JP2008106685A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of appropriately continuing S-regeneration and PM-regeneration even under a low load condition of the internal combustion engine. <P>SOLUTION: The exhaust emission control device for the internal combustion engine adds fuel for recovering an exhaust emission capacity of the exhaust emission control device, or the like. An electric heating type catalyst is arranged in a spray reach section by an injector and raises temperature by electricity supply. A regeneration control means executes control supplying electricity to the electric heating type catalyst and continuing S-regeneration and PM-regeneration when low load operation continues for a predetermined period of time after start of S-regeneration and PM-regeneration. Temperature of the added fuel and exhaust gas is raised and temperature of an exhaust gas passage and the exhaust emission control device rise by supplying electricity to the electric heating type catalyst in such a manner. Consequently, since the exhaust emission control device or the like can be maintained at appropriate temperature even under a low load condition of the internal combustion engine, S-regeneration and PM-regeneration can be appropriately continued. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification control device for an internal combustion engine that performs control for purifying exhaust gas of the internal combustion engine.

  Conventionally, in order to recover the exhaust purification ability of a catalyst provided in an exhaust passage of an internal combustion engine, control for adding fuel as a reducing agent to exhaust gas has been performed. For example, in Patent Document 1, in a system for adding fuel to an exhaust manifold, a fuel reforming catalyst is disposed on the upstream side of a turbocharger to reform the added fuel and to the inner wall of the exhaust passage of the added fuel. Techniques for suppressing adhesion are described. In addition, Patent Documents 2 and 3 describe techniques related to the present invention.

JP 2005-76530 A JP 2005-105828 A JP 2005-61234 A

  However, in the technique described in Patent Document 1 described above, since the temperature of the fuel reforming catalyst is controlled according to the circumstances, the activity tends to be low when the engine is under a low load. For this reason, it has been difficult to properly continue sulfur poisoning recovery (hereinafter also referred to as “S regeneration”) and PM (Particulate Matter) regeneration to the catalyst when the engine is under a low load. In addition, even with the techniques described in Patent Documents 2 and 3 described above, it is difficult to appropriately perform S regeneration and PM regeneration when the engine is under a low load.

  The present invention has been made to solve the above-described problems, and an exhaust purification control device for an internal combustion engine capable of appropriately continuing S regeneration and PM regeneration even in a low load state of the internal combustion engine. The purpose is to provide.

  In one aspect of the present invention, an exhaust gas purification control device for an internal combustion engine that adds fuel to an exhaust gas purification device that purifies exhaust gas provided in an exhaust passage of the internal combustion engine is a spray arrival point by the injector that adds the fuel. An electrically heated catalyst that is heated by being energized, and when the low load operation for a predetermined period is continued after the start of sulfur poisoning recovery or PM regeneration to the exhaust gas purification device, the electrically heated catalyst And a regeneration control means for continuing the sulfur poisoning recovery or PM regeneration.

  The exhaust gas purification control device for an internal combustion engine is preferably used for adding fuel to the exhaust gas purification device in order to recover the exhaust gas purification capability of the exhaust gas purification device that purifies the exhaust gas. The electrically heated catalyst is a catalyst that is disposed at a spray arrival point by an injector to which fuel is added and that is heated when energized. Further, the regeneration control means energizes the electrically heated catalyst when the low load operation for a predetermined period is continued after the start of the sulfur poisoning recovery (S regeneration) or PM regeneration to the exhaust purification device, and the S regeneration or PM Control to continue playback. Since the temperature of the electrically heated catalyst is raised by energizing the electrically heated catalyst in this way, the temperature of the added fuel and exhaust gas rises, and the temperature of the exhaust passage and the exhaust purification device also rises. Therefore, even when the internal combustion engine is in a low load state, the exhaust purification device and the like can be maintained at an appropriate temperature, and therefore it is possible to appropriately continue the S regeneration and PM regeneration of the exhaust purification device. Moreover, when S regeneration or PM regeneration is continued during low load operation as described above, the temperature of the exhaust passage and the like is increased by energizing the electrically heated catalyst. It can be said that it does not adhere. As described above, according to the exhaust purification control apparatus for an internal combustion engine, it is possible to appropriately continue the S regeneration and PM regeneration of the exhaust purification apparatus even when the internal combustion engine is in a low load state or an idle state.

