JP2013050078A - Exhaust purification device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively utilize reduction agent for purification of exhaust gas in an exhaust purification device using a selective reduction catalyst.SOLUTION: The exhaust purification device for an internal combustion engine includes: a selective reduction catalyst 31 provided in an exhaust path 2 of an internal combustion engine; a reduction agent supply device for supplying a reduction agent to exhaust flowing into the selective reduction catalyst at a position upstream of the selective reduction catalyst; a heater 32 for heating the selective reduction catalyst; and a control device for purifying the exhaust in the selective reduction catalyst by supplying the reduction agent into the exhaust through the reduction agent supply device with respect to the selective reduction catalyst heated by the heater. The heater 32 heats the selective reduction catalyst in a cross section of the catalyst relative to a flow direction of the exhaust in the selective reduction catalyst 31 so that the amount of heat supply to a coarse particle area in which the reduction agent supplied from the reduction agent supply device is distributed in a coarse particle state becomes greater than that of an area other than the coarse particle area in the cross section of the catalyst.

Description

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

  In order to purify NOx and the like contained in the exhaust from the internal combustion engine, an exhaust purification catalyst is disposed in the exhaust passage, and various exhaust purification control is performed according to the substance to be purified. For example, Patent Document 1 discloses a technique for purifying NOx in exhaust gas by disposing a selective reduction catalyst as a denitration catalyst in an exhaust passage and supplying a reducing agent into the exhaust gas. In particular, in this technology, in order to shorten the time until the denitration catalyst is activated and to improve the operation rate of the denitration catalyst, a heater for directly heating the denitration catalyst is provided, and the denitration catalyst is operated by heating the heater. A configuration is adopted in which exhaust gas is allowed to flow after the temperature is exceeded.

JP 2003-269149 A

  When purifying NOx or the like in exhaust gas using a selective reduction catalyst, a compound derived from ammonia, a fuel for an internal combustion engine, or the like is used as the reducing agent. In general, when the reducing agent is supplied into the exhaust gas from the upstream side of the selective catalytic reduction catalyst, the reducing agent is supplied to the selective catalytic reduction catalyst together with the exhaust gas, thereby contributing to the selective purification of NOx. However, when the reducing agent supplied into the exhaust gas flows into the selective catalytic reduction catalyst, the reducing agent is not necessarily evenly dispersed in the exhaust gas. It is difficult to be uniform throughout.

  For example, in the selective catalytic reduction catalyst, the particles of the reducing agent are partially coarse and distributed in a large state, and the concentration of the reducing agent is higher than other regions (hereinafter referred to as “coarse particle region”). So, it can be said that the reducing agent is excessively supplied. Therefore, although depending on the NOx concentration in the exhaust gas and the purification capacity of the selective catalytic reduction catalyst, the reducing agent distributed in the coarse particle region flows out downstream of the catalyst according to the exhaust flow without sufficiently contributing to NOx purification. The possibility increases and the effective use of reducing agents is hindered.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to effectively utilize a reducing agent for exhaust purification in an exhaust purification apparatus using a selective reduction catalyst.

  In the present invention, in order to solve the above-mentioned problem, based on how the reducing agent supplied in the exhaust gas is distributed in the selective catalytic reduction catalyst, the selective catalytic reduction catalyst is heated according to the distribution state. Adopted a configuration to adjust. With this configuration, the distribution state of the supplied reducing agent and the active state of the selective catalytic reduction catalyst by heating can be matched, so that the supplied reducing agent can be effectively used for exhaust purification. Thus, the selective reduction catalyst can be efficiently heated.

Therefore, in detail, the present invention relates to a selective reduction catalyst provided in an exhaust passage of an internal combustion engine, and a reduction agent that supplies a reducing agent to exhaust flowing into the selective reduction catalyst upstream of the selective reduction catalyst. Supplying the reducing agent into the exhaust gas via the reducing agent supplying means to the selective reducing catalyst heated by the heating means and the selective reducing catalyst heated by the heating means. And a control means for purifying exhaust gas in the selective catalytic reduction catalyst. The heating means is configured such that, in the catalyst cross section with respect to the exhaust ventilation direction in the selective reduction catalyst, the amount of heat supplied to the coarse particle region in which the reducing agent supplied from the reducing agent supply means is distributed in a coarse particle state is the catalyst. The selective catalytic reduction catalyst is heated so as to be larger than the region other than the coarse particle region in the cross section.

