JP2006017083A - Method of controlling exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology suitably eliminating drop of HC oxidation capacity of rhodium Rh in an exhaust emission control device provided with a catalyst containing rhodium Rh and a particulate filter. <P>SOLUTION: In the exhaust emission control device provided with the occlusion reduction type NOx catalyst containing rhodium Rh and the particulate filter, drop of HC oxidation capacity of rhodium Rh is eliminated by prohibiting rich spike control while temperature of the occlusion reduction type NOx catalyst is a predetermined temperature or higher and putting the occlusion reduction type NOx catalyst in a reduction atmosphere in a process that temperature of the occlusion reduction type NOx catalyst drops after PM forced regeneration process of the particulate filter is performed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control technology for an exhaust emission control device including a catalyst containing rhodium (Rh) and a particulate filter.

2. Description of the Related Art In recent years, an exhaust gas purification device for an internal combustion engine mounted on a vehicle or the like is known in which a catalyst containing platinum (Pt) is deteriorated by making the catalyst rich atmosphere for a predetermined time when the catalyst contains platinum (Pt). (For example, refer to Patent Document 1).
Japanese Utility Model Publication No. 63-128221 JP-A-6-272541 Japanese Patent Laid-Open No. 2003-13777 JP 2000-297633 A

  In a compression ignition type internal combustion engine (diesel engine), a catalyst containing rhodium (Rh) and a particulate filter for collecting particulates (hereinafter referred to as PM) are integrated or separated into an exhaust system. There is known an exhaust purification device arranged in the above.

  In such an exhaust purification device, the catalyst is exposed to a high temperature and lean atmosphere when regenerating the PM trapping ability of the particulate filter. When a catalyst containing rhodium (Rh) is exposed to a high temperature and lean atmosphere, rhodium (Rh) moves to the inside of the catalyst carrier and the purification ability of the catalyst is lowered.

  The decrease in the catalyst purification capability as described above is eliminated when the catalyst is exposed to a high temperature and rich atmosphere of approximately 400 ° C. or higher. However, since the compression ignition type internal combustion engine has a low exhaust temperature, raising the temperature of the catalyst to a high temperature of 400 ° C. or more has a problem that the fuel consumption is deteriorated.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to purify catalyst in an exhaust gas purification apparatus for an internal combustion engine in which a catalyst containing rhodium (Rh) and a particulate filter are provided integrally or separately. An object of the present invention is to provide a technique that can suitably eliminate the decrease in capability.

  The present invention employs the following means in order to solve the above problems. The gist of the present invention is a method of controlling an exhaust purification device in which a catalyst containing rhodium (Rh) and a particulate filter are integrally or separately arranged in an exhaust system of an internal combustion engine, and the PM of the particulate filter In the process of lowering the catalyst temperature after the forced regeneration process, the catalyst is placed in a reducing atmosphere to eliminate the decrease in the catalyst purification capacity.

  When regenerating the PM collection capacity of the particulate filter, the particulate filter is heated by forcibly increasing the exhaust temperature and / or forcibly increasing the amount of reaction heat in the catalyst. A so-called PM forced regeneration process for removing the collected PM by oxidation is performed.

  When the PM forced regeneration process as described above is executed, the catalyst and the particulate filter are exposed to a high temperature and lean atmosphere, so rhodium (Rh) is buried inside the catalyst carrier. When rhodium (Rh) is buried inside the catalyst carrier, the purification capacity of the catalyst is lowered.

  The embedding of rhodium (Rh) in the catalyst carrier is eliminated when the catalyst is exposed to a high temperature reducing atmosphere. That is, when the catalyst is exposed to a high-temperature reducing atmosphere, rhodium (Rh) is exposed again to the surface of the catalyst carrier.

  By the way, if the temperature of the catalyst is forcibly raised only in order to eliminate the reduction in the purification capacity of the catalyst as described above, a marked deterioration in fuel consumption may be induced.

