JP5768767B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

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

In order from the upstream side to the exhaust passage of the internal combustion engine, an oxidation catalyst, a particulate filter, a reducing agent addition valve, a selective reduction type NOx catalyst (hereinafter also referred to as SCR catalyst), and an NH ₃ oxidation catalyst are provided, and the oxidation catalyst is heated. A technique including a heater is known (see, for example, Patent Document 1).

By the way, in an exhaust gas purification apparatus provided with an oxidation catalyst carrying a noble metal (Pt or the like) upstream from the SCR catalyst, the noble metal evaporates from the oxidation catalyst at a high temperature and flows downstream, and this noble metal adheres to the SCR catalyst. Sometimes. When the noble metal adheres to the SCR catalyst in this way, the noble metal increases the oxidation ability of the SCR catalyst. If it does so, since the reducing agent supplied to an SCR catalyst will be oxidized, there exists a possibility that a reducing agent may run short. When NH ₃ is used as the reducing agent, for example, NH ₃ is oxidized by the noble metal attached to the SCR catalyst, and NOx is generated. That is, the SCR catalyst lacks the reducing agent and generates NOx, which may reduce the NOx purification rate.

JP 2010-265862 A JP 2009-062932 A JP 2002-038939 A JP 2003-172185 A

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a selective reduction type NOx catalyst in the case where a catalyst having an oxidation ability is provided upstream of the selective reduction type NOx catalyst. It is in suppressing that the oxidation ability in becomes high.

In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention comprises:
A catalyst provided in the exhaust passage of the internal combustion engine and having an oxidizing ability;
A selective reduction type NOx catalyst provided in an exhaust passage downstream of the catalyst having the oxidation ability;
A trap portion that is provided in an exhaust passage downstream of the catalyst having oxidation ability and upstream of the selective reduction NOx catalyst, and traps a substance that increases the oxidation ability of the selective reduction NOx catalyst;
Supply means for supplying fuel to the catalyst having oxidation ability;
An exhaust gas purification apparatus for an internal combustion engine comprising:
When supplying fuel from the supply means to the catalyst having oxidation ability, the higher the temperature of the trap section, the lower the amount of fuel supplied per time and the higher the frequency of supplying fuel Equipment.

By supplying fuel to a catalyst having oxidation ability, the temperature of the catalyst can be increased, or the temperature of other members provided downstream of the catalyst can be increased. Accordingly, for example, regeneration of the filter and warming up of each catalyst can be performed. Further, when the NOx storage reduction catalyst is provided, sulfur poisoning of the NOx storage reduction catalyst can be recovered. The supply means may discharge unburned fuel from the internal combustion engine, or may add fuel to the exhaust.

Here, a substance (for example, Pt, Pd, Rh) having oxidation ability may evaporate from the catalyst provided upstream of the selective reduction type NOx catalyst (SCR catalyst). When this substance adheres to the SCR catalyst, the oxidation ability of the SCR catalyst becomes high. In this case, the reducing agent supplied to the SCR catalyst is oxidized by the SCR catalyst before acting on the NOx as a reducing agent, so there is a possibility that the reducing agent for reducing NOx is insufficient. In addition, when ammonia (NH ₃ ) is used as the reducing agent, ammonia may be oxidized by the SCR catalyst to generate NOx. For this reason, there is a possibility that NOx that must be purified by the SCR catalyst increases.

  On the other hand, by providing a trap portion upstream of the SCR catalyst, a substance that increases the oxidation ability of the SCR catalyst can be trapped before adhering to the SCR catalyst.

  However, the substance trapped in the trap part may be evaporated by the temperature of the trap part becoming high. That is, the same thing that happened with the catalyst having oxidation ability can occur in the trap part. For example, if fuel adheres to the trap part and is oxidized when the attached fuel has a lean air-fuel ratio, the temperature of the place where the fuel has adhered becomes higher than the surrounding temperature, and the substance evaporates. It becomes easy.

  Therefore, the control device adjusts the temperature of the trap portion so that the temperature does not evaporate. And if a fuel is supplied from a supply means so that a fuel may not adhere to a trap part, the temperature rise of a trap part can be suppressed.

  Here, when supplying the same amount of fuel in a plurality of times, the frequency of supplying the fuel is decreased and the frequency of supplying the fuel is decreased and the frequency of supplying the fuel is decreased. Rather than increasing the amount of fuel supplied per cycle, the fuel is more likely to react with the catalyst having oxidation ability, so that it is difficult for the fuel to adhere to the trap portion. That is, when supplying fuel to a catalyst having oxidation ability, the higher the temperature of the trap portion, the higher the frequency of supplying the fuel and the smaller the amount of fuel supplied per time, the catalyst having oxidation ability. Since the amount of fuel that passes through the fuel tank decreases, it is possible to suppress a local increase in temperature in the trap portion. Thereby, transpiration of the substance can be suppressed.

