JP3334634B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to an exhaust gas purifying apparatus including a catalyst temperature control technique used for removing SOx stored in a storage NOx catalyst. .

[0002]

2. Related Background Art In an internal combustion engine, if the air-fuel ratio is set to a lean air-fuel ratio, there is a problem that the conventional three-way catalyst cannot sufficiently purify NOx (nitrogen oxide) in exhaust gas due to its purification characteristics. A storage NOx catalyst capable of purifying NOx even in an oxygen-excess atmosphere has been developed and put into practical use.

[0003] occlusion-type NOx catalyst occludes deposited in an oxygen excess state (oxidation atmosphere) NOx in the exhaust gas as nitrate X-NO _3, the intake built the NOx CO (carbon monoxide) over state (reduction atmosphere) Thus, the catalyst is configured to have the property of reducing to N ₂ (nitrogen) (carbonate X—CO ₃ is generated at the same time). Speaking of the in-cylinder injection type internal combustion engine, for example, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio or a value close to the stoichiometric air-fuel ratio before the NOx storage amount of the storage NOx catalyst is saturated. (This is referred to as a rich spike), thereby generating a CO-rich reducing atmosphere, purifying and reducing the stored NOx (NOx purge), and regenerating the stored NOx catalyst.

On the other hand, S (sulfur) component (sulfur component) is contained in the fuel, and this S component reacts with oxygen to form SOx (sulfur oxide), which is replaced with NOx instead of NOx. There is a problem that it is stored in the storage NOx catalyst as sulfate. That is, there is a problem that the catalyst carrier is poisoned by SOx and the purification efficiency of the catalyst is reduced. However, it is known that the SOx thus stored is removed (S purge) by setting the air-fuel ratio to a rich state and setting the temperature of the catalyst to a high temperature state. For example, the storage amount of SOx is estimated. If it is determined that the estimated value has reached the predetermined amount, the fuel injection is performed in the retardation or expansion stroke of the ignition timing together with the enrichment of the air-fuel ratio,
A technique is known in which a reducing atmosphere rich in CO is thereby generated, and at the same time, combustibles (fuel) are burned in an exhaust passage to raise the temperature of the exhaust gas to bring the catalyst to a high temperature state and perform an S purge (Japanese Patent Application Laid-Open No. 7-217474). etc).

Further, in the apparatus disclosed in the above publication, the catalyst temperature is detected by an exhaust gas temperature sensor disposed upstream of the catalyst, so that when the S purge is performed, the temperature of the catalyst is reduced. Air-fuel ratio control, ignition timing control, and the like are performed based on this.

[0006]

It is generally known that when detecting the temperature of a catalyst, it is generally better to directly measure the temperature at the center of the catalyst. However, it is actually difficult to dispose a temperature sensor at the center of the catalyst. For example, as disclosed in the above-mentioned publications, a detection unit projects into the exhaust passage immediately upstream of the storage NOx catalyst. The temperature sensor is disposed in such a manner that the temperature of the exhaust gas is detected, and the catalyst temperature is estimated by detecting the exhaust gas temperature. If the temperature sensor is mounted upstream of the catalyst in this way,
An increase in the catalyst temperature can be detected in advance from the exhaust gas temperature upstream of the catalyst, and the temperature control of the catalyst can be easily performed.

However, in order to perform the S purge as described above, the air-fuel ratio is enriched and the ignition timing is retarded or fuel is injected in the expansion stroke, and the amount of combustibles (fuel) in the exhaust passage is increased. Then, a part of the combustibles (unburned fuel components such as unburned HC) flowing through the exhaust passage in the unburned state reaches the storage NOx catalyst without burning in the exhaust passage, and the storage NOx The reaction may occur in the catalyst, that is, it may burn. When a reaction (combustion) occurs in the storage NOx catalyst in this way, the heat of reaction (combustion heat) directly causes the storage N
As the temperature of the Ox catalyst rises, the catalyst temperature becomes higher than the exhaust gas temperature upstream of the catalyst, and the catalyst temperature cannot be accurately estimated from the temperature information from the temperature sensor provided upstream of the catalyst. There is a problem that can not be implemented properly.

