JP4089683B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

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

  In order to purify NOx contained in the exhaust discharged from the internal combustion engine, a NOx purifying catalyst such as a NOx storage reduction catalyst is installed in the exhaust passage. However, SOx is contained in the exhaust gas in addition to NOx, and the NOx purification action of the catalyst may be reduced when this SOx is taken into the NOx purification catalyst.

In view of this, a technique has been disclosed in which an SOx absorbent is installed on the upstream side and an NOx absorbent is installed on the downstream side of the exhaust passage of the internal combustion engine (see, for example, Patent Document 1). According to this technique, when the lean air-fuel mixture is burned, SOx in the exhaust is absorbed by the SOx absorbent, so that only NOx is absorbed by the NOx absorbent disposed downstream of the SOx absorbent. On the other hand, when the oxygen concentration in the exhaust gas flowing into the SOx absorbent and the NOx absorbent is lowered, SOx is released from the SOx absorbent, and NOx is released from the NOx absorbent. As a result, it becomes difficult for SOx to be taken into the NOx absorbent.
JP-A-6-173652

  In the exhaust passage of an internal combustion engine, when an SOx absorbent is installed on the upstream side and a NOx purification catalyst such as NOx absorbent is installed on the downstream side, the SOx in the exhaust gas is exhausted only within the capacity of the SOx absorbent that can be absorbed. Is taken in by the SOx absorbent, and more SOx is taken into the NOx purification catalyst installed on the downstream side. In addition, as the SOx absorbent absorbs SOx therein, the SOx absorption rate decreases, so that SOx that has not been absorbed may be gradually taken into the NOx purification catalyst.

  In view of the above problems, an object of the present invention is to avoid as much as possible the incorporation of SOx into a NOx purification catalyst provided in an exhaust passage in an exhaust gas purification apparatus for an internal combustion engine.

In order to solve the above-described problems, the present invention has a holding ability to hold SOx in exhaust gas inside thereof, the temperature of the inflowing exhaust gas rises, and the air-fuel ratio of the inflowing exhaust gas is leaner than the stoichiometric side. When the air-fuel ratio is reached, the SOx retention agent solution is appropriately supplied to the SOx retention means that recovers its SOx retention ability . More specifically, the present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and is provided in an exhaust passage of the internal combustion engine, and has an SOx holding capacity for holding SOx in the exhaust by carrying an SOx holding agent. At the same time, when the temperature of the inflowing exhaust gas rises and the air-fuel ratio of the inflowing exhaust gas becomes an air-fuel ratio leaner than the stoichiometric ratio, the SOx retention means for recovering its SOx retention capacity, and the SOx retention location for storing the SOx retention agent solution Agent solution storage means, and SOx retention agent supply means for supplying the SOx retention agent solution stored in the SOx retention agent storage means to the SOx retention means.

The SOx holding means is used for exhaust gas purification of an internal combustion engine, has SOx holding ability to hold SOx in the exhaust therein, the temperature of the inflowing exhaust gas rises, and the air-fuel ratio of the inflowing exhaust gas is higher than the stoichiometric ratio. When the lean air-fuel ratio is reached, an SOx retention agent that recovers the SOx retention capacity is supported. This SOx holding means suppresses SOx from flowing downstream. However, since the amount of the SOx holding agent carried on the SOx holding means is finite, its SOx holding capacity is limited, and in some cases, a relatively large amount of SOx may flow out downstream.

Therefore, the amount of SOx retaining agent carried on the SOx retaining means is increased by supplying the SOx retaining agent solution, for example, an aqueous solution or the like, preferably in a sprayed state, to the SOx retaining means by the SOx retaining agent supply means. As a result, the SOx holding capacity of the SOx holding means is increased, and the outflow of SOx to the downstream side can be suppressed as much as possible, so that SOx is taken into, for example, the NOx purification catalyst on the downstream side. Can be avoided as much as possible. Here, the SOx retention agent is supplied in the form of a solution in order to facilitate the loading of the SOx retention agent on the SOx retention means.

  Here, in the exhaust gas purification apparatus for an internal combustion engine, the SOx retention agent solution storage means stores the solution in a state where the SOx retention agent is dissolved in the fuel of the internal combustion engine, and the SOx retention agent supply means The solution may be injected from a fuel injection valve provided in an intake passage or a cylinder of the internal combustion engine. That is, the SOx holding agent is supplied to the SOx holding means via the existing fuel injection system of the internal combustion engine. In this case, a fuel tank of the internal combustion engine can also be used as the SOx retention agent solution storage means.

