JPH07208151A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PURPOSE:To provide an exhaust emission control device of an internal combustion engine which can detect the deterioration of an NOX absorbent accurately depending on the density on the downstream side of the absorbent after reopening the absorption, after the NOX is discharged once. CONSTITUTION:At an exhaust gas passage 17 on the downstream side of an NOX absorbent 18, an NOX sensor 20 to detect the NOX density in the exhaust gas is provided, and it is decided that the NOX absorbent 18 is deteriorated at the time the output of the NOX sensor 20 is raised to a specific value after finishing the regeneration of the NOX absorbent is preliminary decided given time or less.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an air-fuel ratio of the exhaust flowing absorbs NO _X in the exhaust gas when the lean, NO _X absorbent exhaust oxygen concentration to release the absorbed NO _X when lowered The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to an exhaust gas purification device for an internal combustion engine capable of accurately detecting the deterioration of the NO _X absorbent.

[0002]

2. Description of the Related Art NO of this kind_XInternal combustion engine using absorbent
As an exhaust gas purifying apparatus for the above, an international publication WO93-7
There is one described in No. 363. Exhaust gas purification device
Then, when the air-fuel ratio of the inflowing exhaust gas is lean,
NO_XIs absorbed, and the oxygen concentration in the inflowing exhaust gas has decreased.
NO absorbed at times_XReleases NO_XInternal combustion engine with absorbent
Located in the exhaust passage of the Seki
Driving in the above NO_XNO in exhaust gas to absorbent_XAbsorbed
Let Also, NO_XAbsorbent NO_XAs the absorption increases
NO_XAbsorbent NO_XLean because the absorption capacity is reduced
Air-fuel ratio operation continues for a certain time, NO_XAbsorbed of absorbent
NO_XIf the amount increases, change the operating air-fuel ratio of the internal combustion engine.
Switch from lean air-fuel ratio to rich or stoichiometric air-fuel ratio for a short time
By reducing the oxygen concentration in the exhaust gas, NO_XSuck from absorbent
NO collected_XAnd the released N
O_XReduction reduction of unburned HC and CO components in exhaust gas
(In the present specification, the above NO_XAbsorbent
NO from_XThe operation of releasing, reducing, and purifying the_XSucking
It is called "recycling of the collecting agent"). In this way, NO at regular intervals _X
NO by regenerating the absorbent_XAbsorbent NO_X
Absorption capacity is restored and NO_XThe purification ability of the
It

[0003]

As described above, NO _X
The absorbent alternately absorbs, releases, and reduces NO _{x in} the exhaust gas that flows in according to the exhaust air-fuel ratio, and purifies the NO _x in the exhaust gas. However, the above of the NO _X absorbent in some cases deterioration in use to be used in harsh conditions that are exposed to exhaust hot it is disposed in an exhaust passage occurs. For example, deterioration of the catalyst in _the NO _X absorbent as described below (platinum Pt or the like), if due absorbers (e.g. barium oxide BaO, etc.) sulfur poisoning and thermal degradation of the resulting deterioration in the NO _X absorbent, Since the purification capacity of the NO _X absorbent decreases, NO _{X in} the exhaust gas is released to the atmosphere without being purified. For this reason,
_The NO _X absorbent early exchange that has deteriorated to determine the presence or absence of degradation of the NO _X absorbent is required to take measures such as poisoning recovery.

By the way, a three-way catalyst is conventionally known as a device which is arranged in the exhaust passage similarly to the NO _X absorbent and purifies the exhaust gas. Further, since the three-way catalyst also deteriorates during use, various methods for detecting deterioration of the three-way catalyst have been devised. These deterioration detection methods judge the deterioration of the catalyst by detecting a decrease in the O ₂ storage action of the three-way catalyst (for example, Japanese Patent Laid-Open No. 3-331810).
No.).

However, NO_XThe absorbent is N with a three-way catalyst.
O_XThe purification mechanism is different, and like a three-way catalyst
O₂Because it does not have a storage effect,
NO in the same way as deterioration detection_XDetects deterioration of absorbent
I can not do it, NO _XDetects absorbent deterioration
It was difficult. In view of the above problems, the present invention is NO_X
Means that can accurately determine whether or not the absorbent has deteriorated
Is intended to provide.

[0006]

The present invention according to claim 1
According to the inflow is arranged in the exhaust passage of the internal combustion engine
NO when the exhaust air-fuel ratio is lean_XAbsorbs and flows in
NO absorbed when the oxygen concentration in exhaust gas decreases_XEmit
NO to_XAbsorbent and the NO_XExhaust passage on the downstream side of the absorbent
Placed in the road, NO in the exhaust_XNO to detect concentration_XSE
And the NO_XNO absorbed by the absorbent_XEnd the release of
Complete and NO_XNO after resuming absorption _XAbsorbent downstream side
NO_XThe NO based on the temporal change in concentration_XAbsorbent
Internal combustion engine provided with deterioration detecting means for judging presence or absence of deterioration
An exhaust emission control device is provided.

According to the present invention as set forth in claim 2,
The deterioration detecting means, when the NO _X concentration after NO _X absorption resumption of the _the NO _X absorbent is not more than a predetermined time which time is predetermined to be higher than a predetermined value, the NO _X
It is judged that the absorbent has deteriorated. Further, according to the present invention described in claim 3, wherein the deterioration detecting means according to claim 1, comprising means for detecting the NO _X concentration increases the rate of rate of change of the _the NO _X absorbent downstream, the NO _X After resuming absorption, NO _x
It is determined that the NO _X absorbent has deteriorated when the concentration is equal to or higher than a predetermined value and the time until the rate of change in the NO _X concentration increasing rate becomes negative is equal to or less than a predetermined time.

