JP2000087734A - Exhaust emission control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a low quantity of use of the reducing agent used to reduce sulfates. SOLUTION: An exhaust emission control catalyst 17 is placed inside the engine exhaust system. The amount of sulfates absorbed by the exhaust emission control catalyst 17 is determined. If this amount of sulfate exceeds a predetermined quantity, the reducing agent is supplied to the exhaust emission control catalyst 17 by temporarily running auxiliary fuel injection from a fuel injection valve 7. This eliminates absorbed sulfate from the exhaust gas control catalyst 17, and reduces it. The auxiliary fuel injection time is fixed in order to bring the air-fuel ratio into rich state of the exhaust gas that flows into the exhaust gas control catalyst 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, there has been known an internal combustion engine in which a lean air-fuel mixture is burned, in which an oxidizing catalyst is disposed in an exhaust passage. In this internal combustion engine, unburned HC and CO contained in exhaust gas are oxidized by a catalyst in an oxidizing atmosphere to convert the unburned HC and CO into H ₂ O and CO ₂ . However, the exhaust gas flowing into the catalyst also contains sulfur dioxide SO ₂ , and when this SO ₂ reaches the catalyst in an oxidizing atmosphere, sulfur trioxide SO ₃ is generated from this SO ₂ . This SO ₃
Then reacts with H ₂ O in the catalyst to produce H ₂ SO ₄ .

It is not preferable that this H ₂ SO ₄ be discharged as a sulfuric acid mist from the catalyst. Therefore, there is known an exhaust gas purifying apparatus for an internal combustion engine in which a reducing agent is supplied to a catalyst to reduce SO ₃ or H ₂ SO ₄ in the catalyst, that is, sulfate to SO ₂ (JP-A-53-100).
314).

[0004]

In order to effectively reduce sulfate in the catalyst, it is necessary to constantly increase the concentration of the reducing agent in the exhaust gas flowing into the catalyst to some extent. However, when the lean air-fuel mixture is burned, a large amount of the reducing agent is required in order to increase the concentration of the reducing agent in the exhaust gas. There is a problem that it becomes necessary.

[0005]

According to a first aspect of the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine having an oxidizing catalyst disposed in an engine exhaust passage through which excess oxygen exhaust gas flows. In the above, there is provided a reducing agent supply means capable of supplying a reducing agent to the catalyst, the amount of sulfate adsorbed on the catalyst is determined, and when the amount of sulfate exceeds a predetermined amount, the reducing agent is supplied. The reducing agent is temporarily supplied from the supply means, and the sulfate adsorbed thereby is desorbed from the catalyst to be reduced. That is, the catalyst usually has the ability to adsorb sulfate, so that the sulfate produced in the catalyst is adsorbed in the catalyst. On the other hand, if a reducing agent is supplied to the catalyst, sulfate adsorbed from the catalyst is desorbed and reduced. Therefore, in the first invention, when the amount of sulfate adsorbed on the catalyst becomes larger than the set amount, the reducing agent supply action is temporarily performed to desorb and reduce the sulfate in the catalyst. That is, the amount of sulfate discharged from the catalyst without constantly supplying the reducing agent to the catalyst is reduced.

According to a second aspect of the present invention, in the first aspect, the total fuel amount and the total reduction supplied to the exhaust passage, the combustion chamber, and the intake passage upstream of a certain position in the exhaust passage. When the ratio of the total amount of air to the amount of the agent is referred to as the air-fuel ratio of the exhaust gas flowing through the position, when the sulfate is to be desorbed from the catalyst and reduced, the air-fuel ratio of the exhaust gas flowing into the catalyst is made rich so that the catalyst becomes rich. Supplying reducing agent. That is, in the second aspect, the air-fuel ratio of the exhaust gas flowing into the catalyst is made rich, so that the sulfate adsorbed on the catalyst is reliably desorbed and reduced.