  Further, the exhaust gas purification apparatus for an internal combustion engine as described above further comprises SOx retention capability estimation means for estimating the degree of SOx retention capability of the SOx retention means, and the SOx retention capability estimated by the SOx retention capability estimation means is predetermined. When the degree is less than or equal to the degree, the SOx retention agent supply means may supply the SOx retention agent solution. That is, by supplying the solution from the SOx retention agent supply means only when the SOx retention capacity of the SOx retention means is lowered, it becomes possible to avoid unnecessary supply of the SOx retention agent.

  Here, the SOx retention capacity estimation means estimates the degree of the SOx retention capacity of the SOx retention means. For example, the SOx retention capacity is estimated by comparing the SOx amount flowing into the SOx retention means and the SOx amount flowing out. Capability can be estimated. Further, the degree of SOx retention ability of the SOx retention means may be estimated in consideration of the SOx amount discharged from the internal combustion engine, such as a history of the operating state of the internal combustion engine.

  Further, in the exhaust gas purification apparatus for an internal combustion engine up to the above, if the exhaust gas flow rate detecting means for detecting or estimating the exhaust flow rate flowing into the SOx holding means is further provided, the exhaust gas flow rate detected or estimated by the exhaust flow rate detecting means. May be supplied by the SOx retention agent supply means when the flow rate is equal to or higher than a predetermined flow rate. That is, the SOx holding agent supplied from the SOx holding agent supply unit is widely dispersed in the SOx holding unit using the flow of exhaust gas flowing through the exhaust passage. Therefore, the predetermined flow rate is an exhaust flow rate at which the SOx retention agent solution can be widely dispersed by the SOx retention means.

  Further, in the exhaust gas purification apparatus for an internal combustion engine up to the above, when the temperature detection means for detecting or estimating the temperature of the SOx holding means is further provided, the temperature of the SOx holding means detected or estimated by the temperature detection means May belong to a predetermined temperature range, the SOx retention agent supply means may supply a solution of the SOx retention agent. That is, the SOx holding agent supplied from the SOx holding agent supply means is diffused widely into the SOx holding means by the heat energy of the SOx holding means. Therefore, the above-mentioned predetermined temperature range is a temperature range of the SOx holding means such that the SOx holding agent solution can be widely dispersed in the SOx holding means.

  Here, after the SOx holding agent solution is supplied by the SOx holding agent supply means, a temperature raising means for raising the temperature of the SOx holding means may be further provided. Even if the SOx holding means is raised after the supply of the SOx holding agent solution, the dispersion of the SOx holding agent can be promoted. As a method for raising the temperature of the SOx holding means, the exhaust temperature flowing into the SOx holding means may be raised, or the SOx holding means itself may be warmed by a heater or the like.

  Further, in the exhaust gas purification apparatus for an internal combustion engine up to the above, the SOx holding capacity for recovering the SOx holding capacity of the SOx holding means by raising the temperature of the SOx holding means and setting the inflowing exhaust gas to the lean side air-fuel ratio. When the performance recovery means is further provided, when the SOx retention capacity recovery means does not reach the predetermined recovery state of the SOx retention capacity recovery means, the SOx retention agent supply means supplies the SOx retention agent solution. It may be.

  The SOx retaining agent solution is supplied when the predetermined recovery state is not reached, that is, the SOx retaining ability of the SOx retaining means decreases, and the SOx retaining ability is also reduced by the SOx retaining ability recovery means. Is not recovering to the extent that it cannot be sufficiently deterred. In such a case, an SOx holding agent capable of exhibiting SOx holding ability corresponding to the lowered SOx holding ability is supplied. The SOx retention ability recovery means recovers the SOx retention ability by releasing the SOx retained in the SOx retention means.

  In the exhaust gas purification apparatus for an internal combustion engine, it is possible to avoid as much as possible the incorporation of SOx into the NOx purification catalyst provided in the exhaust passage.

