JPH11229849A - Lean burn internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely reduce the discharge amount of NOx into the atmosphere and to improve fuel consumption by expanding the lean operation range through accurate understanding of the deterioration state of the occlusion type NOx catalyst. SOLUTION: Occlusion type NOx catalyst 6A which occludes NOx in oxidation atmosphere and which discharges NOx in reduction atmosphere is provided in the exhaust passage. Also, a NOx sensor 10 for detecting NOx concentration is provided downstream of the occlusion type NOx catalyst 6A. The atmosphere of the occlusion type NOx catalyst 6A is controllable by atmosphere adjustment means 23. The NOx concentration downstream of the occlusion type NOx catalyst 6A when atmosphere adjustment means 23 adjusts the atmosphere of the occlusion type NOx catalyst 6A to reduction atmosphere is detected by the NOx sensor 10. Then, the deterioration state of the occlusion type NOx catalyst 6A is determined by deterioration determination means 22 based on the output value of the NOx sensor 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine having a lean NOx catalyst and capable of lean combustion, and more particularly to a lean burn internal combustion engine capable of detecting deterioration of the lean NOx catalyst.

[0002]

2. Description of the Related Art At present, a NOx catalyst capable of purifying NOx even in an oxygen-excess atmosphere where oxygen in exhaust gas becomes excessive has been developed. In a lean-burn internal combustion engine, by providing this NOx catalyst, NOx during lean-burn is provided. To purify. As this NOx catalyst, a storage type NOx catalyst (trap type NOx catalyst) for purifying NOx in exhaust gas by storing NOx on the catalyst has been developed. This storage type NOx catalyst oxidizes NO in exhaust gas to generate nitrate in an oxidizing atmosphere, that is, an atmosphere with an excessive oxygen concentration, thereby storing NOx, while reducing the atmosphere, that is, an atmosphere in which the oxygen concentration is reduced. Has a function of reacting nitrate stored in the NOx catalyst with CO in exhaust gas to generate carbonate, thereby releasing and decomposing NOx. Of course, the NOx storage amount of the storage NOx catalyst has a limit. Therefore, for example, at appropriate time intervals, N
By setting the atmosphere around the Ox catalyst as a reducing atmosphere, NOx stored on the catalyst can be released.
As a result, the NOx storage performance of the NOx catalyst can be ensured, and NOx in the exhaust gas can be purified during the lean burn operation.

[0003] The operation of releasing the stored NOx and increasing the NOx storage amount of the storage-type NOx catalyst again is called "revival".

[0004]

Incidentally, a sulfur component (S component) is contained in fuel and lubricating oil, and therefore, such a sulfur component is contained in exhaust gas. The NOx catalyst stores NOx in an oxygen-rich atmosphere during the lean burn operation and also stores such sulfur components. In other words, the sulfur component burns,
is oxidized on x catalyst becomes SO _3. And this SO
A part of ₃ further reacts with the NOx storage agent on the NOx catalyst to form sulfate, and is stored in the NOx catalyst.

Therefore, nitrate and sulfate are stored in the NOx catalyst. Sulfate has a higher stability as a salt than nitrate, and even in an atmosphere in which the oxygen concentration is reduced, this is one of the reasons. NOx
The amount of sulfate remaining on the catalyst increases with time. As a result, the NOx storage capacity of the NOx catalyst decreases with time, and the performance of the NOx catalyst deteriorates. This is called S poisoning.

As described above, if the deteriorated NOx catalyst is continuously used, NOx in the exhaust gas which is not purified is released to the atmosphere as it is. Therefore, the deterioration of the NOx catalyst due to S poisoning or the like is determined, and the deteriorated NOx catalyst is determined.
x It is necessary to take measures such as replacing the catalyst and recovering (regenerating) from S poisoning at an early stage. For this reason, conventionally, a technology has been developed which enables the determination of the deterioration of the NOx catalyst in a lean burn internal combustion engine. For example, Japanese Patent Application Laid-Open No. 7-208151 has a NOx sensor provided downstream of the NOx catalyst. The NOx concentration in the lean burn operation after the release of NOx as an atmosphere with a reduced oxygen concentration is detected and the detected N
There is disclosed a technique for determining deterioration (for example, S poisoning) of a NOx catalyst based on a temporal change of an Ox concentration.

