JP2010127182A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine suppressing emission of carbon monoxide and unburnt hydrocarbon. <P>SOLUTION: The exhaust emission control device for an internal combustion engine includes: a NO<SB>x</SB>occlusion catalyst; and an oxidization catalyst disposed downstream of the NO<SB>x</SB>occlusion catalyst and having an oxygen occlusion capacity. The exhaust emission control device calculates an oxygen occlusion amount of the oxidation catalyst by detecting a temperature of the oxidation catalyst, when a temperature of the NO<SB>x</SB>occlusion catalyst is increased to a temperature allowing the release of SO<SB>x</SB>to perform processing of recovery from sulfur poisoning or higher, and a target air-fuel ratio of exhaust gas is calculated based on an oxygen occlusion amount and a target time for performing a predetermined rich control, and the rich control is performed based on the calculated target air-fuel ratio of the exhaust gas. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

In addition to carbon monoxide (CO), unburned hydrocarbons (HC), and particulates (PM), exhaust gases from internal combustion engines such as diesel engines and gasoline engines contain nitrogen oxides (NO _x ). One method of removing nitrogen oxides, NO _X storage catalyst has been proposed to be located in the engine exhaust passage.

_The NO _X storage catalyst, the air-fuel ratio of the exhaust gas is when greater than the stoichiometric air-fuel ratio, i.e., the air-fuel ratio of the exhaust gas is occluded NO _X when the lean. In contrast, when the air-fuel ratio in the exhaust gas is smaller than the stoichiometric air-fuel ratio, that is, when the air-fuel ratio of the exhaust gas is rich or the stoichiometric air-fuel ratio, the stored NO _X is released and included in the exhaust gas. NO _X is reduced and purified by the reducing agent. Diesel engines, etc., during normal operation air-fuel ratio of the exhaust gas is lean, NO _X storage catalyst occludes NO _X in the exhaust gas. After continuing NO _X occlusion, NO _X can be reduced and purified by making the air-fuel ratio of the exhaust gas rich or stoichiometric at a predetermined time.

The exhaust gas of the internal combustion engine may contain sulfur oxide (SO _x ). In this case, the NO _X storage catalyst stores SO _X simultaneously with NO _X storage. When SO _X is occluded, the amount of NO _X that can be occluded decreases. Thus, so-called sulfur poisoning occurs in the NO _X storage catalyst. To overcome this sulfur poisoning, sulfur poisoning recovery process for releasing SO _X is performed. SO _X is occluded in the NO _X storage catalyst in a stable state as compared to the NO _X. Therefore, in the sulfur poisoning recovery process, releasing SO _X by the air-fuel ratio after having heated the _the NO _X storage catalyst supplies a rich exhaust gas or the stoichiometric air-fuel ratio of the exhaust gas.

In Japanese Patent Application Laid-Open No. 2008-51009, a NO _X storage reduction catalyst mounted in the middle of an exhaust pipe, a fuel addition valve for adding fuel to exhaust gas upstream of the NO _X storage reduction catalyst, and NO _X storage An exhaust emission control device is disclosed that includes an oxygen supply means for supplying oxygen to the downstream side of the reduction catalyst. In this exhaust gas purification device, when a reducing agent is added by a fuel addition valve and sulfur poisoning recovery processing is performed, oxygen is supplied by an oxygen supply means to oxidize carbon monoxide and unburned carbon monoxide. Burning the reducing agent is disclosed.

JP 2008-51009 A

In the sulfur poisoning recovery process, a relatively large amount of a reducing agent such as carbon monoxide or unburned hydrocarbon is supplied to the NO _X storage catalyst in order to enrich the air-fuel ratio of the exhaust gas. When the sulfur poisoning recovery process, part of the reducing agent slip through _the NO _X storage catalyst. By NO downstream oxidation catalyst _X storage catalyst is arranged, the reducing agent having passed through the NO _X storage catalyst is oxidized by the oxidation catalyst, the reducing agent can be prevented from being released to the atmosphere.

  Here, some oxidation catalysts have oxygen storage capacity. For example, some oxidation catalysts contain oxygen storage materials. The oxidation catalyst having an oxygen storage capacity stores oxygen when the air-fuel ratio of the exhaust gas is lean. On the other hand, when the air-fuel ratio of the exhaust gas becomes rich, it has a role of assisting the oxidation reaction by releasing the stored oxygen. An oxidation catalyst having an oxygen storage capacity has a characteristic that the oxygen storage amount increases as the temperature rises. That is, as the temperature rises, the oxidation treatment ability of the oxidation catalyst is improved.

In the sulfur poisoning recovery process, when the temperature of the NO _X storage catalyst is raised and the temperature of the NO _X storage catalyst rises above the temperature at which SO _X can be released, the air-fuel ratio of the exhaust gas is set to a predetermined constant air. It was lowered to the fuel ratio. However, in the exhaust purification apparatus oxidation catalyst is arranged downstream of the NO _X storage catalyst, when starting the rich control to make the air-fuel ratio of the exhaust gas rich, the temperature of the oxidation catalyst is he has sufficiently increased In some cases, the oxidation treatment capability was insufficient. As a result, there has been a problem that in the oxidation catalyst, the carbon monoxide and unburned hydrocarbons that have passed through the NO _X storage catalyst cannot be sufficiently oxidized and are released into the atmosphere.

The present invention relates to an exhaust gas purification apparatus for an internal combustion engine that includes an NO _X storage catalyst and an oxidation catalyst that is disposed downstream of the NO _X storage catalyst and has an oxygen storage capacity, and that discharges carbon monoxide and unburned hydrocarbons. It is an object of the present invention to provide an exhaust gas purification apparatus for an internal combustion engine that can suppress the above-described problem.

The exhaust gas purification apparatus for an internal combustion engine of the present invention occludes NO _X contained in exhaust gas when the air-fuel ratio of the exhaust gas flowing into the engine exhaust passage is lean, and the air-fuel ratio of the exhaust gas flowing in is stoichiometric. becomes the ratio or rich is arranged to the NO _X storing catalyst to release the occluded NO _X, placing an oxidation catalyst having an oxygen storage capacity downstream of the engine exhaust passage of the NO _X storage catalyst, stored in the NO _X storage catalyst When the SO _X amount exceeds a predetermined allowable amount, the temperature of the NO _X storage catalyst is increased to a temperature at which SO _X can be released, and the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst is made rich. This is a device that performs sulfur poisoning recovery processing by rich control. The temperature of the NO _X storage catalyst when it should be increased to SO _X releasable temperature, when the air-fuel ratio of the exhaust gas flowing from the NO _X storing catalyst to the NO _X storing catalyst so as to release the SO _X rich oxide Calculating at least one of a target air-fuel ratio of exhaust gas capable of oxidizing the reducing agent flowing out from the NO _X storage catalyst toward the catalyst and a target time for performing rich control, and a target for performing target air-fuel ratio of the exhaust gas and rich control Rich control is performed based on time. With this configuration, emission of carbon monoxide and unburned hydrocarbons can be suppressed.

In the above invention, when the temperature of the NO _X storage catalyst is to be increased to a temperature at which SO _X can be released, the oxygen storage amount of the oxidation catalyst is calculated by detecting the temperature of the oxidation catalyst, and the oxygen storage amount is determined in advance. The target air-fuel ratio of the exhaust gas can be calculated based on the target time for performing the rich control, and the rich control can be performed based on the target air-fuel ratio of the exhaust gas.

