JP2013002388A - Exhaust emission purifier of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission purifier of an internal combustion engine which can preferably reduce clogging of PM on a front end face of an exhaust purifying member.SOLUTION: An engine 1 includes: an oxidation catalyst 31 provided in an exhaust passage 26; a fuel addition valve 5 for supplying the oxidation catalyst 31 with an addition agent; an exhaust return mechanism for returning exhaust to an intake passage 3; and a controller 25 for controlling a return amount of exhaust by the exhaust return mechanism based on an engine operating state. When a clogging amount of the front end face of the oxidation catalyst 31 exceeds a threshold, the controller 25 decreases the return amount of exhaust.

Description

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

In recent years, exhaust systems of some internal combustion engines have been provided with exhaust purification members such as filters that collect PM (particulate matter) in the exhaust.
The exhaust purification member may be supplied with an additive in order to recover the purification function or the like. For example, in the apparatus described in Patent Document 1, when PM collected in the filter accumulates, pressure loss in the filter increases, and thus the fuel is collected by supplying fuel as an additive to the filter. PM is burned out and the filter is regenerated.

JP 2007-23792 A

  By the way, the additive supplied to the exhaust purification member is basically vaporized and burnt down by combustion, oxidation reaction, etc. in the exhaust purification member. However, if some of the additives adhere to the front end surface of the exhaust purification member having a relatively low temperature without being burned off by combustion or oxidation reaction, the additive adhering to the front end surface becomes a binder. Then, PM or the like may be adsorbed, and the front end surface of the exhaust purification member may be clogged with PM.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an exhaust purification device for an internal combustion engine that can suitably reduce clogging of PM on the front end surface of the exhaust purification member.

In the following, means for achieving the above object and its effects are described.
The invention according to claim 1 is an exhaust purification member provided in an exhaust passage, an additive supply mechanism that supplies an additive to the exhaust purification member, an exhaust recirculation mechanism that recirculates exhaust to the intake passage, and the exhaust In an exhaust gas purification device for an internal combustion engine comprising a control unit that controls the recirculation amount of exhaust gas by the recirculation mechanism based on the engine operating state, when the clogging amount of the front end surface of the exhaust purification member exceeds a predetermined threshold value, The gist is to reduce the reflux amount as compared to when the clogging amount does not exceed the threshold value.

  According to this configuration, when the amount of clogging on the front end surface exceeds the threshold value, the amount of exhaust gas flowing into the exhaust gas purification member is increased by reducing the exhaust gas recirculation amount. When the flow rate of the exhaust gas increases in this way, the flow rate of the exhaust gas increases, so that PM clogged in the front end surface of the exhaust gas purification member is blown away by the dynamic pressure of the exhaust gas. Therefore, according to this configuration, it is possible to suitably reduce PM clogging on the front end face of the exhaust purification member.

  Although it is possible to reduce the clogging of the front end face of the exhaust purification member by increasing the exhaust temperature, such a high temperature of the exhaust is not always possible, for example, a low load of an engine having a relatively low exhaust temperature. At times, it is difficult to raise the temperature of the exhaust. On the other hand, in the above configuration, the flow rate of the exhaust gas is increased, and such processing can be executed even when the engine is under a low load. Therefore, according to the configuration, it is possible to increase the execution opportunity of the process for reducing clogging.

  In addition, by reducing the recirculation amount of the exhaust gas, the flow rate of the exhaust gas flowing into the exhaust gas purification member is increased. Therefore, the clogging of the front end surface is reduced without providing a separate mechanism for increasing the exhaust gas flow rate. Can be made.

  According to a second aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the first aspect, the clogging amount includes an increase amount of the clogging amount calculated based on the engine speed and the fuel injection amount, and intake air. The gist is that it is calculated by calculating the difference from the reduction amount of the clogging amount calculated based on the amount.

