JP2000153132A - Exhaust gas purifying apparatus of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To certainly suppress the discharge of H2S to the atmosphere within a wide operation region without bringing about an increase in cost. SOLUTION: A second catalyst (ternary catalyst) having oxygen storage function is provided on the downstream side of a first catalyst (occlusion type NOx catalyst) occluding a sulfur component (S-component) in exhaust gas in a first operation state (lean air/fuel ratio operation) wherein an exhaust gas air/fuel ratio becomes a lean air/fuel ratio and discharging the occluded sulfur component in a second operation state (S purge mode) wherein temp. is high and an exhaust gas air/fuel ratio becomes a rich air/fuel ratio), and an operation state altering means (S16-S22, S26-S32) executing the first operation (lean air/fuel ratio operation) intermittently at the time of the second operation state (S purge mode) is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to an exhaust purifying apparatus for an internal combustion engine, particularly, hydrogen sulfide sulfur component in the exhaust gas is occluded in the catalyst is produced by desorption (H ₂
The present invention relates to a technique for preventing the release of S) into the atmosphere.

[0002]

2. Description of the Related Art Generally, a fuel contains an S (sulfur) component (sulfur component), and this S component reacts with oxygen to form SOx (sulfur oxide). catalytic converter as X-SO ₄ are inserted in the (three-way catalyst, hereinafter referred to as catalyst a NOx catalyst or the like) (S poisoning). SOx thus occluded in the catalyst is:
As disclosed in JP-A-7-217474 and the like,
It is known that when the temperature of the catalyst reaches a predetermined high temperature and the exhaust air-fuel ratio is set to a rich air-fuel ratio state (a reducing atmosphere in which the oxygen concentration is reduced), the catalyst is reduced to sulfur dioxide (SO ₂ ) and released (S purge). I have.

[0003] By the way, the amount of stored SOx is large and
If the degree of enrichment of the rich air-fuel ratio is large, the released S
O_TwoPart of and H_TwoReacts with reducing substances such as hydrogen sulfide
(H _TwoS) is generated and SO_TwoWith the H_TwoS is also in the atmosphere
Is discharged. However, as is well known,
H_TwoS has a characteristic of emitting an unpleasant odor._TwoExpulsion of S
It was an issue to reduce the outflow.

Therefore, for example, Japanese Patent Application Laid-Open No. 8-294618.
As disclosed in Japanese Patent Application Laid-Open Publication No. H10-209, a downstream catalyst containing an H ₂ S trapping agent is disposed downstream of an upstream catalyst provided in an exhaust passage, and an S component (sulfur component) storage amount of the upstream catalyst is provided. Reaches a set value, the air-fuel ratio is alternately changed (air-fuel ratio perturbation) between a rich region and a lean region based on the stoichiometric air-fuel ratio based on the output of the O ₂ sensor under a predetermined condition. The S component is desorbed from the catalyst to form H ₂ S
A technique has been proposed in which H ₂ S is reduced to H ₂ S by a downstream catalyst, and the captured H ₂ S is oxidized in a lean region to suppress the release of H ₂ S into the atmosphere.

[0005]

However, in the technique disclosed in the above publication, desorption of the S component and oxidation of H ₂ S by air-fuel ratio perturbation based on the stoichiometric air-fuel ratio based on the output of the O ₂ sensor are performed. Therefore, the release of H ₂ S can be suppressed only in a specific operation range.

That is, according to the technology disclosed in the above publication,
For example, in an engine operating state in which the catalyst temperature is equal to or higher than a predetermined temperature and the exhaust air-fuel ratio is a rich air-fuel ratio, S component is desorbed from the catalyst and H ₂ S is generated. The air-fuel ratio perturbation based on the stoichiometric air-fuel ratio cannot be performed, that is, H ₂ S cannot be oxidized, and the generated H ₂ S continues to be captured by the downstream catalyst.

[0007] Therefore, H _{2 that is} higher than the capture capacity of the downstream catalyst is required.
When S is generated, the overflowed H ₂ S is released into the atmosphere, and the released H ₂ S also emits an unpleasant odor, which is not preferable. Also, in the case of this technology, H
Must use a special catalyst trapping agent is contained in order to capture ₂ S, there is a problem that leads to high cost.

The present invention has been made in order to solve such problems, and an object of the present invention is to reliably release H ₂ S into the atmosphere over a wide operating range without incurring high costs. It is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine capable of suppressing the occurrence of exhaust gas.

[0009]

In order to achieve the above-mentioned object, according to the first aspect of the present invention, sulfur components in the exhaust gas are stored in the first operating state in which the exhaust air-fuel ratio becomes a lean air-fuel ratio, and the high-temperature and high-temperature operation is performed. A second catalyst having an oxygen storage function is provided downstream of the first catalyst that releases the occluded sulfur component in the second operation state in which the exhaust air-fuel ratio becomes a rich air-fuel ratio. Operating state changing means for intermittently performing the first operation in the state is provided.

For example, in the second operation state, H ₂ S may be generated at the same time when the stored sulfur component is released. At this time, the first operation is performed intermittently. The exhaust air-fuel ratio is set to a lean air-fuel ratio, and surplus oxygen is supplied to a second catalyst provided downstream and stored as appropriate, and H ₂ S is oxidized satisfactorily by the stored oxygen. This reliably prevents the exhaust gas from emitting an off-flavor.

