DE102021205511A1 - Method for operating an internal combustion engine of a vehicle with a storage catalytic converter, as well as a computing unit and computer program - Google Patents

Abstract

The invention relates to a method (200) for operating an internal combustion engine (110) of a vehicle (100) with a storage catalytic converter (142) which is set up at least for storing nitrogen oxides, comprising determining (220) a vehicle speed, determining (210) a current fill level of nitrogen oxides in the storage catalytic converter (142), and a request to empty the storage catalytic converter (142) if the determined vehicle speed falls below a predeterminable speed threshold value and at the same time the determined fill level exceeds a predeterminable fill level threshold value. Furthermore, a computing unit and a computer program product for carrying out such a method are proposed

Description

The present invention relates to a method for operating an internal combustion engine of a vehicle with a storage catalytic converter and a computing unit and a computer program for its implementation.

Background of the Invention

Systems with nitrogen oxide (NO _x ) storage catalysts (NO _x Storage Catalyst, NSC) are known for the aftertreatment of exhaust gas from internal combustion engines, in particular engines with lean combustion (eg diesel engines), for the regeneration of which periodic rich operation of the internal combustion engine is necessary.

Previous application strategies aim at reducing NO _x within a driving cycle. The focus of the prioritization can be on an effective NO _x reduction, but at the same time on limiting the resulting additional fuel consumption. An appropriate "medium" loading threshold (NO _x loading of the storage component of the storage catalyst) can be selected for the requirement of DeNO _x regeneration, which represents a compromise between NO _x reduction efficiency (becomes lower with higher loading threshold) and additional fuel consumption (becomes lower with higher loading threshold). Furthermore, the vehicle speed parameter can be used to increase the prioritization of _NOx regeneration at higher vehicle speeds where there is a greater chance of fuel efficient regeneration.

Disclosure of Invention

According to the invention, a method for operating an internal combustion engine of a vehicle with a storage catalytic converter and a computing unit and a computer program for its implementation with the features of the independent patent claims are proposed. Advantageous configurations are the subject of the dependent claims and the following description.

A special role for the present invention is played by the prioritization of the DeNO _x regeneration requirement based on the vehicle speed and the NO _x loading of the NSC. Both aspects of the previous application strategies described at the beginning are inverted in their previous intention in a new strategic approach with a new objective and can thus fulfill a new objective. The concrete implementation of the strategy takes place through a very high prioritization of the _DeNOx regeneration requirement in the range below a speed threshold value, which is typically always relevant when the vehicle is parked and is not reached, but otherwise does not correspond to the driver's desired use. The speed threshold is preferably at most 30 km/h, 25 km/h, 20 km/h or 15 km/h. A low speed range is passed through each time before the internal combustion engine is switched off, but usually rarely during a journey, so that if the speed falls below such a low threshold value, there is a high probability that the internal combustion engine will be switched off.

Such a regeneration usually lasts a few seconds at most, so that the available time window (from falling below the speed threshold value until the internal combustion engine is switched off) is sufficient for the regeneration. Furthermore, a high prioritization can be applied even at a very low NO _x loading, so that the lowest possible loading with the highest possible NO _x storage efficiency can be made available for the following driving cycle. As a result, the starting emissions, which often make up a large part of the total emissions of NO _x in a driving cycle, can be reliably reduced, since with this strategy the internal combustion engine is almost always switched off with a practically empty NO _x storage device, so that the maximum storage capacity is reached at the beginning of a subsequent driving cycle is available.

In detail, a method according to the invention for operating an internal combustion engine of a vehicle with a storage catalytic converter which is set up at least for storing nitrogen oxides comprises determining a vehicle speed, determining a current filling level of nitrogen oxides in the storage catalytic converter, and requesting emptying of the storage catalytic converter if the vehicle speed falls below a predeterminable speed threshold value and at the same time the ascertained fill level exceeds a predeterminable fill level threshold value. As a result, the storage tank can be emptied before the internal combustion engine is switched off with predictable safety, so that the maximum storage capacity (rated capacity) is available in a subsequent driving cycle, which brings a considerable emission advantage, especially in cold-start phases.

