EP1194683B1 - Method for controlling the operating mode of an internal combustion engine - Google Patents

Abstract

The invention relates to a method for controlling an operating mode of an internal combustion engine. Elements are allocated to the internal combustion engine which at least temporarily influence at least one operating parameter of the internal combustion engine, based on a calculated or measured catalyst temperature of at least one storage catalyst which is located in an exhaust gas channel, in order to set the operating mode of the internal combustion engine. According to the invention: a) the storage catalyst (12) is divided into a number of catalyst cells according to a predetermined matrix; b) a cell temperature is determined for each catalyst cell and c) the operating mode of the internal combustion engine (16) is determined according to the cell temperature of at least one predetermined catalyst cell.

Description

The invention relates to a method for controlling a working mode Internal combustion engine with those mentioned in the preamble of claim 1 Features.

In order to control a working mode of an internal combustion engine, it is known to assign means to the internal combustion engine which allow the working mode to be set by at least temporarily influencing at least one operating parameter of the internal combustion engine. It is also known to clean an exhaust gas from the internal combustion engine by means of suitable catalysts which are arranged in an exhaust gas duct. Such catalysts include NO _x storage catalysts.

During a combustion process of an air-fuel mixture in the internal combustion engine, gaseous pollutants are produced in varying proportions, which can act on the one hand as a reducing agent and on the other hand as an oxidizing agent. Reducing agents, such as CO, HC or H ₂ , arise to an increasing extent under conditions in which a ratio of oxygen to a fuel is sub-stoichiometric or stoichiometric (λ ≤ 1; regeneration mode). If, on the other hand, the oxygen in the air-fuel mixture predominates, the internal combustion engine is in lean operation (λ> 1) and a proportion of the reducing agents in the exhaust gas decrease. In dynamic operation of the internal combustion engine, it is usually still possible to oxidize the reducing agents in the catalytic converter to a sufficient extent with oxygen.

In addition, oxidizing agents such as NO _x and SO _{x are also} formed during a combustion process. These are reduced on the storage catalytic converter in the regeneration mode by the reducing agents. In a lean operation, this is no longer possible to a sufficient degree, but under such conditions the oxidizing agents are stored in the storage catalytic converter. NO _X absorption takes place until a NO _X desorption temperature is reached or until the storage catalytic converter has no NO _X storage capacity. Prior to this time, therefore, a change in the regeneration operation has to take place to a NO _x emission downstream of the storage catalytic converter to reduce.

For this purpose, it is known to control the working mode as a function of an average catalyst temperature. The catalyst temperature can be detected, for example, via sensors additionally introduced into the exhaust gas duct, or can also be calculated in a known manner using suitable models. If the catalyst temperature exceeds a predefinable threshold temperature, a switch to regeneration mode is initiated in order to prevent NO _X desorption without a simultaneous reduction. EP 0 867 604 A describes a method for controlling regeneration intervals of NO _x stores as a function of a calculated or measured temperature of the store and its NO _x loading. A locally differentiated temperature calculation of the NO _x storage is proposed, for which local temperatures are calculated at different positions within the storage and an average storage temperature is calculated from these.

On the other hand, the storage catalytic converter must be heated to a minimum operating temperature in order to ensure sufficient NO _x storage capacity. It is known to operate the internal combustion engine in regeneration mode until a predeterminable minimum temperature is reached. In such an operation, an exhaust gas temperature is generally higher than in lean operation. However, additional fuel consumption must be accepted. To reduce fuel consumption, it is therefore necessary to keep the duration of the regeneration operation as short as possible.

It is also known to desulfurize the storage catalytic converter as required at certain intervals (SO _X regeneration). The regeneration operation of the internal combustion engine is also set for this. However, a significantly higher minimum desulfurization temperature is required for desulfurization. In the previous method, too, only an averaged minimum desulfurization temperature is used here, from which the change to regeneration mode takes place. However, it may make sense to initiate the desulfurization if only individual areas of the storage catalytic converter have exceeded the minimum desulfurization temperature.

The invention has for its object to provide a method that in allows an inhomogeneous temperature curve in a particularly simple and flexible manner within the storage catalytic converter in controlling the working mode of the internal combustion engine to consider. This should go hand in hand with fuel consumption be reduced.

