Method, control device, and computer program product for diagnosing the function of an exhaust gas aftertreatment device of an internal combustion engine

Abstract

The invention relates to a method, a control device (7), and a computer program product (11) for diagnosing the function of an exhaust gas aftertreatment device (2) of an internal combustion engine (1) that has two catalytic converters (3, 4) which are arranged one behind the other in the exhaust gas mass flow (10a) and which are capable of storing oxygen. The method is carried out by means of an electronic control device (7), wherein the internal combustion engine (1) is first operated in a conditioning mode (KBM) in order to pre-condition the two catalytic converters (3, 4), a first and second sensor signal (Sig1, Sig2) being received. The sensor signals (Sig1, Sig2) represent the oxygen content (O2_1, O2_1) in the exhaust gas mass flow (10a) directly after the first catalytic converter (3) and directly after the second catalytic converter (4). When the pre-conditioning process of the catalytic converters (3, 4) is completed, the internal combustion engine (1) is operated in a diagnostic mode (DBM), and an integration over the oxygen mass flow between the catalytic converters (3, 4) or after the second catalytic converter (4) is started in order to ascertain an oxygen mass flow integral (SMI_UFC). The integration over the oxygen mass flow and the diagnostic mode (DBM) are stopped on the basis of different thresholds, and the value of the oxygen mass flow integral (SMI_UFC) is ascertained, said value forming the basis for whether the second catalytic converter (4) is diagnosed as being "fully functional", "still fully functional but in an aged state," or "no longer functional". The aim of the invention is to advantageously allow a selective maintenance operation to be carried out in the event of a failure of the exhaust gas aftertreatment device.

Description

[0001] Description

[0002] Method, control device and computer program product for functional diagnosis of an exhaust gas aftertreatment device of an internal combustion engine

[0003] The invention relates to a method, a control device and a computer program product for carrying out a functional diagnosis of an exhaust gas aftertreatment device of an internal combustion engine, which has at least a first exhaust gas catalyst arranged close to the internal combustion engine and a second exhaust gas catalyst arranged downstream of the first exhaust gas catalyst in the exhaust gas mass flow.

[0004] The increasingly strict European legislation regarding pollutant emissions from internal combustion engines, particularly combustion engines in motor vehicles, requires not only the use and increasingly comprehensive design of exhaust gas aftertreatment devices, but also the constant monitoring of the proper functioning of all device components that influence pollutant emissions.

[0005] To ensure compliance with the required limits, exhaust aftertreatment systems are therefore equipped with combinations of multiple catalytic converters and particulate filters. These include exhaust gas sensors, such as lambda sensors for determining the oxygen content in the exhaust gas, or NOx sensors, whose signals can be used to determine a lambda value in addition to the NOx and NH3 concentrations.

[0006] The values ​​supplied by the various sensors are used, on the one hand, to control and regulate the internal combustion engine, in particular with regard to pollutant emissions, and to monitor pollutant emissions, but on the other hand, they are also used to monitor the function of the individual components of the exhaust gas aftertreatment device.

[0007] In order to comply with the pollutant limits based on the latest legislation, it is essential to install at least one second catalytic converter at the downstream end of the exhaust aftertreatment device, in addition to a first catalytic converter located close to the internal combustion engine at the upstream end of the exhaust aftertreatment device. This catalytic converter eliminates pollutant components that could not be eliminated until then due to malfunctions or inadequate functioning of the upstream catalytic converters relative to the exhaust gas mass flow. For the final monitoring of the exhaust aftertreatment device, a NOx sensor is located downstream of the second catalytic converter. This sensor detects a breakthrough of pollutants, particularly NOx or NH3, and issues an error message accordingly.

[0008] Due to the error message set, a check and, if necessary, repair of the exhaust gas aftertreatment device is then indicated and the operation of the internal combustion engine may be restricted to emergency operation until then.

[0009] However, such an error message does not currently provide any information about which of the individual components of the exhaust aftertreatment system is defective or functionally impaired due to aging. This potentially significantly increases the cost of repairs, and it is desirable for an internal vehicle or control system diagnostic to provide information about which of the exhaust catalysts is defective or functionally impaired. Furthermore, it is desirable that such a diagnostic procedure does not require additional sensors or other costly measures and can be performed solely using the existing resources of the exhaust aftertreatment system.

[0010] The present invention is therefore based on the object of creating a possibility with the aid of which it is possible to determine in a simple manner the functional state or the defectiveness of a component of an exhaust gas aftertreatment device of the type described above.

[0011] This problem is solved by the subject matter of the independent patent claims.

[0012] The advantages of the invention are that in the event of a failure of the exhaust gas aftertreatment device, not only can the failure of the exhaust gas aftertreatment device itself be determined via "On Board Diagnosis", OBD, but also, advantageously, the condition of at least a second catalyst arranged at the downstream end of the exhaust gas aftertreatment device can be diagnosed and thus the component of the exhaust gas aftertreatment device that is responsible for the failure can be more easily identified.

[0013] Advantageous embodiments, developments and details of the present invention emerge from the dependent claims, the description and the drawing.

[0014] The method according to the invention for functional diagnosis of an exhaust gas aftertreatment device of an internal combustion engine relates to an exhaust gas aftertreatment device comprising a first oxygen-storage-capable exhaust gas catalyst and a second oxygen-storage-capable exhaust gas catalyst arranged downstream in the exhaust gas flow. The method is carried out by means of at least one electronic control device associated with the exhaust gas aftertreatment device and the internal combustion engine, by executing the steps described below.

