JP2018087544A - 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: A supply amount of urea water is limited (reduced or stopped) in a situation that an exhaust temperature becomes sufficiently high due to the reduction of NOx when an air-fuel ratio is brought into a rich side, 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), and a sulfur component which is dissolved at a high temperature is dissolved, thus restoring the 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. An exhaust gas purification apparatus using a urea selective reduction system injects urea water into an exhaust passage provided with a selective reduction catalyst, so that urea water is decomposed by the heat of exhaust gas and ammonia is generated and generated. The ammonia reacts with NOx in the exhaust gas on the selective reduction catalyst, and NOx is reduced (purified) to 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, the state of sulfur poisoned by the selective reduction catalyst has a plurality of modes (sulfuric acid ammonium salt, copper sulfide), and some of them are adsorbed on the active site of the selective 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. Urea water supply means for supplying urea water to the exhaust passage on the upstream side, sulfur poisoning judgment means for judging sulfur poisoning of the selective reduction catalyst, and sulfur of the selective reduction catalyst by the sulfur poisoning judgment means When the poisoning is determined, a poisoning recovery means for supplying the urea water from the urea water supply means to the exhaust passage in order to recover sulfur poisoning of the selective reduction catalyst, and detecting an air-fuel ratio of the exhaust And a urea that limits the amount of urea water supplied by the poisoning recovery means when the air-fuel ratio of the exhaust gas is detected to be relatively rich by the air-fuel ratio detection means. With water supply control means And features.

  The present invention according to claim 1 comprises a selective reduction catalyst, poisoning recovery means for the selective reduction catalyst, urea water supply control means, and air / fuel ratio detection means. When it is detected that the fuel ratio has become relatively rich, NOx is reduced. Therefore, the selective reduction catalyst recovers sulfur poisoning by supplying urea water (including NOx purification). (Not done), restrict (reduce) the supply of urea water by poison recovery means, suppress the formation of sulfur components (ammonium salt of sulfuric acid) that decompose at low temperatures, and keep the exhaust temperature high It promotes the decomposition of sulfur components (copper sulfate) that decompose at high temperatures.

  As a result, in a situation where the air-fuel ratio becomes relatively rich and NOx decreases, the supply of urea water is suppressed (decrease in exhaust gas temperature is suppressed), the exhaust gas temperature is maintained high, and decomposition occurs at a high temperature. Sulfur poisoning (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, 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 internal combustion engine exhaust gas purification apparatus according to a second aspect of the present invention is the internal combustion engine exhaust gas purification apparatus according to the first aspect, wherein the urea water supply control means is the air-fuel ratio detection means and the air-fuel ratio of the exhaust gas. Is detected to be rich with respect to the air-fuel ratio during normal operation, the amount of urea water supplied by the poisoning recovery means is limited according to the detected value of the air-fuel ratio. It is characterized by that.

  In the present invention according to claim 2, when it is detected by the air-fuel ratio detection means that the air-fuel ratio of the exhaust gas has become richer than the air-fuel ratio during normal operation, NOx decreases. Therefore, the selective reduction catalyst limits (does not perform) the recovery of sulfur poisoning (including NOx purification) by supplying urea water, and limits the urea water supply by the poisoning recovery means according to the value of the air-fuel ratio. (Adjust), suppress the generation of sulfur component (sulfuric acid ammonium salt) that decomposes at low temperature, promote the decomposition of sulfur component (copper sulfate) that decomposes at high temperature, keeping the exhaust temperature high .

  As a result, in a situation where the air-fuel ratio becomes relatively rich with respect to the air-fuel ratio during normal operation and NOx decreases, the supply of urea water is suppressed (a decrease in exhaust temperature is suppressed), and the exhaust gas is reduced. The sulfur component (copper sulfate) which is maintained at a high temperature and decomposes 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.

  An exhaust gas purification apparatus for an internal combustion engine according to a third aspect of the present invention is the exhaust gas purification apparatus for an internal combustion engine according to the second aspect, wherein the exhaust gas purification apparatus is provided in the exhaust passage upstream of a portion to which the urea water is supplied. NOx occlusion catalyst that stores NOx when exhaust air-fuel ratio is lean, and reduces and purifies NOx occluded when exhaust air-fuel ratio is stoichiometric or rich atmosphere, and NOx occlusion catalyst by adding fuel component to exhaust Enrichment means for raising the temperature of the fuel, and the air-fuel ratio detection means detects the air-fuel ratio of the exhaust when the fuel component is added by the enrichment means and the NOx storage catalyst is heated. Features.

