HK1222214B - Method for operating a driving system and corresponding driving system - Google Patents

Description

Method for operating a drive and corresponding drive

Technical Field

The invention relates to a method for operating a drive unit having an internal combustion engine and an exhaust gas purification device, through which exhaust gas of the internal combustion engine flows for exhaust gas purification, wherein the exhaust gas purification device has at least one catalytic converter element for the catalytic conversion of nitrogen monoxide into nitrogen dioxide at a certain conversion rate. The invention further relates to a drive device.

Background

The drive device is used, for example, for driving a motor vehicle or a ship. For this purpose, the torque is provided by an internal combustion engine, which is designed, for example, as a diesel engine. The exhaust gases produced by the internal combustion engine are supplied to an exhaust gas purification device and at least partially freed of pollutants therein. It is often advantageous here if the exhaust gas flowing through the exhaust gas purification device has a certain content of nitrogen dioxide, for example in order to use it for the regeneration of a particle filter and/or for reacting with nitric oxide in a catalyst.

Just downstream of the internal combustion engine, however, only a small amount or almost no nitrogen dioxide is present in the exhaust gas. In contrast, the content of nitric oxide is relatively high at the exhaust gas. For this reason, the at least one catalytic converter element is arranged in the exhaust gas purification device. It is used for the catalytic conversion of nitric oxide to nitrogen dioxide, wherein this is achieved with a certain conversion. Downstream of the catalyst element (with respect to the main flow direction of the exhaust gas), a higher content of nitrogen dioxide or a larger amount of nitrogen dioxide is present in the exhaust gas of the internal combustion engine than in the case of this upstream of the catalyst element. The catalyst element has at least one catalytically active component or catalyst material, for example platinum or a platinum alloy. As the service life of the catalyst element increases, the catalytic effect of the catalyst material and thus of the catalyst element decreases, in particular due to thermal ageing or chemical poisoning (which is unavoidable due to certain constituents of the lubricant and/or of the fuel used to operate the internal combustion engine). Accordingly, the amount of nitrogen dioxide produced by catalytic conversion is reduced.

For this reason, the catalyst element is typically configured such that it achieves a conversion rate greater than or equal to a minimum conversion rate over its entire specified service life. This, however, leads to a higher conversion at the beginning of the service life of the catalytic converter element and in particular directly at the start of the operation of the drive than is necessary for generating the desired amount of nitrogen dioxide. Accordingly, too large an amount of nitrogen dioxide is present in the exhaust gas downstream of the catalyst element, which may not be available downstream of the catalyst element and is conveyed in accordance with the external environment of the drive device. This results in a higher nitrogen dioxide emission of the drive than necessary.

Disclosure of Invention

The object of the present invention is therefore to provide a method for operating a drive device, which at least partially avoids the disadvantages described at the outset and in particular achieves a low nitrogen dioxide emission of the drive device over the entire service life of the catalytic converter element.

This is achieved according to the invention with a method having the features of claim 1. In order to compensate for the degradation of the conversion of the catalytic converter element caused by aging, the nitrogen monoxide emissions of the internal combustion engine and/or the exhaust gas temperature upstream of the catalytic converter element are adjusted in such a way, depending on the current conversion and/or aging of the catalytic converter element, that the nitrogen dioxide concentration downstream of the catalytic converter element is greater than or equal to a minimum concentration and/or that the molar ratio between nitrogen monoxide and nitrogen dioxide downstream of the catalytic converter element corresponds to a defined ratio. In the first case (in which the nitrogen dioxide concentration should at least correspond to the minimum concentration), the absolute amount of nitrogen dioxide present in the exhaust gas after the catalyst element is influenced. Instead, the molar ratio between nitric oxide and nitrogen dioxide is alternatively or additionally set to a defined ratio for adjusting the amount of nitrogen dioxide in the exhaust gas relative to the amount of nitric oxide. It is of course possible to provide a combination of these two embodiments in which not only the nitrogen dioxide concentration should be greater than or equal to the minimum concentration but also the molar ratio should be equal to the specified ratio.

