JP2014222062A - Exhaust purification device of internal combustion engine - Google Patents

Abstract

Kind Code: A1 The present invention suppresses generation of white smoke from sulfate produced from sulfur oxide deposited on an oxidation catalyst.
The reduction process is executed when the catalyst bed temperature is lower than the target temperature of the catalyst bed temperature in the burn-out process. When the burnout process execution condition is satisfied, the reduction process is executed, and the start timing of the burnout process is delayed until the sulfur oxide deposition amount on the oxidation catalyst becomes equal to or less than the allowable amount due to the execution of the reduction process.
[Selection] Figure 3

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine in which an oxidation catalyst and a filter for capturing particulate matter are provided in an exhaust passage.

  In an exhaust gas purification apparatus in which an exhaust gas oxidation catalyst and a filter are disposed in an exhaust passage, the components contained in the exhaust gas are oxidized and purified by the oxidation catalyst, and particulate matter is captured by the filter. . In such an exhaust purification device, when the amount of particulate matter trapped in the filter is larger than the allowable amount, fuel is added to the exhaust passage to raise the catalyst bed temperature, and the temperature of the filter is raised by the heat of the exhaust. The particulate matter is burned out.

  Further, the exhaust gas from the internal combustion engine contains sulfur oxides in addition to the components and particulate matter. If the state in which such sulfur oxides are adsorbed and deposited on the oxidation catalyst continues, the catalyst function may be lowered. For this reason, in the exhaust emission control device, in addition to the above-described treatment for burning out particulate matter, fuel is added to the exhaust passage to raise the bed temperature of the oxidation catalyst and place the oxidation catalyst in an environment with a low oxygen concentration. Thus, the sulfur oxide deposited on the oxidation catalyst is reduced and desorbed by the added fuel.

  For example, in the exhaust emission control device described in Patent Document 1, when the temperature rise request for the catalyst bed temperature in the burning treatment of the particulate matter is higher than the temperature rise requirement in the reduction treatment for sulfur oxide, the particulate matter is burned out. Thus, the particulate matter captured by the filter is burned out, and the sulfur oxides are reduced and desorbed together.

JP 2006-291823 A

  By the way, in the exhaust gas purification apparatus in which the oxidation catalyst is disposed upstream of the filter, when the sulfur oxide reduction process is performed together with the particulate matter burning process as described above, the following is performed: There's a problem.

  That is, since the bed temperature of the oxidation catalyst also increases during execution of the particulate matter burnout process, sulfur dioxide (SO2) reduced and desorbed in the oxidation catalyst may be oxidized again in the oxidation catalyst. When sulfur dioxide is oxidized in this way, sulfate (sulfur trioxide SO3) is generated, and this sulfate may pass through the filter and be discharged to the outside as white smoke.

  The same problem occurs when sulfur dioxide desorbed from the oxidation catalyst flows into the filter and sulfur dioxide is oxidized again by the heat of the filter. In addition, reoxidation of sulfur dioxide in the filter can be suppressed by increasing the amount of fuel added and placing the filter in an environment having a low oxygen concentration. However, in this case, there are contradictory matters such as deterioration of fuel economy and fuel being discharged as white smoke, which is not appropriate as a solution for the above problem.

  Further, the problem of the generation of white smoke due to the generation of sulfate as described above becomes more prominent when the amount of sulfur contained in the fuel is large and the amount of sulfur oxide to be reduced increases.

  An object of the present invention is to suppress generation of white smoke from sulfate produced from sulfur oxides deposited on an oxidation catalyst.

  In the exhaust emission control device for solving the above-described problems, an oxidation catalyst and a filter that captures particulate matter are sequentially arranged in the exhaust passage from the upstream side. In this exhaust purification device, by adding fuel upstream of the oxidation catalyst, burn-out treatment for burning off particulate matter trapped in the filter and sulfur oxide deposited on the oxidation catalyst are reduced and desorbed. Perform reduction processing.

  Here, in this exhaust purification device, the catalyst bed temperature is lower than the target temperature of the catalyst bed temperature in the burn-out treatment of the particulate matter, and the execution condition of the sulfur oxide reduction treatment is set. Therefore, the sulfur oxide reduction treatment should be performed in an environment where the catalyst bed temperature and the filter temperature are low as compared with the case where the sulfur oxide reduction treatment is performed together with the particulate matter burning-out treatment. It becomes.

  Therefore, it is possible to suppress the generation of sulfate caused by reoxidation of sulfur dioxide with an oxidation catalyst, and the generation of sulfate caused by oxidation of sulfur dioxide flowing from the oxidation catalyst into the filter again. Can also be suppressed.

