ELECTROHYDRAULIC SYSTEM WITH ONE HYDRAULIC AXIS AND AT LEAST ONE CLOSED HYDRAULIC CIRCUIT

Description

[0001] The invention relates to an electro-hydraulic system with a hydraulically actuated axle and at least one closed hydraulic circuit, comprising hydraulic control means which are connected in the closed hydraulic circuit to a hydraulic machine, to a hydraulic consumer and to a hydraulic reservoir.

[0002] Such electro-hydraulic systems with a hydraulic axis can be used in a variety of industrial automation applications, e.g. in presses, plastics machines, bending machines.

[0003] Such hydraulic arrangements are also preferably used underwater at depths of up to several thousand meters to move an element or to refill or change a system with fluid in connection with oil and gas extraction, mining, scientific exploration, or infrastructure projects. For example, oil and gas production facilities at great depths have process valves that can be used to regulate or shut off the flow rate of the medium being extracted.

[0004] DE 10 2015 213695 A discloses such an electrohydraulic system.

[0005] A hydraulic system with an electro-hydraulic actuator for underwater use can comprise a container housing a hydrostatic machine (operable at least as a pump) and an electric motor mechanically coupled to the hydrostatic machine. The actuator is primarily driven by an electric motor, which powers the pump and thus moves a hydraulic cylinder in a linear motion. The actuator adjusts, for example, large production valves in oil or gas wells to regulate the flow rate. The container is filled with a hydraulic fluid, such as oil, as the working fluid. The container is sealed from the surrounding seawater and pressure-compensated against the ambient underwater pressure.The electro-hydraulic system comprises a hydraulic cylinder whose cylinder housing is mounted on the housing of a process valve. The cylinder includes a piston and a piston rod extending from one side of the piston, which moves a process valve spool. The piston divides the interior of the cylinder housing into a cylinder chamber away from the piston rod and a cylinder chamber on the piston rod side. A mechanical spring assembly, such as a helical compression spring, is housed in the cylinder chamber on the piston rod side, which actuates the piston in the manner of closing the process valve. The extension and retraction of such a differential cylinder typically displaces or requires oil equal to the volume of the cylinder rod. A disadvantage of this arrangement is that the large volume of pressurized fluid inside the reservoir can be subject to leakage losses that must be compensated for.Furthermore, a large quantity of pressurized fluid is required for the compression of the hydraulic cylinder. Finally, each machine cycle also creates a stress cycle with respect to the diaphragm of a pressure compensator, which significantly reduces the service life for long-term underwater applications.

[0006] Based on this, the object of the present invention is to create an electrohydraulic system and a method that alleviate or even avoid the aforementioned disadvantages. In particular, the amount of pressurized fluid required for the hydraulic actuator should be reduced in a structurally simple manner, and the amount of oscillation volume generated in the actuator reservoir should be minimized. Furthermore, the operating time should be significantly increased.

[0007] These problems are solved with an electrohydraulic system and a method according to the independent claims. Further embodiments of the invention are specified in the dependent claims. It should be noted that the description, particularly in conjunction with the figures, presents further developments of the invention.

[0008] This is achieved using an electro-hydraulic system with a hydraulic consumer and at least one closed hydraulic circuit, wherein the hydraulic circuit comprises at least one control device, a hydraulic machine, and a closed hydraulic reservoir. The closed hydraulic circuit is filled with degassed hydraulic fluid.

[0009] A hydraulic consumer can be, for example, a movable (positioning) axis, a drive, a valve, or the like. A hydraulically actuated (positioning) axis specifically refers to a hydraulic actuator, such as a hydraulic cylinder, and the hydraulic or electro-hydraulic control arrangement or circuit that actuates the actuator with fluid. Such hydraulic axes are compact and powerful drives. They can be used in a wide variety of industrial automation applications.

[0010] Closed hydraulic circuits can be operated with flow sources (hydraulic pumps). Closed hydraulic circuits generally require systems with hydraulic motors where the return flow rate equals the incoming flow rate. These are working cylinders with piston areas or rotary motors with a rotating output motion. The hydraulic fluid remains in the hydraulic circuit. The hydraulic control devices include, in particular, hydraulic valves. The hydraulic machine (fluid flow generator) is, in particular, a hydraulic pump. The hydraulic reservoir can be a hydraulic accumulator, a refill station, a closed fluid reservoir, or the like. The hydraulic reservoir can also be formed by the internal spaces of the hydraulic circuit, which essentially comprise the hydraulic machine, the hydraulic motor, and / or the hydraulic components. The closed hydraulic circuit is (where technically feasible) completely filled with (a single) hydraulic fluid.For this purpose, the hydraulic circuit may even have been flushed with this hydraulic fluid or previously vacuum-vacuumed to largely or completely remove any air bubbles that may have been present.