[0011] Preferably, the second operation is performed when the sulfur component stored in the first catalyst reaches a predetermined amount, and the first operation is intermittently performed by the operation state changing means in accordance with this. It is better to make it. In this case, SOx but will be released all at once has been heavily H ₂ S is produced, the second catalyst for oxygen is always stored intermittently replenished, thus H ₂ S is Even when a large amount of H ₂ S is generated, H ₂ S is reliably oxidized and deodorized by the oxygen.

[0012] Preferably, the operating state changing means includes:
The first operation is preferably performed periodically in the second operation state, whereby oxygen continues to be stored in the second catalyst without shortage, and H ₂ S is more reliably oxidized and deodorized. You.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, a first embodiment will be described. Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust gas purification device for an internal combustion engine according to the present invention mounted on a vehicle,
Hereinafter, the configuration of the exhaust gas purification apparatus according to the present invention will be described with reference to FIG.

Engine body (hereinafter simply referred to as engine) 1
For example, in-cylinder injection spark ignition capable of performing fuel injection in an intake stroke (intake stroke injection mode) or fuel injection in a compression stroke (compression stroke injection mode) by switching a fuel injection mode (operation mode), for example. It is an inline 4-cylinder gasoline engine. The in-cylinder injection type engine 1 can be easily operated at a stoichiometric air-fuel ratio (stoichiometric ratio), at a rich air-fuel ratio (rich air-fuel ratio operation), or at a lean air-fuel ratio (lean air-fuel ratio). In particular, in the compression stroke injection mode, it is possible to operate at a super lean air-fuel ratio.

As shown in FIG. 1, the cylinder head 2 of the engine 1 is provided with an electromagnetic fuel injection valve 6 together with a spark plug 4 for each cylinder, whereby fuel is injected into the combustion chamber 8. Direct injection is possible. A fuel supply device (both not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe. More specifically, the fuel supply device is provided with a low-pressure fuel pump and a high-pressure fuel pump, whereby the fuel in the fuel tank is supplied to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. From the fuel injection valve 6 into the combustion chamber at a desired fuel pressure. At this time, the fuel injection amount depends on the fuel discharge pressure of the high-pressure fuel pump and the valve opening time of the fuel injection valve 6,
That is, it is determined from the fuel injection time.

An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected to communicate with each intake port. A throttle valve 11 is connected to the other end of the intake manifold 10. The throttle valve 11 is provided with a throttle sensor 11a for detecting a throttle opening θth.

An exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of an exhaust manifold 12 is connected to communicate with each exhaust port. Reference numeral 13 in the figure denotes a crank angle sensor for detecting a crank angle, and the crank angle sensor 13 is capable of detecting an engine rotation speed Ne.

The in-cylinder injection type engine 1 is already known, and the detailed description of its configuration is omitted here. As shown in FIG. 1, an exhaust pipe (exhaust passage) 14 is connected to the exhaust manifold 12, and a small close three-way catalyst 20 and an exhaust purification catalyst device 30 close to the engine 1 are connected to the exhaust pipe 14. A muffler (not shown) is connected via the terminal. The exhaust pipe 14 is provided with a high temperature sensor 16 for detecting the exhaust gas temperature.

The exhaust purification catalyst device 30 includes a storage type NOx catalyst (first catalyst) 30a and a three-way catalyst (second catalyst) 30a.
b, and the three-way catalyst 3
Ob is disposed downstream of the storage NOx catalyst 30a. Occlusion-type NOx catalyst 30a is temporarily occluded as nitrate X-NO ₃ and NOx in an oxidizing atmosphere, N ₂ and NOx in a reducing atmosphere mainly the presence of CO is
(Nitrogen) or the like. More specifically, the storage NOx catalyst 30a uses platinum (P
t), a catalyst having rhodium (Rh) or the like, and an alkali metal such as barium (Ba) or an alkaline earth metal such as barium (Ba) is employed as a storage material.

The storage type NOx catalyst 30a has
Not NOx only, oxides of S (sulfur) component in the fuel contained in the exhaust gas (sulfur component), i.e. SOx also occluded as the sulphate X-SO ₄ as described above. The sulfate X-SO ₄ has a higher stability as a salt than the nitrate X-NO ₃ , and in order to reduce and remove the same, as described above, the storage NOx catalyst 30a is set to a predetermined high temperature and the reducing atmosphere is reduced. It is necessary to

The three-way catalyst 30b is a commonly used three-way catalyst, and has a function of storing oxygen inside as a general characteristic. Ceria (Ce) is preferably added to the three-way catalyst 30b as an additive, so that the oxygen storage capacity is higher. In addition, storage type N
A NOx sensor 32 for detecting a NOx concentration is provided between the Ox catalyst 30a and the three-way catalyst 30b.

Further, an input / output device, a storage device (ROM,
RAM, nonvolatile RAM, etc.), central processing unit (CP
U), an ECU (electronic control unit) 40 including a timer counter and the like is installed.
As a result, comprehensive control of the exhaust gas purification device for the internal combustion engine according to the present invention including the engine 1 is performed. Various sensors such as the above-described throttle sensor 11a, crank angle sensor 13, and high temperature sensor 16 are connected to the input side of the ECU 40, and detection information from these sensors is input.

