JP3838157B2 - 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, an expanded volume chamber is formed in the exhaust passage of an internal combustion engine where combustion is continuously performed under a lean air-fuel ratio, and a particulate filter for collecting particulates in the inflowing exhaust gas is expanded. A bypass passage that is accommodated in the volume chamber, bypasses the expansion volume chamber, and connects the exhaust passage upstream of the expansion volume chamber and the exhaust passage downstream of the expansion volume chamber is provided. 2. Description of the Related Art An exhaust emission control device for an internal combustion engine is known that includes a switching valve that can switch between a collection position that leads to an enlarged volume chamber and all bypass positions that guide almost all exhaust gas into a bypass passage. In this exhaust purification device, the switching valve is held at all bypass positions during engine deceleration operation in which the fuel supply to the engine is temporarily stopped, thereby lowering the temperature of the particulate filter by the relatively low temperature exhaust gas. I try to prevent it.
[0003]
[Problems to be solved by the invention]
When the switching valve is held at the collection position and the exhaust gas is circulating in the particulate filter, the expansion volume chamber acts as an expansion chamber for the muffler or silencer, and as a result, the noise is kept low. However, as described above, when the switching valve is switched to the full bypass position, the expansion volume chamber can no longer function as the expansion chamber, so that there is a possibility that noise increases.
[0004]
SUMMARY OF THE INVENTION An object of the present invention is to provide an internal combustion engine exhaust purification device capable of suppressing noise generated when exhaust gas bypasses an enlarged volume chamber formed in an exhaust passage.
[0005]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, according to the first invention, an enlarged volume chamber is formed in an exhaust passage of an internal combustion engine in which combustion is continuously performed under a lean air-fuel ratio, and in the inflowing exhaust gas Particulate filter for collecting fine particles and NO in 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_XAt least one of the catalyst is accommodated in the expansion volume chamber, a bypass passage is provided to bypass the expansion volume chamber and connect the exhaust passage upstream of the expansion volume chamber and the exhaust passage downstream of the expansion volume chamber, and the bypass passage is shut off An exhaust purification device for an internal combustion engine having a switching valve capable of switching between a collection position for guiding almost all exhaust gas into the enlarged volume chamber and a bypass position for guiding at least part of the exhaust gas into the bypass passage A muffler having an exhaust gas chamber is connected to an exhaust passage downstream of the expansion volume chamber, and the muffler functions as a resonance chamber by switching the flow of the exhaust gas in the muffler or an expansion chamber. The exhaust gas chamber can be switched as a resonance chamber or an expansion chamber depending on the position of the switching valve. It has to.
[0006]
According to the second invention, in the first invention, when the switching valve is held at the collection position, the exhaust gas chamber of the muffler acts as a resonance chamber, and the switching valve is held at the bypass position. The exhaust gas chamber of the muffler functions as an expansion chamber when the vehicle is in operation.
[0007]
According to a third invention, in the second invention, there is provided means for obtaining an amount of exhaust gas flowing through the bypass passage when the switching valve is held at the bypass position, wherein the amount of the exhaust gas is The exhaust gas chamber of the muffler acts as a resonance chamber when it is smaller than a predetermined threshold value, and the exhaust gas chamber of the muffler acts as an expansion chamber when the amount of the exhaust gas is larger than the threshold value. I am doing so.
[0008]
Further, according to the fourth invention, in the second invention, when another particulate filter is arranged in the exhaust gas chamber of the muffler and the exhaust gas chamber should act as an expansion chamber, the exhaust gas flowing through the exhaust gas chamber Is allowed to pass through the other particulate filter.
[0009]
According to a fifth aspect, in the fourth aspect, another NOF is provided on the other particulate filter._XA catalyst is supported.
[0010]
According to the sixth invention, in the first invention, another NO in the exhaust passage between the exhaust passage downstream of the portion where the outflow end of the bypass passage opens and the muffler is provided._XA catalyst is arranged.
[0011]
According to a seventh aspect of the invention for solving the above-described problems, an enlarged volume chamber is formed in an exhaust passage of an internal combustion engine in which combustion is continuously performed under a lean air-fuel ratio, and exhaust gas flowing in Particulate filter for collecting particulates in the exhaust gas and NO in exhaust gas flowing in when the 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_XNO to reduce the amount of_XAt least one of the catalyst is accommodated in the expansion volume chamber, a bypass passage is provided to bypass the expansion volume chamber and connect the exhaust passage upstream of the expansion volume chamber and the exhaust passage downstream of the expansion volume chamber, and the bypass passage is shut off An exhaust purification device for an internal combustion engine having a switching valve capable of switching between a collection position for guiding almost all exhaust gas into the enlarged volume chamber and a bypass position for guiding at least part of the exhaust gas into the bypass passage In the above, it is determined whether or not the noise generated when the switching valve is held in the bypass position exceeds an allowable value, and when it is determined that the noise exceeds the allowable value, the switching valve is held in the collecting position, or The position of the switching valve is controlled so that the amount of exhaust gas flowing through the bypass passage decreases while being held at the bypass position.
[0012]
According to an eighth aspect, in the first or seventh aspect, the particulate filter and the NO in the enlarged volume chamber._XA catalyst is housed together and the NO is placed on the particulate filter._XA catalyst is supported.
[0013]
According to the ninth invention, in the first or seventh invention, the position of the switching valve held at the collection position is the particulate filter or NO stored in the enlarged volume chamber._XDepending on the state of the catalyst, it is temporarily switched to the bypass position.
[0014]
According to the tenth invention, in the first or seventh invention, another particulate filter is arranged in the exhaust passage between the exhaust passage downstream of the portion where the outflow end of the bypass passage opens and the muffler. The switching valve held at the collection position is temporarily switched to the bypass position in accordance with the state of the further particulate filter.
