JP6340864B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus provided with a catalyst provided in an exhaust passage of an internal combustion engine (hereinafter referred to as an engine), which stores a predetermined component in exhaust gas under an oxidizing atmosphere and releases it under a reducing atmosphere.

The exhaust discharged from the engine includes nitrogen oxide (NO), nitrogen oxides (NO ₂ ) containing nitrogen dioxide (NO ₂ ), sulfur components, etc. (hereinafter collectively referred to as predetermined components) Some of the exhaust passages of the engine are provided with a NOx trap catalyst (occlusion reduction catalyst) as an exhaust purification catalyst for purifying NOx among such predetermined components. The NOx trap catalyst stores NOx in the exhaust as nitrate in a lean atmosphere with a relatively high oxygen concentration, and releases NOx stored in a rich atmosphere with a relatively low oxygen concentration to reduce it to nitrogen (N ₂ ). To do.

When the amount of NOx occluded in the NOx trap catalyst increases, the exhaust purification device equipped with the NOx trap catalyst adds a reducing agent to reduce NOx to make the exhaust atmosphere rich, and releases NOx from the NOx trap catalyst. Then, NOx purge control for reducing to N ₂ is performed. In addition to the NOx trap catalyst, the engine exhaust passage may include an oxidation catalyst capable of oxidizing components in the exhaust, and a filter for collecting particulate matter in the exhaust. is there. For example, in Patent Document 1, an oxidation catalyst, a filter, two NOx trap catalysts, and an oxidation catalyst are arranged in this order from the exhaust upstream side. In Patent Document 2, the NOx trap catalyst, the filter, and the NOx trap catalyst are arranged in this order from the exhaust upstream side.

  By the way, it is known that the NOx trap catalyst has a property of storing a sulfur component in the exhaust gas. Since the sulfur component stored in the NOx trap catalyst has higher chemical stability than nitrate and only a small amount is released by the NOx purge control, the sulfur component remaining in the NOx trap catalyst gradually increases, and the NOx trap catalyst. This reduces the ability (performance) to occlude NOx, which is the original function of. Therefore, the temperature of the NOx trap catalyst is raised compared with the NOx purge control, and the S purge control for periodically releasing the sulfur component stored in the NOx trap catalyst is performed to ensure the function of the NOx trap catalyst. Has been done.

JP 2013-53583 A Japanese Patent No. 3812302

  In the above NOx purge control and S purge control, it is necessary to raise the exhaust temperature by injecting additional fuel or the like to raise the temperature of the NOx trap catalyst. . In particular, in the case of an exhaust purification device in which two NOx trap catalysts are arranged in the exhaust passage as in the above-mentioned Patent Documents 1 and 2, since it is necessary to perform purge control on each NOx trap catalyst, There is a possibility that fuel consumption will deteriorate due to control.

  One of the purposes of the present invention was devised in view of the above problems, and it is possible to appropriately release the predetermined components stored in the catalyst while suppressing deterioration in fuel consumption. Is to provide a device. The present invention is not limited to this purpose, and is a function and effect derived from each configuration shown in the embodiments for carrying out the invention described later, and other effects of the present invention are to obtain a function and effect that cannot be obtained by conventional techniques. Can be positioned.

(1) An exhaust purification device for an internal combustion engine disclosed herein is provided in an exhaust passage of the internal combustion engine, and stores a predetermined component in the exhaust in an oxidizing atmosphere and releases it in a reducing atmosphere, A second catalyst that is provided in the exhaust passage on the downstream side of the exhaust flow direction of one catalyst and that occludes the predetermined component in the exhaust in an oxidizing atmosphere and releases it in a reducing atmosphere; the first catalyst and the second catalyst And a filter that collects particulate matter in the exhaust gas .
Further, the exhaust purification device performs a first purge control for supplying a reducing agent and releasing the predetermined component from the first catalyst based on the storage state of the predetermined component stored in the first catalyst, Based on the occlusion status of the predetermined component occluded in the second catalyst when the first purge control is performed, the second purge control is performed to supply the reducing agent and release the predetermined component from the second catalyst. A control means is provided which is continuously executed simultaneously with the one purge control. That is, the control means performs the second purge control together with the first purge control only when the first purge control is performed. The predetermined component is a sulfur component contained in exhaust gas, and the control means removes the particulate matter from the filter based on the amount of the particulate matter collected by the filter; When the first purge control is performed together, the first purge control is performed after the regeneration control is finished. That is, both the first purge control and the second purge control are so-called S purge controls.

(2) It is preferable that the control means changes the execution time of the regeneration control according to the storage amount of the sulfur component stored in the first catalyst and the storage amount of the sulfur component stored in the second catalyst. .
(3) When the first purge control (that is, the first S purge control) is performed, the control means starts exhaust gas temperature increase control for increasing the exhaust gas temperature by decreasing the intake air flow rate. It is preferable to start the exhaust gas temperature increase control at least during the execution of the first purge control.

( 4 ) An exhaust gas purification apparatus for an internal combustion engine disclosed herein is provided in an exhaust passage of the internal combustion engine, stores a predetermined component in the exhaust gas in an oxidizing atmosphere, and releases it in a reducing atmosphere; A second catalyst that is provided in the exhaust passage on the downstream side in the exhaust flow direction of one catalyst and that occludes the predetermined component in the exhaust in an oxidizing atmosphere and releases it in a reducing atmosphere.
Further, the exhaust purification device performs a first purge control for supplying a reducing agent and releasing the predetermined component from the first catalyst based on the storage state of the predetermined component stored in the first catalyst, Based on the occlusion status of the predetermined component occluded in the second catalyst when the first purge control is performed, the second purge control is performed to supply the reducing agent and release the predetermined component from the second catalyst. And a control unit that performs the purge control simultaneously with the one purge control, wherein the predetermined component is a sulfur component contained in the exhaust gas, and the control unit performs the first purge control (that is, the first S purge control). In the case of carrying out, the exhaust gas temperature increase control for increasing the exhaust gas temperature by decreasing the intake air flow rate is started before the start of the first purge control, and at least during the execution of the first purge control, Carry out.

( 5 ) The control means performs the first purge control when the storage amount of the predetermined component stored in the first catalyst is equal to or greater than a predetermined first threshold, and It is preferable that the second purge control is performed when the occlusion amount of the predetermined component occluded in the second catalyst is equal to or greater than a second threshold value that is smaller than the first threshold value .

  According to the disclosed exhaust gas purification apparatus for an internal combustion engine, the purge control (second purge control) of the second catalyst disposed on the exhaust downstream side is performed on the first catalyst disposed on the exhaust upstream side (first purge). This is implemented based on the occlusion status of the predetermined component occluded in the second catalyst when the control is carried out. That is, since the second purge control is not performed alone but is performed simultaneously with the first purge control, it is possible to appropriately release the predetermined component while suppressing deterioration in fuel consumption.

1 is a schematic overall configuration diagram of an internal combustion engine to which an exhaust gas purification apparatus according to a first embodiment is applied. 2 is a graph showing the relationship between the load of the exhaust purification device of FIG. 1 and NOx purification performance. 2 is a graph schematically showing changes in the amount of sulfur component stored in the upstream NOx trap catalyst and the amount of sulfur component stored in the downstream NOx trap catalyst of the exhaust purification device of FIG. 1. 3 is a main flowchart illustrating a control procedure performed by the exhaust purification device of FIG. 1. 5 is a sub-flowchart (flowchart of S purge control) in FIG. 4. FIG. 6 is a graph showing temperature changes and control contents of an upstream NOx trap catalyst and a downstream NOx trap catalyst during S purge control, where (a) shows only upstream S purge control, and (b) shows upstream S purge control and When the downstream S purge control is performed and the downstream S purge control is finished first, (c) is the case where the upstream S purge control and the downstream S purge control are performed, and the upstream S purge control is performed first. This is the case when it ends. It is a typical whole block diagram of the internal combustion engine to which the exhaust gas purification apparatus which concerns on 2nd embodiment was applied.

Hereinafter, embodiments will be described with reference to the drawings. Note that the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described in the following embodiment.
[1. First embodiment]
[1-1. Device configuration]
The exhaust purification device of this embodiment is applied to a diesel engine (internal combustion engine) 1 mounted on a vehicle. FIG. 1 shows one of a plurality of cylinders 2 provided in the engine 1, but the other cylinders 2 have the same configuration. A piston 3 having a cavity formed on the top surface is provided in the cylinder 2 of the engine 1 and slides back and forth in the vertical direction in the cylinder 2.