On the other hand, on the output side of the ECU 40, the above-described ignition plug 4, the fuel injection valve 6, etc. are connected via an ignition coil. The optimum values such as the fuel injection amount and the ignition timing calculated based on the detection information are output.
As a result, an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, and ignition is performed by the spark plug 4 at an appropriate timing.

The ECU 40 determines the target in-cylinder pressure corresponding to the engine load, that is, the target average effective pressure Pe, based on the throttle opening information θth from the throttle sensor 11a and the engine rotation speed information Ne from the crank angle sensor 13. Further, 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 the target average effective pressure Pe and the engine rotation speed Ne are both low, the fuel injection mode is the compression stroke injection mode, and the fuel is injected in the compression stroke, while the target average effective pressure Pe increases or the engine rotation speed increases. When the speed Ne increases, the fuel injection mode is set to the intake stroke injection mode, and fuel is injected during the intake stroke.
The intake stroke injection modes include an intake lean mode that is a lean air-fuel ratio, a stoichiometric feedback mode that is a stoichiometric air-fuel ratio, and an open loop mode that is a rich air-fuel ratio.

From the target average effective pressure Pe and the engine speed Ne, a target air-fuel ratio (target A / A
F) is set, and the appropriate amount of fuel injection is set to the target A /
It is determined based on F. The catalyst temperature Tcat is estimated from the exhaust gas temperature information detected by the high temperature sensor 16. Specifically, the high temperature sensor 16 is connected to the storage NOx catalyst 30.
A temperature difference map (not shown) 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 in order to correct an error that occurs due to the inability to directly install the apparatus in the area a. Therefore, the catalyst temperature Tcat is uniquely estimated when the target average effective pressure Pe and the engine speed information Ne are determined.

The operation of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention will now be described. That is, as described above, the NOx storage catalyst 30a mainly supplies the SOx during the lean air-fuel ratio operation (first operation state).
x is also stored (the air-fuel ratio region where SOx is stored differs depending on the catalyst characteristics), and H ₂ S is generated when the SOx is removed, that is, at the time of S purge.
A control procedure of the purge control will be described, and a method of deodorizing H ₂ S according to the present invention will be described.

Referring to FIG. 2, there is shown a flowchart of the S purge control routine, which will be described below with reference to the flowchart. First, in step S10, N
Whether or not the Ox catalyst has deteriorated by S (sulfur), that is, the amount of SOx occluded by the occlusion type NOx catalyst 30a (poisoning S amount Q
It is determined whether or not s) has reached a predetermined amount. Here, the poisoning S amount Qs is a value obtained by estimation. Hereinafter, an estimation method (detection method) of the poisoning S amount Qs will be briefly described.

The poisoning S amount Qs is basically set based on the fuel injection integrated amount Qf, and is calculated by the following equation for each execution cycle of a fuel injection control routine (not shown). Qs = Qs (n−1) + ΔQf · K−Rs (1) where Qs (n−1) is the previous value of the poisoning S amount, ΔQf is the fuel injection integrated amount per execution cycle, and K is Correction coefficient, Rs
Indicates the amount of released S per execution cycle.

That is, the current poisoning S amount Qs is integrated by correcting the integrated fuel injection amount ΔQf per execution cycle with the correction coefficient K, and subtracting the released S amount Rs per execution cycle from the integrated value. It is required by that. The correction coefficient K is
For example, as shown in the following equation (2), the S poisoning coefficient K1 according to the air-fuel ratio A / F, the S poisoning coefficient K2 according to the S content in the fuel, and the S poisoning according to the catalyst temperature Tcat. It consists of the product of the three correction coefficients K3.

K = K 1 · K 2 · K 3 (2) The released S amount Rs per execution cycle is calculated from the following equation (3). Rs = α · R1 · R2 · dT (3) where α is the release rate (set value) per unit time, dT indicates the execution cycle of the fuel injection control routine, and R1 and R2 are respectively The emission capacity coefficient according to the catalyst temperature Tcat and the emission capacity coefficient according to the air-fuel ratio A / F are shown.

If the result of the determination in step S10 is false (No), and it is determined that the poisoning S amount Qs obtained as described above has not yet reached the predetermined amount, no action is taken. Through. On the other hand, when the determination result of step S10 is true (Yes) and it is determined that the poisoning S amount Qs has reached the predetermined amount, the process proceeds to step S12, and the control mode is switched to the S purge mode. This removes the SOx stored in the storage NOx catalyst 30a, that is, removes SOx.
Purge is started (second operating state).

When the S purge is started, step S14
In, it is determined whether or not the target average effective pressure Pe is smaller than a predetermined value Pe1 (a map for the engine rotation speed Ne). Specifically, based on the main injection mode selection map shown in FIG. 3, it is determined whether or not the target average effective pressure Pe is within the range of the area A in relation to the engine rotation speed Ne.

The result of the determination in step S14 is true (Yes).
If the target average effective pressure Pe is smaller than a predetermined value Pe1 (a map for the engine rotation speed Ne), that is, if the engine load and the engine rotation speed are small such as when idling or running at low speed, the next step Proceed to S16. In step S16, the rich air-fuel ratio operation is performed by setting the fuel injection mode to the intake stroke injection mode.

