Method and device for pressure sensor diagnosis in a fuel tank ventilation system of a motor vehicle with an internal combustion engine in operation

Abstract

The invention relates to a method for pressure sensor diagnosis in a fuel tank ventilation system of a motor vehicle operated by an internal combustion engine, wherein the fuel tank ventilation system has an activated carbon filter, a flushing line arranged between the activated carbon filter and an air intake tract of the motor vehicle, a fuel tank ventilation valve arranged in the flushing line, and a pressure sensor arranged in the flushing line, and wherein the method comprises the following steps: - measuring a prevailing pressure in the flushing line by means of the pressure sensor to determine a starting pressure, - classifying the starting pressure to one of a plurality of pressure ranges depending on the amplitude of the starting pressure, - performing a pressure sensor diagnosis using a diagnosis algorithm assigned to the pressure range in which the starting pressure lies.

Description

Technical Field

[0001] This invention relates to a method and apparatus for diagnosing pressure sensors in the fuel tank ventilation system of a motor vehicle operating an internal combustion engine. Background Technology

[0002] To limit pollutant emissions, modern motor vehicles powered by internal combustion engines are equipped with fuel tank ventilation systems. The purpose of these systems is to absorb and temporarily store fuel vapor formed through evaporation in the fuel tank, preventing it from escaping into the environment. An activated carbon filter is preferably used as the fuel vapor reservoir. However, this activated carbon filter has a limited storage capacity for fuel vapor. To ensure long-term use, the activated carbon filter must be regenerated. For this purpose, a controllable fuel tank ventilation valve is installed in the piping between the activated carbon filter and the intake manifold of the internal combustion engine. Opening this valve initiates regeneration. Consequently, due to the reduced pressure in the intake manifold, the fuel vapor stored in the activated carbon filter escapes into the intake manifold, restoring the filter's ability to absorb fuel vapor.

[0003] exist Figure 1 The image shows a fuel tank ventilation system. This fuel tank ventilation system specifically has the following components:

[0004] Activated carbon filter 3, hydrocarbons emitted from fuel tank 5 are trapped in activated carbon filter 3;

[0005] The flushing mass flow drawn from the activated carbon filter 3 is introduced into the intake manifold 19 through flushing lines 13, 14, 15, and 18;

[0006] The fuel tank ventilation valve 6 is located in the flushing pipe 13 between the activated carbon filter 3 and the intake manifold 19;

[0007] The engine controller (ECU) controls the fuel tank ventilation valve 6 using a pulse-width modulated (PWM) control signal.

[0008] The flushing line is arranged in a branch downstream of the fuel tank vent valve 6, which is a full-load ventilation path 14 and a low-pressure ventilation path 15. They are introduced into the intake manifold 19 at different inlet points, one of which is located between the air filter 20 and the turbocharger compressor 21, while the other inlet is located downstream of the throttle valve 22.

[0009] Venturi nozzles 9 are arranged in the full-load ventilation path 14, which generate the necessary pressure differential in the full-load ventilation path when the load pressure is higher than the ambient level and the engine is operating without throttling.

[0010] Pressure sensor 4 is arranged in flushing line 13 between activated carbon filter 3 and fuel tank vent valve 6 and is configured to perform line diagnostics on full-load ventilation path.

[0011] Fuel tank leak diagnostic component 2, which is configured to perform fuel tank leak diagnostics and is designed, for example, as an electric pump unit;

[0012] The injection system 23 injects the amount of fuel determined by the engine controller ECU into the cylinders of the internal combustion engine;

[0013] Lambda sensor 24 is used to determine the residual oxygen content in the exhaust gas of an internal combustion engine.

[0014] Check valve 7 in full-load ventilation path 14;

[0015] Check valve 8 in low-pressure ventilation path 15.

[0016] Engine controller ECU is especially used

[0017] Determine the target value of the flushing flow based on the current operating status of the internal combustion engine;

[0018] The intake manifold pressure is determined by the pressure sensor 17 in the intake duct;

[0019] The PWM value for controlling the fuel tank vent valve is determined based on the pressure drop between the ambient pressure and the pressure at the corresponding inlet of the pre-given flushing flow.

[0020] Determine the amount of fuel to be injected based on the current operating status of the internal combustion engine;

[0021] For the two inlet points mentioned above, determine the delay time for supplying combustion airflow by opening the fuel tank vent valve 6;

[0022] Fuel correction is calculated based on the hydrocarbon concentration of the flushing mass flow learned using lambda regulator bias.

