JP2014231761A - Exhaust purification device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restore HC poisoning of an oxidation catalyst while curbing emission of NOx into the atmosphere on the occurrence of the HC poisoning of the oxidation catalyst in an exhaust purification device of an internal combustion engine which has the oxidation catalyst and an SCR catalyst, selectively reducing nitrogen oxide in exhaust using ammonia, in series on an exhaust passage of the internal combustion engine.SOLUTION: An exhaust purification device for an internal combustion engine comprises: an oxidation catalyst poisoning amount acquisition section which acquires an HC poisoning amount of an oxidation catalyst; an oxygen concentration increasing section which increases an oxygen concentration in an air-fuel mixture; and an oxidation catalyst poisoning recovering section which recovers the oxidation catalyst from HC poisoning. In a case that the HC poisoning amount of the oxidation catalyst reaches a level where a reduction in oxidation capacity of the oxidation catalyst due to HC poisoning causes a ratio of NO to NOin exhaust flowing out of the oxidation catalyst to be lower than a predetermined threshold ratio, the oxygen concentration in the air-fuel mixture, when a temperature of an SCR catalyst is not less than an activating temperature, is increased larger than the same when the temperature of the SCR catalyst is less than the activating temperature.

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine comprising an oxidation catalyst and a selective reduction catalyst that selectively reduces nitrogen oxides in exhaust using ammonia as a reducing agent.

Conventionally, an oxidation catalyst having an oxidation capability in an exhaust passage of an internal combustion engine, and a selective reduction catalyst that selectively reduces nitrogen oxide (NOx) in exhaust using ammonia as a reducing agent downstream of the oxidation catalyst ( Hereinafter, an exhaust emission control device for an internal combustion engine including an SCR catalyst is also known. In the selective reduction reaction of NOx in this SCR catalyst, it is known that the reaction rate of the reduction reaction in which nitric oxide (NO) and nitrogen dioxide (NO ₂ ) react one-on-one is particularly fast. Therefore, the NOx purification rate of the SCR catalyst is such that the NO ₂ ratio of the exhaust gas flowing into the SCR catalyst (the molar ratio of NO ₂ to NO in the exhaust gas) is a predetermined ratio (for example, approximately 1) that promotes the reduction reaction. The closer you get, the higher. However, since the exhaust discharged from the internal combustion engine usually contains more NO than NO ₂ , the NO ₂ ratio of the exhaust is lower than the above-mentioned predetermined ratio. Therefore, the NOx purification of the SCR catalyst is performed by oxidizing the NO in the exhaust gas to NO ₂ using an oxidation catalyst and bringing the NO ₂ ratio of the exhaust gas flowing out of the oxidation catalyst and flowing into the SCR catalyst close to the above-mentioned predetermined ratio. A technique for increasing the rate is known (see, for example, Patent Document 1).

By the way, when hydrocarbon (HC) contained in exhaust gas adheres to the oxidation catalyst, HC poisoning may occur in which the oxidation ability of the oxidation catalyst is reduced. When the oxidation ability of the oxidation catalyst is lowered, the amount of NO to be oxidized is reduced and the NO ₂ ratio of the exhaust gas flowing out from the oxidation catalyst is lowered. In other words, when HC poisoning occurs in the oxidation catalyst, the NOx purification rate of the SCR catalyst decreases as a result. Here, as a method for recovering HC poisoning, a technique is known that promotes the oxidative removal of hydrocarbons adhering to the oxidation catalyst by switching to lean combustion and increasing the oxygen concentration of the exhaust gas flowing into the oxidation catalyst. (For example, refer to Patent Document 2).

Special table 2011-506818 gazette JP 2000-145506 A

  Here, in the above-described prior art, the oxygen concentration of the air-fuel mixture to be combusted is also increased, so that the amount of NOx in the exhaust gas discharged from the internal combustion engine may increase. Therefore, even if the HC poisoning of the oxidation catalyst can be recovered, the amount of NOx discharged to the atmosphere may increase.

  The present invention has been made in view of such circumstances, and is provided in an exhaust passage of an internal combustion engine with an oxidation catalyst and a downstream side of the oxidation catalyst. In an exhaust gas purification apparatus for an internal combustion engine comprising an SCR catalyst that selectively reduces oxides, when HC poisoning occurs in the oxidation catalyst, HC poisoning of the oxidation catalyst is recovered while suppressing NOx release to the atmosphere. The purpose is to do.

In order to solve the above-described problem, an exhaust gas purification apparatus for an internal combustion engine according to the present invention includes:
An oxidation catalyst provided in an exhaust passage of the internal combustion engine and having an oxidation ability;
A selective reduction catalyst that is provided downstream of the oxidation catalyst in the exhaust passage and selectively reduces nitrogen oxides in the exhaust using ammonia as a reducing agent;
A reducing agent supply unit for supplying ammonia or an ammonia precursor to the selective catalytic reduction catalyst via exhaust;
An oxidation catalyst poisoning amount acquisition unit for acquiring an HC poisoning amount of HC poisoning caused by hydrocarbons adhering to the oxidation catalyst;
An oxygen concentration increasing portion for increasing the oxygen concentration of the air-fuel mixture burned in the combustion chamber of the internal combustion engine;
An oxidation catalyst poisoning recovery portion for recovering HC poisoning of the oxidation catalyst by oxidizing and removing hydrocarbons adhering to the oxidation catalyst;
With
The oxidation catalyst poisoning recovery unit has a predetermined ratio of nitrogen dioxide to nitrogen monoxide in the exhaust gas flowing out of the oxidation catalyst due to a decrease in the oxidation ability of the oxidation catalyst due to HC poisoning. When the temperature of the selective catalytic reduction catalyst is equal to or higher than the active temperature of the selective catalytic reduction catalyst, the oxygen concentration is increased more than when the temperature is lower than the active temperature. I did it.

