JP2006029239A - Exhaust emission control filter overheat prevention device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively prevent overheat of an exhaust emission control filter for an internal combustion engine. <P>SOLUTION: Risk of over heat of the exhaust emission control filter is determined (S102) based on whether estimated maximum bed temperature estimated from a map based on intake air quantity reduction quantity and PM accumulation quantity exceeds over-heat determination temperature or not at a time of PM regeneration control process. If there is a risk of overheat (YES in S102), exhaust gas flow quantity increase process is performed by intake air quantity increase process by fully opening a throttle valve and fully closing an EGR valve (S104). In fuel injection quantity control process, exhaust gas flow quantity is secured by idling speed increase at a time of idling. Consequently, since heat generated in the exhaust emission control filter is positively transmitted and emitted to outside, overheat of the exhaust emission control filter can be effectively prevented. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an apparatus for preventing overheating of an exhaust purification filter that is provided in an exhaust system of an internal combustion engine and filters particulate matter in exhaust gas and burns and purifies particulate matter accumulated by the filtration by a temperature raising process. .

There is known an exhaust purification technology in which a NOx occlusion reduction type catalyst is disposed in an exhaust system of an internal combustion engine, and when the internal combustion engine is decelerated, exhaust gas is enriched to reduce NOx occluded in the catalyst (for example, Patent Document 1). reference). In this technique, when the exhaust gas is enriched, the intake air amount is decreased or the exhaust gas recirculation amount is increased.
JP 2002-371889 A (page 21, FIG. 7, 67)

  As the catalyst disposed in the exhaust system, a catalyst having a filter function for filtering particulate matter may be used instead of or together with the catalyst. In such an exhaust purification filter, the particulate matter gradually accumulates inside as the operation of the internal combustion engine continues. For this reason, in order to prevent clogging, if particulate matter is deposited to some extent, a temperature raising process is required to burn the deposited particulate matter and regenerate the exhaust purification filter.

  However, if the regeneration process by combustion of such particulate matter overlaps with the deceleration state of the internal combustion engine, the exhaust flow rate decreases when the internal combustion engine decelerates, so the amount of heat generated by the regeneration process in the exhaust purification filter is The amount carried out by exhaust will decrease.

For this reason, heat accumulates in the exhaust purification filter, which may cause overheating of the exhaust purification filter, and in some cases may cause deterioration of the exhaust purification filter such as melting.
In addition, as described in Patent Document 1, when the intake air amount is further reduced by the intake throttle valve or the exhaust gas recirculation amount is increased by the exhaust gas recirculation valve at the time of deceleration of the internal combustion engine, the exhaust flow rate decreases. It becomes even larger, and overheating tends to be caused by the exhaust purification filter.

  Although it is conceivable that the regeneration process is immediately stopped when the internal combustion engine is decelerated, oxygen is already present in the exhaust purification filter in some form, and it is difficult to immediately prevent the heat generation itself. .

  An object of the present invention is to effectively prevent overheating in an exhaust purification filter of an internal combustion engine.

In the following, means for achieving the above object and its effects are described.
The exhaust purification filter overheat prevention device according to claim 1 is provided in an exhaust system of an internal combustion engine to filter particulate matter in the exhaust, and to purify the particulate matter deposited by the filtration by heating treatment. An apparatus for preventing overheating of an exhaust purification filter, comprising an overheat prevention means for preventing overheating of the exhaust purification filter by an increase process with respect to an exhaust flow rate when there is a possibility of overheating of the exhaust purification filter. .

  As described above, the overheat prevention means performs an increase process on the exhaust gas flow rate when the exhaust purification filter is likely to be overheated. This increase process only requires that the exhaust flow rate be higher than when the exhaust flow rate is not increased. That is, when the exhaust gas flow rate is decreasing, processing for suppressing the degree of exhaust gas flow rate reduction, maintaining the exhaust gas flow rate so as not to decrease, or increasing the exhaust gas flow rate is included. When the exhaust gas flow rate is increasing, a process for increasing it further is included.

As a result, the heat generated in the exhaust gas purification filter due to the exhaust gas is actively carried out and released to the outside. Thus, overheating of the exhaust purification filter can be effectively prevented.
According to a second aspect of the present invention, in the exhaust purification filter overheat prevention device according to the first aspect, the overheat prevention means realizes the increase process for the exhaust gas flow rate by the increase process for the intake air amount of the internal combustion engine.

  If an increase process for the intake air amount to the internal combustion engine is performed, an exhaust amount that changes in accordance with the intake air amount is discharged to the exhaust pipe side through the combustion chamber. This can be realized by increasing the amount of intake air. This can effectively prevent overheating of the exhaust purification filter.

  According to a third aspect of the present invention, there is provided the exhaust purification filter overheat prevention device according to the second aspect, wherein the overheat prevention means increases the intake air amount of the internal combustion engine by increasing the opening of a throttle valve provided in the intake system and exhaust gas. This is realized by one or both of the processes of reducing the opening degree of the exhaust gas recirculation valve provided in the exhaust gas recirculation path from the system to the intake system.

  The increase process for the intake air amount may be dealt with by increasing the throttle valve opening, or by reducing the exhaust recirculation valve opening. Further, both the increase in the throttle valve opening and the decrease in the exhaust gas recirculation valve opening may be dealt with.

  According to a fourth aspect of the present invention, in the exhaust purification filter overheat prevention device according to the first aspect, the overheat prevention means realizes an increase process for the exhaust flow rate by increasing the idle speed when the internal combustion engine is in an idle state. It is characterized by.

  During idling, an increase process for the exhaust flow rate can be realized by increasing the idling speed. This can effectively prevent overheating of the exhaust purification filter.

  In the exhaust purification filter overheat prevention device according to claim 5, in any one of claims 1 to 4, the overheat prevention means, when the exhaust temperature of the exhaust gas flowing out from the exhaust purification filter is higher than the overheat determination temperature, It is determined that there is a risk of overheating of the exhaust purification filter.

  Since the temperature of the exhaust gas flowing out from the exhaust purification filter reflects the temperature state inside the exhaust purification filter, if the exhaust temperature of the exhaust gas flowing out from the exhaust purification filter is higher than the overheat determination temperature, the exhaust purification filter overheats. It can be determined that there is a risk of this.

  In the exhaust purification filter overheat prevention device according to claim 6, in any one of claims 1 to 4, the overheat prevention means includes a condition that an exhaust temperature of exhaust gas flowing into the exhaust purification filter is higher than an overheat determination temperature, Judgment is made on one or both of the conditions in which the exhaust gas temperature of the exhaust gas flowing out from the purification filter is higher than the overheat determination temperature, and if any one of the conditions is satisfied, the exhaust purification filter may overheat. It is characterized by judging.

  The floor temperature of the exhaust purification filter is also affected by the temperature of the inflowing exhaust. Therefore, it can be determined that the risk of overheating of the downstream exhaust purification filter increases not only by the downstream side of the exhaust purification filter but also by determining the exhaust temperature of the upstream inflow exhaust gas.

