JP5983438B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

2. Description of the Related Art Conventionally, as an exhaust gas purification device provided in an exhaust passage of an internal combustion engine, a filter that carries a selective reduction type NOx catalyst (hereinafter also referred to as “SCR catalyst”) that selectively reduces NOx in exhaust gas is supported. It has been developed (see, for example, Patent Document 1). The filter collects particulate matter (hereinafter referred to as “PM”) in the exhaust. The SCR catalyst reduces NOx in the exhaust gas using ammonia (NH ₃ ) as a reducing agent. Hereinafter, such a filter carrying the SCR catalyst is referred to as “SCRF”. By adopting SCRF as the exhaust purification device, it is possible to make the exhaust purification device more compact and improve its mountability than when the filter and the SCR catalyst are separately provided in the exhaust passage. Further, by adopting SCRF, it becomes possible to arrange the SCR catalyst on the upstream side in the exhaust passage, so that the SCR catalyst is easily heated by the heat of the exhaust, and thus the warm-up property of the SCR catalyst is improved. It is possible to improve the NOx purification rate in the SCR catalyst.

  Here, the collected PM is deposited on the SCRF. For this reason, in an exhaust purification device equipped with SCRF, it is necessary to perform a filter regeneration process for oxidizing and removing the deposited PM. This filter regeneration process is realized by supplying fuel to an oxidation catalyst having an oxidation function provided in an exhaust passage upstream of SCRF. When the fuel is oxidized in the oxidation catalyst, the exhaust gas flowing into the SCRF is heated by the oxidation heat, and the temperature of the SCRF can be raised to the filter regeneration temperature that promotes the oxidation of the collected PM.

Special table 2007-501353 gazette JP 2011-43160 A JP 2009-228618 A JP 2009-7982 A

  By supplying ammonia or an ammonia precursor to the SCRF, NOx in the exhaust gas is selectively reduced using ammonia as a reducing agent in the SCR catalyst supported on the SCRF. Although ammonia is used for NOx reduction purification as described above, NOx may be generated when the ammonia is oxidized. Therefore, in SCRF, it is difficult to support a catalyst having high oxidation ability. . For this reason, the oxidation capability of the SCR catalyst supported by the SCRF having the filter function is generally very low. As a result, the capability of oxidizing and removing PM collected by the SCRF must naturally be lowered. .

  In particular, when the exhaust temperature discharged from the internal combustion engine is low, for example, when performing lean combustion in a diesel engine or a gasoline engine, the influence due to the relative low oxidation capacity in SCRF becomes significant, A relatively long time is required for the filter regeneration process for oxidizing and removing the PM collected there.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to realize rapid filter regeneration processing in an exhaust purification device for an internal combustion engine having SCRF.

  In the present invention, in order to solve the above-described problem, when performing filter regeneration processing on SCRF (a filter carrying an SCR catalyst), a certain amount of fuel component (SOF) is fed into SCRF to capture it in SCRF. A configuration is adopted in which combustion of the collected PM is promoted and a decrease in the NOx purification rate due to the SCR catalyst caused by the fuel component adsorbed on the SCRF is compensated by an increase in the EGR gas amount. By adopting such a configuration, it is possible to suitably achieve both a reduction in the filter regeneration processing time by promoting the combustion of PM in the SCRF and the maintenance of the NOx purification rate as the exhaust purification device.

  Specifically, the present invention provides an oxidation catalyst having an oxidation function provided in an exhaust passage of an internal combustion engine, and a fuel supply unit that supplies fuel components to the oxidation catalyst via exhaust gas flowing into the oxidation catalyst And a filter that is provided in an exhaust passage downstream of the oxidation catalyst and collects particulate matter in the exhaust, and carries a selective reduction type NOx catalyst that selectively reduces NOx in the exhaust using ammonia as a reducing agent. An EGR that recirculates part of the exhaust from the internal combustion engine to the intake system, an ammonia supply unit that supplies ammonia or an ammonia precursor to the filter via exhaust flowing into the filter A predetermined filter regeneration in which oxidation of the particulate matter whose temperature is collected by the filter is promoted by supplying fuel to the oxidation catalyst by the apparatus and the fuel supply unit Allowed to warm to time, comprising a filter regeneration processing unit that performs filter regeneration process to oxidize and remove particulate matter, and an exhaust purification device for an internal combustion engine. When the filter regeneration processing is performed by the filter regeneration processing unit, the amount of EGR gas recirculated to the intake system by the EGR device is increased compared to the amount of EGR gas when the filter regeneration processing is not performed. In this state, the fuel supply unit is configured to supply a predetermined amount of fuel component larger than the amount that can be oxidized by the oxidation catalyst during the filter regeneration process.

  The exhaust emission control apparatus according to the present invention is configured to mainly perform reduction removal of NOx in exhaust gas and collection of PM in exhaust gas by a configuration in which a so-called SCRF filter is provided in the exhaust passage. With respect to the former, ammonia or NOx supplied to the exhaust gas by the ammonia supply unit causes a selective reduction reaction between ammonia and NOx in the selective reduction type NOx catalyst supported on the filter, thereby purifying NOx. On the other hand, for the latter, PM in the exhaust is collected by the filter and the release to the outside is suppressed, but if the collected amount exceeds a predetermined amount, it becomes difficult to maintain the function of the filter, Filter regeneration processing is performed by the filter regeneration processing unit. In the filter regeneration process, the fuel supplied by the fuel supply unit is oxidized by the oxidation catalyst and the temperature of the exhaust gas is raised, and the temperature of the filter located downstream is raised to a predetermined filter regeneration temperature and collected. It promotes the oxidation of PM.

