Patent Description:
When the valve is actuated, the spool can shift or move axially within a bore in a valve body of the valve. As the spool moves, a spool variable area orifice is formed. A cross-sectional area such variable area orifice depends on the extent of axial motion of the spool. For example, when the spool shifts in a given direction, fluid can be allowed to flow from the actuator, then around the spool to a return cavity that is fluidly coupled to the fluid reservoir.

When the spool moves a small axial distance causing a small opening, as fluid flows about the spool, Bernoulli flow forces can be generated. The flow forces oppose the actuation force applied to the spool to shift it within the bore. As a consequence, the valve might not operate as expected, and instabilities might occur as pressure levels fluctuate. Such instabilities can be propagated to the machinery controlled by the valve.

It may thus be desirable to have a spool configured to mitigate the effect of flow forces and enhance stability of the valve. It is with respect to these and other considerations that the invention Freed made herein is presented.

Exemplary arrangements are disclosed in, for example, <CIT>, <CIT> and <CIT>.

The present invention describes implementations that relate to a valve spool with flow force mitigation features.

In a first example implementation, a spool as defined in claim <NUM> is provided.

In a second example implementation, a worksection as defined in claim <NUM> is provided.

In a third example implementation, a hydraulic system as defined in claim <NUM> is provided.

In addition to the illustrative aspects, implementations, and features described above, further aspects, implementations, and features will become apparent by reference to the figures and the following detailed description.

The novel features believed characteristic of the illustrative examples are set forth in the appended claims. The illustrative examples, however, as well as a preferred mode of use, further objectives and descriptions thereof, will best be understood by reference to the following detailed description of an illustrative example of the present invention when read in conjunction with the accompanying Figures.

In certain applications, hydraulic fluid flow in a hydraulic machine can be controlled using hydraulic sectional control valves. A sectional control valve or valve assembly can include a plurality of separate cast and machined metal valve worksections. Each worksection may include internal fluid passages, external ports, and valve bores with valve members slidably disposed within each valve bore. The valve bores may include a spool bore in which a main spool is slidably accommodated. Each worksection may be configured to control flow of fluid to and from a hydraulic actuator of the hydraulic machine.

Particularly, when the valve is actuated and the spool shifts within the spool bore, a variable orifice is formed that allows fluid flow therethrough, e.g., from the hydraulic actuator through a workport in the valve, then through the variable orifice to a return cavity connected to a fluid reservoir. Bernoulli flow forces can result as fluid flows through the variable orifice.

The flow forces can have an axial component that acts on the spool in a closing direction opposing the opening force applied to the spool. In some cases, the flow forces are sufficiently high that instabilities and pressure fluctuations might occur and propagate to the hydraulic actuator and the hydraulic machine. It may thus be desirable to have a spool configured to reduce or mitigate such flow forces and their effect on operation of the valve.

Disclosed herein are spools, systems, valve sections, and valve assemblies that mitigate the effect of flow forces. Particularly, an example spool is configured to have axial grooves that sequentially fluidly couple a workport passage to a return cavity to avoid a sudden, step-wise increase in flow rate and flow forces acting on the spool. In an example, the axial grooves can have variable depths. For instance, the axial grooves that first fluidly couple the workport passage to the return cavity can be shallower than axial grooves that subsequently fluidly couple the workport passage to the return cavity. In another example, each axial groove can have a first portion that is concave and has a first depth and a second portion that is concave and has a second depth, and the first portion is separated from the second portion by a convex or flat portion operating as a restriction that enhances stability of the valve.

<FIG> illustrates a partial, schematic representation of a hydraulic system <NUM>. <FIG> particularly illustrates a perspective cross-sectional view of a worksection <NUM> of a valve assembly that is configured to control multiple hydraulic actuators of the hydraulic system <NUM>. For example, the hydraulic system <NUM> can include a hydraulic actuator <NUM>, and the worksection <NUM> is configured to control fluid flow to and from the hydraulic actuator <NUM>.

The valve assembly can have an inlet section, a plurality of worksections such as the worksection <NUM>, and an outlet section. The worksections can be positioned adjacent one another and can be interposed between the inlet section and the outlet section. The inlet section, the worksections, and the outlet section can be coupled together by fasteners (e.g., bolts screws, clamps, tie rods, etc.) to provide an assembly of valve sections.

The hydraulic system <NUM> can include a source <NUM> of fluid. The source <NUM> of fluid can be a pump (e.g., fixed displacement, variable displacement pump, a load-sense variable displacement pump, etc.), for example. The pump can receive fluid from a fluid tank or fluid reservoir <NUM> of the hydraulic system <NUM>, and the source <NUM> pump then provides fluid flow to the valve assembly.

Particularly, the source <NUM> can be fluidly coupled to an inlet port disposed in an inlet section of the valve assembly. The valve assembly includes fluid passages that can then provide the fluid from the source <NUM> to the worksections of the valve assembly including the worksection <NUM>. The fluid reservoir <NUM> can be fluidly coupled to a reservoir port that can be disposed in the inlet section or an outlet section of the valve assembly.

The worksection <NUM> has a worksection body <NUM> that defines multiple fluid passages, cavities, and bores therein. The worksection <NUM> also includes workports that are configured to be fluidly coupled to respective chambers of the hydraulic actuator <NUM>.

For example, the hydraulic actuator <NUM> can include a cylinder <NUM> and a piston <NUM> slidably accommodated within the cylinder <NUM>. The term "slidably accommodated" is used throughout herein to indicate that a first component (e.g., the piston <NUM>) is positioned relative to a second component (e.g., the cylinder <NUM>) such that the first component is able to move relative to the second component.

