JP2010048131A - Internal combustion engine control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an internal combustion engine control device enabling sure regeneration of a particulate trapping filter by lengthening the time set for a forcible lean air-fuel ratio. <P>SOLUTION: The control device comprises a filter storage catalyst device CwF. The filter storage catalyst device is arranged in an exhaust pipe 52 and stores " first three-way catalyst 53, the particulate trapping filter 54 and a second three-way catalyst 55" in sequence toward the downstream side. The control device sets the air-fuel ratio of mixture to be either a forcible rich air-fuel ratio or a forcible lean air-fuel ratio on request for regenerating a filter. When the air-fuel ratio of the mixture is set to be the forcible lean air-fuel ratio, excessive oxygen flows into the particulate trapping filter 54 to regenerate the particulate trapping filter. When the air-fuel ratio of the mixture is set to be the forcible lean air-fuel ratio, if oxygen flows out of the second three-way catalyst to change the output of a downstream-side air-fuel ratio sensor 67 to be an value corresponding to a lean air-fuel ratio, then the air-fuel ratio of the mixture is set to be the forcible rich air-fuel ratio. <P>COPYRIGHT: (C)2010,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 a three-way catalyst (first three-way catalyst) is provided upstream of the particulate collection filter, oxygen is consumed and stored by the first three-way catalyst, so the amount of oxygen flowing into the particulate collection filter Is extremely low. Therefore, in order to regenerate the particulate collection filter in such 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 “forced lean air-fuel ratio”). By doing so, oxygen must be supplied to the particulate collection filter.

  However, if the air-fuel ratio of the engine is continuously set to the forced lean air-fuel ratio regardless of the state of the three-way catalyst, the nitrogen discharged from the engine is large when the air-fuel ratio of the engine is leaner than the stoichiometric air-fuel ratio. Oxides cannot be purified by a three-way catalyst (for example, when the oxygen storage amount of a three-way catalyst reaches the maximum oxygen storage amount and nitrogen oxides cannot be reduced), and a large amount of nitrogen oxides are discharged into the atmosphere The problem of being done occurs.

  Therefore, when the output of the downstream air-fuel ratio sensor disposed downstream of the particulate collection filter is monitored, and the output of the downstream air-fuel ratio sensor becomes an output corresponding to an air-fuel ratio leaner than the stoichiometric air-fuel ratio. The air-fuel ratio of the engine is temporarily set to an air-fuel ratio richer than the stoichiometric air-fuel ratio (forced rich air-fuel ratio), and then the output of the downstream air-fuel ratio sensor corresponds to an air-fuel ratio richer than the stoichiometric air-fuel ratio. It is considered effective to perform “filter regeneration control” that sets the air-fuel ratio of the engine to the forced lean air-fuel ratio again when the output is obtained. Such air-fuel ratio control is also referred to as “active air-fuel ratio control” in this specification.

  However, when the air-fuel ratio of the engine was set to the forced lean air-fuel ratio in order to regenerate the particulate collection filter, it flowed into the particulate collection filter even though particulates were present in the particulate collection filter. Oxygen may leak from the particulate collection filter without being consumed in the particulate collection filter. In this case, the air-fuel ratio of the engine is immediately changed to a forced rich air-fuel ratio. Therefore, since a large amount of oxygen cannot be allowed to flow into the particulate collection filter at a time, the particulate collection filter cannot be sufficiently regenerated, or “the active space that is not optimal from the viewpoint of emissions”. There arises a problem that the period during which "fuel ratio control" is performed becomes longer.

  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. It is an object of the present invention to provide a control device for an internal combustion engine that can efficiently regenerate a filter (efficiently combusting particulates collected by a particulate collection filter).

  In order to achieve the above object, a control device according to the present invention includes a filter-accommodating catalyst device, a downstream air-fuel ratio sensor, a filter regeneration request generation determination unit, and a filter regeneration unit.

  The filter housing catalyst device is disposed in an exhaust passage of the internal combustion engine. The filter-containing catalyst device includes a “first three-way catalyst, a particulate collection filter, and a second three-way catalyst” arranged in order from the upstream side to the downstream side of the exhaust gas. The first three-way catalyst, the particulate collection filter, and the second three-way catalyst are accommodated in one casing (housing). Here, “the order from the upstream side to the downstream side of the exhaust gas” means “in order from the upstream side to the downstream side of the flow of the exhaust gas in the exhaust passage”.

  The downstream air-fuel ratio sensor is disposed in the exhaust passage and downstream of the filter-accommodating catalyst device. Accordingly, the downstream air-fuel ratio sensor outputs a value corresponding to the air-fuel ratio of “exhaust gas flowing out from the second three-way catalyst and reaching the position where the downstream air-fuel ratio sensor is disposed”.

  The filter regeneration request occurrence determination unit determines whether a filter regeneration request has occurred. The filter regeneration request is “a request to regenerate the particulate collection filter” by burning the particulates collected by the particulate collection filter in the particulate collection filter. The filter regeneration request is generated, for example, when the integrated value of the intake air flow rate after the end of the previous filter regeneration control is equal to or greater than a threshold value.

When it is determined that the filter regeneration request has occurred, the filter regeneration means performs active air-fuel ratio control (filter regeneration control) for a predetermined period.
Active air-fuel ratio control
(1) The air-fuel ratio of the air-fuel mixture supplied to the engine is “a forced rich air-fuel ratio that is an air-fuel ratio richer than the stoichiometric air-fuel ratio” and “forced lean air-fuel that is an air-fuel ratio leaner than the stoichiometric air-fuel ratio. Set to “first air-fuel ratio” of any one of “fuel ratio”,
(2) The output of the downstream air-fuel ratio sensor is changed from a value corresponding to the “second air-fuel ratio” of “the other of the same forced rich air-fuel ratio and the same forced lean air-fuel ratio” to “the first air-fuel ratio” When the air / fuel ratio of the air-fuel mixture supplied to the engine is set to the same second air / fuel ratio,
(3) After that, when the output of the downstream air-fuel ratio sensor changes from “a value corresponding to the first air-fuel ratio” to “a value corresponding to the second air-fuel ratio”, the mixing supplied to the engine The air-fuel ratio of the air is set to “the same first air-fuel ratio”;
Air-fuel ratio control.

  According to this, the second three-way catalyst is disposed downstream of the particulate collection filter. Accordingly, when the air-fuel ratio of the engine is set to the forced lean air-fuel ratio, even if the oxygen flowing into the particulate collection filter leaks downstream without being completely consumed by the particulate collection filter, Oxygen is consumed or stored by the second three-way catalyst. Therefore, the time until the output of the downstream air-fuel ratio sensor changes to a value corresponding to the forced lean air-fuel ratio is delayed. As a result, since the “air-fuel ratio for which the engine air-fuel ratio is set to the forced lean air-fuel ratio” becomes longer, a sufficient amount of oxygen can flow into the particulate collection filter. Therefore, the particulate collection filter can be efficiently regenerated.

  Furthermore, the first three-way catalyst is disposed upstream of the particulate collection filter. Therefore, the first three-way catalyst is warmed up early and activated after the engine is cold started. As a result, the emission after the cold start of the engine can be improved.

