Valve combination for flushing closed hydraulic circuits

Abstract

The invention relates to a loop flushing valve arrangement (10, 40) that comprises a housing with an inner recess, a first fluid port (19) connecting to the inner recess, a second fluid port (20) connecting to the inner recess, a third fluid port (21 ) connecting to the inner recess, and a spool (18) that is slidably movable within the inner recess. A biasing means (29) is provided that biases the spool (18) in a neutral position, in which the first fluid port (19), the second fluid port (20) and the third fluid port (21 ) are fluidly separated from each other. The spool (18) comprises a first pressure surface (22) that moves, when being applied with a pressure, the spool (18) into a first actuated position, in which a first temporary fluid channel is established between the second fluid port (20) and the third fluid port (21 ). Further, the spool (18) comprises a second pressure surface (23) that moves, when being applied with a pressure, the spool (18) into a second actuated position, in which a second temporary fluid channel is established between the first fluid port (19) and the third fluid port (21 ). Further, the first temporary fluid channel and / or the second temporary fluid channel comprise a unidirectional fluid influencing member (35, 36). This way, the loop flushing valve arrangement (10, 40) comprises a loop flushing valve functionality and a minimum pressure check valve functionality in a combined design.

Description

[0001] DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0002] - 1 -

[0003] Valve combination for loop flushing systems

[0004] The invention relates to a loop flushing valve arrangement comprising a housing with an inner recess, a first fluid port connecting to the inner recess, a second fluid port connecting to the inner recess and a third fluid port connecting to the inner recess, and further a spool that is slidably movable within the inner recess.

[0005] The invention further relates to a loop flushing arrangement comprising a loop flushing valve arrangement.

[0006] Even further, the invention relates to a closed loop hydraulic circuit with a loop flushing branch.

[0007] Hydraulic circuits, in particular closed-loop hydraulic circuits, are as such well known in the prior art.

[0008] In particular in case of closed loop hydraulic circuits, frequently so-called loop flushing is regularly employed for various reasons. Basically, loop flushing means to branch off a certain amount of fluid that is circulating inside of the closed loop circuit toward another destination, typically a fluid flow reservoir (possibly via a heat exchanger). This might be required in case that a hydraulic pump is used to pump hydraulic oil into the closed-loop hydraulic fluid circuit. It is to be noted that such a pump is essentially always required to compensate for more or less inevitable fluid losses, in particular fluid losses at machinery with moving parts. To avoid an overpressurisation of the hydraulic circuit, excess amounts of pumped hydraulic fluid has to be removed.

[0009] To compensate for fluid losses, typically a small hydraulic pump is sufficient. However, sometimes the hydraulic pump is scaled to be larger on purpose, in DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0010] - 2 - particular for cooling purposes. It is to be noted that in a closed loop hydraulic circuit, the hydraulic oil will eventually heat up over time. This heat has to be removed. In case of very small thermal energy input, heat dissipation by means of the fluid conduits and the machinery might be sufficient.

[0011] Typically, however, a larger amount of thermal energy has to be removed from the closed hydraulic loop. This may be done by introducing an oil cooler into the closed loop hydraulic circuit. However, such an oil cooler (fluid cooler) introduces a comparatively significant amount of fluid flow resistance, which can be a problem. Furthermore, the heat exchanger has to sustain comparatively high pressures (typically in the order of 30 to 50 bars) and is therefore comparatively costly.

[0012] Therefore, the problem of removing thermal energy is quite often solved by constantly introducing a certain amount of cool hydraulic fluid into the closed loop and removing hot oil from the closed loop circuit.

[0013] For such loop flushing, valves are used that are connected to the low-pressure conduit of the closed-loop hydraulic circuit. The respective valves open only above a certain minimum pressure (cracking pressure). This is to ensure that a sufficient amount of hydraulic fluid will remain in the closed circuit.

[0014] Things become more problematic in case the low-pressure side and the high- pressure side can change in the closed-loop hydraulic circuit. An example for this is a hydraulic transmission where a hydraulic pump drives a hydraulic motor. If, however, the actuated side is to be slowed down, the hydraulic motor will typically function as a hydraulic pump, while the hydraulic pump now acts as a hydraulic motor. It is obvious that now the pressure sides of the closed- loop hydraulic fluid circuit are reversed. To account for this behaviour, an additional selecting valve is required that connects the current low-pressure side to an output conduit, while sealing off the current high-pressure side. DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0015] - 3 -

[0016] While this approach works admittedly well, it nevertheless requires a plurality of different valves for the different functions. This, however, goes along with increased cost. Furthermore, it increases the complexity of the arrangement, requiring more fluid connections and so on, which might also limit the lifetime of the arrangement or may require a more complex manufacturing and / or maintenance of the arrangement.