[0011] A (liquid) hydraulic fluid can be considered "degassed" when it contains little to no free air. In the case of a mineral oil, the remaining air content can be limited to a maximum of, for example, 8% to 9%. Furthermore, measures and / or fluids can be used to reduce the free air content or residual gas content in the degassed state to as low as 2.0% or even 0%. The partial pressure in the fluid can be measured as an indicator of the air content. For example, in the case of the hydraulic fluid HLP 46, the partial pressure is reduced to a level of 0 mbar [millibar] to a maximum of 180 mbar. The specific partial pressure to be set must be determined empirically for each application and should fall within this range. The partial pressure can be measured at a reference fluid temperature of, for example, 50°C or at an ambient temperature of 20°C.

[0012] The proposed electrohydraulic system is designed for operation at great depths underwater. This electrohydraulic system is designed for underwater operation at external ambient pressures above 100 bar or even above 250 bar.

[0013] The reservoir of the electrohydraulic system is pressure-compensated against the ambient pressure prevailing underwater. This is achieved by a pressure compensator in which a membrane is tightly clamped in an opening in the reservoir wall. The membrane thus seals the interior from the environment.

[0014] According to the arrangement presented here, a hydraulic axle for underwater or deep-sea use, or another sealed compact hydraulic axle, such as a servo-hydraulic axle, is filled with degassed oil. This measure reduces the compression volume (i.e., the "loss" of the oil when, in subsea applications, the oil is pressurized to ambient pressure via a pressure compensator) and results in smaller compensators and a smaller oil volume required for compression. More generally, the lower proportion of dissolved oxygen reduces the oxidation of the oil and the hydraulic component, and cavitation or the diesel effect (ignition of oil vapor dissolved in an air bubble) occurs less frequently. Overall, this significantly reduces the need for maintenance or oil changes in tightly sealed hydraulic systems.

[0015] For filling closed systems in underwater hydraulic systems, the compression modulus of the operating fluid is crucial for determining the size of the pressure equalization system. With a degassed operating fluid, the overall compression modulus of the fluid can be increased to a significant advantage, allowing for a smaller pressure equalization system. Simultaneously, the tendency for oxidation and cavitation is reduced, and the risk of diesel effects is minimized. Furthermore, improved control is possible because the higher and nearly linear compression modulus of the oil column positively impacts the control behavior.

[0016] The residual gas content of the degassed hydraulic fluid is at most 10%. In other words, the gas or air content in the hydraulic fluid is limited to a maximum of 10%.

[0017] In a dynamically actuated hydraulic axis, the residual gas content of the degassed hydraulic fluid can range from 7% to 9%. Dynamic axes are subject to frequent and / or rapid movements, for example, with a fluid column acceleration (especially with oil) of at least 20 m / s² (meters per second squared) and / or a pressure rise rate of at least 1,000 bar / s (bar per second). The aforementioned range is advantageous for dynamic axes because it reduces undesirable cavitation and / or erosion phenomena, e.g., in the control elements or the control block. Under high dynamic conditions, water present in the hydraulic fluid can evaporate, which can also lead to undesirable cavitation and / or erosion phenomena. This effect can be partially mitigated by appropriately degassed hydraulic fluid.

[0018] For a static hydraulic axis, a residual gas content of 2% to 5% is advantageous. In a static axis, infrequent and / or slow movements of the axis are performed, for example, with a fluid column acceleration (especially with oil) of less than 20 m / s² (meters per second squared) and / or a pressure rise rate of less than 1,000 bar / s (bar per second). Since no water evaporation is expected in this case, the air content can be further reduced, or even minimized, thus further utilizing the aforementioned properties of low oxidation (aging) and / or compressibility.

