JP2013238205A - Exhaust emission control apparatus for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely detect accumulation of deposits, in an exhaust emission control apparatus for an internal combustion engine with a urea selective reduction catalyst.SOLUTION: An exhaust passage 11 of an engine 10 is provided with a urea selective reduction catalyst 12. A branch passage 20 is connected to an exhaust upstream side of the SCR catalyst 12 in the exhaust passage 11. An addition valve 30 for injecting a reducing agent is mounted to an end of the branch passage 20. The branch passage 20 is provided with a first temperature sensor 41 for detecting deposits accumulated on the branch passage 20. When the temperature detected by the first temperature sensor 41 indicates a value different from the normal temperature when the accumulation of the deposits is not generated, a control unit 50 determines that the accumulation of the deposit is generated, and executes burnout processing of the deposits.

Description

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

  An example of an exhaust gas purification apparatus for an internal combustion engine that is frequently operated with a lean air-fuel ratio, such as a diesel engine, includes a urea-based selective reduction catalyst. In this exhaust purification device, an ammonia-based reducing agent such as an aqueous urea solution is added to the selective reduction catalyst through an addition valve, and NOx (nitrogen oxide) in the exhaust is reduced and purified by the reducing agent. Yes. By the way, in such an exhaust purification device, when the selective reduction catalyst is damaged or the purification performance is deteriorated, it is desirable to quickly detect this.

  Therefore, in the exhaust emission control device described in Patent Document 1, the concentration of NOx discharged from the selective reduction catalyst is monitored, and the concentration of NOx does not change even though the amount of reducing agent added is changed. Is notified that the selective reduction catalyst is not functioning normally. Therefore, in this case, this is dealt with by replacing the selective reduction catalyst.

JP 2004-176719 A

  By the way, in an exhaust gas purification apparatus equipped with such a urea-based selective reduction catalyst, urea-derived deposits may be generated when an aqueous urea solution or the like used as a reducing agent is altered by exhaust heat or the like. If such deposit accumulates in the vicinity of the addition valve, for example, the amount of reducing agent injected from the addition valve and the spray form cannot meet the requirements, so the selective reduction catalyst is not functioning normally. The purification performance of the exhaust emission control device will be reduced as well. However, unlike the case where the function of the selective reduction catalyst itself is lost, such deposit accumulation can be eliminated by increasing the exhaust temperature by performing post injection or the like and burning out the deposit.

  However, in the exhaust gas purification device described in Patent Document 1, it cannot be specified whether the reduction in purification performance in the exhaust gas purification device is caused by deposit accumulation, and there is still room for improvement in this respect. It has become.

  The present invention has been made in view of such conventional circumstances, and an object of the present invention is to provide an exhaust emission control device for an internal combustion engine capable of accurately detecting deposit accumulation.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
An exhaust purification device for an internal combustion engine according to the present invention includes a urea-based selective reduction catalyst provided in an exhaust passage, a branch passage that branches from the exhaust passage upstream of the selective reduction catalyst, and a reducing agent in the branch passage. And an addition valve for injecting and adding to the selective reduction catalyst. The branch passage in which the addition valve is provided is provided with a temperature sensor in which a temperature detection unit is provided at a portion where the deposit is accumulated.

  Normally, the temperature detected by the temperature sensor changes in correlation with the temperature inside the exhaust passage and the branch passage communicating with the exhaust passage. On the other hand, if deposits accumulate on this temperature detector, this correlation decreases due to a decrease in the amount of heat received from the exhaust, so the temperature detected by the temperature sensor is lower than the normal case where no deposits are deposited. Different values. That is, when deposits are accumulated, the temperature detected by the temperature sensor becomes relatively low, and changes with a delay with respect to the temperature change inside the exhaust passage and the branch passage.

  Therefore, by monitoring the detected temperature of this temperature sensor and comparing the monitored detected temperature with the detected temperature in the normal case where no deposit is deposited, deposit deposition can be accurately detected. . Here, if the deposit accumulation portion in the branch passage varies depending on various conditions such as the injection performance of the addition valve and the shape of the branch passage, such deposit deposit portion is specified in advance through experiments, simulations, and the like. be able to.

  Deposit accumulation also occurs when, for example, the reducing agent leaked from the addition valve stays at a specific site. However, if the deposited deposit does not interfere with the spray of the reducing agent injected from the addition valve, The adverse effect on the purification performance is small. On the other hand, when such interference occurs, for example, when the spray form of the reducing agent injected from the addition valve changes due to the deposited deposit, the reducing agent cannot be uniformly added to the selective reduction catalyst. Further, when the injection of the reducing agent from the addition valve is hindered, a required amount of the reducing agent cannot be supplied to the selective reduction catalyst. Therefore, when such interference occurs, the exhaust gas purification performance of the selective reduction catalyst is lowered.

  For this reason, if the deposit in which the temperature detection part of the temperature sensor is deposited and the spray of the reducing agent injected from the addition valve interfere with each other, the deterioration of the exhaust purification performance becomes remarkable. Accumulation can be detected accurately.

