EP4728213A1 - Improved spool for a spool valve - Google Patents

Abstract

The invention relates to a slidable spool (1) for a spool valve (21). The spool (1) comprises at least one annular land (3, 4, 5, 6, 7, 8) around the spool core (9), where the at least one annular land (4, 5, 6, 7) comprises at least 10 one notch (11) in at least one of the side surfaces (12) of the at least one annular land (4, 5, 6, 7). The at least one notch (11) shows an essentially triangular shape. The triangular shape of the at least one notch (11) may show an opening angle (α, β) of at least 90° adjacent to the spool core (9). Additionally or 15 alternatively, a plurality of notches (11) may be arranged along the circumference of the at least one side surface (12) of the at least one annular land (4, 5, 6, 7), wherein along the majority of the circumferential extent of the at least one side surface (12) of the at least one annular land (4, 5, 6, 7) a notch (11) is present.

Description

Improved spool for a spool valve

The invention relates to a slidable spool for a spool valve, the spool comprising at least one annular land around the spool core, wherein the at least one annular land comprises at least one notch in at least one of the side surfaces of the at least one annular land. The invention also relates to a spool valve comprising such a slidable spool.

When it comes to fluid apparatuses, fluid connections have to be established and blocked in a controlled way for a vast variety of reasons. In particular, fluid connections have to be established and blocked depending on an input control signal. Also, fluids have to be directed to different fluid ports in a controlled way.

To realise such a controlled distribution of fluids, a variety of valve designs are around. A particular design is that of so-called spool valves. Spool valves comprise a housing with a bore therein. Inside the bore, a spool is slidably arranged, so that it can be slidably moved inside the bore of the housing. The movement of the spool can be effectuated using a variety of actuators, for example using fluid pressures, electromagnetic forces, mechanical springs or the like. Furthermore, the slidable spool additionally shows one or several annular lands around the central part of the spool, the so-called spool core. Further, the housing additionally shows some recesses around the bore that connect to fluid input and output ports of the spool valve. Typically, the recesses are designed as ringlike grooves that somehow resemble a collarlike design. Using an appropriate design of the spool valve and the housing, varying inlet and outlet fluid ports can be connected to each other and separated from each other, by an appropriate movement and positioning of the spool within the bore of the housing. Such spool valves are well known in the state of the art and are frequently employed for a plethora of applications. Furthermore, depending on the application in question, a vast variety of modifications has already been proposed. While such spool valves are certainly functional in a satisfactory way they do nevertheless sometimes suffer from deficiencies, depending on the application in question.

One such deficiency is for example the force that is needed to move the spool within the housing, in particular if higher fluid pressures are present, and in particular if such higher fluid pressures are only present at some of the fluid ports, while other fluid ports are at significantly lower pressures.

Another possible problem is the operating behaviour, in particular with respect to the fluid flow throughput in dependence of the position of the spool valve. Here, sometimes a certain opening and closing behaviour, in particular a somewhat ’’smooth”, gradual switching behaviour is desired.

It is not surprising that due to the widespread employment of spool valves, a large variety of proposals for designs of spool valves has been proposed to address the aforementioned issues (and other issues as well).

As an example, in United States patent US 4,862,920 a spool for a spool valve is suggested, where the spool comprises a plurality of annular lands having a plurality of notches therein which are in part conical. The notches show an arclike shape (segment of a circle). This way, a more gradual increase of the flow rate through the spool in dependence of the spool displacement can be realised.

Another proposal has been made in European patent EP 0581 156 B, in which a hydraulic directional control valve of a piston spool valve construction is proposed. The spool comprises a spool with annular lands around the spool. Depending on the design, two or four small control notches are arranged in the side surfaces of the annular lands. The circumferential extent of the opening of the notches is small compared to the overall circumference of the respective side surface of the annular land. Therefore, a significant portion of the side surface of the respective annular land does not show a control notch. Using this design, an improved behaviour of the fluid flow throughput in dependence of the displacement of the spool can be realised.

Although spool valves, as they are known in the art, do work in a satisfactory way, such spool valves still show deficiencies, at least for certain areas of application and/or with respect to certain operational characteristics.

It is therefore the object of the present invention to suggest a slidable spool for a spool valve that is improved over slidable spools for spool valves that are known in the prior art.

It is another object of the invention to propose a spool valve with a slidable spool and a housing with a bore for said spool that is improved over spool valves with a slidable spool and a housing with a bore for said spool as they are known in the prior art.

A slidable spool for a spool valve and a spool valve as presently proposed do solve these objects.