The piston <NUM> includes a piston head <NUM> and a piston rod <NUM> extending from the piston head <NUM> along a central longitudinal axis direction of the cylinder <NUM>. The piston head <NUM> divides the inside or internal space of the cylinder <NUM> into a chamber <NUM> and a chamber <NUM>. The chamber <NUM> can be referred to as a cap chamber or head chamber, whereas the chamber <NUM> can be referred to as a rod chamber.

The worksection <NUM> includes a workport <NUM> that is fluidly coupled (e.g., via a fluid lines such as a hose) to the chamber <NUM> of the hydraulic actuator <NUM> and includes a workport <NUM> that is fluidly coupled to the chamber <NUM> of the hydraulic actuator <NUM>. The worksection <NUM> is configured to control supply fluid flow from the source <NUM> to the workports <NUM>, <NUM> and control return fluid flow from the workports <NUM>, <NUM> to the fluid reservoir <NUM>.

The worksection <NUM> has a spool <NUM> slidably accommodated (i.e., axially movable) in a longitudinal bore <NUM> formed in the worksection body <NUM>. The spool <NUM> can be configured to be biased to a neutral or centered position by springs disposed in end caps at the distal and proximal ends of the spool <NUM>. For example, as shown in <FIG>, the worksection <NUM> can include an end cap <NUM> disposed at a distal end of the spool <NUM>. The end cap <NUM> contains biasing springs <NUM> that bias the spool <NUM> in a proximal direction. The worksection <NUM> can similarly include another end cap (not shown) at a proximal end of the spool <NUM> configured to contain biasing springs that bias the spool <NUM> in a distal direction.

As such, the biasing springs on both ends of the spool <NUM> can bias the spool <NUM> to a neutral position at which the spool <NUM> can block fluid flow from the source <NUM> to the workports <NUM>, <NUM>. The term "block" is used throughout herein to indicate substantially preventing fluid flow except for minimal or leakage flow of drops per minute, for example.

The spool <NUM> can be actuated in either direction from the neutral position via various types of mechanisms. As an example for illustration, the spool <NUM> can be controlled by pilot valves such as pilot valve <NUM> that is partially shown in <FIG>.

The pilot valve <NUM> can be solenoid-operated and can be used to actuate or move the spool <NUM> in the longitudinal bore <NUM>. As an example, the pilot valve <NUM> can be configured as a pressure reducing valve that receives pressurized fluid from the source <NUM> then generates a pilot fluid signal that is proportional to a magnitude of an electric command provided thereto.

The pilot valve <NUM> can then provide the pilot fluid signal to a pilot fluid passage <NUM> that communicates the pilot fluid signal to the end cap <NUM>. The pilot fluid signal can apply a fluid force on the spool <NUM> in the proximal direction to shift the spool <NUM> in the proximal direction. The worksection <NUM> can include another pilot valve <NUM> (a portion of which is shown in <FIG>) at the proximal end of the spool <NUM> configured to shift the spool <NUM> in a distal direction when actuated.

In examples, the valve assembly can be configured to be a load-sense (LS) valve. Particularly, the valve assembly can have a shuttle valve network or system that resolves the highest load or the highest load-induced pressure level indicative of the highest load to which the actuators controlled by the valve assembly are subjected. The shuttle valve system then provides the LS signal indicative of the highest load to all the worksections of the valve assembly including the worksection <NUM>.

Fluid provided from the source <NUM> is provided through the inlet section of the valve assembly and fluid passages to an inlet cavity <NUM> in the worksection <NUM>. When the spool <NUM> moves axially in either direction, a variable metering orifice can be formed to allow fluid to flow from the inlet cavity <NUM> to a metered flow chamber <NUM>.

The worksection <NUM> can have a pressure compensator valve <NUM> located downstream from the metered flow chamber <NUM>. The pressure compensator valve <NUM> has a poppet <NUM> that is biased to a closed position by a compensator spring <NUM>. The poppet <NUM> is subjected to various forces such as fluid forces from the LS signal indicative of the highest load to all the worksections of the valve assembly (i.e., a global LS signal), a local LS signal of the worksection <NUM>, and pressurized fluid in the metered flow chamber <NUM> in addition to a spring force by the compensator spring <NUM>.

The poppet <NUM> can then move based on equilibrium between the various forces to allow fluid flow from the metered flow chamber <NUM> to a regulated flow passage <NUM>, which is looped as depicted in <FIG>. With this configuration, the pressure compensator valve <NUM> is configured to maintain a predetermined pressure drop across a variable metering orifice formed when the spool <NUM> is moved axially regardless of the load experienced by the hydraulic actuator <NUM>.

Although the worksection <NUM> used herein has a pressure-compensated, load-sensing configuration, the spool configurations described here that mitigate flow forces on the spools can be used with other types of valves, e.g., a non-pressure compensated valve, a non-load-sensing valve, open center valve, etc..

The spool <NUM> varies in diameter along its length to form lands of variable diameters capable of selectively interconnecting the various passages intercepting the longitudinal bore <NUM> to control flow of fluid to and from the workports <NUM>, <NUM>. The term "land" is used herein to indicate a generally cylindrical spool body portion. The lands of the spool <NUM> cooperate with internal surfaces of the worksection body <NUM> to define variable metering orifices that allows fluid flow therethrough. For example, the spool <NUM> has land <NUM>, land <NUM>, land <NUM>, land <NUM>, and land <NUM> configured to cooperate with the internal surfaces of the worksection body <NUM> to form the variable metering orifices and control the fluid flow rate and fluid direction through the worksection <NUM>. The lands <NUM>-<NUM> can have a first diameter and are separated by lands having a second diameter that is smaller than the first diameter, such that annular grooves are formed between each two lands of the lands <NUM>-<NUM>.

