JP2016109063A - Exhaust emission control device of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an engine capable of properly performing regeneration processing to each of a first exhaust emission control catalyst and a second exhaust emission control catalyst.SOLUTION: An exhaust emission control device of an engine repeats a rich period and a lean period alternately, and executes first regeneration processing of regenerating only a first exhaust emission control catalyst, and second regeneration processing of regenerating only a second exhaust emission control catalyst. When the first regeneration processing is executed, the rich period is longer than the lean period, and when the second regeneration processing is executed, the rich period is shorter than the lean period.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an exhaust purification device for an engine including a first exhaust purification catalyst and a second exhaust purification catalyst, and more particularly, to a regeneration processing technique for the first exhaust purification catalyst and the second exhaust purification catalyst.

  The exhaust gas emitted from engines mounted on automobiles, etc. includes exhausts such as carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM). Contains gas components. For this reason, the engine exhaust passage is provided with a three-way catalyst for decomposing (reducing or the like) the above substances, a particulate filter for capturing PM, and the like.

  For example, in the case of an engine that burns in an oxidizing atmosphere by controlling the air / fuel ratio from the stoichiometric air / fuel ratio (stoichiometric) to a lean air / fuel ratio, such as a diesel engine, a three-way catalyst uses nitrogen oxides in the exhaust gas. (NOx) cannot be sufficiently purified. For this reason, some exhaust passages of this type of engine are provided with a NOx storage catalyst as an exhaust purification catalyst. The NOx storage catalyst stores NOx in the exhaust if the air-fuel ratio of the exhaust is lean, and releases and reduces the stored NOx if the air-fuel ratio of the exhaust is rich. In a diesel engine or the like, normally, since the air-fuel ratio of exhaust gas is lean, nitrogen oxides are stored in the NOx storage catalyst. For this reason, it is necessary to perform a regeneration process (NOx purge) for decomposing (reducing) NOx stored in the NOx storage catalyst by enriching the air-fuel ratio of the exhaust at a predetermined timing.

  Further, since the sulfur component is contained as a harmful component in the fuel, the sulfur component reacts with oxygen to become sulfur oxide (SOx) and is stored in the NOx storage catalyst instead of NOx (S poisoning). . For this reason, it is necessary to perform a regeneration process (S purge) for removing sulfur oxide (SOx) at a predetermined timing. In this regeneration process (S purge), for example, it is necessary to enrich the air-fuel ratio of the exhaust and raise the NOx storage catalyst to a high temperature equal to or higher than a predetermined temperature as in the case of NOx purge.

  There are various proposals for the regeneration process (S purge). For example, while maintaining the NOx storage catalyst in a rich atmosphere, the fuel injection means for injecting fuel (reducing agent) is controlled to control the fuel addition period. However, there is one in which the NOx storage catalyst is heated to a high temperature by alternately repeating a dense period and a sparse period (see, for example, Patent Document 1).

Japanese Patent No. 3972864

  By the way, there is an engine exhaust purification device provided with a plurality of exhaust purification catalysts (for example, NOx storage catalyst). For example, some have a first exhaust purification catalyst near the engine and a second exhaust purification catalyst under the floor of a vehicle on the downstream side of the first exhaust purification catalyst.

  When the regeneration process (S purge) is performed by the exhaust purification device including the first exhaust purification catalyst and the second exhaust purification catalyst in this way, heat is easily generated in the first exhaust purification catalyst, but the second The exhaust gas purification catalyst hardly generates heat, and there is a concern that a temperature difference may occur between the first exhaust gas purification catalyst and the second exhaust gas purification catalyst. When the temperature difference between the first exhaust purification catalyst and the second exhaust purification catalyst becomes large, there is a possibility that the first exhaust purification catalyst and the second exhaust purification catalyst cannot be simultaneously regenerated.

  On the other hand, it may be necessary to regenerate only the first exhaust purification catalyst. For example, if sulfur oxide is adsorbed from the upstream first exhaust purification catalyst, the time required for regeneration of the first exhaust purification catalyst is longer than that of the second exhaust purification catalyst. Further, for example, if the capacity of the first exhaust purification catalyst is larger than that of the second exhaust purification catalyst, the time required for the regeneration process of the first exhaust purification catalyst becomes longer than that of the second exhaust purification catalyst. . In this case, there is a possibility that the first exhaust purification catalyst cannot be sufficiently regenerated by simply regenerating the first exhaust purification catalyst and the second exhaust purification catalyst at the same time.

  For this reason, it is preferable that the first exhaust purification catalyst and the second exhaust purification catalyst are simultaneously regenerated, and only the first exhaust purification catalyst is regenerated as necessary. However, the present situation is that these reproduction processes cannot be appropriately performed.

  The present invention has been made in view of such circumstances, and provides an engine exhaust purification device capable of appropriately regenerating each of the first exhaust purification catalyst and the second exhaust purification catalyst. With the goal.

