JP4674531B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine in which regenerative exhaust gas purification means is provided at each branch portion of an exhaust passage.

In the exhaust purification apparatus having a configuration in which a particulate filter carrying an oxidation catalyst is provided as an exhaust purification means at each of two parallel branch portions provided in the exhaust passage, the accumulated particulate matter deposited on the particulate filter Provided at each of the plurality of branch portions when it is necessary to perform a regeneration process to restore the exhaust gas purification performance of the particulate filter by burning the substance (PM) or reducing the sulfur oxide accumulated in the catalyst. There is known an exhaust emission control device that simultaneously injects fuel as a reducing agent from a reducing agent addition valve and simultaneously raises the temperature of all the particulate filters (see, for example, Patent Document 1). A particulate filter carrying an oxidation catalyst in each of the two branch portions provided in the exhaust passage is arranged as a first exhaust purification means, and a selective reduction catalyst is provided at a collecting portion extending downstream from the junction of the branch portions. In the exhaust gas purification apparatus configured as the second exhaust gas purification means, a switching valve for selectively switching the introduction of exhaust gas to each particulate filter is disposed at the inlet of the branch portion, and exhaust gas is introduced into one of the particulate filters. There is also known an exhaust emission control device that regenerates the other particulate filter while purifying exhaust gas (see, for example, Patent Document 2).
JP 2003-97254 A Japanese Patent Laid-Open No. 2004-162600

  In an exhaust gas purification apparatus in which a regenerative exhaust gas purification unit is disposed in each of the branch portions of the exhaust passage, and another exhaust gas purification unit is provided at a downstream gathering portion thereof, like the exhaust gas purification device described in Patent Document 1. If all the exhaust gas purification means at the branch part are regenerated at the same time, the exhaust gas purification means in the aggregate part may be heated more than necessary by the heat of the exhaust gas introduced into the aggregate part, causing thermal degradation.

  In the exhaust gas purification apparatus described in Patent Document 2, since substantially the entire amount of exhaust gas is purified by only one of the pair of exhaust gas purification units, each exhaust gas purification unit is an abbreviation for exhaust gas. It is necessary to have a capacity capable of processing the entire amount, and the exhaust purification unit becomes larger.

  Therefore, the present invention can regenerate the exhaust gas purification means provided in each of the branch parts while suppressing thermal deterioration of the exhaust gas purification means provided in the gathering part downstream of the branch parts, An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that is advantageous for reducing the capacity of the exhaust gas purification means.

An exhaust gas purification apparatus for an internal combustion engine according to the present invention includes a regenerative first exhaust gas purification unit provided at each of a plurality of branch portions parallel to each other of an exhaust passage, and an exhaust gas extending downstream from a confluence of the plurality of branch portions. The temperature of the second exhaust gas purification means provided in the collective portion of the passage and the first exhaust gas purification means of each of the plurality of branch portions can be individually raised, and the regeneration process can be performed on these first exhaust gas purification means. Each of the regenerative execution means, the determination means for determining whether or not the regeneration processing of all the first exhaust purification means is necessary, the temperature detection means for detecting the temperature of the second exhaust purification means, and each of the branch portions The exhaust flow rate adjusting means for adjusting the exhaust flow rate guided to the engine and the determination means determine that the regeneration process is necessary, the regeneration process for the first exhaust gas purification means is executed, and it is determined that the regeneration process is unnecessary. If all Of a reproduction control means for reproducing processing for the first exhaust gas purification device for controlling the regeneration execution means to be inhibited, comprises a second exhaust gas purification unit, the low-temperature activity than the temperature range suitable for reproduction The regeneration control means excludes the first exhaust gas purification means of at least one branch portion from the target of the regeneration process and determines whether or not the regeneration process is necessary. The processing cycle for executing the regeneration process for the exhaust gas purifying means at the branch portion is repeated while sequentially switching the first exhaust gas purifying means excluded from the target of the regeneration process, whereby all the first exhaust gas purifying means are regenerated. It controls the regeneration execution means to be processed, during execution of the regeneration process, the temperature of the second exhaust gas purifying means is detected by said temperature detecting means is maintained at the activation temperature range Wherein controlling the flow rate of exhaust gas through the exhaust flow rate adjusting means passing through each of the plurality of branch portions as it allows to solve the problems described above (claim 1).

  According to the exhaust emission control device of the present invention, the regeneration control means repeats the processing cycle, whereby the first exhaust purification means of all the branch portions are regenerated. In one processing cycle, the first exhaust purification unit of at least one branch part is excluded from the target of the regeneration process, and the regeneration process is executed on the first exhaust purification unit of the other branch part. The temperature of the exhaust gas flowing into the second exhaust purification unit of the collecting unit is lowered compared with the case where all the first exhaust purification units of the unit are simultaneously regenerated, and as a result, thermal degradation of the second exhaust purification unit is reduced. It is suppressed. In addition, the determination unit determines whether or not the regeneration process for the first exhaust gas purification unit at the branching portion is necessary. When it is determined that regeneration is necessary, the processing cycle is repeated. Since the regeneration process for the first exhaust purification unit is prohibited, all the first exhaust purification units can be used for exhaust purification in a period in which the regeneration process is not required. Thereby, the capacity required for the first exhaust purification unit can be reduced.