  Here, in the exhaust purification device, when the filter regeneration process is performed, the temperature of the filter is increased while the EGR gas amount by the EGR device is increased compared to the EGR gas amount when the filter regeneration process is not performed. The fuel supply by the fuel supply unit is performed so as to supply a predetermined amount of fuel component that is greater than the amount that can be oxidized by the oxidation catalyst during the filter regeneration process. That is, by increasing the amount of EGR gas during the period during which the filter regeneration process is performed, fuel supply exceeding the oxidation capacity of the oxidation catalyst can be achieved while the amount of NOx contained in the exhaust from the internal combustion engine is temporarily reduced. Done. When a predetermined amount of fuel component exceeding the oxidation capability of the oxidation catalyst is supplied, as a result, a part of the fuel component passes through the oxidation catalyst and is sent to a filter located downstream thereof. Then, the fuel component that has flowed into the filter is adsorbed in the SCRF filter at a location where ammonia as a reducing agent is preferably adsorbed from the viewpoint of NOx purification. As a result, the NOx reduction reaction with ammonia in the filter is hindered, so the NOx purification rate by the filter decreases. On the other hand, PM is included in the fuel component in the process of the filter regeneration process, and PM This improves the oxidation efficiency.

  Accordingly, by supplying fuel components exceeding the oxidation capacity of the oxidation catalyst under the temporary increase in EGR gas as described above, the reduction in NOx reduction purification by the selective reduction type NOx catalyst carried on the filter is reduced. It is possible to shorten the time required for the oxidation removal of the collected PM in the filter as the SCRF, that is, the filter regeneration process. The present invention that can improve the oxidation efficiency of PM trapped in the SCRF that has to carry a catalyst having a relatively low oxidation ability from the viewpoint of suppressing oxidation of ammonia has not been solved by the prior art. It solves the problem and is considered extremely useful. The predetermined amount of the fuel component supplied during the filter regeneration process is preferably an amount that provides a suitable state of PM oxidation efficiency by the fuel component adsorbed on the filter. That is, if the amount of the fuel component adsorbed on the filter is too small, it is difficult to efficiently remove the PM by oxidation. On the other hand, if the amount of the fuel component is too large, the filter will be in a poisoned state. For example, it is preferable that the ratio of the amount of the fuel component to the amount of PM collected by the filter is set to a suitable value.

  In the present invention, the fuel component supplied to the SCRF may be a fuel of an internal combustion engine, or may be a fuel lightened by exposure to heat in the internal combustion engine. The amount of fuel component supplied to the SCRF is determined from the viewpoint of supplying energy required for oxidation by the oxidation catalyst and oxidation of PM by the SCRF.

  Here, in the exhaust gas purification apparatus, the increase in the EGR gas amount during the filter regeneration process is in accordance with the decrease in the NOx purification rate in the filter that is caused by supplying the predetermined amount of fuel component. It may be set. As described above, although the oxidation efficiency of PM is improved by the fuel component adsorbed on the filter through the oxidation catalyst, the NOx reduction reaction by the selective reduction type NOx catalyst supported on the filter is inhibited, and the NOx purification is thereby caused. The rate (reduction rate) decreases. Therefore, in order to compensate for the decrease in the NOx purification rate, an increase in the EGR gas amount is set, so that the NOx purification rate of the entire exhaust purification device can be suitably maintained. In addition, by setting the amount of increase in the EGR gas amount in this way, the influence due to the temporary increase in the EGR gas amount, for example, the influence due to the decrease in the combustion temperature, the decrease in the oxygen concentration at the time of combustion, etc. Can be suppressed.

  In the exhaust gas purification apparatus described above, when the filter regeneration processing is performed by the filter regeneration processing unit, the fuel supply unit is located upstream of the oxidation catalyst in a state where the EGR gas amount is increased by the EGR device. At least one of fuel supply to the exhaust gas by a fuel supply valve provided in the exhaust passage on the side and rich combustion that enriches the exhaust air-fuel ratio by controlling the combustion state in the internal combustion engine, A fixed amount of fuel component may be supplied. When the fuel component is supplied by the fuel supply by the fuel supply valve, the fuel supplied to the exhaust is not exposed to the combustion atmosphere, and therefore, generally the heavy fuel component is adsorbed to the filter. . On the other hand, in the fuel supply by rich combustion, generally, a light fuel component exposed to a combustion atmosphere is supplied to the filter. By making it possible to supply fuel components having different properties in this way, it is possible to realize a suitable supply of fuel components according to the oxidation efficiency of PM collected by the filter and the combustion conditions in the internal combustion engine.

  For example, the fuel supply unit may supply the predetermined amount of the fuel component by supplying the fuel component by the fuel supply valve after supplying the fuel component by the rich combustion. By supplying the fuel component in this way, it is possible to send a light fuel component to the filter and form a situation in which PM is easily oxidized, and then send a heavy fuel component. As a result, the oxidation efficiency of PM collected by the filter can be improved, and the time required for the filter regeneration process can be shortened.

