METHOD FOR DETECTING MANIPULATION OF A SENSOR VALUE OF AN EXHAUST ENGINE SENSOR FOR A VEHICLE

Abstract

In a method for detecting manipulation of a sensor value of an exhaust gas sensor of an internal combustion engine for a vehicle, the internal combustion engine (1) is first operated in an overrun fuel cut mode. A first sensor value (ΔNox) of the exhaust gas sensor (70) is determined while a throttle valve (30) is closed. A suspicion of manipulation is established by evaluating the first sensor value (ΔNox) according to a first threshold value (C1). The suspicion of manipulation is verified by measuring a second sensor value (Nox(t2'), NH3(t2'), Nox(t3'), NH3(t3')) of the exhaust gas sensor (70) with an emission increase of the internal combustion engine (1) and by evaluating the second sensor value (Nox(t2'), NH3(t2'), Nox(t3'), NH3(t3')) according to a second threshold value (C2), if the suspicion of manipulation has been previously established.

Description

[0001] Description

[0002] Method for detecting manipulation of a sensor value of an exhaust gas sensor of an internal combustion engine for a vehicle

[0003] The invention relates to a method for detecting tampering with a sensor value of an exhaust gas sensor, in particular a nitrogen oxide sensor, of an internal combustion engine for a vehicle. Furthermore, the invention relates to an internal combustion engine for a vehicle with a function for detecting tampering with a sensor value of an exhaust gas sensor of the internal combustion engine.

[0004] Exhaust gas sensors, such as nitrogen oxide (NOx) sensors, measure the exhaust gas concentration in the exhaust of a vehicle's internal combustion engine. They are used to control SCR (Selective Catalytic Reduction) systems and LNT (Lean NOx Trap) catalysts, and in the future, they will also be used for OBM (On-Board Monitoring) of exhaust emissions. For various reasons, there are repeated attempts to falsify the measured values ​​of exhaust gas sensors, especially NOx sensors, and thus simulate lower exhaust emissions than actually present.

[0005] For example, a multitude of NOx sensor emulators are now freely accessible and available online. These falsify the measured values ​​of the NOx sensors and simulate a functioning exhaust aftertreatment system to a control unit. The goal of these emulators is, for example, to save on the use of a reducing agent in SCR catalysts or to avoid repair costs for exhaust gas purification. Due to the many possible points of attack for circumventing the exhaust aftertreatment system, detecting these emulators is not easy. Another way to falsify the actual emission values ​​is to remove the exhaust sensors so that they only measure ambient air. Furthermore, the protective tube of the exhaust sensors can also be modified so that the exhaust gas mass flow does not reach the sensor element.Not all modifications can be detected by the self-diagnosis of exhaust gas sensors, such as nitrogen oxide sensors, using a so-called gain check. A simple check of a nitrogen oxide sensor is described in the patent specification, for example, by comparing the linear signal of the linear lambda sensor and the linear oxygen signal in a nitrogen oxide sensor.

[0006] DE 102008024177 B3 describes the method described in DE 102008024177 B3. The method described in DE 102008024177 B3 can be used to detect a removed sensor based on a linear lambda sensor and the linear lambda sensor signal of the nitrogen oxide sensor. However, if the sensor value of the exhaust gas sensor itself is manipulated, for example, by an emulator, this can only be detected in the system.

[0007] It is therefore desirable to provide a method for detecting manipulation of a sensor value of an exhaust gas sensor of an internal combustion engine for a vehicle, which method makes it possible to reliably detect manipulation of the sensor value output by the exhaust gas sensor while generating as few emissions as possible.

[0008] A method for reliably detecting manipulation of a sensor value of an exhaust gas sensor of an internal combustion engine for a vehicle is specified in patent claim 1.

[0009] The method can be used in an internal combustion engine having a control device for controlling the internal combustion engine, an intake tract with a throttle valve, a combustion chamber fluidly connected to the intake tract, and an exhaust tract fluidly connected to the combustion chamber with a catalyst. The exhaust gas sensor is arranged in the exhaust tract downstream of the catalyst.

[0010] According to the method, the internal combustion engine is initially operated in overrun cut-off mode. With the throttle valve closed, a first sensor value from the exhaust gas sensor is determined. The control device can initially determine a suspicion of manipulation by evaluating the first sensor value as a function of a first threshold value. Once the suspicion of manipulation has been determined, the control device verifies the suspicion of manipulation by measuring a second sensor value from the exhaust gas sensor when emissions from the internal combustion engine increase and evaluating the second sensor value as a function of a second threshold value.

[0011] According to the invention, a two-stage process is thus used. In the first stage, in which suspicion of manipulation is initially identified, no additional emissions are generated because the internal combustion engine is operated in overrun cut mode. Only if suspicion of manipulation arises in the first stage of the process is the suspicion of manipulation verified in the second stage of the process by increasing the internal combustion engine's emissions. Verification can be achieved, for example, by checking the gain of the exhaust gas sensor signal, for example, the NOx sensor signal, in the second stage of the process.