[0023] According to country-specific laws, the proper functioning of the fuel tank ventilation system is required. Therefore, diagnostics of the fuel tank ventilation system are necessary. The system is considered functional when the mass flow from the activated carbon filter 3 to the intake manifold 19 of the internal combustion engine is sufficiently large to keep hydrocarbon emissions from the fuel tank ventilation system as low as possible. Within the scope of this diagnostics, the operability of the flush line 13 upstream of the pressure sensor 4, the full-load ventilation path 14, the low-pressure ventilation path 15, the high-pressure line 16 leading to the venturi nozzle 9, the flush line 18 downstream of the pressure sensor 4, the fuel tank ventilation valve 6, the check valve 7 located in the full-load ventilation path 14, the check valve 8 located in the low-pressure ventilation path 15, and the venturi nozzle 9 should be checked.

[0024] For this diagnostic, the output signal of pressure sensor 4 is used in the flushing line 13 arranged between activated carbon filter 3 and fuel tank vent valve 6. During the diagnostic process, to determine that the fuel tank venting system is functioning correctly, the output signal provided by pressure sensor 4 is evaluated during the appropriate operating state of fuel tank vent valve 6 when the fuel tank venting function is activated, or after a pressure change in the line is actively introduced by properly operating the fuel tank vent valve. Therefore, a properly functioning pressure sensor 4 is the basis for a correct diagnosis of the fuel tank venting system. If the pressure sensor 4 cannot be guaranteed to operate without failure before starting the internal combustion engine and during the fuel tank venting system diagnostic, inadequate results may result. Thus, if a pressure sensor malfunction is present, the following possibilities may be derived within the scope of interpreting the fuel tank venting line diagnostic results:

[0025] Identify defective flushing piping components;

[0026] The diagnosis was completed, and the result was "system function is normal".

[0027] Both of the above results may be incorrect and cannot accurately describe the actual system state.

[0028] To avoid such erroneous results, it is known that to determine whether the pressure sensor in the fuel tank ventilation system's flush line is functioning correctly, two checks are performed: one for freezing and the other for offset. In the case of freezing (hereinafter referred to as a pressure sensor stall error), the pressure sensor continuously outputs a constant signal. In the case of offset (hereinafter referred to as a pressure sensor offset fault), the pressure sensor indicates a value higher or lower than the actual pressure. Freezing of the pressure sensor is checked by waiting for the following states in the fuel tank ventilation system, in which the pressure sensor will output pressure changes in a fault-free state. To determine pressure sensor offset, the pressure signal in the flush line is compared with a signal from an additional ambient pressure sensor while the internal combustion engine is stationary.

[0029] The drawback of the above process is that it is impossible to distinguish between a flushing line fault and a pressure sensor fault in different pressure sensor areas, because the same pressure signal state or pressure change process may occur under fault conditions. Summary of the Invention

[0030] The objective of this invention is to describe a method and apparatus for performing pressure sensor diagnostics in the fuel tank ventilation system of a motor vehicle operating an internal combustion engine, wherein the aforementioned disadvantages are avoided.

[0031] This task is accomplished by a method having the features described in claim 1. Advantageous designs and extensions of the invention are described in the dependent claims.

[0032] According to the present invention, a method for performing pressure sensor diagnostics in a fuel tank ventilation system of a motor vehicle operating in an internal combustion engine includes the following steps: an activated carbon filter, a flushing line disposed between the activated carbon filter and the intake manifold of the motor vehicle, a fuel tank ventilation valve disposed in the flushing line, and a pressure sensor disposed in the flushing line.

[0033] - The starting pressure is determined by measuring the dominant pressure in the flushing line using the pressure sensor.

[0034] - The initial pressure is classified into one of several pressure ranges based on the magnitude of the initial pressure.

[0035] - Use a diagnostic algorithm assigned to the pressure range of the starting pressure to perform pressure sensor diagnostics.

[0036] A particular advantage of this invention is that the diagnostics according to the invention can be performed without actively interfering with the fuel tank venting function. This increases the fuel tank venting flushing rate during the driving cycle. Furthermore, the diagnostic execution logic ensures precise localization between the presence of a pressure sensor fault and a fault in a section of the flushing line or a component located in the flushing line. Another advantage is that competing diagnostic functions, such as lambda probe diagnostics or catalytic converter diagnostics, do not need to be interrupted to perform the described diagnostics. This eliminates the impact on driving performance and emissions caused by actively reducing the control curve of the fuel tank venting valve. Pressure sensor diagnostics can also be performed with high concentrations of flushing medium, as pressure sensor diagnostics can be completed even with low control levels of the fuel tank venting valve and the resulting changes in flushing line pressure in the nominal system.