According to a third aspect of the present invention, in the second aspect, the rich time is a time during which the air-fuel ratio of the exhaust gas flowing into the catalyst when the sulfate is to be desorbed and reduced from the catalyst is made rich. And the degree of richness of the air-fuel ratio of the exhaust gas are changed according to the engine operating state. That is, in the third aspect, it is possible to reliably desorb and reduce the sulfate adsorbed on the catalyst while reducing the reducing agent discharged from the catalyst.

[0008]

FIG. 1 shows a case where the present invention is applied to a diesel engine. However, the present invention can be applied to a spark ignition type engine. Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber, 3 is an intake port, 4 is an intake valve, 5 is an exhaust port, 6 is an exhaust valve, and 7 is fuel injection for directly injecting fuel into the combustion chamber 2. Each valve is shown. Each electromagnetic fuel injection valve 7 is connected to a fuel pump 9 via a common fuel pressure accumulating chamber 8. In this way, one cylinder
A plurality of fuel injections can be performed in a combustion cycle. The intake port 3 of each cylinder is connected to a common surge tank 11 via a corresponding intake branch pipe 10, and the surge tank 11 is connected to an air cleaner 1 via an intake duct 12.
3 is connected. An intake throttle valve 14 driven by an actuator 14a is arranged in the intake duct 12.
On the other hand, the exhaust port 5 of each cylinder is connected to the common exhaust manifold 1.
5 and an exhaust pipe 16 are connected to a catalytic converter 18 containing an exhaust purification catalyst 17.
Is connected to the exhaust pipe 19. The fuel injection valves 7 and the actuators 14a are respectively controlled based on output signals from the electronic control unit 30.

An electronic control unit (ECU) 30 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 32, R
AM (random access memory) 33, CPU (microprocessor) 34, BR constantly connected to power supply
An AM (backup RAM) 35, an input port 36, and an output port 37 are provided. The engine body 1 is provided with a water temperature sensor 38 for generating an output voltage proportional to the engine cooling water temperature.
Pressure sensor 39 which generates an output voltage proportional to the internal pressure
A temperature sensor 40 for generating an output voltage proportional to the temperature of exhaust gas flowing out of the exhaust purification catalyst 17 is provided in an exhaust pipe 19 adjacent to the exhaust downstream end of the exhaust purification catalyst 17.
Is attached. The temperature of this exhaust is the catalyst temperature TCAT
Is represented. The depression amount sensor 41 generates an output voltage proportional to the depression amount DEP of the accelerator pedal 42. The output voltages of these sensors 38, 39, 40, 41 are input to the input port 36 via the corresponding AD converters 43, respectively. The input port 36 is connected to a crank angle sensor 44 that generates an output pulse every time the crankshaft rotates, for example, 30 degrees. CPU34
Then, the engine speed N is calculated based on this output pulse. On the other hand, the output port 37 is connected to each fuel injection valve 7 and the actuator 14 via the corresponding drive circuit 45.
a.

In the internal combustion engine shown in FIG.
7 is platinum Pt, palladium Pd, rhodium Rh, iridium Ir supported on a porous carrier such as zeolite, ferrierite, mordenite, alumina Al ₂ O _3.
Noble metals such as, or copper Cu, iron Fe, cobalt C
o, including a transition metal such as nickel Ni. As the zeolite, for example, a zeolite having a high silica content such as ZSM-5 type can be used. The exhaust gas purifying catalyst 17 selectively reacts NO _X with HC and CO in an oxygen atmosphere containing a reducing agent such as hydrocarbon HC and carbon monoxide CO, thereby reducing NO _X to nitrogen N ₂ . be able to. That is, the exhaust purification catalyst 17 in the exhaust gas flowing is as containing a reducing agent, even if an oxygen atmosphere to reduce the NO _X in the inflowing exhaust gas. In other words, the exhaust purification catalyst 17 is
It has an oxidizing ability to oxidize HC and CO in the inside to generate H ₂ O or CO ₂ .

On the other hand, in the diesel engine shown in FIG. 1, oxygen excess combustion is always performed in order to reduce smoke and particulates discharged from the engine. Has been maintained. As a result, NO
_X is well reduced. In this case, unburned HC and CO exhausted from the engine can act as a reducing agent for NO _X. However, the amount of NO _X to be purified is overwhelmingly larger than the amount of unburned HC discharged from the diesel engine and the like, that is, the reducing agent for purifying NO _X satisfactorily is insufficient. Therefore, in the internal combustion engine of FIG.
Is supplied secondarily to the NO.
_X is not shortaged.

