Pressure-maintaining system for a hydraulic system of an aircraft, hydraulic system, and aircraft

Abstract

The invention relates to a pressure-maintaining system (1) for a hydraulic system (2) of an aircraft (3), which pressure-maintaining system has a reduced weight and is particularly robust. The pressure-maintaining system (1) has an expansion tank (4) having a hydraulic-side interface (5) for hydraulic connection to a tank interface (6) of the hydraulic system (2), and having a gas-side interface (7), as well as a pressurized gas tank (8) which is fluidically connected to the gas-side interface (7) via a first shut-off member (9). The invention also relates to an associated hydraulic system (2) and to an associated aircraft (3).

Description

[0001] Pressure maintenance system for a hydraulic system of an aircraft, hydraulic system and aircraft

[0002] Description

[0003] The invention relates to a pressure maintenance system for a hydraulic system of an aircraft, comprising an expansion tank with a hydraulic-side interface for hydraulic connection to the hydraulic system and with a gas-side interface. The invention further relates to an associated hydraulic system and an aircraft.

[0004] A classic component of a closed hydraulic system, particularly a fluid circuit, such as a cooling circuit or a hydraulic circuit, is an expansion tank. The reservoir serves as a storage tank for unused hydraulic fluid, such as a coolant, in a circuit of the hydraulic system, and also compensates for volume fluctuations in the hydraulic fluid. In particular, the density of hydraulic fluid in hydraulic systems changes depending on the prevailing temperature within the system. Single-phase media such as liquids can be considered virtually incompressible, which causes the system pressure in the hydraulic system to rise sharply with increasing temperature. To prevent damage to the hydraulic system, the expansion tank is typically provided for the expanding hydraulic fluid.

[0005] Depending on the design of the hydraulic system or the associated pressure maintenance system, pressure equalization tanks are designed to be open or sealed to the environment. In open circuits, the pressure of the hydraulic fluid in the equalization tank is identical to the ambient air pressure, whereas in pressurized hydraulic systems, any pressure can be set in the equalization tank.

[0006] In aircraft applications, pressurized hydraulic systems are often used due to the ambient air pressure varying with altitude. This ensures consistent operating conditions in the hydraulic system, for example, in the cooling circuit. Depending on the operating temperature of the hydraulic system, increasing the operating pressure in the expansion tank also serves to prevent cavitation at the inlet of a hydraulic pump.

[0007] For passive systems, i.e., systems without active control or regulation of the pressure in the expansion tank, large volumes of the expansion tank are disadvantageous. Depending on the volume expansion to be compensated and the desired minimum or maximum pressure in the hydraulic system, the expansion tank can therefore become very large or heavy.

[0008] While actively pressurized systems can be designed significantly smaller, they usually require their own compressor or a high-pressure connection from a hydraulic system to ensure proper function. Both variants also increase system complexity and the likelihood of hydraulic system failure. In particular, compressors designed to actively pressurize a critical aircraft system must be particularly robust, and therefore heavy, and potentially redundant. This can significantly increase the weight of the pressurization system and thus negatively impact the power-to-weight ratio of the entire aircraft.

[0009] WO 2019 / 182498 shows an arrangement for a waste heat recovery system with an expansion tank, which is designed to prevent the ingress of ambient air into the system. US 2017 / 0016383 A1 describes a cooling system with an expansion tank for a vehicle. US 11,085,357 B2 discloses a cooling system for an internal combustion engine with an expansion tank.

[0010] The object of the invention is to propose an improved concept for a pressure maintenance system and a hydraulic system for an aircraft, which are lightweight and particularly robust.

[0011] The object is achieved by the subject matter of the independent patent claims. Advantageous developments of the invention are described by the dependent patent claims, the following description and the figures. A first aspect of the invention provides a pressure maintenance system for a hydraulic system of an aircraft. The pressure maintenance system has at least one expansion tank, wherein the expansion tank has a hydraulic-side interface for hydraulically connecting to a tank interface of the hydraulic system. In addition, the expansion tank has a gas-side interface. The pressure maintenance system has at least one gas pressure tank, which is fluidically connected or fluidically separably connected to the gas-side interface via a first shut-off device.

[0012] Such a pressure maintenance system can be designed to be particularly lightweight and less complex than existing solutions. The low complexity of the pressure maintenance system also allows for a robust system with an extremely low failure probability. In particular, a compressor, which, as an active component for a critical system for aviation applications, must be designed to be particularly robust and therefore heavy during flight operations, can be advantageously omitted.

