JP2008002359A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine having SOx trap material and adopting a measure against SOx flowed out from the SOx trap material. <P>SOLUTION: The exhaust emission control device has the SOx trap material 11 for trapping SOx in an exhaust passage of the internal combustion engine. The exhaust emission control device is provided separately from the SOx trap material with SOx trap means 26, 28, 51, 54 which have a function of trapping SOx flowing out from the SOx trap material when it is judged that a SOx effluence condition that an amount of SOx flowing out from the SOx trap material becomes larger than a predetermined amount is met. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  Patent Document 1 describes an exhaust purification device for an internal combustion engine. This exhaust purification device absorbs NOx (nitrogen oxide) when the air-fuel ratio of the inflowing exhaust gas is lean, and has a NOx absorption / release capability for releasing the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases. The NOx absorbent which has is arrange | positioned in the exhaust passage. Further, in this exhaust purification device, an SOx absorbent having SOx absorption capability for absorbing SOx (sulfur oxide) when the air-fuel ratio of the inflowing exhaust gas is lean is disposed in the exhaust passage upstream of the NOx absorbent. ing. According to this exhaust purification device, the NOx absorption / release capability of the NOx absorbent is maintained high. That is, the NOx absorbent also absorbs SOx when the air-fuel ratio of the inflowing exhaust gas is lean, and in this case, the NOx absorption / release capacity of the NOx absorbent is reduced. However, in the exhaust emission control device described in Patent Document 1, the SOx absorbent is disposed upstream of the NOx absorbent, and SOx is removed from the exhaust gas by the SOx absorbent. For this reason, the SOx flowing into the NOx absorbent is extremely small, and the NOx absorbent capacity of the NOx absorbent is maintained high.

JP-A-6-173652 JP 2005-133610 A JP 2003-65039 A JP 2002-172329 A

  By the way, when the SOx concentration in the exhaust gas is much higher than the assumed concentration or the SOx absorbent capacity of the SOx absorbent is reduced, the SOx absorbent is not absorbed and flows out of the SOx absorbent. The amount of coming SOx may increase. In this case, since the SOx flowing out from the SOx absorbent is absorbed by the NOx absorbent, the NOx absorbent capacity of the NOx absorbent is reduced, and the NOx absorbent is not absorbed by the NOx absorbent. It is also possible that it will leak out of.

  Further, since the SOx absorbent has a function to fulfill the function of absorbing SOx, the SOx that has flowed out of the SOx absorbent even when the NOx absorbent is not disposed downstream of the SOx absorbent. It is not preferable not to perform any treatment. This is generally true even when a so-called SOx trapping material for capturing SOx in the exhaust gas and removing SOx from the exhaust gas is disposed in the exhaust passage.

  Therefore, an object of the present invention is to treat SOx that has flowed out of the SOx trapping material in an exhaust gas purification apparatus for an internal combustion engine that includes the SOx trapping material.

  In order to solve the above-mentioned problem, in the first invention, in the exhaust purification device provided with the SOx trapping material for trapping SOx in the exhaust passage of the internal combustion engine, the amount of SOx flowing out from the SOx trapping material is predetermined. In addition to the SOx trapping material, SOx trapping means is provided that exhibits a function of trapping SOx flowing out from the SOx trapping material when it is determined that a SOx outflow condition greater than the above amount is satisfied.

  According to a second invention, in the first invention, the SOx trapping means is branched from the exhaust passage downstream of the SOx trapping material, the SOx trapping material disposed in the branch passage and capturing SOx, and the exhaust An exhaust gas flow control valve that controls whether or not gas flows into the branch passage, and when it is determined that the SOx outflow condition is satisfied, the SOx trapping means controls the exhaust gas flow control valve. The exhaust gas is controlled to flow into the branch passage.

  In a third aspect, in the second aspect, the SOx trapping means has an air supply device for supplying air to the SOx trapping material disposed in the branch passage, and the SOx trap disposed in the exhaust passage. When the air-fuel ratio of the exhaust gas flowing into the material is a rich air-fuel ratio, it is determined that the SOx outflow condition is satisfied, and when it is determined that the SOx outflow condition is satisfied, the SOx trapping means detects the exhaust gas flow. The control valve is controlled to allow exhaust gas to flow into the branch passage and to supply air from the air supply device to the SOx trapping material disposed in the branch passage.

  According to a fourth invention, in the first invention, a volume space in which the SOx trap means can store exhaust gas, a branch passage that branches from the exhaust passage downstream of the SOx trap and extends to the volume space, An exhaust gas flow control valve that controls whether or not exhaust gas is allowed to flow into the branch passage, and when the SOx outflow condition is determined to be satisfied, the SOx trapping means controls the exhaust gas flow control valve. To control the exhaust gas to flow into the branch passage.

  According to a fifth aspect, in the first aspect, the SOx trapping device generates hydrogen peroxide by supplying hydrogen peroxide, and the reaction between hydrogen peroxide supplied from the hydrogen peroxide supply apparatus and SOx. A sulfuric acid storage chamber for storing sulfuric acid, a branch passage extending from the exhaust passage downstream of the SOx trapping material and extending to the volume space, and an exhaust gas for controlling whether or not exhaust gas flows into the branch passage A flow control valve, and when it is determined that the SOx outflow condition is satisfied, the SOx trapping means controls the exhaust gas flow control valve to flow the exhaust gas into the branch passage, and the branch passage Hydrogen peroxide is supplied from the hydrogen peroxide supply device to the exhaust gas flowing inside.