In the above invention, when the temperature of the NO _X storage catalyst is to be increased to a temperature at which SO _X can be released, the oxygen storage amount of the oxidation catalyst is calculated by detecting the temperature of the oxidation catalyst, and the oxygen storage amount is determined in advance. The target time for performing the rich control can be calculated based on the target air-fuel ratio of the exhaust gas, and the rich control can be performed based on the target time for performing the rich control.

In the above invention, when the temperature of the NO _X storage catalyst should be increased to a temperature at which SO _X can be released, the oxygen release rate of the oxidation catalyst is calculated by detecting the temperature of the oxidation catalyst, and the exhaust gas is exhausted based on the oxygen release rate. The target air-fuel ratio of gas can be calculated, and rich control can be performed based on the target air-fuel ratio of exhaust gas.

In the above invention, when the temperature of the NO _X storage catalyst should be increased to a temperature at which SO _X can be released, the oxygen storage amount of the oxidation catalyst is calculated by detecting the temperature of the oxidation catalyst, and the oxygen storage amount and the exhaust gas It is preferable to calculate a target time for enriching the air-fuel ratio of the exhaust gas from the target air-fuel ratio, and perform the rich control based on the target air-fuel ratio of the exhaust gas and the target time for performing rich control.

In the above invention, when the temperature of the NO _X storage catalyst should be increased to a temperature at which SO _X can be released, it is preferable to gradually reduce the air-fuel ratio of the exhaust gas as the temperature of the oxidation catalyst increases.

In the above invention, when the temperature of the NO _X storage catalyst should be increased to a temperature at which SO _X can be released, the oxygen storage amount of the oxidation catalyst is calculated by detecting the temperature of the oxidation catalyst, and the oxygen storage amount is determined in advance. It is preferable to start the rich control when the determination value becomes equal to or higher than the determined value.

  ADVANTAGE OF THE INVENTION According to this invention, the exhaust gas purification apparatus of the internal combustion engine which can suppress discharge | emission of carbon monoxide and unburned hydrocarbon can be provided.

(Embodiment 1)
With reference to FIGS. 1 to 15, an exhaust gas purification apparatus for an internal combustion engine in the first embodiment will be described.

  FIG. 1 shows an overall view of a compression ignition type internal combustion engine in the present embodiment. In the present embodiment, a diesel engine disposed in an automobile will be described as an example. The internal combustion engine includes an engine body 1. The engine body 1 includes a combustion chamber 2 for each cylinder and an electronically controlled fuel injection valve 3 for injecting fuel into each combustion chamber 2. The engine body 1 includes an intake manifold 4 and an exhaust manifold 5.

  The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6. An inlet of the compressor 7 a is connected to an air cleaner 9 via an intake air amount detector 8. A throttle valve 10 driven by a step motor is disposed in the intake duct 6. Further, an intake air cooling device 11 for cooling intake air flowing through the intake duct 6 is disposed around the intake duct 6.

On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7. The outlet of the exhaust turbine 7 b is connected to the NO _X storage catalyst 17 through the exhaust pipe 12. A particulate filter 16 for collecting particulates in the exhaust gas is disposed in the engine exhaust passage downstream of the NO _X storage catalyst 17. In the embodiment shown in FIG. 1, the oxidation catalyst 13 is disposed in the engine exhaust passage downstream of the particulate filter 16. That is, the oxidation catalyst 13 is disposed downstream of the NO _X storage catalyst 17.

  An EGR passage 18 is arranged between the exhaust manifold 5 and the intake manifold 4 for exhaust gas recirculation (EGR). An electronically controlled EGR control valve 19 is disposed in the EGR passage 18. Further, an EGR cooling device 20 for cooling the EGR gas flowing in the EGR passage 18 is disposed around the EGR passage 18.

  Each fuel injection valve 3 is connected to a common rail 22 via a fuel supply pipe 21. The common rail 22 is connected to a fuel tank 24 via an electronically controlled fuel pump 23 having a variable discharge amount. The fuel stored in the fuel tank 24 is supplied into the common rail 22 by the fuel pump 23. The fuel supplied to the common rail 22 is supplied to the fuel injection valve 3 through each fuel supply pipe 21.

  The electronic control unit 30 is composed of a digital computer. The exhaust purification device for an internal combustion engine in the present embodiment includes an electronic control unit 30. The electronic control unit 30 includes a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35, and an output port 36 connected to each other by a bidirectional bus 31. The ROM 32 is a read-only storage device, and stores information such as a map necessary for performing control in advance. The CPU 34 can perform arbitrary calculations and determinations. The RAM 33 is a readable / writable storage device, and can store information such as an operation history or temporarily store a calculation result.

Downstream of the NO _X storage catalyst 17, a temperature sensor 26 for detecting the temperature of the NO _X storage catalyst 17 is arranged. A temperature sensor 27 for detecting the temperature of the oxidation catalyst 13 or the particulate filter 16 is disposed downstream of the oxidation catalyst 13. The output signals of these temperature sensors 26 and 27 are input to the input port 35 via the corresponding AD converter 37.

The exhaust gas purification apparatus for an internal combustion engine in the present embodiment includes an air-fuel ratio sensor 29 as air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust gas. The air-fuel ratio sensor 29 is disposed downstream of the NO _X storage catalyst 17. The air-fuel ratio sensor 29 is disposed upstream of the oxidation catalyst 13. The air-fuel ratio sensor 29 detects the air-fuel ratio of the exhaust gas flowing out from the NO _X storage catalyst 17 or the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 13. The output signal of the air-fuel ratio sensor 29 is input to the input port 35 via the corresponding AD converter 37.

  The particulate filter 16 is provided with a differential pressure sensor 28 for detecting the differential pressure across the particulate filter 16. Output signals of the differential pressure sensor 28 and the intake air amount detector 8 are input to the input port 35 via the corresponding AD converters 37.

  Connected to the accelerator pedal 40 is a load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40. The output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 15 °. On the other hand, the output port 36 is connected to the fuel injection valve 3, the step motor for driving the throttle valve 10, the EGR control valve 19, and the fuel pump 23 through corresponding drive circuits 38.

  The oxidation catalyst 13 is a catalyst having oxidation ability for purifying exhaust gas. The oxidation catalyst 13 includes, for example, a base body having a partition wall extending in the exhaust gas flow direction inside a cylindrical case body. The substrate is formed in a honeycomb structure, for example. A coating layer made of, for example, porous oxide powder is formed on the surface of the substrate, and a noble metal catalyst such as platinum Pt is supported on the coating layer. Carbon monoxide (CO) and unburned hydrocarbon (HC) contained in the exhaust gas are oxidized by the oxidation catalyst 13 and converted into harmless substances such as water and carbon dioxide. Hereinafter, a substance to be oxidized by an oxidation catalyst such as carbon monoxide and unburned hydrocarbon is referred to as carbon monoxide or the like.

  The oxidation catalyst 13 in the present embodiment has an oxygen storage capacity. The oxidation catalyst 13 has ceria (cerium oxide) as a promoter. The oxidation catalyst 13 stores oxygen when the air-fuel ratio of the exhaust gas is lean. When the air-fuel ratio of the exhaust gas is rich, the stored oxygen is released. By releasing oxygen, the oxidation reaction can be promoted.