In order to perform the S purge, it is necessary to set the storage NOx catalyst 30 in a reducing atmosphere, as described above. Here, first, the rich air-fuel ratio operation is performed so that the exhaust air-fuel ratio becomes the rich air-fuel ratio. To do. In this case, the target A / F
Is set to a predetermined rich air-fuel ratio (for example, value 12). As a result, incomplete combustion occurs under an excessive fuel condition, and CO (carbon monoxide) and H necessary for reducing and removing SOx are removed.
A large amount of C (hydrocarbon) (reducing agent) is generated and storage NO
The S purge is promoted by being supplied to the x catalyst 30a.

By the way, when the S purge is promoted as described above and the reduction of SOx proceeds, H ₂ S which emits an odor simultaneously at a high temperature and under a rich air-fuel ratio is generated. However, the H ₂ S generated in this way is stored in the NOx storage catalyst 3.
Since the three-way catalyst 30b provided downstream of Oa has the oxygen storage capacity as described above, the stored oxygen satisfactorily oxidizes and deodorizes. Thereby, the exhaust gas is preferably prevented from emitting an off-flavor.

In step S18, a predetermined time t1 has elapsed since the start of the rich air-fuel ratio operation in step S16.
It is determined whether or not (for example, 2 seconds) has elapsed. If the determination result is false (No) and it is determined that the predetermined time t1 has not yet elapsed, the rich air-fuel ratio operation is continued until the predetermined time t1 has elapsed. On the other hand, if the determination result is true (Ye
If it is determined in s) that the predetermined time t1 has elapsed, the process proceeds to step S20.

In step S20, the fuel injection mode of the main injection is set to the compression stroke injection mode irrespective of the normal setting described above, and the sub-injection is performed in the expansion stroke (particularly, in the middle stage of the expansion stroke or later). To perform two-stage injection (operation state changing means). In order to perform the S purge, as described above, it is necessary to raise the temperature of the storage NOx catalyst 30 to a predetermined high temperature while performing the rich air-fuel ratio operation. Perform injection. That is, the unburned fuel component (unburned HC
) Is burned in the exhaust pipe 14 or the close three-way catalyst 20 to raise the temperature of the exhaust gas, thereby raising the temperature of the storage NOx catalyst 30. Then, when the target average effective pressure Pe and the engine rotation speed Ne are in the region A in FIG. 3, the two-stage injection is performed by the compression stroke injection and the expansion stroke injection.

Normally, if the target average effective pressure Pe or the engine rotation speed Ne is small, it can be determined that the temperature of the storage NOx catalyst 30a, that is, the catalyst temperature Tcat is low, and it is not easy to raise the temperature of the storage NOx catalyst 30a. Therefore, in this case,
It is preferable to increase the sub-injection amount while minimizing the main injection amount while maintaining the overall A / F at the predetermined air-fuel ratio as described above. However, the air-fuel ratio that can be realized in the intake stroke injection mode has an upper limit (for example, value 22). That is, in the intake stroke, the upper limit value (for example, the value 2
2) Combustion is not established at a larger air-fuel ratio.

Therefore, the target air-fuel ratio of the main injection (main A /
When F) is larger than the upper limit (for example, value 22), the main injection is performed in the compression stroke in which combustion is established at an air-fuel ratio larger than the upper limit (for example, value 22). It is. Further, it can be considered that the lower the engine load and engine speed, the lower the temperature of the storage NOx catalyst 30a, that is, the catalyst temperature Tcat.
Therefore, the value of the main A / F increases as the target average effective pressure Pe or the engine rotation speed Ne decreases, and the air-fuel ratio becomes a leaner air-fuel ratio. That is, the lower the catalyst temperature Tcat, the smaller the main injection amount and the larger the sub injection amount.

Thus, when the engine load and engine speed are small, a large amount of unburned fuel
The exhaust gas is exhausted and strongly burns in the exhaust pipe 14 or the proximity three-way catalyst 20 in the presence of oxygen, thereby increasing the exhaust gas temperature. Even if the catalyst temperature Tcat is low, the occlusion type NOx catalyst 30 a A predetermined high temperature Tcat1 that can be S purged (for example,
650 ° C.).

At this time, the target A / F as a whole of the main injection and the sub-injection, that is, the entire A / F is set to a predetermined lean air-fuel ratio (for example, a value of 15). That is, in step S20, unlike the case of step S16, the target A / F, that is, the entire A / F is set to the lean air-fuel ratio (first operation). Then, while the overall A / F is maintained at the predetermined lean air-fuel ratio (for example, the value 15), the main A / F is set to the target average effective pressure Pe and the engine speed based on the main injection mode selection map of FIG. The fuel injection ratio is determined according to the speed Ne, and the respective fuel injection ratios of the main injection amount and the sub injection amount are appropriately determined.

When the overall A / F is set to the lean air-fuel ratio, excess oxygen is included in the exhaust gas during the two-stage injection because oxygen is excessive as a whole. become. The surplus oxygen discharged as exhaust gas in this way corresponds to the reduced oxygen used for the oxidation of H ₂ S because the three-way catalyst 30b has the oxygen storage capacity as described above. Is stored in the three-way catalyst 30b satisfactorily.

