METHOD FOR OPERATING A FUEL TANK ASSOCIATION FOR A MOTOR VEHICLE AND CORRESPONDING FUEL TANK ASSOCIATION

Description

[0001] The invention relates to a method for operating a fuel tank assembly for a motor vehicle, wherein the fuel tank assembly comprises a fuel tank, a hydrocarbon filter, and a pump, and wherein the fuel tank is connected to the hydrocarbon filter via a tank shut-off valve, and the hydrocarbon filter is fluidically connected, on the one hand, via the pump to an external environment of the fuel tank assembly and, on the other hand, via a purge valve to an intake manifold of an internal combustion engine. The invention further relates to a fuel tank assembly for a motor vehicle.

[0002] For example, German patent application DE 10 2015 221 536 A1 is known from the prior art. This describes a device for diagnosing a fuel tank leak in a motor vehicle, wherein the fuel tank is connected to the intake manifold of an internal combustion engine via a vent line, wherein the internal combustion engine can be charged by means of a pressure generator, wherein the fuel tank can be pressurized with compressed air by means of pressure generated in the pressure generator, wherein a valve is arranged in the vent line through which the fuel tank can be pressurized with compressed air, wherein the valve can be closed after pressurization in such a way that the vent line is blocked, and wherein a pressure sensor for diagnosing the tank leak is arranged in the vent line or in the fuel tank.

[0003] Furthermore, the German patent application DE 10 2012 007 214 A1 describes a device for leak testing a fuel system for a motor vehicle, comprising a first storage reservoir and a second storage reservoir, each containing a storage medium for the irreversible binding of volatile fuel components. The first and second storage reservoirs are connected to a fuel tank via at least one tank vent line and to the intake manifold of an internal combustion engine of the motor vehicle via at least one intake line. The second storage reservoir has a smaller storage volume than the first and, during the leak test, is subjected to a flow of volatile fuel components from the fuel tank to the internal combustion engine via the tank vent line and the intake line. A throttling element is arranged upstream of the second storage reservoir in the direction of flow to reduce the flow cross-sectional area.Other fuel tank arrangements are known from US 2018 / 171938 A1 and US 2020 / 132023 A1.

[0004] The object of the invention is to propose a method for operating a fuel tank assembly for a motor vehicle which has advantages over known methods, in particular enabling a more reliable execution of a leak test of the fuel tank assembly with lower energy requirements.

[0005] According to the invention, this is achieved by a method for operating a fuel tank assembly for a motor vehicle with the features of claim 1. It is provided that, when the pressure in the fuel tank exceeds a pressure threshold, a first leakage test mode is performed, in which a shut-off valve arranged fluidically between the pump and the external environment is closed and the tank shut-off valve is opened. Subsequently, during a test period, the pressure in the fuel tank is measured by means of a pressure sensor arranged in the fuel tank. If a differential threshold is exceeded, a leak in the fuel tank assembly is detected by a pressure difference or a pressure drop over a specific period of time.

[0006] Advantageous embodiments with appropriate further developments of the invention are specified in the dependent claims.

[0007] The fuel tank assembly is preferably an integral part of the motor vehicle, but can of course also be separate. The fuel tank assembly comprises, as essential components, at least the fuel tank, the hydrocarbon filter, and the pump. Additionally, the tank shut-off valve and the purge valve are provided. The fuel tank serves as an intermediate storage unit for fuel, which is used, at least temporarily, to operate the motor vehicle's drive system. The drive system is used to propel the motor vehicle, i.e., to provide the drive torque directed toward propelling the motor vehicle. The drive torque is generated by the drive system using the drive unit, which is supplied with fuel drawn from the fuel tank.

[0008] The fuel tank is designed as a pressure tank. This means it is normally sealed by the tank shut-off valve, which is located between the fuel tank and the hydrocarbon filter. Depending on the ambient conditions of the fuel tank assembly, overpressure can occur within the tank, caused by fuel vaporizing, particularly through evaporation and / or vaporization. Overpressure refers to a pressure within the fuel tank that is higher than the pressure in the surrounding environment. When this description refers to the pressure within the fuel tank, it should be understood as absolute pressure.Preferably, however, the pressure is given as relative pressure with respect to a reference pressure, whereby the pressure in the external environment is preferably used as the reference pressure.

