JP2009215933A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine capable of regenerating a particulate collection filter without increasing the emission of a nitrogen oxide. <P>SOLUTION: The control device comprises an upstream air-fuel ratio sensor 66, a first three-way catalyst 53, the particulate collection filter 54, a first downstream air-fuel ratio sensor 67, a second three-way catalyst 55, a second downstream air-fuel ratio sensor 68, and a third three-way catalyst 56, and they are arranged along an exhaust passage of the internal combustion engine 10 from the upstream to the downstream. When the regeneration of the particulate collection filter is not performed, the control device performs a main feedback control using the upstream air-fuel ratio sensor and a sub feedback control using the first downstream air-fuel ratio sensor. When the regeneration of the particulate collection filter is performed, the control device performs main feedback control using the upstream air-fuel ratio sensor and a sub feedback control using the second downstream air-fuel ratio sensor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device (air-fuel ratio control device) for an internal combustion engine provided with a particulate collection filter and a three-way catalyst in an exhaust passage.

Conventionally, fine particles (particulate matter (PM), that is, nano fine particles such as SOF and Soot) discharged from a diesel engine are collected by a fine particle collecting filter (particulate filter) disposed in an exhaust passage. In addition, there is known a control device for an internal combustion engine that regenerates the particulate collection filter by burning the particulate collected by the particulate collection filter when a predetermined condition is satisfied. One of such conventional control devices detects the upstream air-fuel ratio and the downstream air-fuel ratio of the particulate collection filter, and the particulate collection filter is being regenerated by the detected air-fuel ratio. (Whether or not the collected particulates are in a burning state) and the operation mode of the engine is switched based on the determination result (for example, Patent Document 1). See).
JP-A-2005-240719

  By the way, in order to burn the particulates collected by the particulate collection filter, it is necessary that the particulate collection filter is at a high temperature and that oxygen is supplied to the particulate collection filter. The conventional control device is applied to a diesel engine in which the air-fuel ratio of the supplied air-fuel mixture is very lean. Accordingly, the particulate collection filter is sufficiently supplied with oxygen for burning the particulates. Therefore, the conventional control device raises the temperature of the particulate collection filter by executing the delay of the fuel injection timing, the increase of the fuel injection amount, the decrease of the intake amount by the intake throttle valve, etc. The collected fine particles are burned.

  On the other hand, in recent years, in order to reduce the amount of fine particles discharged from a gasoline engine, it has been studied to arrange a fine particle collecting filter in an exhaust passage of the gasoline engine. On the other hand, in general gasoline engines, there are three exhaust passages in the exhaust passage for the purpose of reducing the amount of unburned substances (HC, CO, etc.) emitted into the atmosphere and the amount of nitrogen oxides (NOx) emitted into the atmosphere. An original catalyst is provided, and the amount of fuel is controlled so that the air-fuel ratio of the air-fuel mixture supplied to the engine (hereinafter also referred to as “engine air-fuel ratio”) becomes an air-fuel ratio in the vicinity of the theoretical air-fuel ratio.

  As described above, in order to regenerate the particulate collection filter (burn the particulates), oxygen must be supplied to the particulate collection filter. However, when the air-fuel ratio of the engine is controlled to be close to the stoichiometric air-fuel ratio, oxygen is hardly supplied to the particulate collection filter. In particular, when an upstream catalyst that is a three-way catalyst is provided upstream of the particulate collection filter, oxygen is consumed and stored by the upstream catalyst, so the amount of oxygen flowing into the particulate collection filter is extremely small. . Accordingly, in order to regenerate the particulate collection filter in a gasoline engine, the air-fuel ratio of the engine is controlled to an air-fuel ratio leaner than the stoichiometric air-fuel ratio (hereinafter also referred to as “lean air-fuel ratio”). Oxygen must be supplied to the particulate collection filter. However, if the air-fuel ratio of the engine is set to a lean air-fuel ratio regardless of the state of the three-way catalyst, nitrogen oxides that are largely discharged from the engine cannot be purified by the three-way catalyst when the air-fuel ratio of the engine is the lean air-fuel ratio. In some cases (for example, when the oxygen storage amount of the three-way catalyst reaches the maximum oxygen storage amount and the nitrogen oxides cannot be reduced), a problem arises that a large amount of nitrogen oxides are discharged into the atmosphere.

  Therefore, an object of the present invention is a control device for an internal combustion engine (gasoline engine) provided with a particulate collection filter and a three-way catalyst in an exhaust passage, and the particulate collection is performed without increasing the amount of nitrogen oxide emission. An object of the present invention is to provide a control device capable of regenerating a filter (burning particulates collected by a particulate collection filter).

  In order to achieve the above object, a control device according to the present invention includes an upstream air-fuel ratio sensor, a first three-way catalyst, and fine particles disposed in the exhaust passage in order from the upstream side to the downstream side of the exhaust passage of the internal combustion engine. The present invention is applied to an internal combustion engine including a collection filter, a first downstream air-fuel ratio sensor, a second three-way catalyst, a second downstream air-fuel ratio sensor, and a third three-way catalyst. Here, “from the upstream side of the exhaust passage toward the downstream side” means “from the upstream side to the downstream side of the flow of the exhaust gas in the exhaust passage”.

  In the case where the internal combustion engine is a multi-cylinder internal combustion engine, the exhaust passage means an exhaust passage formed downstream of a collective portion where branches of exhaust manifolds connected to each cylinder gather.

  Each of the first to third three-way catalysts has a catalytic function for simultaneously purifying unburned substances such as HC and CO and nitrogen oxides (NOx), and an oxygen storage function. The oxygen storage function stores oxygen that has been excessively flowing into the catalyst and oxygen taken from nitrogen oxides, etc., and supplies the stored oxygen to unburned material that flows into the catalyst. It is a function to purify things.

  Each of the upstream air-fuel ratio sensor, the first downstream air-fuel ratio sensor, and the second downstream air-fuel ratio sensor outputs an output corresponding to the air-fuel ratio of the exhaust gas that passes through the portion of the exhaust passage in which the upstream air-fuel ratio sensor is disposed. It is supposed to occur. In a preferred embodiment, the upstream air-fuel ratio sensor is a wide-range air-fuel ratio sensor (for example, a limit current sensor) whose output continuously changes in response to a change in the air-fuel ratio of the detection target gas. Each of the 1 downstream air-fuel ratio sensor and the second downstream air-fuel ratio sensor is a concentration cell type sensor (so-called O2 sensor) whose output changes suddenly at the stoichiometric air-fuel ratio.

  The control apparatus for an internal combustion engine includes filter regeneration request generation determination means and air-fuel ratio feedback control means.

  The filter regeneration request generation determination means generates a “filter regeneration request” that is a request to regenerate the particulate collection filter by burning the particulates collected by the particulate collection filter in the particulate collection filter. It is determined whether or not.

  For example, the filter regeneration request generation determining means generates a request to regenerate the particulate collection filter based on the engine operating state (intake air amount (load), engine air-fuel ratio, travel distance, engine operation time, etc.). It is determined whether or not.

  More specifically, the filter regeneration request occurrence determination means includes a “factory regeneration time” such as a time when the vehicle is shipped from the factory, a time when the particulate collection filter is replaced with a new particulate collection filter, and a time when the previous filter regeneration control is completed. The accumulated intake air amount, the accumulated travel distance, the accumulated engine operating time, etc. from the time when the amount of the particulate matter collected by the particulate collection filter is extremely small (at the time when the collected particulate matter is small) is greater than or equal to a predetermined value. May be configured to determine that a filter regeneration request has occurred. Alternatively, the filter regeneration request occurrence determination means estimates the amount of particulate discharged from the engine per unit time from the intake air amount and the air-fuel ratio of the engine, etc. When the amount of collected particles (estimated amount of particles that will be collected by the particulate collection filter) obtained by integrating from the above becomes a predetermined value or more, it is determined that a filter regeneration request has occurred. Can be configured to.

  The air-fuel ratio feedback control means performs “normal air-fuel ratio feedback control” when it is determined that the filter regeneration request has not occurred. In this normal air-fuel ratio feedback control, the air-fuel ratio represented by the output of the upstream air-fuel ratio sensor matches the first upstream target air-fuel ratio within the “predetermined air-fuel ratio range including the theoretical air-fuel ratio”, and The air / fuel ratio represented by the output of the first downstream air / fuel ratio sensor is supplied to the engine so as to coincide with the first downstream target air / fuel ratio within the “predetermined air / fuel ratio range including the theoretical air / fuel ratio”. This is feedback control for controlling the air-fuel ratio of the air-fuel mixture.

  The “predetermined air-fuel ratio range including the theoretical air-fuel ratio” is a so-called “window” range of the three-way catalyst. This “window” is an air-fuel ratio in which the three-way catalyst can simultaneously purify unburnt substances (HC, CO) and nitrogen oxides (NOx) at a high purification rate (high conversion rate) equal to or higher than a predetermined rate. It is a range.

  According to this, at the normal time (that is, when the filter regeneration request is not generated), the air-fuel ratio represented by the output of the first downstream air-fuel ratio sensor is “within a predetermined air-fuel ratio range including the theoretical air-fuel ratio. The air-fuel ratio of the engine is controlled so as to coincide with the “first downstream target air-fuel ratio”. The first downstream air-fuel ratio sensor is disposed on the downstream side of the first three-way catalyst. Therefore, the first downstream air-fuel ratio sensor is less likely to “degrade (characteristic deviation) due to heat and poisoning” than the upstream air-fuel ratio sensor. Further, the upstream air-fuel ratio sensor may be strongly influenced by a specific cylinder depending on the installation position, and the average air-fuel ratio of the engine may not be detected accurately. On the other hand, the first downstream air-fuel ratio sensor detects the air-fuel ratio of the exhaust gas after passing through the first three-way catalyst, so it is difficult to be affected by the specific cylinder and accurately detects the average of the air-fuel ratio of the engine. can do. Further, in the normal air-fuel ratio feedback control, “transient fluctuation of the engine air-fuel ratio” that is difficult to compensate by the feedback control based only on the output of the first downstream air-fuel ratio sensor is the output of the upstream air-fuel ratio sensor. It can be compensated by feedback control using. Therefore, according to the above configuration, since the air-fuel ratio of the engine is normally controlled within the window with high accuracy, unburned matter and nitrogen oxides discharged from the engine can be purified at a very high purification rate.

  Further, the air-fuel ratio feedback control means performs filter regeneration air-fuel ratio feedback control when it is determined that the filter regeneration request has occurred. In the filter regeneration air-fuel ratio feedback control, when it is determined that the filter regeneration request has occurred, the air-fuel ratio represented by the output of the upstream air-fuel ratio sensor matches a predetermined second upstream target air-fuel ratio, The air-fuel ratio of the engine is adjusted so that the air-fuel ratio represented by the output of the second downstream air-fuel ratio sensor matches the second downstream target air-fuel ratio within the “predetermined air-fuel ratio range including the theoretical air-fuel ratio”. It is feedback control to control.

  In this case, as will be described later, the second upstream target air-fuel ratio may be the same as the first upstream target air-fuel ratio (for example, the stoichiometric air-fuel ratio), and is different from the first upstream target air-fuel ratio. It may be an air-fuel ratio. Similarly, the second downstream target air-fuel ratio may be an air-fuel ratio within the “predetermined air-fuel ratio range including the theoretical air-fuel ratio”, and is the same as the first downstream target air-fuel ratio (for example, the theoretical air-fuel ratio). (Fuel ratio) may be different from the first downstream target air-fuel ratio.

  Now, the air-fuel ratio indicated by the output of the first downstream air-fuel ratio sensor is richer than “the downstream target air-fuel ratio within the predetermined air-fuel ratio range including the theoretical air-fuel ratio (the first downstream target air-fuel ratio)”. It is assumed that the air-fuel ratio of the engine and the air-fuel ratio of the engine continue to be controlled to an air-fuel ratio leaner than the stoichiometric air-fuel ratio. At this time, since excess oxygen flows into the first three-way catalyst, the oxygen storage amount of the first three-way catalyst gradually increases and reaches the maximum oxygen storage amount of the first three-way catalyst. Until this time, oxygen is not supplied to the particulate collection filter. When a short time has elapsed from this point, oxygen is supplied to the particulate collection filter and flows out downstream of the particulate collection filter. As a result, the air-fuel ratio indicated by the output of the first downstream air-fuel ratio sensor changes from the rich air-fuel ratio to the lean air-fuel ratio with respect to the downstream target air-fuel ratio. In other words, the output of the first downstream air-fuel ratio sensor “lean-inverts”. Therefore, if the air-fuel ratio feedback control is executed by the normal air-fuel ratio feedback control so that the output of the first downstream air-fuel ratio sensor matches the downstream target air-fuel ratio, the air-fuel ratio of the engine becomes the lean inversion time point. Immediately after that, the air-fuel ratio is changed to “the air-fuel ratio richer than the theoretical air-fuel ratio” within a relatively short time. As a result, excess oxygen is not discharged from the engine, so oxygen is not supplied to the particulate collection filter. As described above, according to the normal air-fuel ratio feedback control, almost no oxygen flows into the particulate collection filter, so the particulate does not burn and the regeneration of the particulate collection filter does not proceed.

  However, since the second downstream air-fuel ratio sensor is disposed downstream of the second three-way catalyst having an oxygen storage function, the output of the second downstream air-fuel ratio sensor is the output of the first downstream air-fuel ratio sensor. After the lean inversion, the lean inversion does not occur until the oxygen storage amount of the second three-way catalyst reaches the maximum oxygen storage amount of the second three-way catalyst. Therefore, when it is determined that a filter regeneration request has occurred as in the present control device, the air-fuel ratio represented by the output of the second downstream air-fuel ratio sensor is the downstream target air-fuel ratio (second downstream target air-fuel ratio). If the air-fuel ratio of the engine is feedback controlled so as to coincide with (), the timing at which the air-fuel ratio of the engine is changed to a richer air-fuel ratio than the stoichiometric air-fuel ratio is delayed. In other words, since the air-fuel ratio of the engine is controlled to the air-fuel ratio leaner than the stoichiometric air-fuel ratio until the output of the second downstream air-fuel ratio sensor is lean-reversed, a large amount of oxygen is supplied to the particulate collection filter. . As a result, since the particulates burn in the particulate collection filter, the particulate collection filter is regenerated.

