DE102021102457B3 - Method for operating a drive device for a motor vehicle and corresponding drive device - Google Patents

Abstract

The invention relates to a method for operating a drive device (1) for a motor vehicle, the drive device (1) having a drive assembly (2) that produces exhaust gas, an exhaust gas tract (6) for discharging the exhaust gas generated by the drive assembly (2) in the direction of a external environment and an exhaust gas recirculation device (7) for recirculating exhaust gas from the exhaust tract (6) to the drive unit (2) and the drive unit (2) is operated with a fuel-fresh gas mixture with a specific combustion air ratio. It is provided that from a first combustion air ratio of the fuel-fresh gas mixture before a change in the fuel throughput of the fuel supplied to the drive unit (2), a second combustion air ratio of the fuel-fresh gas mixture after the change and one after the change by means of a in the exhaust tract (6) arranged lambda probe (9) measured value describing the residual oxygen content in the exhaust gas, a proportion of the recirculated exhaust gas is determined in the fresh gas. The invention also relates to a drive device (1) for a motor vehicle.

Description

The invention relates to a method for operating a drive device for a motor vehicle, the drive device having a drive unit that generates exhaust gas, an exhaust gas duct for discharging the exhaust gas generated by the drive unit in the direction of an external environment, and an exhaust gas recirculation device for recirculating exhaust gas from the exhaust duct into the exhaust gas unit and the drive unit is operated with a fuel-fresh gas mixture with a specific combustion air ratio. The invention also relates to a drive device for a motor vehicle.

From the prior art, for example, the publication DE 10 2015 207 252 A1 famous. This describes a method for model-based optimization, in particular calibration, of a technical device, in particular an internal combustion engine. The method has the following work steps: detecting at least one first parameter relating to the technical device to be optimized, which parameter characterizes a physical variable; first determining at least one second parameter in relation to the technical device to be optimized by at least one first physical model which characterizes at least one known physical relationship and for which the at least one first parameter is an input parameter; second determination of at least one third parameter using at least one first empirical model, which is based on measurements on a plurality of already known technical devices of the same type, in particular internal combustion engines, and for which at least the at least one second parameter is an input parameter, with the at least one third parameter is suitable for characterizing the technical device to be optimized and/or for making a change to the technical device to be optimized on this basis, in particular for setting a control of the technical device to be optimized; and outputting the at least one third parameter.

Furthermore, the document describes U.S. 10,330,034 B2 a device and a method for determining an exhaust gas recirculation rate based on a position of an exhaust gas recirculation valve, corrected using an exhaust gas composition measured by a sensor.

The pamphlet DE 198 49 272 A1 a method for diagnosing an exhaust gas recirculation system of a combustion process is proposed. It is provided to achieve a predetermined change in the exhaust air ratio lambda by a targeted change in the fresh air/fuel ratio and taking into account the properties of the EGR system, which is evaluated for diagnostic purposes. In particular, a multi-stage progression of the exhaust air ratio is expected with a functioning EGR system in the case of a one-stage abrupt change in the fresh air/fuel ratio.

The publication is also from the state of the art U.S.A. 4,640,257 famous.

The object of the invention is to propose a method for operating a drive device for a motor vehicle which has advantages over known methods, in particular enabling a precise determination of a proportion of the recirculated exhaust gas in the fresh gas supplied to the drive unit in the simplest possible manner.

According to the invention, this is achieved with a method for operating a drive device for a motor vehicle with the features of claim 1 . It is provided that from a first combustion air ratio of the fuel-fresh gas mixture before a change in the fuel throughput of the fuel supplied to the drive unit, a second combustion air ratio of the fuel-fresh gas mixture after the change and one after the change by means of a arranged lambda probe measured, the residual oxygen content in the exhaust gas descriptive measured value, a proportion of the recirculated exhaust gas is determined in the fresh gas.

Advantageous configurations with expedient developments of the invention are specified in the dependent claims.

The drive device is provided and designed to drive the motor vehicle and in this respect serves to provide a drive torque aimed at driving the motor vehicle. The drive device is preferably part of the motor vehicle, but can of course also be present separately from it and in this case is used solely to provide the drive torque.

