Valve assembly and method of providing a liquid flow

Abstract

A valve assembly (100) comprising a main valve unit (110) with a main valve spool (1) is proposed, the main valve spool (1) being configured to be positioned in a resting position and a continuity of metering positions in dependency of a first pilot pressure at a first side (9) of the main valve spool (1) and a second pilot pressure at a second side (10) of the main valve spool (1). The valve assembly (100) further comprises a pilot valve unit (120) comprising a pilot valve spool (5) and a solenoid actuator (7), 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 (7) to adjust the pilot pressure at a second side (10) of the main valve spool (1). An adaptor unit (13) mechanically connecting the main valve unit (110) and the pilot valve unit (120) to form the valve assembly (100, 400) is also provided, the adaptor unit (13) defining a pressure chamber (D) at the second side of the main valve spool (1) for providing the second pilot pressure, and the pilot valve unit (120) being configured to depressurize the pressure chamber (D) depending on the continuity of piloting positions of the pilot valve spool (5) by gradually opening a piloting liquid drain port (12). A method of providing a liquid flow and instrumentalities for implementing the method is also proposed.

Description

[0001] VALVE ASSEMBLY AND METHOD OF PROVIDING A LIQUID FLOW

[0002] Field

[0003] The present disclosure relates to a valve assembly and to a method of providing a liquid flow, as well as to instrumentalities for implementing the proposed method.

[0004] Background

[0005] Traditionally, large spool valves for high flow applications are pilot pressure controlled, i.e. , their control is based on the expectation that a certain pressure drop at the valve will generate a certain flow through the valve. Such valves are, however, often exposed to flow forces that will change the spool position and therefore also change the opening area or liquid cross section. With only pilot pressure control, there is no way of detecting the change in opening area automatically.

[0006] For example, US 6,966,329 A discloses a proportional, pilot operated flow control valve which may include a cage, a hollow compensating spool which is slidably disposed within the cage, a hollow metering guide member which slidably disposed within the compensating spool, a regulating spool which is slidably disposed within the guide member, a dampening guide which is slidably disposed inside the compensating spool to define a dampening chamber, a compensating spring which is disposed inside the dampening chamber and arranged to urge the dampening guide to engage the metering guide and the compensating spool to engage the cage, a regulating spring which is disposed inside the regulating spool and urging the regulating spool to abut the dampening guide, and a cartridge, the cartridge having a pilot valve assembly and an adaptor, the adaptor mounted to the cage, and the pilot valve assembly mounted to the adaptor. The pilot valve assembly includes an actuator. A displacement controlled hydraulic proportional valve disclosed in EP 0 637 692 A1, on the other hand, comprises a dashpot disposed between a main valve spool and a pilot valve spool to stabilize the proportional valve. The dashpot includes a bore in a spring retainer engaging the main valve spool and a plunger axially extending from a spring retainer engaging the pilot valve spool with the plunger extending into the bore to define a dashpot chamber. The plunger is sized to permit restricted fluid flow thereby when the spools move relative to each other thereby dampening relative movement between the valve spools. Dampening the relative movement between the valve spools drastically reduces the amount of overshoot by the main valve spool.

[0007] There is a need for improvements in proportional flow valve assemblies including a pilot valve and a piloted valve, as well as in corresponding methods.

[0008] Summary

[0009] Against this background, a valve assembly and a method of providing a liquid flow, 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.

[0010] A valve assembly 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 first pilot pressure of a pilot liquid at a first side of the main valve spool and a second pilot 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 is configured to slide in the main valve cage or the bore of the valve block.

[0011] The valve assembly 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 the pilot pressure at a second side of the main valve spool. 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 main valve is particularly a proportional valve. 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 selected from the range of hydraulics liquids known by the skilled person, particularly from dedicated hydraulics fluids such as hydraulic oils with a defined viscosity and composition. One or more liquids may be provided in the same or different tanks.

[0012] In a valve assembly proposed herein, the main valve spool is in a neutral or balanced position when the first pilot pressure at a first side of the main valve spool and the second pilot pressure 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 first pilot pressure at a first side of the main valve spool and the second pilot pressure at the second side of the main valve spool. In order to provide the pilot liquid at the first pilot pressure at a first side of the main valve spool and the second pilot pressure at the second side of the main valve spool, pressure chambers or other suitable volumes are provided.

