JP2017106399A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit accumulation of urea-derived deposit onto a front end of a catalyst support filter formed by supporting a selective reduction catalyst for selectively reducing NOx on a filter correcting PMs from causing a temperature rise for burning the PMs.SOLUTION: An ECU 1 acquires a temperature of an SCRF 7 serving as a catalyst support filter and urea addition amount added from an addition valve 5. Based on the temperature and the addition amount, an impact index that indicates a degree of an impact of a differential pressure before and after the SCRF 7 caused by accumulation of urea-derived deposit onto a front end of the SCRF 7 is calculated. Based on an NOx elimination ratio of the SCRF 7 and recent engine stop time, the impact index is corrected. When a differential pressure detected by a differential pressure sensor 8 is a threshold value or larger, whether or not the calculated impact index is equal to or larger than the threshold value is determined. When the impact index is smaller than the threshold value, temperature rise processing for PM removal is performed. When the impact index is the threshold value or larger, instead of the temperature rise processing for PM removal, temperature rise processing for removing the urea-derived deposit is performed.SELECTED DRAWING: Figure 1

Description

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

  Conventionally, a urea SCR (Selective Catalytic Reduction) system is known as one of systems for purifying exhaust gas discharged from an internal combustion engine. In the urea SCR system, a selective reduction catalyst (SCR catalyst) that stores ammonia generated from urea in an exhaust pipe of an internal combustion engine and selectively reduces NOx in the exhaust by the ammonia, and exhaust gas of the selective reduction catalyst An addition valve for adding urea is provided on the upstream side (see, for example, Patent Document 1).

  The exhaust pipe may be provided with a filter that collects particulate matter (particulate matter, PM) in the exhaust. When a certain amount or more of particulate matter is deposited on the filter, a regeneration process is performed in which the particulate matter deposited is burned by raising the temperature of the filter. As the regeneration process, for example, after the main injection for obtaining the torque of the internal combustion engine, after injection or post injection for increasing the temperature of the exhaust gas is performed. Moreover, the differential pressure (pressure loss) of the filter gradually increases as the amount of particulate matter deposited on the filter increases. Therefore, whether or not to perform the regeneration process is determined based on a value acquired by the differential pressure sensor provided with a differential pressure sensor that acquires the differential pressure before and after the filter, for example.

JP 2010-270624 A

  By the way, in the urea SCR system, urea and intermediate products (cyanuric acid) are formed on the inner wall of the exhaust pipe or the front end of the selective reduction catalyst depending on the conditions such as the amount of urea added from the addition valve and the temperature of the selective reduction catalyst. , Melamine, melm, etc.) may be deposited as urea-derived deposits.

  On the other hand, there is a catalyst-carrying filter in which the selective reduction catalyst is carried on the filter. When this catalyst-carrying filter is employed, urea water is added from the upstream side of the catalyst-carrying filter, so that a deposit derived from urea water accumulates in the exhaust pipe, the mixer, and the catalyst front end. When urea-derived deposits accumulate on the front end of the catalyst-carrying filter, the differential pressure across the catalyst-carrying filter increases due to the urea-derived deposit. Due to the increase in differential pressure due to the deposition of urea-derived deposits, even when the amount of particulate matter deposited on the catalyst-carrying filter is small, the temperature rises for burning the particulate matter, and the wasteful temperature rise is repeated to improve fuel efficiency. There is a problem that gets worse.

  The present invention has been made in view of the above problems, and is an internal combustion engine capable of suppressing frequent temperature increase for burning particulate matter due to deposition of urea-derived deposits on the front end of a catalyst-carrying filter. It is an object of the present invention to provide an exhaust emission control device for an engine.

In order to solve the above problems, an exhaust gas purification apparatus for an internal combustion engine according to the present invention includes:
A catalyst provided on an exhaust pipe (3) of an internal combustion engine (2), on which a selective reduction catalyst for selectively reducing NOx in the exhaust is supported on a filter that collects particulate matter in the exhaust of the internal combustion engine A carrier filter (7);
An addition valve (5) for adding urea for reducing NOx in the catalyst-carrying filter to the exhaust upstream side of the catalyst-carrying filter;
A differential pressure sensor (8) for acquiring a differential pressure before and after the catalyst-carrying filter;
A determination unit (S31, 1) that determines execution of regeneration of the catalyst-carrying filter based on a value acquired by the differential pressure sensor;
An index detection unit (S1, 1) for detecting an influence index indicating the magnitude of the influence on the differential pressure by the deposition of urea-derived deposits on the front end of the catalyst-carrying filter;
When the determination unit determines to regenerate the catalyst-carrying filter, when the influence index is less than a predetermined value, the temperature of the catalyst-carrying filter is increased so that particulate matter deposited on the catalyst-carrying filter burns. A first reproduction control unit (S32, S34, S4, 1) for performing the first reproduction process;
When the determination unit determines to regenerate the catalyst-carrying filter and the influence index is equal to or greater than the predetermined value, the urea-derived deposit accumulated on the catalyst-carrying filter is removed instead of the first regeneration process. A second reproduction control unit (S32, S33, S5, 1) for performing the second reproduction process;
Is provided.

  According to the present invention, the influence index indicating the magnitude of the influence on the differential pressure due to the deposition of the urea-derived deposit on the front end of the catalyst-carrying filter is detected. When it is determined to regenerate the catalyst-carrying filter based on the differential pressure before and after the catalyst-carrying filter, the influence index is confirmed before carrying out the regeneration. When the influence index is less than a predetermined value, a temperature rise (first regeneration process) for burning the accumulated particulate matter is performed. On the other hand, when the influence index is equal to or greater than the predetermined value, the first regeneration process is stopped and the second regeneration process for removing the urea-derived deposit is performed, so that the particulate matter is burned by the deposition of the urea-derived deposit. It is possible to suppress frequent temperature increase (first regeneration process). In addition, since the urea-derived deposit accumulated on the catalyst-carrying filter by the second regeneration process can be removed, it is possible to suppress an increase in the differential pressure across the catalyst-carrying filter due to the deposition of the urea-derived deposit.