  Further, in this exhaust purification device, when the execution condition of the particulate matter burning-out process is established, the particulate matter is reduced until the sulfur oxide deposition amount in the oxidation catalyst becomes equal to or less than the allowable amount by executing the sulfur oxide reduction treatment. The start time of the burnout process is delayed. For this reason, the particulate matter is burnt down under a situation where the amount of sulfur oxide deposited on the oxidation catalyst is small, and the amount of sulfur dioxide flowing into the filter from the oxidation catalyst during the burnout treatment is reduced. can do. Therefore, even if sulfur dioxide is reoxidized in the filter, the amount of reoxidation is reduced, and the production of sulfate due to such reoxidation can also be suppressed.

Thus, according to the exhaust emission control device, it is possible to suppress the generation of white smoke due to the generation of sulfate from the sulfur oxide deposited on the oxidation catalyst.
Further, in the above exhaust purification apparatus, the start timing of the burning treatment of the particulate matter is delayed until the amount of sulfur oxide deposited on the oxidation catalyst becomes less than the allowable amount. You may make it prohibit a burning-out process of a particulate matter when the accumulation amount of a sulfur oxide is larger than an allowable amount. Or you may make it delay the start time of the burning-out process of a particulate matter until the execution period of the reduction process of a sulfur oxide reaches a predetermined period.

  Even with these exhaust purification devices, the particulate matter is burned out under the condition that the amount of sulfur oxide deposited on the oxidation catalyst is small, so the sulfur dioxide flowing into the filter from the oxidation catalyst during the burnout treatment is not removed. The amount can be reduced. Therefore, even if sulfur dioxide reoxidation occurs in the filter, the amount of reoxidation decreases, and the production of sulfate due to such reoxidation can be suppressed.

  Further, in the reduction treatment of sulfur oxide, when the catalyst bed temperature is higher than the upper limit temperature at which sulfur dioxide desorbed in the oxidation catalyst is not reoxidized, sulfur dioxide reoxidation frequently occurs in the oxidation catalyst. The generation of sulfate that causes white smoke is likely to proceed. On the other hand, when the catalyst bed temperature is equal to or lower than the upper limit temperature, the amount of sulfur dioxide reoxidized is suppressed to a negligible range in view of the formation of sulfate. For this reason, it is desirable to perform the reduction treatment of the sulfur oxide when the catalyst bed temperature is equal to or lower than the upper limit temperature at which sulfur dioxide desorbed in the oxidation catalyst is not reoxidized. According to such a structure, the production | generation of sulfate when the reduction process of sulfur oxide is performed can be suppressed effectively.

  In the exhaust purification apparatus, it is desirable that the amount of platinum-based metal supported per unit volume of the filter carrier is smaller than the amount of platinum-based metal supported per unit volume of the oxidation catalyst carrier. If the relationship between the amounts of each platinum-based metal supported is set in this way, the oxidizing power of the filter becomes relatively low, while the oxidizing power of the oxidation catalyst becomes relatively high.

  For this reason, in the oxidation catalyst, the amount of sulfur dioxide adsorbed on the carrier increases, and the amount of sulfur dioxide flowing into the filter without being adsorbed by the oxidation catalyst decreases. Therefore, it is possible to suppress the generation of sulfate due to the sulfur dioxide flowing into the heated filter. On the other hand, in the filter, even if sulfur dioxide flows from the oxidation catalyst, its oxidizing power is low, so that reoxidation of sulfur dioxide can be suppressed. Therefore, by employing such a configuration, the amount of sulfate discharged from the filter can be further reduced. In addition, about a filter, the support | carrier which does not carry | support platinum metal can also be employ | adopted.

  In the exhaust purification apparatus, the oxidation catalyst carrier is preferably formed of an alumina-based metal. In this case, it is preferable that the amount of platinum-based metal supported per liter of the oxidation catalyst carrier is 3.0 g or more, and the amount of platinum-based metal supported per liter of the filter carrier is 1.0 g or less.

The schematic diagram which shows schematic structure of an internal combustion engine and its exhaust gas purification device. The flowchart which shows the execution procedure of a burning process and a reduction process. (A) is the burn-out process execution condition, (b) is the amount of fuel added, (c) is the catalyst bed temperature, (d) is the amount of sulfur dioxide flowing into the filter from the oxidation catalyst, and (e) is exhausted from the filter (F) is the time chart which shows those transitions about the quantity of the sulfate to be performed, (f) is the deposition amount of the sulfur oxide in an oxidation catalyst. The flowchart which shows the execution procedure of a reduction process. The flowchart which shows the execution procedure of a burning-out process. (A) is the travel distance, (b) is the amount of sulfur oxide deposited on the oxidation catalyst, (c) is the execution flag for the reduction process, (d) is the prohibition flag for the burnout process, and (e) is the burnout process. The time chart which shows those transitions about an execution mode.

