JP2004036456A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the amount of sulfate to be exhausted into the air. <P>SOLUTION: An auxiliary catalyst is arranged in an exhaust passage on the downstream side of a particulate filter supporting a NOx catalyst. Prior to particulate oxidation control for oxidizing accumulated particulates on the particulate filter, SOx removal control is performed for removing SOx deposited on the auxiliary catalyst. Prior to accumulated SOx reduction control for reducing the accumulated SOx in the NOx catalyst, SOx removal control is performed. In the SOx removal control, an average air-fuel ratio AFA of exhaust gas flowing into the auxiliary catalyst is turned slightly rich. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine.
[0002]
[Prior art]
Conventionally, a particulate filter for trapping fine particles in an inflowing exhaust gas is disposed in an exhaust passage of an internal combustion engine in which combustion is continuously performed under a lean air-fuel ratio, and the NO in exhaust gas flowing in when the air-fuel ratio is lean_XNO when the reducing agent is contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas decreases_XNO stored and reduced_XNO decreases the amount of_XThere is known an internal combustion engine in which a catalyst is supported on the particulate filter and an auxiliary catalyst having oxidizing ability is disposed in an exhaust passage downstream of the particulate filter. This auxiliary catalyst is NO_XThe HC and CO flowing out of the catalyst are oxidized, so that a large amount of HC and CO is prevented from being discharged into the atmosphere.
[0003]
By the way, in such an internal combustion engine, in order to oxidize and remove fine particles deposited on the particulate filter, the temperature of the particulate filter is temporarily increased while maintaining the air-fuel ratio of the exhaust gas flowing into the particulate filter lean. To be increased. On the other hand, as will be described in detail later, NO_XSO in the catalyst_XAre stored without the formation of sulfate and this SO_XIs NO_XNO even if the air-fuel ratio of the exhaust gas flowing into the catalyst is lean_XNO when catalyst temperature rises_XExhausted from the catalyst. Therefore, every time the particulates deposited on the particulate filter are oxidized and removed, NO_XCatalyst to SO_XIs SO₂Will be discharged in the form of
[0004]
[Problems to be solved by the invention]
However, when the particulate matter deposited on the particulate filter is thus oxidized and removed, the temperature of the auxiliary catalyst is also high, and the air-fuel ratio of the exhaust gas flowing into the auxiliary catalyst is lean. Since the amount of reducing agent in the exhaust gas flowing into the_XSO discharged from the catalyst₂Is an auxiliary catalyst with sulfate SO₃And then SO₃There is a problem that it is discharged into the atmosphere in the form of
[0005]
Accordingly, an object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can reduce the amount of sulfate discharged into the atmosphere.
[0006]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a fuel cell system in which SOx in exhaust gas flowing into an exhaust passage of an internal combustion engine in which combustion is continuously performed under a lean air-fuel ratio._XSO that temporarily stores_XA storage agent is arranged and the SO_XAn auxiliary catalyst having oxidizing ability is arranged in the exhaust passage downstream of the storage agent,_XSO adhering to the storage agent_XIs SO_XPrior to being discharged from the storage agent, the SO adhering to the auxiliary catalyst_XIs removed from the auxiliary catalyst.
[0007]
According to a second aspect of the present invention, in the first aspect, there is provided a reducing agent supply means for supplying a reducing agent to the auxiliary catalyst, and the SOx adhering to the auxiliary catalyst is provided._XIs removed from the auxiliary catalyst, the reducing agent is supplied from the reducing agent supply means to the auxiliary catalyst so that the air-fuel ratio of the exhaust gas flowing into the auxiliary catalyst becomes rich.
[0008]
According to a third aspect, in the first aspect, the SO_XThe storage agent is carried on a particulate filter for collecting fine particles in the exhaust gas flowing into the storage device.
[0009]
Further, according to a fourth aspect, in the first aspect, the particulate matter is maintained while maintaining the air-fuel ratio of the exhaust gas flowing into the particulate filter lean so as to oxidize the fine particles deposited on the particulate filter. Prior to raising the temperature of the curated filter, SO2 adhering to the auxiliary catalyst_XIs removed from the auxiliary catalyst.
[0010]
According to a fifth aspect, in the first or third aspect, the SO_XNO in the inflowing exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean_XNO when the reducing agent is contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas decreases_XNO stored and reduced_XNO decreases the amount of_XFormed from catalyst.
[0011]
Further, according to a sixth aspect, in the first aspect, the NO_XSO stored in the form of sulfate in the catalyst_XIs NO_XPrior to being discharged from the catalyst, the SO adhering to the auxiliary catalyst_XIs removed from the auxiliary catalyst.
[0012]
According to a seventh aspect, in the first aspect, the auxiliary catalyst is carried on a particulate filter for collecting fine particles in exhaust gas flowing into the auxiliary catalyst.
[0013]
In the present specification, the ratio of air supplied to the exhaust passage, the combustion chamber, and the intake passage upstream of a certain position in the exhaust passage to a reducing agent such as hydrocarbon HC and carbon monoxide CO is referred to as the ratio. It is called the air-fuel ratio of the exhaust gas at the position.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine. The present invention can also be applied to a spark ignition type internal combustion engine.
[0015]
Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Denotes an exhaust valve, and 10 denotes an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a compressor 15 of an exhaust turbocharger 14 via an intake duct 13. A throttle valve 17 driven by a step motor 16 is arranged in the intake duct 13, and a cooling device 18 for cooling intake air flowing through the intake duct 13 is arranged around the intake duct 13. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 18, and the engine cooling water cools the intake air.
[0016]
On the other hand, the exhaust port 10 is connected to an exhaust turbine 21 of the exhaust turbocharger 14 via an exhaust manifold 19 and an exhaust pipe 20, and an outlet of the exhaust turbine 21 is connected to a catalytic converter 22 via an exhaust pipe 20a.
[0017]
Referring to FIG. 2 together with FIG. 1, the catalytic converter 22 includes a switching valve 61 driven by a step motor 60, and an outlet of the exhaust pipe 20 a is connected to an inflow port 62 of the switching valve 61. Further, an exhaust gas exhaust pipe 64 of the catalytic converter 22 is connected to an outlet port 63 of the switching valve 61 facing the inlet port 62. The switching valve 61 further has a pair of inflow / outflow ports 65 and 66 facing each other on both sides of a straight line connecting the inflow port 62 and the outflow port 63. Both ends of the exhaust pipe 67 are respectively connected. The exhaust pipe 23 is connected to the outlet of the exhaust gas discharge pipe 64.
