JP2888124B2 - Exhaust gas purification device for internal combustion engine - Google Patents

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 It relates to an exhaust purification system of an internal combustion engine with, an exhaust purifying apparatus for an internal combustion engine that can accurately detect the deterioration of the _the NO _X absorbent in detail.

[0002]

2. Description of the Related Art This type of NO_XInternal combustion engine using absorbent
International Patent Publication No. WO93-7
No. 363. The above exhaust gas purification device
Then, when the air-fuel ratio of the inflowing exhaust is lean,
NO_XAbsorbed, and the oxygen concentration in the inflowing exhaust decreased.
NO absorbed sometimes_XReleases NO_XInternal combustion engine with absorbent
Located in the exhaust passage of
Driving with the above NO_XNO in exhaust gas_XAbsorbed
Let NO_XAbsorbent NO_XAs the absorption increases
NO_XAbsorbent NO_XLean due to reduced absorption capacity
If the air-fuel ratio operation continues for a certain period of time and NO_XAbsorbent absorbed
NO_XIf the amount increases, the operating air-fuel ratio of the internal combustion engine
Switch from short lean air-fuel ratio to rich or stoichiometric air-fuel ratio
Lower the oxygen concentration in the exhaust_XAbsorb from absorbent
NO collected_XAnd the released N
O_XPurification by unburned HC and CO in exhaust gas
(In this specification, the above NO_XAbsorbent
NO from_XThe operation of release, reduction, and purification of_XSucking
Regeneration of the sorbent "). In this way, NO _X
By regenerating the absorbent, NO_XAbsorbent NO_X
NO absorption capacity recovers_XPurification capacity is maintained high
You.

[0003]

SUMMARY OF THE INVENTION As described above, NO _x
Absorbent release the absorbed of the NO _X in the exhaust gas flowing in accordance with the exhaust air-fuel ratio, performs reduction alternately, to purify 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 ability of the NO _X absorbent is reduced, NO _{X in} the exhaust gas is released to the atmosphere without purification. 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.

Meanwhile, disposed in the exhaust passage as well as _the NO _X absorbent, it is the three-way catalyst is known conventionally as for purifying similarly exhaust. In addition, since the three-way catalyst also deteriorates during use, various methods for detecting the deterioration of the three-way catalyst have been devised. In these deterioration detection methods, deterioration of the catalyst is determined by detecting a decrease in the O ₂ storage function of the three-way catalyst (for example, see Japanese Unexamined Patent Publication No. 3-331810).
No.).

However, NO_XThe absorbent is a three-way catalyst and N
O_XPurification mechanism is different
Na_TwoBecause it does not have a storage effect,
NO in the same method as the deterioration detection_XDetects absorbent degradation
Can't be _XDetecting absorbent degradation
It was difficult. In view of the above problems, the present invention_X
Means that can accurately determine the presence or absence of deterioration of the absorbent
It is intended to provide.

[0006]

The present invention according to claim 1 is provided.
According to the inflow arranged in the exhaust passage of the internal combustion engine
NO when exhaust air-fuel ratio is lean_XAbsorbs and flows in
NO absorbed when oxygen concentration in exhaust gas decreased_XRelease
NO_XAbsorbent and the NO_XExhaust air downstream of the absorbent
NO on exhaust_XNO for detecting concentration_XC
Sensor and the NO_XNO absorbed by the absorbent_XEnd release of
NO_XNO after resuming absorption _XDownstream of absorbent
NO_XThe NO based on the temporal change of the concentration_XAbsorbent
Internal combustion engine provided with deterioration detecting means for determining the presence or absence of deterioration
Is provided.

Further, 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 determined 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 the absorption restarts, the NO _X
Determines that concentration is less than the predetermined value, and wherein _the NO _X absorbent when the time until NO _X concentration increases speed variation rate is negative is equal to or less than a predetermined time a predetermined deteriorates.

Further, according to the present invention described 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
And absorbent, said _the NO _X absorbent disposed in the exhaust passage downstream, and the downstream-side NO _X sensor for detecting the concentration of NO _X in the exhaust gas, detecting the concentration of NO _X in the exhaust gas of the _the NO _X absorbent upstream 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 exhaust 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 based on the temporal change in the relationship between the side NO _X concentration is provided.