  In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, NOx in the exhaust gas is selectively purified by the selective reduction catalyst provided in the exhaust passage and the reducing agent from the reducing agent supply means provided upstream thereof. Will be. Further, the selective reduction type catalyst is heated by the heating means, so that the catalyst can be quickly brought into an active state suitable for exhaust purification, and the active state is maintained regardless of the operating state of the internal combustion engine. Therefore, the exhaust gas can be efficiently purified by the control means.

  Here, as described above, when the reducing agent supplied into the exhaust gas from the reducing agent supply means reaches the selective catalytic reduction catalyst according to the flow of the exhaust gas, the catalyst is not necessarily distributed uniformly. For example, when the reducing agent supply means supplies the reducing agent into the exhaust, if there is a certain concentration in the reducing agent distribution in the exhaust, the concentration is more specifically selected even in the selective reduction catalyst. This may also be reflected in the cross section of the catalyst with respect to the exhaust ventilation direction in the reduction catalyst. Therefore, a region where the reducing agent is distributed in a coarse particle state in the cross section of the catalyst is referred to as a coarse particle region, and regarding the heating of the catalyst by the heating means, a heat amount supply different from the other regions is supplied to the coarse particle region. I decided to do it.

  In the coarse particle region, since the reducing agent is distributed at a relatively high concentration, in order to effectively use the reducing agent for exhaust gas purification, the purifying ability of the selective catalytic reduction catalyst in the coarse particle region is used in other regions. It is preferable to make it higher than the purifying ability of the selective catalytic reduction catalyst. Therefore, the heating means performs heat treatment according to the portion of the selective catalytic reduction catalyst so that the amount of heat supplied to the coarse particle region is larger than that in the region other than the coarse particle region. Thereby, effective exhaust purification according to the distribution of the reducing agent can be realized, and energy consumption required for catalyst heating can be suppressed as much as possible. Note that the coarse particle region in the selective catalytic reduction catalyst can vary depending on the operating state of the internal combustion engine, the flow rate of exhaust gas flowing through the exhaust passage, and the like. Therefore, the coarse particle region to which the amount of heat is supplied by the heating means may be set on the selective catalytic reduction catalyst so as to include all the coarse particle regions in a variable range. Of the range that can vary from the viewpoint of suppression, a part of the region having a particularly high appearance frequency may be set on the selective catalytic reduction catalyst as a coarse particle region.

  Here, in the exhaust gas purification apparatus for an internal combustion engine, the through-passage connecting the upstream exhaust passage and the downstream exhaust passage of the selective catalytic reduction catalyst is a catalyst supporting portion in the selective catalytic reduction catalyst or the selective catalytic reduction type. The catalyst may be provided in a holding portion that holds and fixes the catalyst in the exhaust passage. Regarding the selective reduction type catalyst installed in the exhaust passage, it is preferable that exhaust gas flowing through the exhaust passage flows into the selective reduction type catalyst to perform effective exhaust purification, but a part of the reducing agent supplied into the exhaust is It may change to a solid substance that is not suitable for exhaust purification with a catalyst and may adhere to the vicinity of the catalyst. If such a solid substance adheres to the vicinity of the catalyst, there is a possibility that the exhaust gas purifying ability of the catalyst may be reduced, and there is a risk of thermal deterioration of the surroundings due to oxidation of the attached substance, which is not preferable. Therefore, as described above, by providing a through-passage in the catalyst supporting part or holding part in the vicinity of the selective catalytic reduction catalyst, it is possible to suppress the adhesion of solid substances and to reduce the functional degradation of the selective catalytic reduction catalyst as much as possible. It can be avoided.

Further, in the exhaust gas purification apparatus for an internal combustion engine up to the above, the heating means may be arranged downstream of the selective reduction catalyst in the exhaust passage. By disposing the heating means on the downstream side of the selective catalytic reduction catalyst, heating of the catalyst can be efficiently realized without inhibiting the flow of the reducing agent into the selective catalytic reduction catalyst. In addition, with such a configuration, the heating means is not directly exposed to the reducing agent, so that it is possible to prevent the reducing agent from being changed to a solid substance that is not suitable for exhaust purification by rapidly raising the temperature of the reducing agent. In addition, it is possible to avoid exposing the heating means itself to a rapid temperature rise.

