JP2001304020A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the stable regeneration of a catalyst device, by low suppressing concentration of H2S generated according to emission of SOx from a catalyst to prevent an offensive odor of exhaust gas while suppressing long extending of a regenerating time of the catalyst, in an exhaust emission control device for an internal combustion engine. SOLUTION: In the case of emitting a sulfuric component from a storage type NOx catalyst 25 by enriching exhaust air/fuel ratio in a high temperature condition, a degree of enriching or a speed of change is controlled in accordance with a frequency (S regenerating frequency) placed in a condition that the storage type NOx catalyst 25 emits the sulfuric component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine having a catalyst having a characteristic of storing sulfur components in exhaust gas in an exhaust passage and releasing the stored sulfur components when the exhaust air-fuel ratio is rich at a high temperature. An exhaust purification device.

[0002]

2. Description of the Related Art In recent years, a lean-burn internal combustion engine has been put to practical use in which the internal combustion engine is operated at a lean air-fuel ratio to improve fuel efficiency. This lean-burn internal combustion engine has a problem that, when operated at a lean air-fuel ratio, the three-way catalyst cannot sufficiently purify NOx (nitrogen oxide) in exhaust gas due to its purification characteristics. A storage type NO that stores NOx in exhaust gas and releases and reduces NOx stored during operation at stoichiometric or rich air-fuel ratio
x catalysts have been employed.

This storage type NOx catalyst converts NOx in exhaust gas into nitrate (X-N
O ₃ ) and the stored NOx is converted to carbon monoxide (C
And released in a state of excess O) nitrogen (N ₂₎ characteristics to be reduced to (simultaneously carbonate X-CO ₃ is a catalyst having a is generated). However, the fuel contains a sulfur (S) component, and this S component reacts with oxygen to form a sulfur oxide (SOx), and this SOx becomes a sulfate instead of NOx and is a storage type instead of nitrate. There is a problem that the catalyst is occluded by the NOx catalyst and the purification efficiency of the catalyst is reduced. However, the SOx occluded in the catalyst can be changed by setting the air-fuel ratio to a rich state and bringing the catalyst to a high temperature state.
It is known that it is released (S purge) as SO ₂ . For example, it is disclosed in Japanese Patent Application Laid-Open No. 7-217474.

[0004]

By the way, when SO ₂ is released, for example, in a reducing atmosphere where the exhaust gas is at a high temperature and a large amount of carbon monoxide and hydrocarbons are present, for example, the following chemical reaction formulas are used. , Hydrogen sulfide (H ₂ S) is generated. SO ₂ + 3H ₂ → H ₂ S + 2H ₂ O SO ₂ + 2CO + H ₂ → H ₂ S + CO ₂ 3SO ₂ + C ₃ H ₆ → 3H ₂ S + 3CO ₂ As is generally known, H ₂ S emits a strong odor and is not generated as much as possible. It is desirable to do so.

However, the technique disclosed in the above publication is
In the technology, the stored SOx is converted to SO2 _TwoInstantly large amount
Is released into the SO._TwoWhen
H around the catalyst_TwoChemical reaction with CO, HC, etc.
To go, H_TwoS was generated in large quantities rapidly
Will be able to. Thus H_TwoS is rapidly generated in large quantities
Then, H_TwoS concentration will increase locally,
The exhaust gas discharged into the air favors an extremely strong odor.
Not a new thing.

[0006] Note that disclosed in Japanese Patent Laid-Open No. 11-107809 "engine control system", with respect to the reproduction control of the NOx catalyst, for H ₂ S is generated when a high exhaust gas temperature, exhaust air A technique for reducing the degree of enrichment of the fuel ratio to about the stoichiometric level is disclosed. However,
As described above, SOx occluded in the catalyst is efficiently released by setting the air-fuel ratio to a rich state and setting the catalyst to a high temperature state. In this case, there is a problem that the regeneration time of the catalyst becomes extremely long even if the large amount of H ₂ S can be suppressed. Further, the generation characteristics of H ₂ S from the catalyst vary depending on the state of the catalyst other than the temperature. However, this publication does not consider such points at all, and there is ample room for improvement.

As a result of the present inventors' research on such a point, the generation of H ₂ S at the time of release of the sulfur component from the catalyst is correlated with the frequency at which the catalyst is in a state of releasing the sulfur component. It was found that there was. Accordingly, the present invention solves the above-described problem by controlling the degree or rate of change of the exhaust air-fuel ratio in accordance with the frequency at which the sulfur component can be released, so that SOx from the catalyst can be reduced. An internal combustion engine capable of reducing the concentration of H ₂ S generated upon release to prevent an odor of exhaust gas and suppressing a prolonged regeneration time of a catalyst to enable stable regeneration of a catalyst device. It is an object of the present invention to provide an exhaust gas purification device.

[0008]

According to the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine which achieves the above-mentioned object by storing a sulfur component in exhaust gas in an exhaust passage of the internal combustion engine, and having a high temperature and an exhaust air-fuel ratio. A catalyst having a characteristic of releasing the sulfur component stored when rich is provided, frequency calculating means calculates the frequency at which the sulfur component stored in the catalyst is released, and regeneration control means controls the catalyst. The exhaust air-fuel ratio is enriched in a high temperature state in which the sulfur component stored in the exhaust gas can be released to release the sulfur component, and the degree or rate of change of the exhaust air-fuel ratio is controlled in accordance with the frequency calculated by the frequency calculation means. Like that.