[0017] A solution to this problem was already proposed in US 10,167,882 B2. Here, a valve arrangement is suggested, where the valve housing includes a cylindrical valve bore with a high-pressure inlet, a low-pressure inlet and a discharge outlet. A first flushing valve spool is arranged elastically pre-stressed within the valve bore for enabling a fluid connection between the low-pressure inlet and the discharge outlet. A shuttle valve spool is arranged elastically prestressed within the valve bore for enabling the fluid connection between the low-pressure inlet and the discharge outlet. The first flushing valve spool is moveable into an open position if the fluid pressure at the low-pressure inlet exceeds a first threshold value, and the shuttle valve spool is moveable into an open position for connecting the low-pressure inlet with the discharge outlet, if the pressure difference between the high-pressure inlet and the low- pressure inlet exceeds a second threshold value. While this valve arrangement realises a combination of a shuttle valve and a minimum pressure valve, therefore simplifying the standard design with separate valves, the manufacture of this valve arrangement is quite complicated and costly. In particular the design with the sleeve like flushing spools that have to be manufactured with a very small play both with respect to the central shuttle valve and the inside surfaces of the housing is cumbersome and costly to manufacture. DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0018] - 4 -

[0019] It is therefore obvious that there is a need for an improved valve arrangement for loop flushing arrangements and / or for improved closed-loop hydraulic circuits with a loop flushing functionality.

[0020] It is therefore an object of the present invention to propose a loop flushing valve arrangement that comprises a housing with an inner recess, a first fluid port connecting to the inner recess, a second fluid port connecting to the inner recess, a third fluid port connecting to the inner recess and a spool that is slidingly movable within the inner recess, and that is improved over such loop flushing valve arrangements as they are known in the state-of-the-art.

[0021] It is another object of the present invention to propose a loop flushing arrangement comprising a loop flushing valve arrangement that is improved over loop flushing arrangements of this type that are known in the state-of-the- art.

[0022] It is yet another object of the invention to propose a closed-loop hydraulic circuit that comprises a hydraulic fluid source, a hydraulic consumer and a fluid flushing branch that is improved over closed-loop hydraulic fluid circuits of this type as they are known in the state-of-the-art.

[0023] A loop flushing valve arrangement, a loop flushing arrangement and / or a closed-loop hydraulic circuit according to the present disclosure solve(s) at least one of these objects.

[0024] It is suggested to design and arrange a loop flushing valve arrangement that comprises a housing with an inner recess, a first fluid port connecting to the inner recess, a second fluid port connecting to the inner recess, a third fluid port connecting to the inner recess, and a spool that is slidably movable within the inner recess, the loop flushing valve arrangement further comprising a biasing means that biases the spool in a neutral position in which the first fluid DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0025] - 5 - port, the second fluid port and the third fluid port are fluidly separated from each other, the spool comprising a first pressure surface that moves, when being applied with a pressure, the spool into a first actuated position, in which a first temporary fluid channel is established between the second fluid port and the third fluid port, and a second pressure surface that moves, when being applied with a pressure, the spool into a second actuated position, in which a second temporary fluid channel is established between the first fluid port and the third fluid port, in a way that the first temporary fluid channel and / or the second temporary fluid channel comprise a unidirectional fluid influencing member.

[0026] This suggested loop flushing valve arrangement may advantageously fulfil the purposes of a loop flushing spool, as it is known in the art, and the formerly separately provided (usually two) minimum pressure check valve(s) together. Nevertheless, it is surprisingly simple in design. In particular, the number of cylindrical surfaces of those parts that are neighbouring each other and that have to be machined with a sufficient preciseness to reduce fluid flow through the remaining gaps to an acceptable level is minimised over different solutions that have already been proposed in the state of the art, in particular by US 10,167,882 B2 that was already mentioned. In particular, essentially only the slidably movable spool and the surrounding bore have to have this machining preciseness. Effectively this means that only two surfaces have to be machined with this accordingly high precision (namely the bore in the housing and the cylindrical middle part of the slidable spool). This is a significant advantage over US 10,167,882 B2, where six surfaces have to be machined with high precision, namely the inner surface of the bore in the housing (one surface), the inner surface and the outer surface of the altogether four sleevelike flushing valve spools (altogether four surfaces), and the outer surface of the slidable central shuttle valve spool (one surface). The advantage is obvious. It becomes even more obvious when considering that the sleeve-like DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0027] - 6 - shuttle valve spools of US 10,167,882 B2 are essentially sheaths with a small thickness, so that the machining becomes complicated.

[0028] The notion of a “temporary fluid channel” is usually to be interpreted in a way that the respective fluid channel is only established when the spool is in an appropriate position (or rather in an appropriate range of positions). In other positions of the spool, the fluid channel is closed and hence not passible for fluid.