In order to adjust the parameters, the nitrogen monoxide emissions of the internal combustion engine and/or the exhaust gas temperature upstream of the catalytic converter element are adjusted accordingly. By matching the nitric oxide emissions of the internal combustion engine, the concentration of nitric oxide in the exhaust gas flow upstream of the catalyst element is increased. Accordingly, the amount of nitrogen dioxide generated by means of the catalyst element from nitrogen monoxide increases even if the current conversion is less than the initial conversion that the catalyst element has at the beginning of its service life, i.e. in the new state.

The current conversion rate is strongly dependent on the exhaust gas temperature during or before the flooding of the catalytic converter element. Accordingly, the molar ratio between nitric oxide and nitrogen dioxide downstream of the catalyst, in particular to a defined ratio, can be adjusted by varying the exhaust gas temperature. The conversion preferably describes the amount of nitrogen dioxide produced by the catalyst per unit time which may be proportional to the amount of nitric oxide present.

The nitric oxide emissions of the internal combustion engine and/or the exhaust gas temperature upstream of the catalyst element are preferably selected as a function of the current conversion of the catalyst element and/or the aging of the catalyst element. The internal combustion engine is then adjusted such that nitric oxide emissions and/or exhaust gas temperatures are achieved. In this way, the degradation of the conversion of the catalytic converter element caused by aging can be compensated. In this case, as already explained above, the absolute amount of nitrogen dioxide or the absolute nitrogen dioxide concentration downstream of the catalytic converter element can be obtained. Alternatively or additionally, it has likewise been discussed for the amount of nitrogen dioxide or the nitrogen dioxide concentration to be influenced downstream of the catalyst with respect to the amount of nitrogen monoxide or the nitrogen monoxide concentration. In this case, the molar ratio between nitric oxide and nitrogen dioxide is particularly preferably set to a predetermined ratio. For example, the ratio one is selected as the prescribed ratio.

The catalytic converter element is, for example, a component of an oxidation catalytic converter of an exhaust gas purification device, in particular a diesel oxidation catalytic converter (DOC). Alternatively, the catalytic converter element can of course also be provided as a separate component in the exhaust gas purification device.

In a preferred embodiment of the invention, provision is made for the nitrogen monoxide emissions to be increased over the service life of the catalytic converter element at a certain operating point of the internal combustion engine in order to compensate for the degradation of the conversion rate caused by aging. As already explained, the current conversion of the catalytic converter element decreases as the catalytic converter element ages over its service life. Accordingly, in order to ensure a certain nitrogen dioxide concentration downstream of the catalyst element, the nitric oxide concentration upstream of the catalyst element has to be increased. By means of such a higher nitric oxide concentration, at the same time, however, with a lower conversion, the nitrogen dioxide concentration downstream of the catalyst element can be kept in the range of a minimum concentration. The nitrogen dioxide concentration should in particular be greater than or equal to the minimum concentration.

Since, of course, different nitric oxide emissions or different exhaust gas temperatures are present at different operating points of the internal combustion engine, the operating point must be selected constantly over the service life of the catalytic converter element for the comparison between the two nitrogen dioxide concentrations at different times. The operating point is characterized, for example, by the rotational speed of the internal combustion engine and/or the torque supplied by the internal combustion engine. Additionally or alternatively, the operating point may also be characterized by at least one other operating parameter.

If the conversion rates of the catalyst elements are now compared with one another at different times, the conversion rate at a later time is less than the conversion rate at an earlier time. In the same operating point, the nitric oxide emissions must be greater at a later time in order to achieve the same or a higher nitrogen dioxide concentration after the catalytic converter element than at an earlier time. It is naturally preferably provided that the nitrogen monoxide emissions are increased over the service life of the catalytic converter element at all operating points of the internal combustion engine in order to compensate for the degradation of the conversion rate caused by aging. This increase is achieved not only in a single operating point, but in all possible operating points. In this case, however, the improvement can be carried out differently for different operating points.