  A first aspect of the present invention that solves the above problems is a fuel injection means for injecting fuel into a cylinder of an engine, a first exhaust purification catalyst provided in an exhaust passage of the engine, and the first of the exhaust passage. Supplied by a second exhaust purification catalyst provided downstream of one exhaust purification catalyst, a reducing agent supply means for supplying a reducing agent to flow into the first exhaust purification catalyst, and at least the reducing agent supply means. A rich period during which the air-fuel ratio of the exhaust gas flowing out from the first exhaust purification catalyst and the second exhaust purification catalyst is enriched by adjusting the amount of reducing agent to be produced, and the first exhaust purification catalyst and the second exhaust And a regeneration process execution means for executing regeneration processing of the first exhaust purification catalyst and the second exhaust purification catalyst by alternately repeating a lean period in which the air-fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst is made lean. And the regeneration process execution means sets the rich period to be longer than the lean period when executing the first regeneration process for regenerating only the first exhaust purification catalyst. In performing the second regeneration process for regenerating the exhaust purification catalyst, the rich exhaust period is made shorter than the lean period.

  According to a second aspect of the present invention, in the exhaust emission control device for an engine according to the first aspect, the regeneration process execution means performs the second regeneration process every time the first regeneration process is performed once or a plurality of times. The engine exhaust gas purification apparatus is characterized by performing the following.

  According to a third aspect of the present invention for solving the above-described problem, in the engine exhaust gas purification apparatus according to the first or second aspect, the regeneration process execution means executes the second regeneration process when the first regeneration process is performed. The exhaust purification device of the engine is characterized in that the lean period is shortened as the degree of deterioration of the exhaust purification catalyst increases.

  According to a fourth aspect of the present invention, in the exhaust emission control device for an engine according to any one of the first to third aspects, the regeneration process executing means is a reduction that is injected from the reducing agent supply means in the first regeneration process. The engine exhaust purification apparatus is characterized in that the amount of the agent is made smaller than the amount of reducing agent injected from the reducing agent supply means in the second regeneration process.

  According to a fifth aspect of the present invention, in the engine exhaust gas purification apparatus according to any one of the first to fourth aspects, the fuel injection unit also serves as the reducing agent supply unit, and the regeneration processing execution unit includes: In the engine exhaust gas purification apparatus, the amount of fuel to be injected is adjusted by post-injection after main injection of the fuel injection means as adjustment of the reducing agent amount.

  According to a sixth aspect of the present invention, in the engine exhaust purification apparatus according to any one of the first to fifth aspects, the first exhaust purification catalyst and the second exhaust purification catalyst are NOx storage catalysts. It is in the exhaust emission control device of the engine.

  According to a seventh aspect of the present invention, in the exhaust purification device for an engine according to the sixth aspect, the regeneration processing executed by the regeneration processing execution means is performed by the first exhaust purification catalyst and the second exhaust purification catalyst. An exhaust emission control device for an engine is characterized in that it is a process for removing sulfur oxides occluded in the engine.

  In the present invention, the first regeneration process for regenerating only the first exhaust purification catalyst and the second regeneration process for regenerating the second exhaust purification catalyst can be performed as necessary. Therefore, each of the first exhaust purification catalyst and the second exhaust purification catalyst can be appropriately regenerated.

1 is a schematic configuration diagram showing an engine including an exhaust purification device according to an embodiment of the present invention. 12 is a graph showing a correspondence relationship between a rich flag, an inlet air-fuel ratio, and an outlet air-fuel ratio in the second regeneration process. It is a figure which shows an example of the fuel injection timing in a 2nd regeneration process. It is a figure explaining the setting procedure of the post injection amount in the rich period in the second regeneration process. 6 is a graph showing a correspondence relationship between a rich flag, an inlet air-fuel ratio, and an outlet air-fuel ratio in the first regeneration process. It is a figure which shows an example of the fuel injection timing in a 1st regeneration process.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
First, the overall configuration of the engine 10 including an exhaust emission control device according to an embodiment of the present invention will be described. An engine 10 shown in FIG. 1 is a diesel engine, and an engine body 11 includes a cylinder head 12 and a cylinder block 13, and a piston 15 is accommodated in each cylinder bore 14 of the cylinder block 13. The piston 15 is connected to the crankshaft 17 via a connecting rod 16. A combustion chamber 18 is formed by the piston 15, the cylinder bore 14, and the cylinder head 12.

  An intake port 19 is formed in the cylinder head 12, and an intake pipe (intake passage) 21 including an intake manifold 20 is connected to the intake port 19. An intake valve 22 is provided in the intake port 19, and the intake port 19 is opened and closed by the intake valve 22. An exhaust port 23 is formed in the cylinder head 12, and an exhaust pipe (exhaust passage) 25 including an exhaust manifold 24 is connected in the exhaust port 23. The exhaust port 23 is provided with an exhaust valve 26. Like the intake port 19, the exhaust port 23 is opened and closed by the exhaust valve 26.