In order to supply the reducing agent to the exhaust purification catalyst 17 secondarily, a reducing agent supply device for supplying the reducing agent into the exhaust passage upstream of the exhaust purification catalyst 17 may be provided. Further, as a reducing agent, for example, gasoline, isooctane, hexane,
Hydrocarbons such as heptane, light oil and kerosene, or hydrocarbons such as butane and propane which can be stored in a liquid state can be used. However, in the internal combustion engine of FIG. 1, the fuel (hydrocarbon) of the engine is used as the reducing agent, and the reducing agent is supplied to the exhaust purification catalyst 17 by injecting fuel from the fuel injection valve 7 into the engine expansion stroke or the exhaust stroke. ing. As described above, the fuel injection performed during the expansion stroke or the exhaust stroke, that is, the auxiliary fuel injection is different from the fuel injection for the normal engine output performed around, for example, the compression top dead center, that is, the main fuel injection. Fuel from the fuel injection hardly contributes to the engine output. This eliminates the need for a separate reductant supply device and reductant tank. The auxiliary fuel injection for reducing NO _X in this manner is referred to as NO _X reducing auxiliary fuel injection.

The sub fuel injection time TAUNO _X in the sub fuel injection for NO _X reduction is, for example, the amount of reducing agent supplied to the exhaust purification catalyst 17 and the amount required to reduce all the NO _X flowing into the exhaust purification catalyst 17. This is the fuel injection time to be obtained. This TAUNOX is stored in the ROM 32 in advance in the form of a map shown in FIG. 2 as a function of the intake air amount Q and the engine speed N, for example.

By the way, as mentioned at the beginning, the exhaust gas
In the exhaust gas flowing into the medium 17, SO_TwoIs also included
SO_TwoReaches the exhaust gas purifying catalyst 17 in an oxidizing atmosphere.
SO _TwoIs oxidized to SO_ThreeIs generated. This SO_ThreeBut
Next, H in the exhaust purification catalyst 17_TwoH reacts with O_TwoS
O_FourIs generated. This H_TwoSO_FourBecomes sulfuric acid mist
Therefore, it is not preferable to flow through the exhaust pipe 19.

On the other hand, the exhaust gas purifying catalyst 17 generally has an ability to adsorb sulfate. The sulfate adsorption action of the exhaust purification catalyst 17 has not been sufficiently elucidated. However, it is considered that this sulfate adsorption action is performed by a mechanism as shown in FIG. That is, when the amount of the reducing agent present in the exhaust purification catalyst 17 is small, as shown in FIG.
Oxygen O _{2 in} 7 adheres to the surface of the catalyst metal M of the exhaust purification catalyst 17 in the form of O ₂ ⁻ or O ²⁻ . On the other hand, SO ₂ in the exhaust purification catalyst 17 reacts with O ₂ ⁻ or O ₂₋ on the surface of the catalyst metal M to become SO ₃ (2SO ₂ + O ₂ → 2S).
O ₃ ). Next, a part of the generated SO ₃ reacts with H ₂ O in the exhaust purification catalyst 17 to become H ₂ SO ₄ , and H ₂ SO _4
It is adsorbed in the pores of the catalyst support in the form of ₄ . Alternatively, part of the SO ₃ is further oxidized and adsorbed in the pores of the catalyst support in the form of MSO ₄ .

It is also considered that the exhaust purification catalyst 17 adsorbs sulfate when the oxygen concentration in the exhaust purification catalyst 17 is high, the pressure in the exhaust purification catalyst 17 is high, or the temperature of the exhaust purification catalyst 17 is low. Have been. Further, when a reducing agent is supplied to the exhaust gas purification catalyst 17, the amount of sulfate adsorbed in the exhaust gas purification catalyst 17 decreases. This is because when a reducing agent is supplied to the exhaust purification catalyst 17,
It is considered that the sulfate adsorbed on the sorbent desorbs.