  In addition, since the air-fuel ratio represented by the output of the second downstream air-fuel ratio sensor is controlled to match the downstream target air-fuel ratio (second downstream target air-fuel ratio) in the window, the third three-way catalyst The average of the air-fuel ratio of the gas flowing into the window becomes the air-fuel ratio in the window. As a result, unburned matter and nitrogen oxides discharged from the engine are purified with high efficiency by the third three-way catalyst. That is, the present control device can regenerate the particulate collection filter while suppressing an increase in the amount of unburned matter and nitrogen oxides discharged.

  In this case, the air-fuel ratio feedback control means may set the first upstream target air-fuel ratio to the stoichiometric air-fuel ratio and set the second upstream target air-fuel ratio to the stoichiometric air-fuel ratio.

  The air-fuel ratio feedback control means sets the first upstream target air-fuel ratio to the stoichiometric air-fuel ratio, and sets the second upstream target air-fuel ratio outside the “predetermined air-fuel ratio range including the stoichiometric air-fuel ratio”. It is outside the "forced rich air-fuel ratio that is the air-fuel ratio richer than the stoichiometric air-fuel ratio" and "the predetermined air-fuel ratio range including the stoichiometric air-fuel ratio" and is "the air-fuel ratio leaner than the stoichiometric air-fuel ratio" It is preferable that any one of the “forced lean air-fuel ratios” is set to an air-fuel ratio that alternately repeats as time elapses.

  According to this, when it is determined that the filter regeneration request has occurred (that is, when the particulate collection filter is regenerated), it is determined that the filter regeneration request has not occurred. It becomes larger than the amplitude of the air / fuel ratio of the engine. Moreover, since the instantaneous air-fuel ratio of the engine in this state oscillates beyond the window, when the second upstream target air-fuel ratio is set to the forced lean air-fuel ratio, high concentration oxygen flows into the particulate collection filter. To do. As a result, since the fine particles burn efficiently in the fine particle collection filter, the fine particle collection filter can be efficiently regenerated within a short period of time. However, as described above, since the air-fuel ratio represented by the output of the second downstream-side air-fuel ratio sensor is controlled so as to coincide with the second downstream-side target air-fuel ratio in the window, it flows into the third three-way catalyst. The average of the air-fuel ratio of the gas to be used becomes the air-fuel ratio in the window. As a result, it is possible to efficiently regenerate the particulate collection filter while avoiding an increase in the discharge amount of unburned substances and nitrogen oxides due to the purification of the third three-way catalyst.

in this case,
The air-fuel ratio feedback control means determines the second upstream target air-fuel ratio from the air-fuel ratio richer than the stoichiometric air-fuel ratio to the lean-side air-fuel ratio expressed by the output of the second downstream air-fuel ratio sensor. When the air-fuel ratio changes, the forced rich air-fuel ratio is set, and the air-fuel ratio represented by the output of the second downstream air-fuel ratio sensor is changed from the lean air-fuel ratio to the rich air-fuel ratio. It is preferable that the forced lean air-fuel ratio is set when the fuel ratio is changed.

  According to this, when the oxygen storage amount of the second three-way catalyst reaches the maximum oxygen storage amount of the second three-way catalyst, the air-fuel ratio represented by the output of the second downstream air-fuel ratio sensor is the theoretical value. The second upstream target air-fuel ratio is set to the forced lean air-fuel ratio until the time when the air-fuel ratio richer than the air-fuel ratio changes to the lean air-fuel ratio (lean reversal time). At the lean inversion time, the oxygen storage amount of the third three-way catalyst does not reach the maximum oxygen storage amount of the third three-way catalyst. Therefore, if the second upstream target air-fuel ratio is changed to the forced rich air-fuel ratio at the lean inversion time, the purification action of the third three-way catalyst can be expected, so that the deterioration of the emission can be avoided. In addition, since the second upstream target air-fuel ratio is set to the forced lean air-fuel ratio until the lean inversion time, the period during which the gas containing high-concentration oxygen is discharged from the engine can be extended. As a result, since a large amount of oxygen is supplied to the particulate collection filter, the particulate collection filter can be efficiently regenerated.

  In this case, the air-fuel ratio feedback control means acquires a filter temperature corresponding value that increases as the temperature of the particulate collection filter increases, and the compulsory lean air-fuel ratio and the value decrease as the acquired filter temperature corresponding value decreases. It is preferable to increase the difference from the stoichiometric air-fuel ratio.

  The lower the temperature of the particulate collection filter, the more difficult the particulate collected by the particulate collection filter burns. On the other hand, the more oxygen is supplied to the particulate collection filter, the more particulates burn. Therefore, the air-fuel ratio feedback control means discharges more oxygen from the engine by setting the forced lean air-fuel ratio to a leaner air-fuel ratio as the temperature of the particulate collection filter is lower, thereby Then, a large amount of oxygen is supplied to the particulate collection filter. As a result, the regeneration of the particulate collection filter can surely proceed regardless of the temperature of the particulate collection filter. Further, when the temperature of the particulate collection filter is high, the instantaneous instantaneous air-fuel ratio of the engine when the second upstream target air-fuel ratio is set to the forced lean air-fuel ratio approaches the stoichiometric air-fuel ratio. The amount of nitrogen oxides emitted from the engine also decreases. Therefore, according to this aspect, the particulate collection filter can be reliably regenerated while suppressing the discharge amount of nitrogen oxide as much as possible.

  Hereinafter, embodiments of a control device for an internal combustion engine according to the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 shows a spark ignition type multi-cylinder (4 cylinders in this example) internal combustion engine (gasoline engine) 10 as an internal combustion engine control apparatus (hereinafter also referred to as “first control apparatus”) according to the first embodiment. The schematic configuration of the applied system is shown. FIG. 1 shows only a cross section of a specific cylinder, but the other cylinders have the same configuration. The internal combustion engine 10 includes a cylinder block portion 20 including a cylinder block, a cylinder block lower case, an oil pan, and the like, a cylinder head portion 30 fixed on the cylinder block portion 20, and a gasoline mixture to the cylinder block portion 20. An intake system 40 for supplying and an exhaust system 50 for releasing exhaust gas from the cylinder block unit 20 to the outside are included.

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

  The cylinder head portion 30 includes an intake port 31 that communicates with the combustion chamber 25, an intake valve 32 that opens and closes the intake port 31, an intake cam shaft that drives the intake valve 32, and continuously changes the phase angle of the intake cam shaft. A variable intake timing device 33, an actuator 33a of the variable intake timing device 33, an exhaust port 34 communicating with the combustion chamber 25, an exhaust valve 35 for opening and closing the exhaust port 34, an exhaust camshaft 36 for driving the exhaust valve 35, an ignition plug 37, An igniter 38 including an ignition coil for generating a high voltage to be applied to the spark plug 37 and an injector (fuel injection means) 39 for injecting fuel into the intake port 31 are provided. An injector 39 as fuel injection means is configured to inject fuel of the indicated injection amount included in the injection instruction signal in response to the injection instruction signal.

  The intake system 40 includes an intake manifold 41, an intake pipe (intake duct) 42, an air filter 43, a throttle valve 44, and a throttle valve actuator 44a.

  The intake manifold 41 is connected to the intake port 31 of the combustion chamber 25 of each cylinder. More specifically, as shown in FIG. 2, the intake manifold 41 includes a plurality of branch portions 41a connected to each intake port, and a surge tank portion 41b in which those branch portions 41a are assembled. As shown in FIGS. 1 and 2, the intake pipe 42 is connected to the surge tank 41b. The intake manifold 41 and the intake pipe 42 constitute an intake passage. The air filter 43 shown in FIG. 1 is provided at the end of the intake pipe 42. The throttle valve 44 is rotatably provided in the intake pipe 42, and changes the opening cross-sectional area of the intake passage formed by the intake pipe 42 by rotating. The throttle valve actuator (throttle valve drive means) 44a is formed of a DC motor, and rotates the throttle valve 44 in response to an instruction signal.

  The exhaust system 50 includes an exhaust manifold 51, an exhaust pipe (exhaust pipe) 52, a first three-way catalyst 53, a particulate collection filter 54, a second three-way catalyst 55, and a third three-way catalyst 56.

  As shown in FIG. 1, the exhaust manifold 51 is connected to the exhaust port 34 of the combustion chamber 25 of each cylinder. More specifically, as shown in FIG. 2, the exhaust manifold 51 includes a plurality of branch portions 51a connected to each exhaust port, and a collective portion 51b in which the branch portions 51a are aggregated. The exhaust pipe 52 is connected to the collective portion 51 b of the exhaust manifold 51. The exhaust manifold 51 and the exhaust pipe 52 constitute an exhaust path. In the present specification, a route through which the exhaust gas formed by the collecting portion 51b of the exhaust manifold 51 and the exhaust pipe 52 is referred to as an “exhaust passage” for convenience.

  The first three-way catalyst (upstream catalyst) 53 carries “noble metal as catalyst material” and “ceria (CeO2)” on a ceramic support, and has a catalytic function and an oxygen storage / release function (simply “ It is also referred to as “oxygen storage function” or “O 2 storage function”. The first three-way catalyst 53 is disposed (intervened) in the exhaust pipe 52. In other words, the first three-way catalyst 53 is disposed in the exhaust passage downstream of the collecting portion 51b. The first three-way catalyst 53 is also referred to as a start catalytic converter (SC).

  The particulate collection filter 54 is a known particulate filter made of ceramic and collects particulates discharged from the engine 10. The particulate collection filter 54 is disposed (intervened) in the exhaust passage (exhaust pipe 52) at a position downstream of the first three-way catalyst 53. The particulate collection filter 54 is also referred to as a particulate matter filter (PMF).

Similar to the first three-way catalyst 53, the second three-way catalyst 55 and the third three-way catalyst 56 carry a noble metal (catalyst substance) and ceria (CeO2) on a ceramic support, and have a catalytic function and oxygen. It is a three-way catalyst having a storage function.
The second three-way catalyst 55 is disposed (intervened) in the exhaust passage (exhaust pipe 52) at a position downstream of the particulate collection filter 54.
The third three-way catalyst 56 is disposed (interposed) in the exhaust passage (exhaust pipe 52) at a position downstream of the second three-way catalyst 55.
Since both the second three-way catalyst 55 and the third three-way catalyst 56 are disposed below the vehicle floor, they are also referred to as an under-floor catalytic converter (UFC). The second three-way catalyst 55 and the third three-way catalyst 56 are also referred to as a first downstream catalyst 55 and a second downstream catalyst 56, respectively.

  As shown in FIG. 3, the three-way catalyst such as the first three-way catalyst 53, the second three-way catalyst 55, and the third three-way catalyst 56 has a so-called “window W”. "When these are within the predetermined air-fuel ratio range including the stoichiometric air-fuel ratio, these undesired components are highly efficient by oxidizing unburnt substances (HC, CO, etc.) and reducing nitrogen oxides (NOx). It has the characteristic (catalyst function) to purify with.

  Further, the three-way catalyst can purify HC, CO and NOx even if the air-fuel ratio shifts from the stoichiometric air-fuel ratio to a certain extent due to the oxygen storage function. That is, if the air-fuel ratio of the engine is leaner than the stoichiometric air-fuel ratio and the gas flowing into the three-way catalyst contains a large amount of NOx, the catalyst deprives the NOx of oxygen molecules (reduces NOx). ), Occlude the lost oxygen molecules. Such a state can also be expressed as “a state in which the three-way catalyst substantially holds a reducing agent (reducing component)”. In addition, when the air-fuel ratio of the engine becomes richer than the stoichiometric air-fuel ratio and the gas flowing into the three-way catalyst contains a large amount of unburned substances (reducing components) such as HC and CO, the three-way catalyst Gives the stored oxygen molecules to these unburned materials and oxidizes (purifies) these components. Such a state can also be expressed as “a state in which the three-way catalyst substantially holds the oxidizing agent (oxidizing component)”.

  Further, as shown in FIG. 1, this system includes a hot-wire air flow meter 61, a throttle position sensor 62, a cam position sensor 63, a crank position sensor 64, a water temperature sensor 65, an upstream air-fuel ratio sensor 66, a first downstream side. An air-fuel ratio sensor 67, a second downstream air-fuel ratio sensor 68, and an accelerator opening sensor 69 are provided.

The hot-wire air flow meter 61 detects the mass flow rate of intake air flowing in the intake pipe 42 and outputs a signal representing the mass flow rate (intake air amount per unit time of the engine 10) Ga.
The throttle position sensor 62 detects the opening of the throttle valve 44 and outputs a signal representing the throttle valve opening TA.

The cam position sensor 63 outputs one pulse every time the intake camshaft rotates 90 degrees, 90 degrees, and 180 degrees from a predetermined angle. This signal is also referred to as a G2 signal.
The crank position sensor 64 has a narrow pulse every time the crankshaft 24 rotates 10 ° and outputs a signal having a wide pulse every time the crankshaft 24 rotates 360 °. A pulse output from the crank position sensor 64 is converted into a signal representing the engine rotational speed NE by an electric control device 70 described later. Further, the electric control device 70 acquires the crank angle (absolute crank angle) of the engine 10 based on signals from the cam position sensor 63 and the crank position sensor 64.
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.

  As shown in FIG. 2, the upstream air-fuel ratio sensor 66 is located at either the exhaust manifold 51 or the exhaust pipe 52 (that is, the exhaust pipe 52) at a position between the collecting portion 51 b of the exhaust manifold 51 and the first three-way catalyst 53. (Passage). The upstream air-fuel ratio sensor 66 outputs an output value corresponding to the air-fuel ratio of exhaust gas (detected gas) flowing through a portion in the exhaust passage where the upstream air-fuel ratio sensor 66 is disposed.

  More specifically, the upstream air-fuel ratio sensor 66 is a limiting current type oxygen concentration sensor. As shown in FIG. 4, 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 (and hence the air-fuel ratio of the air-fuel mixture supplied to the engine). It is supposed to be. 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 gas to be detected increases (lean). That is, 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 to be described later stores the table (map) Mapabyfs shown in FIG. 4 and detects the air-fuel ratio by applying the actual output value Vabyfs to the table (acquires the detected air-fuel ratio abyfs). )

  As shown in FIGS. 1 and 2, the first downstream air-fuel ratio sensor 67 is disposed in the exhaust pipe 52 (exhaust passage) at a position between the particulate collection filter 54 and the second three-way catalyst 55. ing. The first downstream air-fuel ratio sensor 67 is an air-fuel ratio of exhaust gas (gas to be detected, gas flowing into the second three-way catalyst 55) that flows through a portion in the exhaust passage where the first downstream air-fuel ratio sensor 67 is disposed. The output value Voxs1 corresponding to is output.