It is suggested to design a slidable spool for a spool valve, wherein the spool comprises at least one annular land around the spool, and wherein the at least one annular land comprises at least one notch in at least one of the side surfaces of the at least one annular land, where the at least one notch shows an essentially triangular shape in a way that the triangular shape of the at least one notch shows an opening angle of at least 90° adjacent to the spool core. Usually, the slidable spool shows a somewhat elongated design and/or a design with an axis that is usually significantly longer as compared to the other directions. This “main” direction may be addressed as the axial direction of the slidable spool. The cross-sectional shape (i.e. a cross section along a plane that is essentially normal to the axial direction of the slidable spool) may show a variety of shapes, in particular a polygonal shape (with n=3, 4, 5, 6, 7, 8, 9 or 10, with n being the number of edges; possibly comprising sharp and/or rounded comers), a circular or an ellipsoidal shape. It is to be noted that this cross-sectional shape may change along the extent of the slidable spool, in particular along an axial direction of the slidable spool. More particularly, a change may occur between different sections of the slidable spool, in particular between different sections of the annular lands and/or of the spool core of the slidable spool. The spool core may show a somewhat similar dimension of its cross section along the axial direction of the slidable spool, possibly even an (essentially) identical dimension. However, it is also possible to change the dimension of the spool core to a certain extent, in particular between different sections of the spool core. As an example, such differences may be provided due to pressure compensation considerations, which is known in the prior art as such. What has been said about the spool core and/or about different sections of the spool may equally apply to the at least one annular land of the slidable spool, at least in analogy. When talking about different ’’sections" (section of the spool core and/or section of the annular land in particular) different parts that are separated from each other by at least one intermediary means, in particular along the axial direction, may be understood. To give an example: two different sections of the spool core may be defined by an intermediary annular land (or vice versa). Usually, the cross sectional size (in case of a circular cross-section in particular the diameter) of at least one annular land is larger as compared to the cross-sectional size of at least one section of the spool core, preferably of at least one neighbouring section of the spool core, even more preferred of (essentially) all sections of the spool core. According to a typical design of the slidable spool (essentially) all annular lands show a cross-sectional size that is larger than (essentially) all sections of the spool core. A side surface of at least one annular land may be defined as a part of the slidable spool that connects at least one annular land to its adjacent (at least one) section of the spool core. Additionally or alternatively, a side surface may be defined as any part of the slidable spool whose surface is not (essentially) parallel to the axial direction of the slidable spool. However, typically a larger angle between the respective surface and the axial direction of the slidable spool is present, for example an angle larger than (possibly including) 10°, 20°, 30°, 40°, 45°, 50°, 60°, 70° or 80°. More preferably, the respective surfaces are arranged essentially perpendicular (essentially 90°) to the axial direction of the slidable spool. The definition of the angle is based on an appropriate tangential direction of the respective surface part and the axial direction of the slidable spool. When a normal of the respective surface part is considered, the respective relation would be y = 90° - a or 6 = 90° - (3, so that a perpendicular surface part would be a surface part whose normal is parallel to the axial direction of the slidable spool. It is to be noted that the angle between the respective surface part and the axial direction may vary over the extent of the respective side surface of the at least one annular land, in particular in dependence of the radial distance from the centre (centreline) of the slidable spool. Therefore, tapered and - so-to-say - rounded outer corners may be provided. Only for completeness, it should be mentioned that additionally or alternatively, a variation along the circumferential direction of the at least one side surface of the at least one annular land may be used as well. Therefore, sort of a tapering with a varying tapering angle around the circumference of the at least one annular land may be provided for at least one of its side surfaces. It is to be noted that usually one annular land shows two side surfaces.

