JP3826287B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine.
[0002]
[Prior art]
Conventionally, a particulate filter for collecting particulates in the inflowing exhaust gas is disposed in the exhaust passage of the internal combustion engine in which combustion is continuously performed under a lean air-fuel ratio, and the inflowing exhaust gas NO in exhaust gas flowing in when the air-fuel ratio is lean_XNO when storing the reducing agent in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in decreases_XNO is stored and reduced_XNO to reduce the amount of_XThere is known an internal combustion engine in which a catalyst is supported on a 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 from 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 the fine particles accumulated on the particulate filter, the temperature of the particulate filter is temporarily maintained while maintaining the air-fuel ratio of the exhaust gas flowing into the particulate filter lean. Enhanced. On the other hand, as will be described in detail later, NO_XSO is contained in the catalyst._XIs stored without the formation of sulfates._XIs NO_XNO even if the air-fuel ratio of the exhaust gas flowing into the catalyst is lean_XNO at higher catalyst temperatures_XDischarged from the catalyst. Therefore, every time the deposited fine particles on the particulate filter are oxidized and removed, NO is removed._XFrom catalyst to SO_XFor example SO₂Will be discharged.
[0004]
[Problems to be solved by the invention]
However, when the particulates deposited on the particulate filter are oxidized and removed in this way, 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, that is, in the auxiliary catalyst. The amount of reducing agent in the exhaust gas flowing into the_XSO discharged from the catalyst₂Is an auxiliary catalyst, sulfate SO₃Oxidized to SO, then SO₃There is a problem of being discharged into the atmosphere in the form of
[0005]
Accordingly, an object of the present invention is to provide an exhaust purification device for an internal combustion engine that can reduce the amount of sulfate discharged into the atmosphere.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, according to the first invention, SO 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 is provided._XSO to temporarily store_XAn accumulating agent is disposed and the SO_XAn auxiliary catalyst having oxidation ability is arranged in the exhaust passage downstream of the storage agent, and SO_XSO adhering to the storage agent_XIs SO_XPrior to being discharged from the storage agent, SO adhering to the auxiliary catalyst_XIs removed from the auxiliary catalyst.
[0007]
Further, according to a second invention, in the first invention, there is provided a reducing agent supply means for supplying a reducing agent to the auxiliary catalyst, and the SO adhering to the auxiliary catalyst._XIn order to remove the catalyst 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_XIt is carried on a particulate filter for collecting particulates in the exhaust gas into which the storage agent flows.
[0009]
According to a fourth aspect, in the first aspect, in order to oxidize the particulates deposited on the particulate filter, the particulates while maintaining the air-fuel ratio of the exhaust gas flowing into the particulate filter lean. Prior to the temperature of the curate filter being raised, the SO 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 exhaust gas flowing in when the air-fuel ratio of the flowing exhaust gas is lean_XNO when storing the reducing agent in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in decreases_XNO is stored and reduced_XNO to reduce the amount of_XIt is formed from a catalyst.
[0011]
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 particulates in the exhaust gas into which the auxiliary catalyst flows.
[0013]
In this specification, the ratio of the air supplied into the exhaust passage upstream of a certain position of the exhaust passage, the combustion chamber, and the intake passage and the reducing agent such as hydrocarbon HC and carbon monoxide CO This is called the air-fuel ratio of the exhaust gas at the position.
[0014]
DETAILED DESCRIPTION OF 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 Is an exhaust valve, and 10 is 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 disposed in the intake duct 13, and a cooling device 18 for cooling intake air flowing through the intake duct 13 is disposed 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 intake air is cooled by the engine cooling water.
[0016]
On the other hand, the exhaust port 10 is connected to an exhaust turbine 21 of an 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. An exhaust gas discharge pipe 64 of the catalytic converter 22 is connected to the outflow port 63 of the switching valve 61 facing the inflow port 62. The switching valve 61 further has a pair of inflow / outflow ports 65, 66 facing each other on both sides of a straight line connecting the inflow port 62 and the outflow port 63, and the inflow / outflow ports 65, 66 have an annular shape of the catalytic converter 22. Both ends of the exhaust pipe 67 are 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 in the exhaust gas exhaust pipe 64. A particulate filter 69 for collecting fine particles in the exhaust gas is housed in the filter housing 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 longitudinal sectional view of the catalytic converter 22 including the one end surface 69a of the particulate filter 69, and FIG. 2B showing a partial transverse sectional view of the catalytic converter 22, the particulate filter 69 has a honeycomb structure and includes a plurality of exhaust gas passages 70 and 71 extending in parallel with 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 sealing material 72, and an exhaust gas passage 71 having the other end opened and one end closed by a sealing material 73. Is done. Note that the hatched portion in FIG. 2A shows the sealing material 73. The 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 and 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]
As will be described later, NO on the particulate filter 69._XA catalyst 81 is supported. On the other hand, a catalyst storage chamber 75 is formed in the exhaust gas discharge pipe 64 between the outflow port 63 of the switching valve 61 and the portion through which the annular exhaust pipe 67 penetrates. An auxiliary catalyst 76 having an oxidizing ability carried on a substrate having a honeycomb structure is accommodated.
