JP2010048134A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

An object of the present invention is to maintain a high NOx purification rate while maintaining a low fuel consumption.
NOx storage reduction catalysts 27u, 27d are disposed in an exhaust passage, and fuel supply means 32u, 32d for supplying fuel to the NOx storage reduction catalyst are provided. When the NOx occluded from the NOx occlusion reduction catalyst is to be released and reduced, the fuel is supplied from the fuel supply means to the corresponding NOx occlusion reduction catalyst, so that the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich. Like that. The temperature of the NOx storage reduction catalyst is detected. The fuel supply amounts from these fuel supply means are respectively set so that the total value of the fuel supply amounts from the fuel supply means substantially matches the target value, and the set fuel supply amount and the temperature of the NOx storage reduction catalyst are set. The NOx purification rate of the NOx storage reduction catalyst is calculated based on each, and the fuel supply amount from the fuel supply means is set so that the total value of these NOx purification rates exceeds the allowable value.
[Selection] Figure 1

Description

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

  Two NOx occlusion reduction catalysts are arranged in series in the engine exhaust passage, and each NOx occlusion reduction catalyst occludes NOx contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and the air-fuel ratio of the inflowing exhaust gas is theoretically When the air-fuel ratio or rich, the stored NOx is released and reduced, and when the NOx stored from these NOx storage-reduction catalysts should be released and reduced, combustion is performed under the rich air-fuel ratio. Is known (see Patent Document 1). When combustion is performed under a rich air-fuel ratio, the air-fuel ratio of the exhaust gas flowing into the two NOx storage reduction catalysts is switched to rich, so that NOx is released from the two NOx storage reduction catalysts and reduced.

Japanese Patent Laid-Open No. 2004-68731

  However, when combustion is performed under a rich air-fuel ratio, unburned HC and CO contained in the exhaust gas are oxidized by the upstream NOx storage reduction catalyst, and a sufficient amount for the downstream NOx storage reduction catalyst Thus, there is a possibility that NOx is not sufficiently released and reduced in the downstream NOx storage reduction catalyst.

  This problem can be solved by providing fuel supply means for supplying fuel to each of the plurality of NOx storage reduction catalysts arranged in series in the exhaust passage.

  However, in this case, if an attempt is made to increase the NOx purification rate of all NOx storage reduction catalysts, it is necessary to supply a large amount of fuel from each fuel supply means, and there is a risk that the fuel consumption will increase.

  According to the present invention, a plurality of NOx storage reduction catalysts are arranged in series in the engine exhaust passage, and each NOx storage reduction catalyst stores NOx contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, When the air-fuel ratio of the gas becomes the stoichiometric air-fuel ratio or rich, the stored NOx is released and reduced, and fuel supply means for supplying fuel to these NOx storage reduction catalysts is provided, respectively, and the NOx stored from these NOx storage reduction catalysts When the fuel is to be released and reduced, fuel is supplied from the fuel supply means to the corresponding NOx storage reduction catalyst so that the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich. Each temperature is detected, and these fuel supply means are set so that the total value of the fuel supply amount from these fuel supply means substantially matches the target value. And the NOx purification rate of the NOx occlusion reduction catalyst are calculated based on the set fuel supply amount and the detected temperature of the NOx occlusion reduction catalyst, respectively. The amount of fuel supplied from the fuel supply means is set so that the total value exceeds the allowable value.

  The NOx purification rate can be kept high while keeping the fuel consumption low.

  FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine. The present invention can also be applied to a gasoline engine.

  Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electromagnetically 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 c of the exhaust turbocharger 7 via the intake duct 6, and the inlet of the compressor 7 c is sequentially connected to the air flow meter 9 and the air cleaner 10 via the intake introduction pipe 8. An electrically controlled throttle valve 11 is disposed in the intake duct 6, and a cooling device 12 for cooling intake air flowing through the intake duct 6 is disposed around the intake duct 6. On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 t of the exhaust turbocharger 7, and the outlet of the exhaust turbine 7 t is connected to the exhaust aftertreatment device 20.