  The particulate filter 16 is a filter that removes particulate matter (particulates) such as carbon particulates and ionic particulates such as sulfate contained in the exhaust gas. The particulate filter has, for example, a honeycomb structure and has a plurality of flow paths extending in the gas flow direction. In the plurality of channels, the channels whose downstream ends are sealed and the channels whose upstream ends are sealed are alternately formed. The partition walls of the flow path are formed of a porous material such as cordierite. Particulates are captured when the exhaust gas passes through the partition walls.

  Particulate matter is collected on the particulate filter 16 and oxidized. The particulate matter gradually deposited on the particulate filter 16 is oxidized and removed by raising the temperature to, for example, about 600 ° C. in an atmosphere containing excess air.

  In the example of the apparatus shown in FIG. 1, when the differential pressure ΔP before and after the particulate filter 16 detected by the differential pressure sensor 28 exceeds an allowable value, the amount of particulate matter deposited on the particulate filter 16 is an allowable amount. It is judged that it exceeded. When the amount of the particulate matter exceeds the allowable amount, the temperature of the particulate filter 16 is raised under the lean air-fuel ratio of the exhaust gas, thereby oxidizing and removing the deposited particulate matter.

FIG. 2 is a schematic sectional view of the NO _X storage catalyst. The NO _X storage catalyst 17 has a catalyst carrier 45 made of alumina, for example, supported on a substrate. A noble metal catalyst 46 is dispersed and supported on the surface of the catalyst carrier 45. A layer of NO _X absorbent 47 is formed on the surface of the catalyst carrier 45. As the noble metal catalyst 46, for example, platinum Pt is used. The components constituting the NO _X absorbent 47 are selected from, for example, alkali metals such as potassium K, sodium Na and cesium Cs, alkaline earth such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y. At least one of these is used.

In the exhaust gas supplied to the engine intake passage, the combustion chamber, or the engine exhaust passage, when the ratio of air and fuel (hydrocarbon) is referred to as the air-fuel ratio (A / F) of the exhaust gas, it flows into the NO _X storage catalyst. by the time the air-fuel ratio of the exhaust gas is lean (greater time than the stoichiometric air-fuel ratio), NO contained in the exhaust gas is oxidized to NO ₂ on the precious metal catalyst 46. NO ₂ is nitrate ions NO ₃ ^- are occluded in the NO _X absorbent 47 in the form of.

In contrast, when the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst is rich (when smaller than the stoichiometric air-fuel ratio) or when the stoichiometric air-fuel ratio is reached, the oxygen concentration in the exhaust gas decreases and the reaction is reversed. Proceed in the direction (NO ₃ ⁻ → NO ₂ ). _The NO _X absorbent in the 47 nitrate ions NO ₃ ^- are released from _the NO _X absorbent 47 in the form of NO _2. The released NO _X is reduced to N ₂ by unburned HC and CO contained in the exhaust gas.

In the operating example of the present embodiment, to detect the _the NO _X storage amount stored in _the NO _X storage catalyst. For example, a map of the accumulated amount of NO _X per unit time that has the engine speed N and the required torque TQ as functions is built in the ROM 32 of the electronic control unit 30. By integrating the storage amount of the NO _X per unit is calculated time in accordance with the operating conditions, it is possible to detect _the NO _X storage amount stored in the NO _X storage catalyst. Before absorbing capability of the NO _X absorbent 47 becomes saturated, when _the NO _X storage amount reaches the predetermined amount, by temporarily make the air, the NO _X from _the NO _X absorbent 47 It can be released and reduced.

FIG. 3 shows another schematic cross-sectional view of the NO _X storage catalyst. The exhaust gas contains SO _X , that is, SO ₂ . When this SO ₂ flows into the NO _X storage catalyst 17, it is oxidized in the noble metal catalyst 46 to become SO ₃ . The SO ₃ is absorbed in _the NO _X absorbent 47, for example, while bonding with the barium carbonate BaCO _3, and diffuses in the NO _X absorbent 47 in sulfate ions _SO ^{4 2-form,} generating the sulfate BaSO ₄ To do. Since the NO _X absorbent 47 has a strong basicity, the sulfate BaSO ₄ is stable and difficult to decompose. Simply by making the air-fuel ratio of the exhaust gas rich, the sulfate BaSO ₄ remains as it is without being decomposed. . If the use of the NO _X storage catalyst is continued, the sulfate BaSO ₄ in the NO _X absorbent 47 increases. For this reason, the amount of NO _X that can be absorbed by the NO _X storage catalyst decreases. In this way, sulfur poisoning occurs in the NO _X storage catalyst 17.

In order to eliminate the sulfur poisoning, a sulfur poisoning recovery process for releasing SO _X from the NO _X storage catalyst is performed. In the sulfur poisoning recovery process, the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst 17 the temperature of the NO _X storage catalyst 17 in a state of being raised to a temperature capable of SO _X release the stoichiometric air-fuel ratio or rich Thus, a process for releasing SO _X from the NO _X storage catalyst is performed.

  FIG. 4 shows a graph for explaining the relationship between the bed temperature and the oxygen storage amount in an oxidation catalyst having an oxygen storage capacity. The horizontal axis is the bed temperature of the oxidation catalyst, and the vertical axis is the amount of oxygen stored in the oxidation catalyst. The higher the bed temperature, the higher the oxygen storage capacity. Further, since the stored oxygen is easily released when the bed temperature rises to a predetermined temperature, the slope of the graph becomes gentle. In the operating range of the internal combustion engine in the present embodiment, the bed temperature and the oxygen storage amount have a substantially proportional relationship.

In the present embodiment, control when performing sulfur poisoning recovery processing will be described. The exhaust emission control device for an internal combustion engine in the present embodiment detects the SO _X storage amount accumulated in the NO _X storage catalyst. For example, should an internal map of the accumulated amount of SO _X per unit time to the the required torque TQ engine speed N to the function ROM32 of the electronic control unit 30. By integrating the SO _X storage amount per unit is calculated time in accordance with the operating conditions, it is possible to detect the SO _X storage amount stored in the NO _X storage catalyst. When the SO _X storage amount of the NO _X storage catalyst reaches a predetermined amount, a sulfur poisoning recovery process is performed.

For the final stage of the sulfur poisoning recovery process, for example, the remaining SO _X amount is calculated based on the integrated value of the time during which the air-fuel ratio of the exhaust gas is rich. Then, when the SO _X storage amount remaining in the NO _X storage catalyst reaches a predetermined value, the sulfur poisoning recovery process is terminated.

  The exhaust gas purification apparatus for an internal combustion engine in the present embodiment is formed so as to be able to control the injection pattern of fuel injected into the combustion chamber. That is, the fuel injection amount and the injection timing of the fuel injection valve 3 can be controlled. The sulfur poisoning recovery process in the present embodiment is performed by controlling the fuel injection pattern in the combustion chamber. The change of the injection pattern will be described later.

FIG. 5 is a time chart of operation control for performing sulfur poisoning recovery processing in the exhaust gas purification apparatus for an internal combustion engine of the present embodiment. FIG. 5 is an initial time chart of the sulfur poisoning recovery process. Up to time t ₀ is normal operation. The sulfur poisoning recovery process is started upon detecting that the SO _X storage amount of the NO _X storage catalyst has reached a predetermined amount.