  In particular, when another exhaust purification catalyst, such as a NOx occlusion reduction type catalyst, is disposed upstream of the exhaust purification filter, such a catalyst generates heat during the temperature raising process. Therefore, if the upstream exhaust purification catalyst is heated and the exhaust temperature of the inflowing exhaust gas exceeds the limit, it can be determined earlier that the possibility that the downstream exhaust purification filter will be overheated increases.

  Therefore, the overheat prevention means adds a condition that the exhaust gas temperature of the exhaust gas flowing out from the exhaust gas purification filter is higher than the overheat determination temperature and the exhaust gas temperature of the exhaust gas flowing into the exhaust gas purification filter is higher than the overheat determination temperature. Then, either one or both conditions are determined, and if at least one of the conditions is satisfied, it can be determined that the exhaust purification filter may be overheated.

  In this way, by determining the condition that the exhaust temperature of the exhaust gas flowing into the exhaust purification filter is higher than the overheat determination temperature, it is possible to predict overheating of the exhaust purification filter earlier, and by executing the increase process for the exhaust flow rate, Overheating of the exhaust purification filter can be prevented more reliably.

  The exhaust purification filter overheat prevention device according to claim 7, wherein the overheat prevention means is a fuel that flows into an exhaust gas from an addition flow rate provided in an exhaust system of an internal combustion engine. If the floor temperature of the exhaust purification filter is estimated based on the addition amount, the exhaust temperature of the exhaust gas flowing into the exhaust purification filter, and the exhaust temperature of the exhaust gas flowing out of the exhaust purification filter, and the floor temperature is higher than the overheat determination temperature The exhaust purification filter is judged to have a risk of overheating.

  The floor temperature of the exhaust purification filter can be estimated based on the exhaust flow rate, the amount of fuel added from the addition valve into the exhaust, the exhaust temperature of the inflowing exhaust, and the exhaust temperature of the outflowing exhaust. Since the exhaust purification filter floor temperature can be estimated in this way, the exhaust purification filter overheating can be predicted more accurately, and the exhaust purification filter overheating can be more effectively performed by accurately executing the increase processing for the exhaust flow rate. Can be prevented.

  The exhaust purification filter overheat prevention device according to claim 8, wherein the overheat prevention means includes a combustion purification process of particulate matter deposited on the exhaust purification filter. During processing, when the accumulation amount of the particulate matter is larger than the reference accumulation amount, it is determined that the exhaust purification filter may be overheated.

  If the amount of accumulated particulate matter is large, the amount of heat generated per unit time when the particulate matter burns during any exhaust purification filter temperature rise treatment such as combustion purification treatment of particulate matter. Can be estimated to be large. Therefore, when the accumulation amount of the particulate matter is larger than the reference accumulation amount, it may be determined that the exhaust purification filter may be overheated. In this way, a simple determination can be made, and it is easy to determine whether the exhaust purification filter is likely to overheat.

  The exhaust purification filter overheat prevention device according to claim 9, wherein the overheat prevention means performs combustion purification processing of particulate matter deposited on the exhaust purification filter during deceleration of the internal combustion engine. If the predicted maximum floor temperature of the exhaust purification filter estimated based on the operating state of the internal combustion engine is higher than the overheat determination temperature, the exhaust purification filter may overheat. It is characterized by judging.

  Based on the current operating state of the internal combustion engine, it is possible to estimate the expected maximum bed temperature of the exhaust purification filter that occurs immediately after. Therefore, if the predicted maximum bed temperature is higher than the overheat determination temperature when the exhaust gas purification filter temperature raising process such as the combustion purification process of particulate matter is being performed at the time of deceleration of the internal combustion engine, the exhaust gas It may be determined that there is a risk of overheating of the purification filter.

As a result, it is possible to effectively prevent overheating of the exhaust purification filter by executing an increase process for the exhaust flow rate before the bed temperature actually becomes higher than the overheat determination temperature.
The exhaust purification filter overheat prevention device according to claim 10, wherein the overheat prevention means includes a combustion purification process of particulate matter deposited on the exhaust purification filter. It is determined that there is a risk of overheating of the exhaust purification filter when the predicted maximum bed temperature of the exhaust purification filter that is being processed and is estimated based on the operating state of the internal combustion engine is higher than the overheat determination temperature. And

  In addition, not only when the internal combustion engine is decelerated, but based on the current operating state of the internal combustion engine, the estimated maximum bed temperature of the exhaust purification filter that occurs immediately after is estimated, and this predicted maximum bed temperature is higher than the overheat determination temperature. It may be determined that there is a risk of overheating of the exhaust purification filter.

  As a result, overheating of the exhaust purification filter is effectively prevented by executing an increase process for the exhaust flow rate before the bed temperature actually becomes higher than the overheat determination temperature in various operating states, including during deceleration of the internal combustion engine. It comes out.

  In the exhaust purification filter overheat prevention device according to claim 11, in claim 9 or 10, the overheat prevention means captures a reduction amount of the exhaust flow rate per unit time as a reduction amount of the intake air amount per unit time, The predicted maximum bed temperature is estimated based on the amount of decrease in the intake air amount per unit time and the amount of particulate matter deposited.

Thus, the predicted maximum bed temperature can be easily estimated based on the amount of reduction in the intake air amount per unit time and the amount of particulate matter deposited.
In the exhaust purification filter overheat prevention device according to claim 12, in any one of claims 1 to 4, the overheat prevention means performs a combustion purification process of particulate matter deposited on the exhaust purification filter during deceleration of the internal combustion engine. When the temperature of the exhaust gas purification filter is being increased and the accumulation amount of the particulate matter is larger than the reference accumulation amount, it is determined that the exhaust purification filter may be overheated.

  When the internal combustion engine is decelerating, if any exhaust purification filter temperature rise processing such as combustion purification treatment of particulate matter deposited on the exhaust purification filter, or if the particulate matter accumulation amount is greater than the reference deposition amount It is estimated that the amount of heat generated per unit time is large due to the large amount of particulate matter that burns. Therefore, in such a state, it may be determined that the exhaust purification filter may be overheated.

  According to a thirteenth aspect of the present invention, in the exhaust purification filter overheat prevention device according to any one of the eighth to twelfth aspects, the exhaust purification filter temperature increasing process includes a sulfur poisoning recovery control process.

  Not only in the case where the particulate matter combustion purification process is being performed, but also in other exhaust purification filter temperature raising processes such as the sulfur poisoning recovery control process, if the particulate matter remains in the exhaust purification filter May start combustion and overheat. From this, even in the case of sulfur poisoning recovery control processing or the like, the exhaust purification filter overheat prevention device functions as described above, so that overheating of the exhaust purification filter can be effectively prevented.

[Embodiment 1]
FIG. 1 is a configuration explanatory view showing an outline of a vehicular diesel engine to which the above-described invention is applied and a control system thereof. The present invention can also be applied to a case where a similar catalyst configuration is adopted for a lean combustion gasoline engine or the like.

