JP2005030272A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine enabling an NOx catalyst temperature to rise to a target floor temperature without the occurrence of HC poisoning. <P>SOLUTION: An exhaust emission control device comprises a catalyst, having oxidation ability, situated in the exhaust passage of an internal combustion engine; a fuel feeding means to feed fuel to the catalyst from the upstream of the catalyst in the exhaust passage; an arrival droplet calculating means to calculate an arrival driplet amount, being a fuel amount arriving in a driplet state at the catalyst, of fuel fed from the fuel feeding means; a droplet limit amount calculating means to calculate a driplet limit amount being a maximum amount of fuel being oxidized, even if fuel arrivals in a droplet state at a catalyst, based on the temperature of the catalyst; and a feed fuel amount deciding means to decide a fuel amount fed to the catalyst from the fuel feed means such that an arrival droplet amount does not exceed the droplet limit amount. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification device that purifies exhaust gas discharged from an internal combustion engine mounted on an automobile or the like with a catalyst, and in particular, supplies the catalyst to raise the temperature of the catalyst or to remove NOx held by the catalyst. The present invention relates to a technique for preventing fuel from adhering to poisoning of a catalyst.
[0002]
[Prior art]
As a means for purifying nitrogen oxides (hereinafter referred to as “NOx”) discharged from an internal combustion engine before being released into the atmosphere, an NOx storage reduction catalyst (hereinafter simply referred to as “NOx catalyst”) may be provided in the exhaust system. )) And temporarily holding NOx in the exhaust gas on the NOx catalyst during operation at a lean air-fuel ratio is known. Such a NOx catalyst retains sulfur oxide (hereinafter sometimes referred to as “SOx”) together with NOx in the exhaust gas. Therefore, when the amount of retained SOx increases, the NOx in the exhaust gas is increased. This causes so-called SOx poisoning.
[0003]
On the other hand, the NOx catalyst is set to a high temperature of, for example, about 600 ° C., and the fuel as a reducing agent is supplied to the NOx catalyst, so that the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is made rich. A technology is known in which SOx retained in the NOx catalyst is reduced and removed by using a reducing atmosphere, thereby eliminating SOx poisoning of the NOx catalyst and regenerating the NOx catalyst (see, for example, Patent Document 1). ).
[0004]
As a means for raising the temperature of the NOx catalyst to a high temperature of about 600 ° C., post-injection in which fuel is sub-injected into the cylinder during the exhaust stroke or the expansion stroke, or top dead of the intake stroke or the exhaust stroke. The air-fuel ratio of the exhaust gas flowing into the NOx catalyst by performing sub-injection such as big rubber injection for injecting fuel into the cylinder near the point, or by adding a reducing agent such as fuel into the exhaust gas flowing into the catalyst Is used as the rich air-fuel ratio, and the reaction heat that unburned fuel is oxidized by the NOx catalyst is utilized.
[0005]
In addition, in the NOx catalyst, when the lean combustion operation of the internal combustion engine is continued for a long period of time, the NOx retention ability is saturated, and NOx in the exhaust gas is released into the atmosphere without being purified by the NOx catalyst. Therefore, it is necessary to release and reduce the NOx held in the NOx catalyst before the NOx holding ability of the NOx catalyst is saturated.
[0006]
Therefore, the oxygen concentration in the exhaust gas flowing into the NOx catalyst is decreased and the concentration of the reducing agent is increased, and the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is spiked (short time) in a relatively short cycle. It is known that rich spike control is executed (see, for example, Patent Document 2). In such a case, by executing the above-described sub-injection or reducing agent addition, the rich air-fuel ratio can be achieved even at the end of the NOx catalyst in the exhaust direction so that NOx retained in the entire NOx catalyst can be reduced. Unburned fuel is supplied.
[0007]
[Patent Document 1]
JP 2001-82137 A
[Patent Document 2]
Japanese Patent Laid-Open No. 11-210524
[Patent Document 3]
JP-A-11-62559
[Patent Document 4]
JP 2002-38939 A
[0008]
[Problems to be solved by the invention]
However, the ratio of unburned fuel in the exhaust flowing into the NOx catalyst, the exhaust temperature, NOx when the SOx poisoning described above is eliminated or the exhaust air-fuel ratio is made rich when reducing NOx. Depending on the temperature of the catalyst and the like, unburned fuel may not be evaporated and may remain in droplets on the front end of the catalyst.
[0009]
And when the temperature of the NOx catalyst is low, if a large amount of unburned fuel adheres in the form of droplets, the reactivity is poor, so the fuel remains attached, and the NOx purification performance is improved without recovering to the original state. There is a risk of HC poisoning, which is significantly reduced. In particular, under normal diesel engine operating conditions, since the exhaust temperature is lower than that of a gasoline engine, the fuel adhering to the NOx catalyst is difficult to desorb and HC poisoning is likely to occur.
[0010]
The present invention has been made in view of the above-described problems, and an object of the present invention is to exhaust an internal combustion engine that can raise the NOx catalyst to a target bed temperature without causing HC poisoning. It is to provide a purification device. Another object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can reduce NOx from a NOx catalyst without causing HC poisoning.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, a catalyst having oxidizing ability disposed in the exhaust passage of the internal combustion engine, and the catalyst from upstream of the catalyst in the exhaust passage A fuel supply means for supplying fuel to the fuel, and a liquid droplet amount calculating means for calculating an amount of liquid droplets that reaches the catalyst in a liquid droplet state among the fuel supplied from the fuel supply means; Based on the catalyst temperature detecting means for detecting the temperature of the catalyst and the temperature of the catalyst detected by the catalyst temperature detecting means, the maximum amount of fuel that is oxidized even if the catalyst reaches the catalyst in a droplet state. A droplet limit amount calculating means for calculating a droplet limit amount; and the reached droplet amount calculated by the reached droplet amount calculating means exceeds the droplet limit amount calculated by the droplet limit amount calculating means. So that the fuel supply means supplies the catalyst to the catalyst. A supply fuel amount determining means for determining an amount of fuel, characterized in that it comprises a.
[0012]
Examples of the catalyst temperature detecting means include a temperature sensor that directly detects the temperature of the catalyst, or a device that estimates the temperature of the catalyst based on a temperature sensor provided in an exhaust passage downstream of the catalyst. .
[0013]
When fuel is supplied from upstream of the catalyst in order to increase the temperature of the catalyst having oxidation ability or to remove NOx and SOx held in the catalyst, the supplied fuel cannot be vaporized and drops. In some cases, the catalyst may reach and adhere to the catalyst. In addition, since the fuel in the droplet state is less reactive than the vaporized fuel, depending on the temperature of the catalyst, it may remain unreacted (not oxidized) and remain attached, which may cause HC poisoning to the catalyst. There is.