[0019] According to another aspect, degassed oil is used as a hydraulic fluid for an electrohydraulic system with a hydraulic consumer and a closed hydraulic circuit, wherein the hydraulic circuit comprises at least one control device, a hydraulic machine, and a closed hydraulic reservoir. The electrohydraulic system is designed for underwater operation at ambient pressures above 100 bar or even above 250 bar. In an underwater arrangement, a process valve is preferably provided to control a pumpable flow rate of a gaseous or liquid medium. The process valve can be adjusted linearly or rotaryally. A hydraulic cylinder or a rotary hydraulic motor can be used for this purpose.

[0020] According to a further aspect, a method for setting up an electro-hydraulic system with a hydraulic consumer and a closed hydraulic circuit is proposed, wherein the hydraulic circuit comprises at least a control means, a hydraulic machine and a closed hydraulic reservoir, comprising at least the following steps: a) Evacuating the hydraulic circuit, b) Filling the closed hydraulic circuit with degassed hydraulic fluid.

[0021] Before the initial filling or refilling of the hydraulic circuit, the closed part of the hydraulic system can be evacuated using a vacuuming device (e.g., a vacuum pump) as described in step a), so that there is as little or no air in the system as possible. The hydraulic circuit thus prepared is then filled with the degassed hydraulic fluid, for example, via a pipe / hose connection, as described in step b), so that the fill levels specified above can be achieved.

[0022] In step b), the degassed hydraulic fluid can be introduced into the hydraulic circuit using overpressure.

[0023] Preferably, in an additional step c), the hydraulic fluid is degassed. During preparation, the oxygen or air content in the hydraulic fluid to be filled is reduced. Preferably, the oxygen content in the medium is reduced to such an extent that no free oxygen / air remains in the medium. For example, this point is approximately 8.5 to 9% for a mineral oil ISO VG46, although depending on the system design, the oxygen content (remaining gas content) can preferably also be less than 8.5%.

[0024] Preferably, for refilling systems, a residual oxygen content of the hydraulic fluid of less than 8.5% is advantageous, which corresponds, for example, to a partial pressure of less than 180 mbar in the fluid.

[0025] In particular, step c) must be performed before step b) and can overlap with step a), at least temporarily. Specifically, a vacuuming device may be used to act on the hydraulic circuit and / or a hydraulic fluid accumulator. The hydraulic accumulator can interact with the vacuuming device to establish a pressure above the (initially undegassed) hydraulic fluid, for example, 0.2 bar absolute. This causes the hydraulic fluid to foam, resulting from increased bubble formation of the absorbed air and its subsequent release of gas upwards. In this way, the absorbed air can be removed from the hydraulic fluid (degassing). A circulation pump may be provided to further circulate the hydraulic fluid within the accumulator under vacuum, leading to improved and more uniform degassing.Furthermore, this circulation process can also be used to filter and / or clean the hydraulic fluid during degassing.

[0026] If the hydraulic fluid is degassed and the hydraulic circuit is vacuumed, the vacuum in the hydraulic fluid accumulator can be reduced (to atmospheric pressure or above), allowing the degassed hydraulic fluid to be quickly drawn in by the remaining vacuum in the hydraulic circuit and to fill the hydraulic circuit completely (as far as possible).

[0027] Furthermore, an apparatus for setting up a proposed electro-hydraulic system is proposed, which is designed with a hydraulic consumer and a closed hydraulic circuit, wherein the hydraulic circuit comprises at least a control device, a hydraulic machine, and a closed hydraulic reservoir. The apparatus has at least the following: a fluid inlet on the hydraulic reservoir, a vacuuming arrangement that can act on the hydraulic circuit, a device for providing degassed hydraulic fluid, comprising at least a vacuuming arrangement that can act on a separate hydraulic fluid accumulator, and a fluid outlet for degassed hydraulic fluid from the hydraulic fluid accumulator.

[0028] The apparatus can be designed such that the device for supplying degassed hydraulic fluid can be temporarily connected to the electrohydraulic system, particularly via the fluid inlet or outlet and / or a connection to the vacuum assembly. The device for supplying degassed hydraulic fluid is particularly mobile or separately movable and can be connected to different electrohydraulic systems. Setting up an electrohydraulic system here specifically includes filling the hydraulic circuit with a working fluid, namely the degassed hydraulic fluid or degassed oil.

