EP1450048B1 - Valve arrangement - Google Patents

Description

The invention relates to a hydraulic arrangement comprising a hydraulic cylinder having a first chamber and a second chamber and a valve arrangement, the valve arrangement comprising a control valve which selectively connects the first and second chambers of the hydraulic cylinder via a first and a second supply line to a hydraulic pressure source or a container connects, a first switching valve which controls the flow in a first hydraulic line extending between the first chamber and the container and which opens due to a switching signal, a second switching valve, the flow in a running between the second chamber and the container second Hydraulic line controls and which opens due to the switching signal parallel to the first switching valve, wherein by opening the switching valves a floating position is adjustable, in which the first chamber and the second chamber miteinand directly or indirectly via the container he associated with, and a load-holding valve assembly comprising a check valve, which is due to spring force in a closed position and opens in response to the pressure in the second supply line, and a parallel to the check valve arranged check valve, wherein the check valve opens in the direction of the hydraulic cylinder ,

Valve assemblies with implemented float positions, thereby allowing free movement of a hydraulic consumer, are known in the art. Both connection sides of the hydraulic consumer are connected both with each other and with low pressure or without pressure with a tank or hydraulic tank. Such valve arrangements found in construction or loading vehicles Use in which a boom or a loader arm can be raised or lowered by means of a lifting cylinder. The function of the floating position is required, for example, to enable regardless of the position and position of the vehicle that a tool on the boom or loader can follow the contour of the ground contour. The tool is only pressed by gravity on the ground. Such valve assemblies do not include load-holding valves that prevent or greatly slow down inadvertent lowering of the boom or loader arm for safety reasons when leakage occurs in the connection between cylinder and control valve. Since it requires opening or bypassing the load-holding valve of a control pressure, a solution for combining a load-holding valve with a floating position in which there is a non-pressurized state of the hydraulic consumer and thus no control pressure can be built up, is not known.

DE 101 49 787 A1 discloses a valve arrangement with floating position for controlling a double-acting consumer, in which a control valve is acted upon in a flow position and a floating position can be realized by a pressure-connected valve arrangement. A throttling is brought about via the control edges of the control valve, wherein changes in the speed of movement of the consumer during the transition to the floating position should be effectively avoided. The disadvantage here is that the throttling takes place via an elaborately constructed and fed via a pump pressure control of the control valve, whereby a high control inertia is given and it can come at high load when switching to a floating position despite throttling to unwanted or uncontrolled lowering movements. Furthermore the valve assembly contains no load-holding valve to ensure the hydraulic operation of the consumer.

DE 100 06 908 A1 discloses a hydraulic piston-cylinder unit for agricultural machines with a load-holding valve, in which a working position is reached, in which a constant pressure in the piston bottom side cylinder chamber is adjustable. As a result, a boom or a tool located thereon can always rest with preselected contact force on the ground. This working position is achieved by the pressure chambers of the piston-cylinder unit are brought together and via a pressure control valve, a pressure equalization between the two pressure chambers takes place. If the pressure falls below a preselected value, the pressure regulating valve closes. A floating position is only possible if the preselected value is set to zero, so that no pressure control takes place. A disadvantage then has the effect that when switching under load, the boom or the tool would descend unchecked.

DD 205 471 discloses a hydraulic circuit arrangement by means of which a floating position can be established at the driver's request by connecting the chambers of a cylinder to a container by means of a 3/2 valve. A throttled check valve ensures a throttled outflow on the pressure side of the cylinder both in the operating position and in the floating position. The disadvantage is that when switching to the floating position under load of the designed for the operation constant cross section of the throttle a drop in the pressure side is not controllable controlled. Furthermore, such a throttle check valve is not a load-holding valve, which can prevent an undesirable drop in operating position.

JP 09 317706 A discloses a hydraulic arrangement with a valve arrangement in which a resetable load-holding valve connected to a first chamber of a hydraulic cylinder is provided in order to prevent the hydraulic cylinder subjected to a load from falling down unintentionally. The valve arrangement further comprises a special adjustment device for controlling a hydraulic flow effecting the resetting of the load-holding valve. A disadvantage is that the hydraulic arrangement disclosed in JP 09 317706 A is structurally complex and there is no connection of the load-holding valve to the second chamber, with which a control of the load-holding valve by pressurizing the second chamber is made possible.