[0037] According to one embodiment of the present invention, the initial pressure is classified into one of a plurality of ranges, the plurality of ranges including an overpressure range, an ambient pressure range, and an underpressure range.

[0038] According to one embodiment of the present invention, a diagnostic algorithm assigned to the overpressure range determines whether a pressure sensor offset fault or a pressure sensor stall fault exists.

[0039] According to one embodiment of the present invention, the diagnostic algorithm assigned to the overvoltage range includes the following steps:

[0040] - Suspected pressure sensor misalignment fault.

[0041] -Observe the minimum control applied to the fuel tank vent valve using a control value greater than a pre-defined first threshold.

[0042] - Check whether the pressure drop generated on the fuel tank vent valve by the minimum control is greater than a pre-defined second threshold.

[0043] - If the inspection indicates that the pressure drop generated on the fuel tank vent valve by the minimum operation is greater than a pre-defined second threshold, a pressure sensor misalignment fault is identified.

[0044] - If the check indicates that the pressure drop generated on the fuel tank vent valve by the minimum control is not greater than a pre-given second threshold, a pressure sensor stall fault is identified.

[0045] According to one embodiment of the invention, a diagnostic algorithm assigned to the undervoltage range determines whether the pressure sensor is operating without faults or has a pressure sensor offset fault or a pressure sensor stall fault.

[0046] According to one embodiment of the present invention, it is determined whether the area of ​​the flushing pipeline located upstream of the pressure sensor is blocked.

[0047] According to one embodiment of the present invention, the diagnostic algorithm assigned to the undervoltage range includes the following steps:

[0048] - Suspected pressure sensor misalignment fault.

[0049] - Check if the pressure downstream of the fuel tank vent valve is not equal to the initial pressure.

[0050] - During uninterrupted operation of the active fuel tank vent valve, the fuel tank vent volumetric flow rate is integrated until the volume present in the flushing line before the activated carbon filter is reached.

[0051] - Check if the absolute value of the difference between the flush line pressure and the downstream pressure of the fuel tank vent valve is less than a pre-defined third threshold.

[0052] - If this is the case, then a functioning pressure sensor has been identified.

[0053] - If this is not the case, then check whether the maximum absolute value of the difference between the flushing line pressure and the starting pressure is greater than a pre-defined fourth threshold.

[0054] - If this is not the case, then a pressure sensor stall fault is identified.

[0055] - If this is the case, then wait until the fuel tank vent valve closes for the minimum adjustment time.

[0056] - Check whether the absolute value of the difference between the flushing line pressure and the starting pressure is less than a pre-defined fifth threshold.

[0057] - If this is the case, a pressure sensor misalignment fault has been identified.

[0058] - If this is not the case, then a pressure sensor offset fault is identified.

[0059] According to one embodiment of the present invention, a diagnostic algorithm assigned to the environmental pressure range determines whether a pressure sensor stagnation fault exists.

[0060] According to one embodiment of the invention, when it is determined whether a pressure sensor stall failure exists, one or more events in the nominal system that cause pressure changes in the flushing line are evaluated.

[0061] According to one embodiment of the present invention, when it is determined whether a pressure sensor stall fault exists, it is checked whether the absolute value of the difference between the flushing line pressure and the starting pressure is greater than a pre-given sixth threshold.

[0062] According to one embodiment of the present invention, if the absolute value of the difference between the flushing line pressure and the starting pressure is found to be greater than a predetermined sixth threshold, then it is determined that there is no pressure sensor stall fault.

[0063] According to one embodiment of the present invention, if the absolute value of the difference between the flushing line pressure and the starting pressure is not greater than a pre-given sixth threshold, a pressure sensor stall fault is identified.

[0064] According to one embodiment, the device according to the invention has a control unit configured to control the method according to the invention. Attached Figure Description

[0065] The invention is explained below with reference to the accompanying drawings.

[0066] - Figure 1 A sketch of an apparatus for performing pressure sensor diagnostics in the fuel tank ventilation system of a motor vehicle operating an internal combustion engine is shown.

[0067] - Figure 2 It shows Figure 1 A partial sketch illustrating fault symptom A (the flushing line upstream of the pressure sensor is blocked).

[0068] - Figure 3 It shows Figure 1 A partial sketch illustrating symptom B (fuel tank vent valve stuck in the open position).