[0009] A fuel filler line is connected to the fuel tank. On the side facing away from the fuel tank, this filler line has an opening that can be closed with a fuel cap. Fuel can be added to the fuel tank via the filler line, for example, from a pump or similar device. To do this, the filler opening must be uncovered, and the fuel cap must be opened or moved relative to the filler opening. The fuel can then flow through the filler opening into the fuel filler line and from there into the fuel tank. If there is overpressure in the fuel tank when the fuel cap is opened, this pressure is released abruptly through the filler opening to the outside environment.

[0010] To prevent this, the fuel tank is preferably vented periodically, especially before opening the tank cap. For this purpose, the tank shut-off valve is opened, allowing the fluid in the fuel tank, which consists primarily of air and gaseous fuel or hydrocarbons, to flow towards the outside environment of the fuel tank assembly. This fluid flows through the hydrocarbon filter. The filter removes the fuel or hydrocarbons present in the fluid, preventing them from escaping into the environment. The hydrocarbon filter preferably has a filter element made of activated carbon and / or consists at least partially of activated carbon. The fuel or hydrocarbons filtered out of the fluid are temporarily stored in the hydrocarbon filter.The entry of fuel or hydrocarbons into the hydrocarbon filter is therefore reversible. The hydrocarbon filter can thus also be described as a hydrocarbon buffer.

[0011] Since the hydrocarbon filter has a limited capacity for holding fuel or hydrocarbons, it is necessary to purge it periodically. This is achieved using a vacuum created in the intake manifold of the internal combustion engine. During purging, the fuel tank shut-off valve is closed and the purge valve is open. The air pumped through the hydrocarbon filter then carries away the fuel or hydrocarbons temporarily stored within it. Downstream of the hydrocarbon filter, the fluid consists of air and fuel or hydrocarbons in varying proportions. Due to the closed fuel tank shut-off valve and the open purge valve, this fluid flows downstream of the hydrocarbon filter towards the intake stroke of the internal combustion engine and is combusted there.The hydrocarbon filter is rinsed during operation of the drive unit or internal combustion engine.

[0012] To reliably prevent fuel, especially gaseous fuel, from escaping into the environment, it is necessary to perform leak tests at least intermittently, for example, once or repeatedly, and especially periodically. For a fuel tank designed as a pressure tank, this can be done simply by checking whether overpressure builds up in the tank over time with the tank shut-off valve closed. If the overpressure, i.e., the pressure in the fuel tank relative to the ambient pressure, exceeds a certain threshold, it can be concluded that the fuel tank is leak-proof. However, if the overpressure does not exceed the pressure threshold, particularly within a certain time period after the tank shut-off valve is closed, a leak in the fuel tank is detected—purely optionally. In other words, the test preferably detects only the tightness of the tank, not a leak.However, this can also be done additionally. For example, it is assumed that the fuel tank is leaking if its tightness cannot be determined using the described procedure.

[0013] In addition to or as an alternative to the fuel tank itself, other areas of the fuel tank assembly are tested for leak tightness during the leak test, particularly an area located between the tank shut-off valve, the check valve, and the purge valve. This area specifically includes the hydrocarbon filter and / or the pump. To perform the leak test, the tank shut-off valve is opened, the purge valve is closed, and air is pumped towards the fuel tank. The current flowing through the pump is then measured. If the current exceeds a certain threshold, it can be concluded that the fuel tank assembly is sufficiently leak-tight, as the current flow is directly dependent on the pressure within the fuel tank.However, if the current does not reach the current threshold, a leak in the fuel tank assembly is detected.

[0014] The described procedure, however, either only allows for a leak test of the fuel tank or—in the case of comparing the current with the current threshold—is inaccurate. For this reason, it is now planned to first determine the pressure in the fuel tank and compare it with the pressure threshold. The pressure measurement in the fuel tank is carried out with the tank shut-off valve closed. If the pressure is greater than the pressure threshold, the first leak test mode is performed.