[0009] The frequency at which the catalyst releases the sulfur component is correlated with the characteristics of H ₂ S generation from the catalyst, and the degree or rate of change in the exhaust air-fuel ratio is controlled in accordance with this frequency. By doing so, a large amount of H ₂ S is prevented from being generated from the catalyst at one time, the emission concentration is suppressed, and the unpleasant odor of the exhaust gas is prevented. Regeneration of the catalyst device becomes possible.

[0010] In this case, the regeneration control means releases the sulfur component by enriching the exhaust air-fuel ratio at a high temperature when the release frequency of the sulfur component calculated by the frequency calculation means is lower than a predetermined frequency. This is preferable in terms of suppressing deterioration of fuel efficiency and stably regenerating the catalyst.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic configuration of an exhaust gas purifying apparatus for an internal combustion engine according to an embodiment of the present invention, FIG. 2 is a flowchart of S purge control by the exhaust gas purifying apparatus of the present embodiment, and FIG.
FIG. 4 is a time chart of the purge control, and FIG.
x is a graph showing the relationship with the amount of emissions, FIG. 5 is a graph showing the set temperature increase with respect to the S regeneration frequency, FIG. 6 is a graph showing a reflection coefficient for the estimated catalyst temperature, and FIG. FIG. 8 is a time chart showing a time change of the H ₂ S generation amount with respect to a time change of FIG. 8. FIG. FIG. 9 is a time chart showing the time change of the H ₂ S generation amount with respect to the time change of the target A / F in the S purge control, and FIG. 10 is a diagram showing the catalyst when the present embodiment is used and not used in ordinary driving. 3 shows a graph representing the time frequency of temperature.

The internal combustion engine (hereinafter referred to as an engine) of the present embodiment is, for example, in a fuel injection mode (operation mode).
The fuel injection in-cylinder ignition type in-line four-cylinder gasoline engine is capable of performing fuel injection during the intake stroke (intake stroke injection mode) or fuel injection during the compression stroke (compression stroke injection mode). The in-cylinder injection type engine 11 can be easily operated at a stoichiometric air-fuel ratio (stoichiometric), at a rich air-fuel ratio (rich air-fuel ratio operation), or at a lean air-fuel ratio (lean air-fuel ratio). Operation) can be realized, and in particular, in the compression stroke injection mode, operation at an ultra lean air-fuel ratio is possible.

In the present embodiment, as shown in FIG.
An electromagnetic fuel injection valve 14 is attached to a cylinder head 12 of the engine 11 together with an ignition plug 13 for each cylinder, and the fuel injection valve 14 enables direct injection of fuel into a combustion chamber 15. . This fuel injection valve 14
Is connected to a fuel supply device (fuel pump) having a fuel tank via a fuel pipe (not shown). The fuel in the fuel tank is supplied at a high fuel pressure, and the fuel is supplied from a fuel injection valve 14 to a combustion chamber. The fuel is injected at a desired fuel pressure into the fuel cell 15. At this time, the fuel injection amount is determined from the fuel discharge pressure of the fuel pump and the valve opening time (fuel injection time) of the fuel injection valve 14.

An intake port is formed in the cylinder head 12 in a substantially upright direction for each cylinder, and one end of an intake manifold 16 is connected to communicate with each intake port. A drive-by-wire (DBW) type electric throttle valve 17 is connected to the other end of the intake manifold 16.
Has a throttle sensor 1 for detecting the throttle opening θth.
8 are provided. Also, the cylinder head 12 has
An exhaust port is formed in a substantially horizontal direction for each cylinder,
Exhaust manifold 1 so that it communicates with each exhaust port
9 are connected to each other.

The engine 11 is provided with a crank angle sensor 20 for detecting a crank angle, and the crank angle sensor 20 can detect an engine rotation speed Ne. The above-described in-cylinder injection engine 1
1 is already known, and the details of its configuration will not be described here.

The exhaust manifold 1 of the engine 11
An exhaust pipe (exhaust passage) 21 is connected to 9, and a muffler (not shown) is connected to the exhaust pipe 21 via a small three-way catalyst 22 and an exhaust purification catalyst device 23 close to the engine 11. . In the portion of the exhaust pipe 21 between the three-way catalyst 22 and the exhaust purification catalyst device 23, the exhaust pipe 21 is located immediately upstream of the exhaust purification catalyst device 23, that is, immediately upstream of the storage NOx catalyst 25 described later. A high temperature sensor 24 for detecting the exhaust gas temperature is provided.

The exhaust gas purifying catalyst device 23 has a storage type NO.
x catalyst 25 and three-way catalyst 26, and the three-way catalyst 26 is a storage-type NOx catalyst 25.
It is arranged further downstream than. When the storage NOx catalyst 25 has a sufficient function of a three-way catalyst,
The storage NOx catalyst 25 alone may be used. The storage type NOx catalyst 25 has a function of temporarily storing NOx in an oxidizing atmosphere and releasing NOx mainly in a reducing atmosphere where CO is present to reduce it to N ₂ (nitrogen). Specifically, the storage type NOx catalyst 25
Is configured as a catalyst having platinum (Pt), rhodium (Rh) or the like as a noble metal, and an alkali metal such as barium (Ba) or an alkaline earth metal as a storage agent. Further, a NOx sensor 27 for detecting the NOx concentration is provided downstream of the exhaust purification catalyst device 23.