Fuel (HC) contained in the exhaust gas flowing into the oxidation catalyst, that is, hydrocarbon (HC), is oxidized by the oxidation catalyst. Depending on the amount and the catalyst temperature of the oxidation catalyst (hereinafter also referred to as “bed temperature”), the oxidation is performed. It causes HC poisoning that adheres to the catalyst and reduces the oxidation ability of the oxidation catalyst. The oxidation catalyst poisoning amount acquisition unit described above acquires the HC poisoning amount from the amount of HC in the exhaust gas flowing into the oxidation catalyst and the bed temperature of the oxidation catalyst. Here, the oxidation ability of the oxidation catalyst decreases as the HC poisoning amount increases. That is, as the HC poisoning amount increases, the oxidation reaction in which nitrogen dioxide (NO ₂ ) is generated from nitrogen monoxide (NO) in the exhaust is suppressed, so NO _{2 with} respect to NO in the exhaust flowing out from the oxidation catalyst. Ratio (hereinafter also referred to as “NO ₂ ratio”) decreases.

The NOx purification rate of the selective catalytic reduction catalyst (hereinafter, also referred to as “SCR catalyst”) is determined as follows. The NO ₂ ratio of the exhaust gas flowing into the SCR catalyst is a predetermined ratio (hereinafter referred to as “optimal”) in which NOx purification by the SCR catalyst is most accelerated. It is also referred to as a “ratio”.) If it is less than or equal to, it decreases in accordance with a decrease in the NO ₂ ratio of the exhaust. Incidentally, SCR catalysts because they provided downstream of the oxidation catalyst, there is a correlation between the NO ₂ ratio of the exhaust gas flowing out of the NO ₂ ratio and the oxidation catalyst of the exhaust gas flowing into the SCR catalyst. That is, there is a correlation between the NOx purification rate of the SCR catalyst and the NO ₂ ratio of the exhaust gas flowing out from the oxidation catalyst. Therefore, from this correlation, it is possible to determine the NO ₂ ratio of the exhaust gas flowing out from the oxidation catalyst when a desired NOx purification rate (hereinafter also referred to as “target NOx purification rate”) is exhibited by the SCR catalyst. . In the present invention, the NO ₂ ratio can be the above-mentioned “predetermined threshold ratio”. That is, when the NO ₂ ratio of the exhaust gas flowing out from the oxidation catalyst becomes less than the predetermined threshold ratio due to the reduction of the oxidation ability due to HC poisoning, the NOx purification rate of the SCR catalyst becomes less than the target NOx purification rate. As described above, the oxidation ability of the oxidation catalyst decreases according to the amount of HC poisoning. Therefore, from the HC poisoning amount of the oxidation catalyst, it is possible to determine whether or not the oxidation capability of the oxidation catalyst has decreased to a value at which the NO ₂ ratio of the exhaust gas flowing out from the oxidation catalyst becomes less than the predetermined threshold ratio described above. it can.

As described above, according to the present invention, when the NO ₂ ratio of the exhaust gas flowing out from the oxidation catalyst becomes less than the above-mentioned predetermined threshold ratio due to the HC poisoning of the oxidation catalyst, the bed temperature of the SCR catalyst is reduced. When the temperature is equal to or higher than the activation temperature, the oxygen concentration of the air-fuel mixture is increased more than when the bed temperature is lower than the activation temperature. As a result, the oxygen concentration of the exhaust gas flowing into the oxidation catalyst is increased, so that the oxidation removal of HC adhering to the oxidation catalyst is promoted, and the oxidation ability of the oxidation catalyst is restored. As a result, since the NO ₂ ratio of the exhaust gas flowing out from the oxidation catalyst increases, the NOx purification rate of the SCR catalyst can be increased.

Here, when the oxygen concentration of the air-fuel mixture is increased, the amount of NOx discharged from the internal combustion engine may also increase. However, when the oxygen concentration of the air-fuel mixture is increased, the bed temperature of the SCR catalyst is equal to or higher than the activation temperature at which the SCR catalyst is sufficiently activated. Therefore, since the NOx purification ability of the SCR catalyst is maintained, if the NO ₂ ratio of the exhaust gas flowing out to the SCR catalyst increases with the recovery of HC poisoning of the oxidation catalyst, the NOx purification rate of the SCR catalyst also increases. . Therefore, the increase in NOx discharged from the internal combustion engine due to the increase in the oxygen concentration of the air-fuel mixture is purified by the SCR catalyst having an increased NOx purification rate. Therefore, according to the present invention, it becomes possible to recover the HC poisoning of the oxidation catalyst while suppressing the release of NOx to the atmosphere.

  When the exhaust gas purification apparatus according to the present invention further includes an EGR device that recirculates a part of the exhaust gas discharged from the internal combustion engine to the intake passage of the internal combustion engine, the oxygen concentration increasing unit is configured to reduce the exhaust gas from the EGR device. The oxygen concentration of the air-fuel mixture may be increased by decreasing the reflux amount. As a result, the oxygen concentration of the exhaust gas flowing into the oxidation catalyst can be increased more effectively.

  In the present invention, the oxygen concentration increasing unit described above may increase the oxygen concentration of the air-fuel mixture as the bed temperature of the SCR catalyst is higher when the bed temperature of the SCR catalyst is higher than the activation temperature. Good. Here, the higher the bed temperature of the SCR catalyst, the higher the NOx purification ability of the SCR catalyst (however, excluding overheated state). Therefore, the range of increase in the NOx purification rate of the SCR catalyst that increases with the recovery of HC poisoning is larger as the bed temperature of the SCR catalyst is higher. Therefore, according to the present invention, even if the NOx discharged from the internal combustion engine is further increased due to the increase in the oxygen concentration of the air-fuel mixture, the increase is purified by the SCR catalyst having a further increased NOx purification rate. Is done. As a result, it becomes possible to recover HC poisoning of the oxidation catalyst more quickly while suppressing the release of NOx to the atmosphere.

  In addition, an exhaust emission control device according to the present invention is provided between the oxidation catalyst and the SCR catalyst or integrally with the SCR catalyst, and collects particulate matter in the exhaust, and HC poisoning of the filter. A filter poisoning amount acquisition unit that acquires the amount of HC poisoning, a fuel supply unit that supplies fuel to the oxidation catalyst via exhaust, and HC removal of the filter by oxidizing and removing hydrocarbons adhering to the filter And a filter poisoning recovery unit that recovers the poison, the filter poisoning recovery unit is configured such that when the amount of HC poisoning of the filter exceeds a predetermined amount that requires recovery, the bed temperature of the oxidation catalyst is increased. You may make it supply a fuel to this oxidation catalyst when it is more than predetermined temperature. Here, HC poisoning may occur in the filter as well as the HC poisoning of the oxidation catalyst described above. Therefore, the filter poisoning amount acquisition unit described above acquires the HC poisoning amount from the amount of HC in the exhaust gas flowing into the filter and the temperature of the filter. The above-mentioned predetermined temperature may be the bed temperature of the oxidation catalyst necessary for sufficiently oxidizing the supplied fuel.