The drive torque is provided by the drive device using the drive unit. This is operated with the fuel-fresh gas mixture, which is supplied to the drive unit or is only generated in the drive unit. In any case, fresh gas and fuel are supplied to the drive unit, for example separately from one another or together, with the fresh gas being at least temporarily and at least partially contains fresh air from an external environment of the propulsion device. The drive unit is present in particular as an internal combustion engine, particularly preferably as a diesel internal combustion engine or as an Otto internal combustion engine.

During the operation of the drive unit, exhaust gas is produced, which is fed to the exhaust gas tract and discharged via this in the direction of the outside environment. The exhaust tract can—optionally—have an exhaust gas aftertreatment device. This is preferably designed as a vehicle catalytic converter, ie it serves to catalytically convert pollutants contained in the exhaust gas into less hazardous products. The vehicle catalytic converter is present in particular as a three-way catalytic converter or as a storage catalytic converter.

The exhaust gas generated by the drive unit is at least partially recirculated into the drive unit, at least at times, so that the fresh gas supplied to the drive unit is present at least partially as exhaust gas. In this respect, the fresh gas has fresh air at least at times and exhaust gas at least at times, each in any desired proportions. Such a procedure is referred to as exhaust gas recirculation and is carried out using the exhaust gas recirculation device. With the help of the exhaust gas recirculation device, the exhaust gas emitted by the drive unit into the exhaust tract is at least partially added to the fresh gas at least temporarily and fed to the drive unit, so that the exhaust gas already emitted from the drive unit is fed back to the drive unit. To this extent, the exhaust gas recirculation device is an external exhaust gas recirculation system.

In other words, the drive device has a fresh gas line for supplying fresh gas to the drive unit, the drive unit itself and the exhaust line for discharging the exhaust gas from the drive unit. The fresh gas tract is preferably fluidically connected to a combustion chamber of the drive unit via at least one inlet valve, and the exhaust tract via at least one outlet valve. When the intake valve is open, fresh gas flows from the fresh gas tract into the combustion chamber and when the exhaust valve is open, exhaust gas flows out of the combustion chamber into the exhaust tract. The fresh gas tract and the exhaust tract are fluidically connected to one another via an exhaust gas recirculation line, via which at least part of the exhaust gas from the exhaust tract is recirculated at least temporarily into the fresh gas tract.

The mixture of fuel and fresh gas used to operate the drive unit has the specific combustion air ratio. The specific combustion air ratio describes the mass ratio of air to fuel relative to the stoichiometrically ideal ratio. With a combustion air ratio of one, the fuel/fresh gas mixture is stoichiometric in this respect, with a combustion air ratio of less than one there is a lack of air and with a combustion air ratio of greater than one there is excess air.

The combustion air ratio is preferably set using two measured values, namely using a first measured value and a second measured value. The measured values are determined using lambda sensors. To put it more precisely, the first measured value is measured using a first lambda probe, which is assigned to the exhaust gas tract, ie is present downstream of the drive unit with regard to the exhaust gas. For example, the first lambda probe is arranged in terms of flow between the drive assembly and the exhaust gas aftertreatment device. The second measured value, on the other hand, is measured using a second lambda probe, which is located downstream of the first lambda probe, in particular downstream of the exhaust gas aftertreatment device, that is to say downstream of the exhaust gas aftertreatment device in terms of flow. The exhaust gas aftertreatment device is therefore preferably arranged in terms of flow between the first lambda probe and the second lambda probe.

The first measured value describes the residual oxygen content of the exhaust gas downstream of the drive unit, in particular upstream of the exhaust aftertreatment device, and the second measured value describes the residual oxygen content of the exhaust gas downstream of the first lambda probe, preferably downstream of the exhaust aftertreatment device. The first measured value is preferably in the form of a lambda value, ie as a combustion air ratio. The second measured value is, for example, an electrical voltage supplied by the second lambda probe.

It is preferably provided that a broadband lambda probe is used as the first lambda probe and a jump lambda probe is used as the second lambda probe. The broadband lambda probe is preferably composed of several measuring cells, namely a pump cell and a Nernst cell. With such a structure, an accurate measurement of the residual oxygen content of the exhaust gas is also possible outside of a stoichiometric combustion air ratio by means of the broadband lambda probe. The jump lambda probe, on the other hand, preferably has only a single Nernst cell. In this respect, it can also be referred to as a Nernst probe or voltage jump probe. The broadband lambda sensor has the advantage of a large Measuring range, the jump lambda probe has the advantage of higher accuracy. A combination of broadband lambda probe and jump lambda probe can correspondingly achieve high accuracy of a lambda control and thus high efficiency.