Therefore, it is conceivable to provide a temperature sensor downstream of the storage NOx catalyst. However, if such a temperature sensor is provided downstream, there is a problem that a delay in detection of the temperature sensor with respect to the catalyst temperature occurs. For example, when the temperature sensor detects that the catalyst has reached the heat resistant temperature, the catalyst itself may already have exceeded the heat resistant temperature, which is not preferable.

It is also known that the storage NOx catalyst has a lower heat-resistant temperature than the three-way catalyst and is liable to be thermally degraded. Therefore, it is important to accurately determine the catalyst temperature in the storage NOx catalyst. I have. The present invention has been made in order to solve such a problem, and an object of the present invention is to reduce the temperature of the storage NOx catalyst to the exhaust gas temperature in an exhaust purification device for an internal combustion engine having the storage NOx catalyst. An object of the present invention is to provide an exhaust gas purifying apparatus for an internal combustion engine, which can always estimate accurately based on the above.

[0010]

According to the first aspect of the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine having a storage type NOx catalyst.
When it is necessary to raise the temperature of the Ox catalyst, the combustibles increased by the combustible material increasing means to generate combustion in the exhaust passage and raise the exhaust gas temperature are supplied to the exhaust passage. It is caused to react (combust) by combustible substance reaction means provided in the exhaust passage on the upstream side of the storage NOx catalyst. For this reason, when the exhaust gas reaches the storage NOx catalyst, the exhaust gas contains almost no combustibles, the temperature of the storage NOx catalyst is increased by the exhaust gas, and the storage NOx catalyst The temperature rise due to the reaction (combustion) of the material is eliminated or reduced.

Therefore, based on the exhaust gas temperature detected by the exhaust gas temperature detection means provided immediately upstream of the storage NOx catalyst, the temperature of the storage NOx catalyst is determined by the NOx catalyst temperature estimation means.
It is possible to more appropriately estimate, and the temperature control of the storage NOx catalyst by the catalyst temperature control means can be appropriately performed based on the estimated temperature from the detected temperature. Thus, for example, S
If so, such as performing a Atsushi Nobori of the occlusion-type NOx catalyst to purge, the temperature of the occlusion-type NOx catalyst S purgeable predetermined temperature (e.g., 650 ° C.) although there needs to be maintained substantially constant to, NOx Estimated by catalyst temperature estimation means
Catalyst temperature and target temperature of storage NOx catalyst capable of reducing NOx
The deviation from the degree is periodically integrated and the integrated value of the deviation is increased or decreased.
By controlling the combustible substance increasing means in accordance with the integrated value, the temperature feedback of the NOx storage catalyst to the target temperature is controlled.
Thus, the storage type NOx catalyst can be reliably maintained at a predetermined temperature, and the S purge can be satisfactorily performed.

Further, when the temperature of the storage NOx catalyst is accurately estimated as described above, it is possible to reliably prevent thermal deterioration of the storage NOx catalyst.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention mounted on a vehicle. Hereinafter, the configuration of the exhaust gas purifying 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. In the figure, reference numeral 13 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. The exhaust pipe 14 has a small three-way catalyst (combustible substance reaction means) 20 close to the engine 1 and an exhaust pipe. A muffler (not shown) is connected via the purification catalyst device 30. In a portion of the exhaust pipe 14 between the three-way catalyst 20 and the exhaust purification catalyst device 30, a high temperature sensor (exhaust temperature detection means) located immediately upstream of the exhaust purification catalyst device 30 and detecting the exhaust gas temperature is provided. 16 are provided.

The exhaust purification catalyst device 30 includes two catalysts, that is, a storage type NOx catalyst 30a and a three-way catalyst 30b, and the three-way catalyst 30b has a storage type NOx catalyst 3b.
0a is disposed downstream. The storage type NO
When the x catalyst 30a has a three-way catalyst function,
The storage type NOx catalyst 30a alone may be used. The storage type NOx catalyst 30a has a function of temporarily storing NOx in an oxidizing atmosphere and reducing NOx to N ₂ (nitrogen) or the like mainly in a reducing atmosphere where CO is present. More specifically, the storage NOx catalyst 30a is configured as a catalyst having platinum (Pt), rhodium (Rh) or the like as a noble metal, and barium (Ba) as a storage material.
And the like, alkali metals and alkaline earth metals.

