JP4609178B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

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

Particulate filters for collecting particulates contained in exhaust gas discharged from the engine, and NOx in the exhaust gas are occluded when the air-fuel ratio of the inflowing exhaust gas is lean, and the inflowing exhaust gas is empty A NOx trap catalyst that releases the stored NOx when the fuel ratio becomes rich is placed in the engine exhaust passage, and when regenerating the particulate filter, the temperature of the particulate filter is first raised to approximately 600 ° C. or higher so that the temperature can be regenerated. The temperature rise control is performed to raise the temperature, and then the particulate filter deposited on the particulate filter is burned while maintaining the temperature of the particulate filter at about 600 ° C. or higher when the air-fuel ratio of the exhaust gas is lean. An internal combustion engine in which a particulate filter is regenerated is known (for example, See Patent Document 1).
JP 2002-227688 A

  Incidentally, the upper limit temperature of the NOx trap catalyst at which the NOx trap catalyst can store NOx in the exhaust gas is approximately 500 ° C., which is considerably lower than the temperature at which the particulate filter can be regenerated. On the other hand, when the temperature of the particulate filter is maintained at approximately 600 ° C. or higher with the air-fuel ratio of the exhaust gas being lean to regenerate the particulate filter, the temperature of the NOx trap catalyst is such that the NOx trap catalyst can store NOx. The temperature is considerably higher than the temperature. Therefore, when the regeneration action of the particulate filter is performed, the NOx occlusion action is performed by the NOx trap catalyst even though the exhaust gas air-fuel ratio is lean and the exhaust gas contains a large amount of NOx. Therefore, there is a problem that a large amount of NOx is released into the atmosphere.

In order to solve the above problems, according to the present invention, NOx in the exhaust gas is occluded when the air-fuel ratio of the inflowing exhaust gas is lean, and the NOx occluded when the air-fuel ratio of the inflowing exhaust gas becomes rich. A NOx storage reduction catalyst that releases NOx is disposed in the engine exhaust passage, and a particulate filter for collecting particulates contained in the exhaust gas is disposed in the engine exhaust passage downstream of the NOx storage reduction catalyst. In an exhaust gas purification apparatus for an internal combustion engine, temperature increase control is first performed to raise the temperature of the particulate filter to a reproducible temperature when the filter is regenerated, and then regeneration processing is performed to regenerate the particulate filter. during regeneration process of the particulate filter, the temperature of the particulate of the particulate filter Fi As the temperature of the NOx storage reduction catalyst to a temperature capable of occluding lower NOx than the temperature of the particulate filter while maintaining the reproduction target temperature range of data, the air-fuel ratio of the exhaust gas flowing into the NOx storage-reduction catalyst The intermittent rich air-fuel ratio period in which the exhaust gas is intermittently rich repeatedly under lean and the lean air-fuel ratio period in which the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is continuously kept lean are alternately repeated. It is.

Further, in order to solve the above problems, according to the present invention, the first exhaust passage and the second exhaust passage branched from the common exhaust passage are provided, and when the air-fuel ratio of the inflowing exhaust gas is lean. NOx storage reduction catalysts that store NOx in the exhaust gas and release the stored NOx when the air-fuel ratio of the inflowing exhaust gas becomes rich are disposed in the first exhaust passage and the second exhaust passage, respectively. In addition, when a particulate filter for collecting particulates contained in the exhaust gas is disposed in each of the first exhaust passage and the second exhaust passage downstream of the NOx storage reduction catalyst, and the particulate filter is regenerated. First, temperature rise control is performed to raise the temperature of the particulate filter to a recyclable temperature, and then regeneration to regenerate the particulate filter. In the exhaust purification system for an internal combustion engine management is performed, the fuel addition valve disposed in the first exhaust passage and the second exhaust passage common exhaust passage upstream, during regeneration process of the particulate filter, the particulate filter The air-fuel ratio of the exhaust gas is lean so that the temperature of the NOx occlusion reduction catalyst becomes a temperature at which NOx lower than the temperature of the particulate filter can be occluded while maintaining the temperature within the regeneration target temperature range of the particulate filter. The fuel addition period in which fuel is intermittently injected into the exhaust gas from the fuel addition valve and the fuel addition stop period in which the fuel injection from the fuel addition valve is stopped are alternately repeated , and the first The exhaust passage is opened and the second exhaust passage is closed, and the first exhaust passage is closed and the second exhaust passage is opened alternately.

  Even during the regeneration process of the particulate filter, it is possible to purify NOx by the NOx storage reduction catalyst.

FIG. 1 shows an overall view of a compression ignition type internal combustion engine.
Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve for injecting fuel into each combustion chamber 2, 4 is an intake manifold, and 5 is an exhaust manifold. Respectively. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 9 via the air flow meter 8. An electrically controlled throttle valve 10 is arranged in the intake duct 6, and a cooling device 11 for cooling intake air flowing in the intake duct 6 is arranged around the intake duct 6. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 11, and the intake air is cooled by the engine cooling water. On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7, and the outlet of the exhaust turbine 7 b is connected to the exhaust aftertreatment device 20 via the exhaust passage 21.

  The exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 12, and an electrically controlled EGR control valve 13 is disposed in the EGR passage 12. A cooling device 14 for cooling the EGR gas flowing in the EGR passage 12 is disposed around the EGR passage 12. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 14, and the EGR gas is cooled by the engine cooling water. On the other hand, each fuel injection valve 3 is connected to a common rail 16 through a fuel supply pipe 15. Fuel is supplied into the common rail 16 from an electronically controlled fuel pump 17 with variable discharge amount, and the fuel supplied into the common rail 16 is supplied to the fuel injection valve 3 through each fuel supply pipe 15.

  As shown in FIG. 1, a NOx storage reduction catalyst 23, a particulate filter 24, and an oxidation catalyst 25 are arranged in order from the upstream side in the exhaust aftertreatment device 20. Further, in the exhaust aftertreatment device 20, there are a temperature sensor 28 for detecting the temperature of the NOx storage reduction catalyst 23, a differential pressure sensor 29 for detecting the differential pressure across the particulate filter 24, and the oxidation catalyst 25. A temperature sensor 30 and an air-fuel ratio sensor 31 for detecting the temperature and air-fuel ratio of the exhaust gas discharged are arranged. A fuel addition valve 32 is disposed in the exhaust passage 21 upstream of the NOx storage reduction catalyst 23. Fuel is added from the fuel addition valve 32 as shown by F in FIG. In an embodiment according to the invention, this fuel consists of light oil.

