Method and apparatus for checking the functionality, in particular the oxidation capability, of a NO oxidation catalyst installed in the exhaust line of an internal combustion engine operated with excess air

Abstract

Method for verifying the functionality, in particular the oxidation capability, of a NO oxidation catalyst installed in the exhaust line of an internal combustion engine operated with excess air, wherein, for the purpose of verifying the functionality of the NO oxidation catalyst (5), a defined amount of carbon monoxide is added and / or generated as a reducing agent upstream of the NO oxidation catalyst (5), and this carbon monoxide is oxidized at the NO oxidation catalyst (5) with the help of the oxygen contained in the exhaust gas stream upstream of the NO oxidation catalyst, wherein the change in the oxygen content in the exhaust gas stream caused by the oxidation of the added and / or generated carbon monoxide within and / or downstream of the NO oxidation catalyst (5) is recorded and / or determined as the actual oxygen value and compared with a predetermined target oxygen value, and wherein a defined deviation of the actual oxygen value from the target oxygen value indicates a deterioration in the functionality of the NO oxidation catalyst (5), in particular by generating and / or issuing an error message, and wherein the amount of exhaust gas returned to the combustion chamber of the internal combustion engine (2) during the verification phase and the air / fuel ratio Lambda are varied such that the combustion chamber temperature does not exceed 1850K in the range greater than to and including 1.02 Lambda, in particular in the range of 40 to and including 1.02 Lambda, 1600K in the range of 1.02 to and including 0.98 Lambda and 1500K in the range less than 0.98 Lambda.

Description

[0001] The invention relates to a method for verifying the functionality, in particular the oxidation capability, of a NO oxidation catalyst installed in the exhaust line of an internal combustion engine operated with excess air, according to claim 1 or claim 14. Furthermore, the invention relates to a device for verifying the functionality, in particular the oxidation capability, of a NO oxidation catalyst installed in the exhaust line of an internal combustion engine operated with excess air, according to claim 13 or claim 15.

[0002] It is generally known that in combustion engines operating with excess air, catalytically operating aftertreatment systems, such as NOx storage catalysts, SCR catalysts, or particulate filters, are used to comply with legally mandated emission limits. All these systems have in common that nitrogen dioxide (NO2) is an important component of the reactions taking place in the aftertreatment system. This nitrogen dioxide is formed from the nitrogen monoxide emitted by the engine using NO oxidation catalysts, usually containing platinum, with the help of oxygen contained in the exhaust gas. 2NO + O2 ↔2NO2

[0003] In real-world engine operation, however, the sulfurization of these NO oxidation catalysts by the sulfur contained in the fuel and / or engine oil poses a significant problem. During combustion, this sulfur forms SO2, which is then oxidized to SO3 at the NO oxidation catalysts according to the equations below: S + O2 → SO2 2SO2 + O2 → SO3

[0004] It has been shown that the amount of SO3 and NO2 formed are directly related, such that an NO oxidation catalyst, which ideally produces large amounts of NO2, simultaneously and undesirably generates large amounts of SO3. This SO3 reacts with the metal-containing catalyst washcoat to form sulfates, or with water to form sulfuric acid, which are physiosorbed onto the catalyst surface. Both reactions lead to the covering of the catalyst's active sites and thus to a decrease in its activity.

[0005] For this reason, it is necessary to check or monitor the current state of an NO oxidation catalyst and thus its oxidizing capacity.

[0006] A method is known for determining the oxygen storage capacity of three-way catalytic converters by means of periodic oscillations between lean and rich engine operation and by observing the catalyst's reaction using a downstream lambda sensor. The method is such that, in the case of a damped amplitude of the residual oxygen oscillation, the catalyst should still possess oxygen storage capacity, while otherwise it should no longer be able to absorb oxygen (DE 10 2004 009 615 B4). This method cannot be applied to NO oxidation catalysts for two reasons: Firstly, these catalysts do not possess a pronounced oxygen storage capacity, and secondly, diesel-injected or direct-injection gasoline engines, which are usually operated lean, cannot easily be run rich.This leads to an undesirable and extreme increase in both soot emissions and the thermal stress on the engines.