  Thus, it can suppress that the oxidation capability of this SCR catalyst becomes high by suppressing that the substance which makes the oxidation capability of an SCR catalyst evaporate again from a trap part. Thereby, it can suppress that the reducing agent supplied to an SCR catalyst runs short. Moreover, generation | occurrence | production of NOx can be suppressed. By these, it can suppress that the NOx purification rate in an SCR catalyst falls.

  The higher the temperature of the trap section, the smaller the amount of fuel supplied per time and the higher the frequency of fuel supply. This includes changing the supply frequency and the supply amount of fuel per time. In addition, when the temperature of the trap portion is higher than the threshold value, the amount of fuel supplied per time when the fuel is supplied from the supply means is smaller than when the temperature is lower than the threshold value, and the frequency of supplying the fuel Including raising the value.

The fuel supply amount per time may be the fuel supply time per time. That is, the longer the fuel supply time, the greater the fuel supply amount. This may be, for example, the time during which the exhaust air-fuel ratio decreases once. Alternatively, the amount of fuel supplied when the air-fuel ratio of the exhaust gas decreases once may be used. Further, the frequency of supplying the fuel may be a frequency of lowering the air-fuel ratio of the exhaust.

  Further, in the present invention, the control device performs one time when fuel is supplied from the supply means as the amount of the substance that increases the oxidation ability of the selective reduction type NOx catalyst trapped in the trap portion increases. The fuel supply amount per hit can be reduced and the frequency of fuel supply can be increased.

  That is, as the amount of the substance trapped in the trap portion increases, more substance may evaporate. In addition, the more the amount of the substance trapped in the trap portion, the easier it is to generate heat when fuel reaches the trap portion, and thus the temperature tends to rise. On the other hand, by increasing the frequency of supplying the fuel and decreasing the supply amount per time, the substance can be made more difficult to evaporate.

Further, in the present invention, the control device may control the amount of fuel supplied per time when the fuel is supplied from the supply means when the temperature of the trap portion is higher than a threshold value than when the temperature is lower than the threshold value. And increase the frequency of fuel supply,
The control device can lower the threshold value as the amount of the substance that increases the oxidation ability of the selective reduction type NOx catalyst trapped in the trap unit increases.

  The threshold value here can be arbitrarily set as the temperature of the trap portion when switching the amount of fuel supply per one time and the frequency of supplying the fuel. The threshold value may be an upper limit value of the temperature at which the substance does not evaporate from the trap part. Further, the threshold value may be an upper limit value of a temperature that is within an allowable range even if the substance evaporates from the trap portion. And when the temperature of a trap part is higher than a threshold value, it is possible to suppress transpiration of the substance from the trap part by increasing the frequency of supplying fuel and reducing the amount of fuel supplied per time. . However, as the amount of the substance trapped in the trap portion is larger, heat is more likely to be generated, and more substance may be evaporated. On the other hand, transpiration of the substance can be suppressed by lowering the threshold as the amount of the substance trapped in the trap portion increases.

  In the present invention, the supply means performs sub-injection in addition to main injection in the internal combustion engine, thereby discharging unburned fuel from the internal combustion engine and supplying fuel to the catalyst having the oxidation capability. In addition, a fuel addition valve for adding fuel to the exhaust gas can be provided, and fuel can be supplied from the fuel addition valve to the catalyst having the oxidation ability.

  Here, since the fuel supplied from the fuel addition valve hardly reacts in the catalyst having the oxidation ability, it easily passes through the catalyst having the oxidation ability. On the other hand, by carrying out the sub-injection in the internal combustion engine, the unburned fuel discharged from the internal combustion engine is likely to react with the catalyst having oxidation ability. That is, since the unburned fuel discharged from the internal combustion engine is difficult to pass through the oxidation catalyst, it is possible to prevent the temperature from rising locally in the trap portion. And by discharging unburned fuel from the internal combustion engine, the amount of fuel supplied from the fuel addition valve can be reduced accordingly, so that the amount of fuel passing through the catalyst having oxidation ability can be reduced.

  Further, by performing the sub-injection in the internal combustion engine, the gas having a high temperature can be discharged from the internal combustion engine. As a result, the temperature of the catalyst having oxidation ability increases, and accordingly, the amount of fuel supplied from the fuel addition valve into the exhaust gas can be reduced. The sub-injection may be fuel injection performed during the expansion stroke or the exhaust stroke after the main injection.

  Further, in the present invention, the control device supplies the fuel supply amount and fuel per one time when the fuel is supplied from the supply means according to the flow rate of the exhaust gas passing through the catalyst having the oxidation ability. The frequency to do can be determined.

  The flow rate of the exhaust gas may be a space velocity (SV). Here, the higher the exhaust gas flow rate, the more difficult it is for the fuel to react with the catalyst having the oxidation ability, so that the fuel easily passes through the catalyst having the oxidation ability. Therefore, the higher the exhaust gas flow rate, the higher the frequency at which fuel is supplied and the decrease in the amount of fuel supplied per time, so that the fuel can be prevented from passing through the catalyst having oxidation ability.

