JP2004239081A - Exhaust emission control device of internal combustion engine and control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine for restraining generation of white smoke by restraining a discharge quantity of an unburnt fuel component. <P>SOLUTION: When determining that the exhaust air-fuel ratio detected by an air-fuel ratio sensor falls within a target range, an additional quantity of fuel correction is not made (S305). When determining that the exhaust air-fuel ratio detected by the air-fuel ratio sensor does not fall within the target range, determination is made on whether or not a detected value is the high side of the oxygen concentration to the target range. When determining that the oxygen concentration is the high side, processing of a correction A is performed (S307). When determining that the oxygen concentration is the low side, processing of a correction B is performed (S308). A correction quantity is set larger in the correction B than the correction A for restraining the exhaust air-fuel ratio from becoming smaller than the exhaust air-fuel ratio being a target. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to an exhaust gas purification device and a control device for an internal combustion engine, which purifies exhaust substances contained in exhaust gas.
[0002]
[Prior art]
For example, in an internal combustion engine, such as a diesel engine, which operates an engine by burning a mixture having a high air-fuel ratio (lean atmosphere) in a wide operating range, generally, a large amount of nitrogen oxides (hereinafter referred to as NOx) is contained in exhaust gas. ) Is included. A storage-reduction type NOx catalyst (hereinafter referred to as a NOx catalyst) is known as a device that effectively purifies this NOx.
[0003]
The NOx catalyst absorbs NOx contained in the exhaust gas when the oxygen concentration of the exhaust gas is high and releases the absorbed NOx when the oxygen concentration of the exhaust gas is low and in the reducing atmosphere while releasing nitrogen (N ₂ ). When the oxygen concentration of the exhaust gas is high, this NOx catalyst has a characteristic of absorbing not only NOx in the exhaust gas but also sulfur oxides (hereinafter referred to as SOx) in the exhaust gas by the same mechanism as the NOx. When SOx is absorbed by the NOx catalyst in this way, so-called SOx poisoning occurs in which the NOx absorption capacity of the NOx catalyst decreases as the amount of absorption increases.
[0004]
Therefore, in order to eliminate SOx poisoning, it is necessary to remove the SOx absorbed by the NOx catalyst and restore the NOx absorption capacity of the NOx catalyst. As a suitable method for removing SOx, a method of intermittently making the exhaust air-fuel ratio rich is known. In this case, it is common to provide a sensor for detecting the exhaust air-fuel ratio and control the exhaust air-fuel ratio based on the value detected by the sensor (for example, see Patent Document 1).
[0005]
Here, a general air-fuel ratio sensor used for detecting the exhaust air-fuel ratio has a high detection accuracy near the stoichiometry, and the detection accuracy decreases as the distance from the stoichiometry increases. This will be briefly described with reference to FIG. FIG. 12 shows the state of the air-fuel ratio detected by the air-fuel ratio sensor with respect to the actual exhaust air-fuel ratio. As shown in the figure, the median of the values detected by the air-fuel ratio sensor is substantially equal to the actual exhaust air-fuel ratio. However, the air-fuel ratio detected by the air-fuel ratio sensor has an error with respect to the actual exhaust air-fuel ratio due to product variations of the air-fuel ratio sensor and the like. This error increases in a general air-fuel ratio sensor as the distance from the stoichiometry increases, as shown in the figure.
[0006]
Therefore, in the case where the exhaust air-fuel ratio is controlled to be intermittently rich in order to eliminate the SOx poisoning described above, it is difficult to accurately obtain a desired rich atmosphere using such an air-fuel ratio sensor. It is. Therefore, the exhaust air-fuel ratio may be lower than the target rich atmosphere (in other words, the reducing component concentration may be higher) due to variations in the detection accuracy of the air-fuel ratio sensor. As a result, the amount of emission of the unburned fuel component becomes excessively large, and white smoke may be generated. In addition, there is Patent Document 2 as another related technique.
[0007]
[Patent Document 1]
JP 2001-82137 A
[Patent Document 2]
JP-A-11-107827
[0008]
[Problems to be solved by the invention]
As described above, when white smoke is generated, the commercial value of the internal combustion engine or a vehicle equipped with the internal combustion engine is reduced. The cause of the generation of white smoke is that an unburned fuel component is excessively discharged.
[0009]
Therefore, one of the objects of the present invention is to suppress the emission of unburned fuel components.
[0010]
Here, one of the causes of the excessive emission of the unburned fuel component is that the detection accuracy at a desired exhaust air-fuel ratio depends on the characteristics of a general detecting means (sensor) used for detecting the exhaust air-fuel ratio. Low and the exhaust air-fuel ratio may be excessively lower than the desired exhaust air-fuel ratio. However, even when such a sensor is used, it may be possible to reduce the amount of unburned fuel component emission by devising a control method.
[0011]
Therefore, one of the objects of the present invention is to suppress the emission of unburned fuel components even when a sensor having a characteristic of low detection accuracy at a desired exhaust air-fuel ratio is used.
[0012]
In addition, as one of the causes of excessive emission of the unburned fuel component, as described above, the characteristic of a general detecting means (sensor) used for detecting the exhaust air-fuel ratio is determined by the characteristic of the desired exhaust air-fuel ratio. The detection accuracy is low, and it is difficult to accurately control the exhaust air-fuel ratio to a desired value. However, even when such a sensor is used, it may be conceivable to control the desired exhaust air-fuel ratio with high accuracy by utilizing the characteristics of the sensor. Thus, it is conceivable that the emission amount of the unburned fuel component is suppressed.
[0013]
Therefore, one of the objects of the present invention is to accurately control a desired exhaust air-fuel ratio to a desired exhaust air-fuel ratio even when a sensor having a characteristic of low detection accuracy at a desired exhaust air-fuel ratio is used.
[0014]
One of the objects of the present invention is to suppress the generation of white smoke by suppressing the emission of unburned fuel components.
[0015]
[Means for Solving the Problems]
The present invention employs the following means in order to solve the above problems.
[0016]
According to the present invention, when the detected exhaust air-fuel ratio is lower than the target exhaust air-fuel ratio, the correction amount (feedback amount) of the supplied reducing agent is made larger than when the detected exhaust air-fuel ratio is higher. Thereby, it is possible to suppress the exhaust air-fuel ratio from becoming lower than the target exhaust air-fuel ratio. Therefore, it is possible to suppress the release of the excess reducing agent (generally, fuel).
[0017]
Here, the exhaust air-fuel ratio in the specification of the present application means the air-fuel ratio of the exhaust gas. The air-fuel ratio of the exhaust gas refers to the mass of the fuel supplied to the combustion chamber and the mass of the reducing agent when the reducing agent is supplied to the exhaust passage (however, when the reducing agent is other than fuel, Means the ratio of the mass of the air drawn into the combustion chamber (when air is supplied to the exhaust passage, the mass obtained by adding the mass of the air) to the mass obtained by adding the mass converted to fuel. It is.
[0018]
And the exhaust gas purifying apparatus for an internal combustion engine according to the specific present invention,
When the oxidizing component concentration of the exhaust purification section in the exhaust passage is high, the oxidizing exhaust substance contained in the exhaust gas is absorbed, and when the oxidizing component concentration of the exhaust purification section is low and the reducing atmosphere is used, Purifying means for purifying the oxidizing exhaust material by reducing while releasing the absorbed oxidizing exhaust material,
Supply means for supplying a reducing agent to the exhaust gas purification unit,
Detecting means for detecting the exhaust air-fuel ratio downstream of the exhaust purification section;
Feedback control for deriving a correction amount of the supplied reducing agent from a difference between the value detected by the detection unit and a target exhaust air-fuel ratio, and controlling a supply amount of the reducing agent supplied based on the correction amount. And an exhaust purification device for an internal combustion engine comprising:
When exhaust gas is discharged and reduced from the purifying means, when the difference is X, the correction amount when the detection result by the detecting means is higher than a target exhaust air-fuel ratio is Y1, and the exhaust air-fuel ratio is If the correction amount is lower than Y2, the relationship of Y2> Y1 is satisfied regardless of the value of X.
[0019]
According to the configuration of the present invention, the correction amount (feedback amount) of the supplied reducing agent is larger when the detection result of the exhaust air-fuel ratio is lower than the target exhaust air-fuel ratio than when it is higher. Thereby, it is possible to suppress the exhaust air-fuel ratio from becoming lower than the target exhaust air-fuel ratio. Therefore, it is possible to suppress the release of the excess reducing agent (generally, fuel).
[0020]
In another invention, the control is performed such that the exhaust air-fuel ratio (generally, the stoichiometric region) at which the detection accuracy of the sensor is high is performed, and then the control is performed so that the target exhaust air-fuel ratio becomes the target. Thus, since the control for obtaining the target exhaust air-fuel ratio is performed from a state where the detection error detected by the sensor is small, the target exhaust air-fuel ratio can be accurately controlled. Therefore, it is possible to prevent the exhaust air-fuel ratio from becoming excessively lower than the target exhaust air-fuel ratio, and to suppress the release of excessive reducing agent (generally, fuel).