[First Embodiment]
[Configuration of exhaust purification system]
Hereinafter, a first embodiment of an exhaust emission control device will be described with reference to FIGS.

  As shown in FIG. 1, the internal combustion engine 10 is provided with an injection valve 12 that injects fuel into the combustion chamber 11. In the exhaust passage 13, in order from the upstream side thereof, an addition valve 20 for adding fuel to the exhaust passage 13, an oxidation catalyst 21 for oxidizing and purifying the fuel contained in the exhaust, and particulate matter contained in the exhaust are captured. A filter 22 is provided.

  The oxidation catalyst 21 has a carrier formed of an alumina-based metal, and the carrier carries 3.5 g of platinum particles (Pt) per liter. On the other hand, the filter 22 has a carrier formed of, for example, cordierite or silicon carbide, and 0.5 g of platinum particles per liter is carried on the carrier.

  The oxidation catalyst 21 is provided with a bed temperature sensor 30 for detecting the temperature of the carrier, that is, the catalyst bed temperature. A filter temperature sensor 31 for detecting the temperature of the carrier is attached to the filter 22. The exhaust passage 13 is provided with a differential pressure sensor 32 that detects a difference in internal pressure between the upstream portion and the downstream portion of the filter 22. The detection signals of these sensors are taken into the control unit 40 of the exhaust purification device. Based on the detection signals of these sensors, the control unit 40 performs various controls related to exhaust purification by driving actuators such as the injection valve 12 and the addition valve 20.

[Burning treatment of particulate matter]
For example, the control unit 40 performs a burning process for recovering the capturing ability of the particulate matter by burning and burning the particulate matter captured by the filter 22. In this burning process, when the execution condition is satisfied, fuel is added from the addition valve 20 to the exhaust passage 13 to raise the bed temperature of the oxidation catalyst 21 to its target temperature, and the filter 22 is raised by the heat of the exhaust. The particulate matter deposited on the filter 22 is burned out by heating.

Here, the accumulation amount (ΣPM) of the particulate matter in the filter 22 is obtained, for example, by repeating the calculation according to the following equation (1) at a predetermined period.

ΣPM (i) ← ΣPM (i−1) + PMadd−PMsub (1)

In the above equation (1), “ΣPM (i)” is the accumulation amount obtained at the current computation timing, and “ΣPM (i−1)” is the accumulation amount obtained at the previous computation timing. “PMadd” is the amount of particulate matter newly deposited on the filter 22 during the period from the previous calculation timing to the current calculation timing, and “PMsub” is also burned and burned out by the filter 22 during the above period. The amount of particulate matter. These new accumulation amount PMadd and burnout amount PMsub are parameters that correlate with the engine operating state, such as map calculation using fuel injection amount, rotational speed, fuel addition amount of addition valve 20, temperature of filter 22, catalyst bed temperature, etc. Sought through.

  In addition, the burn-out treatment is established by at least one of the accumulation amount of the particulate matter calculated by the above formula (1) being larger than the allowable amount and the differential pressure detected by the differential pressure sensor 32 being a predetermined value or more. The execution condition is to do.

  When the execution condition is satisfied and the burnout process is started, fuel is added from the addition valve 20 and the catalyst bed temperature rises. However, the control unit 40 makes the catalyst bed temperature coincide with the target temperature. Further, the fuel addition mode by the addition valve 20 is controlled while monitoring the catalyst bed temperature and the filter temperature so that the temperature of the filter 22 does not rise excessively. For example, the control unit 40 intermittently adds fuel and adjusts the lengths of the addition period and the rest period to make the catalyst bed temperature coincide with the target temperature.

[Reduction treatment of sulfur oxide]
Further, during operation of the internal combustion engine, sulfur dioxide contained in the exhaust is oxidized and adsorbed and deposited on the oxidation catalyst 21 in the form of sulfur oxide, for example, aluminum sulfate such as Al 2 (SO 4) 3. Therefore, the control unit 40 performs a reduction process for reducing and desorbing the sulfur oxide deposited on the oxidation catalyst 21 in this way.

  In this reduction process, fuel is added to the exhaust passage 13 to raise the catalyst bed temperature, and the oxidation catalyst 21 is placed in an environment with a low oxygen concentration, so that the sulfur oxide deposited on the oxidation catalyst 21 is added. Reduced and eliminated.

  Further, the reduction process performed in this exhaust purification device is executed when the catalyst bed temperature is changing in a temperature range lower than the target temperature of the catalyst bed temperature in the above-described burnout process. Specifically, the reduction process is executed on the condition that the temperature lower than the target temperature is set as the upper limit temperature of the temperature range, and the catalyst bed temperature is equal to or lower than the upper limit temperature.