  A turbocharger 27 is provided in the middle of the intake pipe 21 and the exhaust pipe 25. An intercooler 28 is disposed in the intake pipe 21 on the downstream side of the turbocharger 27. The intake pipe 21 on the downstream side of the intercooler 28 is provided with a throttle valve 29 for opening and closing the intake pipe (intake passage) 21. An EGR pipe (EGR passage) 30 communicating with the exhaust pipe 25 upstream of the turbocharger 27 is connected to the intake pipe 21 downstream of the throttle valve 29. An EGR cooler 31 is provided in the EGR pipe 30, and an EGR valve 32 is provided in a connection portion between the EGR pipe 30 and the intake pipe 21.

  The cylinder head 12 is provided with a fuel injection valve (fuel injection means) 33 for injecting fuel into the combustion chamber 18 of each cylinder. Fuel is supplied to the fuel injection valve 33 from the common rail 34. Fuel in a fuel tank (not shown) is supplied to the common rail 34 by a supply pump 35, and fuel is supplied from the supply pump 35 to the common rail 34 at a predetermined pressure according to the rotational speed of the engine body 11. In the common rail 34, the fuel is adjusted to a predetermined fuel pressure, and high pressure fuel controlled to the predetermined fuel pressure is supplied from the common rail 34 to the fuel injection valve 33.

  In the exhaust pipe 25 on the downstream side of the turbocharger 27, a first NOx storage catalyst 51, which is a first exhaust purification catalyst constituting the exhaust purification device 50, a diesel particulate filter (DPF) 52, and a second A second NOx storage catalyst 53, which is an exhaust purification catalyst, is provided in order from the upstream side. In the present embodiment, the first NOx storage catalyst 51 and the DPF 52 are provided close to the engine body 11, and the second NOx storage catalyst 53 is provided under the floor of the vehicle.

  Since the first and second NOx storage catalysts 51 and 53 and the DPF 52 have an existing structure, a detailed description thereof is omitted here. Further, the arrangement of the first NOx storage catalyst 51, the DPF 52, and the second NOx storage catalyst 53 is not particularly limited. For example, the arrangement of the second NOx storage catalyst 53 may not be under the floor.

  Air-fuel ratio sensors 54 and 55 for detecting the air-fuel ratio of the exhaust are respectively provided in the vicinity of the outlet of the first NOx storage catalyst 51 (for example, in the vicinity of the outlet of the DPF 52) and in the vicinity of the outlet of the second NOx storage catalyst 53. Is provided. That is, the air-fuel ratio sensor 54 detects the air-fuel ratio of the exhaust gas flowing out from the first NOx storage catalyst 51 (first catalyst air-fuel ratio), and the air-fuel ratio sensor 55 is the exhaust gas flowing out of the second NOx storage catalyst 53. The air-fuel ratio (second catalyst air-fuel ratio) is detected. The air-fuel ratio sensors 54 and 55 may detect oxygen concentration in the exhaust gas. The first NOx storage catalyst 51 is provided with a temperature sensor 56 that detects the temperature of the first NOx storage catalyst 51, and the second NOx storage catalyst 53 has a temperature of the second NOx storage catalyst 53. A temperature sensor 57 for detection is provided.

The first NOx occlusion catalyst 51 and the second NOx occlusion catalyst 53 are, for example, supported by a noble metal such as platinum (Pt) and palladium (Pd) on a honeycomb structure carrier made of a ceramic material and occluded. As an agent, an alkali metal such as barium (Ba) or an alkaline earth metal is supported. The first NOx occlusion catalyst 51 and the second NOx occlusion catalyst 53 temporarily occlude nitrogen oxide (NOx) as an exhaust component in an oxidizing atmosphere, and for example, carbon monoxide (CO), hydrocarbon (HC). In a reducing atmosphere containing etc., NOx is released and reduced to nitrogen (N ₂ ) or the like. Since the engine 10 according to the present embodiment is a diesel engine, normally, the first NOx occlusion catalyst 51 and the second NOx occlusion catalyst 53 only occlude NOx, and the occluded NOx is decomposed (reduced). It will never be done.

  For this reason, every time the engine 10 is operated for a predetermined period, for example, a regeneration process (NOx purge) for removing the stored NOx is performed. In this regeneration process (NOx purge), fuel (light oil) as a reducing agent is supplied to the first NOx storage catalyst 51 at a predetermined timing. At that time, the fuel as the reducing agent is also supplied to the second NOx storage catalyst 53. As a result, the inside of the first NOx storage catalyst 51 and the second NOx storage catalyst 53 becomes a reducing atmosphere, and the stored NOx is decomposed (reduced) from the first NOx storage catalyst 51 and the second NOx storage catalyst 53. Removed.