  According to a sixth aspect, in the first aspect, the SOx trapping means is supplied with a hydrogen peroxide supply device for supplying hydrogen peroxide into an exhaust passage downstream of the SOx trapping material, and supplied from the hydrogen peroxide supply device. A sulfuric acid storage chamber for storing sulfuric acid generated by the reaction between hydrogen peroxide and SOx, and when it is determined that the SOx outflow condition is satisfied, the SOx trapping means exhausts from the hydrogen peroxide supply device. Hydrogen peroxide is supplied into the passage.

  According to a seventh aspect, in the first aspect, the SOx trapping means is supplied from a hydrogen peroxide supply device that supplies hydrogen peroxide into an exhaust passage downstream of the SOx capture material, and the hydrogen peroxide supply device. The SOx trapping means supplies hydrogen peroxide into the exhaust passage when it is determined that the SOx outflow condition is satisfied. Let

  In an eighth invention, in any one of the first to seventh inventions, the SOx trap disposed in the exhaust passage has a temperature lower than a constant temperature and the air-fuel ratio of the inflowing exhaust gas is lean. The SOx in the exhaust gas is captured in a region near the surface of the SOx trapping material when the fuel is at the fuel ratio, and when the temperature is higher than the predetermined temperature and the air-fuel ratio of the inflowing exhaust gas is the lean air-fuel ratio, The SOx trapping material diffuses SOx trapped in the vicinity of the surface of the SOx trapping material into the SOx trapping material, and when the SOx trapping rate of the SOx trapping material becomes lower than a predetermined rate, Control is performed so that the temperature of the SOx trapping material is higher than the predetermined temperature and the air-fuel ratio of the exhaust gas flowing into the SOx trapping material is maintained at a lean air-fuel ratio.

  According to the present invention, even if SOx flows out from the SOx trap disposed in the exhaust passage, the SOx is captured by the SOx trapping means.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a compression ignition type internal combustion engine equipped with an exhaust emission control device according to a first embodiment of the present invention. In FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve that injects fuel into each combustion chamber 2, 4 is an intake manifold, and 5 is an exhaust manifold. ing. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 through the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 8. A throttle valve 9 driven by a step motor is disposed in the intake duct 6. Around the intake duct 6, a cooling device 10 for cooling the intake air flowing through the intake duct 6 is disposed. In the internal combustion engine shown in FIG. 1, cooling water is guided into the cooling device 10 and the intake air is cooled by this cooling water. On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7, and the outlet of the exhaust turbine 7 b is connected to the inlet of the SOx trapping material (hereinafter also referred to as “main SOx trapping material”) 11. Further, the outlet of the SOx trap 11 is connected to the inlet of the NOx catalyst 12 via the exhaust pipe 13. The exhaust pipe 13 is provided with a reducing agent supply valve 14 for supplying a reducing agent made of, for example, HC (hydrocarbon) into the exhaust gas flowing through the exhaust pipe 13.

  Further, the outlet of the NOx catalyst 12 is connected to the exhaust pipe 24. A branch pipe 25 branches from the exhaust pipe 24, and a downstream end of the branch pipe 25 is connected to an inlet of a SOx trap (hereinafter also referred to as “backup SOx trap”) 26. The outlet of the SOx trap 26 is connected to the exhaust pipe 24 via the branch pipe 27. Further, an exhaust gas flow control valve 28 for controlling whether or not exhaust gas flows into the branch pipe 25 is attached to a location where the branch pipe 25 branches from the exhaust pipe 24. When the exhaust gas flow control valve 28 is in the state shown in FIG. 1, that is, when the inlet of the branch pipe 25 is closed, the exhaust gas does not flow into the branch pipe 25 and is exhausted as it is. It flows downstream through the tube 24. On the other hand, when the exhaust gas flow control valve 28 is in the state shown in FIG. 2, that is, when the flow path of the exhaust pipe 24 is closed, the exhaust gas flows into the branch pipe 25 and the SOx trapping material. 26 and flows into the exhaust pipe 24 via the branch pipe 27.

  The exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as “EGR”) passage 15, and an electronically controlled EGR control valve 16 is disposed in the EGR passage 15. Further, around the EGR passage 15, a cooling device 17 that cools the exhaust gas (hereinafter also referred to as “EGR gas”) flowing in the EGR passage 15 is disposed. In the internal combustion engine shown in FIG. 1, cooling water is guided into the cooling device 17, and the EGR gas is cooled by this cooling water. On the other hand, each fuel injection valve 3 is connected to a common rail 19 via a fuel supply pipe 18. Fuel is supplied into the common rail 19 from an electronically controlled fuel pump 20 with variable discharge amount. The fuel supplied into the common rail 19 is supplied to the fuel injection valve 3 through each fuel supply pipe 18.

  The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. A ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35, and An output port 36 is provided. A temperature sensor 21 that detects the temperature of the SOx trapping material 11 is attached to the main SOx trapping material 11. On the other hand, a temperature sensor 22 that detects the temperature of the NOx catalyst 12 is attached to the NOx catalyst 12. Further, a temperature sensor 29 that detects the temperature of the SOx trap 26 is attached to the backup SOx trap 26. The output signals of these temperature sensors 21, 22, and 28 are input to the input port 35 via the corresponding AD converters 37. Further, a differential pressure sensor 23 for detecting the differential pressure across the NOx catalyst 12 is attached to the NOx catalyst 12. The output signal of the differential pressure sensor 23 is input to the input port 35 via the corresponding AD converter 37.

