Hydraulic system and method of operating hydraulic system

Abstract

A hydraulic system (100, 200, 300, 400) comprising a main valve unit (110) with a main valve spool (1) is proposed herein. The main valve spool (1) is configured to be positioned in a resting position and a continuity of metering positions in dependency of pressure of a pilot liquid at a first side (C) of the main valve spool (1) and a pressure of the pilot liquid at a second side (D) of the main valve spool (1). The hydraulic system (100) further comprises a pilot valve unit (120) comprising a pilot valve spool (3) and a solenoid actuator (11), the pilot valve spool (5) being configured to be positioned in a base position and a continuity of piloting positions in dependency of a current applied to the actuator (11) to adjust the pressure of the pilot liquid at the second side (D) of the main valve spool (1). The main valve unit (110) comprises a first pilot port (P1) to provide the pilot liquid to the first side (C) of the main valve spool (1) and a second pilot port (P2) to provide the pilot liquid to the second side (D) of the main valve spool (1). The main valve unit (110) provides a main liquid path comprising variable flow cross sections in the metering positions between a main liquid inlet port (B) and a main liquid outlet port (A) for a main liquid supplied to the liquid inlet port (B). The proposed hydraulic system (100, 200, 300, 400) is configured to provide a liquid connection between the main liquid inlet port (B) and the first pilot port (P1) when a pressure of the main liquid supplied to the main liquid inlet port (B) exceeds a threshold pressure. A method of providing a liquid flow and instrumentalities for implementing the method is also proposed.

Description

[0001] R.413340

[0002] HydraForce Hydraulics, Ltd.

[0003] R.413340 - Tag / kun

[0004] Hydraulic system and method of operating hydraulic system

[0005] Field

[0006] The present disclosure relates to a hydraulic system and to a method of operating a hydraulic system, as well as to instrumentalities for implementing the proposed method.

[0007] Background

[0008] In a hydraulic system, there is often a need for a pressure shock relief to protect mechanic structures associated with the hydraulic system or the hydraulic system itself from pressure peaks of a hydraulic liquid. For example, in a system with a hydraulic motor, a sudden load increase to the hydraulic motor, e.g., in the form of an impediment to the rotation of connected wheels caused by an obstacle in the driving path, can impart a shock load to the entire hydraulic transmission. A shock load is associated with excessive pressures, which can negatively affect the components to the hydrostatic transmission. Embodiments disclosed herein, even if discussed mainly in connection with a shock relief as just referred to, can be used for any suitable purposes, such as for secondary pressure relief in order to limit a pump pressure, if necessary.

[0009] For example, and without limiting the present disclosure, US 2007 / 267068 A1 discloses a shock valve assembly for a hydraulic system including a fluid path extending between a first port and a second port with a shock valve disposed in the fluid path to normally block a fluid flow through the fluid path between the first and second ports. The shock valve temporarily opens to permit a fluid flow when a fluid pressure differential between the ports exceeds a predetermined threshold. Fluid flow occurs in a first direction from the first port to the second port through the fluid path when the shock valve is temporarily opened and a fluid pressure in the first port is greater than the second port. R.413340

[0010] In systems with high flow demands and large components like cylinders and motors, shock relief valves may become particularly large and costly, and may add considerable weight to the whole construction. There is also considerable complexity for integration into a machine or larger structure, e.g. for flanging onto a cylinder. Consequently, there is a need for improvements in such hydraulic systems which are suitable to, e.g., cope with pressure peaks of hydraulic liquids in a more effective manner.

[0011] Summary

[0012] Against this background, a hydraulic system and a method of operating a hydraulic system, as well as means for implementing the proposed method with the features of the independent claims are proposed herein. Embodiments are the subject of the dependent claims and of the description that follows hereinbelow.

[0013] A hydraulic system proposed herein comprises a main valve unit with a main valve spool, the main valve spool being configured to be positioned in a resting position and a continuity of metering positions in dependency of a pressure of a pilot liquid (also referred to as “pilot pressure” herein) at a first side of the main valve spool and a pressure of the pilot liquid at a second side of the main valve spool. The main valve spool may, in certain configurations as disclosed herein, be received in a main valve cage or a corresponding bore of a valve block, and may be configured to slide in the main valve cage or the bore of the valve block.