Further, according to the present invention as set forth in claim 5, the contract
The deterioration detecting means according to claim 4, wherein the upstream side NO_XConcentration and
The downstream side NO_XEquipped with a means for calculating the difference from the concentration
Note NO_XAfter the absorption is resumed, the NO_XConcentration difference is below specified value
Is less than or equal to a predetermined time
NO in case_XIt is determined that the absorbent has deteriorated. Also,
According to the present invention described in claim 6, the deterioration detection according to claim 4 is performed.
The means comprises the downstream NO_XConcentration and the upstream NO_Xconcentration
And means for calculating the ratio of _XAfter resumption of absorption
NO_XThe time required for the concentration ratio to exceed the specified value is estimated.
If the time is less than the predetermined time_Xabsorption
It is determined that the agent has deteriorated.

[0010] In the present invention according to claim 7, in the exhaust purification apparatus according to any of claims 4 to 6, the upstream NO _X concentration detecting means, the exhaust of the _the NO _X absorbent upstream consist NO _X sensor provided in the passage. Further, according to the present invention described in claim 8, in the exhaust gas purification device according to 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.
1 (A) to 1 (C), the horizontal axis of each figure indicates time,
FIG. 1A shows the change in the air-fuel ratio of the internal combustion engine, and FIG.
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-
Shows a case where the exhaust gas purification device similar to _the NO _X absorbent regenerating operation described in No. 7363, normal performs the operation of lean air-fuel ratio (for example, about the air-fuel ratio 23), a short time the engine air at regular intervals for reproducing of the NO _X absorbent is switched to fuel ratio to rich (see FIG. 1 (a)). FIG. 1 is for explanation.
This shows a case where the operating conditions are kept constant.

When the air-fuel ratio is changed as described above, 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 for a short time in I), it becomes a substantially constant value during the period when the lean air-fuel ratio operation is 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_XAbsorbent is controlled by the mechanism described below.
NO in exhaust when the exhaust air-fuel ratio is lean_XAbsorbs
When the exhaust air-fuel ratio becomes rich (exhaust oxygen concentration decreases)
NO absorbed_XRelease. NO_XRegeneration of absorbent
(Section II in Fig. 1) NO after completion _XNO absorbed by the absorbent
_XWas released because NO was released_XAbsorbent NO_XAbsorption capacity
High and NO_XNO in exhaust gas flowing into the absorbent
_XMost of NO_XNO in downstream exhaust gas absorbed by the absorbent
_XThe concentration (Fig. 1 (C)) is significantly higher than the upstream side (Fig. 1 (B)).
Lower.

However, 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 flowing out to the downstream side without being absorbed by the O _X absorbent increases, and after a certain period of time after the end of the regeneration, the NO _X concentration in the downstream side exhaust gas starts to increase, and the NO _X concentration in the upstream side exhaust gas increases.
It becomes asymptotic to the _X concentration.

[0016] However, when _the NO _X absorbent is degraded, 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 deteriorates (dotted line in Fig. 1 (C)), it is normal (Fig. 1 (C)
The time until the concentration of NO _X in the downstream exhaust increases shortened after playing compared to solid line).

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) It is determined that it has deteriorated.

Further, as described above, the NO in the exhaust gas on the downstream side is_X
The density change was as shown by the dotted line in Fig. 1 (C).
In order to determine objectively, the deterioration detection means, for example,
NO _XAfter the regeneration of the absorbent (section II), NO_XUnder absorbent
NO in outflow side exhaust_XThe density is a predetermined value (N in FIG. 1 (C)).₁)
Time to reach t₁(Fig. 1 (C)) or the end of playback
After, downstream NO_XChange rate of concentration increase rate changes from positive to negative
Time to reach the changing inflection point (point A in Fig. 1 (C))
Interval t_Two(Fig. 1 (C)) is NO_XA parameter that indicates the deterioration of the absorbent
T as₁Or t_TwoIs a predetermined group
NO when it is less than quasi-hour_XJudge that the absorbent has deteriorated
I do.

Further, when the concentration of NO _X in the exhaust gas flowing to the NO _X absorbent due to changes in the operating conditions change, NO _X
NO _X in the exhaust gas state is also downstream of the same absorbent
Concentrations vary. Therefore, not only the change of the NO _X concentration of the NO _X absorbent downstream exhaust, it is possible to determine more accurately the deterioration of the NO _X absorbent by considering the variation of the NO _X concentration upstream exhaust .

