Method for operating internal combustion engine, computer program and control device

Abstract

The invention relates to a method, a computer program and a control device for operating an internal combustion engine (100) having an exhaust system (130) which has at least one catalytic device (132) and an exhaust gas sensor (134) which is designed to generate an exhaust gas signal indicating an exhaust gas value, the exhaust gas value represents the sum of the nitrogen oxide content and the ammonia gas content in the exhaust gas. The method according to the invention comprises actuating the internal combustion engine (100) in such a way that the internal combustion engine is operated with a thick combustion gas mixture after a thrust shut-off phase of the internal combustion engine (100) that is longer than a predetermined time threshold has occurred. During the actuation of the internal combustion engine (100) with a thick combustion gas mixture: receiving at least one exhaust gas signal (206) of an exhaust gas sensor (134); and ascertaining that the at least one exhaust gas signal (206) satisfies at least one predetermined target criterion. The method according to the invention further comprises actuating the internal combustion engine (100) in such a way that the internal combustion engine is operated with a substantially stoichiometric combustion gas mixture if it is ascertained that the at least one exhaust gas signal (206) meets at least one predetermined target criterion.

Description

Technical Field

[0001] During the thrust cut-off phase of the internal combustion engine of a vehicle, no fuel is usually injected in order to minimize the consumption and untreated emissions of the internal combustion engine. Therefore, the exhaust system is flushed with air during this operating phase of the internal combustion engine. A catalytic device arranged in the exhaust system, such as, for example, a three-way catalytic converter with oxygen storage capacity, can store oxygen contained in the air during this period. If the thrust cut-off phase is long enough, the entire catalytic device consisting of the catalytic converter close to the internal combustion engine and the bottom catalytic converter can be flushed with oxygen and filled almost completely with oxygen. Background Art

[0002] If injection is restarted after the thrust cut-off phase, at least part of the oxygen load must be discharged from the catalytic converter or the catalytic converter must be at least partially reduced in order to be robust both with respect to lean and with respect to rich slip in the subsequent operation. If lean slip occurs (=λ(Lambda)>1), nitrogen oxide emissions will increase. On the other hand, if too much fuel is injected, that is, if rich slip occurs (=λ<1), increased HC, CO and NH3 emissions will occur.

[0003] In order to be able to at least partially discharge part of the stored oxygen after the thrust cut-off phase, it is known to temporarily operate the internal combustion engine with a rich combustion gas mixture. This operation is called catalytic cleaning. During the catalytic cleaning, the carbon oxides (CO) and hydrocarbons (HC) formed can be converted into carbon dioxide (CO2) and water (H2O) with the oxygen stored in the catalytic device. Undesirable by-products such as nitrogen oxides (NOx) and / or ammonia (NH3) can also be produced.

[0004] Since only a portion of the oxygen stored in the catalytic device needs to be discharged during the catalytic purge, it is known from the prior art to use as a target criterion for interrupting the catalytic purge the exceeding of a predetermined lambda voltage of a binary lambda probe arranged downstream of the catalytic device. It is also known to use as a target criterion for interrupting the catalytic purge the undershooting of a modeled oxygen load threshold value by a predetermined oxygen load threshold value.

[0005] A disadvantage here is that the predetermined lambda voltage may be exceeded too late and / or the modeled oxygen load value which is compared with the predetermined oxygen load threshold value may be determined too inaccurately.

[0006] Further methods and devices are known from US 2022 / 0178295 A1, JP 4134398 B2, US 9765715 B2, JP 2022-067790 A, JP 3744373 B2, DE 102021202965 A1 and DE 102021209107 B3. Summary of the invention

[0007] Basically, the object on which the present invention is based is to provide a method and a computer program for operating an internal combustion engine, by means of which the catalytic clean-up after the thrust cut-off phase can be interrupted at an optimized point in time and a switch can be made to normal operation of the internal combustion engine with an essentially stoichiometric combustion gas mixture.

[0008] This object is achieved with a method according to claim 1, a computer program according to claim 9, a computer-readable medium according to claim 10 and a control device according to claim 11. Advantageous embodiments are described in the dependent claims.