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

  FIG. 1 shows a schematic configuration of an exhaust gas purification apparatus for an internal combustion engine according to the present invention. Exhaust gas from the internal combustion engine 1 is discharged to the exhaust passage 2. The exhaust passage 2 is provided with a SOx trap catalyst 3 on the upstream side and a NOx catalyst 4 on the downstream side thereof. The SOx trap catalyst 3 carries an SOx holding agent having SOx holding capacity for holding SOx in exhaust gas inside. Examples of the SOx retention agent include alkali metals such as barium and potassium, and alkaline earth metals. Therefore, the SOx in the exhaust is held inside the SOx trap catalyst 3 as long as the capacity of the SOx trap catalyst 3 permits. The NOx catalyst 4 is a so-called storage reduction type NOx catalyst, and mainly purifies NOx in the exhaust gas.

  In addition, a tank 7 in which an aqueous solution of the SOx trap catalyst 3 of the SOx trap catalyst 3 is stored is provided, and the tank 7 is connected to the exhaust passage 2 upstream of the SOx trap catalyst 3 through the supply passage 5. Here, the supply passage 5 is provided with a pump 6 that pumps an aqueous solution of the SOx retention agent from the tank 7 and pumps it into the exhaust passage 2.

  Here, the internal combustion engine 1 is provided with an electronic control unit (hereinafter referred to as “ECU”) 20 for controlling the internal combustion engine 1. The ECU 20 includes a CPU, a ROM, a RAM, and the like for storing various control routines and maps to be described later. The unit to control. Here, the pump 6 operates according to a control signal from the ECU 20.

  An air flow meter 9 that is provided in the intake passage 8 of the internal combustion engine 1 and detects the intake flow rate is electrically connected to the ECU 20. Further, a temperature sensor 10 that detects the temperature of the exhaust gas flowing through the exhaust passage on the upstream side of the SOx trap catalyst 3 is also electrically connected to the ECU 20. Thus, the ECU 20 receives various signals.

In the exhaust gas purification apparatus of the internal combustion engine 1 configured as described above, the SOx in the exhaust gas is held by the SOx trap catalyst 3, so that the amount of SOx flowing into the NOx catalyst 4 is reduced, and NOx due to SOx poisoning of the NOx catalyst 4 is reduced. A reduction in purification capacity can be avoided. However, the SOx trapping capacity of the SOx trap catalyst 3 is limited, and the SOx holding capacity gradually decreases as the SOx holding amount increases. As a result, the amount of SOx flowing into the NOx catalyst 4 also increases.

  Therefore, the aqueous solution of the SOx retention agent in the tank 7 is pumped by the pump 6, and the SOx retention agent (aqueous solution) is supplied to the SOx trap catalyst 3 through the exhaust passage 2. As a result, the SOx retention capacity of the SOx trap catalyst 3 is restored to some extent, and the amount of SOx flowing into the NOx catalyst 4 can be reduced. Here, FIG. 2 shows a flow of SOx holding agent supply control for supplying the SOx trap catalyst 3 with the SOx holding agent. The control indicated by the flow is executed by the ECU 20.

  First, in S101, the SOx retention capacity of the SOx trap catalyst 3 is estimated. Specifically, based on the operating state of the internal combustion engine 1 and its operating history, the amount of SOx held in the SOx trap catalyst 3 is estimated, and the current SOx holding capacity is estimated from it. To do. Generally, as the amount of SOx held increases, the SOx trapping capacity of the SOx trap catalyst 3 decreases. Therefore, it is possible to estimate the SOx retention capacity in association with the SOx amount retaining the SOx retention capacity.

  In addition, SOx sensors are provided on the upstream side and the downstream side of the SOx trap catalyst 3, respectively, and the ratio between the SOx concentration in the exhaust gas flowing into the SOx trap catalyst 3 and the SOx concentration in the exhaust gas flowing out is determined from the detection values of the sensors. The SOx retention ability, which is the SOx amount actually retained by the SOx trap catalyst 3, may be detected from the calculated ratio. When the process of S101 ends, the process proceeds to S102.

  In S102, it is determined whether or not the SOx trapping capacity of the SOx trap catalyst 3 estimated in S101 is lowered. This determination is made based on whether or not the SOx retention ability estimated in S101 is higher than the reference SOx retention ability. If it is determined that the SOx retention capacity is reduced, the process proceeds to S103, and if it is determined that the SOx retention capacity is not decreased, the present control is terminated.