  In one aspect of the exhaust gas purification control apparatus for an internal combustion engine, the electrically heated catalyst is disposed on the upstream side of the turbocharger.

  In this aspect, the electrically heated catalyst is disposed at the spray arrival point by the injector on the upstream side of the turbocharger. When the electrically heated catalyst is arranged in this way, all the fuel added from the injector passes through the electrically heated catalyst before reaching the turbocharger or the like. Here, since the temperature of the electrically heated catalyst is increased by being energized, the temperature of the fuel and exhaust gas passing through the electrically heated electrically heated catalyst is increased. Further, when the fuel and exhaust gas whose temperature has increased in this way passes through the turbocharger and the exhaust passage, the temperature of the turbocharger and the exhaust passage is also increased. Furthermore, since the temperature of the electrically heated catalyst is also raised by the catalytic reaction of the electrically heated catalyst due to the addition of fuel, this also increases the temperature of the fuel and exhaust gas. As described above, according to the exhaust gas purification control apparatus for an internal combustion engine described above, it is possible to prevent the fuel from flowing in a liquid state when the internal combustion engine has a low temperature and the temperature of the exhaust gas is low. It is possible to effectively prevent the fuel from adhering to the supercharger or the like.

  In another aspect of the exhaust gas purification control apparatus for an internal combustion engine, the electrically heated catalyst is energized when the NOx accumulation amount in the exhaust gas purification apparatus exceeds a first threshold value, and the NOx accumulation amount is First NOx reduction control means for adding fuel from the injector to perform NOx reduction of the exhaust emission control device when it becomes equal to or greater than a second threshold having a value larger than the first threshold. Thereby, it is possible to appropriately perform NOx reduction while preventing fuel added during NOx reduction from adhering to the turbocharger or the exhaust passage.

  Preferably, in the exhaust gas purification control device for an internal combustion engine, the electrically heated catalyst is energized when the NOx accumulation amount in the exhaust gas purification device becomes equal to or greater than a first threshold, and the NOx accumulation amount is equal to the first NOx accumulation amount. NOx reduction of the exhaust gas purification device is performed when the exhaust pipe temperature becomes equal to or higher than a temperature at which the added fuel does not adhere to the exhaust gas passage. Therefore, a second NOx reduction control means for adding fuel from the injector is provided. Thereby, it can prevent more reliably that the fuel added at the time of NOx reduction | restoration adheres to a turbocharger or an exhaust passage.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

[overall structure]
First, the overall configuration of a system to which the exhaust gas purification control apparatus for an internal combustion engine according to the present embodiment is applied will be described.

  FIG. 1 is a schematic configuration diagram of a system to which an exhaust gas purification control apparatus for an internal combustion engine according to this embodiment is applied. In FIG. 1, solid arrows indicate gas flows, and broken arrows indicate input / output of signals.

  The engine (internal combustion engine) 1 includes a plurality of cylinders 1a, and generates power by burning supplied fuel and intake air in the cylinders 1a. The engine 1 is constituted by, for example, a diesel engine. The engine 1 supplies the ECU 20 with a signal S1 corresponding to an operating state, a load, and the like. Further, an exhaust manifold 2 is connected to the engine 1, and exhaust gas generated by combustion is discharged to the exhaust manifold 2. An exhaust passage 4 is connected to the exhaust manifold 2, and the exhaust gas flows through the exhaust passage 4.

