JP2004308525A - Exhaust emission cleaning device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission cleaning device preventing the overheat of a catalyst when interrupted SOx poisoning recovery control is restarted and continued. <P>SOLUTION: This device has an NOx catalyst and a temperature raising means raising a temperature of the NOx catalyst. When a predetermined amount or more of SOx is occluded into the NOx catalyst, an air-fuel ratio of exhaust gas led to flow into the NOx catalyst is made stoichiometric or rich, a catalyst temperature is raised, and SOx occluded into the NOx catalyst is released. This device is provided with a stability determining means determining whether or not a primary factor for controlling catalyst temperature rise by the temperature raising means is stabilized, and a SOx poisoning recovery information maintaining means for maintaining information on SOx poisoning recovery control. In the case that SOx poisoning recovery control is restarted after temporarily interrupted during execution, if the stability determining means determines that the primary factor to control catalyst temperature rise by the temperature raising means is stabilized, SOx poisoning recovery control is restarted based on information on SOx poisoning recovery control maintained by the SOx poisoning recovery information maintaining means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine.
[0002]
[Prior art]
A storage-reduction type NOx catalyst (hereinafter, referred to as a NOx catalyst) having a function of retaining (including storing, absorbing, and adsorbing) sulfur oxides (SOx) and nitrogen oxides (NOx) is provided in an exhaust passage of an internal combustion engine. In such a case, the NOx catalyst or the like holds sulfur oxides (SOx) generated by burning sulfur contained in the fuel. For example, in a NOx catalyst, SOx is held by the same mechanism as that for holding NOx, but the held SOx is less likely to be released than NOx, and NOx is released in a reducing atmosphere having a reduced oxygen concentration. Also, SOx gradually accumulates in the NOx catalyst without desorbing. This is called sulfur poisoning (SOx poisoning) and is a cause of lowering the NOx purification rate of the NOx catalyst. Therefore, it is necessary to perform poisoning recovery processing for recovering the NOx catalyst from SOx poisoning at an appropriate time.
[0003]
At this time, the SOx held by the NOx catalyst can be desorbed only when the exhaust gas with a reduced oxygen concentration is circulated while keeping the NOx catalyst at a high temperature (for example, about 600 to 650 ° C.).
[0004]
However, in an internal combustion engine or the like that can perform lean combustion, the exhaust gas temperature during engine operation is low, so it is necessary to raise the temperature of the NOx catalyst to a temperature at which SOx can be released. Therefore, for example, SOx release is performed by executing control to decrease the oxygen concentration of the exhaust while increasing the bed temperature of the NOx catalyst by adding fuel to the exhaust.
[0005]
By the way, in the above control, when the engine is stopped during the SOx poisoning recovery control, the exhaust temperature is increased based on predetermined control execution conditions, that is, the engine rotation, the engine load, and the catalyst bed temperature after the engine is restarted. When the conditions under which the control for executing the control for executing the control can be performed are established, for example, the execution of the fuel addition into the exhaust gas has been started in order to continue the SOx poisoning recovery control (see Patent Document 1).
[0006]
[Patent Document 1]
JP-A-8-61052 [Patent Document 2]
JP 2000-80914 A
[Problems to be solved by the invention]
However, even after the restart of the engine, even if the above-described control execution conditions are satisfied, the combustion state of the engine and the catalyst bed may be affected by various factors such as the outside air temperature, the in-cylinder temperature, the exhaust manifold temperature, and the responsiveness of the control parts. Temperature may not be stable. In such a case, if the exhaust gas temperature is increased by the above-described fuel addition or the like, the exhaust gas temperature may be increased more than necessary due to the unstable factors, and the catalyst may be overheated. In such a situation, there is a possibility that induction of thermal deterioration of the catalyst or melting of the catalyst may occur.
[0008]
The present invention has been made in view of the above circumstances, and provides an exhaust gas purifying apparatus for an internal combustion engine that prevents overheating of a catalyst when restarting and continuing the suspended SOx poisoning recovery control. Subject.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, at least until the combustion state of the internal combustion engine and the catalyst bed temperature are stabilized, the temperature rise of the catalyst by the temperature raising means is not started.