[0007] For so-called diesel oxidation catalysts, which serve to oxidize unburned hydrocarbons and carbon monoxide, a second method is used: Here, hydrocarbon oxidation is periodically increased, usually by a late post-injection of fuel into the combustion chamber, and the exothermicity of the oxidation of these hydrocarbons at the diesel oxidation catalyst is determined using thermocouples. The detected temperature increase is compared with an expected value derived from the amount of hydrocarbons added. If the measured and expected values ​​deviate too much from each other, damage to the diesel oxidation catalyst can be concluded (EP 1 373 693 B2). The disadvantage of this method is that large quantities of hydrocarbons must be added, as otherwise, due to the large thermal masses and the resulting small temperature increase, no reaction of the system can be observed.This leads to a significant decrease in the efficiency of the internal combustion engine and thus to an increase in fuel consumption. A further disadvantage is the high thermal stress on the catalyst, which, as described above, can lead to damage in NO oxidation catalysts. Especially in internal combustion engines installed in vehicles, the highly variable ambient conditions and the resulting fluctuating temperature losses in the exhaust system create the problem that temperature detection can be subject to a large measurement error.

[0008] From EP 1 936 140 A1, a method for monitoring an exhaust aftertreatment system of an internal combustion engine is already known, in which a first lambda probe for detecting the air-fuel ratio is arranged upstream of the exhaust aftertreatment system and in which a second lambda probe for detecting the air-fuel ratio is arranged further downstream of the exhaust aftertreatment system.To check the functionality of the exhaust aftertreatment system, the internal combustion engine is operated in a state where the exhaust gases discharged from the cylinders have such a high concentration of unburned hydrocarbons that the first sensor malfunctions, indicating a higher air-fuel ratio compared to the actual air-fuel ratio present in the exhaust gas. If the two air-fuel ratios are essentially the same, the exhaust aftertreatment system is considered to be malfunctioning.

[0009] A device for diagnosing the deterioration of a catalyst is known from JP 2005-240 716 A. DE 103 33 337 A1 discloses a method and a device for diagnosing a catalyst system.

[0010] German patent DE 10 2009 000 148 A1 discloses a method for testing an oxidation catalyst and an exhaust aftertreatment arrangement for an internal combustion engine. CH 503 892 A discloses a liquid-based control system for the intake and exhaust valves of internal combustion engines. In contrast, the object of the present invention is to provide a method and a device for testing the functionality, in particular the oxidation capability, of a NO oxidation catalyst installed in the exhaust gas line of an internal combustion engine operating with excess air, which can be carried out reliably and simply with high functional reliability, even at low exhaust gas flow temperatures.

[0011] This problem is solved by the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims relating thereto.

[0012] According to claim 1, a method for verifying the functionality, in particular the oxidation capacity, of a NO oxidation catalyst installed in the exhaust gas line of an internal combustion engine operating with excess air is proposed, in which, according to the invention, a defined quantity of carbon monoxide is added and / or generated as a reducing agent upstream of the NO oxidation catalyst for the purpose of verifying the functionality of the NO oxidation catalyst, and this carbon monoxide is oxidized at the NO oxidation catalyst with the aid of the oxygen contained in the exhaust gas stream upstream of the NO oxidation catalyst. The carbon monoxide produced by the oxidation of the added orThe change in oxygen content in the exhaust gas stream within and / or downstream of the NO oxidation catalyst caused by the carbon monoxide produced is recorded and / or determined as the actual oxygen value and compared with a predetermined target oxygen value, whereby a defined deviation of the actual oxygen value from the target oxygen value indicates a deterioration in the functionality of the NO oxidation catalyst, in particular by generating and / or issuing an error message.