A further development of the invention provides that the adjustment of the nitrogen monoxide emissions and/or the exhaust gas temperature is effected by changing at least one operating parameter of the internal combustion engine, in particular an injection parameter, a charging pressure of the supercharger, an exhaust gas recirculation rate and/or an actuation parameter of at least one intake valve and/or at least one exhaust valve. The nitric oxide emissions or exhaust gas temperature of an internal combustion engine can be influenced by a number of operating parameters of the internal combustion engine. These operating parameters include, for example, injection parameters, boost pressure, exhaust gas recirculation rate and/or actuation parameters of the intake or exhaust valves.

The injection parameter is, for example, the amount of fuel supplied to the internal combustion engine per unit time and/or the period of time during which this supply is effected. The latter is defined by the start of injection, the duration of injection and/or the end of injection. The charging pressure of the supercharger corresponds to the pressure downstream of the supercharger or to the pressure of the fresh charge, in particular fresh air, supplied to the internal combustion engine. The supercharger is, for example, a turbocharger (in particular an exhaust gas turbocharger) or a compressor. The exhaust gas recirculation rate is the amount of exhaust gas which is recirculated to the internal combustion engine per unit time. The control variables of the inlet or outlet valves are, for example, the opening times, the closing times and/or the respective opening periods during which the valves are at least partially open. The actuation parameters of the intake or exhaust valves correspond to the control times (i.e., the opening times, the opening durations and/or the closing times) of the respective valves.

In order to obtain the desired nitrogen monoxide emission or the desired exhaust gas temperature, at least one, but preferably a plurality of, of the operating parameters is now set, wherein this can be controlled and/or regulated, in particular as a function of the nitrogen dioxide concentration or molar ratio downstream of the catalytic converter element.

A further embodiment of the invention provides that the minimum concentration is selected such that the particle filter of the exhaust gas purification device is continuously regenerated with a certain regeneration rate by means of nitrogen dioxide. The exhaust gas purification device has a particulate filter. The internal combustion engine is designed as a diesel engine, for example. Particulate filters are used to filter out particles, in particular soot particles or carbon particles, contained in the exhaust gas of an internal combustion engine from the exhaust gas. Particularly preferably, the particle filter is designed as a Continuously Regenerating particle filter (CRT). The particle filter is now arranged downstream of the catalytic converter element, so that it is not flowed through by the exhaust gas of the internal combustion engine after the catalytic converter element. The nitrogen dioxide present in the exhaust gas at this point, which is generated predominantly by the catalytic converter element from nitrogen monoxide, is now used to continuously regenerate the particle filter at a certain regeneration rate. In the case of a particulate filter, the regeneration rate may also be referred to as a soot burning rate. In this case, regeneration is provided or at least possible over a wide region of the characteristic field of the internal combustion engine.

The regeneration rate is preferably selected in such a way that a reliable filtration of the exhaust gas is always possible over the entire power range of the internal combustion engine by means of the particle filter. In other words, the regeneration rate should be selected such that the regeneration of the particulate filter is always sufficient to achieve a reliable function of the particulate filter. The regeneration rate or the soot burning rate is selected, for example, such that the particulate filter is not clogged or blocked by particles, in particular soot particles, even in the event of a permanently full load of the internal combustion engine. Especially when the particles are present as carbon black particles, they can be converted into carbon dioxide and nitric oxide by means of the nitrogen dioxide contained in the exhaust gas. In order to obtain a certain regeneration rate or soot burn rate, a certain nitrogen dioxide concentration needs to be present. The aforementioned minimum concentration is determined in particular as a function of the regeneration rate, preferably such that the particulate filter is reliably regenerated even in the event of a permanently full load of the internal combustion engine.