A NOx sensor 32 for detecting the NOx concentration is provided between the storage type NOx catalyst 30a and the three-way catalyst 30b.
Is provided. Further, an input / output device, a storage device (R
OM, RAM, nonvolatile RAM, etc.), central processing unit (C
PU), an ECU (electronic control unit) 40 including a timer counter and the like.
With 0, comprehensive control of the exhaust gas purification apparatus according to the present invention including the engine 1 is performed. Various sensors such as the high-temperature sensor 16 and the NOx sensor 32 described above are connected to the input side of the ECU 40, and detection information from these sensors is input.

On the other hand, the output side of the ECU 40 is connected to the above-described ignition plug 4, the fuel injection valve 6, and the like 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.

In practice, the ECU 40 determines the target in-cylinder pressure corresponding to the engine load, that is, the target average effective pressure, based on the throttle opening information θth from the throttle sensor 11a and the engine speed information Ne from the crank angle sensor 13. Pe is determined, 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 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 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 target air-fuel ratio (target A / A), which is a control target, is determined from 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 /
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 and the storage NOx catalyst 30
In order to correct an error caused by the a being arranged at some distance from each other, a temperature difference map (not shown) is prepared in advance according to the target average effective pressure Pe and the engine rotation speed information Ne by an experiment or the like. Therefore, the catalyst temperature Tcat is determined by the target average effective pressure Pe and the engine rotation speed information N.
When e is determined, it is assumed to be unambiguously estimated.

Hereinafter, the operation of the exhaust gas purifying apparatus according to the present invention will be described. As described above, SOx is also stored in the storage-type NOx catalyst 30a in addition to NOx. The SOx is periodically removed (S purge) by raising the temperature of the storage-type NOx catalyst 30a and setting it in a reducing atmosphere. Here, the operation of the exhaust gas purification apparatus according to the present invention will be described while describing the control procedure of the exhaust gas temperature increase control at the time of the S purge.

Referring to FIG. 2, there is shown a flowchart of an exhaust gas temperature raising 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, a method of estimating 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 reproduction S amount per execution cycle.

In other words, 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 regenerated 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 = K1, K2, K3 (2) Further, the reproduction S amount Rs per execution cycle is calculated from the following equation (3). Rs = α · R1 · R2 · dT (3) where α is a regeneration rate (set value) per unit time, dT indicates an execution cycle of the fuel injection control routine, and R1 and R2 are respectively A regeneration capacity coefficient according to the catalyst temperature Tcat and a regeneration 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 in this routine. 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.

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 determination result of step S14 is true (Yes).
In the case where the target average effective pressure Pe is smaller than a predetermined value Pe1 (a map for the engine speed Ne), that is, when the engine load and the engine speed are small immediately after the start of the engine or during low-speed running, Step S16
Proceed to. In step S16, the fuel injection mode of the main injection is set to the compression stroke injection mode regardless of the normal setting described above, and the sub-injection is performed in the expansion stroke (combustible substance increasing means). That is, when performing the S purge, when the target average effective pressure Pe is in the region A in FIG. 3, the two-stage injection is performed by the compression stroke injection and the expansion stroke injection.

The target A / F, that is, the total target A / F including the main injection and the sub-injection, that is, the total A / F
F is set to a predetermined rich air-fuel ratio (a value suitable for the S purge, for example, a value of 12), and is set in accordance with the target average effective pressure Pe and the engine speed Ne based on the main injection mode selection map of FIG. Injection target air-fuel ratio (main A /
F) is determined. At this time, the main A / F is set while the overall A / F is maintained at the predetermined rich air-fuel ratio (for example, value 12). In other words, the fuel injection ratios of the main injection amount and the sub injection amount are appropriately determined while the overall fuel injection amount is kept constant and the reducing atmosphere is well formed.

Normally, if the target average effective pressure Pe or the engine rotation speed Ne is small, the storage type NOx catalyst 30a is in a low temperature state, the catalyst temperature Tcat is low, and the storage type NOx catalyst 3 is low.
It can be determined that the temperature rise of 0a is not easy. Therefore, in this case, while increasing the sub-injection amount, it is preferable to reduce the main injection amount as much as possible while maintaining the overall A / F at the predetermined rich air-fuel ratio as described above.