[0015] In the first leak test mode, the shut-off valve, which is located between the pump and the outside environment, is closed first. Then, the tank shut-off valve is opened. This creates a pressure equalization between the fuel tank and the area of ​​the fuel tank assembly located between the tank shut-off valve, the purge valve, and the shut-off valve. Specifically, the overpressure in the fuel tank is reduced towards this area. However, since the volume of the fuel tank is significantly larger than the volume of the area outside the fuel tank, only a slight pressure reduction occurs in the fuel tank, whereas the pressure in the area outside the fuel tank increases considerably.

[0016] During the test period, the pressure in the fuel tank is measured using the pressure sensor. The tank shut-off valve is kept open and the check valve closed throughout the entire test period. If the pressure in the fuel tank drops over the test period or the specified time interval, the pressure difference of this pressure drop is determined. Pressure drop is defined as a reduction in pressure during the test period or the specified time interval, which comprises at least a portion of the test period.

[0017] The pressure difference describes the extent of the pressure drop. For example, the pressure difference corresponds to the difference between an initial pressure present at the beginning of a specific time period and a subsequent pressure present, particularly at the end of that period. If the pressure difference exceeds the threshold value, i.e., if the pressure difference is greater than the threshold value, it can be assumed that fluid is escaping, or has already escaped, from the fuel tank assembly towards the outside environment. Accordingly, a leak in the fuel tank assembly is detected in this case.

[0018] The described procedure for the first leakage testing mode enables leakage testing of the entire fuel tank assembly, particularly the fuel tank itself and the area surrounding it, and not just the fuel tank. Simultaneously, high accuracy is achieved in the leakage test because it is performed using the pressure sensor and not based on the pump's current. Overall, this results in a fast and reliable leakage test that utilizes the overpressure present in the fuel tank. The first leakage testing mode is essentially based on the fact that the fuel tank is designed as a pressure tank.

[0019] A further development of the invention provides that, if the pressure present in the fuel tank is less than or equal to the pressure threshold, a second leakage test mode is carried out, in which the tank shut-off valve is opened and air from the outside environment is pumped towards the fuel tank until a pressure measured by the pressure sensor reaches a target pressure, and after reaching the target pressure, the shut-off valve is closed by the pressure, whereby after the closing of the shut-off valve, the pressure in the fuel tank is measured by the pressure sensor during the test period and, if the differential threshold is exceeded, the leakage of the fuel tank assembly is detected by the difference in pressure over the specified time period.

[0020] The second leak test mode is performed if the pressure in the fuel tank is insufficient for the first leak test mode. In this case, the second leak test mode is performed instead. This mode also involves opening the tank shut-off valve and closing the purge valve. Then, with the shut-off valve open, air from the outside environment is pumped into the fuel tank, increasing the pressure within the fuel tank assembly. Once the pressure measured in the fuel tank reaches the target pressure, the shut-off valve is closed. The tank shut-off valve remains open, and the purge valve remains closed. The test period then follows, during which the procedure described above is carried out.The described procedure enables leak testing of the fuel tank assembly even if the pressure present in the fuel tank is too low for the first leak testing operating mode.

[0021] A further development of the invention provides that, in the first leakage testing mode, after opening the tank shut-off valve, the pressure in the fuel tank is measured during a monitoring period. If no pressure reduction occurs, a fault in the fuel tank assembly is inferred. The monitoring period precedes the testing period. Preferably, the monitoring period immediately follows the opening of the tank shut-off valve. Thus, the pressure in the fuel tank decreases during the monitoring period. If this pressure reduction does not occur, a fault in the fuel tank assembly is inferred.

[0022] A fault in the fuel tank assembly could, for example, be a fault in the tank shut-off valve or a fault in the pressure sensor. If a pressure sensor has already been diagnosed and this diagnosis confirmed that the pressure sensor is functioning correctly, the fault is immediately attributed to the tank shut-off valve. Otherwise, a fault suspicion is triggered, encompassing a possible fault in both the tank shut-off valve and the pressure sensor. A subsequent diagnosis of the pressure sensor is then performed. If the fault suspicion exists and the diagnosis reveals that the pressure sensor is functioning correctly, the fault is attributed to the tank shut-off valve. Conversely, if the diagnosis reveals a fault in the pressure sensor, and a fault suspicion exists, the fault is attributed to the pressure sensor. Overall, this process enables a highly accurate diagnosis and leak test.