According to this technique, the NOx concentration downstream of the NOx catalyst increases when the NOx catalyst is saturated, and the rate of increase increases as the NOx storage capacity of the NOx catalyst decreases, that is, as the deterioration of the NOx catalyst progresses. The focus is on increasing the size. However, the concentration of NOx released from the NOx catalyst into the atmosphere remains small until the NOx catalyst approaches a saturated state, and changes little, and if the deterioration is determined based on the temporal change in the NOx concentration with such a small amount of change. There is a high risk of erroneous determination. Conversely, when the difference in NOx concentration changes significantly, it is when the NOx catalyst is already near saturation, and in this state, a large amount of NOx is released from the NOx catalyst into the atmosphere. It is possible.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems. By accurately grasping the state of deterioration of a storage-type NOx catalyst, it is possible to reliably reduce the amount of NOx released into the atmosphere and to perform lean operation. It is an object of the present invention to provide a lean-burn internal combustion engine capable of improving fuel efficiency by expanding a range.

[0009]

Therefore, in the lean burn internal combustion engine of the present invention, an NOx storage catalyst is provided in the exhaust passage. This NOx catalyst stores NOx in an oxidizing atmosphere and NOx in a reducing atmosphere. Release. Also,
Nx concentration can be detected downstream of the storage NOx catalyst.
An Ox sensor is provided. The ambient atmosphere of the storage type NOx catalyst can be adjusted by the atmosphere adjusting means, and the storage type NOx catalyst is adjusted by the deterioration determining means based on the NOx sensor output value when the ambient atmosphere of the storage type NOx catalyst is adjusted to the reducing atmosphere. The deterioration state of the NOx catalyst is determined.

This makes it possible to accurately grasp the state of deterioration of the NOx catalyst, thereby making it possible to reliably reduce the amount of NOx released into the atmosphere and to improve fuel efficiency by expanding the lean operation range.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. First, the outline of the configuration of the lean burn internal combustion engine according to one embodiment of the present invention will be described. As shown in FIG. 2, the lean burn internal combustion engine is a four-stroke engine, of a spark ignition type, and It is configured as a direct injection internal combustion engine (direct injection engine) that directly injects fuel into the combustion chamber.

An intake passage 2 and an exhaust passage 3 are connected to the combustion chamber 1 so that they can communicate with each other. The communication between the intake passage 2 and the combustion chamber 1 is controlled by an intake valve 4.
The communication between the exhaust passage 3 and the combustion chamber 1 is controlled by an exhaust valve 5. The intake passage 2 is provided with an air cleaner and a throttle valve (not shown).
The exhaust passage 3 is provided with an exhaust purification device 6 and a muffler (muffler) not shown.

An ignition plug 7 is provided at the upper center of the combustion chamber 1, and an injector 8 is provided at an upper side edge of the combustion chamber 1.
Is provided. This injector (fuel injection valve) 8
Are arranged so that the opening faces the combustion chamber 1. With such a configuration, the air drawn in according to the opening of the throttle valve (not shown) is drawn into the combustion chamber 1 by opening the intake valve 4, and the electronic control unit (ECU) 20
Is mixed with the fuel directly injected from the injector 8 based on the signal from the injector 8. Then, the fuel is burned by ignition of the spark plug 7 at an appropriate timing to generate an engine torque, and then discharged from the combustion chamber 1 to the exhaust passage 3 as exhaust gas. CO, HC, since the purifying three harmful components NO _x, are muted in the muffler so desorbed to the atmosphere side.

This exhaust gas purifying device 6 is a storage type NO_xcatalyst
(Hereinafter simply referred to as NO_x6A and three-way catalyst 6B
Are combined. In other words, the air-fuel ratio is
Exhaust gas contains almost no CO or HC
NO_xAlthough the concentration rapidly increases, this NO_xTo
NO that functions in an oxidizing atmosphere (ie, an oxygen-excess atmosphere) _x
Occluded by the catalyst 6A, the three-way catalyst 6B
CO, HC, NO in exhaust gas by the three-way function_xPurify
It is becoming to be.

By the way, when the NO _x catalyst 6A continues to store NO _x , it eventually reaches a saturated state, and NO _x that can no longer be stored is released into the atmosphere. Therefore, when the NO _x catalyst 6A has reached saturation, it is necessary to'll releasing occluded NO _x once, release of the NO _x is the surrounding atmosphere reducing atmosphere of the NO _x catalyst 6A (i.e., oxygen (Insufficient state), the stored NO _x is desorbed as NO ₂ ,
NO ₂ is reduced by supplying C and CO (reducing agent) to N ₂
The discharge is carried out as follows.