[0021]
Further, 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. A reducing agent is supplied to the reducing agent supply valve 77 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, no reducing agent supply valve is 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. 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 EGR gas is cooled by the engine cooling water.
[0023]
On the other hand, each fuel injection valve 6 is connected to a fuel reservoir, so-called common rail 27, through a fuel supply pipe 6a. Fuel is supplied into the common rail 27 from an electrically controlled fuel pump 28 with variable discharge amount, and the fuel supplied into the common rail 27 is supplied to the fuel injection valve 6 via 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 a fuel pump 28 is set so that the fuel pressure in the common rail 27 becomes a target fuel pressure based on an output signal of the fuel pressure sensor 29. The discharge amount 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. 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 are connected. It comprises. 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 from the auxiliary catalyst 76 is attached to the exhaust gas discharge pipe 64 downstream of the auxiliary catalyst 76, and the output voltage of the temperature sensor 48 passes through the corresponding AD converter 47. To the input port 45. The temperature of the exhaust gas represents the temperature of the auxiliary catalyst 76. A pressure sensor 49 for detecting the pressure in the exhaust pipe 20 a, that is, the engine back pressure, is attached to the exhaust pipe 20 a, and the output voltage of the pressure sensor 49 is input to the input port 45 via the corresponding AD converter 47. The 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. The Further, the input port 45 is connected with a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, 30 °.
[0025]
On the other hand, the output port 46 is connected through the corresponding drive circuit 53 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 normally positioned at one of a position indicated by a solid line and a position indicated by a broken line in FIG. When the switching valve 61 is positioned at the position indicated by the solid line in FIG. 3B, the inflow port 62 communicates with the inflow / outflow port 65 while the communication between the outflow port 63 and the inflow / outflow port 66 is blocked by the switching valve 61. The outflow port 63 is communicated with the inflow / outflow port 66 by the switching valve 61. As a result, as shown by the solid arrows in FIG. 3B, all the exhaust gas flowing through the exhaust pipe 20a flows into the annular exhaust pipe 67 through the inflow port 62 and the inflow / outflow port 65 in sequence, Next, after passing through the particulate filter 69, it flows 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 a position indicated by a broken line in FIG. 3B, the inflow port 62 is inflow / outflow while the communication between the outflow port 63 and the inflow / outflow port 65 is blocked 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 through the inflow port 62 and the inflow / outflow port 66 in sequence, as indicated by the dashed arrows in FIG. Next, after passing through the particulate filter 69, it flows into the exhaust gas discharge pipe 64 through the inflow / outflow port 65 and the outflow port 63 in order.
[0028]
By switching the position of the switching valve 61 in this way, the flow of exhaust gas in the annular exhaust pipe 67 is reversed. In other words, the exhaust gas is NO_XIt flows into the catalyst 81 through its one end face, and NO_XExhaust gas is guided to flow out from the catalyst 81 through the other end face, or NO_XIt flows into the catalyst 81 through the other end face and NO._XIt is possible to switch whether to guide the exhaust gas so as to flow out from the catalyst 81 through its one end face. Hereinafter, the flow of exhaust gas indicated by a solid line in FIG. 3B is referred to as forward flow, and the flow of exhaust gas indicated by a broken line is referred to as reverse flow. In addition, the position of the switching valve 61 indicated by a solid line in FIG. 3B 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 backflow position.