[0014] The hydraulic system further comprises a pilot valve unit comprising a pilot valve spool and a solenoid actuator, the pilot valve spool being configured to be positioned in a base position and a continuity of piloting positions in dependency of a current applied to the actuator to adjust a volume of the pilot liquid at the second side of the main valve spool by allowing the pilot liquid to drain from the second side of the main valve spool.

[0015] Herein, the term “main valve” is intended to refer to a metering valve controlling the flow of a liquid to be metered or provided in a defined flow rate, and the main valve is the valve piloted or hydraulically controlled by a “pilot valve”, said terms being used herein as customary in the field of hydraulics. The liquid to be metered by the main valve is also referred to as “main liquid” herein, in contrast to a “pilot liquid” or “piloting liquid”, which is used to control a position of the main valve spool of the main valve using the pilot valve. Said liquids may be R.413340 selected from the range of hydraulic liquids known by the skilled person, particularly from dedicated hydraulic fluids such as hydraulic oils with a defined viscosity and composition. One or more liquids may be provided in the same or different tanks.

[0016] In a hydraulic system proposed herein, the main valve spool is in a neutral or balanced position when the pressure of the pilot liquid at a first side of the main valve spool and the pressure of the pilot liquid at a second side of the main valve spool are the same or essentially the same. A displacement of the main valve spool is induced by a pressure difference between the pressure of the pilot liquid at a first side of the main valve spool and the pressure of the pilot liquid at the second side of the main valve spool, i.e. by draining liquid from the second side.

[0017] In order to provide the pilot liquid at the at the first side of the main valve spool and at the second side of the main valve spool, pressure chambers are provided, as customary in the field of hydraulics, which may be part of the valve units mentioned or which may be integrated or created in a hydraulic system in which the valve units are mounted. The pilot valve, in the hydraulic system as proposed herein, is configured to release a pilot liquid from the pressure chamber at the second side of the main valve spool in a controlled manner, which is particularly realized by opening or partly opening a drain channel from the corresponding pressure chamber, wherein a cross section for the pilot liquid drain is dependent of a displacement of the pilot valve spool, which in turn is dependent of a current applied to the solenoid actuator.

[0018] In the hydraulic system proposed herein, the main valve unit comprises a first pilot port to provide the pilot liquid to the first side of the main valve spool and a second pilot port to provide the pilot liquid to the second side of the main valve spool. These ports may, as further explained below, connected to corresponding branches of supply lines.

[0019] As proposed herein, the main valve unit provides a main liquid path comprising variable flow cross sections in the metering positions between a first main liquid port and a second main liquid port, or vice versa, for a main liquid supplied to either the first or the second main liquid port. The main valve unit is therefore a proportional or metering valve, and no simple switching valve. The proposed hydraulic system is, furthermore, configured to provide a liquid connection between the main liquid port to which the main liquid is provided on the one R.413340 hand and the first pilot port on the other hand, when a pressure of the main liquid supplied to the respective port exceeds a threshold pressure. It is particularly configured in this sense by by being provided with a further valve unit external to the main valve unit and its main valve spool or integrated into the main valve spool, as further described below in different embodiments. In the understanding used herein, “a liquid connection” between certain ports may also be a connection between lines or any kind of tubing fluidly connected to said ports, as this also provides a liquid path between the ports, or a connection through certain elements of the valve, such as through the main valve spool.

[0020] Embodiments as disclosed herein overcome a plurality of problems related to valve assemblies and corresponding hydraulic arrangements according to the prior art. Conventionally, overpressure protection in hydraulic arrangements for large liquid flows was realized using separate large pressure relief valves which, as mentioned, in such systems were particularly large and costly. As proposed herein, in contrast, a main flow regulating valve as a piloted relief valve may be used for this purpose, saving substantial space, weight and costs in corresponding arrangements.

[0021] In certain embodiments as proposed herein, the pressure threshold may be selected to correspond to a pressure exceeding an design pressure, a standard operating pressure or a predefined pressure, or a corresponding pressure range in each case, at the first or second main liquid port to which the main liquid is supplied by a certain pressure difference or factor, as generally known in the field of hydraulics.