  More specifically, the first downstream air-fuel ratio sensor 67 is an electromotive force type (concentration cell type) oxygen concentration sensor. Therefore, the first downstream air-fuel ratio sensor 67 is also referred to as an oxygen concentration sensor 67. As shown in FIG. 5, the first downstream air-fuel ratio sensor 67 outputs an output value Voxs1, which is a voltage that changes suddenly in the vicinity of the theoretical air-fuel ratio. That is, the first downstream side air-fuel ratio sensor 67 is approximately 0.1 (V) when the air-fuel ratio of the gas to be detected is larger than the stoichiometric air-fuel ratio and is on the lean side, and the air-fuel ratio of the gas to be detected is theoretically A voltage of approximately 0.9 (V) is output when the air-fuel ratio is greater than the air-fuel ratio and rich, and 0.5 (V) when the air-fuel ratio is the stoichiometric air-fuel ratio. Further, the first downstream side air-fuel ratio sensor 67 detects the target gas when the air-fuel ratio of the detected gas is an air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio (the air-fuel ratio substantially corresponding to the three-way catalyst window W described above). A voltage that suddenly decreases (changes from approximately 0.9 (V) to approximately 0.1 (V)) as the air-fuel ratio of the detection gas changes from rich to lean is output. The downstream air-fuel ratio afdown1 of the first three-way catalyst 53 obtained based on the output value Voxs1 of the first downstream air-fuel ratio sensor 67 is the relationship between the output value Voxs and the downstream air-fuel ratio afdown shown in FIG. Where f is a function representing the following, it is obtained by afdown1 = f (Voxs1).

  As shown in FIGS. 1 and 2, the second downstream air-fuel ratio sensor 68 is disposed in the exhaust pipe 52 (exhaust passage) at a position between the second three-way catalyst 55 and the third three-way catalyst 56. Has been. The second downstream air-fuel ratio sensor 68 is an air-fuel ratio of exhaust gas (gas to be detected, gas flowing into the third three-way catalyst 56) flowing through a portion in the exhaust passage where the second downstream air-fuel ratio sensor 68 is disposed. The output value Voxs2 corresponding to is output. The second downstream air-fuel ratio sensor 68 is an electromotive force type oxygen concentration sensor having the same output characteristics as the first downstream air-fuel ratio sensor 67. The downstream air-fuel ratio afdown2 of the second three-way catalyst 55 obtained based on the output value Voxs2 of the second downstream air-fuel ratio sensor 68 represents the relationship between the output value Voxs2 and the downstream air-fuel ratio afdown shown in FIG. When the function is f, it is obtained by afdown2 = f (Voxs2).

  Thus, the upstream air-fuel ratio sensor 66, the first three-way catalyst 53, the particulate collection filter 54, and the first downstream air-fuel ratio sensor 67 are arranged in the exhaust passage of the engine 10 from the upstream side toward the downstream side. The second three-way catalyst 55, the second downstream air-fuel ratio sensor 68, and the third three-way catalyst 56 are sequentially arranged in series.

  Referring to FIG. 1 again, the accelerator opening sensor 69 detects the operation amount of the accelerator pedal 81 operated by the driver, and outputs a signal representing the operation amount Accp of the accelerator pedal 81.

  The electric control device 70 includes a CPU 71 connected by a bus, a routine (program) executed by the CPU 71, a ROM 72 pre-stored with tables (look-up tables, maps), constants, and the like, and the CPU 71 temporarily stores data as necessary. The microcomputer 73 includes a RAM 73 that stores data, a backup RAM 74 that stores data while the power is on, and retains the stored data even when the power is shut off, and an interface 75 that includes an AD converter.

  The interface 75 is connected to the sensors 61 to 69, supplies signals from the sensors 61 to 69 to the CPU 71, and according to instructions from the CPU 71, the actuator 33a, the igniter 38, the injector 39, and the throttle valve of the variable intake timing device 33. A drive signal (instruction signal) is sent to the actuator 44a and the like.

Next, the outline of various air-fuel ratio controls by the first control device will be described.
<Outline of main feedback control>
When the main feedback control condition is satisfied, the first control device sets the upstream air-fuel ratio abyfs acquired based on the output value Vabyfs of the upstream air-fuel ratio sensor 66 to the upstream target air-fuel ratio abyfr (main feedback target value). Feedback control (main feedback control) is performed on the air-fuel ratio of the air-fuel mixture supplied to the engine so as to match. In this example, the main feedback control condition is satisfied when the upstream air-fuel ratio sensor 66 is activated, and is not satisfied in other cases. Other conditions may be added to the main feedback control condition. As will be described later, in the main feedback control, the basic fuel injection amount (feedforward fuel injection amount) Fbase is determined based on the upstream target air-fuel ratio abyfr and the cylinder intake air amount Mc, and the basic fuel injection amount Fbase is determined. Is corrected by the main feedback correction value KFmain calculated based on these values so that the “upstream air-fuel ratio abyfs acquired based on the output value Vabyfs” and the “upstream target air-fuel ratio abyfr” match. The

  The upstream target air-fuel ratio abyfr is the first upstream target air-fuel ratio in “normal air-fuel ratio feedback control” that is executed when a request to regenerate the particulate collection filter 54 is not generated (when no filter regeneration request is generated). The air-fuel ratio is set to the second upstream target air-fuel ratio at the time of “filter regeneration air-fuel ratio feedback control” executed when a request to regenerate the particulate collection filter 54 is generated (when the filter regeneration request is generated). The In the first control device, the first upstream target air-fuel ratio and the second upstream target air-fuel ratio are the same, and both are “air-fuel ratios within a predetermined air-fuel ratio range including the stoichiometric air-fuel ratio (in this example, the stoichiometric air-fuel ratio). Fuel ratio) ”. The “predetermined air / fuel ratio range including the theoretical air / fuel ratio” refers to the “window W” described above. Note that the second upstream target air-fuel ratio is changed alternately to “forced lean air-fuel ratio afenL” and “forced rich air-fuel ratio afenR” with the passage of time in the control device according to the second embodiment described later. Sometimes.

<Outline of sub feedback control>
When the sub feedback control condition is satisfied, the first control device performs sub feedback control in addition to the main feedback control. This sub-feedback control is performed using the output value of either the first downstream air-fuel ratio sensor 67 or the second downstream air-fuel ratio sensor 68.

  More specifically, the first control device selects the first downstream air-fuel ratio sensor 67 as an air-fuel ratio sensor for sub feedback control when no filter regeneration request is generated. Hereinafter, the downstream air-fuel ratio sensor selected for the sub-feedback control is also referred to as “selected air-fuel ratio sensor”. The control for executing the main feedback control described above and the sub feedback control in a state where the first downstream air-fuel ratio sensor 67 is selected as the selected air-fuel ratio sensor is the “normal air-fuel ratio feedback control”.

  When the filter regeneration request is generated, the first control device selects the second downstream air-fuel ratio sensor 68 as an air-fuel ratio sensor for sub feedback control. The control for executing the above-described main feedback control and the sub feedback control in a state where the second downstream air-fuel ratio sensor 68 is selected as the selected air-fuel ratio sensor is the above-mentioned “filter regeneration air-fuel ratio feedback control”.

  In this example, the sub feedback control condition is satisfied when the main feedback control is being performed and the selected air-fuel ratio sensor is activated, and is not satisfied in other cases. Note that other conditions may be added to the sub-feedback control conditions.

  Hereinafter, the output value of the selected air-fuel ratio sensor (that is, the output value Voxs1 of the first downstream air-fuel ratio sensor 67 or the output value Voxs2 of the second downstream air-fuel ratio sensor 68 is selected). Also referred to as “output value Voxs of air-fuel ratio sensor”. In the sub-feedback control, the first control device uses the air-fuel mixture supplied to the engine so that the output value Voxs of the selected air-fuel ratio sensor matches the downstream target value Voxsref that is a value corresponding to the downstream target air-fuel ratio. Feedback control of the air-fuel ratio is performed.

  In other words, the sub-feedback control is supplied to the engine so that the downstream air-fuel ratio afdown represented by the output value Voxs of the selected air-fuel ratio sensor matches the downstream target air-fuel ratio represented by the downstream target value Voxsref. Feedback control for adjusting the air-fuel ratio (fuel amount) of the air-fuel mixture. In the sub feedback control, for example, the deviation (output deviation amount DVoxs) between the output value Voxs of the selected air-fuel ratio sensor and the downstream target value Voxsref is controlled by PI (proportional / integral) control or PID (proportional / integral, differential) control. This is a control that attempts to match “0”.

  The downstream target value Voxsref indicates that the air-fuel ratio of the gas (detected gas) passing through the position where the selected air-fuel ratio sensor is disposed is “a downstream target within a predetermined air-fuel ratio range (window W) including the theoretical air-fuel ratio”. When the air / fuel ratio (theoretical air / fuel ratio in this example) is set, “a value to be output by the selected air / fuel ratio sensor (for example, Voxsref = theoretical air / fuel ratio equivalent value Voxsst = 0.5 V)” is set. The downstream target value Voxsref is set to the stoichiometric air-fuel ratio equivalent value Voxsst both when the filter regeneration request is not generated and when the filter regeneration request is generated. As a result, the air-fuel ratio of the air-fuel mixture supplied to the engine 10 (more precisely, when the selected air-fuel ratio sensor is the first downstream air-fuel ratio sensor 67, the air flow rate of the gas flowing into the second three-way catalyst 55). When the fuel ratio and the selected air-fuel ratio sensor are the second downstream air-fuel ratio sensor 68, the average (center, median) of the air-fuel ratio of the gas flowing into the third three-way catalyst 56 is made to coincide with the stoichiometric air-fuel ratio. . The air-fuel ratio corresponding to the downstream target value Voxsref that is set when no filter regeneration request is generated is also referred to as “first downstream target air-fuel ratio” for convenience. The air-fuel ratio corresponding to the downstream target value Voxsref that is set when the filter regeneration request is generated is also referred to as “second downstream target air-fuel ratio” for convenience.

  As shown in FIG. 5, the downstream target value Voxsref indicates that the air-fuel ratio of the gas passing through the position where the selected air-fuel ratio sensor is arranged is “the air side on the rich side by a predetermined value Δaf slightly smaller than the theoretical air-fuel ratio. It may be set to “a value that the selected air-fuel ratio sensor should output (for example, Voxsref = Vrich = 0.55 V)” when the air-fuel ratio is equivalent to “fuel ratio AFR”. As a result, the air-fuel ratio of the air-fuel mixture supplied to the engine 10 (more precisely, when the selected air-fuel ratio sensor is the first downstream air-fuel ratio sensor 67, the air flow rate of the gas flowing into the second three-way catalyst 55 is reduced. When the fuel ratio and the selected air-fuel ratio sensor are the second downstream side air-fuel ratio sensor 68, the average of the air-fuel ratio of the gas flowing into the third three-way catalyst 56) is slightly richer than the stoichiometric air-fuel ratio (air-fuel ratio) Hereinafter, it is also referred to as “weakly rich air-fuel ratio AFR”).

  As shown in FIG. 3, the weak rich air-fuel ratio AFR is within the window W and is slightly richer than the stoichiometric air-fuel ratio. In this way, the average of the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to the weak rich air-fuel ratio AFR by the first three-way catalyst 53, the second three-way catalyst 55, the third three-way catalyst 56, etc. The “unburned material purification rate” of the three-way catalyst decreases relatively slowly even if the engine air-fuel ratio shifts slightly to the rich side from the window W, whereas the “three-way catalyst” This is because the “purification rate” rapidly decreases when the air-fuel ratio of the engine shifts slightly leaner than the window W.

<Operation of filter regeneration air-fuel ratio feedback control (particulate collection filter regeneration control)>
By the way, the particulate collection filter 54 collects particulates, and the ability to collect particulates decreases. Conversely, if the particulates collected by the particulate collection filter 54 are burned in the particulate collection filter 54, the particulate collection ability of the particulate collection filter 54 is restored. That is, the particulate collection filter 54 can be regenerated. In order to burn the particulates collected in the particulate collection filter 54,
(1) The inside of the particulate collection filter 54 is at a high temperature, and
(2) oxygen is supplied to the particulate collection filter 54;
is required.

  In general, when a gasoline engine operated at an air-fuel ratio near the stoichiometric air-fuel ratio is in a normal operating state (an operating state other than immediately after starting, etc.), the temperature in the particulate collection filter 54 burns the collected particulates. The temperature is high enough to allow On the other hand, when fuel cut (fuel supply stop) control is performed in a predetermined deceleration operation state, air containing a large amount of oxygen is discharged from the engine 10. Therefore, when the fuel cut control is continuously executed for a predetermined time or longer, the oxygen storage amount OSA1 of the first three-way catalyst 53 reaches the maximum oxygen storage amount Cmax1 of the first three-way catalyst 53, and oxygen is stored in the first third-way catalyst 53. It begins to flow out from the original catalyst 53. Oxygen flowing out from the first three-way catalyst 53 flows into the particulate collection filter 54.

  As a result, the inside of the particulate collection filter 54 is at a high temperature and oxygen is supplied to the particulate collection filter 54, so that the particulate collected in the particulate collection filter 54 burns in the particulate collection filter 54, The particulate collection filter 54 is regenerated. However, how often the fuel cut control is executed and how long the fuel cut control time is reached depends on how the engine 10 is operated. Therefore, it is not appropriate to always expect to regenerate the particulate collection filter 54 only by fuel cut control.

  Therefore, when the fuel cut control is not being executed, the air-fuel ratio of the engine 10 is forcibly set to the lean air-fuel ratio, so that a relatively large amount of oxygen is discharged from the engine 10, thereby causing the particulate collection filter 54 to It is considered effective to supply oxygen (burn the fine particles to regenerate the fine particle collecting filter 54).

  By the way, when the air-fuel ratio of the engine is set to the lean air-fuel ratio in this way, in order to supply oxygen to the particulate collection filter 54, first, the oxygen storage amount OSA1 of the first three-way catalyst 53 is set to the first three-way. Oxygen must flow out of the first three-way catalyst 53 by reaching the maximum oxygen storage amount Cmax1 of the catalyst 53. However, if the oxygen storage amount OSA1 of the first three-way catalyst 53 reaches the maximum oxygen storage amount Cmax1 of the first three-way catalyst 53 and the engine air-fuel ratio is a lean air-fuel ratio outside the window W, the first The three-way catalyst 53 cannot effectively purify NOx. Further, since the air-fuel ratio of the engine is set to a lean air-fuel ratio, a large amount of NOx is discharged from the engine.

