EP1203144A1

EP1203144A1 - Method of regulating the operational mode of an internal combustion engine

Info

Publication number: EP1203144A1
Application number: EP00949277A
Authority: EP
Inventors: Ekkehard Pott; Axel Lang
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 1999-07-19
Filing date: 2000-07-06
Publication date: 2002-05-08
Anticipated expiration: 2020-07-06
Also published as: EP1203144B1; WO2001006105A1; DE50008146D1; DE19933712A1

Abstract

The invention relates to a method of regulating the operational mode of an internal combustion engine. The internal combustion engine is linked with means that allow the regulation of the operational mode by at least temporarily influencing at least one operational parameter of the internal combustion engine. The operational mode is regulated depending on the catalyst temperature of at least one NOx storage catalyst that is located in the waste gas duct of the internal combustion engine. According to the inventive method, the operational mode of the internal combustion engine (16) is adjusted if the catalyst temperature exceeds a definable threshold temperature (GT) depending on at least one operational parameter of the internal combustion engine (16) and/or an effective catalyst state of the NOx storage catalyst (12).

Description

Method for controlling an operating mode of an internal combustion engine

The invention relates to a method for controlling a working mode of an internal combustion engine with the features mentioned in the preamble of claim 1.

It is known to assign means to an internal combustion engine which, by at least temporarily influencing at least one operating parameter of the internal combustion engine, permit the control of the working mode. It is also known to arrange an NO _x storage catalytic converter in an exhaust gas duct for cleaning an exhaust gas of the internal combustion engine. In this case, for example, a content of a gas component in the exhaust gas can be detected via sensors additionally arranged in the exhaust gas duct, or a temperature or a temperature profile can also be tracked. In addition, such variables can also be predicted using suitable models, so that it is ultimately possible to quantitatively record selected operating parameters of the internal combustion engine, such as an exhaust gas temperature, a raw emission of selected gas components, a space velocity of the exhaust gas, a vehicle speed, an engine speed or a requested load.

A current catalyst state can be determined in the same way. Thus, either by calculation or by measurements, a catalyst temperature, an NO _x are - or SO _x -Beladungszustand, an NO _x storage capacity, a thermal capacity of the storage catalyst or the like can be detected. The means for controlling the working mode of the internal combustion engine and the methods for detecting the operating parameters of the internal combustion engine and the current catalytic converter state are known and are therefore not explained in more detail in connection with this description.

If there is an excess of oxygen during a combustion process of an air-fuel mixture, the internal combustion engine is in a so-called lean working mode with λ> 1 (lean operation). The educated among others during the combustion process NO _x by the NO _x - Storage catalyst is absorbed as nitrate until a NO _x desorption temperature is reached or a NO _x storage capacity is exhausted. To avoid NO _x emissions downstream of the NO _x storage catalytic converter, a change to a working mode with λ <1 (regeneration mode) must take place before this time. Under such conditions, the absorbed NO _x is desorbed again and reacted on a catalyst component of the storage catalyst with reducing agents such as CO, HC or H2. The proportion of reducing agents increases significantly in the regeneration mode during the combustion process, since in this case there is a deficit of oxygen in the air-fuel mixture.

It is also known to detect the catalyst temperature and, with a view to possible NO _x desorption, to specify a limit value for the temperature at which a change to the regeneration mode must take place. However, operating the internal combustion engine below λ <1 leads to increased fuel consumption, and therefore a regeneration period should be kept as short as possible in practice. Since a NO _x desorption characteristic and thus the NO _x desorption temperature is strongly dependent on the current state of the catalytic converter, the limit temperature is determined with a considerable safety margin to avoid NO _x emissions downstream of the storage catalytic converter. However, a fixed limit temperature is disadvantageous for two reasons. On the one hand, there may be boundary conditions above the limit temperature which allow the internal combustion engine to operate in a lean atmosphere, and this results in unnecessary additional consumption. On the other hand, it is disruptive that the exhaust gas temperature in regeneration operation is generally above the exhaust gas temperature in lean operation and cooling of the storage catalytic converter is thus made more difficult.

The object of the method according to the invention is to make the control of the working mode of the internal combustion engine considerably more flexible, so that a change to lean operation can still take place even after the catalyst temperature has exceeded the limit temperature.

According to the invention, this object is achieved by the method for regulating the working mode of the internal combustion engine with the features mentioned in claim 1. Characterized in that the working mode of the internal combustion engine is set when the catalyst temperature is exceeded above a predetermined limit temperature as a function of at least one operating parameter of the internal combustion engine and / or a current catalytic converter state of the NO _x storage catalytic converter is, it is possible to set a lean operation of the internal combustion engine even above the limit temperature.

In a preferred embodiment of the method according to the invention, at least one of the operating parameters of the internal combustion engine and / or the current catalytic converter state flows into a map, via which the operating mode of the internal combustion engine is determined. In this way, the boundary conditions (current catalytic converter state and operating parameters of the internal combustion engine) can be taken into account in a very simple manner when selecting the working mode.