  Moreover, in the exhaust gas purification apparatus for an internal combustion engine up to the above, the reducing agent is a compound derived from ammonia, and the heating means is the selective reduction type so as to be at a predetermined temperature or higher at which hydrolysis of the reducing agent occurs. The catalyst may be heated. By performing heating by the heating means in this way, ammonia is efficiently generated particularly from the reducing agent supplied to the coarse particle region, and it is selectively reduced by supplying it to other regions of the selective catalytic reduction catalyst. As a whole type catalyst, effective exhaust purification can be realized.

  Further, regarding another aspect of the reducing agent, in the exhaust gas purification apparatus for an internal combustion engine described above, the reducing agent is a compound derived from ammonia, and the heating means removes the solid deposit of the reducing agent. The selective catalytic reduction catalyst may be heated so as to have a predetermined temperature or higher. By performing heating by the heating means in this way, the solid deposit generated from the reducing agent can be removed, such as gas, and deposition of the product from the reducing agent in the selective catalytic reduction catalyst can be avoided. Thus, it is possible to avoid a decrease in catalyst performance and thermal deterioration of the catalyst.

  ADVANTAGE OF THE INVENTION According to this invention, the reducing agent for exhaust gas purification can be effectively utilized in the exhaust gas purification apparatus using the selective reduction catalyst.

It is a figure which shows schematic structure of the exhaust system of the internal combustion engine which concerns on the Example of this invention. It is a 1st figure which shows the specific structure of the exhaust gas purification apparatus shown in FIG. It is a figure regarding the heat supply to the coarse particle area | region formed in the exhaust gas purification apparatus shown in FIG. FIG. 3 is a diagram showing a correlation between catalyst temperature and ammonia adsorption rate in a selective reduction catalyst included in the exhaust purification device shown in FIG. 2. It is a 2nd figure which shows the specific structure of the exhaust gas purification apparatus shown in FIG. It is a figure explaining the change of the form by the temperature regarding the urea as a reducing agent supplied in the exhaust gas purification apparatus shown in FIG.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  An embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described with reference to the drawings attached to the present specification. FIG. 1 is a diagram showing a schematic configuration of an exhaust system of an internal combustion engine according to the present embodiment. The internal combustion engine 1 is a diesel engine for driving a vehicle. An exhaust passage 2 is connected to the internal combustion engine 1. In FIG. 1, the description of the intake system of the internal combustion engine 1 is omitted. The exhaust passage 2 is provided with a particulate filter 4 (hereinafter simply referred to as “filter”) that collects PM in the exhaust. Further, on the upstream side of the filter 4, an exhaust purification device 3 including a selective reduction catalyst and an electrically heated catalyst capable of heating the catalyst is provided. Details of the exhaust purification device 3 will be described later.

Further, a reducing agent supply valve 5 for supplying urea water as a reducing agent contributing to NOx purification in the selective reduction catalyst included in the exhaust purification device 3 into the exhaust is provided upstream of the exhaust purification device 3. Yes. Further, a temperature sensor 6 for measuring the bed temperature of the selective catalytic reduction catalyst included in the exhaust purification device 3 is provided in the catalyst carrier. The internal combustion engine 1 is provided with an electronic control unit (ECU) 10, and the ECU 10 is a unit that controls the operating state and the like of the internal combustion engine 1. In addition to the reducing agent supply valve 5 and the temperature sensor 6 described above, an air flow meter (not shown), a crank position sensor 11 and an accelerator opening sensor 12 are electrically connected to the ECU 10.

  Therefore, the ECU 10 is included in the exhaust flowing through the exhaust passage 2 based on the operating state of the internal combustion engine 1 such as the engine speed based on the detection of the crank position sensor 11 and the engine load based on the detection of the accelerator opening sensor 12. It is possible to estimate the NOx concentration. Then, according to the estimated NOx concentration, the ECU 10 issues an instruction to the reducing agent supply valve 5, and an amount of reducing agent necessary for NOx purification is supplied into the exhaust gas. If the selective catalytic reduction catalyst included in the exhaust purification device 3 is not activated, NOx purification using the supplied reducing agent cannot be performed effectively. The reducing agent is supplied when the bed temperature of the selective catalytic reduction catalyst is equal to or higher than a predetermined temperature at which the catalyst is active by the temperature sensor 6.