[0014]
Accordingly, the exhaust gas purification apparatus for an internal combustion engine according to the present invention includes an arrival droplet amount calculation means for calculating an arrival droplet amount that is the amount of fuel that reaches the catalyst in a droplet state out of the fuel supplied from the fuel supply means. A droplet limit amount calculating means for calculating a droplet limit amount, which is the maximum amount of fuel that is oxidized even when reaching the catalyst in a droplet state, based on the temperature of the catalyst; and Supply fuel amount determining means for determining the amount of fuel supplied from the fuel supply means to the catalyst so as not to exceed a droplet limit amount.
[0015]
With this configuration, the fuel amount determined by the supply fuel amount determination unit is supplied to the catalyst by the fuel supply unit, so that HC poisoning can be prevented from occurring in the catalyst.
[0016]
In addition, the method further comprises: a catalyst-containing gas amount detection means for detecting the amount of exhaust gas flowing into the catalyst; and a catalyst-containing gas temperature detection means for detecting the temperature of the exhaust gas flowing into the catalyst; The means is based on the amount of exhaust gas flowing into the catalyst detected by the catalyst-containing gas amount detection means and the temperature of exhaust gas flowing into the catalyst detected by the catalyst-containing gas temperature detection means. It is preferable to calculate the drop amount.
[0017]
Here, as the catalyst-containing gas amount detection means, the amount of exhaust exhausted from the cylinder is estimated based on the detected value of the air flow meter provided in the intake passage of the internal combustion engine to detect the intake air amount and flows into the catalyst. Estimating the amount of exhaust, estimating the amount of exhaust discharged from the cylinder based on the engine speed, and estimating the amount of exhaust flowing into the catalyst, or exhaust flowing through the exhaust passage upstream of the catalyst Examples include a sensor that directly detects the amount. As the gas temperature detecting means with the catalyst, the temperature of the exhaust is estimated based on the engine speed of the internal combustion engine and the amount of fuel supplied into the cylinder, or the temperature of the exhaust upstream of the catalyst is directly detected. A temperature sensor etc. can be illustrated.
[0018]
Further, it is preferable that the droplet limit amount calculating means calculates the droplet limit amount based on the degree of deterioration of the catalyst. The catalyst may be deteriorated due to SOx poisoning or thermal deterioration. However, when the degree of deterioration increases, the reactivity of the fuel in the catalyst deteriorates. Therefore, when the droplet limit amount is calculated in consideration of the degree of deterioration of the catalyst, the droplet limit amount can be calculated with higher accuracy.
[0019]
Further, activation increases as the temperature of the catalyst rises, and the reactivity of the fuel in the catalyst also improves, so that the droplet limit amount calculating means increases the droplet limit as the temperature of the catalyst increases. Preferably, the amount of fuel to be supplied is calculated, and the supply fuel amount determination means determines to increase the amount of fuel supplied from the fuel supply means as the droplet limit amount increases. .
[0020]
The catalyst is a NOx storage reduction catalyst, and the supply fuel amount determining means determines the amount of fuel supplied by the fuel supply means as a reducing agent for the NOx when the NOx held in the catalyst is to be reduced. It is preferable that the reaching droplet amount is determined so as not to exceed the droplet limit amount. With this configuration, it is possible to reduce NOx retained in the catalyst while preventing the catalyst from causing HC poisoning.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.
[0022]
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine provided with an exhaust gas recirculation device according to an embodiment of the present invention. An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cylinder diesel engine having four cylinders 2.
[0023]
The internal combustion engine 1 includes a fuel injection valve 3 that injects fuel directly into the combustion chamber of each cylinder 2. Each fuel injection valve 3 is connected to a pressure accumulating chamber (common rail) 4, and the common rail 4 communicates with a fuel pump 6 through a fuel supply pipe 5.
[0024]
An intake passage 7 is connected to the internal combustion engine 1, and the intake passage 7 is connected to an air cleaner box 8. An air flow meter 9 that outputs an electrical signal corresponding to the mass of the intake air flowing through the intake passage 7 is attached to the intake passage 7 downstream of the air cleaner box 8.
[0025]
A compressor housing 10 a of a supercharger (turbocharger) 10 is provided in the middle of the intake passage 7. An intercooler 11 is attached to the intake passage 7 downstream of the compressor housing 10a. Further, an intake throttle valve 12 for adjusting the flow rate of intake air flowing through the intake passage 7 is provided in the intake passage 7 downstream of the intercooler 11. An intake throttle actuator 13 that opens and closes the intake throttle valve 12 is attached to the intake throttle valve 12.
[0026]
The intake air that flows into the compressor housing 10a and is compressed in the compressor housing 10a to a high temperature is cooled by the intercooler 11, and then the flow rate is adjusted by the intake throttle valve 12 as necessary. The fuel is distributed to the combustion chambers of the respective cylinders 2 through the passages 7 and burned by using the fuel injected from the fuel injection valves 3 of the respective cylinders 2 as an ignition source.
[0027]
Further, an exhaust passage 14 is connected to the internal combustion engine 1, and this exhaust passage 14 is connected downstream with a muffler (not shown).
[0028]
A turbine housing 10b of the supercharger 10 is disposed in the middle of the exhaust passage 14, and an exhaust purification device 15 is provided in a portion of the exhaust passage 14 downstream from the turbine housing 10b. Unless otherwise specified, the exhaust purification device 15 according to the present embodiment indicates an NOx storage reduction catalyst (hereinafter referred to as “NOx catalyst” unless otherwise specified).
[0029]
The exhaust passage 14 upstream of the NOx catalyst 15 outputs an electric signal corresponding to the air-fuel ratio of the exhaust flowing through the exhaust passage 14 and the temperature of the exhaust flowing through the exhaust passage 14. An exhaust temperature sensor 17 for outputting an electric signal is attached. The exhaust discharged from the turbine housing 10b flows into the NOx catalyst 15 through the exhaust passage 14, and the substance in the exhaust is purified.
[0030]
Further, there is provided a reducing agent supply means for adding fuel (light oil) as a reducing agent into the exhaust gas flowing through the exhaust passage 14 upstream from the NOx catalyst 15. As shown in FIG. 1, this reducing agent supply means is attached to the cylinder head of the internal combustion engine 1 so that its nozzle hole faces the exhaust passage 14, and opens when fuel of a predetermined valve opening pressure or higher is applied. There are provided a reducing agent addition valve 18 for injecting fuel by means of a valve, and a reducing agent supply path 19 for guiding the fuel discharged from the fuel pump 6 to the reducing agent addition valve 18.
[0031]
In the reducing agent supply means configured as described above, the reducing agent added from the reducing agent addition valve 18 into the exhaust passage 14 flows into the turbine housing 10 b together with the exhaust gas flowing from the upstream side of the exhaust passage 14. The exhaust gas flowing into the turbine housing 10b and the reducing agent are agitated by the rotation of the turbine wheel to form a homogeneously mixed exhaust gas.