  The diesel engine 2 is a multiple cylinder engine. Here, four cylinders # 1, # 2, # 3, and # 4 will be described as an example, but the number of cylinders may be less than four or more than four. The combustion chambers 4 of the cylinders # 1 to # 4 are connected to a surge tank 12 via an intake port 8 and an intake manifold 10 that are opened and closed by an intake valve 6. The surge tank 12 is connected via an intake passage 13 to an intercooler 14 and a supercharger, here, an outlet side of a compressor 16 a of an exhaust turbocharger 16. The inlet side of the compressor 16 a is connected to an air cleaner 18. The surge tank 12 has an EGR gas supply port 20 a of an exhaust gas recirculation (hereinafter referred to as “EGR”) path 20. A throttle valve 22 is disposed in the intake path 13 between the surge tank 12 and the intercooler 14, and an intake air amount sensor 24 and an intake air temperature sensor 26 are disposed between the compressor 16 a and the air cleaner 18. .

  The combustion chambers 4 of the cylinders # 1 to # 4 are connected to the inlet side of the exhaust turbine 16b of the exhaust turbocharger 16 via an exhaust port 30 and an exhaust manifold 32 that are opened and closed by an exhaust valve 28, and the outlet of the exhaust turbine 16b. The side is connected to the exhaust path 34. The exhaust turbine 16b introduces exhaust from the fourth cylinder # 4 side in the exhaust manifold 32.

  In the exhaust path 34, three catalytic converters 36, 38 and 40 in which an exhaust purification catalyst is housed are arranged. The most upstream first catalytic converter 36 houses a NOx storage reduction catalyst 36a. When the exhaust gas is in an oxidizing atmosphere (lean) during normal operation of the diesel engine 2, NOx is stored in the NOx storage reduction catalyst 36a. In the reducing atmosphere (stoichiometric or air / fuel ratio lower than stoichiometric), the NOx occluded in the NOx occlusion reduction catalyst 36a is released as NO and is reduced by HC or CO. In this way, NOx is purified.

  The second catalytic converter 38 arranged second is housed with an exhaust purification filter 38a having a wall portion formed in a monolith structure, and is configured so that exhaust gas passes through the minute hole in the wall portion. Since the NOx occlusion reduction catalyst layer is formed on the surface of the minute holes of the exhaust purification filter 38a by coating, it functions as an exhaust purification catalyst and purifies NOx as described above. Furthermore, particulate matter in the exhaust (hereinafter referred to as “PM”) is trapped in the filter wall, so that oxidation of PM is started by active oxygen generated when NOx is occluded in a high-temperature oxidizing atmosphere. The whole PM is oxidized by oxygen. Thus, the purification of PM is performed together with the purification of NOx. Here, the first catalytic converter 36 and the second catalytic converter 38 are integrally formed.

The most downstream third catalytic converter 40 contains an oxidation catalyst 40a, where HC and CO are oxidized and purified.
A first exhaust temperature sensor 44 is disposed between the NOx occlusion reduction catalyst 36a and the exhaust purification filter 38a that are disposed close to each other. Further, between the exhaust purification filter 38a and the oxidation catalyst 40a, a second exhaust temperature sensor 46 is disposed immediately below the exhaust purification filter 38a, and an air-fuel ratio sensor 48 is disposed near the oxidation catalyst 40a.

  The air-fuel ratio sensor 48 is a sensor that detects the air-fuel ratio of the exhaust based on the exhaust component and linearly outputs a voltage signal proportional to the air-fuel ratio. The first exhaust temperature sensor 44 and the second exhaust temperature sensor 46 detect the exhaust temperatures thci and thco at their respective positions.

  A pipe for the differential pressure sensor 50 is provided on the upstream side and the downstream side of the exhaust purification filter 38a, respectively, and the differential pressure sensor 50 is used to detect the degree of clogging of the exhaust purification filter 38a, that is, the degree of PM accumulation. The pressure difference ΔP between the upstream and downstream of the filter 38a is detected.

  In the exhaust manifold 32, an EGR gas inlet 20b of the EGR path 20 is opened. The EGR gas inlet 20b is open on the first cylinder # 1 side, and is on the opposite side to the fourth cylinder # 4 side where the exhaust turbine 16b introduces exhaust.

  In the middle of the EGR path 20, an iron-based EGR catalyst 52 for reforming EGR gas is disposed from the EGR gas inlet 20b side, and an EGR cooler 54 for cooling the EGR gas is further provided. The EGR catalyst 52 also has a function of preventing the EGR cooler 54 from being clogged. An EGR valve 56 is disposed on the EGR gas supply port 20a side. By adjusting the opening degree of the EGR valve 56, the exhaust gas recirculation amount from the EGR gas supply port 20a to the intake system can be adjusted.

  A fuel injection valve 58 disposed in each cylinder # 1 to # 4 and directly injecting fuel into each combustion chamber 4 is connected to a common rail 60 via a fuel supply pipe 58a. Fuel is supplied into the common rail 60 from an electrically controlled discharge variable fuel pump 62, and the high-pressure fuel supplied from the fuel pump 62 into the common rail 60 is supplied to each fuel injection valve 58 through each fuel supply pipe 58a. Distributed supply. A fuel pressure sensor 64 for detecting the fuel pressure is attached to the common rail 60.

  Further, low pressure fuel is separately supplied from the fuel pump 62 to the addition valve 68 via the fuel supply pipe 66. The addition valve 68 is provided in the exhaust port 30 of the fourth cylinder # 4, and adds fuel into the exhaust by injecting fuel toward the exhaust turbine 16b. The catalyst control mode described later is executed by this fuel addition.

  An electronic control unit (hereinafter referred to as “ECU”) 70 is mainly configured by a digital computer including a CPU, a ROM, a RAM, and the like, and a drive circuit for driving various devices. The ECU 70 includes the intake air amount sensor 24, the intake air temperature sensor 26, the first exhaust temperature sensor 44, the second exhaust temperature sensor 46, the air-fuel ratio sensor 48, the differential pressure sensor 50, the EGR opening sensor in the EGR valve 56, Signals from the fuel pressure sensor 64 and the throttle opening sensor 22a are read. Further, signals are read from an accelerator opening sensor 74 that detects the amount of depression of the accelerator pedal 72 (accelerator opening ACCP) and a cooling water temperature sensor 76 that detects the cooling water temperature THW of the diesel engine 2. Further, signals are read from an engine speed sensor 80 that detects the rotational speed NE of the crankshaft 78, and a cylinder discrimination sensor 82 that detects the rotation phase of the crankshaft 78 or the rotation phase of the intake cam and performs cylinder discrimination.

  Based on the engine operating state obtained from these signals, the ECU 70 executes fuel injection amount control and fuel injection timing control by the fuel injection valve 58. Further, the opening degree control of the EGR valve 56, the throttle opening degree control by the motor 22b, the discharge amount control of the fuel pump 62, and the valve opening control of the addition valve 68, PM regeneration control, S (sulfur) poisoning recovery control or NOx described later. Catalyst control such as reduction control, catalyst overheat prevention processing, and other processes are executed.