[0021]
Further, an exhaust gas purifying apparatus for an internal combustion engine according to another specific invention,
When the oxidizing component concentration of the exhaust purification section in the exhaust passage is high, the oxidizing exhaust substance contained in the exhaust gas is absorbed, and when the oxidizing component concentration of the exhaust purification section is low and the reducing atmosphere is used, Purifying means for purifying the oxidizing exhaust material by reducing while releasing the absorbed oxidizing exhaust material,
Supply means for supplying a reducing agent to the exhaust gas purification unit,
Detecting means for detecting the exhaust air-fuel ratio downstream of the exhaust purification section;
Feedback control for deriving a correction amount of the supplied reducing agent from a difference between the value detected by the detection unit and a target exhaust air-fuel ratio, and controlling a supply amount of the reducing agent supplied based on the correction amount. And an exhaust purification device for an internal combustion engine comprising:
When the exhaust gas is released and reduced from the purifying means,
The feedback control means performs control such that the exhaust air-fuel ratio becomes a target air-fuel ratio having a higher reducing component concentration than the stoichiometric air-fuel ratio after performing the control that the exhaust air-fuel ratio becomes stoichiometric.
[0022]
According to the configuration of the present invention, the target air-fuel ratio is generally controlled after stoichiometry with high detection accuracy of the detection means, so that the target exhaust air-fuel ratio can be accurately controlled. Therefore, it is possible to prevent the exhaust air-fuel ratio from becoming excessively lower than the target exhaust air-fuel ratio, and to suppress the release of excessive reducing agent (generally, fuel).
[0023]
Further, an exhaust gas purifying apparatus for an internal combustion engine according to another specific invention,
When the oxidizing component concentration of the exhaust purification section in the exhaust passage is high, the oxidizing exhaust substance contained in the exhaust gas is absorbed, and when the oxidizing component concentration of the exhaust purification section is low and the reducing atmosphere is used, Purifying means for purifying the oxidizing exhaust material by reducing while releasing the absorbed oxidizing exhaust material,
Supply means for supplying a reducing agent to the exhaust gas purification unit,
Detecting means for detecting the exhaust air-fuel ratio downstream of the exhaust purification section;
Feedback control for deriving a correction amount of the supplied reducing agent from a difference between the value detected by the detection unit and a target exhaust air-fuel ratio, and controlling a supply amount of the reducing agent supplied based on the correction amount. And an exhaust purification device for an internal combustion engine comprising:
When the exhaust gas is released and reduced from the purifying means,
The feedback control means, after performing the control that the exhaust air-fuel ratio is stoichiometric, while performing control such that the exhaust air-fuel ratio becomes a target air-fuel ratio having a higher reducing component concentration than the stoichiometric,
When performing the control to achieve the target air-fuel ratio, when the difference is X, the correction amount when the detection result by the detecting means is higher than the target exhaust air-fuel ratio is Y1, and the exhaust air-fuel ratio If the correction amount is lower than Y2, the relationship of Y2> Y1 is satisfied regardless of the value of X.
[0024]
According to the configuration of the present invention, the target air-fuel ratio is generally controlled after stoichiometry with high detection accuracy of the detection means, so that the target exhaust air-fuel ratio can be accurately controlled. Therefore, it is possible to prevent the exhaust air-fuel ratio from becoming excessively lower than the target exhaust air-fuel ratio. Moreover, when the detection result of the exhaust air-fuel ratio is lower than the target exhaust air-fuel ratio, the correction amount (feedback amount) of the supplied reducing agent is larger than when the detection result is higher. Thereby, it is possible to further suppress the exhaust air-fuel ratio from becoming lower than the target exhaust air-fuel ratio. Therefore, it is possible to suppress the release of the excess reducing agent (generally, fuel).
[0025]
Further, the feedback control means performs control such that the exhaust air-fuel ratio becomes stoichiometric, and after the stoichiometric stability determination period elapses, performs control such that the exhaust air-fuel ratio becomes a target air-fuel ratio having a higher reducing component concentration than stoichiometric. It is suitable.
[0026]
Further, the feedback control means performs the stoichiometric control when performing the control in which the exhaust air-fuel ratio becomes the target air-fuel ratio having a higher concentration of the reducing component than the stoichiometric after performing the control in which the exhaust air-fuel ratio becomes stoichiometric. It is preferable to reflect the correction amount at the time of derivation of the correction amount in the case of performing control to achieve the target air-fuel ratio.
[0027]
In this case, the accuracy of the target exhaust air-fuel ratio is further improved.
[0028]
Further, the control device of the present invention,
Receives a signal of exhaust air-fuel ratio data detected by the detection means downstream of the exhaust purification section where the exhaust is purified by the purification means for absorbing or releasing and reducing the oxidizing exhaust substance according to the surrounding atmosphere. Means,
Derivation of deriving a correction amount of a supply amount of a reducing agent supplied by a supply unit that supplies a reducing agent to the exhaust gas purification unit from a difference between the exhaust air-fuel ratio data received by the receiving unit and a target exhaust air-fuel ratio. Means,
Transmitting means for transmitting a signal instructing the supply means, so as to supply at a supply amount corrected by the correction amount derived by the derivation means,
A control device for performing feedback control of the supply amount of the reducing agent by the supply unit,
When exhaust gas is discharged and reduced from the purifying means, when the difference is X, the correction amount when the detection result by the detecting means is higher than a target exhaust air-fuel ratio is Y1, and the exhaust air-fuel ratio is If the correction amount is lower than Y2, the relationship of Y2> Y1 is satisfied regardless of the value of X.
[0029]
Further, the control device of another invention is:
Receives a signal of exhaust air-fuel ratio data detected by the detection means downstream of the exhaust purification section where the exhaust is purified by the purification means for absorbing or releasing and reducing the oxidizing exhaust substance according to the surrounding atmosphere. Means,
Derivation of deriving a correction amount of a supply amount of a reducing agent supplied by a supply unit that supplies a reducing agent to the exhaust gas purification unit from a difference between the exhaust air-fuel ratio data received by the receiving unit and a target exhaust air-fuel ratio. Means,
Transmitting means for transmitting a signal instructing the supply means, so as to supply at a supply amount corrected by the correction amount derived by the derivation means,
A control device for performing feedback control of the supply amount of the reducing agent by the supply unit,
When the exhaust gas is released and reduced from the purifying means,
After performing control to make the exhaust air-fuel ratio stoichiometric, control is performed so that the exhaust air-fuel ratio becomes a target air-fuel ratio having a higher concentration of reducing components than stoichiometric.
[0030]
Here, as a preferable example of the above-mentioned "purifying means", when the concentration of the oxidizing component is high, it absorbs the oxidizing exhaust material (especially NOx) contained in the exhaust gas, reduces the concentration of the oxidizing component and reduces the concentration of the oxidizing component. In the case of an atmosphere, a catalyst that reduces while releasing the oxidizing exhaust material that has been absorbed (hereinafter, referred to as a NOx storage reduction catalyst, abbreviated as NOx catalyst) may be used. In the case of a NOx catalyst, by arranging the catalyst in a part of the exhaust passage, the exhaust gas is purified in the process of passing the exhaust gas through the catalyst. Therefore, the portion where the catalyst is provided and the vicinity thereof serve as an exhaust gas purifying portion.
[0031]
The "supplying means" includes means for supplying a reducing agent to an exhaust passage of the internal combustion engine, means for increasing unburned fuel (functioning as a reducing agent) in exhaust gas discharged from the internal combustion engine through an exhaust passage, And combinations thereof. The latter can be suitably realized, for example, by performing so-called post injection. As the reducing agent, fuel can be suitably used.
[0032]
Further, the "detection means" includes a device capable of detecting an air-fuel ratio that can be converted into an exhaust air-fuel ratio or an exhaust air-fuel ratio can be estimated even when the exhaust air-fuel ratio itself cannot be detected. For example, as an example of a detecting means, an O which detects an oxygen concentration in exhaust gas is detected. ₂ Sensors.
[0033]
The “target exhaust air-fuel ratio” or “target air-fuel ratio” may be a value having no width (for example, 14.2), or a value having a width having a lower limit and an upper limit (for example, 14). .1 to 14.3). Further, the target exhaust air-fuel ratio may be fixed at all times, or may be appropriately changed according to environmental changes or the like. Here, the target exhaust air-fuel ratio is, for example, an exhaust air-fuel ratio required for eliminating SOx poisoning, and may be an exhaust air-fuel ratio at which unburned fuel is not excessively discharged.
[0034]
Regarding the “difference between the value detected by the detection means and the target exhaust air-fuel ratio”, when the latter air-fuel ratio has a wide value, the upper limit value or the lower limit value, or the median value thereof May be selected as appropriate.
[0035]
Further, as a method for the "feedback control means" to derive the correction amount, a method for obtaining the correction amount from a map or a method for obtaining the correction amount by an arithmetic expression can be adopted. For example, in the latter case, if the difference between the value detected by the detection means and the target exhaust air-fuel ratio is input data X and the output data that is the derived correction amount is Y, then Y = aX , Y = bX ² An arithmetic expression such as can be applied. Then, when the difference is X, the correction amount when the detection result by the detection means is higher than a target exhaust air-fuel ratio is Y1, and the correction amount when the detection result is lower than the exhaust air-fuel ratio is Y1. Assuming that Y2 satisfies the relationship of Y2> Y1 regardless of the value of X, the following are specific examples. That is, when Y1 = a1X and Y2 = a2X are adopted from the above equation, if a2> a1, the relationship of Y2> Y1 is satisfied regardless of the value of X. Similarly, Y = b1X ² , Y = b2X ² Is adopted, if b2> b1, the relationship of Y2> Y1 is satisfied regardless of the value of X.
[0036]
In addition, the above-mentioned "control for making the exhaust air-fuel ratio stoichiometric" means control for positively making the exhaust air-fuel ratio stoichiometric, ₂ It does not include the storage effect. For example, it refers to control for positively stabilizing the exhaust air-fuel ratio in the range of 14.6 to 14.8.
