JP2010265754A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of regenerating a filter at low temperature in a short period of time as compared to former devices in exhaust emission control device including a filter capturing particulate matter in exhaust gas. <P>SOLUTION: This device includes an accumulation state determination part 42 determining based on parameters indicating a state of exhaust gas of an engine 1 whether PM captured by and accumulated on DPF 32 are in close contact with a purification catalyst, and a regeneration control part 43 controlling execution of regeneration process. The regeneration control part 43 permits execution of the regeneration process when the accumulation state determination part 42 determines that PM captured by and accumulated on the DPF 32 are in close contact with the purification catalyst. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine. More specifically, the present invention relates to an exhaust gas purification apparatus for an internal combustion engine provided with a filter that captures particulate matter in exhaust gas discharged from the internal combustion engine.

  In an internal combustion engine mounted on an automobile or the like, in particular, a compression ignition type internal combustion engine, a large amount of particulate matter (Particulate Matter) is contained in exhaust gas discharged. This particulate matter is harmful to the human body and is subject to emissions regulations. For this reason, a filter for removing particulate matter is generally provided in the exhaust passage of the internal combustion engine.

  As the filter, a DPF (Diesel Particulate Filter) or a CSF (Catalyzed Soot Filter) in which an oxidation catalyst is supported on the DPF is used. In these filters, when particulate matter accumulates, a differential pressure is generated between the upstream side and the downstream side of the filter, leading to a reduction in output and fuel consumption. For this reason, it is necessary to execute a regeneration process for burning and removing the accumulated particulate matter when the particulate matter has accumulated to some extent. As a result, the filter can be used continuously.

  By the way, it is said that combustion of particulate matter requires a high temperature of 550 ° C. to 650 ° C. Even when a catalyst is used as in the above CSF, particulate matter is efficiently burned at a low temperature. The current situation is not done. This is because the reaction between the particulate matter and the catalyst is a solid-solid reaction, and the combustion reaction of the particulate matter that is not in good contact with the catalyst is difficult to proceed.

For example, the amount of particulate matter collected by the CSF and the amount of particulate matter burned and removed are estimated from the operating state of the internal combustion engine, and the amount of particulate matter deposited is estimated based on the estimation result A continuous regeneration type diesel particulate filter device is disclosed that performs regeneration processing when the estimated accumulation amount exceeds a predetermined accumulation amount (see Patent Document 1).
According to the invention disclosed in Patent Document 1, it is said that by monitoring the accumulation state of the particulate matter, clogging of the filter can be surely prevented and the particulate matter can be efficiently removed.

Further, a filter having a NO ₂ synthesizing catalyst to produce NO ₂ from NO in the exhaust, by contact reaction with NO ₂ generated by the NO ₂ generating catalyst, burning and removing particulate matter deposited on the filter An exhaust purification method is disclosed (see Patent Document 2).
In the invention disclosed in Patent Document 2, since a solid-gas reaction between NO ₂ and particulate matter is used, the particles deposited on the filter are independent of the contact state between the NO ₂ generation catalyst and the particulate matter. It is said that the particulate matter can be efficiently removed by combustion at a relatively low temperature.

Japanese Patent No. 3951619 Patent No. 3012249

However, in Patent Document 1, the amount of particulate matter that can be collected is limited in order to prevent the filter from being melted by the heat of combustion of the particulate matter collected in a large amount. For this reason, the frequency of the regeneration process increases, and the fuel consumption deteriorates.
In addition, as described above, since the reaction between the particulate matter and the catalyst is a solid-solid reaction, the regeneration process is performed without considering the contact state between the particulate matter and the catalyst. Is difficult to remove by combustion, and the regeneration process takes a long time. In addition, since it is necessary to perform the regeneration process at a high temperature, the system becomes complicated and leads to an increase in cost.

On the other hand, as described above, in Patent Document 2, since the solid-gas reaction between the particulate matter and NO ₂ is used, the particulate matter can be burned at a relatively low temperature, but the burning rate is low. The reproduction process takes a long time.

  The present invention has been made in view of the above problems, and an object of the present invention is to regenerate the filter at a lower temperature and in a shorter time than in the past in an exhaust gas purification apparatus equipped with a filter that traps particulate matter in the exhaust gas. The object is to provide a possible exhaust purification device.

  In order to achieve the above object, an invention according to claim 1 is provided in an exhaust passage of an internal combustion engine (1) for capturing particulate matter in exhaust gas of the internal combustion engine and purifying the captured particulate matter. In the exhaust gas purification apparatus for an internal combustion engine including the filter (32) having the purification catalyst, the particulate matter trapped and deposited by the filter is burned and removed by raising the temperature of the exhaust gas flowing into the filter. The regenerating means (9, 21, 31, 40, 41) for executing the regenerating process and whether the particulate matter trapped and deposited by the filter is in close contact with the purification catalyst are determined by the internal combustion engine. A deposition state determination unit (22, 40, 42) for determining based on a parameter indicating an exhaust state; and a regeneration control unit (40, 43) for controlling execution of the regeneration process. The control means permits the execution of the regeneration process when it is determined by the accumulation state determination means that the particulate matter trapped and deposited by the filter is in close contact with the purification catalyst. Features.

As described above, conventionally, the regeneration process has been executed without considering the contact state between the particulate matter and the purification catalyst. For this reason, since the particulate matter burned an amount of particulate matter far exceeding the amount that can ensure good contact with the purification catalyst, a high temperature and long time regeneration treatment was required.
In contrast, in the first aspect of the invention, when it is determined that the particulate matter trapped and deposited by the filter is in intimate contact with the purification catalyst carried by the filter, the regeneration process is performed. Allow execution. Thereby, only the particulate matter in close contact with the purification catalyst among the particulate matter trapped and deposited by the filter can be burned. Therefore, according to the present invention, the purification performance inherent to the purification catalyst can be sufficiently exerted, and the filter can be regenerated by burning the particulate matter at a lower temperature and in a shorter time than conventional. As a result, the energy loss accompanying a regeneration process can be reduced and the deterioration of fuel consumption can be suppressed.

