JP2009041480A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently use catalysts as a whole so that the deviation of the flow velocity of exhaust gas produced by the curved part of an exhaust passage on the upstream side of the catalyst does not partially destroy or deteriorate the catalysts. <P>SOLUTION: In this internal combustion engine, an SOx trap catalyst 24 for capturing SOx is disposed in the engine exhaust passage, and an NOx storage/reduction catalyst 25 is disposed in the exhaust passage on the downstream side of the SOx trap catalyst 24. The engine exhaust passage has the curved part. Since the exhaust gas passes through the outer side of the curved part, the deviation occurs in the flow velocity of the exhaust gas in the exhaust passage, and the exhaust gas in that state flows to the SOx trap catalyst 24. Therefore, partial deviation occurs in the inflow amount of the exhaust gas. A flow velocity control valve 61 is disposed in the exhaust passage where the exhaust gas flows on the outer side of the curved part and the flow velocity is increased on the upstream side of the SOx trap catalyst 24, and controlled to the position predetermined according to the average flow velocity Vav of the exhaust gas. Therefore, the flow velocity control valve so controls the flow of the exhaust gas as to uniformly enter the SOx trap catalyst 24. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  In an internal combustion engine in which a catalyst for purifying harmful components in exhaust gas discharged from the internal combustion engine body is disposed in the exhaust passage, the flow velocity is in a plane perpendicular to the flow direction of the exhaust gas due to the structure of the exhaust pipe or the like. There is a bias. For this reason, the flow rate of exhaust gas per unit time flowing into the catalyst is also partially biased, which causes the catalyst to be partially heated, leading to destruction of the catalyst carrier or partial premature deterioration. There is a problem that it ends up. Even though there are still many usable parts for the catalyst as a whole, it is not possible to sufficiently purify the harmful components in the exhaust gas that has passed through the destroyed part or deteriorated part. Must be replaced.

  In order to solve this problem by making the flow rate deviation of the exhaust gas flowing into the catalyst uniform, the exhaust gas discharged from a plurality of cylinders of the internal combustion engine is collected through the exhaust manifold corresponding to each cylinder. And a plurality of exhaust manifolds are combined at least on the exhaust side of the exhaust manifold, and each exhaust passage of the exhaust manifold is connected to a portion where the plurality of exhaust manifolds are combined. Exhaust manifold that prevents the exhaust gas pulsation from being biased due to the difference in the exhaust timing by forming a communication part that communicates between the exhaust flow passages at the discharge side end part of the partition wall part or in the vicinity of the discharge side end part The discharge port structure is known (see Patent Document 1).

JP 11-148345 A

  However, the structure described in Patent Document 1 achieves a uniform exhaust gas flow rate by a structure in the exhaust side end portion or in the vicinity of the exhaust side end portion of a portion where a plurality of exhaust manifolds are combined. Therefore, it cannot be applied to an internal combustion engine that does not have a plurality of exhaust manifolds.

  Further, as will be described in detail later, a NOx occlusion reduction catalyst that occludes and reduces NOx in the exhaust gas in the engine exhaust passage, and an exhaust passage upstream thereof, are exhausted to the NOx occlusion reduction catalyst. A more specific problem arises in an internal combustion engine in which a SOx trap catalyst that collects SOx so that SOx in the gas does not flow in is arranged. That is, the SOx trap catalyst may need to be heated to an early activation temperature of the catalyst, or may be raised to a high temperature in order to recover the collection ability by diffusing the collected SOx into the interior as described later. is there. Therefore, it is preferable that the exhaust gas is disposed in the exhaust passage in the vicinity of the higher-temperature internal combustion engine body. However, in the vicinity of the main body of the internal combustion engine, the exhaust passage is often curved, and when the exhaust gas passes through the curved portion, the flow velocity is biased in the exhaust passage. Therefore, the deviation of the exhaust gas flow rate due to the catalyst being arranged in the vicinity of the curved portion newly causes the above-mentioned problems of destruction of the catalyst carrier and partial early deterioration due to partial heating of the catalyst. . In order to reduce the size of the vehicle, it is often necessary to arrange the vehicle in such a place from the viewpoint of design.

  In view of the above problems, the present invention is particularly effective because the deviation of the flow rate of the exhaust gas caused by the exhaust passage upstream of the catalyst having a curved portion does not cause partial destruction or deterioration of the catalyst. It is an object of the present invention to provide an exhaust emission control device for an internal combustion engine that can be used.

  According to the first aspect of the present invention, when the SOx trap catalyst for collecting SOx is disposed in the engine exhaust passage, and the air-fuel ratio of the exhaust gas flowing into the SOx trap catalyst downstream exhaust passage is lean, A NOx occlusion reduction catalyst that reduces and purifies the stored NOx when the air-fuel ratio of the exhaust gas that occludes and flows in NOx contained in the exhaust gas becomes the stoichiometric air-fuel ratio or rich is disposed, and the engine exhaust passage has a curved portion. In an internal combustion engine in which the amount of inflow is partially biased by the exhaust gas flowing into the SOx trap catalyst in a state where the flow velocity is biased in the exhaust passage by passing through the curved portion, it passes through the outside of the curved portion. Exhaust gas adjustment that adjusts the flow of exhaust gas so that SOx is evenly collected by the SOx trap catalyst, which is arranged in the area in the exhaust passage where the flow velocity is high Exhaust purifying apparatus for an internal combustion engine equipped with a stage is provided. That is, in the first aspect of the invention, the catalyst can be efficiently used as a whole by adjusting the flow of exhaust gas so that SOx is uniformly collected by the SOx trap catalyst.