  Here, the upper limit temperature is a temperature at which sulfur dioxide desorbed from the oxidation catalyst 21 is not reoxidized in the oxidation catalyst 21. That is, when the catalyst bed temperature is higher than the upper limit temperature, sulfur dioxide re-oxidation frequently occurs in the oxidation catalyst 21, and the generation of sulfate that causes white smoke as described above easily proceeds. On the other hand, when the catalyst bed temperature is equal to or lower than the upper limit temperature, the amount of sulfur dioxide reoxidized can be suppressed to an extremely small range that can be ignored from the viewpoint of the formation of sulfate.

  Further, when the execution condition is satisfied and the reduction process is started, the catalyst bed temperature rises, but the control unit 40 monitors the catalyst bed temperature, and the catalyst bed temperature is in a temperature range below the upper limit temperature. The fuel addition mode by the addition valve 20 is controlled so as to change. For example, the control unit 40 intermittently adds fuel, and adjusts the length of the addition period and the rest period, thereby causing the catalyst bed temperature to change in a temperature range equal to or lower than the upper limit temperature. By performing such a reduction process, the amount of sulfur oxide deposited on the oxidation catalyst 21 is reduced.

Here, the accumulation amount (ΣSO) of the sulfur oxide in the oxidation catalyst 21 is obtained, for example, by repeating the calculation according to the following equation (2) at a predetermined period.

ΣSO (i) ← ΣSO (i−1) + SOadd−SOsub (2)

In the above equation (2), “ΣSO (i)” is the accumulation amount obtained at the current computation timing, and “ΣSO (i−1)” is the accumulation amount obtained at the previous computation timing. “SOadd” is the amount of sulfur oxide newly deposited on the oxidation catalyst 21 during the period from the previous calculation timing to the current calculation timing, and “SOsub” is also reduced by the oxidation catalyst 21 during the above period and desorbed. The amount of sulfur oxide. These new accumulation amount SOadd and desorption amount SOsub are currently used in addition to parameters correlated with engine operating conditions, such as fuel injection amount, rotational speed, fuel addition amount of addition valve 20, temperature of filter 22, catalyst bed temperature, etc. It is obtained through map calculation using parameters correlating with the concentration of sulfur in the fuel.

[Execution procedure for burnout and reduction]
Next, detailed execution procedures of the above-described burnout process and reduction process will be described with reference to FIG.

  As shown in FIG. 2, when the burnout execution condition is satisfied (step S201: YES), it is next determined whether the catalyst bed temperature is equal to or lower than the upper limit temperature described above (step S202).

  When the catalyst bed temperature is equal to or lower than the upper limit temperature (step S202: YES), a reduction process is executed (step S203). Next, the amount of sulfur oxide deposited on the oxidation catalyst 21 is calculated (step S204). If the accumulation amount is equal to or less than the allowable amount (step S205: YES), the burnout process is started (step S206). The burn-out process is continuously executed until the amount of particulate matter deposited on the filter 22 becomes “0”.

  Here, the above-described allowable amount is such that even if the burning process is started and the catalyst temperature rises, and sulfur dioxide desorbed from the oxidation catalyst 21 flows into the filter 22 and is re-oxidized, it does not generate white smoke. This is a threshold value for limiting the amount of sulfur oxide deposited during the burn-out process so as not to affect the process.

  On the other hand, when the burnout execution condition is not satisfied, when the catalyst bed temperature is higher than the upper limit temperature, or when the amount of sulfur oxide deposited on the oxidation catalyst 21 is larger than the allowable amount (step S201: NO, step S202: (NO, step S205: NO), this series of processes ends.

[Operation of exhaust purification system]
Next, the operation of this exhaust purification device will be described with reference to FIG.
As shown in FIG. 3, when the execution condition for the burnout process is satisfied at timing t <b> 1 (FIG. 3A), the catalyst bed temperature is lower than the upper limit temperature, so the reduction process is started and intermittently performed by the addition valve 20. Fuel addition is started (FIG. 3B). When the fuel is added in this way, the catalyst bed temperature gradually rises (FIG. 3 (c)).

  The sulfur oxide adsorbed on the oxidation catalyst 21 is reduced and desorbed by the fuel to generate sulfur dioxide, and the sulfur dioxide flows into the filter 22 from the oxidation catalyst 21 (FIG. 3 (d)). Here, since the catalyst bed temperature is below the upper limit temperature, reoxidation of sulfur dioxide in the oxidation catalyst 21 is suppressed. Moreover, since the temperature of the filter 22 is low, the reoxidation of sulfur dioxide flowing into the filter 22 is also suppressed.