The object underlying the invention is seen to provide a valve assembly of the type mentioned, by which the aforementioned problems are overcome. In particular, a valve arrangement is to be proposed with which a floating position can be realized and when switching from the operating position into the floating position, a controlled lowering or holding the pressure side can take place. A further object of the invention is to combine the valve assembly effectively with a load-holding valve for an operating position.

The object is achieved by the teaching of claim 1. Further advantageous embodiments and modifications of the invention will become apparent from the dependent claims.

According to the invention, a valve arrangement of the type mentioned above is provided with a volume flow-dependent control valve device arranged in the first hydraulic line. A volume-flow-dependent control has the advantage that independent of the hydraulic pressure in the hydraulic line, the volume flow is controllable, so that passes only at a low and high hydraulic load only a certain flow through the hydraulic line and thus a safety function is offered. If, for example, while the first chamber of the hydraulic cylinder is pressurized, the valve assembly is brought into floating position by the switching valve is switched to flow position by a switching signal, then the volume flow-dependent controlling valve device ensures that regardless of the level of pressure, the flow only in certain Can change limits or will not exceed a certain value.

In a preferred embodiment of the invention, the valve device includes a flow opening changing adjusting means, such as a slide or closing elements, which is exposed on the one hand to a pressure of the first chamber and on the other hand, a pressure of the container and optionally a spring force. Depending on a pressure difference between the two flow sides, which varies according to a prevailing one Volumetric flow adjusts or closes the flow opening of the actuating means.

In a particularly preferred embodiment of the invention, the valve device contains means which reduce (expand) the flow cross-section with increasing (decreasing) pressure gradient across the valve device. This has the advantage that if, due to an increasing pressure in the hydraulic line, the volume flow increases, the pressure gradient between the flow inlet and the flow outlet side also increases. At the same time, the flow cross-section over the valve device is reduced so that the pressure gradient drops again. As a result of the falling pressure gradient, in turn, the flow cross-section of the valve device is reduced, so that a controlling or regulating state is established, which keeps the volume flow in the presence of a pressure gradient as far as possible or within certain limits constant.

In a particularly preferred embodiment of the invention, the valve device includes a flow control valve, which changes the flow rate flow-dependent and limited to a predetermined maximum value. Such flow control valves are offered for example by the company "HYDAC International". A detailed description can be found in DIN-ISO 1219. A flow control valve has a differential pressure regulator, which controls or regulates the flow volume-dependent via a control piston, a compression spring, a control orifice and a set screw for adjusting the control pressure difference. With increasing volume flow or increasing flow ie increasing pressure gradient of the cross section of the control panel is increased accordingly Reduced pressure drop until there is an equilibrium of forces again. By the continuous readjustment of the differential pressure regulator, according to the prevailing pressure gradient, a constant volume flow is achieved in a control direction, wherein the control direction preferably the discharge direction of the hydraulic fluid from the high-pressure chamber of the hydraulic cylinder, preferably the lifting side of the hydraulic cylinder, in the direction of the container equivalent. In the opposite direction, the valve can be flowed through unregulated. Such a valve has the advantage that, even with extremely high pressure loads, a volume flow corresponding to the control pressure difference always sets, wherein the control pressure difference can be predetermined via the adjusting screw. This has the consequence that when switching from operating position to floating position under load, a controlled pressure decrease, largely independent of the height of the prevailing pressure, and thus a safety precaution when switching to the floating position is given.

In a particularly preferred embodiment of the invention, the valve device includes a parallel to the flow control valve arranged check valve, which opens in the direction of the first chamber. This ensures that the hydraulic fluid flowing in the direction of the container is forced to flow through the flow control valve and accordingly flows out of the high-pressure chamber in a controlled manner, whereas an inflow from the opposite direction can take place unhindered.

In another preferred embodiment of the invention, the valve means includes means which when exceeded a predeterminable pressure gradient reduce or interrupt the flow. This ensures that upon reaching a volume flow, which causes the predeterminable pressure gradient, the connection is interrupted, so that the pressure in the high-pressure first chamber and in the first hydraulic line is maintained. If the pressure drops again, the connection is restored as soon as the predeterminable pressure gradient is reached or a volume flow is established which causes a pressure gradient which is less than or equal to the predefinable pressure gradient.

