JP2012149624A - Exhaust emission control system of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for controlling an air-fuel ratio, which controls an air-fuel ratio of an air-fuel mixture fed to an engine so that an exhaust gas with an air-fuel ratio that meets a determined air-fuel ratio requirement, flows into a catalyst.SOLUTION: An exhaust emission control system includes: a downstream side air-fuel ratio sensor 56 disposed downstream of a three-way catalyst 43; and a throttle valve 45 disposed downstream of the downstream side air-fuel ratio sensor 56. The system controls the throttle valve 45 to reduce a flow channel cross-sectional area of an exhaust channel, for example, when a variation in intake air volume Ga is accelerated more than a predetermined value. Accordingly, when much NOx (or unburned matter) is generated in the exhaust channel on the upstream side relative to the catalyst 43, the exhaust gas therein is subjected to the catalyst 43 for a longer time, and the NOx (or unburned matter) is more purified, thereby improving the emission.

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine having a three-way catalyst in an exhaust passage.

  Conventionally, in order to purify exhaust gas discharged from an internal combustion engine, a three-way catalyst is disposed in the exhaust passage of the engine. As is well known, the three-way catalyst has an “oxygen storage function” for storing or releasing oxygen in accordance with the components of the exhaust gas flowing into the three-way catalyst. Hereinafter, the three-way catalyst is also simply referred to as “catalyst”, and the gas flowing into the catalyst is also referred to as “catalyst inflow gas”.

  A conventional exhaust gas purification device (conventional device) includes a downstream air-fuel ratio sensor disposed in the exhaust passage of the engine and downstream of the catalyst. The conventional device determines which of the rich request and the lean request is generated based on the output value of the downstream air-fuel ratio sensor. The rich request is a request for an air-fuel ratio indicating that the exhaust gas having an air-fuel ratio smaller than the stoichiometric air-fuel ratio should be supplied to the catalyst. The lean request is a request for an air-fuel ratio indicating that the exhaust gas having an air-fuel ratio larger than the stoichiometric air-fuel ratio should be supplied to the catalyst. The conventional apparatus controls the air-fuel ratio of the air-fuel mixture supplied to the engine so that the air-fuel ratio exhaust gas corresponding to the air-fuel ratio requirement is supplied to the catalyst (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 08-158915

  However, the output value of the downstream air-fuel ratio sensor may not accurately represent the state of the catalyst. As a result, the air-fuel ratio request is not accurate, and the air-fuel ratio of the exhaust gas flowing into the catalyst becomes inappropriate. The emission may deteriorate due to the above.

  More specifically, for example, when the output value of the downstream air-fuel ratio sensor is “a value corresponding to an air-fuel ratio smaller than the theoretical air-fuel ratio (hereinafter also simply referred to as“ rich air-fuel ratio ”)” The conventional apparatus determines that a lean request has occurred, and controls the air / fuel ratio of the engine to “an air / fuel ratio larger than the theoretical air / fuel ratio (hereinafter simply referred to as“ lean air / fuel ratio ”)”.

  Thereafter, the output value of the downstream air-fuel ratio sensor changes to “a value corresponding to the lean air-fuel ratio” when a predetermined time elapses from “when the air-fuel ratio of the engine starts to be controlled to the lean air-fuel ratio”. . This is because an inevitable time (exhaust gas transport delay time Td) is required for the exhaust gas discharged from the engine to reach the downstream air-fuel ratio sensor, and the catalyst stores excess oxygen in the exhaust gas. Therefore, it takes time for oxygen to flow out downstream of the catalyst.

  Therefore, when the output value of the downstream air-fuel ratio sensor is a value corresponding to the rich air-fuel ratio (that is, when the air-fuel ratio of the engine is controlled to the lean air-fuel ratio based on the lean request), the operating state of the engine When the intake air amount (and hence the exhaust gas amount) increases rapidly due to the acceleration operation state, “a large amount of oxygen that cannot be stored by the catalyst and the catalyst can be purified. There may be a case where a large amount of NOx that cannot be obtained exists. As a result, a large amount of NOx is discharged from the catalyst.

  The present invention has been made to cope with such problems, and one of the purposes is to provide a throttle valve downstream of the downstream air-fuel ratio sensor and when a predetermined condition is satisfied. Provided is an exhaust gas purifying device for an internal combustion engine that can reduce the flow cross-sectional area of the exhaust passage by using the throttle valve, thereby promoting the exhaust gas purifying action in the catalyst and thereby improving the emission. There is.

An exhaust gas purifying device for an internal combustion engine of the present invention that achieves the above-mentioned object,
A three-way catalyst disposed in the exhaust passage of the internal combustion engine;
A downstream air-fuel ratio sensor disposed downstream of the catalyst in the exhaust passage;
Based on the output value of the downstream air-fuel ratio sensor, “a rich request to supply exhaust gas having an air-fuel ratio (rich air-fuel ratio) smaller than the stoichiometric air-fuel ratio to the catalyst” and “greater than the stoichiometric air-fuel ratio to the catalyst It is determined which of the air-fuel ratio requests among the “lean requests to supply exhaust gas having an air-fuel ratio (lean air-fuel ratio)”, and the air-fuel ratio exhaust gas corresponding to the determined air-fuel ratio request is Air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine so as to flow into the catalyst;
Is provided.

Furthermore, the exhaust gas purification apparatus for an internal combustion engine of the present invention is
A throttle valve that is arranged downstream of the downstream air-fuel ratio sensor of the exhaust passage and is configured to be able to change the flow passage cross-sectional area of the exhaust passage according to an instruction signal;
Throttle valve opening control means for sending an instruction signal for operating the throttle valve to the throttle valve when a predetermined condition is satisfied;
Is provided.

  According to this, when a predetermined condition is satisfied, for example, when the output value of the downstream side air-fuel ratio sensor does not accurately represent the state of the catalyst (appropriate air-fuel ratio request), the flow passage cross-sectional area of the exhaust passage is satisfied. Can be reduced. As a result, the pressure downstream of the catalyst becomes higher, and the time during which the exhaust gas stays in the catalyst becomes longer. As a result, the amount of NOx or unburned matter discharged from the catalyst without purification can be reduced. That is, the emission can be improved. Furthermore, the degree of deviation between the air-fuel ratio of the exhaust gas reaching the downstream air-fuel ratio sensor and the air-fuel ratio of “the exhaust gas in the catalyst and the exhaust gas in the exhaust passage upstream of the catalyst” can be reduced. . As a result, it is possible to generate an appropriate air-fuel ratio request.