[0012] According to an advantageous embodiment of the method, in the first step of the method, a zero point of the exhaust gas sensor is calibrated after the internal combustion engine has been operated in overrun cutoff mode. The first sensor value is determined as a function of the calibration of the zero point of the exhaust gas sensor.

[0013] Due to aging and / or contamination, the measurement accuracy of the exhaust gas sensor may decrease over time. The proposed calibration allows a zero point of the exhaust gas sensor to be reset, which corresponds to a sensor value when essentially pollutant-free, particularly nitrogen dioxide-free, gases flow past the sensor. The subsequently determined sensor values ​​then refer to the newly learned zero point.

[0014] According to one possible embodiment of the method, to calibrate the zero point of the exhaust gas sensor, the throttle valve is first opened. A third sensor value is determined at a first point in time after the throttle valve is opened.

[0015] When the throttle valve opens, ambient pressure is established in the intake tract, increasing the air mass drawn in. Since the internal combustion engine is in overrun cut mode, in which no fuel is burned, the air drawn in through the intake tract essentially flows through the combustion chamber into the exhaust tract, as the internal combustion engine is dragged and moved by the vehicle's movement. At the same time, the influence of so-called blow-by gases, which can enter the intake tract through a crankcase ventilation line, remains minimal. Therefore, after the initial time after the throttle valve opens, primarily ambient air flows past the exhaust gas sensor.

[0016] According to a further development of the method, the third sensor value is determined by calculating an average of the exhaust gas sensor values ​​between the first point in time and a second point in time after the first point in time. Averaging can minimize errors in the zero point determination.

[0017] According to one embodiment of the method, in order to determine the first sensor value of the exhaust gas sensor in the first stage of the method, the throttle valve is closed again at a third time after the second time. A fourth sensor value is determined after a period of time following the closing of the throttle valve.

[0018] Closing the throttle valve increases the ratio of blow-by gases to fresh air in the engine's exhaust system. Thus, a high proportion of blow-by gases flows from the engine's crankcase through the crankcase ventilation into the intake system and from there, due to the engine's drag, into the exhaust system. Consequently, nitrogen emissions in the exhaust system rise again after the throttle valve closes. If the exhaust gas sensor has not been tampered with, the measured fourth sensor value should indicate the increase in nitrogen emissions.

[0019] According to an advantageous embodiment of the method, the fourth sensor value is calculated by calculating an average of the sensor values ​​of the exhaust gas sensor between a fourth point in time after the third point in time and a fifth point in time after the fourth point in time. Averaging minimizes errors in determining the fourth sensor value. According to a further embodiment of the method, the first sensor value is determined by calculating a difference between the fourth sensor value and the third sensor value. By evaluating the difference between the fourth sensor value and the third sensor value, a suspicion of possible sensor manipulation can be determined.

[0020] According to one embodiment of the method, the control device determines suspicion of manipulation if the control device determines that the first sensor value is below the first threshold. Since the first sensor value corresponds to the previously calculated difference between the fourth sensor value and the third sensor value, the control device determines suspicion of manipulation if the difference between the fourth sensor value and the third sensor value is smaller than the first threshold.

[0021] If the suspicion of manipulation is detected by the control device, the second stage of the procedure is carried out in which the suspicion of manipulation is verified.

[0022] According to one possible embodiment of the method, to verify the suspicion of manipulation, the overrun cut-off operation of the internal combustion engine is terminated at a sixth time after the fifth time. After the sixth time, the internal combustion engine is operated with a lean combustion air ratio. According to this embodiment of the method, the second sensor value is measured at a seventh time after the sixth time. The suspicion of manipulation is verified if the control device determines that the second sensor value is below the second threshold value.

[0023] At the seventh time point, the engine's raw emissions are measured because the catalyst is operating lean and saturated with oxygen. Therefore, no NOx conversion takes place in the catalyst. Therefore, if the sensor is fault-free, the second sensor signal must be above the second threshold at the seventh time point. However, if the second sensor value is below the second threshold, the control unit detects tampering with the exhaust gas sensor.

[0024] According to another embodiment of the method, an integral over a curve of the second sensor value is evaluated to verify the suspected manipulation. After a suspected manipulation has been identified in the first stage of the method, the overrun cut-off mode of the internal combustion engine is initially terminated at a sixth point in time after the fifth point in time to verify the suspected manipulation. After the sixth point in time, the internal combustion engine is operated with a lean combustion air ratio. The second sensor value is measured starting at a seventh point in time after the sixth point in time, and an integral over a curve of the second sensor value between the sixth point in time and the seventh point in time is determined. The suspected manipulation is verified if the control device determines that a value of the integral is below the second threshold value.

[0025] In this embodiment of the method, the exhaust gas sensor signal is not evaluated at a specific point in time, but rather an integral of the sensor signal is evaluated over a period of time. This makes the measurement less dependent on noise signals.

[0026] In the previously described variants of the process for verifying suspected manipulation, a nitrogen concentration in the exhaust tract is determined using the second sensor value. The removal of the catalyst after the end of overrun cutoff is deliberately delayed until the verification of the suspected manipulation is completed. The catalyst thus remains saturated with oxygen even after the engine's overrun cutoff operation has ended. Therefore, no nitrogen oxide conversion takes place in the catalyst, so that, with an unmanipulated sensor, the second sensor value or the integral over the NOx curve of the second sensor value must be above a threshold value.