In a preferred embodiment of the invention, the valve device includes a raw rupture valve, which closes upon reaching or exceeding a predetermined pressure gradient or opens when falling below the predetermined pressure gradient. Such Rohbruchsicherungsventile are offered for example by the company "HYDAC International" and are described in detail in a company catalog "HYDAC INTERNATIONAL - FLUTEC Pipe Fittings RBE". "Flutec" pipe rupture valves are volume-flow-dependent switching flat seat valves that prevent inadmissible and uncontrolled movements of a load under load. A pipe rupture valve has a closing element, for example a closing piston in the form of a poppet valve, which has an open switching position in the normal operating state. The closing element, is preferably held by a spring in the open state, as long as the spring force is greater than the force caused by the flow resistance when flowing through the closing element or on the plate surface of the poppet valve. The valve remains open and can be flown through in both directions. Exceeds the prevailing Volume flow when flowing through the valve in a predetermined direction defined by the predeterminable pressure drop, maximum allowable value is overcome by the flow resistance increase the spring force and the closing element abruptly pressed onto the valve seat, so that the flow is interrupted. The valve opens automatically as soon as a pressure equalization takes place and the pressure force in front of the valve falls below the force resulting from spring force and compressive force behind the valve.

In a preferred embodiment of the invention, the valve device includes a parallel to the pipe rupture valve arranged throttle or orifice, which allows a reduced volume flow when the pipe rupture valve is closed. This ensures that always a certain proportion of the volume flow is passed on, so that the pressure in front of the valve device can not build up. The throttle or orifice can be arranged in a bypass line parallel to the pipe break safety valve or be formed, for example, in the form of a bore directly on the pipe rupture valve, in particular directly on the poppet valve. At high flow rates is thus ensured that the closing of the pipe rupture valve much of the flow is intercepted and only a small portion of the hydraulic fluid passes through the throttle, so that a total of controlled pressure decrease is achieved when switching to the floating position.

In a further embodiment of the invention, the control valve connects a second chamber of the hydraulic cylinder via a second supply line optionally with the hydraulic pressure source or the container. Thus, both chambers of a double-acting hydraulic cylinder can be pressurized, which allows accelerated emptying of the chambers and thus the extension and retraction of a hydraulic cylinder piston is made possible at shorter intervals. Preferably, a second switching valve is included, which controls the flow in a running between the second chamber and the container second hydraulic line, and which opens in parallel to the first switching valve due to the switching signal, whereby a floating position is adjustable, in which the first chamber and the second Chamber communicate directly or indirectly via the container with each other. The hydraulic cylinder can be brought in this way from each operating position to a floating position or be brought immediately after accidental switching to a floating position without significant pressure loss back to an operating position.

In a further embodiment of the invention, the first and / or the second supply line includes a load-holding valve arrangement. Load-holding valve arrangements are state of the art and are introduced in most modern valve arrangements as a safety precaution in supply lines in order to prevent an unwanted pressure drop in the consumer or in the hydraulic cylinder. If leaks occur, be it on the control valve, on the connecting lines or on seals, etc., it can, especially under load, come to rapid pressure losses in the hydraulic chambers of the hydraulic cylinder, which in turn represents a safety risk. To prevent pressure drops under load such load-holding valve arrangements are as close as possible to the Positioned hydraulic cylinder, so that as few components are included between the hydraulic cylinder and load-holding valve assembly, which could have leaks. Usually, these load-holding valve assemblies are located directly on the hydraulic cylinder and are part of this assembly, so that no easily damaged components such. As hoses, must be used. Furthermore, load-holding valve arrangements make it possible to ensure a tight seal that prevents even the smallest pressure losses over a longer period under load. Intended pressure change is achieved by bypassing or opening such load hold valve assemblies by hydraulic circuitry.

In combination with the first and second hydraulic line, which connect the chambers of the hydraulic cylinder in floating position with the container, can be achieved in a particularly advantageous manner, on the one hand, an operating position with integrated load-holding valve arrangement, on the other hand in a floating position with the described safety features of a controlled flow control be switched.

As load holding valve arrangements z. B. pipe rupture devices used, the various components such. B. lowering brake valves, hydraulically releasable check valves, Overcenter valves öder similar contain.

