JP2015075003A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of suppressing an end of an addition valve exposed to an inside of an injection passage from being exposed to high temperature exhaust gas and overheated.SOLUTION: The exhaust emission control device includes an exhaust passage 10, a selective reduction catalyst 30, and an injection passage 11 branched from a portion on an upstream side of the selective reduction catalyst 30 in the exhaust passage 10. A urea addition valve 40 is attached to the injection passage 11. A communication passage 12 directly communicating a portion on the upstream side of a branch part in which the injection passage 11 is branched in the exhaust passage 10 with the injection passage 11 without passing through the branch part is provided in the exhaust emission control device. The exhaust emission control device further includes a cooling device 50 for cooling exhaust gas flowing through the communication passage 12, a cooling water pump 51 for circulating the cooling water to the cooling device 50, and a control device 100 for controlling the cooling water pump 51. The control device 100 controls the cooling water pump 51 so that a temperature in the injection passage 11 is maintained to a prescribed level.

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine including an addition valve for injecting an additive into exhaust gas.

  Patent Document 1 discloses an exhaust gas purification device for an internal combustion engine that includes an addition valve that injects an additive toward a catalyst provided in the middle of an exhaust passage. In the exhaust purification device of Patent Document 1, an injection path branched from the exhaust passage is provided upstream of the catalyst in the exhaust passage, and an addition valve is provided in this injection path. Patent Document 1 discloses a configuration in which a gas introduction pipe is provided for directing exhaust gas directly into the injection path from the exhaust path upstream of the branch part between the exhaust passage and the injection path without passing through the branch part. Has been.

  Moreover, in the exhaust gas purification apparatus of Patent Document 1, a cooling water passage is provided inside a pedestal to which the addition valve is attached, and the addition valve is cooled by cooling water flowing through the cooling water passage. .

JP 2009-156073 A

  However, when the addition valve is cooled by the cooling water flowing through the cooling passage provided inside the pedestal as described above, the tip of the addition valve exposed in the exhaust passage and exposed to high-temperature exhaust is removed. It cannot be cooled directly. For this reason, the tip of the addition valve may be overheated.

  The present invention has been made in view of the above circumstances, and an object thereof is an internal combustion engine capable of suppressing overheating due to exposure of the tip of the addition valve exposed in the injection path to high-temperature exhaust gas. An object of the present invention is to provide an exhaust emission control device for an engine.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
An exhaust emission control device for solving the above problems includes an exhaust passage connected to an internal combustion engine, a catalyst provided in the middle of the exhaust passage, and an injection branched from a portion upstream of the catalyst in the exhaust passage. A branch valve, an addition valve attached to the injection path, for injecting an additive, an exhaust passage upstream of the branch section where the injection path is branched in the exhaust passage, and the injection path. A communication path that directly communicates without passing through, a cooling device that cools exhaust gas flowing through the communication path by circulating cooling water in a cooling water path that surrounds the communication path, and circulating cooling water to the cooling water device And a control device that controls the cooling water pump, and controls the cooling water pump so as to maintain the temperature in the injection path at a predetermined level.

  According to the above configuration, the exhaust gas cooled by the cooling device is supplied into the injection path. And in the said structure, the cooling water pump which circulates cooling water to a cooling device is controlled so that the temperature in an injection path may be maintained at a predetermined | prescribed level. Therefore, the temperature in the injection path can be controlled, and the tip of the addition valve exposed in the injection path can be prevented from being exposed to high-temperature exhaust gas and overheating.

The schematic diagram which shows the whole structure about one Embodiment of the exhaust gas purification apparatus of an internal combustion engine. The graph which shows the change by the temperature of the residual ratio of the precipitate derived from urea. The graph which shows the change by the temperature of the liquid phase ratio in the precipitate derived from urea. The flowchart which shows the flow of a series of processes concerning addition valve protection control implemented in addition to control of a cooling water pump. The schematic diagram which shows the example of a change of the exhaust gas purification apparatus of an internal combustion engine.

Hereinafter, an embodiment of an exhaust gas purification apparatus for an internal combustion engine will be described with reference to FIGS.
As shown in FIG. 1, in this exhaust gas purification apparatus for an internal combustion engine, an oxidation catalyst 20 and a selective reduction catalyst 30 are provided in this order from the upstream side in an exhaust passage 10 connected to the internal combustion engine. In FIG. 1, the flow direction of the exhaust gas flowing through the exhaust passage 10 is indicated by a white arrow.

