JP2003035132A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely maintain the amount of hydrogen sulfide generated per unit time to be a fixed amount or less, when making sulfur element discharged from the exhaust purification catalyst. SOLUTION: The device is provided with an exhaust purification catalyst 23 for purifying element in exhaust gas. The sulfur element in the exhaust gas is occluded in the exhaust purifying catalyst; when discharging the occluded sulfur element, the temperature of the exhaust purification catalyst is set at the prescribed temperature or higher, and the air fuel ratio of the exhaust gas is set to almost the theoretical air/fuel ratio or richer. A hydrogen sulfide quantity control means is provided, by which the amount of the hydrogen sulfide generated from the sulfur element discharged from the exhaust purification catalyst during discharging the sulfur element is maintained to be the fixed amount. On the basis of output by a hydrogen sulfide amount detecting means 29 for detecting the amount of hydrogen sulfide, which flows out of the exhaust purification catalyst, actuation of the hydrogen sulfide amount control means is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification device for an internal combustion engine.

[0002]

2. Description of the Related Art In an internal combustion engine, NO _x is stored when the air-fuel ratio of the inflowing exhaust gas is lean, and the stored NO _x is released when the air-fuel ratio of the inflowing exhaust gas becomes rich. NO _X catalysts that can purify NO _X by the reducing agent therein are known.

The NO _X catalyst stores not only NO _X but also the sulfur component contained in the exhaust gas in the form of sulfur oxide SO _X. The occluded SO _X is is _the NO _X storage ability of many becomes the NO _X catalyst decreases the NO _X absorbent. Thus the air-fuel ratio of the exhaust gas _the NO _X storage capability flowing to the NO _X catalyst when reduced may NO _X catalyst becomes unable to occlude NO _X longer while in lean. In this case, NO _X flows out from the NO _X catalyst to the downstream side, and exhaust emission deteriorates.

[0004] sulfur component stored in the NO _X catalyst is released from the NO _X catalyst when the air-fuel ratio of the exhaust gas temperature of the NO _X catalyst flows into and NO _X catalyst becomes a certain temperature or higher becomes rich . So when it should emit sulfur component stored in the NO _X catalyst is occluded if the air-fuel ratio of the exhaust gas flowing into and NO _X catalyst increases the temperature of the NO _X catalyst above a certain temperature and rich The sulfur components present are released from the NO _x storage agent, and thus N
The NO _X storage capacity of the O _X catalyst is restored.

When SO _X is released from the NO _X catalyst, part of the released SO _X reacts with HC and CO in the exhaust gas to produce hydrogen sulfide H ₂ S. This H ₂ S gives off a strong odor when a large amount is generated in a short time. Therefore, in order to avoid this, it is necessary to release SO _X from the NO _X catalyst while maintaining the amount of H ₂ S generated per unit time below a certain fixed amount. As described above, there is a technique for keeping the amount of H ₂ S generated below a certain level.
No. 74232. In the technique described in the above publication, as the rich degree of the exhaust gas flowing into the NO _x catalyst increases, the H ₂ S generation amount increases, so the rich degree of the air-fuel ratio of the exhaust gas is periodically changed at predetermined intervals. By increasing or decreasing, the amount of SO _X released from the NO _X catalyst per unit time is kept below a certain amount on average, so that a large amount of H ₂ S is not generated at one time.

[0006]

As described above, in the technique described in the above publication, the rich degree of the air-fuel ratio of the exhaust gas is cycled at a predetermined interval so that a large amount of H ₂ S is not generated at one time. Increase or decrease. In other words, the average rich degree of the air-fuel ratio of the exhaust gas is set to a predetermined value and is not controlled based on the H ₂ S generation amount. That is, the average rich degree of the air-fuel ratio of the exhaust gas is set regardless of the amount of H ₂ S generated. However, the amount of H ₂ S generated changes depending on factors other than the rich degree of the air-fuel ratio of the exhaust gas. Therefore, even if the rich degree of the air-fuel ratio of the exhaust gas is periodically increased or decreased at a predetermined interval so that the average air-fuel ratio of the exhaust gas becomes the predetermined rich degree, H ₂ S may increase depending on the engine operating state. Can occur in large numbers. This is because not only the NO _x catalyst but also the exhaust purification catalyst whose exhaust gas purifying function has its purification function deteriorated by occluding the sulfur components in the exhaust gas, in order to release the sulfur components from the exhaust purification catalyst. This is also a problem that applies equally when the air-fuel ratio of the inflowing exhaust gas is made rich.

In view of such circumstances, an object of the present invention is to reliably maintain the amount of hydrogen sulfide generated per unit time at the time of releasing the sulfur component from the exhaust purification catalyst to be a certain amount or less.

[0008]

In order to solve the above problems, in the first invention, an exhaust purification catalyst for purifying components in exhaust gas, and a sulfur component in exhaust gas are contained in the exhaust purification catalyst. When the stored sulfur component is to be released from the exhaust purification catalyst, the temperature of the exhaust purification catalyst is set to a predetermined temperature or higher and the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is set to be approximately the theoretical air-fuel ratio or rich. And a sulfur component for performing a sulfur component release process for maintaining the amount of hydrogen sulfide generated from the sulfur component released from the exhaust gas purification catalyst during the sulfur component release process below a certain amount. In an exhaust gas purification device for an internal combustion engine equipped with a hydrogen amount control means, the amount of hydrogen sulfide flowing out from the exhaust gas purification catalyst or the amount of hydrogen sulfide expected to flow out from the exhaust gas purification catalyst. Comprises a hydrogen sulfide amount detecting means for detecting, for controlling the operation of the hydrogen sulfide amount control means based on the output of hydrogen sulfide amount detecting means.

As described above, in the past, a large amount of hydrogen sulfide was not generated at one time by controlling the release of sulfur components that was preset during manufacturing. However, although the amount of hydrogen sulfide generated varies depending on various factors such as the operating state of the internal combustion engine, these factors are not taken into consideration in the preset sulfur component release control, and a large amount of hydrogen sulfide is generated. It could happen. On the other hand, the first
In the exhaust gas purification device of the invention described above, the operation of the hydrogen sulfide amount control means is controlled based on the amount of hydrogen sulfide detected by the hydrogen sulfide amount detection means, that is, the amount of hydrogen sulfide changed by the various factors described above. Therefore, the operation of the hydrogen sulfide amount control means is not controlled regardless of the amount of hydrogen sulfide flowing out from the exhaust purification catalyst.

According to a second aspect of the present invention, in the first aspect of the present invention, the hydrogen sulfide amount detecting means directly detects the actual amount of hydrogen sulfide flowing out from the exhaust purification catalyst by a hydrogen sulfide sensor. That is, in the exhaust gas purification device of the second invention, the amount of hydrogen sulfide actually generated is detected, so the amount of hydrogen sulfide flowing out from the exhaust gas purification catalyst is accurately detected.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the hydrogen sulfide amount control means controls the temperature of the exhaust purification catalyst so that the amount of hydrogen sulfide flowing out of the exhaust purification catalyst during the sulfur component release process is increased. Keep the amount below a certain amount.

According to a fourth aspect of the present invention, in any one of the first to third aspects of the present invention, the hydrogen sulfide amount control means controls the characteristics of the exhaust gas flowing into the exhaust purification catalyst, so that the sulfur component release process is performed. The amount of hydrogen sulfide flowing out from the exhaust purification catalyst is maintained below a certain amount.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects of the present invention, when the hydrogen sulfide amount detecting means detects a certain amount or more of hydrogen sulfide during the sulfur component releasing process, the hydrogen sulfide is detected. Activate the quantity control means.

According to a sixth aspect of the present invention, in any one of the first to fourth aspects of the present invention, the hydrogen sulfide amount control means controls the amount of hydrogen sulfide flowing out from the exhaust purification catalyst during a sulfur component release process to be below a certain amount. The temperature of the exhaust purification catalyst that can be maintained is set as a target temperature based on the output of the hydrogen sulfide amount detection means, and the temperature of the exhaust purification catalyst is controlled so that the temperature of the exhaust purification catalyst becomes the target temperature.

In a seventh aspect based on the sixth aspect, the hydrogen sulfide amount control means lowers the target temperature when the hydrogen sulfide amount detection means detects a certain amount or more of hydrogen sulfide.

In an eighth aspect based on the first aspect, the hydrogen sulfide amount control means is provided when the amount of hydrogen sulfide detected by the hydrogen sulfide amount detection means during the sulfur component releasing process becomes a certain amount or more. Keeps the amount of hydrogen sulfide flowing out of the exhaust purification catalyst below a certain amount by lowering the temperature of at least the highest temperature portion of the exhaust purification catalyst.

In a ninth aspect based on the eighth aspect, the hydrogen sulfide amount control means is one of the flow rate of the exhaust gas flowing into the exhaust purification catalyst and the passage direction when the exhaust gas passes through the exhaust purification catalyst. By changing at least one of them, the temperature of at least the hottest part of the exhaust purification catalyst is lowered.

In a tenth aspect of the invention, in the eighth or ninth aspect of the invention, a bypass passage for bypassing the exhaust purification catalyst, a flow rate of the exhaust gas flowing into the exhaust purification catalyst and an exhaust gas flowing into the bypass passage are provided. A flow rate adjusting valve for adjusting the flow rate and a reducing agent addition device for adding fuel to the exhaust gas flowing into the exhaust purification catalyst are further provided, and the sulfur component release processing means flows into the exhaust purification catalyst. The amount of hydrogen sulfide is adjusted by adjusting the flow rate adjusting valve so that the flow rate of the exhaust gas to be set is lower than the flow rate of the exhaust gas discharged from the internal combustion engine, and adding fuel to the exhaust gas flowing into the exhaust purification catalyst. When the amount of hydrogen sulfide detected by the hydrogen sulfide amount detection unit is equal to or more than the certain amount, the control unit determines that the flow rate of the exhaust gas flowing into the exhaust purification catalyst is the sulfur component release process. Adjust the flow control valve to be larger than set flow rate to lower the temperature of the exhaust purification catalyst by means.

Usually, when performing the sulfur component release treatment,
Operating parameters of the internal combustion engine (for example, ignition timing, fuel injection amount, intake valve and Exhaust valve opening timing, etc.) will be changed. Further, the operating parameters of the internal combustion engine are similarly changed when the temperature of the exhaust purification catalyst is lowered during the sulfur component release processing. However, if the operating parameter of the internal combustion engine is changed in this way, the operating parameter becomes a value different from the optimum value for the operating state of the internal combustion engine. On the other hand, according to the tenth aspect, since the sulfur component release processing is performed by adding the reducing agent (for example, fuel, HC, CO) by the reducing agent addition device (for example, the fuel addition device), the sulfur component release is performed. It is not necessary to change the operating parameters of the internal combustion engine to execute the processing. Further, the hydrogen sulfide amount control means also reduces the amount of hydrogen sulfide flowing out of the exhaust purification catalyst to a certain amount or less simply by adjusting the flow rate adjusting valve without changing the operating parameters of the internal combustion engine or the fuel addition amount from the fuel addition device. Can be maintained. Therefore, it is possible to prevent the operating parameter of the internal combustion vaporization from becoming a value different from the optimum value for the operating state of the internal combustion engine.

In addition, in the exhaust purification device in which the temperature of the exhaust purification catalyst is raised by adding the fuel from the fuel addition device and reducing the flow rate of the exhaust gas flowing into the exhaust purification catalyst, the sulfur component of the exhaust purification catalyst is released. The temperature of the exhaust purification catalyst can also be lowered by stopping the fuel addition from the fuel addition device during the processing. However, in this case, since the flow rate of the exhaust gas flowing into the exhaust purification catalyst is small, the heat of the exhaust purification catalyst is difficult to be transferred to the exhaust gas, and thus the temperature of the exhaust purification catalyst is hard to decrease. On the other hand, according to the tenth aspect, since the flow rate of the exhaust gas flowing into the exhaust purification catalyst is increased, the heat of the exhaust purification catalyst is easily transferred to the exhaust gas, so that the temperature of the exhaust purification catalyst is rapidly lowered. To be

In an eleventh aspect of the invention, in the tenth aspect of the invention, an exhaust purification catalyst for purifying the components in the exhaust gas is further arranged on the bypass passage. According to the eleventh aspect, the flow rate adjusting valve is adjusted so that the flow rate of the exhaust gas flowing into the exhaust purification catalyst during the sulfur component release processing is set to be lower than the flow rate of the exhaust gas discharged from the internal combustion engine. The exhaust gas that has sometimes flown into the bypass passage is also purified.