  As the combustion mode control executed by the ECU 70, a combustion mode selected from two types of a normal combustion mode and a low temperature combustion mode is executed according to the operating state. Here, the low-temperature combustion mode is a combustion mode in which NOx and smoke are simultaneously reduced by slowing the increase in the combustion temperature by a large amount of exhaust gas recirculation using the EGR valve opening map for low-temperature combustion mode. This low-temperature combustion mode is executed in the low-load low-medium rotation region, and air-fuel ratio feedback control is performed by adjusting the throttle opening TA based on the air-fuel ratio AF detected by the air-fuel ratio sensor 48. The combustion mode other than this is a normal combustion mode in which normal EGR control (including the case where EGR is not performed) is executed using the normal combustion mode EGR valve opening degree map.

  There are four types of catalyst control modes for performing catalyst control on the exhaust purification catalyst: a PM regeneration control mode, an S poison recovery control mode, a NOx reduction control mode, and a normal control mode.

  In the PM regeneration control mode, when the estimated accumulation amount of PM reaches the PM regeneration reference value, in particular, the PM accumulated on the exhaust purification filter 38a in the second catalytic converter 38 is combusted as described above by increasing the temperature, and CO2. And a temperature raising process for PM purification that is discharged as H2O. In this mode, fuel addition from the addition valve 68 is repeated in an air-fuel ratio state higher than stoichiometric (theoretical air-fuel ratio) to raise the catalyst bed temperature (for example, 600 to 700 ° C.). There is a case where after-injection that is fuel injection into the combustion chamber 4 in the stroke or exhaust stroke is added.

  The S poisoning recovery control mode is a mode in which when the NOx storage reduction catalyst 36a and the exhaust purification filter 38a are poisoned with S and the NOx storage capacity is reduced, the S component is released to recover from the S poisoning. In this mode, fuel addition is repeated from the addition valve 68 to execute a temperature raising process for raising the catalyst bed temperature (for example, 650 ° C.), and the air-fuel ratio is stoichiometrically or stoichiometrically by intermittent fuel addition from the addition valve 68. The air-fuel ratio lowering process is performed to make the air-fuel ratio slightly lower than that. Here, enrichment is performed to make the air-fuel ratio slightly lower than stoichiometric. In this mode, after-injection by the fuel injection valve 58 may be added.

  The NOx reduction control mode is a mode in which NOx occluded in the NOx occlusion reduction catalyst 36a and the exhaust purification filter 38a is reduced to N2, CO2 and H2O and released. In this mode, by intermittent fuel addition from the addition valve 68 with a relatively long time, the catalyst bed temperature is relatively low (for example, 250 to 500 ° C.), and the air-fuel ratio is reduced or lower than the stoichiometry. .

It should be noted that states other than these three catalyst control modes become the normal control mode, and in this normal control mode, fuel addition from the addition valve 68 and after-injection by the fuel injection valve 58 are not performed.
Next, the catalyst overheating prevention process among the processes executed by the ECU 70 will be described. FIG. 2 shows a flowchart of the catalyst overheat prevention process. This process is a process that is repeatedly executed at a constant time period. The steps in the flowchart corresponding to the individual processing contents are represented by “S˜”.

  When this process is started, it is first determined whether or not the exhaust purification filter 38a is likely to be overheated (S102). In this determination, it is determined that there is a possibility of overheating when both of the following conditions (1) and (2) are satisfied.

(1) By the catalyst control described above, the PM regeneration control mode, that is, the PM regeneration control process for burning the accumulated PM by raising the temperature of the exhaust purification filter 38a is executed.
(2) The predicted maximum bed temperature CTmax of the exhaust purification filter 38a, which is obtained from the relationship between the intake air amount decrease amount ΔGA per unit time and the PM accumulation amount in the exhaust purification filter 38a, exceeds the overheat determination temperature OT. . This predicted maximum bed temperature CTmax is the maximum bed temperature that occurs immediately after the reduction of the intake air amount GA.

  Here, the intake air amount decrease amount ΔGA (g / s / s) is obtained as a change amount in unit time (s) from the intake air amount GA (g / s) detected by the intake air amount sensor 24. Note that ΔGA> 0 when the intake air amount GA decreases.

  The PM accumulation amount of the exhaust purification filter 38a is always obtained by the PM accumulation amount calculation process separately executed by the ECU 70 based on the operating state of the diesel engine 2 (intake air temperature, combustion air-fuel ratio, exhaust temperature thci, thco, etc.). It has been. Specifically, it was obtained by calculating the balance between the amount of PM discharged from the diesel engine 2 calculated at a constant time period based on the engine operating state and the amount of PM lost due to oxidation in the exhaust purification filter 38a. It is obtained by integrating the values.

  Then, based on the intake air amount decrease amount ΔGA and the PM accumulation amount, the predicted maximum bed temperature CTmax is calculated from the map MapCT shown by a solid line in FIG. 3, and whether or not the predicted maximum bed temperature CTmax exceeds the overheat determination temperature OT. Is determined. If CTmax> OT, the condition (2) is satisfied.

  The map MapCT is created in advance by experimentally measuring the maximum bed temperature of the exhaust purification filter 38a in the period immediately after the decrease in the intake air amount during PM regeneration control, using the intake air amount decrease amount ΔGA and the PM accumulation amount as parameters. Map. As shown in FIG. 3, as the PM accumulation amount increases, the sensitivity of the predicted maximum bed temperature CTmax based on the intake air amount decrease amount ΔGA increases. That is, when the intake air amount decrease amount ΔGA = ΔGA1, the predicted maximum bed temperature CTmax = PM1a when the PM accumulation amount is small, and the predicted maximum bed temperature CTmax = PM1b when the PM accumulation amount is large, both of which are the overheat determination temperature. Lower than OT.

  However, if the intake air amount decrease amount ΔGA = ΔGA2 and the degree of decrease in the exhaust flow rate increases, the predicted maximum bed temperature CTmax = PM2a when the PM accumulation amount is small, which is lower than the overheat determination temperature OT, When the accumulation amount is large, the predicted maximum bed temperature CTmax = PM2b, which is higher than the overheat determination temperature OT.

  If both (1) and (2) are satisfied, it is determined that the exhaust purification filter 38a may be overheated (YES in S102), and an exhaust flow rate increasing process for preventing catalyst overheating is executed (S104).

Here, in the catalyst overheat prevention exhaust gas flow rate increasing process, both of the following processes (a) and (b) are executed.
(A) The opening degree TA of the throttle valve 22 is increased as compared with normal control.

  In order to cause the diesel engine 2 to burn properly, the throttle valve 22 is controlled in its opening degree according to the engine operating state. In order to increase the throttle opening degree TA, for example, the throttle opening degree TA is fully opened (100 %) Or increase by the opening degree set for overheating prevention, and make the opening degree larger than usual.

  In the present embodiment, the throttle valve 22 is fully opened. As a result, the intake air amount GA sucked into the combustion chamber 4 is increased, and as a result, the exhaust flow rate discharged to the exhaust passage 34 is increased.

  The increase processing of the intake air amount GA and the exhaust gas flow rate means an increase compared to the case where the throttle valve 22 is subjected to normal opening control. That is, when the intake air amount GA and the exhaust flow rate are reduced, the degree of reduction of the intake air amount GA and the exhaust flow rate is suppressed, the intake air amount GA and the exhaust flow rate are not reduced, or A process of increasing the intake air amount GA and the exhaust flow rate is included. When the intake air amount GA and the exhaust gas flow rate are increased, a process for further increasing the intake air amount GA and the exhaust gas flow rate is included.

