NO20180204A1

NO20180204A1 - Pressurisation module and secondary-controlled hydraulic system

Info

Publication number: NO20180204A1
Application number: NO20180204A
Authority: NO
Inventors: Sander Boeijen
Original assignee: Bosch Gmbh Robert
Priority date: 2017-02-08
Filing date: 2018-02-08
Publication date: 2018-08-09
Also published as: CN108397428A; CN108397428B; DE102017203280A1

Abstract

A pressurisation module, and a secondary- controlled hydraulic system which is pro-vided with such a pressurisation module, are disclosed. By means of the pressurisa-tion module, a feed pressure can be built up, without a feed pump, in the low-pressure branch of the system.A pressurisation module, and a secondary controlled hydraulic system which is provided with such a pressurisation module, are disclosed. By means of the pressurisation module, a feed pressure can be built up, without a feed pump, in the low-pressure branch of the system.

Description

Pressurisation module and secondary-controlled hydraulic system

Description

The invention relates to a pressurisation module and a secondary-controlled hydraulic drive system with a pressurisation module of the same kind.

A secondary control system is an energy-saving drive concept with high dynamics for setting up speed, position, and torque closed-loop controls with energy recovery. The basic structure of such a secondary-controlled drive concept, which can, for example, be used to drive a winch or other functional unit, is described in the article, "Investigation of hydraulic systems", in the journal o p 1-2/2011. Accordingly, a secondarycontrolled drive has a primary unit preferably designed as a variable-displacement pump, which is preferably pressure-controlled and which feeds a high-pressure network on which the secondary units operate, which are designed, for example, as hydrostatic axial piston units. Power is drawn as required from the high-pressure network and returned to it without throttling by adjusting the stroke volume of the axial piston units to the load case in question. Here, several units operating as motor or pump can be connected in parallel, wherein a four-quadrant operation is possible, wherein the units for speed or torque reversal can be pivoted about "zero". If required, a high-pressure accumulator (energy accumulator) can be arranged between the primary and secondary units, which serves to cover volume peaks and which, in addition, is used to store the energy which is fed back into the hydraulic network by the secondary unit during pump operation, when no other consumers are present. Together with the pressure-controlled primary unit and the operating state of the secondary unit, the loading state of the accumulator and its pressurisation pressure determine the injected high pressure of the system. The low-pressure branch is pressurised by a feed pump to a minimum pressure (feed pressure). An energy accumulator can also be provided on the low-pressure side to store energy.

A disadvantage of such drive systems is that, to pressurise the low-pressure branch, considerable outlay on device technology is required.

In marine and offshore applications, a variety of winch drives are often disposed on each offshore platform or vessel. In principle, two main possibilities exist. Firstly, the individual winch drives can each be operated in a closed circuit, with one pump each and one hydraulic motor each. Such a solution is extremely complicated, since a plurality of pumps and the corresponding pipework must be provided for the closed circuits of the winch drives.

To reduce the outlay on device technology, it is known for such winch drives to be arranged in an open hydraulic circuit, wherein the pressure medium is supplied via a central pump, which then supplies pressure medium to the secondary units connected to the constant pressure network of the ship or the platform. Such a solution can be relatively easily connected to the central pressure-medium supply of the ship or offshore platform. Of course, apart from ships, the principle of secondary control is also applied on land and to hydraulic consumers other than winches. However, the problem is the pressurisation of the low-pressure branch, since a separate feedpressure circuit must be provided for this.

In contrast, the invention is based upon the aim of creating a pressurisation module, as well as a secondary-controlled hydraulic system with such a pressurisation module, wherein a pressurisation of the low-pressure branch is made possible with little outlay on device technology.

This aim is achieved with respect to the pressurisation module by the combination of the features of claim 1 and, with respect to the secondary-controlled hydraulic system, by the combination of the features of independent claim 11. In most cases, the low-pressure circuit can be a standard return line, as is used in connection with constant pressure circuits.

Advantageous developments of the invention are the subject matter of the dependent claims.

The pressurisation module according to the invention for a secondary-controlled hydraulic system - preferably, a drive system - has a pressure channel (high-pressure line) and a low-pressure channel (low-pressure line), wherein the latter is pressurised to a feed pressure. According to the invention, in a pressurisation channel between the pressure channel and the low-pressure channel, a flow control valve is provided via which a predetermined volume flow flows from the high-pressure side to the lowpressure side, wherein the pressure drop at the flow control valve is selected such that the desired supply pressure is established on the low-pressure side.