  The cylinder head above the cylinder 2 is provided with an in-cylinder injection valve (injector) 4 for fuel injection. The in-cylinder injection valve 4 has a tip projecting from the in-cylinder space of the cylinder 2 and injects fuel directly into the cylinder 2. A fuel pipe is connected to the base end portion of the in-cylinder injection valve 4, and fuel pressurized from the fuel pipe is supplied to the in-cylinder injection valve 4. The fuel injection amount from the in-cylinder injection valve 4 and the injection timing thereof are controlled by an engine control device 40 described later.

  The cylinder head is provided with an intake port 5 and an exhaust port 6 communicating with the in-cylinder space of the cylinder 2, and an intake valve 7 and an exhaust valve 8 for opening and closing each of these ports 5 and 6 are provided. An intake manifold 9 (hereinafter referred to as intake manifold 9) is provided on the upstream side of the intake port 5, and the intake manifold 9 is provided with a surge tank 10 for temporarily storing air flowing to the intake port 5 side. A throttle body (not shown) incorporating an electronically controlled throttle valve 11 is connected to the upstream end of the intake manifold 9 and flows to the intake manifold 9 side according to the opening (throttle opening) of the throttle valve 11. Air volume is adjusted. The throttle opening is controlled by the engine control device 40. An intake passage 12 is connected to the upstream side of the throttle body. An air filter 13 is provided in the uppermost stream of the intake passage 12, and fresh air filtered by the air filter 13 is introduced into the intake passage 12.

  On the other hand, an exhaust manifold 15 (hereinafter referred to as an exhaust manifold 15) formed so as to merge from the plurality of cylinders 2 is provided on the exhaust downstream side of the exhaust port 6, and an exhaust passage 16 is provided on the downstream side of the exhaust manifold 15. Connected. The intake / exhaust system of the engine 1 is provided with a turbocharger (supercharger) 17 that supercharges intake air into the cylinder 2 using exhaust pressure. The turbocharger 17 is a supercharger interposed between both the intake passage 12 and the exhaust passage 16. The turbocharger 17 compresses the intake air on the side of the intake passage 12 by rotating the turbine on the exhaust passage 16 with the exhaust pressure in the exhaust passage 16 and driving the compressor on the intake passage 12 using the rotational force. Then, the engine 1 is supercharged. An intercooler 14 is provided on the downstream side of the intake air flow with respect to the compressor in the intake passage 12 to cool the compressed air.

  The engine 1 according to the present embodiment is provided with an EGR passage 18 (also referred to as an exhaust gas recirculation passage or a reflux passage) that recirculates exhaust gas flowing through the exhaust passage 16 to the intake passage 12. The EGR passage 18 communicates the exhaust passage 16 upstream of the turbine of the turbocharger 17 and the intake passage 12 downstream of the compressor to form a so-called high pressure EGR passage. An EGR valve 19 is built in a connection portion between the EGR passage 18 and the intake passage 12, and the amount of recirculation gas flowing through the EGR passage 18 is adjusted according to the opening degree of the EGR valve 19. The opening degree of the EGR valve 19 is controlled by the engine control device 40. The EGR passage 18 is provided with an EGR cooler 20 for cooling the reflux gas.

  An upstream NOx trap catalyst (first catalyst) 31, a filter 32, and a downstream NOx trap catalyst (second catalyst) 33 are arranged in order from the upstream side in the exhaust flow direction as an exhaust purification device 30 on the downstream side of the turbine in the exhaust passage 16. Intervened. Exhaust gas flowing through the exhaust passage 16 is purified by the exhaust purification device 30 and then discharged outside the vehicle. The exhaust purification device 30 includes an engine control device 40 described later.

The upstream NOx trap catalyst 31 and the downstream NOx trap catalyst 33 both store NOx (predetermined component) in the exhaust as nitrate on the carrier in an oxidizing atmosphere (the exhaust air / fuel ratio is leaner than the stoichiometric air / fuel ratio). It has the function of releasing the stored NOx and reducing it to N ₂ under a reducing atmosphere (exhaust air / fuel ratio is richer than the stoichiometric air / fuel ratio). Corresponding to these functions, the upstream NOx trap catalyst 31 and the downstream NOx trap catalyst 33 carry a storage material responsible for NOx storage, a noble metal element responsible for a reduction function, and the like.

  Here, the upstream NOx trap catalyst 31 and the downstream NOx trap catalyst 33 have the same constituent components (types and amounts of occlusion material, noble metal element, etc.). Represent. 1 illustrates a case where the downstream NOx trap catalyst 33 has a larger capacity than the upstream NOx trap catalyst 31, but the NOx trap catalysts 31 and 33 may have the same capacity. These NOx trap catalysts 31, 33 have the property of having excellent NOx purification performance in a certain temperature range (having a peak of NOx purification performance in a certain temperature range). In other words, the NOx purification performance is not always constant, but changes according to the temperature of the NOx trap catalysts 31, 33, and exhibits the highest NOx purification performance in a certain temperature range.

The upstream NOx trap catalyst 31 and the downstream NOx trap catalyst 33 each have a determined amount (maximum amount) of NOx that can be stored according to the capacity. When the amount of each NOx stored in the upstream NOx trap catalyst 31 and the downstream NOx trap catalyst 33 approaches the maximum amount (saturated state), the NOx stored in the upstream NOx trap catalyst 31 or the downstream NOx trap catalyst 33 by the engine control device 40. Is controlled to reduce to N ₂ (hereinafter referred to as NOx purge control).

  Further, these NOx trap catalysts 31 and 33 have the property that a sulfur component (predetermined component, also simply referred to as S) in exhaust gas can be stored. Since only a small amount of the sulfur component occluded in the NOx trap catalysts 31 and 33 is released by the above NOx purge control, the NOx trap catalysts 31 and 33 are originally functioning by the gradually increasing sulfur component. The ability (performance) to occlude is reduced. This is called S poisoning, and in order to eliminate the S poisoning of the NOx trap catalysts 31 and 33, the engine controller 40 releases the sulfur component from the NOx trap catalysts 31 and 33 (hereinafter referred to as S purge). Control) is performed separately from the above NOx purge control. In the following description, the amount of sulfur component stored in the NOx trap catalysts 31 and 33 (storage amount) is referred to as storage S amount.

  The filter 32 is a porous filter that collects particulate matter (hereinafter referred to as PM) in the exhaust gas, and has a relatively large heat capacity. The interior of the filter 32 is divided into a plurality along the flow direction of the exhaust by a porous wall. A large number of pores having a size corresponding to the particulates of PM are formed in the wall body, and PM is collected on the wall body and the surface of the wall body when exhaust passes near or inside the wall body. In the filter 32, continuous regeneration in which the collected PM is continuously oxidized and regeneration control in which the PM is forcibly burned by the engine control device 40 to regenerate the filter 32 are performed.

  In the exhaust purification device 30, the upstream NOx trap catalyst 31 and the downstream NOx trap catalyst 33 are disposed in the exhaust passage 16 with the filter 32 interposed therebetween. Different. This is because the upstream NOx trap catalyst 31 is more likely to be heated by the exhaust heat than the downstream NOx trap catalyst 33 because the exhaust temperature is higher upstream of the exhaust passage 16. The high-temperature exhaust gas passes through the upstream NOx trap catalyst 31 and is deprived of the temperature, and further passes through the downstream NOx trap catalyst 33 after being cooled by passing through the filter 32 having a large heat capacity. Therefore, the downstream NOx trap catalyst 33 is less likely to be heated than the upstream NOx trap catalyst 31 and has a lower temperature than the upstream NOx trap catalyst 31. The exhaust temperature changes according to the operating state (engine load) of the engine 1, and the exhaust temperature tends to increase as the load increases.

  As described above, since the NOx trap catalysts 31 and 33 have a peak NOx purification performance in a certain temperature range, the upstream NOx trap catalyst 31 and the downstream NOx trap catalyst 33 are arranged in different temperature zones, The operation state in which the upstream NOx trap catalyst 31 exhibits high NOx purification performance and the operation state in which the downstream NOx trap catalyst 33 exhibits high NOx purification performance can be differentiated. Thereby, it becomes possible to improve the NOx purification performance of the whole system. This will be described with reference to FIG. 2 indicate the NOx purification performance of the upstream NOx trap catalyst 31 and the downstream NOx trap catalyst 33, respectively, and the solid line indicates the NOx purification performance of the entire system. The engine load on the horizontal axis has a positive correlation with the exhaust temperature as described above, and the exhaust temperature increases as the load increases.