However, the air-fuel ratio achievable in the intake stroke injection mode has an upper limit (for example, value 22), and the upper limit (for example, value 2) in the intake stroke injection mode.
2) Combustion is not established at a larger air-fuel ratio. Therefore,
When the main A / F becomes larger than the upper limit (for example, the value 22), the upper limit (for example,
The main injection is performed in the compression stroke in which combustion is established at an air-fuel ratio larger than the value 22).

The temperature of the storage NOx catalyst 30a, that is, the catalyst temperature Tcat, can be considered to be lower as the engine load or the engine speed is smaller. 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.

By the way, when the fuel (combustible material) is injected in the expansion stroke by the sub-injection in such a two-stage injection, most of the fuel remains unburned, that is, the unburned fuel component (unburned HC) As a result, the fuel is discharged into the exhaust pipe 14 and flows into the three-way catalyst 20. However, unburned fuel components (combustibles) flowing into the three-way catalyst 20
Causes an oxidation reaction (combustion) in the three-way catalyst 20 by the action of the catalyst. That is, the fuel supplied by the sub-injection burns without reaching the storage type NOx catalyst 30a, and the exhaust gas flowing into the storage type NOx catalyst 30a is sufficiently heated.

As a result, even if the catalyst temperature Tcat is low, the exhaust gas temperature is raised and the storage NOx catalyst 30a is quickly heated to a predetermined high temperature Tcat1 (for example, 650 ° C.) at which S purging is possible. The S purge can be favorably performed. In the next step S18, feedback control of the catalyst temperature according to the catalyst temperature Tcat, that is, catalyst temperature F / B control (catalyst F / B), while maintaining the overall A / F at a predetermined rich air-fuel ratio (for example, value 12) Temperature control means).

Here, first, after a predetermined time t1 (for example, 2 minutes) has elapsed since the start of the S purge by the execution of the step S12 and the catalyst temperature Tcat has reached a predetermined high temperature T.
It is determined whether or not cat1 (for example, 650 ° C.) has been reached.
If the determination result is true (Yes) and the predetermined time t1
Has elapsed and the catalyst temperature Tcat has reached the predetermined high temperature Tcat1, the main A / F set based on the main injection mode selection map of FIG.
Is corrected in accordance with the temperature deviation integration ΣΔTcat.

Specifically, the temperature deviation integration ΣΔTcat is given by the following equation:
It is calculated from (4). ΣΔTcat = ΣΔTcat (n−1) + ΔTcat (4) where ΔTcat is a temperature deviation, and the ΔTcat is the predetermined high temperature Tcat1 (for example, 650 ° C.) and the high temperature sensor 16.
Is calculated from the following equation (5) based on the current catalyst temperature Tcat estimated based on

ΔTcat = Tcat1−Tcat (5) As described above, the sub-injected fuel reacts (combustes) in the three-way catalyst 20 and reacts (combustes) in the storage NOx catalyst 30a. Therefore, the temperature of the storage NOx catalyst 30a, that is, the catalyst temperature Tcat
Is always properly estimated based on the exhaust gas temperature detected by Therefore, the ΔTcat, and thus the temperature deviation integration Σ
ΔTcat is a very appropriate value corresponding to the actual temperature of the storage NOx catalyst 30a.

Actually, the temperature deviation integration ΣΔTcat and the correction value of the main A / F are mapped in advance as shown in Table 1 by experiments or the like, and the main A / F is
The correction is performed based on the correction value map of F (integral correction).

[0042]

[Table 1]

Here, of the correction values of the main A / F, a plus sign (+) indicates a correction toward the lean side, and a minus sign (-) indicates a correction toward the rich side. That is, if the storage NOx catalyst 30a is heated by overshoot exceeding a predetermined high temperature Tcat1 (for example, 650 ° C.), the temperature deviation integrated ΣΔTcat becomes a negative value, and in this case, the main A / F Is corrected to the negative side, that is, the rich side, that is, the fuel amount of the sub-injection is reduced and returned to the predetermined high temperature Tcat1. Thereafter, when the undershoot occurs and the temperature deviation integration ΣΔTcat becomes a positive value, the main A / F is corrected to the positive side, that is, the lean side, that is, the fuel amount of the sub injection is increased and the catalyst temperature Tcat is increased. Is again raised to a predetermined high temperature Tcat1.