[0029]
The exhaust gas that has flowed into the exhaust gas discharge pipe 64 through the outflow port 66 then passes through the catalyst 76 and travels 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]
Exhaust gas flow in the particulate filter 69 will be described. During forward flow, the exhaust gas flows into the particulate filter 69 through the one end surface 69a, and flows out of the particulate filter 69 through the other end surface 69b. At this time, the exhaust gas flows into the exhaust gas passage 70 opened in the one end surface 69 a, and then flows into the adjacent exhaust gas passage 71 through the surrounding partition wall 74. On the other hand, at the time of reverse flow, the exhaust gas flows into the particulate filter 69 through the other end surface 69b, and flows out from the particulate filter 69 through the one end surface 69a. At this time, the exhaust gas flows into the exhaust gas passage 71 opened in the other end surface 69 b, and then flows 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, on both side surfaces of the partition wall 74 and the inner wall surface of the pore, as shown in FIG._XEach catalyst 81 is supported. This NO_XThe catalyst 81 has, for example, alumina as a carrier, and an alkali metal such as potassium K, sodium Na, lithium Li, and cesium Cs, an alkaline earth such as barium Ba and calcium Ca, lanthanum La, and yttrium Y are supported on the carrier. At least one selected from rare earths and a noble metal such as platinum Pt, palladium Pd, rhodium Rh, and iridium Ir are supported.
[0032]
NO_XThe catalyst is NO when the average air-fuel ratio of the exhaust gas flowing in is lean._XNO when storing the reducing agent in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in decreases_XNO is stored and reduced_XAccumulation and reduction action to reduce the amount of.
[0033]
NO_XThe detailed mechanism of the accumulation and reduction action of the catalyst has not been fully clarified. However, the mechanism currently considered can be briefly described as follows, taking as an example the case where platinum Pt and barium Ba are supported on a support.
[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 inflowing exhaust gas greatly increases and oxygen O₂Is O₂ ⁻Or O^2-It adheres to 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). Then the generated NO₂Part of the NO is being oxidized further on platinum Pt_XNitrate ion NO while being absorbed in the catalyst and combined with barium oxide BaO₃ ⁻NO in the form of_XIt diffuses into the catalyst. In this way NO_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 NO₂Production amount decreases and the reaction proceeds in the reverse direction (NO₃ ⁻→ NO + 2O^*) And thus NO_XNitrate ion NO in the catalyst₃ ⁻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 can be reduced by reacting with the HC and CO. In this way, NO on the surface of platinum Pt._XNO when no longer exists_XNO from catalyst to next_XIs released and reduced, NO_XNO stored in the catalyst_XThe amount of is gradually reduced.
[0036]
NO without forming nitrate_XStore NO_XNO without releasing_XIt is also possible to reduce In addition, active oxygen O^*If you pay attention to, NO_XThe catalyst is NO_XWith the accumulation and release of oxygen^*It can also be regarded as an active oxygen generating catalyst that generates
[0037]
Meanwhile, in the embodiment according to the present invention, the auxiliary catalyst 76 is formed from a noble metal catalyst containing noble metal such as platinum Pt without containing alkali metal, alkaline earth, and rare earth. However, the auxiliary catalyst 76 is the NO described above._XYou may form 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 hardly changes between when the switching valve 61 is in the forward flow position and when it is in 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 it is in the reverse flow position. Does not require control.
[0039]
In the embodiment according to the present invention, each time the engine low load operation is performed, the switching valve 61 is switched from the forward flow position to the reverse flow position or vice versa. In this way, as will be understood from the following description, the particulate filter 69 and the NO._XFine particles bypassing the catalyst 81 and NO_XThe amount of can be reduced.
[0040]
As described above, the exhaust gas passes through the particulate filter 69 regardless of whether it is forward flow or reverse flow. Further, the internal combustion engine shown in FIG. 1 is continuously combusted under a 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 accumulated in catalyst 81_XThe amount increases gradually. Therefore, in the embodiment according to the present invention, for example, NO._XNO accumulated in catalyst 81_XNO when the amount exceeds the allowable amount_XNO stored in catalyst 81_XNO_XNO accumulated in catalyst 81_XIn order to reduce the amount, the reducing agent supply valve 77_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 carbon contained in the exhaust gas are collected on the particulate filter 69. That is, schematically, fine particles are collected on the side surface and the pores of the partition wall 74 on the exhaust gas passage 70 side in the forward flow, and on the side surface and the pores of the partition wall 74 on the exhaust gas passage 71 side in the reverse flow. Fine particles are collected. The internal combustion engine shown in FIG. 1 continues to burn under a lean air-fuel ratio, and NO_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 more, the particulates are oxidized on the particulate filter 69 and removed. The
[0043]
In this case, the above-mentioned NO_XNO of catalyst 81_XAccording to the accumulation and reduction mechanism of NO_XNO in catalyst 81_XNO is also stored when_XActive oxygen is also generated when is released. This active oxygen is oxygen O₂Therefore, the fine particles deposited on the particulate filter 69 are rapidly oxidized. That is, NO on the particulate filter 69._XWhen the catalyst 81 is supported, fine particles 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, if the temperature of the particulate filter 69 is not maintained at a temperature that can oxidize the particulates, or the amount of particulates flowing into the particulate filter 69 per unit time becomes considerably large, the particulates that accumulate on the particulate filter 69. 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 particulates deposited 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 lean while the particulate filter 69 Fine particle oxidation control is performed in which the temperature is raised to the fine particle oxidation required temperature TNP, for example, 600 ° C. or higher, and then maintained at the fine particle oxidation required temperature TNP or higher. 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 exceeds the allowable value when the switching valve 61 is held in the forward flow position or the reverse flow position, the particulate filter 69 It is determined that the amount of deposited fine particles exceeded the allowable maximum amount.
