阅读说明：本技术 检测车辆液体储箱的至少一个内部增强元件的状态的方法 (Method for detecting the condition of at least one internal reinforcing element of a liquid tank of a vehicle ) 是由 保罗·丹尼尔·鲁瑟 大卫·希尔 安托万·肖锡南 于 2019-08-06 设计创作，主要内容包括：所述方法检测车辆的液体储箱(2)的至少一个内部增强元件(1)的状态。所述至少一个内部增强元件(1)连接所述液体储箱(2)的至少两个相对的壁(3,4),该液体储箱(2)包含至少可由液位传感器(5)测量的液体(6)的初始量。所述方法包括以下步骤：a)根据所述液位传感器(5)测量的液体(6)的初始量和压强传感器(7)测量的所述液体储箱的初始内部压强,确定第一阈值；b)监控液位传感器的输出和压强传感器的输出；c)如果所述压强传感器的输出高于所述第一阈值,根据所述压强传感器的输出、所述液位传感器的初始输出和所述初始内部压强输出确定第二阈值和第三阈值；d)将所述液位传感器的输出与所述第二和第三阈值进行比较；e)-如果所述液位传感器的输出高于所述第二阈值,发送表示至少一个连接所述相对的壁的内部增强元件被损坏或可能被损坏的第一预定信号,和/或-如果所述液位传感器的输出低于第三阈值,发送表示至少一个连接所述相对的壁的内部增强元件被损坏或可能被损坏的第二预定信号。(The method detects the condition of at least one internal reinforcing element (1) of a liquid tank (2) of a vehicle. Said at least one internal reinforcing element (1) connects at least two opposite walls (3,4) of said liquid tank (2), which liquid tank (2) contains at least an initial quantity of liquid (6) measurable by a level sensor (5). The method comprises the following steps: a) determining a first threshold value as a function of an initial quantity of liquid (6) measured by the level sensor (5) and an initial internal pressure of the liquid tank measured by a pressure sensor (7); b) monitoring the output of the liquid level sensor and the output of the pressure sensor; c) determining a second threshold value and a third threshold value based on the output of the pressure sensor, the initial output of the level sensor, and the initial internal pressure output if the output of the pressure sensor is above the first threshold value; d) comparing the output of the level sensor to the second and third thresholds; e) -if the output of said level sensor is higher than said second threshold value, sending a first predetermined signal indicating that at least one internal reinforcing element connected to said opposite wall is damaged or possibly damaged, and/or-if the output of said level sensor is lower than a third threshold value, sending a second predetermined signal indicating that at least one internal reinforcing element connected to said opposite wall is damaged or possibly damaged.)

1. Method of detecting the condition of at least one internal reinforcing element (1) of a liquid tank (2) of a vehicle, which connects at least two opposite walls (3,4) of said liquid tank, which comprises at least an initial quantity of liquid (6) measurable by a level sensor (5), said method comprising the steps of:

a) determining a first threshold value based on an initial quantity of liquid measured by the level sensor and an initial internal pressure of the liquid tank measured by a pressure sensor (7);

b) monitoring the output of the liquid level sensor and the output of the pressure sensor;

c) determining a second pressure threshold and a third pressure threshold based on the output of the pressure sensor, the initial output of the level sensor, and the initial output of the internal pressure sensor if the output of the pressure sensor is above the first pressure threshold;

d) comparing the output of the level sensor to the second and third level thresholds;

e) -if the output of said level sensor is higher than said second level threshold, sending a first predetermined signal indicating that at least one internal reinforcing element connecting said opposite walls is damaged or possibly damaged, and/or;

-sending a second predetermined signal indicating that at least one internal reinforcing element connecting said opposite walls is damaged or possibly damaged, if the output of said level sensor is lower than a third level threshold.

2. Method according to claim 1, wherein during said step c) the determination of said second and third threshold values is also dependent on the temperature of the liquid in said tank (2).

3. The method of any of the preceding claims, comprising the steps of: -incrementing a counter (9) if the output of the level sensor (5) is between the second threshold and the third threshold.

