Alternating Current Solenoids

Abstract

A solenoid construction for use as a flow control valve having a coil, and an armature in the form of a valve plunger which is disposed in a housing which forms a fluid barrier between the coil and plunger, and is formed of magnetic material to provide a flux path of low reluctance linking the coil with the immersed valve plunger.

Description

BACKGROUND

This invention relates to alternating current electromagnets useful in solenoid devices such as relays, actuators, and particularly in magnetic fluid control valves of the type used to control the flow of gases or liquids under pressure in a closed system.

In the design of solenoid fluid control valves it has been the practice to provide a cylindrical plunger guide or cup member of nonmagnetic material to serve as a housing for the movable valve plunger and a return biasing spring. The housing with appropriate gasketed assembly to the valve body, confines within the cup whatever fluid is controlled by the valve. Such constructions are often referred to as "wet armature" valves. The exciting coil is provided with a magnetic shell and cylindrical pole members, designed to conduct the flux to the vicinity of the plunger housing with a minimum of gaps or magnetic discontinuities, to thereby attain a relatively high magnetic efficiency. The coil is commonly assembled about the housing, such that when energized, the magnetic flux path is through the wall of the nonmagnetic housing and the plunger-armature. U.S. Pat. Nos. 2,627,544 and 2,936,790 illustrate typical examples of solenoid valves constructed as described.

Because of the nonmagnetic cup between the plunger and the pole members, a truly closed magnetic circuit is not possible of attainment. The wall thickness of the cup forms a gap across which the flux must pass twice, on entering and leaving the armature. To be capable of withstanding the fluid or hydraulic forces encountered, it is necessary that the plunger cup be of appreciable wall thickness, a typical value for a brass or bronze housing being 0.026 inch for a fluid pressure of 125 p.s.i. The wall thickness represents an equivalent gap of 0.052 inch in an otherwise closed magnetic circuit. The presence of such a substantial gap in a closed AC magnetic circuit has the two fold effect of causing sharp reductions in inductive reactance, and in total flux flowing in the system. Thus for a given applied voltage, a high current will flow in the solenoid, coupled with a material weakening in the mechanical pull force attained by the armature. A result of these combined effects is to cause electromagnets so constructed to operate at relatively high levels of input wattage, and to therefore require in the solenoid, a relatively large number of costly copper windings for a given value of mechanical force exerted by the armature. High input wattage and rapid temperature rise have commonly been accepted as unavoidable incidences of wet armature valve constructions heretofore available.

Past efforts to overcome those limitations have included the use of high-strength nonmagnetic materials such as 18-8 stainless steel for thinner housing wall constructions, and also at a considerable manufacturing cost, the use of immersed magnetic poles provided with annular shading rings. But these approaches yielded only slight improvements in magnetic efficiency.

THE PRESENT INVENTION

In accordance with this invention it has been found that in fluid control valves of the type described above, the cup or guide housing the armature may be constructed of thin ferromagnetic material such as A.I.S.I. type 430 stainless steel, chosen from the group known as "straight chrome ferritic." Using this type of material, armature housings can be constructed with thin wall sections of adequate strength to withstand the fluid pressures encountered in such valves. Moreover, the use of a magnetic material has the effect of essentially eliminating the magnetic gap invariably encountered in previous wet armature valves. As a result, there is obtained a large increase in total flux and in flux linking the armature, as well as in the value of inductive reactance of the solenoid. The consequent decrease in current value, input wattage, and temperature rise enable significant savings in the weight, size, and cost of the copper winding required for a given mechanical force exerted by the armature.

It is accordingly an important object of the present invention to provide for a fluid control valve of the immersed armature type, a solenoid construction having an essentially "gapless" or closed magnetic circuit with resulting improvement, at reduced cost, in electromagnetic efficiency and mechanical force attained by the armature, for a given electrical input.

Another object is to provide for a magnetic fluid valve of the above type, a construction wherein for a given fluid load on the armature, the required electrical power is reduced whereby the amount of copper in the solenoid winding can be greatly reduced.