In a twelfth invention, in the eighth or ninth invention, the passage direction when the exhaust gas passes through the exhaust purification catalyst is switched between a forward direction and a reverse direction opposite to the forward direction. The hydrogen sulfide amount control means can be
When the amount of hydrogen sulfide detected by the hydrogen sulfide amount detection means is equal to or more than the certain amount when the passage direction of the exhaust gas is flowing in one of the forward direction and the reverse direction, the exhaust gas By switching the passage direction to the opposite direction to the passage direction at that time, the temperature of at least the highest temperature portion of the exhaust purification catalyst is lowered.

Usually, when an exhaust gas having an air-fuel ratio of substantially stoichiometric air-fuel ratio or rich flows through the exhaust purification catalyst as in the case of executing the sulfur component release process, an exothermic reaction occurs in the exhaust purification catalyst, and therefore the exhaust purification catalyst. The temperature of the downstream portion of the exhaust gas becomes high. Therefore, when hydrogen sulfide flows out from the exhaust purification catalyst by the sulfur component release processing, hydrogen sulfide is generated in the portion of the exhaust purification catalyst on the exhaust downstream side. On the other hand, the temperature of the exhaust upstream side of the exhaust purification catalyst is relatively low, and hydrogen sulfide is not generated in this part. According to the exhaust gas purification apparatus of the eleventh aspect of the invention, the temperature of the portion of the exhaust gas purification catalyst, which was on the exhaust gas downstream side before the passage direction of the exhaust gas was switched, is high, and the amount of hydrogen sulfide is equal to or more than the predetermined amount. In this case, the exhaust purification catalyst portion becomes the upstream side of the exhaust gas by switching the passage direction of the exhaust gas, and the temperature is gradually lowered. On the other hand, the temperature of the portion of the exhaust purification catalyst that was on the upstream side of the exhaust gas before switching the passage direction of the exhaust gas is low inside the catalyst, and this portion of the exhaust purification catalyst is changed by switching the passage direction of the exhaust gas. It becomes the downstream side of the exhaust gas and the temperature is raised. By performing such control, the amount of hydrogen sulfide that flows out can be maintained below a certain amount simply by switching the flow direction of the exhaust gas, so in order to keep the amount of hydrogen sulfide that flows out below a certain amount. There is no need to change the operating parameters of the internal combustion engine or the amount of fuel added from the fuel addition device.

According to a thirteenth aspect of the present invention, in any one of the eighth to twelfth aspects, the hydrogen sulfide amount detecting means is a parameter relating to the operation of the internal combustion engine other than the actual amount of hydrogen sulfide flowing out from the exhaust purification catalyst. And a parameter detection means for detecting at least one parameter of the characteristics of the exhaust gas flowing into the exhaust purification catalyst and the parameters of the state of the exhaust purification catalyst, and the value of the parameter detected by the parameter detection means. Estimate the amount of hydrogen sulfide expected to flow from the exhaust purification catalyst from. According to the exhaust purification system of the thirteenth invention, the amount of hydrogen sulfide expected to flow out from the exhaust purification catalyst can be estimated, so that the amount of hydrogen sulfide actually flowing out from the exhaust purification catalyst becomes the above-mentioned fixed amount. The hydrogen sulfide amount control means can be activated before reaching. The parameters relating to the operation of the internal combustion engine mean, for example, the ignition timing, the fuel injection amount, the opening timing of the intake and exhaust valves, and the parameters relating to the characteristics of the exhaust gas mean, for example, the air-fuel ratio of the exhaust gas, the temperature and the flow rate. In addition, the parameter relating to the state of the exhaust purification catalyst means, for example, the temperature of the exhaust purification catalyst and the deposition amount of the sulfur component.

In a fourteenth aspect based on the thirteenth aspect, the parameter detecting means comprises at least an exhaust temperature sensor for detecting the temperature of the exhaust gas in the vicinity of the exhaust purification catalyst.

According to a fifteenth invention, in the eighth to fourteenth inventions, the constant amount is zero. Usually, the temperature of the exhaust purification catalyst from which hydrogen sulfide flows out is higher than the temperature of the exhaust purification catalyst from which the sulfur component is released from the exhaust purification catalyst.
Therefore, according to the exhaust gas purification device of the fifteenth invention, the amount of hydrogen sulfide generated can be reduced to zero while releasing the sulfur component from the exhaust gas purification catalyst.

[0027]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings. The engine body 1 schematically shown in FIG. 1 is a cylinder injection type spark ignition internal combustion engine. However, the present invention may be applied to another spark ignition type internal combustion engine or compression ignition type internal combustion engine.

As shown in FIG. 1, in the first embodiment of the present invention, the engine body 1 includes a cylinder block 2, a piston 3 that reciprocates in the cylinder block 2, and a cylinder fixed on the cylinder block 2. And a head 4. A combustion chamber 5 is formed between the piston 3 and the cylinder head 4. The cylinder head 4 has an intake valve 6 for each cylinder,
An intake port 7, an exhaust valve 8 and an exhaust port 9 are arranged. Further, as shown in FIG. 1, an ignition plug 10 is arranged in the center of the inner wall surface of the cylinder head 4, and a fuel injection valve 11 is arranged in the peripheral portion of the inner wall surface of the cylinder head 4. A cavity 12 extending from below the fuel injection valve 11 to below the spark plug 10 is formed on the top surface of the piston 3.

The intake port 7 of each cylinder is connected to a surge tank 14 via a corresponding intake branch pipe 13, and the surge tank 14 includes an intake duct 15 and an air flow meter 16.
Via an air cleaner (not shown). A throttle valve 18 driven by a step motor 17 is arranged in the intake duct 15. On the other hand, the exhaust port 9 of each cylinder is connected to an exhaust manifold 19, and this exhaust manifold 19 is a casing containing a NO _x storage agent 23 via a catalytic converter 21 containing an oxidation catalyst or a three-way catalyst 20 and an exhaust pipe 22. 24 is connected. The exhaust manifold 19 and the surge tank 14 are connected to each other via a recirculation exhaust gas (hereinafter referred to as EGR gas) conduit 26, and an EGR gas control valve 27 is arranged in the EGR gas conduit 26.

The electronic control unit (ECU) 31 is composed of a digital computer, and RAM (random access memory) 3 connected to each other via a bidirectional bus 32.
3, a ROM (read only memory) 34, a CPU (microprocessor) 35, an input port 36 and an output port 37. The air flow meter 16 generates an output voltage proportional to the intake air amount, and this output voltage corresponds to A
It is input to the input port 36 via the D converter 38. An air-fuel ratio sensor 28 for detecting the air-fuel ratio is attached to the exhaust manifold 19, and the output signal of this air-fuel ratio sensor 28 is input to the input port 36 via the corresponding AD converter 38. Further, an H ₂ S sensor 29 and a conventional NO _X sensor 30 capable of detecting the NO _X concentration in the exhaust gas are provided in the exhaust pipe 25 connected to the outlet of the casing 24 containing the NO _X storage agent 23. Are arranged and these H ₂ S sensors 2
9 and the output signals of the NO _X sensor 30 are input to the input port 36 via the corresponding AD converters 38.

A load sensor 41 for generating an output voltage proportional to the depression amount of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is input to the input port 36 via the corresponding AD converter 38. Is entered. The crank angle sensor 42 generates an output pulse each time the crankshaft rotates 30 degrees, for example, and the output pulse is input to the input port 36. The CPU 35 calculates the engine speed from the output pulse of the crank angle sensor 42. On the other hand, the output port 37 corresponds to the corresponding drive circuit 3
A spark plug 10, a fuel injection valve 11, a step motor 17, and an EGR gas control valve 27 are connected via 9.

Next, the structure of the H ₂ S sensor 29 will be briefly described with reference to FIG. The H ₂ S sensor 29 has a reference electrode 52 made of a noble metal electrode on one surface of the oxygen ion conductive solid electrolyte 51, and a detection electrode 53 made of a noble metal electrode on the other surface thereof. 53 is sintered, and the surface of the detection electrode 53 is further covered with the metal oxide semiconductor layer 5
It is formed by coating with 4 and firing. A conductor 55 made of a noble metal is connected to both electrodes 52 and 53, and a voltmeter 56 is connected to these conductors 55. The oxygen ion conductive solid electrolyte 51 is yttrium oxide Y ₂ O ₃ or calcium oxide CaO.
It is made of zirconium oxide ZrO ₂ or cerium oxide CeO ₂ which is stabilized with, and has a tube shape or a flat plate shape. The reference electrode 52 and the detection electrode 53 are made of a noble metal such as platinum Pt, rhodium Rh, palladium Pd, iridium Ir, ruthenium Ru, osmium Os or alloys thereof. The metal oxide semiconductor layer 54 is made of tungsten oxide WO ₃ , tin oxide SnO ₂ , indium oxide In ₂ O _3.
Consists of.

The detection mechanism of the H ₂ S concentration of the above H ₂ S sensor will be described. Oxygen O ₂ is ionized into ² oxygen ions O in the detection electrode 53 made on one noble metal disposed on the surface of the oxygen ion conductive solid electrolyte 51.
A potential is generated by the ionization reaction of oxygen O _{2 at} the detection electrode 53. Further, in the metal oxide semiconductor layer 54, H ₂ S is oxidized by this oxygen ion O ^2-, and changed to water vapor H ₂ O, sulfur oxide SO _2, or the like. A potential is also generated by the H ₂ S oxidation reaction in the metal oxide semiconductor 54. The potential and H caused by the ionization reaction of oxygen
The mixed potential with the potential due to the ₂ S oxidation reaction is a potential depending on the concentration of H ₂ S, and the reference electrode 52 does not contribute to the ionization reaction of oxygen and the oxidation reaction of H ₂ S. Therefore, if this mixed potential is detected by the voltmeter 56 as a potential difference from the reference potential of the reference electrode 52, the concentration of H ₂ S can be directly detected.

Next, the fuel injection control of the internal combustion engine shown in FIG. 1 will be described with reference to FIG. Figure 3
In (A), the vertical axis represents engine load Q / N (intake air amount Q /
The engine speed N) is shown, and the horizontal axis shows the engine speed N.

In FIG. 3 (A), stratified charge combustion is performed in the operating region on the lower load side than the solid line X ₁ . That is, at this time, as shown in FIG. 1, at the end of the compression stroke, the fuel injection valve 1
Fuel F is injected from 1 toward the inside of the cavity 12.
This fuel is guided by the inner peripheral surface of the cavity 12 to form an air-fuel mixture around the spark plug 10, and the air-fuel mixture is ignited and burned by the spark plug 10. At this time, the average air-fuel ratio in the combustion chamber 5 is lean.

On the other hand, in the region on the higher load side than the solid line X ₁ in FIG. 3 (A), fuel is injected from the fuel injection valve 11 during the intake stroke, and at this time homogeneous mixture combustion is performed. It should be noted that between the solid line X ₁ and the chain line X ₂ , uniform air-fuel mixture combustion is performed under a lean air-fuel ratio, and between the chain line X ₂ and the chain line X ₃ homogeneous air-fuel mixture combustion is performed under a theoretical air-fuel ratio. When the load is higher than the chain line X ₃ , the homogeneous mixture combustion is performed under the rich air-fuel ratio.

In the present invention, the basic fuel injection amount TAU required for making the air-fuel ratio the stoichiometric air-fuel ratio is a map shape as a function of the engine load Q / N and the engine speed N as shown in FIG. 3B. Is stored in the ROM 34 in advance, and basically, the basic fuel injection amount TAU is multiplied by the correction coefficient KA to obtain the final fuel injection amount TAUO (= KA · T
AU) is calculated. The correction coefficient KA is stored in advance in the ROM 34 in the form of a map as a function of the engine load Q / N and the engine speed N as shown in FIG.

The value of the correction coefficient KA is smaller than 1.0 in the operating region on the low load side of the chain line X ₂ of FIG. 3A where combustion is performed under a lean air-fuel ratio, and the rich air-fuel ratio It becomes larger than 1.0 in the operating region on the higher load side than the chain line X ₃ of FIG. Further, the correction coefficient KA is set to 1.0 in the operating region between the chain line X ₂ and the chain line X _3, and at this time, the air-fuel ratio is feedback-controlled based on the output signal of the air-fuel ratio sensor 28 so that it becomes the stoichiometric air-fuel ratio. To be done.