  In the present invention, the control device determines a fuel supply amount per one time and a fuel supply frequency when supplying the fuel from the supply means according to the temperature of the catalyst having the oxidation ability. can do.

  Here, the higher the temperature of the catalyst having oxidation ability, the easier the fuel passes through the catalyst having oxidation ability. Therefore, the higher the temperature of the catalyst having oxidation ability, the more frequently the fuel is supplied and the amount of fuel supplied per time is reduced, thereby preventing the fuel from passing through the catalyst having oxidation ability. it can.

  According to the present invention, when the catalyst having the oxidation ability is provided on the upstream side of the selective reduction type NOx catalyst, it is possible to suppress the oxidation ability of the selective reduction type NOx catalyst from becoming high.

It is a figure which shows schematic structure of the internal combustion engine which concerns on an Example, and its exhaust system. It is the time chart which showed the relationship between the addition signal of a fuel addition valve, and the temperature of a trap part. 3 is a flowchart showing a flow of fuel addition control according to the first embodiment. 6 is a flowchart showing a flow of fuel addition control according to a second embodiment. 10 is a flowchart showing a flow of fuel addition control according to a third embodiment.

  Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings.

<Example 1>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine according to the present embodiment and an exhaust system thereof. The internal combustion engine 1 shown in FIG. 1 is a diesel engine, but may be a gasoline engine. The internal combustion engine 1 is mounted on a vehicle, for example.

  An exhaust passage 2 is connected to the internal combustion engine 1. In the middle of the exhaust passage 2, an oxidation catalyst 3, a trap unit 5, and a selective reduction type NOx catalyst 6 (hereinafter referred to as SCR catalyst 6) are provided in order from the upstream side.

The oxidation catalyst 3 is a catalyst having oxidation ability, and oxidizes, for example, HC or CO in exhaust gas. The oxidation catalyst 3 may be another catalyst having oxidation ability (for example, a three-way catalyst or an occlusion reduction type NOx catalyst). The oxidation catalyst 3 carries a noble metal such as Pt, Pd, or Rh. In the following description, it is assumed that Pt is supported on the oxidation catalyst 3. However, even if Pd or Rh is supported, the present invention can be applied similarly to Pt. In this embodiment, the oxidation catalyst 3 corresponds to a catalyst having oxidation ability in the present invention. In this embodiment, Pt, Pd, and Rh correspond to “substances that increase the oxidation ability of the selective reduction NOx catalyst” in the present invention.

  The filter 4 collects particulate matter (PM) in the exhaust gas. The oxidation catalyst 3 may be carried on the filter 4.

  The trap unit 5 is a device that traps a substance (Pt) evaporated from the oxidation catalyst 3. The trap unit 5 includes at least one of Ni, Pd, and Au. Ni, Pd, and Au have a face-centered cubic lattice structure that is the same crystal structure as Pt, Pd, and Rh, and are easily bonded to Pt, Pd, and Rh.

The trap unit 5 may include at least one of CeO ₂ , TiO ₂ , and CZY instead of including at least one of Ni, Pd, and Au. Further, it may be configured to include at least one of Ni, Pd, and Au and at least one of CeO ₂ , TiO ₂ , and CZY. CeO ₂ , TiO ₂ , and CZY are materials that have high affinity with Pt, and have the property that the electrons of Pt are shared via oxygen and bind to Pt.

Moreover, the trap part 5 may be comprised including the material which has the property which takes in a noble metal in a crystal structure instead of including at least one of Ni, Pd, and Au. Note that it may be configured to include at least one of Ni, Pd, and Au and a material having a property of incorporating a noble metal into the crystal structure. Furthermore, it may be configured to include at least one of CeO ₂ , TiO ₂ , and CZY and a material having a property of incorporating a noble metal into the crystal structure. Further, it may be configured to include at least one of Ni, Pd, and Au, at least one of CeO ₂ , TiO ₂ , and CZY, and a material that has a property of incorporating a noble metal into the crystal structure. As a material (precious metal recovery material) having a property of incorporating a noble metal into the crystal structure, a perovskite complex oxide can be exemplified.

  The trap unit 5 may be a device that chemically traps the material evaporated from the oxidation catalyst 3. The trap may be any method such as adsorption, occlusion, or absorption.

The SCR catalyst 6 adsorbs a reducing agent and selectively reduces NOx by the adsorbing reducing agent when NOx passes. NH ₃ can be used as a reducing agent supplied to the SCR catalyst 6.

  The filter 4 can also be provided downstream of the trap portion 5 and upstream of the SCR catalyst 6. The filter 4 can also be provided downstream of the SCR catalyst 6.

  A fuel addition valve 7 for injecting fuel (HC) into the exhaust gas flowing through the exhaust passage 2 is provided in the exhaust passage 2 upstream of the oxidation catalyst 3. By adding HC to the exhaust gas from the fuel addition valve 7, HC can be reacted with the oxidation catalyst 3, and the temperature of the exhaust gas can be raised by this reaction heat. For example, when raising the temperature of the oxidation catalyst 3, the filter 4, and the SCR catalyst 6, HC is added from the fuel addition valve 7.