[0032]
The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 20 for controlling the internal combustion engine 1. The ECU 20 is an arithmetic logic operation circuit including a CPU, a ROM, a RAM, a backup RAM, and the like.
[0033]
Various sensors such as a crank position sensor 21 and a water temperature sensor 22 attached to the internal combustion engine 1 are connected to the ECU 20 through electric wiring in addition to the air flow meter 9, the air-fuel ratio sensor 16, and the exhaust gas temperature sensor 17 described above. Output signals from the various sensors described above are input to the ECU 20.
[0034]
On the other hand, the fuel injection valve 3, the intake throttle actuator 13, the reducing agent addition valve 18 and the like are connected to the ECU 20 via electric wiring, and the ECU 20 is connected to the fuel injection valve 3, the intake throttle actuator 13 and the reducing agent addition valve. 18 etc. can be controlled.
[0035]
For example, the ECU 20 executes input of output signals of various sensors, calculation of engine speed, calculation of fuel injection amount, calculation of fuel injection timing, and the like in a basic routine to be executed at regular intervals. Various signals input by the ECU 20 and various control values obtained by the ECU 20 in the basic routine are temporarily stored in the RAM of the ECU 20.
[0036]
Next, the NOx storage reduction catalyst 15 according to the present embodiment will be described.
When the air-fuel ratio of the exhaust gas flowing into the catalyst is a lean air-fuel ratio (greater than the theoretical air-fuel ratio), the NOx catalyst 15 retains NOx in the exhaust gas so as not to be released into the atmosphere, and the exhaust gas flowing into the catalyst When the air-fuel ratio becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio (below the stoichiometric air-fuel ratio), the retained NOx is released and reduced.
[0037]
For this reason, when the internal combustion engine 1 is operated in lean combustion, the air-fuel ratio of the exhaust exhausted from the internal combustion engine 1 becomes a lean atmosphere, and the oxygen concentration of the exhaust becomes high, so that NOx contained in the exhaust becomes NOx catalyst 15. However, if the lean combustion operation of the internal combustion engine 1 is continued for a long period of time, the NOx retention capacity of the NOx catalyst 15 is saturated, and the NOx in the exhaust gas is not purified by the NOx catalyst 15 and is not purified. It will be released inside.
[0038]
In particular, in a diesel engine such as the internal combustion engine 1, the lean air-fuel ratio mixture is combusted in the most operating region, and the exhaust air-fuel ratio becomes the lean air-fuel ratio in the most operating region accordingly. The NOx retention capacity of the catalyst 15 is easily saturated.
[0039]
Further, since the NOx catalyst 15 holds SOx in the exhaust gas by the same mechanism as in the case of NOx, when the amount of SOx held increases, the NOx holding capacity of the NOx catalyst 15 decreases accordingly, so-called SOx poisoning. Will occur.
[0040]
When SOx poisoning occurs in the NOx catalyst 15 in this way, the NOx retention capacity is saturated, and NOx in the exhaust gas is released into the atmosphere without being purified by the NOx catalyst 15. Therefore, in the present embodiment, the SOx poisoning elimination control is executed to release and reduce the SOx poisoned by the NOx catalyst 15.
[0041]
In this SOx poisoning elimination control, when the ECU 20 determines that the SOx poisoning amount is a predetermined amount or more based on the heat history of the exhaust gas flowing into the NOx catalyst 15, first, the bed temperature of the NOx catalyst 15 is set to about 600 ° C. In order to increase the temperature, the catalyst temperature raising control as described below is executed. When the bed temperature of the NOx catalyst 15 rises to about 600 ° C. by the catalyst temperature increase control, the fuel as the reducing agent is added from the reducing agent addition valve 18 so that the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 becomes a rich air-fuel ratio. The reducing agent addition control is executed.
[0042]
[First embodiment of catalyst temperature rise control]
Hereinafter, a first example of catalyst temperature increase control according to the present embodiment will be specifically described.
[0043]
In the catalyst temperature increase control according to the present embodiment, in order to increase the temperature of the NOx catalyst 15 at an early stage, in addition to the normal main fuel injection in the compression stroke of the internal combustion engine 1, the cylinder during the exhaust stroke or the expansion stroke Sub-injection such as post-injection in which fuel is injected into the cylinder or injection into the cylinder in the vicinity of the top dead center of the intake or exhaust stroke is performed.
[0044]
In the post-injection, fuel injected during the exhaust stroke or the expansion stroke flows into the NOx catalyst 15 as unburned fuel, and the temperature of the catalyst rises due to heat of reaction with the catalyst. On the other hand, in the rubber injection, the fuel injected near the top dead center of the intake stroke or the exhaust stroke evaporates in the subsequent stroke and easily ignites and stabilizes the combustion. The amount of energy consumed for the piston motion decreases, and the exhaust gas whose temperature has increased accordingly reaches the NOx catalyst 15, whereby the temperature of the catalyst increases. Further, the unburned portion of the injected fuel is supplied to the NOx catalyst 15, which causes an oxidation reaction on the catalyst, and the temperature of the catalyst rises. In addition, it is not always necessary to provide an interval between the main fuel injection and the secondary injection such as post injection and big rubber injection.
[0045]
Further, by adding fuel as a reducing agent into the exhaust gas from the reducing agent addition valve 18 in place of or in addition to the above-described auxiliary injection, the unburned fuel is oxidized in the NOx catalyst 15 and is oxidized. The bed temperature of the NOx catalyst 15 may be increased by the generated heat.
[0046]
However, depending on the HC concentration in the exhaust gas flowing into the NOx catalyst 15, the temperature and amount of exhaust gas flowing into the catalyst, the bed temperature of the NOx catalyst, etc., the sub-injection or the addition of the reducing agent addition valve 18 described above causes the NOx catalyst 15 to There is a possibility that all of the supplied fuel does not evaporate and reaches the front end portion of the catalyst in a liquid state and adheres. And when the temperature of the NOx catalyst 15 is low, if a large amount of unburned fuel adheres in the form of droplets, the reactivity is poor, so the fuel remains attached and the NOx purification performance is not restored to its original state. May cause HC poisoning.
[0047]
Even if HC poisoning occurs in the NOx catalyst 15 in this way, when the temperature of the exhaust gas flowing into the catalyst rises and the temperature of the catalyst rises, the attached fuel is oxidized and desorbed, and the HC poisoning is However, under normal operating conditions of a diesel engine, the exhaust temperature is lower than that of a gasoline engine, so that the fuel adhering to the NOx catalyst 15 is difficult to desorb and HC poisoning is difficult to eliminate.