According to the present invention as defined in claim 4,
Disposed in an exhaust passage of an internal combustion engine, air-fuel ratio of the exhaust gas flowing into absorbs NO _X when the lean, the oxygen concentration of the exhaust gas flowing to release NO _X absorbed when reduced NO _X
An absorbent, a downstream NO _x sensor arranged in the exhaust passage downstream of the NO _x absorbent to detect the NO _x concentration in the exhaust, and a NO _x concentration in the exhaust upstream of the NO _x absorbent. an upstream NO _X concentration detecting means for the _the NO _X absorbent is after resuming NO _X absorption end the release of the absorbed NO _{X, the} NO _X absorbent downstream NO _X concentration and _the NO _X absorbent upstream There is provided an exhaust emission control device for an internal combustion engine, comprising: a deterioration detecting unit that determines whether or not the NO _X absorbent is deteriorated based on a temporal change in a relationship with a side NO _X concentration.

Further, in the present invention according to claim 5, the contract
The deterioration detecting means of claim 4 is the upstream NO_XConcentration and
Downstream NO_XA means for calculating the difference from the concentration is provided,
Note NO_XNO after resuming absorption_XConcentration difference is less than the specified value
Is less than or equal to a predetermined time
In case of NO_XIt is judged that the absorbent has deteriorated. Also,
In the present invention according to claim 6, the deterioration detection according to claim 4 is performed.
The means is the downstream NO_XConcentration and the upstream NO_Xconcentration
And a means for calculating the ratio of _XAfter resuming absorption
Said NO_XThe time required for the concentration ratio to reach or exceed the specified value
If the time is less than or equal to the specified time, the NO_Xabsorption
It is determined that the agent has deteriorated.

Further, in the present invention according to claim 7, in the exhaust emission control device according to any one of claims 4 to 6, the upstream side NO _x concentration detecting means is the exhaust gas on the upstream side of the NO _x absorbent. consist NO _X sensor provided in the passage. Further, according to the present invention as set forth in claim 8, in the exhaust gas purification device as set forth in any one of claims 4 to 6,
The upstream NO _X concentration detecting means includes means for detecting an operating condition of the engine, based on the detected operating conditions, and means for calculating the upstream-side NO _X concentration from a predetermined relationship .

[0011]

The operation of the present invention will be described below with reference to FIG.
In Figures 1 (A) to (C), the horizontal axis of each figure represents time,
Fig. 1 (A) shows changes in the air-fuel ratio of the internal combustion engine, and Fig. 1 (B) shows NO.
The concentration of NO _X in the exhaust gas _(the NO _X absorbent upstream exhaust) flowing into the _X absorbent, FIG 1 (C) is NO _X in the exhaust gas passing through the _the NO _X absorbent _(the NO _X absorbent downstream exhaust) The respective concentrations are shown.

FIG. 1 shows the above-mentioned International Publication No. WO93-.
The case where the NO _x absorbent regeneration operation similar to that of the exhaust gas purification device described in No. 7363 is performed is shown. Normally, a lean air-fuel ratio (for example, an air-fuel ratio of about 23) is operated, and the engine air is exhausted for a short period at regular intervals. for reproducing of the NO _X absorbent is switched to fuel ratio to rich (see FIG. 1 (a)). Further, FIG. 1 is for explanation,
It shows the case where the operating conditions are kept constant.

When the air-fuel ratio is changed in this way, FIG.
As shown in (B), NO _X when the exhaust concentration of NO _X absorbent upstream of the engine air-fuel ratio is switched to rich (Figure 1 interval I
Although it increases to I) for a short period of time, it remains almost constant during the period when lean air-fuel ratio operation is being performed. Further, FIG. 1 (C) shows the differences due to the presence or absence of deterioration of the NO _X absorbent downstream side of the exhaust NO _X concentration change of the NO _X absorbent in the case of changing the engine air-fuel ratio as described above, FIG. 1 where the solid line is _the NO _X absorbent is normal (C), the dotted line indicates the case where _the NO _X absorbent is deteriorated, respectively.

NO_XAbsorber has the following mechanism
NO in exhaust gas when exhaust air-fuel ratio is lean_XAbsorbs
When the exhaust air-fuel ratio becomes rich (exhaust oxygen concentration decreases)
NO absorbed_XTo release. Also, NO_XRegeneration of absorbent
(Figure 1 Section II) NO after the end _XNO absorbed by the absorbent
_XNO is released_XAbsorbent NO_XAbsorption capacity
It is getting higher, NO_XNO in the exhaust flowing into the absorbent
_XMost of them are NO_XNO of the exhaust gas on the downstream side absorbed by the absorbent
_XThe concentration (Fig. 1 (C)) is much larger than that on the upstream side (Fig. 1 (B)).
It becomes low.

However, the NO absorbed in the NO _x absorbent
Maximum amount of NO _X can be absorbed in _the NO _X absorbent _X amount is increased because the NO _X absorbing capacity of the NO _X absorbent toward the (saturation amount) is reduced, N out of the NO _X in the exhaust gas flowing
The amount of NO _X that is not absorbed by the O _X absorbent and flows out to the downstream side increases, and after a certain amount of time has elapsed after the end of regeneration, the NO _X concentration in the downstream exhaust gas begins to rise, and the NO _X in the upstream exhaust gas
It becomes asymptotic to the _X concentration.