  When sulfur dioxide is desorbed from the oxidation catalyst 21 in this way, the amount of sulfur oxide deposited on the oxidation catalyst 21 gradually decreases (FIG. 3 (f)). At timing t2, when the amount of sulfur oxide deposited becomes equal to or less than the allowable amount, the reduction process ends and the burnout process starts. As a result, the catalyst bed temperature further rises and gradually converges to the target temperature for the burnout treatment (FIG. 3 (c)). Even if the burnout process is performed and the catalyst temperature rises, the amount of sulfur oxide deposited on the oxidation catalyst 21 is reduced by the reduction process performed prior to the burnout process. The amount of sulfur dioxide flowing into the filter 22 whose temperature has been increased from the above becomes a very limited amount. Accordingly, the emission of white smoke due to the generation of sulfate in the filter 22 is suppressed (FIG. 3 (e)).

  As described above, in this exhaust purification apparatus, when the burnout process execution condition is satisfied, the start timing of the burnout process is delayed until the sulfur oxide deposition amount becomes equal to or less than the allowable amount due to the execution of the reduction process. Yes.

[Effect of exhaust purification system]
The exhaust purification device described above can achieve the following effects.
(1a) When the catalyst bed temperature is lower than the target temperature of the catalyst bed temperature in the burnout process, the reduction process is executed. For this reason, compared with the case where the reduction process is performed together with the burning process, the reduction process is performed in an environment where the catalyst bed temperature and the filter temperature are low. Therefore, it is possible to suppress the generation of sulfate due to the reoxidation of sulfur dioxide by the oxidation catalyst 21. Furthermore, it is possible to suppress the generation of sulfate due to the sulfur dioxide flowing into the filter 22 from the oxidation catalyst 21 being oxidized again by the filter 22.

  (1b) Further, when the execution condition of the burnout process is satisfied, the start timing of the burnout process is delayed until the sulfur oxide deposition amount on the oxidation catalyst 21 becomes equal to or less than the allowable amount by executing the reduction process. For this reason, the burn-out process is performed under a situation where the amount of sulfur oxide deposited on the oxidation catalyst 21 is small, and the amount of sulfur dioxide flowing into the filter 22 from the oxidation catalyst 21 during the burn-out process is reduced. be able to. For this reason, the production | generation of the sulfate resulting from sulfur dioxide oxidizing again with the filter 22 can also be suppressed now.

Therefore, according to the present exhaust purification device, it is possible to suppress the generation of white smoke due to the generation of sulfate from the sulfur oxide deposited on the oxidation catalyst.
(2) Further, the reduction treatment is executed when the catalyst bed temperature is equal to or lower than the upper limit temperature at which sulfur dioxide desorbed from the oxidation catalyst 21 is not reoxidized in the oxidation catalyst 21. For this reason, the reoxidation amount of sulfur dioxide in the oxidation catalyst 21 can be suppressed to an extremely small range that can be ignored, and the generation of sulfate when the reduction treatment is performed can be effectively suppressed.

  (3) Since the supported amount of platinum particles per unit volume of the carrier of the filter 22 is smaller than the supported amount of platinum particles per unit volume of the carrier of the oxidation catalyst 21, the oxidizing power of the filter 22 becomes relatively low. On the other hand, the oxidizing power of the oxidation catalyst 21 is relatively high.

  Therefore, in the oxidation catalyst 21, the amount of sulfur dioxide adsorbed on the carrier increases, and the amount of sulfur dioxide that flows into the filter 22 without being adsorbed on the oxidation catalyst 21 decreases. As a result, it is possible to suppress the generation of sulfate due to the sulfur dioxide flowing into the heated filter 22. On the other hand, in the filter 22, even if sulfur dioxide flows from the oxidation catalyst 21, the oxidizing power thereof is low, so that reoxidation of sulfur dioxide can be suppressed. Therefore, the amount of sulfate discharged from the filter 22 can be further reduced.

  (4) Further, since the support of the oxidation catalyst 21 is formed of an alumina-based metal, sulfur dioxide contained in the exhaust can be efficiently adsorbed on the support. Therefore, it is possible to prevent sulfur dioxide from flowing from the oxidation catalyst 21 into the heated filter 22 during the burning process, and to suppress the generation of sulfate in the filter 22.

[Second Embodiment]
Next, a second embodiment of the exhaust emission control device will be described with reference to FIGS. It should be noted that the configuration of the exhaust gas purification device such as the addition valve 20, the oxidation catalyst 21, the filter 22, etc., the method for calculating the amount of particulate matter deposited, the method for calculating the amount of sulfur oxide deposited, Since the fuel addition mode in the reduction process is the same as that of the first embodiment, the description thereof is omitted. In this example, it is assumed that the internal combustion engine to which the exhaust emission control device is applied is mounted on a vehicle.