  In the present invention according to claim 3, when the fuel component is added from the enrichment means to raise the temperature of the NOx storage catalyst and the air-fuel ratio becomes richer than the air-fuel ratio during normal operation, the urea water Is suppressed and the exhaust temperature is kept high. The situation in which the fuel component is added from the enrichment means includes a time when the NOx storage catalyst is regenerated or a rich purge in which the fuel component is intermittently supplied.

  According to a fourth aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the third aspect of the present invention, wherein the internal combustion engine exhaust gas purification apparatus comprises a catalyst temperature grasping means for detecting a temperature state of the selective reduction catalyst, The poisoning recovery means determines the sulfur poisoning mode based on information including the temperature state of the selective reduction catalyst grasped by the catalyst temperature grasping means, and the urea water supply control means The degree of restriction of the supply of the urea water is controlled according to the aspect of sulfur poisoning determined by the poison recovery means.

  In the present invention according to claim 4, 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 are many sulfur components decomposed in the low temperature range (ammonium salt of sulfuric acid), increase the restriction of urea water supply to reduce the supply amount of urea water (suppress the discharge of ammonia), Suppresses the exhaust temperature drop due to latent heat, keeps the exhaust temperature high, and decomposes sulfur components that are decomposed at high temperatures.

  The exhaust gas purification apparatus for an internal combustion engine of the present invention according to claim 5 is the exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein the poisoning recovery means decomposes the ammonium salt of sulfuric acid with the selective reduction catalyst. Determining the state of sulfur poisoning by determining a first temperature that is higher than the first temperature and a second temperature that is higher than the first temperature and decomposing copper sulfate, and controlling the urea water supply The means controls the degree of restriction of the supply of the urea water based on a history of a state where the temperature of the selective reduction catalyst is equal to or higher than the first temperature and lower than the second temperature. To do.

  In the present invention according to claim 5, the history of the temperature of the selective reduction catalyst is grasped, and the history of the state (state in which the ammonium salt of sulfuric acid is decomposed) that is higher than the first temperature and lower than the second temperature is Control the degree of restriction of urea water supply. That is, by grasping the temperature state of the selective reduction catalyst, the ammonium salt of sulfuric acid and the copper sulfate are classified, and the degree of restriction of the supply of urea water is changed.

  The internal combustion engine exhaust gas purification apparatus according to claim 6 is the internal combustion engine exhaust gas purification apparatus according to claim 5, wherein the urea water supply control means is configured such that the temperature of the selective reduction catalyst is the first The degree of restriction of the supply of the urea water is increased as the time that is higher than the temperature and lower than the second temperature becomes longer.

  In the present invention according to claim 6, when the temperature of the state in which the ammonium salt of sulfuric acid is decomposed is long, the degree of restriction of the supply of urea water is increased as the state in which ammonium sulfate is decomposed (the supply of urea water is reduced). Greatly reduced), the exhaust temperature is kept low and the exhaust temperature is kept high, and the copper sulfate decomposed in the high temperature region is decomposed to recover sulfur poisoning.

  An exhaust gas purification apparatus for an internal combustion engine according to a seventh aspect of the present invention is the exhaust gas purification apparatus for an internal combustion engine according to any one of the third to sixth aspects, wherein the enrichment means is fuel for exhaust gas. It is a means for regenerating the NOx storage catalyst by adding a component to raise the temperature of the NOx storage catalyst.

  In the present invention according to claim 7, when the regeneration of the NOx storage catalyst is performed, when the fuel component is added and the air-fuel ratio becomes rich, the supply degree of urea water is increased by increasing the degree of restriction of urea water supply. Reduce the amount.

  An exhaust gas purification apparatus for an internal combustion engine according to an eighth aspect of the present invention is the exhaust gas purification apparatus for an internal combustion engine according to any one of the third to seventh aspects, wherein the enrichment means is a fuel for exhaust gas. It is means for intermittently releasing NOx from the NOx storage catalyst by adding components intermittently to raise the temperature of the NOx storage catalyst.