[0027] According to another embodiment of the method, to verify the suspicion of manipulation, the overrun cut-off operation of the internal combustion engine is first terminated at a sixth time after the fifth time. However, the clearing of the catalyst is not delayed; instead, the catalyst is cleared by purging the catalyst for a period of time greater than the time required to consume the oxygen present in the catalyst. After the sixth time, the internal combustion engine is operated with a rich combustion air ratio. At a seventh time after the sixth time, the second sensor value is measured. The suspicion of manipulation is verified if the control device determines that the second sensor value is below the second threshold value.

[0028] While in the previously described embodiments, the nitrogen oxide concentration (NOx concentration) in the exhaust gas determined by the exhaust gas sensor is evaluated to verify suspected manipulation, in the last-mentioned embodiment of the method for verifying suspected manipulation, an ammonia concentration (NH3 concentration) in the exhaust gas is measured and evaluated. If the catalytic converter is operated in the rich operating range with the oxygen storage empty, ammonia is produced, whereby the ammonia concentration depends on the lambda, the temperature, and the aging state of the catalytic converter. The exhaust gas sensor, in particular a NOx exhaust gas sensor, is cross-sensitive to ammonia. If the catalytic converter is operated in an operating range in which ammonia is produced, the exhaust gas sensor must indicate this concentration in the exhaust gas stream.

[0029] An embodiment of an internal combustion engine for a vehicle with detection of tampering with a sensor value of an exhaust gas sensor is specified in claim 15. The internal combustion engine comprises a control device for controlling the internal combustion engine, an intake tract with a throttle valve, a combustion chamber fluidly connected to the intake tract, and an exhaust tract with a catalytic converter fluidly connected to the combustion chamber. The exhaust gas sensor is arranged in the exhaust tract downstream of the catalytic converter. The control device is designed to carry out the above-described method for detecting tampering with a sensor value of the exhaust gas sensor.

[0030] Such a fuel engine allows for the detection of suspected manipulation of an exhaust gas sensor reading in a first stage without the fuel engine generating additional emissions. Only when suspicion of manipulation of the exhaust gas sensor reading is confirmed does the control unit verify the suspected manipulation in a second stage by generating additional emissions.

[0031] The invention is explained in more detail below with reference to figures showing embodiments of the invention. They show:

[0032] Figure 1 is a schematic view of an internal combustion engine of a vehicle,

[0033] Figure 2 is a flowchart of a first stage of a method according to the invention for detecting a manipulation of a sensor value of an exhaust gas sensor of an internal combustion engine,

[0034] Figure 3 shows signal curves to illustrate the first stage of the method for detecting manipulation of a sensor value of an exhaust gas sensor of an internal combustion engine, Figure 4 shows a first embodiment of a second stage of the method for detecting manipulation of a sensor value of an exhaust gas sensor of an internal combustion engine,

[0035] Figure 5 shows signal curves to illustrate the first embodiment of the second stage of the method for detecting a manipulation of a sensor value of an exhaust gas sensor of an internal combustion engine,

[0036] Figure 6 shows a further embodiment of a second stage of a method for detecting a manipulation of a sensor value of an exhaust gas sensor of an internal combustion engine, and

[0037] Figure 7 Signal curves to illustrate the further embodiment of the second stage of the method for detecting a manipulation of a sensor value of an exhaust gas sensor of an internal combustion engine.

[0038] Figure 1 shows a schematic view of an internal combustion engine 1 for a vehicle, which has a functionality for detecting manipulation of a sensor value of an exhaust gas sensor 70, in particular a nitrogen oxide sensor (NOx sensor). The internal combustion engine 1 comprises a control device 10 for controlling the internal combustion engine and its components. The internal combustion engine 1 further has an intake tract 20, for example an intake manifold, in which a throttle valve 30 is arranged. Fluidically connected to the intake tract 20 is a combustion chamber 40 with cylinders in which pistons move. The pistons are at least partially arranged in a crankcase 41 and mechanically coupled therein to a crankshaft. Intake air can reach the combustion chamber 40 via the intake tract 20, where the intake air is mixed with fuel and burned.

[0039] The internal combustion engine 1 further comprises an exhaust tract 50, which is fluidly connected to the combustion chamber 40. A catalytic converter 60 is arranged in the exhaust tract 50, and the exhaust gas sensor 70, in particular a nitrogen oxide sensor, is arranged downstream of the catalytic converter 60. A lambda probe 80 can be arranged in the exhaust tract 50 between the combustion chamber 40 and the catalytic converter 60.

[0040] During operation of the internal combustion engine 1, exhaust gases from the cylinders of the combustion chamber 40 enter the crankcase 41. To prevent these so-called blow-by gases from being expelled untreated into the atmosphere, a ventilation device 90 with a ventilation line 91 is provided, which connects the crankcase 41 to the intake tract 20. The ventilation device 90 further comprises a ventilation valve 92, with which the ventilation of the crankcase 41 into the intake tract 20 can be controlled.