  Connected to the accelerator pedal 40 is a load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40. The output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. Further, a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates by 15 °, for example, is connected to the input port 35. On the other hand, the output port 36 is connected to the fuel injection valve 3, the step motor for driving the throttle valve 9, the reducing agent supply valve 14, the EGR control valve 16, and the fuel pump 20 via the corresponding drive circuit 38.

  The NOx catalyst 12 will be described. The NOx catalyst 12 is supported on a monolith support or pellet support having a three-dimensional network structure, or is supported on a particulate filter having a honeycomb structure. As described above, the NOx catalyst 12 can be supported on various carriers. Hereinafter, a case where the NOx catalyst 12 is supported on the particulate filter will be described.

  3A and 3B show the structure of a particulate filter (hereinafter referred to as “filter”) 12a carrying a NOx catalyst 12. FIG. 3A shows a front view of the filter 12a, and FIG. 3B shows a side sectional view of the filter 12a. As shown in FIGS. 3A and 3B, the filter 12a has a honeycomb structure and has a plurality of exhaust flow passages 60 and 61 extending in parallel with each other. These exhaust flow passages are constituted by an exhaust gas inflow passage 60 whose downstream end is closed by a plug 62 and an exhaust gas outflow passage 61 whose upstream end is closed by a plug 63. In FIG. 3A, the hatched portion shows a plug 63. Therefore, the exhaust gas inflow passages 60 and the exhaust gas outflow passages 61 are alternately arranged via the thin partition walls 64. In other words, in the exhaust gas inflow passage 60 and the exhaust gas outflow passage 61, each exhaust gas inflow passage 60 is surrounded by four exhaust gas outflow passages 61, and each exhaust gas outflow passage 61 is surrounded by four exhaust gas inflow passages 60. To be arranged. The filter 12a is made of, for example, a porous material such as cordierite. Therefore, the exhaust gas flowing into the exhaust gas inflow passage 60 is indicated by an arrow in FIG. Then, the gas flows out into the adjacent exhaust gas outflow passage 61 through the surrounding partition wall 64.

  Here, when the NOx catalyst 12 is supported on such a filter 12 a, the peripheral wall surfaces of the exhaust gas inflow passages 60 and the exhaust gas outflow passages 61, that is, on the both side surfaces of the partition walls 64 and the pore inner wall surfaces in the partition walls 64. On the top, for example, a catalyst carrier made of alumina is supported. FIG. 4 schematically shows a cross section of the surface portion of such a catalyst carrier 45. As shown in FIG. 4, a noble metal catalyst 46 is dispersedly supported on the surface of the catalyst carrier 45, and a layer of NOx absorbent 47 is formed on the surface of the catalyst carrier 45. Has been.

  In the embodiment of the present invention, platinum (Pt) is used as the noble metal catalyst 46, and examples of components constituting the NOx absorbent 47 include potassium (K), sodium (Na), and cesium (Cs). At least one selected from such alkali metals, alkaline earths such as barium (Ba) and calcium (Ca), and rare earths such as lanthanum (La) and yttrium (Y) is used.

When the ratio of air and fuel (hydrocarbon) supplied into the intake passage of the internal combustion engine, the combustion chamber 2 and the exhaust passage upstream of the NOx catalyst 12 is referred to as the air-fuel ratio of the exhaust gas, the NOx absorbent 47 is the NOx catalyst. When the air-fuel ratio of the exhaust gas flowing into the exhaust gas 12 is a lean air-fuel ratio, it has the ability to absorb and release NOx and to release the absorbed NOx when the oxygen concentration in the exhaust gas decreases. That is, the case where barium (Ba) is used as an example of the component constituting the NOx absorbent 47 will be described as an example. When the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 12 is a lean air-fuel ratio, that is, in the exhaust gas When the oxygen concentration of the exhaust gas is high, NO in the exhaust gas is oxidized on the platinum 46 to become NO ₂ as shown in FIG. 4, and then is absorbed into the NOx absorbent 47 to be barium oxide (BaO). ) And the NOx absorbent 47 in the form of nitrate ions (NO ₃ ⁻ ). Thus, NOx is absorbed in the NOx absorbent 47. As long as the oxygen concentration in the exhaust gas is high, NO ₂ is generated on the surface of the platinum 46, and as long as the NOx absorption capacity of the NOx absorbent 47 is not saturated, NO ₂ is absorbed in the NOx absorbent 47 and nitrate ions are generated. Is done.

On the other hand, if the air-fuel ratio of the exhaust gas is made rich or stoichiometric by supplying the reducing agent from the reducing agent supply valve 14, the oxygen concentration in the exhaust gas decreases, so the reaction proceeds in the reverse direction ( NO ₃ ⁻ → NO ₂ ), and thus nitrate ions in the NOx absorbent 47 are released from the NOx absorbent 47 in the form of NO ₂ . Next, the released NOx is reduced by unburned HC and CO in the exhaust gas.

  Thus, when the air-fuel ratio of the exhaust gas is a lean air-fuel ratio, that is, when combustion is performed with the air-fuel ratio of the air-fuel mixture in the combustion chamber 2 being set to the lean air-fuel ratio, NOx in the exhaust gas is reduced. Absorbed in the NOx absorbent 47. However, if the air-fuel ratio of the air-fuel mixture in the combustion chamber 2 is made to be a lean air-fuel ratio and combustion is continued, the NOx absorption capacity of the NOx absorbent 47 is saturated during that time, and therefore the NOx The absorbent 47 cannot absorb NOx. Therefore, in the embodiment of the present invention, the air-fuel ratio of the exhaust gas is temporarily made rich by supplying the reducing agent from the reducing agent supply valve 14 before the NOx absorption capacity of the NOx absorbent 47 is saturated. Thereby, NOx is released from the NOx absorbent 47.