A duration of a working mode, in particular after the change to lean operation, can be determined taking into account the current catalytic converter state and the operating parameters of the internal combustion engine. It is also conceivable to determine a frequency for the change from regeneration mode to lean mode and back (wobble frequency) in accordance with these boundary conditions.

Furthermore, it has proven to be advantageous after a change to the lean operation downstream of the storage catalytic converter to detect a NO _x concentration or a NO _x emission accumulated over a predefinable period of time using a suitable sensor. If the NO _x concentration exceeds a predeterminable threshold value or the cumulative NO _x emission exceeds a predeterminable threshold value within the predeterminable period of time, the lean operation can be interrupted. In this way it is possible to keep the NO _x emission downstream of the storage catalytic converter as low as possible and to comply with the legal standards that may be present.

Furthermore, it is conceivable if a predefinable threshold value for a raw NO _x emission (NO _x emission upstream of the storage catalytic converter), the NO _x concentration or the cumulative NO _x emission is a NO _x reduction measure by influencing the operating parameters of the internal combustion engine to take. Of course, the NO _x reduction measure can also be initiated as a function of the NO _x emission detected downstream of the storage catalytic converter.

Further preferred embodiments of the invention result from the other features mentioned in the subclaims. The invention is explained in more detail below in exemplary embodiments with reference to the associated drawings. Show it:

Figure 1 shows an arrangement of a NO _x storage catalyst in an exhaust duct of an internal combustion engine;

Figure 2 shows a course of a catalyst temperature and

Figure 3 is a flow chart of an embodiment of the invention

Method for controlling a working mode of the internal combustion engine.

An arrangement 10 of a NO _x storage catalytic converter 12 in an exhaust gas duct 14 of an internal combustion engine 16 is shown schematically in FIG. Furthermore, sensors 18, 20 are arranged in the exhaust gas duct, which make it possible to determine a content of a gas component in the exhaust gas (gas sensors) or to record a temperature (temperature sensors). The number, position and type of such sensors 18, 20 are highly variable. A detection and evaluation of the signals of such sensors 18, 20 is known and will not be explained in more detail in the context of this description. In addition, it is possible in a known manner to calculate the content of the gas components or the temperature in selected areas of the arrangement 10 using suitable models.

For reasons of clarity, a representation of means assigned to the internal combustion engine has been dispensed with, which means that a working mode can be controlled by at least temporarily influencing at least one operating parameter of the internal combustion engine. Such means for influencing the operating parameters are well known and are therefore not explained in more detail here. It is also known to detect a catalytic converter temperature, for example by means of the sensor 20, and to control the operating parameters of the internal combustion engine 16 as a function of this catalytic converter temperature.

If there is an excess of oxygen in excess of a fuel in the internal combustion engine 16 during a combustion process, the internal combustion engine is in a working mode with λ> 1 (lean operation). During lean operation, the NO _x in generated during the combustion process absorbs the NO _x storage catalyst 12 until either an NO _x desorption temperature is reached or a NO _x storage capacity is exceeded.

Under stoichiometric conditions or when the fuel has an excess of oxygen (λ <1; regeneration mode), reducing agents such as CO, HC or H2 are generally produced to an increased extent. In regeneration mode, the absorbed NO _{x is} swapped out again (NO _x desorption) and converted in the NO _x storage catalytic converter 12 with the aid of the reducing agents.

As already mentioned, the NO _x storage capacity of the NO _x storage catalytic converter 12 is temperature-dependent. In order to avoid NO _x emission downstream of the NO _x storage catalytic converter 12, the internal combustion engine 16 is therefore set to the working mode with λ <1 (regeneration mode) in the method according to the invention after a predetermined limit temperature GT has been exceeded. A course of the temperature during such a regulation of the working mode of the internal combustion engine 16 is shown as an example in FIG. 2. At the end of a lean phase t _m ι, for example, a switch is made to the working mode with λ <1 due to an increased power requirement on the internal combustion engine 16.

During a fat phase tf- | the limit temperature GT of the catalyst is exceeded. During this fat phase tf- | a current catalytic converter state and / or at least one operating parameter of the internal combustion engine 16 is continuously detected. Selected operating parameters of the internal combustion engine 16 can be, for example, an exhaust gas temperature, a raw emission of selected gas components, a space velocity of the exhaust gas, a vehicle speed, an engine speed or a requested load. The catalytic converter state can be determined via the sensors 18, 20 or via suitable models and includes, for example, a NO _x or SO _x loading state, the NO _x storage capacity, a heat capacity of the storage catalytic converter or the catalytic converter temperature. Methods for detecting the operating parameters of the internal combustion engine 16 and the current catalytic converter state are known and are therefore not explained in more detail here.

After the detection of the boundary conditions (catalytic converter state and operating parameters), the working mode of the internal combustion engine 16 is assigned via a map, so that, for example, from a time T- | because of the admissibility of a lean work mode in the operation of the internal combustion engine, a change to lean operation can be initiated. As can be seen, the catalyst temperature is above the limit temperature GT and only drops below this threshold from a time T2. The regeneration operation of the internal combustion engine 16 is hereby significantly shortened compared to the known methods, which at least over the phases t _m 2 and tf- | a rich exhaust gas is applied to the storage catalytic converter 12, with a duration of the phase t _m 2 being extended due to the higher exhaust gas temperatures in the regeneration mode.