That is, in step S20, the temperature of the storage NOx catalyst 30 is raised by performing two-stage injection, and at the same time, the reduced three-way catalyst used for oxidizing H ₂ S by performing the lean air-fuel ratio operation. The oxygen in 30b is replenished. In the next step S22, a predetermined time t after the two-stage injection is started in step S20.
It is determined whether or not 2 (for example, 2 seconds) has elapsed. If the result of the determination is false (No) and it is determined that the predetermined time t2 has not yet elapsed, 2
Continue step injection. On the other hand, if the result of the determination is true (Yes) and it is determined that the predetermined time t2 has elapsed, then step S
Proceed to 24.

On the other hand, when the result of the determination in step S14 is false (No), and the target average effective pressure Pe is determined to be equal to or higher than the predetermined value Pe1 (a map for the engine speed Ne), that is, when the vehicle is running at a middle speed. If the engine load and the engine speed are relatively large, the process proceeds to step S26. In step S26, similarly to step S16, the fuel injection mode is set to the intake stroke injection mode, and the rich air-fuel ratio operation is performed. As a result, a large amount of CO or HC (reducing agent) is discharged, and S purge is promoted.

[0045] At this time, although will be H ₂ S is produced under high temperature and rich air-fuel ratio as described above, the H ₂ S
Is well oxidized and deodorized by the oxygen stored in the three-way catalyst 30b as described above. Thereby, the exhaust gas is preferably prevented from emitting an off-flavor. In step S28, similarly to step S18, it is determined whether or not a predetermined time t1 (for example, 2 seconds) has elapsed since the start of the rich air-fuel ratio operation in step S26. The determination result is false (No) and the predetermined time t
If it is determined that 1 has not elapsed, the predetermined time t1
The rich air-fuel ratio operation is continued until elapses. On the other hand, if it is determined that the predetermined time t1 has elapsed since the determination result is true (Yes), the process proceeds to step S30.

In step S30, the fuel injection mode of the main injection is set to the intake stroke injection mode regardless of the normal setting described above, and the sub-injection is performed in the expansion stroke. That is, when the engine load and the engine rotation speed are relatively large and the target average effective pressure Pe and the engine rotation speed Ne are in the region B in FIG. 3, the two-stage injection is performed by the intake stroke injection and the expansion stroke injection. (Operation state changing means).

Normally, if the engine load and the engine speed are relatively large, the storage type NOx catalyst 30a is heated to a certain high temperature, and the storage type NOx catalyst 30a is heated to a predetermined high temperature Tcat1 (for example, 650). ℃)
It can be easily determined that the temperature can be raised. Therefore, in this case, it is preferable to reduce the sub-injection amount while increasing the main injection amount to maintain the overall A / F at a predetermined rich air-fuel ratio. However, the air-fuel ratio that can be realized in the compression stroke injection mode has a lower limit (for example, value 22). That is,
In the compression stroke, in contrast to the above case, combustion is not established at an air-fuel ratio equal to or lower than the lower limit (for example, value 22).

Therefore, when the air-fuel ratio of the main injection is equal to or lower than the lower limit (for example, value 22), the main fuel is injected in the intake stroke in which combustion is established at the air-fuel ratio equal to or lower than the lower limit (for example, value 22). The injection is performed. As a result, the storage NOx catalyst 30a
Is a predetermined high temperature Tcat1 that can be S purged (for example, 650).
° C).

At this time, as in the case of step S20, the total target A / A including the main injection and the sub injection is combined.
F, that is, the overall A / F is set to a predetermined lean air-fuel ratio (for example, a value of 15). That is, even in step S30,
Unlike the case of step S26, the target A / F, that is, the overall A / F is set to the lean air-fuel ratio (first operation).
Then, while the overall A / F is maintained at the predetermined lean air-fuel ratio (for example, the value 15), the main A / F is switched to the state shown in FIG.
Target effective pressure P based on the main injection mode selection map of
It is determined according to e and the engine speed Ne, and the respective fuel injection ratios of the main injection amount and the sub injection amount are properly determined.

As a result, oxygen is satisfactorily stored in the three-way catalyst 30b so as to compensate for the reduced amount of oxygen used in the oxidation of H ₂ S. That is,
Also in step S30, similarly to the case of step S20, the temperature of the storage NOx catalyst 30 is raised by performing two-stage injection, and the lean air-fuel ratio operation is performed by performing the lean air-fuel ratio operation.
Oxygen of the three-way catalyst within 30b that is used to decrease the oxidation of ₂ S with each other to as to refill.

In the next step S32, the above step S
Similarly to 22, it is determined whether or not a predetermined time t2 (for example, 2 seconds) has elapsed since the start of the two-stage injection in step S30. If the determination result is false (No) and it is determined that the predetermined time t2 has not yet elapsed, the two-stage injection is continued until the predetermined time t2 has elapsed. On the other hand, if the result of the determination is true (Yes) and it is determined that the predetermined time t2 has elapsed, then the flow proceeds to step S24.