[0015] First, the internal combustion engine is operated in a conditioning operating mode to precondition both exhaust gas catalysts for functional diagnosis.

[0016] A first sensor signal and a second sensor signal are continuously received in parallel with the process. The first sensor signal is representative of a first oxygen content in the exhaust stream immediately downstream of the first catalytic converter, and the second sensor signal is representative of a second oxygen content in the exhaust stream immediately downstream of the second catalytic converter. During the process, the first and second sensor signals are evaluated to continuously determine the first and second oxygen content.

[0017] If, during operation in the conditioning operating mode, the first oxygen fraction and the second oxygen fraction indicate that the preconditioning of the exhaust gas catalysts is completed, the internal combustion engine is operated in a diagnostic operating mode, i.e. the conditioning operating mode is ended and the diagnostic operating mode is started.

[0018] If then, during operation of the internal combustion engine in

[0019] Diagnostic operating mode, if the first oxygen fraction reaches a first threshold value, an integration is started over the oxygen mass flow between the first and second exhaust catalyst or downstream of the second exhaust catalyst in order to determine an oxygen mass flow integral.

[0020] If the value of the oxygen mass flow integral reaches an upper integral limit or the second oxygen content in the exhaust gas immediately downstream of the second catalytic converter reaches a second threshold, the integration based on the oxygen mass flow and the diagnostic operating mode of the internal combustion engine is stopped, and the value of the oxygen mass flow integral reached up to that point is determined. This value provides information about the oxygen storage capacity of the second catalytic converter, which in turn is an indicator of the functionality of the second catalytic converter.

[0021] Based on the value of the oxygen mass flow integral determined in this way, the functional diagnosis of the second exhaust gas catalyst can now be carried out.

[0022] The second exhaust gas catalyst of the exhaust aftertreatment device is diagnosed as “fully functional” when the value of the oxygen mass flow integral has reached the upper integral limit.

[0023] If the value of the oxygen mass flow integral falls below the upper integral limit but does not fall below a lower integral limit, the second exhaust gas catalyst is diagnosed as “still functional but in an aged condition”.

[0024] However, if the value of the oxygen mass flow integral does not reach or falls below the lower storage capacity limit, the second exhaust gas catalyst is diagnosed as “no longer functional”.

[0025] Using the method described above, a second exhaust catalyst arranged downstream of a first exhaust catalyst in the exhaust gas aftertreatment device can now also be advantageously tested for proper functioning, independently of the function of the other components of the exhaust gas aftertreatment device, and can be specifically repaired or replaced in the event of a failure. The designations "first exhaust catalyst" and "second exhaust catalyst" refer to two exhaust catalysts arranged consecutively in the exhaust gas mass flow, between which additional components of the exhaust gas aftertreatment device, such as a particulate filter, may be arranged, but no additional oxygen-storage-capable component may be arranged. However, these designations are not intended to limit the total number of exhaust catalysts arranged in the exhaust gas aftertreatment device to two.In a common constellation, however, the first exhaust catalyst is a three-way catalyst (TWC) located close to the engine, i.e. in the immediate vicinity of the internal combustion engine, and the second exhaust catalyst is a so-called underbody catalyst (UFC) located far from the engine, on the underbody of a motor vehicle powered by the internal combustion engine.

[0026] A first embodiment of the method according to the invention for functional diagnosis of an exhaust gas aftertreatment device of an internal combustion engine is characterized in that the conditioning operating mode for preconditioning both exhaust catalysts is characterized by enriching the combustion mixture (oxygen deficiency). In other words, both exhaust catalysts are purged, i.e., the oxygen load is removed or at least reduced to a minimum. Accordingly, the preconditioning of the exhaust catalysts is completed when the first sensor signal and the second sensor signal indicate that the first oxygen content and the second oxygen content have reached a minimum. The diagnostic operating mode following this preconditioning is then characterized by leaning the combustion mixture (oxygen excess).Oxygen is therefore initially stored in the first catalytic converter until its oxygen storage capacity is exhausted and an oxygen breakthrough is detected by the first exhaust gas sensor located immediately downstream of the first catalytic converter. In this embodiment, the oxygen mass flow integral is calculated based on the oxygen mass flow between the first and second catalytic converters until the second oxygen content in the exhaust gas immediately downstream of the second catalytic converter reaches a second threshold value, which indicates an oxygen breakthrough immediately downstream of the second catalytic converter. Thus, the amount of oxygen that can be stored in the second catalytic converter is determined.

[0027] A second embodiment of the method according to the invention for functional diagnosis of an exhaust gas aftertreatment device of an internal combustion engine is to be understood as an alternative to the first embodiment and is characterized in that the conditioning operating mode for preconditioning both exhaust gas catalysts is characterized by combustion mixture leaning or overrun fuel cut-off (excess oxygen). In contrast to the first embodiment, both exhaust gas catalysts are therefore fully loaded with oxygen or up to a maximum value. Accordingly, the preconditioning of the exhaust gas catalysts is to be considered complete when the first oxygen content and the second oxygen content have reached a maximum, which means that the storage capacity of the respective exhaust gas catalyst is exhausted and an oxygen breakthrough occurs.The diagnostic operating mode is then characterized by enriched combustion mixture (oxygen deficiency), whereby the oxygen stored in the exhaust catalysts is flushed out again. First, the oxygen stored in the first exhaust catalyst is flushed out. If the first sensor signal from the exhaust sensor located immediately downstream of the first exhaust catalyst indicates that the first oxygen content reaches a first threshold value, where the first threshold value in this case indicates a minimum amount of oxygen in the exhaust gas mass flow, the integration is performed over the oxygen mass flow, in this case downstream of the second exhaust catalyst. Thus, the amount of oxygen flushed out of the second exhaust catalyst is determined.The formation of the oxygen mass flow integral is stopped when the second oxygen fraction in the exhaust gas immediately downstream of the second exhaust gas catalyst reaches a second threshold value which indicates a minimum of oxygen in the exhaust gas mass flow.

