JP2018141411A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine capable of suppressing occurence of HC slip even when cooling addition processing is performed during execution of desorption processing.SOLUTION: A control device 80 of an exhaust emission control device executes desorption processing for desorbing a sulfur compound accumulated on a NSR catalyst by making an air fuel ratio of an exhaust gas flowing into the NSR catalyst 20 in a state of increasing a temperature of the NSR catalyst 20 to a desorption temperature to desorb the sulfur compound accumulated on the NSR catalyst 20, richer than a theoretical air fuel ratio, and cooling addition processing for cooling an addition valve 35 by injecting an engine fuel from the addition valve 35 disposed on an exhaust passage 14. The control device 80 adjusts an amount of the fuel injected from a cylinder injection valve 11 so that the sum of the amount of the fuel supplied to the exhaust gas from the cylinder injection valve 11 and an amount of the fuel injected from the addition valve 35 becomes smaller than an amount of the fuel causing occurrence of HC slip in the NSR catalyst 20 when executing the cooling addition processing during executing the desorption processing.SELECTED DRAWING: Figure 1

Description

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

  Some exhaust gas purification apparatuses for internal combustion engines are equipped with a NOx storage reduction catalyst. In such an exhaust purification device, while combustion is being performed at an air-fuel ratio leaner than the stoichiometric air-fuel ratio in the internal combustion engine, NOx in the exhaust is occluded in the catalyst, and the air-fuel ratio of the air-fuel mixture combusted in the internal combustion engine is reduced. When the air-fuel ratio is temporarily rich, the NOx occluded by the catalyst is reduced and purified, thereby suppressing NOx discharge to the outside air.

  In the NOx occlusion reduction type catalyst, NOx and sulfur oxide (SOx) in the exhaust gas are occluded in the form of sulfur compounds such as sulfides. As the sulfur compound is deposited, the NOx occlusion capacity of the catalyst decreases, so-called sulfur poisoning occurs. For this reason, in the exhaust purification apparatus as described above, poisoning recovery control is performed to desorb sulfur compounds deposited on the catalyst. In this poisoning recovery control, the air-fuel ratio of the exhaust gas flowing into the catalyst is made richer than the stoichiometric air-fuel ratio in a state where the temperature of the catalyst is raised to a temperature necessary for desorption of sulfur compounds (for example, 600 ° C). Is performed to supply a reducing agent necessary for the sulfur compound elimination reaction to the catalyst (for example, Patent Document 1).

  In the desorption process, the catalyst is adjusted by adjusting the fuel injection amount of the in-cylinder injection valve that directly injects fuel into the cylinder and the fuel injection amount of the addition valve that is provided in the exhaust passage and adds fuel to the exhaust. The air-fuel ratio of the exhaust gas flowing into the engine is made richer than the stoichiometric air-fuel ratio.

  Here, during the execution of the desorption treatment, the temperature of the exhaust gas is raised to a temperature necessary for desorption of the sulfur compound, so that the addition valve provided in the exhaust passage is heated and the heat damage is caused to the addition valve. May occur. Therefore, for example, as described in Patent Document 2, when there is a concern about a high temperature of the addition valve, a so-called cooling addition process is performed in which the addition valve is cooled by injecting fuel from the addition valve. It is conceivable to execute in the apparatus.

International Publication No. 2010/116535 Japanese Patent No. 4922899

  However, if the above cooling addition process is performed during the desorption process, the amount of unburned fuel contained in the exhaust gas becomes excessive, and as a result, a phenomenon in which the unburned fuel in the exhaust gas slips through the catalyst, a so-called phenomenon. HC slip may occur.

  The present invention has been made in view of such circumstances, and it is an object of the present invention to provide an exhaust gas purification apparatus for an internal combustion engine that can suppress the occurrence of HC slip even if a cooling addition process is performed during the desorption process. .