  Further, as another method for supplying a predetermined amount of fuel component by the fuel supply unit, the fuel supply unit has a case in which the value of the predetermined amount exceeds a smoke generation threshold that can cause smoke when the rich combustion is performed. Alternatively, the fuel component may be supplied by the fuel supply valve without supplying the fuel component by the rich combustion. According to the supply of fuel components by rich combustion, light fuel components can be sent to the filter, so it is expected to improve the oxidation efficiency of PM. On the other hand, supply of fuel components through combustion of the internal combustion engine Therefore, there is a concern about the generation of smoke when the supply amount increases. Therefore, if it is necessary to supply a fuel component that is expected to generate smoke, that is, an amount that exceeds the smoke generation threshold, for the filter regeneration process, supply of the fuel component by rich combustion By performing the supply by the fuel supply valve without performing the above, it is possible to suppress the generation of smoke.

  Here, in the exhaust gas purification apparatus described above, the predetermined amount of fuel component may be increased as the amount of particulate matter that is oxidized and removed by the filter regeneration processing unit increases. Thereby, the oxidation removal of PM collected by the filter can be performed effectively. Further, regarding the increase limit of the fuel component supplied for the filter regeneration process, the predetermined amount of the fuel component may be increased up to an amount that can oxidize the particulate matter in the filter during the filter regeneration process. Good. By setting the increase limit of the fuel component in this way, it is possible to suppress the influence caused by the excessive supply of the fuel component, for example, the decrease in the oxidation efficiency of PM due to fuel poisoning or the release of the fuel component to the outside. it can.

  In the exhaust gas purification apparatus described above, the predetermined amount of fuel component may be set to be smaller as the air-fuel ratio of the exhaust gas flowing into the filter is the leaner air-fuel ratio. This is because, as the exhaust air-fuel ratio is the leaner air-fuel ratio, more oxygen is supplied to the filter, so that it is possible to favorably maintain the PM oxidation efficiency with fewer fuel components. .

  According to the present invention, rapid filter regeneration processing can be realized in an exhaust gas purification apparatus for an internal combustion engine having SCRF.

It is a figure showing a schematic structure of an exhaust-air-purification device of an internal-combustion engine concerning the present invention. 3 is a first flowchart regarding filter regeneration processing control executed in the exhaust gas purification apparatus for an internal combustion engine according to the present invention. FIG. 3 is a diagram for explaining a determination process of the supply amount with respect to the supply amount of the fuel component calculated by the filter regeneration processing control shown in FIG. 2. FIG. 3 is a first diagram for explaining a determination process of an increase amount of EGR gas calculated by the filter regeneration processing control shown in FIG. 2. FIG. 6 is a second diagram for explaining a determination process of the increase amount of the EGR gas calculated by the filter regeneration process control shown in FIG. 2. It is a 2nd flowchart regarding the filter regeneration process control performed in the exhaust gas purification apparatus of the internal combustion engine which concerns on this invention. 6 is a third flowchart regarding filter regeneration processing control executed in the exhaust gas purification apparatus for an internal combustion engine according to the present invention.

  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.

  An embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described with reference to the drawings attached to the present specification. FIG. 1 is a diagram showing a schematic configuration of an exhaust system and a part of an intake system of an internal combustion engine according to the present embodiment. The internal combustion engine 1 is a diesel engine for driving a vehicle. However, the internal combustion engine according to the present invention is not limited to a diesel engine, and may be a gasoline engine or the like.

  An intake passage 15 and an exhaust passage 2 are connected to the internal combustion engine 1. An air flow meter 16 and a throttle valve 17 are provided in the intake passage 15. The air flow meter 16 detects the intake air amount of the internal combustion engine 1. The throttle valve 17 adjusts the intake air amount of the internal combustion engine 1.

  In the exhaust passage 2, a selective reduction NOx catalyst (hereinafter simply referred to as “SCR catalyst”) that selectively reduces NOx in the exhaust using ammonia as a reducing agent collects particulate matter (PM) in the exhaust. SCRF4 formed by being supported by a wall flow type filter is provided. Then, in order to generate ammonia that acts as a reducing agent in the SCR catalyst supported on the SCRF 4, urea water that is a precursor of ammonia stored in the urea tank 8 is located upstream of the SCRF 4. It is supplied into the exhaust by a valve 7. The urea water supplied from the supply valve 7 is hydrolyzed by the heat of the exhaust to generate ammonia, and the ammonia is adsorbed on the SCR catalyst supported on the SCRF 4, thereby reducing the ammonia and NOx in the exhaust. And NOx purification is performed. In the present embodiment, urea water is supplied from the supply valve 7 as described above, but ammonia or ammonia water may be directly supplied to the exhaust gas instead.

An oxidation catalyst (hereinafter referred to as “ASC catalyst”) 5 for oxidizing ammonia slipping from SCRF 4 is provided downstream of SCRF 4. The ASC catalyst 5 may be a catalyst configured by combining an oxidation catalyst and an SCR catalyst that reduces ammonia in exhaust gas using ammonia as a reducing agent. In this case, for example, an oxidation catalyst is formed by supporting a noble metal such as platinum (Pt) on a carrier made of aluminum oxide (Al ₂ O ₃ ), zeolite, or the like, and copper (Cu SCR catalyst may be formed by supporting a base metal such as iron or iron (Fe). By using the ASC catalyst 5 as a catalyst having such a configuration, HC, CO, and ammonia in the exhaust can be oxidized, and further, NOx is generated and generated by oxidizing a part of ammonia. NOx can also be reduced with excess ammonia.