It is a block diagram of the exhaust gas purification device of an internal combustion engine. It is the figure which showed the state in which the urea deposit was deposited on the SCRF front end. It is the figure which showed the breakdown of the differential pressure by PM deposition, and the differential pressure by urea deposition when a differential pressure reaches a threshold value. It is the figure which showed the state which the urea deposit deposited in the narrow range of the SCRF front end. It is a block diagram of each process which comprises SCRF reproduction processing. It is the block diagram which showed the process of calculating an influence parameter | index from SCRF temperature and urea addition amount. It is the figure which showed the relationship between SCRF temperature and an influence parameter | index. It is the figure which showed the relationship between the urea addition amount when SCRF temperature is low, and an influence parameter | index. It is the figure which showed the relationship between the urea addition amount when SCRF temperature is high, and an influence parameter | index. It is the figure which illustrated transition of the SCRF temperature in the upper stage, and showed transition of the influence index in the form corresponding to the transition of the temperature. It is the block diagram which showed the process of calculating the influence parameter | index which considered the NOx purification rate in addition to SCRF temperature and urea addition amount. It is the figure which showed the relationship between the NOx purification rate and the correction | amendment term of an influence parameter | index. It is the figure which showed the relationship between SCRF temperature and the NOx purification capability in SCRF. It is the block diagram which showed the process of calculating the influence parameter | index which considered engine stop time in addition to SCRF temperature and urea addition amount. It is the figure which showed the relationship between an engine stop time and the correction | amendment term of an influence parameter | index. It is a flowchart of temperature rising implementation determination of whether temperature raising for PM removal is implemented, or temperature raising for urea deposit removal is implemented. It is a time chart of each parameter relevant to the reproduction process of SCRF.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an exhaust emission control device for an internal combustion engine to which the present invention is applied. 1 is an apparatus that is mounted on a vehicle and removes harmful substances in the exhaust discharged from the engine 2 (internal combustion engine) of the vehicle. The exhaust purification device includes a urea SCR system that purifies NOx in the exhaust. Further, the exhaust purification device is also a device for removing PM (Soot) in the exhaust.

  The engine 2 is, for example, a diesel engine that includes an injector that directly injects fuel into a cylinder, and the fuel injected from the injector self-ignites in the cylinder to generate torque for driving the vehicle.

  An exhaust pipe 3 of the engine 2 is provided with an oxidation catalyst 4 (DOC: Diesel Oxidation Catalyst) that oxidizes and purifies HC and CO that are one of harmful components in the exhaust. The oxidation catalyst 4 carries, for example, a catalyst component (for example, Pt (platinum) or Pd (palladium)) that promotes the oxidation reaction of HC and CO on a wall-through type ceramic honeycomb or metal mesh. It has a structure. The oxidation catalyst 4 raises the temperature of the exhaust gas by an oxidation reaction with unburned fuel (unburned HC) supplied to the oxidation catalyst 4 in order to burn and remove PM and urea-derived deposits deposited on the SCRF 7 described later. It also has a role.

  An addition valve 5 for adding urea water as a reducing agent is disposed in the exhaust pipe 3 in the exhaust pipe 3 downstream of the oxidation catalyst 4. The addition valve 5 has the same structure as a fuel injection valve (injector) that injects fuel into a cylinder or an intake port of a gasoline engine. That is, the addition valve 5 is an electromagnetic on-off valve provided with a nozzle formed with an injection hole, a drive unit including an electromagnetic solenoid, and a urea water passage through which urea water flows and a needle for opening and closing the nozzle. It is configured. When the electromagnetic solenoid is energized, the needle moves in the valve opening direction along with the energization, and urea water is injected from the nozzle hole formed at the tip of the nozzle as the needle moves.

  A mixer 6 is disposed in the exhaust pipe 3 downstream of the addition valve 5. The mixer 6 is a device that atomizes the urea water added from the addition valve 5 and disperses it in the exhaust gas. The mixer 6 is configured, for example, as a passage that generates a swirling flow or a meandering flow of exhaust.

  An SCRF (Selective Catalytic Reduction Filter) 7 as a catalyst carrying filter is disposed in the exhaust pipe 3 downstream of the mixer 6. The SCRF 7 collects PM in exhaust gas, for example, a SCR as a selective reduction catalyst that selectively reduces NOx in exhaust gas to a filter (DPF: Diesel Particulate Filter) configured in a wall-through type ceramic honeycomb. It has a structure in which a catalyst is supported. That is, the SCRF 7 has both a function of removing PM and a function of reducing and purifying NOx. The exhaust gas flows downstream while passing through the porous partition walls of SCRF 7, while PM in the exhaust gas is collected by SCRF 7.

The SCR catalyst supported on the SCRF 7 promotes the reduction reaction of, for example, the following formula 1, formula 2, and formula 3 as a reduction reaction between ammonia (NH 3) generated from urea water and NOx, such as vanadium, Base metal oxides such as molybdenum and tungsten, zeolite and noble metals. In this way, while the exhaust gas passes through the SCRF 7, NOx is decomposed (purified) into water and nitrogen by, for example, the following formula 1, formula 2, and formula 3.
4NO + 4NH3 + O2 → 4N2 + 6H2O (Formula 1)
6NO2 + 8NH3 → 7N2 + 3H2O (Formula 2)
NO + NO2 + 2NH3 → 2N2 + 3H2O (Formula 3)

  Further, the exhaust gas purification device is provided with a urea water supply device (not shown) that supplies urea water to the addition valve 5. The urea water supply device includes a urea water tank that stores urea water, a pipe that connects the urea water tank and the addition valve 5, and a pump that pumps the urea water from the urea water tank and discharges it to the addition valve 5 side through the pipe. And a regulator that adjusts the pressure of the urea water in the pipe to a predetermined pressure.

  Further, various sensors are provided in the exhaust purification device. Specifically, a differential pressure sensor 8 that detects a differential pressure before and after the SCRF 7 (a difference between a pressure upstream and a downstream pressure of the SCRF 7) is provided. Further, an exhaust temperature sensor 9 for detecting the temperature of the exhaust gas flowing into the SCRF 7 and an upstream NOx sensor 10 for detecting the NOx concentration are provided upstream of the SCRF 7. If the ECU 1 has a function for estimating the NOx concentration flowing into the SCRF 7, the upstream NOx sensor 10 may not be provided. The sensor 9 is provided downstream of the mixer 6. When the sensor 10 is mounted, it is provided upstream of the addition valve 5. A downstream NOx sensor 11 that detects the NOx concentration in the exhaust gas flowing out from the SCRF 7 is provided downstream of the SCRF 7. Furthermore, the air flow meter 12 that detects the flow rate (for example, mass flow rate) of the intake gas flowing through the intake pipe of the engine 2, the rotation speed sensor 13 that detects the rotation speed of the engine 2, and the vehicle driver's required torque are notified to the vehicle side. For example, an accelerator pedal sensor 14 for detecting an operation amount (depression amount) of the accelerator pedal is provided. The detection values of these sensors 8 to 14 are input to the ECU 1.

  The exhaust purification device includes an ECU (Electronic Control Unit) 1 that controls the entire exhaust purification device. The ECU 1 has a normal computer structure, and includes a CPU (not shown) for performing various calculations and a memory 15 such as a ROM and a RAM for storing various information. For example, the ECU 1 detects the operating conditions of the engine 2 based on detection signals from the various sensors, calculates an optimal fuel injection amount, injection timing, injection pressure, etc. according to the operating conditions, Control fuel injection. Further, the ECU 1 may have a function of estimating the NOx concentration flowing into the SCRF 7.