The first measured value is preferably regulated by setting the combustion air ratio to a target value. This process is also referred to as lambda control. In this case, the target value is particularly preferably defined on the basis of the second measured value. In order to achieve efficient operation of the drive assembly, as soon as the second measured value reaches a threshold value, the combustion air ratio is adjusted by a differential value in a specific direction within a first time period. The combustion air ratio is then adjusted in the same direction at a specific speed over a second period of time. Incidentally, the threshold value can also be referred to as a lambda threshold value or control threshold value.

It is therefore preferably provided that the combustion air ratio is set in different ways during the two time periods. In this case, the second period of time preferably follows directly after the first period of time. During the first period of time, the combustion air ratio is changed by the differential value. The first period of time has a specific period of time, which is particularly preferably significantly less than a period of time of the second period of time. In particular, the combustion air ratio is adjusted instantaneously or essentially instantaneously by the differential value, so that the first time period is very short, in particular infinitesimally short.

In contrast, the adjustment of the combustion air ratio within the second period of time takes place over a longer period of time. There is no provision here for the combustion air ratio to be changed directly by a specific value, rather the combustion air ratio is adjusted at the specific speed. The speed is to be understood in particular as a gradient of the combustion air ratio over time. For example, both the difference value and the speed are permanently stored values.

The combustion air ratio is adjusted in particular by adjusting the setpoint value already mentioned. It is therefore provided that when the second measured value reaches the threshold value, the target value is understood to be in the specific direction by the difference value within the first time period and then with the speed in the same direction over the second time period. The first measured value is then regulated to the desired value as part of the lambda control explained, namely by adjusting the combustion air ratio.

Basically, the direction in which the combustion air ratio is adjusted depends on the direction in which the second measured value reaches the threshold value. If the second measured value reaches the threshold value in a first direction, for example from below, the combustion air ratio is adjusted in a first specific direction. If, on the other hand, the second measured value reaches the threshold value from a second direction that is different from the first direction, for example from above, the combustion air ratio is adjusted in a second specific direction opposite to the first specific direction. As a result, a so-called natural frequency control of the combustion air ratio is implemented. The threshold value required for this can basically be chosen in any way, for example it corresponds to a combustion air ratio of one or at least almost one or a corresponding voltage of the second lambda probe.

With the help of the already described exhaust gas recirculation, raw emissions from the drive unit can be significantly reduced. When carrying out the exhaust gas recirculation, it is necessary to be able to determine the proportion of the recirculated exhaust gas, the so-called exhaust gas recirculation rate, as precisely as possible. However, direct measurement of the exhaust gas recirculation rate is difficult to implement due to the high temperature of the exhaust gas that is recirculated.

For this reason, the exhaust gas recirculation rate or the proportion of the recirculated exhaust gas in the fresh gas should be determined indirectly, namely using the first combustion air ratio, the second combustion air ratio and the measured value measured using the lambda probe. In principle, therefore, the proportion of the recirculated exhaust gas is available as a function of the first combustion air ratio, the second combustion air ratio and the measured value. The lambda probe is to be understood in particular as the first lambda probe already mentioned above, which is preferably arranged upstream of the exhaust gas aftertreatment device, if this is present. The lambda probe is preferably arranged in such a way that it is reached by the exhaust gas emitted from the drive unit after a maximum of 100 ms, a maximum of 50 ms, a maximum of 25 ms or a maximum of 10 ms, i.e. more generally after a maximum of 10 ms to a maximum of 100 ms. This period of time is here in particular which depends on an operating point of the drive unit and the associated exhaust gas mass flow.

During stationary operation of the drive device or the drive assembly, the recirculated exhaust gas has the same combustion air ratio or the same residual oxygen content as the fuel/fresh gas mixture with which the drive assembly is operated. This follows from the fact that during the combustion of the fuel/fresh gas mixture in the combustion chamber, the combustion air ratio is set precisely, which is also subsequently present in the exhaust gas. When the exhaust gas is recirculated, two fluid streams with the same combustion air ratio are mixed so that the fuel-fresh gas mixture present in the combustion chamber has the same combustion air ratio, regardless of the proportion of the recirculated exhaust gas.