[0013] With such a method according to the invention, the functionality of a NO oxidation catalyst can be checked in a simple and reliable manner, since the reduction in the oxygen content of the exhaust gas stream can be easily detected and determined using a sensor, for example a lambda sensor, located downstream or within the catalyst. This is then compared with the target oxygen value as the expected value. The target oxygen value is preferably a function of the catalyst temperature and / or the exhaust gas volume and / or the amount of reducing agent supplied and / or the oxygen content of the exhaust gas stream upstream of the NO oxidation catalyst and is stored, for example, in the form of a mathematical model and / or in the form of characteristic maps in an electronic control unit of a device for checking the functionality of the NO oxidation catalyst.Both an absolute value and the change in oxygen concentration or lambda value caused by the oxidation of carbon monoxide can be used as the actual and / or target / expected value. As an alternative to the previously described example of measuring the oxygen content upstream of the NO oxidation catalyst using sensors, this can also be determined using appropriate mathematical models, either alternatively or additionally.

[0014] It should be explicitly mentioned here that any suitable measuring or sensor device can be used to determine the oxygen content, for example, in addition to lambda probes, NOx sensors can also be used, which can also be used to determine the oxygen content, to name just one further example.

[0015] If the internal combustion engine is in a defined operating mode, especially in a steady-state operating mode, it is also possible to determine the change downstream of the NO oxidation catalyst after increasing the carbon monoxide concentration using the value before increasing the carbon monoxide concentration and to compare this value with the target or expected value.

[0016] The use of carbon monoxide according to the invention in relation to hydrocarbons, as is the case in the prior art, has the advantage that carbon monoxide is oxidized at significantly lower temperatures than long-chain hydrocarbons from the fuel. This means that, in the prior art, below a certain temperature, no conversion and therefore no verification using hydrocarbons is possible, since both the target value and the actual value are zero. Therefore, the use of carbon monoxide as a reducing agent is particularly advantageous at such low temperatures as those occurring in internal combustion engines where at least one exhaust gas turbocharger is used. A further problem with the use of hydrocarbons is the coking of the catalysts by long-chain hydrocarbon compounds, especially at low temperatures.

[0017] By using the oxygen or lambda value as an evaluation criterion, significantly smaller amounts of reducing agent are sufficient compared to temperature as an evaluation criterion, as is the case with EP 1 373 693 B2, since the reaction of the system is considerably faster than in thermally based measurements, which react much more slowly due to the heat capacity of the NO oxidation catalyst.

[0018] Overall, the inventive method allows for a quick and low-temperature verification of the functionality, in particular the oxidation capacity, of a NO oxidation catalyst installed in the exhaust gas line of an internal combustion engine operated with excess air, without placing a large thermal load on the NO oxidation catalyst.

[0019] According to a particularly preferred method, it is proposed that the amount of carbon monoxide added and / or generated is defined and / or specified such that it completely reduces the oxygen contained in the exhaust gas stream upstream of the NO oxidation catalyst. In the event that only carbon monoxide is present as a reducing agent upstream of the NO oxidation catalyst, this is ensured by making the carbon monoxide concentration upstream of the NO oxidation catalyst twice as high as the oxygen concentration upstream of the NO oxidation catalyst. However, since technical combustion processes are always incomplete, small amounts of unburned hydrocarbons, which also act as reducing agents, must also be taken into account upstream of the NO oxidation catalysts. This reduces the amount of carbon monoxide required for the complete reduction of the residual oxygen accordingly.With this method, an exact determination of the oxygen concentration can be dispensed with, and instead, a case distinction between "oxygen still present / no oxygen present" downstream of the NO oxidation catalyst can be used. Accordingly, very cost-effective step-wave lambda sensors, which provide an abrupt signal change at the transition between "oxygen still present / no oxygen present," can be used. If, however, the method is designed such that residual oxygen is still present downstream of the NO oxidation catalysts, the use of broadband lambda sensors becomes necessary. These can determine the oxygen content over a wide range, but due to their more complex design, they are considerably more expensive and less robust.

[0020] The carbon monoxide required to monitor the functionality of the NO oxidation catalyst is preferably generated by homogeneous charge compression ignition (HCCI) of the internal combustion engine or by semi-homogeneous combustion engine operation. Homogeneous charge compression ignition (HCCI, also known as controlled auto ignition, or CAI) of the internal combustion engine, used to increase carbon monoxide emissions during the testing phase, is a combustion process in which the fuel is distributed as homogeneously as possible in the combustion chamber and then ignited by compression. This is usually achieved through a defined mixing of fuel and fresh air in front of the cylinders of the internal combustion engine. The aim of this homogeneous charge compression ignition is to initiate combustion as simultaneously as possible throughout the entire combustion chamber. This combustion process makes it possible to reduce NO emissions. X- and significantly reduce soot emissions, while on the other hand there is an increase in carbon monoxide emissions.

