JP2003519744A - Method and apparatus for controlling desulfurization of a NOx storage catalyst disposed in an exhaust gas passage of an internal combustion engine - Google Patents

Abstract

(57) Abstract: The present invention is disposed downstream of the NO _X storage catalyst, using at least one of the NO _X sonde depending on the concentration of NO _X in the exhaust gas and sends a signal, the exhaust gas of the internal combustion engine The present invention relates to a method and an apparatus for controlling the desulfurization of a NO _X storage catalyst disposed in a gas passage. NO _X storage catalyst (18) the NO _X storage NO _X catalyst activity (18) (NOA) were determined from the NO _X concentration measured downstream of, NO _X storage NO _X catalyst activity (18) of (NOA) when below a predetermined threshold value (SW), to start the desulfurization by a predetermined desulfurization parameters, based on the desulfurization performance to determine the irreversible deterioration of the NO _X storage catalyst (18), a predetermined degradation limit (SW _IR) the initiates a strong desulfurization when more than at least one of desulfurization parameters are selected corresponding to the case high desulfurizing effect, the subsequent operation of the internal combustion engine 10, the recovered NO _X initial activity after a strong desulfurization (NOAMX) Depend on height.

Description

Detailed Description of the Invention

The present invention relates to a method and a device for controlling the desulfurization of a NO _X storage catalyst arranged in the exhaust gas passage of an internal combustion engine, having the features recited in independent claims 1 and 13.

The exhaust gas of an internal combustion engine that is operated in a lean burn operation mode at least temporarily is
O _X aftertreatment be operated with the aid of the storage catalyst is known. At this time, the lean-burn operation mode, the nitrogen oxides NOx in this stage is present in excess in the exhaust gas as compared with the reducing exhaust gas components such as carbon monoxide or unburned hydrocarbons, thus, NO _X storage catalyst, the fully not converted nitrogen oxides nO _X stored in the form of nitrates. N
When the Ox storage capacity is lowered, at regular intervals, NO _X regeneration is performed in the storage catalyst. Therefore, a rich exhaust gas atmosphere is sent to the storage catalyst to adjust the minimum catalyst temperature.

In addition to the absorption of NO _X , NO _X storage catalysts also have an undesired accumulation of sulfur oxides. Since the accumulation of sulfur is irreversible under the conditions of the NO _X regeneration, sulfide increased the storage catalyst, NO _X storage capacity is lowered. Therefore, the aggregation of sulfur may lead to the formation of sulfate particles, which may irreversibly deteriorate the catalytic activity of the NO _X storage catalyst. Removal of such sulfate particles becomes increasingly difficult as the particle size increases.
Therefore, the NO _X storage catalyst is desulfurized at regular intervals, at which time a rich exhaust gas atmosphere is fed at a catalyst temperature of over 650 ° C, and the accumulated sulfur is mainly formed into sulfur dioxide SO ₂ and hydrogen sulfide H ₂ S. It is known to be discharged in.

In addition to irreversible degradation due to the formation of sulfate particles, other permanent types of degradation leading to a loss of storage capacity of the catalyst are known. In this case, thermal degradation is of primary importance.

[0005] Underlying the present invention is to identify the irreversible deterioration of the NO _X storage catalyst, a problem is proposed a method for controlling the desulphurization of the NO _X storage catalyst which can be tracked.

According to the invention, this problem is solved by a method and a device for controlling the desulfurization of NO _X storage catalysts having the features recited in the independent claims. According to the method of the present invention, N
O _X determine the NO _X storage activity of the NO _X storage catalyst from NO _X concentration measured downstream of the storage catalyst, when the NO _X activity of the NO _X storage catalyst falls below a predetermined threshold, desulfurization by a predetermined desulfurization parameters To start. Also, irreversible deterioration of the NO _X storage catalyst is tracked based on the desulfurization performance, and when the predetermined deterioration limit value is exceeded, strong desulfurization is started,
At least one desulfurization parameter corresponding to a high desulfurization effect is then selected, which makes the subsequent operation of the internal combustion engine dependent on the high NO _X activity recovered after strong desulfurization.
Even if the preceding standard desulfurization is incomplete, the implementation of heavy desulfurization allows quantitative sulfur emissions. Thus, the NO _x storage activity recovered after strong desulfurization is
It can be directly correlated to the current irreversible deterioration of the NO _X storage catalyst. As a result, permanent deterioration of the NO _X storage catalyst which is no longer acceptable can be identified.