[0013] In particular, the pressure maintenance system can be designed such that no element actuated by a motor, e.g. pistons, and / or hydraulic actuators are required and / or that the pressure in the hydraulic system can be regulated, adjusted and / or maintained exclusively by means of one or more shut-off devices, in particular the first shut-off device and / or a second shut-off device, in particular valves, and a gas pressure vessel.

[0014] The pressure maintenance system is particularly designed and configured to be used for closed hydraulic systems in aviation applications. The pressure maintenance system can be used, in particular, to maintain a pressure in the hydraulic system, which may be higher than ambient pressure, and in particular to actively control or regulate the pressure. For this purpose, the pressure in the expansion tank, and thus also in the hydraulic system, can be increased by means of the gas pressure tank by opening the first shut-off device in a controlled manner so that gas can flow into the expansion tank and the pressure in the gas pressure tank increases. For this purpose, the expansion tank can be a container having a gas side and a hydraulic side inside it, which can interact with each other in terms of pressure.In particular, the pressure on the gas side essentially corresponds to the pressure on the hydraulic side, so that by actively adjusting the pressure on the gas side, the pressure on the hydraulic side can be adjusted.

[0015] For example, the pressure to be maintained in the gas pressure vessel can be between two and three bar. For example, the gas pressure vessel can be set at a pressure that is higher than the pressure to be maintained in the gas pressure vessel, preferably significantly higher, and in particular between 20 and 200 bar. By opening the first shut-off device, the gas can thus flow, preferably in a controlled manner, from the gas pressure vessel into the expansion vessel, in particular into the gas side of the expansion vessel, in order to increase the pressure in the expansion vessel.

[0016] For this purpose, the expansion tank has a gas-side interface that is fluidically connected to the first shut-off device, for example, directly or via a pipe or line. The gas pressure vessel can also have an interface that is fluidically connected to the first shut-off device, for example, directly or via a pipe or line. When the first shut-off device is at least partially open, the gas can flow from the gas pressure vessel into the gas side of the expansion tank. When the first shut-off device is closed, gas flow between the gas pressure vessel and the gas side of the expansion tank is prevented.

[0017] The gas can be air, for example. Alternatively, the gas can be a weakly or non-reactive gas, such as nitrogen or a noble gas.

[0018] By means of the first shut-off device in a closed position, the fluidic connection can be interrupted, so that no gas can flow. The fluidic connection can be established when the first shut-off device is open or partially open. The same applies to all shut-off devices, in particular to the second to fifth shut-off devices, of the pressure maintenance system. The first shut-off device can preferably be designed as a valve. The valve can, in particular, be a pressure reducing valve or a throttle valve, whose gas flow can also be controlled or regulated.

[0019] The expansion tank also has a hydraulic-side interface that can be connected to the tank interface of the hydraulic system. The hydraulic-side interface and the tank interface can each represent hydraulic connections that can be fluidically connected to one another directly or indirectly via a pipe or line. In particular, such a fluidic connection can allow hydraulic fluid to flow from a hydraulic circuit of the hydraulic system into the expansion tank, or hydraulic fluid to flow from the expansion tank into the hydraulic circuit, so that the expansion tank can be used both as a reservoir for excess hydraulic fluid and for pressure equalization or hydraulic fluid equalization in the hydraulic system.In particular, when the temperature rises, the hydraulic fluid can expand, so that any resulting increase in pressure can be compensated for by the hydraulic fluid flowing out into the expansion tank, and vice versa.

[0020] In particular, it can be designed so that when the temperature in the hydraulic circuit of the hydraulic system drops, the volume of hydraulic fluid decreases, thus threatening to cause a drop in pressure. In this case, reserved hydraulic fluid can flow from the expansion tank into the hydraulic circuit until a balanced pressure is established between the expansion tank and the hydraulic circuit. If this pressure is too low, the pressure in the expansion tank can be increased to a predetermined level by introducing gas into the gas side.