  By the way, a wall flow type particulate collection filter may be employed as the particulate collection filter. The wall flow type particulate collection filter includes a wall portion that forms a plurality of passages extending along the flow direction of the exhaust gas flowing into the particulate collection filter. The wall portion is made of, for example, a porous thin plate, and is configured so that the exhaust gas can pass (permeate). Some of the plurality of passages are closed (sealed) at the most upstream end. Further, the remaining passages that are not closed at the most upstream end among the plurality of passages are closed (sealed) at the most downstream end. The exhaust gas flows into the passage that is not closed at the most upstream end, passes through the wall, and then flows out from the passage that is not closed at the most downstream end. Fine particles in the exhaust gas are collected when the exhaust gas passes through the wall.

  As described above, when a “wall flow type particulate collection filter” is employed as the particulate collection filter, the filter-containing catalyst device is provided between the first three-way catalyst and the particulate collection filter. It is preferable that the first space is provided and the second space is provided between the particulate collection filter and the second three-way catalyst.

  As a result, the exhaust gas flowing out from the first three-way catalyst once flows out into the first space, and then from the first space to the “passage that is not closed at the most upstream end among the plurality of passages of the particulate collection filter”. And flows efficiently. Further, the exhaust gas flowing out from the “passage that is not closed at the most downstream end among the plurality of passages of the particulate collection filter” once flows out into the second space, and then from the second space to the second three-way catalyst. Inflow efficiently. Accordingly, the exhaust gas can be efficiently and evenly (uniformly) flowed into the particulate collection filter and the second three-way catalyst.

  In the filter housing catalyst device used by the control device of the present invention, it is preferable that the palladium loading rate of the first three-way catalyst is larger than the palladium loading rate of the second three-way catalyst.

  Typical examples of noble metals supported on the catalyst to oxidize unburned substances (HC, CO, etc.) are platinum (Pt) and palladium (Pd). Platinum is easily deteriorated by sintering when a gas having an air-fuel ratio that is higher than lean and is leaner than the stoichiometric air-fuel ratio flows (hereinafter also referred to as “high temperature / lean gas atmosphere”). On the other hand, platinum is unlikely to deteriorate when a strong rich air-fuel ratio gas flows at a higher temperature and is richer than the stoichiometric air-fuel ratio and has a higher degree of richness than palladium.

  On the other hand, in the filter regeneration control (active air-fuel ratio control), the air-fuel ratio of the exhaust gas changes into a forced lean air-fuel ratio with a relatively small degree of lean and a forced rich air-fuel ratio with a relatively small degree of richness. Therefore, if the “first three-way catalyst that tends to become high temperature when high-temperature exhaust gas first flows” carries a large amount of platinum, when the engine air-fuel ratio is set to the forced lean air-fuel ratio, the first The three-way catalyst is easily deteriorated because it is exposed to a “high temperature / lean gas atmosphere”. Therefore, as described above, the first three-way catalyst is preferably configured to have a higher palladium loading rate than the second three-way catalyst. As a result, it is possible to suppress the progress of deterioration during the filter regeneration control of the first three-way catalyst.

  Furthermore, in the filter containing catalyst device used by the control device of the present invention, even if the activation degree (temperature) of the first three-way catalyst and the second three-way catalyst is the same, the second three-way catalyst is the first one. It is preferable that the maximum oxygen storage amount is larger than that of the three-way catalyst (the oxygen storage capacity is large).

  According to this, since the maximum oxygen storage amount of the first three-way catalyst is small, oxygen starts to be supplied to the particulate collection filter within a short time after the air-fuel ratio of the engine is switched to the forced lean air-fuel ratio. Therefore, the regeneration start time of the particulate collection filter is advanced. Further, since the maximum oxygen storage amount of the second three-way catalyst is large, the time from when the air-fuel ratio of the engine is switched to the forced lean air-fuel ratio until oxygen flows out downstream of the second three-way catalyst becomes longer.

  That is, the time from “when the air-fuel ratio of the engine is set to the forced lean air-fuel ratio” to “the time from when the downstream air-fuel ratio sensor changes from the value corresponding to the forced rich air-fuel ratio to the value corresponding to the forced lean air-fuel ratio” is become longer. Accordingly, since the time during which the air-fuel ratio of the engine is set to the forced lean air-fuel ratio becomes longer, a large amount of oxygen can be allowed to flow into the particulate collection filter. As a result, the particulate collection filter can be efficiently regenerated.

  In addition, in the filter-containing catalyst device used by the control device of the present invention, the second three-way catalyst has a zone coat three formed such that the upstream portion has a higher palladium loading ratio than the downstream portion. It is preferable that it is a raw catalyst.

  As described above, palladium is less susceptible to deterioration than platinum in a “high temperature / lean gas atmosphere”. In addition, in the second three-way catalyst, the upstream portion has a higher temperature than the downstream portion. Further, as described above, in the filter regeneration control, the air-fuel ratio of the exhaust gas changes to a forced lean air-fuel ratio with a relatively small degree of lean and a forced rich air-fuel ratio with a relatively small degree of richness. Therefore, if the upstream part of the second three-way catalyst, which tends to be high in temperature, carries a large amount of platinum, when the engine air-fuel ratio is set to the forced lean air-fuel ratio, the upstream part may deteriorate. Increases nature. Therefore, as in the above configuration, a zone coat catalyst is employed as the second three-way catalyst, and the palladium loading rate of the upstream portion of the second three-way catalyst is made larger than the palladium loading rate of the downstream portion. . Thereby, the progress of the deterioration of the second three-way catalyst (deterioration of the upstream portion) during the filter regeneration control can be suppressed.

  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 schematic configuration of a system in which a control device according to the first embodiment (hereinafter also referred to as “first control device”) is applied to an internal combustion engine 10. The engine 10 is a spark ignition type, multi-cylinder (4 cylinders in this example), gasoline fuel engine. FIG. 1 shows only a cross section of a specific cylinder, but the other cylinders have the same configuration.

  The engine 10 supplies a gasoline mixture to the cylinder block portion 20 including a cylinder block, a cylinder block lower case, an oil pan, etc., a cylinder head portion 30 fixed on the cylinder block portion 20, and the cylinder block portion 20. And an exhaust system 50 for releasing the exhaust gas from the cylinder block unit 20 to the outside.

  The cylinder block unit 20 includes a cylinder 21, a piston 22, a connecting rod 23, and a crankshaft 24. The piston 22 reciprocates in the cylinder 21, and the reciprocating motion of the piston 22 is transmitted to the crankshaft 24 through the connecting rod 23, whereby the crankshaft 24 rotates. The 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 that generates a high voltage to be applied to the spark plug 37 and a fuel injection valve 39 for injecting fuel into the intake port 31 are provided. The fuel injection valve 39 serving as the fuel injection means is configured to inject the 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 filter-accommodating catalyst device CwF including a first three-way catalyst 53, a particulate collection filter 54, and a second three-way catalyst 55; The original catalyst 56 is provided.

  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, the “path for allowing the exhaust gas to pass” 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.