A variable metering orifice is used herein to indicate a spool-to-bore cylindrical area opening that forms between a land of the spool <NUM> and the internal surfaces of the worksection body <NUM> when the spool <NUM> shifts axially therein. Thus, the variable metering orifice is a flow area that forms between the spool <NUM> and the internal surface of the worksection body <NUM>, and the flow area can vary in size based on the axial position of the spool <NUM> within the longitudinal bore <NUM>, e.g., the farther the spool <NUM> shifts axially, the larger the flow area.

The worksection <NUM> has a return cavity <NUM> and a return cavity <NUM> that are fluidly coupled to the fluid reservoir <NUM>. The fluid reservoir <NUM> is drawn in two locations on <FIG> to reduce visual clutter but it should be understood that that return cavities <NUM>, <NUM> are connected through fluid passages in the valve assembly to an outlet port that is fluidly coupled to the fluid reservoir <NUM>.

The worksection <NUM> has a workport passage <NUM> that is fluidly coupled to the workport <NUM>. The worksection <NUM> also has a workport passage <NUM> that is fluidly coupled to the workport <NUM>. The worksection <NUM> can include workport relief valves, such as workport relief valve <NUM> fluidly coupled to the workport passage <NUM>, configured to relieve fluid if pressure level in the workport passage <NUM> exceeds a threshold pressure value. The worksection <NUM> can also include plugs, such as plug <NUM>, if pressure level is not expected to increase beyond a threshold value, for example.

When the spool <NUM> is in a neutral position, fluid flow to the various chambers, cavities, and passages can be blocked. Particularly, the land <NUM> can block fluid flow from the inlet cavity <NUM> to the metered flow chamber <NUM>, the land <NUM> blocks fluid flow from the regulated flow passage <NUM> to the workport passage <NUM>, the land <NUM> blocks fluid flow from the regulated flow passage <NUM> to the workport passage <NUM>, the land <NUM> blocks fluid flow from the workport passage <NUM> to the return cavity <NUM>, and the land <NUM> blocks fluid flow from the workport passage <NUM> to the return cavity <NUM>. As such, the piston <NUM> of the hydraulic actuator <NUM> might not move.

Actuating the pilot valve <NUM> or pilot valve <NUM> causes the spool <NUM> to move axially, thereby providing fluid flow to the hydraulic actuator <NUM> to move the piston <NUM>. For instance, if the pilot valve <NUM> is actuated and the spool <NUM> shifts axially in the proximal direction, the land <NUM> can move in the proximal direction to the extent that it moves past an edge of the internal surface of the worksection body <NUM> interfacing therewith. As a result, a metering orifice is formed, allowing fluid flow from inlet cavity <NUM> to the metered flow chamber <NUM>. Fluid in the metered flow chamber <NUM> can then push the poppet <NUM> and flow to the regulated flow passage <NUM>.

Also, the land <NUM> moves past the edge of the internal surface of the worksection body <NUM>, and another metering orifice is formed that allows fluid flow from the regulated flow passage <NUM> to the workport passage <NUM>. The workport passage <NUM> is fluidly coupled to the workport <NUM>, and thus fluid flows through the workport passage <NUM> to the workport <NUM>, and then to the chamber <NUM> of the hydraulic actuator <NUM> to extend the piston <NUM> (e.g., move the piston <NUM> to the left in <FIG>). Fluid discharged from the chamber <NUM> of the hydraulic actuator <NUM> flows through the workport <NUM> and the workport passage <NUM>, then through another metering orifice formed between the land <NUM> and the internal surface of the worksection body <NUM> to the return cavity <NUM>, which is fluidly coupled to the reservoir <NUM> as depicted in <FIG>.

On the other hand, if the pilot valve <NUM> is actuated and the spool <NUM> shifts axially in the distal direction, the land <NUM> can move in the distal direction to the extent that it moves past an edge of the internal surface of the worksection body <NUM> interfacing therewith. As a result, a metering orifice is formed, allowing fluid flow from the inlet cavity <NUM> to the metered flow chamber <NUM>. Fluid in the metered flow chamber <NUM> can then push the poppet <NUM> and flow to the regulated flow passage <NUM>.

Also, the land <NUM> moves past the edge of the internal surface of the worksection body <NUM>, and another metering orifice is formed, allowing fluid flow from the regulated flow passage <NUM> to the workport passage <NUM>. The workport passage <NUM> is fluidly coupled to the workport <NUM>, and thus fluid flows through the workport passage <NUM> to the workport <NUM>, and then to the chamber <NUM> of the hydraulic actuator <NUM> to retract the piston <NUM> (e.g., move the piston <NUM> to the right in <FIG>). Fluid discharged from the chamber <NUM> of the hydraulic actuator <NUM> flows through the workport <NUM> and the workport passage <NUM>, then through another metering orifice formed between the land <NUM> and the internal surface of the worksection body <NUM> to the return cavity <NUM>, which is fluidly coupled to the reservoir <NUM> as depicted in <FIG>.