However, when the NO _x absorbent deteriorates, N
The saturation amount of O _X absorbent is lowered, the absorption capacity of the NO _X absorbent in the low NO _X absorption as compared with the case _the NO _X absorbent is normal will be lowered. Therefore, NO _X
When the absorbent is deteriorated (dotted line in Fig. 1 (C)), it is normal (Fig. 1 (C)).
As compared with the solid line, the time until the NO _x concentration in the downstream side exhaust increases after the regeneration is completed becomes shorter.

The present invention, by detecting the differences in temporal variation of the NO _X concentration downstream in the exhaust with and without deterioration of the _the NO _X absorbent, and performs determination of deterioration of the NO _X absorbent . That is, in the present invention, by disposing the NO _X sensor the NO _X absorbent downstream by the deterioration detection means, NO
Monitoring the change in concentration of NO _{X X} absorbent regeneration (section II) after completion of the _the NO _X absorbent when the NO _X concentration change of the downstream side exhaust showed changes such as the dotted line shown in FIG. 1 (C) Determined as degraded.

Further, as described above, NO in the exhaust gas on the downstream side is_X
The change in concentration became as shown by the dotted line in Fig. 1 (C).
In order to objectively judge that
NO _XNO after regeneration of absorbent (section II)_XUnder absorbent
NO in the exhaust gas on the flow side_XConcentration is a predetermined value (N in Fig. 1 (C))₁) To
Time t to reach₁(Fig. 1 (C)) or playback end
After, NO on the downstream side_XThe rate of change of concentration increase rate changes from positive to negative
Time to reach the changing inflection point (point A in Figure 1 (C))
Interval t₂(Figure 1 (C)) NO_XParameter indicating deterioration of absorbent
Used as a₁Or t₂Is a predetermined group
NO when it is less than the quasi-time_XDetermined that the absorbent has deteriorated
To do.

Further, when the NO _x concentration in the exhaust gas flowing into the NO _x absorbent changes due to changes in operating conditions, etc., NO _x
NO _X in the exhaust gas state is also downstream of the same absorbent
The concentration varies. Therefore, the deterioration of the NO _X absorbent can be determined more accurately by considering not only the change in the NO _X concentration in the exhaust gas on the downstream side of the NO _X absorbent but also the change in the NO _X concentration in the exhaust gas on the upstream side. .

[0020] In the present invention according to claims 4 8, downstream NO _X sensor in addition to _the NO _X absorbent N in the upstream side exhaust
O _X concentration means for detecting provided to detect the deterioration of the NO _X absorbent based on the temporal change in the relationship between the downstream NO _X concentration upstream concentration of NO _X regeneration after the end of the NO _X absorbent.
That is, the absorption capacity of the NO _X absorbent, since represented by it can absorb and how much of the NO _X out of the NO _X in the exhaust gas flowing, the upstream NO _X concentration and the downstream concentration of NO _X after regeneration obtains the absorption capacity of the NO _X absorbent from the temporal change in relationships, and to detect the presence or absence of deterioration of _the NO _X absorbent by time until the absorption capacity of the NO _X absorbent becomes lower than a certain value .

[0021] For example, until the difference between the NO _X concentration and the concentration of NO _X in the downstream exhaust in upstream exhaust becomes a predetermined value or less time, or in the downstream exhaust NO _X concentration and the upstream side in the exhaust the time until the ratio of the NO _X concentration becomes equal to or greater than a predetermined value N
Using as a parameter representing the degradation of O _X absorbent, NO _X absorbent is determined to have deteriorated when this time becomes equal to or less than a predetermined reference time.

[0022] In addition, NO _X absorbent NO _X in the upstream side exhaust
Concentration, that is, the rotational speed of the engine for a concentration of NO _X exhaust gas discharged from the engine, depending on the engine operating conditions such as a load. Therefore, the concentration of NO _X in _the NO _X absorbent upstream exhaust, other detected directly by providing a NO _X sensor the NO _X absorbent upstream exhaust passage, in the exhaust gas in each operating condition of the engine in advance by actual measurement The NO _X concentration can be obtained in advance and indirectly obtained from the operating conditions of the engine.

[0023]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 2 is an overall view of an internal combustion engine to which the exhaust emission control device of the present invention is applied. In FIG. 2, reference numeral 1 is an internal combustion engine such as a gasoline engine that burns at a lean air-fuel ratio, 3 is a combustion chamber of the engine 1, 6 is an intake port of the engine, and 8 is an exhaust port. Each intake port 6 is connected to a surge tank 10 via an intake branch pipe 9, and a fuel injection valve 11 for injecting fuel into each intake port 6 is arranged in each branch pipe 9.

Further, the surge tank 10 is connected to an air cleaner 13 via an intake passage 12, and a throttle valve 14 having an opening degree corresponding to an operation of an accelerator pedal (not shown) by a driver is provided in the intake passage 12. It is arranged. Also,
The surge tank 10 is provided with an intake pressure sensor 15 that generates an output voltage proportional to the absolute pressure in the surge tank 10.

On the other hand, the exhaust port 8 of the engine 1 is connected to an exhaust passage 17 via an exhaust manifold 16, and the exhaust passage 17 is connected to a casing 19 containing a NO _x absorbent 18 described later. Further, reference numeral 20 in FIG. 2 denotes a NO _X sensor provided in the exhaust passage downstream of the NO _X absorbent 18 for detecting the NO _X concentration in the exhaust gas.

