US2809253A - Electrical control devices - Google Patents

Description

OCt- 8. 1957 w. c. BRoEKHuYsEN ELECTRICAL CONTROL DEVICES 2 Sheets-Sheet l Filed Nov. 28, 1952 Oct. 8, 1957 w. c. BRoEKHUYsEN ELECTRICAL CONTROL DEVICES 2 Sheets-Sheet 2 Filed Nov. 2B, 1952 70 BY @L70 KP i 2,809,253 Patented Oct. 8, 1957 ELECTRICAL CONTRL DEVICES William C. Broekhuysen, Brooklyn, N. Y., assignor to G-V Controls Inc., a corporation of New Jersey Application November 28, 1952, Serial No. 322,905

25 Claims. (Cl. 200-113) This invention relates to electrical control devices, and more particularly to electro-thermally actuated relays of the directly heated type, known as hot wire relays.

On account of the difficulty in obtaining and maintaining adequate spacing between several strands of resistance wire which are connected electrically in series but mechanically in multiple, hot-wire relays heretofore known in the art have usually been limited for use with relatively low voltages requiring only a single loop of wire. The construction of this type of relay for higher voltages involved a more or less complicated arrangement of pulleys over which the wire was strung back and forth. rfhe use of this type of relay has also been limited because they were not suitable for timing periods of more than two to three seconds. Thermal relays of the socalled indirectly heated type are not satisfactory for many uses because they cannot be used below ten seconds if reasonably fast recycling is required. This left a range in which thermal relays could not be used effectively except under certain limitations.

The above limitations are substantially completely overcome by my invention. The construction of my novel relay enables me to use many loops of resistance wire due to my novel method of forming the heating assembly or expanding element, which method is simple and lends itself readily to quantity production. The construction of a relay made in accordance with my invention also provides means for increasing the time constant of the directly heated expanding assembly or element so that the relay can be used eciently for timing periods as high as twenty seconds without sacrificing the fast recycling characteristic of a hot-wire relay.

In addition my novel relay can also be compensated substantially completely for wide variations in ambient temperature, and it can be adjusted externally for a wide range of timing periods even though it is enclosed in an hermetically sealed housing or casing.

Accordingly it is an object of my invention to provide a novel method of constructing a hot-wire thermal relay having a heating element employing a plurality of loops of resistance wire, which method is simple and readily adaptable for quantity production.

The invention also consists of a simple and novel method of forming a hot-wire relay heating element having a plurality of loops of resistance wire, and wherein all strands lie in substantially the same plane.

Another object of the invention is to provide a novel hot-wire relay having means for extending the timing range or the time constant thereof to as high as ten times the normal range or constant of hot-wire relays heretofore known in the art, without sacrificing its fast recycling characteristics.

An `additional important object of the invention is to provide a novel highly efficient hot-wire thermal timedelay relay which is smaller in size than other devices of this type, and yet one which is rugged and substantially vibration resistant.

Another object of the invention is to provide an hermetically sealed hot-wire relay which can be adjusted simply and repeatedly over a wide range, not only when and where it is made, but also wherever it is in use, without destroying the hermetic seal, and wherein the adjustment remains unchanged at all times even under adverse operating conditions.

The invention also consists in the provision of a device of the type described which is fully compensated for changes in ambient temperature over a wide range. The invention is also characterized by the provision of a device l in which, if desired, the timing or regulation can vary with ambient temperature in a predetermined manner.

Other objects of my invention will be set forth in the following description and drawings which illustrate preferred embodiments thereof, it being undertsood that the above statement of the objects of the invention is intended generally to explain the same without limiting it in any manner.

Referring now to the following detailed description taken in conjunction with the accompanying drawings, which form la part of this specification, and in which like characters of reference indicate the same or like parts:

Figure 1 is a vertical central sectional view, with parts in elevation, showing a preferred form of my invention.

Figure 2 is a bottom view of the structure shown in Figure 1.

Figure 3 is a sectional view taken along line 3-3 of Figure l.

Figure 4 is a sectional view taken along line 4--4 of Figure l.

Figure 5 is a sectional view taken along line 5--5 of Figure l.

Figure 6 is a sectional view taken along line 6---6 of Figure 1.

Figure 7 is a diagrammatic representation of the operative elements of the form of invention shown in Figure l.

Figure 8 is a sectional view taken along line 8 8 of Figure l.

Figures 9, l0, and l1 are face views of insulating parts.

Figure 12 is a face view of the heating element as first wound.