Requesting that the storage catalytic converter be emptied can, in particular, directly include activation of the internal combustion engine to generate a rich exhaust gas. However, as an alternative or in addition, an indirect determination and output can also be made ben include a requirement value depending on the vehicle speed and the fill level. In this way, other vehicle functions that can request NSC regeneration/memory emptying using their own request values can also be taken into account. For example, a request can be made depending on different parameters or driving conditions such as exhaust gas temperatures, engine operating point, environmental conditions, driving profile, etc., and a feasibility evaluation can be carried out in a "regeneration logic" and an NSC regeneration can be bundled in a final request based on several request values from different sources and then finally requested.

The dependency of the required value on the fill level can, for example, increase monotonically, e.g. linearly or generally polynomial, with the required value increasing as the fill level rises.

The dependency of the requirement value on the speed can, for example, be monotonically decreasing, e.g. linear or generally polynomial, with the requirement value decreasing as the speed increases.

Advantageously, the filling level threshold value can also be defined as a function of the vehicle speed, with the dependency increasing monotonically, e.g. linearly or generally polynomially, with the filling level threshold value increasing with increasing speed. As a result, regeneration can be carried out in a particularly targeted manner and unnecessary increases in consumption due to increased or frequent regeneration requests can be avoided.

The method can also determine at least one operating parameter, which includes in particular a current speed of the internal combustion engine and/or a current geographic position of the vehicle and/or a current temperature of the storage catalytic converter or another component of the vehicle, and setting the speed threshold value and/or Level threshold depending on the at least include one operating parameter. These are particularly meaningful parameters for predicting an impending shutdown of the internal combustion engine or for assessing the storage level.

In some forms, the method may include preventing the internal combustion engine from producing a rich exhaust gas when an SCR catalyst downstream of the storage catalyst is at a temperature below its minimum operating temperature. As a result, regeneration of the storage component can only be carried out when nitrogen oxide released by the regeneration (eg desorbed NO _x ) can be converted downstream of the storage catalyst. In contrast to conventional methods, when the exhaust aftertreatment system is already hot (e.g. T > 200 °C), a high priority can still be given to regeneration at low speed in order to prepare the exhaust aftertreatment system accordingly for a subsequent cold start (after switching off the internal combustion engine and cooling down).

In some configurations, the method can include controlling an electric machine to generate a torque that enables or supports rich operation of the internal combustion engine. This is particularly advantageous for lean-burn engines with self-ignition or external ignition (e.g. diesel engines), as these would otherwise be difficult to operate in rich mode. However, this can also be used in Otto engines. For example, when driving uphill, a high torque may be required, which may rule out rich operation of the internal combustion engine in pure combustion operation. If an electric machine is used in such a situation to provide (additional) torque, regeneration can also be carried out in situations in which this would otherwise be impossible or only at the expense of other disadvantages (e.g. greatly increased fuel consumption, drop in performance, ...). it is possible. This is particularly advantageous in the case of hybrid-electric vehicles (traction motor), but under certain circumstances it can also be implemented using an electrical cranking device (e.g. starter motor, starter generator).

A computing unit according to the invention, e.g. a control unit of a motor vehicle, is set up, in particular in terms of programming, to carry out a method according to the invention.

The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is advantageous because this causes particularly low costs, especially if an executing control unit is also used for other tasks and is therefore available anyway. Suitable data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard drives, flash memories, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and refinements of the invention result from the description and the attached drawing.

The invention is shown schematically in the drawing using an exemplary embodiment and is described below with reference to the drawing.

character list

• 1 shows a vehicle with an internal combustion engine and an exhaust gas aftertreatment system in a schematic representation.
• 2 shows a greatly simplified flowchart of an advantageous embodiment of a method according to the invention.

embodiment(s) of the invention

In 1 1 is a vehicle that can be used within the scope of the invention, shown schematically and denoted by 100 in its entirety. Vehicle 100 has an internal combustion engine 110, an exhaust gas aftertreatment system 140 with at least one catalytic converter 142 and a drive axle 150, which is supplied with drive energy by the internal combustion engine. A control unit 115 controls the operation of internal combustion engine 110. In the example shown, vehicle 100 also has a transmission 120, which is connected between internal combustion engine 110 and drive axle 150 and is optionally connected to the control unit in a data-conducting manner.