Reference numeral 30 in FIG. 2 denotes an electronic control circuit of the engine 1. The electronic control circuit 30 includes a ROM (read only memory) 32, a RAM (random access memory) 3
3, CPU (microprocessor) 34, input port 3
5. A digital computer having a known structure in which the output ports 36 are connected to each other by the bidirectional bus 31.
In addition to performing basic control of the engine such as fuel injection amount control of the engine 1 and ignition timing control, in the present embodiment, it plays a role as deterioration detecting means for detecting deterioration of the NO _X absorbent 18.

For the above purpose, the input port 35 of the control circuit 30 has a voltage signal corresponding to the intake pressure from the intake pressure sensor 15 and the NO _x concentration in the exhaust gas downstream of the NO _x absorbent from the NO _x sensor 20. In addition to the voltage signals representing the respective values being input through the AD converter 37, the engine speed sensor 21 provided in the distributor (not shown) of the engine.
A pulse signal indicating the engine speed is input from.

The output port 36 of the control circuit 30 is
The fuel injection valve 11 is driven through the corresponding drive circuit 38.
Is connected to the ignition plug 4 to control the fuel injection from the fuel injection valve 11 and the ignition timing of the engine. The NO _x absorbent 18 contained in the casing 19 uses, for example, a carrier such as alumina, on which potassium K, sodium Na, lithium Li, an alkali metal such as cesium Cs, barium Ba or calcium Ca. At least one selected from such alkaline earths, lanthanum La, and rare earths such as yttrium Y and a noble metal such as platinum Pt are supported. This NO _X absorbent 18 is NO _X when the air-fuel ratio of the inflowing exhaust gas is lean.
That absorbs NO and releases NO _X when the oxygen concentration decreases
_It absorbs and releases _X.

The above-mentioned exhaust air-fuel ratio is N in this case.
It means the ratio of the total amount of air and the total amount of fuel supplied to the exhaust passage on the upstream side of the O _X absorbent 18, the engine combustion chamber, the intake passage, and the like. Therefore, NO _X absorbent 1
When fuel or air is not supplied to the upstream exhaust passage 8 of No. 8, the exhaust air-fuel ratio becomes equal to the air-fuel ratio of the engine (air-fuel ratio in combustion in the engine combustion chamber).

In this embodiment, an engine that burns lean air-fuel ratio is used, so the exhaust air-fuel ratio during normal operation is lean, and the NO _X absorbent 18 absorbs NO _{X in} the exhaust. Further, when the air-fuel ratio of the engine is switched from the lean air-fuel ratio to the rich or stoichiometric air-fuel ratio and the oxygen concentration in the exhaust gas decreases, the NO _X absorbent 18 releases the absorbed NO _X.

There are some points where the detailed mechanism of this absorption and release action is not clear. However, it is considered that this absorbing / releasing action is performed by the mechanism shown in FIG. Next, regarding this mechanism, platinum P on the carrier
A case of supporting t and barium Ba will be described as an example, but other precious metals, alkali metals, alkaline earth metals,
The same mechanism can be achieved by using rare earths.

That is, when the inflow exhaust becomes considerably lean, the oxygen concentration in the inflow exhaust greatly increases, and as shown in FIG. 3 (A), these oxygen O ₂ are in the form of O ₂ ⁻ or O ^{2 −.} It adheres to the surface of platinum Pt. On the other hand, most of NO _x is discharged from the engine in the form of NO, but NO in the exhaust flowing into the NO _x absorbent reacts with this O ₂ ⁻ or O ^{2 −} on the surface of platinum Pt, It becomes NO ₂ (2NO + O ₂ → 2NO
₂ ). Then, a part of the NO ₂ produced is oxidized on the platinum Pt, absorbed in the absorbent and combined with the barium oxide BaO, and as shown in FIG.
It diffuses into the absorbent in the form of O ₃ ⁻ . NO in this way
_X is absorbed in the NO _X absorbent 18.

[0033] Thus, NO ₂ is produced on the surface of the platinum Pt so long as the oxygen concentration is high in the inflowing exhaust gas, so long as NO ₂ to NO _X absorbing capacity of the absorbent is not saturated is absorbed in the absorbent and nitrate ions NO ₃ ^- is generated. Organization 1
When the air-fuel ratio of is switched to rich or stoichiometric air-fuel ratio,
The oxygen concentration in the inflowing exhaust gas decreases and the amount of NO ₂ produced decreases. Thus the reaction is reverse (NO ₃ ^- → NO ₂₎ proceeds, the nitrate ions NO in absorbent ₃ ^- are released from the absorbent in the form of NO _2.

On the other hand, when unburned HC, CO, and other components are present in the inflowing exhaust gas, these components cause oxygen O ₂ on platinum Pt.
^- or O ^2- reacts with oxidized to consume oxygen on the platinum Pt. In addition, the NO released from the NO _X absorbent 18
₂ is reduced by reacting with HC and CO as shown in FIG. 3 (B). When NO ₂ is no longer present on the surface of platinum Pt in this manner, NO ₂ is released from the absorbent one after another.

That is, HC and CO in the inflowing exhaust gas first react with O ₂ ⁻ or O ²⁻ on platinum Pt immediately to be oxidized, and then O ₂ ⁻ or O ²⁻ on platinum Pt are consumed. If HC and CO still remain, the NO _X released from the absorbent by the HC and CO and the NO _X that flows in with the exhaust gas are reduced. In this embodiment, the control circuit 30 is similar to the WO WO93-7363 described above, the fuel injection when the lean air-fuel ratio operation is NO _X absorption of the NO _X absorbent 18 continues for a predetermined period of time has increased by increasing the amount, NO _X from the _the NO _X absorbent increases unburnt HC, CO components in the exhaust with lowering the oxygen concentration in the exhaust gas by switching the short engine air-fuel ratio to a rich air-fuel ratio Is released and reduction purification is performed.