Furthermore, an input / output device and a storage device (ROM, R
AM, nonvolatile RAM, etc.), central processing unit (CPU),
An ECU (Electronic Control Unit) 28 having a timer counter and the like is provided, and the ECU 28 controls the exhaust gas purifying apparatus of the present embodiment including the engine 11 comprehensively. That is, on the input side of the ECU 28,
Various sensors such as the high temperature sensor 24 and the NOx sensor 27 described above are connected, and detection information from these sensors is input. On the other hand, on the output side of the ECU 28, the above-described ignition plug 13 and fuel injection valve 14 are connected via an ignition coil.
The ignition coil, the fuel injection valve 1 and the like are connected.
4 and the like, the optimum values such as the fuel injection amount and the ignition timing calculated based on the detection information from the various sensors are output. As a result, an appropriate amount of fuel is injected from the fuel injection valve 14 at an appropriate timing, and ignition is performed by the spark plug 13 at an appropriate timing.

Actually, the ECU 28 determines the target in-cylinder pressure corresponding to the engine load, that is, the target average effective pressure, based on the accelerator opening information from the accelerator opening sensor (not shown) and the engine speed information Ne from the crank angle sensor 20. The pressure Pe is obtained, and the fuel injection mode is set from a map (not shown) according to the target average effective pressure Pe and the engine rotation speed information Ne. For example, when both the target average effective pressure Pe and the engine rotation speed Ne are small, the fuel injection mode is set to the compression stroke injection mode, and fuel is injected in the compression stroke.
On the other hand, when the target average effective pressure Pe increases or the engine speed Ne increases, the fuel injection mode is set to the intake stroke injection mode, and fuel is injected in the intake stroke.

The target air-fuel ratio (target A / A) is a control target based on the target average effective pressure Pe and the engine speed Ne.
F) is set, and the appropriate amount of fuel injection is set to the target A / F
Is determined based on Further, from the exhaust gas temperature information detected by the high temperature sensor 24, the catalyst temperature Tcat is estimated. Specifically, the high-temperature sensor 24 and the storage NOx catalyst 25
In order to correct an error caused by being arranged at least a little apart from each other, a temperature difference map is set in advance by an experiment or the like in accordance with the target average effective pressure Pe and the engine rotation speed information Ne. The catalyst temperature Tcat is uniquely estimated when the target average effective pressure Pe and the engine speed information Ne are determined.

Hereinafter, the operation of the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment configured as described above will be described.

In the storage type NOx catalyst 25 of the exhaust purification catalyst device 23, nitrate is generated from NOx in the exhaust gas in an atmosphere having an excessive oxygen concentration such as in the super-lean combustion operation in the lean mode, whereby NOx is stored. Exhaust gas purification is performed. On the other hand, in the three-way catalyst 26, the nitrate stored in the storage NOx catalyst 25 reacts with CO in the exhaust gas in an atmosphere having a reduced oxygen concentration to generate carbonate and release NOx. Therefore, the storage type NOx catalyst 25
As the NOx occlusion proceeds, the oxygen concentration is reduced by enriching the air-fuel ratio or performing additional fuel injection to reduce
O is supplied into the exhaust gas, and NOx is stored in the NOx storage catalyst 25.
To maintain its function.

Incidentally, sulfur components (SOx) contained in fuel and lubricating oil are also present in exhaust gas, and the storage type NOx catalyst 25 stores SOx as well as NOx in an oxygen-rich atmosphere. That is, the sulfur component is oxidized to S
Ox, and a part of this SOx is stored in the NOx storage catalyst 25.
Further, it reacts with an occluding agent originally used for occluding NOx, becomes a sulfate, and is stored in the storage type NOx catalyst 25 instead of NOx.

The storage type NOx catalyst 25 has a tendency to release the stored SOx when the oxygen concentration decreases. That is, in an atmosphere in which the oxygen concentration is reduced and the CO becomes excessive, a part of the sulfate stored in the storage NOx catalyst 25 and CO in the exhaust react with each other to easily generate a carbonate and reduce the SOx. It is easily detached. However, sulfate has a higher stability as a salt than nitrate, and only a part of the sulfate is decomposed in an atmosphere having a reduced oxygen concentration. Therefore, the amount of sulfate remaining in the storage NOx catalyst 25 increases with time. To increase. As a result, the storage capacity of the storage NOx catalyst 25 decreases with time, and the performance of the storage NOx catalyst 25 deteriorates (S poisoning).

In order to regenerate the NOx storage capacity, the amount of SOx stored in the storage type NOx catalyst 25 is estimated to estimate the state of S poisoning. When S poisoning progresses to a certain extent or more, the temperature of the catalyst is raised. In addition, there is a method of releasing SOx by enriching the air-fuel ratio. However, in the present embodiment, when the catalyst temperature Tcat becomes equal to or higher than a catalyst temperature setting temperature correlated with the S regeneration frequency, the regeneration control means Raises the temperature of the catalyst and enriches the air-fuel ratio to release the stored SOx, thereby restoring the NOx storage capacity.