  According to the present invention, when it is necessary to recover the HC poisoning of the filter, the fuel supplied from the fuel supply unit is more effectively oxidized by the oxidation catalyst. As a result, the temperature of the exhaust gas flowing out from the oxidation catalyst increases, and the temperature of the exhaust gas flowing into the filter increases. As a result, oxidation removal of HC adhering to the filter is promoted, so that HC poisoning of the filter is more effectively recovered.

  In the present invention, the filter poisoning recovery unit described above is configured such that when the HC poisoning amount of the filter is equal to or more than the predetermined amount, the bed temperature of the oxidation catalyst is less than the predetermined temperature. The oxygen concentration of the air-fuel mixture may be increased more than when the temperature is equal to or higher than the predetermined temperature. As a result, the oxygen concentration of the exhaust gas flowing into the oxidation catalyst is increased, whereby the temperature of the exhaust gas flowing out from the oxidation catalyst is raised, and the oxygen concentration of the exhaust gas is increased. As a result, oxidation removal of HC adhering to the filter is promoted, so that the HC poisoning of the filter can be recovered without performing fuel supply by the fuel supply unit.

  According to the present invention, an oxidation catalyst and an SCR catalyst that is provided downstream of the oxidation catalyst and selectively reduces nitrogen oxides in the exhaust gas using ammonia as a reducing agent are provided in the exhaust passage of the internal combustion engine. In the exhaust gas purification apparatus for an internal combustion engine provided, when HC poisoning occurs in the oxidation catalyst, it becomes possible to recover the HC poisoning of the oxidation catalyst while suppressing the release of NOx to the atmosphere.

1 is a diagram illustrating a schematic configuration of an exhaust gas purification apparatus for an internal combustion engine according to a first embodiment. 3 is a flowchart showing a flow of HC poisoning recovery control of an oxidation catalyst according to Embodiment 1. 6 is a time chart showing the transition of each physical quantity when HC poisoning recovery control of the oxidation catalyst according to Example 1 is executed. It is a figure explaining the map used at the time of the update of the HC poisoning amount of the oxidation catalyst which concerns on Example 1. FIG. It is a figure which shows the relationship between the bed temperature in the oxidation catalyst which concerns on Example 1, and HC poisoning amount. It is a figure which shows the relationship between the amount of HC inflow in the oxidation catalyst which concerns on Example 1, and the amount of HC poisoning. 6 is a flowchart showing a flow of HC poisoning recovery control of an oxidation catalyst according to a second embodiment. 10 is a flowchart showing a flow of HC poisoning recovery control of an oxidation catalyst and a filter according to Embodiment 3. It is a fragmentary figure which shows schematic structure of the oxidation catalyst and filter which concern on a modification.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

[Example 1]
First, a first embodiment of the present invention will be described. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied and its exhaust purification device. An internal combustion engine 1 shown in FIG. 1 is a compression ignition type internal combustion engine (diesel engine) for an automobile having a plurality of cylinders.

  The internal combustion engine 1 includes a fuel injection valve 1a that injects fuel into a combustion chamber in a cylinder. An intake passage 2 and an exhaust passage 3 are connected to the internal combustion engine 1. The intake passage 2 is a passage that guides air taken from the atmosphere to the cylinder of the internal combustion engine 1, and a throttle valve 4 that adjusts the amount of air taken into the cylinder of the internal combustion engine 1 is disposed. Further, the exhaust passage 3 is a passage for circulating the exhaust discharged from the cylinder of the internal combustion engine 1.

In the exhaust passage 3, in order from the upstream side, the catalyst casing 5, the first exhaust temperature sensor 6, the reducing agent addition valve 7, the first NOx sensor 8, the selective reduction catalyst (SCR catalyst) 9, the second NOx sensor 10, and the second An exhaust temperature sensor 11 is disposed. The internal combustion engine 1 is also provided with an ECU 100 that is an electronic control unit for controlling the internal combustion engine 1. The fuel injection valve 1a, the throttle valve 4, and the reducing agent addition valve 7 described above are electrically connected to the ECU 100 and controlled by the ECU 100. In addition to the exhaust gas temperature sensor 6 and the NOx sensor described above, the ECU 100 is electrically provided with a crank position sensor 12 that detects the engine speed and an accelerator position sensor 13 that detects the amount of depression of the accelerator pedal by the driver. These output signals are input to the ECU 100. Note that. ECU1
00 estimates the operating state of the internal combustion engine 10 based on the detection values of the crank position sensor 12, the accelerator position sensor 13, and the like.

In the catalyst casing 5, an oxidation catalyst 5a having oxidation ability and a filter 5b for collecting particulate matter (PM) in the exhaust are accommodated. The oxidation catalyst 5a oxidizes unburned fuel, carbon monoxide and the like discharged from the internal combustion engine 1, and suppresses them from being discharged to the atmosphere. Further, the oxidation catalyst 5a oxidizes nitrogen monoxide (NO) contained in the exhaust to generate nitrogen dioxide (NO ₂ ). The first exhaust temperature sensor 6 detects the temperature of the exhaust gas flowing out from the catalyst casing 5. From the detection value of the first exhaust temperature sensor 6, the catalyst temperature (bed temperature) of the oxidation catalyst 5a is estimated. As schematically shown in FIG. 1, the oxidation catalyst 5a is arranged upstream of the filter 5b in the catalyst casing 5, but as long as the oxidation catalyst 5a is arranged upstream of the filter 5b. , Each may be housed in a separate casing.