The fluid volume in the chamber <NUM> and the fluid flow rate of fluid discharged from the chamber <NUM> can be large in some applications. For instance, the hydraulic actuator <NUM> can represent one or two cylinders of a boom actuator of a wheel loader or skid steer, and as the boom actuator retracts, fluid is discharged from the cap or head chambers of the cylinders large at a large flow rate. The discharged fluid flows through the workport <NUM> and the workport passage <NUM>, then through a metering orifice formed between the land <NUM> and the internal surfaces of the worksection body <NUM> to the return cavity <NUM>.

Bernoulli flow forces can result from fluid flowing through the metering orifice formed between the land <NUM> and the internal surfaces of the worksection body <NUM> to the return cavity <NUM>. The flow forces can have an axial component that acts on the spool <NUM> in a closing (proximal) direction opposing the opening force applied to the spool <NUM> (e.g., the force of the pilot fluid signal at the proximal end of the spool <NUM>). In some cases, the flow forces are sufficiently high that they can cause oscillations of the spool <NUM> and oscillations in pressure levels can occur and propagate through the worksection <NUM> and the hydraulic actuator <NUM>.

Such oscillations can cause instabilities in the hydraulic actuator <NUM> and the machine that the hydraulic actuator <NUM> controls. For example, such oscillations can cause the bucket of a wheel loader to oscillate as the boom actuator is retracting (e.g., as the piston <NUM> is retracting) to lower the bucket. Such oscillations and instabilities are undesirable.

It may thus be desirable to control (e.g., reduce or limit) fluid flow rate through the worksection <NUM> to reduce the flow forces and maintain stability. For example, the worksection <NUM> can include an orifice plate <NUM> disposed at the workport <NUM> and having a hole <NUM> formed therethrough. The hole <NUM> operates as a fixed orifice that limits fluid flow through the workport <NUM>.

With this configuration, the orifice plate <NUM> can generate backpressure in the chamber <NUM> of the hydraulic actuator <NUM>, which can prevent cavitation in the chamber <NUM> when the piston <NUM> is retracting at a high speed. The orifice plate <NUM> can also limit fluid flow rate of fluid discharged from the chamber <NUM> and flowing through the variable metering orifice formed by the land <NUM> and the internal surfaces of the worksection body <NUM>. As a result, the flow forces generated and acting on the spool <NUM> may be reduced.

However, the orifice plate <NUM> can cause pressure level in the chamber <NUM> to increase, which may reduce efficiency of the hydraulic system. Also, as fluid flows through the hole <NUM>, a pressure drop occurs (i.e., pressure level decreases as fluid flows therethrough such that pressure level in the chamber <NUM> is higher than pressure level in the workport passage <NUM>). Such pressure drop causes power loss.

Particularly, power loss Pwr resulting from fluid flow through the hole <NUM> can be determined as Pwr = Q(P<NUM> - P<NUM>), where Q is the flow rate through the hole <NUM>, P<NUM> is pressure level in the chamber <NUM>, and P<NUM> is pressure level in the workport passage <NUM>. The higher the flow rate Q, the greater the power loss Pwr. The power loss is dissipated through the worksection <NUM> in the form of heat generated at the orifice plate <NUM>. Such power loss may be undesirable as it reduces efficiency of the hydraulic system.

Further, when the spool <NUM> shifts in the other direction (in the proximal direction) to extend the piston <NUM> (e.g., to raise the bucket of the wheel loader by the boom actuators), fluid is provided through the workport passage <NUM>, the orifice plate <NUM>, the workport <NUM> to the chamber <NUM>. The orifice plate <NUM> restricts fluid flow therethrough causing pressure levels to increase and efficiency to be reduced. In other words, while the orifice plate <NUM> may help reduce instabilities while lowering a load (retracting the piston <NUM>), it can also reduce efficiency while raising the load (extending the piston <NUM>).

It may thus be desirable to have a spool that is configured to reduce flow forces and instabilities while retracting the piston <NUM> without affecting extension of the piston <NUM>. In particular, the land <NUM> of the spool <NUM> can be configured in a manner that controls fluid flow from the workport passage <NUM> to the return cavity <NUM> to reduce the flow forces. This way, the orifice plate <NUM> might be eliminated or the size of the hole <NUM> can be increased so as to enhance efficiency of the system. It may further be desirable that the configuration of the land <NUM> that restricts fluid flow from the workport passage <NUM> to the return cavity <NUM> does not affect operation of the worksection <NUM> while extending the piston <NUM>.

<FIG> illustrates a perspective cross-sectional view of a worksection <NUM> of a valve assembly having a spool <NUM> with flow force reduction features, in accordance with an example implementation. The worksection <NUM> is similar to the worksection <NUM> and components that are the same in both worksections are designated with the same reference numbers. For example, the worksection body <NUM> can be configured similarly in both worksections. The spool <NUM>, however, is different from the spool <NUM> in that the spool <NUM> has features that control fluid flow from the workport passage <NUM> to the return cavity <NUM> when retracting the piston <NUM> so as to reduce flow forces acting on the spool <NUM>.

<FIG> illustrates a side view of the spool <NUM>, in accordance with an example implementation. The spool <NUM> has a spool body <NUM> that is generally cylindrical and varies in diameter along its length to form lands of variable diameters capable of selectively interconnecting the various passages intercepting the longitudinal bore <NUM> to control flow of fluid to and from the workports <NUM>, <NUM>.

Particularly, the lands of the spool <NUM> cooperate with internal surfaces of the worksection body <NUM> to define variable metering orifices that allows fluid flow therethrough. For example, the spool <NUM> comprises land <NUM> at its distal end configured to control fluid flow from the workport passage <NUM> to the return cavity <NUM> when the piston <NUM> is retracting and control fluid flow from the regulated flow passage <NUM> to the workport passage <NUM> when the piston <NUM> is extending.