[0029] The slidably movable spool, in combination with the altogether three fluid ports, serve to provide the loop flushing spool functionality of the loop flushing valve arrangement. For clarifying, a loop flushing spool is a shuttle valve that connects the lower pressurised conduit of a closed loop hydraulic fluid circuit with a flushing conduit. Typically, the first fluid port and the second fluid port are connected to the differently pressurised fluid conduits of such a closed loop hydraulic fluid circuit. As already noted, at least for certain designs of closed loop hydraulic fluid circuits, the pressure situation can reverse, so that the formerly lower pressurised conduit becomes the higher pressurised conduit and vice versa. This is, for example, the case if a fluid pump propels a fluid motor. If the device that is driven by the fluid motor has to be slowed down, a situation occurs where the fluid motor temporarily becomes a fluid pump, while the (usual) fluid pump temporarily becomes a fluid motor. Therefore, to “continuously” connect the lower pressurised fluid conduit (which may change, as described) to the fluid flushing port, a loop flushing spool that has to be provided.

[0030] Only for completeness: the third fluid port, which may also be addressed as a central fluid port, will be connected to a fluid flushing conduit. Consequently, one can describe the third fluid port as a fluid outlet port (temporal fluid output port). Hence, the first fluid port and the second fluid port may be addressed as side fluid ports or (temporal) fluid input ports. DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0031] - 7 -

[0032] The functionality of the loop flushing spool is provided by a first pressure surface that is fluidly connected with the first fluid port. If this port is connected to the higher pressurised conduit, the spool moves into a position in which the then lower pressurised fluid port (the second fluid port) is connected to the central fluid port / third fluid port and consequently to the fluid flushing fluid conduit. At this time, the first fluid port / the higher pressurised conduit is cut off from the third fluid port.

[0033] The same applies mutatis mutandis by means of the second pressure surface when the second fluid port is connected to the higher pressurised conduit of the closed loop hydraulic fluid circuit (at a particular point in time). In particular, not not only a first pressure surface is fluidly connected with the first fluid port but additionally or alternatively, a second pressure surface is fluidly connected with the second fluid port.

[0034] A further advantageous characteristics, which is as such also known in the prior art, lies in that in case the pressures at the first fluid port and the second fluid port are (essentially) the same, the spool will be in a neutral position, in which all three fluid ports are separated from each other. This way, an undesired emptying of the closed-loop hydraulic fluid circuit (running dry) can be avoided, or at least delayed. This may apply if the closed-loop hydraulic fluid circuit is switched off, but also during certain operational states of the closed-loop hydraulic fluid circuit.

[0035] It is to be noted that it is possible to design the biasing means in a way that a minimum pressure difference between first fluid port and second fluid port will be required to move the spool in one or both opening positions, in which the third fluid port is connected to either the first fluid port or the second fluid port. Actually, this will be typically the case, in particular in case a biasing means (in particular two opposing biasing means) are in a neutral, unbiased position, DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0036] - 8 - when the spool is in its neutral position (or in an equally biased, pre-tensioned position). Then, a certain force is required to move the spool in either direction, i.e. in the direction of a position in which a fluid connection is established between the third fluid port and one of the first fluid port and the second fluid port.

[0037] Usually, the at least one unidirectional fluid influencing member is arranged to lie within and / or in series with the respective temporary fluid channel (first temporary fluid channel and / or second temporal fluid channel. In particular, if the respective temporary fluid channel is in a temporarily open position, a large fraction, the majority of and / or (essentially) all of the the fluid flow through the temporary fluid channel will flow through the respective unidirectional fluid influencing member as well. In particular, this does not rule out the possibility that a certain fraction is led around the respective unidirectional fluid influencing member, in particular a leakage flow due to unavoidable manufacturing tolerances. In particular, the percentage of the fluid flow that does not flow through the respective unidirectional fluid influencing member when the temporary fluid channel is open should be less than 0.1 %, 0.2%, 0.5%, 1 %, 2%, 5%, 10%, 15%, 20% or 25%.

[0038] More particularly, if a first unidirectional fluid influencing member is arranged within / as part of / in series with a first temporary fluid channel between the second fluid port and the third fluid port, a large fraction, the majority of and / or (essentially) all of the the fluid flow through the first temporary fluid channel will also flow through the first unidirectional fluid influencing member (and not through a parallel fluid channel or the like). Furthermore, if the first temporary fluid channel is closed, usually (essentially) no fluid will flow through the first unidirectional fluid influencing member.

[0039] Additionally or alternatively, if a second unidirectional fluid influencing member is arranged within / as part of / in series with a second temporary fluid channel DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0040] - 9 - between the first fluid port and the third fluid port, a large fraction, the majority of and / or (essentially) all of the the fluid flow through the second temporary fluid channel will also flow through the second unidirectional fluid influencing member (and not through a parallel fluid channel or the like). Furthermore, if the second temporary fluid channel is closed, usually (essentially) no fluid will flow through the second unidirectional fluid influencing member.