[0028] A further embodiment of the method according to the invention and its previously described embodiments is characterized in that the first sensor signal is received by a binary sensor and the second sensor signal is received by a NOx sensor. A conventional binary lambda sensor can be used as the binary sensor; it measures the oxygen content in the exhaust gas mass flow and provides it as a binary lambda signal. In addition to pollutant concentrations, a NOx sensor typically measures the A value, i.e., the oxygen content in the exhaust gas mass flow, as a further variable and provides it as a binary or linear lambda signal.A technical difficulty is that the NOx sensor delivers a total value of at least two of the pollutants to be monitored, which requires a calculation model in a control device with the help of which the measurement signal can be broken down into the different pollutant components.

[0029] This has the advantage that such sensors are usually provided at the relevant positions in the exhaust aftertreatment system anyway and no additional, costly exhaust gas sensor is required.

[0030] A further embodiment of the method according to the invention and its previously described embodiments is characterized in that the oxygen mass flow is determined based on an exhaust gas mass flow, its temperature, and its A-value. To determine the respective oxygen mass flow integral, the A-value and the temperature value of the exhaust gas mass flow at the corresponding point of the exhaust gas aftertreatment device are naturally used. Therefore, if the oxygen mass flow integral is formed via the oxygen mass flow between the first and second exhaust gas catalytic converters, the A-value determinable from the first sensor signal must be used accordingly. If, on the other hand, the oxygen mass flow integral is formed via the oxygen mass flow downstream of the second exhaust gas catalytic converter, the A-value determinable from the second sensor signal must be used.The temperature of the exhaust gas mass flow can be determined using a temperature sensor located at the corresponding location in the exhaust gas aftertreatment device and transmitted to the control device. Model calculations based, for example, on a temperature sensor located anywhere in the exhaust gas aftertreatment device can also provide temperature values ​​of the exhaust gas mass flow at the respective position in the exhaust gas aftertreatment device.

[0031] A further refinement of the first embodiment of the method according to the invention is characterized in that, after the diagnostic operating mode has been completed, the internal combustion engine is operated in an operating mode characterized by enriched combustion mixture (oxygen deficiency) until the second oxygen fraction again reaches a minimum. This flushes out the oxygen stored in the exhaust gas catalysts, advantageously ensuring that optimal conditions for catalytic exhaust gas aftertreatment prevail during proper operation of the internal combustion engine following the functional diagnosis.A further embodiment of the method according to the invention and its previously described embodiments is characterized in that the method is only carried out when an evaluation of the second sensor signal shows that a pollutant component in the exhaust gas flow downstream of the second exhaust gas catalyst has exceeded a predetermined limit value and / or the internal combustion engine is operated in a workshop diagnostic mode.

[0032] Since the method described above can in itself have a negative impact on the overall pollutant emissions (real-time emissions) of the internal combustion engine and, if applicable, of a corresponding motor vehicle, it is advantageous to only carry out the method if there is reason to suspect a defective component in the exhaust gas aftertreatment device. This is the case if the exhaust gas sensor downstream of the second exhaust gas catalytic converter in the exhaust gas mass flow, for example a NOx sensor, indicates that a limit value for a pollutant, for example NOx or NH3, has been exceeded. Such a limit value violation usually generates an entry in the error memory of the control device, a warning message to the operator of the internal combustion engine, and requires the exhaust gas aftertreatment device to be checked or repaired by a specialist company or workshop.In this respect, the implementation of the method according to the invention can also be limited to a workshop diagnostic operation that is only carried out within the scope of a stationary inspection or repair.

[0033] This has the advantage that the impact on the overall pollutant emissions is kept small or, if carried out only in workshop diagnostic mode, the pollutant emissions during this time are not included in the overall pollutant emissions (real-time emissions) of the internal combustion engine.

[0034] The electronic control device according to the invention for functional diagnosis of an exhaust gas aftertreatment device of an internal combustion engine has at least the following components:

[0035] - An electronic storage device in which at least one computer program product with program instructions for carrying out the method is provided and

[0036] - an input / output interface which is configured to receive and output electrical signals, and - an electronic computing unit (processor) for executing program instructions, with access to the at least one electronic storage device and the input / output interface.

[0037] When the program instructions are then executed by means of the electronic computing unit, they cause the electronic control device to carry out the method according to the invention, as described above.

[0038] The above-mentioned advantages of the method according to the invention can be realized with the electronic control device.

[0039] The computer program product according to the invention for functional diagnosis of an exhaust gas aftertreatment device of an internal combustion engine comprises program instructions for execution by the electronic processing unit of the electronic control device described above, wherein the program instructions, when executed by the electronic processing unit, cause the electronic control device to carry out the method according to the invention in accordance with one of the embodiments and configurations described above.

