JP2006161789A - Sox poisoning regeneration method for exhaust gas purifying catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology for suppressing worsening of SO<SB>x</SB>poisoning regeneration efficiency by suppressing fluctuation of temperature of absorption reduction type NOx catalyst in SO<SB>x</SB>poisoning regeneration and suppressing worsening of fuel economy in SO<SB>x</SB>poisoning regeneration. <P>SOLUTION: When performing SO<SB>x</SB>poisoning regeneration, a SO<SB>x</SB>poisoning regeneration place is decided (S102) and target combustion A/F and target amount of reducing agent addition are set (S105, S106) in accordance with a position of the decided SO<SB>x</SB>poisoning regeneration place (S104) in the absorption reduction type NO<SB>x</SB>catalyst 10. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an SOx poisoning regeneration method for an exhaust purification catalyst.

  The exhaust gas of an internal combustion engine usually contains harmful NOx and the like. For this reason, in order to purify NOx in the exhaust, a NOx catalyst is provided in the exhaust system of the internal combustion engine. However, for example, in the case of a NOx storage reduction catalyst, it is known that SOx poisoning in which the purification performance deteriorates occurs due to SOx in the exhaust gas being stored in the NOx storage reduction catalyst. In order to eliminate this SOx poisoning, the temperature of the NOx storage reduction catalyst is raised to a temperature higher than the sulfur separation desorption temperature, and the reducing agent is supplied to reduce and release SOx stored in the NOx storage reduction catalyst. A process is being performed (hereinafter, this process is referred to as “SOx poisoning regeneration”).

  Here, as the SOx poisoning regeneration, the temperature adjustment step of adjusting the temperature of the NOx storage reduction catalyst to a temperature within a predetermined temperature range equal to or higher than the sulfur separation desorption temperature, and the exhaust gas air-fuel ratio is made rich. A method of performing SOx poisoning regeneration, etc. has been proposed by repeating a sulfur separation and desorption process for removing sulfur from the NOx storage reduction catalyst by controlling and without excessive temperature rise in a wider range of engine operating conditions. (For example, refer to Patent Document 1).

  In the conventional SOx poisoning regeneration method as described above, when the air separation ratio of the exhaust discharged from the cylinder of the internal combustion engine is lean and the sulfur separation and desorption step is performed, and the exhaust air / fuel ratio is controlled to be rich, In particular, when the air-fuel ratio of the exhaust gas is controlled to be rich by intermittently supplying a relatively large amount of reducing agent to the exhaust gas, the temperature fluctuation increases in the upstream portion of the storage reduction type NOx catalyst. It was considered that the temperature of the NOx storage reduction catalyst was lower than the sulfur separation desorption temperature during the period of part. As a result, it was considered that the reduction efficiency of SOx in the NOx storage reduction catalyst was lowered.

On the other hand, in order to suppress the temperature fluctuation in the NOx storage reduction catalyst described above, the sulfur separation / desorption process is performed in a state where the air-fuel ratio of the exhaust discharged from the cylinder of the internal combustion engine is rich, and a relatively small amount of reducing agent is added. If the air-fuel ratio of the exhaust gas is controlled to be rich by intermittently supplying it to the exhaust gas, the fuel consumption in SOx poisoning regeneration may be deteriorated, and the emission may be deteriorated due to the occurrence of smoke. It was.
JP 2004-068700 A JP 2002-303176 A

  The object of the present invention is to suppress the temperature fluctuation of the NOx storage reduction catalyst during SOx poisoning regeneration to suppress the deterioration of SOx poisoning regeneration efficiency and to suppress the deterioration of fuel consumption during SOx poisoning regeneration. Is to provide technology.

  In order to achieve the above object, according to the present invention, when performing SOx poisoning regeneration, in the NOx storage reduction catalyst, a portion to be subjected to SOx poisoning regeneration is determined, and the determined portion to be subjected to SOx poisoning regeneration is determined. The greatest feature is that the air-fuel ratio of the exhaust gas discharged from the cylinder of the internal combustion engine and the amount of reducing agent supplied to the NOx storage reduction catalyst are controlled according to the position.

More specifically, by controlling the air-fuel ratio of the exhaust gas discharged from the cylinder of the internal combustion engine and supplying the reducing agent from the upstream to the NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine, the storage reduction A method for SOx poisoning regeneration of an exhaust purification catalyst for removing sulfur content in a NOx type catalyst,
In the NOx storage reduction catalyst, a SOx poisoning regeneration part determining step for determining a part to be SOx poisoning regeneration;
The air-fuel ratio of the exhaust gas discharged from the cylinder of the internal combustion engine is controlled to the target air-fuel ratio, and the target reduction per unit time for the portion to be SOx poisoned regeneration determined in the SOx poisoning regeneration portion determination step A reducing agent supply step for intermittently supplying a reducing agent in an amount,
The values of the target air-fuel ratio and the target reducing agent amount in the reducing agent supply step are set according to the position of the portion to be SOx poisoning regenerated determined in the SOx poisoning regeneration portion determining step. And

  Here, in SOx poisoning regeneration, the air-fuel ratio of the exhaust discharged from the cylinder of the internal combustion engine is controlled, and the reducing agent is supplied from the upstream to the NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine. Thus, the temperature of the NOx storage reduction catalyst is raised to a temperature higher than the sulfur separation desorption temperature (actually, the reaction heat of the reducing agent in the oxidation catalyst supported on or separately provided on the NOx storage reduction catalyst) In addition, the atmosphere is often high in reducing agent concentration, and the sulfur content occluded or adsorbed by the NOx storage reduction catalyst is reduced and removed.

  At this time, in the NOx storage reduction catalyst, the reducing agent is intermittently applied to the NOx storage reduction catalyst so that the temperature of the NOx storage reduction catalyst does not rise excessively due to heat of reaction when SOx is reduced. In general, this is generally performed (hereinafter referred to as “rich spike”).

  In performing the rich spike, when the air-fuel ratio of the exhaust discharged from the cylinder of the internal combustion engine is set to a relatively lean state and the amount of the reducing agent supplied by the rich spike is increased, the reducing agent is supplied. Since the difference between the reducing agent supply amounts during the suspension of the reducing agent supply becomes large, particularly in the upstream portion of the NOx storage reduction catalyst, the temperature fluctuation accompanying the execution of the rich spike becomes large. As a result, the temperature of the NOx storage reduction catalyst falls below the sulfur separation desorption temperature (or regeneration lower limit temperature) as the SOx purifying threshold temperature during a part of the period, and as a result, the SOx poisoning regeneration efficiency may decrease. There is.

  On the other hand, when the air-fuel ratio of the exhaust discharged from the cylinder of the internal combustion engine is set to a relatively rich state and the amount of reducing agent supplied by the rich spike is reduced, the upstream side in the NOx storage reduction catalyst Although the temperature fluctuation of the portion can be reduced, the fuel consumption at the time of SOx poisoning regeneration may deteriorate, and the air-fuel ratio in the cylinder of the internal combustion engine becomes rich, so the emission deteriorates, etc. May cause problems.

On the other hand, in the present invention, in the SOx poisoning regeneration part determination step, the part to be SOx poisoning regeneration in the NOx storage reduction catalyst is determined,
In the reducing agent supply step, the values of the target air-fuel ratio and the target reducing agent amount are set according to the position of the portion to be SOx poisoned and regenerated determined in the SOx poisoning and regenerating portion determining step. did.

Here, a case will be described in which the heat capacity of the portion to be SOx poisoned and regenerated differs depending on the position of the portion to be SOx poisoned and regenerated determined in the SOx poisoned and regenerated portion determination step. For example, when the heat capacity of the portion to be SOx poisoned regeneration determined in the SOx poisoning regeneration portion determination step is small, the air-fuel ratio of the exhaust discharged from the cylinder of the internal combustion engine is set to a relatively lean state, When the amount of reducing agent supplied by the rich spike is set to be large, the temperature fluctuation accompanying the execution of the rich spike becomes large. As a result, in some periods, the temperature of the NOx storage reduction catalyst falls below the sulfur desorption temperature (or the regeneration lower limit temperature) as the SOx purifying threshold temperature, and SOx poisoning regeneration efficiency may be reduced. Arise.