[0069] - Figure 4 It shows Figure 1A partial sketch illustrating fault symptom C (the flush line between the pressure sensor and the fuel tank vent valve is blocked / the fuel tank vent valve is stuck in the closed position / the flush line assembly downstream of the fuel tank vent valve is blocked or open to the environment).

[0070] - Figure 5 A chart illustrating the classification of flushing line pressures is shown.

[0071] - Figure 6 A sketch illustrating the division of pressure sensor diagnostics into diagnostic algorithms assigned to pressure ranges is shown.

[0072] - Figure 7 A flowchart of the diagnostic algorithm assigned to the pressure range W is shown.

[0073] - Figure 8 A flowchart of the diagnostic algorithm assigned to pressure range X is shown.

[0074] - Figure 9 A flowchart of the diagnostic algorithm assigned to the pressure range Y is shown.

[0075] - Figure 10 A flowchart illustrating other events that can be evaluated to identify pressure sensor stall failure is shown, as well as

[0076] - Figure 11 A flowchart of the diagnostic algorithm assigned to pressure region Z is shown. Detailed Implementation

[0077] In order to describe the present invention, firstly... Figure 1 Based on the equipment shown, the possible pressure signal states in the event of a flushing line failure are discussed.

[0078] exist Figure 1 In the fuel tank ventilation system shown, the following fault conditions or symptoms affecting the change process of the pressure sensor signal should be considered:

[0079] Flushing line 13 is upstream of fuel tank vent valve 6 by Figure 2 The area indicated by the letter "A" is blocked (symptom A):

[0080] If flush line 13 becomes blocked in region A between activated carbon filter 3 and fuel tank vent valve 6, pressure is generated at pressure sensor 4 after fuel tank vent valve 6 opens. This pressure corresponds to the pressure in the active flush line region downstream of fuel tank vent valve 6, i.e., the pressure in full-load ventilation path 15 or low-pressure ventilation path 14. If fuel tank vent valve 6 is closed during or after internal combustion engine operation, the pressure remains at the level that last dominated under the control of the active fuel tank vent valve. This described behavior makes it impossible to directly distinguish a pressure sensor offset fault from a blocked flush line upstream of the pressure sensor after internal combustion engine startup, when fuel tank vent valve 6 is always closed during internal combustion engine startup. Furthermore, in order to determine Figure 2 During a diagnostic process where region A is functioning normally, the pressure level reached may occasionally remain constant (the sensor may "stagnate"), leading to misinterpretation of the output pressure.

[0081] Fuel tank vent valve 6 is stuck in the open position, such as Figure 3 The letter "B" indicates symptom B:

[0082] When the fuel tank vent valve 6 is stuck in the open position and the internal combustion engine is activated, a pressure drop has already occurred between the pressure present at pressure sensor 4 and the ambient pressure in the non-operational state. If the pressure sensor signal deviates from the level of the pressure drop in the described fault condition (symptom B), it is impossible to accurately pinpoint between a flush line fault and a pressure sensor fault. This also applies to a pressure signal that is output at a constant pressure level of the aforementioned pressure drop in the current fault condition (symptom B) (sensor "stalled").

[0083] The flush line 18 upstream of the fuel tank vent valve 6 is blocked. The fuel tank vent valve 6 is stuck in the closed position. Components 7, 8, 9, 14, 15, and 16 of the flush line system downstream of the fuel tank vent valve 6 are blocked or open to the environment (symptom C), such as... Figure 4 The letter "C" is shown in the image.

[0084] If the mass flow rate through the fuel tank ventilation system cannot be achieved due to a system malfunction, no pressure drop compared to ambient pressure will occur at sensor 4 when the fuel tank ventilation valve 6 is actively operated. Furthermore, with a constant output pressure signal close to ambient pressure (sensor "stalled"), it is impossible to accurately pinpoint the location between a flushing line malfunction and a pressure sensor malfunction.

[0085] The potential overlay of diagnostic results based on the above system and pressure sensor conditions is illustrated in Table 1 below:

[0086]

[0087] Table 1

[0088] To resolve the superposition of described diagnostic results and allow for precise location of the actual faulty component in the fuel tank ventilation system, the diagnostic procedure for determining the proper functioning of pressure sensor 4 is described below. This involves classifying the pressure measured by pressure sensor 4 into different ranges W, X, Y, and Z directly after the engine control unit is switched on, such as... Figure 5 As shown.