In this case, the sulfate elimination reducing action is also sufficient.
Not elucidated in minutes. However, this sulfur
The reduction action is performed by the mechanism shown in FIG.
It is thought that it is. That is, the exhaust purification catalyst 1
When the amount of the reducing agent in the exhaust gas 7 increases,
H_TwoSO_FourIs H_TwoSO_FourDesorbed and released in the form of
You. Alternatively, the MSO adsorbed on the exhaust purification catalyst 17
_FourIs H in the exhaust purification catalyst 17._TwoH reacts with O_TwoSO_Four
Is released and released from the exhaust purification catalyst 17.
Next, the H desorbed and released from the exhaust purification catalyst 17_TwoS
O_FourReacts with the reducing agent (HC),
Is reduced. Alternatively, the reducing agent (HC)
Adsorbed on the medium 17 and then adsorbed on the exhaust purification catalyst 17
H _TwoSO_FourOr MSO_FourAnd thus reacts
Reduce rufate. Furthermore, at this time, the exhaust purification catalyst
SO in 17_ThreeCan also be reduced by the reducing agent.

When the oxygen concentration in the exhaust purification catalyst 17 decreases, the pressure in the exhaust purification catalyst 17 decreases, or the temperature of the exhaust purification catalyst 17 increases, the oxygen is adsorbed in the exhaust purification catalyst 17. It is considered that sulfate is desorbed and released, and at this time, if a reducing agent is present in the exhaust purification catalyst 17, the sulfate is desorbed and reduced by the reducing agent.

As described above, in the diesel engine shown in FIG. 1, oxygen excess combustion is usually performed, and therefore, the concentration of the reducing agent in the exhaust gas flowing into the exhaust purification catalyst 17 is kept low. Therefore, the sulfate generated in the exhaust purification catalyst 17 at this time is adsorbed in the exhaust purification catalyst 17, and the amount of sulfate discharged from the exhaust purification catalyst 17 is reduced. However, the sulfate adsorption capacity of the exhaust gas purification catalyst 17 has a limit, so it is necessary to desorb the sulfate from the exhaust gas purification catalyst 17 before the sulfate adsorption capacity of the exhaust gas purification catalyst 17 is saturated.

Therefore, in this embodiment, the exhaust purification catalyst 17
The amount of sulfate adsorbed in the fuel cell is determined, and when the amount of adsorbed sulfate exceeds a predetermined amount, the reducing agent is supplied to the exhaust gas purification catalyst 17 by temporarily performing auxiliary fuel injection. The sulfate is desorbed from the exhaust purification catalyst 17 and reduced. The auxiliary fuel injection for desorbing and reducing the sulfate in the exhaust purification catalyst 17 in this manner is referred to as a sulfate reducing auxiliary fuel injection.

It is difficult to directly determine the amount of sulfate adsorbed on the exhaust purification catalyst 17. Therefore, in the present embodiment, the amount of adsorbed sulfate is estimated based on the operating state of the engine. That is, the amount of sulfate flowing into the exhaust purification catalyst 17 can be obtained based on the engine operating state. FIG. 4 shows the inflow sulfate amount QSUL flowing into the exhaust purification catalyst 17 per unit time unit fuel injection time. As shown in FIG. 4A, QSUL increases as the depression amount DEP of the accelerator pedal increases, and QSUL decreases as DEP increases when DEP is considerably large. FIG.
As shown in (B), QSUL increases as the engine speed N increases, and when the engine speed N is considerably high, QSUL decreases as N increases. The inflow sulfate amount QSUL is stored in the ROM 32 in the form of a map shown in FIG.

Therefore, the integrated values of the main fuel injection time and the NOx reduction auxiliary fuel injection time during the normal operation are STAUM, STAUS, STAUM and STAUM, respectively.
When the sum with TAUS is expressed by STAU and the estimated time interval of the adsorbed sulfate amount is expressed by DLT, the estimated adsorbed sulfate amount S
QSUL is represented by the following equation. SQUL = SQSUL + QSUL / STAU / DLT This estimated adsorption sulfate amount SQUL is equal to the set value SQ1.
When it becomes larger, the secondary fuel injection for sulfate reduction is started. While the secondary fuel injection for sulfate reduction is being performed secondary fuel injection for NO _X reduction is stopped.