In a particularly preferred embodiment of the invention, the load holding valve assembly includes a check valve, such as a hydraulically releasable check valve, which is in a closed position and in response to the pressure of the first and / or the second Supply line opens. Furthermore, an additional check valve is included parallel to the check valve, wherein the additional check valve opens in the direction of the hydraulic cylinder. The load holding valve arrangement is preferably arranged on the lifting side of the hydraulic cylinder, ie on the usually safety-relevant pressure side of the lifting cylinder, at which a high operating pressure due to a load will occur. About the corresponding supply line, the first chamber of the hydraulic cylinder can be filled by the pump. The check valve effectively prevents escape of the hydraulic fluid from this filled chamber. A first pressure line connects the second supply line to the check valve. If now the chamber to be emptied, the second chamber is filled via the second supply line, whereby a pressure builds up in the second supply line, which moves the check valve via the first pressure line from the closed position into a passage position. The hydraulic fluid can now flow from the first chamber into the container. As soon as the pressure in the second supply line degrades, for example by switching to another operating position, the check valve resumes its closed position. Furthermore, a second pressure line is provided as an overload protection hydraulic cylinder side in the first supply line, which opens at high pressure conditions on the lift side of the hydraulic cylinder, regardless of the switching position of the control valve, the check valve.

In a particularly preferred embodiment of the invention, the first and second switching valve are designed as electromagnetically switchable seat valves. As a result, by generating an electrical switching signal, the switching valves controlled and switched at any time in a floating position. Conceivable here is the use of other types of switching valves, which are, for example, pneumatically, hydraulically or mechanically controlled switchable.

Preferably, the valve arrangements shown in the various embodiments are used for use for a hydraulic cylinder for raising and lowering a boom on a loader or construction vehicle, in particular on a telescopic loader. For example, in a telehandler in any operating position, even under load with raised boom, be switched to floating position. A floating position without described volume flow control would cause the boom would shut down more or less uncontrollably with increasing load, which represents an increased safety risk. At the same time it is possible to use the floating position when working on the ground surface. Furthermore, the possibility is given with integrated load-holding valve, the hydraulic cylinder with raised boom by appropriate control via the control valve to pressurize the lower side, so that an accelerated shutdown of the boom entry. In all operating positions while a secure switching is given in a floating position.

It is particularly advantageous that is given by the embodiments of the invention, a floating position for a telescopic loader while maintaining a safety-relevant load-holding valve assembly (pipe rupture protection). Furthermore, the realization of a floating position is given, which dispenses with elaborate designs, so that the most already existing on a telescopic loader Hubsektionen the main valve blocks do not need to be changed. Thereby, the number of valve blocks can be kept low and also be given the possibility of retrofitting or upgrading using the same lifting cylinder with different options. Furthermore, other variations are conceivable that combine a floating position function, for example, with a hydraulic suspension version, so that starting from a basic version with load-holding valve assembly a modular extension with floating position function and beyond a modular extension with suspension function is possible.

Reference to the drawing, which shows two embodiments of the invention, the invention and further advantages and advantageous developments and refinements of the invention are described and explained in more detail below.

Fig. 1

einen Schaltplan einer ersten erfindungsgemäßen Ventilanordnung mit einem Stromregelventil,

Fig. 2

einen Schaltplan einer zweiten erfindungsgemäßen Ventilanordnung mit einem Rohrbruchsicherungsventil und

Fig. 3

eine schematische Seitenansicht eines Teleskopladers mit erfindungsgemäßer Ventilanordnung zur Verwendung für einen Hydraulikzylinder.

It shows:

Fig. 1

a circuit diagram of a first valve assembly according to the invention with a flow control valve,

Fig. 2

a circuit diagram of a second valve assembly according to the invention with a pipe rupture valve and

Fig. 3

a schematic side view of a telescopic loader with inventive valve assembly for use for a hydraulic cylinder.

The circuit diagram shown in Fig. 1 shows an embodiment of a valve assembly 10 for the realization of a floating position. The valve assembly 10 includes a switchable control valve 12, for example a slide valve, which is connected via hydraulic lines 14, 16 with a pump 18 and a hydraulic reservoir 20, wherein the control valve 12 in three operating positions, lift, neutral and lowered position, is switchable. The switching of the control valve 12 is preferably carried out manually, but can also be done electrically, hydraulically or pneumatically.