  Therefore, if the catalyst is brought into a reducing atmosphere before the catalyst temperature is sufficiently lowered in the process of the catalyst temperature decreasing after the execution of the forced PM regeneration process, the heat of the PM forced regeneration process is used to purify the catalyst. It becomes possible to eliminate the capacity drop. As a result, it is not necessary to perform a separate temperature raising process in order to eliminate the decrease in the purification capacity of the catalyst, and the deterioration of fuel consumption is suppressed.

  Note that the reduction in the purification capacity of the catalyst is preferably eliminated when the catalyst is exposed to a high-temperature reducing atmosphere of approximately 400 ° C. or higher. Therefore, in the process in which the catalyst temperature decreases after the PM forced regeneration process is performed. You may make it make a catalyst into a reducing atmosphere in the period when a catalyst temperature becomes 400 degreeC or more. In this case, the amount of reducing agent required to form a reducing atmosphere can be minimized.

  In the present invention, as a catalyst containing rhodium (Rh), an NOx storage reduction catalyst can be exemplified. Since the NOx storage capacity of the NOx storage reduction catalyst is limited, it is necessary to appropriately regenerate the NOx storage capacity in an exhaust purification device equipped with the NOx storage reduction catalyst.

  As a method for regenerating the NOx storage capacity of the NOx storage reduction catalyst, so-called rich spike control is effective in which the reducing agent is added to the exhaust gas upstream of the catalyst so that the exhaust gas flowing into the catalyst has a rich atmosphere.

  By the way, in the exhaust emission control device provided with the particulate filter and the NOx storage reduction catalyst, there is a possibility that the rich spike control is executed after the PM forced regeneration process of the particulate filter is performed.

  When rich spike control is performed in a state where the catalyst purification capacity is reduced, the NOx stored in the NOx storage reduction catalyst is released, but the released NOx cannot be sufficiently reduced. There is a risk of being released into the atmosphere. Furthermore, when the unpurified NOx increases, there is a possibility that the unpurified reducing agent (that is, the reducing agent that could not react with NOx) also increases accordingly.

  On the other hand, if rich spike control is performed after the execution of the forced PM regeneration process, the catalyst is exposed to a high-temperature rich atmosphere, and thus it is conceivable that the decrease in the catalyst purification capability is eliminated. However, the rich spike control is a control that makes the exhaust gas intermittently rich, and since the rich atmosphere time per time is relatively short, it is difficult to sufficiently eliminate the decrease in the catalyst purification capability. Furthermore, since the conventional rich spike control does not consider the rhodium (Rh) characteristics, the catalyst does not always have a rich atmosphere when the catalyst temperature is in an appropriate temperature range.

Therefore, in the present invention, when the catalyst containing rhodium (Rh) is an NOx storage reduction catalyst, the rich spike control after the execution of the PM forced regeneration process is prohibited and the catalyst is placed in a reducing atmosphere. Good.

  In addition, it is preferable to make the rich degree at the time of making a catalyst into a reducing atmosphere lower than the rich degree at the time of setting it as rich atmosphere by rich spike control.

  This is because, when the purification capacity of the catalyst is reduced, if a rich atmosphere similar to the rich spike control is formed, a relatively large amount of NOx is released from the NOx storage reduction catalyst and released into the atmosphere. This is because the amount of unpurified NOx to be increased may increase.

  Examples of the method for bringing the catalyst into the reducing atmosphere include a method for adding a small amount of reducing agent into the exhaust in a shorter cycle than the rich spike control, and a method for making the air-fuel ratio of the internal combustion engine rich.

  In addition, in an exhaust purification device that includes an NOx storage reduction catalyst and a particulate filter, a sulfur poisoning elimination process for the NOx storage reduction catalyst may be executed following the forced PM regeneration process.

  In the control according to the present invention and the sulfur poisoning elimination process, the control according to the present invention sets the catalyst in a reducing atmosphere without forcibly raising the catalyst temperature or maintaining the temperature, whereas the sulfur poisoning elimination process. However, it is different in that the catalyst is brought into a reducing atmosphere while forcibly raising the temperature of the catalyst or maintaining the temperature.