[0009] Basically, the invention is based on the idea of ​​using an exhaust gas signal of an exhaust gas sensor arranged downstream of a catalytic device, in particular a three-way catalytic device, which indicates the sum of the nitrogen oxide content and the ammonia content in the exhaust gas of an internal combustion engine; detecting the optimal time point for interrupting the so-called catalytic cleanup after a thrust cut-off operation of the internal combustion engine. In particular, according to the invention, the exhaust gas signal is evaluated during operation of the internal combustion engine with a rich combustion gas mixture, which operation immediately follows a sufficiently long thrust cut-off phase of the internal combustion engine, and an investigation is conducted to determine whether at least one predetermined target criterion for interrupting the catalytic cleanup exists. As a result, the catalytic cleanup phase can be regulated, that is to say not controlled, by evaluating the exhaust gas signal of the exhaust gas sensor. In addition, the catalytic cleanup phase can be terminated earlier based on the evaluation of the exhaust gas signal of the exhaust gas sensor than by evaluating the signal of the lambda probe, which can lead to lower emissions.

[0010] Therefore, according to a first aspect of the invention, a method for operating an internal combustion engine with an exhaust gas system is disclosed, the exhaust gas system having: at least one catalytic device, which is designed to at least partially store oxygen; and an exhaust gas sensor arranged downstream of the at least one catalytic device, which is designed to generate an exhaust gas signal indicating an exhaust gas value, which represents the sum of the nitrogen oxide content and the ammonia content in the exhaust gas. The method according to the invention includes controlling the internal combustion engine in such a way that the internal combustion engine is operated with a rich combustion gas mixture after a thrust cut-off phase of the internal combustion engine that is longer than a predetermined time threshold has occurred. According to the invention, during the operation of the internal combustion engine with a rich combustion mixture, at least one exhaust gas signal of the exhaust gas sensor is received and it is determined that the at least one exhaust gas signal meets at least one predetermined target criterion. The method according to the invention also includes controlling the internal combustion engine in such a way that if it is determined that the at least one exhaust gas signal meets at least one predetermined target criterion, the internal combustion engine is operated with a substantially stoichiometric combustion gas mixture.

[0011] According to the invention, the exhaust gas signal of the exhaust gas sensor is therefore evaluated as to whether at least one predetermined target criterion for switching the operation of the internal combustion engine with a rich combustion mixture to the operation of the internal combustion engine with a substantially stoichiometric combustion gas mixture is met, and thus the so-called catalytic clean-up immediately after the sufficiently long-lasting power-off operation of the internal combustion engine can be interrupted. In particular, it can be shown at this point in time that the catalytic device, which was completely loaded with oxygen during the power-off phase of the internal combustion engine, is now sufficiently reduced so that a switch to normal operation with a substantially stoichiometric combustion gas mixture is possible. In this case, utilization is made of the fact that during the operation of the internal combustion engine with a rich combustion gas mixture (that is to say during the catalytic clean-up), the oxygen loading of the catalytic device decreases, and thus the generation of ammonia in the catalytic device increases. During the catalytic clean-up, initially an inevitable nitrogen oxide peak occurs in the exhaust gas signal, which decreases as the oxygen loading of the catalytic device decreases. However, the continuous reduction of the oxygen load in the catalytic converter due to the operation of the internal combustion engine with a rich combustion gas mixture leads to the production of ammonia in the catalytic converter, which is reflected in the exhaust gas signal in the ammonia peak that is temporally behind the nitrogen oxide peak. Therefore, the corresponding exhaust gas signal of the exhaust gas sensor, which represents the sum of the nitrogen oxide content and the ammonia content in the exhaust gas, first shows an increase in the nitrogen oxide content up to a maximum value. Subsequently, the nitrogen oxide content in the exhaust gas decreases again, which is reflected in the decreasing exhaust gas signal of the exhaust gas sensor. The subsequent increase in the exhaust gas signal of the exhaust gas sensor after passing the minimum value is based on the production of ammonia due to the continuously decreasing oxygen load of the catalyst.

