United States Patent 3735301

A solenoid construction for use as a power relay in which a phase-splitting magnetic core element in combination with a bi-stable snap-switch element enables a compact relay construction yielding a forward power control ratio of 4,800 : 1, or an equivalent power gain in excess of 36 decibels, without amplification.

Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
335/99, 335/297
International Classes:
H01H50/20; (IPC1-7): H01F7/10
Field of Search:
335/244,297,243,99,101,100,102,255,131,258 310
View Patent Images:
US Patent References:
3281741Magnetic leak relay1966-10-25Beliveau
3249823Electromagnetic actuator1966-05-03Beardow
3210616Solenoid mechanisms1965-10-05Severn
2458957Temperature compensator for electrical regulators1949-01-11Neild

Primary Examiner:
Broome, Harold
Having described my invention, I claim

1. In a magnetic relay the combination including switch means, adjacent solenoid means having an armature, a core, a coil, and a unitary ferrous structure exterior of said coil forming with said armature and said core a magnetic circuit, said core being of substantially cylindrical form, said external ferrous structure comprising a strip of ferrous material forming a closed loop of substantially quadrate form having the strip-ends abuttingly disposed intermediate one side of said loop, the axis of said core substantially corresponding with said abutment, and being substantially perpendicular thereto, said core being disposed inwardly of said external ferrous structure.

2. In a magnetic relay the combination including switch means, adjacent solenoid means having a coil, an axially disposed core substantially within said coil, an armature disposed as a plunger for axial operative motion, and a unitary ferrous structure exterior of said coil forming with said core and said armature a substantially closed loop magnetic circuit linking said coil, said exterior structure forming a plurality of magnetically continuous divisional flux paths therethrough disposed about said coil in substantial symmetry and being characterized by substantially co-equal magnetic cross-section.

3. A magnetic relay as set forth in claim 2 wherein said core includes a composite flux conducting element comprising a plurality of ferro-magnetic portions defining spaced magnetically parallel flux paths, said portions being relatively disparate in the electro-magnetic properties thereof including magnetic hysteresis and eddy-current susceptibility, said portions being magnetically separated over a substantial portion of their common length by non-magnetic gap means extending therebetween.

4. A magnetic relay as set forth in claim 2 wherein said switch means is of the enclosed bi-stable snap-acting type having outwardly spring-biased plunger actuating means extending outwardly thereof, and means including screw means joining said armature with said switch plunger actuating means in threadedly adjustable operative association.

5. A magnetic relay as set forth in claim 2 wherein said armature is of substantially cylindrical form arranged for axial operative motion substantially within said coil and said exterior ferrous structure, means including screw means joining said armature with said switch means in threadedly adjustable operative association, a portion of said screw means extending outwardly of said ferrous structure whereby said operative association may be adjusted externally of said solenoid means.

6. A magnetic relay as set forth in claim 2 wherein said armature and said core are of substantially cylindrical form disposed in an axially co-extensive manner, said armature being arranged for axial operative motion, cover means enclosing at least one side of said solenoid means, said core defining the energized limit of motion of said armature, a portion of said cover means providing stop means defining the de-energized limit of motion of said armature.


This invention relates to improvements in alternating current electromagnets useful in solenoid devices such as valves, clutches, actuators, and particularly in power relays used to control substantial electrical loads. While useful in compact light-duty general purpose relays, it is particularly applicable to power circuit relays whereby loads of hundreds or thousands of watts are controlled by actuating signals of relatively low power, and for convenience is herein shown and described as applied thereto.

This application contains subject matter in common with my copending application No. 783,035 for Phase Splitting Core for electro-magnetic Devices, filed Dec. 11, 1968. (To issue Jan. 5, 1971, U.S. Pat. No. 3,553,618.)

Power relays of the present type have evolved over many years within a common body of prior art, and are available from many sources in relatively standardized forms. Structures, mountings, terminals, contact arrangements, solenoid designs and other principal elements are similar. The functional parameters including contact current rating, response time, solenoid input wattage, temperature rise and service life are quite uniform for a given load rating. Switching contacts have been found to require substantial mechanical forces thus requiring actuating solenoids of relatively high power. It is common practice to provide from 8.0 to 16.0 ounces of solenoid tractive force per switch pole, in relays used in load circuits involving 20 to 30 amperes at 200 to 500 volts.

Prior art solenoids for the present use almost invariably utilize laminated magnetic cores, provided with copper shading rings to attain phase-splitting necessary to overcome the weak tractive forces and objectionable buzz which is otherwise characteristic of single phase electromagnets. Shading-ring solenoids operate at low values of efficiency therefor requiring relatively high values of input power, per unit of tractive force attained. It is well known that D.C. solenoids yield as much as 10 ounces of tractive force per watt of input, whereas A.C. shading-ring solenoids produce only 3.0 to 4.0 ounces per watt. Thus for a given force requirement a relatively high wattage must be dissipated by the solenoid, therefor requiring relatively large solenoid assemblies having large numbers of costly copper windings in the magnet coil. High input wattage and the associated rapid and detrimental temperature rise have been commonly accepted as unavoidable incidences of A.C. relay constructions heretofore available.

A further problem has evolved with the growing usage of power relays as control elements in complex "automated" electro-mechanical systems for industrial process control, automatic machine control, and like applications. Command signals for the power relays are commonly derived from relatively sensitive or delicate sources such as electronic computers, or sensing devices responsive to thermal, speed, pressure, flow, or weight variables. Such sensors frequently yield signals of limited power, inadequate to directly energize a power relay unless added amplification or an intermediate relay are employed. Such accessories add materially to system costs, and impair the overall system reliability.

Power relays for such applications are frequently viewed as control amplifiers whereby a given load circuit maximum power is controlled by a much lower input or solenoid wattage. The ratio of output power to control or input power represents a forward gain or power-amplification ratio which numerically describes the merit of the device. As an example, a commercial prior art A.C. relay of D.P.D.T. type has a switch rating of 25 amperes resistive load at 250 V. r.m.s, or 6,250 watts. The solenoid operates at 11.0 VA. or 7.0 watts, producing 21 ounces of force at rated voltage. The control ratio is: 6,250/7 = 890 : 1, equivalent to 29.5 decibels. Much higher power ratios are desirable and have long been sought in the prior art. In this regard it is noted that a relay of similar load rating actuated by a D.C. solenoid would operate at 2.5 watts coil input, yielding a power ratio of 2,500 : 1, or 33.9 decibels power gain, however usually requiring a D.C. power supply.

Past efforts to overcome the above limitations have included careful attention to design details of A.C. solenoids, as well as resort to D.C. solenoids supplied from auxiliary power supplies, or energized by A.C. applied through full-wave diode bridge rectifiers. Pre-amplification is also sometimes applied, but is subject to similar cost, reliability, and power supply objections. Efforts to reduce solenoid wattage requirements by reducing relay spring forces and contact pressures have generally resulted only in decreased reliability and contact life expectancy, slower response time, and increased susceptibility to malfunction due to mechanical shock loads or vibration.

The basic and long standing problem is clearly that of providing means of constructing a relay actuator operated by A.C., which yields a greatly increased value of tractive force per watt of input, and which is producible at costs comparable to prior art shading ring solenoids.


My copending application No. 783,035 referenced above discloses a general purpose A.C. solenoid actuator incorporating a novel magnetic core element having inherent phase-splitting properties whereby the use of copper shading-rings is avoided. The simple and low cost solenoid construction disclosed has been found to yield tractive force values in excess of 10 ounces per watt. I have discovered that a modification of the above structure enables its use in combination with various switch arrangements for relay constructions. The preferred form disclosed herein embodies the modified solenoid in combination with a commercially available snap-switch element of high power handling capability. Power relays so constructed have been found to yield control ratios of greater than 4,500 : 1, or the equivalent power gain of 36.5 decibels.