  The selective reduction catalyst 30 is a selective reduction type catalyst that reduces and purifies NOx (nitrogen oxide) in exhaust gas by using ammonia supplied as a reducing agent. The oxidation catalyst 20 is a catalyst for bringing the ratio of NO (nitrogen monoxide) and NO2 (nitrogen dioxide) in NOx contained in the exhaust gas closer to “1.0”. The part is oxidized to NO2. Thus, the oxidation catalyst 20 is provided upstream of the selective reduction catalyst 30 because the NOx purification rate in the selective reduction catalyst 30 is high by making the ratio of NO and NO2 contained in the exhaust gas close to “1.0”. It is to become.

  An injection passage 11 branched from the exhaust passage 10 is connected to a portion of the exhaust passage 10 located between the oxidation catalyst 20 and the selective reduction catalyst 30. A urea addition valve 40 that injects urea water as an additive is attached to the injection path 11. The urea addition valve 40 is connected to a urea pump 41 via a supply pipe 42, and urea water pumped from the tank by the urea pump 41 is supplied to the urea addition valve 40.

  The exhaust passage 10 is provided with a communication passage 12 that branches from a portion upstream of the oxidation catalyst 20 and communicates directly with the injection passage 11. That is, the communication passage 12 is a passage that directly introduces exhaust gas into the injection passage 11 without going through a branching portion where the injection passage 11 in the exhaust passage 10 is branched.

  The exhaust purification device is provided with a cooling device 50 that cools the portion of the communication passage 12 connected to the injection passage 11 and the tip of the urea addition valve 40. A cooling water passage is provided inside the cooling device 50. The cooling water passage of the cooling device 50 is connected to the cooling water pump 51, and the cooling water is circulated by driving the cooling water pump 51. The cooling water pump 51 is controlled by the control device 100.

  An exhaust temperature sensor 60 that detects the temperature of the exhaust gas flowing through the exhaust passage 10 is connected to the control device 100. The exhaust gas temperature sensor 60 detects the temperature of the exhaust gas flowing through the upstream side of the oxidation catalyst 20 in the exhaust gas passage 10.

  The control device 100 estimates the temperature in the vicinity of the urea addition valve 40, for example, the temperature in the injection path 11 based on the temperature detected by the exhaust temperature sensor 60. Further, the control device 100 estimates the adsorption amount of ammonia adsorbed on the selective reduction catalyst 30 based on the control history of the urea addition valve 40, the temperature history detected by the exhaust temperature sensor 60, and the like. The addition valve 40 and the urea pump 41 are controlled.

  In this exhaust purification device, the urea water injected from the urea addition valve 40 is hydrolyzed by the heat of the exhaust to become ammonia and is adsorbed by the selective reduction catalyst 30. The NOx in the exhaust is reduced and purified by the ammonia adsorbed on the selective reduction catalyst 30.

By the way, if urea water injected from the urea addition valve 40 adheres to the tip of the urea addition valve 40, the injection path 11, or the exhaust passage 10, urea-derived precipitates may accumulate.
As shown in FIG. 2, the urea-derived precipitate cannot be completely pyrolyzed unless the temperature is raised to about 350.degree. FIG. 2 shows the residual ratio of precipitates based on the amount of precipitates deposited at 100 ° C.

  If it is a deposit deposited in the exhaust passage 10 instead of the injection passage 11, it is decomposed by raising the temperature to 350 ° C. or higher in a high temperature environment during high load operation or regeneration processing such as a diesel particulate filter. Is possible. However, if the urea addition valve 40 reaches 120 ° C. or higher, reliability problems may occur. Therefore, the injection path 11 near the urea addition valve 40 rises to 350 ° C. or higher from the viewpoint of protecting the urea addition valve 40. It is difficult to heat.

However, if the deposit deposited in the vicinity of the urea addition valve 40 is left as it is, the injection path 11 may be blocked and ammonia may not be supplied to the selective reduction catalyst 30.
In response to such a problem, the spray angle of the urea water sprayed from the urea addition valve 40 is narrowed to increase the penetration force, and the urea spray is physically formed in the injection path 11 by making the urea water spray into a liquid column shape. It can also be prevented from adhering to. However, if the spray of urea water is in the form of a liquid column, the urea water will not sufficiently diffuse into the exhaust gas before reaching the selective reduction catalyst 30. As a result, hydrolysis to ammonia does not proceed, the NOx purification rate decreases, or ammonia cannot be adsorbed by the selective reduction catalyst 30, and ammonia is discharged downstream from the selective reduction catalyst 30. There is a fear.