[0012] In a preferred embodiment of the method according to the invention, ascertaining that at least one exhaust gas signal meets at least one predetermined target criterion includes ascertaining that at least one received exhaust gas signal indicates an exhaust gas value that exceeds a predetermined exhaust gas threshold value.

[0013] Therefore, in this preferred embodiment of the method according to the invention, the catalytic cleaning is interrupted as soon as at least one received exhaust gas signal exceeds a predetermined exhaust gas threshold value. This means that the inevitable generation of nitrogen oxides at the start of the catalytic cleaning can be used to end the catalytic cleaning process. Depending on the engine operating point (exhaust gas temperature, exhaust gas mass flow, lambda value, etc.) and the embodiment of the catalytic device, such as, for example, size, precious metal loading, oxygen storage capacity, etc., it can be meaningful to interrupt the catalytic cleaning prematurely, because there is still a dense exhaust gas mixture in the exhaust system upstream of the catalytic device. A typical threshold value is about 100 ppm.

[0014] In a further advantageous embodiment of the method according to the invention, ascertaining that the at least one exhaust gas signal meets at least one predetermined target criterion further comprises ascertaining that the exhaust gas signal has reached a local maximum.

[0015] In this advantageous embodiment, the catalytic clean-up is therefore interrupted and the internal combustion engine is switched to operation with a substantially stoichiometric combustion gas mixture as soon as the exhaust gas signal has reached a local maximum. A local maximum describes a state of the catalytic device in which the nitrogen oxide peaks in the exhaust gas signal of the exhaust gas sensor, which are inevitable due to the oxygen load, have reached a maximum. In this case, the catalytic device begins to convert more and more nitrogen oxides produced by the combustion or in the catalytic device.

[0016] It may further be preferred here that determining that the at least one exhaust gas signal meets at least one predetermined target criterion further comprises receiving at least one further exhaust gas signal of the exhaust gas sensor after reaching the local maximum and determining that a gradient of the at least one received further exhaust gas signal has reached a predetermined gradient threshold value.

[0017] In this preferred embodiment of the method according to the invention, after reaching a local maximum, the catalytic cleaning is interrupted only if the gradient of at least one further received exhaust gas signal has additionally reached a predetermined gradient threshold value. This serves to increase the robustness of the detection of local maxima in the exhaust gas signal of the exhaust gas sensor and can also be used to define an optimal time for interrupting the catalytic cleaning.

[0018] In an advantageous embodiment of the method according to the invention, the gradient threshold value is negative or positive. Thus, in addition to the exhaust gas signal of the exhaust gas sensor, which indicates the exhaust gas value in the exhaust gas of the internal combustion engine, the gradient of the exhaust gas signal can also be evaluated. In this case, the gradient can drop negatively (drop of the exhaust gas signal immediately after the nitrogen oxide maximum) or lie in a range between a local maximum of the nitrogen oxide content and a local maximum of the ammonia content, wherein a local minimum exists between these two local maxima. Furthermore, further criteria, such as, for example, the oxygen integral from the time when the gradient falls below an oxygen threshold value, can be taken into account as an interruption criterion in order to define an optimal time for interrupting the catalytic cleanup.

[0019] Preferably, a substantially stoichiometric combustion gas mixture has a lambda value of between approximately 0.998 and 1.002. It is also preferred that a rich combustion gas mixture has a lambda value of approximately 0.8.

[0020] In a preferred embodiment of the method according to the invention, the predetermined time threshold for identifying the thrust reduction phase is approximately 1 to 5 seconds. Alternatively or additionally, a sufficiently long thrust reduction phase of the internal combustion engine can be determined if the oxygen mass supplied to the catalytic device exceeds a predetermined oxygen mass threshold. The oxygen mass supplied to the catalytic device can be detected by means of a linear lambda signal of a lambda probe arranged upstream of the catalytic device and / or can be estimated by a suitable model that can additionally take into account the exhaust gas mass flow.

[0021] According to a further aspect of the present invention, a computer program is disclosed which has instructions which, when executed by a processor or a control unit of a control unit, cause the control unit to carry out the method according to the present invention for operating an internal combustion engine.