When the main A / F is corrected in this way, the catalyst temperature Tcat stabilizes at a predetermined high temperature Tcat1 (for example, 650 ° C.).
a is maintained at the predetermined high temperature Tcat1. When the catalyst temperature Tcat is stabilized in this way, thereafter, it is only necessary to perform a temperature increase control for maintaining the predetermined high temperature Tcat1. In other words, the main injection amount is increased by setting the main A / F to a small value, while the auxiliary injection amount is reduced.

When fuel injection is performed in the compression stroke injection mode, the air-fuel ratio at which combustion is established is restricted due to the structure, and when the main A / F becomes the lower limit (for example, value 24). While maintaining the overall A / F at a predetermined rich air-fuel ratio (for example, a value of 12), only the main injection is performed in the intake stroke without performing the two-stage injection, and the temperature increase control is continued by correcting the ignition timing. To do.

The ignition timing correction amount is set in accordance with the above-mentioned temperature deviation integration ΣΔTcat. Actually, the temperature deviation integration ΣΔTcat and the ignition timing correction amount are mapped in advance as shown in Table 2 by experiments or the like, and the ignition timing is corrected based on the ignition timing correction amount map (integration correction). . During normal combustion control, the reference ignition timing is set to the advanced side as much as possible so that the torque becomes large. However, when performing the ignition timing correction, there is a margin for correcting the ignition timing to the advanced side. Therefore, the reference ignition timing for performing the correction is set to a neutral position between the advance and the retard.

[0047]

[Table 2]

Here, in the ignition timing correction amount, a positive sign (+) indicates correction to the advance side, and a negative sign (-) indicates correction to the retard side. That is, as described above, when the storage NOx catalyst 30a is heated by overshoot exceeding a predetermined high temperature Tcat1 (for example, 650 ° C.), the temperature deviation integration ΣΔTcat becomes a negative value,
In this case, the ignition timing correction amount is corrected to the positive side, that is, the advance side, and the temperature raising effect is reduced. Thereafter, when the undershoot occurs and the temperature deviation integration ΣΔTcat becomes a positive value, the ignition timing correction amount is corrected to the negative side, that is, the retard side, the temperature increasing effect is enhanced, and the catalyst temperature Tcat is again set to the predetermined value. Is raised to the high temperature Tcat1.

As a result, the storage NOx catalyst 30a is stably maintained at a predetermined high temperature Tcat1 (for example, 650 ° C.), and the S purge is continued satisfactorily. On the other hand, if 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 greater than the predetermined value Pe1 (a map for the engine speed Ne), that is, the engine load, If the engine speed is relatively high, the process proceeds to step S20.

In step S20, 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 during 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. I do.

Then, similarly to the above, the overall A / F is a predetermined rich air-fuel ratio (a value suitable for S purge, for example, a value of 12).
And the target air-fuel ratio (main A / F) of the main injection is determined while maintaining the overall A / F at the predetermined rich air-fuel ratio (for example, value 12). Each fuel injection ratio of the injection amount is properly determined.

Normally, when the engine load and the engine speed are relatively high, the storage NOx catalyst 30a is heated to a high temperature to some extent, and it can be determined that the temperature of the storage NOx catalyst 30a can be easily 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, as described above, the air-fuel ratio that can be realized in the compression stroke injection mode has a lower limit (for example, a value of 24), and in the compression stroke injection mode, the lower limit is opposite to the above case. Combustion is not established at an air-fuel ratio equal to or less than (for example, value 24). Therefore, when the air-fuel ratio of the main injection is equal to or lower than the lower limit (for example, value 24), the intake stroke in which combustion is established at the air-fuel ratio equal to or lower than the lower limit (for example, value 24). The main injection is performed.

In this case, as in the above,
The unburned fuel components (combustible substances) flowing into the three-way catalyst 20 cause an oxidation reaction (combustion) in the three-way catalyst 20 by the action of the catalyst. That is, the fuel supplied by the sub-injection burns without reaching the storage type NOx catalyst 30a, and the exhaust gas flowing into the storage type NOx catalyst 30a is sufficiently heated.

