JP2012137096A - Control device of internal combustion engine equipped with exhaust treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine provided with an exhaust treatment device capable of avoiding the risk of solidification and deposition of a reducing agent added to exhaust, thereby exerting an adverse influence on an exhaust system including a reducing agent addition system.SOLUTION: When an internal combustion engine 1 shifts to deceleration condition, addition of urea aqueous solution from a urea aqueous solution injection nozzle 4A, in S3 is stopped. Furthermore, in order to maintain an exhaust temperature at a predetermined level, and to suppress water content from added urea aqueous solution from evaporating, a urea powder from solidifying and depositing near a jetting hole of the urea aqueous solution injection nozzle 4A or inside an exhaust passage 2, fuel supply in a predetermined quantity to the internal combustion engine 1 is performed for a predetermined period of time, instead of fuel cut. Further, in order to prevent fresh air at relatively low temperature from being introduced into cylinders of the internal combustion engine 1 and from being discharged as low temperature exhaust, intake air quantity is limited by an intake throttle valve 20 for a predetermined period of time. In addition, an exhaust brake valve 30 is operated to suppress fall of exhaust temperatures. Furthermore, an EGR valve 41 is opened for a predetermined period of time.

Description

  The present invention relates to a control device for an internal combustion engine provided with an exhaust treatment device that processes gas (exhaust gas) discharged from the internal combustion engine and containing various exhaust substances.

  Purifying the exhaust from the combustion device to suppress the spread of environmental pollution is an important issue. For example, in the case of a diesel combustion engine, PM (particulate matter: particulate matter = mainly black smoke) in the exhaust (Soot), to suppress the emission of unburned fuel called SOF and components of lubricating oil, components generated from sulfur in diesel fuel called sulfate, and other solid substances) to the atmosphere In addition, for example, a diesel particulate filter (CSF) or a CSF (catalyzed soot filter) is installed in the exhaust passage, and the exhaust gas is passed through the diesel particulate filter or CSF so that the PM in the exhaust gas is passed. While collecting, diesel particulate filter and CSF It has been made to be reproduced by the people of the way.

  Further, for example, in Patent Document 1, in order to realize simultaneous reduction of NOx and PM contained in exhaust gas, a diesel particulate filter and CSF are interposed in the exhaust passage, and at the downstream side, NOx reduction is performed. It has been proposed to interpose an effective urea SCR (Selective Catalytic Reduction). Urea SCR is a selective reduction-type NOx catalyst that has the property of selectively reacting NOx with a reducing agent even in the presence of oxygen. And NOx in the exhaust gas is reduced and purified on the selective reduction type NOx catalyst using the generated ammonia as a reducing agent.

More specifically, in the conventional exhaust treatment apparatus as described in Patent Document 1, for example, as shown in FIG. 4, the exhaust gas temperature at the most upstream side of the exhaust passage 2 of the internal combustion engine 1 such as a diesel combustion engine is used. A diesel particulate filter 3 with an oxidation catalyst is installed at a relatively high position from the viewpoint of regeneration efficiency, etc., and a urea water addition device 4 and urea SCR 5 are installed downstream thereof, and leakage occurs from the urea SCR 5. An ammonia oxidation catalyst 6 for oxidizing excess ammonia (NH ₃ ) was interposed.

  However, in such a conventional exhaust treatment device, before the urea water added to the exhaust gas from the urea water addition device 4 is thermally decomposed into ammonia and carbon dioxide gas, the exhaust temperature decreases, for example, the exhaust temperature is 150 ° C. or less. In such a case, moisture may evaporate from the urea water and urea powder may be deposited as a solid component. This may be, for example, the vicinity of the nozzle hole of the urea water injection nozzle constituting the urea water addition device 4 or the exhaust gas. Since there is a possibility of accumulation in the passage, there is a risk of adversely affecting the exhaust system including the urea water addition system.