The sub fuel injection time TAUS in the sub fuel injection for sulfate reduction is set to TAUSUL.
USUL is calculated by the following equation, for example. TAUSUL = TAUSB · KSUL Here, TAUSB represents a basic auxiliary fuel injection time, and KSUL represents a correction coefficient. The basic sub-fuel injection time TAUSB is a sub-fuel injection time required for setting the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 17 to the stoichiometric air-fuel ratio. The basic auxiliary fuel injection time TAUSB is determined in advance in the form of a map shown in FIG.
It is stored in M32.

The correction coefficient KSUL is for controlling the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 17 when the sulfate-reducing auxiliary fuel injection is performed. KSUL =
If 1.0, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 17 becomes the stoichiometric air-fuel ratio. On the other hand, KSUL <1.0
, The air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 17 becomes larger than the stoichiometric air-fuel ratio, that is, becomes lean, and K
When SUL> 1.0, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 17 becomes smaller than the stoichiometric air-fuel ratio, that is, becomes rich.

In this embodiment, KSUL> 1.0.
That is, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 17 when the sulfate-reducing auxiliary fuel injection is performed is made rich. In this way, the sulfate in the exhaust purification catalyst 17 can be quickly desorbed and reduced. However, when the temperature TCAT of the exhaust purification catalyst 17 decreases, the desorption speed and the reduction speed of the sulfate decrease, and even if a large amount of the reducing agent is supplied to the exhaust purification catalyst 17 at this time, most of the reducing agent remains in the exhaust purification catalyst. 17 and the fuel consumption rate also deteriorates. Therefore, in the present embodiment, as shown in FIG. 6 (A), the correction coefficient KSUL is reduced as the catalyst temperature TCAT decreases, and thus the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 17 as the catalyst temperature TCAT decreases. Is made to be low.

On the other hand, since the auxiliary fuel injection for sulfate reduction is performed in synchronization with the main fuel injection, when the engine speed N increases, the amount of the reducing agent supplied to the exhaust purification catalyst 17 per unit time becomes excessive, and as a result, the exhaust gas A large amount of the reducing agent may flow out of the purification catalyst 17. Therefore, in this embodiment, as shown in FIG. 6 (B), the correction coefficient KSUL is reduced as the engine speed N increases, whereby the exhaust gas flowing into the exhaust purification catalyst 17 as the engine speed N increases. The richness of the air-fuel ratio is reduced. The correction coefficient KSUL is stored in the ROM 32 in advance in the form of a map shown in FIG. 6C as a function of the catalyst temperature TCAT and the engine speed N. Therefore, a reducing agent can be effectively used for elimination and reduction of sulfate.

By the way, the sulfate reducing auxiliary fuel injection is performed only for the rich time. In this case, the catalyst temperature TCA
As T increases, the desorption and reduction rates of sulfate increase, so that the desorption and reduction actions of sulfate are completed in a short time. If the sulfate-reducing auxiliary fuel injection is continued despite the completion of the sulfate desorption and reduction actions, not only does the reducing agent flow out of the exhaust purification catalyst 17 but the fuel consumption rate deteriorates. Therefore, in this embodiment,
As shown in FIG. 7A, the rich time coefficient CSUL representing the rich time is determined so that the rich time coefficient CSUL decreases as the catalyst temperature TCAT increases.

On the other hand, as described above, when the engine speed N is high, a large amount of reducing agent may flow out of the exhaust purification catalyst 17. Therefore, when the engine speed N is high, the auxiliary fuel injection for sulfate reduction is performed for a long time. Is not preferred. Therefore, in the present embodiment, as shown in FIG. 7B, the rich time coefficient CSUL is determined so as to decrease as the engine speed N increases. Note that the rich time coefficient CSU
L is stored in the ROM 32 in advance in the form of a map shown in FIG. 7C as a function of the catalyst temperature TCAT and the engine speed N. Therefore, a reducing agent can be used more effectively for elimination and reduction of sulfate.