  Each fuel injection valve 3 is connected to a common rail 14 via a fuel supply pipe 13, and this common rail 14 is connected to a fuel tank 16 via an electrically controlled fuel pump 15 having a variable discharge amount. The fuel in the fuel tank 16 is supplied into the common rail 14 by the fuel pump 15, and the fuel supplied into the common rail 14 is supplied to the fuel injection valve 3 through each fuel supply pipe 13. A fuel pressure sensor (not shown) for detecting the fuel pressure in the common rail 14 is attached to the common rail 14 so that the fuel pressure in the common rail 14 matches the target pressure based on a signal from the fuel pressure sensor. The fuel discharge amount of the fuel pump 15 is controlled.

  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 17, and an electrically controlled EGR control valve 18 is disposed in the EGR passage 17. A cooling device 19 for cooling the EGR gas flowing in the EGR passage 17 is disposed around the EGR passage 17.

  The exhaust aftertreatment device 20 includes an exhaust pipe 21 connected to an outlet of the exhaust turbine 7t, and the exhaust pipe 21 is connected to a casing 22. A three-way catalyst 23 is accommodated in the casing 22. The casing 22 is connected to the casing 25 via the exhaust pipe 24. The SOx trap catalyst 26 is accommodated on the upstream side in the casing 25, and the NOx occlusion reduction catalyst 27u is accommodated on the downstream side. The casing 25 is connected to the casing 29 via the exhaust pipe 28. The NOx occlusion reduction catalyst 27d is accommodated on the upstream side of the casing 29, and the particulate filter 30 is accommodated on the downstream side. Further, an exhaust pipe 31 is connected to the casing 29. In the embodiment according to the present invention, the casings 22 and 25 are disposed adjacent to the engine body 1 and the casing 29 is disposed below the vehicle floor.

  Fuel supply means 32u and 32d such as fuel addition valves for supplying fuel (hydrocarbon) into the corresponding exhaust pipes 21 and 28 are attached to the exhaust pipes 21 and 28, respectively. The fuel supply means 32u may be disposed in the casing 25 downstream of the exhaust pipe 24 or the SOx trap catalyst 26 and upstream of the NOx storage reduction catalyst 27u. The exhaust pipe 28 is provided with a temperature sensor 33u for detecting the temperature of the exhaust gas flowing out from the casing 25. The temperature of the exhaust gas represents the temperature TNu of the NOx storage reduction catalyst 27u. The exhaust pipe 31 is provided with a temperature sensor 33d for detecting the temperature of the exhaust gas flowing out from the casing 29. The temperature of the exhaust gas represents the temperature TNd of the NOx storage reduction catalyst 27d.

  The electronic control unit 40 is composed of 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 voltages of the air flow meter 9 and the temperature sensors 33u and 33d are input to the input port 45 via the corresponding AD converters 47, respectively. A load sensor 50 that generates an output voltage proportional to the amount of depression of the accelerator pedal 49 is connected to 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. The Further, a crank angle sensor 51 that generates an output pulse every time the crankshaft rotates, for example, 30 degrees is connected to the input port 45. The CPU 44 calculates the engine speed based on the output pulse from the crank angle sensor 51. On the other hand, the output port 46 is connected to the fuel injection valve 3, the drive device of the throttle valve 11, the fuel pump 15, the EGR control valve 18, and the fuel supply means 32u and 32d through corresponding drive circuits 48.

  The particulate filter 30 has a honeycomb structure and includes a plurality of exhaust flow passages extending in parallel with each other. These exhaust flow passages include an exhaust gas inflow passage whose downstream end is closed by a plug, and an exhaust gas outflow passage whose upstream end is closed by a plug. Therefore, the exhaust gas inflow passages and the exhaust gas outflow passages are alternately arranged through thin partition walls. In other words, the exhaust gas inflow passage and the exhaust gas outflow passage are arranged such that each exhaust gas inflow passage is surrounded by four exhaust gas outflow passages, and each exhaust gas outflow passage is surrounded by four exhaust gas inflow passages. . The particulate filter 30 is made of, for example, a porous material such as cordierite. Therefore, the exhaust gas flowing into the exhaust gas inflow passage flows out into the adjacent exhaust gas outflow passage through the surrounding partition wall.