[0046]
More specifically, in the embodiment shown in FIG. 1, the temperature of the particulate filter 69 is maintained while the air-fuel ratio of the exhaust gas flowing into the particulate filter 69 is maintained lean while holding the switching valve 61 in the forward flow position. The reducing agent is supplied from the reducing agent supply valve 77 so that is raised to the fine particle oxidation requirement temperature TNP or higher and then maintained at the fine particle oxidation requirement temperature TNP or higher. 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 the fine particle oxidation required temperature TNP and maintained.
[0047]
By the way, sulfur content is SO._XIs included in the form of NO_XNO in the catalyst 81_XNot only SO_XCan also be stored. This SO_XNO_XThe accumulation mechanism in the catalyst 81 is NO._XThis is considered 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 simply described as an example, NO_XWhen the air-fuel ratio of the exhaust gas flowing into the catalyst 81 is lean, as described above, the oxygen O₂Is O₂ ⁻Or O^2-Attached to the surface of platinum Pt in the form of SO₂Adheres to the surface of platinum Pt and O on the surface of platinum Pt.₂ ⁻Or O^2-Reacts with SO₃It becomes. The generated SO₃NO is being oxidized on platinum Pt_XWhile being absorbed into the catalyst 81 and combined with barium oxide BaO, sulfate ions SO₄ ⁻NO in the form of_XIt diffuses into the catalyst 81. This sulfate ion SO₄ ⁻Then barium ion Ba⁺Combined with sulfate BaSO₄Is generated.
[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 81₄The amount of does not decrease. For this reason, as time passes, NO_XSulfate BaSO in catalyst 81₄The amount of NO increases, resulting in NO_XNO that the catalyst 81 can store_XThe amount of will decrease.
[0049]
However, NO_XWhile maintaining the temperature of the catalyst 81 at 550 ° C. or higher, NO_XWhen the average air-fuel ratio of the exhaust gas flowing into the catalyst 81 is made the stoichiometric air-fuel ratio or rich, NO_XSulfate BaSO in catalyst 81₄Decomposes into SO₃NO in the form of_XReleased from the catalyst 81. This released SO₃If exhaust gas contains a reducing agent, ie, HC or CO, it reacts with HC and CO to react with SO.₂To be reduced. In this way NO_XIn the catalyst 81, sulfate BaSO₄SO stored in the form of_XThe amount of NO decreases gradually, at this time NO_XFrom catalyst 81 to SO_XIs SO₃It will not leak out.
[0050]
Therefore, in the embodiment according to the present invention, for example, NO._XAccumulated SO in catalyst 81_XWhen the amount exceeds the allowable amount, NO_XAccumulated SO 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, SO_XVolume reduction required temperature TNS For example, accumulated SO maintained at 550 ° C or higher_XVolume reduction control is performed.
[0051]
More specifically, in the embodiment shown in FIG. 1, while holding the switching valve 61 in the weak forward flow position as shown in FIG._XWhile the average air-fuel ratio of the exhaust gas flowing into the catalyst 81 is kept slightly rich, NO_XThe temperature of the catalyst 81 is SO_XThe reducing agent may be supplied from the reducing agent supply valve 77 so that the amount reduction required temperature TNS is maintained. When the switching valve 61 is held at the weak forward flow position, as shown by an arrow in FIG. 5, only a small amount of the exhaust gas flowing through the exhaust pipe 20 a passes through the inflow / outflow port 65 and enters the annular exhaust pipe 67. And then NO_XThe catalyst 81 circulates in the forward direction, and most of the remaining exhaust gas flows out from the inflow port 62 directly into the exhaust gas discharge pipe 64 through the outflow port 63, that is, NO._XThe catalyst 81 bypasses the catalyst 81 and flows into the auxiliary catalyst 76. In the embodiment according to the present invention, an 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 determined in advance. NO when the value is exceeded_XAccumulated SO in catalyst 81_XIt is determined that the amount has exceeded the allowable amount.
