1370: The CPU 71 stores the output deviation amount DVoxlow after the low pass filter at the present time in the output deviation amount DVoxlow 1 after the low pass filter used in the next processing at step 1340.

  As described above, the sub-feedback correction coefficient KFi is obtained by the proportional-integral-integral control (PID control), and the basic fuel injection amount Fbase is corrected by the sub-feedback correction coefficient KFi (see step 1130 in FIG. 11). The main feedback correction amount DFi is added to the corrected basic fuel injection amount Fbase (sub-feedback control fuel injection amount Fbasesb) to determine the final fuel injection amount Fi (see step 1140 in FIG. 11). .)

  On the other hand, when the sub feedback control condition is not satisfied at the time of determination in step 1310, the CPU 71 determines “No” in step 1310, proceeds to step 1380, and sets the value of the sub feedback correction coefficient KFi to zero. Next, the CPU 71 proceeds to step 1390 to set the value of the output deviation amount DVoxslow after passing through the low-pass filter to zero. Thereafter, the CPU 71 proceeds to step 1395 to end the present routine tentatively. Thus, when the sub feedback control condition is not satisfied, the sub feedback correction coefficient KFi is set to zero. Accordingly, at this time, the basic fuel injection amount Fbase is not corrected by the sub feedback correction coefficient KFi.

  Here, it is assumed that the upstream air-fuel ratio sensor 66 has asymmetrically deteriorated due to reasons such as aging. Furthermore, it is assumed that the sensor deterioration diagnosis execution condition is also satisfied at the present time. According to the above assumption (the condition for executing the sensor deterioration diagnosis is established), when the CPU 71 starts the process from step 1200 in FIG. 12, it determines “Yes” in step 1205, and then steps 1210 to 1230. These processes are sequentially executed, and the process proceeds to step 1235. If the above assumption (the upstream air-fuel ratio sensor 66 is asymmetrically degraded), the CPU 71 determines “Yes” in step 1235 and proceeds to step 1260.

  When the upstream air-fuel ratio sensor 66 is asymmetrically deteriorated, the third control device replaces the above-described first feedback control coefficient with the “second feedback control coefficient” as a control coefficient for calculating the main feedback correction amount DFi. Is adopted. In the third control device, as the second feedback control coefficient, “second feedback control composed of a second proportional gain Gpsmall smaller than the first proportional gain Gp and a second integral gain Giamall smaller than the first integral gain Gi”. "Coefficient" is adopted.

  That is, the CPU 71 stores the second proportional gain Gpsmall as the value of the first proportional gain Gp at step 1260, and stores the second integral gain Giamall as the value of the first integral gain Gi at step 1265 following step 1260. To do.

  Then, the CPU 71 proceeds to step 1240 to acquire the main feedback correction amount DFi based on the second feedback control coefficient. Next, the CPU 71 proceeds to step 1245 to acquire (update) the integrated value SDFchi of the in-cylinder fuel supply amount deviation after passing through the high-pass filter, and proceeds to step 1295 to end the present routine tentatively.

  Furthermore, when the CPU 71 starts the process from step 1300 in FIG. 13, if the above-described sub feedback control condition is satisfied, the CPU 71 determines “Yes” in step 1310 and proceeds to step 1320 and subsequent steps. Next, as described above, the CPU 71 sequentially performs the processing from step 1320 to step 1370 to obtain the sub feedback correction coefficient KFi.

  As described above, the sub feedback correction coefficient KFi is obtained by the proportional integral differential control (PID control), and the basic fuel injection amount Fbase is corrected by the sub feedback correction coefficient KFi (see step 1130 in FIG. 11). The main feedback correction amount DFi is added to the corrected basic fuel injection amount Fbase (sub-feedback control fuel injection amount Fbasesb) to determine the final fuel injection amount Fi (see step 1140 in FIG. 11). .)

As described above, the third control device
A catalyst 53 disposed in an exhaust passage of the internal combustion engine 10;
An upstream air-fuel ratio sensor 66 that is disposed in a portion upstream of the catalyst 53 in the exhaust passage and outputs an output value Vabyfs corresponding to an air-fuel ratio of exhaust gas flowing through the disposed portion;
A downstream air-fuel ratio sensor 67 that is disposed in a portion downstream of the catalyst 53 in the exhaust passage and outputs an output value Voxs corresponding to an air-fuel ratio of exhaust gas flowing through the disposed portion;
It is applied to the internal combustion engine provided with.