In the exhaust gas purification apparatus according to the present invention,
The predetermined condition is a condition that is satisfied when an increase amount per unit time of the intake air amount of the engine becomes a predetermined amount or more,
The throttle valve opening control means is configured to send an instruction signal for operating the throttle valve to the throttle valve so that a flow passage cross-sectional area of the exhaust passage becomes small when the predetermined condition is satisfied. The

  Even if the increase amount per unit time of the intake air amount of the engine becomes a predetermined amount or more, the output value of the downstream air-fuel ratio sensor corresponds to the lean air-fuel ratio for a period until a certain time elapses from that point. In some cases, the value or the value corresponding to the rich air-fuel ratio does not change. Therefore, during that period, an amount of “NOx or unburned matter” that cannot be purified by the catalyst is exhausted from the engine in the exhaust passage upstream of the catalyst. According to the above configuration, when the increase amount per unit time of the intake air amount of the engine becomes a predetermined amount or more, the flow passage cross-sectional area of the exhaust passage is decreased. Therefore, the exhaust gas in the exhaust passage upstream of the catalyst can be retained in the catalyst for a long time. As a result, the amount of “NOx or unburned matter” discharged from the catalyst without being purified can be reduced.

1 is a schematic view of an internal combustion engine to which an exhaust gas purification apparatus (first apparatus) according to a first embodiment of the present invention is applied. 2 is a graph showing the relationship between the output voltage of the upstream air-fuel ratio sensor shown in FIG. 1 and the air-fuel ratio. 2 is a graph showing the relationship between the output voltage of the downstream air-fuel ratio sensor shown in FIG. 1 and the air-fuel ratio. It is the flowchart which showed the "fuel injection control routine" which CPU of 1st apparatus performs. 7 is a flowchart showing a “catalyst state determination routine” executed by the CPU of the first device. 7 is a flowchart showing a “throttle valve control routine (1)” executed by the CPU of the first device. It is the flowchart which showed the "throttle valve control routine (2)" which CPU of the 1st device performs. It is the flowchart which showed the "throttle valve control routine (1)" which CPU of the exhaust gas purification apparatus (2nd apparatus) which concerns on 2nd Embodiment of this invention performs. It is the flowchart which showed the "throttle valve control routine (2)" which CPU of the 2nd device executes. It is the flowchart which showed the "throttle valve control routine" which CPU of the exhaust gas purification apparatus (3rd apparatus) which concerns on 3rd Embodiment of this invention performs.

  Hereinafter, an exhaust gas purifying apparatus for an internal combustion engine according to each embodiment of the present invention will be described with reference to the drawings.

<First Embodiment>
(Constitution)
FIG. 1 shows a schematic configuration of an internal combustion engine 10 to which an exhaust gas purifying apparatus (hereinafter also referred to as “first apparatus”) according to a first embodiment of the present invention is applied. The engine 10 is a four-cycle / spark ignition type / multi-cylinder (four cylinders in this example) / gasoline fuel engine. The engine 10 includes a main body 20, an intake system 30, and an exhaust system 40.

  The main body portion 20 includes a cylinder block portion and a cylinder head portion. The main body portion 20 includes a plurality (four) of combustion chambers (first cylinder # 1 to fourth cylinder # 4) 21 including a piston top surface, a cylinder wall surface, and a lower surface of the cylinder head portion.

  In the cylinder head portion, an intake port 22 for supplying “a mixture of air and fuel” to each combustion chamber (each cylinder) 21, and an exhaust gas (burned gas) from each combustion chamber 21 are discharged. An exhaust port 23 is formed. The intake port 22 is opened and closed by an unillustrated intake valve, and the exhaust port 23 is opened and closed by an unillustrated exhaust valve.

  A plurality (four) of spark plugs 24 are fixed to the cylinder head portion. Each spark plug 24 is disposed such that its spark generating part is exposed at the center of each combustion chamber 21 and in the vicinity of the lower surface of the cylinder head part. Each spark plug 24 generates an ignition spark from the spark generating portion in response to the ignition signal.

  A plurality (four) of fuel injection valves (injectors) 25 are further fixed to the cylinder head portion. One fuel injection valve 25 is provided for each intake port 22 (that is, one for each cylinder). In response to the injection instruction signal, the fuel injection valve 25 injects “the fuel of the indicated injection amount included in the injection instruction signal” into the corresponding intake port 22.

  Further, an intake valve control device 26 is provided in the cylinder head portion. The intake valve control device 26 has a known configuration that adjusts and controls the relative rotation angle (phase angle) between an intake camshaft (not shown) and an intake cam (not shown) by hydraulic pressure. The intake valve control device 26 operates based on an instruction signal (drive signal), and can change the valve opening timing (intake valve opening timing) of the intake valve.

  The intake system 30 includes an intake manifold 31, an intake pipe 32, an air filter 33, a throttle valve 34, and a throttle valve actuator 34a.

  The intake manifold 31 includes a plurality of branch portions connected to each intake port 22 and a surge tank portion in which the branch portions are gathered. The intake pipe 32 is connected to the surge tank portion. The intake manifold 31, the intake pipe 32, and the plurality of intake ports 22 constitute an intake passage. The air filter 33 is provided at the end of the intake pipe 32.

  The throttle valve 34 is rotatably attached to the intake pipe 32 at a position between the air filter 33 and the intake manifold 31. The throttle valve 34 is configured to change the flow passage cross-sectional area (opening cross-sectional area) of the intake passage formed by the intake pipe 32 by rotating. The throttle valve actuator 34a is formed of a DC motor, and rotates the throttle valve 34 in response to an instruction signal (drive signal).

  The exhaust system 40 includes an exhaust manifold 41, an exhaust pipe (exhaust pipe) 42, an upstream catalyst 43, a downstream catalyst 44, a throttle valve (exhaust throttle valve) 45, and a throttle valve actuator 45a.

  The exhaust manifold 41 includes a plurality of branch portions 41a connected to each exhaust port 23, and a collection portion (exhaust collection portion) 41b in which the branch portions 41a are gathered. The exhaust pipe 42 is connected to a collective portion 41 b of the exhaust manifold 41. The exhaust manifold 41, the exhaust pipe 42, and the plurality of exhaust ports 23 constitute a passage (exhaust passage) through which exhaust gas passes.

The upstream catalyst 43 supports “noble metals (palladium Pd and platinum Pt, rhodium Rd, etc.)” and “ceria (CeO ₂ ) as an oxygen storage material” on a support made of ceramic. It is a three-way catalyst having a storage / release function (oxygen storage function). The upstream catalyst 43 is disposed (intervened) in the exhaust pipe 42. When the upstream catalyst 43 reaches a predetermined activation temperature, it exhibits a “catalytic function for simultaneously purifying unburned substances (HC, CO, H _2, etc.) and nitrogen oxides (NOx)” and “oxygen storage function”. . The upstream catalyst 43 is also referred to as a start catalytic converter (SC) or a first catalyst.

  The downstream catalyst 44 is a three-way catalyst similar to the upstream catalyst 43. The downstream catalyst 44 is disposed (intervened) in the exhaust pipe 42 downstream of the upstream catalyst 43. Since the downstream side catalyst 44 is disposed below the floor of the vehicle, it is also referred to as an under-floor catalytic converter (UFC) or a second catalyst. In the present specification, when the term “catalyst” is simply used, the “catalyst” means the upstream catalyst 43.

  The throttle valve (exhaust throttle valve) 45 is rotatably attached to the exhaust pipe 42 downstream of the downstream side air-fuel ratio sensor 56 and the downstream side catalyst 44. The throttle valve 45 changes the flow passage cross-sectional area (opening cross-sectional area) of the exhaust passage formed by the exhaust pipe 42 by rotating. The throttle valve actuator 45a is formed of a DC motor, and rotates the throttle valve 45 in response to an instruction signal (drive signal).