[0040] In other words, the subject matter of the invention relates to a method, a control device, and a computer program product for functional diagnosis of an exhaust gas aftertreatment device of an internal combustion engine having two oxygen-storage-capable exhaust gas catalysts arranged one behind the other in the exhaust gas mass flow. The method is carried out by means of an electronic control device, wherein the internal combustion engine is initially operated in a conditioning mode for preconditioning both exhaust gas catalysts, wherein a first and a second sensor signal are received and evaluated. The sensor signals are representative of the oxygen content in the exhaust gas mass flow immediately downstream of the first exhaust gas catalyst and immediately downstream of the second exhaust gas catalyst.Once preconditioning of the exhaust catalysts is complete, the internal combustion engine is operated in a diagnostic mode, and an integration of the oxygen mass flow between the exhaust catalysts or downstream of the second exhaust catalyst is initiated to determine an oxygen mass flow integral. Depending on various limit values, the integration of the oxygen mass flow and the diagnostic mode are stopped, and the value of the oxygen mass flow integral is determined. Based on this value, the second exhaust catalyst is diagnosed as "fully functional," "still functional but in an aged condition," or "no longer functional."

[0041] The features and combinations of features of the embodiments of the subject matter according to the invention mentioned above in the description or below in the description of the figures are, insofar as they are not applicable alternatively or even mutually exclusive, to be used individually, in part or in whole, also in mutual combination or mutual supplementation, in further development of the subject matter according to the invention, without departing from the scope of the invention.

[0042] Features and details that are described in connection with the method naturally also apply in connection with the electronic control device and the computer program product, and vice versa, so that with regard to the disclosure of this invention, reference can always be made to the individual aspects of the invention.

[0043] Particularly advantageous embodiments, details or developments of the invention are explained in more detail below with reference to the figures, although the subject matter of the invention is not intended to be limited to these examples.

[0044] They show:

[0045] Fig. 1 is a simplified schematic representation of an internal combustion engine with exhaust gas aftertreatment device.

[0046] Fig. 2 shows a simplified flow diagram of the method according to the invention.

[0047] Fig. 3 shows a simplified signal diagram of the sequence of a first embodiment of the method.

[0048] Fig. 4 shows a further simplified signal diagram of the sequence of a first embodiment of the method.

[0049] Fig. 5 shows a further simplified signal diagram illustrating the sequence of a first embodiment of the method. Fig. 6 shows a simplified signal diagram illustrating the sequence of a second embodiment of the method.

[0050] The figures in the drawings of this application are to be viewed merely as schematic, and the proportions of the individual figures and the elements depicted in the figures are not to be considered to scale. Rather, individual elements may be exaggerated for clarity and / or clarity. Elements with the same function, designation, type, or effect are identified by the same reference numerals throughout the figures. Individual reference numerals may be omitted in individual figures to improve clarity.

[0051] Figure 1 shows an internal combustion engine 1, which can be designed, for example, as a reciprocating piston internal combustion engine with four cylinders (indicated). Connected to the internal combustion engine 1 is an exhaust gas aftertreatment device 2 with a first exhaust gas catalytic converter 3 (TWC), a second exhaust gas catalytic converter 4 (UFC), and a particulate filter 5 (GPF), which are connected to the internal combustion engine 1 and interconnected via an exhaust pipe 10. The exhaust gas mass flow 10a is guided through the exhaust pipe 10 to the aforementioned components of the exhaust gas aftertreatment device 2. The exhaust gas mass flow 10a is represented by arrow symbols that indicate the flow direction of the exhaust gas mass flow 10a. The first exhaust gas catalytic converter 3 is arranged close to the engine, directly at the exhaust outlet of the internal combustion engine 1 and is designed here, for example, as a three-way catalytic converter (TWC).The first exhaust gas catalyst 3 is followed downstream of the exhaust gas mass flow 10a by a particulate filter 5 (PF) and then by the second exhaust gas catalyst 4 (UFC), which can be arranged, for example, on the underbody of a motor vehicle and can also be designed as a three-way catalyst.

[0052] In the exhaust pipe 10, a first exhaust gas sensor 6a is arranged downstream of the first catalytic converter 3, and a second exhaust gas sensor 6b is arranged downstream of the second catalytic converter 4. Another exhaust gas sensor 6c is arranged upstream of the first catalytic converter 3 in the exhaust pipe 10. A temperature sensor 9 for measuring the temperature of the exhaust gas mass flow 10a is arranged in the exhaust pipe 10 between the first catalytic converter 3 and the particulate filter 5.

[0053] The aforementioned sensors 6a-c and 9 are connected via electrical signal lines 8 to the input / output interface 7c of an electronic control device 7 according to the invention for transmitting the sensor signals to the control device 7. The internal combustion engine 1 is also connected via electrical signal lines 8 to the input / output interface 7c of the electronic control device 7 according to the invention.

[0054] The electronic control device 7 has an electronic processing unit 7a, also referred to as a processor, an electronic storage device 7b, and an input / output interface 7c. In this embodiment, the electronic storage device 7b comprises a program memory 7b1 in which a computer program product 11 according to the invention with program instructions is available. Furthermore, the electronic storage device 7b has an operating data memory 7b2 in which predetermined operating data 12 as well as operating data recorded during operation are stored, for example, organized in characteristic maps. This memory area also stores, for example, the various threshold values ​​for the oxygen content in the exhaust gas mass flow as well as the integral limit values ​​for the oxygen mass integral, for retrieval by the electronic processing unit.