[0010]
That is, the first invention provides a NOx catalyst installed in an exhaust system,
Temperature raising means for raising the temperature of the NOx catalyst;
Has,
When a predetermined amount or more of SOx is stored in the NOx catalyst, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is set to stoichiometric or rich, and the temperature of the NOx catalyst is increased by the temperature raising means. Internal combustion engine that performs SOx poisoning recovery control that releases SOx stored in
Stability determining means for determining whether the factor for controlling the increase in the temperature of the catalyst by the temperature raising means is stable,
SOx poisoning recovery information holding means for holding information of the SOx poisoning recovery control even after the internal combustion engine is stopped,
When the SOx poisoning recovery control is temporarily interrupted during its execution and then restarted, when the stability determining means determines that the factor for controlling the temperature rise of the catalyst by the temperature raising means has stabilized, The SOx poisoning recovery control is restarted and continued based on the information on the SOx poisoning recovery control held in the SOx poisoning recovery information holding means.
[0011]
By restarting the SOx poisoning recovery control after the factor for controlling the increase in the temperature of the catalyst is stabilized in this way, it is possible to prevent the catalyst temperature from abruptly increasing and the catalyst from being overheated.
[0012]
A second invention provides a NOx catalyst installed in an exhaust system,
Fuel supply means for supplying fuel to the NOx catalyst;
Has,
When a predetermined amount or more of SOx is stored in the NOx catalyst, the air-fuel ratio of exhaust gas flowing into the NOx catalyst is set to stoichiometric or rich by the fuel supply means, and the temperature of the NOx catalyst is increased to increase the NOx catalyst. Internal combustion engine that performs SOx poisoning recovery control that releases SOx stored in
Stability determining means for determining whether the factor determining the amount of fuel supplied by the fuel supply means is stable,
SOx poisoning recovery information holding means for holding information of the SOx poisoning recovery control even after the internal combustion engine is stopped,
When the stability determination means determines that the factor determining the fuel amount supplied by the fuel supply means has become stable when the SOx poisoning recovery control is temporarily interrupted during execution and then restarted. In addition, the SOx poisoning recovery control is restarted and continued based on the information of the SOx poisoning recovery control held in the SOx poisoning recovery information holding means.
[0013]
In this manner, after the SOx poisoning recovery control is restarted, it is possible to suppress an increase in the amount of fuel to be added more than necessary, a rise in the catalyst temperature, and an overheating of the catalyst.
[0014]
The SOx poisoning recovery control is interrupted, for example, when the internal combustion engine is stopped or when a predetermined SOx poisoning recovery condition is not satisfied. Examples of when the execution conditions of the SOx poisoning recovery control are not satisfied are as follows: when the engine speed falls below a predetermined value, when the engine load decreases, or when the exhaust gas temperature becomes high and the catalyst bed temperature rises excessively. And so on.
[0015]
When the SOx poisoning recovery control is interrupted due to the stop of the internal combustion engine, the stability determination means can determine that the factor has stabilized when a predetermined time has elapsed after the restart of the internal combustion engine. For example, the catalyst bed temperature becomes unstable due to the temperature variation depending on the position of the catalyst. However, the exhaust gas flows through the catalyst after the internal combustion engine is restarted, and the entire temperature is made uniform. The temperature stabilizes.
[0016]
Factors controlling the increase in the temperature of the catalyst by the temperature raising means include, for example, a catalyst temperature and an engine combustion state.
[0017]
The factors that determine the amount of fuel supplied by the fuel supply means include, for example, the catalyst temperature and the combustion state of the engine, as described above.
[0018]
According to the present invention, when the S0x poisoning recovery control is interrupted and restarted, the S0x poisoning recovery condition and the condition for increasing the catalyst temperature are satisfied until the catalyst bed temperature and the engine combustion are stabilized. Even if it is, the S0x poisoning recovery control is not immediately started, and the control is started after the above-described factor for controlling the catalyst temperature is determined to be stable, so that the catalyst temperature may excessively increase. Be suppressed.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, specific embodiments of the exhaust gas purification apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 to which an exhaust purification device according to the present embodiment is applied, and an intake and exhaust system thereof.
[0020]
The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.
[0021]
The internal combustion engine 1 includes a fuel injection valve 3 for directly injecting fuel into a combustion chamber of each cylinder 2. Each fuel injection valve 3 is connected to a pressure accumulation chamber (common rail) 4 for accumulating fuel up to a predetermined pressure.
[0022]
The common rail 4 communicates with a fuel pump 6 via a fuel supply pipe 5. Fuel discharged from the fuel pump 6 is accumulated to a predetermined pressure by the common rail 4 and distributed to the fuel injection valve 3 of each cylinder 2. Is done.