A notch in at least one of the side surfaces of the at least one annular land may be considered to be a recess/void/cut-out of material within the respective side surface of the at least one annular land. Its shape - presently an essentially triangular shape - may be considered within a cross-sectional plane, wherein the respective plane is arranged in a way that one of its tangential directions lies essentially parallel to the axial direction of the slidable spool and/or whose normal lies essentially parallel to a radial direction of the slidable spool and/or whose normal lies essentially perpendicular to the axial direction of the slidable spool. Therefore, additionally or alternatively, the notch may show a cross-sectional shape that is so-to-say visible to an outside observer when he looks at the slidable spool, in particular when he looks at the slidable spool with a viewing direction that is essentially perpendicular to the axial direction of the slidable spool (where the observer has to turn the spool along its axial direction into an appropriate viewing position). It is suggested to design and arrange at least one notch with an essentially triangular shape. When talking about a ’’triangular shape", in particular the ’’missing material" (cut-out material) of the at least one annular land is considered. When talking about a ’’triangular shape" rounded comers are possible, of course. For example, such ’’rounded corners" may be a result of the production techniques involved. If, for example, a milling cutter is used to machine the spool valve/the side surface of the at least one annular land/at least one notch, it is essentially inevitable that the tip of the triangle pointing in the direction of the annular land and/or away from its base line has a certain rounded tip with a radius that is usually comparable to the diameter of the milling head. Therefore, rounded corners with a radius of the rounded tip of a less than 5 mm, 4 mm, 3 mm, 2 mm, 1 mm, 0.75 mm, 0.5 mm or 0.25 mm shall be considered to be a so-to-say ’’sharp tip" in the sense of this disclosure. An additional or alternative definition of a triangular shape with rounded tips may be that the length of the straight sections of the triangular shape (in particular of those parts defining the cut-out, usually yielding two straight lines) is larger than the length of the rounded section (top tip of the triangular shape, ’’pointing" in the direction of the annular land). “Longer” may mean that the length of the straight sections is at least 1 , 1 .5, 2, 2.5, 3, 4, 5, 7.5 or 10 times larger than the length of the rounded section. First experiments do surprisingly indicate that in particular straight sections of the essentially triangular shaped notches have an influence on reducing fluid-induced forces on the slidable pool. Therefore, there is a surprising advantageous effect over notches with shapes that do not show straight sections (or show only very short straight sections), like it is the case for parabolic shapes, circle segment shapes or the like. It is to be noted that more or less rounded corners (even if they may be considered to be a “sharp tip” in the sense of the present disclosure) typically occur in a direction, pointing towards an annular land. In fact, such more or less rounded comers may be essentially unavoidably present due to machining reasons, as stated above. Nevertheless, such more or less rounded comers may be present in a direction, pointing towards a spool core section as well or alternatively. Furthermore, it is possible - and maybe even advantageous - to realise “real sharp” tips, in particular in a direction, pointing towards a spool core section of the slidable spool. The triangular shape may be arranged (essentially) symmetrically with respect to an axial direction of the slidable spool (which is typically the preferred design); however, it is also possible to arrange the triangular shape in a non-symmetrical way with respect to the axial direction of the slidable spool. As proposed, the opening angle of the at least one notch shows an angle of at least 90° adjacent to the spool core. For completeness it should be mentioned that this does not necessarily rule out the possibility that due to manufacturing issues there might be some kind of a rounded shape in the change-over section from the notche’s sidewall to the spool core in the ultimate vicinity of the spool core. In this ultimate vicinity section, the notch angle may or may not be larger than the presently proposed 90° (or some other angle, as proposed later on). Therefore, a sort of flat triangle with an obtuse angle at the top is employed. Using the presently proposed design, it is surprisingly possible to reduce operating forces that occur in the axial direction of the slidable spool due to fluid pressures (both static and/or dynamic) that are applied on the various inlet and outlet ports of the spool valve (fluid-induced forces), when the slidable spool is used within the intended machinery. Therefore, the respective actuators can be dimensioned smaller and/or with lower operating forces. This, in turn, may result in fast operating speeds, in energy savings when operating the spool valve, in less noise, in smaller dimensioned actuating devices and the like. All of this is advantageous. Furthermore, possibly even the lifetime of the spool valve and/or of the actuating devices may be increased based on the presently proposed design.

Additionally or alternatively to the previous suggestion, it is proposed to design a slidable spool for a spool valve, the spool comprising at least one annular land around the spool core, the at least one annular land comprising at least one notch in at least one of the side surfaces of the at least one annular land, the at least one notch showing an essentially triangular shape, in a way that a plurality of notches is provided along the circumference of the at least one side surface of the at least one annular land, wherein along the majority of the circumferential extent of the at least one side surface of the at least one annular land a notch is present. While in principle it is possible that only one notch is provided on the at least one side surface of the at least one annular land (resulting in a triangle, where a single flank of the triangular notch extends for about half of the circumference of the annular land, at least in case an essentially equiangularly shaped triangle is used as a notch), it is preferred if a plurality of notches is used. In general (which applies to the whole disclosure of this document, as well) 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12 or even more notches may be used on at least one of the side surfaces of the at least one annular land. It is to be noted that the number of notches that is present on one side surface of at least one annular land may vary between the side surfaces and/or the directions of the side surfaces and/or the control surfaces that are formed by the annular land in the housing of the spool valve and/or may depend on the annular land(s) in question. Put in other words, only an accordingly small circumferential extent of the at least one side surface of the at least one annular land is formed by a so-to-say undisturbed/unmodified/unaltered/ungrooved/non-machined side surface (i.e. a surface part that is arranged essentially normal to the axial direction of the spool valve; where in this context an inclination due to a tapering/rounding of the respective part of the surface side may or may not be present). When using the present aspect of the disclosure (with or without combining it with the aforementioned aspect of the present disclosure, in particular with respect to the angle of the at least one notch) it is also possible to decrease any forces that may occur in the axial direction of the slidable spool in case different pressure levels are applied to the different fluid ports, and thus to reduce actuation forces and consequently actuation times or the like.