By the way, if a reducing agent is constantly supplied to the exhaust purification catalyst 17, the production of sulfate by the exhaust purification catalyst 17 is suppressed, so that the discharge of the sulfate from the exhaust purification catalyst 17 is prevented. However, the proportion of the reducing agent that is actually consumed to reduce the sulfate among the reducing agent flowing into the exhaust purification catalyst 17 is relatively low. It is necessary to increase the concentration of the reducing agent in the exhaust gas flowing into the purification catalyst 17. However, when the concentration of the reducing agent in the exhaust gas flowing into the exhaust purification catalyst 17 is increased, a large amount of the reducing agent is discharged from the exhaust purification catalyst 17. In addition, the fuel consumption rate also deteriorates.

On the other hand, in this embodiment, the secondary fuel injection for sulfate reduction is temporarily performed, so that a large amount of reducing agent is prevented from being discharged from the exhaust purification catalyst 17 and the fuel consumption rate is reduced. While preventing it from getting worse,
The amount of sulfate discharged from the exhaust purification catalyst 17 can be reduced favorably. FIG. 8 is a routine for controlling the sulfate-reducing auxiliary fuel injection. This routine is executed by interruption every predetermined set time.

Referring to FIG. 8, first, at step 50, it is determined whether or not the sulfate flag XSUL1 is set. This sulfate flag XSUL1 is set when the sulfate-reducing auxiliary fuel injection is to be performed (XSUL1 = "1"), and is reset when the sulfate-reducing auxiliary fuel injection is to be stopped (XSUL1).
= "0"). When sulfate flag XSUL1 is reset, the process proceeds to step 51, the sum STAU the integrated value STAUS integrated value STAUM and NO _X reduction for the sub fuel injection time of the main fuel injection time is calculated. In addition,
Integrated value STAUS integrated value STAUM and NO _X reduction for the sub fuel injection time of the main fuel injection time is calculated by a routine described later. In the following step 52, STAUM and STAUS are cleared. In the following step 53, FIG.
Based on the map shown in (C), the inflow sulfate amount QS
UL is calculated. In the following step 54, the estimated adsorption sulfate amount SQSUL is calculated based on the following equation.

SQUL = SQSUL + QSUL / STAU / DLT where DLT is a time interval from the previous routine to the current routine. In a succeeding step 55, it is determined whether or not the estimated adsorption sulfate amount SQSUL is larger than a set value SQ1. When SQUL ≦ SQ1, the processing cycle ends. On the other hand, when SQUL> SQ1, the routine proceeds to step 56, where the sulfate flag XS
UL1 is set (XSUL1 = "1"). In the following step 57, the rich time coefficient CSUL is calculated from the map of FIG. Next, the processing cycle ends.

When the sulfate flag XSUL1 is set, the process proceeds from step 50 to step 58, where the count value C indicating the time during which the sulfate-reducing auxiliary fuel injection is being performed is incremented by one. In a succeeding step 59, it is determined whether or not the count value C is larger than the rich time coefficient CSUL. When C ≦ CSUL, the processing cycle ends. On the other hand, C> CSUL
In the case of, the routine proceeds to step 60, where the sulfate flag X
Reset SUL1. In the following step 61, the count value C and the estimated adsorption sulfate amount SQSUL are cleared.

FIG. 9 shows a routine for calculating the main fuel injection time TAUM. This routine is executed by interruption every predetermined crank angle. Referring to FIG. 9, first, at step 70, the basic main fuel injection time TAUMB is calculated. This basic main fuel injection time TA
UMB is, for example, the fuel injection time required to obtain the required output torque, and is stored in the ROM 32 in advance in the form of a map shown in FIG. 10 as a function of the accelerator pedal depression amount DEP and the engine speed N. Subsequent step 71
In step 72, the main fuel injection time TAUMB is calculated by multiplying the basic main fuel injection time TAUMB by the correction coefficient K. The correction coefficient K represents, for example, an acceleration increase correction coefficient, a warm-up increase correction coefficient, and the like. Next step 7
In 3, the integrated value STAUM of the main fuel injection time TAUM is calculated.