[0029] The separate hydraulic fluid accumulator can be designed like a tank in which the hydraulic fluid is stored, for example, at least partially at atmospheric pressure. Before filling, a vacuum (approx. 0.2 bar) can be applied using a vacuum system to degasse the stored hydraulic fluid. Once the desired degassing state is reached, the degassed hydraulic fluid can be transferred from the fluid outlet of the accumulator, via the fluid inlet on the hydraulic reservoir, into the hydraulic circuit. This can be achieved by reducing or eliminating the vacuum in the accumulator after connecting the fluid outlet and inlet.

[0030] It is possible that the vacuuming arrangement of the device for supplying degassed hydraulic fluid can also be coupled to the hydraulic circuit. In this way, the vacuuming arrangement can also be used for evacuating the hydraulic circuit.

[0031] The device for providing degassed hydraulic fluid can be equipped with a circulation pump for the separate hydraulic fluid accumulator, which can implement a circular flow of the hydraulic fluid, possibly through at least one filter.

[0032] The explanations of the electrohydraulic system, the use of degassed oil as hydraulic fluid, the method for setting up an electrohydraulic system, and the apparatus for setting up an electrohydraulic system can be used interchangeably for further characterization.

[0033] The invention and its technical context are explained in more detail below with reference to the figures. Identical components are identified by the same reference numerals. The illustrations are schematic and not intended to demonstrate size relationships. The explanations given with reference to individual details of a figure can be extracted and freely combined with information from other figures or the preceding description, unless a person skilled in the art necessarily derives a different conclusion or such a combination is explicitly prohibited here. The figures schematically show: Fig. 1 : a side view of the electro-hydraulic system with one hydraulic axis and a closed hydraulic circuit with the process valve closed; Fig. 2 : a block diagram with a device for evacuating and filling a closed hydraulic circuit with degassed hydraulic fluid and flow directions of fluids; Fig. 3 : a circuit diagram of a hydraulic axle with a hydraulic circuit for a closed hydraulic circuit and Fig. 4a , 4b : in front view ( Fig. 4a ) and in side view ( Fig. 4b ) a device for degassing a hydraulic fluid and for filling a closed hydraulic circuit.

[0034] In Fig. 1 Figure 7 shows an electrohydraulic system with a hydraulic axis as a hydraulic consumer and a closed hydraulic circuit with a closed process valve 1.

[0035] The Fig. 1 Figure 1 shows an electro-hydraulic actuator 29 for a process valve 1 with a process valve housing 2 through which a process valve channel 3 passes, which continues at its outlets through pipes (not shown) and in which a gaseous or liquid medium flows from the seabed to a part of a drilling rig or a drilling ship protruding from the sea. The direction of flow is indicated by arrow 4.

[0036] A cavity is formed in the process valve housing 2, which crosses the process valve channel 3 and in which a process valve spool 5 with a flow opening 6 is movable transversely to the longitudinal direction of the process valve channel 3. In the state after the Fig. 1 In this state, the process valve channel 3 and the flow opening 6 in the process valve spool 5 do not overlap. The process valve 1 is therefore closed. In another state (not shown), the flow opening 6 and the process valve channel 3 largely overlap. The process valve 1 is almost closed.

[0037] A process valve 1 of the type shown and described for use should, on the one hand, be capable of controlled actuation and, on the other hand, also contribute to safety by quickly and reliably assuming a position corresponding to a safe state in the event of a malfunction. In this case, this safe state is a closed process valve 1.

[0038] The process valve 1 is actuated by a compact electro-hydraulic system 7, which is located underwater directly on the process valve 1. The hydraulic system 7 includes a reservoir 9, which is attached to the process valve 1 at one open end, creating an interior space 10 sealed from the environment. This interior space is filled with a hydraulic pressure fluid, e.g., oil, as the working fluid. For attachment to the process valve housing 2, the reservoir 9 has an internal flange on its open end, to which it is screwed. Radially outside the screw connections, a circumferential seal 11 is arranged between the internal flange of the reservoir 9 and the process valve housing 2. This seal is inserted into a circumferential groove in the process valve housing 2.

[0039] Container 9 is pressure-compensated against the ambient pressure prevailing underwater (seawater area 12). For this purpose, a membrane 14 is tightly clamped in an opening in the container wall of a pressure compensator 13. The interior 10 is thus sealed off from the environment by the membrane 14. A cable 8 leads out of container 9.