Further , according to the exhaust gas purification apparatus of the present invention, the flow rate of the high-temperature exhaust gas that is led from the branch part during the regeneration process to the collecting part and the low-temperature gas that is led from the branch part excluded from the regeneration process to the gathering part. By adjusting the ratio of the exhaust flow rate with the exhaust flow rate adjusting means, it is possible to change the temperature of the exhaust gas introduced into the second exhaust purification means of the collecting portion. Then, by controlling the exhaust flow rate adjusting means so that the temperature introduced into the second exhaust purification means is maintained in the activation temperature range of the catalyst included in the second exhaust purification means, the first of the collecting portions is also generated during the regeneration process. (2) The purification performance of the exhaust gas purification means can be fully exerted and deterioration of exhaust emission can be suppressed.

In one aspect of the present invention, the exhaust gas purification device includes an air-fuel ratio detection unit that detects an air-fuel ratio of the exhaust gas flowing into the second exhaust gas purification unit, and an exhaust gas flow rate adjustment that adjusts an exhaust gas flow rate that is led to each of the branch portions. And the regeneration executing means has a fuel addition valve for individually adding fuel to the first exhaust purification means of each of the plurality of branch portions, and the second exhaust purification means Including a catalyst that exhibits purification performance in an air-fuel ratio range, wherein the regeneration control means maintains the air-fuel ratio detected by the air-fuel ratio detection means within the predetermined air-fuel ratio range during execution of the regeneration process. In addition, the exhaust flow rate passing through each of the plurality of branch portions may be controlled via the exhaust flow rate adjusting means ( claim 2 ).

  According to this aspect, the flow rate of the exhaust gas having a large amount of fuel guided from the branch part during regeneration processing to the collecting part, and the exhaust amount of the fuel having a small fuel amount guided from the branch part excluded from the regeneration process target to the collecting part. By adjusting the ratio with the flow rate by the exhaust flow rate adjusting means, the air-fuel ratio of the exhaust gas introduced into the second exhaust purification means of the collecting portion can be changed. Then, by controlling the air-fuel ratio of the exhaust gas introduced into the second exhaust gas purification unit to an air-fuel ratio range in which the catalyst included in the second exhaust gas purification unit exhibits the purification performance, the second portion of the collecting portion is also in the regeneration process. It is possible to sufficiently exhibit the purification performance of the exhaust purification means and suppress the deterioration of exhaust emission.

In a mode in which the air-fuel ratio of the exhaust gas introduced into the second exhaust gas purification unit is controlled using the exhaust gas flow rate adjusting unit, the first exhaust gas purification unit further includes an NOx storage reduction catalyst, and the second exhaust gas purification unit. It means, as the predetermined air-fuel ratio range, which may contain a catalyst which exerts purification performance against sulphate in many lean region air quantity than the stoichiometric air-fuel ratio (claim 3).

  When the first exhaust purification means at the branching portion contains a NOx occlusion reduction type catalyst, the regeneration process for eliminating the sulfur poisoning is performed by heating the catalyst to a temperature higher than the activation temperature range and introducing it into the catalyst. It is necessary to control the air-fuel ratio of the exhaust gas to a rich region where the fuel amount is larger than the stoichiometric air-fuel ratio. However, when all the first exhaust purification means are regenerated at the same time, or when a single first exhaust purification means is disposed upstream of the second exhaust purification means without providing a branch portion, the first exhaust purification means is provided. If the air-fuel ratio of the exhaust gas introduced into the means is controlled to a deep rich state, that is, the ratio of the fuel amount is greatly biased to the rich side from the stoichiometric air-fuel ratio, the exhaust gas introduced into the downstream (downstream) exhaust purification means The air-fuel ratio is also biased to the rich side, and the sulfate generated by the sulfur poisoning regeneration process of the upstream (upstream) exhaust purification means cannot be purified by the subsequent exhaust purification means, resulting in sulfate white smoke or bad odor. As a means for solving such inconvenience, it is conceivable to limit the air-fuel ratio during the regeneration process of the exhaust purification unit in the preceding stage to a relatively shallow rich state, that is, a rich state close to the theoretical air-fuel ratio. In an environment controlled in a shallow rich state, the elimination of sulfur poisoning proceeds slowly, so that the time required for regeneration increases. If the regeneration process is lengthened, the risk of thermal deterioration of the exhaust gas purification means during the regeneration process increases, or the amount of fuel supplied as a reducing agent increases, resulting in inconvenience of fuel consumption.

  On the other hand, according to the above aspect of the present invention, the first exhaust gas purification means of at least one branch part is excluded from the target of the regeneration process, and the exhaust flow rate of the branch part during the regeneration process and the non-regeneration target Since the ratio with the exhaust flow rate of the branching portion is adjusted by the exhaust flow rate adjusting valve, the air-fuel ratio of the exhaust led to the second exhaust purification means of the collecting portion is the lean necessary for the sulfate purification even during the regeneration process. Can be controlled. For this reason, it is possible to control the air-fuel ratio of the exhaust gas flowing into the first exhaust gas purification means to be regenerated into a relatively deep rich state, whereby the sulfur poisoning regeneration is completed in a short time, and the first It is possible to improve the fuel consumption by preventing thermal deterioration of the exhaust purification means or reducing the amount of fuel added by regeneration. Further, since it is not necessary to limit the air-fuel ratio of the exhaust gas flowing into the first exhaust purification means during the regeneration to a shallow rich state, the range of the target air-fuel ratio at the time of regeneration is expanded, and the stability of the control relating to the regeneration processing is improved. To do.