  On the other hand, when the heat capacity of the portion to be SOx poisoned and regenerated determined in the SOx poisoning and regenerating portion determination step is large, the air-fuel ratio of the exhaust discharged from the cylinder of the internal combustion engine is set to a relatively lean state. Even if the amount of the reducing agent supplied by the rich spike is set to be large, the temperature fluctuation accompanying the execution of the rich spike is relatively small.

  Therefore, for example, when the heat capacity of the portion to be SOx poisoned and regenerated determined in the SOx poisoning and regeneration portion determining step is small, the target air-fuel ratio in the reducing agent supply step is set low, and the target reducing agent is set. It is good to set the value of quantity small. On the other hand, when the heat capacity of the SOx poisoning regeneration portion determined in the SOx poisoning regeneration portion determination step is large, the target air-fuel ratio in the reducing agent supply step is set high, and the target reducing agent amount It is good to set many values.

  Next, a case will be described in which the bed temperature of the portion to be SOx poisoned and regenerated differs depending on the position of the portion to be SOx poisoned and regenerated determined in the SOx poisoned and regenerated portion determination step. For example, when the bed temperature of the portion to be SOx poisoned and regenerated determined in the SOx poisoning and regenerating portion determination step is low, the air-fuel ratio of the exhaust discharged from the cylinder of the internal combustion engine is set to a relatively lean state. If a large amount of reducing agent is supplied by the rich spike, the temperature of the NOx storage reduction catalyst falls below the sulfur separation desorption temperature (or regeneration lower limit temperature) in a certain period, and the SOx poisoning regeneration efficiency decreases. Is more likely to do.

  On the other hand, when the bed temperature of the portion to be SOx poisoned and regenerated determined in the SOx poisoning and regenerating portion determination step is sufficiently high, the air-fuel ratio of the exhaust discharged from the cylinder of the internal combustion engine is made relatively lean. Even if the amount of reducing agent supplied by the rich spike is set to be large, the temperature of the NOx storage reduction catalyst falls below the sulfur separation desorption temperature (or regeneration lower limit temperature), and the SOx poisoning regeneration efficiency decreases. Unlikely.

  Therefore, for example, when the bed temperature of the portion to be SOx poisoned and regenerated determined in the SOx poisoning and regeneration portion determining step is low, the target air-fuel ratio in the reducing agent supply step is set low, and the target reduction is performed. It is advisable to set a small amount of agent. On the other hand, when the bed temperature of the portion to be SOx poisoned and regenerated determined in the SOx poisoning and regeneration portion determining step is high, the target air-fuel ratio in the reducing agent supply step is set high, and the target reducing agent amount It is good to set many values of.

  As described above, the target air-fuel ratio and the target reducing agent amount in the reducing agent supply step are set in accordance with the position of the portion to be SOx poisoning regenerated determined in the SOx poisoning regeneration determining step. Thus, when the temperature of the SOx poisoning regeneration portion of the NOx storage reduction catalyst is likely to be lower than the sulfur separation desorption temperature (or regeneration lower limit temperature), the target air-fuel ratio in the reducing agent supply step is set. Setting the value lower and setting the target reducing agent amount to a smaller value prevents the temperature of the SOx poisoning regeneration portion of the NOx storage reduction catalyst from falling below the sulfur separation desorption temperature (or regeneration lower limit temperature). When the temperature of the portion of the NOx catalyst that is undergoing SOx poisoning regeneration is less likely to fall below the sulfur separation desorption temperature (or regeneration lower limit temperature), the return is performed. By setting the target air-fuel ratio in the agent supply process high and setting the value of the target reducing agent amount to a large value, it is possible to suppress the deterioration of fuel consumption in SOx poisoning regeneration and further suppress the deterioration of emissions. .

  Further, in the present invention, compared with the case where the SOx poisoning regeneration portion determined in the SOx poisoning regeneration portion determination step is in a predetermined upstream region on the upstream side in the NOx storage reduction catalyst, When the portion to be SOx poisoned and regenerated is in the predetermined downstream region on the downstream side of the NOx storage reduction catalyst, the target air-fuel ratio is set high and the target reducing agent amount is set large. It may be.

  Here, when the SOx poisoning regeneration portion determined in the SOx poisoning regeneration portion determination step is on the upstream side of the NOx storage reduction catalyst, the heat capacity of the SOx poisoning regeneration portion is small. In addition, the change in the supply amount of the reducing agent during the rich spike operation directly affects the change in the temperature of the portion to be regenerated by SOx poisoning. Therefore, in this case, it is desirable that the target air-fuel ratio in the reducing agent supply step is set low and the target reducing agent amount is set small. On the other hand, when the portion to be SOx poisoned and regenerated determined in the SOx poisoning and regenerating portion determination step is on the downstream side of the NOx storage reduction catalyst, the heat capacity is relatively large, and when rich spike is performed The change in the supply amount of the reducing agent is also effected while the reducing agent passes through the upstream side of the NOx storage reduction catalyst, so that the change in the temperature of the portion to be SOx poisoned and regenerated is not greatly affected. Absent. Therefore, in this case, the target air-fuel ratio in the reducing agent supply step may be set high, and the target reducing agent amount may be set large.

  Here, the predetermined upstream region on the upstream side in the NOx storage reduction catalyst and the predetermined downstream region on the downstream side in the NOx storage reduction catalyst are respectively the supply amount of the reducing agent in the NOx storage reduction catalyst. The effect of the change on the temperature change of the portion to be regenerated by SOx poisoning may be an upstream region and a downstream region where there is a significant difference between them.

  That is, when there is almost no difference between the upstream side and the downstream side of the NOx storage reduction catalyst in the influence of the change in the supply amount of the reducing agent on the temperature change in the SOx poisoning regeneration portion. For example, the upstream half of the NOx storage reduction catalyst may be the predetermined upstream region, and the downstream half of the NOx storage reduction catalyst may be the predetermined downstream region.

  Further, when there is a large difference between the upstream side and the downstream side of the NOx storage reduction catalyst due to the change in the supply amount of the reducing agent with respect to the change in the temperature of the SOx poisoning regeneration portion. If the NOx storage reduction catalyst is relatively upstream, all may be a predetermined upstream region, and if it is relatively downstream, all may be a predetermined downstream region. In this case, as a result, when the portion to be SOx poisoned and regenerated determined in the SOx poisoning and regenerating portion determination step is relatively downstream in the NOx storage reduction catalyst, it is relatively upstream. The target air-fuel ratio may be set higher and the target reducing agent amount may be set higher than in the case of the above.

  More specifically, the target air-fuel ratio is set higher as the SOx poisoning / regeneration portion determined in the SOx poisoning / regeneration portion determination step is located downstream of the NOx storage reduction catalyst. At the same time, the target reducing agent amount may be set larger.

  In this way, it is possible to more reliably suppress changes in the temperature of the portion where SOx poisoning regeneration should be performed with simpler control, suppress deterioration in SOx poisoning regeneration efficiency, and improve fuel efficiency in SOx poisoning regeneration. Can be suppressed.

  Further, in the present invention, in the SOx poisoning regeneration part determining step, the part where the amount of sulfur in the NOx storage reduction catalyst is equal to or greater than a predetermined sulfur amount is determined as the part to be SOx poisoning regeneration. You may make it do.

  Here, the predetermined sulfur amount is the SOx occlusion amount as a threshold at which the deterioration of the NOx occlusion capacity is expected to increase in a portion where the amount of sulfur in the occlusion reduction type NOx catalyst exceeds this value. is there. Therefore, according to the present invention, the SOx poisoning and regeneration can be selectively performed on the portion where the deterioration of the NOx storage capacity becomes large, so that the NOx storage capacity of the NOx storage reduction catalyst is more efficiently maintained. be able to.

  In the present invention, an upper limit may be provided for the value of the target air-fuel ratio. Here, the case where the portion to be SOx poisoned and regenerated determined in the SOx poisoning and regenerating portion determination step is a predetermined downstream region on the downstream side of the NOx storage reduction catalyst will be described. In this case, in the present invention, as described above, the value of the target air-fuel ratio may be set high and the target reducing agent amount may be set large. This is because in this case, the influence of the change in the amount of the reducing agent supplied to the NOx storage reduction catalyst on the temperature change of the portion to be regenerated by SOx poisoning is small.