  The first device includes a hot-wire air flow meter 51, a throttle position sensor 52, an engine speed sensor 53, a water temperature sensor 54, an upstream air-fuel ratio sensor 55, a downstream air-fuel ratio sensor 56, and an accelerator opening sensor 57.

  The hot-wire air flow meter 51 detects the mass flow rate of the intake air flowing through the intake pipe 32 and outputs a signal representing the mass flow rate (intake air amount per unit time of the engine 10) Ga.

  The throttle position sensor 52 detects the opening degree of the throttle valve 34 and outputs a signal representing the throttle valve opening degree TA.

  The engine rotational speed sensor 53 outputs a signal having a narrow pulse every time the intake camshaft rotates 5 ° and a wide pulse every time the intake camshaft rotates 360 °. A signal output from the engine rotational speed sensor 53 is converted into a signal representing the engine rotational speed NE by an electric control device 60 described later. Further, the electric control device 60 acquires the crank angle (absolute crank angle) of the engine 10 based on signals from the engine rotation speed sensor 53 and a crank angle sensor (not shown).

  The water temperature sensor 54 detects the temperature of the cooling water of the internal combustion engine 10 and outputs a signal representing the cooling water temperature THW.

  The upstream air-fuel ratio sensor 55 is disposed in either the exhaust manifold 41 or the exhaust pipe 42 (that is, the exhaust passage) at a position between the collecting portion 41 b of the exhaust manifold 41 and the upstream catalyst 43. The upstream air-fuel ratio sensor 55 is disclosed in, for example, “limit current type wide area air-fuel ratio including a diffusion resistance layer” disclosed in JP-A-11-72473, JP-A-2000-65782, JP-A-2004-69547, and the like. Sensor ".

  As shown in FIG. 2, the upstream air-fuel ratio sensor 55 is an air-fuel ratio of exhaust gas flowing through the position where the upstream air-fuel ratio sensor 55 is disposed (the air-fuel ratio of “catalyst inflow gas” which is a gas flowing into the catalyst 43, The output value Vabyfs corresponding to the detected upstream air-fuel ratio abyfs) is output. The output value Vabyfs increases as the air-fuel ratio of the catalyst inflow gas increases (that is, as the air-fuel ratio of the catalyst inflow gas becomes leaner).

  The electric control device 60 stores the air-fuel ratio conversion table (map) Mapabyfs shown in FIG. The electric control device 60 detects the actual upstream air-fuel ratio abyfs (obtains the detected upstream air-fuel ratio abyfs) by applying the output value Vabyfs to the air-fuel ratio conversion table Mapabyfs.

Referring again to FIG. 1, the downstream air-fuel ratio sensor 56 is disposed in the exhaust pipe 42 (that is, the exhaust passage) at a position between the upstream catalyst 43 and the downstream catalyst 44. The downstream air-fuel ratio sensor 56 is a well-known concentration cell type oxygen concentration sensor (O ₂ sensor). The downstream air-fuel ratio sensor 56 is responsive to the air-fuel ratio (downstream air-fuel ratio afdown) of the exhaust gas flowing through the position where the downstream air-fuel ratio sensor 56 is disposed (that is, the “catalyst outflow gas” that is the gas flowing out from the catalyst 43). The output value Voxs is output.

  As shown in FIG. 3, the output value Voxs of the downstream air-fuel ratio sensor 56 is such that the air-fuel ratio of the catalyst outflow gas (detected gas) is richer than the stoichiometric air-fuel ratio, When the oxygen partial pressure of the gas after oxidation equilibrium is small, the maximum output value max (for example, about 0.9 to 1.0 V) is obtained. That is, the downstream air-fuel ratio sensor 56 outputs the maximum output value max when the catalyst outflow gas does not contain excessive oxygen.

  The output value Voxs is the minimum output value min (for example, when the air-fuel ratio of the catalyst outflow gas is leaner than the stoichiometric air-fuel ratio and the oxygen partial pressure of the gas after oxidation equilibrium of the catalyst outflow gas is large) , About 0 to 0.1 V). That is, the downstream air-fuel ratio sensor 56 outputs the minimum output value min when the catalyst outflow gas contains excessive oxygen.

  Further, this output value Voxs is suddenly changed from the maximum output value max to the minimum output value min when the air-fuel ratio of the catalyst outflow gas changes from the rich air-fuel ratio to the lean air-fuel ratio with respect to the stoichiometric air-fuel ratio. Decrease. Conversely, the output value Voxs is abruptly changed from the minimum output value min to the maximum output value max when the air-fuel ratio of the catalyst outflow gas changes from the lean air-fuel ratio to the rich air-fuel ratio. Increase. The average value of the minimum output value min and the maximum output value max is referred to as a median value Vmid (= (max + min) / 2). Median value Vmid is also referred to as stoichiometric air-fuel ratio equivalent voltage Vst.

  The accelerator opening sensor 57 shown in FIG. 1 detects the operation amount of the accelerator pedal AP operated by the driver, and outputs a signal indicating the operation amount Accp of the accelerator pedal AP.

  The electric control device 60 is an electronic circuit including a “well-known microcomputer” including “an interface including a CPU, a ROM, a RAM, a backup RAM, and an AD converter”.

  The backup RAM included in the electric control device 60 is a battery mounted on the vehicle regardless of the position of an ignition key switch (not shown) of the vehicle on which the engine 10 is mounted (any one of an off position, a start position, an on position, etc.). It is supposed to receive power supply from. When receiving power from the battery, the backup RAM stores data according to an instruction from the CPU (data is written) and holds (stores) the data so that the data can be read. The backup RAM cannot retain data when the power supply from the battery is interrupted, for example, when the battery is removed from the vehicle. In other words, the data held so far is lost (destroyed).

  The interface of the electric control device 60 is connected to the sensors 51 to 57 so as to supply signals from the sensors 51 to 57 to the CPU. Further, in accordance with an instruction from the CPU, the interface sends an instruction signal (drive signal) to the ignition plug 24 of each cylinder, the fuel injection valve 25 of each cylinder, the intake valve control device 26, the throttle valve actuator 34a, the throttle valve actuator 45a, and the like. ) Etc. are sent out. The electric control device 60 sends an instruction signal to the throttle valve actuator 34a so that the throttle valve opening TA increases as the acquired accelerator pedal operation amount Accp increases.

(Operation)
Next, details of the actual operation of the apparatus will be described.
<Fuel injection control>
The CPU repeats the fuel injection control routine shown in the flowchart of FIG. 4 every time the crank angle of an arbitrary cylinder reaches a predetermined crank angle before the intake top dead center of the arbitrary cylinder (for example, BTDC 90 ° CA). It is supposed to run. Therefore, when the crank angle of any cylinder reaches the predetermined crank angle, the CPU starts the process from step 400, and determines whether or not the value of the fuel cut flag XFC is “0” in step 410.