[0041] In the following, a method for detecting manipulation of a sensor value of the exhaust gas sensor 70, in particular a nitrogen oxide sensor, is explained in more detail with reference to Figures 2 to 6. In the following, Nox(t) refers to a nitrogen oxide concentration at time t, and NH3(t) refers to an ammonia concentration at time t. The individual method steps as well as the control of the necessary components of the internal combustion engine 1 are carried out by means of the control device 10. The

[0042] The method has a two-stage process. In the first stage of the process, the control device 10 first checks whether there is any suspicion of tampering. For this purpose, the internal combustion engine 1 is operated in overrun cut mode. In overrun cut mode, the fuel supply to the internal combustion engine is intentionally and temporarily interrupted when the engine is not intended to deliver power but is being dragged by the moving vehicle mass. Since the internal combustion engine is dragged and moved due to the vehicle movement, the air drawn in through the intake tract 20 passes through the combustion chamber 40 into the exhaust tract 50.

[0043] In this so-called overrun mode of the internal combustion engine, a first sensor value ANOx from the exhaust gas sensor 70 is determined with the throttle valve 30 closed. With the throttle valve closed, blow-by gases from the crankcase 41 pass through the crankcase ventilation line 91 into the intake tract 20 of the internal combustion engine. This increases the ratio of blow-by gases to fresh air. Due to the engine's dragging motion, the blow-by gases pass from the intake tract 20 through the combustion chamber 40 into the exhaust tract 50, where they flow past the exhaust gas sensor / NOx sensor 70.

[0044] In the case of a non-tampered exhaust gas sensor 70, the determined first sensor value ANOx should indicate an increase in the nitrogen oxide concentration. In the first stage of the method, a suspicion of tampering can thus be determined by the control device 10 evaluating the sensor value ANOx as a function of a threshold value C1. Suspicion of tampering is determined in particular if the evaluated sensor value ANOx is below the threshold value C1.

[0045] In the second stage of the method, the control device 10 then verifies the suspicion of manipulation. The second stage of the method is based on a gain check of the (NOx) exhaust gas sensor 70 with an increase in emissions from the internal combustion engine if a suspicion of manipulation was detected in the first stage of the method.

[0046] For this purpose, the engine's overrun cutoff mode is terminated and the engine is operated in normal mode. During normal mode, fuel and fresh air are supplied to the engine, and the fuel-air mixture is combusted in the combustion chamber 40. In the second stage of the process, in contrast to the first stage, in which no additional emissions were generated, the engine's emissions are thus increased. In the second stage of the process, a sensor value of NOx(t2') or NH3(t2') is measured when the engine's emissions increase.

[0047] As explained in more detail below, the sensor value measured in the second stage of the method can be a nitrogen oxide concentration NOx(t2') or an ammonia concentration NH3(t2'). By evaluating the measured sensor value NOx(t2') or NH3(t2') as a function of a second threshold value C2, a previously identified suspicion of manipulation can be verified by the control device 10. Manipulation is present in particular if the measured second sensor value NOx(t2') or NH3(t2') is below the second threshold value C2.

[0048] The individual steps of the two-stage process are examined in more detail below. Figure 2 illustrates the steps during the first stage of the process. The various points in time are shown in Figure 3.

[0049] After starting the method, in a step S11, at a time t0 (Figure 3), the control device 10 initially switches the internal combustion engine from normal operation to overrun cutoff mode and continues to operate there. Overrun cutoff mode describes an operating state of the internal combustion engine in which no fuel combustion occurs. Instead, the internal combustion engine is towed and moved due to the vehicle movement, so that the air drawn in through the intake tract 20 flows through the combustion chamber 40 into the exhaust tract 50.

[0050] In order to carry out the further method steps, the control device 110 further checks in method step S11 whether the speed of the vehicle is above a threshold value, for example above a threshold value of 50 km / h, and whether the engine speed is above a further threshold value, for example above 1800 revolutions per minute. Only if these conditions are met can it be ensured that the further method steps can be carried out before the vehicle comes to a standstill and are not aborted by the resumption of normal operation of the internal combustion engine, i.e., fuel supply with combustion of the fuel-air mixture, after the overrun fuel cut-off. If the exhaust gas sensor 70 is arranged in the exhaust tract 50 downstream of a gas particle filter, it is additionally checked in method step S11 whether the temperature of the gas particle filter is below a threshold value, for example below 550 °C, in order to avoid soot oxidation.In method step S12, at time t1 (Figure 3), the exhaust gas sensor is calibrated by determining a zero point of the exhaust gas sensor after the internal combustion engine has been operating in overrun cutoff mode (zero point adaptation). This allows a signal shift in the sensor signal of exhaust gas sensor 70 resulting from aging effects and / or contamination effects of the exhaust gas sensor to be compensated. The exhaust gas sensor 70 is thus calibrated with respect to its actual zero point in method step S12. The sensor value ANOx can thus be determined later in an error-compensated manner depending on the calibration of the zero point of exhaust gas sensor 70.