  However, in this case, it is considered that a large temperature change occurs in the upstream portion of the NOx storage reduction catalyst. Then, the temperature of the upstream portion of the NOx storage reduction catalyst becomes excessively high during a part of the period, and the NOx storage reduction catalyst may cause thermal deterioration. Therefore, for each part of the NOx storage reduction catalyst, a temperature rise limit air-fuel ratio is set as a threshold value at which an excessive temperature rise does not occur in the upstream portion, and the target air fuel ratio is the temperature rise limit air-fuel ratio. When it becomes higher, the target air-fuel ratio may be set to the temperature rise limit air-fuel ratio. If it does so, the excessive temperature rise in the upstream part in the NOx storage reduction catalyst can be suppressed.

  In the above description, when the portion to be SOx poisoned and regenerated determined in the SOx poisoning and regenerating portion determination step is a predetermined downstream region on the downstream side of the NOx storage reduction catalyst, the NOx storage reduction type Although the case where the excessive temperature rise in the downstream portion of the catalyst is suppressed has been described, the present invention is based on the NOx storage reduction type catalyst where the SOx poisoning regeneration portion determined in the SOx poisoning regeneration portion determination step When the heat capacity of the NOx storage reduction type NOx catalyst is suppressed when excessive heat rise is suppressed, or the SOx poisoning regeneration portion determined in the SOx poisoning regeneration portion determination step However, when the bed temperature in the NOx storage reduction catalyst is a low part, the excessive temperature increase in the part of the NOx storage reduction catalyst having a high bed temperature is suppressed. It is also possible to apply to the case.

  Further, in the present invention, when there are a plurality of portions determined as SOx poisoning regeneration portions in the SOx poisoning regeneration portion determination step, the target air-fuel ratio and the target reduction in the reducing agent supply step The value of the dose may be set to a value that should be set for the most upstream portion of the plurality of SOx poisoning and regeneration portions.

  Here, comparing the upstream portion and the downstream portion of the NOx storage reduction catalyst, for the reasons described above, the temperature of the upstream portion accompanying the change in the amount of reducing agent supplied during the rich spike operation is The change is greater than the temperature change in the downstream portion in the same case. In other words, when comparing the upstream portion of the NOx storage reduction catalyst with the downstream portion, it can be said that the restrictions on the target air-fuel ratio and the target reducing agent amount are stricter.

Therefore, when there are a plurality of portions determined as SOx poisoning regeneration portions in the SOx poisoning regeneration portion determination step, the values of the target air-fuel ratio and the target reducing agent amount in the reducing agent supply step are the plurality of portions. If the value to be set for the most upstream part of the part to be SOx poisoned and regenerated is, the temperature change is excessive in the part to be SOx poisoned and regenerated located on the downstream side. The temperature of the portion to be regenerated by SOx poisoning that is located on the downstream side is lower than the sulfur separation desorption temperature (or the regeneration lower limit temperature), so that the SOx poisoning regeneration efficiency is reduced or excessively increased. Heating can be suppressed. As a result, the SOx poisoning regeneration process can be performed more reliably regardless of the number of parts determined to be SOx poisoning regeneration in the SOx poisoning regeneration part determining step.

  In the present invention, the portion to be SOx poisoned and regenerated determined in the SOx poisoning and regeneration portion determining step is sequentially changed from the upstream side to the downstream side in the NOx storage reduction catalyst, and the SOx The poisoning regeneration portion determination step and the reducing agent supply step may be repeatedly executed.

  That is, the target air-fuel ratio and the target reduction for each SOx poisoning regeneration portion are moved while moving the SOx poisoning regeneration portion from the upstream side to the downstream side of the NOx storage reduction catalyst. The amount of the agent is set, and the reducing agent supply step is sequentially performed. In this way, the values of the target air-fuel ratio and the target reducing agent amount in the reducing agent supply step described above are always located on the most upstream side of the plurality of SOx poisoning regeneration portions. SOx poisoning regeneration can be performed on the entire NOx storage reduction catalyst while automatically satisfying the condition that the value should be set for the portion. In addition, since SOx poisoning regeneration is performed sequentially from the upstream side of the NOx storage reduction catalyst, SOx re-poisoning on the downstream side can be suppressed.

Further, in the present invention, the NOx storage reduction catalyst is a NOx storage reduction group consisting of a plurality of NOx reduction catalysts provided in series in the exhaust passage,
In the SOx poisoning regeneration part determining step, the NOx storage reduction catalyst to be SOx poisoned and regenerated is determined from the plurality of NOx storage reduction catalysts as the SOx poisoning regeneration part. Also good.

  That is, when a plurality of storage reduction NOx catalysts are provided in series in the exhaust passage of the internal combustion engine, the storage reduction NOx catalyst group consisting of a plurality of storage reduction NOx catalysts is replaced with the above storage reduction NOx catalyst. From the plurality of NOx storage reduction catalysts, the NOx storage reduction catalyst that should be SOx poisoned and regenerated is considered as the part that should be SOx poisoned and regenerated. The same control as that performed on the NOx catalyst can be applied to the plurality of NOx storage reduction catalysts as a whole.

  In this way, among the plurality of storage reduction type NOx catalysts provided in series in the exhaust passage, in some of the storage reduction type NOx catalysts, the temperature does not fall below the sulfur separation desorption temperature (or the regeneration lower limit temperature). Further, SOx poisoning regeneration can be performed on all the NOx storage reduction catalysts provided in the exhaust passage while improving fuel efficiency and emission in SOx poisoning regeneration.

  The means for solving the problems in the present invention can be used in combination as much as possible.

  In the present invention, temperature fluctuation of the NOx storage reduction catalyst during SOx poisoning regeneration can be suppressed to suppress deterioration in SOx poisoning regeneration efficiency, and fuel consumption deterioration during SOx poisoning regeneration can be suppressed. can do.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine according to the present embodiment and its exhaust system and control system. An internal combustion engine 1 shown in FIG. 1 is a diesel engine. In FIG. 1, the inside of the internal combustion engine 1 and its intake system are omitted.

  In FIG. 1, an exhaust pipe 5 through which exhaust gas discharged from the internal combustion engine 1 flows is connected to the internal combustion engine 1, and this exhaust pipe 5 is connected downstream to a muffler (not shown). Further, an occlusion reduction type NOx catalyst (hereinafter simply referred to as NOx catalyst) 10 for purifying NOx in the exhaust is disposed in the middle of the exhaust pipe 5.

  A fuel addition valve 13 for supplying fuel as a reducing agent to the NOx catalyst 10 is disposed upstream of the NOx catalyst 10 in the exhaust pipe 5 during NOx reduction processing of the NOx catalyst 10 and SOx poisoning regeneration. Has been. The fuel injected from the fuel addition valve 13 is introduced into the NOx catalyst 10 together with the exhaust from the internal combustion engine 1.

  The NOx catalyst 10 in this embodiment is selected from alkali metals such as potassium K, sodium Na, lithium Li and cesium Cs, alkaline earth such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y. And at least one of the above and a noble metal such as platinum Pt. The NOx catalyst 10 occludes NOx when the air-fuel ratio of the exhaust gas passing through the NOx catalyst 10 is lean, and occludes if the air-fuel ratio of the exhaust gas that passes through the NOx catalyst 10 becomes rich and a reducing agent is present. It has the effect of reducing and purifying by removing NOx. The NOx catalyst 10 carries an oxidation catalyst that causes an oxidation reaction when fuel as a reducing agent is introduced and raises the temperature of the NOx catalyst 10 itself by the heat of reaction.

  The internal combustion engine 1 is also provided with an electronic control unit (ECU) 20 for controlling the internal combustion engine 1 and the exhaust system. The ECU 20 is a unit that performs control related to the NOx catalyst 10 of the internal combustion engine 1 in addition to controlling the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  Sensors related to control of the operation state of the internal combustion engine 1 such as an air flow meter, a crank position sensor, and an accelerator position sensor (not shown) are connected to the ECU 20 via electric wiring so that an output signal is input to the ECU 20. It has become. On the other hand, a fuel injection valve (not shown) in the internal combustion engine 1 is connected to the ECU 20 via an electric wiring, and a fuel addition valve 13 in this embodiment is connected via an electric wiring and is controlled by the ECU 20. It has become so.