4. Method according to claim 3, wherein at least the steps a), b) and c) of claim 1 are carried out again, preferably with a plurality of first thresholds, if the counter (9) is lower than a fourth predetermined threshold.

5. Method according to claim 4, wherein, if said counter (9) is higher than said fourth threshold value, said method comprises the step of sending a signal indicating that at least one internal reinforcing element (1) connecting said opposite walls (3,4) is not damaged.

6. Method according to any of the preceding claims, wherein the monitoring step b) depends only on an increase or decrease of the pressure inside the tank (2) caused by an increase or decrease of the temperature outside the tank.

7. Method according to any of claims 1 to 5, wherein the monitoring step b) comprises the step of sending an instruction to means to raise or lower the pressure in the tank (2), said means preferably being responsive to a signal from a vehicle collision sensor.

8. Method according to claim 7, wherein said step of sending an instruction to means to raise or lower the pressure in said tank (2) is carried out by:

-using an external pump, which does not form part of the vehicle;

-using a device forming part of the vehicle, such as a pump or a heater; and/or

-controlling the pressure inside the relief tank using a valve of said tank.

9. A method according to any preceding claim, wherein the method is carried out when the vehicle is de-energised, preferably only when the vehicle is de-energised.

10. A method as claimed in any preceding claim, wherein the method is carried out while the vehicle is in service mode.

11. The method according to any one of the preceding claims, wherein a leak detection step is carried out before step a).

12. Method of detecting the condition of at least one internal reinforcing element (1) of a liquid tank (2) of a vehicle, which connects at least two opposite walls (3,4) of the liquid tank, comprising the steps of:

-performing a leak detection step, and

-sending a signal indicating that at least one internal reinforcing element (1) connecting at least two opposite walls (3,4) of the liquid tank may be damaged if the result of the leak detection step is of a predetermined type.

13. A vehicular liquid tank (2) comprising control means (8) arranged to implement the method according to any one of the preceding claims.

14. A vehicle comprising a liquid tank (2) and a control device (8) arranged to implement the method according to any one of claims 1 to 12.

15. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method according to any one of claims 1 to 12.

Technical Field

The present invention relates to a method for testing a liquid tank, for example a fuel tank of a vehicle.

Background

Fuel tanks often require internal reinforcing (strengthening) structures, such as weld posts, or external structures, such as weld patches. During an accident that is not severe enough to require significant tank replacement, the internal reinforcing structure may be damaged, so that if not discovered, this may cause noise or, in the worst case, after recycling, the integrity of the tank may be impaired. We do not know any way to detect such damage without disassembling the tank and inspecting the inside. Disassembling the tank is undesirable because it is time consuming, costly and complicated. However, depending on the nature of the damage, detecting damage to the internal reinforcing elements in the tank can protect the driver from the risk of future leaks, liquid residues or ventilation losses and bursts.

Disclosure of Invention

The present invention aims to provide a test method that addresses these drawbacks.

The invention provides a method of detecting the condition of at least one internal reinforcing element of a liquid tank of a vehicle, said at least one internal reinforcing element connecting at least two opposite walls of the liquid tank containing at least an initial quantity of liquid measurable by a level sensor, said method comprising the steps of:

a) determining a first threshold value based on an initial amount of liquid measured by the liquid level sensor and an initial internal pressure of the liquid tank measured by the pressure sensor;

b) monitoring the output of the liquid level sensor and the output of the pressure sensor;

c) determining a second pressure threshold and a third pressure threshold based on the output of the pressure sensor, the initial output of the level sensor, and the initial output of the internal pressure sensor if the output of the pressure sensor is above the first pressure threshold;

d) comparing the output of the level sensor to second and third level thresholds;

e) -if the output of the level sensor is higher than a second level threshold, sending a first predetermined signal indicating that at least one internal reinforcing element connecting the opposite walls is damaged or possibly damaged, and/or;

-sending a second predetermined signal indicating that at least one internal reinforcing element connecting the opposite walls is damaged or possibly damaged, if the output of the level sensor is lower than a third level threshold.

