JP2018087542A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the discharge of ammonia by restoring sulfur poisoning with the supply of a minimum necessary amount of urea water.SOLUTION: When a temperature of a catalyst (NOx occlusion catalyst 4) is raised for the purpose of regeneration, a supply amount of urea water is limited (reduced or stopped) in a situation that an exhaust temperature becomes sufficiently high, the supply of the urea water at the restoration of the sulfur poisoning of a selective reduction catalyst 11 is suppressed (the lowering of the exhaust temperature caused by latent heat is suppressed), the generation of a sulfur component (ammonium salt of sulfuric acid) which is dissolved at a low temperature is suppressed, and a sulfur component (sulfate of copper) which is dissolved at a high temperature is dissolved, thus restoring sulfur poisoning.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust purification device that reduces nitrogen oxides (NOx) in exhaust gas of an internal combustion engine.

  As a technique for reducing nitrogen oxide (NOx) contained in exhaust gas of an internal combustion engine (engine), an exhaust purification device using a selective catalytic reduction system is known. The exhaust gas purification apparatus using the selective reduction system is produced by injecting urea water into the exhaust passage provided with the selective reduction catalyst, whereby the urea water is decomposed by the heat of the exhaust gas to generate ammonia. Ammonia reacts with NOx in the exhaust gas on the selective reduction catalyst, and NOx is reduced (purified) into nitrogen and water.

  In the above-described exhaust purification device, if the operation is continued, sulfur poisoning occurs in which the sulfur content in the fuel adheres to the selective reduction catalyst. When sulfur poisoning occurs in the selective reduction catalyst, the NOx purification performance decreases, and therefore, poisoning recovery operation for recovering the sulfur poisoning of the selective reduction catalyst is performed (for example, see Patent Document 1). In the technique described in Patent Document 1, when sulfur poisoning occurs in the selective reduction catalyst, the selective reduction catalyst is heated to decompose the sulfur component. As the temperature of the selective reduction catalyst increases, the urea water supply is stopped to prevent overheating of the urea water injector.

  By the way, in the state of sulfur poisoned by the selective reduction catalyst, the state of sulfur poisoned by the selective reduction catalyst has multiple modes (sulfuric acid ammonium salt, copper sulfide), some of which are selected. Adsorbed on the active site of the reduction catalyst. For this reason, depending on the amount of sulfur poisoning, when sulfur poisoning occurs in the selective reduction catalyst, urea water is supplied to produce a large amount of ammonium salt of sulfuric acid, and a low temperature (for example, about 400 ° C. to 500 ° C. ) Can be decomposed into nitrogen, sulfur dioxide and water. Therefore, by supplying urea water, the ammonium salt of sulfuric acid can be decomposed and sulfur poisoning can be recovered.

  As described above, when sulfur poisoning occurs in the selective reduction catalyst, the sulfur poisoning can be recovered at an early stage by supplying urea water and generating a large amount of ammonium salt of sulfuric acid. However, if urea water is supplied at the time of recovery of sulfur poisoning of the selective reduction catalyst, there is a possibility that ammonia may be discharged. Therefore, it is desired to suppress the discharge of ammonia to the environment.

Japanese Patent Laying-Open No. 2015-63936

  The present invention has been made in view of the above situation, and in an exhaust purification device that recovers sulfur poisoning by supplying urea water when sulfur poisoning occurs in the selective reduction catalyst, the minimum necessary amount of urea water It is an object of the present invention to provide an exhaust gas purification apparatus for an internal combustion engine that can recover sulfur poisoning by supplying.

  In order to achieve the above object, an exhaust emission control device for an internal combustion engine according to claim 1 of the present invention is provided in an exhaust passage of the internal combustion engine and selectively reduces and purifies NOx contained in the exhaust, and the selective reduction catalyst. A urea water supply means for supplying urea water to the exhaust passage on the upstream side, a catalyst or filter provided in the exhaust passage for purifying exhaust, and sulfur poisoning determination for judging sulfur poisoning of the selective reduction catalyst Means, poisoning recovery means for recovering sulfur poisoning of the selective reduction catalyst by raising the temperature of the selective reduction catalyst, and heating the catalyst or the filter to regenerate the catalyst or the upstream filter. During regeneration of the catalyst or the filter by the regeneration means, or until a predetermined time elapses after regeneration of the catalyst or the filter is completed by the regeneration means During the case of executing the recovery of the sulfur poisoning of the selective reduction catalyst by poisoning recovery means it is characterized in that a urea water supply control means for limiting the supply amount of the urea water.