[0023] A further development of the invention provides that during the monitoring period, a pressure gradient over time is determined and compared with a gradient threshold. If the pressure falls below the gradient threshold, the gradient determines the pressure, and if the pressure falls below a minimum threshold, the system switches from the first leakage testing mode to the second leakage testing mode. During the monitoring period, in addition to or as an alternative to checking for the absence of pressure reduction, the pressure gradient over time is determined. The pressure gradient is calculated from the measured pressure. The gradient is determined continuously or periodically, in particular until it falls below the gradient threshold.

[0024] When the gradient falls below the threshold value, the current pressure is determined. In other words, the current pressure is determined as soon as the gradient falls below the threshold value. This pressure is then compared to the minimum pressure. If the pressure falls below the minimum pressure, it is concluded that the pressure in the fuel tank before the tank shut-off valve was opened was not high enough to perform the first leak test mode. Therefore, the system switches to the second leak test mode.

[0025] Switching to the second leak test operating mode means that the shut-off valve is opened and the pump is operated to pump air from the outside environment towards the fuel tank until the pressure measured in the fuel tank reaches the target pressure. The shut-off valve is closed when or immediately after the target pressure is reached. The test period then begins, during which the procedures described above are carried out.

[0026] A further development of the invention provides that the test period is initiated if the pressure is greater than or equal to the minimum pressure. Thus, if the pressure present when the gradient threshold is undershot is at least equal to the minimum pressure, the test period is initiated, preferably immediately, so that the test period directly follows the monitoring period. This ensures that the pressure present in the fuel tank assembly is still sufficient to carry out the leakage test.

[0027] A further development of the invention provides that the leakage is classified based on the pressure difference of the pressure drop over a specific time period. For example, several leakage classes are defined, each assigned a threshold value for the pressure difference. After determining the pressure difference, the leakage class with the highest threshold value, which is at least reached or exceeded by the pressure difference, is selected. Preferably, each leakage class is assigned an equivalent diameter of a leak. For example, a first leakage class exists for an equivalent diameter of 0.5 mm and a second leakage class for an equivalent diameter of 1.0 mm. Using the leakage classes, a sufficiently accurate assessment of the extent of the leakage is possible.Preferably, depending on the selected leakage class, an error is entered into a fault memory of the motor vehicle.

[0028] A further development of the invention provides that in the first leakage test operating mode and the second leakage test operating mode, the purge valve located between the hydrocarbon filter and the intake tract is closed. This prevents fluid from escaping from the fuel tank assembly towards the intake stroke and thereby impairing the leakage test.

[0029] A further development of the invention provides that a check valve of a pump assembly containing the pump is used as the shut-off valve. The pump assembly thus includes both the pump and the shut-off valve. The shut-off valve is designed as a check valve that allows flow only from the external environment into the fuel tank assembly, but not vice versa. The method can therefore be implemented with minimal effort. The check valve can, of course, be a purely mechanical check valve or an electrically controlled check valve that can be selectively opened and closed by means of an actuator.

[0030] A further development of the invention provides that, after the test period, the tank shut-off valve is closed and the check valve is opened, so that the fluid containing air and gaseous fuel, which is present between the tank shut-off valve and the hydrocarbon filter, flows through the hydrocarbon filter towards the outside environment. Thus, after completion of the leak test, the fuel tank is fluidically separated from the other area of ​​the fuel tank assembly by closing the tank shut-off valve. To relieve the overpressure present in this other area, the check valve is opened. Accordingly, the fluid present there flows towards the outside environment, namely through the hydrocarbon filter, so that any fuel contained in the fluid is separated and temporarily stored in it.