According to the invention, various variants are possible for setting the deterioration limit value. In a preferred embodiment, the threshold to be proportional to the NO _X initial activity of the NO _X storage catalyst recovered after the end of the desulfurization, is set each time the desulfurization, the desulfurization is activated below which. In this case, the deterioration limit value is the lowest limit value that must not be lower than the NO _X storage activity, and the threshold value is larger than the deterioration limit value. According to an alternative embodiment, the threshold below which desulfurization is triggered remains unchanged. In this modified method, the desulfurization frequency increases as the irreversible deterioration of the catalyst increases, so a predetermined maximum desulfurization frequency is used as the deterioration limit value. Threshold in another alternative embodiment which is also a constant, degradation limit is the lower limit of the NO _X initial activity was recovered after desulfurization.

The implementation of desulfurization, in particular heavy desulfurization, is associated with high fuel consumption and in some cases can influence the driving behavior of the vehicle. Therefore, it is not desirable to start desulfurization under any operating conditions. Thus, an advantageous embodiment of the method first inhibits lean burn operation of the internal combustion engine when the deterioration threshold is exceeded and only initiates strong desulfurization when suitable predetermined ambient conditions are present. The boundary conditions is the lowest speed for compliance between the minimum temperature and / or minimum time eg NO _X storage catalyst.

[0009] The method of the present invention are those which depend a further operation of the internal combustion engine after a strong desulfurization desulfurization performance, i.e. the height of the NO _X initial activity was recovered after desulfurization. A preferred embodiment is that if the NO _X initial activity recovered after the end of the strong desulfurization is nearly complete or at least within a given range of sulfur and NO _X- free intact NO _X storage catalysts.
The lean-burn operation of the internal combustion engine is configured to continue to be permitted. In this case, that is, loss of the observed NO _X storage activity prior strong desulfurized cause desulfurization of the preceding ended in accumulation i.e. incomplete sulfur, because not due irreversible deterioration of the NO _X storage catalyst. Therefore, it is preferable to adjust the desulfurization parameters so that the subsequent desulfurization is effectively performed after the effective strong desulfurization treatment.

On the other hand, if the strong desulfurization has little effect and the recovered NO _x initial activity is not much higher than the NO _x initial activity after the last desulfurization, a severe irreversible deterioration of the NO _x storage catalyst is presumed. Therefore, the lean burn operation of the internal combustion engine is limited or cut off in order to reduce NO _X emission. It is also conceivable to inform the vehicle driver of the necessity of catalyst maintenance by an alarm indicator.

It is also preferable that the apparatus is configured to include means, for example, a control unit, in which the control procedure of the desulfurization treatment of the NO _X storage catalyst is stored in digital form. Such control units are often preferably incorporated into existing engine control systems.

Other preferred embodiments of the invention are apparent from the other features recited in the dependent claims.

[0013]   Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0014]   FIG. 1 shows an outline of an internal combustion engine 10 and an exhaust gas system 12 which is installed downstream. Exhaust gas
Pre-catalyst 16 and NO in the exhaust gas passage 14 of the system 12_XWith the storage catalyst 18
There is. In addition, the exhaust gas passage 14 is provided with various types of exhaust gas for detecting selected operating parameters.
Built-in instrument. For example, gas sondes 20 and 22 show the concentration of gas components in exhaust gas.
To detect. In this example, a gas sonde 20 designed as a lambda sonde is an internal combustion engine 1
Used for the detection of oxygen content behind 0 and in front of the catalytic components 16, 18, while
, NO_XSonde 22 is NO_XNO behind storage catalyst 18_XMeasure the concentration. NO
_XTemperature probes 24 and 26 arranged before and after the storage catalyst 18 detect the catalyst temperature.
Used for As an alternative, one or both of the temperature sondes 24 and 26 may be eliminated and N
O_XIt is also possible to empirically derive the temperature of the storage catalyst. Gassonde 20, 22 and
All signals detected by the temperature probe and temperature sonde 24, 26 enter the engine controller 28.
Input, where it is first digitized and then the operating mode of the internal combustion engine 10 is controlled.
Is further processed for. For this purpose, the engine control unit 28 is provided with, for example, the intake pipe 3
To adjust the position of the second throttle valve 30 and / or the exhaust gas return device 34.
Therefore, the air-fuel mixture supplied to the internal combustion engine 10 is adjusted. Illustrated operation unit 30
, 34 for adjusting the lean or rich mode of the internal combustion engine 10, for example.
it can.