[0022] Embodiments as proposed herein are used in connection with piloted valves with mechanical spool position feedback. Traditional large spool valves for high flow applications are pilot pressure controlled, but in such valves, when being exposed to varying flow forces, the spool position and therefore also change the opening area or liquid cross section may change. That is, with only pilot pressure control there is no way of detecting the change in opening area automatically, and, in such arrangements, the pilot valve and main spool need to be calibrated to perform the best possible way. The piloted valves with mechanical spool position feedback used in the context of the embodiments proposed herein, in contrast to conventional valves with pilot pressure control, provide a mechanical feedback and a liquid flow rate which can be defined by a current applied to the solenoid. R.413340

[0023] Conventionally, valve units are integrated into mono block or sectional type of casted housings which restricts the design possibilities (for the spool and body). This may also be the case in certain embodiments proposed herein. Further embodiments as proposed herein, on the other hand, provide for a modular assembly and, as also explained below in connection with certain embodiments, allow for a particularly easy, reliable and straightforward manufacturing process. In such embodiments, the valve units may be modular units which may be connected by an adaptor unit.

[0024] As proposed herein, a main liquid supply line may be provided to supply the main liquid to the first or the second main liquid port, and a pilot liquid supply line is provided to supply the pilot liquid to the first and the second pilot liquid ports. A further valve unit is fluidly interposed between the main liquid port to which the main liquid is supplied, i.e., the first or the second main liquid port as the case may be, and the first pilot liquid port. A backflow restrictor may be provided to reduce or avoid a backflow from said first pilot liquid port and the main liquid port to which the main liquid is supplied.

[0025] The further valve unit, which may be a relief valve or sequence valve as described below, is configured to implement the functionality of providing said liquid connection between the main liquid port to which the main liquid is supplied and the first pilot port when the pressure of the main liquid supplied exceeds the threshold pressure.

[0026] In one configuration including a relief valve, the main liquid supply line may comprise a first branch to the main liquid port to which the main liquid is supplied and a second branch to an inlet port of the relief valve, and a pilot liquid supply line is provided to supply the pilot liquid to the pilot liquid ports, the pilot liquid supply line comprising a first branch to the first pilot liquid port and a second branch to the second pilot liquid port. The first branch of the pilot liquid supply line, in this configuration, comprises or may comprise the backflow restrictor. In the latter configuration, an outlet port of the relief valve is connected to the first branch of the pilot liquid supply line downstream of the backflow restrictor. In such configurations, the relief valve is external to the main valve unit and its main valve spool.

[0027] In a different configuration, avoiding an external further valve unit, the further valve unit may also be integrated into the main valve spool and may comprise connections to the main liquid port to which the main liquid is supplied on an inlet side and to the first pressure chamber on R.413340 an outlet side. Also a backflow restrictor may be integrated into the main valve spool. In such embodiments, the pressure relief or limit function is integrated into the main valve unit, creating some kind of multifunctional valve.

[0028] The term “backflow restrictor”, in the language used herein, may relate to any means of restricting, or in other configurations completely blocking, a backflow against the direction indicated. A backflow restrictor may particularly be provided as a small orifice or a throttle valve restricting a liquid flow.

[0029] The term “relief valve” is used herein as customary in the field of hydraulics. A relief valve may particularly block a flow of a liquid between its inlet port and its outlet port when in a first position and allow a flow of a liquid between its inlet port and its outlet port when in a second position, the inlet port and the outlet port particularly being the only ports of a relief valve in such a case. This means that all liquid used in such a configuration passes through the relief valve to its outlet port, including a liquid provided in a spring chamber of the relief valve, as the case may be. This means that a pressure prevailing at the outlet port, or a pressure chamber connected therewith, has to be included in the determination of the opening pressure of the relief valve. In other configurations, a different type of relief valve may be provided, in which the spring chamber drains to atmosphere or to tank. This avoids the pressure at the outlet port having to be added to the relief valve setting.

[0030] In embodiments proposed herein, the relief valve switches from the first position to the second position in case of the inlet pressure, i.e., the pressure of the main liquid supplied to the main liquid inlet port, and therefore the pressure in the second branch of the main liquid supply line, exceeds the threshold pressure which is defined by the relief valve.

[0031] Embodiments including a relief valve require a backflow restrictor but allow for using particularly simple valve technology. Certain embodiments of relief valves proposed in certain embodiments include the capability of leakage free load holding, if the main valve spool is likewise designed leakage free or comprising low leakage. This allows, for example, a hydraulically operated appliance, such as a digger arm for example, to stay in position.