  The value of the fuel cut flag XFC is set to “1” when a fuel cut condition (fuel supply cutoff condition, fuel cut start condition) is satisfied by a fuel cut condition determination routine (not shown), and the value of the fuel cut flag XFC is If the fuel cut end condition is satisfied when it is “1”, it is set to “0”. The value of the fuel cut flag XFC is set to “0” in the initial routine. The initial routine is a routine executed by the CPU when the ignition key switch of the vehicle on which the engine 10 is mounted is changed from OFF to ON.

  Assume that the value of the fuel cut flag XFC is “0”. In this case, the CPU makes a “Yes” determination at step 410 to proceed to step 420, where the in-cylinder intake air amount Mc that is drawn into the “cylinder that reaches the current intake stroke” based on the table MapMc (Ga, NE). (K) is acquired (estimated / determined). The cylinder that reaches this intake stroke is also referred to as a “fuel injection cylinder”. Ga is the intake air amount measured by the air flow meter 51. NE is an engine speed that is separately required. The in-cylinder intake air amount Mc (k) is stored in the RAM while corresponding to the intake stroke of each cylinder. The CPU may estimate the in-cylinder intake air amount Mc (k) using a known “air model”.

Next, the CPU proceeds to step 430 to determine whether or not the value of the sub feedback control flag XSFB is “1”. The value of the sub feedback control flag XSFB 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. The sub-feedback control condition is satisfied when all of the following conditions are satisfied, and is not satisfied when at least one of the following conditions is not satisfied.
(S1) The main feedback control condition is satisfied.
(S2) The downstream air-fuel ratio sensor 56 is activated.

Note that. The main feedback control condition is satisfied when all of the following conditions are satisfied, and is not satisfied when at least one of the following conditions is not satisfied.
(M1) The upstream air-fuel ratio sensor 55 is activated.
(M2) The engine load (load factor) KL is less than or equal to the threshold KLth.
(M3) Fuel cut is not in progress.

  The load factor KL is obtained by an equation of KL = (Mc (k) / (ρ · L / 4)) · 100%. In this equation, Mc (k) is the in-cylinder intake air amount, ρ is the air density (unit is (g / l)), L is the displacement of the engine 10 (unit is (l)), and “4” is The number of cylinders of the engine 10. Note that the accelerator pedal operation amount Accp may be used as the engine load instead of the load factor KL.

  If the sub feedback control condition is not satisfied, the value of the sub feedback control flag XSFB is “0”. Therefore, in this case, the CPU makes a “No” determination at step 430 to proceed to step 440 to divide the in-cylinder intake air amount Mc (k) by the theoretical air-fuel ratio stoich (14.7 in this example). Thus, the basic fuel injection amount Fb for making the air-fuel ratio of the engine coincide with the stoichiometric air-fuel ratio stoich is obtained. In other words, the CPU sets the target air-fuel ratio abyfr to the stoichiometric air-fuel ratio stoich. Thereafter, the CPU proceeds to step 480.

  On the other hand, if the sub feedback control condition is satisfied at the time when the CPU executes the process of step 430, the value of the sub feedback control flag XSFB is “1”. Accordingly, in this case, the CPU makes a “Yes” determination at step 430 to proceed to step 450 to determine whether or not the value of the rich request flag XRichreq is “1”. The value of the rich request flag XRichreq is set to “1” in the above-described initial routine.

  Further, the value of the rich request flag XRichreq is set by the routine of FIG. That is, the CPU executes the “catalyst state determination routine (air-fuel ratio request determination routine)” shown in the flowchart of FIG. 5 every time a predetermined time elapses. Accordingly, when the predetermined timing comes, the CPU starts the process from step 500 in FIG. 5 and proceeds to step 510 to determine whether or not the output value Voxs of the downstream air-fuel ratio sensor 56 is smaller than the theoretical air-fuel ratio equivalent voltage Vst. judge. In other words, the CPU determines whether or not the air-fuel ratio (downstream air-fuel ratio) indicated by the output value Voxs is larger (lean) than the stoichiometric air-fuel ratio stoich.

  When the output value Voxs is smaller than the stoichiometric air-fuel ratio equivalent voltage Vst, the CPU determines that the state of the catalyst 43 is an oxygen excess state (lean state), and thus determines that a rich request has occurred. . That is, when the output value Voxs is smaller than the theoretical air-fuel ratio equivalent voltage Vst, the CPU makes a “Yes” determination at step 510 to proceed to step 520, sets the value of the rich request flag XRichreq to “1”, Thereafter, the routine proceeds to step 595, where the present routine is temporarily terminated.

  On the other hand, when the output value Voxs is equal to or higher than the theoretical air-fuel ratio equivalent voltage Vst, the CPU determines that the state of the catalyst 43 is in an oxygen-deficient state (rich state), and accordingly, a lean request is generated. judge. That is, when the output value Voxs is equal to or higher than the theoretical air-fuel ratio equivalent voltage Vst, the CPU makes a “No” determination at step 510 to proceed to step 530 to set the value of the rich request flag XRichreq to “0”. Thereafter, the routine proceeds to step 595, where the present routine is temporarily terminated.

  As described above, the value of the rich request flag XRichreq is set to “1” when the state of the catalyst 43 is in an excessive oxygen state (a state in which exhaust gas having a rich air-fuel ratio should flow into the catalyst 43). Is an oxygen-deficient state (a state in which a lean air-fuel ratio exhaust gas should flow into the catalyst 43).

  When the value of the rich request flag XRichreq is set to “1”, the CPU makes a “Yes” determination at step 450 in FIG. 4 and proceeds to step 460 to set the in-cylinder intake air amount Mc (k) to a predetermined rich value. By dividing by the air-fuel ratio afRich (14.2 in this example), the basic fuel injection amount Fb for making the engine air-fuel ratio coincide with the predetermined rich air-fuel ratio afRich is obtained. In other words, the CPU sets the target air-fuel ratio abyfr to the predetermined rich air-fuel ratio afRich. The predetermined rich air-fuel ratio afRich is smaller than the theoretical air-fuel ratio. Thereafter, the CPU proceeds to step 480.

  On the other hand, if the value of the rich request flag XRichreq is set to “0”, the CPU makes a “No” determination at step 450 in FIG. 4 to proceed to step 470, where the in-cylinder intake air amount Mc (k ) Is divided by a predetermined lean air-fuel ratio afLean (15.2 in this example) to obtain a basic fuel injection amount Fb for making the air-fuel ratio of the engine coincide with the predetermined lean air-fuel ratio afLean. In other words, the CPU sets the target air-fuel ratio abyfr to the predetermined lean air-fuel ratio afLean. The predetermined lean air-fuel ratio afLean is larger than the theoretical air-fuel ratio. Thereafter, the CPU proceeds to step 480.

  When the CPU proceeds to step 480, the CPU multiplies the basic fuel injection amount Fb calculated in any one of steps 440, 460, and 470 by the main feedback amount KFmain (the basic fuel injection amount Fb is used as the main feedback amount). The commanded fuel injection amount Fi is calculated by correcting with KFmain.

