Method for detecting combustion misfires during operation of an internal combustion engine

Abstract

A method for detecting combustion misfires (126) during operation of an internal combustion engine is proposed. The internal combustion engine has a lambda probe (100), in particular a broadband lambda probe, for exhaust gas aftertreatment, in particular of a motor vehicle. The lambda probe (100) has a pump cell (106) with at least one measuring gas chamber (108). The method comprises detecting a measurement signal (128) indicating a pump current of the lambda probe (100), evaluating the measurement signal (128), and detecting combustion misfires (126) based on a change in the measurement signal (130).

Description

State of the art

[0001] The invention relates to a method for detecting combustion misfires during operation of an internal combustion engine having exhaust gas aftertreatment, in particular of a motor vehicle, and to a corresponding control unit.

[0002] For exhaust aftertreatment in motor vehicles, lambda control, in conjunction with a catalytic converter, is currently the most effective exhaust gas purification method for gasoline engines. In combination with currently available ignition and injection systems, this can achieve very low emissions.

[0003] The particularly effective three-way or selective catalysts have the property of breaking down hydrocarbons, carbon monoxide and nitrogen oxides by up to more than 98% if the engine is operated within a range of approximately 1% of the stoichiometric air-fuel ratio with LAMBDA = 1. The LAMBDA value, also known as the "air ratio", indicates how far the actual air-fuel mixture deviates from the value LAMBDA = 1, which corresponds to a mass ratio of 14.7 kg of air to 1 kg of petrol theoretically necessary for complete combustion, ie LAMBDA is the quotient of the supplied air mass and the theoretical air requirement.

[0004] With lambda control, the respective exhaust gas is measured, and the supplied fuel quantity is immediately corrected according to the measurement result, for example, by the injection system. A lambda sensor is used as the sensor; it exhibits a voltage jump exactly at LAMBDA = 1, thus providing a signal indicating whether the mixture is richer or leaner than LAMBDA = 1. The lambda sensor's operation is based on the principle of a galvanic oxygen concentration cell with a solid-state electrolyte.

[0005] Lambda sensors designed as two-point sensors operate in a well-known manner according to the Nernst principle, based on a Nernst cell. The solid-state electrolyte consists of two interfaces separated by a ceramic. The ceramic material used becomes conductive to oxygen ions at around 350°C, so that when the oxygen content on either side of the ceramic differs, the so-called Nernst potential is generated between the interfaces. This electrical voltage is a measure of the difference in the oxygen content on either side of the ceramic. Since the residual oxygen content in the exhaust gas of an internal combustion engine is highly dependent on the air-fuel ratio of the mixture supplied to the engine, it is possible to use the oxygen content in the exhaust gas as a measure of the actual air-fuel ratio.

[0006] The lambda sensors are operated with a Nernst voltage statically adjusted to 450 mV. The air ratio LAMBDA is calculated from a stored lambda characteristic curve of the broadband sensor LAMBDA = f(Ip) from the measured pump current Ip.

[0007] In so-called broadband probes, the measuring sensor is designed as a broadband sensor. This is formed by solid electrolyte layers and a number of electrodes. Such a structure is described in DE 19 912 102 A1, to which reference is made in its entirety in this context. In this sensor, one part of the electrodes forms a so-called pump cell, the other part a so-called concentration cell. Furthermore, the solid electrolyte layers form a so-called measuring gas chamber.

[0008] A pump voltage is applied to the electrodes of the pump cell, which is used to establish a constant oxygen partial pressure, i.e., a corresponding air ratio (LAMBDA), in the sample gas chamber by pumping oxygen in or out. The pump voltage is regulated such that a constant voltage of 450 mV is established at the electrodes of the concentration cell. This voltage corresponds to a value of LAMBDA = 1 when the oxygen partial pressure in the reference channel is 20%.

[0009] In broadband lambda sensors based on the aforementioned double-cell principle, the air ratio in the measuring gas chamber of the pump cell is regulated to a specific value, which is preferably kept constant at LAMBDA = 1. The air ratio in the aforementioned measuring gas chamber is predetermined by the aforementioned reference voltage for the Nernst cell generated by a control unit of the internal combustion engine.

[0010] It is known that due to individual combustion misfires during operation of the internal combustion engine, called "misfire", unburned fuel enters the catalytic converter and creates unwanted heating there, which in the worst case leads to damage to the catalytic converter.