Here, the NO in the lean burn internal combustion engine
The release of NO _x from the _x catalyst 6A will be described in more detail. In a direct injection engine such as the present lean-burn internal combustion engine, as a mode of fuel injection, a late injection mode in which fuel is injected during a compression stroke in order to realize lean operation by the above-described stratified super-lean combustion and improve fuel efficiency. , Realizing lean operation by premixed combustion and achieving fuel injection during the intake stroke in order to obtain output by gentle acceleration, and stoichiometric operation by premixed combustion to achieve higher output than the previous injection mode For this purpose, a stoichiometric mode in which fuel is injected during the intake stroke and an enriched mode in which rich operation by premixed combustion is realized and the output is improved from the stoichiometric operation mode are provided, and are switched according to the operating state of the engine. It is supposed to be.

[0017] Then, under the lean operation as described above, NO _x since the periphery of the catalyst 6A is in the oxidizing atmosphere, NO produced by lean combustion in the NO _x catalyst 6A _x
Although but will be occluded, thus it occluded NOx is released in a reducing atmosphere, because it is decomposed, in order to release the NOx stored in the NO _x catalyst 6A, atmosphere adjuster 23 for the exhaust passage to a reducing atmosphere Is provided. The atmosphere adjusting means 23 is configured to create a reducing atmosphere by using fuel injection control.

That is, the ECU 20 of the lean-burn internal combustion engine according to the present embodiment is provided with a mode selecting means 24 and a fuel injection control means 25, as shown in the functional block diagram of FIG. The mode selecting means 24 selects one of the above modes according to the engine speed Ne and the average effective pressure Pe.

The fuel injection control means 25 includes a normal fuel injection control means 26 for injecting fuel to perform normal combustion for obtaining an engine output, and an additional fuel injection control means 27 for creating a reducing atmosphere. Is provided.
The normal fuel injection control means 26 selects a fuel injection control map corresponding to the mode set by the mode selection means 24 and uses the selected fuel injection control map to determine the engine speed Ne and the average effective pressure Pe. Accordingly, the fuel injection amount and the injection timing for performing the normal combustion (that is, the fuel injection end timing and the fuel injection start timing) are set.

The detection information (or calculation information) of the engine speed sensor 13 is used for the engine speed Ne, and the calculation information of the effective pressure calculation means 28 is used for the average effective pressure Pe. In the effective pressure calculating means 28, the engine speed Ne and the accelerator position sensor (AP
S) The average effective pressure Pe is calculated from each information of the accelerator opening θ detected in 14.

The additional fuel injection control means 27 controls the fuel injection performed for restoring and regenerating the NOx catalyst 6A. This additional fuel injection is based on HC, C
Additional fuel injection is performed during the expansion stroke of each cylinder (preferably a timing close to the end of the expansion stroke is also preferable) in consideration of securing O and the effect on the output torque of the engine.

The restoration of the NOx catalyst 6A means that the NOx
By releasing the NOx stored in the catalyst 6A, NO
This is a process for ensuring the NOx occlusion performance of the x catalyst 6A (this process is referred to as restoration control).
The regeneration of A is a process for releasing the SOx stored in the NOx catalyst 6A to improve again the NOx storage performance reduced (deteriorated) by the NOx catalyst 6A storing the SOx (this process). Is called playback control).

Therefore, the additional fuel injection performed under the control of the additional fuel injection control means 27 is performed by the NOx catalyst 6A.
And additional fuel injection for regeneration of the NOx catalyst 6A (this is referred to as regeneration additional fuel injection). Although details will be described later, in the reuse additional fuel injection, the surroundings of the NOx catalyst 6A are reduced in oxygen concentration by the additional fuel injection, that is, the NOx catalyst 6A is set to a reducing atmosphere.
In the additional fuel injection for regeneration, the surroundings of the NOx catalyst 6A are heated to a high temperature equal to or higher than a predetermined temperature and the oxygen concentration is reduced by the additional fuel injection, that is, the NOx catalyst 6A is turned into a reducing atmosphere. It is designed to promote SOx release.

In order to regenerate and regenerate the NOx catalyst 6A, the atmosphere around the catalyst is changed to a reducing atmosphere.
A method of enriching the air-fuel ratio in normal fuel injection without using additional fuel injection may be used. In addition, as a method of raising the atmosphere around the catalyst to a high temperature equal to or higher than the predetermined temperature for regeneration of the NOx catalyst 6A, a method of retarding the ignition timing in normal fuel injection may be used.