  The PM that causes clogging of the front end surface of the exhaust purification member is derived from the fuel of the engine. Basically, the larger the fuel injection amount, the greater the clogging amount of the front end surface. Further, the higher the engine rotational speed, the larger the exhaust amount per unit time and the PM exhaust amount. Therefore, basically, the higher the engine rotational speed, the greater the amount of clogging at the front end face. On the other hand, since the flow rate of the exhaust gas flowing through the exhaust passage increases as the intake air amount increases, PM is easily blown off from the front end surface. Therefore, as the intake air amount increases, the amount of clogging at the front end surface decreases. Therefore, in this configuration, the increase amount of the clogging amount is calculated based on the engine speed and the fuel injection amount, and the decrease amount of the clogging amount is calculated based on the intake air amount, and the difference between the increase amount and the decrease amount is calculated. Thus, the amount of clogging of the PM at the front end face is calculated, and according to this configuration, the amount of clogging of the front end face can be estimated appropriately.

The invention according to claim 3 is the exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the increase amount is increased as the atmospheric pressure is lower.
Soot, which is one of the components constituting PM, is more easily discharged from the engine as the atmospheric pressure is lower and the oxygen density is lower. Therefore, in the same configuration, as the atmospheric pressure is lower, the calculated increase amount of the clogging amount is increased so that the influence of the atmospheric pressure on the increase amount of the clogging amount can be suitably corrected. it can.

  According to a fourth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the second or third aspect, the reduction amount is increased as the temperature of the front end surface of the exhaust gas purification member is higher. To do.

  The amount of the PM adhering to the front end surface decreases as the temperature of the front end surface of the exhaust purification member increases, so that oxidation and burning are promoted. Therefore, in the same configuration, as the temperature of the front end surface of the exhaust purification member is higher, the calculated reduction amount of the clogging amount is increased, so that the front end surface of the exhaust purification member is reduced with respect to the reduction amount of the clogging amount. The influence of temperature can be suitably corrected.

  The fifth aspect of the present invention is the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to fourth aspects, wherein the reduction amount of the recirculation amount is increased as the engine speed is lower. And

  Since the amount of exhaust discharged from the internal combustion engine decreases as the engine speed decreases, the effect of reducing the clogging of the front end surface caused by exhaust becomes small. In this regard, according to the same configuration, the amount of exhaust gas flowing into the exhaust purification member increases by increasing the amount of decrease in the exhaust gas recirculation amount as the engine speed decreases. Therefore, according to the configuration, clogging of the front end face can be suitably reduced regardless of the engine rotation speed.

  According to a sixth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to fifth aspects, the reduction amount of the recirculation amount increases as the clogging amount increases. The gist.

  According to this configuration, the flow rate of the exhaust gas flowing into the exhaust gas purification member is increased as the amount of clogging is larger and more PM needs to be blown away. Therefore, it is possible to appropriately set the reduction amount of the reflux amount according to the clogging amount.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the internal combustion engine to which this is applied, and its periphery structure about one Embodiment of the exhaust gas purification device of the internal combustion engine concerning this invention. The flowchart which shows the procedure of the calculation process of clogging amount. The graph which shows the relationship between engine rotation speed, fuel injection amount, and basic clogging amount. The graph which shows the relationship between atmospheric pressure and basic clogging amount. The graph which shows the relationship between air quantity ratio and an air quantity correction coefficient. The graph which shows the relationship between intake air amount and front end surface temperature, and clogging reduction amount. The flowchart which shows the procedure of the reduction process of clogging. The graph which shows the relationship between an engine speed and an EGR reduction value. The graph which shows the relationship between the amount of clogging, and a clogging correction coefficient.

Hereinafter, an embodiment in which an exhaust gas purification apparatus for an internal combustion engine according to the present invention is embodied in an exhaust gas purification apparatus for a diesel engine will be described with reference to FIGS.
As shown in FIG. 1, the engine 1 is provided with a plurality of cylinders # 1 to # 4. A plurality of fuel injection valves 4 a to 4 d are attached to the cylinder head 2. These fuel injection valves 4a to 4d inject fuel into the combustion chambers of the cylinders # 1 to # 4. Further, the cylinder head 2 is provided with intake ports for introducing outside air into the cylinders and exhaust ports 6a to 6d for discharging combustion gas outside the cylinders corresponding to the respective cylinders # 1 to # 4. ing.

  The fuel injection valves 4a to 4d are connected to a common rail 9 that accumulates high-pressure fuel. The common rail 9 is connected to the supply pump 10. The supply pump 10 sucks fuel in the fuel tank and supplies high-pressure fuel to the common rail 9. The high-pressure fuel supplied to the common rail 9 is injected into the cylinder from the fuel injection valves 4a to 4d when the fuel injection valves 4a to 4d are opened.