  Here, the exhaust emission control device 3 will be described with reference to FIGS. 2 and 3. FIG. 2 is a diagram showing a schematic configuration of the exhaust gas purification device 3, and FIG. 3 is formed in the selective reduction catalyst when the urea water as the reducing agent is supplied from the reducing agent supply valve 5. It is a figure regarding the heat supply to a coarse particle area | region. As shown in FIG. 2, the exhaust purification device 3 includes a selective reduction catalyst 31 that is selectively attached to the housing 2 a of the exhaust passage 2 via a holding portion 21 and selectively reduces NOx in the exhaust, and the catalyst 31. The electrically heated catalyst 32 is attached to the exhaust passage 2 via a fixed portion 33 on the downstream side. In the electrically heated catalyst 32, a catalyst having an oxidation function is supported on a catalyst carrier made of a material that generates electrical resistance and generates heat when energized. The catalyst carrier has a plurality of passages that extend in the direction in which the exhaust flows and whose cross section perpendicular to the direction in which the exhaust flows forms a honeycomb. By exhaust gas flowing through this passage, exhaust gas purification by the supported catalyst is performed. Examples of the catalyst include an oxidation catalyst, a three-way catalyst, an occlusion reduction type NOx catalyst, and a selective reduction type NOx catalyst. The selective reduction catalyst 31 and the electrically heated catalyst 32 are connected by a plurality of heat transfer pins 34 so that the thermal energy of the electrically heated catalyst 32 can be transferred to the selective reduction catalyst 31 side. Yes.

  Here, as shown in FIG. 3, when the reducing agent supply valve 5 is provided on the upstream side of the exhaust purification device 3 and the bed temperature of the selective catalytic reduction catalyst 31 exceeds a predetermined temperature indicating the active state as described above. Then, the reducing agent is supplied from the reducing agent supply valve 5 to the exhaust gas. The reducing agent injected from the reducing agent supply valve 5 diffuses into the exhaust gas and flows into the selective reduction catalyst 31 together with the exhaust gas, whereby the NOx in the exhaust gas is reduced and purified. Depending on the direction, the injection angle, the flow rate of the exhaust gas flowing through the exhaust passage 2, the diffusion state of the injected reducing agent in the exhaust gas is not uniform. For example, in the exhaust gas supplied with the reducing agent, there may be some unevenness of the reducing agent, such as a portion where the particles of the reducing agent are coarse and diffused in a large state, or a portion where there is not much reducing agent. . Therefore, when the reducing agent flows into the selective catalytic reduction catalyst 31, the particles of the reducing agent are coarse and relatively large in the catalyst cross section perpendicular to the longitudinal direction of the selective catalytic reduction catalyst 31 (the direction in which the exhaust gas flows). There is a tendency to form a coarse particle region that flows into a particle state and a non-coarse particle region in which the reducing agent particles are finer than the coarse particle region.

In the example shown in FIG. 3, since the reducing agent is injected from the reducing agent supply valve 5 so as to diffuse into the exhaust gas in a conical shape, the tip central portion and the tip outer peripheral portion of the spray by the injected reducing agent are In comparison, the reducing agent is distributed at a high density. Since there is a certain distance from the reducing agent supply valve 5 to the selective catalytic reduction catalyst 31, the spray gradually diffuses into the exhaust gas. However, uneven distribution of the reducing agent at the tip of the spraying is still in the selective catalytic reduction catalyst 31. It will be reflected as unevenness of the reducing agent flowing in. In the example of FIG. 3, as shown in the front view of the catalyst, in the ring-shaped region having a certain width in the catalyst cross section of the selective catalytic reduction catalyst 31 corresponding to the shape of the outer periphery of the tip of the spray, A coarse particle region R1 in which the particles are in a coarse particle state is formed. The substantially circular region R2 inside the coarse particle region R1 is not a state where no reducing agent is supplied at all, but is a region in which the particles of the reducing agent are finer than the coarse particle region R1. . The reducing agent that has flown into the front surface of the selective catalytic reduction catalyst 31 proceeds to some extent along the exhaust flow, but the coarse particle region R1 is formed near the front surface of the selective catalytic reduction catalyst 31. The