  In S103, it is determined whether or not the exhaust flow rate through the exhaust passage is equal to or greater than a predetermined flow rate SV0. The exhaust flow rate is estimated based on a signal from the air flow meter 9. The predetermined flow rate SV0 is an exhaust flow rate threshold value for allowing the SOx retaining agent aqueous solution pumped by the pump 6 to sufficiently diffuse in the SOx trap catalyst 3. That is, when the exhaust flow rate is less than SV0, the supplied SOx retention agent aqueous solution adheres only to the exhaust inlet side of the SOx trap catalyst 3 and is difficult to diffuse throughout, so the determination in S103 is performed. Is called. Therefore, if the exhaust flow rate is equal to or higher than the predetermined flow rate SV0, the process proceeds to S104, and if it is less than the predetermined flow rate SV0, the present control is terminated.

  In S104, it is determined whether or not the catalyst temperature of the SOx trap catalyst 3 is equal to or higher than a predetermined temperature T0. The catalyst temperature is estimated based on a signal from the temperature sensor 10. The predetermined temperature T0 is a threshold value for sufficiently diffusing the SOx holding agent aqueous solution pumped by the pump 6 with the SOx trap catalyst 3 by the thermal energy of the SOx trap catalyst 3. That is, when the catalyst temperature is lower than T0, the determination in S104 is performed in view of the fact that the supplied aqueous solution of SOx retention agent is difficult to diffuse throughout. Therefore, when the catalyst temperature is equal to or higher than the predetermined temperature T0, the process proceeds to S105, and when it is lower than the predetermined temperature T0, this control is terminated.

  In S105, the pump 6 pumps the SOx retention agent aqueous solution. As a result, the SOx retention agent is supplied to the SOx trap catalyst 3. As a result, the SOx retention capacity of the SOx trap catalyst 3 increases. In addition, after the SOx holding agent is supplied, the exhaust temperature of the internal combustion engine 1 may be controlled to increase the temperature of the SOx trap catalyst 3 in order to diffuse the SOx holding agent in the SOx trap catalyst 3. After the process of S105, this control is terminated.

  According to this control, when the SOx retention capacity of the SOx trap catalyst 3 decreases, the SOx retention capacity is recovered by supplying an SOx retention agent aqueous solution to the SOx trap catalyst 3, and SOx is taken into the NOx catalyst 4. Can be avoided as much as possible.

  FIG. 3 shows another SOx holding agent supply control flow for supplying the SOx trapping catalyst 3 with the SOx holding agent. The control indicated by the flow is executed by the ECU 20. Of the processes in the SOx retention agent supply control, the same processes as those in the SOx retention agent supply control shown in FIG. 2 are denoted by the same reference numerals and description thereof is omitted.

  In the SOx retention agent supply control shown in FIG. 3, if it is determined in S102 that the SOx retention ability is reduced, the process proceeds to S201. In S201, a process for recovering the SOx retention ability of the SOx trap catalyst 3 is performed. Specifically, the combustion conditions of the internal combustion engine 1 are controlled so that the exhaust gas temperature flowing into the SOx trap catalyst 3 is raised and the air-fuel ratio of the exhaust gas is made leaner than the stoichiometric air-fuel ratio. By doing so, the SOx held in the SOx trap catalyst 3 is released, and the SOx holding ability of the SOx trap catalyst 3 is recovered. When the process of S201 ends, the process proceeds to S202.

  In S202, it is determined whether or not the SOx trapping capacity of the SOx trap catalyst 3 has been recovered to a predetermined recovery state by the process of S201. Here, the predetermined recovery state refers to a state in which the SOx retention capability of the SOx trap catalyst 3 has been recovered to such an extent that it is not determined that the retention capability is reduced in S102. If it is determined in S202 that the SOx trapping capacity of the SOx trap catalyst 3 has not recovered to the predetermined recovery state, the processing after S103 is performed. Further, when it is determined that the SOx retention capacity of the SOx trap catalyst 3 has been recovered to the predetermined recovery state, this control is terminated.

  According to this control, the supply of the SOx retention agent to the SOx trap catalyst 3 is performed when the SOx retention capacity is not sufficiently recovered, for example, when the SOx retention capacity is reduced due to deterioration of the SOx trap catalyst 3 or the like. Only done. Accordingly, it is possible to suppress the consumption of the SOx retention agent.