Figure 13 is a side or edge View of heater and mounting and clamping parts in exploded relationship.

Figure 14 is a perspective view of a completed heater element ready for assembly with the remainder of the structure.

Figure 15 is a sectional View taken along line 15-15 of Figure 14.

Figure 16 is a sectional view taken along line 1,6 16 of Figure 14.

Figure 17 is a diagrammatic representation of the structure of a relay having normally open contacts.

The structure made in accordance with the invention, is referred to herein as a thermal time-delay relay. However, it may also find application in other functions. such as for example, a discriminator or regulator for potential, current or frequency in electrical circuits. Therefore, wherever in the following specification the device embodying the invention is referred to as a timedelay relay, such other functions are meant to be included, since the construction of the device is substantially the same for al1 purposes.

In a preferred embodiment of the invention selected for purposes of illustration and shown in Figures l-16, the entire internal operating structure is supported on seven pins, numbered 1 to 7. Unless otherwise specified, all mechanical and electrical connections may conveniently be made by spotwelding. Pins l to 7 are insulated from, and hermetically sealed into a suitable base, such as a disc-shaped metal base 8 by glass beads 10. Base 8 is provided with a rim 12, Figure 1, which is rigidly crimped in the lower edge of casing 14, preferably cylindrical in form. The seam is hermetically sealed by solder as at la.

The heated timing member designated generally consists of a grid of tine resistance wire 22 wound originally on a frame 24 of suitable shape and thickness made of a suitable insulating and heat resistant material with high mechanical strength and rigidity, such as mica (Figures 9 and l2). As illustrated in Figures 9 and 12, frame 24 is substantially rectangular in shape and is provided wlth an extension 23 at each end. Frame 24 is also formed with a central cut out portion, such as window 21, which in the preferred form is rectangular in shape. The w1re 22 is wound around the full length of frame 24 back and forth over end projections 23, and between ears formed on projections or extensions 23, as many times as 1s required for the desired resistance. The two ends of the winding are secured in V-shaped notches 25 as shown in Figure l2.

Each end extension 23 of frame 24 is provided with two spaced slots 26. The frame is supported at top and bottom on two at staples 28 and 30 made of a suitable material, such as stainless steel, which extend through the slots. Staple 30 is connected to a short liexible leaf spring secured to a strip 42. Staple 28 is connected to another tiexible leaf spring 44 attached to a U-shaped bracket 46. Parts 40-46 preferably are also made of stainless steel.

Also supported on staples 28 and 30 are four pieces 32 (Figure l0), two on each side of grid 22, and four pieces 34 (Figure l1), two on each side of grid 22. Parts 32 and 34 are made of a suitable insulating and heat resistant material, such as rnica. These parts are assembled or stacked on staples 28 and 30 in the order shown in Figure 13, after which the long arms, and then the short arms of the staples are bent over, tightly clamping pieces 32 and 34 together with frame 24.

Bent over arms of staples 28 and 30 also secure the strands of grid 22 in proper spaced relationship on frame 24. The overlapping central parts of mica leaves 32 are held together by a small flat staple of nickel ribbon or other suitable material 36. After this assembly, shown complete in Figure 14, has been attached to the rest of the structure, which holds it under tension, as will be explained hereinafter, the two sides of frame 24 are cut off along broken lines 38 shown in Figure 12. This leaves the wire grid 22 as the only member to take up this tension. This completes the formation of heating element 20.

From a reference to Figures l, l2 and 14 to 16, it will be evident that the heating element 20 may be termed substantially uniplanar. Thus when a current is passed through the wire of grid 22, the elongation thereof is longitudinal only, and there is substantially no tiexing.

Pins 6 and 7 support the lower end of compensating member 43. This member preferably is channel shaped for rigidity. A flat leaf spring forms a flexible connection between compensating member 48 and strip 52, rigidly fixed to pins 6 and 7. temperature compensation member 48 is made of a metal having substantially the same coefficient of thermal expansion as the wire of grid 22. Compensating member 48 is substantially the same length as the free length of wire grid 22.