  The first NOx storage catalyst 51 and the second NOx storage catalyst 53 store sulfur oxide (SOx), which is an exhaust component, similarly to nitrogen oxide (NOx), and therefore remove SOx at a predetermined timing. A regeneration process (S purge) is performed. In this regeneration process (S purge), fuel (light oil) as a reducing agent is appropriately supplied to the exhaust, and accordingly, the first NOx storage catalyst 51 and the second NOx storage catalyst 53 are kept at a predetermined temperature (for example, about 700 ° C.). ) Increase the temperature to above. As a result, the stored sulfur oxide (SOx) is decomposed (reduced) and removed from the first NOx storage catalyst 51 and the second NOx storage catalyst 53.

The DPF 52 is, for example, a honeycomb structure filter formed of a ceramic material. PM trapped in the DPF 52 is oxidized (combusted) by NO ₂ in the exhaust gas and discharged as CO ₂ , and NO ₂ is decomposed into N ₂ and discharged.

  The engine 10 includes an electronic control unit (ECU) 70. The ECU 70 includes an input / output device, a storage device that stores a control program, a control map, and the like, a central processing unit, timers, and counters. Yes. The ECU 70 performs comprehensive control of the engine 10 on which the exhaust purification device 50 is mounted based on information from various sensors (not shown).

  The ECU 70 also functions as a part of the exhaust purification device 50 and appropriately controls the fuel injection valve 33 based on information from various sensors such as the air-fuel ratio sensors 54 and 55 and the temperature sensors 56 and 57. Specifically, the ECU 70 includes a regeneration processing execution means 71, which controls the fuel injection valve 33 that serves as both the fuel injection means and the reducing agent supply means, and is injected from the fuel injection valve 33. By adjusting the fuel amount (reducing agent amount), regeneration processing such as S purge of the first NOx storage catalyst 51 and the second NOx storage catalyst 53 described above is executed.

  Here, the regeneration process execution means 71 executes, as regeneration processes, a first regeneration process for regenerating only the first NOx storage catalyst 51 and a second regeneration process for regenerating the second NOx storage catalyst 53. To do. In the second regeneration process, in the present embodiment, the first NOx storage catalyst 51 and the second NOx storage catalyst 53 are simultaneously regenerated. Of course, the second regeneration process may be a process for regenerating only the second NOx storage catalyst 53.

  As described above, the regeneration processing execution means 71 executes regeneration processing (for example, S purge) every time the engine 10 is operated for a predetermined period. At this time, either the first regeneration processing or the second regeneration processing is performed. Whether to execute the determination is determined based on the amount of sulfur oxide (SOx) accumulated in the first NOx storage catalyst 51 and the second NOx storage catalyst 53.

  Specifically, when the regeneration process is performed, the amount of SOx accumulated in each of the first NOx storage catalyst 51 and the second NOx storage catalyst 53 is estimated, and is the difference between them a predetermined amount or more? Whether or not to execute the first reproduction process or the second reproduction process is determined depending on whether or not. When the difference in the amount of SOx accumulated in each of the first NOx storage catalyst 51 and the second NOx storage catalyst 53 is a predetermined amount or more, that is, the first NOx storage catalyst 51 stores the second NOx storage. When SOx more than the catalyst 53 is accumulated by a predetermined amount or more, the first regeneration process is executed, and when it is smaller than the predetermined amount, the second regeneration process is executed.

  Thus, each of the first NOx storage catalyst 51 and the second NOx storage catalyst 53 can be appropriately regenerated.

  The method for estimating the amount of SOx accumulated in the first NOx storage catalyst 51 and the second NOx storage catalyst 53 is not particularly limited. For example, it is estimated based on the fuel consumption, the capacity of each catalyst, and the like. Can do.

  The determination of whether to execute the first reproduction process or the second reproduction process may be performed as described above as appropriate, but may be determined in advance. For example, the second reproduction process may be executed every time the first reproduction process is executed once or a plurality of times.

  It is considered that the sulfur oxide is adsorbed from the first NOx storage catalyst 51 on the upstream side. For this reason, the time required for the regeneration process of the first NOx storage catalyst 51 is longer than the time required for the regeneration process of the second exhaust purification catalyst 53. For this reason, each time the first regeneration process is executed once or a plurality of times, the second NOx storage catalyst 51 and the second NOx storage catalyst 53 are appropriately set by executing the second regeneration process. Can be played back.

  Hereinafter, the first reproduction process and the second reproduction process will be described in detail. First, the second regeneration process for regenerating the first NOx storage catalyst 51 and the second NOx storage catalyst 53 simultaneously will be described.

  When the second regeneration process (S purge) is performed by the regeneration process execution means 71, the air-fuel ratio of the exhaust gas flowing into the first NOx storage catalyst 51 and the second NOx storage catalyst 53 as shown in FIG. Is a rich period (a period in which the rich flag is ON) Ta1, and a lean period in which the air-fuel ratio of the exhaust gas flowing into the first NOx storage catalyst 51 and the second NOx storage catalyst 53 is a lean air-fuel ratio ( The cycle including the rich flag OFF period) Tb1 is repeated. That is, one rich period Ta1 and one lean period Tb1 are defined as one cycle period Tc, and the rich period Ta1 and lean period Tb1 are alternately repeated. In the second reproduction process, the rich period Ta1 and the lean period Tb1 are switched in a so-called short cycle, and the rich period Ta1 is set shorter than the lean period Tb1.