  In the present invention according to claim 1, a selective reduction catalyst, a catalyst (for example, a NOx storage catalyst), a filter (for example, a diesel particulate filter), a selective reduction catalyst poisoning recovery means, a catalyst, a filter regeneration means, urea When the temperature of the catalyst or the filter is raised, the urea water supply control means restricts (reduces) the supply of urea water by the poisoning recovery means, and sulfur components that decompose at a low temperature ( (Sulfuric acid ammonium salt) is suppressed, and the decomposition of the sulfur component (copper sulfate) that decomposes at a high temperature is maintained by keeping the exhaust temperature high.

  As a result, in a situation where the temperature of the exhaust gas is sufficiently high by raising the temperature of the catalyst or filter during regeneration of the catalyst or filter, the supply of urea water is suppressed (a decrease in the exhaust gas temperature is suppressed), and the exhaust gas temperature is kept high. The sulfur component (copper sulfate) decomposed at a high temperature is decomposed to recover sulfur poisoning. At this time, since supply of urea water is suppressed, discharge of ammonia is suppressed.

  Therefore, when sulfur poisoning occurs in the selective reduction catalyst, the sulfur poisoning can be recovered by supplying the minimum amount of urea water in the exhaust purification apparatus that recovers sulfur poisoning by supplying urea water. It becomes possible.

  An exhaust gas purification apparatus for an internal combustion engine according to a second aspect of the present invention is the exhaust gas purification apparatus for an internal combustion engine according to the first aspect, wherein sulfur poisoning estimation means for estimating the sulfur poisoning amount of the selective reduction catalyst is provided. The urea water supply control means is characterized in that the greater the estimated sulfur poisoning amount, the greater the degree of restriction for limiting the supply amount of urea water to reduce the supply amount of urea water.

  In the present invention according to claim 2, as the sulfur poisoning amount increases, the degree of restriction for limiting the supply amount of urea water can be increased to decrease the supply amount of urea water, thereby suppressing ammonia discharge.

  According to a third aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the first aspect, wherein the sulfur poisoning estimation means for estimating the sulfur poisoning amount of the selective reduction catalyst is provided. The urea water supply control means is characterized in that the urea water supply time decreases as the estimated sulfur poisoning amount increases, thereby reducing the urea water supply amount.

  In the present invention according to claim 3, as the sulfur poisoning amount increases, the urea water supply time can be reduced to decrease the urea water supply amount, thereby suppressing ammonia discharge.

  In addition, while increasing the restriction | limiting degree which restrict | limits the supply amount of urea water, the supply time of urea water can also be decreased and the supply amount of urea water can also be reduced.

  An exhaust gas purification apparatus for an internal combustion engine according to a fourth aspect of the present invention is the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to third aspects, wherein the catalyst has a lean exhaust air-fuel ratio. A NOx occlusion catalyst that occludes NOx when the atmosphere is exhausted and reduces and purifies NOx occluded when the exhaust air-fuel ratio is stoichiometric or rich; and the regeneration means is means for raising the temperature of the NOx occlusion catalyst It is characterized by.

  In the present invention according to claim 4, the NOx storage catalyst is regenerated by raising the temperature of the NOx storage catalyst by the regeneration means (controlling the exhaust air / fuel ratio to a stoichiometric or rich atmosphere), and regeneration of the NOx storage catalyst. As a result, the exhaust temperature increases (for example, 700 ° C.). That is, when the temperature of the NOx occlusion catalyst, which is a catalyst, is regenerated and raised, the exhaust temperature becomes high. Therefore, the supply amount of urea water by the poisoning recovery means is limited to suppress a decrease in the exhaust temperature.