(a) der Speicherkatalysator entsprechend einer vorgebbaren Matrix in einer Anzahl von Katalysatorzellen aufgeteilt wird;

(b) eine Zellentemperatur für jede Katalysatorzelle ermittelt wird und

(c) der Arbeitsmodus der Verbrennungskraftmaschine in Abhängigkeit von der Zellentemperatur von wenigstens einer vorgebbaren Katalysatorzelle bestimmt wird derart,

• dass ein Magerbetrieb mit λ > 1 eingestellt wird, wenn in wenigstens einer Katalysatorzelle die Zellentemperatur zwischen einer vorgebbaren unteren Grenztemperatur und einer vorgebbaren oberen Grenztemperatur liegt und/oder
• dass beim Überschreiten der Zellentemperatur in wenigstens einer Katalysatorzelle über eine Mindestentschwefelungstemperatur eine Entschwefelung eingeleitet wird.

According to the invention, this object is achieved by the method for controlling the working mode of the internal combustion engine with the features mentioned in claim 1. As a result of that

(a) the storage catalytic converter is divided into a number of catalytic converter cells in accordance with a predeterminable matrix;

(b) a cell temperature is determined for each catalyst cell and

(c) the working mode of the internal combustion engine is determined as a function of the cell temperature of at least one predefinable catalyst cell,

• that lean operation is set to λ> 1 if the cell temperature in at least one catalyst cell lies between a predeterminable lower limit temperature and a predeterminable upper limit temperature and / or
• that when the cell temperature is exceeded in at least one catalyst cell above a minimum desulfurization temperature, desulfurization is initiated.

it is possible to make the working mode of the internal combustion engine an actual one Adapt catalyst state.

The lower limit temperature is selected such that the minimum operating temperature is exceeded and there is an overall sufficient NO _x storage capacity of the storage catalytic converter. The upper limit temperature is below the NO _X desorption temperature. The lean operation of the internal combustion engine can therefore still be maintained if the mean catalyst temperature has already exceeded the upper limit temperature, but is still at least one catalyst cell below the predefinable upper limit temperature, and the internal combustion engine can already start lean operation in at least one catalyst cell after the minimum operating temperature has been exceeded be switched, even if the mean catalyst temperature is below the minimum operating temperature.

It has proven to be advantageous to determine the NO _x storage capacity for each catalyst cell as a function of the NO _x and SO _x loading state and the cell temperature. The NO _x storage capacity can be used as a further criterion for maintaining lean operation. To this end, it is conceivable, on the one hand, to specify a threshold value for the NO _x storage capacity and to start the regeneration operation of the internal combustion engine when the threshold value is exceeded. On the other hand, a cumulative raw NO _x emission of the internal combustion engine over a predefinable period and the NO _x desorption of each catalyst cell can be calculated over the same period. Subsequently, depending on the NO _x storage capacity, the NO _x desorption and a spatial position of each catalyst cell and the cumulative raw NO _x emission, a cumulative NO _x emission downstream of the storage catalytic converter can be calculated. If the calculated cumulative NO _x emission exceeds a predeterminable threshold value, the regeneration operation of the internal combustion engine is also set.

It is also provided that the desulfurization is initiated when the cell temperature is exceeded in at least one catalyst cell above the minimum desulfurization temperature. Of course, the desulfurization can also be made dependent on a predefinable threshold value for the SO _X loading state. In this way, it is possible to initiate the desulfurization even before an average minimum desulfurization temperature is exceeded, thus shortening a heating-up phase.

A duration of the heating phase to reach the minimum desulfurization temperature in Catalyst cells located further downstream can depend on the cell temperature Catalyst cells located further upstream are calculated since these are their Excess heat (difference between the cell temperature and the minimum desulfurization temperature) pass downstream during desulfurization. So that becomes a Desulphurization time is shortened and an additional consumption due to desulphurization reduced.

It has proven to be advantageous to use a storage catalyst model for a spatial extension, a temperature profile, a profile of a regeneration speed, a profile of the NO _x storage capacity, a profile of the NO _x -, SO _x - or O ₂ -load condition or a combination thereof.

Further preferred refinements of the invention result from the others in the Characteristics mentioned subclaims.

Figur 1

eine Anordnung eines NO_X-Speicherkatalysators in einem Abgaskanal einer Verbrennungskraftmaschine;

Figur 2

eine schematische Darstellung einer Aufteilung des Speicherkatalysators anhand einer Matrix;

Figur 3

eine schematische Darstellung eines Verlaufes eines Lambdawertes während einer NO_X-Regeneration;

Figur 4

eine schematische Darstellung des Verlaufes des Lambdawertes während einer Aufheizphase kurz nach Start der Verbrennungskraftmaschine;

Figur 5

ein Flußdiagramm eines Ausführungsbeispiels des erfindungsgemäßen Verfahrens zur Steuerung eines Arbeitsmodus der Verbrennungskraftmaschine und

Figur 6

ein Flußdiagramm eines Ausführungsbeispiels des erfindungsgemäßen Verfahrens zur Steuerung eines Arbeitsmodus der Verbrennungskraftmaschine während einer Entschwefelung.