  According to the invention of claim 2, in the invention of claim 1, the exhaust gas adjusting means is disposed upstream of the SOx trap catalyst, and is a predetermined position corresponding to the average flow velocity of the exhaust gas. Thus, an exhaust gas purification apparatus for an internal combustion engine, which is a movable member that controls the flow of exhaust gas so as to uniformly flow into the SOx trap catalyst, is provided. That is, according to the second aspect of the invention, the movable member is positioned each time according to the average flow rate of the exhaust gas, so that the flow rate of the exhaust gas flowing into the SOx trap catalyst is always uniform, and the entire catalyst is Can be used efficiently.

  According to the invention of claim 3, in the invention of claim 1, the exhaust gas adjusting means is disposed upstream of the SOx trap catalyst or downstream of the NOx storage reduction catalyst, and the SOx trap catalyst. The exhaust gas purifying device for an internal combustion engine according to claim 1, wherein the exhaust gas purifying device is a movable member that is controlled to a position that restricts the exhaust gas from flowing into a portion where the collection capacity of the exhaust gas is saturated. That is, in the invention described in claim 3, it is possible to finally use the catalyst efficiently as a whole by gradually adjusting the flow of the exhaust gas as the service period elapses.

  According to the fourth aspect of the present invention, the SOx trap catalyst that collects SOx is disposed in the engine exhaust passage, and the air-fuel ratio of the exhaust gas that flows into the SOx trap catalyst downstream exhaust passage is lean. In this case, a NOx occlusion reduction catalyst that reduces and purifies the stored NOx when the air-fuel ratio of the exhaust gas that occludes and flows into the exhaust gas becomes richer than the stoichiometric air-fuel ratio or rich, and the engine exhaust passage has a curved portion. In the internal combustion engine in which the inflow amount is partially biased by the exhaust gas flowing into the SOx trap catalyst in a state where the flow velocity is biased in the exhaust passage by passing through the curved portion, the SOx trap catalyst An exhaust purification device for an internal combustion engine is provided in which the amount of SOx that can be collected is biased in advance according to the bias. That is, in the invention described in claim 4, by pre-biasing the SOx trappable amount, it is possible to efficiently use the catalyst as a whole without requiring an additional mechanism in the exhaust passage. Become.

  According to the fifth aspect of the present invention, the SOx trap catalyst for collecting SOx is disposed in the engine exhaust passage, and the air-fuel ratio of the exhaust gas flowing into the SOx trap catalyst downstream exhaust passage is lean. In this case, a NOx occlusion reduction catalyst that reduces and purifies the stored NOx when the air-fuel ratio of the exhaust gas that occludes and flows into the exhaust gas becomes richer than the stoichiometric air-fuel ratio or rich, and the engine exhaust passage has a curved portion. In the internal combustion engine in which the inflow amount is partially biased by the exhaust gas flowing into the SOx trap catalyst in a state where the flow velocity is biased in the exhaust passage by passing through the curved portion, the SOx trap catalyst An exhaust purification device for an internal combustion engine in which the tendency of the pressure loss of the exhaust gas flowing into the engine is preliminarily biased according to the bias is provided. That is, in the invention described in claim 5, by pre-biasing the tendency of pressure loss, it is possible to efficiently use the catalyst as a whole without requiring an additional mechanism in the exhaust passage. Become.

  According to the invention described in each claim, in particular, the deviation of the flow velocity of the exhaust gas caused by the exhaust passage upstream of the catalyst having a curved portion does not cause partial destruction or deterioration of the catalyst, and the catalyst as a whole. There is a common effect that it can be used efficiently.

  FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine. However, the present invention can also be applied to a spark ignition type internal combustion engine.

  Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve for injecting fuel into each combustion chamber 2, 4 is an intake manifold, and 5 is an exhaust manifold. Respectively. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 9 via the air flow meter 8. An electrically controlled throttle valve 10 is arranged in the intake duct 6, and a cooling device 11 for cooling intake air flowing in the intake duct 6 is arranged around the intake duct 6. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 11, and the intake air is cooled by the engine 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 exhaust aftertreatment device 20.

  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 12, and an electrically controlled EGR control valve 13 is disposed in the EGR passage 12. A cooling device 14 for cooling the EGR gas flowing in the EGR passage 12 is disposed around the EGR passage 12. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 14, and the EGR gas is cooled by the engine cooling water. On the other hand, each fuel injection valve 3 is connected to a common rail 16 through a fuel supply pipe 15. Fuel is supplied into the common rail 16 from an electronically controlled fuel pump 17 with variable discharge amount, and the fuel supplied into the common rail 16 is supplied to the fuel injection valve 3 through each fuel supply pipe 15.