  The reducing agent addition valve 7 injects urea water into the exhaust gas flowing through the exhaust passage 3 based on a command from the ECU 100, and supplies urea as an ammonia precursor to the SCR catalyst 9. The SCR catalyst 9 purifies NOx in the exhaust gas using ammonia generated from urea as a reducing agent. Here, the ECU 100 detects NOx in the SCR catalyst 9 based on the NOx concentration of the exhaust gas detected by the first NOx sensor 8 disposed on the upstream side of the SCR catalyst 9 and the second NOx sensor 10 disposed on the downstream side. The amount of urea water added by the reducing agent addition valve 7 is controlled so as to be effectively reduced. The reducing agent addition valve 7 may add ammonia water instead of urea water. The second exhaust temperature sensor 11 detects the temperature of the exhaust gas flowing out from the SCR catalyst 9. From the detection value of the second exhaust temperature sensor 11, the bed temperature of the SCR catalyst 9 is estimated.

Here, the NOx purification capacity of the SCR catalyst 9 increases as the bed temperature rises (except when the bed temperature rises excessively). In particular, when the bed temperature of the SCR catalyst 9 is equal to or higher than the activation temperature at which the SCR catalyst 9 is sufficiently activated, the NOx purification ability is sufficiently increased. However, the NOx purification rate actually exhibited by the SCR catalyst 9 (the ratio of the NOx amount purified by the SCR catalyst to the NOx amount flowing into the SCR catalyst) is the NO ₂ ratio of exhaust gas flowing into the SCR catalyst 9 (inside the exhaust gas). Mole ratio of NO ₂ to NO). Specifically, in the selective reduction reaction of NOx using ammonia as a reducing agent by the SCR catalyst 9, the reaction of the reduction reaction 1 represented by the following reaction formula (1) in which NO and NO ₂ react one-to-one. The speed is particularly fast.
NO + NO ₂ + NH ₃ → 2N ₂ + 3H ₂ O (1)
Therefore, as the NO ₂ ratio of the exhaust gas flowing into the SCR catalyst 9 approaches a predetermined ratio (for example, approximately 1. Hereinafter, also referred to as “optimum ratio”) in which the reduction reaction 1 is most promoted, the actual SCR catalyst 9 becomes more actual. The NOx purification rate (hereinafter also simply referred to as “NOx purification rate”) increases.

  The exhaust passage 3 configured as described above is provided with an EGR device 20 that recirculates a part of the exhaust discharged from the internal combustion engine 1 to the intake passage of the internal combustion engine 1. The EGR device 20 includes an EGR passage 21 that communicates the intake passage 2 and the exhaust passage 3, and an EGR valve 22 that adjusts the amount of EGR gas to be recirculated. The EGR valve 22 adjusts the amount of EGR gas based on a command from the electrically connected ECU 100.

By the way, in the exhaust emission control device of the internal combustion engine 1 according to the present embodiment, when the operation of the internal combustion engine 1 continues, hydrocarbon (HC) as unburned fuel adheres to the oxidation catalyst 5a, and the oxidation of the oxidation catalyst 5a. HC poisoning that reduces the ability may occur. More specifically, this HC poisoning is a phenomenon in which the activity of the catalyst is reduced by the HC in the exhaust gas flowing into the oxidation catalyst 5a adhering to active sites such as platinum carried on the oxidation catalyst 5a. is there. Therefore, if the amount of HC adhering to the oxidation catalyst 5a is defined as the HC poisoning amount (hereinafter also simply referred to as “poisoning amount”), the oxidation ability of the oxidation catalyst 5a increases as the poisoning amount increases. Will decline. When the oxidation capability of the oxidation catalyst 5a decreases, the amount of NO ₂ generated by the oxidation of NO by the oxidation catalyst 5a decreases. Here, the exhaust gas discharged from the internal combustion engine 1 usually contains more NO than NO ₂ . Therefore, when the HC poisoning of the oxidation catalyst 5a progresses and the poisoning amount increases, the increase in the NO ₂ ratio due to the action of the oxidation catalyst 5a decreases. That is, as the poisoning amount of the oxidation catalyst 5a increases, the NO ₂ ratio of the exhaust gas flowing out from the oxidation catalyst 5a decreases. As a result, the NO ₂ ratio of the exhaust gas flowing into the SCR catalyst 9 deviates from the above-described optimal ratio, so that the NOx purification rate of the SCR catalyst 9 decreases. Here, in order to sufficiently suppress the release of NOx into the atmosphere, the NOx purification rate of the SCR catalyst 9 is required to be equal to or higher than a desired target NOx purification rate. It is necessary to recover HC poisoning.

  The recovery of the HC poisoning of the oxidation catalyst 5a is performed by oxidizing and removing the HC adhering to the oxidation catalyst 5a. Here, if the temperature of the exhaust gas flowing into the oxidation catalyst 5a is raised by performing after-injection or the like on the fuel injection valve 1a, HC oxidation removal can be promoted. However, the temperature rise of the exhaust gas is not preferable because fuel is consumed. Therefore, a method of promoting the oxidative removal of adhering HC by increasing the oxygen concentration of the exhaust gas flowing into the oxidation catalyst 5a can be considered. Here, the oxygen concentration of the exhaust gas flowing into the oxidation catalyst 5a can be increased by increasing the oxygen concentration of the air-fuel mixture combusted in the internal combustion engine 1. However, this method may increase the amount of NOx in the exhaust discharged from the internal combustion engine 1. Therefore, in the poisoning recovery control of the oxidation catalyst 5a according to the present embodiment, the SCR catalyst 9 is accompanied with the poisoning recovery of the oxidation catalyst 5a so that the increased amount of NOx discharged from the internal combustion engine 1 is purified. The NOx purification rate is also increased. Hereinafter, this HC poisoning recovery control will be described with reference to the drawings.

  FIG. 2 is a flowchart showing a flow of HC poisoning recovery control of the oxidation catalyst 5a according to the present embodiment. This flow is executed by the ECU 100 at predetermined time intervals or as necessary. FIG. 3 is a time chart showing the transition of each physical quantity at the time of executing the recovery control of the oxidation catalyst 5a.