[0032] This advantage can particularly be provided when using a relief valve as this may typically be provided as a seating valve. R.413340

[0033] In other embodiments as proposed herein, the sequence valve already mentioned may be used as the further valve unit. In this case, as above, the main liquid supply line comprises a first branch to the main liquid port to which the main liquid is supplied and a second branch to a first inlet port of the sequence valve, and a pilot liquid supply line is provided to supply the pilot liquid to the the pilot liquid ports, the pilot liquid supply line comprising a first branch to a second inlet port of the sequence valve and a second branch to the second pilot liquid port. An outlet port of the sequence valve is connected to the first pilot liquid port, the sequence valve providing a first flow path between its first inlet port and its outlet port in a first valve position and a second flow path between its second inlet port and its outlet port in a second valve position and the sequence valve being configured to switch from the first valve position to the second valve position when the pressure of the main liquid supplied to the main liquid inlet port exceeds the threshold pressure.

[0034] Also the term “sequence valve” is used herein as customary in the field of hydraulics. In contrast to a simpler relief valve, a sequence valve as used in the alternative embodiments disclosed herein comprises two inlet ports which, depending on the valve position, are selectively connected to an outlet port. Embodiments including a relief valve may dispose of a backflow restrictor but the sequence valve comprises three valve ports. Furthermore, a sequence valve is typically provided as a spool valve, in contrast to a typical relief valve, which is typically a poppet valve. Poppet valves are typically leakage free or exhibit only low leakage, enabling load holding as discussed previously already.

[0035] In certain embodiments as proposed herein, the main valve spool comprises a sealing section and a passage section, passage section defining a space between the main valve spool and an inner surface of a main valve cage providing the main liquid path comprising the variable flow cross sections. This allows for a particularly easy provision of a metered flow according to such embodiments, and a particularly easy manufacture by, e.g., casting and turning to form a rotational symmetric geometry.

[0036] In certain embodiments as proposed herein, between the main valve spool and the pilot valve spool there are arranged a neutral spring and a feedback spring, the main valve spool being biased towards the resting position by the neutral spring against the pressure of the pilot liquid, and the pilot valve spool being biased towards the base position by the feedback R.413340 spring against a force provided by the actuator. The counterforces provided by said springs serve the purpose of holding the respective spools in defined positions.

[0037] In certain embodiments as proposed herein, the feedback spring is coaxially arranged within the neutral spring. This provides a particularly space saving design and allows for a particularly easy and straightforward manufacturing process.

[0038] In certain embodiments as proposed herein, the main valve spool and the pilot valve spool are provided in a coaxial arrangement in the hydraulic system. Particularly such an arrangement allows for the hydraulic system to be created by using turned parts. Turned parts in comparison to casted parts can be manufactured with higher precision and hardened where required, providing a further advantage.

[0039] A method of operating a hydraulic system includes providing a hydraulic system as described hereinabove in different embodiments, providing a pilot liquid to the first pilot port and to the second pilot port, providing a main liquid to the main liquid inlet port, and energizing the actuator depending on predefined a flow rate of the liquid flow. Particularly, a liquid connection between the main liquid inlet port and the first pilot port is provided in such a method when a pressure of the main liquid supplied to the main liquid inlet port exceeds a threshold pressure.

[0040] As to further details and advantages of such a method, reference is made to the explanations above and below regarding the hydraulic system proposed herein and its different embodiments. Particularly, such a method may, in embodiments as proposed herein, use a hydraulic system according to any of the embodiments as discussed herein.

[0041] The method proposed herein, and the hydraulic system used in such a method, allow for controlling a flow in two directions to high flow levels, e.g., at more than 600 litres per minute. With mechanical position feedback, the hydraulic system will keep its intended position and therefore also the opening area which makes the valve compensating for flow forces. The seat in neutral position will enable the hydraulic system to have low leakage at closed position and capability of holding a load for long time. R.413340

[0042] Embodiments as proposed herein may also be used in connection with electronic load compensation systems. As the position of the valve spools is rather close to controlled current, the valve position is known, which enables for calculating a current flow (when knowing the differential pressure across the valve) and optimize energy efficiency. In consequence, no compensator is required, leading to higher availability and lower cost in comparison to spool valves with electronic position feedback sensor (LVDT). Electronic flow sharing is possible, in connection with embodiments proposed herein, with highest energy efficiency (configurable margin pressure).