  As shown in FIG. 2, the upstream NOx trap catalyst 31 has a peak of NOx purification performance on the low load side, and the downstream NOx trap catalyst 33 has a peak of NOx purification performance on the high load side. This is because, when the load on the engine 1 is low, the upstream NOx trap catalyst 31 is heated to a temperature range where high NOx purification performance can be exhibited by exhaust heat, while the downstream NOx trap catalyst 33 exhibits high NOx purification performance. This is because the temperature is not raised to a possible temperature range. On the other hand, when the load on the engine 1 is high, the upstream NOx trap catalyst 31 is heated to a temperature higher than the temperature range where high NOx purification performance can be exhibited due to exhaust heat, and the NOx purification performance decreases. This is because the downstream NOx trap catalyst 33 is heated to a temperature range where high-temperature exhaust gas reaches and can exhibit high NOx purification performance.

  Therefore, NOx is mainly purified by the upstream NOx trap catalyst 31 in the low load operation region of the engine 1, and NOx is mainly purified by the downstream NOx trap catalyst 33 in the high load operation region of the engine 1. When viewed from the entire system, high NOx purification performance can be ensured over the entire operation region of the engine 1.

  The exhaust purification device 30 is provided in an upstream injector 34 provided in the exhaust passage 16 immediately upstream of the upstream NOx trap catalyst 31 and in the exhaust passage 16 downstream of the filter 32 and immediately upstream of the downstream NOx trap catalyst 33. And a downstream injector 35. These injectors 34 and 35 are injection valves that directly supply a reducing agent such as carbon monoxide (CO) or hydrocarbon (HC) to the exhaust passage 16, and both of the injectors 34 and 35 protrude into the exhaust passage 16. Provided. Further, fuel pipes connected to the fuel pump are connected to the base ends of the injectors 34 and 35, and fuel is used as a reducing agent here.

  The injectors 34 and 35 supply a reducing agent to the upstream NOx trap catalyst 31 and the downstream NOx trap catalyst 33 in the NOx purge control and the S purge control, respectively, and each periphery of the upstream NOx trap catalyst 31 and the downstream NOx trap catalyst 33. While the atmosphere is reduced (rich atmosphere), the upstream NOx trap catalyst 31 and the downstream NOx trap catalyst 33 are heated. The injection amount of the reducing agent from the injectors 34 and 35 and the injection timing thereof are controlled by the engine control device 40.

  Between the air filter 13 in the intake passage 12 and the compressor, an air flow sensor 21 for detecting the intake flow rate is provided. The intake air flow rate is a parameter corresponding to the flow rate of air that has passed through the air filter 13. An air-fuel ratio sensor 22 for detecting the air-fuel ratio of the intake air is provided between the EGR valve 19 in the intake passage 12 and the surge tank 10. The air-fuel ratio sensor 22 is a so-called linear air-fuel ratio sensor that detects the oxygen concentration of intake air flowing through the intake passage 12 and outputs a value proportional to the oxygen concentration. An intake manifold pressure sensor 23 and an intake air temperature sensor 24 are provided in the surge tank 10. The intake manifold pressure sensor 23 detects the pressure in the surge tank 10 as intake manifold pressure, and the intake air temperature sensor 24 detects the intake air temperature in the surge tank 10.

  An air-fuel ratio sensor 25 that detects the air-fuel ratio of the exhaust gas and an exhaust temperature sensor 26 that detects the exhaust gas temperature are provided downstream of the upstream injector 34 in the exhaust passage 16 and upstream of the upstream NOx trap catalyst 31. Further, an air-fuel ratio sensor 27 for detecting the air-fuel ratio of exhaust gas and an exhaust temperature sensor 28 for detecting the exhaust temperature are provided downstream of the downstream injector 35 in the exhaust passage 16 and upstream of the downstream NOx trap catalyst 33. In addition to these, for example, an engine rotation speed sensor that detects the rotation speed of the engine 1, a cooling water temperature sensor that detects the temperature of the cooling water of the engine 1, the in-cylinder injection valve 4, and the injectors 34 and 35 are injected. A fuel pressure sensor or the like for detecting the pressure of the fuel may be provided. Various information detected by the various sensors 21 to 28 is transmitted to the engine control device 40.

  A vehicle equipped with the engine 1 is provided with an engine control device (control means) 40. The engine control device 40 is configured as, for example, an LSI device or an embedded electronic device in which a microprocessor, ROM, RAM, and the like are integrated, and is connected to a communication line of an in-vehicle network provided in the vehicle. Note that other electronic control devices such as a brake control device and an air conditioning control device are communicably connected to each other on the in-vehicle network.

  The engine control device 40 is an electronic control device that comprehensively controls a wide range of systems such as an ignition system, a fuel system, an intake / exhaust system, and a valve system related to the engine 1, and is supplied to each cylinder 2 of the engine 1. It controls the air amount, fuel injection amount, ignition timing of each cylinder 2, supercharging pressure, and the like. The aforementioned various sensors 21 to 28 are connected to the input port of the engine control device 40. Specific control objects of the engine control device 40 include the fuel injection amount injected from the in-cylinder injection valve 4 and its injection timing, the operating state of the turbocharger 17, the throttle opening, the opening of the EGR valve 19, and the upstream injector. 34 and the reducing agent injection amount injected from the downstream injector 35 and the injection timing thereof. In the present embodiment, the two controls of the S purge control of the NOx trap catalysts 31 and 33 and the regeneration control of the filter 32 will be described in detail.

[1-2. Control configuration]
As shown in FIG. 1, the engine control device 40 includes an estimation unit 41, an upstream S purge control unit 42, a downstream S purge control unit 43, and a regeneration control unit 44 as elements for performing the above two controls. Provided. Each of these elements may be realized by an electronic circuit (hardware), may be programmed as software, or some of these functions are provided as hardware, and the other part is software. It may be a thing.

  The estimation unit 41 stores the amount of the sulfur component stored in the upstream NOx trap catalyst 31 (referred to as storage S amount A), the amount of the sulfur component stored in the downstream NOx trap catalyst 33 (referred to as storage S amount B), and the filter 32. The amount of accumulated PM (referred to as PM accumulation amount D) is estimated. Various known techniques can be applied to these estimation methods. An example of a method for estimating the storage amounts A and B will be described. The engine control device 40 includes a ratio R1 (amount of stored S A / total amount) of the amount of sulfur component that can be stored in the upstream NOx trap catalyst 31 with respect to the total amount of sulfur component discharged from the engine 1, and downstream. The ratio R2 of the amount of sulfur component that can be stored in the NOx trap catalyst 33 (storage amount S / total amount) is stored in advance. Since the upstream NOx trap catalyst 31 located upstream of the exhaust stores more sulfur components than the downstream NOx trap catalyst 33, R1> R2 is set. Further, the total amount of the sulfur component discharged from the engine 1 depends on the amount of fuel used in the engine 1 and the type of fuel.

  The estimation unit 41 accumulates the amount of fuel that has been used since the end of the previous S purge control, and estimates the total amount of sulfur component by multiplying the accumulated amount of used fuel by a coefficient corresponding to the type of fuel. The estimated total amount is multiplied by the ratio R1 to estimate the storage S amount A of the upstream NOx trap catalyst 31, and the total amount is multiplied by the ratio R2 to estimate the storage S amount B of the downstream NOx trap catalyst 33. . Further, when the S purge control described later is being performed, the estimation unit 41 calculates the amount of the sulfur component released during the S purge control from the value obtained by multiplying the total amount of the sulfur component by the ratios R1 and R2. Are respectively subtracted to estimate the storage amounts A and B. The amount of sulfur component released during the S purge control can be estimated by a known method based on, for example, the stored S amounts A and B, the air-fuel ratio, temperature, and flow rate of the exhaust gas.

  Further, as an example of a method for estimating the PM accumulation amount D, the estimation unit 41 estimates the amount of PM discharged from the engine 1 based on the rotation speed of the engine 1, the engine load, and the like, and uses this to control the previous regeneration control. PM accumulation amount D is estimated by integrating from the end of the process. Alternatively, a method for detecting or estimating the differential pressure upstream and downstream of the filter 32 and estimating the PM deposition amount D based on the differential pressure is also known, and the estimation unit 41 uses the above method to calculate the PM deposition amount D. It may be estimated. The estimation unit 41 transmits the estimated occlusion S amounts A and B and the PM accumulation amount D to the upstream S purge control unit 42, the downstream S purge control unit 43, and the regeneration control unit 44.