This regeneration control means includes a storage NOx catalyst 2
5 so that the degree of regeneration for releasing SOx is maintained in a predetermined range. That is, the temperature of the storage NOx catalyst 25 is higher than the activation temperature (for example, 250 to 350 ° C.), and the temperature (for example, 650 to 800 ° C.) suitable for desorbing the stored SOx or lower. When the temperature becomes equal to or higher than the set temperature (for example, 600 ° C.),
The temperature of the storage NOx catalyst 25 is raised and the air-fuel ratio is made rich to release SOx. In other words, when the original catalyst temperature is high to some extent, the S regeneration speed is made to reach the catalyst temperature range quickly by operating the temperature raising means slightly in an assist manner, and the SOx is efficiently increased at a low temperature rise (a small fuel consumption deterioration degree). Is to be released.

Further, with respect to SOx occluded in the occlusion-type NOx catalyst 25, when releasing SOx by the air-fuel ratio causes the temperature of the the occlusion-type NOx catalyst 25 rich, SOx is released as SO ₂ Therefore, in a reducing atmosphere in which the exhaust gas is at a high temperature and a large amount of hydrogen, carbon monoxide, hydrocarbons and the like are present, hydrogen sulfide (H ₂ S) is generated and emits an odor. Then, as the degree of richness increases, the amount of reducing agent such as hydrogen increases, and H ₂ S is rapidly and largely generated from SO ₂ . For this reason, in the present embodiment, the regeneration control means controls the degree of enrichment or the rate of change of the exhaust air-fuel ratio in accordance with the S regeneration frequency.

Here, the S purge control will be described in detail with reference to the flowchart shown in FIG. 2 and the time chart shown in FIG. As shown in FIG. 2, first, in step S1, the catalyst temperature Tcat of the storage NOx catalyst 25 is estimated from the exhaust gas temperature information detected by the high temperature sensor 24. In this case, as described above, the target average effective pressure Pe
An error between the high-temperature sensor 24 and the actual catalyst temperature is corrected based on a temperature difference map set according to the engine speed information Ne.

Next, in step S2, the S regeneration frequency indicating the degree of regeneration (S regeneration) from the S poisoning of the storage NOx catalyst 25 is calculated (frequency calculation means). The calculation method will be described below. I do. This S reproduction frequency is calculated based on the following equation (1). S regeneration frequency (s / km) = S-regeneration time converted to 700 ° C./travel distance (1) Here, the S-regeneration time converted to 700 ° C. is the storage-type NOx catalyst at the estimated catalyst temperature Tcat. 25
Is the total time converted into the S regeneration time when the catalyst temperature Tcat is 700 ° C., and by dividing the 700 ° C. converted S regeneration time by the traveling distance, the S regeneration time per 1 km of the traveling distance, that is, S The regeneration frequency can be obtained. When the S regeneration frequency increases, SOx is released (purge) well.
That is, it is well reproduced from S poisoning.

As a specific method of calculating the 700 ° C. converted S regeneration time, it is calculated based on the following equation (2). 700 ° C conversion S regeneration time _(n) = 700 ° C conversion S regeneration time _(n-1) + S regeneration speed coefficient × calculation cycle × A / F coefficient (2) Here, the S regeneration speed coefficient is the storage type NOx. This is for correcting that the S regeneration speed varies depending on the temperature of the catalyst 25, and is for converting the S regeneration time at each catalyst temperature into an S regeneration time equivalent to 700 ° C. Since the S regeneration rate increases exponentially as the temperature of the storage NOx catalyst 25 increases, the catalyst temperature Tcat of the storage NOx catalyst 25 increases.
Is 0 when the temperature is low at 580 ° C. or lower, and is calculated using the following equation (3) approximated by an exponential function when the temperature is higher than 580 ° C. S regeneration speed coefficient = exp {-kk × (1 / T ₁ ) − (1 / T ₀ )} (3) where kk is set according to the S regeneration reaction of the storage NOx catalyst 25. The predetermined coefficient, T _1, is the catalyst temperature Tcat (K) of the storage NOx catalyst 25, and T ₀ is 973 (70
0 + 273) (K). In the present embodiment, E
In the CU 28, a calculation based on an exponential function is not performed, but a value calculated in advance is obtained from a stored S regeneration speed coefficient map for the catalyst temperature. The above-mentioned A / F coefficient indicates the degree of S regeneration by the A / F, and is set to 0 when the air-fuel ratio is in the lean mode or fuel cut, and is set to 1 in other modes. In addition, it is often classified finely, and A
/ F coefficient is 1/4 when the air-fuel ratio is in the lean mode or fuel cut, and 2/3 in the stoichiometric F / B mode.
In the rich (O / L) mode, it may be set to 1.

The S reproduction frequency is a predetermined value D (for example,
It is reset at 1.5 s / km or more, the S regeneration time at 700 ° C. is set to 0 s, and the traveling distance is set to 0 km. That is, if the S regeneration frequency is equal to or greater than the predetermined value D, the regeneration is stopped because the storage NOx catalyst 25 has been sufficiently purged. The method of setting the threshold value D when resetting the S reproduction frequency may be as follows. That is, as shown in FIG.
It is known that the higher the S regeneration frequency, the lower the NOx emission value.
What is necessary is just to set the reproduction frequency. Although the threshold value D is affected by the catalyst characteristics and the NOx emission regulation value, it is generally known that the threshold value D may be set to approximately 1.5 s / km or more.