  In the present invention according to claim 8, when purging the NOx storage catalyst, when the fuel component is intermittently added and the air-fuel ratio becomes rich, the degree of restriction of urea water supply is increased to increase the urea concentration. Reduce water supply.

  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 a flowchart explaining basic operation | movement 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. It is a graph explaining the time-dependent change of the air fuel ratio and the supply amount of urea water. It is a graph explaining the time-dependent change of the air fuel ratio and the supply amount 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, and a large amount of ammonium salt of sulfuric acid is produced, and the temperature is low (for example, about 400 ° C. to 550 ° C .: first temperature). It decomposes into nitrogen, sulfur dioxide, and water to decompose the ammonium salt of sulfuric acid to recover sulfur poisoning of the selective reduction catalyst.

  When it is detected that the air-fuel ratio has become relatively rich (when the air-fuel ratio has become rich with respect to the air-fuel ratio during normal operation), the supply amount of urea water is limited. (Decrease and stop), suppress the exhaust temperature drop due to latent heat, maintain the exhaust temperature at a high temperature (for example, about 600 ° C. to 650 ° C .: the second temperature), copper in a high temperature atmosphere It decomposes the sulfate of the catalyst 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.

  Note that the air-fuel ratio at the time of normal operation is an air-fuel ratio in a state where fuel is supplied for traveling, and the value of the air-fuel ratio varies depending on the operation state. Except during normal operation, this is a state in which fuel is supplied separately from running, for example, a case where additional fuel is supplied to activate the catalyst.

  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 includes a purification device 6 having a NOx storage catalyst 4 and a diesel particulate 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 filter 5 are poisoned by sulfur, additional fuel is injected into the exhaust pipe 2 (riching means), and the NOx storage catalyst 4 and the diesel particulate collection. The filter 5 is heated to remove sulfur and regenerate (regeneration operation). Further, additional fuel is intermittently injected into the exhaust pipe 2 (riching means), the NOx of the NOx storage catalyst 4 is purged, and the particulates of the diesel particulate collection filter 5 are purged (purge operation).

  A urea selective reduction (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.

  An air-fuel ratio detection sensor 15 as an air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust gas is provided in the passage on the downstream side of the purification device 6 on the upstream side of the urea water injection valve 12. As the air-fuel ratio detection sensor 15, for example, an oxygen sensor that determines the theoretical air-fuel ratio by detecting oxygen or a linear air-fuel ratio sensor that continuously detects the air-fuel ratio can be applied.

  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.

  When the air-fuel ratio detection sensor 15 detects that the air-fuel ratio of the exhaust gas is relatively rich, the supply amount of urea water is limited. Specifically, as will be described later, when the air-fuel ratio of the exhaust gas becomes relatively rich, NOx decreases, so the supply of urea water is limited and sulfur poisoning due to the supply of urea water Recovery (including NOx purification) is restricted (not performed), the exhaust temperature is prevented from lowering due to latent heat, and the sulfur component (copper sulfate) that decomposes at a high temperature is maintained while maintaining the exhaust temperature high. Facilitate. At this time, the degree of restriction of the supply of urea water is adjusted according to the temperature state (history) of the selective reduction catalyst 11.

  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, when the NOx storage catalyst 4 and the diesel particulate filter 5 are poisoned by sulfur, the control means 10 is supplied with additional fuel to supply the NOx storage catalyst 4 and the diesel particulate collection filter. Regeneration means 25 for performing a regeneration operation by raising the temperature of 5 is provided. Further, the regeneration unit 25 intermittently supplies additional fuel to raise the temperature of the NOx storage catalyst 4 and perform the NOx purge operation of the NOx storage catalyst 4.

  Information about 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.

  When additional fuel is supplied by the regeneration means 25, the air-fuel ratio detection sensor 15 detects that the air-fuel ratio has become rich. When it is detected that the air-fuel ratio has become rich, the amount of urea water supplied (supplied for poisoning recovery) in accordance with a command from the poisoning recovery means 23 is limited.

  For example, when the NOx storage catalyst 4 is being regenerated, the air-fuel ratio of the exhaust gas becomes rich and the exhaust gas temperature is raised. Therefore, the supply amount of urea water is limited to reduce (stop) the exhaust gas due to latent heat. Reduces temperature drop. By maintaining the exhaust temperature high, for example, decomposition of copper sulfate is promoted. The state of restriction of the supply amount of urea water is set according to the temperature history (sulfur poisoning mode) of the selective reduction catalyst 11 (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). To figure out.

