JP5062069B2 - 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.

As a technique for raising the temperature of a catalyst provided in an exhaust system of an internal combustion engine, unburned fuel (hydrocarbon, hereinafter referred to as HC) is supplied to the catalyst by adding fuel to the exhaust system or performing sub-injection, and HC is oxidized in the catalyst. There is a technology that uses reaction heat at the time of reaction. Here, when the catalyst temperature is so low that it is difficult for HC to undergo an oxidation reaction, even if HC is supplied to the catalyst, an effect of raising the temperature of the catalyst due to the heat of oxidation reaction of HC is not obtained, but also the unreacted HC passes through the catalyst and is discharged into the atmosphere in the form of white smoke. On the other hand, when the catalyst temperature is so low that it is difficult to oxidize HC, a technique is proposed in which HC is not supplied to the catalyst (Patent Document 1).
JP 2006-274907 A JP 2001-164928 A JP 2004-346877 A JP 2003-172185 A

  In this prior art, when the catalyst temperature is so low that it is difficult to oxidize HC, the temperature raising process of the catalyst cannot be performed. For this reason, there is a problem that it is not possible to start control that requires prior catalyst temperature raising processing, such as regeneration processing of a filter that collects PM and sulfur poisoning recovery processing of the NOx storage reduction catalyst.

  Further, a large amount of HC needs to be supplied to the catalyst during the regeneration process of the filter and the sulfur poisoning recovery process of the NOx catalyst. Here, in order for HC supplied to the catalyst to react, HC needs to be adsorbed on the active site of the catalyst and vaporized. However, when a large amount of HC is supplied to the catalyst, the rate at which new HC is supplied exceeds the progress rate of the HC adsorption and vaporization process, and the active sites of the catalyst are covered with unreacted HC. There is. As a result, even when the catalyst temperature is high enough to oxidize HC, the activity of the catalyst is lost, the oxidation reaction of HC does not progress, and the filter regeneration process and the sulfur poisoning recovery process may not be performed properly. there were.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a technique that enables the temperature of a catalyst to be increased even when the catalyst temperature is low as HC is difficult to oxidize. It is another object of the present invention to provide a technique capable of suppressing the loss of catalyst activity during the execution of filter regeneration processing and sulfur poisoning recovery processing.

In order to achieve the above object, an exhaust emission control device for an internal combustion engine of the present invention comprises:
A catalyst having oxidation ability disposed in the exhaust passage of the internal combustion engine;
HC supply means for supplying HC into the exhaust gas flowing into the catalyst;
CO supply means for supplying CO into the exhaust gas flowing into the catalyst;
Temperature acquisition means for acquiring the temperature of the catalyst;
Catalyst temperature increase control means for performing catalyst temperature increase control for increasing the temperature of the catalyst by supplying HC by the HC supply means and / or supplying CO by the CO supply means;
With
When the catalyst temperature increase control execution condition is satisfied, the catalyst temperature increase control means
When the temperature of the catalyst is lower than a predetermined first reference temperature, the catalyst temperature increase control is not executed,
When the temperature of the catalyst is equal to or higher than the first reference temperature and lower than a predetermined second reference temperature, the catalyst temperature increase control is executed by supplying CO by the CO supply means,
When the temperature of the catalyst is equal to or higher than the second reference temperature and lower than a predetermined third reference temperature, the catalyst temperature increase control is performed by supplying CO by the CO supply means and supplying HC by the HC supply means. Run,
When the temperature of the catalyst is equal to or higher than the third reference temperature, the catalyst temperature increase control is executed by supplying HC by the HC supply means.

  The present invention has been made paying attention to the fact that the temperature at which CO can be oxidized in the catalyst is lower than the temperature at which HC can be oxidized in the catalyst. The temperature at which CO can undergo an oxidation reaction and the temperature at which HC can undergo an oxidation reaction vary depending on the air-fuel ratio of the exhaust, the flow rate of the exhaust, the operating state of the internal combustion engine, etc. It is about 50 ° C. lower than the reaction temperature. Therefore, even when the catalyst temperature is so low that it is difficult for HC to undergo an oxidation reaction, the oxidation reaction of CO may be possible. In such a case, by supplying CO to the catalyst, the CO can be oxidized in the catalyst, and the temperature of the catalyst can be raised by the reaction heat.

  In the present invention, the first reference temperature is a temperature determined based on the lower limit value of the temperature at which the catalyst can be heated by the heat of CO oxidation reaction in the catalyst. The first reference temperature depends on various conditions such as the possibility of CO oxidation reaction in the catalyst, the removal of heat by exhaust passing through the catalyst, the air-fuel ratio of exhaust flowing into the catalyst, the flow rate of exhaust, and the operating conditions of the internal combustion engine. Can be determined based on. The first reference temperature may vary depending on such various conditions, but is approximately 150 ° C.

  When the temperature of the catalyst is lower than the first reference temperature, it is difficult to raise the temperature of the catalyst by the heat of oxidation reaction of CO or the heat of oxidation reaction of HC. Temperature increase control is not executed. In the case where the temperature of the catalyst can be raised by other means, it is not hindered to raise the temperature of the catalyst using that, but at least the supply of CO by the CO supply means or the supply of HC by the HC supply means The temperature of the catalyst is not increased.

  When CO is supplied to the catalyst when the catalyst temperature is so low that the reaction of CO is difficult, the CO is supplied as a gas to the catalyst, so that the supplied CO passes through the catalyst and is discharged to the atmosphere as it is. Since CO has toxicity, it is preferable to suppress emission to the atmosphere as much as possible. According to the present invention, when the catalyst temperature is so low that the oxidation reaction of CO is difficult, neither CO nor HC is supplied. Therefore, toxic CO and unburned HC white smoke are discharged to the atmosphere. Can be suppressed.

  In the present invention, the second reference temperature is a temperature of the catalyst determined based on a lower limit value of a temperature at which HC can undergo an oxidation reaction in the catalyst. The second reference temperature is determined based on various conditions such as the air-fuel ratio of the exhaust, the flow rate of the exhaust, and the operating conditions of the internal combustion engine. The second reference temperature may vary depending on such various conditions, but is approximately 50 ° C. higher than the temperature at which CO can be oxidized in the catalyst, and is approximately 200 ° C. or so.

When the temperature of the catalyst is equal to or higher than the first reference temperature and lower than the second reference temperature, the temperature of the catalyst can be raised by the heat of the oxidation reaction of CO, but the oxidation reaction of HC in the catalyst is difficult. The catalyst temperature increase control is performed by supplying CO to the catalyst. Thus, even when the catalyst is at a low temperature so that the oxidation reaction of HC is difficult, the temperature of the catalyst can be raised by supplying CO. Therefore, it is possible to perform processing requiring a prior catalyst temperature rise, such as filter regeneration processing and sulfur poisoning recovery processing of the NOx catalyst, under a wider range of operating conditions.