[0040] Inside the interior 10 of the container 9 is a hydraulic cylinder 15 (as a hydraulic consumer or actuating axis) with a cylinder housing 16, which is closed at its end by a cylinder base 17 and a cylinder head 18, with a piston 19 which is displaceable longitudinally within the cylinder housing 16, and with a first piston rod 20 which is rigidly connected to the piston 19 and projects away from the piston 19 on one side, is sealed, and passes through the cylinder head 18 in a manner not shown. The gap between the piston rod 20 and the cylinder head 18 is sealed by two seals (not shown) arranged axially apart from each other in the cylinder head 18. The process valve disc 5 is attached to the free end of the piston rod 20.Furthermore, a second piston rod 21 is rigidly connected to the piston 19 and projects away from the other side of the piston 19. This rod is guided in a sealed manner and passes through the cylinder base 17. The piston 19 divides the interior of the cylinder housing 16 into a first cylinder chamber 22 on the cylinder head side and a second cylinder chamber 23 on the bottom side, the volume of which depends on the position of the piston 19.

[0041] In the cylinder chamber 22 a helical compression spring 24 is housed, which surrounds the piston rod 20 and is clamped between the cylinder head 18 and the piston 19, acting on the piston 19 in a direction in which the piston rod 20 is retracted and the valve slide 5 is moved to close the process valve 1.

[0042] Inside the interior 10 of the container 9 is a hydraulic machine 25, which can be operated as a pump with two delivery directions. The hydraulic machine 25 has a pressure port 26 and a suction port 27, which is open to the interior 10. When operating as a pump, the hydraulic machine 25 can pump hydraulic fluid drawn from the interior 10 to the cylinder chamber 23 via the pressure port 26. Conversely, hydraulic fluid can be displaced from the cylinder chamber 23 into the interior 10 of the container 9 via the hydraulic machine 25. An electric motor 28 is mechanically coupled to the hydraulic machine 25 for a common rotary motion, e.g., via a shaft.

[0043] Furthermore, a hydraulic coupling is provided, which allows degassed hydraulic fluid or oil to be transferred underwater from a first system (e.g., storage tank or refill station, or emergency actuation robot) to a second system (closed hydraulic circuit) without contamination by seawater.

[0044] The hydraulic coupling comprises a block 33 and a filling rod 34 (hot rod). The block 33 is located inside the interior 10 of the reservoir 9, while, in the example shown, a rod-shaped filling part 35 is located inside the block 33 and a connection part 36 is located outside the block 33. A remotely controlled underwater vehicle 37 is connected to the connection part 33. The underwater vehicle 37 includes a storage tank 38 for degassed hydraulic fluid or oil as its hydraulic reservoir. Reference numeral 39 designates a control device for the oil flow from the underwater vehicle 37 to the coupling. The control device 39 includes, or is connected to, an on / off switching device for the flow of the degassed fluid from the storage tank 38. Reference numeral 40 designates an outlet area.

[0045] The underwater vehicle 37 can be configured as a Remote Operated Vehicle (ROV), Autonomous Underwater Vehicle (AUV) or Subsea Crawler (e.g. mining or cable laying).

[0046] A (hydraulic) arrangement of the type presented here can be installed in a new (hydraulic) device or retrofitted into an existing (hydraulic) device.

[0047] Fig. 2 Figure 1 shows a block diagram of an apparatus for setting up an electrohydraulic system. A device 41 for supplying degassed hydraulic fluid is connected to a vacuum pump or vacuuming unit 43, which serves to degas the hydraulic fluid. The hydraulic circuit 42 is also optionally connected to the same vacuum pump or vacuuming unit 43, which can be used to evacuate the hydraulic circuit 42. Alternatively (not shown), two separate vacuum pumps can be connected, one each to the device 41 and to the closed hydraulic circuit 42. Furthermore, a draining device 44 is connected to the hydraulic circuit 42, which is used to drain used oil. Additionally, a venting device 45 can be connected to the hydraulic circuit 42. Arrows 46 and 47 each indicate a hydraulic fluid flow, and arrows 48, 49, and 50 each indicate an air flow.The arrowheads indicate the direction of the current.

[0048] Fig. 3 shows a circuit diagram of a hydraulic axle 51 with a hydraulic circuit for a closed hydraulic circuit. In Fig. 3 A compact axle is shown. In this axle, a hydraulic pump, an electric motor, and a multi-surface cylinder are combined into a single unit. Several control valves are provided in the control block for controlling the multi-surface cylinder.