[0011] Furthermore, combustion misfires have a significant impact on the functional diagnosis of the catalytic converter, as the control unit requires the most precise information possible about which engine settings lead to combustion misfires. For the actual diagnosis of the catalytic converter, the internal combustion engine is operated in a conventional manner, sometimes slightly lean and sometimes slightly rich, so that, integrated over time, an exhaust gas with an air / fuel ratio of '1' is produced. The amplitude of the change at a sensor downstream of the catalytic converter is then used to evaluate the storage capacity of the catalytic converter, and conclusions are drawn about the functionality of the catalytic converter based on this value.

[0012] Detecting misfiring in combustion engines caused by insufficient spark or fuel injection due to a component failure is a key task for the company to prevent increased emissions and damage to the catalytic converter. In many countries, this detection and display is therefore required by law as part of the OBD (On Board Diagnostics) system.

[0013] The legal requirement for detection defines a range in which misfire detection must be activated. Outside of this range, robust detection is not possible because - especially at the operating point of low engine torque - the typically used detection parameter "rough running" is not sufficiently meaningful to indicate the absence of combustion. Rough running detects the torque resulting from combustion via the crankshaft acceleration and detects misfires if the torque is absent. At very low torques, the resulting crankshaft acceleration cannot be sufficiently differentiated between the fault-free and faulty cases.

[0014] From WO 91 / 11599 A1 a method for detecting combustion misfires in an internal combustion engine is known, in which, in order to determine a cylinder with misfires in an internal combustion engine with z cylinders, for each cylinder z (z from 1 - Z) a time period T(z) is measured within which the crankshaft rotates by a predetermined crank angle in the combustion stroke of the cylinder, and the time difference value DT(z) = T(z) - T(z - 1) is formed for each cylinder.

[0015] From US 6 584 834 A a method for detecting combustion misfires of an internal combustion engine is known, in which a measure of the rough running of the internal combustion engine is formed and compared with a threshold value which depends on the load of the internal combustion engine, and wherein exceeding the threshold value is evaluated as a misfire.

[0016] Methods based on other approaches, such as ion current or cylinder pressure, are known, but are not widely used due to the significant additional costs for the additional components required. The method based on rough running is therefore the most widely used. Various approaches to improving detection based on advanced signal analysis have been investigated, but none have proven significantly more robust than the simple analysis of crankshaft acceleration and have been widely adopted.

[0017] The potential of new data processing methods based on artificial intelligence (AI) has also been considered, although there has been no indication so far that any of the AI-based methods has significant advantages and is being widely used in series production.

[0018] Since misfiring detection is a long-standing and intensively researched signal analysis task, the expectation of improved detection quality must be based on the previously only assumed advantages of AI, without, however, being able to demonstrate the core advantage – proof of the improvement achieved by AI is still pending. Therefore, among all methods, the rough running method based on the analysis of combustion engine speed has been established to date as cost-effective and high-performance.

[0019] Nevertheless, there are limitations in the detection quality due to the physical characteristics of the combustion engine's operation, primarily, as described above, at operating points with low combustion torque or in operating situations with sluggish, possibly incomplete combustion without sufficient torque development. The fundamental problem with insufficient torque development is that this type of combustion cannot be distinguished from misfires, which also produce no torque.

[0020] A possible alternative approach to detect misfires is to use exhaust back pressure, if such a signal is available in the system.

[0021] DE 10 2013 014 674 A1 discloses a method for detecting misfires based on comparing the exhaust gas with a threshold value. It is proposed to individually measure the exhaust gas of each cylinder of the internal combustion engine using at least one exhaust gas sensor and to measure at least one actual exhaust gas value from the exhaust gas of each cylinder. According to a further development of the invention, the actual exhaust gas value for each cylinder is measured using at least one cylinder-specific exhaust gas sensor, with the respective exhaust gas sensor of the respective cylinder measuring the respective actual exhaust gas value exclusively within a cylinder-specific crankshaft angle range.

[0022] DE 10 2008 031 696 A1 describes a device for detecting a combustion misfire in an internal combustion engine, in particular a gasoline engine, comprising a first sensor upstream of the catalytic converter and a second sensor downstream of the catalytic converter for measuring a first residual oxygen concentration. The method claims to detect a misfire when there is a peak toward a lean mixture, measured by the first lambda sensor upstream of the catalytic converter.