[0018]
The annular exhaust pipe 67 extends through the exhaust gas exhaust pipe 64, and a filter housing chamber 68 is formed in a portion of the annular exhaust pipe 67 located inside the exhaust gas exhaust pipe 64. A particulate filter 69 for collecting fine particles in exhaust gas is accommodated in the filter accommodation chamber 68. In FIG. 2, reference numerals 69a and 69b denote one end face and the other end face of the particulate filter 69, respectively.
[0019]
As shown in FIG. 2A showing a partial vertical cross-sectional view of the catalytic converter 22 including one end surface 69a of the particulate filter 69, and FIG. A honeycomb structure 69 has a plurality of exhaust gas passages 70 and 71 extending parallel to each other. These exhaust gas passages are constituted by an exhaust gas passage 70 having one end opened and the other end closed by a seal member 72, and an exhaust gas passage 71 having the other end opened and one end closed by a seal member 73. Is done. In FIG. 2A, a hatched portion indicates the sealing material 73. These exhaust gas passages 70 and 71 are alternately arranged via thin partition walls 74 formed of a porous material such as cordierite. In other words, the exhaust gas passages 70, 71 are arranged such that each exhaust gas passage 70 is surrounded by four exhaust gas passages 71, and each exhaust gas passage 71 is surrounded by four exhaust gas passages 70.
[0020]
The NO on the particulate filter 69 is described later._XA catalyst 81 is supported. On the other hand, a catalyst accommodating chamber 75 is formed in the exhaust gas exhaust pipe 64 between the outflow port 63 of the switching valve 61 and a portion through which the annular exhaust pipe 67 penetrates. An auxiliary catalyst 76 having an oxidizing ability and supported on a substrate having a honeycomb structure is accommodated therein.
[0021]
An electrically controlled reducing agent supply valve 77 for supplying a reducing agent to the particulate filter 69 is attached to the annular exhaust pipe 67 between the inflow / outflow port 65 of the switching valve 61 and the particulate filter 69. The reducing agent supply valve 77 is supplied with a reducing agent from an electrically controlled reducing agent pump 78. In the embodiment according to the present invention, the fuel of the internal combustion engine, that is, light oil, is used as the reducing agent. In the embodiment according to the present invention, the reducing agent supply valve is not disposed in the annular exhaust pipe 67 between the inflow / outflow port 66 and the particulate filter 69.
[0022]
Still referring to FIG. 1, the exhaust manifold 19 and the surge tank 12 are connected to each other via an exhaust gas recirculation (hereinafter, referred to as EGR) passage 24, and an electrically controlled EGR control valve 25 is provided in the EGR passage 24. Be placed. Further, a cooling device 26 for cooling the EGR gas flowing in the EGR passage 24 is disposed around the EGR passage 24. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 26, and the engine cooling water cools the EGR gas.
[0023]
On the other hand, each fuel injection valve 6 is connected to a fuel reservoir, a so-called common rail 27, via a fuel supply pipe 6a. Fuel is supplied into the common rail 27 from a fuel pump 28 of an electrically controlled variable discharge amount, and the fuel supplied into the common rail 27 is supplied to the fuel injection valve 6 through each fuel supply pipe 6a. A fuel pressure sensor 29 for detecting the fuel pressure in the common rail 27 is attached to the common rail 27, and the fuel pump 28 is controlled so that the fuel pressure in the common rail 27 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 29. Is controlled.
[0024]
The electronic control unit 40 is composed of a digital computer, and is connected to each other by a bidirectional bus 41 such as a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a CPU (Microprocessor) 44, an input port 45 and an output port 46. Is provided. The output signal of the fuel pressure sensor 29 is input to the input port 45 via the corresponding AD converter 47. A temperature sensor 48 for detecting the temperature of the exhaust gas flowing out of the auxiliary catalyst 76 is attached to the exhaust gas exhaust pipe 64 downstream of the auxiliary catalyst 76, and the output voltage of the temperature sensor 48 is supplied via a corresponding AD converter 47. Input to the input port 45. The temperature of the exhaust gas indicates the temperature of the auxiliary catalyst 76. A pressure sensor 49 for detecting the pressure in the exhaust pipe 20a, that is, the engine back pressure, is attached to the exhaust pipe 20a, and the output voltage of the pressure sensor 49 is input to the input port 45 via the corresponding AD converter 47. You. A load sensor 51 that generates an output voltage proportional to the amount of depression of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. You. Further, the input port 45 is connected to a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, by 30 °.
[0025]
On the other hand, the output port 46 is connected to the fuel injection valve 6, the throttle valve driving step motor 16, the EGR control valve 25, the fuel pump 28, the switching valve driving step motor 60, the reducing agent supply valve 77, And a reducing agent pump 78.
[0026]
The switching valve 61 is usually located at one of the position indicated by the solid line and the position indicated by the broken line in FIG. When the switching valve 61 is positioned at the position shown by the solid line in FIG. 3B, the inflow port 62 communicates with the inflow / outflow port 65 while the communication with the outflow port 63 and the inflow / outflow port 66 is cut off by the switching valve 61. The outflow port 63 is connected to the inflow / outflow port 66 by the switching valve 61. As a result, all the exhaust gas flowing through the exhaust pipe 20a flows into the annular exhaust pipe 67 via the inflow port 62 and the inflow / outflow port 65 sequentially as indicated by the solid arrow in FIG. Next, after passing through the particulate filter 69, it flows out into the exhaust gas discharge pipe 64 through the inflow / outflow port 66 and the outflow port 63 in order.
[0027]
On the other hand, when the switching valve 61 is positioned at the position shown by the broken line in FIG. 3B, the inflow port 62 is inflowed and outflowed while the communication between the outflow port 63 and the inflow / outflow port 65 is cut off by the switching valve 61. The outflow port 63 is communicated with the inflow / outflow port 65 by the switching valve 61. As a result, all the exhaust gas flowing through the exhaust pipe 20a flows into the annular exhaust pipe 67 via the inflow port 62 and the inflow / outflow port 66 sequentially as indicated by the broken arrow in FIG. Next, after passing through the particulate filter 69, it flows out into the exhaust gas discharge pipe 64 via the inflow / outflow port 65 and the outflow port 63 in order.
[0028]
By switching the position of the switching valve 61 in this manner, the flow of the exhaust gas in the annular exhaust pipe 67 is reversed. In other words, if the exhaust gas is NO_XNO flows into the catalyst 81 through one end surface thereof and_XThe exhaust gas is guided to flow out of the catalyst 81 through the other end face, or NO_XNO flows into the catalyst 81 through the other end face._XIt is possible to switch whether to guide the exhaust gas so as to flow out of the catalyst 81 via one end surface thereof. Hereinafter, the flow of the exhaust gas indicated by a solid line in FIG. 3B is referred to as a forward flow, and the flow of the exhaust gas indicated by a broken line is referred to as a reverse flow. In FIG. 3B, the position of the switching valve 61 indicated by a solid line is referred to as a forward flow position, and the position of the switching valve 61 indicated by a broken line is referred to as a reverse flow position.