  An internal combustion engine exhaust gas purification apparatus according to a fifth aspect of the present invention is the internal combustion engine exhaust gas purification apparatus according to any one of the first to fourth aspects, wherein the temperature condition of the selective reduction catalyst is determined. A catalyst temperature grasping means for detecting, wherein the poisoning recovery means determines the sulfur poisoning mode based on information including the temperature status of the selective reduction catalyst grasped by the catalyst temperature grasping means, The urea water supply control means controls the degree of restriction of the urea water supply according to the sulfur poisoning mode determined by the poisoning recovery means.

  In the present invention according to claim 5, the catalyst temperature grasping means grasps at least the conditions such as the temperature of the selective reduction catalyst, the temperature history, etc., and determines the sulfur poisoning mode of the selective reduction catalyst. In other words, regarding the sulfur poisoning of the selective reduction catalyst, the status of the sulfur component (sulfuric acid ammonium salt) decomposed in the low temperature range and the sulfur component (copper sulfate salt) decomposed in the high temperature range are determined from the temperature history, etc. However, if there is a large amount of sulfur component (ammonium salt of sulfuric acid) decomposed in the low temperature range, increase the degree of restriction of urea water supply or reduce the supply time of urea water to supply urea water Reduce the amount (suppress ammonia discharge), suppress the exhaust temperature drop due to latent heat, keep the exhaust temperature high, and decompose the sulfur component decomposed in the high temperature range.

  According to a sixth aspect of the present invention, there is provided the exhaust gas purification apparatus for an internal combustion engine according to the fifth aspect, wherein the sulfur poisoning mode includes an ammonium salt, and the urea water supply control is performed. The means limits the supply amount of the urea water so as to increase the degree of restriction of the supply of the urea water as the amount of poisoning of the ammonium salt relative to the total amount of the sulfur poisoning is relatively large. It is characterized by.

  In the present invention according to claim 6, the amount of ammonium salt relative to the total amount of sulfur poisoning (catalytic sulfur poisoning amount) increases as the ammonium salt poisoning amount / catalyst sulfur poisoning amount = 1. The restriction is set so that the degree of restriction of water supply is high (the restriction is set so that the supply amount of urea water approaches 0). That is, when an ammonium salt that can be decomposed at a low temperature is sufficiently produced, it is not necessary to increase the ammonium salt to decompose sulfur, so the supply of urea water is reduced (stopped). By reducing the supply of urea water, a decrease in exhaust temperature due to latent heat is suppressed (exhaust temperature is maintained at about 600 ° C.), and the exhaust temperature is maintained at a temperature at which copper sulfate can be decomposed.

  An exhaust gas purification apparatus for an internal combustion engine of the present invention according to claim 7 for achieving the above object is provided in an exhaust passage of the internal combustion engine, the selective reduction catalyst for reducing and purifying NOx contained in the exhaust, and the selection A urea water supply unit that supplies urea water to the exhaust passage upstream of the reduction catalyst; and a sulfur poisoning determination unit that determines sulfur poisoning of the selective reduction catalyst. The urea water supply unit includes the sulfur water The supply amount of the urea water supplied from the urea water supply unit is limited according to the sulfur poisoning estimated by the poisoning determination unit.

  In the present invention according to claim 7, when the sulfur poisoning determination means determines that the selective reduction catalyst is sulfur poisoned, urea water is supplied from the urea water supply means to the exhaust passage. In this case, the supply of urea water is controlled according to the sulfur poisoning status determined by the sulfur poisoning determination means.

  As a result, when sulfur poisoning occurs in the selective reduction catalyst, the sulfur poisoning can be recovered by supplying the minimum amount of urea water in the exhaust gas purification device that recovers sulfur poisoning by supplying urea water. Is possible.

  The exhaust gas purification apparatus for an internal combustion engine according to the present invention supplies a minimum amount of urea water in an exhaust gas purification apparatus that recovers sulfur poisoning by supplying urea water when sulfur poisoning occurs in the selective reduction catalyst. This makes it possible to recover sulfur poisoning. As a result, the supply of urea water is suppressed and ammonia discharge is suppressed.