The structure includes movable arm 54 which, as shown in the illustrated embodiment, consists of an open channel partly surrounding member 48. See Figures l, 4 and 6. One end of arm S4 is pivotally connected to the top of member 48 at a point designated P by two crossed springs 56 and 58. Spring 58 is positioned substantially horizontally, and extends through a suitable opening 59 formed in the center of spring 56. As shown in Figure 8, opening 59 may be circular, and of a size such as to prevent any engagement between springs 56 and 58. One end of spring 58 is secured to a bent over tip 60 of member 48. The other end of spring 58 is attached to a flange of bracket 62 rigidly secured to movable arm 54. Spring 56 is arranged substantially at right angles For complete ambient to spring 58, and is also secured to member 48 and bracket 62. Bracket 46 of heated timing member or heater assembly 20 likewise is secured to the upper end of arm 54. Bracket 42 at the lower end of heated timing member 20 is rigidly secured to pins 1 and 4. The two ends of wire grid 22 are connected to pins 2 and 3.

A leaf spring 64 carrying at its lower free end a contact 66, is connected to the outer face of arm 54, at a point designated L. Spring 64 is biased in such manner that, when free, it bears with a positive resilent pressure against the lower edge of arm S4. Normally, as shown in Figure l, it is held a sort distance away from this edge of arm S4 because of the engagement of contact 66 with lixed contact 68 on bracket 70 rigidly attached to pin 5.

A V-shaped leaf spring 72, the free ends of which arc secured to the inner face of movable arm 54 and the outer face of compensating member 48, respectively, tends to push the lower end of arm 54 away from member 4S. A U-shaped bracket 74, made of a suitable metal such as stainless steel, is secured to the open side of member 48 or the back face thereof a short distance below the top. See Figure 1.

At a suitable distance below the upper rim of casing 14, as shown in Figure 1, a diaphragm 76 is brazed to the inner wall thereof, forming an hermetic closure for the operating parts of the structure. An L-shaped lever 78 having an arm 77 extending downwardly into casing 14, is brazed into an opening 79 in diaphragm 76 and near its edge. A glass bead 80 mounted on a short wire 81 secured to the lower tip of downwardly extending arm 77 of lever 78 engages the inner face of U-bracket 74. The other arm of lever 78 extends substantially horizontally above diaphragm 76 and is drilled, tapped, and slotted at its end in such manner that adjusting screw 82 can be clamped sufficiently tightly therein in order to prevent it from turning due to vibration. However, screw 82 can be easily adjusted with a suitable tool, such as a screwdriver. A small hole 84 in diaphragm 76 provides an opening to the interior of casing 14. This opening makes its possible to evacuate casing 14 and till it with a dry atmosphere such as nitrogen or other inert gas, or with dry air, after which opening 84 is sealed off with a drop of solder. Cover 86 closes ol the top of casing 14, and protects lever 78 and adjusting screw 82. The latter can be adjusted by inserting the end of a screwdriver through opening 88 formed in cover 86.

Referring now to the diagrammatic representation in Figure 7, it is apparent that the pressure exerted by spring 72 serves not only to maintain bracket 74 in contact with bead 80 at all times, but also functions to maintain heating element 20 under tension at all times. Hence, when member 20 expands longitudinally due to a current passing through and heating wire grid 22, arm 54 will pivot around P and move contact 66 on spring 64 out of engagement with fixed contact 68. When current through wire grid 22 is cut off and member 20 starts to cool, contact 66 is again brought into engagement with contact 68 by means of spring 72. Further cooling of grid 22 results in arm 54 moving away from spring 64 and returning to the position shown in Figure l. Thus the stresses that can be set up in the structure arc limited to safe values by the bias tension of spring 64.

Turning screw 82 so as to raise the horizontal arm of lever 78 moves the lower edge of arm 54 closer to spring 64, thereby reducing the time required for contacts 66 and 68 to be disengaged when current is passed through wire grid 22. It will be clear that, since members 20 and 48 are nearly parallel, the horizontal movement of the lower end of arm 54 as a result of adjustment of lever 78 is substantially equal to the horizontal movement of P. On the other hand, the vertical movement of point Q, which is the point on member 20 opposite P, due to the thermal expansion of member 20 causes a horizontal movement of the lower end of arm 54 which is amplified in the ratio of distance P-66 to PQ. As the crossedspring pivot at P is free from backlash and friction this ratio can be made quite substantial.

So long as grid 22 and member 48 are substantially equal in effective length and are made of materials having substantially the same coefficients of thermal expansion, a change in ambient temperature causes no appreciable change in the relative positions of P and Q, and in the position of arm 54. Therefore, there will be no change in the time delay between the application of heating current to grid 22 and the opening of contacts 66 and 68. lf it is desired that the time delay should vary in n certain manner with changes in ambient temperature, this can be accomplished by making grid 22 and member 48 of different metals, having substantially diierent coefcients of thermal expansion.