  Further, the ECU 1 calculates the addition amount of urea water necessary for NOx purification in the SCRF 7, and drives the addition valve 5 so that the addition amount of urea water is added. Regarding the calculation of the urea water addition amount, for example, the ammonia amount necessary to purify NOx flowing into the SCRF 7, the ammonia supply amount to the SCRF 7 determined from the urea water addition amount added so far, and the ammonia consumption at the SCRF 7 Based on the balance with the amount, the ammonia adsorption amount at SCRF 7 is calculated. Then, the urea water addition amount corresponding to the deviation between the ammonia adsorption amount and the target adsorption amount is calculated as the addition amount at this time. The ammonia consumption at SCRF 7 is based on, for example, the upstream NOx sensor 10 or the operating conditions of the engine 2 (engine speed determined from the rotational speed sensor 13 and engine load (fuel injection amount) determined from the accelerator pedal sensor 14). The NOx amount flowing into the SCRF 7 is calculated, the NOx concentration flowing out from the downstream NOx sensor 11 from the SCRF 7 is calculated, and obtained from the NOx amount upstream of the SCRF and the NOx amount downstream of the SCRF.

  Furthermore, when the differential pressure detected by the differential pressure sensor 8 becomes large, the ECU 1 executes a regeneration process in which the PM accumulated on the SCRF 7 is removed by combustion to regenerate the SCRF 7. Details of this reproduction processing will be described later.

  Before describing the details of the regeneration process, the urea-derived deposit will be described. The urea water added from the addition valve 5 is thermally decomposed by the exhaust heat, so that ammonia and cyanuric acid are generated. Here, in the process in which ammonia or cyanuric acid is generated from urea water, intermediate products such as melamine and melm are generated. The intermediate product is usually decomposed by heat, but depending on conditions, it may solidify without disappearing. In some cases, only the water of urea water evaporates and urea precipitates and solidifies. Below, the urea origin deposit which is the precipitation solid substance of urea and the intermediate product derived from urea is called urea deposition. Urea deposits are likely to occur, for example, when the temperature of SCRF 7 is low (specifically, for example, 250 ° C. or lower). In addition, urea deposits are more likely to occur as the amount of urea water added by the addition valve 5 increases.

  The urea deposit is deposited on the inner wall of the exhaust pipe 3, the mixer 6, the SCRF 7, and the like. Speaking of the SCRF 7, as shown in FIG. 2, the urea deposit is likely to be deposited at the front end (end on the exhaust upstream side) of the SCRF 7. This is because when the urea water is not evaporated or decomposed by the front end of the SCRF 7, urea water is accumulated at the front end of the SCRF and solidified urea is generated.

  When urea deposits are deposited on the SCRF 7, the flow of the exhaust is inhibited by the deposition, and as a result, the differential pressure (pressure loss) before and after the SCRF 7 increases. At this time, even when the differential pressure reaches the determination threshold value for performing the regeneration process of SCRF 7 (temperature increase for PM removal), as shown in FIG. In some cases, the pressure is large and the differential pressure due to the urea depot is small. On the contrary, the differential pressure due to the PM amount is small and the differential pressure due to the urea depot is large. The temperature increase for burning and removing PM is preferably performed when the amount of PM deposited on the SCRF 7 is as large as possible as shown in the breakdown shown on the left in FIG. This is because the temperature necessary for removing PM is higher than the temperature necessary for removing urea depot, so that a large amount of fuel is required to raise the temperature of the exhaust gas. For this reason, as shown in the breakdown on the right side of FIG. 3, if the temperature is raised even when the amount of PM is small, fuel is wasted for raising the temperature of the exhaust, resulting in deterioration of fuel consumption.

  As shown in FIG. 4, when the urea deposit is deposited in a narrow range at the front end of the SCRF 7, the urea deposit has a smaller degree of hindering the exhaust flow in the SCRF 7, compared with the case of FIG. The effect on differential pressure is small. In this case, when the differential pressure reaches the determination threshold value, it is considered that the left breakdown in FIG.

  The SCRF 7 regeneration process described below suppresses the temperature increase for PM removal when the urea deposit is deposited at the front end of SCRF 7 as shown in FIG. It is configured for the purpose of doing. The details of the SCRF 7 regeneration process executed by the ECU 1 will be described below.

  FIG. 5 shows a block diagram of each process constituting the reproduction process. The regeneration process shown in FIG. 5 starts, for example, simultaneously with the start of the engine 2 and is repeatedly executed at a predetermined cycle. In the regeneration process of FIG. 5, an influence index indicating the magnitude of the influence on the differential pressure due to the urea deposit deposition on the front end of the SCRF 7 is calculated (S1). In other words, the influence index is an index indicating the contribution to the differential pressure due to urea deposition at the front end of the SCRF 7, and the larger the value, the greater the contribution.

  Specifically, the influence index is calculated according to the process of FIG. In FIG. 6, the temperature of the SCRF 7 at each time point is acquired (S11). Specifically, since the temperature of the SCRF 7 changes according to the temperature of the exhaust, for example, the temperature of the SCRF 7 is estimated based on the temperature of the exhaust detected by the exhaust temperature sensor 9. More specifically, for example, the inside of SCRF 7 is virtually divided into a plurality of regions (cells) from the upstream side to the downstream side, and the temperature distribution in SCRF 7 is obtained by estimating the temperature of each cell. For example, the average value of the obtained temperature distribution is set as the temperature of SCRF7. As the number of cell divisions, the higher the number of divisions, the more accurate the temperature can be obtained, but the calculation amount increases. In view of the accuracy of temperature and the amount of calculation, the number of cell divisions is set appropriately.

  Hereinafter, a method for estimating the temperature of each cell will be described. For example, the temperature of each cell is estimated in order from the upstream side. In addition, what is necessary is just to let the temperature of a cell be the temperature of the base material of the cell part. A process for estimating all cell temperatures at each time point is referred to as a single process, a process performed once before is referred to as a previous process, and a process currently performed is referred to as a current process. In addition, one cell that is a target of cell temperature estimation is referred to as the cell, one upstream cell adjacent to the cell is referred to as an upstream cell, and one downstream cell adjacent to the cell is referred to as a downstream cell.

  Specifically, the heat transfer amount Q1 from the exhaust gas flowing through the cell to the cell is obtained. The heat transfer amount Q1 is a heat transfer coefficient indicating the temperature of exhaust gas flowing through the cell (hereinafter referred to as cell gas temperature), the temperature of the cell, the flow rate of exhaust gas flowing through the cell, and the ease of heat transfer between the exhaust gas and the cell. And obtained. The exhaust flow rate is obtained from the detected value of the air flow meter 12. The cell gas temperature may be the value obtained in the previous process or the cell gas temperature in the upstream cell obtained in the current process. The method for obtaining the cell gas temperature will be described later. Moreover, what is necessary is just to use the value obtained by the last process for the temperature of the said cell. The heat transfer coefficient may be a predetermined fixed value or a value corresponding to the exhaust flow rate. The relationship between the cell gas temperature, the temperature and exhaust flow rate of the cell, and the heat transfer amount Q1 is obtained in advance and stored in the memory 15 as a map, for example, and the heat transfer amount Q1 is calculated using the map.