In this context it should be mentioned that along the majority of the circumferential extent of the at least one side surface of the at least one annular land triangular-shaped notches should be present. This, however, does not rule out the possibility that the respective at least one side surface might comprise additional notches with a shape that differs from a triangular shape. Nevertheless, it is preferred if (essentially) all notches do show a triangular shape.

According to a preferred embodiment of the present disclosure, the slidable spool is designed in a way that the triangular shape of the at least one notch shows an opening angle of at least 90° along the majority of the radial extent of the at least one notch, preferably at least along (essentially) the complete radial extent of the at least one notch. As previously mentioned, this may or may not include an ultimate vicinity section, i.e. a change-over section from the notche’s sidewall to the spool core in the ultimate vicinity of the spool core. In particular, if such an ultimate vicinity section is excluded, the opening angle may be at least 90° (or another lower limit angle) along the full radial extent of the at least one notch. Nevertheless, some constriction of the so-to-say waistline of the notch may be present. Further, the opening angle of at least one notch may broaden along the radial direction (the “height”) of the notch. The increase in angle may be between 5°, 10°, 15°, 20°, 25°, 30°, 35°, 40° and 45° (lower limit) and 10°, 15°, 20°, 25°, 30°, 35°, 40°, 45° and 50° (upper limit). When designing a slidable spool as presently proposed, a particularly advantageous fluid flow pattern around the slidable spool, and hence of the final spool valve can be achieved. This, in turn, may result in particularly low fluid-induced forces in the axial direction of the slidable spool. When talking about a majority of the radial extent of the at least one notch, in particular at least 50%, 60%, 70%, 80%, 90% or 95% of its full radial extent (“height” of the notch) may be envisaged. In this context, it should be noted that irrespective of whether the majority of the radial extent of at least one notch shows an opening angle of at least 90° or not, the opening angle may vary along the radial direction of the at least one notch (or put in other words: along the height of the respective notch), or not. Preferably, however, an at least slight widening of the opening angle is preferred, when going in the radially outward direction. In particular, a lower opening angle a (or radially inner opening angle a, core neighbouring opening angle a, or the like) and an upper opening angle [3 (or radially outer opening angle (3, outer surface opening angle (3, circumferential opening angle (3, housing neighbouring opening angle (3, or the like) might be limiting at least one of the at least one notches in a radial direction. First experiments indicated that this design results in an advantageous fluid flow pattern. Again, it should be noted that the opening angle (including its variation along the radial direction) may be the same for two, a plurality or (essentially) all notches, or may differ between at least some notches. As previously mentioned, the angle a may be measured including or excluding an ultimate vicinity section, i.e. a change-over section from the notche’s sidewall to the spool core in the ultimate vicinity of the spool core.

In particular, it is proposed to design the slidable spool in a way that the opening angle has a size of at least 100°, preferably at least 110°, more preferably at least 120°. It is to be noted that it is also possible to employ different angles as well, for example an angle of larger than (and possibly including) 95°, 100°, 105°, 110°, 115°, 120°, 125°, 130°, 135°, 140°, 145° or 150°. Further, it should be noted that the angle may be the same for at least two or more notches, in case a plurality of notches is used (even if angles are used, having a different value than the aforementioned ones). This statement may relate to notches that are arranged at the same side surface of at least one annular land and/or at different side surfaces of at least one annular land and/or at side surfaces of different annular lands (where the side surfaces with the notches show in the same direction and/or in different directions, as seen in the axial direction of the slidable spool; preferably those side surfaces might be facing each other, at least in part) and/or on both side surfaces of at least one annular land. However, it has been shown that it is usually preferred if the notches that are arranged at one side surface of one annular land show essentially the same shape, in particular the same opening angle. First experiments have shown that these angles result in a particularly good reduction of (fluid-induced) forces that may occur in the axial direction due to different pressure levels at the different fluid inlet/outlet ports of the slidable spool/spool valve.