[0023]
An intake branch pipe 8 is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe 8 communicates with a combustion chamber of each cylinder 2 via an intake port (not shown).
[0024]
The intake branch pipe 8 is connected to the intake pipe 9, and an intake throttle valve 13 for adjusting the flow rate of intake air flowing through the intake pipe 9 is provided at a position located immediately upstream of the intake branch pipe 8. .
[0025]
The intake pipe 9 located between the air flow meter 11 and the intake throttle valve 13 installed upstream of the intake pipe 9 is provided with a centrifugal supercharger (turbocharger) 15 that operates using the energy of exhaust gas as a driving source. A compressor housing 15a is provided.
[0026]
On the other hand, an exhaust branch pipe 18 is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe 18 communicates with the combustion chamber of each cylinder 2 via an exhaust port 1b.
[0027]
The exhaust branch pipe 18 is connected to a turbine housing 15 b of the centrifugal supercharger 15. The turbine housing 15b is connected to an exhaust pipe 19, which communicates downstream with the atmosphere.
[0028]
A storage-reduction type NOx catalyst 20 (hereinafter simply referred to as a NOx catalyst) including a NOx holding material is provided in the exhaust pipe 19. The NOx catalyst 20 is formed of a porous material such as cordierite, for example, using alumina as a carrier and, on the carrier, potassium (K), sodium (Na), lithium (Li), cesium (Cs), or the like. And at least one selected from alkaline earths such as barium (Ba) or calcium (Ca), rare earths such as lanthanum (La) or yttrium (Y), and a noble metal such as platinum (Pt). Is carried. In the present embodiment, barium (Ba) and platinum (Pt) are supported on a carrier made of alumina, and a transition metal such as ceria (CeO ₂ ) having an oxygen storage (O ₂ storage) ability is used. Has been added.
[0029]
When the oxygen concentration of the exhaust gas flowing into the NOx catalyst 20 is high, the NOx catalyst 20 retains nitrogen oxides (NOx) in the exhaust gas, while the oxygen concentration of the exhaust gas flowing into the NOx catalyst 20 decreases. In some cases, the retained NOx is released. At that time, if reducing components such as hydrocarbons (HC) and carbon monoxide (CO) are present in the exhaust gas, NOx released from the NOx catalyst 20 is reduced. Further, a transition metal such as ceria (CeO ₂ ) has the ability to temporarily hold oxygen according to the characteristics of exhaust gas and release it as activated oxygen.
[0030]
An exhaust temperature sensor 24 that outputs an electric signal corresponding to the temperature of exhaust flowing through the exhaust pipe 19 is attached to the exhaust pipe 19 upstream of the NOx catalyst 20. In addition, a NOx sensor 22 that outputs an electric signal corresponding to the NOx concentration in the exhaust gas flowing through the exhaust pipe 19 and an electric signal corresponding to the air-fuel ratio of the exhaust gas are output to the exhaust pipe 19 downstream of the NOx catalyst 20. The air-fuel ratio sensor 23 is mounted.
[0031]
By the way, when the internal combustion engine 1 is performing the lean burn operation, the air-fuel ratio of the exhaust gas discharged from the internal combustion engine 1 becomes a lean atmosphere, and the oxygen concentration in the exhaust gas becomes high, so that NOx contained in the exhaust gas becomes NOx catalyst. However, if the lean burn operation of the internal combustion engine 1 is continued for a long time, the NOx holding capacity of the NOx catalyst is saturated, and NOx in the exhaust is released to the atmosphere without being held by the NOx catalyst. Could be done.
[0032]
In particular, in a diesel engine such as the internal combustion engine 1, a mixture having a lean air-fuel ratio is burned in most of the operating region, and the air-fuel ratio of the exhaust gas becomes a lean air-fuel ratio in most of the operating region. The NOx holding capacity of the catalyst is likely to be saturated.
[0033]
Note that the lean air-fuel ratio here is, for example, in the range of 20 to 50 in a diesel engine, and means a region in which NOx cannot be purified by a three-way catalyst. Therefore, when the internal combustion engine 1 is performing the lean burn operation, the oxygen concentration in the exhaust gas flowing into the NOx catalyst is reduced and the concentration of the fuel as the reducing agent is increased before the NOx holding capacity of the NOx catalyst is saturated, so that the NOx It is necessary to reduce NOx retained in the catalyst.
