JP5206597B2 - 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.

  An NOx storage reduction catalyst that stores NOx contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean and reduces and purifies the stored NOx when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich An internal combustion engine arranged in an exhaust passage is known. In this internal combustion engine, NOx generated when combustion is performed under a lean air-fuel ratio is stored in the NOx storage reduction catalyst. On the other hand, when the NOx occlusion capacity of the NOx occlusion reduction catalyst approaches saturation, the air-fuel ratio of the exhaust gas is temporarily made rich, whereby NOx is reduced and purified from the NOx occlusion reduction catalyst.

By the way, sulfur is contained in the fuel and the lubricating oil. Therefore, the exhaust gas contains a sulfur compound (SOx, for example, SO ₂ ). This SOx is stored in the NOx storage reduction catalyst together with NOx. However, this SOx is not released from the NOx occlusion reduction catalyst by simply making the air-fuel ratio of the exhaust gas rich, and therefore the amount of SOx occluded in the NOx occlusion reduction catalyst gradually increases (hereinafter referred to as “sulfur”). Called poisoning). As a result, the amount of NOx that can be stored in the NOx storage reduction catalyst gradually decreases.

  In order to release SOx from the NOx storage reduction catalyst (that is, to perform sulfur poisoning recovery), the catalyst temperature of the NOx storage reduction catalyst is increased to the temperature at which SOx is released, that is, the SOx release temperature (for example, 600 ° C.). It is necessary to perform a sulfur poisoning recovery process in which the air-fuel ratio of the exhaust gas flowing into the NOx storage-reduction catalyst is made to be the stoichiometric air-fuel ratio or the rich air-fuel ratio while the temperature is increased.

  Therefore, in an exhaust gas purification apparatus for an internal combustion engine that includes a NOx storage reduction catalyst in the engine exhaust passage and includes a reducing agent addition valve that adds a reducing agent to the upstream exhaust passage of the NOx storage reduction catalyst, the NOx storage reduction catalyst An exhaust purification device for an internal combustion engine that raises the temperature of a NOx storage reduction catalyst and supplies a reducing agent during sulfur poisoning recovery processing is known (Patent Document 1).

  Incidentally, there is a configuration in which a NOx storage reduction catalyst having an oxygen storage function is used instead of the NOx storage reduction catalyst in the above configuration. Here, the oxygen storage function is a function of storing oxygen contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean and releasing the stored oxygen when the air-fuel ratio of the inflowing exhaust gas becomes rich. For example, a three-way catalyst has its function.

JP 2003-176715 A

  In this configuration, when the sulfur poisoning recovery process is to be performed, if the reducing agent is supplied and the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is made rich, the supplied reducing agent is released from the NOx storage reduction catalyst. Reaction heat is generated by reacting with oxygen. This reaction heat is transmitted to the downstream portion of the NOx storage reduction catalyst via the flow of the exhaust gas, whereby the temperature of the downstream portion rises more than the upstream portion of the NOx storage reduction catalyst. On the other hand, the degree of sulfur poisoning of the NOx storage reduction catalyst is larger in the upstream part than in the downstream part, and in order to effectively recover the sulfur poisoning, the upstream part of the NOx storage reduction catalyst is more fully used. It is necessary to raise the temperature.

  Therefore, in this state, if it is attempted to raise the temperature of the upstream portion of the NOx storage reduction catalyst to the SOx release temperature, the downstream portion is excessively heated and the catalyst function is deteriorated. On the other hand, if it is attempted to prevent the deterioration of the catalyst in the downstream portion of the NOx storage reduction catalyst, the temperature increase in the upstream portion becomes insufficient, the efficiency of the sulfur poisoning recovery process deteriorates, the processing time becomes longer, and the fuel consumption also deteriorates. The problem also arises.

  Further, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is made rich, the air-fuel ratio of the gas in the combustion chamber, that is, the air-fuel ratio of the in-cylinder gas is made rich in the reaction in the sulfur poisoning recovery process. From the viewpoint of sex. However, while the reactivity is improved, the reactivity with oxygen released from the NOx occlusion reduction catalyst is also improved, and the temperature rise in the downstream portion becomes larger, so the above problem becomes more remarkable.

  Further, when the intake air amount is small, the amount of heat exhausted to the outside of the NOx storage reduction catalyst via the exhaust gas also decreases, so the temperature difference between the upstream side portion and the downstream side portion of the NOx storage reduction catalyst is Become bigger.