[0031] The tank shut-off valve closes before the check valve opens. Specifically, the check valve only opens once the tank shut-off valve is completely closed. This prevents a large amount of fluid from flowing from the fuel tank through the hydrocarbon filter, thus preventing a large amount of fuel from accumulating in it.

[0032] The invention further relates to a fuel tank arrangement for a motor vehicle, in particular for carrying out the method according to the descriptions in this document, comprising a fuel tank, a hydrocarbon filter and a pump, wherein the fuel tank is connected to the hydrocarbon filter via a tank shut-off valve and the hydrocarbon filter is connected to an external environment of the fuel tank arrangement via the pump and to an intake manifold of an internal combustion engine via a purge valve.

[0033] The fuel tank arrangement is designed and configured to perform a first leakage test mode when the pressure in the fuel tank exceeds a pressure threshold. In this mode, a shut-off valve located between the pump and the outside environment is closed, the tank shut-off valve is opened, and the pressure in the fuel tank is measured by a pressure sensor located in the fuel tank during a test period. If a differential threshold is exceeded, a pressure difference or a pressure drop over a specific period of time indicates a leak in the fuel tank arrangement.

[0034] The advantages of this fuel tank configuration and this procedure have already been mentioned. Both the fuel tank configuration and the method for operating it can be further developed as described in this document, and reference is made to these details.

[0035] The features and combinations of features described in the description, in particular those described in the following figure description and / or shown in the figures, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention. Thus, embodiments that are not explicitly shown or explained in the description and / or the figures, but which emerge from or can be derived from the explained embodiments, are also to be considered as encompassed by the invention.

[0036] The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing, without limiting the invention. The drawing shows: Figure 1 is a schematic representation of a fuel tank arrangement for a motor vehicle, and Figure 2 is a flowchart of a method for operating the fuel tank arrangement.

[0037] The Figure 1Figure 1 shows a schematic representation of a fuel tank assembly 1, which is preferably a component of a motor vehicle (not shown in detail here). The fuel tank assembly 1 comprises a fuel tank 2, a hydrocarbon filter 3, and a pump 4. The fuel tank 2 is fluidically connected to the hydrocarbon filter 3 via a tank shut-off valve 5. The hydrocarbon filter 3 is also fluidically connected, on the one hand, to an external environment 8 of the fuel tank assembly 1 via the pump 4, a shut-off valve 6, and an air filter 7, and on the other hand, to an intake manifold 10 of an internal combustion engine 11 via a purge valve 9. The internal combustion engine 11 forms part of a drive system 12 of the motor vehicle.

[0038] The tank shut-off valve 5, the shut-off valve 6, and the purge valve 9, or their respective actuators, are electrically connected to a control unit 13. This also applies to the pump 4. Furthermore, a pressure sensor 14, located in the fuel tank 2, is connected to the control unit 13 and serves to measure the pressure present in the fuel tank 2. A fuel filler line 15 is connected to the fuel tank 2. On its end facing away from the fuel tank 2, the fuel filler line 15 has a tank opening 16 which is closed by means of a tank cap 17.

[0039] The Figure 2Figure 1 shows a flowchart of a procedure for operating the fuel tank assembly 1. The procedure begins at a starting point 18. After starting point 18, a delay step 19 follows, during which a defined time interval is observed. Subsequently, in step 20, a decision is made as to whether only fuel tank 2 or the entire fuel tank assembly 1 should be subjected to a leak test. If the former is the case, a query 21 checks whether the pressure present in fuel tank 2 is greater than a pressure threshold value. If so, the process branches to step 22, in which a first leak test operating mode is initiated. Otherwise, the process branches to step 23, in which a second leak test operating mode is initiated.

[0040] During the first leak test mode, the shut-off valve 6 is closed and the tank shut-off valve 5 is opened. If a subsequent query 24 detects that the pressure in the fuel tank 2 is dropping, the system proceeds to query 25; otherwise, it proceeds to step 26. In step 26, a test for a defect in the tank shut-off valve 5 and the pressure sensor 14 is initiated.