  During the execution of the second regeneration process, the exhaust air / fuel ratio (inlet air / fuel ratio) in the vicinity of the inlet of the second NOx storage catalyst 53 detected by the air / fuel ratio sensor 54 depends on the rich period Ta1 and the lean period Tb1. To switch between the rich air-fuel ratio and the lean air-fuel ratio. On the other hand, the air-fuel ratio (outlet air-fuel ratio) in the vicinity of the outlet of the second NOx storage catalyst 53 detected by the air-fuel ratio sensor 55 changes according to the switching between the rich period Ta1 and the lean period Tb1, but is always rich. The fuel ratio is maintained.

  Further, as shown in FIG. 3A, during the rich period Ta1, the pre-injection Pu and the main injection Ma, which are the main injections by the fuel injection valve 33, and the early post-injection Po1, which is the post-injection after the main injection, and the post-combustion Post injection Po2 is performed.

The early post-injection Po1 is a post-injection that is performed at a timing at which combustion can be continued following the combustion by the main injection, and an amount of fuel that substantially consumes all the oxygen (O ₂ ) in the combustion chamber 18 is consumed. Spray. That is, an amount of fuel in which the calculated in-cylinder air-fuel ratio becomes stoichiometric or slightly rich is injected by the early post-injection Po1.

  The post-combustion post-injection Po2 is a post-injection that is performed at the timing when the combustion in the combustion chamber 18 ends after the early post-injection Po1. By performing the post-combustion post-injection Po2, fuel (hydrocarbon: HC) as a reducing agent is added to the exhaust gas. As a result, the air-fuel ratio of the exhaust gas flowing into the first NOx storage catalyst 51 and the second NOx storage catalyst 53 during the rich period Ta1 becomes the rich air-fuel ratio.

  On the other hand, during the lean period Tb1, only the pre-injection Pu and the main injection Ma as the main injection by the fuel injection valve 33 are performed, and the post-injection is not performed. For this reason, the air-fuel ratio of the exhaust gas flowing into the first NOx storage catalyst 51 and the second NOx storage catalyst 53 during the lean period Tb becomes the lean air-fuel ratio.

  During the execution of the second regeneration process, that is, while the rich period Ta1 and the lean period Tb1 are repeated, each of the first NOx storage catalyst 51 and the second NOx storage catalyst 53 flows into the inflowing exhaust gas. The temperature rises due to heat generation when the air-fuel ratio of the air-fuel ratio switches between the rich air-fuel ratio and the lean air-fuel ratio. Thereby, the temperature of the first NOx storage catalyst 51 and the second NOx storage catalyst 53 can be raised to substantially the same temperature.

  By the way, when the regeneration process execution means 71 executes the second regeneration process (S purge), for example, as shown in FIG. 4, the air-fuel ratio of exhaust gas discharged from the second NOx storage catalyst 53 (second The target average air-fuel ratio during one cycle period Tc of the exhaust gas air-fuel ratio) is set, and the fuel amount (additive amount) injected from the fuel injection valve 33 during the rich period Ta1 based on this target average air-fuel ratio, In the embodiment, the fuel amount by post injection (early post injection Po1 and post-combustion post injection Po2) is determined.

By injecting the fuel amount determined in this way as post-injection from the fuel injection valve 33, when the temperature of the second NOx occlusion catalyst 53 is reliably raised at the target temperature, the accuracy can be improved. Furthermore, the temperature of the second NOx storage catalyst 53 can be adjusted while suppressing the temperature change of the first NOx storage catalyst 51. Even if the injection amount injected from the fuel injection valve 33 is not changed during the lean period Tb1, the first NOx storage catalyst 51 is stored by changing the fuel amount injected from the fuel injection valve 33 during the rich period Ta1. The amount of O ₂ flowing into the second NOx occlusion catalyst 53 is changed by changing the speed at which the downstream of the first NOx occlusion catalyst 51 is leaned when the rich period Ta1 shifts to the lean period Tb1. And the temperature of the second NOx storage catalyst 53 can be adjusted relatively easily.

  Therefore, even when a temperature difference between the first NOx storage catalyst 51 and the second NOx storage catalyst 53 occurs due to some factor, by adjusting the temperature of the second NOx storage catalyst 53, both The temperature difference can be kept small.

  When the regeneration process execution means 71 performs the second regeneration process, first, the state of the first NOx storage catalyst 51 and the second NOx storage catalyst 53, for example, the first and second NOx storage catalysts 51, 53. Based on the temperature or the like, the length of one cycle period Tc (the rich period Ta1 and the lean period Tb1) is set. At that time, the reproduction processing execution means 71 sets the rich period Ta1 to be shorter than the lean period Tb1. Thereby, the temperature of the first NOx storage catalyst 51 and the second NOx storage catalyst 53 can be raised to substantially the same temperature.