  An intake manifold 7 is connected to the intake port. The intake manifold 7 is connected to the intake passage 3. An intake throttle valve 16 for adjusting the intake air amount is provided in the intake passage 3.

An exhaust manifold 8 is connected to the exhaust ports 6a to 6d. The exhaust manifold 8 is connected to the exhaust passage 26.
In the middle of the exhaust passage 26, a catalyst device 30 for purifying exhaust components is provided. Inside the catalyst device 30, an oxidation catalyst 31 and a filter 32 are arranged in series with respect to the flow direction of the exhaust gas.

  The oxidation catalyst 31 carries a catalyst for oxidizing HC in the exhaust. The filter 32 is a member that collects PM (particulate matter) in the exhaust gas, and is made of a porous ceramic. The PM in the exhaust gas is collected when it passes through the porous wall. Is done.

  The cylinder head 2 is provided with a fuel addition valve 5 for supplying fuel as an additive to the oxidation catalyst 31 and the filter 32. The fuel addition valve 5 is connected to the supply pump 10 via a fuel supply pipe 27, and fuel is injected from the fuel addition valve 5 into the exhaust port 6d of the fourth cylinder # 4. The injected fuel reaches the oxidation catalyst 31 and the filter 32 together with the exhaust gas. The position of the fuel addition valve 5 can be changed as appropriate as long as it is in the exhaust system and upstream of the catalyst device 30. The fuel addition valve 5, the fuel supply pipe 27, and the supply pump 10 constitute the additive supply mechanism.

  In addition, the engine 1 is provided with an exhaust gas recirculation mechanism (hereinafter referred to as an EGR device). This EGR device is a device that reduces the amount of NOx generated by lowering the combustion temperature in the cylinder by introducing part of the exhaust gas into the intake air. This device is composed of an EGR passage 13 communicating the intake passage 3 and the exhaust passage 26, an EGR valve 15 provided in the EGR passage 13, an EGR cooler 14, and the like. The EGR valve 15 adjusts the recirculation amount of the exhaust gas introduced from the exhaust passage 26 into the intake passage 3, that is, the EGR amount EK, by adjusting the opening degree thereof. The EGR cooler 14 reduces the temperature of the exhaust gas flowing in the EGR passage 13. The EGR valve 15 is provided with an EGR valve opening sensor 22, and the EGR valve opening sensor 22 detects the opening of the EGR valve 15, that is, the EGR valve opening EA. The opening degree of the EGR valve 15 is controlled to be an opening degree corresponding to the EGR rate set based on the engine operating state. Note that the higher the EGR rate, the larger the opening of the EGR valve 15, thereby increasing the EGR amount EK. Incidentally, the EGR rate is a value obtained by “the amount of EGR flowing into the cylinder / (the amount of fresh air flowing into the cylinder + the amount of EGR flowing into the cylinder)”.

  The engine 1 also includes a turbocharger 11 that supercharges intake air introduced into the cylinder using exhaust pressure. An intercooler 18 is provided in the intake passage 3 between the intake side turbine and the intake throttle valve 16 in order to reduce the temperature of intake air whose temperature rises due to supercharging of the turbocharger 11.

  Various sensors for detecting the engine operation state are attached to the engine 1. For example, the air flow meter 19 detects the intake air amount GA in the intake passage 3. The throttle valve sensor 20 detects a throttle valve opening TA that is the opening of the intake throttle valve 16. The first temperature sensor 33 provided on the exhaust gas downstream side of the oxidation catalyst 31 measures a first exhaust temperature Thi that is the temperature of the exhaust gas immediately after passing through the oxidation catalyst 31. A second temperature sensor 34 provided on the exhaust downstream side of the filter 32 provided on the exhaust downstream side of the oxidation catalyst 31 detects a second exhaust temperature Tho that is the temperature of the exhaust immediately after passing through the filter 32. The engine rotation speed sensor 23 detects the rotation speed of the crankshaft, that is, the engine rotation speed NE. The accelerator sensor 24 detects an accelerator pedal depression amount, that is, an accelerator operation amount ACCP. The air-fuel ratio sensor 21 detects the air-fuel ratio λ of the exhaust.