The spool <NUM> also comprises land <NUM> configured to meter fluid flow from the inlet cavity <NUM> to the metered flow chamber <NUM>. The spool <NUM> further includes land <NUM> configured to control fluid flow from the metered flow passage <NUM> to the workport passage <NUM> when the piston <NUM> is retracting, and land <NUM> configured to control fluid flow from the workport passage <NUM> to the return cavity <NUM> when the piston is extending. The lands <NUM>-<NUM> are configured as generally cylindrical portions of the spool body <NUM> and are separated by lands having a smaller diameter, such that annular grooves are formed therebetween, i.e., the lands <NUM>-<NUM> can have a first diameter and are separated by lands having a second diameter that is smaller than the first diameter, such that annular grooves are formed at the areas of the spool <NUM> having the smaller diameter lands.

To reduce the flow forces acting on the spool <NUM> when the piston <NUM> is retracting and a large amount of fluid flow is flowing from the chamber <NUM> to the fluid reservoir <NUM> via the worksection <NUM>, the land <NUM> includes a plurality of axial grooves <NUM> that extend longitudinally along a portion of an axial length of the land <NUM>. The plurality of axial grooves <NUM> are disposed in a circular array about a circumference of the land <NUM>.

<FIG> illustrates a cross-sectional view labelled "A-A" in <FIG>, in accordance with an example implementation. As an example implementation shown in <FIG>, the land <NUM> can include eight axial grooves that are disposed at <NUM> degree angles from each other about the circumference of the land <NUM>. Eight axial grooves are used herein as an example; however, more or fewer axial grooves can be used based on the application.

The axial grooves are configured differently. In particular, the land <NUM> comprises a first set of axial grooves including axial groove <NUM>, axial groove <NUM>, axial groove <NUM>, and axial groove <NUM>. The axial grooves <NUM>, <NUM>, <NUM>, and <NUM> can be configured similarly and are disposed at <NUM> degree angles from each other about the circumference of the land <NUM>.

The land <NUM> also comprises a second set of axial grooves including axial groove <NUM>, axial groove <NUM>, axial groove <NUM>, and axial groove <NUM> that can be configured similar to each other and are disposed at <NUM> degree angles from each other about the circumference of the land <NUM>.

The axial grooves <NUM>, <NUM>, <NUM>, and <NUM> of the first set of axial grooves are intermeshed or interleaved with the axial grooves <NUM>, <NUM>, <NUM>, and <NUM> of the second first set of axial grooves. In other words, each of the axial grooves <NUM>, <NUM>, <NUM>, and <NUM> is circumferentially-interposed between two axial grooves of the axial grooves <NUM>, <NUM>, <NUM>, and <NUM> (i.e., the axial groove <NUM> is interposed between the axial grooves <NUM>, <NUM>; the axial groove <NUM> is interposed between the axial grooves <NUM>, <NUM>; the axial groove <NUM> is interposed between the axial grooves <NUM>, <NUM>; and the axial groove <NUM> is interposed between the axial grooves <NUM>, <NUM>).

Similarly, each of the axial grooves <NUM>, <NUM>, <NUM>, and <NUM> is circumferentially-interposed between two axial grooves of the axial grooves <NUM>, <NUM>, <NUM>, and <NUM> (i.e., the axial groove <NUM> is interposed between the axial grooves <NUM>, <NUM>; the axial groove <NUM> is interposed between the axial grooves <NUM>, <NUM>; the axial groove <NUM> is interposed between the axial grooves <NUM>, <NUM>; and the axial groove <NUM> is interposed between the axial grooves <NUM>, <NUM>). This configuration renders the spool <NUM> radially-balanced as fluid forces of fluid traversing the axial grooves applies equal radially-inward forces on the spool body <NUM>.

The axial grooves of <NUM>, <NUM>, <NUM>, and <NUM> of the second set of axial grooves are configured differently from the axial grooves <NUM>, <NUM>, <NUM>, and <NUM> of the first set of axial grooves. Particularly, the first set of axial grooves have axial lengths that are different from respective axial lengths of the second set of axial grooves. Further, the first set of axial grooves have depths that are different from respective depths of the second set of axial grooves.

<FIG> illustrates a cross-sectional view labelled "B-B" in <FIG> depicting the axial groove <NUM> and the axial groove <NUM> of the first set of axial grooves, in accordance with an example implementation. The axial grooves <NUM>, <NUM> are configured similar to each other and the axial grooves <NUM>, <NUM> not shown in the cross-sectional view of <FIG> are similar to the axial grooves <NUM>, <NUM>.

The axial groove <NUM> can have an axial length L1 (i.e., the longitudinal distance from the distal edge of the axial groove <NUM> to the proximal edge of the axial groove <NUM>). The axial groove <NUM> has a distal concave portion <NUM> and a proximal concave portion <NUM>, that are separated from each other by a convex or straight portion, such as straight portion <NUM>. The distal concave portion <NUM> and the proximal concave portion <NUM> can have concave of flat bases.

Tracing a contour of the axial groove <NUM> from its distal end to its proximal end, the distal concave portion <NUM> begins with a vertical plunge cut <NUM>, followed by a curved portion <NUM>, then a base or flat portion <NUM>, then another curved portion <NUM>. The curved portion <NUM> can include an inflection point of the distal concave portion <NUM> and turns into the straight portion <NUM>.