  Furthermore, an oxidation catalyst 3 having an oxidation function is provided upstream of the SCRF 4 and the supply valve 7. A fuel supply valve 6 that can supply the fuel of the internal combustion engine 1 to the oxidation catalyst 3 through the exhaust gas flowing into the oxidation catalyst 3 is disposed on the upstream side of the oxidation catalyst 3. The fuel supplied to the exhaust from the fuel supply valve 6 is oxidized by the oxidation catalyst 3, and the temperature of the exhaust flowing into the SCRF 4 located downstream can be raised.

Further, a temperature sensor 9 for detecting the temperature of the exhaust gas flowing out from the oxidation catalyst 3 is provided on the downstream side of the oxidation catalyst 3, and a NOx sensor 10 for detecting NOx in the exhaust gas flowing into the SCRF 4 is provided on the upstream side of the SCRF 4. Provided on the downstream side of the SCRF 4 are a NOx sensor 11 for detecting NOx in the exhaust gas flowing out from the SCRF 4 and a temperature sensor 12 for detecting the exhaust gas temperature. The internal combustion engine 1 is also provided with an electronic control unit (ECU) 20 that controls the operating state of the internal combustion engine 1, an exhaust purification device, and the like. In addition to the temperature sensors 9 and 12 and the NOx sensors 10 and 11 described above, the ECU 20 is electrically connected to an air flow meter 16, a crank position sensor 21, and an accelerator opening sensor 22, and detection values of the sensors are passed to the ECU 20. It is. Therefore, the ECU 20 determines the operating state of the internal combustion engine 1 such as the intake air amount based on the detected value of the air flow meter, the engine speed based on the detection of the crank position sensor 21, and the engine load based on the detection of the accelerator opening sensor 22. It is possible to grasp.

  In this embodiment, the NOx in the exhaust gas flowing into the SCRF 4 can be detected by the NOx sensor 10, but the exhaust gas exhausted from the internal combustion engine 1 (the exhaust gas before being purified by the SCRF 4, that is, the exhaust gas flowing into the SCRF 4). NOx included in the internal combustion engine 1 is related to the operation state of the internal combustion engine, and can be estimated based on the operation state of the internal combustion engine 1. Further, the ECU 20 can estimate the temperature of the oxidation catalyst 3 based on the exhaust temperature detected by the temperature sensor 9 or a temperature sensor (not shown) provided on the upstream side of the oxidation catalyst 3. Further, it is possible to estimate the temperatures of the SCRF 4 and the ASC catalyst 5 based on the exhaust temperature detected by the temperature sensor 12 or a temperature sensor (not shown) provided on the upstream side of the SCRF 4.

Then, according to the NOx amount (NOx concentration) in the exhaust gas detected and estimated in this way, the ECU 20 issues an instruction to the supply valve 7, and an amount of urea water necessary for NOx reduction purification is supplied into the exhaust gas. The Specifically, the urea water supply from the supply valve 7 is controlled so that the NOx purification rate by the SCRF 4 determined by the following equation 1 falls within a predetermined range (Pmin to Pmax shown in FIG. 4A). .
NOx purification rate = 1- (detected value of NOx sensor 11) / (detected value of NOx sensor 10) (Expression 1)
Note that when the SCRF 4 is not in an activated state, NOx purification using the supplied urea water cannot be performed effectively, so the urea water supply from the supply valve 7 is the estimated temperature of the SCRF 4 Is carried out when the catalyst is at or above a predetermined temperature at which it is active.

  Further, one end of the EGR passage 13 is connected to the exhaust passage 2 upstream of the fuel supply valve 6. The other end of the EGR passage 13 is connected downstream of the throttle valve 17 in the intake passage 15. Further, an EGR valve 14 is provided in the EGR passage 13. With such a configuration, a part of the exhaust discharged from the internal combustion engine 1 is introduced into the intake passage 15 through the EGR passage 13 as EGR gas. Thereby, the EGR gas is supplied to the internal combustion engine 1, and the amount of NOx in the exhaust gas is suppressed through the control of the combustion temperature and the like in the internal combustion engine 1. The amount of EGR gas introduced into the intake passage 15 through the EGR passage 13 is adjusted by an EGR valve 14 that is electrically connected to the ECU 20.

  In the exhaust gas purification apparatus for the internal combustion engine 1 configured as described above, the NOx purification and PM removal in the exhaust gas are performed by the SCRF 4. Here, when the collected PM gradually accumulates on the SCRF 4 and the accumulated amount exceeds a certain amount, the operation of the internal combustion engine 1 may be hindered. Therefore, in the present embodiment, the filter regeneration process for removing the PM deposited on the SCRF 4 is executed by the ECU 20. The filter regeneration process according to the present embodiment is realized by supplying fuel from the fuel supply valve 6 and thereby supplying the fuel to the oxidation catalyst 3. When the fuel is oxidized in the oxidation catalyst 3, heat of oxidation is generated. The exhaust heat flowing into SCRF 4 is heated by this oxidation heat, and the temperature of SCRF 4 rises. At the time of executing the filter regeneration process, the temperature of the SCRF 4 is raised to a predetermined filter regeneration temperature (for example, 600 to 650 ° C.) that promotes the oxidation of PM by controlling the amount of fuel supplied from the fuel supply valve 6. Let As a result, the PM deposited on SCRF4 is oxidized and removed, and the PM collection ability of SCRF4 is regenerated.