[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 to previously obtain the NO _X concentration can be indirectly determined 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 gas purification device of the present invention is applied. 2, reference numeral 1 denotes an internal combustion engine such as a gasoline engine that performs combustion at a lean air-fuel ratio, 3 denotes a combustion chamber of the engine 1, 6 denotes an intake port of the engine, and 8 denotes an exhaust port. Each intake port 6 is connected to a surge tank 10 via an intake branch pipe 9, and each branch pipe 9 is provided with a fuel injection valve 11 for injecting fuel into each intake port 6.

The surge tank 10 is connected to an air cleaner 13 through an intake passage 12, and a throttle valve 14 having an opening corresponding to the operation of an accelerator pedal (not shown) by a driver is provided in the intake passage 12. Are located. 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 a casing 19 containing a NO _X absorbent 18 described later is connected to the exhaust passage 17. Also, the illustrated 20 in Fig. 2, provided in the exhaust passage downstream of the NO _X absorbent 18 is NO _X sensor for detecting the concentration of NO _X in the exhaust gas.

In FIG. 2, reference numeral 30 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 configuration in which the output ports 36 are connected to each other by the bidirectional bus 31,
Fuel injection amount control of the engine 1, besides performing basic control of the engine ignition timing control and the like, in the present embodiment plays a role as a deterioration detecting means for detecting deterioration of the NO _X absorbent 18.

[0027] For the above object, the input port 35 of the control circuit 30, NO _X concentrations voltage signal and, NO _X absorbent in the downstream exhaust from NO _X sensor 20 in accordance with the intake pressure from the intake pressure sensor 15 Are input via the AD converter 37, and an engine speed sensor 21 provided in a distributor (not shown) of the engine.
, A pulse signal representing the engine speed is input.

The output port 36 of the control circuit 30
The fuel injection valve 11 is connected via the corresponding drive circuit 38.
And the ignition plug 4, and controls the fuel injection from the fuel injection valve 11 and the ignition timing of the engine. _The NO _X absorbent 18 built in the casing 19, for example using a carrier such as alumina, alkali metal, such as the carrier on, for example, potassium K, sodium Na, lithium Li, cesium Cs, barium Ba, calcium Ca At least one selected from alkaline earths, rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt are supported. NO _X when the air-fuel ratio of the _the NO _X absorbent 18 is inflowing exhaust is lean
Absorb NO and release NO _X when the oxygen concentration decreases
_X absorbs and releases.

The above-mentioned exhaust air-fuel ratio is defined as N
O _X absorbent 18 upstream of the exhaust passage and the engine combustion chamber is intended to mean the ratio of the sum of the sum and fuel respectively to the intake passage or the like supplied air quantity. Therefore, NO _X absorbent 1
When no fuel or air is supplied to the upstream exhaust passage 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, since an engine that performs combustion at a lean air-fuel ratio is used, the exhaust air-fuel ratio during normal operation is lean, and the NO _X absorbent 18 absorbs NO _{X in} the exhaust gas. Further, when the air-fuel ratio of the engine is the oxygen concentration in the exhaust gas is switched from the lean air-fuel ratio to the rich or the stoichiometric air-fuel ratio decreases, NO _X absorbent 18 performs the release of the absorbed NO _X.

The detailed mechanism of the absorption / release action is not clear in some parts. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, regarding this mechanism, platinum P
The case where t and barium Ba are supported will be described as an example, but other noble metals, alkali metals, alkaline earths,
The same mechanism is obtained even when rare earth elements are used.

That is, when the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases, and as shown in FIG. 3 (A), the oxygen O ₂ is converted into O ₂ ⁻ or O ²⁻ . It adheres to the surface of platinum Pt. On the other hand, NO _X from the engine is largely discharged in the form of NO, NO in the exhaust gas flowing to the NO _X absorbent on the surface of the platinum Pt this reacts with the O ₂ ^- or O ^2- as, NO ₂ (2NO + O ₂ → 2NO
₂ ). Next, a part of the generated NO ₂ is absorbed in the absorbent while being oxidized on the platinum Pt and combined with the barium oxide BaO, and as shown in FIG.
O ₃ ^- is diffused in the absorbent in the form of. NO in this way
_X is absorbed into the NO _x absorbent 18.