The straight portion <NUM> operates as a "bump" between the distal concave portion <NUM> and the proximal concave portion <NUM> as the straight portion <NUM> is raised up from the deeper concave portions <NUM>, <NUM>. Continuing with tracing the profile of the axial groove <NUM>, the straight portion <NUM> turns into or connects with a curved portion <NUM> of the proximal concave portion <NUM>, which then turns into a base or flat portion <NUM>, followed by a curved portion <NUM>, which connects with a vertical plunge cut <NUM> at the proximal edge of the axial groove <NUM>. The curved portions <NUM>, <NUM> can instead be sloped straight surfaces.

Further, the distal concave portion <NUM> can have a depth D1 (i.e., a radial distance from the surface of the land <NUM> to the flat portion <NUM> is D1), the straight portion <NUM> can have a depth D2 (i.e., a radial distance from the surface of the land <NUM> to the straight portion <NUM> is D2), and the proximal concave portion <NUM> can have a depth D3 (i.e., a radial distance from the surface of the land <NUM> to the flat portion <NUM> is D3).

In examples, the depth D1 can be equal to the depth D3; however, in other examples, D1 and D3 can be different. As an example for illustration, the length L1 (longitudinal distance from the vertical plunge cut <NUM> and the vertical plunge cut <NUM>) can be about <NUM> (<NUM> inches), the depths D1 and D3 can be about <NUM> (<NUM> inches), and the depth D2 can be about <NUM> (<NUM> inches). The axial groove <NUM> (as well as the axial grooves <NUM>, <NUM> of the first set of axial grooves) is configured similar to the axial groove <NUM>. However, the second set of axial grooves (the axial grooves <NUM>, <NUM>, <NUM>, and <NUM>) can be configured with different depths and lengths.

<FIG> illustrates a cross-sectional view labelled "C-C" in <FIG> depicting the axial groove <NUM> and the axial groove <NUM> of the second set of axial grooves, in accordance with an example implementation. The axial grooves <NUM>, <NUM> are configured similar to each other and the axial grooves <NUM>, <NUM> not shown in the cross-sectional view of <FIG> are similar to the axial grooves <NUM>, <NUM>.

The axial groove <NUM> can have an axial length L2 (i.e., the longitudinal distance from the distal edge of the axial groove <NUM> to the proximal edge of the axial groove <NUM>). The axial groove <NUM> has a profile similar to the profile of the axial groove <NUM> described above. Particularly, the axial groove <NUM> has a distal concave portion <NUM> and a proximal concave portion <NUM>, that are separated from each other by a convex or straight portion, such as straight portion <NUM>. The distal concave portion <NUM> and the proximal concave portion <NUM> can have concave or flat bases.

For instance, tracing a contour of the axial groove <NUM> from its distal end to its proximal end, the distal concave portion <NUM> begins with a vertical plunge cut <NUM>, followed by a curved portion <NUM>, then a base or flat portion <NUM>, then another curved portion <NUM>. The curved portion <NUM> can include an inflection point of the distal concave portion <NUM> and turns into the straight portion <NUM>.

The straight portion <NUM> operates as a "bump" between the distal concave portion <NUM> and the proximal concave portion <NUM>. The straight portion <NUM> can then turn into or connects with a curved portion <NUM> of the proximal concave portion <NUM>, then turns into a base or flat portion <NUM>, followed by a curved portion <NUM>, which connects with a vertical plunge cut <NUM>. The curved portions <NUM>, <NUM> can instead be sloped straight surfaces.

Further, the distal concave portion <NUM> can have a depth D4 (i.e., a radial distance from the surface of the land <NUM> to the flat portion <NUM> is D4), the straight portion <NUM> can have a depth D5 (i.e., a radial distance from the surface of the land <NUM> to the straight portion <NUM> is D5), and the proximal concave portion <NUM> can have a depth D6 (i.e., a radial distance from the surface of the land <NUM> to the flat portion <NUM> is D6).

In examples, the depth D4 can be equal to the depth D6; however, in other examples, D4 and D6 can be different. As an example for illustration, the length L2 (longitudinal distance from the vertical plunge cut <NUM> or distal end of the axial groove <NUM> and the vertical plunge cut <NUM> or proximal end of the axial groove <NUM>) can be about <NUM> (<NUM> inch), the depths D4 and D6 can be about <NUM> (<NUM> inches), and the depth D5 can be about <NUM> (<NUM> inches). The axial groove <NUM> (as well as the axial grooves <NUM>, <NUM>) is configured similar to the axial groove <NUM>.

As such, the axial length L2 of the second set of axial grooves (i.e., the axial grooves <NUM>, <NUM>, <NUM>, and <NUM>) is greater than the respective axial length L1 of the first set of axial grooves (i.e., the axial grooves <NUM>, <NUM>, <NUM>, and <NUM>). Further, the depths (e.g., D4, D5, and/or D6) of the axial grooves <NUM>, <NUM>, <NUM>, and <NUM> of the second set of axial grooves are smaller than the respective depths (e.g., D1, D2, and/or D3) of the axial grooves <NUM>, <NUM>, <NUM>, and <NUM> of the first set of axial grooves. In other words, the axial grooves <NUM>, <NUM>, <NUM>, and <NUM> of the second set of axial grooves can be longer but shallower than the axial grooves <NUM>, <NUM>, <NUM>, and <NUM> of the first set of axial grooves.