In step S24, the storage NOx catalyst 3
It is determined whether 0a has reached a high temperature (for example, 650 ° C.) suitable for SOx removal and a predetermined time t3 has elapsed. The predetermined time t3 is a time preset by experiments or the like as a time during which SOx can be sufficiently removed when the storage NOx catalyst 30a is maintained at a predetermined high temperature Tcat1 in a reducing atmosphere.

The determination result of step S24 is false (No)
If it is determined that the predetermined time t3 has not elapsed, the process returns to step S14 to continue the operation in the S purge mode. That is, step S16 and step S2
6 and the two-stage injection in steps S20 and S30, that is, the lean air-fuel ratio operation, are alternately and repeatedly performed.
The S purge is continued while the catalyst temperature feedback control is performed so that the temperature does not fall below a predetermined high temperature Tcat1 suitable for Ox removal. In the catalyst temperature feedback control, the main A / F and the ignition timing are changed based on information from the high temperature sensor 16 within a range that does not affect the H ₂ S oxidation process, in order to maintain the predetermined high temperature Tcat1. In this case, the sub-injection amount of the two-stage injection may be adjusted, and the predetermined time t2
May be changed.

By alternately repeating the rich air-fuel ratio operation for discharging a large amount of CO and the two-stage injection having a large temperature-raising effect for each of the predetermined time t1 and the predetermined time t2, the storage NOx catalyst 30a can be efficiently switched to the predetermined operation. The temperature can be raised to a high temperature Tcat1 to remove SOx, and further, the entire A / F
By performing the two-stage injection to achieve a lean air-fuel ratio,
Oxygen can always be stored in the three-way catalyst 30b, so that H ₂ S generated during the execution of the S purge can be almost completely and reliably oxidized and deodorized.

On the other hand, if the result of the determination in step S24 is true (Y
If it is determined to be es), it is considered that SOx has been sufficiently removed, and the routine exits from the routine and ends the S purge control.
Note that the rich air-fuel ratio operation (steps S16, S2
Actually, adjustment of the intake air amount and ignition timing by an air bypass valve or a drive-by-wire type throttle valve (not shown) so that the output torque becomes equal between the case of 6) and the case of the two-stage injection (steps S20 and S30). Is adjusted.

Here, whether or not SOx has been sufficiently removed is determined based on whether or not the predetermined time t3 has elapsed. However, the poisoning S amount Qs is calculated from the above equation (1). The determination may be made based on whether the poisoning S amount Qs is equal to or less than a predetermined value. By the way, although not shown in FIG. 2, the vehicle is running at a high speed, the engine speed Ne and the target average effective pressure Pe are large, and the main A / F is smaller than the lower limit value 16 and becomes close to stoichio. In other words, when the determination result of step S14 is false (No) and the target average effective pressure Pe and the engine rotation speed Ne are in the region C in FIG. 3, it is difficult to perform the two-stage injection due to restrictions of the injector driver and the like. On the other hand, the combustion heat is large, the exhaust gas temperature is sufficiently high, and the storage NOx catalyst 3
It can be determined that Oa can be heated to a predetermined high temperature Tcat1 at which S purge can be performed. Therefore, in this case, the rich air-fuel ratio operation is performed in step S26, and in step S30, only the main injection is performed in the intake stroke instead of the two-stage injection, and the exhaust gas temperature is increased by retarding the ignition timing. I do. Note that, in this case as well,
/ F is set to a predetermined lean air-fuel ratio (for example, a value of 15) (first operation), and excess oxygen is satisfactorily replenished and stored in the three-way catalyst 30b, so that H ₂ S is also reliably oxidized. Deodorized.

Similarly, when the engine rotational speed Ne and the target average effective pressure Pe are extremely large and the main A / F has a rich air-fuel ratio, that is, step S14.
Is false (No) and the target average effective pressure Pe,
When the engine rotational speed Ne is in the region D in FIG. 3, it can be determined that the combustion heat is extremely large and the exhaust gas temperature is so high that the S purge can be performed without performing the temperature increase control. Therefore,
In this case, the rich air-fuel ratio operation is performed in step S26, and in step S30, only the main injection is performed in the intake stroke instead of the two-stage injection. In this case as well, the overall A / F is set to a predetermined lean air-fuel ratio (for example, a value of 15) (first operation), and excess oxygen is satisfactorily replenished and stored in the three-way catalyst 30b. Again, H ₂ S is reliably oxidized and deodorized.

In the first embodiment, after performing the rich air-fuel ratio operation for a predetermined time t1 (for example, 2 seconds), the two-stage injection (lean air-fuel ratio operation) is performed for a predetermined time t1 (for example, 2se).
c) The rich air-fuel ratio operation and the two-stage injection (lean air-fuel ratio operation) are performed for a predetermined number of strokes (one or more strokes).
It may be performed alternately every time. That is, the rich air-fuel ratio operation and the two-stage injection may be repeated each time the predetermined number of strokes elapses in each cylinder.

Here, the predetermined time t1 and the predetermined time t2 are both set to, for example, 2 seconds. However, the predetermined time t1 and the predetermined time t2 are taken into consideration in consideration of the balance between the required temperature increase, the required CO amount and the required oxygen amount. t2 may be set separately. Further, these may be varied according to operating conditions (target average effective pressure Pe, engine rotation speed Ne, etc.) and catalyst temperature Tcat. Thus, the S purge can be performed more appropriately, and the H ₂ S can be more reliably oxidized and deodorized.