However, during transient operation of the drive device or the drive unit, the combustion air ratio of the recirculated exhaust gas and the combustion air ratio of the fuel/fresh gas mixture temporarily differ due to the running time of the exhaust gas within the exhaust gas recirculation device. When the fuel throughput of the fuel supplied to the drive unit changes due to a change in the specific combustion air ratio of the fuel/fresh gas mixture, the measured value measured using the lambda probe changes in a characteristic manner.

If the combustion air ratio is changed from the first combustion air ratio to the second combustion air ratio, the measured value, which initially corresponds to the first combustion air ratio, only reacts with a time delay. This means that the measured value initially remains at the first combustion air ratio due to the transit time of the exhaust gas downstream of the drive unit through the exhaust tract to the lambda probe, then within a short time it adjusts to a value between the first combustion air ratio and the second combustion air ratio and only subsequently changed in the direction of the second air-fuel ratio.

In this case, the first combustion air ratio is present before the change in the fuel throughput, in particular immediately before the change in the fuel throughput. In contrast, the second combustion air ratio is present after the change in the fuel throughput, in particular immediately after the change. The first combustion air ratio preferably corresponds to the combustion air ratio of the fuel-fresh gas mixture immediately before the change and the second combustion air ratio corresponds to the combustion air ratio of the fuel-fresh gas mixture immediately after the change.

Alternatively, it can of course also be provided to determine the first combustion air ratio and/or the second combustion air ratio by means of the lambda probe. In this case, the first combustion air ratio corresponds to the measured value before the change or immediately before the change in the fuel throughput. The second combustion air ratio corresponds to the measured value with a sufficient time interval to the change, for example at least 0.5 s, at least 1 s or at least 2 s after the change.

The measured value measured by means of the lambda probe is preferably used as the second combustion air ratio if the measured value has remained constant again over a certain period of time after the change in the fuel throughput, for example over a period of at least 50 ms, at least 75 ms or at least 100 ms. The measured value, which is used to determine the proportion of the recirculated exhaust gas, is preferably measured immediately after a sudden change in the residual oxygen content in the exhaust gas after the change in the fuel throughput. From the ratio between the first combustion air ratio, the second combustion air ratio and the measured value, the proportion of the recirculated exhaust gas in the fresh gas can then be determined with high accuracy in a simple manner.

A further development of the invention provides that there is an exhaust gas cleaning device in the exhaust tract and the measured value describes the residual oxygen content in the exhaust gas upstream of the exhaust gas cleaning device. The optional exhaust gas cleaning device has already been discussed. The exhaust gas purification device is preferably supplied with all of the exhaust gas generated by the drive unit. In terms of flow, the exhaust gas purification device is located between the drive assembly and a tailpipe of an exhaust line of the exhaust tract. The exhaust gas is discharged downstream of the exhaust gas cleaning device via the tailpipe into the outside environment of the drive device.

The lambda probe is arranged in such a way that the measured value indicates the residual oxygen content of the exhaust gas upstream of the exhaust gas cleaning device and thus in terms of flow between the Drive unit and the emission control device describes. This ensures that the measured value quickly follows the combustion air ratio of the fuel/fresh gas mixture. It has already been explained above that the lambda probe is arranged in such a way that the measured value lags behind the combustion air ratio by at most 100 ms, at most 50 ms, at most 25 ms or at most 10 ms. This achieves a high temporal resolution when determining the proportion of the recirculated exhaust gas.

A further development of the invention provides that the first combustion air ratio is measured by means of the lambda probe before the change in the fuel throughput and/or that the combustion air ratio present before the change in the fuel throughput is used as the first combustion air ratio. To this extent, the first combustion air ratio can be present as a measured value. For this purpose, the measured value measured using the lambda probe before the change in the fuel throughput is used as the first combustion air ratio. In other words, the first combustion air ratio is set equal to the measured value of the lambda probe before the change in the fuel throughput, in particular immediately before.

In addition or as an alternative, it is provided that the combustion air ratio set on the drive unit is used as the first combustion air ratio. The combustion air ratio set on the drive unit describes the combustion air ratio of the fuel/fresh gas mixture or corresponds to it. The combustion air ratio is calculated from the fuel quantity supplied to the drive unit and the fresh gas quantity or fresh air quantity supplied to the drive unit. The procedure described enables an exact determination of the proportion of the recirculated exhaust gas in the fresh gas.