[0037]
Further, the “stoichiometric stability determination period” means a period until it is determined that the stoichiometric state is stable. This period varies as appropriate according to various configurations, environments, and the like, and a value corresponding to various configurations may be determined. Note that, for this period, a value fixed in advance may be used, a value that fluctuates depending on the environment, deterioration over time, or the like may be used, or may be estimated from a detection result of the exhaust air-fuel ratio. .
[0038]
It should be noted that the above configurations can be employed in combination as much as possible.
[0039]
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention thereto unless otherwise specified. Absent. In the following description, an embodiment in which the exhaust gas purification device for an internal combustion engine is applied to a diesel engine system will be described.
[0040]
(First Embodiment)
With reference to FIGS. 1 to 5, an exhaust gas purifying apparatus for an internal combustion engine according to a first embodiment of the present invention will be described.
[0041]
[Structure and function of engine system]
FIG. 1 is a schematic configuration diagram of an exhaust gas purification device for an internal combustion engine according to an embodiment of the present invention. As shown in FIG. 1, a diesel engine system (hereinafter, referred to as an engine) 1 as an internal combustion engine according to the present embodiment includes a fuel supply system 10, a combustion chamber 20, an intake system 30, and an exhaust system 40 as main components. It is an in-line four-cylinder diesel engine system configured.
[0042]
First, the fuel supply system 10 includes a supply pump 11, a common rail 12, a fuel injection valve 13, a shutoff valve 14, a metering valve 16, a reducing agent addition valve 17, an engine fuel passage P1, an addition fuel passage P2, and the like.
[0043]
The supply pump 11 increases the pressure of the fuel pumped from a fuel tank (not shown) and supplies the fuel to the common rail 12 via the engine fuel passage P1. The common rail 12 has a function as a pressure accumulating chamber that holds (accumulates) the high-pressure fuel supplied from the supply pump 11 at a predetermined pressure, and distributes the accumulated fuel to the fuel injection valves 13. The fuel injection valve 13 is an electromagnetic valve provided with an electromagnetic solenoid (not shown) therein, and opens the valve appropriately to inject and supply fuel into the combustion chamber 20.
[0044]
The supply pump 11 supplies a part of the fuel pumped from the fuel tank to the reducing agent addition valve 17 via the additional fuel passage P2. In the added fuel passage P2, a shutoff valve 14 and a metering valve 16 are sequentially provided from the supply pump 11 toward the reducing agent addition valve 17. The shutoff valve 14 has a function of shutting off the fuel supply by shutting off the additional fuel passage P2 in an emergency. The metering valve 16 has a function of controlling the pressure (fuel pressure) PG of the fuel supplied to the reducing agent addition valve 17. The reducing agent addition valve 17 is an electromagnetic valve provided with an electromagnetic solenoid (not shown) inside the same as the fuel injection valve 13. The reducing agent addition valve 17 in the present embodiment adds and supplies a fuel functioning as a reducing agent to the upstream side of the catalyst casing 42 of the exhaust system 40 at an appropriate amount and at an appropriate timing.
[0045]
The intake system 30 includes a passage (intake passage) for intake air supplied into each combustion chamber 20. On the other hand, the exhaust system 40 includes a passage (exhaust passage) for exhaust gas discharged from each combustion chamber 20.
[0046]
Further, the engine 1 is provided with a supercharger (hereinafter, referred to as a turbocharger) 50. The turbocharger 50 includes a pair of rotating bodies connected via a shaft 51, that is, a turbine wheel 52 and a compressor wheel 53. The turbine wheel 52 is exposed to exhaust gas in the exhaust system 40, and the compressor wheel 53 is exposed to intake air in the intake system 30. The turbocharger 50 having such a configuration performs so-called supercharging such that the compressor wheel 53 is rotated by using the exhaust flow (exhaust pressure) received by the turbine wheel 52 to increase the intake pressure.
[0047]
In the intake system 30, an intercooler 31 provided in the turbocharger 50 forcibly cools the intake air whose temperature has been increased by supercharging. The throttle valve 32 provided further downstream than the intercooler 31 is an electronically controlled opening / closing valve whose opening can be continuously adjusted. The throttle valve 32 has a function of changing the flow area of the intake air under predetermined conditions and adjusting the supply amount (flow rate) of the intake air.
[0048]
Further, the engine 1 is provided with an exhaust gas recirculation passage (hereinafter, referred to as an EGR passage) 60 that bypasses the intake system 30 on the upstream side of the combustion chamber 20 and the exhaust system 40 on the downstream side. The EGR passage 60 has a function of appropriately returning a part of the exhaust gas to the intake system 30. The EGR passage 60 is provided with an EGR valve 61 which is opened and closed in a stepless manner by electronic control and which can freely adjust the flow rate of exhaust gas (EGR gas) flowing through the EGR passage 60, and exhaust gas which passes (recirculates) through the EGR passage 60. An EGR cooler 62 for cooling is provided.
[0049]
Further, in the exhaust system 40, a catalyst casing 42 containing an occlusion-reduction type NOx catalyst (hereinafter, simply referred to as a NOx catalyst) is provided downstream of a communication portion between the exhaust system 40 and the EGR passage 60.
[0050]
In addition, various sensors are attached to each part of the engine 1, and output a signal relating to an environmental condition of the part and an operation state of the engine 1.
[0051]
That is, the rail pressure sensor 70 outputs a detection signal corresponding to the pressure of the fuel stored in the common rail 12. The fuel pressure sensor 71 outputs a detection signal corresponding to the pressure (fuel pressure) PG of the fuel introduced into the reducing agent addition valve 17 via the metering valve 16 among the fuel flowing through the addition fuel passage P2. The air flow meter 72 outputs a detection signal corresponding to the flow rate (intake amount) GN of air (intake air) introduced into the intake system 30. The exhaust gas temperature sensor 73 is attached to the exhaust gas inflow portion of the catalyst casing 42 in the exhaust system 40, and outputs a detection signal corresponding to the temperature of the exhaust gas (exhaust gas temperature) TEX at the portion.
[0052]
An air-fuel ratio (A / F) sensor (O ₂ The sensor 74 outputs a detection signal that continuously changes in accordance with the oxygen concentration in the exhaust downstream of the catalyst casing 42 of the exhaust system 40. Here, the air-fuel ratio sensor 74 in the present embodiment employs a general sensor, and as described with reference to FIG. 12, the detection accuracy is high near the stoichiometric. As the distance increases, the detection accuracy decreases.
[0053]
The NOx sensor 75 outputs a detection signal that continuously changes in accordance with the NOx concentration in the exhaust downstream of the catalyst casing 42 of the exhaust system 40.
[0054]
The accelerator position sensor 76 is attached to an accelerator pedal (not shown) of the engine 1 and outputs a detection signal corresponding to the depression amount ACC of the pedal. The crank angle sensor 77 outputs a detection signal (pulse) every time the output shaft (crankshaft) of the engine 1 rotates by a certain angle. These sensors 70 to 77 are electrically connected to an electronic control unit (hereinafter, referred to as an ECU) 90.
[0055]
The ECU 90 as a control device or control means includes a central processing unit (hereinafter, referred to as CPU) 91, a read-only memory (hereinafter, referred to as ROM) 92, a random access memory (hereinafter, referred to as RAM) 93, a backup RAM 94, and A timer counter 95 and the like are provided.
[0056]
The ECU 90 includes a CPU 91, a ROM 92, a RAM 93, a backup RAM 94, a timer counter 95, and the like, an external input circuit 96 including an A / D converter, and an external output circuit 97 connected by a bidirectional bus 98. Logic operation circuit.
[0057]
The ECU 90 configured as described above inputs the detection signals of the various sensors via an external input circuit, and controls the opening / closing operation of the fuel injection valve 13 based on these signals, adjusts the opening of the EGR valve 61, Alternatively, various controls relating to the operating state of the engine 1, such as adjustment of the opening of the throttle valve 32, are performed.
[0058]
[Structure and function of catalyst casing]
Next, among the components of the engine 1 described above, the structure and function of the catalyst casing 42 provided in the exhaust system 40 will be described in detail.
[0059]
The catalyst casing 42 contains a NOx storage reduction catalyst (hereinafter, referred to as a NOx catalyst).
[0060]
The NOx catalyst is configured by supporting a material that functions as a NOx absorbent and a material that functions as an oxidation catalyst on the surface of a carrier. Here, as the carrier, for example, alumina (Al ₂ O ₃ ) As a main material (a particulate filter). Materials that function as NOx absorbents include, for example, alkali metals such as potassium (K), sodium (Na), lithium (Li) and cesium Cs, alkaline earth metals such as barium Ba and calcium Ca, and lanthanum (La). ), Yttrium (Y) and the like. In addition, examples of a material that functions as an oxidation catalyst (a noble metal catalyst) include a noble metal such as platinum Pt.
[0061]
The NOx catalyst has a characteristic of absorbing NOx under the condition that the exhaust gas contains a large amount of oxidizing components (oxidizing atmosphere) and releasing NOx under the condition of a low oxidizing component in the exhaust gas. Further, when NOx is released into the exhaust gas, under the condition where HC and CO are present in the exhaust gas (reducing atmosphere), the noble metal catalyst promotes the oxidation reaction of these HC and CO, thereby converting NOx into an oxidizing component. An oxidation-reduction reaction using HC and CO as reducing components occurs between the two. That is, HC and CO are converted to CO ₂ And H ₂ Oxidized to O and NOx becomes N ₂ Is reduced to
[0062]
On the other hand, when the NOx catalyst absorbs a predetermined limit amount of NOx, it no longer absorbs NOx.