[0055] The electronic processing unit 7a is configured to carry out the method according to the invention in the previously described and possibly additional embodiments. For this purpose, the electronic processing unit 7a has access to, or is in data communication with (symbolized by connecting arrows) the input / output interface 7c, the program memory 7b1, and the operating data memory 7b2. Upon execution of the program instructions by means of the electronic processing unit 7a, using the relevant operating data 12 and the various threshold values ​​for the oxygen content in the exhaust gas mass flow as well as the integral limit values ​​for the oxygen mass integral, the electronic control device 7 is prompted to execute the method according to the invention for functional diagnosis of the exhaust gas aftertreatment device 2 of the internal combustion engine 1.

[0056] According to the program instructions, sensor data or operating data 12, for example, the signals from exhaust gas sensors 6a-c, which represent the oxygen content in exhaust gas mass flow 10a, and signals from temperature sensor 9, are received via the input / output interface 7c, and the arithmetic operations specified by the program are executed. Based on these, control commands, for example, for controlling internal combustion engine 1 according to the various operating modes, such as the conditioning operating mode or the diagnostic operating mode, are then output to the internal combustion engine via the input / output interface 7c.

[0057] Figure 2 shows a simplified flow diagram illustrating the essential method steps 20 - 26 of an embodiment of the method according to the invention.

[0058] Before the method itself is started, according to this embodiment, a query can first be performed to determine whether an evaluation of the second sensor signal Sig2 indicates that a pollutant component, for example, NOx or NH3 as shown, in the exhaust gas mass flow 10a downstream of the second exhaust gas catalyst 4 has exceeded a predetermined exhaust gas limit value AG_Gw and / or whether the internal combustion engine 1 is operating in a workshop diagnostic mode W-DBM. If at least one of these two criteria is met, the method is started.

[0059] In the first method step 20, by appropriately controlling the internal combustion engine 1, i.e. by issuing corresponding control commands from the electronic control device 7, the internal combustion engine 1 is operated in a conditioning operating mode KBM for preconditioning both exhaust gas catalysts 3, 4 for the functional diagnosis.

[0060] In the subsequent method step 21, a first sensor signal Sig1, which is representative of a first oxygen content Ü2_1 in the exhaust gas mass flow 10a immediately after the first exhaust gas catalyst 3, is received and evaluated, and a second sensor signal Sig2, which is representative of a second oxygen content C_2 in the exhaust gas mass flow 10a immediately after the second exhaust gas catalyst 4, is received and evaluated. The respective oxygen content is obtained by evaluating the signals Sig1, Sig2 by means of the control device 7.

[0061] If, in method step 22, the first oxygen fraction Ü2_1 and the second oxygen fraction C_2 reach a conditioning threshold value K-SW and thereby indicate that the preconditioning of the exhaust gas catalytic converters 3, 4 is completed, the conditioning operating mode KBM is ended and the internal combustion engine 1 is switched to a diagnostic operating mode DBM and operated in this. The conditioning threshold value K-SW can be fixed and stored in the operating data memory 7b2 and can be read out from the operating data memory 7b2 by the electronic processing unit 7a. In this example, the same conditioning threshold value K-SW is used as a basis for the oxygen fraction Ü2_1 and the oxygen fraction C_2, but different conditioning threshold values ​​K-SW can also be specified for the respective oxygen fraction Ü2_1, O2_2.

[0062] If in method step 23 during operation of the internal combustion engine 1 in the diagnostic operating mode DBM the first oxygen proportion Ü2_1 reaches a first threshold value SW1, which can also be read out from the operating data memory 7b2, an integration via the oxygen mass flow 10a between the first and the second exhaust gas catalytic converter 3, 4 or downstream of the second exhaust gas catalytic converter 4 is started to determine an oxygen mass flow integral SMI_UFC.

[0063] If in method step 24 the value of the oxygen mass flow integral SMI_UFC reaches an upper integral limit value IGw_o or the second oxygen fraction C_2 in the exhaust gas immediately downstream of the second exhaust gas catalyst 4 reaches a second threshold value SW2, the integration via the oxygen mass flow and the diagnostic operating mode DBM of the internal combustion engine 1 is stopped, and the achieved value of the oxygen mass flow integral SMIJJFC is determined.

[0064] In method step 25, the second exhaust gas catalyst 4 of the exhaust gas aftertreatment device 2 is now diagnosed.

[0065] The exhaust gas catalyst 4 is diagnosed as “fully functional”, OK, in a sub-step 25a if the value of the oxygen mass flow integral SMIJJFC has reached or exceeds the upper integral limit value IGw_o.

[0066] In sub-step 25b, the exhaust gas catalytic converter 4 is diagnosed as "still functional but in an aged condition," OK / aged, if the value of the oxygen mass flow integral SMI_UFC falls below the upper integral limit value IGw_o but does not fall below a lower integral limit value IGw_u. In sub-step 25c, the exhaust gas catalytic converter 4 is diagnosed as "no longer functional," nOK, if the value of the oxygen mass flow integral SMIJJFC falls below the lower integral limit value IGw_u.

[0067] All required limit values ​​IGw_o, IGw_u and threshold values ​​K_SW, SW1, SW2 and AG_Gw are stored in the operating data memory 7b2 and can be read out as required during the process.

[0068] Figures 3 to 5 each show a simplified signal diagram of the sequence of a first embodiment of the method, but for different diagnostic results.