[0041] First, a query (27) checks whether the pressure sensor 14 has already undergone a diagnostic check and whether this resulted in a positive result. If this is the case, thus ensuring that the pressure sensor 14 is functioning correctly, then in step 28 a fault in the tank shut-off valve 5 is detected. Otherwise, the process proceeds to step 29, in which a suspected fault in the tank shut-off valve 5 and a fault in the pressure sensor 14 are recorded.

[0042] A diagnostic check of pressure sensor 14 is then performed. Once this is complete, the result of this diagnostic check is verified in step 30. If the diagnostic check confirms that pressure sensor 14 is functioning correctly, the fault of the tank shut-off valve 5 is detected in step 28. Otherwise, a fault in pressure sensor 14 is detected in step 31.

[0043] During query 25, a pressure gradient over time is determined during a monitoring period and compared to a gradient threshold. If the pressure gradient falls below a gradient threshold, the pressure at which this threshold is crossed is determined. If the pressure is less than a minimum pressure, the process proceeds to step 32; otherwise, it proceeds to step 33. In step 32, a suspected defect in the shut-off valve 6 or a major leak is recorded.

[0044] The system then switches to the second leakage testing mode. In step 34, air from the external environment 8 is pumped towards fuel tank 2 using pump 4. The shut-off valve 6 is opened beforehand. During this pumping process, the pressure in fuel tank 2 is measured using pressure sensor 14. If the pressure reaches a target pressure after a certain period, which is checked in query 35, the shut-off valve 6 is closed and the system proceeds to step 33. Otherwise, step 36 detects a fault in the shut-off valve 6 or a major leak in the fuel tank assembly 1.

[0045] Step 33 initiates a test period. First, a delay step 37 is performed. Then, the pressure in fuel tank 2 is measured and recorded. If a pressure drop occurs, the pressure difference is determined in step 38. The test period is then ended in step 39, and the pressure or pressure difference is evaluated in a subsequent step 40.

[0046] In a subsequent query 41, the pressure difference is determined. If the pressure difference is less than a first difference threshold, the process proceeds to step 42. If the pressure difference is at least as large as the first difference threshold, the process proceeds to step 43. If, however, the pressure difference is at least as large as a second difference threshold that is greater than the first difference threshold, the process proceeds to step 44.

[0047] Step 42 is followed by step 45, in which it is determined that there is no leakage from the fuel tank assembly 1. Step 43 is followed by step 46, according to which a leakage from the fuel tank assembly 1 is detected with a first leakage class. Step 44 is followed by step 47, in which the leakage from the fuel tank assembly 1 is determined with a second leakage class. After each of steps 45, 46, and 47, the described procedure is terminated.

[0048] The described procedure enables a highly reliable leak test of the fuel tank assembly 1. It preferably utilizes the overpressure already present in the fuel tank 2, so that pump 4 is not operated in the first leak test mode. Pump 4 is only used in the second leak test mode. REFERENCE MARK LIST:

[0049] 1 Fuel tank assembly 2 Fuel tank 3 Hydrocarbon filter 4 Pump 5 Tank shut-off valve 6 Shut-off valve 7 Air filter 8 External environment 9 Purge valve 10 Intake manifold 11 Internal combustion engine 12 Drive unit 13 Control unit 14 Pressure sensor 15 Fuel filler pipe 16 Tank opening 17 Tank cap 18 Starting point 19 Delay step 20 Step 21 Query 22 Step 23 Step 24 Query 25 Query 26 Step 27 Query 28 Step 29 Step 30 Query 31 Step 32 Step 33 Step 34 Step 35 Query 36 Step 37 Delay step 38 Step 39 Step 40 Step 41 Query 42 Step 43 Step 44 Step 45 Step 46 Step 47