The third control device
A value obtained by performing high-pass filter processing on a deviation DFc (see step 1225 in FIG. 12) between a value corresponding to the output value Vabyfs of the upstream air-fuel ratio sensor 66 and an upstream target value corresponding to the theoretical air-fuel ratio. DFchi (see step 1230 in FIG. 12) and a value obtained by performing high-pass filter processing on a value corresponding to the output value Vabyfs of the upstream air-fuel ratio sensor 66 and an upstream target value corresponding to the theoretical air-fuel ratio The main feedback correction amount DFi for feedback control of the air-fuel ratio of the air-fuel mixture supplied to the engine 10 based on one of the deviations from the first feedback control coefficient including at least one gain (see FIG. 12) Main feedback correction amount calculating means for calculating using Gp and Gi) in step 1240;
A value obtained by subjecting the deviation DVoxs (see step 1320 in FIG. 13) between the value corresponding to the output value Voxs of the downstream air-fuel ratio sensor 67 and the downstream target value corresponding to the theoretical air-fuel ratio to low-pass filter processing. Based on DVoxslow (see step 1330 in FIG. 13), the sub feedback correction amount Fbasesb for feedback control of the air-fuel ratio of the air-fuel mixture supplied to the engine 10 is independent of the calculation of the main feedback correction amount. Sub feedback correction amount calculating means for calculating
Based on the main feedback correction amount DFi and the sub feedback correction amount Fbasesb, feedback control is performed so that the air-fuel ratio of the air-fuel mixture supplied to the engine 10 matches the stoichiometric air-fuel ratio (see the routine of FIG. 11). Fuel ratio control means;
The lean direction response time constant Taflean, which is the response time constant of the upstream air-fuel ratio sensor 66 when the exhaust gas air-fuel ratio increases, and the upstream air-fuel ratio sensor 66 when the exhaust gas air-fuel ratio decreases. Response time constant acquisition means (see step 620 in FIG. 6) for acquiring a rich direction response time constant Tafrich which is a response time constant;
It is determined whether or not a diagnostic index value that is an absolute value of a difference between the lean direction response time constant Taflean and the rich direction response time constant Tafrich is larger than a predetermined allowable value δ (see step 630 in FIG. 6). ) Air-fuel ratio sensor diagnostic means;
Is provided.

In the third control device,
The main feedback correction amount calculating means includes
When the air-fuel ratio sensor diagnosing means determines that the diagnostic index value is larger than the allowable value δ (when it is determined “Yes” in step 630 in FIG. 6), it replaces the first feedback control coefficient. The second feedback control coefficient (Gpsmall and Gismall; see step 1260 and step 1265 in FIG. 12) obtained by reducing at least one of the gains included in the first feedback control coefficient. The main feedback correction amount DFi is calculated (see step 1240 in FIG. 12).

  In this way, the third control device evaluates the degree of deterioration of the air-fuel ratio sensor based on the magnitudes of the lean direction response time constant Taflean and the rich direction response time constant Tafrich. Here, when it is not determined that the upstream air-fuel ratio sensor 66 is asymmetrically deteriorated, main feedback control is executed based on the first feedback control coefficient (including Gp and Gi as gains). On the other hand, when it is determined that the upstream air-fuel ratio sensor 66 has asymmetrically deteriorated, the second feedback control coefficient including a gain smaller than the first feedback control coefficient (as gains Gpsmall and Gi smaller than Gp) Main feedback control is executed on the basis of the small Gi).

  The magnitude of the gain included in the feedback control coefficient affects the magnitude of the feedback correction amount. Further, by applying high-pass filter processing to the value based on the output value Vabyfs of the upstream air-fuel ratio sensor 66, the high-frequency component (the high-frequency component of the fluctuation of the air-fuel ratio of the exhaust gas) is the main feedback control. Used for. Therefore, by adopting the “second feedback control coefficient” when the upstream air-fuel ratio sensor is asymmetrically deteriorated (responsiveness to high-frequency components is deteriorated), the high-frequency component of the fluctuation of the air-fuel ratio of the exhaust gas is adopted. The correction amount based on (main feedback correction amount) becomes small. Thereby, the influence of the main feedback correction amount on the sub feedback correction amount can be reduced. As a result, the influence of the asymmetric response of the upstream air-fuel ratio sensor can be reduced as much as possible, so that the engine emission can be maintained satisfactorily.