For this reason, for example, in Patent Document 2, a heating means such as an electric heater is provided on the exhaust upstream side of the urea water injection nozzle, and the exhaust temperature is controlled to a temperature equal to or higher than the melting point of the reducing agent (urea water) by the heating means. In such a state, an exhaust treatment device has been proposed in which urea is injected and added to exhaust gas from a urea water injection nozzle.
JP 2007-2697 A JP 2005-105940 A

  However, in the exhaust treatment device described in Patent Document 2, a heating means must be provided on the exhaust upstream side of the urea water injection nozzle, and there is a possibility that the configuration becomes complicated, the device becomes large, and the product cost increases. Actually, no consideration has been given to the case where the operating state of the internal combustion engine changes (exhaust temperature changes). In addition, when the heating means is provided, the power consumption is large and the exhaust resistance and the like may be increased, which may cause adverse effects on fuel consumption and performance.

  The present invention has been made in view of such circumstances, and has a simple and inexpensive configuration, but the reducing agent (for example, urea water) added to the exhaust gas is solidified and deposited to adversely affect the exhaust system including the reducing agent addition system. An object of the present invention is to provide a control device for an internal combustion engine provided with an exhaust treatment device having a selective reduction catalyst capable of avoiding fears.

For this reason, the control device for an internal combustion engine provided with the exhaust treatment device according to the present invention includes:
A control device for an internal combustion engine comprising an exhaust treatment device that selectively adds a reducing agent to exhaust gas discharged from the internal combustion engine via a reducing agent addition means and selectively reduces a specific component in the exhaust gas by a selective reduction catalyst. Because
When the reducing agent is urea water and the selective catalytic reduction catalyst is a urea selective catalytic reduction NOx catalyst,
The exhaust gas temperature control is executed to maintain the exhaust gas temperature at a predetermined level or higher for a predetermined period when it is determined that the exhaust gas temperature is likely to drop to a predetermined level or lower during the NOx reduction process. To do.

  The present invention can be characterized in that the exhaust gas temperature control is executed when the internal combustion engine is decelerated.

  In the present invention, the exhaust temperature control is configured to supply a predetermined amount of fuel into the cylinder of the internal combustion engine, to close the intake throttle valve to a predetermined level, to close the exhaust throttle valve to a predetermined level, It is made by performing at least one of opening a predetermined valve, operating exhaust heating means for heating exhaust, operating fuel addition means for adding fuel to exhaust, can do.

  According to the present invention, the exhaust gas temperature control is executed so that the exhaust gas temperature can be maintained at 150 ° C. or higher for about 15 seconds after the addition of urea water to the exhaust gas via the reducing agent adding unit is stopped. Can be a feature.

  According to the present invention, it is possible to avoid the possibility that the reducing agent (for example, urea water) added to the exhaust gas solidifies and accumulates and has an adverse effect on the exhaust system including the reducing agent addition system, although the configuration is simple and inexpensive. It is possible to provide a control device for an internal combustion engine including an exhaust treatment device having a selective catalytic reduction catalyst.

It is a figure which shows the structural example of the internal combustion engine provided with the exhaust-gas treatment apparatus which concerns on one embodiment of this invention. It is a flowchart for demonstrating the exhaust temperature control performed in embodiment same as the above. It is a flowchart explaining the conventional NOx reduction process control. It is a figure which shows the structural example of the internal combustion engine provided with the conventional exhaust-air-treatment apparatus.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments according to the present invention will be described with reference to the accompanying drawings. The present invention is not limited to the embodiments described below.

A first embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 1, an exhaust treatment apparatus according to an embodiment of the present invention has a regeneration efficiency or the like at a relatively high exhaust temperature position on the most upstream side of an exhaust passage 2 of an internal combustion engine 1 such as a diesel combustion engine. From the viewpoint of the above, a diesel particulate filter 3 with an oxidation catalyst is interposed, a urea water addition device 4 and a urea SCR catalyst 5 are interposed downstream thereof, and excess ammonia (NH ₃ ) An ammonia oxidation catalyst 6 for oxidizing the product is interposed.