  As described above, according to the present invention, the first exhaust purification unit of at least one branch part is excluded from the target of the regeneration process, and the regeneration process is performed on the first exhaust purification unit of the other branch part. Since the processing cycle to be executed is repeated to regenerate the first exhaust purification means of all the branch portions, the first exhaust purification means of all the branch portions is regenerated at the same time as compared with the case where all the first exhaust purification means of the branch portions are simultaneously regenerated. (2) The temperature of the exhaust gas flowing into the exhaust gas purification means can be lowered, thereby suppressing the thermal deterioration of the second exhaust gas purification means. In addition, the processing cycle is repeated when it is determined that regeneration of the first exhaust purification unit at the branch portion is necessary. On the other hand, when it is determined that regeneration is unnecessary, regeneration processing for all the first exhaust purification units is prohibited. Therefore, all the first exhaust gas purification means can be used for exhaust gas purification during a period when the regeneration process is not required. Thereby, the capacity required for the first exhaust purification unit can be reduced.

  FIG. 1 shows an outline of an exhaust emission control device according to one embodiment of the present invention and an internal combustion engine to which the exhaust purification device is applied. The internal combustion engine 1 is configured as a four-cylinder in-line type diesel engine that is used as a power source for driving a vehicle. Hereinafter, the internal combustion engine 1 is abbreviated as the engine 1. The exhaust passage 2 of the engine 1 is provided with a pair of branch portions 3A and 3B that are parallel to each other and a collective portion 5 that extends downstream from the junction 4 of the branch portions 3A and 3B. The branch portions 3A and 3B are provided directly below the exhaust manifold 2a. Each of the branch portions 3A and 3B is provided with front-stage catalyst devices 6A and 6B as first exhaust purification means, and the collecting portion 5 is provided with a rear-stage catalyst device 7 as second exhaust purification means. The pre-catalyst devices 6A and 6B each have a configuration in which a catalyst having an oxidation function is supported on a particulate filter having a function of capturing particulate matter contained in exhaust gas from a diesel engine. As a catalyst having an oxidation function, there are a storage reduction type NOx catalyst, a selective reduction type NOx catalyst, and the like. However, in the following description, it is assumed that a storage reduction type NOx catalyst is used in the pre-stage catalyst devices 6A and 6B. . On the other hand, the post-catalyst device 7 is for treating exhaust emissions that cannot be completely processed by the pre-catalyst devices 6A and 6B, and is sometimes called a sweeper catalyst. The post-catalyst device 7 includes a catalyst capable of purifying sulfate.

  The pre-catalyst devices 6A and 6B are so-called maniverter-type catalyst devices arranged immediately below the exhaust manifold 2a. On the other hand, the rear catalyst device 7 is installed under the floor of the vehicle as an example. The respective capacities of the pre-catalyst devices 6A and 6B are obtained by replacing the pre-catalyst devices 6A and 6B with a single pre-catalyst device without providing the branch portions 3A and 3B in the exhaust passage 2, Assuming that the exhaust gas is purified by the apparatus and the post-catalyst device 7 and the capacity required for the single pre-catalyst device is defined as the required capacity, it is larger than 1/2 of the required capacity and more than the required capacity Set to a small range. The capacity of the post-catalyst device 7 is set larger than that of each of the pre-catalyst devices 6A and 6B.

  The pre-catalyst devices 6A and 6B are regenerative catalyst devices that require periodic regeneration treatment to oxidize accumulated particulates or eliminate sulfur poisoning. In the PM regeneration process for the purpose of particulate oxidation or the sulfur poisoning regeneration process for the purpose of eliminating sulfur poisoning, the pre-catalyst devices 6A and 6B are suitable for exhaust purification, more specifically for storing NOx. It is necessary to raise the temperature to a regeneration temperature range higher than the activation temperature range. Furthermore, in the sulfur poisoning regeneration process, it is necessary to control the air-fuel ratio of the exhaust gas flowing into the upstream catalyst devices 6A and 6B to a rich region where the fuel amount is larger than the stoichiometric air-fuel ratio. In order to execute such a regeneration process, fuel addition valves 8A and 8B for adding fuel to the exhaust gas flowing into the upstream catalyst devices 6A and 6B are provided upstream of the upstream catalyst devices 6A and 6B of the branch portions 3A and 3B, respectively. Is provided. These fuel addition valves 8A and 8B function as regeneration executing means capable of individually performing regeneration processing on the preceding catalyst devices 6A and 6B of the branch portions 3A and 3B. Further, the branch portions 3A and 3B have temperature sensors 9A and 9B for detecting the temperatures of the preceding catalyst devices 6A and 6B, and exhaust flow rate adjusting means for adjusting the exhaust flow rates led to the branch portions 3A and 3B, respectively. The flow regulating valves 10A and 10B are provided. On the other hand, an air-fuel ratio sensor 11 as an air-fuel ratio detecting means for detecting the air-fuel ratio of the exhaust gas flowing into the rear-stage catalyst device 7 is provided upstream of the rear-stage catalyst device 7 of the collecting section 5. A temperature sensor 12 is provided as temperature detecting means for detecting the temperature of the rear catalyst device 7.