  In the present invention, the third reference temperature is a temperature of the catalyst determined based on a lower limit value of the temperature at which the catalyst can be heated by the heat of HC oxidation reaction in the catalyst. The third reference temperature is the amount of HC supplied to the catalyst, the supply speed, the vaporization rate of HC adsorbed on the catalyst, and various factors that affect them, such as the air-fuel ratio of exhaust, the flow rate of exhaust, the operating conditions of the internal combustion engine It can be determined based on various conditions such as. The third reference temperature may vary depending on such various conditions, but is generally a temperature of 300 ° C to 330 ° C.

  When the temperature of the catalyst is equal to or higher than the second reference temperature and lower than the third reference temperature, both CO and HC can be oxidized in the catalyst. However, if the temperature of the catalyst is increased only by supplying HC, as described above, Depending on conditions such as HC vaporization rate, HC supply rate, HC supply amount, exhaust flow rate, exhaust air-fuel ratio, operating conditions of internal combustion engine, etc., there is a possibility of catalyst poisoning and deactivation by unreacted HC . Therefore, in such a temperature condition, the temperature of the catalyst is raised using both the heat of oxidation reaction of CO and the heat of oxidation reaction of HC. As a result, it is possible to suitably raise the temperature of the catalyst while suppressing the deactivation of the catalyst due to mass adsorption of unreacted HC.

  Under this temperature condition, the amount of CO and the amount of HC supplied to the catalyst may be fixed to a constant value, or may be changed according to the temperature of the catalyst. For example, the higher the temperature of the catalyst, the higher the HC vaporization rate. Therefore, the higher the temperature of the catalyst, the higher the supply amount of HC. At this time, the supply amount of CO may be decreased as the supply amount of HC increases, or the supply of a predetermined amount of CO may be continued until the third reference temperature is reached. The method of changing the supply amount of HC and the supply amount of CO may be continuous or stepwise. Since the exhaust gas flow rate is also related to the HC vaporization speed, the CO supply amount and the HC supply amount may be changed in consideration of the intake air amount and the engine speed.

  When the temperature of the catalyst is equal to or higher than the third reference temperature, it is possible to raise the temperature of the catalyst by both supply of HC and supply of CO, but it may be difficult to supply a large amount of CO to the catalyst. . In order to supply more CO to the catalyst, as described above, it is necessary to increase the ratio of incomplete combustion by intake throttle or EGR gas introduction, or to increase the fuel injection amount to lower the air-fuel ratio. If the required CO supply amount increases, problems such as an increase in the amount of PM generated, oil dilution, and fuel consumption deterioration may occur. When the temperature of the catalyst is raised by supplying CO, there is a merit that the lower limit of the catalyst temperature at which the temperature of the catalyst can be raised is lower than that when raising the temperature of the catalyst by supplying HC. In the present invention, when the temperature of the catalyst is equal to or higher than the third reference temperature, the temperature of the catalyst is increased by supplying HC. This makes it possible to raise the temperature of the catalyst while suppressing the occurrence of problems such as an increase in the amount of PM generated, oil dilution, and deterioration in fuel consumption.

  According to the present invention, when the catalyst temperature is so low that the HC oxidation reaction is difficult, the temperature of the catalyst is raised mainly by supplying CO, and when the catalyst temperature is high enough to enable the HC oxidation reaction, HC is supplied. Thus, it is possible to suitably raise the temperature of the catalyst under a wider range of operating conditions by controlling the temperature of the catalyst to raise the temperature of the catalyst. Therefore, processes that require the filter and NOx catalyst to be heated to a high target temperature in advance, such as filter regeneration and sulfur poisoning recovery of the NOx storage reduction catalyst, can be performed under a wider range of operating conditions. It becomes possible to implement in.

By the way, when HC undergoes an oxidation reaction in the catalyst, the supplied HC is adsorbed on the active site of the catalyst and then vaporizes, so that the reaction rate of HC in the catalyst is slower than the reaction rate of CO. Therefore, even if the catalyst temperature is high enough to allow HC oxidation reaction, if a large amount of HC is supplied to the catalyst in a short time exceeding the rate of HC oxidation reaction supplied to the catalyst, unreacted There is a possibility that a large amount of HC is adsorbed on the active site of the catalyst, the catalyst is poisoned by HC, and the activity of the catalyst is lost. In that case, since the oxidation reaction of HC in the catalyst does not proceed appropriately, the catalyst temperature may be lowered.

  In this way, when performing catalyst temperature control that requires supplying a large amount of HC, it is possible to select whether to supply HC or CO to the catalyst according to only the catalyst temperature. It is not sufficient to efficiently raise the temperature of the catalyst to the target temperature or to suitably maintain the temperature of the raised catalyst at the target temperature.

Accordingly, an exhaust emission control device for an internal combustion engine according to the present invention is:
A catalyst having oxidation ability disposed in the exhaust passage of the internal combustion engine;
HC supply means for supplying HC into the exhaust gas flowing into the catalyst;
CO supply means for supplying CO into the exhaust gas flowing into the catalyst;
Temperature acquisition means for acquiring the temperature of the catalyst;
Catalyst temperature control means for performing catalyst temperature control for controlling the temperature of the catalyst to a predetermined target temperature by supply of HC by the HC supply means and / or supply of CO by the CO supply means,
The catalyst temperature control means adjusts the supply amount of HC by the HC supply means and the supply amount of CO by the CO supply means according to the difference between the temperature of the catalyst acquired by the temperature acquisition means and the target temperature. It is characterized by controlling.

  According to this invention, the supply amount of HC and the supply amount of CO to the catalyst in the catalyst temperature control are controlled according to the difference between the actual catalyst temperature and the target temperature. For example, when performing catalyst temperature control for maintaining the catalyst temperature at a certain target temperature, the CO supply amount and the HC supply amount can be controlled in accordance with the magnitude of the temperature difference between the target temperature and the catalyst temperature. Thereby, the deviation of the catalyst temperature from the target temperature can be detected, and based on this, the active state of the catalyst can be determined, and if necessary, the temperature of the catalyst can be raised or the deactivated state can be eliminated by supplying CO.

  In addition, when performing catalyst temperature control in which the catalyst temperature is raised toward a certain target temperature, the supply amount of CO and the supply amount of HC may be controlled according to the changing tendency of the temperature difference between the target temperature and the catalyst temperature. it can. When the catalyst temperature is raised toward the target temperature, the temperature difference is reduced if the catalyst is activated, but when the catalyst is deactivated, the rate of change (decrease rate) of the temperature difference is large. Since it becomes smaller and the change speed of the temperature difference becomes positive (changes in the direction in which the temperature difference widens), this is detected, and if necessary, the temperature rise or deactivation of the catalyst by supplying CO is eliminated. It can be performed.

  As described above, since CO flows into the catalyst in the state of gas molecules, there is no need to go through the process of adsorption and vaporization on the catalyst as in HC, and it immediately oxidizes when it reaches the active point of the catalyst. . Therefore, the temperature of the catalyst can be raised with good responsiveness. As a result, the catalyst temperature can be prevented from greatly deviating from the target temperature, and the catalyst temperature can be quickly returned to the target temperature even when the catalyst temperature deviates from the target temperature. Further, when the temperature of the catalyst is raised, even when the catalyst temperature does not rise favorably or the catalyst temperature starts to fall, it can be quickly and suitably returned to the state where the catalyst temperature rises.