  By the way, when the reducing agent is injected from the addition valve, most of the reducing agent is sprayed and introduced into the exhaust passage, but a part of the reducing agent remains in the vicinity of the addition valve nozzle. . In particular, when the injection of the reducing agent by the addition valve is stopped, the reducing agent having a reduced penetrating force as the injection is stopped often stays in the vicinity of the injection port of the addition valve. Therefore, in the vicinity of the nozzle hole of the addition valve, the staying reducing agent may be altered and deposited as deposits.

  When such deposits are deposited, the nozzle of the addition valve is narrowed by the deposits, so that the required amount of reducing agent cannot be supplied to the selective reduction catalyst, leading to a reduction in exhaust purification performance. For this reason, if the temperature detection part of a temperature sensor is arrange | positioned in the site | part adjacent to the nozzle hole of an addition valve, deposit accumulation in the vicinity of such nozzle hole can be detected exactly.

  Further, in the part where the reducing agent injected from the addition valve directly adheres in the branch passage, a part of the reducing agent stays in a liquid state, so that the staying reducing agent changes in quality and easily deposits as deposits. Therefore, if the temperature detection part of the temperature sensor is arranged at the site where the reducing agent injected from the addition valve directly adheres in the branch passage, deposit accumulation can be accurately detected.

  Further, the deposit depositing portion in the branch passage may change irregularly every time, or the deposit may be deposited starting from a specific portion, and the deposit amount may gradually increase. For this reason, in the latter case, deposit accumulation can be detected earlier by disposing the temperature detection portion of the temperature sensor at a site that is the starting point when such deposit is deposited. In addition, about the site | part used as the starting point at the time of depositing, this can be previously specified through experiment, simulation, etc.

  Here, when the reducing agent injected into the branch passage merges with the exhaust flowing through the exhaust passage, the reducing agent is altered due to vaporization or phase change of a part of the reducing agent due to the heat of the exhaust. As a result, a deposit is easily generated. Therefore, there is a concern that the generated deposit accumulates at a communication portion communicating with the exhaust passage in the branch passage. For this reason, if the temperature detection part of a temperature sensor is arrange | positioned in the communicating part connected with an exhaust passage in a branch passage, deposit accumulation can be detected exactly.

  Here, since the reducing agent injected into the branch passage flows to the exhaust downstream side while joining the exhaust gas flowing through the exhaust passage, deposit accumulation becomes prominent also at the communication portion, particularly at the exhaust downstream side. For this reason, in order to detect deposit accumulation earlier, it is desirable that the temperature detection part of the temperature sensor is disposed on the exhaust downstream side in the communication part.

  In the exhaust emission control device according to the present invention, for example, the detected temperature of the temperature sensor in a normal time when no deposit is accumulated is estimated based on the engine operating state, and the estimated temperature is compared with the actual detected temperature of the temperature sensor. It is also possible to detect deposit accumulation. However, such an estimated temperature includes an error, and the estimated error becomes larger during a transient operation in which the engine operating state changes.

  Therefore, in addition to the above-described temperature sensor for detecting deposit accumulation (hereinafter referred to as “first temperature sensor”), the deposit accumulation amount is higher than the portion where the temperature detection unit of the first temperature sensor is disposed. It is desirable to employ a configuration that further includes a second temperature sensor in which the temperature detection unit is disposed in a portion with a small amount.

  According to such a configuration, the detected temperature of the first temperature sensor is significantly lower than the detected temperature of the second temperature sensor, or the change in the detected temperature of the first temperature sensor is delayed with respect to the change in the detected temperature of the second temperature sensor. Deposits can be detected on the basis of a decrease in the correlation between the detected temperatures of the temperature sensors, such as an increase in the temperature. That is, deposit accumulation is detected through a comparison of the temperatures actually detected by each temperature sensor, so there is no influence of the estimation error as described above, and deposit accumulation is detected with high accuracy even during transient operation. can do.

  Here, in order to increase the accuracy in detecting deposit accumulation, the temperature detection unit of the second temperature sensor does not deposit or deposits the amount compared to the temperature detection unit of the first temperature sensor. It is necessary to arrange in very few parts. For this reason, it is desirable to arrange | position a 2nd temperature sensor in exhaust_gas | exhaustion upstream rather than a communication part with a branch channel | path in an exhaust passage. According to such a configuration, the reducing agent introduced into the exhaust passage from the branch passage flows along the exhaust flow to the exhaust downstream side of the communication portion, and therefore, the first reductant disposed on the exhaust upstream side of the communication portion. It becomes difficult for the reducing agent to adhere to the temperature detection part of the two-temperature sensor, and deposition of deposits on the temperature detection part can be suppressed.

  Similarly, even if the temperature detection unit of the second temperature sensor is disposed at a site that avoids the spray region of the reducing agent injected from the addition valve, the reducing agent hardly adheres to the temperature detection unit. Therefore, the deposit can be suppressed.