In a further embodiment of the invention, it is provided that a catalytic converter of the exhaust gas purification device, which catalytic converter is arranged downstream of the catalytic converter element, is designed or becomes an SCR catalytic converter. For example, the exhaust gas purification device has a catalyst disposed downstream of a catalyst element. The catalyst is used for carrying out a selective catalytic reduction of pollutants contained in the exhaust gas, in particular nitrogen oxides, i.e. in particular nitrogen monoxide and/or nitrogen dioxide. It is particularly advantageous when a reducing agent, for example in the form of ammonia or an aqueous urea solution, from which ammonia is formed in the exhaust gas, is introduced into the exhaust gas upstream of the catalyst. The reducing agent passes with the exhaust gas into the catalytic converter and is used there to carry out the reduction of the nitrogen oxides.

The reaction carried out here can be carried out, for example, by the following reaction equation:

4NO₂+4NH₃+O₂->4N₂+6H₂o (Eq.1)

6NO₂+8NH₃->7N₂+ 12H₂O (Eq.2)

NO₂+NO+2NH₃->2N₂+3H₂O (Eq.3)

To illustrate. Equation 3 illustrates a particularly efficient reaction path in which nitrogen dioxide reacts directly with nitric oxide. In order that this reaction path may preferably be carried out, it is required that the exhaust gas contains the same amount of nitric oxide and nitrogen dioxide. Accordingly, the molar ratio is chosen to be equal to one. Preferably, at least approximately one nitrogen dioxide molecule per nitric oxide molecule is available for the reaction. In other words, the defined ratio is selected such that at least the reaction path of the selective catalytic reaction of the exhaust gas in the catalytic converter of the exhaust gas purification device continues according to equation 3 (in which the nitrogen monoxide reacts with the nitrogen dioxide in the presence of the reducing agent introduced into the exhaust gas), but at least over the largest possible temperature range.

A particularly advantageous embodiment of the invention provides that the adjustment is carried out such that the nitrogen dioxide concentration after the catalytic converter element is less than or equal to the maximum concentration. I.e. not only to ensure that the nitrogen dioxide concentration is greater than or equal to the aforementioned minimum concentration (which is important in particular for the regeneration of the particle filter). The highest concentration should also be noted. This is important because excess nitrogen dioxide present downstream of the catalytic converter element cannot be utilized and can accordingly enter the external environment of the drive. Furthermore, N is generated in the case of excess nitrogen dioxide at the SCR catalyst mentioned above₂And O. However, this is undesirable. I.e. an excess of nitrogen dioxide should be avoided, in particular to comply with emission limits for nitrogen dioxide.

In the ideal case, the nitrogen dioxide concentration after the catalytic converter element is set or adjusted to a certain value. In this case, the maximum concentration corresponds to the minimum concentration, so that the concentration of nitrogen dioxide present after the catalyst element is not only equal to the minimum concentration but also equal to the maximum concentration. However, since this is technically difficult to achieve, a certain gap is provided in which the highest concentration is selected to be greater than the smallest concentration. For example, the minimum concentration is below the desired value of the nitrogen dioxide concentration by a certain difference and the maximum concentration is above the desired nitrogen dioxide concentration by a certain difference.

A refinement of the invention provides that the first nitrogen oxide concentration parameter is determined by means of a first nitrogen oxide sensor upstream of the catalyst element and the second nitrogen oxide concentration parameter is determined by means of a second nitrogen oxide sensor downstream of the catalyst element, wherein the nitrogen dioxide concentration is determined from the difference between the first nitrogen oxide concentration parameter and the second nitrogen oxide concentration parameter. The first and second nitrogen oxide sensors are designed such that they detect any nitrogen oxides, i.e. in particular not only nitrogen monoxide but also nitrogen dioxide, and provide a concentration in the form of the first or second nitrogen oxide concentration parameter. Since the amount of nitrogen dioxide formed by the internal combustion engine is negligible, however, the nitrogen dioxide concentration converted by the catalyst element from nitrogen monoxide and thus present in the exhaust gas downstream of the catalyst element can be directly deduced from the difference between these two nitrogen oxide concentration parameters.