  As described above, the filter-containing catalyst device CwF includes the first three-way catalyst 53, the particulate collection filter 54, and the second three-way catalyst 55. The filter-accommodating catalyst device CwF accommodates these in one casing (housing, case) C. The filter containing catalyst device CwF is disposed in the exhaust passage (exhaust pipe 52). That is, the filter containing catalyst device CwF is disposed on the downstream side of the collecting portion 51b. When the filter containing catalyst device CwF is disposed in the exhaust passage, the first three-way catalyst 53 is located on the most upstream side, the particulate collection filter 54 is located on the downstream side of the first three-way catalyst 53, and the second The three-way catalyst 55 is positioned downstream of the particulate collection filter 54.

The first three-way catalyst 53 supports “noble metals (palladium Pd and platinum Pt, rhodium Rd) as catalyst materials” and “ceria (CeO ₂ )” on a support made of ceramic. With these substances, the first three-way catalyst 53 has a catalytic function and an oxygen storage / release function (also simply referred to as “oxygen storage function” or “O 2 storage function”). The first three-way catalyst 53 is also referred to as a front start catalytic converter (FrSC).

  The particulate collection filter 54 is a known particulate filter made of a porous ceramic (for example, cordierite). The particulate collection filter 54 collects particulates discharged from the engine 10. The particulate collection filter 54 is also referred to as a particulate matter filter (PMF) (see, for example, JP-A-2005-83346).

  Similar to the first three-way catalyst 53, the second three-way catalyst 55 is a three-way catalyst having a catalytic function and an oxygen storage function, in which a noble metal (catalyst substance) and ceria are supported on a ceramic support. The second three-way catalyst 55 is also referred to as a rear start catalytic converter (RrSC).

  The third three-way catalyst 56 is disposed (intervened) in the exhaust passage (exhaust pipe 52) at a position downstream of the filter containing catalyst device CwF. Similar to the first three-way catalyst 53, the third three-way catalyst 56 is a three-way catalyst having a catalytic function and an oxygen storage function in which a noble metal (catalyst substance) and ceria are supported on a ceramic support. Since the third three-way catalyst 56 is disposed below the floor of the vehicle on which the engine 10 is mounted, it is also called an underfloor catalytic converter (UFC).

  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” (predetermined value including the theoretical air-fuel ratio). In the air / fuel ratio range), unburned substances (HC, CO, etc.) are oxidized and nitrogen oxides (NOx) are reduced. Thereby, the three-way catalyst has a characteristic (catalytic function) for purifying these harmful components with high efficiency.

  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 becomes leaner than the stoichiometric air-fuel ratio and the gas flowing into the three-way catalyst contains excess oxygen and NOx, the catalyst will deprive the oxygen (reducing NOx). ), Store the deprived oxygen. Furthermore, when the air-fuel ratio of the engine is 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 Provides the stored oxygen to these unburned materials and oxidizes these components.

  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, and a downstream air-fuel ratio. A sensor 67 and an accelerator opening sensor 68 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.
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 disposed between the exhaust manifold 51 and the exhaust gas at a position between the collecting portion 51b of the exhaust manifold 51 and the first three-way catalyst 53 (accordingly, the filter housing catalyst device CwF). It is disposed in any one of the pipes 52 (that is, the exhaust passage). The upstream air-fuel ratio sensor 66 outputs a value (current value, voltage value, etc.) corresponding to the air-fuel ratio of the exhaust gas (detected gas) flowing through the portion in the exhaust passage where the upstream air-fuel ratio sensor 66 is disposed. It is like that.

  More specifically, the upstream air-fuel ratio sensor 66 is a limiting current type oxygen concentration sensor. 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 gas to be detected (accordingly, the air-fuel ratio of the air-fuel mixture supplied to the engine). 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.

  An electric control device 70 to be described later stores an air-fuel ratio conversion table (map) Mapabyfs, and detects the air-fuel ratio (obtains the detected air-fuel ratio abyfs) by applying the actual output value Vabyfs to the table. It has become.

  As shown in FIGS. 1 and 2, the downstream air-fuel ratio sensor 67 is connected to the exhaust pipe 52 at a position between the second three-way catalyst 55 (accordingly, the filter housing catalyst device CwF) and the third three-way catalyst 56. (Exhaust passage). The downstream air-fuel ratio sensor 67 outputs an output corresponding to the 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 downstream air-fuel ratio sensor 67 is disposed. The value Voxs is output.

  More specifically, the downstream air-fuel ratio sensor 67 is an electromotive force type (concentration cell type) oxygen concentration sensor. Therefore, the downstream air-fuel ratio sensor 67 is also referred to as an oxygen concentration sensor 67. The downstream air-fuel ratio sensor 67 outputs an output value Voxs that is a voltage that changes suddenly in the vicinity of the theoretical air-fuel ratio. That is, the output value Voxs is approximately 0.1 (V) when the air-fuel ratio of the detected gas is larger than the stoichiometric air-fuel ratio and is on the lean side, and the air-fuel ratio of the detected gas is greater than the stoichiometric air-fuel ratio. When the air-fuel ratio is on the rich side, it is approximately 0.9 (V), and when the air-fuel ratio is the stoichiometric air-fuel ratio, it is 0.5 (V).

  Further, the output value Voxs is the air-fuel ratio of the gas to be detected when the air-fuel ratio of the gas to be detected is an air-fuel ratio in the vicinity of the theoretical air-fuel ratio (the air-fuel ratio substantially corresponding to the window W of the three-way catalyst described above). Decreases rapidly as it changes from rich to lean (changes from approximately 0.9 (V) to approximately 0.1 (V)). The output value Voxs rapidly increases as the air-fuel ratio of the gas to be detected changes from lean to rich when the air-fuel ratio of the gas to be detected is close to the stoichiometric air-fuel ratio (from approximately 0.1 (V)). It changes toward about 0.9 (V).) When the downstream air-fuel ratio afdown of the second three-way catalyst 55 obtained based on the output value Voxs of the downstream air-fuel ratio sensor 67 is f, a function representing the relationship between the output value Voxs and the downstream air-fuel ratio afdown is assumed. , Afdown = f (Voxs).

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

  Referring to FIG. 1 again, the accelerator opening sensor 68 detects the operation amount of the accelerator pedal AP operated by the driver, and outputs a signal representing the operation amount Accp of the accelerator pedal AP.

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

  The interface 75 is connected to the sensors 61 to 68 and supplies signals from the sensors 61 to 68 to the CPU 71. Further, the interface 75 sends a drive signal (instruction signal) to the actuator 33a of the variable intake timing device 33, the igniter 38 of each cylinder, the fuel injection valve 39 of each cylinder, the throttle valve actuator 44a, etc. in accordance with the instruction of the CPU 71. It is supposed to be.

Next, an outline of air-fuel ratio control 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 (feed forward fuel injection amount) Fbase is determined based on the upstream target air-fuel ratio abyfr and the cylinder intake air amount Mc. The basic fuel injection amount Fbase is corrected by the main feedback correction value KFmain. The main feedback correction value KFmain is a feedback amount calculated so that “the upstream air-fuel ratio abyfs acquired based on the output value Vabyfs” matches the “upstream target air-fuel ratio abyfr”.