[0021] The disadvantage of the homogeneous combustion process in direct-injection internal combustion engines, where fuel is injected directly into the combustion chamber during normal operation, is that additional devices for fuel injection must be provided in the intake manifold. This results in a significant increase in costs.

[0022] This is avoided with so-called semi-homogeneous compression ignition: In direct-injection internal combustion engines, the injection timing is advanced significantly, so that fuel and air only mix in the combustion chamber. Due to the advanced injection timing, ignition of the fuel droplets is prevented, and instead, their vaporization is promoted by a relatively long residence time. However, complete homogeneous mixing of fuel and air is usually not achieved, which is why it is referred to as semi-homogeneous compression ignition. Nevertheless, this also leads to a significant increase in carbon monoxide emissions. At the same time, hydrocarbon emissions typically increase, but with two significant differences compared to a process based on retarding the injection timing: Firstly, the carbon monoxide concentrations are considerably higher than the hydrocarbon concentrations during homogeneous or semi-homogeneous compression ignition, while the ratio shifts towards hydrocarbons when the ignition timing is adjusted late, and these are usually considerably higher than the carbon monoxide concentrations. Secondly, the hydrocarbons emitted during homogeneous or semi-homogeneous compression ignition are considerably shorter-chain, usually in the range of 1 to 5 carbon atoms, so that fouling of the oxidation catalysts by long-chain, pyrolyzed and condensed hydrocarbons can be avoided.

[0023] Particularly preferred, especially in semi-homogeneous internal combustion engine operation, is a method in which the injection timing in the verification phase is advanced, in particular to at least 15° crank angle up to a maximum of 370° crank angle before top dead center, most preferably to a value of 20° crank angle up to 350° crank angle before top dead center.

[0024] Alternatively or preferably additionally, it can be provided during the verification phase, during homogeneous or semi-homogeneous operation of the internal combustion engine, that the amount of exhaust gas recirculated from the exhaust side to the charge air side of the internal combustion engine is increased so that the proportion of exhaust gas in the charge air supplied to the internal combustion engine is at least 30% and at most 80%.

[0025] According to a first embodiment of the invention, the amount of exhaust gas recirculated to the combustion chamber of the internal combustion engine during the testing phase and the air / fuel ratio (lambda) are varied such that the combustion chamber temperature does not exceed 1850 K in the range of lambda greater than or including 1.02, 1600 K in the range of lambda greater than or equal to 1.02, and 1500 K in the range of lambda less than or equal to 0.98. As a further additional measure, it can be ensured that the air / fuel ratio does not fall below a lambda value of 1 or is less than or equal to 1, although residual oxygen is still present in the exhaust gas upstream of the NO oxidation catalyst.

[0026] Alternatively or additionally, it can be provided that the injection pressure of the fuel into the cylinder is increased by at least 20% and / or to at least 1200 bar, but no more than 3500 bar, during the verification phase.

[0027] The ratio of carbon monoxide to hydrocarbon concentration is usually at least 2:1.

[0028] According to a further specific procedure, as an alternative or in addition to increasing carbon monoxide emissions, it may be provided that the compression ratio in the review phase is reduced by at least 20%, but at most by 75% and / or not below 6:1.