A control unit 36, which stores a desulfurization control procedure for the NO _X storage catalyst, which will be described in detail below, is incorporated in the engine control device 28. Alternatively, the control unit 36 can be realized independently of the engine control 28.

[0016]   2 is NO_XRelative NO of storage catalyst 18_XActive NOA_relShows the time course of.
At that time, relative NO_XActive NOA_relIs this NO_XNO of storage catalyst 18_XActive NO
A and NO_XAnd intact NO without sulfur_XNO of storage catalyst_XRepresents the ratio to activity. This
If NO_XActive NOA itself is NO_XNO behind the storage catalyst 18_XSonde 22
Measured NO_XConcentration and NO_XNO in front of the storage catalyst 18_XDefined as the ratio of concentrations
. NO_XNO in front of the storage catalyst 18_XConcentration ie NO_XCoarse emission is especially
Calculated by the engine control device 28 based on actual operating parameters of the internal combustion engine 10.
. Instead, NO_XNO disposed in the exhaust gas system 14 in front of the storage catalyst 18_X It can also be measured with a sonde. NO_XActive NOA or relative NO_XActive NOA_{re l} Is calculated by the engine control unit 28. NO for the engine control unit 28
_XAnd intact NO containing no sulfur_XNO of storage catalyst_XActive NOA is also remembered
It NO at the beginning of vehicle operation_XThe storage catalyst 18 has the same NO as the fresh catalyst._XActive NO
Relative NO because it has A_XActive NOA_relTakes a value close to "1" per difference. So
Since the sulfurization of the catalyst 18 increases in the later process, the relative NO_XActive NOA_relDepends on
Fall to. Relative NO_XBelow the initial activation threshold SW, time t₁And NO_XSavings
The first desulfurization of the stored catalyst 18 is started. Required for desulfurization according to prescribed desulfurization parameters
The required minimum catalyst temperature is adjusted so that the internal combustion engine 10 has a predetermined or adjusted desulfurization time.
Meanwhile, the engine is operated in the rich operation mode corresponding to the excess air ratio rich setting. H₂S
It is possible to operate desulfurization at rich lean intervals to control emissions.
Are known. In this case, as the auxiliary desulfurization parameter, for example, the
Chi-lean excess air ratio setting, switching frequency or NO_XRich behind the storage catalyst 18
・ The lean switching state can be set. Relatives recovered after the end of desulfurization 40
NO_XAccording to the initial active NOAMX, the position of the threshold value SW is newly changed to the control unit 36.
Confirm by. In that case, the threshold value SW has recovered to NO._XCompared to initial active NOAMX
It is preferable to exemplify. NO after desulfurization_XThe initial activation NOAMX is the operating time t
NO as the progress of_XIt gradually becomes less compatible with stored catalysts,
It will decrease. The cause is NO, for example._XIncomplete desulfurization and / or storage catalyst 18
It is irreversible thermal deterioration. NO_XAs a result of the decrease in initial active NOAMX,
If it turns, the threshold value SW at which desulfurization starts is further decreased. Time t_FiveNO_XActive NO
A is a lower limit value that must not fall below, deterioration limit value SW_IRUntil it reaches 38
And the desulfurization 40 cycle is repeated. Deterioration limit value SW_IRBelow, NO_Xrelease
First, the internal combustion engine 10 is changed from the lean operation mode to the stoichiometric or
It is switched to the rich operation mode. Predetermined peripheral conditions, such as NO_XStorage catalyst 18
When the lowest vehicle speed that complies with the minimum temperature and / or the minimum time of
It is preferable to start strong desulfurization. Powerful with enormous energy problems
Fuel consumption for desulfurization can thus be relatively low. Strong desulfurization 42
Compared to the preceding desulfurization 40, the desulfurization parameters described above (eg catalyst temperature, air
At least one of (excess ratio, time setting) is selected to correspond to a high desulfurization effect.
Is different. Long desulfurization time and / or low emptyness due to high strength desulfurization 42, for example.
You can specify the overkill rich setting.