[0063]
Therefore, in the engine 1, before the NOx absorption amount by the NOx catalyst housed in the catalyst casing 42 reaches the limit amount, the reducing agent addition valve 17 moves the reducing agent (in the present embodiment, upstream of the catalyst casing 42 in the exhaust passage). Fuel). Thereby, the control of releasing and reducing and purifying the NOx absorbed by the NOx catalyst and restoring the NOx storage capacity of the NOx catalyst is repeated at predetermined intervals.
[0064]
Further, the particulate filter serving as a carrier for the NOx absorbent and the noble metal catalyst purifies fine particles such as soot and harmful components such as NOx contained in exhaust gas based on the following mechanism.
[0065]
As described above, the NOx catalyst repeatedly performs the absorption, release, and purification of NOx in accordance with the concentration of the oxidizing component and the amount of the reducing component in the exhaust gas by the cooperation of the NOx absorbent and the noble metal catalyst which are the components. It is on the street. On the other hand, the NOx catalyst has a characteristic of secondary generation of active oxygen in the process of purifying NOx. When the exhaust gas passes through the particulate filter, fine particles such as soot contained in the exhaust gas are captured by the structure (porous material). Here, since the active oxygen generated by the NOx catalyst has extremely high reactivity (activity) as an oxidizing agent, of the captured fine particles, the fine particles deposited on the surface of or near the NOx catalyst are the active oxygen. And react quickly (without luminous flame) to be purified.
[0066]
[Overview of fuel injection control]
The ECU 90 performs the fuel injection control based on the operation state of the engine 1 that is grasped from the detection signals of the various sensors. In the present embodiment, the fuel injection control refers to the execution of fuel injection into each combustion chamber 20 through each fuel injection valve 13 by setting parameters such as a fuel injection amount Q, an injection timing, and an injection pattern. It refers to a series of processing for executing the operation of opening and closing the individual fuel injection valves 13 based on the parameters set.
[0067]
The ECU 90 repeatedly performs such a series of processes at predetermined time intervals during the operation of the engine 1. The fuel injection amount Q and the injection timing are basically set in advance based on the depression amount ACC to the accelerator pedal and the engine speed NE (a parameter that can be calculated based on the pulse signal of the crank angle sensor). The determination is made with reference to a map (not shown).
[0068]
Further, regarding the setting of the fuel injection pattern, the ECU 90 obtains the engine output by performing the fuel injection near the compression top dead center as the main injection for each cylinder, and also obtains the fuel injection prior to the main injection (hereinafter referred to as pilot injection). ) And a fuel injection subsequent to the main injection (hereinafter, referred to as post injection) is performed for the selected cylinder at a time appropriately selected as a sub-injection.
[0069]
[Pilot injection]
In a diesel engine, in general, at the end of the compression stroke, the temperature in the combustion chamber reaches a temperature that induces self-ignition of fuel. In particular, when the operating state of the engine is in the middle to high load range, when the fuel supplied for combustion is injected and supplied collectively into the combustion chamber, this fuel explosively burns with noise. Therefore, by executing the pilot injection, the fuel supplied prior to the main injection becomes a heat source (or a pilot flame), and the heat source gradually expands in the combustion chamber to reach combustion. The combustion state of the fuel becomes relatively slow, and the ignition delay time is shortened. For this reason, noise accompanying engine operation is reduced, and the amount of NOx in exhaust gas is also reduced.
[0070]
[Post injection]
The fuel supplied into the combustion chamber 20 by the post injection is reformed into light HC in the combustion gas, and is discharged to the exhaust system 40. That is, light HC that functions as a reducing agent is added to the exhaust system 40 through post-injection, thereby increasing the concentration of reducing components in the exhaust. The reducing component added to the exhaust system 40 reacts with the NOx released from the NOx catalyst and other oxidizing components contained in the exhaust via the NOx catalyst in the catalyst casing 42. The reaction heat generated at this time raises the bed temperature of the NOx catalyst.
[0071]
[Overview of EGR control]
The ECU 90 performs EGR control based on the operating state of the engine 1 that is grasped from detection signals of various sensors. In the present embodiment, the EGR control refers to the operation of an electronically controlled EGR valve 61 provided in the EGR passage so that the gas flows through the EGR passage, in other words, is returned from the exhaust system 40 to the intake system 30. This refers to the process of adjusting the flow rate of exhaust gas.
[0072]
A target opening amount of the EGR valve 61 (hereinafter, referred to as a target opening amount) is basically based on an operating state such as a load and a rotation speed of the engine 1 and refers to a preset map (not shown). Is determined. The ECU 90 updates the target opening amount at predetermined time intervals during the operation of the engine 1 and sequentially drives the EGR valve 61 so that the actual opening amount of the EGR valve 61 matches the updated target opening amount. Outputs a command signal to the circuit.
[0073]
[Low temperature combustion based on EGR control]
When a part of the exhaust gas is recirculated to the intake system 30 by such a series of processes, the amount of the inert gas component in the air-fuel mixture supplied to the engine combustion increases according to the recirculated amount. As a result, under predetermined conditions, the amount of NOx in the exhaust gas is reduced, and smoke is hardly generated.
[0074]
As the low-temperature combustion is performed, the amount of unburned HC (reducing component) in the exhaust gas increases. As a result, light HC functioning as a reducing agent is added to the exhaust system 40 and the concentration of the reducing component in the exhaust gas is increased. Will be increased.
[0075]
(Fuel addition control)
By directly adding the fuel (reducing agent) to the exhaust system 40 through the reducing agent addition valve 17, the concentration of the reducing component in the exhaust gas is increased similarly to the post injection, and as a result, the bed temperature of the NOx catalyst is reduced. Can be raised. The fuel added by the reducing agent addition valve 17 tends to be unevenly distributed while maintaining a higher polymer state in the exhaust gas, as compared with the fuel added by the post injection. In addition, in the fuel addition by the reducing agent addition valve 17, the amount of fuel that can be added at once and the degree of freedom of the addition timing are larger than in the case of post injection.
[0076]
[Overview of SOx poisoning recovery control]
The pilot injection, post-injection, low-temperature combustion, and fuel addition control commonly act to increase the amount of reducing components in the exhaust gas. Therefore, by repeatedly performing any control at predetermined intervals, the NOx catalyst The NOx absorbed in the NOx can be released, reduced and purified, and the NOx absorbing ability of the NOx catalyst can be restored.
[0077]
The ECU 90 raises the temperature of the NOx catalyst to a predetermined temperature range (for example, about 600 to 700 ° C.) in order to remove SOx and the like that gradually accumulate on the NOx catalyst as the engine 1 continues to operate. Then, control for supplying a large amount of reducing components to the catalyst (hereinafter referred to as SOx poisoning recovery control) is performed. By performing the SOx poisoning recovery control, a large amount of the reducing component supplied to the NOx catalyst decomposes and removes the SOx deposited on the catalyst under a high temperature condition. Here, as part of the SOx poisoning recovery control, the ECU 90 performs any of the above-described pilot injection, post-injection, low-temperature combustion and fuel addition control, or a combination of two or more of these to raise the temperature of the NOx catalyst to a predetermined temperature. Or implement. In addition, in the present embodiment, a larger amount of the fuel, which is a reducing component than the amount required for release and reduction purification of NOx absorbed by the NOx catalyst, is supplied to the exhaust system (exhaust passage) through the reducing agent addition valve 17. The control for supplying to the upstream of the NOx catalyst is performed. Thereby, SOx poisoning is eliminated.
[0078]
[Specific execution procedure of SOx poisoning recovery control]
In particular, a specific execution procedure of the SOx poisoning recovery control will be described with reference to FIGS. FIG. 2 is a diagram showing how the exhaust air-fuel ratio varies with elapsed time when performing SOx poisoning recovery control. FIG. 3 is a partially enlarged view of FIG. 2 (an enlarged view of a portion indicated by a circle in FIG. 2), and shows an example of a change in the exhaust air-fuel ratio. FIG. 4 is a flowchart showing a schematic procedure of the SOx poisoning recovery control. FIG. 5 is a flowchart showing a schematic procedure of the addition control in FIG.
[0079]
In order to eliminate SOx poisoning, it is necessary to set the exhaust air-fuel ratio to a rich air-fuel ratio (air-fuel ratio having a reducing component concentration higher than stoichiometric ratio) in a predetermined temperature range as described above. In this case, it is preferable to perform control (rich spike control) to make the exhaust air-fuel ratio intermittently rich air-fuel ratio, and this embodiment also employs this control. The reason that the exhaust air-fuel ratio is intermittently set to the rich air-fuel ratio is that although the exhaust air-fuel ratio is continuously changed to the air-fuel ratio, SOx can be purified, but the catalyst bed temperature excessively rises due to reaction heat when SOx is purified. This may cause thermal degradation.
[0080]
In the upper part of FIG. 2, the ON / OFF timing of the fuel addition command signal with respect to the elapsed time is shown. B1 indicates a period during which the addition of fuel is suspended (pause period). Then, as shown in the lower part of FIG. 2, the addition period substantially corresponds to a period in which the atmosphere becomes rich (reducing atmosphere), and the pause period substantially corresponds to a period in which the atmosphere becomes lean (oxidizing atmosphere). In the present embodiment, the fuel addition command signal during the addition period is transmitted as a pulse signal. Thus, by appropriately adjusting the pulse width, fine adjustment of the fuel supply amount can be easily performed, and fine feedback control can be performed.
