JP2003500595A - Method for controlling regeneration of NOx absorption catalyst - Google Patents

Abstract

(57) Abstract: The present invention, NO _X NO _X concentration of an exhaust gas by placed NO _X sensor downstream of the absorption catalyst is detected, at least one of the NO _X disposed in the exhaust passage of a combustion engine A method for controlling regeneration of an absorption catalyst. NO _X concentration measured after the (a) absorption catalyst is compared with the NO _X target density, compared value correspondingly to the deviation of the concentration of NO _X from the NO _X target concentration is determined, (b) comparison value Is greater than a configurable threshold, wherein at least one operating parameter of the combustion engine (14) is at least temporarily affected, and (c) the regeneration means is possibly The selection is made depending on the previously implemented reproduction means.

Description

Detailed Description of the Invention

The invention relates to a method for controlling the regeneration of at least one NO _x absorption catalyst arranged in the exhaust passage of a combustion engine, having the features of the preamble of claim 1.

It is known to purify the exhaust gas of a combustion engine by means of a suitable catalyst arranged in the exhaust passage of the combustion engine. During the combustion process, gaseous toxic substances are generated. The harmful substances can be divided into reducing agents such as CO, HC or H ₂ or oxidizing agents such as NO _x or SO _x . This reducing agent is catalytically oxidized by oxygen and the oxidizing agent is converted by the reducing agent.

The combustion engine can then be operated in various operating modes. Then, if there is an excess of oxygen to the fuel in the mixture of fuel and air to be burned, λ> 1 (lean operating mode). Under the theoretical mixing ratio condition, λ = 1, while the lambda value is smaller than 1 when the fuel is in excess of oxygen (rich operation mode).
In the rich operation mode, the reducing agent increases due to incomplete combustion, whereas in the lean operation mode, the proportion of the reducing agent in the exhaust gas decreases significantly. Nevertheless, the conversion of at least part of the reducing agent is possible with the catalyst even in a rich atmosphere when the oxygen concentration is sufficient.

[0004]   On the other hand, NO_XOr SO_XCan be reduced only when λ ≦ 1.
Nevertheless, NO_XN in the exhaust passage in order to suppress the emission of as much as possible.
O_XIt is known to arrange a reservoir. This NO_XReservoir NO with catalyst _X Storage catalyst (NO_XAbsorption catalyst). NO_XAbsorption catalyst is λ>
NO when 1_XAbsorbs as nitrate, and NO_XAbsorption temperature and / or N
O_XCan be absorbed until it exceeds its storage capacity.

Therefore, it is known to regenerate the NO _x absorption catalyst in a regular cycle (
NO _X reproduction). During NO _x regeneration, switching to the operating mode of λ ≦ 1 is performed in a short time. Under such conditions, the stored NO _x is reabsorbed and catalytically reduced by the reducing agent. Regeneration is then required depending on the individual operating parameters.
This operating parameter can be detected directly by suitable measuring equipment. It is known, for example, from German Patent Application DE 197 29 676 A1 to start regeneration in dependence on a predetermined limit temperature. A complex model for such a control can be deduced from the German patent DE 19716275. In this case, in particular, the actual driving situation, the load condition and the actual lambda value (excess air ratio) can be taken into consideration. Furthermore, the condition during reproduction can be tied to a certain parameter. From the German Patent Application Publication No. 19744409,
Depending on the storage capacity of the oxygen storage capacity and or NO _X reservoir of catalysts are known to change the time of the regeneration cycle. Federal Republic of Germany Patent 19830
It is further known from Japanese Patent No. 829 to control the reducing agent flow rate required for regeneration of the NO _X absorption catalyst depending on the signal detected by the NO _X sensor.

In the course of operation of the NO _X absorption catalyst, of course, various damages may impair the NO _X storage capacity and the functionality related to catalytic activity. Such damage occurs in both the catalyst and the reservoir and is reversible or irreversible depending on its nature.

Reversible damage is achieved, for example, by covering the catalyst with condensate or soot. In addition, SO _X is formed during the combustion of fuels containing sulfur. This SO _x , like NO _x , is absorbed by the reservoir. The storage of SO _X as nitrate in particular reduces the NO _X storage capacity and over a long period of time leads to catalyst damage, for example by the formation of sulfite. Furthermore, formation of sulfites granules would cause distortion of the tissue of the NO _X absorbent catalyst upon absorption. This distortion can lead to irreversible damage of the NO _X absorbent catalyst.