  The ECU 20 includes a CPU, a ROM, a RAM, and the like. The ROM stores a program for performing various controls of the internal combustion engine 1 and a map storing data. The NOx reduction processing routine (reduction is omitted) for reducing and releasing NOx stored in the NOx catalyst 10 and the SOx poisoning regeneration routine in the present embodiment, which will be described later, are also programs stored in the ROM of the ECU 20. is there.

In the diesel engine as shown in FIG. 1, the air-fuel ratio of the exhaust at normal time is lean, and the NOx catalyst 10 can purify NOx in the exhaust by storing NOx in the exhaust. . However, when the amount of NOx stored in the NOx catalyst 10 increases, the NOx purification ability of the NOx catalyst 10 deteriorates. Therefore, when the amount of NOx occluded in the NOx catalyst 10 exceeds a predetermined amount, NOx reduction processing is performed in which fuel as a reducing agent is supplied from the fuel addition valve 13 to the exhaust pipe 5 upstream of the NOx catalyst 10. Do. As a result, the air-fuel ratio of the exhaust gas passing through the NOx catalyst 10 is reduced and the reducing agent is present.
The NOx stored in the x catalyst 10 is reduced and released.

In addition, if the SOx component is contained in the exhaust gas, the NOx catalyst 10 stores SOx in the exhaust gas by the same mechanism as that for storing NOx. When the air-fuel ratio of the exhaust gas is lean, SOx (eg, SO ₂ ) in the exhaust gas is oxidized on, for example, platinum Pt to become SO ₃ ⁻ , SO ₄ ⁻ , and is combined with, for example, barium oxide BaO to form BaSO ₄ . To do. In this case, BaSO ₄ is relatively stable, and since crystals tend to be coarse, once produced, they are difficult to be decomposed and separated. For this reason, when the amount of BaSO ₄ produced in the NOx catalyst 10 increases, the amount of BaO that can participate in NOx storage decreases, and the NOx storage capacity decreases.

In order to eliminate this SOx poisoning, BaSO ₄ generated in the NOx catalyst 10 is decomposed at a high temperature, and SO ₃ ⁻ and SO ₄ ⁻ sulfate ions generated thereby are reduced in a rich atmosphere, It is necessary to convert it into gaseous SO ₂ to be separated from the NOx catalyst 10. Therefore, in order to perform SOx poisoning regeneration, it is necessary to make the NOx catalyst 10 in a high temperature and rich atmosphere.

  As a method for carrying out such SOx poisoning regeneration, fuel as a reducing agent is added from the fuel addition valve 13 to the exhaust pipe 5 upstream of the NOx catalyst 10, and the NOx catalyst 10 is made to react by the reaction heat in the oxidation catalyst of the fuel. There is a method to create a rich atmosphere while raising the temperature. However, in this method, if the air-fuel ratio of the exhaust gas passing through the NOx catalyst 10 is to be maintained in a rich state, the temperature of the NOx catalyst 10 rises due to the reaction of fuel or the like in the NOx catalyst 10, and the engine operating state Depending on the condition, there is a risk of overheating.

  Therefore, at the time of SOx poisoning regeneration, the air-fuel ratio of exhaust discharged from a cylinder (not shown) of the internal combustion engine 1 is controlled to the target air-fuel ratio, and the reducing agent is supplied from the fuel addition valve 13 to the exhaust pipe 5 by rich spike. The NOx catalyst 10 is intermittently supplied, so that a large amount of reducing agent does not react in a short period of time and does not overheat.

  Here, since combustion in the internal combustion engine 1 is normally performed at a lean air-fuel ratio, the air-fuel ratio of exhaust discharged from the cylinders of the internal combustion engine 1 is lean at normal times. In that case, in order to supply sufficient reducing agent to the NOx catalyst 10, it is necessary to relatively increase the amount of reducing agent intermittently added from the fuel addition valve 13. As a result, in the NOx catalyst 10, the difference between the temperature during which the fuel added from the fuel addition valve 13 reacts and the temperature during the period during which the fuel is not added increases, and thus the temperature variation in the NOx catalyst 10 increases.

  As a result, during the period when the temperature of the NOx catalyst 10 is low, the temperature of the NOx catalyst 10 may be lower than the sulfur separation / desorption temperature (or regeneration lower limit temperature) required for the reduction reaction of SOx at the minimum, and SOx poisoning may occur. Reproduction efficiency may decrease. Therefore, in reality, when SOx poisoning regeneration of the NOx catalyst 10 is performed, the air-fuel ratio of the exhaust discharged from the cylinder of the internal combustion engine 1 is controlled to the rich side, and fuel is added from the fuel addition valve 13 at the rich spike. By suppressing the amount of fuel added per unit time during this time, temperature fluctuations in the NOx catalyst 10 are suppressed, and the reduction in SOx poisoning regeneration efficiency is suppressed.

  However, in this case, in the internal combustion engine 1, combustion occurs at a rich air-fuel ratio, so that the fuel consumption related to the entire SOx poisoning regeneration process is deteriorated, and further, the exhaust emission during this period may be deteriorated. It was.

Therefore, in this embodiment, even if a relatively large amount of fuel is intermittently supplied as described above in the downstream portion of the NOx catalyst 10, the influence is reduced, and the NOx catalyst It is noted that, in the downstream portion of the NOx catalyst 10, the heat capacity is larger than that of the upstream end portion of the NOx catalyst 10, so that the temperature change is smaller than that of the upstream portion of the NOx catalyst 10. did. When the downstream portion of the NOx catalyst 10 is subjected to SOx poisoning regeneration, the air-fuel ratio of the exhaust discharged from the internal combustion engine 1 is controlled to the lean side and is intermittently added from the fuel addition valve 13. The amount of fuel added per unit time was increased. On the other hand, when SOx poisoning regeneration is performed on the upstream portion of the NOx catalyst 10, the air-fuel ratio of the exhaust gas discharged from the internal combustion engine 1 is controlled to the rich side and added intermittently from the fuel addition valve 13. The amount of fuel added per unit time was reduced.

  This will be described with reference to FIG. FIG. 2 shows the exhaust gas introduced into the NOx catalyst 10 when SOx poisoning regeneration is performed on the upstream end A of the NOx catalyst 10 and when SOx poisoning regeneration is performed on the downstream portion B of the NOx catalyst 10. 4 is a time chart showing an air-fuel ratio, an addition pulse sent to the fuel addition valve 13 by a command from the ECU 20, a temperature at an upstream end A, and a temperature at a downstream portion B. Here, the left column of FIG. 2 controls the air-fuel ratio of the exhaust discharged from the cylinder of the internal combustion engine 1 to the rich side (target combustion A / F = rich) and is intermittently added from the fuel addition valve 13. The time chart when the amount of fuel added per unit time is reduced (target reducing agent addition amount = low), the right column controls the air-fuel ratio of exhaust discharged from the cylinder of the internal combustion engine 1 to the lean side (target) It is a time chart when the amount of fuel added per unit time of fuel added intermittently from the fuel addition valve 13 is increased (target reducing agent addition amount = high). Here, the target combustion A / F is the target air-fuel ratio in the present embodiment, and the target reducing agent addition amount is the target reducing agent amount in the present embodiment.

  In this embodiment, when SOx poisoning regeneration is performed for the portion B on the downstream side of the NOx catalyst 10, the air-fuel ratio of the exhaust discharged from the cylinder of the internal combustion engine 1 as shown in the right column of FIG. Is controlled to the lean side, and the addition amount of fuel added intermittently from the fuel addition valve 13 per unit time is increased. In this case, the amplitude of the fluctuation of the air-fuel ratio of the exhaust gas introduced into the NOx catalyst 10 increases. As a result, the temperature fluctuation at the upstream end portion A of the NOx catalyst 10 becomes large and falls below the sulfur separation desorption temperature (or regeneration limit temperature) during a part of the period. However, at point B, which is the downstream portion of the NOx catalyst 10, the air-fuel ratio of the exhaust gas introduced into the NOx catalyst 10 is varied and the heat capacity is large, so the temperature variation is relatively small. It has become.