[0048]
Therefore, in the present embodiment, in consideration of the temperature and amount of exhaust gas flowing into the NOx catalyst 15, the bed temperature of the NOx catalyst 15, and the like, supply to the NOx catalyst 15 as follows so as not to cause HC poisoning. Decide how much fuel to use.
[0049]
The fuel supplied by the sub-injection or the addition by the reducing agent addition valve 18 is liquid, but when it is exposed to a high-temperature gas thereafter, a part of the fuel is evaporated and vaporized. Then, the fuel that could not be evaporated reaches the NOx catalyst 15 as droplets. That is, a relationship of “amount of supplied fuel−amount of fuel evaporated = amount of droplets reached” is established.
[0050]
On the other hand, when the fuel reaches the NOx catalyst 15 as droplets, it adheres to the catalyst. However, depending on the temperature of the NOx catalyst 15, the attached fuel does not remain attached to the catalyst but reacts (oxidizes) with the catalyst. Detach. The maximum amount of fuel that does not remain attached to the catalyst (oxidized) even if it reaches the NOx catalyst 15 as a droplet is defined as a “droplet limit amount”, and the relationship with the bed temperature of the NOx catalyst 15 is expressed as follows. This is shown in FIG. As shown in the figure, the droplet limit amount increases as the temperature of the NOx catalyst 15 increases.
[0051]
In determining the amount of fuel to be supplied in order to execute the catalyst temperature increase control, the amount of fuel that reaches the NOx catalyst 15 in the form of droplets among the supplied fuel is the bed temperature of the NOx catalyst 15 at that time. Do not exceed the droplet limit. In other words, “amount of reached droplets ≦ the limit amount of droplets” is set. On the other hand, since it is preferable to supply more fuel in order to raise the temperature early, the reached droplet amount is made as close to the droplet limit amount as possible.
[0052]
Based on the above, the amount of fuel to be supplied is determined to be an amount obtained by adding the droplet evaporation amount to the fuel evaporation amount, that is, “supply fuel amount = fuel evaporation amount + droplet limit amount”.
[0053]
Next, the fuel evaporation amount will be described. This fuel evaporation amount has a three-dimensional correlation between the amount of exhaust gas flowing into the NOx catalyst 15 and the temperature of exhaust gas flowing into the catalyst. Then, the intake air amount that is the amount of air sucked into the cylinder is detected based on the detection value of the air flow meter 9, the amount of exhaust exhausted from the cylinder is estimated, and this is set as the amount of gas containing the catalyst. In this case, a three-dimensional correlation as shown in FIG. 3 is established among the intake air amount, the catalyst-containing gas temperature, and the fuel evaporation amount.
[0054]
FIG. 4 is a two-dimensional representation of the correlation between the fuel evaporation amount and the intake air amount, and the correlation between the fuel evaporation amount and the catalyst-containing gas temperature. Thus, even if the same amount of fuel is supplied, the amount of fuel that evaporates increases as the amount of air drawn into the cylinder increases, and the amount of fuel that evaporates increases as the temperature of the exhaust gas flowing into the catalyst increases.
[0055]
In view of the above points, in the catalyst temperature raising control according to the present embodiment, the amount of fuel to be supplied is determined according to the control routine shown in the flowchart of FIG. 5, and the fuel is supplied only for the determined amount of fuel. .
[0056]
This control routine is a routine that is stored in advance in the ROM of the ECU 20 and is a routine that is executed by the ECU 20 as an interrupt process triggered by elapse of a fixed time or input of a pulse signal from the crank position sensor 21.
[0057]
In this routine, the ECU 20 first grasps the catalyst bed temperature of the NOx catalyst 15 in S100. This is based on the detection value of a catalyst bed temperature sensor (not shown) that outputs an electrical signal corresponding to the temperature of the catalyst. If the catalyst temperature is not detected directly by the catalyst bed temperature sensor, it may be grasped based on the detection value of the exhaust temperature sensor 17 provided downstream of the catalyst.
[0058]
Thereafter, the process proceeds to step 101, and the droplet limit amount is calculated. As described above, since the catalyst bed temperature and the droplet limit amount have a correlation as shown in FIG. 2, this relationship is previously mapped based on an empirical rule and stored in the ROM. The catalyst bed temperature ascertained at 100 is substituted into this map to calculate the droplet limit amount.
[0059]
Then, it progresses to step 102 and grasps | ascertains the amount of intake air. This is grasped based on the detected value of the air flow meter 9. Then, it progresses to step 103 and estimates the gas temperature containing a catalyst. This is derived from the map and estimated based on the main injection fuel amount and the engine speed. Alternatively, a temperature sensor may be provided in the exhaust passage upstream of the NOx catalyst 15 for detection.
[0060]
Thereafter, the routine proceeds to step 104 where the fuel evaporation amount is calculated. As described above, there is a correlation as shown in FIG. 3 between the fuel evaporation amount, the intake air amount, and the catalyst-containing gas temperature. Then, the amount of intake air obtained in step 102 and the gas temperature with catalyst estimated in step 103 are substituted into this map to calculate the fuel evaporation amount.
[0061]
However, when fuel is supplied by sub-injection in order to set the air-fuel ratio of the exhaust gas to a desired value, the post-injection and big rubber injection evaporate even if the supplied fuel amount is the same because the injection timing is different. The amount of fuel is different. For this reason, it is preferable that the map for post injection and the map for rubber injection are separately provided. Similarly, the sub-injection for supplying fuel into the cylinder and the supply of fuel from the reducing agent addition valve 18 into the exhaust exhausted from the cylinder differ not only in the timing for supplying the fuel but also in the supply location. Therefore, even if the supplied fuel amount is the same, the amount of fuel to be evaporated is different. Therefore, it is preferable to use a unique map for supply from the reducing agent addition valve 18.
[0062]
Thereafter, the process proceeds to step 105, and the amount of supplied fuel is calculated. As described above, the supplied fuel amount is an amount determined based on the expression “supply fuel amount = fuel evaporation amount + droplet limit amount”, and is calculated in step 104 and the droplet limit amount calculated in step 101. The supplied fuel amount is calculated by adding the evaporated fuel amount.
[0063]
And it progresses to step 106 and performs fuel supply. That is, in this step, the supplied fuel amount calculated in step 105 is actually supplied, but the fuel injection valve 3 or the reducing agent is added in consideration of the fuel pressure at that time (pressure in the common rail 4). The amount is controlled in the valve opening period of the valve 18.
[0064]
Then, the process proceeds to Step 107, where it is determined whether or not the catalyst bed temperature of the NOx catalyst 15 has reached the target temperature. As described in Step 100, the catalyst bed temperature is grasped and compared with a target catalyst bed temperature (for example, about 600 ° C.).
[0065]
If it is determined that the target catalyst bed temperature has been reached, the execution of this routine is terminated. On the other hand, if it is determined that the target catalyst bed temperature has not been reached, the processing from step 100 is executed until the catalyst bed temperature reaches the target temperature.