[0008]   Therefore, depending on the desulfurization needs, NO_XIs known to desulfurize (SO _X Playback). However, for that purpose, the thermodynamic stability of sulfate is higher than that of nitrate.
On the basis of high temperature is required. Desulfurization needs, degree of sulfurization, actual excess air
Determined based on parameters that represent the actual catalyst state, such as rate or catalyst temperature
be able to. For example, the degree of sulfurization is NO_XNO downstream of absorption catalyst_XDepending on the concentration
You can decide. NO_XNO for concentration detection_XSensor-like component
A unique sensor is suitable. German Patent Application Publication No. 19837074
From the publication, methods are inferred to influence the control of the air to fuel ratio during the desulfurization phase.
. At that time, the actual value of oxygen concentration was compared with the target value during desulfurization, and
The error signal newly determines the fuel concentration supplied during desulfurization.

In general, the fuel consumption of the combustion engine in the rich operation mode is higher than that in the lean operation mode. Thereby, the additional heating of the exhaust gas performed by the case, in NO _X regeneration or SO _X regeneration is further enhanced fuel consumption. Therefore,
As research continues to reduce fuel consumption in combustion engines, it is desirable to have λ> 1 operation as long as possible.

The known method has the disadvantage that the order of the individual regeneration means is poorly coordinated. As a result, fuel consumption increases, and it is impossible to select the regeneration means according to the actual catalyst state.

The task of the method according to the invention is to continuously monitor the functionality of the NO _x absorption catalyst with respect to its NO _x storage capacity and catalytic activity and to adapt the regeneration means to the actual catalytic conditions.

According to the present invention, the object is to provide an exhaust passage of a combustion engine having a feature of claim 1, in which the NO _x concentration of exhaust gas is detected by a NO _x sensor arranged downstream of the NO _x absorption catalyst. It is solved by a method for controlling the regeneration of at least one NO _x absorption catalyst arranged. NO _X concentration measured after the (a) absorption catalyst is compared with the NO _X target density, compared value correspondingly to the deviation of the concentration of NO _X from the NO _X target concentration is determined, (b) comparison value Is above a configurable threshold, at least one operating parameter of the combustion engine is at least temporarily affected in this regeneration step, and (c) the regeneration means is optionally before it. Depending on the regeneration means carried out in step 1, the progress of successive regeneration means can be coordinated and adapted to the actual catalytic conditions.

In a preferred embodiment of the method, the comparison value is newly determined during or after the regeneration means. When this comparison value exceeds the threshold value, at least one other regeneration measure is taken. In addition, it is possible to change the content of the reducing agent in the exhaust gas during NO _X regeneration or SO _X regeneration depending on the comparison value. This makes it possible to easily take into consideration the actual catalyst state.

Furthermore, it is advantageous if a regeneration means is provided during NO _x regeneration when the comparison value exceeds a threshold value, ie in a rich atmosphere or a stoichiometric mixture ratio, which subsequently raises the exhaust gas temperature without changing to a lean operating mode. is there. If the comparison value exceeds the threshold,
The catalyst component of the NO _x absorption catalyst is damaged.

Furthermore, it is advantageous to detect the comparison value after changing to a lean atmosphere. First N
Starting from O _X regeneration, after each playback means, whether the comparison value is greater than the threshold is examined again, other playback means are taken in some cases. At that time, it has been found a new NO _X regeneration after the first of the NO _X regeneration, and may continue to increase in temperature of the exhaust gas is advantageous. Furthermore, if the comparison value is too high, SO _X regeneration can be started. This SO _X regeneration is repeated in some cases. By comparison value even after a new SO _X regeneration is greater than the threshold, NO _X absorbent catalyst is damaged irreversibly with high probability.

Other advantageous embodiments of the invention are apparent from the other features of the dependent claims.

[0017]   Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 schematically shows an arrangement structure of the catalyst system 10 in the exhaust passage 12 of the combustion engine 14. The catalyst system 10 includes a NO _x absorption catalyst (storage catalyst) 16, a primary catalyst (pre-catalyst) 18, and a temperature sensor 22.