When the S regeneration frequency is obtained in this manner, in step S3, a set temperature rise temperature ZSTEMP (° C.) is calculated. In this case, as shown in FIG. 5, a map of ZSTEMP with respect to the S reproduction frequency is set in advance. According to this map, when the S reproduction frequency is low, ZSTE
MP is set to 600 ° C., and ZSTEMP increases with an increase in the frequency of S regeneration, and is set to 800 ° C. at a predetermined value D. That is, the set heating temperature ZSTEMP is changed based on the S regeneration frequency.

Then, in step S4, the storage type N
It is determined whether or not the catalyst temperature Tcat of the Ox catalyst 25 is equal to or higher than ZSTEMP. If the catalyst temperature Tcat is equal to or higher than ZSTEMP, the S regeneration frequency is low to some extent and the temperature of the storage NOx catalyst 25 is raised to some extent. Since it is estimated that the purging is easy, the process proceeds to step S5, and the control mode is switched to the S purge mode. Thus, the removal of SOx stored in the storage NOx catalyst 25 (S purge control) is started.

That is, in step S6, the ignition timing is controlled, that is, retarded (retarded), so that the storage NO
The temperature of the x catalyst 25 is raised. That is, by sufficiently raising the temperature of the exhaust gas flowing into the storage type NOx catalyst 25 by the ignition timing retard, the storage type NOx catalyst 25 quickly rises to a temperature (for example, 650 ° C. to 800 ° C.) suitable for the S purge control. Will be warmed. In this case, the ignition timing is set to retard according to the following equation (4). Ignition timing = base ignition timing−ZSSA × reflection coefficient (4) Here, ZSSA is set based on a retard map set according to the target average effective pressure Pe and the engine rotation speed information Ne. Yes, it is set as an amount that takes into account the amount of allowance for the retard amount that becomes the combustion limit. Further, as shown in FIG. 6, the reflection coefficient is set based on a catalyst temperature estimated value, that is, a map corresponding to the catalyst temperature Tcat. The reflection coefficient is set to 0 when the fuel is cut or when the throttle opening is equal to or more than a predetermined value.

Subsequently, in step S7, control is performed so that the air-fuel ratio becomes a predetermined rich A / F. In this case, a process of gradually changing the target A / F toward a predetermined rich A / F is performed, and the speed of change of the target A / F is low in accordance with the degree of S reproduction (S reproduction frequency). The setting is made such that the richer the speed becomes, the lower the speed becomes.

SO released by S purge control
₂ reacts in a reducing atmosphere to form H
₂ S is generated. If the target air-fuel ratio at the time of S regeneration is gradually enriched in accordance with the degree of S regeneration (S regeneration frequency), the amount of SO ₂ released increases at a stretch and H ₂ is generated. At the start of the S purge control in which a large amount of S is likely to be generated, the supply amounts of CO and HC can be limited, and SO ₂
H ₂ S generation concentration can be suppressed low by suppressing the amount of H ₂ S released.

That is, FIG. 7 shows the results of the execution of steps S1 to S4, the time change (a) of the target A / F and the H ₂ S when the S purge control is executed after step S5.
Is shown as a time chart. In this case, the target air-fuel ratio AF ₁ (for example, the value of the target air-fuel ratio AF ₁ ) is set immediately (or, even if the target air-fuel ratio is gradually changed, about several cycles) immediately after the start of the S purge control. shows the case of a 12) with a broken line, the target a / F according to the S regeneration frequency as in the present embodiment initially a small value of enrichment degree in the vicinity of stoichiometric, gradually to a predetermined rich air-fuel ratio AF ₁ The case of shifting toward is shown by a solid line. As can be seen from this time chart, in the conventional control (broken line), a large amount of H ₂ S was generated temporarily immediately after the start of the S purge control, but in the control of the present embodiment (solid line), the S purge phenomenon of large amounts of H ₂ S immediately after the start of the control is not, this state it is possible to hold the exhaust gas odor in suppressing the concentration of H ₂ S as well as reduce the occurrence concentration of H ₂ S immediately after the start of the S purge Can be reliably prevented from being released.

In particular, by gradually shifting the target A / F toward a predetermined rich air-fuel ratio AF ₁ , H ₂ S
Generation concentration was kept low while the value can promote efficient release of SO _2, it is possible to reach quickly the target A / F to a predetermined rich air-fuel ratio AF _1. As a result, it is possible to prevent the S purge control from being prolonged as much as possible and to suppress the H ₂ S concentration to a low level while suitably preventing the deterioration of fuel efficiency.

Returning to FIG. 2, in step S8,
When the state where the catalyst temperature Tcat is lower than the predetermined value K (for example, 650 ° C.) has passed for a predetermined time C (for example, 45 seconds), in step S9, the temperature rise of the storage NOx catalyst 25 is stopped and the air-fuel ratio is reduced. Lean and exit this routine. That is, even in the S purge mode, the catalyst temperature Tca
t is the optimal temperature for desorbing sulfur components (eg, 650 ° C.)
In the case where it is difficult to approach the above, the S-purge mode is stopped in order to suppress deterioration of fuel efficiency.
On the other hand, if the catalyst temperature Tcat becomes equal to or higher than the predetermined value K before the predetermined time C elapses, the temperature rise of the storage NOx catalyst 25 and the enrichment of the air-fuel ratio are continued.