  The upstream S purge control unit 42 supplies the reducing agent and releases the sulfur component from the upstream NOx trap catalyst 31 based on the storage state of the sulfur component of the upstream NOx trap catalyst 31 (storage S amount A). 1 purge control, hereinafter referred to as upstream S purge control). Specifically, the upstream S purge control unit 42 determines that the upstream injector when the occlusion S amount A estimated by the estimation unit 41 is greater than or equal to a predetermined upstream S purge start threshold (first threshold) As (A ≧ As). By intermittently injecting a predetermined amount of reducing agent from 34, the ambient atmosphere of the upstream NOx trap catalyst 31 is enriched and the upstream NOx trap catalyst 31 is heated to a temperature equal to or higher than the S purgeable temperature Tp to release sulfur components. Let me reduce.

The upstream S purge start threshold value As is a threshold value for determining whether or not the sulfur component stored in the upstream NOx trap catalyst 31 needs to be removed (allowable limit for S poisoning), and storing NOx. It is set in advance based on the degree of decrease in the ability to perform the operation. Moreover, generation of hydrogen sulfide (H ₂ S) is suppressed by intermittently injecting the reducing agent. The upstream S purge control unit 42 starts the upstream injector when the occlusion S amount A estimated by the estimation unit 41 after starting the upstream S purge control becomes less than a predetermined upstream S purge end threshold Af (A <Af). The injection of the reducing agent from 34 is stopped and the upstream S purge control is terminated.

  If the regeneration control unit 44 described later determines that the regeneration control is necessary, the upstream S purge control unit 42 does not stop the regeneration control even if the occlusion S amount A is equal to or greater than the upstream S purge start threshold value As. The upstream S purge control is waited for, and the upstream S purge control is started after the regeneration control is completed. That is, in the regeneration control of the filter 32 and the upstream S purge control of the upstream NOx trap catalyst 31, the former priority is higher. This is because the S purgeable temperature Tp is higher than the temperature at which PM accumulated on the filter 32 is combusted during the regeneration control of the filter 32, and the upstream S purge control is performed before the regeneration control of the filter 32. This is to prevent PM from burning excessively and causing the filter 32 to generate abnormal heat. In addition, by starting the upstream S purge control after performing the regeneration control, the upstream NOx trap catalyst 31 can be quickly raised to the S purgeable temperature Tp or more, and the time for performing the upstream S purge control can be shortened. Is possible.

  Further, the upstream S purge control unit 42 throttles the intake air flow rate prior to the upstream S purge control when the occlusion S amount A estimated by the estimation unit 41 is equal to or greater than the upstream S purge start threshold value As (A ≧ As). The exhaust temperature increase control for increasing the exhaust temperature is started. This is because it is difficult to obtain a temperature rise effect due to combustion of the reducing agent in the upstream part of the upstream NOx trap catalyst 31, and it takes time until the sulfur component stored in the upstream part starts to be released. Increase the exhaust temperature. In the exhaust S temperature rise control, the upstream S purge control unit 42 controls the operating state of the throttle valve 11 and the turbocharger 17, for example, to reduce the intake flow rate and increase the heat amount per unit exhaust flow rate to increase the exhaust temperature. Raise. Note that the upstream S purge control unit 42 ends the exhaust gas temperature increase control upon completion of the upstream S purge control.

  The downstream S purge control unit 43 supplies a reducing agent based on the storage state (storage S amount B) of the sulfur component of the downstream NOx trap catalyst 33 when the upstream S purge control is performed by the upstream S purge control unit 42. Thus, S purge control for releasing the sulfur component from the downstream NOx trap catalyst 33 (second purge control, hereinafter referred to as downstream S purge control) is performed. That is, the downstream S purge control unit 43 starts the downstream S purge control after the upstream S purge control by the upstream S purge control unit 42 is started (that is, only when the upstream S purge control is performed). Thus, the upstream S purge control and the downstream S purge control are performed simultaneously and continuously. Note that simultaneous and continuous means that the upstream and downstream S purge control is performed at the same timing, but the upstream side is started in advance and the downstream side is started continuously.

  Specifically, the downstream S purge control unit 43 determines that the storage S amount B estimated by the estimation unit 41 after the upstream S purge control by the upstream S purge control unit 42 is a predetermined downstream S purge start threshold (first When two threshold values) Bs or more (B ≧ Bs), a predetermined amount of reducing agent is intermittently injected from the downstream injector 35 to enrich the ambient atmosphere of the downstream NOx trap catalyst 33 and to set the downstream NOx trap catalyst 33 to S Raise the temperature to the purgeable temperature Tp or higher. The downstream S purge start threshold value Bs is a threshold value for determining whether or not the sulfur component stored in the downstream NOx trap catalyst 33 needs to be removed, and is smaller than the upstream S purge start threshold value As described above. The value (Bs <As) is preset. This is to prevent the ability of the downstream NOx trap catalyst 33 to store NOx from greatly decreasing.

This will be described with reference to FIG. FIG. 3 is a graph schematically showing changes in the storage S amount A of the upstream NOx trap catalyst 31 and the storage S amount B of the downstream NOx trap catalyst 33. The upstream S purge control unit 42 performs the upstream S purge control from the time (time t _X , t _Z ) when the occlusion S amount A of the upstream NOx trap catalyst 31 becomes equal to or higher than the upstream S purge start threshold value As, and removes the sulfur component. Release. When the occlusion S amount A becomes less than the upstream S purge end threshold Af, the upstream S purge control is ended.

On the other hand, the downstream occlusion S of NOx trap catalyst 33 B is to continue to gradually increase the upstream NOx trap catalyst 31, the time of the upstream S purge control at the time t _X does not reach the downstream S purge start threshold Bs, downstream S purge control unit 43 does not implement the downstream S purge control in which time t _X. The occlusion S amount B of the downstream NOx trap catalyst 33 further increases and reaches the downstream S purge start threshold Bs at time t _Y. At this point, the upstream S purge control is not performed, so the downstream S purge control unit 43 Does not start downstream S purge control. In other words, the downstream S purge control unit 43 waits for the downstream S purge control until the next upstream S purge control is started. When the upstream S purge control is executed at time t _Z, since the storage amount of S B of the downstream NOx trap catalyst 33 is downstream S purge start threshold Bs above, the downstream S purge control section 43 downstream S purge control To start.

As described above, the downstream NOx trap catalyst 33 may have a period (time t _{Y to} t _{Z in} FIG. 3) in which the downstream S purge control is not performed until the upstream S purge control is performed. Therefore, by setting the downstream S purge start threshold value Bs to a value smaller than the upstream S purge start threshold value As, it is possible to prevent an excessive increase in the storage S amount B of the downstream NOx trap catalyst 33 and to reduce the NOx of the downstream NOx trap catalyst 33. The ability to occlude can be secured.

  The downstream S purge controller 43 starts the downstream injector when the occlusion S amount B estimated by the estimation unit 41 after starting the downstream S purge control is less than a predetermined downstream S purge end threshold Bf (B <Bf). The injection of the reducing agent from 35 is stopped and the downstream S purge control is terminated. The downstream S purge end threshold value Bf may be the same value as the upstream S purge end threshold value Af, or may be set to a different value.

  Further, when the upstream S purge control is terminated by the upstream S purge control unit 42 before the downstream S purge control is terminated, the downstream S purge control unit 43 does not contribute to torque in the in-cylinder injection valve 4 (for example, expansion) The fuel is injected in the second half of the stroke and the exhaust stroke). That is, the downstream S purge control unit 43 supplies the fuel to the exhaust passage 16 by causing the in-cylinder injection valve 4 to post-inject the fuel when the upstream S purge control is finished, and the temperature of the downstream NOx trap catalyst 33 is increased. Hold above S purgeable temperature Tp. The downstream S purge control unit 43 ends the post injection together with the end of the downstream S purge control.

  When the regeneration control unit 44 determines the necessity of regeneration control for removing PM from the filter 32 based on the amount of PM collected by the filter 32 (PM accumulation amount D), and determines that regeneration control is necessary The reproduction control is performed. Specifically, the regeneration control unit 44 determines that regeneration control is necessary when the PM accumulation amount D estimated by the estimation unit 41 is equal to or greater than a predetermined regeneration start threshold Ds (D ≧ Ds), and the PM accumulation is determined. When the amount D is less than the regeneration start threshold value Ds, it is determined that the regeneration control is unnecessary.