  The exhaust manifold 2 is provided with a fuel addition injector 5 for adding fuel. The fuel addition injector 5 executes the addition of fuel as indicated by reference numeral 5a in FIG. 1 in response to a control signal S5 supplied from the ECU 20. In addition, an electrically heated catalyst (hereinafter referred to as “EHC (Electrical Heated Catalyst)”) 6 is disposed downstream of the fuel addition injector 5. Specifically, the EHC 6 has the same size as the diameter of the exhaust passage 4 and is disposed at a position immediately downstream of the fuel addition injector 5, that is, at a fuel spray arrival point. Further, the EHC 6 is configured as a catalyst having an exhaust gas purifying action, and raises the temperature when energized. Specifically, energization of the EHC 6 is controlled by a control signal S6 supplied from the ECU 20.

  Further, a turbocharger 7 is provided on the downstream side of the EHC 6. The turbocharger 7 is supercharged by rotating an internal turbine (not shown) by exhaust gas exhausted from the engine 1 and transmitting the rotational torque of the turbine to a compressor (not shown). I do. Further, an exhaust gas purification device 8 for purifying exhaust gas is provided on the exhaust passage 4 on the downstream side of the turbocharger 7. The exhaust purification device 8 includes an NSR (NOx Storage Reduction) 9 and a DPNR (Diesel Particulate NOx Reduction system) 10. NSR9 is a NOx occlusion / reduction catalyst that performs NOx occlusion / reduction, and DPNR10 is a device that can continuously purify NOx and PM simultaneously.

  Here, the effect by disposing the fuel addition injector 5, the EHC 6, and the turbocharger 7 as described above will be described. First, a problem that may occur when the EHC 6 is not provided on the downstream side of the fuel addition injector 5 will be described. The addition of fuel by the fuel addition injector 5 is executed in order to recover the exhaust purification capability of the exhaust purification device 8, and when the fuel is added in this way, the fuel added from the fuel addition injector 5 becomes the exhaust purification device. Before reaching 8, it may adhere to the turbine in the turbocharger 7 or the inner wall of the exhaust passage 4. In particular, when the engine 1 has a low exhaust gas temperature and the load is low, the fuel is likely to be in a liquid state, and the fuel tends to adhere. When fuel adheres in this way (in other words, when “fuel pool” occurs), the turbocharger 7 has a problem in rotation, or the fuel adhering to the sudden acceleration suddenly evaporates, This may react with the exhaust gas purification device 8 and become high temperature (OT; Over Temperature).

  In this embodiment, the EHC 6 is disposed at the spray arrival point by the fuel addition injector 5 to prevent the fuel from adhering. Specifically, the adhesion of the fuel is prevented by suppressing the fuel from flowing in a liquid state. More specifically, fuel adhesion is mainly prevented by the following procedure. Since the EHC 6 is disposed at the spray arrival point by the fuel addition injector 5, all the fuel added from the fuel addition injector 5 passes through the EHC 6 before reaching the turbocharger 7 or the like. Here, since the temperature of the EHC 6 is increased by being energized, the temperature of the fuel and exhaust gas passing through the energized EHC 6 will be increased. Further, the fuel and exhaust gas whose temperature has increased in this way passes through the turbocharger 7 and the exhaust passage 4, so that the turbocharger 7 and the exhaust passage 4 are also heated. Furthermore, the temperature of the EHC 6 also rises due to the catalytic reaction of the EHC 6 due to the addition of fuel, which also increases the temperature of the fuel and exhaust gas. With the above configuration, the fuel can be prevented from flowing in a liquid state at a low load of the internal combustion engine where the temperature of the exhaust gas is low. It becomes.