[0043] Applications of embodiments disclosed herein include electronic “dampening” (active dampening feature, e.g. for cranes, wheel loaders, etc.). Because of the cartridge design of a hydraulic system proposed herein, there is a high flexibility of use, either in main control, but also in “add on” functionality (in parallel to main control), e.g. in energy recovery functions. Applications of embodiments disclosed herein include “big machines”, like forestry harvesters, wheel loaders, cranes (all terrain, forestry, etc.), off shore hydraulic apparatus, excavators, reach stackers, material handlers, ship loading cranes, “general cargo-handling machines”, presses, harvesting heads of forestry machines (due to high flow rates and high precision) and functions like slewing and winching.

[0044] Particularly, embodiments as proposed herein include load holding applications, with, e.g., independent metering control valves directly flanged to cylinders. This allows to be able to dispose of additional load holding valves. Also anti-shock relief functions included into typical load holding valves may be provided in connection with valve systems proposed herein, without extra space consumption. Also “distributed hydraulics” applications may be envisaged in the context of the present disclosure, where valve systems are not, or not completely, centralized in, e.g., a vehicle or machine.

[0045] Embodiments as proposed herein may particularly be used in connection with control systems operating on the basis of characteristic curves or look up tables. Due to the possibility for reliable calibration which is essentially uninfluenced by pressure differences, such characteristic curves or look up tables may provide for metering precisions of valve assemblies essentially comparable to sensor based control. R.413340

[0046] A computer or computing unit according to the present disclosure, e.g., a valve controller, is set up, in particular in terms of programming, to carry out a method as proposed herein.

[0047] The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, since this causes particularly low costs, especially if an executing control unit is still used for other tasks and is therefore available anyway. Suitable data carriers for providing the computer program are in particular magnetic, optical and electrical memories, as generally known in the field. It is also possible to download a programme via local or global computer networks.

[0048] Figures

[0049] Further advantages and embodiments disclosed herein are explained in connection with the accompanying drawings, in which

[0050] Figure 1 schematically illustrates a longitudinal section through a hydraulic system as proposed herein according to an embodiment,

[0051] Figure 2 schematically illustrates a longitudinal section through a hydraulic system as proposed herein according to an embodiment,

[0052] Figures 3a and 3b schematically illustrate a longitudinal section through a hydraulic system as proposed herein according to an embodiment,

[0053] Figure 4 is a schematic valving diagram including a hydraulic system, and

[0054] Figure 4a is a valve unit usable in an arrangement according to the valving diagram.

[0055] Embodiments

[0056] In the Figures, elements of identical, essentially identical, functionally comparable, or technically compatible function and / or purpose may be identified with identical reference numerals, and repeated explanations may be omitted for reasons of conciseness. R.413340

[0057] Explanations herein relating to devices, apparatus, assemblies, arrangements, systems, etc., according to certain embodiments disclosed herein likewise may apply to methods, processes, procedures, etc. according to corresponding embodiments.

[0058] The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and / or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the scope of the claimed invention.

[0059] Various embodiments as disclosed herein may suitably comprise, consist of, or consist essentially of, appropriate and technically sensible combinations of the disclosed elements, components, features, parts, steps, means, etc., other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future, particularly when encompassed by the scope of the independent claims.

[0060] The conjunction “and / or”, when used in a list of elements before the last element of the list, should be understood to mean that all elements mentioned in the list before and after can be combined with each other as desired. In other words, “A, B and / or C” may mean “A and / or B and / or C” or “at least one of the elements A, B and C in any combination” and each of these alternative expression can be used exchangeably.

[0061] Figure 1 schematically illustrates a longitudinal section through a hydraulic system 100 as proposed herein according to an embodiment.

[0062] The hydraulic system 100 includes valves provided in a cartridge design and includes a main valve unit 110 and a pilot valve unit 120. The main valve unit 110 includes a main valve spool 1 arranged to slide in a main valve cage 10 and biased to its neutral position by a neutral spring 2. The control of the main valve spool 1 is regulated by an electro proportional controlled pilot valve 3 of the pilot valve unit 120, wherein a solenoid of the pilot valve unit R.413340

[0063] 120 is indicated with 110. A feedback spring 4 is also provided. It should be understood that other configurations of the main valve cage, e.g., in connection with a cartridge type valve, are also envisaged in connection with the present disclosure.

[0064] A pilot pressure of the same pressure level of a piloting liquid is acting on both sides C and D, i.e. , a first pressure and a second pressure is acting on a first side C and a second side D of the main valve spool 1, said pressures typically acting on the same effective area. Pressure chambers or spaces at the first side C and a second side D are provided to hold the piloting liquid at the corresponding pressures.