  If the regeneration control unit 44 determines that regeneration control is necessary, the filter 32 is regenerated by intermittently injecting a predetermined amount of reducing agent from the upstream injector 34 and combusting it on the upstream NOx trap catalyst 31. The PM is burned by raising the temperature above the possible temperature Tr. The regeneration start threshold value Ds is a threshold value for determining whether or not the PM accumulated on the filter 32 needs to be forcibly burned and removed, and depends on the degree of increase in pressure loss of the filter 32 and PM overdeposition. It is set in advance based on the risk of melting of the filter 32 and the like. In the regeneration control, fuel may be supplied to the exhaust passage 16 by post-injecting the in-cylinder injection valve 4 instead of injecting the reducing agent from the upstream injector 34.

  When the PM accumulation amount D estimated by the estimation unit 41 after starting the regeneration control becomes less than a predetermined regeneration end threshold value Df (D <Df), the regeneration control unit 44 supplies the reducing agent from the upstream injector 34. The injection or post injection by the in-cylinder injection valve 4 is stopped, and the regeneration control is finished. The regeneration end threshold value Df is a value set according to the storage state of the sulfur component of the upstream NOx trap catalyst 31 and the storage state of the sulfur component of the downstream NOx trap catalyst 33, and thus regeneration control is performed. The time (implementation time) is changed according to the storage amounts A and B of the NOx trap catalysts 31 and 33.

  Specifically, the regeneration control unit 44 is normal when the occlusion S amount A estimated by the estimation unit 41 is less than the upstream S purge start threshold value As (A <As), that is, when the upstream S purge control is not performed. This threshold value D1 is set as the reproduction end threshold value Df. The normal threshold value D1 is a value for causing almost no PM to remain in the filter 32, and is a value close to zero. The regeneration control unit 44 determines that the storage S amount A is equal to or greater than the upstream S purge start threshold value As (A ≧ As) and the storage S amount B is equal to or greater than the downstream S purge start threshold value Bs (B ≧ Bs), that is, Even when both the upstream S purge control and the downstream S purge control are performed, the normal threshold D1 is set as the regeneration end threshold Df.

  The regeneration control unit 44 determines that the storage S amount A is equal to or higher than the upstream S purge start threshold value As (A ≧ As) and the storage S amount B is less than the downstream S purge start threshold value Bs (B <Bs), that is, When the upstream S purge control is performed but the downstream S purge control is not performed, a value D2 slightly larger than the normal threshold D1 is set as the regeneration end threshold Df. As a result, only in this case, the regeneration control is terminated with a small amount of PM remaining in the filter 32. This is because PM remaining in the filter 32 is burned and removed from the filter 32 by the upstream S purge control performed after the regeneration control of the filter 32.

  That is, only in this case, the regeneration control is terminated before removing all PM from the filter 32, thereby suppressing the amount of fuel used for the regeneration control and improving the fuel consumption. Removal by the upstream S purge control that is performed completes regeneration of the filter 32. When the downstream S purge control is also performed, if PM remains in the filter 32, the filter 32 may become excessively hot. Therefore, when the downstream S purge control is also performed, a normal threshold value is used. The filter 32 is protected by setting D1 as the regeneration end threshold value Df.

[1-3. flowchart]
4 and 5 are flowcharts for explaining the procedure of the above-described S purge control and regeneration control. These flows are repeatedly performed in the engine control device 40 at a predetermined calculation cycle. Apart from these flows, the estimation unit 41 always estimates the storage S amounts A and B and the PM deposition amount D, and the upstream S purge control unit 42, the downstream S purge control unit 43 and the regeneration are performed. The control unit 44 reads each estimated value and performs upstream S purge control, downstream S purge control, and regeneration control.

As shown in FIG. 4, first, the reproduction control section 44, PM accumulation amount D estimated by the estimation unit 41 is read (step S10), and the flag F _D is determined whether F _D = 0 (Step S20). The flag F _D is used to determine whether or not the regeneration control is necessary. F _D = 1 corresponds to necessity, and F _D = 0 corresponds to no necessity. When the flag F _D = 0, it is determined whether or not the PM accumulation amount D is equal to or greater than the regeneration start threshold Ds (D ≧ Ds) (step S30). If D ≧ Ds, the flag F _D is F _D = It is set to 1 (step S40), and it is determined whether or not it is an operation state in which regeneration control can be performed (step S50).

In addition, when the flag F _D = 1 in step S20, regeneration control is necessary, and in this case, the process also proceeds to step S50. That is, when there is a need for regeneration control, regeneration control is performed with priority over S purge control. If it is determined in step S50 that the regeneration control can be performed based on, for example, the exhaust temperature, the accelerator opening, the engine speed, etc., the regeneration control of the filter 32 is performed (step S60). When the operation state is not regeneratively controlled, this flow is returned, and the processes of steps S10, S20, and S50 are repeated until the operation state is reproducible in the next and subsequent calculation cycles.

  The subsequent steps S70 to S105 are processes for changing the execution time of the regeneration control in accordance with the occlusion S amounts A and B. In step S70, the storage S amounts A and B estimated by the estimation unit 41 are read, and it is determined whether or not the storage S amount A is equal to or higher than the upstream S purge start threshold value As (A ≧ As) (step S80). . If A ≧ As, it is determined whether the occlusion S amount B is equal to or greater than the downstream S purge start threshold Bs (B ≧ Bs). (Step S90). When A ≧ As and B ≧ Bs, and when A <As, the regeneration end threshold value Df is set to the normal threshold value D1 (step S100). When A ≧ As and B <Bs, the regeneration end threshold value is set. Df is set to a value D2 larger than the normal threshold value D1 (step S105).

In step S110, it is determined whether the PM accumulation amount D is less than the regeneration end threshold Df set in step S100 or S105 (D <Df), and regeneration control is continued until D <Df. . Note that, during the regeneration control, the NOx trap catalysts 31 and 33 can occlude sulfur components, so the regeneration end threshold Df may change during the regeneration control. If the D <Df in step S110, the reproduction control is terminated (step S120), the flag F _D is reset to F _D = 0 (step S130), it returns the flow.

When the flag F _D = 0 in step S20 and the PM accumulation amount D is less than the regeneration start threshold value Ds (D <Ds) in step S30, the process proceeds to step S140, and the flow of S purge control (FIG. 5) is performed. To be implemented. As shown in FIG. 5, the upstream S purge control section 42, storage S amount A of the upstream NOx trap catalyst 31 estimated by the estimator 41 is read (step W10), the flag F _A is a F _A = 0 Is determined (step W15). Flag F _A is for the starting condition of the upstream S purge control is determined whether or not satisfied, F _A = 1 corresponds to the starting condition is satisfied (Yes request upstream S purge control), F _A = 0 corresponds to failure of start condition (no request for upstream S purge control).

When the flag F _A = 0, whether occluded S amount A is upstream S purge start threshold As above (A ≧ As) is determined (step W20), if A ≧ As flag F _A is F _A = 1 is set (step W25), and exhaust gas temperature rise control is performed (step W30). In the subsequent step W35, it is determined whether or not the operation state is such that the upstream S purge control can be performed, for example, from the exhaust temperature, the accelerator opening, the engine speed, and the like. Thus, the injection of the reducing agent is started, and the upstream S purge control is performed (step W40). On the other hand, when the upstream S purge control is not possible, this flow is returned, and the processes of steps W10, W15, W30, and W35 are repeated until the upstream S purge control is possible in the next and subsequent calculation cycles. .

After the upstream S purge control is started, it is determined whether or not the occlusion S amount A is less than the upstream S purge end threshold Af (A <Af) (step W45). Since the storage S amount A does not immediately become less than the upstream S purge end threshold Af, the downstream S purge control unit 43 reads the storage S amount B of the downstream NOx trap catalyst 33 estimated by the estimation unit 41 this time. (Step W75), it is determined whether or not the flag F _B is F _B = 0 (Step W80). The flag F _B is used to determine whether or not the downstream S purge control start condition is satisfied. F _B = 1 corresponds to the start condition satisfied (the downstream S purge control is requested), and F _B = 0 corresponds to failure of starting condition (no request for downstream S purge control).

When the flag F _B = 0, it is determined whether or not the storage S amount B is equal to or greater than the downstream S purge start threshold Bs (B ≧ Bs) (step W85). If B <Bs, the downstream S purge control is performed. Since this is unnecessary, this flow is returned. After the next cycle, if B ≧ Bs is not satisfied while upstream S purge control is being performed (before the condition of step W45 is satisfied), downstream S purge control is not performed. On the other hand, when B ≧ Bs is satisfied while the upstream S purge control is being performed (before the condition of step W45 is satisfied), the flag F _B is set to F _B = 1 (step W90).