In the present embodiment, the execution of the filter regeneration processing may be requested every time a predetermined time has elapsed since the previous execution of the filter regeneration processing has ended. As an alternative, a vehicle on which the internal combustion engine 1 is mounted is predetermined. You may request | require execution of a filter reproduction | regeneration process every time it travels a travel distance. Alternatively, the filter regeneration process may be requested every time the PM deposition amount in the SCRF 4 reaches a predetermined deposition amount. Note that the PM accumulation amount in the SCRF 4 can be estimated based on the history of the fuel injection amount in the internal combustion engine 1, the flow rate of the exhaust gas flowing into the SCRF 4, the temperature of the SCRF 4, and the like. When execution of the filter regeneration process is requested, if the temperature of the oxidation catalyst 3 is equal to or higher than a predetermined activation temperature, the filter regeneration process is performed (that is, fuel supply from the fuel supply valve 6 is performed). . The predetermined activation temperature is a temperature at which the fuel supplied from the fuel supply valve 6 can be oxidized to some extent in the oxidation catalyst 3. This predetermined activation temperature is a temperature determined according to the type and configuration of the oxidation catalyst 3, and is determined in advance based on experiments and the like.

  Here, the SCR catalyst supported on the SCRF 4 is set to have a very low oxidation capacity in order to make it difficult for the ammonia used for the reduction reaction to be oxidized. Therefore, as described above, there is a tendency that a relatively long time is required for the filter regeneration process required for oxidizing and removing the PM collected by the SCRF 4. Therefore, in this embodiment, the ECU 20 executes filter regeneration processing control for oxidizing and removing PM collected by the SCRF 4 shown in FIG. 2, thereby reducing the time required for the filter regeneration processing. The NOx purification rate of the whole exhaust gas purification device of the internal combustion engine 1 is maintained. The control is performed by executing a control program stored in the ECU 20.

  First, in S101, it is determined whether a condition for executing the filter regeneration process is satisfied. For example, as described above, it can be determined that the condition is satisfied when a predetermined time has elapsed since the previous execution of the filter regeneration process was completed. If a positive determination is made in S101, the process proceeds to S102, and if a negative determination is made, the process of S101 is performed again. As for other conditions for executing the filter regeneration processing, the vehicle mounted with the internal combustion engine 1 travels a predetermined travel distance, the operation history of the internal combustion engine 1 (fuel injection amount, exhaust flow rate, SCRF 4 temperature, etc.). When the PM deposition amount at SCRF 4 estimated from the history reaches a predetermined deposition amount, it may be determined that the condition is satisfied.

  Next, in S102, the supply amount X0 of the fuel component from the fuel supply valve 6 required for oxidizing and removing the collected PM in the SCRF 4 is calculated in the filter regeneration process. Here, calculation of the supply amount of the fuel component will be described with reference to FIG. As described above, in order to oxidize and remove PM collected by SCRF4, the temperature of the exhaust gas flowing into SCRF4 is raised, and the temperature of SCRF4 is increased to a predetermined filter regeneration temperature at which PM oxidation is promoted. It is necessary to let However, the present inventor does not simply increase the temperature of SCRF4 in PM oxidation at SCRF4, but increases the temperature of SCRF4 in a state where PM collected in SCRF4 coexists with a predetermined amount of fuel components. We focused on the fact that the time required for the filter regeneration processing can be shortened. This is considered to be due to the fact that the fuel component adsorbed on SCRF 4 is present to some extent with respect to PM, so that PM is efficiently oxidized. In this embodiment, the fuel component coexisting with PM in SCRF 4 during the filter regeneration process is referred to as “coexisting fuel”.

  Therefore, in S102, the fuel component supply amount X0 is calculated as an amount exceeding the amount X2 of the fuel component amount X1 that can be oxidized by the oxidation catalyst 3 at the time when the filter regeneration process is performed (see FIG. 3). That is, the fuel component of the amount X1 is a fuel component that is assumed to raise the exhaust gas temperature by being oxidized by the oxidation catalyst 3, and is referred to as “exhaust temperature rising fuel” in this embodiment. The fuel component of the amount X2, which exceeds the amount X1 of the exhaust temperature rising fuel among the fuel components of the supply amount X0, is not oxidized by the oxidation catalyst 3, and thus flows through the oxidation catalyst 3 and flows into the SCRF 4 located downstream thereof, and PM oxidation It is assumed that it will be a co-existing fuel for promotion of

More specifically, the amount X1 of the exhaust gas temperature raising fuel is set based on the temperature of the oxidation catalyst 3 estimated based on the detection value of the temperature sensor 9. In general, if the temperature of the oxidation catalyst 3 has reached the activation temperature, the higher the temperature of the oxidation catalyst 3, the greater the amount X1 of the exhaust temperature raising fuel. On the other hand, the amount X2 of the coexisting fuel is set to an amount corresponding to the oxidation removal of PM collected in the SCRF4. The inventor of the present application finds that the collected PM is oxidized and removed particularly efficiently when a predetermined ratio of the fuel component to the amount of PM collected in the SCRF 4 is supplied as the coexisting fuel. It was. Therefore, in this embodiment, the predetermined ratio for SCRF4 is determined by a prior experiment or the like, and based on the amount of PM collected in SCRF4 at the time when filter regeneration processing control is performed, and this predetermined ratio. The amount X2 of the coexisting fuel is calculated.