  The electronic control unit 40 comprises a digital computer and is connected to each other by a bidirectional bus 41. A ROM (read only memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 44, an input port 45 and an output port 46 are connected. It comprises. The output signals of the air flow meter 8, the temperature sensors 28 and 30, the differential pressure sensor 29, and the air-fuel ratio sensor 31 are input to the input port 45 via the corresponding AD converters 47. The accelerator pedal 49 is connected to a load sensor 50 that generates an output voltage proportional to the depression amount L of the accelerator pedal 49, and the output voltage of the load sensor 50 is input to the input port 45 via the corresponding AD converter 47. Is done. Further, a crank angle sensor 51 that generates an output pulse every time the crankshaft rotates, for example, 15 ° is connected to the input port 45. On the other hand, the output port 46 is connected to the fuel injection valve 3, the throttle valve 10 drive device, the EGR control valve 13, the fuel pump 17, and the fuel addition valve 32 via corresponding drive circuits 48.

  FIG. 2 shows the structure of the NOx storage reduction catalyst 23. In the embodiment shown in FIG. 2, the NOx occlusion reduction catalyst 23 has a honeycomb structure and includes a plurality of exhaust gas flow passages 61 separated from each other by thin partition walls 60. A catalyst carrier made of alumina, for example, is supported on both surfaces of each partition wall 60, and FIGS. 3A and 3B schematically show a cross section of the surface portion of the catalyst carrier 65. As shown in FIGS. 3A and 3B, a noble metal catalyst 66 is dispersedly supported on the surface of the catalyst carrier 65, and a layer of NOx absorbent 67 is further formed on the surface of the catalyst carrier 65. Is formed.

In the embodiment according to the present invention, platinum Pt is used as the noble metal catalyst 66, and the components constituting the NOx absorbent 67 are, for example, alkali metals such as potassium K, sodium Na, cesium Cs, barium Ba, and calcium Ca. At least one selected from rare earths such as alkaline earth, lanthanum La, and yttrium Y is used.
When the ratio of air and fuel (hydrocarbon) supplied into the engine intake passage, the combustion chamber 2 and the exhaust passage upstream of the NOx storage reduction catalyst 23 is referred to as the air-fuel ratio of the exhaust gas, the NOx absorbent 67 When the fuel ratio is lean, NOx is absorbed, and when the oxygen concentration in the exhaust gas decreases, the NOx is absorbed and released to release the absorbed NOx.

That is, the case where barium Ba is used as a component constituting the NOx absorbent 67 will be described as an example. When the air-fuel ratio of the exhaust gas is lean, that is, when the oxygen concentration in the exhaust gas is high, the NO contained in the exhaust gas 3A is oxidized on platinum Pt66 to become NO ₂ as shown in FIG. 3 (A), and then is absorbed into the NOx absorbent 67 and combined with barium oxide BaO to form a NOx absorbent in the form of nitrate ions NO ₃ ^−. It diffuses in 67. In this way, NOx is absorbed in the NOx absorbent 67. Exhaust oxygen concentration in the _gas, NO ₂ is produced on a high as long as the surface of the platinum PT66, unless NO ₂ to NOx absorbing capability of the NOx absorbent 67 is not saturated is absorbed in the NOx absorbent 67 nitrate ions NO ₃ ^- is Generated.

On the other hand, when the air-fuel ratio of the exhaust gas is made rich or stoichiometric, the oxidation concentration in the exhaust gas decreases, so that the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ). As shown in (B), nitrate ions NO ₃ ⁻ in the NOx absorbent 67 are released from the NOx absorbent 67 in the form of NO ₂ . Next, the released NOx is reduced by unburned HC and CO contained in the exhaust gas.

  Thus, when the air-fuel ratio of the exhaust gas is lean, that is, when combustion is performed under the lean air-fuel ratio, NOx in the exhaust gas is absorbed into the NOx absorbent 67. However, if combustion under a lean air-fuel ratio is continuously performed, the NOx absorbent capacity of the NOx absorbent 67 is saturated during that time, and therefore the NOx absorbent 67 cannot absorb NOx. Therefore, in the embodiment according to the present invention, the air-fuel ratio of the exhaust gas is temporarily made rich by adding fuel from the fuel addition valve 32 before the absorption capacity of the NOx absorbent 67 is saturated, and thereby the NOx absorbent 67 to the NOx. To be released.

  4A and 4B show the structure of the particulate filter 24. FIG. 4A shows a front view of the particulate filter 24, and FIG. 4B shows a side sectional view of the particulate filter 24. As shown in FIGS. 4A and 4B, the particulate filter 24 has a honeycomb structure and includes a plurality of exhaust flow passages 70 and 71 extending in parallel with each other. These exhaust flow passages include an exhaust gas inflow passage 70 whose downstream end is closed by a plug 72 and an exhaust gas outflow passage 71 whose upstream end is closed by a plug 73. In addition, the hatched part in FIG. Therefore, the exhaust gas inflow passages 70 and the exhaust gas outflow passages 71 are alternately arranged via the thin partition walls 74. In other words, in the exhaust gas inflow passage 70 and the exhaust gas outflow passage 71, each exhaust gas inflow passage 70 is surrounded by four exhaust gas outflow passages 71, and each exhaust gas outflow passage 71 is surrounded by four exhaust gas inflow passages 70. Arranged so that.

  The particulate filter 24 is made of, for example, a porous material such as cordierite. Therefore, the exhaust gas flowing into the exhaust gas inflow passage 70 is contained in the surrounding partition wall 74 as shown by an arrow in FIG. And flows into the adjacent exhaust gas outflow passage 71.

  In the embodiment according to the present invention, catalyst carriers made of alumina, for example, are also provided on the peripheral wall surfaces of the exhaust gas inflow passages 70 and the exhaust gas outflow passages 71, that is, on both side surfaces of the partition walls 74 and on the pore inner wall surfaces of the partition walls 74. As shown in FIGS. 3A and 3B, a noble metal catalyst 66 made of platinum Pt is dispersed and supported on the surface of the catalyst carrier 65, and a layer of NOx absorbent 67 is supported. Is formed. Therefore, when combustion is performed under a lean air-fuel ratio, NOx in the exhaust gas is also absorbed in the NOx absorbent 67 on the particulate filter 24. The NOx absorbed in the NOx absorbent 67 is also released by adding fuel from the fuel addition valve 32. In this case, a particulate filter that does not carry the NOx absorbent 67 may be used as the particulate filter 24.