  At this time, if the respective oxygen storage amounts of the second three-way catalyst 55 and the third three-way catalyst 56 are somewhat smaller than the respective maximum oxygen storage amounts, these three-way catalysts will be discharged from the first three-way catalyst 53. Can be purified. On the other hand, when the respective oxygen storage amounts of the second three-way catalyst 55 and the third three-way catalyst 56 have reached their respective maximum oxygen storage amounts, just after the fuel cut is restored (immediately after the end of the fuel cut). These three-way catalysts cannot sufficiently purify NOx, causing a problem that a large amount of NOx is released into the atmosphere.

  Therefore, as described above, when the first control device requests to regenerate the particulate collection filter 54, the first downstream air-fuel ratio sensor 67 is used as the air-fuel ratio sensor (selected air-fuel ratio sensor) used for the sub-feedback control. To the second downstream air-fuel ratio sensor 68. As a result, a large amount of oxygen flows into the particulate collection filter 54 as described below, so that the particulates burn in the particulate collection filter 54 and the particulate collection filter 54 is regenerated. At this time, the average of the air-fuel ratio of the gas flowing into the third three-way catalyst 56 is maintained at a substantially stoichiometric air-fuel ratio by sub-feedback control, so that unburned matter and nitrogen oxides are purified by the third three-way catalyst 56. Is done. As a result, the particulate collection filter 54 can be regenerated without deteriorating emissions. This control is the “filter regeneration air-fuel ratio feedback control” described above.

  Here, the reason why the particulate filter 54 is regenerated by employing the second downstream air-fuel ratio sensor 68 as the selected air-fuel ratio sensor will be described.

  Now, the normal air-fuel ratio feedback control is being performed, and the air-fuel ratio afdown1 indicated by the output value Voxs1 of the first downstream air-fuel ratio sensor 67 as the selected air-fuel ratio sensor is richer than the stoichiometric air-fuel ratio that is the downstream target air-fuel ratio. It is assumed that the air-fuel ratio of the engine and the air-fuel ratio of the engine continue to be controlled to a leaner air-fuel ratio than the stoichiometric air-fuel ratio by sub-feedback control. In this case, since excess oxygen is discharged from the engine 10, oxygen flows into the first three-way catalyst 53. Accordingly, as shown at time t1 to time t2 in FIGS. 6A and 6B, the oxygen storage amount OSA1 of the first three-way catalyst 53 gradually increases, and at time t2, the first three-way catalyst. The maximum oxygen storage amount Cmax1 of 53 is reached. Thereafter, at time t3 when a slight time has elapsed from time t2, oxygen leaks through the particulate collection filter 54 to the downstream of the particulate collection filter 54.

  As a result, as shown at time t3 in FIG. 6A, the air-fuel ratio afdown1 indicated by the output of the first downstream air-fuel ratio sensor 67 is richer than the downstream target air-fuel ratio (theoretical air-fuel ratio). The air-fuel ratio changes from the air-fuel ratio to the lean side. That is, the output value Voxs1 of the first air-fuel ratio sensor “lean-inverts”. At this time, since the sub-feedback control is executed so that the output value Voxs1 of the first air-fuel ratio sensor 67 coincides with the downstream target air-fuel ratio (theoretical air-fuel ratio), the air-fuel ratio of the engine is richer than the stoichiometric air-fuel ratio. The air / fuel ratio is changed. Accordingly, excess oxygen is not discharged from the engine 10. Thus, in the “normal air-fuel ratio feedback control” in which the first downstream air-fuel ratio sensor 67 is selected as the selected air-fuel ratio sensor, oxygen hardly flows into the particulate collection filter 54. Accordingly, the particulates do not burn and the regeneration of the particulate collection filter 54 does not proceed.

  On the other hand, it is assumed that the same state as the above-described times t1 to t2 occurs during the filter regeneration air-fuel ratio feedback control (that is, while the second downstream air-fuel ratio sensor 68 is selected as the selected air-fuel ratio sensor). . In this case, since the second downstream air-fuel ratio sensor 68 is disposed downstream of the second three-way catalyst 55 having an oxygen storage function, the output value Voxs2 of the second downstream air-fuel ratio sensor 68 is the first downstream After the lean inversion of the output value Voxs1 of the side air-fuel ratio sensor 67 (after time t3), as shown in FIGS. 6C, 6D, and 6E, the oxygen storage amount of the second three-way catalyst 56 The lean inversion is not performed (time t5) until immediately after the time (time t4) when OSA2 reaches the maximum oxygen storage amount Cmax2 of the second three-way catalyst 56.

  That is, according to the filter regeneration air-fuel ratio feedback control, the timing when the air-fuel ratio of the engine is changed to a richer air-fuel ratio than the stoichiometric air-fuel ratio is the lean reversal time (time t3) of the first downstream air-fuel ratio sensor 67. ) Later than time t5. In other words, the air-fuel ratio of the engine is maintained at an air-fuel ratio leaner than the stoichiometric air-fuel ratio until the output value Voxs2 of the second downstream air-fuel ratio sensor 68 is lean-reversed. Therefore, during the period from the lean inversion time (time t3) of the first downstream air-fuel ratio sensor 67 to the lean inversion time (time t5) of the second downstream air-fuel ratio sensor 68, a large amount of oxygen is present in the particulate collection filter 54. Supplied. As a result, since the particulates burn in the particulate collection filter 54, the particulate collection filter 54 is regenerated.

  In addition, the output value Voxs2 of the second downstream air-fuel ratio sensor 68 that is the selected air-fuel ratio sensor is controlled to coincide with the “value Voxsst corresponding to the theoretical air-fuel ratio that is the downstream target air-fuel ratio in the window W”. Therefore, the temporal average value of the air-fuel ratio of the gas flowing into the third three-way catalyst 56 becomes the air-fuel ratio in the window W. As a result, unburned matter and nitrogen oxides discharged from the engine 10 are purified with high efficiency by the third three-way catalyst 56. The above is the outline of the filter regeneration air-fuel ratio feedback control.

<Operation>
Next, the operation of the first control device will be described. The CPU 71 of the first controller performs the above-described various controls by repeating the procedure shown in the flowchart of FIG. 7 every elapse of a predetermined time. In the following description, it is assumed that the upstream air-fuel ratio sensor 66, the first downstream air-fuel ratio sensor 67, and the second downstream air-fuel ratio sensor 68 are all activated.

  The CPU 71 starts processing from step 700 at a predetermined timing, proceeds to step 710, and determines whether or not the value of the filter regeneration request flag XPM is “1”. The value of the filter regeneration request flag XPM is set to “1” when a request to regenerate the particulate collection filter 54 (filter regeneration request) is generated, and when it is not necessary to regenerate the particulate collection filter 54 “ 0 "is set. The operation of the filter regeneration request flag XPM will be described later (see FIG. 8).

  Assume that the value of the filter regeneration request flag XPM is “0”. In this case, the CPU 71 makes a “No” determination at step 710 and proceeds to step 720 to execute the “normal air-fuel ratio feedback control” described above.

  More specifically, in step 720, the CPU 71 executes both main feedback control and sub feedback control. In this case, the upstream target air-fuel ratio (first upstream target air-fuel ratio) abyfr of the main feedback control is set to the stoichiometric air-fuel ratio stoich, and the downstream target value Voxsref (corresponding to the first downstream target air-fuel ratio) of the sub-feedback control. Is set to a stoichiometric air-fuel ratio equivalent value Voxsst corresponding to the stoichiometric air-fuel ratio. Further, the CPU 71 selects the first downstream air-fuel ratio sensor 67 as the selected air-fuel ratio sensor used for the sub feedback control.

  As described above, the main feedback control is feedback control in which the upstream air-fuel ratio abyfs obtained based on the output value Vabyfs of the upstream air-fuel ratio sensor 66 matches the upstream target air-fuel ratio abyfr. Further, the sub-feedback control in this case is feedback control in which the output value Voxs1 of the first downstream air-fuel ratio sensor 67 is matched with the downstream target value Voxsref (theoretical air-fuel ratio equivalent value Voxsst). Thereafter, the CPU 71 proceeds to step 795 to end the present routine tentatively. As a result, the average air-fuel ratio of the engine substantially matches the stoichiometric air-fuel ratio. That is, based on the upstream air-fuel ratio abyfs and the downstream air-fuel ratio afdown1, the engine air-fuel ratio is adjusted so that the air-fuel ratio of the air-fuel mixture supplied to the engine becomes an air-fuel ratio within a predetermined air-fuel ratio range including the stoichiometric air-fuel ratio. The fuel ratio is feedback controlled.

  Incidentally, the CPU 71 executes the “filter regeneration request determination routine” shown by the flowchart in FIG. 8 every elapse of a predetermined time. Therefore, the CPU 71 starts the process from step 800 at a predetermined timing, proceeds to step 810, and the integrated value SGa of the intake air amount Ga after completing the “previous filter regeneration control” is a predetermined threshold (filter regeneration). It is determined whether or not the control execution threshold value) is greater than or equal to SGath.

  The integrated value SGa is updated by an intake air amount integrating routine (not shown) that is executed every elapse of the predetermined time Δts. That is, the CPU 71 updates the integrated value SGa by adding the intake air amount Ga detected by the air flow meter 61 at that time to the integrated value SGa at that time every elapse of the predetermined time Δts. The integrated value SGa is stored in the backup RAM 74. Since the amount of fine particles generated by the operation of the engine 10 increases as the intake air amount Ga increases, the integrated value SGa is an amount representing the amount of fine particles collected by the fine particle collection filter 54. The integrated value SGa is set (cleared) to “0” by the intake air amount integration routine when the execution of the filter regeneration air-fuel ratio feedback control (filter regeneration control) is completed.

  At this time, if the integrated value SGa is smaller than the threshold value SGath, the CPU 71 makes a “No” determination at step 810 to directly proceed to step 830, where the value of the filter regeneration request flag XPM is finally “0” to “1”. It is determined whether or not a predetermined time (filter regeneration control execution time) has elapsed after the change to. As will be described later, the value of the filter regeneration request flag XPM is set to “1” when the integrated value SGa becomes equal to or greater than a threshold value SGath (that is, when the filter regeneration air-fuel ratio feedback control is started). (See step 820 in FIG. 8).

  At present, since the integrated value SGa is smaller than the threshold value SGath, the value of the filter regeneration request flag XPM is maintained at “0”. Therefore, the CPU 71 makes a “No” determination at step 830 to directly proceed to step 895 to end the present routine tentatively. As a result, since the value of the filter regeneration request flag XPM is maintained at “0”, the normal air / fuel ratio feedback control is continued, and the filter regeneration air / fuel ratio feedback control is not started (see step 710 and step 720 in FIG. 7). .)

  On the other hand, if the integrated value SGa is equal to or greater than the threshold value SGath during the processing of step 810 in FIG. 8, the CPU 71 determines “Yes” in step 810 and proceeds to step 820 to set the value of the filter regeneration request flag XPM. Is set to “1”. At this time, the predetermined time (filter regeneration control execution time) has not elapsed after the value of the filter regeneration request flag XPM has changed from “0” to “1”. Therefore, the CPU 71 proceeds directly from step 830 to step 895 to end the present routine tentatively. At this time, when the CPU 71 executes the processing of step 710 in FIG. 7, the CPU 71 determines “Yes” in step 710 and proceeds to step 730 to execute the “filter regeneration air-fuel ratio feedback control” described above.

  More specifically, the CPU 71 executes main feedback control in step 730. In this case, the upstream target air-fuel ratio (second upstream target air-fuel ratio) abyfr of the main feedback control is set to the stoichiometric air-fuel ratio stoich. Further, the CPU 71 selects the second downstream air-fuel ratio sensor 68 as the selected air-fuel ratio sensor used for the sub-feedback control, and executes the sub-feedback control. In this case, the downstream target value Voxsref (value corresponding to the second downstream target air-fuel ratio) of the sub feedback control is set to the stoichiometric air-fuel ratio equivalent value Voxsst corresponding to the stoichiometric air-fuel ratio. As a result, the “filter regeneration air-fuel ratio feedback control” described above is executed, so that a large amount of oxygen is supplied into the particulate collection filter 54. As a result, the particulates burn and the regeneration of the particulate collection filter 54 starts. Thereafter, the CPU 71 proceeds to step 795 to end the present routine tentatively.

  If this state continues, regeneration of the particulate collection filter 54 proceeds, and a predetermined time (filter regeneration control execution time) elapses after the value of the filter regeneration request flag XPM changes from “0” to “1”. To do. Accordingly, when the CPU 71 proceeds to step 830 in FIG. 8, the CPU 71 determines “Yes” at step 830 and proceeds to step 840 to set the value of the filter regeneration request flag XPM to “0”. Then, the CPU 71 proceeds to step 895 to end the present routine tentatively.

  As a result, the CPU 71 determines “No” in step 710 of FIG. 7 and proceeds to step 720. Therefore, the filter regeneration air-fuel ratio feedback control is stopped, and the normal air-fuel ratio feedback control is resumed.

<Details of air-fuel ratio feedback control>
Here, details of the main feedback control and the sub feedback control will be described. The first control device performs these controls (air-fuel ratio feedback control) by a plurality of means shown in FIG. 9 which is a functional block diagram. Hereinafter, a description will be given with reference to FIG.

<Calculation of basic fuel injection amount>
The cylinder intake air amount calculation means A1 includes an intake air amount Ga measured by the air flow meter 61, an engine speed NE obtained based on the output of the crank position sensor 64, and a table MapMc stored in the ROM 72. Based on the above, the in-cylinder intake air amount Mc (k) that is the intake air amount of the cylinder that reaches the current intake stroke is obtained. Here, the subscript (k) indicates a value for the current intake stroke. The in-cylinder intake air amount Mc (k) is stored in the RAM 73 while corresponding to the intake stroke of each cylinder. The first control device may determine the in-cylinder intake air amount Mc (k) by a known air amount estimation model (air model) that models the behavior of air in the intake passage of the engine 10.

  The upstream target air-fuel ratio setting (determination) means A2 sets the upstream target air-fuel ratio abyfr (k) to the theoretical air-fuel ratio. The upstream target air-fuel ratio setting (determining) means A2 stores the upstream target air-fuel ratio abyfr (k) in the RAM 73 while corresponding to the intake stroke of each cylinder.