  Thus, in the selective reduction catalyst 31, the reducing agent supplied from the reducing agent supply valve 5 into the exhaust does not necessarily flow uniformly. And in coarse particle area | region R1, since the density | concentration of a reducing agent becomes high compared with area | region R2, compared with area | region R2, it becomes difficult to hydrolyze urea water which is a reducing agent efficiently. As a result, a certain amount of reducing agent is caused to flow downstream without the formation of ammonia contributing to NOx reduction due to the hydrolysis of urea water, and the effective utilization of the reducing agent can be hindered.

  Therefore, the exhaust gas purification apparatus 3 according to the present embodiment uses the thermal energy generated in the electrically heated catalyst 32 to increase the coarse particle region of the selective reduction catalyst 31 in order to promote effective utilization of the reducing agent in the coarse particle region R1. The electrically heated catalyst 32 and the selective reduction catalyst 31 are connected via a plurality of heat transfer pins 34 arranged so as to be preferentially transmitted to R1. Specifically, as shown in the catalyst rear view of FIG. 3, the rear surface of the selective catalytic reduction catalyst 31 is provided with an insertion hole 34a into which the heat transfer pin 34 is inserted at a portion overlapping the coarse particle region R1. ing. The insertion hole 34a extends to a position close to the coarse particle region R1 formed in the vicinity of the front surface of the selective catalytic reduction catalyst 31, and the heat transfer pin 34 is inserted therein to realize the connection of the two catalysts. Is done. By connecting the two catalysts in this way, when the electrically heated catalyst 32 generates heat by energization, the thermal energy is preferentially transmitted to the coarse particle region R1 of the selective catalytic reduction catalyst 31 and then to other regions. Go. As a result, in the selective catalytic reduction catalyst 31, the amount of heat supplied to the coarse particle region R1 can be made larger than the amount of heat supplied to other regions (for example, the region R2), and therefore the coarse particle region R1 is preferential. Heating can be achieved.

  If the coarse particle region R1 is preferentially heated in this way, it is possible to efficiently supply heat energy required for hydrolysis to the reducing agent distributed at a relatively high concentration therein. Thus, the hydrolysis can be promoted, and the amount of the reducing agent that flows downstream can be reduced without hydrolysis as described above. Further, by performing heating in accordance with the distribution of the reducing agent supplied to the selective catalytic reduction catalyst 31, that is, not performing heating of the selective catalytic reduction catalyst 31 as a whole, but performing only necessary and sufficient heating. Therefore, energy required for the heating, that is, power consumption in the electrically heated catalyst 32 can be suppressed.

Here, in the selective reduction catalyst 31, the correlation between the catalyst temperature (bed temperature) and the adsorption rate of ammonia produced from urea water as the reducing agent is shown in FIG. When the catalyst temperature exceeds the hydrolysis temperature, generation of ammonia is promoted by hydrolysis of the supplied urea water. At this time, if the catalyst temperature is near the hydrolysis temperature, the ammonia adsorption rate is relatively high. Therefore, as described above, the energization of the electrically heated catalyst 32 is controlled so that the temperature of the coarse particle region R1 becomes at least the hydrolysis temperature shown in FIG. 4 as a result of the heating by the electrically heated catalyst 32. Thus, it is possible to avoid a state in which ammonia is not generated (is difficult to generate) from the reducing agent. As the temperature of the selective catalytic reduction catalyst 31 further rises, the ammonia adsorption rate becomes very close to zero, and ammonia generated from the reducing agent is purged sequentially without being substantially adsorbed by the catalyst. Therefore, by setting the temperature of the coarse particle region R1 to a temperature belonging to the ammonia purge region shown in FIG. 4, it becomes possible to positively supply ammonia to the rear stage side of the selective catalytic reduction catalyst 31 and promote NOx purification. You can plan. Thus, the generation of ammonia from the reducing agent in the selective reduction catalyst 31 and the supply of ammonia to the downstream side of the catalyst can be controlled via the catalyst temperature. Therefore, by controlling the amount of current supplied to the electrically heated catalyst 32 according to the concentration of NOx contained in the exhaust, it is possible to appropriately control the supply of ammonia required for NOx reduction while effectively using the reducing agent. Is possible.