  On the other hand, particulates contained in the exhaust gas, that is, particulate matter, are collected on the particulate filter 24 and sequentially oxidized. However, when the amount of particulate matter collected is larger than the amount of particulate matter to be oxidized, particulate matter gradually accumulates on the particulate filter 24. In this case, if the amount of particulate matter deposited increases, the engine output Will be reduced. Therefore, when the amount of accumulated particulate matter increases, the deposited particulate matter must be removed. In this case, if the temperature of the particulate filter 24 is maintained at approximately 600 ° C. or higher under excess air, the deposited particulate matter is oxidized and removed.

  Therefore, in the embodiment according to the present invention, when the amount of the particulate matter deposited on the particulate filter 24 exceeds the allowable amount, for example, the differential pressure ΔP before and after the particulate filter 24 detected by the differential pressure sensor 29 has an allowable value. When exceeding, the fuel is added from the fuel addition valve 32 while keeping the air-fuel ratio of the exhaust gas flowing into the particulate filter 24 lean, and the temperature of the particulate filter 24 is set to about 600 by the oxidation reaction heat of the added fuel. The temperature is kept above ℃.

  FIG. 5 shows a time chart of NOx release control from the NOx storage reduction catalyst 23 and the particulate filter 24, or NOx release control from the NOx storage reduction catalyst 23, and regeneration control of the particulate filter 24. As indicated by X in FIG. 5, the air-fuel ratio A / F of the exhaust gas flowing into the NOx absorbent 67 temporarily changes from lean to rich every time the amount of NOx absorbed in the NOx absorbent 67 exceeds the allowable value. Is switched to. At this time, NOx is released from the NOx absorbent 67 and reduced.

  On the other hand, when the differential pressure ΔP across the particulate filter 24 exceeds the allowable value PX, first, as shown in FIG. 5, the temperature at which the temperature of the particulate filter 24 can be regenerated with the air-fuel ratio of the exhaust gas being lean is shown. The temperature rise control is performed to raise the temperature up to. This temperature increase control is performed by adding fuel from the fuel addition valve 32 or by retarding the fuel injection timing from the fuel injection valve 3 to the compression top dead center.

  Next, when the temperature of the particulate filter 24 reaches a reproducible temperature, that is, approximately 600 ° C. or higher, a regeneration process for regenerating the particulate filter 24 is performed. As can be seen from FIG. 5, in the present invention, during the regeneration process of the particulate filter 24, the air-fuel ratio of the exhaust gas is occasionally rich in order to remove NOx in the exhaust gas while maintaining the temperature of the particulate filter 24 at or above the regeneration temperature. It is said. Next, when the regeneration process is completed, the air-fuel ratio of the exhaust gas is returned to lean.

  FIG. 6 shows the fuel addition method from the fuel addition valve 32 during the regeneration process shown in FIG. 5 and the fluctuation of the air-fuel ratio A / F of the exhaust gas flowing into the NOx storage reduction catalyst 23. Further, FIG. 6 also shows changes in the temperature Tn of the NOx storage reduction catalyst 23 and changes in the temperature Tf of the particulate filter 24.

  Referring to FIG. 6, according to the present invention, the intermittent rich air in which the air-fuel ratio of the exhaust gas flowing into the NOx occlusion reduction catalyst 23 is repeatedly made rich repeatedly intermittently during the regeneration process of the particulate filter 24. The fuel ratio period F and the lean air-fuel ratio period R in which the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 23 is continuously kept lean are alternately repeated.

  More specifically, when the fuel addition valve 32 is arranged in the engine exhaust passage 21 upstream of the NOx storage reduction catalyst 23 as shown in FIG. The fuel is intermittently injected, and the air-fuel ratio of the exhaust gas is intermittently made rich. During the lean air-fuel ratio period R, intermittent fuel injection from the fuel addition valve 32 is stopped. In FIG. 6, the air-fuel ratio A / F of the exhaust gas in the lean air-fuel ratio period R indicates the air-fuel ratio in the combustion chamber 2, that is, the base air-fuel ratio, and the intervals of each fuel addition in the form of pulses are shown in FIG. As shown, the air-fuel ratio of the exhaust gas is set at a relatively long interval that can return from rich to almost this base air-fuel ratio during each fuel addition.

  When fuel is added from the fuel addition valve 32, a part of the added fuel is oxidized in the NOx storage reduction catalyst 23, and the remaining added fuel passes through the NOx storage reduction catalyst 23 and flows into the particulate filter 24. Then, it is oxidized in the particulate filter 24. In this case, when fuel is added from the fuel addition valve 32, that is, in the intermittent rich air-fuel ratio period F, the temperature Tn of the NOx occlusion reduction catalyst 23 is raised by the oxidation reaction heat of the added fuel as shown in FIG. On the other hand, the temperature Tf of the particulate filter 24 is maintained at a high temperature without changing as much as Tn of the NOx storage reduction catalyst 23. On the other hand, when the fuel addition action is stopped, that is, during the lean air-fuel ratio period R, the oxidation reaction of the added fuel is not performed in the NOx storage reduction catalyst 23, so the temperature Tn of the NOx storage reduction catalyst 23 decreases. However, since the oxidation reaction of the particulate matter on the particulate filter 24 continues, the temperature Tf of the particulate filter 24 does not change much.

  In order to perform the regeneration of the particulate filter 24 satisfactorily, the temperature Tf of the particulate filter 24 is maintained at a temperature equal to or higher than a recyclable lower limit temperature TL and lower than an upper limit temperature TH that causes deterioration of the particulate filter 24. is required. That is, it is necessary to maintain the temperature Tf of the particulate filter 24 within the regeneration target temperature range between the lower limit temperature TL and the upper limit temperature TH. However, the temperature Tf of the particulate filter 24 increases when the intermittent rich air-fuel ratio period F is lengthened and decreases when the lean air-fuel ratio period R is lengthened. Therefore, in the embodiment according to the present invention, the intermittent rich air-fuel ratio period F is lengthened when the temperature Tf of the particulate filter 24 falls to the lower limit temperature TL of the regeneration target temperature range, and the temperature Tf of the particulate filter 24 becomes the regeneration target temperature range. When the temperature rises to the upper limit temperature TH, the intermittent rich air-fuel ratio period F is shortened.

  As described above, according to the present invention, when the particulate filter 24 is regenerated, the temperature Tf of the particulate filter 24 is maintained within the regeneration target temperature range, so that the particulate matter deposited on the particulate filter 24 is surely oxidized and removed. Is done.