[0034]
As a method of reducing the oxygen concentration in this way, the amount of EGR gas is further increased after adding the fuel in the exhaust gas or increasing the amount of recirculated EGR gas to increase the amount of generated soot to a maximum. Low-temperature combustion (see Japanese Patent No. 3116876), a secondary injection method for injecting fuel again during an expansion stroke or an exhaust stroke after a main injection for injecting fuel for engine output, and the like can be considered. In the fuel addition in the exhaust, a fuel supply mechanism for adding a fuel (light oil) as a reducing agent to the exhaust flowing through the exhaust pipe 19 upstream of the NOx catalyst 20 is provided, and the fuel is added from the fuel supply mechanism to the exhaust. Thus, the oxygen concentration of the exhaust gas flowing into the NOx catalyst 20 can be reduced and the fuel concentration can be increased.
[0035]
As shown in FIG. 1, the fuel supply mechanism is mounted so that its injection hole faces the exhaust branch pipe 18, and the fuel supply mechanism opens a valve from a signal from an ECU 35 described later to inject fuel, and A fuel supply passage 29 for guiding the fuel discharged from the fuel pump 6 to the fuel addition valve 28;
[0036]
In such a fuel supply mechanism, high-pressure fuel discharged from the fuel pump 6 is applied to the fuel addition valve 28 via the fuel supply path 29. Then, the fuel addition valve 28 is opened by a signal from the ECU 35 and fuel as a reducing agent is injected into the exhaust branch pipe 18.
[0037]
The fuel injected from the fuel addition valve 28 into the exhaust branch pipe 18 reduces the oxygen concentration of the exhaust gas flowing from the upstream of the exhaust branch pipe 18, reaches the NOx catalyst 20, and is retained by the NOx catalyst 20. NOx will be reduced.
[0038]
Thereafter, the fuel addition valve 28 is closed by a signal from the ECU 35, and the addition of fuel into the exhaust branch pipe 18 is stopped.
[0039]
Further, the internal combustion engine 1 is provided with a crank position sensor 33 that outputs an electric signal corresponding to the rotational position of the crankshaft.
[0040]
The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU: Electronic Control Unit) 35 for controlling the internal combustion engine 1. The ECU 35 is a unit that controls the operating state of the internal combustion engine 1 according to the operating conditions of the internal combustion engine 1 and the driver's requirements.
[0041]
Various sensors are connected to the ECU 35 via electric wiring. In addition to the output signals of the various sensors described above, an output signal of an accelerator opening sensor 36 that outputs an electric signal according to the amount of depression of the accelerator pedal by the driver is output. Is to be entered.
[0042]
On the other hand, the fuel injection valve 3, the fuel addition valve 28, and the like are connected to the ECU 35 via electric wiring, so that the above-described components can be controlled by the ECU 35.
[0043]
By the way, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 20 is spiked to be the target rich air-fuel ratio, so that the NOx stored in the NOx storage reduction catalyst can be reduced. However, in the NOx catalyst, SOx is held by the same mechanism as that for holding NOx, but the held SOx is less likely to be released than NOx, and NOx is released in a reducing atmosphere having a reduced oxygen concentration. Also, SOx gradually accumulates in the NOx catalyst without desorbing. This is called sulfur poisoning (SOx poisoning), and the NOx purification rate of the NOx catalyst decreases. Therefore, it is necessary to perform poisoning recovery processing for recovering the NOx catalyst from SOx poisoning at an appropriate time. In such SOx poisoning recovery control, the ECU 35 performs SOx poisoning elimination processing to eliminate poisoning of the NOx catalyst 20 by SOx.
[0044]
Here, the fuel of the internal combustion engine 1 may contain sulfur (S), and when such fuel is burned in the internal combustion engine 1, sulfur dioxide (SO ₂ ), sulfur trioxide (SO ₃ ), or the like is used. Of sulfur oxide (SOx) is produced.
[0045]
When the oxygen concentration of the exhaust gas flowing into the NOx catalyst 20 is high, SOx such as sulfur dioxide (SO ₂ ) or sulfur trioxide (SO ₃ ) in the inflowing exhaust gas is oxidized on the surface of platinum (Pt), It is held on the NOx catalyst 20 in the form of sulfate ions (SO ₄ ²⁻ ). Further, the sulfate ions (SO ₄ ²⁻ ) absorbed by the NOx catalyst 20 combine with barium oxide (BaO) to form sulfate (BaSO ₄ ). This sulfate (BaSO ₄ ) is stable compared to barium nitrate (Ba (NO ₃ ) ₂ ) and is not easily decomposed. Even if the oxygen concentration of the exhaust gas flowing into the NOx catalyst 20 becomes low, it is not decomposed. It remains in the NOx catalyst 20.