  Returning to FIG. 1, the description will be resumed. The ECU (Engine Control Unit) 20 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like (not shown). The ECU 20 executes control for recovering the exhaust purification capability of the exhaust purification device 8 described above. Specifically, the ECU 20 performs control to add fuel from the fuel addition injector 5 in order to perform S regeneration (sulfur poisoning recovery), PM regeneration, and NOx reduction for the exhaust gas purification device 8. In the present embodiment, the ECU 20 performs energization of the EHC 6 mainly based on an operating condition such as a load of the engine 1 to perform the above-described S regeneration, PM regeneration, and NOx reduction. Thus, the ECU 20 functions as a regeneration control means, a first NOx reduction control means, and a second NOx reduction control means in the present invention.

[S regeneration process / PM regeneration process]
Next, the S regeneration process and the PM regeneration process performed for the S regeneration and PM regeneration of the exhaust purification device 8 will be described.

  In the present embodiment, when the low load operation for a predetermined period continues after the start of S regeneration or PM regeneration for the exhaust gas purification device 8, control is performed to continue S regeneration or PM regeneration by energizing the EHC 6. The reason why the EHC 6 is energized and the S regeneration or PM regeneration is continued is as follows. S regeneration and PM regeneration are performed by adding fuel to the exhaust gas purification device 8. Here, these regenerations are preferably performed when the exhaust purification device 8 is at a relatively high temperature (for example, 600 to 650 ° C.). That is, when the engine 1 is in a low load state, it can be said that it is difficult to appropriately continue the S regeneration and the PM regeneration.

  In this embodiment, when low load operation for a predetermined period continues after the start of S regeneration or PM regeneration, control is performed to energize the EHC 6 and continue S regeneration or PM regeneration. In other words, the EHC 6 is energized to continue S regeneration or PM regeneration. Since the EHC 6 is heated by energizing the EHC 6 in this manner, the temperature of the added fuel and exhaust gas is increased, and the turbocharger 7, the exhaust passage 4, and the exhaust purification device 8 are also heated. It becomes. Therefore, even when the engine 1 is in a low load state, the exhaust purification device 8 and the like can be maintained at an appropriate temperature, so that it is possible to appropriately continue the S regeneration and PM regeneration of the exhaust purification device 8. . Further, when the S regeneration or PM regeneration is continued during the low load operation as described above, the turbocharger 7 and the exhaust passage 4 are heated by energizing the EHC 6, so that the added fuel is the turbo It can be said that it hardly adheres to the supercharger 7 or the like. As described above, according to the S regeneration process and the PM regeneration process according to the present embodiment, it is possible to appropriately continue the S regeneration and PM regeneration of the exhaust purification device 8 even when the engine 1 is in a low load state or an idle state. It becomes possible.

  FIG. 2 is a flowchart showing the S reproduction process according to the present embodiment. This process is executed by the ECU 20 described above.

  First, in step S101, the ECU 20 executes S regeneration for the exhaust purification device 8. Specifically, the ECU 20 performs control to add fuel from the fuel addition injector 5. Then, the process proceeds to step S102.

  In step S102, the ECU 20 determines whether or not the low load operation of the engine 1 has continued for a certain time or more. Here, it is determined whether or not it is necessary to energize the EHC 6 in order to continue the S regeneration. When the low-load operation continues for a certain time or longer (step S102; Yes), the process proceeds to step S103. On the other hand, when the low load operation has not continued for a certain time or longer (step S102; No), the process returns to step S102. In this case, it can be said that it is not necessary to energize the EHC 6. Therefore, the ECU 20 continues the S regeneration without energizing the EHC 6.

  In step S103, the ECU 20 energizes the EHC 6 because the low load operation has continued for a certain time or longer. Specifically, the ECU 20 energizes the EHC 6 by supplying a control signal S6. As a result, the temperature of the EHC 6 is raised and the temperature of the added fuel and exhaust gas rises, so that the turbocharger 7, the exhaust passage 4, and the exhaust purification device 8 can be heated. When the above process ends, the process proceeds to step S104.