The first and second nitrogen oxide sensors are preferably nitric oxide sensors, however with lateral sensitivity to nitrogen dioxide. The nitrogen oxide sensor therefore reacts not only to nitric oxide but also to nitrogen dioxide. As a measuring method, for example, an IR measuring method, a chemiluminescence measuring method, and/or an electrochemical measuring method can be used for the nitrogen oxide sensor. The nitrogen dioxide concentration can be adjusted to a concentration greater than or equal to the minimum concentration or a concentration corresponding thereto, depending on the nitrogen dioxide concentration thus determined.

A further advantageous embodiment of the invention provides that the calibration of the first nox sensor and the second nox sensor is carried out at exhaust gas temperatures at which the conversion is less than a certain conversion. Since the nox sensor is subject to ageing processes, as is the case with the catalytic converter element, it needs to be corrected, for example, at regular time intervals. The exhaust gas temperature upstream of the catalytic converter element is to be selected such that the conversion rate directly dependent on the exhaust gas temperature is small, for example less than 10%, in particular less than 5%, less than 2.5%, less than 1% or less than 0.5%; the conversion determined corresponds to one of the values mentioned above. In this case, only a small amount of nitrogen dioxide is generated during the time the catalyst element is flowed through by nitric oxide. Of course, the conversion determined can be significantly less than the values already mentioned and preferably corresponds to 0.25%, 0.1% or 0.05%.

Accordingly, calibration of the NOx sensor may be implemented such that the first NOx concentration parameter is equivalent to the second NOx concentration parameter or vice versa. The aging of the sensor and/or the series dispersion of the sensor (series treeuung) can thus be compensated. The conversion must be less than the determined conversion throughout the calibration process to avoid errors. Accordingly, the exhaust gas temperature must also be selected accordingly during the entire correction process, preferably less than the determined exhaust gas temperature which satisfies the condition. Alternatively, the exhaust gas temperature may be greater than the determined exhaust gas temperature, since the conversion is also reduced for high exhaust gas temperatures. Particularly preferably, the exhaust gas temperature is kept constant during the entire correction process.

Finally, it may be provided that a second nox sensor is arranged downstream of the catalytic converter and/or the particle filter and that the second nox concentration parameter is determined from the measured values of the second nox sensor and from a correction value taking into account the catalytic converter and/or the particle filter. Preferably, of course, the second nox sensor is arranged directly downstream of the catalytic converter element, at least upstream of the catalytic converter and/or the particle filter. However, this is not possible in any case. Accordingly, a second nox sensor is arranged in this case downstream of the catalytic converter and/or the particle filter and detects the measured values at this point.

This means, however, that the exhaust gas no longer has the nitrogen dioxide concentration present directly downstream of the catalytic converter element, since nitrogen dioxide is already consumed in the catalytic converter or in the particle filter. For this reason, the correction value must be taken into account when determining the second nitrous oxide concentration parameter from the measured values. The correction value specifies, for example, the amount of nitrogen dioxide in the exhaust gas consumed by the catalytic converter and/or the particle filter. The correction values are determined, for example, by means of mathematical relationships, tables and/or characteristic fields. The correction value is dependent in particular on the temperature of the exhaust gas.