[0023] DE 10 2009 049 544 A1 describes a method for detecting misfires. To reliably identify misfires as such, at least one additional misfire signal is used to determine whether a detected rotational irregularity is due to a misfire. A misfire is only recognized as such if both an engine speed signal and at least one additional misfire signal are detected. If the engine speed signal and the additional misfire signal occur simultaneously, this is a clear indication that a misfire is indeed occurring.

[0024] DE 10 2006 006 114 A1 describes a method for detecting combustion misfires in internal combustion engines with exhaust aftertreatment. The method described in the application proposes using the dynamic pressure dependence of the lambda sensor to detect combustion misfires by detecting missing combustions (misfires) through the absence of deflections in the pumping current. The method is based on the basic assumption that, synchronous with each combustion, the combustion engine speed causes gas to enter the measuring gas chamber of the sensor as a result of the pressure increase when the cylinder volume is discharged. This leads to a measurable pumping current with a suitable Nernst voltage setting, whereas the pressure increase and pumping current are absent in the case of combustion misfires.

[0025] Despite the numerous advantages of the state-of-the-art methods for detecting combustion misfires during operation of an internal combustion engine, they still have potential for improvement. For example, the known methods do not reliably detect misfires at every operating point. For example, DE 10 2006 006 114 A1 fails to take into account the fact that the composition of the exhaust gas depends on whether combustion has occurred (low oxygen content) or not (high oxygen content). Disclosure of the invention

[0026] A method for detecting combustion misfires during operation of an internal combustion engine is therefore proposed, which at least largely avoids the disadvantages of known methods for detecting combustion misfires during operation of an internal combustion engine and, in particular, improves the robustness of conventional misfire detection. In particular, the existing misfire detection of the internal combustion engine in systems with a suitable lambda sensor is to be supplemented in such a way that the risk of misfires being incorrectly detected (slow combustion with low torque development) or not being detected is minimized by linking the additional information with the existing misfire detection method. The weighting of the respective individual signal in the overall evaluation can depend on the detection quality and robustness at the current operating point.Under suitable boundary conditions, the evaluation of the pump current signal can be used as the sole means of failure detection.

[0027] The method according to the invention comprises the following steps, preferably in the order mentioned: - Recording a measurement signal indicating a pumping current of the lambda probe, - Evaluation of the measurement signal and - Detection of combustion misfires based on a change in the measurement signal.

[0028] The proposed method improves the state of the art primarily by using the pumping current instead of the exhaust gas probe signal. A basic idea of ​​the method is the assumption that the composition of the exhaust gas during unsuccessful combustion, and thus the pumping current signal, differs noticeably from the state of correct combustion. A change in the signal or a deviation from the expected signal curve can be used as an indication of misfires. The evaluation of the pumping current, with its better temporal resolution, thus provides more precise information about the presence of (individual) misfires.

[0029] The method can further comprise detecting combustion misfires based on a temporal change in the measurement signal. As a result of a misfire—with fuel actually not being burned—a significant change in a pumping current is observable. Generally speaking, the basic idea and advantage of the invention lies in the use of the probe's pumping current signal, which has a higher temporal resolution than the smoothed signal of a pre-evaluated variable—for example, exhaust lambda—and its change compared to the behavior when combustion has occurred. In combination with the above applications, the advantage of the invention further arises from the use of the pumping current signal to detect misfires in all cylinders and for the more robust detection of actual misfires in the presence of a powerful electric motor in a hybrid engine.The basic idea can generally be applied where there is a meaningful relationship between the high-resolution pump current signal and the combustion process. If a significant exhaust gas mixture occurs, for example, due to an exhaust turbocharger or an unsuitable exhaust routing to the sensor, only limited detection of misfires is possible through the evaluation of the pump current signal.

[0030] The change in the measurement signal may include an increase in the measurement signal. Triggered by dropouts, the pump current reacts in the form of a significant increase, which can be used as an indicator for the presence of dropouts.

[0031] Combustion misfires can be detected if the change in the measurement signal exceeds a predetermined threshold. As a result of a misfire—with fuel actually not combusted—a significant change in the pumping current can be observed, which can be easily achieved, for example, by comparing the calculated temporal gradient of the signal with a suitably determined threshold.

[0032] The predetermined threshold can be a predetermined temporal change in the measurement signal and / or an expected change in the measurement signal. With fuel injection and ignition in the combustion chamber, a change in the pumping current is expected; a deviation from the expected change should be interpreted as an indication of misfiring in all (or some) cylinders.