(Normal air-fuel ratio feedback control)
The upstream target air-fuel ratio abyfr is equal to the stoichiometric air-fuel ratio stoich in the “normal air-fuel ratio feedback control” executed when the request for regenerating the particulate collection filter 54 is not generated (when the filter regeneration request is not generated). A certain first upstream target air-fuel ratio is set.

(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, the first control device executes “filter regeneration control (active air-fuel ratio control)” when a request to regenerate the particulate collection filter 54 is generated (when the filter regeneration request is generated). In this filter regeneration control, the upstream target air-fuel ratio abyfr is alternately changed at a predetermined timing to either the forced lean air-fuel ratio afenL or the forced rich air-fuel ratio afenR.

  More specifically, as shown in FIG. 3, when “the upstream target air-fuel ratio abyfr is set to the forced lean air-fuel ratio afenL” during the filter regeneration control, the upstream target air-fuel ratio abyfr is set to the downstream side. Forced rich air-fuel ratio when the output value Voxs of the air-fuel ratio sensor 67 changes from a value representing an air-fuel ratio richer than the stoichiometric air-fuel ratio to a value representing an air-fuel ratio leaner than the stoichiometric air-fuel ratio (at the time of lean reversal) It is changed to afenR (see time t2 and time t4 in FIG. 3). Further, when “the upstream target air-fuel ratio abyfr is set to the forced rich air-fuel ratio afenR” during the filter regeneration control, the output value Voxs of the downstream air-fuel ratio sensor 67 is equal to the stoichiometric air-fuel ratio. 3 is changed to the forced lean air-fuel ratio afenL at the time of changing from a value representing a leaner air-fuel ratio to a value representing an air-fuel ratio richer than the stoichiometric air-fuel ratio (during rich inversion) (time t3 in FIG. 3 is changed). reference.).

The forced lean air-fuel ratio afenL is outside the predetermined air-fuel ratio range (the three-way catalyst window W) including the stoichiometric air-fuel ratio, and is an air-fuel ratio leaner than the stoichiometric air-fuel ratio by an air-fuel ratio ΔafL (ΔafL> 0). is there. 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 (three-way catalyst 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). is there. 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.

<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 Voxs of the downstream air-fuel ratio sensor 67.

  In this example, the sub feedback control condition is satisfied when the main feedback control is being executed and the downstream air-fuel ratio sensor 67 is activated, and is not satisfied in other cases. The sub-feedback control is executed both in the normal air-fuel ratio feedback control and the filter regeneration control. Note that other conditions may be added to the sub-feedback control conditions.

  In the sub-feedback control, the first control device is supplied to the engine so that the output value Voxs of the downstream air-fuel ratio sensor 67 matches the downstream target value Voxsref that is a value corresponding to the downstream target air-fuel ratio. The air-fuel ratio of the mixture is feedback controlled.

  In other words, the sub-feedback control is performed so that the downstream air-fuel ratio afdown represented by the output value Voxs of the downstream air-fuel ratio sensor 67 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 supplied to the engine. The sub-feedback control is based on PI (proportional / integral) control or PID (proportional / integral) based on “the deviation (output deviation amount DVoxs) between the output value Voxs of the downstream air-fuel ratio sensor 67 and the downstream target value Voxsref”. , Differentiation) control to make it coincide with “0”.

  The downstream target value Voxsref is set to a theoretical air-fuel ratio equivalent value (Voxsst = 0.5V). As a result, the average (center, median) of the air-fuel ratio of the air-fuel mixture supplied to the engine 10 (more precisely, 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. .

<Operation>
Next, the operation of the first control device will be described. The CPU 71 of the first control device performs the above-described various controls by repeating the procedure shown in the schematic flowchart of FIG. 4 every elapse of a predetermined time. In the following description, it is assumed that the upstream air-fuel ratio sensor 66 and the downstream air-fuel ratio sensor 67 are all activated.

  The CPU 71 starts processing from step 400 at a predetermined timing, proceeds to step 410, 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. 5).

  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 410 and proceeds to step 430 to execute the “normal air-fuel ratio feedback control” described above.

  More specifically, in step 430, the CPU 71 executes both main feedback control and sub feedback control. In this case, the 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 (a value corresponding to the downstream target air-fuel ratio) of the sub-feedback control is a theory corresponding to the stoichiometric air-fuel ratio. The air-fuel ratio equivalent value Voxsst is set.

  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 is feedback control in which the output value Voxs of the 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 495 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, feedback control is performed based on the upstream air-fuel ratio abyfs and the downstream air-fuel ratio afdown so that the air-fuel ratio of the engine becomes the stoichiometric air-fuel ratio (the air-fuel ratio within a predetermined air-fuel ratio range including the stoichiometric air-fuel ratio).

  By the way, the CPU 71 executes the “filter regeneration request determination routine” shown by the flowchart in FIG. 5 every elapse of a predetermined time. Accordingly, the CPU 71 starts the process from step 500 at a predetermined timing, proceeds to step 510, 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 time the predetermined time Δts elapses. To do. 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 control (filter regeneration control) is completed (and when the fuel cut control is performed). It has become.

  At this time, if the integrated value SGa is smaller than the threshold value SGath, the CPU 71 makes a “No” determination at step 510 to directly proceed to step 530, where the value of the filter regeneration request flag XPM is finally changed from “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 the threshold value SGath (that is, when filter regeneration control is started) (FIG. 5). (See step 520).

  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”. Accordingly, the CPU 71 makes a “No” determination at step 530 to directly proceed to step 595 to end the present routine tentatively. As a result, the value of the filter regeneration request flag XPM is maintained at “0”, so that the normal air-fuel ratio feedback control is continued and the filter regeneration control is not started (see step 410 and step 430 in FIG. 4).

  On the other hand, if the integrated value SGa is greater than or equal to the threshold value SGath during the process of step 510 in FIG. 5, the CPU 71 determines “Yes” in step 510 and proceeds to step 520 to 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 530 to step 595 to end the present routine tentatively. At this time, when the CPU 71 executes the process of step 410 in FIG. 4, the CPU 71 determines “Yes” in step 410 and proceeds to step 420 to execute the “filter regeneration control” described above.

  More specifically, the CPU 71 executes main feedback control in step 420. In this case, as shown in FIG. 3, the upstream target air-fuel ratio abyfr of the main feedback control is set to an air-fuel ratio that alternately repeats the forced lean air-fuel ratio afenL and the forced rich air-fuel ratio afenR over time.

  That is, when the output value Voxs of the downstream air-fuel ratio sensor 67 changes from a value smaller than the stoichiometric air-fuel ratio equivalent value Voxsst to a larger value as shown at time t1 in FIG. The fuel ratio abyfr is set to the forced lean air-fuel ratio afenL. This timing is the time when the air-fuel ratio afdown represented by the output value Voxs of the downstream air-fuel ratio sensor 67 is reversed from the lean air-fuel ratio to the rich air-fuel ratio from the stoichiometric air-fuel ratio. That is, this timing is also referred to as “when the output value Voxs is richly inverted” in which the output value Voxs changes from a value corresponding to the forced lean air-fuel ratio afenL to a value corresponding to the forced rich air-fuel ratio afenR.