The invention further relates to a drive device, in particular for carrying out the method according to the above-described embodiment, having an internal combustion engine and an exhaust gas purification device (which is flowed through by the exhaust gas of the internal combustion engine for exhaust gas purification), wherein the exhaust gas purification device has at least one catalytic converter element for the catalytic conversion of nitrogen monoxide and nitrogen dioxide with a certain conversion. In this case, it is provided that the drive device is designed to adjust the nitrogen monoxide emissions of the internal combustion engine and/or the exhaust gas temperature upstream of the catalytic converter element in accordance with the current conversion and/or the aging of the catalytic converter element in order to compensate for a reduction in the conversion of the catalytic converter element caused by aging, such that the nitrogen dioxide concentration downstream of the catalytic converter element is greater than or equal to a minimum concentration and/or the molar ratio between nitrogen monoxide and nitrogen dioxide downstream of the catalytic converter corresponds to a defined ratio. Such a design of the drive device or the advantages of such a design have already been discussed. The drive device and the corresponding method can be modified according to the embodiments described above, so that reference is made to these embodiments in this respect.

Drawings

The invention will be explained in more detail below with the aid of embodiments illustrated in the drawings, without limiting the invention. Wherein:

figure 1 shows a schematic view of a drive unit with an internal combustion engine and an exhaust gas cleaning device,

FIG. 2 shows a schematic view of an exhaust gas purification apparatus and

fig. 3 shows a diagram in which the conversion of a catalyst element of an exhaust gas purification device is plotted against the temperature of the exhaust gas of an internal combustion engine.

Detailed Description

Fig. 1 shows a schematic representation of a drive 1 with an internal combustion engine 2, of which only one cylinder 3 with a piston 4 is shown here. A fresh charge, i.e. for example fresh air or a fresh air-fuel mixture, can be supplied to the cylinders 3 via the intake valves 5. In the exemplary embodiment shown here, an injection valve 6 is furthermore provided, which serves to introduce fuel into the cylinder 3 or into the combustion chamber of the cylinder 3. Finally, at least one exhaust valve 7 is associated with the cylinder 3, via which exhaust gas is supplied from the cylinder 3 or the combustion chamber, for example via an exhaust manifold 8, to an exhaust gas purification device 9.

The exhaust gas purification device 9 has, for example, an oxidation catalyst 10 or a Diesel Oxidation Catalyst (DOC), a particle filter 11, and a catalyst 12 for selective catalytic reduction (SCR catalyst). The oxidation catalyst 10, the particulate filter 11 and the catalyst 12 are flowed through by the exhaust gas of the internal combustion engine 2 in this order. Downstream of the catalytic converter 12, the exhaust gases are carried out into the environment 13 outside the drive 1, in particular via a tail pipe 14. A catalytic converter element, which is not shown in detail here, is provided in the oxidation catalytic converter 10, which catalytic converter element is embodied, for example, in the form of a coating, in particular a precious metal coating, in the oxidation catalytic converter 10. As the noble metal, for example, platinum or a platinum alloy is used. The catalyst element serves to convert the nitrogen monoxide contained in the exhaust gas into nitrogen dioxide with a certain conversion. The nitrogen dioxide is then used, i.e., downstream of the oxidation catalytic converter 10, to achieve a continuously performed regeneration of the particle filter 11 with a certain regeneration rate and/or to execute a fast reaction path in the catalytic converter 12 for decomposing the nitrogen monoxide contained in the exhaust gas.

In the particle filter 11, the particles, in particular carbon particles, are according to the reaction equation

2NO₂+C ->CO₂+2NO

Is decomposed into carbon dioxide and nitric oxide. Accordingly, the particle filter is always available for absorbing additional particles conveyed through the exhaust gas. Conversely, the reaction path in the catalyst 12 should be according to the reaction equation

NO₂+NO+2NH₃->2N₂+3H₂O

Wherein ammonia (NH)₃) Preferably introduced into the exhaust gas upstream of catalyst 12. The introduction is effected, for example, in the form of urea, which is based on the reaction equation

(NH₂)₂CO+H₂O ->2NH₃+2CO₂

Together with the water contained in the exhaust gas, to ammonia and carbon dioxide.