Next, a second embodiment will be described. In the first embodiment, the rich air-fuel ratio operation and the two-stage injection (lean air-fuel ratio operation) are switched every predetermined time or every predetermined number of strokes. In the second embodiment, the engine 1 is a multi-cylinder engine. In this case, the rich air-fuel ratio operation and the two-stage injection (lean air-fuel ratio operation) are repeated for each cylinder instead of the predetermined number of strokes for a predetermined time.

Referring to FIG. 4, there is shown a part of a flow chart showing an S purge control routine according to the second embodiment following the flow chart of FIG. 2. Based on this flow chart, only parts different from the first embodiment will be described. explain. In the second embodiment, in step S14,
It is determined whether or not the target average effective pressure Pe is smaller than a predetermined value Pe1, and if the determination result is true (Yes), the process proceeds to step S16 '.

In step S16 ', a rich air-fuel ratio operation is performed in some cylinders. Then, in step S20 ', two-stage injection (lean air-fuel ratio operation) is performed in the remaining cylinder (first operation). That is, here, since the engine 1 is, for example, an in-cylinder injection spark ignition type in-line four-cylinder gasoline engine, the rich air-fuel ratio operation is performed in some of the four cylinders (for example, two cylinders), and the remaining cylinders (for example, 2 in 2 cylinders)
Step injection (lean air-fuel ratio operation) is performed. In this case, for the two-stage injection, the main injection is performed in the compression stroke and the sub-injection is performed in the expansion stroke, as in the first embodiment, based on the determination in step S14.

It is preferable that the rich air-fuel ratio operation and the two-stage injection are alternately and equally performed. When the engine 1 is, for example, a V-type gasoline engine, the rich air-fuel ratio operation is performed in each cylinder of one bank. And the two-stage injection is performed in each cylinder of the other one bank. on the other hand,
If the result of the determination in step S14 is false (No), the process proceeds to step S26 '.

In step S26 ', a rich air-fuel ratio operation is performed in a part of the cylinders in the same manner as described above. Then, step S3
At 0 ', two-stage injection (lean air-fuel ratio operation) is performed in the remaining cylinder (first operation). In this case, for the two-stage injection, the main injection is performed in the intake stroke and the sub-injection is performed in the expansion stroke, as in the first embodiment, based on the determination in step S14.

Then, in step S24, the storage type NOx catalyst 30a is heated to a high temperature (for example, 6 ° C.) suitable for SOx removal.
50 ° C.), and it is determined whether or not a predetermined time t3 has elapsed. Also in this case, the poisoning S amount Qs is obtained from the above equation (1), and whether or not SOx has been sufficiently removed is determined based on whether or not the poisoning S amount Qs has become a predetermined value or less. Good.

The determination result of step S24 is false (No)
If it is determined that the predetermined time t3 has not elapsed, the process returns to step S14. Thereby, step S16 'and step S20' or step S26 '
In step S30 ', the rich air-fuel ratio operation and the two-stage injection (lean air-fuel ratio operation) are performed such that the catalyst temperature Tcat is maintained at the predetermined high temperature Tcat1 by the catalyst temperature feedback control, and the storage NOx catalyst 30a is maintained in the SOx removal atmosphere.
Is continuously performed for each cylinder.

In this manner, the rich air-fuel ratio operation for discharging a large amount of CO and HC and the two-stage injection having a large temperature raising effect are carried out in a well-balanced manner. The predetermined high temperature Tcat
The temperature can be satisfactorily raised to 1 and SOx can be reliably removed. In addition, by performing two-stage injection so that the overall A / F has a lean air-fuel ratio, it is generated during the execution of the S purge. The H ₂ S to be oxidized can be almost completely and reliably oxidized and deodorized as in the case of the first embodiment.

In this case, both the partial cylinder and the remaining cylinder are, for example, two cylinders. However, as in the case where the predetermined time t1 and the predetermined time t2 are separately set in the first embodiment, the necessary temperature increase amount is required. Alternatively, the number of partial cylinders and the number of remaining cylinders may be set to different numbers of cylinders while considering the balance between the required amount of CO and the required amount of oxygen. Further, these are adjusted to operating conditions (target average effective pressure Pe, engine speed Ne, etc.) and catalyst temperature T.
You may make it change according to cat. Thus, the S purge can be performed more appropriately, and the H ₂ S can be more reliably oxidized and deodorized.

In the rich air-fuel ratio operation, the ignition timing may be retarded.
The temperature increasing effect can be obtained not only during the stage injection operation but also during the rich air-fuel ratio operation. By the way, in the above embodiment, two-stage injection is performed in steps S20 and S30 as the exhaust gas temperature raising control. However, instead of the two-stage injection, the entire A / F is set to a predetermined lean air-fuel ratio (for example,
The ignition timing may be retarded as the exhaust gas temperature raising control while setting the value 15). Even in this case,
H ₂ S is reliably oxidized and deodorized.