[0013] The pilot valve, in the valve assembly proposed herein, is configured to depressurize the pressure chamber at the second side of the main valve spool in a controlled manner, which is particularly done 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. That is, in configurations as proposed herein, a pressure difference between both sides of the main valve spool is not, as according to conventional systems, provided by increasing the pressure at one side, but by a reduction of a volume of the piloting liquid relief. This has considerable advantages with regard to the switching speed.

[0014] The valve assembly proposed herein comprises an adaptor unit mechanically connecting the main valve unit and the pilot valve unit to form the valve assembly. The adaptor unit defines, or contributes to define, a pressure chamber at the second side of the main valve spool for providing the second pilot pressure, and the pilot valve unit is being configured to depressurize the pressure chamber at the second side of the main valve spool depending on the continuity of piloting positions of the pilot valve spool by gradually opening a piloting liquid drain port. The pilot liquid drain port may be connected to a tank for a hydraulic liquid.

[0015] This allows for the complete valve assembly to be provided in a cartridge type assembly which enables a system designer to create a hydraulic integrated circuit with high flexibility. Due to the cartridge design, the valve assembly can be directly mounted into, e.g., cylinders, motors, pumps, etc. The cartridge design also allows a flexible system design when combining multiple valves into a system.

[0016] In other words, large spool valves may conventionally be integrated into mono block or sectional type of casted housings which restricts the design possibilities (for the spool and body). Embodiments of the present invention rather 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.

[0017] However, in some configurations, instead of a cartridge design and the adapter solution described above, the elements of the main valve unit, particularly the main valve spool, may also be provided in a casing block configured to carry a plurality of such units. Such a casing block may be formed by suitable manufacturing techniques such as casting, particularly core casting, for example, and may include prefabricated fluid channels, ports, etc. Use of a casing block facilitates manufacturing valve arrangements including a plurality of valve assemblies, particularly for serial production.

[0018] Embodiments as disclosed herein overcome a plurality of problems related to valve assemblies according to the prior art. As mentioned, traditionally 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.

[0019] Even if a proper calibration is performed, there still is the risk of the valve reacting to varying flow forces, so that the calibration is no longer correct. A valve assembly as proposed herein, in contrast, allows for a calibration that is valid for a larger range of operating conditions which, e.g., allows for providing a characteristic curve and controlling the valve assembly via a look up table with essentially the same reliability and reproducibility as conventionally achieved using a position sensor for spool monitoring.

[0020] Conventionally, large spool valves also have a relatively large spool leakages due to their large diameters. A conventional solution to this problem is to pair spools and bodies for minimizing leakages, which involves considerable effort and costs. This disadvantage is overcome according to certain embodiments further explained below due to sealing means. This allows for an effective and essentially leak free blocking of the main liquid when the main valve spool is in the resting position. Generally, as the valve assemblies proposed herein do not operate on the basis of a differential pressure of a liquid upstream and downstream of the valve assemblies, the main liquid path can be completely closed in a resting position of the main valve spool and no additional pressurizing must be performed.

[0021] Embodiments as proposed herein offer advantages over the two main types of proportional valves for larger flow rates and volumes which either include an external pilot valve, which has to be dimensioned accordingly, or which comprise an integrated pilot valve and which operate on the basis of a pressure difference.

[0022] In conventional arrangements, a response time of a valve is increasing with the size of the spool diameter due to higher oil flow requirements, requiring bigger electric proportional pilot valves. Generally, a relationship between size and speed still exists according to embodiments proposed herein, but due to the proposed relief of the piloting liquid from the pressure chamber, which is much faster than a pressure build up according to the prior art, switching is nevertheless faster according to the proposed embodiments. Common today is, in conventional valves, the use of hydraulic pilot joysticks, which cannot handle the increased need of pilot flow. Also this problem is overcome with the embodiments proposed herein.