If it is suggested to modify the slidable spool for a spool valve in a way that along at least a 60%, preferably at least 70%, more preferably at least 80%, even more preferably at least 90%, yet more preferably at least 95% of the circumferential extent of the at least one side surface of the at least one annular land a notch is present. According to the present suggestion, however, when talking about a majority of the circumferential extent of the at least one side surface, this may also mean that at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95% (lower limit) to 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% (upper limit) of the respective circumferential extent of the respective side surface is occupied by a notch (a single one or preferably a plurality of notches). First experimental embodiments of such a slidable spool/spool valve have shown to have particularly low fluid-induced axial forces.

Furthermore, it is suggested to design the slidable spool for a spool valve according to the present disclosure in a way that the spool comprises a plurality of annular lands along the spool core. This way, it is possible to enhance the fluid flow throughput through the resulting spool valve in a simple and efficient way. Furthermore, using this design, it is usually particularly simple to achieve a pressure compensation effect, i.e. the necessary actuation force becomes comparatively independent of the various fluid pressures that are applied to the various fluid flow ports. Furthermore, providing a plurality of annular lands along the spool core, certain control tasks can be achieved. Using a directional valve as an example, a fluid input port is selectively connected to a first or a second fluid output port (where an intermediary position, where the fluid input port is fluidly connected to both first and second fluid output port, may or may not be present). As previously mentioned, in case a plurality of annular lands along the (axial extent of the) spool core is provided, the cross-sectional size and/or the cross-sectional shape of the respective annular lands may be (essentially) the same or may be (essentially) different, at least for some of the annular lands.

Is it further suggested to design the slidable spool in a way that at least one of the annular lands shows notches on only one side surface thereof. First experiments have shown that this design is sufficient to significantly reduce any axial forces due to different pressure levels at the different fluid inlet and outlet ports. At the same time, machining efforts (and therefore cost) can be reduced, because only fewer notches have to be machined. Another advantage is that the slidable spool (and therefore the final spool valve) may be more compact, if this design is applied. For completeness, it should be mentioned that the side surface with the notches should usually point towards fluid chambers where in an assembled state of the spool valve particularly high fluid flow pressures are to be expected.

Yet further, it is proposed that the notches of at least two annular lands are arranged in different axial directions. This way, again a particularly versatile and yet compact slidable spool/spool valve can be achieved. In particular, using this approach, the notches of neighbouring annular lands can be directed facing each other. Therefore, the notches may be directed in the direction of the same fluid chamber (at least in the usual design of a spool valve), so that for the respective fluid chamber, a reduction of fluid-induced axial forces that are exerted on the slidable spool can be achieved, even for particularly high fluid pressures.

Furthermore, it is suggested that the slidable spool is designed in a way that at least one annular land comprises essentially no notches, wherein said at least one annular land essentially without any notches is arranged at an axially outer portion of the slidable spool. First experiments have shown that such side surfaces essentially without notches do not introduce noticeable disadvantages with respect to fluid-induced axial forces occurring on the slidable spool, at least at certain positions. Even if some forces occur, the usually negligible trade-off by this is frequently easily outweighed by the cost savings for manufacture and by the reduced size of the slidable spool, and hence of the resulting spool valve. While the annular land essentially without notches may be arranged at any position, placing them (at least) at an axially outer portion of the slidable spool is usually advantageous, since, for example, the respective lands can be used as actuating surfaces for providing a defined, actuated movement of the slidable spool in an axial direction. Hence for typical designs of fluid distribution valves, a high-pressure fluid input may be directed to one of two lower pressure fluid output ports in a controlled way.

According to another suggestion, at least one annular land is camfered and/or tapered and/or rounded in a radial direction. This way, a design can be realised that provides a fluid control behaviour that is frequently requested in the market. In particular, some smoother fluid flow transitions in dependence of the axial position/displacement of the slidable spool can be realised, which is usually a desired behaviour. It is further suggested to design a spool valve with a slidable spool and a housing with a bore for said slidable spool, wherein the slidable spool is a slidable spool according to the presently disclosed design. Then, the spool valve can show the same features and characteristics as the presently suggested slidable spool, at least in analogy. Furthermore, the corresponding spool valve can be modified in the sense, as described in connection with the slidable spool, at least in analogy, as well, resulting in at least similar characteristics and advantages.

Furthermore, it is suggested to design the spool valve in a way that it is designed and arranged as a fluid distribution valve. Such a valve is designed in a way that one fluid input port is selectively connected to a first or a second fluid output port, depending on the axial position/displacement of the valve spool. An intermediary position, where the fluid input port is simultaneously fluidly connected to both first and second fluid output port may or may not be realised. Similarly, it is also possible that for a certain range of axial positions of the valve spool, no fluid connection is established between the fluid input and the fluid output ports. The spool valve may be actively or passively controlled, depending on the application in question.