  On the other hand, when fuel is added from the fuel addition valve 32, the added fuel is oxidized in the NOx storage reduction catalyst 23 and the particulate filter 24 as described above. Therefore, the temperature Tn of the NOx storage reduction catalyst 23 rises due to the oxidation reaction heat of the added fuel, and the exhaust gas temperature flowing out from the NOx storage reduction catalyst 23 becomes higher than the temperature of the NOx storage reduction catalyst 23. At this time, the particulate filter 24 is heated by the high-temperature exhaust gas, and the heat of oxidation reaction of the added fuel is generated in the particulate filter 24. Therefore, as shown in FIG. 6, the temperature Tf of the particulate filter 24 is NOx. It becomes considerably higher than the temperature Tn of the storage reduction catalyst 23. In other words, the temperature Tn of the NOx storage reduction catalyst 23 is lower than the temperature Tf of the particulate filter 24.

  By the way, if the NOx absorbent 67 carried on the NOx occlusion reduction catalyst 23 is in the temperature range of 200 ° C. to 250 ° C. and 450 ° C. to 500 ° C., if the air-fuel ratio of the exhaust gas is lean, It has the property of absorbing NOx. That is, when the temperature of the NOx absorbent 67 is 200 ° C. to 250 ° C. or less, platinum Pt is not sufficiently activated, so that NO is not sufficiently oxidized, and as a result, NOx absorption action is not performed. On the other hand, when the temperature of the NOx absorbent 67 is changed from 450 ° C. to 500 ° C., the NOx absorbed by the NOx absorbent 67 is decomposed in the NOx absorbent 67 and spontaneously released from the NOx absorbent 67. At this time, NOx absorption is not performed.

  As can be seen from FIG. 6, in the second half of the lean air-fuel ratio period R, the temperature Tn of the NOx occlusion reduction catalyst 23 decreases to 500 ° C. or less, and for a while even in the intermittent rich air-fuel ratio period F, that is, intermittent In the first half of the rich air-fuel ratio period F, the temperature Tn of the NOx storage reduction catalyst 23 is 500 ° C. or less. Accordingly, when the air-fuel ratio A / F of the exhaust gas is lean in the first half of the lean air-fuel ratio period R and the second half of the intermittent rich air-fuel ratio period F, NOx contained in the exhaust gas is stored in the NOx storage reduction catalyst 23. Thus, NOx in the exhaust gas can be purified while the particulate filter 24 is regenerated. Note that NOx occluded in the NOx occlusion reduction catalyst 23 is released and reduced when the air-fuel ratio of the exhaust gas becomes rich in the intermittent air-fuel ratio rich period F.

FIG. 7 shows the regeneration control of the particulate filter 24.
Referring to FIG. 7, first, at step 100, it is judged if the differential pressure ΔP across the particulate filter 24 has exceeded the allowable value PX. Next, at step 101, the temperature rise control shown in FIG. 5 is performed. Next, at step 102, it is determined whether or not the temperature raising control is completed. When the temperature raising control is completed, the routine proceeds to step 103 where regeneration processing of the particulate filter 24 is performed. This reproduction processing routine is shown in FIG. Next, at step 104, it is determined whether or not the differential pressure ΔP across the particulate filter 24 has become equal to or smaller than the minimum value MIN. When ΔP <MIN, the regeneration process is completed.

  In the embodiment shown in FIG. 6, a reference fuel addition period Fv in which fuel is added in a pulsed manner, that is, a reference intermittent rich air-fuel ratio period F, is predetermined, and this fuel addition period Fv is as shown in FIG. As the intake air amount Ga increases, it becomes longer.

FIG. 9 shows a time interrupt routine.
Referring to FIG. 9, first, at step 110, whether or not the temperature T of the particulate filter 24 estimated from one or both of the temperature sensor 28 and the temperature sensor 30 is lower than the lower limit temperature TL of the regeneration target temperature range. When T <TL, the routine proceeds to step 111 where the set value α is added to the correction value ΔF for the fuel addition period Fv. On the other hand, when it is judged at step 110 that T ≧ TL, the routine proceeds to step 112, where it is judged if the temperature T of the particulate filter 24 is higher than the upper limit temperature TH of the regeneration target temperature range, and T> TH. Sometimes, the routine proceeds to step 113, where the set value α is subtracted from the correction value ΔF for the fuel addition period Fv.

  Referring to FIG. 10, first, at step 120, the fuel addition period Fv is calculated from FIG. Next, at step 121, the final fuel addition period F, that is, the intermittent rich air-fuel ratio period F, is obtained by adding the correction value ΔF to the fuel addition period Fv, and the fuel addition operation is performed based on the fuel addition period F. . Next, the routine proceeds to step 104 in FIG.

  FIG. 11 shows a modification. In this modification, a smaller amount of fuel is intermittently and repeatedly injected during the lean air-fuel ratio period R than during the intermittent rich air-fuel ratio period F.

  In another modified example, during the intermittent rich air-fuel ratio period F, additional fuel is injected into the combustion chamber 2 during the latter half of the expansion stroke or during the exhaust stroke after a predetermined period. Is repeatedly made rich so that the injection of additional fuel is stopped during the lean air-fuel ratio period R. In this case, intermittent rich in the combustion chamber 2 during the latter half of the expansion stroke or during the exhaust stroke with a predetermined period during the lean air-fuel ratio period R so that the same air-fuel ratio change as that shown in FIG. 11 occurs. It is also possible to inject a small amount of additional fuel as compared to during the air-fuel ratio period F.

FIG. 12 shows another embodiment.
In this embodiment, the exhaust aftertreatment device 20 includes a first exhaust passage 22a and a second exhaust passage 22b branched from a common exhaust passage 21 connected to the outlet of the exhaust turbine 7b. In the first exhaust passage 22a, a first exhaust control valve driven by the first NOx storage reduction catalyst 23a, the first particulate filter 24a, the first oxidation catalyst 25a, and the actuator 27a in order from the upstream side. 26a is disposed in the second exhaust passage 22b in order from the upstream side by the second NOx storage reduction catalyst 23b, the second particulate filter 24b, the second oxidation catalyst 25b, and the actuator 27b. Two exhaust control valves 26b are arranged. The first exhaust passage 22a and the second exhaust passage 22b are joined to a common exhaust pipe 27 downstream of the first exhaust control valve 26a and the second exhaust control valve 26b.

  The first exhaust passage 22a has a temperature sensor 28a for detecting the temperature of the first NOx storage reduction catalyst 23a and a first difference for detecting the differential pressure across the first particulate filter 24a. A pressure sensor 29a, a temperature sensor 30a and an air-fuel ratio sensor 31a for detecting the temperature and air-fuel ratio of the exhaust gas discharged from the first oxidation catalyst 25a, respectively, are disposed, and a second exhaust passage 22b is provided with a second sensor. A temperature sensor 28b for detecting the temperature of the NOx storage reduction catalyst 23b, a second differential pressure sensor 29b for detecting the differential pressure across the second particulate filter 24b, and the second oxidation catalyst 25b. A temperature sensor 30b and an air-fuel ratio sensor 31b are provided for detecting the temperature of the exhaust gas and the air-fuel ratio, respectively. Further, in this embodiment, a common fuel addition valve 32 is provided in the common exhaust passage 21 upstream of the first exhaust passage 22a and the second exhaust passage 22b with respect to the first exhaust passage 22a and the second exhaust passage 22b. Is arranged.