  The exhaust aftertreatment device 20 includes an exhaust pipe 21 connected to the outlet of the exhaust turbine 7 b, a catalytic converter 22 connected to the exhaust pipe 21, and an exhaust pipe 23 connected to the catalytic converter 22. In the catalytic converter 22, an SOx trap catalyst 24 and a NOx storage reduction catalyst 25 are arranged in this order from the upstream side. The exhaust pipe 23 includes a temperature sensor 26 for detecting the temperature of the exhaust gas discharged from the catalytic converter 22, and an air-fuel ratio sensor 27 for detecting the air-fuel ratio of the exhaust gas discharged from the catalytic converter 22. Is placed. The temperature of the exhaust gas discharged from the catalytic converter 22 represents the temperature of the SOx trap catalyst 24 and the NOx storage reduction catalyst 25.

  On the other hand, a fuel addition valve 28 is attached to the exhaust manifold 5 as shown in FIG. Fuel is added to the fuel addition valve 28 from the common rail 16, and fuel is added from the fuel addition valve 28 into the exhaust manifold 5. In an embodiment according to the invention, this fuel consists of light oil. The fuel addition valve 28 can be attached to the exhaust pipe 21.

  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. It comprises. Output signals of the air flow meter 8, the temperature sensor 26, and the air-fuel ratio sensor 27 are input to the input port 35 via the corresponding AD converters 37, respectively. The accelerator pedal 39 is connected to a load sensor 40 that generates an output voltage proportional to the depression amount L of the accelerator pedal 39. The output voltage of the load sensor 40 is input to the input port 35 via the corresponding AD converter 37. Is done. Further, the input port 35 is connected to a crank angle sensor 41 that generates an output pulse every time the crankshaft rotates, for example, 15 °. The CPU 34 calculates the engine speed N based on the output pulse from the crank angle sensor 41. On the other hand, the output port 36 is connected to the fuel injection valve 3, the throttle valve 10 drive device, the EGR control valve 13, the fuel pump 17, and the fuel addition valve 28 via corresponding drive circuits 38.

  First, the NOx storage reduction catalyst 25 shown in FIG. 1 will be described. The NOx occlusion reduction catalyst 25 has a catalyst carrier made of alumina, for example, and FIG. 2 schematically shows a cross section of the surface portion of the catalyst carrier 45. As shown in FIG. 2, 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.

  In the embodiment according to the present invention, platinum Pt is used as the noble metal catalyst 46, and the constituent elements of the NOx absorbent 47 are, for example, alkali metals such as potassium K, sodium Na, cesium Cs, barium Ba, and calcium Ca. At least one selected from rare earths such as alkaline earth, lanthanum La, and yttrium Y is used.

  When the ratio of air and fuel (hydrocarbon) supplied into the engine intake passage, the combustion chamber 2 and the exhaust passage upstream of the NOx occlusion reduction catalyst 25 is referred to as the air-fuel ratio of the exhaust gas, the NOx absorbent 47 is exhausted from the exhaust gas. When the fuel ratio is lean, NOx is absorbed, and when the oxygen concentration in the exhaust gas decreases, the absorbed and released NOx is reduced and released. However, if combustion under a lean air-fuel ratio is continuously performed, the NOx absorbent capacity of the NOx absorbent 47 is saturated during that time, and the NOx absorbent 47 cannot absorb NOx. Therefore, in the embodiment according to the present invention, the air-fuel ratio of the exhaust gas is temporarily made rich by supplying the fuel from the fuel addition valve 28 before the absorption capacity of the NOx absorbent 47 is saturated, and thereby the NOx absorbent 47 to the NOx. Is reduced and released. Further, since the temperature of exhaust gas is low in the compression ignition type internal combustion engine, the catalyst temperature may not rise and the reactivity of the catalyst may be poor. Even in such a case, the fuel can be supplied from the fuel addition valve 28 and the temperature of the catalyst can be raised by the reaction heat.

Meanwhile, the exhaust gas contains SOx, that is, SO _2, the SO ₂ When this SO ₂ flows into the NOx storing and reducing catalyst 25 is the is oxidized SO ₃ in the platinum Pt 46. Next, this SO ₃ is absorbed into 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⁻ to produce stable sulfate BaSO ₄ . However, since the NOx absorbent 47 has a strong basicity, this sulfate BaSO ₄ is stable and difficult to decompose. If the air-fuel ratio of the exhaust gas is simply made rich, the sulfate BaSO ₄ remains as it is without being decomposed. . Therefore, the sulfate BaSO ₄ increases in the NOx absorbent 47 as time elapses, and thus the amount of NOx that can be absorbed by the NOx absorbent 47 decreases as time elapses.

  Therefore, in the present invention, the SOx trap catalyst 24 is disposed upstream of the NOx storage reduction catalyst 25, and SOx contained in the exhaust gas is collected by the SOx trap catalyst 24, so that SOx does not flow into the NOx storage reduction catalyst 25. I am doing so. Next, the SOx trap catalyst 24 will be described.

  3A and 3B show the structure of the SOx trap catalyst 24. FIG. 3A is a front view of the SOx trap catalyst 24, and FIG. 3B is a side sectional view taken along line AA in FIG. 3A passing through the central axis of the SOx trap catalyst 24. Show. In the embodiment shown in FIGS. 3 (A) and 3 (B), the SOx trap catalyst 24 is composed of a monolith catalyst having a honeycomb structure, extends straight in the axial direction of the SOx trap catalyst 24, and is separated from each other by a thin partition wall 48. A plurality of exhaust gas flow passages 49 are provided. A catalyst carrier made of alumina, for example, is supported on both surfaces of each partition wall 48. FIG. 4 schematically shows a cross section of the surface portion of the catalyst carrier 50. As shown in FIG. 4, an SOx trap 51 is formed on the surface of the catalyst carrier 50, and the noble metal catalyst 52 is dispersed and held on the surface of the SOx trap 51.