Notably, referring back to <FIG>, while the distal ends of the axial grooves <NUM>, <NUM>, <NUM>, and <NUM> of the first set of axial grooves are misaligned with respective distal ends of the axial grooves <NUM>, <NUM>, <NUM>, and <NUM> of the second set of axial grooves (due to a difference between the lengths L1 and L2), all eight axial grooves are aligned at their proximal ends.

Particularly, the distal ends of the four axial grooves of the first set of axial grooves (e.g., the axial groove <NUM>) are disposed at a distance E1 measured from a distal end <NUM> of the spool body <NUM>. The distal ends of the four axial grooves of the second set of axial grooves (e.g., the axial grooves <NUM>, <NUM>) are disposed at a distance E2 measured from the distal end <NUM> of the spool body <NUM>.

However, proximal ends of all eight axial grooves are disposed at a distance E3 measured from the distal end <NUM> of the spool body <NUM>. The distance E1 is greater than E2 because the axial grooves of the first set of axial grooves (e.g., the axial groove <NUM>) are shorter than axial grooves of the second set of axial grooves (e.g., the axial grooves <NUM>, <NUM>). With this configuration, the axial grooves can engage (i.e., allow fluid flow to) the return cavity <NUM> in a sequential manner when the spool <NUM> moves in a first axial direction (e.g., the distal direction) to retract the piston <NUM>, while all the axial grooves engage the regulated flow passage <NUM> at the same time when the spool <NUM> moves in a second axial direction (e.g., the proximal direction) opposite the first axial direction to extend the piston <NUM>.

<FIG>, <FIG> illustrate sequential engagement of the axial grooves <NUM>-<NUM> with the return cavity <NUM> when the spool <NUM> moves in the distal direction, in accordance with an example implementation. Particularly, <FIG> illustrates a partial cross-sectional view of the worksection <NUM> with the spool <NUM> in a neutral position. At the neutral position of the spool <NUM> shown in <FIG>, the land <NUM> blocks the workport passage <NUM> and prevent fluid flow to the return cavity <NUM> as none of the axial grooves <NUM>-<NUM> is exposed to or engaged with the return cavity <NUM>. In other words, the workport passage <NUM> is fluidly decoupled from the return cavity <NUM> when the spool <NUM> is in the neutral position. The term "fluidly decoupled" is used herein to indicate that no substantial fluid flow (e.g., except for minimal leakage flow of drops per minute) occurs between two fluid passages or openings that are fluidly decoupled. Conversely, the term "fluidly coupled" indicates that fluid can flow or be communicated between two fluid passages or openings.

<FIG> illustrates a partial cross-sectional view of the worksection <NUM> where the spool <NUM> has moved axially in the distal direction through a first portion of its stroke to a first axial position. As the spool <NUM> moves in the distal direction to retract the piston <NUM>, distal ends of the longer axial grooves of the second set of axial grooves (the axial grooves <NUM>, <NUM>) start to move past an edge <NUM> of the return cavity <NUM>.

As such, the longer axial grooves of the second set of axial grooves (the axial grooves <NUM>, <NUM>) fluidly couple the workport passage <NUM> to the return cavity <NUM> and allow fluid flow from the workport passage <NUM> to the return cavity <NUM>. However, at the first axial position of the spool <NUM>, the shorter axial grooves of the first set of axial grooves (e.g., the axial groove <NUM>) have not reached the edge <NUM> of the return cavity <NUM> and remain disengaged therefrom.

Thus, a limited amount of fluid flow is allowed through the second set of axial grooves (e.g., the axial grooves <NUM>, <NUM>) from the workport passage <NUM> to the return cavity <NUM>. As a result, the flow forces acting on the spool <NUM> may be reduced compared to a configuration where all axial grooves engage at the same time.

<FIG> illustrates a partial cross-sectional view of the worksection <NUM> where the spool <NUM> has moved axially in the distal direction through a second portion of its stroke to a second axial position. As the spool <NUM> moves further in the distal direction, distal ends of the shorter axial grooves of the first set of axial grooves (the axial groove <NUM>) also move past an edge <NUM> of the return cavity <NUM>. This way, the first set of axial grooves also fluidly couple the workport passage <NUM> to the return cavity <NUM>, thereby increasing the fluid flow rate from the workport passage <NUM> to the return cavity <NUM>.

However, such gradual increase in fluid flow rate by first engaging the second set of axial grooves then later engaging the first set of axial grooves may correspond to a gradual increase in the flow forces acting on the spool <NUM>. In other words, a step-wise or sudden increase in the flow forces is avoided by sequentially engaging of the axial grooves, and thus the effect of flow forces on stability may be mitigated. Additionally, further movement of the spool <NUM> in the distal direction creates a flow restriction that may further enhance stability.

<FIG> illustrates a partial cross-sectional view of the worksection <NUM> where the spool <NUM> has moved axially in the distal direction through a third portion of its stroke to a third axial position. As the spool <NUM> moves further in the distal direction, the "bumps" of the axial grooves (e.g., the straight portion <NUM>) overlaps an interior surface portion <NUM> of the worksection body <NUM>, and a flow restriction is created therebetween.

The flow restriction can restrict fluid flow rate from the workport passage <NUM> to the return cavity <NUM>, further enhancing stability. For example, a backpressure is generated in the workport passage <NUM> and the chamber <NUM> to prevent cavitation and retract the piston <NUM> in a controlled manner. Additionally, the flow restriction redirecting the flow forces in the desired direction, thereby mitigating the instability caused by Bernoulli flow forces.

Notably, the straight portion <NUM> can be shifted axially relative to the distal concave portion <NUM> and the proximal concave portion <NUM> (see <FIG>) based on desired performance, and thus the spool configuration can be tuned specifically to a particular application.