  Therefore, in this exhaust purification device, attention is paid to the fact that the urea-derived precipitate exists in the liquid phase in the temperature range of 130 ° C. to 160 ° C. as shown in FIG. 3, and the urea-derived precipitate is always kept in the liquid phase. And is discharged into the exhaust passage 10.

  In addition, since hydrolysis hardly arises at the temperature of 100 degrees C or less, urea water exists as it is, and the precipitate derived from urea does not generate | occur | produce. Urea changes in quality in a temperature field of 100 ° C. or higher, and changes from urea to biuret and further to triuret. Furthermore, it transforms in order from cyanuric acid, ammelide, and melamine existing in the solid phase even in a temperature field of 130 ° C. to 160 ° C. from triuret. Therefore, even if the urea-derived precipitates deposited for a long period of time are exposed to a temperature field of 130 ° C. to 160 ° C., if the transformation progresses to cyanuric acid, ammelide, and melamine, the liquid is discharged from the injection path 11 as a liquid. It becomes difficult to do. In other words, it is necessary to create a temperature environment of 130 ° C. to 160 ° C. before the alteration proceeds to cyanuric acid, and to make the precipitate into a liquid to be discharged from the injection path 11. On the other hand, the alteration rate of urea increases as the temperature increases, so it is not preferable to expose the urea-derived precipitate to a high temperature field of 160 ° C. or higher.

  Therefore, in order to keep urea-derived precipitates in the liquid phase at all times, in this exhaust purification device, the exhaust gas introduced into the injection passage 11 through the communication passage 12 is cooled by the cooling device 50, and the urea in the injection passage 11 is cooled. The temperature of the region to which the deposit derived from the source adheres is maintained at 130 ° C to 160 ° C. Specifically, the control device 100 controls the cooling water pump 51 to control the circulation amount of the cooling water that circulates through the cooling device 50, so that the temperature of the region in which the precipitate derived from urea in the injection path 11 adheres. Is maintained at 130 ° C to 160 ° C. The cooling device 50 basically has a temperature at the tip of the urea addition valve 40 as long as the cooling water is circulated so as to maintain the temperature in the injection path 11 at 130 ° C. to 160 ° C. It is designed to be 120 ° C or lower.

  Further, in this exhaust purification device, the temperature in the vicinity of the urea addition valve 40 is usually managed by the above method, but when the temperature cannot be managed only by circulating the cooling water by the cooling device 50, the exhaust purification device can also be used. Add valve protection control is executed.

The addition valve protection control is executed through a series of processes shown in FIG. This series of processes is repeatedly executed at a predetermined control cycle by the control device 100 during operation of the internal combustion engine.
When starting this series of processing, the control device 100 determines whether or not the temperature in the vicinity of the urea addition valve 40 is 160 ° C. or higher in step S101.

  When it is determined in step S101 that the temperature in the vicinity of the urea addition valve 40 is lower than 160 ° C. (step S101: NO), the control device 100 executes normal urea addition control in step S102. When the normal urea addition control is executed in this way, the control device 100 once ends this series of processes.

  On the other hand, when it is determined in step S101 that the temperature in the vicinity of the urea addition valve 40 is 160 ° C. or higher (step S101: YES), the control device 100 executes addition valve protection control after step S103.

  In step S <b> 103, the control device 100 determines the current ammonia adsorption amount in the selective reduction catalyst 30. And the control apparatus 100 determines whether cooling addition is possible in step S104 based on the determined adsorption amount. Specifically, it is determined whether the ammonia adsorption amount in the selective reduction catalyst 30 is greater than or equal to a reference value. If the ammonia adsorption amount is less than the reference value, it is determined that the cooling addition can be performed. If the ammonia adsorption amount is equal to or greater than the reference value, it is determined that the cooling addition cannot be performed.