  The third control device performs high-pass filter processing on “deviation DFc between the value corresponding to the output value Vabyfs of the upstream air-fuel ratio sensor 66 and the upstream target value corresponding to the theoretical air-fuel ratio”, and is obtained by this processing. The main feedback control is executed based on the value DFi and the first feedback control coefficient or the second feedback control coefficient. However, the third control device first performs a high-pass filter process on the “value corresponding to the output value Vabyfs of the upstream air-fuel ratio sensor 66”, and the upstream target corresponding to the processed output value Vabyfs and the theoretical air-fuel ratio. The main feedback control may be executed based on the deviation from the value and the first feedback control coefficient or the second feedback control coefficient.

  The third control device performs main feedback control by proportional-integral control (PI control). However, the third control device may be configured to execute main feedback control by, for example, proportional integral derivative control (PID control). Further, when the first feedback control coefficient described above includes a differential gain (D gain), the second feedback control coefficient may be configured to reduce only the differential gain.

  In addition, this invention is not limited to said each embodiment, A various modification can be employ | adopted within the scope of the present invention.

  The air-fuel ratio control apparatus for an internal combustion engine of the present invention can also be configured as follows.

That is, the air-fuel ratio control apparatus for an internal combustion engine of the present invention is
(1) an air-fuel ratio sensor that is disposed in an exhaust passage of the internal combustion engine and outputs an output value corresponding to the air-fuel ratio of exhaust gas flowing through the disposed portion;
(2) air-fuel ratio control means for performing air-fuel ratio feedback control for matching the air-fuel ratio of the air-fuel mixture supplied to the engine with the target air-fuel ratio based on the output value of the air-fuel ratio sensor;
Is applied to an air-fuel ratio control device for an internal combustion engine comprising:
(3) A lean direction response time constant that is a response time constant of the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas increases, and a response time constant of the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas decreases. Response time constant acquisition means for acquiring a certain rich direction response time constant;
(4) an air-fuel ratio sensor diagnostic means for determining whether or not a diagnostic index value that is an absolute value of a difference between the lean direction response time constant and the rich direction response time constant is greater than a predetermined allowable value;
(5) When the air-fuel ratio sensor diagnosis means determines that the diagnostic index value is larger than the allowable value, the target air-fuel ratio is determined when the lean direction response time constant is larger than the rich direction response time constant. Air-fuel ratio correction means for reducing the target air-fuel ratio by a second correction amount when the rich direction response time constant is larger than the lean direction response time constant;
It can also comprise.

  As described above, when the air-fuel ratio sensor is asymmetrically deteriorated, the output value of the air-fuel ratio sensor cannot sufficiently follow the fluctuation of the air-fuel ratio of the exhaust gas in the direction of low responsiveness. In this case, the detected air-fuel ratio shows a behavior different from the fluctuation of the actual air-fuel ratio. As a result, the air-fuel ratio feedback control that is executed based on the detected air-fuel ratio is also not appropriately executed.

  For example, when only the rich direction response of the air-fuel ratio sensor is deteriorated (that is, when the rich direction response time constant is larger than the lean direction response time constant), the output value of the air-fuel ratio sensor is the rich value of the exhaust gas air-fuel ratio. It is not possible to sufficiently follow the change in direction. In this case, during a period in which the output value of the air-fuel ratio sensor cannot follow the actual air-fuel ratio, the detected air-fuel ratio becomes larger than the actual air-fuel ratio (becomes a lean value). Therefore, during this period, excessive feedback control (control to make the air-fuel ratio turn to the rich side) that is not actually required is performed. As a result, the center of the air-fuel ratio of the exhaust gas flowing into the catalyst (hereinafter also referred to as “average air-fuel ratio”) becomes an air-fuel ratio richer than the target air-fuel ratio, and engine emissions deteriorate.