  Accordingly, since the temperature of the NOx catalyst 10 does not fall below the sulfur separation desorption temperature (or regeneration limit temperature) at the place where the SOx poisoning regeneration is actually performed, it is possible to suppress the deterioration of the SOx poisoning regeneration efficiency.

  On the other hand, when SOx poisoning regeneration is performed on the upstream end A of the NOx catalyst 10, the air-fuel ratio of the exhaust discharged from the internal combustion engine 1 is controlled to the rich side and intermittently from the fuel addition valve 13. The amount of fuel added per unit time is reduced. By doing so, the amplitude of the fluctuation of the air-fuel ratio of the exhaust gas introduced into the NOx catalyst 10 is reduced, and the temperature change in A is also reduced. As a result, also in A, the temperature of the NOx catalyst 10 does not fall below the sulfur separation desorption temperature (or regeneration limit temperature), and the reduction in SOx poisoning regeneration efficiency can be suppressed.

  Next, the SOx poisoning regeneration routine in this embodiment will be described. FIG. 3 is a flowchart showing the SOx poisoning regeneration routine in this embodiment. This routine is a program stored in the ROM of the ECU 20 and is executed at predetermined intervals while the internal combustion engine 1 is in operation.

  When the SOx poisoning regeneration routine in the present embodiment is executed, first, in S101, the SOx occlusion amount at each location of the NOx catalyst 10 is calculated. Specifically, a plurality of detection points are defined in the NOx catalyst 10, and the previous plurality of detection points are determined based on the SOx occlusion amount at the start of the previous SOx poisoning regeneration and the temperature distribution of the NOx catalyst. The remaining SOx amount at the end of SOx poisoning regeneration is estimated, and each detection point at the present time is determined from the remaining SOx amount at each detection point and the fuel consumption in the internal combustion engine 1 after the previous SOx poisoning regeneration end. The SOx occlusion amount may be estimated. When the processing of S101 ends, the process proceeds to S102.

  In S102, the SOx poisoning regeneration location is determined from the SOx occlusion amount at each detection point calculated in S101. Specifically, it is determined that SOx poisoning regeneration is performed at a detection point where the SOx occlusion amount is determined to be equal to or greater than a limit SOx occlusion amount that is a threshold that is considered to affect the NOx purification performance of the NOx catalyst 10. . When the process of S102 ends, the process proceeds to S103. Here, the above-described limit SOx occlusion amount corresponds to the predetermined sulfur amount in the present embodiment.

  In S103, it is determined whether or not there is a SOx poisoning regeneration place in S102. Here, there was no SOx poisoning regeneration place. That is, when it is determined that there is no place where the SOx occlusion amount is greater than or equal to the limit SOx occlusion amount, this routine is terminated as it is. On the other hand, if there is a SOx poisoning regeneration place, the process proceeds to S104.

  In S104, the target combustion A / F and the target reducing agent addition amount are derived. Specifically, it corresponds to the position of the SOx poisoning regeneration place determined in S102 from the map storing the relationship between the position of the SOx poisoning regeneration place, the target combustion A / F, and the target reducing agent addition amount. The target combustion A / F to be performed and the value of the target reducing agent addition amount are read out.

  Here, as described above, the target combustion A / F is the target air-fuel ratio in the present embodiment, and corresponds to the air-fuel ratio of the exhaust discharged from the cylinder of the internal combustion engine 1. The target reducing agent addition amount is the target reducing agent amount in the present embodiment, and per unit time during the period of adding fuel when fuel is intermittently added from the fuel addition valve 13 in the rich spike. This corresponds to the amount of fuel added to.

  Here, the relationship between the position of the SOx poisoning regeneration site, the target combustion A / F, and the target reducing agent addition amount is experimentally obtained in advance. A method for obtaining the relationship between the position of the SOx poisoning regeneration location, the target combustion A / F, and the target reducing agent addition amount will be described with reference to FIG. FIG. 4 is a graph showing the position of the NOx catalyst 10 in the axial direction, the temperature that can be secured at that position, and the target combustion A / F.

  The upper graph in FIG. 4 shows the relationship between the axial position of the NOx catalyst 10 and the secureable temperature. According to the curve drawn in this figure, for example, when combustion A / F = 25, the fuel addition valve 13 is used to supply the NOx catalyst 10 with sufficient reducing agent for SOx poisoning regeneration. Therefore, it is necessary to increase the amount of the reducing agent supplied intermittently. As a result, the temperature fluctuation at the upstream end A of the NOx catalyst 10 becomes large, and the ensureable temperature becomes low. Conversely, when combustion A / F = 18, the amount of reducing agent that should be intermittently supplied from the fuel addition valve 13 may be small, so the temperature fluctuation at the upstream end A is small. As a result, the temperature that can be secured is higher than that in the case of combustion A / F = 25.

The lower side of FIG. 4 is a graph showing the combustion A / F necessary for making the temperature of the NOx catalyst 10 equal to or higher than the sulfur separation desorption temperature (or the regeneration lower limit temperature) in the above-described state. That is, at the upstream end A, in order to ensure a temperature equal to or higher than the sulfur separation desorption temperature (or regeneration lower limit temperature) in the upper graph of FIG. On the other hand, in the portion B on the downstream side, the temperature fluctuation is small, so that the sulfur separation / desorption temperature (or regeneration lower limit temperature) can be secured even when the combustion A / F = 25.

  Thus, the relationship between the axial position of the NOx catalyst 10 and the target combustion A / F can be obtained from the lower graph of FIG. When the target combustion A / F value is determined, the target reducing agent addition amount to be added per unit time from the fuel addition valve 13 is determined from the difference from the reducing agent amount value necessary for SOx poisoning regeneration. Obtainable.

  Returning to FIG. In S104, when the target combustion A / F and the target reducing agent addition amount are derived from the map created based on the above concept, the combustion A / F is controlled to become the target combustion A / F in S105. The Specifically, the combustion A / F is controlled by controlling the amount of intake air introduced into the cylinder of the internal combustion engine 1 by controlling the opening of an intake throttle valve (not shown) or an EGR valve (not shown). .

  Next, in S106, a reducing agent corresponding to the target reducing agent addition amount is intermittently added from the fuel addition valve 13 per unit time. When the process of S106 ends, this routine is temporarily ended.

  As described above, in the present embodiment, a location where SOx poisoning regeneration is necessary is determined from the amount of SOx stored in each detection unit of the NOx catalyst 10, and SOx poisoning regeneration is necessary. At the place, the lowest target combustion A / F at which the temperature of the NOx catalyst can ensure the sulfur separation desorption temperature (or the regeneration lower limit temperature) or higher is obtained, and the actual combustion A / F is controlled to be the target A / F. The minimum amount of reducing agent that can be subjected to SOx regeneration processing is added from the fuel addition valve 13 as the target reducing agent addition amount.

  Therefore, the temperature of the NOx catalyst 10 at the SOx poisoning regeneration site can be suppressed from falling below the sulfur separation desorption temperature (or the regeneration lower limit temperature), and the reduction in SOx poisoning regeneration efficiency can be suppressed. At the same time, since it is possible to prevent the air-fuel ratio of the exhaust gas discharged from the cylinder of the internal combustion engine 1 from being unnecessarily controlled to a low combustion A / F, it is possible to suppress deterioration in fuel consumption and emission in SOx poisoning regeneration. Can do.

  In the flowchart shown in FIG. 3, the processing of S101 and S102 corresponds to the SOx poisoning reproduction portion determination step in this embodiment. The processing from S104 to S106 corresponds to the reducing agent supply step in the present embodiment.

  In S102 in FIG. 3, when there are a plurality of SOx poisoning regeneration sites, the target combustion A / F and the target reducing agent addition amount obtained for the SOx poisoning regeneration site located on the most upstream side are obtained. The value of may be adopted. This is because the more the SOx poisoning regeneration site is located upstream of the NOx catalyst 10, the smaller the combustion A / F value at which the temperature of the SOx poisoning regeneration site can be maintained at or above the sulfur separation desorption temperature (or regeneration lower limit temperature). In other words, since the conditions for the combustion A / F are severe, by adopting the target combustion A / F and the value of the target reducing agent addition amount obtained for the SOx poisoning regeneration position located at the most upstream side, a plurality of values can be obtained. It is possible to simultaneously perform SOx poisoning regeneration while suppressing a decrease in SOx poisoning regeneration efficiency with respect to the SOx poisoning regeneration site.