Due to this irreversible deterioration of the NO _X storage catalyst 18, various heights of NO _X initially active NOAMX are recovered after strong desulfurization. In the scenario shown in 44, NO _X activity NOAMX the recovered corresponds substantially intact catalyst containing no sulfur. In this case, the catalyst 18 has virtually no permanent deterioration and it can be assumed that the preceding loss of activity is due to an incomplete preceding desulfurization 40. The initial of the NO _X activity by a strong desulfurization 42 In scenario 46 completely Nide not be large extent recovered. This suggests that there was an irreversible deterioration of the catalyst and the desulfurization 40 was incomplete. Any lean burn operation scenarios 44,46 even the internal combustion engine 10 is subsequently permitted, can be set more thresholds below to NO _X initial activity NOAMX be recovered. In either case 44 or 46, it is preferable to adaptively modify the desulfurization parameters for the subsequent desulfurization so that the subsequent improvement of the desulfurization performance is expected. NO _X storage catalyst 1
Less 8 irreversible degradation of, the higher the recovered NO _X activity NOA after strong desulfurization 42, it is important to fix the much desulfurization parameters. According to scenario 48,
Strong desulfurization 42 was practically ineffective. Therefore, in this case, extensive irreversible deterioration of the storage catalyst 18 must be estimated. In order to stop the subsequent NO _X emission,
In this case, the lean burn operation of the internal combustion engine 10 is finally cut off. An alarm indicator may be optionally provided to inform the vehicle driver of the condition of the catalyst or to indicate necessary maintenance.

[0018]   Relative NO corresponding to another preferred embodiment of the present invention_XActive NOA_relThe progress of
3 shows. In this case, NO while all vehicles are operating._XThe threshold value SW of the active NOA is kept constant
Be done. NO_XNO recovers after desulfurization 40 as the aging of storage catalyst 18 increases _X Initially active NOAMX decreases. As a result, NO in the lean mode of the internal combustion engine 10 _X The period τ for accumulating sulfur until the storage catalyst 18 reaches the threshold value SW becomes shorter and shorter.
Become. In other words, the frequency with which desulfurization 40 is required increases. The need for strong desulfurization 42
The criterion for the recognition of sex is the specified maximum desulfurization frequency or NO recovered after desulfurization._XInitial activity
It is the lower limit of NOAMX. Other method features of this embodiment of the invention are:
Since all of them correspond to the features shown in FIG. 2, they will not be described again here.

FIG. 4 shows a flow chart for explaining the embodiment of the method shown in FIG. The procedure starts in step S1. Here, a lean atmosphere, that is, a lambda value> 1 is sent to the internal combustion engine 10. In step S2, calculating of the NO _X activity NOA basis to the NO _X concentration NO _X sonde 22 is measured at the rear of the NO _X storage catalyst 18 is performed. In step S3, the NO _X storage active NOA is compared with the threshold value SW. If the NO _X active NOA is higher than the threshold value SW, the process moves to step S1 and the internal combustion engine 10 is continuously operated in the lean mode. On the other hand, when the threshold value SW is reached or falls below the threshold value, step S3
If confirmed in step 4, the NO _x active NOA is compared with the deterioration limit value SW _IR in step 4. If the deterioration limit value SW _IR has not yet been reached or falls below, the desulfurization is started in step S5 with predetermined desulfurization parameters. After the desulfurization is completed, the recovered NO _X active NOAMX is determined in step S6, and the threshold value SW is newly calculated according to the determined initial active NOAMX. On the other hand, if it is confirmed in step S4 that the NO _X active NOA reaches or falls below the deterioration limit value SW _IR , strong desulfurization is started in step S7. NO _X active NOAMX recovered in step S8 after completion of strong desulfurization
Is smaller than a predetermined threshold value SWMX. If this question is denied, a new threshold value SW is calculated in connection with the NO _X initial activation NOAMX in step S6, on the basis of which the lean burn operation is again permitted in step S1. However, if the desulfurization result cannot be confirmed in step S8, the lean burn operation is finally shut off in step S9.