A development of the invention provides that the second combustion air ratio is measured by means of the lambda probe after the change in the fuel throughput and/or that the combustion air ratio present after the change in the fuel throughput is used as the second combustion air ratio. Basically the same applies to the second combustion air ratio as to the first combustion air ratio with the only difference that it is determined after the change in the fuel throughput and not before the change, as is the case for the first combustion air ratio. Reference is therefore made in full to the corresponding explanations for the first combustion air ratio. Again, the procedure described allows the reliable and rapid determination of the proportion of the recirculated exhaust gas.

A development of the invention provides that the measured value is determined during or immediately after a step response of the residual oxygen content in the exhaust gas caused by the change. It has already been explained that the change in fuel flow results in a change in the measured value, which is slightly delayed. This change is in the form of the step response of the residual oxygen content, so the measured value changes suddenly or within a very short period of time.

If, when the fuel throughput changes, exhaust gas is fed back from the exhaust tract into the drive unit, the residual oxygen content in the exhaust gas does not change to a value that corresponds to the second combustion air ratio, but to a value which corresponds to a combustion air ratio between the first combustion air ratio and the second combustion air ratio corresponds.

In order to determine the proportion of the recirculated exhaust gas in the fresh gas, the measured value is determined at or immediately after the step response, ie at or after the sudden change in the measured value. For example, that measured value is used which is present after a first threshold value has been exceeded and a gradient of the residual oxygen content or the measured value has subsequently fallen below the threshold value. In this way, an exact determination of the proportion of the recirculated exhaust gas is realized.

A development of the invention provides that a fresh gas throughput of the fresh gas supplied to the drive unit is kept constant throughout the change. The combustion air ratio of the fuel/fresh gas mixture therefore changes exclusively as a result of the change in the fuel flow rate, not as a result of a change in the fresh gas flow rate. For example, to keep the fresh gas throughput constant, a throttle valve position of the drive unit remains unchanged. This ensures a high degree of accuracy of the determined proportion.

A development of the invention provides that an exhaust gas recirculation throughput of the exhaust gas recirculated into the drive unit is kept constant over the change. In addition or as an alternative to the fresh gas throughput, the exhaust gas recirculation throughput is kept constant, namely in particular at least until the proportion of the recirculated exhaust gas in the fresh gas is determined. Keeping the exhaust gas recirculation constant throughput is realized in particular by maintaining a specific position of an actuator of the exhaust gas recirculation device. This procedure also ensures a high degree of accuracy in determining the proportion of the recirculated exhaust gas.

ermittelt wird, wobei λ₁ das erste Verbrennungsluftverhältnis, λ₂ das zweite Verbrennungsluftverhältnis und λ₃ ein aus dem Messwert ermitteltes drittes Verbrennungsluftverhältnis beschreibt.A development of the invention provides that the proportion of the recirculated exhaust gas using the relationship $${\text{x}}_{\text{A}}=1-{\mathrm{\lambda }}_1\left({\mathrm{<figure-callout\; id="2"\; label="\lambda "\; filenames="DE102021102457B3\_0005.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_2-{\mathrm{\lambda }}_3\right)/\left({\mathrm{\lambda }}_3\left({\mathrm{<figure-callout\; id="2"\; label="\lambda "\; filenames="DE102021102457B3\_0005.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_2-{\mathrm{\lambda }}_1\right)\right)$$

is determined, where λ ₁ describes the first combustion air ratio, λ ₂ describes the second combustion air ratio and λ ₃ describes a third combustion air ratio determined from the measured value.

Basically, for a molar concentration of oxygen _CO2 , the relationship _CO2 = 0.21 (λ - 1) / λ applies. The molar concentration of the oxygen is dependent on the combustion air ratio. The relationship C ₃ = x _L C ₁ + (1 - x _L ) C ₂ applies to the oxygen concentration of a mixture of the exhaust gas generated by the drive unit and the exhaust gas recirculated from the exhaust tract into the drive unit, where C ₁ is the molar concentration of oxygen for the first airflow ratio, C ₂ is the molar concentration of oxygen for the second airflow ratio, and C ₃ is the molar concentration of oxygen for the third airflow ratio. The variable x _L describes the proportion of fresh air in the exhaust gas.