The atmosphere adjusting means 23 has a function of bringing the surroundings of the NOx catalyst 6A into a reducing atmosphere (a state in which the oxygen concentration is reduced) by such additional fuel injection. The additional fuel injection control means 27 and the additional fuel injection Injector (fuel injection valve) 8 driven by an injector driver (not shown) under the control of control means 27 to perform additional fuel injection
It is composed of

The recycle additional fuel injection is performed based on the determination of the rejuvenation control determining means 21, and the regeneration additional fuel injection is performed by the regeneration control determining means 2 as a deterioration determining means.
2 is performed based on the determination. The rejuvenation control determining means 21 performs operation in a lean mode such as an intake lean mode or a compression lean mode for a predetermined time (for example, about 6
(0 seconds). For this reason, the count value of the timer 12 is read into the recovery control determination means 21.

The operation in the lean mode is performed for a predetermined time (for example, about 6
(0 seconds), it is determined that the resurrection control needs to be performed, and a control signal relating to the recycle additional fuel injection is output to the additional fuel injection control means 27. Reproduction control determining means (deterioration determining means) 22
Is to determine whether it is necessary to perform playback control,
This is for determining the deterioration of the NOx catalyst 6A. Although the details of the deterioration determination will be described later, when the regeneration control determining means (deterioration determining means) 22 determines that the NOx catalyst is deteriorated, it is necessary to perform the regeneration control. A control signal relating to the additional fuel injection is output to the additional fuel injection control means 27.

By the way, the above-mentioned resurrection control is performed by:
When an operation is performed in a lean mode such as the intake lean mode or the compression lean mode, the vicinity of the NOx catalyst 6A becomes an oxygen-excess atmosphere, and the NOx storage reaction proceeds, so that these lean modes are performed for a predetermined time (for example, about 60 seconds). If the above operation is performed, a large amount of NOx will be stored in the NOx catalyst 6A, and the NOx purification efficiency of the NOx catalyst 6A will gradually decrease.

Accordingly, in the resurrection control, the lean mode is set for a predetermined time (for example, about 60
Second), the additional fuel injection is performed such that the vicinity of the NOx catalyst 6A becomes a reducing atmosphere with a reduced oxygen concentration. In this additional fuel injection, the air-fuel ratio is slightly higher than the stoichiometric air-fuel ratio. By performing fuel injection for a short time (for example, about 2 seconds) so as to be small (for example, about 13), a reducing atmosphere is set in the exhaust passage.

Further, the above-mentioned regeneration control is performed even if the reactivation control of the NOx catalyst 6A is performed every predetermined time (for example, about 60 seconds), if the atmosphere near the NOx catalyst 6A becomes an oxygen-excessive atmosphere, For example, SOx
Is gradually stored, and even if the oxygen concentration in the vicinity of the NOx catalyst 6A decreases and the exhaust air-fuel ratio becomes a reducing atmosphere, this SOx is still stored in the NOx catalyst 6A. N by the NOx catalyst 6A only for the storage amount
This is because there are deterioration factors that cannot be removed by the restoration control, such as a decrease in the purification ability of Ox (S poisoning).

Therefore, in the regeneration control, if the regeneration control determining means (deterioration determining means) 22 determines that the NOx catalyst 6A has deteriorated, the atmosphere near the NOx catalyst 6A (for example, A / F = about 12), and additional fuel injection is performed for a predetermined time (for example, about 3 minutes) so as to be equal to or higher than a predetermined temperature (for example, about 600 ° C.).

Incidentally, in the deterioration determining means 22, NOx
Sensor 10, NOx catalyst temperature sensor (high temperature sensor) 1
1, engine speed sensor 13, effective pressure calculating means 28
The deterioration of the NOx catalyst 6A is determined while evaluating the NOx concentration α obtained during the period of performing the additional fuel injection for the recovery control based on the information from the above.

That is, as shown in FIG. 3, when the start signal of the additional fuel injection for reuse is input (time t ₀ ), the deterioration determining means 22 starts counting of the timer 12 and
The NOx concentration α input from the NOx sensor 10 is sampled at a predetermined cycle from the time (time t ₁ ) after the lapse of a predetermined time tt ₀₁ from the input of the recovery control signal (time t ₀ ). Then, the time tt from the start of sampling (time t ₁ )
At the time when _{12 has} elapsed (time t ₂ ), sampling is completed,
The average value β of each sampled NOx concentration is calculated.