[0066]
By doing in this way, at the time of catalyst temperature increase control, the amount of fuel that does not cause HC poisoning is determined and supplied according to the catalyst bed temperature or the like. Thereafter, as the catalyst bed temperature rises, even if the amount of fuel supplied increases and the amount of fuel that reaches the catalyst as droplets increases, the tolerance for non-HC poisoning increases, so the amount of fuel supplied increases. The For this reason, the amount of fuel supplied per unit time increases as compared to the case where the catalyst is supplied first, so that the catalyst bed temperature also increases as compared with the case where the catalyst is supplied first. By repeating such a process, the catalyst can be quickly raised to the target catalyst bed temperature without causing HC poisoning.
[0067]
[Second Example of Catalyst Temperature Raising Control]
In the present embodiment, the degree of deterioration of the NOx catalyst 15 is also taken into consideration when determining the amount of fuel to be supplied. If the degree of deterioration of the catalyst is large, it becomes difficult for unburned fuel to react with the catalyst, and the fuel supplied to the catalyst adheres to the catalyst as droplets, and the rate at which the catalyst remains unreacted and remains attached to the catalyst increases. Therefore, the amount of fuel to be supplied is determined in consideration of the degree of deterioration of the catalyst.
[0068]
The degree of catalyst deterioration has a three-dimensional relationship between the SOx poisoning amount and the thermal deterioration of the catalyst, and FIG. 6 shows these relationships two-dimensionally. As shown in the figure, the degree of catalyst deterioration increases as the SOx poisoning amount increases, and the degree of catalyst deterioration increases as the catalyst thermally deteriorates.
[0069]
In the first embodiment, the droplet limit amount is determined based on only the catalyst bed temperature without considering the deterioration of the NOx catalyst 15, and the droplet amount reaching the catalyst is determined as the droplet limit amount. Although the amount of supplied fuel is determined so as not to exceed the amount, in this embodiment, the droplet limit amount is determined in consideration of catalyst deterioration.
[0070]
The determination method is as follows. First, the maximum droplet that does not remain attached to the catalyst even if the fuel reaches the NOx catalyst without considering the catalyst degradation, that is, the NOx catalyst when the catalyst deterioration is not considered. In this embodiment, the amount is “maximum droplet amount”.
[0071]
In determining the droplet limit amount, a catalyst deterioration coefficient having a three-dimensional relationship with the degree of catalyst deterioration and the catalyst bed temperature is used. Limit amount. That is, “droplet limit amount = maximum droplet amount × catalyst deterioration coefficient”. FIG. 7 shows the two-dimensional relationship between the catalyst deterioration coefficient and the catalyst deterioration degree and the two-dimensional relationship between the catalyst deterioration coefficient and the catalyst bed temperature. As shown in FIG. There is a relationship such that the catalyst deterioration coefficient decreases as the value increases, and the catalyst deterioration coefficient increases as the catalyst bed temperature increases. That is, the greater the degree of catalyst deterioration, the smaller the catalyst deterioration coefficient and the smaller the droplet limit amount. Further, the higher the catalyst bed temperature, the larger the catalyst deterioration coefficient and the larger the droplet limit amount.
[0072]
Further, the amount of fuel to be supplied is determined by using the formula “supply fuel amount = fuel evaporation amount + droplet limit amount” as in the first embodiment.
[0073]
In view of the above points, in the catalyst temperature increase control according to this embodiment, the amount of fuel to be supplied is determined according to the control routine shown in the flowchart of FIG. 8, and the fuel is supplied by the determined amount of fuel.
[0074]
This control routine is a routine that is stored in advance in the ROM of the ECU 20 and is a routine that is executed by the ECU 20 as an interrupt process triggered by elapse of a fixed time or input of a pulse signal from the crank position sensor 21.
[0075]
In this routine, the ECU 20 first calculates the degree of deterioration of the NOx catalyst 15 in S200. As described above, since there is a correlation among the degree of catalyst deterioration, the amount of SOx poisoning, and the degree of thermal deterioration of the catalyst, this relation is previously mapped based on empirical rules and stored in the ROM. The degree of thermal deterioration of the catalyst derived based on the SOx poisoning amount already derived in executing the SOx poisoning elimination process and the heat history of the exhaust gas discharged from the internal combustion engine and flowing into the catalyst is substituted into the map. Thus, the degree of catalyst deterioration is calculated.
[0076]
Thereafter, the routine proceeds to step 201 where the catalyst bed temperature of the NOx catalyst 15 is grasped. Since this is the same as step 100 of the first embodiment, a description thereof will be omitted. Thereafter, the process proceeds to step 202, and the maximum droplet amount is calculated. This is the same as the droplet limit amount not considering the catalyst deterioration in the first embodiment, and the calculation method is the same as that described above, so that the description thereof is omitted.
[0077]
Thereafter, the routine proceeds to step 203, where the catalyst deterioration coefficient of the NOx catalyst 15 is calculated. As described above, since there is a correlation between the catalyst deterioration coefficient, the catalyst deterioration degree, and the catalyst bed temperature, this relationship is previously mapped based on an empirical rule and stored in the ROM, and is calculated in step 200. The catalyst deterioration coefficient is calculated by substituting the degree of catalyst deterioration and the catalyst bed temperature grasped in step 201 into the map.
[0078]
Thereafter, the process proceeds to step 204, and the droplet limit amount is calculated. As described above, this is to add the catalyst deterioration coefficient calculated in step 203 to the maximum droplet amount calculated in step 202.
[0079]
Thereafter, the process proceeds to step 205, the intake air amount is grasped, the process proceeds to step 206, the gas temperature with catalyst is estimated, the process proceeds to step 207, and the fuel evaporation amount is calculated. Since these are the same as steps 102 to 104 in the first embodiment, the description thereof will be omitted.
[0080]
Thereafter, the process proceeds to step 208, and the amount of supplied fuel is calculated. As described above, the supplied fuel amount is obtained by adding the droplet evaporation amount to the fuel evaporation amount. Therefore, the supply fuel amount is obtained by adding the droplet evaporation amount calculated in step 204 to the fuel evaporation amount calculated in step 207. Is calculated.
[0081]
Thereafter, the process proceeds to step 209, where fuel supply is executed. In step 210, it is determined whether or not the catalyst bed temperature has reached the target catalyst bed temperature. Since these are the same as steps 106 and 107 in the first embodiment, the description thereof is omitted. If it is determined in step 210 that the catalyst bed temperature has reached the target catalyst bed temperature, the execution of this routine is terminated. On the other hand, if it is determined that the target catalyst bed temperature has not been reached, the processing from step 201 is executed again.