[0029]
The exhaust gas that has flowed into the exhaust gas exhaust pipe 64 via the outflow port 66 then passes through the catalyst 76 and proceeds along the outer peripheral surface of the annular exhaust pipe 67 as shown in FIGS. After that, it flows out into the exhaust pipe 23.
[0030]
Explaining the flow of the exhaust gas in the particulate filter 69, the exhaust gas flows into the particulate filter 69 via one end surface 69a and flows out of the particulate filter 69 via the other end surface 69b at the time of forward flow. At this time, the exhaust gas flows into the exhaust gas passage 70 opened in the one end surface 69a, and then flows out into the adjacent exhaust gas passage 71 through the surrounding partition wall 74. On the other hand, at the time of backflow, the exhaust gas flows into the particulate filter 69 via the other end surface 69b, and flows out of the particulate filter 69 via the one end surface 69a. At this time, the exhaust gas flows into the exhaust gas passage 71 opened in the other end surface 69b, and then flows out into the adjacent exhaust gas passage 70 through the surrounding partition wall 74.
[0031]
On the partition wall 74 of the particulate filter 69, that is, for example, on both side surfaces of the partition wall 74 and the inner wall surface of the pores, as shown in FIG._XCatalysts 81 are respectively supported. This NO_XThe catalyst 81 is made of, for example, alumina as a carrier. On this carrier, for example, alkali metals such as potassium K, sodium Na, lithium Li, and cesium Cs, alkaline earths such as barium Ba and calcium Ca, lanthanum La, and yttrium Y are used. And at least one selected from rare earth elements and a noble metal such as platinum Pt, palladium Pd, rhodium Rh, and iridium Ir.
[0032]
NO_XThe catalyst is NO when the average air-fuel ratio of the inflowing exhaust gas is lean._XNO when the reducing agent is contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas decreases_XNO stored and reduced_XPerforms an accumulation reducing action to reduce the amount of
[0033]
NO_XThe detailed mechanism of the accumulation and reduction of the catalyst has not been fully elucidated. However, the mechanism currently considered is briefly described below, taking the case where platinum Pt and barium Ba are carried on a carrier as an example.
[0034]
That is, NO_XWhen the air-fuel ratio of the exhaust gas flowing into the catalyst becomes considerably leaner than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas flowing into the catalyst greatly increases, and the oxygen O₂Is O₂ ⁻Or O^2-On the surface of platinum Pt. On the other hand, NO in the inflowing exhaust gas adheres to the surface of platinum Pt, and O on the surface of platinum Pt.₂ ⁻Or O^2-Reacts with NO₂(NO + O₂→ NO₂+ O^*, Where O^*Is active oxygen). NO generated next₂Is partially oxidized on platinum Pt while NO_XWhile being absorbed in the catalyst and binding to barium oxide BaO, nitrate ions NO₃ ⁻NO in the form of_XDiffusion into the catalyst. NO in this way_XIs NO_XStored in the catalyst.
[0035]
In contrast, NO_XWhen the air-fuel ratio of the exhaust gas flowing into the catalyst becomes rich or stoichiometric, the oxygen concentration in the exhaust gas decreases and NO₂Is reduced and the reaction proceeds in the opposite direction (NO₃ ⁻→ NO + 2O^*) And thus NO_XNitrate ion NO in catalyst₃ ⁻Is NO in the form of NO_XReleased from the catalyst. This released NO_XIf the exhaust gas contains a reducing agent, that is, HC or CO, it reacts with these HC and CO to be reduced. Thus, NO on the surface of platinum Pt_XNO when no longer exists_XNO from catalyst to catalyst_XIs released and reduced, and NO_XNO stored in the catalyst_XGradually decreases.
[0036]
It should be noted that NO is formed without forming nitrate._XAnd store NO_XNO without releasing_XIt is also possible to reduce Also, active oxygen O^*Focusing on, NO_XThe catalyst is NO_XOf active oxygen O along with the accumulation and release of oxygen^*It can also be regarded as an active oxygen generation catalyst that generates OH.
[0037]
On the other hand, in the embodiment according to the present invention, the auxiliary catalyst 76 is formed of a noble metal catalyst containing noble metal, for example, platinum Pt without containing alkali metals, alkaline earths, and rare earths. However, when the auxiliary catalyst 76 is_XIt may be formed from a catalyst.
[0038]
Here, the particulate filter 69 is disposed substantially at the center of the annular exhaust pipe 67, that is, the distance from the inflow port 62 of the switching valve 61 to the particulate filter 69, and the distance from the particulate filter 69 to the outflow port 63. The distance is almost the same between when the switching valve 61 is at the forward flow position and when it is at the reverse flow position. This means that the state of the particulate filter 69, for example, the temperature hardly changes between when the switching valve 61 is in the forward flow position and when the switching valve 61 is in the reverse flow position. No control required.
[0039]
In the embodiment according to the present invention, the switching valve 61 is switched from the forward flow position to the reverse flow position or vice versa each time the engine low load operation is performed. By doing so, as will be understood from the following description, the particulate filter 69 and the NO_XParticles and NO bypassing the catalyst 81_XCan be reduced.
[0040]
As described above, the exhaust gas passes through the particulate filter 69 regardless of whether the flow is in the forward flow or in the reverse flow. Further, in the internal combustion engine shown in FIG. 1, the combustion is continuously performed under the lean air-fuel ratio, and therefore, the air-fuel ratio of the exhaust gas flowing into the particulate filter 69 is maintained lean. As a result, NO in the exhaust gas_XIs NO on the particulate filter 69_XIt is stored in the catalyst 81.
[0041]
NO over time_XNO stored in catalyst 81_XThe amount increases gradually. Therefore, in the embodiment according to the present invention, for example, NO_XNO stored in catalyst 81_XNO when the amount exceeds the allowable amount_XNO stored in catalyst 81_XIs reduced to NO_XNO stored in catalyst 81_XNO from the reducing agent supply valve 77 to reduce the amount_XA reducing agent, that is, a reducing agent is temporarily supplied to the catalyst 81. In this case, NO_XThe air-fuel ratio of the exhaust gas flowing into the catalyst 81 is temporarily switched to rich.
[0042]
On the other hand, fine particles mainly composed of solid carbon contained in the exhaust gas are collected on the particulate filter 69. That is, when roughly described, fine particles are trapped on the side surface of the partition wall 74 on the exhaust gas passage 70 side and in the pores during the forward flow, and on the side surface of the partition wall 74 and the pores on the exhaust gas passage 71 side during the reverse flow. Fine particles are collected. In the internal combustion engine shown in FIG. 1, combustion is continuously performed under a lean air-fuel ratio._XSince the catalyst 81 has an oxidizing ability, if the temperature of the particulate filter 69 is maintained at a temperature at which the particulates can be oxidized, for example, 250 ° C. or higher, the particulates are oxidized and removed on the particulate filter 69. You.