  According to a second aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the first aspect, the parameter indicating the exhaust state of the internal combustion engine includes a differential pressure between the upstream side and the downstream side of the filter, and It is a cumulative time of the time when the differential pressure occurs.

According to the second aspect of the present invention, the particulate matter trapped and deposited on the filter based on the differential pressure between the upstream side and the downstream side of the filter and the accumulated time of the time when the differential pressure is generated is purified catalyst. It is determined whether it is in close contact with.
As will be described later, the contact state between the particulate matter trapped and deposited by the filter and the purification catalyst is determined by the differential pressure between the upstream side and the downstream side of the filter, and the accumulated time of the time when this differential pressure occurs. Determined by. Therefore, according to the present invention, since the particulate matter accumulation state is determined on the basis of the differential pressure generated in the filter and the accumulated time of the time when the differential pressure is generated, the particulate matter is in close contact with the purification catalyst. It is possible to accurately determine whether or not it is touching. Therefore, it is possible to reliably burn only the particulate matter that is in close contact with the purification catalyst, and the effect of the invention of claim 1 is exhibited to a higher degree.

  According to a third aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the first or second aspect, the particulate matter trapped and deposited by the filter is in close contact with the purification catalyst by the accumulation state determining means. A deposit amount judging means (40, 44) for judging whether or not the deposit amount of the particulate matter has reached the maximum deposit amount that can be deposited in the pores of the filter when it is judged that And the regeneration control means executes the regeneration process when it is determined by the accumulation amount determination means that the accumulation amount of the particulate matter trapped and deposited by the filter has reached the maximum accumulation amount. It is characterized by permitting.

According to the third aspect of the present invention, it is determined that the particulate matter trapped and deposited by the filter is in intimate contact with the purification catalyst, and the amount of particulate matter deposited is within the pores of the filter. When it is determined that the maximum deposition amount that can be deposited is reached, the execution of the regeneration process is permitted.
This is based on the fact that the particulate matter can come into close contact with the purification catalyst when the particulate matter is trapped and deposited in the pores of the filter. That is, the particulate matter deposited on the surface of the filter cannot be in close contact with the purification catalyst, unlike the particulate matter deposited in the pores of the filter. For this reason, after the amount of particulate matter deposited reaches the maximum amount that can be deposited in the pores of the filter, the particulate matter only accumulates on the surface of the filter and is in close contact with the purification catalyst. Since the amount of particulate matter that can be reached has reached saturation, the regeneration process is performed. Therefore, according to the present invention, only the particulate matter that has reached the saturation amount and is in close contact with the purification catalyst can be burned, so that the frequency of the regeneration process can be further reduced and the deterioration of fuel consumption can be further suppressed. it can.

  According to a fourth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the third aspect, the regeneration control means takes a time required for burning and removing the particulate matter in close contact with the purification catalyst. When the time has elapsed, execution of the reproduction process is prohibited.

In the fourth aspect of the present invention, the particulate matter trapped and deposited by the filter is in intimate contact with the purification catalyst, and the amount of particulate matter deposited reaches the maximum deposition amount that can be deposited in the pores of the filter. When it is determined that the particulate matter is in contact with the purifying catalyst and the regeneration process is executed, the regeneration process is prohibited when the time necessary for burning and removing the particulate matter has passed.
Thereby, the execution of the regeneration process can be stopped when the particulate matter in close contact with the purification catalyst is burned and removed. Therefore, according to the present invention, the energy loss associated with the regeneration process can be further reduced, and the deterioration of fuel consumption can be further suppressed.
Here, the “time necessary for burning and removing the particulate matter in close contact with the purification catalyst” in the present invention is calculated in advance by conducting a predetermined experiment. Specifically, it is calculated from the burning rate of the particulate matter according to the regeneration temperature and the maximum amount of particulate matter that can be deposited in the pores of the filter. This is because the particulate matter in intimate contact with the purification catalyst is generated only in the pores of the filter.

  According to a fifth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to fourth aspects, the regeneration means is configured to increase the main injection amount and provide an oxidation catalyst upstream of the filter. The regeneration process is performed by increasing the temperature of the exhaust gas flowing into the filter by performing post injection or heating by a heater.

  In the fifth aspect of the invention, the regeneration process is executed by increasing the temperature of the exhaust gas flowing into the filter by increasing the main injection amount. Alternatively, post-injection is performed to contain the fuel component in the exhaust, and the fuel component is oxidized by an oxidation catalyst provided on the upstream side of the filter, so that the regeneration process is performed using the generated heat. Alternatively, the regeneration process is executed by heating the filter using a heater. Therefore, according to the present invention, the particulate matter that is in intimate contact with the purification catalyst can be surely burned and removed by these regeneration treatments, and the effect of the invention according to any one of claims 1 to 4 can be reliably exhibited. The

  According to a sixth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to fifth aspects, the purification catalyst comprises Ag and Pd supported on a complex oxide having an oxygen releasing ability. Features.

  In the invention described in claim 6, a purification catalyst is used in which Ag and Pd are supported on a complex oxide having oxygen releasing ability. Ag has excellent PM combustion performance at low temperatures, and by using a composite oxide having oxygen releasing ability and Pd in combination, better PM purification performance can be obtained at low temperatures.

A seventh aspect of the present invention is the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to sixth aspects, wherein the filter further includes a NO ₂ generation catalyst that generates NO ₂ from NO in the exhaust gas. To do.