For completeness, it should be mentioned that a “fluid” in the present context may be a gas, a liquid, or a mixture thereof. Also, a “fluid” might relate to a supercritical fluid, where a distinction between the gasous and the liquid state may not be made any more. Even further, the fluid may contain solid particles to a certain extent, as well.

Further advantages, features, and objects of the invention will be apparent from the following detailed description of the invention in conjunction with the associated drawings, wherein the drawings show: Fig. 1 : a schematic top view of a possible embodiment of a slidable spool according to the present disclosure according to a possible embodiment;

Fig. 2: a schematic top view of a possible embodiment of a slidable spool according to the present disclosure, as seen in a different rotational position;

Fig. 3: a possible embodiment of a spool valve in a partial cross-section, comprising a possible embodiment of a slidable spool according to Fig. 1 ;

Fig. 4: a cross-sectional view through the slidable spool of the possible embodiment of the slidable spool in a plane, being normal to the axial direction.

Fig. 1 shows a top view of a slidable spool 1 that is particularly suited for being used in combination with an appropriate housing 20 to form a fluid distribution valve 21 (see Fig. 3).

The presently shown embodiment of the slidable spool 1 is designed to be essentially circular in cross-section, where the cross-section is aligned along planes that are normal to the centreline 2 of the slidable spool 1 , where the centreline 2 runs in an axial direction of the slidable spool 1. As can be seen in Fig. 1 , the presently shown embodiment of the slidable spool 1 shows altogether six annular lands 3, 4, 5, 6, 7, 8 that protrude from a central spool core 9, respectively. In particular, non-notched annular lands 3 and 8 are arranged at axially outer portions of the slidable spool 1 (i.e. neighbouring both axial ends of the slidable spool 1 ). They mainly function as a sealing means to the (axial) outside. This functionality (and possibly an additional valve type functionally), however, is dependent on the design and dimensioning of the housing 20, as will become clear later on, particularly with respect to Fig. 3. Notched annular lands 4, 5, 6, 7, however, are arranged so-to-say in the middle or an “inner” side/position of the slidable spool 1 , and function as an opening/closing control surface for enabling or disrupting a fluid flow through the respective control opening of the spool valve 21 , depending on the actual position/displacement of the slidable spool 1 in the housing 20 of the spool valve 21 .

As can be seen from Fig. 1 , all ’’inner" notched annular lands 4, 5, 6, 7 do show an essentially perpendicular sidewall 10 on one of their respective sidewalls 10, 12. The perpendicular sidewalls 10 essentially do not show any notches 11 and further essentially do not show any tapering 16, apart from a small, rounded transition between the perpendicular sidewall 10 and the respective part of the spool core 9, which is mainly due to the manufacturing process. Is to be noted, however, that a tapering could be provided as well, both on the radial inside (transition to the spool core 9), or to the radial outside (similar to the rounding 16 of the notched side surfaces 12 with the notches 11 and the tapering/rounding 16; see following description).

On the respective other side surfaces 12, opposing the perpendicular sidewalls 10, the ’’inner" notched annular lands 4, 5, 6, 7, do show a series of consecutive triangular notches 11 (see also Fig. 2) that are arranged following each other in a circumferential direction of the notched sidewall 12 of the respective notched annular lands 4, 5, 6, 7.

Each individual notch 11 shows an essentially triangular shape in a cross- sectional plane that is appropriately positioned therein and comprises a tangent that runs parallel to the centreline 2 of the slidable spool 1 (the suitable arrangement of the cross-sectional plane, in particular with respect to its “rotative” position in the circumferential direction, is obvious to a person skilled in the art). Each individual notch 11 has a peripheral plane 13 that limits the void of the notch 11 towards the spool core 9. In the presently shown embodiment, the respective peripheral planes 13 are indeed planar, so that the spool core 9 is flattened in this area, thus deviating somewhat from the circular curvature of the basic shape of the slidable spool 1 . However, the plane 13 might also follow the original curvature of a so-to-say “undisturbed” spool core 9, therefore deviating from a “real planar shape” of the plane 13 to a certain extent. The lower opening angle a at the peripheral plane 13 is presently chosen to be a = 100° (or radially inner opening angle a, core neighbouring opening angle a, or the like).