[0052]
However, accumulated SO_XIf particulates 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 particulates while the temperature of the deposited particulates is raised. As a result, the deposited fine particles cause so-called abnormal combustion, and the particulate filter 69 may be melted.
[0053]
Therefore, the SO according to the embodiment of the present invention._XIn control, NO_XAccumulated SO in catalyst 81_XWhen the amount exceeds the allowable amount, the particulate oxidation control is performed first, and then the accumulated SO_XVolume reduction control is performed. That is, accumulated SO_XThe particulate deposits on the particulate filter 69 are removed before the amount reduction control is performed.
[0054]
Next, an embodiment according to the present invention will be described with reference to FIG. In FIG. 6, QR is the amount of 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._XThe average air-fuel ratio of the exhaust gas flowing into the catalyst 81 or the particulate filter 69, TA is the temperature of the auxiliary catalyst 76, and TN is NO_XThe temperature of the catalyst 81 or the particulate filter 69, Tin is NO_XThe temperature of the exhaust gas flowing into the catalyst 81 or the particulate filter 69 is shown.
[0055]
As shown by the arrow X in FIG._XAccumulated SO in catalyst 81_XWhen the amount QS exceeds the allowable amount QSU, first, the SO adhering to the auxiliary catalyst 76_XSO to remove_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 the arrow R. As a result, the reducing agent becomes particulate filter 69 and NO._XIt 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 to slightly enrich 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. 6, the attached SO in the auxiliary catalyst 76._XWhen the amount is almost zero, for example, SO_XRemoval control is completed, and particulate oxidation control is started immediately. That is, the switching valve 61 is switched from the reverse flow position to the forward flow position and is held, and as indicated by the arrow R, the reducing agent is intermittently supplied from the reducing agent supply valve 77. 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 the above-mentioned fine particle 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 request 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 is slightly reduced.
[0057]
Next, as shown by the arrow Y in FIG. 6, when the amount of deposited particulate on the particulate filter 69 becomes, for example, approximately zero, particulate oxidation control is completed, and immediately the SO_XRemoval control is performed again. That is, as described above, the switching valve 61 is switched and held from the forward flow position to the reverse flow position, and the reducing agent supply operation is performed under QR = QRR. At this time, the exhaust gas flowing into the auxiliary catalyst 76 The average air-fuel ratio AFA is slightly enriched.
[0058]
Next, as shown by the arrow YY in FIG. 6, the attached SO in the auxiliary catalyst 76._XWhen the amount is almost zero, for example, SO_XRemoval control is completed and immediately accumulated SO_XThe amount reduction control is started. That is, the reducing agent is intermittently supplied from the reducing agent supply valve 77 as indicated by the arrow R while holding the switching valve 61 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 maintaining 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 changed to SO._XThe QRS is required to maintain the amount reduction required temperature at or above the TNS. In this case, a relatively large amount of exhaust gas is NO._XTherefore, the average air-fuel ratio AFA of the exhaust gas flowing into the auxiliary catalyst 76 is kept lean. NO_XSince the temperature of the exhaust gas that bypasses the catalyst 81 is low, the accumulated SO_XWhen the amount reduction control is performed, the temperature TA of the auxiliary catalyst 76 decreases.
[0059]
Next, as shown by the arrow Z in FIG._XAccumulated SO in catalyst 81_XFor example, when the amount becomes almost zero, the accumulated SO_XThe amount reduction control is completed. In this case, the switching valve 61 is switched to the forward flow position, for example, and the reducing agent supply action from the reducing agent supply valve 77 is stopped.
[0060]
Thus, in the embodiment according to the present invention, the SO is controlled prior to the fine particle oxidation control._XRemoval control is performed and accumulated SO_XPrior to the volume reduction control being performed, SO_XRemoval control is performed. In this way, the sulfate SO discharged from the auxiliary catalyst 76.₃The amount of can be reduced. This is due to the following reason.
[0061]
That is, according to the inventors of the present application, NO_XNO even if the average air-fuel ratio AFN of the exhaust gas flowing into the catalyst 81 is kept lean_XWhen the temperature TN of the catalyst 81 increases, NO_XSO in exhaust gas flowing out of catalyst 81_XConcentration is NO_XSO in the exhaust gas flowing into the catalyst 81_XIt has been confirmed that the concentration is temporarily higher than the concentration. This is NO_XNO when the temperature of the catalyst 81 increases_XSO stored in the catalyst 81_XIs discharged and this SO_XIs sulfate BaSO₄It means that it is stored without forming.