The NO _x storage agent 23 arranged in the engine exhaust passage uses, for example, alumina as a carrier, and potassium K, sodium Na, lithium Li, alkali metals such as cesium Cs, barium Ba, calcium Ca are provided on the carrier. And at least one selected from rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt. in this case,
It is also possible to dispose a particulate filter made of cordierite, for example, in the casing 24, and carry the NO _x storage agent 23 having alumina as a carrier on the particulate filter.

In any case, the ratio of the amount of air to the amount of fuel (hydrocarbon) supplied to the engine intake passage, the combustion chamber 5 and the exhaust passage upstream of the NO _x storage agent 23 is N.
When referred to as the air-fuel ratio of the exhaust gas flowing into the O _X storage agent 23,
This _the NO _X storage agent 23 when the air-fuel ratio of the inflowing exhaust gas is lean occludes NO _X, absorbing and releasing action of the NO _X air-fuel ratio of the inflowing exhaust gas to release the NO _X occluding becomes the stoichiometric air-fuel ratio or rich I do.

[0041] The _the NO _X storage ability of the NO _X absorbent 23 way is limited, therefore it is necessary to _the NO _X storage ability of the NO _X absorbent 23 to release the NO _X from _the NO _X storage agent 23 prior to saturation . However, the NO _X storage agent 23 stores almost all the NO _X contained in the exhaust gas while the NO _X storage capacity is sufficient, but when the NO _X storage capacity reaches the limit, it becomes impossible to store some NO _X. Thus, when the NO _X storage agent 23 approaches the limit of the NO _X storage capacity, the NO _X storage agent 23
The amount of NO _X flowing out from the downstream begins to increase.

Therefore, the total NO _X storage amount stored in the NO _X storage agent 23 is estimated, and the exhaust gas flowing into the NO _X storage agent 23 when this NO _X storage amount approaches the maximum NO _X storage amount. the air-fuel ratio (hereinafter, the exhaust air-fuel ratio hereinafter) to temporarily release the NO _X from _the NO _X storage agent 23 in the rich and. In this case, there are various methods for making the exhaust air-fuel ratio flowing into the NO _X storage agent 23 rich. For example, the exhaust air-fuel ratio can be made rich by increasing the average air-fuel ratio of the air-fuel mixture in the combustion chamber 5, or the exhaust air-fuel ratio can be increased by injecting additional fuel at the end of the expansion stroke or during the exhaust stroke. It can be made rich, or the exhaust air-fuel ratio can be made rich by adding additional fuel into the exhaust passage upstream of the NO _x storage agent 23.

If this NO _X storage agent 23 is arranged in the engine exhaust passage, the NO _X storage agent 23 actually performs the NO _X absorption and release action, but there are some parts where the detailed mechanism of this NO _X storage action is not clear. . However, it is considered that this absorbing / releasing action is performed by the mechanism as shown in FIG. Next, this mechanism will be described by taking as an example the case where platinum Pt and barium Ba are supported on a carrier, but other precious metals, alkali metals, alkaline earth metals,
The same mechanism can be achieved by using rare earths.

The internal combustion engine shown in FIG. 1 is frequently used.
Combustion with lean air-fuel ratio in most operating conditions
Is done. In this way, combustion can be performed when the air-fuel ratio is lean.
If so, the oxygen concentration in the exhaust gas is high and this
At this time, as shown in FIG.₂But
O₂ ^-Or O^2-It adheres to the surface of platinum Pt in the form of. one
On the other hand, NO in the inflowing exhaust gas is O on the surface of platinum Pt.₂ ^-Well
Or O^2-Reacts with NO ₂Becomes (2NO + O₂→ 2 NO
₂). NO generated next₂Part of is oxidized on platinum Pt
While being stored, it is occluded in the occluding agent and binds with barium oxide BaO.
As shown in FIG. 4 (A), the nitrate ion NO₃ ^-
Diffuses into the occlusion agent in the form of. NO in this way_XIs N
O_XIt is occluded in the occluding agent 23. Oxygen in the inflowing exhaust gas
NO on the surface of platinum Pt as long as the concentration is high₂Is generated and sucked
NO of storage agent_XNO unless the storage capacity is saturated₂Inside the storage agent
Nitrate NO stored in the₃ ^-Is generated.

On the other hand, when the inflow exhaust air-fuel ratio is made rich, the oxygen concentration in the inflow exhaust gas decreases, and as a result, the platinum P
The amount of NO ₂ produced on the surface of t decreases. NO ₂ with the reaction the reverse generation amount is reduced ^- proceed to (NO ₃ → NO _2),
Thus, the nitrate ion NO ₃ ⁻ in the storage agent is released from the storage agent in the form of NO ₂ . In this case _the NO _X storage agent NO _X released from 23 large amount of unburned HC contained in the inflowing exhaust gas as shown in FIG. 4 (B), is caused to reduction by reaction with CO. In this way, NO ₂ is formed on the surface of platinum Pt.
When NO is no longer present, NO ₂ is released from the occluding agent one after another. Therefore, when the inflow exhaust air-fuel ratio is made rich, NO _X is released from the NO _X storage agent 23 in a short time, and the released NO _X is reduced, so that NO _X is exhausted to the atmosphere. There is no such thing.

In this case, the inflow exhaust air-fuel ratio is set to the theoretical air-fuel ratio.
Even if the ratio is NO_XNO from occluding agent 23_XIs released. Shi
However, when the inflow exhaust air-fuel ratio is set to the theoretical air-fuel ratio,
NO_XNO from occluding agent 23_XWas released only gradually
To say NO_XAll NO stored in the storage agent 23_XEmitted
It takes a little longer time to get it done. By the way in the exhaust gas
Is mainly SO_XIncluded in the form of NO_XOcclusion
NO for agent 23_XNot only SO_XIs also occluded. this
NO_XSO for storage agent 23_XNO storage mechanism_Xof
It is considered to be the same as the storage mechanism. Ie N
O_XOn the carrier in the same way as when explaining the storage mechanism of
Taking the case of supporting platinum Pt and barium Ba as an example,
As described above, the inflow exhaust air-fuel ratio is lean.
Oxygen O when₂Is O₂ ^-Or O^2-In the form of platinum Pt
SO in the exhaust gas that adheres to the surface₂Is platinum P
O on the surface of t₂ ^-Or O^2-Reacts with SO₃Becomes
SO generated next₃Some of the acid on platinum Pt
While being converted into barium oxide BaO
Sulfate ion SO while binding _Four ^2-In the form of
Scattered and stable sulfate BaSO_FourTo generate.

However, the sulfate BaSO ₄ is stable and difficult to decompose, and the sulfate BaSO ₄ remains without being decomposed simply by making the inflow exhaust air-fuel ratio rich. Thus will be sulfates BaSO ₄ increases as time in _the NO _X storage agent 23 has elapsed, that _the NO _X storage agent 23 as thus to time has passed _the amount of NO _X can be occluded is reduced Become. That is, the NO _x storage agent 23 deteriorates as time passes.

[0048] In this case, however the temperature is a constant temperature of the NO _X absorbent 23, decomposed sulfate BaSO ₄ in the _the NO _X storage agent 23 when for example a 600 ° C. or higher, flows into the NO _X absorbent 23 at this time exhaust When the air-fuel ratio is made rich, SO _X can be released from the NO _X storage agent 23. Therefore, in the embodiment of the present invention, the NO _X storage agent 23 to S
When O _X should be released, the temperature of the NO _X storage agent 23 is raised and the exhaust air-fuel ratio flowing into the NO _X storage agent 23 is made rich so that the sulfur component or the SO _{X is} discharged from the NO _X storage agent 23.
The SO _X releasing process for releasing is emitted.

Next, referring to FIG. 5, the SO _{X of} the first embodiment
The release process will be described. In FIG. 5, ΣSOX is N
The total amount of SO _X stored in the O _X storage agent 23 (hereinafter referred to as the total SO _X storage amount), SOXmax is the maximum amount of SO _X stored in the NO _X storage agent 23 (hereinafter, referred to as a limit value). A / F is the exhaust air-fuel ratio, T _cat is the temperature of the NO _x storage agent 23 (hereinafter referred to as the storage agent temperature), and T ₁ is the SO _x NO _x.
The temperature at which the occluding agent 23 can be released (hereinafter, S
O _X referred to as release temperature), H ₂ S per the unit time NO _X
The amount of H ₂ S generated in the storage agent 23 is shown. As shown in FIG. 5, while the exhaust air-fuel ratio A / F is lean R ₁ , S
Since O _X continues to be stored in the NO _X storage agent 23, the total SO _X storage amount ΣSOX gradually increases. In this embodiment, when the total SO _X storage amount ΣSOX exceeds a value (hereinafter, referred to as a determination value) SOXlow which is slightly smaller than the limit value SOXmax, the exhaust air-fuel ratio becomes slightly smaller than the stoichiometric air-fuel ratio from lean R _1. Switch to a rich rich R ₂ that is rich. When the exhaust air-fuel ratio is switched from lean R ₁ to weak rich R ₂ in this way, the unburned fuel in the exhaust gas burns in the NO _X storage agent 23, which raises the storage agent temperature T _cat . Absorbent temperature T _cat is SO _X release temperature T to reach ₁ SO _X is NO _X when it continues to be occluded by the occluding agent 23 absorbing agent temperature T _cat once reached SO _X release temperature T ₁ SO _X is NO _X The total SO _X storage amount ΣSOX since it begins to be released from the storage agent 23
Begins to decrease.

After that, the exhaust air-fuel ratio A / F is determined by the storage agent temperature T.
_{The cat} is controlled to be equal to or higher than the SO _X release temperature T ₁ and the H ₂ S generation amount is controlled to be within the allowable range. The control of the exhaust air-fuel ratio A / F will be described later. As described above, when the storage agent temperature T _cat is maintained at the SO _X release temperature T ₁ or higher, SO _X continues to be released from the NO _X storage agent 23, and therefore the total SO _X storage amount ΣSOX gradually decreases. Then, when the total SO _X storage amount ΣSOX becomes zero, the exhaust air-fuel ratio A / F is returned to the lean R1, whereby the SO _X release processing is ended. Thus, according to this embodiment, N
All the SO _X is released from the O _X storage agent 23, whereby the NO _X storage capacity of the NO _X storage agent 23 is restored.

By the way, during execution of the SO _X releasing process, SO _X is released from the NO _X occluding agent 23, and a part of this released SO _X is the HC or the like contained in the exhaust gas according to the following chemical reaction formula. Reacts with CO, hydrogen sulfide (H ₂ S)
To generate. SO ₂ + 3H ₂ → H ₂ S + 2H ₂ O (1) SO ₂ + 2CO + H ₂ → H ₂ S + 2CO ₂ (2) 3SO ₂ + C ₃ H ₆ → 3H ₂ S + 3CO ₂ (3) These reaction formulas (1) to ( H ₂ S generation amount as can be seen from the 3) the amount of sO _X released from _the NO _X storage agent 23 per unit time (hereinafter, proportional to the referred to as sO _X release amount), S
The larger the amount of released O _{X, the} larger the amount of H ₂ S generated. And SO _X
Amount released is proportional to the temperature of the NO _X absorbent 23, as the temperature of the NO _X absorbent 23 is high SO _X release amount is large. That is, H ₂
The amount of S generated increases as the temperature of the NO _X storage agent 23 increases. If a large amount of H ₂ S is generated in a short period of time, it causes an offensive odor in the atmosphere. Therefore, in order to prevent this, it is necessary to suppress the amount of H ₂ S generated to a certain amount or less. Exhaust air-fuel ratio A / F excess fuel if the greater richness of absorbing heat from the air-fuel mixture in the combustion chamber when vaporized in the combustion chamber, NO _X occluding resulting Therefore, since the temperature of the exhaust gas is reduced The temperature of the agent 23 can be lowered. Therefore, basically, if the temperature of the NO _X storage agent 23 is lowered by setting the rich degree of the exhaust air-fuel ratio A / F to a strong rich that is larger than a weak rich, the SO _X release amount decreases, and thus H _The amount of ₂ S generated should decrease.