[0069] Above the time axis t, in the upper area of ​​the respective diagram, the course of the A value of the exhaust gas mass flow 10a leaving the internal combustion engine 1, also referred to as EOut_A, is shown in the individual operating phases of the internal combustion engine 1.

[0070] Below, the signal curves S ig 1 and Sig2 of the first exhaust gas sensor 6a, which is arranged downstream of the first exhaust gas catalyst 3, and of the second exhaust gas sensor 6b, which is arranged downstream of the second exhaust gas catalyst 4, are recorded in their course over time t.

[0071] In the lower part of the respective diagram, the course of the oxygen mass flow integral SMI_TWC, SMIJJFC and the various integral limit values ​​IGw_o and IGw_u are shown, to which the respective diagnostic results OK, OK-aged and nOK are assigned.

[0072] Figure 3 shows a first “operating phase” in which the internal combustion engine 1 is used in normal operation. In this example, this operating phase is characterized by an A value greater than 1, A >1, i.e. by a lean combustion mixture. The signals Sig 1 and Sig 2 are each initially in the upper range, which indicates a low oxygen content O2 I, C _2. Towards the end of the “operating phase,” the first sensor signal Sig1 of the first exhaust gas sensor 6a drops sharply, which indicates that the storage capacity of the first catalytic converter 3 is exhausted and an oxygen breakthrough is occurring at the first catalytic converter 3. The second sensor signal Sig2, which indicates the second oxygen content C _2 downstream of the second catalytic converter 4, remains at a roughly constant, high level until then, since the excess oxygen is still being stored in the second catalytic converter 4.With the start of "preconditioning," internal combustion engine 1 switches to the conditioning operating mode KBM for the "preconditioning" of both exhaust catalysts 3, 4, which is characterized by a rich combustion mixture, i.e., A <1. Oxygen is now purged from the exhaust catalysts, and the signal curves increase until the first sensor signal Sig1 and the second sensor signal Sig2 reach the conditioning threshold value K_SW. At this point, both exhaust catalysts 3, 4 are virtually completely free of oxygen.

[0073] The internal combustion engine 1 is now switched to the diagnostic operating mode DBM, and the "diagnostic mode" begins, which is characterized by a lean combustion mixture, A>1. The excess oxygen leaving the internal combustion engine is then initially stored in the first oxygen catalyst 3 until its oxygen storage capacity is exhausted. This is recognizable by the sharp drop in the first sensor signal Sig 1 , which indicates an oxygen breakthrough at the first exhaust catalyst 3.

[0074] As soon as the first sensor signal Sig 1 reaches the first threshold value SW1, the integration of the oxygen mass flow between the first exhaust catalyst 3 and the second exhaust catalyst 4 begins to form the oxygen mass flow integral SMIJJFC, represented by a solid arrow symbol, which indicates the amount of oxygen supplied to the second exhaust catalyst 4 (UFC). For this purpose, the current A value of the exhaust gas mass flow 10a is provided at this point by the first exhaust gas sensor 6a and used to calculate the oxygen mass flow.

[0075] The value progression of the oxygen mass flow integral SMI_TWC of the second catalytic converter 4 is shown in the lower section of the diagram. In this example, it can be seen that the second sensor signal Sig2 does not decrease until the oxygen mass flow integral SMI_TWC reaches the upper integral limit IGw_o. As soon as the oxygen mass flow integral SMI_TWC reaches the upper integral limit IGw_o, the integration and the DBM diagnostic operating mode are terminated, and the function of the second catalytic converter 4 can be diagnosed as OK.

[0076] Following the “diagnostic operation”, the internal combustion engine 1 can now be operated again with a rich combustion mixture, for example in a “post-conditioning” phase, in order to reduce the oxygen loading of the exhaust gas catalysts 3, 4 again and, for example, to restore the initial situation before the diagnosis was carried out.

[0077] Furthermore, Figure 3 shows that an integration can also be carried out via the oxygen mass flow upstream of the first exhaust gas catalytic converter 3 (TWC), represented by a bordered arrow, to form an oxygen mass flow integral SMI_TWC, from the start of diagnostic operation until the time at which the first sensor signal Sig1 reaches the first threshold value SW1, i.e. the first exhaust gas catalytic converter is completely loaded with oxygen or its oxygen storage capacity is exhausted. For this purpose, the A value of the exhaust gas mass flow 10a upstream of the first exhaust gas catalytic converter 3, which is supplied, for example, by the further exhaust gas sensor 6c, must be used. The value of the oxygen mass flow integral SMI_TWC can now be used in a similar way to diagnose the first exhaust gas catalytic converter 3. Here, too, integral limit values ​​can be specified which enable the first exhaust gas catalytic converter 3 to be classified as OK, OK-aged, or nOK.

[0078] Figure 4 now shows, in a representation analogous to Figure 3, a diagnosis according to the first embodiment of the method, according to claim 2, but for the case of a second exhaust gas catalytic converter 4 that is to be classified as OK-aged. Here, the second sensor signal Sig2 drops to a second threshold value SW2, which indicates an oxygen breakthrough at the second exhaust gas catalytic converter 4, before the oxygen mass flow integral SMIJJFC reaches the upper integral limit value IGw_o. At this point, the diagnostic operation and integral formation are stopped, and the value of the oxygen mass flow integral SMI_UFC reached up to that point is used to diagnose the second exhaust gas catalytic converter 4, which leads to a classification as still OK but in an aged state, OK-aged.