  Subsequently, for example, it is determined whether or not the operation state is such that the downstream S purge control can be performed based on the exhaust temperature, the accelerator opening, the engine speed, and the like (step W95), and if the downstream S purge control can be performed, the downstream injector The injection of the reducing agent by 35 is started, and the downstream S purge control is performed (step W100). On the other hand, when the operation state in which the downstream S purge control is not possible, this flow is returned, and when the operation state in which the downstream S purge control is possible, the downstream S purge control is performed. After the downstream S purge control is started, it is determined whether or not the occlusion S amount B is less than the downstream S purge end threshold Bf (B <Bf) (step W105).

When B <Bf is satisfied while the upstream S purge control is being performed (that is, when step W105 is established before step W45), the injection of the downstream injector 35 is stopped and the downstream S purge control is terminated. (Step W110). Then, the flag F _B is reset to F _B = 0 (step W115), and this flow is returned. Thereafter, exhaust temperature rise control and upstream S purge control are performed until A <Af is established in step W45, and when A <Af, injection of the upstream injector 34 is stopped (step W50). Then, the flag F _A is reset to F _A = 0 (step W55), and the exhaust gas temperature increase control is ended (step W60). If the downstream S purge control is not performed at this time, the flag F _B is set to F _B = 0, and this flow is returned.

On the other hand, when A <Af is satisfied while the downstream S purge control is being performed (that is, when step W45 is established before step W105), the injection of the upstream injector 34 is stopped and the upstream S purge control is performed. The process is terminated (step W50). Then, the flag F _A is reset to F _A = 0 (step W55), and the exhaust gas temperature increase control is ended (step W60). In this case, since the flag F _B is set to F _B = 1, the process proceeds from step W65 to step W70, post injection is started, and this flow is returned.

In the next cycle, the process proceeds from step W20 to step W120, it is determined whether or not the flag F _B is F _B = 1, the stored S amount B is read (step W125), and whether or not B <Bf is satisfied. Is determined (step W130). This process is repeated until B <Bf, and when B <Bf, the injection of the downstream injector 35 is stopped and the downstream S purge control is terminated (step W135). Then, the post injection is also stopped (step W140), the flag F _B is reset to F _B = 0 (step W145), and this flow is returned.

[1-4. Action]
FIGS. 6A to 6C show temperature changes and control details of the upstream NOx trap catalyst 31 and the downstream NOx trap catalyst 33 during the S purge control. As shown in FIG. 6A, when the storage amount A of the upstream NOx trap catalyst 31 becomes equal to or greater than the upstream S purge start threshold value As (A ≧ As) at time t ₀ , first, the exhaust temperature is controlled by the upstream S purge control unit 42. Ascending control is started, and as a result, the temperatures of the NOx trap catalysts 31, 33 gradually increase. If the feasible operating conditions of upstream S purge control at time t _1, the upstream S purge control is started. The reducing agent injected from the upstream injector 34 enriches the atmosphere around the upstream NOx trap catalyst 31 and burns on the upstream NOx trap catalyst 31 to further increase the temperature of the upstream NOx trap catalyst 31.

From the vicinity of the time t ₂ the temperature of the upstream NOx trap catalyst 31 becomes equal to or higher than S purgeable temperature Tp, the sulfur component was occluded upstream NOx trap catalyst 31 starts to be released. If the stored S amount B of the downstream NOx trap catalyst 33 does not exceed the downstream S purge start threshold Bs (B ≧ Bs) during the upstream S purge control, the downstream S purge control is performed as shown in FIG. Is not implemented. In this case, the temperature of the downstream NOx trap catalyst 33 rises due to the upstream S purge control, but does not exceed the S purge possible temperature Tp. When the storage amount A becomes less than the upstream S purge end threshold Af (A <Af) at time t ₃ , the exhaust temperature rise control is terminated, and the reducing agent injection by the upstream injector 34 is also stopped and the upstream S purge is performed. Control is terminated. As a result, the temperature of the upstream NOx trap catalyst 31 gradually decreases.

Also, during the upstream S purge control, when the stored S amount B of the downstream NOx trap catalyst 33 is equal to or greater than the downstream S purge start threshold Bs (B ≧ Bs), it is shown in FIGS. 6B and 6C. as shown, from the time t ₄ when became feasible operating state of the downstream S purge control, the downstream S purge control is started. The reducing agent injected from the downstream injector 35 enriches the atmosphere around the downstream NOx trap catalyst 33 and burns on the downstream NOx trap catalyst 33 to increase the temperature of the downstream NOx trap catalyst 33.

Even when the downstream S purge control is performed, first, the temperature of the upstream NOx trap catalyst 31 becomes equal to or higher than the S purgeable temperature Tp (time t ₅ ), and the sulfur component stored in the upstream NOx trap catalyst 31 from this point It begins to be released. Note that the temperature of the upstream NOx trap catalyst 31 is higher than when the downstream S purge control is not performed. Subsequently, at time t ₆ , the temperature of the downstream NOx trap catalyst 33 becomes equal to or higher than the S purgeable temperature Tp, and the sulfur component starts to be released from the downstream NOx trap catalyst 33 as well.

When the storage amount B of the downstream NOx trap catalyst 33 falls below the downstream S purge end threshold Bf during the upstream S purge control, as shown in FIG. 6B, the downstream S purge is performed before the upstream S purge control. Control is terminated (time t ₇ ). Thereby, since the reducing agent injection by the downstream injector 35 is stopped, the temperature of the downstream NOx trap catalyst 33 is lowered. After time t ₇ , in order to suppress thermal deterioration of the upstream NOx trap catalyst 31, the injection amount and injection timing of the upstream injector 34 are adjusted, and the temperature of the upstream NOx trap catalyst 31 is lowered to near the S purgeable temperature Tp. Let Thereafter, when the occlusion S amount A of the upstream NOx trap catalyst 31 falls below the upstream S purge end threshold Af, the exhaust temperature increase control and the upstream S purge control are ended (time t ₈ ).

On the other hand, if the stored S amount A of the upstream NOx trap catalyst 31 falls below the upstream S purge end threshold Af before the downstream S purge control ends, the downstream S purge control is in progress as shown in FIG. Then, the exhaust gas temperature increase control and the upstream S purge control are finished (time t ₉ ), whereby the temperature of the upstream NOx trap catalyst 31 gradually decreases. On the other hand, since the temperature of the downstream NOx trap catalyst 33 needs to be maintained at a temperature equal to or higher than the S purgeable temperature Tp, the post by the in-cylinder injection valve 4 from the time when the upstream S purge control is finished (time t ₉ ). Injection is performed. When the storage S amount B of the downstream NOx trap catalyst 33 falls below the downstream S purge end threshold Bf, the downstream S purge control and the post injection are ended (time t ₁₀ ).

[1-5. effect]
Therefore, according to the exhaust purification device 30 described above, the S purge control (downstream S purge control, second purge control) of the downstream NOx trap catalyst 33 is performed on the upstream NOx trap catalyst 31 (upstream S purge control, second purge control). Based on the storage status of the sulfur component (predetermined component) of the downstream NOx trap catalyst 33 when one purge control) is performed, this is performed together with the upstream S purge control. That is, since the downstream S purge control is not performed alone, but is performed simultaneously with the upstream S purge control, the sulfur component can be appropriately released while suppressing deterioration in fuel consumption.

  In the exhaust purification device 30 described above, since the downstream S purge start threshold (second threshold) Bs is set to a smaller value than the upstream NOx trap catalyst S purge start threshold (first threshold) As, the downstream NOx trap. It is possible to prevent the storage S amount B of the catalyst 33 from excessively increasing, and to prevent the NOx storage capacity of the downstream NOx trap catalyst 33 from being lowered.

  Further, in the above exhaust purification device 30, the upstream NOx trap catalyst 31, the filter 32, and the downstream NOx trap catalyst 33 are provided in the exhaust passage 16 in order from the upstream side in the exhaust flow direction. In other words, the upstream NOx trap catalyst 31 and the downstream NOx trap catalyst 33 are disposed apart from each other in the exhaust passage 16, and the filter 32 having a large heat capacity is disposed therebetween, so that the upstream NOx trap catalyst 31 and the downstream NOx trap catalyst are disposed. The catalyst 33 and the catalyst 33 can be arranged at different temperatures. Thereby, the operation state in which the upstream NOx trap catalyst 31 exhibits high NOx purification performance and the operation state in which the downstream NOx trap catalyst 33 exhibits high NOx purification performance can be differentiated, and the NOx purification performance of the entire system can be reduced. Can be increased. That is, high NOx purification performance can be ensured over the entire operation region of the engine 1.