[0029] Alternatively or additionally, the valve opening times can be modified during the verification phase. These measures aim, firstly, to extend the ignition delay, resulting in a longer homogenization phase, and secondly, to prevent excessive pressure increases by reducing the combustion speed. For example, at least one intake valve can be closed before bottom dead center (BDC). This reduces the combustion chamber pressure and consequently the combustion chamber temperature when the exhaust valve is closed. Another possibility is to close the intake valve very late after BDC, thereby expelling already drawn-in air through the intake valves. This process is known as the Miller cycle and, due to the reduced cylinder filling, leads to lower peak pressures during combustion.Another possibility is to modify the valve opening times during the verification phase so that at least one exhaust valve remains open longer, thereby increasing the residual gas fraction through backflow of exhaust gas from the exhaust tract and consequently reducing the combustion speed. The valve opening times can be varied, in particular, by means of a variable valve train, which is state of the art and therefore will not be discussed further here (EP 0 279 265, DE 38 233 32 A1, DE 39 20 895 A1).

[0030] In connection with the teaching according to the invention, it is particularly important to consider that the previously shown engine measures for increasing carbon monoxide emissions during the testing phase, such as injection timing, recirculated exhaust gas volume, compression ratio, valve opening times, injection pressure, etc., have always been varied in the prior art in such a way as to keep the amount of carbon monoxide formed as low as possible in order to avoid increased carbon monoxide emissions, or to achieve the temperature increase through the catalytic oxidation of long-chain hydrocarbons, which is only possible with sufficiently high exhaust gas temperatures without coking of the catalysts. In contrast, in the solution according to the invention, the engine parameters are changed in such a way that exactly the opposite occurs, but the CO emissions are increased significantly more than the HC emissions during the testing phase.Furthermore, the process according to the invention ensures that a large proportion of the hydrocarbons are considerably smaller, typically in the range of 1 to 5 carbon atoms per molecule, than is the case with the aforementioned prior art processes, thereby additionally avoiding the risk of catalyst coking by large quantities of long-chain hydrocarbons. Since carbon monoxide and short-chain hydrocarbons are significantly easier to oxidize than the long-chain, unburned hydrocarbons from the fuel fraction, as formed by late injection according to the prior art, the catalyst activation temperature can be lowered according to the invention. This allows the functionality of the NO oxidation catalysts to be verified even at low exhaust gas temperatures upstream of them.

[0031] Furthermore, an advantageous device for verifying the functionality of a NO oxidation catalyst installed in the exhaust pipe of an internal combustion engine operating with excess air is proposed. The advantages to be achieved with the device according to the invention have already been explained in detail previously in connection with the process. In this respect, reference is made to the preceding explanations.

[0032] The advantageous embodiments and further developments of the invention described above and / or described in the dependent claims can be applied individually or in any combination, except, for example, in cases of clear dependencies or incompatible alternatives.

[0033] The invention is explained in more detail below with reference to a drawing only as an example.

[0034] They show: Fig. 1 schematically the structure of an exhaust gas aftertreatment device for carrying out a process according to the invention, and Fig. 2 schematically a flowchart for an exemplary explanation of a process according to the invention in a stationary internal combustion engine.

[0035] The Fig. Figure 1 schematically shows an exhaust aftertreatment device 1 for an internal combustion engine 2, which is shown here only in a highly schematic manner, to which charge air 12 is supplied via a charge air line 3 in a manner known per se.

[0036] From the internal combustion engine 2, an exhaust gas line 4 leads away, in which, as an example, a NO oxidation catalyst 5, an SCR catalyst 6, and a particulate filter 7 are arranged one after the other in the direction of exhaust gas flow. Upstream of the SCR catalyst 6, as indicated here only very schematically by the arrow, a reducing agent, for example an aqueous ammonia solution, is added.

[0037] Furthermore, an oxygen measuring device 18, for example a lambda probe, is arranged upstream of the SCR catalyst 6 in the exhaust line 4, specifically downstream of the NO oxidation catalyst 5.

[0038] Upstream of the NO oxidation catalyst 5, an exhaust gas turbine 9 of an exhaust gas turbocharger 10 is arranged in the exhaust line 4, by means of which a compressor 11 in the charge air line 3 is driven in the usual manner to compress the charge air 12.

[0039] Furthermore, an exhaust gas recirculation line 13 leads from the exhaust pipe 4 to the charge air pipe 3, by means of which exhaust gas can be recirculated from the exhaust pipe 4 to the charge air pipe 3 according to predefined, defined recirculation parameters in a manner known per se. To enable or disable the exhaust gas recirculation line 13, a shut-off element 14, for example an exhaust flap or the like, is arranged in this exhaust gas recirculation line 13 (shown here only in a highly schematic way).