[0079] Figure 5 also shows, in a representation analogous to Figure 3, a diagnosis according to the first embodiment of the method, according to claim 2, but for the case of a second exhaust gas catalytic converter 4 that is to be classified as defective or inoperative, nOK. Here, the drop in the second sensor signal Sig2 to a second threshold value SW2 occurs more quickly than in the previously shown examples, and the oxygen breakthrough at the second exhaust gas catalytic converter 4 is indicated earlier, and before the oxygen mass flow integral SMI_UFC reaches the lower integral limit value IGw_u. At this point, the diagnostic operation and integral formation are stopped, and the value of the oxygen mass flow integral SMI_UFC reached up to that point is used to diagnose the second exhaust gas catalytic converter 4, which leads to a classification as inoperative, nOK.

[0080] Figure 5, on the other hand, shows a diagnosis according to the second embodiment of the method, according to claim 3, in a representation analogous to Figure 3. Here, the conditioning operating mode KBM is used to “precondition” both exhaust gas catalytic converters 3, 4 by leaning out the combustion mixture or overrun fuel cut-off, which in both cases creates an excess of oxygen. Both exhaust gas catalytic converters are therefore initially loaded with oxygen until their oxygen storage capacity is exhausted and an oxygen breakthrough occurs, i.e. when the first oxygen fraction Ü2_1 and the second oxygen fraction C _2 reach a maximum. This is indicated by both sensor signals Sig1, Sig2 reaching the conditioning threshold value K_SW. In contrast to the previously shown examples, the diagnostic operating mode DBM here is characterized by enriching the combustion mixture, i.e. a lack of oxygen.In this case, the integration of the oxygen mass flow is started when the first sensor signal Sig1 indicates that the first exhaust gas catalyst 3 is completely free of oxygen. This is the case when the first sensor signal Sig1 reaches the first threshold value SW1.

[0081] The oxygen mass flow integral SMIJJFC over the oxygen mass flow is formed here downstream of the second exhaust catalyst 4 and indicates the amount of oxygen purged from the second exhaust catalyst 4. Of course, the A value downstream of the second exhaust catalyst 4, which is supplied by the second exhaust sensor 6b, is used for this purpose.

[0082] As soon as the second sensor signal Sig2, which indicates the oxygen content C_2 in the exhaust gas mass flow 10a downstream of the second catalytic converter 4, reaches the second threshold value SW2, which indicates that the second catalytic converter is now also completely free of oxygen, the integration of the oxygen mass flow is stopped and the value of the oxygen mass flow integral SMI_UFC reached up to that point is used to diagnose the second catalytic converter 4, in the same way as in the examples described above. In the case shown in Fig. 6, this leads to the second catalytic converter 4 being classified as OK-aged. Reconditioning of the catalytic converters 3, 4 is not necessary in this case, since they are already in an oxygen-free state at the end of the diagnostic mode. After the end of the diagnostic mode, the system can therefore continue in a neutral operating phase with A=1.