[0015]
According to the eleventh invention, in the first or seventh invention, the exhaust gas flows into the exhaust passage upstream of the portion where the inflow end of the bypass passage opens when the air-fuel ratio of the exhaust gas flowing in is lean. A sulfur storage agent that stores sulfur in the exhaust gas and releases the stored sulfur when the air-fuel ratio of the inflowing exhaust gas decreases is disposed. The position can be temporarily switched to the bypass position in accordance with the state of the minute accumulating agent.
[0016]
According to the twelfth invention, in the first or seventh invention, the switching valve held in the collection position is temporarily switched to the bypass position in accordance with the engine operating state.
[0017]
According to the thirteenth invention, in the first or seventh invention, the particulate filter or NO_XExhaust gas passing through the catalyst is in the particulate filter or NO_XParticulate filter or NO flows into the catalyst only through its one end face._XThe exhaust gas is guided so as to flow out from the catalyst only through the other end face.
[0018]
According to the fourteenth invention, in the first or seventh invention, the particulate filter or NO_XExhaust gas passing through the catalyst is in the particulate filter or NO_XIt flows into the catalyst through its one end face, and the particulate filter or NO_XGuide the exhaust gas to flow out from the catalyst through the other end face, or in the particulate filter or NO_XParticulate filter or NO flows into the catalyst through the other end face_XSwitching means for switching whether to guide the exhaust gas so as to flow out from the catalyst through one end face thereof is provided.
[0019]
In the present specification, the ratio of the air supplied to the exhaust passage upstream of a certain position of the exhaust passage, the combustion chamber, and the intake passage and the hydrocarbon HC and carbon monoxide CO is determined by the ratio of the exhaust gas at that position. This is called the air-fuel ratio.
[0020]
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.
[0021]
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.
[0022]
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.
[0023]
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. A muffler 90 is connected to the outlet of the exhaust gas discharge pipe 64 through the exhaust pipe 23.
[0024]
The annular exhaust pipe 67 extends through the exhaust gas discharge pipe 64, and a filter housing chamber 68 having a relatively large capacity is formed in a portion of the annular exhaust pipe 67 located in the exhaust gas discharge pipe 64. The 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.
[0025]
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.
[0026]
In the embodiment according to the present invention, NO is applied on the particulate filter 69 as will be described later._XA catalyst 81 is supported. However, the particulate filter 69 and NO in the filter storage chamber 68 are provided._XThe present invention can also be applied when either one of the catalysts 81 is accommodated.
[0027]
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. Additional NO supported on a honeycomb substrate_XA catalyst 76 is accommodated.
[0028]
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.
[0029]
Referring to FIGS. 1 and 3, the muffler 90 includes a casing 91 and an exhaust pipe 92 connected to the exhaust pipe 23 and extending through the casing 91. The muffler 90 is disposed in the casing 91 internal space around the exhaust pipe 92. An annular exhaust gas chamber 93 having a relatively large volume is formed. A large number of small holes 94 are formed on the downstream side of the exhaust pipe 92, and the internal space of the exhaust pipe 92 and the exhaust gas chamber 93 communicate with each other through the small holes 94. In addition, a communication hole 96 that is opened or closed by a silence control valve 95 driven by an actuator 94 is provided on the upstream side of the exhaust pipe 92. As will be described later, when the communication hole 96 is opened, the internal space of the exhaust pipe 92 is communicated with the exhaust gas chamber 93 through the communication hole 96. On the other hand, a large number of small holes 97 are formed on the downstream side of the exhaust pipe 92. These small holes 97 always communicate the internal space of the exhaust pipe 92 with the exhaust gas chamber 93. Further, an additional particulate filter 98 having an annular shape is accommodated in the exhaust gas chamber 93 between the communication hole 96 and the small hole 97, and the NO on the additional particulate filter 98._XA catalyst 99 is supported.
[0030]
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.
[0031]
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.
[0032]
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. For example, a temperature sensor 48 for detecting the temperature of the particulate filter 69 is attached to the center of the particulate filter 69, and the output voltage of the temperature sensor 48 is input to the input port 45 via the corresponding AD converter 47. The 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 °.
[0033]
On the other hand, the output port 46 is connected through a corresponding drive circuit 48 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, The reductant agent pump 78 and the silencing control valve driving actuator 94 are connected to each other.
[0034]
The switching valve 61 of the catalytic converter 22 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 arrow in FIG. 3B, all the exhaust gas flowing into the exhaust pipe 20a flows into the annular exhaust pipe 67 through the inflow port 62 and the inflow / outflow port 65 sequentially, 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.
[0035]
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 flows into the annular exhaust pipe 67 sequentially through the inflow port 62 and the inflow / outflow port 66 as shown by the broken arrows in FIG. 3B, and then passes through the particulate filter 69. After that, the gas flows out into the exhaust gas discharge pipe 64 through the inflow / outflow port 65 and the outflow port 63 sequentially.
[0036]
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 guided so that the exhaust gas flows into the particulate filter 69 through one end face thereof and flows out from the particulate filter 69 through the other end face, or the exhaust gas is introduced into the particulate filter 69 through the other end face. It is possible to switch whether to guide the exhaust gas so that it flows in and flows out from the particulate filter 69 through one end face thereof. 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.
[0037]
The exhaust gas flowing into the exhaust gas discharge pipe 64 through the outflow port 66 is then added to the additional NO as shown in FIGS. 3 (A) and (B)._XAfter passing through the catalyst 76 and progressing along the outer peripheral surface of the annular exhaust pipe 67, it flows into the exhaust pipe 23.