By the way, the exhaust gas contains SOx, that is, SO _{2. When} this SO ₂ flows into the NOx catalyst 12, this SO ₂ is oxidized in the platinum 46 to become SO ₃ . Next, this SO ₃ is absorbed in the NOx absorbent 47 and bonded to the barium oxide (BaO), while diffusing into the NOx absorbent 47 in the form of sulfate ions (SO ₄ ²⁻ ), and a stable sulfate. (BaSO ₄ ) is generated. And since the NOx absorbent 47 has a strong basicity, this sulfate is stable and difficult to be decomposed. By simply setting the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 12 to a rich air-fuel ratio, The sulfate remains intact without being decomposed. Therefore, as time elapses, the amount of sulfate in the NOx absorbent 47 increases, and in this case, the amount of NOx that can be absorbed by the NOx absorbent 47 decreases.

  In this case, if the temperature of the NOx catalyst 12 is raised to a temperature of 600 ° C. or higher and the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 12 is made rich, the SOx is released from the NOx absorbent 47. However, in this case, SOx is released from the NOx absorbent 47 little by little. Therefore, in order to release all SOx from the NOx absorbent 47, the air-fuel ratio of the exhaust gas flowing into the NOx absorbent 47 must be made rich for a long time. In this case, a large amount of fuel is required. Or a reducing agent is needed. Further, the SOx released from the NOx absorbent 47 is discharged into the atmosphere, which is not preferable.

  Therefore, in the embodiment of the present invention, the main SOx trapping material 11 is arranged upstream of the NOx catalyst 12, and the SOx trapping material 11 captures SOx in the exhaust gas, so that SOx does not flow into the NOx catalyst 12. I am doing so. Next, the main SOx trapping material 11 will be described.

  The main SOx trapping material 11 is made of, for example, a monolithic catalyst having a honeycomb structure, and has a large number of exhaust gas circulation holes extending straight in the axial direction of the SOx trapping material 11. Thus, when the SOx trapping material 11 is formed from a monolithic catalyst having a honeycomb structure, a catalyst carrier made of alumina, for example, is supported on the inner peripheral wall surface of each exhaust gas circulation hole. FIG. A cross section of the surface portion of the carrier 50 is shown schematically. As shown in FIG. 5, a coat layer 51 is formed on the surface of the catalyst carrier 50, and the noble metal catalyst 52 is dispersed and supported on the surface of the coat layer 51.

  In the embodiment of the present invention, platinum (Pt) is used as the noble metal catalyst 52, and examples of the component constituting the coat layer 51 include potassium (K), sodium (Na), and cesium (Cs). At least one selected from alkali metals, alkaline earths such as barium (Ba) and calcium (Ca), and rare earths such as lanthanum (La) and yttrium (Y) is used. That is, the coat layer 51 of the main SOx trapping material 11 exhibits strong basicity.

By the way, SOx in the exhaust gas, that is, SO ₂ is oxidized in the platinum 52 and then trapped in the coat layer 51 as shown in FIG. That is, SO ₂ diffuses into the coat layer 51 in the form of sulfate ions (SO ₄ ²⁻ ) to form sulfate. As described above, the coat layer 51 has a strong basicity. Therefore, as shown in FIG. 5, a part of SO ₂ in the exhaust gas is directly captured in the coat layer 51. Is done.

  In FIG. 5, the shading in the coat layer 51 indicates the concentration of the captured SOx. As can be seen from FIG. 5, the SOx concentration in the coat layer 51 is highest near the surface of the coat layer 51 and gradually decreases toward the back. When the SOx concentration in the vicinity of the surface of the coat layer 51 is increased, the basicity of the surface of the coat layer 51 is weakened, and the SOx capturing ability is weakened. Here, the ratio of SOx trapped in the main SOx trapping material 11 in the SOx in the exhaust gas is referred to as the SOx trapping rate. If the basicity of the surface of the coat layer 51 is weakened, the SOx trapping rate is accordingly increased. Will drop.

  FIG. 6 shows the temporal change in the SOx capture rate. As shown in FIG. 6, the SOx capture rate is initially close to 100%, but as time passes, the SOx capture rate decreases rapidly. Therefore, in the embodiment of the present invention, as shown in FIG. 7, when the SOx trapping rate is lower than a predetermined rate, the air-fuel ratio of the exhaust gas flowing into the main SOx trapping material 11 is made lean. The temperature rise control is performed to raise the temperature of the SOx trapping material 11 to a constant temperature after the air-fuel ratio is set, thereby recovering the SOx trapping rate.

  That is, if the air-fuel ratio of the exhaust gas flowing into the main SOx trapping material 11 is set to a lean air-fuel ratio and the temperature of the SOx trapping material 11 is raised to a certain temperature, it is concentrated near the surface in the coat layer 51. The SOx diffuses toward the back of the coat layer 51 so that the SOx concentration in the coat layer 51 is uniform. That is, the sulfate produced in the coat layer 51 changes from an unstable state concentrated near the surface in the coat layer 51 to a stable state uniformly dispersed throughout the coat layer 51. To do. When SOx existing in the vicinity of the surface in the coat layer 51 diffuses toward the inner part of the coat layer 51, the SOx concentration in the vicinity of the surface in the coat layer 51 decreases, and therefore, the temperature increase control of the SOx trap 11 is performed. When is completed, the SOx trapping rate is recovered as shown in FIG.