[0021] In at least one exemplary embodiment, the pressure maintenance system is provided with a second shut-off device, via which the gas-side interface of the gas pressure vessel is fluidically connected or fluidically separably connected to an external environment. Advantageously, gas can thus be released from the gas pressure vessel, in particular from the gas side of the gas pressure vessel, to the external environment or released. As a result, the pressure in the gas side, as well as in the hydraulic side, and thus in the entire hydraulic system, can be advantageously reduced if necessary. For example, a pressure to be maintained in the gas pressure vessel can have a value between two and three bar. For example, this pressure of the gas pressure vessel can be higher than the pressure of the external environment (ambient pressure). In particular, the ambient pressure is approximately one bar and can be significantly lower than one bar, especially at higher altitudes in aviation applications.By opening the second shut-off device, the gas can flow from the gas side of the expansion tank into the outside environment, preferably in a controlled manner, in order to reduce the pressure in the expansion tank.

[0022] The gas-side interface can be fluidically connected to the second shut-off device, for example, directly or via a pipe or line. When the second shut-off device is at least partially open, the gas can flow from the expansion tank into the external environment. When the second shut-off device is closed, gas flow between the expansion tank and the external environment is prevented.

[0023] The second shut-off device can preferably be designed as a drain valve. The drain valve can be a throttle valve whose gas flow can also be controlled or regulated.

[0024] In particular, it can be designed so that as the temperature in the hydraulic circuit of the hydraulic system increases, the volume of hydraulic fluid increases, thus threatening to increase the pressure. In this case, hydraulic fluid from the hydraulic circuit can flow into the expansion tank until a balanced pressure is established between the expansion tank and the hydraulic circuit. If this pressure is too high, the pressure in the expansion tank can be reduced to a predetermined level by releasing gas from the gas side into the outside environment.

[0025] In at least one embodiment, the pressure maintenance system is provided with a first fluid distributor, via which the gas-side interface is connected in parallel to the first shut-off device and the second shut-off device. This allows the gas-side interface to be fluidically connected to the first and second shut-off devices in a particularly simple and thus less complex manner. The gas-side interface can accordingly be designed as a gas connection.

[0026] In particular, the first fluid distributor and the first and second shut-off elements can be designed as a common component, for example as a controllable directional control valve.

[0027] In at least one alternative embodiment, the gas-side interface comprises an inlet fluidically connected to the first shut-off device, and an outlet formed separately from the inlet and fluidically connected to the second shut-off device. This allows the gas-side interface to be fluidically connected to the first and second shut-off devices in a particularly simple and thus less complex manner. The inlet and outlet, respectively, can be configured as a gas connection.

[0028] In at least one exemplary embodiment, the pressure maintenance system comprises a compressor fluidically connected to the gas pressure vessel and configured to provide compressed ambient air for the gas pressure vessel. This advantageously extends the operating time of the gas pressure vessel and thus of the pressure maintenance system between two maintenance appointments.

[0029] In particular, the compressor, especially an air compressor, is intended to be activated only on the ground, i.e., not during flight operations. Because the compressor is not designed to supply the critical pressurization system with compressed air during flight operations, it does not need to be designed to be robust, safe, and redundant for aviation applications. A simple compressor design thus allows component weight to be kept low and the overall complexity of the pressurization system to be reduced.

[0030] Additionally or alternatively, a fluidic connection between the gas pressure vessel and the compressor can be designed to be detachable, allowing the compressor to be completely separated from the rest of the pressure-maintaining system (so that the compressor does not need to be carried during flight operations, for example) and reconnected to the rest of the pressure-maintaining system in a fluid-tight manner (for example, to pressurize or refill the gas pressure vessel). For this purpose, a shut-off device can be provided on the rest of the system beyond the interface to the compressor.

[0031] The compressor is designed, in particular, to fill the gas pressure vessel with compressed ambient air on the ground in order to restore any dropped pressure in the gas pressure vessel to a setpoint. For example, it may be provided that the gas pressure vessel can be restored to the setpoint pressure by means of the compressor before the aircraft takes off, and during flight operations, only the gas pressure vessel is designed to increase the pressure in the expansion tank if necessary.

[0032] In particular, a third shut-off device can be provided, via which the gas pressure vessel is fluidically connected to the compressor. The gas pressure vessel can be fluidically connected to the third shut-off device, for example, directly or via a pipe or line. When the third shut-off device is at least partially open, the compressed gas can flow from the active compressor into the gas pressure vessel. When the third shut-off device is closed, backflow from the gas pressure vessel into the inactive compressor is prevented.