[0082]
As described above, in this embodiment, the amount of fuel to be supplied is determined in consideration of the degree of catalyst deterioration, so that it is possible to prevent HC poisoning from occurring in the NOx catalyst 15 with higher accuracy, and to early the catalyst bed. The temperature can be raised to the target floor temperature.
[0083]
In this embodiment, the SOx poisoning amount and the thermal deterioration of the catalyst are exemplified as the factors of catalyst deterioration. However, the following cases are also considered as factors of catalyst deterioration. That is, the catalyst may be poisoned by SOF contained in the exhaust gas from the internal combustion engine. Even if the catalyst temperature increase control is performed using this embodiment or the first embodiment of the catalyst temperature increase control, the fuel injection valve 3 or the reducing agent addition valve 18 does not open properly, and the fuel is desired. There is a possibility that the catalyst may be subjected to HC poisoning because the amount is not supplied. When the amount of poisoning of such SOF poisoning or HC poisoning is large, the fuel supplied to the catalyst adheres to the catalyst as droplets, and remains attached to the catalyst without reacting as it is. The rate increases. Therefore, in this embodiment, the degree of catalyst deterioration is calculated based on the correlation between the SOx poisoning amount and the thermal deterioration of the catalyst, but further includes the SOF poisoning amount and the HC poisoning amount. It is preferable to calculate the degree of catalyst deterioration and determine the amount of fuel to be supplied based on the degree of catalyst deterioration.
[0084]
The above has described the catalyst temperature increase control in the SOx poisoning elimination control for eliminating the SOx poisoning using the NOx catalyst as the exhaust purification device 15, but the first and second of the catalyst temperature increase control described above. This embodiment can also be applied when raising the bed temperature of the catalyst during warm-up.
[0085]
Further, in order to reduce particulates such as soot in the exhaust from the internal combustion engine (PM: Particulate Matter, hereinafter referred to as “PM”), the exhaust purification device 15 is referred to as a particulate filter (hereinafter referred to as “filter”). ) Or a filter carrying an oxidation catalyst, a NOx storage reduction catalyst, a three-way catalyst, etc., in order to prevent the filter from trapping PM excessively and causing the filter to become clogged. It is necessary to remove the collected PM and regenerate the filter. As a method for regenerating the filter, it is common to raise the temperature of the filter to a temperature range where PM can be oxidized (about 500 ° C. to 700 ° C.) while making the inside of the filter an oxidizing atmosphere (ie, an oxygen-excess atmosphere) Is.
[0086]
Even when the temperature of the filter is raised to a temperature range where PM can be oxidized, as described in the first and second embodiments of the catalyst temperature increase control described above, the catalyst carried on the filter or the filter It is possible to prevent HC poisoning from occurring in the catalyst provided in the vicinity, and to raise the catalyst bed temperature to the target bed temperature at an early stage.
[0087]
[First Example of NOx Reduction Processing Control]
As described above, when the lean combustion operation of the internal combustion engine 1 is continued for a long period of time, the NOx retention capacity of the NOx catalyst 15 is saturated, and NOx in the exhaust is released into the atmosphere without being purified by the NOx catalyst 15. End up.
[0088]
Therefore, when the internal combustion engine 1 is operating in lean burn, before the NOx retention capacity of the NOx catalyst 15 is saturated, the oxygen concentration in the exhaust gas flowing into the NOx catalyst 15 is reduced and the concentration of the reducing agent is increased. It is necessary to perform a so-called NOx reduction process for releasing and reducing the NOx held in the catalyst 15. Therefore, in the present embodiment, as the NOx reduction processing, the rich spike control in which the ECU 20 changes the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 to a rich air-fuel ratio in a spike manner (short time) in a relatively short cycle. Execute.
[0089]
In the rich spike control, the ECU 20 determines whether or not the rich spike control execution condition is satisfied when it is time to reduce NOx held in the NOx catalyst. As the rich spike control execution condition, for example, whether the NOx catalyst 15 is in an active state, the output signal value (exhaust temperature) of the exhaust temperature sensor 17 is equal to or lower than a predetermined upper limit value, or SOx poisoning elimination control described later. The condition such as whether or not is executed can be exemplified.
[0090]
When it is determined that the rich spike control execution condition as described above is satisfied, the ECU 20 adds the fuel as the reducing agent in a spike manner from the reducing agent addition valve 18 so that the exhaust gas flowing into the NOx catalyst 15 is added. Is temporarily set to a rich air-fuel ratio. Then, the rich air-fuel ratio exhaust gas thus formed flows into the NOx catalyst 15 and releases and reduces the NOx held in the catalyst.
[0091]
In this way, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 15 alternately repeats “lean” and “spike-like rich air-fuel ratio” in a relatively short cycle, so that the NOx catalyst 15 holds NOx. And release / reduction can be alternately repeated in a short cycle.
[0092]
In determining the amount of fuel as the reducing agent added by the reducing agent addition valve 18, the above catalyst is used so that the NOx catalyst 15 is not subjected to HC poisoning by the fuel added by the reducing agent addition valve 18. The determination is made by the method described in the first and second embodiments of the temperature rise control.
[0093]
Specifically, in the case of the first embodiment, the droplet limit amount is calculated based on the catalyst bed temperature, and the fuel evaporation amount is calculated based on the intake air amount and the catalyst-containing gas temperature. Then, the supply fuel amount is determined by adding the droplet limit amount to the fuel evaporation amount.
[0094]
In the case of the second embodiment, the degree of catalyst deterioration is calculated based on the SOx poisoning amount of the catalyst and the degree of thermal deterioration, and the catalyst deterioration coefficient is calculated based on the catalyst bed temperature and the degree of catalyst deterioration. Then, the droplet maximum amount is calculated based on the catalyst bed temperature, and the droplet limit amount is calculated by adding the catalyst deterioration coefficient to the droplet maximum amount. On the other hand, the fuel evaporation amount is calculated based on the intake air amount and the catalyst inflow gas temperature. Then, the supply fuel amount is determined by adding the droplet limit amount to the fuel evaporation amount.
[0095]
Thus, by adding only the fuel amount determined as described above, NOx can be released and reduced while the NOx catalyst is not subject to HC poisoning.
[0096]
However, as described above, even if the catalyst temperature increase control is performed using the first embodiment or the second embodiment of the catalyst temperature increase control, the fuel injection valve 3 or the reducing agent addition valve 18 is properly opened. Without the desired amount of fuel being supplied, or the fuel adhering to the exhaust passage or the like while the internal combustion engine is stopped operating adheres to the NOx catalyst 15 when the internal combustion engine is started, etc. When performing the NOx reduction process, there is a possibility that HC poisoning has already occurred in the front end portion of the NOx catalyst. In such a case, even if a fuel amount that does not cause HC poisoning to the NOx catalyst is supplied as described above, there is a possibility that NOx is not efficiently reduced and the HC poisoning is worsened.