[0041] The at least one unidirectional fluid influencing member that is suggested will in turn provide a (minimum pressure) check valve functionality. That means that (usually) a minimum pressure is required in the lower pressurised conduit of the closed-loop hydraulic fluid circuit to open the unidirectional fluid influencing member. Such a minimum pressure check valve functionality may be provided for only one of the fluid ports (first fluid port or second fluid port), i.e. one of the fluid conduits of the closed-loop hydraulic fluid circuit. Preferably, however, a (possibly minimum pressure) unidirectional fluid influencing member / (minimum pressure) check valve functionality is preferably provided for both the first fluid port and the second fluid port, i.e. for both conduits of the closed-loop hydraulic fluid circuit, the loop flushing valve arrangement is intended to be used for. This minimum pressure check valve functionality is generally used to prevent an under-pressurisation and / or an under-filling of the closed-loop hydraulic fluid circuit. Such an under-fling could lead to a significant mechanical failure of hydraulic components, in particular of hydraulic pumps and / or hydraulic motors in light of their plurality of fast-moving parts.

[0042] Further, it is to be noted that the presently proposed loop flushing valve arrangement usually does serve both functionalities of a loop flushing spool and of a (one or more) minimum pressure check valve, and nevertheless a single, more or less unitary / monolithic loop flushing valve arrangement design may be provided that is comparatively easy to manufacture and / or that uses DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0043] - 10 - less mounting space. Further, less fluid connections between various parts are needed, too, which is an advantage as well.

[0044] Only for completeness it is to be pointed out that a closed-loop hydraulic fluid circuit might be pressurised, even to a comparatively high level of several tens of bars, and nevertheless no pressure difference between both sides of the closed-loop hydraulic fluid circuit may be present. Similarly, a pressure difference between the two sides of the closed-loop hydraulic fluid circuit may be present, and nevertheless the pressure in the lower pressurised conduit of the closed-loop hydraulic fluid circuit might be comparatively small, in particular quite close to ambient pressure. In both conditions, the loop flushing valve arrangement typically does not allow a fluid passage towards the third fluid port. This is actually a desired characteristicsin the present technological field.

[0045] Usually, it is preferred if at least two unidirectional fluid influencing members are provided, in particular at least one unidirectional fluid influencing member that is (so to say) assigned per respective fluid port (typically first fluid port and second fluid port) and / or per respective temporary fluid channel.

[0046] However, in certain cases it might be preferred to provide only a single unidirectional fluid influencing memberforthe loop flushing valve arrangement. This way, the design of the loop flushing valve arrangement may be simpler and hence may be cheaper to produce. Admittedly, usually such a design of a loop flushing valve arrangement will usually be inferior to a design with at least two unidirectional fluid influencing members when it comes to operational, particular fluid flow considerations. As an example, such a “simple” loop flushing valve arrangement may cause a certain energy loss and / or may not allow a continuous operation in the respective operational state, when the loop flushing valve arrangement is used in the hydraulic circuit it is intended for. However, at least for certain use cases this might not be problematic. As an DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0047] - 11 - example: if a car is operated in a reverse direction only rarely and only for short distances, a missing oil cooling effect due to a non-presence of a hydraulic fluid flush for cooling purposes is usually not problematic. The respective built up of heat by 1 °C or 2°C (or the like) is typically not problematic; further, the temperature will drop back to normal when the car is operated in the forward direction again.

[0048] Preferably, the loop flushing valve arrangement may be designed and arranged in a way that the first temporary fluid channel and / or the second temporary fluid channel comprises a unidirectional fluid influencing member that opens in the direction towards the third fluid port. Additionally or alternatively, the loop flushing valve arrangement may be designed and arranged in a way that at least one unidirectional fluid influencing member is designed as a check valve (possibly as a minimum pressure / minimum pressure difference check valve). Using these design features, the loop flushing valve arrangement fulfils the usually desired switching characteristics for loop flushing valve arrangements for closed-loop hydraulic fluid circuit arrangements.

[0049] Yet further, it is suggested to design and arrange the loop flushing valve arrangement in a way that at least one unidirectional fluid influencing member is designed and arranged to open at a certain pressure level. Preferably, at least two unidirectional fluid influencing members are designed and arranged in a way to open at a certain pressure level. This way a minimum pressure in the lower pressurised conduit of the closed-loop hydraulic fluid circuit is required, before the loop flushing functionality is initiated. This may increase the effectiveness of the closed-loop hydraulic fluid circuit and / or may prevent damage, in particular of moving parts within the closed-loop hydraulic fluid circuit (in particular hydraulic motors / hydraulic pumps). DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0050] - 12 -

[0051] Further, it is suggested to design and arrange the loop flushing valve arrangement in a way that at least parts of the loop flushing valve arrangement comprise an axially elongated design and / or is at least partially rotationally symmetric. This may be particularly valid for the inner recess, the spool, and possibly one or more (all) unidirectional fluid influencing members. In particular with respect to a rotational symmetry, this may particularly relate to the first pressure surface and the second pressure surface, and possibly to a conduit that is provided within the spool (if present). With respect to a partially rotational symmetry, this may also relate to a n-count symmetry. This way, triangular shapes, rectangular shapes, pentagonal shapes, hexagonal shapes, heptagonal shapes, octagonal shapes, general polygonal shapes, and so on may be employed. With respect to a partial rotational symmetry, this may relate to certain sections of the respective part, in particular to certain sections along the axial extent of the respective part. Further, it is to be noted that some sidewardly directed bores or the like are usually not to be considered as breaking the general rotational symmetry of the respective part.