The method helps to determine the condition of the tank, more specifically of the internal reinforcing element. For example, it may indicate that at least one internal reinforcing element is suspected of breaking. The method relies on pressure evolution and volume evolution, which information is captured by sensors commonly available on the system. Accordingly, it is not costly.

The two opposing walls are preferably a bottom wall and a top wall. Opposite walls may be provided, being the two side walls of the tank.

The initial amount of liquid, which can be measured by the liquid level sensor, ensures that at least a minimum detectable amount of liquid is present in the tank before the method is carried out, so that the method can be carried out. For example, if the tank does not contain any liquid, the method may be ineffective.

The initial internal pressure of the liquid tank is preferably equal to atmospheric pressure. Since the initial liquid amount is measured at atmospheric pressure, the tank is not initially deformed, which improves the accuracy of the method.

The first threshold may be higher, lower or equal to atmospheric pressure. For example, the first threshold may be +50mbar higher or-50 mbar lower than the initial pressure. Preferably, the first threshold is +100mbar higher or-100 mbar lower than the initial pressure. More preferably, the first threshold is +200mbar higher or-200 mbar lower than the initial pressure.

"initial" refers to the first measurement, whenever a measurement is taken. For example, the measurement may be performed before the vehicle is powered on or before an accident or collision.

The signal may be, for example, an audio or visual signal.

Thereby, the signal alerts the operator or driver by, for example, indicating that the at least one internal reinforcing element is damaged or is likely to be damaged. The operator or driver may then take action to determine and/or repair the fault. For example, the visual signal may be a message or light displayed on the dashboard. In an alternative embodiment, the settable signal does not exclusively indicate that at least one internal reinforcing element is damaged or is likely to be damaged, but merely indicates that there is a fault requiring repair.

The monitoring of the output of the level sensor and the output of the pressure sensor may be continuous or timed monitoring.

The evaluation of the second and third threshold values may be performed by mapping. A table relating the initial internal pressure and the initial liquid amount to a first threshold value may be provided. Thereby, the level of the liquid in the tank may be compared with a desired level as a function of the pressure in the tank.

It may be arranged to send a predetermined signal indicating that at least one internal reinforcing element is not damaged if neither of the conditions of step e) is met.

The liquid tank may for example be a tank for fuel, urea or water.

Preferably, during step c), the second and third thresholds are also determined as a function of the temperature of the liquid in the tank.

Thereby, the evaluation of the second threshold or the third threshold is more accurate, since the temperature may affect the liquid level in the tank. In fact, the temperature rise causes the liquid to expand, i.e. causes thermal expansion of the liquid. Thus, for example, a temperature increase results in an expected increase in the liquid level in the tank.

Advantageously, the method comprises the step of incrementing a counter if the output of the level sensor is between the second threshold and a third threshold.

Preferably, if the counter is below a fourth predetermined threshold, at least steps a), b) and c) of the method are carried out again, preferably at a plurality of first thresholds.

This increases the significance of the method.

Advantageously, if the counter is higher than the fourth threshold, the method comprises a step of sending a signal indicating that at least one internal reinforcing element connecting the opposite walls is not damaged.

Thereby, the method is forcibly repeated to ensure that the method has been run a statistically sufficient number of times to ensure that conditions are met to verify that at least one internal strength component has not been damaged. This is particularly relevant when the method relies on natural pressure variations within the tank.

Preferably, the monitoring step b) relies on an increase or decrease in pressure within the tank caused only by an increase or decrease in temperature outside the tank.

Thereby, the method relies on temperature changes caused by the environment of the tank, possibly natural changes, which makes the method unnecessary for additional elements. In this case, the first threshold value is preferably +100mbar higher or-100 mbar lower than the initial pressure.

Preferably, the monitoring step b) comprises the step of sending an instruction to a device to raise or lower the pressure in said tank, said device preferably being responsive to a signal from a vehicle collision sensor.