[0052] However in proportion to the amount of the reaction formula (3) as seen from the H ₂ S emissions is unburned hydrocarbons C ₃ H ₆ flowing to the NO _X absorbent 23 per unit time, _the NO _X storage agent As the amount of unburned hydrocarbons C ₃ H ₆ flowing into 23 increases, H ₂
The amount of S generated increases. Therefore, simply exhaust air-fuel ratio A / F
Even if the rich degree of is made larger than the weak rich, the SO _X release amount is increased rather, and thus the H ₂ S generation amount may not be suppressed to a predetermined amount or less. That is, as shown in FIG. 6, the H ₂ S generation amount is a function of the temperature of the NO _x storage agent 23 and the rich degree Dr of the exhaust air-fuel ratio A / F, and the higher the storage agent temperature T _cat , the more the H ₂ S generation amount. The amount of H ₂ S generated tends to increase as the rich degree Dr of the exhaust air-fuel ratio A / F increases. However, as the rich degree Dr of the exhaust air-fuel ratio A / F becomes larger, the storage agent temperature T _cat becomes lower. As a result, as shown in FIG. 7, when the rich degree Dr becomes large, the amount of H ₂ S generated tends to decrease. is there. Therefore, in order to suppress the H ₂ S generation amount to a predetermined amount or less, when the rich degree of the exhaust air-fuel ratio A / F is increased, the decrease value of the H ₂ S generation amount due to the temperature decrease of the NO _X storage agent 23 is the NO _X storage amount. H ₂ due to increase in unburned hydrocarbons flowing into the agent
It is necessary to select the rich degree of the exhaust air-fuel ratio A / F so as to exceed the increase value of the S generation amount.

Next, a method of selecting a rich degree that can reduce the amount of H ₂ S generated will be described with reference to FIG. 7. The horizontal axis of FIG. 7 represents the exhaust air-fuel ratio rich degree Dr,
The vertical axis represents the amount of H ₂ S generated, and the line Ta represents the rich degree Dr and H ₂ S when the storage agent temperature is the first temperature Ta.
The line Tb shows the relationship between the rich degree Dr and the H ₂ S generation amount when the storage agent temperature is the second temperature Tb, and the line Tc shows the relationship with the generation amount. T
The relationship between the rich degree Dr and the amount of H ₂ S generation when the value is c is shown. The first temperature Ta, the second temperature Tb,
The relationship between the third temperature Tc and Ta <Tb <Tc. In the following description, the rich degree is the first degree Dr1.
The temperature of the NO _X storage agent 23 becomes the first temperature Ta when the above is set, and the temperature of the NO _X storage agent 23 becomes the second temperature T when the rich degree is set to the second degree Dr2.
b, and it is assumed that the temperature of the NO _X storage agent 23 becomes the third temperature Tc when the rich degree is the third degree Dr3.

First, the rich degree Dr is the first degree Dr1.
Is 0, the storage agent temperature T _cat becomes the first temperature Ta, and the point representing the H ₂ S generation amount at this time is the point X.
Here, if the rich degree Dr is switched from the first degree Dr1 to the second degree Dr2, the point representing the H ₂ S generation amount shifts from the point X to the point Y1. That is, the amount of H ₂ S generated increases. However, the rich degree Dr is the second degree Dr
When it is set to 2, the storage agent temperature T _cat decreases from the first temperature Ta to the second temperature Tb, so that the point representing the H ₂ S generation amount shifts from the point Y1 to the point Z1. That is, the amount of H ₂ S generated is reduced. However in this case, H ₂ S emissions at point Z1 is larger than H ₂ S emissions at point X. Therefore, the rich degree Dr is changed from the first degree Dr1 to the second degree D.
Even if switched to r2, the amount of H ₂ S generated does not decrease in the end.

On the other hand, if the rich degree Dr is switched from the first degree D1 to the third degree Dr3, the point representing the H ₂ S generation amount shifts from the point X to the point Y2. That is, H ₂ S
The amount of generation increases. Moreover third degree Dr3 are H ₂ S generation amount at the point Y2 is greater than the second degree Dr2 is greater than H ₂ S emissions at point Y1. But the third degree Dr3 is large because storage agent temperature T _cat than the second degree Dr2 drops to a third temperature Tc is lower than the second temperature Tb, point points representing H ₂ S emissions Transition from Y2 to point Z2. Here, the amount of H ₂ S generated at the point Z2 is smaller than the amount of H ₂ S generated at the point X. Therefore, in this case, by increasing the rich degree, H ₂
The amount of S generated is suppressed.

As described above, the amount of H ₂ S generated depends on the rich degree Dr.
Increase with increasing temperature, the rate of increase is the storage agent temperature T _cat
Becomes smaller, and the storage agent temperature T _cat becomes lower as the rich degree Dr increases. Therefore, the amount of H ₂ S generated can be reduced by appropriately selecting the rich degree. In this embodiment, the rich degree capable of reducing the amount of H ₂ S generated is previously obtained by an experiment, and RO is shown in the form of a map.
Store in M.

Next, by increasing the rich degree of the exhaust air-fuel ratio to the rich degree selected as described above, H ₂ S
Phenomena when the generated amount is suppressed below a predetermined amount Fig. 5
Will be described with reference to. As described above, the SO _{X of} this embodiment is
According to the release processing, the total SO _X storage amount ΣSOX is the determination value SO
When it reaches Xlow, the exhaust air-fuel ratio is switched from lean to weak rich. After that, when the storage agent temperature T _cat reaches the SO _X release temperature T ₁ , SO _X begins to be released from the NO _X storage agent 23. At the same time, the H ₂ S generation amount H ₂ S starts to rise. After that, since the exhaust air-fuel ratio is maintained to be slightly rich, the storage agent temperature T _cat continues to rise. Therefore, H ₂ S
The generated amount increases, and eventually reaches the determination value H2Slow. At this time, in the present embodiment, the degree of richness of the exhaust air-fuel ratio is increased in order to lower the storage agent temperature _Tcat . That is, the exhaust air-fuel ratio is set to be strong rich, which has a larger rich degree than the rich degree of weak rich. At this time, the H ₂ S generation amount H ₂ S temporarily increases, but thereafter the storage agent temperature T _cat decreases, so that the H ₂ S generation amount gradually decreases.

If the temperature of the NO _X storage agent 23 is lowered more than necessary, the temperature of the NO _X storage agent 23 may become lower than the SO _X release temperature T _1. Therefore, the exhaust air-fuel ratio is set for a predetermined period. After being made a strong rich over a period of time, it is returned to a weak rich. As a result, the storage agent temperature T _cat rises again, and with this, the H ₂ S generation amount H ₂ S also rises again, and eventually reaches the determination value H2Slow. Also at this time, in this embodiment, the degree of richness of the exhaust air-fuel ratio is increased in order to lower the storage agent temperature _Tcat . Also at this time, temporarily H ₂ S
The generated amount H ₂ S increases, but the storage agent temperature T _cat decreases, so the H ₂ S generated amount H ₂ S gradually decreases. Here too, the exhaust air-fuel ratio is made rich for a predetermined period and then returned to weak rich. As a result, the storage agent temperature T _cat rises again, and the H ₂ S generation amount H ₂ S also increases accordingly. However, this time, the total SO _X storage amount ΣSOX is small, and therefore the SO _X release amount is small. Therefore, even if the storage agent temperature T _cat rises, the H ₂ S generation amount H _2
2 S does not reach the determination value H2Slow, and after a certain period of time, begins to decrease gradually as the total SO _X storage amount ΣSOX decreases, and finally reaches the minimum value H2Smin.

By the way, the temperature T _cat of the NO _X storage agent 23 is S
The fact that the H ₂ S generation amount H ₂ S has reached the minimum value H2Smin even though it is higher than the O _X release temperature T ₁ is due to the NO _X storage agent 2.
This means that the amount of SO _x released from 3 is extremely small.
Therefore, in this embodiment, the H ₂ S generation amount H ₂ S is the minimum value H ₂ Smi.
When it reaches n, the exhaust air-fuel ratio is returned to lean, and thus the SO _X release processing is ended. That is, according to this embodiment, the output timing of the H ₂ S sensor determines the end timing of the SO _X releasing process. Thus, according to this embodiment, SO _X is reduced to N while suppressing the H ₂ S generation amount to a certain amount or less.
It can be released from the O _X storage agent.

In the present embodiment, SO_XRelease process
Total SO to determine when to start a row_XOcclusion
Estimate the amount as_X
NO when the storage amount reaches the judgment value_XStorage agent 23 to S
O_XIt should be released. Almost one in fuel
Contains a fixed proportion of sulfur and therefore NO_XSucking
SO stored in storage agent 23 from time to time_XQuantity is the final jet
It is a function of the fuel injection amount TAUO. Also included in fuel
The proportion of sulfur components varies from fuel to fuel and therefore NO _XSucking
SO stored in storage agent 23 from time to time_XThe amount is fixed for each fuel
It is also a function of the total sulfur content. Further NO_XStorage agent 2
SO stored in 3_XThe amount depends on the exhaust air-fuel ratio
And therefore NO_XIt is occluded in the occluding agent 23 from time to time
SO_XThe quantity is also a function of the exhaust air-fuel ratio. Also NO_XOcclusion
No easiness of occlusion in agent 23_XDepending on the temperature of the occluding agent 23
Is different, so NO_XIn the occlusion agent 23 from time to time
SO stored_XThe amount is NO_XEven as a function of the temperature of the occluding agent 23
is there.

Therefore, if the coefficient relating to the sulfur content determined for each fuel is KB _a and the coefficient relating to the exhaust air-fuel ratio and the temperature of the NO _x storage agent 23 is KB _b , the SO stored in the NO _x storage agent 23 at each moment. _X amount is the final injected fuel amount T
The product of AUO and coefficient KB _a and coefficient KB _b TAUO · KB _a
It can be expressed as KB _b . Therefore, the total SO _X storage amount ΣSOX is the final injected fuel amount TAUO and the coefficient KB.
is calculated as the integrated value obtained by integrating the product TAUO · KB _a · KB _b of _a and coefficient _{KB b Σ (TAUO · KB a} · KB b). The coefficient KB _b is previously obtained by an experiment and is stored in advance in the ROM 34 in the form of a map as a function of the exhaust air-fuel ratio and the temperature of the NO _X storage agent 23 as shown in FIG. In addition, the above three parameters (sulfur content, exhaust air-fuel ratio, and NO _x) are used to calculate the total SO _x storage amount.
In addition to (the temperature of the storage agent), for example, the EGR rate, which is the ratio of exhaust gas recirculation (EGR), may be used as a parameter.

By the way, total SO_XStorage amount ΣSOX is the judgment value
Exhaust air-fuel ratio becomes lean R when SOXlow is reached.₁To weak
Rich R₂Even if it is switched to
Is NO _XThe temperature of the occlusion agent 23 is SO_XRelease temperature T₁Lower than
So total SO_XThe storage amount ΣSOX continues to increase. Therefore
The above judgment value SOXlow has an exhaust air-fuel ratio of lean R₁From weak
R₂NO after switching to_XThe temperature of the occlusion agent 23
SO_XRelease temperature T₁To reach total SO_XStorage capacity is limited
It is set so as not to exceed the value SOXmax. in this way
Total SO can be set by setting the judgment value SOXlow._XStorage amount Σ
NO before SOX exceeds the limit value SOXmax_XStorage agent 23
To SO_XBegins to be released.

Further, as described above, when the exhaust air-fuel ratio is switched from the weak rich R ₂ to the strong rich R ₃ , the H ₂ S generation amount temporarily increases greatly. Therefore, in the present embodiment, the determination value H2Slow is the exhaust air Fuel ratio is weak rich R ₂ to strong rich R ₃
Even if the H ₂ S generation amount is temporarily increased, the H ₂ S generation amount is set so as not to exceed the allowable value H2Smax. Further, the amount of increase in the H ₂ S generation amount when the exhaust air-fuel ratio is switched from the weak rich R ₂ to the strong rich R ₃ becomes larger as the temperature of the NO _x storage agent 23 becomes higher, so a predetermined judgment value is set. H2Slow may be corrected by the temperature of the NO _X storage agent 23 detected by the temperature sensor of the second embodiment described later.