In the invention described in claim 7, in addition to the purification catalyst, a filter having a NO ₂ production catalyst is used. NO ₂ generated from NO in the exhaust by the action of NO ₂ generation catalysts have superior PM oxidation performance. Therefore, by the synergistic effect of the purification catalyst and NO ₂ generation catalysts, excellent PM purification performance at low temperatures is obtained.

The invention according to claim 8 is the exhaust gas purification apparatus for an internal combustion engine according to claim 7, wherein the NO ₂ generation catalyst is at least one selected from the group consisting of Pt, Pd, and Rh as a high specific surface area carrier. It is characterized by being carried.

In the invention according to claim 8, the NO ₂ generation catalyst formed by supporting at least one selected from the group consisting of Pt, Pd, and Rh on the high specific surface area support is used. Since these noble metal elements are excellent in NO ₂ generation ability, the effect of the invention of claim 7 is exhibited more highly.

It is a figure showing composition of an exhaust-air-purification device of an internal-combustion engine concerning one embodiment of the present invention. It is a cross-sectional schematic diagram of DPF used by one Embodiment of this invention. It is a flowchart which shows the procedure of the reproduction | regeneration control which concerns on one Embodiment of this invention. It is a schematic diagram of tight contact PM. It is a schematic diagram of loose contact PM. It is a figure which shows a tight contact area | region. It is a figure which shows the relationship between differential pressure | voltage (DELTA) P and accumulation PM amount. It is a TG-DTA chart of an Ag type purification catalyst. It is a figure which shows the relationship between reproduction | regeneration temperature and reproduction | regeneration time.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of an exhaust emission control device for an internal combustion engine according to an embodiment of the present invention. An internal combustion engine (hereinafter referred to as an engine) 1 is a diesel engine that directly injects fuel into a combustion chamber of each cylinder 7, and each cylinder 7 is provided with a fuel injection valve (not shown). These fuel injection valves are electrically connected by an electronic control unit (hereinafter referred to as ECU) 40, and the valve opening time and valve closing time of the fuel injection valve are controlled by the ECU 40.

  The engine 1 includes an intake pipe 2 through which intake air flows, an exhaust pipe 4 through which exhaust flows, an EGR passage 6 that recirculates part of the exhaust to the intake air, and a supercharger 8 that pumps intake air into the intake pipe 2. , Is provided.

  The intake pipe 2 is connected to the intake port of each cylinder 7 of the engine 1 through a plurality of branch portions of the intake manifold 3. The exhaust pipe 4 is connected to the exhaust port of each cylinder 7 of the engine 1 through a plurality of branch portions of the exhaust manifold 5.

  The supercharger 8 includes a turbine 81 provided in the exhaust pipe 4 and a compressor 82 provided in the intake pipe 2. The turbine 81 is driven by the kinetic energy of the exhaust flowing through the exhaust pipe 4. The compressor 82 is driven by the rotation of the turbine 81 to pressurize the intake air and pump it into the intake pipe 2. The turbine 81 includes a plurality of variable vanes (not shown), and is configured to change the rotational speed of the turbine by changing the opening of the variable vanes. The vane opening degree is electromagnetically controlled by the ECU 40.

  A throttle valve 9 for controlling the intake air amount of the engine 1 is provided on the upstream side of the supercharger 8 in the intake pipe 2. The throttle valve 9 is connected to the ECU 40 via an actuator, and the opening degree is electromagnetically controlled by the ECU 40. The intake air amount controlled by the throttle valve 9 is detected by the air flow meter 21.

  The EGR passage 6 connects the exhaust manifold 5 and the intake manifold 3 to return a part of the exhaust upstream of the turbine 81 to the downstream of the compressor 82 in the intake pipe 2. The EGR passage 6 is provided with an EGR valve 11 that controls the flow rate of the recirculated exhaust gas. The EGR valve 11 is connected to the ECU 40 via an actuator (not shown), and the valve opening degree is electromagnetically controlled by the ECU 40.

  Further, an oxidation catalyst 31 and a DPF 32 are provided in this order from the upstream side in the exhaust pipe 4 downstream of the turbine 81.

The oxidation catalyst 31 oxidizes a fuel component introduced into the exhaust gas by post injection, which will be described later, and raises the temperature of the exhaust gas with generated heat. As this oxidation catalyst 31, for example, platinum (Pt) acting as a catalyst is supported on an alumina (Al ₂ O ₃ ) support, zeolite having an excellent HC adsorption action, and steam reforming action of HC. In addition, a material constituted by adding rhodium (Rh) excellent in the above is used.

When the exhaust gas passes through the pores of the filter, the DPF 32 collects particulate matter (Particulate Matter, hereinafter referred to as “PM”) by depositing it on the surface of the filter and in the pores of the filter. For example, a wall flow type DPF using a honeycomb structure made of a ceramic porous body such as silicon carbide (SiC) is used. The wall flow type DPF includes an exhaust inflow passage sealed on the downstream side, an exhaust outflow passage adjacent to the exhaust inflow passage and plugged on the upstream side, and a filter wall that partitions the exhaust inflow passage and the exhaust outflow passage. Is composed of.
Note that, in the DPF 32, the pressure loss of the exhaust pipe 4 increases as PM is collected, so that a regeneration process to be described later for burning the collected PM is executed.

The DPF 32 carries a purification catalyst for purifying the PM trapped and deposited by the filter. As the purification catalyst, a PM combustion catalyst for burning the deposited PM is used.
Specifically, a PM combustion catalyst in which Ag and Pd are supported on a complex oxide having oxygen releasing ability is preferably used as the purification catalyst.
The complex oxide having oxygen releasing ability includes at least one crystal structure selected from the group consisting of perovskite type, spinel type, rutile type, delafossite type, magnetoplumbite type, ilmenite type, and fluorite type. A composite oxide comprising is preferably used. Of these complex oxides having a crystal structure, a complex oxide containing at least one element selected from the group consisting of Al, Si, Ti, Ce, and Zr as a main constituent element is preferably used.
In addition, a composite oxide obtained by adding at least one element selected from the group consisting of alkali metals, alkaline earth metals, rare earths, transition metals, and noble metals is more preferably used. By adding these elements to the composite oxide, the valence of the constituent elements changes and oxygen can be absorbed and released.