[0023] A further problem solved by embodiments proposed herein is that of increasing hysteresis in connection with the spool diameter because of spool weight and friction due to larger sealings. In addition to the directional control valves, traditionally a counterbalance valve, load holding valve or seated logic element is required to achieve leakage free load holding of a cylinder. This is no more the case in embodiments as proposed herein. Particularly, in the valve assembly proposed herein, the main valve spool, in the resting position and all of the continuity of metering positions, blocks a fluid passage between the first side of the main valve spool and the second side of the main valve spool, and the pressure chamber at the second side of the main valve spool is pressurized, or configured to be pressurized, via a channel in the adaptor unit and a pilot port to provide the second pilot pressure. The pilot port is an orifice to the channel in the adapter unit.This is a substantially different configuration than disclosed in US 6,966,329 B2 mentioned at the outset, where pressure difference on both sides of a regulating spool is created by fluid being allowed to pass through the regulating spool via an orifice therein, and therefore these pressures are always dependent from another.

[0024] In certain embodiments of the valve assembly proposed herein, the main valve spool comprises a spool shoulder configured to rest on a spool seat provided in a receptacle for the main valve spool, such as a main valve cage or a bore of a valve block. The spool shoulder rests on the spool seat when the main valve spool is in the resting position, blocking a liquid passage between liquid ports for a main liquid. The spool shoulder particularly is provided as a circular contiguous rim or step in a plane perpendicularly to a longitudinal axis of the main valve spool. The spool seat, on the other hand, is particularly provided as a circular contiguous ridge or rim in a plane perpendicularly to a longitudinal axis of the receptacle. The spool shoulder and the spool seat are in contact with or abut each other in the resting position in order to block a liquid flow therebetween. The spool seat is provided between the liquid ports for the main liquid. Advantages of providing a spool shoulder and a spool seat in a spool receptacle include a complete, or essentially complete, blockage of the main liquid in the resting position of the main spool.

[0025] In certain embodiments, the main valve spool is an assembly comprising a first part and a second part. This assembly is provided by inserting one of the first part and the second part into the receptacle from a first side thereof and thereafter inserting the other one of the first part and the second part into the receptacle from a second side thereof. The first and second sides are opposite sides and the first and the second part may be connected to each other by any suitable connection, e.g., by press fitting, screwing, welding or soldering. An assembly of this type is particularly useful if the spool seat is formed integrally with the receptacle, creating a reduced diameter. The main valve spool may, in such situations, nevertheless contact an inner surface of the receptacle on both sides of the spool seat, and a region therebetween may be provided with a smaller diameter.

[0026] In certain embodiments of the valve assembly proposed herein, the receptacle for the main valve spool comprises a sealing section configured to be in a sealing relationship with an outer surface of the main valve spool when the main valve spool is positioned at a continuity of intermediate positions between the resting position and each of the metering positions, also blocking a liquid passage between the liquid ports for the main liquid in the intermediate positions, i.e. , when the main valve spool is moved from its resting position towards the metering positions.

[0027] The term “sealing relationship” shall, herein, particularly refer to a distance between the sealing section of the receptacle for the main valve spool and the outer surface of the main valve spool which provides for a substantial restriction of a liquid flow therebetween but which, particularly due to operational limitations, such as a required motility, may be less tight than the contact between the spool shoulder and the spool seat. The spool shoulder, in other words, rests on the spool seat to provide an essentially complete sealing when the main valve spool is in the resting position, but also when the main valve spool is moved into an opening direction, there is, initially, a certain amount of sealing when the main valve spool is displaced from the resting position and moved into the direction of the metering positions. The sealing section may include indentations, rims, recesses, grooves and other structuring elements as may be required for proper sealing and motility.

[0028] In certain embodiments as proposed herein, the sealing section extends from the spool seat in a first direction and the main valve spool comprises a passage section defining a clearance between the main valve spool and an inner surface of the receptacle, the passage section extending from the spool shoulder in a second direction opposite to the first direction and the clearance providing a liquid passage between the liquid ports for the main liquid in each of the metering positions. This allows for providing a metered flow proportional to a current flowing through the solenoid of the pilot valve, which in turn hydraulically controls or pilots a position of the main valve spool.