  In the embodiment according to the present invention, platinum is used as the noble metal catalyst 52, and the components constituting the SOx trap 51 are, for example, alkali metals such as potassium K, sodium Na, cesium Cs, barium Ba, and calcium Ca. At least one selected from rare earths such as alkaline earth, lanthanum La, and yttrium Y is used. That is, the SOx trap 51 of the SOx trap catalyst 24 has a strong basicity.

Now, SOx contained in the exhaust gas, that is, SO ₂ is oxidized in platinum Pt 52 as shown in FIG. 4 and then collected in the SOx collection material 51. That is, SO ₂ diffuses into the SOx trap 51 in the form of sulfate ions SO ₄ ²⁻ to form sulfate. As described above, the SOx trap 51 has a strong basicity. Therefore, as shown in FIG. 4, a part of SO ₂ contained in the exhaust gas is directly trapped in the SOx trap 51. Is done.

  In FIG. 4, the density in the SOx collection material 51 indicates the concentration of the collected SOx. As can be seen from FIG. 4, the SOx concentration in the SOx collection material 51 is highest near the surface of the SOx collection material 51 and gradually decreases toward the back. When the SOx concentration in the vicinity of the surface of the SOx collection material 51 is increased, the basicity of the surface of the SOx collection material 51 is weakened, and the SOx collection capability is weakened. Here, of the SOx contained in the exhaust gas, the ratio of SOx trapped in the SOx trap catalyst 24 is referred to as the SOx trap ratio. If the basicity of the surface of the SOx trap 51 is weakened, the SOx traps accordingly. The trap rate will decrease. In the embodiment according to the present invention, when the SOx trap rate is lower than a predetermined rate, the temperature rise control is performed to raise the temperature of the SOx trap catalyst 24 under the lean air-fuel ratio of the exhaust gas, thereby the SOx trap. I try to recover the rate. Here, as temperature increase control, fuel is supplied from the fuel addition valve 28, and the temperature of the catalyst is increased by the reaction heat.

  In other words, when the temperature of the SOx trap catalyst 24 is raised while the air-fuel ratio of the exhaust gas is lean, the SOx concentrated in the vicinity of the surface in the SOx trap 51 has a SOx concentration in the SOx trap 51. It diffuses toward the back of the SOx collection material 51 so as to be uniform. That is, the nitrate produced in the SOx collection material 51 is uniformly dispersed from the unstable state where the nitrate is concentrated in the vicinity of the surface of the SOx collection material 51 over the entire SOx collection material 51. Change to state. When SOx existing in the vicinity of the surface in the SOx collection material 51 diffuses toward the back of the SOx collection material 51, the SOx concentration in the vicinity of the surface of the SOx collection material 51 is lowered, and thus the SOx trap catalyst 24. When the temperature rise control is completed, the SOx trap rate is recovered.

  If the temperature of the SOx trap catalyst 24 is set to about 450 ° C. when the temperature rise control of the SOx trap catalyst 24 is performed, SOx existing near the surface of the SOx trap 51 is diffused into the SOx trap 51. If the temperature of the SOx trap catalyst 24 is raised to about 600 ° C., the SOx concentration in the SOx trap 51 can be made fairly uniform. Therefore, during the temperature increase control of the SOx trap catalyst 24, it is preferable to raise the temperature of the SOx trap catalyst 24 to about 600 ° C. while the air-fuel ratio of the exhaust gas is lean.

  Now, FIG. 5 schematically shows the flow rate of the exhaust gas when the exhaust pipe 21 is curved in the vicinity of the connecting portion with the catalytic converter 22 as shown in FIG. The arrow represents the flow of exhaust gas, and the higher the density of the arrow, the greater the flow velocity. The flow rate of the exhaust gas increases the flow velocity outside the curved portion due to its inertial force. Therefore, the flow rate of the exhaust gas flowing into the SOx trap catalyst 24 is also increased in the corresponding portion, that is, the left side in FIG. When this is referred to as the a side and the opposite side, ie, the right side is referred to as the b side, as described above, the a side of the SOx trap catalyst 24 is partially heated to destroy the catalyst carrier and partially prematurely deteriorate. Problems arise. This problem will be described in more detail below.

  FIG. 6A shows a cross section of the distribution of the total inflow amount of SOx contained in the exhaust gas flowing into the SOx trap catalyst 24 during the operation of the internal combustion engine for a long time as shown in FIG. It is shown schematically as a distribution curve at. 6A, the left side corresponds to the a side in FIG. 5, and the right side corresponds to the b side in FIG. Here, the amount by which the SOx trap catalyst 24 cannot absorb SOx and the collection ability is saturated, that is, the limit collection amount is shown as SOX0 in FIG. When the distribution curve is compared with the limit collection amount SOX0, the distribution curve exceeds the limit collection amount SOX0 in a part of the region a. That is, in this region, the SOx trap catalyst 24 cannot collect only the amount of SOx whose distribution curve exceeds the limit collection amount SOX0 and discharges it as it is to the downstream NOx storage reduction catalyst 25. . As a result, in the region of the NOx occlusion reduction catalyst 25 at the corresponding position, that amount of SOx flows into the NOx absorbent 47 (FIG. 6B), and the NOx absorbent 47 as described above can absorb it. The problem of a decrease in the amount of NOx occurs.