However, since the catalyst element is subjected to an aging process, so that the achievable conversion decreases with increasing aging of the catalyst element, the aforementioned reaction cannot be easily maintained without special measures. It is known, for example, to design the catalytic converter element such that the nitrogen dioxide concentration downstream of the catalytic converter element is greater than or equal to a minimum concentration over the entire service lifeAnd/or the molar ratio between nitric oxide and nitrogen dioxide after the catalyst element corresponds to a defined ratio. This means, however, that the nitrogen dioxide concentration present after the catalyst element at the beginning of the service life of the catalyst element may be too high. Such a high nitrogen dioxide concentration leads to the formation of laughing gas (N) in the catalytic converter 12₂O) or especially if no nitrogen dioxide is released from the catalyst 12 into the external environment 13. However, this is undesirable.

For this reason, in order to compensate for the reduction in the conversion of the catalytic converter element caused by aging, the nitric oxide emissions of the internal combustion engine 2 and/or the exhaust gas temperature upstream of the catalytic converter element are adjusted as a function of the current conversion and/or the aging of the catalytic converter element such that the nitrogen dioxide concentration downstream of the catalytic converter element is greater than or equal to a minimum concentration and/or the molar ratio between nitric oxide and nitrogen dioxide downstream of the catalytic converter element corresponds to a defined ratio. In this case, for example, it is provided to measure the nitrogen dioxide concentration and, as a function of this measured nitrogen dioxide concentration, to set the nitrogen monoxide emission and/or the exhaust gas temperature of the internal combustion engine in a controlled and/or regulated manner, for example as a function of the measured values determined by means of the nitrogen oxide sensor, such that the desired minimum concentration is achieved by the nitrogen dioxide concentration.

Fig. 2 shows a further schematic illustration of a drive 1 with an internal combustion engine 2 and an exhaust gas purification device 9, which has at least an oxidation catalytic converter 10 and a particle filter 11 and/or catalytic converter 12. Upstream of the oxidation catalytic converter 10 (in which the catalytic converter element is present), a first nitrogen oxide sensor 15 is provided, by means of which a first nitrogen oxide concentration parameter is determined. Downstream of the oxidation catalytic converter 10 or between the oxidation catalytic converter 10 on the one hand and the particle filter 11 and/or catalytic converter 12 on the other hand or downstream of the particle filter 11 or catalytic converter 12, a second nox sensor 16 is arranged, which serves to determine a second nox concentration parameter.

In the case of a second nitrogen oxide sensor 16 arranged upstream of the particle filter 11 and the catalytic converter 12, the current nitrogen dioxide concentration can be determined directly from the difference between the first nitrogen oxide concentration parameter and the second nitrogen oxide concentration parameter, since the amount of nitrogen dioxide which is usually generated directly by the internal combustion engine 2 is negligible. If, on the other hand, the second nox sensor 16 is arranged downstream of the particulate filter 11 and/or the catalytic converter 12, the second nox concentration parameter is determined from the measured value of the second nox sensor 16 and a correction value, wherein the correction value takes into account the particulate filter 11 or the catalytic converter 12. For example, the first nox concentration parameter and the second nox concentration parameter are preferably supplied to a control unit 17 of the drive 1, which is used to control the internal combustion engine 2 in the manner described above.

fig. 3 shows a diagram in which a first curve 18 shows the conversion η at the beginning of the service life of the catalytic converter element with respect to the temperature T of the exhaust gas, and conversely a curve 19 shows the conversion η with respect to the temperature T for an aged catalytic converter element, which diagram therefore clearly shows that not only does the conversion η decrease, but there is a shift in the temperature T of the maximum of the conversion as the aging of the catalytic converter element increases.