Wird diese Gleichung nach x aufgelöst ergibt sich die Beziehung $${\text{x}}_{\text{L}}={\mathrm{\lambda }}_1\left({\mathrm{\lambda }}_2-{\mathrm{\lambda }}_3\right)/\left({\mathrm{\lambda }}_3\left({\mathrm{\lambda }}_2-{\mathrm{\lambda }}_1\right)\right)$$

für den Anteil x_L der Frischluft an dem Frischgas, und x_A = 1 - x_L für den Anteil des Abgases an dem Frischgas. Die genannte Beziehung ermöglicht eine rasche und genaue Berechnung des Abgasanteils an dem Frischgas.The third combustion air ratio is determined or calculated from the measured value. Using the above relationship, the equation is obtained $$\left({\mathrm{<figure-callout\; id="3"\; label="\lambda "\; filenames="DE102021102457B3\_0005.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_3-{\mathrm{\lambda }}_1\right)/{\mathrm{<figure-callout\; id="3"\; label="\lambda "\; filenames="DE102021102457B3\_0005.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_3={\text{x}}_{\text{L}}\left({\mathrm{<figure-callout\; id="1"\; label="\lambda "\; filenames="DE102021102457B3\_0005.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_1-1\right)/{\mathrm{<figure-callout\; id="1"\; label="\lambda "\; filenames="DE102021102457B3\_0005.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_1+\left(1-{\text{x}}_{\text{L}}\right)\left({\mathrm{<figure-callout\; id="2"\; label="\lambda "\; filenames="DE102021102457B3\_0005.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_2-1\right)/{\mathrm{<figure-callout\; id="2"\; label="\lambda "\; filenames="DE102021102457B3\_0005.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_2.$$

If this equation is solved for x, the relationship results $${\text{x}}_{\text{L}}={\mathrm{\lambda }}_1\left({\mathrm{<figure-callout\; id="2"\; label="\lambda "\; filenames="DE102021102457B3\_0005.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_2-{\mathrm{\lambda }}_3\right)/\left({\mathrm{\lambda }}_3\left({\mathrm{<figure-callout\; id="2"\; label="\lambda "\; filenames="DE102021102457B3\_0005.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_2-{\mathrm{\lambda }}_1\right)\right)$$

for the proportion x _L of the fresh air in the fresh gas, and x _A = 1 - x _L for the proportion of the exhaust gas in the fresh gas. The relationship mentioned enables the proportion of exhaust gas in the fresh gas to be calculated quickly and accurately.

A development of the invention provides that if the proportion of the recirculated exhaust gas deviates from an exhaust gas recirculation target value, the proportion is adjusted in the direction of the exhaust gas recirculation target value. The exhaust gas recirculation target value is used to determine how much exhaust gas is to be recirculated from the exhaust tract to the drive unit. If, after determining the proportion of the recirculated exhaust gas in the fresh gas, it is determined that the proportion deviates from the exhaust gas recirculation target value, the proportion is adjusted in such a way that it changes in the direction of the exhaust gas recirculation target value, in particular until it corresponds to the exhaust gas recirculation target value. The proportion of the recirculated exhaust gas is therefore particularly preferably regulated to the exhaust gas recirculation target value. As a result, a particularly efficient operation of the drive device is realized.

The invention also relates to a drive device for a motor vehicle, in particular for carrying out the method according to the statements in this description, with a drive assembly that generates exhaust gas, an exhaust tract for discharging the exhaust gas generated by the drive assembly in the direction of an external environment, and an exhaust gas recirculation device for recirculating exhaust gas from the exhaust tract into the drive unit, the drive device being provided and designed to be operated with a fuel-fresh gas mixture with a specific combustion air ratio.

The drive device is also provided and configured to select from a first combustion air ratio of the fuel-fresh gas mixture before a change in the fuel throughput of the fuel supplied to the drive assembly, a second combustion air ratio of the fuel-fresh gas mixture after the change and one after the change to determine a proportion of the recirculated exhaust gas in the fresh gas by means of a lambda probe arranged in the exhaust tract and which describes the residual oxygen content in the exhaust gas.