Here, the pressure variations are controlled, not only as a result of (or more precisely as a result of) the variations from the environment. Thereby, the implementation of the method is more controlled, since the pressure target, i.e. the first threshold value, will be reached on command. Accordingly, the method can be triggered whenever desired or needed. This method is shorter than the method based on ambient pressure evolution (or more precisely, environmentally driven). In this embodiment (in which the step of sending an instruction to a device to raise or lower the pressure in said tank is carried out in response to a signal from a vehicle crash sensor), said method is enforced when an event monitored by an external sensor (e.g. a crash sensor) suspects that an impact has occurred. The sensor is for example an accelerometer for an airbag or dedicated.

More preferably, said step of sending an instruction to a device to raise or lower the pressure in said tank is carried out by:

-using an external pump, which does not form part of the vehicle;

using devices forming part of the vehicle, such as pumps or heaters; and/or

-controlling the pressure inside the relief tank using a vehicle valve.

When an external pump is used, which does not form part of the vehicle, the external device can exert pressure in the tank during maintenance and require diagnostics to be carried out. Control of a valve of the system, such as a Fuel Tank Isolation Valve (FTIV) or a purge valve, may be provided to allow pressure from an external pump to be applied to the system. The external pump can apply positive and/or negative pressure. When an external pump is used which does not form part of the vehicle, the first threshold value may for example be +100mbar higher than the initial pressure, preferably +200mbar higher than the initial pressure.

Devices that form part of the vehicle are devices that are already present in the vehicle for other purposes, such as leak detection pumps, canister purge (vent) pumps, engine manifold vacuums, or other devices. Thus, it is not costly and requires no external intervention. When using the device forming part of the vehicle, the first threshold value is preferably +50mbar higher or-50 mbar lower than the initial pressure.

When the tank valve is used to effect controlled release of the pressure inside the tank, the use of existing valves, such as FTIV or E valves, is feasible and inexpensive without external intervention. The valve may be used only to reduce the pressure, but the pressure release may occur, for example, in connection with a fueling event. In this case, the first threshold value is preferably equal to the atmospheric pressure.

Advantageously, the method is implemented when the vehicle is powered off, preferably only when the vehicle is powered off.

Thereby, sloshing of the liquid in the tank is limited. Sloshing refers to liquid fluctuation within the tank that produces fuel level measurement noise. In order to make the method as accurate as possible, the level sensor should not be moved dynamically. From this, avoid rocking in order to improve the accuracy of liquid level measurement.

Preferably, the method is carried out while the vehicle is in service (or maintenance) mode.

Thus, the method is implemented when the information is particularly useful. The tank can thus be inspected more deeply and, if necessary, replaced. The method is triggered, for example, by an external computer.

Advantageously, a leak detection step is carried out before step a).

The leak detection step verifies the integrity of the tank shell. In the case of passive systems (for example pressure increase or decrease based on changes in the external temperature), the tests carried out with a constant tank volume generally do not work, since a volume change occurs due to breakage of the internal reinforcing element.

The leak detection method is intended to detect a leak in a liquid tank of a vehicle. An example of a leak detection method is described in JP 2013-.

The invention also relates to a method of checking the condition of at least one internal reinforcing element of a liquid tank of a vehicle, which connects at least two opposite walls of the liquid tank, comprising the steps of:

-performing a leak detection step, and

-if the result of the leak detection step is of a predetermined type, sending a signal indicating that at least one internal reinforcing element connecting at least two opposite walls of the liquid tank may be damaged.

Advantageously, the predetermined type of result is a result indicative of a suspected leak. The result may be derived from the results of the leak detection method. If leak detection indicates a problem, this may be due to an unexpected change in volume caused by damage to the internal reinforcing elements. Thereby, the method may facilitate servicing of a liquid tank, also referred to as a liquid system, e.g. a fuel system.