The pressure-medium flow from the high-pressure side to the low-pressure side via the flow control valve has the further advantage that fresh pressure medium flows into the low-pressure branch, thereby ensuring that the temperature of the pressure medium does not increase excessively when flowing through the secondary unit. A pressurisation module of this kind can be readily integrated as a "plug-and-play" solution into existing drive concepts, so that, for example, even an installation in a central pressure-medium supply system of a ship or offshore platform is made possible in a simple manner, with no need to provide an additional feed-pressure supply, such as, for example, feed-pressure pumps, with their associated closed-loop control system and pipework.

In one embodiment of the invention, a check valve, which must be activated to build up the feed pressure, is installed upstream of the flow control valve.

Such a check valve may, for example, be a pilot-controlled non-return valve or a directional seated valve with a blocking position and an open position.

The flow control valve for limiting the pressure medium flow between the pressure channel and the low-pressure channel can be designed as an adjustable aperture / throttle or as a flow regulation valve.

In the second alternative, it is preferred for a pressure transducer and a temperature sensor to be assigned to the flow regulation valve so that the flow regulation valve can be regulated as a function of the pressure and the temperature in the lowpressure branch. In this way, it is ensured that the pressure medium in the lowpressure branch is not excessively heated and, moreover, that the required feed pressure is present. The particular advantage of the second alternative is the fact that the exact amount of pressure medium is supplied to the low-pressure side which is needed to keep the pressure there at the desired level and the temperature within a favourable range, and thus keep energy losses low. In the first alternative, however, the quantity of pressure medium is set in accordance with the maximum power, so that energy losses will occur whenever the maximum power is not provided.

To cover volumetric flow peaks and to store energy, an energy accumulator can be provided in the low-pressure branch and/or in the high-pressure branch.

One embodiment of the invention envisages providing a filter in a control line branching off from the pressure channel and leading to the secondary unit.

The pressure in the low-pressure branch can be limited via a low-pressure pressurerelief valve.

The pressurisation module can furthermore be designed with a secondary unit and/or an electronic control unit for controlling the primary and secondary units, and also the functionally-relevant valve devices such as, for example, the flow regulation valve.

The secondary-controlled hydraulic system according to the invention has, as mentioned at the beginning, a primary unit which is connected via the pressure medium in a pressure channel to a secondary unit for driving a functional unit, such as a winch, wherein the secondary unit is connected via a low-pressure channel to a tank or other pressure medium sink. Furthermore, the secondary-controlled system has a pressurisation module in the sense of the above statements.

Here, the secondary unit, i.e., the hydraulic motor, can also be integrated in the pressurisation module so that this, in principle, includes the motor, the controller, and the valves required for control.

Preferred embodiments of the invention will be explained in more detail below, with reference to the figures.

The drawings show:

Figure 1 a circuit diagram of a secondary-controlled hydraulic system/drive realised with a pressurisation module according to the invention, wherein a feed pressure is set by a constant flushing flow from the high-pressure side to the lowpressure side, and

Figure 2 a variant in which the feed pressure is set via an adjustable flushing flow.

The invention is explained below with reference to a secondary-controlled winch drive 1, which is installed, for example, on an offshore platform or a ship. This has, for example, a central pressure-medium supply unit 2, to which the winch drive is connected. The pressure-medium supply unit 2 has at least one pressure-controlled variable displacement pump 4, which sucks the pressure medium from a tank T. The pressure port of the variable displacement pump 4 is connected to a central pressure line 6, through which, as shown in Figure 1, the individual hydraulic consumers, e.g., the winch drive 1 and, optionally, additional winch drives or consumers, are supplied with pressure medium. The pressure medium flowing back from these consumers flows via a ring tank line 8 back to the tank T.

A pressure channel 10, through which the winch drive 1 is supplied with pressure medium, branches off from the central pressure line 6 of the pressure medium supply unit 2. In the embodiment shown in Figure 1, this has a pressurisation module 12, indicated by a dash-dotted line, in which the valve devices required for operating the winch are arranged; these will be discussed in more detail below. The secondary unit - specifically, an axial piston unit - which can operate as both a motor and pump, is connected to the pressurisation module 12 such that a four-quadrant operation is possible, wherein the units need to be swivelled about "zero" for speed or torque reversal. The adjustment of the swivel angle of the axial piston unit, referred to in the following as hydraulic motor 14, is effected via a final control element, not shown in more detail in Figure 1, which is supplied with pressure medium from the pressurisation module via a control line 66. The design and control of such axial piston units are known, making further explanations unnecessary.