  An exhaust gas purification apparatus for an internal combustion engine that solves the above problems is applied to an internal combustion engine that includes an in-cylinder injection valve that directly injects fuel into a cylinder. The exhaust emission control device includes a NOx storage reduction type catalyst provided in an exhaust passage of the internal combustion engine, and an addition valve provided in an exhaust passage upstream of the catalyst to add engine fuel to the exhaust. And by enriching the air-fuel ratio of the exhaust gas flowing into the catalyst with a temperature higher than the stoichiometric air-fuel ratio in a state where the temperature of the catalyst is raised to a desorbable temperature at which the sulfur compound deposited on the catalyst is desorbed A desorption process for desorbing the sulfur compound deposited on the engine and a cooling addition process for cooling the addition valve by injecting engine fuel from the addition valve are executed. When the cooling addition process is executed during the desorption process, the exhaust gas purification apparatus is configured to supply the fuel amount supplied from the in-cylinder injection valve to the exhaust gas and the fuel amount added from the addition valve to the exhaust gas. The amount of fuel injected from the in-cylinder injection valve is adjusted so that the sum of the above and the amount of fuel that causes HC slip in the catalyst becomes smaller.

  According to this configuration, when the cooling addition process is performed during the desorption process, the amount of unburned fuel contained in the exhaust gas flowing into the catalyst is reduced so that the amount of unburned fuel is smaller than the amount of fuel causing HC slip. The amount of fuel injected from the injection valve is metered. Therefore, even if the desorption process and the cooling addition process are performed simultaneously, the occurrence of HC slip can be suppressed.

The schematic diagram which shows the structure of one Embodiment of the exhaust gas purification apparatus of an internal combustion engine. The time chart which shows the embodiment of the poisoning recovery | restoration control in the embodiment. The time chart which shows the drive signal of the addition valve in the embodiment. The flowchart which shows a series of processing procedures implemented when performing the detachment | desorption process in the embodiment. 6 is a time chart showing the transition of the pre-catalyst exhaust air-fuel ratio during execution of the desorption process of the same embodiment. The time chart which shows transition of the before-catalyst exhaust air-fuel ratio in execution of the desorption process in the modification of the embodiment.

  Hereinafter, an embodiment of an exhaust gas purification apparatus for an internal combustion engine will be described with reference to FIGS. The exhaust purification device of this embodiment is applied to a compression ignition type internal combustion engine that burns fuel injected into a cylinder by self-ignition by compression, so-called diesel engine.

  As shown in FIG. 1, an internal combustion engine 10 to which the exhaust purification system of this embodiment is applied is provided with a plurality of in-cylinder injection valves 11 that directly inject fuel into the cylinder. The intake passage of the internal combustion engine 10 is provided with an intake throttle valve that adjusts the amount of air taken into the cylinder.

  The exhaust passage 14 of the internal combustion engine 10 is provided with a NOx storage reduction catalyst (hereinafter referred to as NSR catalyst) 20. The NSR catalyst 20 stores surrounding nitrogen oxides in an oxidizing atmosphere, while releasing the stored nitrogen oxides in a reducing atmosphere for reduction purification.

  An electromagnetically driven addition valve 35 for adding the fuel of the internal combustion engine 10 to the exhaust is installed in a portion of the exhaust passage 14 upstream of the NSR catalyst 20. The addition valve 35 is provided with a water-cooling type cooling device 60 that shares the cooling water of the internal combustion engine 10.

  In the vicinity of the exhaust inlet of the NSR catalyst 20 in the exhaust passage 14, a temperature sensor 73 that detects the temperature of exhaust gas flowing into the NSR catalyst 20 (hereinafter referred to as exhaust temperature THE) and exhaust gas flowing into the NSR catalyst 20. An air-fuel ratio sensor 74 for detecting the air-fuel ratio (hereinafter referred to as pre-catalyst exhaust air-fuel ratio AF1) is installed.