  If SOx of the same amount as the SOx amount shown in the distribution curve flows uniformly into the SOx trap catalyst 24 without being biased, a straight line as shown by SOXE is obtained. That is, when the exhaust gas uniformly flows into the SOx trap catalyst 24, the limit collection amount SOX0 is not exceeded at any part of the SOx trap catalyst 24, and the NOx amount that the NOx absorbent 47 can absorb is reduced. There is no problem.

  Therefore, in the first embodiment according to the present invention, since the limit collection amount of SOx of the SOx trap catalyst 24 is biased in advance, only the portion where the flow rate of inflowing exhaust gas is large exceeds the limit collection amount. The above problem is solved.

  First, before explaining the method of biasing the limit collection amount, how to determine a bias tendency as a reference will be described. For this purpose, the distribution of the exhaust gas amount actually flowing into the SOx trap catalyst 24 is measured, and the deviation of the SOx amount is determined on the assumption that the ratio of SOx contained in the exhaust gas is constant. As a matter of course, the tendency of deviation of the amount of exhaust gas actually flowing into the SOx trap catalyst 24 is largely related to the configuration of the internal combustion engine, that is, the degree of curvature of the exhaust pipe, the length and thickness of the exhaust pipe, and the like. Therefore, it is necessary to individually measure and determine according to the configuration. Furthermore, although it changes variously also according to the driving | running state of an engine, this assumes driving | running conditions. One method is to measure the distribution of the amount of exhaust gas flowing into the SOx trap catalyst 24 when the throttle valve is fully open and the load is high, where the exhaust gas flow velocity is considered to be the fastest and most uneven. . As another method, it is conceivable to operate the internal combustion engine in accordance with a predetermined traveling pattern of the vehicle and measure the distribution of the amount of exhaust gas flowing into the SOx trap catalyst 24 at that time. By these methods, an actual bias tendency as shown in the distribution curve of FIG. It will be described in the following embodiment on the assumption that the obtained actual bias tendency is shown in the distribution curve of FIG.

  A method for biasing the amount of catalyst carrier will be described with reference to FIG. 7 as one of the methods for realizing the tendency to bias the limit collection amount. FIG. 7 schematically shows a cross section of a surface portion on the inner peripheral wall surface of the exhaust gas flow passage of the SOx trap catalyst 24. When this is further enlarged, FIG. 4 shown above is obtained. The catalyst carrier 50 on the substrate 53 has a plurality of pores 54. As shown in the enlarged view of FIG. 4, the noble metal catalyst 52 is dispersed and supported on the surface portion of the catalyst carrier 50 through the SOx trapping material 51. Therefore, if the amount of the catalyst carrier 50 is increased and the catalyst carrier 50 is deposited thicker on the substrate, the number of pores increases and the surface area increases. As a result, the area of the SOx collection material 51 on the surface of the catalyst carrier 50 and the amount of the noble metal catalyst 52 also increase, and the limit collection amount of SOx is improved.

  By this method, the amount of the catalyst carrier 50 on the a side is relatively increased compared to the side b, and finally, as shown in FIG. 8, the amount of the catalyst carrier 50 between the a side and the b side, that is, the distribution tendency of the surface area is illustrated. 6 (A) is formed so as to have a tendency similar to the tendency of the distribution curve. As a result, even if more exhaust gas flows into the a side than the b side, the operation time until the limit collection amount is reached is substantially the same between the a side and the b side. Accordingly, the SOx trap catalyst 24 is not partially disabled, and the catalyst can be used as a whole without waste.

  As another method, in order to improve the reactivity of the catalyst, the distribution tendency of the noble metal activity of the catalyst (for example, the amount of the noble metal catalyst 52) and the amount of the SOx trap 51 is formed as shown in FIG. By doing so, the same purpose can be achieved. Further, the number of exhaust gas flow passages 49 of the honeycomb structure of the SOx trap catalyst 24 per unit area, that is, the density of the arrangement of the exhaust gas flow passages 49 is increased, and the surface area tendency in the exhaust gas flow passages 49 is shown in FIG. The same purpose can be achieved by forming the same tendency as in FIG. 8 as shown in FIG.

  In the second embodiment according to the present invention, the above problem is caused by allowing the exhaust gas to uniformly flow into the entire SOx trap catalyst 24 by biasing the tendency of pressure loss when the exhaust gas flows into the SOx trap catalyst 24. Has solved. That is, if the pressure loss is increased on the side a where the flow rate of exhaust gas is large, the amount of exhaust gas flowing into the portion inevitably decreases. Then, the flow of exhaust gas shifts to the b side where the pressure loss is smaller, and the amount of exhaust gas flowing into the SOx trap catalyst 24 becomes uniform as a whole. Thereby, the catalyst can be efficiently used as a whole.

