JP3266100B2 - Exhaust gas purification device for internal combustion engine - Google Patents

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 an lean air-fuel mixture is burned, in which an oxidation catalyst is disposed in an exhaust passage. In this internal combustion engine,
The unburned HC and CO contained in the exhaust gas are oxidized by an oxidation catalyst in an oxidizing atmosphere to convert these unburned HC and CO into H ₂ O.
And so as to convert and CO _2. However, the exhaust gas flowing into the oxidation catalyst also contains sulfur dioxide SO ₂ , and when the SO ₂ reaches the oxidation catalyst in an oxidizing atmosphere, sulfur trioxide SO ₃ is generated from the SO ₂ . This SO
₃ then reacts with H ₂ O in the oxidation catalyst to produce H ₂ SO ₄
Is generated.

It is not preferable that this H ₂ SO ₄ be converted into sulfuric acid mist and discharged from the oxidation catalyst. Therefore, a reducing agent is supplied to the oxidation catalyst to cause SO ₃ or H
_2. Description of the Related Art An exhaust gas purifying apparatus for an internal combustion engine in which ₂ SO ₄ , that is, sulfate is reduced to SO ₂ is known (see Japanese Patent Application Laid-Open No. 53-100314).

[0004]

In an internal combustion engine designed to burn a lean mixture having a high lean degree, a large amount of oxygen is present in the exhaust gas. In this case, oxygen in the exhaust gas flowing into the catalyst is removed. For this purpose, a large amount of a reducing agent such as fuel is required, and the fuel consumption rate is deteriorated. Therefore, an attempt has been made to include a reducing agent in the exhaust gas with excess oxygen flowing into the catalyst, and to reduce the sulfate with the reducing agent.

However, when a reducing agent is supplied to the oxidation catalyst at a high catalyst temperature, the reducing agent reacts more actively with oxygen than sulfate, and as a result, the amount of sulfuric acid mist discharged from the oxidation catalyst is sufficiently reduced. There is a problem that can not be. In other words, in a certain catalyst temperature range, almost all of the reducing agent actively reacts with substances other than sulfate. The above publication does not suggest this problem at all.

[0006]

According To solve the above problems SUMMARY OF THE INVENTION to the first invention, the oxidation catalyst in the engine exhaust passage
And the oxidation catalyst is always maintained in an oxidizing atmosphere.
In the exhaust purification apparatus for an internal combustion engine that, with an oxidation catalyst comprising an oxidation catalyst comprising platinum, sulfate in the inflowing exhaust gas
Is held by the adsorption action, and the catalyst temperature is
Reducing agent supplied when the temperature is within the optimal temperature range for fate reduction
The amount of adsorbed sulfate decreases and
The sulfate can be formed from an oxidation catalyst adapted to be reduced, and a reducing agent can be supplied to the oxidation catalyst.
A reducing agent supply means, catalyst temperature; and a catalyst temperature determining means for determining whether in the sulfate reducing the optimum temperature range of the oxidation catalyst, the catalyst temperature is determined to be within the sulfate reduction optimum temperature range Sometimes adsorbed on oxidation catalyst
Reduce the amount of sulfate that has been
The reducing agent is temporarily supplied from the reducing agent supply means to the oxidation catalyst in order to reduce the load. That is, in the first invention, when it is determined that the catalyst temperature is within the optimum sulfate reduction optimum temperature range for reducing sulfate, the reducing agent is supplied to the oxidation catalyst. The amount of sulfate that is reacted and thus discharged from the oxidation catalyst is reduced favorably.

Further, in the first aspect according to the second aspect of the invention, NO in the supplies of the reducing agent to the oxidation catalyst in the oxidation catalyst when the catalyst temperature is within NO _X reduction optimum temperature range of the oxidation catalyst _X being adapted to reduce, the upper threshold of the sulfate reducing optimum temperature range defined higher than the upper threshold of the NO _X reduction optimum temperature range, and the lower threshold of the sulfate reducing optimum temperature range It is set higher than the lower limit threshold value of the NO _x reduction optimum temperature range. That is, in the second invention, sulfate-reducing optimum temperature range is determined on the higher temperature side than the NO _X reduction optimum temperature range.

According to a third aspect of the present invention, in the second aspect, a fuel injection valve for directly injecting fuel into an engine combustion chamber is provided, and the auxiliary fuel is injected from the fuel injection valve to an engine expansion stroke or an exhaust stroke. the so as to supply fuel as a reducing agent to the oxidation catalyst, the secondary fuel injection in comparison with the time to perform the secondary fuel injection for reducing the NO _X when should perform sub fuel injection in order to reduce the sulfate by I try to make it late. That is, in the third invention, a relatively heavy fuel is supplied to the oxidation catalyst because the auxiliary fuel injection timing is delayed, so that even when the catalyst temperature is within the comparatively high sulfate reduction optimum temperature range, The agent reaches the vicinity of the exhaust downstream end of the oxidation catalyst without being completely oxidized, and thus the reducing agent is supplied to the entire oxidation catalyst.

Further, in the second aspect according to the fourth invention, when to be supplied with the reducing agent to the oxidation catalyst for the reduction of sulfates to supply the oxidation catalyst a reducing agent to reduce NO _X The concentration of the reducing agent in the exhaust gas flowing into the oxidation catalyst is made higher than when it should be. That is, in the fourth invention, even when the catalyst temperature is within the optimum temperature range for sulfate reduction, which is relatively high, the reducing agent does not completely oxidize and reaches the vicinity of the exhaust gas downstream end of the oxidation catalyst. Is supplied with a reducing agent.

According to a fifth aspect of the present invention, in the fourth aspect, when a reducing agent is to be supplied to the oxidation catalyst in order to reduce sulfate, the concentration of the reducing agent in the exhaust gas flowing out of the oxidation catalyst is predetermined. The concentration of the reducing agent in the exhaust gas flowing into the oxidation catalyst is determined so as not to exceed the allowable value. That is, in the fourth invention, the high concentration of the reducing agent is prevented from being discharged from the oxidation catalyst.

According to a sixth aspect, in the first aspect, when a reducing agent is to be supplied to the oxidation catalyst in order to reduce sulfate, the reducing agent is intermittently supplied to the oxidation catalyst. . That is, when the reducing agent is continuously supplied, the catalyst temperature may increase due to the heat of reaction of the reducing agent and may deviate from the optimum sulfate reduction temperature range. Therefore, in the sixth invention, the catalyst temperature is maintained within the optimum sulfate reduction temperature range by intermittently supplying the reducing agent.

According to a seventh aspect, in the first aspect, there is provided a rapid acceleration determining means for determining whether or not the engine rapid acceleration operation has been performed, and the catalyst temperature determining means comprises an engine rapid acceleration operation. It is determined that the catalyst temperature is within the optimum sulfate reduction temperature range within a second set period immediately after a lapse of the first set period after it is determined that has been performed. When the engine rapid acceleration operation is performed, the temperature of the exhaust gas flowing into the oxidation catalyst increases, so that the catalyst temperature is raised to an optimum temperature range for sulfate reduction. However, even if the engine rapid acceleration operation is performed, the catalyst temperature does not immediately rise, and after a while, falls within the optimum sulfate reduction temperature range. Therefore, in the seventh invention, it is determined that the catalyst temperature is within the optimum sulfate reduction temperature range during the second set period immediately after the lapse of the first set period after it is determined that the engine rapid acceleration operation has been performed. At this time, the reducing agent is supplied.

According to an eighth aspect of the present invention, in the first aspect, there is provided a catalyst temperature control means capable of controlling a catalyst temperature within the above-mentioned optimum sulfate reduction temperature range. That is, in the eighth invention, the sulfate reducing action can be performed at any time. Further, the ninth in the first aspect according to the invention, agencies often and catalyst temperature than the allowable adsorption amount of amount adsorbed sulfates predetermined seeking adsorbed sulfate amount of the oxidation catalyst based on the operating condition sulfate reduction When the temperature is within the optimum temperature range, the reducing agent is supplied to the oxidation catalyst. That is, in the ninth invention, the sulfate adsorption capacity of the oxidation catalyst is prevented from being saturated.

Further, in the first aspect according to the tenth invention, comprising a NO _X reduction catalyst and sulfate reduction catalyst wherein the oxidation catalyst is arranged in sequential series in the engine exhaust passage, NO _X reduction catalyst Has a high oxidizing ability and a low sulfate adsorbing ability, and the sulfate reducing catalyst has a low oxidizing ability and a high sulfate adsorbing ability. When the reducing agent is supplied, the sulfate in the sulfate reduction catalyst is reduced to reduce the amount of sulfate adsorbed on the sulfate reduction catalyst, and the catalyst temperature determining means determines that the temperature of the sulfate reduction catalyst is Determine whether the temperature is within the optimum temperature range for sulfate reduction of the catalyst, and The reducing agent is supplied to the sulfate reduction catalyst when it is determined that the temperature of the source catalyst is within the optimum sulfate reduction temperature range of the sulfate reduction catalyst. That is, in the tenth invention, when it is determined that the temperature of the sulfate reduction catalyst is within the optimum sulfate reduction temperature range for reducing sulfate, the reducing agent is supplied to the sulfate reduction catalyst. It reacts vigorously with the agent, thus favorably reducing the amount of sulfate discharged from the sulfate reduction catalyst.