However, this average value β is averaged for each sampled NOx concentration and appropriately corrected in order to more accurately estimate the amount of NOx released from the NOx catalyst 6A. That is, the NOx concentration α detected by the NOx sensor 10 is determined by the amount of N released from the NOx catalyst 6A.
Since it contains not only the Ox concentration but also the NOx concentration α ₀ discharged from the engine body during the resurrection control, the latter NOx concentration
The concentration α ₀ is measured in advance, and is divided from the average of each sampled NOx concentration.

Further, in order to correct individual variations and changes over time of the NOx sensor 10 itself, the NOx sensor output value and the NOx sensor
The difference from the x concentration, that is, the correction amount, is obtained, and is divided from the average value of each sampled NOx concentration. By making an appropriate correction in this way, the average value β of the concentration of only NOx released from the NOx catalyst 6A is calculated.

This average value β is the value of NOx for restoring the catalyst.
NOx released from NOx catalyst 6A in release process
It is an evaluation value of the concentration.
x The amount of NOx released from the catalyst 6A is also small, that is, N
It is estimated that the amount of SOx stored in the Ox catalyst 6A is large. Then, the average value (hereinafter referred to as an evaluation value) β is compared with a predetermined reference value β _0, and if β ≦ β ₀ , it can be determined that the battery has deteriorated.

The above-mentioned time t ₀₁ is a time until the NOx concentration α becomes a stable state, and a time tt ₁₂ is a sufficient sampling time for accurately evaluating the concentration of NOx released from the NOx catalyst 6A. It is time to take numbers. Also,
The judgment reference value β ₀ is stored in the deterioration judgment means 22 in advance. By the way, in order to properly evaluate the NOx concentration during the restoration control, various conditions are required. Therefore, the deterioration determining means 22 determines that the NOx catalyst 6A is deteriorated when various conditions are satisfied, including the evaluation of the NOx concentration.

That is, the deterioration determining means 22 determines that the NOx catalyst 6A is deteriorated when all of the following conditions are satisfied. First, the first condition is that the effective pressure Pe input from the effective pressure calculating means 24 and the engine speed Ne input from the speed sensor 15 are determined for a predetermined time during the additional fuel injection control process for NOx release. During tt _a (sampling time tt ₁₂ or more), it is substantially constant (that is, the fluctuation of the effective pressure Pe is within a predetermined value and the engine speed N
e is within a predetermined range).

As described above, in order to accurately evaluate the concentration α of NOx released from the NOx catalyst 6A, it is necessary to take a sufficient sample of the NOx concentration α.
Since it changes the load conditions and the rotational speed condition of the engine, in order to evaluate the NOx concentration α is the inside of at least a sampling time tt ₁₂ load state and the rotational speed condition of the engine is required to be constant. In the present embodiment, the effective pressure Pe is used as the load state of the engine.
The precondition is that the effective pressure Pe and the engine speed Ne are substantially constant (that is, each fluctuation range is within a predetermined value).

Next, the second condition is that the evaluation value β is equal to the judgment reference value.
β₀It is as follows. That is, the NOx catalyst 6A
If it has deteriorated, it is possible to store enough NOx
Since it is not possible, the evaluation value (NOx concentration average
Value) β is the judgment reference value β ₀It should drop below. This
Therefore, the evaluation value β is₀Less than
It is a condition for conversion.

The third condition is that the catalyst temperature θ _CC detected by the high temperature sensor 11 is within a predetermined temperature range in which the NOx catalyst 6A functions effectively. This is to confirm that the NOx catalyst 6A is functioning effectively. The fourth condition is that the high temperature sensor 11 is normal, and the fifth condition is that the NOx sensor 10 is normal.

The sixth condition is that the above-mentioned first to fifth conditions are continuously satisfied for a predetermined number of times n ₀ or more. This is to prevent erroneous determination when the second condition is accidentally satisfied, and to prevent the driver from feeling uncomfortable due to fuel consumption deterioration due to useless additional fuel injection and output torque fluctuation. When all of the above first to sixth conditions are satisfied, the deterioration determining means 22 determines that the NOx catalyst 6A is deteriorated. Then, the deterioration determining means 22
Releases SOx and the like stored in the NOx catalyst 6A,
In order to recover the NOx storage capacity of the Ox catalyst 6A, that is, perform the regeneration process of the NOx catalyst 6A, the additional fuel injection control means 2
7, a signal (additional fuel injection signal for regeneration processing) is sent.