The catalyst system 10 is further provided with gas sensors 19, 20, 21. This gas sensor can detect the gas content of the gas component of the exhaust gas. For example, a lambda oxygen sensor or a component-specific sensor is suitable. At that time, the gas sensor 2
1 allows for detection of at least NO _X concentration, and thus is NO _X sensor.

The operating mode of the combustion engine 14 can be controlled by the engine controller 24. If a mode of operation, for example λ <1 (rich atmosphere) is desired, the oxygen concentration in the intake pipe 26 must be reduced before combustion of the fuel-air mixture. At the same time, the content of reducing agents such as CO, HC and H _{2 in} the exhaust gas is increased compared with the content of oxygen. For example, such an operating mode can be adjusted by reducing the flow rate of the air sucked in by the throttle valve 28 and by simultaneously supplying the exhaust gas low in oxygen via the exhaust gas check valve 30.

During combustion, gaseous pollutants such as CO, HC, NO _x or SO _x are formed in varying proportions. The reducing agent can be oxidized by oxygen in the primary catalyst 18.
With sufficient oxygen concentration, complete or sufficient conversion is possible in almost all operating modes.

In the operating mode of λ> 1 (lean atmosphere), SO _X is absorbed by the NO _X absorption catalyst 16 in addition to NO _X , while a small proportion of the reducing agent is almost absorbed in the primary catalyst 18 at least at a low space velocity. Completely converted. Depending on the NO _X storage capacity of the NO _X absorption catalyst 16 and the NO _X desorption temperature, the combustion engine 14 must operate at λ ≦ 1 for NO _X regeneration. In this mode of operation, the previously absorbed NO _x is N
It is reduced on the catalytic surface of the O _x absorption catalyst 16.

Similarly, the absorbed SO _X is stored in the NO _X absorption catalyst 16 in the form of sulfate.
Of course in this case, reversibility of the storage process requires temperatures much higher Unlike storage NO _X. Therefore, there must be a minimum sulfidation temperature and an air excess of λ ≦ 1 for desulfurization (SO _x regeneration temperature). By providing at least temporary influence on at least one operating parameter of the combustion engine 14, it is possible to increase the exhaust gas temperature, it is possible to heat the NO _X absorbent catalyst 16 to the lowest temperature.

The gas sensor 21 continuously detects the NO _X concentration of the exhaust gas behind the NO _X absorption catalyst 16. This concentration is compared with NO _X target density, compared value correspondingly to the deviation of the concentration from the target concentration is obtained. If the comparison value exceeds a configurable threshold,
Regeneration measures are taken. Reproducing means, in order to remove a coating of absorbent catalyst by condensate or soot, SO _X regeneration (desulfurization), it includes an increase of the NO _X regeneration or exhaust gas temperature. In selecting the regenerating means, it is important that this regenerating means be adapted to the regenerating means which was previously performed. As a result, the individual regeneration means can be harmonized and the regeneration of the absorption catalyst 16 can be controlled extremely efficiently. When the comparison value after implementing the reproducing means further exceeds the threshold value, another reproducing means is selected and implemented.

FIG. 2 is a block diagram for controlling the regeneration of the NO _X absorption catalyst 16 in the rich atmosphere. In such an atmosphere, NO _X regeneration of the NO _X absorption catalyst 16 can be already performed. If the comparison value falls below the threshold value during comparison 40, another means (42)
Cannot be taken. However, when the comparison value reaches the threshold value, the operating temperature of the combustion engine 14 is at least temporarily affected so that the exhaust gas temperature is increased (exhaust gas temperature increase 44). Then, a comparison 40 between the comparison value and the threshold value is performed. When the comparison value exceeds the threshold value, irreversible damage to the NO _X absorption catalyst 16 is estimated.

In addition to the detection of NO _X concentration during NO _X regeneration, as shown in the block diagram of FIG.
Detection of the NO _X concentration can be carried out in a lean atmosphere. In that case, first, as already mentioned, the comparison 40 between the comparison value and the threshold value is carried out, and in some cases the NO _X regeneration 48 is started as regeneration means. In the subsequent comparison 40, if the comparison value is again greater than the threshold value, the second NO _X regeneration 50 is started. After the second NO _X regeneration 50 is completed, the comparison value and the threshold value are compared again. When the regenerating means is successful, the other means 42 are not taken. For example, to compensate for small irreversible damage to the NO _x absorption catalyst 16, optionally depending on the previously detected comparison value, N
O _X content of exhaust gas can be newly adapted 52 to the reproduction in the reducing agent.