  Further, the length of one cycle period Tc (the rich period Ta1 and the lean period Tb1) may be always constant, but it is preferable to shorten the length of the lean period Tb1 as the degree of deterioration of the first NOx storage catalyst 51 increases. . As the degree of deterioration increases, the temperature rise of the first NOx storage catalyst 51 becomes slower. Therefore, by shortening the length of the lean period Tb1 and increasing the timing of switching between the rich air-fuel ratio and the lean air-fuel ratio, the first It becomes easy to raise the temperature of the NOx storage catalyst 51.

Here, if the length of the lean period Tb1 is shortened, the amount of O ₂ supplied to the second NOx occlusion catalyst 53 is reduced, and the temperature of the second NOx occlusion catalyst 53 may not be easily raised. As the degree of deterioration of the NOx storage catalyst 51 increases, the HC storage capacity generally decreases. Therefore, the amount of O ₂ supplied to the second NOx storage catalyst 53 during the lean period Tb1 does not decrease so much, and the second NOx storage is performed. The temperature rise of the catalyst 53 can be ensured.

  The method for determining the degree of deterioration of the first NOx storage catalyst 51 is not particularly limited, but can be determined based on, for example, the accumulated usage time.

Furthermore, it is preferable to shorten the length of the lean period as the outside air temperature is lower. When the outside air temperature is low, the temperature rise of the second NOx storage catalyst 53 together with the first NOx storage catalyst 51 is also slowed. Therefore, the length of the lean period Tb1 is shortened, and the rich air fuel ratio and the lean air fuel ratio are reduced. Increasing the switching timing makes it easier to raise the temperature of the first NOx storage catalyst 51 and the second NOx storage catalyst 53. However, if the length of the lean period Tb1 is excessively shortened, the amount of O ₂ supplied to the second NOx storage catalyst 53 is reduced, and the temperature of the second NOx storage catalyst 53 may not be easily raised. It is necessary to set Tb1 appropriately.

Thereafter, the regeneration process execution means 71 performs the one cycle period Tc (the rich period Ta1 and the lean period) so that the second NOx occlusion catalyst 53 required for the second regeneration process (S purge) can be raised to the target temperature. A target average air-fuel ratio is set based on Tb1). At this time, the target average air-fuel ratio is also preferably set in consideration of the degree of deterioration of the first NOx storage catalyst 51. For example, it is preferable to set the target average air-fuel ratio to the lean side as the degree of deterioration of the first NOx storage catalyst 51 increases. As the degree of deterioration increases, the temperature rise of the first NOx storage catalyst 51 becomes slower. For this reason, it is easy to raise the temperature of the second NOx storage catalyst 53 by increasing the amount of O ₂ supplied to the second NOx storage catalyst 53 by setting the target average air-fuel ratio to the lean side.

  Then, based on the set target average air-fuel ratio, the amount of fuel (reducing agent amount) injected from the fuel injection valve 33 as the reducing agent supply means during the rich period Ta1 is determined. That is, based on the target average air-fuel ratio, the amount of fuel that is injected as post injection from the fuel injection valve 33 during the rich period Ta1 is determined.

  For example, as shown in FIG. 4, when the target average air-fuel ratio is set, the total fuel injection amount Fa necessary to achieve the target air-fuel ratio is determined. The total fuel injection amount Fa is a fuel injection amount Fm by main injection (pre-injection Pu and main injection Ma) during one cycle period Tc, and fuel injection by post-injection (early post-injection Po1 and post-combustion post-injection Po2). It is the sum of the quantity Fp1. Therefore, by subtracting the fuel injection amount Fm by the main injection from the total fuel injection amount Fa, the fuel injection amount Fp1 by the post injection required during the one cycle period Tc is calculated. The fuel injection amount Fp1 by post injection required during the one cycle period Tc is set as the fuel injection amount Fp2 injected by post injection during the rich period Ta1. And it injects as early post-injection Po1 and post-combustion post-injection Po2.

  During the lean period Tb1, post injection is not performed as described above, and only pre-injection Pu and main injection Ma, which are main injections by the fuel injection valve 33, are performed.

  As described above, in the present embodiment, during the second regeneration process, the fuel injection amount (reduction) by the post-injection during the rich period Ta1 based on the target average air-fuel ratio during the one-cycle period Tc of the second catalyst air-fuel ratio. Dose amount) Fp2 was determined. As a result, during the second regeneration process (S purge), the first NOx storage catalyst 51 and the second NOx storage catalyst 53 can each be heated to a desired target temperature. That is, by calculating the fuel injection amount Fp by post injection during the rich period Ta1 from the target average air-fuel ratio, the required fuel injection amount Fp can be set with high accuracy, and the first NOx storage catalyst 51 and the second NOx storage catalyst 51 When the temperature of the NOx storage catalyst 53 is raised, an error from the target temperature can be suppressed small.