In the radial direction 14 pointing away and outwards from the centreline 2, the void of the notch 11 broadens, so that at an outside rim 15 of the respective notch 11 , an upper opening angle [3 of presently = 125° is reached (or radially outer opening angle (3, outer surface opening angle (3, circumferential opening angle (3, housing neighbouring opening angle (3, or the like). Hence, when looking in an axial direction onto a notched sidewall 12 of one of the notched annular lands 4, 5, 6, 7, each notch 11 has a somewhat trough-like appearance (which can be particularly seen in Fig. 4). Presently, the changeover from the lower opening angle a at the peripheral plane 13 to the upper opening angle [3 at the outside rim 15 is non-linear and particularly shows a step 34. However, a different type of changeover could be used as well.

Following the outside rim 15 of the triangular notches 11 , a rounding 16 is provided at the notched sidewall 12 of each notched annular land 4, 5, 6, 7 (starting with an angle with respect to the axial centreline 2 of presently 50°). The rounding 16 transitions towards the circumferential surface 17 of the notched annular lands 4, 5, 6, 7. These circumferential surfaces 17 typically define the outer diameter of the slidable spool 1. In the presently shown embodiment, the outside diameter of the notched annular lands 4, 5, 6, 7 is identical to the outside diameter of the non-notched “outer” annular lands 3, 8. For simplicity, the same reference number 17 is used for the circumferential surfaces 17. Fig. 2 shows the slidable spool 1 of Fig. 1 in a different top view, namely in a different rotational position. In other words, the slidable spool 1 is rotated around its centreline 2 by a certain angle, as compared to the position, as shown in Fig. 1 . In particular, it can be seen that in the circumferential direction on all notched sidewalls 12 of all notched annular lands 4, 5, 6, 7, one notch 11 follows the next neighbouring notch 11 directly. Therefore, the notched sidewalls 12 do not show a perpendicular surface part (a surface part, lying in a plane that is normal to the axial centreline 2), in particular in between two neighbouring notches 11 .

As can be further deferred from Fig. 1 , 2 or 3, the top pikes 18 of every triangular notch 11 are not forming a sharp pike. Instead, they show a rounded shape 32. This is due to the manufacturing technique used for the slidable spool 1 , using rotating milling heads. The diameter of the top pike 18 is presently equivalent to the diameter of the milling head. Nevertheless, it is clear from the Figs., that the triangular notches 11 show straight legs 19 for a substantive fraction of the overall length of the respective sidelines. In particular, the length of the straight legs 19 of a single notch 11 is longer than the length of the rounded section 32 of the top pike 18 of the respective triangular notch 11 . In particular, the straight length 19 is longer by a factor of 2, 3, 4, 5, 7.5 or 10, as compared to the length of the rounded portion 18.

Further, the limiting corners of the triangular notches 11 that are directed towards the spool core sections (away from the annular lands 4, 5, 6, 7) do show sharp corners 33 in the presently shown embodiment, at least for certain parts along the radial 14 extent thereof. Certainly, this may be designed differently as well.

Fig. 3 shows the slidable spool 1 being arranged in the bore 27 of a housing 20, thus forming a spool valve 21 . Presently, the spool valve 21 is designed as a fluid distribution valve. As usual, the slidable spool 1 can be moved in an axial direction within a bore 27 that is provided inside the housing 20 of the spool valve 21 . Depending on the axial position (displacement) of the slidable spool 1 inside the housing 20, different fluid connections can be established in a controlled way, while other fluid connections are interrupted. The slidable spool 1 can be moved using an actuator of any type that is known in the state-of-the-art. Presently, the actuator is not shown for simplicity.

The housing 20 of the spool valve 21 shows several annular fluid chambers 22, 23, 24, 25, 26 that surround the slidable spool 1 (or to be more precise the bore 27 in which the spool 1 is placed).

Annular fluid chambers 22 and 26 are connected to each other via a fluid conduit 28 that in turn is fluidly connected to a first fluid outlet port 29. Annular fluid chambers 23, 25 connect fluidly to fluid inlet port 30, while annular fluid conduit 24 fluidly connects to a second fluid outlet port 31 .

Depending on the axial position of the spool 1 within the housing 20, fluid inlet port 29 is either fluidly connected to first fluid outlet port 28 or to second fluid outlet port 31 . Such a fluid distribution valve 21 is known in the state of the art as such, so that for brevity no detailed explanations are presently presented.

To show the advantage of a slidable spool 1 and a spool valve 21 according to the present disclosure, Table 1 shows the fluid-induced axial force that acts on the slidable spool 1 for various strokes (indicated in percent of the maximum stroke) and for different opening angles of the triangular notches 11 , where a suitable combination of lower opening angle a and upper opening angle [3 is shown. The applied pressures were 60 bars at the fluid inlet port 30 with a pressure drop of 5 bar over the respective control surface of the spool valve 21. Therefore, in the position shown in Fig. 3, in which a fluid connection is established between fluid inlet port 30 and first fluid outlet port 29, the pressure level at the first fluid outlet port 29 is 55 bars. Is obvious from Table 1 that the forces are significantly lower for a slidable spool 21 according to the present disclosure for higher strokes, as compared to a spool, as known in the prior art. For smaller strokes they are at least comparable in size.