[0036] However, since _the NO _X absorbent is absorbing and releasing action of degradation to the above of the NO _X in a variety of causes is reduced, so _the amount of NO _X flowing out to _the NO _X absorbent downstream without being purified increases Become. The deterioration of the NO _x absorbent is caused by the platinum P
It is caused by a decrease in catalytic action such as t and a decrease in NO _x absorption capacity of the absorbent BaO and the like. For example, the reduction of the catalytic action of platinum Pt occurs due to thermal deterioration, etc., and when the catalytic action is reduced, the oxidation reaction of NO in the inflowing exhaust gas (2NO + O ₂ → 2N
O ₂ ) decreases and NO ₂ is no longer produced. In this case, since NO is not absorbed by the absorbent BaO as it is, it passes through the NO _X absorbent as it is and flows out to the downstream side. Therefore, if the platinum Pt deteriorates, the NO concentration in the exhaust gas on the downstream side of the NO _x absorbent will increase as compared with the normal case.

Also, a decrease in the absorption capacity of the absorbent BaO is an example.
For example, it is caused by heat deterioration and sulfur poisoning. For example, institution
A small amount of sulfur oxide (SO_X) Is included,
SO in the exhaust_XIs the above NO_XSame mechanism as absorption of
And NO_XNO is absorbed by the absorbent_XAbsorbed in absorbent
SO_XDue to NO_XWhen the sulfur poisoning of the absorbent occurs
There is a match. That is, when the exhaust air-fuel ratio is lean
SO_X(Eg SO ₂) Is oxidized on platinum Pt to give S
O₃ ^-, SO_Four ^-And binds to barium oxide BaO
BaSO_FourTo form. However, BaSO_FourIs a comparison
Is stable, and the crystals tend to become coarse, so once
Once formed, it is difficult to decompose and release. Because of this, it was absorbed
SO_XIs normal NO_XNot released during absorbent regeneration operation
NO_XIt tends to accumulate in the absorbent. in this way
NO_XBaSO in the absorbent_FourNO increases when the amount of
_XThe amount of BaO that can be involved in the absorption of
O _XThe so-called sulfur poisoning that reduces the absorption capacity of
(Or SO_XPoisoning) occurs. Also, NO_X
When the absorbent is used for a long time, the high temperature causes the absorbent BaO itself to
Even if it deteriorates, the absorption capacity is the same as the above sulfur poisoning.
The amount may decrease.

In the case such as NO _X absorbing capacity of the thus _the NO _X absorbent is lowered, the oxidation reaction of NO in the exhaust gas platinum Pt flows if normal _{(2NO + O 2 → 2NO 2} )
Is normally performed, but the NO _X absorbent immediately becomes NO _X.
In saturated will be, the NO ₂ generated in the generated NO ₂ to the platinum Pt to become unable to absorb it to flow out to leave the downstream side is not absorbed by the absorbent, also in this case NO _X
The NO ₂ concentration in the exhaust gas on the downstream side of the absorbent increases.

Therefore, in any case, when the NO _X absorbent deteriorates, the NO _X (NO or NO ₂ ) in the exhaust gas on the downstream side of the NO _X absorbent will increase in a short time after the end of the regeneration. Moreover, the deterioration of the NO _X absorbent can be detected by monitoring the change in the exhaust NO _X concentration downstream of the NO _X absorbent after the regeneration. In this embodiment, NO
_X absorbent 18 NO _X sensor 20 provided on the downstream side exhaust passage
By monitoring the concentration of NO _X in the downstream exhaust, and determine the presence or absence of deterioration of the NO _X absorbent 18.

[0040] NO for detecting the NO _X component concentration in the exhaust gas _X
There are various types of sensors, but in this embodiment,
NO _X component concentration in exhaust gas is detected in real time to detect NO _X
Any type of NO _x sensor capable of generating an electric signal according to the component concentration can be used. The NO _X sensor of this type, for example, a sensor using a N-type oxide semiconductor ceramics titania (titanium oxide) as a main component as the detection element. The semiconductor-type sensor, NO _X in the exhaust gas from a change in electrical resistance caused by trapping electrons element ceramics in NO _X in the exhaust (NO or NO ₂₎ is adsorbed to the sensor surface
Next, the operation of determining the deterioration of the NO _X absorbent 18 using the output of the NO _X sensor 20 will be described.

FIG. 4 shows an example of a flowchart of a NO _x absorbent deterioration determination routine executed by the control circuit 30 at regular intervals. As described above, when the NO _X absorbent deteriorates, the NO _{X in the} exhaust gas on the downstream side is exhausted in a short time after the NO _X absorbent regeneration is completed.
_{The X} concentration will increase. In this embodiment, the presence or absence of deterioration of the NO _X absorbent is determined by the time until the NO _X concentration of the downstream side exhaust rises to a certain level after the end of regeneration.

When the routine starts in FIG. 4,
At step 401, it is judged if the regeneration operation of the NO _X absorbent 18 is currently being executed. If the regeneration operation is currently being executed, the routine proceeds to step 403, where the counter C is cleared and the routine is ended. If the reproduction operation is not being executed in step 401, the process proceeds to step 405 and the value of the counter C is incremented by one. Since this routine is executed at regular time intervals, the value of the counter C is
_The value corresponds to the elapsed time from the end of the regenerating operation of the _X absorbent 18.