[0089] exist Figure 5 In the diagram, the flushing line pressure is plotted at the top and time t is plotted on the right. Range W corresponds to the overpressure range, where the flushing line pressure is positioned above the ambient pressure range Z. Range X corresponds to the underpressure range, where the flushing line pressure is positioned below the ambient pressure range Z. An additional underpressure range Y is positioned between underpressure range X and ambient pressure range Z.

[0090] The following is based on Figure 6-11 The diagnostic principle is explained, and it is used to determine that the pressure sensor 4 is functioning normally.

[0091] Figure 6 The diagram illustrates how, after the engine controller is turned on, a pressure sensor signal is measured using pressure sensor 4 in the flushing line, and the measured flushing line pressure is categorized based on this signal. In this categorization, the pressure sensor signal corresponding to the measured flushing line pressure, hereinafter referred to as the starting pressure, is assigned to and stored within a relevant pressure range W, Z, Y, or X. Diagnostics then commence.

[0092] Figure 7 A flowchart is shown illustrating the diagnostic process when the initial pressure is within the overpressure range W. The initial pressure is considered overpressured when the pressure value measured by the pressure sensor, after subtracting the ambient pressure, exceeds a pre-defined adjustable threshold: p - p1 > sw. Here, p is the measured pressure value, p1 is the ambient pressure value, and sw is the pre-defined threshold.

[0093] If the initial value is within the overpressure range W, a pressure sensor offset fault is suspected in step W1 immediately after the engine controller is turned on. This is because even if the flush line upstream of pressure sensor 4 is blocked, a pressure signal greater than ambient pressure is impossible, as there is only underpressure downstream of fuel tank vent valve 6 when the internal combustion engine is activated. In a further diagnostic process, to differentiate between a pressure sensor offset fault and a pressure sensor stall fault, step W2 waits for minimal actuation of fuel tank vent valve 6 with the minimum required pressure drop. Here, the actuation value of the fuel tank vent valve and the pressure drop (i.e., the difference between ambient pressure and the dominant pressure downstream of the fuel tank vent valve (pressure in the low-pressure or high-pressure flush line)) are checked to see if they exceed a pre-defined threshold. In a further step W3, the pressure change (p0 - p > sw) that occurs during the active minimum actuation of the fuel tank vent valve is compared to the minimum threshold, where p corresponds to the measured pressure value and p0 corresponds to the initial value.

[0094] If the pressure change does not reach the minimum threshold, proceed to step W4, where a pressure sensor offset fault is recorded. Then proceed to step W6, at which point the method ends.

[0095] However, if the aforementioned pressure change reaches a minimum threshold, the process proceeds to step W5, where a pressure sensor malfunction is recorded. Then, the process proceeds to step W6, at which point the method terminates.

[0096] Figure 8 A flowchart is shown illustrating the diagnostic process when the initial pressure is within the underpressure range X. The initial pressure is considered underpressure when the difference between the ambient pressure and the pressure value measured by the pressure sensor exceeds a pre-defined adjustable threshold.

[0097] If the initial value is within the underpressure range X, a pressure sensor offset fault is suspected in step X1 immediately after the engine controller is turned on. Therefore, the absolute initial pressure must be less than the minimum pressure that would be generated when the fuel tank vent valve 6 is stuck in the open position. The goal of this diagnostic is to differentiate between a blockage in the flush line 13 upstream of pressure sensor 4 and a pressure sensor stall fault or a pressure sensor offset fault. To do this, the fuel tank vent volume flow rate during uninterrupted active fuel tank vent valve operation is first integrated until the volume present in the flush line 13 before the activated carbon filter 3 is reached. The pressure downstream of fuel tank vent valve 6 must not be equal to the initial pressure. The following relationship must be satisfied:

[0098] |Initial pressure - Pressure downstream of fuel tank vent valve| > Adjustable threshold.

[0099] In step X2, check if the relationship is satisfied. If the relationship is not satisfied, jump back to step X2. Conversely, if the relationship is satisfied, proceed to step X3.

[0100] In step X3, check whether the volumetric flow rate integral is greater than a pre-defined threshold:

[0101] Volumetric flow rate integral > threshold

[0102] If the relationship is not satisfied, jump back to step X3. Conversely, if the relationship is satisfied, proceed to step X4.