  Further, in the exhaust purification device 30 described above, regeneration control for forcibly burning PM accumulated on the filter 32 located between the two NOx trap catalysts 31 and 33 is performed prior to the upstream S purge control. . In other words, the regeneration control has a higher priority than the upstream S purge control, and the upstream S purge control is performed after the regeneration control ends. Thereby, abnormal heat generation of the filter 32 is prevented, and the filter 32 can be protected. In addition, since the upstream S purge control is performed after the regeneration control of the filter 32, the temperature of the upstream NOx trap catalyst 31 can be increased at an early stage, so the time for performing the upstream S purge control can be shortened. Since the amount of fuel consumed by the S purge control can be reduced, fuel consumption deterioration can be suppressed.

  In addition, in the regeneration control of the filter 32, it depends on the amount of sulfur component stored in the upstream NOx trap catalyst 31 (storage S amount A) and the amount of sulfur component stored in the downstream NOx trap catalyst 33 (storage S amount B). Thus, the execution time of the regeneration control is changed. That is, during the S purge control that can be performed after the regeneration control, the amount of fuel consumed in the regeneration control can be reduced by changing the time for performing the regeneration control in anticipation that the PM accumulated in the filter 32 burns. Deterioration can be suppressed.

  In particular, in the present embodiment, when only the upstream S purge control is performed after the regeneration control, the regeneration end threshold value Df is set to a value D2 that is larger than the normal threshold value D1, and therefore the regeneration control execution time is shortened. , Fuel consumption can be reduced. In addition, when the upstream S purge control and the downstream S purge control are performed after the regeneration control, the regeneration end threshold value Df is set to the normal threshold value D1, so that excessive thermal deterioration of the filter 32 can be prevented. The filter 32 can be protected.

  Further, in the exhaust purification device 30 described above, exhaust temperature increase control for increasing the exhaust temperature serving as a base is performed before the upstream S purge control is started, so that a temperature increase effect by combustion of the reducing agent is obtained. It is possible to increase the temperature of the upstream portion of the upstream NOx trap catalyst 31 that is difficult. The upstream portion of the upstream NOx trap catalyst 31 is a portion where the sulfur component is first stored and can store a large amount of sulfur component. Therefore, the sulfur component from the upstream NOx trap catalyst 31 is improved by increasing the temperature rise performance of the upstream portion. Release and reduction can be promoted.

  In the above embodiment, the upstream injector 34 is provided immediately upstream of the upstream NOx trap catalyst 31, and the reducing agent is injected from the upstream injector 34 in the upstream S purge control. Can be warmed. Further, since the distance from the upstream injector 34 to the upstream NOx trap catalyst 31 is short, the reactivity between the sulfur component occluded in the upstream NOx trap catalyst 31 and the reducing agent can be increased, and thereby the upstream NOx trap catalyst 31 occludes. The sulfur component thus removed can be efficiently removed.

  In the above embodiment, the downstream injector 35 is provided immediately upstream of the downstream NOx trap catalyst 33. In the downstream S purge control, the reducing agent is injected from the downstream injector 35, so that the reducing agent can be used effectively. The downstream NOx trap catalyst 33 can be effectively heated. Further, since the reducing agent is injected on the downstream side of the upstream NOx trap catalyst 31, excessive thermal deterioration of the upstream NOx trap catalyst 31 can be suppressed.

  In the above embodiment, since the downstream S purge control is started after the upstream S purge control is started, the downstream S purge control is started when the temperature of the downstream NOx trap catalyst 33 is increased by the upstream S purge control. Become. Thereby, since the temperature of the downstream NOx trap catalyst 33 can be raised early, the implementation time of the downstream S purge control can be shortened. Therefore, the amount of fuel consumed by the downstream S purge control can be reduced, and fuel consumption deterioration can be suppressed.

  In the above embodiment, in the downstream S purge control, when the upstream S purge control is finished first, the post injection by the in-cylinder injection valve 4 is performed and the fuel is supplied to the exhaust passage 16, so the upstream S purge control is finished. The temperature of the downstream downstream NOx trap catalyst 33 can be maintained at the S purgeable temperature Tp or higher, and excessive thermal deterioration of the upstream NOx trap catalyst 31 can be suppressed.

[2. Second embodiment]
Next, an exhaust purification device 30 'according to the second embodiment will be described with reference to FIG. This exhaust purification device 30 ′ is configured in the same manner as in the first embodiment except that the filter 32 is not provided between the upstream NOx trap catalyst 31 and the downstream NOx trap catalyst 33. Note that the regeneration control unit 44 for controlling the regeneration of the filter 32 is also not provided in the engine control device 40 of the present embodiment. Hereinafter, about the apparatus and structure similar to 1st embodiment, the code | symbol similar to 1st embodiment is attached | subjected, and the overlapping description is simplified.

  As shown in FIG. 7, the exhaust purification device 30 ′ according to the present embodiment has an upstream NOx trap catalyst (first catalyst) 31 and a downstream NOx in order from the upstream side in the exhaust flow direction to the downstream side of the turbine in the exhaust passage 16. A trap catalyst (second catalyst) 33 is provided. The storage S amount A stored in the upstream NOx trap catalyst 31 and the storage S amount B stored in the downstream NOx trap catalyst 33 are estimated by the estimation unit 41 of the engine control device (control means) 40 as in the above embodiment.

  When the upstream S purge control unit 42 performs the upstream S purge control (first purge control) on the basis of the storage S amount A (storage state) of the upstream NOx trap catalyst 31, and when the upstream S purge control is performed. The downstream S purge control unit 43 performs downstream S purge control (second purge control) based on the storage S amount B (storage state) of the downstream NOx trap catalyst 33. That is, in the exhaust purification device 30 ′ as well, the downstream S purge control is started after the upstream S purge control is started (that is, only when the upstream S purge control is performed) as in the exhaust purification device 30 described above. Thus, the upstream S purge control and the downstream S purge control are performed simultaneously and continuously.

  Specifically, the upstream S purge control unit 42, when the storage S amount A estimated by the estimation unit 41 is equal to or greater than the upstream S purge start threshold (first threshold) As (A ≧ As), as in the above embodiment. In addition, by intermittently injecting a predetermined amount of reducing agent from the upstream injector 34, the ambient atmosphere of the upstream NOx trap catalyst 31 is enriched and the upstream NOx trap catalyst 31 is heated to a temperature equal to or higher than the S purgeable temperature Tp, Release sulfur component to reduce.

Similarly to the above embodiment, the downstream S purge control unit 43 determines that the stored S amount B estimated by the estimation unit 41 after the upstream S purge control by the upstream S purge control unit 42 is the downstream S purge start threshold value. (Second threshold) When Bs is equal to or greater than Bs (B ≧ Bs), a predetermined amount of reducing agent is intermittently injected from the downstream injector 35 to enrich the ambient atmosphere of the downstream NOx trap catalyst 33 and the downstream NOx trap catalyst 33. Is raised to an S purgeable temperature Tp or higher. Here, the downstream S purge start threshold value Bs is preset to a value (Bs <As) smaller than the upstream S purge start threshold value As.
Similar to the above embodiment, the upstream S purge control unit 42 prior to the upstream S purge control when the occlusion S amount A estimated by the estimation unit 41 is equal to or greater than the upstream S purge start threshold value As (A ≧ As). Then, exhaust temperature increase control for increasing the exhaust temperature by reducing the intake flow rate is started.

  Even with such an exhaust purification device 30 ′, the S purge control (downstream S purge control, second purge control) of the downstream NOx trap catalyst 33 is performed on the upstream NOx trap catalyst 31 (upstream S purge control, first purge). Based on the storage status of the sulfur component (predetermined component) of the downstream NOx trap catalyst 33 when the purge control is performed, the purge control is performed together with the upstream S purge control. That is, since the downstream S purge control is not performed alone, but is performed simultaneously with the upstream S purge control, the sulfur component can be appropriately released while suppressing deterioration in fuel consumption.