[0051] To calibrate the zero point of the exhaust gas sensor 70, in method step S12, the throttle valve 30 is opened at time t1 so that ambient pressure is established in the intake tract or intake manifold 20 and the intake air mass is increased. At time t1, or after a period t1 after the opening of the throttle valve 30 at time t0, it can be assumed that fresh air has reliably reached the exhaust gas sensor 70 due to the engine's drag motion and that the sensor signal of the exhaust gas sensor 70 has stabilized. Typical values ​​for a time period from the activation of overrun mode at time t0 to time t1 are approximately 3-5 seconds and depend on the volume of the exhaust system.

[0052] After the throttle valve 30 opens, a sensor value N0x(t2-t1) is determined after time t1. The sensor value N0x(t2-t1) is preferably calculated by calculating an average of the sensor values ​​of the exhaust gas sensor 70 between time t1 and a time t2 after time t1. During this time, mainly ambient air flows past the exhaust gas sensor 70. The sensor value N0x(t2-t1) corresponds to the actual zero point of the exhaust gas sensor 70, which is now learned by the control device 10. If the average of the newly learned zero point of the sensor signal of the exhaust gas sensor 70 is greater than the tolerance of the sensor, for example 10 ppm, the zero point adaptation is implausible and is not performed. Implausible adaptation can arise from the burning of oil or from the oxidation of soot. After calibrating the exhaust gas sensor 70, the throttle valve 30 is closed in method step S13 at a time t3 after the time t2.While the influence of blow-by gases on the exhaust gas sensor 70 during zero point calibration or zero point adaptation by the open throttle valve is minimal, the ratio of blow-by gases to fresh air is increased by closing the throttle valve 30 at time t3. As a result, a high proportion of blow-by gases flows from the crankcase 41 through the crankcase ventilation line 91 into the intake tract 20 and from there into the exhaust tract 50 due to the engine's drag motion.

[0053] At a time t4 after the throttle valve 30 closes and a gas runtime has elapsed, the exhaust gas sensor 70, if it has not been tampered with, must indicate elevated nitrogen concentrations. At or after the time t4 after the throttle valve 30 closes, the sensor value of the exhaust gas sensor 70 is therefore determined again by the control device 10 in a method step S14. According to a preferred embodiment of the method, this sensor value NOx (t4-t5) is determined in method step S14 by calculating an average of the sensor values ​​of the exhaust gas sensor 70 between the time t4 and a subsequent time t5.

[0054] In a method step S15, the sensor value ANOx is determined by calculating a difference between the sensor value NOx(t4-t5) and the sensor value N0x(t2-t1) determined by the control device 10 during the zero point adaptation or calibration of the exhaust gas sensor (ANOx = NOx(t5-t4) - N0x(t2-t1)).

[0055] If the exhaust gas sensor 70 has not been tampered with, the sensor value ANOx must be greater than a threshold value. Therefore, in method step S16, the control device 10 checks whether the sensor value ANOx is greater than a threshold value C1 (ANOx > C1?). If the control device 10 determines that the sensor value ANOx is greater than the threshold value C1, there is no suspicion that the sensor value, in particular the NOx sensor value, of the exhaust gas sensor 70 has been tampered with, and the method is terminated. If, however, the control device 10 determines that the sensor value ANOx is below the threshold value C1, the control device 10 determines a suspicion of tampering in method step S16.

[0056] Once the suspicion of manipulation has been established, the second stage of the process, in which the suspicion of manipulation is verified, is carried out in process step S17. After this, the process is terminated.

[0057] In the following, various embodiments for the second stage of the method for verifying suspected tampering are explained in more detail using Figures 4 to 6. The individual times for the method steps can be seen in Figure 3 and, in particular, Figure 5. The times t1', t2', and t3' shown in Figure 5 occur after time t6 in Figure 3.

[0058] The verification of the suspected manipulation, which was determined in method step S16 in the first stage of the method, takes place in the second stage of the method with an increase in emissions from the internal combustion engine, whereas the first stage of the method took place by operating the internal combustion engine in overrun cutoff mode without emissions. The verification of the suspected manipulation takes place if, in method step S16 of the first stage of the method, the control device 10 has determined that the condition ANOx = NOx (t5-t4) - NOx (t2-t1) < C1 is met. The verification of the suspected manipulation can then take place, for example, when the internal combustion engine reaches a resumption of idle speed at time t6 (Figure 3) after overrun cutoff.

[0059] According to the sequence for the second process stage shown in Figure 4, after the start of the second process stage, the overrun cutoff operation of internal combustion engine 1 is terminated at a time t1 ' (Figure 5) after time t5 or t6 (Figure 3). The internal combustion engine is thus operated again in normal mode with fuel supply and combustion of the fuel-air mixture. At idle, NOx emissions are still low, and the mass flow rate is also low.

[0060] In a method step S22, the catalyst clearing function, which normally occurs immediately after the end of overrun cutoff and in which the oxygen stored in the catalyst is expelled by briefly operating the engine in a rich mode, is deliberately and intentionally delayed. The clearing of the catalyst 60 is delayed until the verification of the suspected manipulation is completed at time t3' (Figure 5).