  The main feedback amount KFmain is determined based on the output value Vabyfs of the upstream air-fuel ratio sensor 55 when the main feedback control condition described above is satisfied. More specifically, the main feedback amount KFmain is determined as follows.

  (1) When the value of the sub feedback control flag XSFB is “0” (that is, when the basic fuel injection amount Fb is a value obtained by dividing the in-cylinder intake air amount Mc (k) by the stoichiometric air-fuel ratio stoich). The main feedback amount KFmain is decreased when the upstream air-fuel ratio abyfs expressed by the output value Vabyfs of the upstream air-fuel ratio sensor 55 is smaller (rich) than the stoichiometric air-fuel ratio stoich, and the upstream air-fuel ratio abyfs is theoretically decreased. Increased when air-fuel ratio is greater than stoich (lean).

  (2) When the value of the sub feedback control flag XSFB is “1” and the value of the rich request flag XRichreq is “1” (that is, the basic fuel injection amount Fb is the in-cylinder intake air amount Mc (k ) Is divided by the predetermined rich air-fuel ratio afRich), the main feedback amount KFmain is decreased when the upstream air-fuel ratio abyfs is smaller (rich) than the predetermined rich air-fuel ratio afRich, and the upstream air-fuel ratio Increased when abyfs is greater (lean) than the predetermined rich air-fuel ratio afRich.

  (3) When the value of the sub feedback control flag XSFB is “1” and the value of the rich request flag XRichreq is “0” (that is, the basic fuel injection amount Fb is the in-cylinder intake air amount Mc (k The main feedback amount KFmain is decreased when the upstream air-fuel ratio abyfs is smaller (rich) than the predetermined lean air-fuel ratio afLean, and the upstream air-fuel ratio abyfs is It is increased when it is larger than the predetermined lean air-fuel ratio afLean (is lean).

(4) When the main feedback control condition is not satisfied, the main feedback amount KFmain is set to “1”.
Thus, the main feedback amount KFmain is decreased when the actual upstream air-fuel ratio abyfs is smaller than the target air-fuel ratio abyfr, and is increased when the actual upstream air-fuel ratio abyfs is larger than the target air-fuel ratio abyfr.

  Next, the CPU proceeds to step 490, and instructs the fuel injection valve 25 to inject fuel so that the fuel of the indicated fuel injection amount Fi is injected from the fuel injection valve 25 for the fuel injection cylinder. Thereafter, the CPU proceeds to step 495 to end the present routine tentatively.

  On the other hand, if the value of the fuel cut flag XFC is “1” at the time when the CPU performs the process of step 410, the CPU makes a “No” determination at step 410 and proceeds directly to step 495 to execute this routine. Exit once. Therefore, since the process of step 490 is not executed, the fuel cut operation is executed.

  Further, the CPU executes the “throttle valve control routine (1)” shown by the flowchart in FIG. 6 every time a predetermined time elapses. Therefore, at the predetermined timing, the CPU starts the process from step 600 in FIG. 6 and proceeds to step 610 to read the intake air amount Ga.

  Next, the CPU proceeds to step 620 to calculate a value ΔGa obtained by subtracting “the intake air amount Gaold of a predetermined time before (previous)” from the “current intake air amount Ga” read in step 610. The value ΔGa is also referred to as “intake air change amount ΔGa or intake air increase amount ΔGa”. Next, the CPU proceeds to step 630 to store “the current intake air amount Ga” read in step 610 as “the intake air amount Gaold before (previous) a predetermined time”.

  Next, the CPU proceeds to step 640 to determine whether or not the value of the throttle valve control execution flag XC is “0”. The value of the throttle valve control execution flag XC is set to “0” in the above-described initial routine. Therefore, it is assumed here that the value of the throttle valve control execution flag XC is “0”.

  In this case, the CPU makes a “Yes” determination at step 640 to proceed to step 650 to determine whether or not the intake air change amount ΔGa is larger than the intake air change amount threshold value ΔGath. At this time, it is assumed that the intake air change amount ΔGa is equal to or less than the intake air change amount threshold value ΔGath. In this case, the CPU makes a “No” determination at step 650 to directly proceed to step 695 to end the present routine tentatively. Therefore, the value of the throttle valve control execution flag XC is maintained at “0”.

  Furthermore, the CPU executes the “throttle valve control routine (2)” shown by the flowchart in FIG. 7 every time a predetermined time elapses. Therefore, when the predetermined timing comes, the CPU starts the process from step 700 of FIG. 7 and proceeds to step 710 to determine whether or not the value of the throttle valve control execution flag XC is “1”.

  At the present time, the value of the throttle valve control execution flag XC is maintained at “0”. Accordingly, the CPU makes a “No” determination at step 705 to directly proceed to step 795 to end the present routine tentatively.

  In this state, when the acceleration operation is performed and the intake air change amount ΔGa becomes larger than the intake air change amount threshold value ΔGath, the CPU determines “Yes” in step 650 of FIG. 6 and proceeds to step 660. In step 660, the CPU sets the value of the throttle valve control execution flag XC to “1”, proceeds to step 670, and sets the value of the post-acceleration time counter CCL to “0”. Thereafter, the CPU proceeds to step 695 to end the present routine tentatively.

  In this state, when the CPU proceeds to step 705 in FIG. 7, the CPU makes a “Yes” determination at step 705 to proceed to step 710, and increases the value of the post-acceleration time counter CCL by “1”. Next, the CPU proceeds to step 715 to determine whether or not the value of the post-acceleration time counter CCL is equal to or less than the counter threshold value CCLth. The counter threshold CCLth is set to a predetermined value of “2” or more.

  The present time is immediately after the value of the post-acceleration time counter CCL is increased from “0” by “1”. Therefore, the CPU makes a “Yes” determination at step 715 to proceed to step 720 to calculate the exhaust gas transport delay time td based on the intake air amount Ga. The exhaust gas transport delay time td is calculated so as to decrease as the intake air amount Ga increases.

  Next, the CPU proceeds to step 725 to determine the throttle amount CLOSE of the throttle valve 45 based on the exhaust gas transport delay time td. More specifically, the CPU sets the throttle amount CLOSE to “0” when the exhaust gas transport delay time td is equal to or shorter than the predetermined time tdth. Further, the CPU determines the throttle amount CLOSE so that when the exhaust gas transport delay time td is equal to or longer than the predetermined time tdth, the throttle amount CLOSE increases as the exhaust gas transport delay time td increases. The larger the throttle amount CLOSE, the more the throttle valve 45 is rotated by a larger angle, so that the cross-sectional area of the exhaust passage formed by the exhaust pipe 42 becomes smaller. However, even if the throttle amount CLOSE matches the maximum throttle amount CLmax, the flow passage cross-sectional area of the exhaust passage formed by the exhaust pipe 42 does not become “0”.

  Next, the CPU proceeds to step 730 and sends an instruction signal to the throttle valve actuator 45a so as to rotate the throttle valve 45 by an angle corresponding to the throttle amount CLOSE, thereby causing the flow of the exhaust passage formed by the exhaust pipe 42 to flow. Change the road cross-sectional area. Thereafter, the CPU proceeds to step 795 to end the present routine tentatively.