Also in the exhaust purification device 30 ′ according to the present embodiment, the downstream S purge start threshold (second threshold) Bs is set to a smaller value than the upstream NOx trap catalyst S purge start threshold (first threshold) As. Therefore, it is possible to prevent the storage S amount B of the downstream NOx trap catalyst 33 from excessively increasing, and it is possible to prevent the NOx storage capability of the downstream NOx trap catalyst 33 from being lowered.
Also in the present exhaust purification device 30 ′, the exhaust temperature increase control for increasing the exhaust temperature as the base is performed before the upstream S purge control is started, so that the temperature increase effect due to the combustion of the reducing agent is obtained. It is possible to increase the temperature of the upstream portion of the upstream NOx trap catalyst 31 that is difficult. Thereby, the release and reduction of the sulfur component from the upstream NOx trap catalyst 31 can be promoted.

[3. Modified example]
Regardless of the embodiment described above, various modifications can be made without departing from the spirit of the invention. Each structure of this embodiment can be selected as needed, or may be combined appropriately.
For example, the supply of the reducing agent in the upstream S purge control and the downstream S purge control may be performed by post injection by the in-cylinder injection valve 4. In this case, since the upstream injector 34 and the downstream injector 35 can be omitted, the configuration of the apparatus can be simplified and the cost can be reduced.

  Further, in the first and second embodiments, the exhaust gas temperature increase control is finished together with the end of the upstream S purge control, but when the downstream S purge control is executed after the end of the upstream S purge control, The exhaust gas temperature increase control may be continued, and the exhaust gas temperature increase control may be terminated simultaneously with the end of the downstream S purge control. Alternatively, the exhaust temperature increase control itself can be omitted. For example, if the fact that the exhaust gas temperature is high is added to the condition for starting the upstream S purge control, injection of the reducing agent is started in a state where the temperature of the upstream portion of the upstream NOx trap catalyst 31 is high. Can also release and reduce sulfur components.

Further, when the upstream S purge control is finished before the downstream S purge control, instead of maintaining the temperature of the downstream NOx trap catalyst 33 by post injection, the downstream NOx is injected by injecting the reducing agent from the upstream injector 34. The temperature of the trap catalyst 33 may be maintained at the S purgeable temperature Tp or higher. Further, the downstream S purge start threshold value Bs may be set to the same value as the upstream S purge start threshold value As.
Further, in the first embodiment, the execution time of the regeneration control of the filter 32 is changed according to the storage state of the sulfur component of the NOx trap catalysts 31, 33, but the regeneration control is performed regardless of the storage state of the sulfur component. The implementation time may be constant. Thereby, the control configuration can be simplified.

  Further, in determining whether to start the upstream / downstream S purge control, the NOx trap is used by using the time elapsed from the end of the previous S purge control instead of estimating the storage amounts A and B by the estimation unit 41. You may judge the occlusion condition of the sulfur component occluded in the catalysts 31 and 33. FIG. The upstream / downstream S purge control end condition may not be determined based on the occluded S amounts A and B, but may be determined based on the execution time of the S purge control, for example. Similarly, the start condition and end condition of the regeneration control are not limited to those described above, and may be determined based on, for example, a differential pressure upstream or downstream of the filter 32, time, or the like.

In the first embodiment, the engine control device 40 includes four functional elements, that is, the estimation unit 41, the upstream S purge control unit 42, the downstream S purge control unit 43, and the regeneration control unit 44. In the second embodiment, the estimation unit 41, the upstream S purge control unit 42, and the downstream S purge control unit 43 are illustrated as having three functional elements. For example, the configuration may include one S purge control unit that performs upstream and downstream S purge control.
The upstream NOx trap catalyst 31 and the downstream NOx trap catalyst 33 do not have to have the same constituent components (types and amounts of the occlusion body and the noble metal element). The engine 1 is not limited to the diesel engine having the above configuration, and may be a diesel engine having another configuration or a gasoline engine.

  In the first and second embodiments, the sulfur component is cited as the predetermined component contained in the exhaust gas, and the S purge control of the NOx trap catalysts 31 and 33 for storing this is described in detail. However, the predetermined component in the exhaust gas is For example, NOx may be used. That is, for the NOx trap catalysts 31, 33 that store NOx in the exhaust under an oxidizing atmosphere and release under a reducing atmosphere, the engine control device 40 reduces the NOx amount stored in the upstream NOx trap catalyst 31 based on the storage state of the NOx. An upstream side NOx purge control (first purge control) for supplying the agent and releasing NOx from the upstream NOx trap catalyst 31 is performed. The reducing agent is supplied based on the storage state of the NOx amount stored in the downstream NOx trap catalyst 33 when the upstream NOx purge control is performed, and the downstream NOx is released from the downstream NOx trap catalyst 33. Purge control (second purge control) is performed. Even in such a configuration, the NOx purge control of the downstream NOx trap catalyst 33 is performed together with the NOx purge control of the upstream NOx trap catalyst 31, and fuel consumption deterioration can be suppressed.

1 engine (internal combustion engine)
4 In-cylinder injection valve 16 Exhaust passage 30, 30 'Exhaust gas purification device 31 Upstream NOx trap catalyst (first catalyst)
32 Filter 33 Downstream NOx trap catalyst (second catalyst)
34 Upstream injector 35 Downstream injector 40 Engine control device (control means)
41 Estimator 42 Upstream S Purge Control Unit 43 Downstream S Purge Control Unit 44 Regeneration Control Unit
As Upper S purge start threshold (first threshold)
Bs Downstream S purge start threshold (second threshold)

Claims (5)

A first catalyst provided in an exhaust passage of the internal combustion engine, storing a predetermined component in the exhaust under an oxidizing atmosphere and releasing it under a reducing atmosphere;
A second catalyst provided in the exhaust passage on the downstream side in the exhaust flow direction of the first catalyst, storing the predetermined component in the exhaust under an oxidizing atmosphere and releasing it under a reducing atmosphere;
A filter that is provided in the exhaust passage between the first catalyst and the second catalyst and collects particulate matter in the exhaust;
When performing the first purge control by supplying a reducing agent and releasing the predetermined component from the first catalyst based on the storage state of the predetermined component stored in the first catalyst, and performing the first purge control The second purge control for supplying the reducing agent and releasing the predetermined component from the second catalyst based on the occlusion status of the predetermined component occluded in the second catalyst simultaneously with the first purge control. Control means to implement ,
The predetermined component is a sulfur component contained in exhaust gas,
The control means ends the regeneration control when performing both regeneration control for removing particulate matter from the filter and the first purge control based on the amount of particulate matter collected by the filter. The exhaust gas purifying apparatus for an internal combustion engine , wherein the first purge control is performed after the operation . The control means changes the execution time of the regeneration control according to the storage amount of the sulfur component stored in the first catalyst and the storage amount of the sulfur component stored in the second catalyst. The exhaust emission control device for an internal combustion engine according to claim 1 . Before SL control unit, the case of implementing the first purge control to start the exhaust temperature rise control to raise the exhaust gas temperature by reducing the intake air flow rate before the start of the first purge control, at least the first purge The exhaust emission control device for an internal combustion engine according to claim 1 or 2 , wherein the exhaust gas temperature rise control is performed during the control. A first catalyst provided in an exhaust passage of the internal combustion engine, storing a predetermined component in the exhaust under an oxidizing atmosphere and releasing it under a reducing atmosphere;
A second catalyst provided in the exhaust passage on the downstream side in the exhaust flow direction of the first catalyst, storing the predetermined component in the exhaust under an oxidizing atmosphere and releasing it under a reducing atmosphere;
When performing the first purge control by supplying a reducing agent and releasing the predetermined component from the first catalyst based on the storage state of the predetermined component stored in the first catalyst, and performing the first purge control The second purge control for supplying the reducing agent and releasing the predetermined component from the second catalyst based on the occlusion status of the predetermined component occluded in the second catalyst simultaneously with the first purge control. Control means to implement ,
The predetermined component is a sulfur component contained in exhaust gas,
When the first purge control is performed, the control means starts exhaust temperature increase control for increasing the exhaust temperature by decreasing the intake flow rate before starting the first purge control, and at least the first purge control The exhaust gas purification device for an internal combustion engine, wherein the exhaust gas temperature rise control is performed during the operation of the engine. The control means includes
The first purge control is performed when the storage amount of the predetermined component stored in the first catalyst is greater than or equal to a predetermined first threshold, and the second catalyst stored in the second catalyst when performing the first purge control 5. The internal combustion engine according to claim 1, wherein the second purge control is performed when an occlusion amount of a predetermined component is equal to or greater than a second threshold value that is smaller than the first threshold value. Exhaust purification device.

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