In addition, an ammonia addition valve 8 for adding urea water or ammonia (NH ₃ ) to the exhaust gas is provided in the exhaust passage 2 downstream from the trap unit 5 and upstream from the SCR catalyst 6. The urea water is hydrolyzed by the heat of the exhaust to become NH ₃ . The ammonia addition valve 8 may be provided upstream from the oxidation catalyst 3, or may be provided downstream from the oxidation catalyst 3 and upstream from the trap unit 5. Ammonia is used as a reducing agent in the SCR catalyst 6.

  If the trap portion 5 is provided downstream of the ammonia addition valve 8, ammonia may be oxidized by Pt trapped by the trap portion 5. Therefore, in this embodiment, the ammonia addition valve is provided downstream of the trap portion 5. 8 is provided.

  A first temperature sensor 11 that detects the temperature of exhaust gas and an air-fuel ratio sensor 12 that detects the air-fuel ratio of exhaust gas are attached to the exhaust passage 2 downstream of the oxidation catalyst 3 and upstream of the trap portion 5. Yes. The first temperature sensor 11 can detect the temperature of the oxidation catalyst 3 or the temperature of the filter 4. Further, the air-fuel ratio sensor 12 can detect the air-fuel ratio of the exhaust gas flowing out from the oxidation catalyst 3 or the air-fuel ratio of the exhaust gas flowing into the filter 4. A second temperature sensor 13 for detecting the temperature of the exhaust is attached to the exhaust passage 2 downstream from the trap unit 5 and upstream from the ammonia addition valve 8. The second temperature sensor 13 can detect the temperature of the trap unit 5 or the temperature of the SCR catalyst 6. In addition, a temperature sensor may be attached to each of the oxidation catalyst 3, the filter 4, the trap unit 5, and the SCR catalyst 6 to directly detect the temperature of each member.

  Note that it is not necessary to attach all of the above sensors, and they may be appropriately selected and attached.

  The internal combustion engine 1 is provided with an in-cylinder injection valve 9 for injecting fuel into the cylinder.

  The internal combustion engine 1 configured as described above is provided with an ECU 10 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 10 controls the internal combustion engine 1 in accordance with the operating conditions of the internal combustion engine 1 and the driver's request.

  The sensors are connected to the ECU 10 via electric wiring, and output signals from these sensors are input to the ECU 10. Further, the ECU 10 is connected with a fuel addition valve 7, an ammonia addition valve 8, and an in-cylinder injection valve 9 through electric wiring, and these devices are controlled by the ECU 10.

  The ECU 10 can raise the temperature of the oxidation catalyst 3 and the exhaust gas by supplying HC to the oxidation catalyst 3 from the upstream side of the oxidation catalyst 3. For example, when the NOx purification rate is low because the temperature of the SCR catalyst 6 is low, the temperature of the SCR catalyst 6 can be raised by supplying HC to the oxidation catalyst 3. Further, when it is desired to increase the purification rate by raising the temperature of the oxidation catalyst 3, the temperature of the oxidation catalyst 3 can be raised by supplying HC to the oxidation catalyst 3.

  In addition, when the amount of PM collected by the filter 4 reaches a threshold value, the ECU 10 supplies HC to the oxidation catalyst 3 to increase the temperature of the exhaust. Then, since the temperature of the filter 4 rises, PM is oxidized. Thereby, PM can be removed from the filter 4. In this way, the regeneration of the filter 4 is performed. In the case where the NOx storage reduction catalyst is provided downstream of the oxidation catalyst 3, by supplying HC to the oxidation catalyst 3, the temperature of the NOx storage reduction catalyst is raised and the sulfur coverage is reduced. Can restore poison.

In this way, the ECU 10 adds fuel from the fuel addition valve 7 in order to supply HC to the oxidation catalyst 3. The ECU 10 can also supply HC to the oxidation catalyst 3 by discharging unburned fuel from the internal combustion engine 1. That is, the secondary injection (post injection or after injection) is performed again during the expansion stroke or the exhaust stroke after the main injection from the in-cylinder injection valve 9, or the timing of the main injection is delayed. Accordingly, the gas containing a large amount of HC can be discharged from the internal combustion engine 1. Therefore, in this embodiment, the fuel addition valve 7 or the in-cylinder injection valve 9 corresponds to the supply means in the present invention.

  By the way, when the HC added to the exhaust gas from the fuel addition valve 7 reaches the oxidation catalyst 3 before being dispersed in the exhaust gas, the oxidation catalyst 3 has a location where the concentration of HC is high and a location where the concentration is low. And in the location where the concentration of HC is high, more heat is generated than in the location where the concentration of HC is low, so the temperature becomes high. If it does so, Pt contained in the oxidation catalyst 3 may evaporate in the location where temperature is high. The Pt evaporated in this way flows downstream with the exhaust.