[0033] The evaluation of the measured signal can include comparisons with an expected and / or modeled pump current signal curve. For example, in the event of a fault or misfire, the pump current will not change with the (expected) start of combustion. A difference from the expected / modeled pump current curve thus indicates the presence of a fault.

[0034] The expected and / or modeled curve of the pumping current signal can take into account the curve of a target ignition angle. Thus, the evaluation of the pumping current as a result of the change in the ignition angle during engine start-up allows the detection of combustion, such as a non-misfire condition on all cylinders.

[0035] The method may further comprise using the method to verify the plausibility of another method for detecting combustion misfires. Combining a different or additional misfire detection method with the proposed pump current evaluation reduces the probability of misfire detection errors.

[0036] The other method may involve evaluating the engine speed of the internal combustion engine. Combining the classic misfire detection with the proposed pump current analysis reduces the probability of misfire detections (false failures).

[0037] Furthermore, a computer program is proposed which is configured to carry out each step of the method according to one of the embodiments described above or below.

[0038] Furthermore, an electronic storage medium is proposed on which a computer program according to the previous embodiment is stored.

[0039] Furthermore, an electronic control device is proposed which comprises an electronic storage medium according to the previous embodiment.

[0040] For the purposes of the present invention, an internal combustion engine is understood to be a heat engine (thermal fluid energy engine) that performs mechanical work through the internal combustion of fuel. Unlike steam engines and hot-air engines, all work processes take place in a single working chamber, the working cylinder. Chemical energy from a fuel-air mixture is converted into pressure (force) and expansion (displacement) via the temperature of the working gas, and thus into mechanical energy (force times displacement).

[0041] An internal combustion engine can be an internal combustion engine. An internal combustion engine is a heat engine based on the principle of the internal combustion engine, which converts chemical energy into mechanical work through fuel combustion. To achieve this, an ignitable mixture of fuel and air (oxygen) is burned in a combustion chamber. The hallmark of all internal combustion engines is internal combustion, i.e., the generation of combustion heat within the engine, which is why the acronym ICE (Internal Combustion Engine) is used for internal combustion engines in vehicles. The thermal expansion of the resulting hot gas is used to move pistons (rotary pistons, so-called rotors in the Wankel engine). The most common types of internal combustion engines are spark-ignition (SI) and compression-ignition (DSI) engines.A typical application of these engines is the propulsion of motor vehicles (motor vehicles for short), such as cars or motorcycles, ships, and aircraft. The fuel to be burned can be liquid fuels, such as gasoline, diesel, or methanol, or gaseous fuels, such as methane, LPG, or hydrogen.

[0042] In the context of the present invention, a combustion misfire, or misfire for short, can be understood as the lack of fuel combustion in the working chamber. Due to individual combustion misfires during operation of the internal combustion engine, known as "misfire", unburned fuel enters the catalytic converter and creates unwanted heating, which in the worst case leads to damage to the catalytic converter. Possible causes include leaky valves. Minor valve leaks can lead to serious engine malfunctions over time. Leaking intake valves change the intake manifold pressure and thus also the values ​​of the intake manifold pressure sensor. If unburned gas mixtures reach the lambda sensor via leaky exhaust valves, a residual oxygen content is measured there and the engine mixture is enriched. Over time, this can lead to fuel deposits in the combustion chamber and in the valve guides.In extreme cases, the valves can become stuck in the valve guides. Therefore, misfiring detection should be part of every vehicle's OBD monitoring system.

[0043] In the context of the present invention, a measurement signal indicating a pump current can be understood as a signal that indicates the detected pump current or a variable derived therefrom, such as the pump voltage.

[0044] In the context of the present invention, a change in the measurement signal can be understood as an anomaly in the course of the measurement signal and thus in the observed pump current. Such an anomaly can be a particularly high value of the observed pump current compared to previous measured values, equivalent to a temporarily high oxygen concentration. Alternatively or additionally, a high gradient of the pump current or a pronounced peak or a characteristic course of the pump current can also be considered an indication of a misfire.