[0038]
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.
[0039]
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.
[0040]
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.
[0041]
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.
[0042]
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 is 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.
[0043]
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.
[0044]
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
[0045]
The additional particulate filter 98 is configured in the same manner as the particulate filter 69, and an additional NO is added on the partition wall of the additional particulate filter 98._XA catalyst 99 is supported. Also, additional NO_XCatalysts 76 and 99 are also NO_XThe configuration is the same as that of the catalyst 81.
[0046]
As described above, the exhaust gas passes through the particulate filter 69 regardless of whether the switching valve 61 is held in the forward flow position or the reverse flow position. 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.
[0047]
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 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.
[0048]
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
[0049]
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.
[0050]
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.
[0051]
Therefore, in the embodiment according to the present invention, for example, when the amount of deposited fine particles on the particulate filter 69 exceeds the allowable maximum amount, the switching valve 61 is switched from the forward flow position to the reverse flow position or vice versa and flows into the particulate filter 69. A temperature rise control is performed in which the temperature of the particulate filter 69 is increased to 600 ° C. or higher while the air-fuel ratio of the exhaust gas is maintained lean, and then maintained at 600 ° C. or higher. When this temperature increase control is performed, the fine particles deposited on the particulate filter 69 are ignited and burned and removed. In this case, since the flow of the exhaust gas is reversed, the ash formed by burning the fine particles is easily removed from the particulate filter 69.
[0052]
In the embodiment shown in FIG. 1, the accumulation on the particulate filter 69 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. It is determined that the amount of fine particles has exceeded the allowable maximum amount. In addition, a reducing agent is supplied from a reducing agent supply valve 77 to raise the temperature of the particulate filter 69, and this reducing agent burns on the particulate filter 69.
[0053]
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.
[0054]
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 SO₂Is 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.
[0055]
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.
[0056]
However, NO_XWhile maintaining the temperature of the catalyst 81 at 550 ° C. or higher, NO_XWhen the air-fuel ratio of the exhaust gas flowing into the catalyst 81 is rich or stoichiometric, 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_XSO stored in the catalyst 81_XThe amount of NO decreases gradually, at this time NO_XFrom catalyst 81 to SO_XIs SO₃It will not leak out.
[0057]
Therefore, in the embodiment shown in FIG._XAccumulated SO in catalyst 81_XNO when the amount exceeds the allowable amount_XSO stored in the catalyst 81_XNO_XAccumulated SO in catalyst 81_XIn order to reduce the amount, the reducing agent supply valve 77_XA 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 the stoichiometric air-fuel ratio or rich.
[0058]
In this case, in the embodiment shown in FIG._XAccumulated SO in catalyst 81_XWhen the amount is to be reduced, the switching valve 61 is held at the weak forward flow position shown in FIG. When the switching valve 61 is held in this weak forward flow position, as shown in FIG. 5, most of the exhaust gas flows directly from the inflow port 62 into the exhaust gas discharge pipe 64 through the outflow port 63, that is, NO._XThe catalyst 81 is bypassed, and a small amount of the remaining exhaust gas flows into the annular exhaust pipe 67 via the inflow / outflow port 65, and then NO._XThe catalyst 81 flows in the forward flow direction. That is, when the switching valve 61 is held at the weak forward flow position, the NO is compared with the case where the switching valve 61 is held at the forward flow position or the reverse flow position._XThe amount of exhaust gas flowing into the catalyst 81 is reduced, and NO_XThe space velocity of the exhaust gas in the catalyst 81 decreases.
[0059]
Accordingly, if the switching valve 61 is held at the weak forward flow position, NO_XThe amount of reducing agent required to switch the air-fuel ratio of the exhaust gas flowing into the catalyst 81 to the stoichiometric air-fuel ratio or rich can be reduced. NO_XNO of the reducing agent supplied to the catalyst 81_XThe residence time in the catalyst 81 is increased, so that the reducing agent is SO._XIt can be used effectively for reduction. Here, 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.
[0060]
On the other hand, the muffling control valve 95 of the muffler 90 is held at either one of the resonance position indicated by the solid line and the extended position indicated by the broken line in FIG. When the silencing control valve 95 is held at the resonance position, the communication hole 96 is closed, and as a result, the exhaust gas chamber 93 acts as a resonance chamber. Therefore, in this case, noise is suppressed by the resonance effect of the exhaust gas chamber 93. Note that the flow of the exhaust gas when the muffler control valve 95 is at the resonance position is indicated by a solid arrow in FIG.
[0061]
On the other hand, when the silencing control valve 95 is held in the extended position, the communication hole 96 is opened, and the exhaust pipe 92 between the communication hole 96 and the small hole 97 is closed by the silencing control valve 92. As a result, the exhaust gas that has flowed into the exhaust pipe 92 flows into the exhaust gas chamber 93 through the communication hole 96 and then passes through the additional particulate filter 98, as indicated by the broken dashed line in FIG. Later, it returns to the exhaust pipe 92 through the small hole 97. As described above, the volume of the exhaust gas chamber 93 is relatively large, and as a result, the exhaust gas chamber 93 acts as an expansion chamber. Therefore, in this case, noise is suppressed by the expansion action of the exhaust gas chamber 93.
[0062]
When the switching valve 61 is held in the forward flow position or the reverse flow position, the exhaust gas passes through the particulate filter 69, that is, passes through the filter housing chamber 68. As described above, the volume of the filter housing chamber 68 is relatively large, and as a result, the filter housing chamber 68 functions as an expansion chamber. In other words, when the switching valve 61 is held in the forward flow position or the reverse flow position, noise is suppressed by the expansion action of the filter housing chamber 68.