[0043]
In this case, the above-mentioned NO_XNO of catalyst 81_XAccording to the accumulation reduction mechanism of NO, NO_XNO in catalyst 81_XNO when is stored_XActive oxygen is also generated when is released. This active oxygen is oxygen O₂Therefore, the fine particles deposited on the particulate filter 69 are quickly oxidized. That is, NO on the particulate filter 69_XWhen the catalyst 81 is carried, the particulates deposited on the particulate filter 69 are oxidized regardless of whether the air-fuel ratio of the exhaust gas flowing into the particulate filter 69 is lean or rich. In this way, the fine particles are continuously oxidized.
[0044]
However, when the temperature of the particulate filter 69 is not maintained at a temperature at which the particulates can be oxidized, or when the amount of the particulates flowing into the particulate filter 69 per unit time becomes considerably large, the particulates deposited on the particulate filter 69 become large. Gradually increases, and the pressure loss of the particulate filter 69 increases.
[0045]
Therefore, in the embodiment according to the present invention, for example, when the amount of deposited particulates on the particulate filter 69 exceeds the allowable maximum amount, the air-fuel ratio of the exhaust gas flowing into the particulate filter 69 is maintained while maintaining a lean air-fuel ratio. Fine particle oxidation control is performed in which the temperature is raised to a required particle oxidation temperature TNP, for example, 600 ° C. or higher, and then maintained at or above the required particle oxidation temperature TNP. When the particulate oxidation control is performed, the particulates deposited on the particulate filter 69 are ignited and burned and removed. In the embodiment shown in FIG. 1, when the engine back pressure detected by the pressure sensor 49 when the switching valve 61 is held at the forward flow position or the backward flow position exceeds the allowable value, the particulate filter 69 Is determined to have exceeded the maximum allowable amount.
[0046]
More specifically, in the embodiment shown in FIG. 1, while maintaining the switching valve 61 at the forward flow position, while maintaining the air-fuel ratio of the exhaust gas flowing into the particulate filter 69 lean, the temperature of the particulate filter 69 The reducing agent is supplied from the reducing agent supply valve 77 so that the temperature is increased to or higher than the required particle oxidation temperature TNP and then maintained at or above the required particle oxidation temperature TNP. This reducing agent is oxidized on the particulate filter 69, and as a result, the temperature TN of the particulate filter 69 is raised to and maintained at the particulate oxidation required temperature TNP or higher.
[0047]
By the way, the sulfur content in the exhaust gas is SO_XIn the form of NO_XNO in the catalyst 81_XNot only SO_XIs also stored. This SO_XNO_XThe accumulation mechanism in the catalyst 81 is NO_XIt is thought to be the same as the accumulation mechanism. That is, when the case where platinum Pt and barium Ba are supported on a carrier is briefly described as an example, NO_XWhen the air-fuel ratio of the exhaust gas flowing into the catalyst 81 is lean, the oxygen O₂Is O₂ ⁻Or O^2-Is attached to the surface of platinum Pt in the form of₂Adheres to the surface of platinum Pt, and O₂ ⁻Or O^2-Reacts with SO₃It becomes. Then the generated SO₃Is further oxidized on platinum Pt_XWhile being absorbed in the catalyst 81 and binding to barium oxide BaO, sulfate ions SO₄ ⁻NO in the form of_XIt diffuses into the catalyst 81. This sulfate ion SO₄ ⁻Is then barium ion Ba⁺Combined with sulfate BaSO₄Generate
[0048]
This sulfate BaSO₄Is difficult to decompose, NO_XEven if the air-fuel ratio of the exhaust gas flowing into the catalyst 81 is simply rich, NO_XSulfate BaSO in catalyst 81₄Does not decrease. Therefore, as time passes, NO_XSulfate BaSO in catalyst 81₄Increases, resulting in NO_XNO that can be stored in the catalyst 81_XWill be reduced.
[0049]
However, NO_XNO while maintaining the temperature of the catalyst 81 at 550 ° C. or higher_XIf the average air-fuel ratio of the exhaust gas flowing into the catalyst 81 is set to the stoichiometric air-fuel ratio or rich, NO_XSulfate BaSO in catalyst 81₄Is decomposed into SO₃NO in the form of_XReleased from the catalyst 81. This released SO₃If the exhaust gas contains a reducing agent, that is, HC or CO, it reacts with these HC and CO and reacts with SO.₂It is reduced to. NO in this way_XSulfate BaSO in catalyst 81₄SO stored in the form of_XGradually decreases, and at this time NO_XCatalyst 81 to SO_XIs SO₃No spill in the form of
[0050]
Therefore, in the embodiment according to the present invention, for example, NO_XSO stored in catalyst 81_XIf the amount exceeds the allowable amount, NO_XSO stored in catalyst 81_XNO to reduce the amount_XWhile maintaining the average air-fuel ratio of the exhaust gas flowing into the catalyst 81 at the stoichiometric air-fuel ratio or rich,_XAccumulated SO that is maintained at the required amount decrease temperature TNS, for example, 550 ° C. or higher._XThe amount reduction control is performed.
[0051]
More specifically, in the embodiment shown in FIG. 1, while the switching valve 61 is held at the weak forward flow position as shown in FIG._XWhile maintaining the average air-fuel ratio of the exhaust gas flowing into the catalyst 81 slightly rich, the NO_XWhen the temperature of the catalyst 81 is SO_XThe reducing agent may be supplied from the reducing agent supply valve 77 so as to be maintained at or above the required amount decrease temperature TNS. When the switching valve 61 is held at the weak forward flow position, only a small amount of the exhaust gas flowing through the exhaust pipe 20a flows through the inflow / outflow port 65 into the annular exhaust pipe 67 as indicated by an arrow in FIG. And then NO_XThe remaining most of the exhaust gas flows through the catalyst 81 in the forward flow direction, and most of the remaining exhaust gas flows directly from the inflow port 62 through the outflow port 63 into the exhaust gas exhaust pipe 64, that is, NO._XIt flows into the auxiliary catalyst 76 bypassing the catalyst 81. In the embodiment according to the present invention, the integrated value of the fuel supplied from the fuel injection valve 6 and the reducing agent (fuel) supplied from the reducing agent supply valve 77 is obtained, and this integrated value is a predetermined threshold. NO when exceeded_XSO stored in catalyst 81_XIt is determined that the amount has exceeded the allowable amount.