  However, when the sulfur poisoning elimination process is executed, the catalyst is exposed to a high-temperature rich atmosphere, so it is possible to eliminate the reduction in the purification capacity of the catalyst.

  Therefore, the control of the present invention is prohibited when the sulfur poisoning elimination process is executed following the PM forced regeneration process, and when the sulfur poisoning elimination process is not executed following the PM forced regeneration process, What is necessary is just to perform control. In this case, the catalyst is not unnecessarily brought into a reducing atmosphere, so that deterioration of fuel consumption is prevented.

  According to the present invention, in an exhaust purification device in which a catalyst containing rhodium (Rh) and a particulate filter are provided integrally or separately, the deterioration of the purification capability of the catalyst is eliminated while suppressing deterioration of fuel consumption. Can do.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied.

  An internal combustion engine 1 shown in FIG. 1 is a compression ignition type internal combustion engine (diesel engine). The internal combustion engine 1 includes an intake passage 2 and an exhaust passage 3. An intake throttle valve 4 is provided in the intake passage 2. A particulate filter 5 is provided in the exhaust passage 3. The particulate filter 5 carries an NOx storage reduction catalyst containing rhodium (Rh).

  The exhaust passage 3 upstream of the particulate filter 5 is provided with a reducing agent addition valve 6 that injects fuel of the internal combustion engine 1 as a reducing agent. An exhaust temperature sensor 7 is provided in the exhaust passage 3 downstream of the particulate filter 5.

  The intake passage 2 and the exhaust passage 3 are communicated with each other by an EGR passage 8. An EGR valve 9 is provided in the EGR passage 8.

  The intake throttle valve 4, the reducing agent addition valve 6, the exhaust temperature sensor 7, and the EGR valve 9 are each electrically connected to the ECU 10.

  The ECU 10 performs known controls such as fuel injection control and EGR control based on the exhaust temperature sensor 7 and the operating state of the internal combustion engine 1, and also executes catalyst purification capacity regeneration control that is the gist of the present invention. Hereinafter, the catalyst purification capacity regeneration control will be described.

  Since the PM collection capability of the particulate filter 5 is limited, the ECU 10 executes the PM forced regeneration process before the PM collection capability is saturated. In the PM forced regeneration process, the ECU 10 uses post injection and / or fuel addition from the reducing agent addition valve 6 into the exhaust to increase the exhaust temperature and / or increase the reaction heat amount in the NOx storage reduction catalyst. The particulate filter 5 is forcibly raised in temperature.

  When the PM forced regeneration process of the particulate filter 5 is executed, the NOx storage reduction catalyst supported on the particulate filter 5 is also exposed to a high temperature and lean atmosphere. At this time, the rhodium (Rh) of the NOx storage reduction catalyst is buried inside the catalyst carrier, so that the purification capacity of the NOx storage reduction catalyst (particularly, the ability to oxidize hydrocarbons (HC)) decreases.

  When the HC oxidation capacity of the NOx storage reduction catalyst decreases, the NOx purification capacity of the NOx storage reduction catalyst decreases. That is, when the HC oxidation capacity of the NOx storage reduction catalyst is reduced, the NOx storage capacity of the NOx storage reduction catalyst is regenerated, that is, the fuel (hydrocarbon (HC)) is intermittently discharged from the reducing agent addition valve 6 into the exhaust gas. When rich spike control for adding NO is performed, hydrocarbon (HC) is not easily transformed into an active species in the NOx storage reduction catalyst, so NOx released from the NOx storage reduction catalyst or NOx storage reduction catalyst There is a risk that the supplied hydrocarbon (HC) may be released into the atmosphere without being purified.

  FIG. 2 is a diagram showing a temperature at which the NOx purification ability of the NOx storage reduction catalyst is activated. Before the forced PM regeneration process of the particulate filter 5 is executed, the NOx purification capacity of the NOx storage reduction catalyst is activated at around 300 ° C., but after the forced PM regeneration process is performed, it is activated up to about 350 ° C. or more. It is gone.