  Next, another aspect in the present embodiment will be described. This aspect is different in terms of the map in which the target combustion A / F and the target reducing agent addition amount are derived in S104 of FIG. That is, when deriving the target combustion A / F, it is ensured that the temperature of the SOx poisoning regeneration place in the NOx catalyst 10 is equal to or higher than the sulfur separation desorption temperature (or regeneration lower limit temperature), and the temperature of the NOx catalyst 10. Is a mode that takes into consideration that the temperature does not overheat.

  FIG. 5 is a graph showing the concept of a map showing the relationship between the position of the SOx poisoning regeneration location in the NOx catalyst 10 and the target combustion A / F in this embodiment.

  In FIG. 5, the graph written second from the top shows the relationship between the position of the SOx poisoning regeneration position in the NOx catalyst 10 and the maximum catalyst temperature. That is, as described above, if the combustion A / F is the same, the temperature variation at the SOx poisoning regeneration site increases as the position of the SOx poisoning regeneration site in the NOx catalyst 10 is upstream. This indicates that the maximum temperature at the SOx poisoning regeneration site also increases. According to the second graph from the top in FIG. 5, it can be seen that if the SOx poisoning regeneration place in the NOx catalyst 10 is the same, the higher the combustion A / F, the higher the maximum temperature. The catalyst limit temperature shown here is a catalyst temperature as a threshold value at which it is determined that there is a possibility that thermal degradation will occur due to excessive temperature rise of the NOx catalyst 10 when the temperature of the NOx catalyst 10 exceeds this temperature.

  The graph shown third from the top in FIG. 5 is a restriction that the maximum catalyst temperature of the NOx catalyst 10 does not exceed the catalyst limit temperature, that is, the NOx catalyst 10 does not overheat, with respect to the lower graph in FIG. It is the graph which calculated | required target combustion A / F in consideration of this. For example, considering the upstream end A of the NOx catalyst 10, the combustion A / F condition obtained from the condition that the temperature of the NOx catalyst 10 does not fall below the sulfur separation desorption temperature (or the regeneration lower limit temperature) is the combustion A / F. F ≦ 18. On the other hand, the combustion A / F condition obtained from the condition that the maximum catalyst temperature of the NOx catalyst 10 does not exceed the catalyst limit temperature is combustion A / F ≦ 16. Accordingly, the target combustion A / F in this case is 16. Here, the value of combustion A / F = 16 corresponds to the above-described temperature rise limit air-fuel ratio.

  As described above, in this embodiment of the present embodiment, when the target combustion A / F is derived, the upper limit of the target fuel A / F is taken into consideration that the NOx catalyst 10 does not overheat. Therefore, in the SOx poisoning regeneration, it is possible to suppress the decrease in SOx poisoning regeneration efficiency and the deterioration of fuel consumption and emission, and it is possible to suppress the NOx catalyst 10 from being excessively heated.

  In this embodiment, the SOx poisoning regeneration place in the NOx catalyst 10 is changed to the SOx poisoning regeneration place on the basis of the influence of the change in the heat capacity and the supply amount of the reducing agent when the rich spike is performed. Accordingly, the target fuel A / F and the target reducing agent addition amount are set. However, when only the heat capacity is different depending on the SOx poisoning regeneration place in the NOx catalyst 10, or the NOx catalyst is different depending on the SOx poisoning regeneration place in the NOx catalyst 10. The same control may be applied to the case where the bed temperature of 10 is different.

  Next, a second embodiment of the present invention will be described. In the second embodiment, as in the first embodiment, the SOx poisoning regeneration is not performed under appropriate conditions for the specific SOx poisoning regeneration place in the NOx catalyst 10, but the upstream end portion of the NOx catalyst 10 is used. A description will be given of an example in which SOx poisoning and regeneration locations are sequentially designated as positions from the downstream end to the downstream end, and SOx poisoning and regeneration are sequentially performed under appropriate conditions for the determined SOx poisoning and regeneration locations.

  The internal combustion engine to which this embodiment is applied and its exhaust system and control system are the same as those shown in FIG. FIG. 6 shows the SOx poisoning regeneration routine in this embodiment.

When the SOx poisoning regeneration routine in the present embodiment is executed, first, the SOx occlusion amount of the entire NOx catalyst is calculated in S201. The difference from S101 in FIG. 3 is that, in this routine, the SOx occlusion amount at a predetermined detection point of the NOx catalyst 10 is not calculated individually,
The point is that the SOx occlusion amount of the entire NOx catalyst 10 is calculated. Specifically, it may be calculated from the amount of fuel consumed after the end of the previous SOx poisoning regeneration. When the process of S201 ends, the process proceeds to S202.

  In S202, it is determined whether SOx poisoning regeneration is necessary. Specifically, it is determined whether or not the total SOx storage amount calculated in S201 is equal to or greater than the catalyst limit SOx storage amount. Here, the catalyst limit SOx occlusion amount is the SOx occlusion amount as a threshold at which it is determined that the deterioration of the NOx purification performance of the NOx catalyst 10 becomes large when the entire NOx catalyst 10 is occluded.

  If it is determined in S202 that SOx poisoning regeneration is not required, that is, the SOx occlusion amount of the NOx catalyst 10 as a whole is less than the catalyst limit SOx occlusion amount, this routine is immediately terminated. On the other hand, if it is determined that SOx poisoning regeneration is necessary, that is, the SOx occlusion amount of the NOx catalyst 10 as a whole is equal to or greater than the catalyst limit SOx occlusion amount, the process proceeds to S203.

  In S203, when performing SOx poisoning regeneration of the entire NOx catalyst 10, first, the target combustion A / F and the target reducing agent addition amount at the upstream end of the NOx catalyst 10 are derived. Here, the target combustion A / F corresponding to the upstream end of the NOx catalyst 10 is stored from a map storing the relationship between the position of the SOx poisoning regeneration location, the target combustion A / F, and the target reducing agent addition amount. And it derives | leads-out by reading the value of target reducing agent addition amount. Regarding this map, the same map as used in S104 of FIG. 3 may be used.

  Next, the process proceeds to S204, where the combustion A / F is controlled to the target combustion A / F derived in S203, and the process proceeds to S205 from the fuel addition valve 13 with the target reducing agent addition amount derived in S203. Add. The contents of this process are the same as the processes of S105 and S106 shown in FIG. Here, a predetermined waiting time is set after the addition of the reducing agent in S205 until the process proceeds to S206. This waiting time can be considered as an interval from when SOx poisoning regeneration is performed on a predetermined SOx poisoning regeneration place of the NOx catalyst 10 until SOx poisoning regeneration is performed on the next SOx poisoning regeneration place. it can. With regard to this waiting time, the interval at which SOx poisoning regeneration is most efficiently performed may be obtained experimentally in consideration of the control speed of the combustion A / F, the response speed of the fuel addition valve 13, and the like.

  In S206, it is determined whether the target combustion A / F derived in S203 and the target reducing agent addition amount are for the downstream end of the NOx catalyst 10. That is, in this routine, the SOx poisoning regeneration is sequentially performed on the positions from the upstream end portion to the downstream end portion of the NOx catalyst 10, so that the upstream end portion of the NOx catalyst 10 is downstream from the upstream end portion. It is determined whether or not the SOx poisoning regeneration has been completed for the position up to the end of. Here, when it is determined that the target combustion A / F derived in S203 and the target reducing agent addition amount are for the downstream end of the NOx catalyst 10, the upstream end of the NOx catalyst 10 is determined. Since it is determined that the SOx poisoning regeneration has been completed from the first to the downstream end, this routine is temporarily terminated. On the other hand, if it is determined that the target combustion A / F derived in S203 and the target reducing agent addition amount are not for the downstream end of the NOx catalyst 10, the upstream end of the NOx catalyst 10 is determined. Since it is determined that the SOx poisoning regeneration has not been completed from the downstream end to the downstream end, the process proceeds to S207.