  In the exhaust gas purification apparatus of the first embodiment, the start timing of the burnout process is delayed until the amount of sulfur oxide deposited on the oxidation catalyst 21 becomes equal to or less than the allowable amount, but in the exhaust gas purification apparatus of the present embodiment, The burn-out process is prohibited when the amount of sulfur oxide deposited on the oxidation catalyst 21 is larger than the allowable amount.

  Further, in the exhaust purification apparatus of the first embodiment, the reduction process is executed under a predetermined condition when the burnout process execution condition is satisfied, but the exhaust purification apparatus of the present embodiment Then, every time the vehicle travels a predetermined distance, a reduction process is executed.

Hereinafter, with reference to FIG.4 and FIG.5, the reduction | restoration process and burning process performed by the exhaust gas purification apparatus of this embodiment are demonstrated.
[Reduction process execution procedure]
First, a detailed execution procedure of the reduction process will be described.

  As shown in FIG. 4, when the travel distance of the vehicle reaches a predetermined distance (step S401: YES), the travel distance is reset to “0” (step S402). Then, the execution flag for the reduction process is set to “ON” (step S403), and the process proceeds to step S404. On the other hand, when the travel distance of the vehicle has not reached the predetermined distance (step S401: NO), the process similarly proceeds to step S404.

  Here, the predetermined distance is set to a value sufficiently shorter than the average distance traveled by the vehicle in the period from the amount of particulate matter deposited on the filter 22 to the allowable amount from “0”. .

  In step S404, the amount of sulfur oxide deposited on the oxidation catalyst 21 is calculated. If the accumulation amount is larger than the allowable amount (step S405: YES), the prohibition flag for the burnout process is set to “ON” (step S406). Next, when the execution flag is “ON” (step S407: YES), it is further determined whether or not the catalyst bed temperature is equal to or lower than the upper limit temperature (step S408). When the catalyst bed temperature is equal to or lower than the upper limit temperature (step S408: YES), a reduction process is executed (step S409).

Further, when the execution flag is “OFF” (step S407: NO), and when the catalyst bed temperature is higher than the upper limit temperature (step S408: NO), the processing is terminated.
On the other hand, when the accumulation amount is equal to or less than the allowable amount (step S405: NO), the prohibition flag is set to “OFF” (step S416), the execution flag is set to “OFF”, and this process ends (step S416). S417).

  As described above, in the exhaust purification apparatus, the burn-in prohibition flag is set to “ON” when the accumulation amount is larger than the allowable amount, and is set to “OFF” when the accumulation amount is less than the allowable amount. Is done. Further, the execution flag for the reduction process is set to “ON” when the travel distance of the vehicle reaches a predetermined distance, and is set to “OFF” when the accumulation amount is equal to or less than the allowable amount.

[Execution procedure for burnout processing]
Next, a detailed execution procedure of the burnout process will be described.
As shown in FIG. 5, when the burnout process execution condition is satisfied (step S501: YES), it is next determined whether or not the prohibition flag set in the previous reduction process is "OFF" (step S501). S502). When the prohibition flag is “OFF”, the burnout process is started. As in the first embodiment, the burnout process is continuously executed until the amount of particulate matter deposited on the filter 22 reaches “0”.

  On the other hand, when the execution condition for the burnout process is not satisfied (step S501: NO), and when the prohibition flag is “ON” (step S502: NO), the series of processes ends. That is, even if the execution condition described above for the burnout process is satisfied (step S501: YES), if the prohibition flag is “ON” (step S502: NO), the burnout process is not executed. That is, in this exhaust purification apparatus, when the amount of sulfur oxide deposited on the oxidation catalyst 21 is larger than the allowable amount, the burnout process is prohibited.

[Operation of exhaust purification system]
Next, the operation of this exhaust purification device will be described with reference to FIG.
As shown in FIG. 6, when the travel distance reaches a predetermined distance at timing t1 (FIG. 6A), the execution flag for the return process is switched from “OFF” to “ON” (FIG. 6C). ). Therefore, if other execution conditions for the reduction process are satisfied, the reduction process is executed.

  Here, since the prohibition flag for the burnout process is “ON” (FIG. 6D), even if the execution condition is satisfied, the burnout process is not executed (FIG. 6E). That is, in the present embodiment, at least one of the above-described accumulation amount of the particulate matter is larger than the allowable amount and that the differential pressure detected by the differential pressure sensor 32 is a predetermined value or more is established. As a precondition, in addition to the establishment of the precondition, the prohibition flag being “OFF” is a substantial execution condition of the burnout process.