  The method for preparing and supporting the purification catalyst is not particularly limited, and for example, a conventionally known wash coat method can be employed. Specifically, a slurry containing the material constituting the purification catalyst is prepared, and the honeycomb structure is immersed in the slurry for a predetermined time. After a predetermined time has passed, the purification structure can be supported on the honeycomb structure by lifting the honeycomb structure to remove excess slurry and drying it.

In addition to the purification catalyst, the DPF 32 preferably supports a NO ₂ generation catalyst that generates NO ₂ from NO contained in the exhaust gas.
The NO ₂ synthesizing catalyst, the high specific surface area support, Pt, Pd, and NO ₂ generation catalyst comprising carrying at least one member selected from the group consisting of Rh is preferably used.
The high specific surface area carrier is not particularly limited, and conventionally known oxides and composite oxides are used.

In the present embodiment, as shown in FIG. 2, a purification catalyst layer 34 formed on the filter wall 33 constituting the DPF 32 and a NO ₂ generation catalyst layer 35 formed on the purification catalyst layer 34 are provided. A two-layer structure having the same is preferably used.
The two-layer DPF 32 is obtained by sequentially forming the purification catalyst layer 34 and the NO ₂ generation catalyst layer 35 on the filter wall 33 by the wash coat method.

  Returning to FIG. 1, a differential pressure sensor 22 connected via a pressure introduction pipe 23 is provided in the exhaust pipe 4 upstream and downstream of the DPF 32. The differential pressure sensor 22 detects a differential pressure between the upstream pressure and the downstream pressure of the DPF 32. The differential pressure sensor 22 is connected to an ECU 40 described later, and a detection signal thereof is supplied to the ECU 40.

  The ECU 40 shapes an input signal waveform from various sensors, corrects a voltage level to a predetermined level, converts an analog signal value into a digital signal value, and a central processing unit (hereinafter, referred to as a central processing unit). CPU). In addition, the ECU 40 includes a storage circuit that stores various calculation programs executed by the CPU, calculation results, and the like, a throttle valve 9, a fuel injection valve of the engine 1, a heater (not shown) for heating the DPF 32, and the like. And an output circuit for outputting a control signal.

With the hardware configuration described above, the ECU 40 includes modules of a regeneration unit 41, a deposition state determination unit 42, a regeneration control unit 43, and a deposition amount determination unit 44.
The regeneration unit 41 increases the temperature of the exhaust gas flowing into the DPF 32, thereby executing a regeneration process for burning and removing the PM trapped and accumulated in the DPF 32.
The accumulation state determination unit 42 determines whether PM trapped and accumulated in the DPF 32 is in close contact with the purification catalyst based on a parameter indicating the exhaust state of the engine 1.
When the accumulation state determination unit 42 determines that the PM trapped and accumulated in the DPF 32 is in close contact with the purification catalyst, the accumulation amount determination unit 44 determines that the PM accumulation amount is smaller than that of the DPF 32. It is determined whether or not the maximum deposition amount that can be deposited in the hole has been reached.
When the accumulation state determination unit 42 determines that the PM deposited on the DPF 32 is in close contact with the purification catalyst, the regeneration control unit 43 captures the PM accumulated by being captured by the DPF 32 by the accumulation amount determination unit 44. When it is determined that the deposition amount has reached the maximum deposition amount that can be deposited in the pores of the DPF 32, execution of the regeneration process is permitted.

  FIG. 3 is a flowchart showing a playback control procedure according to this embodiment. This regeneration control is repeatedly executed by the ECU 40 described above.

In step S <b> 11, first, a differential pressure ΔP between the upstream pressure and the downstream pressure of the DPF 32 is detected by the differential pressure sensor 22. Next, an average differential pressure ΔPave is calculated from the detected value of the differential pressure ΔP.
Further, the accumulated time Tp of the time when the differential pressure ΔP occurs is measured. After the measurement, the process proceeds to step S12.

In step S12, the PM accumulated in the DPF 32 is in intimate contact with the purification catalyst based on the average differential pressure ΔPave calculated in step S11 and the accumulated time Tp of the time when the differential pressure ΔP measured in step S11 occurs. (Hereinafter referred to as “tight contact”).
Specifically, it is determined by referring to a tight contact region determination map, which will be described later, whether or not the PM deposited on the DPF 32 has become a tight contact. If this determination is YES, the process proceeds to step S13, and if NO, the process returns to step S11 again.

Here, the tight contact PM and the PM not in close contact with the purification catalyst (hereinafter referred to as “loose contact”) will be described.
FIG. 4 is a diagram schematically showing the tight contact PM. FIG. 5 is a diagram schematically showing the loose contact PM. As shown in FIG. 4, the tight contact PM is in intimate contact with the purification catalyst supported on the DPF 32 (in the example shown in FIG. 4, the PM combustion catalyst in which Ag and Pd are supported on CeZrO ₂ ). Therefore, the combustion reaction proceeds smoothly, so that the combustion is removed at a low temperature in a short time. On the other hand, as shown in FIG. 5, in the loose contact PM, since a gap is formed between the purification catalyst and the combustion catalyst, the combustion reaction does not proceed smoothly, and combustion requires a high temperature and a long time. The loose contact PM as shown in FIG. 5 is seen immediately after the tight contact PM is burned and removed by the regeneration process.
The present invention has been made paying attention to the difference in characteristics between the tight contact PM and the loose contact PM. In the present invention, only the tight contact PM is burned, so that the regeneration process can be performed at a low temperature in a short time. It is said.