  The urea water adding device 4 corresponds to a reducing agent adding means according to the present invention, and urea as a reducing agent for exhaust gas based on a signal from an engine control unit (ECU: Engine Control Unit) (not shown). A urea water injection nozzle 4A that supplies water at a predetermined timing, a urea water tank 4B that stores urea water, and the urea water that supplies urea water stored in the urea water tank 4B to exhaust gas And a supply pump 4C that supplies the jet nozzle 4A with a predetermined pressure.

  Here, before the urea water injected and added to the exhaust gas from the urea water injection nozzle 4A constituting the urea water adding device 4 is thermally decomposed into ammonia and carbon dioxide gas, the exhaust temperature is lowered, for example, the exhaust temperature is 150 °. In the case of C or less, moisture evaporates from the urea water and urea powder precipitates as a solid component, which is deposited, for example, near the nozzle hole of the urea water injection nozzle 4A or inside the exhaust passage, Although there is a risk of adversely affecting the exhaust system including the water addition system, in order to avoid such a concern, in the present embodiment, the exhaust temperature control for maintaining the exhaust temperature as follows is executed. To do.

That is,
As shown in the flowchart of FIG. 2, the exhaust gas temperature control according to the present embodiment is performed by adding urea water to the exhaust gas from the urea water injection nozzle 4A and thermally decomposing it into ammonia and carbon dioxide gas. It is executed during the execution of the NOx reduction process that uses the urea SCR catalyst 5 as a reducing agent to reduce and purify NOx in the exhaust gas.

  In S (step, the same applies hereinafter) 1, accelerator operation determination is performed. For example, it is determined whether or not the time change of the accelerator opening (Δ accelerator opening) is positive (Δ accelerator opening> 0). In other words, in S1, it is determined whether or not the exhaust gas temperature has shifted to an operating state in which there is a possibility that the exhaust gas temperature may fall below a predetermined level.

  If Yes, it is determined that the vehicle is accelerating, for example, and it is determined that the exhaust temperature is not likely to drop to a predetermined level or less, and the process proceeds to S2 to continue the NOx reduction process.

  In S2, for example, a prescribed amount of fuel is injected into the cylinder (that is, the combustion chamber) of the internal combustion machine 1 based on the rotational speed of the internal combustion engine 1, the accelerator opening, and the like, and the prescribed amount from the urea water injection nozzle 4A. After a control signal is transmitted to the drive unit of the urea water injection nozzle 4A so as to inject and add an amount of urea water into the exhaust passage 2, this flow is ended and the next routine is prepared.

  On the other hand, when it is determined No in S1, for example, the internal combustion engine 1 shifts to a deceleration state, and it is determined that the exhaust temperature may be lowered to a predetermined level or less, and the process proceeds to S3.

  In S3, since the operation state of the internal combustion engine 1 is in a decelerating state, the NOx emission amount is small and the necessity of continuing the NOx reduction process is low. Therefore, the conventional control of the NOx reduction process as shown in FIG. 3 will be described. Similarly to the flowchart, the addition of urea water into the exhaust gas from the urea water injection nozzle 4A is stopped.

  Further, in S3, the exhaust temperature is set to a predetermined value (for example, 180 °) without immediately cutting off the fuel injection into the cylinder of the internal combustion engine 1 as in the flowchart for explaining the control of the conventional NOx reduction process shown in FIG. C) or higher), the water is evaporated from the urea water already added to the exhaust gas, and urea powder accumulates in the vicinity of the nozzle hole of the urea water injection nozzle 4A and in the exhaust passage 2 to include the urea water addition system. In order to avoid the possibility of adverse effects on the system, even during deceleration, fuel injection into the cylinder is continued for a predetermined amount of fuel to be supplied to the internal combustion engine 1 for the first predetermined period.