The invention is explained in more detail below in exemplary embodiments with reference to the associated drawings. Show it:

Figure 1

an arrangement of a NO _x storage catalyst in an exhaust duct of an internal combustion engine;

Figure 2

a schematic representation of a division of the storage catalyst using a matrix;

Figure 3

a schematic representation of a course of a lambda value during a NO _X regeneration;

Figure 4

a schematic representation of the course of the lambda value during a heating phase shortly after the start of the internal combustion engine;

Figure 5

a flowchart of an embodiment of the inventive method for controlling a working mode of the internal combustion engine and

Figure 6

a flowchart of an embodiment of the inventive method for controlling a working mode of the internal combustion engine during desulfurization.

FIG. 1 shows a schematic representation of an arrangement 10 with a NO _x storage catalytic converter 12 in an exhaust gas duct 14 of an internal combustion engine 16. Of course, the arrangement 10 is only a greatly simplified exemplary embodiment, and additional NO _x storage catalytic converters or precatalysts can also be used in the area of the exhaust duct 14 are arranged. Such arrangements are known and will not be explained in more detail here.

In addition, sensors are arranged in the exhaust gas channel, which allow a conclusion to be drawn about a current catalytic converter condition, for example by detecting a content of a gas component in an exhaust gas or a temperature. For this purpose, a gas sensor 18 and a temperature sensor 20 are shown in the arrangement 10, which are located downstream of the NO _x storage catalytic converter 12. The sensors 18, 20 deliver signals that can be evaluated within an engine control unit 22. Furthermore, means 24 are assigned to the internal combustion engine 16, which enable at least a temporary influencing of at least one operating parameter of the internal combustion engine 16. In this way, an exhaust gas temperature, a working mode of the internal combustion engine 16 and / or the proportion of the individual gas components in the exhaust gas can be varied. Such influencing of the operating parameters of the internal combustion engine 16 is known and will not be explained in more detail in this context.

During a combustion process of an air-fuel mixture in the internal combustion engine 16, reducing agents, such as CO, HC and H ₂ , and oxidizing agents, such as NO _x and SO _x, are produced in varying proportions. In a working mode with λ 1 1 (rich or stoichiometric atmosphere, regeneration mode), a fuel fraction outweighs an oxygen fraction in the air / fuel mixture or these are in stoichiometric ratios. As a result, reducing agents are formed to an increased degree. If the working mode changes in a range with λ> 1 (lean atmosphere, lean operation), the proportion of reducing agents in the exhaust gas decreases. In the NO _x storage catalytic converter 12, the reducing agents are oxidized with oxygen. A reduction in a reducing agent emission is therefore always possible to a sufficient extent if an oxygen concentration in the NO _x storage catalytic converter 12 is correspondingly high.

In contrast, the oxidizing agents are converted in the NO _x storage catalytic converter 12 by the reducing agents. To a sufficient degree, this can only be done in a working mode with λ ≤ 1. In a lean atmosphere, the NO _{X is} absorbed as nitrate and the SO _X as sulfate until a NO _X desorption temperature is reached or a NO _X storage capacity is exhausted. Accordingly, at least one NO _x regeneration must be carried out before this point in time.

Due to a higher SO _X desorption temperature, SO _X regeneration (desulfurization) generally does not take place during NO _X regeneration. An operating mode with λ ≤ 1, and a regeneration temperature (in dependence on the NO _X or SO _X desorption temperature) necessary to form the combined regeneration parameters - Overall, however, are for regeneration (and SO _x regeneration NO _X). The regeneration parameters can be set in a known manner by influencing the operating parameters of the internal combustion engine 16. It is also known to determine a need for regeneration of the NO _x storage catalytic converter 12. This will not be explained in more detail in this context.