  In calculating the amount X2 of the coexisting fuel, the amount of the fuel component that can be oxidized by the SCRF 4 is set as the upper limit value. This is because when the fuel component exceeding the amount that can be oxidized by SCRF4 is supplied to SCRF4 as the coexisting fuel, the SCR catalyst carried on SCRF4 is poisoned by the fuel, the NOx purification rate is remarkably lowered, and the coexisting fuel This is because the oxidization and removal of PM cannot be effectively performed. Therefore, specifically, an upper limit value X3 corresponding to the oxidation capability of SCRF4 is set according to the temperature of SCRF4 estimated based on the detection value of temperature sensor 12 (see FIG. 3). When the amount X2 of the coexisting fuel calculated based on the collected PM amount and the predetermined ratio as described above does not exceed the upper limit, the calculated amount is set as the final amount of the coexisting fuel, When the calculated amount X2 of the coexisting fuel exceeds the upper limit value, the amount (X3) of the upper limit value is set as the final coexisting fuel amount.

  When the process of S102 ends, the process proceeds to S103. In S103, the increase amount ΔY is calculated in order to increase the EGR gas amount during the filter regeneration process from the EGR gas amount when the filter regeneration process is not performed (during the non-filter regeneration process). As described above, in this embodiment, the coexisting fuel is fed into the SCRF 4 in order to promote the combustion of the collected PM. At this time, the coexisting fuel that has reached SCRF4 is adsorbed on the SCR catalyst site where ammonia is adsorbed for NOx reduction. As a result, while improving the oxidation efficiency of PM, the NOx purification ability by SCRF4 is reduced as shown in FIG. 4A. In FIG. 4A, the reduced NOx purification rate (corresponding to the NOx purification capacity) of SCRF4 is represented by ΔP, the reduced NOx purification rate becomes P1, and the range of the NOx purification rate (Pmin˜ Pmax). Therefore, in order to compensate for the decrease ΔP in the NOx purification rate, the increase amount ΔY of EGR gas is calculated in S103.

  Specifically, it is considered that the decrease ΔP of the NOx purification rate due to SCRF4 increases as the amount X2 of the coexisting fuel increases. Therefore, as shown in FIG. 4B, the increase ΔY in the EGR gas as the coexisting fuel X2 increases. To increase. As a result, the amount of EGR gas provided for combustion of the internal combustion engine 1 is increased from the amount during non-filter regeneration processing, and the amount of NOx in the exhaust can be reduced. The reduction in the NOx amount due to the increase in the EGR gas compensates for the decrease in the NOx purification rate due to the above-mentioned coexisting fuel. In general, the EGR gas amount is supplied with an amount of EGR gas suitable for combustion based on the operating state of the internal combustion engine 1, such as the engine load and the engine speed. Therefore, when the amount of EGR gas is increased to compensate for the NOx purification ability as described above, there is a possibility that the influence will appear not a little. However, since the increase in the EGR gas is temporarily performed during the filter regeneration process, the affected range can be made as small as possible. Further, if an increase in EGR gas for compensating the NOx purification capacity can adversely affect the operating state of the internal combustion engine 1, the maximum increase in EGR gas can be performed within the allowable range of influence. Good.

When the process of S103 ends, the process proceeds to S104. In S104, fuel is supplied from the fuel supply valve 6 in order to supply the fuel component of the supply amount X0 (X1 + X2) calculated in S102, and the EGR gas is increased by ΔY calculated in S103. EGR
By performing the opening degree adjustment of the valve 14, the filter regeneration process in the present embodiment is executed. In S105, it is determined whether or not it is the end timing of the filter regeneration process. Specifically, the end timing of the filter regeneration process is determined based on the elapsed time from the start of the filter regeneration process, the exhaust gas temperature transition detected by the temperature sensor 12, and the like. If a positive determination is made in S105, the process proceeds to S106, and if a negative determination is made, the determination in S105 is performed again.

  In S106, the fuel supply from the fuel supply valve 6 and the increase in EGR gas for the filter regeneration process started in S104 are stopped. Thereby, the amount of EGR gas in the internal combustion engine 1 is returned to an amount corresponding to the operating state of the internal combustion engine 1 during the non-filter regeneration process. When the process of S106 ends, this control is repeated again.

  According to this control, the fuel component is positively supplied to the SCRF 4 as a coexisting fuel, whereby the PM trapped in the SCRF 4 is efficiently burned, and the NOx purification ability by the SCRF 4 due to the coexisting fuel is reduced. By compensating for the temporary increase in the EGR gas, it is possible to suitably maintain the NOx purification ability of the entire exhaust gas purification device. Therefore, it is possible to shorten the time required for the filter regeneration process of the SCRF 4 without deteriorating the NOx purification ability of the exhaust purification device.

