Spool valve and piston geometry to reduce cavitation effects in a linear actuator

A linear actuator system has a rotary spool valve configuration having a spool, a piston, and a cylinder. The spool and piston have return apertures so positioned, configured and angled to direct return flow towards the center of a spool central return port and spool pressure ports to direct pressurized flow into upper or lower chambers. Rotation of the spool synchronizes and aligns ports and apertures to reverse flows and effect upward and downward translation of the cylinder to vibrationally drive an implement to perform work. The positioned and angled apertures direct the fluid to a region demarcated by a total length of 1.5 times the interior diameter of the spool central return port centered about a piston shoulder. A base plug member having a bull-nose tip, baffles and cavities is disposed within the spool central return port to reduce or eliminate cavitation.

TECHNICAL FIELD

The present invention relates generally to hydraulic spool valves controlling cyclic flow reversal. More specifically, the present invention relates to a hydraulic spool valve used for rapid-flow cycling in a hydraulic system with combined flow rates and pressure differentials to induce cavitation effects. Cavitation is a devastating problem that may result in rapid wear and degradation of hydraulic components. High speed flow reversals and pressure differentials generate conditions that are at a high risk of sustaining cavitation damage.

Various exemplary embodiments of the present invention are described below. Use of the term “exemplary” means illustrative or by way of example only, and any reference herein to “the invention” is not intended to restrict or limit the invention to exact features or steps of any one or more of the exemplary embodiments disclosed in the present specification. References to “exemplary embodiment,” “one embodiment,” “an embodiment,” “some embodiments,” “various embodiments,” and the like, may indicate that the embodiment(s) of the invention so described may include a particular structure, feature, property, or characteristic, but not every embodiment necessarily includes the particular structure, feature, property, or characteristic. Further, repeated use of the phrase “in one embodiment,” or “in an exemplary embodiment,” does not necessarily refer to the same embodiment, although they may.

BACKGROUND

Many hydraulic applications require rapid-flow reversals which are accomplished using servo or spool valves to redirect fluid from one direction or port to another. At low-flow rates or pressure differentials this task is accomplished easily using conventional servo and spool technology. As the flow rates and pressure differentials increase, this task becomes challenging both in terms of generating efficient flow regimes and in preventing cavitation.

For example, current servo and spool technology, at frequencies above 50 Hz and flow rates above 300 liters per minute, typically experience a combination of poor efficiency (high heat production), noisy valve performance (poor harmonics and non-sinusoidal flow regimes), poor frequency response (slow valve opening) and high cavitation of the valve and downstream hydraulic component materials.

Further, servo and spool valves typically comprise a cylindrical valve element housed within a precisely machined bore with very small annular gaps between the two. The small annular gaps act as, or assist, in sealing the high-and-low pressure environments from one another. In larger valves capable of flow rates above 300 liters per minute, the tolerances and clearances make it difficult to achieve an effective seal.

Such a system is described in U.S. Pat. No. 5,136,926 issued to Bies et al. (“Bies”). The system described uses a rotating spool valve with axial grooves to deliver pressurized fluid medium to the linear piston cylinder system and a central return cavity to return the spent fluid to the source for recirculation as pressurized fluid.

Bies teaches a valve with radially distributed and positioned porting, having axial grooves used as distribution chambers for the pressurized fluid situated immediately adjacent to the return porting. Such a geometry relies upon a journal-type seal, or simply a tight tolerance resulting in a narrow annulus, to deter high-pressure fluid medium from leaking from the high-pressure region to the low-pressure, return flow, region. The valve geometry taught by Bies results in a short-circumferential sealing area between the pressure and return circuits. In addition, the long axial grooves for delivery of the pressurized fluid results in a broad valve edge with increased leakage path potential and decreased efficiency.

Further, as the valve rotates, the sealing annular path between the pressure and return circuits reduces significantly, resulting in high leakage rates as the valve is about to open or shortly after valve closure. Such leakage may represent 40% or more of the total flow of the system with resulting high losses and inefficiency.

It will also be appreciated that when using presently available systems, at higher pressures and flow rates, the stop/start cyclic flow regime may result in rapidly reducing pressures followed by rapidly increasing pressures, which increase the risk of cavitation. As flow rates and pressure differentials increase, the potential for cavitation increases as well. With rapid flow interruption or reversals, hydraulic hammer effects can take place which contribute significantly to cavitation.

Porting geometries and flow velocities also influence cavitation potential. These effects have been studied and tested by the inventors resulting in advances made in the understanding of how geometry may influence and reduce cavitation potential.

Accordingly, a need exists for a new system and method for rapid flow switching spool technology that addresses one or more known problematic issues. Specifically, a new system and method is needed that will allow for high flow rate and pressure differential flow switching with high efficiency that reduces or eliminates cavitation of the host materials. Such systems and methods are disclosed herein.

SUMMARY OF THE INVENTION

The exemplary embodiments of the present disclosure have been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been resolved fully by currently available hydraulic servo or spool valves.

A fluid driven piston/cylinder system may be configured to act as an uni-axial, high-frequency (above 30 Hz) vibrator using an internal spool valve. Fluid is directed by a spool valve above or below a shoulder mounted on either the piston or the cylinder to generate axial movement. Such axial movement, reacting against a mass, will generate cyclic, axial motion and force.

It is desirable to separate the pressure and return circuits to avoid backward and forward shuttling of flow, which requires energy to move the mass of fluid and causes heat accumulation as the fluid is not replenished with new, cooled fluid.

The exemplary embodiments of the current invention alter significantly the geometry of the spool valve porting and flow paths to increase efficiency and to reduce cavitation potential. In summary, the spool valve features: 1) pressure and return port separation; 2) isolated pressure porting; 3) spool valve return port location and projection; and, 4) spool interior baffling that dissipates pressure pulses to specifically address, reduce, or eliminate the conditions that cause cavitation.

Cavitation may be caused by stress waves emanating from a rapidly collapsing bubble in high-pressure hydraulic fluids (such as hydraulic oil). Two events must occur to generate cavitation causing stress waves: 1) bubbles must form in the hydraulic fluid in a low-pressure environment, and 2) the bubbles must collapse rapidly in a high-pressure environment. Thus, cavitation may be prevented by eliminating the bubbles that lead to cavitation or by preventing the bubbles from collapsing rapidly, or by some combination thereof.

Separation of the pressure and return ports reduces system leakage from high to low pressure. A highly cyclic pressure regime may result in pulsing flows within these annular gaps. Separation of the porting reduces the opportunity to generate pulsing flows that may lead to cavitation. In addition, the separation reduces leakage volume and enhances efficiency. Separation of the pressure and return ports may be achieved by re-locating the pressure porting axially along the valve to the top and bottom of the cylinder chamber and maintaining the return porting towards the center of the cylinder assembly, at the other end of each chamber.

Return port location and geometry strongly influences cavitation potential. Correct selection of port sizing and orientation of the return flow path may reduce cavitation potential significantly.

The central spool return porting tends to be long with respect to the spool diameter. High frequency flow switching and dynamic vibrator loading, from the work or implement the linear vibrator is mobilizing, may result in very high return cylinder cavity pressures at the moment the return valve opens. High pressures within the return cylinder cavity and low return spool porting results in immediate, high pressure pulses and flow rates within the partially open valve. Such high-pressure pulses can result in stress wave propagation and reflection within the central, long valve port. Stress wave reflection and superposition at the valve ends can develop high, rapidly changing pressures with the consequence of high cavitation potential and damage. Such stress waves are worsened by axial separation of the return ports, which may be desirable in order to maintain port location on either side of the piston or cylinder shoulder. Separation of the return ports results in two locations of stress pulses which are separated in time by the period of vibration.

Further, the return flow possesses mass; and thus, momentum when flowing out of the valve. As the lower port closes, the momentum of the flow column away from the lower valve generates a low pressure or vacuum condition that is more susceptible to bubble formation. With the onset of the upper return valve opening under high pressure, the resulting high-pressure stress wave and superposition at the lower valve plug results in bubble collapse and higher cavitation power and damage.

Clustering the return ports within the same region and angling the ports to a common target within the spool central return port results in a reduction of the flow momentum and a resulting reduction in vacuum or low-pressure events. The subsequent opening of the upper return valve, which occurs as soon as the lower return valve closes, feeds fluid medium (hydraulic oil) immediately into the potentially low-pressure region.

Introduction of a spool end plug, featuring a bullnose and/or porting with a plethora of baffles will dissipate any stress waves traveling within the valve central return port.

These and other features of the present disclosure will become more fully apparent from the following description, or may be learned by the practice of the invention as set forth hereinafter.

REFERENCE NUMERALS

DETAILED DESCRIPTION

The exemplary embodiments of the present disclosure will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. It will be readily understood that the components, and their equivalents, of the present invention, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the exemplary embodiments, as represented in the Figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of exemplary embodiments of the invention.

In this application, the phrases “connected to”, “coupled to”, and “in communication with” refer to any form of interaction between two or more entities, including but not limited to mechanical, capillary, electrical, magnetic, electromagnetic, pneumatic, hydraulic, fluidic, and thermal interactions.

The phrases “attached to”, “secured to”, and “mounted to” refer to a form of mechanical coupling that restricts relative translation or rotation between the attached, secured, or mounted objects, respectively. The phrase “slidably attached to” refer to a form of mechanical coupling that permits relative translation, respectively, while restricting other relative motions. The phrase “attached directly to” refers to a form of securement in which the secured items are in direct contact and retained in that state of securement.

The term “abutting” refers to items that are in direct physical contact with each other, although the items may not be attached together. The term “grip” refers to items that are in direct physical contact with one of the items firmly holding the other. The term “integrally formed” refers to a body that is manufactured as a single piece, without requiring the assembly of constituent elements. Multiple elements may be integrally formed with each other, when attached directly to each other from a single work piece. Thus, elements that are “coupled to” each other may be formed together as a single piece.

FIG.1depicts an exemplary embodiment of a linear actuator system10having spool valve and piston geometry designed to reduce cavitation effects within the system10. The linear actuator system10comprises a spool12, a piston14, a cylinder16having an upper cylinder member18and a lower cylinder member20, a spool bulkhead22, and a base plug member24. The spool12is rotated (as shown by Arrow R) by an external source (not shown, but known by those skilled in the art) mounted to a supporting housing (not shown) or dominant mass (such as backing mass26). In this example, the piston14is fixedly connected to the backing mass26, via a piston anchorage28(a threaded or any other suitable connection). The backing mass26acts as a reaction mass against which the linear actuator10will pull, as for every action there is an equal and opposite reaction. The spool12rotates freely within the piston14with a narrow annular gap30(spacing of the gap30is not shown for overall clarity due to relative dimensions) between the two. Such narrow gap30effects a seal whose efficiency is based upon the length and width of the annular area or space. Piston14also has a shoulder32extending outward from the body34of the piston14.

It should be understood that in an alternative exemplary embodiment, the cylinder16may have a shoulder32similar to, and in lieu of, the shoulder32connected to and extending from the piston14as depicted in the drawings.

Although the linear actuator system10is described herein such that the system10has a longitudinal axis that extends vertically, it should be understood that the linear actuator system10need not necessarily operate in a vertical disposition. However, to simplify this disclosure a vertical disposition is described and terms such as “upper”, “lower”, “upward”, and “downward” are used to facilitate understanding the invention, but may not otherwise technically be accurate if the linear actuator system10were not oriented vertically. Hence, the use of such directional terms in the claims should not be limited to a vertical disposition, but should be interpreted as if the system10were oriented vertically.

The cylinder16slidably engages both the body34of piston14and the shoulder32. The upper cylinder member18has an enclosed end36and a closing end38, wherein the upper cylinder member18and its enclosed end36, together with the body34of piston14and its shoulder32forms an upper chamber40having an expandable/contractable volume. The closing end38of upper cylinder member18is attached fixedly to the lower cylinder member20, via a cylinder coupling42(a threaded or any other suitable connection). The upper cylinder member18and connected lower cylinder member20, together with the body34of piston14and its shoulder32forms a lower chamber44having an expandable/contractable volume. Lower cylinder member20extends below the piston14and may be connected fixedly to some implement (not shown, but working implements such as clamps, piles, drill bits, chisels and the like are known to those skilled in the art) via an implement coupling46(a threaded or any other suitable connection).

The spool12is ported (referred to herein as spool pressure port48) to permit a high-pres sure fluid medium50to flow from the rotatable spool12through spool pressure aperture52and communicating through the piston14via piston pressure aperture54, into the upper chamber40(as depicted by directional flow indicator arrows define fluidic communication between the referenced passages and such directional arrows are not numbered so to differentiate non-flow and lead-line arrows). It is to be noted, the spool pressure port48is enclosed within the body of the spool12, via rifle bore or similar method, and is not an annular passageway formed by a groove or other means between the outer diameter of the spool12and the inner diameter of the piston14. Simultaneously, lower chamber44communicates through piston return aperture(s)56and spool return aperture(s)58to release low-pressure fluid medium50from within lower chamber44into the spool central return port60and back to the power medium source (not shown, but known to those experienced in the art) and sometimes referred to herein as the fluid-pressurizing source. The rotation of spool12is timed or synchronized to open and close the spool pressure aperture52and piston pressure aperture54and the spool return aperture(s)58and piston return aperture(s)56, respectively, such that the introduction of pressurized fluid medium50into the upper chamber40is simultaneous, or nearly so, with the evacuation of the lower chamber44. The pressurized flow of the fluid medium50into upper chamber40taken together with the evacuation of fluid medium50from lower chamber44, forces the cylinder16upward and thus spool bulkhead22upward in the direction depicted by Arrow D.

The spool return aperture(s)58and piston return aperture(s)56are located, positioned through their respective spool12and piston14member bodies such that the discharge into the central return port60of the spool12within 1.5 times the internal diameter of the central spool return port60centered on the midpoint62of the shoulder32. Further, spool return aperture(s)58and piston return aperture(s)56are angled within the respective spool12and piston14member bodies such that the discharge is directed towards the central spool return port60and the midpoint62of the shoulder32.

For purposes of this disclosure, the term “midpoint” is a small region in the near vicinity to where the center-transverse plane of the shoulder32intersects the longitudinal axis of the linear actuator system10(the spool12has the same longitudinal axis). Also, it should be understood that the cylinder16may have a shoulder32similar to, and in lieu of, the shoulder32connected to and extending from the piston14as depicted in the drawings. With a shoulder32extending from the cylinder16and the piston14having an enclosing end and a closing end, the functionality of the linear actuator system10would be the same. Certainly, those skilled in the art, armed with this disclosure, will know how to fashion a shoulder32extending inwardly from the body of the cylinder16, separating upper chamber40and lower chamber44, and together with the piston14having an enclosing end and a closing end would define the expandable/contractable upper chamber40and lower chamber44.

The base of the spool12is fitted with a base plug member24fixedly attached to the spool12at plug anchorage64by threaded or any other suitable connection. In another exemplary embodiment, the base plug member24may be fixedly attached to the spool bulkhead22or the piston14.

The spool base plug member24may feature a bull-nose tip66and one or more small diameter baffles68to permit the passage of fluid medium50pressure waves and/or flow (as a result of fluid medium50compression within the interior of the body of the base plug member24) to enter into a series of expanded cavities70within the body of the base plug member24. The effect of the baffles68and cavities70is to dissipate both the stress waves and flow, thereby reducing or eliminating cavitation.

FIG.2depicts the exemplary embodiment of the linear actuator system10when the rotatably attached spool12has rotated one valve progression (for example, 60 degrees clockwise in a three-ported valve configuration) positioning the spool12to translate the cylinder16and the upper cylinder member18as connected to the lower cylinder member20downwards as depicted by directional Arrow D. The vertical section is cut along the central axis but rotated 60 degrees clockwise (see Arrow R) to depict the valve communication for a downward translation.

As depicted in this embodiment, the piston14is connected fixedly to the backing mass26, via piston anchorage28. Again, the backing mass26acts as a reaction mass against which the linear actuator10will push, as for every action there is an equal and opposite reaction. The spool12rotates freely within the piston14with the narrow annular gap30between the two. As discussed above regardingFIG.1, the narrow gap30effects a seal whose efficiency is based upon the length of and width of the annular area or space.

Cylinder16is connected slidably to the piston14. The upper cylinder member18has an enclosed end36and a closing end38, wherein the upper cylinder member18and its enclosed end36, together with the body34of piston14and its shoulder32forms an upper chamber40having an expandable/contractable volume. The closing end38of upper cylinder member18is attached fixedly to the lower cylinder member20, via a cylinder coupling42. The upper cylinder member18and connected lower cylinder member20, together with the body34of piston14and its shoulder32forms a lower chamber44having an expandable/contractable volume. Lower cylinder member20extends below the piston14and may be connected fixedly to some implement (not shown, but working implements such as clamps, piles, drill bits, chisels and the like are known to those skilled in the art) via the implement coupling46.

The spool12is ported, having another spool pressure port48positioned 60 degrees clockwise from spool pressure port48shown inFIG.1, to permit a high-pressure fluid medium50to flow from the rotatable spool12through spool pressure aperture52and communicating through the piston14via piston pressure aperture54, into the lower chamber44(as depicted by directional flow indicator arrows not numbered so to differentiate non-flow and lead-line arrows). It is to be noted, the spool pressure port48is enclosed within the body of the spool12, via rifle bore or similar method, and is not an annular passageway formed by a groove or other means between the outer diameter of the spool12and the inner diameter of the piston14. Simultaneously, upper chamber40communicates through piston return aperture(s)56and spool return aperture(s)58to release low-pressure fluid medium50from within upper chamber40into the spool central return port60and back to the power medium source (not shown, but known to those experienced in the art). The rotation of spool12is timed or synchronized to open and close the spool pressure aperture52and piston pressure aperture54and the spool return aperture(s)58and piston return aperture(s)56, respectively, such that the introduction of pressurized fluid medium50into the lower chamber44is simultaneous, or nearly so, with the evacuation of the upper chamber44. The pressurized flow of the fluid medium50into lower chamber44taken together with the evacuation of fluid medium50from upper chamber40, forces the cylinder16downward and thus spool bulkhead22downward in the direction depicted by Arrow D.

The spool return aperture(s)58and piston return aperture(s)56are located, positioned through their respective spool12and piston14member bodies such that the discharge into the central return port60of the spool12within 1.5 times the internal diameter of the central spool return port60centered on the midpoint62of the shoulder32. Further, spool return aperture(s)58and piston return aperture(s)56are angled within the respective spool12and piston14member bodies such that the discharge is directed towards the central spool return port60and the midpoint62of the shoulder32.

As discussed above regarding theFIG.1, the base of the spool12remains unchanged. It is fitted with a base plug member24fixedly attached to the spool12at plug anchorage64by threaded or any other suitable connection. In another exemplary embodiment, the base plug member24may be fixedly attached to the spool bulkhead22or the piston14. The spool base plug member24may feature a bull-nose tip66and one or more small diameter baffles68to permit the passage of fluid medium50pressure waves and/or flow (as a result of fluid medium50compression within the interior of the body of the base plug member24) to enter into a series of expanded cavities70within the body of the base plug member24. The effect of the baffles68and cavities70is to dissipate both the stress waves and flow, thereby reducing or eliminating cavitation.

FIG.3depicts a horizontal plane cross-sectional view along line A-A ofFIG.1of the exemplary linear actuator system10having a three-ported valve configuration. Line A-A passes through the upper chamber40when the spool12is in the position depicted. The configuration of this exemplary embodiment demonstrates the geometry of the spool valve12and piston14when spool pressure aperture52and piston pressure aperture54have been rotated into position for maximum communication. The spool12may rotate into the position shown which depicts full synchronization of the rotatable spool12and the fixed piston14. The spool pressure port48is shown communicating pressurized medium flow50from the source to the upper chamber40of the linear actuator10to pressurize and enlarge the volume of the upper chamber40.

It should be understood that the linear actuator system10of the present invention may have other configurations without departing from the spirit of the invention. For example, two-ported, four-ported, up to n-ported valve configurations (where n is factor of 360) are possible depending on the size of the linear actuator system10and its component spool12, piston14and cylinder16parts. Those skilled in the art, armed with this disclosure will readily understand how to make and use each multi-port configuration of the linear actuator system10depicted and/or described herein. Also, although for the purposes of this disclosure the exemplary embodiment depicted has the piston14attached fixedly to the backing mass26, it should be understood that with only slight modification (easily performed by those skilled in the art armed with this disclosure) another exemplary embodiment may have the cylinder16attached fixedly to the backing mass26and any implement being connected to a slidably movable piston14disposed within the cylinder16.

In the exemplary embodiment of the three-ported valve configuration depicted inFIG.3, spool pressure ports48are disposed at 60-degree intervals clockwise from the spool pressure port48depicted inFIG.1. Every other spool pressure port48is shown to communicated pressurized medium50flow from the source into the upper chamber40of the linear actuator10during theFIG.3depicted cycle. The cylinder16is translated upward (see Arrow D) when the spool12is so positioned. In this three-ported valve configuration, the linear actuator10will repeat a complete upward and downward cycle three times with each full revolution of the spool12.

By rotating the spool1260 degrees clockwise into the next-cycle configuration, the spool pressure ports48will communicate pressurized medium50flow from the source to the lower chamber44of the linear actuator during the next cycle. The cylinder16is translated downward (see Arrow D inFIG.2) when the spool12is so positioned.

FIG.4depicts a horizontal plane cross-sectional view along line B-B ofFIGS.1and2of the exemplary linear actuator system10at the center of the shoulder32when the spool12is in the position depicted in bothFIGS.1and2. Those skilled in the art will appreciate that the exemplary embodiment shows 1) an upward cycle configuration inFIG.1when the spool pressure ports48are positioned for activating the upper chamber40during the upward translation (see Arrow D inFIG.1) of the cylinder16, and 2) a downward cycle configuration inFIG.2when the spool pressure ports48are positioned for activating the lower chamber44during the downward translation (see Arrow D inFIG.2) of the cylinder16.

FIG.5depicts a transverse along non-linear line C-C ofFIG.1of the exemplary linear actuator10having a three-ported valve configuration. Line C-C passes through the lower chamber44when the spool12is in the position depicted. The configuration of this exemplary embodiment demonstrates the geometry of the spool valve12and piston14when spool return aperture(s)58and piston return aperture(s)56have been rotated into position for maximum evacuation from lower chamber44. It should be noted that non-linear line C-C passes at an angle through spool return aperture58and piston return aperture56so to depict the angled passageway through which low-pressure fluid medium50flows from the lower chamber into the spool central return port60. The cylinder16is translated upward (see Arrow D ofFIG.1) when the spool12is so positioned.

For exemplary methods or processes of the invention, the sequence and/or arrangement of steps described herein are illustrative and not restrictive. Accordingly, although steps of various processes or methods may be shown and described as being in a sequence or temporal arrangement, the steps of any such processes or methods are not limited to being carried out in any specific sequence or arrangement, absent an indication otherwise. Indeed, the steps in such processes or methods generally may be carried out in different sequences and arrangements while still falling within the scope of the present invention.

Exemplary embodiments of the present invention are described above. No element, act, or instruction used in this description should be construed as important, necessary, critical, or essential to the invention unless explicitly described as such. Although only a few of the exemplary embodiments have been described in detail herein, those skilled in the art will readily appreciate that many modifications are possible in these exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the appended claims.

In the claims, any means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. Unless the exact language “means for” (performing a particular function or step) is recited in the claims, a construction under Section 112 is not intended. Additionally, it is not intended that the scope of patent protection afforded the present invention be defined by reading into any claim a limitation found herein that does not explicitly appear in the claim itself.