  The operations of the fuel addition valves 8A and 8B and the flow rate adjustment valves 10A and 10B are controlled by an engine control unit (ECU) 15. The ECU 15 is configured as a computer unit for controlling the fuel injection amount, intake air amount, valve operating characteristics, and the like of the engine 1. During normal operation of the engine 1, the ECU 15 controls the air-fuel ratio of the exhaust gas flowing into the front-stage catalyst devices 6A and 6B to a lean region where the air amount is larger than the stoichiometric air-fuel ratio, and the temperature of the front-stage catalysts 6A and 6B is NOx purified. Keep the temperature in the active temperature range. Further, the ECU 15 temporarily injects fuel from the fuel addition valves 8A and 8B for a short period of time so that the NOx occlusion amounts of the upstream catalytic devices 6A and 6B are not saturated, and temporarily sets the air-fuel ratio of the exhaust gas flowing into the upstream catalytic devices 6A and 6B. The so-called rich spike control for changing to the rich region is also executed. These controls may be the same as those of a known exhaust purification device. Note that the ECU 15 controls the flow rate adjusting valves 10A, 10B so that substantially the same amount of exhaust gas is led to the branch portions 3A, 3B during normal operation, that is, during a period when regeneration processing for the upstream catalytic devices 6A, 6B is not required. Adjust the opening of each. For example, the flow rate adjusting valves 10A and 10B are each controlled to be fully opened. During the execution of the rich spike control, the flow rate adjustment valves 10A and 10B may be controlled in the same manner as during normal operation, but the flow rate adjustment valves 10A and 10B are alternately opened and closed alternately for each of the branch portions 3A and 3B. Rich spike control may be executed.

  Further, the ECU 15 executes the PM regeneration processing routine shown in FIGS. 2 and 3 and the sulfur poisoning regeneration routine shown in FIGS. 4 and 5 to perform the PM regeneration processing or moving poisoning of the pre-stage catalyst devices 6A and 6B. Perform playback processing. First, the PM regeneration processing routine will be described with reference to FIGS. The PM regeneration processing routine is repeatedly executed at an appropriate period in parallel with various other processes executed by the ECU 15.

  In the PM regeneration processing routine of FIG. 2, the ECU 15 first determines in step S11 whether or not PM regeneration processing is necessary for the pre-catalyst devices 6A and 6B. The necessity of the PM regeneration process can be performed in the same manner as a known exhaust purification device. For example, the accumulated amount of particulates in the preceding catalyst devices 6A and 6B is based on physical quantities that correlate with the accumulated amount of particulates such as pressure loss before and after the preceding catalyst devices 6A and 6B, the operating time of the engine 1, and the travel distance of the vehicle. It is possible to estimate that PM regeneration is necessary when the estimated value exceeds a predetermined allowable value. It should be noted that even if the amount of accumulated particulates exceeds the allowable value, it is also determined whether the PM regeneration process should not be executed for some reason, that is, whether the prohibition condition for the PM regeneration process is satisfied. Then, the case where the prohibition condition is satisfied may be determined as one aspect when the PM regeneration process is unnecessary.

  When it is determined that the PM regeneration process is necessary, the ECU 15 proceeds to step S12, in which the target regeneration temperature Ttrg_M during the PM regeneration process of the preceding catalyst devices 6A and 6B and the target temperature upper limit Ttrg_UF_H of the subsequent catalyst device 7 during the PM regeneration process are determined. And the target temperature lower limit Ttrg_UF_L, respectively. The target regeneration temperature Ttrg_M is set to a temperature range (about 600 ° C. as an example) necessary for particulate combustion, and the temperature range is generally higher than the activation temperature suitable for the NOx purification treatment of the pre-stage catalyst devices 6A and 6B. is there. On the other hand, the rear catalyst target temperature upper limit Ttrg_UF_H is set to a temperature lower than the temperature at which the rear catalyst device 7 undergoes thermal degradation, and more preferably, the upper limit temperature in the activation temperature range (350 ° C ± α as an example) of the rear catalyst device 7 or Somewhat lower than this is set. The target temperature lower limit Ttrg_UF_L is set to the lower limit temperature of the activation temperature range of the post-catalyst device 7 or somewhat higher than this.

  In the subsequent step S13, the ECU 15 targets only one of the pre-catalyst devices 6A for PM regeneration processing, adds fuel from the fuel addition valve 8A of the branch portion 3A provided with the pre-catalyst device 6A, and performs the pre-catalyst device 6A. Is started, the PM regeneration process of the pre-catalyst device 6A is started. In this case, the amount of fuel added from the fuel addition valve 8A is controlled so that the temperature Tb_Ma of the upstream catalytic device 6A detected by the temperature sensor 9A matches the upstream catalytic target regeneration temperature Ttrg_M. The other front-stage catalyst device 6B is excluded from the target of the PM regeneration process, and no fuel is added from the fuel addition valve 8B of the branch portion 3B provided with the front-stage catalyst device 6B.