  Further, a heat transfer amount Q2 from the cell adjacent to the cell upstream and downstream to the cell is obtained. This heat transfer amount Q2 is obtained from the temperature of the upstream cell, the temperature of the downstream cell, the temperature of the cell, and the heat conduction coefficient indicating the ease of heat transfer in the SCRF 7. As the temperature of the upstream cell, the value obtained by the current process may be used, assuming that the cell temperature is obtained in order from the upstream cell. A value obtained by the previous process may be used for the temperature of the downstream cell and the temperature of the cell. The heat conduction coefficient may be a predetermined fixed value. The relationship between the temperature of the upstream cell, the temperature of the downstream cell, the temperature of the cell, and the heat transfer amount Q2 is obtained in advance and stored in the memory 15 as a map, for example, and the heat transfer amount Q2 is stored using the map. Is calculated.

  The total value of the two obtained heat transfer amounts Q1 and Q2 is calculated. Thereby, the total amount of heat transferred to the cell is obtained. Next, the temperature rise value of the cell is calculated from the total value of the heat transfer amount to the cell. In this calculation, the total amount of heat transfer may be divided by a predetermined heat capacity of the cell. Further, the obtained temperature rise value is added to the previously calculated temperature of the cell. Thereby, the current temperature of the cell is obtained.

  Next, how to obtain the cell gas temperature necessary for obtaining the temperature of each cell will be described. The basic idea for calculating the cell gas temperature of the cell is obtained by dividing the temperature drop due to the heat transfer amount Q1 from the gas flowing through the cell to the cell (the heat transfer amount Q is divided by the heat capacity of the gas). ) Is subtracted from the cell gas temperature of the upstream cell. That is, the cell gas temperature of the cell is obtained from the heat transfer amount Q1 and the cell gas temperature of the upstream cell. The heat transfer amount Q1 and the cell gas temperature of the upstream cell have already been obtained in this process. When there is no cell upstream from the cell, that is, when the cell is the most upstream cell, the detected value of the exhaust temperature sensor 9 may be used as the cell gas temperature of the upstream cell. The relationship between the heat transfer amount Q1 and the cell gas temperature of the upstream cell and the cell gas temperature of the cell is obtained in advance and stored in the memory 15 as a map, for example, and the cell gas temperature of the cell is calculated using the map. .

  Eventually, the temperature of SCRF7 becomes a value corresponding to the temperature and flow rate of the exhaust gas flowing into SCRF7. Therefore, in S11, it means that an estimated model of the temperature of the SCRF 7 based on the exhaust gas temperature and the flow rate is stored in the memory 15 and the temperature of the SCRF 7 is estimated based on the estimated model.

  In the above description, the calculation of the temperature of the SCRF 7 is described on the assumption that the PM deposited on the SCRF 7 does not burn. However, when the temperature of the SCRF 7 is high and the PM burns, the temperature of the SCRF 7 also changes depending on the amount of heat generated by the combustion. . Therefore, the temperature of SCRF 7 may be estimated in consideration of the amount of heat generated by PM combustion. In the step of S11 in FIG. 6, a temperature sensor may be provided inside the SCRF 7, and the detection value of the temperature sensor may be acquired as the temperature of the SCRF 7.

  Returning to FIG. 6, the urea addition amount per unit time added from the addition valve 5 at each time point is acquired (S12). The urea addition amount may be an addition amount command value to the addition valve 5 obtained by the ECU 1 itself at each time point.

  Based on the temperature of the SCRF 7 at each time point and the urea addition amount (conditions related to urea deposition) obtained in S11 and S12, an influence index on the differential pressure due to the urea depot at each time point is calculated (S13). The influence index calculated here is an index corresponding to the change amount per unit time of the urea deposition amount on the SCRF 7 at each time point, that is, the urea deposition rate. In other words, the influence index of S13 is an index indicating the ease of urea deposition on the SCRF 7 at each time point.

  Here, FIGS. 7 to 9 illustrate the relationship between the SCRF temperature or urea addition amount and the influence index. Urea deposits tend to occur when the temperature is low, and decompose when the temperature is high. Therefore, as shown in FIG. 7, the influence index has a large value in the region where the SCRF temperature is low, and the influence index becomes smaller as the SCRF temperature becomes higher. Further, when the SCRF temperature becomes high to some extent, the deposited urea deposit is decomposed and disappears. Therefore, in FIG. 7, in the region where the SCRF temperature is equal to or higher than the predetermined temperature, the influence index is a negative value indicating that the urea depot disappears. The influence index indicates that the larger the value on the positive side, the greater the amount of accumulated urea depot, and the greater the value on the negative side, the greater the amount of the urea depot deposited and dissociated.

  Also, as shown in FIGS. 8 and 9, the influence index increases as the urea addition amount increases. This is because the larger the amount of urea added, the greater the amount of intermediate product that causes urea deposition. Further, when the urea addition amount is large, the temperature of the SCRF 7 is likely to decrease due to the urea water supplied to the SCRF 7 as compared with the case where the urea addition amount is small, and urea deposition is likely to occur due to the temperature decrease.

  Comparing FIG. 8 and FIG. 9, when the SCRF temperature in FIG. 8 is low, the degree of increase in the influence index with respect to the increase in the urea addition amount is large, whereas when the SCRF temperature in FIG. 9 is high, the degree of increase is small. In other words, even when the urea water addition amount is the same, the influence index when the SCRF temperature is low in FIG. 8 is larger than the influence index when the SCRF temperature is high in FIG. As described with reference to FIG. 7, this is because urea deposition tends to occur when the SCRF temperature is low. In FIGS. 8 and 9, the influence index can take a negative value. For example, when the amount of urea added is small, the decomposition of the urea deposit already deposited due to the influence of the SCRF temperature is superior to the new deposition of the urea deposit. In this case, the impact index is a negative value.

  In step S13, the relationship between the SCRF temperature and urea addition amount and the influence index is obtained in advance and stored in the memory 15 as a map 101 (see FIG. 6), for example. Then, from this map 101 and the SCRF temperature and urea addition amount obtained in S11 and S12, an influence index corresponding to the SCRF temperature and urea addition amount is calculated for each time point. The map 101 corresponds to the integrated relationship of FIGS.

  After performing the process of S13, next, the influence index in each time obtained by S13 is integrated | accumulated (S14). That is, the influence index obtained in S13 at the present time is added to the integrated value of the influence index obtained in S14 up to the previous time point, and is set as the integrated value at the present time. This integrated value corresponds to the integrated amount of urea deposits accumulated at the front end of SCRF7. The integrated value obtained in S14 is set as the output value in the step S1 in FIG. The integrated value varies between the lower limit and the upper limit, for example, assuming that the lower limit is zero and the upper limit is a predetermined value (for example, 100).