As shown in the following equation (1), the basic fuel injection amount calculating means A3 uses the in-cylinder intake air amount Mc (k) obtained by the in-cylinder intake air amount calculating means A1 as the upstream target air-fuel ratio setting means. By dividing by the upstream target air-fuel ratio abyfr (k) set by A2, the basic fuel injection amount Fbase (for the current intake stroke is set to make the engine air-fuel ratio the upstream target air-fuel ratio abyfr (k). k) ". The basic fuel injection amount calculation means A3 stores the basic fuel injection amount Fbase (k) in the RAM 73 while corresponding to the intake stroke of each cylinder.
Fbase (k) = Mc (k) / abyfr (k) (1)

<Calculation of final fuel injection amount>
As shown by the following equation (2), the final fuel injection amount calculation means A4 uses the main feedback correction value KFmain obtained by the main feedback correction value update means A15 described later as the basic fuel injection amount Fbase (k). Multiply and add the product (= Fbase (k) · KFmain) to a sub-feedback correction value Fisub determined by the PID controller A10, which will be described later, to determine the final fuel injection amount Fi (k) for this time.
Fi (k) = Fbase (k) · KFmain + Fisub (2)

  As described above, the first control device corrects the basic fuel injection amount Fbase (k) based on the main feedback correction value KFmain and the sub feedback correction value Fisub by the final fuel injection amount calculation means A4. Find the quantity Fi (k). Further, the first control device sends an injection instruction signal to the injector 39 so that the fuel of the final fuel injection amount Fi (k) is injected from the injector 39 of the cylinder that reaches the current intake stroke. . In other words, the injection instruction signal includes information on the final fuel injection amount Fi (k) as the instruction injection amount.

<Calculation of sub feedback correction value>
The filter regeneration request occurrence determination means A5 achieves the function of step 810 in FIG. That is, the filter regeneration request generation determination unit A5 determines whether or not the integrated value SGa of the intake air amount Ga after the completion of the “previous filter regeneration control” is equal to or greater than a predetermined threshold (filter regeneration control execution threshold) SGath. Determine whether. The filter regeneration request occurrence determination means A5 sets the value of the filter regeneration request flag XPM to “1” when the integrated value SGa is equal to or greater than the threshold value SGath. Further, the filter regeneration request generation determining means A5 determines whether or not the filter regeneration control execution time is equal to or longer than a predetermined time (filter regeneration control execution time). The value of the filter regeneration request flag XPM is set to “0”.

  When the value of the filter regeneration request flag XPM output from the filter regeneration request generation determining unit A5 is “0”, the selecting unit A6 is the first downstream side as the air / fuel ratio sensor (selected air / fuel ratio sensor) used for the sub feedback control. The air-fuel ratio sensor 67 is selected. When the value of the filter regeneration request flag XPM output from the filter regeneration request generation determining unit A5 is “1”, the selecting unit A6 is the second downstream side as an air / fuel ratio sensor (selected air / fuel ratio sensor) used for sub feedback control. The air-fuel ratio sensor 68 is selected. The selection means A6 outputs the output value Voxs1 or Voxs2 of the selected downstream air-fuel ratio sensor as the output value Voxs.

  The downstream target value setting means A7 outputs the downstream target value Voxsref. The downstream target value Voxsref is set to a value Voxsst (for example, 0.5 (V)) corresponding to the theoretical air-fuel ratio. The downstream target value Voxsref may be set to a value Vrich (for example, 0.55 (V)) corresponding to the above-described weak rich air-fuel ratio AFR.

Based on the following equation (3), the output deviation amount calculation means A8 is output from the downstream target value Voxsref at the current time set by the downstream target value setting means A7 from the selection means A6. The output deviation amount DVoxs is obtained by subtracting the output value Voxs of the downstream air-fuel ratio sensor. The output deviation amount calculation means A8 outputs the obtained output deviation amount DVoxs to the low-pass filter A9.
DVoxs = Voxsref−Voxs (3)

The low-pass filter A9 is a primary digital filter. A transfer function A9 (s) representing the characteristics of the low-pass filter A9 is expressed by the following equation (4). In the equation (4), s is a Laplace operator, and τ1 is a time constant. The low-pass filter A9 passes a low-frequency component having a frequency (1 / τ1) or lower and does not pass a high-frequency component having a frequency (1 / τ1) or higher. The low-pass filter A9 inputs the value of the output deviation amount DVoxs and outputs the output deviation amount DVoxslow after passing through the low-pass filter, which is a value after low-pass filtering the output deviation amount DVoxs, to the PID controller A10.
A9 (s) = 1 / (1 + τ1 · s) (4)

The PID controller A10 performs proportional / integral / differential processing (PID processing) on the output deviation amount DVoxslow after passing through the low-pass filter based on the following equation (5) to obtain a sub feedback correction value Fisub.
Fisub = Kp · DVoxslow + Ki · SDVoxslow + Kd · DDVoxslow… (5)

  In the above equation (5), Kp is a preset proportional gain (proportional constant), Ki is a preset integral gain (integral constant), and Kd is a preset differential gain (differential constant). SDVoxslow is a time integral value of the output deviation amount DVoxslow after passing through the low-pass filter, and DDVoxslow is a time differential value of the output deviation amount DVoxslow after passing through the low-pass filter. Thus, the sub feedback correction value Fisub is obtained. Note that the PID controller A10 includes a normal air-fuel ratio feedback control gain (proportional gain Kp1, integral gain Ki1, differential gain Kd1) at which the first downstream air-fuel ratio sensor 67 is selected as the selected air-fuel ratio sensor, and the selected air-fuel ratio. There are two types of gains (proportional gain Kp2, integral gain Ki2, differential gain Kd2) for filter regeneration air-fuel ratio feedback control in which the second downstream air-fuel ratio sensor 68 is selected as the sensor, and which one is controlled? The gain may be switched in accordance with. In this case, it is desirable that the gain for filter regeneration air-fuel ratio feedback control is set smaller than the gain for normal air-fuel ratio feedback control.

  As is clear from the above, the filter regeneration request generation determination means A5, the selection means A6, the downstream target value setting means A7, the output deviation amount calculation means A8, the low-pass filter A9, and the PID controller A10 constitute sub-feedback correction value calculation means. is doing.

<Calculation of main feedback correction value>
Based on the output value Vabyfs of the upstream air-fuel ratio sensor 66 and the table Mapabyfs representing the relationship between the upstream air-fuel ratio sensor output value Vabyfs and the air-fuel ratio A / F shown in FIG. The present detected air-fuel ratio abyfs (k) detected by the upstream air-fuel ratio sensor 66 is obtained.

  The target air-fuel ratio delay means A12 reads the upstream target air-fuel ratio abyfr stored in the RAM 73 from the RAM 73 at the time before the N stroke (N intake strokes) from the current time. Is set as the upstream target air-fuel ratio abyfr (kN). Here, the subscript (kN) indicates a value relative to the intake stroke before the N stroke (N · 180 ° CA, CA: crank angle in a four-cylinder engine) from the current intake stroke. . The upstream target air-fuel ratio abyfr (kN) is used to calculate the basic fuel injection amount Fbase (kN) (= Mc (kN) / abyfr (kN)) of the cylinder that has reached the intake stroke N strokes before the present time. The upstream target air-fuel ratio thus obtained (see the above formula (1)).

  Here, the value N differs depending on the displacement of the internal combustion engine 10, the distance from the combustion chamber 25 to the upstream air-fuel ratio sensor 66, and the like. Thus, the upstream target air-fuel ratio abyfr (kN) N strokes before the current stroke is used for calculating the main feedback correction value because the fuel containing the fuel injected from the injector 39 and mixed in the combustion chamber 25 is used. This is because a dead time L1 corresponding to the N stroke is required until the air reaches the upstream air-fuel ratio sensor 66. The value N is desirably changed so as to decrease as the engine rotational speed NE increases and to decrease as the engine load (for example, the cylinder intake air amount Mc) increases.

The upstream air-fuel ratio deviation calculating means A13 is based on the following expression (6) and detects the present time obtained by the table converting means A11 from the “upstream target air-fuel ratio abyfr (kN) output from the delay means A12”. The air-fuel ratio deviation Daf is obtained by subtracting the “air-fuel ratio abyfs (k)”. This air-fuel ratio deviation Daf is an amount representing a deviation from the target air-fuel ratio of the air-fuel ratio of the air-fuel mixture supplied into the cylinder at a time point before the N stroke.
Daf = abyfrtgt (k) −abyfs (k) (6)

The high-pass filter A14 is a primary filter. A transfer function A14 (s) representing the characteristics of the high-pass filter A14 is expressed by equation (7). In equation (7), s is a Laplace operator, and τ1 is a time constant. The time constant τ1 is the same time constant as the time constant τ1 of the low-pass filter A9. The high-pass filter A14 passes a high-frequency component having a frequency (1 / τ1) or higher and does not pass a low-frequency component having a frequency (1 / τ1) or lower.
A14 (s) = {1-1 / (1 + τ1 · s)} (7)

  The high-pass filter A14 receives the air-fuel ratio deviation Daf obtained by the upstream-side air-fuel ratio deviation calculating means A13, and after high-pass filtering the air-fuel ratio deviation Daf according to the characteristic expression expressed by the above equation (7). The main feedback control deviation DafHi, which is a value, is output.

  The main feedback correction value updating means A15 performs proportional processing on the main feedback control deviation DafHi, which is the output value of the high-pass filter A14. That is, the main feedback correction value updating unit A15 obtains the main feedback correction value KFmain by multiplying the main feedback control deviation DafHi by the proportional gain GpHi. The main feedback correction value KFmain is used when determining the final fuel injection amount Fi (k) as shown by the equation (2).

The main feedback correction value updating unit A15 performs main feedback correction by performing proportional / integral processing (PI processing) on the main feedback control deviation DafHi, which is an output value of the high-pass filter A14, based on the following equation (8). The value KFmain may be obtained.
KFmain = Gphi / DafHi + Gihi / SDafHi (8)

  In the above equation (8), Gphi is a preset proportional gain (proportional constant), and Gihi is a preset integral gain (integral constant). SDafHi is a time integral value of the deviation DafHi for main feedback control.

  As is apparent from the above, the upstream target air-fuel ratio setting means A2, table conversion means A11, target air-fuel ratio delay means A12, upstream air-fuel ratio deviation calculation means A13, high-pass filter A14, and main feedback correction value update means A15 are: Main feedback correction value calculation means is configured.

  In this way, the first control device connects the main feedback control system and the sub feedback control system in parallel and independently to the calculation system for the basic fuel injection amount Fbase. That is, the first control device independently executes main feedback control that multiplies the basic fuel injection amount Fbase by the main feedback correction value KFmain and sub feedback control that adds the sub feedback correction value Fisub.

  Further, the main feedback control deviation DafHi is a value obtained by subjecting the air-fuel ratio deviation Daf to the high-pass filter processing by the high-pass filter A14 and reflecting the air-fuel ratio fluctuation that does not appear downstream of the first three-way catalyst 53. . Therefore, the main feedback correction value KFmain and the sub feedback correction value Fisub are not corrected so as to interfere with the fluctuation of the air-fuel ratio of the air-fuel mixture supplied to the engine. In addition, a sudden change in the air-fuel ratio in the transient operation state is suppressed by the main feedback control, and a gradual air-fuel ratio that appears as “a fluctuation in the air-fuel ratio downstream of the first three-way catalyst 53 or the second three-way catalyst 55 by the sub-feedback control. Is eliminated. Further, the detection error of the upstream air-fuel ratio sensor 66 with respect to the average of the air-fuel ratio caused by the “characteristic deviation of the upstream air-fuel ratio sensor 66”, the “position of the upstream air-fuel ratio sensor 66”, etc. "Can prevent the engine air-fuel ratio average from deviating from the window W". Details of such air-fuel ratio feedback control are disclosed in, for example, Japanese Patent Application Laid-Open No. 2005-273524.

(Detailed operation)
Next, the operation of the first control device will be described in detail. Hereinafter, for convenience of explanation, “MapX (a1, a2,...)” Represents a table for obtaining a value X having a1, a2,. If the argument value is a sensor detection value, the current value is applied to the argument value.

<Calculation of final fuel injection amount Fi (k)>
The CPU 71 performs the routine for calculating the final fuel injection amount Fi and the injection instruction shown in the flowchart of FIG. 10. The CPU 71 performs a predetermined crank angle before the intake top dead center of each cylinder (for example, BTDC 90 ° CA). Each time it becomes, it is executed repeatedly. Therefore, when the crank angle of an arbitrary cylinder reaches the predetermined crank angle, the CPU 71 starts processing from step 1000, sequentially performs the processing of steps 1010 to 1050 described below, and proceeds to step 1095 to temporarily execute this routine. finish.

Step 1010: The CPU 71 performs the current in-cylinder intake air amount Mc to be drawn into a cylinder (hereinafter, also referred to as “fuel injection cylinder”) that reaches the current intake stroke based on the table MapMc (NE, Ga). Estimate and determine (k).
Step 1020: The CPU 71 sets the stoichiometric air-fuel ratio stoich to the current upstream target air-fuel ratio abyfr (k).
Step 1030: The CPU 71 calculates the basic fuel injection amount Fbase (k) by dividing the in-cylinder intake air amount Mc (k) by the upstream target air-fuel ratio abyfr (k) according to the equation (1). To do.

Step 1040: The CPU 71 adds the sub-feedback correction value Fisub to the product of the basic fuel injection amount Fbase and the main feedback correction value KFmain obtained in the routine to be described later, according to the above equation (2). Find the quantity Fi (k).
Step 1050: The CPU 71 issues an injection instruction to the injector 39 so that the fuel of the final fuel injection amount Fi (k) is injected from the injector 39 for the fuel injection cylinder.

  As described above, the basic fuel injection amount Fbase is acquired based on the upstream target air-fuel ratio abyfr (k) and the current in-cylinder intake air amount Mc (k), and the basic fuel injection amount Fbase is obtained from the main feedback correction value KFmain. The final fuel injection amount (final fuel injection amount) Fi is obtained by correcting with the sub-feedback correction value Fisub, and the fuel injection instruction of the final fuel injection amount Fi is sent to the injector 39 of the fuel injection cylinder. Made.

<Calculation of main feedback correction value>
Next, the operation for calculating the main feedback correction value KFmain will be described. The CPU 71 is configured to repeatedly execute the routine shown in the flowchart of FIG. 11 every elapse of a predetermined time. Accordingly, the CPU 71 starts processing from step 1100 at a predetermined timing, and determines whether or not the value of the main feedback control condition satisfaction flag XmainFB is “1” in step 1110. The value of the main feedback control condition satisfaction flag XmainFB is set to “1” when the main feedback control condition is satisfied, and is set to “0” when the main feedback control condition is not satisfied. Assuming that the value of the main feedback control condition satisfaction flag XmainFB is “1”, the CPU 71 sequentially performs the processing from step 1120 to step 1160 described below, proceeds to step 1195, and temporarily terminates this routine.