From time t ₀ to time t _3, the temperature of the NO _X storage catalyst is performing a Atsushi Nobori control for raising the temperature of the NO _X storing catalyst to be equal to or greater than the SO _X release temperature. In order to release SO _X , for example, the NO _X storage catalyst is heated to 600 ° C. or higher. After time t ₃ , temperature maintenance control is performed to maintain the temperature of the NO _X storage catalyst at or above the SO _X release temperature. Further, after time t ₂ , SO _X is released by performing rich control that makes the air-fuel ratio of the exhaust gas rich or the stoichiometric air-fuel ratio while performing temperature rise control and temperature maintenance control. Rich control is performed intermittently.

6, in the exhaust purification system of an internal combustion engine in the present embodiment, a flowchart of when raising the temperature of the NO _X storage catalyst. Figure 6 is a flow chart of a control that is performed in a period from the time t ₁ in FIG. 5 to time t _3.

In step 111, the bed temperature _TN of the NO _X storage catalyst 17 is detected. Temperature of the NO _X storage catalyst 17, with reference to FIG. 1, for example, can be detected by a temperature sensor 26 disposed downstream of the NO _X storage catalyst 17.

In step 112, it is determined whether or not the bed temperature T _N of the NO _X storage catalyst is _{equal to} or higher than the temperature T _NX at which SO _X can be released. If the bed temperature _TN of the NO _X storage catalyst is equal to or higher than this determination value, the routine proceeds to step 113. If the bed temperature _TN is less than the determination value, this control is terminated, and step 111 is repeated again after a predetermined time has elapsed.

Referring to FIG. 5, at time _{t 1,} the temperature of the NO _X storage catalyst has reached the SO _X releasable temperature _{T NX.} In the present embodiment, since the temperature of the oxidation catalyst time t ₁ is not high enough, not to start rich control at time t _1, it has sustained temperature increase control. In the present embodiment, control is performed to wait for the oxidation catalyst temperature to rise and the oxidation treatment capability of the oxidation catalyst to improve.

Referring to FIG. 6, in step 113, the bed temperature T _O of the oxidation catalyst is detected. The bed temperature of the oxidation catalyst can be detected by, for example, a temperature sensor 27 disposed downstream of the oxidation catalyst 13 with reference to FIG.

  Next, in step 114, the oxygen storage amount S of the oxidation catalyst 13 is calculated. The oxygen storage amount can be calculated from the relationship between the oxidation catalyst bed temperature and the oxidation storage amount shown in FIG. For example, a map of the oxygen storage amount as a function of the bed temperature is stored in the ROM 32 of the electronic control unit 30. By detecting the bed temperature of the oxidation catalyst 13, the amount of oxygen stored in the oxidation catalyst can be detected.

Next, in step 115, it is determined whether or not the calculated oxygen storage amount is equal to or greater than a predetermined determination value. In step 115, it is determined whether or not the catalyst has sufficient oxygen to suppress the emission of carbon monoxide or the like into the atmosphere when the oxidation catalyst makes the air-fuel ratio of the exhaust gas rich. . In the present embodiment, a determination value for the oxygen storage amount is predetermined. The determination value of the oxygen storage amount can be stored in the ROM 32 of the electronic control unit 30, for example. The determination value in the present embodiment is set to an oxygen storage amount that can oxidize substantially all of carbon monoxide flowing out from the NO _X storage catalyst when the air-fuel ratio of the exhaust gas is made slightly rich. Yes. As the determination value, an oxygen storage amount that can be processed by carbon monoxide or the like when the air-fuel ratio of the exhaust gas is set to the stoichiometric air-fuel ratio may be set.

If it is determined in step 115 that the oxygen storage amount is less than the determination value, this control is terminated, and processing is performed again from step 111 after a predetermined time. If the oxygen storage amount is greater than or equal to the determination value, the routine proceeds to step 116. In the time chart of FIG. 5, at time t _2, the oxygen storage amount is equal to or greater than the determination value. The bed temperature T _O of the oxidation catalyst at this time is the temperature T _OX .

  In the present embodiment, the oxygen storage amount is calculated from the bed temperature of the oxidation catalyst, and it is determined whether or not rich control is performed based on this oxygen storage amount. It may be determined whether or not rich control is performed based on the bed temperature of the oxidation catalyst.

  Referring to FIG. 6, when the oxygen storage amount is not less than the determination value in step 115, the process proceeds to step 116. In step 116, the target air-fuel ratio of the exhaust gas is calculated from the calculated oxygen storage amount.

  FIG. 7 shows an enlarged view of the time chart of the air-fuel ratio of the exhaust gas when rich control is performed. The horizontal axis is time, and the vertical axis is the air-fuel ratio of the exhaust gas. When performing the rich control, the air-fuel ratio of the exhaust gas is lowered to the target value, and the air-fuel ratio of the exhaust gas is maintained for the enrichment time during which one rich control is continued. In the present embodiment, the enrichment time is set in advance. An enrichment area Sr surrounded by the enrichment time and an air-fuel ratio region equal to or lower than the stoichiometric air-fuel ratio is defined.

  FIG. 8 is a graph showing the relationship between the area Sr when the air-fuel ratio of the exhaust gas is made rich and the amount of carbon monoxide or the like flowing into the oxidation catalyst. The horizontal axis is the area Sr of enrichment, and the vertical axis is the amount of carbon monoxide or the like flowing into the oxidation catalyst. As the area Sr increases, the amount of carbon monoxide and the like flowing into the oxidation catalyst increases. From the relationship of FIG. 8, the other is obtained by specifying either the area Sr or the amount of carbon monoxide or the like flowing into the oxidation catalyst. That is, the amount of carbon monoxide or the like flowing into the oxidation catalyst can be calculated from the air-fuel ratio of the exhaust gas and the enrichment time. Here, the oxygen storage amount of the oxidation catalyst corresponds to the oxidation treatment amount of the oxidation catalyst. If the oxygen storage amount is greater than or equal to the amount of carbon monoxide or the like flowing into the oxidation catalyst, substantially all of the carbon monoxide or the like can be oxidized.

  Referring to FIG. 6, in the present embodiment, in step 114, the oxygen storage amount of the oxidation catalyst is calculated. From the oxygen storage amount of the oxidation catalyst, the amount of carbon monoxide or the like that can be made to flow into the oxidation catalyst and be oxidized almost entirely is calculated. Referring to FIG. 8, area Sr can be obtained from the amount of carbon monoxide or the like flowing into the oxidation catalyst. Referring to FIG. 7, in the present embodiment, since the enrichment time for one time is determined in advance, the target air-fuel ratio of the exhaust gas can be calculated from the enrichment area Sr.

  Thus, in step 116, the target air-fuel ratio of the exhaust gas is calculated. Next, at step 117, rich control is performed so that the calculated target air-fuel ratio of the exhaust gas is obtained.

Referring to FIG. 5, in the period from time t ₂ to time t _3, the rich control and the temperature maintaining control is carried out alternately. In the present embodiment, temperature maintenance control for a predetermined time is performed after performing rich control once. During the temperature maintenance control period, the air-fuel ratio of the exhaust gas becomes lean, and the oxidation catalyst occludes oxygen. The temperature maintenance control is preferably performed for a time longer than the time when the oxygen stored in the oxidation catalyst is saturated.