  As the reduction process is performed, the amount of sulfur oxide deposited on the oxidation catalyst 21 gradually decreases (FIG. 6 (b)). When the amount deposited becomes equal to or less than the allowable amount at timing t2, the execution flag is set. “OFF” is set, and the reduction process ends. On the other hand, at the timing t2, the prohibition flag is set to “OFF”. Therefore, when the above-mentioned preconditions for the burnout process are established, the burnout process is started.

[Effect of exhaust purification system]
As described above, according to this exhaust gas purification apparatus, in addition to (1a) and (2) to (4) in the first embodiment, the following effects can be further achieved.

  (1c) When the amount of sulfur oxide deposited on the oxidation catalyst 21 is larger than the allowable amount, the burning process is prohibited. For this reason, the burn-out process is performed under a situation where the amount of sulfur oxide deposited on the oxidation catalyst 21 is small, and the amount of sulfur dioxide flowing into the filter 22 from the oxidation catalyst 21 during the burn-out process is reduced. be able to. For this reason, the production | generation of the sulfate resulting from sulfur dioxide oxidizing again with the filter 22 can also be suppressed now.

  (5) Since the reduction process is executed when the catalyst bed temperature is equal to or lower than the upper limit temperature, the reduction process can be executed when the burnout process execution condition is satisfied. There is a concern that sufficient processing opportunities cannot be secured.

  On the other hand, in this embodiment, the reduction process is executed every time the vehicle travels a predetermined distance, and the amount of the particulate matter deposited on the filter 22 during this predetermined distance is a period from “0” to the allowable amount. The value was set to be sufficiently shorter than the average distance traveled by the vehicle. For this reason, there are multiple opportunities for execution of the reduction process during the period from when the execution condition for the burnout process is not satisfied until the execution condition is satisfied. As a result, it is possible to increase the execution opportunity of the reduction process, and thus increase the execution opportunity of the burnout process.

[Other Embodiments]
Each embodiment mentioned above can also be implemented in the following modes. Moreover, it can also implement combining each embodiment and each deformation | transformation structure shown below suitably.

  In the first embodiment, when the burnout process execution condition is satisfied, the amount of sulfur oxide deposited is monitored, and the start timing of the burnout process is delayed until the deposition amount falls below the allowable amount. However, for example, the start timing of the burnout process may be delayed until the execution period of the reduction process reaches a predetermined period. Even in such a configuration, the predetermined period is set to a period sufficient to reduce the amount of sulfur oxide deposited, so that the burn-out process is performed under a situation where the amount of sulfur oxide deposited on the oxidation catalyst 21 is small. Can do. For this reason, the effect equivalent to 1st Embodiment can be acquired.

  In the above modification, when the reduction process is executed intermittently, it is desirable to delay the start timing of the burnout process until the accumulated value of the execution period reaches a predetermined period. Alternatively, the start timing of the burnout process can be delayed until the period in which the reduction process is continuously executed reaches a predetermined period.

  -Moreover, in the said modification, you may make it change the said predetermined period according to the deposition amount of the sulfur oxide when a reduction process is started. That is, if the predetermined period is made longer as the amount of deposition increases, the amount of deposition can be appropriately reduced through the reduction treatment regardless of the amount of sulfur oxide deposited. Burnout treatment can be performed under conditions where the amount is small.

  In each embodiment, the amount of sulfur oxide deposited on the oxidation catalyst 21 is monitored. However, for example, the total amount of sulfur oxide deposited on both the oxidation catalyst 21 and the filter 22 may be monitored. Since the total amount of sulfur oxide deposited on both the oxidation catalyst 21 and the filter 22 has a correlation with the amount of sulfur oxide deposited on the oxidation catalyst 21, the control of each embodiment is executed based on the total amount. Even in this case, the effect of each embodiment can be obtained.

  The fuel is added in the reduction process or the burnout process using the addition valve 20, but in addition to the fuel addition by the addition valve 20, the exhaust is performed by the injection of the injection valve 12 (also referred to as after injection) performed in the exhaust stroke. Fuel can also be added to the passage 13. Further, if the exhaust purification device does not include the addition valve 20, fuel can be added by after-injection of the injection valve 12.

  ・ In the reduction process and the burnout process, fuel is added intermittently, and the catalyst bed temperature and filter temperature are controlled by adjusting the length of the addition period and the rest period. The aspect is not limited to this. For example, the catalyst bed temperature or the filter temperature may be controlled by adjusting the amount of fuel added by the addition valve 20 or the injection amount of the injection valve 12 in the case of after injection.

  In the second embodiment, every time the travel distance of the vehicle reaches a predetermined distance, an opportunity for execution of the reduction process arrives. However, for example, every time the cumulative operation time of the internal combustion engine 10 reaches a predetermined time, An opportunity to execute processing may be provided. Alternatively, the reduction process is performed when the amount of sulfur oxide deposited on the oxidation catalyst 21 has increased to a predetermined amount (> allowable amount) or more, or when the catalyst bed temperature has become the upper limit temperature or less. May be.