Step 1120: The CPU 71 obtains the current detected air-fuel ratio abyfs (k) by converting the current output value Vabyfs of the upstream air-fuel ratio sensor 66 based on the table Mapabyfs (Vabyfs) shown in FIG.
Step 1130: The CPU 71 sets the upstream target air-fuel ratio abyfr (k−N) N strokes before the current time as the main feedback target air-fuel ratio abyfrtgt (k).
Step 1140: The CPU 71 obtains the air-fuel ratio deviation Daf by subtracting the current detected air-fuel ratio abyfs (k) from the main feedback target air-fuel ratio abyfrtgt (k) according to the above equation (6).
Step 1150: The CPU 71 obtains a main feedback control deviation DafHi by subjecting the air-fuel ratio deviation Daf to high-pass filter processing having the characteristic expressed by the above equation (7).
Step 1160: The CPU 71 obtains a main feedback correction value KFmain by adding a value “1” to the product obtained by multiplying the main feedback control deviation DafHi by the proportional gain GpHi.

  On the other hand, if the value of the main feedback control condition satisfaction flag XmainFB is “0”, the CPU 71 determines “No” in step 1110 and proceeds to step 1170 to set the main feedback correction value KFmain to “1”. To do. Thereafter, the CPU 71 proceeds to step 1195 to end the present routine tentatively. As described above, the main feedback correction value KFmain is updated.

<Calculation of sub feedback correction value>
Next, an operation for calculating the sub feedback correction value Fisub will be described. The CPU 71 repeatedly executes the routine shown in the flowchart of FIG. 12 every time a predetermined time elapses. Accordingly, when the predetermined timing comes, the CPU 71 starts the process from step 1200 and proceeds to step 1205 to determine whether or not the value of the sub feedback control condition satisfaction flag XsubFB is “1”.

  The value of the sub feedback control condition satisfaction flag XsubFB is set to “1” when the sub feedback control condition is satisfied, and is set to “0” when the sub feedback control condition is not satisfied.

  Now, assuming that the value of the sub feedback control condition satisfaction flag XsubFB is “1”, the CPU 71 determines “Yes” in step 1205 and proceeds to step 1210, and the value of the filter regeneration request flag XPM is “1”. It is determined whether or not there is. The value of the filter regeneration request flag XPM is manipulated by the routine shown in FIG.

  At this time, if the value of the filter regeneration request flag XPM is “1”, the CPU 71 determines “Yes” in step 1210 and proceeds to step 1215 to set the output value Voxs of the selected air-fuel ratio sensor to the second downstream side empty air. The output value Voxs2 of the fuel ratio sensor 68 is stored. That is, the CPU 71 selects the second downstream air-fuel ratio sensor 68 as the selected air-fuel ratio sensor. On the other hand, if the value of the filter regeneration request flag XPM is “0”, the CPU 71 makes a “No” determination at step 1210 to proceed to step 1220 to set the output value Voxs of the selected air-fuel ratio sensor to the first downstream side. The output value Voxs1 of the air-fuel ratio sensor 67 is stored. That is, the CPU 71 selects the first downstream air-fuel ratio sensor 67 as the selected air-fuel ratio sensor. Thereafter, the CPU 71 sequentially performs the processing from step 1225 to step 1250 described below, proceeds to step 1295, and once ends this routine.

Step 1225: The CPU 71 determines 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 according to the above equation (3). As described above, the downstream target value Voxsref is set to a value Voxsst corresponding to the theoretical air-fuel ratio.
Step 1230: The CPU 71 calculates the output deviation amount DVoxslow after passing through the low-pass filter by performing low-pass filter processing having the characteristic expressed by the above equation (4) on the output deviation amount DVoxs.

Step 1235: The CPU 71 obtains a differential value DDVoxslow of the output deviation amount DVoxslow after passing through the low-pass filter based on the following equation (9). In the equation (9), DVoxslow1 is the previous value of “the output deviation amount DVoxslow after passing through the low-pass filter” updated in step 1235 (described later) at the previous execution of this routine. Δt is the time from the time when this routine was executed last time to the time when this routine was executed this time.
DDVoxslow = (DVoxslow-DVoxslow1) / Δt (9)

Step 1240: The CPU 71 obtains a sub feedback correction value Fisub according to the above equation (5).
Step 1245: The CPU 71 adds the output deviation amount DVoxslow after passing through the low-pass filter obtained in the above step 1230 to the integrated value SDVoxslow of the output deviation amount DVoxslow after passing through the low-pass filter at that time point, thereby obtaining a new output deviation amount after passing through the low-pass filter. Find the integrated value SDVoxslow of DVoxslow.
Step 1250: The CPU 71 stores the output deviation amount DVoxslow after passing through the low pass filter obtained in the above step 1230 in the previous value DVoxslow1 of the output deviation amount DVoxslow after passing through the low pass filter.

  On the other hand, if the value of the sub feedback control condition establishment flag XsubFB is “0” at the time of determination in step 1205, the CPU 71 determines “No” in step 1205 and proceeds to step 1255 to execute the sub feedback correction value Fisub. Is set to “0”, and in step 1260, the integrated value SDVoxslow of the output deviation DVoxslow after passing through the low-pass filter is set to “0”. Then, the process proceeds to step 1295, and this routine is temporarily ended.

  Thus, when the sub-feedback control condition is not satisfied (XsubFB = 0), the sub-feedback correction value Fisub is set to “0”, so the air-fuel ratio corresponding to the output value Voxs of the downstream air-fuel ratio sensor 67 is reduced. Feedback control is not performed.

  As described above, when the filter regeneration request is not generated (filter regeneration request flag XPM = 0), the first control device determines that the air-fuel ratio abyfs expressed by the output Vabyfs of the upstream air-fuel ratio sensor 66 is “theoretical air-fuel ratio”. Is equal to the first upstream target air-fuel ratio (abyfr, stoichiometric air-fuel ratio) within a predetermined air-fuel ratio range including the air-fuel ratio afdown1 (= f) expressed by the output value Voxs1 of the first downstream air-fuel ratio sensor 67 (Voxs1)) is made equal to the second downstream target air-fuel ratio (theoretical air-fuel ratio equivalent value Voxsst) within a predetermined air-fuel ratio range including the stoichiometric air-fuel ratio. In addition, the first control device performs an air-fuel ratio abyfs represented by the output Vabyfs of the upstream air-fuel ratio sensor 66 when a filter regeneration request is generated (filter regeneration request flag XPM = 1). Predetermined second upstream target The air-fuel ratio (the same theoretical air-fuel ratio as the first upstream target air-fuel ratio) coincides with the air-fuel ratio afdown2 (= f (Voxs2)) expressed by the output value Voxs2 of the second downstream air-fuel ratio sensor 68. Filter regeneration air-fuel ratio feedback control for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine 10 so as to coincide with the downstream target air-fuel ratio (the same stoichiometric air-fuel ratio equivalent value Voxsst as the first downstream target air-fuel ratio). Do.

  As a result, unburned matter and nitrogen oxides discharged from the engine are purified at high efficiency by at least the second three-way catalyst 55 and the third three-way catalyst 56 during normal air-fuel ratio feedback control, and are used for filter regeneration. At the time of air-fuel ratio feedback control, at least the third three-way catalyst 56 is purified with high efficiency. In addition, during the filter regeneration air-fuel ratio feedback control, a large amount of oxygen flows into the particulate collection filter 54. Therefore, the first control device can regenerate the particulate collection filter 54 while suppressing an increase in the discharge amount of unburned matter and nitrogen oxides.

(Second Embodiment)
Next, a control device for an internal combustion engine according to a second embodiment of the present invention (hereinafter also referred to as “second control device”) will be described. The second control device is the first control device only in that the upstream target air-fuel ratio abyfr in the filter regeneration air-fuel ratio feedback control is alternately changed over time with the forced lean air-fuel ratio afenL and the forced rich air-fuel ratio afenR. Is different. Such control is referred to as “air-fuel ratio active control”.

  More specifically, the CPU 71 of the second control device is the first controller only in that the routine shown in the flowchart of FIG. 13 is executed instead of the routine shown in FIG. 7 executed by the CPU 71 of the first control device. It is different from the control device. Therefore, the following description will be made with this difference as the center. In FIG. 13, steps for performing the same processing as the steps shown in FIG. 7 are denoted by the same reference numerals as those assigned to such steps in FIG. 7. A detailed description of these steps is omitted.

  The routine shown in FIG. 13 is different from the routine shown in FIG. 7 only in that step 730 of the routine shown in FIG. The processing in step 1310 is performed when the value of the filter regeneration request flag XPM is “1” (when a filter regeneration request is generated).

  More specifically, when the CPU 71 proceeds to step 1310, it performs regeneration air-fuel ratio feedback control to regenerate the particulate collection filter 54. In this case, the CPU 71 executes main feedback control and sub feedback control. As shown in FIG. 14, the upstream target air-fuel ratio (that is, the second upstream target air-fuel ratio) abyfr of the main feedback control is changed between the forced lean air-fuel ratio afenL and the forced rich air-fuel ratio afenR as time elapses. It is set to an air-fuel ratio that repeats alternately.

  That is, when the output value Voxs2 of the second downstream air-fuel ratio sensor 68 changes from a value smaller than the theoretical air-fuel ratio equivalent value Voxsst to a larger value as shown at time t1 in FIG. The target air-fuel ratio abyfr is set to the forced lean air-fuel ratio afenL. This timing is the time when the air-fuel ratio afdown2 represented by the output value Voxs2 of the second downstream air-fuel ratio sensor 68 is reversed from the lean air-fuel ratio to the rich air-fuel ratio from the stoichiometric air-fuel ratio. Also referred to as “rich inversion of Voxs2.”

  Thereafter, when the output value Voxs2 of the second downstream air-fuel ratio sensor 68 changes from a value larger than the theoretical air-fuel ratio equivalent value Voxsst to a smaller value as shown at time t2 in FIG. The target air-fuel ratio abyfr is set to the forced rich air-fuel ratio afenR. This timing is the time when the air-fuel ratio afdown2 represented by the output value Voxs2 of the second downstream air-fuel ratio sensor 68 reverses from the rich air-fuel ratio to the lean air-fuel ratio from the stoichiometric air-fuel ratio. Also referred to as “Voxs2 lean reversal”.

  Further, as shown at time t3 in FIG. 14, the CPU 71 sets the upstream target air-fuel ratio abyfr to the forced lean air-fuel ratio afenL at the next “at the time of rich inversion of the output value Voxs2,” and at time t4 in FIG. As shown, the upstream target air-fuel ratio abyfr is set to the forced rich air-fuel ratio afenR at the next “at the time of lean inversion of the output value Voxs2.” Thereafter, the CPU 71 repeats such an operation.

The forced lean air-fuel ratio afenL is an air-fuel ratio that is outside the predetermined air-fuel ratio range (window W) including the stoichiometric air-fuel ratio and is leaner than the stoichiometric air-fuel ratio by the air-fuel ratio ΔafL (ΔafL> 0). That is, forced lean air-fuel ratio afenL = theoretical air-fuel ratio stoich + ΔafL.
The forced rich air-fuel ratio afenR is outside the predetermined air-fuel ratio range (window W) including the stoichiometric air-fuel ratio and is richer than the stoichiometric air-fuel ratio by the air-fuel ratio ΔafR (ΔafR> 0). That is, forced rich air-fuel ratio afenR = theoretical air-fuel ratio stoich−ΔafR.
As a result, the upstream target air-fuel ratio abyfr changes in a rectangular waveform while having a width AC1 (= ΔafL + ΔafR).
In this example, the air-fuel ratio ΔafL and the air-fuel ratio ΔafR are equal, but the air-fuel ratio ΔafL is preferably set to be equal to or higher than the air-fuel ratio ΔafR.

  Further, in step 1310 of FIG. 13, the CPU 71 selects the second downstream air-fuel ratio sensor 68 as the selected air-fuel ratio sensor used for the sub-feedback control, and executes the sub-feedback control. In this case, the downstream target value Voxsref (the value corresponding to the second downstream target air-fuel ratio) of the sub feedback control is set to the stoichiometric air-fuel ratio equivalent value Voxsst corresponding to the stoichiometric air-fuel ratio.

  With the above control, the air-fuel ratio of the exhaust gas (exhaust gas flowing into the first three-way catalyst 53) passing through the location where the upstream air-fuel ratio sensor 66 is disposed is basically the same as the upstream target air-fuel ratio abyfr changes. By changing the injection amount Fbase and main feedback control, the forced lean air-fuel ratio afenL and the forced rich air-fuel ratio afenR are changed alternately. Accordingly, during the period when the upstream target air-fuel ratio abyfr is set to the forced lean air-fuel ratio afenL, a large amount and high concentration of oxygen is discharged from the engine 10 and flows into the particulate collection filter 54 via the first three-way catalyst 53. To do. As a result, the particulate collection filter 54 is efficiently regenerated.

  On the other hand, similarly to the first control device, the sub feedback control is executed so that the output value Voxs2 of the second downstream air-fuel ratio sensor 68 becomes the stoichiometric air-fuel ratio equivalent value Voxsst. Therefore, the average of the exhaust gas flowing into the third three-way catalyst 56 matches the stoichiometric air fuel ratio. As a result, the emission can be maintained satisfactorily.

  FIG. 15 is one of detailed flowcharts executed by the CPU 71 of the second control device. The CPU 71 of the second control device executes the routine shown in FIGS. 8, 11 and 12 in the same manner as the CPU 71 of the first control device, in addition to executing the routine of FIG. 15 instead of the routine of FIG.

  The routine of FIG. 15 is a routine in which step 1020 of FIG. 10 is replaced with steps 1510 to 1530. More specifically, the CPU 71 determines in step 1510 whether or not the value of the filter regeneration request flag XPM is “1”. If the value of the filter regeneration request flag XPM is “1”, the CPU 71 proceeds from step 1510 to step 1520 to set the air-fuel ratio (forced lean) for the air-fuel ratio active control described above to the upstream target air-fuel ratio abyfr (k). The air-fuel ratio (air-fuel ratio) in which the air-fuel ratio afenL and the forced rich air-fuel ratio afenR are alternately repeated is set. That is, when the output value Voxs2 of the second downstream air-fuel ratio sensor 68 is smaller than the theoretical air-fuel ratio equivalent value Voxsst, the CPU 71 sets the upstream target air-fuel ratio abyfr (k) to the forced rich air-fuel ratio afenR. Further, when the output value Voxs2 of the second downstream air-fuel ratio sensor 68 is larger than the theoretical air-fuel ratio equivalent value Voxsst, the CPU 71 sets the upstream target air-fuel ratio abyfr (k) to the forced lean air-fuel ratio afenL.