It is a schematic block diagram showing the system | strain of the exhaust gas purification apparatus of the internal combustion engine which concerns on one Example of this invention. It is a block block diagram of a control means. It is an operation | movement flowchart of the exhaust gas purification apparatus of the internal combustion engine which concerns on one Example of this invention. It is a map explaining the supply restriction | limiting of urea water.

  The exhaust gas purification apparatus for an internal combustion engine according to the present embodiment is an exhaust gas purification apparatus using a selective catalytic reduction system. That is, in order to reduce nitrogen oxide (NOx) contained in the exhaust gas, a selective reduction catalyst is provided, and urea water is injected into the exhaust passage from the urea water injection valve, so that the urea water is heated by the exhaust gas. Is a device that generates ammonia by being decomposed by the above, and the generated ammonia reacts with NOx in the exhaust gas on the selective reduction catalyst, and NOx is reduced (purified) to nitrogen and water.

  When sulfur poisoning occurs in the selective reduction catalyst, urea water is supplied from the urea water injection valve to produce a large amount of ammonium sulfate, and nitrogen and sulfur dioxide at low temperatures (eg, about 400 ° C to 550 ° C) It is decomposed into water to decompose the ammonium salt of sulfuric acid to recover sulfur poisoning of the selective reduction catalyst.

  When the temperature of the upstream catalyst of the selective catalytic reduction catalyst is regenerated and raised, the supply amount of urea water is limited (reduced and stopped), and the temperature of the exhaust gas due to latent heat is suppressed from decreasing, and a high temperature (about The temperature of the exhaust gas is maintained at 600 ° C. to 650 ° C., and the copper sulfate is decomposed in a high temperature atmosphere to recover the sulfur poisoning of the selective reduction catalyst. At this time, since the supply amount of urea water is limited, the discharge of ammonia can be suppressed.

  The configuration of an embodiment of the present invention will be described with reference to FIG. FIG. 1 shows a schematic configuration representing a system of an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention.

  As shown in the figure, an exhaust purification device 3 is provided in an exhaust pipe 2 as an exhaust passage of a multi-cylinder diesel engine (engine) 1 as an internal combustion engine mounted on a vehicle. The exhaust purification device 3 is provided with a purification device 6 (catalyst or filter) having a NOx storage catalyst 4 and a diesel particulate collection filter 5.

  The NOx storage catalyst 4 stores NOx when the exhaust air-fuel ratio is a lean atmosphere, and reduces and purifies NOx stored when the exhaust air-fuel ratio is a stoichiometric or rich atmosphere. The diesel particulate filter 5 is a device that collects particulates.

  When the NOx storage catalyst 4 and the diesel particulate collection filter 5 are poisoned by sulfur, the NOx storage catalyst 4 and the diesel particulate collection filter 5 are heated (for example, by injection of additional fuel), and sulfur is removed. It is removed and reproduced (reproducing means).

  A urea selective reduction catalyst (Selective Catalytic Reduction) system is provided on the downstream side of the purification device 6 as the exhaust purification device 3. That is, the selective reduction catalyst 11 is provided in the exhaust pipe 2 on the downstream side of the purification device 6, and the urea water injection valve 12 (urea water supply means) is provided in the exhaust pipe 2 on the upstream side of the selective reduction catalyst 11. ing.

  The urea water injection valve 12 is supplied with urea water from a urea water tank (not shown), and the urea water injection valve 12 injects (supply) urea water into the exhaust pipe 2 according to an instruction from the control means 10. That is, by supplying urea water, urea water is decomposed by the heat of the exhaust gas to generate ammonia, and the generated ammonia reacts with NOx in the exhaust gas by the selective reduction catalyst 11, and NOx is converted into nitrogen. Reduced (purified) to water.

  The selective reduction catalyst 11 is provided with a temperature sensor 13 that detects the temperature of the catalyst, and a NOx sensor that detects the state of NOx in the exhaust gas that has exited the selective reduction catalyst 11 is disposed in a downstream passage of the selective reduction catalyst 11. 14 is provided. Detection information of the temperature sensor 13 and the NOx sensor 14 is input to the control means 10. Further, the operating state of the engine 1 is input to the control means 10.