(B) The opening degree EGRa of the EGR valve 56 is decreased as compared with the normal control.
The opening degree of the EGR valve 56 is controlled in accordance with the engine operating state in order to cause the diesel engine 2 to burn properly. In order to decrease the EGR opening degree EGRa, for example, the target EGR opening degree EGRt is fully closed. (0%) or decrease by the opening degree set for preventing overheating to make the opening degree smaller than normal.

  In the present embodiment, the EGR valve 56 is fully closed. As a result, the intake air amount GA taken into the combustion chamber 4 is increased, and as a result, the exhaust flow rate discharged to the exhaust passage 34 is increased.

  As a result, as shown in the timing chart of FIG. 4, after the start of the PM regeneration control mode (t0), the catalyst bed temperature becomes the overheat determination temperature OT due to the decrease in the exhaust flow rate, here the intake air amount GA due to deceleration or the like. When predicted to exceed (t1), the throttle valve 22 is fully opened and the EGR valve 56 is fully closed.

  As a result, a decrease in the exhaust flow rate is suppressed by suppressing the decrease in the intake air amount GA, and the exhaust purification filter 38a does not rise to the overheat determination temperature OT. Unless the throttle opening degree TA is increased and the EGR opening degree EGRa is not reduced, the intake air amount GA rapidly decreases as shown by the broken line, the catalyst bed temperature rises and exceeds the overheat determination temperature OT (t2).

  (1) If at least one of the conditions (2) is not satisfied, it is determined that there is no risk of overheating of the exhaust purification filter 38a (NO in S102). Is determined (S106). If the exhaust gas flow rate increasing process for preventing catalyst overheating has not been performed (NO in S106), this process is temporarily terminated as it is.

  If the above-described catalyst overheat prevention exhaust flow rate increase process is being executed (YES in S106), it is next determined whether or not a stop condition for the catalyst overheat prevention exhaust flow rate increase process is satisfied ( S108).

This stop condition is satisfied when either of the following (e1) and (e2) is satisfied.
(E1) A sufficient time has elapsed since the PM regeneration control process was completed.

  If the PM regeneration control process is completed, heat generation due to PM combustion in the exhaust purification filter 38a is stopped, and if a sufficient time that can be cooled by the exhaust has elapsed, normal throttle opening control and EGR are performed. It is because there is no fear of overheating even if it returns to opening degree control.

(E2) The predicted maximum bed temperature CTmax of the exhaust purification filter 38a is sufficiently lower than the overheat determination temperature OT.
For example, this is a case where the predicted maximum bed temperature CTmax obtained from the map MapCT based on the current intake air amount decrease amount ΔGA and the PM accumulation amount satisfies the relationship of Equation 1 using the hysteresis H.

If Expression 1 is satisfied, there is no risk of hunting even when returning to normal throttle opening control and EGR opening control.
[Formula 1] CTmax <OT-H
If any of the above (e1) and (e2) is satisfied (YES in S108), the exhaust flow rate increasing process for preventing catalyst overheating is stopped (S110).

  If none of the above (e1) and (e2) is satisfied (NO in S108), this process is temporarily stopped as it is. Therefore, the exhaust gas flow rate increasing process for preventing catalyst overheating is continued.

  Next, the fuel injection amount control process executed by the ECU 70 is shown in the flowchart of FIG. In this fuel injection amount control process, if an exhaust flow rate increasing process for preventing catalyst overheating is being performed during idling, a process for performing idle up is added. This process is executed at intervals of the injection interval, in this case, the 4-cylinder diesel engine 2, and therefore is executed every crank angle of 180 °.

  When the fuel injection amount control process is started, it is first determined whether or not the current engine operating state is not the deceleration fuel cut region (S152). The deceleration fuel cut region is determined from the engine operating state (for example, the accelerator opening ACCP and the engine speed NE). If this is the deceleration fuel cut region (NO in S152), the present process is temporarily terminated. To do. Therefore, fuel is not injected from the fuel injection valve 58.

  If it is not the deceleration fuel cut region (YES in S152), the idle governor injection amount QGOV1 and the traveling governor injection amount QGOV2 are determined from the governor pattern map shown in FIG. 6 in which the relationship between the engine speed NE and the accelerator opening ACCP is set. Calculate (S154). The idle governor injection amount QGOV1 is an injection amount when the engine is in a low rotation range, that is, when the automobile is mainly in the idle rotation state, and is indicated by a broken line in FIG. Further, the traveling governor injection amount QGOV2 is an injection amount when the engine is in a high rotation range, that is, when the automobile is mainly in a traveling state, and is indicated by a solid line in FIG.

  Next, it is determined whether the exhaust gas flow rate increasing process for preventing catalyst overheating is being executed (S156). If the exhaust gas flow rate increasing process for preventing catalyst overheating has not been executed (NO in S156), the governor injection amount QGOV is then calculated (S158). The governor injection amount QGOV is calculated as shown in Equation 2.

[Formula 2] QGOV ←
Max (QGOV1 + QII + QIPB + QIPNT, QGOV2 + QIPB)
That is, a value obtained by adding the integral correction amount QII, the ISC expected load correction term QIPB and the ISC expected rotation speed correction term QIPNT to the idle governor injection amount QGOV1, and further calculating the ISC expected load correction term QIPB to the travel governor injection amount QGOV2. Calculate the added value. Then, the two values are compared, and the larger value is set as the governor injection amount QGOV.

  Therefore, at the time of normal fuel injection amount control in which the exhaust gas flow rate increasing process for preventing catalyst overheating is not executed, the governor injection amount QGOV is set as roughly determined from FIG. That is, in the low speed range of the engine 2 (when the engine 2 is mainly in the idling state), the integral governor injection amount QGOV1, the integral correction amount QII, the ISC expected load correction term QIPB and the ISC expected rotational speed correction term QIPNT are set. The added value is selected as the governor injection amount QGOV. In a high rotation range of the engine 2 (when the automobile is mainly in a traveling state), a value obtained by adding the ISC expected load correction term QIPB to the traveling governor injection amount QGOV2 is selected as the governor injection amount QGOV.

On the other hand, if the exhaust gas flow increase processing for preventing catalyst overheating is being executed (YES in S156), the governor injection amount QGOV is calculated as shown in Equation 3.
[Formula 3] QGOV ←
Max (QGOV1 + QII + QINC, QGOV2 + QIPB)
Formula 3 differs from Formula 2 in that the value obtained by adding the integral correction amount QII and the ISC rotation speed correction term QINC for idling up at the time of catalyst overheating to the idle governor injection amount QGOV1 set mainly at idling is the governor injection. This is the point that is selected as the quantity QGOV.

  As a result, during the exhaust gas flow increase process for preventing catalyst overheating, the engine speed is always higher than that during normal idling, as indicated by the broken line shown as “Idle Up” in FIG. 6 by the ISC speed correction term QINC. Thus, the fuel injection amount is increased. As a result, even when the exhaust flow rate increasing process for preventing catalyst overheating is in an idle state, a sufficient exhaust flow rate is ensured to prevent the exhaust purification filter 38a from being overheated.