A drive shaft of the hydraulic motor 14 drives a winch 18, with which a load 20 can be hoisted or lowered (reeling in the winch rope, uncoiling the winch rope). The winch 18 has a brake, not shown in more detail, which can be released by means of a brake release cylinder 16. The pressure channel 10 is connected to a connection of the hydraulic motor 14. A low-pressure channel 22 leading to the ring tank line 8 has a pressure-medium connection to the other connection of the hydraulic motor 14. As used herein, the term, "channel", covers any pressure medium line.

In accordance with the illustration in Figure 1, between the pressure channel 10 and the low-pressure channel 22, a bypass channel 24 is provided, in which a pressurerelief valve 26 is arranged which limits the maximum pressure in the pressure line 10 to, for example, 320 bar, and, if this maximum pressure is exceeded, activates a pressure-medium connection from the pressure channel 10 to the low-pressure channel 22. Seen in the direction of pressure build-up, an optional non-return valve 28 is arranged upstream of the bypass line 24, by means of which a return flow of pressure medium in the direction of the central pressure supply is prevented. In the case in which a return flow of the pressure medium (energy feedback) to the central pressure line 6 is to be enabled, this non-return valve 28 can be dispensed with. This is, for example, the case when the energy recovered from the winch drive can be used for driving other hydraulic consumers which are connected to the pressure line 6. In this case, the bypass channel 24 together with the pressure-relief valve 26 can be removed from the module 12 and arranged centrally in the hydraulic system.

Furthermore, a pressure accumulator 30 is arranged in the pressure line 10, whose pressure is monitored by a pressure transducer 32. In the embodiment according to Figure 1, upstream of the non-return valve 28, a pressurisation channel 34 branches off from the pressure channel 10, discharges into the low-pressure channel 22, and thus, from the hydraulic point of view, runs parallel to the bypass channel 24. In this pressurisation channel 34, a flow control valve is arranged which, in the illustrated embodiment, takes the form of an adjustable aperture / throttle 36, whose crosssection can be adjusted to allow pressure medium - referred to below as flushing flow - to flow from the high-pressure side to the low-pressure side. The cross-section is adjusted so that, on the low-pressure side, a feed pressure is set in the low-pressure channel 22, which is necessary for the optimal operation of the winch drive 1. This feed pressure can, for example, be 16 bar. Overheating of the hydraulic motor 14 is also prevented by the flushing flow.

In the embodiment illustrated, the feed pressure in the low-pressure channel 22 is limited by a low-pressure pressure-relief valve 38 to which, as indicated in Figure 1, is applied the pressure difference in the low-pressure channel 22 and in a leakage line 40 which is explained in more detail below. Accordingly, the low-pressure pressure-relief valve 38 is set to a pressure of, for example, 16 bar. Downstream (towards the tank T) a pressurisation valve 42 is provided in the low-pressure channel 22 or in the region of the ring tank line 8, which, for example, takes the form of a springtensioned non-return valve and which opens the pressure-medium connection to the tank T when a pressure of, for example, 6 bar is exceeded. If the non-return valve 42 is located in the between the tank and the branches to the individual hydraulic consumers, the pressurisation generated by the non-return valve 8 will be effective for all branches. A non-return valve 8 can also be inserted so that it is effective for several, but not for all, branches.

A pilot-controlled non-return valve 44 is assigned to the flow control valve 36, and, in the blocking state, blocks a flow of pressure medium from the high-pressure side to the low-pressure side. Unblocking takes place via an unblocking line 46, to which, as explained below, the pump pressure is applied.

When the non-return valve 44 is open, a flushing flow, which corresponds, for example, to 25 to 30% of the maximum pressure-medium volume flow required to operate the winch 18, flows via the flow control valve 36. A constant supply of fresh pressure medium which has not been heated by the hydraulic motor 14 is supplied via the flushing flow to the low-pressure side, thereby resulting in a constant flushing action there, which also prevents any excessive heating of the pressure medium during winching operation.