[0052]
However, the accumulated SO_XIf fine particles are deposited on the particulate filter 69 when the amount reduction control is performed, a relatively large amount of reducing agent is supplied to the deposited fine particles while the temperature of the deposited fine particles is increased. As a result, the deposited fine particles cause abnormal combustion, and the particulate filter 69 may be damaged.
[0053]
Therefore, the SO of the embodiment according to the present invention_XIn control, NO_XSO stored in catalyst 81_XWhen the amount exceeds the permissible amount, firstly, oxidation control of fine particles is performed, and then the accumulated SO is controlled._XThe amount decrease control is performed. That is, the accumulated SO_XBefore the amount reduction control is performed, the deposited fine particles on the particulate filter 69 are removed.
[0054]
Next, an embodiment according to the present invention will be described with reference to FIG. In FIG. 6, QR is the amount of the reducing agent supplied from the reducing agent supply valve 77, AFA is the average air-fuel ratio of the exhaust gas flowing into the auxiliary catalyst 76, and AFN is NO._XAverage air-fuel ratio of exhaust gas flowing into the catalyst 81 or the particulate filter 69, TA is the temperature of the auxiliary catalyst 76, TN is NO_XTemperature of catalyst 81 or particulate filter 69, Tin is NO_XThe temperature of the exhaust gas flowing into the catalyst 81 or into the particulate filter 69 is shown.
[0055]
As shown by arrow X in FIG._XSO stored in catalyst 81_XWhen the amount QS exceeds the allowable amount QSU, first, the SO adhering to the auxiliary catalyst 76_XSO for removing_XRemoval control is performed. That is, the switching valve 61 is switched and held, for example, from the forward flow position to the reverse flow position, and the reducing agent is intermittently supplied from the reducing agent supply valve 77 as indicated by an arrow R. As a result, the reducing agent becomes particulate filter 69 and NO_XThe catalyst flows into the auxiliary catalyst 76 without reaching the catalyst 81. At this time, the amount QR of the reducing agent supplied from the reducing agent supply valve 77 is a QRR necessary for slightly increasing the average air-fuel ratio AFA of the exhaust gas flowing into the auxiliary catalyst 76. In this case, NO_XThe average air-fuel ratio AFN of the exhaust gas flowing into the catalyst 81 is maintained lean. Further, since the reducing agent is oxidized in the auxiliary catalyst 76, the temperature TA of the auxiliary catalyst 76 slightly increases.
[0056]
Next, as shown by an arrow XX in FIG._XWhen the amount becomes almost zero, for example, SO_XThe removal control is completed, and the particulate oxidation control is immediately started. That is, the switching valve 61 is switched from the reverse flow position to the forward flow position and held, and the reducing agent is intermittently supplied from the reducing agent supply valve 77 as shown by the arrow R. At this time, the amount QR of the reducing agent supplied from the reducing agent supply valve 77 is necessary to maintain the temperature TN of the particulate filter 69 at or above the particulate oxidation required temperature TNP when the switching valve 61 is in the forward flow position. QRP. As a result, the temperature TN of the particulate filter 69 rises and is maintained at or above the particulate oxidation required temperature TNP. In this case, the temperature TA of the auxiliary catalyst 76 is substantially the same as the temperature TN of the particulate filter 69. Further, the average air-fuel ratio AFA of the exhaust gas flowing into the auxiliary catalyst 76 is returned to lean, and NO_XThe average air-fuel ratio AFN of the exhaust gas flowing into the catalyst 81 becomes slightly smaller.
[0057]
Next, as shown by an arrow Y in FIG. 6, when the amount of the deposited particulate on the particulate filter 69 becomes substantially zero, for example, the particulate oxidation control is completed, and the SO_XThe removal control is performed again. That is, as described above, the switching valve 61 is switched from the forward flow position to the reverse flow position and held, and the reducing agent supply operation is performed under QR = QRR. At this time, the exhaust gas flowing into the auxiliary catalyst 76 Is slightly enriched.
[0058]
Next, as shown by an arrow YY in FIG._XWhen the amount becomes almost zero, for example, SO_XThe removal control is completed and the stored SO_XThe quantity reduction control is started. That is, the reducing agent is intermittently supplied from the reducing agent supply valve 77 as shown by the arrow R while the switching valve 61 is maintained at the weak forward flow position. At this time, the amount QR of the reducing agent supplied from the reducing agent supply valve 77 is NO._XWhile keeping the average air-fuel ratio AFN of the exhaust gas flowing into the catalyst 81 slightly rich, NO_XThe temperature TN of the catalyst 81 is set to SO_XThe QRS is required to maintain the temperature at or above the required amount decrease temperature TNS. In this case, a relatively large amount of exhaust gas is NO_XThe average air-fuel ratio AFA of the exhaust gas that bypasses the catalyst 81 and thus flows into the auxiliary catalyst 76 is kept lean. NO_XSince the temperature of the exhaust gas bypassing the catalyst 81 is low, the accumulated SO_XWhen the amount decrease control is performed, the temperature TA of the auxiliary catalyst 76 decreases.
[0059]
Next, as shown by arrow Z in FIG._XSO stored in catalyst 81_XWhen the amount becomes almost zero, for example, the accumulated SO_XThe amount reduction control is completed. In this case, the switching valve 61 is switched to, for example, the forward flow position, and the reducing agent supply operation from the reducing agent supply valve 77 is stopped.
[0060]
As described above, in the embodiment according to the present invention, the SO control is performed before the particulate oxidation control is performed._XRemoval control is performed and the accumulated SO_XBefore the amount decrease control is performed, SO_XRemoval control is performed. By doing so, the sulfate SO discharged from the auxiliary catalyst 76₃Can be reduced. This is for the following reason.
[0061]
That is, according to the present inventors, NO_XEven if the average air-fuel ratio AFN of the exhaust gas flowing into the catalyst 81 is maintained lean, NO_XWhen the temperature TN of the catalyst 81 increases, NO_XSO in the exhaust gas flowing out of the catalyst 81_XNO concentration_XSO in the exhaust gas flowing into the catalyst 81_XIt has been confirmed that the concentration is temporarily higher than the concentration. This means NO_XNO when the temperature of the catalyst 81 rises_XSO stored in the catalyst 81_XIs discharged and this SO_XIs the sulfate BaSO₄Means that they are stored without forming
[0062]
Such SO_XIs NO in any form_XWhether it is stored in the catalyst 81 is not always clear, but it is considered that it is stored as follows. That is, as described above,_XSO in the exhaust gas flowing into the catalyst 81₂Is first deposited on, for example, platinum Pt surface and then sulfate BaSO₄It is stored in the form of However, sulfate BaSO₄SO stored in the form of_XIncreases the amount of SO adhering on the platinum Pt surface.₂Is sulfate BaSO₄And SO₂Continue to adhere to the platinum Pt surface as it is. Thus SO_XIs sulfate BaSO₄Is stored without forming
[0063]
Then, NO_XIn the catalyst 81, sulfate BaSO₄SO stored in the form of_XIf any, sulfate BaSO₄SO stored without forming_XThere is also. Therefore, generally speaking, NO_XThe catalyst 81 removes SO_XStoring SO in either sulfate or non-sulfate form_XIt will act as a storage agent.