[0065] Pilot valve spool 3 is controlled by solenoid actuator 11 against a feedback spring 4. When current is applied to the actuator 11, the pilot valve spool 33 is pushed against the feedback spring 4 which is therefore compressed with the force which the current to the actuator 11 can provide. When the pilot valve spool 3 moves, the pressure chamber at the second side D of the main valve spool 1 will be opened to tank, via a drain port 12, and the pilot pressure on this side D of the main valve spool 1 will decrease. Due to the pilot pressure remaining unchanged on the first side C of the main valve spool 1 , however, the main valve spool 1 will start to move and compress the neutral spring 4.

[0066] In consequence, a passage section 16 of the main valve spool 1 defining a clearance 17 provides an opening between a first main valve port and a second main valve port A and B. For ease of reference only, reference is made to a “main liquid inlet port” B and a “main liquid outlet port” A hereinbelow, assuming that a main liquid is supplied to the inlet port B. It should be understood, however, that a main liquid can be supplied to either of these ports. Only one alternative is described hereinbelow for reasons of conciseness. Both configurations are intended for allowing a metered flow of a metered or “main” liquid between these ports A, B in either direction.

[0067] Due to a movement of the main spool 1 , the feedback spring 4 is compressed and pushes the pilot spool 3 against the force of the actuator 11 until the pilot valve spool 3 is in neutral position. A certain pilot pressure of a pilot liquid will therefore again be present at the spring side or second side D of the main valve spool 1 and the main valve spool 1 will therefore not move further, being in a balanced state and providing a certain liquid cross section for the main liquid. R.413340

[0068] If any flow forces act on the main valve spool 1 and create movements, the balance between the feedback spring 4 and the solenoid actuator 11 will be changed. This change will shift the pilot valve spool 3 to either open the spring side or second side D of the main spool 1 to tank, via drain port 12, allowing the main spool to shift against the neutral spring 2, or add pilot pressure to the spring side or second side C of the main spool 1 , allowing the main spool 1 to shift away from the second side D. The same will happen if the current to the solenoid actuator 11 will increase or decrease, thus providing the possibility to proportionally control the position of the main spool 1 and further to control the opening area or fluid cross section between main valve ports A and B.

[0069] The main valve unit 110 comprises a first pilot port P1 to provide the pilot liquid to the first side C of the main valve spool 1 and a second pilot port P2 to provide the pilot liquid to the second side D of the main valve spool 1. The main valve unit 110 provides a main liquid path comprising variable flow cross sections in the metering positions between a main liquid inlet port B and a main liquid outlet port A for a main liquid supplied to the liquid inlet port B, as mentioned. As now will be further explained, the hydraulic system 100 is configured to provide a liquid connection between the main liquid inlet port B and the first pilot port P1 when a pressure of the main liquid supplied to the main liquid inlet port B exceeds a threshold pressure. This is shown in Figure 1 in a first alternative.

[0070] As shown in Figure 1 in connection with hydraulic system 100, a main liquid supply line X is provided to supply the main liquid to the main liquid inlet port B, the main liquid supply line X comprising a first branch X1 to the main liquid inlet port B and a second branch X2 to an inlet port of a relief valve 5. In the relief valve 5, the spring chamber drains to an outlet port thereof, the consequences of which have been described above. Alternatively, a relief valve 5a may be provided instead of the relief valve 5, in which the spring chamber drains to the atmosphere or to tank. This avoids the pressure at the outlet port having to be added to the relief valve setting, as also described above.

[0071] Furthermore, a pilot liquid supply line Y is provided to supply the pilot liquid to the first pilot liquid port P1 and to supply the pilot liquid to the second pilot liquid port P2, the pilot liquid supply line Y comprising a first branch Y1 to the first pilot liquid port P1 and a second branch Y2 to the second pilot liquid port P2. The first branch Y1 of the pilot liquid supply line Y R.413340 comprises a backflow restrictor 6 and an outlet port of the relief valve 5 is connected to the first branch Y1 of the pilot liquid supply line Y downstream of the backflow restrictor 6. As mentioned, backflow restrictor 6 can be a small orifice.

[0072] Figure 2 schematically illustrates a longitudinal section through a hydraulic system 200 as proposed herein according to an embodiment.

