Method for operating a fuel gas tank system, and control device

Abstract

The invention relates to a method for operating a fuel gas tank system (1), which comprises at least one fuel gas tank (2) for storing fuel gas under high pressure and one valve assembly (3) for removing fuel gas from the fuel gas tank (2), said valve assembly being inserted in the fuel gas tank (2), wherein, in order to remove fuel gas, a shut-off valve (4) is actuated and opened, said shut-off valve being integrated, downstream of a flow-limiting valve (5) with respect to the removal direction, in a removal path (6) of the valve assembly (3), said removal path leading into a gas line (7). According to the invention, before the shut-off valve (4) is actuated, in a step (a) it is checked whether an activation of the flow-limiting valve (5) is expected, and, if an activation of the flow-limiting valve (5) is expected, in a step (b) the shut-off valve (4) is actuated multiple times one after the other at specific time intervals. The invention also relates to a control device for carrying out steps of the method.

Description

[0001] Description

[0002] Method for operating a fuel gas tank system, control unit

[0003] The invention relates to a method for operating a fuel gas tank system, comprising at least one fuel gas tank for storing fuel gas under high pressure and a valve assembly inserted into the fuel gas tank for removing fuel gas from the fuel gas tank. Furthermore, the invention relates to a control unit for a fuel gas tank system.

[0004] The preferred area of ​​application is mobile fuel gas tank systems, particularly fuel cell and / or gas vehicles powered by a fuel gas. The fuel gas can be, in particular, hydrogen or natural gas, which is stored under high pressure in a fuel gas tank.

[0005] State of the art

[0006] Mobile fuel gas tank systems are known, comprising at least one fuel gas tank for storing fuel gas, such as hydrogen or natural gas. The fuel gas tank is typically designed as a high-pressure tank. A high-pressure tank always requires a shut-off valve to seal the tank tightly when the vehicle is not in use. For safety reasons, the shut-off valve is generally designed as a normally closed valve. For further protection, a flow-limiting valve can be installed upstream of the shut-off valve. This valve significantly restricts the flow in the event of a malfunction, thus enabling controlled release of fuel gas from the fuel gas tank.

[0007] The shut-off valve and the flow limiting valve are typically integrated into a valve assembly that can be installed as a compact unit in the fuel gas tank, particularly in the area of ​​a cylinder neck of the fuel gas tank. The valve assembly is integrated into a withdrawal path of the valve assembly that leads into a gas line. In addition to the shut-off valve and the flow limiting valve, other components, particularly additional valves, are typically integrated into the withdrawal path.

[0008] The pressure loss when withdrawing fuel gas from the fuel gas tank increases with the number of components in the withdrawal path. The pressure threshold for activating the flow limiting valve, hereinafter referred to as the activation threshold, must therefore be selected to be lower than the differential pressure across the entire valve assembly. This increases the risk that the flow limiting valve will be inadvertently activated when the shut-off valve is activated and that the flow will be limited by the open shut-off valve. This risk is particularly present when there is a pressure increase in the fuel gas tank and / or a pressure drop in the gas line, so that the difference between the pressure in the fuel gas tank and the pressure in the gas line is particularly high. If the flow limiting valve is activated, the flow is limited, meaning that the requested amount of fuel gas cannot be withdrawn from the fuel gas tank.In a fuel gas tank system with multiple fuel gas tanks, this results in the missing quantity being drawn from a fuel gas tank where activation of the flow limiting valve is least likely. This can result in uneven emptying of the multiple fuel gas tanks.

[0009] The present invention addresses the problem of preventing flow limitation due to an activated flow limiting valve when withdrawing fuel gas from a fuel gas tank, or at least mitigating the negative consequences of such flow limitation. To achieve this problem, the method with the features of claim 1 is proposed. Advantageous further developments of the invention can be found in the subclaims. Furthermore, a control device for executing steps of the method according to the invention is specified.

[0010] Disclosure of the invention

[0011] A method is proposed for operating a fuel gas tank system which comprises at least one fuel gas tank for storing fuel gas under high pressure and a valve assembly inserted into the fuel gas tank for withdrawing fuel gas from the fuel gas tank. In the method, a shut-off valve is activated and opened to withdraw fuel gas. The shut-off valve is integrated into a withdrawal path of the valve assembly, which opens into a gas line, downstream of a flow limiting valve in the withdrawal direction. According to the invention, before the shut-off valve is activated, a check is carried out in step (a) to determine whether activation of the flow limiting valve is to be expected. If activation of the flow limiting valve is to be expected, the shut-off valve is activated several times in succession at specific time intervals in step (b).