  Therefore, an object of the present invention is to provide an exhaust purification device for an internal combustion engine that can perform the sulfur poisoning recovery process of the NOx storage reduction catalyst having an oxygen storage function without causing deterioration of the catalyst function.

  In order to solve the above problem, according to the first aspect of the present invention, when the air-fuel ratio of the exhaust gas flowing into the engine exhaust passage is lean, the NOx contained in the exhaust gas is occluded and the exhaust gas flowing in A NOx storage reduction catalyst that reduces and purifies the stored NOx when the air-fuel ratio becomes the stoichiometric air-fuel ratio or rich, and a reducing agent supply means is disposed in the engine exhaust passage upstream of the NOx storage reduction catalyst, and the NOx storage reduction catalyst However, when the air-fuel ratio of the inflowing exhaust gas is lean, it further has an oxygen storage function that stores oxygen contained in the exhaust gas and releases the stored oxygen when the air-fuel ratio of the inflowing exhaust gas becomes rich, and stores NOx When the SOx stored in the reduction catalyst should be released, the catalyst temperature of the NOx storage reduction catalyst is raised to the SOx release temperature and the air-fuel ratio of the exhaust gas flowing in is reduced. In the exhaust gas purification apparatus for an internal combustion engine having a sulfur poisoning recovery processing means for performing a sulfur poisoning recovery process, when the sulfur poisoning recovery processing means is to execute the sulfur poisoning recovery process, a cylinder During the lean combustion period in which the air-fuel ratio of the internal gas is made lean, the reducing agent is supplied from the reducing agent supply means, and after the lean combustion period has passed, control is performed to make the air-fuel ratio of the in-cylinder gas rich. An exhaust gas purification apparatus for an internal combustion engine is provided in which the exhaust gas amount is set longer as the exhaust gas amount is smaller.

  According to the first aspect of the present invention, there is an effect that the sulfur poisoning recovery process of the NOx occlusion reduction catalyst having an oxygen storage function can be performed without causing deterioration of the catalyst function.

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 map of SOx amount SOXA occluded per unit time. It is a figure which shows the relationship between the position of NOx storage reduction catalyst, and temperature. It is a time chart which shows the relationship between the addition control in a sulfur poisoning recovery process, and combustion control. It is a time chart which shows the relationship between the addition control in a sulfur poisoning recovery process, and combustion control.

  FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine. However, the present invention can also be applied to a spark 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 7a of the exhaust turbocharger 7 through the intake duct 6, and the inlet of the compressor 7a is connected to the air cleaner 9 through the air flow meter 8 for detecting the intake air amount. The intake air amount detected by the air flow meter 8 is equal to the exhaust gas amount SV. A throttle valve 10 driven by a step motor is disposed in the intake duct 6, and a cooling device 11 for cooling intake air flowing through the intake duct 6 is disposed 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.

  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 electronically 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.

  The exhaust aftertreatment device 20 includes an exhaust pipe 21 connected to the outlet of the exhaust turbine 7b, a NOx storage reduction catalyst 22 connected to the exhaust pipe 21, and an exhaust pipe 23 connected to the NOx storage reduction catalyst 22. . A reducing agent addition valve 24 is attached to the exhaust pipe 21. An air-fuel ratio sensor 25 for detecting the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 22 is arranged, and a temperature sensor 26 for detecting the catalyst temperature T is attached to the NOx storage reduction catalyst 22.

  Fuel as a reducing agent is added from the common rail 16 to the reducing agent addition valve 24, and fuel is added from the reducing agent addition valve 24 into the exhaust pipe 21. In an embodiment according to the invention, this fuel consists of light oil. The reducing agent addition valve 24 can be attached to the exhaust manifold 5. Further, in the embodiment according to the present invention, in addition to adding fuel from the reducing agent addition valve 24, exhaust gas containing CO (carbon monoxide) as a reducing agent may be generated to generate a rich air-fuel ratio exhaust gas. it can. CO is more reducible than fuel and can be generated by making the air-fuel ratio of the air-fuel mixture in the combustion chamber rich and burning at a high temperature.