（２）結果
ＳＣＲＦにおける酸化除去されたＰＭ量は、ＳＣＲＦから流れ出る排気に含まれる二酸化炭素および一酸化炭素の量から算出した。したがって、排気に本来的に含まれている二酸化炭素等の影響が下記の実施例１と比較例１の実験結果には含まれているが、両者を比べるにあったては、支障はないと考えられる。

Here, this inventor performed the following experiment regarding a present Example, and confirmed the effect.
(1) Experimental method After uniformly filling carbon black into SCRF formed by supporting β zeolite, the exhaust temperature flowing into SCRF is raised from 150 ° C. to 800 ° C. assuming filter regeneration processing. At this time, in the SCRF according to this embodiment, the following fuel components are supplied before the exhaust temperature rises, and in the SCRF according to the comparative example, the fuel components before the exhaust temperature rises are not supplied.

(2) Results The amount of PM removed by oxidation in SCRF was calculated from the amounts of carbon dioxide and carbon monoxide contained in the exhaust gas flowing out from SCRF. Therefore, the influence of carbon dioxide and the like inherently contained in the exhaust gas is included in the experimental results of Example 1 and Comparative Example 1 below, but there is no problem in comparing the two. Conceivable.

  As a result, it can be understood that the PM is efficiently oxidized and removed by raising the exhaust gas temperature while supplying the coexisting fuel to the SCRF as in this embodiment. This contributes to shortening the time required for the filter regeneration process. Further, the supply of coexisting fuel to the SCRF results in a decrease in the SCRF NOx purification capacity, but this decrease in the NOx purification capacity can be compensated by temporarily increasing the EGR gas. The present inventors have confirmed this through experiments.

<Modification>
In the filter regeneration processing control described above, the supply amount X0 may be corrected in consideration of the air-fuel ratio of the exhaust gas flowing into the SCRF 4 when calculating the fuel component supply amount X0 in S102. In general, it is considered that if the amount of oxygen in the exhaust gas increases, the oxidation efficiency of PM collected in SCRF 4 is improved. Therefore, the fuel component supply amount X0 may be corrected so as to decrease as the exhaust air-fuel ratio flowing into the SCRF 4 becomes a leaner air-fuel ratio. By doing in this way, the quantity of the fuel component consumed for filter regeneration processing can be controlled.

  In the first embodiment, the fuel component is supplied to the SCRF 4 via the fuel supply valve 6, but instead of or together with it, the air-fuel ratio of the exhaust discharged from the internal combustion engine 1 is rich. By performing rich combustion by changing the combustion conditions so that the air / fuel ratio becomes the same, it is possible to include more fuel components (SOF) in the exhaust and deliver the fuel components as the coexisting fuel to the SCRF 4. One example of rich combustion is retarding the fuel injection timing in the internal combustion engine 1.

  Based on the above, in this embodiment, filter regeneration processing control for supplying fuel components via the fuel supply valve 6 and supplying fuel components via rich combustion in the internal combustion engine 1 will be described with reference to FIG. To do. Of the processes performed in the filter regeneration process control shown in FIG. 5, the same processes as those performed in the filter regeneration process control shown in FIG. .

  In the control shown in FIG. 5, when the process of S103 is completed, the process proceeds to S201. In S201, the EGR gas increase is executed according to the EGR gas increase ΔY calculated in S103. Then, in the state where the amount of EGR gas is increased in this way, the subsequent processes of S202 and S203 are performed. First, in S202, a fuel component is supplied by rich combustion. Since the fuel component supplied by rich combustion is exposed to the combustion environment in the internal combustion engine 1, it becomes a relatively light fuel component. Therefore, the fuel component by rich combustion that passes through the oxidation catalyst 3 and reaches the SCRF 4 easily enters the inside of the SCRF 4 and is considered to contribute to oxidizing and removing the collected PM from the inside.

  In S203 performed after S202, the fuel component is supplied by the fuel supply valve 6. Since the fuel component supplied by the fuel supply valve 6 is not exposed to the combustion environment in the internal combustion engine 1, it becomes a relatively heavy fuel component. Therefore, the PM collected together with the light fuel component that has reached the inside of the SCRF 4 in S202 is wrapped in the heavy fuel component, and the PM being oxidized by the light fuel component is converted into the heavy fuel component. Can be expected to be oxidized and removed quickly. When the process of S203 is completed, the processes after S105 are performed.

  Since the processing of S202 and S203 is performed in the state where the amount of EGR gas is increased in S201, even if the fuel component as the coexisting fuel reaches SCRF4, the NOx purification rate as the exhaust purification device is suitably maintained. The The fuel component supply amount in S202 and the fuel component supply amount in S203 are the same as the amount X2 of the coexisting fuel in the supply amount X0 calculated in S102 (FIG. 3). It is sufficient to adjust appropriately so that In particular, when fuel components are supplied by rich combustion, it is necessary to change the combustion conditions in the internal combustion engine 1, and therefore it may be difficult to supply sufficient fuel components depending on the combustion conditions. In such a case, the amount of fuel component supplied by rich combustion may be relatively reduced.