As described above, in the S purge mode, the S purge control routine is repeated.
When the SOx occluded in the NOx 5 is released, the frequency of S regeneration of the occluded NOx catalyst 25 increases, and ZSTEMP also increases based on the map of FIG. Then, when ZSTEMP exceeds the catalyst temperature Tcat, in step S4, the catalyst temperature Tcat of the storage NOx catalyst 25 becomes lower than ZSTEMP, the process exits the control routine, proceeds to step S9, and the S purge control is stopped.

As described above, since the three-way catalyst 26 has the function of storing oxygen inside, the three-way catalyst
x H ₂ S generated in the catalyst 25 is the three-way catalyst 2
6 is oxidized well by the oxygen inside. This also reliably prevents the exhaust gas from emitting an odor.

By the way, in the embodiment described above, during the S purge control, but the target A / F was set to be gradually migrated toward a predetermined rich air-fuel ratio AF ₁ according to the S regeneration frequency, limited to It is not something that can be done. That is, as another embodiment, for example, in the above step S7,
When the S purge control is started, the target A / F of the S purge control is first determined as a fixed value from the map shown in FIG. 8 (the graph on the right side in FIG. 8).
The purge control time t _s may be set uniquely (graph on the left side in FIG. 8).

[0044] That is, as shown by the solid line in FIG. 9, richer than the rich air-fuel ratio AF ₁ given the lower S regeneration frequency according to the S regeneration frequency a target A / F when the S purge control is started The target A / F is set to a small value
The S purge control may be performed over the S purge control time t _s while maintaining a constant.

In this case, as shown by the solid line in FIG. 9, although the release time of SO ₂ becomes longer, H ₂ S has conventionally been generated in a large amount temporarily immediately after the start of the S purge control. And the generation concentration of H ₂ S (broken line) can be made sufficiently low, and the H ₂ S concentration can be kept low to reliably prevent the exhaust gas from emitting an odor.

[0046] In the embodiment described above, but were smooth transition continuously toward the target A / F to a predetermined rich air-fuel ratio AF ₁ according to the S regeneration frequency during S purge control, is divided into a plurality it may be transferred to the rich air-fuel ratio AF ₁ stepwise (step-like). Further, both the degree of enrichment and the speed of change may be controlled in accordance with the S reproduction frequency. Further, the method of enriching the air-fuel ratio is not limited to the method of changing the target A / F. For example, in stoichiometric feedback control using an O ₂ sensor, the integral gain (coefficient) for feedback control is set to the rich side. It is also possible to use a method of changing the value to a larger value on the lean side. In this case, by setting the speed of the integral gain or the proportional gain in accordance with the S regeneration frequency, the average air-fuel ratio can be gradually enriched in accordance with the S regeneration frequency, or the gain value itself can be changed to the S value.
By setting the average air-fuel ratio in accordance with the regeneration frequency, the average air-fuel ratio may be controlled to be a rich air-fuel ratio in accordance with the S regeneration frequency.

Here, the switching control to the S purge mode described above will be specifically described with reference to the time chart of FIG. As shown in FIG. 3, when the S purge mode is OFF,
When the regeneration frequency is low, the set heating temperature ZSTEMP is 60
It is set to 0 ° C. And the driving state of the driver,
For example, when accelerating or traveling on a highway or mountain road, the catalyst temperature Tcat rises, and this catalyst temperature Tcat
When STEMP is exceeded, the S purge mode is turned on (Yes in step S4). Then, the ignition timing is retarded to raise the temperature of the storage NOx catalyst 25 and to enrich the air-fuel ratio, so that the SOx stored in the storage NOx catalyst 25 is reduced.
x is released. When the S purge mode is continued, the S regeneration proceeds, the S regeneration time at 700 ° C. increases, the S regeneration frequency increases, and when the S regeneration frequency increases,
Based on the map of FIG. 4, ZSTEMP increases and exceeds the catalyst temperature Tcat.

Then, the S purge mode is turned off (No in step S4), and the temperature of the storage NOx catalyst 25 is stopped, so that the catalyst temperature Tcat decreases. Thereafter, when the traveling distance increases with the catalyst temperature Tcat being low, the S regeneration frequency decreases and ZSTEMP decreases to 600
Return to ° C.

Also, the catalyst temperature Tcat rises again due to the driving state of the driver, and when the catalyst temperature Tcat exceeds ZSTEMP, the S purge mode is turned on (Ye in step S4).
s). At this time, if the driver is in a driving state of repeating acceleration and deceleration in a place such as an urban area, the storage type N
The Ox catalyst 25 is unlikely to reach a high temperature state required for releasing SOx. That is, in this case, the catalyst temperature Tcat is initially Z
Although the temperature exceeds STEMP (600 ° C.), the temperature is lower than 650 ° C., and S regeneration is performed in this temperature range, but the S regeneration efficiency is low. Therefore, when the continuation time of this state has elapsed the set time C, the S purge mode is turned off (No in step S4), thereby stopping the ignition timing retard and enrichment, and reducing the fuel consumption in a temperature range where the S regeneration efficiency is low. Deterioration can be suppressed.

In the S purge mode, the air-fuel ratio is set to the rich air-fuel ratio mode and the transition to the lean air-fuel ratio mode is prohibited. However, when the storage NOx catalyst 25 is at a high temperature, the storage NOx catalyst 25 In some cases, the lean air-fuel ratio mode is already prohibited to prevent thermal degradation.