[0063]
Therefore, in the embodiment shown in FIG. 1, when the switching valve 61 is held at the forward flow position or the reverse flow position, the muffler control valve 95 is held at the resonance position so that the exhaust gas chamber 93 acts as the resonance chamber. Yes. As a result, noise in a wide frequency range can be suppressed.
[0064]
However, as described above, for example, NO_XAccumulated SO in catalyst 81_XWhen the amount should be decreased, the switching valve 61 is switched to the weak forward flow position, and at this time, a large amount of exhaust gas bypasses the filter housing chamber 68. For this reason, the noise suppressing action of the filter housing chamber 68 is weakened.
[0065]
Therefore, in the embodiment shown in FIG. 1, when the switching valve 61 is switched to the weak forward flow position, the silencing control valve 95 is switched to the extended position. As a result, as described above, the exhaust gas chamber 93 acts as an expansion chamber, and noise can be continuously suppressed. At this time, the particulate filter 69 and NO_XExhaust gas that bypasses the catalyst 81 passes through an additional particulate filter 98 and additional NO._XNO and particulates that pass through the catalyst 99 and are therefore discharged into the atmosphere when the switching valve 61 is held in the weak forward flow position._XThe amount of can be reduced.
[0066]
That is, as shown in FIG. 7, the switching valve 61 is alternately switched between the forward flow position and the reverse flow position, for example, according to the amount of deposited fine particles on the particulate filter 69, and at this time, the silencing control valve 95 is set to the resonance position. Retained. Next, when the switching valve 61 is switched to the weak forward flow position, the silencing control valve 95 is switched to the extended position. For example, when the switching valve 61 is returned to the forward flow position, the mute control valve 95 is also returned to the resonance position.
[0067]
FIG. 8 shows a routine for executing the silencing control valve control in the embodiment shown in FIG. This routine is executed by interruption every predetermined time. Referring to FIG. 8, first, at step 200, it is judged if the switching valve 61 is held at the weak forward flow position. When the switching valve 61 is held at the forward flow position or the reverse flow position, the routine proceeds to step 201 where the mute control valve 95 is held at the resonance position. On the other hand, when the switching valve 61 is held at the weak forward flow position, the routine proceeds to step 202, where the mute control valve 95 is held at the extended position.
[0068]
When the switching valve 61 is held at the weak forward flow position, NO in the exhaust gas_XIs an additional NO_XAccumulated in the catalyst 76, 99, the particulates accumulate on the additional particulate filter 98. However, the time for which the switching valve 61 is held at the weak forward flow position is not so long, and therefore additional NO._XAccumulated NO in catalyst 76,99_XSpecial control to reduce the amount or to reduce the amount of particulate deposited on the additional particulate filter 98 is not necessarily required.
[0069]
Further, the weak forward flow position of the switching valve 61 in the embodiment shown in FIG. 1 is a position where the amount of exhaust gas flowing through the particulate filter 69 is made substantially constant, and therefore the engine operating state fluctuates and is discharged from the internal combustion engine. Considering that the amount of exhaust gas to be changed fluctuates, the weak forward flow position in this case is not necessarily a constant angular position.
[0070]
FIG. 9 shows another embodiment according to the present invention. In the embodiment shown in FIG. 9, a casing 168 of the catalytic converter 22 is connected to the outlet of the exhaust pipe 20a._XA particulate filter 69 carrying a catalyst 81 is accommodated. The outlet of the casing 168 is connected to the muffler 90 via the exhaust pipe 123.
[0071]
A bypass pipe 185 is branched from the exhaust pipe 20 a, and the outflow end of the bypass pipe 185 opens into the exhaust pipe 123. In addition, a switching valve 161 is disposed in the portion of the exhaust pipe 20a where the inflow end of the bypass pipe 185 is open. The switching valve 161 is closed as shown by a solid line in FIG. 9 to close the bypass pipe 185 and guide almost all exhaust gas into the casing 168, and a large amount of exhaust gas as shown by a broken line in FIG. A portion flows into the bypass pipe 185 and can be switched between an open position where the remaining slight amount of exhaust gas flows into the casing 168. Therefore, in the embodiment shown in FIG. 9, the particulate filter 69 or the NO is obtained both when the switching valve 161 is in the closed position and in the open position._XExhaust gas passing through the catalyst 81 is in the particulate filter 69 or NO._XIt flows into the catalyst 81 only through one end face thereof, and the particulate filter 69 or NO_XThe exhaust gas is guided from the catalyst 81 so as to flow out only through the other end face.
[0072]
Here, in the embodiment shown in FIG. 9, the angular position or opening of the switching valve 61 when held in the open position is kept constant.
[0073]
A flow rate sensor 186 for detecting the amount of exhaust gas flowing through the bypass pipe 185 is attached to the bypass pipe 185. The actuator for driving the switching valve 161 and the flow sensor 186 are connected to an electronic control unit (not shown). Further, a reducing agent supply valve 77 is disposed in the exhaust pipe 20 a between the switching valve 161 and the casing 168.
[0074]
Usually, the switching valve 161 is held at the closed position, and the mute control valve 95 of the muffler 90 is held at the resonance position. For example NO_XSO in catalyst 81_XReduce and accumulate SO_XWhen the amount should be decreased, the switching valve 161 is temporarily switched to the open position, and at this time, the mute control valve 95 is temporarily switched to the extended position.
[0075]
Here, as described above, the angular position or opening of the switching valve 61 when held in the open position is kept constant. Therefore, when the engine operating state fluctuates, the amount of exhaust gas flowing through the bypass pipe 185 fluctuates, that is, the amount of exhaust gas that bypasses the casing 168 that forms the enlarged volume chamber fluctuates.