[0022] According to yet another aspect of the present invention, a computer-readable medium is disclosed, on which a computer program according to the present invention is stored.

[0023] According to yet another aspect of the present invention, a control device for operating an internal combustion engine is disclosed, the internal combustion engine having an exhaust system, the exhaust system having: at least one catalytic device, the catalytic device being configured to at least partially store oxygen; and an exhaust gas sensor arranged downstream of the at least one catalytic device, the exhaust gas sensor being configured to generate an exhaust gas signal indicating an exhaust gas value, the exhaust gas value representing the sum of the nitrogen oxide content and the ammonia content in the exhaust gas. In this case, the control device according to the present invention is configured to implement the method according to the present invention for operating an internal combustion engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Additional advantages and features of the present invention will become apparent to those skilled in the art upon practicing the teachings described herein and upon consideration of the sole accompanying drawings, in which:

[0025] Figure 1 shows a schematic diagram of an internal combustion engine with an exhaust system, a catalytic device and an exhaust gas sensor,

[0026] Figure 2 Shows Figure 1 An exemplary diagram of the time curve of the nitrogen oxide content and the ammonia content in the exhaust gas of an internal combustion engine of

[0027] Figure 3 Shows Figure 1 Comparison of the nitrogen oxide content and ammonia content of the exhaust gas signal of the exhaust gas sensor of the internal combustion engine Figure 2 The time trend of the relevant trend,

[0028] Figure 4 Shows Figure 3 The time trend of the gradient of the exhaust gas signal,

[0029] Figure 5 Shows Figure 1 Comparison of the nitrogen oxide content and ammonia content of the exhaust gas signal of the exhaust gas sensor of the internal combustion engine Figure 2 The time trend of the relevant trend,

[0030] Figure 6 Shows Figure 5 The time trend of the gradient of the exhaust gas signal,

[0031] Figure 7 Shows Figure 1 Comparison of the nitrogen oxide content and ammonia content of the exhaust gas signal of the exhaust gas sensor of the internal combustion engine Figure 2 The time trend of the relevant trend,

[0032] Figure 8 Shows Figure 7 The time course of the gradient of the exhaust gas signal, and

[0033] Fig. 9 Shown is the operation Figure 1 An exemplary flow chart of the method according to the invention for an internal combustion engine of FIG. DETAILED DESCRIPTION

[0034] In the context of the present disclosure, the term "catalytic clean-up" describes a temporary operating mode of an internal combustion engine, which follows a sufficiently long power-off phase of the internal combustion engine before the internal combustion engine switches to normal operation with an essentially stoichiometric combustion gas mixture. During the catalytic clean-up, the internal combustion engine is operated with a rich combustion gas mixture in order to at least partially reduce the catalytic device that was almost completely filled with oxygen during the power-off phase of the internal combustion engine and thereby provide conditions for the subsequent normal operation of the internal combustion engine.

[0035] In the context of the present disclosure, the term "combustion gas mixture" describes a mixture of fuel and air which is burned in an internal combustion engine. A "rich combustion gas mixture" is characterized by a combustion air ratio of λ (also called air ratio or air factor) less than 1. The λ value describes the mass ratio of air to fuel relative to the respectively stoichiometric ideal ratio for a theoretically complete combustion process. In addition, an essentially stoichiometric combustion gas mixture is characterized by a λ value in the range of approximately 0.998 and 1.002.

[0036] Figure 1 1 shows a schematic diagram of an internal combustion engine 100, the operation of which is controlled by a control device 110. In particular, the internal combustion engine 100 comprises a combustion line section 120, which has an intake device (not explicitly shown) and at least one combustion chamber (also not explicitly shown) and an exhaust device 130 connected downstream thereof, in which a catalytic device 132 and an exhaust gas sensor 134 arranged downstream of the catalytic device 132 are arranged. The flow direction of the exhaust gas through the exhaust device 130 is Figure 1 This is indicated by arrow 102.

[0037] The control device 110 can be designed as hardware and / or software or can have hardware components and / or software components. In addition, the control device 110 has a processor or controller configured to execute instructions. In particular, the control device can contain at least one computer program configured to control the operation of the internal combustion engine 100.