  Here, FIG. 10 is a diagram exemplifying the transition with respect to time of the influence index obtained in the process of S1 (process of FIG. 6). Specifically, the upper stage illustrates the transition of the SCRF temperature, and the transition of the temperature. The transition of the impact index is shown in the bottom row in a form corresponding to Note that the symbol “m” in FIG. 10 indicates the influence index calculated in S13 in FIG. In the example of FIG. 10, when the SCRF temperature is low, the influence index (integrated value) gradually increases with the passage of time, and the increase amount per unit time (the influence index m at each time point) Larger than medium or high. Further, when the SCRF temperature is medium, the influence index (integrated value) gradually increases with the passage of time, but the increase amount per unit time is smaller than when the SCRF temperature is low. Further, when the SCRF temperature is high, the influence index (integrated value) gradually decreases with the passage of time. Thus, the integrated value of the influence index does not continue to increase monotonously as time elapses, and the rate of increase changes or decreases depending on the conditions of the SCRF temperature and urea addition amount.

  Note that at the start of the influence index integration in FIG. 10 (zero point), that is, at the time of calculation of the influence index in S13 of FIG. 6 and the start of integration in S14, a temperature increase for PM removal is performed in S4 of FIG. Or when the temperature is increased for removing the urea depot in S5. That is, in the process of S1, the integrated value of the influence index from the previous temperature increase of S4 or S5 to the current time is calculated. This is because the urea deposition deposited on the SCRF 7 is removed and the influence index is reset to zero by increasing the temperature.

  As described above, in FIG. 6, the influence index is obtained from the SCRF temperature and the urea addition amount at each time point. In other words, the influence index is based on the history of the SCRF temperature and the history of the urea addition amount. Seeking.

  By the way, the urea deposit is influenced not only by the SCRF temperature and the urea addition amount but also by the NOx purification rate at SCRF 7 and the recent engine stop time. Therefore, in addition to the SCRF temperature and the urea addition amount, the influence index may be obtained in consideration of the NOx purification rate and the engine stop time as described below.

  First, calculation of an influence index considering the NOx purification rate will be described. When urea deposits are deposited at the front end of the SCRF 7 as shown in FIG. 2, the accumulation range of the exhaust gas in the SCRF 7 is narrowed due to the deposition, and as a result, the NOx purification rate is lower than expected. Conversely, when the NOx purification rate is lower than expected, it can be considered that the influence of urea deposition is large. Based on this concept, the influence index obtained from the SCRF temperature and the urea addition amount is corrected according to the NOx purification rate.

  FIG. 11 is a block diagram in which steps related to correction by the NOx purification rate are added to each step of FIG. In FIG. 11, the NOx purification rate at each time point in SCRF7 is acquired (S15). The NOx purification rate is obtained by acquiring the NOx amount B1 flowing into the SCRF 7 and the NOx amount B2 flowing out from the SCRF 7, and dividing the difference between the NOx amounts B1 and B2 by the inflowing NOx amount B1. That is, NOx purification rate = (B1-B2) / B1 is calculated. Here, the inflow NOx amount B1 may be obtained from, for example, a detection value of the upstream NOx sensor 10, or may be estimated from engine operating conditions (engine speed, engine load, etc.). Further, the outflow NOx amount B2 is obtained from the detection value of the downstream NOx sensor 11, for example. When the inflow NOx amount B1 is estimated from the engine operating condition, the engine speed as the engine operating condition is obtained from the speed sensor 13. The engine load may be a command value for the fuel injection amount to the injector set by the ECU 1 itself based on the detected value (accelerator pedal operation amount) of the accelerator pedal sensor 14 and the engine speed. The relationship between the engine operating condition and the inflow NOx amount B1 is obtained in advance and stored in the memory 15, for example, as a map, and the inflow NOx amount B1 can be obtained based on this map.

  Next, a correction term (correction coefficient) for correcting the influence index obtained in steps S11 to S14 based on the NOx purification rate is calculated (S16). The correction term is a coefficient for correcting the influence index to the increase side by multiplying the influence index, and is set to a value of 1 or more. When the correction term = 1, it means that the influence index is not corrected.

  Here, FIG. 12 shows the relationship between the NOx purification rate and the correction term. In FIG. 12, line 103 shows the relationship when the SCRF temperature is high, and line 104 shows the relationship when the SCRF temperature is low. FIG. 13 shows the relationship between the SCRF temperature and the NOx purification capacity (NOx purification rate) at SCRF7. As shown in FIG. 13, in the region where the SCRF temperature is low (region where the temperature is T1 or less), the catalyst activity at SCRF 7 is low, so the NOx purification capacity is low. Further, when the SCRF temperature is increased to some extent, the activity of the catalyst is increased, so that the NOx purification capability is increased. However, if the SCRF temperature becomes too high (region of temperature T2 or higher), the NOx purification capacity is reduced.

  When the SCRF temperature is high (in the example of FIG. 13, the temperature is between T1 and T2), the NOx purification rate is low even though the NOx purification capacity is normally high. It can be considered that the NOx purification rate is lowered due to the influence of deposition. Further, it can be considered that the lower the NOx purification rate, the higher the degree of influence due to urea deposition. Based on this concept, in the line 103 of FIG. 12, the correction term increases as the NOx purification rate decreases. On the other hand, when the NOx purification rate is high when the SCRF temperature is high, the NOx purification capacity is originally high (see FIG. 13), and the urea depot that requires correction of the influence index obtained from the SCRF temperature and the urea water addition amount is required. In the line 103, the correction term is 1 in the region where the NOx purification rate is equal to or greater than a certain value.

  Also, when the SCRF temperature is low (temperature T1 or lower in FIG. 13), the NOx purification capacity is originally low, so it cannot be determined that the effect of urea deposition is large just because the actual NOx purification rate is low. . Therefore, the correction term is set smaller in the line 104 in FIG.

  In step S16, the relationship shown in FIG. 12, that is, the relationship between the SCRF temperature and NOx purification rate, and the correction term is obtained in advance and stored in the memory 15 as a map 102 (see FIG. 11). Then, a correction term is calculated based on the map 102 and the SCRF temperature and NOx purification rate obtained in the steps S11 and S15. In FIG. 12, two examples of the relationship 103 when the SCRF temperature is high and the relationship 104 when the SCRF temperature is low are illustrated, but the map 102 shows the NOx purification rate and the correction term for each region of more than two SCRF temperatures. It is a map in which the relationship is set. Note that it is particularly necessary to correct the influence index when the NOx purification rate is low when the SCRF temperature is high. Therefore, the map 102 is configured only from the line 103 in FIG. 12, and the SCRF temperature acquired in S11 is equal to or higher than a predetermined value. In this case, the calculation of the correction term in S16 and the correction in S17 described later may be performed. If the SCRF temperature is less than a predetermined value, the steps S16 and S17 may be omitted.