  Further, when a temperature difference between the first NOx storage catalyst 51 and the second NOx storage catalyst 53 has occurred, by adjusting the temperature of the second NOx storage catalyst 53 (adjustment of heat generation), both The temperature difference can be kept small. For example, when the temperature of the second NOx occlusion catalyst 53 has decreased, the target average air-fuel ratio is set to the lean side, thereby suppressing the temperature rise of the first NOx occlusion catalyst 51 and the second NOx occlusion catalyst 51. The NOx storage catalyst 53 can be raised in temperature early.

  Accordingly, the first NOx storage catalyst 51 and the second NOx storage catalyst 53 can be appropriately regenerated.

Next, a first regeneration process for regenerating only the first exhaust purification catalyst will be described.
When the first regeneration process (S purge) is executed by the regeneration process execution means 71, as shown in FIG. 5, the first NOx storage catalyst 51 and the first NOx storage catalyst 51 and the second regeneration process are executed as in the case where the second regeneration process is executed. A rich period (a period when the rich flag is ON) Ta2 in which the air-fuel ratio of the exhaust gas flowing into the second NOx storage catalyst 53 is a rich air-fuel ratio, and the first NOx storage catalyst 51 and the second NOx storage catalyst 53 A cycle including a lean period (a period during which the rich flag is OFF) Tb2 in which the air-fuel ratio of the exhaust is set to be a lean air-fuel ratio is repeated.

  However, unlike the case of the second reproduction process, the first reproduction process does not switch between the rich period Ta2 and the lean period Tb2 in a so-called short cycle, and the rich period Ta2 is set longer than the lean period Tb2. Has been. That is, in the first regeneration process, the rich period Ta2 occupies most, but the generation of hydrogen sulfide is suppressed by repeating the rich period Ta2 and the lean period Tb2 shorter than the rich period Ta2.

  Further, during the first regeneration process, the exhaust air / fuel ratio (inlet air / fuel ratio) near the inlet of the second NOx storage catalyst 53 detected by the air / fuel ratio sensor 54 and the second NOx storage catalyst detected by the air / fuel ratio sensor 55 are detected. The air-fuel ratio in the vicinity of the outlet 53 (exit air-fuel ratio) is switched between the rich air-fuel ratio and the lean air-fuel ratio in accordance with the rich period Ta2 and the lean period Tb2.

  Also in the first regeneration process as in the second regeneration process, during the rich period Ta2, as shown in FIG. 6, the pre-injection Pu and the main injection Ma, which are the main injections by the fuel injection valve 33, and the main injection Early post-injection Po3 and post-combustion post-injection Po4, which are subsequent post-injections, are performed. However, the injection amount of the early post-injection Po3 in the first regeneration process is smaller than the injection amount of the early post-injection Po1 in the second regeneration process (shown by a dotted line in the figure). That is, the injection period of the early post-injection Po3 in the first regeneration process is shorter than the injection period of the early post-injection Po1 in the second regeneration process.

Therefore, in the first regeneration process, oxygen (O ₂ ) in the combustion chamber 18 remains even if fuel is injected by the early post-injection Po3. When post-combustion post-injection Po4 is executed, unburned fuel is present in the combustion chamber 18 together with oxygen (O ₂ ). Note that the amount of post-combustion post-injection Po4 in the first regeneration process may be smaller than the amount of post-combustion post-injection Po2 in the second regeneration process (shown by the dotted line in the figure).

  On the other hand, during the lean period Tb2, only the pre-injection Pu and the main injection Ma as the main injection by the fuel injection valve 33 are performed as in the second regeneration process, and the post-injection is not performed (see FIG. 3B). .

In such a first regeneration process, during the rich period Ta2, HC contained in the fuel together with O ₂ contained in the exhaust gas is simultaneously supplied to the first NOx storage catalyst 51, and the first NOx storage catalyst. The temperature of 51 rises due to heat generated by the reaction of these HC and O ₂ . On the other hand, the second NOx storage catalyst 53 disposed on the downstream side consumes O ₂ in the first NOx storage catalyst 51, and therefore generates very little heat when HC and O ₂ are supplied simultaneously. . In the first reproduction process, there is little switching between the rich period Ta2 and the lean period Tb2. Therefore, in the first regeneration process, both the first NOx storage catalyst 51 and the second NOx storage catalyst 53 generate very little heat due to switching between the rich air-fuel ratio and the lean air-fuel ratio. Therefore, in the first regeneration process, only the first NOx storage catalyst 51 can be efficiently heated while suppressing the temperature increase of the second NOx storage catalyst 53. That is, only the first NOx storage catalyst 51 can be efficiently regenerated.