  The internal combustion engine 10 is provided with various sensors in addition to the above sensors. For example, an air flow meter 70 that detects the intake air amount GA, a crank angle sensor 71 that detects the engine rotational speed NE, a water temperature sensor 72 that detects the cooling water temperature THW that is the temperature of the cooling water that cools the internal combustion engine 10, and the like. Is provided.

  The internal combustion engine 10 includes a control device 80. The control device 80 includes a central processing unit that performs various types of arithmetic processing, a read-only memory that stores control programs and data, a memory that temporarily stores arithmetic results of the central processing unit, an input port, and an output. It has a port. The output signals of the various sensors described above are input to the input port of the control device 80. In addition, a drive circuit for various devices such as the in-cylinder injection valve 11 and the addition valve 35 is connected to the output port of the control device 80.

  The control device 80 performs various controls such as fuel injection control for controlling the fuel injection amount and fuel injection timing of the in-cylinder injection valve 11 and exhaust purification control for suitably performing exhaust purification by the NSR catalyst 20.

  In such an internal combustion engine 10, while combustion is being performed in a state where the air-fuel ratio of the air-fuel mixture is larger than the stoichiometric air-fuel ratio ST, the value of the pre-catalyst exhaust air-fuel ratio AF1 becomes a value larger than the value of the stoichiometric air-fuel ratio ST. In the NSR catalyst 20 at this time, NOx in the exhaust is occluded, so that release of NOx to the outside air is suppressed. However, the amount of NOx that can be stored in the NSR catalyst 20 is limited. Therefore, in the exhaust purification device of the present embodiment, before the NOx storage amount of the NSR catalyst 20 reaches the limit, post injection is performed from the in-cylinder injection valve 11 and fuel is supplied from the in-cylinder injection valve 11 to the exhaust. As a result, the air-fuel ratio of the exhaust gas flowing into the NSR catalyst 20 is made richer than the stoichiometric air-fuel ratio ST, and the reducing agent (fuel) is supplied to the NSR catalyst 20. Then, using the supplied reducing agent, the stored NOx is released from the NSR catalyst 20 to perform NOx reduction processing for reduction purification. In addition, when the fuel supply to the exhaust by post injection is insufficient, the fuel addition from the addition valve 35 is also used.

  On the other hand, sulfur oxide (SOx) is contained in the fuel, and the NSR catalyst 20 also stores fuel-derived sulfur oxide (SOx) together with NOx in an oxidizing atmosphere. The SOx at this time is stored in the NSR catalyst 20 in the form of a sulfur compound such as sulfate. The sulfur compound stored in the NSR catalyst 20 is not desorbed from the NSR catalyst 20 under the conditions during the NOx reduction treatment. Therefore, sulfur compounds gradually accumulate on the NSR catalyst 20, and if left untreated, a phenomenon in which the NOx storage capacity of the NSR catalyst 20 decreases, so-called sulfur poisoning, occurs. Therefore, the control device 80 performs sulfur recovery control for desorbing the sulfur compound deposited on the NSR catalyst 20.

FIG. 2 shows an embodiment of sulfur recovery control.
The control device 80 accumulates on the NSR catalyst 20 based on the amount of fuel supplied to the exhaust, the temperature of the NSR catalyst 20 determined from the exhaust temperature THE, the exhaust flow rate determined from the intake air amount GA, and the like. The amount of sulfur compound (hereinafter referred to as sulfur deposition amount) is calculated.

  When the sulfur accumulation amount S reaches a predetermined start determination value S1 at time t1 in the same figure, poisoning recovery control is started. When poisoning recovery control is started, first, fuel addition from the addition valve 35 is executed, so that the temperature of the NSR catalyst 20 is raised to a detachable temperature at which the sulfur compound deposited on the NSR catalyst 20 is desorbed. For this purpose, a temperature raising process is performed.