  Since the exhaust temperature of the compression ignition internal combustion engine is around 300 ° C. except during high-load operation, if the activation temperature of the NOx purification capacity increases as described above, it is released into the atmosphere when rich spike control is executed. The possibility that NOx and HC to be increased increases.

  Therefore, when the PM forced regeneration process is executed, it is necessary to eliminate the decrease in the HC oxidation ability of the NOx storage reduction catalyst. In order to eliminate the decrease in the HC oxidizing ability, it is necessary to expose again the rhodium (Rh) embedded in the catalyst carrier.

  Since rhodium (Rh) embedded in the catalyst carrier is exposed to the surface of the catalyst carrier when exposed to a high temperature reducing atmosphere of 400 ° C. or higher, the temperature of the NOx storage reduction catalyst is raised to 400 ° C. or higher. If the exhaust gas flowing into the NOx storage reduction catalyst is used as a reducing atmosphere, the reduction in the HC oxidizing ability can be eliminated.

  By the way, as a method of raising the temperature of the NOx storage reduction catalyst to a high temperature range of 400 ° C. or higher, a method of increasing the exhaust temperature by post injection or adding fuel to the exhaust to increase the reaction heat of the NOx storage reduction catalyst. However, each method has a drawback that it causes a deterioration in fuel consumption.

  Therefore, in the catalyst purification capacity regeneration control according to the present embodiment, the particulate filter 5 is in the period when the temperature of the NOx storage reduction catalyst is 400 ° C. or higher in the process in which the catalyst temperature decreases after the execution of the PM forced regeneration process. A reducing atmosphere was created.

  Hereinafter, the catalyst purification capacity regeneration control will be described with reference to FIG. FIG. 3 is a flowchart showing a catalyst purification capacity regeneration control routine. The catalyst purification capacity regeneration control routine is a routine that is stored in advance in the ROM of the ECU 10 and is an interrupt routine that is executed by the ECU 10 with the completion of execution of the PM forced regeneration process as a trigger.

  In the catalyst purification capacity regeneration control routine, the ECU 10 first determines in S101 whether or not the value of the PM forced regeneration completion flag is “1”. The PM forced regeneration completion flag is a storage area set in advance in the RAM or the like, and is stored as “1” when the execution of the PM forced regeneration process is completed, and “0” when the execution of the catalyst purification capacity regeneration control is completed. Is memorized.

  When it is determined in S101 that the PM forced regeneration completion flag is “0”, the ECU 10 ends the execution of this routine. On the other hand, if it is determined in S101 that the PM forced regeneration completion flag is “1”, the ECU 10 proceeds to S102.

  In S102, the ECU 10 inputs an output signal (outflow exhaust gas temperature): Tout of the exhaust gas temperature sensor 7.

  In S103, it is determined whether or not the outflow exhaust gas temperature Tout input in S102 is equal to or higher than a predetermined temperature Ts (for example, 400 ° C.).

  When the outflow exhaust gas temperature: Tout is not equal to or higher than the predetermined temperature: Ts in S103 (Tout <Ts), the ECU 10 estimates that the bed temperature of the NOx storage reduction catalyst is lower than the predetermined temperature: Ts, and proceeds to S110. move on. In S110, the ECU 10 changes the value of the PM forced regeneration completion flag to “0” and ends the execution of this routine.

  When it is determined in S103 that the outflow exhaust gas temperature: Tout is equal to or higher than the predetermined temperature: Ts (Tout ≧ Ts), the ECU 10 determines that the bed temperature of the NOx storage reduction catalyst is equal to or higher than the predetermined temperature: Ts. Estimate and proceed to S104.

  In S104, the ECU 10 prohibits execution of rich spike control.

  In S105, the ECU 10 executes an exhaust enrichment process for making the exhaust gas flowing into the particulate filter 5 into a reducing atmosphere (rich atmosphere). In the exhaust enrichment process, the ECU 10 controls the reducing agent addition valve 6 to intermittently add fuel into the exhaust.