The lean-burn internal combustion engine according to one embodiment of the present invention is configured as described above.
As shown in the flowchart, the deterioration determination of the NOx catalyst 6A and the regeneration process at the time of deterioration are performed. First, the revival control determination means 21 obtains the operating time in the lean mode from the count information of the timer 12, and when the lean operating time reaches a predetermined time (for example, 60 seconds), it is necessary to release NOx from the NOx catalyst 6A. Is determined. In the additional fuel injection control means 27, the NOx catalyst 6A
Then, additional fuel injection control for releasing NOx is performed (step S10).

The additional fuel injection from the injector 8 by the additional fuel injection control is continuously performed for a predetermined time (for example, about 2 seconds). The deterioration determining means 22 determines the predetermined time tt _a during the additional fuel injection and the effective pressure. It is determined whether the effective pressure Pe input from the calculating means 28 and the engine speed Ne input from the speed sensor 13 are substantially constant (first condition, step S20).

In step S20, a predetermined time tt _a ,
If the combustion pressure Pe and the engine speed Ne was almost constant, further, the deterioration determining unit 22, from the time when the start of the additional fuel injection a predetermined time tt ₀₁ elapses, the predetermined time period
NOx concentration α input from NOx sensor 10 during tt ₁₂
Are sampled at a predetermined cycle. As a result, an average value β of the sampled NOx concentration α is calculated, and this average value (evaluation value) β is compared with a determination reference value β ₀ . The determination reference value β ₀ is set by referring to a correspondence map stored in advance so as to correspond to the effective pressure Pe and the engine speed Ne (second condition, above, step S30).

When the evaluation value β becomes equal to or less than the judgment reference value β ₀ , it is possible to judge that the NOx catalyst 6A has deteriorated beyond the reference value. Whether it is correct or not from step S40 to step S80
Confirmation is made in the processing of. First, in step S40, the catalyst temperature θ _CC detected by the high temperature sensor 11 is NO.
x It is determined whether or not the temperature is within a predetermined temperature range in which the catalyst 6A functions effectively (third condition).

In step S50, it is determined whether the high temperature sensor 11 is normal (fourth condition), and in step S60, it is determined whether the NOx sensor 10 is normal (fifth condition). When any of the conditions from step S40 to step S60 is satisfied, 1 is added to the number n of times the condition is satisfied (step S70), and the number n of times that the condition is satisfied becomes the predetermined number n.
_It is determined whether or not ₀ has been reached (sixth condition, step S8
0).

[0048] Then, when the condition satisfaction count n has reached a predetermined number n _0, i.e., condition 1 to consecutively a predetermined number of times n ₀
6 is satisfied, the deterioration determining means 22 determines that the NOx catalyst 6A has truly deteriorated beyond the reference value, and NO
It is determined that additional fuel injection is required to release SOx and the like stored in the x catalyst 6A. Additional fuel injection control means 27
Then, the NOx catalyst 6A
An additional fuel injection control for discharging SOx and the like from the fuel cell is performed, and an additional fuel injection for releasing the SOx and the like is performed from the injector 8 for a predetermined time.

The additional fuel injection for the SOx such release, as in the case revival control, although the fuel injection for ordinary combustion is injected separate additional fuel, further NO _X catalyst than when revived control The vicinity of 6A is set to a rich atmosphere (for example, A / F = about 12) in which the oxygen concentration is reduced, and a predetermined time (for example, about 3 minutes) is added so that the temperature becomes higher than a predetermined temperature (for example, about 600 ° C.). Fuel injection is performed. As a result, SOx and the like are released from the NOx catalyst 6A, and the regeneration process of the NOx catalyst 6A is performed (step S9).
0).

After the regeneration process of the NOx catalyst 6A is completed, the number n of satisfied conditions is reset to 0 (step S10).
0), preparing for the next regeneration process of the NOx catalyst 6A. Note that, in step S80, if the condition satisfaction count n has not reached the predetermined number of times n _0, returns to leave the step S10 to hold the condition satisfaction count n, that the additional fuel injection for the next of the NO _x emission is performed Wait and step S20 again
It is determined whether the conditions from Step S60 to Step S60 are satisfied.