  The first predetermined period is, for example, a period during which the urea water added in the exhaust gas can be thermally decomposed into ammonia and carbon dioxide gas. For example, the urea water discharged from the urea water injection nozzle 4A into the exhaust gas of the urea water. The addition can be stopped (since urea water is added at the end), and the exhaust temperature can be set to a period required to maintain the exhaust temperature from 150 ° C. to about 200 ° C. for about 15 seconds. be able to.

In S3, in order to maintain the exhaust temperature at a predetermined level, the exhaust temperature is lowered by introducing relatively low temperature fresh air (outside air) into the cylinder of the internal combustion engine 1 and exhausting it as low temperature exhaust. In order to prevent this, the control for limiting the amount of intake air by the intake throttle valve 20 interposed in the intake passage of the internal combustion engine 1 (a low λ control for suppressing the excess air ratio λ) is executed for a second predetermined period. .
The second predetermined period is, for example, a period during which the urea water added in the exhaust gas can be thermally decomposed into ammonia and carbon dioxide gas. For example, the urea water is discharged into the exhaust gas from the urea water injection nozzle 4A. The addition can be stopped (since urea water is added at the end), and the exhaust temperature can be set to a period required to maintain the exhaust temperature from 150 ° C. to about 200 ° C. for about 15 seconds. be able to.

In addition, in S3, an exhaust throttle valve 30 (for example, a so-called exhaust brake valve) that is interposed in the exhaust passage 2 and controls the passage cross-sectional area of the exhaust passage 2 to control the exhaust pressure is operated, so that the third By keeping the relatively hot exhaust gas in the exhaust passage 2 for a predetermined period, a decrease in the exhaust temperature in the exhaust passage 2 including the vicinity of the nozzle hole of the urea water injection nozzle 4A is suppressed.
The third predetermined period is, for example, a period during which the urea water added in the exhaust gas can be thermally decomposed into ammonia and carbon dioxide gas. For example, the urea water discharged from the urea water injection nozzle 4A into the exhaust gas of the urea water. The addition can be stopped (since urea water is added at the end), and the exhaust temperature can be set to a period required to maintain the exhaust temperature from 150 ° C. to about 200 ° C. for about 15 seconds. be able to.

Further, in S3, a so-called EGR (Exhaust Gas Recirculation) system that recirculates at least a part of the exhaust gas from the internal combustion engine 1 as EGR gas into the cylinder of the internal combustion engine 1 in order to lower the combustion temperature and suppress the amount of NOx generated. The EGR valve 41 constituting 40 is opened for a fourth predetermined period. As a result, at least a part of the exhaust gas is recirculated as EGR gas into the cylinder of the internal combustion engine 1, and the rate at which relatively low temperature fresh air (outside air) is introduced into the cylinder of the internal combustion engine 1 is reduced, thereby This contributes to maintaining the temperature of the exhaust gas from the engine 1 at a predetermined level. Here, the opening degree of the EGR valve 41 can be fully opened (100%), for example, but can be changed as necessary.
The fourth predetermined period is, for example, a period during which the urea water added in the exhaust gas can be thermally decomposed into ammonia and carbon dioxide gas. For example, the urea water discharged from the urea water injection nozzle 4A into the exhaust gas of the urea water. The addition can be stopped (since urea water is added at the end), and the exhaust temperature can be set to a period required to maintain the exhaust temperature from 150 ° C. to about 200 ° C. for about 15 seconds. be able to.

  By the way, in order to regenerate the diesel particulate filter 3 with an oxidation catalyst according to the present embodiment, an exhaust heating means for heating the exhaust by an electric heater, a burner or the like and a fuel addition means for adding fuel to the exhaust are provided. In this case, a configuration in which the exhaust heating unit and the fuel addition unit are used in combination with the exhaust temperature control described above can be adopted. When the operation shifts to an operating state where the exhaust temperature may drop to a predetermined level or less after the reduction process is stopped, the heating means and the fuel addition means are operated for a predetermined period in S3 of the flowchart of FIG. By maintaining it at a predetermined level (for example, 180 ° C. or higher), water is evaporated from the urea water already added into the exhaust gas, and urea powder is sprayed into the urea water injection nozzle 4. May also be configured to deposit around or inside of the exhaust passage 2 injection hole exhaust system including a urea water addition system to avoid Re adversely affect fear.