  Particulate matter contained in the exhaust gas is collected on the particulate filter 30 and sequentially oxidized. However, when the amount of the collected particulate matter is larger than the amount of the particulate matter to be oxidized, the particulate matter gradually accumulates on the particulate filter 30. In this case, when the amount of the particulate matter deposited increases, the engine output is increased. Will be reduced.

  Therefore, in the embodiment according to the present invention, when the amount of the particulate matter deposited on the particulate filter 30 exceeds the allowable amount, the temperature of the particulate filter 30 is set to, for example, 600 ° C. while keeping the air-fuel ratio of the exhaust gas lean. The temperature rise control is performed to raise the temperature to a certain extent, and the particulate matter thus deposited is removed by oxidation. Whether or not the amount of the particulate matter deposited on the particulate filter 30 exceeds an allowable amount can be determined based on, for example, the differential pressure across the particulate filter 30. Further, the temperature rise control can be performed, for example, by supplying fuel from the fuel supply means 32d and oxidizing the supplied fuel in the NOx storage reduction catalyst 27d or the particulate filter 30.

  The NOx occlusion reduction catalysts 27u and 27d have a honeycomb structure and include a plurality of exhaust gas flow passages separated from each other by thin partition walls. A catalyst carrier made of alumina, for example, is supported on both side surfaces of each partition wall. FIGS. 2A and 2B schematically show a cross section of the surface portion of the catalyst carrier 55. As shown in FIGS. 2 (A) and 2 (B), a noble metal catalyst 56 is dispersedly supported on the surface of the catalyst carrier 55, and a layer of NOx absorbent 57 is further provided on the surface of the catalyst carrier 55. Is formed.

  In the embodiment according to the present invention, at least one selected from platinum Pt, palladium Pd, osmium Os, gold Au, rhodium Rh, iridium Ir, and ruthenium Ru is used as the noble metal catalyst 56, and the component constituting the NOx absorbent 57 is used. For example, at least one selected from alkali metals such as potassium K, sodium Na and cesium Cs, alkaline earth such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y is used.

  If the ratio of air and fuel (hydrocarbon) supplied into the intake passage, the combustion chamber 5 and the exhaust passage upstream of a certain position in the exhaust passage is referred to as the air-fuel ratio of the exhaust gas at that position, NOx absorption The agent 57 absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and performs the NOx absorption / release action of releasing the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases.

That is, the case where platinum Pt is used as the noble metal catalyst 56 and barium Ba is used as a component constituting the NOx absorbent 57 will be described as an example. When the air-fuel ratio of the exhaust gas is lean, that is, the oxygen concentration in the exhaust gas is high. Sometimes the NO contained in the exhaust gas is oxidized on the platinum Pt 56 to become NO ₂ as shown in FIG. 2 (A), and then absorbed into the NOx absorbent 57 and combined with barium carbonate BaCO ₃ and nitrate ions. It diffuses into the NOx absorbent 57 in the form of NO ₃ ⁻ . In this way, NOx is absorbed in the NOx absorbent 57. Exhaust oxygen concentration in the gas at the surface as far as the platinum Pt56 _high, NO ₂ is generated, as long as NO ₂ to NOx absorbing capability of the NOx absorbent 57 is not saturated is absorbed in the NOx absorbent 57 nitrate ions NO ₃ ^- is Generated.

In contrast, reactions opposite direction to the air-fuel ratio of the exhaust gas is oxidized concentration in the exhaust gas is made rich to decrease ^- proceed to (NO ₃ → NO _2), in Figure 2 and thus (B) As shown, nitrate ions NO ₃ ⁻ in the NOx absorbent 57 are released from the NOx absorbent 57 in the form of NO ₂ . Next, the released NOx is reduced by HC and CO contained in the exhaust gas.

In an embodiment according to the present invention, combustion under an excess of oxygen continues. Therefore, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalysts 27u, 27d is maintained lean, and at this time, NOx in the exhaust gas is stored in the NOx storage reduction catalysts 27u, 27d. However, if the engine operation is continued, the amount of NOx stored in the NOx storage reduction catalysts 27u, 27d increases, and eventually the NOx storage reduction catalysts 27u, 27d cannot store NOx. Therefore, in the embodiment according to the present invention, the air-fuel ratio of the exhaust gas is temporarily enriched before the NOx storage reduction catalysts 27u, 27d are saturated with NOx, thereby releasing NOx from the NOx storage reduction catalysts 27u, 27d, and the exhaust gas. It is reduced to N ₂ etc. by HC and CO inside.