[0049] The hydraulic axle 51 (servo-hydraulic compact axle) has a control block 52 to which a hydraulic cylinder 54 is connected via an intermediate block 53. A hydraulic machine 55, which can be used as a hydraulic pump and hydraulic motor in both directions, is also connected to the control block 52. The hydraulic machine 55 can be driven by an electric motor 56. A hydraulic accumulator 57 is also connected to the control block 52.

[0050] The hydraulic cylinder 54 is a multi-surface cylinder whose piston 58 has an extension surface 59, a first retraction surface 60, and a second retraction surface 61. The piston 58 can be extended and retracted in rapid traverse and power traverse via the control block 52 and the intermediate block 53. Furthermore, decompression can occur after the power traverse in both the extension and retraction directions. The piston 48 can also be clamped in a pressure holding phase. Additionally, a storage charging mode can be provided.

[0051] The hydraulic machine 55 is connected to the control block 2 via a first pump connection 62 and a second pump connection 61. The first pump connection 62 is fluidically connected to the extension surface 59 via a first control valve 64 of the control block 52. The first control valve 64 is designed as a switching valve, the valve spool of which is actuated in its closed position by a valve spring and can be moved to its open position by an electromagnetic actuator or manually. The second pump connection 63 is fluidly connected to the second retraction surface 61 via a second control valve 65, which is designed in accordance with the first control valve 64. The extension surface 59 is fluidly connected to the first retraction surface 60 via a third control valve 66, which is designed in accordance with the control valves 64 and 65.A flow path between the first pump port 62 and the first control valve 64 can be fluidically connected to the hydraulic accumulator 57 via a fourth control valve 64. Furthermore, the hydraulic accumulator 57 can be connected to the first pump port 62 via a first check valve 60 and to the second pump port 63 via a second check valve 69. The check valves 68 and 69 each open in a flow direction away from the hydraulic accumulator 57. Additionally, the first pump port 62 can be connected to the hydraulic accumulator 57 via a pressure relief valve 70, and the second pump port 63 via a pressure relief valve 71. Furthermore, the extension surface 59 can also be fluidically connected to the hydraulic accumulator 57 via a pressure relief valve 72, and the second inlet surface 61 via a pressure relief valve 73. Two switching valves 74 and 75 are arranged in series in the intermediate block 53. These are designed accordingly for control valves 64 to 67.The hydraulic fluid connection between the second pump port 63 and the first entry surface 60 can be opened and closed via the control valves 74 and 75. The hydraulic fluid connection is open when both control valves 74 and 75 are in their open position. If the hydraulic cylinder 54 is mounted vertically, the piston 58 can be held up by the control valves 74 and 75 when they are closed. Thus, these valves act as hold-up valves to protect an annular chamber of the hydraulic cylinder 54, which can be used as a press cylinder and is bounded by the first entry surface 60. The second control valve 75 is located between the control valve 74 and the hydraulic cylinder 54. A pressure relief valve 76 is connected between the first entry surface 60 and the second control valve 75. This is located in the intermediate block 53 and is connected to the hydraulic accumulator 57 via the control block 52.

[0052] The intermediate block 53 further comprises a first connection surface 77 and a second connection surface 78. The first connection surface 77 is connected to a connection surface 79 or end surface of the control block 52. The hydraulic cylinder 54 is connected to the second connection surface 78. The connection surfaces 77, 78, and 79 have the same hole pattern. Thus, the hydraulic cylinder 54 could also be connected directly to the control block 52 without the intermediate block 53.

[0053] Number 80 designates a filter, and numbers 81 to 84 designate check valves (without pressure drop).

[0054] The Fig. 4a , 4b schematically show in front view ( Fig. 4a ) and in side view ( Fig. 4b ) a device 41 for providing degassed hydraulic fluid and for filling a closed hydraulic circuit 42 (see Fig. 2 ) with the degassed hydraulic fluid.

[0055] Device 41 can be used to prepare the degassed oil required for filling a hydraulic system. Evacuation of the hydraulic bores in the control block, the interiors of the superstructure, and the cylinder (electrohydraulic system) is possible with device 41. Filling with the prepared hydraulic fluid is then possible. If device 41 is connected to a hydraulic system using pressure-resistant hydraulic hoses 88 (not shown), the system can be flushed, and the hydraulic fluid can be evacuated and filtered in a bypass flow.

[0056] The maximum flow rate of the installed pump (filter pump 92) is 7.5 l / min. The operating temperature range is +10 °C to 60 °C. Suitable for hydraulic fluids with a viscosity of 10 to 300 m² / s.