  Therefore, when the air-fuel ratio sensor is asymmetrically deteriorated, the third air-fuel ratio control apparatus corrects the “target air-fuel ratio” so as to cope with the deterioration of the air-fuel ratio sensor. Specifically, in the third air-fuel ratio control device, the lean direction response time constant of the air-fuel ratio sensor is larger than the rich direction response time constant (that is, the lean direction response is lower than the rich direction response). ) “Decrease” the target air-fuel ratio by the first correction amount. The third air-fuel ratio control apparatus sets the target air-fuel ratio to the first value when the rich direction response time constant is larger than the lean direction response time constant (that is, when the rich direction response is lower than the lean direction response). “Increase” by two corrections.

  Even if the target air-fuel ratio is corrected as described above, the asymmetric response of the output value of the air-fuel ratio sensor is not eliminated. However, the above correction makes it possible to bring the “average air-fuel ratio” of the exhaust gas flowing into the catalyst as close as possible to the original target air-fuel ratio. The reason for this will be described below with reference to the above-mentioned “when only the rich direction responsiveness of the air-fuel ratio sensor deteriorates”.

  As described above, when only the rich direction responsiveness of the air-fuel ratio sensor deteriorates, the average air-fuel ratio of the exhaust gas flowing into the catalyst becomes an air-fuel ratio (abyfr-β1) richer than the target air-fuel ratio abyfr. At this time, if the target air-fuel ratio abyfr is corrected so as to increase by a predetermined correction amount (γ), the subsequent feedback control is executed based on the corrected target air-fuel ratio (abyfr + γ). As described above, even if the target air-fuel ratio is corrected, the asymmetric response of the output value of the air-fuel ratio sensor is not eliminated. Accordingly, as described above, the average air-fuel ratio of the exhaust gas flowing into the catalyst becomes “the air-fuel ratio richer than the corrected target air-fuel ratio (abyfr + γ) (abyfr + γ−β2)”. Here, by appropriately setting the correction amount (γ) of the target air-fuel ratio abyfr, the average air-fuel ratio of the exhaust gas flowing into the catalyst can be brought as close as possible to the original target air-fuel ratio abyfr (for example, γ = β2). The average air / fuel ratio matches the target air / fuel ratio).

  Contrary to the above, even when the lean direction responsiveness of the air-fuel ratio sensor is lower than the rich direction responsiveness, the average air-fuel ratio of the exhaust gas flowing into the catalyst is set to the original target air-fuel ratio abyfr by the same method as described above. As close as possible. Therefore, the emission of the engine can be maintained satisfactorily.

  Here, the “first correction amount” and the “second correction amount” can be determined as follows, for example. First, “the rich direction response time constant and the lean direction response time constant of the non-degraded air-fuel ratio sensor” are acquired in advance. Next, by comparing these response time constants with the respective response time constants at the time of deterioration diagnosis, the “degree of responsiveness deterioration” is evaluated. Then, the “first correction amount” and the “second correction amount” are appropriately determined so as to correspond to the degree of deterioration of the responsiveness.

  Furthermore, the air-fuel ratio control apparatus for an internal combustion engine of the present invention can also be configured as follows.

That is, the air-fuel ratio control apparatus for an internal combustion engine of the present invention is
(1) an air-fuel ratio sensor that is disposed in an exhaust passage of the internal combustion engine and outputs an output value corresponding to the air-fuel ratio of exhaust gas flowing through the disposed portion;
(2) air-fuel ratio control means for performing air-fuel ratio feedback control for matching the air-fuel ratio of the air-fuel mixture supplied to the engine with the target air-fuel ratio based on the output value of the air-fuel ratio sensor;
Is applied to an air-fuel ratio control device for an internal combustion engine comprising:
(3) A lean direction response time constant that is a response time constant of the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas increases, and a response time constant of the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas decreases. Response time constant acquisition means for acquiring a certain rich direction response time constant;
(4) an air-fuel ratio sensor diagnostic means for determining whether or not a diagnostic index value that is an absolute value of a difference between the lean direction response time constant and the rich direction response time constant is greater than a predetermined allowable value;
(5) When the air-fuel ratio sensor diagnosis means determines that the diagnostic index value is larger than the allowable value, the air-fuel ratio sensor is used when the lean direction response time constant is larger than the rich direction response time constant. When the output value of the air-fuel ratio sensor decreases, the high frequency component is amplified, and when the rich direction response time constant is larger than the lean direction response time constant, the high frequency component Sensor output correction means for amplifying components;
It can also comprise.