FIG. 11 shows a routine for calculating the sub fuel injection time TAUS. This routine is executed by interruption every predetermined set time. Referring to FIG. 11, first, at step 80, the sulfate flag XSUL set or reset in the routine of FIG.
It is determined whether 1 is set (XSUL1 = "1"). Sulfates flag XSUL1 proceeds to then step 81 is when it is reset (XSUL1 = "0"), the map from the NO _X reduction for the secondary fuel injection time in FIG. 2 TAUNOX is calculated. Subsequent step 82
In this case, this TAUNOX is set as the sub fuel injection time TAUS. In the following step 83, the integrated value STAUS of the sub fuel injection time TAUS is calculated.

On the other hand, when the sulfate flag XSUL1 is set at step 80, the routine proceeds to step 84, where the basic auxiliary fuel injection T
AUSB is calculated. In the following step 85, FIG.
The correction coefficient KSUL is calculated from the map (C). In the following step 86, the sulfate reduction auxiliary fuel injection time TAUSUL is calculated (TAUSUL = TAUSB).
-KSUL). In the following step 87, this TAUSUL
Is the auxiliary fuel injection time TAUS.

[0037]

According to the present invention, the amount of sulfate discharged from the oxidizing catalyst can be reduced while the amount of reducing agent required for reducing sulfate is kept small.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

2 is a diagram showing a secondary fuel injection time TAUNOX for NO _X reduction.

3A is a schematic diagram illustrating a sulfate adsorption action of an exhaust purification catalyst, and FIG. 3B is a schematic view illustrating sulfate desorption and reduction actions of an exhaust purification catalyst.

FIG. 4 is a diagram showing an amount of sulfate flowing into an exhaust purification catalyst per unit time unit fuel injection amount.

FIG. 5 is a diagram showing a basic auxiliary fuel injection time TAUSB.

FIG. 6 is a diagram showing a correction coefficient KSUL.

FIG. 7 is a diagram showing a rich time coefficient CSUL.

FIG. 8 is a flowchart for controlling sulfate reduction auxiliary fuel injection.

FIG. 9 is a flowchart for calculating a main fuel injection time.

FIG. 10 is a diagram showing a basic main fuel injection time.

FIG. 11 is a flowchart for calculating an auxiliary fuel injection time.

[Explanation of symbols]

 2: Combustion chamber 7: Fuel injection valve 15: Exhaust manifold 17: Exhaust purification catalyst

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G091 AA02 AA12 AA17 AA18 AB02 AB05 BA11 BA14 BA15 BA19 CA18 CB02 CB03 CB07 DB06 DB10 DB13 EA01 EA06 EA16 EA17 EA31 FB10 FB12 FC02 GB01W GB01X GB05W GB06W GB07 HA GB JA25 JA26 LB01 LB11 MA01 MA11 MA18 MA19 MA20 MA23 NE13 NE15 PA07A PD11A PE01A PE03A PE04A PE05A PE08A PF03A

Claims (3)

[Claims] 1. An exhaust gas purification apparatus for an internal combustion engine in which a catalyst having oxidizing ability is disposed in an engine exhaust passage through which exhaust gas with excess oxygen flows, comprising reducing agent supply means capable of supplying a reducing agent to the catalyst. Determining the amount of sulfate adsorbed on the catalyst and temporarily supplying the reducing agent from the reducing agent supply means when the amount of sulfate exceeds a predetermined set amount; An exhaust gas purification device for an internal combustion engine, which is configured to desorb and reduce the catalyst. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a reducing agent is supplied to the catalyst so that the air-fuel ratio of exhaust gas flowing into the catalyst becomes rich when sulfate is to be desorbed and reduced from the catalyst. . 3. An engine according to claim 1, wherein a rich time is a time during which the air-fuel ratio of the exhaust gas flowing into the catalyst when the sulfate is to be desorbed and reduced from the catalyst is rich, and an air-fuel ratio of the exhaust gas is rich. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein said apparatus is changed according to an operation state.