In step S101, the ECU 100 updates Q _{hc_doc} which is the amount of HC poisoning of the oxidation catalyst 5a. _{Q Hc_doc} in this flow, the _{Q Hc_doc} at the end of the previous flow is determined by adding the poisoning amount Delta] Q _{Hc_doc} that occurred in the period Δt from the end of the previous flow to the start of the flow. Here, the ECU 100 obtains ΔQ _{hc_doc} from the bed temperature T _doc of the oxidation catalyst 5a at the time of execution of this flow and the HC inflow amount that is the HC amount contained in the exhaust gas flowing into the oxidation catalyst 5a during Δt. Note that T _doc is estimated from a value detected by the first exhaust temperature sensor 6. Further, the HC inflow amount is estimated from the amount of fuel discharged from the internal combustion engine 1 during Δt. The amount of fuel increases as the amount of fuel injected by the fuel injection valve 1a increases (that is, the engine load increases) and as the amount of EGR gas recirculated by the EGR device 20 increases. Therefore, the ECU 100 acquires the amount of fuel discharged from the internal combustion engine 1 during Δt from a map or calculation model prepared in advance based on the acquired engine speed, fuel injection amount, and EGR gas recirculation amount. When the T _doc and the HC inflow amount are acquired in this manner, the ECU 100 acquires the corresponding ΔQ _{hc_doc} from the map schematically shown in FIG.

Here, FIG. 4 shows a map in which the value of ΔQ _{hc_doc} is stored in association with T _doc and the HC inflow amount. This map is created based on the relationship between T _doc and the poisoning amount of the oxidation catalyst 5a shown in FIG. 5, and the relationship between the HC inflow amount and the poisoning amount shown in FIG. The ECU 100 is prepared in advance.

Here, FIG. 5 is a diagram showing the relationship between T _doc and the poisoning amount of the oxidation catalyst 5a when the HC inflow amount is constant. When T _doc increases, the activity of the oxidation catalyst 5a increases and the oxidation ability increases, so the poisoning amount of the oxidation catalyst 5a decreases. In FIG. 5, when T _doc is equal to or higher than temperature T1, the poisoning amount is a negative value. In this temperature range, the oxidation catalyst 5a has a sufficient oxidation capability, so HC poisoning does not proceed, and if HC poisoning has already occurred, it will be recovered. Means. FIG. 6 is a diagram showing the relationship between the HC inflow amount and the poisoning amount when T _doc is constant. As shown in FIG. 6, when the HC inflow amount increases, the poisoning amount of the oxidation catalyst 5a increases. Then, the map shown in FIG. 4 is created by _{obtaining the} relationship shown in FIG. 5 in an appropriate T _doc range and further finding the relationship shown in FIG. 6 in an appropriate HC inflow range. Incidentally, as shown in FIG. 4, for example, when T _doc is low and the HC inflow amount is large, ΔQ _{hc_doc} becomes large. Further, when T _doc is high and the amount of HC inflow is small, ΔQ _{hc_doc} becomes negative, so that HC poisoning of the oxidation catalyst 5a is recovered.

In step S102, the ECU 100 determines whether or not the Q _{hc_doc} updated in the previous step is equal to or greater than a predetermined determination poisoning amount. This determined poisoning amount is a poisoning amount when the NO ₂ ratio of the exhaust gas flowing out from the oxidation catalyst 5a becomes a predetermined threshold ratio. This threshold ratio is the NO ₂ ratio of the exhaust gas flowing out from the oxidation catalyst 5a corresponding to the target NOx purification rate of the SCR catalyst 9. In other words, when the poisoning amount of the oxidation catalyst 5a is equal to or greater than the determined poisoning amount, the NOx purification rate of the SCR catalyst 9 becomes less than the target NOx purification rate, so that the release of NOx into the atmosphere may not be sufficiently suppressed. There is. Therefore, when an affirmative determination is made in this step, the ECU 100 proceeds to step S103 in order to execute poisoning recovery of the oxidation catalyst 5a. On the other hand, if a negative determination is made in this step, the ECU 100 determines that there is no need to increase the NOx purification rate of the SCR catalyst 9, and ends this flow. For example, when this flow is executed within a period from time t0 to t1 in FIG. 3, that is, within a certain period immediately after the operation of the internal combustion engine 1 is started in a state where the poisoning amount of the oxidation catalyst 5a is low. Since the HC poisoning of the oxidation catalyst 5a has not progressed, this flow is terminated without executing the recovery process.

  In step S103, the ECU 100 determines whether or not the bed temperature of the SCR catalyst 9 in the present flow is equal to or higher than the activity determination temperature of the SCR catalyst 9. The bed temperature of the SCR catalyst 9 is estimated from the detection value of the second exhaust temperature sensor 11. The activity determination temperature of the SCR catalyst 9 is a threshold temperature when the SCR catalyst 9 exhibits a sufficient NOx purification ability, and may be prepared in advance by experiments or the like. This activity determination temperature corresponds to the activation temperature in the present invention. If a negative determination is made in this step, this flow ends. For example, during the period from time t1 to time t2 in FIG. 3, the poisoning amount of the oxidation catalyst 5a exceeds the determined poisoning amount, but the bed temperature of the SCR catalyst 9 does not reach the activity determination temperature. In such a case, it is not preferable that the NOx amount of the exhaust gas discharged from the internal combustion engine 1 increases. Therefore, the ECU 100 ends this flow without executing the HC poisoning recovery process. On the other hand, if an affirmative determination is made in this step, it is determined that the NOx purification ability of the SCR catalyst 9 is sufficiently high, and the ECU 100 proceeds to step S104.

In step S104, the ECU 100 determines an increase amount of the oxygen concentration of the air-fuel mixture. This increase amount is an amount necessary for making the oxygen concentration of the exhaust gas flowing into the oxidation catalyst 5a sufficient to restore poisoning. The ECU 100 determines the amount of increase from a map or model prepared in advance based on _{Qhc_doc} acquired in step S101, the operating state of the internal combustion engine 1, and the like.

In step S105, the ECU 100 decreases the amount of EGR gas recirculated by the EGR device 20 so that the oxygen concentration of the air-fuel mixture increases by the increase amount determined in the previous step. Note that the decrease amount of the EGR gas corresponding to the increase amount of the oxygen concentration may be acquired from a map or model prepared in advance based on the operating state of the internal combustion engine 1 or the like. When the EGR gas amount is decreased, the NOx concentration (SCR catalyst inlet concentration) of the exhaust gas flowing into the SCR catalyst 9 temporarily increases as shown in the period from time t2 to t3 in FIG. However, as the poisoning amount of the oxidation catalyst 5a decreases, the NOx purification rate of the SCR catalyst 9 increases. As a result, the NOx concentration (tail pipe concentration) of the exhaust gas flowing out from the SCR catalyst 9 is lowered, so that release of unpurified NOx into the atmosphere is sufficiently suppressed.