  When the temperature rise control of the main SOx trapping material 11 is performed, if the temperature of the SOx trapping material 11 is set to about 450 ° C., the SOx existing in the vicinity of the surface in the coat layer 51 is directed toward the back of the coat layer 51. When the temperature of the SOx trapping material 11 is raised to about 600 ° C., the SOx concentration in the coat layer 51 can be made fairly uniform. Therefore, when executing the temperature increase control of the SOx 11, it is preferable to raise the temperature of the SOx capture material 11 to about 600 ° C. while setting the air-fuel ratio of the exhaust gas flowing into the SOx capture material 11 to be a lean air-fuel ratio.

  In this way, if the air-fuel ratio of the exhaust gas flowing into the SOx trapping material 11 when the temperature of the main SOx trapping material 11 is raised to a certain temperature is a rich air-fuel ratio, the SOx trapping material 11 releases SOx. It will be released. Therefore, when the temperature of the SOx trapping material 11 is raised to a certain temperature, the air-fuel ratio of the exhaust gas flowing into the SOx trapping material 11 must not be a rich air-fuel ratio. Further, when the SOx concentration in the vicinity of the surface in the coat layer 51 becomes high, the air-fuel ratio of the exhaust gas flowing into the SOx trapping material 11 becomes the rich air-fuel ratio even if the temperature of the SOx trapping material 11 is not raised to a certain temperature. Then, SOx is released from the SOx trapping material 11. Therefore, in the embodiment of the present invention, when the temperature of the SOx trapping material 11 is equal to or higher than the temperature at which SOx may be released, the air-fuel ratio of the exhaust gas flowing into the SOx trapping material 11 does not become a rich air-fuel ratio. I am doing so.

  Further, the backup SOx trapping material 26 is basically the same as the main SOx trapping material 11.

  By the way, as described above, SOx is removed from the exhaust gas by the main SOx trapping material 11. Therefore, when the SOx trapping rate of the SOx trapping material 11 is high, there is little or no SOx flowing into the NOx catalyst 12, and there is little or no SOx flowing downstream from the NOx catalyst 12. Therefore, at this time, even if the exhaust gas flow control valve 28 is maintained in the state shown in FIG. 1, that is, even if the inlet of the branch pipe 25 is closed and the flow path of the exhaust pipe 24 is kept open, There is little or no SOx outflowing from the tube 24 to the atmosphere. Therefore, the exhaust gas flow control valve 28 is normally maintained in the state shown in FIG.

  However, if the SOx trapping rate of the main SOx trapping material 11 becomes low or so much SOx flows into the SOx trapping material 11 that the main SOx trapping material 11 cannot be trapped, the SOx traps out of the SOx trapping material 11. , The NOx catalyst 12 may flow out of the NOx catalyst downstream.

  Therefore, in the first embodiment, when it is determined that the condition that the amount of SOx flowing out from the main SOx trapping material 11 is larger than a predetermined amount (hereinafter referred to as “SOx outflow condition”) is satisfied, the exhaust gas flow control is performed. The valve 28 is switched from the state shown in FIG. 1 to the state shown in FIG. 2, that is, the state where the flow path of the exhaust pipe 24 is closed and the inlet of the branch pipe 25 is opened. According to this, the SOx flowing out from the main SOx capturing material 11 flows into the backup SOx capturing material 26 together with the exhaust gas via the branch pipe 25 and is captured by the backup SOx capturing material 26. For this reason, there is no or almost no SOx flowing out from the backup SOx capturing material 26. In the embodiment of the present invention, the exhaust gas flowing out from the backup SOx trap 26 is returned to the exhaust pipe 24 via the branch pipe 27, but there is no or almost no SOx flowing out from the backup SOx trap 26. For this reason, SOx is prevented from flowing out from the exhaust pipe 24 to the atmosphere.

  In the above-described embodiment, for example, when the amount of sulfur component contained in the fuel injected from the fuel injection valve 3 (hereinafter referred to as “fuel-containing sulfur component amount”) is larger than a predetermined amount, Alternatively, when the air-fuel ratio of the exhaust gas flowing into the main SOx trapping material 11 is a rich air-fuel ratio, or an SOx concentration sensor that detects the SOx concentration in the exhaust gas is disposed in the exhaust pipe 13 downstream of the main SOx trapping material 11. In this case, it is determined that the SOx outflow condition is satisfied when the SOx concentration in the exhaust gas detected by the SOx concentration sensor is higher than a predetermined concentration. Further, when it is determined that the SOx outflow condition is satisfied when the fuel-containing sulfur component amount is larger than a predetermined amount, for example, the NOx catalyst 12 can be held to the maximum as the fuel-containing sulfur component amount increases. Since the NOx amount decreases early, when the NOx amount that the NOx catalyst 12 can hold to the maximum decreases to a predetermined amount within a predetermined period, the fuel-containing sulfur component amount is determined in advance. Judged to be greater than the amount given. Alternatively, as the amount of sulfur component containing fuel increases, the amount of SOx flowing out from the main SOx trapping material 11 increases, so that the amount of SOx flowing out from the main SOx trapping material 11 is larger than a predetermined amount. Sometimes, it may be determined that the fuel-containing sulfur component amount is larger than a predetermined amount. Alternatively, a region that provides fuel with a fuel-containing sulfur component amount larger than a predetermined amount is stored in advance in a so-called navigation system as map information, and the fuel-containing sulfur component amount is determined in advance based on this map information. When the fuel is provided in a region where the amount is greater than the determined amount, it may be determined that the fuel-containing sulfur component amount is greater than a predetermined amount.