If the conditions are not satisfied in steps S20 to S60, the NOx
Assuming that SOx or the like is not occluded enough to perform the regeneration process of the catalyst 6A or that the sensors 10 and 11 are abnormal, the number n of satisfied conditions is reset to 0 (step S1).
10) A determination process as to whether or not to perform the regeneration process of the NOx catalyst 6A is performed again.

As described above, according to the lean burn internal combustion engine, the deterioration state of the NOx catalyst is determined based on the level of the NOx concentration during the reactivation control by the additional fuel injection.
Since the difference in NOx concentration during the restoration control is larger than the difference in NOx concentration during lean operation,
There is an advantage that the deterioration state of the catalyst can be accurately grasped without erroneous determination.

As a result, it is possible to reliably reduce the amount of NOx released into the atmosphere, to prevent erroneous determinations and to reduce fuel consumption due to unnecessary additional fuel injection based on the lack of determination criteria, and to achieve lean operation. There is an advantage that fuel economy can be improved by expanding the area. In this embodiment, the NOx concentration α for the deterioration determination is sampled during the recovery control time. However, when the NOx concentration α for the deterioration determination is sampled, the sampling is performed more than during the recovery control. The fuel injection time may be set longer so that a sufficient number of samplings can be taken to accurately evaluate the concentration of NOx released from the NOx catalyst 6A.

As the conditions for determining the deterioration of the NOx catalyst 6A, the following conditions may be added to the above-described first to sixth conditions as a seventh condition. That is, the fuel integrated value in the lean mode after the previous regeneration process of the NOx catalyst 6A becomes the predetermined value X
That is the seventh condition. However, the predetermined value X is the fuel integration in the lean mode at the time when it is determined that the NOx catalyst has deteriorated when the fuel with the largest sulfur content is used for the lower limit product of the NOx catalyst variation. Value.

The integrated fuel value can be calculated from the integrated value of the driving time of the injector 8, and the fuel integrated value in the lean mode can be calculated in combination with the mode determination by the ECU 20. Note that NOx
The fuel integrated value is reset when the catalyst 6A is regenerated, and the fuel integrated value is backed up by a battery when the engine is stopped.

By adding the seventh condition, the NOx catalyst 6
A further improvement in the accuracy of the deterioration determination of A can be expected. Further, with respect to the above first to seventh conditions, the following condition
It may be added as an R condition. That is, when the fuel integrated value when operating in the lean mode becomes equal to or more than the predetermined value Y (Y ≧ X) from the previous NOx catalyst 6A regeneration process,
It is determined that the NOx catalyst 6A has deteriorated irrespective of whether the first to seventh conditions are satisfied, and the regeneration process of the NOx catalyst 6A is performed. However, this predetermined value Y is the fuel in the lean mode at the time when it is determined that the NOx catalyst has deteriorated when the fuel with the lowest sulfur content that is assumed to be used for the upper limit product of the NOx catalyst variation is used. It is an integrated value.

This condition is usually the first to seventh conditions described above.
The regeneration process of the NOx catalyst 6A is performed when the conditions are satisfied. For example, if an abnormality occurs in the NOx sensor 10 or the high temperature sensor 11, all the conditions are not satisfied no matter how long, and the regeneration of the NOx catalyst 6A is performed. This is to prevent a situation in which NOx is released into the atmosphere without processing.

That is, by adding the above conditions as OR conditions to the first to seventh conditions, the regeneration process of the NOx catalyst 6A is forcibly performed when the integrated fuel value when operating in the lean mode exceeds the predetermined value Y. It is intended to be performed on a regular basis. Further, by setting the predetermined value Y as described above, it is possible to avoid a problem that the deterioration is determined even though the deterioration has not yet occurred.

Since some NOx catalysts occlude NOx not only in the oxidizing atmosphere but also in the vicinity of the stoichiometric atmosphere, the above-mentioned integrated fuel value is only the integrated fuel value when operating in the lean mode. Alternatively, the integrated fuel value when operating in the stoichiometric mode may be added. At this time, the integrated fuel value when operating in the stoichiometric mode may have a predetermined coefficient a (0 <a <1). May be applied. This makes it possible to more accurately determine the degree of deterioration of the NOx catalyst 6A. Further, the degree of deterioration of the NOx catalyst 6A may be determined based on the traveling distance in each mode instead of the integrated fuel value.