As a result, while the overall fuel injection amount is maintained constant and the reducing atmosphere is well formed, a predetermined high temperature Tcat1 ( For example, the temperature is rapidly increased to 650 ° C.), and the S purge can be satisfactorily performed. By the way, when the vehicle is running at high speed and the engine rotation speed Ne and the target average effective pressure Pe are large, that is, the target average effective pressure Pe is C in FIG.
When it is in the range, it is difficult to perform two-stage injection due to restrictions of an injector driver or the like, but the exhaust gas temperature is originally relatively high, and the storage NOx catalyst 30 can be obtained only by retarding the ignition timing.
It can be determined that a can be heated to a predetermined high temperature Tcat1 at which S can be purged. Therefore, in this case, only the main injection is performed in the intake stroke instead of the two-stage injection in step S20, and the temperature rise control is performed by retarding the ignition timing. Note that, also in this case, the overall A / F is set to a predetermined rich air-fuel ratio (for example, a value of 12).

In the case where the engine 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, the target average effective pressure Pe and the engine speed Ne in FIG. When it is in the D region, it can be determined that the combustion heat is extremely large and the exhaust gas temperature is high enough to perform the S purge without performing the temperature increase control. In this case,
Step S20 is skipped.

Then, in the next step S22, similarly to step S18, the catalyst temperature Tca is maintained while the overall A / F is maintained at a predetermined rich air-fuel ratio (for example, a value of 12).
Feedback control of the catalyst temperature, that is, catalyst temperature F / B control (catalyst temperature control means) is performed according to t. Since the details of the control are as described above, the description is omitted here. However, when the fuel injection is performed in the intake stroke injection mode, the air-fuel ratio is set to the upper limit value (for example, value 22) as described above. Therefore, when the main A / F reaches the upper limit (for example, value 22), the entire A / F is maintained at a predetermined rich air-fuel ratio (for example, value 12) as described above. However, only the main injection is performed in the intake stroke without performing the two-stage injection, and the temperature increase control is continued by correcting the ignition timing. The ignition timing correction is as described above.

Thus, the storage NOx catalyst 3
0a is stably maintained at a predetermined high temperature Tcat1 (for example, 650 ° C.), and the S purge is favorably continued.
In step S24, it is determined whether a predetermined time t2 has elapsed since the start of the S purge mode. The predetermined time t2 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 t2 has not yet elapsed, the process returns to step S12 to continue the temperature increase control in the S purge mode. On the other hand, if the determination result of step S24 is true (Yes) and it is determined that the predetermined time t2 has elapsed, it is assumed that SOx has been sufficiently removed, and the routine exits to terminate the exhaust gas temperature raising control.

As described above, in the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the three-way catalyst (combustible substance reaction means) 20 is provided upstream of the storage NOx catalyst 30a, and the S purge Is performed, that is, when fuel (combustible material) is supplied into the exhaust pipe 14 to raise the temperature of the storage NOx catalyst 30a, the fuel (combustible material) is stored in the three-way catalyst 20. The reaction (burn) is performed. That is, the exhaust gas flowing into the storage NOx catalyst 30a is heated to a sufficiently high temperature without containing fuel (combustible material), and the fuel (combustible material) is stored so as not to react (burn) in the storage NOx catalyst 30a. Type NOx catalyst 30a
There is no or little temperature rise due to the internal reaction.

Therefore, according to the exhaust gas purifying apparatus of the present invention, the catalyst temperature Tca is determined based on the exhaust gas temperature information from the high temperature sensor 16 provided immediately upstream of the NOx storage catalyst 30a.
Since t can be estimated appropriately, the catalyst temperature F / B control can be performed extremely accurately. Therefore, when performing the S purge, the storage type NOx catalyst 30a can be surely maintained at a predetermined temperature (for example, 650 ° C.), and the S purge is reliably performed and the storage type NOx catalyst 30a It is possible to always maintain good NOx purification efficiency.

Further, as described above, the storage type NOx catalyst 30a
When the temperature of the NOx catalyst 3 is accurately estimated,
0a can be reliably prevented beforehand.
In the above embodiment, the storage type NOx is obtained by two-stage injection.
The case where the S purge is performed by raising the temperature of the catalyst 30a has been described. However, the purpose of raising the temperature of the storage type NOx catalyst 30a may be not only for the S purge but also for the activity of the catalyst. If the fuel (combustible material) is supplied into the fuel cell 14 to raise the temperature of the storage type NOx catalyst 30a, the combustible material increasing means is not limited to the enrichment of the air-fuel ratio, the two-stage injection, and the retard of the ignition timing. Alternatively, the fuel may be directly injected into the exhaust pipe 14 upstream of the three-way catalyst 20.