  Further, as described above, normally, the exhaust gas does not flow into the backup SOx trap 26. Therefore, when it is determined that the SOx outflow condition is satisfied, the temperature of the SOx trap 26 is lower than the temperature at which the SOx trap 26 exhibits the ability to trap SOx (hereinafter referred to as “active temperature”). There is a possibility. When the temperature of the SOx trap 26 is lower than the activation temperature, even if it is determined that the SOx outflow condition is satisfied and the exhaust gas flows into the SOx trap 26, the SOx trap 26 captures SOx. I can't. Of course, if the exhaust gas flows into the SOx trap 26 and a certain period of time elapses, the temperature of the SOx trap 26 is increased by the heat of the exhaust gas and reaches the activation temperature. 26 can capture SOx. However, in order to minimize the amount of SOx flowing out from the SOx capturing material 26 as much as possible, when it is determined that the SOx outflow condition is satisfied, the SOx capturing material 26 is at a temperature lower than the activation temperature. The material 26 may be heated by a heater or the like.

  Further, the backup SOx trap 26 captures SOx when the air-fuel ratio of the exhaust gas flowing into the backup SOx trap is a lean air-fuel ratio. Therefore, when it is determined that the SOx outflow condition is satisfied and the exhaust gas is allowed to flow into the SOx trapping material 26, it is preferable that the air-fuel ratio of the exhaust gas flowing into the SOx trapping material 26 is surely a lean air-fuel ratio. . In particular, when it is determined that the SOx outflow condition is satisfied because the air-fuel ratio of the exhaust gas flowing into the main SOx trapping material 11 is a rich air-fuel ratio, the air-fuel ratio of the exhaust gas flowing into the backup SOx trapping material 26 is rich. Since the air-fuel ratio is set, it is necessary to set the air-fuel ratio of the exhaust gas flowing into the backup SOx trap 26 to the lean air-fuel ratio. Therefore, as shown in FIG. 9, when the air injection device 50 for injecting air is attached to the branch pipe 25 and it is determined that the SOx outflow condition is satisfied, in particular, the exhaust of exhaust gas flowing into the main SOx trapping material 11 is empty. The air injection device 50 may inject air when it is determined that the SOx outflow condition is satisfied because the fuel ratio is a rich air-fuel ratio. According to this, since the air-fuel ratio of the exhaust gas flowing into the backup SOx trapping material 26 becomes a lean air-fuel ratio more reliably, the backup SOx trapping material 26 can sufficiently capture SOx.

  FIG. 8 is a diagram showing an example of a routine for controlling the exhaust emission control device of the first embodiment. In the routine of FIG. 8, first, in step 10, the amount of SOx trapped in the main SOx trapping material 11 and the amount of SOx retained in the NOx catalyst 12 (hereinafter referred to as “total SOx trapped amount”) are calculated. It is determined whether or not the total ΣSOX is larger than a predetermined amount α (ΣSOX> α). Here, the total SOx trapping amount is based on the amount of fuel injected from the fuel injection valve 3 because the amount of SOx discharged from the combustion chamber 2 is proportional to the amount of fuel injected from the fuel injection valve 3, for example. Is calculated. In step 10, the total SOx trapping amount is taken into account because it is difficult for SOx to flow out of the main SOx trapping material 11 when the total SOx trapping amount is relatively small.

  When it is determined at step 10 that ΣSOX> α, the routine proceeds to step 11 where it is determined whether or not the SOx outflow condition is satisfied. Here, when it is determined that the SOx outflow condition is satisfied, the routine proceeds to step 12 where the control I of the exhaust gas flow control valve is executed. That is, here, the exhaust gas flow control valve 28 is in the state shown in FIG. 2, that is, the state in which the inlet of the branch pipe 25 is opened and the flow path of the exhaust pipe 24 is closed. On the other hand, when it is determined in step 11 that the SOx outflow condition is not satisfied, the routine proceeds to step 13 where the control II of the exhaust gas flow control valve is executed. That is, here, the exhaust gas flow control valve 28 is in the state shown in FIG. 1, that is, the state where the inlet of the branch pipe 25 is closed and the flow path of the exhaust valve 24 is opened. Even when it is determined at step 10 that ΣSOX ≦ α, the routine proceeds to step 13 where the control II of the exhaust gas flow control valve is executed.

  Next, an exhaust emission control device according to a second embodiment of the present invention will be described. FIG. 10 shows a compression ignition type internal combustion engine provided with the exhaust emission control device of the second embodiment. In the second embodiment, the branch pipe 25 branched from the exhaust pipe 24 is connected to the inlet of the SOx trapping container 51 having a certain volume space. The outlet of the SOx trap 51 is connected to the exhaust pipe upstream of the main SOx trap 11 via the branch pipe 27. In the second embodiment, an exhaust flow rate control valve 52 that controls the amount of exhaust gas flowing into the exhaust pipe upstream of the main SOx trap 11 through the branch pipe 27 is disposed in the branch pipe 27. The exhaust flow control valve 51 is normally in a state in which the branch pipe 27 is closed as shown in FIG.