  In the subsequent step S14, the ECU 15 causes the temperature Tb_UF of the rear catalyst device 7 detected by the temperature sensor 12 to fall within the range from the target temperature lower limit Ttrg_UF_L to the target temperature upper limit Ttrg_UF_H (hereinafter referred to as the target temperature range of the rear catalyst device 7). It is determined whether or not there is. When it is determined that the temperature Tb_UF is higher than the target temperature upper limit Ttrg_UF_H or lower than the target temperature lower limit Ttrg_UF_L, the ECU 15 proceeds to step S15 so that the temperature Tb_UF of the post-catalyst device 7 changes within the target temperature range. The opening degree of the flow regulating valves 10A and 10B is adjusted. For example, when the temperature Tb_UF is shifted to a higher temperature side than the target temperature upper limit Ttrg_UF_H, an operation for reducing the opening degree of the flow rate adjustment valve 10A on the same side as the preceding-stage catalyst device 6A that is the target of the PM regeneration process. , And at least one of the operations for increasing the opening degree of the flow rate adjustment valve 10B on the same side as the pre-catalyst device 6B excluded from the target of the PM regeneration process. When the temperature Tb_UF is shifted to a lower temperature side than the target temperature lower limit Ttrg_UF_L, an operation of increasing the opening of the flow rate adjustment valve 10A on the same side as the preceding stage catalyst device 6A that is the target of the PM regeneration process, and At least one of the operations of decreasing the opening degree of the flow rate adjustment valve 10B on the same side as the preceding stage catalyst device 6B excluded from the target of the PM regeneration process is executed. In this case, the operation amount of the flow rate adjusting valves 10A and 10B may be set based on the deviation amount of the catalyst temperature Tb_UF with respect to the target temperature range. After executing step S15, the ECU 15 returns to step S14.

  On the other hand, when it is determined in step S14 that the temperature Tb_UF of the rear catalyst device 7 is within the target temperature range, the ECU 15 proceeds to step S16 and determines whether or not the PM regeneration process is finished. The end of the PM regeneration process is, for example, the progress of particulate combustion such as the duration of the PM regeneration process, the temperature history detected by the temperature sensor 9A during the PM regeneration process, and the integrated value of the fuel addition amount from the fuel addition valve 8A. It can be determined based on a physical quantity correlated with. The ECU 15 returns to step S14 if it is determined in step S16 that the PM regeneration process has not ended, and proceeds to step S17 in FIG. 3 if it determines that the PM regeneration process has ended.

  In step S17, the ECU 15 replaces the pre-stage catalyst device to be subjected to the PM regeneration process from the pre-stage catalyst device 6A to the pre-stage catalyst device 6B, and from the fuel addition valve 8B of the branch section 3B provided with the pre-stage catalyst device 6B. The PM regeneration process of the pre-catalyst device 6B is started by adding fuel and raising the temperature of the pre-catalyst device 6B. In this case, the amount of fuel added from the fuel addition valve 8B is controlled so that the temperature Tb_Mb of the pre-stage catalyst device 6B detected by the temperature sensor 9B matches the pre-stage catalyst target regeneration temperature Ttrg_M. The pre-catalyst device 6A that has previously executed the PM regeneration process is excluded from the target of the PM regeneration process, and no fuel is added from the fuel addition valve 8A of the branch section 3A in which the pre-catalyst device 6A is provided.

  After starting the PM regeneration process, the ECU 15 proceeds to step S18. The processes from Steps S18 to S20 are the same as Steps S14 to S16 in FIG. 2 except that the target of the PM regeneration process is changed to the pre-catalyst device 6B and the flow rate adjusting valves 10A and 10B are replaced accordingly. The description is omitted. If the ECU 15 determines in step S20 that the PM regeneration processing of the pre-catalyst device 6B has been completed, the ECU 15 proceeds to step S21. In step S21, the ECU 15 resets the opening degree of the flow rate adjusting valves 10A, 10B, that is, returns the opening degree before executing the PM regeneration process, and then ends the PM regeneration process routine. If it is determined in step S11 in FIG. 2 that the PM regeneration process is not necessary, the ECU 15 skips the processes in and after step S12 and ends the PM regeneration process routine. Thereby, when the PM regeneration process is unnecessary, the PM regeneration process for all the pre-catalyst devices 6A and 6B is prohibited.

  Next, the sulfur poisoning regeneration processing routine will be described with reference to FIGS. The sulfur poisoning regeneration processing routine is repeatedly executed at an appropriate cycle in parallel with various other processes executed by the ECU 15. In the sulfur poisoning regeneration processing routine of FIG. 4, the ECU 15 first determines in step S31 whether or not sulfur poisoning regeneration processing is necessary for the pre-stage catalyst devices 6A and 6B. Necessity of the sulfur poisoning regeneration treatment can be performed in the same manner as in a known exhaust purification device. For example, since the sulfur component in the fuel is closely related to the sulfur poisoning amount, the sulfur poisoning amount is estimated using the integrated value of the fuel injection amount calculated by the ECU 15, and the estimated value is a predetermined allowable value. When it exceeds, it can be determined that the sulfur poisoning regeneration process is necessary. The concentration of sulfur components in the fuel stored in the fuel tank of the vehicle may be detected by a sensor to improve the estimation accuracy of the sulfur poisoning amount. Even if the sulfur poisoning amount exceeds the allowable value, if the sulfur poisoning regeneration process should not be executed for some reason, that is, whether or not the prohibition condition for the sulfur poisoning regeneration process is satisfied. In addition, the determination may be made and the case where the prohibition condition is satisfied may be determined as an aspect in the case where the sulfur poisoning regeneration process is unnecessary.