  In other words, regarding the sulfur poisoning of the selective reduction catalyst 11, the situation of the sulfur component (sulfuric acid ammonium salt) decomposed in the low temperature region and the sulfur component (copper sulfate salt) decomposed in the high temperature region is determined from the temperature history. However, if there are many sulfur components (ammonium salt of sulfuric acid) decomposed in a low temperature region, the supply amount of urea water is reduced by increasing the degree of restriction of supply of urea water.

  Specifically, according to the history of the state in which the selective reduction catalyst 11 was at or above the first temperature (for example, about 400 ° C. to 550 ° C.) and less than the second temperature (for example, about 600 ° C. to 650 ° C.), Change the degree of restriction of urea water supply. For example, the degree of restriction on the supply of urea water is increased as the ammonium salt of sulfuric acid is in a state where a large amount of ammonium salt is decomposed as the time of the state that is higher than the first temperature and lower than the second temperature becomes longer. And greatly reduce the urea water supply.

  By reducing the supply of urea water (by stopping), the exhaust temperature is kept low by suppressing the exhaust temperature drop due to latent heat, and the copper sulfate decomposed in the high temperature range is decomposed. By reducing the supply of urea water (by stopping), the discharge of ammonia is suppressed.

  That is, the temperature of the selective reduction catalyst 11 is grasped, the ammonium salt of sulfuric acid and the copper sulfate are classified, the degree of restriction of the supply of urea water is changed, and the exhaust temperature is suppressed by suppressing the decrease in the exhaust temperature. Is maintained at a high temperature, and the sulfur sulfate is recovered by decomposing copper sulfate, which is decomposed at high temperatures.

  As described above, the urea water supply control means 24 restricts the supply of urea water when the regeneration means 25 is operated and the exhaust air temperature is rich and the exhaust gas temperature is raised. Then, the degree of restriction of the supply of urea water is controlled based on the temperature history information of the selective reduction catalyst 11. For example, when the decomposition of ammonium sulfate is increased, the supply of urea water is limited to reduce (stop) the supply, and the decrease in exhaust temperature due to latent heat is suppressed to promote 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, it is determined in step S4 whether or not the air-fuel ratio of the exhaust has become relatively rich. For example, during the regeneration operation of the NOx storage catalyst 4 (see FIG. 1), when additional fuel is supplied by the regeneration means 25 (see FIG. 2), the air-fuel ratio is rich by the air-fuel ratio detection sensor 15 (see FIG. 1). It is determined whether or not it has been detected that the vehicle has become the side. Alternatively, when the NOx purge operation of the NOx storage catalyst 4 (see FIG. 1) is performed, when additional fuel is supplied by the regeneration means 25 (see FIG. 2), the air-fuel ratio detection sensor 15 (see FIG. 1) It is determined whether or not it has been detected that the air-fuel ratio has become rich.

  If it is determined in step S4 that the air-fuel ratio of the exhaust gas has become relatively rich, NOx decreases, so the supply of urea water is limited in step S5.

  In step S5, the supply of urea water is restricted, and recovery from sulfur poisoning (including NOx purification) due to the supply of urea water is not performed, so that a decrease in exhaust temperature due to latent heat is suppressed, and the exhaust temperature is maintained high. It promotes the decomposition of sulfur components (copper sulfate) that decompose at high temperatures. At this time, the degree of restriction of the supply of urea water is adjusted according to the temperature state (history) of the selective reduction catalyst 11.

  For example, the time during which the selective reduction catalyst 11 (see FIG. 1) is at or above a first temperature (eg, about 400 ° C. to 550 ° C.) and below a second temperature (eg, about 600 ° C. to 650 ° C.). As the length of the water becomes longer, the supply of urea water is greatly reduced by increasing the degree of restriction of the supply of urea water, assuming that a large amount of the ammonium salt of sulfuric acid is decomposed.

  When limiting the supply amount of urea water in step S5, it is implemented based on the map shown in FIG.