  A second embodiment of the exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described below. FIG. 4 is a schematic view of an exhaust gas purification apparatus for an internal combustion engine according to the second embodiment. The same components as those of the exhaust gas purification apparatus for an internal combustion engine shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  The feature of the exhaust emission control device for the internal combustion engine 1 according to this embodiment is that the SOx retention agent is dissolved in the fuel of the internal combustion engine 1 and supplied from the fuel injection valve 11 together with the fuel. That is, the fuel injection valve 11 provided in the internal combustion engine 1 is connected to the pressure accumulation chamber 12, and the pressure accumulation chamber 12 is connected to the fuel tank 14 via the fuel supply passage 13. The SOx holding agent to be supplied to the SOx trap catalyst 3 is dissolved in the fuel stored in the fuel tank 14.

  Accordingly, the SOx holding agent is also injected together with the fuel injection from the fuel injection valve 11, and the SOx holding agent in the exhaust continues to be supplied to the SOx trap catalyst 3 provided in the exhaust passage 2. As a result, the SOx retention ability of the SOx trap catalyst 3 is maintained, and it is possible to avoid taking SOx into the NOx catalyst 4 as much as possible.

It is a figure showing schematic structure of the exhaust gas purification device of the internal combustion engine which concerns on 1st Example of this invention. It is a 1st flowchart of SOx retention agent supply control performed in the exhaust gas purification apparatus of the internal combustion engine which concerns on 1st Example of this invention. It is a 2nd flowchart of SOx retention agent supply control performed in the exhaust gas purification apparatus of the internal combustion engine which concerns on 1st Example of this invention. It is a figure showing schematic structure of the exhaust gas purification device of the internal combustion engine which concerns on the 2nd Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 .... Internal combustion engine 2 .... Exhaust passage 3 .... SOx trap catalyst 4 .... NOx catalyst 5 .... Supply passage 6 .... Pump 7 .... Tank 8 .... ... Intake passage 9 ... Air flow meter 10 ... Temperature sensor 11 ... Fuel injection valve 14 ... Fuel tank

Claims (7)

Provided in the exhaust passage of the internal combustion engine, the SOx retention agent is supported and has SOx retention capability for retaining SOx in the exhaust therein, and the temperature of the inflowing exhaust gas rises and the air-fuel ratio of the inflowing exhaust gas is stoichiometric. SOx holding means for recovering the SOx holding ability when the air-fuel ratio on the lean side is reached,
SOx retention agent solution storage means for storing the SOx retention agent solution;
SOx retention agent supply means for supplying the SOx retention agent solution stored in the SOx retention agent storage means to the SOx retention means;
An exhaust emission control device for an internal combustion engine, comprising: The SOx retention agent solution storage means stores the solution in a state where the SOx retention agent is dissolved in the fuel of the internal combustion engine,
The exhaust purification device for an internal combustion engine according to claim 1, wherein the SOx retention agent supply means injects the solution from a fuel injection valve provided in an intake passage or a cylinder of the internal combustion engine. SOx holding capacity estimating means for estimating the degree of SOx holding capacity of the SOx holding means is further provided,
3. The SOx retention agent solution is supplied by the SOx retention agent supply unit when the SOx retention capability estimated by the SOx retention capability estimation unit is equal to or less than a predetermined level. 4. Exhaust gas purification device for internal combustion engine. Exhaust flow rate detection means for detecting or estimating the exhaust flow rate flowing into the SOx holding means is further provided,
3. The SOx retention agent solution is supplied by the SOx retention agent supply means when the exhaust flow rate detected or estimated by the exhaust flow rate detection means is equal to or higher than a predetermined flow rate. 2. An exhaust gas purification apparatus for an internal combustion engine according to 1. Temperature detecting means for detecting or estimating the temperature of the SOx holding means, further comprising:
The SOx retention agent solution is supplied by the SOx retention agent supply means when the temperature of the SOx retention means detected or estimated by the temperature detection means belongs to a predetermined temperature range. The exhaust emission control device for an internal combustion engine according to claim 1 or 2. The temperature rising means for raising the temperature of the SOx holding means after the SOx holding agent solution is supplied by the SOx holding agent supply means is further provided. An exhaust gas purification apparatus for an internal combustion engine as described. SOx holding capacity recovery means for recovering the SOx holding capacity of the SOx holding means by increasing the temperature of the SOx holding means to make the exhaust air flowing into the lean side air-fuel ratio,
2. The SOx retention agent supply means supplies the SOx retention agent solution when the SOx retention capacity recovery means does not reach a predetermined recovery state by the SOx retention capacity recovery means. Item 7. An exhaust emission control device for an internal combustion engine according to any one of Items 6 to 6.

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