  Although details will be described later, in the control means 10, the temperature state (history) of the selective reduction catalyst 11 detected by the temperature sensor 13, the purification state of NOx detected by the NOx sensor 14, and the urea from the urea water injection valve 12. The sulfur poisoning of the selective reduction catalyst 11 is determined based on the water injection status, the operating status of the engine 1, and the like. When sulfur poisoning is determined, urea water is supplied to recover sulfur poisoning.

  The control means 10 will be specifically described based on FIG. FIG. 2 shows a block configuration of the control means 10.

  As shown in the figure, the control means 10 is provided with sulfur poisoning estimation means 21. In the sulfur poisoning estimation means 21, the fuel consumption rate for operating the engine 1, the estimated sulfur concentration, and the accumulation ratio of sulfur (sulfuric acid ammonium salt, copper sulfate) according to the temperature of the selective reduction catalyst 11. Based on this, the sulfur poisoning amount of the selective reduction catalyst 11 is estimated. Further, the sulfur poisoning amount of the selective reduction catalyst 11 is estimated from the relationship between the urea water injection amount at a specific temperature of the selective reduction catalyst 11 and the NOx purification rate.

  The control means 10 is provided with sulfur poisoning determination means 22 for determining whether or not the sulfur poisoning amount estimated by the sulfur poisoning estimation means 21 exceeds a determination value. Further, when the sulfur poisoning determination means 22 determines that the selective reduction catalyst 11 is sulfur poisoned (when it is determined that the sulfur poisoning amount exceeds the determination value), the sulfur poisoning of the selective reduction catalyst 11 is reduced. In order to recover, poisoning recovery means 23 for injecting urea water from the urea water injection valve 12 is provided. The poisoning recovery means 23 sends a command for injecting urea water from the urea water injection valve 12 via the urea water supply control means 24.

  On the other hand, the control means 10 includes a regeneration means for raising the temperature of the NOx storage catalyst 4 and the diesel particulate collection filter 5 when the NOx storage catalyst 4 and the diesel particulate collection filter 5 are poisoned by sulfur. 25, and information on the temperature rise of the NOx storage catalyst 4 and the diesel particulate filter 5 by the regeneration means 25 is sent to the urea water supply control means 24. Sulfur poisoning of the selective reduction catalyst 11 is recovered by injecting urea water from the urea water injection valve 12 via the urea water supply control means 24.

  The urea water supply control unit 24 operates when the regeneration unit 25 is operated and the NOx storage catalyst 4 (diesel particulate collection filter 5) is heated (when the catalyst or filter is heated by the regeneration unit 25), Alternatively, when the NOx storage catalyst 4 (diesel particulate collection filter 5) is kept in a high state for a predetermined time after the regeneration is completed, it is supplied according to a command from the poisoning recovery means 23 ( The supply amount of urea water (supplied for poisoning recovery) is limited.

  For example, when the temperature of the NOx occlusion catalyst 4 is raised, the exhaust gas temperature is increased. Therefore, the supply amount of urea water is limited to reduce (stop) the supply amount, thereby suppressing a decrease in exhaust gas temperature due to latent heat. By maintaining the exhaust temperature high, for example, decomposition of copper sulfate is promoted. The situation of restriction of the supply amount of urea water is set according to the mode of sulfur poisoning (specifically, described later).

  As described above, the sulfur poisoning state is estimated by the sulfur poisoning estimation means 21 provided in the control means 10. Then, the supply amount of urea water supplied from the urea water supply control means 24 is set according to the sulfur poisoning state estimated by the sulfur poisoning estimation means 21. Specifically, the amount of urea water to be supplied is increased by increasing the degree of limiting the amount of urea water supplied from the urea water supply control means 24 as the sulfur poisoning amount increases. Decrease. Further, poisoning is progressing, that is, the amount of urea water to be supplied is reduced by shortening the time for supplying urea water as the amount of sulfur poisoning increases. Here, the expression “restricting the supply amount of urea water” includes the meaning of reducing the supply amount of urea water to zero.