Further, in the first embodiment, the total SO _X storage amount ΣS
Although the timing for performing the SO _X release processing is determined from the value of OX, this timing may be determined by another method. For example exhaust air-fuel ratio switching to rich from lean, thereby NO stored in the NO _X absorbent 23 _X
From the execution interval of so-called rich spike that releases SO
You may decide the timing which performs an _X release process. That amount of the NO _X that can be occluded in the NO _X absorbent 23 when the SO _X storage amount stored in the NO _X storage agent 23 as described above is increased is reduced, since the rich spike execution interval gradually becomes shorter When the rich spike execution interval becomes shorter than the predetermined interval, it can be determined that the total SO _X storage amount exceeds the determination value. The SO _X sensor in the exhaust pipe between the engine body and _the NO _X storage agent 23 in addition to this provided, SO _X of the SO _X sensor flows out _the NO _X storage agent
When the amount of is greater than the predetermined amount, the total SO
It is also possible to judge that the _X storage amount exceeds the judgment value.

[0065] Although in the first embodiment is made to raise the temperature of the NO _X absorbent 23 by switching the exhaust air-fuel ratio from lean R ₁ to a slightly rich R _{2, the} NO _X storage agent 23 by other methods The temperature may be increased. For example, the first method is to retard the ignition timing. When the ignition timing is retarded, a part of the fuel is not burned in the combustion chamber and is discharged from the combustion chamber as unburned fuel, and this unburned fuel is burned in the engine exhaust passage, and thus exhausted. The temperature of the gas rises. Therefore, this can raise the temperature of the NO _X storage agent 23. In this method, the temperature of the NO _X storage agent 23 can be increased largely as the ignition timing is delayed. Further, when this method is adopted to raise the temperature of the NO _X storage agent, if the ignition timing is advanced when the H ₂ S generation amount exceeds the determination value, the temperature of the NO _X storage agent is increased. Can be lowered. The second method is to inject additional fuel in the expansion stroke after injecting fuel in the intake stroke or compression stroke. The additional fuel injected in the expansion stroke does not burn in the combustion chamber and is discharged as unburned fuel from the combustion chamber,
This unburned fuel burns in the engine exhaust passage, thus raising the temperature of the exhaust gas. Therefore this will result in NO
The temperature of the _X storage agent 23 can be raised. In this method, the temperature of the NO _X storage agent 23 can be increased more as the amount of additional fuel increases. Also if you have to raise the temperature of the NO _X absorbent adopts this method, _the NO _X storage agent if reduce the amount of additional fuel to be injected when the H ₂ S generation amount exceeds the judgment value The temperature can be lowered.

As a third method, the internal combustion engine is exhaustive.
The order in which the expansion stroke is performed in the case of a cylinder internal combustion engine
Alternating the engine air-fuel ratio between rich and lean for each cylinder according to
There is a method of switching to. For example, the internal combustion engine is 4
In case of a cylinder internal combustion engine, the crankshaft is 180 °
The combustion process is performed sequentially in each cylinder as it rotates.
However, in this case, according to this method, for example, the first expansion
The cylinder in which the stroke is performed and the cylinder in which the expansion stroke is performed third
And the engine air-fuel ratio becomes rich, and the second expansion
And the cylinder in which the expansion stroke is performed fourth.
In, the engine air-fuel ratio is made lean. According to this
Unburned fuel is included from the cylinder whose engine air-fuel ratio is rich.
Exhaust gas is exhausted and the engine air-fuel ratio becomes lean.
Exhaust gas containing a large amount of oxygen is discharged from the cylinder.
Unburned fuel by combining exhaust gas in the engine exhaust passage
Are combusted, thus raising the temperature of the exhaust gas. But
That's NO_XTo raise the temperature of the occlusion agent 23
You can Note that in this method,
The larger the difference between the air-fuel ratio and the lean air-fuel ratio, the more NO _XSucking
The temperature of the storage agent can be raised significantly. Again this
No method adopted_XTo raise the temperature of the occlusion agent
If yes, H₂When the S generation amount exceeds the judgment value,
NO if the difference between the air-fuel ratio and lean air-fuel ratio is reduced_X
The temperature of the occluding agent can be lowered.

FIG. 9 shows a control routine for executing the SO _X releasing process of the first embodiment. First, at step 100, reference the final fuel injection amount TAUO and correction coefficient _{KB (= KB a · KB b} ) is calculated to FIG. Then in step 101, step 10
The total SO _X storage amount ΣSOX is calculated from the final injected fuel amount TAUO calculated at 0 and the correction coefficient KB. Then whether SO _X release flag indicating that the _the NO _X storage agent 23 should be released SO _X in step 102 is set or not. When the SO _X release flag is not set, the routine proceeds to step 103, where it is judged if the total SO _X storage amount ΣSOX of the NO _X storage agent 23 exceeds the judgment value SOX low. When it is determined in step 103 that ΣSOX ≦ SOXlow, the processing cycle of the control routine is completed. On the other hand, step 1
When it is determined that ΣSOX> SOXlow in 03, the routine proceeds to step 104. In step 104, S
O _X release flag is set, and the control routine of the processing cycle is completed.

When the SO _X release flag is set in step 104, step 102 is executed in the next processing cycle.
To step 105. In step 105, the exhaust air-fuel ratio A / F is switched from lean R ₁ to weak rich R ₂ . Next, at step 106, it is judged if the H ₂ S generation amount exceeds the minimum value H2Smin. That is, at step 106, it is judged if SO _X has started to be released from the NO _X storage agent 23. While it is determined in step 106 that H ₂ S ≦ H2Smin, step 106 is repeated. On the other hand, if it is determined in step 106 that H ₂ S> H2Smin, step 1
Proceed to 07. At step 107, it is judged if the H ₂ S generation amount is smaller than the minimum value H ₂ Smin. Step 1
When it is determined at 07 that H ₂ S <H2Smin, the routine proceeds to step 108, where the SO _X release flag is reset and ΣSOX is made zero, and the processing cycle of the control routine is completed.

In step 107, H ₂ S ≧ H2Smin
When it is determined that the value is, the process proceeds to step 109. At step 109, it is judged if the H ₂ S generation amount is smaller than the judgment value H2Slow. H _{2 in} step 109
If it is determined that S ≦ H2Slow, step 1
Returned to 07. In step 109, H ₂ S> H2
If it is determined to be Slow, the routine proceeds to step 110. In step 110, the exhaust air-fuel ratio A / F is switched from the weak rich R ₂ to the strong rich R ₃ for a predetermined period, and then is returned to the weak rich R ₂ again. Then, the process returns to step 107 again. Note combustion means capable of detecting the temperature of the NO _X absorbent because H ₂ S emissions temporarily increase when the exhaust air-fuel ratio from lean to slightly rich varies depending on the temperature of the NO _X absorbent If the engine is provided, the determination value H2Slow may be set from the temperature of the NO _X storage agent before executing step 106.

Next, a second embodiment of the present invention will be described. The second embodiment of the present invention is shown in FIG. Temperature sensor 43 for detecting the temperature of the NO _X absorbent 23 is mounted in the NO _X absorbent 23 in the second embodiment.
The temperature sensor 43 is connected to the input port 36 of the electronic control unit 31 via the A / D converter 38.

Next, referring to FIG. 11, the SO of the second embodiment
_{The X} release processing will be described. FIG. 11 is a time chart similar to FIG. Also in the second embodiment, the total SO _X amount stored in the NO _X storage agent 23 (total SO _X
When the storage amount ΣSOX exceeds the determination value SOXlow, the air-fuel ratio of the exhaust gas is switched from lean to weak rich. Temperature T _cat of the NO _X absorbent 23 is SO _X reaches the SO _X release temperature T ₁ is started to be released from _the NO _X storage agent 23, and at the same time H ₂ S generation amount increases. When the temperature of the NO _X storage agent 23 reaches the target temperature T _catl at that time, the air-fuel ratio of the exhaust gas is switched between weak rich and strong rich, whereby the temperature of the NO _X storage agent 23 is set to the target temperature T _catl. Maintained at.

By the way, when the amount of H ₂ S generation continues to increase and reaches the allowable value H2Sbmax, the target temperature T _catl of the NO _X storage agent 23 is lowered according to this embodiment. Therefore, the air-fuel ratio of the exhaust gas is made strongly rich over a predetermined period, and the temperature of the NO _X storage agent 23 is set to the low target temperature T _catl . This reduces the amount of H ₂ S generated. Furthermore N
When the temperature of the O _X storage agent 23 reaches the low target temperature T _catl , the air-fuel ratio of the exhaust gas is switched between the weak rich and the strong rich, whereby the temperature of the NO _X storage agent 23 reaches the low target temperature T _catl . Maintained. Further, when the H ₂ S generation amount does not reach the allowable value H2Sbmax while the temperature of the NO _X storage agent 23 is maintained at the low target temperature T _catl , the target temperature T _catl is increased in this embodiment. At this time, the air-fuel ratio of the exhaust gas is maintained to be slightly rich, and the temperature of the NO _X storage agent 23 is raised. Therefore, the amount of H ₂ S generated rises, and reaches the allowable value H2Sbmax again. At this time as well, the target temperature T _catl is similarly lowered, so that the air-fuel ratio of the exhaust gas is made strongly rich over a predetermined period, and N
The temperature of the O _X storage agent 23 is set to a low target temperature T _catl .

Further, when the H ₂ S generation amount does not reach the allowable value H2Sbmax while the temperature of the NO _x storage agent 23 is maintained at the low target temperature T _catl , as described above, the target temperature T _catl is set in the present embodiment. To be raised. However, at this time, the total SO _X storage amount ΣSOX has already decreased, and even if the target temperature T _catl is gradually increased, H
_The amount of ₂ S generated does not reach the allowable value H2Sbmax.

By the way, in this embodiment, the target temperature T _catl is increased when the H ₂ S generation amount is smaller than the allowable value H2Sbmax. However, if the target temperature T _catl becomes excessively high, the NO _X storage agent 23 may deteriorate due to heat. So the target temperature T _cat l in this example is guarded to some guard value T _CATLG does not cause thermal deterioration of _the NO _X storage agent 23. According to the present embodiment, all the SO _X is reduced to NO _X within a short period while suppressing the H ₂ S generation amount to a certain amount or less.
It can be released from the occlusion agent 23.

Next, referring to FIG. 12, the SO of the second embodiment is
A control routine for executing the _X release processing will be described. In FIG. 12, steps 200 to 204
Is the same as steps 100 to 104 of the control routine shown in FIG. When it is determined in step 202 of FIG. 12 that the SO _X release flag is set, the process proceeds to step 205. In step 205, the exhaust air-fuel ratio A / F is switched from lean R ₁ to weak rich R ₂ . Then, step 206
Then, it is determined whether or not the H ₂ S generation amount exceeds the minimum value H2Smin. In step 206, H ₂ S ≦ H2Sm
Step 206 is repeated while it is determined to be in. On the other hand, if it is determined that H ₂ S> H2Smin, then the routine proceeds to step 207.

At step 207, the target temperature T set in the routine for setting the target temperature described later is set.
Get the _CatL, temperature of the NO _X absorbent 23 is a temperature of the NO _X absorbent 23 is controlled to be the target temperature T _CatL. Specifically, the temperature of the NO _X storage agent 23 is controlled to the target temperature T _catl by switching the air-fuel ratio of the exhaust gas flowing into the NO _X storage agent 23 between weak rich and strong rich. Next, at step 208, it is judged if the H ₂ S generation amount exceeds the minimum value H2Smin. When it is determined in step 208 that H ₂ S ≧ H2Smin, the process returns to step 207. On the other hand, H ₂ S <H2Sm
If it is determined to be in, the process proceeds to step 209.
In step 209, the SO _X release flag is reset and ΣSOX is returned to zero. Thus, the SO _X releasing process is completed.

Next, a routine for setting the target temperature will be described with reference to FIG. In FIG. 13, first, in step 301, the H ₂ S generation amount is the allowable value H 2
It is determined whether or not Sbmax is exceeded. Step 30
When it is determined that H ₂ S> H2Sbmax in 1, it is determined that the target temperature of the NO _x storage agent 23 is too high,
In step 303, the target temperature T _catl is lowered by the predetermined value ΔT. On the other hand, in step 301, H ₂ S ≦
NO _x storage agent 2 when it is determined to be H2Sbmax
It is determined that a large amount of H ₂ S will not be generated even if the temperature of 3 is further increased, and the _routine proceeds to step 303, where the target temperature T _catl is increased by a predetermined value ΔT. Then, the target temperature T _CatL step 304 is excessively high become not the target temperature T _{ca tl} as a guard to a certain temperature.