  In the first reproduction process, the rich period Ta2 is set longer than the rich period Ta1 in the second reproduction process. For this reason, the first reproduction process requires a shorter processing time than the second reproduction process. For this reason, by executing not only the second regeneration process but also the first regeneration process at a predetermined timing, the fuel efficiency can be improved as compared with the case where the second regeneration process is always performed.

  Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment.

  For example, in the above-described embodiment, the fuel injection amount by the post injection is changed based on the target average air-fuel ratio. However, for example, if the influence of the change in the generated torque of the engine is not a problem in the running of the vehicle. For example, the fuel injection amount by the main injection may be further changed.

  Further, for example, although the S purge is exemplified as the regeneration process in the above-described embodiment, the present invention is not limited to this embodiment. For example, the present invention can be applied to NOx purge.

  In the above-described embodiment, fuel as a reducing agent is supplied by performing post injection from the fuel injection valve. However, a separate injector is provided at a predetermined position of the exhaust pipe, for example, near the inlet of the first NOx storage catalyst. The fuel as the reducing agent may be injected from the injector into the exhaust pipe instead of the post injection. In this case, a reducing agent (hydrocarbon) other than fuel may be injected from the injector.

  Moreover, although the diesel engine was illustrated in the above-described embodiment, the present invention can also be applied to a gasoline engine that performs combustion in an oxidizing atmosphere by controlling the lean air-fuel ratio side rather than the stoichiometric air-fuel ratio.

DESCRIPTION OF SYMBOLS 10 Engine 11 Engine main body 12 Cylinder head 13 Cylinder block 14 Cylinder bore 15 Piston 16 Connecting rod 17 Crankshaft 18 Combustion chamber 19 Intake port 20 Intake manifold 21 Intake pipe 22 Intake valve 23 Exhaust port 24 Exhaust manifold 25 Exhaust pipe 26 Exhaust valve 27 Turbocharger 28 Intercooler 29 Throttle valve 30 EGR pipe 31 EGR cooler 32 EGR valve 33 Fuel injection valve 34 Common rail 35 Supply pump 50 Exhaust gas purification device 51 First NOx storage catalyst 52 DPF
53 Second NOx storage catalyst 54, 55 Air-fuel ratio sensor 56, 57 Temperature sensor 71 Regeneration processing execution means

Claims (7)

Fuel injection means for injecting fuel into the cylinder of the engine;
A first exhaust purification catalyst provided in the exhaust passage of the engine;
A second exhaust purification catalyst provided downstream of the first exhaust purification catalyst in the exhaust passage;
Reducing agent supply means for supplying a reducing agent to flow into the first exhaust purification catalyst;
A rich period during which the air-fuel ratio of the exhaust gas flowing out from the first exhaust purification catalyst and the second exhaust purification catalyst is enriched by adjusting at least the amount of the reducing agent supplied by the reducing agent supply means; Regeneration of the first exhaust gas purification catalyst and the second exhaust gas purification catalyst by alternately repeating a lean period in which the air-fuel ratio of the exhaust gas flowing out from the first exhaust gas purification catalyst and the second exhaust gas purification catalyst is made lean. Reproduction processing execution means for executing processing,
When performing the first regeneration process for regenerating only the first exhaust purification catalyst, the regeneration process execution means makes the rich period longer than the lean period, and sets the second exhaust purification catalyst to An exhaust emission control device for an engine, wherein when executing the second regeneration process for regeneration, the rich period is made shorter than the lean period. The exhaust emission control device for an engine according to claim 1,
The engine exhaust gas purification apparatus according to claim 1, wherein the regeneration process execution means executes the second regeneration process every time the first regeneration process is performed once or a plurality of times. The engine exhaust gas purification apparatus according to claim 1 or 2,
The regeneration process execution means shortens the length of the lean period as the degree of deterioration of the first exhaust purification catalyst is larger when the second regeneration process is performed. apparatus. The engine exhaust gas purification apparatus according to any one of claims 1 to 3,
The regeneration process executing means makes the amount of reducing agent injected from the reducing agent supply means in the first regeneration process smaller than the amount of reducing agent injected from the reducing agent supply means in the second regeneration process. An exhaust purification device for an engine characterized by the above. The engine exhaust gas purification apparatus according to any one of claims 1 to 4,
The fuel injection means also serves as the reducing agent supply means;
The engine exhaust purification apparatus according to claim 1, wherein the regeneration processing execution means adjusts the amount of fuel injected by post-injection after main injection of the fuel injection means as adjustment of the reducing agent amount. The engine exhaust gas purification apparatus according to any one of claims 1 to 5,
The engine exhaust gas purification apparatus, wherein the first exhaust gas purification catalyst and the second exhaust gas purification catalyst are NOx storage catalysts. The engine exhaust gas purification apparatus according to claim 6,
The engine exhaust characterized in that the regeneration process executed by the regeneration process execution means is a process of removing sulfur oxides stored in the first exhaust purification catalyst and the second exhaust purification catalyst. Purification equipment.