[0040] If, starting from normal operation or non-test operation of the internal combustion engine 2, it is determined or specified that a check of the functionality or oxidation capacity of the NO oxidation catalyst 5 is to be carried out, then at the beginning of the test phase, a homogeneous compression ignition of the internal combustion engine or a partially homogeneous internal combustion engine operation can be specified by means of the control device 15, which is shown here only in a very schematic way, or at least one defined internal combustion engine operating parameter can be changed compared to a setting in the non-test phase such that the carbon monoxide emissions of the internal combustion engine 2 are increased. Preferably, the carbon monoxide concentration upstream of the NO oxidation catalyst 5 is increased to at most twice the oxygen concentration upstream of the NO oxidation catalyst 5.

[0041] Because the SCR catalyst 6 downstream of the NO oxidation catalyst 5 preferably has no CO oxidation activity, it is ensured that there is no significant temperature rise at the SCR catalyst 6, so that its thermal damage can be reliably avoided.

[0042] To increase carbon monoxide emissions as desired, the control unit 15 can, for example, actuate the shut-off element 14 via the control line 16 (shown here in dashed lines) such that the exhaust gas recirculation rate is increased to over 30%, relative to the amount of charge air supplied to the combustion engine 2. The amount of recirculated exhaust gas can be further increased by providing a throttling device (not shown here) in the fresh air supply 3 to increase the pressure differential between the exhaust and fresh air sides. Alternatively or additionally, as is only schematically indicated by the control line 17, the air / fuel ratio lambda can be reduced, for example, to below 1.05 and / or the injection pressure can be increased by, for example, at least 20% or to at least 1200 bar.Alternatively or additionally, a shift in the injection timing, for example to at least 20° crank angle, but not more than 370° crank angle before top dead center (ignition TDC), and / or a reduction in the compression ratio, in particular by at least 20%, and / or a change in the valve opening times may be provided.

[0043] This process generates large quantities of carbon monoxide, which are oxidized at the NO oxidation catalyst 5 with the help of the oxygen contained in the exhaust gas stream upstream of the NO oxidation catalyst 5. The change in the oxygen content in the exhaust gas stream downstream of the NO oxidation catalyst 5 caused by the oxidation of the carbon monoxide is recorded as the actual oxygen value by the oxygen measuring device 18 and supplied to the control unit 15 via the control or signal line 19. In the control unit 15 or a comparator unit of the control unit 15, this recorded value is used to calculate the oxygen content.The measured actual oxygen value is compared with an expected value, for example, one specified via a characteristic map or a calculated target oxygen value. A defined deviation of the actual oxygen value from the target oxygen value, and thus the degree of deviation, indicates either impaired functionality of the NO oxidation catalyst or confirms its proper functioning. In the event of a detected deficiency or impaired functionality exceeding defined thresholds, an error signal can be output, for example, via control line 20, stored in the vehicle, and / or displayed to the driver via a display device. This is explained below using the following example. Fig. 2. This is explained in more detail using a specific example procedure.

[0044] It is understood that at the end of this verification phase, conventional internal combustion engine operation can be resumed, meaning in particular that the homogeneous compression ignition of the internal combustion engine or a semi-homogeneous internal combustion engine operation will be terminated.

[0045] The control unit 15 can, for example, be a separate control unit. However, the control unit 15 can also be part of the engine control unit of the internal combustion engine 2.