[0045] In the context of the present invention, a lambda probe can be understood as a sensor designed to detect the oxygen content in a measurement gas. The oxygen content can be detected, for example, in the form of a partial pressure and / or in the form of a percentage. The measurement gas can be exhaust gas from an internal combustion engine. The lambda probe (λ-probe) is the main sensor in the control loop of the lambda control for catalytic exhaust gas purification (colloquially: controlled catalyst). The aim is to minimize the release of pollutants such as nitrogen oxides, hydrocarbons, and soot. It compares the residual oxygen content in the exhaust gas with the oxygen content of a reference, usually the current atmospheric air. From this, the combustion air ratio λ (ratio of combustion air to fuel) can be determined and thus adjusted.Two measurement principles are used: voltage of a solid-state electrolyte (Nernst probe) and resistance change of a ceramic (resistance probe). The lambda sensors usable within the scope of the present invention can, in principle, be designed as known, for example, from Konrad Reif (ed.): Sensors in Motor Vehicles, 3rd edition 2010, pp. 128-137. With broadband lambda sensors, in particular planar broadband lambda sensors, the oxygen concentration in the exhaust gas can be determined over a wide range, thus determining the air-fuel ratio in the combustion chamber. The air / fuel ratio λ describes this air / fuel ratio. Short description of the drawings

[0046] Further optional details and features of the invention will become apparent from the following description of preferred embodiments, which are schematically illustrated in the figures. In the drawings, identical reference numerals indicate identical or comparable components or features.

[0047] They show: Fig. 1 shows an embodiment of a broadband lambda sensor suitable for implementing the invention; Fig. 2 exemplary signal curves over time; Fig. 3 exemplary signal curves over time; Fig. 4 exemplary signal curves over time; Fig. 5 exemplary signal curves over time; Fig. 6 exemplary signal curves over time; and Fig. 7 example signal curves over time. Embodiments of the invention

[0048] Fig. 1 shows an embodiment of a lambda sensor 100 suitable for implementing the invention. The lambda sensor is in particular a broadband lambda sensor. Fig. In the broadband lambda probe 100 shown in Figure 1, exhaust gas 102 passes through a small opening 104 of a pump cell 106 and a diffusion barrier into the actual measuring gas chamber 108 of a concentration cell 110 in the form of a Nernst cell. Adjacent to the concentration cell 110 is a reference gas chamber 112 containing an oxygen reference gas. A stoichiometric air-fuel ratio is always set in the measuring gas chamber 108. An evaluation and control circuit 116 arranged in a control unit 114 or the like regulates a pump voltage U_Pump applied to the pump cell 106 such that the composition of the gas in the measuring gas chamber 108 remains constant at LAMBDA = 1. When the exhaust gas 102 is lean, the pump cell 106 pumps oxygen from the measuring gas chamber 108 to the outside. In contrast, when the exhaust gas 102 is rich, the oxygen from the exhaust gas 102 of the environment is pumped into the measuring gas chamber 108 and thereby the direction of the electrical pumping current I_Pump is reversed.The pumping current is proportional to the oxygen concentration or oxygen demand. Thus, the pumping current 1 Pump is a measure of the lambda in the exhaust gas. An integrated heater 118 ensures an operating temperature of at least 600°C, which, however, is only reached after a certain preheating period after a cold start.

[0049] The pump current is adjusted via the evaluation and control circuit 116, which compares the Nernst voltage U_Nernst with an internally generated reference voltage U_Ref of 450 mV. As soon as a deviation Delta (U_Nernst, U_Ref) occurs, this deviation is amplified in the circuit 116 and fed into the pump cell 106 as the pump current I_Pump. This pumps oxygen into or out of the sample gas chamber 108, and the Nernst voltage U_Nernst stabilizes at 450 mV. The required pump current I_Pump or the output voltage U_Sonde dropped across a resistor (R1) 120 is evaluated as the output signal of the probe 100.

[0050] It should be noted that for the operation of a broadband lambda probe 100 with a pumped reference, the reference electrode is connected to +5 V via a fixed resistor of, for example, 100 kOhm in order to continuously supply oxygen to the reference gas chamber 112 via the Nernst cell 110.

[0051] The output signal I_Pump is transmitted to another electronic control unit (not shown), which in turn signals a mixture-forming device, such as an injection system or an electronically controlled carburetor, via a control signal whether the mixture needs to be enriched or leaned. If the mixture is too lean, more fuel is added; if the mixture is too rich, the amount of fuel supplied to the engine is reduced again.