[0081]
Next, the procedure of the SOx poisoning recovery control will be described with reference to the flowchart of FIG. When the conditions for performing the SOx poisoning recovery control are satisfied, the SOx poisoning recovery control is performed according to the flowchart shown in FIG. The determination as to whether or not the condition for performing the SOx poisoning recovery control is satisfied is performed according to another flowchart (routine). When the condition is satisfied, the operation illustrated in the flowchart illustrated in FIG. 4 is performed. Whether the condition for performing the SOx poisoning recovery control is satisfied is determined by assuming that the concentration of the SOx component in the fuel is constant, estimating the amount of SOx deposited on the NOx catalyst from the fuel consumption, or determining the NOx It can be performed by detecting the purification rate of the NOx catalyst from the detection result by the sensor.
[0082]
When the SOx poisoning recovery control is started, first, conditions for adding a fuel as a reducing agent are derived (S100). Specifically, an intermittent rich condition necessary for appropriately performing SOx poisoning recovery is derived from the current operating state of the engine. The intermittent rich conditions mainly include a fuel addition amount, an addition period, and a pause period. More specifically, the addition period, a pulse width during the period, an ON / OFF cycle, an ON / OFF count, and a pause period And the number of repetitions of the addition period and the suspension period (corresponding to the entire period in which the SOx poisoning recovery control is performed (SOx poisoning recovery control period)). The suspension period is determined by estimating how many seconds the addition should be suspended to keep the catalyst bed temperature at the target temperature with respect to the previous addition amount.
[0083]
Next, it is determined according to the derived condition whether or not the current period is the addition period (S200). If during the addition period, addition control is performed (S300). Then, the addition control operation is repeated as long as it is during the addition period (S200, S300). If it is determined in S200 that the fuel is not being added, the fuel addition is stopped (S400). Then, according to the derived condition, it is determined whether or not the current period is the suspension period (S500). If it is a suspension period, it is monitored whether or not the suspension period is present until the suspension period ends (S500).
[0084]
If it is determined in S500 that it is not the suspension period, it is determined whether or not the current SOx poisoning recovery control period is in accordance with the derived condition (S600). If it is determined that the period is not the SOx poisoning recovery control period, the SOx poisoning recovery control ends. On the other hand, if it is determined in S600 that the period is the SOx poisoning recovery control period, the process returns to S200 and repeats the same procedure. However, if it is determined in S600 that the period is the SOx poisoning recovery control period, the process may return to S100 and repeat the derivation of the new addition condition.
[0085]
As described above, based on the derived addition conditions, the addition period in which the addition control is sequentially performed and the suspension period in which the addition is stopped are repeated until the SOx poisoning recovery control period ends. Thus, the intermittent rich control based on the derived addition condition is performed.
[0086]
Next, the procedure of the addition control (S300) will be described with reference to the flowchart shown in FIG.
[0087]
When the addition control is started, it is determined whether or not the addition flag is currently ON (S301). That is, it is determined whether or not the addition is currently being performed. If the addition flag is not ON, the addition flag is turned ON (S302). That is, the fuel addition command signal is turned on (transmitted) to start the fuel addition. After starting the fuel addition, O ₂ Monitoring is performed until the storage ends (S303). Where O ₂ The determination as to whether or not the storage has been completed can be made, for example, by monitoring the fluctuation (slope) of the detection value detected by the air-fuel ratio sensor 74. That is, if a state where the air-fuel ratio does not fluctuate near the stoichiometric state appears, ₂ It is determined to be storage, and when it changes, ₂ It can be determined that the storage has been completed. It can also be estimated from the integrated intake air amount. Or O ₂ If the time until the end of the storage is constant to some extent, the O ₂ It is also possible to determine that the storage has been completed.
[0088]
O ₂ When the storage is completed, it is determined whether or not the exhaust air-fuel ratio detected by the air-fuel ratio sensor 74 is within a target range (for example, the air-fuel ratio 14.1 to 14.3) (S304). If it is determined in S301 that the addition flag is ON, the process jumps to S304. Because, if it is determined in S301 that the addition flag is ON, the flow shown in FIG. 5 has already been repeated one or more times. ₂ This is because the storage has been completed. Here, the target range of the exhaust air-fuel ratio in the present embodiment is determined by the air-fuel ratio that can effectively eliminate SOx poisoning, does not discharge excessive unburned fuel, and does not generate white smoke.
[0089]
Then, if it is determined in S304 that the exhaust air-fuel ratio detected by the air-fuel ratio sensor 74 is within the target range, the addition control is terminated without correcting the fuel addition amount (S305).
[0090]
On the other hand, if it is determined in step S304 that the exhaust air-fuel ratio detected by the air-fuel ratio sensor 74 is not within the target range, the detected value is determined by comparing the target value with the oxygen concentration of the target range. It is determined whether it is on the high side (S306). When it is determined that the oxygen concentration is on the high side (lean side), the process of the correction A is performed (S307), and the addition control is ended. On the other hand, when it is determined that the oxygen concentration is on the low side (rich side), the process of the correction B is performed (S308), and the addition control is ended.
[0091]
Here, the processing of the correction A and the processing of the correction B will be described in detail. In the present embodiment, in order to keep the exhaust air-fuel ratio within the target range, a so-called feedback control is performed in which the exhaust air-fuel ratio is detected and the fuel addition amount is sequentially corrected based on the detected data. I have. That is, since the exhaust air-fuel ratio detected by the air-fuel ratio sensor 74 is not within the target range, the above correction processing corrects the fuel supply amount so that the exhaust air-fuel ratio falls within the target range. It is.
[0092]
In the correction process, a difference between the detected exhaust air-fuel ratio and a target exhaust air-fuel ratio (for example, the intermediate value of the target range, 14.2 in the above specific example) is obtained, and the correction amount of the supplied fuel is determined from the difference. I try to guide. Therefore, the correction processing in the present embodiment uses a process of deriving (outputting) a correction amount by inputting a value (input data) detected by the air-fuel ratio sensor 74. Specific examples of this process include one using a map and one using an arithmetic expression. In the former case, for example, a predetermined map is stored in advance in a storage device (for example, the ROM 92) provided in the ECU 90, and a correction amount serving as output data can be selected from input data. In the latter case, for example, a predetermined arithmetic expression is stored in advance in a storage device (for example, the ROM 92) provided in the ECU 90, and input data is substituted into the arithmetic expression to calculate a correction amount serving as output data. be able to.
[0093]
Then, in the case of the correction A, a process of adding the derived correction amount to the supply amount up to that time and performing a process to approach the target exhaust air-fuel ratio is performed. That is, a command signal is transmitted to add fuel at the supply amount obtained by adding the correction amount. On the other hand, in the case of performing the correction B, a process of subtracting the derived correction amount from the supplied amount up to that time to approach the target exhaust air-fuel ratio is performed. That is, a command signal is transmitted to add fuel at the supply amount obtained by subtracting the correction amount.
[0094]
Here, in the present embodiment, the derivation process is different for correction A and correction B. That is, in the above specific example, the correction A and the correction B use different maps or arithmetic expressions. Therefore, the storage device provided in the ECU 90 stores the map or the arithmetic expression used for the correction A and the map or the arithmetic expression used for the correction B, and the map or the arithmetic expression to be used depends on which correction is performed. It is necessary to select an arithmetic expression as appropriate.
[0095]
In this embodiment, in order to prevent the exhaust air-fuel ratio from being smaller than the target exhaust air-fuel ratio, the correction amount is larger in the correction B than in the correction A. Specifically, for example, let X be the difference between the detected exhaust air-fuel ratio and the target exhaust air-fuel ratio. When this X is input data, the correction amount (output data) Y1 derived in the process of the correction A and the correction amount Y2 derived in the process of the correction B can be any value of X. It is set so that the relationship of Y2> Y1 is always satisfied.
[0096]
As described above, in the present embodiment, when the exhaust air-fuel ratio is lower and higher than the target exhaust air-fuel ratio, the former performs the feedback control in which the correction amount is larger than the target exhaust air-fuel ratio. This makes it possible to quickly exit from a situation where the exhaust air-fuel ratio is lower than the target exhaust air-fuel ratio. Further, even when the fuel addition amount is corrected by the feedback control in a situation where the exhaust air-fuel ratio is higher than the target exhaust air-fuel ratio, the deviation from the target exhaust air-fuel ratio to a side lower than the target exhaust air-fuel ratio can be prevented. Absent. From these facts, in the present embodiment, it is possible to prevent the exhaust air-fuel ratio from becoming excessively lower than the target exhaust air-fuel ratio. Therefore, it is possible to suppress the discharge of the excess unburned fuel component, and it is possible to suppress the generation of white smoke and the generation of odor.
[0097]
An example of a change in the exhaust air-fuel ratio when the above-described feedback control is performed will be described along the procedure of the feedback control with reference to FIGS.
[0098]
When the SOx poisoning recovery control is started, as shown in FIG. 4, the conditions for adding the reducing agent are derived (S100). Specifically, as shown in the upper part of FIG. 2, the ON / OFF timing of the fuel addition command signal is derived. In an actual product, control is performed in which an addition period and a pause period appear alternately many times. Here, for the sake of simplicity, it is assumed that the addition period is twice and a pause period appears once during that period. An example will be described. Further, in an actual product, feedback control (correction) is performed many times during one addition period. However, here, for simplification of description, a case where only three times are performed will be described as an example. Note that the period indicated by C in FIG. ₂ This is a storage period, and a period indicated by D indicates a period in which feedback control is performed. Here, the period during which the feedback control is performed is, specifically, during the addition period and when O ₂ This corresponds to a period after the end of the storage period.