In step S106, the ECU 100 _acquires Q _{hc_doc} after the decrease in the EGR gas amount by the same method as the processing in step S101.

In step S107, ECU 100 determines whether or not Q _{hc_doc} updated in the previous step is less than a predetermined end determination poisoning amount for determining the end of the HC poisoning recovery process. This end determination poisoning amount is a poisoning amount set to determine whether or not the HC poisoning of the oxidation catalyst 5a has been sufficiently recovered. If an affirmative determination is made in this step, it is determined that the HC poisoning of the oxidation catalyst 5a has been sufficiently recovered, and this flow is ended. On the other hand, when a negative determination is made, it is determined that it is necessary to additionally perform the HC poisoning recovery process, and the process from step S103 is executed again.

  In this embodiment, the ECU 100 that updates the HC poisoning amount of the oxidation catalyst 5a in step S101 corresponds to the oxidation catalyst poisoning amount acquisition unit in the present invention. In step S105, the ECU 100 that increases the oxygen concentration of the air-fuel mixture by reducing the amount of EGR gas corresponds to the oxygen concentration increasing portion in the present invention. And ECU100 which performs this flow is equivalent to the oxidation catalyst poisoning recovery part in the present invention.

  As described above, according to the present embodiment, when HC poisoning occurs in the oxidation catalyst 5a, the poisoning recovery is executed by increasing the oxygen concentration of the air-fuel mixture. In this case, even if the amount of NOx discharged from the internal combustion engine 1 increases, the increase is purified by the SCR catalyst 9 whose NOx purification rate has further increased. As a result, it becomes possible to recover the HC poisoning of the oxidation catalyst 5a while suppressing the release of NOx to the atmosphere.

[Example 2]
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 7 is a flowchart showing a flow of HC poisoning recovery control of the oxidation catalyst 5a executed in the present embodiment. In the recovery control according to the present embodiment, when the necessity of recovery of poisoning of the oxidation catalyst 5a is higher, that is, when the amount of poisoning of the oxidation catalyst 5a is further increased, poisoning recovery is performed. In order to execute it more quickly, early poisoning recovery control is executed in which the oxygen concentration of the air-fuel mixture is increased as the bed temperature of the SCR catalyst 9 is higher. The flow of this early poisoning recovery control is different from the flow of the first embodiment described above in that steps S204 to S207 are executed after step S103. Therefore, in the following description, description of the same configuration as that of the first embodiment will be omitted. In the following, the recovery control executed in the first embodiment is referred to as normal poisoning recovery control.

If it is determined in step S103 that the bed temperature of the SCR catalyst 9 is _equal to or higher than the activation determination temperature, the ECU 100 determines in step S204 that _{Qhc_doc} updated in step S101 is equal to or greater than a predetermined second determination poisoning amount. It is determined whether or not. This second determination poisoning amount is a value larger than the determination poisoning amount used in step S102 described above, and the poisoning amount of the oxidation catalyst 5a is increased, so that the oxidation catalyst 5a is poisoned. This value is set to determine whether or not the necessity for recovery is higher. That is, if the negative determination is made in step S103 of the flow executed before this flow, the poisoning amount of the oxidation catalyst 5a exceeds the determined poisoning amount (that is, affirmative in step S102). Even in the case of determination), there is a possibility that the poisoning recovery of the oxidation catalyst 5a has not been executed because the bed temperature of the SCR catalyst 9 is lower than the activity determination temperature. Therefore, in this flow, when it is determined that the bed temperature of the SCR catalyst 9 is equal to or higher than the activity determination temperature, it is possible that the poisoning amount of the oxidation catalyst 5a has increased from the normal time. When the poisoning amount is further increased, it is necessary to recover the poisoning of the oxidation catalyst 5a more quickly. Therefore, if an affirmative determination is made in this step, the ECU 100 proceeds to step S205 in order to perform early poisoning recovery control. On the other hand, if a negative determination is made in this step, there is no need to quickly recover the poisoning of the oxidation catalyst 5a, so the ECU 100 proceeds to step S104 and continues the normal poisoning recovery control.

  In step S205, the ECU 100 determines whether or not the bed temperature of the SCR catalyst 9 is equal to or higher than a predetermined second activity determination temperature. This second activity determination temperature is higher than the activity determination temperature used in step S103 described above. That is, in the early poisoning recovery control, the oxygen concentration of the air-fuel mixture is further increased as compared with the normal poisoning recovery control, and therefore it is determined whether or not the activity of the SCR catalyst 9 is sufficient. If an affirmative determination is made in this step, the ECU 100 determines that the activity of the SCR catalyst 9 is sufficiently high, and proceeds to step S206. On the other hand, if a negative determination is made in this step, the ECU 100 proceeds to step S104 and returns to normal poisoning recovery control.

  In step S206, the ECU 100 determines whether or not the oxygen concentration of the air-fuel mixture during execution of this flow is less than a predetermined determination oxygen concentration. This determination oxygen concentration is a value that is set to determine whether or not the oxygen concentration of the exhaust at the time of execution of this flow can be increased with an increase that is larger than the increase in the normal poisoning recovery control. It is. That is, in the early poisoning recovery control, the oxygen concentration of the air-fuel mixture is increased as compared with the time when the normal poisoning recovery control is executed. The Therefore, the ECU 100 acquires the oxygen concentration of the air-fuel mixture in this flow from the operating state of the internal combustion engine 1, the recirculation amount (or EGR gas rate) of the EGR gas, and compares it with the above-described determination oxygen concentration. If an affirmative determination is made in this step, the ECU 100 determines that the oxygen concentration can be further increased by further reducing the EGR gas, and proceeds to step S207. On the other hand, if a negative determination is made in this step, the ECU 100 proceeds to step S104 and returns to normal poisoning recovery control.