Via a first and second supply line 22, 24, the control valve 12 is connected to a hydraulic cylinder 26, wherein the first supply line 22 leads into a first chamber 28 of the hydraulic cylinder 26 and the second supply line 24 into a second chamber 30 of the hydraulic cylinder 26. The first chamber 28 of the hydraulic cylinder 26 represents the piston bottom side and the stroke side chamber, whereas the second chamber 30 represents the piston rod side and the lower side chamber of the hydraulic cylinder.

In the first supply line 22, a load holding valve assembly 32 is provided. The load-holding valve arrangement 32 includes a pressure-controlled and spring-controlled shut-off valve 34, and a non-return valve 36 which opens to the hydraulic cylinder side and is arranged parallel to the shut-off valve 34 via a bypass line 38. Via a first pressure line 40, a pressure connection is made from the check valve 34 to the hydraulic cylinder side portion of the first supply line 22. Via a second pressure line 42 is a further pressure connection from the check valve 34 to the second Supply line 24 made. Furthermore, a spring 44 holds the check valve 34 in the closed position.

A first hydraulic line 46 connects the first chamber 28 and the first supply line 22 to the hydraulic tank 20, wherein the not connected to the hydraulic tank 20 end 48 of the first hydraulic line 46 between the first chamber 28 and the load-holding valve assembly 32 is arranged.

In the first hydraulic line 46, a first switching valve 50 and a in the direction of the hydraulic tank 20 connected in series valve means 52 is arranged. The first switching valve 50 is an electrically switchable seat valve, which is held by a spring 54 in the closed position and can be brought via a magnetic coil 56 in an open passage position. The switching valve 50 seals off in one or both directions without leakage. The valve device 52 includes a flow control valve 58 which is arranged in parallel to a check valve 60, wherein the check valve 60 opens in the hydraulic cylinder direction. In this case, it is also possible to arrange the valve device 52 in the direction of the hydraulic container 20 upstream of the switching valve 50.

Furthermore, a second hydraulic line 62 is provided, which connects the second supply line 24 to the first hydraulic line 46, wherein the connection point 64 is arranged with the first hydraulic line 46 between the hydraulic tank 20 and the valve device 52.

Further, the second hydraulic line 62 includes a second switching valve 66, which is similar to the first switching valve 50 in construction and function.

The individual operating states can now be controlled as follows via the control valve 12 and via the switching valves 50 and 66. As shown in Fig. 1, the control valve 12 is held by the control springs 68, 70 in neutral position. The switching valves 50 and 66 are in a closed position. Via a control signal, the control valve 12 is brought out of the neutral position by means of an actuator 72 in the lifting or lowering position. This may be a manual, electrical, hydraulic or pneumatic actuator 72.

In the stroke position, the connection of the first supply line 22 to the pump 18 and the connection of the second supply line 24 to the hydraulic container 20 is produced. The connected to the hydraulic tank 20 pump 18 filled via the first supply line 22 and the check valve 36 of the load-holding valve assembly 32 (the check valve 34 of the load-holding arrangement 32 is in the closed position), the first chamber 28 of the hydraulic cylinder 26. As a result, the piston 74 moves in the direction of the second chamber 30 and pushes the existing there oil through the second supply line 24 out in the hydraulic tank 20. If now switched back to the neutral position, the control valve 12 interrupts the connections to the pump 18 and the hydraulic tank 20, so that the pressure maintained in the two chambers 28, 30 of the hydraulic cylinder 26 and the movement of the piston 74 is released. The piston 74 stops.

In the lowered position, the connection of the first supply line 22 to the hydraulic reservoir 20 and the connection of the second supply line 24 to the pump 18 is established. The pump delivers oil into the second chamber 30 of the hydraulic cylinder 26, wherein the pressure building up in the second supply line 24 opens the check valve 34 via the second pressure line 42 of the load holding valve arrangement 32. At the same time, the piston 74 is moved in the direction of the first chamber 28, so that the oil flowing out of the first chamber 28 passes via the first supply line 22 and via the opened shut-off valve 34 into the hydraulic container 20.