[0099]
When the addition condition is derived, it is determined whether or not it is during the addition period (S200). Since the addition period (A0 in FIG. 2) is selected here, the addition control operation is performed (S300). In the addition control, first, it is determined whether or not the addition flag is ON (S301). Here, fuel addition has not been performed yet, and the addition flag is OFF. Therefore, the addition flag is turned ON and the addition of fuel is started (S302). Then, the NOx catalyst ₂ Due to the storage effect, the exhaust air-fuel ratio is O ₂ The storage state is established (the period indicated by C in FIG. 3).
[0100]
O ₂ When the storage is completed (S303), it is determined whether or not the exhaust air-fuel ratio detected by the air-fuel ratio sensor 74 is within the range of the target air-fuel ratio (S304). Here, the determination is performed at the timing of D1 shown in FIG. 3, and the detected exhaust air-fuel ratio is lower than the target air-fuel ratio region (the oxygen concentration is low). (S306, S308), the addition control ends. In the case of the process using the correction B, since the correction amount is large as described above, control is performed to relatively rapidly increase the exhaust air-fuel ratio as shown in FIG.
[0101]
Thereafter, it is determined again whether or not it is the addition period (S200). In this case, since the addition period is still in progress, the addition control is performed again (S300). When the addition control is started, it is determined whether or not the addition flag is ON (S301). Since the addition flag is already ON this time, the process jumps to S304 and is detected by the air-fuel ratio sensor 74. It is determined whether the exhaust air-fuel ratio is within the range of the target air-fuel ratio. Here, the determination is performed at the timing of D2 shown in FIG. 3, and the detected exhaust air-fuel ratio is higher than the target air-fuel ratio region (the oxygen concentration is high). (S306, S307), the addition control ends. In the case of the process using the correction A, since the correction amount is small as described above, control is performed to relatively slowly lower the exhaust air-fuel ratio as shown in FIG.
[0102]
Thereafter, it is determined again whether or not it is the addition period (S200). Also in this case, since the addition period is still in progress, the addition control is performed again (S300). When the addition control is started, it is determined whether or not the addition flag is ON (S301). Since the addition flag is already ON this time, the process jumps to S304 and is detected by the air-fuel ratio sensor 74. It is determined whether the exhaust air-fuel ratio is within the range of the target air-fuel ratio. Here, the determination is performed at the timing of D3 shown in FIG. 3, and the detected exhaust air-fuel ratio is in the target air-fuel ratio range, so that the correction process is not performed (S305), and the addition control ends. Therefore, as shown in FIG. 3, the exhaust air-fuel ratio does not change much thereafter.
[0103]
Thereafter, it is determined again whether or not it is the addition period (S200). This time is the timing of E shown in FIG. 3 and the addition period has passed, so the addition of fuel is stopped (S400), and the operation shifts to the stop period (the period indicated by B1 in FIG. 2). Then, it is monitored whether or not it is a suspension period (S500), and after the suspension period, it is determined whether or not it is a SOx poisoning recovery control period (S600). In this case, since it is the period indicated by A1 shown in FIG. 2 and is still within the control period, it is determined again whether or not it is the addition period (S200). Here, since it is the addition period (A1), the addition control (S300) is started.
[0104]
Then, feedback control is performed in the same manner as in the case of the addition period indicated by A0, and after the A1 period ends, fuel addition is stopped (S400). After the suspension period ends, the SOx poisoning recovery control period starts. It is determined whether or not there is (S600). Here, since the SOx poisoning recovery control period has passed, the SOx poisoning recovery control ends.
[0105]
As described above, in the present embodiment, it is possible to suppress the exhaust air-fuel ratio from becoming excessively lower than the target exhaust air-fuel ratio, and to suppress the discharge of the excessive unburned fuel component. The generation of white smoke and the generation of odor can be suppressed.
[0106]
(Second embodiment)
6 to 9 show a second embodiment. In this embodiment, an embodiment in which the specific execution procedure of the SOx poisoning recovery control is different from that of the first embodiment will be described. The other configuration and operation, such as the configuration of the internal combustion engine and the outline of the SOx poisoning recovery control, are the same as those of the first embodiment, and thus the description thereof is omitted.
[0107]
[Specific execution procedure of SOx poisoning recovery control]
FIG. 6 is a flowchart showing a schematic procedure of the SOx poisoning recovery control. FIG. 7 is a flowchart showing a schematic procedure of the addition control in FIG. FIG. 8 is a flowchart showing a schematic procedure of the stoichiometric control in FIG. FIG. 9 is a flowchart showing a schematic procedure of the target control in FIG.
[0108]
Also in the present embodiment, similarly to the case of the first embodiment, a control (rich spike control) for intermittently setting the exhaust air-fuel ratio to a rich air-fuel ratio is performed. Also in the present embodiment, as in the case of the first embodiment, the fuel addition command signal in the addition period is transmitted as a pulse signal. The details thereof are as described above, and the description thereof will be omitted.
[0109]
The procedure of the SOx poisoning recovery control will be described with reference to the flowchart of FIG. When the conditions for performing the SOx poisoning recovery control are satisfied, the SOx poisoning recovery control is performed according to the flowchart shown in FIG. The conditions for performing the SOx poisoning recovery control are as described above, and thus the description thereof is omitted. When the SOx poisoning recovery control is started, first, conditions for adding a fuel as a reducing agent are derived (S150). The conditions for addition are the same as those described in the first embodiment, and a description thereof will be omitted.
[0110]
Next, it is determined whether or not it is the current addition period according to the derived condition (S250). If during the addition period, addition control is performed (S350). Then, the fuel addition is stopped during the addition period or after the addition control ends (S450). Then, according to the derived condition, it is determined whether or not the current period is the suspension period (S550). If it is a suspension period, it is monitored whether or not the suspension period is present until the suspension period ends (S550).
[0111]
If it is determined in S550 that the current period is not the suspension period, it is determined whether or not the current period is the SOx poisoning recovery control period according to the derived condition (S650). If it is determined that the period is not the SOx poisoning recovery control period, the SOx poisoning recovery control ends. On the other hand, if it is determined in S650 that the period is the SOx poisoning recovery control period, the process returns to S250 and repeats the same procedure. However, if it is determined in S650 that the period is the SOx poisoning recovery control period, the process may return to S150 and repeat the derivation of the new addition condition.
[0112]
As described above, based on the derived addition conditions, the addition period in which the addition control is sequentially performed and the suspension period in which the addition is stopped are repeated until the SOx poisoning recovery control period ends. Thus, the intermittent rich control based on the derived addition condition is performed.
[0113]
Next, the procedure of the addition control (S350) will be described with reference to the flowchart shown in FIG.
[0114]
When the addition control starts, the addition flag is turned ON (S360). That is, the fuel addition command signal is turned on (transmitted) to start the fuel addition. After starting the fuel addition, O ₂ Monitoring is performed until the storage is completed (S370). Where O ₂ The determination as to whether or not the storage has been completed has already been described in the first embodiment. ₂ Since the stoichiometric control is performed after the storage is completed (S380), if the determination using the air-fuel ratio sensor 74 is performed, ₂ It is difficult to determine whether the storage is due to stoichiometric control. Therefore, in the present embodiment, O ₂ Whether storage is completed or not is determined by a certain time after the start of addition. ₂ It is preferable to determine that the storage has been completed. This fixed time is appropriately set according to various configurations such as the characteristics of the NOx catalyst.
[0115]
O ₂ When the storage is completed, stoichiometric control is performed as described above (S380). This stoichiometric control ₂ Unlike storage, it actively controls for stoichiometry. Here, feedback control for stoichiometric aim is performed until the stoichiometric state becomes stable. Thereafter, control is performed so that the exhaust air-fuel ratio becomes a target air-fuel ratio lower than the stoichiometric ratio (higher reducing component concentration) (S390), and the addition control ends.
[0116]
Next, the procedure of the stoichiometric control (S380) will be described with reference to the flowchart shown in FIG. Here, O ₂ It is sufficient that the exhaust air-fuel ratio stabilizes in the stoichiometric state after the storage ends, and the flowchart shown in FIG. 8 is merely an example of control for stabilizing the exhaust air-fuel ratio to the stoichiometric state.
[0117]
When the stoichiometric control starts, it is determined whether or not the exhaust air-fuel ratio detected by the air-fuel ratio sensor 74 is within a target stoichiometric range (for example, 14.6 to 14.8) (S381). If it is not within the target stoichiometric range, the addition amount is corrected, that is, feedback control is performed to make the target stoichiometric range (S382). When the exhaust air-fuel ratio detected in S381 is within the target stoichiometric range, one is added to the counter value of a counter (not shown) (provided in the ECU 90) (S383). Then, it is determined whether or not the total of the counter values is larger than the threshold (S384). If it is not larger than the threshold, the process returns to S381, and the same procedure is repeated again. If it is determined in step S384 that the value is larger than the threshold value, the stoichiometric control ends.
[0118]
In the stoichiometric control, as described above, after the O2 storage is completed, control for actively aiming for stoichiometry is performed, and control is performed to stabilize the stoichiometric state. Therefore, after the end of the O2 storage, it is necessary to perform feedback control targeting stoichiometry until it is determined that the stoichiometric state is stabilized. That is, during the period until the stoichiometric state is determined to be stable (stoichiometric stability determination period), it is necessary to perform feedback control targeting stoichiometric conditions. In the present embodiment, the determination as to whether or not the stoichiometric state is stabilized utilizes the value of the exhaust air-fuel ratio detected by the air-fuel ratio sensor 74. In other words, it is considered that the stoichiometric state is stable if the state in which the detected air-fuel ratio is within the target stoichiometric range continues for a certain period or more.