  As a result, the basic fuel injection amount Fbase (k) obtained in step 1030 also changes in accordance with either the forced lean air-fuel ratio afenL or the forced rich air-fuel ratio afenR. Further, in the main feedback correction value calculation routine shown in FIG. 11, since the upstream target air-fuel ratio abyfr (k) becomes the air-fuel ratio for air-fuel ratio active control, the main feedback correction value KFmain also sets “the air-fuel ratio of the engine It is calculated so as to coincide with the air-fuel ratio for air-fuel ratio active control.

  At this time (that is, when the value of the filter regeneration request flag XPM is “1”), the CPU 71 makes a “Yes” determination at step 1210 in FIG. 12 and proceeds to step 1215 to select the second downstream as the selected air-fuel ratio sensor. The side air-fuel ratio sensor 68 is selected. Accordingly, the sub feedback correction value Fisub is calculated based on the output value Voxs2 of the second downstream air-fuel ratio sensor 68 (sub feedback control is executed).

  On the other hand, when the CPU 71 executes step 1510 in FIG. 15, if the value of the filter regeneration request flag XPM is “0”, the CPU 71 proceeds from step 1510 to step 1530 and theoretically sets the upstream target air-fuel ratio abyfr (k). Set the air-fuel ratio stoich.

  Further, if the value of the filter regeneration request flag XPM is “0”, the CPU 71 makes a “No” determination at step 1210 in FIG. 12 to proceed to step 1220, where the first downstream-side empty sensor is selected as the selected air-fuel ratio sensor. The fuel ratio sensor 67 is selected. Therefore, the sub feedback correction value Fisub is calculated based on the output value Voxs1 of the first downstream air-fuel ratio sensor 67 (sub feedback control is executed). As a result, the normal air-fuel ratio feedback control that is the same as the normal air-fuel ratio feedback control executed by the first control device is executed.

  As described above, according to the second control device, the amplitude of the air-fuel ratio of the engine when it is determined that the filter regeneration request has occurred (when the filter regeneration request is generated) This is larger than the amplitude of the air-fuel ratio of the engine when it is determined that there is no (normal time, when no filter regeneration request is generated). Moreover, the engine air-fuel ratio (instantaneous instantaneous air-fuel ratio instead of the average) at the time of this filter regeneration request oscillates over the window W, and the upstream target air-fuel ratio abyfr is set to the forced lean air-fuel ratio afenL. When the engine 10 is on, a large amount of high concentration oxygen is discharged.

  Therefore, when a filter regeneration request is generated, high-concentration oxygen flows into the particulate collection filter 54, so that the particulates burn efficiently. Furthermore, since the amount of fine particles combusted per unit time is increased by this high concentration of oxygen, more heat is generated. Therefore, the temperature of the particulate collection filter 54 is further increased by this heat, so that the combustion efficiency of the particulates is further improved. As a result, the second control device can efficiently regenerate the particulate collection filter 54 within a short period of time.

  In addition, according to the second control apparatus, the upstream target air-fuel ratio abyfr is set to the forced lean air-fuel ratio afenL at the time of rich inversion of the output value Voxs2, and the upstream target at the time of “at the time of lean inversion of the output value Voxs2". The air-fuel ratio abyfr is set to the forced rich air-fuel ratio afenR. Therefore, when the oxygen storage amount OSA2 of the second three-way catalyst 55 reaches “0” (when the output value Voxs2 is richly inverted), the point when the maximum oxygen storage amount Cmax2 of the second three-way catalyst 55 is reached (output value). The upstream target air-fuel ratio abyfr is set to the forced lean air-fuel ratio afenL during the period until the lean reversal of Voxs2. Further, the oxygen storage amount OSA3 of the third three-way catalyst 56 does not reach the maximum oxygen storage amount Cmax3 of the third three-way catalyst 56 at the time of the lean reversal of the output value Voxs2. Since the upstream target air-fuel ratio abyfr is changed to the forced rich air-fuel ratio afenR when the output value Voxs2 is lean-reversed, NOx that cannot be purified by the third three-way catalyst 56 flows into the third three-way catalyst 56. do not do.

  As a result, it is possible to lengthen the period during which high-concentration oxygen is discharged from the engine 10 (the period in which the upstream target air-fuel ratio abyfr is set to the forced lean air-fuel ratio afenL) within a range where the emission is not deteriorated. Therefore, since a large amount and high concentration of oxygen is supplied to the particulate collection filter 54, the particulate collection filter 54 can be efficiently regenerated while avoiding the deterioration of emission.

(First Modification of Second Embodiment)
Next, a first modification of the second embodiment (hereinafter also referred to as “first modification”) will be described. In the first modification, the upstream target air-fuel ratio abyfr in the filter regeneration air-fuel ratio feedback control is alternately changed over time with the forced lean air-fuel ratio afenL and the forced rich air-fuel ratio afenR, as in the second control device. . That is, the first modification also performs “air-fuel ratio active control”. However, in the first modification, the upstream target air-fuel ratio abyfr is changed to the forced rich air-fuel ratio afenR at the timing based on the lean inversion of the output value Voxs1 of the first downstream air-fuel ratio sensor 67, and the first downstream The second control device is different from the second control device only in that the upstream target air-fuel ratio abyfr is changed to the forced lean air-fuel ratio afenL at the timing based on the rich inversion of the output value Voxs1 of the side air-fuel ratio sensor 67.

  More specifically, in the first modification, when the filter regeneration air-fuel ratio feedback control is executed, the upstream target air-fuel ratio abyfr is set as shown in FIG. That is, the CPU 71 changes the output value Voxs1 of the first downstream air-fuel ratio sensor 67 from a value larger than the theoretical air-fuel ratio equivalent value Voxst to a smaller value (when the output value Voxs1 is lean-reversed, the time t2 in FIG. 16). ) After the elapse of a predetermined time T1 (time t3), the upstream target air-fuel ratio abyfr is changed from the forced lean air-fuel ratio afenL to the forced rich air-fuel ratio afenR. Further, the CPU 71 changes the output value Voxs1 of the first downstream air-fuel ratio sensor 67 from a value smaller than the theoretical air-fuel ratio equivalent value Voxst to a larger value (when the output value Voxs1 is richly inverted, time t4 in FIG. 16). ) After the elapse of a predetermined time T2 (time t5), the upstream target air-fuel ratio abyfr is changed from the forced rich air-fuel ratio afenR to the forced lean air-fuel ratio afenL.

  In this case, the time T1 and the time T2 may be the same or different. However, the time T1 is set to a time shorter than the time required for the oxygen storage amount OSA2 of the second three-way catalyst 55 to reach the maximum oxygen storage amount Cmax2 of the second three-way catalyst 55 from “0”. Is more preferable. In order to set the time T1 in this way, the CPU 71 estimates the maximum oxygen storage amount Cmax2 of the second three-way catalyst 55, and sets the time T1 to a longer time as the estimated maximum oxygen storage amount Cmax2 increases. Good. The time T1 may be “0”. That is, at the time of lean inversion of the output value Voxs1, the upstream target air-fuel ratio abyfr may be changed from the forced lean air-fuel ratio afenL to the forced rich air-fuel ratio afenR.

  Similarly, the time T2 is set to a time shorter than the time required for the oxygen storage amount OSA2 of the second three-way catalyst 55 to reach “0” from the maximum oxygen storage amount Cmax2 of the second three-way catalyst 55. More preferably. In order to set the time T2 in this way, the CPU 71 estimates the maximum oxygen storage amount Cmax2 of the second three-way catalyst 55, and sets the time T2 to a longer time as the estimated maximum oxygen storage amount Cmax2 increases. Good. Further, the time T2 may be “0”. That is, when the output value Voxs1 is richly inverted, the upstream target air-fuel ratio abyfr may be changed from the forced rich air-fuel ratio afenR to the forced lean air-fuel ratio afenL.

  Also according to the first modification, high concentration oxygen can be caused to flow into the particulate collection filter 54 by the air-fuel ratio active control, so that the particulate collection filter 54 can be efficiently regenerated. Furthermore, since the sub-feedback control is executed in a state where the second downstream air-fuel ratio sensor 68 is selected as the selected air-fuel ratio sensor, the particulate collection filter 54 can be regenerated while avoiding deterioration of emissions.

(Second Modification of Second Embodiment)
Next, a second modified example (hereinafter also referred to as “second modified example”) of the second embodiment will be described. In the second modification, as in the second control device, the upstream target air-fuel ratio abyfr in the filter regeneration air-fuel ratio feedback control is alternately changed over time with the forced lean air-fuel ratio afenL and the forced rich air-fuel ratio afenR. . That is, the second modification also performs “air-fuel ratio active control”. However, in the second modified example, as shown in FIG. 17, the upstream target air-fuel ratio abyfr is set to the forced lean air after a predetermined time TL has elapsed since the upstream target air-fuel ratio abyfr is set to the forced lean air-fuel ratio afenL. The fuel ratio is changed from the fuel ratio afenL to the forced rich air-fuel ratio afenR. Further, in the second modified example, the upstream target air-fuel ratio abyfr is changed from the forced rich air-fuel ratio afenR to the forced lean air-fuel ratio afenL after a predetermined time TR has elapsed since the upstream target air-fuel ratio abyfr was set to the forced rich air-fuel ratio afenR. Change to

  In this case, during the predetermined time TL, when the upstream target air-fuel ratio abyfr is set to the forced lean air-fuel ratio afenL, the oxygen storage amount OSA1 of the first three-way catalyst 53 is changed from “0” to the first three-way catalyst 53. Is reached in a time shorter than the time TL1 when the oxygen storage amount OSA2 of the second three-way catalyst 55 reaches the maximum oxygen storage amount Cmax2 of the second three-way catalyst 55 after that. It is desirable that the time is as close as possible to the time TL1.

  Similarly, for a predetermined time TR, when the upstream target air-fuel ratio abyfr is set to the forced rich air-fuel ratio afenR, the oxygen storage amount OSA1 of the first three-way catalyst 53 is the maximum oxygen storage amount of the first three-way catalyst 53. After reaching the amount Cmax1 to “0”, the oxygen storage amount OSA2 of the second three-way catalyst 55 is shorter than the time TR1 until the maximum oxygen storage amount Cmax2 of the second three-way catalyst 55 reaches “0”. It is desirable that the time is as close as possible to the time TR1.

  Also according to the second modification, since the high concentration oxygen can be caused to flow into the particulate collection filter 54 by the air-fuel ratio active control, the particulate collection filter 54 can be efficiently regenerated. Furthermore, since the sub-feedback control is executed in a state where the second downstream air-fuel ratio sensor 68 is selected as the selected air-fuel ratio sensor, the particulate collection filter 54 can be regenerated while avoiding deterioration of emissions.

(Third embodiment)
Next, a control device for an internal combustion engine according to a third embodiment of the present invention (hereinafter also referred to as “third control device”) will be described. Similar to the second control device, the third control device performs air-fuel ratio active control to regenerate the particulate collection filter 54. However, the third control device performs the second control only in changing the values of the forced lean air-fuel ratio afenL and the forced rich air-fuel ratio afenR according to the temperature TempPMF of the particulate collection filter 54 during execution of the air-fuel ratio active control. It is different from the device.

  More specifically, the CPU 71 of the third control device is the second controller only in that the routine shown in the flowchart of FIG. 18 is executed instead of the routine shown in FIG. 15 executed by the CPU 71 of the second control device. It is different from the control device. Therefore, the following description will be made with this difference as the center. Note that steps for performing the same processing as the steps described above in FIG. 18 are denoted by the same reference numerals as those given to such steps. A detailed description of these steps is omitted.

  The routine shown in FIG. 18 differs from the routine shown in FIG. 15 only in that Steps 1810 and 1820 are added between Step 1510 and Step 1520 of the routine shown in FIG. The processing of these steps is performed when the value of the filter regeneration request flag XPM is “1” (when a filter regeneration request is generated).

  More specifically, the CPU 71 determines in step 1510 whether or not the value of the filter regeneration request flag XPM is “1”. If the value of the filter regeneration request flag XPM is “1”, the CPU 71 proceeds from step 1510 to step 1810 to acquire the temperature TempPMF of the particulate collection filter 54. The temperature TempPMF of the particulate collection filter 54 is a value that increases as the temperature of the particulate collection filter 54 increases.

  In practice, the CPU 71 sets the temperature of the gas flowing into the particulate collection filter 54 (hereinafter referred to as “filter inflow gas temperature”) Tempg as the current engine rotational speed NE and the current engine load KL (intake air). This may be estimated by applying the amount Ga or the accelerator pedal operation amount Accp) and the current ignition timing Aig to the table MapTempg (NE, KL, Aig). The table MapTempg (NE, KL, Aig) is obtained in advance by experiments and stored in the ROM 72. Then, the CPU 71 acquires the filter inflow gas temperature Tempg as the temperature TempPMF of the particulate collection filter 54. A temperature sensor may be provided at the exhaust gas inlet of the particulate collection filter 54, and the CPU 71 may acquire the filter inflow gas temperature Tempg as the temperature TempPMF of the particulate collection filter 54 based on the output of the temperature sensor. .

  Next, the CPU 71 proceeds to step 1820 and determines the forced lean air-fuel ratio afenL and the forced rich air-fuel ratio afenR by applying the acquired temperature TempPMF of the particulate collection filter 54 to the table shown in the block of step 1820. . According to this table, the forced lean air-fuel ratio afenL is determined to be the rich air-fuel ratio and approach the stoichiometric air-fuel ratio as the temperature TempPMF of the particulate collection filter 54 increases. Further, according to this table, as the temperature TempPMF of the particulate collection filter 54 increases, the forced rich air-fuel ratio afenR is determined to become the lean air-fuel ratio and approach the stoichiometric air-fuel ratio.

  Thereafter, the CPU 71 proceeds to step 1520 to set the forced lean air-fuel ratio afenL and forced rich air-fuel ratio afenR (air-fuel ratio for air-fuel ratio active control) determined in step 1820 to the upstream target air-fuel ratio abyfr (k). To do.

  As a result, the basic fuel injection amount Fbase (k) obtained in step 1030 of FIG. 10 also changes according to either the forced lean air-fuel ratio afenL or the forced rich air-fuel ratio afenR. Further, in the main feedback correction value calculation routine shown in FIG. 11, since the upstream target air-fuel ratio abyfr (k) becomes the air-fuel ratio for air-fuel ratio active control, the main feedback correction value KFmain also sets “the air-fuel ratio of the engine It is calculated so as to coincide with the air-fuel ratio for air-fuel ratio active control.