  ・ It was decided that the condition that the sulfur dioxide desorbed in the oxidation catalyst was below the upper limit temperature at which it was not reoxidized was included as the reduction treatment execution condition, but if the catalyst bed temperature was lower than the target temperature in the burnout treatment, The reduction process may be executed when the temperature is higher than the upper limit temperature. Even with such a configuration, it is possible to achieve each effect except for (2) shown in the first embodiment.

  The oxidation catalyst 21 employs a carrier on which 3.5 g of platinum particles (Pt) are supported per liter, but the amount supported can be appropriately changed as long as it is 3.0 g or more. The filter 22 employs a carrier carrying 0.5 g of platinum particles (Pt) per liter, but this carrying amount can be appropriately changed as long as it is 1.0 g or less. For the filter 22, a carrier on which no platinum particles are supported can be used.

  Furthermore, the amount of platinum particles supported on the carrier of the filter 22 may be equal to or greater than the amount of oxidation catalyst 21 supported. Even with such a configuration, it is possible to achieve each effect except for (3) shown in the first embodiment. The platinum particles carried on the carrier of the oxidation catalyst 21 and the filter 22 may be particles of other platinum-based metals such as palladium (Pd) and rhodium (Rh).

  In the oxidation catalyst 21, an alumina-based metal carrier is used, but a carrier made of another metal such as titanium oxide can also be adopted.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Combustion chamber, 12 ... Injection valve, 13 ... Exhaust passage, 20 ... Addition valve, 21 ... Oxidation catalyst, 22 ... Filter, 30 ... Bed temperature sensor, 31 ... Filter temperature sensor, 32 ... Differential pressure Sensor, 40 ... control unit.

Claims (6)

An oxidation catalyst and a filter that traps particulate matter are arranged in order from the upstream side in the exhaust passage, and a burnout process that burns away particulate matter trapped in the filter by adding fuel upstream of the oxidation catalyst; In an exhaust gas purification apparatus for an internal combustion engine that performs a reduction process for reducing and desorbing sulfur oxides deposited on an oxidation catalyst,
The reduction treatment includes, as its execution condition, that the catalyst bed temperature is lower than the target temperature of the catalyst bed temperature in the burnout treatment,
An exhaust gas purification apparatus for an internal combustion engine that delays the start timing of the burnout process until the amount of sulfur oxide deposited on the oxidation catalyst becomes equal to or less than an allowable amount due to the execution of the reduction process when the execution condition of the burnout process is satisfied. An oxidation catalyst and a filter that traps particulate matter are arranged in order from the upstream side in the exhaust passage, and a burnout process that burns away particulate matter trapped in the filter by adding fuel upstream of the oxidation catalyst; In an exhaust gas purification apparatus for an internal combustion engine that performs a reduction process for reducing and desorbing sulfur oxides deposited on an oxidation catalyst,
The reduction treatment includes, as its execution condition, that the catalyst bed temperature is lower than the target temperature of the catalyst bed temperature in the burnout treatment,
An exhaust gas purification apparatus for an internal combustion engine that prohibits the execution of the burn-out process when the amount of sulfur oxide deposited on the oxidation catalyst is larger than an allowable amount. An oxidation catalyst and a filter that traps particulate matter are arranged in order from the upstream side in the exhaust passage, and a burnout process that burns away particulate matter trapped in the filter by adding fuel upstream of the oxidation catalyst; In an exhaust gas purification apparatus for an internal combustion engine that performs a reduction process for reducing and desorbing sulfur oxides deposited on an oxidation catalyst,
The reduction treatment includes, as its execution condition, that the catalyst bed temperature is lower than the target temperature of the catalyst bed temperature in the burnout treatment,
An exhaust gas purification apparatus for an internal combustion engine that delays the start timing of the burnout process until the execution period of the reduction process reaches a predetermined period when the execution condition of the burnout process is satisfied. 4. The reduction treatment includes, as its execution condition, that the catalyst bed temperature is lower than the target temperature and not more than an upper limit temperature at which sulfur dioxide desorbed in the oxidation catalyst is not reoxidized. 2. An exhaust gas purification apparatus for an internal combustion engine according to 1. The amount of platinum-based metal supported per unit volume of the carrier of the filter is smaller than the amount of platinum-based metal supported per unit volume of the carrier of the oxidation catalyst. Exhaust purification device. In the oxidation catalyst, the carrier is an alumina-based metal, and the supported amount of platinum-based metal per liter of the carrier is 3.0 g or more. The filter is supported in the amount of platinum-based metal per liter of the carrier. The exhaust emission control device for an internal combustion engine according to claim 5, wherein: