Abstract:
A valve construction relies upon solenoid-driven axial elongation of an annular magnetostrictive core element for opening displacement of an elongate poppet-valve member that is carried within the annulus of the core element. A first stiffly compliant preload independently urges the poppet-valve member into its seated position of lock-up at valve closure, and a second stiffly compliant preload independently prestresses the annular magnetostrictive core element into a fixed referencing abutment with valve-body structure. The currently preferred material of the core is Terfenol-D, which offers a strong elongation response to inductively coupled excitation. The elongation response is sufficient to serve the purposes of (1) closing a pretravel clearance prior to a flange engagement with the poppet-valve member and (2) also, via the flange engagement, displacing the poppet-valve member out of its normal valve-closing engagement with the valve seat. In the preferred embodiments, inlet and outlet ports for the valve are centered at the respective axial ends of the valve-body structure.

Description:
RELATED CASE 
     This application is a continuation of original application Ser. No. 08/540,919, filed Oct. 11, 1995, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a valve construction wherein solenoid excitation of an elongate magnetostrictive core element is relied upon to actuate a valve for control of fluid flow, as for controlling the flow of a pressure fluid from an upstream source to an outlet for downstream storage or utilization at reduced pressure. 
     Pending application Ser. No. 309,776, filed Sep. 21, 1994 now U.S. Pat. No. 5,501,425 issued Mar. 26, 1996 describes several embodiments of magnetostrictive valves of the character indicated, with specific utility and application to spacecraft, wherein the valve is necessarily of normally closed variety and a very high seating force is desired, to provide positive sealing and very low leakage under lock-up (i.e. valve-closed) conditions. Pressurized propellant gas for maneuvering must be conserved at all costs, relying upon valves with superior (i.e., very low) leakage resistance under lock-up conditions, yet offering fast response to instant demand. Thus, shut-off, isolation, low friction, mechanical simplicity and small size are important considerations in a valve of the character indicated. A magnetically latching and magnetically actuated valve of the nature described in U.S. Pat. No. 3,814,376 or in pending application Ser. No. 08/184,484 now U.S. Pat. No. 5,375,811 issued Dec. 27, 1994 has properties approaching the desired low-leakage of a valve-closed condition, but the time constant for valve actuation (opening or closing) is greater than would be desired, and the seating force is less than desired. 
     The disclosure of said pending application Ser. No. 309,776 is hereby incorporated by reference, and it suffices here to note that all of the disclosed embodiments of said application relied upon a central cylindrical core element of magnetostrictive material, forming part of a toroidal path of magnetic flux, wherein the toroidal path surrounds an excitation winding. One axial end of the core element has reference to the valve housing, and the other axial end is poised to drive an actuating stem into abutment with and valve-opening displacement of a valve member which is otherwise spring-loaded into its closed relation of engagement with a valve seat. Disc washers or Belleville springs are utilized for axial-force preloading and to center component parts for minimum friction and/or mechanical hysteresis, but the constructions are more than is believed strictly necessary. Moreover, inlet and outlet parts serve valve-chamber regions at one axial end of magnetostrictive actuating system. 
     BRIEF STATEMENT OF THE INVENTION 
     It is an object of the invention to provide an improved valve construction of the character indicated. 
     A specific object is to provide a valve construction having superior lock-up properties of sealing against leakage of pressure fluid for the valve-closed condition. 
     Another specific object is to meet the above objects with a basically simple miniaturizable configuration, having application for control of propellant gas stored under high pressure for use in maneuvered orientation of a spacecraft. 
     A further specific object is to meet the above objects with a construction having a fast time constant of valve opening and closing, and exhibiting inherently little mechanical hysteresis, under a wide range of ambient temperature conditions and offering a fail safe condition of superior valve lock-up against leakage of pressure fluid. 
     It is a general object to meet the above objects with simpler construction offering economies of manufacture without sacrifice of performance capability. 
     The invention achieves these objects in a valve construction which relies upon solenoid-driven axial elongation of an annular magnetostrictive core element, for opening displacement of an elongate poppet-valve member that is carried within the annulus of the core element. A first stiffly compliant preload independently urges the poppet-valve member into its seated position of lock-up at valve closure, and a second stiffly compliant preload independently prestresses the annular magnetostrictive core element into a fixed referencing abutment with valve-body structure. The currently preferred material of the core is Terfenol-D, which offers a strong elongation response to inductively coupled excitation. The elongation response is sufficient to serve the purposes of (1) closing a pretravel clearance prior to a flange engagement with the poppet-valve member and (2) also, via the flange engagement, displacing the poppet-valve member out of its normal valve-closing engagement with the valve seat. In the preferred embodiments, inlet and outlet ports for the valve are centered at the respective axial ends of the valve-body structure. 
     In the present description, for convenience of reference, the central axis of the valve system will be sometimes referred to as &#34;horizontal&#34;, extending from a left or inlet-end port, to a right or outlet-end port. But it is to be understood that a &#34;horizontal&#34; orientation is no more significant than the &#34;vertical&#34; orientations shown for the embodiments of said pending application Ser. No. 309,776, in that valve operation is not in any sense dependent upon any relation to the instantaneous gravity vector. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred and illustrative embodiments of the invention will be described in detail, in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a view in longitudinal section of a first valve embodiment of the invention, shown for the closed condition of the valve; 
     FIG. 2 is a view as in FIG. 1 for an actuated condition of the valve, with schematic indication of the flow of electromagnetically induced excitation flux; 
     FIG. 3 is a view similar to FIG. 1, for a modified construction, shown for the closed condition of the valve; 
     FIG. 4 is a view as in FIG. 3 for an actuated condition of the valve of FIG. 3; 
     FIG. 5 is another view similar to FIG. 1, for another modification; and 
     FIG. 6 is a further view similar to FIG. 1, for a further modification. 
    
    
     DETAILED DESCRIPTION 
     Referring initially to the embodiment of FIGS. 1 and 2, the invention is shown to comprise a body 10, consisting of an upstream cup-shaped part 11 having a central inlet-port connection 12 to its closed left-end wall 13, and annular downstream parts 19, 21, 33, collectively marked 14, and having a central outlet-port connection 15 to a closed right-end wall 16. The body parts 11, 16, 19 and 21 are of ferromagnetic material, and the part 33 is an inner sleeve of a material which is not ferromagnetic. The part 19 is an outer sleeve or skirt portion of body 10 and has an inwardly flanged upstream end which telescopically laps the upstream body part 11; the body parts 11, 19 are shown connected by a circumferential weldment 17, the overlapping engagement being additionally sealed by an elastomeric O-ring 18. An inlet filter 12&#39; in port 12 assures that particles borne by inlet pressure-fluid flow will not impair valve operation. 
     More specifically, the outer sleeve or skirt part 19 of body part 14 features a counterbore for reception and location of a winding or solenoid coil 20. The inner sleeve 33 provides coaxial support of winding 20, and the downstream annulus 21 closes the counterbore for axial retention of winding 20. The downstream end-wall part 16 seats against the inner end of a counterbore in annulus 21 and is centrally formed at its upstream end with an annular valve-seat configuration, which surrounds a passage to outlet port 15 and which projects from an annular manifolding concavity. One or more radial grooves 25 communicate inlet-gas flow to the manifold 24. 
     It is important to the invention that the end-closure walls 13, 16 shall be securely connected to withstand internal axially compressional loading of valve parts yet to be described. This can be done by circumferentially welding the fit of parts 19, 21 to each other and by providing a circumferential weld 27 of end-wall part 16 to the annulus 21; however, in the preferred arrangement shown in FIGS. 1 and 2, parts 19, 21 have only an axially extending telescopic fit that is sealed by an elastomeric O-ring 26, and the material of inner sleeve is selected not only for its non-ferromagnetic properties, but also for its compatibility with the ferromagnetic material of axially adjacent parts 11, 21 for welding purposes. Suitably, the material of ferromagnetic body parts 11, 19, 21, 16 is magnetic-quality stainless steel, and the material of non-magnetic sleeve 33 is an austenitic stainless steel (such as 304L), circumferentially welded at both axial ends, as suggested by thickened lines of connection to parts 11 and 21 in FIGS. 1 and 2. After such welding of sleeve 33, a single continuous bore is defined and is preferably finish-ground after the described welding of sleeve 33 and prior to assembly of internal valve components (yet to be described) and of the downstream end-closure part 16. It will be understood that once these internal valve components have been assembled, and end-closure part 16 has been welded at 27 to annulus 21, the continuously finished bore within welded parts 11, 33, 21 establishes an axially direct continuous permanent interconnection of the end-closure walls at 13 and 16. 
     In accordance with a feature of the invention, a cylindrical annulus or core 30 of magnetostrictive material is retained, preferably with close clearance, within the continuous bore of parts 11, 33 and 21; and a stiffly compliant spring 31, seated within body part 11, applies prestressing compressional force, via a shouldered (and preferably ferromagnetic) plate 32, to the upstream end face of the magnetostrictive annulus 30. The fit of parts 30, 32 to the described continuous bore of parts 11, 33, 21 will be understood to be sufficiently loose, to allow for magnetostrictive elongation of part 30, pursuant to electrical excitation of coil 20. As best seen in FIG. 2, such excitation of coil 20 establishes toroidal circulation of magnetic flux, via inductive coupling to the magnetostrictive part 20 along an inner axial path leg a, with resultant path completion radially outward via a path leg b, an outer axial path leg c, and back to path leg a via a radially inward path leg d. 
     One or more longitudinal grooves 34 in the periphery of plate 32 and of core 20 align with the one or more radial grooves 25 of body-closure wall 16, to provide for pressure fluid (e.g. gas) communication from inlet port 12 to the manifold 24. 
     An elongate cylindrical poppet-valve member 35 has guided support for limited longitudinal displaceability from its normally closed downstream-end contact with the valve-seat formation 22. Preferably, this downstream end of the valve member is coated or otherwise finished with a closure pad or coating 30 of elastomeric material such as nylon or Teflon*. And valve member or poppet 35 features a radial-flange formation 37 at its upstream end for shouldered reception of stiffly compliant preloading force, shown to be provided by a coil spring 38 that is nested within the prestressing spring 31 and independently referenced to the body-closure wall 13. 
    
     The normally closed valve condition of FIG. 1 reveals, with some exaggeration, an axial clearance or pretravel allowance δ 1 , to assure the independent action of spring 38, for fail-safe closure of poppet end 36 against the annular rim of seat 22. This pretravel allowance must be overcome by magnetostrictive elongation of core element 30, in response to a sufficient electrical excitation of winding 20, before the magnetostrictive elongation can further be expected to lift the poppet-valve element 30 into a valve-opening axial clearance δ 2  from seat 22. Thus, the total elongation of element 30 is the sum of δ 1  and δ 2  ; but, for the indicated usage in spacecraft applications, the values of these axial clearances are indeed small, in view of flow rates of 0 to 12 mg/sec, for the case of Xenon as the pressure fluid. With proper choice of materials, the extent of pretravel clearance (i.e. thermal-stroke error) can be reduced to near-zero, in view of the fact that in use, the stem of the poppet-valve member 35 and the magnetostrictive core element 30 will be at essentially the same steady-state temperature. At present, a preference is stated for use of a magnetostrictive material known as Terfenol-D as the material of core element 30; this is a specially formulated alloy of terbium, dysprosium and iron, and it is commercially available from Etrema Products, Inc., of Ames, Iowa. Preferably, the material of poppet-valve member 35 has substantially the same temperature coefficient of expansion as the material of core element 30; and for the indicated use of Terfenol-D, the desired substantial match of thermal coefficients results from use of the titanium alloy Ti-6Al-4V as the material of valve member 35, thereby effectively neutralizing the effects of differential thermal expansion of parts 30/35, and reducing allowance for pre-travel δ 1  to near-zero. 
     As with ferromagnetic body parts 11, 14 (19, 21, 16), plate 32 is also suitably of magnetic-quality stainless steel. And the bore of plate 32 may have a coating of Teflon or other low-friction material for smooth axially slidable displaceability with respect to the upstream (i.e. flanged) end of poppet 30. Preferably also, winding 20 is itself a sub-assembly, pre-potted in suitable plastic and defining a solid cylindrical annulus, with precisely spaced end-wall surfaces, and with a bore having a closely supporting fit to the nonmagnetic sleeve 33. 
     The modification of FIGS. 3 and 4 will be seen to closely correspond with the embodiment of FIGS. 1 and 2, and, therefore, identical reference numbers have been used for both embodiments, as far as possible. The difference in FIGS. 3 and 4 is that the length of body part 19 has been slightly extended to provide a region Δ of axial-end overlap of core element 30 within the ferromagnetic body parts 11 and 19, in which case plate 32 need not be of magnetic-quality stainless steel, in that the toroidal path of magnetic flux, upon excitation of winding 20, can avoid reliance upon plate 32, as schematically indicated in FIG. 4. 
     In the description thus far, it will be appreciated that the reference to body parts 11 and 14, as being telescopically or otherwise fitted shapes, has been for convenience purposes, in that the main point is that the magnetostrictive core element 30 shall be the axially extending portion of the toroidal flux path established via the body parts, upon excitation of the winding 20 which is enclosed within the toroidal flux path. 
     For mechanical assembly purposes, the central axis of the upstream body part 11 is advisedly oriented vertically, so as to present an upwardly open skirt, for axial reception of the independent springs 31, 37 and for their coaxial location by radially spaced shoulders of the annularly grooved profile 40 of the inner wall of end closure 13. This upwardly open skirt may be a sub-assembly which includes the outer body part 19, permanently welded (at 41, FIG. 5); the axially limiting position of such a sub-assembly of parts 11 and 19 is best seen in FIG. 5, where the body part 19&#39; has a radially inward flange 39 for axially limiting abutment with the skirt of body member 11, prior to welding at 41. In this connection, part 19 may advisedly have been pre-assembled with winding 20, sleeve 33, and body-ring part 21, with permanently welded connection of parts 19 and 21 via sleeve 33, thus presenting a clean open cavity into which poppet 35 and its flange 37 can be inserted for its shoulder location of engagement to spring 38, and into which plate 32 can be inserted for its shoulder location of engagement to spring 31. At this point, the way is clear for insertion of core element 30 over the stem of poppet 35 and within the aligned bores of ring 21 and sleeve 33. All that remains is for the downstream end-closure body part 16 to be inserted into the counterbore 42 of ring 21 and for application of axially compressive force to the point of achieving a fully seated relation of part 16 at the bottom of counterbore 42, at which point, both of springs 31 and 38 will have been preloaded, and the weld 27 may be applied, to complete a permanent assembly of the valve. 
     FIG. 6 serves to illustrate that the non-magnetic sleeve 33 may be a separate plastic component; preferably, however, the potting in which winding is consolidated (as explained above) takes place within a cavity (not shown) having an inner cylindrical surface such that sleeve 33 is produced as an integral feature of the potted winding, with a precision bore that is capable of providing axially elongate, low-friction, cylindrical support of core element 30. Of course, the use of plastic as the material of sleeve 33 means that sleeve 33 in FIG. 6 cannot be relied upon as a means of connecting parts 19 and 21, under the prestressing and preload conditions expected of springs 31, 38; therefore in FIG. 6, the desired establishment of axially rigid connection of end-closure walls at 13 and 16 is via a circumferential weld 28 of the lapped fit of parts 19, 21 to each other. 
     FIG. 6 also serves to illustrate that the inlet and outlet ports for pressure-fluid flow controlled by the valve may both exist at a single axial end of the valve, thereby avoiding need for the grooves 25/34 of FIGS. 1 to 5. 
     Specifically, in FIG. 6, the end closure 16 is shown with an inlet passage 25&#39; having direct communication with the annular manifold 24 which surrounds the annular valve-seat formation 22. Structure, assembly and operation may otherwise be as described for FIG. 5 and the other embodiments. 
     The described constructions will be seen to meet all stated objects and to provide a simplified collocation of elemental parts which lend themselves to facile assembly and reliable performance. In particular, all necessary clearances and preloads are automatically achieved for the method of assembly which has been described, and no further adjustments are needed. It is particularly notable that the two independently operative springs are in nested radial clearance with each other; that they each derive compressive reference from the single end-closure wall 13; and that the other closure wall 16 of the body or housing 11, 14 provides reactive reference for the prestressed core element 30 and for the valve-seat formation 22, in the normally closed condition of the valve. When winding 20 is sufficiently excited, magnetostrictive elongation of core element 30 is a jacking action wherein core member 20 has axial-abutment reference to the said other closure wall 16; the jacking action opens the valve by axially &#34;lifting&#34; poppet 35 upon core member (20) engagement with the flanged end of the poppet, against the preloading force of spring 38.