[0038] In an alternative embodiment, exhaust system 130 may additionally have a further catalytic device arranged downstream of exhaust gas sensor 134 and a further exhaust gas sensor arranged downstream of the further catalytic device.

[0039] Catalytic device 132 is a catalytic device configured to store oxygen. Catalytic device 132 is, for example, a three-way catalytic converter, a particle filter equipped with a catalytically active coating, a combination of a three-way catalytic converter and a particle filter without a coating, or a combination of a three-way catalytic converter and a particle filter with a coating. In addition, another three-way catalytic converter and / or a particle filter can also be arranged downstream.

[0040] Exhaust gas sensor 134 is designed to generate an exhaust gas signal that indicates an exhaust gas value that represents the sum of the nitrogen oxide content and the ammonia content in the exhaust gas. Thus, the exhaust gas sensor can be, for example, a nitrogen oxide sensor based on the amperometric measurement principle that is cross-sensitive to ammonia and therefore measures the sum of the nitrogen oxide content and the ammonia content in the exhaust gas.

[0041] Figure 2The diagram shows the position of the exhaust gas sensor 134 during the catalytic clean-out phase of the internal combustion engine 100. Figure 1 202 and ammonia content 204 in the exhaust gas of an internal combustion engine 100, the catalytic clean-up phase being started at time t0. Exemplary profile 202 of the nitrogen oxide content in the exhaust gas of internal combustion engine 100 has a maximum value M_NOx before it drops to a value of approximately zero. Figure 2 Exemplary profile 204 of the ammonia content in the exhaust gas of internal combustion engine 100 also has a maximum value M_NH3, which, however, occurs later in time than maximum value M_NOx of profile 202 of the nitrogen oxide content.

[0042] Figure 2 The trends 202, 204 are based on the fact that during the catalytic clean-up, the catalytic device 132 is first reduced, that is, the oxygen stored therein is depleted by converting the fuel injected in excess relative to the stoichiometric ratio (λ < 1). Since the catalytic device 132 is almost completely loaded with oxygen after the boost phase, no nitrogen oxide conversion occurs at first (starting from the time t_NOx). As the oxygen load decreases, the nitrogen oxide conversion efficiency of the catalytic device 132 increases continuously, so that an increasing portion of the nitrogen oxides produced by the internal combustion engine 100 is converted. The result is Figure 2 The inevitable nitrogen oxide peak shown in . The more intensely the oxygen is depleted in the catalytic device, the better the conditions for the production of ammonia. With the aid of the carbon monoxide present in abundance due to the rich combustion, hydrogen is increasingly formed in the catalytic device 132 by the water gas shift reaction, whereby the nitrogen oxides can be converted into ammonia. Since the exhaust gas sensor 134 is cross-sensitive to ammonia and therefore detects the sum of the nitrogen oxide concentration and the ammonia concentration, the second peak shown is thus generated, which is mainly due to the existing ammonia concentration. The ammonia production ends with the interruption of the catalytic purge.

[0043] Figure 3 A time curve 206 of the exhaust gas sensor 134 is shown, which is similar to the time curve 206 of the exhaust gas sensor 134. Figure 2 The trends 202 and 204 of the nitrogen oxide content and the ammonia content are related. In particular, Figure 3 It can be seen from FIG. 2 that the exhaust gas signal 206 has two local maxima M1 and M3, namely the local maximum M1 at time t1 and the local maximum M3 at time t3. In addition, Figure 3 The trend 206 of the exhaust gas signal of the exhaust gas sensor 134 has a local minimum M2 at a time t2 which is arranged between the local maxima M1, M3. As already mentioned, Figure 3 The trend of the exhaust gas signal 206 shows Figure 2The sum signal of the two curves 202 , 204 of the nitrogen oxide content and the ammonia content is thus a curve 206 of the exhaust gas signal of the exhaust gas sensor only in the positive range.