  In particular, in the exhaust emission control device 3 shown in FIG. 3, the electrically heated catalyst 32 is disposed on the downstream side of the selective catalytic reduction catalyst 31 so that the reducing agent supplied from the reducing agent supply valve 5 into the exhaust gas. Can be allowed to flow into the selective catalytic reduction catalyst 31 without being inhibited by the electrically heated catalyst 32. Therefore, generation and release of ammonia in the selective catalytic reduction catalyst 31 can be controlled more easily and accurately.

  Regarding the preferential heat supply to the coarse particle region R1 described above, even if the electrically heated catalyst 32 is arranged upstream of the selective catalytic reduction catalyst 31, an effective reducing agent can be used as in the above example. Utilization can be realized. However, in this case, due to the presence of the electrically heated catalyst 32, the shape and position of the coarse particle region R1 generated in the selective catalytic reduction catalyst 31 may be different from that shown in FIG. Therefore, the heat transfer pins 34 are arranged so that the thermal energy from the electrically heated catalyst 32 is transmitted to the coarse particle region R1 that is assumed based on the presence of the electrically heated catalyst 32 located on the upstream side. Just decide.

  In the example shown in FIG. 3, the position where the reducing agent particles are formed in a coarse particle state in the vicinity of the front surface of the selective catalytic reduction catalyst 31 is supplied from the flow rate of the exhaust gas flowing through the exhaust passage 2 or the reducing agent supply valve 5. It may vary depending on the operating state of the internal combustion engine 1 related to the amount of reducing agent etc. to be performed. Therefore, the region set as the coarse particle region R1 may be a region including all of the regions where the coarse particle state occurs as long as the operating state of the internal combustion engine 1 can be changed. As another method, a region in which a coarse particle state corresponding to an operation state when the frequency of appearance is relatively high in a range where the operation state of the internal combustion engine 1 can be changed is set as the coarse particle region R1. Good.

  Further, in the example shown in FIG. 3, since the electrically heated catalyst 32 is disposed on the downstream side of the selective catalytic reduction catalyst 31, unburned HC and PM (particulate matter) contained in the exhaust gas are discharged to the electrically heated catalyst 32. Becomes difficult to adhere. Therefore, the rapid temperature rise of the electrically heated catalyst 32 due to the oxidation of the deposit can be suppressed, and the thermal deterioration can be avoided. On the other hand, as described above, the electrically heated catalyst 32 is formed by supporting a catalyst having oxidizing ability on a carrier. Therefore, by utilizing the temperature increase due to the oxidation heat of the oxidation catalyst in addition to the temperature increase due to energization, more thermal energy can be transmitted to the selective catalytic reduction catalyst 31, and the above-described preferential heating of the coarse particle region R1 It is also possible to recover sulfur poisoning generated in the selective catalytic reduction catalyst 31 without being limited to NOx purification including the above.

Further, in the example shown in FIG. 3, since the electrically heated catalyst 32 is disposed on the downstream side of the selective catalytic reduction catalyst 31, it is basically generated by the oxidation catalyst supported on the electrically heated catalyst 32. Oxidation heat is only transmitted to the selective catalytic reduction catalyst 31 via the heat transfer pins 34. Here, as shown in FIG. 6, when the temperature of urea water as a reducing agent rises, the form can be changed from liquid burette, solid cyanuric acid, and gaseous cyanic acid. In particular, when it is changed to solid cyanuric acid, the reducing agent supplied in the selective catalytic reduction catalyst 31 becomes a solid deposit, which is not preferable because it causes clogging. However, as described above, in the example shown in FIG. 3, the exhaust that has been heated by the heat of oxidation in the electrically heated catalyst 32 is not configured to flow into the selective catalytic reduction catalyst 31. It avoids being placed in an environment where the temperature is rapidly increased. Therefore, since the temperature of the urea water that is the reducing agent is not rapidly increased, it is possible to suppress the urea water from being changed to a solid burette or cyanuric acid as much as possible. In addition, when the urea water which is a reducing agent solidifies, it is preferable to raise and raise to the temperature (about 360 degreeC) which it vaporizes. For example, when the operating state of the internal combustion engine 1 is in a decelerating state, the deposited solid substance can be removed by reducing the space velocity (SV) without stopping the heating by the electrically heated catalyst 32.