Next, the tight contact region determination map will be described.
FIG. 6 shows a tight contact region determined by an average differential pressure ΔPave of DPF 32 supporting a purification catalyst containing Ag and an accumulated time (hereinafter referred to as “PM compression time”) Tp when the differential pressure ΔP occurs. This is a determination map. This judgment map shows that when PM is deposited on the DPF 32 until a predetermined differential pressure is reached, the PM is compressed for a predetermined time using N ₂ gas and then switched to the Air gas, the test is started for 30 seconds from the start of the test. The PM combustion speed is calculated from the burned PM, and is created based on the result of the calculated PM combustion speed becoming the saturation combustion speed. This determination map is created in advance by the above experiment and stored in the ECU 40.
As shown in FIG. 6, the condition for the saturation of the PM deposited on the DPF 32 and the purification catalyst to reach saturation is determined by the average differential pressure ΔPAve of the DPF 32 and the PM compression time Tp. The upper right region of the curve in FIG. 6 is the condition of the average differential pressure ΔPave and the PM compression time Tp for making PM tight contact. As shown in FIG. 6, as the average differential pressure ΔPAve of the DPF 32 is larger and the PM compression time Tp is longer, the PM deposited on the DPF 32 becomes tight contact.
Here, “PM becomes tight contact” means that the contact property between PM and the purification catalyst reaches saturation.

Returning to FIG. 3, in step S <b> 13, it is determined whether or not the accumulated PM amount W accumulated in the DPF 32 has reached the maximum accumulated amount Wp that can be accumulated in the pores of the DPF 32. If this determination is NO, the process returns to step S11 again. In the case of YES, the process proceeds to step S14 and the reproduction process is executed.
This is based on the finding of the inventors that combustion of the tight contact PM occurs only in the pores of the DPF 32. That is, the PM deposited on the surface of the DPF 32 cannot contact the purification catalyst closely unlike the PM deposited in the pores. For this reason, after the deposited PM amount W reaches the maximum deposit amount Wp that can be deposited in the pores of the DPF 32, PM is deposited on the surface of the DPF 32, so the regeneration process is executed. .

Here, the accumulated PM amount W accumulated in the DPF 32 is calculated by referring to the map shown in FIG. 7 based on the differential pressure ΔP of the DPF 32 detected by the differential pressure sensor 22. The map shown in FIG. 7 shows the relationship between the differential pressure ΔP of the DPF 32 and the amount of accumulated PM when a purification catalyst containing Ag is used. The map is created in advance by a predetermined experiment and stored in the ECU 40.
Further, the maximum deposition amount Wp that can be deposited in the pores of the DPF 32 is calculated in advance by a predetermined experiment and stored in the ECU 40. Specifically, it is the amount of accumulated PM at P where the increase in the differential pressure ΔP becomes gradual in the curve of FIG. That is, the differential pressure ΔP of the DPF 32 increases rapidly up to P in the curve of FIG. 7, but this is because PM is trapped and deposited in the pores of the DPF 32, and the pressure loss increases greatly with a small amount of accumulated PM. It is to rise. Therefore, the amount of deposited PM at P in the curve of FIG. 7 is the maximum amount of deposition Wp that can be deposited in the pores of the DPF 32.

In step S <b> 14, a regeneration process is performed in which the temperature of the exhaust gas flowing into the DPF 32 is raised to burn and remove the PM trapped and accumulated in the DPF 32. After starting the reproduction process, the process proceeds to step S15.
Specifically, by outputting a control signal to the throttle valve 9, the fuel injection valve of the engine 1, or a heater for heating the DPF 32, the intake air amount is reduced, the main injection amount is increased, the post injection is performed, Alternatively, the regeneration process is executed by heating with a heater to raise the temperature of the exhaust gas flowing into the DPF 32.

In the regeneration treatment of the present embodiment, it is preferable to raise the temperature to a temperature at which the purification performance inherent in the purification catalyst can be sufficiently exhibited and the tight contact PM can be burned at a high combustion rate.
Hereinafter, a specific example will be described.
FIG. 8 shows a TG-DTA chart of a purification catalyst in which 30 mass% of Ag and 1 mass% of Pd are supported on CeZrO ₂ . FIG. 8 shows TG− when PM powder is mixed in a mortar so as to be 5% by mass with respect to the catalyst powder to make tight contact, and then air is flowed to raise the temperature at 20 ° C./min. It is a DTA chart.
As shown in FIG. 8, the combustion of PM is started at the temperature T1, the combustion speed is dramatically increased at the temperature T2, and the combustion speed reaches a peak at the temperature T3. Therefore, in the regeneration process of the present embodiment, it is preferable to increase the temperature to a predetermined temperature equal to or higher than T1, which is the PM combustion start temperature. Further, it is more preferable to increase the temperature to a predetermined temperature equal to or higher than T2 at which the PM combustion rate starts to increase dramatically, and further preferable to increase to a predetermined temperature equal to or higher than the PM combustion peak temperature T3.

In step S15, after the time necessary for burning and removing the tight contact PM has elapsed, execution of the regeneration process is prohibited.
The time required to burn and remove the tight contact PM is calculated in advance by a predetermined experiment and stored in the ECU 40. Specifically, the time required to burn and remove the tight contact PM is calculated from the PM burning rate according to the regeneration temperature and the maximum amount of PM that can be deposited in the pores of the DPF 32. This is because the tight contact PM occurs only in the pores of the DPF 32.
FIG. 9 is a diagram showing the relationship between the regeneration temperature and the regeneration time when a regeneration process is executed by burning only a predetermined amount of tight contact PM using a purification catalyst containing Ag. Thus, based on the PM combustion rate at each regeneration temperature, the time required for combustion of the tight contact PM, that is, the regeneration time is obtained.