  As shown in FIG. 4, when the detected air-fuel ratio becomes richer than the stoichiometric air-fuel ratio, the urea water supply amount is reduced (stopped) with respect to the normal supply amount. In other words, when the air-fuel ratio of the exhaust gas becomes richer, the state of NOx decreases, so the supply of urea water is restricted and the recovery of sulfur poisoning (including NOx purification) by the supply of urea water is restricted. (Not done) Suppresses the decrease in exhaust temperature due to latent heat, promotes the decomposition of sulfur components (copper sulfate) that decompose at a high temperature while maintaining the exhaust temperature high.

  The normal supply amount of urea water is set by setting 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 supplied amount is set as a 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.

  Returning to the flowchart of FIG. 3, when it is determined in step S4 that the air-fuel ratio of the exhaust gas is not relatively rich, or in step S5, the supply of urea water is limited (stopped) and the exhaust temperature decreases. When the sulfur poisoning recovery process is executed in a state where the S is suppressed, it is determined in step S6 whether or not the sulfur poisoning of the selective reduction catalyst 11 has been recovered. 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 S6 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 S6 that the sulfur poisoning of the selective reduction catalyst 11 has been recovered, the recovery end process is executed in step S7, and the process ends. That is, the information on the estimated sulfur poisoning amount is reset, and the sulfur poisoning recovery process is ended.

  Instead of the determination in step S6, it is also possible to shift to the sulfur poisoning recovery end process (step S7) using the sulfur poisoning recovery processing time as a threshold value.

  The supply amount of urea water according to the value of the air-fuel ratio detected by the air-fuel ratio detection sensor 15 (following the change in the air-fuel ratio) during the regeneration operation of the NOx storage catalyst 4 (see FIG. 1) and the NOx purge operation Can be limited.

  Based on FIGS. 5 and 6, the relationship between the air-fuel ratio and the urea water supply amount in the regeneration operation and NOx purge operation of the NOx storage catalyst 4 (see FIG. 1) will be described. FIG. 5 is a graph for explaining temporal changes in the air-fuel ratio and urea water supply amount during the regeneration operation, and FIG. 6 is a graph for explaining temporal changes in the air-fuel ratio and urea water supply amount during the NOx purge operation. It is.

  As shown in FIG. 5 (a), the regeneration operation of the NOx storage catalyst 4 (see FIG. 1) is started at time ts and additional fuel is supplied until the regeneration operation ends at time te. The air-fuel ratio is maintained in a range between the richer side and the slightly leaner side than the fuel ratio. As a result, the NOx storage catalyst 4 (see FIG. 1) is heated and regenerated.

  As shown in FIG. 5 (b), the supply of urea water is limited and reduced at time ts, and until the time te when the regeneration operation ends, according to the value of the air-fuel ratio (following the change of the air-fuel ratio). The supply amount of urea water is adjusted. That is, if the air-fuel ratio becomes rich, the supply amount of urea water is reduced according to the degree of change, and if it changes to the lean side, the supply amount is increased according to the degree of change.

  Since the supply amount of urea water is adjusted according to the value of the air-fuel ratio, during the regeneration operation of the NOx storage catalyst 4 (see FIG. 1), the supply of urea water can be limited by an optimal limit amount, and the minimum necessary amount The urea water can be supplied as long as possible.

  As shown in FIG. 6A, additional fuel is supplied from time t1 to time t2, and the NOx purge operation of the NOx storage catalyst 4 (see FIG. 1) is executed. Further, additional fuel is supplied from time t3 to time t4, and the NOx purge operation of the NOx storage catalyst 4 (see FIG. 1) is executed. For example, in contrast to the NOx purge operation from time t1 to time t2, in the NOx purge operation from time t3 to time t4, additional fuel is supplied so that the air-fuel ratio becomes rich. Then, in the NOx purge operation, additional fuel is supplied so that the air-fuel ratio becomes richer than the regeneration operation (so that the rich becomes deeper).

  As shown in FIG. 6 (b), the supply of urea water is limited and reduced between time t1 and time t2 and between time t3 and time t4, depending on the value of the air / fuel ratio (air / fuel ratio). The supply amount of urea water is adjusted following the change in That is, the restriction between time t1 and time t2 is greatly restricted between time t3 and time t4.

  Since the supply amount of urea water is adjusted according to the value of the air-fuel ratio, it is possible to limit the supply of urea water with an optimal limit amount during the NOx purge operation of the NOx storage catalyst 4 (see FIG. 1). Urea water can be supplied at a minimum.