[0062]
Such SO_XWhat is NO_XWhether it is stored in the catalyst 81 is not necessarily clear, but is considered to be stored as follows. That is, as described above, NO_XSO in the exhaust gas flowing into the catalyst 81₂First, for example, after depositing on the platinum Pt surface, the sulfate BaSO₄Are stored in the form of However, sulfate BaSO₄SO stored in the form of_XAs the amount of SO increases, the SO adhering to the platinum Pt surface₂Is sulfate BaSO₄SO₂It continues to adhere on the platinum Pt surface. In this way SO_XIs sulfate BaSO₄Can be stored without forming.
[0063]
Then NO_XIn the catalyst 81, sulfate BaSO₄SO stored in the form of_XIf there is a sulfate BaSO₄Can be stored without forming_XThere will be. So generally speaking, NO_XThe catalyst 81 contains SO in the exhaust gas flowing in._XStored in either sulfate or non-sulfate form_XIt will act as an accumulating agent.
[0064]
Fine particle oxidation control is started and NO_XWhen the temperature TN of the catalyst 81 increases, the sulfate BaSO₄SO stored without forming_XIs NO_XIt is released from the catalyst 81 at once, and this SO_XThen flows into the auxiliary catalyst 76.
[0065]
On the other hand, the SO that has flowed into the auxiliary catalyst 76._XTemporarily adheres to, for example, the platinum surface of the auxiliary catalyst 76, leaves the platinum surface and is discharged from the auxiliary catalyst 76. At this time, the SO_XIs attached to the auxiliary catalyst 76 while the SO is attached to the auxiliary catalyst 76._XIt is thought that it will become shorter as the amount of increases. Also, SO_XThe amount of the reducing agent in the exhaust gas flowing into the auxiliary catalyst 76 is small or the average of the exhaust gas flowing into the auxiliary catalyst 76 when is adhering to the platinum surface of the auxiliary catalyst 76 or detached from the platinum surface If the air-fuel ratio AFA is lean, SO_XSulfate SO₃There is a risk of being discharged from the auxiliary catalyst 76 in the form of.
[0066]
In the auxiliary catalyst 76 before the particulate oxidation control is started, the accumulated SO_XNO during volume reduction control_XSO discharged from the catalyst 81_XOr NO during normal operation_XSO that passed through the catalyst 81_XTherefore, a large amount of SO is contained in the auxiliary catalyst 76 when the particulate oxidation control should be started._XIs attached.
[0067]
Accordingly, the particulate oxidation control is performed in this state, and a large amount of SO is contained in the auxiliary catalyst 76._XWhen SO flows in, this SO_XIs immediately discharged from the auxiliary catalyst 76. At this time, as described above, the amount of 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. Large amount of sulfate SO₃May be discharged from the auxiliary catalyst 76.
[0068]
On the other hand, when 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 increased._XIs removed from the auxiliary catalyst 76, at which time SO_XIs SO₂Is discharged from the auxiliary catalyst 76.
[0069]
Therefore, in the embodiment according to the present invention, the SO adhering to the auxiliary catalyst 76 prior to the fine particle oxidation control as shown in FIG._XSO to remove_XRemoval control is performed. Specifically, as described above, the reducing agent is supplied so 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 of the auxiliary catalyst 76_XThe amount is reduced, for example, to almost zero, when the auxiliary catalyst 76₃Is not discharged.
[0070]
SO_XWhen the removal control is completed, fine particle oxidation control is subsequently started. At this time, a large amount of SO flowing into the auxiliary catalyst 76 is started._XAdheres to the auxiliary catalyst 76 and is gradually discharged from the auxiliary catalyst 76. Therefore, a large amount of sulfate SO from the auxiliary catalyst 76.₃Can be prevented from being discharged.
[0071]
Similarly, accumulated SO_XWhen the amount reduction control should be started, a large amount of SO is added to the auxiliary catalyst 76._XIs attached and accumulated SO_XNO when volume reduction control is performed_XIn the catalyst 81, sulfate BaSO₄SO stored in the form of_XIs NO_XThe catalyst 81 is discharged at once, 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, after the particulate oxidation control is completed as shown in FIG._XPrior to the volume reduction control_XRemoval control is performed. Accordingly, in this case as well, a large amount of sulfate SO is removed from the auxiliary catalyst 76.₃Can be 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 the deposited particulate on the particulate filter 69 exceeds the allowable maximum amount. Also in this case, SO is controlled prior to fine particle oxidation control._XRemoval control is performed.