[0029] In certain embodiments, the passage section is provided as a section of the main valve spool having a reduced diameter as compared to a section of the main valve spool extending from the spool shoulder in the first direction. 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.

[0030] In certain embodiments as proposed herein, the continuity of metering positions defines a continuity of different liquid cross sections between the liquid ports for the main liquid, in order to provide different flow rates of the main liquid. Due to the piloted operation in embodiments as proposed herein, these positions are particularly well defined and there is no displacement by pressure or flow fluctuations as in the prior art.

[0031] In certain embodiments as proposed herein, the valve assembly comprises a neutral spring and a feedback spring, the main valve spool being biased towards the resting position by the neutral spring against the second pilot pressure, and the pilot valve spool being biased towards the base position by the feedback 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.

[0032] 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.

[0033] In certain embodiments as proposed herein, the assembly comprises an adaptor unit mechanically connecting the main valve unit and the pilot valve unit to form the valve assembly, the adaptor unit defining a pressure chamber at the second side of the main valve spool for providing the second pilot pressure. This allows for the complete valve assembly to be provided in a cartridge type assembly which enables a system designer to create a manifold quicker and with more flexibility. Due to the cartridge design, the valve assembly can be directly mounted into, e.g., cylinders, motors, pumps, etc. The cartridge design also allows a flexible system design when combining multiple valves into a system.

[0034] The pilot valve unit is, as already mentioned, particularly configured to depressurize the pressure chamber at the second side of the main valve spool depending on the continuity of piloting positions of the pilot valve spool by gradually opening a piloting liquid drain port. In contrast to conventional mono block designs, the modular design as provided according to such embodiments is particularly advantageous and serviceable.

[0035] In certain embodiments as proposed herein, the main valve spool and the pilot valve spool are provided in a coaxial arrangement in the valve assembly. Particularly such an arrangement allows for the valve assembly to be created by using turned parts. Turned parts, in comparison to casted parts, for example, can be manufactured with higher precision and hardened where required.

[0036] A method of providing a liquid flow as proposed herein comprises providing a valve assembly as described in different embodiments above, providing the first pilot pressure and the second pilot pressure at the first and second sides of the main valve spool, and energizing the actuator depending on predefined a flow rate of the liquid flow.

[0037] As to further details and advantages of such a method, reference is made to the explanations above and below regarding the valve assembly proposed herein and its different embodiments. Particularly, such a method may, in embodiments as proposed herein, use a valve assembly according to any of the embodiments as discussed herein.

[0038] The method proposed herein, and the valve assembly 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. The internal mechanical position feedback increases the response time and improves the hysteresis. With mechanical position feedback, the valve assembly 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 valve assembly to have low leakage at closed position and capability of holding a load for long time. The unique design of the valve assemblies disclosed herein enables tailored flow versus current behaviour. In comparison to known technology, the valve assembly does not require any differential pressure (pressure drop) in “regulating” mode. A simple calibration process of the pilot valve solenoid actuator with force feedback before combining with the spool is possible.

[0039] Certain embodiments as proposed herein include a multi chamber cylinder control with independent metering of flows to and from the valve assembly and load holding without parasitic losses through spool control valves. Certain embodiments may also include a hydraulic cylinder operated using a regeneration circuit or regeneration control. Regeneration includes, as known to the skilled person, connecting the bottom and rod sides of a cylinder. This can be achieved through valve technology. Regeneration means that the fluid flowing out of the rod end of the cylinder during extension is returned to the inlet side of the cylinder in order to increase the extension velocity. This concept allows the extension speed to be increased significantly without increasing the pump flow output. This means that regeneration circuits save investment and operating costs because a smaller pump, motor, and tank can produce the desired cycle time.

[0040] Valve assemblies and methods as proposed herein may particularly be used in any hydraulic arrangements such as, without limitation, energy optimized, electrified machines and energy recovery systems with restrictive leakage requirements, load holding devices, independent metering or bridge circuits, directional control systems, as well as on / off and proportional control arrangements combined with an “intelligent” pump (e.g. digital pump).