[0078] Note that the first target temperature T _CatL step 302 or step 303 at the time the routine of FIG. 13 is performed to the last target temperature T _CatL of the previous SO _X release process. Of course, the target temperature at this time may be a predetermined temperature irrelevant to the target temperature set at the previous SO _X release processing. Further, as described above, the H ₂ S sensor directly detects the H ₂ S concentration by oxidizing H ₂ S in the exhaust gas with oxygen ions generated by ionizing oxygen in the exhaust gas. That is, in order for the H ₂ S sensor to detect the H ₂ S concentration, the exhaust gas must contain sufficient oxygen. However, the oxygen concentration in the exhaust gas flowing out from the NO _X storage agent 23 during the SO _X release processing is relatively low. Therefore, in the above-described two embodiments, a means for supplying air into the exhaust gas is provided downstream of the NO _x storage agent 23 in order to reliably detect the H ₂ S concentration by the H ₂ S sensor during the SO _x release processing. Alternatively, the air may be supplied into the exhaust gas by the means during the SO _X release process.

Next, a third embodiment will be described. FIG. 14 shows an exhaust purification system of a third embodiment of the present invention. The structure of the exhaust gas purification apparatus of the third embodiment is almost the same as the structure of the exhaust gas purification apparatus of the first embodiment, but unlike the first embodiment, instead of the casing 24, the bypass type exhaust gas purification unit 5 is used.
0 is provided.

FIG. 1 is an enlarged view of the bypass type exhaust purification unit 50.
5 shows. As shown in FIG. 15, the bypass type exhaust purification unit 50 is connected to the exhaust pipe 22 and has an upstream side exhaust pipe 50 a.
And a branching portion 50b located on the exhaust pipe 50a substantially upstream.
And a casing 50c containing the NO _x storage agent 23,
The bypass pipe 50d and the downstream exhaust pipe 50e are provided. The upstream side exhaust pipe 50a and the casing 50c are connected to each other, and the casing 50c and the downstream side exhaust pipe 50e.
Are connected to each other, and the upstream exhaust pipe 50a, the casing 50c, and the downstream exhaust pipe 50e extend substantially in a straight line. A bypass pipe 50d branches from the branch portion 50b of the upstream exhaust pipe 50a, and the branched bypass pipe 50d is connected to the downstream exhaust pipe 50e. Air-fuel ratio sensor 53 for detecting an air-fuel ratio of the exhaust gas flowing into the NO _x absorbent 23 in the immediately upstream of the NO _x absorbent 23 is provided on the upstream exhaust pipe 50a, the downstream side of the NO _x absorbent 23 At the end, a temperature sensor 5 for detecting the temperature of the NO _x storage agent 23.
4 are provided. The output signals of these sensors are the corresponding A
It is input to the input port 36 via the D converter 38. Further, a flow rate adjusting valve 51 is provided at the branch portion 50b.

The flow rate adjusting valve 51 can be rotated so as to change the angle with respect to the direction of the exhaust gas flowing through the upstream side exhaust pipe 50a, and is accommodated in the casing 50c according to the angle of the flow rate adjusting valve 51. NO _x storage agent 23
It is possible to adjust the flow rate of exhaust gas flowing into the bypass pipe and the flow rate of exhaust gas flowing into the bypass pipe 50d. In other words, by rotating the flow rate adjusting valve 51, it is possible to adjust the ratio of the exhaust gas that flows into the NO _x storage agent 23 in the exhaust gas that reaches the branch portion 50b via the upstream exhaust pipe 50a. . In particular, the flow rate adjusting valve 51 is shown in FIG.
In the position shown by the solid line, all of the exhaust gas that reaches the branch portion 50b has flowed into the NO _x storage agent 23, and therefore the flow rate of the exhaust gas that reaches the branch portion 50b and N
The flow rates of the exhaust gas flowing into the O _x storage agent 23 are equal. On the other hand, when the flow rate adjusting valve 51 is in the position shown by the chain line in FIG. 15, all of the exhaust gas that reaches the branch portion 50b has flowed into the bypass pipe 50d, and therefore the NO _x storage agent 23.
The exhaust gas flow through the is zero.

Furthermore, the branch portion 50 of the upstream exhaust pipe 50a
A fuel addition device 52 is provided between b and the NO _x storage agent 23. The fuel addition device 52 is provided in the upstream exhaust pipe 50.
NO of the exhaust gas that reaches the branching portion 50b via a
_{x The} fuel can be added only to the exhaust gas flowing into the occlusion agent 23. The addition of fuel from the fuel addition device 52 to the exhaust gas flowing into the NO _x absorbent 23, as well as the exhaust air-fuel ratio of the exhaust gas flowing into the NO _x absorbent 23 can be made substantially stoichiometric or rich since the fuel added from the fuel addition device 52 for combustion in the upstream and _the NO _x storage material 23 of the NO _x absorbent 23 _the NO _x storage agent 2
The temperature of 3 also rises. In particular, if the flow rate of the exhaust gas flowing into the NO _x storage agent is the same, the temperature of the NO _x storage agent 23 can be greatly increased as the amount of fuel added from the fuel addition device 52 increases. Therefore, in the third embodiment, fuel is added to exhaust gas to release the SO _x from _the NO _x storage material 23 flows from the fuel addition device 52 to _the NO _x storage material 23, thereby _the NO _x storage agent The exhaust air-fuel ratio of the exhaust gas flowing into 23 is made approximately the stoichiometric air-fuel ratio or rich, and the temperature of the NO _x storage agent 23 is raised.

At this time, when all the exhaust gas discharged from the internal combustion engine flows into the NO _x storage agent 23, a large amount of fuel is added from the fuel addition device 52 in order to make the exhaust gas substantially stoichiometric air-fuel ratio or rich. There must be. Also, when this large amount of fuel is added as the large amount of fuel to generate heat by burning in the upstream and _the NO _x storage material 23 of the NO _x absorbent 23, thereby a high temperature more than necessary _the NO _x storage material 23 Become. Therefore, as the sulfur component processing means in the present embodiment, the flow control valve 51 so that the flow rate of the exhaust gas flowing into the NO _x absorbent 23 is reduced in the case of releasing the SO _x from _the NO _x storage agent 23 times The amount of fuel added from the fuel addition device 52 is adjusted in accordance with the flow rate of the exhaust gas that is operated and flows into the NO _x storage agent 23. This results in NO _x
While the exhaust gas air-fuel ratio of the exhaust gas flowing into the absorbent 23 is not substantially stoichiometric air-fuel ratio or a high temperature more than necessary temperature of the NO _x absorbent 23 along with becomes richer becomes more release SO _x temperature, _the NO _x storage agent SO _x is released from 23.

By the way, in the above embodiment, the amount of H ₂ S generated is proportional to the amount of SO _x released from the NO _x storage agent 23 per unit time, and it is as if the NO _x storage agent 23 releases SO _x. with H ₂ but S has been described as always occurs, conditions sO _x starts to be released in detail (hereinafter, S
O _x release start condition hereinafter) and H ₂ S starts to Condition (hereinafter, referred to as H ₂ S generation starting condition) is different. That is, while SO _x is released from the NO _x storage agent 23,
₂ S may not occur.

Further, in the above-mentioned embodiment, it is shown in FIG.
H like₂The amount of S generated is NO_xTemperature of the storage agent 23 and discharge
Although it is a function of the air-fuel ratio, for example, NO_xOcclusion
When the flow rate of the exhaust gas flowing through the agent 23 is small, NO
_xH accumulated in the storage agent 23₂Because the amount of S is large,
And NO_xH in the occlusion agent 23₂High S concentration, and as a result,
H₂Since the amount of S generated decreases, H₂S generation amount is N
O_xDepending on the flow rate of exhaust gas flowing through the occlusion agent 23,
I can say. Further, in the above embodiment, the S deposition amount is SO _xrelease
Used only to determine when to start processing
But H₂S generation amount is SO_xChanges momentarily during the release process
Depending on the amount of deposited S, specifically, H₂S generation amount is S
The greater the amount of deposition, the greater. Therefore, H₂S generation open
The starting condition is the above-mentioned four parameters, namely NO_xSucking
Storage agent temperature, exhaust air-fuel ratio, exhaust gas flow rate, S deposition
Determined from quantity.

Therefore, in the SO _x releasing process of this embodiment,
When SO _x is released from the NO _x storage agent 23, by controlling the above-mentioned four parameters to values that do not generate H ₂ S even when SO _x is released, NO is generated without H ₂ S being generated. SO _x is released from the _x storage agent 23. In addition,
The SO _x release start condition is similarly determined from the above four parameters. Particularly, when the parameters other than the temperature of the NO _x storage agent 23 are the same, the NO _x when H ₂ S starts to be generated.
Temperature of storage agent 23 (hereinafter referred to as H ₂ S generation start temperature)
T _catm is higher than the temperature of the NO _x storage agent 23 when SO _x starts to be released (hereinafter, referred to as SO _x release start temperature) T _cats .

In order to control these four parameters to such values, in the third embodiment, the total SO _x storage amount ΣSOX is estimated in a mode different from that of the above embodiment, and specifically, the SO _x release is performed. When the process is not executed, the fuel injection amount TAUO and the correction coefficient KB are the same as in the above embodiment.
(= KB _a · KB _b ) and total SO _x storage amount Σ
Calculating the SOX, release SO _x During processing, thus calculated total SO _x storage amount ShigumaSOX from release SO _x processed by _the NO _x storage agent total SO _x storage amount by subtracting the amount of SO _x released from 23 ShigumaSOX To calculate. Here, the amount of SO _x released from the NO _x storage agent 23 is experimentally obtained in advance for each value of the above four parameters, and is stored in the ROM 34 in advance in the form of a map as a function of these four parameters. In the example of the sign, the exhaust air-fuel ratio A
/ F and storage agent temperature T _cat , in addition to NO _x storage agent 23
The flow rate F of the exhaust gas flowing through is measured. Exhaust air-fuel ratio A
/ F and the storage agent temperature T _cat are the air-fuel ratio sensor 5 respectively.
3 and the temperature sensor 54. The flow rate F of exhaust gas is calculated from the rotation speed of the internal combustion engine. further,
Release SO _x starting temperature T _cats are experimentally obtained in advance as a function of three parameters other than the temperature stored in advance in the ROM34 in the form of a map, also, H ₂ S generation starting temperature T
_catm is experimentally obtained in advance as a function of three parameters other than temperature and is stored in the ROM ₃₄ in advance in the form of a map.

Next, the SO _x releasing process of the third embodiment will be described. In the third embodiment, as in the first embodiment, when the total SO _x storage amount ΣSOX exceeds the determination value SOXlow, the flow rate of the exhaust gas flowing into the NO _x storage agent 23 decreases so as to decrease. the valve 51 is made to rotate, the flow rate to become such a position suitable for the flow rate of the exhaust gas flowing into the NO _x absorbent 23 releases sO _x from _the NO _x storage agent 23 (hereinafter, the release of sO _x position It is positioned). For example, the SO _x release position is a position where the flow rate of the exhaust gas flowing into the NO _x storage agent 23 is about 10% of the flow rate of the exhaust gas discharged from the internal combustion engine. Then, a certain amount of fuel is introduced from the fuel addition device 52 into the exhaust gas so that the exhaust air-fuel ratio of the exhaust gas flowing into the NO _x storage agent 23 becomes substantially stoichiometric or rich and the temperature of the NO _x storage agent 23 rises. Is added.

Thus NO_xThe temperature of the occluding agent 23 gradually increases.
SO getting higher_xReaching the release start temperature, SO_xIs released
Begin to be. SO_xFuel addition device 5
If fuel is continuously added to the exhaust gas from No. 2, NO
_xThe temperature of the occlusion agent 23 gradually rises to H₂S generation start temperature
T_catmWill reach. Therefore, in this embodiment, NO
_xThe temperature of the occlusion agent 23 is H₂S generation start temperature T_catmReached
When SO_xNO than release position_xInflow into storage agent 23
At a position where the flow rate of exhaust gas increases
The flow rate adjusting valve 51 is rotated to a position (referred to as a position).
For example, the occlusion agent cooling position of the flow rate adjustment valve 51 is the branch portion 5
0b exhaust gas flow rate and NO _xFlow to the occlusion agent 23
This is the position where the flow rate of the exhaust gas entering the same. Furthermore
At the same time that the flow rate adjusting valve 51 rotates,
The addition of these fuels is stopped. Usually from an internal combustion engine
Emitted and NO_xExhaust gas temperature reaching the occlusion agent 23
Is NO_xH of storage agent 23₂Lower than the S generation start temperature,
The fuel addition from the fuel addition device 52 is stopped.
Unburned fuel added from the fuel addition device 52 by
No longer burns and the temperature of the exhaust gas rises
No_xThe occlusion agent 23 is cooled.