  The outputs of these various sensors are input to the control device 25. The control device 25 includes a central processing control device (CPU), a read only memory (ROM) that stores various programs and maps in advance, a random access memory (RAM) that temporarily stores CPU calculation results, a timer counter, an input The microcomputer is mainly configured with an interface, an output interface, and the like. The control device 25 controls, for example, fuel injection amount control and fuel injection timing control of the fuel injection valves 4a to 4d, discharge pressure control of the supply pump 10, drive amount control of the actuator 17 that opens and closes the intake throttle valve 16, EGR Various controls of the engine 1 such as opening control of the valve 15 and injection control of the fuel addition valve 5 are performed. The control device 25 constitutes the control unit that controls the exhaust gas recirculation amount based on the engine operating state. Various exhaust purification controls such as a regeneration process for a filter that burns the PM collected by the filter 32 are also performed by the controller 25.

  Since the regeneration process of the filter 32 is well known, the outline thereof will be described below. In this regeneration process, the PM accumulation amount of the filter 32 is estimated based on the engine operating state and the like. When the estimated PM accumulation amount exceeds a predetermined value, fuel is injected from the fuel addition valve 5 as an additive. The injected fuel is oxidized by the oxidation catalyst 31, and the exhaust gas is heated by the oxidation heat. When the exhaust gas heated by the oxidation catalyst 31 flows into the filter 32, the temperature rise of the filter 32 is promoted to reach the PM reproducible temperature, whereby the PM collected by the filter 32 is oxidized. It will decrease as it is burned. When the PM collected in the filter 32 through the temperature increasing process decreases and the PM accumulation amount decreases to a predetermined value, the fuel addition from the fuel addition valve 5 is terminated, and the regeneration process of the filter 32 is performed. finish.

  Incidentally, the additive injected from the fuel addition valve 5 is oxidized in the process of passing through the oxidation catalyst 31. Therefore, the temperature of the front end surface of the oxidation catalyst 31 is relatively low. For this reason, some additives may not be burned off by combustion, oxidation reaction, or the like, and may directly adhere to the front end surface of the oxidation catalyst 31 having a relatively low temperature. When the additive adheres to the front end face in this way, the additive becomes a binder and adsorbs PM or the like, and the front end face of the oxidation catalyst 31 may be clogged with PM.

  When the front end face of the oxidation catalyst 31 is clogged in this way, the additive passage area in the oxidation catalyst 31 is reduced, so that the amount of additive oxidized by the oxidation catalyst 31 is reduced. The amount of additive that passes through without being oxidized increases. If the amount of the additive that passes without being oxidized in the oxidation catalyst 31 in this way increases, the temperature of the exhaust gas flowing into the filter 32 becomes insufficient, and the regeneration process of the filter 32 is delayed.

  Further, when the front end face of the oxidation catalyst 31 is clogged, the flow of exhaust gas passing through the oxidation catalyst 31 tends to drift, and as a result, the exhaust gas is exhausted to the first temperature sensor 33 provided on the exhaust gas downstream side of the oxidation catalyst 31. May be difficult to hit. If the exhaust gas does not easily hit the first temperature sensor 33 in this way, the temperature of the exhaust gas detected by the first temperature sensor 33 becomes inaccurate. For example, for the exhaust gas temperature control performed during the regeneration process. There is also the possibility of adverse effects.

Therefore, in the present embodiment, the clogging of PM on the front end face of the oxidation catalyst 31 is reduced through the execution of the clogging amount calculation process and the reduction process described below.
FIG. 2 shows a procedure for calculating the clogging amount M on the front end face of the oxidation catalyst 31. This process is repeatedly executed at predetermined intervals by the control device 25.

  When this processing is started, first, a basic clogging amount Mb, which is a basic value of the clogging amount M, is calculated based on the engine speed NE, the fuel injection amount Q, and the atmospheric pressure P (S100). Here, as shown in FIG. 3, the basic clogging amount Mb is calculated to be larger as the engine rotational speed NE is higher or the fuel injection amount Q is larger. Further, even if the engine speed NE and the fuel injection amount Q are the same, the basic clogging amount Mb is calculated to be larger as the atmospheric pressure P is lower, as shown in FIG.