[0033] For example, a second fluid distributor may be provided, via which the gas pressure vessel is connected in parallel to the first shut-off device and the third shut-off device, wherein alternative devices may be provided.

[0034] In particular, appropriate lines, interfaces, shut-off devices, and corresponding circuits can be provided to fluidically connect the compressor to the gas-side interface of the expansion tank and to directly pressurize the gas side with compressed ambient air. Preferably, the compressor is fluidically connected to the first shut-off device, so that the gas side can be pressurized by the active compressor by opening the second shut-off device.

[0035] In at least one exemplary embodiment, the pressure maintenance system comprises a gas pressure interface for fluidic connection to an external gas pressure supply device, wherein the gas pressure interface is fluidic connected to the gas pressure vessel. The gas pressure supply device is configured, in particular, to supply compressed gas. By fluidic connection of the gas supply device to the gas pressure interface, the gas pressure vessel can be filled with compressed gas, thus advantageously extending the operating time of the gas pressure vessel and thus of the pressure maintenance system between two maintenance appointments.

[0036] In particular, it is intended that the gas pressure interface is fluidically connected to the external gas pressure supply device only on the ground, i.e. not during flight operations.

[0037] The external gas pressure supply device can, for example, be a ground-based compressed air reservoir or a ground-based compressor that can generate compressed air from the ambient air. "External" here means that the gas pressure supply device is not part of the pressurization system, but can simply be connected to it via the gas pressure interface. In particular, the external gas pressure supply device can be separated from the gas pressure interface for flight operations, so that it advantageously does not contribute to the weight of the pressurization system or the aircraft.

[0038] The external gas pressure supply device is configured, in particular, to fill the gas pressure vessel on the ground with compressed gas, in particular compressed air, in order to restore any dropped pressure in the gas pressure vessel to a desired value. For example, it may be provided that the gas pressure vessel can be restored to the desired pressure by means of the external gas pressure supply device before the aircraft takes off, and during flight operations, only the gas pressure vessel is configured to increase the pressure in the equalization vessel if necessary.

[0039] In particular, a fourth shut-off device can be provided, via which the gas pressure vessel is fluidically separably connected to the gas pressure interface. The gas pressure vessel can be fluidically connected to the fourth shut-off device, for example, directly or via a pipe or line. When the fourth shut-off device is at least partially open, the compressed gas can flow from the coupled gas pressure supply device into the gas pressure vessel. When the fourth shut-off device is closed, backflow from the gas pressure vessel to the gas pressure interface is prevented.

[0040] In particular, appropriate lines, interfaces, shut-off devices, and corresponding circuits can be provided to fluidically connect the gas pressure interface to the gas-side interface of the expansion tank and to directly pressurize the gas side with compressed ambient air. Preferably, the gas pressure interface is fluidically connected to the first shut-off device, so that by opening the second shut-off device, the gas side can be pressurized by the connected gas pressure supply device.

[0041] In at least one embodiment, the second fluid distributor is configured to connect the gas pressure vessel to the first shut-off device, and to the compressor and / or to the gas pressure interface in parallel. For example, the second fluid distributor can be configured to connect the gas pressure vessel to the first shut-off device and the fourth shut-off device and / or the third shut-off device in parallel, although alternative devices may be provided.

[0042] In at least one exemplary embodiment, it is provided that the pressure maintenance system has an electronic control device which is designed to control and / or regulate a pressure in the expansion tank at least via the first shut-off device. Furthermore, the electronic control device can be designed to control and / or regulate the pressure in the expansion tank and / or in the gas pressure vessel via the second shut-off device and / or the third shut-off device and / or the fourth shut-off device and / or the compressor. In particular, the control device can be designed to open and close a respective shut-off device by a certain degree of opening, as well as to activate and deactivate the compressor at a certain power level.

[0043] For this purpose, the electronic control unit can be connected to the shut-off devices and the compressor to send corresponding control signals. Furthermore, pressure sensors can be provided in the expansion tank and the gas pressure vessel, which can be connected to the electronic control unit and can provide a corresponding sensor signal for a measured pressure. In particular, the control unit sends the control signals automatically depending on the sensor signals.

[0044] In at least one embodiment, the expansion tank is a diaphragm expansion tank. This advantageously allows the hydraulic side to be separated from the gas side by a diaphragm, in particular to prevent a chemical reaction between the hydraulic fluid and the gas or a transfer of the gas into the hydraulic fluid. This can then extend the service life of the hydraulic fluid.