[0103] In step X4, it is checked whether the flushing line pressure measured by pressure sensor 4 after the aforementioned volumetric flow rate integration has approached the pressure downstream of fuel tank vent valve 6. The following query is performed for this purpose:

[0104] |Flush line pressure - Pressure downstream of fuel tank vent valve| < threshold

[0105] If the query indicates that the absolute value of the difference between the flush line pressure and the pressure downstream of the fuel tank vent valve is less than the mentioned adjustable threshold, then in step X5 it is inferred that a functioning pressure sensor 4 exists and in step X6 the diagnosis ends with a good inspection result.

[0106] If this is not the case, then the minimum flushing line pressure change is evaluated during the calculation of the volumetric flow rate integral described above. For this purpose, proceed to step X7, where it is checked whether the absolute value of the difference between the flushing line pressure and the initial pressure is greater than a threshold:

[0107] |Flush line pressure - initial pressure| > threshold.

[0108] If no minimum flushing line pressure change is given, a pressure sensor stall fault is inferred in step X8. The process proceeds to step X9, where it is identified that no pressure sensor offset fault exists. The method terminates in the subsequent step X10.

[0109] Conversely, if the aforementioned minimum flushing line pressure change is reached, a pressure sensor stall fault is identified in step X11 and the process proceeds to step X12.

[0110] In step X12, to identify the presence of a pressure sensor offset fault, the fuel tank vent valve 6 is waited for an adjustable minimum time to close. To do this, step X12 queries whether the time for which the fuel tank vent valve is closed is greater than a pre-defined threshold. If this is not the case, the process jumps back to step X12. Conversely, if this is the case, the process proceeds to step X13.

[0111] In step X13, the set flushing line pressure is checked to ensure it is the same as the initial pressure according to the following relationship:

[0112] |Flush line pressure - initial pressure| < adjustable threshold

[0113] If this is not the case, it is deduced in step X15 that there is no pressure sensor offset fault. Then proceed to step X10, and the method ends with step X10.

[0114] Conversely, if this is the case, a pressure sensor offset fault is identified in step X14. The process then proceeds to step X10, at which point the method concludes.

[0115] Figure 9 A flowchart is shown illustrating the diagnostic process when the initial pressure is within the underpressure range Y. If the initial pressure is within the underpressure range extending from the pressure generated when symptom B is present (ambient pressure - sensor value < predefined threshold) to the lower limit of the aforementioned ambient pressure range Z, a diagnostic sequence for pressure range Y is initiated. In principle, the diagnostic sequence for pressure range Y yields the same execution logic as the diagnostic sequence for pressure range X.

[0116] If the initial value is within the underpressure range Y, a pressure sensor offset fault is suspected in step Y1 immediately after the engine controller is turned on. In principle, the diagnostic sequence for pressure range Y yields the same execution logic as the diagnostic sequence for pressure range X.

[0117] Therefore, the fuel tank vent volumetric flow rate during uninterrupted active fuel tank vent valve operation is first integrated until the volume present in the flush line 13 before the activated carbon filter 3 is reached. The pressure downstream of the fuel tank vent valve 6 must not be equal to the initial pressure. The following relationship must be satisfied:

[0118] |Initial pressure - Pressure downstream of fuel tank vent valve| > Threshold.

[0119] In step Y2, check if the relationship is satisfied. If the relationship is not satisfied, return to step Y2. Conversely, if the relationship is satisfied, proceed to step Y3.

[0120] In step Y3, check whether the volumetric flow rate integral is greater than a pre-defined threshold:

[0121] Volumetric flow rate integral > threshold

[0122] If the relationship is not satisfied, jump back to step Y3. Conversely, if the relationship is satisfied, proceed to step Y4.

[0123] In step Y4, it is checked whether the flushing line pressure measured by pressure sensor 4 after the above-mentioned volumetric flow rate integration has approached the pressure downstream of fuel tank vent valve 6. The following query is performed for this purpose:

[0124] |Flush line pressure - Pressure downstream of fuel tank vent valve| < threshold

[0125] If the query indicates that the absolute value of the difference between the flush line pressure and the pressure downstream of the fuel tank vent valve is less than the mentioned threshold, then in step Y5 it is inferred that a functioning pressure sensor 4 exists and in step Y6 the diagnosis ends with a good inspection result.

[0126] If this is not the case, then the minimum flushing line pressure change is evaluated during the calculation of the volumetric flow rate integral described above. For this purpose, proceed to step Y7, where it is checked whether the absolute value of the difference between the flushing line pressure and the initial pressure is greater than a pre-defined threshold:

[0127] |Flush line pressure - initial pressure| > threshold.