[0052] Further, it is suggested to design and arrange the loop flushing valve arrangement in a way that the first pressure surface is fluidly connected to the first fluid port, at least in the neutral position of the spool and preferably in the first actuated position of the spool. Additionally or alternatively, the second pressure surface may be fluidly connected to the second fluid port, at least in the neutral position of the spool and preferably in the second actuated position of the spool. This way, a good loop flushing spool-like switching behaviour can be realised for the loop flushing valve.

[0053] It is possible, although not necessarily required, that the fluid flow crosssection between the first fluid port and the first pressure surface and / or the second fluid port and the second pressure surface is different between the neutral position and the first actuated position and / or between the neutral position and second actuated position, respectively. In particular, the DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0054] - 13 - respective fluid flow cross-section may increase when the spool is repositioned from the neutral position into the first actuated position and / or the second actuated position, respectively. This may be particularly advantageous for a faster return of the spool into its neutral position (possibly into its opposite position), if the pressures at the first fluid port and the second fluid port are equilibrated or even reversed. Such a fast switching behaviour is usually desired in the present technical field.

[0055] Further, it is suggested to design and arrange the loop flushing valve arrangement in a way that the first pressure surface is fluidly disconnected from the first fluid port in the second actuated position of the spool. Additionally or alternatively, it is possible that the second pressure surface is fluidly disconnected from the second fluid port in the first actuated position of the spool. This way usually noise due to a mechanical impact of the spool at a limiting surface of the recess in the housing of the loop flushing valve arrangement can be avoided. In particular, any remaining fluid in the vicinity of the first pressure surface or second pressure surface may act as a fluid damper.

[0056] However, it is also possible to design and arrange the loop fluid valve arrangement in a way that the first pressure surface remains fluidly connected to the first fluid port in the second actuated position of the spool and / or that the second pressure surface remains fluidly connected to the second fluid port in the first actuated position of the spool. This design might support a faster switching behaviour of the loop flushing valve arrangement in case the pressures at the first fluid port and the second fluid port change, in particular exchange.

[0057] Even further, it is suggested to design and arrange the loop flushing valve arrangement in a way that the biasing means and / or at least one unidirectional fluid influencing member comprise a mechanical biasing means, in particular DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0058] - 14 - a mechanical spring, more particularly a helical spring. This way a mechanical biasing can be realised in a comparatively cheap and yet durable and effective way.

[0059] Even further, the loop flushing valve arrangement may be designed and arranged in a way that the first temporary fluid channel and / or the second temporary fluid channel and / or at least one unidirectional fluid influencing means are, at least in part, provided inside of the spool. This way, a very compact and effective design can be realised. In particular, a fluid flow between the center channel and the first fluid port, the second fluid port and / or the third fluid port may be realised by a circumferentially and / or sidewardly arranged bore in the sheath of the spool (then at least usually a partially sheath-like spool).

[0060] Yet further, a loop flushing arrangement is suggested that comprises a loop flushing valve arrangement according to the present disclosure, and that further comprises an additional fluid flux variation means and / or an additional fluid switching means. In particular an additional actuated fluid flux variation means and / or an additional actuated fluid switching means may be provided. This way, it is possible to vary the permitted loop flushing fluid flux, at least within certain limits. This may be done to increase the effectivity of the closed- loop hydraulic fluid circuit, the loop flushing arrangement is used for. Furthermore, it may increase operational safety as well. The flushing fluid flux might be regulated depending on the temperature of the hydraulic fluid inside of the closed loop hydraulic circuit.

[0061] Yet further it is suggested to design and arrange a closed-loop hydraulic circuit in a way that it comprises a hydraulic fluid source, in particular hydraulic a fluid pump, a hydraulic consumer, in particular a fluid motor, and a loop flushing fluid conduit, and that further comprises at least one loop flushing valve arrangement according to the present disclosure and / or at least one loop DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0062] - 15 - flushing arrangement according to the present disclosure. This way, a very effective closed loop hydraulic fluid circuit can be realised with a simpler and more cost efficient design.

[0063] Both the presently proposed loop flushing arrangement and / or the closed-loop hydraulic fluid circuit may be modified in the presently disclosed sense. Such modifications may result in the already described characteristics and advantages, at least in analogy.