Here, the amount of CO supplied by the CO supply means may be increased as the temperature difference between the catalyst temperature and the target temperature increases. By doing so, even when the difference between the catalyst temperature and the target temperature is large, the catalyst temperature can be matched with the target temperature at an early stage. In this case, the supply amount of CO may be continuously changed with respect to the temperature difference between the catalyst temperature and the target temperature, or may be changed stepwise.

  Further, the supply of CO by the CO supply means may be started on the condition that the temperature difference between the catalyst temperature and the target temperature has become larger than a predetermined first reference value. In this case, the supply of CO by the CO supply means is stopped on the condition that the temperature difference between the catalyst temperature and the target temperature is reduced as the CO supply starts and the temperature difference becomes smaller than a predetermined second reference value. Anyway. For example, the supply of CO may be continued after the start of the supply of CO by the CO supply means until the temperature difference becomes small enough to determine that the catalyst temperature substantially matches the target temperature. At this time, the CO supply amount by the CO supply means may be a constant amount, or the CO supply amount may be reduced in accordance with the reduction of the temperature difference.

  Further, when the supply of CO by the CO supply unit is started, the supply amount of HC by the HC supply unit may be adjusted according to the supply amount of CO. For example, the supply amount of HC may be the same before and after the supply of CO, or the supply amount of HC may be reduced as the supply amount of CO increases. Alternatively, the supply of HC by the HC supply unit may be stopped when CO is supplied by the CO supply unit.

  According to the present invention, even when the catalyst temperature is high enough to oxidize HC (for example, higher than the third reference temperature described above), if there is a difference between the catalyst temperature and the target temperature, CO is supplied by the CO supply means. Therefore, in the catalyst temperature control that requires supplying a large amount of reducing agent, even when the catalyst is deactivated by supplying a large amount of HC, it is possible to suppress the rapid recovery of the active state of the catalyst. Further, even when the catalyst is deactivated, the activated state can be recovered early, and the catalyst temperature can be matched with the target temperature.

  The present invention makes it possible to raise the temperature of the catalyst even when the catalyst temperature is so low that HC is difficult to oxidize. In addition, during the execution of control that increases the temperature of the catalyst, control that maintains the catalyst temperature at the target temperature, or control that requires supply of a large amount of reducing agent, such as filter regeneration processing or sulfur poisoning recovery processing, Inactivation can be suppressed.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  FIG. 1 is a conceptual diagram schematically showing the schematic configuration of an internal combustion engine to which the exhaust gas purification apparatus for an internal combustion engine according to this embodiment is applied, and its intake system and exhaust system. The internal combustion engine 1 is a diesel engine having four cylinders 49. Each cylinder 49 is provided with an injector 29 for injecting and supplying fuel into the cylinder. Each cylinder 49 communicates with the intake manifold 17 via an intake port (not shown). An intake passage 42 is connected to the intake manifold 17. Each cylinder 49 communicates with the exhaust manifold 18 through an exhaust port (not shown). An exhaust passage 43 is connected to the exhaust manifold 18. The exhaust manifold 18 is provided with a fuel addition valve 19 that adds fuel to the exhaust.

The exhaust passage 43 and the intake passage 42 communicate with each other through the EGR passage 15. A part of the exhaust gas from the internal combustion engine 1 flows into the intake passage 42 as EGR gas via the EGR passage 15. An EGR valve 14 that adjusts the amount of EGR gas is disposed in the EGR passage 15. The intake passage 42 has an intake throttle valve 22 for adjusting the intake air amount and an air flow meter 7 for measuring the intake air amount.
Is provided. The exhaust passage 43 is provided with a NOx storage reduction catalyst 41. The NOx catalyst 41 occludes NOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean, and releases NOx when the air-fuel ratio of the inflowing exhaust is stoichiometric or rich. Then, if there is a reducing agent around the NOx catalyst to reduce and purify the released was NOx to N _2. The NOx catalyst 41 of this embodiment corresponds to the catalyst in the present invention. An exhaust gas temperature sensor 50 that measures the temperature of the exhaust gas flowing out from the NOx catalyst 41 is provided in the exhaust passage 43 on the downstream side of the NOx catalyst 41.

  The internal combustion engine 1 is provided with an ECU 26 that is a computer that controls the operation of the internal combustion engine 1. In addition to the air flow meter 7 and the exhaust gas temperature sensor 50, sensors such as a crank angle sensor and an accelerator opening sensor are connected to the ECU 26, and measurement data of each sensor is input. The ECU 26 is connected to an injector 29, a fuel addition valve 19, an intake throttle valve 22, an EGR valve 14 and other devices, and a control signal for controlling the operation of each device is output from the ECU 26.

  The NOx catalyst 41 also stores SOx in the exhaust gas, and the NOx purification capacity decreases as the SOx storage amount increases. Therefore, it is necessary to recover the NOx purification ability of the NOx catalyst 41 by periodically performing a sulfur poisoning recovery process for desorbing the SOx stored in the NOx catalyst 41 from the NOx catalyst 41.

  In the sulfur poisoning recovery process, the temperature of the NOx catalyst 41 is first raised to a temperature equal to or higher than a predetermined target temperature, and then the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 41 is maintained while maintaining the temperature of the NOx catalyst 41 at the target temperature. By enriching, the SOx stored in the NOx catalyst 41 is desorbed from the NOx catalyst 41. Here, the target temperature is a temperature (around 700 ° C.) determined based on the lower limit value of the catalyst temperature at which SOx can be desorbed from the NOx catalyst 41, and the NOx catalyst 41 reaches a temperature significantly higher than the exhaust temperature. It is necessary to raise the temperature.

  The temperature of the NOx catalyst 41 can be increased by supplying HC as a reducing agent from the upstream side of the NOx catalyst 41. In the present embodiment, as means for supplying HC to the NOx catalyst 41, fuel is added to the exhaust gas by the fuel addition valve 19, or at a relatively late time (for example, 100 ° ATDC) after compression top dead center by the injector 29. Post-injection with sub-injection of a small amount of fuel. The HC supplied to the NOx catalyst 41 in this way undergoes an oxidation reaction in the NOx catalyst 41, and the temperature of the NOx catalyst 41 rises due to the reaction heat generated at that time. In this embodiment, the fuel addition valve 19 or the injector 29 that performs post injection corresponds to the HC supply means in the present invention.

  The temperature rise of the NOx catalyst 41 can also be performed by supplying CO as a reducing agent from the upstream side of the NOx catalyst 41. As a means for supplying CO to the NOx catalyst 41, in this embodiment, after-injection, exhaust top dead, in which a small amount of fuel is sub-injected by the injector 29 at a relatively early time after compression top dead center (eg, 40 ° ATDC). Vibra rubber injection that sub-injects a small amount of fuel in the vicinity of the point, low-temperature combustion realized by opening the EGR valve 14 and introducing a large amount of EGR gas, and reducing the intake air amount by restricting the intake throttle valve 22 Then, the air-fuel ratio is enriched by increasing the fuel injection amount. The CO supplied to the NOx catalyst 41 in this way undergoes an oxidation reaction in the NOx catalyst 41, and the temperature of the NOx catalyst 41 rises due to the reaction heat generated at that time. In this embodiment, an injector 29 that performs after-injection, an injector 29 that performs bi-rubber injection, an ECU 26 that performs low-temperature combustion control by opening the EGR valve 14, an ECU 26 that performs intake air amount reduction control by restricting the intake throttle valve 22, The ECU 26 that performs air-fuel ratio enrichment control corresponds to the CO supply means in the present invention.