  Note that, for example, the air-fuel ratio of the gas in the exhaust manifold 5 that does not include the fuel added from the reducing agent addition valve 24 indicates the air-fuel ratio of the gas in the combustion chamber 5 (in-cylinder). It is called an air-fuel ratio. Therefore, generating the exhaust gas containing CO described above makes the air-fuel ratio of the in-cylinder gas rich.

  The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. It comprises. Output signals of the air flow meter 8, the air-fuel ratio sensor 25, and the temperature sensor 26 are input to the input port 35 via corresponding AD converters 37, respectively. A load sensor 40 that generates an output voltage proportional to the depression amount L of the accelerator pedal 39 is connected to the accelerator pedal 39, and the output voltage of the load sensor 40 is input to the input port 35 via the corresponding AD converter 37. Is done. Further, the input port 35 is connected to a crank angle sensor 41 that generates an output pulse every time the crankshaft rotates, for example, 15 °. On the other hand, the output port 36 is connected to the fuel injection valve 3, the throttle valve 10 drive step motor, the EGR control valve 13, the fuel pump 17, and the reducing agent addition valve 24 through corresponding drive circuits 38.

  FIG. 2 shows the structure of the NOx storage reduction catalyst 22. In the embodiment shown in FIG. 2, the NOx occlusion reduction catalyst 22 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, the noble metal catalyst 66 is dispersed and supported on the surface of the catalyst carrier 65, and a layer of NOx absorbent 67 is further provided 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 22 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 the stoichiometric air-fuel ratio, 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, such as fuel added from the reducing agent addition valve 24 or CO generated by combustion in the combustion chamber.

Further, according to the embodiment of the present invention, the NOx occlusion reduction catalyst 22 stores the oxygen contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and stores it when the air-fuel ratio of the inflowing exhaust gas becomes rich. It has an oxygen storage function to release the oxygen that has been produced. That is, in order to realize the oxygen storage function, an example in which the oxygen storage material is made of cerium Ce will be described as an example. When the air-fuel ratio of the inflowing exhaust gas is lean, oxygen molecules O ₂ contained in the exhaust gas is CeO ₂ . Incorporated in the form (Ce ₂ O _3- > 2CeO ₂ ). On the other hand, when the air-fuel ratio of the inflowing exhaust gas becomes rich, the reaction proceeds in the reverse direction (2CeO _2- > Ce ₂ O ₃ ), and oxygen molecules O ₂ are released.

By the way, the exhaust gas contains SOx (for example, SO ₂ ). When this SO ₂ flows into the NOx occlusion reduction catalyst 22, this SO ₂ is oxidized at platinum Pt 66 to become SO ₃ . Next, this SO ₃ is absorbed in the NOx absorbent 67 and bonded to the barium carbonate BaCO ₃ while diffusing into the NOx absorbent 67 in the form of sulfate ions SO ₄ ^2- to form a stable sulfate BaSO ₄ . To do. However, since the NOx absorbent 67 has a strong basicity, this sulfate BaSO ₄ is stable and difficult to decompose. If the air-fuel ratio of the exhaust gas is simply made rich, the sulfate BaSO ₄ remains as it is without being decomposed. . Accordingly, in the NOx absorbent 67, the sulfate BaSO ₄ increases (that is, sulfur poisoning) as time passes, and the amount of NOx that can be absorbed by the NOx absorbent 67 decreases as time passes. become.

  Therefore, in this case, when the stored SOx is to be released, that is, when the sulfur poisoning recovery process is to be performed, the NOx storage reduction catalyst 22 is heated to a SOx release temperature of 600 ° C. or higher in the state where the NOx storage reduction catalyst 22 is raised. By making the air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst 22 rich (hereinafter referred to as “rich processing”), SOx is released from the NOx absorbent 67 and the amount of NOx that can be absorbed by the NOx absorbent 67 is recovered. To do.

  Here, the time when the sulfur poisoning recovery process should be performed is when the estimated SOx amount ΣS stored in the NOx storage reduction catalyst 22 exceeds a predetermined value SOX0. Sulfur is contained in the fuel at a certain ratio. Therefore, the amount of SOx contained in the exhaust gas, that is, the amount of SOx stored in the NOx storage reduction catalyst 22 is proportional to the fuel injection amount. The fuel injection amount is a function of the required torque TQ and the engine speed N. Therefore, the SOx amount stored in the NOx storage reduction catalyst 22 is also a function of the required torque TQ and the engine speed N. In the embodiment according to the present invention, the SOx amount SOXA stored in the NOx storage reduction catalyst 22 per unit time is stored in advance in the ROM 32 as a function of the required torque TQ and the engine speed N in the form of a map as shown in FIG. ing. By integrating the SOx amount SOXA per unit time, the estimated SOx amount ΣS stored in the NOx storage reduction catalyst 22 is calculated.