In a period of time t ₃ from the time t _2, the temperature of the oxidation catalyst is further increased. Referring to FIG. 4, the oxygen storage amount increases as the bed temperature of the oxidation catalyst increases. For this reason, the air-fuel ratio of the exhaust gas when performing rich control can be further reduced. That is, by repeating the control shown in FIG. 6, at time t ₃ from the time t ₂ with increasing temperature of the oxidation catalyst, while maintaining the suppression of the carbon monoxide and the like to be discharged, the air-fuel ratio of the exhaust gas Can be gradually reduced.

In the present embodiment, the lower limit value of the air-fuel ratio of the exhaust gas is set in advance. When the target air-fuel ratio of the exhaust gas reaches the lower limit value, the control shown in FIG. That is, when the air-fuel ratio of the exhaust gas for which the rich control is constantly performed is reached, the control shown in FIG. 6 is terminated. At time t _3, the target air-fuel ratio of the exhaust gas has reached the lower limit. In time t ₃ or later, is performed sulfur poisoning recovery process by the air-fuel ratio constant exhaust gas. In time t ₃ after the oxygen storage amount when the temperature rises of the oxidation catalyst has become sufficiently large, it is possible to treat substantially all of the carbon monoxide to slip through _the NO _X storage catalyst.

In the present embodiment, the oxygen storage amount of the oxidation catalyst is calculated by detecting the temperature of the oxidation catalyst, and rich control is started when the oxygen storage amount becomes equal to or greater than the determination value. Until the time t ₂ is delaying the start time of the rich control. By performing this control, it is possible to avoid performing rich control when oxygen storage or the like of the oxidation catalyst is insufficient. Or it can suppress that carbon monoxide etc. are discharged | emitted in air | atmosphere due to there being little oxidation treatment amount of an oxidation catalyst.

In the present embodiment, in the period of time t ₃ from the time t _2, the based on the target time for the oxygen storage amount and a predetermined rich control, and calculates the target air-fuel ratio of the exhaust gas. The air-fuel ratio of the exhaust gas is changed in accordance with the oxygen storage amount of the oxidation catalyst. For this reason, carbon monoxide etc. which are released into the atmosphere can be suppressed.

  FIG. 9 shows a graph for explaining the relationship between the bed temperature of the oxidation catalyst and the amount of carbon monoxide or the like flowing into the oxidation catalyst in the present embodiment. The bar graph is the amount of carbon monoxide or the like flowing into the oxidation catalyst, and the straight line is the treatable amount of the oxidation catalyst, that is, the oxygen storage amount of the oxidation catalyst. In the present embodiment, the amount of carbon monoxide or the like flowing into the oxidation catalyst is controlled so as to be within the range of the processable amount depending on the bed temperature. For this reason, the amount of carbon monoxide and the like released to the outside air can be made substantially zero.

In the present embodiment, the oxidation treatment capability of the oxidation catalyst is calculated, the target air-fuel ratio of the exhaust gas is calculated based on the oxidation treatment capability of the oxidation catalyst, and rich control is performed based on the target air-fuel ratio of this exhaust gas. Is doing. Alternatively, at least one of the target air-fuel ratio of exhaust gas that can oxidize the reducing agent flowing out from the NO _X storage catalyst and the target time for performing rich control is calculated, and rich control is performed based on the calculated target value. . By this control, carbon monoxide and the like released into the atmosphere can be suppressed.

Here, FIG. 10 shows a time chart of a comparative example when the temperature is raised at the start of the sulfur poisoning recovery process. The normal operation until time t ₀ and the temperature increase control from time t ₀ to time t ₁ are the same as the control of the exhaust gas purification apparatus in the present embodiment.

In the control of the exhaust gas purification apparatus of the comparative example, at time t _1, it has started rich control by detecting that _the NO _X storage catalyst has reached the SO _X releasable temperature T _NX. At time t _1, and the air-fuel ratio of the exhaust gas up to a certain air-fuel ratio to a predetermined performing rich control to rich.

In this control, during the period from time t ₁ to time t _2, the temperature T _O of the oxidation catalyst is not sufficiently raised, the oxygen storage amount occluded in the oxidation catalyst is insufficient. For this reason, the amount of carbon monoxide or the like flowing into the oxidation catalyst exceeds the oxygen storage amount, and untreated carbon monoxide or the like is released to the outside air. Similarly, during the period from time t ₂ to time t ₃ , carbon monoxide and the like are released because the air / fuel ratio of the exhaust gas is controlled to a predetermined target air / fuel ratio without adjustment. Will be.

FIG. 11 shows a graph for explaining the relationship between the bed temperature of the oxidation catalyst and the amount of carbon monoxide or the like flowing into the oxidation catalyst in the control of the comparative example of the exhaust purification device. In the control of the comparative example, the amount of carbon monoxide or the like flowing into the oxidation catalyst is constant with respect to the amount that can be oxidized by the oxidation catalyst. In the region where the bed temperature of the oxidation catalyst is low, the amount of carbon monoxide or the like flowing into the oxidation catalyst exceeds the treatable amount. For this reason, carbon monoxide etc. which cannot be processed are emitted. Thus, in the comparative example, in the period of time t ₃ from the time t _1, carbon monoxide from being emitted into the atmosphere.

Referring to FIG. 5, in the present embodiment, from time t ₁ to time t ₂ , even if the NO _X storage catalyst reaches a temperature at which SO _X can be released, the rich oxidation control is not performed immediately without performing rich control. Waiting for temperature to rise. Further, in the period from time t ₂ at time t _3, in correspondence with the bed temperature of the oxidation catalyst, and the air-fuel ratio of the exhaust gas is gradually decreased. By performing this control, carbon monoxide and the like released during the temperature rise can be suppressed.

  Next, a method for adjusting the air-fuel ratio of the exhaust gas in the present embodiment will be described. The sulfur poisoning recovery process in the present embodiment is performed by controlling the fuel injection pattern in the combustion chamber. In other words, this is done by controlling the injection amount and injection timing of the fuel injected into the combustion chamber.

  FIG. 12 shows a fuel injection pattern during normal operation of the internal combustion engine in the present embodiment. The injection pattern A is a fuel injection pattern during normal operation. During normal operation, the main injection FM is performed at a compression top dead center TDC. That is, main injection FM is performed when the crank angle is approximately 0 °. Further, in order to stabilize the combustion of the main injection FM, the pilot injection FP is performed before the main injection FM. The pilot injection FP is performed, for example, in a range where the crank angle is approximately 10 ° to approximately 40 ° before the compression top dead center TDC. During normal operation, as shown in the injection pattern B, the pilot injection FP may not be performed, and the operation may be performed only with the main injection FM. In this embodiment, an injection pattern in which pilot injection FP is performed will be described as an example.

Referring to FIG. 5, during the normal operation up to time t ₀ , the operation is performed with the injection pattern A. At this time, the air-fuel ratio of the exhaust gas is lean. Then, to start raising the temperature of the NO _X storage catalyst at time t _0, it performs the Atsushi Nobori control to raise the temperature of the NO _X storage catalyst at time t ₃ from time t _0.