  Here, in a normal time when no deposit is deposited on the temperature detection unit of the first temperature sensor, the degree of deviation of the detection temperature of each temperature sensor is small and changes synchronously, in other words, their correlation is high. desirable. In other words, if the correlation between the detected temperatures of each temperature sensor is high in such a normal time, it can be determined that when the degree of divergence or response delay occurs, it is not due to other factors, but due to the accumulation of deposits. it can.

  For this reason, it is desirable to arrange the temperature detection unit of the second temperature sensor adjacent to the temperature detection unit of the first temperature sensor while avoiding the spray region of the reducing agent injected from the addition valve. According to such a configuration, the correlation between the temperatures detected by the temperature sensors can be increased in a normal time when no deposit is deposited on the temperature detection unit of the first temperature sensor. It becomes possible to detect accurately.

  By the way, in general, in an exhaust purification device in which a filter for capturing particulate matter in exhaust is provided in the exhaust passage, the filter function is regenerated by burning away particulate matter captured by the filter by raising the exhaust temperature. The filter regeneration process is executed. During the filter regeneration process, the temperature of the filter may be excessively increased due to the combustion of the particulate matter. To avoid this, the temperature of the filter is monitored based on the temperature of the exhaust gas passing through the filter. There is a need. In such an exhaust purification device, since the second temperature sensor can be used as a temperature sensor for monitoring the exhaust temperature during the filter regeneration process, an exhaust temperature sensor for the filter regeneration process is separately provided in the exhaust passage. Is no longer necessary.

  Further, in the exhaust purification apparatus, by providing a dispersion member on the exhaust upstream side of the selective reduction catalyst, the reducing agent introduced into the exhaust passage through the branch passage is dispersed by the dispersion member, and the reducing agent is reduced with respect to the selective reduction catalyst. Can be added uniformly. However, deposits are also a concern in this dispersing member as in the branch passage. When deposit is deposited on the dispersion member, the dispersion function is lowered, and the resistance when exhaust gas or the reducing agent passes through the dispersion member increases, so that the required amount of reducing agent cannot be added to the selective reduction catalyst. There is a fear. For this reason, when such a dispersion member is provided in the exhaust passage, it is desirable to provide a third temperature sensor in the exhaust passage for detecting the temperature of the dispersion member in order to detect that deposits have accumulated on the dispersion member.

  Normally, the temperature detected by the third temperature sensor that detects the temperature of the dispersion member changes in correlation with the temperature of the exhaust gas. On the other hand, when deposits are deposited on the dispersion member, this correlation is lowered, so that the temperature detected by the third temperature sensor is different from that in a normal case where no deposits are deposited. That is, when deposit is accumulated, the temperature detected by the third temperature sensor becomes relatively low, and changes with a delay with respect to the temperature change of the exhaust gas. Therefore, by monitoring the detected temperature of the third temperature sensor and comparing the monitored detected temperature with the detected temperature in the normal case where no deposit is deposited, the deposit accumulated on the dispersion member is also detected. Can be accurately detected.

1 is a cross-sectional view of an exhaust purification device according to an embodiment of the present invention. Sectional drawing which expands and shows the communicating part of a branch passage and an exhaust passage. The graph which shows the time transition of the temperature detected by each temperature sensor. Sectional drawing which shows the arrangement | positioning state of each temperature sensor of the exhaust gas purification apparatus concerning other embodiment. Sectional drawing which shows the arrangement | positioning state of each temperature sensor of the exhaust gas purification apparatus concerning other embodiment. Sectional drawing which shows the arrangement | positioning state of each temperature sensor of the exhaust gas purification apparatus concerning other embodiment. Sectional drawing of the exhaust passage of the exhaust gas purification apparatus concerning other embodiment. Sectional drawing of the exhaust passage of the exhaust gas purification apparatus concerning other embodiment. Sectional drawing of the branch channel | path of the exhaust gas purification apparatus concerning other embodiment.

Hereinafter, an embodiment in which the present invention is embodied in an exhaust emission control device for a diesel engine will be described with reference to FIGS.
As shown in FIG. 1, a urea-based selective reduction catalyst (hereinafter referred to as “SCR catalyst 12”) is provided in the exhaust passage 11 of the engine 10. A branch passage 20 is connected to the exhaust gas upstream side of the SCR catalyst 12 in the exhaust passage 11.

  An addition valve 30 for injecting a reducing agent is attached to the end of the branch passage 20. Here, an aqueous urea solution is used as the reducing agent added to the SCR catalyst 12. The reducing agent injected from the injection port 31 of the addition valve 30 is introduced into the exhaust passage 11 through the branch passage 20, hydrolyzed into ammonia by the heat of the exhaust, and added to the SCR catalyst 12. As a result, in the SCR catalyst 12, NOx in the exhaust gas is purified to nitrogen through a reduction reaction with ammonia.