Alternatively, the predetermined type of result is a result derived from a result of the leak detection method, the result indicating that the at least one internal reinforcing element may be damaged while no leak is detected. This may be accomplished by pumping air into or out of the liquid tank to pressurize or depressurize it, and measuring the internal pressure of the liquid tank. If after the implementation of the leak detection method no leak is suspected, the method comprises the step of determining a relation between:

volume of air, denoted V, pumped into or out of the liquid reservoir_air(t)；

-vapor dome volume, denoted V_dome(t); and

-the internal pressure of the liquid tank, denoted P_int(t) and comparing the value c (t) calculated using the above relationship with a predetermined threshold, wherein t in brackets indicates that the parameter of interest is time dependent. The predetermined threshold may be, for example, a calibration value calculated using the above-mentioned relationship when the tank condition is known to be intact.

From pump performance F_pump(t) and Pump activation time duration Δ t_actVolume of expelled air V_air(t) wherein the vapor dome volume V_dome(t) is the total volume V of the liquid tank as follows_tot(t) and liquidVolume V of liquid in tank_liquid(t) difference calculation:

V_dome(t)＝V_total(t)-V_liquid(t)

pump Performance F_pump(t) is defined as being dependent on the following parameters: for example volume of air V_air(t), pump efficiency, and pump current consumption.

For example, the value c (t) may be calculated according to the following steps:

-step 1: by pump performance F_pump(t) (this is dependent on the volume of air V_airParameter of (t) and tank internal pressure P_int(t) multiplication by energy consumption E of the pump_pump(t) to obtain A (t).

A(t)＝E_pump(t)*F_pump(t)*P_int(t)

-step 2: during pump activation time Δ t_act(this is dependent on the volume of air V_airParameter (t) is integrated on A (t) to obtain B (t).

-step 3: with volume V of vapour dome_do_me(t) multiplying B (t) to obtain C (t).

C(t)＝B(t)*V_dome(t)

If the value c (t) is greater than the predetermined threshold, the method comprises a step of indicating that at least one internal reinforcing element may be damaged.

Conversely, no signal is sent indicating that at least one internal reinforcing element connecting at least two opposite walls of the liquid tank may be damaged.

The invention also relates to a vehicular liquid tank comprising control means arranged to implement the method as described above.

The invention also relates to a vehicle comprising a liquid tank and a control device arranged to implement the method as described above.

The invention also relates to a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method as described above.

Drawings

The above and other features, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The reference figures quoted below refer to the attached drawings, in which:

figure 1 is a schematic view of an embodiment of a tank that can be used for implementing the method according to the invention;

figure 2 is a schematic view of another embodiment of tank that can be used for implementing the method according to the invention;

figure 3 is a flow chart illustrating a first embodiment of the method according to the invention;

figure 4 is a flow chart illustrating a second embodiment of the method according to the invention; and

fig. 5 is a flow chart illustrating a third embodiment of the method according to the invention.

Detailed Description

The present invention will be described based upon a specific embodiment and with reference to certain drawings but the invention is not limited thereto.

First embodiment (FIGS. 1 and 3)

The first embodiment describes a method for detecting the condition of at least one internal reinforcing element 1 of a liquid tank 2 of a vehicle, wherein the internal reinforcing element 1 connects at least two opposite walls, preferably the bottom and top walls 3,4, of the liquid tank 2. The reinforcing element 1 is, for example, a column.

The tank 2 has a level sensor 5 for measuring the level of the liquid 6 inside the tank 2.

The tank 2 has a pressure sensor 7 for measuring the internal pressure of the tank 2.

The tank 2 is associated to control means 8 able to process the data provided by the level sensor 5 and the pressure sensor 7 and to control the steps of the method.

The tank 2 comprises at least an initial amount of liquid 6 measurable by a level sensor 5. For example, the tank 2 comprises at least 2mL of liquid 6, for example 20L of liquid 6. The first threshold value is determined by the control means 8 on the basis of the initial amount of liquid 6 measured by the liquid level sensor 5 and the initial internal pressure of the liquid tank 2 measured by the pressure sensor 7 (step a, not shown). For example, the first threshold value may be determined using a two-dimensional look-up table using the initial internal pressure and the initial amount of liquid as input data.