[0061] In a method step S23, a sensor value of a lambda probe 80 located upstream of the catalytic converter 60 and / or the lambda signal of the exhaust gas sensor 70 is measured at time tT. The lambda signal of the lambda probe 80 upstream of the catalytic converter 60 and / or the lambda signal of the exhaust gas sensor or NOx sensor 70 must be lean or greater than a threshold value C0.

[0062] Therefore, if the control device 10 determines in method step S24 that the sensor value LS of the lambda probe 80 and / or a lambda value LS of the exhaust gas sensor 70 is below a threshold value C0, the verification of the suspected manipulation is terminated. This means that if the lambda signal of the lambda probe 80 or the lambda signal of the exhaust gas sensor 70 indicates a non-lean operating state, the function of verifying the suspected manipulation is not executed because the internal combustion engine was in overrun cutoff mode for too short a time, and thus the catalytic converter 60 was not saturated with oxygen.

[0063] If it is determined in method step S24 that the sensor value or the lambda signal LS of the lambda probe 80 and / or the sensor value or lambda value LS of the exhaust gas sensor 70 is lean at time t1', the internal combustion engine 1 is operated with a lean air-fuel ratio after time tT in method step S25. For this purpose, a lambda setpoint value can be set to lean, for example to 1.06, at time t. In a subsequent method step S26, a sensor value NOx(t3') of the exhaust gas sensor 70 is measured at a time t3' after time t1'. Since the catalytic converter 60 is operated lean and is saturated with oxygen, the raw emissions of the internal combustion engine are measured at time t3'. No nitrogen oxide conversion takes place in the catalytic converter 60.Therefore, if the measured NOx(t3') sensor value of the exhaust gas sensor 70 does not exceed a certain threshold value, for example, 300 ppm, at time t3', it can be assumed that the exhaust gas sensor or NOx sensor 70 has been tampered with. The threshold value of, for example, 300 ppm depends on the respective engine, in particular the compression ratio, the ignition timing, an internal exhaust gas recirculation system, etc., and represents the raw emissions at idle.

[0064] In a method step S27, the control device 10 therefore checks whether the sensor value NOx(t3') at time t3' is above a threshold value C2. If the control device 10 determines that the sensor value NOx(t3') is above the threshold value C2, the suspicion of manipulation has not been confirmed, which is determined by the control device 10 in method step S28. If, however, the control device 10 determines in method step S27 that the sensor value NOx(t3') of the exhaust gas sensor 70 is below the threshold value C2, the control device 10 verifies the suspicion of manipulation in method step S29, thus concluding the second stage of the method for detecting manipulation of the sensor values ​​of the exhaust gas sensor 70.

[0065] To terminate the method, a lambda value of the exhaust gas sensor 70 is measured after time t2'. If the control device 10 determines that the lambda value has reached or fallen below the lambda target value, the verification of the suspected manipulation by the control device 10 is terminated after method step S28 or S29. Subsequently, the catalytic converter 60 is purged by briefly operating the internal combustion engine 1 rich in order to consume the oxygen stored in the catalytic converter. The internal combustion engine is subsequently operated in stoichiometric mode. In the example shown in Figure 5 for the second method stage, in which the suspected manipulation is verified, the sensor or lambda signal NOx(t3') of the exhaust gas sensor 70 reaches the lambda target value at time t3'.At time t3' at the latest, the verification of suspected manipulation or the gain check of exhaust gas sensor 70 is terminated, and the purging function of catalyst 60 is started. This occurs as after normal overrun cutoff operation by briefly operating the engine with a rich lambda in order to consume the stored oxygen in the catalyst as quickly as possible and thus enable nitrogen oxide conversion again. In the example shown, the purging function is performed with A = 0.9, but can also be performed with an even more enriched mixture. After the purging function, the lambda setpoint is adjusted back to stoichiometric operation.

[0066] The method advantageously also makes it possible to determine or at least isolate the cause of the manipulation. If the gradient of the sensor value of the exhaust gas sensor 70 has not exceeded the threshold value C1 at time t2', the control device 10 can determine that the sensor's protective tube has been tampered with, causing a delay in the exhaust gas reaching the exhaust gas sensor 70. If, however, the control device 10 determines that the threshold value C1 is not exceeded at all, this is an indication that the exhaust gas sensor 70 has been tampered with or is defective. In this case, the exhaust gas sensor 70 can be tampered with, for example, by a NOx emulator, which halves the values ​​of the exhaust gas sensor.