Further, when performing the S purge, the throttle valve 17 is operated according to the ignition timing retard to adjust the throttle opening θth with respect to the base throttle opening, thereby operating the intake air amount. The control is performed such that the torque decrease due to the ignition timing retard is compensated and the torque is substantially constant. In this case, the throttle opening is set by the following equation (5). Throttle opening = base throttle opening−ZSETV × reflection coefficient (5) Here, ZSETV is based on a throttle opening correction map set according to the target average effective pressure Pe and the engine rotation speed information Ne. The reflection coefficient is set based on the map shown in FIG. 6, as described above. In this case, the throttle opening θth with respect to the corrected ignition timing (the ignition timing after the retard).
May be set according to the map.

As described above, in this embodiment, the storage type NOx
Control is performed so that the degree of regeneration for releasing SOx from the catalyst 25 is kept within a predetermined range, that is, the catalyst temperature Tcat of the storage type NOx catalyst 25 becomes the activation temperature (for example, 250 to 350 ° C.).
When the temperature becomes higher (e.g., 650 ° C. to 800 ° C.) suitable for desorbing the stored SOx or higher than the set temperature ZSTEMP set lower than that, the ignition timing is retarded. NOx storage catalyst 2
5 and the air-fuel ratio is enriched to release SOx.

Then, the storage type NOx catalyst 25 is subjected to S purge control or NOx purge control (when the temperature of the catalyst is high and the sulfur component is released when enriched for NOx purge), natural S purge (operation) When the catalyst becomes rich due to the high temperature umbrella due to natural operation such as acceleration of the person and the sulfur component is released), the frequency at which the sulfur component is released in the case of)) or the like is determined by the storage type NOx catalyst 25 as H _2. It has been found that there is a correlation with the characteristic in which S is generated, and the degree or rate of change of the exhaust air-fuel ratio is controlled in accordance with the frequency at which the sulfur component is released (S regeneration frequency). . That is, in the example of FIG. 7, so that the target A / F initially is set to a small value of enrichment degree in the vicinity of stoichiometric according to the S regeneration frequency, is gradually shifts toward a predetermined rich air-fuel ratio AF ₁ In the example of FIG. 8, the degree of enrichment with a low S reproduction frequency is reduced. In these cases, the catalyst regeneration time slightly increases as the S regeneration frequency decreases, but does not significantly increase.

Therefore, when the storage type NOx catalyst 25 is at a high temperature to some extent, the temperature of the storage type NOx catalyst 25 is assisted to release SOx in a catalyst temperature range suitable for SOx release to regenerate. . Therefore, the storage type NO
When it takes a long time to raise the temperature of the x catalyst 25 to the optimum temperature for releasing SOx in a low temperature state, the S regeneration is not forcibly performed. As a result, it is not necessary to perform a long-time enrichment and retardation of the ignition timing, and a large retardation for greatly increasing the temperature from a low temperature, and it is possible to suppress the deterioration of fuel efficiency.

[0055] and, at the time of the S-regeneration, rather than occurrence phenomenon of large amounts of H ₂ S immediately after the change of the target A / F, H ₂ at this time
It is possible to keep the concentration of S generated low and keep H ₂ S at a low concentration, and to keep the H ₂ S concentration low to reliably prevent the exhaust gas from emitting an odor.
It is possible to suppress the prolonged regeneration time of the x catalyst 25 and to perform stable regeneration of the catalyst.

FIG. 10 shows the time of the catalyst bed temperature of the storage-type NOx catalyst 25 when the S regeneration control by the assisted temperature increase according to the present embodiment is used during normal driving and when it is not used. 2 shows a comparison of frequencies. By using this control, the time frequency of 650 ° C. or higher, which is suitable for S reproduction, is increased greatly, and the time frequency of 700 ° C., which is higher in S reproduction speed, is also increased. You can see that it has been played.

If the catalyst temperature Tcat does not approach the optimum temperature (for example, 650 ° C. or more) for sulfur component desorption in the S purge mode, the S purge mode is stopped after the set time C has elapsed. I have. Therefore, for example, when the vehicle is in an operating state in which acceleration and deceleration are repeated in a place such as an urban area, the storage type NOx catalyst 25 is unlikely to be in a high temperature state that is optimal for releasing SOx. In this manner, the S purge mode is stopped, and thereby, in a temperature range where the S regeneration efficiency is not good, the deterioration of fuel efficiency can be suppressed by providing a limit to the enrichment and the continuation of the temperature increase.

In the present embodiment, the temperature of the storage NOx catalyst 25 is set to an activation temperature of 250 ° C. to 350 ° C., and a temperature suitable for desorbing the stored SOx is set to 650 ° C. to 800 ° C. (more preferably). Is set to 700 ° C. or higher), and the temperature setting temperature ZSTEMP is changed from the temperature of 600 ° C. according to the S regeneration frequency, but each temperature is appropriately set according to the characteristics of the storage NOx catalyst 25, the engine configuration, the exhaust temperature, and the like. It is good to do.