[0043] Next, the NO _X sensor 20 in step 407 of the NO _X absorbent 18 downstream exhaust NO _X concentration NR
Is read, and in step 409, the above NO _x concentration NR is read.
Is greater than or equal to a predetermined value N ₁ (see FIG. 1 (C)), and if NR <N ₁ , the routine is ended. If NR ≧ N ₁ in step 409, it is further determined in step 411 whether the value of the counter C is less than or equal to the predetermined value C ₁ .

If C ≦ C _{1 in} step 411, N
The NO _x concentration on the downstream side is N _{1 within a} short time after the regeneration of the O _x absorbent
Since it is considered that the NO _x absorbent has deteriorated, it proceeds to step 413 and sets the value of the alarm flag ALM to 1 and terminates the routine. If C> C ₁ in step 411, the downstream NO _x concentration rises slowly, and it is considered that the NO _x absorbent is functioning normally. Therefore, the value of the alarm flag ALM is left unchanged and the routine is executed. finish.

The value of the alarm flag ALM is set to 1.
When executed, the control circuit 30 separately executes the drawing.
Routines that do not
NO _XThe deterioration of the absorbent is notified. Also shown in FIG.
I haven't done so, but I turned off the main switch to the control circuit 30
A backup RAM that can hold and store
The value of the flag ALM in this backup RAM for reasons
May be stored. The predetermined value N₁Over
And C₁Value is NO_XDepends on the type and size of the absorbent
Therefore, it is preferable to decide by experiment etc.
Yes.

FIG. 5 shows another embodiment of the routine for determining the deterioration of the NO _X absorbent. This routine is also executed by the control circuit 30 at regular intervals. Figure In fourth embodiments, although the downstream NO _X concentration after _the NO _X absorbent playback end has been determined whether the degradation by time to rise to a predetermined value N _{1, the} NO _X absorbent regeneration in this embodiment The deterioration of the NO _X absorbent is determined by detecting the time until the downstream side NO _X concentration increase curve after reaching the inflection point.

As shown in FIG. 1 (C), N
Concentration of NO _X O _X absorbent downstream, begin to rise from a certain point in time, NO _X absorption of the NO _X absorbent becomes asymptotic to a constant value as it approaches saturation. For this reason, the rate of increase of the downstream NO _x concentration after the end of regeneration is high at first and then decreases, so that there is an inflection point (point A in FIG. 1 (C)) on the change curve of the downstream side NO _x concentration. . Therefore, after the playback end in this embodiment, is the increasing speed of the downstream NO _X concentration is negative, and the downstream-side NO _X concentration with time to occurring state is a predetermined value or more, of the NO _X absorbent 18 Whether or not there is deterioration is determined.

In FIG. 5, when the routine is started, steps 501 to 505 are performed in FIG.
The counter C is operated in the same manner as 01 to 403.
Further, in steps 507 to 513, the rate of change of the increasing rate of the downstream NO _X concentration is calculated. In other words, the NO _X sensor 20 in step 507 is NO _X concentration NR loaded, N last time routine executed in step 509
Using the O _X concentration NR _i-1 , the increasing rate DN of the NO _X concentration
R is calculated as DNR = NR-NR _i-1 .

Further, in step 509, step 50
The change rate D2NR of the NO _X concentration increase rate is calculated as D2NR = DNR−DNR _i−1 by using the increase rate DNR calculated in step 7 and the increase rate DNR _i−1 at the time of executing the previous routine, and step 513 Then, the values of NR _i-1 and DNR _i-1 are updated in preparation for the next routine execution. Next, in steps 515 to 519, the NO _x absorbent 1 is calculated from the values of the NO _x concentration NR and the D2NR calculated above.
The presence or absence of deterioration of No. 8 is determined. That is, when the D2NR is zero or negative (step 515) and the NR is equal to or more than the predetermined value N ₁ (step 517), the NO _X absorbent 18 is deteriorated when the elapsed time from the end of regeneration is C ₁ or less. The determination is made, and the alarm flag ALM is set (= 1) in step 521. The other operations are the same as those in FIG. 4, so the description thereof is omitted here.

[0050] In the above embodiment, based only on the downstream NO _X concentration change of the NO _X absorbent after playback NO
Although not detect the presence or absence of degradation of _X absorbent, NO _X concentration of the NO _X absorbent downstream, even in the state of deterioration of the NO _X absorbent is the same, of the exhaust gas flowing to the NO _X absorbent If the NO _X concentration changes, it changes accordingly. That is, due to changes in engine operating conditions, increases or decreases accordingly also concentration of NO _X downstream if increase or decrease concentration of NO _X exhaust gas flowing to the NO _X absorbent. Therefore, N on the downstream side
If the presence or absence of deterioration of the NO _X absorbent is determined based only on the O _X concentration, there is a risk of erroneous determination due to changes in engine operating conditions. Therefore, in the embodiment described below, in addition to the downstream NO _x concentration, the NO _x absorbent upstream NO
_{The X} concentration is also detected, and the presence or absence of deterioration of the NO _X absorbent is determined based on the change in the relationship of these NO _X concentrations.

[0051] Figure 6 shows an example of a configuration of an exhaust purification device which performs _the NO _X absorbent deterioration determination based the NO _X concentration upstream and downstream of _the NO _X absorbent is a view similar to FIG. 2. 6, elements similar to those in FIG. 2 are designated by the same reference numerals. In the embodiment of FIG. 6, the same NO as the downstream NO _X sensor 20 is provided in the exhaust passage on the upstream side of the NO _X absorbent 18.
_The point that the _X sensor 25 is provided is different from the embodiment of FIG. Further, FIG. 7 shows NO _x of the exhaust purification system of FIG.
An example of an absorbent deterioration determination routine is shown. This routine is executed by the control circuit 30 at regular intervals.