[0119]
Therefore, in the present embodiment, if the exhaust air-fuel ratio detected by the air-fuel ratio sensor 74 is within the target stoichiometric range, the counter is added, and if the added value exceeds the threshold, the state of being within the stoichiometric range is constant. It is considered that this has continued for more than the period, and such a determination method was used. However, as for the threshold value, an appropriate value differs depending on the feedback timing and other characteristics of the configuration, and may be set individually. Further, the threshold value may be a fixed value or a variation value that varies according to the environment or the like.
[0120]
Here, as described above, since the air-fuel ratio sensor 74 has high detection accuracy near the stoichiometric state, the exhaust air-fuel ratio is accurately detected while the stoichiometric state is stable.
[0121]
Next, the procedure of the target control (S390) performed after the stoichiometric control (S380) ends will be described with reference to the flowchart shown in FIG. When the target control is started, the fuel supply amount increase correction amount Qα required to change the current stoichiometric (14.7) to the target exhaust air-fuel ratio (for example, 14.2 or 14.1-14.3) is obtained. Derivation is performed (S391). Here, the target air-fuel ratio in the present embodiment is determined by an air-fuel ratio that can effectively eliminate SOx poisoning, does not discharge excessive unburned fuel, and does not generate white smoke. Further, the increase correction amount Qα can be derived based on the intake air amount or the like. The derivation process can be performed using a map or an arithmetic expression. Then, when the increase correction amount Qα is derived, a process of adding the increase correction amount Qα to the current addition amount Qad to approach the target exhaust air-fuel ratio is performed. That is, a command signal is transmitted to add fuel at the supply amount obtained by adding the correction amount. Thereafter, it is monitored whether or not the addition period is in progress (S393), and when the addition period ends, the target control is ended. During the addition period, the addition of the fuel is continued at the supply amount obtained by adding the correction amount. However, also in this case, it is more effective to perform feedback control for repeating the correction.
[0122]
As described above, in the present embodiment, control is performed such that the target exhaust air-fuel ratio is changed from a stoichiometrically stable state. Therefore, the amount of fuel supplied is controlled so as to reach the target exhaust air-fuel ratio from the state where the exhaust air-fuel ratio is accurately detected by the air-fuel ratio sensor 74, and the target exhaust air-fuel ratio is accurately achieved. Is done. That is, as described above, although the air-fuel ratio sensor 74 has a high detection accuracy near the stoichiometry, the air-fuel ratio sensor 74 has a characteristic that the detection accuracy decreases as the air-fuel ratio sensor moves away from the stoichiometry. Therefore, as is generally done in the past, when control is performed to aim at the target exhaust air-fuel ratio from a state where the air-fuel ratio is higher than stoichiometric, control is performed to aim at the target exhaust air-fuel ratio from a state where the detection accuracy is low. , The accuracy of the target exhaust air-fuel ratio deteriorates.
[0123]
On the other hand, in the present embodiment, since the control for aiming at the target exhaust air-fuel ratio is performed from the state of high detection accuracy, the accuracy of the target exhaust air-fuel ratio increases. Therefore, it is possible to prevent the exhaust air-fuel ratio from becoming excessively lower than the target exhaust air-fuel ratio, and to suppress the release of excessive fuel.
[0124]
(Third embodiment)
FIG. 10 shows a third embodiment. The present embodiment is different from the above-described second embodiment only in that the correction amount at the time of performing the stoichiometric control is stored as a learning value, and this is reflected in the target control. The other parts are the same as those in the second embodiment, and the description thereof is omitted.
[0125]
[Specific execution procedure of SOx poisoning recovery control]
FIG. 10 is a flowchart showing a schematic procedure of the addition control (corresponding to the addition control S350 in FIG. 6) according to the third embodiment of the present invention. The procedures shown in the flowcharts of FIGS. 6 and 8 described in the second embodiment are the same in the present embodiment, and thus description thereof will be omitted. Also, there is not much difference in the procedure shown in the flowchart of FIG.
[0126]
In the present embodiment, the addition control S350 in the flowchart shown in FIG. 6 is different from that of the second embodiment. Therefore, in the present embodiment, the addition control will be described as addition control S350A with reference to FIG. When the addition control starts, the addition flag is turned ON (S360), and ₂ A series of operations from the end of storage (S370) to the execution of stoichiometric control (S380) are the same as in the second embodiment (see FIG. 7).
[0127]
In the present embodiment, the correction value of the addition amount (see S381 and S382 in FIG. 8) at the time of performing the feedback control so that the exhaust air-fuel ratio becomes stoichiometric in the stoichiometric control (S380) is set as the learning value. It is stored (S700). After that, target control is performed (S390A), and the addition control ends. Here, in the present embodiment, when performing the target control (S390A), the stored learning value is reflected when deriving the increase correction.
[0128]
In other words, feedback control (correction) is required when performing stoichiometric control because, even if fuel is added at a supply amount considered to be necessary for stoichiometric control, in reality, dimensional errors and environmental This is because an error is generated based on aging and the like, and it is necessary to correct this error. Since such an error is considered to occur based on the same phenomenon even when the control for achieving the target air-fuel ratio is performed thereafter, the correction value used for the feedback control for performing the stoichiometric control should be reflected. Thus, such an error can be reduced in advance. Therefore, in the present embodiment, such a method is adopted.
[0129]
One specific example will be briefly described. If the stoichiometric supply amount is assumed to be Q, and if it is necessary to increase the supply amount to Q + q in order to actually achieve stoichiometry, the correction amount is q. In this case, if the supply amount for the target exhaust air-fuel ratio is derived as Qα (see S391 in FIG. 9), the increase correction amount is set to Qα × ((Q + q) / Q), and this is added to the current addition amount Qad. What is necessary is just to make it increase correction. In addition, when feedback control for stoichiometric aim is performed, it is generally considered that correction is performed many times. In this case, as for the correction amount stored as the learning value, the correction amount can be updated each time the correction is performed, or the average value of a plurality of correction amounts (for example, the correction amount for the latest 10 times) can be calculated. It may be stored as a correction amount.
[0130]
As described above, in the present embodiment, when performing the control aimed at the target exhaust air-fuel ratio, the correction value used immediately before the feedback control for the stoichiometric aim is reflected as the learning value. As compared with the second embodiment, the accuracy of the target exhaust air-fuel ratio is further improved. Therefore, it is possible to prevent the exhaust air-fuel ratio from becoming excessively lower than the target exhaust air-fuel ratio, and to suppress the release of excessive fuel.
[0131]
(Fourth embodiment)
FIG. 11 shows a fourth embodiment. In the present embodiment, the concept of the feedback control described in the first embodiment is adopted when performing the target control in the second embodiment. The other parts are the same as those in the second embodiment, and the description thereof is omitted.
[0132]
FIG. 11 is a flowchart showing a schematic procedure of target control according to the fourth embodiment of the present invention. The procedure shown in the flowcharts of FIGS. 6 to 8 described in the second embodiment is the same in the present embodiment, and therefore the description thereof is omitted here. In the present embodiment, the target control S390 in the flowchart shown in FIG. 7 is different from that of the second embodiment. Therefore, in the present embodiment, target control will be described as addition control S390A with reference to FIG.
[0133]
When the target control is started, an increase correction amount Qα up to the target exhaust air-fuel ratio is derived (S391), and a series of operations from increasing the Qα to the current addition amount Qad (S392) is described in the second operation. This is the same as the embodiment (see FIG. 9). However, in deriving the increase correction, as described in the third embodiment, it is more effective to reflect the correction value used in the stoichiometric control as the learning value.
[0134]
Then, in the present embodiment, after the increase correction amount Qα up to the target exhaust air-fuel ratio is increased and corrected, the exhaust air-fuel ratio detected by the air-fuel ratio sensor 74 falls within a target range (for example, the air-fuel ratio 14.1 to 14.1). It is determined whether or not 14.3) is present (S393A). If it is determined that the exhaust air-fuel ratio detected by the air-fuel ratio sensor 74 is within the target range, the correction of the fuel addition amount is not performed (S395A). On the other hand, if it is determined in S393A that the exhaust air-fuel ratio detected by the air-fuel ratio sensor 74 is not within the target range, the detected value is determined to be higher than the target range in the oxygen concentration side. Is determined (S394A). When it is determined that the oxygen concentration is on the high side (lean side), the processing of the correction A is performed (S396A), and when it is determined that the oxygen concentration is on the low side (rich side), the correction B is performed. (S397A).
[0135]
Thereafter, it is determined whether or not it is the current addition period (S398A). If it is determined that the current period is the addition period, the process returns to S393A and the same processing is repeated, and it is determined that the current period is not the addition period in S398A. If so, the target control ends. The correction processing (feedback control) for setting the exhaust air-fuel ratio to the target air-fuel ratio in steps S393A to S398A is the same as that described in the first embodiment, and a description thereof will be omitted. I do.