  After calculating the correction term in the step S16, the influence index is corrected by multiplying the correction term by the influence index obtained in the step S14 (S17). Thereby, in addition to the SCRF temperature and the urea addition amount, it is possible to obtain an influence index considering the NOx purification rate. For example, when the SCRF temperature is high and the NOx purification rate is low, the influence index is corrected to increase. The corrected influence index is set as the output value in the step S1 in FIG.

  Next, calculation of an influence index considering recent engine stop time will be described. When the engine 2 stops, the SCRF temperature decreases. However, the longer the engine stop time, that is, the longer the state in which the SCRF temperature decreases, the more likely urea depots are generated. Therefore, the influence index obtained from the SCRF temperature and the urea addition amount is corrected according to the latest engine stop time.

  Specifically, as shown in FIG. 14, the latest engine stop time is acquired (S18). The ECU 1 has a clock. Every time the engine 2 stops, the ECU 1 calculates an engine stop time, which is a time from when the engine 2 is stopped to the next start by the clock, and stores it in the memory 15. deep. In step S18, the engine stop time stored in the memory 15 is read.

  Next, a correction term (correction coefficient) for correcting the influence index obtained in steps S11 to S14 based on the engine stop time is calculated (S19). Similarly to the correction term calculated in S16, this correction term is a coefficient for correcting the influence index to the increase side by multiplying the influence index, and is set to a value of 1 or more.

  Here, FIG. 15 shows the relationship between the engine stop time and the correction term. As shown in FIG. 15, in the region where the engine stop time is short, the correction term is 1 or a value close to 1, but when the engine stop time becomes long, the correction term increases rapidly. This is because urea depot hardly occurs during the engine stop when the engine stop time is short such as the engine stop by the idle stop function in which the engine automatically stops by waiting for a signal or the like. On the other hand, when the engine is stopped for a long time such as when the vehicle is stopped overnight, urea supplied from the addition valve 5 and remaining in the SCRF 7 before the engine is stopped does not solidify when the engine is operating. Even if it is the amount of urea addition, it may solidify because a state with a low SCRF temperature continues for a long time. At this time, the differential pressure before and after SCRF 7 at the end of engine stop (when the engine is started) is a value that is increased from the differential pressure before and after the engine is stopped by an amount corresponding to the amount of accumulated urea deposits during engine stop. . This increase corresponds to the correction term in FIG.

  In step S19, the relationship shown in FIG. 15 is obtained in advance and stored in the memory 15 as a map 105 (see FIG. 14). Then, a correction term is calculated based on the map 105 and the engine stop time acquired in S18.

  Next, the influence index is corrected by multiplying the influence index obtained in the step S14 by the correction term obtained in the step S19 (S20). As a result, in addition to the SCRF temperature and the urea addition amount, it is possible to obtain an influence index that considers the recent engine stop time. For example, when the engine stop time is long, the influence index is corrected to increase. The corrected influence index is set as the output value in the step S1 in FIG.

  As long as the engine stop time acquired in S15 is the engine stop time for the engine stop that occurred at the same time, the correction of S20 based on the engine stop time is performed only once. That is, for example, when the engine is stopped at a certain time t1, the correction of S20 based on the engine stop time for the engine stop is performed only once. Thereafter, when the engine is stopped at another time t2, the correction of S20 based on the engine stop time for the engine stop is also performed only once.

  Further, when the engine is stopped based on the idle stop function, the engine stop time is very short, and urea depot is hardly generated while the engine is stopped. Therefore, in the steps S18 to S20, the influence index may be corrected in consideration of only engine stop based on vehicle key-off excluding engine stop by the idle stop function. In this case, in the process of S18, the engine stop time at the latest engine stop among the engine stops based on the key-off of the vehicle is acquired. Even when the correction is performed in consideration of the engine stop based on the idle stop function, the engine stop time based on the idle stop function is very short. May not correct the influence index.

  Note that only one or both of the correction of the influence index based on the NOx purification rate and the correction of the influence index based on the engine stop time may be performed. When both are implemented, for example, both the correction term calculated in S16 of FIG. 11 and the correction term calculated in S19 of FIG. 14 are multiplied by the influence index calculated in S14. Alternatively, a map of the SCRF temperature, the NOx purification rate, the engine stop time, and the correction term obtained by integrating the map 102 of FIG. 11 and the map 105 of FIG. 14 is obtained and stored in the memory 15. Then, one correction term corresponding to the SCRF temperature, the NOx purification rate, and the engine stop time may be calculated based on this map, and the influence index may be corrected based on this correction term.

  Thus, in addition to the SCRF temperature and the urea addition amount, the NOx purification rate and the engine stop time are also taken into consideration, whereby a highly accurate influence index can be obtained.

  The above is the content of the process of S1 of FIG. In addition, ECU1 which performs the process of S1 is equivalent to a parameter | index detection part. Moreover, ECU1 which performs the process of S11 corresponds to a temperature acquisition part. ECU1 which performs the process of S12 is equivalent to an addition amount acquisition part. ECU1 which performs the process of S13 is equivalent to a calculation part. The ECU 1 that executes the process of S14 corresponds to an integrating unit. ECU1 which performs the process of S15 is equivalent to a purification rate acquisition part. ECU1 which performs the process of S16 and S17 is equivalent to a correction | amendment part. ECU1 which performs the process of S18 is equivalent to a stop time acquisition part. ECU1 which performs the process of S19 and S20 corresponds to a correction | amendment part.

  Returning to the description of FIG. 5, the differential pressure across the SCRF 7 is acquired from the differential pressure sensor 8 (S2). After acquiring the influence index and the differential pressure in S1 and S2, next, based on these, it is determined whether to perform the temperature increase for PM removal or the temperature increase for urea depot removal (S3). Specifically, the process of the flowchart in FIG. 16 is executed.

  In FIG. 16, it is first determined whether or not the differential pressure acquired in the step S2 is equal to or greater than a predetermined threshold (S31). Note that the differential pressure varies depending on the flow rate of the exhaust gas passing through the SCRF 7 even when the same PM amount is accumulated, and specifically, the differential pressure increases as the flow rate increases. Therefore, in S31, for example, a threshold corresponding to the exhaust gas flow rate is set in order to exclude the influence of the differential pressure due to the exhaust gas flow rate. This threshold is set to a larger value as the flow rate is higher. The flow rate of the exhaust gas is obtained by the air flow meter 12, the exhaust gas temperature sensor 9 and the differential pressure sensor 8 upstream of the SCRF. Then, the threshold corresponding to the flow rate is compared with the differential pressure. Alternatively, the detection value of the differential pressure sensor 8 may be converted into a differential pressure per unit flow rate based on the exhaust flow rate, and the differential pressure per unit flow rate may be compared with a threshold value. In addition, ECU1 which implements the process of S31 is equivalent to a judgment part.