In step S207, the ECU 100 determines a second increase amount that is an increase amount of the oxygen concentration of the air-fuel mixture. Here, this increase amount is an amount larger than the increase amount determined in step S104 of the normal poisoning recovery control. That is, in the early poisoning recovery control, the oxygen concentration of the air-fuel mixture increases as the bed temperature of the SCR catalyst 9 increases. Therefore, the ECU 100 determines the second increase amount from a map or model prepared in advance based on the bed temperature of the SCR catalyst 9 acquired in the previous step, Q _{hc_doc} , the operating state of the internal combustion engine 1, and the like. When the second increase amount is determined, the ECU 100 proceeds to step S105 and decreases the EGR gas amount so that the oxygen concentration of the air-fuel mixture increases by the second increase amount.

  As described above, according to this embodiment, when it is necessary to quickly recover the HC poisoning of the oxidation catalyst 5a, the oxygen concentration of the air-fuel mixture increases as the bed temperature of the SCR catalyst 9 increases. Here, even if the amount of NOx discharged from the internal combustion engine 1 is further increased due to the increase in the oxygen concentration of the air-fuel mixture, this increase is purified by the SCR catalyst 9 whose NOx purification rate is further increased. . As a result, it becomes possible to recover HC poisoning of the oxidation catalyst more quickly while suppressing the release of NOx to the atmosphere.

[Example 3]
Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 8 is a flowchart showing a flow of HC poisoning recovery control of the oxidation catalyst 5a and the filter 5b executed in the present embodiment. In the recovery control according to the present embodiment, even if the oxidation catalyst 5a does not need to be poisoned, if the filter 5b needs to do so, the poisoning recovery process of the oxidation catalyst 5a or the filter 5b It differs from the poisoning recovery control according to the first embodiment described above in that the poison recovery process is executed. Therefore, in the following description, description of the same configuration as that of the first embodiment will be omitted. Also, description of the same steps as those in the flow according to the first embodiment shown in FIG. 2 is omitted.

If a negative determination is made in step S102, the ECU 100 determines that it is not necessary to increase the NOx purification rate of the SCR catalyst 9 by performing poisoning recovery of the oxidation catalyst 5a, and proceeds to step S303. In step S303, the ECU 100 updates Q _{hc_dpf} , which is the amount of HC poisoning occurring in the filter 5b. Q _{hc_dpf} in this flow is obtained by adding the poisoning amount ΔQ _{hc_dpf} generated in the period Δt ′ from the acquisition of the relevant Q _{hc_dpf} to the execution time of this flow to the latest Q _{hc_dpf} acquired in the past flow. Desired. Here, in the same way as the method of obtaining ΔQ _{hc_doc} described above, the ECU 100 determines from the temperature of the filter 5b at the time of execution of this flow and the filter HC inflow amount that is the amount of HC contained in the exhaust gas flowing into the filter 5b during Δt ′. ΔQ _{hc_dpf} is acquired. In the present embodiment, the bed temperature T _doc of the oxidation catalyst 5a is used as the temperature of the filter 5b. Further, the filter HC inflow amount can be obtained by correcting the value acquired by the same method or the same method as the HC inflow amount related to the oxidation catalyst 5a described above. Further, in the present embodiment, a map is prepared in which the value of ΔQ _{hc_dpf} is stored in association with T _doc and the filter HC inflow amount. Similar to the map relating to ΔQ _{hc_doc} shown in FIG. 4, the map is created based on the relationship between T _doc and the poisoning amount of the filter 5b and the relationship between the filter HC inflow amount and the poisoning amount. Is.

In step S304, the ECU 100 determines whether or not the updated Q _{hc_dpf} is greater than or _equal to a predetermined third determination poisoning amount. The third determination poisoning amount is a threshold value for determining whether or not it is necessary to execute the poisoning recovery of the filter 5b, and is obtained in advance by an experiment or the like. If a negative determination is made in this step, the ECU 100 determines that it is not necessary to execute the poisoning recovery process of the filter 5b, and ends this flow. On the other hand, if an affirmative determination is made in this step, the ECU 100 proceeds to step S305.

In step S305, the ECU 100 determines whether or not the bed temperature T _doc of the oxidation catalyst 5a in the present flow is _equal to or higher than a predetermined third activity determination temperature. Here, this third activity determination temperature determines whether or not the oxidation capability of the oxidation catalyst 5a has increased to such an extent that the fuel supplied from the fuel injection valve 1a by after injection or the like can be sufficiently oxidized. For the threshold temperature. If a negative determination is made in this step, the ECU 100 determines that the temperature of the exhaust gas flowing into the filter 5b cannot be increased by adding fuel from the fuel injection valve 1a, and returns to the normal poisoning recovery control described above. To do. Here, also in the normal poisoning recovery control, the exhaust gas flowing out from the oxidation catalyst 5a (that is, the exhaust gas flowing into the filter 5b) is heated by oxidative removal of HC adhering to the oxidation catalyst 5a. The HC poisoning of the filter 5b is recovered. Further, when the oxidation catalyst 5a is poisoned in a low amount, oxygen is not consumed in the oxidation catalyst 5a, so that the oxygen concentration of the exhaust gas flowing into the filter 5b is increased, so that the HC poisoning of the filter 5b is recovered. The On the other hand, if a positive determination is made in this step, the ECU 100 proceeds to step S306.

In step S306, the ECU 100 executes fuel supply by the fuel injection valve 1a. The amount of fuel to be supplied may be acquired from a map or model prepared in advance based on T _doc or Q _{hc_dpf} . When the fuel supplied in this step flows into the oxidation catalyst 5a, the exhaust temperature rises because the fuel is oxidized by the oxidation catalyst 5a. When the exhaust gas whose temperature has increased in this way flows out of the oxidation catalyst 5a and flows into the filter 5b, the HC adhering to the filter 5b is oxidized, so that the HC poisoning of the filter 5b is recovered.

In step S307, the ECU 100 _{updates Qhc_dpf} after the fuel supply in the previous step by the same method as the process in step S303.

In step S308, the ECU 100 determines whether or not the Q _{hc_dpf} updated in the previous step is less than a predetermined second end determination poisoning amount for determining the end of the poisoning recovery process of the filter 5b. If an affirmative determination is made in this step, it is determined that the HC poisoning of the filter 5b has been sufficiently recovered, and this flow is ended. On the other hand, if a negative determination is made, it is determined that it is necessary to additionally execute the HC poisoning recovery process, and the process from step S304 is executed again.