  Here, a part of the reducing agent injected from the addition valve 30 may be transformed into biuret, cyanuric acid or the like due to the influence of exhaust heat or the like, and may be deposited in the branch passage 20 as a deposit. For this reason, the first temperature sensor 41 for detecting such deposit accumulation is provided in the branch passage 20 of the exhaust gas purification apparatus. On the other hand, the exhaust passage 11 is provided with a second temperature sensor 42 for detecting the temperature of the exhaust. The output values of the temperature sensors 41 and 42 are taken into the control unit 50, respectively.

  The control unit 50 calculates the detected temperatures of the temperature sensors 41 and 42 based on the output values that are taken in, and detects deposit accumulation based on the detected temperatures. Further, the controller 50 opens and closes the addition valve 30 to inject an amount of reducing agent from the addition valve 30 in accordance with the engine operating state.

  In addition, when the control unit 50 determines that deposits are accumulated in the branch passage 20 and the amount of the reducing agent injected from the addition valve 30 and the spray form cannot meet the requirements, the burnout process of the deposits is performed. Run. That is, the control unit 50 increases the exhaust temperature by performing post injection or the like, thereby burning out deposits accumulated in the branch passage 20 and the exhaust passage 11.

  As shown in FIG. 2, the temperature detector 41 a of the first temperature sensor 41 is disposed in a portion that is exposed to the inside of the branch passage 20 and is adjacent to the injection port 31 of the addition valve 30. When the reducing agent is injected from the addition valve 30, most of the reducing agent is sprayed and introduced into the exhaust passage 11, but a part of the reducing agent stays in the vicinity of the nozzle 31 of the addition valve 30. . In particular, when the injection of the reducing agent by the addition valve 30 is stopped, the reducing agent having a reduced penetrating force as the injection is stopped often stays in the vicinity of the nozzle 31 of the addition valve 30 in a liquid state. Therefore, in the vicinity of the nozzle hole 31 of the addition valve 30, the staying reducing agent is altered and easily deposited as a deposit.

  Then, as shown by a two-dot chain line in FIG. 2, when deposit is deposited in the vicinity of the injection port 31 of the addition valve 30, the spraying and depositing of the reducing agent injected from the addition valve 30, such as narrowing the injection port 31 by the deposit, etc. Interference will occur. Thus, the temperature detection part 41a of the 1st temperature sensor 41 is arrange | positioned at the depositing site | part of the deposit which interferes with the spray of a reducing agent while adjoining the nozzle 31 of the addition valve 30. FIG.

  On the other hand, as shown in FIG. 2, the second temperature sensor 42 has a temperature detection unit at a site on the exhaust upstream side of the communication portion 21 between the branch passage 20 and the exhaust passage 11 and avoiding the reducing agent spray region. 42a is disposed. Accordingly, of the first temperature sensor 41 and the second temperature sensor 42, deposits are deposited on the temperature detection unit 41a of the first temperature sensor 41, while no deposits are deposited on the temperature detection unit 42a of the second temperature sensor 42. Even if it is deposited, the amount thereof is negligible as compared with the temperature detecting portion 41a of the first temperature sensor 41.

Next, the operation of such an exhaust purification device will be described.
As shown in FIG. 3, since the exhaust directly contacts the temperature detection unit 42 a of the second temperature sensor 42, the detected temperature θ <b> 2 (two-dot chain line) of the second temperature sensor 42 is the detected temperature of the first temperature sensor 41. It is always higher than θ1 (dashed line / solid line). Further, when deposit is accumulated on the temperature detecting portion 41a of the first temperature sensor 41, the detected temperature θ1 of the first temperature sensor 41 is lowered and has a predetermined delay time Δt with respect to the detected temperature θ2 of the second temperature sensor 42. To change.

  That is, the detected temperature θ1 of the first temperature sensor 41 usually changes in correlation with the temperature inside the exhaust passage 11 and the branch passage 20 connected to the exhaust passage 11, but when deposits are accumulated in the temperature detecting portion 41a. The correlation decreases due to a decrease in the amount of heat received from the exhaust. Accordingly, when deposits are accumulated on the temperature detecting portion 41a of the first temperature sensor 41, the detected temperature θ1 of the first temperature sensor 41 becomes relatively low, and the second temperature sensor 42 having a high correlation with the exhaust temperature. It changes with a delay with respect to the detected temperature θ2.

  Therefore, the control unit 50 compares the detected temperature θ1 of the first temperature sensor 41 with the detected temperature θ2 of the second temperature sensor 42, and when one of the following conditions a and b is satisfied, the above-described burnout Execute the process.

Condition a: degree of deviation (θ2−θ1)> determination value Δθa
Condition b: Delay time Δt> determination value Δtb

When the burning process is performed in this way, the deposits accumulated in the branch passage 20 and the exhaust passage 11 including the vicinity of the injection port 31 of the addition valve 30 are burned out. For this reason, the quantity of the reducing agent injected from the addition valve 30 and the spray form can be made to meet the requirements.