In the routine of FIG. 7, NO _X after the end of reproduction is completed.
Based on the time until the difference between the upstream NO _x concentration and the downstream NO _x concentration falls below a predetermined value, the NO _x absorbent 18
The presence or absence of deterioration is determined. Upstream NO _X in _the NO _X absorbent
The difference between the concentration and the downstream-side NO _X concentration, i.e. by monitoring the NO _X concentration difference of the NO _X absorbent upstream and downstream to represent the amount of NO _X which is actually absorbed in the NO _X absorbent,
A change in the absorption capacity of the NO _X absorbent can be detected regardless of fluctuations in the NO _X concentration on the upstream side.

When the routine starts in FIG. 7,
In steps 701 to 705, the counter C is operated in the same manner as in steps 401 to 405 in FIG. Next, at steps 707 and 709, the downstream NO _x sensor 2
0 and the upstream NO _x sensor 25, and the downstream N
The O _X concentration NRD and the upstream NO _X concentration NRU are read, and in step 711, the difference ΔNR between the NRD read in the above and the NRU is calculated.

Next, at step 713, ΔNR is a predetermined value.
ΔNR₁It is determined whether or not the following. ΔNR> ΔNR₁so
If yes, ie downstream NO_XConcentration is upstream NO_XDark
NO if it is sufficiently lower than_XAbsorbency of absorbent 18
Since the power is not yet reduced, the routine ends as it is
To do. On the other hand, ΔNR ≦ ΔNR₁NO if_XSucking
NO of collecting agent 18_XAbsorption capacity has dropped below a specified value
Therefore, in step 715, the value of the counter C is C₁Whether or not
To determine. In step 715, C ≦ C ₁in the case of
Is NO_XThe absorption capacity of the absorbent has deteriorated in a short time.
No, no_XSince it is considered that the absorbent 18 has deteriorated,
Proceed to step 717 and set alarm flag ALM (=
1) Then, the routine ends. The above-mentioned predetermined value ΔNR
₁And C ₁Is NO_XDepending on the type and size of the absorbent
Differently, it is preferable to determine by experiment. Also,
Since the other operations in FIG. 7 are substantially the same as those in the routine in FIG.
Then, the description is omitted.

In the above embodiment, the NO Δ is monitored by monitoring the difference ΔNR between the upstream NO _x concentration and the downstream NO _x concentration.
The absorption capacity of the _X absorbent is determined, but the difference in concentration ΔNR
It is also possible to determine the absorption capacity of the NO _X absorbent using parameters other than. For example, the downstream NO _X concentration N
Ratio of RD and upstream NO _X concentration NRU RNR = NRD /
It is also possible to determine the absorption capacity of the NO _x absorbent by NRU. That is, the concentration ratio RNR is N out of the NO _x in the inflowing exhaust gas that is not absorbed and flows out to the downstream side.
Since it represents the ratio of O _x , when the concentration ratio RNR increases, it means that the absorption capacity of the NO _x absorbent decreases. Therefore, instead of detecting the time until the density difference ΔNR becomes a predetermined value or less, the density ratio RNR is set to a predetermined value RNR.
The presence or absence of deterioration of the NO _X absorbent may be determined by detecting the time until it becomes NR ₁ (for example, about 0.8) or more.

FIG. 8 shows a flowchart of the NO _x absorbent deterioration determination routine based on the concentration ratio RNR. In the routine of FIG. 8, and calculate the ratio RNR of the NO _X concentration of the NO _X absorbent downstream side and upstream side (step 811), RNR predetermined value R
If the elapsed time C from the end of regeneration is equal to or less than the predetermined value C ₀ when NR ₁ or more (step 813) (step 815), it is determined that the NO _x absorbent 18 has deteriorated and the alarm flag ALM is set. Is set (= 1). The other steps of FIG. 8 are substantially the same as those of the routine of FIG. 7, and therefore detailed description thereof is omitted here.

By the way, in the embodiment of FIGS. 6 to 8, NO
Upstream NO _x installed in the upstream exhaust passage of the _X absorbent 18
The sensor 25, the upstream side of the NO _X absorbent 18 NO _X
Although not detect the concentration, upstream concentration of NO _{X the} NO _X absorbent, namely NO _X in the exhaust gas discharged from the engine
The concentration. In addition, NO of exhaust gas discharged from the engine
_{The X} concentration is determined by engine operating conditions such as engine load and intake air amount. Therefore, as described above, the NO _X absorbent 18
It is also possible to the upstream side to calculate the concentration of NO _{X the} NO _X absorbent upstream from the engine operating condition without providing the NO _X sensor 25.

In this case, the NO _x concentration RNU in the exhaust gas of the engine is actually measured under the condition that the engine intake pressure PM (that is, engine load) and the rotational speed N (that is, intake air amount) are changed in advance, and the intake pressure PM The NO _x concentration RNU is stored in the ROM 32 of the control circuit 30 in the form of a numerical table having a format as shown in FIG. 9 as a function of the rotational speed N and NO in step 709 of FIG. 7 and step 809 of FIG. _X sensor 25
Instead of reading the NO _X absorbent 18 upstream NO _X concentration from, the engine intake pressure PM and the engine speed N are read from the intake pressure sensor 15 and the engine speed sensor 21, respectively,
From the numerical table of FIG. 9 stored in the ROM 32, the upstream side N
O _X concentration can be so read the RNU.