  A second embodiment of the exhaust emission control device 3 for the internal combustion engine 1 according to the present invention will be described with reference to FIG. In the exhaust purification apparatus according to this embodiment, the holding portion 21 that holds the selective reduction catalyst 31 in the exhaust passage housing 2a connects the through-passage that connects the upstream exhaust passage and the downstream exhaust passage of the selective reduction catalyst 31. 21a is provided. Therefore, a part of the exhaust discharged from the internal combustion engine 1 flows into the selective reduction catalyst 31 of the exhaust purification device 3 in the exhaust passage 2 and the other passes through the through passage 21a and is downstream of the selective reduction catalyst 31. Will flow into.

  In the configuration according to the first embodiment, in the vicinity of the holding portion 21 that holds the selective catalytic reduction catalyst 31, a structure that easily traps exhaust flowing in the exhaust passage 2, for example, slightly depressed as shown in FIG. 2. A space is formed. For this reason, solid cyanuric acid or the like generated from urea water as the reducing agent supplied from the reducing agent supply valve 5 adheres to the selective reducing catalyst 31 and the exhaust passage housing 2a and causes thermal deterioration. . However, as shown in FIG. 5, by providing the through passage 21 a with respect to the holding portion 21, it becomes difficult to trap exhaust gas in the vicinity of the holding portion 21, so that generation and adhesion of cyanuric acid and the like are effectively suppressed. Can do.

  In the configuration shown in FIG. 5, the through passage 21a is provided for the holding portion 21 on the exhaust passage 2 side. However, such a through passage may be provided on the selective reduction catalyst 31 side. For example, the through passage 21a may be provided in a portion of the carrier of the selective catalytic reduction catalyst 31 that does not interfere with the coarse particle region R1 described above.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Exhaust passage 3 ... Exhaust gas purification device 4 ... Filter 5 ... Reducing agent supply valve 6 ... Temperature sensor 10 ... ECU
11 .... Crank position sensor 12 .... Accelerator opening sensor 31 ... Selective reduction type catalyst 32 ... Electric heating catalyst 34 ... Heat transfer pin R1 ... Coarse particles region

Claims (5)

A selective reduction catalyst provided in an exhaust passage of the internal combustion engine;
Reducing agent supply means for supplying a reducing agent to the exhaust flowing into the selective catalytic reduction catalyst on the upstream side of the selective catalytic reduction catalyst;
Heating means for heating the selective catalytic reduction catalyst;
Control means for purifying exhaust gas in the selective reduction catalyst by supplying a reducing agent into the exhaust gas via the reducing agent supply means with respect to the selective reduction catalyst heated by the heating means;
An exhaust purification device for an internal combustion engine comprising:
In the catalyst cross section with respect to the exhaust ventilation direction in the selective reduction catalyst, the heating means has a supply heat amount in the coarse particle region where the reducing agent supplied from the reducing agent supply means is distributed in a coarse particle state in the catalyst cross section. Heating the selective catalytic reduction catalyst so as to be larger than the region other than the coarse particle region
An exhaust purification device for an internal combustion engine. A through passage connecting the upstream exhaust passage and the downstream exhaust passage of the selective catalytic reduction catalyst serves as a catalyst supporting portion in the selective catalytic reduction catalyst or a holding portion that holds and fixes the selective catalytic reduction catalyst in the exhaust passage. Provided,
The exhaust emission control device for an internal combustion engine according to claim 1. The heating means is disposed on the downstream side of the selective catalytic reduction catalyst in the exhaust passage.
An exhaust emission control device for an internal combustion engine according to claim 1 or 2. The reducing agent is a compound derived from ammonia,
The heating means heats the selective catalytic reduction catalyst so as to be at or above a predetermined temperature at which hydrolysis of the reducing agent occurs;
The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3. The reducing agent is a compound derived from ammonia,
The heating means heats the selective catalytic reduction catalyst so as to be at or above a predetermined temperature at which the solid deposit of the reducing agent can be removed
The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3.

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