As described above, according to the exhaust gas purification apparatus according to the present embodiment, the following effects can be obtained.
(1) The temperature detection unit 41a of the first temperature sensor 41 is disposed at a portion where deposits are deposited, and the detection temperature θ1 of the first temperature sensor 41 changes when deposits are deposited on the temperature detection unit 41a. Since deposit accumulation is detected by using this, such deposit accumulation can be accurately detected.

  When deposit accumulation is detected, the deposit is burned out through the burning process, so that the exhaust purification performance of the exhaust purification device can be quickly restored to its original capacity. Further, unlike the case where the burnout process is frequently executed assuming that the deposit is most prominent regardless of the detection result of the first temperature sensor 41, unnecessary deterioration of fuel consumption is avoided. Will be able to.

  (2) Further, the temperature detector 41a is disposed adjacent to the nozzle hole 31 of the addition valve 30 and at a deposit accumulation site that interferes with the spray of the reducing agent. For this reason, the reducing agent staying in the liquid state in the vicinity of the nozzle 31 of the addition valve 30 changes in quality and deposits and deposits. The reduction of the purification performance is remarkable due to interference with the spray of the reducing agent injected from the nozzle 31. Prior to this, deposition of such deposits can be quickly detected and burned out.

  (3) For example, the detected temperature θ1 of the first temperature sensor 41 in the normal time when no deposit is accumulated based on the engine operating state is estimated, and this estimated temperature and the detected temperature actually detected by the first temperature sensor 41 By comparing with θ1, deposit deposition can also be detected. In other words, the burnout process can be executed based only on the detection result of the first temperature sensor 41 without using the second temperature sensor 42. However, such an estimated temperature includes an error, and the estimated error becomes larger during a transient operation in which the engine operating state changes.

  In this regard, in the exhaust purification apparatus according to the present embodiment, a second temperature sensor 42 that detects the exhaust temperature of the exhaust passage 11 is provided separately from the first temperature sensor 41, and the detected temperature θ2 of the second temperature sensor 42 is A reference temperature to be compared with the detected temperature θ1 of the first temperature sensor 41 is set. Accordingly, for each detected temperature θ1, θ2, the correlation between the first temperature sensor 41 and the exhaust temperature decreases such that the degree of deviation (θ2-θ1) increases or the delay time Δt increases. This can be detected through a comparison of temperatures actually detected by the sensors 41 and 42. For this reason, there is no influence of the estimation error as described above, and deposit accumulation can be accurately detected with high accuracy even during transient operation.

  (4) Further, when the deposit accumulation is detected based on the fact that the correlation between the detected temperatures θ1 and θ2 detected by the temperature sensors 41 and 42 is lowered in this way, the temperature detection of the second temperature sensor 42 is performed. It is desirable that the portion 42a is provided at a site where no deposit is deposited or even if deposited, the amount is negligible. In this respect, the temperature detecting portion 42a of the second temperature sensor 42 is located upstream of the communication portion 21 between the branch passage 20 and the exhaust passage 11, and avoids the spray region of the reducing agent injected from the addition valve 30. It is supposed to be arranged at the site. For this reason, it can suppress that the reducing agent adhering to the temperature detection part 42a changes in quality and deposits and deposits, and deposit accumulation can be detected with a higher precision.

  As mentioned above, although one Embodiment of this invention was described, this Embodiment can also be implemented as a modification which changed this as follows. In any of the modifications described below, the basic configuration of the exhaust gas purification device, the processing procedure when the deposit is burnt down, and the like are the same as those in the above embodiment, and therefore, the description will focus on the differences from the above embodiment.

  As shown in FIG. 4, for example, when the injection pressure of the addition valve 30 is high, in other words, when the penetrating force of the reducing agent injected is large, the reducing agent injected from the addition valve 30 flows through the branch passage 20. It comes to adhere directly to the inner surface. In this way, at the portion where the injected reducing agent directly adheres, a part of the reducing agent stays in a liquid state, so that the staying reducing agent changes in quality and is easily deposited as a deposit. Therefore, as shown in FIG. 4, if the temperature detector 41 a of the first temperature sensor 41 is disposed in the branch passage 20 where the reducing agent injected from the addition valve 30 directly attaches, Accumulation can be detected accurately.

  Further, in the branch passage 20 where the reducing agent injected into the branch passage 20 joins with the exhaust flowing through the exhaust passage 11 such as the communication portion 21 communicating with the exhaust passage 11, moisture of the reducing agent is caused by the heat of the exhaust. Evaporation deposits urea, and the deposited urea is further altered to easily generate deposits. For this reason, as shown in FIG. 4, if the temperature detecting portion 41a of the first temperature sensor 41 is disposed in the communication portion 21, the deposit accumulation generated by the exhaust heat as described above is accurately detected. can do.

  Further, since the reducing agent injected into the branch passage 20 flows downstream of the exhaust gas while joining the exhaust gas flowing through the exhaust passage 11, deposits as described above become conspicuous also at the communication portion 21, particularly on the downstream side of the exhaust gas. . For this reason, as shown in FIG. 4, depositing of the deposit can be detected earlier by disposing the temperature detecting portion 41 a of the first temperature sensor 41 in the communication portion 21 particularly on the exhaust downstream side.