[0052] A typical qualitative curve of the pumping current I_Pump as a function of LAMBDA is, for example, such that with lean exhaust gas, a positive pumping current is established in order to maintain a stoichiometric composition in the sample gas chamber or in the diffusion barrier. With rich exhaust gas, in contrast, a negative pumping current is present. Since one is no longer dependent on the stepped voltage characteristic of the Nernst cell, LAMBDA can be measured continuously in a range from 0.7 to infinity. A measurement for LAMBDA equal to infinity is required, for example, for overrun calibration.

[0053] Such lambda sensors feature software-implemented logic to improve the accuracy of the measured lambda signal. The Nernst cell's pumping current, which is subject to a higher sampling rate (and higher variance), is converted into an exhaust lambda value using temporal averaging and then made available to the emissions control system.

[0054] A method according to the invention for detecting combustion misfires during operation of an internal combustion engine is described below. In the method, a measurement signal indicating a pumping current of the lambda sensor is recorded. Furthermore, it is provided to evaluate the pumping current and detect a combustion misfire based on a change in the measurement signal. If the temporal profile of the measurement signal is unusual, it can be concluded that combustion is intermittent. The unusual characteristic of the profile can be a particularly high value of the observed pumping current, which is equivalent to a temporarily high oxygen concentration. Alternatively, a high gradient of the pumping current or a pronounced peak or a characteristic profile of the pumping current can also be interpreted as an indication of a misfire.

[0055] The proposed method improves the state of the art primarily by using the pump current as the measurement signal instead of the exhaust gas probe signal. The core of the method is the assumption that the composition of the exhaust gas during unsuccessful combustion, and thus the pump current signal, differs noticeably from the state of correct combustion. A change in the measurement signal or a deviation from the expected signal curve can be used as an indication of misfires. The evaluation of the pump current, with its better temporal resolution, thus provides more precise information about the presence of (individual) misfires.

[0056] Fig. Figure 2 shows exemplary signal curves over time. Time is plotted on the x-axis 122, and the respective signal values ​​are plotted on the y-axis 124. Fig. Figure 2 shows, in particular, the basic relationship between misfires 126, which, as indicated by signal 127, are stimulated or imposed, for example, electronically stimulated or imposed, the pumping current 128, the change in the pumping current 130 compared to the classic misfire detection based on a change in the speed 132 with the associated detection threshold 134, and the suppression condition 136. Detection is also possible in areas where the classic misfire detection 136 is suppressed, for example, at low engine torque, which is indicated by signal 137. The evaluation of the pumping current 128 clearly shows a relationship to the imposed misfires 126 due to the temporal change in the pumping current 130.

[0057] In the event of a misfire, the oxygen concentration in the exhaust gas is higher than in the case of a combustion event, since the amount of oxygen in the cylinder remains largely unburned. This increased concentration is detected as an increased pumping current 128. An increase in the pumping current 128 can thus be used as a basis for detecting misfires 126.

[0058] An alternative approach to operating internal combustion engines currently being pursued compared to existing gasoline and diesel internal combustion engines is to design the engines for hydrogen. The detection of defects that lead to incomplete combustion and hydrogen discharge or potentially critical catalyst temperatures is also advantageous for hydrogen internal combustion engines, regardless of legal requirements. Hydrogen engines may pose a particular challenge in distinguishing combustion processes with a slow combustion process and a low torque contribution – correspondingly low impact on crankshaft acceleration – from misfires 126. In these cases, the limit of robust detection of misfires 126 using torque- or speed-based methods is reached.The problem of insufficient differentiation between misfires 126 and the described slow, low-torque combustion processes cannot be eliminated with conventional methods due to their nature.

[0059] Furthermore, a particular challenge in plug-in hybrids (PHEVs - Plug-in Hybrid Electric Vehicles) with powerful electric motors is the robust detection of misfires 126 on all cylinders when the engine speed 132 is reached with the help of the electric motor, but no change in the segment time or torque change can be observed due to lack of combustion, so that misfires are not detected at all, or when the electric motor causes severe disturbances in the engine speed signal 132, resulting in false detections. At catalyst temperatures beyond light-off, undetected massive damage can occur in the first case. In the second case, detection can lead to unauthorized entries and driver warnings or even cylinder deactivation.

[0060] The proposed method of evaluating the pumping current of the lambda sensor could ensure improved detection of actual combustion misfires and avoid the problems described.