Hereinafter, the effect of the exhaust emission control device for the internal combustion engine according to the present embodiment will be described.
As described above, conventionally, the regeneration process is executed without considering the contact state between the PM and the purification catalyst. For this reason, since the amount of PM that burned far exceeded the amount that could ensure good contact with the purification catalyst, high temperature and long time regeneration treatment was required.
On the other hand, in this embodiment, when it is determined that the PM trapped and deposited by the DPF 32 is in tight contact, the regeneration process is permitted to be executed. Thereby, only the tight contact PM can be burned out of the PM trapped and deposited by the DPF 32.
Therefore, according to the present embodiment, the purification performance inherent to the purification catalyst can be sufficiently exerted, and the DPF 32 can be regenerated by burning PM at a lower temperature and in a shorter time than conventional. Specifically, by executing the regeneration process that burns only the tight contacts PM, the regeneration process that conventionally required a high temperature of 550 ° C. to 650 ° C. can be performed at a low temperature of 400 ° C. or less ( (See FIG. 9). For this reason, the energy loss accompanying a regeneration process can be reduced and the deterioration of a fuel consumption can be suppressed.

In the present embodiment, whether the PM trapped and accumulated in the DPF 32 is tightly contacted based on the differential pressure between the upstream side and the downstream side of the DPF 32 and the accumulated time when the differential pressure occurs. Determine whether or not.
As described above, the contact state between the PM trapped and accumulated in the DPF 32 and the purification catalyst is determined by the differential pressure between the upstream side and the downstream side of the DPF 32 and the accumulated time of the time when the differential pressure is generated. Is done. For this reason, according to the present embodiment, whether or not the PM is in tight contact is determined because the PM accumulation state is determined based on the differential pressure generated in the DPF 32 and the accumulated time of the time when the differential pressure is generated. Can be determined accurately. Therefore, only the tight contact PM can be surely burned, and the above effect is exhibited more highly.

Further, in the present embodiment, it is determined that the PM trapped and deposited by the DPF 32 is in tight contact, and the PM deposition amount reaches the maximum deposition amount that can be deposited in the pores of the DPF 32. When it is determined that the playback process is being performed, the execution of the playback process is permitted.
This is based on the fact that PM can be tightly contacted when PM is trapped and deposited in the pores of DPF 32. That is, the PM deposited on the surface of the DPF 32 cannot be made tight contact unlike the PM deposited in the pores of the DPF 32. For this reason, after the PM deposition amount reaches the maximum deposition amount that can be deposited in the pores of the DPF 32, only PM accumulates on the surface of the DPF 32, and the tight contact PM amount has already reached saturation. Therefore, the reproduction process is executed. Therefore, according to the present embodiment, only the tight contact PM that has reached the saturation amount can be burned, so that the frequency of the regeneration process can be further reduced and the deterioration of fuel consumption can be further suppressed.

Further, in this embodiment, the PM trapped and deposited by the DPF 32 is made into a tight contact, and it is determined that the PM deposition amount has reached the maximum deposition amount that can be deposited in the pores of the DPF 32, and the regeneration process is executed. In such a case, when the time necessary for burning and removing the tight contact PM has elapsed, the regeneration process is prohibited.
Thereby, the execution of the regeneration process can be stopped when the tight contact PM is removed by combustion. Therefore, according to this embodiment, the energy loss accompanying a regeneration process can be further reduced, and deterioration of fuel consumption can be further suppressed.

  In the present embodiment, the temperature of the exhaust gas flowing into the DPF 32 is raised by increasing the main injection amount, performing the post injection with the oxidation catalyst 31 provided upstream of the DPF 32, or heating by the heater. Perform playback processing. Therefore, according to the present embodiment, PM that is in close contact with the purification catalyst can be reliably burned and removed by these regeneration processes, and the above-described effects are reliably exhibited.

  In the present embodiment, a purification catalyst is used in which Ag and Pd are supported on a complex oxide having oxygen releasing ability. Ag has excellent PM combustion performance at low temperatures, and by using a composite oxide having oxygen releasing ability and Pd in combination, better PM purification performance can be obtained at low temperatures.

In this embodiment, in addition to the purification catalyst, DPF 32 having a NO ₂ production catalyst is used. NO ₂ generated from NO in the exhaust by the action of NO ₂ generation catalysts have superior PM oxidation performance. Therefore, by the synergistic effect of the purification catalyst and NO ₂ generation catalysts, excellent PM purification performance at low temperatures is obtained.

In this embodiment, a NO ₂ generation catalyst is used in which at least one selected from the group consisting of Pt, Pd, and Rh is supported on the high specific surface area support. Since these noble metal elements are excellent in NO ₂ generation ability, the above effects are exhibited more highly.

  In the present embodiment, the ECU 40 constitutes a regeneration unit, a deposition state determination unit, a regeneration control unit, and a deposition amount determination unit of the present invention. Specifically, the regeneration unit 41 corresponds to the regeneration unit, the deposition state determination unit 42 corresponds to the deposition state determination unit, the regeneration control unit 43 corresponds to the regeneration control unit, and the deposition amount determination unit 44 determines the deposition amount. Corresponds to means. Further, the means related to the execution of step S12 in FIG. 3 corresponds to the accumulation state determination means, the means related to the execution of step S13 corresponds to the accumulation amount determination means, and the means related to the execution of step S14 corresponds to the regeneration means and the regeneration control. The means for executing step S15 corresponds to the reproduction control means.

  It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.

  EXAMPLES Next, although this invention is demonstrated in detail based on an Example, this invention is not limited to these Examples.