  As shown in FIG. 5, the temperature detector 41 a of the first temperature sensor 41 is disposed in the branch passage 20 where the reducing agent injected from the addition valve 30 directly adheres, while the branch passage 20 and the exhaust passage 11. The temperature detection unit 42a of the second temperature sensor 42 is disposed at a site that is upstream of the exhaust portion of the communicating portion 21 and avoids the spray region of the reducing agent injected from the addition valve 30. Here, in order to detect deposit accumulation with high accuracy based on the detected temperatures θ1 and θ2 of the temperature sensors 41 and 42, in a normal time when no deposit accumulates on the temperature detection unit 41a of the first temperature sensor 41, It is desirable that the degree of divergence between the detected temperatures θ1 and θ2 is small and changes in synchronization, in other words, the correlation between the detected temperatures θ1 and θ2 is high.

  For this reason, as shown in FIG. 5, the temperature detection units 41a and 42a are arranged adjacent to each other so that the distance between the temperature detection units 41a and 42a of the temperature sensors 41 and 42 is as short as possible. Thus, by making the temperature detection parts 41a and 42a approach, the correlation between the detected temperatures θ1 and θ2 of the temperature sensors 41 and 42 can be increased. Therefore, when deviations or response delays occur in the detected temperatures θ1 and θ2, it can be determined that they are not caused by other factors, but deposits, and deposit deposits can be detected more accurately. Will be able to.

  -The part where deposits accumulate in the branch passage 20 may change irregularly each time, or the deposits may always accumulate starting from a specific part, and the amount of the deposits may gradually increase. FIG. 6 shows an example in which the temperature detection unit 41a of the first temperature sensor 41 is disposed at a site that is a starting point when deposits are deposited as in the latter case. As indicated by a two-dot chain line in FIG. 6, in the portion where the temperature detecting portion 41 a of the first temperature sensor 41 is disposed in the branch passage 20, deposits start to be accumulated starting from the portion, and the amount of accumulation gradually increases. To increase.

  Therefore, if the temperature detector 41a of the first temperature sensor 41 is disposed at the site that is the starting point when deposits are deposited in this way, deposit deposition can be detected earlier. It should be noted that the starting point for depositing such deposits can be specified in advance through experiments, simulations, and the like.

  In the above-described embodiment and its modification, as shown in FIG. 7, a filter 14 that captures particulate matter in the exhaust gas can be provided on the exhaust gas upstream side of the first temperature sensor 41 in the exhaust passage 11. In this case, the amount of the particulate matter trapped by the filter 14 is monitored, and when the amount exceeds a predetermined amount, the exhaust temperature is increased by performing post injection or the like, thereby being trapped by the filter 14. A filter regeneration process for restoring the function of the filter 14 by burning off the particulate matter is performed.

  Here, during the execution of such filter regeneration processing, the temperature of the filter 14 may rise excessively as the particulate matter burns. Therefore, in order to avoid this, the temperature of the filter 14 is set to, for example, the exhaust gas passing through the filter 14. Need to be monitored based on the temperature. According to the above configuration, since the second temperature sensor 42 can be used as a temperature sensor for monitoring the exhaust temperature during the execution of such filter regeneration processing, an exhaust temperature sensor for filter regeneration processing is separately provided in the exhaust passage 11. It is not necessary to provide it.

  Further, in such a configuration, the deposit burning process may be combined with the filter regeneration process, and the deposit may be burned out through the filter regeneration process. In this case, when either one of the condition c: deposit deposition is detected, or the condition d: the amount of particulate matter trapped in the filter 14 exceeds a predetermined amount, the filter is satisfied. The playback process is executed. Even when deposits deposited through the filter regeneration process are burned out in this manner, the deposition of deposits is most noticeable because the condition c is determined based on the detection results of the temperature sensors 41 and 42. Unlike the case where the filter regeneration processing is frequently executed assuming the situation, unnecessary fuel consumption deterioration can be avoided.

  In the above-described embodiment and its modifications, as shown in FIG. 8, a dispersion member 15 that disperses the reducing agent in the exhaust passage 11 upstream of the SCR catalyst 12 may be provided. As this dispersion member 15, for example, a member having a plurality of blades for dispersing the reducing agent introduced into the exhaust passage 11 from the branch passage 20 can be employed. In such a dispersion member 15, a swirl force is applied to the exhaust gas that passes through the dispersion member 15 by a plurality of blades, so that a swirl flow of the exhaust gas is generated on the exhaust downstream side of the dispersion member 15. When such a swirl flow is generated, the reducing agent is dispersed and mixed with the exhaust gas, so that the reducing agent is uniformly added to the end surface of the SCR catalyst 12 on the exhaust upstream side.