[Brief description of drawings]

FIG. 1 is a principle diagram of a means for controlling desulfurization of an NO _X storage catalyst and an exhaust gas purification facility.

FIG. 2 is a diagram of the NO _X storage activity over time of a NO _X storage catalyst according to a preferred embodiment of the present invention.

FIG. 3 is a diagram of the NO _X storage activity over time of a NO _X storage catalyst according to another preferred embodiment of the present invention.

4 is a flow chart of a procedure according to the present invention based on the embodiment shown in FIG.

[Explanation of symbols]

10 Internal combustion engine 18 NO _X storage catalyst NOA NO _X activity NOAMX NO _X initial activity SW threshold SW _IR deterioration limit value

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02D 45/00 314 F02D 45/00 314Z (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE, TR), AE, AG, AL, AM, AU, AZ, BA, BB, BG, BR , BY, BZ, CA, CN, CR, CU, CZ, DM, DZ, EE, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LV, MA, MD, MG, MK, MN, MW, MX, MZ, NO, NZ, PL, R , RU, SD, SG, SI, SK, SL, TJ, TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW (72) Inventor Hiinze, Zellen Federal Republic of Germany 38114 Braunschweig, Eichtalstraße 4 Ar. (72) Inventor Zilmer, Michael Gicte 38173, Federal Republic of Germany 18173 Im Schrotmogen 18 (72) Inventor, Lang, Axel German Republic 38302 Wolfen Buttel, Nerkenweg 29 (72) Inventor, Schulz, Frank Fordolf, Federal Republic of Germany 38533, Rosengarten 35 (72) Inventor Drukkhammer, Yens 3838 Germany Braunschweig, Wiehlungstrasse 47 B. F term (reference) 3G084 BA09 DA10 EA11 EB12 EC03 FA27 FA28 FA29 3G091 AA02 AA11 AB06 BA11 BA14 CB01 DA01 DA02 DB10 DB11 EA18 EA33 EA34 FB10 FB12 FC02 HA08 HA36 HA37 HA42 HB05

Claims (15)