When the catalyst temperature of the NOx catalyst 41 is raised to a target temperature or higher, the NOx catalyst 41
While maintaining the catalyst temperature at the target temperature, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 41 is enriched. As a result, the SOx stored in the NOx catalyst 41 is desorbed from the NOx catalyst 41. In this embodiment, by supplying HC and / or CO as a reducing agent from the upstream side of the NOx catalyst 41, the temperature of the NOx catalyst 41 is maintained and the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 41 is enriched. Thus, the SOx desorption process is performed.

  Here, when HC undergoes an oxidation reaction in the NOx catalyst 41, a process in which HC is first adsorbed to the active point of the oxidation reaction of the NOx catalyst 41, the adsorbed HC is vaporized, and the vaporized HC undergoes an oxidation reaction. It passes. For this reason, the rate of the oxidation reaction of HC in the NOx catalyst 41 is relatively slow, and this tendency is particularly remarkable in a low temperature state where HC is hard to vaporize. In addition, since there is a delay from the time when HC is adsorbed to the active point until the active point is released by the oxidation reaction, the supply rate of HC to the NOx catalyst 41 is high or a large amount of HC is supplied. In some cases, the active point of the oxidation reaction of the NOx catalyst 41 is covered by the adsorption of unreacted HC, and the NOx catalyst 41 is deactivated. Even when the temperature of the NOx catalyst 41 is sufficiently high so that HC can undergo an oxidation reaction, the NOx catalyst 41 may be deactivated in this manner depending on the supply speed and supply amount of HC. On the contrary, when the temperature of the NOx catalyst 41 is not high enough to oxidize HC, the HC supplied to the NOx catalyst 41 is adsorbed by the NOx catalyst 41, and a large amount of unreacted HC enters the atmosphere. There is little risk of being discharged.

  On the other hand, when CO undergoes an oxidation reaction in the NOx catalyst 41, since CO is supplied to the NOx catalyst 41 in a gaseous state, the oxidation reaction occurs immediately when CO arrives at the active point of the oxidation reaction of the NOx catalyst 41. To do. For this reason, the rate of the oxidation reaction of CO in the NOx catalyst 41 is relatively fast, and even if the NOx catalyst 41 is at a low temperature so that the oxidation reaction of HC is difficult, the CO may be capable of an oxidation reaction. The temperature at which CO can be oxidized in the NOx catalyst 41 is approximately 50 ° C. lower than the temperature at which HC can be oxidized in the NOx catalyst 41. Further, since the active sites of the oxidation reaction of the NOx catalyst 41 are not covered as in the case of HC, there is little possibility that the NOx catalyst 41 is deactivated by supplying a large amount of CO. On the other hand, when the temperature of the NOx catalyst 41 is not high enough for CO to undergo an oxidation reaction, the CO supplied to the NOx catalyst 41 passes through the NOx catalyst 41 as it is without reacting with the NOx catalyst 41 and enters the atmosphere. Discharged. In this case, the emission of toxic CO increases, which is not preferable.

  In the sulfur poisoning recovery process of this embodiment, paying attention to the difference in properties as described above when HC or CO undergoes an oxidation reaction in the NOx catalyst 41, the temperature increase control of the NOx catalyst 41 and the NOx catalyst after the temperature increase are performed. The exhaust gas flowing into the engine 41 is controlled to be enriched. Hereinafter, the sulfur poisoning recovery process of the present embodiment will be described. FIG. 2 is a flowchart showing a temperature increase control routine of the NOx catalyst 41 in the sulfur poisoning recovery process of this embodiment. This routine is periodically executed by the ECU 26 during operation of the internal combustion engine 1.

  In step S101, the ECU 26 determines whether or not an execution condition for the sulfur poisoning recovery process is satisfied. In the present embodiment, when the integrated value of the fuel injection amount from the previous execution of the sulfur poisoning recovery process exceeds a predetermined reference value, it is determined that the execution condition for the sulfur poisoning recovery process is satisfied. If it is determined in step S101 that the execution condition for the sulfur poisoning recovery process is satisfied (Yes), the ECU 26 proceeds to step S102. If it is determined in step S101 that the execution condition for the sulfur poisoning recovery process is not satisfied (No), the ECU 26 once exits this routine.

In step S102, the ECU 26 acquires the catalyst temperature Tcat of the NOx catalyst 41. In this embodiment, the catalyst temperature of the NOx catalyst 41 is estimated based on the output gas temperature of the NOx catalyst 41 measured by the exhaust temperature sensor 50. In this embodiment, the ECU 26 that executes step S102 to acquire the catalyst temperature Tcat corresponds to the temperature acquisition means in the present invention.

  In step S103 to step S106, the ECU 26 compares the catalyst temperature Tcat acquired in step S102 with a predetermined reference temperature, and performs temperature increase control of the NOx catalyst 41 based on the comparison result. In this embodiment, three reference temperatures, ie, a first reference temperature T1, a second reference temperature T2, and a third reference temperature T3, are defined as the reference temperatures.

  The first reference temperature T1 is determined based on the lower limit value of the catalyst temperature at which the NOx catalyst 41 can be heated by supplying CO to the NOx catalyst 41. As the first reference temperature, a temperature at which CO can be oxidized in the NOx catalyst 41 can be used. However, even if the NOx catalyst 41 can perform the CO oxidation reaction itself, the NOx catalyst 41 is raised by the reaction heat. Whether or not the temperature can be increased is considered to be affected by the removal of heat caused by the exhaust gas passing through the NOx catalyst 41. Therefore, in the present embodiment, the first reference temperature is determined as a variable value corresponding to the exhaust gas flow rate, the exhaust air-fuel ratio, and the operating state of the internal combustion engine 1. The first reference temperature T1 is a temperature around 150 ° C.

  The second reference temperature T2 is determined based on the lower limit value of the catalyst temperature at which HC can oxidize in the NOx catalyst 41. Since the HC oxidation reaction in the NOx catalyst 41 includes the HC adsorption and vaporization process as described above, the second reference temperature is also the first, for example, the HC is more easily vaporized when the flow rate of the exhaust gas is larger. As with the reference temperature, the variable value is determined according to various conditions. The second reference temperature T2 is approximately 50 ° C. higher than the first reference temperature T1, and is a temperature around 200 ° C.

  The third reference temperature T3 is determined based on the lower limit value of the catalyst temperature at which the NOx catalyst 41 can be heated by supplying HC to the NOx catalyst 41. As described above, even if the temperature of the NOx catalyst 41 is so high that HC can undergo an oxidation reaction, a large amount of HC is supplied, or the HC adsorption / vaporization / oxidation process speed catches up with the HC supply speed. If not, the active point of the NOx catalyst 41 is poisoned by unreacted HC, and the NOx catalyst 41 may be deactivated. In such a case, it is difficult to suitably raise the temperature of the NOx catalyst 41 by supplying only HC. In consideration of such circumstances, in this embodiment, the third reference temperature is set to a temperature higher than the second reference temperature. The third reference temperature T3 is about 300 to 330 ° C.