  In the second embodiment, while it is determined that the SOx outflow condition is not satisfied, the exhaust gas flow control valve 28 is in the state shown in FIG. 10, that is, the outlet of the branch pipe 25 is closed. The flow path of the tube 24 is kept open. On the other hand, when it is determined that the SOx outflow condition is satisfied, the exhaust gas flow control valve 28 closes the flow path of the exhaust pipe 24 by opening the inlet of the branch pipe 25 as shown in FIG. Switch to state. At this time, the exhaust gas flow rate control valve 52 is maintained in a state in which the branch pipe 27 is closed, as shown in FIG. According to this, the SOx flowing out from the main SOx capturing material 11 flows into the SOx capturing container 51 through the branch pipe 25 together with the exhaust gas, and is collected in the SOx capturing container 51. According to this, the outflow of SOx from the exhaust pipe 24 to the atmosphere is suppressed.

  In the second embodiment, when it is determined that the SOx outflow condition is not satisfied, that is, when the main SOx trapping material 11 can sufficiently capture SOx, the exhaust gas flow control valve 28 is returned to the state shown in FIG. 10, and the exhaust gas flow control valve 52 is opened. According to this, the SOx in the SOx capture container 52 flows into the main SOx capture material 11 through the branch pipe 27 together with the exhaust gas, and is captured by the main SOx capture material 11.

Next, an exhaust emission control device according to a third embodiment of the present invention will be described. FIG. 12 shows a compression ignition type internal combustion engine provided with the exhaust emission control device of the third embodiment. In the third embodiment, the branch pipe 25 branched from the exhaust pipe 24 is connected to the inlet of the SOx processing container 53. The outlet of the SOx processing container 53 is connected to the exhaust pipe 24 via the branch pipe 27. An H ₂ O ₂ supply device 54 that supplies mist-like H ₂ O ₂ (hydrogen peroxide) into the SOx processing container 53 is attached to the SOx processing container 53.

In the third embodiment, while it is determined that the SOx outflow condition is not satisfied, the exhaust gas flow control valve 28 is exhausted by closing the inlet of the branch pipe 25 as shown in FIG. The flow path of the tube 24 is kept open. On the other hand, when it is determined that the SOx outflow condition is satisfied, the exhaust gas flow control valve 28 opens the inlet of the branch pipe 25 from the state shown in FIG. 12 to the state shown in FIG. The flow path of the tube 24 is switched to a closed state. At this time, mist-like H ₂ O ₂ is supplied from the H ₂ O ₂ supply device 54 into the SOx processing container 53. According to this, the SOx flowing out from the main SOx trapping material 11 flows into the SOx processing device 53 through the branch pipe 25 together with the exhaust gas, and reacts with H ₂ O ₂ to become sulfuric acid (SO ₂ + H ₂ O ₂ → H ₂ SO ₄ ). The sulfuric acid is stored in a sulfuric acid storage chamber formed in the SOx processing device 53. In this way, SOx is prevented from flowing out from the exhaust pipe 24 to the atmosphere.

  In the first embodiment, when the amount of SOx trapped in the backup SOx trapping material 26 reaches or approaches the limit value of the amount of SOx that can be captured by the backup SOx trapping material 26, or In the third embodiment, when the amount of sulfuric acid stored in the sulfuric acid storage chamber of the SOx treatment container 53 reaches or near the limit value of the sulfuric acid amount that can be stored by the sulfuric acid storage device, When the alarm device is activated, the amount of SOx trapped in the backup SOx trap 26 has reached or approached the limit value, or the amount of sulfuric acid stored in the SOx processing container 53 is the limit value. The vehicle driver or the like may be notified that the vehicle has reached or is approaching.

Moreover, you may employ | adopt the exhaust gas purification apparatus shown in FIG. 14 as another example of the exhaust gas purification apparatus of 3rd Embodiment. In the example shown in FIG. 14, the SOx processing container 53 is directly attached to the exhaust pipe 24. In this example, while it is determined that the SOx outflow condition is not satisfied, mist-like H ₂ O ₂ is not supplied from the H ₂ O ₂ supply device 54. On the other hand, when the SOx flowing out condition is determined to be _satisfied, then fed from the H 2 _{O 2} supply device 54 mist of _H 2 _{O 2} into the SOx processing container _53, and SOx in the exhaust gas H 2 _{O 2} React to sulfuric acid. Thereby, it is suppressed that SOx flows out from the exhaust pipe 24 to the atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a compression ignition type internal combustion engine equipped with an exhaust emission control device according to a first embodiment of the present invention, where an exhaust gas flow control valve is in a state of closing an inlet of a branch pipe. FIG. 2 is a view showing a compression ignition type internal combustion engine equipped with the exhaust purification device of the first embodiment as in FIG. 1, but here, the exhaust gas flow control valve is in a state where the inlet of the branch pipe is opened. It is the figure which showed the structure of the particulate filter. It is sectional drawing of the surface part of the catalyst support | carrier of a NOx catalyst. It is sectional drawing of the surface part of the catalyst support | carrier of SOx trapping material. It is the figure which showed the SOx capture rate. It is a figure for demonstrating temperature rising control. It is the figure which showed an example of the routine which controls the exhaust gas purification device of 1st Embodiment. It is the figure which showed another example of the exhaust gas purification apparatus of 1st Embodiment. It is the figure which showed the compression ignition type internal combustion engine provided with the exhaust gas purification device of 2nd Embodiment, and is in the state which the exhaust gas flow control valve closed the inlet of the branch pipe here. It is the figure which showed the compression ignition type internal combustion engine provided with the exhaust gas purification device of 2nd Embodiment similarly to FIG. 10, Here, the exhaust gas flow control valve exists in the state which opened the inlet_port | entrance of the branch pipe. It is the figure which showed the compression ignition type internal combustion engine provided with the exhaust gas purification device of 3rd Embodiment, and is in the state which the exhaust gas flow control valve closed the inlet of the branch pipe here. FIG. 13 is a view showing a compression ignition type internal combustion engine equipped with an exhaust emission control device according to a third embodiment as in FIG. 12, in which an exhaust gas flow control valve is in a state where an inlet of a branch pipe is opened. It is the figure which showed another example of the exhaust gas purification device of 3rd Embodiment.