[0012] By repeatedly activating the shut-off valve, the shut-off valve is opened several times in succession. Between two opening phases, the shut-off valve is closed so that no fuel gas is drawn from the fuel gas tank. This means that between two opening phases, the high flow through the flow limiting valve and thus its activation are stopped. The flow limiting valve then opens again so that the shut-off valve can be activated or opened again to draw fuel gas. If the flow limiting valve is activated again, the control of the shut-off valve is interrupted again until the activation of the flow limiting valve is finished and the drawing of fuel gas from the fuel gas tank can continue.

[0013] The proposed control strategy prevents flow limitation due to unintentional activation of the flow limiting valve. If the flow limiting valve is already activated, the flow limitation can be quickly removed using the proposed control strategy, so that fuel gas can be withdrawn from the fuel gas tank even under unfavorable pressure conditions. In mobile fuel gas tank systems, system availability and thus the full range of the vehicle are thus restored. In fuel gas tank systems with multiple fuel gas tanks, the proposed control strategy can be used to prevent uneven emptying of the fuel gas tanks. The proposed control strategy results in reduced requirements for the valve assembly installed in the fuel gas tank. The design of the valve assembly is correspondingly simplified.

[0014] For testing in step (a), the current pressure in the fuel gas tank and / or the current pressure in the gas line is preferably measured by sensors. Based on the current pressure in the fuel gas tank or the current pressure in the gas line, it can be estimated in certain cases whether activation of the flow limiting valve is to be expected.

[0015] Such a case could arise, for example, if the fuel gas tank was exposed to sunlight for an extended period while the vehicle was parked, causing a noticeably high pressure increase in the fuel gas tank. This can be detected by sensors and, if necessary, compared with a maximum pressure value that is normally reached. A significantly higher value then indicates an expected activation of the flow limiting valve when the shut-off valve is activated, even without knowing the current pressure in the gas line.

[0016] Such a situation can also arise if the gas line is leaking, resulting in a noticeably high pressure drop in the gas line. This can also be detected by sensors and, if necessary, compared with a minimum pressure value that is normally reached. A significantly lower value then indicates an expected activation of the flow limiting valve when the shut-off valve is activated. Knowledge of the current pressure in the fuel gas tank is not required for this.

[0017] The sensory detection of the pressure in the fuel gas tank and in the gas line requires appropriate sensors. However, a fuel gas tank is not always equipped with appropriate sensors, in particular a tank pressure sensor. As an alternative or in addition, it is therefore proposed that the pressure in the fuel gas tank be determined based on another parameter, in particular the temperature. The pressure in the fuel gas tank can then be estimated based on the temperature curve. In the absence of a tank pressure sensor, the temperature in the fuel gas tank and the pressure in the gas line can be detected and stored by sensors, for example, before the vehicle is parked and before the shut-off valve is closed.Before the vehicle is started again, the temperature in the fuel gas tank is repeatedly recorded by sensors so that, taking into account the temperature change during the shutdown phase and the pressure in the gas line, the expected pressure in the fuel gas tank can be calculated using the following formula: p2 = p1 x T2 / T1 with p1 = the pressure in the gas line before shutdown p2 = the current pressure in the fuel gas tank.

[0018] T1 = the temperature in the fuel gas tank before switching off

[0019] T2 = the current temperature in the fuel gas tank

[0020] In a further development of the invention, it is proposed that for the test in step (a), the differential pressure across the valve assembly, i.e., the difference between the pressure in the fuel gas tank and the pressure in the gas line, be determined. The following formula can be used for this purpose: dp = p2 - p3, where p2 = the current pressure in the fuel gas tank, p3 = the current pressure in the gas line.

[0021] Based on the differential pressure determined before the shut-off valve is activated, it can be checked very precisely whether activation of the flow limiting valve is to be expected when the shut-off valve is activated and opened. This is because the higher the differential pressure, the greater the flow through the flow limiting valve and thus the risk of unintentional activation of the flow limiting valve or flow limitation. Furthermore, it is proposed that after the shut-off valve has been activated in step (b), the activation of the shut-off valve is interrupted until the activation of the flow limiting valve has ended. This means that the shut-off valve is only opened again when the flow limitation no longer applies. This ensures that fuel gas can be withdrawn from the fuel gas tank again, at least until the flow limiting valve is activated again.This is because the flow limiting valve is activated with a certain delay. This delay allows for a certain pressure equalization between the pressure in the fuel gas tank and the pressure in the gas line, potentially preventing further activation of the flow limiting valve.