  FIG. 13 shows another embodiment of the compression ignition type internal combustion engine. In this embodiment, a fuel addition valve 32 is attached to the exhaust manifold 5, and fuel, that is, light oil, is added into the exhaust manifold 5 from the fuel addition valve 32. 12 and FIG. 13 is substantially the same as the NOx storage reduction catalyst 23 shown in FIG. 1, and each particulate filter 24a shown in FIG. 12 and FIG. 24b are substantially the same as the particulate filter 24 shown in FIG.

  14 shows the fuel addition action from the fuel addition valve 32 during particulate filter regeneration, the opening / closing operation of the exhaust control valves 26a, 26b, and the air-fuel ratio A / of the exhaust gas flowing into the NOx storage reduction catalysts 23a, 23b. F, temperature Tf of each particulate filter 24a, 24b, and temperature Tn of each NOx storage reduction catalyst 23a, 23b are shown. In FIG. 14, I indicates the first exhaust passage 22a, and II indicates the second exhaust passage 22b.

  Referring to FIG. 14, in this embodiment, during the regeneration process of the particulate filter, the fuel addition period F during which fuel is intermittently injected from the fuel addition valve 32 and the fuel injection from the fuel addition valve 32 are suspended. The fuel addition suspension period R is alternately repeated. Also in this embodiment, the fuel addition period F is controlled so that the temperature Tf of the particulate filters 24a, 24b is within the regeneration target temperature range. That is, when the temperature Tf of the particulate filters 24a and 24b is reduced to the lower limit temperature TL of the regeneration target temperature range, the fuel addition period F is lengthened, and the temperature Tf of the particulate filters 24a and 24b is increased to the upper limit temperature TH of the regeneration target temperature range. The fuel addition period F is shortened when it rises to.

  In this embodiment, as shown in FIG. 14, the first exhaust control valve 26a and the second exhaust control valve 26b are repeatedly opened and closed. In this case, the first exhaust control valve 26a is opened. When the valve is opened, the second exhaust control valve 26b is closed, and when the first exhaust control valve 26a is closed, the second exhaust control valve 26b is opened. That is, the state where the first exhaust passage 22a is opened and the second exhaust passage 22b is closed and the state where the first exhaust passage 22a is closed and the second exhaust passage 22b is opened are alternately repeated.

  At this time, the first exhaust control valve 26a and the second exhaust control valve 26b are opened or closed during the fuel addition period F, and the first exhaust control valve 26a and the second exhaust control valve 26b are opened. When the valve was opened during the fuel addition period F, the valve continued to be opened during the fuel addition suspension period R, and the first exhaust control valve 26a and the second exhaust control valve 26b were closed during the fuel addition period F. Sometimes it remains closed during the fuel addition suspension period R. That is, the first exhaust passage 22a and the second exhaust passage 22b are opened or closed during the fuel addition period F, and kept open or closed during the fuel addition suspension period R.

  As described above, when the first exhaust passage 22a and the second exhaust passage 22b are opened or closed during the fuel addition period F and kept open or closed during the fuel addition suspension period R, the particulate filters 24a and 24b are regenerated. NOx in the exhaust gas can be purified. That is, paying attention to the first fuel addition period F in FIG. 14, when the fuel addition is started, the first exhaust control valve 26a is closed and the second exhaust control valve 26b is opened. The gas flows only into the second exhaust passage 22b. Therefore, the fuel added from the fuel addition valve 32, that is, light oil, flows only into the second exhaust passage 22b. The fuel that has flowed into the second exhaust passage 22b temporarily adheres to the second NOx storage reduction catalyst 23b and the first particulate filter 24b, and then evaporates and is oxidized.

  On the other hand, as shown in FIG. 14, as soon as the first fuel addition is performed, the first exhaust control valve 26a is opened and the second exhaust control valve 26b is closed. Therefore, the fuel added from the fuel addition valve 32, that is, light oil, flows only into the first exhaust passage 22a. The fuel that has flowed into the first exhaust passage 22a temporarily adheres to the first NOx storage reduction catalyst 23a and the first particulate filter 24a, and then is evaporated and oxidized.

  As a result, as shown in FIG. 14I, the temperature Tn of the first NOx storage reduction catalyst 23a rises, and the temperature Tf of the first particulate filter 24a continues to be maintained at a high temperature. Next, when the fuel addition period F shifts to the fuel addition suspension period R, the generation of heat of oxidation reaction is interrupted in the NOx storage reduction catalyst 23a, so the temperature Tn of the NOx storage reduction catalyst 23a decreases. At this time, since the particulate matter oxidation reaction continues in the particulate filter 24a, the temperature Tf of the particulate filter 24a does not change much.

  Next, the fuel addition period F is reached again. When the first fuel addition is completed, the second exhaust control valve 26b is opened, and the first exhaust control valve 26a is closed. At this time, as shown in II of FIG. 14, the temperature Tn of the second NOx storage reduction catalyst 23b rises, and the temperature Tf of the second particulate filter 24b is kept at a high temperature. Next, when the fuel addition period F shifts to the fuel addition suspension period R, the generation of heat of oxidation reaction is interrupted in the NOx storage reduction catalyst 23b, so the temperature Tn of the NOx storage reduction catalyst 23b decreases. At this time, since the particulate matter oxidation reaction continues in the particulate filter 24b, the temperature Tf of the particulate filter 24b does not change much.

  On the other hand, when attention is again paid to the first fuel addition period F in FIG. 14, the second exhaust control valve 26b is closed immediately after the first fuel addition. When the second exhaust control valve 26b is closed, only the heat of oxidation reaction due to the oxygen present in the limited volume in the second exhaust passage 22b is generated, so the temperature Tn of the second NOx storage reduction catalyst 23b is It is kept at a relatively low temperature. Accordingly, in this embodiment, as can be seen from FIG. 14, the temperature Tn of the second NOx occlusion reduction catalyst 23b is 500 ° C. or less for a while after the second exhaust control valve 26b is opened, and the fuel addition In the rest period R, the temperature Tn of the second NOx storage reduction catalyst 23b becomes 500 ° C. or less.