The method is triggered by an operator when the vehicle is in a maintenance mode and the vehicle is powered off. After triggering the method, the pressure in the tank is increased by external means, for example by an external pump, and an overpressure (overpressure) in the tank is initiated. Of course, it is possible to provide for the use of other means, for example forming part of the vehicle, for increasing the pressure in the tank. One or more steps of raising the pressure may be employed, as may steps of gradually raising the pressure (gradual pressure change). In another embodiment, it may be provided to use a reduced pressure, which induces a negative pressure (depression) in the tank. Such a negative pressure may be induced, for example, by an external pump.

The pressure and the liquid level are monitored with the aid of the sensors using the control device (step b) until the tank pressure measured by the pressure sensor 7 is above a first threshold value.

If the output of the pressure sensor 7 is above the first threshold value, second and third threshold values are determined by the control means 8 on the basis of the output of the pressure sensor 7, the initial output of the level sensor 5 and the initial output of the internal pressure sensor 7 (step c, not shown). For example, the second and third threshold values may be determined using a three-dimensional look-up table using the output of the pressure sensor 7, the initial output of the level sensor 5, and the initial output of the internal pressure sensor 7 as input data. The look-up table may be arranged to include a fourth dimension consisting of the temperature of the liquid in the tank. As described above, thermal expansion of the liquid can thereby be taken into account.

The control device 8 then compares the output of the level sensor 5 with the second and third threshold values to check whether the output of the level sensor 5 differs from the desired level value (step d).

If the output of the level sensor 5 is above the second threshold value, this may indicate that the inner reinforcing member 1 (or at least one of the inner reinforcing members 1) is damaged. Thereby, a signal is sent indicating that at least one internal reinforcing element 1 is damaged or possibly damaged (step e). Preferably, the signal is sent to the driver at a first time. The signal may be a visual signal, for example the signal may consist of a message or light displayed on the dashboard. The signal corresponding to the diagnosis may be stored in a storage medium to alert a service operator during an internal electrical inspection of the vehicle.

If the output of the level sensor is below the third threshold value, this may indicate that the internal reinforcing element 1 (or at least one of the internal reinforcing elements 1) is damaged. Thereby, a signal is transmitted indicating that the at least one internal reinforcing element is damaged or may be damaged.

If the output of the level sensor 5 is below the second threshold value but above a third threshold value, this may indicate that the column 1 is intact. Thereby, it may be arranged to send a signal indicating that the internal reinforcing member 1 (or at least one internal reinforcing member 1) is intact (step e).

Second embodiment (FIGS. 2 and 4)

In this embodiment, the method is also used for detecting the condition of at least one internal reinforcing element 1 of a liquid tank 2 of a vehicle, wherein the internal reinforcing element 1 connects at least two opposite walls of the liquid tank, preferably a bottom wall 3 and a top wall 4. For example, the at least one reinforcing element is a post.

The tank 2 may for example be the same as described above for the first embodiment.

The first step of the method consists in implementing a leak detection method. In the present example, the leak detection method used is an active leak detection method. Of course, it may be provided to use any suitable leak detection method, such as the leak detection methods described in WO 2018/002054 or WO 2013/164463, the contents of which are incorporated herein by reference.

If the result of the leak detection method indicates that a leak may be present, a predetermined signal is sent by the control device 8 indicating that at least one internal reinforcing element 1 is damaged or may be damaged. In fact, the result may actually be a false positive result caused by a damaged internal reinforcing element 1. Thereafter, the operator may perform further checks to verify or verify that there is a leak in the tank. If it is shown that no leak is present, there is a high probability that the leak detection result is caused by a damaged reinforcing element.

If the result of the leak detection method shows that no leak is present in the tank 2, a counter 9, for example a predetermined counter 9 of the control device 8, is reset and the state of the vehicle is observed.