The advantages of such a procedure or such a configuration of the drive device have already been pointed out. Both the drive device and the method for operating it can be further developed according to the statements made within the scope of this description, so that reference is made to them in this respect.

The features and feature combinations described in the description, in particular the features and feature combinations described in the following description of the figures and/or shown in the figures, can be used not only in the combination specified in each case, but also in other combinations or on their own, without going beyond the scope of the leave invention. Embodiments are therefore also to be regarded as covered by the invention which are not explicitly shown or explained in the description and/or the figures, but emerge from the explained embodiments or can be derived from them.

• 1 eine schematische Darstellung einer Antriebseinrichtung für ein Kraftfahrzeug, welche über ein Antriebsaggregat, einen Abgastrakt sowie eine Abgasrückführeinrichtung verfügt, sowie
• 2 mehrere Diagramme, in welchen ein Kraftstoffdurchsatz des dem Antriebsaggregat zugeführten Kraftstoffs und ein mittels einer in dem Abgastrakt angeordneten Lambdasonde gemessener Messwert über der Zeit aufgetragen sind.

The invention is explained in more detail below with reference to the exemplary embodiments illustrated in the drawing, without the invention being restricted. while showing

• 1 a schematic representation of a drive device for a motor vehicle, which has a drive unit, an exhaust tract and an exhaust gas recirculation device, and
• 2 several diagrams in which a fuel throughput of the fuel supplied to the drive assembly and a measured value measured by means of a lambda probe arranged in the exhaust tract are plotted over time.

the 1 shows a schematic representation of a drive device 1 for a motor vehicle not shown in detail. The drive device 1 comprises a drive unit 2, by means of which a drive torque of the drive device 1 can be generated or made available. The drive assembly 2 is preferably in the form of an internal combustion engine, in particular an Otto internal combustion engine or a diesel internal combustion engine. The drive assembly 2 is operated using a fuel-fresh gas mixture, which is put together while maintaining a specific combustion air ratio. For this purpose, the drive unit 2 is supplied with fresh gas according to the arrow 3 and fuel according to the arrow 4 . At least some of the fresh gas has fresh air, which is supplied according to arrow 5 .

During the operation of the drive assembly 2, exhaust gas is produced, which is completely supplied to an exhaust gas duct 6 of the drive device 1 and is discharged via this in the direction of an external environment of the drive device 1. The drive device 1 also has an exhaust gas recirculation device 7, of which an exhaust gas recirculation line 8 is shown here merely as an example. Exhaust gas from the exhaust tract 6 can be fed back to the drive unit 2 by means of the exhaust gas recirculation device 7 . For this purpose, the exhaust gas from the exhaust tract 6 is at least partially added to the fresh gas at least temporarily, so that the fresh gas is composed of fresh air and exhaust gas at least temporarily. In addition, there is at least one lambda probe 9 in the exhaust tract 6 , by means of which a measured value is measured which describes a residual oxygen content of the exhaust gas in the exhaust tract 6 .

the 2 FIG. 12 shows two diagrams, a curve 10 of a fuel throughput of the fuel supplied to the drive unit 2 over time t being shown in an upper one of the diagrams. It can be seen that the fuel throughput changes at time t ₁ , for example it increases, namely—purely by way of example—from 1 kg/h to 2 kg/h.

In the 2 two curves 11 and 12 of the measured value measured by means of the lambda probe 9 are plotted, also over time t. Before the change in the fuel throughput at time t ₁ , the measured value corresponds to a combustion air ratio of 4 according to both curves 11 and 12. This combustion air ratio changes with the change in the fuel throughput.

Curve 11 shows the measured value without recirculated exhaust gas, so the proportion of the recirculated exhaust gas in the fresh gas is zero. In this case, the air/fuel ratio drops abruptly from the first air/fuel ratio before the change in the fuel throughput to a second air/fuel ratio of 2 after the change.

If, on the other hand, exhaust gas is recirculated from the exhaust tract 6 to the drive assembly 2 by means of the exhaust gas recirculation device 7, the combustion air ratio or the residual oxygen content changes immediately during or after the change in the fuel throughput only partially in the direction of the second combustion air ratio. With a ratio of 1:1 between fresh air and exhaust gas in the fresh gas, the combustion air ratio drops rapidly to a value of 2.6 according to curve 12 and then slowly continues to decrease in the direction of the combustion air ratio of 2.