With this configuration of the axial grooves in the land <NUM>, the effect of flow forces on the spool <NUM> when the spool <NUM> moves in the distal direction to retract the piston <NUM> can be mitigated, and spool stability may be enhanced. Notably, the sequential engagement of the axial grooves and the flow restriction caused by the "bumps" in the axial grooves are pertinent to retraction of the piston <NUM> and movement of the spool <NUM> in the distal direction. However, they do not affect operation when the spool <NUM> moves in the proximal direction to extend the piston <NUM>.

Referring to <FIG> together, as mentioned above, the proximal ends of all eight axial grooves are axially aligned and are disposed at the distance E3 from the distal end <NUM> of the spool <NUM>. Thus, when the spool <NUM> moves in the proximal direction to extend the piston <NUM>, all eight axial grooves engage the regulated flow passage <NUM> at the same time to fluidly couple the regulated flow passage <NUM> to the workport passage <NUM>.

Further, the "bumps" caused by the straight portions (e.g., straight portion <NUM>, <NUM>) do not cause flow restriction as is the case when the spool <NUM> moves in the distal direction. As such, the configuration of the spool <NUM> avoids the drawbacks of the orifice plate <NUM> which limits fluid flow in both directions.

It should be understood that the disclosed configuration of the spool <NUM> can be used as an alternative or in addition to using the orifice plate <NUM>. In the case where both the spool <NUM> and the orifice plate <NUM> are used, a bigger hole <NUM> can be used (e.g.,<NUM> ( <NUM> inch) rather than <NUM> (<NUM> inch) as the spool <NUM> enhances stability and a more restrictive orifice plate might not be needed.

<FIG> is a flowchart of a method <NUM> for operating a worksection of a valve assembly, in accordance with an example implementation. The method <NUM> is used with the worksection <NUM> and the spool <NUM>.

The method <NUM> may include one or more operations, functions, or actions as illustrated by one or more of blocks <NUM>-<NUM>. Although the blocks are illustrated in a sequential order, these blocks may also be performed in parallel, and/or in a different order than those described herein.

At block <NUM>, the method <NUM> includes positioning the spool <NUM> in the neutral position within the longitudinal bore <NUM> formed in the worksection <NUM> of a valve assembly, wherein the worksection <NUM> comprises the workport passage <NUM> fluidly coupled to the hydraulic actuator <NUM> and the return cavity <NUM> fluidly coupled to the fluid reservoir <NUM>, wherein the spool <NUM> has the land <NUM> configured to control fluid flow from the workport passage <NUM> to the return cavity <NUM>, wherein the land <NUM> comprises the plurality of axial grooves <NUM> formed in a circular array about a circumference of the land <NUM>, wherein the plurality of axial grooves <NUM> comprises the first set of axial grooves (i.e., the axial grooves <NUM>-<NUM>) and the second set of axial grooves (i.e., the axial grooves <NUM>-<NUM>), wherein an axial length of the axial grooves of the second set of axial grooves is greater than a respective axial length of the axial grooves of the first set of axial grooves, and wherein in the neutral position of the spool <NUM>, the plurality of axial grooves <NUM> are disengaged from the return cavity <NUM> and the land <NUM> fluidly decouples the workport passage <NUM> from the return cavity <NUM> (see <FIG>).

At block <NUM>, the method <NUM> includes moving the spool <NUM> to a first axial position (see <FIG>), wherein at the first axial position of the spool, the axial grooves of the second set of axial grooves engage the return cavity <NUM>, thereby fluidly coupling the workport passage <NUM> to the return cavity <NUM>, whereas the axial grooves of the first set of axial grooves remain disengaged from the return cavity <NUM>.

At block <NUM>, the method <NUM> includes moving the spool <NUM> to a second axial position (see <FIG>), wherein at the second axial position of the spool <NUM>, the axial grooves of the first set of axial grooves engage the return cavity <NUM> such that both the first set of axial grooves and the second set of axial grooves fluidly couple the workport passage <NUM> to the return cavity <NUM>.

The detailed description above describes various features and operations of the disclosed systems with reference to the accompanying figures. The illustrative implementations described herein are not meant to be limiting.

Claim 1:
A spool (<NUM>) configured to be movable in a worksection (<NUM>, <NUM>) of a valve assembly, the spool comprising:
a spool body (<NUM>) varying in diameter along a length of the spool body, thereby forming a plurality of lands (<NUM>-<NUM>) of variable diameters, wherein a land of the plurality of lands is configured to control fluid flow from a workport passage (<NUM>, <NUM>) formed in the worksection to a return cavity (<NUM>, <NUM>) formed in the worksection; and
a plurality of axial grooves (<NUM>) formed in a circular array about a circumference of the land (<NUM>), wherein the plurality of axial grooves comprises a first set of axial grooves (<NUM>, <NUM>, <NUM>, <NUM>) and a second set of axial grooves (<NUM>, <NUM>, <NUM>, and <NUM>), wherein an axial length of axial grooves of the second set of axial grooves is greater than a respective axial length of axial grooves of the first set of axial grooves, allowing the axial grooves of the second set of axial grooves to engage the return cavity before the axial grooves of the first set of axial grooves when the spool is shifted within the worksection in a distal axial direction; characterised in that, a maximal depth of the axial grooves of the second set of axial grooves is smaller than a respective maximal depth of the axial grooves of the first set of axial grooves such that the axial grooves of the second set of axial grooves are shallower than the axial grooves of the first set of axial grooves.