[Claims] Is disposed downstream of claim 1] NO _X storage catalyst, using at least one of the NO _X sonde transmits a signal in accordance with concentration of NO _X in the exhaust gas, disposed in an exhaust gas passage of an internal combustion engine a method for controlling a desulphurization of the NO _X storage catalyst, a) NO _X storage catalyst (18) downstream in NO _X determine the activity (NOA) of the NO _X storage catalyst from the measured NO _X concentration (18) of B) When the NO _x activity (NOA) of the NO _x storage catalyst (18) is below a predetermined threshold value (SW), desulfurization is started with a predetermined desulfurization parameter, and c) the NO _x storage catalyst (based on the desulfurization performance ( 18) irreversible deterioration is determined, and when a predetermined deterioration limit value (SW _IR ) is exceeded, strong desulfurization is started, whereby at least one desulfurization parameter corresponding to a high desulfurization effect is selected, and d) internal combustion After the institution The operation was recovered after a strong desulfurization NO _X initial activity (NO
AMX) height dependent. 2. A NO _X storage catalyst (18) whose threshold value (SW) is restored after the end of desulfurization.
), The threshold value (SW) of desulfurization is proportional to the NOX initial activity (NOAMX).
And the deterioration limit value (SW _IR ) is a minimum limit value that must not be lower than the NO _X activity (NOA), and the threshold value (SW) is larger than the deterioration limit value (SW _IR ). The method according to Item 1. 3. Process according to claim 1, characterized in that when the threshold value (SW) is unchanged, the deterioration limit value (SW _IR ) is a predetermined maximum desulfurization frequency. 4. The deterioration limit value (SW _IR ) is a predetermined lower limit of NO _X initial activity (NOAMX) recovered after desulfurization when the threshold value (SW) is unchanged. the method of. 5. When the deterioration limit value (SW _IR ) is exceeded, first, lean combustion operation of the internal combustion engine (10) is limited or prohibited, and predetermined ambient conditions such as a NO _x storage catalyst (18).
The method according to any one of the preceding claims, characterized in that strong desulfurization is started only when the minimum vehicle speed to be observed is established during the minimum temperature and / or the minimum time. 6. _{If the} initial NO _X activity (NOAMX) recovered after the end of strong desulfurization corresponds almost completely or at least to a certain extent to a sulfur and NO _X- free intact NO _X storage catalyst (18). A method as claimed in any one of the preceding claims, characterized in that a lean burn operation of the internal combustion engine (10) is still allowed. 7. A strong desulfurization of restored NO _X initial activity after completion (NOAMX) is almost completely or at least in a predetermined range, if corresponding to the intact of the NO _X storage catalyst without sulfur and NO _X (18) The method according to any one of the preceding claims, characterized in that the desulfurization parameters are adjusted so that the subsequent desulfurization takes place effectively. 8. If the NO _X initial activity (NOAMX) recovered after the end of the strong desulfurization is not significantly higher than that after the immediately preceding desulfurization, a severe irreversible deterioration of the NO _X storage catalyst (18) is estimated and the internal combustion engine A method according to any one of the preceding claims, characterized in that the lean burn operation of (10) is limited or interrupted. And NO _X concentration NO _X activity (NOA) was measured downstream of the NO _X storage catalyst (18) according to claim 9 NO _X storage catalyst (18), the actual operating parameters of the measured or engine (10) NO _X storage catalyst (18) upstream of the NO _X calculated based on the
Method according to any one of the preceding claims, characterized in that it corresponds to the ratio with the concentration. 10. NO _X activity (NOA) and the NO _X concentrations measured behind of the NO _X storage catalyst (18), of the NO _X concentrations modeled based on intact of the NO _X storage catalyst without sulfur (18) Method according to any one of the preceding claims, characterized in that it is a ratio. 11. The desulfurization parameter according to claim 1, wherein the desulfurization parameters are a desulfurization temperature, an excess air ratio rich setting (Lambda-Fettvorgabe) and a desulfurization time of the NO _X storage catalyst (18). Method. 12. Controlled rich lean desulfurization (Fett-Manager-E).
In the case of ntschwefung, the rich / lean excess air ratio setting (Fe
tt-Mager-Lambdavorgaben), behind the rich lean switching limit switching frequency and NO _X storage catalyst (18) (Fett-Mager- U
Method according to any one of the preceding claims, characterized in that the state of mschaltschwellen) is an auxiliary desulfurization parameter. 13. is disposed downstream of the NO _X storage catalyst, using at least one of the NO _X sonde transmits a signal in accordance with concentration of NO _X in the exhaust gas, disposed in an exhaust gas passage of an internal combustion engine an apparatus for controlling the desulphurization of the NO _X storage catalyst, the following procedure, namely (a) NO _X storage NO _X catalyst activity NO _X storage catalyst from NO _X concentration measured downstream of (18) (18) (NOA) is determined, and (b) when it falls below a predetermined threshold value (SW) of the NO _X activity (NOA) of the NO _X storage catalyst (18), desulfurization is started with a predetermined desulfurization parameter, and (c) desulfurization The irreversible deterioration of the NO _X storage catalyst (18) is determined based on the results, and when the predetermined deterioration limit value (SW _IR ) is exceeded, strong desulfurization is started, and at this time, at least one desulfurization corresponding to a high desulfurization effect is achieved. The parameter is selected, ( apparatus characterized by means capable of performing determining with respect to the subsequent operation of the internal combustion engine according to the level of d) was recovered after a strong desulfurization NO _X activity (NOAMX) is provided. 14. Apparatus according to claim 13, characterized in that said means comprises a control unit (36) storing in digital form the control procedure for the desulfurization treatment of the NO _X storage catalyst (18). 15. A method according to claim 14, characterized in that the control unit (36) is integrated in the engine control (28).