[0067] In order to minimize the impact on emissions, the function for verifying suspected manipulation can also be carried out on a time-controlled basis. The NOx emissions are calculated and integrated in mg / s. The process sequence is initially identical to the sequence outlined in Figure 4 up to process step S25. In process step S26, the NOx emissions are integrated from time t1' and evaluated at time t2'. A NOx emission can be calculated in mg / s based on the exhaust gas mass and the NOx concentration in ppm. From time t1', an integral of the nitrogen oxide emission is formed. In particular, the control device 10 determines an integral over a curve of the NOx emissions between time t1' and the subsequent time t2'. In process step S27, the control device checks whether the value of the integral at time t2' is greater than a threshold value C2.If control device 10 determines that the value of the integral is above threshold C2, no manipulation of the exhaust gas sensor is detected in method step S28. If, however, control device 10 determines that the value of the integral is below threshold C2, the suspected manipulation is verified by control device 10 in method step S29. A purge function for purging the catalytic converter 60 is started when the lambda sensor signal downstream of the catalytic converter has fallen below a specific value, for example, A = 1.2, or after a defined period of time or after a defined exhaust gas mass flow rate.

[0068] The process sequence described in Figures 4 and 5 for implementing the second stage of the method for detecting tampering with a sensor value from an exhaust gas or nitrogen oxide sensor leads to an increase in NOx emissions. An alternative method, if there is only a suspicion of tampering with the NOx sensor signal, is to flush the catalyst more intensively than necessary at time tT. This means that a purge function for the catalyst is performed even though the oxygen in the catalyst has already been depleted.

[0069] If the catalyst is operated in the rich operating range with the oxygen reservoir depleted, ammonia (NH3) is produced both after overrun cutoff and during normal engine operation. The NH3 concentration depends on the lambda, the temperature, and the aging state of the catalyst. The maximum concentration is at approximately A = 0.95 and decreases continuously to A = 1. No NH3 is produced during lean operation.

[0070] The NOx exhaust sensor has a cross-sensitivity to NH3, which is also used to calculate NH3 emissions. If the catalytic converter is operated in an operating range where NH3 is produced, the exhaust sensor 70 must also indicate this concentration. If the sensor value of the NOx sensor signal is higher than a certain threshold, for example, 50 ppm, it can be assumed that the exhaust sensor has not been tampered with.

[0071] A process variant for implementing the second stage of the process, in which the NH3 emission is evaluated to verify the suspicion of manipulation of the sensor values ​​of the exhaust gas sensor 70, is explained below using the process flow outlined in Figure 6 and the signal curves shown in Figure 7.

[0072] In method step S31, the overrun cutoff operation of the internal combustion engine is terminated at time t1' after time t5 or t6 (Figure 3). In contrast to the method sequence outlined in Figure 4, in which the clearing of the catalyst 60 is delayed, in the method outlined in Figure 6, the clearing of the catalyst 60 is intensified in method step S32. This can be achieved by clearing the catalyst 60 for a period of time that is longer than the period necessary to consume the oxygen present in the catalyst.

[0073] In method step S33, the internal combustion engine 1 is operated with a rich combustion air ratio after the time t1 '.

[0074] In method step S34, a sensor value NH3(t3') is measured at time t3' after time t1'. In contrast to the method outlined in Figure 4, in which the nitrogen oxide concentration NOx is measured, the cross-sensitivity of the exhaust gas sensor 70 to NH3 is utilized in the method sequence outlined in Figure 6, and thus the NH3 concentration in the exhaust gas is measured as the sensor value NH3(t3') at time t3'.

[0075] In method step S35, the control device 10 checks whether the measured sensor value NH3(t3'), i.e., the NH3 concentration at time t3', is less than a threshold value C2. If the control device 10 determines that the sensor value NH3(t3') is not below the threshold value C2 or is above the threshold value C2, the suspected manipulation is not verified by the control device 10 in method step S36. If, however, the control device 10 determines in method step S35 that the sensor value NH3(t3') is below the threshold value C2, the suspected manipulation is verified by the control device 10 in method step S37.

[0076] Similar to the first embodiment of the second stage of the method explained above, in which the NOx emission is evaluated using an integral to check for suspected tampering, an integral of the NH3 sensor value can also be evaluated in the method variant of Figures 6 and 7. As outlined in Figure 7 (curve G), in this method variant the integral of the NH3 emission is evaluated from time t1' to time t2'. If the control device 10 determines that the value of the integral of the NH3 emission is above a threshold value C2, the control device 10 does not detect any tampering with the exhaust gas sensor. If, on the other hand, the control device 10 determines that the value of the NH3 integral is below the threshold value C2, the control device 10 verifies the suspected tampering.

Claims

Patent claims 1. Method for detecting manipulation of a sensor value of an exhaust gas sensor of an internal combustion engine for a vehicle, wherein the internal combustion engine (1) comprises a control device (10) for controlling the internal combustion engine, an intake tract (20) with a throttle valve (30), a combustion chamber (40) fluid-connected to the intake tract, and an exhaust tract (50) fluid-connected to the combustion chamber with a catalyst (60), wherein the exhaust gas sensor (70) is arranged in the exhaust tract (50) downstream of the catalyst (60), wherein the method comprises the following steps: Operating the internal combustion engine (1) in overrun cut-off mode, determining a first sensor value (ANox) of the exhaust gas sensor (70) with the throttle valve (30) closed, Determining a suspicion of manipulation by the control unit (10) by evaluating the first sensor value (ANox) depending on a first threshold value (C1 ), Verification of the suspicion of manipulation by the control unit (10) by measuring a second sensor value (Nox(t2'), NH3(t2'), Nox(t3'), NH3(t3')) of the exhaust gas sensor (70) in the event of an increase in emissions from the internal combustion engine (1 ) and by evaluating the second sensor value (Nox(t2'), NH3(t2'), Nox(t3'), NH3(t3')) as a function of a second threshold value (C2) if the suspicion of manipulation has been previously detected.