In S207, the target combustion A / F and the target reducing agent addition amount at a position downstream by a predetermined amount from the position in the NOx catalyst corresponding to the currently set target combustion A / F and the target reducing agent addition amount. Is derived from the aforementioned map. Here, the predetermined amount is a length set in advance, and may be, for example, 1 / n of the axial length of the NOx catalyst 10. Here, the more n, the more finely the NOx catalyst 10 is divided into appropriate target combustion A at each location.
Since SOx poisoning regeneration is performed with / F and the target reducing agent addition amount, SOx poisoning regeneration can be completed more reliably.

  When the processing of S207 is completed, the processing of S204 to S206 is executed again, and until it is determined in S206 that the target combustion A / F and the target reducing agent addition amount are for the downstream end of the NOx catalyst 10, The process is repeated. In S206, if it is determined that the target combustion A / F and the target reducing agent addition amount are for the downstream end portion of the NOx catalyst 10, the downstream end portion from the upstream end portion of the NOx catalyst 10 is determined. Since it is determined that the SOx poisoning regeneration has been performed up to the end with the appropriate target combustion A / F and the target reducing agent addition amount, this routine is temporarily terminated.

  As described above, in the present embodiment, the upstream end portion to the downstream end portion of the NOx catalyst 10 is appropriately divided, and the sulfur separation desorption temperature (or regeneration lower limit temperature) or higher is obtained for each location. SOx poisoning regeneration is performed with an appropriate target combustion A / F that can be ensured and a target reducing agent addition amount. Therefore, the SOx poisoning regeneration can be completed more reliably for the entire NOx catalyst 10. In addition, the NOx catalyst 10 may be divided into two, that is, SOx poisoning regeneration may be performed at two locations on the upstream side and the downstream side by appropriate target combustion A / F and target reducing agent addition amount. .

  Further, in this embodiment, since SOx poisoning regeneration proceeds sequentially from the upstream end of the NOx catalyst 10 toward the downstream, the SOx poisoning regeneration always located on the most upstream side where the conditions for combustion A / F are severe are always high. The target combustion A / F obtained for the place and the value of the target reducing agent addition amount are adopted. Accordingly, it is possible to perform SOx poisoning regeneration while suppressing a decrease in SOx poisoning regeneration efficiency for all SOx poisoning regeneration sites. In addition, the occurrence of SOx re-poisoning on the downstream side of the NOx catalyst 10 can be suppressed.

  Next, a third embodiment of the present invention will be described. In the third embodiment, an example in which a single NOx catalyst 10 is not arranged in the exhaust pipe 5 of the internal combustion engine 1 as in the first embodiment but a plurality of NOx catalysts are arranged in series will be described. To do.

  FIG. 7 is a diagram showing the internal combustion engine 1 and its exhaust system and control system in this embodiment. In FIG. 7, a downstream NOx catalyst 12 is provided on the downstream side of the upstream NOx catalyst 11. The upstream exhaust pipe 5 of the upstream NOx catalyst 11 is provided with a first NOx sensor 14 that detects the upstream NOx concentration of the upstream NOx catalyst 11. Similarly, a second NOx sensor 15 is provided in the exhaust pipe 5 between the upstream NOx catalyst 11 and the downstream NOx catalyst 12, and a third NOx sensor 16 is provided in the exhaust pipe 5 downstream of the downstream NOx catalyst 12. ing.

  Next, SOx poisoning regeneration in the present embodiment will be described. FIG. 8 shows the SOx poisoning regeneration routine in this embodiment. When this routine is executed, first, in S301, the SOx occlusion amounts in the upstream NOx catalyst 11 and the downstream NOx catalyst 12 are calculated. Specifically, the SOx occlusion amount in the upstream NOx catalyst 11 is detected from the difference between the outputs of the first NOx sensor 14 and the second NOx sensor 15. That is, the NOx purification performance in the upstream NOx catalyst 11 is detected from the difference between the outputs of the first NOx sensor 14 and the second NOx sensor 15, and the SOx occlusion amount highly correlated with the NOx purification performance is detected. Similarly, the SOx occlusion amount in the downstream side NOx catalyst 12 is detected from the difference between the output of the second NOx sensor 15 and the output of the third NOx sensor 16. When the process of S301 ends, the process proceeds to S302.

In S302, the SOx poisoning regeneration target NOx catalyst is determined. Specifically, it is determined that the SOx poisoning regeneration is performed on the NOx catalyst that is determined to be equal to or more than the limit SOx storage amount as a threshold that the NOx purification performance of the NOx catalyst is considered to deteriorate significantly. For example, when only the SOx occlusion amount in the upstream NOx catalyst 11 is equal to or greater than the limit SOx occlusion amount, only the upstream NOx catalyst 11 becomes the SOx poisoning regeneration target NOx catalyst. When the process of S302 ends, the process proceeds to S303.

  In S303, it is determined whether or not there is a SOx poisoning regeneration target NOx catalyst in S302. Here, there was no SOx poisoning regeneration target NOx catalyst. That is, when it is determined that there is no NOx catalyst having the SOx occlusion amount equal to or greater than the limit SOx occlusion amount, this routine is terminated as it is. On the other hand, if there is a SOx poisoning target NOx catalyst, the process proceeds to S304.

  In S304, the target combustion A / F and the target reducing agent addition amount are derived. That is, the target combustion corresponding to the SOx poisoning regeneration target NOx catalyst determined in S302 from the map storing the relationship between the SOx poisoning regeneration target NOx catalyst, the target combustion A / F, and the target reducing agent addition amount. It is derived by reading out the values of A / F and target reducing agent addition amount. In other words, depending on whether the SOx poisoning regeneration target NOx catalyst is the upstream NOx catalyst 11 or the downstream NOx catalyst 12, an appropriate target combustion A / F and target reducing agent addition amount are derived in each case.

  Here, the relationship between the SOx poisoning regeneration target NOx catalyst, the target combustion A / F, and the target reducing agent addition amount is experimentally obtained in advance. For this relationship, the same idea as shown in FIG. 4 is applied.

  FIG. 9 is a graph showing two NOx catalysts arranged in series in the exhaust pipe 5, the temperatures that can be secured in these NOx catalysts, and the target A / F.

  The upper graph of FIG. 9 shows the relationship between two NOx catalysts arranged in series in the exhaust pipe 5 and the secureable temperature. In this graph, for example, for the upstream side NOx catalyst 11, for the same reason as described in FIG. 4, when the combustion A / F = 25, a sufficient reducing agent for SOx poisoning regeneration is added to the NOx catalyst. 10, it is necessary to increase the amount of the reducing agent intermittently supplied from the fuel addition valve 13. As a result, the temperature fluctuation in the upstream side NOx catalyst 11 becomes large, and the secureable temperature becomes low. On the other hand, when combustion A / F = 18, the amount of reducing agent to be intermittently supplied from the fuel addition valve 13 is small, and therefore the temperature fluctuation in the upstream side NOx catalyst 11 becomes small. As a result, the temperature that can be secured is higher than that in the case of combustion A / F = 25.

  On the other hand, in the downstream side NOx catalyst 12, the effect of the reducing agent intermittently supplied from the fuel addition valve 13 during execution of the rich spike on the temperature change of the downstream side NOx catalyst 12 is higher than that in the upstream side NOx catalyst 11. Since it is small, the temperature that can be secured becomes high for each combustion A / F value, and even when the combustion A / F = 25, the sulfur separation desorption temperature (or regeneration lower limit temperature) can be secured.

  The graph shown in the lower side of FIG. 9 shows the combustion A / N necessary for setting the temperatures of the upstream NOx catalyst 11 and the downstream NOx catalyst 12 to be equal to or higher than the sulfur separation desorption temperature (or regeneration lower limit temperature) in the above-described state. FIG. That is, in the upstream side NOx catalyst 11, in order to ensure a temperature equal to or higher than the sulfur separation desorption temperature (or regeneration lower limit temperature) in the upper graph of FIG. On the other hand, in the downstream side NOx catalyst 12, the temperature fluctuation is small, so that the sulfur separation desorption temperature (or regeneration lower limit temperature) can be secured even when the combustion A / F = 25.