Also, the present invention is characterized in that the regeneration control means controls the degree of enrichment or the rate of change of the exhaust air-fuel ratio based on the estimated frequency during S regeneration. The S regeneration frequency may not be used as a condition for starting the S purge control. For example, SO stored in the storage NOx catalyst 25 in order to regenerate the NOx storage capacity.
The S purge control may be started on condition that the x amount (S poisoning amount) is equal to or more than a predetermined amount. Further, the temperature rise of the catalyst of the present invention is not limited to the above-described embodiment. For example, two-stage injection for performing additional fuel injection during the expansion stroke or the exhaust pipe 21 upstream of the NOx storage catalyst 25 may be provided. The fuel may be directly injected, or a heating means such as an electric heating catalyst may be used. Also,
The above-described two-stage injection or exhaust pipe 2 can be used as the enrichment means.
A direct fuel injection into 1 may be used. Further, depending on the operating state, when the temperature of the catalyst is already high, it may not be necessary to operate the temperature raising means again.

As a method of obtaining the catalyst temperature, in addition to the method of obtaining the catalyst temperature from the high temperature sensor 24 as in the above-described embodiment, a map of the target average effective pressure Pe (engine load) and the engine rotation speed Ne is set in advance. The catalyst temperature to EC
It may be obtained from the value stored in U28. Further, the catalyst temperature may be obtained from a value stored in the ECU 28 experimentally in advance as a map for vehicle speed in a simplified manner.
In this case, although the accuracy is slightly lowered, there is an advantage that the cost is reduced because the high temperature sensor 24 is not required.

Further, in the above embodiment, the engine 11
Is an in-cylinder injection type gasoline engine, but the present invention is not limited to this, and may be an intake pipe injection type gasoline engine. In the above-described embodiment, the three-way catalyst 22 is provided to improve exhaust gas purification efficiency. However, the three-way catalyst 22 is not necessarily
Need not be provided, and the present invention can be suitably realized without the three-way catalyst 20. Although the storage type NOx catalyst 25 has been described as a catalyst for storing and releasing sulfur components in the above-described embodiment, other types of catalysts may be used, and an adsorption piece for directly reducing the adsorbed NOx may be used. It may be a NOx catalyst or a three-way catalyst of a type that easily absorbs sulfur components. Further, the present invention can be applied to a diesel engine.

[0062]

As described in detail in the above embodiment, according to the exhaust gas purifying apparatus for an internal combustion engine of the present invention, the exhaust air is purged according to the frequency at which the sulfur component stored in the catalyst is released. Since the degree of fuel enrichment or the rate of change is controlled, H ₂ S is prevented from being generated in large quantities from the catalyst at a time, and the emission concentration is suppressed to a low level. It is possible to suppress the prolonged regeneration time of the catalyst and to enable stable regeneration of the catalyst device.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an exhaust gas purification device for an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a flowchart of S purge control by the exhaust gas purification device of the present embodiment.

FIG. 3 is a time chart of S purge control.

FIG. 4 is a graph showing a relationship between S regeneration frequency and NOx emission amount.

FIG. 5 is a graph showing a temperature rise set temperature with respect to an S regeneration frequency.

FIG. 6 is a graph showing a reflection coefficient with respect to a catalyst temperature estimated value.

FIG. 7 is a time chart showing a time change of an H ₂ S generation amount with respect to a time change of a target A / F in the S purge control.

FIG. 8 is a setting map of a target A / F, an S purge time, and a NOx purge time according to the S regeneration frequency according to another embodiment of the present invention.

FIG. 9 is a time chart showing a time change of the H ₂ S generation amount with respect to a time change of the target A / F in the NOx purge control during the S purge control.

FIG. 10 is a graph showing the time frequency of the catalyst temperature when the present embodiment is used and when it is not used in ordinary driving.

[Explanation of symbols]

Reference Signs List 11 engine (internal combustion engine) 21 exhaust pipe (exhaust passage) 22 three-way catalyst 23 exhaust purification catalyst device (catalyst) 24 high temperature sensor 25 storage type NOx catalyst 26 three-way catalyst 27 NOx sensor 28 electronic control unit, ECU (frequency calculation,
Means reproduction control means)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/04 305 B01D 53/36 101B (72) Inventor Takashi Dogahara 5-33 Shiba 5-chome, Minato-ku, Tokyo No. 8 Mitsubishi Motors Corporation F term (reference) 3G091 AA12 AA17 AA24 AB03 AB06 BA00 BA11 BA14 CA16 CB01 CB02 CB05 CB06 CB07 CB08 CB09 DA07 DB11 DB13 DB15 EA00 EA01 EA03 EA07 EA10 EA17 GB03 FB03 GB02 HA09 HA10 HA12 HA37 3G301 HA01 HA04 HA06 HA15 JA21 JA25 MA01 MA03 MA11 NA03 NA04 NA06 NA08 NA09 NC01 NC04 ND02 ND05 ND07 NE13 NE21 PA11Z PB03A PB03Z PD01Z PD11A PD11Z PE01Z PE03Z 4D048 AA06 AA02 DA03 AB03 DA03 DA01 DA03 DA20 EA04

Claims (1)

[Claims] 1. A catalyst provided in an exhaust passage of an internal combustion engine for storing sulfur components in exhaust gas and releasing the stored sulfur components when the temperature of the exhaust gas is high and the exhaust air-fuel ratio is rich. Frequency calculating means for calculating the frequency at which the sulfur component stored in the catalyst is released, and the exhaust air-fuel ratio is enriched in a high temperature state in which the sulfur component stored in the catalyst can be released to release the sulfur component. And an exhaust gas purification device for an internal combustion engine, comprising: regeneration control means for controlling the degree or rate of change of the exhaust air-fuel ratio in accordance with the frequency calculated by the frequency calculation means.