[0076]
On the other hand, when the amount of exhaust gas flowing through the bypass pipe 185 is not so large, the noise suppression effect of the casing 168 is not necessarily weakened, and the exhaust gas chamber 93 of the muffler 90 does not need to act as an expansion chamber. Rather, in such a case, the noise can be suppressed by using the exhaust gas chamber 93 as a resonance chamber.
[0077]
Therefore, in the embodiment shown in FIG. 9, the amount of exhaust gas flowing through the bypass pipe 185 is obtained, and when the amount of exhaust gas is larger than a predetermined threshold value, the silencing control valve 95 is set to the extended position. When it is less than the threshold value, the mute control valve 95 is held at the resonance position. In this way, it is possible to further prevent the noise suppression action from deteriorating when the switching valve 161 is switched to the open position.
[0078]
FIG. 10 shows a routine for executing the silencing control valve control in the embodiment shown in FIG. This routine is executed by interruption every predetermined time. Referring to FIG. 10, first, at step 210, it is judged if the switching valve 161 is held in the open position. When the switching valve 161 is held at the closed position, the routine proceeds to step 211 where the mute control valve 95 is held at the resonance position. On the other hand, when the switching valve 161 is held at the open position, the routine proceeds to step 212, where it is determined whether or not the amount QB of the exhaust gas flowing through the bypass pipe 185 is larger than a predetermined threshold value Q0. Is done. When QB ≦ Q0, the routine proceeds to step 211 where the mute control valve 95 is held at the resonance position. On the other hand, when QB> Q0, the routine proceeds to step 213, where the mute control valve 95 is held in the extended position.
[0079]
In the embodiment shown in FIG. 9, a flow sensor 186 is attached to the bypass pipe 185 in order to obtain the amount of exhaust gas flowing through the bypass pipe 185. However, as shown in FIG. 11, a pressure sensor 187 for detecting the pressure in the bypass pipe 185 is attached to the bypass pipe 185, and the amount of exhaust gas flowing through the bypass pipe 185 based on the pressure in the bypass pipe 185. QB can also be estimated. The pressure sensor 187 is connected to an electronic control unit (not shown).
[0080]
In the embodiment described so far, the muffler 90 includes a single exhaust gas chamber 93. However, the muffler 90 can be provided with an additional exhaust gas chamber that acts as a resonance chamber or an expansion chamber.
[0081]
FIG. 12 shows still another embodiment according to the present invention. In the embodiment shown in FIG. 12, the SO pipe 20a has SO._XAn accumulating agent 188 is disposed, and an additional particulate filter 189 is disposed in the exhaust pipe 23. In this embodiment, the reducing agent supply valve and the muffler shown in FIG. 1 are not provided.
[0082]
SO_XThe accumulating agent 188 uses, for example, alumina as a carrier, and at least one selected from transition metals such as iron Fe, manganese Mn, nickel Ni, tin Sn and lithium Li is supported on the carrier. This SO_XAccumulating agent 188 is NO_XSimilar to the catalyst, the SO in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean_XAnd the stored SO when the air-fuel ratio of the inflowing exhaust gas decreases_XRelease. However, SO_XAccumulating agent 188 is NO_XStored SO rather than catalyst_XCan be easily released. This is SO_XIs sulfate ion SO₄ ^2-In the form of SO_XPresent in the storage agent or sulfate BaSO₄Even if is produced, the sulfate BaSO₄SO is not stable_XIt is thought that it is because it exists in the accumulating agent.
[0083]
SO_XThe air-fuel ratio of the exhaust gas flowing into the storage agent 188 is maintained lean, so that the SO in the exhaust gas is maintained._XIs SO_XIt is stored in the storage agent 188. As a result, NO_XSO in catalyst 81_XCan be prevented from flowing in.
[0084]
SO over time_XAccumulated SO in the accumulator 188_XThe amount increases gradually. In the embodiment shown in FIG._XAccumulated SO in the accumulator 188_XSO when the amount exceeds the allowable amount_XSO stored in storage agent 188_XSO to release_XThe average air-fuel ratio of the exhaust gas flowing into the storage agent 188 is temporarily switched to the stoichiometric air-fuel ratio or rich. In the embodiment shown in FIG._XIn order to make the average air-fuel ratio of the exhaust gas flowing into the storage agent 188 the stoichiometric air-fuel ratio or rich, a second fuel injection is performed from the fuel injection valve 6 during the engine expansion stroke or the exhaust stroke.
[0085]
SO_XSO released from the storage agent 188_XReaches the switching valve 61 via the exhaust pipe 20a. At this time, if the switching valve 61 is held in the forward flow position or the reverse flow position, that is, the exhaust gas is NO._XWhen guided into the catalyst 81, this SO_XIs NO_XThere is a risk of being stored in the catalyst 81.
[0086]
Therefore, in the embodiment shown in FIG._XAccumulating agent 188 to SO_XThe switch valve 61 is temporarily switched to the full bypass position shown in FIG. When the switching valve 61 is held in this all bypass position, almost all the exhaust gas flows out from the inflow port 62 directly into the exhaust gas discharge pipe 64 through the outflow port 63 as shown in FIG._XBypass the catalyst 81, NO_XThe exhaust gas flowing into the catalyst 81 becomes almost zero.
[0087]
As a result, SO_XSO released from the storage agent 188_XIs NO_XBypass catalyst 81 and therefore NO_XIt is not stored in the catalyst 81.