[0073] The embodiment of hydraulic system 200 shown in Figure 2 is an alternative to hydraulic system 100 as shown in Figure 1. In hydraulic system 200, as an alternative to the relief valve 5 of hydraulic system 100, a three ported sequence valve 7 is used. The function with the sequence valve 7 includes that, when the pressure in port B exceeds the setting, the valve will shift and let flow and pressure into the pilot chamber at side C and at the same time block the flow path to the pilot chamber. The need for the restrictor 6 is avoided.

[0074] More precisely, in the hydraulic system 200 according to claim 1 , a main liquid supply line X is provided to supply the main liquid to the main liquid inlet port B, the main liquid supply line X comprising a first branch X1 to the main liquid inlet port B and a second branch X2 to a first inlet port of a sequence valve 7. Furthermore, a pilot liquid supply line Y is provided to supply the pilot liquid to the first pilot liquid port P1 and to supply the pilot liquid to the second pilot liquid port P2, the pilot liquid supply line Y comprising a first branch Y1 to the first pilot liquid port P1 and a second branch Y2 to a second inlet port of the sequence valve 7. An outlet port of the sequence valve 7 is connected to the first pilot liquid port P1, the sequence valve 7 providing a first flow path between its first inlet port and its outlet port in a first valve position and a second flow path between its second inlet port and its outlet port in a second valve position and the sequence valve 7 being configured to switch from the first valve position to the second valve position when the pressure of the main liquid supplied to the main liquid inlet port B exceeds the threshold pressure.

[0075] Figures 3a and 3b schematically illustrate longitudinal sections through hydraulic systems 300, 400 as proposed herein according to a further embodiment. As to the elements already shown in Figures 1 and 2 in connection with hydraulic systems 100, 200, reference is made to the explanations above. As shown in Figures 3a and 3b, additional valve units 9 with relief function may be provided within the main valve spool 1, wherein Figure 3a shows a R.413340 configuration for a pressure relief from port A to port B and Figure 3b shows a configuration for a pressure relief from port B to port A.

[0076] Figure 4 is a schematic valving diagram 500 of an arrangement which may include a hydraulic system 100 or 200 as proposed herein. As encircled by a dash dotted line 310, a system of four bidirectional proportional flow control valves 311 , 312, 313, 314 is provided, of which control valves 312 and 314 are shown in Figure 4 in a simplified matter. These may be provided as a hydraulic system 100, 200, 300 or 400 as proposed herein and as shown in Figures 1, 2, 3a and 3b. The arrangement is used to operate a double acting hydraulic cylinder 320 including a piston 321 and a cylinder 322 connected to the valve system 310 by a first hydraulic connection 301 and a second hydraulic connection 302. Valve system 310 is connected to a pressure port or line P and a drain or tank port or line T. The valves 312 and 314 are shown in Figure 4A in the Form of valve diagrams.

[0077] Operation of the arrangement shown in Figure 4 will now be explained. If an upward movement of piston 321 is intended (“upward”, “above”, “downward” and “below” referring to the illustration in Figure 3), valve 311 may be switched to pass hydraulic liquid from pressure port P and hydraulic connection 301 to a pressure chamber below the piston 321 and valve 314 may be switched to pass hydraulic liquid from a pressure chamber above the piston 321 and hydraulic connection 302 to tank port P while valves 312 and 313 may remain closed. On the other hand, if a downward movement of piston 321 is intended, valve 313 may be switched to pass hydraulic liquid from pressure port P and hydraulic connection 302 to the pressure chamber above the piston 321 and valve 312 may be switched to pass hydraulic liquid from a pressure chamber below the piston 321 and hydraulic connection 301 to tank port P while valves 311 and 314 may remain closed.

Claims

R.413340Claims1. A hydraulic system (100, 200, 300, 400) comprising a main valve unit (110) with a main valve spool (1), the main valve spool (1) being configured to be positioned in a resting position and a continuity of metering positions in dependency of a pressure of a pilot liquid at a first side (C) of the main valve spool (1) and a pressure of the pilot liquid at a second side (D) of the main valve spool (1), and a pilot valve unit (120) comprising a pilot valve spool (3) and a solenoid actuator (11), the pilot valve spool (5) being configured to be positioned in a base position and a continuity of piloting positions in dependency of a current applied to the actuator (11) to adjust the pressure of the pilot liquid at the second side (D) of the main valve spool (1), wherein the main valve unit (110) comprises a first pilot port (P1) to provide the pilot liquid to the first side (C) of the main valve spool (1) and a second pilot port (P2) to provide the pilot liquid to the second side (D) of the main valve spool (1), wherein the main valve unit (110) provides a main liquid path comprising variable flow cross sections in the metering positions between a first main liquid port (A, B) and a second main liquid port (A, B), or vice versa, for a main liquid supplied to the first main liquid inlet port (A, B) or the second main liquid port (A, B), and wherein the hydraulic system (100, 200, 300, 400) is configured to provide a liquid connection between the main liquid inlet port (A, B) to which the main liquid is supplied and the first pilot port (P1) when a pressure of the main liquid supplied exceeds a threshold pressure.