In this embodiment, the judgment reference value β₀To
Determined by effective pressure (load information) Pe and engine speed Ne
Is set based on a map
(No SOx or the like is stored in the NOx catalyst 6A)
Evaluation value β calculated by the deterioration determining means 22 in the state
Multiplied by a predetermined deterioration coefficient b (b <1)
Value β₀And the effective pressure Pe and the engine speed N at that time
e and store it in a separate storage means
Is also good. Then, when determining whether the second condition is satisfied or not,
Corresponding to the input effective pressure Pe and the engine speed Ne
Criterion value β ₀From the storage means, and the evaluation value β and
You may make it compare.

Further, in the present embodiment, the revival control determining means 21 determines the revival based on the integrated value of the lean operation time (N
However, the restoration determination (estimation of the NOx storage amount) is not limited to this. The NOx concentration during the lean operation is detected by the NOx sensor 10, and the detected NOx concentration is determined to be high. The configuration may be such that the amount of NOx stored in the NOx catalyst 6A is estimated based on the degree of pod rise. Further, the configuration may be such that the estimation is performed based on an integrated value of the injector driving time during the lean operation or the like.

In this embodiment, the NOx sensor 10
The concentration of NOx in exhaust gas is detected by
While performing the deterioration determination of the NOx catalyst 6A based on the concentration, by catalytic some cases part of the NOx released from the NOx catalyst in a reducing atmosphere is NH ₃ by the reaction on the catalyst. Since this NH ₃ is obtained by changing the NOx originally stored in the NOx catalyst, the NH ₃ concentration can also be detected and used for the deterioration judgment.

[0063] In this case, if the NOx sensor is intended to detect NH ₃ concentration in addition to the NOx concentration, the NOx sensor output value is output as the sum of both may be performed deterioration determination based. Conversely, if the NOx sensor
x If only the concentration is to be detected, a new NH ₃
A sensor is provided to detect the concentration of NH _{3 in} the exhaust gas,
The deterioration determination may be performed based on both the sensor output value and the NH ₃ sensor output value. Further, the deterioration determination of the NOx catalyst 6A may be performed only by the NH ₃ sensor.

In this embodiment, the case of the direct injection engine, which is one of the lean burn internal combustion engines, has been described. However, the lean burn internal combustion engine of the present invention is not limited to this direct injection engine. Any internal combustion engine capable of lean combustion may be used.

[0065]

As described above in detail, according to the lean burn internal combustion engine of the present invention, the determination of the deterioration of the NOx catalyst is made by the storage type N.
NO when the surrounding atmosphere of the Ox catalyst becomes a reducing atmosphere
Although the determination is made based on the output value of the x sensor, the difference between the NOx sensor output value and the catalyst deterioration during the lean atmosphere is the difference between the NOx sensor output value and the catalyst deterioration during the lean burn operation. Because the difference is larger than
The state of deterioration of the NOx catalyst can be accurately grasped without erroneous determination, the amount of NOx released into the atmosphere can be reliably reduced, and the fuel efficiency can be improved by expanding the lean operation region.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing a main configuration of a control system for additional fuel injection control of a lean burn internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a configuration of a lean burn internal combustion engine according to one embodiment of the present invention.

FIG. 3 is a diagram showing a NO for determining the start of a NOx catalyst regeneration process.
FIG. 7 is a diagram for explaining detection timing of x density.

FIG. 4 is a flowchart showing a flow of a regeneration process of the NOx catalyst of the lean burn internal combustion engine according to one embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 3 exhaust passage 6 exhaust gas purification device 6A NOx catalyst 6B three-way catalyst 8 injection (fuel injection valve) 10 NOx sensor 20 ECU 21 restoration control determination means 22 regeneration control determination means (deterioration determination means) 23 atmosphere adjustment means 25 fuel injection Control means 27 Additional fuel injection control means

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI F02D 41/02 301 F02D 41/02 301A

Claims (1)

[Claims] 1. An internal combustion engine capable of lean combustion in an exhaust passage having an oxidizing atmosphere, provided in the exhaust passage for storing NOx in an oxidizing atmosphere and releasing NOx in a reducing atmosphere. A NOx sensor provided downstream of the NOx storage catalyst for detecting NOx concentration; atmosphere adjusting means for adjusting the ambient atmosphere of the NOx storage catalyst; and the atmosphere adjusting means reducing the ambient atmosphere of the NOx storage catalyst. A lean-burn internal combustion engine comprising: a deterioration determining means for determining a deterioration state of the storage-type NOx catalyst based on an output value of the NOx sensor when the atmosphere is set.