[0088]
On the other hand, in the embodiment shown in FIG. 12, the fuel supply operation to the engine is temporarily stopped during the engine deceleration operation, and the temperature of the exhaust gas at this time is relatively low. Therefore, if the switching valve 61 is held at the forward flow position or the reverse flow position at this time, the temperature of the particulate filter 69 may be lowered by the low temperature exhaust gas.
[0089]
Therefore, in the embodiment shown in FIG. 12, the switching valve 61 is temporarily switched to the full bypass position during engine deceleration operation where the temperature of the particulate filter 69 is lower than a predetermined threshold value. As a result, the low-temperature exhaust gas does not flow into the particulate filter 69, and the temperature of the particulate filter 69 is maintained high.
[0090]
However, when the switching valve 61 is held at the full bypass position in this way, the particulates contained in the exhaust gas at this time bypass the particulate filter 69.
[0091]
Therefore, in the embodiment shown in FIG. 12, an additional particulate filter 189 is arranged in the exhaust pipe 23 so that the particulates are not discharged into the atmosphere when the switching valve 61 is held at the full bypass position.
[0092]
The amount of deposited particles on the additional particulate filter 189 also increases with time. In the embodiment shown in FIG. 12, for example, when the amount of particulate matter deposited on the additional particulate filter 189 exceeds the allowable amount, the air-fuel ratio of the exhaust gas flowing into the additional particulate filter 189 is maintained while keeping lean. The temperature rise control is performed such that the temperature of the particulate filter 189 is raised to 600 ° C. or higher and then maintained at 600 ° C. or higher. When this temperature rise control is performed, the fine particles deposited on the additional particulate filter 189 are ignited and burned and removed. In the embodiment shown in FIG. 12, in order to increase the temperature of the additional particulate filter 189, an additional, ie, second fuel injection is performed from the fuel injection valve 6 during the engine expansion stroke or the exhaust stroke. The temperature of the exhaust gas flowing into the additional particulate filter 189 is raised. The temperature of the particulate filter 69 is similarly raised.
[0093]
In this case, if the switching valve 61 is held in the forward flow position or the reverse flow position, that is, if the exhaust gas is introduced into the particulate filter 69, the temperature of the particulate filter 69 is first increased, and the additional particulate filter It takes time to raise the temperature of 189.
[0094]
Therefore, in the embodiment shown in FIG. 12, the switching valve 61 is temporarily switched to the full bypass position even when the amount of accumulated particulates on the additional particulate filter 189 should be reduced.
[0095]
Thus, SO_XAccumulating agent 188 to SO_XWhen the amount of accumulated particulate matter on the additional particulate filter 189 is to be decreased during engine deceleration operation, the switching valve 61 is temporarily switched to the full bypass position.
[0096]
However, when the switching valve 61 is switched to the full bypass position, the noise suppressing action of the filter housing chamber 68 is weakened as described above, and the noise increases.
[0097]
However, when the engine load is low or the engine speed is low, the noise does not increase so much even if the switching valve 61 is switched to the full bypass position. That is, as shown in FIG. 14, when the engine operating state is in the region NS, the noise generated when the switching valve 61 is held in the full bypass position is kept smaller than the allowable value, however, the engine operating state is in the region NL. When inside, the noise generated when the switching valve 61 is held at all bypass positions increases beyond an allowable value.
[0098]
Therefore, in the embodiment shown in FIG. 12, it is determined whether the engine operating state is in the region NS or the region NL when the switching valve 61 is to be switched to the full bypass position or to be held, and the engine operating state is determined. When the engine is in the region NS, the switching valve 61 is switched or held to the full bypass position, and when the engine operating state is in the region NS, the switching valve 61 is held or switched to the forward flow position or the reverse flow position.
[0099]
As a result, noise can be suppressed when the engine operating state is within the region NL, and when the engine operating state is within the region NS, for example, SO._XAccumulating agent 188 to SO_XCan be reliably released. When the switching valve 61 is held or switched to the forward flow position or the reverse flow position, the second fuel injection by the fuel injection valve 6 is not started or stopped. Therefore, SO_XSO from storage agent 188_XThe discharge action and the temperature increase control of the additional particulate filter 189 are not started or interrupted. Region NS and region NL are obtained in advance as a function of accelerator pedal depression amount L and engine speed N representing engine load, and are stored in advance in ROM 32 in the form of a map shown in FIG. Yes.
[0100]
FIG. 15 shows a routine for executing the switching valve control in the embodiment shown in FIG. This routine is executed by interruption every predetermined time. Referring to FIG. 15, first, at step 220, it is determined whether or not the switching valve 61 should be switched to the full bypass position. When the switching valve 61 is to be held at the forward flow position or the reverse flow position, the routine proceeds to step 221 where the switching valve 61 is held at the forward flow position or the reverse flow position. On the other hand, when the switching valve 61 is to be switched to the full bypass position or to be held, the routine proceeds to step 222, where it is determined whether or not the current engine operating state is within the region NS. When the current engine operating state is within the area NS, the routine then proceeds to step 223, where the switching valve 61 is switched or held at the full bypass position. On the other hand, when the current engine operating state is in the region NL, the routine proceeds to step 221 where the switching valve 61 is switched or held at the forward flow position or the reverse flow position.
[0101]
Next, another embodiment of the embodiment shown in FIG. 12 will be described with reference to the routine shown in FIG. This routine is executed by interruption every predetermined time.
[0102]
Referring to FIG. 16, first, in step 230, it is determined whether or not the switching valve 61 should be switched to the full bypass position. When the switching valve 61 should be held in the forward flow position or the backward flow position, the process proceeds to step 231 where the switching valve 61 is held in the forward flow position or the backward flow position. On the other hand, when the switching valve 61 is to be switched to the full bypass position or to be held, the routine proceeds to step 232, where it is determined whether or not the current engine operating state is within the region NS. When the current engine operating state is within the region NS, the routine proceeds to step 233, where the switching valve 61 is switched or held at the full bypass position. On the other hand, when the current engine operating state is in the region NL, the routine proceeds to step 234, where the switching valve 61 is switched or held at the weak forward flow position.