  As a method for increasing the pressure loss, for example, as shown in FIG. 9, it is conceivable to reduce the diameter of the exhaust gas flow passage 49 and increase the number of the exhaust gas flow passages 49 and increase the density accordingly. If the diameter of the exhaust gas flow passage 49 is reduced and the density of the arrangement is increased, the pressure loss in that portion increases accordingly. It is also conceivable to increase the amount of the catalyst carrier 50 and substantially increase the thickness of the partition wall 48 without changing the diameter and arrangement density of the exhaust gas flow passage 49. That is, when the amount of the catalyst carrier 50 is increased, as described in the first embodiment, the surface area is increased. On the contrary, the partition wall 48 is thickened as a whole, so that the diameter of the exhaust gas passage is reduced and the pressure loss is reduced. growing. As another method, the usable portion of the catalyst as a whole is reduced, but it is also conceivable to prevent the exhaust gas from physically passing through by closing the exhaust gas flow passage 49 with a plug 55 as shown in FIG. It is done. In this case, it is possible to select whether the inlet side upstream of the SOx trap catalyst 24 is closed or the outlet side which is downstream is closed, but there is little catalyst in the exhaust gas flow passage 49 itself which is closed when the outlet side is closed. It is more preferable because it can be used.

  The pressure loss can be adjusted by these methods, and the tendency of the pressure loss between the a side and the b side can be formed to have the same tendency as the tendency of the distribution curve of FIG. It becomes possible. More specifically, in the method of reducing the diameter of the exhaust gas flow passage 49 and increasing the arrangement density, the diameter of the exhaust gas flow path 49 on the a side is made smaller, the arrangement density is made higher, and the catalyst In the method of increasing the amount of the carrier 50, the number of catalyst carriers 50 on the a side is increased, and in the method of closing the exhaust gas flow passage with the plug 55, the arrangement, ratio, interval, and the like of the holes to be closed are changed. Accordingly, the tendency of pressure loss as shown in FIG. 11 can be realized, and the amount of exhaust gas flowing into the SOx trap catalyst 24 becomes uniform as a whole. Thereby, the catalyst can be efficiently used as a whole.

  Next, a third embodiment will be described. In the present embodiment, as shown in FIG. 12, the planar flow rate control valve 61 that is disposed in the exhaust passage upstream of the SOx trap catalyst 24 and can be controlled by the actuator 60 is used to flow into the SOx trap catalyst 24. The flow of exhaust gas is adjusted so that the flow rate of exhaust gas to be made uniform. Unlike the above-described embodiment, the SOx trap catalyst 24 is a catalyst that has no bias in the amount of limit collection or pressure loss.

  The flow rate control valve 61 is driven stepwise or steplessly by the actuator 60 between a closed position indicated by a solid line and an open position indicated by a broken line. The actuator 60 is controlled based on an output signal from an electronic control unit (ECU) 30. The closed position is a position where the flow rate control valve 61 is located in a cross section substantially orthogonal to the central axis of the exhaust passage and receives the exhaust gas substantially perpendicularly to the flow to block the flow. The open position is The flow rate control valve 61 is located in a cross section substantially parallel to the flow of exhaust gas and does not block the exhaust gas.

  When exhaust gas collides with the flow rate control valve 61 during operation of the internal combustion engine, a wake vortex 62 is generated behind the flow rate control valve 61. By changing the wake vortex 62 using a flow rate control valve 61 as shown below, the exhaust gas in the downstream exhaust passage is rectified and flows into the SOx trap catalyst 24 at a substantially uniform flow rate without any deviation. Will be.

  Next, design items and control principles of the flow rate control valve 61 will be described. A cross section perpendicular to the central axis of the exhaust passage is referred to as a reference plane, and the average value of the exhaust gas flow velocity distribution in the reference plane is referred to as an average flow velocity Vav (FIG. 13). As for various design matters such as the shape and size of the flow rate control valve 61 and the mounting position in the exhaust passage, the flow rate control valve 61 in the closed position flows into the SOx trap catalyst 24 when the average flow rate Vav of the exhaust gas is maximum. The flow velocity distribution of the exhaust gas is determined to be uniform. As a matter of course, various design items of the flow rate control valve 61 must be determined in accordance with the shape, size, length, and arrangement of the catalyst of the exhaust passage to be applied.

  Here, an embodiment of the flow rate control valve 61 is shown in FIGS. According to these embodiments, the flow rate control valve 61 is a half-moon shaped thin plate, and is in a closed position (FIGS. 14A and 15A) and an open position (FIG. 14B) and FIG. 15 (B)) is positioned by the actuator 60.

  Further, the control target value C of the flow velocity control valve 61 positioned by the actuator 60 generates the wake vortex 62 in which the exhaust gas flowing into the SOx trap catalyst 24 becomes uniform when the average flow velocity Vav is a certain value. The position is determined. The control target value C can be expressed by an angle around the rotation axis X with the angle of the flow rate control valve 61 in the closed position being 0 degrees. In this embodiment, when the cross section in the exhaust passage including the flow rate control valve 61 in the closed position is used as a reference plane, the average flow velocity Vav on the reference plane changes according to the required torque TQ and the engine speed N. Therefore, the control target value C corresponding to the average flow velocity Vav can also be expressed as a function of the required torque TQ and the engine speed N, and is stored in advance in the ROM 32 in the form of a map as shown in FIG.

  Next, a flowchart of the flow velocity equalization operation will be described with reference to FIG. This operation is performed as a routine executed by interruption every predetermined time set in advance by the electronic control unit (ECU) 30.