[0061] In general terms, the basic idea and advantage of the invention lies in the use of the pump current signal of the probe 100, which has a higher temporal resolution than the smoothed signal of a pre-evaluated variable - for example the exhaust gas lambda - and its change compared to the behavior when combustion has taken place.

[0062] In combination with the above applications, the advantage of the invention further results from the use of the pump current signal to detect misfires 126 on all cylinders and to more robustly detect actual misfires 126 in the presence of a powerful electric machine in a hybrid engine.

[0063] The pump current analysis can be used, in particular, to confirm the detection of a potential misfire using the classic speed-based method. A lack of change in speed 132 and thus a low torque development is then evaluated as a misfire if the sensor current analysis also indicates a failed combustion. Combining the classic misfire detection with the proposed pump current analysis thus reduces the probability of false detections (false fails) of misfires 126.

[0064] In this case, it is obvious to identify defined operating points or operating ranges during the development and application phase of the project that, for physical or methodological reasons, exhibit a lower detection quality for misfire detection using conventional, rough-running-based methods. In these operating ranges, the pump current-based signal is used in the manner described above as a supplement or alternative to the conventional, e.g., speed-based signal 132 for misfire detection 126.

[0065] These areas can be determined without or in an extended form of the proposal using artificial intelligence methods; in the second case, the AI ​​process can automatically learn from the measurements of the application phase which operating points - characterized by which operating parameters - mean a lower robustness of the misfire detection.

[0066] Fig. Figure 3 shows exemplary signal curves over time. Time is plotted on the x-axis 122, and the respective signal values ​​are plotted on the y-axis 124. Fig. 3 shows, in particular, by way of example, the change in the pump current 130 compared to the pump current 138 delayed by 20 samples. Triggered by stimulated dropouts, a reaction of the pump current 128 is shown - in the form of a significant increase - which can be used as an indicator for the presence of the dropouts.

[0067] The response of the pump current 128 can be used as an additional criterion for confirming the detection with the conventional method in order to avoid false detections during slow combustion. Thus, in the upper part of the Fig. 3 shows the classic misfire detection based on a change in the speed 132 with the associated detection threshold 134.

[0068] Fig. Figure 4 shows exemplary signal curves over time. Time is plotted on the x-axis 122, and the respective signal values ​​are plotted on the y-axis 124. Fig. In particular, Figure 4 shows, by way of example, the change in the pumping current compared to the pumping current 138, which is delayed by 20 sample values, in a phase with lower combustion torque. The reaction of the pumping current 128 can be used as an indicator for the presence of misfires 126, possibly even if the characteristic variable 132 does not exceed the detection threshold 134 with the conventional speed-based method.

[0069] The characteristics of the conventional signal 132 and the pumping current 128 or the change in the pumping current 130 depending on the operating point and type of misfire indicate that a combination depending on other known input conditions, such as load and speed, possibly with machine learning methods, can be advantageous in terms of high detection accuracy.

[0070] Fig. Figure 5 shows exemplary signal curves over time. Time is plotted on the x-axis 122, and the respective signal values ​​are plotted on the y-axis 124. Fig. 5 shows, in particular, the waveforms of the conventional signal 132 and the change in the pump current 130 for two sequences of multiple dropouts 126. In both cases, the amplitude of the signal formed based on the pump current 128 is not constant. Clear detection of dropouts 126 based solely on the pump current signal may therefore not be possible under certain circumstances. One possible concrete implementation of the method is therefore the use of the signal based on the pump current 128 to confirm detections with the conventional method, for example, in a borderline range below a clear detection threshold.

[0071] Fig. 6 illustrates this approach. Fig. Figure 6 shows exemplary signal curves over time. Time is plotted on the x-axis 122, and the respective signal values ​​are plotted on the y-axis 124. Fig. 6 shows, in particular, the evaluation of the change in pump current 130 to confirm a suspected fault from conventional, speed-based detection. Suspicion arises when the lower threshold is exceeded. The signal based on speed 132 lies in a transition range 140 between clear detection of misfires 126 and clear detection of non-misfires. While the speed-based signal 132 does not exceed the threshold for reliable misfire detection 132 in the event of the first misfire, which would not be detected conventionally, a lower-data threshold for the same signal can generate a suspected misfire, and this suspected misfire can be confirmed by testing the pump current-based signal as a secondary signal. A misfire is present if the evaluation of pump current signal 128 also indicates this.The method allows a lowering of the threshold for suspected errors or, alternatively, an raising of the threshold for the reliable detection of dropouts 126 and thus offers the possibility of reducing false detections (false fail / false pass) through the suspicion test based on the second signal.