According to the present invention, in an exhaust gas purification system in which exhaust gas containing oxygen flows into an exhaust gas purification catalyst, it is possible to adjust the amount of a reducing agent in the exhaust gas while oxygen is present in the exhaust gas. Limited to systems that can.

[0016]

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.

The 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 that 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 zeolite comprises a supported platinum P t on a porous support such as alumina Al ₂ O _3. As the zeolite, for example, a zeolite containing high silica such as ZSM-5 type, ferrierite, and mordenite 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, when the exhaust purification catalyst 17 exhaust flowing contains a reducing agent, NO in the exhaust gas even flows be oxygen atmosphere
_{Reduce X.} In other words, the exhaust purification catalyst 17
Functions as an oxidation catalyst that oxidizes HC and CO in the exhaust purification catalyst 17 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 secondary supply the reducing agent to the exhaust purification catalyst 17, 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 reducing agent supply device and reducing agent tank.

[0021] FIG. 2 (A) shows the NO _X purification rate PENOX of the exhaust purification catalyst 17, the relationship between the temperature i.e. the catalyst temperature TCAT of the exhaust purification catalyst 17. Here CNI the concentration of NO _X in the exhaust gas flowing into the exhaust purification catalyst 17, the concentration of NO _X in the exhaust gas discharged from the exhaust purifying catalyst 17 CN
When O NO _X purification rate PENOX is (CNI-CN
O) / CNI. Referring to FIG. 2 (A), the the catalyst temperature TCAT is in the range from LTNOX to UTNOX NO _X purification rate PENOX allowable minimum purification efficiency MN
It turns out that it becomes higher than OX. The temperature range of the LTNOX to UTNOX NO _X reduction optimum temperature range O
When referred to TNOX, the catalyst temperature TCAT is the exhaust purification catalyst 17 not been activated for of the NO _X reduction when less than NO _X reduction optimum temperature range OTNOX, also the catalyst temperature TCAT is higher than NO _X reduction optimum temperature range OTNOX When high, the reducing agent supplied to the exhaust purification catalyst 17 is NO
Substances other than NO _X than _X, in particular O ₂ and actively longer present in an amount of reducing agent required reaction to for of the NO _X reduction, than thus to NO _X reduction rate PENOX to allowable minimum purification efficiency MNOX Will also be lower. On the other hand, the catalyst temperature TCA
T has been activated for the exhaust purification catalyst 17 of the NO _X reduction at the NO _X reduction optimum temperature range OTNOX,
In addition, the reducing agent reacts more actively with NO _X than O ₂ , so that the NO _X reduction rate PENOX becomes higher than the minimum allowable purification rate MNOX.

[0022] Therefore, it is impossible to catalyst temperature TCAT is to effectively utilize the reducing agent a reducing agent for of the NO _X reduction action be supplied when outside OTNOX NO _X reduction optimum temperature range. Therefore, in this embodiment, the catalyst temperature TCAT
N but when in the NO _X reduction optimum temperature range OTNOX
Performs O _X reduction for the sub fuel injection, the catalyst temperature TCAT is NO
_{When the} temperature is outside the _X- reduction optimum temperature range OTNOX, the auxiliary fuel injection for NO _X reduction is stopped. as a result,
Amount of NO _X discharged from the exhaust purifying catalyst 17 while effectively utilizing the reducing agent can be sufficiently reduced. In the example shown in FIG. 2A, the lower threshold value LTNOX of the optimum NO _X reduction temperature range OTNOX is about 200 ° C., and the upper threshold value UTNOX is about 350 ° C.

By the way, as mentioned at the beginning,
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.

Therefore, in the present embodiment, a reducing agent is supplied to the exhaust purification catalyst 17 by the auxiliary fuel injection, and the exhaust purification catalyst 17 is supplied.
To reduce the sulfate within, ie, SO ₃ or H ₂ SO ₄ . In this case, the sulfate reduction auxiliary fuel injection is performed when the catalyst temperature TCAT is within the sulfate reduction optimum temperature range. Next, the optimum temperature range for sulfate reduction will be described with reference to FIG.

FIG. 2B shows the catalyst temperature TCAT when it is considered that NO _X is not contained in the exhaust gas flowing into the exhaust purification catalyst 17, and the reducing agent in the exhaust gas at the inlet and the outlet of the exhaust purification catalyst 17. The relationship between the concentration ratio RRED (solid line) and the sulfate concentration ratio RSUL in exhaust gas at the inlet and outlet of the exhaust purification catalyst 17 (broken line) is shown.
Referring to FIG. 2 (B), when the catalyst temperature TCAT is as low as a, the reducing agent concentration ratio RRED is maintained at approximately 1, that is, almost all of the reducing agent supplied to the exhaust purification catalyst 17 does not react. It is discharged from the exhaust purification catalyst 17. On the other hand, the sulfate concentration ratio RSUL is maintained at substantially zero, that is, almost no sulfate is discharged from the exhaust purification catalyst 17. It is considered that this is because the exhaust purification catalyst 17 has a sulfate adsorption action. Next, the sulfate adsorbing action of the exhaust purification catalyst 17 will be described with reference to FIGS. 3 (A) and 3 (B).

Sulfate adsorption action of the exhaust purification catalyst 17
Is not fully understood. However, this sulfe
The adsorbing action is performed by the mechanism shown in FIG.
It is thought that it is done. That is, the catalyst temperature TC
When the AT is low, as shown in FIG.
O in the purification catalyst 17_TwoIs the catalytic metal M of the exhaust purification catalyst 17
O on the surface of_Two ^-Or O^2-Adheres in the form of On the other hand,
SO in the gas purification catalyst 17_TwoIs O on the surface of the catalyst metal M._Two
^-Or O^2-Reacts with SO_Three(2SO _Two+ O_Two
→ 2SO_Three). Then the generated SO_ThreePart of the exhaust is clean
H in the conversion catalyst 17_TwoH reacts with O_TwoSO_FourAnd H
_TwoSO_FourIs adsorbed in the pores of the catalyst support.
Or SO_ThreeIs partially oxidized to MSO_FourForm of
Is absorbed in the pores of the catalyst carrier.

When the oxygen concentration in the exhaust purification catalyst 17 is high, the pressure in the exhaust purification catalyst 17 is high, or the amount of the reducing agent present in the exhaust purification catalyst 17 is small, the sulfate of the exhaust purification catalyst 17 is reduced. It is also thought to adsorb. As described above, when the catalyst temperature TCAT is as low as a, the sulfate is adsorbed by the exhaust purification catalyst 17, so that RSUL is maintained at almost zero, and since the reducing agent hardly reacts with the sulfate, RRED is maintained at approximately 1.

Referring again to FIG. 2, the catalyst temperature TCAT
Becomes higher as shown by b, RRED decreases while RSUL is maintained at almost zero, and when TCAT becomes greater than or equal to LTSUL, RRED becomes smaller than the allowable maximum ratio MRED. This is presumably because the reducing agent reduces the sulfate when the catalyst temperature TCAT increases, and the proportion of the reducing agent that reacts with the sulfate increases as the catalyst temperature TCAT increases.

The sulfate reducing action in this case has not been sufficiently elucidated. However, it is considered that this sulfate reducing action is performed by a mechanism as shown in FIG. That is, when the catalyst temperature TCAT increases, the H ₂ SO
₄ is desorbed and released in the form of H ₂ SO ₄ . Alternatively, the MSO ₄ adsorbed on the exhaust gas purification catalyst 17 is released from the exhaust gas purification catalyst 17 while reacting with H ₂ O in the exhaust gas purification catalyst 17 to generate H ₂ SO ₄ . Next, the H ₂ SO ₄ released and released from the exhaust purification catalyst 17 is used as a reducing agent (H
C), whereby the sulfate is reduced.
Alternatively, the reducing agent (HC) is adsorbed on the exhaust purification catalyst 17 and then the H ₂ SO
₄ or MSO ₄ , thus reducing sulfate. In any case, in the catalyst temperature region, the amount of sulfate adsorbed on the exhaust purification catalyst 17 is reduced. Further, at this time, the SO ₃ in the exhaust purification catalyst 17
Can 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 amount of the reducing agent present in the exhaust purification catalyst 17 increases, the exhaust purification catalyst 17 It is considered that the sulfate adsorbed on the catalyst is released and released, and at this time, if a reducing agent is present in the exhaust purification catalyst 17, the sulfate is reduced by the reducing agent.

When the catalyst temperature TCAT further increases as shown in FIG. 2B, both RRED and RSUL are maintained at almost zero. It is considered that this is because almost all of the reducing agent supplied to the exhaust purification catalyst 17 is used for the sulfate reducing action. In this catalyst temperature region, the amount of sulfate adsorbed on the exhaust gas purification catalyst 17 is reduced.