<Single PM combustion performance evaluation>
[Example 1: Ag-based catalyst]
(Preparation of Ag-based catalyst)
A predetermined amount of silver nitrate and Pd nitrate were dissolved in water such that Ag was 30% by mass and Pd was 1% by mass with respect to CeZrO ₂ . Next, CeZrO ₂ powder, silver nitrate, and a Pd nitrate mixed aqueous solution were placed in an eggplant flask and evaporated to dryness with a rotary evaporator. This was calcined at 700 ° C. for 2 hours to produce AgPd / CeZrO ₂ .

(Catalyst loading on wall flow type DPF)
To the AgPd / CeZrO ₂ prepared above, a SiO ₂ sol was added together with a predetermined amount of water and stirred with a ball mill to form a slurry. A 300-cell SiC-DPF honeycomb was prepared, and this honeycomb was immersed in the slurry. After soaking, the honeycomb was pulled up and the excess slurry was cut well with an air knife, and then drying at 200 ° C. was repeated until a predetermined weight was reached, so that the slurry was supported by the dried solid product. Next, by baking at 700 ° C. for 2 hours, a DPF with catalyst carrying 60 g / L of catalyst per 1 L of DPF with catalyst was obtained.

(PM combustion performance evaluation)
The PM combustion test was conducted under the following conditions. The test was conducted in the initial state, that is, using the DPF with catalyst obtained above as it was.
The PM was collected by circulating the exhaust of the diesel generator through a 15 cc DPF with catalyst. Simultaneously with the collection, the PM deposited on the DPF with the catalyst was compressed at 5 to 10 kPa for 60 minutes to make the PM and the catalyst into tight contact. The weight of the collected PM was determined by measuring the weight of the DPF with catalyst before and after the collection. Moreover, in order to exclude the influence of water or HC, weight measurement was performed after drying in a dryer at 200 ° C. for 15 minutes.
The test piece DPF with a catalyst after the PM trapping, by using the PM combustion performance evaluation device, PM is by measuring the concentration of CO and CO ₂ produced during the combustion was carried out PM combustion performance evaluation. Specifically, after heating up to 400 ° C. with N ₂ gas so that PM does not burn, the gas composition is O: 25%, NOx: 700 ppm, N ₂ : balance (linear velocity SV = 50000 ^h−1 ). The high combustion speed when the tight contact PM burns for 30 seconds from the start of combustion is defined as the tight contact combustion speed, and then the PM combustion speed until 90% of the PM burns is loose contact. PM combustion performance was evaluated as the burning rate.

[Example 2: Ag / Pt catalyst]
(Preparation of Ag-based catalyst)
The Ag-based catalyst was prepared in the same manner as in Example 1 except that citric acid was mixed during slurry preparation so as to increase the amount of PM that can be made into tight contact by increasing the specific surface area of the catalyst.

(Preparation of Pt catalyst)
Predetermined amounts of Pt nitrate and Pd nitrate were dissolved in water such that Pt was 9.3 mass% and Pd was 4.7 mass% with respect to Al ₂ O ₃ . Next, an Al ₂ O ₃ powder, Pt nitrate, and a Pd nitrate mixed aqueous solution were placed in an eggplant flask and evaporated to dryness with a rotary evaporator. PtPd / Al ₂ O ₃ was produced by firing this at 700 ° C. for 2 hours.

(Catalyst loading on wall flow type DPF)
The same operation as in Example 1 was carried out except that the above Pt catalyst was supported at 20 g / L per 1 L of DPF on the upper layer of an Ag catalyst DPF produced in the same manner as in Example 1, and an Ag / Pt catalyst was added. A DPF was obtained.

(PM combustion performance evaluation)
The obtained PMD with catalyst was subjected to the same PM combustion performance evaluation as in Example 1.

[Comparative Example 1: Pt catalyst]
Using a commercial Pt / _Al 2 _{O 3} catalyst was carried out in the same manner as the PM combustion performance evaluation as in Example 1.

<Evaluation of actual PM combustion performance>
[Example 3: Ag-based catalyst]
(Preparation of Ag-based catalyst)
In order to increase the amount of PM that can be tightly contacted by increasing the specific surface area of the catalyst, the same operation as in Example 1 was carried out except that citric acid was mixed during slurry preparation to prepare an Ag-based catalyst.

(Catalyst loading on wall flow type DPF)
Catalyst loading on the wall flow type DPF was carried out in the same manner as in Example 1 except that the capacity of the DPF was 2.1 L to obtain a DPF with catalyst.

(PM combustion performance evaluation)
The PM combustion test was conducted under the following conditions. The test was conducted in the initial state, that is, using the DPF with catalyst obtained above as it was.
Using an automobile diesel engine, the engine speed and torque were controlled so that the temperature immediately before the DPF with catalyst was about 400 ° C., and exhaust gas was introduced into the DPF with catalyst. The differential pressure (pressure loss) at this time was about 5 to 10 kPa. Measure the weight before and after the introduction of exhaust for two types: the exhaust introduction time set to 30 minutes and not tight contact, and the exhaust introduction time set to 120 minutes and tight contact. Thus, PM combustion performance was evaluated. In addition, in order to exclude the influence of water and HC, weight measurement was performed after drying at 200 ° C. × 2.5 hours.

[Comparative Example 2: Pt catalyst]
PM combustion performance evaluation similar to Example 3 was performed using a commercially available Pt / Al ₂ O ₃ catalyst in the same manner as in Comparative Example 1.