As described above, by calculating the NO _X concentration on the upstream side of the NO _X absorbent from the engine operating conditions, the NO _X sensor 25 on the upstream side of the NO _X absorbent is omitted and the apparatus is simplified. It becomes possible.

[0060]

According Effects of the Invention Claims 1 to the present invention described in 3, by monitoring the changes of the NO _X concentration of the NO _X absorbent in the downstream exhaust after reproduction end, which has heretofore been difficult NO
It becomes possible to easily detect the deterioration of the _X absorbent. Further, according to the present invention as set forth in claims 4 to 8, by monitoring the NO _x concentration in the exhaust gas on the upstream side and the downstream side of the NO _x absorbent after completion of regeneration, regardless of changes in engine operating conditions. It is possible to accurately detect the deterioration of the NO _X absorbent.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a method for detecting deterioration of a NO _x absorbent according to the present invention.

FIG. 2 is a schematic diagram of an embodiment of an internal combustion engine to which the exhaust emission control device of the present invention is applied.

FIG. 3 is a diagram illustrating a NO _X absorption / release action of a NO _X absorbent.

FIG. 4 is a flowchart showing an example of an operation of detecting deterioration of the NO _X absorbent of the embodiment of FIG.

5 is a flow chart showing an example of an operation for detecting deterioration of the NO _X absorbent of the embodiment of FIG.

FIG. 6 is a schematic view of another embodiment of an internal combustion engine to which the exhaust emission control device of the present invention is applied.

FIG. 7 is a flow chart showing an example of a deterioration detection operation of the NO _X absorbent of the embodiment of FIG.

8 is a flow chart showing an example of a deterioration detection operation of the NO _X absorbent of the embodiment of FIG.

FIG. 9 is a diagram showing a format of a numerical table representing NO _X concentration in engine exhaust.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 17 ... Exhaust passage 18 ... NO _X absorbent 20, 25 ... NO _X sensor 30 ... Control circuit

Front page continuation (72) Inventor Satoshi Iguchi 1 Toyota-cho, Toyota-shi, Aichi Toyota Automobile Co., Ltd.

Claims (8)

[Claims] 1. A NO disposed in an exhaust passage of an internal combustion engine, which absorbs NO _X when the inflowing exhaust air-fuel ratio is lean, and releases the absorbed NO _X when the inflowing exhaust gas has a reduced oxygen concentration. and _X absorbent, the disposed in an exhaust passage of the NO _X absorbent downstream, the NO _X sensor for detecting the concentration of NO _X in the exhaust gas, to exit the release of the NO _X wherein _the NO _X absorbent has absorbed N
The O _X absorption based on the temporal variation of the NO _X absorbent downstream concentration of NO _X after restarting, the exhaust gas purification apparatus for an internal combustion engine having a determining deterioration detecting means the presence or absence of deterioration of the _the NO _X absorbent . Wherein said deterioration detecting means, wherein, when the NO _X concentration after the NO _X absorbent resumption of the NO _X absorbent is not more than a predetermined time in which the time until the predetermined value or more predetermined said The exhaust emission control device according to claim 1, wherein it is determined that the NO _x absorbent has deteriorated. Wherein said deterioration detecting means, by said comprising means for detecting the rate of increase in the rate of change of the NO _X concentration of the NO _X absorbent downstream, the NO _X concentration after the NO _X absorbent restart is equal to or higher than a predetermined value The exhaust emission control device according to claim 1, wherein when the time until the rate of change of the NO _x concentration increasing rate becomes negative is a predetermined time or less, the NO _x absorbent is determined to have deteriorated. . 4. An NO arranged in an exhaust passage of an internal combustion engine, which absorbs NO _X when the inflowing exhaust air-fuel ratio is lean, and releases the absorbed NO _X when the inflowing exhaust gas has a reduced oxygen concentration. _{An X} absorbent, a downstream NO _X sensor arranged in the exhaust passage downstream of the NO _X absorbent to detect the NO _X concentration in the exhaust, and a NO _X concentration in the exhaust upstream of the NO _X absorbent. an upstream NO _X concentration detecting means for detecting the _the NO _X absorbent is completed the release of the absorbed NO _X N
The O _X absorption based on the temporal change of the relationship between _the NO _X absorbent downstream NO _X concentration and _the NO _X absorbent upstream concentration of NO _X after restarting, determines the presence or absence of deterioration of the _the NO _X absorbent An exhaust gas purification device for an internal combustion engine, comprising: a deterioration detecting means. 5. The deterioration detecting means is configured to provide the upstream NO _x.
And means for calculating the difference between the concentration and the downstream NO _X concentration, the case difference between the NO _X concentration after NO _X absorbent restart is equal to or less than a predetermined time that the time until a predetermined value or less predetermined The exhaust emission control device according to claim 4, wherein it is determined that the NO _x absorbent has deteriorated. 6. The deterioration detecting means is configured to provide the downstream NO _x.
And means for calculating the ratio between the concentration and the upstream-side NO _X concentration, the NO _X when the ratio of the NO _X concentration after absorption restart is equal to or less than a predetermined time which time is predetermined to be greater than a predetermined value The exhaust emission control device according to claim 4, wherein it is determined that the NO _x absorbent has deteriorated. 7. The exhaust emission control device according to claim 4, wherein the upstream NO _x concentration detecting means is a NO _x sensor provided in an exhaust passage upstream of the NO _x absorbent. . 8. The upstream NO _x concentration detecting means detects the operating state of the engine, and calculates the upstream NO _x concentration from a predetermined relationship based on the detected operating state. 7. The method according to claim 4, further comprising:
The exhaust emission control device according to the item.