  The control means 10 is provided with a catalyst temperature grasping means 26, and information on the temperature state of the selective reduction catalyst 11 grasped by the catalyst temperature grasping means 26 is sent to the poisoning recovery means 23. The poisoning recovery means 23 determines the state of sulfur poisoning based on the information including the temperature state of the selective reduction catalyst 11 grasped by the catalyst temperature grasping means 26 (state of ammonium sulfate and copper sulfate). Determine.

  That is, in the poisoning recovery means 23, as the sulfur poisoning of the selective reduction catalyst 11, the amount of sulfur component (sulfuric acid ammonium salt) decomposed in the low temperature range, the sulfur component decomposed in high temperature range (copper sulfate) Determine the amount of situation. Information determined by the poisoning recovery means 23 is sent to the urea water supply control means 24.

  The urea water supply control means 24 is operated when the regeneration means 25 is operated and the NOx storage catalyst 4 (diesel particulate collection filter 5) is heated (when the upstream catalyst is heated by the regeneration means 25), That is, when the exhaust gas temperature is raised, the degree of restriction of urea water supply is controlled based on the information of the sulfur poisoning mode determined by the poisoning recovery means 23.

  For example, when the sulfur poisoning amount of the selective reduction catalyst 11 is high in the proportion of ammonium salt of sulfuric acid, the supply amount is reduced (stopped) by restricting the supply of urea water, and the decrease in the exhaust temperature due to latent heat is suppressed. Promotes the decomposition of copper sulfate. By reducing the supply of urea water (by stopping), the discharge of ammonia is suppressed.

  Therefore, when sulfur poisoning occurs in the selective reduction catalyst 11, the sulfur poisoning is recovered by supplying the minimum amount of urea water in the exhaust purification device that supplies urea water to recover the sulfur poisoning. Is possible.

  The operation of the exhaust emission control device described above will be specifically described with reference to FIGS. FIG. 3 is a flowchart for explaining the flow of recovery processing for sulfur poisoning of the selective reduction catalyst 11 in the exhaust gas purification apparatus for an internal combustion engine according to one embodiment of the present invention, and FIG. 4 is a map for explaining the supply restriction of urea water. Is shown.

  As shown in FIG. 3, the sulfur poisoning amount of the selective reduction catalyst 11 is estimated in step S1. That is, selective reduction based on the fuel consumption rate for operating the engine 1, the estimated sulfur concentration, and the accumulation ratio of sulfur (ammonium salt of sulfuric acid, copper sulfate) by temperature of the selective reduction catalyst 11. The sulfur poisoning amount of the catalyst 11 is estimated. Further, the sulfur poisoning amount of the selective reduction catalyst 11 is estimated from the relationship between the urea water injection amount at a specific temperature of the selective reduction catalyst 11 and the NOx purification rate.

  In step S2, it is determined whether or not the estimated sulfur poisoning amount is greater than or equal to the amount that needs to be recovered (determination value or more), and if it is determined that the sulfur poisoning amount is greater than or equal to the determination value, In step S3, a recovery process (a process for supplying urea water) is started. If it is determined in step S2 that the sulfur poisoning amount is less than the determination value, the process proceeds to the sulfur poisoning amount estimation process in step S1.

  When the recovery process is started in step S3, in step S4, the upstream catalyst (for example, the NOx storage catalyst 4 and the diesel particulate collection filter 5 or the NOx storage catalyst 4 whose regeneration temperature is higher than that of the diesel particulate collection filter 5). It is determined whether or not the regeneration operation is being performed. When it is determined in step S4 that the upstream catalyst is in the regeneration operation, the process proceeds to a process of limiting the supply amount of urea water.

  If it is determined in step S4 that the upstream catalyst is in the regeneration operation, an ammonium salt is estimated in step S5. That is, the status of the temperature at which the selective reduction catalyst 11 is operated is grasped, and the amount of ammonium salt in the sulfur poisoning of the selective reduction catalyst 11 is estimated. The ammonium salt can be estimated from the integrated value of the fuel consumption rate, the estimated sulfur poisoning concentration, the sulfur component accumulation rate (by temperature: may be negative), and the ammonia coverage of the selective reduction catalyst 11. .

  After estimating the ammonium salt in step S5, the supply amount of urea water is limited in step S6. The rate of restriction of the urea water supply amount is implemented based on the map shown in FIG.