[0064] Further advantages, features, and objects of the invention will be apparent from the following detailed description of the invention in connection with the associated drawings, wherein the drawings show:

[0065] Fig. 1 : a schematic circuitry of a closed-loop hydraulic fluid circuit with a loop flushing functionality;

[0066] Fig. 2: an equivalent hydraulic schematic graphic symbol of a first possible embodiment of a loop flushing valve arrangement according to the present disclosure;

[0067] Fig. 3: a schematic cross-section of the first possible embodiment of a loop flushing valve arrangement according to the present disclosure in its neutral position;

[0068] Fig. 4: the first possible embodiment of a loop flushing valve arrangement according to Fig. 3 in a first actuated position;

[0069] Fig. 5: an equivalent hydraulic schematic graphic symbol of a second possible embodiment of a loop flushing valve arrangement according to the present disclosure;

[0070] Fig. 6: a schematic cross-section of the second possible embodiment of a loop flushing valve arrangement according to the present disclosure in its neutral position. DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0071] - 16 -

[0072] Fig. 1 shows a schematic circuitry of a closed-loop hydraulic fluid circuit 1 with a loop flushing functionality according to a basic design that is known as such in the prior art. The closed-loop hydraulic fluid circuit 1 comprises a hydraulic pump 2 and a hydraulic motor 3. The hydraulic pump 2 is moved by a primary mover (not shown), for example by a combustion engine. The hydraulic motor 3 drives a part to be moved (also not shown). Hydraulic pump 2 and hydraulic motor 3 are connected to each other by two main hydraulic fluid lines 4, 5, namely first main hydraulic fluid line 4 and second main hydraulic fluid line 5. This constitutes the main hydraulic circuit 8.

[0073] In the typical mode of operation, where the hydraulic pump 2 is pumping hydraulic oil, first main hydraulic fluid line 4 shows a higher pressure as compared to the second main hydraulic fluid line 5. If, however, hydraulic pump 2 is stopped and the mechanical load connected to hydraulic motor 3 is driving the hydraulic motor 3 (so that it acts as a hydraulic pump, while “usual” hydraulic pump 2 acts as a hydraulic motor), the pressure situation is inverted.

[0074] Further, an auxiliary hydraulic pump 6 is provided that pumps hydraulic oil from a fluid reservoir 7 into the main hydraulic circuit 8, comprising hydraulic pump 2, first main hydraulic fluid line 4, hydraulic motor 3 and second main hydraulic fluid line 5. The auxiliary fluid line 9 that is supplied by the auxiliary hydraulic pump 6 feeds a pair of antiparallelly arranged check valves 10, so that the current lower pressure line 4, 5 of main hydraulic circuit 8 is fed with hydraulic oil.

[0075] Since there is a constant influx of oil into the main hydraulic circuit 8 (which is necessary, for example to account for fluid losses, in particular in the moving parts 2, 3 of the main hydraulic circuit 8), a loop flushing valve arrangement 10 is required. DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0076] - 17 -

[0077] According to the usual state of the art (as shown in Fig. 1 ), this loop flushing valve arrangement 10 is realised by an arrangement of separate valves, namely a loop flushing valve 11 and a minimum pressure check valve 12 (where sometimes two or even more minimum pressure check valves 12 are used).

[0078] The loop flushing valve 11 is designed and arranged in a way that it connects the main hydraulic circuit 8 either via a first feed line 13 or a second feed line 14 to a fluid flush line 15. In particular, the loop flushing valve 11 is designed and arranged in a way that it is pressure actuated by the two pressures in the first main hydraulic fluid line 4 and the second main hydraulic fluid line 5 so that the current low (lower) pressure main hydraulic fluid line 4, 5 will be connected to the fluid flush line 15.

[0079] To avoid the situation that the current low (lower) pressure line 4, 5 of main hydraulic circuit 8 drops below a certain minimum pressure, an additional minimum pressure check valve 12 is arranged in line with the loop flushing valve 11 (serial arrangement). Minimum pressure check valve 12 cracks open only when a certain minimum design pressure is present at incoming fluid flush line 15 (i.e. directly coming from the loop flushing valve 11 ). The control of minimum pressure check valve 12 is made by the fluid pressure itself.

[0080] Further, in the presently shown embodiment, in a section 16 of the fluid flush line 15 past the minimum pressure check valve 12, an additional, presently electrically actuated fluid control valve 17 is arranged. By means of the fluid control valve 17, the flushing fluid flow may be interrupted and, depending on the design of the fluid control valve 17, a flushing fluid flux through fluid flushing line 15 may be controlled in size.

[0081] According to the present disclosure, instead of using two (or even more) separate valves 11 , 12, the loop flushing valve arrangement 10 is designed as DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0082] - 18 - a single, so-to-say monolithic loop flushing valve arrangement 10, but it nevertheless provides both functionalities. This is indicated by the dashed box in Fig. 1. It is to be noted that fluid control valve 17 is presently still designed as a separate valve.

[0083] A more appropriate and descriptive equivalent fluid flow schematic graphic symbol 38 of a loop flushing valve arrangement 10 according to a first embodiment of a loop flushing valve arrangement 10 according to the present disclosure is shown in Fig. 2. This graphic symbol may so to say replace the dashed box that is shown in Fig. 1 .

[0084] A possible mechanical design setup of the first embodiment of a combined loop flushing valve arrangement 10 as symbolized by Fig. 2 is shown in Figs.

[0085] 3 and 4 in a schematic cross-section. However, the position of the spool 18 of the loop flushing valve arrangement 10 is different between Figs. 3 and 4; namely Fig. 3 shows the spool 18 in a neutral position, while Fig. 4 shows the spool 18 in a first actuated position.