  In step S104, the ECU 20 continues the S regeneration. That is, the ECU 20 continues to add fuel from the fuel addition injector 5. In this case, since the turbocharger 7, the exhaust passage 4, and the exhaust purification device 8 are heated by the action of the EHC 6, the S regeneration of the exhaust purification device 8 can be appropriately continued. Moreover, it can be said that adhesion of the fuel added in the S regeneration hardly occurs. When the above process ends, the process proceeds to step S105.

  In step S105, the ECU 20 determines whether or not the load of the engine 1 is equal to or greater than a predetermined value. Here, it is determined whether or not it is possible to end the energization of the EHC 6. If the load on the engine 1 is greater than or equal to the predetermined value (step S105; Yes), the process proceeds to step S106. On the other hand, when the load of the engine 1 is less than the predetermined value (step S105; No), the process returns to step S103. In this case, energization of the EHC 6 is continued. That is, the S regeneration is continued with the EHC 6 energized.

  In step S106, the ECU 20 ends energization of the EHC 6 because the load of the engine 1 is equal to or greater than a predetermined value. In this case, it can be said that it is not necessary to raise the temperature of the exhaust purification device 8 etc. by energizing the EHC 6 since the exhaust purification device 8 etc. can be brought to a desired temperature by the exhaust gas. Therefore, the ECU 20 ends the energization of the EHC 6 and continues the S regeneration. When the above process ends, the process exits the flow.

  According to the above S regeneration processing, it is possible to appropriately continue the S regeneration of the exhaust purification device 8 even when the engine 1 is in a low load state or an idle state.

  Although only the S regeneration process for the exhaust gas purification device 8 has been described above, the PM regeneration process for the exhaust gas purification device 8 can also be executed in the same manner. That is, when the low load operation continues for a certain time or longer after the start of PM regeneration for the exhaust gas purification device 8, control is performed to continue PM regeneration by energizing the EHC 6. When the load on the engine 1 becomes equal to or greater than a predetermined value during energization of the EHC 6, the energization of the EHC 6 is terminated. According to such a PM regeneration process, it is possible to appropriately continue the PM regeneration of the exhaust purification device 8 even when the engine 1 is in a low load state or an idle state.

[NOx reduction treatment]
Next, the NOx reduction process performed for NOx reduction of the exhaust purification device 8 will be described. In the present embodiment, control for energizing the EHC 6 is executed before the NOx reduction for the exhaust gas purification device 8 is executed. That is, after energizing the EHC 6, NOx reduction is executed. This is to prevent the fuel added at the time of NOx reduction from adhering to the turbocharger 7 or the exhaust passage 4.

(First example)
First, a first example of NOx reduction processing will be described. In the first example, the EHC 6 is energized when the NOx accumulation amount in the exhaust purification device 8 becomes equal to or greater than the first threshold, and the NOx accumulation amount exceeds the second threshold having a value larger than the first threshold. When it becomes, NOx reduction is executed. That is, the EHC 6 is energized before the NOx reduction is performed.

  FIG. 3 is a flowchart showing the NOx reduction process according to the first example. This process is executed by the ECU 20 described above.

  First, in step S201, the ECU 20 operates the engine 1 at a low load for a predetermined time or longer. That is, as a preparation for NOx reduction, the engine 1 is operated at a low load. Then, the process proceeds to step S202.

  In step S202, the ECU 20 determines whether or not the NOx accumulation amount of the exhaust purification device 8 is equal to or greater than the first threshold value. The determination in step S202 is performed to determine whether or not the EHC 6 is to be energized. Specifically, the ECU 20 estimates the NOx accumulation amount by referring to a map defined by, for example, the intake air amount. Further, the first threshold value is set to a value smaller than the NOx accumulation amount (corresponding to the second threshold value) in a situation where NOx reduction should be performed. If the NOx accumulation amount is greater than or equal to the first threshold (step S202; Yes), the process proceeds to step S203. On the other hand, when the NOx accumulation amount is less than the first threshold (step S202; No), the process returns to step S202. In this case, it cannot be said that the EHC 6 is to be energized. Therefore, it waits until the NOx accumulation amount becomes equal to or greater than the first threshold value.