[0022] Therefore, the time interval between two control phases for opening the shut-off valve is preferably selected depending on the reaction time of the flow limiting valve.

[0023] Furthermore, the pressure difference across the valve assembly is preferably determined before each actuation of the shut-off valve in step (b). This procedure has the advantage that the actuation strategy can be adapted to the currently determined pressure difference ("dynamic actuation strategy"), particularly with regard to the actuation duration and / or the duration of the actuation interruption. The pressure equalization between the pressure in the fuel gas tank and the pressure in the gas line can be accelerated in this way.

[0024] Preferably, the frequency of actuation of the shut-off valve and / or interruptions is determined depending on the pressure difference across the valve assembly before the first actuation.

[0025] According to a preferred embodiment of the invention, an activation threshold of the flow limiting valve is determined, and the shut-off valve for withdrawing fuel gas is only activated when the activation threshold is undershot, preferably taking a safety margin into account. This measure ensures that flow limitation does not occur. Appropriate consideration of the activation threshold of the flow limiting valve is particularly useful in fuel gas tank systems with multiple fuel gas tanks. In this case, the requested amount of fuel gas can be withdrawn from another fuel gas tank, provided that it is ensured that activation of the shut-off valve is not expected to activate the flow limiting valve. Therefore, the fuel gas is preferably withdrawn from the fuel gas tank in which the lowest pressure prevails.The removal of fuel gas leads to an increase in pressure in the gas line, so that a certain pressure equalization is achieved between the pressure in the gas line and the tank pressure of the other fuel gas tanks.

[0026] As pressure equalization progresses, the shut-off valves of the other fuel gas tanks can then also be controlled and opened so that they are emptied evenly.

[0027] Furthermore, it is proposed that a deactivation threshold for the flow limiting valve be determined, and that the shut-off valve is only reactivated after an interruption of control when the flow falls below the deactivation threshold. This measure ensures that the flow limitation is removed before the shut-off valve is reactivated or opened.

[0028] To achieve the aforementioned object, a control unit for a fuel gas tank system is also proposed, which is configured to execute steps of a method according to the invention. The control unit can be used to determine the time and frequency of actuation of a shut-off valve. For this purpose, an activation threshold and / or a deactivation threshold of a flow limiting valve can be stored in the control unit. In a fuel gas tank system with multiple fuel gas tanks, the order of actuation of the shut-off valves can be determined depending on the differential pressures determined for each tank.

[0029] The method according to the invention and its advantages are explained in more detail below with reference to the accompanying drawings. These show:

[0030] Fig. 1 is a schematic representation of a fuel gas tank system which can be operated according to the method according to the invention, Fig. 2 is a schematic longitudinal section through a valve assembly of a fuel gas tank of the fuel gas tank system of Figure 1 and

[0031] Fig. 3 is a diagram illustrating the control of the shut-off valve integrated in the valve assembly of Figure 2 as a function of the differential pressure (dp) between the fuel gas tank and the gas line.

[0032] Detailed description of the drawings

[0033] Figure 1 shows a simplified representation of a fuel gas tank system 1 with several fuel gas tanks 2. The fuel gas tank system 1 shown serves to supply a fuel cell stack 8 with fuel gas, preferably hydrogen.

[0034] A valve assembly 3 is inserted into each fuel gas tank 2, via which the respective fuel gas tank 2 is connected to a gas line 7. The gas lines 7 are joined together so that essentially the same pressure prevails in the gas lines 7. This pressure is measured using a pressure sensor 9. A further pressure sensor 9 is integrated into each fuel gas tank 2. Instead of a pressure sensor 9, each fuel gas tank 2 can also be provided with just one temperature sensor 10.

[0035] Figure 2 shows an enlarged view of a valve assembly 3 of a fuel gas tank 2. A withdrawal path 6 leads through the valve assembly 3 and opens into the gas line 7. A shut-off valve 4 and—upstream of the shut-off valve 4 in the withdrawal direction—a flow-limiting valve 5 are integrated into the withdrawal path 6. Between the flow-limiting valve 5 and the shut-off valve 4, a further flow-limiting valve 11 for limiting the flow in the reverse flow direction and a filter 12 are arranged. Downstream of the shut-off valve 4, a manually operable valve 13 and another filter 14 are also integrated.

[0036] In the withdrawal direction, downstream of the shut-off valve 4, a refueling path 15 branches off from the withdrawal path 6. The flow direction in the refueling path 15 is determined by an integrated check valve 16. The check valve 16 thus prevents fuel gas from flowing out of the fuel gas tank 2 via the refueling path 15.