  Here, as with the branch passage 20, there is a concern that deposits are deposited on the dispersion member 15. When deposit is deposited on the dispersion member 15, the dispersion function is lowered, and the resistance when the reducing agent passes through the dispersion member 15 increases. Therefore, the required amount of reducing agent cannot be added to the SCR catalyst 12. There is a fear. Therefore, the exhaust passage 11 is provided with a third temperature sensor 43 that detects the temperature of the dispersion member 15 in order to detect that deposits have accumulated on the dispersion member 15.

  Here, the detected temperature θ3 of the third temperature sensor 43 normally changes in correlation with the temperature inside the exhaust passage 11, but when deposits accumulate on the dispersion member 15, the amount of heat received from the exhaust decreases. This correlation decreases. Accordingly, when deposits are accumulated on the dispersion member 15, the detected temperature θ3 of the third temperature sensor 43 is relatively low, and is predetermined with respect to the detected temperature θ2 of the second temperature sensor 42 having a high correlation with the exhaust gas temperature. Changes with a delay time Δt. That is, the same tendency as the detected temperature θ1 of the first temperature sensor 41 when deposit accumulation occurs is exhibited.

  Therefore, as in the comparison of the detected temperatures θ1 and θ2, the condition e: the degree of deviation (θ2-θ3)> the determination value Δθe and the condition f: the delay time Δt> the determination value Δtf are satisfied. In addition, the burnout process of the deposit is executed. According to such a configuration, it is possible to accurately detect that deposits have accumulated on the dispersion member 15. When deposit accumulation is detected, the deposit can be burned down through the burning process, so that the exhaust gas purification performance of the exhaust gas purification device can be quickly restored to its original capacity.

  In the above-described embodiment and its modification, when the second temperature sensor 42 is provided in the exhaust passage 11, the temperature detection portion 42 a is located on the exhaust upstream side of the communication portion 21 between the branch passage 20 and the exhaust passage 11. It arrange | positioned in the site | part which avoided the spray area | region of the reducing agent. However, if the deposit amount can always be smaller than the temperature detection unit 41 a of the first temperature sensor 41, for example, the temperature detection unit 42 a of the second temperature sensor 42 is connected to the branch passage 20 and the exhaust passage 11. You may make it arrange | position to the exhaust_gas | exhaustion downstream rather than the site | part 21. FIG. In addition, the temperature detector 42 a of the second temperature sensor 42 may be disposed in the branch passage 20 similarly to the first temperature sensor 41.

  In the above-described embodiment and its modification, the deposit burnout process is executed when either one of the condition a and the condition b is satisfied. However, when both the condition a and the condition b are satisfied. In addition, the deposit burning process may be executed. This is the same even in the case where the burnout process is executed based on the condition of the condition e and the condition f in the modified example including the dispersion member 15 described above.

  In the above-described embodiment and its modification, the correlation between the detected temperature θ1 of the first temperature sensor 41 and the detected temperature θ2 of the second temperature sensor 42 is monitored, and the burnout process of the deposit is executed when the correlation decreases. However, it is also possible to determine whether or not to perform such burnout processing based only on the detected temperature θ1 of the first temperature sensor 41 without providing the second temperature sensor 42.

  In this case, the detected temperature θ1 of the first temperature sensor 41 in a normal time when no deposit is accumulated is estimated based on the engine operating state, and the degree of divergence between the estimated temperature and the detected temperature θ1 of the first temperature sensor 41 When the (estimated temperature−detected temperature θ1) is equal to or higher than a predetermined determination value, the burnout process is executed. That is, the burnout process is executed when the detected temperature θ1 becomes relatively low and the degree of deviation from the estimated temperature becomes large. Alternatively, when the detected temperature θ1 of the first temperature sensor 41 changes with a predetermined delay time Δt with respect to the estimated temperature, the burnout process is executed when the delay time Δt is equal to or greater than a predetermined determination value. . That is, the burnout process is executed when the response of the detected temperature θ1 is reduced due to deposit accumulation and the delay time Δt becomes longer.

  In the above-described embodiment and its modification, the degree of deviation between the detected temperature θ1 of the first temperature sensor 41 and the detected temperature θ2 of the second temperature sensor 42 is determined based on the deviation of each temperature (θ2−θ1). However, for example, the determination can be made based on the ratio of each temperature (θ2 / θ1, θ1 / θ2). This is actually detected from the estimated temperature of the first temperature sensor 41 estimated based on the degree of deviation between the detected temperature θ3 of the third temperature sensor 43 and the detected temperature θ2 of the second temperature sensor 42, and the engine operating state. The same applies to the degree of deviation from the detected temperature θ1.

  As shown in FIG. 9, it is also possible to adopt a configuration in which a recessed portion 20a is formed in a part of the branch passage 20, and the temperature detecting portion 41a of the first temperature sensor 41 is disposed in the recessed portion 20a. it can. Since the reducing agent tends to stay in the recessed portion 20a, deposit deposition is likely to occur compared to other portions. That is, if no deposit is deposited in the recessed portion 20a where deposits are likely to be deposited, it can be determined that no deposit is deposited in other portions of the branch passage 20 as well.