FIG. 2 schematically shows a division of the storage catalytic converter 12 into any number of catalytic converter cells using a predeterminable matrix. The matrix for dividing the storage catalytic converter 12 into the catalyst cells can be determined using a storage catalytic converter model. This model can include, for example, a spatial extension of the storage catalytic converter 12, a temperature profile or a profile of a regeneration speed within the storage catalytic converter 12. It is also conceivable to use a course of the NO _x storage capacity and a course of a loading state for NO _x , SO _x or O ₂ within the storage catalytic converter 12. The loading state is a measure of an absorbed NO _X , SO _X or O ₂ mass of a catalyst cell. Of course it is possible to incorporate a combination of the parameters mentioned in a calculation of the matrix. In the example shown, the storage catalytic converter 12 has been divided into a total of six catalyst cells Z ₁ to Z ₆ (zones), the cell Z _{1 being arranged} on a side facing the internal combustion engine 16.

FIG. 3 shows a course of the lambda value during the regeneration of the storage catalytic converter 12 (dashed line). A curve of the lambda value according to a conventional method (solid line) is also shown for clarification. Here, the internal combustion engine 16 is initially in a lean mode for a phase t _m1 . After a predefinable threshold temperature for the average catalyst temperature of the storage catalytic converter 12 has been exceeded, the regeneration mode is set in a phase t _f1 , at least until the threshold temperature is again fallen below. Lean operation is then started again in a phase t _m2 .

In the method according to the invention, the course of the lambda value (dashed line) is significantly different. In a phase t _f1 ', the regeneration operation can be started later on the one hand and ended earlier on the other hand. In the lean phases t _m1 'and t _m2 ', the mean catalyst temperature may occasionally be above the limit temperature that can be specified using the conventional method, but the temperature in selected catalyst cells (cell temperature) can still be low enough to ensure sufficient NO _x storage capacity , The type of control will be explained in more detail below.

FIG. 4 shows a course of the lambda value during a heating phase of the storage catalytic converter 12 (dashed line). Again, a solid line shows the course of the lambda value according to a conventional method. In order to bring the storage catalytic converter 12 to a necessary operating temperature shortly after the internal combustion engine 16 has started, a rich or stoichiometric exhaust gas (λ 1 1) is initially applied to it for a phase t _f2 , since the exhaust gas temperatures are generally significantly increased here. The regeneration operation is maintained until the average catalyst temperature has exceeded a minimum temperature. In contrast, a phase t _f2 'is shortened in the process according to the invention, and lean operation can already be started when selected catalyst cells have exceeded the minimum temperature.

FIG. 5 is a flow chart for controlling the working mode of the Internal combustion engine 16 shown. First, in a step S1 Storage catalytic converter 12 in any number according to the predeterminable matrix divided by catalyst cells. Subsequently, in a step S2 Cell temperature determined for each catalyst cell. The cell temperature will either measured directly, for example using additional temperature sensors, or it is calculated using known models.

In a step S3, it is determined whether the cell temperature in a selected number of catalytic converter cells, which is dependent on exhaust gas mass flow and lambda and NOx raw emissions, lies between a predeterminable lower limit temperature G ₁ and a predefinable upper limit temperature G ₂ . The lower limit temperature G ₁ represents the minimum operating temperature of the storage catalytic converter 12, which is necessary in order to allow sufficient NO _x storage capacity at all. The upper limit temperature G ₂ is selected such that it lies below the NO _X desorption temperature so that NO _X emissions downstream of the storage catalytic converter 12 are avoided. If the cell temperature in the selected catalyst cells is below the lower limit temperature G ₁ , a heating measure can be initiated in a step S4, for example by changing to regeneration mode. If the cell temperature in the selected catalyst cells is above the upper limit temperature G ₂ , a cooling measure can optionally be carried out in step S4 by influencing the operating parameters of the internal combustion engine 16 in a known manner.

In a step S5, the NO _x storage capacity of selected catalyst cells is determined. This can in turn be carried out using known storage catalytic converter models for the NO _x , SO _x or O ₂ loading state. If the NO _x storage capacity does not reach a predefinable threshold value S ₁ (step S6), the regeneration operation is started in a step S7.

In a step S8, depending on the NO _x storage capacity, the NO _x desorption and a spatial position of each catalyst cell and a NO _x raw emission of the internal combustion engine 16, a cumulative NO _x emission downstream of the storage catalytic converter is calculated in a predeterminable period of time. Thus, the catalyst cells shown in Figure 2 Z ₄ to Z _6, the downstream further need are arranged in the exhaust passage 14, possibly also accommodate addition to the heat generated by the internal combustion engine 16 NO _X -Rohemission NO _X that by NO _X desorption in earlier lying catalyst cells (Z ₁ to Z ₃ ) is released. If the calculated cumulative NO _x emission downstream of the storage catalytic converter 12 exceeds a predeterminable threshold value S ₂ , the regeneration operation is started again (step S7). If this is not the case, the internal combustion engine 16 remains in the lean operation or is adjusted to the lean operation (step S10).