  Following step S158 or step S160, the smaller one of the maximum injection amount QFULL and the governor injection amount QGOV is set as the final injection amount QFIN (S162). Then, an injection amount command value (time conversion value) TSP corresponding to the final injection amount QFIN is calculated, and this injection amount command value TSP is output (S164). In this way, this process is once completed. Based on the output of the injection amount command value TSP, the fuel injection valve 58 is driven and fuel injection is performed.

  Therefore, as shown in the timing chart of FIG. 4, after the idling state is reached (t3), the catalyst overheating prevention is performed unless the PM regeneration control mode continues and the predicted maximum bed temperature CTmax is not sufficiently low. Therefore, the throttle opening fully open, the EGR opening fully closed, and the idle-up process are continued.

  In the above-described configuration, the relationship with the claims is that the processes of steps S156 and S160 of the catalyst overheat prevention process (FIG. 2) and the fuel injection amount control process (FIG. 5) among the processes executed by the ECU 70 are the overheat prevention means. It corresponds to the process.

According to the first embodiment described above, the following effects can be obtained.
(I). In the process of the catalyst overheat prevention process (FIG. 2), when there is a possibility of overheating of the exhaust purification filter 38a, the exhaust flow rate is increased by the process of increasing the intake air amount with the throttle valve 22 fully open and the EGR valve 56 fully closed. Yes. In steps S156 and S160 of the fuel injection amount control process (FIG. 5), the exhaust flow rate is secured by increasing the idle speed during idling. For this reason, since the heat generated in the exhaust purification filter 38a is actively carried out and released to the outside, overheating of the exhaust purification filter 38a can be effectively prevented.

  (B). The possibility of overheating of the exhaust purification filter 38a is during PM regeneration control processing, and the predicted maximum bed temperature CTmax estimated from the map MapCT (FIG. 3) based on the intake air amount decrease amount ΔGA and the PM accumulation amount is The determination is made based on whether or not the overheat determination temperature OT is exceeded.

  As a result, the exhaust flow rate can be easily increased before the bed temperature actually becomes higher than the overheat determination temperature OT in various operating conditions such as when the accelerator pedal 72 is returned during deceleration of the engine or downhill. Thus, overheating of the exhaust purification filter 38a can be effectively prevented.

[Embodiment 2]
In the present embodiment, in the catalyst overheat prevention process (FIG. 2), only the determination condition of the possibility of overheating in step S102 and the stop condition of the exhaust gas flow increase process for catalyst overheat prevention in step S108 are different. The same as in the first embodiment. Therefore, description will be made with reference to FIGS.

In the present embodiment, the risk of overheating is determined by the following conditions (1) and (2).
(1) The exhaust temperature thci on the upstream side of the exhaust purification filter 38a (that is, the exhaust temperature on the downstream side of the NOx storage reduction catalyst 36a) is higher than the upstream overheat determination temperature OTi.

(2) The exhaust temperature thco on the downstream side of the exhaust purification filter 38a is higher than the overheat determination temperature OTo for the downstream side.
When at least one of (1) and (2) is satisfied, the exhaust purification filter 38a determines that there is a possibility of overheating.

The stop condition is established when the following (e1) is satisfied.
(E1) The upstream exhaust temperature thci is sufficiently lower than the overheat determination temperature OTi, and the downstream exhaust temperature thco is sufficiently lower than the overheat determination temperature OTo.

  As a result, as shown in the timing chart of FIG. 7, when the exhaust gas flow thco exceeds the overheat determination temperature OTo due to a decrease in the exhaust flow rate during the PM regeneration control mode, here, due to a decrease in the intake air amount GA due to deceleration or the like. At (t11), the throttle valve 22 is fully opened and the EGR valve 56 is fully closed. As a result, the intake air amount GA is increased to suppress a decrease in the exhaust flow rate, and the exhaust purification filter 38a does not rise to the overheat determination temperature OT. Unless the throttle opening degree TA is increased or the EGR opening degree EGRa is not reduced, the intake air amount GA rapidly decreases as shown by the broken line, the catalyst bed temperature rises and exceeds the overheat determination temperature OT (t12). The point of idling up during idling (from t13) is as described in the fuel injection amount control process (FIG. 5).

According to the second embodiment described above, the following effects can be obtained.
(I). The same effect as (a) of the first embodiment is produced.
(B). The presence or absence of the possibility of overheating of the exhaust purification filter 38 a is based on the upstream exhaust temperature thci detected by the first exhaust temperature sensor 44 and the downstream exhaust temperature thco detected by the second exhaust temperature sensor 46. .

  The floor temperature of the exhaust purification filter 38a is affected by the temperature of the inflowing exhaust. Therefore, it can be determined that the risk of overheating of the downstream exhaust purification filter 38a is increased by determining the exhaust temperature thci upstream of the exhaust purification filter 38a.

  In particular, a NOx occlusion reduction catalyst 36a, which is another exhaust purification catalyst, is disposed upstream of the exhaust purification filter 38a. Even if this NOx occlusion reduction catalyst 36a does not function as a filter, it generates heat due to the added fuel from the addition valve 68 during the temperature raising process for the PM regeneration control process. Therefore, if the upstream exhaust gas temperature thci exceeds the limit when the upstream NOx occlusion reduction catalyst 36a rises in temperature, the downstream exhaust purification filter 38a is likely to be overheated.

Furthermore, since the exhaust temperature thco on the downstream side is a temperature immediately below the exhaust purification filter 38a, the possibility of overheating of the exhaust purification filter 38a can be almost directly grasped.
Therefore, when at least one of thci> OTi and thco> OTo is satisfied, it can be determined that there is a possibility of overheating.

  In particular, by determining the exhaust gas temperature thci flowing into the exhaust gas purification filter 38a, the overheating of the exhaust gas purification filter 38a can be predicted earlier, and the exhaust gas flow rate can be increased at an early stage to further overheat the exhaust gas purification filter 38a. It can be surely prevented.

[Embodiment 3]
In the present embodiment, in the catalyst overheat prevention process (FIG. 2), only the determination condition of the possibility of overheating in step S102 and the stop condition of the exhaust gas flow increase process for catalyst overheat prevention in step S108 are different. The same as in the first embodiment. Therefore, description will be made with reference to FIGS.

In the present embodiment, the risk of overheating is determined by the following condition (1).
(1) The estimated bed temperature thcf of the exhaust purification filter 38a is higher than the overheat determination temperature OTf.
The estimated bed temperature thcf is calculated by the ECU 70 at regular time intervals according to Equation 4.

[Formula 4] thcf ← thcfold + (Cf−Ce) / Hcp
Here, the previous estimated bed temperature thcfold is the estimated bed temperature thcf calculated one cycle before.

  The amount of heat generated by the exhaust purification filter Cf is the amount of heat generated from the exhaust purification filter 38a during one cycle, and the amount of added fuel that has not been consumed by the upstream NOx occlusion reduction catalyst 36a due to the addition of fuel from the addition valve 68. The amount of heat generated by The added fuel consumed by the upstream NOx storage reduction catalyst 36a can be estimated from the upstream exhaust temperature thci and the intake air amount GA. Therefore, by subtracting this consumed added fuel amount from the added fuel amount from the addition valve 68, the added fuel amount combusted in the exhaust purification filter 38a is found, and the exhaust purification filter generated heat amount Cf is obtained from this added fuel amount. Can do.