Accordingly, as long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is generated on the surface of the platinum Pt, and as long as the NO _x absorption capacity of the absorbent is not saturated, NO ₂ is absorbed in the absorbent and nitrate ions NO ₃ ^- is generated. Institution 1
When the air-fuel ratio is switched to rich or stoichiometric,
The oxygen concentration in the inflow exhaust gas decreases, and the amount of generated NO ₂ decreases. As a result, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and nitrate ions NO ₃ ⁻ in the absorbent are released from the absorbent in the form of NO ₂ .

On the other hand, if components such as unburned HC and CO are present in the inflow exhaust gas, these components become the oxygen O ₂ on the platinum Pt.
^- or O ^2- reacts with oxidized to consume oxygen on the platinum Pt. Further, 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 the platinum Pt, NO ₂ is released from the absorbent one after another.

[0035] That is, HC in the inflowing exhaust gas, CO, first O ₂ on the platinum Pt ^- immediately react with oxidized or O ^2-, and then on the platinum Pt O ₂ ^- or O ^2- is consumed the HC, NO _X flowing into NO _X released from the absorbent by CO, and with the exhaust gas is reduced even yet HC, any remaining CO is. 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 Release and reduction purification.

[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. Deterioration of the NO _X absorbent, the platinum P
This is caused by a decrease in the catalytic action such as t and a decrease in the NO _x absorption capacity of the absorbent BaO or the like. For example, the catalytic action of platinum Pt decreases due to thermal degradation and the like. When the catalytic action decreases, the oxidation reaction of NO in the inflowing exhaust gas (2NO + O ₂ → 2N
O ₂ ) decreases and NO ₂ is not generated. In this case, NO is intact because it is not absorbed by the absorbent BaO, and passes through the _the NO _X absorbent flowing downstream. Therefore, so that the NO _X NO concentration of the absorbent in the downstream exhaust increases as compared with the case of platinum Pt is normal when deteriorated.

Further, the decrease in the absorption capacity of the absorbent BaO is an example.
For example, it is caused by thermal deterioration, sulfur poisoning, and the like. For example, institution
A small amount of sulfur oxides (SO_X) Is included,
SO in exhaust_XIs the above NO_XSame mechanism as absorption
NO_XNO is absorbed by the absorbent_XAbsorbed by absorbent
SO_XNO_XWhere sulfur poisoning of the absorbent occurs
There is a case. That is, when the exhaust air-fuel ratio is lean,
SO_X(Eg SO _Two) Is oxidized on platinum Pt to form S
O_Three ^-, SO_Four ^-And binds to barium oxide BaO
BaSO_FourTo form However, BaSO_FourIs a comparison
Is stable, and the crystal tends to be coarse.
Once formed, it is difficult to decompose and release. Because of this, it was absorbed
SO_XIs normal NO_XNot released by absorbent regeneration operation
NO_XTends to accumulate in the absorbent. in this way
NO_XBaSO in absorbent_FourNO when the amount of
_XThe amount of BaO that can participate in the absorption of
O _XSo-called sulfur poisoning that reduces the absorption capacity of
(Or SO_XPoisoning) occurs. NO_X
Using the absorbent for a long time and the high temperature caused the absorbent BaO itself
In the case of deterioration, the absorption capacity is the same as for sulfur poisoning described above.
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} )
Although is successful, NO _X absorbent is immediately NO _X
And the generated NO ₂ cannot be absorbed, so that the NO ₂ generated on the platinum Pt flows downstream without being absorbed by the absorbent. In this case also, NO _X
The NO ₂ concentration in the exhaust gas downstream of the absorbent increases.

[0039] Therefore, since the NO _X when the absorption agent is either when deteriorated in a short time after playing _the NO _X absorbent NO _X in the downstream exhaust (NO or NO ₂₎ is to increase, as described above it is possible to detect the deterioration of the NO _X absorbent by monitoring the change in the exhaust concentration of NO _X in _the NO _X absorbent downstream of after playing the. 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,
Detecting the NO _X component concentration in the exhaust gas in real time NO _X
It may be used as long as the type of the NO _X sensor capable of generating an electrical signal corresponding to the component concentration. 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. In this semiconductor type sensor, when NO _x (NO or NO ₂ ) in the exhaust gas is adsorbed on the sensor surface, the change in the electric resistance value caused by capturing the electrons in the element ceramics causes the NO _{x in the} exhaust gas to change.
The following is of a type that detects the concentration, described deterioration determination operation of the NO _X absorbent 18 using the output of the NO _X sensor 20.