[0046]
When the amount of sulfate (BaSO ₄ ) in the NOx catalyst 20 increases, the amount of barium oxide (BaO) that can participate in holding NOx decreases accordingly, so that the NOx holding capacity of the NOx catalyst 20 decreases. , So-called SOx poisoning occurs.
[0047]
A method for eliminating SOx poisoning of the NOx catalyst 20 is to raise the ambient temperature of the NOx catalyst 20 to a high temperature range of about 600 to 650 ° C. and lower the oxygen concentration of the exhaust gas flowing into the NOx catalyst 20. , barium sulfate absorbed in the NOx catalyst 20 (BaSO ₄₎ SO ₃ ^- then pyrolyzed, then SO ₃ ^{- -} and SO ₄ and SO ₄ ^- hydrocarbons in the exhaust gas (HC) and carbon monoxide ( CO) is reacted gaseous by SO ₂ ^- a method of reducing can be exemplified.
[0048]
The ECU 35 oxidizes those unburned fuel components in the NOx catalyst 20, for example, by adding fuel to the exhaust gas from the fuel addition valve 28, and raises the bed temperature of the NOx catalyst 20 by the heat generated during the oxidation. To do. At the same time, fuel may be secondarily injected from the fuel injection valve 3 during the expansion stroke or the exhaust stroke of each cylinder.
[0049]
By the above-described fuel addition, the bed temperature of the NOx catalyst 20 rises from 600 ° C. to a high temperature range of about 650 ° C. After that, the ECU 35 injects fuel from the fuel addition valve 28 so as to continuously reduce the oxygen concentration of the exhaust gas flowing into the NOx catalyst 20.
[0050]
When the poisoning recovery process is performed as described above, the oxygen concentration of the exhaust gas flowing into the NOx catalyst 20 becomes low under the condition that the bed temperature of the NOx catalyst 20 is high. (BaSO ₄₎ is SO ₃ ^- and SO ₄ ^- are thermally decomposed, they SO ₃ ^- and SO ₄ ^- are reduced by reaction with hydrocarbons (HC) and carbon monoxide in the exhaust gas (CO), Te following SOx poisoning of the NOx catalyst 20 is recovered.
[0051]
In the above-mentioned SOx poisoning recovery processing, the rich spike is executed to reduce the oxygen concentration of the exhaust gas.
[0052]
Further, one rich spike is formed by a plurality of fuel injections so that the air-fuel ratio does not become excessively rich. Here, there is a possibility that the air-fuel ratio for injecting a large amount of fuel at one time becomes excessively rich, and a part of the fuel that cannot be completely reacted by the NOx catalyst 20 may flow downstream. Therefore, in the present embodiment, by injecting a small amount of fuel in a plurality of times, a rich atmosphere is formed while suppressing excessive richness.
[0053]
As shown in FIG. 2, such SOx poisoning recovery control can be determined to be executed in a region where the engine speed NE and the engine output torque T are at predetermined values. This region substantially indicates a case where the temperature of the exhaust gas discharged from the internal combustion engine 1 is within a predetermined range. The SOx poisoning recovery control is executed only when it is within the executable region a, and is stopped when the operating state of the internal combustion engine 1 deviates from this region a. Also, naturally, the SOx poisoning recovery control is stopped when the internal combustion engine 1 is stopped.
[0054]
Thereafter, when the operation of the internal combustion engine 1 is restarted and the operating state again shifts into the SOx poisoning recovery control executable area a shown in FIG. 2, this control can be restarted and continued. Become.
[0055]
However, even within the region a, if the internal combustion engine 1 is restarted after a certain period of time has elapsed after the internal combustion engine 1 has been stopped, for example, in the case of a catalyst, the inlet portion where exhaust gas flows in becomes hot, Temperature differences from other parts may occur. As described above, when the catalyst temperature fluctuates or when the combustion state of the internal combustion engine 1 is unstable, the temperature increase control is executed based on the unstable parameter, and the catalyst temperature is unnecessarily increased. There is a possibility that the control for raising may be performed. That is, when the catalyst bed temperature is measured or estimated and fuel is added to the exhaust gas to increase the temperature, the catalyst temperature is recognized as lower than the actual value due to the variation in the catalyst bed temperature, and the required amount is exceeded. If fuel addition is performed, the catalyst temperature may rise excessively.