[0057] The device 41 consists of a reservoir or separate hydraulic fluid accumulator 90 (oil reservoir), which is vacuum-tight and pressure-tight. A filter pump unit (or circulation pump) 91 is mounted on the lower part of the hydraulic fluid accumulator 90 and piped to the hydraulic fluid accumulator 90 (tank) via a bypass pipe 89 with a pressure of 3 bar. The filter pump unit 91 consists of an electrically operated filter pump 92, e.g., an internal gear pump with a replaceable low-pressure filter, which is monitored by an optical maintenance indicator. 93 designates an electric motor (motor "main pump") and 94 designates a line filter.

[0058] A low-pressure distribution block is piped to the filter pump unit 91 and the upper part of the hydraulic fluid accumulator 90. The distribution block has low-pressure push-in connections (e.g., for filling a hydraulic system) that can be switched on and off using ball valves 95, and a leak-free hydraulic quick-release coupling for refilling. A mobile frame supports the hydraulic fluid accumulator 90 with the filter pump unit 91 and the distribution block, as well as a vacuum pump or vacuuming unit 43. This vacuuming unit 43 is connected to the upper part of the hydraulic fluid accumulator 90 via a low-pressure hose and an oil separator. A 3 / 2-way ball valve 97 allows the hydraulic fluid accumulator 90 to be connected to the atmosphere or to the vacuum pump or vacuuming unit 43. The pressure hoses are each fitted with a hydraulic quick-release coupling at one end. The number 96 designates a coupling sleeve (hydraulic filling).

[0059] The hydraulic machine 25; 55 is in Fig. 1 as a hydraulic pump with two delivery directions and in Fig. 3 The hydraulic consumer 86 is shown as a hydraulic pump and / or hydraulic motor. Fig. 1 as a double-acting hydraulic cylinder 15 with a double-sided piston rod and in Fig. 3 depicted as a multi-surface cylinder. The hydraulic reservoir 87 is in Fig. 1 as container 9 and in Fig. 3 shown as hydraulic accumulator 57.

Claims

1. Electrohydraulic system (7) having a container (9) which can be pressure-compensated with respect to an ambient pressure prevailing under water of above 100 bar and has a pressure compensator (13) with a membrane (14) which is tightly clamped in an opening in a container wall and partitions off the interior (10) of the container (9) from the environment, wherein the electrohydraulic system (7) is designed with a hydraulic consumer (86) and at least one closed hydraulic circuit (42), wherein the hydraulic circuit (42) comprises at least a control means, a hydraulic machine (25; 55) and a closed hydraulic reservoir, characterized in that the closed hydraulic circuit (42) is filled with degassed hydraulic fluid, the residual gas content of which is 10% at most.

2. Electrohydraulic system (7) according to Claim 1, wherein the hydraulic machine (25; 55) draws hydraulic fluid for the hydraulic circuit (42) or displaces hydraulic fluid from the hydraulic circuit (42) via a connection in the interior (10) of the container (9).

3. Electrohydraulic system (7) according to Claim 1 or 2, wherein the hydraulic consumer (86) comprises a dynamically actuable axle (51) and a residual gas content of the degassed hydraulic fluid lies in the range of 7% to 9%.

4. Electrohydraulic system (7) according to Claim 1 or 2, wherein the hydraulic consumer (86) comprises a statically actuable axle (51) and a residual gas content of the degassed hydraulic fluid lies in the range of 2% to 5%.

5. Use of degassed oil as a hydraulic fluid for an electrohydraulic system (7) having a hydraulic consumer (86) and a closed hydraulic circuit (42), wherein the hydraulic circuit (42) comprises at least a control means, a hydraulic machine (25; 55) and a closed hydraulic reservoir (87), for reducing the compression volume of the oil when ambient pressure above 100 bar is applied to the oil by a pressure compensator in an underwater application.

6. Use according to Claim 5 for extending the service life of the membrane of a pressure compensator under water.

7. Method for setting up an electrohydraulic system (7) according to Claim 1 comprising at least the following steps: a) evacuating the hydraulic circuit (42), b) filling the closed hydraulic circuit (42) with degassed hydraulic fluid.

8. Method according to Claim 7, wherein the degassed hydraulic fluid is introduced into the hydraulic circuit (42) by means of excess pressure in step b).