  At time t2, when the temperature of the NSR catalyst 20 becomes equal to or higher than the desorbable temperature and the temperature raising process is completed, the desorption process is started. This desorption process ends once at time t3 when a predetermined execution time DT elapses. Thereafter, the desorption process is started again at time t4 when a predetermined rest period RT has elapsed. Thereafter, the desorption process is repeatedly executed with the rest period RT until the poisoning recovery control is completed.

  When the desorption process is started, post injection from the in-cylinder injection valve 11 is executed, so that the temperature of the NSR catalyst 20 is increased to the desorbable temperature by the temperature increase process. The pre-catalyst exhaust air-fuel ratio AF1 is made richer than the theoretical air-fuel ratio ST, and fuel as a reducing agent is supplied to the NSR catalyst 20. The fuel supply to the NSR catalyst 20 starts desorption of sulfur compounds from the NSR catalyst 20.

  Note that, during the desorption process, the amount of fuel supplied to the NSR catalyst 20 can be increased as the degree of enrichment of the pre-catalyst exhaust air-fuel ratio AF1 is increased. However, if the pre-catalyst exhaust air-fuel ratio AF1 is excessively enriched, HC slip occurs in the NSR catalyst 20, and white smoke may be discharged from the end of the exhaust passage 14 to the outside air, for example. Therefore, when the minimum air-fuel ratio that can suppress the occurrence of HC slip in the NSR catalyst 20 is the limit air-fuel ratio LT, the exhaust air-fuel ratio exceeds the limit air-fuel ratio LT during the desorption process. Therefore, it is necessary to adjust the amount of unburned fuel contained in the exhaust gas so that the fuel does not become rich. Therefore, in this embodiment, the basic post-injection amount QPb when the air-fuel ratio of the exhaust gas flowing into the NSR catalyst 20 becomes the limit air-fuel ratio LT is obtained through a preliminary experiment or the like, and the basic post-injection thus obtained is obtained. The amount QPb is set as the post injection amount during execution of the desorption process.

  Then, during the execution period of each desorption process (t2 to t3, t4 to t5, t6 to t7, t8 to t9), the value of the sulfur accumulation amount S depends on the desorption amount of the sulfur compound from the NSR catalyst 20. Will be reduced. Then, at the time t9 when the value of the sulfur accumulation amount S decreases to the end determination value S3 (for example, set to “0” in the present embodiment), the poisoning recovery control is ended.

  On the other hand, since the addition valve 35 is provided in the exhaust passage 14 as described above, the temperature of the addition valve 35 increases due to exposure to the exhaust. If the temperature is excessively high, the addition valve 35 may be thermally damaged. Therefore, the control device 80 performs a cooling addition process for suppressing the temperature increase of the addition valve 35.

  As shown in FIG. 3, when such cooling addition processing is performed, intermittent addition is performed in which fuel is periodically and repeatedly injected from the addition valve 35 to the exhaust. When this intermittent addition is performed, the addition valve 35 is energized only during a predetermined drive time τ for each drive interval time Tint that is variably set according to the temperature state of the addition valve 35. The drive time τ is a time for causing the addition valve 35 to perform the valve opening operation by holding the drive signal output from the control device 80 toward the drive circuit of the addition valve 35 in the “ON” state. A time (for example, a minimum value that can be set as the drive time of the addition valve 35) that can suppress the fuel consumption as much as possible while ensuring the cooling effect of the valve 35 is set. Further, as the degree of cooling request of the addition valve 35 is higher, the value of the drive interval time Tint is shortened, so that the amount of fuel injected from the addition valve 35 per unit time increases, and thereby the addition valve 35 due to fuel addition. The cooling effect is enhanced.

  By the way, if the cooling addition process of the addition valve 35 is executed during the above-described desorption process, both the post-injection fuel and the cooling addition process fuel are supplied to the exhaust gas, so the amount of unburned fuel contained in the exhaust gas As a result, HC slip may occur. Therefore, the exhaust purification apparatus of this embodiment is configured to suppress the occurrence of such inconvenience by executing a series of processing procedures shown in FIG. Note that the control device 80 performs the processing procedure shown in FIG. 4 until the internal combustion engine 10 is started after the internal combustion engine 10 is started.