  Thereafter, when the output value Voxs of the downstream air-fuel ratio sensor 67 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 fuel ratio abyfr is set to the forced rich air-fuel ratio afenR. This timing is the time when the air-fuel ratio afdown represented by the output value Voxs of the downstream air-fuel ratio sensor 67 is reversed from the air-fuel ratio richer than the stoichiometric air-fuel ratio to the lean air-fuel ratio. That is, this timing is also referred to as “at the time of lean inversion of the output value Voxs” in which the output value Voxs changes from a value corresponding to the forced rich air-fuel ratio afenR to a value corresponding to the forced lean air-fuel ratio afenL.

  Further, as shown at time t3 in FIG. 3, 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 Voxs”, and at time t4 in FIG. As described above, 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 reversal of the output value Voxs”. Thereafter, the CPU 71 repeats such an operation.

  Then, the CPU 71 executes main feedback control for the upstream target air-fuel ratio abyfr set in this way. Further, the CPU 71 executes 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. As a result, the “filter regeneration 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.

  When this state continues, regeneration of the particulate collection filter 54 proceeds. When the CPU 71 proceeds to step 530 in FIG. 5 immediately after a predetermined time (filter regeneration control execution time) has elapsed after the value of the filter regeneration request flag XPM has changed from “0” to “1”, the CPU 71 In step 530, “Yes” is determined. Then, the CPU 71 proceeds to step 540 and sets the value of the filter regeneration request flag XPM to “0”. Thereafter, the CPU 71 proceeds to step 595 to end the present routine tentatively.

  As a result, the CPU 71 determines “No” in step 410 in FIG. 4 and proceeds to step 430. Therefore, the filter regeneration control is stopped, and the normal air-fuel ratio feedback control is resumed.

(Details of operation)
FIG. 6 shows the details of the fuel injection control routine executed by the CPU 71. Hereinafter, the processing by this routine will be briefly described.

  The CPU 71 repeatedly executes the routine shown in FIG. 6 every time the crank angle of each cylinder reaches a predetermined crank angle (for example, BTDC 90 ° CA) before the intake top dead center of each cylinder. . Therefore, when the crank angle of an arbitrary cylinder reaches the predetermined crank angle, the CPU 71 starts the process from step 600 and proceeds to step 610, based on the engine speed NE, the intake air amount Ga, and the table MapMc (NE, Ga). Then, “this in-cylinder intake air amount Mc to be sucked into a cylinder (hereinafter, also referred to as“ fuel injection cylinder ”) that reaches the intake stroke” is estimated and determined.

  Next, the CPU 71 proceeds to step 620 to determine whether or not the value of the filter regeneration request flag XPM is “0”. If the value of the filter regeneration request flag XPM is “0”, the CPU 71 sequentially performs the processing from step 630 to step 680 described below, proceeds to step 695, and once ends this routine.

Step 630: The CPU 71 sets the stoichiometric air-fuel ratio stoich to the upstream target air-fuel ratio abyfr.
Step 640: The CPU 71 calculates the basic fuel injection amount Fbase by dividing the in-cylinder intake air amount Mc by the upstream target air-fuel ratio abyfr.
Step 650: The CPU 71 reads a main feedback correction value KFmain separately obtained by a routine not shown.
Step 660: The CPU 71 reads a sub feedback correction value Fisub separately obtained by a routine not shown.
Step 670: The CPU 71 obtains the final fuel injection amount Fi according to the following equation (1).
Fi = Fbase · KFmain + Fisub (1)
Step 680: The CPU 71 issues an injection instruction to the fuel injection valve 39 so that the fuel of the final fuel injection amount Fi is injected from the fuel injection valve 39 for the fuel injection cylinder.

  The calculation method of the main feedback correction value KFmain read in step 650 is well known as described in, for example, JP-A-2005-273524.

In brief, the CPU 71 detects the current detected air-fuel ratio abyfs detected by the upstream air-fuel ratio sensor 66 based on the output value Vabyfs of the upstream air-fuel ratio sensor 66 and the table Mapabyfs stored in advance. Ask for.
The CPU 71 obtains the air-fuel ratio deviation Daf by subtracting the detected air-fuel ratio abyfs from the upstream target air-fuel ratio abyfr.
The CPU 71 performs a high-pass filter process on the air-fuel ratio deviation Daf to obtain a main feedback control deviation DafHi. As a result of the high-pass filter processing, the main feedback control deviation DafHi becomes a value representing air-fuel ratio fluctuation that does not appear downstream of the filter-accommodating catalyst device CwF.
The CPU 71 obtains the main feedback correction value KFmain by multiplying the main feedback control deviation DafHi by the proportional gain GpHi.

  Furthermore, the calculation method of the sub feedback correction value Fisub read in step 660 is also well known as described in, for example, JP-A-2005-273524.

  In brief, the CPU 71 determines that the current downstream output value Voxs of the downstream air-fuel ratio sensor from the “downstream target value Voxsref set to a value corresponding to the theoretical air-fuel ratio (for example, 0.5 (V))”. The output deviation amount DVoxs (DVoxs = Voxsref−Voxs) is obtained. The downstream target value Voxsref is slightly richer than the stoichiometric air-fuel ratio, and is a value Vrich (for example, 0.55 (for example, 0.55 (equivalent to the rich air-fuel ratio AFR) within the window W described above). V)) may be set.

The CPU 71 obtains the output deviation amount DVoxslow after passing through the low-pass filter by performing a low-pass filter process on the output deviation amount DVoxs.
The CPU 71 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 (2) to obtain a sub feedback correction value Fisub.
Fisub = Kp · DVoxslow + Ki · SDVoxslow + Kd · DDVoxslow… (2)

  In the above equation (2), 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.

  On the other hand, if the value of the filter regeneration request flag XPM is “1” at the time when the process of step 620 in FIG. 6 is executed, the CPU 71 determines “No” in step 620. Then, the CPU 71 proceeds to step 690 and sets the upstream target air-fuel ratio abyfr to “forced lean air-fuel ratio afenL” or “forced rich air-fuel ratio afenR” as shown in FIG. 3 (see step 420 in FIG. 4). ). Thereafter, the CPU 71 executes the processing of step 640 to step 680.

  In this case, when the output value Voxs of the downstream air-fuel ratio sensor 67 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 air-fuel ratio abyfr is set to the forced lean air-fuel ratio afenL. As a result, excess oxygen flows into the first three-way catalyst 53 of the filter containing catalyst device CwF, and then oxygen flows out from the first three-way catalyst 53. This oxygen flows into the particulate collection filter 54 of the filter containing catalyst device CwF. Thereby, the particulates collected by the particulate collection filter 54 are burned, and the particulate collection filter 54 is regenerated.