In addition to the catalytic converter 142, the exhaust gas aftertreatment system 140 in the example shown includes an exhaust gas sensor upstream 145 and downstream 147 of the catalytic converter 142. The exhaust gas sensors 145, 147 are set up to monitor the composition of the exhaust gas from the internal combustion engine 110 and can be provided, for example, in the form of lambda sensors. The catalytic converter 142 comprises at least one storage component for the temporary storage of nitrogen oxide(s) NO _x . Exhaust gas aftertreatment system 140 or catalytic converter 142 preferably includes a catalytic converter for the selective catalytic reduction of nitrogen oxides (SCR; not explicitly shown) downstream of the storage component.

In 2 an advantageous embodiment of a method according to the invention is shown schematically using a greatly simplified flow chart and is denoted overall by 200 .

In a first step 210 of method 200, a filling level of catalytic converter 142 with regard to NO _x is determined. For this purpose, for example, data from the exhaust gas sensors 145, 147 can be used and, for example on the basis of a model of the catalytic converter, a relative proportion of occupied storage locations of the storage component can be calculated. If the fill level is higher than a predetermined threshold value, which can be 10% of the storage capacity, for example, then the method 200 continues with a second step 220 .

In the second step 220, at least one operating parameter of the vehicle 100 is determined, from which a probability of an impending shutdown of the internal combustion engine 110 can be derived. The at least one operating parameter includes at least one vehicle speed, which can be determined, for example, using data from transmission 120 and/or internal combustion engine 110 . For example, the speed of vehicle 100 can be calculated using a currently set transmission ratio and a current speed. Of course, the speed of the vehicle can also be measured directly using a correspondingly calibrated sensor, for example using a rotational speed of an output shaft of transmission 120 in conjunction with a fixed conversion factor that depends on the wheel size and is specific to the vehicle. The speed of the vehicle is a very suitable parameter for predicting an imminent shutdown of the internal combustion engine 110, since a certain range of low speeds is practically always passed before the internal combustion engine 110 is switched off. For example, the vehicle 100 will typically be moving at a speed of less than 20 km/h before the engine 110 is switched off. At the same time, such a speed is to be expected rather seldom if the internal combustion engine is not about to be switched off.

Other operating parameters can also be additionally used in order to predict the impending shutdown of internal combustion engine 110 as reliably as possible, for example a current geographic position or learned movement patterns, which can typically be individual to the driver. However, the speed of the vehicle is a particularly reliable indicator, since it does not depend on the individual driver's behavior and thus also functions reliably with a larger group of users of a vehicle (for example a fleet vehicle).

If the operating parameter(s) determined in step 220 indicate an imminent shutdown of the internal combustion engine, ie if the speed falls below a predetermined threshold, for example, then the method calls for regeneration of the storage catalytic converter 142 on. For this purpose, for example, a request value can be output to control unit 115 . The requirement value can be all the higher, the more the corresponding threshold value is exceeded or not reached, which results in a correspondingly stronger prioritization of the regeneration, in particular compared to other control objectives. In particular, after a regeneration of storage catalytic converter 142 has been requested, method 200 continues with a regeneration step 230 according to the prioritization. However, if the internal combustion engine is not about to be switched off on the basis of the operating parameter(s) determined, method 200 can return to first step 210 .

In regeneration step 230, the internal combustion engine is activated to produce a rich exhaust gas in order to reduce nitrogen oxides _NOx stored in catalytic converter 142. As a result, the nitrogen oxide store can be emptied before the internal combustion engine 110 is switched off, so that at the beginning of a subsequent operating cycle (i.e. in particular in an operating phase in which the exhaust gas aftertreatment system 140 is still cold and therefore not ready for the conversion of nitrogen oxides) essentially the entire Storage capacity for nitrogen oxides is available, so that the cold start emissions of the vehicle 100, which usually make up a large part of the total emissions in terms of nitrogen oxides, can be significantly reduced. In particular, the method 200 can include a step 225 in which a temperature of the exhaust gas aftertreatment system 140 is determined, and only continue with step 230 if the temperature is above a minimum operating temperature.