  The reason why the addition of cooling is determined based on the ammonia adsorption amount in the selective reduction catalyst 30 is because there is an upper limit in the amount of ammonia that the selective reduction catalyst 30 can adsorb. If the amount of ammonia adsorbed on the selective reduction catalyst 30 exceeds the upper limit and ammonia generated by the execution of cooling addition cannot be adsorbed by the selective reduction catalyst 30, ammonia is discharged downstream from the selective reduction catalyst 30. Therefore, here, the reference value is set as a value indicating the upper limit of a range in which ammonia is not discharged downstream from the selective reduction catalyst 30 in consideration of the amount of ammonia generated by cooling addition.

  When it is determined in step S104 that cooling addition is possible (step S104: YES), the control device 100 executes cooling addition in step S105. Here, the control apparatus 100 injects urea water from the urea addition valve 40. Thereby, the temperature of the urea addition valve 40 vicinity falls by the vaporization latent heat of urea spray. Also, the heated urea water is discharged from the urea addition valve 40 and new urea water is supplied from the urea pump 41, and the urea addition valve 40 is cooled by heat exchange with the new urea water. .

When the cooling addition is executed in this way, the control device 100 once ends this series of processes.
On the other hand, when it is determined in step S104 that the cooling addition is impossible (step S104: NO), the control device 100 executes the urea water suction back in step S106. Here, the control device 100 sucks back the urea water remaining in the urea addition valve 40 by rotating the urea pump 41 in the reverse direction with the urea addition valve 40 opened. By preventing the urea water from remaining in the high temperature urea addition valve 40 in this way, the urea water remaining in the urea addition valve 40 evaporates to a high temperature and high pressure, and the seat portion of the urea addition valve 40 is corroded. Can be suppressed.

When the urea water is sucked back in this way, the control device 100 once ends this series of processes.
Next, the operation of the exhaust gas purification apparatus for an internal combustion engine according to this embodiment will be described.

  The exhaust gas cooled by the cooling device 50 is supplied into the injection path 11. Moreover, the cooling water pump 51 is controlled so that the temperature in the injection path 11 can be maintained at 130 ° C to 160 ° C.

  Further, when the temperature cannot be controlled by the cooling device 50, the addition valve protection control is executed. Through this addition valve protection control, if cooling addition is possible, cooling addition is executed to cool the urea addition valve 40 and its vicinity, and even if cooling addition is impossible, the urea addition valve 40 can be The remaining urea water is sucked back.

According to the embodiment described above, the following effects can be obtained.
(1) Since the temperature in the injection path 11 can be controlled by controlling the cooling water pump 51, the tip of the urea addition valve 40 exposed in the injection path 11 is exposed to high-temperature exhaust. And overheating can be suppressed.

  (2) Since the temperature in the vicinity of the urea addition valve 40 is maintained in a range of 130 ° C. to 160 ° C. at which urea-derived precipitates are in a liquid phase, the liquid precipitates are transferred from the injection path 11 to the exhaust passage 10. It will be discharged. Therefore, it is possible to suppress deposits from being deposited near the urea addition valve 40 and blocking the injection path 11.

  (3) When the temperature in the vicinity of the urea addition valve 40 is 160 ° C. or higher and the cooling addition can be executed, the cooling addition is executed together with the cooling by the cooling device 50, so the urea addition valve 40 is overheated. It can suppress more reliably.

  (4) When the adsorption amount of ammonia in the selective reduction catalyst 30 is large, the cooling addition is not performed, and therefore, the ammonia injected by the cooling addition is not completely adsorbed by the selective reduction catalyst 30 and is discharged downstream. Can be suppressed.

  (5) When the amount of adsorbed ammonia is large and cooling addition is not feasible, the urea water is reconstituted. Therefore, even if the temperature in the vicinity of the urea addition valve 40 is 160 ° C. or higher, the sheet portion is corroded. It can suppress and can protect the urea addition valve 40.

In addition, the said embodiment can also be implemented with the following forms which changed this suitably.
In the above embodiment, an example in which the temperature in the injection path 11 is estimated based on the temperature detected by the exhaust temperature sensor 60 has been described, but the method for estimating and detecting the temperature can be changed as appropriate. For example, the structure which provides a temperature sensor in the injection path 11, and the structure which estimates the temperature in the injection path 11 based on the injection quantity of the fuel in an internal combustion engine and the engine cooling water temperature are also employable.

  In the above embodiment, it is exemplified that the adsorption amount of ammonia in the selective reduction catalyst 30 is estimated based on the control history of the urea addition valve 40, the temperature history detected by the exhaust temperature sensor 60, and the like. The means for estimating the adsorption amount may be changed as appropriate.