[0037] The valve assembly 3 shown in Figure 2 also has a relief path 17 in which additional valves 18, 19 are arranged. Firstly, another manually operable valve 18 is provided, which bypasses all valves and is also referred to as a "bleed valve." Valve 19 is a safety valve for relieving any excess pressure.

[0038] Essential components for carrying out the method according to the invention are the shut-off valve 4 shown in Figure 2 and the upstream flow limiting valve 5. The further components shown are optional and not absolutely necessary for carrying out the method according to the invention.

[0039] The method according to the invention is explained below with reference to Figure 3.

[0040] With the shut-off valve 4 initially still closed (see curve A), there is a pressure pTank in the fuel gas tank 2 and a pressure pi_eitun in the gas line 7 g which is significantly below the pressure pTank, resulting in a differential pressure dp. If the shut-off valve 4 is now activated to open it (see curve A), fuel gas flows from the fuel gas tank 2 into the gas line 7, so that the pressure pi_eitun grises steeply. This means that the flow through the shut-off valve 4 and the flow limiting valve 5 is very high. This leads, with a slight delay (see arrow 20), to the activation of the flow limiting valve 5 (see curve B), so that the flow is limited. The pressure pi_eitun g in the gas line 7 therefore only increases slightly. To quickly remove the flow limitation, the control of the shut-off valve 4 is interrupted (see curve A), so that the flow is completely blocked and the pressure Pline g in the gas line 7 no longer increases. This ultimately leads to the cancellation of the activation of the flow limiting valve 5, so that the shut-off valve 4 can be activated and opened again until a pressure equalization between the pressure pTank and the pressure pi_eitun g is reached.

[0041] If the pressure relief valve 5 is activated again on the way to pressure equalization, the control of the shut-off valve 4 can be interrupted repeatedly.

Claims

Claims 1. Method for operating a fuel gas tank system (1), comprising at least one fuel gas tank (2) for storing fuel gas under high pressure and a valve assembly (3) inserted into the fuel gas tank (2) for withdrawing fuel gas from the fuel gas tank (2), wherein a shut-off valve (4) is activated and opened for withdrawing fuel gas, which shut-off valve is integrated in the withdrawal direction downstream of a flow limiting valve (5) in a withdrawal path (6) of the valve assembly (3), which opens into a gas line (7), characterized in that before the shut-off valve (4) is activated, a check is carried out in a step (a) to determine whether activation of the flow limiting valve (5) is to be expected, and if activation of the flow limiting valve (5) is to be expected, the shut-off valve (4) is activated several times in succession at specific time intervals in a step (b).

2. Method according to claim 1, characterized in that for the test in step (a) the current pressure (pTank) in the fuel gas tank (2) and / or the current pressure (pi_eitun g ) in the gas line (7) is or are detected by sensors.

3. Method according to claim 2, characterized in that the current pressure (pTank) in the fuel gas tank (2) is determined on the basis of a further parameter, in particular the temperature.

4. Method according to claim 2 or 3, characterized in that for the test in step (a) the current differential pressure (dp) across the valve assembly (3), that is to say the difference between the pressure (pTank) in the fuel gas tank (2) and the pressure (pi_eitun g ) in the gas line (7).

5. Method according to one of the preceding claims, characterized in that after activation of the shut-off valve (4) in step (b), the activation of the shut-off valve (4) is interrupted until the activation of the flow limiting valve (5) is completed.

6. Method according to one of the preceding claims, characterized in that before each activation of the shut-off valve (4) in step (b), the pressure difference (dp) across the valve assembly (3) is determined.

7. Method according to claim 6, characterized in that the frequency of the actuation of the shut-off valve (4) and / or the interruptions is determined as a function of the pressure difference (dp) across the valve assembly (3) before the first actuation.

8. Method according to one of the preceding claims, characterized in that an activation threshold (dpActive) of the flow limiting valve (5) is determined and the shut-off valve (4) is only activated for the removal of fuel gas when the activation threshold (dpActive) is undershot, preferably taking into account a safety margin.

9. Method according to one of the preceding claims, characterized in that a deactivation threshold (dpDeaktiv) of the flow limiting valve (5) is determined and the shut-off valve (4) is only activated again after an interruption of the activation when the deactivation threshold (dpDeaktiv) is undershot.

10. Control device for a fuel gas tank system (1) which is designed to carry out steps of a method according to one of the preceding claims.

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