  As shown in FIG. 4, when this process is started, it is first determined whether or not there is a request for execution of poisoning recovery control (S100). In this step S100, when the sulfur accumulation amount S has reached the start determination value S1, it is determined that there is a request for execution of poisoning recovery control. And when there is no execution request | requirement of poisoning recovery control (S100: NO), the process of step S100 is repeatedly performed.

  On the other hand, when there is a request for execution of poisoning recovery control (S100: YES), it is determined whether or not the above-described temperature raising process has ended (S110). In this step S110, when the temperature of the NSR catalyst 20 is equal to or higher than the desorbable temperature, it is determined that the temperature raising process has been completed. When the temperature raising process is not completed (S110: NO), the process of step S110 is repeatedly executed.

  On the other hand, when the temperature raising process is completed (S110: YES), the predicted maximum temperature Tm of the addition valve 35 during the execution of the desorption process is calculated (S120). . In step S120, the predicted maximum temperature Tm is calculated from the current cooling water temperature THW, the current exhaust temperature THE, the current intake air amount, the target exhaust temperature during the desorption process, the target intake air amount during the desorption process, and the like. Is calculated.

  Next, it is determined whether or not the calculated predicted maximum temperature Tm exceeds the allowable upper limit temperature Tc (S130). The allowable upper limit temperature Tc is set to a maximum temperature at which the occurrence of heat damage due to the high temperature of the addition valve 35 can be suppressed. When the predicted maximum temperature Tm exceeds the allowable upper limit temperature Tc (S130: YES), the total cooling addition amount CAT during the desorption process is set (S140). The total cooling addition amount CAT is obtained when the above-described cooling addition process is performed during the desorption process, thereby suppressing the maximum temperature of the addition valve 35 during the desorption process to the allowable upper limit temperature Tc. This is the total amount of cooling addition required per desorption treatment. The relationship between the total cooling addition amount CAT and the predicted maximum temperature Tm is obtained through a prior experiment or the like so that the total cooling addition amount CAT increases as the predicted maximum temperature Tm increases. When the total cooling addition amount CAT is set in this way, the total cooling addition amount CAT is divided by the amount of fuel injected from the addition valve 35 within the driving time τ (hereinafter referred to as a single fuel amount CQ). Thus, the number of times of fuel addition during the desorption process is obtained. A value obtained by dividing the execution time DT by the number of times of fuel addition is set as the drive interval time Tint when the cooling addition is executed during the desorption process.

  Next, the post-injection amount QPD at the time of reduction is calculated based on the fuel amount of cooling addition (S150). In step S150, the post-injection amount QPD at the time of reduction is calculated as follows.

  As shown in FIG. 5, the amount of fuel supplied to the exhaust when the post-injection with the basic post-injection amount QPb is performed for the time T1 corresponding to one drive time τ when the cooling addition is performed is the first fuel. An amount Q1 is set, and a fuel amount obtained by subtracting the single fuel amount CQ at the time of cooling addition from the first fuel amount Q1 is set as a second fuel amount Q2. Then, a post injection amount that can supply the second fuel amount Q2 to the exhaust gas within the time T1 is obtained in advance, and the post injection amount corresponding to the second fuel amount Q2 is the post-reduction amount QPD when decreasing. Set as

  Next, the desorption process based on the calculated post-injection amount QPD during reduction is executed once (S160). In the present embodiment, as shown in FIG. 5, the post-injection amount during the execution period of the desorption process is fixed to the post-injection amount QPD when decreasing. Then, during the desorption process, cooling addition of the addition valve 35 is also performed (S170).

  In the previous step S130, when the predicted maximum temperature Tm is equal to or lower than the allowable upper limit temperature Tc (S130: NO), the desorption process with the basic post injection amount QPb is executed (S220).