  For example, when the filter 4 is regenerated, the temperature of the oxidation catalyst 3 increases, so that Pt may evaporate from the oxidation catalyst 3. When the catalyst is supported on the filter 4, Pt may evaporate from the catalyst supported on the filter 4.

  Here, when the trap part 5 is not provided, the evaporated Pt adheres to the SCR catalyst 6. As described above, since Pt adhering to the SCR catalyst 6 has a small amount but has an oxidation ability, the oxidation ability of the SCR catalyst 6 becomes high. And when the oxidation capability in the SCR catalyst 6 becomes high, ammonia added from the ammonia addition valve 8 may be oxidized and NOx may be generated. That is, ammonia as a reducing agent necessary for reducing NOx decreases, and NOx to be reduced increases. For this reason, there exists a possibility that the NOx purification rate in the SCR catalyst 6 may fall.

  On the other hand, in the present embodiment, Pt evaporated from the oxidation catalyst 3 can be trapped by the trap unit 5, so that it is possible to suppress Pt from adhering to the SCR catalyst 6.

  However, when the filter 4 is being regenerated, the temperature of the trap unit 5 rises due to high-temperature exhaust gas passing through the trap unit 5. And when the temperature of the trap part 5 becomes high, Pt trapped easily evaporates, so that Pt easily flows out downstream of the trap part 5.

  On the other hand, in this embodiment, when HC is supplied from the fuel addition valve 7, the temperature rise of the trap portion 5 is suppressed. The fuel addition valve 7 may be controlled so that the temperature of the trap unit 5 is lower than the temperature at which Pt evaporates.

  Here, FIG. 2 is a time chart showing the relationship between the addition signal of the fuel addition valve 7 and the temperature of the trap unit 5. The alternate long and short dash line indicates the case where the frequency of fuel addition is reduced and the addition amount per time is increased, and the solid line indicates that the frequency of fuel addition is higher and the addition per time than in the case of A The case where the amount is reduced is shown. In addition, the temperature of the trap part 5 is the temperature in the location where temperature becomes the highest. When the addition signal of the fuel addition valve 7 is ON, the fuel addition valve 7 is energized to open the fuel addition valve and add fuel. When OFF, the fuel addition valve 7 is closed and fuel addition is stopped. The time that is ON is proportional to the fuel injection amount. Moreover, if the temperature of the trap part 5 is 600 degreeC, for example, it will become the temperature at which PM is oxidized in the filter 4.

  When adding fuel from the fuel addition valve 7, as the amount of addition per time increases, the fuel is more likely to pass through the oxidation catalyst 3 and the filter 4, so that the fuel is more likely to adhere to the trap portion 5. For this reason, it becomes easy to raise temperature locally in the trap part 5, and Pt tends to evaporate.

On the other hand, by reducing the addition amount per time, it is possible to suppress the fuel from passing through the oxidation catalyst 3 and the filter 4. Note that if the amount of addition per one time is reduced, the heat generated in the oxidation catalyst 3 is reduced, and the filter 4 cannot be regenerated. For this reason, when reducing the addition amount per time, the frequency of fuel addition is also increased. That is, the amount of addition per one time is reduced, and the addition frequency is increased so that the heat generated in the oxidation catalyst 3 is not reduced. By doing in this way, regeneration of filter 4 can be implemented, suppressing a local temperature rise in trap part 5.

  For example, as the temperature of the trap unit 5 is higher, the addition amount per time may be decreased and the frequency of fuel addition may be increased. Moreover, when the temperature of the trap part 5 is higher than a threshold value, the addition amount per time may be decreased and the frequency of fuel addition may be increased as compared with the case where the temperature is lower than the threshold value. This threshold value is obtained in advance by experiments or the like as the temperature of the trap portion 5 at which Pt does not evaporate even if the addition amount per time is increased and the frequency of fuel addition is reduced.

  Here, the higher the average temperature inside the trap portion 5, the easier it is for Pt to evaporate when there is a local temperature rise. The average temperature inside the trap unit 5 may be the temperature of the entire trap unit 5. Further, the temperature of the exhaust gas downstream from the trap unit 5 may be used.

  FIG. 3 is a flowchart showing a flow of fuel addition control according to the present embodiment. This routine is executed every predetermined time by the ECU 10.

  In step S101, it is determined whether or not to add fuel from the fuel addition valve 7. In this step, it may be determined whether to regenerate the filter 4, warm up the oxidation catalyst 3, or warm up the SCR catalyst 6. If an affirmative determination is made in step S101, the process proceeds to step S102. On the other hand, if a negative determination is made, this routine is terminated.

  In step S102, the temperature of the oxidation catalyst 3 or the temperature of the filter 4 is detected. These temperatures are detected by the first temperature sensor 11. Note that these temperatures may be estimated based on the operating state of the internal combustion engine 1. When the process of step S102 is completed, the process proceeds to step S103.