However, when the comparison value 40 further exceeds the threshold value, the exhaust gas having the increased exhaust gas temperature is supplied to the NO _X absorption catalyst 16 (exhaust gas temperature increase 44). If this regeneration means does not reduce the comparison value, the first SO _X regeneration 54 is started and, if appropriate, a second SO _X regeneration 56 follows. Then, the comparison 40 between the comparison value and the threshold value is performed again. When the comparison value again falls below the threshold value, similar to the process in NO _X regeneration, it is possible to adapt the content with respect to SO _X regeneration the reducing agent (compatible 58).

It can be inferred that the NO _X -absorbing catalyst 16 is irreversibly damaged unless all the regenerating measures taken reduce the comparison value below the threshold value. In addition, the degree of this damage can be estimated from the situation of comparative values. The maintenance work that may be required may depend on the extent of this damage.

[Brief description of drawings]

[Figure 1]   It is a figure which shows the arrangement structure of the catalyst system in the exhaust passage of a combustion engine.

FIG. 2 is a block diagram for controlling regeneration of the NO _X absorption catalyst in a rich operation mode.

FIG. 3 is a block diagram for controlling regeneration of the NO _X absorption catalyst in a lean operation mode.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/20 F01N 3/28 301C 3/24 F02D 45/00 314Z 3/28 301 368F F02D 45/00 314 B01D 53/36 K 368 101B F-term (reference) 3G084 AA04 BA09 DA10 EA11 FA27 FA30 3G091 AA11 AA12 AA17 AA28 AB06 BA11 BA14 CA13 CB01 DA01 DA02 DA03 DA04 DB11 EA17 EA18 EA33 EA34 FB02 FB10 FB11 FB12 FC04 FC07 GA06 HA03 HA08 HA36 HA37 HA42 HB03 HB05 3G301 HA15 JA25 MA01 NA08 NE17 PD02 PD09 PD11Z 4D048 AA06 AB07 BC01 BD01 BD03 CC51 DA01 DA02 DA06 DA08 DA20 EA04

Claims (10)

[Claims] 1. A concentration of NO _X exhaust gas by NO _X sensor arranged downstream of the NO _X absorbent catalyst is detected, reproduction of at least one of the NO _X absorbent catalyst disposed in an exhaust passage of a combustion engine a method for controlling, (a) NO _X concentration measured after the absorbent catalyst is compared with the NO _X target density, compared value correspondingly to the deviation of the NO _X concentration is determined from the NO _X target concentration (B) regenerative measures are taken when the comparison value exceeds a settable threshold, at which at least one operating parameter of the combustion engine (14) is at least temporarily influenced, and ( c) A method characterized in that the reproduction means are optionally selected depending on the reproduction means carried out before it. 2. A comparison value is newly determined during or after the reproduction means, and at least one other reproduction means is taken when the comparison value exceeds a threshold value. The method described. When the comparison value exceeds the threshold value 3. A lean operating mode of the combustion engine (14), according to claim 1 and method of claim 2, characterized in that the NO _X regeneration is initiated as a regeneration unit. 4. The method according to claim 1, wherein the exhaust gas temperature is increased as the regeneration means when the comparison value exceeds a threshold value in the rich operating mode of the combustion engine (14). 5. The method according to claim 3, wherein NO _x regeneration is repeated as the regeneration means when the comparison value newly exceeds the threshold value. 6. The method according to claim 5, wherein the exhaust gas temperature is raised as the regeneration means when the comparison value is newly above the threshold value. 7. The method according to claim 6, characterized in that when the comparison value newly exceeds the threshold value, SO _X regeneration is started as regeneration means. 8. The method according to claim 6, wherein SO _x regeneration is repeated as regeneration means when the comparison value newly exceeds the threshold value. 9. The method according to claim 4, wherein the irreversible damage to the NO _x -absorbing catalyst is determinable when the comparison value is above the threshold value. 10. The content of the reducing agent in the exhaust gas during NO _X regeneration or SO _X regeneration is changed depending on the comparison value. the method of.