[0074]
FIG. 7 shows an example SO according to the present invention._XA control routine is shown. This routine is executed by interruption every predetermined time. Referring to FIG. 7, first in step 200, NO._XAccumulated SO in catalyst 81_XIt is determined whether or not the amount QS exceeds the allowable amount QSU. When QS ≦ QSU, the processing cycle is terminated, and when QS> QSU, the process proceeds to step 201, and the SO is described later with reference to FIG._XA removal control routine is executed. In the subsequent step 202, a particulate oxidation control routine described later with reference to FIG. 10 is executed. In the following step 203, the SO described later with reference to FIG._XThe removal control routine is executed again. In the following step 204, the accumulated SO described later with reference to FIG._XAn amount reduction control routine is executed.
[0075]
FIG. 8 shows a fine particle control routine according to an embodiment of the present invention. This routine is executed by interruption every predetermined time. Referring to FIG. 8, first, at step 210, it is judged if the amount of accumulated particulates QPM on the particulate filter 69 has exceeded the allowable amount QPMU. When QPM ≦ QPMU, the processing cycle is terminated. When QPM> QPMU, the routine proceeds to step 211, where the SO is described later with reference to FIG._XA removal control routine is executed. In the subsequent step 212, a particulate oxidation control routine described later with reference to FIG. 10 is executed.
[0076]
FIG. 9 shows the SO described above._XThe removal control routine is shown. Referring to FIG. 9, first, at step 220, the switching valve 61 is switched or held at the backflow position. In the subsequent step 221, the reducing agent supply amount QR is set to the above-mentioned QRR. In the subsequent 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 present invention, SO_XSince the removal control is started, the SO adhering to the auxiliary catalyst 76_XWhen the time necessary to bring the amount of water to almost zero has elapsed_XIt is determined that the removal control should be completed. This necessary time can be obtained in advance by experiments. SO_XUntil it is determined that the removal control should be completed, the process returns to step 222 to repeatedly supply the reducing agent, and the SO_XWhen it is determined that the removal control should be completed, the processing cycle is terminated.
[0077]
FIG. 10 shows the fine particle oxidation control routine described above. Referring to FIG. 10, first, at step 230, the switching valve 61 is switched or held at the forward flow position. In the subsequent step 231, the reducing agent supply amount QR is set to the above-described QRP. In the subsequent 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 almost zero. Until it is determined that the fine particle oxidation control should be completed, the process returns to step 232 and the reducing agent is repeatedly supplied. When it is determined that the fine particle oxidation control should be completed, the processing cycle is terminated.
[0078]
FIG. 11 shows the accumulated SO described above._XAn amount reduction control routine is shown. Referring to FIG. 11, first, at step 240, the switching valve 61 is switched to the weak forward flow position. In the subsequent step 241, the reducing agent supply amount QR is set to the QRS described above. In the subsequent 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 an embodiment according to the present invention, NO_XAccumulated SO in catalyst 81_XAccumulated SO when quantity is almost zero_XIt is determined that the amount reduction control should be completed. Accumulated SO_XThe process returns to step 242 until it is determined that the amount reduction control should be completed, and the reducing agent is repeatedly supplied to accumulate SO._XWhen it is determined that the amount reduction control should be completed, the processing cycle is terminated.
[0079]
Next, another embodiment of SO according to the present invention will be 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, a reducing agent is supplied into the exhaust manifold 19 or into 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, there is a combustion stroke or an 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 average air-fuel ratio AFA of the exhaust gas flowing into the auxiliary catalyst 76 is made slightly rich by this method of injecting additional fuel. Next, another embodiment according to the present invention will be described in detail with reference to FIG. In FIG. 12, QP indicates the amount of additional fuel injected from the fuel injection valve 6 during the combustion stroke or exhaust stroke, and AFE indicates the plain air-fuel ratio of the exhaust gas discharged from the internal combustion engine.
[0083]
As shown by the arrow X in FIG._XAccumulated SO in catalyst 81_XWhen the amount QS exceeds the allowable amount QSU, or when the particulate oxidation control is completed as indicated by the arrow Y, the SO_XRemoval control is performed. That is, the switching valve 61 is held, for example, by switching from the forward flow position to the bypass position, and as shown by the arrow P, additional fuel is injected from the fuel injection valve 6 into the combustion stroke or the exhaust stroke. 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 20a directly enters the exhaust gas discharge pipe 64 from the inflow port 62 through the outflow port 63. Outflow or NO_XBypassing the catalyst 81 and the particulate filter 69, the exhaust gas is NO._XThe catalyst 81 and the particulate filter 69 are not circulated. Thus, when the switching valve 61 is held in 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 that bypasses the particulate filter 69. . As a result, a large amount of reducing agent contained in the exhaust gas discharged from the internal combustion engine is NO._XBefore bypassing the catalyst 81 and thus flowing into the auxiliary catalyst 76, NO_XIt is prevented from being oxidized and consumed in the catalyst 81.