  In step S203, the ECU 20 energizes the EHC 6 because the NOx accumulation amount is not less than the first threshold value. Specifically, the ECU 20 energizes the EHC 6 by supplying a control signal S6. As a result, the turbocharger 7 and the exhaust passage 4 and the like are heated by the action of the EHC 6 (temperature rise due to energization and temperature rise due to catalytic reaction), so that the fuel added during NOx reduction is prevented from adhering. Is possible. When the above process ends, the process proceeds to step S204.

  In step S204, the ECU 20 determines whether or not the NOx accumulation amount of the exhaust purification device 8 is equal to or greater than a second threshold value. The determination in step S204 is performed to determine whether or not it is a situation where NOx reduction should be performed. Specifically, the ECU 20 estimates the NOx accumulation amount by referring to a map defined by, for example, the intake air amount. The second threshold value is set to the NOx accumulation amount in a situation where NOx reduction should be executed. In other words, the second threshold value is set near the limit value of the amount by which the exhaust purification device 8 can store NOx. If the NOx accumulation amount is equal to or greater than the second threshold (step S204; Yes), the process proceeds to step S205. On the other hand, when the NOx accumulation amount is less than the second threshold (step S204; No), the process returns to step S203. In this case, since there is no situation in which NOx reduction should be performed, energization of the EHC 6 is continued and the process waits until the NOx accumulation amount becomes equal to or greater than the second threshold value.

  In step S205, the ECU 20 executes control for adding fuel from the fuel addition injector 5 to perform NOx reduction. In this case, since the exhaust gas and fuel, and the turbocharger 7 and the exhaust passage 4 are heated by the action of the EHC 6, the added fuel is prevented from adhering to the turbocharger 7 and the like. Can do. When the above process ends, the process exits the flow.

  According to the NOx reduction process according to the first example described above, the NOx reduction is appropriately performed while preventing the fuel added at the time of NOx reduction from adhering to the turbocharger 7 and the exhaust passage 4. Can do.

(Second example)
Next, a second example of the NOx reduction process will be described. The second example is the same as the first example described above in that the EHC 6 is energized when the NOx accumulation amount in the exhaust purification device 8 becomes equal to or greater than the first threshold, but the NOx accumulation amount is the second. When the temperature of the exhaust passage 4 becomes equal to or higher than the temperature at which the added fuel does not adhere to the fuel (hereinafter referred to as “the upper limit temperature of the piping adhesion”), NOx reduction is performed. This is different from the first example described above. That is, in the second example, even if the NOx accumulation amount is equal to or greater than the second threshold value, NOx reduction is not performed if the pipe temperature is lower than the pipe adhesion upper limit temperature. Such control is executed in order to more reliably prevent fuel from adhering to the exhaust passage 4 and the like.

  FIG. 4 is a flowchart showing the NOx reduction process according to the second example. This process is executed by the ECU 20 described above. In addition, since the process of step S301-S304 and the process of step S306 are the same as the process of step S201-S204 and the process of step S205 which were respectively shown in FIG. 3, the description is abbreviate | omitted. Here, the process of step S305 will be described in detail.

  In step S305, the ECU 20 determines whether or not the pipe temperature of the exhaust passage 4 is equal to or higher than the pipe adhesion upper limit temperature. The situation that has proceeded to the process of step S305 can be said to be a situation in which NOx reduction should be performed because the NOx accumulation amount is equal to or greater than the second threshold (step S304; Yes). However, in the second example, priority is given to preventing fuel adhesion. Therefore, even if the NOx accumulation amount is equal to or higher than the second threshold value, NOx reduction is performed until the pipe temperature becomes equal to or higher than the pipe adhesion upper limit temperature. do not do. That is, the determination in step S305 is performed to determine whether or not the situation is such that fuel adhesion does not occur reliably. Note that the piping temperature of the exhaust passage 4 is acquired by referring to a map defined by operating conditions such as the load of the engine 1.