FIG. 3 shows a flow chart for regulating the working mode of the internal combustion engine according to the method according to the invention, taking into account the NO _x emission downstream of the storage catalytic converter 12. In a first step S1 - as already mentioned - the operating parameters of the internal combustion engine, for example the space velocity of the exhaust gas, the exhaust gas temperature, the requested load or the NO _x raw emission, are recorded quantitatively.

At the same time, the current catalytic converter state is measured in a second step S2, for example via sensors 18, 20, or calculated using suitable models. If the current catalyst temperature exceeds the limit temperature (step S3), this can lead to the initiation of a map-controlled change in the setting of the working mode of the internal combustion engine 16 in a step S4. Here, selected operating parameters of the internal combustion engine as well as selected parameters of the current catalytic converter state, such as, for example, a NO _x desorption characteristic for a current NO _x or SO _x loading state, flow into the characteristic diagram.

In step S4, it is determined on the basis of the parameters made available whether it makes sense at all to switch internal combustion engine 16 to lean operation or to leave it in lean operation. For example, it can first be checked whether it is possible with a motor to allow the working mode with λ> 1 with regard to the requested load. It is also conceivable to calculate a maximum permissible duration of a cooling phase, that is to say the lean operation until the regeneration operation has to be stopped, on the basis of a cumulative raw NO _x emission predicted over a predeterminable period of time and the NO _x storage capacity determined. If the duration of the cooling phase falls below a predefinable minimum duration, the regeneration operation is started. In a step S5, the NO _x emission detected in a step S6 downstream of the NO _x storage catalytic converter 12 is compared with a predefinable threshold value for the NO _x emission downstream of the NO _x storage catalytic converter 12. In the same way, a comparison of an accumulated NO _x emission downstream of the NO _x storage catalytic converter 12 is also possible. If the (cumulative) emission exceeds the threshold value, it can be checked in a step S7 whether a NO _x reduction measure can be taken by influencing the operating parameters of the internal combustion engine 16. If this is not possible, the regeneration mode is set with λ <1. If the NO _x reduction measure is possible or if the (cumulative) emission threshold has not yet been exceeded, lean operation with λ> 1 is possible. Via step S5, it is possible to continuously check the NO _x emission or the cumulative NO _x emission downstream of the storage catalytic converter 12. In addition, a threshold value for a cumulative raw NO _x emission upstream of the NO _x storage catalytic converter 22 can also be specified and, if possible, the NO _x reduction measure can be initiated if this threshold value is exceeded.

Claims

PATENT CLAIMS

1. A method for regulating a working mode of an internal combustion engine, the internal combustion engine being assigned means which allow the working mode to be regulated by at least temporarily influencing at least one operating parameter of the internal combustion engine, and the regulating the working mode depending on a catalyst temperature of at least one in an exhaust gas duct the internal combustion engine arranged NO _x storage catalyst, characterized in that the operating mode of the internal combustion engine (16) when the catalyst temperature is exceeded above a predetermined limit temperature (GT) depending on at least one operating parameter of the internal combustion engine (16) and / or a current catalyst state of the NO _x storage catalyst (12) is set.

2. The method according to claim 1, characterized in that the at least one operating parameter of the internal combustion engine (16) and / or the current catalyst state flow into a map and the operating mode of the internal combustion engine (16) is determined via the map.

3. The method according to claims 1 or 2, characterized in that the operating parameters of the internal combustion engine (16) at least one exhaust gas temperature, an engine speed, a requested load, a space velocity of an exhaust gas, a content of at least one gas component in the exhaust gas (raw emission) or a vehicle speed include.

4. The method according to claims 1 and 2, characterized in that the current catalyst state comprises the catalyst temperature, a NO _x - storage capacity, a NO _x conversion rate or a thermal conductivity of the storage catalyst.

5. The method according to any one of the preceding claims, characterized in that a duration of a working mode with λ> 1 (lean operation) in Depending on the current state of the catalyst and the operating parameters of the internal combustion engine (16) is determined.

6. The method according to claim 5, characterized in that a working mode of the internal combustion engine (16) with λ <1 (regeneration operation) is set when the calculated duration of the lean operation falls below a predetermined minimum duration.

7. The method according to any one of the preceding claims, characterized in that a frequency of a change (wobble frequency) of the working mode is determined as a function of the current catalyst state and the operating parameters of the internal combustion engine (16).

8. The method according to any one of the preceding claims, characterized in that the lean operation is maintained until a predeterminable threshold value for NO _x emission downstream of the NO _x storage catalyst (12) is exceeded.

9. The method according to any one of claims 1 to 7, characterized in that the lean operation is maintained until a predeterminable threshold value is exceeded for a cumulative NO _x emission downstream of the NO _x storage catalytic converter (12).

10. The method according to any one of the preceding claims, characterized in that when a predeterminable threshold value for a raw NO _x emission, the NO _x emission or the cumulative NO _x emission downstream of the NO _x storage catalytic converter (12) a NO _x - Reduction measure is taken by influencing the operating parameters of the internal combustion engine (16).