The tank 2 comprises at least an initial amount of liquid 6 measurable by a level sensor 5. For example, the tank comprises at least 2mL of liquid 6, for example 20L of liquid 6. The first threshold value is determined by the control means 8 on the basis of the initial amount of liquid 6 measured by the liquid level sensor 5 and the initial internal pressure of the liquid tank 2 measured by the pressure sensor 7 (step a, not shown). For example, the first threshold value may be determined using a two-dimensional look-up table using the initial internal pressure and the initial amount of liquid as input data.

If the vehicle is powered on, the valve or pump 10 is activated to release pressure from inside the tank 2 and the method can be carried out again from the leak detection step. The valve is for example an FTIV or E valve. If the vehicle is powered off, the control means 8 controls the pressure in the tank to be raised using, for example, means forming part of the vehicle, such as an on-board pump. This results in an overpressure in the tank 2. One or more steps of raising the pressure may be employed, as may steps of gradually raising the pressure (gradual pressure change). In another embodiment, a reduced pressure may be provided, causing a negative pressure in the tank 2. Such negative pressure may be induced by an on-board pump, for example.

The pressure and the liquid level are monitored by means of the sensors 5, 7 using the control means 8 (step b) until the tank pressure measured by the pressure sensor 7 is above a first threshold value.

If the control means 8 determines that the output of the pressure sensor 7 is above the first threshold value, the second and third threshold values are determined by the control means 8 on the basis of the output of the pressure sensor 7, the initial output of the level sensor 5 and the initial output of the internal pressure sensor 7 (step c, not shown). For example, the second and third threshold values may be determined using a three-dimensional look-up table using the output of the pressure sensor 7, the initial output of the level sensor 5, and the initial output of the internal pressure sensor 7 as input data. The look-up table may be arranged to include a fourth dimension consisting of the temperature of the liquid in the tank. As described above, thermal expansion of the liquid can thereby be taken into account.

The control device 8 then compares the output of the level sensor with the second and third threshold values to check whether the output of the level sensor differs from the desired level value (step d).

If the output of the level sensor is above the second threshold value, this may indicate that the inner reinforcing member 1 (or at least one of the inner reinforcing members 1) is damaged. Thereby, a signal is sent indicating that at least one internal reinforcing element 1 is damaged or possibly damaged (step e).

If the output of the level sensor 5 is below the third threshold value, this may indicate that the internal reinforcing element 1 (or at least one of the internal reinforcing elements 1) is damaged. Thereby, a signal is sent indicating that at least one internal reinforcing element 1 is damaged or possibly damaged (step e, not shown).

If the output of the level sensor 5 is below the second threshold value and above a third threshold value, the counter 9 is incremented. If the counter 9 is below a fourth predetermined threshold value, at least steps a), b) and c) of the method are carried out again, preferably at a plurality of first threshold values, under the control of the control device 8. If the counter 9 is higher than the fourth threshold value, the method comprises the step of sending a signal indicating that at least one internal reinforcing element 1 connecting the opposite walls 3,4 is not damaged.

Third embodiment (FIGS. 2 and 5)

The third embodiment is the same as the second embodiment except for the points discussed below.

In a third embodiment, the leak detection method is not an active leak detection method, but a method based on pressure and temperature analysis, such as described in EP 17305638. Moreover, the leak detection test is carried out by the control device 8 in parallel with the test of the condition of at least one internal reinforcing element 1 of the liquid tank 2 of the vehicle. Thus, in contrast to the second embodiment, the test is conducted even if the leak detection method detects a leak.

In the third embodiment, there is no step of actively increasing the internal pressure in the tank after a vehicle power-off is observed. Instead, the monitoring step b) depends only on an increase or decrease of the pressure inside the tank 2 caused by an increase or decrease of the temperature outside the tank. When the ambient temperature rises, the pressure in the tank rises. When the ambient temperature decreases, the pressure in the tank decreases.

Similarly to the second embodiment, the temperature and the liquid level inside the tank 2 are monitored by the control means 8 until the output of the pressure sensor 7 is higher than the first threshold, all the following steps being identical to those of the second embodiment.

While the principles of the invention have been described above in connection with specific embodiments, it is to be understood that this description is made only by way of example and not as a limitation on the scope of the invention, as defined in the appended claims.