The load holding valve assembly 32 thus ensures that the hydraulic cylinder 26 maintains its position in the neutral position or escape in the lifting and neutral position no oil from the pressurized first chamber 28 and that in the lowered position, the oil from the first chamber 28 can flow through the open check valve 34 , To ensure this, the load-holding valve arrangement should or should be arranged as shown on the lifting side of the hydraulic cylinder 26, wherein the lifting side is the side of the hydraulic cylinder 26, in which a pressure for lifting a load is built up. In the embodiments shown here, the lifting side is the first chamber 28 of the hydraulic cylinder 26, wherein by turning the hydraulic cylinder 26 and the second chamber 30 could serve as a lifting side. The first pressure line 40 is an overload protection, so that at high operating pressures in the first chamber 28 of the hydraulic cylinder 26, which may arise, for example, by excessive loads, in the first pressure line 40, a limiting pressure is reached, which opens the check valve 34 to reduce pressure ,

About the switching valves 50 and 66 can be switched in any operating position in the floating position. For this purpose, the switching valves 50 and 66 are driven in parallel by means of a switching signal, so that the magnetic coils 56 counteract the spring force of the springs 54 and the switching valves 50, 66 are brought out of the closed position substantially at the same time in the flow position. The result of this is that the first chamber 28 and the second chamber 30 are communicated with one another and with the hydraulic tank 20 so that an exchange of the hydraulic fluid or of the oil takes place and the piston 74 can be moved freely. If switching takes place from an operating position under load, then the oil flows out of the pressurized first chamber 28 under increased pressure, which leads to an accelerated piston movement. In order to limit this piston movement in its speed, the flow control valve 58 comes into force, which limits the volume flow or controls the flow of the oil or regulates. If the volume flow exceeds an approved value, the passage cross-section of the flow control valve 58 narrows so that the volume flow does not increase any further. As a result, uncontrolled movements of the hydraulic cylinder piston 74 are effectively avoided. With an opposite pressure action in the direction of the first chamber 28, the check valve 60 allows bypassing the flow control valve 58 and thus an uncontrolled flow in the direction of the first chamber 28. Switching from the floating position to an operating position is at any time by switching the switching valves 50, 66 in a closed position possible.

2, a second embodiment will be described. This will be the same for similar components Reference numerals as used in Fig. 1. 2, a pipe rupture valve 76 is used in combination with a throttle 78 connected in parallel for the valve device 52 instead of the flow control valve 58 and the check valve 60. Instead of the throttle 78 can also be used a similar effect aperture. Is switched by switching the switching valves 50, 66 in the floating position, the pipe rupture valve 76 also causes a flow-dependent reduction or limitation of the volume flow. If the volume flow in the floating position in the first hydraulic line 46, due to excessive pressure in the first chamber 28, a limit value predeterminable on the pipe rupture valve 76, then acting from the adjusting pressure difference force acting on the pipe rupture valve 76 spring force of a closing spring 80 counteracts and At the same time, the oil flowing out of the first chamber 28 is diverted through the throttle 78, so that a greatly reduced, controllable volume flow flows and only low movement speeds of the piston 74 are permitted. In this case, it is also possible to arrange the valve device 52 in the direction of the hydraulic container 20 upstream of the switching valve 50.

A use for the embodiments illustrated in FIG. 1 and FIG. 2 is illustrated in FIG. 3. FIG. 3 shows a mobile telescopic loader 82 with a telescopically extendable boom 86 pivotably articulated to a housing 84 or frame of the telescopic handler 82. A hydraulic cylinder 26 for raising and lowering the boom 86 is arranged between the arm 86 and the housing 84. The hydraulic cylinder 26 is at a first and a second bearing point 88, 90th hinged pivotally, wherein the piston rod side 92 is hinged to the second bearing point 90 on the arm 86 and the piston bottom side 94 at the first bearing 88 on the housing 84. Furthermore, the hydraulic tank 20, the pump 18 and the valve assembly 10 are positioned on or in the housing 84 and connected to each other via hydraulic lines 14, 16, 46, 96. Furthermore, the supply lines 22, 24 between valve assembly 10 and hydraulic cylinder 26 in Fig. 3 can be seen. Control or switching signals are generated by means of a control, not shown, with which the control valve 12 and the switching valves 50, 66 (see FIGS. 1 and 2) are controlled or switched. According to the operating positions described above, the hydraulic cylinder 26 can be operated such that the boom 86 can be raised, held or lowered. Further, it is possible to switch to floating position, so that the piston is freely movable and the boom 86 is floatingly movable. The floating position ensures that a tool 98 fastened to the arm 86 and lowered onto the ground can float, following the ground contour, over the ground surface. The contact pressure of the tool 98 relative to the ground is determined essentially by the weight of the arm 86 and the tool 98. A safety function is given by the fact that a lowering of the boom 86 under load can be volume-controlled, so that no unwanted, sudden changes in movement occur. Is z. As the boom 86 in the raised position under load and is then switched to floating position, the flow control valve 58 and the pipe rupture valve 76 in conjunction with the throttle 78 ensures that the boom 86 is lowered in a presettable, controllable speed becomes. With this realized by the valve assembly 10 safety precaution for a floating position, can be switched from each operating position out in a floating position, without causing uncontrolled movement changes on the boom 86. Furthermore, hereby a valve arrangement 10 with integrated floating position is realized in conjunction with a load holding device 32, with which a pressurized lowering of the arm 86 by switching the control valve 12 in lowered position with closed switching valves 50, 66 is possible.