When the catalyst temperature TCAT further increases as shown in FIG. 2B, RRED is maintained at almost zero while RRED is maintained at almost zero.
When SUL rises and TCAT exceeds UTSUL, R
SUL becomes larger than the maximum allowable ratio MSUL. This is because when the catalyst temperature TCAT further increases, the reducing agent supplied to the exhaust gas purification catalyst 17 reacts more actively with substances other than sulfate, particularly O ₂ , than sulfate, and as the catalyst temperature TCAT increases, O ₂ decreases. It is considered that this is because the ratio of the reducing agent that reacts with increases.

When the catalyst temperature TCAT is further increased as shown by e, RRED is maintained at almost zero, and RSUL is substantially one.
Is maintained. It is considered that this is because almost all of the reducing agent supplied to the exhaust purification catalyst 17 reacts with O ₂ . That is, LTSUL to UTSUL in FIG.
The optimal temperature range OTS for sulfate reduction
When the catalyst temperature TCAT is within the sulfate reduction optimum temperature range OTSUL, the exhaust purification catalyst 1
When the reducing agent is supplied to the exhaust gas purifying catalyst 7, the sulfate in the exhaust gas purifying catalyst 17 is reduced, and the amount of the sulfate adsorbed on the exhaust gas purifying catalyst 17 decreases. At this time, the amount of the reducing agent discharged from the exhaust gas purifying catalyst 17 and the sulfate The amount can be sufficiently reduced. Therefore, in this embodiment, TCAT
Is in the OTSUL, the sulfate-reducing auxiliary fuel is injected to supply the reducing agent to the exhaust purification catalyst 17. As a result, the amount of sulfate discharged from the exhaust gas purification catalyst 17 can be sufficiently reduced while effectively using the reducing agent for sulfate reduction. In addition, since the amount of sulfate adsorbed on the exhaust purification catalyst 17 is reduced, the sulfate can be surely adsorbed on the exhaust purification catalyst 17 when the TCAT becomes lower than OTSUL again. The amount of sulfate can be further reduced. In the example shown in FIG. 2 (B), the lower limit threshold value LTNO of the sulfate reduction optimum temperature range OTSUL
X is about 350 ° C. and the upper threshold value UTNOX is about 4
50 ° C.

[0034] FIG. 2 (A) and FIG. 2 upper threshold UTNOX and sulfate reducing optimum temperature range in the example shown in (B) NO _X reduction optimum temperature range OTNOX OTSUL
Is equal to the lower threshold value LTSUL. However, for example, depending on the configuration of the exhaust purification catalyst 17, U
TNOX> LTSUL or UTNOX <LT
It may be SUL. However, OTSU
The upper threshold value UTSUL of L is higher than the upper threshold value UTNOX of OTNOX, and the lower threshold value L of OTSUL is lower.
TSUL is also higher than the lower threshold value LTNOX of OTNOX. That is, OTSUL is set to a higher temperature side than OTNOX.

The catalyst temperature TCAT is compared has become higher, thus the secondary fuel injection for sulfate reduction when the secondary fuel injection for NO _X reduction is performed at the time when the thus sulphate reduction for the sub fuel injection is carried out is performed At times, the proportion of the reducing agent that reacts with oxygen O ₂ in the reducing agent supplied to the exhaust gas purification catalyst 17 becomes higher than when the NO _X reducing auxiliary fuel injection is performed. For this reason, when the sulfate-reducing auxiliary fuel injection is performed, the reducing agent concentration CRED in the exhaust gas flowing into the exhaust purification catalyst 17 is set to, for example, NO _X
If the reducing agent concentration is determined to be equal to that when the reducing auxiliary fuel injection is performed, the reducing agent is completely oxidized before reaching the exhaust downstream end of the exhaust purification catalyst 17, that is, the reducing agent cannot be supplied to the entire exhaust purification catalyst 17. There is fear.

On the other hand, the sulfate is
Sulfate secondary fuel injection is performed because it is almost completely absorbed.
H when_TwoSO_FourIs almost all of the exhaust purification catalyst 17
You will be separated from your body. Therefore, the exhaust purification catalyst
H discharged from 17_TwoSO _FourReduction in order to reduce
It is necessary to supply the agent to the entire exhaust purification catalyst 17. There
In this embodiment, the secondary fuel injection for sulfate reduction is performed.
When the auxiliary fuel injection for NOx reduction is performed
The concentration of reducing agent CRED is set higher than
You. That is, for example, NO_XThe auxiliary fuel injection for reduction is performed
The reducing agent concentration CRED at the time of
Return when the secondary fuel injection for sulfate reduction is performed
The base agent concentration CRED is set to about 3000 ppmC. That
As a result, when the secondary fuel injection for sulfate reduction is performed
Then, the reducing agent supplied to the exhaust purification catalyst 17
Exhaust without complete oxidation at the exhaust upstream side of the medium 17
Can reach near the downstream end, thus reducing agent
It can be supplied to the entire exhaust purification catalyst 17.

[0037] In terms Specifically, the NO _X reduction for the sub fuel injection, as a reducing agent concentration CRED is higher than when the secondary fuel injection for NO _X reduction is performed when the secondary fuel injection for sulfate reduction is performed Sub fuel injection time TA
The auxiliary fuel injection time TAUSUL in UNOX and sulfate reduction auxiliary fuel injection is predetermined. This T
AUNOX is stored in advance as a function of the intake air amount Q and the engine speed N in the form of a map shown in FIG.
It is stored in M32. TAUSUL is also a function of the intake air amount Q and the engine speed N, for example, as shown in FIG.
It is stored in the ROM 32 in advance in the form of a map shown in FIG.

[0038] Furthermore, in this embodiment, so that slow the secondary fuel injection timing compared to when the secondary fuel injection for NO _X reduction is performed when the secondary fuel injection for sulfate reduction is performed. That is, part of the fuel injected into the combustion chamber 2 by the auxiliary fuel injection is partially oxidized or completely oxidized. In this case, the amount of fuel partially or completely oxidized in the combustion chamber 2 decreases or the degree of partial oxidation decreases as the auxiliary fuel injection timing is delayed. In other words, when the auxiliary fuel injection timing is delayed, the amount of the reducing agent oxidized in the combustion chamber 2 is suppressed, so that the reducing agent concentration CRED can be maintained high, and at the same time, the heavy reducing agent (high Molecular weight hydrocarbons). Therefore, the reducing agent can reach the vicinity of the exhaust downstream end of the exhaust purification catalyst 17. On the other hand, when NO _X is to be reduced, it is not always necessary to supply the reducing agent to the entire exhaust purification catalyst 17. Rather, the light of the reducing agent (low molecular weight hydrocarbons) are suitable for reducing the NO _X. Therefore, the secondary fuel injection timing when the secondary fuel injection for sulfate reduction in the present embodiment is the sub-fuel injection timing CASUL the NO _X reduction for the sub fuel injection when performed performed CANO
It is set later than X. That is, for example, CANOX
Is approximately 120 ° C. from the approximately 90 ° crank angle (hereinafter, referred to as CA) after compression top dead center (hereinafter, referred to as ATDC).
A, whereas CASUL is, for example, from about 150 ° CA ATDC to about 210 ° C. ATDC.
It is determined within the range up to A.

Incidentally, a porous material such as zeolite has a function of adsorbing hydrocarbons, and the hydrocarbons adsorbed by the porous material are released when the temperature of the porous material increases. Therefore, hydrocarbons are also adsorbed on the exhaust purification catalyst 17, and when the catalyst temperature TCAT increases, the adsorbed hydrocarbons are released. For this reason, when the catalyst temperature TCAT is high, such as when it is within the sulfate reduction optimum temperature range OTSUL, the hydrocarbons adsorbed from the exhaust purification catalyst 17 are released. In this case, if the sub fuel injection is performed by TAUSUL determined according to the engine operating state, excess hydrocarbon is supplied to the exhaust purification catalyst 17, and thus the high-purity hydrocarbon is supplied from the exhaust purification catalyst 17. May be discharged.

Therefore, in this embodiment, when the sulfate-reducing auxiliary fuel injection is performed, the reducing agent concentration CRED is set so that the reducing agent concentration in the exhaust gas flowing out of the exhaust purification catalyst 17 does not exceed a predetermined allowable value. Has been established.
That is, the amount of the reducing agent flowing out of the exhaust purification catalyst 17 is the sum of the amount of the reducing agent leaving the exhaust purification catalyst 17 and the amount of the reducing agent by the sulfate-reducing auxiliary fuel injection, and the reaction rate of the reducing agent in the exhaust purification catalyst 17. , And the conversion of the reducing agent depends on the catalyst temperature TCAT. On the other hand, the amount of the reducing agent released from the exhaust gas purification catalyst 17 depends on the amount of the reducing agent adsorbed on the exhaust gas purification catalyst 17 and the catalyst temperature TCAT. Depends on. Therefore, the engine operation history and the catalyst temperature TC
From the AT, the auxiliary fuel injection time during which the concentration of the reducing agent in the exhaust flowing out of the exhaust purification catalyst 17 becomes an allowable value can be obtained. Therefore, if this auxiliary fuel injection time is referred to as an allowable maximum auxiliary fuel injection time MTAUS, if the fuel injection time in the sulfate reduction auxiliary fuel injection does not exceed MTAUS, the reducing agent in the exhaust gas flowing out of the exhaust purification catalyst 17 The concentration does not exceed the above-mentioned tolerance.