[0103]
That is, this embodiment is different from the embodiment shown in FIG. 12 in that the switching valve 61 is switched to the weak forward flow position (FIG. 5) when the engine operating state is in the region NL. In other words, almost all exhaust gas flows around the particulate filter 69 when the engine operating state is in the region NS, and one part of the exhaust gas flows into the particulate filter 69 when the engine operating state is in the region NL. The amount of exhaust gas that flows into the part and bypasses the particulate filter 69 is reduced as compared to when it is in the region NS.
[0104]
In this way, when the engine operating state is within the region NL, the amount of exhaust gas flowing into the particulate filter 69 can be kept small while suppressing noise by the expansion action of the filter housing chamber 68. . Therefore, in this case, even when the engine operating state is within the region NL, the SO_XSO from storage agent 188_XThe discharge action and the temperature increase control of the additional particulate filter 189 can be started or continued.
[0105]
By the way, the forward flow position and the reverse flow position in the embodiment of FIGS. 1 and 12 and the closed position in the embodiment of FIG. 9 are referred to as a collection position, and the weak forward flow position in the embodiment of FIG. 1 and the open position in the embodiment of FIG. When the switching valve is held at the collection position, the bypass passage is blocked and almost all exhaust gas is guided into the enlarged volume chamber. When the switching valve is held at the bypass position, at least a part of the exhaust gas is guided into the bypass passage.
[0106]
In addition, in the embodiment shown in FIGS. 1 and 9, when the switching valve is held at the collection position, the exhaust gas chamber of the muffler acts as a resonance chamber, and the switching valve is held at the bypass position. This means that the exhaust gas chamber of the muffler acts as an expansion chamber. On the other hand, in the embodiment shown in FIGS. 12 and 16, it is determined whether or not the noise generated when the switching valve is held in the bypass position exceeds the allowable value, and when it is determined that the noise exceeds the allowable value. In the embodiment shown in FIG. 12, the position of the switching valve is controlled so as to hold the switching valve in the collecting position, and in the embodiment shown in FIG. 16, the exhaust gas flowing in the bypass passage is held in the bypass position. This means that the position of the switching valve is controlled so that the amount decreases.
[0107]
Further, in the embodiment shown in FIGS. 1 and 9, for example, NO_XAccumulated SO in catalyst 81_XWhen the amount exceeds the allowable amount, the switching valve is temporarily switched to the bypass position. In the embodiment shown in FIGS. 12 and 16, for example, SO_XAccumulated SO in the accumulator 188_XWhen the amount exceeds the allowable amount, when the engine is decelerating when the temperature of the particulate filter 69 is higher than the threshold value, or when the amount of accumulated particulates on the additional particulate filter 189 exceeds the allowable amount, the switching valve Is temporarily switched to the bypass position.
[0108]
So, generally speaking, NO_XState of catalyst 81, state of particulate filter 69, SO_XThis means that the switching valve is temporarily switched to the bypass position in accordance with the state of the storage agent 188, the state of the additional particulate filter 189, or the engine operating state.
[0109]
【The invention's effect】
Noise generated when the exhaust gas bypasses the enlarged volume chamber formed in the exhaust passage can be suppressed.
[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 view for explaining the flow of exhaust gas in the muffler.
7 is a diagram for explaining control of a muffler control valve in the embodiment shown in FIG. 1; FIG.
FIG. 8 is a flowchart for executing control of the silencing control valve in the embodiment shown in FIG. 1;
FIG. 9 shows another embodiment according to the present invention.
10 is a flowchart for executing control of the silencing control valve in the embodiment shown in FIG. 9; FIG.
FIG. 11 is a diagram showing still another embodiment according to the present invention.
FIG. 12 is a diagram showing still 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 full bypass position.
FIG. 14 is a diagram showing an operation region.
FIG. 15 is a flowchart for executing control of the silencing control valve in the embodiment shown in FIG. 12;
FIG. 16 is a flowchart for executing control of a mute control valve in still another embodiment of the present invention.