  As described above, when the air-fuel ratio sensor deteriorates asymmetrically, the output value of the air-fuel ratio sensor shows an asymmetric response. Here, as described above, when the “high frequency component amplification compensation” is performed on the output value “whole” indicating the asymmetric response, the high frequency component of the output value in the direction in which the degree of deterioration is small is excessively amplified, As a result, the engine emissions deteriorate. Therefore, the fourth air-fuel ratio control apparatus performs a correction for amplifying the high frequency component only for the “output value in the direction in which the degree of deterioration is large” among the output values showing the asymmetric response.

  Specifically, when the lean direction response time constant is larger than the rich direction response time constant (that is, when the lean direction response is lower than the rich direction response), the fourth air-fuel ratio control device When the output value of the sensor increases (when the output value fluctuates in the lean direction), the output value of the air-fuel ratio sensor is corrected so as to amplify the high frequency component. Further, the fourth air-fuel ratio control device outputs the output of the air-fuel ratio sensor when the rich direction response time constant is larger than the lean direction response time constant (that is, when the rich direction response is lower than the lean direction response). When the value decreases (when the output value fluctuates in the rich direction), the output value of the air-fuel ratio sensor is corrected so as to amplify the high frequency component.

  By the above correction, only the output value in the direction in which the degree of deterioration is large is amplified, so that the asymmetric response of the output value of the air-fuel ratio sensor can be eliminated. Further, with the above correction, it is possible to obtain an output value without delay with respect to fluctuations in the actual air-fuel ratio. As a result, the emission of the engine can be maintained well.

  Here, in performing the correction, it is necessary to specify the direction in which the output value of the air-fuel ratio sensor fluctuates. The “direction in which the output value of the air-fuel ratio sensor fluctuates” can be determined as follows, for example. First, the output value of the air-fuel ratio sensor is acquired at every elapse of a predetermined time, and a time number (1, 2, 3,... N−1, N, N + 1...) Is assigned to the acquired output value. The Next, the output value acquired at time N and the output value acquired at time N−1 are compared. By this comparison, “the direction in which the output value of the air-fuel ratio sensor varies” is determined.

  The “degree of amplification” when the high frequency component of the output value is amplified can be determined as follows, for example. First, the degree of deterioration of the air-fuel ratio sensor is evaluated by the same method as the third air-fuel ratio control device. Next, an appropriate “degree of amplification” is determined so as to correspond to the degree of deterioration of the responsiveness.

1 is a schematic cross-sectional view of an internal combustion engine to which a control device of the present invention is applied. 2 is a graph showing a relationship between an air-fuel ratio and an output value of an upstream air-fuel ratio sensor shown in FIG. 2 is a graph showing a relationship between an air-fuel ratio and an output value of a downstream air-fuel ratio sensor shown in FIG. 2 is a time chart showing a relationship between an air-fuel ratio and a detected air-fuel ratio obtained based on an output value of an upstream air-fuel ratio sensor shown in FIG. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on the 1st control apparatus of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on the 1st control apparatus of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on the 1st control apparatus of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on the 1st control apparatus of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on the 2nd control apparatus of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on the 3rd control apparatus of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on the 3rd control apparatus of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on the 3rd control apparatus of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on the 3rd control apparatus of this invention performs.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 25 ... Combustion chamber, 39 ... Injector, 52 ... Exhaust pipe (exhaust pipe), 53 ... Three-way catalyst (first catalyst), 54 ... Three-way catalyst (second catalyst), 66 ... Empty upstream Fuel ratio sensor, 67 ... downstream air-fuel ratio sensor, 70 ... electric control device, 71 ... CPU

Claims (4)