Therefore, in this embodiment, the allowable maximum fuel injection time MTAUS is determined from the engine operation history and the catalyst temperature TCAT.
Is calculated, and the TAUSU obtained according to the engine operating state is calculated.
When L is smaller than MTAUS, the fuel injection time in the sulfate reduction auxiliary fuel injection is set to TAUSUL. When TAUSUL is larger than MTAUS, the fuel injection time in the sulfate reduction auxiliary fuel injection is set to M.
TAUS.

The exhaust pipe 19 may be provided with a sensor for detecting the concentration of the reducing agent in the exhaust gas, and the fuel injection time in the sulfate-reducing auxiliary fuel injection may be controlled according to the output of this sensor. By the way, as described above, excessive oxygen combustion is performed in the diesel engine, and therefore, the exhaust gas flowing into the catalytic converter 19 contains a large amount of oxygen. For this reason, a large amount of reducing agent is required to increase the reducing agent concentration CRED to, for example, 3000 ppmC, and as a result, the fuel consumption rate is deteriorated.

Therefore, in the present embodiment, when the sulfate-reducing sub-fuel injection is performed, the opening degree VOP of the intake throttle valve 14 is determined by the opening degree VOPU during normal operation, that is, when the sulfate-reducing sub-fuel injection is stopped. Also, the opening degree VOPS is made small, so that the amount of oxygen flowing into the catalytic converter 19 is reduced. as a result,
It is possible to reduce the amount of fuel in the sulfate-reducing sub-fuel injection, thereby preventing the fuel consumption rate from deteriorating. The intake throttle valve 1 during normal operation
The opening degree VOPU of 4 is, for example, an opening degree required to set the engine output to the required output. For example, the opening degree VOPU is a function of the depression amount DEP of the accelerator pedal and the engine speed N in the form of a map shown in FIG. It is stored in the ROM 32 in advance. On the other hand, the opening degree VOPS of the intake throttle valve 14 when the sulfate reducing auxiliary fuel injection is performed is the optimum opening degree for increasing the reducing agent concentration CRED without deteriorating the combustion.
For example, as a function of the depression amount DEP of the accelerator pedal and the engine speed N, R
It is stored in the OM32.

In a diesel engine equipped with an EGR device, the catalytic converter 1 is increased by increasing the EGR amount.
The concentration of oxygen in the exhaust gas flowing into the exhaust gas 9 may be reduced. 6 and 7 show a sub fuel injection amount calculation routine according to this embodiment. The routine shown in FIGS. 6 and 7 is executed by interruption every predetermined set time.

Referring to FIGS. 6 and 7, first, at step 50, it is determined whether or not the catalyst temperature TCAT is equal to or lower than the upper threshold value UTSUL and equal to or higher than the lower threshold value LTSUL of the sulfate reduction optimum temperature range OTSUL. Is determined. UTSUL
If <TCAT or TCAT <LTSUL, that is, if TCAT is out of OTSUL, then step 5
Proceeds to 1, the catalyst temperature TCAT is NO _X reduction optimum temperature range OTNOX and the upper limit threshold UTNOX follows and whether or not the lower threshold LTNOX above, i.e. OT
It is determined whether or not it is within NOX. UTNOX ≧ TC
When AT ≧ LTNOX, that is, when TCAT is OTNO
If it is within X, then the routine proceeds to step 52, where the auxiliary fuel injection timing CAS is set to the above-mentioned CANOX. In the following step 53, TAUNOX is calculated from the map of FIG. In the following step 54, this TAUNOX is set as the auxiliary fuel injection time TAUS. That is, TCAT is OT
Is the secondary fuel injection for NO _X reduction is performed when the NOX.

On the other hand, in step 51, UTN
When OX <TCAT or TCAT <LTNOX, that is, when TCAT is out of OTNOX, the routine proceeds to step 55, where the auxiliary fuel injection time TAUS is set to zero.
That is, UTSUL <TCAT or LTNOX <T
At the time of CAT, both the NOx reduction auxiliary fuel injection and the sulfate reduction auxiliary fuel injection are stopped.

On the other hand, in step 50, UTSUL ≧
When TCAT ≧ LTSUL, that is, when TCAT is within the optimum sulfate reduction temperature range OTSUL, the routine proceeds to step 56, where the auxiliary fuel injection timing CAS is set to the above CASUL. In the following step 57, FIG.
TAUSUL is calculated from the map. In the following step 58, the allowable maximum fuel injection time MTAUS is calculated from the engine operation history and the catalyst temperature TCAT. Next step 59
Then, it is determined whether or not TAUSUL calculated in step 57 is smaller than the allowable maximum fuel injection time MTAUS. If TAUSUL <MTAUS, then the routine proceeds to step 59a, where TAUSUL is set to the sub fuel injection time TAU.
S. On the other hand, when TAUSUL ≧ MTAUS, the routine proceeds to step 59b, where MTAUS is set to the sub fuel injection time TAUS. That is, when TCAT is within OTSUL, sulfate reducing auxiliary fuel injection is performed.

FIG. 8 shows a routine for calculating the opening degree VOP of the intake throttle valve 14. This routine is executed by interruption every predetermined set time.
Referring to FIG. 8, first, at step 150, the catalyst temperature T
It is determined whether the CAT is within the sulfate reduction optimum temperature range OTSUL. When UTSUL <TCAT or TCAT <LTSUL, that is, the catalyst temperature TCAT
If is not within the OTSUL, then go to step 151. That is, when the normal operation is performed, the VOPU is calculated from the map of FIG. 5A in step 151, and this VOPU is set as the opening degree VOP of the intake throttle valve 14 in the subsequent step 152.

On the other hand, UTSUL ≧ TCAT ≧ LT
At the time of SUL, that is, when TCAT is within OTSUL, the process proceeds to step 153. That is, when the sulfate-reducing auxiliary fuel injection is performed, step 1 is performed.
In step 53, the VOPS is calculated from the map shown in FIG.

Next, a second embodiment of the exhaust gas purification method according to the present invention will be described. In the above-described first embodiment, the catalyst temperature TCAT is determined according to the engine operating state, and therefore, the sulfate reducing auxiliary fuel injection is controlled according to the engine operating state. However, in this case, when the engine low load operation or the idling operation is continued, the catalyst temperature TCAT is maintained outside the sulfate reduction optimum temperature range OTSUL, and the amount of sulfate S adsorbed on the exhaust gas purification catalyst 17 is maintained.
QSUL gradually increases, and thus the exhaust gas purifying catalyst 17 may be saturated with sulfate. When the exhaust purification catalyst 17 is saturated with sulfate, the catalyst temperature TCAT
Is low, the sulfate is discharged from the exhaust purification catalyst 17. In the first embodiment, TCAT is O
When it is within TSUL, sub-fuel injection is performed regardless of the amount of adsorbed sulfate. When the amount of adsorbed sulfate is extremely small, the reducing agent cannot be effectively used for sulfate reduction.

Therefore, in the present embodiment, the amount of adsorbed sulfate is determined, and when the determined amount of adsorbed sulfate exceeds a certain amount, the auxiliary fuel for sulfate reduction is injected, and the catalyst temperature for controlling the catalyst temperature TCAT is controlled. When a control device is provided to perform sulfate reduction sub-fuel injection, the catalyst temperature control device maintains the catalyst temperature TCAT within the sulfate reduction optimum temperature range OTSUL. Further, the sulfate reducing auxiliary fuel injection is performed in an amount required to reduce the fixed amount of sulfate.

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, when the catalyst temperature TCAT is lower than the sulfate reduction optimum temperature OTSUL, it is considered that almost all of the sulfate flowing into the exhaust purification catalyst 17 is adsorbed in the exhaust purification catalyst 17. On the other hand, the amount of sulfate flowing into the exhaust purification catalyst 17 can be obtained based on the engine operating state.

FIG. 9 shows the inflow sulfate amount QSU flowing into the exhaust purification catalyst 17 per unit time and unit fuel injection time.
L is shown. As shown in FIG. 9A, QS increases as the depression amount DEP of the accelerator pedal increases.
When UL is large and DEP is quite large, DE
QSUL decreases as P increases. Also,
As shown in FIG. 9 (B), QSUL increases as the engine speed N increases, and QSUL decreases as N increases when the engine speed N is considerably high. The inflow sulfate amount QSUL is stored in the ROM 32 in advance in the form of a map shown in FIG.

Therefore, when the catalyst temperature TCAT is lower than the sulfate reduction optimum temperature range OTSUL, the integrated values of the main fuel injection time and the auxiliary fuel injection time are respectively represented by S
TAUM, STAUS, these STAUM and STAUS
Is expressed by STAU and the estimated time interval of the adsorbed sulfate amount is expressed by DLT, the estimated adsorbed sulfate amount SQSUL is expressed by the following equation.

SQSUL = SQSUL + QSUL · STAU · DLT When the estimated adsorption sulfate amount SQSUL becomes larger than a predetermined set value SQ1, the catalyst temperature T
When the CAT is within the sulfate reduction optimum temperature range OTSUL, the sulfate reduction auxiliary fuel injection is performed immediately. On the other hand, when the temperature is lower than TCATOTSUL, TCAT is raised to the inside of OTSUL by the catalyst temperature control device, and then the secondary fuel injection for sulfate reduction is performed.