  As described above, the sulfur poisoning recovery process is started by first raising the temperature of the NOx storage reduction catalyst 22 to the SOx release temperature. When this temperature raising process is performed by making the air-fuel ratio of the in-cylinder gas rich, it reacts well with the oxygen stored by the oxygen storage function of the NOx storage reduction catalyst 22 to generate a large amount of reaction heat. This reaction heat is transmitted to the downstream portion of the NOx storage reduction catalyst 22 via the exhaust gas, so that the downstream portion of the NOx storage reduction catalyst 22 is heated more than the upstream portion, and as a result, the upstream side A temperature difference is generated between the portion and the downstream portion.

  In this regard, FIG. 5 shows the temperature relationship at each site in the exhaust gas flow direction of the NOx storage reduction catalyst 22. The curve shown by A in FIG. 5 shows a state where the downstream portion of the NOx storage reduction catalyst 22 is heated more than the upstream portion when the sulfur poisoning recovery process according to the present invention is not performed. . As a result, the above-described problems such as catalyst deterioration and fuel consumption deterioration occur.

  On the other hand, the curve shown by B in FIG. 5 shows a state in which the sulfur poisoning recovery process according to the present invention is performed. In the curve B, the temperature of the upstream portion of the NOx storage reduction catalyst 22 is increased and the temperature of the downstream portion is decreased as compared with the curve A. As a result, it is possible to prevent deterioration of the catalyst due to excessive temperature rise in the downstream portion and to sufficiently perform the sulfur poisoning recovery process in the upstream portion having a high degree of sulfur poisoning.

  The sulfur poisoning recovery process according to the embodiment of the present invention for realizing the temperature state as shown by the curve B in FIG. 5 will be described with reference to FIG. FIG. 6 is a time chart showing the relationship between the control of the timing for adding the reducing agent from the reducing agent addition valve 24 in the sulfur poisoning recovery process, that is, the addition control, and the control of the air-fuel ratio of the in-cylinder gas, that is, the combustion control. It is.

  Referring to FIG. 6, when sulfur poisoning recovery processing is to be performed, combustion control is performed so that lean combustion is performed so that the air-fuel ratio of the in-cylinder gas becomes lean, and a reducing agent is added from a reducing agent addition valve 24. . At this time, the added fuel undergoes an oxidation reaction on the NOx storage reduction catalyst 22, whereby the temperature of the NOx storage reduction catalyst 22 gradually increases as a whole. Further, as the temperature of the NOx occlusion reduction catalyst 22 rises, oxygen stored in the NOx occlusion reduction catalyst 22 is gradually released, so that the oxygen storage amount gradually decreases. The oxygen released here reacts with the reducing agent.

  If a reducing agent is added during lean combustion, the NOx storage reduction catalyst 22 can be heated while the exhaust gas contains almost no highly reducible CO, and the NOx storage reduction catalyst 22 A large amount of heat generated by the reaction between stored oxygen and CO can be suppressed. In addition, the reaction heat generated by the reaction between the added reducing agent and the stored oxygen is transmitted to the downstream portion of the NOx storage reduction catalyst 22 by exhaust gas having a temperature lower than that of rich combustion described later, and finally. The NOx occlusion reduction catalyst 22 is discharged into the downstream exhaust passage. Therefore, it is possible to suppress an excessive temperature rise in the downstream portion of the NOx storage reduction catalyst 22 and reduce the temperature difference between the upstream portion and the downstream portion.

  Next, when the temperature of the upstream portion of the NOx storage reduction catalyst 22 has sufficiently reached the SOx release temperature, the combustion control is switched from lean combustion to rich combustion that makes the air-fuel ratio of the in-cylinder gas rich. By performing the rich combustion, a lot of highly reducible CO is contained in the exhaust gas, and the sulfur poisoning that releases the stored SOx is well recovered. Further, since most of the oxygen stored in the NOx storage reduction catalyst 22 is released by the lean combustion before the rich combustion, little reaction heat is generated due to the reaction between the CO in the exhaust gas and the released oxygen. .