[0072] The example of the reaction to the 6th stimulated dropout shows that, even with the described extension, the detection is not completely robust against non-detection of dropouts 126. However, with appropriate activation / data of the procedure, it can be expected that an increase in robustness can be achieved. In the specific case of Fig. 5, only one of the 10 dropouts would not be detected using the described procedure.

[0073] A more general solution can use the probe pump current signal (or the probe pump voltage) as input for a combined evaluation, for example, via combined decision tables with the statement "dropout / no dropout" depending on whether the combination of the indicators formed from the speed and probe pump current, possibly standardized, lies within a range of values ​​(cell of a table / map), whereby load and speed 132 can also be taken into account (different tables). Alternatively, the statement about dropout / no dropout can be derived from the variables using a model generated by machine learning.

[0074] The evaluation of pumping current 128 can be used to detect misfires 126 on all cylinders, for example, by observing the change in pumping current depending on the change in injection and, if applicable, ignition. With fuel injection and ignition in the combustion chamber, a change in pumping current 130 is expected; a deviation from the expected change should be interpreted as an indication of misfires on all, or possibly some, cylinders.

[0075] Fig. Figure 7 shows exemplary signal curves over time. Time is plotted on the x-axis 122, and the respective signal values ​​are plotted on the y-axis 124. Fig.Figure 7 shows, in particular, the curve of the pumping current 128 during a start of the combustion engine with the curve of the target ignition angle 142 and the ignition angle release status after start 144. The error-free case is shown. In the event of an error, the pumping current 128 will not change with the (expected) start of combustion. A difference from the expected / modeled curve of the pumping current 128 indicates the presence of the error.

[0076] The invention can be demonstrated through the relationship between pump current and misfire detection. Systems that utilize the additional signal will have specific requirements regarding the information provided by the lambda sensor, and changes in the sensor signal, such as the absence / filtering / interference of the signal value, will affect the detection of misfires 126. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 19 912 102 A1

[0007] WO 91 / 11599 A1

[0014] US 6 584 834 A

[0015] DE 10 2013 014 674 A1

[0021] DE 10 2008 031 696 A1

[0022] DE 10 2009 049 544 A1

[0023] DE 10 2006 006 114 A1 [0024, 0025] Cited non-patent literature

[0000] Konrad Reif (ed.): Sensors in motor vehicles, 3rd edition 2010, pp. 128-137

[0045]

Claims

[1] Method for detecting combustion misfires (126) during operation of an internal combustion engine, wherein the internal combustion engine has a lambda probe (100), in particular a broadband lambda probe, for exhaust gas aftertreatment, in particular of a motor vehicle, wherein the lambda probe (100) has a pump cell (106) with at least one measuring gas chamber (108), the method comprising the following steps: - detecting a measurement signal (128) indicating a pumping current of the lambda probe (100), - Evaluation of the measurement signal (128) and - Detecting combustion misfires (126) based on a change in the measurement signal (130). [2] Method according to the preceding claim, further comprising detecting combustion misfires (126) based on a temporal change in the measurement signal (130). [3] Method according to one of the preceding claims, wherein the change in the measurement signal (130) comprises an increase in the measurement signal. [4] Method according to one of the preceding claims, wherein combustion misfires (126) are detected if the change in the measurement signal (130) exceeds a predetermined threshold value. [5] Method according to the preceding claim, wherein the predetermined threshold value is a predetermined temporal change of the measurement signal (130) and / or an expected change of the measurement signal (130). [6] Method according to one of the preceding claims, wherein the evaluation of the measurement signal (128) comprises comparison with an expected and / or modeled course of a pump current signal. [7] Method according to the preceding claim, wherein the expected and / or modeled course of the pump current signal takes into account a course of a desired ignition angle (142). [8] Method according to one of the preceding claims, further comprising using the method for checking the plausibility of another method for detecting combustion misfires. [9] Method according to the preceding claim, wherein the other method comprises evaluating an engine speed (132) of the internal combustion engine. [10] A computer program arranged to carry out each step of the method according to any one of the preceding claims. [11] An electronic storage medium on which a computer program according to claim 10 is stored. [12] An electronic control device (114) comprising an electronic storage medium according to claim 11.

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