The catalyst temperature control device of this embodiment is provided with a fuel injection valve 7, and performs TCAT by performing auxiliary fuel injection from the fuel injection valve 7 at the beginning of an engine expansion stroke or an exhaust stroke.
To increase. That is, as described above,
As the auxiliary fuel injection timing advances, the amount of fuel burned in the combustion chamber 2 increases, so that the temperature of the exhaust gas flowing into the exhaust purification catalyst 17 increases, so that the catalyst temperature TCAT can be increased. Therefore, in the present embodiment, the auxiliary fuel injection is performed in the early stage of the engine expansion stroke or the exhaust stroke, whereby T
CAT ≧ LTSUL. The auxiliary fuel injection for increasing the catalyst temperature TCAT to within the sulfate reduction optimum temperature range OTSUL is referred to as heating auxiliary fuel injection.

It can be considered that the amount of adsorbed sulfate when the auxiliary fuel injection for sulfate reduction should be started is almost SQ1. Thus, in the present embodiment, the sulfate-reducing auxiliary fuel injection is performed in an amount necessary to reduce the sulfate by SQ1. As a result, the reducing agent can be effectively used for sulfate reduction.

Next, the exhaust gas purification method according to this embodiment will be described in more detail with reference to the time chart of FIG.
Referring to FIG. 10, when the estimated adsorption sulfate amount SQSUL becomes larger than the set value SQ1 as indicated by time a, and when the catalyst temperature TCAT is lower than the lower threshold LTSUL of the sulfate reduction optimum temperature range OTSUL. That is, when TCAT is lower than OTSUL, heating auxiliary fuel injection is first performed (ON). Next, at time b, when TCAT ≧ LTSUL, that is, when TCAT is within OTSUL, the auxiliary heating fuel injection is stopped (OFF), and the auxiliary fuel injection for sulfate reduction is performed (ON). When the sulfate-reducing secondary fuel injection is started, the calculation of the integrated value STAUSS of the sulfate-reducing secondary fuel injection amount is started. When the accumulated value STAUSS becomes larger than the predetermined set value ST1 at the time c, the sulfate reduction auxiliary fuel injection is stopped (OFF), and the estimated adsorption sulfate amount SQSUL is cleared. This set value ST1 is an auxiliary fuel injection amount necessary to reduce sulfate by SQ1. That is,
When STAUSS> ST1, exhaust purification catalyst 1
It is determined that the sulfate desorption reduction operation of 7 has been completed, and the sulfate reduction auxiliary fuel injection is stopped.

On the other hand, as shown by time d, SQ
When SUL> SQ1 and TCAT ≧ LTSUL, the auxiliary fuel injection for sulfate reduction is performed without performing the auxiliary fuel injection for heating. Then, at time e, S
When TAUSS> ST1, the auxiliary fuel injection for sulfate reduction is stopped, and the estimated adsorption sulfate amount SQSUL is cleared.

FIG. 11 is a routine for controlling the sulfate-reducing auxiliary fuel injection. The routine shown in FIG. 11 is executed by interruption every predetermined time. Referring to FIG. 11, first, in step 60, it is determined whether or not the sulfate flag XSUL1 is set. The sulfate flag XSUL1 is set when the sulfate reduction auxiliary fuel injection is to be performed (XSUL1 = "1"), and is reset when the sulfate reduction auxiliary fuel injection is to be stopped (XSUL1 =
“0”). When the sulfate flag XSUL1 is reset, the routine proceeds to step 61, where the integrated value STAUM of the main fuel injection time and the integrated value S of the auxiliary fuel injection time are set.
The sum STAU with TAUS is calculated. The integrated value STAUM of the main fuel injection time and the integrated value STAUS of the auxiliary fuel injection time are calculated by a routine described later. In the following step 62, STAUM and STAUS are cleared. In the following step 63, the inflow sulfate amount QSUL is calculated based on the map shown in FIG. In the following step 64, the estimated adsorption sulfate amount SQSUL
Is calculated based on the following equation.

SQUL = SQSUL + QSUL / STAU / DLT Here, DLT is a time interval from the previous routine to the current routine. In the following step 65, it is determined whether or not the estimated adsorption sulfate amount SQSUL is larger than the set value SQ1. If SQUL> SQ1, the routine proceeds to step 66, where the sulfate flag XSUL1 is set (XSUL1 = "1"), and the processing cycle ends. On the other hand, when SQUL ≦ SQ1, the processing cycle ends while the sulfate flag XSUL1 is held at the reset.

When the sulfate flag XSUL1 is set, the process proceeds from step 60 to step 67, where the integrated value STA of the sulfate reducing auxiliary fuel injection time is set.
It is determined whether USS is greater than set value ST1. When STAUSS ≦ ST1, it is determined that the sulfate desorbing and reducing action is insufficient, and the processing cycle ends while the sulfate flag XSUL1 is kept set. On the other hand, when STAUSS> ST1, it is determined that the sulfate release / reduction action is sufficient, and the routine proceeds to step 68, where the sulfate flag XSUL1 is reset. Next, the routine proceeds to step 69, where the accumulated value STAUSS of the sulfate reduction auxiliary fuel injection time and the estimated adsorption sulfate amount SQSUL are cleared, and the processing cycle ends. It should be noted that the integrated value STAUSS of the sulfate reduction auxiliary fuel injection time is calculated in a routine described later.

FIG. 12 is a routine for calculating the main fuel injection time TAUM. The routine shown in FIG. 12 is executed by interruption every predetermined crank angle. Referring to FIG. 12, first, at step 70, the basic main fuel injection time TAUMB is calculated. The basic main fuel injection time TAUMB is determined by the accelerator pedal depression amount DE.
It is stored in the ROM 32 in advance in the form of a map shown in FIG. 13 as a function of P and the engine speed N. In the following step 71, a correction coefficient K is calculated. In the following step 72, the main fuel injection time TAUM is calculated by multiplying the basic main fuel injection time TAUMB by the correction coefficient K. In the following step 73, the integrated value S of the main fuel injection time TAUM
TAUM is calculated.

FIGS. 14 and 15 show the auxiliary fuel injection time TA.
This is a routine for calculating US. This routine is executed by interruption every predetermined set time. Referring to FIG. 14 and FIG.
At 0, the sulfate flag XSUL1 set or reset in the routine of FIG. 11 is set (XSUL1 =
"1") is determined. When the sulfate flag XSUL1 is reset (XSUL1 = "0"), the routine proceeds to step 81, where UTNO
It is determined whether or not X ≧ TCAT ≧ LTNOX, that is, whether or not the catalyst temperature TCAT is within the NO _X reduction optimum temperature range OTNOX. UTNOX ≧ TCAT ≧ LT
If NOx, the process proceeds to step 82, where the auxiliary fuel injection timing CAS is set to the above-described CANOX. In the following step 83, TAUNOX is calculated from the map of FIG. In the following step 84, this TAUNOX is set as the auxiliary fuel injection time TAUS. Thus the secondary fuel injection is performed for NO _X reduction. In the following step 85, the integrated value STAUS of the sub fuel injection time TAUS is calculated.

On the other hand, in step 81, UTN
OX <When TCAT or TCAT <LTNOX, i.e. TCAT is routine goes to step 86 when the outside NO _X reduction optimum temperature range OTNOX, the secondary fuel injection time TAUS is made zero. On the other hand, when the sulfate flag XSUL1 is set in step 80, the routine proceeds to 87, where the catalyst temperature TCAT is set to the upper limit threshold value UTSUL of the sulfate reduction optimum temperature range OTSUL.
It is determined whether or not: UTSUL <TCAT
, Ie, when TCAT is outside OTSUL, the routine proceeds to step 86, where the auxiliary fuel injection time TAUS is set to zero. On the other hand, when UTSUL ≧ TCAT, the routine proceeds to step 88, where the catalyst temperature TCAT becomes OT
It is determined whether or not the value is equal to or more than the lower threshold value LTSUL of SUL, that is, whether or not the value is within the OTSUL. TCAT
If <LTSUL, that is, if TCAT is outside OTSUL, then the routine proceeds to step 89, where the auxiliary fuel injection timing CAS is set to CAH. This CAH is the catalyst temperature TCA
T is an optimum auxiliary fuel injection timing for rapidly increasing T, for example, from about 90 ° CA to about 120 ° CA of ATDC.
It is determined within the range up to. In the following step 90, FIG.
6, the TAUH is calculated. This TAUH is a fuel injection time that gives the optimum auxiliary fuel injection amount for rapidly raising the catalyst temperature TCAT, and is, for example, in the form of a map shown in FIG. 16 as a function of the intake air amount Q and the engine speed N. It is stored in the ROM 32 in advance. Therefore, heating auxiliary fuel injection is performed.