  Referring to FIG. 17, first, at step 100, the control target value C is read from the map shown in FIG. 16 stored in the ROM 32 based on the required torque TQ and the engine speed N at the time of execution of the routine. Next, at step 101, the flow rate control valve 61 is positioned by the actuator 60 so as to reach the control target value C, and the routine is terminated.

  Next, a fourth embodiment will be described. In the present embodiment, as shown in FIG. 18, an inflow restriction valve 66 that can be controlled by the actuator 65 is disposed immediately downstream of the NOx storage reduction catalyst 25 and on the a side where the flow velocity is fast. The actuator 65 is controlled based on an output signal from an electronic control unit (ECU) 30. By using the inflow restricting valve 66, control is performed so that the exhaust gas does not flow into the portion where the collection capability of the SOx trap catalyst 24 is saturated and becomes unusable.

  The function of the inflow restriction valve 66 will be specifically described with reference to FIG. The inflow restriction valve 66 is driven stepwise or steplessly by the actuator 65 between a closed position indicated by a solid line and an open position indicated by a broken line. The closed position is a position where the inflow restricting valve 66 is disposed in a plane parallel to the planar end surface on the discharge side of the NOx storage reduction catalyst 25, and the open position is the inflow limiting valve 66. This is a position where the flow of the exhaust gas discharged from 25 is not blocked. The inflow restricting valve 66 positioned other than the open position blocks the flow of exhaust gas discharged from the exhaust gas flow passage of the NOx storage reduction catalyst 25 corresponding to that position and makes it difficult to discharge. Then, the resistance when the exhaust gas flowing into the exhaust gas flow passage of the SOx trap catalyst 24 corresponding to the portion where the exhaust is blocked becomes large. As a result, the flow of inflowing exhaust gas changes in the direction of the b side where the exhaust gas discharge is not blocked, and the amount of inflow can be adjusted.

  An actual usage method using this function will be described with reference to FIG. 19 showing the SOx trapping amount of the SOx trap catalyst 24. In an unused internal combustion engine, the inflow restriction valve 66 is in the open position. The amount of SOx trapped in the SOx trap catalyst 24 in proportion to the operation time of the internal combustion engine gradually increases as a whole with a bias on the a side as shown by line I in FIG. When the operation is continued in such a state, the portion of the SOx trap catalyst 24 closest to the outermost side on the a side reaches the limit collection amount, and the collection ability is saturated (line II). Then, since this part can no longer be used, the inflow restricting valve 66 is driven so as to block the discharge of the exhaust gas. Then, the exhaust gas no longer flows into that portion, and the flow of the exhaust gas changes further to the b side. Accordingly, when the further inner portion reaches the limit collection amount (line III), the inflow restricting valve 66 is further driven to restrict the inflow. By repeating this, the SOx trap catalyst 24 can be efficiently used as a whole by controlling the inflow restricting valve 66 so as to restrict the inflow of exhaust gas in the portion that has reached the limit collection amount.

  Next, a method for estimating the distribution of SOx flowing into the SOx trap catalyst 24 according to the average flow velocity Vav and operating the inflow restriction valve 66 based on the estimated SOx amount will be described. In this embodiment, the cross section in the exhaust passage including the inflow restriction valve 66 in the closed position is taken as a reference plane. The average flow velocity Vav is stored in advance in the ROM 32 as a function of the required torque TQ and the engine speed N in the form of a map as shown in FIG. The SOx amount SOX flowing into the SOx trap catalyst 24 per unit time is stored in advance in the ROM 32 in the form of a map as shown in FIG. 21 as a function of the position X indicated by the coordinate axis from the a side to the b side and the average flow velocity Vav. Is stored within. Therefore, the total collection amount ΣSOX of SOx at a certain point in time at a certain position is calculated by integrating the SOx amount SOX.

  When the total trapped amount ΣSOX calculated in this way exceeds the limit trapped amount SOX0, it is determined that the SOx trap catalyst 24 in that portion cannot be used, and the inflow restricting valve 66 is positioned to determine the above-described amount. The inflow of exhaust gas is limited like this. Note that the opening position of the inflow restricting valve 66 is set to an angle of 0 degrees, and the control target value C represented by an angle around the rotation axis X and the corresponding position X that can restrict the inflow of exhaust gas are stored in the ROM 32 in advance. ing.

  Next, a flowchart of the inflow restriction operation will be described with reference to FIG. This operation is performed as a routine executed by interruption every predetermined time set in advance by the electronic control unit (ECU) 30.

  Referring to FIG. 22, first, at step 200, based on the required torque TQ and the engine speed N at the time of execution of the routine, the average flow velocity Vav is read from the map shown in FIG. Next, at step 201, the SOx amount SOX at the position X closest to the a side in the still usable range is read from the read average flow velocity Vav. Next, at step 202, the read SOx amount SOX is added to the total collection amount ΣSOX. Next, at step 203, it is determined whether or not the calculated total collection amount ΣSOX exceeds the limit collection amount SOX0. As a result, if the limit collection amount SOX0 is not yet exceeded, the routine is terminated. On the other hand, when the total collection amount ΣSOX exceeds the limit collection amount SOX0, the process proceeds to step 204. In step 204, the control target value C corresponding to the position X exceeding the limit collection amount SOX0 is read. Next, at step 205, the inflow restricting valve 66 is positioned by the actuator 65 so as to reach the control target value C, and the routine is ended.