In the above embodiment, the engine 1 is an in-cylinder injection spark ignition type in-line four-cylinder gasoline engine. However, the engine 1 may be an intake pipe lean-burn engine. Further, in the above-described embodiment, the combustible substance reaction means is configured using the three-way catalyst 20. However, the combustible substance reaction means is not limited to the three-way catalyst 20, and the combustible substance reaction means may be a SOx trap similar to a three-way catalyst. It may be constituted by a device or the like. Further, the same effect as described above can be obtained even if a small three-way catalyst provided almost integrally with the vicinity of the exhaust manifold is used as the combustible substance reaction means.

Further, the combustible substance reaction means may not be a catalyst as in the present embodiment. For example, the combustible substance reaction means may be provided with a volume for retaining the exhaust gas in the exhaust manifold, and may be provided in the exhaust passage. The ignition means may be provided to burn combustibles in the exhaust passage.

[0065]

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, the storage NO
The temperature of the storage NOx catalyst is determined based on the exhaust gas temperature detected by the exhaust gas temperature detecting means provided immediately upstream of the x catalyst.
The NOx catalyst temperature estimating means can satisfactorily estimate, and the estimated catalyst temperature and NOx can be reduced.
The deviation from the target temperature of the storage NOx catalyst is integrated periodically.
To increase or decrease the integrated value of the deviation,
Controlling the mass increasing means to increase the temperature of the storage NOx catalyst to the target temperature.
By performing temperature feedback, temperature control of the occlusion-type NOx catalyst according to the catalyst temperature control means it can be positively carried out suitable.

Therefore, for example, when the temperature of the storage NOx catalyst is increased to perform the S purge, the NOx catalyst temperature estimation
The means for increasing the amount of combustibles is controlled based on the catalyst temperature estimated by the means, so that the storage NOx catalyst can be surely maintained at a predetermined temperature (for example, 650 ° C.) and purged with S. The NOx purification efficiency of the catalyst can always be kept good. Moreover, in this way the temperature of the occlusion-type NOx catalyst Ri accurately estimated capable Na, to a predetermined temperature
When securely retainable in ing, can be prevented reliably advance the thermal degradation of the occlusion-type NOx catalyst.

[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 shows a catalyst temperature F in the exhaust gas purifying apparatus according to the present invention.
4 is a flowchart illustrating a control routine of exhaust gas temperature increase control including / B control.

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

[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 (exhaust gas temperature detecting means) 20 Three-way catalyst (combustible substance reaction means) 30a Storage NOx catalyst 40 Electronic control Unit (ECU)

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-10-306717 (JP, A) JP-A-10-30430 (JP, A) International Publication 93/7363 (WO, A1) (58) Fields surveyed (Int.Cl. ⁷ , DB name) F01N 3/08-3/36 B01D 53/86

Claims (1)

(57) [Claims] 1. An occluding type NOx catalyst which is interposed in an exhaust passage and stores NOx when the exhaust passage is in an oxidizing atmosphere and reduces the stored NOx when the exhausting passage is in a reducing atmosphere. When it is necessary to raise the temperature of
A combustible substance increasing means for increasing the amount of combustible material supplied into the exhaust passage; and a combustible substance provided in the exhaust passage upstream of the storage type NOx catalyst for reacting the combustible substance increased by the combustible substance increase means. A substance reacting means, provided in an exhaust passage upstream of the storage NOx catalyst in close proximity to the storage NOx catalyst, and detecting a temperature of exhaust gas flowing into the storage NOx catalyst via the combustible substance reaction means. Exhaust temperature detecting means, and a NOx catalyst temperature for estimating the temperature of the storage NOx catalyst based on the exhaust temperature detected by the exhaust temperature detecting means.
Estimating means, and the catalyst temperature estimated by the NOx catalyst temperature estimating means.
The target temperature of the storage NOx catalyst capable of reducing NOx
The deviation is periodically integrated to increase or decrease the integrated value of the deviation,
In particular for controlling the combustibles increasing unit in response to the integrated value
Temperature of the storage NOx catalyst to the target temperature.
An exhaust gas purification device for an internal combustion engine, comprising: catalyst temperature control means for performing feedback .