  That is, in the embodiment according to the present invention, the amount of NOx stored per unit time in the NOx storage reduction catalysts 27u, 27d is stored in advance in the ROM 42 in the form of a map as a function of the engine operating state such as the engine load factor KL and the engine speed Ne. The total NOx amount stored in the NOx storage reduction catalysts 27u and 27d is calculated by accumulating the NOx amount. In addition, every time the total NOx occlusion amount of the NOx occlusion reduction catalysts 27u, 27d exceeds the upper limit NOx amount, fuel (hydrocarbon) is supplied from the fuel supply means 32u, 32d and flows into the NOx occlusion reduction catalysts 27u, 27d. The air-fuel ratio of the exhaust gas is temporarily switched to rich. As a result, NOx is released from the NOx storage reduction catalysts 27u and 27d and reduced. The engine load factor KL is the ratio of the engine load to the total load.

However, the exhaust gas contains SOx That SO _2, the SO ₂ When this SO ₂ flows into the NOx occlusion reduction catalyst 27 u, the 27d become oxidized SO ₃ in platinum PT56. Next, this SO ₃ is absorbed into the NOx absorbent 57 and diffuses into the NOx absorbent 57 in the form of sulfate ions SO ₄ ²⁻ while being combined with the barium carbonate BaCO ₃ , thereby generating a stable sulfate BaSO ₄ . However, the sulfate BaSO ₄ is stable and difficult to decompose, and the sulfate BaSO ₄ remains as it is without being decomposed simply by making the air-fuel ratio of the exhaust gas rich. Therefore, the sulfate BaSO ₄ increases in the NOx absorbent 57 as time elapses, and thus the storage capacity of the NOx occlusion reduction catalysts 27u and 27d decreases as time elapses.

  Therefore, in the embodiment according to the present invention, the SOx trap catalyst 26 is disposed upstream of the NOx storage reduction catalysts 27u, 27d, and the SOx trap catalyst 26 captures SOx contained in the exhaust gas, thereby the NOx storage reduction catalyst 27u. , 27d is prevented from flowing into SOd. Next, the SOx trap catalyst 26 will be described.

  The SOx trap catalyst 26 has, for example, a honeycomb structure and includes a plurality of exhaust gas flow passages separated from each other by thin partition walls. A catalyst carrier made of alumina, for example, is supported on both side surfaces of each partition wall, and FIG. 3 schematically shows a cross section of the surface portion of the catalyst carrier 60. As shown in FIG. 3, a coat layer 61 is formed on the surface of the catalyst carrier 60, and a noble metal catalyst 62 is dispersed and supported on the surface of the coat layer 61.

  In the embodiment according to the present invention, platinum is used as the noble metal catalyst 62, and the components constituting the coating layer 61 are, for example, alkali metals such as potassium K, sodium Na, cesium Cs, barium Ba, and calcium Ca. At least one selected from alkaline earths, rare earths such as lanthanum La and yttrium Y is used. That is, the coat layer 61 of the SOx trap catalyst 26 exhibits strong basicity.

As shown in FIG. 3, SOx contained in the exhaust gas, that is, SO ₂ is oxidized in platinum Pt 62 and then trapped in the coat layer 61. That is, SO ₂ diffuses into the coat layer 61 in the form of sulfate ions SO ₄ ²⁻ to form sulfate. As described above, the coat layer 61 has a strong basicity. Therefore, as shown in FIG. 3, a part of SO ₂ contained in the exhaust gas is directly captured in the coat layer 61. In this way, SOx is trapped in the SOx trap catalyst 26 and SOx is prevented from being stored in the NOx storage reduction catalysts 27u and 27d.