  The exhaust heat amount Ce is the amount of heat taken from the exhaust purification filter 38a by exhaust during one cycle, and is obtained from the intake air amount GA reflecting the exhaust flow rate, the upstream exhaust temperature thci, and the previous estimated bed temperature thcfold. Can do.

The exhaust purification filter heat capacity Hcp is a heat capacity of the exhaust purification filter 38a that is actually measured in advance.
The stop condition is established when the following (e1) is satisfied.

(E1) The estimated bed temperature thcf is sufficiently lower than the overheat determination temperature OTf.
As a result, as shown in the timing chart of FIG. 8, when the estimated bed temperature thcf exceeds the overheat determination temperature OTf due to a decrease in the exhaust flow rate during the PM regeneration control mode, here, a decrease in the intake air amount GA due to deceleration or the like (t21 ), The throttle valve 22 is fully opened and the EGR valve 56 is fully closed. As a result, a decrease in the exhaust flow rate is suppressed by the process of increasing the intake air amount GA, and the exhaust purification filter 38a does not rise to the overheat determination temperature OT. Unless the throttle opening degree TA is increased and the EGR opening degree EGRa is not reduced, the intake air amount GA rapidly decreases as shown by the broken line, the catalyst bed temperature rises and exceeds the overheat determination temperature OT (t22). The point of idling up during idling (from t23) is as described in the fuel injection amount control process (FIG. 5).

According to the third embodiment described above, the following effects can be obtained.
(I). The same effect as (a) of the first embodiment is produced.
(B). The possibility of overheating of the exhaust purification filter 38a is determined by the estimated bed temperature thcf estimated based on the intake air amount GA, the fuel addition amount, the upstream exhaust temperature thci, and the downstream exhaust temperature thco.

  Thus, since the determination is made based on the estimated bed temperature thcf of the exhaust purification filter 38a, the overheating of the exhaust purification filter 38a can be predicted more accurately, and the exhaust purification filter 38a is overheated by accurately increasing the exhaust gas flow rate. Can be more effectively prevented.

[Embodiment 4]
In the present embodiment, in the catalyst overheat prevention process (FIG. 2), only the determination condition of the possibility of overheating in step S102 and the stop condition of the exhaust gas flow increase process for catalyst overheat prevention in step S108 are different. The same as in the first embodiment. Therefore, description will be made with reference to FIGS.

In the present embodiment, the risk of overheating is determined by the following condition (1).
(1) The PM regeneration control process is in progress, and the PM accumulation amount is larger than the reference accumulation amount.
That is, if the PM accumulation amount is large and the amount of heat generated by the PM regeneration control process is large and the exhaust gas flow rate is reduced, the exhaust purification filter 38a may be overheated. PM accumulation amount> reference accumulation amount Is judged.

The stop condition is satisfied when either of the following (e1) and (e2) is satisfied.
(E1) The PM deposition amount is sufficiently smaller than the reference deposition amount.

  That is, it is determined that there is no risk that the exhaust purification filter 38a is overheated even when the exhaust gas flow rate is reduced because the amount of PM that has been combusted is reduced.

(E2) The PM regeneration control process has been completed and sufficient time has elapsed.
It is determined that there is no possibility of overheating of the exhaust gas purification filter 38a even if the exhaust gas flow rate is lowered because sufficient time has passed since PM is no longer burned.

According to the fourth embodiment described above, the following effects can be obtained.
(I). The same effect as (a) of the first embodiment is produced.
(B). Since the determination is based on the PM accumulation amount at the time of PM regeneration control, the determination becomes simple, and it is possible to easily determine whether or not the exhaust purification filter may be overheated.

[Other embodiments]
(A). In each of the above embodiments, the intake air amount increasing process is executed by correcting the opening degree of both the throttle valve and the EGR valve. Alternatively, it may be dealt with by an opening reduction process of the EGR valve.

  Further, although the throttle valve is fully opened in each of the above embodiments, the opening degree set for preventing overheating may be increased and corrected. Although the EGR valve is also fully closed, the opening degree set for preventing overheating may be corrected to decrease.

  (B). In the second embodiment, the risk of overheating may be determined only by the condition (2). In this case, the stop condition is satisfied when the “downstream exhaust temperature thco is sufficiently lower than the overheat determination temperature OTo”.

  (C). In the first embodiment, it may be determined that there is a possibility of overheating when the following conditions (1) and (2) are satisfied as conditions for determining the possibility of overheating. The condition (2) is the same as in the first embodiment.

(1) The exhaust purification filter temperature raising process in either the PM regeneration control mode or the S poison recovery control mode is executed by the catalyst control described above.
(2) Expected maximum bed temperature CTmax> overheat determination temperature OT.

In this case, the stop condition is as follows. The condition (e2) is the same as in the first embodiment.
(E1) The PM regeneration control process and the S poison recovery control process are both completed, and sufficient time has elapsed.

(E2) The predicted maximum bed temperature CTmax is sufficiently lower than the overheat determination temperature OT.
Also in the fourth embodiment, as a condition for determining the possibility of overheating, it may be determined that there is a possibility of overheating when the following condition (1) is satisfied.

(1) The exhaust purification filter temperature raising process in either the PM regeneration control mode or the S poison recovery control mode is in progress, and the PM accumulation amount is larger than the reference accumulation amount.
In this case, the stop condition is as follows. The condition (e1) is the same as in the fourth embodiment.

(E1) The PM deposition amount is sufficiently smaller than the reference deposition amount.
(E2) The PM regeneration control process and the S poison recovery control process are both completed, and sufficient time has elapsed.

  As described above, in both the first and fourth embodiments, when the S poison recovery control mode is executed in the condition (1), PM is contained in the exhaust purification filter 38a during the S poison recovery control process. Even when the exhaust gas remains, overheating of the exhaust purification filter can be effectively prevented.

  (D). The condition for determining the possibility of overheating in each embodiment does not include the condition “when the engine is decelerating”, but the condition “when the engine is decelerating” is included in the condition for determining the possibility of overheating. In this case, it functions effectively especially during engine deceleration.

  (E). In each embodiment, at the time of idling when there is a possibility of overheating, the idle opening process is executed together with the throttle opening increasing process and the EGR opening decreasing process. In this way, the exhaust gas flow rate can be increased to effectively prevent overheating of the exhaust gas purification filter.

  (F). In step S156 of the fuel injection amount control process of FIG. 5, it is determined whether or not the engine is to be idled up by determining whether or not the catalyst overheat prevention exhaust gas flow rate increasing process is being executed. In addition to this, in step S156, it may be determined whether or not there is an idle up using the same conditions as the execution condition and stop condition of the exhaust gas flow increase processing for preventing catalyst overheating described in the above embodiments.