This is a significant difference from conventional solutions in which the feed pressure in the low-pressure branch must be generated by a dedicated feed pump, wherein no - or only a minor degree of - pressure-medium exchange takes place, with the result that the pressure medium can heat up considerably with high winch loads. Furthermore, this kind of feed pressure network is not provided in the central pressuremedium supply system 2 which is usually present on a ship, so that the outlay on device technology required to install the additional feed pump and associated pipework is considerable.

In the low-pressure channel 22, a low-pressure accumulator 48 is provided, whose pressure is also monitored via a pressure transducer 50. Furthermore, the temperature of the pressure medium in the low-pressure branch is monitored via a temperature sensor 52, so that the valve elements described can also be controlled as a function of these pressure and temperature signals. In the embodiment shown in Figure 1, this control is effected via a central control unit or a controller, which is indicated in Figure 1 by the reference number 54.

The brake release cylinder 16 for releasing the brake of the winch 18 is controlled via a brake release valve 56 controlled by the controller 54 and, in the illustrated embodiment, designed as a 3/2-way valve. The provision of a brake and the components provided for releasing the brake are typical of winch drives and are optional.

An input port P of the brake release valve 56 is connected via a line 58 to the pressure channel 10. An output port A of the brake release valve 56 leads via a brake line 60 to the brake release cylinder 16. The pressure in the brake line 60, and thus in the brake release cylinder 16, is monitored by a further pressure transducer 62. It can be determined on the basis of the detected pressure whether the brake is released or not. The aforementioned unblocking line 46 branches off from the line 60, so that the non-return valve 44 is always unblocked when the brake is released.

The brake release valve 56 has, in addition, a tank port T, which is connected via a channel 64 to the low-pressure channel 22. In its basic, spring-tensioned position, marked (a), the brake release valve 56 connects the brake line 60 to the channel 64, so that the brake release cylinder 16 is depressurised - the brake is thus active. The input port P is shut off, leakage-free. The brake release valve 56 can be switched, via the controller 54, into its position (B), in which the output port A is connected to the pressure port P. In this case, the brake line 60 is connected via the line 58 to the pressure line 10, so that the brake release cylinder 16 extends, and the brake releases. In the switching position (b), the tank port T is shut off, leakage-free. The basic structure and the function of a final control element of this kind and its control are, per se, known, making further explanations unnecessary.

The control line 66, by which the final control element of the hydraulic motor 14 is supplied with pressure medium, branches off from the line 58. A swivel-angle transducer may be provided which detects the swivel angle of the hydraulic motor 14 and sends a corresponding control signal to the controller 54. A filter unit 68, by means of which the pressure medium is filtered, is provided in the control line 66. The pressure loss across the filter unit 68 is monitored, so that, in the event of an increasing pressure loss due to clogging of the filter, a signal is sent to the controller 54 via a switch 70 in the filter unit 68, indicating that the filter element must be replaced or cleaned.

The pressurisation module 12 described thus contains all of the valve units and functional elements required for the operation of the winch 1 and can be integrated into an existing central pressure-medium supply unit 2 with little outlay on device technology and control technology.

The secondary-controlled hydraulic system according to the invention with the pressurisation module 12 described thus includes a hydraulic motor 14 whose stroke volume can be adjusted. Furthermore, a device for releasing a brake (not shown), by which the winch is held in a predetermined position, and a control unit for regulating the stroke volume of the motor should be installed. The pressurisation module 12 is, as described above, designed to build up the required feed pressure on the lowpressure side.

Both the high-pressure side and the low-pressure side are protected by pressurerelief valves. The secondary-controlled system also has devices for cooling and flushing, so that contamination of the pressure medium and of the components through which it flows is prevented, as is excessive heating of the pressure medium.

All of the required safety functions for the operation of the winch are present. Pressure, temperature, swivel angle, speed of rotation of the winch, and so on can, depending upon requirements, be detected by suitable sensors.

The controller 54 is designed to control the winch drive 1 by means of software functions that make the usual winch functions possible. These are, for example, hauling and paying out the winch 18, applying a constant tension to the load 20 or winch rope (mooring), implementing an overload protection, and a freewheel function. Furthermore, a high-speed hauling or paying-out function is to be implemented, which, for example, is activated when no load is attached (empty-hook mode). In addition, a load-dependent control is to be made possible.

All of this can be installed in the system according to the invention with relatively little effort.