Thus, from the lower diagram of FIG. 9, the target combustion A / F for the case where the SOx poisoning regeneration target NOx catalyst is the upstream NOx catalyst 11 and the downstream NOx catalyst 12, respectively.
Can be obtained. When the target combustion A / F value is determined, the target reducing agent addition amount to be added per unit time from the fuel addition valve 13 is determined from the difference from the reducing agent amount value necessary for SOx poisoning regeneration. Obtainable.

  In this description, the upstream NOx catalyst 11 and the downstream NOx catalyst 12 are described on the premise that the heat capacities are almost the same. However, if these heat capacities are different, the target combustion is taken into consideration. It is necessary to derive A / F. For example, when the heat capacity of the downstream NOx catalyst 12 is extremely small, the effect of the reducing agent intermittently supplied from the fuel addition valve 13 on the temperature change of the downstream NOx catalyst 12 is not necessarily the upstream NOx catalyst. This is because the influence on the temperature change of 11 is not reduced.

  Here, the description returns to FIG. When the target combustion A / F and the target reducing agent addition amount are derived in S304, the combustion A / F is controlled to become the target combustion A / F in S305, and the process proceeds to S306. The reducing agent corresponding to the target reducing agent addition amount is intermittently added. When the process of S306 ends, this routine is temporarily ended.

  As described above, in this embodiment, the amount of SOx occluded in the upstream NOx catalyst 11 and the downstream NOx catalyst 12 from the outputs of the first NOx sensor 14, the second NOx sensor 15, and the third NOx sensor 16. From which NOx catalyst to be subjected to SOx poisoning regeneration is determined. Then, for the NOx catalyst to be subjected to SOx poisoning regeneration, the lowest target combustion A / F that can ensure that the temperature is equal to or higher than the sulfur separation desorption temperature (or regeneration limit temperature) is obtained, and the actual combustion A / F Is controlled to be the target combustion A / F. Further, the minimum amount of reducing agent capable of SOx poisoning regeneration is added from the fuel addition valve 13.

  Therefore, in the exhaust system of an internal combustion engine having a plurality of NOx catalysts, the temperature of the NOx catalyst that is the target of SOx poisoning regeneration is suppressed from falling below the sulfur separation desorption temperature (or regeneration limit temperature), and SOx poisoning regeneration efficiency is reduced. Can be suppressed. At the same time, since it is possible to suppress control to uselessly low combustion A / F, it is possible to suppress deterioration in fuel consumption and emission in SOx poisoning regeneration.

  In the embodiment described above, an example in which fuel as a reducing agent is supplied to the NOx catalyst 10 during SOx poisoning regeneration has been described, but exhaust purification using, for example, urea or the like other than fuel as the reducing agent. You may apply the control similar to the said Example with respect to a catalyst. Moreover, in the said Example, although the case where the internal combustion engine 1 was a diesel engine was demonstrated, when the internal combustion engine 1 is a diesel engine other than a diesel engine, for example, even if the same control as the said Example is applied. Good. Further, in the above-described embodiment, the example in which the reducing agent is supplied from the fuel addition valve 13 provided in the exhaust pipe 5 of the internal combustion engine 1 has been described. However, the fuel as the reducing agent is sub-injection such as post injection or big rubber injection. You may apply the control similar to the said Example with respect to the case where it supplies by injection.

1 is a diagram illustrating a schematic configuration of an internal combustion engine and an exhaust system and a control system thereof in Embodiment 1 of the present invention. The air-fuel ratio of the exhaust gas introduced into the NOx catalyst and the fuel addition valve in the case where the upstream end of the NOx catalyst is SOx poisoned and the downstream part of the NOx catalyst is SOx poisoned and regenerated 6 is a time chart showing an addition pulse, a temperature at an upstream end, and a temperature at a downstream portion sent in accordance with the command. It is a flowchart which shows the SOx poisoning reproduction | regeneration routine in Example 1 of this invention. It is a graph which shows the position of the SOx poisoning reproduction | regeneration place in the NOx catalyst in Example 1 of this invention, the temperature which can be ensured in the position, and target combustion A / F. It is a graph which shows the position of the SOx poisoning reproduction | regeneration place in the NOx catalyst in another aspect of Example 1 of this invention, the temperature which can be ensured in the position, the maximum catalyst temperature, and target combustion A / F. It is a flowchart which shows the SOx poisoning reproduction | regeneration routine in Example 2 of this invention. It is a figure which shows schematic structure of the internal combustion engine in Example 3 of this invention, its exhaust system, and a control system. It is a flowchart which shows the SOx poisoning reproduction | regeneration routine in Example 3 of this invention. 7 is a graph showing a NOx catalyst to be subjected to SOx poisoning regeneration, a temperature that can be secured by the NOx catalyst, and a target combustion A / F in Example 3 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 5 ... Exhaust pipe 10 ... NOx catalyst 11 ... Upstream side NOx catalyst 12 ... Downstream side NOx catalyst 13 ... Fuel addition valve 14 ... 1st NOx sensor 15. ..Second NOx sensor 16 ... Third NOx sensor 20 ... ECU

Claims (7)

In the NOx storage reduction catalyst, the air-fuel ratio of the exhaust gas discharged from the cylinder of the internal combustion engine is controlled and a reducing agent is supplied from upstream to the NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine. A method for SOx poisoning regeneration of an exhaust purification catalyst that removes sulfur,
In the NOx storage reduction catalyst, a SOx poisoning regeneration part determining step for determining a part to be SOx poisoning regeneration;
The air-fuel ratio of the exhaust gas discharged from the cylinder of the internal combustion engine is controlled to the target air-fuel ratio, and the target reduction per unit time for the portion to be SOx poisoned regeneration determined in the SOx poisoning regeneration portion determination step A reducing agent supply step for intermittently supplying a reducing agent in an amount,
The values of the target air-fuel ratio and the target reducing agent amount in the reducing agent supply step are set according to the position of the portion to be SOx poisoning regenerated determined in the SOx poisoning regeneration portion determining step. A method for SOx poisoning regeneration of an exhaust purification catalyst.   Compared with the case where the SOx poisoning / regeneration portion determined in the SOx poisoning / regeneration portion determination step is within a predetermined upstream region upstream of the NOx storage reduction catalyst, the portion to be SOx poisoned / regenerated However, when the NOx storage reduction type NOx catalyst is within a predetermined downstream region on the downstream side, the target air-fuel ratio is set high and the target reducing agent amount is set large. The SOx poisoning regeneration method of the exhaust purification catalyst as described in 1.   In the SOx poisoning regeneration part determining step, a part where the amount of sulfur content in the NOx storage reduction catalyst is equal to or greater than a predetermined sulfur amount is determined as a part to be SOx poisoning regeneration. Item 3. A method for SOx poisoning regeneration of an exhaust purification catalyst according to Item 1 or 2.   4. The SOx poisoning regeneration method for an exhaust purification catalyst according to claim 1, wherein an upper limit is set for the value of the target air-fuel ratio.   When there are a plurality of portions determined as SOx poisoning regeneration portions in the SOx poisoning regeneration portion determination step, the values of the target air-fuel ratio and the target reducing agent amount in the reducing agent supply step are The exhaust purification catalyst according to any one of claims 1 to 4, wherein a value to be set with respect to a portion located on the most upstream side among a plurality of portions to be subjected to SOx poisoning regeneration is set. SOx poisoning regeneration method.   The SOx poisoning regeneration part determination step determined in the SOx poisoning regeneration part determination step is sequentially changed from the upstream side to the downstream side in the NOx storage reduction catalyst, and the SOx poisoning regeneration part determination step and 5. The SOx poisoning regeneration method for an exhaust purification catalyst according to any one of claims 1 to 4, wherein the reducing agent supply step is repeatedly executed. The NOx storage reduction catalyst is a NOx storage reduction group consisting of a plurality of NOx storage reduction catalysts provided in series in the exhaust passage,
In the SOx poisoning regeneration portion determining step, the NOx storage reduction catalyst to be SOx poisoning regenerated is determined as the portion to be SOx poisoning regeneration of the plurality of NOx storage reduction catalysts. A method for SOx poisoning regeneration of an exhaust purification catalyst according to any one of claims 1 to 6.

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