[0045] The diaphragm expansion tank, also known as a bladder accumulator, has a flexible rubber diaphragm that fluidically separates the hydraulic fluid and the gas and can deform depending on the pressure or the fill level of the hydraulic fluid in the expansion tank.

[0046] In at least one embodiment, the gas pressure vessel is a gas cylinder. Gas cylinders are advantageously readily available and interchangeable. The gas cylinder can, in particular, have a steel casing and a gas cylinder valve as an interface.

[0047] A further aspect of the invention relates to a hydraulic system for an aircraft, wherein the hydraulic system comprises a pressure maintenance system according to the invention. The hydraulic-side interface of the expansion tank is fluidly connected to the tank interface of the hydraulic system, so that the hydraulic side of the expansion tank is fluidly connected to the hydraulic circuit.

[0048] In at least one exemplary embodiment, the hydraulic system is a cooling circuit system, in particular for a fuel cell drive of the aircraft. Accordingly, the hydraulic circuit is a cooling circuit, preferably for cooling the fuel cell drive, in particular heat-generating components of the fuel cell drive.

[0049] A further aspect of the invention relates to an aircraft, in particular an airplane, which has a hydraulic system according to the invention. In particular, the aircraft can have a fuel cell drive. The aircraft can, in particular, be a commercial aircraft. However, the aircraft can also be designed as a helicopter, drone, or the like.

[0050] The invention also includes combinations of the features of the described embodiments.

[0051] The invention is explained in more detail below using specific embodiments and associated schematic drawings. In the figures, identical or functionally equivalent elements may be provided with the same reference numerals. The description of identical or functionally equivalent elements may not necessarily be repeated for different figures. In this regard, the following shows:

[0052] FIG. 1 shows a schematic representation of a simple embodiment of a hydraulic system according to the invention with a pressure maintenance system;

[0053] FIG. 2 shows a schematic representation of an expanded embodiment of a hydraulic system according to the invention with a pressure maintenance system;

[0054] FIG. 3 shows a schematic representation of an expanded embodiment of a hydraulic system according to the invention with an electronic control device;

[0055] FIG. 4 is a schematic representation of an embodiment of an aircraft according to the invention.

[0056] FIG. 1 shows a schematic representation of a simple embodiment of a hydraulic system 2 according to the invention with a pressure maintenance system 1, in particular for an aircraft 3.

[0057] The pressure maintenance system 1 can have an expansion tank 4, which can have a hydraulic side 18 and a gas side 19 inside. In this example, the expansion tank 4 is designed as a diaphragm expansion tank, which in particular has a flexible rubber diaphragm 17 inside that fluidically separates the hydraulic side 18 from the gas side 19, but couples them together with respect to a pressure in the expansion tank 4. A pressure in the expansion tank 4 can be, for example, one to five bar, preferably 2 to 3 bar.

[0058] The hydraulic side 18, which is at least partially filled with hydraulic fluid, in particular cooling fluid such as water, is fluidly connected via a hydraulic-side interface 5 of the expansion tank 4 to a tank interface 6 of the hydraulic system 2, in particular a hydraulic circuit 22 of the hydraulic system, so that the hydraulic fluid can flow from the hydraulic circuit 22 into the expansion tank 4 or from the expansion tank 4 into the hydraulic circuit 22. The hydraulic circuit 22 can, for example, be a cooling circuit for a fuel cell drive of the aircraft 3.

[0059] The gas side 19, which is at least partially filled with gas such as air, is in this exemplary embodiment fluidically connected to a gas pressure vessel 8 via a gas-side interface 7 of the expansion tank 4 and via a first shut-off device 9 so that, depending on a position of the first shut-off device 9, compressed gas can flow from the gas pressure vessel 8 into the expansion tank 4 in order to increase the pressure in the expansion tank 4 and thus in the hydraulic circuit 22. The gas pressure vessel 8 can be designed in particular as a gas bottle or as a gas cartridge and can store pressurized gas, in particular compressed air, in its interior. The pressure in the gas pressure vessel is greater, preferably significantly greater, than in the expansion tank 4, preferably 20 bar to 200 bar.