FIG. 13 shows an injection pattern for increasing the temperature of the NO _X storage catalyst or maintaining the increased temperature. In the injection pattern C, the injection timing of the main injection FM is delayed from the compression top dead center TDC. That is, the injection timing of the main injection FM is retarded. As the injection timing of the main injection FM is retarded, the injection timing of the pilot injection FP is also retarded. By delaying the injection timing of the main injection FM, the temperature of the exhaust gas can be raised. Further, after the main injection FM, after injection FA as auxiliary injection is performed. The after injection FA is performed at a combustible time after the main injection. The after injection FA is performed, for example, in a range where the crank angle after compression top dead center is approximately 40 °, for example, in the range where the crank angle after compression top dead center is approximately 20 ° to approximately 30 °. By performing after-injection FA, the afterburning period becomes longer and the temperature of the exhaust gas can be raised. Further, the amount of combustion in the combustion chamber can be increased and the temperature of the exhaust gas can be raised.

Referring to FIG. 5, in the period from time t ₀ to time t _3, by heating the exhaust gas, it is possible to raise the temperature of the _the NO _X storage catalyst. At time t ₃ after the period, by performing the injection pattern C, it is possible to perform the temperature maintaining control for maintaining _the NO _X storage catalyst or the SO _X release temperature. When operating with the injection pattern C, the air-fuel ratio of the exhaust gas is lean. Note that the temperature increase of the NO _X storage catalyst, but the invention is not limited to this, it is possible to employ any method.

FIG. 14 shows an injection pattern when rich control is performed in the present embodiment. At time t ₂ after the period, in order to release the SO _X, it performs rich control to make the air-fuel ratio of the exhaust gas rich or the stoichiometric air-fuel ratio. When compared with the injection pattern C, the injection pattern D increases the injection amount of the after injection FA. The after injection FA is auxiliary injection. By increasing the injection amount of the after injection FA, the air-fuel ratio of the exhaust gas can be reduced (to the rich side).

  Referring to FIG. 1, a throttle valve 10 is disposed in the engine intake passage. The amount of air flowing into the combustion chamber 2 can be adjusted by adjusting the opening of the throttle valve 10. The air-fuel ratio in the combustion chamber can be adjusted by adjusting the amount of air flowing into the combustion chamber 2 with respect to the amount of fuel injected into the combustion chamber 2. For example, by reducing the amount of air flowing into the combustion chamber 2, the air-fuel ratio in the combustion chamber can be reduced. As a result, the air-fuel ratio of the exhaust gas can be reduced.

  Further, in the present embodiment, the air-fuel ratio sensor 29 detects the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 13, and the injection pattern and combustion in the combustion chamber 2 so that the air-fuel ratio of the exhaust gas becomes the target value. The amount of air flowing into the chamber 2 can be changed. In other words, the feedback control is performed so that the amount of fuel injected into the combustion chamber 2 and the intake air amount can be controlled. Thus, the air-fuel ratio of the exhaust gas can be adjusted by adjusting the air-fuel ratio in the combustion chamber.

Referring to FIG. 5, at time t ₂ after the period, the rich control is performed at regular intervals when the temperature raising control or temperature maintenance control is performed. SO _X is released while repeating the injection pattern D and the injection pattern C. In the control of the air-fuel ratio of the exhaust gas from time t ₂ to time t _3, by adjusting the injection amount of the after injection FA, and perform the adjustment of the air-fuel ratio of the exhaust gas. After completion of the sulfur poisoning recovery process, the injection pattern is returned to the injection pattern A and normal operation is performed.

  FIG. 15 shows another injection pattern when performing rich control in the present embodiment. In the injection pattern E, post injection FPO is further performed after the main injection FM and after injection FA. The post-injection FPO is an injection that hardly participates in the combustion of fuel. The post-injection FPO is an auxiliary injection similar to the after-injection, but the post-injection affects the engine output, while the post-injection has a feature that does not contribute to the engine output. The post-injection FPO is an injection performed, for example, when the crank angle after compression top dead center is in the range of approximately 90 ° to approximately 120 °. By injecting the post-injection FPO, the air-fuel ratio of the exhaust gas can be made rich.

  When the post injection FPO is performed, the air-fuel ratio of the exhaust gas can be controlled by adjusting the injection amount of the post injection FPO. For example, the air-fuel ratio of the exhaust gas can be increased (to the lean side) by reducing the injection amount of the post injection FPO.

  Alternatively, control of the injection amount of after injection and the injection amount of post injection may be performed simultaneously. That is, the air-fuel ratio of the exhaust gas can be controlled by adjusting the injection amount of the auxiliary injection. Thus, the air-fuel ratio of the exhaust gas can be adjusted by adjusting the amount of any one of the auxiliary injections performed after the main injection. Alternatively, any control that adjusts the amount of fuel injected into the combustion chamber can be employed.

  In the present embodiment, rich control is performed by adjusting the amount of fuel injected into the combustion chamber of the internal combustion engine. However, the present invention is not limited to this mode, and any control that can control the air-fuel ratio of exhaust gas is performed. Can be adopted.

For example, in the engine exhaust passage, reducing agent supply means for adding a reducing agent may be arranged upstream of the NO _X storage catalyst. For example, a fuel addition valve that injects the same fuel as that of the engine body may be disposed in the exhaust pipe. By changing the injection amount injected from the fuel addition valve, the air-fuel ratio of the exhaust gas can be adjusted.

When the fuel addition valve is disposed in the exhaust passage by injecting the fuel from the fuel addition valve, it may be heated to _the NO _X storage catalyst. Since the NO _X storage catalyst carries a noble metal, oxidation is also performed in the NO _X storage catalyst. The temperature of the NO _X storage catalyst can be increased by this oxidation reaction heat. At this time, the amount of fuel injected from the fuel addition valve is preferably limited so as not to excessively prevent oxygen storage of the oxidation catalyst. For example, it is preferable to control so that the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst does not become a predetermined value or less.

  In the present embodiment, the bed temperature of each catalyst is detected by the temperature sensor arranged downstream of each catalyst. However, the present invention is not limited to this mode, and the bed temperature of the catalyst can be detected. Any device can be employed.

The oxidation catalyst may be any oxidation catalyst having an oxygen storage capacity. For example, a three-way catalyst on which an oxidation catalyst is supported may be used. Alternatively, an oxidation catalyst may be supported on the particulate filter. The NO _X storage catalyst may be any catalyst that can temporarily store NO _X and release it. For example, NO _X absorbent and the noble metal in order to carry out the insertion and extraction of the NO _X is may be supported on a particulate filter.

(Embodiment 2)
With reference to FIG. 16 and FIG. 17, the exhaust gas purification apparatus for an internal combustion engine in the second embodiment will be described. The internal combustion engine in the present embodiment is the same as the internal combustion engine in the first embodiment (see FIG. 1).

FIG. 16 shows a time chart of control of the exhaust gas purification apparatus for the internal combustion engine in the present embodiment. FIG. 17 shows a flowchart of control of the exhaust gas purification apparatus for an internal combustion engine in the present embodiment. Normal operation from time t _0, the Atsushi Nobori control of the temperature increase control from time t ₀ to time t _1, and from time t ₁ to time t _2, the is the same as in the first embodiment. In the present embodiment, different rich control period _the NO _X storage catalyst from time t ₂ to time t ₃ is Atsushi Nobori in the first embodiment.