[0136]
As described above, in the present embodiment, similarly to the above-described second embodiment, control is performed after the stoichiometric control to aim at the target exhaust air-fuel ratio. Therefore, the accuracy of the target exhaust air-fuel ratio is increased. Further, in the present embodiment, as in the case of the first embodiment, when the exhaust air-fuel ratio is lower than the target exhaust air-fuel ratio and when the exhaust air-fuel ratio is higher than the target exhaust air-fuel ratio, the former has a larger correction amount. Control is performed. This makes it possible to quickly exit from a situation where the exhaust air-fuel ratio is lower than the target exhaust air-fuel ratio. Therefore, in the present embodiment, it is possible to synergistically suppress the exhaust air-fuel ratio from becoming excessively lower than the target exhaust air-fuel ratio. Therefore, the discharge of the excess unburned fuel component can be further suppressed, and the generation of white smoke and the generation of odor can be suppressed.
[0137]
(Other)
In the embodiments described above, only the case where the intermittent rich system is employed when performing the SOx poisoning recovery control has been described. However, the control concept in each embodiment is also applied to the continuous rich system. It is also possible. That is, as described in the first embodiment, the correction A and the correction B can be used when the feedback control is performed to achieve the target exhaust air-fuel ratio in the continuous rich method as described in the first embodiment. Further, as described in the second embodiment, in the method of continuously enriching, it is also possible to perform control aiming at stoichiometry before setting the target rich exhaust air-fuel ratio. Further, the learning values described in the third embodiment can be used, and the control concepts of the first and second embodiments can be combined as described in the fourth embodiment. .
[0138]
【The invention's effect】
As described above, according to the present invention, the amount of unburned fuel component emissions can be reduced. This can also suppress the generation of white smoke.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an exhaust gas purification device for an internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a state of a change in an exhaust air-fuel ratio with respect to an elapsed time when performing SOx poisoning recovery control according to the first embodiment of the present invention.
FIG. 3 is a partially enlarged view of FIG. 2;
FIG. 4 is a flowchart illustrating a schematic procedure of SOx poisoning recovery control according to the first embodiment of the present invention.
FIG. 5 is a flowchart showing a schematic procedure of addition control in FIG.
FIG. 6 is a flowchart illustrating a schematic procedure of SOx poisoning recovery control according to the second embodiment of the present invention.
FIG. 7 is a flowchart showing a schematic procedure of addition control in FIG.
FIG. 8 is a flowchart showing a schematic procedure of stoichiometric control in FIG. 7;
FIG. 9 is a flowchart showing a schematic procedure of target control in FIG. 7;
FIG. 10 is a flowchart illustrating a schematic procedure of addition control according to a third embodiment of the present invention.
FIG. 11 is a flowchart illustrating a schematic procedure of target control according to a fourth embodiment of the present invention.
FIG. 12 shows a state of an air-fuel ratio detected by an air-fuel ratio sensor with respect to an actual exhaust air-fuel ratio.
[Explanation of symbols]
1 engine
10 Fuel supply system
11 Supply pump
12 common rail
13 Fuel injection valve
14 Shut-off valve
16 Metering valve
17 Reducing agent addition valve
20 Combustion chamber
30 Intake system
31 Intercooler
32 Throttle valve
40 Exhaust system
42 Catalyst casing
50 Turbocharger
51 shaft
52 Turbine wheel
53 Compressor wheel
60 EGR passage
61 EGR valve
62 Cooler
70 Rail pressure sensor
71 Fuel pressure sensor
72 air flow meter
73 Exhaust gas temperature sensor
74 air-fuel ratio sensor
75 NOx sensor
76 Accelerator position sensor
77 Crank angle sensor
90 ECU
91 CPU
92 ROM
93 RAM
94 Backup RAM
95 Timer counter
96 External input circuit
97 External output circuit
98 Bidirectional bus

Claims (7)

When the oxidizing component concentration of the exhaust purification section in the exhaust passage is high, the oxidizing exhaust substance contained in the exhaust gas is absorbed, and when the oxidizing component concentration of the exhaust purification section is low and the reducing atmosphere is used, Purifying means for purifying the oxidizing exhaust material by reducing while releasing the absorbed oxidizing exhaust material,
Supply means for supplying a reducing agent to the exhaust gas purification unit,
Detecting means for detecting the exhaust air-fuel ratio downstream of the exhaust purification section;
Feedback control for deriving a correction amount of the supplied reducing agent from a difference between the value detected by the detection unit and a target exhaust air-fuel ratio, and controlling a supply amount of the reducing agent supplied based on the correction amount. And an exhaust purification device for an internal combustion engine comprising:
When exhaust gas is discharged and reduced from the purifying means, when the difference is X, the correction amount when the detection result by the detecting means is higher than a target exhaust air-fuel ratio is Y1, and the exhaust air-fuel ratio is If the correction amount is lower than Y2, the relationship of Y2> Y1 is satisfied regardless of the value of X. When the oxidizing component concentration of the exhaust purification section in the exhaust passage is high, the oxidizing exhaust substance contained in the exhaust gas is absorbed, and when the oxidizing component concentration of the exhaust purification section is low and the reducing atmosphere is used, Purifying means for purifying the oxidizing exhaust material by reducing while releasing the absorbed oxidizing exhaust material,
Supply means for supplying a reducing agent to the exhaust gas purification unit,
Detecting means for detecting the exhaust air-fuel ratio downstream of the exhaust purification section;
Feedback control for deriving a correction amount of the supplied reducing agent from a difference between the value detected by the detection unit and a target exhaust air-fuel ratio, and controlling a supply amount of the reducing agent supplied based on the correction amount. And an exhaust purification device for an internal combustion engine comprising:
When the exhaust gas is released and reduced from the purifying means,
The exhaust gas purification of an internal combustion engine according to claim 1, wherein the feedback control means performs control such that the exhaust air-fuel ratio becomes a target air-fuel ratio having a higher reducing component concentration than the stoichiometric ratio after performing the control such that the exhaust air-fuel ratio becomes stoichiometric. apparatus. When the oxidizing component concentration of the exhaust purification section in the exhaust passage is high, the oxidizing exhaust substance contained in the exhaust gas is absorbed, and when the oxidizing component concentration of the exhaust purification section is low and the reducing atmosphere is used, Purifying means for purifying the oxidizing exhaust material by reducing while releasing the absorbed oxidizing exhaust material,
Supply means for supplying a reducing agent to the exhaust gas purification unit,
Detecting means for detecting the exhaust air-fuel ratio downstream of the exhaust purification section;
Feedback control for deriving a correction amount of the supplied reducing agent from a difference between the value detected by the detection unit and a target exhaust air-fuel ratio, and controlling a supply amount of the reducing agent supplied based on the correction amount. And an exhaust purification device for an internal combustion engine comprising:
When the exhaust gas is released and reduced from the purifying means,
The feedback control means, after performing the control that the exhaust air-fuel ratio is stoichiometric, while performing control such that the exhaust air-fuel ratio becomes a target air-fuel ratio having a higher reducing component concentration than the stoichiometric,
When performing the control to achieve the target air-fuel ratio, when the difference is X, the correction amount when the detection result by the detecting means is higher than the target exhaust air-fuel ratio is Y1, and the exhaust air-fuel ratio If the correction amount is lower than Y2, the relationship of Y2> Y1 is satisfied regardless of the value of X. The feedback control means performs control such that the exhaust air-fuel ratio becomes a stoichiometric control, and then, after the stoichiometric stability determination period elapses, performs control such that the exhaust air-fuel ratio becomes a target air-fuel ratio having a higher reducing component concentration than the stoichiometric. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2 or 3. The feedback control means, after performing the control that the exhaust air-fuel ratio becomes stoichiometric, when performing the control that the exhaust air-fuel ratio becomes the target air-fuel ratio having a higher reducing component concentration than the stoichiometric, when performing the stoichiometric control 5. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the correction amount is reflected at the time of deriving the correction amount when performing control to achieve the target air-fuel ratio. Receives a signal of exhaust air-fuel ratio data detected by the detection means downstream of the exhaust purification section where the exhaust is purified by the purification means for absorbing or releasing and reducing the oxidizing exhaust substance according to the surrounding atmosphere. Means,
Derivation of deriving a correction amount of a supply amount of a reducing agent supplied by a supply unit that supplies a reducing agent to the exhaust gas purification unit from a difference between the exhaust air-fuel ratio data received by the receiving unit and a target exhaust air-fuel ratio. Means,
Transmitting means for transmitting a signal instructing the supply means, so as to supply at a supply amount corrected by the correction amount derived by the derivation means,
A control device for performing feedback control of the supply amount of the reducing agent by the supply unit,
When exhaust gas is discharged and reduced from the purifying means, when the difference is X, the correction amount when the detection result by the detecting means is higher than a target exhaust air-fuel ratio is Y1, and the exhaust air-fuel ratio is If the correction amount is lower than Y2, the relationship of Y2> Y1 is satisfied regardless of the value of X. Receives a signal of exhaust air-fuel ratio data detected by the detection means downstream of the exhaust purification section where the exhaust is purified by the purification means for absorbing or releasing and reducing the oxidizing exhaust substance according to the surrounding atmosphere. Means,
Derivation of deriving a correction amount of a supply amount of a reducing agent supplied by a supply unit that supplies a reducing agent to the exhaust gas purification unit from a difference between the exhaust air-fuel ratio data received by the receiving unit and a target exhaust air-fuel ratio. Means,
Transmitting means for transmitting a signal instructing the supply means, so as to supply at a supply amount corrected by the correction amount derived by the derivation means,
A control device for performing feedback control of the supply amount of the reducing agent by the supply unit,
When the exhaust gas is released and reduced from the purifying means,
A control device, wherein after performing control to make the exhaust air-fuel ratio stoichiometric, control is performed so that the exhaust air-fuel ratio becomes a target air-fuel ratio having a higher concentration of reducing components than stoichiometric.

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