[0060] The gas side 19 can also be fluidically connected to an external environment 11, in particular to ambient air, via the gas-side interface 7 and via a second shut-off device 10, so that depending on a position of the second shut-off device 10, gas can flow from the expansion tank 4 into the external environment 11 in order to reduce the pressure in the expansion tank 4 and thus in the hydraulic circuit 22.

[0061] Optionally, a compressor 13 of the pressure maintenance system 2 can be provided, which is fluidically connected to the gas pressure vessel 8 and is designed to provide compressed ambient air from the external environment 11 for the gas pressure vessel 8. The compressor 13 can be designed to be activated only during ground operation of the aircraft, so that it does not represent an aviation-critical component and can be designed accordingly smaller and lighter.

[0062] Furthermore, the compressor 13 can be separably fluidically connected to the expansion tank 4 via the first shut-off device 9 in order to be able to increase the pressure in the expansion tank directly via the compressor 13 if necessary.

[0063] FIG. 2 shows a schematic representation of an expanded embodiment of the hydraulic system 2 according to the invention, wherein the description for FIG. 1 applies correspondingly to FIG. 2.

[0064] In this example, the gas-side interface 7 is fluidically connected to a first fluid distributor 12, so that the gas-side interface 7 is connected in parallel to the first shut-off device 9 and the second shut-off device 10 via the first fluid distributor 12. For example, the first shut-off device 9, the second shut-off device 10, and the first fluid distributor 12 can be jointly configured as a directional control valve.

[0065] Alternatively, the gas-side interface 7 may have an inlet which is fluidically connected to the first shut-off device 9 and an outlet formed separately from the inlet which is fluidically connected to the second shut-off device 10.

[0066] In particular, in addition to or as an alternative to the compressor 13, a gas pressure interface 14 can be provided for fluidic connection to an external gas pressure supply device (not shown), wherein the gas pressure interface 14 is fluidic connected to the gas pressure vessel 8.

[0067] According to this example, a second fluid distributor 15 can be provided, via which the gas pressure vessel 8 can be connected in parallel to the first shut-off device 9, to the compressor 13, and to the gas pressure interface 14. Preferably, a third shut-off device 20 can be provided for this purpose, which fluidically separably connects the compressor 13 to the second fluid distributor 15, as well as a fourth shut-off device 21, which fluidically separably connects the gas pressure interface 14 to the second fluid distributor 15, and a fifth shut-off device 23, which fluidically separably connects the gas pressure vessel 8 to the second fluid distributor 15. For example, the first to fifth shut-off devices and the first and second fluid distributors can be designed together as a directional control valve. Alternatively, the third to fifth shut-off devices and the second fluid distributor can be designed together as a second directional control valve.

[0068] FIG. 3 shows a schematic representation of an expanded embodiment of the hydraulic system 2 according to the invention with an electronic control device 16, wherein the description for FIG. 3 applies correspondingly to FIG. 3.

[0069] The electronic control device 16 or control and regulation device can generally be designed to control and / or regulate the pressure in the expansion tank 4. For this purpose, the electronic control device 16 can be signal-connected to a first pressure sensor 24 and a second pressure sensor 25. The first pressure sensor 24 can be designed to determine the pressure in the expansion tank 4, in particular in the hydraulic side 18, and to send a corresponding first sensor signal to the control device 16. The second pressure sensor 25 can be designed to determine the pressure in the gas pressure tank 8 and to send a corresponding second sensor signal to the control device 16.

[0070] In addition, the control device 16 can be connected in terms of signaling at least to the first shut-off device 9, and preferably also to the second shut-off device 10, the third shut-off device 20, the fourth shut-off device 21 and the fifth shut-off device 23, as well as to the compressor 13.

[0071] Depending on the first and / or second sensor signal, the control device 16 can be designed, in particular, to send corresponding control signals to the shut-off devices or to the compressor 13, so that a respective shut-off device assumes a corresponding position, for example an open, a partially open, or a closed position, or the compressor 13 is activated or deactivated. As a result, the pressure in the expansion tank 4 can be controlled or regulated, in particular increased, decreased, or maintained at a constant level. Furthermore, the pressure in the gas pressure tank 8 can be increased or gas can be released from the gas pressure tank 8 by means of the control device 16.

[0072] FIG. 4 shows a schematic representation of an embodiment of an aircraft 3 according to the invention. The aircraft 3 has, in particular, the hydraulic system 2 according to the invention with the pressure maintenance system 1 according to the invention.