It is accordingly a principal object of the present invention to provide in an A.C. actuated relay an actuating solenoid of greatly increased magnetic efficiency whereby current switching contacts are operable with substantially lower solenoid input wattage than has heretofore been required.

Another object is to provide a new and improved A.C. relay construction which utilizes a novel electromagnetic structure of linear acting type which combines high magnetic efficiency with low heat dissipation and temperature rise, while yielding an increased value of actuating force for given dimensions.

A further object is to provide an improved A.C. relay of reduced size for a given load switching capacity wherein a novel magnetic actuator of linear acting type enables construction at low cost with a minimum of parts, and with wearing parts such as hinge pins, bearings and the like substantially avoided.

An additional object is to provide a novel relay construction of relatively high power-switching capacity in which the mass of moving parts is held to a minimum, thus enabling long mechanical life and rapid response to energizing signals of low power, yet which operates quietly and with less impact noise than has commonly been attained by prior constructions.

Still another object is to provide a relay of a low cost and compact construction having a high power switching capability, embodying a novel solenoid actuator of improved efficiency, such that the volume and weight of copper winding required is substantially reduced over prior constructions of similar power switching capacity.

A further object is to provide a novel relay construction of relatively high efficiency and power switching capacity having external means whereby manual actuation of the switch means may be conveniently and safely performed without exposure to shock or other hazard.

The foregoing and other objects and advantages of the invention will become apparent from the following description and the accompanying drawings describing various embodiments thereof.

In the drawings,

FIG. 1 is a side elevation of an assembled relay according to the present invention; and,

FIG. 2 is an enlarged partially sectioned view of the relay of FIG. 1 showing a median section of a solenoid assembly in general accordance with my above referenced copending application, as modified for the present relay usage; and,

FIG. 3 is an enlarged partially sectioned view of the phase-splitting core assembly of FIG. 2.

Alternating current relay constructions heretofore available have universally attained flux phase-splitting by the use of copper shading rings placed in slots in the magnetic pole face abutting the the attracted member or armature, in a manner such as to encircle a major portion of the pole-face area. The flux wave flowing in the encircled pole area is caused to lag in phase behind that of the wave flowing in the unshaded pole area by the opposing and phase retarding effects of the heavy current circulating in the shading ring. A two-phase flux wave is thus generated. While such methods attain a moderately effective split-phase result, the relatively low efficiency and high characteristic temperature rise enforce the requirement for relatively large and costly solenoid assemblies, for a given mechanical force.

Generally speaking the present invention makes use of my prior discovery that flux phase splitting may be attained by the use in a solenoid core portion, of two or more ferro-magnetic members in a parallel spaced arrangement, and having dissimilar electromagnetic properties including magnetic hysteresis and eddy-current susceptibility. Those properties combined in one of said members cause the flux wave flowing therein to lag materially behind the wave flowing in the companion member which is designed to be relatively less susceptible to those retardant properties. The above mentioned spacing between members enables the maintenance of interphase magnetic separation to avoid commingling or inter-phase coupling.

The foregoing art has enabled the attainment of very high values of efficiency thus permitting compact solenoid constructions yielding high values of force per watt with low temperature rise. The above referenced copending application contains a more detailed description of the art in various applications, as well as a discussion of the properties of various magnetic materials usable therein. Common reference characters are used in FIGS. 2, and 3, of the drawings of both applications wherever applicable.

The preferred exemplification of the present present invention makes use of a bi-stable plunger actuated snap-switch, long available from a number of sources in relatively standardized forms and sizes. Such are available with contact ratings of from 5 to 25 amperes, having long been accepted as reliable and conservatively rated, and having found wide use due to their compactness, low cost, and ease of replacement. Their use for relay purposes has been inhibited presumably by the relatively high plunger force necessary to overcome the internal return spring.