  In addition, each process performed in said S3 is not restricted to performing all, For example, according to a request | requirement, at least one can be selected from each process, or it can also perform combining suitably. It is.

  Further, the present invention is not limited to the above-described embodiment. For example, when the exhaust gas temperature detecting means is provided and the exhaust gas temperature becomes a predetermined level or lower, the urea water is discharged from the urea water injection nozzle 4A. The present invention is also applicable to the case where the addition to the inside is stopped and the execution of the NOx reduction process is stopped.

  That is, after the exhaust gas temperature falls below a predetermined level and the urea water injection from the urea water injection nozzle 4A is stopped in the exhaust gas and the execution of the NOx reduction process is stopped, the urea water added up to that point is ammonia. 2 can be configured to perform the process of S3 in the flowchart shown in FIG. 2 so as to maintain the exhaust temperature for a predetermined period so that it can be thermally decomposed into carbon dioxide gas.

  By the way, in the exhaust gas temperature control according to the present embodiment, when the exhaust gas temperature rises to a predetermined level or higher during the process of S3 in the flowchart shown in FIG. However, the process of S3 can be stopped or interrupted on the way.

  By the way, in each said embodiment, although the internal combustion engine 1 can be set as the diesel engine which performs diesel combustion, for example, it is not limited to this, It is set as the internal combustion engine which uses gasoline and other substances as fuel. In addition, a mobile / stationary internal combustion engine can be obtained.

  Each embodiment described above is only an example for explaining the present invention, and various modifications can be made without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Exhaust passage 4 Urea water addition apparatus (equivalent to reducing agent addition means)
4A Urea water injection nozzle 4B Urea water tank 4C Supply pump 5 Urea selective reduction type NOx catalyst (equivalent to selective reduction type catalyst)
6 Ammonia oxidation catalyst (NH ₃ anti-slip catalyst)
20 Intake throttle valve 30 Exhaust brake valve (Exhaust throttle valve)
40 RGR system 41 EGR valve

Claims (4)

A control device for an internal combustion engine comprising an exhaust treatment device that selectively adds a reducing agent to exhaust gas discharged from the internal combustion engine via a reducing agent addition means and selectively reduces a specific component in the exhaust gas by a selective reduction catalyst. Because
When the reducing agent is urea water and the selective catalytic reduction catalyst is a urea selective catalytic reduction NOx catalyst,
The exhaust gas temperature control is executed to maintain the exhaust gas temperature at a predetermined level or higher for a predetermined period when it is determined that the exhaust gas temperature is likely to drop to a predetermined level or lower during the NOx reduction process. The control apparatus of the internal combustion engine provided with the exhaust-gas processing apparatus which performs.   The control apparatus for an internal combustion engine provided with the exhaust processing apparatus according to claim 1, wherein the exhaust gas temperature control is executed when the internal combustion engine is decelerated.   The exhaust temperature control supplies a predetermined amount of fuel into the cylinder of the internal combustion engine, closes the intake throttle valve, closes the exhaust throttle valve, and opens the EGR valve. 2. The method according to claim 1, wherein at least one of operating the exhaust heating means for heating the exhaust and operating the fuel addition means for adding fuel to the exhaust is performed. Or the control apparatus of the internal combustion engine provided with the exhaust-gas treatment apparatus of Claim 2. The exhaust gas temperature control is performed so that the exhaust gas temperature can be maintained at 150 ° C. or higher for about 15 seconds after the addition of urea water to the exhaust gas through the reducing agent adding unit is stopped. A control device for an internal combustion engine, comprising the exhaust treatment device according to any one of claims 1 to 3.