  In this embodiment, the ECU 100 that updates the HC poisoning amount of the filter 5b in step S303 corresponds to the filter poisoning amount acquisition unit in the present invention. In step S306, the fuel injection valve 1a that supplies fuel to the oxidation catalyst 5a via exhaust corresponds to the fuel supply unit in the present invention. And ECU100 which performs this flow is equivalent to a filter poisoning recovery part in the present invention.

  As described above, according to the present embodiment, when the HC poisoning to the extent that the filter 5b needs to be recovered has occurred, the oxygen concentration of the fuel supply or the inflowing exhaust gas is increased, so that the filter 5b HC poisoning is restored. As a result, the HC poisoning of the filter can be more reliably recovered by a method corresponding to the bed temperature of the oxidation catalyst 5a.

[Modification]
In the modification according to the present invention, an SCRF catalyst in which an SCR catalyst and a filter for collecting PM in exhaust gas are integrally provided is used instead of the filter 5b and the SCR catalyst 9 in the above-described embodiment. . Here, as an aspect in which the SCR catalyst and the filter are integrally provided, for example, an aspect in which the SCR catalyst is supported on the particulate filter is conceivable. The present modification is different from the exhaust purification apparatus according to the above-described embodiment in that the oxidation catalyst and the SCRF catalyst are accommodated in one casing provided in the exhaust passage 3. Therefore, in the following, description of the same configuration as that of the above-described embodiment is omitted.

  FIG. 9 is a partial view showing a part of the exhaust passage 3 of the exhaust emission control device according to this modification. As shown in FIG. 9, an oxidation catalyst 5a is provided on the upstream side in the casing 5c, and an SCRF catalyst 9a in which an SCR catalyst and a filter are integrally provided is provided on the downstream side of the oxidation catalyst 5a. The reducing agent addition valve 7 is provided between the oxidation catalyst 5a and the SCRF catalyst 9a. As illustrated in FIG. 9, the first exhaust temperature sensor 6 is provided on the downstream side of the oxidation catalyst 5a, and the second exhaust temperature sensor 11 is provided on the downstream side of the SCRF catalyst 9a. Further, as illustrated in FIG. 9, the first NOx sensor 8 and the second NOx sensor 10 are disposed on the upstream side and the downstream side of the SCRF catalyst 9a, respectively.

Also in the exhaust gas purification apparatus for an internal combustion engine according to this modification, the poisoning recovery control of the oxidation catalyst 5a and the poisoning recovery control of the SCRF catalyst 9a are executed by the same method as described in the first to third embodiments. The As a result, the same effects as in the above embodiment are achieved. In particular, in this modification, since the interval between the oxidation catalyst 5a and the SCRF catalyst 9a is smaller than the interval between the oxidation catalyst 5a and the SCR catalyst 9 in the above-described embodiment, HC poisoning occurs in the oxidation catalyst 5a. In such a state, the SCRF catalyst 9a is likely to reach the activation temperature. Therefore, in this modified example, the chance of performing poisoning recovery control of the oxidation catalyst 5a is increased, and NOx discharged from the internal combustion engine 1 is more effectively purified. As a result, it becomes possible to more effectively execute the suppression of NOx release and the recovery of HC poisoning of the oxidation catalyst 5a.

1 Internal combustion engine 3 Exhaust passage 5a Oxidation catalyst 5b Filter 9 SCR catalyst 20 EGR device 100 ECU

Claims (5)

An oxidation catalyst provided in an exhaust passage of the internal combustion engine and having an oxidation ability;
A selective reduction catalyst that is provided downstream of the oxidation catalyst in the exhaust passage and selectively reduces nitrogen oxides in the exhaust using ammonia as a reducing agent;
A reducing agent supply unit for supplying ammonia or an ammonia precursor to the selective catalytic reduction catalyst via exhaust;
An oxidation catalyst poisoning amount acquisition unit for acquiring an HC poisoning amount of HC poisoning caused by hydrocarbons adhering to the oxidation catalyst;
An oxygen concentration increasing portion for increasing the oxygen concentration of the air-fuel mixture burned in the combustion chamber of the internal combustion engine;
An oxidation catalyst poisoning recovery portion for recovering HC poisoning of the oxidation catalyst by oxidizing and removing hydrocarbons adhering to the oxidation catalyst;
With
The oxidation catalyst poisoning recovery unit has a predetermined ratio of nitrogen dioxide to nitrogen monoxide in the exhaust gas flowing out of the oxidation catalyst due to a decrease in the oxidation ability of the oxidation catalyst due to HC poisoning. When the temperature of the selective catalytic reduction catalyst is equal to or higher than the active temperature of the selective catalytic reduction catalyst, the oxygen concentration is increased more than when the temperature is lower than the active temperature. An exhaust purification device for an internal combustion engine. In claim 1,
An EGR device for recirculating a part of the exhaust discharged from the internal combustion engine to the intake passage of the internal combustion engine;
The oxygen concentration increasing unit increases the oxygen concentration by decreasing an exhaust gas recirculation amount by the EGR device. In claim 1 or 2,
The oxygen concentration increasing unit increases the oxygen concentration as the temperature of the selective catalytic reduction catalyst increases. In any one of Claims 1-3,
A filter that is provided between the oxidation catalyst and the selective reduction catalyst or integrated with the selective reduction catalyst and collects particulate matter in the exhaust;
A filter poisoning amount acquisition unit for acquiring an HC poisoning amount of HC poisoning caused by hydrocarbons adhering to the filter;
A fuel supply section for supplying fuel to the oxidation catalyst via exhaust;
A filter poisoning recovery unit that recovers HC poisoning of the filter by oxidizing and removing hydrocarbons adhering to the filter;
Further comprising
The filter poisoning recovery unit supplies fuel to the oxidation catalyst when the temperature of the oxidation catalyst is equal to or higher than a predetermined temperature when the HC poisoning amount of the filter is equal to or higher than a predetermined amount that needs to be recovered. An exhaust purification device for an internal combustion engine. In claim 4,
The filter poisoning recovery unit, when the HC poisoning amount of the filter is equal to or higher than the predetermined amount, when the temperature of the oxidation catalyst is lower than the predetermined temperature, than when the temperature is higher than the predetermined temperature. An exhaust purification device for an internal combustion engine that increases the oxygen concentration.

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