In step S103, when the catalyst temperature Tcat is lower than the first reference temperature T1 (Tcat <T1), the ECU 26 temporarily exits from the execution of this routine. That is, in this case, the temperature increase control of the NOx catalyst 41 is not performed, and therefore the sulfur poisoning recovery process is temporarily stopped at this point. When the catalyst temperature is lower than the first reference temperature, the CO oxidation reaction does not proceed favorably in the NOx catalyst 41. As described above, supplying CO to the NOx catalyst 41 under such temperature conditions is not preferable because unreacted CO may pass through the NOx catalyst 41 and be released to the atmosphere as it is. Therefore, the temperature of the catalyst is not increased by at least CO supply or HC supply. As a result, it is possible to avoid a situation in which emissions are deteriorated due to the supply of CO in a low temperature state where neither a temperature increase due to CO nor a temperature increase due to HC can be expected. In this embodiment, neither the catalyst temperature rise nor the sulfur poisoning recovery process is performed in this case, but this means that the catalyst temperature rise by the supply of CO or the supply of HC is not performed. If a means for raising the temperature of the catalyst 41 is provided, it does not prevent the temperature of the catalyst from being raised by that means. In that case, the NOx catalyst 41 may be heated to the target temperature by the temperature raising means, and the sulfur poisoning recovery process may be continued. Even if the routine once exits from this routine, this routine is repeatedly executed periodically. If the catalyst temperature Tcat becomes equal to or higher than the first reference temperature, for example, when the internal combustion engine 1 is operated at a high load, the temperature increase control in steps S104 to S106 is executed.

  In step S103, if the catalyst temperature Tcat is equal to or higher than the first reference temperature T1 and lower than the second reference temperature T2 (T1 ≦ Tcat <T2), the ECU 26 proceeds to step S104 and supplies NOx to the NOx catalyst 41 by supplying CO. The catalyst 41 is heated. In this temperature region, it is possible to raise the temperature of the NOx catalyst 41 by the heat of oxidation reaction of CO, but since the oxidation reaction of HC is difficult, the temperature of the catalyst is raised by supplying only CO. As a result, even when the NOx catalyst 41 is so cold that the HC oxidation reaction is difficult, the temperature of the catalyst can be raised by supplying CO. After executing step S104, the ECU 26 returns to step S102.

  In step S102, when the catalyst temperature Tcat is equal to or higher than the second reference temperature T2 and lower than the third reference temperature T3 (T2 ≦ Tcat <T3), the ECU 26 proceeds to step S105 and supplies CO and HC to the NOx catalyst 41. To raise the temperature of the NOx catalyst 41. In this temperature range, both CO and HC can be oxidized in the NOx catalyst 41. However, if the temperature of the catalyst is increased only by supplying HC, as described above, the HC vaporization rate, HC supply rate, HC Depending on the supply amount, exhaust flow rate, exhaust air-fuel ratio, operating conditions of the internal combustion engine 1, etc., there is a possibility that the NOx catalyst 41 is poisoned and deactivated by unreacted HC. If the supply rate of HC is slowed, it is not impossible to raise the temperature of the NOx catalyst 41 by supplying only HC and preventing the NOx catalyst 41 from being deactivated. Since it is preferable to complete the temperature increase of the NOx catalyst 41 in the sulfur poisoning recovery process as early as possible, in this embodiment, the temperature of the NOx catalyst 41 is increased by using both CO and HC in this temperature range. . Thereby, the temperature of the NOx catalyst 41 can be rapidly raised while suppressing the deactivation of the NOx catalyst 41. In step S105, the amount of CO and the amount of HC supplied to the NOx catalyst 41 or the ratio of CO and HC in the total amount of reducing components to be supplied to the NOx catalyst 41 may be a certain constant value. It is good also as a variable value according to the temperature of the NOx catalyst 41. For example, as the temperature of the NOx catalyst 41 increases, the CO supply amount may be reduced and the HC supply amount may be increased. In this case, how to change the supply amount of CO and HC may be continuous with respect to the temperature of the NOx catalyst 41 or may be stepwise. Further, the CO supply amount may be maintained while increasing the HC supply amount as the temperature of the NOx catalyst 41 rises. After executing step S105, the ECU 26 returns to step S102.

  In step S103, when the catalyst temperature Tcat is equal to or higher than the third reference temperature T3 and lower than the target temperature Ttrg (T3 ≦ Tcat <Ttrg), the ECU 26 proceeds to step S106 and supplies the HC to the NOx catalyst 41, thereby supplying the NOx catalyst 41. The temperature is increased. In this temperature region, it is possible to raise the temperature of the NOx catalyst 41 by both the CO oxidation reaction and the HC oxidation reaction. However, in the case of a diesel engine, there is a tradeoff in generating a large amount of CO. That is, when CO is supplied to the NOx catalyst 41, the ratio of incomplete combustion is increased by decreasing the intake air amount or increasing the EGR gas amount, or the fuel injection amount is increased to enrich the air-fuel ratio. Therefore, if a large amount of CO is generated, problems such as an increase in the amount of PM generated, oil dilution, and deterioration in fuel efficiency may occur. On the other hand, when HC is supplied, there is an advantage that a relatively large amount can be supplied to the NOx catalyst 41 without causing such a problem. Therefore, even if a large amount of HC is supplied to the NOx catalyst 41, the temperature of the NOx catalyst 41 is increased only by supplying HC in this temperature range where there is no possibility of poisoning and deactivation of the NOx catalyst 41 by unreacted HC. It was decided. After executing step S106, the ECU 26 returns to step S102.

  In step S103, when the catalyst temperature Tcat is equal to or higher than the target temperature Ttrg (Ttrg ≦ Tcat), the ECU 26 determines that the temperature increase control is completed, and the process after the catalyst temperature increase in the sulfur poisoning recovery process, that is, the step of FIG. The process proceeds to S201 and subsequent steps.

  In this embodiment, the ECU 26 that executes steps S104 to S106 corresponds to the catalyst temperature increase control means in the present invention.

  FIG. 3 shows an example of temporal changes in the catalyst temperature increase Tcat, the CO supply amount, and the HC supply amount of the NOx catalyst 41 when the temperature increase control described above is executed.

  In the example of FIG. 3, it is assumed that it is determined that the execution condition of the sulfur poisoning recovery process is satisfied at time t0. At this time, it is assumed that the catalyst temperature Tcat is lower than the first reference temperature T1, as shown in FIG. In this case, since the temperature of the NOx catalyst 41 cannot be suitably raised by either CO supply or HC supply, as shown in FIGS. 3B and 3C, CO supply and HC supply are also possible. Also not done. Therefore, the temperature rise of the NOx catalyst 41 by supplying CO or HC is not performed at this time. Here, the exhaust gas temperature increases due to other factors such as the internal combustion engine 1 operating at a high load, and as a result, the catalyst temperature gradually rises, and the catalyst temperature Tcat reaches the first reference temperature T1 at time t1. And

  When the catalyst temperature Tcat reaches the first reference temperature T1, the supply of CO is started as shown in FIG. At this temperature, since HC is still difficult to oxidize in the NOx catalyst 41, as shown in FIG. 3C, HC is not supplied. Thus, even in a low temperature state where it is difficult to raise the temperature of the NOx catalyst 41 by the heat of oxidation reaction of HC, the temperature of the NOx catalyst 41 can be raised as shown in FIG.