  When it is determined that the sulfur poisoning regeneration process is necessary, the ECU 15 proceeds to step S32, and the target regeneration temperature Ttrg_M at the time of the sulfur poisoning regeneration process of the preceding catalyst apparatuses 6A and 6B and the subsequent catalyst apparatus during the sulfur poisoning regeneration process. 7 target temperature upper limit Ttrg_UF_H and target temperature lower limit Ttrg_UF_L are set. The target regeneration temperature Ttrg_M is set to a temperature range (about 650 ° C. as an example) necessary for removing the sulfur component accumulated in the pre-catalyst device 6A, and this temperature range is generally suitable for the NOx purification treatment of the pre-catalyst devices 6A and 6B. Higher than the activation temperature. The post-catalyst target temperature upper limit Ttrg_UF_H and the target temperature lower limit Ttrg_UF_L may be equivalent to those in the PM regeneration process.

  In subsequent step S33, the ECU 15 treats only one of the front-stage catalyst devices 6A as a target for sulfur poisoning regeneration processing, and adds fuel from the fuel addition valve 8A of the branch section 3A provided with the front-stage catalyst device 6A. By raising the temperature of the apparatus 6A, the sulfur poisoning regeneration process of the pre-catalyst apparatus 6A is started. In this case, the temperature Tb_Ma of the pre-catalyst device 6A detected by the temperature sensor 9A coincides with the pre-catalyst target regeneration temperature Ttrg_M, and the air-fuel ratio of the exhaust gas flowing into the pre-catalyst device 6A becomes the target air-fuel ratio set in the rich region. The amount of fuel added from the fuel addition valve 8A is controlled so as to match. The other front-stage catalyst device 6B is excluded from the sulfur poisoning regeneration process, and no fuel is added from the fuel addition valve 8B of the branching section 3B provided with the front-stage catalyst device 6B. In order to control the air-fuel ratio, the opening degree of the flow rate adjusting valve 10A may be further adjusted.

  In the subsequent step S34, the ECU 15 brings the temperature Tb_UF of the rear catalyst device 7 detected by the temperature sensor 12 into a range from the target temperature lower limit Ttrg_UF_L to the target temperature upper limit Ttrg_UF_H (hereinafter referred to as the target temperature range of the rear catalyst device 7). It is determined whether or not the air-fuel ratio A / F detected by the air-fuel ratio sensor 11 is greater than the target air-fuel ratio A / Ftrg_UF in the rear catalyst device 7. The target air-fuel ratio A / Ftrg_UF is set to a value that is somewhat biased toward the lean region from the stoichiometric air-fuel ratio. That is, in step S34, in addition to the temperature of the post-catalyst device 7, it is determined whether or not the air-fuel ratio of the exhaust gas flowing into the post-catalyst device 7 is controlled to a predetermined lean region, as shown in FIG. Is different. When it is determined that the temperature Tb_UF is higher than the target temperature upper limit Ttrg_UF_H, lower than the target temperature lower limit Ttrg_UF_L, or the air-fuel ratio A / F is higher than the target air-fuel ratio A / Ftrg_UF, the ECU 15 proceeds to step S35, and the subsequent stage The opening degree of the flow rate adjusting valves 10A, 10B is controlled so that the temperature Tb_UF of the catalyst device 7 is controlled within the target temperature range, and the air-fuel ratio A / F is controlled to the target air-fuel ratio A / Ftrg_UF or less, that is, the lean region. adjust. In this case, the operation for the temperature shift may be performed by operating the flow rate adjusting valves 10A and 10B in the same manner as in step S15 of FIG. When the air-fuel ratio A / F is larger than the target air-fuel ratio A / Ftrg, an operation for decreasing the opening degree of the flow rate adjustment valve 10A on the same side as the front-stage catalyst device 6A that is the target of the sulfur poisoning regeneration process. And at least one of the operations for increasing the opening degree of the flow rate adjustment valve 10B on the same side as the pre-catalyst device 6B excluded from the target of the sulfur poisoning regeneration process may be executed. After executing step S35, the ECU 15 returns to step S34.

  On the other hand, when it is determined in step S34 that the temperature Tb_UF of the post-catalyst device 7 is within the target temperature range and the air-fuel ratio A / F is equal to or less than the target air-fuel ratio A / Ftrg_UF, the ECU 15 proceeds to step S36. It is determined whether or not the sulfur poisoning regeneration process is completed. The end of the sulfur poisoning regeneration process is, for example, the sulfur poisoning regeneration process, such as the duration of the sulfur poisoning regeneration process, the temperature history detected by the temperature sensor 9A during the sulfur poisoning regeneration process, and the integrated value of the fuel addition amount from the fuel addition valve 8A. The determination can be made based on a physical quantity that correlates with the progress of component removal. If the ECU 15 determines in step S36 that the sulfur poisoning regeneration process has not ended, the ECU 15 returns to step S34. If the ECU 15 determines that the sulfur poisoning regeneration process has ended, the ECU 15 proceeds to step S37 in FIG.