  Next, an air amount correction coefficient Ka is calculated based on the air amount ratio GAH (S110). This air amount ratio GAH is a value obtained by “intake air amount GA / target air amount GAp”. That is, it is a value indicating the ratio of the current intake air amount GA to the target air amount GAp set based on the engine operating state. Therefore, when the intake air amount GA and the target air amount GAp coincide with each other, such as when the engine is stationary, the air amount ratio GAH is “1”. Further, when the intake air amount GA is smaller than the target air amount GAp, such as during engine transition, the air amount ratio GAH becomes a value smaller than “1”. As shown in FIG. 5, the air amount correction coefficient Ka is set to a larger value as the air amount ratio GAH is smaller, that is, as the intake air amount GA is insufficient with respect to the target air amount GAp.

  Next, the clogging increase amount Mi is calculated by multiplying the basic clogging amount Mb by the air amount correction coefficient Ka (S120). The clogging increase amount Mi is calculated as a clogging amount M increased from the previous main processing execution cycle to the current main processing execution cycle.

  Next, a clogging reduction amount Md is calculated based on the intake air amount GA and the front end surface temperature Thm (S130). The front end surface temperature Thm is the temperature of the front end surface of the oxidation catalyst 31 and is estimated from the first exhaust temperature Thi detected by the first temperature sensor 33. Note that a temperature sensor may be provided in the vicinity of the front end face of the oxidation catalyst 31 to directly measure the front end face temperature Thm. The clogging reduction amount Md is calculated as a clogging amount M that has decreased from the previous main processing execution cycle to the current main processing execution cycle. As shown in FIG. 6, the clogging reduction amount Md is calculated to be larger as the intake air amount GA is larger or the front end surface temperature Thm is higher.

  Next, the clogging amount M in the current process execution cycle is calculated (S140), and the process is temporarily terminated. In step S140, the clogging increase amount Mi calculated in step S120 is added to the clogging amount M calculated in the previous main processing execution cycle, and the clogging reduction amount Md calculated in step S130 is subtracted. By doing so, the clogging amount M in the current processing execution cycle is calculated.

Next, the procedure of the clogging amount reduction process will be described with reference to FIG. This reduction process is also repeatedly executed by the control device 25 at predetermined intervals.
When this process is started, it is first determined whether or not the clogging amount M obtained by the above-described calculation process exceeds the threshold value α (S200). This threshold value α is a value for determining whether or not the current clogging amount M is a value that causes the above-described inconvenience. When the clogging amount M is equal to or less than the threshold value α (S200: NO), this process is temporarily terminated. As described above, when a negative determination is made in step S200, the basic EGR rate Eb is set based on the engine operating state (for example, the engine rotation speed and the engine load), and the target EGR rate Ep is set according to the basic EGR rate Eb. Thus, the opening degree of the EGR valve 15 is controlled. The basic EGR rate Eb is set to a smaller value as the engine operating state becomes a higher load and higher speed.

  On the other hand, when the clogging amount M exceeds the threshold value α (S200: YES), there is a possibility that inconvenience due to clogging of the front end surface may occur, and therefore, the processing after step S210 is performed in order to reduce such clogging.

  In step S210, an EGR decrease value Ed is calculated based on the engine speed NE. Here, as shown in FIG. 8, the EGR reduction value Ed is set to a larger value as the engine speed NE is higher.

  Next, a clogging correction coefficient Kc is calculated based on the clogging amount M (S220). Here, as shown in FIG. 9, the clogging correction coefficient Kc increases toward “1” as the clogging amount M increases until the clogging amount M reaches a predetermined amount M1. After the clogging amount M reaches the predetermined amount M1, the clogging correction coefficient Kc is fixed to “1”.

  Next, an EGR correction value H is calculated (S230). Here, the EGR correction value H is calculated by multiplying the EGR decrease value Ed calculated in step S210 by the clogging correction coefficient Kc calculated in step S220. Therefore, the EGR correction value H is set to a larger value as the engine speed NE is higher. Further, the EGR correction value H is set to a large value as the clogging amount M increases until the clogging amount M reaches the predetermined amount M1. After the clogging amount M reaches the predetermined amount M1, the EGR reduction value Ed is set as the EGR correction value H as it is.