  At this time, even if oxygen leaks from the particulate collection filter 54 before all of the particulates are combusted, the oxygen is occluded or consumed by the second three-way catalyst 55 of the filter containing catalyst device CwF. Therefore, it does not reach the downstream air-fuel ratio sensor 67. Accordingly, since the time point when the output value Voxs of the downstream air-fuel ratio sensor 67 changes from a value larger than the theoretical air-fuel ratio equivalent value Voxsst to a smaller value (when the output value Voxs is lean-reversed) is delayed, the upstream target air-fuel ratio abyfr Is set to the forced lean air-fuel ratio afenL. As a result, a large amount of oxygen can be made to flow into the particulate collection filter 54 (oxygen can be made to flow continuously), so that the particulate collection filter 54 can be efficiently regenerated.

  As described above, when it is determined that the filter regeneration request has occurred (when XPM = 1 at step 520 in FIG. 5), the first control device “the air-fuel mixture supplied to the engine 10”. Is set to “first air-fuel ratio” of “one of forced rich air-fuel ratio afenR and forced lean air-fuel ratio afenL”, and output Voxs of downstream air-fuel ratio sensor 67 is set to “forced rich air-fuel ratio”. The air-fuel mixture supplied to the engine 10 when the value corresponding to the “second air-fuel ratio” of the other one of the fuel ratio afenR and the forced lean air-fuel ratio afenL changes from the value corresponding to the “first air-fuel ratio”. After that, the output Voxs of the downstream air-fuel ratio sensor 67 has changed from a value corresponding to the “first air-fuel ratio” to a value corresponding to the “second air-fuel ratio”. The air-fuel ratio of the air-fuel mixture supplied to the engine 10 is set to the “first air-fuel ratio”. “Filter regeneration means” for executing the active air-fuel ratio control for a predetermined period (see step 420 in FIG. 4, step 530 and step 540 in FIG. 5).

  Further, the filter-containing catalyst device CwF includes a first three-way catalyst 53, a particulate collection filter 54, and a second three-way catalyst 55 from upstream to downstream. That is, the second three-way catalyst 55 is disposed downstream of the particulate collection filter 54. Therefore, when the air-fuel ratio of the engine is set to the forced lean air-fuel ratio afenL, it is assumed that oxygen flowing into the particulate collection filter 54 leaks downstream without being completely consumed by the particulate collection filter 54. However, the oxygen is consumed or stored by the second three-way catalyst 55. Accordingly, the time until the output Voxs of the downstream air-fuel ratio sensor 67 changes to a value corresponding to the forced lean air-fuel ratio afenL is delayed. As a result, the time during which the air-fuel ratio of the engine is set to the forced lean air-fuel ratio afenL becomes longer, so that a sufficient amount of oxygen can flow into the particulate collection filter 54. Therefore, the particulate collection filter 54 can be efficiently regenerated.

  Further, the first three-way catalyst 53 is disposed upstream of the particulate collection filter 54. Accordingly, the first three-way catalyst 53 is warmed up and activated early after the cold start of the engine. As a result, the emission after the cold start of the engine can be improved.

(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 different from the filter storage catalyst device CwF of the first control device in the structure of the filter storage catalyst device. Hereinafter, the filter housing catalyst device CwF employed by the second control device is referred to as a filter housing catalyst device CwF2.

  As shown in FIG. 7, the filter housing catalyst device CwF2 includes a first three-way catalyst 53, a particulate collection filter 54a, and a second three-way catalyst 55.

  The first three-way catalyst 53 and the second three-way catalyst 55 are the same as the first three-way catalyst 53 and the second three-way catalyst 55 provided in the filter housing catalyst device CwF of the first control device, respectively.

  The particulate collection filter 54a is a known “wall flow type particulate collection filter”. FIG. 8 is a schematic cross-sectional view of the particulate collection filter 54a. FIG. 9 is a schematic front view of the particulate collection filter 54a as viewed from the downstream side of the particulate collection filter 54a. As shown in FIGS. 8 and 9, the particulate collection filter 54a includes a plurality of wall portions 54a1, a plurality of upstream side closing portions 54a2, a plurality of downstream side closing portions 54a3, and an outer frame body 54a4. Contains.

  The plurality of wall portions 54a1 form a plurality of “first passages P1 and second passages P2” extending along the direction of the flow of the exhaust gas flowing into the particulate collection filter 54a. The wall 54a1 is made of a porous thin plate (for example, a porous ceramic such as cordierite) and is configured so that exhaust gas can pass through.

Each cross-sectional shape of "the 1st channel | path P1 and the 2nd channel | path P2" is substantially square. The first passage P1 and the second passage P2 are arranged so as to be adjacent to each other while sharing one side of a square in a sectional view.
The upstream closing portion 54a2 is disposed so as to close the second passage P2 at the upstream end portion (most upstream end) of the second passage P2.
The downstream closing portion 54a3 is disposed so as to close the first passage P1 at the downstream end (most downstream end) of the first passage P2.

  Thus, the particulate collection filter 54a forms a plurality of passages (P1 and P2) extending along the flow direction of the exhaust gas flowing into the particulate collection filter 54a, and the “wall portion 54a1” through which the exhaust gas can pass. And some (about half in this example) of the plurality of passages (P1 and P2) are closed at the most upstream end and closed at the most upstream end of the plurality of passages (P2). The remaining unpassed passage is closed at the most downstream end.

  Exhaust gas flows into the first passage P1 through the particulate collection filter 54a configured as described above. Then, as shown by the arrow in FIG. 8, the inflowing exhaust gas passes through the wall 54a1 and flows into the second passage P2, and then is discharged from the second passage P2 to the outside. The fine particles in the exhaust gas are collected at the wall 54a1 when the exhaust gas flows from the first passage P1 through the wall 54a1 into the second passage P2.

  Referring to FIG. 7 again, in the filter containing catalyst device CwF2, a space (gap, first space) SP1 is formed between the first three-way catalyst 53 and the particulate collection filter 54a. Further, a space (gap, second space) SP2 is also formed between the particulate collection filter 54a and the second three-way catalyst 55.

  Accordingly, the exhaust gas flowing out from the first three-way catalyst 53 once flows out into the first space SP1, and then from the first space SP1, “the first non-closed end of the plurality of passages of the particulate collection filter is closed. It flows into 1 passage P1 ". Therefore, the exhaust gas can be efficiently and evenly (uniformly) flowed into the particulate collection filter 54a. Further, the exhaust gas flowing out from the “second passage P2 that is not closed at the most downstream end among the plurality of passages of the particulate collection filter 54a” once flows out into the second space SP2, and then from the second space SP2 into the second space SP2. 2 It flows into the three-way catalyst 55. Therefore, the exhaust gas can be efficiently and evenly (uniformly) flowed into the second three-way catalyst 55.

(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. In the third control device, the first three-way catalyst and the second three-way catalyst of the filter containing catalyst device are different from those of the filter containing catalyst device CwF2 of the second control device. Hereinafter, the filter housing catalyst device employed by the third control device is referred to as a filter housing catalyst device CwF3.

  As shown in FIG. 10, the filter-containing catalyst device CwF3 includes a first three-way catalyst 53a, a particulate collection filter 54a, and a second three-way catalyst 55a. The particulate collection filter 54a is the same filter as the wall flow type particulate collection filter 54a provided in the filter-containing catalyst device CwF2. The first three-way catalyst 53a and the second three-way catalyst 55a are three-way catalysts similar to the “first three-way catalyst 53 and the second three-way catalyst 55” included in the filter housing catalyst devices CwF and CwF2.