[0056]
Therefore, in the following first embodiment of the present invention, when the S poisoning recovery control is interrupted due to the stop of the internal combustion engine 1, after the internal combustion engine 1 is restarted, until a predetermined time elapses, The above control is not restarted until the time required for the catalyst bed temperature to disperse and the engine combustion to stabilize has elapsed.
[0057]
Next, the control of the present invention will be described based on the flowchart of the SOx poisoning recovery control shown in FIG.
[0058]
In step S101, it is determined whether the SOx poisoning recovery condition is satisfied. Examples of the condition include whether the SOx amount held in the NOx catalyst 20 exceeds a predetermined amount. Here, the SOx holding amount can be calculated based on a two-dimensional map of engine speed NE × fuel injection amount Q.
[0059]
In addition, it can be obtained from the fuel consumption, the output signal from the NOx sensor 22, the vehicle travel distance, and the like. Since the NOx catalyst 20 is poisoned by the sulfur component in the fuel, the fuel consumption may be integrated and stored in the ECU 35, and the SOx holding amount may be obtained from the fuel consumption.
[0060]
As the SOx poisoning progresses, the NOx holding amount of the NOx storage reduction catalyst decreases, and the amount of NOx flowing downstream of the NOx catalyst 20 increases. Therefore, the NOx sensor 22 may be provided downstream of the NOx catalyst 20, and the SOx holding amount may be obtained based on the output signal. Further, assuming that the SOx holding amount increases according to the vehicle running distance, the SOx holding amount can be obtained based on the vehicle running distance.
[0061]
If an affirmative determination is made in step S101, the process proceeds to step S102, while if a negative determination is made, this routine ends.
[0062]
In step S102, the elapsed time of restart of the internal combustion engine 1 is Xsec. It is determined whether or not this is the case.
[0063]
If an affirmative determination is made in step S102, the process proceeds to step S103, while if a negative determination is made, this routine ends.
[0064]
In step S103, it is determined whether a condition for determining fuel addition to exhaust gas is satisfied. As conditions, the internal combustion engine 1 is in an operating state suitable for SOx poisoning recovery, or the temperature of the NOx catalyst 20 is in a range from A ° C to B ° C suitable for SOx poisoning recovery (for example, 550 to 700 ° C). Range), and whether or not the air-fuel ratio of the exhaust gas is smaller than the stoichiometric ratio.
[0065]
When an affirmative determination is made in step S103, the process proceeds to step S104, and fuel addition is performed. On the other hand, if a negative determination is made in step S103, this routine ends.
[0066]
As described above, in the present control, after the restart of the internal combustion engine 1, a time equal to or longer than a certain threshold value has elapsed, and the fuel addition is performed when the fuel addition execution condition is satisfied. Therefore, after the catalyst bed temperature and the combustion of the internal combustion engine 1 are stabilized, the catalyst temperature is increased by the addition of fuel, and the catalyst temperature by the addition of the fuel is increased as intended and the catalyst bed temperature is adjusted to an appropriate temperature. SOx poisoning recovery is performed while being controlled within the range.
(Other embodiments)
In the above-described embodiment, the case where the SOx poisoning recovery control is interrupted due to the stop of the engine has been described. However, other causes, for example, the internal combustion engine 1 is in an idling state, or the exhaust temperature is extremely high at high speed traveling. Due to the high level, the SOx poisoning recovery control may be interrupted. Even in such a case, as described in the above embodiment, after the internal combustion engine 1 is restarted, the fuel addition is not started and the SOx poisoning recovery control is not restarted until a predetermined time has elapsed. Can be controlled. Note that the SOx poisoning recovery control is interrupted in any case outside the range of the region a shown in FIG.
[0067]
However, among the causes of the interruption of the SOx poisoning recovery control, when the internal combustion engine 1 is in the idling state, the fuel temperature is maintained until the catalyst temperature does not fluctuate by continuing fuel addition so as not to lower the catalyst temperature even during idling. If so, the fuel addition may be started without waiting for a predetermined time to elapse. Further, when the exhaust gas temperature is high during high-speed running or the like, and when the exhaust gas temperature falls to a temperature range where the SOx poisoning recovery control can be performed, the combustion state of the internal combustion engine 1 and the catalyst bed temperature are not unstable. Can restart SOx poisoning recovery control immediately. Therefore, such a determination may be made in the present control, and a case may be set in which fuel addition is started within a predetermined time due to the cause of the interruption.