  Next, the target EGR rate Ep is calculated based on the basic EGR rate Eb and the EGR correction value H described above (S240). In step S240, a value obtained by subtracting the EGR correction value H from the basic EGR rate Eb is set as the target EGR rate Ep. Therefore, the target EGR rate Ep becomes smaller as the EGR correction value H becomes larger, and the EGR amount EK becomes smaller. When the EGR amount EK does not decrease in this way, the amount of exhaust gas returned to the intake passage decreases, and the flow rate of exhaust gas flowing into the oxidation catalyst 31 increases.

Next, the operation of this embodiment will be described.
When it is determined in step S200 of FIG. 7 that the clogging amount M does not exceed the threshold value α, the target EGR rate Ep corresponding to the basic EGR rate Eb is set. On the other hand, if it is determined in step S200 that the clogging amount M has increased beyond the threshold α, the value obtained by subtracting the EGR correction value H from the basic EGR rate Eb is the target EGR rate Ep in step S240. Is done. Therefore, when the clogging amount M exceeds the threshold value α, the target EGR rate Ep is made smaller than when the clogging amount M does not exceed the threshold value α. As described above, when the target EGR rate Ep is reduced, the flow rate of the exhaust gas flowing into the oxidation catalyst 31 is increased by reducing the recirculation amount of the exhaust gas. When the flow rate of the exhaust gas increases in this way, the flow rate of the exhaust gas increases, so that PM clogged in the front end surface of the oxidation catalyst 31 is blown away by the dynamic pressure of the exhaust gas. Therefore, clogging of PM on the front end surface of the oxidation catalyst 31 is reduced.

  It is also possible to reduce clogging at the front end face of the oxidation catalyst 31 by increasing the temperature of the exhaust. However, it is not always possible to raise the exhaust temperature. For example, it is difficult to raise the exhaust temperature when the engine temperature is low and the engine is under a low load. Opportunities are limited to some extent. On the other hand, in this embodiment, the flow rate of the exhaust gas is increased, and such processing can be executed even when the engine is under a low load. Therefore, it is also possible to increase the execution opportunity for the process of reducing the clogging of the front end face.

  Further, the flow rate of the exhaust gas flowing into the oxidation catalyst 31 is increased by decreasing the EGR amount EK. Therefore, it is possible to reduce the clogging of the front end face without separately providing a mechanism only for increasing the exhaust flow rate.

  Further, the PM that causes clogging of the front end face of the oxidation catalyst 31 is derived from the engine fuel. Basically, the larger the fuel injection amount Q, the greater the clogging amount of the front end face. Further, as the engine rotational speed NE is higher, the exhaust amount per unit time is increased and the PM exhaust amount is also increased. Therefore, basically, the higher the engine rotational speed is, the larger the clogging amount of the front end face is. On the other hand, as the intake air amount GA increases, the flow rate of the exhaust gas flowing through the exhaust passage 26 increases, so that PM is easily blown off from the front end surface. Therefore, as the intake air amount GA increases, the amount of clogging of the front end surface decreases. Therefore, in the present embodiment, the clogging increase amount Mi is calculated based on the engine rotational speed NE and the fuel injection amount Q, and the clogging reduction amount Md is calculated based on the intake air amount GA, and the clogging increase amount Mi and clogging are calculated. The amount of PM clogging at the front end face is calculated by obtaining the difference from the decrease amount Md. Therefore, the amount M of clogging of the front end face can be estimated appropriately.

  In addition, soot, which is one of the components constituting PM, is more easily discharged from the engine as the atmospheric pressure is lower and the oxygen density is lower. Thus, the basic clogging amount MB is increased as the atmospheric pressure P is lower, so that the clogging increase amount Mi is increased. Therefore, it is possible to appropriately correct the influence of the atmospheric pressure P on the clogging increase amount Mi.

  Further, as the air amount ratio GAH is smaller, that is, when the intake air amount GA is insufficient with respect to the target air amount GAp, soot is likely to be generated and the clogging amount M is likely to increase. Therefore, by increasing the air amount correction coefficient Ka as the air amount ratio GAH is smaller, the clogging increase amount Mi calculated in step S120 is increased. Therefore, the estimation accuracy of the clogging increase amount Mi at the time of engine transition in which the intake air amount GA is likely to be insufficient with respect to the target air amount GAp is improved.