  Here, in the sulfur poisoning recovery process, if the time for performing lean combustion before switching to rich combustion is referred to as a lean combustion period t1, the lean combustion period t1 is set longer as the exhaust gas amount is smaller. That is, the small exhaust gas amount means that when the temperature of the downstream portion of the NOx storage reduction catalyst 22 is higher than that of the upstream portion, the amount of heat released per unit time to the outside of the NOx storage reduction catalyst 22 is small. Become. Therefore, by setting the lean combustion period t1 longer, the heat release to the outside of the NOx storage reduction catalyst 22 is promoted, and the temperature difference between the upstream portion and the downstream portion of the NOx storage reduction catalyst 22 is reduced as much as possible. I am doing so.

  The addition timing of the reducing agent by addition control during lean combustion is determined according to, for example, the catalyst temperature T, and is obtained in advance through experiments or the like together with the lean combustion period t1 corresponding to the amount of exhaust gas, and stored in the ROM 32.

  As described above, according to the present invention, in the sulfur poisoning recovery process of the NOx storage reduction catalyst 22 having an oxygen storage function, the temperature in the NOx storage reduction catalyst 22 can be made more uniform. Thus, there is an effect that it is possible to improve the processing efficiency of sulfur poisoning recovery and shorten the processing time without causing deterioration.

  Subsequently, a sulfur poisoning recovery process according to another embodiment of the present invention will be described. FIG. 7 is a time chart different from FIG. 6 showing the relationship between the addition control and the combustion control in the sulfur poisoning recovery process.

  The difference from FIG. 6 will be described with reference to FIG. 7. In the present embodiment, the addition time t2 is set longer in the latter half of the lean combustion period t1. As a result, more reducing agent is added to the NOx occlusion reduction catalyst 22, the air-fuel ratio of the exhaust gas flowing into the NOx occlusion reduction catalyst 22 becomes temporarily rich, and almost all of the stored oxygen is released. As a result, during the next rich combustion, it becomes possible to minimize the heat of reaction due to oxygen stored in the NOx storage reduction catalyst 22, and therefore, the temperature in the NOx storage reduction catalyst 22 can be made uniform. It becomes possible. The addition time t2 is obtained in advance by experiments or the like according to the catalyst temperature T, for example, and is stored in the ROM 32.

  As described above, according to the present embodiment, in addition to the effects of the present invention described above, the temperature in the NOx storage reduction catalyst 22 can be further uniformized. Further, since the air-fuel ratio of the exhaust gas flowing into the NOx occlusion reduction catalyst 22 during the lean combustion temporarily becomes rich, a part of the occluded SOx is released and the sulfur poisoning recovery at the time of further rich combustion is performed. It is possible to improve the processing efficiency and shorten the processing time.

4 Intake manifold 5 Exhaust manifold 7 Exhaust turbocharger 21 Exhaust pipe 22 NOx storage reduction catalyst 24 Reductant supply valve

Claims (1)

  NOx for storing NOx contained in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the engine exhaust passage is lean, and reducing and purifying the stored NOx when the air-fuel ratio of the exhaust gas flowing in becomes the stoichiometric air-fuel ratio or rich The NOx storage reduction catalyst is disposed in the engine exhaust passage upstream of the NOx storage reduction catalyst, and the NOx storage reduction catalyst is included in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean. The NOx storage-reduction catalyst is further provided with an oxygen storage function for releasing the stored oxygen when the air-fuel ratio of the exhaust gas that stores and flows in is rich, and the NOx storage-reduction catalyst should release SOx. The sulfur poisoning recovery processing means for performing the sulfur poisoning recovery processing for raising the catalyst temperature to the SOx release temperature and enriching the air-fuel ratio of the inflowing exhaust gas In the exhaust gas purification apparatus for an internal combustion engine, the reducing agent supply means during the lean combustion period in which the sulfur poisoning recovery processing means leans the air-fuel ratio of the in-cylinder gas when the sulfur poisoning recovery processing is to be executed. An internal combustion engine characterized in that a reducing agent is supplied from the exhaust gas and control is performed to enrich the air-fuel ratio of the in-cylinder gas after the lean combustion period, and the lean combustion period is set longer as the exhaust gas amount is smaller. Exhaust purification equipment.

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