  When the CPU proceeds to step 640 in FIG. 6 in this state, the CPU makes a “No” determination at step 640 to directly proceed to step 695 to end the present routine tentatively. Further, in this state, when the CPU proceeds to step 705 in FIG. 7, the CPU makes a “Yes” determination at step 705 to proceed to step 710 and step 715. Accordingly, the processing from step 720 to step 730 is repeatedly executed until the value of the post-acceleration time counter CCL becomes larger than the counter threshold CCLth.

  Thereafter, when the value of the post-acceleration time counter CCL becomes larger than the counter threshold CCLth, the CPU makes a “No” determination at step 715 to proceed to step 735 to decrease the aperture amount CLOSE by a certain amount dC. Next, the CPU proceeds to step 740 to determine whether or not the aperture amount CLOSE is “0” or less. At this time, if the aperture amount CLOSE is larger than “0”, the CPU makes a “No” determination at step 740 to directly proceed to step 730.

  On the other hand, if the aperture amount CLOSE is equal to or less than “0” at the time when the CPU executes the process of step 740, the CPU makes a “Yes” determination at step 740 to proceed to step 745, and the aperture amount CLOSE. Is set to “0”. Further, the CPU proceeds to step 750 to set the value of the throttle valve control execution flag XC to “0”. Thereafter, the CPU proceeds to step 730.

As described above, the first device is
Based on the output value Voxs of the downstream air-fuel ratio sensor 56, “a rich request to supply exhaust gas having an air-fuel ratio smaller than the stoichiometric air-fuel ratio to the catalyst 43” and “exhaust gas having an air-fuel ratio larger than the stoichiometric air-fuel ratio to the catalyst 43 It is determined which air-fuel ratio request among the "lean requests to supply" is generated (see the routine of FIG. 5), and the exhaust gas of the air-fuel ratio corresponding to the determined air-fuel ratio request is Air-fuel ratio control means (see steps 450 to 490 in FIG. 4) for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine 10 so as to flow into the catalyst;
A throttle valve (45, 45a) disposed downstream of the air-fuel ratio sensor 56 on the downstream side of the exhaust passage of the engine 10 and configured to be able to change the cross-sectional area of the exhaust passage according to an instruction signal;
Throttle valve opening control means (see the routines of FIGS. 6 and 7) for sending an instruction signal for operating the throttle valve to the throttle valve when a predetermined condition is satisfied;
Is provided.

Further, the throttle valve opening control means includes:
When the increase amount (intake air change amount ΔGa) per unit time of the intake air amount of the engine exceeds a predetermined amount (intake air change amount threshold value ΔGath), the flow passage cross-sectional area of the exhaust passage is reduced. An instruction signal for operating the throttle valve is sent to the throttle valve (see Steps 650 and 660 in FIG. 6 and “Yes” determination in Step 705 in FIG. 7). Further, the throttle valve opening control means sends an instruction signal for operating the throttle valve to the throttle valve until a predetermined time elapses after the intake air change amount ΔGa becomes equal to or greater than the intake air change amount threshold value ΔGath. It is configured to send (see step 715 to step 750 in FIG. 7).

  As a result, when the lean request is generated, the intake air amount Ga increases rapidly, and when a large amount of NOx is exhausted into the exhaust passage upstream of the catalyst 43, the exhaust gas enters the catalyst 43 (and the downstream catalyst 44). Can be retained for a long time. Therefore, since NOx in the exhaust gas is further purified in the catalyst 43 (and the downstream catalyst 44), the amount of NOx released into the atmosphere can be reduced.

  Alternatively, when the rich request is generated, the intake air amount Ga increases rapidly, and when a large amount of unburned matter is discharged into the exhaust passage upstream of the catalyst 43, the catalyst 43 (and the downstream catalyst 44) enters. The exhaust gas can be retained for a long time. Therefore, the unburned matter in the exhaust gas is further purified in the catalyst 43 (and the downstream catalyst 44), so the amount of unburned matter released into the atmosphere can be reduced.

  The CPU determines whether or not the output value Voxs of the downstream air-fuel ratio sensor 56 is greater than the theoretical air-fuel ratio equivalent voltage Vst between step 650 and step 660 of FIG. Any of the steps of determining whether or not the flag XRichreq is “0” may be added. In this case, the CPU proceeds to step 660 when the output value Voxs of the downstream air-fuel ratio sensor 56 is larger than the theoretical air-fuel ratio equivalent voltage Vst (that is, when a lean request is generated), and the output value Voxs is the theoretical air-fuel ratio. When it is equal to or lower than the fuel ratio equivalent voltage Vst (when a rich request is generated), the process proceeds directly to step 695. According to this, the throttle valve 45 is closed only when there is a high possibility that NOx will be discharged, so the amount of NOx discharged can be reduced.

Second Embodiment
Next, an exhaust gas purification apparatus (hereinafter also referred to as “second apparatus”) according to a second embodiment of the present invention will be described. The second device is such that the CPU executes “throttle valve control routines (1) and (2)” shown in the flowcharts in “FIGS. 8 and 9” instead of “FIGS. 6 and 7”. Only in the first device. Therefore, hereinafter, this difference will be mainly described. Of the steps of the routines shown in FIGS. 8 and 9, steps that perform the same processing as the steps already described are assigned the same reference numerals as those given to those steps.

  The routine shown in FIG. 8 differs from the routine shown in FIG. 6 only in that step 810 is added after step 670. That is, when the CPU ends the process of step 670, the process proceeds to step 810, and calculates the counter threshold value CCLth based on the intake air amount Ga. The counter threshold CCLth is determined so as to decrease as the intake air amount Ga increases. In other words, the counter threshold CCLth is equal to the air-fuel ratio request at the time of sudden increase in intake air when a time corresponding to the counter threshold CCLth has elapsed from “when the intake air change amount ΔGa becomes larger than the intake air change amount threshold ΔGath”. Is set to a value at which an opposite air-fuel ratio requirement will occur.

  In other words, when the output value Voxs of the downstream air-fuel ratio sensor 56 is greater than the theoretical air-fuel ratio equivalent voltage Vst at “when the intake air change amount ΔGa becomes larger than the intake air change amount threshold value ΔGath” (a lean request is generated). When the time corresponding to the counter threshold CCLth elapses from “when the intake air change amount ΔGa becomes larger than the intake air change amount threshold value ΔGath”, the output value Voxs becomes smaller than the theoretical air-fuel ratio equivalent voltage Vst. (Rich request occurs) Similarly, when the output value Voxs of the downstream air-fuel ratio sensor 56 is smaller than the stoichiometric air-fuel ratio equivalent voltage Vst at “when the intake air change amount ΔGa becomes larger than the intake air change amount threshold value ΔGath” (the rich request is When the time corresponding to the counter threshold value CCLth has elapsed from “when the intake air change amount ΔGa becomes larger than the intake air change amount threshold value ΔGath”, the output value Voxs becomes lower than the theoretical air-fuel ratio equivalent voltage Vst. It becomes large (a lean request occurs). Thereafter, the CPU proceeds to step 895 to end the present routine tentatively.