[0128] If no minimum flushing line pressure change is given, a pressure sensor stall fault is inferred in step Y8. The process proceeds to step Y9, where it is identified that no pressure sensor offset fault exists. The method terminates in the subsequent step Y10.

[0129] Conversely, if the aforementioned minimum flush line pressure change is reached, step Y11 identifies no pressure sensor stall fault and proceeds to step Y12. In step Y12, to identify the presence of a pressure sensor offset fault, the fuel tank vent valve 6 is waited for an adjustable minimum time to close. For this purpose, step Y12 queries whether the time for closing the fuel tank vent valve is greater than a pre-defined threshold. If not, it jumps back to step Y12. Conversely, if it is, it proceeds to step Y13.

[0130] In step Y13, the set flushing line pressure is checked to ensure it is the same as the initial pressure according to the following relationship:

[0131] |Flush line pressure - initial pressure| < threshold

[0132] If this is not the case, it is deduced in step Y15 that there is no pressure sensor offset fault. Then proceed to step Y10, and the method ends with step Y10.

[0133] Conversely, if this is the case, a pressure sensor offset fault is identified in step Y14. The process then proceeds to step Y10, at which point the method concludes.

[0134] and Figure 8 The difference between the methods described in [the document] and [the document] lies in [the fact that] in [the context of] [the process]... Figure 9 The described method does not include pressure levels within pressure range Y that would lead to incorrect inputs about components or piping sections during flushing line diagnostics. This fact allows for the evaluation or waiting for additional events that generate pressure changes in the nominal system before a pressure sensor stall fault is ultimately identified. Examples of such events include... Figure 10 As shown in the image.

[0135] For example, if a speed gradient greater than a pre-defined threshold is identified within the query range, the process moves to a further query that checks whether the maximum absolute value of the difference between the flush line pressure and the starting pressure is greater than a pre-defined threshold, or if this is not the case. If this is the case, it is inferred that there is no pressure sensor stagnation fault. Conversely, if this is not the case, it is inferred that there is a pressure sensor stagnation fault.

[0136] For example, if a change in ambient pressure exceeding a predefined threshold is identified within the query range, the process moves to a further query that checks whether the maximum absolute value of the difference between the flush line pressure and the starting pressure exceeds the predefined threshold, or if this is not the case. If this is the case, it is inferred that there is no pressure sensor stagnation fault. Conversely, if this is not the case, it is inferred that there is a pressure sensor stagnation fault.

[0137] For example, if refueling is identified within the query range, the process moves to a further query that checks whether the maximum absolute value of the difference between the flush line pressure and the starting pressure is greater than a predefined threshold, or if this is not the case. If this is the case, it is inferred that there is no pressure sensor stagnation fault. Conversely, if this is not the case, it is inferred that there is a pressure sensor stagnation fault.

[0138] Figure 11 A flowchart is shown illustrating the diagnostic process when the initial pressure is within the ambient range Z. This ambient range Z is sandwiched between two adjustable pressure thresholds, one below the currently measured ambient pressure and the other above the currently measured ambient pressure.

[0139] If the initial pressure is within the ambient range Z, a good check result for pressure sensor offset diagnosis can be obtained directly after the engine controller is turned on. Further steps require checking whether the pressure sensor signal is frozen. This can be done by observing events that would cause pressure changes in the flush lines within the nominal system. Examples of such events are... Figure 11As shown in the diagram. These or other events can be used to check for pressure sensor stalling faults, either by choice or in any logical combination. This also applies to... Figure 11 The event shown.

[0140] Combination Figure 7-11 The threshold described is a calibration threshold, which must be adjustable to adapt diagnostic functions to the underlying system (pipe length, pipe diameter, etc.).

[0141] In one particular implementation of pressure sensor diagnostics, the current diagnostic status between flush line diagnostics and pressure sensor diagnostics is synchronized to achieve optimal coordination of diagnostic results and precise location of faulty system components.

[0142] The diagnostics described above, based on the accompanying drawings, can be performed without actively interfering with the fuel tank venting function. This has the advantage of increasing the fuel tank venting flushing rate during the driving cycle. Furthermore, the diagnostic execution logic ensures precise localization between the presence of a pressure sensor fault and a fault in a section of the flushing line or a component located in the flushing line. Another advantage is that competing diagnostic functions, such as lambda probe diagnostics or catalytic converter diagnostics, do not need to be interrupted to perform the described diagnostics. This eliminates the driving performance and emissions impacts caused by actively reducing the control curve of the fuel tank venting valve. Pressure sensor diagnostics can also be performed with high concentrations of flushing medium, as pressure sensor diagnostics can already be performed at low control levels of fuel tank venting valve 6 and the resulting changes in flushing line pressure in the nominal system.