  In the present embodiment, the inflow restriction valve 66 is disposed downstream of the NOx storage reduction catalyst 25. However, the inflow restriction valve 66 is disposed immediately upstream of the SOx trap catalyst 24, and the portion of the SOx trap catalyst 24 in which the collection ability is saturated is saturated. The exhaust gas flow passage 49 may be blocked so that the exhaust gas does not flow into the exhaust gas.

1 is an overall view of an internal combustion engine. It is sectional drawing of the surface part of the catalyst support | carrier of a NOx storage reduction catalyst. It is a figure which shows the structure of a SOx trap catalyst. It is sectional drawing of the surface part of the catalyst support | carrier of a SOx trap catalyst. It is an image figure of the flow velocity of the exhaust gas which flows into a SOx trap catalyst. It is a figure which shows the SOx amount which flows into a SOx trap catalyst and a NOx occlusion reduction catalyst. It is sectional drawing of the surface part of the catalyst support | carrier of a SOx trap catalyst. It is a figure which shows the bias | inclination of SOx collection amount. It is a figure which shows the structure of the SOx trap catalyst by this invention. It is a figure which shows the structure of the SOx trap catalyst by this invention. It is a figure which shows the bias | inclination of pressure loss. It is a figure which shows the structure of a flow velocity control valve, and the flow of exhaust gas. It is a figure which shows the basic idea of an average flow velocity. It is a figure which shows the shape and structure of a flow control valve. It is another figure which shows the shape and structure of a flow control valve. It is a figure which shows the map of the control target value C. It is a flowchart for controlling the flow rate control valve to make the flow rate uniform. It is a figure which shows the structure of the inflow restriction valve 66, and the flow of exhaust gas. It is a figure which shows the transition of SOx collection amount. It is a figure which shows the map of average flow velocity Vav. It is a figure which shows the map of the SOx amount which flows in per unit time. It is a flowchart for controlling an inflow restricting valve to restrict inflow of exhaust gas.

Explanation of symbols

1 Engine body 21 Exhaust pipe 24 SOx trap catalyst 25 NOx storage reduction catalyst

Claims (5)

  An SOx trap catalyst that collects SOx is disposed in the engine exhaust passage, and NOx contained in the exhaust gas is occluded and flows into the SOx trap catalyst downstream exhaust passage when the air-fuel ratio of the inflowing exhaust gas is lean. A NOx occlusion reduction catalyst that reduces and purifies the stored NOx when the air-fuel ratio of the exhaust gas that is exhausted becomes rich or rich, the engine exhaust passage has a curved portion, and passes through the curved portion to thereby enter the exhaust passage. In an internal combustion engine in which the inflow amount is partially biased by the exhaust gas flowing into the SOx trap catalyst in a state where the flow velocity is biased, the flow rate in the exhaust passage is increased through the outside of the curved portion. Exhaust gas purification of an internal combustion engine provided with an exhaust gas adjusting means arranged in the region and adjusting exhaust gas flow so that SOx is uniformly collected by the SOx trap catalyst Apparatus.   The exhaust gas adjusting means is disposed upstream of the SOx trap catalyst, and is controlled to a predetermined position corresponding to the average flow velocity of the exhaust gas, so that the exhaust gas flow uniformly flows into the SOx trap catalyst. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purification apparatus is a movable member controlled as described above.   The exhaust gas adjusting means is disposed upstream of the SOx trap catalyst or downstream of the NOx storage reduction catalyst, and is controlled to a position that restricts exhaust gas from flowing into a portion where the trapping capacity of the SOx trap catalyst is saturated. The exhaust purification device for an internal combustion engine according to claim 1, wherein the exhaust purification device is a movable member.   An SOx trap catalyst that collects SOx is disposed in the engine exhaust passage, and NOx contained in the exhaust gas is occluded and flows into the SOx trap catalyst downstream exhaust passage when the air-fuel ratio of the inflowing exhaust gas is lean. A NOx occlusion reduction catalyst that reduces and purifies the stored NOx when the air-fuel ratio of the exhaust gas that is exhausted becomes rich or rich, the engine exhaust passage has a curved portion, and passes through the curved portion to thereby enter the exhaust passage. In an internal combustion engine in which the exhaust gas flows into the SOx trap catalyst in a state where the flow velocity is biased, the inflow amount is partially biased, and the SOx trappable amount of the SOx trap catalyst is previously determined according to the bias. Biased internal combustion engine exhaust gas purification device.   An SOx trap catalyst that collects SOx is disposed in the engine exhaust passage, and NOx contained in the exhaust gas is occluded and flows into the SOx trap catalyst downstream exhaust passage when the air-fuel ratio of the inflowing exhaust gas is lean. A NOx occlusion reduction catalyst that reduces and purifies the stored NOx when the air-fuel ratio of the exhaust gas that is exhausted becomes rich or rich, the engine exhaust passage has a curved portion, and passes through the curved portion to thereby enter the exhaust passage. In an internal combustion engine in which the exhaust gas flows into the SOx trap catalyst in a state where the flow velocity is biased, the inflow amount is partially biased, and the tendency of the pressure loss of the exhaust gas flowing into the SOx trap catalyst is An exhaust purification device for an internal combustion engine biased in advance according to

Images