  Therefore, when the correlation between the detected temperature θ1 of the first temperature sensor 41 and the detected temperature θ2 of the second temperature sensor 42 is not lowered, it is determined that no deposit is deposited in other parts. This makes it possible to avoid the deterioration of fuel consumption caused by the deposit burnout process and the filter regeneration process being performed more than necessary. About this point, without using the 2nd temperature sensor 42, the estimated temperature concerning the detection temperature (theta) 1 of the 1st temperature sensor 41 estimated based on an engine operating state, and the detection actually detected by the 1st temperature sensor 41 The same applies to the configuration in which the correlation with the temperature θ1 is monitored.

  In the above-described embodiment and its modification, an example in which a decrease in the correlation between the detected temperature θ1 of the first temperature sensor 41 and the detected temperature θ2 of the second temperature sensor 42 is determined based on the degree of deviation or the delay time has been shown. . In addition, as a method of monitoring such correlation, a correlation function that uses the values of the detected temperatures θ1 and θ2 in a predetermined period as arguments and returns their correlation coefficients is used. It is also possible to detect the accumulation of the. Regarding this point, the estimated temperature applied to the detected temperature θ1 of the first temperature sensor 41 estimated based on the correlation between the detected temperature θ3 of the third temperature sensor 43 and the detected temperature θ2 of the second temperature sensor 42 and the engine operating state. The same applies to the determination of a decrease in the correlation between the detected temperature θ1 and the detected temperature θ1 actually detected by the first temperature sensor 41.

-Although the example which uses urea aqueous solution as a reducing agent added to the SCR catalyst 12 was shown, other ammonia-type reducing agents, such as an ammonia compound, can also be used, for example.
-Although the diesel engine was illustrated as an internal combustion engine used as the application object of the exhaust gas purification apparatus concerning this invention, this internal combustion engine is not limited to a diesel engine, For example, it is a gasoline engine in which the driving | running which makes an air fuel ratio lean is performed frequently. There may be.

  DESCRIPTION OF SYMBOLS 10 ... Engine, 11 ... Exhaust passage, 12 ... SCR catalyst, 14 ... Filter, 15 ... Dispersing member, 20 ... Branching passage, 20a ... Recessed part, 21 ... Communication part, 30 ... Addition valve, 31 ... Injection hole, 41 ... 1st temperature sensor, 41a ... temperature detection part, 42 ... 2nd temperature sensor, 42a ... temperature detection part, 43 ... 3rd temperature sensor, 50 ... control part.

Claims (13)

  Urea-based selective reduction catalyst provided in an exhaust passage of an internal combustion engine, a branch passage branched from the exhaust passage on the exhaust upstream side of the selective reduction catalyst, and the selective reduction catalyst by injecting a reducing agent into the branch passage An exhaust gas purification apparatus for an internal combustion engine, comprising: an addition valve to be added to a gas sensor; and a temperature sensor in which a temperature detector is disposed at a portion where deposits are accumulated in the branch passage. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the temperature detection unit is disposed at a portion where the accumulated deposit interferes with the spray of the reducing agent injected from the addition valve. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the temperature detection unit is disposed in a portion adjacent to the injection port of the addition valve. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the temperature detection unit is disposed at a portion to which the reducing agent injected from the addition valve directly adheres. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the temperature detection unit is disposed at a site that is a starting point when deposits are deposited. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the temperature detection unit is disposed in a communication portion that communicates with the exhaust passage in the branch passage. The exhaust gas purification apparatus for an internal combustion engine according to claim 6, wherein the temperature detection unit is disposed on the exhaust downstream side in the communication portion. When the temperature sensor is a first temperature sensor, a second temperature at which the temperature detection unit is disposed at a portion of the first temperature sensor where the deposited amount of deposit is smaller than the portion at which the temperature detection unit is disposed. The exhaust purification device for an internal combustion engine according to any one of claims 1 to 7, further comprising a sensor. The exhaust gas purification apparatus for an internal combustion engine according to claim 8, wherein the temperature detection unit of the second temperature sensor is disposed upstream of the branch passage and the communication portion in the exhaust passage. The exhaust emission control device for an internal combustion engine according to claim 8, wherein the temperature detection unit of the second temperature sensor is disposed at a portion that avoids a spray region of the reducing agent injected from the addition valve. The exhaust emission control device for an internal combustion engine according to claim 9 or 10, wherein the temperature detection unit of the second temperature sensor is disposed adjacent to the temperature detection unit of the first temperature sensor. The exhaust emission control device for an internal combustion engine according to any one of claims 8 to 11, wherein a filter for capturing particulate matter in the exhaust gas is provided on the exhaust gas upstream side of the second temperature sensor in the exhaust passage. A dispersion member provided on the exhaust upstream side of the selective reduction catalyst for dispersing the reducing agent introduced into the exhaust passage from the branch passage; and a third temperature sensor for detecting a temperature of the dispersion member; The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 12.