  When the differential pressure is less than the threshold value (S31: No), the process waits until the differential pressure becomes equal to or greater than the threshold value. If the differential pressure is equal to or greater than the threshold (S31: Yes), it is next determined whether or not the influence index obtained in the step S1 is equal to or greater than a predetermined threshold. If it is less than the threshold value (S32: No), it is determined that the temperature increase for PM removal is performed on the assumption that the influence on the differential pressure due to urea deposition is small and the breakdown of the differential pressure is the breakdown on the left in FIG. S34). Thereafter, the process of FIG. 16 is terminated.

  On the other hand, if the influence index is equal to or greater than the threshold (S32: Yes), the effect on the differential pressure due to urea deposition is large, and the breakdown of the differential pressure is the breakdown on the right in FIG. The temperature implementation is determined (S33). Thereafter, the process of FIG. 16 is terminated.

  Returning to FIG. 5, based on the result of the execution determination in S3, either the temperature increase for PM removal (S4) or the temperature increase for urea depot removal (S5) is performed. Specifically, when it is determined in S34 in FIG. 16 that the temperature removal for PM removal is performed, the temperature removal for PM removal is performed (S4). For example, after the main injection for obtaining the torque of the engine 2, this temperature increase is performed after injection or post injection. Here, the after injection is a small amount of fuel injection performed immediately after the main injection for the purpose of increasing the temperature of the exhaust gas. The post-injection is a small amount of fuel injection performed immediately before the exhaust valve is opened in order to send unburned fuel into the exhaust pipe 3. Further, a fuel addition valve for adding fuel may be provided upstream of the oxidation catalyst 4 in the exhaust pipe 3, and unburned fuel may be added directly into the exhaust pipe 3 by this fuel addition valve.

  Unburnt fuel is supplied to the oxidation catalyst 4 by after-injection, post-injection, or fuel addition by a fuel addition valve, and the unburnt fuel undergoes an oxidation reaction in the oxidation catalyst 4 to raise the temperature of the exhaust gas. The exhaust gas whose temperature has risen flows into SCRF 7, whereby the SCRF temperature rises. The target temperature of the SCRF temperature at the time of temperature increase for PM removal is set to be higher than the target temperature at the time of temperature increase for depot removal, which will be described later. ). The ECU 1 monitors the SCRF temperature during the temperature rise for PM removal, and adjusts the post injection amount and the like so that the SCRF temperature becomes the target temperature. For example, when the SCRF temperature is lower than the target temperature, the post injection amount is increased. Conversely, when the SCRF temperature is higher than the target temperature, the post injection amount is decreased. The monitoring (acquisition) of the SCRF temperature may be performed in the same manner as the step S11 of FIG. Further, since the SCRF temperature correlates with the exhaust temperature, the injection amount may be adjusted so that the detected value of the exhaust temperature sensor 9 becomes the target temperature. In this way, by performing the temperature increase while monitoring the SCRF temperature, it is possible to suppress the SCRF 7 from being excessively heated, and it is possible to suppress the SCRF 7 from being melted by heat due to the excessive temperature increase.

  Further, the temperature increase for PM removal may be continued for a predetermined fixed time (for example, 20 minutes to 30 minutes), or the detection value of the differential pressure sensor 8 is a predetermined value (than the threshold value of S31 in FIG. 16). You may continue until it becomes less than (small value). The duration of temperature rise for removing PM is longer than the duration of temperature raising for removing urea depot.

  In this way, the PM deposited on the SCRF 7 can be burned and removed by raising the temperature for removing the PM. In addition, since the urea depot burns at a lower temperature than PM, the urea depot can also be removed by combustion.

  On the other hand, if it is determined in S33 in FIG. 16 that the temperature increase for urea depot removal is determined, the temperature increase for urea depot removal is performed (S5). This temperature increase is performed, for example, after injection, post injection, or fuel addition by a fuel addition valve, similarly to the temperature increase for PM removal. However, the target temperature of the SCRF temperature and the duration of the temperature increase are different from the temperature increase for PM removal. Specifically, the target temperature of the SCRF temperature at the time of temperature increase for urea depot removal is set to be lower than the target temperature at the time of temperature increase for PM removal, and specifically, PM is allowed not to be removed by combustion. However, the urea deposit is set to a temperature at which combustion is removed (for example, about 350 ° C. to 400 ° C.).

  In the temperature increase for urea depot removal, it is difficult to assume that the SCRF temperature becomes excessively high. For example, the fuel injection amount such as post injection is fixed in advance for each operating condition so as to become the target temperature. Value. That is, the monitoring of the SCRF temperature during the temperature raising process and the adjustment of the injection amount based on the SCRF temperature are not performed. Similarly to the temperature increase for PM removal, the SCRF temperature may be monitored and the injection amount may be adjusted so that the SCRF temperature becomes the target temperature.

  In addition, the duration of the temperature increase for urea deposition removal is set to a time shorter than the duration for PM removal (for example, about 5 to 10 minutes). That is, the temperature increase for urea deposition removal ends after a predetermined fixed time that is shorter than the temperature increase duration for PM removal. It should be noted that the duration of the temperature increase for urea deposition removal may be set to a time corresponding to the influence index, and specifically may be set to a longer time as the influence index is larger. Even when the duration is set according to the influence index, the duration is set to be shorter than the duration in the temperature increase for PM removal. Thus, by setting the duration according to the influence index, it is possible to suppress the temperature rise from being completed before the urea depot accumulated on the SCRF 7 is completely burned and removed, and the urea depot is burned and removed. However, it is possible to prevent the temperature increase from being unnecessarily continued despite the completion of. In this way, by performing the temperature increase for removing the urea deposit, the urea deposit deposited on the SCRF 7 can be removed by combustion.

  In addition, ECU1 which performs the process of S32, S34, and S4 corresponds to a 1st reproduction | regeneration control part. The ECU 1 that executes the processes of S32, S33, and S5 corresponds to a second regeneration control unit. Further, the temperature increase for PM removal corresponds to the first regeneration process, and the temperature increase for urea deposition removal corresponds to the second regeneration process.

  Here, FIG. 17 is a diagram for explaining the operation of the present embodiment, and shows a time chart of each parameter related to the reproduction processing of SCRF7. Specifically, FIG. 17 shows, from the top, the differential pressure before and after the SCRF (FIG. (A)), the PM amount in the SCRF (FIG. (B)), and the differential pressure due to urea depot to the front end of the SCRF (influence index) (FIG. 3C), SCRF temperature (FIG. 4D), and temperature increase injection amount (FIG. 2E) are time charts. In FIG. 17, the dotted line indicates the present example, and the solid line indicates the conventional example.