  The routine shown in FIG. 9 is different from the routine shown in FIG. 7 only in that Steps 720 and 725 in FIG. 7 are replaced with Steps 910 to 930. That is, if the CPU makes a “Yes” determination at step 715, the CPU proceeds to step 910 to increase the aperture amount CLOSE by a fixed amount dC. Next, the CPU proceeds to step 920 to determine whether or not the aperture amount CLOSE is greater than or equal to the maximum aperture amount CLmax. At this time, if the aperture amount CLOSE is less than the maximum aperture amount CLmax, the CPU makes a “No” determination at step 920 to directly proceed to step 730.

  On the other hand, when the CPU executes the process of step 920, if the aperture amount CLOSE is equal to or larger than the maximum aperture amount CLmax, the CPU makes a “Yes” determination at step 920 to proceed to step 930, and the aperture amount CLOSE is set to the maximum aperture amount CLmax. Thereafter, the CPU proceeds to step 730.

  As a result, the throttle amount CLOSE is “the time when the predetermined time has elapsed from the time when the intake air change amount ΔGa becomes larger than the intake air change amount threshold ΔGath” (that is, the post-acceleration time counter CCL reaches the counter threshold CCLth). It gradually increases from “0” during the period until “

  Further, the aperture amount CLOSE gradually decreases after “the time when the predetermined time elapses (that is, the time when the post-acceleration time counter CCL reaches the counter threshold CCLth)” by the processing of step 715 and steps 735 to 750. . Further, the predetermined time becomes shorter as the intake air amount Ga is larger (see step 810 in FIG. 8 and step 715 in FIG. 9).

  As a result, when the lean request is generated, the intake air amount Ga increases rapidly, and when a large amount of NOx is discharged into the exhaust passage upstream of the catalyst 43, the longer the amount of NOx discharged, the longer the time. The exhaust gas can stay in the catalyst 43 (and the downstream catalyst 44). Therefore, since NOx in the exhaust gas is further purified in the catalyst 43 and (and the downstream catalyst 44), the amount of NOx released into the atmosphere can be reduced.

  Alternatively, when the rich request is generated, the intake air amount Ga increases rapidly, and when a large amount of unburned material is discharged into the exhaust passage upstream of the catalyst 43, the larger the amount of discharged unburned material, The exhaust gas can stay in the catalyst 43 (and the downstream catalyst 44) for a longer time. Therefore, the unburned matter in the exhaust gas is further purified in the catalyst 43 and (and the downstream catalyst 44), so that the amount of unburned matter released into the atmosphere can be reduced.

<Third Embodiment>
Next, an exhaust gas purification apparatus (hereinafter, also referred to as “third apparatus”) according to a third embodiment of the present invention will be described. The third device is different from the first device only in that the “throttle valve control routine” shown in the flowchart of FIG. 10 instead of “FIGS. 6 and 7” is executed every time a predetermined time elapses. It is different from the device. Therefore, hereinafter, this difference will be mainly described.

When the predetermined timing is reached, the CPU starts processing from step 1000 in FIG. 10 and proceeds to step 1010 to calculate “oxygen change amount DOSA” per unit time according to the following equation (1). The oxygen change amount DOSA is a change amount per unit time of oxygen discharged from the engine 10 in the exhaust passage upstream of the catalyst 43. In the following formula (1), the value “0.23” is the weight ratio of oxygen contained in the atmosphere. SFi is the total fuel injection amount (indicated fuel injection amount Fi) injected within the unit time. abyfr is the predetermined rich air-fuel ratio afRich (14.2 in this example) when the value of the rich request flag XRichreq is “1”, and the predetermined lean when the value of the rich request flag XRichreq is “0”. The air-fuel ratio is afLean (15.2 in this example). stoich is the stoichiometric air-fuel ratio.

DOSA = 0.23 · SFi · (abyfr-stoich) (1)

  Note that abyfr in equation (1) may be replaced with abyfs. abyfs is the upstream air-fuel ratio abyfs obtained by applying the output value Vabyfs of the upstream air-fuel ratio sensor 55 to the air-fuel ratio conversion table Mapabyfs (Vabyfs) shown in FIG.

  Next, the CPU proceeds to step 1020 to update the exhaust passage oxygen amount OSA by adding the change amount DOSA to the exhaust passage oxygen amount OSA at that time. Next, the CPU proceeds to step 1030 to determine whether or not the exhaust passage oxygen amount OSA is equal to or greater than the maximum oxygen storage amount Cmax.

  The maximum oxygen storage amount Cmax is the maximum value of the amount of oxygen that can be stored by the upstream catalyst 43, and is acquired separately by so-called “active air-fuel ratio control”. The active air-fuel ratio control is a well-known control described in, for example, JP-A-5-133264. For example, the maximum oxygen storage amount Cmax is acquired as follows.

The CPU keeps the exhaust gas having an air-fuel ratio richer than the stoichiometric air-fuel ratio stoich flowing into the upstream catalyst 43, and matches the oxygen storage amount of the upstream catalyst 43 to “0”. At this time, the output value Voxs of the downstream air-fuel ratio sensor 56 becomes the maximum output value max.

The CPU continues to flow the exhaust gas having an air-fuel ratio leaner than the stoichiometric air-fuel ratio stoich from that time onward, and the output value Voxs of the downstream-side air-fuel ratio sensor 56 from the time point becomes higher than the stoichiometric air-fuel ratio equivalent voltage Vst. “Oxygen storage amount change amount ΔOSA per unit time” is calculated in a period up to the time point when the value becomes smaller, and the maximum oxygen storage amount Cmax is obtained by integrating the oxygen storage amount change amount ΔOSA. The oxygen storage amount change amount ΔOSA is calculated by SFi (fuel amount per unit time) · 0.23 · (abyfs−stoich).

  When the CPU executes the process of step 1030, if the oxygen amount OSA in the exhaust passage is equal to or greater than the maximum oxygen storage amount Cmax, the catalyst 43 cannot store all the oxygen in the exhaust passage, and at the same time, the exhaust passage. The inside NOx cannot be sufficiently purified. Therefore, in this case, the CPU makes a “Yes” determination at step 1030 to proceed to step 1040, where the value k · obtained by multiplying the value obtained by subtracting the maximum oxygen storage amount Cmax from the oxygen amount OSA in the exhaust passage is multiplied by a positive constant k. (OSA-Cmax) is set as the throttle amount CLOSE of the throttle valve 45.

  Next, the CPU proceeds to step 1050 to determine whether or not the aperture amount CLOSE is greater than or equal to the maximum aperture amount CLmax. At this time, if the aperture amount CLOSE is less than the maximum aperture amount CLmax, the CPU makes a “No” determination at step 1050 to directly proceed to step 1070.

  On the other hand, when the CPU executes the process of step 1050 and the aperture amount CLOSE is equal to or larger than the maximum aperture amount CLmax, the CPU makes a “Yes” determination at step 1050 to proceed to step 1060, and the aperture amount CLOSE is set to the maximum aperture amount CLmax. Thereafter, the CPU proceeds to step 1070.