[0046] As this is shown in the Fig. As shown in section 2, the first step in checking functionality can be to determine whether the internal combustion engine (in the Fig.2 (referred to as the engine) is in a steady-state or stable operating mode, i.e., not in an unstable start-up mode. If this is confirmed, the oxygen content downstream of the NO oxidation catalyst 5 is measured by the oxygen measuring device 18 in a subsequent process step. This value is stored as oxygen content O2.0. The CO concentration upstream of the NO oxidation catalyst 5 is then increased in the manner described above, in particular by adjusting engine parameters to transition to HCCI operation, and the oxygen content O2.1 downstream of the NO oxidation catalyst 5 is again measured by the oxygen measuring device 18.The current oxygen content (O2.1) determined in this way is then compared, for example, by calculating the difference with the stored value for the oxygen content (O2.0). If the difference between the two values ​​is less than a predefined target or expected value, an error message is displayed. If this is not the case, the system shuts down operation with increased CO emissions, the check is stopped, and no error message is displayed. After this step, the system returns to normal combustion engine operation, in which the CO emissions of the combustion engine are again at the same level as before the functionality check of the NO oxidation catalyst, or significantly lower than during this check, ideally at no more than twenty percent of the value during the check.

[0047] The operating parameters for determining a steady-state operating condition (the term steady-state expressly includes a quasi-steady-state operating condition) may advantageously include the coolant temperature and / or the oil temperature and / or the fuel temperature and / or the fuel injection pressure and / or the intake air temperature and / or the charge air temperature and / or the turbocharger speed and / or the boost pressure and / or the vehicle speed and / or the engine speed and / or the fuel injection quantity and / or the exhaust gas temperatures and / or the catalyst temperature and / or the reducing agent injection quantity and / or the exhaust gas recirculation rate and / or the emissions and / or the fuel / air ratio and / or the change over time of these quantities.

Claims

[1] Method for testing the functionality, in particular the oxidation capability, of a NO oxidation catalyst installed in the exhaust pipe of an internal combustion engine operated with excess air, wherein, for testing the functionality of the NO oxidation catalyst (5), a defined amount of carbon monoxide is added and / or generated as a reducing agent upstream of the NO oxidation catalyst (5), this carbon monoxide is oxidized on the NO oxidation catalyst (5) with the aid of the oxygen contained in the exhaust gas stream upstream of the NO oxidation catalyst, wherein the change in the oxygen content in the exhaust gas flow caused by the oxidation of the added and / or generated carbon monoxide is recorded and / or determined as an actual oxygen value within and / or downstream of the NO oxidation catalyst (5) and is compared with a predetermined oxygen target value, and wherein, in the event of a defined deviation of the actual oxygen value from the desired oxygen value, it is concluded that the functionality of the NO oxidation catalyst (5) is impaired, in particular in such a way that an error message is generated and / or output, and wherein the exhaust gas quantity returned to the combustion chamber of the internal combustion engine (2) in the checking phase and the air / fuel ratio lambda are varied such that the combustion chamber temperature does not exceed 1850K in the range greater than and including 1.02 lambda, in particular in the range from 40 up to and including 1.02 lambda, 1600K in the range from 1.02 up to and including 0.98 lambda and 1500K in the range less than 0.98 lambda. [2] Method according to claim 1, characterized by that the amount of carbon monoxide added and / or produced is defined and / or specified in such a way that it completely reduces the oxygen contained in the exhaust gas stream upstream of the NO oxidation catalyst. [3] Method according to claim 1 or 2, characterized by that the carbon monoxide concentration upstream of the NO oxidation catalyst (5) is at most twice as high as the oxygen concentration upstream of the NO oxidation catalyst (5) and / or that the ratio of carbon monoxide to hydrocarbon concentration is at least 2:

1. [4] Method according to one of the preceding claims, characterized by that the carbon monoxide is generated by homogeneous compression ignition of the internal combustion engine or by partially homogeneous internal combustion engine operation. [5] Method according to one of the preceding claims, characterized bythat the injection point of the fuel in the test phase, in particular in the case of partially homogeneous internal combustion engine operation, is shifted towards an earlier point, in particular to 15° crank angle up to a maximum of 370° crank angle before top dead center of ignition, advantageously to 20° crank angle up to 350° crank angle before top dead center of ignition. [6] Method according to one of the preceding claims, characterized by that in the test phase, in particular during partially homogeneous internal combustion engine operation, an exhaust gas quantity recirculated from the exhaust side to the charge air side of the internal combustion engine (2) is increased such that the proportion of exhaust gas in the charge air supplied to the internal combustion engine (2) is at least 30% and at most 80%. [7] Method according to one of the preceding claims, characterized bythat the air / fuel ratio does not fall below a lambda value of one or less than one, provided that residual oxygen is still present in the exhaust gas upstream of the NO oxidation catalyst. [8] Method according to one of the preceding claims, characterized by that the injection pressure is increased by at least 20% and / or to at least 1200 bar up to a maximum of 3500 bar during the verification phase. [9] Method according to one of the preceding claims, characterized by that the compression ratio is reduced by at least 20% to a maximum of 75% and / or not less than 6:1 during the verification phase. [10] Method according to one of the preceding claims, characterized by that the valve opening times are changed during the check phase in such a way that the residual gas quantity is increased and / or the combustion chamber temperature is reduced. [11] Method according to claim 10, characterized bythat the valve opening times are changed in the checking phase in such a way that, in particular with the aid of a variable valve train, at least one exhaust valve remains open for a longer time and / or at least one intake valve is opened and / or closed later. [12] Method according to one of the preceding claims, characterized by that the actual oxygen value is determined from an oxygen measurement upstream and an oxygen measurement downstream of the NO oxidation catalyst (5), wherein it is preferably provided that the oxygen concentration is determined with the aid of a sensor device (18) mounted downstream of the NO oxidation catalyst (5). [13] Device for carrying out a method for checking the functionality, in particular the oxidation capability, of a NO oxidation catalyst installed in the exhaust pipe of an internal combustion engine operated with excess air, in particular for carrying out a method according to one of the preceding method claims, wherein a control device (15) is provided, by means of which the functionality of the NO oxidation catalyst (5) the addition and / or production of a defined amount of carbon monoxide as a reducing agent upstream of the NO oxidation catalyst (5) can be introduced and / or carried out, which carbon monoxide is oxidized on the NO oxidation catalyst (5) with the aid of the oxygen contained in the exhaust gas stream upstream of the NO oxidation catalyst (5), wherein at least one sensor device and / or at least one computer device is provided, by means of which the change in the oxygen content in the exhaust gas flow within and / or downstream of the NO oxidation catalyst (5) caused by the oxidation of the added and / or generated carbon monoxide can be detected and / or determined as an actual oxygen value, and wherein at least one comparator device is provided, by means of which the actual oxygen value can be compared with an oxygen target value, wherein preferably a storage and / or output and / or display device is provided, by means of which an error message can be generated and / or output in the event of a detected and / or determined lack of functionality, and wherein the exhaust gas quantity returned to the combustion chamber of the internal combustion engine (2) in the check phase and the air / fuel ratio lambda are variable such that the combustion chamber temperature does not exceed 1850K in the range greater than and including 1.02 lambda, in particular in the range from 40 up to and including 1.02 lambda, 1600K in the range from 1.02 up to and including 0.98 lambda and 1500K in the range less than 0.98 lambda. [14] Method for testing the functionality, in particular the oxidation capability, of a NO oxidation catalyst installed in the exhaust line of an internal combustion engine operated with excess air, wherein, for testing the functionality of the NO oxidation catalyst (5), a defined amount of carbon monoxide is added and / or generated as a reducing agent upstream of the NO oxidation catalyst (5), this carbon monoxide is oxidized on the NO oxidation catalyst (5) with the aid of the oxygen contained in the exhaust gas stream upstream of the NO oxidation catalyst, and wherein in a first step of the method it is detected whether the internal combustion engine is in a stationary or stable operating mode, wherein in a second step of the method, if the internal combustion engine is in a stationary or stable operating mode, the oxygen content downstream of the NO oxidation catalyst is detected by means of the oxygen measuring device (18) and stored as the first oxygen content O2.0, wherein the carbon monoxide concentration upstream of the NO oxidation catalyst is then increased and the second oxygen content 02.1 of the NO oxidation catalyst is detected by means of the oxygen measuring device (18), wherein the second oxygen content 02.1 is compared with the first oxygen content O2.0 by difference, and where, in the event that the difference between the two values ​​is smaller than a given target or expected value an error message is displayed. [15] Apparatus adapted to carry out a method according to claim 14.

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