[0041] Figure 4 shows an example of a flowchart of the NO _X absorbent deterioration determining routine executed by the control circuit 30 at predetermined intervals. As described above, NO _X when the absorbent is degraded _the NO _X absorbent playback end after a short time on the downstream side exhaust NO
_X concentration increases. In this embodiment, it is determined whether the deterioration of the NO _X absorbent by time to concentration of NO _X after playback downstream exhaust rises to a certain level.

When the routine starts in FIG.
In step 401, it is determined whether or not the regeneration operation of the NO _X absorbent 18 is currently being executed. If the regeneration operation is being executed, the process proceeds to step 403, where the counter C is cleared and the routine ends. If it is determined in step 401 that the reproduction operation is not being performed, the flow advances to step 405 to increment the value of the counter C by one. Since this routine is executed at regular time intervals, the value of the counter C becomes NO
_The value corresponds to the elapsed time from the end of the _X absorbent 18 regeneration operation.

[0043] Next, the NO _X sensor 20 in step 407 of the NO _X absorbent 18 downstream exhaust NO _X concentration NR
It is read, in step 409 the NO _X concentration NR
Is greater than or equal to a predetermined value N ₁ (see FIG. 1C). If NR <N ₁ , the routine is terminated. In the case of NR ≧ N ₁ in step 409, further the value of the counter C at step 411 whether or not a predetermined value C ₁ or less is determined.

If C ≦ C _{1 in} step 411, N
O _X absorbent downstream NO _X concentration in a short time after playing is N ₁
Has been raised to, for _the NO _X absorbent is considered to have deteriorated, the routine ends is set to 1 the value of the alarm flag ALM proceeds to step 413. Also, slow increase in the downstream NO _X concentration in the case of C> C ₁ at step 411, it is considered that _the NO _X absorbent is functioning normally, the routine is left as the value of the alarm flag ALM finish.

When the value of the alarm flag ALM is set to 1,
Is set by the control circuit 30.
A routine that does not trigger, for example, an alarm
NO _XDeterioration of the absorbent is reported. Also shown in FIG.
But the main circuit is turned off to the control circuit 30
A backup RAM that can hold and store
The value of the flag ALM is stored in this backup RAM for
May be stored. The predetermined value N₁Passing
And C₁Is NO_XDepends on the type and size of the absorbent
Therefore, it is preferable to decide by experiment
No.

[0046] Figure 5 shows another embodiment of a deterioration determination routine 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 and determining the deterioration of the NO _X absorbent by increasing curve of the downstream concentration of NO _X after the end is detected the time to reach 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. Therefore, increasing the speed of the downstream concentration of NO _X after playing is initially large, the change curve of the downstream NO _X concentration for then decreases there is the inflection point (A point in FIG. 1 (C)) . 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 The presence or absence of deterioration is determined.

In FIG. 5, when the routine is started, in steps 501 to 505, the processing in FIG.
The operation of the counter C is performed in the same manner as in steps 01 to 403.
Further, in steps 507 513, the rate of increase in the rate of change of the downstream-side 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 rate of increase of the NO _X concentration DN
R is calculated as DNR = NR−NR _i−1 .

In Step 509, Step 50
An increase rate DNR calculated in 7, with an increase rate DNR _i-1 at the previous routine is executed, the change rate D2NR of the NO _X concentration increases the rate is calculated as _{D2NR = DNR-DNR i-1} , step 513 Then, the values of NR _i-1 and DNR _i-1 are updated in preparation for the next routine execution. Next, at steps 515 519, NO _X concentration NR and _the NO _X absorbent from the value of D2NR and calculated by the 1
8 is determined. That, D2NR zero or negative (step 515), and NR is _the NO _X absorbent 18 when the elapsed time from the playback ends when a predetermined value N ₁ or more (step 517) is a C ₁ or less is deteriorated It is determined, and the alarm flag ALM is set (= 1) in step 521. Other operations are the same as those in FIG. 4, and the description 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, the downstream N
O _X concentration alone than was determine the presence or absence of deterioration of the NO _X absorbent based on, which may cause an erroneous determination due to changes in engine operating conditions. Therefore, in the embodiment described below, NO _X absorbent upstream NO In addition to the downstream NO _X concentration
_{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 between 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, the same elements as those in FIG. 2 are denoted by the same reference numerals. In the embodiment of FIG. 6, on the upstream side of the exhaust passage of the NO _X absorbent 18, the downstream-side NO _X sensor 20 a similar NO
_The point that the _X sensor 25 is provided is different from the embodiment of FIG. FIG. 7 shows the NO _X of the exhaust gas purification apparatus of FIG.
4 shows an example of an absorbent deterioration determination routine. This routine is executed by the control circuit 30 at regular intervals.