  The exhaust purification device described above is in a state where NOx is reduced when the air-fuel ratio becomes rich during the regeneration operation of the NOx storage catalyst 4 (see FIG. 1) or during the NOx purge operation. The catalyst limits (does not perform) recovery of sulfur poisoning due to the supply of urea water (including NOx purification) and limits (decreases, stops) the supply amount of urea water, so sulfur that is decomposed at low temperatures Generation of the component (ammonium salt of sulfuric acid) is suppressed, and the exhaust temperature is kept high.

  As a result, when the air-fuel ratio becomes rich, the NOx decreases and the exhaust temperature becomes sufficiently high, so that the supply of urea water is suppressed (a decrease in the exhaust temperature due to latent heat is suppressed) and the temperature is high. The sulfur component to be decomposed (copper sulfate) is decomposed to restore 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 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)
2 exhaust pipe 3 exhaust purification device 4 NOx storage catalyst 5 diesel particulate filter 6 purification device 10 control means 11 selective reduction catalyst 12 urea water injection valve 13 temperature sensor 14 NOx sensor 15 air-fuel ratio detection sensor 21 sulfur poisoning estimation means 22 Sulfur poisoning determination means 23 poisoning recovery means 24 urea water supply control means 25 regeneration means 26 catalyst temperature grasping means

Claims (8)

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;
Sulfur poisoning determination means for determining sulfur poisoning of the selective reduction catalyst;
When the sulfur poisoning determination unit determines that the selective reduction catalyst is sulfur poisoned, the urea water supply unit supplies the urea water to the exhaust passage in order to recover the sulfur poisoning of the selective reduction catalyst. Poisoning recovery means,
Air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust;
Urea water supply control means for limiting the supply amount of the urea water by the poisoning recovery means when the air-fuel ratio detection means detects that the air-fuel ratio of the exhaust gas has become relatively rich. An exhaust emission control device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
The urea water supply control means includes
When it is detected by the air-fuel ratio detection means that the air-fuel ratio of the exhaust gas is richer than the air-fuel ratio during normal operation, the poisoning recovery means is determined according to the detected value of the air-fuel ratio. An exhaust purification device for an internal combustion engine, characterized in that the supply amount of the urea water is limited. The exhaust gas purification apparatus for an internal combustion engine according to claim 2,
Provided in the exhaust passage upstream of the portion to which the urea water is supplied, stores NOx when the exhaust air-fuel ratio is lean, and reduces and purifies NOx stored when the exhaust air-fuel ratio is stoichiometric or rich. NOx storage catalyst to
Enriching means for adding a fuel component to the exhaust to raise the temperature of the NOx storage catalyst;
The air-fuel ratio detection means includes
An exhaust gas purification apparatus for an internal combustion engine, wherein an air-fuel ratio of exhaust gas when the fuel component is added by the enrichment means and the NOx storage catalyst is heated is detected. The exhaust gas purification apparatus for an internal combustion engine according to claim 3,
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 4,
The poisoning recovery means includes
The sulfur poisoning is determined by determining a first temperature for decomposing the ammonium salt of sulfuric acid with the selective reduction catalyst and a second temperature higher than the first temperature for decomposing the copper sulfate. Determine the mode of
The urea water supply control means includes
The degree of restriction of the supply of the urea water is controlled based on a history of a state in which the temperature of the selective reduction catalyst is equal to or higher than the first temperature and lower than the second temperature. Exhaust purification equipment. The exhaust gas purification apparatus for an internal combustion engine according to claim 5,
The urea water supply control means includes
The degree of restriction of the supply of urea water is increased as the time during which the temperature of the selective reduction catalyst is equal to or higher than the first temperature and lower than the second temperature is increased. Exhaust purification device. The exhaust emission control device for an internal combustion engine according to any one of claims 3 to 6,
The enrichment means includes
An exhaust gas purification apparatus for an internal combustion engine, characterized in that the NOx storage catalyst is regenerated by adding a fuel component to exhaust gas to raise the temperature of the NOx storage catalyst. The exhaust emission control device for an internal combustion engine according to any one of claims 3 to 7,
The enrichment means includes
An exhaust gas purification apparatus for an internal combustion engine, characterized by intermittently releasing NOx from the NOx storage catalyst by intermittently adding a fuel component to exhaust gas to raise the temperature of the NOx storage catalyst.

Images