  That is, as shown in FIG. 4, as the ammonium salt increases with respect to the total amount of sulfur poisoning (estimated sulfur poisoning amount) (the closer to the poisoning amount of ammonium salt / the sulfur poisoning amount = 1). A restriction is set for the normal supply amount so that the degree of restriction of the urea water supply becomes high (a restriction is set so that the supply amount of urea water approaches 0). In other words, if enough ammonium salt that can be decomposed at low temperature is generated and decomposed, it is not necessary to increase the ammonium salt by supplying urea water any more, so reduce the supply of unnecessary urea water (stop) ).

  The normal supply amount of urea water is set as the supply amount of urea water at the time of recovery based on the NOx passage amount detected by the NOx sensor 14 (see FIG. 1) and the ammonia adsorption amount of the selective reduction catalyst 11. The target supply amount of water is the normal supply amount.

  By reducing (stopping) the supply of urea water, a decrease in the exhaust temperature due to latent heat is suppressed, and the exhaust temperature is maintained at a high temperature of about 600 ° C., for example. Thus, the exhaust temperature is maintained at a temperature at which the copper sulfate can be decomposed, and the copper sulfate is decomposed to recover the sulfur poisoning. And since supply of urea water is restrict | limited (stop), discharge | emission of ammonia can be suppressed.

  In the above-described embodiment, the amount of ammonium salt is estimated to change the degree of restriction of urea water supply. However, when it is determined that the upstream catalyst is in the regeneration operation, urea water is reduced. Various controls can be applied to control the restriction of the supply of urea water, such as performing a control that reduces (stops) a certain rate for a certain time and suppresses a decrease in exhaust gas temperature.

  Returning to the flowchart of FIG. 3, if it is determined in step S4 that the upstream catalyst is not in the regeneration operation and urea water is supplied at a normal supply amount and the sulfur poisoning recovery process is executed, or step S6. When the sulfur poisoning recovery process is executed in a state where the supply of urea water is limited (stopped) and the decrease in the exhaust temperature is suppressed, whether or not the sulfur poisoning of the selective reduction catalyst 11 has been recovered in step S7. Is judged. That is, it is determined whether or not the sulfur poisoning amount is less than or equal to the amount at which the recovery process is completed (below the end determination value).

  If it is determined in step S7 that the sulfur poisoning of the selective reduction catalyst 11 has not been recovered, the process proceeds to step S3 and the sulfur poisoning recovery process is continued. If it is determined in step S7 that the sulfur poisoning of the selective reduction catalyst 11 has been recovered, the recovery end process is executed in step S8, and the process ends. That is, the information on the estimated sulfur poisoning amount and the information on the estimated ammonium salt are reset, and the sulfur poisoning recovery process ends.

  Instead of the determination in step S7, it is also possible to shift to the sulfur poisoning recovery end process (step S8) using the sulfur poisoning recovery processing time as a threshold value. It is also possible to shift to the sulfur poisoning recovery end process (step S8) when the upstream catalyst regeneration operation ends.

  Since the exhaust purification device described above limits (decreases, stops) the supply amount of urea water when the temperature of the upstream catalyst (for example, the NOx storage catalyst 4) is increased for regeneration, the exhaust purification device has a low temperature. The generation of sulfur components (ammonium salt of sulfuric acid) decomposed in is suppressed, and the exhaust temperature is kept high.

  As a result, in a situation where the exhaust temperature becomes sufficiently high when the upstream catalyst (for example, the NOx storage catalyst 4) is regenerated, the supply of urea water is suppressed (a decrease in the exhaust temperature due to latent heat is suppressed) and the decomposition is performed at a high temperature. The sulfur component (copper sulfate) is decomposed and sulfur poisoning is recovered. At this time, since supply of urea water is suppressed, discharge of ammonia is suppressed.

  Therefore, when sulfur poisoning occurs in the selective reduction catalyst 11, the sulfur poisoning is recovered by supplying the minimum amount of urea water in the exhaust purification device that supplies urea water to recover the sulfur poisoning. And ammonia emission can be suppressed.