[0044] Figure 4 Shows Figure 3 1 . The graph of FIG. 20 shows a time curve 208 of a gradient of an exhaust gas signal 206 of an exhaust gas sensor 134. Correspondingly, the gradient curve 208 has a zero value at each of the time points t1, t2 and t3, wherein the gradient undergoes a sign change at these time points due to the local maximum value M1, M3 and the local minimum value M2. The gradient curve 208 of the exhaust gas signal 206 of the exhaust gas sensor 134 is a mathematical derivative of the exhaust gas signal 206 as a function of time t.

[0045] Reference below Figure 5 A first exemplary embodiment of the method according to the present invention for operating internal combustion engine 100 is explained, in particular the point in time at which the catalytic clean-up can be terminated. For this purpose, Figure 5 Again, it shows Figure 3 An exemplary time profile 206 of an exhaust gas signal of exhaust gas sensor 134 of internal combustion engine 100 is shown.

[0046] According to a first exemplary embodiment, the catalytic clean-up can be terminated when the exhaust gas signal 206 of the exhaust gas sensor 134 reaches a predetermined exhaust gas threshold value C1. Figure 5 This is shown with the aid of point P1. Figure 5 It is shown that at time t4, exhaust gas signal 206 of exhaust gas sensor 134 reaches and exceeds a predetermined exhaust gas threshold value C1 (e.g., approximately 100 ppm). This means that the exhaust gas signal increases and an unavoidable nitrogen oxide peak occurs. If this is detected, the operation of internal combustion engine 100 with a rich combustion mixture can be terminated at this time t4, that is, the catalytic clean-up can be terminated, and internal combustion engine 100 can be switched to normal operation with an essentially stoichiometric combustion gas mixture.

[0047] In another exemplary embodiment of the method according to the present invention, when exhaust gas signal 206 reaches a local maximum P2 (see also Figure 3 When M1 is reached, the catalytic clean-up can be terminated. The reaching of the local maximum value P2 can be performed by evaluating the gradient 208 of the exhaust gas signal 206. In particular, (see also Figure 6 ) The local maximum P2 of the exhaust gas signal 206 can be determined by reaching the zero point of the course of the gradient 208 of the exhaust gas signal 206 at time t5, wherein at the same time a change from a positive gradient to a negative gradient must occur at the zero point. This makes it possible to exclude that the point P2 is a so-called saddle point (or plateau point) at which the preceding and succeeding gradients have the same mathematical sign.

[0048] If it is then ascertained at time t5 that exhaust gas signal 206 of exhaust gas signal 134 has reached a local maximum value P2, the catalytic clean-up can be terminated and the internal combustion engine can be switched back to normal operation with a substantially stoichiometric combustion gas mixture. The local maximum value P2 is preferably the first maximum value after time t_NOx at which the exhaust gas signal 206 increased during the catalytic clean-up. Reaching the local maximum value P2 means that the exhaust gas signal has reached an unavoidable nitrogen oxide peak and then begins to drop thereafter.

[0049] refer to Figure 7 and Figure 8 , two further exemplary embodiments of the method according to the present invention are described below. Figure 7 Again, the exhaust gas signal 206 is shown as having been Figure 3 and Figure 5 Known trends, and Figure 8 shows that the gradient 208 of the exhaust gas signal 206 of the exhaust gas sensor 134 has been Figure 4 and Figure 6 Known time trends.

[0050] According to the third and fourth exemplary embodiments of the method according to the invention, during the catalytic clean-up, the local maximum value P2 can again be first determined, as already described in reference to Figure 5 and Figure 6 However, in a third embodiment of the method according to the invention, instead of interrupting the catalytic clean-up when the local maximum value P2 is reached, a further exhaust gas signal of the exhaust gas sensor 134 is evaluated below. In particular, the gradient of the exhaust gas signal 206 of the exhaust gas sensor 134 which is generated after the local maximum value P2 is reached is additionally studied and evaluated to determine whether the gradient reaches a predetermined gradient threshold value S1, S2 (see Figure 8 ).

[0051] According to a third specific embodiment of the method according to the invention, the catalytic clean-up can be terminated when the gradient of the exhaust gas signal 206 reaches and falls below a predetermined negative gradient threshold value S1 at a time t6 after reaching the local maximum value P2. Reaching the negative gradient threshold value S1 indicates that an unavoidable nitrogen oxide peak has been exceeded and the exhaust gas signal subsequently drops again. An increase in the exhaust gas signal due to the generation of ammonia can thus be expected.