  When the pipe temperature is equal to or higher than the pipe attachment upper limit temperature (step S305; Yes), the process proceeds to step S306. In this case, since the possibility of fuel adhesion is very low, the ECU 20 executes control for adding fuel from the fuel addition injector 5 to perform NOx reduction (step S306). On the other hand, when the pipe temperature is lower than the pipe adhesion upper limit temperature (step S305; No), the process returns to step S303. In this case, there is a possibility that fuel adheres, so that energization to the EHC 6 is continued without performing NOx reduction. That is, the process waits until the pipe temperature becomes equal to or higher than the upper limit temperature of the pipe attachment.

  According to the NOx reduction process according to the second example described above, it is possible to more reliably prevent the fuel added at the time of NOx reduction from adhering to the turbocharger 7 and the exhaust passage 4.

[Modification]
Next, a modified example of the present invention will be described. In the above, the embodiment in which the EHC 6 is arranged on the upstream side of the turbocharger 7 is shown, but instead, an EHC (electrically heated catalyst) can be arranged on the downstream side of the turbocharger 7. Specifically, a fuel addition injector can be provided on the downstream side of the turbocharger 7, and an EHC can be disposed at a fuel spray arrival point by the fuel addition injector.

  FIG. 5 is a schematic configuration diagram of a system to which an exhaust gas purification control apparatus for an internal combustion engine according to a modification is applied. The same components as those of the system shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  In the configuration according to the modification, the fuel addition injector 12 and the EHC 13 are disposed on the exhaust passage 4 on the downstream side of the turbocharger 7. The fuel addition injector 12 performs fuel addition as indicated by reference numeral 12a in FIG. 5 in response to a control signal S12 supplied from the ECU 20. An EHC 13 is disposed downstream of the fuel addition injector 12. Specifically, the EHC 13 has the same size as the diameter of the exhaust passage 4 and is provided at a position immediately downstream of the fuel addition injector 12 on the upstream side of the exhaust purification device 8. That is, the EHC 13 is disposed at the fuel spray arrival point of the fuel addition injector 12. Further, the EHC 13 is configured as a catalyst having an exhaust gas purifying action, and raises the temperature when energized. Specifically, the energization of the EHC 13 is controlled by a control signal S13 supplied from the ECU 20.

  Here, the effect by arranging the turbocharger 7, the fuel addition injector 12, and the EHC 13 as described above will be described. First, a problem that may occur when the EHC 13 is not provided on the downstream side of the fuel addition injector 12 will be described. The fuel addition by the fuel addition injector 12 is executed to recover the exhaust purification capability of the exhaust purification device 8. When the fuel is added in this way, the fuel added from the fuel addition injector 12 is exhausted from the exhaust passage 4. And may adhere to a conical portion of the exhaust purification device 8 (a portion indicated by reference numeral 8a in FIG. 5; hereinafter, simply referred to as “cone portion 8a”). In particular, when the engine 1 has a low exhaust gas temperature and the load is low, the fuel is likely to be in a liquid state, and the fuel tends to adhere. When the fuel adheres in this way, when the adhering fuel suddenly accelerates, it rapidly evaporates, and this may react with the exhaust purification device 8 and become high temperature (OT; Over Temperature).