  In step S103, the required fuel addition amount is calculated. This required fuel addition amount is a fuel addition amount required to raise the current temperature of the oxidation catalyst 3 or the filter 4 to the target temperature. This required fuel addition amount is calculated using a map based on the temperature of the oxidation catalyst 3 or the temperature of the filter 4 detected in step S102. This map is obtained in advance by experiments or the like and stored in the ECU 10. When the process of step S103 is completed, the process proceeds to step S104.

  In step S104, the temperature of the trap unit 5 is detected. This temperature is detected by the second temperature sensor 13.

  In step S105, the fuel addition amount per time is calculated. At this time, the fuel addition amount per time is calculated so that the fuel addition amount per time decreases as the temperature of the trap unit 5 detected in step S104 increases. This fuel addition amount per time is obtained from a map using the temperature of the trap section 5. This map is obtained in advance by experiments or the like and stored in the ECU 10. Then, the fuel addition frequency is calculated according to the fuel addition amount per one time. This fuel addition frequency is also obtained from the map. In these maps, the amount of fuel added per unit time is set so that heat necessary for regeneration of the filter 4 can be obtained. When the process of step S105 is completed, the process proceeds to step S106. In this embodiment, the ECU 10 that processes step S105 corresponds to the control device in the present invention.

In step S106, fuel is added from the fuel addition valve 7. When the process of step S106 is completed, this routine is terminated.

  Thus, since it can suppress that the temperature of the trap part 5 becomes high locally, it can suppress that Pt evaporates from the trap part 5. FIG. Thereby, it can suppress that Pt adheres to the SCR catalyst 6. FIG.

  In this embodiment, the ECU 10 may decrease the amount of fuel added per time and increase the frequency of fuel addition as the amount of Pt trapped in the trap unit 5 increases.

  That is, as the amount of Pt trapped in the trap portion 5 increases, more Pt may evaporate. In addition, as the amount of Pt trapped in the trap unit 5 increases, heat is more easily generated when the fuel reaches the trap unit 5, and thus the temperature is likely to rise. On the other hand, transpiration of Pt can be suppressed by increasing the frequency of fuel addition and decreasing the amount of fuel added per time.

  Note that the amount of Pt trapped in the trap unit 5 can be estimated using a well-known technique that is used, for example, for determining deterioration of the oxidation catalyst. That is, the amount of Pt trapped in the trap unit 5 can be estimated by detecting the oxidation ability in the trap unit 5. Further, the amount of Pt trapped in the trap unit 5 may be estimated based on the transition of the temperature of the oxidation catalyst 3. Furthermore, it is considered that the amount of Pt trapped in the trap unit 5 increases as the operating time of the internal combustion engine 1 or the travel distance of the vehicle increases, and these relationships may be obtained in advance by experiments or the like. . Then, the fuel addition amount per time calculated in step S105 is changed according to the amount of Pt trapped in the trap unit 5. Optimum values for the amount of Pt trapped in the trap unit 5 and the change amount or change rate of the fuel addition amount per time calculated in step S105 are obtained in advance through experiments or the like.

  Further, in the present embodiment, the ECU 10 reduces the amount of fuel added per time and increases the frequency of fuel addition when the temperature of the trap unit 5 is higher than the threshold value than when the temperature is below the threshold value. May be. Then, the ECU 10 may lower this threshold as the amount of Pt trapped in the trap unit 5 increases.

  The threshold value here can be arbitrarily set as the temperature of the trap unit 5 when the fuel addition amount per one time and the frequency of fuel addition are switched. The threshold value may be an upper limit value of the temperature at which Pt does not evaporate from the trap unit 5. The threshold value may be an upper limit value of the temperature that is within the allowable range even if Pt evaporates from the trap unit 5. And when the temperature of the trap part 5 is higher than a threshold value, transpiration of Pt from the trap part 5 can be suppressed by increasing the frequency of fuel addition and decreasing the fuel addition amount per time. However, as the amount of Pt trapped in the trap portion 5 increases, heat is more likely to be generated, and more Pt may evaporate. On the other hand, the greater the amount of Pt trapped in the trap unit 5, the lower the threshold value, thereby increasing the frequency of fuel addition at a lower temperature and reducing the amount of fuel added per time. Therefore, transpiration of Pt can be suppressed.

<Example 2>
In this embodiment, when fuel is added from the fuel addition valve 7, sub-injection (post-injection) in the internal combustion engine 1 is used together. Since other devices are the same as those in the first embodiment, the description thereof is omitted.

  Here, the post-injection is fuel injection performed in the cylinder of the internal combustion engine 1 and is performed during the expansion stroke or the exhaust stroke after the main injection. By performing the post-injection, it is possible to discharge a gas having a high temperature from the internal combustion engine 1 or to discharge unburned fuel that is easily reacted in the oxidation catalyst 3.