  However, the first three-way catalyst 53a has a higher loading ratio of “palladium (Pd)” than the second three-way catalyst 55a.

  Typical examples of noble metals supported on the catalyst to oxidize unburned substances (HC, CO, etc.) are platinum (Pt) and palladium (Pd). Platinum is easily deteriorated by sintering when a gas having an air-fuel ratio that is higher in temperature than that of palladium and leaner than the stoichiometric air-fuel ratio flows (also referred to as “high temperature / lean gas atmosphere”). On the other hand, platinum is unlikely to deteriorate when a strong rich air-fuel ratio gas flows at a higher temperature and is richer than the stoichiometric air-fuel ratio and has a higher degree of richness than palladium.

  On the other hand, in the above-described filter regeneration control (active air-fuel ratio control), the air-fuel ratio of the exhaust gas is “forced lean air-fuel ratio afenL with a relatively small degree of lean” and “forced rich air-fuel ratio afenR with a relatively small degree of richness”. And change. Therefore, if the first three-way catalyst 53a, which is likely to become high temperature by being arranged upstream, carries a large amount of platinum, the first three-way catalyst 53a is easily exposed to a "high temperature / lean gas atmosphere" and deteriorates easily. . Therefore, as described above, the first three-way catalyst 53a is configured to have a higher palladium loading rate than the second three-way catalyst 55a. Further, the first three-way catalyst 53a is configured to have a lower platinum loading rate than the second three-way catalyst 55a. As a result, the third control device can suppress the progress of deterioration of the first three-way catalyst 53a during the filter regeneration control.

(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. In the fourth control device, the first three-way catalyst and the second three-way catalyst of the filter containing catalyst device are different from those of the filter containing catalyst device CwF2 of the second control device. Hereinafter, the filter housing catalyst device employed by the fourth control device is referred to as a filter housing catalyst device CwF4.

  As shown in FIG. 11, the filter-accommodating catalyst device CwF4 includes a first three-way catalyst 53b, a particulate collection filter 54a, and a second three-way catalyst 55b. The particulate collection filter 54a is the same filter as the wall flow type particulate collection filter 54a provided in the filter-containing catalyst device CwF2. The first three-way catalyst 53b and the second three-way catalyst 55b are the same three-way catalysts as the “first three-way catalyst 53 and the second three-way catalyst 55” provided in the filter housing catalyst devices CwF and CwF2.

However, the second three-way catalyst 55b is configured such that its maximum oxygen storage amount is larger than the maximum oxygen storage amount of the first three-way catalyst 53b. That is, if the temperature of the first three-way catalyst 53b and the temperature of the second three-way catalyst 55b are the same, the second three-way catalyst 55b stores more oxygen than the first three-way catalyst 53b. It is configured to be able to. More specifically, the supported amount of ceria (CeO ₂ ) that is the oxygen storage material of the second three-way catalyst 55b is larger than the supported amount of ceria of the first three-way catalyst 53b.

  In this case, the “ceria loading amount per unit catalyst volume (ceria loading rate)” of the second three-way catalyst 55b is larger than the ceria loading rate of the first three-way catalyst 53b and the capacity of the second three-way catalyst 55b. Is more than the capacity of the first three-way catalyst 53b. However, the ceria loading ratio of the second three-way catalyst 55b is equal to or lower than the loading ratio of the first three-way catalyst 53b, but the capacity of the second three-way catalyst 55b is larger than the capacity of the first three-way catalyst 53b. As a result, the amount of ceria supported by the second three-way catalyst 55b may be larger than the amount of ceria supported by the first three-way catalyst 53b. That is, the total supported amount of ceria (that is, the maximum oxygen storage amount and the oxygen storage capacity) determined by the ceria support rate and the capacity of the three-way catalyst is larger than that of the first three-way catalyst 53b in the second three-way catalyst 55b. Should also be large.

  According to this, since the maximum oxygen storage amount of the first three-way catalyst 53b is small, oxygen starts to be supplied to the particulate collection filter 54a within a short time after the air-fuel ratio of the engine is switched to the forced lean air-fuel ratio afenL. . Therefore, the reproduction disclosure time of the particulate collection filter 54a is advanced.

  Furthermore, since the maximum oxygen storage amount of the second three-way catalyst 55b is large, the time from when the air-fuel ratio of the engine is switched to the forced lean air-fuel ratio afenL becomes longer until oxygen flows out downstream of the second three-way catalyst 55b. . That is, from “when the air-fuel ratio of the engine is set to the forced lean air-fuel ratio afenL” to “from the value corresponding to the forced rich air-fuel ratio afenR to the value corresponding to the forced lean air-fuel ratio afenL” "Time" becomes longer. Accordingly, since the time during which the air-fuel ratio of the engine is set to the forced lean air-fuel ratio afenL becomes longer, a large amount of oxygen can be caused to flow into the particulate collection filter 54a. As a result, the particulate collection filter 54a can be efficiently regenerated.

(Fifth embodiment)
Next, a control device for an internal combustion engine according to a fifth embodiment of the present invention (hereinafter also referred to as “fifth control device”) will be described. In the fifth control device, the second three-way catalyst of the filter containing catalyst device is different from the second three way catalyst 55a of the filter containing catalyst device CwF3 of the third control device. Hereinafter, the filter housing catalyst device employed by the fifth control device is referred to as a filter housing catalyst device CwF5.

  As shown in FIG. 12, the filter-accommodating catalyst device CwF5 includes a first three-way catalyst 53a, a particulate collection filter 54a, and a second three-way catalyst 55c. The particulate collection filter 54a is the same filter as the wall flow type particulate collection filter 54a included in the filter-containing catalyst device CwF3. The first three-way catalyst 53a and the second three-way catalyst 55c are the same three-way catalysts as the “first three-way catalyst 53a and the second three-way catalyst 55a” provided in the filter housing catalyst device CwF3.

  However, the second three-way catalyst 55c is a zone coat three-way catalyst in which the loading ratio of each noble metal can be set for each region (zone). The second three-way catalyst 55c is formed such that the upstream portion 55c1 has a higher palladium loading rate (and a lower platinum loading rate) than the downstream portion 55c2. The downstream portion 55c2 is a portion located downstream of the upstream portion 55c1 in the axial direction (exhaust gas passage direction) of the second three-way catalyst 55c.

  As described above, palladium is less susceptible to deterioration than platinum in a “high temperature / lean gas atmosphere”. In the second three-way catalyst 55c, the upstream portion 55c1 has a higher temperature than the downstream portion 55c2. Further, as described above, in the filter regeneration control, the air-fuel ratio of the exhaust gas changes to the forced lean air-fuel ratio afenL that has a relatively low degree of lean and the forced rich air-fuel ratio afenR that has a relatively low degree of richness. Accordingly, if the portion 55c1 on the upstream side of the second three-way catalyst 55c, which is likely to become high temperature, carries a large amount of platinum, the possibility that the portion deteriorates increases. However, in the second three-way catalyst 55c of the fifth control device, the upstream portion 55c1 has a higher palladium loading rate and a lower platinum loading rate than the downstream portion 55c2, and therefore the second three-way catalyst 55c during the filter regeneration control. The progress of the deterioration of the three-way catalyst 55c can be suppressed.