A further object is to provide for a magnetic fluid valve of the above type, a solenoid and magnetic circuit construction of such new and novel character that the required electrical input power per unit of fluid pressure or fluid flow is decreased, whereby the heat dissipation and time rate of temperature rise of said solenoid is reduced over prior constructions.

Another object is to provide for a magnetic fluid valve of the immersed armature type, a solenoid and magnetic circuit of new and novel character enabling increased armature forces, and increased fluid loads, pressures, and flow rates, for a given value of electrical input power.

A still further object is to provide for a magnetic fluid control valve, an armature housing constructed of ferromagnetic material having the property of hysteresis, to coact with a phase splitting core of the type described in my copending application Ser. No. 783,035, filed Dec. 11, 1968, now U.S. Pat. No. 3,553,618. In this combination the phase-shifting effectiveness is further improved with resulting further improvement of the solenoid magnetic efficiency.

Another important object is to provide an electromagnetic construction of high efficiency for use in hermetically sealed devices commonly used in vacuum or explosionproof systems wherein complete isolation by an impermeable barrier is requisite between the electrical energizing and magnetically actuated elements of said devices.

An additional object is to provide a solenoid construction wherein a housing or guide for the armature is constructed of ferromagnetic material, whereby the distribution of magnetic flux in and around said armature is controlled to yield an improved force-versus-distance characteristic, to thereby increase the wide gap pull value attained by said solenoid.

Yet another object is the provision in a flow control valve, of an armature and a closely fitting magnetic housing which is characterized by a motion-inhibiting piston or dashpot effect, serving to reduce the tendency of the valve to produce hydraulic noise or " water hammer" effects.

The foregoing and other objects and advantages of the invention will become apparent from the following description, and the accompanying drawings of a preferred embodiment, in which:

FIG. 1 is a cross-sectional view of a fluid valve embodying a solenoid according to this invention; and,

FIG. 2 is a sectioned partial view showing an alternative solenoid construction according to my copending application Ser. No. 783,035 for Phase Splitting Core, in combination herewith.

FIG. 3 is an enlarged partially sectioned view of the assembly of the magnetic core of FIG. 2.

Wet armature valve constructions heretofore available were presumably based on the premise that the use of magnetic material as an armature-plunger housing would act adversely as a magnetic shunt, bypassing a large portion of the available flux, thus reducing the tractive force exerted by the plunger.

The basis of this invention is my discovery that a valve solenoid having an armature housing constructed of ferromagnetic material of relatively thin wall section, behaves in an unexpectedly opposite manner to that previously postulated. The pulling force per unit of input power is greatly in excess of the values obtained with the use of nonmagnetic material in said housing.

This apparently anomalous behavior is explained; first by the virtual elimination of the dual magnetic gaps, with a major increase in flux flowing in the magnetic circuit due to the decrease in the reluctance thereof; and secondly by the fact that pole-to-pole shunting of flux by the housing wall has a limited adverse effect because the thin ferromagnetic housing wall becomes saturated at relatively low values of flux. As a result of the above saturation effect, the balance of the available flux comprising the greater part thereof, therefore flows through the best alternate magnetic path which in the present case is represented by the plunger-armature, as will be hereafter described. It has been discovered that the relatively small loss of flux due to parallel shunting by the housing wall is more than compensated by the large increase in total magnetic circuit flux due to the above-mentioned elimination of the housing wall gaps. The resulting tradeoff yields a substantial net gain in armature force available per unit of electrical input power. I have observed gains in excess of 100 percent during tests of the present invention.

The combination of an armature and a closely fitted ferromagnetic housing yields a further benefit whereby the armature stroke vs. force characteristic is modified in a manner favoring the initial, or wide gap pull value, which I have found to be a desirable characteristic in fluid valve usage, and in some other applications. This effect is believed explainable as a modification of flux distribution in and around the armature by the close proximity of my ferromagnetic housing, with said flux distribution varying progressively as the armature moves from the initial or open gap position, to the sealed, or closed gap position.

It will be apparent to those skilled in the art that many changes may be made in the arrangement of parts and details of construction of the solenoid devices described herein without departing from the spirit of the invention. Moreover, it will be understood that the applications shown as applied to fluid control valves are by way of illustration only, and that the several advantages of the invention are applicable to other tractive solenoid devices such as relays and clutches, as well as to hermetically sealed and explosionproof magnetic devices.

Referring more particularly to the drawings wherein similar reference characters designate corresponding parts throughout the various views; FIG. 1 is a median sectional view of a solenoid flow control valve according to the present invention in which cylindrical armature 1, and bias spring 2, are enclosed by armature housing 3, said housing being constructed of ferromagnetic material, and so dimensioned as to permit free axially slidable motion therein by plunger-armature 1. Armature 1 is formed with a projecting valve stem portion 4, having at its lower end an integrally formed conical valve portion 5 designed to enter and seal fluid orifice 6 under the influence of bias spring 2, when the valve is deenergized or closed. Bias spring 2 is of the conical compression type having its large diameter upper end supported by annular shoulder portion 11 formed in housing member 3, and having its small diameter end engaged with valve stem 4 by snapring 7, or other suitable means. Compression spring 2 thus biases armature 1 in a downward direction such as to seal fluid orifice 6 when the valve is deenergized. When so biased the upper surface of armature 1 is separated from the inner abutting surface of magnetic cup 3, thus forming working gap 8 which allows upward motion of armature 1, when the solenoid is energized.

Valve body 9 is formed of plastic or metal, and is provided with inlet pipefitting 14, and outlet fitting 22, which are connected by integrally formed fluid passages with the appropriate sides of the valve means. Inlet 14 is provided with an annular recess 16, adapted to receive wire mesh inlet strainer 15 which serves to prevent fluid-borne particulate matter from entering the valve. Inlet 14 is connected by fluid duct 17 to annular fluid channel 18, whereby the incoming fluid is conducted to the pressure chamber formed by the inside of the conical portion 12 of plunger housing 3. The peripheral flange portion 13 of housing 3 is pressed into sealing contact with elastic sealing ring 20, by the downward force exerted on annular pressure plate 19, by a number of appropriately spaced assembly screws, not shown. Fluid seal ring 20, formed of an elastomer is seated in annular channel 21 formed in valve body 9. Elastic ring 20 thus forms a compressibly deformed seal which confines the pressurized incoming fluid to the inside of said conical pressure chamber.

Outlet fitting 22 is formed by a downward projecting portion of valve body 9, generally tubular in form, and positioned coaxial with armature plunger 1. Outlet fluid duct 23 extends upward to connect with fluid passage 24 which passes vertically through annular valve seat member 25. Valve member 25 is molded of elastomeric material and is dimensioned to fit snugly in annular recess 26 formed in valve body 9, coaxial with fluid duct 23, and forming the upper extremity thereof. Fluid orifice 6 forms the valve seat proper, being normally sealed by the engagement thereagainst of valve cone 5, when the solenoid is deenergized. Fluid passage 24 forms a flow limiting restriction, the diameter being appropriate to the fluid pressure, viscosity, and flow rate desired.

The magnetic solenoid is assembled over the cylinder cup portion of housing 3, coaxial therewith. The solenoid is comprised of copper winding 27, on insulating spool 28, and is connected to the external power source by terminals or leads 29. The winding encloses soft iron core piece 30, and is enclosed by mild steel magnetic outer shell 31, to which pole piece 30 is attached at top center 32. Magnetic shell 31 has in its lower surface a bore or hole dimensioned to fit snugly over the cylindrical cup portion of housing 3 which extends into winding spool 28 to abut the lower end of core piece 30, thus completing the magnetic circuit linking solenoid 27 in an effectively closed manner. A dimensional length of core 30 equal to 75 percent of the length of solenoid winding 27 has yielded good results in tests.

FIG. 1 depicts the valve in deenergized state, with armature 1 in the downward position thus forming axial gap 8 separating armature 1 from the diaphragm portion 33 of housing 3. Upon energization, the magnetomotive force deriving from the current flowing in solenoid 27 gives rise to a concentration of flux flowing axially in the thin cylindrical wall of housing 3, with a resulting saturation of the wall. The excess of available flux lines beyond the saturation level is thus diverted radially through the wall of housing 3, thence axially through armature 1, across gap 8 and through diaphragm 33 to core 30, thus developing a pulling force which raises armature 1, compressing spring 2, and opening passage 24 to allow the flow of fluid therethrough.

It can be noted that the upward travel of armature 1 causes working gap 8 to vanish, with the previous gap space then becoming occupied by the upper portion of armature 1, thus completing a low-reluctance link in the solenoid magnetic circuit, of relatively large cross section and low susceptibility to saturation. As a result there occurs a redistribution of flux whereby the greater part of the total flux will pass through armature 1, with a minor portion of the flux flowing in the wall of housing 3 due to its small cross secton. A preponderance of the available flux will thus flow in armature 1 under both the open gap and closed gap conditions.

It is therefore postulated that the housing wall operates in two differing and sequential magnetic states, varied by the motion or position of armature 1. The housing wall becomes saturated by the high inrush current at energization, followed by a transition into a less saturated state as armature 1 reaches the full stroke or zero gap position, with coil current dropping to the lower steady-state value. Both states result in the transfer of major values of flux into and through armature 1, thereby causing said armature to develop useful values of mechanical pulling force.

The arrangement of armature 1 with a closely fitted housing 3, as disclosed in FIG. 1 provides further functional benefits resulting from an inherent dashpot or fluid damping effect. Said damping effect serves to reduce the tendency of an AC solenoid to produce intermittent pull forces and buzzing sounds, when phase-splitting means are not employed, as in FIG. 1 where core piece 30 is of the simple cylindrical type. The diametral clearance between armature 1 and housing 3 may be varied to control the damping and rate of movement of armature 1, as the controlled fluid enters and leaves gap area 8. The force and rate of bias spring 2 becomes an important design factor, since spring force together with the above armature diametral clearance, are basic in determining the rate at which armature 1 moves downward after deenergization of solenoid 27. The above damping effect may be further modified for fluids of varying viscosity by providing an axially aligned fluid passage through armature 1, or by providing axially aligned leakage grooves in the periphery of said armature. The fluid damping serves beneficially to reduce the tendency of the valve to produce hydraulic-hammer and other fluid surge or transient effects arising from rapid armature motion.

FIG. 2 depicts a solenoid construction in which a phase splitting core of a self-shading type described in my copending patent application Ser. No. 783,035 is used in lieu of the plain cylindrical core 30 of FIG. 1, yielding a further major improvement in magnetic efficiency and pull force, over the values obtainable with said cylindrical iron core. The solenoid construction of FIG. 2 is directly usable with the valve construction of FIG. 1, the related valve description thus being applicable to FIG. 2.

The two-piece annular core 34 and 35 makes use of the discovered fact that hysteresis and eddy currents in flux carrying core members may be economically and efficiently used to obtain phase retardation and resultant phase splitting in AC devices in lieu of shading rings previously used for that purpose. The core assembly including soft iron outer sleeve 34, and mild steel inner cylindrical member 35, is shown in section in FIG. 2, and also in an enlarged partially sectioned view in FIG. 3 which discloses the annular and peripheral gap means which contribute to the phase splitting function and high magnetic efficiency of said core assembly.

Outer cylindrical core member 34 is the leading phase flux path, being designed to introduce a minimum of phase retardation of the flux wave flowing therein. To that end it is constructed of a low hysteresis material such as silicon steel of annealed ingot iron. It is further provided with a longitudinal slot 36, which extends the full length of said sleeve thus interrupting the phase retarding circumferential circulating current which would otherwise flow therein. The flux wave flowing in sleeve 34 is thus substantially in phase with the alternating magnetomotive force established by the current flowing in exciting coil 27.

Inner cylindrical core member 35 is the lagging phase or retardant flux path, being designed to obtain a substantial value of flux wave phase retardation by the combined effects of hysteresis and internal circulating currents. Member 35 is constructed of a milk steel such as cold-rolled A.I.S.I. C-1117 which is characterized by a moderate degree of inherent hysteresis or remanence, such as to cause an effective phase retardation of the flux wave flowing therethrough. Moreover, member 35 is designed as an unbroken cylindrical body which is subject to the flow of circular induced eddy currents throughout its length. Said eddy currents serve to oppose changes in the instantaneous flux value flowing in said member, thus retarding the phase of the resultant flux wave, in addition to the hysteretic phase retardation aforesaid. The resultant angular phase shift is thus a composite value which may be considered as the vector sum of the two phase lag angles obtained separately from the retarding effects of magnetic hysteresis and eddy current flow.