In the routine of FIG. 7, NO _X after the end of the reproduction
The difference between the absorber upstream NO _X concentration and the downstream NO _X concentration is based on the time until a predetermined value or less _the NO _X absorbent 18
Is determined as to whether or not there is any deterioration. 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,
It is possible to detect a change in the absorption capacity of the NO _X absorbent regardless of a change in the NO _X concentration on the upstream side.

When the routine starts in FIG.
In steps 701 to 705, the same operation of the counter C as in FIG. 4 and steps 401 to 405 is performed. Then, the downstream step 707 and 709 side NO _X sensor 2
0 upstream NO _X sensor 25. Each downstream N
O _X concentration NRD and the upstream NO _X concentration NRU is read, the difference ΔNR the read NRD and NRU by the step 711 is calculated.

Next, at step 713, ΔNR is set to a predetermined value.
ΔNR₁It is determined whether or not: ΔNR> ΔNR₁so
In some cases, ie downstream NO_XConcentration is upstream NO_XDark
NO if low enough_XAbsorbency of absorbent 18
The routine ends because the power has not yet decreased
I do. On the other hand, ΔNR ≦ ΔNR₁NO if_XSucking
NO for collector 18_XAbsorption capacity has fallen below a specified value
Therefore, at step 715, the value of the counter C becomes C₁Less than or equal
Is determined. In step 715, C ≦ C ₁in the case of
Is NO_XIf the absorption capacity of the absorbent decreases
No_XSince it is considered that the absorbent 18 has deteriorated,
Proceed to step 717 to set the alarm flag ALM (=
1) Then, the routine ends. The predetermined value ΔNR
₁And C ₁Is NO_XDepending on the type and size of the absorbent
Differently, it is preferable to determine by experiment or the like. Also,
The other operations in FIG. 7 are substantially the same as the routine in FIG.
Then, the description is omitted.

[0055] In the above embodiment, by monitoring the difference ΔNR the upstream NO _X concentration and the downstream NO _X concentration, NO
_Although the absorption capacity of the _X absorbent is determined, the concentration difference ΔNR
It is also possible to determine the absorption capacity of the NO _X absorbent with parameters other than. For example, the downstream NO _X concentration N
RD upstream NO _X concentration NRU and the ratio 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 flowing downstream without being absorbed out of the NO _X in the exhaust gas flowing N
To represent the proportion of O _X, if the concentration ratio RNR is increased which means that the absorption capacity of the NO _X absorbent is lowered. Therefore, instead of detecting the time until the density difference ΔNR becomes equal to or smaller than the predetermined value, the density ratio RNR is set to the predetermined value RNR.
May determine the presence or absence of deterioration of the NO _X absorbent by detecting the time until more NR ₁ (e.g., about 0.8).

[0056] Figure 8 shows a flowchart of the NO _X absorbent deterioration determining routine according to 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
NR ₁ or when the elapsed time C from the playback end time when it is (step 813) is equal to or less than the predetermined value C ₀ (step 815), the alarm flag is judged that _the NO _X absorbent 18 is deteriorated ALM Is set (= 1). Note that the other steps in FIG. 8 are substantially the same as those in the routine in FIG.

In the embodiments shown in FIGS. 6 to 8, NO
Upstream NO _X installed in the exhaust passage upstream of the _X absorbent 18
The sensor 25 detects the NO _X on the upstream side of the NO _X absorbent 18.
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
Concentration. In addition, NO of exhaust gas discharged from the engine
_{The X} concentration is determined by engine operating conditions such as the engine load and the amount of intake air. Therefore, as described above _the NO _X absorbent 18
It is also possible to calculate the NO _X concentration upstream of the NO _X absorbent from the engine operating conditions without providing the NO _X sensor 25 on the upstream side.