[0064]
Start of particulate oxidation control and NO_XWhen the temperature TN of the catalyst 81 increases, the sulfate BaSO₄SO stored without forming_XIs NO_XIt is released at once from the catalyst 81, and this SO_XThen flows into the auxiliary catalyst 76.
[0065]
On the other hand, the SO flowing into the auxiliary catalyst 76_XOnce adheres to, for example, the platinum surface of the auxiliary catalyst 76, is separated from the platinum surface, and is discharged from the auxiliary catalyst 76._XIs attached to the auxiliary catalyst 76 during the time when SO is attached to the auxiliary catalyst 76._XIt is believed that the larger the amount, the shorter it becomes. Also, SO_XWhen the amount of the reducing agent in the exhaust gas flowing into the auxiliary catalyst 76 when is adhered to or separated from the platinum surface of the auxiliary catalyst 76, or the average of the exhaust gas flowing into the auxiliary catalyst 76 If the air-fuel ratio AFA is lean, SO_XIs sulfate SO₃May be discharged from the auxiliary catalyst 76 in the form of
[0066]
Before the start of the particulate oxidation control, the auxiliary catalyst 76 contains the previously accumulated SO._XNO during amount decrease control_XSO discharged from the catalyst 81_XOr NO during normal operation_XSO passed through catalyst 81_XIs flowing into the auxiliary catalyst 76 when the particulate oxidation control should be started._XIs attached.
[0067]
Therefore, in this state, the particulate oxidation control is performed and a large amount of SO_XFlows in, this SO_XIs immediately discharged from the auxiliary catalyst 76, and since the amount of the reducing agent flowing into the auxiliary catalyst 76 is small or the average air-fuel ratio AFA of the exhaust gas flowing into the auxiliary catalyst 76 is lean as described above, Large amount of sulfate SO₃May be discharged from the auxiliary catalyst 76.
[0068]
On the other hand, if the amount of the reducing agent flowing into the auxiliary catalyst 76 is increased or the average air-fuel ratio AFA of the exhaust gas flowing into the auxiliary catalyst 76 is made rich, the SO adhering to the auxiliary catalyst 76 is_XIs removed from the auxiliary catalyst 76, at which time SO 2_XIs SO₂Is discharged from the auxiliary catalyst 76 in the form of
[0069]
Therefore, in the embodiment according to the present invention, as shown in FIG._XSO to remove_XRemoval control is performed. Specifically, as described above, the reducing agent is supplied such that the average air-fuel ratio AFA of the exhaust gas flowing into the auxiliary catalyst 76 becomes slightly rich. As a result, the adhering SO_XThe amount decreases to, for example, almost zero, and the sulfate SO₃Is not emitted.
[0070]
SO_XWhen the removal control is completed, the particulate oxidation control is subsequently started. At this time, a large amount of SO flowing into the auxiliary catalyst 76 is removed._XAdheres to the auxiliary catalyst 76 and is gradually discharged from the auxiliary catalyst 76. Therefore, a large amount of sulfate SO₃Is prevented from being discharged.
[0071]
Similarly, the accumulated SO_XEven when the amount reduction control should be started, a large amount of SO_XIs attached and the accumulated SO_XNO if amount reduction control is performed_XSulfate BaSO in catalyst 81₄SO stored in the form of_XIs NO_XThe gas is exhausted from the catalyst 81 at a stretch, and then flows into the auxiliary catalyst 76. At this time, the average air-fuel ratio AFA of the exhaust gas flowing into the auxiliary catalyst 76 is lean.
[0072]
Therefore, in the embodiment according to the present invention, as shown in FIG._XPrior to performing the quantity reduction control, SO_XRemoval control is performed. Therefore, also in this case, a large amount of sulfate SO₃Is prevented from being discharged.
[0073]
In the embodiment according to the present invention, as described above, the particulate oxidation control is also performed when the amount of particulates deposited on the particulate filter 69 exceeds the maximum allowable amount. Also in this case, SO control is performed before the particulate oxidation control is performed._XRemoval control is performed.
[0074]
FIG. 7 shows an SO according to an embodiment of the present invention._X4 shows a control routine. This routine is executed by interruption every predetermined set time. Referring to FIG. 7, first, in step 200, NO_XSO stored in catalyst 81_XIt is determined whether the amount QS has exceeded the allowable amount QSU. When QS ≦ QSU, the processing cycle is ended, and when QS> QSU, the process proceeds to step 201, where SO is described later with reference to FIG._XA removal control routine is executed. In the following step 202, a particulate oxidation control routine described later with reference to FIG. 10 is executed. In the following step 203, SO 3 described later with reference to FIG._XThe removal control routine is executed again. In the following step 204, the stored SO, which will be described later with reference to FIG._XAn amount decrease control routine is executed.
[0075]
FIG. 8 shows a particle control routine according to the embodiment of the present invention. This routine is executed by interruption every predetermined set time. Referring to FIG. 8, first, at step 210, it is determined whether or not the amount QPM of deposited particulate on the particulate filter 69 has exceeded the allowable amount QPMU. When QPM ≦ QPMU, the processing cycle is ended, and when QPM> QPMU, the process proceeds to step 211, where SO is described later with reference to FIG._XA removal control routine is executed. In the following step 212, a particulate oxidation control routine described later with reference to FIG. 10 is executed.
[0076]
FIG. 9 shows the above-described SO._X9 shows a removal control routine. Referring to FIG. 9, first, at step 220, the switching valve 61 is switched to or held at the reverse flow position. In the following step 221, the reducing agent supply amount QR is set to the above-mentioned QRR. In the following step 222, the reducing agent is supplied from the reducing agent supply valve 77 by the reducing agent supply amount QR. In the following step 223, SO_XIt is determined whether or not the removal control should be completed. In an embodiment according to the invention, SO_XAfter the removal control is started, the SO adhering to the auxiliary catalyst 76_XWhen the time required to make the amount of_XIt is determined that the removal control should be completed. This necessary time can be obtained in advance by an experiment. SO_XUntil it is determined that the removal control should be completed, the flow returns to step 222 to repeatedly supply the reducing agent,_XWhen it is determined that the removal control should be completed, the processing cycle ends.