An annular gap 37 provides for magnetic separation of the two core members 34 and 35, to avoid interphase shunting of flux components due to the proximity of the two members. Gap 37 is indicated in FIG. 3, produced by forming member 35 with a step or shoulder 38 whereby the lower portion of core 35 is slightly smaller in diameter than the inside of sleeve 34. A satisfactory dimension for said gap has been found to be provided by forming shoulder 38 with a radial dimension equal to 21/2 percent of the outside diameter of sleeve 34. The axial length of gap 37 may be between 70 and 90 percent of the length of sleeve member 34. While the annular gap space 37 is shown in the drawing as an airgap, it will be apparent to those skilled in the art that the gap space may alternatively be filled with an appropriate nonmagnetic material such as plastic or cement, to maintain concentricity and secure adhesion.

In the absence of mathematical expressions reliable applicable to the present invention, an experimental test program was undertaken to provide a basis for mathematical definition, and to establish optimum or near-optimum dimensions, materials, and size ratios for a water valve application similar to that shown in FIGS. 1 and 2. A flow rate of 1.0 g.p.m. was chosen, with operation on 115 v. 60-cycle AC with a water gauge pressure of 60 p.s.i. The diameter of fluid passage 24 was established as 0.072 inch, and an armature travel of 0.063 inch was chosen, thus setting the axial dimension of working gap 8 at 0.063 inch. An armature open-gap (inrush) pull requirement of 10 oz. was established to allow a reserve over the maximum load values to be encountered.

The following dimensions and size ratios were established:

Coil spool 28, length o.a., 0.820 inch, winding length 0.760 inch.

Coil 27 3,900 turns, No. 39 or 40 B&S ga. copper, weight 8 or 11 gm.

Core 30, 0.600 inch long, 0.437 inch dia., magnetic ingot iron.

Core sleeve 34, 0.600 inch long, 0.437 dia, 0.062 wall, ingot iron.

Core 35, 0.600 inch long, dias. 0.296 inch & 0.316 inch, C-1117 c.r.s.

Housing 3, cup 0.437 inch o.d., 0.405 inch i.d., wall 0.016 inch, 430 S.S.

Armature 1, dia. 0.395 inch to 0.400 inch, plunger length 0.325 inch, 430 S.S.

Magnetic shell 31, 12 ga. .times. 0.812 inch w. 1,012 h.r.s. Butt at top center.

For evaluation purposes a numerical performance factor of merit "P " was devised as an expression of open gap pull in ounces attainable, per watt of steady state electrical input. For the present examples "P" becomes 10 (oz.) divided by the measured input watts (w.) for the closed gap steady-state condition. A commercial prior art water valve of similar capacity was included in the test series as a comparison base, with the supply voltage adjusted to obtain 10 Oz. of armature pull at inrush. At that voltage it consumed 16 watts, steady state, for a value P=0.625.

Values obtained for the present invention were:

Assembly of FIG. 2 with nonmagnetic housing 3, w.=7.80, P=1.28 Assembly of FIG. 1, with magnetic housing 3, w.=5.85, P=1.71 Assembly of FIG. 2, with magnetic housing 3, w.=3.10, P=3.22

in the combination construction of FIG. 2, I have observed that the use of hysteretic material in the construction of housing 3 adds further to the pull values obtainable. This result presumably arises from a cooperative phase shifting effect whereby the hysteretic property of housing 3 adds to the angular phase shift produced by core assembly 34, and 35.

The use in this invention of hysteretic materials has been found not to cause undue difficulties with "sticking armature" due to remanence or residual flux. Although annealing of outer shell 31 after forming is desirable, attention to the force and rate of spring 2, has provided freedom from residual flux problems. It thus appears that housing 3 serves beneficially as a saturable magnetic shunt, bypassing around armature 1 a portion of the residual flux originating in parts such as core 30, shell 31, or core 35. The bypassing of residual flux is effective up to the saturation level of the cylindrical wall of housing 3, thus representing a further benefit accruing to the present invention.