After the regeneration 230 has taken place, the method 200 can return to the step 210 .

In summary, this results in a regeneration strategy that is inverse to conventional strategies, since regeneration is usually preferred at high speeds in order to enable the lowest possible additional fuel consumption. Furthermore, if possible, no regeneration can be carried out when the exhaust gas aftertreatment system 140 is cold, in order to avoid emissions due to desorbing nitrogen oxides. This also represents an inversion of conventional strategies, since usually when the exhaust gas aftertreatment system 140 is cold (i.e. also cold SCR catalytic converters; not shown in the figure), a low maximum filling level or a high regeneration prioritization is specified in order to ensure the highest possible storage efficiency. In the context of the invention, however, such a high regeneration prioritization can be dispensed with, since essentially the complete storage capacity of the NOx storage component is available and it can thus be ensured that the exhaust gas aftertreatment system 140 is heated to operating temperature before the total storage capacity is exhausted. Therefore, an emission advantage is also achieved here compared to conventional procedures, since a regeneration 230 within the scope of the invention is usually only carried out when the SCR catalytic converter downstream of the storage catalytic converter 142 is ready for operation and can thus render any desorbing nitrogen oxides harmless.

It should be emphasized that the order of the steps given herein is to be understood as purely exemplary for purposes of illustration and that some of the steps may also be performed in a different order, for example in reverse, or in parallel with one another. Continuous implementation, ie doing without defined steps, may also be advantageous. For example, threshold values given as an example can also influence one another, so that, for example, the filling level threshold value mentioned can depend on the probability that internal combustion engine 110 will be switched off. In particular, for example at very low speeds (e.g. below 12 km/h) a lower level threshold value (e.g. 10%) can be used than at higher speeds (e.g. between 15 and 25 km/h; 20%). When the exhaust aftertreatment system is cold, the filling level threshold can also be raised very drastically (e.g. 90%) in order to avoid regeneration with a risk of unconverted desorption of nitrogen oxides.

Claims (11)

Method (200) for operating an internal combustion engine (110) of a vehicle (100) with a storage catalytic converter (142), which is set up at least for storing nitrogen oxides, comprising: determining (220) a vehicle speed, Determining (210) a current fill level of nitrogen oxides in the storage catalytic converter (142), and Requesting that the storage catalytic converter (142) be emptied if the determined vehicle speed falls below a predeterminable speed threshold value and at the same time the determined fill level exceeds a predeterminable fill level threshold value. Method (200) according to claim 1 , wherein the request for emptying the storage catalytic converter (142) includes a triggering (230) of the internal combustion engine (110) to generate a rich exhaust gas. Method (200) according to claim 1 or 2 , wherein the request for emptying the storage catalytic converter (142) comprises determining and outputting a request value as a function of the determined vehicle speed and the determined filling level. Method (200) according to any one of the preceding claims, comprising setting the level threshold as a function of the vehicle speed. A method (200) according to any one of the preceding claims, wherein the speed threshold is at most 30 km/h, 25 km/h, 20 km/h or 15 km/h. A method (200) according to any one of the preceding claims, further comprising Detecting at least one operating parameter, which includes in particular a current speed of the internal combustion engine (110) and/or a current geographic position of the vehicle (100) and/or a current temperature of the storage catalytic converter (142) or another component of the vehicle (100), and Defining the speed threshold and/or the filling level threshold as a function of the at least one operating parameter. Method (200) according to any one of the preceding claims, comprising preventing the internal combustion engine (110) from producing a rich exhaust gas when an SCR catalytic converter downstream of a storage component of the storage catalytic converter (142) has a temperature below its minimum operating temperature (225). Method (200) according to any one of the preceding claims, comprising driving an electric machine to generate a torque to support the internal combustion engine (110). Arithmetic unit (115) which is set up to carry out all method steps of a method (200) according to one of the preceding claims. Computer program that causes a computing unit (115) to perform all method steps of a method (200) according to one of Claims 1 until 8th to be performed when it is executed on the computing unit (115). Machine-readable storage medium with a computer program stored on it claim 10 .

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