[0058] In this case, the actually measured NO _X concentration RNU in the exhaust gas of the engine under conditions changed and advance engine intake pressure PM (i.e. engine load) and the rotational speed N (i.e. intake air amount), the intake pressure PM and as a function of the rotational speed N, the NO _X concentration RNU be stored in the ROM32 in the form control circuit 30 in the form of a numerical table such as shown in FIG. 9, FIG. 7 step 709 and FIG. 8 step 809, NO _X sensor 25
From Instead of loading the _the NO _X absorbent 18 upstream NO _X concentration, the rotational speed sensor 21. the intake pressure sensor 15, respectively reads the engine intake pressure PM and the engine speed N,
From the numerical table of FIG.
O _X concentration can be so read the RNU.

As described above, by calculating the NO _X concentration upstream of the NO _X absorbent from the engine operating conditions, the NO _X sensor 25 upstream of the NO _X absorbent is omitted to simplify the apparatus. 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 according to claims 4 8, by monitoring the concentration of NO _X in the exhaust gas in _the NO _X absorbent upstream side and the downstream side of the playback ends, regardless of changes in engine operating conditions precisely it is possible to detect the deterioration of the NO _X absorbent.

[Brief description of the 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 gas purification device of the present invention is applied.

FIG. 3 is a diagram for explaining the NO _X absorbing / releasing action of a NO _X absorbent.

FIG. 4 is a flowchart illustrating an example of an operation for detecting deterioration of the NO _X absorbent in the embodiment of FIG. 2;

FIG. 5 is a flowchart showing an example of an operation for detecting deterioration of the NO _X absorbent in the embodiment of FIG. 2;

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

FIG. 7 is a flowchart illustrating an example of an operation for detecting deterioration of the NO _X absorbent in the embodiment of FIG. 6;

FIG. 8 is a flowchart showing an example of an operation for detecting deterioration of the NO _X absorbent in the embodiment of FIG. 6;

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

[Explanation of symbols]

1 ... engine 17 ... exhaust passage 18 ... NO _X absorbent 20, 25 ... NO _X sensor 30 ... control circuit

Continued on the front page (51) Int.Cl. ⁶ Identification code FI G01M 15/00 G01M 15/00 Z (72) Inventor Tetsu Iguchi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (56) References JP-A-5-302508 (JP, A) JP-A-2-207159 (JP, A) JP-A-5-312109 (JP, A) JP-A-6-93843 (JP, A) (58) Fields investigated (Int.Cl. ⁶ , DB name) F01N 3/08-3/20 F02B 77/08 F02D 45/00 368 G01M 15/00

Claims (8)

(57) [Claims] An NO arranged in an exhaust passage of an internal combustion engine absorbs NO _X when the inflowing exhaust air-fuel ratio is lean, and releases the absorbed NO _X when the oxygen concentration of the inflowing exhaust decreases. 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 exhaust purifying apparatus according to claim 1 determines that _the NO _X absorbent is 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 and wherein the NO _X concentration exhaust purifying apparatus according to the NO claim 1 determines that the _X absorbent is deteriorated when the rate of increase of the rate of change is the time until the negative is below a predetermined time to a predetermined . 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 _{An X} absorbent, a downstream NO _X sensor disposed in an exhaust passage on the downstream side 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 detection unit. 5. The apparatus according to claim 1, wherein the deterioration detecting means includes an 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 exhaust purifying apparatus according to _the NO _X absorbent is determined according to claim 4 and is degraded. Wherein said deterioration detecting means, 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 exhaust purifying apparatus according to _the NO _X absorbent is determined according to claim 4 and is degraded. Wherein said upstream NO _X concentration detecting means, an exhaust purifying apparatus according to any one of the _the NO _X absorbent claims 4 to 6 comprising a NO _X sensor provided on the upstream side of the exhaust passage . Wherein said upstream NO _X concentration detecting means includes means for detecting an operating condition of the engine, based on the detected operating condition, means for calculating the upstream-side NO _X concentration from a predetermined relationship 7. The method according to claim 1, further comprising:
Exhaust gas purifying apparatus according to the item.