  Here, the NOx purification rate EFF of the NOx storage reduction catalyst will be described with reference to FIG. As can be seen from FIG. 4, when the catalyst temperature TN is low, the NOx purification rate EFF increases as the catalyst temperature TN increases, and when the catalyst temperature TN is high, the NOx purification rate EFF decreases as the catalyst temperature TN increases. Further, the NOx purification rate EFF increases as the fuel supply amount QAF increases. That is, the NOx purification rate EFF is determined according to the temperature TN of the NOx storage reduction catalyst and the fuel supply amount QAF to the NOx storage reduction catalyst. When the NOx amount flowing into the NOx storage reduction catalyst is represented by NOXi and the NOx amount flowing out from the NOx storage reduction catalyst is represented by NOXo, the NOx purification rate EFF can be represented by (NOXi−NOXo) / NOXi.

  In the embodiment according to the present invention, as described above, when NOx should be released and reduced from the NOx storage reduction catalysts 27u, 27d, fuel is supplied from the fuel supply means 32u, 32d to the corresponding NOx storage reduction catalysts 27u, 27d, respectively. Is supplied. The fuel supply amounts QAFu and QAFd from the fuel supply means 32u and 32d in this case are set so as to satisfy the following two conditions in the embodiment according to the present invention.

  The first condition is that the total value SQAF (= QAFu + QAFd) of the fuel supply amounts QAFu and QAFd substantially coincides with a predetermined target value TGT.

  The second condition is that the total value SEFF (= EFFu + EFFd) of the NOx purification rates EFFu and EFFd of the NOx storage reduction catalysts 27u and 27d is larger than the allowable value ALW.

  In this way, the NOx purification rate of the entire NOx storage reduction catalyst 27u, 27d represented by the total NOx purification rate value SEFF can be maintained high while maintaining the fuel consumption low.

  Specifically, since the NOx purification rates EFFu and EFFd are functions of the catalyst temperatures TNu and TNd and the fuel supply amounts QAFu and QAFd as described above, if the catalyst temperatures TNu and TNd are detected by the temperature sensors 33u and 33d, NOx is detected. The purification rates EFFu and EFFd are functions fu (QAFu) and fd (QAFd) of the fuel supply amounts QAFu and QAFd, respectively. Then, QAFu and QAFd that satisfy SEFF (= EFFu + EFFd)> ALW while satisfying SQAF (= QAFu + QAFd) = TGT are obtained.

  The NOx purification rates EFFu and EFFd can be approximated by, for example, the following logarithmic function.

EFFu = au · log (bu · QAFu + 1)
EFFd = ad · log (bd · QAFd + 1)
Here, au and bu are coefficients determined according to the catalyst temperature TNu, and ad and bd are coefficients determined according to the catalyst temperature TNd.

  Therefore, when the catalyst temperatures TNu and TNd are detected and the coefficients au, bu, ad, and bd are determined, functions fu (QAFu) and fd (QAFd) representing the NOx purification rates EFFu and EFFd are determined.

  Referring to the examples shown in FIGS. 5A and 5B, when the fuel supply amounts QAFu and QAFd are set to TGT / 2 + q and TGT / 2-q, respectively (X), the NOx purification rates EFFu and EFFd Are EFFuX and EFFdX, respectively, and in this case, the total NOx purification rate value SEFF is smaller than the allowable value ALW. On the other hand, when the fuel supply amounts QAFu and QAFd are set to TGT / 2−q and TGT / 2 + q, respectively (Y), the NOx purification rates EFFu and EFFd become EFFuY and EFFdY, respectively, and the total NOx purification rate SEFF Becomes larger than the allowable value ALW. Therefore, the fuel supply amounts QAFu and QAFd can be set to TGT / 2−q and TGT / 2 + q, respectively.

  In the example indicated by Y, the NOx purification rate EFFu is smaller than in the example indicated by X. However, the concept of the present invention is not to consider the NOx purification rates EFFu and EFFd, but to increase the NOx purification rates of the entire NOx storage reduction catalysts 27u and 27d represented by the total NOx purification rate value SEFF. .

  There may be a plurality of sets of fuel supply amounts QAFu and QAFd that satisfy the two conditions described above. In this case, for example, the fuel supply amounts QAFu and QAFd that maximize the NOx purification rate total value SEFF can be selected, or the fuel to the NOx storage reduction catalysts 27u and 27d with the higher NOx purification rates EFFu and EFFd is selected. The fuel supply amounts QAFu and QAFd having the largest supply amounts QAFu and QAFd can also be selected.