[0041] Embodiments as proposed herein may also be used in connection with electronic load sensing systems. As the position of the valve spools is in rather close relation to controlled current, the valve position is known, which enables for calculating a current flow, if knowing the differential pressure 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, with highest energy efficiency (configurable margin pressure).

[0042] 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.

[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 valve assembly 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”, harvesting heads of forestry machines (due to high flow rates and high precision) and functions like slewing and winching.

[0044] 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.

[0045] 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.

[0046] Figures

[0047] Further advantages and embodiments disclosed herein are explained in connection with the accompanying drawings, in which

[0048] Figure 1 schematically illustrates a longitudinal section through a valve assembly as proposed herein according to an embodiment,

[0049] Figures 2A and 2B are detail views of valve assemblies as proposed according to certain embodiments,

[0050] Figure 3 schematically illustrates a longitudinal section through a valve assembly as proposed herein according to further embodiment, and

[0051] Figure 4 is a schematic valving diagram including a valve assembly.

[0052] Embodiments 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.

[0053] 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, and repetitions may be omitted for reasons of conciseness only.

[0054] 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.

[0055] 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 as they stand.

[0056] 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.

[0057] Figure 1 schematically illustrates a longitudinal section through a valve assembly 100 as proposed herein according to an embodiment. Valve assembly 100 is a two way, two position electrical proportional flow control valve assembly with mechanical position feedback. Essential features include a two piece spool design with a seated resting position which enables low leakage (load holding) feature. The special spool and cage design enables tailored flow versus current metering behavior.

[0058] Valve assembly 100 comprises a main valve 110 including a main valve spool 1 inside a main valve cage 2 biased to a resting position by a neutral spring 4. A pilot valve 110 is operated with a solenoid 7, and the main valve 110 and the pilot valve 110 are mechanically connected by an adaptor 13. The adaptor 13, more precisely, holds the pilot valve 12 and the main valve cage 2 together, to form, in the example illustrated, a screw in valve assembly 100. The main valve spool 1 is composed of a first part 1a and a second part 1b enabling the mounting of the main valve spool 1 from two ends of the main valve cage 2 in order to provide a functionality of a seat 8 for the main valve spool 1 , as already explained before and further below.

[0059] The functionality of the valve unit 100 will now be described. A pilot pressure of the same pressure level of a piloting liquid is acting on both sides 9 and 10, i.e. , a first pressure and a second pressure is acting on a first side 9 and a second side 10 of the main valve spool 1 , said pressures typically acting on the same effective area. Pressure chambers or spaces at the first side 9 and a second side 10 of the main valve spool 1 are indicated by C and D. They may be included in a larger arrangement or may be part of assembly 100.

[0060] A pilot valve spool 5 is controlled by solenoid actuator 7 against a feedback spring 6. When current is applied to the actuator 7, the pilot valve spool 5 is pushed against the feedback spring 6 which is therefore compressed with the force which the current to the actuator 7 can provide. When the pilot valve spool 5 moves, the pressure chamber D at the second side 10 of the main valve spool 1 will be opened to tank, via a drain port 12, and the pilot pressure on this side of the main valve spool 1 will decrease. Due to the pilot pressure remaining unchanged on the first side 9 of the main valve spool 1, however, the main valve spool 1 will start to move and compress the neutral spring 4.

[0061] In consequence, a passage section 16 of the main valve spool 1 defining a clearance 17 between the main valve spool 1 and an inner surface of the main valve cage 2 provides an opening between main valve ports A and B allowing a metered flow of a metered or “main” liquid. At the same time, due to a movement of the main spool 1 , the feedback spring 6 is compressed and pushes the pilot spool 5 against the force of the actuator 7 until the pilot valve spool 5 is in neutral position. A certain pilot pressure of a pilot liquid will therefore again be present at the spring side or second side 10 of the main valve spool 1 and the main valve spool 1 will therefore not move further.

[0062] If any flow forces act on the main valve spool 1 and create movements, the balance between the feedback spring 6 and the solenoid actuator 7 will be changed. This change will shift the pilot valve spool 5 to either open the spring side or second side 10 of the main spool 1 to tank, via drain port 12, allowing the main spool to shift against the neutral spring 4, or add pilot pressure, via pilot port 11, to the spring side or second side 10 of the main spool 1, allowing the main spool 1 to shift away from the second side 10. The same will happen if the current to the solenoid actuator 7 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.