  By using this post injection together, the amount of fuel added from the fuel addition valve 7 can be reduced. That is, by discharging unburned fuel from the internal combustion engine 1, fuel can be supplied to the oxidation catalyst 3, so that the amount of fuel added from the fuel addition valve 7 can be reduced accordingly. Moreover, since the temperature of the oxidation catalyst 3 can be raised by discharging high temperature gas from the internal combustion engine 1, the amount of fuel added from the fuel addition valve 7 can be reduced accordingly. Then, the fuel discharged from the internal combustion engine 1 is more likely to react in the oxidation catalyst 3 than the fuel added from the fuel addition valve 7, and therefore is less likely to pass through the oxidation catalyst 3.

  Thus, by performing post-injection in the internal combustion engine 1, the amount of fuel added per time when fuel is added from the fuel addition valve 7 can be reduced, so that the oxidation catalyst 3 and the filter 4 can be reduced. The fuel passing through can be reduced. Thereby, since the local temperature rise of the trap part 5 can be suppressed, it can suppress more that Pt evaporates from the trap part 5. FIG. For example, the temperature of the oxidation catalyst 3 and the filter 4 is increased mainly by post injection, and when the temperature increase of the oxidation catalyst 3 or the filter 4 is insufficient only by the post injection, the insufficient temperature increase is compensated. The fuel may be added from the fuel addition valve 7.

  FIG. 4 is a flowchart showing a flow of fuel addition control according to the present embodiment. This routine is executed every predetermined time by the ECU 10. In addition, about the step in which the said float same process is made, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In this routine, when the process of step S104 is completed, the process proceeds to step S201. In step S201, the post injection amount is calculated. That is, the amount of fuel injected into the cylinder when post-injection is performed in the internal combustion engine 1 is calculated. The post injection amount may be a fixed value set in advance, may be a value obtained by multiplying the required fuel addition amount calculated in step S103 by a predetermined value, or may be a value that maximizes the post injection amount. Further, the post injection amount may be determined according to the operating state of the internal combustion engine 1 (for example, the engine speed and the engine load). These post-injection amounts are determined in advance by experiments and the like. When the process of step S201 is completed, the process proceeds to step S202.

  In step S202, a value obtained by subtracting the post-injection amount calculated in step S201 from the required fuel addition amount calculated in step S103 is set as a total fuel amount to be added from the fuel addition valve 7. From the total fuel amount, 1 Calculate the amount of fuel added per cycle. The frequency of fuel addition is calculated as the frequency of supplying fuel to the oxidation catalyst 3 from either post injection or fuel addition from the fuel addition valve 7. That is, if post injection and fuel addition from the fuel addition valve 7 overlap, the fuel supply amount per unit time to the oxidation catalyst 3 increases, so that they do not overlap. Then, when it is time to add fuel, either post injection or fuel addition from the fuel addition valve 7 is performed. A value obtained by adding the fuel amount supplied by the post injection and the fuel addition amount from the fuel addition valve 7 so that the post injection and the fuel addition from the fuel addition valve 7 overlap with each other is 1 Each fuel addition amount may be determined so as to be equal to the fuel addition amount per round. Then, when the process of step S202 is completed, the process proceeds to step S106. In this embodiment, the ECU 10 that processes step S202 corresponds to the control device in the present invention.

  As described above, according to the present embodiment, the post-injection can be used together to further reduce the fuel injection amount per one time from the fuel addition valve 7, so that the local area of the trap unit 5 can be reduced. Temperature rise can be further suppressed.

<Example 3>
In this embodiment, the amount of fuel added from the fuel addition valve 7 and the frequency of fuel addition are determined based on the flow rate or space velocity (SV) of the exhaust gas or the temperature of the oxidation catalyst 3. Since other devices are the same as those in the first embodiment, the description thereof is omitted.

  Here, the higher the temperature of the oxidation catalyst 3, the more HC passes through the oxidation catalyst 3. Further, the larger the SV of the exhaust gas in the oxidation catalyst 3 or the larger the flow rate of the exhaust gas passing through the oxidation catalyst 3, the greater the amount of HC that passes through the oxidation catalyst 3. Thus, the degree to which HC passes through the oxidation catalyst 3 varies depending on the temperature of the oxidation catalyst 3 and the exhaust gas flow rate or SV.

  On the other hand, in this embodiment, the fuel addition amount per one time and the frequency of fuel addition are adjusted according to the temperature of the oxidation catalyst 3, the flow rate of exhaust gas or SV.

  FIG. 5 is a flowchart showing a flow of fuel addition control according to the present embodiment. This routine is executed every predetermined time by the ECU 10. In addition, about the step in which the said float same process is made, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In this routine, when the process of step S104 is completed, the process proceeds to step S301. In step S301, the flow rate of the SV or the exhaust gas in the oxidation catalyst 3 is detected. For example, the intake air amount may be detected, and the SV or exhaust flow rate may be calculated based on the intake air amount. Further, since the flow rate of the SV or the exhaust gas changes depending on the operation state of the internal combustion engine 1 (for example, the engine speed and the engine load), the relationship between the operation state of the internal combustion engine 1 and the flow rate of the SV or the exhaust gas is tested in advance. For example, the map may be calculated and stored in the ECU 10, and the flow rate of the SV or the exhaust gas may be obtained using the map. Further, a sensor for detecting the flow rate of SV or exhaust may be attached to directly detect the flow rate of SV or exhaust. When the process of step S301 is completed, the process proceeds to step S302.