[0077]
FIG. 10 shows the above-described particulate oxidation control routine. Referring to FIG. 10, first, at step 230, the switching valve 61 is switched to or held at the forward flow position. In the following step 231, the reducing agent supply amount QR is set to the above-described QRP. In the following step 232, the reducing agent is supplied from the reducing agent supply valve 77 by the reducing agent supply amount QR. In the following step 233, it is determined whether or not the particulate oxidation control should be completed. In the embodiment according to the present invention, it is determined that the particulate oxidation control should be completed when the amount of the deposited particulate on the particulate filter 69 becomes substantially zero. The process returns to step 232 until it is determined that the particulate oxidation control should be completed, and the reducing agent is repeatedly supplied. When it is determined that the particulate oxidation control should be completed, the processing cycle ends.
[0078]
FIG. 11 shows the above-described accumulated SO._X9 shows a quantity reduction control routine. Referring to FIG. 11, first, at step 240, the switching valve 61 is switched to the weak forward flow position. In the following step 241, the reducing agent supply amount QR is set to the above-described QRS. In the following step 242, the reducing agent is supplied from the reducing agent supply valve 77 by the reducing agent supply amount QR. In the following step 243, the accumulated SO_XIt is determined whether or not the amount reduction control should be completed. In the embodiment according to the present invention, NO_XSO stored in catalyst 81_XWhen the amount becomes almost zero, the accumulated SO_XIt is determined that the amount reduction control should be completed. Accumulated SO_XUntil it is determined that the amount reduction control should be completed, the process returns to step 242 to repeatedly supply the reducing agent,_XWhen it is determined that the amount reduction control should be completed, the processing cycle ends.
[0079]
Next, the SO of another embodiment according to the present invention is described._XThe removal control will be described.
[0080]
SO mentioned above_XIn the removal control, the reducing agent is supplied from the reducing agent supply valve 77 in order to make the average air-fuel ratio AFA of the exhaust gas flowing into the auxiliary catalyst 76 rich.
[0081]
However, for this purpose, the average air-fuel ratio of the exhaust gas flowing through the exhaust pipe 20a may be made rich, that is, by supplying a reducing agent into the exhaust manifold 19 or the exhaust pipes 20 and 21. Alternatively, the average air-fuel ratio of the exhaust gas discharged from the internal combustion engine may be made rich. Here, in order to make the average air-fuel ratio of the exhaust gas discharged from the internal combustion engine rich, there is a method of making the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 5 rich, and there is also a method of making the combustion stroke or the exhaust stroke. There is also a method of injecting additional fuel from the fuel injection valve 6.
[0082]
In another embodiment according to the present invention, the method of injecting the additional fuel causes the average air-fuel ratio AFA of the exhaust gas flowing into the auxiliary catalyst 76 to be slightly rich. Next, another embodiment of the present invention will be described in detail with reference to FIG. In FIG. 12, QP indicates an additional amount of fuel injected from the fuel injection valve 6 during a combustion stroke or an exhaust stroke, and AFE indicates a normal air-fuel ratio of exhaust gas discharged from the internal combustion engine.
[0083]
As indicated by arrow X in FIG._XSO stored in catalyst 81_XWhen the amount QS exceeds the allowable amount QSU, or when the particulate oxidation control is completed as indicated by an arrow Y, SO_XRemoval control is performed. That is, the switching valve 61 is switched and held, for example, from the forward flow position to the bypass position, and additional fuel is injected from the fuel injection valve 6 into the combustion stroke or the exhaust stroke as shown by the arrow P. When the switching valve 61 is held at the bypass position, as shown in FIG. 13, all the exhaust gas flowing through the exhaust pipe 20 a flows directly from the inflow port 62 through the outflow port 63 into the exhaust gas exhaust pipe 64. Spilled or NO_XBypassing the catalyst 81 and the particulate filter 69, the exhaust gas is NO_XIt does not flow through the inside of the catalyst 81 and the inside of the particulate filter 69. Thus, when the switching valve 61 is held at the bypass position, the exhaust gas flow path from the inflow port 62 to the outflow port 63 of the switching valve 61 acts as a bypass passage bypassing the particulate filter 69. . As a result, a large amount of the reducing agent contained in the exhaust gas discharged from the internal combustion engine becomes NO._XBypassing the catalyst 81 and therefore NO before flowing into the auxiliary catalyst 76_XOxidation and consumption in the catalyst 81 are prevented.
[0084]
At this time, the additional fuel amount QP is QRR 'necessary for slightly increasing the average air-fuel ratio AFA of the exhaust gas flowing into the auxiliary catalyst 76. In this case, the average air-fuel ratio AFA of the exhaust gas flowing into the auxiliary catalyst 76 matches the average air-fuel ratio AFE of the exhaust gas discharged from the internal combustion engine.
[0085]
FIG. 14 shows another embodiment of the SO according to the present invention._X9 shows a removal control routine. In this embodiment, the SO shown in FIG._XThe control routine and the particle control routine shown in FIG. 8 are executed, and in steps 201, 203 and 211 of these routines, the SO control shown in FIG._XA removal control routine is executed. Referring to FIG. 14, first, at step 250, the switching valve 61 is switched to the bypass position. In the following step 251, the additional fuel injection amount QP is set to the above-mentioned QRR '. In the following step 252, additional fuel is injected from the fuel injection valve 6 by QP during the combustion stroke or the exhaust stroke. In the following step 253, SO_XIt is determined whether or not the removal control should be completed. SO_XThe process returns to step 252 until additional fuel is repeatedly injected until it is determined that the removal control should be completed._XWhen it is determined that the removal control should be completed, the processing cycle ends.
[0086]
The embodiment according to the present invention described so far can be applied to, for example, an internal combustion engine shown in FIG.
[0087]
In the internal combustion engine shown in FIG. 15, a casing 168 is connected to the outlet of the exhaust pipe 20a, and the casing 167 is connected to the casing 175 via the exhaust pipe 20c, and the casing 175 is connected to the exhaust pipe 23. NO is contained in these casings 168 and 175._XThe particulate filter 69 supporting the catalyst 81 and the auxiliary catalyst 76 are housed therein.
[0088]
A bypass pipe 185 is branched from the exhaust pipe 20a, and an outflow end of the bypass pipe 185 opens to the exhaust pipe 20c. Further, a switching valve 161 controlled by an electronic control unit (not shown) is disposed in a portion of the exhaust pipe 20a where the inflow end of the bypass pipe 185 is open. Further, a reducing agent supply valve 77 is disposed in the exhaust pipe 20a between the inflow end of the bypass pipe 185 and the particulate filter 69.
[0089]
The switching valve 161 is normally held at a normal position shown by a solid line in FIG. When the switching valve 161 is held at the normal position, the bypass pipe 185 is shut off, and almost all the exhaust gas flowing into the exhaust pipe 20a is guided into the particulate filter 69. Therefore, the normal position of the switching valve 161 corresponds to the forward flow position or the reverse flow position of the switching valve 61 in the internal combustion engine of FIG.