[0063] Summarizing what was just explained, valve assembly 100 comprises a main valve unit 110 with a main valve spool 1 and a main valve cage 2, the main valve spool 1 being arranged to slide in the main valve cage 2 and being configured to be positioned in a resting position and a continuity of metering positions in dependency of a first pilot pressure of a pilot liquid at a first side 9 of the main valve spool 1 and a second pilot pressure of the pilot liquid at a second side 10 of the main valve spool 1. Valve assembly 100 further comprises a pilot valve unit 120 comprising a pilot valve spool 5 and a solenoid actuator 7, 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 7 to adjust the pilot pressure at a second side 10 of the main valve spool 1.

[0064] Figures 2A and 2B show detail views 101 and 102 of valve assemblies according to certain embodiments disclosed herein.

[0065] As particularly visible from Figure 2A, showing a detail view 101 of the assembly 100 illustrated in Figure 1, the position of which is also referred to by a box 101 in Figure 1, when the main spool 1 is in its resting position, the seat 8 for the main valve spool 1 enables a leak free path between the ports A and B. Due to the design of the seat 8 and the cage opening B the flow versus current metering behaviour can be modified.

[0066] In other words, the main valve spool 1 comprises a spool shoulder 3 and the main valve cage 2 comprises spool seat 8. The spool shoulder 3 rests on the spool seat 8 when the main valve spool 1 is in the resting position, as illustrated in Figures 1 and 2A, blocking a liquid passage between the main liquid ports A and B as shown in Figure 1.

[0067] When shoulder 3 of the main valve spool 1 rests on the seat 8, as shown in Figure 2A, the flow is zero and essentially leak free. When the main valve spool 1 has shifted from this position to the left, such that the main valve spool 1 lifts off the seat 8, the metering opening 12 opens a passage between main liquid ports A and B.

[0068] A further embodiment is shown in Figure 2B. The features shown in Figure 2B can be alternatively implemented in the valve assembly 100 according to Figure 1. In this embodiment, when the main valve spool 1 lifts off the seat 8, the passage between main liquid ports A and B is still closed between positions E and F of the main valve spool 1 , but the leakage has increased to spool leakage. When the main valve spool 1 has reached position G, the metering opening 12 starts and flow increases. The shape of the opening can be formed differently to get the desired behaviour of the valve.

[0069] That is, in the embodiment shown in Figure 2B, the main valve cage 2 comprises a sealing section 15 configured to be in a sealing relationship with an outer surface of the main valve spool 1 when the main valve spool 1 is positioned at a continuity of intermediate positions E, F, G between the resting position and each of the metering positions to block a liquid passage between the main liquid ports in the intermediate positions.

[0070] Figure 3 schematically illustrates a longitudinal section through a valve assembly 200 as proposed herein according to further embodiment. Elements already explained above in connection with Figure 1 are not explained again for reasons of conciseness and may be indicated with identical reference numerals.

[0071] As shown in Figure 3, in an embodiment a valve assembly may also be provided without a a spool seat on which a spool shoulder rests in the resting position. Figure 4 is a schematic valving diagram 300 of an arrangement which may include a valve assembly 100 or 200 as proposed herein and as described in connection with Figures 1 and 3. As encircled by a dash dotted line 310, a system of four bidirectional proportional flow control valves 311, 312, 313, 314, each of which may be provided as a valve assembly 100 as proposed herein, is used to operate a double acting hydraulic cylinder arrangement 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.

[0072] 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 4), 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.

[0073] A valve 315 may further be present establish a regeneration circuit or to allow for regeneration control as described before, i.e. , for connecting the bottom and rod sides of cylinder 320 as described before in detail already.