The switch model chosen for initial development and shown herein is of a S.P.D.T. type, rated at 20 amperes A.C. resistive load at voltages to 480 r.m.s. The linear actuating force required is 18.0 to 20.0 ounces, a value clearly not attainable with prior art solenoids of suitably compact size and low input wattage. Conversely, the solenoid construction disclosed herein has a volume of 0.58 cubic inch, and yields a linear force of 21 ounces with power input of 2.0 watts, thus being ideally suited to the present combination.

The above circumstances have enabled the construction disclosed which is of the straight-through linear acting type, in which levers, bearings, hinge-pins and other commonly used parts are avoided. Relays of the type disclosed have exhibited exceptional life and reliability characteristics, test models having attained 1.5 × 108 operational cycles without failure. Switching response has been found to be exceptionally rapid, presumably due to the relatively high value of solenoid force available, combined with the relatively low mass or weight of the moving parts of the solenoid and switch, taken separately or together.

It will be apparent from the above recited ratings and performance values that the relay herein described attains a control ratio of 9,000/2 = 4,500 : 1, or 36.5 decibels power gain, a result heretofore unattainable in an A.C. actuated power relay.

It will be understood that many changes may be made in details of solenoid construction, choice of switching arrangement, and arrangement of parts without departing from the spirit of the invention as expressed in the appended claims. It will also be understood that the application shown as applied to a specific power relay application is by way of illustration only, and that the art disclosed is also beneficially applicable to many other electrical control devices having current switching as an important function. I therefore do not wish to be limited to the exact details of construction, or arrangement of parts as shown and described.

Referring more particularly to the drawing wherein similar reference characters designate corresponding parts throughout the several views; FIG. 1 depicts a side elevation of the assembled relay showing the manner in which the solenoid unit is mounted atop the commercial snap-switch 4, being enclosed by sheet-metal cover 1, which is held in assembled condition by fastening screw 7 which passes through one of the two mounting holes 21 in snap-switch 4, being retained by a nut on the reverse side of the assembly, not shown. Sheet-metal cover 1 is of a generally U form, inverted to enclose both front and back sides of the assembly, and passing across the top of the solenoid unit to enclose and confine the armature. The cover 1 is characterized mainly by the centrally located raised or domed portion 22 which confines the armature, and which has a centrally located clearance hole through which the head of the armature actuating screw 3 projects upwardly, thus being externally accessible for adjustment, or for manual operation of the relay, as for testing. Solenoid connecting leads 10 for connection to the external control circuit pass through the solenoid magnetic shell through appropriate insulating means, and may be at any desirable location.

FIG. 2 is a partially sectioned view of the relay similar in plan to FIG. 1, in which the upper solenoid structure is sectioned on its median plane to disclose details of construction. Switch 4 is also partially sectioned to show the arrangement of switch actuating plunger 5. The entire magnetic structure is contained within magnetic outer shell 15 constructed of annealed low-carbon mild steel flat strip formed into a closed rectangular loop with the abutting ends joined at bottom center by welding, or by a locking dovetail joint, not shown. Shell 15 has in its lower surface a centrally located hole through which magnetic core assembly 13 and 14 is firmly attached by spin-over 16, or other suitable means. Shell 15 has in its upper surface a bore or hole, also centrally located, and so dimensioned as to retain cylindrical mild steel armature 2 for free vertically slidable motion therethrough. Armature 2 is thus positioned substantially coaxial with phase-splitting core assembly 13--14, and engages the upper pole-face thereof when in the downward or attracted position.