This circumstance is now used to determine the proportion of the recirculated exhaust gas in the fresh gas from the first combustion air ratio, the second combustion air ratio and the measured value. This enables this proportion to be determined very precisely in an indirect way, i.e. without a complex direct measurement of the proportion.

Reference List

1

drive device

2

drive unit

3

Arrow

4

Arrow

5

Arrow

6

exhaust tract

7

exhaust gas recirculation device

8th

exhaust gas recirculation line

9

lambda probe

10

Course

Claims (10)

A method for operating a drive device (1) for a motor vehicle, the drive device (1) having a drive assembly (2) that generates exhaust gas, an exhaust tract (6) for discharging the exhaust gas generated by the drive assembly (2) in the direction of an external environment, and an exhaust gas recirculation device (7) for recirculating exhaust gas from the exhaust tract (6) into the drive unit (2) and the drive unit (2) is operated with a fuel-fresh gas mixture with a specific combustion air ratio, characterized in that from a prior to a change of a fuel throughput of the fuel supplied to the drive unit (2), a first combustion air ratio of the fuel/fresh gas mixture that is present after the change, and a second combustion air ratio of the fuel/fresh gas mixture that is present after the change, and a lambda probe (9) that is arranged after the change by means of a lambda probe (9) arranged in the exhaust tract (6) measured, the residual oxygen content in the A bgas descriptive measured value a proportion of the recirculated exhaust gas is determined at the fresh gas. procedure after claim 1 , characterized in that in the exhaust tract (6) there is an exhaust gas cleaning device and the measured value describes the residual oxygen content in the exhaust gas upstream of the exhaust gas cleaning device. Method according to one of the preceding claims, characterized in that the first combustion air ratio is measured by means of the lambda probe (9) before the change in the fuel throughput and/or that the combustion air ratio before the change in the fuel throughput is used as the first combustion air ratio. Method according to one of the preceding claims, characterized in that the second combustion air ratio is measured after the change in the fuel throughput by means of the lambda probe (9) and/or that the combustion air ratio present after the change in the fuel throughput is used as the second combustion air ratio. Method according to one of the preceding claims, characterized in that the measured value is determined during or immediately after a step response of the residual oxygen content in the exhaust gas caused by the change. Method according to one of the preceding claims, characterized in that a fresh gas throughput of the fresh gas supplied to the drive unit (2) is kept constant throughout the change. Method according to one of the preceding claims, characterized in that an exhaust gas recirculation throughput of the exhaust gas recirculated into the drive unit (2) is kept constant throughout the change. Method according to one of the preceding claims, characterized in that the proportion of the recirculated exhaust gas using the relationship $${\text{x}}_{\text{A}}=1-{\mathrm{\lambda }}_1\left({\mathrm{\lambda }}_2-{\mathrm{\lambda }}_3\right)/\left({\mathrm{\lambda }}_3\left({\mathrm{\lambda }}_2-{\mathrm{\lambda }}_1\right)\right)$$

is determined, where λ ₁ describes the first combustion air ratio, λ ₂ describes the second combustion air ratio and λ ₃ describes a third combustion air ratio determined from the measured value. Method according to one of the preceding claims, characterized in that if the proportion of the recirculated exhaust gas deviates from an exhaust gas recirculation target value, the proportion is adjusted in the direction of the exhaust gas recirculation target value. Drive device (1) for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, with a drive assembly (2) generating exhaust gas, an exhaust tract (6) for discharging the exhaust gas generated by the drive assembly (2) in the direction of an external environment and an exhaust gas recirculation device (7) for recirculating exhaust gas from the exhaust tract (6) into the drive assembly (2), the drive device (1) being provided and designed to be operated with a fuel-fresh gas mixture with a specific combustion air ratio, characterized in that the drive device (1) is further provided and designed to calculate from a first combustion air ratio of the fuel-fresh gas mixture that is present before a change in the fuel throughput of the fuel supplied to the drive unit (2), a second combustion air ratio of the fuel that is present after the change -Fresh h-gas mixture and a measured value describing the residual oxygen content in the exhaust gas, measured after the change by means of a lambda probe (9) arranged in the exhaust gas tract (6), a proportion of the to determine recirculated exhaust gas on the fresh gas.

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