[0090]
Also in this internal combustion engine, SOx is controlled before particulate oxidation control is performed._XRemoval control is performed and the accumulated SO_XBefore the amount decrease control is performed, SO_XRemoval control is performed. When the particulate oxidation control is to be performed, the reducing agent is supplied from the reducing agent supply valve 77 while holding the switching valve 161 at the normal position. Also, the accumulated SO_XWhen the amount decrease control is to be performed, the reducing agent is supplied from the reducing agent supply valve 77 while the switching valve 161 is maintained at the weak flow position indicated by the dashed line in FIG. When the switching valve 161 is held at the weak flow position, a small part of the exhaust gas flowing into the exhaust pipe 20a is guided into the particulate filter 69, and the remaining exhaust gas is guided into the bypass pipe 185. Therefore, the weak flow position of the switching valve 161 corresponds to the weak forward flow position of the switching valve 61 in the internal combustion engine of FIG.
[0091]
SO_XWhen the removal control is to be performed, the average air-fuel ratio of the exhaust gas discharged from the internal combustion engine is made rich while holding the switching valve 161 at the bypass position shown by the broken line in FIG. When the switching valve 161 is held at the bypass position, the bypass pipe 185 is opened, and almost all the exhaust gas flowing into the exhaust pipe 20a bypasses the particulate filter 69. Therefore, the bypass position of the switching valve 161 corresponds to the bypass position of the switching valve 61 in the internal combustion engine of FIG.
[0092]
As shown in FIG._XThe particulate filter 69 which accommodates the catalyst 81 and carries the auxiliary catalyst 76 in the casing 175 can also be accommodated.
[0093]
Therefore, generally speaking, NO_XNO with catalyst_XAn auxiliary catalyst is arranged in the exhaust passage downstream of the catalyst, and NO_XNO from the exhaust passage upstream of the catalyst_XBy providing a bypass passage to the exhaust passage between the catalyst and the auxiliary catalyst and controlling the amount of exhaust gas flowing in the bypass passage, NO_XA switching valve for controlling the amount of exhaust gas flowing through the catalyst is provided._XThis means that a reducing agent supply valve for supplying the reducing agent is disposed in the exhaust passage between the catalysts.
[0094]
In addition, in the internal combustion engine shown in FIG._XNO flows into the catalyst through one end_XGuide the exhaust gas out of the catalyst through the other end face or NO_XNO flowing into the catalyst through the other end face_XThat is, it is switched whether the exhaust gas is guided so as to flow out of the catalyst through one end surface thereof.
[0095]
【The invention's effect】
The amount of sulfate discharged into the atmosphere can be reduced.
[Brief description of the drawings]
FIG. 1 is an overall view of an internal combustion engine.
FIG. 2 is a diagram showing a structure of a catalytic converter.
FIG. 3 is a diagram for explaining a flow of exhaust gas when a switching valve is at a forward flow position or a reverse flow position.
FIG. 4 is a partially enlarged sectional view of a partition wall of the particulate filter.
FIG. 5 is a diagram for explaining the flow of exhaust gas when the switching valve is at a weak forward flow position.
FIG. 6 is a time chart for explaining an embodiment according to the present invention.
FIG. 7 shows an SO according to an embodiment of the present invention._X5 is a flowchart illustrating a control routine.
FIG. 8 is a flowchart showing a particulate oxidation control routine according to the embodiment of the present invention.
FIG. 9 shows an SO according to an embodiment of the present invention._XIt is a flowchart which shows a removal control routine.
FIG. 10 is a flowchart illustrating a particulate oxidation control routine according to an embodiment of the present invention.
FIG. 11 shows a storage SO of an embodiment according to the present invention;_XIt is a flowchart which shows a quantity reduction control routine.
FIG. 12 is a time chart for explaining another embodiment according to the present invention.
FIG. 13 is a diagram for explaining the flow of exhaust gas when the switching valve is at a bypass position.
FIG. 14 shows an SO according to another embodiment of the present invention._XIt is a flowchart which shows a removal control routine.
FIG. 15 is a view showing another embodiment.
FIG. 16 is a diagram for explaining the position of the switching valve of the embodiment shown in FIG.
FIG. 17 is a diagram showing another embodiment.
[Explanation of symbols]
1. Engine body
20a ... exhaust pipe
22 ... catalytic converter
61 ... Switching valve
64 ... exhaust gas exhaust pipe
67 ... Annular exhaust pipe
69 ... Particulate filter
76 ... Auxiliary catalyst
77… Reducing agent supply valve
81 ... NO_Xcatalyst

Claims (7)

With arranging the SO _X storage agent storing SO _X in the exhaust gas flowing into the exhaust passage of an internal combustion engine combustion continues under a lean air-fuel ratio is made temporarily the SO _X storage agent downstream an auxiliary catalyst having oxidizing ability in the exhaust passage is arranged, prior to SO _X that is stored in the SO _X storage agent is discharged from the SO _X storage agent, the SO _X adhering to the cocatalyst An exhaust gas purification device for an internal combustion engine that is removed from an auxiliary catalyst. The auxiliary catalyst is provided with a reducing agent supply means for supplying a reducing agent to the auxiliary catalyst. The air-fuel ratio of the exhaust gas flowing into the auxiliary catalyst is rich in order to remove the SO _X attached to the auxiliary catalyst from the auxiliary catalyst. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the reducing agent is supplied from the reducing agent supply means to the auxiliary catalyst such that The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the SO _X accumulating agent is carried on a particulate filter for trapping fine particles in exhaust gas flowing into the SO _X accumulating agent. Prior to increasing the temperature of the particulate filter while maintaining a lean air-fuel ratio of the exhaust gas flowing into the particulate filter to oxidize the particulates deposited on the particulate filter, the auxiliary 4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 3, wherein SO _X adhering to the catalyst is removed from the auxiliary catalyst. The SO _X storage agent, the air-fuel ratio of the inflowing exhaust gas is stored in the NO _X in the exhaust gas flowing at the time of the lean air-fuel ratio of the inflowing exhaust gas includes the reducing agent in the exhaust gas when the reduced an exhaust purification system of an internal combustion engine according to claim 1 or 3 formed from NO _X catalyst is the amount of the NO _X are stored by reducing NO _X which the accumulated and have to decrease. Claims the NO _X catalyst SO _X that is stored in the form of sulfate in the prior to being discharged from the NO _X catalyst was the SO _X adhering to the auxiliary catalyst to be removed from the auxiliary catalyst Item 6. An exhaust gas purification device for an internal combustion engine according to item 5. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said auxiliary catalyst is carried on a particulate filter for collecting particulates in exhaust gas flowing into said auxiliary catalyst.

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