  As shown in FIG. 17, when the differential pressure reaches the threshold value, the temperature rise for PM removal is always performed as shown by the solid lines in FIGS. In the embodiment, an influence index due to urea deposition on the front end of the SCRF is confirmed before the temperature is raised. When the influence index has reached a predetermined value (see FIG. 17C), the temperature increase for urea depot removal is performed instead of the temperature increase for PM removal (FIGS. 17D and 17D). (See the dotted line in e)). Although the amount of PM in the SCRF does not decrease by performing the temperature increase for urea deposition removal (see the dotted line in FIG. 17B), the differential pressure due to the urea deposition decreases (see FIG. 17C). As a result, the differential pressure indicated by the dotted line in FIG. 17A decreases by the amount that the differential pressure in FIG. However, since the PM amount is not burned and removed, the dotted line in FIG. 17A is higher than the solid line.

  As described above, according to the present embodiment, the influence index due to urea deposition at the SCRF front end is calculated, and when the differential pressure reaches the threshold, the influence index is confirmed. Instead of the temperature increase for PM removal, the temperature increase for urea depot removal is performed. Thereby, it can suppress that the temperature increase for PM removal will be implemented frequently by the influence of urea deposition. The temperature increase for urea deposition removal is a temperature increase with good fuel consumption because the target temperature is lower and the duration is shorter than the temperature increase for PM removal. Since it can suppress that the temperature rise for PM removal is implemented frequently, deterioration of a fuel consumption can be suppressed. Further, by performing the temperature increase for removing the urea deposit, the urea deposit deposited on the SCRF can be removed, and an increase in the differential pressure due to urea deposit deposition can be suppressed.

  In addition, although it is difficult to accurately detect the amount of urea deposit deposited on the SCRF, in this embodiment, since both the detected value of the differential pressure sensor and the influence index are used, the SCRF as shown in FIG. It is possible to accurately capture a state in which the amount of urea deposition deposited on the front end is large and the differential pressure due to urea deposition is large. Also, as shown in FIG. 4, there is a possibility that the temperature for removing the urea depot may be increased even when the urea depot accumulates in a narrow range at the front end of the SCRF and the differential pressure due to the urea depot is small. In this case, although the influence on the vehicle performance and the SCRF catalyst performance is small, the temperature increase for urea deposition removal is frequently performed, and the fuel consumption is deteriorated. In the present embodiment, it is possible to prevent the temperature increase for removing urea deposits from being frequently (wastely) performed.

  In addition, this invention is not limited to the said embodiment, A various change is possible to the limit which does not deviate from description of a claim. For example, in the above embodiment, the temperature increase process of the SCRF temperature based on post injection or the like is exemplified as a means for removing the urea deposit deposited on the SCRF. However, for example, the urea flow rate is increased by increasing the exhaust gas flow rate, You may skip from SCRF. The increase in the exhaust gas flow rate is caused, for example, by operating the engine under conditions of a high rotational speed and a high load.

  Moreover, although the example which arrange | positioned the oxidation catalyst upstream of SCRF was shown in the said embodiment, you may carry | support an oxidation catalyst on the base material of SCRF. Also by this, the SCRF temperature can be raised by supplying unburned fuel to the oxidation catalyst supported on the SCRF.

1 ECU (determination unit, index detection unit, temperature acquisition unit, addition amount acquisition unit, calculation unit, integration unit, purification rate acquisition unit, stop time acquisition unit, correction unit, first regeneration control unit, second regeneration control Part)
2 Engine (Internal combustion engine)
3 Exhaust pipe 5 Addition valve 7 SCRF (Catalyst carrying filter)
8 Differential pressure sensor

Claims (7)

A catalyst provided on an exhaust pipe (3) of an internal combustion engine (2), on which a selective reduction catalyst for selectively reducing NOx in the exhaust is supported on a filter that collects particulate matter in the exhaust of the internal combustion engine A carrier filter (7);
An addition valve (5) for adding urea for reducing NOx in the catalyst-carrying filter to the exhaust upstream side of the catalyst-carrying filter;
A differential pressure sensor (8) for acquiring a differential pressure before and after the catalyst-carrying filter;
A determination unit (S31, 1) that determines execution of regeneration of the catalyst-carrying filter based on a value acquired by the differential pressure sensor;
An index detection unit (S1, 1) for detecting an influence index indicating the magnitude of the influence on the differential pressure by the deposition of urea-derived deposits on the front end of the catalyst-carrying filter;
When the determination unit determines to regenerate the catalyst-carrying filter, when the influence index is less than a predetermined value, the temperature of the catalyst-carrying filter is increased so that particulate matter deposited on the catalyst-carrying filter burns. A first reproduction control unit (S32, S34, S4, 1) for performing the first reproduction process;
When the determination unit determines to regenerate the catalyst-carrying filter and the influence index is equal to or greater than the predetermined value, the urea-derived deposit accumulated on the catalyst-carrying filter is removed instead of the first regeneration process. A second reproduction control unit (S32, S33, S5, 1) for performing the second reproduction process;
An exhaust gas purification apparatus for an internal combustion engine.   The index detection unit acquires the temperature of the catalyst-carrying filter and the amount of urea added from the addition valve, and calculates the influence index based on the temperature and the amount of addition. An exhaust gas purification apparatus for an internal combustion engine as described. The index detection unit
A temperature acquisition unit (S11) for acquiring the temperature at each time of the catalyst-carrying filter;
An addition amount acquisition unit (S12) for acquiring the addition amount of urea at each time point added from the addition valve;
A calculation unit (S13) for calculating the influence index according to the temperature and the addition amount for each time point;
An integration unit (S14) that integrates the influence index for each time point calculated by the calculation unit;
The first regeneration control unit performs the first regeneration process based on when the influence index of integration obtained by the integration unit is less than the predetermined value,
The exhaust purification device for an internal combustion engine according to claim 2, wherein the second regeneration control unit performs the second regeneration process when the influence index of integration obtained by the integration unit is equal to or greater than the predetermined value. The index detection unit
A purification rate acquisition unit (S15) for acquiring a NOx purification rate in the catalyst-carrying filter;
The exhaust gas purification apparatus for an internal combustion engine according to claim 2 or 3, further comprising a correction unit (S16, S17) that corrects the influence index based on the NOx purification rate acquired by the purification rate acquisition unit. The index detection unit
A stop time acquisition unit (S18) for acquiring a recent stop time of the internal combustion engine;
The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 2 to 4, further comprising a correction unit (S19, S20) that corrects the influence index based on the stop time acquired by the stop time acquisition unit.   The second regeneration process is a process of raising the temperature of the catalyst-carrying filter so that urea-derived deposits are combusted, and the target temperature of the catalyst-carrying filter when the second regeneration process is performed is the same as that of the first regeneration process. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 5, wherein the temperature is lower than a target temperature of the catalyst-carrying filter during operation. The exhaust purification device for an internal combustion engine according to any one of claims 1 to 6, wherein the second regeneration control unit ends the second regeneration process after continuing for a predetermined time.

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