  FIG. 6 shows a routine for executing the NOx release control of the embodiment according to the present invention. This routine is executed by interruption every predetermined time.

  Referring to FIG. 6, first, at step 100, it is judged if NOx should be released from the NOx storage reduction catalysts 27u, 27d and reduced. When NOx should be released from the storage reduction catalysts 27u and 27d and not reduced, the processing cycle is terminated. When NOx is to be released from the storage reduction catalysts 27u and 27d and reduced, the routine proceeds to step 101 where the catalyst temperatures TNu and TNd are detected by the temperature sensors 33u and 33d. In the subsequent step 102, functions fu (QAFu) and fd (QAFd) representing the NOx purification rates EFFu and EFFd are determined based on the catalyst temperatures TNu and TNd. In the following step 103, the fuel supply amount QAFu is used so that the fuel supply amount total value SQAF matches the target value and the NOx purification rate total value SEFF exceeds the allowable value using the functional expressions fu (QAFu) and fd (QAFd). , QAFd are set. In the following step 104, fuel is supplied from the fuel supply means 32u and 32d by QAFu and QAFd, respectively.

  In the embodiments according to the present invention described so far, two NOx storage reduction catalysts and two fuel supply means are provided in the exhaust passage. However, three or more NOx storage reduction catalysts and fuel supply means may be provided.

  Further, the three-way catalyst 23, the SOx trap catalyst 26, and the particulate filter 30 can be omitted. Alternatively, the NOx occlusion reduction catalyst 27d can be formed on the particulate filter 30.

  Further, as the SOx trap catalyst 26, a catalyst in which at least one selected from a transition metal such as iron Fe, manganese Mn, nickel Ni, tin Sn and lithium Li is supported on a support made of alumina may be used.

  In addition, in order to make the exhaust gas flowing into the NOx storage reduction catalyst arranged at the uppermost stream in the exhaust passage into the stoichiometric air-fuel ratio or rich, the air-fuel ratio of the exhaust gas discharged from the combustion chamber is made to the stoichiometric air-fuel ratio or rich. You may make it do. In this case, the air-fuel ratio of the combustion mixture is made the stoichiometric air-fuel ratio or rich, or additional fuel is injected from the fuel injection valve in the expansion stroke or the exhaust stroke, so that the air-fuel ratio of the exhaust gas discharged from the combustion chamber is the theoretical air-fuel ratio. It can be fuel ratio or rich.

1 is an overall view of an internal combustion engine. It is sectional drawing of the surface part of the catalyst support | carrier of a NOx storage reduction catalyst. It is sectional drawing of the surface part of the catalyst support | carrier of a SOx trap catalyst. It is a diagram which shows the NOx purification rate of a NOx storage reduction catalyst. It is a diagram for demonstrating the setting method of fuel supply amount. It is a flowchart for performing the NOx release control routine of the Example by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine main body 20 Exhaust after-treatment apparatus 27u, 27d NOx storage reduction catalyst 32u, 32d Fuel supply means 33u, 33d Temperature sensor

Claims (1)

  A plurality of NOx occlusion reduction catalysts are arranged in series in the engine exhaust passage, and each NOx occlusion reduction catalyst occludes NOx contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and the air-fuel ratio of the inflowing exhaust gas is theoretically When the air-fuel ratio becomes rich, the stored NOx is released and reduced, and fuel supply means for supplying fuel to these NOx storage and reduction catalysts is provided, respectively, and the NOx stored from these NOx storage and reduction catalysts is released and reduced. When the fuel should be supplied from the fuel supply means to the corresponding NOx storage reduction catalyst, the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich, and the temperatures of these NOx storage reduction catalysts are detected respectively. The fuel supply from these fuel supply means so that the total value of the fuel supply amount from these fuel supply means substantially matches the target value. , And the NOx purification rate of the NOx storage reduction catalyst is calculated based on the set fuel supply amount and the detected temperature of the NOx storage reduction catalyst, and the total value of these NOx purification rates is an allowable value. An exhaust purification device for an internal combustion engine in which the amount of fuel supplied from the fuel supply means is set so as to exceed.

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