[0086] Now reverting to Fig. 3, in which the loop flushing valve arrangement 10 is in its neutral position, the spool 18 is in a neutral, center position, in which a fluid flow between first fluid port 19 (which is presently fluidly connected to first main fluid hydraulic fluid line 4) and third fluid port 21 (presently fluidly connected to fluid flushing line 15 / 16) is inhibited. At the same time fluid flow between second fluid port 20 (fluidly connected to second main hydraulic fluid line 5) and third fluid port 21 is also inhibited.

[0087] The spool 18 is held in its neutral position, as shown in Fig. 3, by means of two counteracting helical springs 29. Only for completeness it is noted that the presently depicted neutral position of spool 18 occurs if no pressure is present at the three fluid ports 19, 20, 21 (or rather no significant pressure differences are present between the three fluid ports 19, 20, 21 ). DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0088] - 19 -

[0089] The spool 18 shows a first pressure surface 22 and a second pressure surface 23 on opposite sides of the spool 18.

[0090] First pressure surface 22 is fluidly connected to first fluid port 19 by means of a first fluid through port 24, while second pressure surface 23 is fluidly connected to second fluid port via a second fluid through port 25.

[0091] Further, one can see that spool 18 comprises two radial steps 27 that form respective valve seats 27 for antiparallelly arranged valve poppets 28. In a neutral position the valve poppets 28 are pressed onto their valve seats 27 by means of additional biased helical springs 30.

[0092] Now let's consider the situation that the closed-loop hydraulic circuit 1 is switched on into a standard operational mode and the fluid pressure in first main hydraulic fluid line 4 becomes (significantly) higher as compared to the pressure in second main hydraulic fluid line 5 and fluid flushing line 15 / 16 (where the pressures in the three different fluid ports 19, 20, 21 that are connected to the respective fluid lines 4, 5, 15 are accordingly high).

[0093] Due to the high pressure in first fluid port 19 of loop flushing valve arrangement 10, the spool 18 is pushed towards the left into first actuated position (according to Fig. 4) due to the high pressure acting on the first pressure surface 22 (initially conveyed through first fluid through port 24, later by an additional fluid connection through ring-like orifice 31 ).

[0094] Fig. 4 shows the leftmost position. A further movement to the left is hindered by a mechanical contact between the left surface face of spool 18 and an inner surface face of one of the plugs 32, presently left plug 32. DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0095] - 20 -

[0096] As can be seen, in this leftmost position according to Fig. 4, a second tangential bore arrangement 34 will allow fluid flow between second fluid port 20 and inner bore 26 of spool 18, in particular towards valve poppet 28 of second unidirectional fluid influencing member 36 (essentially a minimum pressure check valve).

[0097] Since the bias of helical spring 30 is chosen comparatively high, the respective valve poppet 28 of second unidirectional fluid influencing means 36 will initially remain on its corresponding valve seat 27. Only once a certain minimum pressure has been reached (cracking pressure), the respective poppet 28 will open and second unidirectional fluid influencing member 36 will allow a fluid flow through the remainder of inner bore 26 toward third tangential bore arrangement 37 and into third fluid port 21. To be more precise: second unidirectional fluid influencing means 36 will open if a sufficient pressure difference is present between second fluid port 20 and third fluid port 21 .

[0098] It is obvious to a person skilled in the art that the loop flushing valve arrangement 10 will return to its neutral position according to Fig. 3 if the pressure differences cease to exist.

[0099] Further, the spool 18 of loop flushing valve arrangement 10 will move to its rightmost position (not shown) by pressure acting on the second pressure surface 23 via second fluid through bore 25 if the second main hydraulic fluid line 5 becomes the higher pressurised line of main hydraulic circuit 8, and consequently second fluid port 20 shows a higher pressure as compared to first fluid port 19 and third fluid port 21 .

[0100] If the pressure in first fluid port 19 (lower pressurised port) is sufficiently high, fluid flow will then be established through first tangential bore arrangement 33, inner bore 26, passing open first unidirectional fluid influencing means 35, third tangential bore arrangement 37 into third fluid port 21 . DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025

[0101] - 21 -

[0102] Fig. 5 shows a descriptive equivalent fluid flow schematic graphic symbol 39 of a loop flushing valve arrangement 40 according to a second embodiment of a loop flushing valve arrangement 40 according to the present disclosure. Again, this graphic symbol may so to say replace the dashed box that is shown in Fig. 1 .

[0103] As a person skilled in the art can already conclude from Fig. 6, the mechanical design setup of the second embodiment of a combined loop flushing valve arrangement 40 is somewhat equivalent to the first embodiment of a combined loop flushing valve arrangement 10 as shown in Figs. 3 and 4. In particular, it can be seen from Fig. 6 (only the middle, neutral position of the loop flushing valve arrangement 40 is shown for brevity) that presently replaces one of the unidirectional fluid influencing means 35, 36 (presently the second fluid flow influencing means 36) is replaced by a fixed fluid throughput orifice 41 of a certain fluid flow cross-section. It is to be noted that instead of a fixed fluid throughput orifice 41 a fluid blockage might be envisaged as well (an in particular irrespective of other detailed design considerations).