[0083] List of reference symbols

[0084] 1 internal combustion engine

[0085] 2 exhaust aftertreatment device

[0086] 3 first exhaust catalyst

[0087] 4 second exhaust catalyst

[0088] 5 particle filters

[0089] 6a - c Exhaust gas sensors

[0090] 7 Control device

[0091] 7a Electronic computing unit

[0092] 7b Electronic storage device

[0093] 7b1 Program memory

[0094] 7b2 Operating data memory

[0095] 7c Input / output interface

[0096] 8 signal lines

[0097] 9 Temperature sensor

[0098] 10 Exhaust pipe

[0099] 10a Exhaust gas mass flow

[0100] 11 Computer program product

[0101] 12 Operating data

[0102] 20-27 procedural steps

[0103] PF particle filter

[0104] Ap pressure difference sensor

[0105] TWC three-way catalyst

[0106] UFC underbody catalyst

[0107] AG_Gw exhaust gas limit value

[0108] W-DBM workshop diagnostic mode

[0109] KBM conditioning operating mode

[0110] DBM diagnostic mode

[0111] Sig1 first sensor signal

[0112] Sig2 second sensor signal

[0113] Ü2_1 first oxygen portion

[0114] Ö2_2 second oxygen component

[0115] K_SW conditioning threshold

[0116] SW1 first threshold

[0117] SW2 second threshold

[0118] IGw_o upper integral limit

[0119] IGw_u lower integral limit SMI_TWC oxygen mass flow integral TWC

[0120] SMIJJFC oxygen mass flow integral UFC

[0121] EOut_AA value of the exhaust gas mass flow at the engine outlet t time

Claims

Patent claims 1. A method for functional diagnosis of an exhaust gas aftertreatment device (2) of an internal combustion engine (1) having a first oxygen-storage-capable exhaust gas catalyst (3) and a second oxygen-storage-capable exhaust gas catalyst (4) arranged downstream in the exhaust gas mass flow (10), by carrying out the following steps by means of at least one electronic control device (7) associated with the exhaust gas aftertreatment device (2) and the internal combustion engine (1): - Operating the internal combustion engine (1) in a conditioning operating mode (KBM) for preconditioning both exhaust gas catalysts (3, 4) for functional diagnosis; - receiving and evaluating a first sensor signal (Sig1 ) which is representative of a first oxygen content (Ü2_1 ) in the exhaust gas mass flow (10a) immediately after the first exhaust gas catalyst (3) and receiving and evaluating a second sensor signal (Sig2) which is representative of a second oxygen content (Ü2_2) in the exhaust gas mass flow (10a) immediately after the second exhaust gas catalyst (4); - When the first oxygen fraction (Ü2_1 ) and the second oxygen fraction (O2_2) indicate that the preconditioning of the exhaust gas catalysts (3, 4) is completed, operate the internal combustion engine (1 ) in a diagnostic operating mode (DBM); - If, during operation of the internal combustion engine in the diagnostic operating mode (DBM), the first oxygen fraction (Ü2_1) reaches a first threshold value (SW1), an integration via the oxygen mass flow between the first and the second exhaust gas catalytic converter (3, 4) or downstream of the second exhaust gas catalytic converter (4) is started to determine an oxygen mass flow integral (SMIJJFC); - When the value of the oxygen mass flow integral (SMIJJFC) reaches an upper integral limit value (IGw_o) or the second oxygen fraction (O2_2) in the exhaust gas immediately downstream of the second exhaust gas catalyst (4) reaches a second threshold value (SW2), stopping the integration via the oxygen mass flow, stopping the diagnostic operating mode (DBM) of the internal combustion engine (1 ) and determining a reached value of the oxygen mass flow integral (SMIJJFC); - Diagnosing the second exhaust gas catalyst (4) of the exhaust gas aftertreatment device (2) as “fully functional” if the value of the oxygen mass flow integral (SMIJJFC) has reached the upper integral limit (IGw_o); or “still functional but in an aged condition” if the value of the oxygen mass flow integral (SMI_UFC) falls below the upper integral limit but does not fall below a lower integral limit (IGw_u); or - “no longer functional” if the value of the oxygen mass flow integral (SMI_UFC) falls below the lower integral limit (IGw_u).

2. Method for functional diagnosis of an exhaust gas aftertreatment device (2) of an internal combustion engine (1) according to claim 1, characterized in that - the conditioning operating mode (KBM) for preconditioning both exhaust gas catalysts (3, 4) is characterized by enrichment of the combustion mixture (oxygen deficiency), - that the preconditioning of the exhaust gas catalysts (3, 4) is completed when the first oxygen content (O2_1) and the second oxygen content (O2_2) reach a minimum and - that the diagnostic operating mode (DBM) is characterized by lean combustion mixture (excess oxygen) and - the oxygen mass flow integral (SMIJJFC) is formed via the oxygen mass flow between the first and the second exhaust gas catalyst (3, 4).

3. Method for functional diagnosis of an exhaust gas aftertreatment device (2) of an internal combustion engine (1) according to claim 1, characterized in that - the conditioning operating mode (KBM) for preconditioning both exhaust gas catalysts (3, 4) is characterized by leaning of the combustion mixture or overrun cut-off (excess oxygen); - that the preconditioning of the exhaust gas catalysts (3, 4) is completed when the first oxygen fraction (O2_1) and the second oxygen fraction (O2_2) reach a maximum and - that the diagnostic operating mode (DBM) is characterized by enriched combustion mixture (oxygen deficiency) and the oxygen mass flow integral (SMIJJFC) is formed via the oxygen mass flow downstream of the second exhaust gas catalyst (4).

4. Method for functional diagnosis of an exhaust gas aftertreatment device (2) of an internal combustion engine (1) according to one of claims 1 or 2, characterized in that the first sensor signal (Sig1) is received by a binary sensor and that the second sensor signal (Sig2) is received by a NOx sensor.

5. Method for functional diagnosis of an exhaust gas aftertreatment device (2) of an internal combustion engine according to one of the preceding claims, characterized in that the oxygen mass flow is determined on the basis of an exhaust gas mass flow (10a), its temperature and its A value.

6. Method for functional diagnosis of an exhaust gas aftertreatment device (2) of an internal combustion engine (1) according to claim 2, characterized in that after completion of the diagnostic operating mode (DBM), the internal combustion engine (1) is operated in an operating mode which is characterized by enrichment of the combustion mixture (oxygen deficiency) until the second oxygen proportion (Ü2_2) again reaches a minimum.

7. Method for functional diagnosis of an exhaust gas aftertreatment device (2) of an internal combustion engine (1) according to one of the preceding claims, characterized in that the method is only carried out when an evaluation of the second sensor signal (Sig2) shows that a pollutant proportion in the exhaust gas mass flow (10a) downstream of the second exhaust gas catalytic converter (4) has exceeded a predetermined limit value (AG_Gw) and / or the internal combustion engine (1) is operated in a workshop diagnostic mode (W-DBM).

8. Electronic control device (7) for functional diagnosis of an exhaust gas aftertreatment device (2) of an internal combustion engine (1), with at least - an electronic storage device (7b) in which at least one computer program product (11) with program instructions for carrying out the method is provided and - an input / output interface (7c) configured to receive and output electrical signals, and - an electronic processing unit (processor) (7a) for executing program instructions, with access to the at least one electronic memory device (7b) and the input / output interface (7c); wherein the program instructions, when executed by means of the electronic processing unit (7a), cause the electronic control device (7) to execute the method according to one of the preceding claims.

9. Computer program product (11) for functional diagnosis of an exhaust gas aftertreatment device (2) of an internal combustion engine (1), comprising program instructions for execution by the electronic computing unit (7a) of the electronic control device (7) according to claim 8, wherein the program instructions, when executed by the electronic computing unit (7a), cause the electronic control device (7) to carry out the method according to one of claims 1 to 7.

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