[0084]
At this time, the additional fuel amount QP is set to QRR ′ necessary to slightly enrich 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 the SO according to another embodiment of the present invention described above._XThe removal control routine is shown. In this embodiment as well, the SO shown in FIG._XThe control routine and the particulate control routine shown in FIG. 8 are executed. In steps 201, 203, and 211 of these routines, the SO 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 subsequent 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 in 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, and SO_XWhen it is determined that the removal control should be completed, the processing cycle is terminated.
[0086]
The embodiment according to the present invention described so far can also be applied to the internal combustion engine shown in FIG. 15, for example.
[0087]
In the internal combustion engine shown in FIG. 15, a casing 168 is connected to the outlet of the exhaust pipe 20 a, the casing 167 is connected to the casing 175 via the exhaust pipe 20 c, and the casing 175 is connected to the exhaust pipe 23. These casings 168 and 175 have NO inside_XThe particulate filter 69 carrying the catalyst 81 and the auxiliary catalyst 76 are accommodated.
[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. In addition, 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 20 a between the inflow end of the bypass pipe 185 and the particulate filter 69.
[0089]
The switching valve 161 is normally held in the normal position shown by the solid line in FIG. When the switching valve 161 is held in this 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]
Even in this internal combustion engine, SO is controlled prior to fine particle oxidation control._XRemoval control is performed and accumulated SO_XPrior to the volume reduction control being performed, SO_XRemoval control is performed. When fine particle 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. Accumulated SO_XWhen the amount reduction 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 weak flow position indicated by the one-dot chain 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 20 a 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 indicated 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 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. 17, NO in casing 168_XA particulate filter 69 that accommodates the catalyst 81 and carries the auxiliary catalyst 76 in the casing 175 can also be accommodated.
[0093]
Therefore, generally speaking, NO in the exhaust passage_XPlace catalyst and NO_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 through the bypass passage, NO_XA switching valve is provided for controlling the amount of exhaust gas flowing through the catalyst, and the branch portion of the bypass passage and the NO_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 its one end face_XGuide the exhaust gas to flow out from the catalyst through the other end face, or NO_XNO flows into the catalyst through the other end face_XThis means that the exhaust gas is switched so as to flow out from the catalyst through one end face 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 view for explaining the flow of exhaust gas when the switching valve is in a forward flow position or a reverse flow position.
FIG. 4 is a partial enlarged cross-sectional view of a partition wall of a particulate filter.
FIG. 5 is a diagram for explaining the flow of exhaust gas when the switching valve is in a weak forward flow position.
FIG. 6 is a time chart for explaining an embodiment according to the present invention.
FIG. 7 shows an example SO according to the present invention._XIt is a flowchart which shows a control routine.
FIG. 8 is a flowchart showing a fine particle oxidation control routine according to an embodiment of the present invention.
FIG. 9 shows an example SO according to the present invention._XIt is a flowchart which shows a removal control routine.
FIG. 10 is a flowchart showing a fine particle oxidation control routine according to an embodiment of the present invention.
FIG. 11 shows an example of storage SO of 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 view for explaining the flow of exhaust gas when the switching valve is in the bypass position.
FIG. 14 shows another embodiment of SO according to the present invention._XIt is a flowchart which shows a removal control routine.
FIG. 15 is a diagram showing another embodiment.
FIG. 16 is a view for explaining the position of the switching valve of the embodiment shown in FIG. 15;
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 apparatus for an internal combustion engine that is removed from an auxiliary catalyst. A reducing agent supply means for supplying a reducing agent to the auxiliary catalyst is provided, and the air-fuel ratio of exhaust gas flowing into the auxiliary catalyst is rich in order to remove SO _X adhering to the auxiliary catalyst from the auxiliary catalyst. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the reducing agent is supplied to the auxiliary catalyst from the reducing agent supply means. The exhaust emission control device for an internal combustion engine according to claim 1, which is carried on a particulate filter for collecting particulates in exhaust gas into which the SO _X accumulation agent flows. Before the temperature of the particulate filter is raised while maintaining the air-fuel ratio of the exhaust gas flowing into the particulate filter lean to oxidize the particulates deposited on the particulate filter, the auxiliary The exhaust purification device 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 stores NO _X in the exhaust gas flowing in when the air-fuel ratio of the inflowing exhaust gas is lean, and the reductant is contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas decreases. 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 emission control device for an internal combustion engine according to Item 5. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, which is carried on a particulate filter for collecting particulates in exhaust gas into which the auxiliary catalyst flows.

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