[0104] It is noted that identical reference numerals are used throughout the present disclosure for parts that are sufficiently similar in design and / or in function to justify the use of identical reference numerals, although the respective parts may not be identical. This is done for brevity and to improve the understandability of the description.

[0105] It is also to be noted that a single one or a plurality of the features of one, several or all of the presently disclosed detailed embodiments may be used in combination with the generic description of the present disclosure.

Claims

DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025- 22 -C l a i m s1 . Loop flushing valve arrangement (10, 40) comprising a housing with an inner recess, a first fluid port (19) connecting to the inner recess, a second fluid port (20) connecting to the inner recess, a third fluid port (21 ) connecting to the inner recess, and a spool (18) that is slidably movable within the inner recess, further comprising a biasing means (29) that biases the spool (18) in a neutral position in which the first fluid port (19), the second fluid port (20) and the third fluid port (21 ) are fluidly separated from each other, the spool (18) comprising a first pressure surface (22) that moves, when being applied with a pressure, the spool (18) into a first actuated position, in which a first temporary fluid channel is established between the second fluid port (20) and the third fluid port (21 ), and a second pressure surface (23) that moves, when being applied with a pressure, the spool (18) into a second actuated position, in which a second temporary fluid channel is established between the first fluid port (19) and the third fluid port (21 ), characterised in that the first temporary fluid channel and / or the second temporary fluid channel comprise a unidirectional fluid influencing member (35, 36).

2. Loop flushing valve arrangement (10, 40) according to claim 1 , characterised in that the first temporary fluid channel and / or the second temporary fluid channel comprise a unidirectional fluid influencing member (35, 36) that opens in the direction toward the third fluid port (21 ) and / or characterised in that at least one unidirectional fluid influencing member (35, 36) is designed as a check valve.

3. Loop flushing valve arrangement (10, 40) according to claim 1 or 2, in particular according to claim 2, characterised in that at least oneDAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025- 23 - unidirectional fluid influencing member (35, 36) is designed and arranged to open at a certain pressure level.

4. Loop flushing valve arrangement (10, 40) according to any of the preceding claims, characterised in that at least parts of the loop flushing valve arrangement (10, 40) comprise an axially elongated design and / or are at least partially rotationally symmetric.

5. Loop flushing valve arrangement (10, 40) according to any of the preceding claims, characterised in that the first pressure surface (22) is fluidly connected to the first fluid port (19), at least in the neutral position of the spool (18) and preferably in the first actuated position of the spool (18) and / or characterised in that the second pressure surface (23) is fluidly connected to the second fluid port (20), at least in the neutral position of the spool (18) and preferably in the second actuated position of the spool (18).

6. Loop flushing valve arrangement (10, 40) according to any of the preceding claims, in particular according to claim 5, characterised in that the first pressure surface (22) is fluidly disconnected from the first fluid port (19) in the second actuated position of the spool (18) and / or characterised in that the second pressure surface (23) is fluidly disconnected from the second fluid port (20) in the first actuated position of the spool (18).

7. Loop flushing valve arrangement (10, 40) according to any of claims 1 to 5, in particular according to claim 5, characterised in that the first pressure surface (22) remains fluidly connected to the first fluid port (19) in the second actuated position of the spool (18) and / or characterised in that the second pressure surface (23) remains fluidly connected to the second fluid port (20) in the first actuated position of the spool (18).DAN2412DEWO - PA18803W001 loop flushing system with flushing valve 19 December 2025- 24 -8. Loop flushing valve arrangement (10, 40) according to any of the preceding claims, characterised in that the biasing means (29) and / or at least one unidirectional fluid influencing member (35, 36) comprise a mechanical biasing means (29, 30), in particular a mechanical spring (29, 30), more particularly a helical spring (29, 30).

9. Loop flushing valve arrangement (10, 40) according to any of the preceding claims, characterised in that the first temporary fluid channel and / or the second temporary fluid channel and / or at least one unidirectional fluid influencing means are, at least in part, provided inside of the spool.

10. Loop flushing arrangement, comprising a loop flushing valve arrangement (10, 40) according to any of the preceding claims characterised by an additional fluid flux variation means (17) and / or an additional fluid switching means (17), in particular an additional actuated fluid flux variation means (17) and / or an additional actuated fluid switching means (17).11 . Closed loop hydraulic circuit (1 ), comprising a hydraulic fluid source (2, 6), in particular a hydraulic fluid pump (2, 6), a hydraulic consumer (3), in particular a fluid motor (3), and a loop flushing fluid conduit, characterised by at least one loop flushing valve arrangement (10, 40) according to any of claims 1 to 9 and / or by at least one loop flushing arrangement according to claim 10.

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