  That is, when the exhaust gas flows through the second NOx storage reduction catalyst 23b, the temperature Tn of the second NOx storage reduction catalyst 23b becomes 500 ° C. or less over a relatively long time, so that the NOx in the exhaust gas. Is occluded satisfactorily in the second NOx occlusion reduction catalyst 23b. Similarly, when the exhaust gas is flowing through the first NOx storage reduction catalyst 23a, the temperature Tn of the first NOx storage reduction catalyst 23a becomes 500 ° C. or less over a relatively long time, so that NOx is occluded well in the first NOx occlusion reduction catalyst 23a.

  Referring again to the first fuel addition period F in FIG. 14, when the first fuel addition is performed, the second exhaust control valve 26b is opened, and at this time, the fuel added from the fuel addition valve 32 is the second fuel added. The NOx occlusion reduction catalyst 23b and the first particulate filter 24b are attached, and the attached fuel evaporates after the second exhaust control valve 26b is closed. At this time, the exhaust gas does not flow in the second exhaust passage 22b, and the attached fuel evaporates in the exhaust gas within a limited volume in the second exhaust passage 22b. Therefore, as shown in FIG. The air-fuel ratio A / F of the exhaust gas in the two exhaust passages 22b becomes rich. As a result, NOx is released from the second NOx storage reduction catalyst 23b and reduced.

  The same is true when the first exhaust control valve 26a is closed. That is, as shown in FIG. 14, when the first exhaust control valve 26a is closed, the air-fuel ratio A / F of the exhaust gas in the first exhaust passage 22a becomes rich, and therefore the first NOx. NOx is released from the storage reduction catalyst 23a and reduced.

  Further, in the embodiment shown in FIG. 14, the air-fuel ratio A / F of the exhaust gas is intermittently changed by the fuel injected from the fuel addition valve 32 when the exhaust gas is flowing through the NOx storage reduction catalysts 23a and 23b. To be rich. Accordingly, at this time as well, NOx is released from the NOx storage reduction catalysts 23a and 23b and reduced.

  Looking again at the first fuel addition period F in FIG. 14, the fuel injection performed when the first exhaust control valve 26a is closed is mainly the air-fuel ratio of the exhaust gas in the second exhaust passage 22b. Used to make the A / F rich, fuel injection performed when the first exhaust control valve 26b is open is used to keep the temperature Tf of the particulate filter 24a above the lower limit temperature TL. Is done. In this case, it is necessary to maintain the temperature Tf of the particulate filter 24a at or above the lower limit temperature TL compared to the amount of fuel necessary to make the air-fuel ratio A / F of the exhaust gas in the second exhaust passage 22b rich. Since the amount of fuel is much larger, the first exhaust passage 22a and the second exhaust passage 22b are opened or closed at the beginning of the fuel addition period F as shown in FIG. That is, the first exhaust control valve 26a and the second exhaust control valve 26b are opened or closed at the beginning of the fuel addition period F.

  Also in this embodiment, the reference fuel addition period Ft is determined in advance, and this fuel addition period Ft becomes longer as the intake air amount Ga increases as shown in FIG. As for each exhaust control valve 26a, 26b, when one exhaust control valve is opened, the other exhaust control valve can be closed regardless of the intake air amount. However, if one of the exhaust control valves is closed when the amount of intake air is large, the back pressure increases and the output decreases. Therefore, in the example shown in FIG. 15B, the opening degree S when the exhaust control valve is closed is increased when the intake air amount Ga is increased.

FIG. 16 shows a time interrupt routine.
Referring to FIG. 16, first, in step 200, the temperature T ₁ of the particulate filter 24a or the temperature T _{2 of the} particulate filter 24b estimated from the temperature sensors 28a and 28b or the temperature sensors 30a and 30b is within the regeneration target temperature range. It is determined whether or not the temperature is lower than the lower limit temperature TL. When T ₁ or T ₂ <TL, the routine proceeds to step 201 where the set value β is added to the correction value ΔF for the fuel addition period Ft. On the other hand, when it is determined in step 200 that T ₁ and T ₂ ≧ TL, the routine proceeds to step 202 where the temperature T ₁ of the particulate filter 24a or the temperature T ₂ of the particulate filter 24b is the upper limit temperature TH of the regeneration target temperature range. If T ₁ or T ₂ > TH, the routine proceeds to step 203 where the set value β is subtracted from the correction value ΔF for the fuel addition period Ft.

FIG. 17 shows the reproduction process performed in step 103 of FIG.
Referring to FIG. 17, first, at step 210, the fuel addition period Ft is calculated from FIG. 15 (A). Next, at step 211, the final fuel addition period F is obtained by adding the correction value ΔF to the fuel addition period Ft, and the fuel addition operation is performed based on the fuel addition period F. Next, at step 212, the opening degree θ when the exhaust control valve is closed is obtained from FIG. 15B, and the opening degree when the exhaust control valve is closed is set to this opening degree θ. Next, the routine proceeds to step 104 in FIG.

  FIG. 18 shows another embodiment. In this embodiment, as shown in FIG. 18, a smaller amount of fuel is intermittently injected from the fuel addition valve 32 during the fuel addition suspension period R than during the fuel addition period F.

In the embodiment shown in FIG. 19, the same amount of fuel is injected from the fuel addition valve 32 at equal intervals. Also in this embodiment, at the time of each fuel injection performed intermittently, the air-fuel ratio A / F of the exhaust gas in the opened exhaust passages 22a, 22b becomes rich and the exhaust passage 22a, The air-fuel ratio A / F of the exhaust gas in 22b also becomes rich.

  In this embodiment, the temperature of the particulate filters 24a, 24b is maintained within the regeneration target temperature range of the particulate filters 24a, 24b by controlling the amount of fuel intermittently injected from the fuel addition valve 32. That is, in this embodiment, when the temperature of the particulate filters 24a and 24b is reduced to the lower limit temperature TL of the regeneration target temperature range, the fuel addition amount is increased, and the temperature of the particulate filters 24a and 24b is increased to the upper limit of the regeneration target temperature range. When the temperature rises to TH, the fuel addition amount is decreased.

  In this embodiment, a reference fuel addition amount Qo is determined in advance, and the fuel addition amount Qo increases as the intake air amount Ga increases as shown in FIG. Also in this embodiment, as shown in FIG. 20B, the opening degree S when the exhaust control valve is closed is increased as the intake air amount Ga increases.