Explanation of symbols

11 main SOx trap member 12 NOx catalyst 24 an exhaust pipe 25, 27 branch pipe 26 back up SOx capturing material 28 exhaust gas flow control valve 50 an air injection device 51 SOx trap container 53 SOx processing vessel 54 H ₂ O ₂ supply device

Claims (8)

  In the exhaust emission control device provided with the SOx capturing material that captures SOx in the exhaust passage of the internal combustion engine, it is determined that the SOx outflow condition in which the amount of SOx flowing out from the SOx capturing material is larger than a predetermined amount is satisfied. An exhaust gas purification apparatus for an internal combustion engine, comprising: a SOx capturing means that exhibits a function of capturing SOx flowing out of the SOx trapping material when being performed, separately from the SOx trapping material.   Whether the SOx trapping means is branched from the exhaust passage downstream of the SOx trap; the SOx trap that is disposed in the branch passage and captures SOx; and whether exhaust gas is allowed to flow into the branch passage An exhaust gas flow control valve for controlling the exhaust gas flow, and when it is determined that the SOx outflow condition is satisfied, the SOx capture means controls the exhaust gas flow control valve to flow the exhaust gas into the branch passage The exhaust emission control device for an internal combustion engine according to claim 1, wherein   The SOx trapping means has an air supply device for supplying air to the SOx trapping material disposed in the branch passage, and the air-fuel ratio of the exhaust gas flowing into the SOx trapping material disposed in the exhaust passage is rich. It is determined that the SOx outflow condition is satisfied when the fuel ratio is the fuel ratio, and when it is determined that the SOx outflow condition is satisfied, the SOx capturing means controls the exhaust gas flow control valve so that the exhaust gas is supplied to the branch passage. The exhaust gas purification device for an internal combustion engine according to claim 2, wherein the air is supplied into the SOx trapping material disposed in the branch passage from the air supply device.   A volume space in which the SOx capturing means can store exhaust gas, a branch passage that branches from the exhaust passage downstream of the SOx trapping material and extends to the volume space, and whether exhaust gas is allowed to flow into the branch passage An exhaust gas flow control valve for controlling the exhaust gas flow control valve, and when it is determined that the SOx outflow condition is satisfied, the SOx trapping means controls the exhaust gas flow control valve to cause the exhaust gas to enter the branch passage. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purification apparatus is made to flow.   A hydrogen peroxide supply device for supplying hydrogen peroxide by the SOx trapping means; a sulfuric acid storage chamber for storing sulfuric acid produced by the reaction of hydrogen peroxide and SOx supplied from the hydrogen peroxide supply device; A branch passage that branches from the exhaust passage downstream of the SOx trapping material and extends to the volume space; and an exhaust gas flow control valve that controls whether or not exhaust gas flows into the branch passage. The SOx trapping means controls the exhaust gas flow control valve to cause the exhaust gas to flow into the branch passage and to supply the hydrogen peroxide to the exhaust gas flowing through the branch passage. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein hydrogen peroxide is supplied from the engine.   The SOx trapping means is generated by a hydrogen peroxide supply device that supplies hydrogen peroxide into the exhaust passage downstream of the SOx capture material, and a reaction between the hydrogen peroxide supplied from the hydrogen peroxide supply device and SOx. A sulfuric acid storage chamber for storing sulfuric acid, and when it is determined that the SOx outflow condition is satisfied, the SOx trapping means supplies hydrogen peroxide into the exhaust passage from the hydrogen peroxide supply device. The exhaust emission control device for an internal combustion engine according to claim 1.   The SOx trapping means is generated by a hydrogen peroxide supply device that supplies hydrogen peroxide into the exhaust passage downstream of the SOx capture material, and a reaction between the hydrogen peroxide supplied from the hydrogen peroxide supply device and SOx. The volumetric space for containing sulfuric acid, and when it is determined that the SOx outflow condition is satisfied, the SOx trapping means supplies hydrogen peroxide into the exhaust passage. An exhaust purification device for an internal combustion engine.   When the temperature of the SOx trapping material disposed in the exhaust passage is lower than a certain temperature and the air-fuel ratio of the inflowing exhaust gas is a lean air-fuel ratio, the SOx in the exhaust gas is converted to the vicinity of the surface of the SOx trapping material. The SOx trapped in the vicinity of the surface of the SOx trapping material when the temperature is higher than the constant temperature and the air-fuel ratio of the inflowing exhaust gas is a lean air-fuel ratio. The SOx trapping material diffused into the SOx trapping material, and when the SOx trapping rate of the SOx trapping material becomes lower than a predetermined rate, the temperature of the SOx trapping material is made higher than the constant temperature and The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 7, wherein control for maintaining the air-fuel ratio of the inflowing exhaust gas at a lean air-fuel ratio is executed.

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