  For example, in step S156, if the condition is not satisfied under the condition that “the expected maximum bed temperature CTmax is lower than the overheat determination temperature OT for a certain period of time”, the idle-up (S160) is continued and satisfied. If so, the idle-up may be stopped and step S158 may be executed.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing showing the outline of the diesel engine for vehicles of Embodiment 1, and its control system. 4 is a flowchart of a catalyst overheat prevention process executed by the ECU according to the first embodiment. The structure explanatory drawing of map MapCT used in the said catalyst overheat prevention process. 4 is a timing chart illustrating an example of processing according to the first embodiment. 4 is a flowchart of fuel injection amount control processing executed by the ECU according to the first embodiment. The structure explanatory view of the governor pattern used in the above-mentioned fuel injection amount control processing. 9 is a timing chart illustrating an example of processing according to the second embodiment. 10 is a timing chart illustrating an example of processing according to the third embodiment.

Explanation of symbols

  2 ... Diesel engine, 4 ... Combustion chamber, 6 ... Intake valve, 8 ... Intake port, 10 ... Intake manifold, 12 ... Surge tank, 13 ... Intake passage, 14 ... Intercooler, 16 ... Exhaust turbocharger, 16a ... Compressor, 16b ... exhaust turbine, 18 ... air cleaner, 20 ... EGR path, 20a ... EGR gas supply port, 20b ... EGR gas intake port, 22 ... throttle valve, 22a ... throttle opening sensor, 22b ... motor, 24 ... intake air amount sensor , 26 ... intake temperature sensor, 28 ... exhaust valve, 30 ... exhaust port, 32 ... exhaust manifold, 34 ... exhaust path, 36 ... first catalytic converter, 36a ... NOx occlusion reduction catalyst, 38 ... second catalytic converter, 38a ... Exhaust purification filter, 40 ... third catalytic converter, 40a ... oxidation catalyst, 44 ... first exhaust temperature sensor, 4 ... second exhaust temperature sensor, 48 ... air-fuel ratio sensor, 50 ... differential pressure sensor, 52 ... EGR catalyst, 54 ... EGR cooler, 56 ... EGR valve, 58 ... fuel injection valve, 58a ... fuel supply pipe, 60 ... common rail, 62 ... Fuel pump, 64 ... Fuel pressure sensor, 66 ... Fuel supply pipe, 68 ... Addition valve, 70 ... ECU, 72 ... Accelerator pedal, 74 ... Accelerator opening sensor, 76 ... Cooling water temperature sensor, 78 ... Crankshaft, 80 ... engine speed sensor, 82 ... cylinder discrimination sensor.

Claims (13)

An apparatus provided in an exhaust system of an internal combustion engine for filtering particulate matter in exhaust gas and preventing overheating in an exhaust purification filter that burns and purifies particulate matter deposited by the filtration by a temperature raising process,
An exhaust purification filter overheat prevention device comprising overheat prevention means for preventing overheating of the exhaust purification filter by an increase process with respect to the exhaust flow rate when there is a possibility of overheating of the exhaust purification filter. 2. The exhaust purification filter overheat prevention device according to claim 1, wherein the overheat prevention means realizes an increase process for the exhaust flow rate by an increase process for the intake air amount of the internal combustion engine. The overheat prevention means according to claim 2, wherein an increase process for the intake air amount of the internal combustion engine is provided in an increase in the opening of a throttle valve provided in the intake system and an exhaust recirculation path from the exhaust system to the intake system. An exhaust purification filter overheat prevention device, which is realized by one or both of the processes of reducing the opening of the exhaust gas recirculation valve. 2. The exhaust purification filter overheat prevention device according to claim 1, wherein the overheat prevention means realizes an increase process for the exhaust gas flow rate by an increase in the idle speed when the internal combustion engine is in an idle state. 5. The overheat prevention means according to claim 1, wherein the exhaust purification filter determines that there is a risk of overheating of the exhaust purification filter when the exhaust temperature of the exhaust gas flowing out from the exhaust purification filter is higher than the overheat determination temperature. Exhaust purification filter overheat prevention device. 5. The overheat prevention means according to claim 1, wherein the overheat prevention means is configured such that the exhaust temperature of the exhaust gas flowing into the exhaust purification filter is higher than the overheat determination temperature, and the exhaust temperature of the exhaust gas flowing out from the exhaust purification filter is higher than the overheat determination temperature. Exhaust purification filter overheat prevention device characterized in that one or both of the high conditions is judged and if any one of the conditions is satisfied, it is judged that there is a risk of overheating of the exhaust purification filter . The overheat prevention means according to any one of claims 1 to 4, wherein an exhaust flow rate, an amount of fuel added into an exhaust gas from an addition valve provided in an exhaust system of an internal combustion engine, an exhaust temperature of exhaust gas flowing into an exhaust purification filter, The exhaust temperature of the exhaust gas purification filter is estimated based on the exhaust gas temperature of the exhaust gas flowing out from the exhaust gas purification filter. If the floor temperature is higher than the overheat determination temperature, it is determined that the exhaust gas purification filter may be overheated. An exhaust purification filter overheat prevention device characterized by the above. 5. The overheating prevention means according to claim 1, wherein the overheat prevention means is performing an exhaust purification filter temperature raising process including a combustion purification process of particulate matter deposited on the exhaust purification filter, and the amount of the particulate matter deposited is An exhaust purification filter overheat prevention device, characterized in that it is determined that there is a risk of overheating of the exhaust purification filter when the amount is greater than a reference accumulation amount. 5. The overheat prevention means according to claim 1, wherein the overheat prevention means is performing an exhaust purification filter temperature raising process including a combustion purification process of particulate matter deposited on the exhaust purification filter when the internal combustion engine is decelerated. An exhaust purification filter overheat prevention device characterized in that, when the predicted maximum bed temperature of the exhaust purification filter estimated based on the operating state of the exhaust purification filter is higher than the overheat determination temperature, it is determined that there is a risk of overheating of the exhaust purification filter. . 5. The overheat prevention means according to claim 1, wherein the overheat prevention means is in an exhaust purification filter temperature raising process including a combustion purification process of particulate matter deposited on the exhaust purification filter, and is based on an operating state of the internal combustion engine. An exhaust purification filter overheat prevention device, characterized in that, when the estimated maximum floor temperature of the estimated exhaust purification filter is higher than an overheat determination temperature, it is determined that the exhaust purification filter may be overheated. 11. The overheat prevention means according to claim 9 or 10, wherein the overheat prevention means captures the amount of decrease in the exhaust flow rate per unit time as the amount of decrease in the intake air amount per unit time, and the amount of decrease in the intake air amount per unit time and the particulate form. An exhaust purification filter overheat prevention device, wherein the predicted maximum bed temperature is estimated based on the amount of accumulated substances. 5. The overheat prevention means according to claim 1, wherein the overheat prevention means is performing an exhaust purification filter temperature raising process including a combustion purification process of particulate matter deposited on the exhaust purification filter when the internal combustion engine is decelerated. An exhaust purification filter overheat prevention device, characterized in that, when the accumulation amount of the particulate matter is larger than the reference accumulation amount, it is determined that the exhaust purification filter may be overheated. The exhaust purification filter overheat prevention device according to any one of claims 8 to 12, wherein the exhaust purification filter temperature raising process includes a sulfur poisoning recovery control process.

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