[0074] It should be understood that the valve symbols shown in Figure 4 for the valves 311 to 315 are simplified representations of more complex arrangements. Particularly, pilot and drain lines are not shown for reasons of conciseness

Claims

Claims1. A valve assembly (100, 200) 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 first pilot pressure of a pilot liquid at a first side (9) of the main valve spool (1) and a second pilot pressure of the pilot liquid at a second side (10) of the main valve spool (1), a pilot valve unit (120) comprising a pilot valve spool (5) and a solenoid actuator (7), 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 solenoid actuator (7) to adjust the pilot pressure at a second side (10) of the main valve spool (1), and an adaptor unit (13) mechanically connecting the main valve unit (110) and the pilot valve unit (120) to form the valve assembly (100, 400), the adaptor unit (13) defining or contributing to define a pressure chamber (D) at the second side (10) of the main valve spool (1) for providing the second pilot pressure, and the pilot valve unit (120) being configured to depressurize the pressure chamber (D) depending on the continuity of piloting positions of the pilot valve spool (5) by gradually opening a piloting liquid drain port (12).

2. The valve assembly (100, 200) according to claim 1 , wherein the main valve spool (1), in the resting position and all of the continuity of metering positions, blocks a fluid passage between the first side (9) of the main valve spool (1) and the second side (10) of the main valve spool (1), and wherein the pressure chamber (D) at the second side of the main valve spool (1) is pressurized, or configured to be pressurized, via a channel in the adaptor unit (13) and a pilot port (11) to provide the second pilot pressure.

3. The valve assembly (100) according to claim 1 or 2, the main valve spool (1) comprising a spool shoulder (3) and a receptacle (2) for the main valve spool (1) comprising a spool seat (8), wherein the spool shoulder (3) rests on the spool seat (8) when the main valve spool (1) is in the resting position, blocking a liquid passage through the valve assembly (100, 400).

4. The valve assembly (100, 200) according to claim 3,wherein the main valve spool (1) is an assembly comprising a first part (1a) and a second part (1b) provided by inserting one of the first part (1a) and the second part (1b) into the receptacle (2) from a first side thereof and thereafter inserting the other one of the first part (1a) and the second part (1b) into the receptacle (2) from a second side thereof.

5. The valve assembly (100) according to claim 3 or 4, the receptacle (2) for the main valve (1) spool being provided as a valve cage or a bore in a valve block used to form the valve assembly (100).

6. The valve assembly (100) according to any one of claims 3 to 5, the receptacle (2) comprising a sealing section (15) configured to be in a sealing relationship with an outer surface of the main valve spool (1) when the main valve spool (1) is positioned at a continuity of intermediate positions between the resting position and each of the metering positions in order to block a liquid passage between the main liquid ports (A, B) in the intermediate positions.

7. The valve assembly (100) according to claim 6, the sealing section (15) extending from the cage seat (8) in a first direction and the main valve spool (1) comprising a passage section (16) defining a clearance (17) between the main valve spool (1) and an inner surface of the main valve cage (2) the passage section (16) extending from the spool shoulder (3) in a second direction opposite to the first direction providing and the clearance (17) providing a liquid passage between the main liquid ports (A, B) in each of the metering positions.

8. The valve assembly (100, 200) according to any one of the preceding claims, the continuity of metering positions defining a continuity of different liquid cross sections through the valve assembly (100, 400).

9. The valve assembly (100, 200) according to any one of the preceding claims, comprising a neutral spring (4) and a feedback spring (6), the main valve spool (1) being biased towards the resting position by the neutral spring (4) against the second pilot pressure, and the pilot valve spool (7) being biased towards the base position by the feedback spring (6) against a force provided by the actuator.

10. The valve assembly (100, 200) according to claim 9, the feedback spring (6) being coaxially arranged within the neutral spring (4).

11. The valve assembly (100, 200) according to any one of the preceding claims, the main valve spool (1) and the pilot valve spool (5) being provided in a coaxial arrangement in the valve assembly (100).

12. A method of providing a liquid flow, the method comprising providing a valve assembly (100, 200) according to any one of the preceding claims, providing the first pilot pressure and the second pilot pressure, energizing the actuator (7) depending on predefined a flow rate of the liquid flow.

13. A computer comprising a processor configured to execute the method of claim 12.

14. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to execute the method of claim 12.

15. A computer readable data carrier storing the computer program of claim 14.

Images