[0097]
Therefore, in the NOx reduction process control according to the present embodiment, first, the rich spike control described above is executed after the HC poisoning of the front end portion of the NOx catalyst 15 is eliminated. Hereinafter, the control routine of the NOx reduction process control according to the present embodiment will be specifically described with reference to the flowchart of FIG.
[0098]
This control routine is a routine that is stored in advance in the ROM of the ECU 20 and is a routine that is executed by the ECU 20 as an interrupt process triggered by elapse of a fixed time or input of a pulse signal from the crank position sensor 21.
[0099]
First, in step 300, it is determined whether or not it is time to reduce NOx held in the NOx catalyst 15. This determination is to determine whether or not the NOx retention amount of the NOx catalyst 15 exceeds a predetermined amount, but means that the NOx retention amount by the NOx catalyst 15 has approached its limit value to some extent. This holding amount is estimated based on the elapsed time from the previous NOx reduction process, the operation history, or the like, or estimated based on the differential pressure across the NOx catalyst 15. If it is determined that it is time to reduce NOx, the process proceeds to step 301. If not, the execution of this routine is terminated.
[0100]
In step 301, it is determined whether HC poisoning has occurred in the NOx catalyst 15 or not. This is determined based on the operation history, temperature history, etc. of the internal combustion engine so far. For example, when the fuel is added to the exhaust for the NOx reduction process or the SOx poisoning elimination process, the internal combustion engine is used. The engine is stopped, and the added fuel adheres to the exhaust passage as a liquid, and determination is made based on whether or not HC has adhered to the catalyst at the next start-up. If it is determined that HC poisoning has occurred in the catalyst, the process proceeds to step 302. If it is determined that poisoning has not occurred, the process proceeds to step 304.
[0101]
In step 302, HC poisoning recovery process control is executed. In this HC poisoning recovery process control, fuel is added so that the air-fuel ratio at the end of the catalyst is about 13.5 which is a rich air-fuel ratio in the conventional NOx reduction process, whereas FIG. 10 shows Thus, the fuel is added so that the air-fuel ratio at the front end of the catalyst becomes 18. As a result, unburned fuel reacts with oxygen on the NOx catalyst 15, and the temperature of the front end of the catalyst rises due to the reaction heat. When the temperature of the NOx catalyst 15 exceeds a predetermined value, the HC adhering to the catalyst is oxidized and removed. Instead of fuel addition by the reducing agent addition valve 18, post injection may be performed so that the air-fuel ratio at the front end portion of the NOx catalyst 15 becomes 18. Further, the HC adhering to the catalyst may be removed by oxidation by directly increasing the temperature of the catalyst by increasing the temperature of the gas flowing into the catalyst by executing the big rubber injection.
[0102]
Thereafter, the process proceeds to step 303 to determine whether or not HC poisoning has been recovered. This is determined based on the history of the temperature and time of the HC poisoning recovery process according to the current degree of poisoning that can be grasped in step 300 based on the map that is the judgment of poisoning recovery. If it is determined that the HC poisoning has been recovered, the process proceeds to step 304 to start executing the rich spike control described above. On the other hand, if it is determined that the HC poisoning has not recovered, the processing from step 302 is executed again. Even if it is not determined whether or not the HC poisoning has been recovered in step 303, the process may proceed to step 304 after a predetermined time has elapsed from the start of the execution of the HC poisoning recovery process in step 302.
[0103]
As described above, in the NOx reduction processing according to the present embodiment, the rich spike control is executed after the HC poisoning at the front end of the catalyst is recovered. Therefore, compared with the case where the rich spike control is executed with the HC poisoning occurring. Thus, the NOx reduction efficiency can be increased. In addition, since the catalytic activity at the front end of the catalyst is increased by the HC poisoning recovery process at the front end of the catalyst, the NOx reduction efficiency in the subsequent rich spike control is also increased.
[0104]
In executing the rich spike control, it is preferable to supply the amount of fuel determined as described above so that the fuel added by the reducing agent addition valve 18 does not cause HC poisoning in the NOx catalyst. However, the amount of fuel may be supplied so that the exhaust air-fuel ratio at the end of the catalyst is 13.5. This is because the catalyst bed temperature at the front end of the catalyst has risen due to the HC poisoning recovery process at the front end of the catalyst, so that the possibility of re-poisoning of the catalyst is low.
[0105]
[Second Example of NOx Reduction Processing Control]
In the first embodiment, the rich spike control is executed by determining the amount of fuel to be supplied by the same method as in the first and second embodiments of the catalyst temperature increase control. After reducing the NOx at the front end, a fuel amount is supplied so that the NOx at the catalyst rear end can be reduced.
[0106]
Hereinafter, the control routine of the NOx reduction process control according to the present embodiment will be specifically described with reference to the flowchart of FIG.
[0107]
This control routine is a routine that is stored in advance in the ROM of the ECU 20 and is a routine that is executed by the ECU 20 as an interrupt process triggered by elapse of a fixed time or input of a pulse signal from the crank position sensor 21.
[0108]
First, in step 400, it is determined whether or not it is time to reduce NOx held in the NOx catalyst 15. Since this is the same as step 300 in the first embodiment of the NOx reduction process control, its description is omitted. If it is determined that it is time to reduce NOx, the process proceeds to step 401; otherwise, the execution of this routine is terminated.
[0109]
In step 401, rich spike control is executed only at the front end portion of the NOx catalyst 15. As shown in FIG. 12, the fuel is supplied so that the air-fuel ratio at the center of the catalyst becomes about 13.5, which is the air-fuel ratio capable of reducing NOx. In this case, NOx held at the front end of the catalyst is reduced by unburned fuel flowing into the catalyst, but is held at a portion where the air-fuel ratio of the exhaust flowing into the rear end of the catalyst is higher than the stoichiometric air-fuel ratio. NOx is not reduced.
[0110]
Therefore, compared with the conventional case where the amount of fuel is supplied so that the air-fuel ratio at the rearmost end of the catalyst becomes 13.5, the amount of fuel supply decreases, so that the front end of the catalyst is poisoned with HC. Can be reduced. Further, since the air-fuel ratio at the catalyst rear end is lean, NOx generated by NOx discharge generated at the initial stage of NOx reduction can be held at the catalyst rear end.
[0111]
Thereafter, the process proceeds to step 402, where it is determined whether or not the NOx reduction at the front end of the catalyst has been completed. This is determined based on the detection value and map of the air-fuel ratio sensor provided in the center of the catalyst. If the air-fuel ratio sensor is provided only in the exhaust passage downstream of the catalyst without providing the air-fuel ratio sensor in the center of the catalyst, the determination may be made based on the detected value and map of the air-fuel ratio sensor downstream of the catalyst. Good. Further, it may be determined that the NOx reduction at the catalyst front end is completed if the elapsed time from the execution of the catalyst front end NOx reduction processing is a predetermined time or more.