  INDUSTRIAL APPLICABILITY The present invention can be used in the industrial field of exhaust purification devices that reduce nitrogen oxides (NOx) in exhaust gases of internal combustion engines.

1 Multi-cylinder diesel engine (engine)
DESCRIPTION OF SYMBOLS 2 Exhaust pipe 3 Exhaust gas purification device 4 NOx occlusion catalyst 5 Diesel particulate collection filter 6 Purification device 10 Control means 11 Selective reduction catalyst 12 Urea water injection valve 13 Temperature sensor 14 NOx sensor 21 Sulfur poisoning estimation means 22 Sulfur poisoning judgment means 22 23 poisoning recovery means 24 urea water supply control means 25 regeneration means 26 catalyst temperature grasping means

Claims (7)

A selective reduction catalyst provided in an exhaust passage of the internal combustion engine for reducing and purifying NOx contained in the exhaust;
Urea water supply means for supplying urea water to the exhaust passage on the upstream side of the selective reduction catalyst;
A catalyst or filter provided in the exhaust passage for purifying exhaust;
Sulfur poisoning determination means for determining sulfur poisoning of the selective reduction catalyst;
Poisoning recovery means for recovering sulfur poisoning of the selective reduction catalyst by raising the temperature of the selective reduction catalyst;
Regenerating means for regenerating the catalyst or the upstream filter by raising the temperature of the catalyst or the filter;
While the catalyst or the filter is regenerated by the regeneration means, or until a predetermined time elapses after the regeneration of the catalyst or the filter is completed by the regeneration means, the poisoning recovery means An exhaust gas purification apparatus for an internal combustion engine, comprising: urea water supply control means for restricting the supply amount of the urea water when performing recovery of sulfur poisoning of the selective reduction catalyst. The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
Comprising sulfur poisoning estimation means for estimating the sulfur poisoning amount of the selective reduction catalyst,
The urea water supply control means includes
An exhaust emission control device for an internal combustion engine, wherein the amount of urea water supplied is reduced by increasing the degree of restriction for limiting the amount of urea water supplied as the estimated sulfur poisoning amount increases. The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
Comprising sulfur poisoning estimation means for estimating the sulfur poisoning amount of the selective reduction catalyst,
The urea water supply control means includes
An exhaust gas purification apparatus for an internal combustion engine, characterized in that as the estimated amount of sulfur poisoning increases, the supply time of urea water is reduced to reduce the supply amount of urea water. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3,
The catalyst is
A NOx storage catalyst that stores NOx when the exhaust air-fuel ratio is a lean atmosphere and reduces and purifies NOx stored when the exhaust air-fuel ratio is a stoichiometric or rich atmosphere;
The reproducing means includes
An exhaust gas purifying apparatus for an internal combustion engine, characterized in that it is means for raising the temperature of the NOx storage catalyst. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 4,
A catalyst temperature grasping means for detecting a temperature state of the selective reduction catalyst;
The poisoning recovery means includes
Determining the mode of sulfur poisoning based on information including the temperature status of the selective reduction catalyst grasped by the catalyst temperature grasping means;
The urea water supply control means includes
An exhaust emission control device for an internal combustion engine, wherein the degree of restriction of the supply of urea water is controlled in accordance with the aspect of sulfur poisoning determined by the poisoning recovery means. The exhaust gas purification apparatus for an internal combustion engine according to claim 5,
Said sulfur poisoning embodiment comprises an ammonium salt,
The urea water supply control means includes
The urea water supply amount is limited so as to increase the degree of restriction of the urea water supply as the amount of poisoning of the ammonium salt relative to the total amount of the sulfur poisoning increases. An exhaust purification device for an internal combustion engine. A selective reduction catalyst provided in an exhaust passage of the internal combustion engine for reducing and purifying NOx contained in the exhaust;
Urea water supply means for supplying urea water to the exhaust passage on the upstream side of the selective reduction catalyst;
Comprising sulfur poisoning determination means for determining sulfur poisoning of the selective reduction catalyst,
The urea water supply means includes
An exhaust gas purification apparatus for an internal combustion engine, wherein the supply amount of the urea water supplied from the urea water supply means is limited according to the sulfur poisoning estimated by the sulfur poisoning determination means.

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