2. The hydraulic system (100, 200, 300, 400) according to claim 1 , wherein the threshold pressure is selected to correspond to a pressure exceeding a design pressure, a standard operating pressure or a predefined pressure or pressure range at the first main liquid port (A, B) or the second main liquid port (A, B) to which the main liquid is supplied by a certain pressure difference or factor.

3. The hydraulic system (100, 200, 300, 400) according to claim 1 or 2, wherein a main liquid supply line (X) is provided to supply the main liquid to the first main liquid port (A, B) or to the second main liquid port (A, B), wherein a pilot liquid supply line (Y) is provided to supply the pilot liquid to the first pilot liquid port (P1) and to supply the pilot liquid to the second pilot liquid port (P2),R.413340 wherein a further valve unit (5, 7, 9) is fluidly interposed between the main liquid port (A, B) to which the main liquid is supplied and the first pilot liquid port (P1 ), wherein said further valve unit (5, 7, 9) is configured to provide said liquid connection between the main liquid inlet port (A, B) to which the main liquid is supplied and the first pilot port (P1) when the pressure of the main liquid supplied exceeds the threshold pressure.

4. The hydraulic system (100) according to claim 3, wherein the further valve unit (5) is provided as or comprises a relief valve (5), wherein the main liquid supply line (X) comprises a first branch (X1) to the main liquid port (A, B) to which the main liquid is supplied and a second branch (X2) to an inlet port of the relief valve (5), and wherein the pilot liquid supply line (Y) comprises a first branch (Y1) to the first pilot liquid port (P1) and a second branch (Y2) to the second pilot liquid port (P2).

5. The hydraulic system (100) according to claim 4, wherein the first branch (Y1) of the pilot liquid supply line (Y) comprises a backflow restrictor (6) and an outlet port of the relief valve (5) is connected to the first branch (Y1) of the pilot liquid supply line (Y) downstream of the backflow restrictor (6).

6. The hydraulic system (300, 400) according to claim 3, wherein the further valve (9) is integrated into the main valve spool (1).

7. The hydraulic system (200) according to claim 3, wherein the further valve unit (5) is provided as or comprises a sequence valve (7), wherein the main liquid supply line (X) comprises a first branch (X1) to the main liquid port (A, B) to which the main liquid is supplied and a second branch (X2) to a first inlet port of the sequence valve (7), wherein a pilot liquid supply line (Y) is provided to supply the pilot liquid to the first pilot liquid port (P1) and to supply the pilot liquid to the second pilot liquid port (P2), the pilot liquid supply line (Y) comprising a first branch (Y1) to the first pilot liquid port (P1) and a second branch (Y2) to a second inlet port of the sequence valve (7), and wherein an outlet port of the sequence valve (7) is connected to the first pilot liquid port (P1), the sequence valve (7) providing a first flow path between its first inlet port and its outlet port in a first valve position and a second flow path between its second inlet port andR.413340 its outlet port in a second valve position and the sequence valve (7) being configured to switch from the first valve position to the second valve position when the pressure of the main liquid supplied to the main liquid inlet port (B) exceeds the threshold pressure.

8. A method of operating a hydraulic system (100, 200, 300, 400), the method comprising providing a hydraulic system (100, 200, 300, 400) according to any one of the preceding claims, providing a pilot liquid to the first pilot port (P1) and to the second pilot port (P2), providing a main liquid to the first main liquid port (A, B) or the second main liquid port (A, B), and energizing the actuator (7) depending on predefined a flow rate of the liquid flow.

9. The method according to claim 8, further comprising providing a liquid connection between the main liquid port (A, B) to which the main liquid is supplied and the first pilot port (P1) when a pressure of the main liquid supplied exceeds a threshold pressure.

10. A computer comprising a processor configured to execute the method of claim 8 or 9.

11. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to execute the method of claim 8 or 9.

12. A computer readable data carrier storing the computer program of claim 11.

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