Claims

1. A method for pressure sensor diagnostics in a fuel tank ventilation system of a motor vehicle operating an internal combustion engine, wherein the fuel tank ventilation system comprises an activated carbon filter, a flushing conduit disposed between the activated carbon filter and the intake manifold of the motor vehicle, a fuel tank ventilation valve disposed in the flushing conduit, and a pressure sensor disposed in the flushing conduit, characterized in that, The method includes the following steps: -The pressure sensor (4) is used to measure the dominant pressure in the flushing line to determine the starting pressure. - The initial pressure is classified into one of several pressure ranges (W; Z; Y; X) based on the magnitude of the initial pressure, wherein the initial pressure is classified into one of several ranges, including an overpressure range (W), an ambient pressure range (Z), and an underpressure range (X; Y). - Perform pressure sensor diagnostics using a diagnostic algorithm assigned to the pressure range in which the starting pressure falls. The diagnostic algorithm assigned to the overpressure range (W) includes the following steps: - Suspected pressure sensor misalignment fault. -Observe the minimum control applied to the fuel tank vent valve (6) using a control value greater than a pre-defined first threshold. - Check whether the pressure drop generated on the fuel tank vent valve (6) by the minimum control is greater than a pre-given second threshold. - If the inspection indicates that the pressure drop generated on the fuel tank vent valve by the minimum control is greater than the pre-defined second threshold, a pressure sensor misalignment fault is identified. - If the check indicates that the pressure drop generated on the fuel tank vent valve by the minimum control is not greater than the pre-given second threshold, then a pressure sensor stall fault is identified.

2. The method according to claim 1, characterized in that, The diagnostic algorithm assigned to the undervoltage range (X; Y) determines whether the pressure sensor (4) is working without fault or has a pressure sensor offset fault or a pressure sensor stall fault.

3. The method according to claim 2, characterized in that, Determine whether the area (13) of the flushing line upstream of the pressure sensor (4) is blocked.

4. The method according to claim 2 or 3, characterized in that, The diagnostic algorithm assigned to the undervoltage range (X) includes the following steps: - Suspected pressure sensor misalignment fault. - Check whether the pressure downstream of the fuel tank vent valve (6) is not equal to the starting pressure, and if the pressure downstream of the fuel tank vent valve (6) is not equal to the starting pressure, then - During uninterrupted operation of the active fuel tank vent valve, the fuel tank vent volumetric flow rate is integrated until the volume present in the flushing line before the activated carbon filter (3) is reached. - Check whether the absolute value of the difference between the flush line pressure and the pressure downstream of the fuel tank vent valve is less than a pre-defined third threshold. - If this is the case, then a functioning pressure sensor has been identified. - If this is not the case, then check whether the maximum absolute value of the difference between the flushing line pressure and the starting pressure is greater than a pre-defined fourth threshold. - If this is not the case, then a pressure sensor stall fault is identified. - If this is the case, then wait until the fuel tank vent valve closes for the minimum adjustment time. - Check whether the absolute value of the difference between the flushing line pressure and the starting pressure is less than a pre-defined fifth threshold. - If this is the case, a pressure sensor misalignment fault has been identified. - If this is not the case, then a pressure sensor offset fault is identified.

5. The method according to claim 1, characterized in that, The diagnostic algorithm assigned to the ambient pressure range (Z) determines whether a pressure sensor stall fault exists.

6. The method according to claim 5, characterized in that, When determining whether a pressure sensor stall failure exists, evaluate one or more events in the nominal system that cause pressure changes in the flushing line.

7. The method according to claim 5 or 6, characterized in that, When it is determined whether there is a pressure sensor stall fault, check whether the absolute value of the difference between the flushing line pressure and the starting pressure is greater than a pre-given sixth threshold.

8. The method according to claim 7, characterized in that, If the absolute value of the difference between the flushing line pressure and the starting pressure is found to be greater than the pre-defined sixth threshold, then a pressure sensor stall fault is identified.

9. The method according to claim 7, characterized in that, If the absolute value of the difference between the flushing line pressure and the starting pressure is not greater than the pre-defined sixth threshold, a pressure sensor stall fault is identified.

10. An apparatus for performing the method according to any one of the preceding claims, characterized in that, The device has a control unit (ECU) configured to control the method according to any one of the preceding claims.

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