  When the process of step S170 or the process of step S220 is executed, it is next determined whether or not the poisoning recovery control is completed (S180). In this step S180, it is determined that the poisoning recovery control has ended when the sulfur accumulation amount S has decreased to the end determination value S3. When it is determined that the poisoning recovery control has ended (S180: YES), the process returns to step S100.

  On the other hand, when the poisoning recovery control has not ended (S180: NO), it is determined whether or not the desorption process has been executed a predetermined number of times N (S190). As the specified number N, the number of executions of the desorption process corresponding to the time required for the coolant temperature THW to change to such an extent that the calculation of the predicted maximum temperature Tm is affected is set.

  Then, when the desorption process has not been executed for the specified number N yet (S190: NO), the desorption process is stopped only during the pause period RT (S200), and then the processes after step S160 are executed again. . That is, in this case, the desorption process and the cooling addition based on the currently set post-injection amount QPD at the time of reduction are performed again.

  On the other hand, when the desorption process is executed for the specified number N (S190: YES), the desorption process is stopped only during the pause period RT (S210), and then the processes after step S120 are executed again. That is, in this case, the predicted maximum temperature Tm is calculated again, and when the calculated predicted maximum temperature Tm is equal to or lower than the allowable upper limit temperature Tc (S130: NO), the desorption process using the basic post injection amount QPb is performed. On the other hand, the cooling addition process of the addition valve 35 is not executed. Further, when the calculated predicted maximum temperature Tm exceeds the allowable upper limit temperature Tc (S130: YES), the total cooling addition amount CAT and the post-injection amount QPD at the time of reduction are set based on the newly calculated predicted maximum temperature Tm. The renewal is performed, and the desorption process by the updated post injection amount QPD at the time of the decrease and the cooling addition of the addition valve 35 by the updated total cooling addition amount CAT are executed.

According to this embodiment described above, the following operations and effects can be obtained.
(1) As shown in FIG. 5 above, when the cooling addition process of the addition valve 35 is executed during the desorption process, the amount of fuel supplied from the in-cylinder injection valve 11 to the exhaust gas (second fuel quantity) The sum of Q2) and the amount of fuel added to the exhaust from the addition valve 35 (single fuel amount CQ) is smaller than the amount of fuel that causes HC slip in the NSR catalyst 20 (amount exceeding the first fuel amount Q1). In addition, the amount of fuel injected from the in-cylinder injection valve 11 (post injection amount) is adjusted. As described above, when the cooling addition process is performed during the desorption process, the amount of unburned fuel contained in the exhaust gas flowing into the NSR catalyst 20 is reduced so that the amount of unburned fuel is smaller than the amount of fuel causing HC slip. The amount of fuel injected from the injection valve 11 (post injection amount) is adjusted. Therefore, even if the desorption process and the cooling addition process are performed simultaneously, the occurrence of HC slip can be suppressed.

  (2) If the pre-catalyst exhaust air-fuel ratio AF1 during the desorption process is excessively rich, the efficiency of desorbing the sulfur compound from the NSR catalyst 20 may be reduced. In this regard, according to the present embodiment, even if the desorption process and the cooling addition process are performed at the same time, the pre-catalyst exhaust air-fuel ratio AF1 is prevented from being excessively enriched beyond the limit air-fuel ratio LT. Therefore, it is possible to suppress a decrease in the efficiency of desorbing the sulfur compound from the NSR catalyst 20.

  (3) When the desorption process has not been executed the specified number N (S190: NO in FIG. 5), the processes after step S160 are executed again. That is, the detachment process is performed again while maintaining the currently set post-injection amount QPD during reduction. Therefore, the calculation load of the control device 80 can be reduced as compared with the case of calculating the post-injection amount QPD during reduction every time the desorption process is performed once.