[0052] According to a fourth embodiment of the method according to the invention, the catalytic clean-up can be terminated when the gradient of the exhaust gas signal 206 reaches and exceeds a predetermined positive gradient threshold value S2 at time t7 after reaching the local maximum value P2. However, the gradient threshold value S2 can also be predetermined as a negative value.

[0053] Furthermore, due to the underlying mathematical principle, this is reflected in the exhaust gas signal 206 passing through the local minimum M2 (see Figure 3 ) and therefore the gradient of the exhaust gas signal 206 passes through zero at time t2 (see Figure 4 ) is the prerequisite. This means that the increase in ammonia emissions now exceeds the decline in nitrogen oxide emissions.

[0054] Fig. 9 Shown is the operation Figure 1 An exemplary flow chart of the method according to the present invention for internal combustion engine 100 is shown.

[0055] Fig. 9 The method starts in step 300 and then reaches step 310, in which a thrust cut-off phase of internal combustion engine 100 is detected. For example, the thrust cut-off phase of internal combustion engine 100 can be detected based on the position of the accelerator pedal and / or based on the speed of internal combustion engine 100.

[0056] In the following step 320 , it is checked whether the internal combustion engine 100 is in the thrust cut-off phase for a sufficient time. If it is detected in step 320 that a predetermined time threshold (depending on the operating point of the internal combustion engine 100 , for example 2 seconds) has not been reached, the method returns to step 310 .

[0057] However, if it is determined in step 320 that the internal combustion engine 100 has been in the thrust cut-off phase for longer than a predetermined time threshold, the method proceeds to step 330, in which the internal combustion engine 100 is controlled in such a way that it is operated with a rich combustion gas mixture. In particular, it can be assumed that the catalytic device 132 is completely filled with oxygen when the predetermined time threshold has elapsed, so that the operation with a rich combustion gas mixture carried out in step 330 is initiated in order to reduce the oxygen. This operation of the internal combustion engine 100 with a rich combustion mixture after the thrust cut-off phase is referred to as catalytic clean-up.

[0058] In a subsequent step 340 , at least one exhaust gas signal from exhaust gas sensor 134 is received.

[0059] In a subsequent step 350, at least one exhaust gas signal of exhaust gas sensor 134 received in step 340 is evaluated. In particular, in step 350, the trend of exhaust gas signal 206 (see Figure 5 and Figure 7 ) and the trend of the gradient 208 of the exhaust gas signal 206 (see Figure 6 and Figure 8 ) and are checked for achievement of predetermined target standards.

[0060] In a subsequent step 360 , it is checked whether a predetermined target criterion has been met. If, for example, it is ascertained in step 360 that the predetermined target criterion has not yet been met, the method returns to step 340 .

[0061] However, if it is determined in step 360 that the predetermined target criterion is met, the method proceeds to step 370 in which the internal combustion engine 100 is switched from operation with a rich combustion gas mixture to normal operation with a substantially stoichiometric combustion gas mixture, and the method is then terminated in step 380 .

[0062] The target criterion to be met in step 360 can be exceeding or reaching a predetermined exhaust gas threshold value C1 (see also Figure 5 Alternatively, the target criterion can be to reach a local maximum P2 (see Figure 5 and Figure 6 ), reaches a predetermined gradient threshold S1 or reaches a predetermined gradient threshold S2.

[0063] The predetermined target criterion may include a predetermined section, a preferred point, which exhaust gas signal 206 must reach in order to meet the predetermined target criterion.

[0064] If any of the mentioned target criteria are not met, according to the invention the catalytic cleaning is interrupted again based on the lambda signal of the binary lambda probe and / or based on a known load model of the catalytic device 132 .