  As described above, each embodiment of the control apparatus for an internal combustion engine according to the present invention includes the second three-way catalyst downstream of the particulate collection filter, and the air-fuel ratio forced rich air-fuel ratio afenR in the filter regeneration control. Is switched based on the output value Voxs of the downstream air-fuel ratio sensor 67 disposed downstream of the second three-way catalyst. Accordingly, since the time during which the air-fuel ratio of the engine is set to the forced lean air-fuel ratio afenL during the filter regeneration control can be lengthened, the particulate collection filter can be efficiently regenerated.

  When it is determined that a filter regeneration request has not occurred (XPM = 0), each of the above control devices determines that the air-fuel ratio determined based on the output value Vabyfs of the upstream air-fuel ratio sensor 66 is “theoretical air-fuel ratio”. And the air-fuel ratio represented by the output value Voxs of the downstream air-fuel ratio sensor is `` within the predetermined air-fuel ratio range including the theoretical air-fuel ratio ''. It is also a device that performs “normal air-fuel ratio feedback control for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine” so as to coincide with the “downstream target air-fuel ratio”.

  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 main and sub feedback control, for example, as disclosed in Japanese Patent Application Laid-Open No. 2007-278186, the upstream air-fuel ratio 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 sensor 66 is apparently corrected may be employed. Further, as disclosed in Japanese Patent Application Laid-Open No. 06-010738, 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.

  Further, in the fifth control device, the first three-way catalyst 53a, the upstream portion 55c1 of the second three-way catalyst 55c, the downstream portion 55c2 of the second three-way catalyst 55c, and the third three-way catalyst 56, in this order, You may comprise so that the loading rate of palladium may fall. At the same time, the platinum loading decreases in the order of the third three-way catalyst 56, the downstream portion 55c2 of the second three-way catalyst 55c, the upstream portion 55c1 of the second three-way catalyst 55c, and the first three-way catalyst 53a. It may be configured to. Furthermore, the embodiments can be combined within a range that is consistent with each other. For example, you may combine the characteristic of the filter accommodation catalyst apparatus CwF3 of a 3rd control apparatus, and the characteristic of the filter accommodation catalyst apparatus CwF4 of a 4th control apparatus. Further, in the filter containing catalyst device CwF3, the filter containing catalyst device CwF4 and the filter containing catalyst device CwF5, the first space SP1 and the second space SP2 may be omitted as appropriate, and the particulate collection filter 54a is provided with a wall flow. A particulate collection filter other than the type may be used.

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. It is a time chart for demonstrating the action | operation in the filter reproduction | regeneration control 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 the flowchart which showed the detail of the fuel-injection control routine which CPU of a 1st control apparatus performs. It is a schematic block diagram of the internal combustion engine to which the control apparatus (2nd control apparatus) which concerns on 2nd Embodiment of this invention is applied. It is a fragmentary sectional view of the particulate collection filter shown in FIG. It is a front view of the particulate collection filter shown in FIG. It is the schematic of the filter accommodation catalyst apparatus which the control apparatus (3rd control apparatus) which concerns on 3rd Embodiment of this invention employ | adopted. It is the schematic of the filter accommodation catalyst apparatus which the control apparatus (4th control apparatus) which concerns on 4th Embodiment of this invention employ | adopted. It is the schematic of the filter accommodation catalyst apparatus which the control apparatus (5th control apparatus) which concerns on 5th Embodiment of this invention employ | adopted.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 20 ... Cylinder block part, 25 ... Combustion chamber, 30 ... Cylinder head part, 34 ... Exhaust port, 40 ... Intake system, 50 ... Exhaust system, 51 ... Exhaust manifold, 52 ... Exhaust pipe, 53, 53a , 53b ... first three-way catalyst, 54, 54a ... particulate collection filter, 54a1 ... wall part, 54a2 ... upstream side closing part, 54a3 ... downstream side closing part, 54a4 ... outer frame body, 55, 55a, 55b, 55c 1st three-way catalyst, 56 3rd three-way catalyst, 66 upstream air-fuel ratio sensor, 67 downstream air-fuel ratio sensor, 70 electric control device.

Claims (5)

A filter-containing catalyst device in which a first three-way catalyst, a particulate collection filter, and a second three-way catalyst, which are disposed in an exhaust passage of an internal combustion engine and are arranged in order from the upstream side to the downstream side, are housed in one casing. When,
A downstream air-fuel ratio sensor disposed in the exhaust passage and downstream of the filter-containing catalyst device;
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 occurred, the air-fuel ratio of the air-fuel mixture supplied to the engine is changed to a rich air-fuel ratio that is richer than the stoichiometric air-fuel ratio and a lean air-fuel ratio that is leaner than the stoichiometric air-fuel ratio. One of the forced lean air-fuel ratios, which is an air-fuel ratio, is set to the first air-fuel ratio, and the output of the downstream air-fuel ratio sensor is the other of the forced rich air-fuel ratio and the forced lean air-fuel ratio. When the value according to the second air-fuel ratio changes from the value according to the first air-fuel ratio, the air-fuel ratio of the air-fuel mixture supplied to the engine is set to the second air-fuel ratio, and then the downstream side air-fuel ratio is set. When the output of the fuel ratio sensor changes from a value corresponding to the first air / fuel ratio to a value corresponding to the second air / fuel ratio, the air / fuel ratio of the air-fuel mixture supplied to the engine is set to the first air / fuel ratio. Filter regeneration means for executing air-fuel ratio control for a predetermined period;
The control apparatus of the internal combustion engine provided with. The control apparatus for an internal combustion engine according to claim 1,
The particulate collection filter includes a plurality of passages extending along the flow direction of the exhaust gas flowing into the particulate collection filter and includes a wall portion through which the exhaust gas can pass, and some of the plurality of passages Is a wall flow type particulate collection filter closed at its uppermost stream end, and the remaining passages not closed at the uppermost stream end of the plurality of passages are closed at the lowermost stream end,
The filter-containing catalyst device includes a first space between the first three-way catalyst and the particulate collection filter, and a second space between the particulate collection filter and the second three-way catalyst. A control apparatus for an internal combustion engine configured to include the internal combustion engine. A control device for an internal combustion engine according to claim 1 or 2,
The control apparatus for an internal combustion engine, wherein the first three-way catalyst has a higher palladium loading rate than the second three-way catalyst. A control device for an internal combustion engine according to claim 1 or 2,
The control apparatus for an internal combustion engine, wherein the second three-way catalyst is configured to have a maximum oxygen storage amount larger than that of the first three-way catalyst. A control device for an internal combustion engine according to claim 1 or 2,
The control apparatus for an internal combustion engine, wherein the second three-way catalyst is a zone coat three-way catalyst formed such that the upstream portion has a higher palladium loading ratio than the downstream portion.

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