In the above embodiment, first, the rich air-fuel ratio operation (steps S16, S26, S16 ', S2
6 '), the lean air-fuel ratio operation by two-stage injection (steps S20, S30, S20', S30 ') is performed, and thereafter, the operation is repeated. After performing the lean air-fuel ratio operation by the two-stage injection, the rich air-fuel ratio operation may be performed, and thereafter, the operation may be repeated.

In the above embodiment, the three-way catalyst 30b is disposed downstream of the storage NOx catalyst 30a, and the close three-way catalyst 20 is disposed upstream of the storage NOx catalyst 30a. Upstream of a NOx catalyst (not limited to a storage type NOx catalyst but may be a selective reduction type NOx catalyst),
S capable of absorbing Ox and releasing in a reducing atmosphere
A (sulfur) trap may be provided.

In this case, the NOx catalyst and the three-way catalyst may be individually arranged in order downstream of the S trap,
The NOx catalyst may be a three-way catalyst-equipped NOx catalyst and a separate three-way catalyst may not be provided. Further, instead of the S trap, a two-layer trap having both the S trap function and the function of the NOx catalyst may be provided, and a three-way catalyst may be provided downstream of the two-layer trap.

The present invention can be satisfactorily carried out even if the proximity three-way catalyst 20 is omitted. Further, in the above embodiment, it is determined whether or not the poisoning S amount Qs of the occlusion type NOx catalyst 30a has reached a predetermined amount, and when the poisoning S amount Qs exceeds the predetermined amount, the S purge of the occlusion type NOx catalyst 30a is performed. Is described as an example, but in practice, even during normal driving, the storage NOx catalyst 30a naturally becomes hot during a high load operation and the exhaust air-fuel ratio becomes rich air-fuel ratio. In such a case, the S 2 purge may be performed to reduce the H ₂ S by intermittently performing the first operation in which the exhaust air-fuel ratio becomes a lean air-fuel ratio. Can be.

Specifically, regardless of the poisoning S amount Qs, if the storage NOx catalyst 30a reaches a predetermined high temperature Tcat1 and the target A / F reaches a predetermined rich air-fuel ratio (for example, a value of 12), As described above, the lean air-fuel ratio operation may be performed periodically. As a result, H ₂ S is oxidized and deodorized satisfactorily whenever the S purge is performed.
In this case, the overall A / F at the time of the lean air-fuel ratio operation is a predetermined lean air-fuel ratio (for example, a value of about 15) near stoichio and the lean air-fuel ratio operation is a short time. Even if there is, the output torque hardly decreases.

[0075]

As described above in detail, according to the exhaust gas purifying apparatus for an internal combustion engine of the first aspect of the present invention, H ₂ S can be oxidized satisfactorily in a wide operating range without increasing the cost. It is possible to reliably prevent the exhaust gas from emitting an odor.

[Brief description of the drawings]

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

FIG. 2 is a flowchart illustrating a control routine of the exhaust gas purifying apparatus for an internal combustion engine according to the first embodiment of the present invention.

FIG. 3 is a main injection mode selection map when performing two-stage injection.

FIG. 4 is a part of a flowchart illustrating a control routine of the exhaust gas purification device for an internal combustion engine according to the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine (internal combustion engine) 4 Spark plug 6 Fuel injection valve 11 Throttle valve 11a Throttle sensor 13 Crank angle sensor 16 High temperature sensor 30a Storage type NOx catalyst (first catalyst) 30b Three-way catalyst (second catalyst) 40 Electronic control Unit (ECU)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/04 305 B01D 53/36 102H 104A (72) Inventor Katsuhiko Miyamoto 5-33 Shiba 5-chome, Minato-ku, Tokyo No. 8 F term in Mitsubishi Motors Corporation (reference) 3G091 AA02 AA12 AA13 AA17 AA24 AA28 AA29 AB03 AB05 AB06 AB11 BA04 BA11 BA14 BA15 BA19 BA20 BA33 CA18 CB02 CB03 CB05 DA03 DA07 DA10 DB06 DB10 DC01 EA01 EA31 FA13 EA30 FA30 FA14 FB02 FB03 FB10 FB11 FB12 FC01 FC07 FC08 GB02Y GB04W GB04Y GB05W GB06W HA03 HA08 HA12 HA36 HA37 HA38 HA47 3G301 HA01 HA04 HA06 HA08 HA15 HA18 JA21 JA25 JB09 LB04 MA01 MA11 MA18 MA23 MA26 NA06 NE02 NE15 NE12 NE15 NE12 NE15 NE12 NE15 NE21 PA11A PD11A PE01A PE03A 4D048 AA02 AA03 AA06 AA18 AB05 BA30Y BA33Y BC01 BD10 CA01 CC32 CC38 CC4 4 DA01 DA02 EA04

Claims (1)

[Claims] 1. An exhaust passage, wherein a sulfur component in exhaust gas is occluded in a first operation state in which an exhaust air-fuel ratio is a lean air-fuel ratio, and in a second operation state in which the exhaust air-fuel ratio is high and the exhaust air-fuel ratio is a rich air-fuel ratio. A first catalyst for releasing the stored sulfur component, and a first catalyst provided in the exhaust passage downstream of the first catalyst;
An exhaust gas purification apparatus for an internal combustion engine, comprising: a second catalyst having an oxygen storage function; and an operation state changing unit that intermittently performs the first operation in the second operation state. .