Magnetic shell 15 has a primary function of providing a closed magnetic circuit functioning to divert the flux into two separate oppositely disposed unbroken flux paths of relatively reduced cross-section linking the lower end of core assembly 13-14 with the upper peripheral area of armature 2, external to solenoid winding 8 which is of insulated copper wire, wound on an appropriate insulating bobbin, shown in section. Cylindrical Armature 2 has a central axially aligned threaded hole therethrough in which the threaded actuating screw 3 is engaged. Actuating screw 3 is constructed of 18-8 stainless steel, bronze, or other suitable non-magnetic material, and has threads limited to the upper portion engaging with armature 2. The rod-like lower portion of screw 3 extends downwardly for the full length of inner core member 14 through the axial clearance hole 12 passing therethrough.

Core member 14 has in its lower end an annular recess which tightly accepts axial guide bushing 11 of Nylon or other wear resistant material, which has a central bearing hole dimensioned to permit the lower end portion of screw 3 to slide axially therein. The lower end of screw 3 is thus guided and positioned in proper axial abutting engagement with the switch actuating plunger 5. Actuating screw 3 thus has the plural functions of operatively connecting armature 2 with switch plunger 5, of providing an external means of adjusting the axial motion of plunger 5 for proper switch actuation when the solenoid is energized, and to provide axial alignment of armature 2 to avoid cocking or binding. The head of screw 3 also provides a convenient means of manually actuating switch 4 for test purposes. Screw 3 may be locked in the adjusted position by the application of thread-locking compound which "sets" after a short period of time.

Switch 4 is provided with a substantial internal normalizing spring which normally biases plunger 5 in an upward direction thereby acting on screw 3 to raise armature 2 upwardly against the domed portion 22 of cover 1, when the solenoid is deenergized. A gap is thus created between the bottom face of armature 2 and the juxtaposed upper pole face formed by core members 13 and 14. Upon passage of alternating current through solenoid winding 8, armature 2 is drawn downward into engagement with pole members 13 and 14 by the two-phase flux generated therein, being thereafter held in firm contact thereagainst by said flux. During the downward travel, plunger 5 is depressed thus actuating switch 4.

The mode of operation of core members 13 and 14 in generating a split or two-phase flux wave is based on my earlier discovery that a core member constructed of hysteretic material subjected to an alternating magnetomotive force, will respond with a flux wave lagging in phase behind that of the magnetizing current by an amount dependent on the degree of hysteretic remanance which is characteristic of that material. It was further determined that if the foregoing corepiece be of proper cross-section it will be subject to a further phase retardation due to the phase retardant effects of eddy or circulating currents flowing therein. The total phase lag angle thus attained is a composite lag which is the vector sum of the two lag angles obtained separately by the effects of eddy-currents and hysteresis. Very substantial phase lag angles have been found to be thus attainable. The foregoing corepiece is used in company with a companion corepiece constructed of a material having a lesser hysteresis characteristic, and configured to be less susceptible to eddy-currents.

The two corepieces are arranged in a parallel manner, and separated by a small gap or spacing to avoid inter-phase shunting or bypassing effects. When the two members are magnetized by the alternating current flowing in the common exciting coil, the resulting flux wave is split, with the leading phase flowing in the less retardant member, and the lagging phase flowing in the more retardant member.

Referring to FIG. 3, the outer sleeve member 13 is the leading phase member, being constructed of annealed magnetic iron, a low hysteresis material. It is also provided with a longitudinal slot 17 which interrupts the circumferential circulating or eddy current which would otherwise flow therein. The inner core portion 14 is the retardant or lagging-phase member, being constructed of a moderately hysteretic material such as partially annealed A.I.S.I. mechanical steels C-1115, or C-1117 which are low cost and readily available steels characterized by a substantial value of hysteresis. Inner core 14 is constructed as an unbroken cylindrical part, thus being subject to the flow of circular induced eddy-currents throughout its length, adding further to the phase retardation obtained.

The above mentioned interphase gap or separation is obtained by forming inner member 14 with a small annular step or shoulder 18 whereby the diameter of member 14 is made slightly smaller than the inside diameter of sleeve 13. A gap thickness dimension of 21/2 percent of the outside diameter of sleeve 13 has been found to yield effective phase separation, and a highly efficient solenoid.

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