  Further, as the temperature of the front end surface of the oxidation catalyst 31 increases, the amount of PM adhering to the front end surface is promoted to be oxidized and burned, and the amount thereof is reduced. Therefore, in the present embodiment, the calculated clogging reduction amount Md increases as the front end surface temperature Thm of the oxidation catalyst 31 increases. Therefore, it is possible to appropriately correct the influence of the front end face temperature Thm on the clogging reduction amount Md.

  Further, since the amount of exhaust discharged from the engine 1 decreases as the engine speed NE decreases, the effect of reducing the clogging of the front end surface caused by exhaust becomes small. In this respect, in the present embodiment, the EGR reduction value Ed is increased as the engine rotational speed NE is decreased, so that the reduction amount of the exhaust gas recirculation amount is increased. The flow rate of exhaust gas flowing in increases. Therefore, it is possible to appropriately reduce clogging of the front end face regardless of the engine rotational speed NE.

  Further, as the clogging amount M is larger, the clogging correction coefficient Kc is increased so that the EGR correction value H becomes larger, thereby reducing the target EGR rate Ep and reducing the EGR amount EK. I am doing so. That is, the amount of reduction in the exhaust gas recirculation amount (EGR amount EK) increases as the clogging amount M increases. Therefore, the flow rate of the exhaust gas flowing into the oxidation catalyst 31 is increased as the clogging amount M is larger and more PM needs to be blown away. In this way, the reduction amount of the exhaust gas recirculation amount can be appropriately set according to the clogging amount M.

As described above, according to the present embodiment, the following effects can be obtained.
(1) When the clogging amount M on the front end face of the oxidation catalyst 31 exceeds the threshold value α, the EGR amount EK is decreased.

  Therefore, PM clogging on the front end face of the oxidation catalyst 31 can be suitably reduced. In addition, it is possible to increase the execution opportunity of processing for reducing clogging. Then, the clogging of the front end face of the oxidation catalyst 31 can be reduced without providing a separate mechanism for increasing the exhaust flow rate.

  (2) The clogging amount M is calculated by calculating the difference between the clogging increase amount Mi calculated based on the engine speed NE and the fuel injection amount Q and the clogging reduction amount Md calculated based on the intake air amount GA. Like to do. Therefore, the amount M of clogging of the front end face can be estimated appropriately.

(3) The clogging increase amount Mi increases as the atmospheric pressure P decreases. Therefore, the influence of the atmospheric pressure P on the increase amount of the clogging amount M can be suitably corrected.
(4) The clogging reduction amount Md increases as the front end face temperature Thm of the oxidation catalyst 31 increases. Therefore, it is possible to suitably correct the influence of the front end face temperature Thm of the oxidation catalyst 31 on the reduction amount of the clogging amount M.

(5) The EGR decrease value Ed increases as the engine speed NE decreases. Therefore, clogging of the front end face can be suitably reduced regardless of the engine speed NE.
(6) By increasing the clogging correction coefficient Kc as the clogging amount M increases, the reduction amount of the EGR amount EK increases as the clogging amount M increases. Therefore, the amount of decrease in the EGR amount EK can be set appropriately according to the clogging amount M.

In addition, the said embodiment can also be changed and implemented as follows.
In step S210, the EGR reduction value Ed is calculated based on the engine speed NE. Here, generally, when the fuel injection amount is small, that is, when the engine load is low, the EGR amount EK is often increased. Therefore, the EGR decrease value Ed that decreases the EGR amount EK can be increased as the engine load is lower. Therefore, an engine load may be added in addition to the engine speed NE as a parameter for setting the EGR decrease value Ed. In this case, the EGR reduction value Ed is set to a larger value as the engine load is lower (for example, as the fuel injection amount Q is smaller). According to this modification, it is possible to introduce more exhaust gas into the oxidation catalyst 31 as compared with the case where the EGR decrease value Ed is calculated based only on the engine rotational speed NE.

  -The clogging amount M may be obtained in another manner. For example, the pressure difference between the exhaust upstream side and the exhaust downstream side of the oxidation catalyst 31 may be measured, and it may be estimated that the larger the pressure difference, the larger the clogging amount.