Claims

1. Method for operating a fuel tank arrangement (1) for a motor vehicle, wherein the fuel tank arrangement (1) has a fuel tank (2), a hydrocarbon filter (3) and a pump (4), and wherein the fuel tank (2) is fluidically connected via a tank shut-off valve (5) to the hydrocarbon filter (3) and the hydrocarbon filter (3) is fluidically connected, on the one hand, via the pump (4) to an external environment (8) of the fuel tank arrangement (1) and, on the other hand, via a purge valve (9) to an intake tract (10) of an internal combustion engine (11), characterised in that when the pressure present in the fuel tank (2) is greater than a pressure threshold value while the tank shut-off valve (5) is closed, a first leakage test mode is carried out, in which a shut-off valve (6) arranged in terms of flow between the pump (4) and the external environment (8) is closed and the tank shut-off valve (5) is opened, and subsequently, during a test period, the pressure in the fuel tank (2) is measured by means of a pressure sensor (14) arranged in the fuel tank (2), and, if a differential threshold value is exceeded by a pressure difference of a pressure drop of the pressure over a specific period of time, a leakage of the fuel tank arrangement (1) is detected.

2. Method according to claim 1, characterised in that, when the pressure in the fuel tank (2) is less than or equal to the pressure threshold value while the tank shut-off valve (5) is closed, a second leakage test mode is carried out, in which the tank shut-off valve (5) is opened and air is pumped by means of the pump (4) from the external environment (8) towards the fuel tank (2) until a pressure measured by means of the pressure sensor (14) reaches a target pressure and, after the target pressure has been reached by the pressure, the shut-off valve (6) is closed, wherein after the shut-off valve (6) has closed the pressure in the fuel tank (2) is being measured by means of the pressure sensor (14) during the test period and the leakage of the fuel tank arrangement (1) is detected, if the differential threshold value is exceeded by the difference in pressure over the specific period of time.

3. Method according to one of the preceding claims, characterised in that in the first leakage test mode, after the tank shut-off valve (5) has opened during a monitoring period preceding the test period, the pressure in the fuel tank (2) is measured and, in the absence of a pressure reduction, a fault in the fuel tank arrangement (1) is concluded.

4. Method according to claim 3, characterised in that during the monitoring period a gradient of the pressure over time is determined and compared with a gradient threshold value, wherein the pressure is determined when the gradient falls below the gradient threshold value and, when the pressure falls below a minimum pressure, a switch from the first leakage test mode to the second leakage test mode is carried out.

5. Method according to claim 4, characterised in that the test period is initiated if the pressure is greater than or equal to the minimum pressure.

6. Method according to one of the preceding claims, characterised in that a classification of the leakage is carried out based on the pressure difference of the pressure drop over the specific period of time.

7. A method according to any one of the claims 2 to 6, characterised in that in the first leakage test mode and the second leakage test mode the purge valve (9) present between the hydrocarbon filter (3) and the intake tract (10) is closed.

8. Method according to one of the preceding claims, characterised in that a check valve of a pump arrangement comprising the pump (4) is used as the shut-off valve (6).

9. Method according to one of the preceding claims, characterised in that, after the test period, the tank shut-off valve (5) is closed and the shut-off valve (6) is opened so that fluid comprising air and gaseous fuel present between the tank shut-off valve (5) and the hydrocarbon filter (3) flows through the hydrocarbon filter (3) towards the external environment.

10. Fuel tank arrangement (1) for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, with a fuel tank (2), a hydrocarbon filter (3) and a pump (4), wherein the fuel tank (2) is fluidically connected via a tank shut-off valve (5) to the hydrocarbon filter (3) and the hydrocarbon filter (3) is fluidically connected, on the one hand, via the pump (4) to an external environment (8) of the fuel tank arrangement (1) and, on the other hand, via a purge valve (9) to an intake tract (10) of an internal combustion engine (11), characterized in that the fuel tank arrangement (1) is provided and designed to carry out a first leakage test mode, when the pressure present in the fuel tank (2) is greater than a pressure threshold value while the tank shut-off valve (5) is closed, in which a shut-off valve (6) arranged in terms of flow between the pump (4) and the external environment (8) is closed and the tank shut-off valve (5) is opened, and subsequently, during a test period, the pressure in the fuel tank (2) is measured by means of a pressure sensor (14) arranged in the fuel tank (2), and, if a differential threshold value is exceeded by a pressure difference of a pressure drop of the pressure over a specific period of time, a leakage of the fuel tank arrangement (1) is detected.