From the foregoing it will be apparent that I have provided novel, simple, and economical means of attaining the objects and advantages recited.

Claims

Having described my invention, I claim:

1. In a magnetomotive device having a coil with a core and an armature arranged to form a magnetic circuit, a housing for said armature, said core including a composite flux conducting element comprising a plurality of ferromagnetic portions defining spaced magnetically parallel flux paths, said portions incorporating relative variations in at least one of the electromagnetic properties thereof including magnetic hysteresis and eddy current susceptibility, said portions being in fixed relative position and being magnetically separated over a substantial portion of their common length by substantially nonmagnetic gap means extending therebetween.

2. A magnetomotive device as set forth in claim 1 in which said housing is a fluid confining barrier interposed between said armature and said coil.

3. In a magnetomotive device having a coil with a core and an armature arranged to form a flux path, a substantially closed magnetic circuit including a tubular housing for said armature, said housing being of unitary construction having one and closed by a transverse diaphragm portion, said housing including said diaphragm portion being formed throughout of ferromagnetic material providing an uninterrupted flux path throughout the tubular wall and diaphragm portions thereof and in which at least the tubular wall portion thereof is substantially the same thickness throughout its entire length.

4. A magnetomotive device as set in claim 3 in which said housing is a fluid confining barrier interposed between said armature and said coil.

5. A magnetomotive device as set forth in claim 3 in which said housing is arranged as a fluid confining element of an associated fluid control valve, said armature being immersed in the fluid controlled by said valve.

6. In a magnetomotive device having a coil with a core and an armature arranged to form a magnetic circuit, a housing for said armature, said core including a composite flux conducting element comprising a plurality of ferromagnetic portions defining spaced magnetically parallel flux paths, said portions incorporating relative variations in at least one of the electromagnetic properties thereof including magnetic hysteresis and eddy-current susceptibility, said portions being magnetically separated over a substantial portion of their common length by substantially nonmagnetic gap means extending therebetween, said portions including an inner cylindrical member and an outer sleeve member arranged in an annular coaxial manner, said sleeve member having its circumferential electrical continuity substantially interrupted.

7. In a magnetomotive device having a coil with a core and an armature arranged to form a magnetic circuit, a housing for said armature arranged as a fluid confining element of an associated fluid control valve, said core including a composite flux conducting element comprising a plurality of ferromagnetic portions defining spaced magnetically parallel flux paths, said portions incorporating relative variations in at least one of the electromagnetic properties thereof including magnetic hysteresis and eddy current susceptibility, said portions being magnetically separated over a substantial portion of their common length by substantially nonmagnetic gap means extending therebetween, said armature being immersed in the fluid controlled by said valve.

8. In a magnetomotive device having a coil with a core and an armature arranged to form a magnetic circuit, a housing for said armature, said core including a composite flux conducting element comprising a plurality of ferromagnetic portions defining spaced magnetically parallel flux paths, said portions incorporating relative variations in at least one of the electromagnetic properties thereof including magnetic hysteresis and eddy current susceptibility, said portions being magnetically separated over a substantial portion of their common length by substantially nonmagnetic gap means extending therebetween, said housing being of tubular form and of integral construction having one end closed by a transverse diaphragm portion, said housing being formed of ferromagnetic material of substantially uniform thickness, said core and said armature forming a substantially closed flux path including said housing.

9. In a magnetic fluid valve having a coil with a core and an armature arranged to form a flux path, a substantially closed magnetic circuit including a tubular housing for said armature, said housing being of integral construction having one end closed by a transverse diaphragm portion, said housing being formed of ferromagnetic material of substantially uniform thickness, said armature being disposed within said housing for operative movement and having fluid valving means in operative association therewith, said core including a composite flux conducting element comprising a plurality of ferromagnetic portions defining spaced magnetically parallel flux paths, said portions incorporating relative variations in at least one of the magnetic properties thereof including magnetic hysteresis and eddy current susceptibility, said portions being magnetically separated over a substantial portion of their common length by substantially nonmagnetic gap means extending therebetween.