In addition, the said embodiment can also be changed and implemented as follows.
-The process of step S190 and step S200 shown in previous FIG. 5 is abbreviate | omitted. Then, when a negative judgment is made at step S180, the processing after step S210 may be executed. That is, the post-injection amount QPD at the time of reduction may be calculated every time the desorption process is executed once. Even in this case, effects other than the above (3) can be obtained.

  In the above-described embodiment, in order to inject fuel corresponding to the total cooling addition amount CAT from the addition valve 35 within the desorption processing execution time DT, the drive interval time Tint is determined according to the total cooling addition amount CAT. Was changed. In addition, by changing the drive time τ of the addition valve 35 according to the total cooling addition amount CAT, the fuel corresponding to the total cooling addition amount CAT is added from the addition valve 35 within the execution time DT of the desorption process. You may make it be injected.

  In step S160 of the above embodiment, when the desorption process based on the post-injection amount QPD during reduction is executed, as shown in FIG. 5, the post injection amount during the execution period of the desorption process is reduced. The post injection amount was fixed to QPD.

  In addition, as shown in FIG. 6, when the fuel injection of the addition valve 35 by the cooling addition is being executed during the execution of the desorption process, the post injection amount is set to the post injection amount QPD at the time of reduction. On the other hand, when the fuel injection of the addition valve 35 by cooling addition is not executed (a period excluding the drive time τ within the drive interval time Tint shown in FIG. 3), the post injection amount is changed to the basic post injection amount QPb. You may make it set to. In this case, since the pre-catalyst exhaust air-fuel ratio AF1 is maintained at the limit air-fuel ratio LT during the desorption process execution period, the post-injection amount during the desorption process execution period is fixed to the post-deceleration amount QPD during reduction. Compared with the case where it does, the fluctuation | variation of the before-catalyst exhaust air-fuel ratio AF1 can be suppressed.

  In the above embodiment, post-injection is performed in order to make the air-fuel ratio of the exhaust gas flowing into the NSR catalyst 20 richer than the stoichiometric air-fuel ratio when performing the desorption process. In addition, a rich spike that temporarily enriches the air-fuel ratio of the air-fuel mixture may be implemented. Even in this case, the sum of the amount of fuel supplied from the in-cylinder injection valve 11 to the exhaust and the amount of fuel injected from the addition valve 35 is smaller than the amount of fuel causing HC slip in the NSR catalyst 20. By adjusting the amount of fuel injected from the injection valve 11, the effect (1) can be obtained.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... In-cylinder injection valve, 14 ... Exhaust passage, 20 ... NOx occlusion reduction type catalyst (NSR catalyst), 35 ... Addition valve, 60 ... Cooling device, 70 ... Air flow meter, 71 ... Crank angle sensor, 72 ... Water temperature sensor, 73 ... Temperature sensor, 74 ... Air-fuel ratio sensor, 80 ... Control device.

Claims (1)

Applied to an internal combustion engine having an in-cylinder injection valve that directly injects fuel into a cylinder, a NOx occlusion reduction type catalyst provided in an exhaust passage of the internal combustion engine, and provided in an exhaust passage upstream of the catalyst. And an addition valve for adding engine fuel to the exhaust,
The sulfur compound deposited on the catalyst was deposited on the catalyst by making the air-fuel ratio of the exhaust gas flowing into the catalyst richer than the stoichiometric air-fuel ratio in a state where the temperature of the catalyst was raised to the desorbable temperature. An exhaust purification device that performs a desorption process for desorbing a sulfur compound and a cooling addition process for cooling the addition valve by injecting engine fuel from the addition valve,
When the cooling addition process is performed during the desorption process, the sum of the amount of fuel supplied from the in-cylinder injection valve to the exhaust and the amount of fuel added from the addition valve to the exhaust is determined by the catalyst. An exhaust emission control device for an internal combustion engine, wherein the amount of fuel injected from the in-cylinder injection valve is adjusted so that the amount of fuel generated by HC slip becomes smaller.

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