On the other hand, at step 88 TCA
When T ≧ LTSUL, that is, when TCAT is within the sulfate reduction optimum temperature range OTSUL, the routine proceeds to step 91, where the sub fuel injection timing CAS is set to the above CAS.
UL. In the following step 92, TAUSUL is calculated from the map of FIG. In the following step 93, this TAUSUL is set as the auxiliary fuel injection time TAUS. Therefore, sulfate reduction auxiliary fuel injection is performed. In the following step 94, the integrated value STAUSS of the sulfate reduction auxiliary fuel injection time is calculated.

Next, a description will be given of a third embodiment of the exhaust gas purification method according to the present invention. This embodiment is different from the above-described embodiment in that it does not include a temperature sensor and a catalyst temperature control device. In this embodiment, the catalyst temperature TCAT depends on the operating state of the engine, as in the first embodiment. In this case, since the temperature of the exhaust gas flowing into the exhaust purification catalyst 17 is relatively low when the engine steady operation or the slow acceleration operation is performed, the catalyst temperature TCAT is set to the sulfate reduction optimum temperature range O.
It is not raised to within TSUL. On the other hand, when the engine rapid acceleration operation is performed, the temperature of the exhaust gas flowing into the exhaust purification catalyst 17 increases, so that the catalyst temperature TCAT is raised to within the sulfate reduction optimum temperature range OTSUL and is maintained within OTSUL for a certain period. . However, the exhaust purification catalyst 17
Even if the temperature of the exhaust gas flowing into the
A delay time is required for the AT to be raised to within OTSUL.

Therefore, in this embodiment, it is determined whether or not the engine rapid acceleration operation has been performed, and the second set immediately after the lapse of the first set period from the determination that the engine rapid acceleration operation has been performed.
It is determined that the catalyst temperature TCAT is within the sulfate optimum temperature range OTSUL within the set period of, and at this time, the sulfate reducing auxiliary fuel injection is performed. On the other hand, when it is determined that the engine is not rapidly accelerating,
The catalyst temperature TCAT is NO _X reduction optimum temperature range OTNOX
Is the secondary fuel injection for NO _X reduction is performed when it is determined that within. That is, for example, when the intake air amount Q is longer than a certain time and smaller than a certain value, or when the engine speed N is longer than a certain time and smaller than a certain value, it is determined that the TCAT is outside the OTNOX. It is determined that it is within OTNOX.

Incidentally, since the sulfate reducing action is an exothermic reaction, if the sulfate reducing auxiliary fuel injection is continuously performed, there is a possibility that the catalyst temperature TCAT may be raised outside the sulfate optimum temperature range OTSUL. This embodiment does not include a temperature sensor for detecting the catalyst temperature, and therefore, even if TCAT is raised outside OTSUL, the secondary fuel injection for sulfate reduction can be performed as long as it is within the second set period. However, in this case, as described above, the reducing agent cannot be effectively used for sulfate reduction.

Therefore, in this embodiment, the catalyst temperature TCAT
Is determined to be within the sulfate optimum temperature range OTSUL, the sulfate reducing auxiliary fuel injection is intermittently performed. As a result, TCAT becomes OTSU
It can be prevented from being raised out of L, and thus sulfate can be sufficiently reduced. next,
18 to 20 with reference to the time chart of FIG.
The exhaust gas purification method according to the present embodiment will be described in further detail with reference to the flowchart of FIG.

FIG. 18 shows a control routine for the secondary fuel injection for sulfate reduction. This routine is executed by interruption every predetermined set time. FIG.
First, at step 100, it is determined whether or not the sulfate flag XSUL2 is set. This sulfate flag XSUL2 is set when it is within the above-described second set period (XSUL2 =
"1"), and reset when the time is outside the second set period (XSUL2 = "0"). Sulfate flag XSUL
If 2 has been reset, then step 101
It is determined whether or not the rapid acceleration flag XACC is set. This rapid acceleration flag XACC is set when the engine rapid acceleration operation is performed (XACC =
"1"), reset when the engine rapid acceleration operation is not being performed (XACC = "0"). Rapid acceleration flag XAC
If C is reset, then step 102
And the rate of change Δ of the accelerator pedal depression amount DEP
It is determined whether or not DEP is greater than the set value D1 (> 0), that is, whether or not the engine rapid acceleration operation has been performed. Δ
When DEP ≦ D1, that is, when the engine rapid acceleration operation is not being performed, the processing cycle ends. On the other hand, when ΔDEP> D1, that is, when the engine rapid acceleration operation is performed, the routine proceeds to step 103, where the rapid acceleration flag XACC is set.

When the rapid acceleration flag XACC is set, the routine proceeds from step 101 to step 104, where it is determined whether or not the count value CF is larger than the set value CF1. This count value CF represents the elapsed time since it was determined that the engine rapid acceleration operation was performed, and the set value CF1
Represents the first set period described above. When CF ≦ CF1, that is, when the first set period has not yet elapsed since it was determined that the engine rapid acceleration operation was performed, the process proceeds to step 105, where the count value CF is incremented by one. On the other hand, when CF> CF1, it is determined that the first set period has elapsed since it was determined that the engine rapid acceleration operation was performed, and then the routine proceeds to step 106, where the sulfate flag XSUL2 is set. That is, it is determined that it is within the second set period, and accordingly, it is determined that TCAT is within OTSUL, and therefore, the secondary fuel injection for sulfate reduction is started. In the following step 107, the rapid acceleration flag XACC is reset, and in the following step 108, the count value CF is cleared.

When the sulfate flag XSUL2 is set, the process proceeds from step 100 to step 109, where the count value CS is incremented by one. In the following step 110, it is determined whether or not the count value CS is larger than the set value CS1. The count value CS is the first
Represents the elapsed time after the completion of the set period, and the set value CS1 represents the above-described second set period. CS
When ≤ CS1, that is, when the second setting period has not yet elapsed since the completion of the first setting period, the processing cycle ends. Therefore, the intermittent sulfate-reducing auxiliary fuel injection is continued. On the other hand, CS> C
In the case of S1, it is determined that the second set period has elapsed since the completion of the first set period, and then the routine proceeds to step 111, where the sulfate flag XSUL2 is reset.
The intermittent sulfate reduction auxiliary fuel injection is stopped.
Therefore, in the subsequent step 112, the count value CS is cleared.

That is, when ΔDEP becomes larger than the set value D1, as shown at time a in FIG. 17, the rapid acceleration flag XACC is set, and the count value CF starts to be incremented. Next, when the count value CF becomes larger than the set value CF1 as at time b in FIG. 17, the rapid acceleration flag XACC is reset, the sulfate flag XSUL2 is set, and the intermittent sulfate reduction auxiliary fuel injection is started, and the count value The CS increment is started. Next, when the count value CS becomes larger than the set value CS1 as at time c in FIG. 17, the sulfate flag XSUL2 is reset, and the intermittent sulfate reduction auxiliary fuel injection is stopped.

FIGS. 19 and 20 show the auxiliary fuel injection time TA.
This is a routine for calculating US. This routine is executed by interruption every predetermined set time. Referring to FIG. 19 and FIG.
At 20, the sulfate flag XSUL2 set or reset in the routine of FIG. 18 is set (XSUL2
= “1”) is determined. The sulfate flag XSUL2 is reset (XSUL2 = "0")
When that is the routine goes to step 121, whether the catalyst temperature TCAT is within NO _X reduction optimum temperature range OTNOX is determined based on the engine operating state. As described above, in the present embodiment, when the intake air amount Q is equal to or more than a certain time and smaller than a certain value, or when the engine speed N is equal to or more than a certain time and smaller than a certain value, TCAT is set to O.
TCAT is determined to be out of TNOX, otherwise TCAT is O
It is determined that it is within TNOX. TCAT is OTNOX
If it is determined that it is within the range, then the routine proceeds to step 122, where the auxiliary fuel injection timing CAS is set to the above-described CANOX. In the following step 123, TAUNOX is calculated from the map of FIG. In the following step 124, this TAU
NOX is set as the auxiliary fuel injection time TAUS. On the other hand, when it is determined in step 121 that TCAT is out of OTNOX, the routine proceeds to step 125, where the sub fuel injection time TAUS is set to zero. Therefore, the auxiliary fuel injection is stopped.

On the other hand, when the sulfate flag XSUL2 is set in step 120, the process proceeds to 126, where it is determined whether or not the stop flag XSTP is set. The stop flag XSTP is set when the sulfate reduction auxiliary fuel injection is to be temporarily stopped (XSTP = "1"), and is reset when the sulfate reduction auxiliary fuel injection is to be performed (XSTP =
“0”). When the stop flag XSTP has been reset, the process then proceeds to step 127, where the count value CPFM representing the continuation execution time of the sulfate reduction auxiliary fuel injection
Is larger than the set value CPF1. C
When PFM ≦ CPF1, the routine proceeds to step 128, where the count value CPFM is incremented by one. In the following step 129, the auxiliary fuel injection timing CAS is set to the above CASUL. In the following step 130, TA
USUL is calculated from the map of FIG. In the following step 131, this TAUSUL is set to the sub fuel injection time TAUS
It is said. Therefore, sulfate reduction auxiliary fuel injection is performed.