  At that time, as shown in FIG. 4, the ECU 10 reduces the amount of fuel added from the reducing agent addition valve 6 at one time as compared with the rich spike control, and the fuel addition interval is shorter than that during the rich spike control. Thus, the reducing agent addition valve 6 is controlled.

  The reason why the amount of fuel injected by the reducing agent addition valve 6 at one time is smaller than that during rich spike control is that the amount of carbonization is the same as that during rich spike control when the HC oxidation capacity of the NOx storage reduction catalyst is reduced. When hydrogen (HC) is supplied to the NOx storage reduction catalyst, the amount of NOx released from the NOx storage reduction catalyst increases, and the amount of unpurified NOx released into the atmosphere increases accordingly. is there.

Further, another reason for reducing the amount of fuel injected by the reducing agent addition valve 6 at one time than during the rich spike control is that during the rich spike control when the HC oxidation capacity of the NOx storage reduction catalyst is reduced. This is because if the same amount of fuel is added to the exhaust gas, the amount of hydrocarbons (HC) that cannot be reacted with NOx and released into the atmosphere may increase.

  The reason why the fuel addition interval of the reducing agent addition valve 6 is made shorter than that during the rich spike control is that the temperature of the particulate filter 5 and the NOx storage reduction catalyst rapidly decreases after the completion of the PM forced regeneration process. This is because if the fuel is added at the same addition interval as in the rich spike control, the temperature of the NOx storage reduction catalyst may be reduced to a temperature lower than the predetermined temperature: Ts before the HC oxidizing ability is regenerated.

  In S106, the ECU 10 inputs the output signal (outflow exhaust gas temperature): Tout of the exhaust gas temperature sensor 7 again.

  In S107, the ECU 10 determines whether or not the outflow exhaust gas temperature Tout input in S106 has decreased below a predetermined temperature Ts.

  If it is determined in S107 that the exhaust gas exhaust temperature: Tout has not fallen below the predetermined temperature: Ts (Tout ≧ Ts), the ECU 10 determines that the bed temperature of the NOx storage reduction catalyst is still equal to or higher than the predetermined temperature: Ts. It is assumed that there is, and the processes after S105 described above are executed again.

  If it is determined in S107 that the exhaust gas exhaust temperature Tout has decreased below the predetermined temperature Ts (Tout <Ts), the ECU 10 determines that the bed temperature of the NOx storage reduction catalyst has decreased below the predetermined temperature Ts. Regardless, the process proceeds to S108.

  In S108, the ECU 10 ends the execution of the exhaust enrichment process.

  In S109, the ECU 10 cancels the prohibition of execution of the rich spike control.

  In S110, the ECU 10 changes the value of the PM forced regeneration process execution completion flag to “0”.

  As described above, when the ECU 10 executes the catalyst purification capacity regeneration control routine, the HC oxidation capacity of the NOx storage reduction catalyst can be regenerated using the heat at the time of performing the PM forced regeneration process. For this reason, the fuel consumption deterioration accompanying the temperature rise of the NOx storage reduction catalyst can be suppressed.

  Further, in the present embodiment, since a small amount of fuel is added to the exhaust gas in a shorter cycle than during the rich spike control, the occlusion reduction is performed within a period in which the bed temperature of the NOx storage reduction catalyst is equal to or higher than the predetermined temperature: Ts. It is possible to regenerate the HC oxidizing ability of the NOx catalyst, and to reduce unpurified NOx and hydrocarbons (HC) released into the atmosphere.

  When the exhaust enrichment process is performed after the forced PM regeneration process, the bed temperature of the NOx storage reduction catalyst exceeds the predetermined temperature: Ts over a long period of time due to the reaction heat of rhodium (Rh) and hydrocarbon (HC). There is also the possibility of maintaining. In such a case, (1) the execution of the exhaust enrichment process is terminated when the execution time of the exhaust enrichment process reaches a predetermined time or more, and (2) the fuel addition amount is increased. The temperature of the NOx storage reduction catalyst is gradually reduced by reducing the amount of the NOx storage according to the above, and (3) the temperature of the NOx storage reduction catalyst is lowered stepwise by providing an interval for every predetermined number of times of fuel addition. May be adopted.