  In this embodiment, the EHC 13 is disposed at the spray arrival point by the fuel addition injector 12 to prevent the above-described fuel adhesion. Specifically, the fuel is prevented from adhering by suppressing the fuel from flowing in a liquid state. More specifically, fuel adhesion is mainly prevented by the following procedure. Since the EHC 13 is disposed at the spray arrival position by the fuel addition injector 12, all the fuel added from the fuel addition injector 12 passes through the EHC 13 before reaching the exhaust purification device 8. Here, since the temperature of the EHC 13 is increased by being energized, the temperature of the fuel and exhaust gas that passes through the energized EHC 13 will also increase. Further, when the fuel and exhaust gas whose temperature has increased in this way passes through the exhaust passage 4 and the cone portion 8a, the exhaust passage 4 and the cone portion 8a are also heated. Furthermore, since the temperature of the EHC 13 is also raised by the catalytic reaction of the EHC 13 due to the addition of fuel, this also raises the temperature of the fuel and exhaust gas. According to the above configuration, the fuel can be prevented from flowing in a liquid state at a low load of the internal combustion engine where the temperature of the exhaust gas is low. Is possible.

  Even in the configuration according to the modification, the above-described S regeneration process (see FIG. 2) and PM regeneration process can be executed. That is, the ECU 20 performs control to continue S regeneration or PM regeneration by energizing the EHC 13 when low load operation for a predetermined period continues after the start of S regeneration or PM regeneration for the exhaust gas purification device 8. Thereby, even if the engine 1 is in a low load state or an idle state, it is possible to appropriately continue the S regeneration and PM regeneration of the exhaust purification device 8.

  In addition, the NOx reduction process according to the first example (see FIG. 3) and the NOx reduction process according to the second example (see FIG. 4) can also be executed. That is, the ECU 20 executes NOx reduction for the exhaust gas purification device 8 after energizing the EHC 13. Thereby, it can prevent effectively that the fuel added at the time of NOx reduction | restoration adheres to the exhaust passage 4 or the cone part 8a.

1 is a schematic configuration diagram of a system to which an exhaust gas purification control device for an internal combustion engine according to the present embodiment is applied. It is a flowchart which shows S reproduction | regeneration processing based on this embodiment. It is a flowchart which shows the NOx reduction process which concerns on a 1st example. It is a flowchart which shows the NOx reduction process which concerns on a 2nd example. The schematic block diagram of the system with which the exhaust gas purification control apparatus of the internal combustion engine which concerns on a modification is applied is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Exhaust manifold 4 Exhaust passage 5, 12 Fuel addition injector 6, 13 Electric heating type catalyst (EHC)
7 Turbocharger 8 Exhaust gas purification device 20 ECU

Claims (4)

In an exhaust gas purification control device for an internal combustion engine that adds fuel to an exhaust gas purification device that purifies exhaust gas provided in an exhaust passage of the internal combustion engine,
An electrically heated catalyst that is disposed at the spray arrival point by the injector to which the fuel is added and is heated by being energized,
Regeneration control for energizing the electrically heated catalyst and continuing the sulfur poisoning recovery or PM regeneration when low load operation for a predetermined period continues after the start of sulfur poisoning recovery or PM regeneration to the exhaust gas purification device And an exhaust gas purification control apparatus for an internal combustion engine.   The exhaust gas purification control apparatus for an internal combustion engine according to claim 1, wherein the electrically heated catalyst is disposed upstream of the turbocharger.   When the NOx accumulation amount in the exhaust purification apparatus becomes equal to or greater than a first threshold value, the electric heating type catalyst is energized, and the NOx accumulation amount becomes equal to or greater than a second threshold value having a value larger than the first threshold value. The exhaust purification of an internal combustion engine according to claim 1 or 2, further comprising first NOx reduction control means for adding fuel from the injector to perform NOx reduction of the exhaust purification device. Control device.   When the NOx accumulation amount in the exhaust purification device becomes equal to or greater than a first threshold value, the electric heating type catalyst is energized, and the NOx accumulation amount becomes equal to or greater than a second threshold value having a value larger than the first threshold value. And a second NOx reduction in which fuel is added from the injector to perform NOx reduction of the exhaust purification device when the piping temperature of the exhaust passage exceeds a temperature at which the added fuel does not adhere. The exhaust gas purification control apparatus for an internal combustion engine according to claim 1 or 2, further comprising a control means.

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