When the NO _x storage agent 23 is cooled down to the SO _x release start temperature T _cats or less, the flow rate adjusting valve 51 is returned to the SO _x release position again, and the fuel addition device 5 is operated.
From 2 fuel is added to the exhaust gas. As a result, the temperature of the NO _x storage agent 23 starts to rise again. By repeating such control, SO _x can be released from the NO _x storage agent 23 without generating H ₂ S.
Then, the judgment value Σ that the total SO _x storage amount ΣSOX is almost zero
The SO _x releasing process is terminated when the amount becomes less than or equal to SOX min.

Next, referring to FIG. 16, S of the third embodiment
A control routine for executing the _Ox releasing process will be described. Since steps 400 to 404 are the same as steps 100 to 104 shown in FIG. 9, description thereof will be omitted. In step 405, the fuel addition device 52
A fixed amount of fuel is started and the process proceeds to step 406. In step 406, the flow rate adjusting valve 51 is rotated to the SO _x releasing position. Then, step 407
Then, from the estimated or measured total SO _x storage amount ΣSOX, the exhaust air-fuel ratio A / F and the flow rate F, the SO _x release start temperature T _cats and the H ₂ S generation start temperature T _catm are calculated from the map stored in the ROM _34. To be done. At step 408, it is judged if the storage agent temperature T _cat is _{equal to} or higher than the H ₂ S generation start temperature T _catm . If it is determined that the storage agent temperature T _cat is _{equal to} or higher than the H ₂ S generation start temperature T _catm , step 40.
Proceed to 9. In step 409, the flow rate adjusting valve 51 is rotated to the storage agent cooling position and the fuel addition device 5
The fuel addition from 2 is stopped, and the routine proceeds to step 412.

On the other hand, if it is determined in step 408 that the storage agent temperature T _cat is lower than the H ₂ S generation start temperature T _catm , the process proceeds to step 410. At step 410, it is judged if the storage agent temperature T _cat is not _higher than the SO _x release start temperature T _cats . When it is determined in step 410 that the storage agent temperature T _cat is equal to or lower than the SO _x release start temperature T _cats , the process proceeds to step 411. Step 411
Then, the flow rate adjusting valve 51 is rotated to the SO _x releasing position, a fixed amount of fuel is added from the fuel adding device 52, and the routine proceeds to step 412. On the other hand, in step 410, the storage agent temperature T _cat is changed to the SO _x release start temperature T
If it is determined that it is higher than _cats , the process proceeds to step 412. In step 412, it is determined whether the total SO _x storage amount ΣSOX is less than or equal to the determination value ΣSOXmin, and the total SO _x is determined.
When the stored amount ΣSOX is larger than the determination value ΣSOXmin, the process returns to step 407. On the other hand, step 41
2, the total SO _x storage amount ΣSOX is the judgment value ΣSOXmin
In the case of the following, proceed to step 413. In step 413, the SO _x release flag is reset, fuel addition from the fuel addition device 52 is terminated, and the control routine is completed.

Next, the advantages of the third embodiment will be described. Conventionally, in the above-described configuration, when the temperature of the NO _x storage agent is lowered, the amount of fuel added from the fuel addition device is simply reduced. However, the cooling of the _the NO _x storage material to reduce the amount of fuel to be added from the fuel addition device when the flow rate of the exhaust gas flowing into the NO _x absorbent is small, the ambient environment of the NO _x absorbent, i.e. in air I had to wait for it to cool down due to the natural heat dissipation to.
However, the amount of heat radiated to the atmosphere per unit time is not large, and it takes a long time to cool the NO _x storage agent. On the other hand, in the present invention,
Since _the NO _x storage material is an adjustable arrangement the flow rate of the exhaust gas flowing into, NO _x storage agent usually lower the exhaust gas most supplied rapidly _the NO _x storage material than the temperature at which H ₂ S generation conditions The temperature can be lowered.

The flow rate F of the exhaust gas depends on the NO _x storage agent 2
It may be detected by a flow rate sensor (not shown) arranged immediately upstream of 3.

Next, a modification of the third embodiment will be described with reference to FIG. As shown in FIG. 17, in the modification of the third embodiment, the bypass type exhaust purification unit 5 of the third embodiment is used.
0 is changed to the two-branch exhaust purification unit 55. The two-branch exhaust purification unit 55 includes an upstream exhaust pipe 56a connected to the exhaust pipe 22, and a branch 56b from the upstream exhaust pipe 56a.
In, the first exhaust pipe 56c and the second exhaust pipe 56d are branched into two, and the exhaust pipe 56e where the two branched exhaust pipes 56c and 56d join. The NO _x storage agent 23 is incorporated in each of the first exhaust pipe 56c and the second exhaust pipe 56d. A flow rate adjusting valve 57 is provided at the branch portion 56b. The flow rate adjusting valve 57 adjusts the flow rate of the exhaust gas flowing into the first exhaust pipe 56c and the flow rate of the exhaust gas flowing into the second exhaust pipe 56d, like the flow rate adjusting valve 51 of the third embodiment. Further, the fuel addition device 52, the air-fuel ratio sensor 53, and the temperature sensor 54 are arranged for each NO _x storage agent 23.

In the exhaust gas purifying apparatus of the modification of the third embodiment having such a configuration, when the SO _x releasing process of the NO _x storage agent 23 is executed, the bypass passage 50d is used in the third embodiment.
The exhaust gas that has passed through passes through the other NO _x storage agent 23. In the third embodiment, when the exhaust gas passes through the bypass passage 50d, the exhaust gas passing through the bypass passage 50d is not purified, thus polluting the atmosphere. On the other hand, in this modified example, the bypass passage 50
Since _the NO _x storage material 23 is arranged in place of d, it can not be made to flow in one of the NO _x absorbent _the NO _x storage agent 23 running release SO _x treating exhaust gas of all one of the 23 Also, the other NO _x storage agent 23 can purify the exhaust gas.

Next, a fourth embodiment will be described. The configuration of the exhaust purification system of the fourth embodiment of the present invention is almost the same as the configuration of the exhaust purification system of the third embodiment, but the direction switching is performed instead of the bypass type exhaust purification unit 50 of the third embodiment. A mold exhaust gas purification unit 60 is provided.

FIG. 18 shows the direction switching type exhaust purification unit 60. As shown in FIG. 18, the direction switching type exhaust purification unit 60
Is an upstream exhaust pipe 60a connected to the exhaust pipe 22, a branch portion 60b, and a casing 6 containing the NO _x storage agent 23 therein.
0d, a first branch pipe 60c connecting the branch portion 60b and one end of the casing 60d, and a second branch connecting the branch portion 60b and the end of the casing 60d opposite to the one end. A pipe 60e and a downstream exhaust pipe 60f are provided. The NO _x storage agent 23 has a first end portion 23a on the first branch pipe 60c side and a second end portion 23b on the second branch pipe 60e side.
Have. The first branch pipe 60c is provided with a first temperature sensor 62 near the first end 23a of the NO _x storage agent 23, and the second branch pipe 60e is provided at the second end 23b of the NO _x storage agent 23. The second temperature sensor 63 is provided in close proximity. The output signals of these temperature sensors are input to the input port 36 via the corresponding AD converters 38. In addition, the branch unit 60
A switching valve 61 is provided at b.

The switching valve 61 is switched between a first position shown by a solid line in FIG. 18 and a second position shown by a chain line in FIG. When the switching valve 61 is at the first position, the exhaust gas that reaches the branch portion 60b via the upstream exhaust pipe 60a flows into the first branch pipe 60c, and the NO _x storage agent 23 is discharged from the first end portion 23a. It passes in the direction toward the second end portion 23b, and again through the second branch pipe 60e, the branch portion 60b.
And flows out to the downstream side exhaust pipe 60f. The flow direction of the exhaust gas in the NO _x storage agent 23 at this time is referred to as a forward direction. On the other hand, when the switching valve 61 is in the second position, the exhaust gas that reaches the branch portion 60b via the upstream exhaust pipe 60a flows into the second branch pipe 60e, and the NO _x storage agent 23 is discharged to the second end portion. It passes in the direction from 23b toward the first end portion 23a, returns to the branch portion 60b again via the first branch pipe 60c, and flows out to the downstream side exhaust pipe 60f. Therefore, the flow direction of the exhaust gas in the NO _x storage agent 23 at this time is opposite to the above-mentioned forward direction.

By the way, NO_xSO of storage agent 23_xRelease process
NO when performing_xExhaust gas flowing into the occlusion agent 23
If the air-fuel ratio of is almost stoichiometric or rich, N
O_xThe temperature distribution in the occlusion agent 23 is not uniform,
NO_xThere is a temperature difference in the direction in which the exhaust gas passes through the occlusion agent 23.
it can. Generally, SO_xExhaust when performing release processing
The gas air-fuel ratio is almost stoichiometric or rich.
Therefore, NO_xIn the exhaust gas flowing into the storage agent 23,
Burned fuel is included, and this unburned fuel is NO_xOn the occlusion agent 23
To burn. Therefore, SO_xWhen performing a release process, an example
For example, when the switching valve 61 is in the first position, NO_xStorage agent 23
If exhaust gas is flowing in the forward direction, NO_xStorage agent 23
As shown in FIG. 19 (a), the first end 23a
The temperature gradually increases toward the end 23b. Word
In other words, NO_xIn the occluding agent 23, from the exhaust upstream side to the downstream side
The temperature gradually increases toward the side. That is,
NO on the most exhaust downstream side_xThe second end, which is the part of the occlusion agent 23
Part 23b has the highest temperature, and H₂S generation start temperature
To reach. On the other hand, NO on the most exhaust downstream side_xStorage agent 23
The temperature of the second end 23b, which is the part of₂S generation start temperature
Even if it reaches_xThe upstream temperature of the occlusion agent 23 is
Is relatively low, and in some cases NO on the most upstream side of exhaust gas _xOcclusion
The temperature of the first end portion 23a, which is the portion of the agent 23, is SO_xrelease
It may be lower than the starting temperature.

Therefore, in the fourth embodiment of the present invention, SO
_{During the x} emission process, for example, when the switching valve 61 is at the first position, the temperature of the second end portion 23b, which is the portion of the NO _x storage agent 23 on the exhaust downstream side, reaches the H ₂ S generation start temperature T _catm . In this case, that is, when the temperature measured by the second temperature sensor 63 reaches the H ₂ S generation start temperature T _catm , the switching valve 61 is switched to the second position. This reverses the direction of the exhaust gas flowing through the NO _x storage agent 23,
NO _x that was on the upstream side of the exhaust until the switching valve 61 was switched
The first end 23a of the storage agent 23 is on the exhaust downstream side, and the second end 23b of the NO _x storage agent 23, which was on the exhaust downstream side until the switching valve 61 was switched, is on the exhaust upstream side. Therefore, the temperature of the second end portion 23b of the NO _x storage agent 23, which is at a high temperature on the exhaust downstream side until the switching valve 61 is switched, decreases, and conversely, the exhaust gas is on the exhaust upstream side until the switching valve 61 is switched. The temperature of the first end portion 23a of the NO _x storage agent 23, which has a low temperature in the agent 23, rises, as shown in FIG.
As shown in (b), the temperature of the NO _x storage agent 23 temporarily becomes almost uniform. Of course, if the switching valve 61 is maintained at the second position as it is during the sulfur component release processing, the first end portion 23, which is the portion of the NO _x storage agent 23 on the exhaust gas downstream side, will eventually be provided.
The temperature of a reaches the H ₂ S generation start temperature T _catm , and the temperature measured by the first temperature sensor 62 becomes the H ₂ S generation start temperature T _catm . In this case, the switching valve 61 is switched to the first position again. In the fourth embodiment, the switching valve 61 is switched during the SO _x release processing as described above, whereby the sulfur component can be released from the entire NO _x storage agent 23 without generating H ₂ S.