[Explanation of symbols]
1 ... Engine body
20a ... exhaust pipe
22 ... Catalytic converter
61, 161 ... switching valve
64 ... Exhaust gas exhaust pipe
67 ... Annular exhaust pipe
68. Filter accommodation room
76,99 ... additional NO_Xcatalyst
77 ... Reducing agent supply valve
81 ... NO_Xcatalyst
90 ... Muffler
93 ... exhaust gas chamber
95 ... Silencer control valve
98,189 ... additional particulate filter
185 ... Bypass pipe
186 ... Flow sensor
187 ... Pressure sensor
188 ... SO_XAccumulating agent

Claims (14)

An expanded volume chamber is formed in an exhaust passage of an internal combustion engine where combustion is continuously performed under a lean air-fuel ratio, a particulate filter for collecting particulates in the inflowing exhaust gas, and inflowing exhaust gas store up NO _X in the exhaust gas air-fuel ratio of the gas flows at the time of lean, the NO _X when the air-fuel ratio of the inflowing exhaust gas is stored that contains a reducing agent in the exhaust gas when the reduced At least one of the NO _X catalyst in which the amount of NO _X stored by reduction is reduced is accommodated in the expansion volume chamber, bypassing the expansion volume chamber, and the exhaust passage upstream of the expansion volume chamber and the exhaust downstream of the expansion volume chamber A bypass passage that connects the passages to each other, a collection position that blocks the bypass passage and guides almost all exhaust gas into the enlarged volume chamber, and a bypass position that guides at least a part of the exhaust gas into the bypass passage. In an exhaust gas purification apparatus for an internal combustion engine having a switching valve capable of switching between, a muffler provided with an exhaust gas chamber is connected to an exhaust passage downstream of the expansion volume chamber, and the muffler controls the flow of exhaust gas in the muffler. By switching, it is possible to switch whether the exhaust gas chamber functions as a resonance chamber or an expansion chamber, and the position of the switching valve determines whether the exhaust gas chamber functions as a resonance chamber or an expansion chamber. An exhaust purification device for an internal combustion engine that is switched according to the conditions. When the switching valve is held at the collection position, the exhaust gas chamber of the muffler acts as a resonance chamber, and when the switching valve is held at the bypass position, the exhaust gas chamber of the muffler acts as an expansion chamber. The exhaust emission control device for an internal combustion engine according to claim 1. Means for determining the amount of exhaust gas flowing through the bypass passage when the switching valve is held at the bypass position, and when the amount of exhaust gas is less than a predetermined threshold value, exhaust gas of the muffler The exhaust purification device for an internal combustion engine according to claim 2, wherein the chamber acts as a resonance chamber, and when the amount of the exhaust gas is larger than the threshold value, the exhaust gas chamber of the muffler acts as an expansion chamber. . A separate particulate filter is arranged in the exhaust gas chamber of the muffler, and the exhaust gas flowing through the exhaust gas chamber passes through the separate particulate filter when the exhaust gas chamber should act as an expansion chamber. 2. An exhaust emission control device for an internal combustion engine according to 2. Said another on the particulate filter, the exhaust purification system of an internal combustion engine according to claim 4 in which another of the NO _X catalyst. In the exhaust passage between the exhaust passage downstream of the muffler than the portion outlet end of the bypass passage is opened, the exhaust purification system of an internal combustion engine according to claim 1, further arranged another of the NO _X catalyst. An expanded volume chamber is formed in an exhaust passage of an internal combustion engine where combustion is continuously performed under a lean air-fuel ratio, a particulate filter for collecting particulates in the inflowing exhaust gas, and inflowing exhaust gas store up NO _X in the exhaust gas air-fuel ratio of the gas flows at the time of lean, the NO _X when the air-fuel ratio of the inflowing exhaust gas is stored that contains a reducing agent in the exhaust gas when the reduced At least one of the NO _X catalyst in which the amount of NO _X stored by reduction is reduced is accommodated in the expansion volume chamber, bypassing the expansion volume chamber, and the exhaust passage upstream of the expansion volume chamber and the exhaust downstream of the expansion volume chamber A bypass passage that connects the passages to each other, a collection position that blocks the bypass passage and guides almost all exhaust gas into the enlarged volume chamber, and a bypass position that guides at least a part of the exhaust gas into the bypass passage. In an exhaust gas purification apparatus for an internal combustion engine equipped with a switching valve capable of switching between the two, a determination is made as to whether or not the noise generated when the switching valve is held in the bypass position exceeds an allowable value, and if the noise exceeds the allowable value An exhaust purification device for an internal combustion engine that controls the position of the switching valve so as to reduce the amount of exhaust gas flowing in the bypass passage while holding the switching valve in the collecting position when judged or holding the switching valve in the bypass position . The expansion volume and the indoors particulate filter and the NO _X catalyst is accommodated together, the exhaust purification system of an internal combustion engine according to claim 1 or 7 wherein the NO _X catalyst on the particulate filter is carried . Position of the switching valve which is held in the collection position, claim wherein is adapted to be switched to temporarily bypass position according to the state of the particulate filter or NO _X catalyst is housed in the enlarged volume chamber 1 Or an exhaust emission control device for an internal combustion engine according to claim 7. A further particulate filter is disposed in the exhaust passage between the exhaust passage downstream of the portion where the outflow end of the bypass passage opens and the muffler, and the switching valve held in the collecting position is provided with the further separate valve. The exhaust emission control device for an internal combustion engine according to claim 1 or 7, wherein the exhaust gas purification device is temporarily switched to a bypass position in accordance with the state of the particulate filter. In the exhaust passage upstream from the portion where the inflow end of the bypass passage opens, the sulfur content in the exhaust gas flowing in when the air-fuel ratio of the inflowing exhaust gas is lean is stored, and the air-fuel ratio of the inflowing exhaust gas is lowered Then, a sulfur accumulation agent that releases the stored sulfur component is arranged, and the switching valve held at the collection position is temporarily switched to the bypass position according to the state of the sulfur accumulation agent. The exhaust emission control device for an internal combustion engine according to claim 1 or 7, wherein The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 7, wherein the switching valve held at the collection position is temporarily switched to the bypass position in accordance with the engine operating state. Exhaust gas so that the exhaust gas passing through the particulate filter or NO _X catalyst flows out only via the other end surface from inside the particulate filter, or one end face in the NO _X catalyst only flows through the particulate filter or NO _X catalyst The exhaust emission control device for an internal combustion engine according to claim 1 or 7, wherein Guiding the exhaust gas so that the exhaust gas passing through the particulate filter or NO _X catalyst flows out through the other end surface from the inflow and the particulate filter or NO _X catalyst through its one end surface in the or NO _X catalyst particulate filter either, or a switching means for flowing through the other end face in the particulate in the particulate filter or NO _X in the catalyst switching to and guides the exhaust gases to flow out through the one end face from the particulate filter or NO _X catalyst The exhaust emission control device for an internal combustion engine according to claim 1 or 7, which is provided.

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