Claims (12)

1. method for operating a drive unit (1) having an internal combustion engine (2) and an exhaust gas purification device (9) through which exhaust gases of the internal combustion engine (2) flow in order to be purified, wherein the exhaust gas purification device (9) has at least one catalyst element for the catalytic conversion of nitrogen monoxide into nitrogen dioxide with a certain conversion (η), characterized in that, in order to compensate for a reduction in the conversion (η) of the catalyst element caused by ageing, the nitrogen monoxide emission of the internal combustion engine (2) and/or the exhaust gas temperature upstream of the catalyst element is/are adjusted in dependence on the current conversion (η) and/or the ageing of the catalyst element such that the nitrogen dioxide concentration downstream of the catalyst element is greater than or equal to a minimum concentration and/or the molar ratio between nitrogen monoxide and nitrogen dioxide downstream of the catalyst element corresponds to a defined ratio.

2. a method according to claim 1, characterised in that in order to compensate for the reduction in the conversion (η) caused by ageing, the nitric oxide emissions are increased over the service life of the catalyst element in a certain operating point of the internal combustion engine (2).

3. Method according to claim 1 or 2, characterized in that the adjustment of the nitric oxide emissions and/or the exhaust gas temperature is effected by changing at least one operating parameter of the combustion engine.

4. A method according to claim 3, characterised in that the at least one operating parameter of the internal combustion engine is an injection parameter, a boost pressure of a supercharger, an exhaust gas recirculation rate and/or a manipulation parameter of at least one inlet valve (5) and/or of at least one exhaust valve (6).

5. A method according to claim 1 or 2, characterized in that the minimum concentration is selected such that the particle filter (11) of the exhaust gas cleaning device (9) is continuously regenerated with a certain regeneration rate by means of nitrogen dioxide.

6. Method according to claim 1 or 2, characterized in that a catalyst of the exhaust gas purification device (9) arranged downstream of the catalyst element is configured as an SCR catalyst.

7. A method according to claim 1 or 2, characterised in that the adjustment is effected such that the nitrogen dioxide concentration after the catalyst element is less than or equal to the highest concentration.

8. A method according to claim 1 or 2, characterized in that a first nitrogen oxide concentration parameter is determined by means of a first nitrogen oxide sensor (15) upstream of the catalyst element and a second nitrogen oxide concentration parameter is determined by means of a second nitrogen oxide sensor (16) downstream of the catalyst element, wherein the nitrogen dioxide concentration is determined from the difference between the first nitrogen oxide concentration parameter and the second nitrogen oxide concentration parameter.

9. method according to claim 8, characterized in that the correction of the first nitrogen oxide sensor (15) and the second nitrogen oxide sensor (16) is carried out at exhaust gas temperatures at which the conversion (η) is less than a certain conversion.

10. Method according to claim 8, characterized in that the second nox sensor (16) is arranged downstream of a catalyst (12) and/or a particle filter (11) of the exhaust gas purification device (9) and the second nox concentration parameter is determined from the measured values of the second nox sensor (16) and from a correction value taking into account the catalyst (12) and/or the particle filter (11).

11. a drive arrangement (1) having an internal combustion engine (2) and an exhaust gas purification device (9) through which exhaust gases of the internal combustion engine (2) flow for purification, wherein the exhaust gas purification device (9) has at least one catalyst element for the catalytic conversion of nitrogen monoxide into nitrogen dioxide with a conversion (η), characterized in that, in order to compensate for a reduction in the conversion (η) of the catalyst element caused by ageing, the drive arrangement (1) is configured to adjust the nitrogen monoxide emission of the internal combustion engine (2) and/or the exhaust gas temperature before the catalyst element as a function of the current conversion (η) and/or the ageing of the catalyst element such that the nitrogen dioxide concentration after the catalyst element is greater than or equal to a minimum concentration and/or the molar ratio between nitrogen monoxide and nitrogen dioxide after the catalyst element corresponds to a prescribed ratio.

12. Drive arrangement (1) according to claim 11, characterized in that the drive arrangement (1) is adapted to perform a method according to any of claims 1-10.