On the other hand, in step 127, CPF
If M> CPF1, then the routine proceeds to step 132,
The stop flag XSTP is set. Subsequent step 13
At 3, the count value CPFM is cleared. In the following step 134, the count value CSTP representing the continuation stop time of the sulfate reduction auxiliary fuel injection is incremented by one. In the following step 135, the auxiliary fuel injection time TAU
S is set to zero. Therefore, when the sulfate-reducing auxiliary fuel injection is performed for the time represented by the set value CPF1, the fuel is temporarily stopped.

When the stop flag XSTP is set, the process proceeds from step 126 to step 136, where it is determined whether or not the count value CSTP is larger than the set value CST1. When CSTP ≦ CST1, the routine proceeds to step 134, where the count value CSTP is incremented, and then the sub fuel injection time TAUS is set to zero. On the other hand, when CSTP> CST1 in step 136, the process proceeds to step 137, where the stop flag XSTP
Is reset. In the following step 138, the count value CSTP is cleared. In the following step 128, the count value CPFM is incremented.
At 29, CAS is set to CASUL, and the following step 13
At 0, TAUSUL is calculated, and at step 131, TAUS is set to TAUSUL. Therefore, when the sulfate-reducing auxiliary fuel injection is stopped for the time represented by the set value CST1, the fuel is restarted.

Next, a fourth embodiment of the exhaust gas purification method according to the present invention will be described with reference to FIG. NO _X reduction catalyst 17a and the sulfate reducing catalyst 17 in the diesel engine which is connected in series exhaust purification catalyst 17 sequentially shown in FIG. 21
b. That is, the exhaust pipe 16 is connected to a casing 18a housing the NO _X reduction catalyst 17a, the casing 18a is connected to the casing 18b housing the sulfate reducing catalyst 17b via the exhaust pipe 20. Further, a reducing agent supply device 21 for supplying a reducing agent comprising, for example, a fuel to the sulfate reducing catalyst 17b is attached in the exhaust pipe 20. In addition, NO _X reduction catalyst 17
The exhaust pipe 20 adjacent to the exhaust downstream end of a temperature sensor 40a is attached that generates an output voltage proportional to the temperature of the exhaust gas flowing out from the NO _X reduction catalyst 17a. The temperature of this exhaust gas is the catalyst temperature of the NO _x reduction catalyst 17a (hereinafter referred to as N
O _X catalyst temperature referred to) represent TCATN. Further, a temperature sensor 40b for generating an output voltage proportional to the temperature of the exhaust gas flowing out of the sulfate reduction catalyst 17b is mounted in the exhaust pipe 19 adjacent to the exhaust downstream end of the sulfate reduction catalyst 17b. The temperature of the exhaust gas represents the catalyst temperature of the sulfate reduction catalyst 17b (hereinafter, referred to as sulfate catalyst temperature) TCATS. The output voltages of the temperature sensors 40a and 40b are input to the input port 36 via the corresponding AD converters 43, respectively.
On the other hand, the output port 37 is connected to the reducing agent supply device 21 via the corresponding drive circuit 45. The other configuration is the same as that of the diesel engine shown in FIG.

The NO _x reduction catalyst 17a is composed of platinum Pt, palladium Pd, rhodium Rh, iridium Ir supported on a porous carrier such as zeolite and 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 containing high silica such as ZSM-5 type, ferrierite, and mordenite can be used. This NO _X reduction catalyst 17a is, like the exhaust purification catalyst 17 of the above-described embodiment, an optimum NO _X reduction temperature range O
It has TNOX, i.e. NO _X catalyst temperature TCA
TN is reducing NO _X with at the high purification rate reducing agent is supplied to the NO _X reduction catalyst 17a when in the NO _X reduction optimum temperature range OTNOX, purify. However,
NO _X reduction catalyst 17a does not have a sulfate adsorbing ability, such as the exhaust gas purifying catalyst 17 of the above embodiments.

On the other hand, the sulfate reduction catalyst 17b comprises platinum Pt, palladium Pd, rhodium Rh supported on a porous carrier such as silica SiO ₂ and titania TiO ₂ .
Noble metals such as iridium Ir, or copper Cu, iron F
e, a transition metal such as cobalt Co and nickel Ni. This sulfate reduction catalyst 17b has a sulfate adsorption capacity and a sulfate reduction optimum temperature range OTSUL similarly to the exhaust purification catalyst 17 of the above-described embodiment, that is, the sulfate catalyst temperature TCATS is within the sulfate reduction optimum temperature range OTSUL. Sometimes, when the reducing agent is supplied, the sulfate in the sulfate reduction catalyst 17b is reduced at a high purification rate, and the amount of sulfate adsorbed on the sulfate reduction catalyst 17b is reduced. However, the sulfate reduction catalyst 17b is different from the exhaust purification catalyst 1 of the above-described embodiment.
It does not have the NO _X reduction action or oxidizing ability, such as 7. Since the sulfate adsorption mechanism and the sulfate desorption / reduction mechanism of the sulfate reduction catalyst 17b are considered to be the same as those in the exhaust gas purification catalyst 17 of the above-described embodiment, the description will be omitted.

[0082] In other words, NO _X reduction catalyst 17a is low is high and sulfates adsorptivity oxidizing ability, sulfate reducing catalyst 17b will be high and sulfate adsorbing ability low oxidizing ability. In this embodiment, NO _X
The lower threshold value LTNOX of the optimal NO _X reduction temperature range OTNOX of the reduction catalyst 17a is about 200 ° C, and the upper threshold value UTNOX is about 350 ° C. The optimum temperature range OT for sulfate reduction of the sulfate reduction catalyst 17b
The lower threshold LTNOX of SUL is about 350 ° C.
The upper threshold value UTNOX is about 450 ° C., and is set to be higher than the optimal NO _X reduction temperature range OTNOX of the NO _X reduction catalyst 17a.

Next, an exhaust gas purification method according to the present embodiment will be described. Fuel injection valves 7 when the NO _X catalyst temperature TCATN is within NO _X reduction optimum temperature range OTNOX
Is the secondary fuel injection for NO _X reduction is performed from, whereby NO
_The reducing agent is supplied to the _X reduction catalyst 17a, and TCATN becomes O
Is the secondary fuel injection for NO _X reduction is stopped when the outside TNOX. As a result, reducing agent can be favorably reduce NO _X in the NO _X reduction catalyst 17a effectively while utilizing for of the NO _X reduction.

When the sulfate catalyst temperature TCATS is within the optimum sulfate reduction temperature range OTSUL, a reducing agent (fuel) is injected from the reducing agent supply device 21 into the exhaust pipe 20, whereby the sulfate reducing catalyst 17
When the reducing agent is supplied to b and the TCATS is outside the OTSUL, the reducing agent injection of the reducing agent supply device 21 is stopped.
As a result, sulfate can be satisfactorily reduced in the sulfate reduction catalyst 17b while effectively using the reducing agent for sulfate reduction.

As described above, in the present embodiment, since the NO _X reducing action and the sulfate reducing action are performed by separate catalysts, it is possible to simultaneously perform the NO _X reducing action and the sulfate reducing action. That, NO _X when the reduction reaction NO _X reduction reaction occurs in the NO _X reduction catalyst 17a because it is exothermic sulfate reducing catalyst 1
Temperature of the exhaust gas flowing into 7b is higher than the temperature of the exhaust gas flowing to the NO _X reduction catalyst 17a. As a result, NO _X catalyst temperature TCATN is NO _X reduction optimum temperature range OTNOX
And the sulfate catalyst temperature TCATS is OT
Optimum temperature range O for sulfate reduction higher than NOX
It can be maintained in TSUL. Therefore, the NO _X reduction action and sulfate reducing action are performed simultaneously.

Incidentally, the sulfate catalyst temperature TCAT
S is of the NO _X reduction catalyst 17a upstream when in the sulfate reducing optimum temperature range OTSUL, for example from the fuel injection valve 7 performs a secondary fuel injection, if thereby to supply the reducing agent to the sulfate reducing catalyst 17b, NO _{Since the X} reduction catalyst 17a has a high oxidizing ability, the reducing agent due to the auxiliary fuel injection is almost completely oxidized in the NO _X reduction catalyst 17a, and thus may not reach the sulfate reduction catalyst 17b. . Therefore, in the present embodiment, NO _X reduction catalyst 17a and the sulfate reducing catalyst 17
b, a reducing agent supply device 21 is disposed in the exhaust pipe 20, and the reducing agent supply device 21
Is supplied with a reducing agent.

FIG. 22 shows a control routine of the reducing agent supply operation in this embodiment. This routine is executed by interruption every predetermined set time. Referring to FIG. 22, whether or not first step 130 the NO _X catalyst temperature TCATN is not more than the upper threshold UTNOX of the NO _X reduction optimum temperature range OTNOX of the NO _X reduction catalyst 17a and the lower threshold LTNOX more That is, it is determined whether or not it is within OTNOX. UTN
When OX ≧ TCATN ≧ LTNOX, that is, TCA
TN proceeds to then step 131 when in OTNOX, for NO _X reduction from the fuel injection valve 7 secondary fuel injection is performed. The auxiliary fuel injection timing and the auxiliary fuel injection time in this case are obtained in the same manner as in the above-described embodiment. Next, the routine proceeds to step 133. On the other hand, in step 130, UTNOX <TCATN or TCATN <LTNOX
When, namely TCATN proceeds to then step 132 when outside OTNOX, the secondary fuel injection for NO _X reduction is stopped. Next, the routine proceeds to step 133.