Referring to FIG. 17, step 111 to step 115 are the same as the control in the first embodiment (see FIG. 6). In the control from time t ₂ to time t _3, when the oxygen storage amount is not less than the determination value in step 115, the process proceeds to step 118. In the present embodiment, a constant target air-fuel ratio of exhaust gas when performing rich control is determined in advance. In step 118, a target time for performing rich control is calculated based on the calculated oxygen storage amount.

  In step 118, referring to FIG. 8, the amount of carbon monoxide or the like that can be oxidized in the oxidation catalyst is calculated from the calculated oxygen storage amount S, and the enrichment area Sr is further calculated. . Referring to FIG. 7, a target time for enrichment for performing rich control once is calculated from this area Sr and a predetermined air-fuel ratio of exhaust gas.

  In step 119, the operation pattern is changed based on the calculated target time for performing the rich control and a predetermined target air-fuel ratio of the exhaust gas. When changing the time for performing the rich control, the time for performing the rich control can be changed, for example, by changing the length of the operation period in which the injection pattern D shown in FIG. 14 is performed.

Referring to FIG. 16, the rich control is started at time t _2. Air-fuel ratio of the exhaust gas at time t ₂ after the time is constant. In the period from time t ₂ to time t _3, as the temperature rise of the bed temperature of the oxidation catalyst, the time for performing the rich control is gradually increased.

  In the present embodiment, the oxygen storage amount of the oxidation catalyst is calculated, and the target time for performing the rich control is calculated based on a predetermined target air-fuel ratio of the exhaust gas. By controlling the time during which rich control is performed, the amount of carbon monoxide or the like flowing into the oxidation catalyst can be controlled.

Thus, in the present embodiment, the oxidation treatment capability of the oxidation catalyst is calculated, and the target time for performing rich control is calculated based on the oxidation treatment capability of the oxidation catalyst. A target time for performing rich control capable of oxidizing carbon monoxide or the like flowing out from the NO _X storage catalyst is calculated. Almost all of carbon monoxide and the like flowing into the oxidation catalyst can be oxidized, and carbon monoxide and the like released into the atmosphere can be suppressed.

  Other configurations, operations, and effects are the same as those in the first embodiment, and thus description thereof will not be repeated here.

(Embodiment 3)
With reference to FIGS. 18 to 21, an exhaust gas purification apparatus for an internal combustion engine according to Embodiment 3 will be described. The internal combustion engine in the present embodiment is the same as the internal combustion engine in the first embodiment (see FIG. 1).

FIG. 18 shows a time chart of control of the exhaust gas purification apparatus for an internal combustion engine in the present embodiment. FIG. 19 shows a flowchart of the control of the exhaust gas purification apparatus for the internal combustion engine in the present embodiment. Normal operation from time t _0, the Atsushi Nobori control of the temperature increase control from time t ₀ to time t _1, and from time t ₁ to time t _2, the is the same as in the first embodiment. In the present embodiment, the control of the period during which the NO _X storage catalyst is heated from time t ₂ to time t ₃ is different from that in the first embodiment.

Referring to FIG. 19, steps 111 to 115 are the same as the control of the exhaust purification device in the first embodiment (see FIG. 6). In the control from time t ₂ to time t ₃ , if the oxygen storage amount is not less than the determination value in step 115, the process proceeds to step 121. In the present embodiment, in step 121, an oxygen release rate V when oxygen stored in the oxidation catalyst is released is calculated.

  FIG. 20 shows a graph for explaining the relationship between the bed temperature of the oxidation catalyst and the oxygen release rate of the oxidation catalyst. The horizontal axis is the bed temperature of the oxidation catalyst, and the vertical axis is the oxygen release rate V. It can be seen that the higher the bed temperature of the oxidation catalyst, the higher the oxygen release rate. The oxygen release rate corresponds to the rate of oxidizing carbon monoxide and the like. Here, depending on the type of the oxidation catalyst and the like, when the bed temperature is low, the oxygen release rate is slow, and the rate at which carbon monoxide or the like flows may not be reached. That is, there are cases where the oxygen release rate is slow and all carbon monoxide and the like cannot be oxidized. In FIG. 20, for one carbon monoxide inflow rate, a region where carbon monoxide or the like passes through the oxidation catalyst in a region where the bed temperature is low is defined.

  In the present embodiment, control is performed in consideration of the oxygen release rate of the oxidation catalyst. From the graph shown in FIG. 20, the oxygen release rate V can be calculated by specifying the bed temperature of the oxidation catalyst. For example, a map of the oxygen release rate as a function of the bed temperature of the oxidation catalyst can be stored in the ROM 32 of the electronic control unit 30. By detecting the bed temperature of the oxidation catalyst, the oxygen release rate can be calculated.

  Referring to FIG. 19, when oxygen release rate V is calculated in step 121, the process proceeds to step 122. In step 122, a target air-fuel ratio of exhaust gas that can oxidize all carbon monoxide and the like within the calculated oxygen release rate is calculated. For example, a map of the target air-fuel ratio of exhaust gas as a function of the oxygen release rate V is stored in the ROM 32 of the electronic control unit 30. By specifying the oxygen release rate V, the air-fuel ratio of the corresponding exhaust gas can be calculated. As the oxygen release rate V increases, the air-fuel ratio of the exhaust gas that can be set can also be reduced.

  Next, in step 123, the time for performing rich control is calculated based on the oxygen storage amount S calculated in step 114 and the target air-fuel ratio of the exhaust gas calculated in step 122. The calculation of the time for performing the rich control can be obtained by calculating the area Sr when the rich control is performed, as in the above-described embodiment. Next, the routine proceeds to step 124, where the operation pattern is changed based on the calculated target air-fuel ratio of exhaust gas and the time during which rich control is performed.

Referring to FIG. 18, in a period of time t ₃ from the time t _2, the air-fuel ratio of the exhaust gas is gradually decreased. In this embodiment, since the time for performing one rich control is calculated, the time for each rich control is different. For example, when the air-fuel ratio of exhaust gas when performing rich control is limited by the oxygen release rate of the oxidation catalyst, the time for performing one rich control becomes longer. With this control, more of the stored oxygen can be used for the oxidation treatment. Note that when the air-fuel ratio of the exhaust gas when performing rich control is limited, the number of times of performing rich control may be increased.

  FIG. 21 shows the relationship between the oxidation catalyst bed temperature and the time during which rich control is performed and the target air-fuel ratio of exhaust gas when the oxidation catalyst bed temperature and rich control are performed in the control of the exhaust gas purification apparatus according to the present embodiment. It is a graph explaining a relationship. In the region where the bed temperature is low, a region through which carbon monoxide or the like shown in FIG. 20 passes is defined.

  In a region where carbon monoxide or the like passes through, the target air-fuel ratio of the exhaust gas gradually increases as the bed temperature increases. Further, as the bed temperature rises, the enrichment time for performing rich control is gradually shortened. In the region where the bed temperature is higher than the region where carbon monoxide or the like passes through, both the enrichment time and the target air-fuel ratio of the exhaust gas are made constant.