An air-fuel ratio sensor that outputs an output value corresponding to the air-fuel ratio of the exhaust gas that is disposed in the exhaust passage of the internal combustion engine and that flows through the disposed portion;
A lean direction response time constant that is a response time constant of the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas increases, and a rich direction that is a response time constant of the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas decreases A response time constant acquisition means for acquiring a response time constant;
The reference response time constant is equal to or greater than the deterioration side response time constant based on the deterioration side response time constant which is the larger one of the lean direction response time constant and the rich direction response time constant. Sensor output processing means for obtaining a post-processing output value by applying low pass filter processing having a time constant corresponding to the reference response time constant to the output value of the air-fuel ratio sensor,
Air-fuel ratio control means for performing air-fuel ratio feedback control for matching the air-fuel ratio of the air-fuel mixture supplied to the engine with the target air-fuel ratio based on the post-processing output value;
An air-fuel ratio control apparatus for an internal combustion engine comprising: The air-fuel ratio control apparatus for an internal combustion engine according to claim 1,
The sensor output processing means includes
The reference response time constant is configured to be determined based on the deterioration side response time constant when the engine is in the first operating state; and
When the engine is in a second operating state different from the first operating state, a time constant corresponding to a value obtained by correcting the deterioration-side response time constant based on a parameter corresponding to the second operating state is set. An air-fuel ratio control device configured to be adopted as a time constant of the low-pass filter. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1,
The sensor output processing means includes
The reference response time constant is configured to be determined based on the deterioration side response time constant when the engine is in the first operating state; and
When the engine is in a second operating state different from the first operating state, a time constant corresponding to a value obtained by correcting the reference response time constant based on a parameter corresponding to the second operating state is An air-fuel ratio control apparatus configured to be employed as a time constant of a low-pass filter. A catalyst disposed in an exhaust passage of the internal combustion engine;
An upstream air-fuel ratio sensor that outputs an output value corresponding to the air-fuel ratio of exhaust gas that is disposed in the exhaust passage and upstream of the catalyst and flows through the disposed portion;
A downstream air-fuel ratio sensor which is disposed in a portion downstream of the catalyst in the exhaust passage and outputs an output value corresponding to an air-fuel ratio of exhaust gas flowing through the disposed portion;
Applied to an internal combustion engine with
A value obtained by performing high-pass filter processing on a deviation between a value corresponding to the output value of the upstream air-fuel ratio sensor and an upstream target value corresponding to the theoretical air-fuel ratio, and an output value of the upstream air-fuel ratio sensor For feedback control of the air-fuel ratio of the air-fuel mixture supplied to the engine based on one of the deviations between the value obtained by subjecting the corresponding value to the high-pass filter processing and the upstream target value corresponding to the theoretical air-fuel ratio Main feedback correction amount calculating means for calculating the main feedback correction amount of the first feedback control coefficient using a first feedback control coefficient including at least one gain;
Based on a value obtained by performing low-pass filter processing on a deviation between a value corresponding to the output value of the downstream air-fuel ratio sensor and a downstream target value corresponding to the theoretical air-fuel ratio, the air-fuel mixture supplied to the engine is emptied. Sub feedback correction amount calculating means for calculating a sub feedback correction amount for feedback control of the fuel ratio independently of the calculation of the main feedback correction amount;
Air-fuel ratio control means for performing feedback control so that the air-fuel ratio of the air-fuel mixture supplied to the engine matches the stoichiometric air-fuel ratio based on the main feedback correction amount and the sub-feedback correction amount;
The lean direction response time constant, which is the response time constant of the upstream air-fuel ratio sensor when the air-fuel ratio of the exhaust gas increases, and the response time constant of the upstream air-fuel ratio sensor when the air-fuel ratio of the exhaust gas decreases A response time constant acquiring means for acquiring a rich direction response time constant,
An air-fuel ratio sensor diagnostic means for determining whether or not a diagnostic index value that is an absolute value of a difference between the lean direction response time constant and the rich direction response time constant is greater than a predetermined allowable value;
With
The main feedback correction amount calculating means includes
When the air-fuel ratio sensor diagnosing means determines that the diagnostic index value is greater than the allowable value, at least one gain of the gains included in the first feedback control coefficient instead of the first feedback control coefficient An air-fuel ratio control apparatus for an internal combustion engine configured to calculate the main feedback correction amount by using a second feedback control coefficient obtained by reducing the value of.

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