<Single PM combustion performance evaluation results: Examples 1 and 2 and Comparative Example 1>
Table 1 shows the PM combustion performance evaluation results of Examples 1 and 2 and Comparative Example 1. Comparison between Example 1 and Comparative Example 1 revealed that the Ag-based catalyst had a higher PM combustion rate for 30 seconds after the start of the test, that is, the tight contact PM combustion rate. This is a result of the high purification performance inherently possessed by the Ag-based catalyst being exhibited by the tight contact PM burning in the pores of the DPF.
On the other hand, no significant difference was observed between the Ag-based catalyst and the Pt-based catalyst in the combustion rate until 90% of PM combusted after 30 seconds from the start of the test, that is, the loose contact PM combustion rate. This is a result of the combustion reaction mainly using NO ₂ being advanced by the loose contact PM burning. For this reason, the influence by the difference in the purification | cleaning performance of a catalyst and the influence by the contact state of PM and a catalyst are hardly seen, and it is thought that the PM combustion speed substantially equivalent was obtained in all.
From this result, it was found that a high PM combustion rate can be obtained by making the PM and the catalyst tight contact, particularly in the case of an Ag-based catalyst.

Further, in comparison between Example 1 and Example 2, a higher PM combustion rate was obtained by combining a Pt-based catalyst that is a NO ₂ production catalyst than an Ag-based catalyst that is a PM combustion catalyst alone. This was thought to be due to a synergistic effect due to the addition of NO ₂ excellent in PM oxidation performance to tight contact PM combustion that proceeds at the interface where the Ag-based catalyst and PM are in close contact.
Moreover, the significant difference was not recognized by Example 1 and Example 2 about the loose contact PM combustion rate. This is considered to be because PM is mainly burned by NO ₂ and the influence of the contact state between PM and the catalyst is extremely small.

<Evaluation of actual PM combustion performance: Example 3 and Comparative Example 2>
Table 2 shows the PM combustion performance evaluation results of Example 3 and Comparative Example 2. The PM combustion rate when exhaust introduction time was 30 minutes in Example 3 was 0%. This is considered to be because PM combustion reaction did not proceed under conditions of an average differential pressure of 3.8 kPa and an exhaust introduction time, that is, a PM compression time of 30 minutes, because it was outside the tight contact region (see FIG. 6). ). On the other hand, the PM combustion rate when the exhaust introduction time was 120 minutes was 40%. This was considered that the PM combustion reaction progressed because the average pressure loss of 3.9 kPa and the exhaust introduction time, that is, the PM compression time of 120 minutes were in the tight contact region (see FIG. 6).
On the other hand, the PM combustion rate when the exhaust introduction time was 30 minutes in Comparative Example 2 was 6%. This is probably because Pt-based catalyst is used in Comparative Example 2, and therefore PM is burned mainly by gas-solid reaction by NO _2, so there is almost no influence by the contact state between PM and catalyst. It was. Further, the PM combustion rate when the exhaust introduction time was 120 minutes was 17%, and the combustion was less than half compared with the exhaust introduction time of 120 minutes in Example 3. This was considered because the combustion performance when the Ag-based catalyst was tightly contacted with PM had higher combustion performance than combustion with NO ₂ .

1. Engine (internal combustion engine)
9 ... Throttle valve (regeneration means)
21 ... Air flow meter (regeneration means)
22 ... Differential pressure sensor (deposition state judging means)
31 ... Oxidation catalyst (regeneration means)
32 ... DPF (filter)
40 ... ECU (regeneration means, accumulation state determination means, regeneration control means, accumulation amount determination means)

Claims (8)

In an exhaust gas purification apparatus for an internal combustion engine, which is provided in an exhaust passage of the internal combustion engine and includes a filter having a purification catalyst for purifying particulate matter in the exhaust gas of the internal combustion engine and purifying the captured particulate matter.
A regeneration means for performing a regeneration process for burning and removing particulate matter trapped and deposited by the filter by raising the temperature of the exhaust gas flowing into the filter;
Deposition state determination means for determining whether particulate matter trapped and deposited by the filter is in intimate contact with the purification catalyst based on a parameter indicating an exhaust state of the internal combustion engine;
Playback control means for controlling execution of the playback process,
The regeneration control unit permits the regeneration process to be executed when the accumulation state determination unit determines that the particulate matter trapped and deposited by the filter is in close contact with the purification catalyst. An exhaust emission control device for an internal combustion engine.   The parameter indicating the exhaust state of the internal combustion engine is a differential pressure between the upstream side and the downstream side of the filter and an accumulated time of a time when the differential pressure is generated. An exhaust purification device for an internal combustion engine. When it is determined by the deposition state determination means that the particulate matter trapped and deposited by the filter is in close contact with the purification catalyst, the amount of particulate matter deposited is determined in the pores of the filter. And further comprising a deposit amount judging means for judging whether or not the maximum deposit amount that can be deposited is reached.
The regeneration control means permits execution of the regeneration process when the accumulation amount determination means determines that the accumulation amount of the particulate matter trapped and accumulated by the filter has reached the maximum accumulation amount. The exhaust emission control device for an internal combustion engine according to claim 1 or 2, characterized in that:   4. The regeneration control unit prohibits execution of the regeneration process when a time necessary for burning and removing particulate matter in close contact with the purification catalyst has elapsed. An exhaust gas purification apparatus for an internal combustion engine as described.   The regeneration means increases the temperature of the exhaust gas flowing into the filter by increasing the main injection amount, performing post injection after providing an oxidation catalyst upstream of the filter, or heating by a heater, and The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein regeneration processing is executed.   The exhaust purification device of an internal combustion engine according to any one of claims 1 to 5, wherein the purification catalyst comprises Ag and Pd supported on a complex oxide having an oxygen releasing ability. The exhaust purification device for an internal combustion engine according to any one of claims 1 to 6, wherein the filter further includes a NO ₂ generation catalyst that generates NO ₂ from NO in the exhaust gas. 8. The exhaust gas purification apparatus for an internal combustion engine according to claim 7, wherein the NO ₂ generation catalyst carries at least one selected from the group consisting of Pt, Pd, and Rh on a high specific surface area carrier. .

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