  When the catalyst temperature Tcat reaches the second reference temperature T2 at the time t2, the HC can be oxidized in the NOx catalyst 41. Therefore, as shown in FIGS. 3B and 3C, the supply of HC Is started, and the supply amount of HC increases as the catalyst temperature Tcat rises. At this temperature, if all the required amount of reducing agent is supplied by HC, there is a possibility of poisoning and deactivation of the NOx catalyst 41 by unreacted HC. The supply amount of CO is decreased as the supply amount increases.

  When the catalyst temperature Tcat reaches the third reference temperature T3 at time t3, the NOx catalyst 41 is less likely to be deactivated even if the total amount of reducing agent required for raising the catalyst temperature is supplied by HC. As shown in FIG. 3B, the supply of CO is stopped, and only HC is supplied to the NOx catalyst 41, whereby the catalyst temperature is raised to the target temperature Ttrg.

  Here, in FIG. 3, when both the HC and the CO are supplied and the NOx catalyst 41 is heated, the HC supply amount is gradually increased and the CO supply amount is gradually decreased according to the catalyst temperature Tcat. However, as shown in FIG. 4, during the period until the catalyst temperature Tcat reaches the third reference temperature, CO and HC may be supplied by a certain amount. In short, in the temperature range where the NOx catalyst 41 may be deactivated when the total amount of reducing agent required for rapid catalyst temperature rise is supplied by HC, the oxidation reaction rate is high and the deactivation of the NOx catalyst 41 is performed. The effect of the present invention can be obtained by supplying the NOx catalyst 41 with a combination of CO that is less likely to cause and HC that is more advantageous than CO in terms of smoke and fuel consumption.

Next, control for enriching the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 41 in the sulfur poisoning recovery process of this embodiment will be described. In the sulfur poisoning recovery process after the temperature increase of the NOx catalyst 41 is completed, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 41 is changed to a rich air-fuel ratio capable of SOx desorption while maintaining the NOx catalyst 41 at the target temperature Ttrg. There is a need. In such SOx desorption processing after the catalyst temperature rise, it is necessary to supply a large amount of reducing components to the NOx catalyst 41. When a large amount of HC is supplied, the active sites of the NOx catalyst 41 may be poisoned by unreacted HC and deactivated as described above. In this case, even if the catalyst temperature of the NOx catalyst 41 is equal to or higher than the third reference temperature, the NOx catalyst 41 is in a state in which the oxidation reaction of HC does not proceed appropriately, so that the temperature of the NOx catalyst 41 decreases and the catalyst temperature May not be maintained at the target temperature.

  Therefore, in the SOx desorption process of this embodiment, attention is paid to the temperature difference ΔT between the temperature Tcat of the NOx catalyst 41 and the target temperature Ttrg. That is, when the temperature difference ΔT spreads beyond the predetermined reference temperature difference in the SOx desorption process after the temperature raising process is completed, it is determined that the NOx catalyst 41 is deactivated as described above, and the SOx desorption is performed. In the separation process, CO was supplied to the NOx catalyst 41.

  As described above, CO undergoes an oxidation reaction without being adsorbed to the NOx catalyst 41. Therefore, even in a situation where many of the active sites of the NOx catalyst 41 are covered with unreacted HC, an oxidation reaction is possible. The temperature of the NOx catalyst 41 that has decreased due to the heat of reaction can be increased again. As the temperature of the NOx catalyst 41 rises, the vaporization and oxidation reaction of unreacted HC adsorbed on the NOx catalyst 41 is promoted, and the NOx catalyst 41 can be activated again. When the temperature difference ΔT between the temperature Tcat of the NOx catalyst 41 and the target temperature Ttrg becomes sufficiently small, the supply of CO is stopped and the SOx desorption process by supplying only HC is resumed.

  Thus, in the SOx desorption process, by supplying CO as a reducing agent to the NOx catalyst 41 based on not only the temperature of the NOx catalyst 41 but also the temperature difference between the temperature of the NOx catalyst 41 and the target temperature, SOx It is possible to suppress the deactivation of the NOx catalyst 41 in the desorption process, and it is possible to more appropriately perform the sulfur poisoning recovery process.

  FIG. 5 is a flowchart showing a control routine of the SOx desorption process in the sulfur poisoning recovery process of the present embodiment. This routine is executed when it is determined in step S103 in the flow of FIG. 2 that the catalyst temperature Tcat is equal to or higher than the target temperature Ttrg.

  In step S201, the ECU 26 determines whether or not an end condition for the sulfur poisoning recovery process is satisfied. In this embodiment, when the execution time of the SOx desorption process after the completion of the temperature raising process of the NOx catalyst 41 has passed a predetermined time, it is determined that the end condition for the sulfur poisoning recovery process is satisfied. This predetermined time is a time during which it can be determined that the SOx occluded in the NOx catalyst 41 has almost completely desorbed, and is obtained in advance by experiments. Note that the end of the sulfur poisoning recovery process may be determined by other methods. If it is determined in step S201 that the sulfur poisoning recovery process end condition is satisfied (Yes), the ECU 26 once exits this routine. On the other hand, when it is determined that the sulfur poisoning recovery process termination condition is not satisfied (No), the ECU 26 proceeds to step S202.

  In step S202, the ECU 26 supplies HC to the NOx catalyst 41. The supply amount of HC is determined so that the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 41 becomes a rich air-fuel ratio capable of SOx desorption while maintaining the temperature Tcat of the NOx catalyst 41 at the target temperature Ttrg.

  In step S203, the ECU 26 acquires the temperature Tcat of the NOx catalyst 41.

  In step S204, the ECU 26 calculates a temperature difference ΔT between the catalyst temperature Tcat acquired in step S203 and the target temperature Ttrg.

In step S205, the ECU 26 determines whether or not the temperature difference ΔT calculated in step S204 exceeds a predetermined reference temperature difference ΔTc. Here, the reference temperature difference ΔTc is
This is the reference value of the temperature difference that can be determined that the oxidation activity of the NOx catalyst 41 is deactivated by unreacted HC. If the temperature difference ΔT is equal to or smaller than the reference temperature difference ΔTc in step S205 (No), the ECU 26 determines that the NOx catalyst 41 is not deactivated, and returns to step S201. On the other hand, if the temperature difference ΔT exceeds the reference temperature difference ΔTc in step S205 (Yes), the ECU 26 determines that the NOx catalyst 41 is deactivated by unreacted HC, and proceeds to step S206.

  In step S206, the ECU 26 reduces the amount of HC supplied to the NOx catalyst 41 and starts supplying CO. As a result, as described above, the oxidation reaction of CO having a high reaction rate proceeds in the NOx catalyst 41, and the temperature of the NOx catalyst 41 rises due to the heat of reaction.