  In step S302, the fuel addition amount per one time and the frequency of fuel addition when fuel is added from the fuel addition valve 7 are calculated. In this step, the fuel addition amount per time set in step S105 is changed in accordance with the flow rate of SV or exhaust. Here, as the flow rate of SV or exhaust becomes larger, the fuel easily passes through, so the amount of fuel added per time is reduced. Note that when the SV or exhaust flow rate is equal to or greater than the threshold value, the amount of fuel added per time may be less than when the flow rate is less than the threshold value. The relationship between the flow rate of the SV or exhaust and the change amount or change rate of the fuel addition amount per time is obtained in advance by experiments or the like and stored in the ECU 10. When the fuel addition amount per time is calculated, the frequency of fuel addition is determined accordingly. When the process of step S302 is completed, the process proceeds to step S106.

  In step S302, as the temperature of the oxidation catalyst 3 is higher, the amount of fuel added per time may be reduced and the frequency of fuel addition may be increased. At this time, the fuel addition amount per time set in step S105 is changed according to the temperature of the oxidation catalyst 3. Further, when the temperature of the oxidation catalyst 3 is equal to or higher than the threshold value, the amount of fuel added per time may be less than when the temperature is lower than the threshold value. The relationship between the temperature of the oxidation catalyst 3 and the amount of change or rate of change of the amount of fuel added per time may be obtained in advance through experiments or the like and mapped and stored in the ECU 10. In step S302, the fuel addition amount per time set in step S105 may be changed based on any one of the exhaust gas flow rate or SV, or the temperature of the oxidation catalyst 3. It may be changed based on one of the flow rate or SV and the temperature of the oxidation catalyst 3. In this embodiment, the ECU 10 that processes step S302 corresponds to the control device in the present invention.

In this way, since the fuel flowing out from the oxidation catalyst 3 can be further reduced, the local temperature rise in the trap portion 5 can be further suppressed.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Exhaust passage 3 Oxidation catalyst 4 Filter 5 Trap part 6 Selective reduction type NOx catalyst (SCR catalyst)
7 Fuel addition valve 8 Ammonia addition valve 9 In-cylinder injection valve 10 ECU
11 First temperature sensor 12 Air-fuel ratio sensor 13 Second temperature sensor

Claims (6)

A catalyst provided in the exhaust passage of the internal combustion engine and having an oxidizing ability;
A selective reduction type NOx catalyst provided in an exhaust passage downstream of the catalyst having the oxidation ability;
A trap portion that is provided in an exhaust passage downstream of the catalyst having oxidation ability and upstream of the selective reduction NOx catalyst, and traps a substance that increases the oxidation ability of the selective reduction NOx catalyst;
Supply means for supplying fuel to the catalyst having oxidation ability;
An exhaust gas purification apparatus for an internal combustion engine comprising:
When supplying fuel from the supply means to the catalyst having oxidation ability, the higher the temperature of the trap section, the lower the amount of fuel supplied per time and the higher the frequency of supplying fuel An exhaust emission control device for an internal combustion engine comprising the device.   The controller increases the amount of fuel supplied per time when the fuel is supplied from the supply means, as the amount of the substance that increases the oxidation ability of the selective reduction type NOx catalyst trapped in the trap portion is larger. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the frequency is reduced and the frequency of supplying fuel is increased. When the temperature of the trap unit is higher than a threshold value, the control device reduces the amount of fuel supplied per time when supplying fuel from the supply means and lowers the fuel than when the temperature is lower than the threshold value. Increase the frequency of supply,
2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the control device lowers the threshold value as the amount of a substance that increases the oxidation capability of the selective reduction type NOx catalyst trapped in the trap unit increases.   The supply means performs sub-injection in addition to main injection in the internal combustion engine, thereby discharging unburned fuel from the internal combustion engine to supply fuel to the catalyst having the oxidation ability, and supplying fuel into the exhaust gas. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3, further comprising a fuel addition valve to be added and supplying fuel from the fuel addition valve to the catalyst having the oxidation ability.   The control device determines a fuel supply amount per one time and a fuel supply frequency when fuel is supplied from the supply means according to a flow rate of exhaust gas passing through the catalyst having the oxidation ability. 5. An exhaust emission control device for an internal combustion engine according to any one of 1 to 4.   6. The control device according to claim 1, wherein the control device determines a fuel supply amount per one time and a fuel supply frequency when fuel is supplied from the supply means according to a temperature of the catalyst having the oxidation ability. The exhaust emission control device for an internal combustion engine according to any one of the preceding claims.

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