2. The method of claim 1, comprising the following steps: Calibrating a zero point of the exhaust gas sensor (70) after operating the internal combustion engine (1) in the overrun cut-off mode, Determining the first sensor value (ANox) depending on the calibration of the zero point of the exhaust gas sensor (70).

3. The method of claim 2, wherein the following steps are performed to calibrate the zero point of the exhaust gas sensor (70): Opening the throttle valve (30), Determining a third sensor value (Nox(t2-t1 )) after a first time point (t1 ) after opening the throttle valve (30).

4. The method of claim 3, comprising the following step: Determining the third sensor value (Nox(t2-t1 )) by calculating an average of the sensor values ​​of the exhaust gas sensor (70) between the first time (t1 ) and a second time (t2) after the first time (t1 ).

5. Method according to any one of claims 1 to 4, wherein the following steps are carried out to determine the first sensor value (ANox) of the exhaust gas sensor (70): Closing of the throttle valve (30) at a third time point (t3) after the second time point (t2), Determining a fourth sensor value (Nox(t4-t5)) after a time period following the closing of the throttle valve (30).

6. The method of claim 5, comprising the following step: Determining the fourth sensor value (Nox(t4-t5)) by calculating an average of the sensor values ​​of the exhaust gas sensor (70) between a fourth time point (t4) after the third time point (t3) and a fifth time point (t5) after the fourth time point (t4).

7. Method according to one of claims 5 or 6, wherein the first sensor value (ANox) is determined by calculating a difference between the fourth sensor value (Nox(t4-t5)) and the third sensor value (Nox(t2-t1)).

8. Method according to any one of claims 1 to 7 wherein the suspicion of manipulation is detected by the control device (10) when the control device (10) determines that the first sensor value (ANox) is below the first threshold value (C1 ).

9. Method according to any one of claims 1 to 8, The following steps are carried out to verify the suspicion of manipulation: Termination of the thrust-cutting operation of the internal combustion engine (1 ) at a sixth time point (t1 ') after the fifth time point (t5), Operating the internal combustion engine (1 ) with a lean air-fuel ratio after the sixth time (t1 '), Measuring the second sensor value (Nox(t3')) at a seventh time point (t3') after the sixth time point (t1'), Verifying the suspicion of manipulation when the control unit (10) determines that the second sensor value (Nox(t3')) is below the second threshold (C2).

10. Method according to any one of claims 1 to 8, wherein the following steps are performed to verify the suspicion of manipulation: Termination of the thrust-cutting operation of the internal combustion engine (1 ) at a sixth time point (t1 ') after the fifth time point (t5), Operating the internal combustion engine (1 ) with a lean air-fuel ratio after the sixth time (t1 '), Measuring the second sensor value (Nox(t2')) from a seventh time point (t2') after the sixth time point (t1') and determining an integral over a course of the second sensor value between the sixth time point (t1') and the seventh time point (t2'), Verifying the suspicion of manipulation when the control unit (10) detects that a value of the integral is below the second threshold (C2).

11. Method according to any one of claims 1 to 10, wherein the second sensor value indicates a nitrogen concentration in the exhaust tract (50).

12. Method according to any one of claims 1 to 11 , wherein the removal of the catalyst (60) after the end of the thrust cut-off is delayed until the verification of the suspicion of tampering is completed.

13. Method according to any one of claims 1 to 8, wherein the following steps are performed to verify the suspicion of manipulation: Termination of the thrust-cutting operation of the internal combustion engine (1) at a sixth time point (t1 ') after the fifth time point (t5), Eliminating the catalyst (60) by rinsing the catalyst for a period of time longer than the period of time necessary to consume the oxygen present in the catalyst, Operating the internal combustion engine (1) with a rich air-fuel ratio after the sixth time (t1 '), Measuring the second sensor value (NH3(t3')) at a seventh time point (t3') after the sixth time point (t1'), Verifying the suspicion of manipulation when the control unit (10) determines that the second sensor value (NH3(t3')) is below the second threshold (C2).

14. Method according to one of claims 1 to 8 or 13, wherein the second sensor value indicates an ammonia concentration in the exhaust tract (50).

15. Internal combustion engine for a vehicle with detection of manipulation of a sensor value of an exhaust gas sensor, comprising: a control device (10) for controlling the internal combustion engine (1), an intake tract (20) with a throttle valve, (30) a combustion chamber (40) fluidly connected to the intake tract, an exhaust tract (50) fluidly connected to the combustion chamber (40) with a catalyst (60), wherein the exhaust gas sensor (70) is arranged in the exhaust tract (50) downstream of the catalyst (60), wherein the control device (10) is configured to perform a method for detecting a manipulation of a sensor value of the exhaust gas sensor (70) according to one of claims 1 to 14.