[0073] In this example, aircraft 3 is designed as a commercial aircraft.

[0074] List of reference symbols:

[0075] 1 pressure maintenance system

[0076] 2 hydraulic system

[0077] 3 aircraft

[0078] 4 expansion tanks

[0079] 5 Hydraulic interface

[0080] 6 Container Interface

[0081] 7 Gas-side interface

[0082] 8 gas pressure vessels

[0083] 9 first shut-off device

[0084] 10 second shut-off device

[0085] 11 external environment

[0086] 12 first fluid distributor

[0087] 13 compressors

[0088] 14 Gas pressure interface

[0089] 15 second fluid distributor

[0090] 16 electronic control device

[0091] 17 Rubber membrane

[0092] 18 Hydraulic side

[0093] 19 Gas side

[0094] 20 Third shut-off device

[0095] 21 Fourth shut-off device

[0096] 22 Hydraulic circuit

[0097] 23 Fifth shut-off device

[0098] 24 First pressure sensor

[0099] 25 Second pressure sensor

Claims

Patent claims 1. Pressure maintenance system (1) for a hydraulic system (2) of an aircraft (3), comprising - a compensation tank (4) with a hydraulic-side interface (5) for hydraulic connection to a tank interface (6) of the hydraulic system (2), and with a gas-side interface (7), characterized by - a gas pressure vessel (8) which is fluidically connected to the gas-side interface (7) via a first shut-off device (9).

2. Pressure maintenance system (1) according to claim 1, characterized by a second shut-off device (10) via which the gas-side interface (7) of the gas pressure vessel (8) is fluidically connected to an external environment (11).

3. Pressure maintenance system (1) according to claim 1 or 2, characterized in that the pressure maintenance system (1) is designed such that a pressure in the hydraulic system can be regulated, adjusted and / or maintained exclusively with the aid of one or more shut-off devices, in particular the first shut-off device (9) and / or the second shut-off device (10), and the gas pressure container.

4. Pressure maintenance system (1) according to claim 2 or 3, characterized by a first fluid distributor (12) via which the gas-side interface (7) is connected in parallel to the first shut-off device (9) and the second shut-off device (10).

5. Pressure maintenance system (1) according to claim 2 or 3, characterized in that the gas-side interface (7) has an inlet which is fluidically connected to the first shut-off device (9) and has an outlet formed separately from the inlet which is fluidically connected to the second shut-off device (10).

6. Pressure maintenance system (1) according to one of the preceding claims, characterized by a compressor (13) which is fluidically connected to the gas pressure vessel (8) and is designed to provide compressed ambient air for the gas pressure vessel (8), wherein preferably the fluidic connection between the gas pressure vessel and the compressor is detachable in such a way that the compressor can optionally be completely separated from the rest of the pressure maintenance system and can be reconnected to the rest of the pressure maintenance system in a fluid-tight manner.

7. Pressure maintenance system (1) according to one of the preceding claims, characterized by a gas pressure interface (14) for fluidic connection to an external gas pressure supply device for providing compressed gas, wherein the gas pressure interface (14) is fluidic connected to the gas pressure container (8).

8. Pressure maintenance system (1) according to claim 6 and / or 7, characterized by a second fluid distributor (15), via which the gas pressure vessel (8) is connected in parallel to the first shut-off device (9), and to the compressor (13) and / or to the gas pressure interface (14).

9. Pressure maintenance system (1) according to one of the preceding claims, characterized by an electronic control device (16) which is designed to control and / or regulate a pressure in the compensation tank (4) at least via the first shut-off device (9).

10. Pressure maintenance system (1) according to one of the preceding claims, characterized in that the compensation tank (4) is a diaphragm expansion tank.

11. Pressure maintenance system (1) according to one of the preceding claims, characterized in that the gas pressure vessel (8) is a gas cylinder.

12. Hydraulic system (2) for an aircraft (3), characterized by a pressure maintenance system (1) according to one of the preceding claims, wherein the hydraulic-side interface (5) of the compensation tank (4) is fluidically connected to the tank interface (6) of the hydraulic system (2).

13. Hydraulic system (2) according to claim 12, characterized in that the hydraulic system (2) is a cooling circuit system, in particular for a fuel cell drive of the aircraft (3).

14. Aircraft (3), in particular an airplane, characterized by a hydraulic system (2) according to claim 12 or 13.

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