  In the above-described embodiment, the example in which the cooling water pump 51 is controlled so as to maintain the temperature in the injection path 11 at 130 ° C. to 160 ° C. is shown, but the purpose is to protect the urea addition valve 40. For example, the level of the temperature to be maintained can be changed as appropriate, and is not limited to the above temperature range. For example, the temperature of the tip of the urea addition valve 40 may be maintained in a temperature range that is 120 ° C. or lower. In short, the level of the temperature to be maintained may be set to a level that can guarantee the function of the urea addition valve 40 in accordance with the standard of the urea addition valve 40.

  In addition valve protection control, cooling addition is not performed when the amount of ammonia adsorbed on the selective reduction catalyst 30 is large, but the processing in steps S103, S104, and S106 is omitted, and the temperature is high regardless of the amount of adsorption. Sometimes cooling addition may be performed.

  An example is shown in which the addition valve protection control is executed when the temperature in the vicinity of the urea addition valve 40 is 160 ° C. or higher. May be.

-Although the example which performs cooling addition in addition valve protection control was shown, cooling addition may be abbreviate | omitted and it may be made to always perform the sucking-back of cooling water in addition valve protection control.
-The addition valve protection control itself may be omitted.

  In the above embodiment, an exhaust purification device that injects urea water as an additive is illustrated, but the technical idea disclosed in the above embodiment can also be applied to an exhaust purification device that injects additives other than urea water. .

  -Although the cooling device 50 showed the example comprised so that the front-end | tip part of the urea addition valve 40 and the communication path 12 might be cooled, the cooling device which cools the urea addition valve 40, and the cooling which cools the communication path 12 The apparatus may be provided separately. Further, if at least a cooling device for cooling the communication passage 12 is provided, it is possible to prevent the tip portion of the urea addition valve 40 exposed in the injection passage 11 from being exposed to high-temperature exhaust gas and overheating. Therefore, the cooling device for cooling the urea addition valve 40 may not be provided.

  The shape of the exhaust passage 10 can be changed as appropriate. For example, the technical idea disclosed in the above embodiment is an exhaust gas in which the angle θ formed by the central axis of the oxidation catalyst 20 and the central axis of the selective reduction catalyst 30 is in the range of −90 ° to 90 ° as shown in FIG. It is particularly effective when applied to a purification device. When it is outside this range, the exhaust passage 10 is folded back from the oxidation catalyst 20 toward the selective reduction catalyst 30. Therefore, the flow rate of the exhaust gas that has passed through the oxidation catalyst 20 is slowed down before flowing into the selective reduction catalyst 30, and it is possible to secure a time until the urea water injected from the urea addition valve 40 evaporates and diffuses. Since it is easy to evaporate and diffuse urea water by this, spray can be made into a liquid column shape and adhesion of urea water to the urea addition valve 40 vicinity can be suppressed. On the other hand, when the angle θ is in the range of −90 ° to 90 °, the flow rate of the exhaust gas is difficult to reduce, so it is difficult to secure time for evaporating and diffusing the urea water. That is, since it is difficult to make urea spray into a liquid column shape, it is preferable to apply the technical idea disclosed in the above embodiment to suppress deposition of urea-derived precipitates in the vicinity of the urea addition valve 40.

DESCRIPTION OF SYMBOLS 10 ... Exhaust path, 11 ... Injection path, 12 ... Communication path, 20 ... Oxidation catalyst, 30 ... Selective reduction catalyst, 40 ... Urea addition valve, 41 ... Urea pump, 42 ... Supply pipe, 50 ... Cooling device, 51 ... Cooling Water pump, 60 ... exhaust temperature sensor, 100 ... control device.

Claims (1)

An exhaust passage connected to the internal combustion engine;
A catalyst provided in the middle of the exhaust passage;
An injection path branched from a portion upstream of the catalyst in the exhaust passage;
An addition valve attached to the injection path for injecting the additive;
A communication passage that directly connects the exhaust passage upstream of the branch portion where the injection passage in the exhaust passage branches and the injection passage without passing through the branch portion;
A cooling device that cools exhaust gas flowing in the communication path by circulating cooling water in a cooling water path surrounding the communication path;
A cooling water pump for circulating cooling water through the cooling device;
A control device for controlling the cooling water pump,
An exhaust gas purification apparatus for an internal combustion engine that controls the cooling water pump so as to maintain a temperature in the injection path at a predetermined level.