FIG. 21 shows a time interrupt routine.
Referring to FIG. 21, first, in step 300, the temperature T ₁ of the particulate filter 24a or the temperature T _{2 of the} particulate filter 24b estimated from the temperature sensors 28a and 28b or the temperature sensors 30a and 30b is within the regeneration target temperature range. It is determined whether or not the temperature is lower than the lower limit temperature TL. When T ₁ or T ₂ <TL, the routine proceeds to step 301 where the set value γ is added to the correction value ΔQ for the fuel addition amount Qo. On the other hand, when it is determined in step 300 that T ₁ and T ₂ ≧ TL, the routine proceeds to step 302 where the temperature T ₁ of the particulate filter 24a or the temperature T ₂ of the particulate filter 24b is the upper limit temperature TH of the regeneration target temperature range. If T ₁ or T ₂ > TH, the routine proceeds to step 303 where the set value γ is subtracted from the correction value ΔQ for the fuel addition amount Qo.

FIG. 22 shows the reproduction process performed in step 103 of FIG.
Referring to FIG. 22, first, at step 310, the fuel addition amount Qo is calculated from FIG. Next, at step 311, the final fuel addition amount Q is obtained by adding the correction value ΔQ to the fuel addition amount Qo, and the fuel addition action is performed based on this fuel addition amount Q. Next, at step 312, the opening degree θ when the exhaust control valve is closed is obtained from FIG. 20B, and the opening degree when the exhaust control valve is closed is this opening degree θ. Next, the routine proceeds to step 104 in FIG.

A modification is shown in FIGS.
In the example shown in FIG. 23 (A), one exhaust control valve 26 is arranged at the junction of the downstream end of the first exhaust passage 22a and the downstream end of the second exhaust passage 22b to the exhaust passage 27. The exhaust control valve 26 opens both the first exhaust passage 22a and the second exhaust passage 22b as shown by the solid line, and only the first exhaust passage 22a is closed as shown by the broken line a. And a state in which only the second exhaust passage 22b is closed as indicated by a broken line b.

  In the example shown in FIG. 23B, the first exhaust control valve 26a is disposed in the first exhaust passage 22a upstream of the first NOx storage reduction catalyst 23a, and the second NOx storage reduction catalyst 23b upstream. A second exhaust control valve 26b is disposed in the exhaust passage 22b. Even in this case, if the first exhaust control valve 26a is closed when the added fuel adheres to the first NOx storage reduction catalyst 23a and the first particulate filter 24a, the exhaust gas in the first exhaust passage 22a. Becomes rich, and if the second exhaust control valve 26b is closed when the added fuel adheres to the second NOx storage reduction catalyst 23b and the second particulate filter 24b, the inside of the second exhaust passage 22b Exhaust gas becomes rich.

  FIG. 24 shows still another embodiment. As shown in FIG. 24, in this embodiment, the first fuel addition valve 32a is disposed in the first exhaust passage 22a upstream of the first NOx storage reduction catalyst 23a, and the second NOx storage reduction catalyst 23b upstream. The second fuel addition valve 32b is disposed in the second exhaust passage 22b. In this embodiment, the fuel addition period F and the fuel addition stop period R by the first fuel addition valve 32a are completely synchronized with the fuel addition period F and the fuel addition stop period R by the second fuel addition valve 32b, respectively. The first exhaust control valve 26a and the second exhaust control valve 26b are closed when one is opened, and the other is closed when the other is opened.

1 is an overall view of a compression ignition type internal combustion engine. It is side surface sectional drawing of a NOx storage reduction catalyst. It is sectional drawing of the surface part of a catalyst support | carrier. It is a figure which shows the structure of a particulate filter. It is a time chart for demonstrating the temperature rising control and regeneration process of a particulate filter. 6 is a time chart showing fuel addition timing, fluctuations in the air-fuel ratio of exhaust gas, and the like. It is a flowchart for performing regeneration control of a particulate filter. It is a figure which shows the fuel addition period Fv used as a reference | standard. It is a flowchart which shows a time interruption. It is a flowchart for performing reproduction processing. It is a figure which shows the fuel addition time etc. in a modification. It is a figure which shows another Example of a compression ignition type internal combustion engine. It is a figure which shows another Example of a compression ignition type internal combustion engine. It is a figure which shows the fluctuation | variation of the fuel addition time, the on-off valve timing of an exhaust control valve, the air fuel ratio of exhaust gas, etc. It is a figure which shows the fuel addition period Ft etc. used as a reference | standard. It is a flowchart which shows a time interruption. It is a flowchart for performing reproduction processing. It is a figure which shows the fluctuation | variation of the fuel addition time, the on-off valve timing of an exhaust control valve, the air fuel ratio of exhaust gas, etc. It is a figure which shows the fluctuation | variation of the fuel addition time, the on-off valve timing of an exhaust control valve, the air fuel ratio of exhaust gas, etc. It is a figure which shows fuel addition amount Qo etc. used as a reference | standard. It is a flowchart which shows a time interruption. It is a flowchart for performing reproduction processing. It is a figure which shows the various modifications of a compression ignition type internal combustion engine. It is a figure which shows another Example of a compression ignition type internal combustion engine.

Explanation of symbols

5 Exhaust manifold 20 Exhaust aftertreatment device 21, 27 Common exhaust passage 22a First exhaust passage 22b Second exhaust passage 23 NOx storage reduction catalyst 23a First NOx storage reduction catalyst 23b Second NOx storage reduction catalyst 24 Patty Curate filter 24a First particulate filter 24b Second particulate filter 25 Oxidation catalyst 25a First oxidation catalyst 25b Second oxidation catalyst 26 Exhaust control valve 26a First exhaust control valve 26b Second exhaust control valve 32 Fuel addition valve

Claims (18)