At step 133, the sulfate catalyst temperature TCATT is set to the upper limit threshold value UTSU of the sulfate reduction optimum temperature range OTSUL of the sulfate reduction catalyst 17b.
It is determined whether the value is equal to or less than L and equal to or more than the lower limit threshold value LTSUL, that is, whether the value is within the OTSUL. When UTSUL ≧ TCATS ≧ LTSUL, that is, TCATS is in the sulfate reduction optimum temperature range OTS
When it is within the UL, the routine then proceeds to step 134, where the reducing agent supply operation of the reducing agent supply device 21 is executed. In this case, the reducing agent amount corresponding to the sulfate reducing auxiliary fuel injection time in the above embodiment is supplied. On the other hand, when UTSUL <TCATs or TCATs <LTSUL in step 133, that is, TCAT
When S is outside the OTSUL, the process proceeds to step 135, where the reducing agent supply operation of the reducing agent supply device 21 is stopped.

The particulate filter may be accommodated in the casing 18b, and the above-mentioned sulfate reduction catalyst 17b may be carried on the particulate filter. It is known that the particulate matter collected by the particulate filter easily adsorbs sulfate. Therefore, the amount of sulfate discharged into the exhaust pipe 19 is further reduced by combining the particulate filter with the sulfate reduction catalyst 17b. can do.

[0090]

The reducing agent is supplied to the oxidation catalyst when it is determined that the catalyst temperature is within the optimum sulfate reduction temperature range, so that the reducing agent actively reacts with the sulfate, and therefore, the sulfate can be reduced well. Thus, the amount of sulfate discharged from the oxidation catalyst can be favorably reduced.

[Brief description of the drawings]

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

2A is a graph showing a relationship between a catalyst temperature and a NO _X purification rate of an exhaust purification catalyst, and FIG. 2B is a graph showing a relationship between a catalyst temperature and a reducing agent concentration ratio RRED and a sulfate concentration ratio RSUL. FIG.

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

[4] (A) NO _X reduction for the secondary fuel injection time TAUNO
It is a diagram showing X, (B) is a diagram showing sulfate reduction auxiliary fuel injection time TAUSUL.

5A is a diagram showing the opening of the intake throttle valve during normal operation, and FIG. 5B is a diagram showing the opening of the intake throttle valve when sulfate-reducing auxiliary fuel injection is performed.

FIG. 6 is a flowchart for calculating an auxiliary fuel injection time.

FIG. 7 is a flowchart for calculating an auxiliary fuel injection time.

FIG. 8 is a flowchart for calculating an opening degree of an intake throttle valve.

FIG. 9 is a graph showing the amount of sulfate flowing into the exhaust purification catalyst per unit time unit fuel injection amount.

FIG. 10 is a time chart illustrating an exhaust gas purification method according to a second embodiment.

FIG. 11 is a flowchart for controlling sulfate reduction auxiliary fuel injection in the second embodiment.

FIG. 12 is a flowchart for calculating a main fuel injection time.

FIG. 13 is a diagram showing a main basic fuel injection time.

FIG. 14 is a flowchart for calculating an auxiliary fuel injection time in a second embodiment.

FIG. 15 is a flowchart for calculating an auxiliary fuel injection time in a second embodiment.

FIG. 16 is a diagram showing a heating auxiliary fuel injection time.

FIG. 17 is a time chart illustrating an exhaust gas purification method according to a third embodiment.

FIG. 18 is a flowchart for controlling the sulfate-reducing secondary fuel injection in the third embodiment.

FIG. 19 is a flowchart for calculating an auxiliary fuel injection time in a third embodiment.

FIG. 20 is a flowchart for calculating an auxiliary fuel injection time in a third embodiment.

FIG. 21 is an overall view of an internal combustion engine according to a fourth embodiment.

FIG. 22 is a flowchart for controlling a reducing agent supply operation in a fourth embodiment.

[Explanation of symbols]

 2: Combustion chamber 7: Fuel injection valve 15: Exhaust manifold 17: Exhaust purification catalyst 40: Temperature sensor

Continuation of the front page (51) Int.Cl. ⁷ Identification code FI F02D 45/00 360 B01D 53/36 D ZAB 101Z (56) References JP-A-9-32619 (JP, A) JP-A-9-287436 ( JP, A) WO 97/41336 (WO, A1) WO 98/12423 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/08-3/24 B01D 53 / 86 B01D 53/94 F02D 45/00

Claims (10)

(57) [Claims] [Claim 1] Place oxidation catalyst in the engine exhaust passage, the
In an exhaust gas purifying apparatus for an internal combustion engine in which the oxidation catalyst is constantly maintained in an oxidizing atmosphere , the oxidation catalyst is an oxidation catalyst containing platinum, and has an action of adsorbing sulfate in inflowing exhaust gas.
The catalyst temperature is adjusted to the sulfate return of the oxidation catalyst.
If the reducing agent is supplied while the temperature is within the
The amount of sulfate being worn is reduced and the sulfate
The reducing agent is formed from an oxidation catalyst that is designed to reduce the amount of the reducing agent.
And feeding means, and the catalyst temperature comprises a <br/> the catalyst temperature determining means for determining whether in the sulfate reducing the optimum temperature range of the oxidation catalyst, the catalyst temperature is within sulfate reducing optimum temperature range determined When it is adsorbed on the oxidation catalyst
Reduce the amount of sulfate and reduce the sulfate
Temporarily reducing agent into the oxidation catalyst from a reducing agent supply means to
An exhaust gas purification device for an internal combustion engine that is supplied in a continuous manner . 2. A are adapted to the catalyst temperature is reduced to NO _X in the oxidation catalyst by supplying reducing agent to the oxidation catalyst when in the NO _X reduction optimum temperature range of the oxidation catalyst, the sulfate reduction The upper threshold of the optimum temperature range is
_X is set higher than the upper limit threshold value of the optimum temperature range for reduction, and the lower limit threshold value of the optimum temperature range for sulfate reduction is NO.
_2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purifying apparatus is set higher than a lower limit threshold value of the _X reduction optimum temperature range. 3. A fuel injection valve for directly injecting fuel into an engine combustion chamber, and a fuel as a reducing agent is supplied to the oxidation catalyst by performing auxiliary fuel injection from the fuel injection valve during an engine expansion stroke or an exhaust stroke. NO _X when sub-fuel injection should be performed to reduce sulfate
3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the auxiliary fuel injection timing is delayed as compared with when the auxiliary fuel injection is to be performed to reduce the fuel consumption. 4. When a reducing agent to reduce the sulfate to be supplied to the oxidation catalyst in the exhaust gas flowing into the oxidation catalyst as compared to when to supply the reducing agent to the oxidation catalyst to reduce the NO _X 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the reducing agent concentration is increased. 5. When the reducing agent is to be supplied to the oxidation catalyst in order to reduce the sulfate, the concentration of the reducing agent in the exhaust gas flowing out of the oxidation catalyst does not exceed a predetermined allowable value. The exhaust gas purifying apparatus for an internal combustion engine according to claim 4, wherein a concentration of the reducing agent in the exhaust gas flowing into the exhaust gas is determined. 6. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a reducing agent is intermittently supplied to the oxidation catalyst when a reducing agent is to be supplied to the oxidation catalyst in order to reduce sulfate. 7. A rapid acceleration judging means for judging whether or not the engine rapid acceleration operation has been performed, wherein the catalyst temperature judging means has a first set period after it is judged that the engine rapid acceleration operation has been performed. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein it is determined that the catalyst temperature is within the optimum sulfate reduction temperature range within a second set period immediately after the elapse of the predetermined time. 8. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, further comprising catalyst temperature control means capable of controlling a catalyst temperature within the optimum sulfate reduction temperature range. Oxidation catalyst when 9. Many and catalyst temperature than the allowable adsorption amount of amount adsorbed sulfates predetermined seeking adsorbed sulfate amount of the oxidation catalyst based on the institution operating condition is in the sulfate reducing optimum temperature range The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a reducing agent is supplied to the exhaust gas. 10. A and a said oxidation catalyst arranged in sequential series in the engine exhaust passage an NO _X reduction catalyst and sulfate reducing catalyst, the NO _X reduction catalyst is low is high and sulfates adsorptivity oxidizing ability, The sulfate reduction catalyst has low oxidizing ability and high sulfate adsorbing ability,
If the reducing agent is supplied when the temperature of the sulfate reduction catalyst is within the optimum temperature range for sulfate reduction of the sulfate reduction catalyst, the sulfate in the sulfate reduction catalyst is reduced, and the amount of sulfate adsorbed on the sulfate reduction catalyst decreases. The catalyst temperature determination means determines whether the temperature of the sulfate reduction catalyst is within the optimum temperature range for sulfate reduction of the sulfate reduction catalyst, and determines whether the temperature of the sulfate reduction catalyst is optimal for the sulfate reduction of the sulfate reduction catalyst. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein a reducing agent is supplied to the sulfate reduction catalyst when it is determined that the temperature falls within the temperature range.