FIG. 6 shows a flow chart for controlling the operating mode of the internal combustion engine 16 during the desulfurization. In steps S1 and S2 - as already explained - the storage catalytic converter 12 is first divided into individual catalytic converter cells and the cell temperature of selected catalytic converter cells is recorded. If the cell temperature in the selected catalyst cells is below a minimum desulfurization temperature (step S11), no further action is taken (step S12). Otherwise it is checked in a step S13 whether the SO _X loading state exceeds a predeterminable threshold value S ₃ . If necessary, a duration of the heating phase for the desulfurization is then determined in a step S14. The duration of the heating phase for reaching the minimum desulfurization temperature in further downstream catalyst cells (for example the catalyst cells Z ₄ to Z ₆ in FIG. 2) can be determined as a function of the cell temperature in further upstream catalyst cells (for example the catalyst cells Z ₁ to Z ₃ in FIG. 2) become. In addition to a heat flow through the exhaust gas, a heat flow can also take place within the storage catalytic converter 12 between the individual catalyst cells. in general, the further upstream catalyst cells have a higher cell temperature. Overall, the regeneration time during desulfurization can be significantly reduced in this way. The desulfurization is then carried out in a step S15.

Claims (7)

1. Method for controlling an operating mode of a combustion engine (16), wherein means are allocated to the combustion engine (16), which, in dependence upon a calculated or measured catalyst temperature of at least one storage catalyst (12) arranged in an exhaust duct, influence at least one operating parameter of the combustion engine (16) in order to adjust the operating mode of the combustion engine (16) at least temporarily, characterised in that

   (a) the storage catalyst (12) is subdivided according to a preselectable matrix into a number of catalyst cells;

   (b) a cell temperature is determined for each catalyst cell;

   (c) the operating mode of the combustion engine (16) is determined in dependence upon the cell temperature of at least one preselectable catalyst cell in such a manner that

   a lean operating mode with λ > 1 is set, whenever the cell temperature in at least one catalyst cell, lies between a preselectable lower threshold temperature (G₁) and a preselectable upper threshold temperature (G₂) and/or

   desulfuration is initiated whenever the cell temperature in at least one catalyst cell rises above a minimum desulfuration temperature.
2. Method according to claim 1, characterised in that

   (a) an NO_x storage capacity for each catalyst cell is determined in dependence upon a NO_x and SO_x loading status and the cell temperature, and

   (b) the operating mode of the combustion engine (16) is determined in dependence upon the NO_x storage capacity of at least one preselectable catalyst cell.
3. Method according to claim 2, characterised in that a threshold value (S₁) for the NO_x storage capacity is preselected and that whenever the threshold value (S₁) of at least one catalyst cell is exceeded, a regeneration mode of the combustion engine (16) with λ ≤ 1 is adjusted.
4. Method according to claim 2 or 3, characterised in that

   (a) a cumulative NO_x raw emission from the combustion engine (16) and an alteration of the NO_x loading status of selected catalyst cells are calculated for a preselectable period;

   (b) a cumulative NO_x emission downstream of the storage catalyst (12) is calculated in dependence upon the NO_x storage capacity, the alteration of the NO_x loading status, a spatial location of the selected catalyst cells and the cumulative NO_x raw emission;

   (c) a threshold value (S₂) for the cumulative NO_x emission is preselected and

   (d) whenever the threshold value (S₂) is exceeded, the regeneration operating mode of the combustion engine (16) is set.
5. Method according to any one of the preceding claims, characterised in that the desulfuration is initiated in dependence upon a preselectable threshold value (S₃) for the SO_x loading status.
6. Method according to any one of the preceding claims, characterised in that a duration of a warm-up phase to reach the minimum desulfuration temperature in catalyst cells located further downstream is determined in dependence upon the cell temperature of catalyst cells located further upstream.
7. Method according to any one of the preceding claims, characterised in that the matrix for subdivision of the storage catalyst (12) into catalyst cells is established on the basis of a storage-catalyst model for a spatial extension, a temperature characteristic, a characteristic for a regeneration rate, a characteristic for the NO_x storage capacity, a characteristic for the NO_x, SO_x or O₂ loading status or a combination of the same.

Images