A control routine for executing the SO _x releasing process of the fourth embodiment will be described with reference to FIG. Steps 500 to 504 are the same as steps 100 to 104 shown in FIG. 9, so description thereof will be omitted. In step 505, temperature raising / rich control for raising the exhaust gas by various methods shown in the first embodiment and for making the exhaust air-fuel ratio of the exhaust gas flowing into the NO _x storage agent 23 rich is started. Be punished. Next, in step 506, as in step 407 of FIG. 16, the H ₂ S generation start temperature T _catm is stored in the ROM ₃₄ from the estimated or measured total SO _x storage amount ΣSOX, exhaust air-fuel ratio A / F and flow rate F. It is calculated from the created map. In step 507, the two storage agent temperatures T _cat1 and T _cat2 respectively detected by the first temperature sensor 62 and the second temperature sensor 63 are the H ₂ S generation start temperature T _catm.
It is determined whether it is lower. When it is determined that the storage agent temperatures T _cat1 and T _cat2 are lower than the H ₂ S generation start temperature T _catm , the process proceeds to step 509.

On the other hand, if it is determined in step 507 that the storage agent temperature T _cat1 or T _cat2 is _{equal to} or higher than the H ₂ S generation start temperature T _catm , the process proceeds to step 508. In step 508, the switching valve 61 is switched between the first position and the second position, and the process proceeds to step 509. At step 509, the total SO _x storage amount ΣSOX is the determination value ΣSO.
It is determined whether or not it is less than or equal to Xmin, and the total SO _x storage amount ΣS
If OX is larger than the determination value ΣSOXmin, the process returns to step 506. On the other hand, when the total SO _x storage amount ΣSOX is equal to or smaller than the determination value ΣSOXmin in step 509, the process proceeds to step 510. In step 510, the SO _x release flag is reset, the temperature raising / rich control is ended, and the control routine is completed.

In the fourth embodiment, the switching valve 61 is not a valve that can be switched between two positions, and the angle can be continuously adjusted with respect to the flow direction of the exhaust gas flowing from the upstream exhaust pipe 55a, for example. It may be any valve. In this case, N
It is possible to change not only the direction of the exhaust gas passing through the O _x storage agent 23 but also the flow rate.

Further, the NO _x storage agent 23 of the present invention may be a particulate filter having a NO _x storage function capable of collecting fine particles in exhaust gas. In this case, by oxidizing the particulates trapped by the particulate filter by the active oxygen produced when releasing the occluded NO _x and when the particulate filter occludes NO _x, to purify the exhaust gas You can

Further, in this specification, the term "storage" relating to NO _x and sulfur components means "absorption" and "adsorption".
Including both meanings of. Therefore, "NO _x storage agent"
Contains both "NO _x absorbent" and "NO _x adsorbent". The former retains NO _x by accumulating NO _x in the form of nitrate, etc., and the latter adsorbs in the form of NO ₂ etc. The NO _x is retained by causing the above. Further, the term “release” from the NO _x retention agent includes “release” corresponding to “absorption” and “desorption” corresponding to “adsorption”.

[0107]

According to the first to fifteenth aspects of the present invention, the operation of the hydrogen sulfide amount control means is controlled based on the amount of hydrogen sulfide detected by the hydrogen sulfide amount detection means. The amount of hydrogen sulfide generated per unit time when releasing is reliably maintained below a certain amount.

According to the fifteenth aspect of the invention, since the amount of hydrogen sulfide generated is made zero while the sulfur component is released from the exhaust purification catalyst, the exhaust gas is released even when the sulfur component is released from the exhaust purification catalyst. It prevents the odor of gas from becoming too strong.

[Brief description of drawings]

FIG. 1 is an overall view of an internal combustion engine of a first embodiment.

FIG. 2 is a diagram showing a structure of an H ₂ S sensor.

FIG. 3 is a diagram showing a basic fuel injection amount, a correction coefficient, and the like.

4 is a diagram for explaining the NO _X absorbing and releasing action of the NO _X absorbent.

FIG. 5 is a time chart for explaining SO _X release processing of the first embodiment.

FIG. 6 is a diagram showing a relationship between a temperature of a NO _x storage agent, a rich degree of exhaust gas, and an H ₂ S generation amount.

FIG. 7 is a diagram showing a relationship between a rich degree of exhaust gas, an H ₂ S generation amount, and a temperature of a NO _x storage agent.

FIG. 8 is a diagram showing a map of correction coefficients.

FIG. 9 is a flowchart for performing SO _X release processing of the first embodiment.

FIG. 10 is an overall view of an internal combustion engine of a second embodiment.

FIG. 11 is a time chart for explaining the SO _X releasing process of the second embodiment.

FIG. 12 is a flow chart for performing SO _X release processing of the second embodiment.

FIG. 13 is a flowchart for setting a target temperature.

FIG. 14 is an overall view of an internal combustion engine of a third embodiment.

FIG. 15 is an enlarged view of an exhaust gas purification unit of a third embodiment.

FIG. 16 is a flow chart for performing SO _x release processing of the third embodiment.

FIG. 17 is an enlarged view of an exhaust gas purification unit of a modification of the third embodiment.

FIG. 18 is an enlarged view of an exhaust gas purification unit of a fourth embodiment.

FIG. 19 is a diagram showing a temperature distribution of a NO _x storage agent.

FIG. 20 is a flow chart for performing SO _x release processing of the fourth embodiment.

[Explanation of symbols]

11 ... Fuel injection valve 23 ... NO _X storage agent 28 ... Air-fuel ratio sensor 29 ... H ₂ S sensor 31 ... Electronic control unit

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 7/08 F01N 7/08 B F02D 41/04 305 F02D 41/04 305Z 45/00 360 45/00 360C 360Z (72 ) Inventor Toshiaki Tanaka 1 Toyota-cho, Toyota-shi, Aichi F-term in Toyota Motor Corporation (reference) 3G004 AA01 BA06 DA24 EA01 EA06 3G084 AA04 BA05 BA11 BA16 BA20 BA24 DA10 EA07 EB12 EC03 FA10 FA26 FA27 FA28 FA33 FA38 3G091 AA02 AA02 A AA12 AA17 AB06 AB11 BA11 BA14 CA18 CB01 CB05 DA02 DB11 DB13 DC03 EA01 EA07 EA18 EA33 EA34 FB07 FB12 FC08 GA06 GB02W GB03W GB04W GB06W HA10 HA36 HA39 HA42 HB03 HB05 3G301 HA01 HA04 HA06 HA13 HA16 JA25 LA03 LB04 LC01 MA01 MA11 NA09 NC02 ND02 NE06 PD01A PD02A PD12A PE03Z PF03Z

Claims (15)

[Claims] 1. An exhaust purification catalyst for purifying components in exhaust gas, and a sulfur component in exhaust gas stored in the exhaust purification catalyst, when the stored sulfur component should be released from the exhaust purification catalyst. Sulfur component release processing means for performing a sulfur component release process for making the temperature of the exhaust purification catalyst equal to or higher than a predetermined temperature and for making the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst substantially stoichiometric air-fuel ratio or rich; In an exhaust gas purification apparatus for an internal combustion engine, comprising: a hydrogen sulfide amount control means for maintaining the amount of hydrogen sulfide generated from a sulfur component released from an exhaust gas purification catalyst during a component release process A hydrogen sulfide amount detecting means for detecting the amount of hydrogen sulfide flowing out from the catalyst or the amount of hydrogen sulfide expected to flow out from the exhaust purification catalyst is provided, and the hydrogen sulfide amount is detected. An exhaust gas purification apparatus for an internal combustion engine, wherein the operation of the hydrogen sulfide amount control means is controlled based on the output of the means. 2. The exhaust gas purification device for an internal combustion engine according to claim 1, wherein the hydrogen sulfide amount detection means directly detects the actual amount of hydrogen sulfide flowing out from the exhaust gas purification catalyst by a hydrogen sulfide sensor. 3. The hydrogen sulfide amount control means controls the temperature of the exhaust purification catalyst to maintain the amount of hydrogen sulfide flowing out from the exhaust purification catalyst at a certain amount or less during the sulfur component release process. An exhaust emission control device for an internal combustion engine as set forth in. 4. The hydrogen sulfide amount control means controls the characteristics of the exhaust gas flowing into the exhaust purification catalyst to maintain the amount of hydrogen sulfide flowing out from the exhaust purification catalyst during a sulfur component release process to be below a certain amount. An exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3. 5. The hydrogen sulfide amount detecting means is adapted to operate the hydrogen sulfide amount controlling means when detecting a certain amount or more of hydrogen sulfide during the sulfur component releasing process. An exhaust purification device for an internal combustion engine according to one. 6. The hydrogen sulfide amount control means controls the temperature of the exhaust purification catalyst, which can maintain the amount of hydrogen sulfide flowing out from the exhaust purification catalyst to a certain amount or less during the sulfur component release process, by the hydrogen sulfide amount detection means. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the temperature is set as a target temperature based on the output, and the temperature of the exhaust gas purification catalyst is controlled so that the temperature of the exhaust gas purification catalyst becomes the target temperature. . 7. The exhaust gas purification apparatus for an internal combustion engine according to claim 6, wherein the hydrogen sulfide amount control means lowers the target temperature when the hydrogen sulfide amount detection means detects a certain amount or more of hydrogen sulfide. 8. The hydrogen sulfide amount control means is at least the hottest part of the exhaust purification catalyst when the amount of hydrogen sulfide detected by the hydrogen sulfide amount detection means during the sulfur component release processing is a certain amount or more. The exhaust gas purification device for an internal combustion engine according to claim 1, wherein the amount of hydrogen sulfide flowing out from the exhaust gas purification catalyst is maintained below a certain amount by lowering the temperature of. 9. The exhaust gas purification means controls the hydrogen sulfide amount by changing at least one of a flow rate of the exhaust gas flowing into the exhaust gas purification catalyst and a passage direction when the exhaust gas passes through the exhaust gas purification catalyst. The exhaust gas purification device for an internal combustion engine according to claim 8, wherein the temperature of at least the hottest portion of the catalyst is lowered. 10. A bypass passage for bypassing the exhaust purification catalyst, a flow rate adjusting valve for adjusting a flow rate of the exhaust gas flowing into the exhaust purification catalyst and a flow rate of the exhaust gas flowing into the bypass passage, and an exhaust gas. The sulfur component release processing means further comprises a reducing agent addition device for adding fuel to the exhaust gas flowing into the purification catalyst, wherein the flow rate of the exhaust gas flowing into the exhaust purification catalyst is the exhaust gas discharged from the internal combustion engine. The flow rate adjusting valve is adjusted so that the flow rate is set to be lower than the flow rate of gas, and fuel is added to the exhaust gas flowing into the exhaust purification catalyst, and the hydrogen sulfide amount control means is detected by the hydrogen sulfide amount detecting means. When the amount of hydrogen sulfide exceeds the above-mentioned fixed amount, the flow rate of the exhaust gas flowing into the exhaust purification catalyst should be higher than the flow rate set by the sulfur component release processing means. The exhaust gas purification device for an internal combustion engine according to claim 8 or 9, wherein the flow rate adjustment valve is adjusted to lower the temperature of the exhaust gas purification catalyst. 11. The exhaust gas purification device for an internal combustion engine according to claim 10, further comprising an exhaust gas purification device disposed on the bypass passage for purifying the components in the exhaust gas. 12. The passage direction of exhaust gas passing through an exhaust purification catalyst can be switched between a forward direction and a reverse direction opposite to the forward direction, and the hydrogen sulfide amount control means can control the exhaust gas. When the amount of hydrogen sulfide detected by the hydrogen sulfide amount detecting means is equal to or more than the above-mentioned certain amount when the gas is flowing in one of the forward direction and the reverse direction, the passage of exhaust gas 10. The temperature of at least the hottest part of the exhaust purification catalyst is lowered by making the direction different from the one of the forward direction and the reverse direction. Exhaust gas purification device for internal combustion engine. 13. The hydrogen sulfide amount detecting means detects at least one of the parameters relating to the operation of the internal combustion engine and the parameters relating to the characteristics of the exhaust gas other than the actual amount of hydrogen sulfide flowing out from the exhaust purification catalyst. 13. The internal combustion engine according to any one of claims 8 to 12, further comprising: a parameter detecting means for estimating the amount of hydrogen sulfide expected to flow out from the exhaust purification catalyst from the value of the parameter detected by the parameter detecting means. Exhaust gas purification device for engines. 14. The exhaust gas purifying apparatus for an internal combustion engine according to claim 13, wherein the parameter detecting means includes at least an exhaust gas temperature sensor for detecting the temperature of the exhaust gas in the vicinity of the exhaust gas purifying catalyst. 15. The method according to claim 8, wherein the constant amount is zero.
2. An exhaust gas purification device for an internal combustion engine according to any one of 1.