In the present embodiment, as a specific execution method of the exhaust enrichment process, the reducing agent addition valve 6 is used.
Although an example in which fuel is added to the exhaust gas from the engine is described, the air-fuel ratio of the exhaust gas discharged from the internal combustion engine 1 may be decreased by increasing the amount of EGR gas.

  Further, in the present embodiment, the example in which the particulate filter 5 and the NOx storage reduction catalyst are integrally provided in the exhaust passage 3 has been described. However, the particulate filter 5 and the NOx storage reduction catalyst are separately provided in the exhaust passage 3. It may be provided.

For example, the particulate filter 5 and the NOx storage reduction catalyst may be arranged in series in the exhaust passage 3 (preferably the NOx storage reduction catalyst is preferably arranged upstream of the particulate filter 5). However, it is assumed that the reducing agent addition valve 6 is disposed upstream of the NOx storage reduction catalyst.
<Other embodiments>

  When the amount of sulfur component contained in the fuel used in the internal combustion engine 1 is large, the NOx storage reduction catalyst is sulfur poisoned (S poisoning), so the S poisoning elimination process is executed following the PM forced regeneration process. There is a possibility.

  Since the sulfur poisoning elimination process is a process of making the catalyst rich atmosphere while maintaining the NOx storage reduction catalyst at a high temperature, it is possible to eliminate the reduction in the HC oxidation performance of the NOx storage reduction catalyst.

  Therefore, the ECU 10 prohibits the execution of the catalyst purification ability regeneration control when executing the sulfur poisoning elimination process following the PM forced regeneration process, and does not execute the sulfur poisoning elimination process following the PM forced regeneration process. For this, the catalyst purification capacity regeneration control may be executed.

  In this case, since the catalyst purification capacity regeneration control is not executed unnecessarily, it is possible to suppress fuel consumption related to the catalyst purification capacity regeneration control.

The figure which shows schematic structure of the internal combustion engine to which this invention is applied. The figure which shows the result of having measured the temperature which NOx purification ability of a NOx storage reduction catalyst activates Flowchart showing a catalyst purification capacity regeneration control routine The figure which shows the concrete execution method of exhaust gas enrichment processing

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 3 ... Exhaust passage 5 ... Particulate filter 6 ... Reducing agent addition valve 7 ... Exhaust temperature sensor 10 ... ECU

Claims (6)

A control method for an exhaust gas purification device in which a catalyst containing rhodium and a particulate filter that collects particulates in an exhaust system of an internal combustion engine are arranged integrally or separately.
Exhaust gas characterized in that the particulate filter and the catalyst are heated to forcibly regenerate the trapping capacity of the particulate filter, and the catalyst is brought into a reducing atmosphere in the process of lowering the catalyst temperature after the forced regeneration is completed. Control method of purification device. 2. The method of controlling an exhaust purification device according to claim 1, wherein the catalyst is placed in a reducing atmosphere during a period when the catalyst temperature is equal to or higher than a predetermined temperature. 3. The method of controlling an exhaust purification device according to claim 2, wherein the predetermined temperature is about 400.degree. The catalyst according to any one of claims 1 to 3, wherein the catalyst is an NOx storage reduction catalyst.
When the catalyst is in a reducing atmosphere, the exhaust purification device control method is characterized by prohibiting execution of a process for regenerating the NOx storage capacity of the catalyst. 5. The method of controlling an exhaust purification device according to claim 4, wherein when the catalyst is in a reducing atmosphere, the degree of richness is made lower than that during the regeneration processing of the NOx storage capacity. A particulate filter provided in the exhaust system of the internal combustion engine;
A catalyst containing rhodium provided in the exhaust system integrally or separately from the particulate filter;
Regenerating means for forcibly regenerating the particulate filter's collection ability by raising the temperature of the particulate filter and the catalyst;
In the process in which the catalyst temperature after the forced regeneration of the particulate filter ends, the deterioration eliminating means that makes the catalyst a reducing atmosphere;
A control device for an exhaust gas purification device.

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