In the case of the embodiment described above, the controller 54 or the control unit is arranged centrally. Figure 2 shows a variant in which the controller 54 is integrated into the pressurisation module 12. In the embodiment according to Figure 2, the pressurisation module 12 also includes the hydraulic motor 14 with the winch 18, as well as the brake release cylinder 16 and the valve elements necessary for its operation. Apart from the increased functionality of the pressurisation module 12, the basic structure of the winch drive 1 shown in Figure 2 corresponds to that of the embodiment shown in Figure 1, so that only the essential differences will be discussed here, and, other than that, reference can be made to the descriptions provided above.

As in the previously described embodiment, the winch drive - in the present case, the pressurisation module 12 - is connected to the central pressure-medium supply, which provides a constant pressure. For the sake of simplicity, this central pressuremedium supply system is no longer shown in Figure 2. The pressure medium is supplied to the hydraulic motor 14 and its actuation mechanism and to the brake release cylinder 16 in the same way as in the previously described embodiment, so that a description will be dispensed with. Components which correspond to each other have been given the same reference numbers in Figure 1 and Figure 2.

As in the previously described embodiment, the high-pressure branch is safeguarded via the pressure-relief valve 26 in the bypass channel 24. The pressure in the lowpressure channel 22 is limited via the low-pressure pressure-relief valve 38. In the embodiment according to Figure 2, parallel to this bypass channel 24, there extends a feeder line 72 in which a feeder valve 74 is provided, so that pressure medium can be fed into the high-pressure branch from the low-pressure branch to prevent cavitation in the event of a pressure drop in the pressure channel 10, which may have been caused by, for example, a rapid lowering of the load 20 due to its weight.

As in the previously described embodiment, upstream of the non-return valve 28, the pressurisation channel 34 branches off from the pressure channel 10. In the illustrated embodiment example, the flow control valve takes the form of a flow regulation valve 74 with a continuously adjustable throttle cross-section. Pressure and temperature are, once again, registered by the pressure transducer 50 and temperature sensor 52 respectively and reported to the controller 54, which then sets the throttle cross-section of the flow control valve 74 accordingly. The flushing flow can be set variably via this flow control valve 74, such that the desired pressurisation pressure / feed pressure is set in the low-pressure branch, i.e., in the low-pressure channel 22, wherein the pressure medium can be kept within a predetermined temperature range. In the illustrated embodiment, the flow control valve 74 is designed in such a way that, starting from the maximum throttle cross-section, it can be closed down completely, so that the flushing flow is then, accordingly, equal to zero. Since, however, no leakage-free shut-off is possible, a check valve is, in turn, installed upstream of the flow regulation valve 74. In the embodiment shown in Figure 2, this takes the form of a 2/2-way valve 76, which is pretensioned in the blocking position by a spring and which can be shifted into an open position by means of an electromagnet (controlled via the controller 24).

The winch drive 1 shown in Figure 2 is thus of modular design and can be very easily connected to the existing constant-pressure supply of a ship, an offshore platform, or another installation. The advantages of the modular concept described above are that, for one, a plug-and-play solution is provided, which can be connected to an ex isting, central pressure-medium supply of a ship or the like only via the hydraulic interfaces of pressure connection, tank connection, and, if applicable, a control connection. The electrical interfaces are extremely simple in design and can, for example, be connected via a bus interface to the main control system.

The modular solution is also very cost-effective, since the hydraulic motor, the hydraulic components, the control system, and the software can be put together on a modular basis to create a single unit. This also results in an extremely compact design which can be installed with low space requirements. Optimal adjustment to the winch in question can improve the efficiency of the winch, wherein a variety of operating modes are made available by an appropriate programming of the controller. Due to the integral implementation adapted to the winch in question, the energy consumption of the modular system is optimised. Depending upon whether the described non-return valve 28 is provided, an energy feedback to the central supply can be provided or not.

Due to the perfectly mutually matched hydraulic components of the module and the local intelligence which can be supplied with the built-in controller 54, the ship-side control system can have a comparatively simple design, wherein all safety functions are integrated into the module. The modular design reduces the pipework required, thus lowering costs further. The large number of connection components required by conventional solutions for the safety functions and control of the function elements is also minimised in the case of the modular solution, since all necessary connections are integrated into the module.