Although the invention has been described by way of two embodiments only, many different alternatives, modifications and variations that are within the scope of the present invention will become apparent to those skilled in the art in light of the foregoing description and the drawings. Thus, for example, the valve assembly can be applied to other vehicles, such as excavators or cranes, which have hydraulically actuated components that need to be raised or lowered and where a floating position seems useful.

Claims (10)

1. Hydraulic arrangement, having a hydraulic cylinder (26), which has a first chamber (28) and a second chamber (30), and having a valve arrangement, the valve arrangement comprising a control valve (12), which connects the first and the second chamber (28, 30) of the hydraulic cylinder (26) via a first and a second supply line (22, 24) optionally to a hydraulic pressure source (18) or to a container (20), a first on-off valve (50), which controls the flow in a first hydraulic line (46) extending between the first chamber (28) and the container (20) and which opens on the basis of a switch signal, a second on-off valve (66), which controls the flow in a second hydraulic line (62) extending between the second chamber (30) and the container (20) and which opens on the basis of the switch signal parallel to the first on-off valve (50), a floating position being able to be set by opening the on-off valves (50, 66), in which floating position the first chamber (28) and the second chamber (30) are in communication directly or indirectly with each other via the container (20), and a load-holding valve arrangement (32), which has a stop valve (34), which is in a closed position as a result of spring force and opens as a function of the pressure in the second supply line (24), and has a check valve (36) disposed parallel to the stop valve (34), the check valve (36) opening in the direction of the hydraulic cylinder (26), characterised in that the valve arrangement has a valve device (52) which is disposed in the first hydraulic line (46) and controls as a function of the volume flow.
2. Hydraulic arrangement according to claim 1, characterised in that the valve arrangement (52) contains an adjustment means (58, 76, 78) which changes the flow opening, said adjustment means being subjected on the one hand to a pressure of the first chamber (28) and on the other hand to a pressure of the container (20) and also if necessary to a spring force.
3. Hydraulic arrangement according to one of the preceding claims, characterised in that the valve device (52) contains means (58, 76, 78) which, with increasing (reducing) pressure head across the valve device (52), reduce (increase) the flow cross-section.
4. Hydraulic arrangement according to one of the preceding claims, characterised in that the valve device (52) contains a flow-control valve (58) which changes the volume flow as a function of the flow and restricts it to a prescribable maximum value.
5. Hydraulic arrangement according to claim 4, characterised in that the valve device (52) contains a check valve (60) which is disposed parallel to the flow-control valve (58) and opens in the direction of the first chamber (28).
6. Hydraulic arrangement according to one of the claims 1 to 3, characterised in that the valve device (52) contains means (76, 78) which reduce or interrupt the volume flow when a prescribable pressure head is exceeded.
7. Hydraulic arrangement according to claim 6, characterised in that the valve device (52) contains an isolating safety valve (76) which closes when a prescribable pressure head is reached or exceeded or opens when the prescribable pressure head is fallen below.
8. Hydraulic arrangement according to claim 7, characterised in that the valve device (52) contains a throttle (78) or diaphragm which is disposed parallel to the isolating safety valve (76) and permits a reduced volume flow with a closed isolating safety valve (76).
9. Hydraulic arrangement according to one of the preceding claims, characterised in that the first and/or second on-off valve (50, 66) are electromagnetically switchable seat valves.
10. Hydraulic arrangement according to one of the preceding claims for use with a hydraulic cylinder (26) for raising and lowering a jib (86) on a loader or construction vehicle, in particular on a telescopic loader (82).

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