[0065] The method according to the invention for operating an internal combustion engine, in particular for interrupting a catalytic purge after a thrust cut-off phase, can be carried out during each sufficiently long thrust cut-off phase. Alternatively or additionally, the method according to the invention can be used to adjust a model-based catalytic purge strategy in order to minimize any model errors over the life of the internal combustion engine. The basis of the model-based catalytic purge strategy is that the catalytic purge is interrupted when a calculated oxygen load value is below a predetermined oxygen load threshold value, which oxygen load value is reduced in addition to the stoichiometric ratio based on the injected fuel mass. Since the calculation has a model error due to deviations in the input parameters (e.g. measured lambda value, measured exhaust gas mass flow, aging state of the catalytic device that can influence the threshold value, etc.), the adjustment based on the measured nitrogen oxide value can at least largely compensate for this.

[0066] The method according to the invention makes it possible to achieve a maximum minimization of pollutant emissions, in particular nitrogen oxide, ammonia, carbon oxide and / or hydrocarbon emissions, of an internal combustion engine during catalytic cleaning.

Claims

1. A method for operating an internal combustion engine (100), the internal combustion engine having an exhaust gas device (130), the exhaust gas device having: at least one catalytic device (132), the catalytic device being configured to at least partially store oxygen; and an exhaust gas sensor (134) arranged downstream of the at least one catalytic device (132), the exhaust gas sensor being configured to generate an exhaust gas signal indicating an exhaust gas value, the exhaust gas value representing the sum of a nitrogen oxide content and an ammonia content in the exhaust gas, wherein: The method comprises: - controlling the internal combustion engine (100) in such a way that, after a thrust cut-off phase of the internal combustion engine (100) which lasts longer than a predetermined time threshold has occurred, the internal combustion engine (100) is operated with a rich combustion gas mixture, wherein, during the control of the internal combustion engine (100) with the rich combustion gas mixture: - receiving at least one exhaust gas signal (206) from the exhaust gas sensor (134), and - ascertaining that the at least one exhaust gas signal (206) meets at least one predetermined target criterion, and If it is ascertained that the at least one exhaust gas signal (206) meets at least one predetermined target criterion, the internal combustion engine (100) is controlled in such a way that it is operated with a substantially stoichiometric combustion gas mixture.

2. The method according to claim 1, wherein: Determining that the at least one exhaust signal (206) satisfies at least one predetermined target criterion includes: - ascertaining that at least one received exhaust gas signal (206) indicates an exhaust gas value which exceeds a predetermined exhaust gas threshold value (C1).

3. A method according to any one of the preceding claims, wherein: Determining that the at least one exhaust signal (206) satisfies at least one predetermined target criterion further comprises: - determining that the exhaust gas signal (206) has reached a local maximum (P2).

4. The method according to claim 3, wherein: Determining that the at least one exhaust signal (206) satisfies at least one predetermined target criterion further comprises: - after reaching the local maximum (P2), receiving at least one further exhaust gas signal (206) of the exhaust gas sensor (134), and - determining that a gradient (208) of the at least one further exhaust gas signal (206) has reached a predetermined gradient threshold value (S1, S2).

5. The method according to claim 4, wherein: The gradient thresholds (S1, S2) are negative or positive.

6. A method according to any one of the preceding claims, wherein: The substantially stoichiometric combustion gas mixture has a lambda value between approximately 0.998 and 1.

002.

7. A method according to any one of the preceding claims, wherein: The rich combustion gas mixture has a lambda value of approximately 0.

8.

8. A method according to any one of the preceding claims, wherein: The predetermined time threshold is between approximately 1 second and 5 seconds.

9. A computer program having instructions which, when executed by a processor or a controller of a control device (110), cause the control device (110) to carry out the method according to any one of the preceding claims.

10. A computer-readable medium having stored thereon the computer program according to claim 9.

11. A control device (110) for operating an internal combustion engine, the internal combustion engine having an exhaust device (130), the exhaust device having: at least one catalytic device (132), the catalytic device being configured to at least partially store oxygen; and an exhaust gas sensor (134) arranged downstream of the at least one catalytic device (132), the exhaust gas sensor being configured to generate an exhaust gas signal (206) indicating an exhaust gas value, the exhaust gas value representing the sum of a nitrogen oxide content and an ammonia content in the exhaust gas, wherein: The control device (110) is designed to carry out a method according to any one of claims 1 to 8.

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