  In step S37, the ECU 15 replaces the pre-stage catalyst device to be subjected to the sulfur poisoning regeneration process from the pre-stage catalyst device 6A to the pre-stage catalyst device 6B, and the fuel addition valve of the branch portion 3B provided with the pre-stage catalyst device 6B. By adding fuel from 8B and raising the temperature of the pre-catalyst device 6B, the sulfur poisoning regeneration process of the pre-catalyst device 6B is started. In this case, the temperature Tb_Mb of the pre-catalyst device 6B detected by the temperature sensor 9B coincides with the pre-catalyst target regeneration temperature Ttrg_M, and the air-fuel ratio of the exhaust gas flowing into the pre-catalyst device 6B becomes the target air-fuel ratio set in the rich region. The amount of fuel added from the fuel addition valve 8B is controlled so as to match. Further, the pre-catalyst device 6A previously subjected to the sulfur poisoning regeneration process is excluded from the target of the sulfur poisoning regeneration process, and fuel is supplied from the fuel addition valve 8A of the branch portion 3A provided with the pre-catalyst device 6A. Not added. In order to control the air-fuel ratio, the opening degree of the flow rate adjustment valve 10B may be further adjusted.

  After starting the sulfur poisoning regeneration process, the ECU 15 proceeds to step S38. The processes from Step S38 to S40 are the same as Steps S34 to S36 in FIG. 4 except that the target of the sulfur poisoning regeneration process is changed to the pre-catalyst device 6B and the flow control valves 10A and 10B are replaced accordingly. Therefore, the description is omitted. If the ECU 15 determines in step S40 that the sulfur poisoning regeneration process of the pre-catalyst device 6B has been completed, the ECU 15 proceeds to step S41 and resets the opening of the flow rate adjustment valves 10A and 10B, that is, executes the sulfur poisoning regeneration process. The opening is returned to the previous opening, and then the sulfur poisoning regeneration processing routine is terminated. Further, when it is determined in step S31 in FIG. 4 that the sulfur poisoning regeneration process is not necessary, the ECU 15 skips the processes after step S32 and ends the sulfur poisoning regeneration process routine. Thereby, when the sulfur poisoning regeneration process is unnecessary, the sulfur poisoning regeneration process for all the pre-catalyst devices 6A and 6B is prohibited.

  According to the above embodiment, the PM regeneration process or the sulfur poisoning regeneration process of the pre-catalyst devices 6A and 6B provided in the pair of branch parts 3A and 3B is alternately executed for each branch part. The temperature of the exhaust gas flowing into the rear catalyst device 7 can be greatly reduced as compared with the case where the regeneration processing is executed by simultaneously raising the temperature of the front catalyst devices 6A and 6B on both sides. As a result, the temperature of the post-catalyst device 7 can be suppressed to a temperature lower than the temperature at which thermal degradation occurs even during the regeneration process of the pre-catalyst devices 6A and 6B. Further, during the regeneration process, the opening degree of the flow rate adjusting valves 10A and 10B is adjusted to maintain the temperature of the post-catalyst device 7 in the active temperature range, and its exhaust purification performance is fully exhibited to release exhaust emissions to the atmosphere. Can be suppressed.

  Further, in the sulfur poisoning regeneration process, the air-fuel ratio of the exhaust gas flowing into the rear catalyst device 7 is maintained in the lean region by controlling the opening degree of the flow rate adjusting valves 10A, 10B. Can be purified. Therefore, it is not necessary to limit the air-fuel ratio of the pre-catalyst devices 6A and 6B to the shallow rich state during the sulfur poisoning regeneration process for the purpose of preventing sulfate white smoke or offensive odor, and the air-fuel ratio is controlled to a relatively deep rich state. Thus, the sulfur poisoning regeneration process can be completed in a short time. As a result, it is possible to suppress the thermal deterioration of the pre-catalyst devices 6A and 6B or the deterioration of fuel consumption during the sulfur poisoning regeneration process. Further, since it is not necessary to limit the air-fuel ratio during the sulfur poisoning regeneration process to a shallow rich state, it is possible to expand the range of the target air-fuel ratio of the exhaust gas flowing into the upstream catalyst devices 6A, 6B during the sulfur regeneration poisoning. it can. The stability of playback control is improved.

  In the above embodiment, the ECU 15 functions as the determination means of the present invention by executing step S11 in FIG. 2 and step S31 in FIG. 4, and the ECU 15 performs steps S12 to S21 in FIG. 2 and FIG. 5 is executed, and when steps S11 and S31 are negatively determined, the processes of steps S12 to S21 and S32 to S41 are skipped, thereby functioning as a reproduction control unit of the present invention. To do. In the PM regeneration processing routine of FIGS. 2 and 3, steps S13 to S16 correspond to one processing cycle, and steps S17 to S20 correspond to another one processing cycle. In the sulfur poisoning regeneration processing routine of FIG. 4 and FIG. 5, steps S33 to S36 correspond to one processing cycle, and steps S37 to S40 correspond to another one processing cycle.