  In step S207, the ECU 26 acquires the temperature Tcat of the NOx catalyst 41.

  In step S208, the ECU 26 calculates a temperature difference ΔT between the catalyst temperature Tcat acquired in step S207 and the target temperature Ttrg.

  In step S209, the ECU 26 determines whether or not the temperature difference ΔT calculated in step S208 has become equal to or smaller than a predetermined reference temperature difference ΔT0. Here, the reference temperature difference ΔT0 is a reference value of a temperature difference that can be determined that the deactivated state of the NOx catalyst 41 due to poisoning of unreacted HC has been eliminated. More simply, in step S209, it may be determined whether or not the catalyst temperature Tcat has reached the target temperature Ttrg (ΔT≈0). If the temperature difference ΔT is larger than the reference temperature difference ΔT0 in step S209 (No), the ECU 26 returns to step S207. On the other hand, if the temperature difference ΔT is equal to or smaller than the reference temperature difference ΔT0 in step S209 (Yes), the ECU 26 proceeds to step S210.

  In step S210, the ECU 26 stops the supply of CO to the NOx catalyst 41, and increases the supply amount of HC to an amount capable of maintaining and enriching the temperature of the NOx catalyst 41 by supplying only HC as a reducing agent.

  FIG. 6 shows an example of temporal changes in the catalyst temperature Tcat, the CO supply amount, and the HC supply amount of the NOx catalyst 41 when the SOx desorption process described above is executed.

  In the example of FIG. 6, it is assumed that the temperature Tcat of the NOx catalyst 41 starts to decrease at the time t1 during execution of the SOx desorption process after the temperature increase process of the NOx catalyst 41 is completed. At this time, HC is supplied to the NOx catalyst 41 in order to maintain the temperature of the NOx catalyst 41 at the target temperature Ttrg and create a rich atmosphere in which SOx can be desorbed from the NOx catalyst 41.

  It is assumed that the catalyst temperature Tcat gradually decreases and the temperature difference ΔT between the catalyst temperature Tcat and the target temperature Ttrg exceeds the reference temperature difference ΔTc at time t2. Then, it is determined that the NOx catalyst 41 is poisoned by the unreacted HC and is in an inactivated state, and as shown in FIGS. 6B and 6C, the supply of CO is started and the HC is started. Is stopped. Thereby, CO having a high reaction rate is supplied to the NOx catalyst 41, and the temperature of the NOx catalyst 41 starts to rise due to the oxidation reaction heat of CO, as shown in FIG.

  Then, when the temperature difference ΔT reaches the reference temperature difference ΔT0 at time t3, it is determined that the deactivated state of the NOx catalyst 41 has been eliminated, and the supply of HC is started again and the supply of CO is stopped.

  Here, FIG. 6 shows an example in which the supply of HC is stopped during the period from when the temperature difference ΔT exceeds the reference temperature difference ΔTc until it reaches the reference temperature difference ΔT0. good. 6 shows an example in which the supply amount of CO and the supply amount of HC are constant values (the supply amount of HC is a constant value 0) in the period, but FIG. 7B and FIG. As shown in (), during the period, the supply amount of CO may be decreased and the supply amount of HC may be increased in accordance with the reduction of the temperature difference ΔT. In this case, although FIGS. 7B and 7C show an example in which the HC supply amount and the CO supply amount are continuously changed, they may be changed stepwise. In addition, the HC supply amount may not be changed during the period, but only the CO supply amount may be changed according to the temperature difference ΔT. In short, during the SOx desorption process, if CO is supplied when the NOx catalyst 41 is determined to be in an inactive state even though the catalyst temperature Tcat of the NOx catalyst 41 is sufficiently high, the present invention can be used. The effect can be obtained.

  In Example 1, in the SOx desorption process of the sulfur poisoning recovery process, when the catalyst temperature control is performed to maintain the temperature of the NOx catalyst 41 at the target temperature, the temperature difference between the catalyst temperature and the target temperature is increased. The control for supplying CO in response to this has been described. Specifically, in Example 1, even if the catalyst temperature Tcat is equal to or higher than the third reference temperature T3, the NOx catalyst 41 is supplied by supplying CO for a certain period after the temperature difference ΔT exceeds the reference temperature difference ΔTc. Eliminate the inactive state.

  In this embodiment, in the catalyst temperature increase process of the sulfur poisoning recovery process, when the catalyst temperature control is performed to increase the temperature of the NOx catalyst 41 toward the target temperature, the temperature difference between the catalyst temperature and the target temperature is changed. Control for supplying CO in accordance with the changing speed will be described.

  In the present embodiment, in the flow of FIG. 2 of the first embodiment, it is determined in step S103 that the catalyst temperature Tcat is equal to or higher than the third reference temperature and lower than the target temperature Ttrg, and the NOx catalyst 41 is heated by supplying HC. The temperature difference ΔT between the catalyst temperature Tcat and the target temperature Ttrg is calculated. Based on the calculated temperature difference ΔT and the previously calculated temperature difference ΔT, a current change rate (dΔT / dt) of the temperature difference ΔT is calculated. When the calculated change speed is a negative value and the magnitude thereof is lower than a predetermined target value, or when the calculated speed is a positive value, the NOx catalyst 41 is in a deactivated state. Judgment is made and the supply of CO is started. Here, the target value of the change rate is a change rate assumed from the supply amount of HC, the operating condition of the internal combustion engine, and the like when the NOx catalyst 41 is in a normal active state.

  When the calculated change rate is a negative value and its magnitude is lower than the target value, it means that the catalyst temperature Tcat is rising, but the rate of increase is slowing down. Further, when the calculated change rate is a positive value, it means that the catalyst temperature that should have been increased is decreased. In such a case, in this embodiment, it is determined that the NOx catalyst 41 is poisoned and deactivated by the HC supplied to the NOx catalyst 41, and the catalyst temperature Tcat belongs to a temperature range equal to or higher than the third reference value. Even if it is, CO is supplied. This supply of CO continues until the rate of change is a negative value and the magnitude thereof exceeds a target value.

  Thus, when CO is supplied to the NOx catalyst 41, the CO rapidly undergoes an oxidation reaction, and the temperature rise rate of the NOx catalyst 41 is recovered by the reaction heat, and the deactivated state is canceled as the temperature of the NOx catalyst 41 rises. The Therefore, it is possible to suppress a decrease in the efficiency of the catalyst temperature increasing process due to the deactivation of the NOx catalyst 41.

  FIG. 8 is a diagram illustrating an example of temporal changes in the catalyst temperature increase Tcat, the CO supply amount, and the HC supply amount of the NOx catalyst 41 when the temperature increase control in the present embodiment described above is executed.

8, since it is the same as that of FIG. 3 of Example 1 until it determines with the catalyst temperature Tcat becoming more than 3rd reference temperature T3, description is abbreviate | omitted. As shown in FIG. 8 (A), at time ta after it is determined that the catalyst temperature Tcat has become equal to or higher than the third reference temperature T3, the rate of change dΔT / dt of the temperature difference ΔT between the catalyst temperature Tcat and the target temperature Ttrg. Is a negative value and its magnitude falls below the target value, and then becomes a positive value (that is, the rate of increase of the catalyst temperature Tcat slows down, and then starts to decrease).