Table 1

Fig. 4 shows a cross-sectional view through the slidable spool 1 of the embodiment according to Fig. 1 and 2 through plane IV as indicated in Fig. 1. The view is depicted to elucidate the geometrical design of the slidable spool 1 for a person skilled in the art.

In particular, further details of the notches 11 can be seen. In particular, the rounded tips 32 and the sharp tips 33 (only at the very radially outside part in the presently shown view) of the triangular notches 11 are visible. Furthermore, the tapering of the opening angle starting from the lower peripheral plane 13 (lower opening angle a) towards the outside rim 15 (upper opening angle [3) is visible, where a clear step 34 of the change of the opening angle is visible. Nevertheless, even in the presently shown embodiment the opening angle broadens monotonically in a radial direction 14 towards the outside. It is to be noted that a single one or a plurality of the features of the presently disclosed detailed embodiment may be used in combination with the generic description of the present disclosure.

Claims

C l a i m s

1 . Slidable spool (1 ) for a spool valve (21 ), the spool (1 ) comprising at least one annular land (3, 4, 5, 6, 7, 8) around the spool core (9), the at least one annular land (4, 5, 6, 7) comprising at least one notch (11 ) in at least one of the side surfaces (12) of the at least one annular land (4, 5, 6, 7), the at least one notch (11 ) showing an essentially triangular shape, characterised in that the triangular shape of the at least one notch (11 ) shows an opening angle (a, [3) of at least 90° adjacent to the spool core (9).

2. Slidable spool (1 ) for a spool valve (21 ) according to the preamble of claim 1 , in particular according to claim 1 , characterised by a plurality of notches (11 ) along the circumference of the at least one side surface (12) of the at least one annular land (4, 5, 6, 7), wherein along the majority of the circumferential extent of the at least one side surface (12) of the at least one annular land (4, 5, 6, 7) a notch (11 ) is present.

3. Slidable spool (1 ) for a spool valve (21 ) according to claim 1 or claim 2, in particular according to claim 1 , characterised in that the triangular shape of the at least one notch (11 ) shows an opening angle (a, (3) of at least 90° along the majority of the radial extent (14) of the at least one notch (11 ), preferably at least along essentially the complete radial extent (14) of the at least one notch (11 ).

4. Slidable spool (1 ) for a spool valve (21 ) according to any of the preceding claims, characterised in that the opening angle (a, [3) is at least 100°, preferably at least one 110°, more preferably at least 120°.

5. Slidable spool (1 ) for a spool valve (21 ) according to any of the preceding claims, in particular according to any of claims 2 to 4, characterised in that along at least 60%, preferably at least 70%, more preferably at least 80%, even more preferably at least 90%, yet more preferably at least 95% of the circumferential extent of the at least one side surface (12) of the at least one annular land (4, 5, 6, 7) a notch is present.

6. Slidable spool (1 ) for a spool valve (21 ) according to any of the preceding claims, characterised in that the slidable spool (1 ) comprises a plurality of annular lands (3, 4, 5, 6, 7, 8) along the spool core (9).

7. Slidable spool (1 ) for a spool valve (21 ) according to any of the preceding claims, characterised in that at least one of the annular lands (4, 5, 6, 7) shows notches (11 ) on only one side surface (12) thereof.

8. Slidable spool (1 ) for a spool valve (21 ) according to claims 6 or 7, characterised in that the notches (11 ) of at least two annular lands (4, 5, 6, 7) are arranged in different axial directions.

9. Slidable spool (1 ) for a spool valve (21 ), characterised by at least one annular land (3, 8) essentially without notches, wherein said at least one annular land (3, 8) essentially without notches is arranged at an axially outer portion of the slidable spool (9).

10. Slidable spool (1 ) for a spool valve (21 ), characterised in that at least one annular land (3, 4, 5, 6, 7, 8) is chamfered and/or tapered and/or rounded (16) in a radial direction (14).

11 . Spool valve (21 ) with a slidable spool (1 ) and a housing (20) with a bore (27) for said slidable spool (1 ), characterised in that said slidable spool (1 ) is a slidable spool (1 ) according to any of the preceding claims.

12. Spool valve (21 ) according to claim 11 , characterized in that said spool valve (21 ) is designed and arranged as a fluid distribution valve (21 ).