  The clogging increase amount Mi is obtained from the engine rotational speed NE, the fuel injection amount Q, and the atmospheric pressure P. However, the atmospheric pressure P may be omitted and the engine rotational speed NE and the fuel injection amount Q may be obtained. Good.

The clogging reduction amount Md may be determined based on the intake air amount GA and the front end surface temperature Thm, but may be determined only from the intake air amount GA while omitting the front end surface temperature Thm.
Although the EGR decrease value Ed is variably set based on the engine rotational speed NE, it may be set to a fixed value set as appropriate.

  Although the value of the clogging correction coefficient Kc is fixed after the clogging amount M exceeds the predetermined amount M1, the clogging correction coefficient Kc may be increased as the clogging amount M increases.

-Calculation of the clogging correction coefficient Kc may be omitted.
The calculation of the air amount correction coefficient Ka may be omitted.
The fuel for raising the temperature of the filter 32 is supplied from the fuel addition valve 5. In addition, the temperature of the filter 32 may be increased by executing post-injection (fuel injection performed again at a timing delayed from the execution timing of the main injection) by the fuel injection valves 4a to 4d. Further, the fuel supply by the fuel addition valve 5 and the fuel supply by post injection may be used in combination.

-Although the said additive was the fuel of the engine 1, what kind of thing may be sufficient as long as the effect | action similar to this is acquired.
The number of catalysts and filters arranged in the catalyst device 30 can be arbitrarily set. For example, even when only the filter 32 is provided, the front end face may be clogged due to the additive addition. However, by applying the present invention, even when only the filter 32 is provided, clogging of the front end face can be reduced.

A NOx purification catalyst may be provided instead of the oxidation catalyst 31.
Although the engine 1 is an in-line four-cylinder internal combustion engine, the present invention can be similarly applied to an exhaust gas purification apparatus for an internal combustion engine having other numbers of cylinders or cylinder arrangements.

  DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Cylinder head, 3 ... Intake passage, 4a-4d ... Fuel injection valve, 5 ... Injection nozzle, 6a-6d ... Exhaust port, 7 ... Intake manifold, 8 ... Exhaust manifold, 9 ... Common rail, 10 ... Supply pump, 11 ... turbocharger, 13 ... EGR passage, 14 ... EGR cooler, 15 ... EGR valve, 16 ... throttle valve, 17 ... actuator, 18 ... intercooler, 19 ... air flow meter, 20 ... throttle opening sensor, 21 DESCRIPTION OF SYMBOLS ... Air-fuel ratio sensor, 22 ... EGR valve opening sensor, 23 ... Engine rotational speed sensor, 24 ... Accelerator sensor, 25 ... Control device, 26 ... Exhaust passage, 27 ... Fuel supply pipe, 30 ... Catalyst device, 31 ... Oxidation catalyst 32 ... Filter, 33 ... First temperature sensor, 34 ... Second temperature sensor.

Claims (6)

An exhaust purification member provided in the exhaust passage, an additive supply mechanism for supplying an additive to the exhaust purification member, an exhaust recirculation mechanism for recirculating exhaust gas to the intake passage, and an exhaust recirculation amount by the exhaust recirculation mechanism In an exhaust gas purification apparatus for an internal combustion engine comprising a control unit that controls based on an operating state,
When the amount of clogging of the front end surface of the exhaust purification member exceeds a predetermined threshold, the recirculation amount is reduced compared to when the amount of clogging does not exceed the threshold. Exhaust purification device. The clogging amount is calculated by obtaining a difference between an increase amount of the clogging amount calculated based on the engine speed and the fuel injection amount and a reduction amount of the clogging amount calculated based on the intake air amount. Item 6. An exhaust emission control device for an internal combustion engine according to Item 1. The exhaust purification device for an internal combustion engine according to claim 2, wherein the increase amount is increased as the atmospheric pressure is lower. The exhaust purification device for an internal combustion engine according to claim 2 or 3, wherein the amount of decrease is increased as the temperature of the front end face of the exhaust purification member is higher. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the reduction amount of the recirculation amount is reduced as the engine rotational speed is higher. The exhaust purification device for an internal combustion engine according to any one of claims 1 to 5, wherein the amount of decrease in the recirculation amount is increased as the clogging amount increases.

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