  On the other hand, when the CPU 71 executes step 1510 in FIG. 18, if the value of the filter regeneration request flag XPM is “0”, the CPU 71 proceeds from step 1510 to step 1530 to theoretically set the upstream target air-fuel ratio abyfr (k). Set the air-fuel ratio stoich. Therefore, in this case, the same normal air-fuel ratio feedback control as the normal air-fuel ratio feedback control executed by the first control device is executed.

  As described above, when it is determined that a filter regeneration request has occurred (ie, when the particulate collection filter 54 is regenerated, when the filter regeneration request is generated), the third controller is similar to the second controller. Then, air-fuel ratio active control is executed. Accordingly, the third control device can cause a large amount and high concentration of oxygen to flow through the particulate collection filter 54 as in the second control device. As a result, the particulate collection filter 54 can be reliably regenerated within a short period of time.

  Further, the third control device acquires a filter temperature corresponding value (in this case, the temperature TempPMF of the particulate collection filter 54) that increases as the temperature TempPMF of the particulate collection filter 54 increases, and corresponds to the acquired filter temperature. The smaller the value TempPMF, the greater the difference between the forced lean air-fuel ratio afenL and the stoichiometric air-fuel ratio (see ΔafL in step 1820 in FIG. 18).

  As the temperature TempPMF of the particulate collection filter 54 is lower, the particulates collected by the particulate collection filter 54 are more difficult to burn. On the other hand, the more oxygen is supplied to the particulate collection filter 54, the more particulates burn. Therefore, the third control device sets the forced lean air-fuel ratio to a leaner air-fuel ratio as the temperature TempPMF of the particulate collection filter 54 is lower. Accordingly, a higher concentration of oxygen is exhausted from the engine 10, whereby more oxygen can be supplied to the particulate collection filter 54. As a result, the regeneration of the particulate collection filter 54 can surely proceed regardless of the temperature TempPMF of the particulate collection filter 54. Further, when the temperature TempPMF of the particulate collection filter 54 is high, the air-fuel ratio (forced lean air-fuel ratio afenL) of the engine 10 during the air-fuel ratio active control approaches the stoichiometric air-fuel ratio. The amount of things also decreases. Therefore, according to the third control device, it is possible to reliably regenerate the particulate collection filter 54 while suppressing the discharge amount of nitrogen oxide as much as possible.

  Also in this example, the air-fuel ratio ΔafL (difference between the forced lean air-fuel ratio afenL and the stoichiometric air-fuel ratio stoich) and the air-fuel ratio ΔafR (the stoichiometric air-fuel ratio stoich and the forced rich air-fuel ratio afenR) with respect to the temperature TempPMF of a certain particulate collection filter 54 Is the same as However, the air-fuel ratio ΔafL with respect to the temperature TempPMF of a certain particulate collection filter 54 is preferably set larger than the air-fuel ratio ΔafR with respect to the temperature TempPMF. Further, the third control device may switch between the forced lean air-fuel ratio afenL and the forced rich air-fuel ratio afenR at the same timing as in the first and second modifications of the second control device.

(Fourth embodiment)
Next, a control device for an internal combustion engine according to a fourth embodiment of the present invention (hereinafter also referred to as “fourth control device”) will be described. As shown in FIG. 19, the fourth control device eliminates the first downstream air-fuel ratio sensor 67, and “in the air-fuel ratio active control for regenerating the particulate collection filter 54” and “normal air-fuel ratio”. The difference from the second control device is that the sub-feedback control using the output value Voxs2 of the second downstream air-fuel ratio sensor 68 is performed both in “during feedback control”.

  More specifically, the CPU 71 of the fourth control device is the second controller only in that the routine shown in the flowchart of FIG. 20 is executed instead of the routine shown in FIG. 13 executed by the CPU 71 of the second control device. It is different from the control device. Therefore, the following description will be made with this difference as the center. Note that steps for performing the same processing as the steps described above in FIG. 20 are denoted by the same reference numerals as those given to such steps. A detailed description of these steps is omitted.

  The routine shown in FIG. 20 is different from the routine shown in FIG. 13 only in that step 1310 and step 720 of the routine shown in FIG. 13 are replaced with step 2010 and step 2020, respectively.

  According to this routine, the CPU 71 determines in step 710 whether or not the value of the filter regeneration request flag XPM is “1”. If the value of the filter regeneration request flag XPM is “1”, the CPU 71 proceeds from step 710 to step 2010 and executes main feedback control. This step 2010 is a step for performing substantially the same processing as step 1310 in FIG. That is, the CPU 71 alternates the upstream target air-fuel ratio (that is, the second upstream target air-fuel ratio) abyfr of the main feedback control between the forced lean air-fuel ratio afenL and the forced rich air-fuel ratio afenR as shown in FIG. The air-fuel ratio is set to repeat.

  Further, in step 2010, the CPU 71 uses the output value Voxs2 of the second downstream air-fuel ratio sensor 68 for the sub feedback control. In this case, the downstream target value Voxsref of the sub feedback control is set to the stoichiometric air fuel ratio equivalent value Voxsst corresponding to the stoichiometric air fuel ratio.

  On the other hand, if the value of the filter regeneration request flag XPM is “0”, the CPU 71 proceeds from step 710 to step 2020 and executes main feedback control. In this case, the upstream target air-fuel ratio (that is, the first upstream target air-fuel ratio) abyfr of the main feedback control is set to the stoichiometric air-fuel ratio stoich.

  Further, also in step 2020, the CPU 71 uses the output value Voxs2 of the second downstream air-fuel ratio sensor 68 for the sub feedback control. In this case, the downstream target value Voxsref of the sub feedback control is set to the stoichiometric air fuel ratio equivalent value Voxsst corresponding to the stoichiometric air fuel ratio. Thereby, normal air-fuel ratio feedback control is executed.

  The fourth control device also executes air-fuel ratio active control when the particulate collection filter 54 is regenerated. Therefore, the particulate collection filter 54 can be efficiently regenerated. Moreover, since the 4th control apparatus can abbreviate | omit the 1st downstream air-fuel-ratio sensor 67 with respect to a 2nd control apparatus, it can reduce the cost of an apparatus. However, when compared with the fourth control device, the second control device has a period of sub-feedback control in the normal air-fuel ratio feedback that is not so long. 1 It is possible to avoid flowing into the three-way catalyst 53 for a long period of time. Therefore, the 2nd control device can control that the deterioration by sintering of the 1st three way catalyst 55 advances rather than the 4th control device.

  As described above, the control device for an internal combustion engine according to the embodiment of the present invention can regenerate the particulate collection filter 54 at an appropriate timing without increasing the emission amount of nitrogen oxides.

  The present invention is not limited to the above embodiments, and various modifications can be adopted within the scope of the present invention. For example, in the sub feedback control, for example, as disclosed in JP 2007-278186 A, the upstream air-fuel ratio sensor 66 is set so that the output value Voxs of the downstream air-fuel ratio sensor 67 matches the downstream target value. A mode in which the air-fuel ratio detected by the above is apparently corrected may be employed. Further, as disclosed in JP-A-6-010738, an air-fuel ratio correction coefficient created based on the output value of the upstream air-fuel ratio sensor 66 based on the output value Voxs of the downstream air-fuel ratio sensor 67. It is also possible to change the mode.

  In addition, in the first embodiment, the upstream target air-fuel ratio abyfr (that is, the second upstream target air-fuel ratio) in the regeneration air-fuel ratio feedback control is equal to the upstream target air-fuel ratio abyfr in the normal air-fuel ratio feedback control (that is, The air / fuel ratio may be different from the first upstream target air / fuel ratio. Similarly, the downstream target value corresponding to the downstream target air-fuel ratio (that is, the second downstream target air-fuel ratio) in the regeneration air-fuel ratio feedback control is the value of the window W of the three-way catalyst as in the above embodiments. If the value corresponds to the air-fuel ratio within the range, it is the same as the downstream target value corresponding to the downstream target air-fuel ratio (that is, the first downstream target air-fuel ratio) in the normal air-fuel ratio feedback control (for example, the stoichiometric air-fuel ratio). (Voxsst) or a different value.

1 is a schematic view of an internal combustion engine to which a control device (first control device) according to a first embodiment of the present invention is applied. It is a schematic block diagram of the internal combustion engine shown in FIG. 2 is a graph showing the purification rate of unburned components and nitrogen oxides with respect to the air-fuel ratio of the first to third three-way catalysts shown in FIG. 1. 3 is a graph showing the relationship between the output of the upstream air-fuel ratio sensor shown in FIG. 1 and the air-fuel ratio. 3 is a graph showing the relationship between the output of the first downstream air-fuel ratio sensor and the second downstream air-fuel ratio sensor shown in FIG. 1 and the air-fuel ratio. It is a time chart for demonstrating the action | operation of a 1st control apparatus. It is the flowchart which showed the routine which CPU of a 1st control apparatus performs. It is the flowchart which showed the routine which CPU of a 1st control apparatus performs. It is a functional block diagram of the 1st control device for performing air fuel ratio feedback control. It is the flowchart which showed the routine for performing calculation of the last fuel injection amount and injection instruction which CPU of a 1st control apparatus performs. It is the flowchart which showed the routine for calculating the main feedback correction value which CPU of the 1st control device performs. It is the flowchart which showed the routine for calculating the sub feedback correction value which CPU of the 1st control unit executes. It is the flowchart which showed the routine which CPU of the control apparatus (2nd control apparatus) concerning 2nd Embodiment of this invention performs. It is a time chart for demonstrating the upstream target air fuel ratio in the air fuel ratio active control which a 2nd control apparatus performs. It is the flowchart which showed the routine for performing calculation of the final fuel injection amount and the injection instruction which CPU of a 2nd control apparatus performs. It is a time chart for demonstrating the upstream target air fuel ratio in the air fuel ratio active control which the 1st modification of a 2nd control apparatus performs. It is a time chart for demonstrating the upstream target air fuel ratio in the air fuel ratio active control which the 2nd modification of a 2nd control apparatus performs. It is the flowchart which showed the routine for performing calculation of the last fuel injection amount and the injection instruction which CPU of the control apparatus (3rd control apparatus) concerning 3rd Embodiment of this invention performs. It is a schematic block diagram of the internal combustion engine to which the control apparatus (4th control apparatus) which concerns on 4th Embodiment of this invention is applied. It is the flowchart which showed the routine which CPU of the 4th control unit performs.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 20 ... Cylinder block part, 25 ... Combustion chamber, 34 ... Exhaust port, 41 ... Intake manifold, 42 ... Intake pipe, 50 ... Exhaust system, 51 ... Exhaust manifold, 51a ... Branch part, 51b ... Collecting part , 52 ... Exhaust pipe, 53 ... First three-way catalyst, 54 ... Fine particle collecting filter, 55 ... Second three-way catalyst, 56 ... Third three-way catalyst, 66 ... Upstream air-fuel ratio sensor, 67 ... First downstream Side air-fuel ratio sensor, 68... Second downstream air-fuel ratio sensor, 70.

Claims (5)

An upstream air-fuel ratio sensor, a first three-way catalyst, a particulate collection filter, a first downstream air-fuel ratio sensor, a second three-way catalyst, which are sequentially arranged from the upstream side to the downstream side of the exhaust passage of the internal combustion engine; A control device for an internal combustion engine comprising a second downstream air-fuel ratio sensor and a third three-way catalyst,
A filter regeneration request is generated to determine whether a filter regeneration request, which is a request to regenerate the particulate collection filter, is generated by burning the particulates collected by the particulate collection filter in the particulate collection filter. A determination means;
When it is determined that the filter regeneration request has not occurred, the air-fuel ratio represented by the output of the upstream air-fuel ratio sensor becomes the first upstream target air-fuel ratio within a predetermined air-fuel ratio range including the stoichiometric air-fuel ratio. And the air-fuel ratio represented by the output of the first downstream air-fuel ratio sensor is supplied to the engine so as to coincide with a first downstream target air-fuel ratio within a predetermined air-fuel ratio range including the theoretical air-fuel ratio. The normal air-fuel ratio feedback control for controlling the air-fuel ratio of the air-fuel mixture is performed, and when it is determined that the filter regeneration request has occurred, the air-fuel ratio represented by the output of the upstream air-fuel ratio sensor is a predetermined second upstream side The air-fuel ratio that matches the target air-fuel ratio and that is represented by the output of the second downstream air-fuel ratio sensor matches the second downstream-side target air-fuel ratio within a predetermined air-fuel ratio range that includes the theoretical air-fuel ratio. Machine And air-fuel ratio feedback control means for performing filter regeneration air-fuel ratio feedback control for controlling the air-fuel ratio of the mixture supplied to the,
A control device comprising: The control apparatus for an internal combustion engine according to claim 1,
The control device, wherein the air-fuel ratio feedback control means sets the first upstream target air-fuel ratio to the stoichiometric air-fuel ratio and sets the second upstream target air-fuel ratio to the stoichiometric air-fuel ratio. A control device for an internal combustion engine according to claim 1,
The air-fuel ratio feedback control means sets the first upstream target air-fuel ratio to the stoichiometric air-fuel ratio, and sets the second upstream target air-fuel ratio outside a predetermined air-fuel ratio range including the stoichiometric air-fuel ratio. A forced rich air-fuel ratio that is an air-fuel ratio richer than the stoichiometric air-fuel ratio and a forced lean air-fuel ratio that is outside the predetermined air-fuel ratio range including the stoichiometric air-fuel ratio and is leaner than the stoichiometric air-fuel ratio A control device configured to set an air-fuel ratio that repeats alternately as time elapses. The control apparatus for an internal combustion engine according to claim 3,
The air-fuel ratio feedback control means determines the second upstream target air-fuel ratio from the air-fuel ratio richer than the stoichiometric air-fuel ratio to the lean-side air-fuel ratio expressed by the output of the second downstream air-fuel ratio sensor. When the air-fuel ratio changes, the forced rich air-fuel ratio is set, and the air-fuel ratio represented by the output of the second downstream air-fuel ratio sensor is changed from the lean air-fuel ratio to the rich air-fuel ratio. A control device configured to set the forced lean air-fuel ratio when the fuel ratio changes to the fuel ratio. The control apparatus for an internal combustion engine according to claim 3 or 4,
The air-fuel ratio feedback control means acquires a filter temperature corresponding value that increases as the temperature of the particulate collection filter increases, and the forced lean air-fuel ratio and the stoichiometric air-fuel ratio decrease as the acquired filter temperature corresponding value decreases. A control device that changes the forced lean air-fuel ratio so that the difference between the two increases.

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