An NOx occlusion reduction catalyst that stores NOx in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean and releases the stored NOx when the air-fuel ratio of the inflowing exhaust gas becomes rich is disposed in the engine exhaust passage. When a particulate filter for collecting particulates contained in the exhaust gas is disposed in the engine exhaust passage downstream of the NOx storage reduction catalyst, and the particulate filter is regenerated, first, the temperature of the particulate filter In the exhaust gas purification apparatus for an internal combustion engine in which the temperature raising control for raising the temperature to a recyclable temperature is performed, and then the regeneration process for regenerating the particulate filter is performed, during the regeneration process of the particulate filter , the particulate filter While maintaining the temperature of the particulate filter within the regeneration target temperature range of the particulate filter As the temperature of the Ox storage reduction catalyst to a temperature capable of occluding lower NOx than the temperature of the particulate filter, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is intermittently repeated rich under a lean The internal combustion engine exhaust gas purification apparatus in which the intermittent rich air-fuel ratio period and the lean air-fuel ratio period in which the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is continuously maintained lean are alternately repeated.   During the lean air-fuel ratio period, the temperature of the NOx occlusion reduction catalyst decreases, NOx contained in the exhaust gas is occluded in the NOx occlusion reduction catalyst, and NOx occluded in the NOx occlusion reduction catalyst is exhausted in the intermittent air fuel ratio rich period. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the exhaust gas purification device releases and reduces when the air-fuel ratio of the gas becomes rich.   A fuel addition valve is disposed in the engine exhaust passage upstream of the NOx storage reduction catalyst. During the intermittent rich air-fuel ratio period, fuel is intermittently injected from the fuel addition valve, and the air-fuel ratio of the exhaust gas is intermittently repeatedly rich. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein intermittent fuel injection from the fuel addition valve is stopped during the lean air-fuel ratio period.   A fuel addition valve is disposed in the engine exhaust passage upstream of the NOx storage reduction catalyst. During the intermittent rich air-fuel ratio period, fuel is intermittently injected from the fuel addition valve, and the air-fuel ratio of the exhaust gas is intermittently repeatedly rich. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein a small amount of fuel is intermittently and repeatedly injected during the lean air-fuel ratio period as compared with the intermittent rich air-fuel ratio period.   During the intermittent rich air-fuel ratio period, the air-fuel ratio of the exhaust gas is intermittently made rich repeatedly by injecting additional fuel into the combustion chamber during the latter half of the expansion stroke or during the exhaust stroke after a predetermined period. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the injection action of the additional fuel is stopped during the lean air-fuel ratio period.   During the intermittent rich air-fuel ratio period, the air-fuel ratio of the exhaust gas is intermittently made rich repeatedly by injecting additional fuel into the combustion chamber during the latter half of the expansion stroke or during the exhaust stroke after a predetermined period. 2. A small amount of additional fuel is injected into the combustion chamber during the second half of the expansion stroke or during the exhaust stroke at a lean air-fuel ratio period, as compared to the intermittent rich air-fuel ratio period. Exhaust gas purification device for internal combustion engine. The intermittent rich air-fuel ratio period is lengthened when the temperature of the particulate filter falls to the lower limit temperature of the regeneration target temperature range, and the intermittent rich air-fuel ratio period when the temperature of the particulate filter rises to the upper limit temperature of the regeneration target temperature range. 2. An exhaust emission control device for an internal combustion engine according to claim 1, wherein The first exhaust passage and the second exhaust passage branched from the common exhaust passage are provided. When the air-fuel ratio of the inflowing exhaust gas is lean, NOx in the exhaust gas is occluded and the air-fuel ratio of the inflowing exhaust gas is stored. NOx occlusion reduction catalysts that release NOx occluded when the gas becomes rich are disposed in the first exhaust passage and the second exhaust passage, respectively, and the first exhaust passage and the second exhaust gas downstream of the NOx occlusion reduction catalyst are arranged. In order to regenerate the particulate filter, the temperature of the particulate filter is first raised to a recyclable temperature when a particulate filter for collecting particulates contained in the exhaust gas is arranged in each exhaust passage. In an exhaust gas purification apparatus for an internal combustion engine in which a temperature raising control is performed, and then a regeneration process for regenerating the particulate filter is performed, A fuel addition valve is disposed in the common exhaust passage upstream of the exhaust passage and the second exhaust passage, and during the regeneration process of the particulate filter, the temperature of the particulate filter is within the regeneration target temperature range of the particulate filter. While maintaining the temperature of the NOx occlusion reduction catalyst so that the temperature at which NOx is lower than the temperature of the particulate filter can be occluded, the fuel is added to the exhaust gas from the fuel addition valve with the air-fuel ratio of the exhaust gas being lean. The fuel addition period intermittently injected into the fuel supply period and the fuel addition stop period during which fuel injection from the fuel addition valve is stopped are alternately repeated, and the first exhaust passage is opened and the second exhaust passage is opened. An exhaust purification device for an internal combustion engine in which a closed state and a state in which a first exhaust passage is closed and a second exhaust passage is opened alternately are repeated . When either one of the exhaust passages is closed, the temperature of the NOx storage reduction catalyst disposed in the closed exhaust passage decreases and the air-fuel ratio of the exhaust gas in the closed exhaust passage becomes rich. Therefore, NOx is released and reduced from the NOx occlusion reduction catalyst arranged in the closed exhaust passage, and the NOx occlusion reduction is arranged in the opened exhaust passage when the closed exhaust passage is opened. The exhaust gas purification apparatus for an internal combustion engine according to claim 8 , wherein NOx contained in the exhaust gas is occluded in the catalyst . 9. The air-fuel ratio of exhaust gas in the open exhaust passage is intermittently made rich when fuel is intermittently injected from the fuel addition valve during the regeneration process of the particulate filter. 2. An exhaust gas purification apparatus for an internal combustion engine according to 1. 9. The exhaust emission control device for an internal combustion engine according to claim 8 , wherein the first exhaust passage and the second exhaust passage are opened or closed during the fuel addition period and kept open or closed during the fuel addition suspension period . The exhaust emission control device for an internal combustion engine according to claim 11 , wherein the first exhaust passage and the second exhaust passage are opened or closed at an initial stage of the fuel addition period . The temperature of the particulate filter is controlled by controlling the fuel addition period. When the temperature of the particulate filter decreases to the lower limit temperature of the regeneration target temperature range, the fuel addition period is lengthened, and the temperature of the particulate filter is The exhaust purification device of an internal combustion engine according to claim 8 , wherein the fuel addition period is shortened when the temperature rises to the upper limit temperature of the regeneration target temperature range . The exhaust emission control device for an internal combustion engine according to claim 8 , wherein a smaller amount of fuel is intermittently injected from the fuel addition valve during the fuel addition suspension period than during the fuel addition period . The exhaust emission control device for an internal combustion engine according to claim 8 , wherein the temperature of the particulate filter is maintained within the regeneration target temperature range of the particulate filter by controlling the amount of fuel injected intermittently from the fuel addition valve . When the temperature of the particulate filter falls to the lower limit temperature of the regeneration target temperature range, the fuel addition amount is increased. When the temperature of the particulate filter rises to the upper limit temperature of the regeneration target temperature range, the fuel addition amount is decreased. 16. An exhaust emission control device for an internal combustion engine according to claim 15 , wherein the exhaust gas purification device is an internal combustion engine. The fuel addition valve includes a first fuel addition valve and a second fuel addition valve, the first fuel addition valve is disposed in the first exhaust passage upstream of the NOx storage reduction catalyst, and the second fuel addition valve is The exhaust emission control device for an internal combustion engine according to claim 8 , which is disposed in the second exhaust passage upstream of the NOx storage reduction catalyst . The exhaust emission control device for an internal combustion engine according to claim 8 , further comprising at least one exhaust control valve for closing or opening the first exhaust passage and the second exhaust passage .

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