[0112]
If it is determined that the NOx reduction has been completed, the process proceeds to step 403. If it is determined that the NOx reduction has not been completed, the processes after step 401 are executed again. As a result, the rich spike control is executed until it is determined that the NOx reduction at the front end of the catalyst is completed.
[0113]
In step 403, rich spike control at the rear end of the catalyst is executed. As shown in FIG. 12, the fuel is supplied so that the air-fuel ratio at the rearmost end of the catalyst is about 13.5, but the amount of fuel purified at the inner front end of the fuel supplied to the catalyst. Therefore, the amount of fuel supplied for the front end rich spike control executed in step 401 is increased in consideration of that amount, so that the unburned fuel reaches the last end. As a result, NOx held at the rear end of the catalyst is reduced. In addition, since the temperature of the front end of the catalyst has already risen due to the heat of reaction when NOx at the front end of the catalyst is reduced, even if fuel is supplied for NOx reduction at the rear end, HC poisoning occurs at the front end of the catalyst. Is less likely to occur.
[0114]
Thereafter, the routine proceeds to step 404, where it is determined whether or not the NOx reduction at the rear end of the catalyst has ended. This is determined based on the detection value and map of the air-fuel ratio sensor provided downstream of the catalyst. Further, if the elapsed time from the execution of the catalyst rear end NOx reduction process is a predetermined time or more, it may be determined that the NOx reduction at the catalyst rear end is completed. When it is determined that the NOx reduction at the catalyst rear end is completed, the execution of this routine is terminated. On the other hand, if it is determined that the processing has not ended, the processing from step 403 is executed again. Thus, the NOx reduction process is executed until it is determined that the NOx reduction at the catalyst rear end is completed.
[0115]
Thus, after reducing NOx at the front end of the catalyst and then reducing NOx at the rear end of the catalyst, conventionally, the amount of fuel is reduced so that the air-fuel ratio at the rearmost end of the catalyst becomes 13.5. Since the amount of fuel supply is reduced as compared with the case where it is supplied, it is possible to reduce the occurrence of HC poisoning at the front end of the catalyst. Further, when NOx at the rear end of the catalyst is reduced by rich spike control, the temperature at the front end of the catalyst has already risen, so that HC poisoning is less likely to occur.
[0116]
【The invention's effect】
As described above, according to the present invention, the NOx catalyst can be raised to the target bed temperature without causing HC poisoning. Further, NOx can be reduced from the NOx catalyst without causing HC poisoning.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a diagram showing a correlation between a catalyst bed temperature and a droplet limit amount.
FIG. 3 is a diagram showing a correlation among catalyst-containing gas temperature, intake air amount, and fuel evaporation amount.
4A is a diagram showing a correlation between an intake air amount and a fuel evaporation amount, and FIG. 4B is a diagram showing a correlation between a catalyst-containing gas temperature and a fuel evaporation amount.
FIG. 5 is a flowchart showing a control routine according to a first embodiment of catalyst temperature raising control.
6A is a diagram showing the correlation between the SOx poisoning amount and the degree of catalyst deterioration, and FIG. 6B is a diagram showing the correlation between the thermal deterioration of the catalyst and the degree of catalyst deterioration.
7A is a diagram showing the correlation between the degree of catalyst deterioration and the catalyst deterioration coefficient, and FIG. 7B is a diagram showing the correlation between the catalyst bed temperature and the catalyst deterioration coefficient.
FIG. 8 is a flowchart showing a control routine according to a second embodiment of catalyst temperature increase control.
FIG. 9 is a flowchart showing a control routine according to a first embodiment of NOx reduction process control;
FIG. 10 is a diagram schematically showing a processing method according to a first example of NOx reduction processing control.
FIG. 11 is a flowchart showing a control routine according to a second embodiment of NOx reduction process control;
FIG. 12 is a diagram schematically showing a processing method according to a second example of NOx reduction processing control;
[Explanation of symbols]
1 Internal combustion engine
2-cylinder
3 Fuel injection valve
4 Common rail
5 Fuel supply pipe
6 Fuel pump
7 Intake passage
8 Air cleaner box
9 Air flow meter
10 Turbocharger
11 Intercooler
12 Inlet throttle valve
13 Inlet throttle actuator
14 Exhaust passage
15 Exhaust purification device
16 Air-fuel ratio sensor
17 Exhaust temperature sensor
18 Reducing agent addition valve
19 Reducing agent supply path
20 ECU
21 Crank position sensor

Claims (5)

A catalyst having oxidation ability disposed in the exhaust passage of the internal combustion engine;
Fuel supply means for supplying fuel to the catalyst from upstream of the catalyst in the exhaust passage;
An reached droplet amount calculating means for calculating an reached droplet amount that is a fuel amount that reaches the catalyst in a droplet state among the fuel supplied from the fuel supply means;
Catalyst temperature detection means for detecting the temperature of the catalyst;
Based on the temperature of the catalyst detected by the catalyst temperature detecting means, a droplet limit amount calculating means for calculating a droplet limit amount that is the maximum amount of fuel that is oxidized even if the catalyst reaches the catalyst in a droplet state. When,
The amount of fuel supplied from the fuel supply unit to the catalyst so that the reached droplet amount calculated by the reached droplet amount calculation unit does not exceed the droplet limit amount calculated by the droplet limit amount calculation unit Fuel supply amount determining means for determining
An exhaust emission control device for an internal combustion engine, comprising: Catalyst-containing gas amount detection means for detecting the amount of exhaust gas flowing into the catalyst;
A catalyst-containing gas temperature detecting means for detecting the temperature of the exhaust gas flowing into the catalyst,
The reaching droplet amount calculating means is configured to adjust the amount of exhaust flowing into the catalyst detected by the catalyst-containing gas amount detecting means and the temperature of exhaust flowing into the catalyst detected by the catalyst-containing gas temperature detecting means. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the amount of liquid droplets reached is calculated on the basis of the amount. 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the droplet limit amount calculating means calculates the droplet limit amount based on a degree of deterioration of the catalyst. The droplet limit amount calculating means calculates so as to increase the droplet limit amount as the temperature of the catalyst rises,
The said supply fuel amount determination means determines so that the amount of fuel supplied from the said fuel supply means may be increased according to the said droplet limit amount increasing. Exhaust gas purification device for internal combustion engine. The catalyst is a NOx storage reduction catalyst,
The fuel supply amount determining means determines the amount of fuel that the fuel supply means supplies as a reducing agent for the NOx when the NOx held in the catalyst is to be reduced, and the amount of liquid reached reaches the droplet limit amount. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 4, wherein it is determined so as not to exceed.

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