  In the present embodiment, the oxygen release rate of the oxidation catalyst is calculated by detecting the temperature of the oxidation catalyst, and the target air-fuel ratio of the exhaust gas is calculated based on the oxygen release rate. This control can suppress the release of carbon monoxide or the like into the atmosphere even when the oxygen release rate is slow.

  In the present embodiment, the target time for enriching the air-fuel ratio of the exhaust gas is calculated from the calculated oxygen storage amount and the calculated target air-fuel ratio. By performing this control, more oxygen stored in the oxidation catalyst can be discharged. The rich control is not limited to this form, and the enrichment time may be set in advance.

  Since other configurations, operations, and effects are the same as those in the first or second embodiment, description thereof will not be repeated here.

  In the respective drawings described above, the same or corresponding parts are denoted by the same reference numerals. In addition, said embodiment is an illustration and does not limit invention. Further, in the embodiment, changes included in the scope of claims are intended.

1 is a schematic diagram of an internal combustion engine in a first embodiment. It is an enlarged schematic sectional view of the NO _X storage catalyst when absorbing NO _X. It is an enlarged schematic sectional view of the NO _X storage catalyst when absorbing the SO _X. It is a graph explaining the relationship between the bed temperature and the oxygen storage amount in the oxidation catalyst which has oxygen storage capability. 6 is a time chart when the temperature is raised in order to perform sulfur poisoning recovery processing in the exhaust gas purification apparatus in the first embodiment. 6 is a flowchart when the temperature is raised in order to perform sulfur poisoning recovery processing in the exhaust gas purification apparatus in the first embodiment. It is an enlarged view of the air-fuel ratio of exhaust gas when performing rich control. It is a graph explaining the relationship between the area Sr when rich control is performed and the amount of carbon monoxide or the like flowing into the oxidation catalyst. 4 is a graph showing the relationship between the bed temperature of the oxidation catalyst in Embodiment 1 and the amount of carbon monoxide or the like flowing into the oxidation catalyst. 3 is a time chart for explaining the control of the exhaust emission control device of the comparative example in the first embodiment. 3 is a graph showing the relationship between the bed temperature of an oxidation catalyst of a comparative example in Embodiment 1 and the amount of carbon monoxide or the like flowing into the oxidation catalyst. It is an injection pattern in the combustion chamber in a normal operation state. It is an injection pattern in the combustion chamber at the time of raising the temperature of _the NO _X storage catalyst in the sulfur poisoning recovery process. It is an injection pattern in a combustion chamber when performing rich control in the sulfur poisoning recovery process. It is another injection pattern in the combustion chamber when performing rich control in the sulfur poisoning recovery process. 6 is a time chart when the temperature is raised to perform the sulfur poisoning recovery process in the second embodiment. 6 is a flowchart when a temperature is raised to perform a sulfur poisoning recovery process in the second embodiment. 10 is a time chart when the temperature is raised to perform the sulfur poisoning recovery process in the third embodiment. 10 is a flowchart when the temperature is raised to perform the sulfur poisoning recovery process in the third embodiment. It is a graph explaining the relationship between the bed temperature of an oxidation catalyst, and an oxygen release rate. It is a graph explaining the relationship between the bed temperature of an oxidation catalyst, the target air fuel ratio of exhaust gas, or the time which performs rich control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine body 2 Combustion chamber 3 Fuel injection valve 8 Intake air amount detector 10 Throttle valve 12 Exhaust pipe 13 Oxidation catalyst 17 NO _X storage catalyst 21 Fuel supply pipe 26 Temperature sensor 27 Temperature sensor 28 Differential pressure sensor 29 Air-fuel ratio sensor 30 Electron Control unit 31 Bilateral bus 32 ROM
33 RAM
34 CPU

Claims (7)

When the air-fuel ratio of the exhaust gas flowing into the engine exhaust passage is lean, the NO _X contained in the exhaust gas is occluded, and when the air-fuel ratio of the exhaust gas flowing in becomes the stoichiometric air-fuel ratio or rich, the stored NO _X is released. _the NO _X storage catalyst is arranged, an oxidation catalyst is arranged having an oxygen storage capacity downstream of the engine exhaust passage of the NO _X storage catalyst, the allowable amount of SO _X amount stored in the NO _X storage catalyst is predetermined to When NO is exceeded, the temperature of the NO _X storage catalyst is raised to a temperature at which SO _X can be released, and at the same time, the sulfur poisoning recovery process is performed by rich control that makes the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst rich. In the exhaust gas purification apparatus for an internal combustion engine,
The temperature of the NO _X storage catalyst when it should be increased to SO _X releasable temperature, when the air-fuel ratio of the exhaust gas flowing from the NO _X storing catalyst to the NO _X storing catalyst so as to release the SO _X rich oxide Calculating at least one of a target air-fuel ratio of exhaust gas capable of oxidizing the reducing agent flowing out from the NO _X storage catalyst toward the catalyst and a target time for performing rich control, and calculating the target air-fuel ratio of the exhaust gas and rich control; An exhaust emission control device for an internal combustion engine, wherein the rich control is performed based on a target time to be performed. When the temperature of the NO _X storage catalyst should be raised to a temperature at which SO _X can be released, the oxygen storage amount of the oxidation catalyst is calculated by detecting the temperature of the oxidation catalyst, and the oxygen storage amount and predetermined rich control are performed. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein a target air-fuel ratio of the exhaust gas is calculated based on a target time, and the rich control is performed based on the target air-fuel ratio of the exhaust gas. When the temperature of the NO _X storage catalyst is to be increased to a temperature at which SO _X can be released, the oxygen storage amount of the oxidation catalyst is calculated by detecting the temperature of the oxidation catalyst, and the oxygen storage amount and a predetermined exhaust gas target are calculated. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein a target time for performing rich control is calculated based on an air-fuel ratio, and the rich control is performed based on the target time for performing rich control. When the temperature of the NO _X storage catalyst should be increased to a temperature at which SO _X can be released, the oxygen release rate of the oxidation catalyst is calculated by detecting the temperature of the oxidation catalyst, and the target air-fuel ratio of the exhaust gas is calculated based on the oxygen release rate The exhaust purification device for an internal combustion engine according to claim 1, wherein the rich control is performed based on a target air-fuel ratio of the exhaust gas. When the temperature of the NO _X storage catalyst should be increased to a temperature at which SO _X can be released, the oxygen storage amount of the oxidation catalyst is calculated by detecting the temperature of the oxidation catalyst, and the exhaust gas is calculated from the oxygen storage amount and the target air-fuel ratio of the exhaust gas. The target time for enriching the gas air-fuel ratio is calculated, and the rich control is performed based on the target air-fuel ratio of the exhaust gas and the target time for performing the rich control. An exhaust purification device for an internal combustion engine. 6. The exhaust gas air-fuel ratio is gradually reduced as the temperature of the oxidation catalyst increases when the temperature of the NO _X storage catalyst should be increased to a temperature at which SO _X can be released. An exhaust purification device for an internal combustion engine according to claim 1. When the temperature of the NO _X storage catalyst should be increased to a temperature at which SO _X can be released, the oxygen storage amount of the oxidation catalyst is calculated by detecting the temperature of the oxidation catalyst, and the oxygen storage amount exceeds a predetermined determination value. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein the rich control is started when the engine becomes an exhaust gas.

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