  The present invention is not limited to the above form, and may be implemented in an appropriate form. For example, the first exhaust gas purification means arranged at the branching portion may be any device that requires a regeneration process with a temperature raising operation, and is not limited to a catalyst device in which a NOx storage reduction catalyst is supported on a particulate filter. . For example, only the particulate filter or only the NOx catalyst may be provided as the first exhaust purification means, or a configuration in which the particulate filter and the NOx catalyst are arranged in series in the exhaust flow direction is adopted as the first exhaust purification means. May be.

The second exhaust gas purification means arranged in the gathering part can be changed as appropriate. In the above embodiment, the air-fuel ratio in the second exhaust purification unit is controlled to the lean region in order to purify the sulfate generated during the sulfur poisoning regeneration process. For example, the second exhaust purification unit is a three-way catalyst. If the catalyst includes a catalyst that exhibits purification performance at the stoichiometric air-fuel ratio, the exhaust flow rate adjusting means may be operated so that the air-fuel ratio of the second exhaust purification means during the regeneration process is controlled to the stoichiometric air-fuel ratio. If the first exhaust purification unit does not require the sulfur poisoning regeneration process, the operation of the exhaust flow rate adjusting unit in consideration of the air-fuel ratio in the second exhaust purification unit may be omitted .

  The number of branch portions is not limited to two, and may be three or more. When three or more branch portions are provided, the first exhaust purification means in at least one branch portion is excluded from the regeneration process target in one processing cycle, and the first exhaust purification means in the other branch portions is regenerated. The reproduction process may be executed as a target of the above. The temperature increase for the regeneration process is not limited to the example realized by the fuel addition valve, and may be realized by a heating means such as a heater provided at the branch portion.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows the outline of the exhaust gas purification apparatus which concerns on one form of this invention, and the internal combustion engine to which this is applied. The flowchart which shows PM regeneration process routine performed with ECU of FIG. The flowchart following FIG. The flowchart which shows the sulfur poisoning reproduction | regeneration processing routine performed with ECU of FIG. The flowchart following FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Exhaust passage 3A, 3B Branch part 4 Junction part of a branch part 5 Aggregation part 6A, 6B Pre-stage catalyst apparatus (1st exhaust purification means)
7 Subsequent catalyst device (second exhaust purification means)
8A, 8B Fuel addition valve (regeneration execution means)
9A, 9B Temperature sensor 10A, 10B Flow rate adjusting valve 11 Air-fuel ratio sensor 12 Temperature sensor 15 Engine control unit (determination means, regeneration control means)

Claims (3)

Regenerative first exhaust gas purification means provided in each of a plurality of branch portions parallel to each other in the exhaust passage;
A second exhaust purification means provided at a collection portion of exhaust passages extending downstream from a confluence of the plurality of branch portions;
Regeneration executing means capable of individually raising the temperature of the first exhaust purification means of each of the plurality of branch portions and executing regeneration processing on the first exhaust purification means;
Determination means for determining whether or not regeneration processing of all the first exhaust purification means is necessary;
Temperature detecting means for detecting the temperature of the second exhaust purification means;
Exhaust flow rate adjusting means for adjusting the exhaust flow rate guided to each of the branch portions;
When the determination unit determines that the regeneration process is necessary, the regeneration process for the first exhaust purification unit is executed, and when it is determined that the regeneration process is unnecessary, the regeneration process for all the first exhaust purification units. Replay control means for controlling the replay execution means so that is prohibited,
The second exhaust purification means includes a catalyst that exhibits purification performance in an active temperature range lower than a temperature range suitable for regeneration,
When it is determined that the regeneration process is necessary, the regeneration control means excludes the first exhaust purification means of at least one branch part from the target of the regeneration process and performs the regeneration process on the exhaust purification means of the other branch part. Is repeated while sequentially switching the first exhaust purification means excluded from the regeneration process target, thereby controlling the regeneration execution means so that all the first exhaust purification means are regenerated. In addition, during execution of the regeneration process, the plurality of branch portions are provided via the exhaust flow rate adjusting means so that the temperature of the second exhaust purification means detected by the temperature detecting means is maintained in the active temperature range. An exhaust gas purification apparatus for an internal combustion engine, wherein the exhaust gas flow rate passing through each of the engine is controlled .   The regeneration execution means further comprises: an air-fuel ratio detection means for detecting an air-fuel ratio of the exhaust flowing into the second exhaust purification means; and an exhaust flow rate adjustment means for adjusting an exhaust flow rate guided to each of the branch portions. Has a fuel addition valve for individually adding fuel to the first exhaust purification means of each of the plurality of branch portions, and the second exhaust purification means includes a catalyst that exhibits purification performance in a predetermined air-fuel ratio range. The regeneration control means, via the exhaust flow rate adjusting means, controls the plurality of air flow ratios so that the air-fuel ratio detected by the air-fuel ratio detection means is maintained within the predetermined air-fuel ratio range during execution of the regeneration process. The exhaust emission control device according to claim 1, wherein the exhaust gas flow rate passing through each of the branch portions is controlled. The first exhaust purification means includes an NOx storage reduction catalyst, and the second exhaust purification means exhibits a purification performance against sulfate in a lean region where the air amount is larger than the stoichiometric air-fuel ratio as the predetermined air-fuel ratio range. The exhaust emission control device according to claim 2 , further comprising a catalyst.

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