  In the second embodiment, in the filter regeneration processing control, the fuel component is supplied through the fuel supply valve 6 and the fuel component is supplied through the rich combustion in the internal combustion engine 1. From the viewpoint of suppressing smoke during the filter regeneration process, the filter regeneration process control for selectively supplying the fuel component via the fuel supply valve 6 and the fuel component via the rich combustion in the internal combustion engine 1 will be described. This will be described with reference to FIG. Of the processes performed in the filter regeneration process control shown in FIG. 6, the same processes as those performed in the filter regeneration process control shown in FIG. .

  In the control shown in FIG. 6, when the process of S103 is completed, the process proceeds to S301. In S301, as in S201, the EGR gas increase is executed according to the EGR gas increase ΔY calculated in S103. Then, in the state where the amount of EGR gas is increased in this way, the following processes of S302 to S304 are performed. In S302, it is determined whether or not the fuel component supply amount X0 calculated in S102 is larger than the reference amount Xsmk for generating smoke. When the fuel component is supplied by rich combustion, smoke may be generated if the supply amount is too large. Therefore, the threshold value of the supply amount of the fuel component that may cause smoke in the internal combustion engine 1 is calculated in advance by experiments or the like and set as the reference amount Xsmk. If a positive determination is made in S302, the process proceeds to S303, and if a negative determination is made, the process proceeds to S304. When the process proceeds to S303, the fuel supply valve 6 supplies the fuel component of the supply amount X0. When the routine proceeds to S304, the fuel component of the supply amount X0 is supplied by the rich combustion in the internal combustion engine 1. When S303 or S304 ends, the processing after S105 is performed.

  According to this control, the processing of S303 and S304 is performed in a state where the amount of EGR gas is increased in S301. Therefore, even if the fuel component as the coexisting fuel reaches SCRF4, the NOx purification rate as the exhaust purification device is Preferably maintained. In this case, considering the generation of smoke, either the supply of the fuel component by the fuel supply valve 6 or the supply of the fuel component by rich combustion is performed, so that the PM can be promptly suppressed while suppressing the generation of smoke. Oxidation removal of is realized.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Exhaust passage 3 Oxidation catalyst 4 Selective reduction type NOx catalyst (SCR catalyst)
5 ASC catalyst 6 Fuel supply valve 7 Supply valve 9, 12 Temperature sensor 10, 11 NOx sensor 13 EGR passage 14 EGR valve 20 ECU
21 Crank position sensor 22 Accelerator position sensor

Claims (8)

An oxidation catalyst provided in the exhaust passage of the internal combustion engine and having an oxidation function;
A fuel supply unit that supplies fuel components to the oxidation catalyst via exhaust gas flowing into the oxidation catalyst;
A filter that is provided in an exhaust passage downstream of the oxidation catalyst and collects particulate matter in the exhaust, and carries a selective reduction type NOx catalyst that selectively reduces NOx in the exhaust using ammonia as a reducing agent. Filters,
An ammonia supply unit for supplying ammonia or an ammonia precursor to the filter via exhaust flowing into the filter;
An EGR device that recirculates part of the exhaust from the internal combustion engine to an intake system;
When the fuel is supplied to the oxidation catalyst by the fuel supply unit, the temperature of the filter is raised to a predetermined filter regeneration temperature that promotes oxidation of the collected particulate matter, and the particulate matter A filter regeneration processing unit that performs a filter regeneration process for oxidizing and removing
When the filter regeneration processing is performed by the filter regeneration processing unit, the amount of EGR gas recirculated to the intake system by the EGR device is increased in comparison with the amount of EGR gas when the filter regeneration processing is not performed. The fuel supply unit supplies a predetermined amount of fuel component larger than the amount that can be oxidized by the oxidation catalyst during the filter regeneration process.
An exhaust purification device for an internal combustion engine. The increased amount of the EGR gas amount at the time of the filter regeneration process is set according to a decrease in the NOx purification rate in the filter that is caused by supplying the predetermined amount of fuel component.
The exhaust emission control device for an internal combustion engine according to claim 1. When the filter regeneration processing is performed by the filter regeneration processing unit, the fuel supply unit provides a fuel supply provided in an exhaust passage upstream of the oxidation catalyst in a state where the EGR gas amount is increased by the EGR device. Supplying the predetermined amount of fuel component by at least one of fuel supply to exhaust by a valve and rich combustion to enrich the exhaust air-fuel ratio by controlling the combustion state in the internal combustion engine;
An exhaust emission control device for an internal combustion engine according to claim 1 or 2. The fuel supply unit supplies the predetermined amount of the fuel component by supplying the fuel component by the fuel supply valve after supplying the fuel component by the rich combustion.
The exhaust emission control device for an internal combustion engine according to claim 3. The fuel supply unit does not supply the fuel component by the rich combustion and does not supply the fuel component when the value of the predetermined amount exceeds a smoke generation threshold value that may cause smoke when the rich combustion is performed. Supplying fuel components by valves,
The exhaust emission control device for an internal combustion engine according to claim 3. The predetermined amount of fuel component is increased as the amount of particulate matter collected by oxidation removal by the filter regeneration processing unit increases.
The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 5. The predetermined amount of fuel component is increased up to an amount that can oxidize particulate matter in the filter during the filter regeneration process,
The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 6. The predetermined amount of fuel component is set to be smaller as the air-fuel ratio of the exhaust gas flowing into the filter is the lean-side air-fuel ratio.
The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 7.

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