[0068]
Further, in the above embodiment, the case where the fuel is added by the fuel addition valve 28 into the exhaust passage upstream of the catalyst in order to raise the catalyst temperature has been described. For example, a method of supplying unburned components to exhaust gas by sub-injection and a method of increasing unburned components in exhaust gas by low-temperature combustion are included.
[0069]
Further, without adding fuel by the fuel addition valve 28, unburned components are supplied to the exhaust gas by sub-injection such as post injection, or the catalyst bed temperature is increased by a method of increasing the unburned component in the exhaust gas by low-temperature combustion. , The control of the present invention can be applied.
[0070]
【The invention's effect】
According to the present invention, when restarting and continuing the interrupted SOx poisoning recovery control, overheating of the catalyst can be prevented.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a diagram showing an area in which SOx poisoning recovery control can be executed.
FIG. 3 is a flowchart illustrating an execution flow of SOx poisoning recovery control according to the embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 ... Cylinder 3 ... Fuel injection valve 4 ... Common rail 5 ... Fuel supply pipe 6 ... Fuel pump 8 ... Intake branch pipe 9 ... Intake pipe 18 Exhaust branch pipe 19 Exhaust pipe 20 NOx catalyst 22 NOx sensor 23 Air-fuel ratio sensor 24 Exhaust temperature sensor 28 Fuel addition valve 29 ... Fuel supply path 33 ... Crank position sensor 35 ... ECU
36 ・ ・ ・ Accelerator opening sensor

Claims (6)

An NOx storage reduction catalyst installed in the exhaust system;
Temperature raising means for raising the temperature of the NOx catalyst;
Has,
When a predetermined amount or more of SOx is stored in the NOx catalyst, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is set to stoichiometric or rich, and the temperature of the NOx catalyst is increased by the temperature raising means. In an internal combustion engine that executes SOx poisoning regeneration control for releasing SOx stored in a catalyst,
Stability determining means for determining whether a factor for controlling the temperature rise of the NOx catalyst by the temperature raising means has been stabilized;
SOx poisoning recovery information holding means for holding information of the SOx poisoning recovery control even after the engine is stopped,
When the stability determining means determines that the factor for controlling the increase in the temperature of the catalyst by the temperature increasing means has stabilized when the SOx poisoning regeneration control is temporarily interrupted during its execution, the SOx An exhaust gas purification apparatus for an internal combustion engine, characterized in that SOx poisoning recovery control is restarted and continued based on information on SOx poisoning regeneration control held in poisoning recovery information holding means. An NOx storage reduction catalyst installed in the exhaust system;
Fuel supply means for supplying fuel to the NOx catalyst;
Has,
When a predetermined amount or more of SOx is stored in the NOx catalyst, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is set to stoichiometric or rich by the fuel supply means, and the temperature of the NOx catalyst is increased. In an internal combustion engine that performs SOx poisoning regeneration control for releasing SOx stored in a catalyst,
Stability determining means for determining whether the factor determining the amount of fuel supplied by the fuel supply means is stable,
SOx poisoning recovery information holding means for holding information of the SOx poisoning recovery control even after the engine is stopped,
When the stability determining means determines that the factor determining the amount of fuel supplied by the fuel supply means is stable when the SOx poisoning regeneration control is temporarily interrupted during execution and then restarted. The exhaust gas purifying apparatus for an internal combustion engine, wherein the SOx poisoning recovery control is restarted and continued based on the information on the SOx poisoning regeneration control held in the SOx poisoning recovery information holding means. 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the SOx poisoning regeneration control is interrupted when the engine is stopped or when predetermined SOx poisoning regeneration conditions are not satisfied. 4. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the stability determination unit determines that the factor has stabilized when a predetermined time has elapsed after restarting the engine. 5. 5. The exhaust gas of an internal combustion engine according to claim 1, wherein a factor for controlling a rise in the temperature of the storage reduction catalyst by the temperature raising means is at least one of a catalyst temperature and an engine combustion state. Purification device. 5. The internal combustion engine according to claim 2, wherein the factor determining the amount of fuel supplied by the fuel supply means is at least one of a catalyst temperature and an engine combustion state. Exhaust purification equipment.

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