  Next, in step 1070, the CPU sends an instruction signal to the throttle valve actuator 45a so as to rotate the throttle valve 45 by an angle corresponding to the throttle amount CLOSE, thereby causing the flow of the exhaust passage formed by the exhaust pipe 42 to flow. Change the road cross-sectional area. Thereafter, the CPU proceeds to step 1095 to end the present routine tentatively.

  As a result, when the oxygen amount OSA in the exhaust passage in the exhaust passage upstream of the catalyst 43 becomes equal to or greater than the maximum oxygen storage amount Cmax, “the value obtained by subtracting the maximum oxygen storage amount Cmax from the oxygen amount OSA in the exhaust passage” is The larger the size, the smaller the cross-sectional area of the exhaust passage.

  On the other hand, when the CPU performs the process of step 1030, if the oxygen amount OSA in the exhaust passage is less than the maximum oxygen storage amount Cmax, the CPU makes a “No” determination at step 1030 to proceed to step 1080, where the exhaust passage It is determined whether or not the internal oxygen amount OSA is smaller than “0”.

  When the oxygen amount OSA in the exhaust passage is smaller than “0”, the catalyst 43 cannot sufficiently purify the unburned matter in the exhaust passage. Therefore, in this case, the CPU makes a “Yes” determination at step 1080 to proceed to step 1085, where the throttle valve is set to a value k · | OSA | obtained by multiplying the absolute value | OSA | A diaphragm amount CLOSE of 45 is set. Thereafter, the CPU proceeds to step 1050 and thereafter.

  On the other hand, when the CPU performs the process of step 1080 and the oxygen amount OSA in the exhaust passage is equal to or greater than “0”, the CPU determines “No” in step 1080 and proceeds to step 1090. Set CLOSE to "0". Thereafter, the CPU proceeds to step 1050 and thereafter.

  As a result, when the oxygen amount OSA in the exhaust passage in the exhaust passage upstream of the catalyst 43 is less than “0”, the flow rate of the exhaust passage increases as the absolute value | OSA | of the “oxygen amount in exhaust passage OSA” increases. The cross-sectional area becomes smaller.

  As described above, the exhaust gas purification apparatus for an internal combustion engine according to each embodiment of the present invention reduces the flow passage cross-sectional area of the exhaust passage by rotating the throttle valve 45 when a predetermined condition is satisfied. As a result, the time during which the exhaust gas stays in the catalyst 43 and the downstream catalyst 44 becomes longer, so that the emission can be improved.

  The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention. For example, the throttle valve 45 may be disposed in the exhaust pipe 42 (exhaust passage) between the downstream air-fuel ratio sensor 56 and the downstream catalyst 44.

  Further, each exhaust purification device is configured to perform known sub-feedback control for making the output value Voxs of the downstream air-fuel ratio sensor 56 coincide with the downstream target value Voxsref (usually the theoretical air-fuel ratio equivalent voltage Vst). May be. That is, each exhaust purification device determines the sub feedback amount KSFB so that the deviation between the output value Voxs of the downstream air-fuel ratio sensor 56 and the downstream target value Voxsref is reduced by PID control, and sub-feedback from the stoichiometric air-fuel ratio stoich. A value obtained by subtracting the amount KSFB may be set as the target air-fuel ratio abyfr.

  In this case, if the output value Voxs is smaller than the downstream target value Voxsref, the sub feedback amount KSFB is increased. As a result, the target air-fuel ratio abyfr becomes smaller than the stoichiometric air-fuel ratio stoich (set to a rich air-fuel ratio). On the other hand, if the output value Voxs is larger than the downstream target value Voxsref, the sub feedback amount KSFB is decreased and becomes a negative value. As a result, the target air-fuel ratio abyfr becomes larger than the stoichiometric air-fuel ratio stoich (set to a lean air-fuel ratio).

  In this case, each device automatically and substantially determines which of the “rich request and lean request” air-fuel ratio is generated based on the output value Voxs of the downstream air-fuel ratio sensor 56, It can be said that the air-fuel ratio of the engine is controlled according to the air-fuel ratio request.

  Furthermore, each device immediately stops the reduction of the cross-sectional area of the exhaust passage by the throttle valve 45 when the predetermined condition that gives priority to the drivability of the engine 10 is satisfied (the throttle amount CLOSE is set to “0”). Thus, the throttle valve 45 can be fully opened. An example of the predetermined condition that prioritizes drivability is when the engine 10 is decelerated. If the cross-sectional area of the exhaust passage is reduced by the throttle valve 45 when the engine 10 is decelerated, the pressure in the exhaust passage becomes higher than the pressure in the cylinder, and the exhaust gas flows back into the cylinder. Combustion becomes unstable and the drivability of the engine 10 decreases. Furthermore, in general, a constant delay is incorporated in the operating speed of the throttle valve actuator 45a (configured so that the rotational speed of the throttle valve 45 is below a certain value), but priority is given to the drivability of the engine 10. When a predetermined condition to be satisfied is satisfied, it is desirable to minimize the delay and immediately stop the reduction of the flow passage cross-sectional area of the exhaust passage.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 21 ... Combustion chamber, 23 ... Exhaust port, 25 ... Fuel injection valve, 40 ... Exhaust system, 41 ... Exhaust manifold, 41a ... Branch part, 41b ... Collecting part, 42 ... Exhaust pipe, 43 ... Upstream side Catalyst, 44 ... downstream catalyst, 45 ... throttle valve, 45a ... throttle valve actuator, 55 ... upstream air-fuel ratio sensor, 56 ... downstream air-fuel ratio sensor, 60 ... electric control device.

Claims (2)

A three-way catalyst disposed in the exhaust passage of the internal combustion engine;
A downstream air-fuel ratio sensor disposed downstream of the catalyst in the exhaust passage;
Based on the output value of the downstream air-fuel ratio sensor, a rich request to supply an exhaust gas with an air-fuel ratio smaller than the stoichiometric air-fuel ratio to the catalyst and an exhaust gas with an air-fuel ratio greater than the stoichiometric air-fuel ratio to the catalyst should be supplied It is determined which air-fuel ratio request among the lean requests is generated, and mixing that is supplied to the engine so that exhaust gas having an air-fuel ratio corresponding to the determined air-fuel ratio request flows into the catalyst Air-fuel ratio control means for controlling the air-fuel ratio of the air;
An exhaust gas purification apparatus for an internal combustion engine comprising:
A throttle valve that is arranged downstream of the downstream air-fuel ratio sensor of the exhaust passage and is configured to be able to change the flow passage cross-sectional area of the exhaust passage according to an instruction signal;
Throttle valve opening control means for sending an instruction signal for operating the throttle valve to the throttle valve when a predetermined condition is satisfied;
Exhaust gas purification device with The exhaust gas purification apparatus according to claim 1,
The predetermined condition is a condition that is satisfied when an increase amount per unit time of the intake air amount of the engine becomes a predetermined amount or more,
The throttle valve opening control means is configured to send an instruction signal for operating the throttle valve to the throttle valve so that a flow passage cross-sectional area of the exhaust passage becomes small when the predetermined condition is satisfied. Exhaust gas purification device.

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