  Then, as shown in FIG. 8B, the supply of CO that has been stopped is started. At this time, as shown in FIG. 8C, the supply amount of HC may not be changed, or the supply amount of HC may be decreased in accordance with the start of supply of CO. In any case, when CO is supplied to the NOx catalyst 41, the temperature reduction of the NOx catalyst 41 is suppressed by the oxidation reaction heat of CO, and the active state of the NOx catalyst 41 starts to recover.

  As a result, as shown in FIG. 8A, the change rate of the temperature difference ΔT changes from a positive value to a negative value, and the change rate is a negative value at time tb and the magnitude thereof is equal to or greater than the target value. become. Then, it is determined that the deactivated state of the NOx catalyst 41 has been eliminated, and the supply of CO is stopped as shown in FIG. After time tb, as shown in FIG. 8 (A), ΔT decreases at a reduction rate that is equal to or higher than the target value assumed from the HC supply amount and the operating conditions of the internal combustion engine 1, and the catalyst temperature Tcat becomes the target temperature Ttrg. It rises favorably toward.

  As described above, also in the catalyst temperature increasing process, by controlling not only the catalyst temperature of the NOx catalyst 41 but also the temperature difference between the catalyst temperature and the target temperature, the HC supply amount and the CO supply amount are controlled. Thus, the temperature of the NOx catalyst 41 can be raised more reliably.

  The above-described embodiment is an example for explaining the present invention, and various modifications can be made to the above-described embodiment without departing from the gist of the present invention. For example, in each of the above embodiments, the case where the present invention is applied to a system configured to raise the temperature of the NOx catalyst by oxidizing CO and HC by the oxidation ability of the NOx catalyst has been described. The present invention can also be applied to a system configured to arrange an oxidation catalyst on the side and to raise the temperature of the catalyst by supplying CO and HC to the oxidation catalyst. Further, the present invention can be applied not only to the catalyst temperature rise and rich control accompanying the sulfur poisoning recovery process of the NOx catalyst, but also to the catalyst temperature rise accompanying the regeneration process of the filter that collects particulate matter in the exhaust gas. .

It is a figure which shows schematic structure of the internal combustion engine to which the exhaust gas purification apparatus which concerns on an Example, its intake system, and an exhaust system is applied. 3 is a flowchart illustrating a temperature increase control routine for a NOx catalyst in the sulfur poisoning recovery process of the first embodiment. It is a figure which shows an example of the time change of the catalyst temperature of NOx catalyst, CO supply amount, and HC supply amount at the time of performing temperature rising control of the NOx catalyst in the sulfur poisoning recovery process of Example 1. It is a figure which shows an example of the time change of the catalyst temperature of NOx catalyst, CO supply amount, and HC supply amount at the time of performing temperature rising control of the NOx catalyst in the sulfur poisoning recovery process of Example 1. 3 is a flowchart illustrating a control routine for SOx desorption processing in the sulfur poisoning recovery processing according to the first embodiment. It is a figure which shows an example of the time change of the catalyst temperature of NOx catalyst, CO supply amount, and HC supply amount at the time of performing SOx desorption process in the sulfur poisoning recovery process of Example 1. It is a figure which shows an example of the time change of the catalyst temperature of NOx catalyst, CO supply amount, and HC supply amount at the time of performing SOx desorption process in the sulfur poisoning recovery process of Example 1. It is a figure which shows an example of the time change of the catalyst temperature of NOx catalyst, CO supply amount, and HC supply amount at the time of performing temperature rising control of NOx catalyst in the sulfur poisoning recovery process of Example 2.

Explanation of symbols

1 Internal combustion engine 7 Air flow meter 14 EGR valve 15 EGR passage 17 Intake manifold 18 Exhaust manifold 19 Fuel addition valve 22 Inlet throttle valve 26 ECU
29 Injector 41 NOx catalyst 42 Intake passage 43 Exhaust passage 49 Cylinder 50 Exhaust temperature sensor

Claims (5)

A catalyst having oxidation ability disposed in the exhaust passage of the internal combustion engine;
HC supply means for supplying HC into the exhaust gas flowing into the catalyst;
CO supply means for supplying CO into the exhaust gas flowing into the catalyst;
Temperature acquisition means for acquiring the temperature of the catalyst;
Catalyst temperature increase control means for performing catalyst temperature increase control for increasing the temperature of the catalyst by supplying HC by the HC supply means and / or supplying CO by the CO supply means;
With
When the catalyst temperature increase control execution condition is satisfied, the catalyst temperature increase control means
When the temperature of the catalyst is lower than a predetermined first reference temperature, the catalyst temperature increase control is not executed,
When the temperature of the catalyst is equal to or higher than the first reference temperature and lower than a predetermined second reference temperature, the catalyst temperature increase control is executed by supplying CO by the CO supply means,
When the temperature of the catalyst is equal to or higher than the second reference temperature and lower than a predetermined third reference temperature, the catalyst temperature increase control is performed by supplying CO by the CO supply means and supplying HC by the HC supply means. Run,
An exhaust gas purification apparatus for an internal combustion engine, wherein when the temperature of the catalyst is equal to or higher than the third reference temperature, the catalyst temperature increase control is executed by supplying HC by the HC supply means. In claim 1,
In the catalyst temperature increase control performed when the temperature of the catalyst acquired by the temperature acquisition means is equal to or higher than the second reference temperature and lower than the third reference temperature, the catalyst temperature increase control means The exhaust gas purification apparatus for an internal combustion engine, characterized by increasing the amount of HC supplied by the HC supply means and decreasing the amount of CO supplied by the CO supply means as the value of the HC supply means increases. A catalyst having oxidation ability disposed in the exhaust passage of the internal combustion engine;
HC supply means for supplying HC into the exhaust gas flowing into the catalyst;
CO supply means for supplying CO into the exhaust gas flowing into the catalyst;
Temperature acquisition means for acquiring the temperature of the catalyst;
Catalyst temperature control means for performing catalyst temperature control for controlling the temperature of the catalyst to a predetermined target temperature by supply of HC by the HC supply means and / or supply of CO by the CO supply means,
In accordance with the difference between the temperature of the catalyst acquired by the temperature acquisition unit and the target temperature, the catalyst temperature control unit increases the amount of CO supplied by the CO supply unit as the difference increases. An exhaust emission control device for an internal combustion engine, which controls an HC supply amount by an HC supply means and a CO supply amount by the CO supply means. In claim 3,
The catalyst temperature control means starts the supply of CO by the CO supply means on the condition that the temperature difference becomes larger than a predetermined first reference value, and then the temperature difference becomes a predetermined second reference value. An exhaust gas purification apparatus for an internal combustion engine, characterized in that the supply of CO by the CO supply means is stopped on the condition that it becomes smaller. In claim 4 ,
The catalyst temperature control means adjusts the supply of HC by the HC supply means according to the supply amount of CO when the CO supply by the CO supply means is performed. .

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