The system according to the invention can therefore be used particularly advantageously with winch drives when there are performance requirements and winch capacity requirements which cannot be satisfied with conventional winch control systems.

The concept according to the invention can also be implemented with winches which are driven by several motors.

A pressurisation module, and a secondary-controlled hydraulic system which is provided with such a pressurisation module, are disclosed. By means of the pressurisation module, a feed pressure can be built up, without a feed pump, in the lowpressure branch of the system.

The examples shown are hydraulic winch drives. The pressurisation module can, however, be used for all secondary-controlled hydrostatic drives which are connected to a central pressure line. The system can be made even more efficient by omitting the non-return valve 28 and connecting the pressure-relief valve 26 to the central pressure line. In this case, energy recovered by the secondary units can be used by any other hydraulic consumer connected to the central pressure line, or at least stored in a central hydraulic accumulator connected to the central pressure line. This opens up new possibilities for using secondary-controlled hydrostatic units for energy recovery in systems with many hydraulic consumers connected to the central pressure line. This can greatly reduce the amount of oil that is necessary for pressurising the hydraulic motor. A local flushing to ensure compliance with the temperature does not appear absolutely necessary. Measurements of temperature can then also be done centrally instead of locally. All that appears necessary is local measurement of the pressure using a pressure transducer 50.

List of reference numbers

1 Winch drive

2 Central pressure medium supply (constant pressure) 4 Variable displacement pump

6 Central pressure line

8 Ring tank line

10 Pressure channel

12 Pressurisation module

14 Hydraulic motor

16 Brake release cylinder

18 Winch

20 Load

22 Low-pressure channel

24 Bypass channel

26 Pressure-relief valve

28 Non-return valve

30 Pressure accumulator

32 Pressure transducer

34 Pressurisation channel

36 Throttle/aperture

38 Low-pressure pressure-relief valve

40 Leakage line

42 Pressurisation valve

44 Pilot-controlled non-return valve

46 Unblocking line

48 Low-pressure accumulator

50 Pressure transducer

52 Temperature sensor

54 Controller

56 Brake release valve

58 Line

60 Brake line

62 Pressure transducer 64 Channel

66 Control line

68 Filter unit

70 Switch

72 Feeder line

74 Flow regulation valve 76 Directional seated valve

Claims

1. Pressurisation module for a hydraulic drive system with secondary regulation, with a pressure channel (10) and a low-pressure channel (22) that is pressurised to a feed pressure, wherein, in a pressurisation channel (34) between the pressure channel (10) and the low-pressure channel (22), a flow control valve is provided by means of which a flushing flow from the pressure channel (10) to the low-pressure channel (22) can be adjusted for the purpose of pressurisation.

2. Pressurisation module according to claim 1, wherein a check valve is pressurised with respect to the flow control valve.

3. Pressurisation module according to claim 2, wherein the check valve is a pilot-controlled non-return valve (44) or a directional seated valve (76) with a blocking position and an open position.

4. Pressurisation module according to one of the preceding claims, wherein the flow control valve is an adjustable throttle or orifice (36), or a flow regulation valve (74).

5. Pressurisation module according to claim 3 or 4, wherein a pressure transducer (50) and a temperature sensor (52) are assigned to the flow control valve so that this can be adjusted or regulated as a function of pressure and temperature.

6. Pressurisation module according to one of the preceding claims, wherein a pressure accumulator (30) is provided in the pressure channel (10) and/or a lowpressure accumulator (48) is provided in the low-pressure channel (22).

7. Pressurisation module according to one of the preceding claims, with a bypass channel (24) between the pressure channel (10) and the low-pressure channel (22), in which a pressure-relief valve (26) is arranged to limit the maximum pressure.

8. Pressurisation module according to one of the preceding claims, with a control line (66) which branches off from the pressure channel (10) and in which a filter unit (68) is arranged.

9. Pressurisation module according to one of the preceding claims, wherein, on the low-pressure side, a low-pressure pressure-relief valve (38) is provided which limits the feed pressure.

10. Pressurisation module according to one of the preceding claims, with a secondary unit and/or a controller (54).

11. Secondary-controlled drive system with a primary unit, which is connected by pressure medium via a pressure channel (10) to a secondary unit for driving a functional unit, such as a winch (18), wherein the secondary unit is connected via a low-pressure channel to a tank (T) or the like via a low-pressure channel (22) and to a pressurisation module (12) according to one of the preceding claims.