The rate of longitudinal thermal expansion of grid 22 when a fixed current is passed through it, is determined not only by the size of wire and its resistivity, but also by the thickness and the number of overlapping mica leaves 32. lt these leaves are omitted entirely, the time constant of grid 22 is essentially that of the wire of the grid. The function of the mica leaves 32 is not so much to provide thermal insulation around the grid 22, but to increase the thermal capacity of grid 22 without intertering with its thermal expansion. This requires a fair degree of physical contact between the grid and the mica leaves which is assured by clamping ribbon 36. The minimum number of mica leaves 32, disregarding total omission. is two. For example, the lower one on one side of the element or member 20, and the upper one on the other side thereof. This will still provide the neces sary electrical insulation between clamp 36 and grid 22. To obtain longer delays, any multiple of two pieces or leaves 32 may be used, or their thickness may be increased. Or if desired, metal leaves of the same shape as mica leaves 32 may be added to the outside of element Ztl. Mica pieces 34 are used only for additional electrical insulation between grid 22 and staples 28 and 30.

As the wire ot` grid 22 is always at least as hot or hotter than any other part of heating member 20, its expansion will cease instantly when the heating current is cutoff, thus eliminating any tendency to overshoot which is usually encountered in thermal relays of the indirectly heated type with considerable time constants.

The structure shown in Figures l-16 may be modified in many ways within the scope of my invention. For example, it is quite possible to reverse the positions of contacts 66 and 68 so that the circuit between them is normally open, and is closed as the result of passing a current through and heating grid 22. This modification is shown diagrsmmatically in Figure 17 in which contacts 166 and are normally open. For this purpose spring 6tlis placed between bias spring 72 and the inner face of movable arm or channel 54.

The invention above described may be varied in construction within the scope of the claims, for the particular embodiments selected to illustrate the invention are but a few of the possible concrete forms which my invention may assume. The invention, therefore, is not to be restricted to the precise details of the structure shown and described.

What l claim is:

l. A thermal time delay electrical control device comprising supporting means, a xed contact secured to said supporting means, a movable arm, a contact on said arm adapted to coact with said Iixed contact, an elongated compensating member spaced from and generally parallel with said arm and having one end mounted on said supporting means, an elongated heated timing member, means mounting said heated timing member on said supporting means in generally parallel relationship with said movable arm, resilient means pivotally connecting said movable arm and the other end of said compensating member and said heated timing member, and a wire grid in said heated timing member, said grid comprising a plurality of continuous loops of resistance wire, said grid being operative in response to a current passing therethrough to elongate longitudinally and swing said arm on said resilient pivot means, and effect a displacement of one of said contacts relative to the other.

2. A thermal time delay relay comprising supporting means, a fixed contact mounted on said supporting means, an elongated timing member, said timing member including opposed wire supporting elements movable relative one to the other, a plurality of loops of resistance wire passing back and forth over said elements and forming an elongated wire grid, means supporting one of said elements on said supporting means, a movable contact, an arm supporting said movable Contact, a compensating member, means mounting one end of said compensating member on said supporting means, pivotal means connecting the other end of said compensating member with said arm and the other of said elements of said timing member, means operatively connected to said arm and to said compensating member for biasing said arm away from said compensating member, and for continuously maintaining said grid of said timing member under tension, whereby when said grid is heateed by a current passing therethrough, said grid elongates and eiiects a movement of one contact relative to the other.

3. A device of the type described comprising an elongated heated timing member, said member having a fixed end and a free end, an elongated compensating member substantially equal in length to said timing member, a resilicntly pivoted member linking said free end of said timing member and one end of said compensating member, a movable arm having one end rigidly connected to said resilicntly pivoted member and the other end free, a movable contact on the free end of said movable arm, a fixed contact adapted to ccact with said movable contact, fixed support means for said heated timing member, said compensating member, and said fixed contact, and a device in said heated timing member for heating and elongating said timing member, said device including a Wire grid consisting of a plurality of continuous loops of resistance wire, and opposed longitudinally movable supports holding said wire, and means seecuring said grid and opposed supports iu assembled arrangement for elongation when a current is passed through said wire.

4. The invention defined in claim 3, including spring means engaging said movable arm and said compensating member for biasing said arm and said compensating member apart, means engaging the top of said compensating member for preventing substantial movement of the top of said compensating member, said spring means being adapted to maintain said heated timing membere constantly under tension.

5. The invention deiined in claim 4 including an adjusting mechanism for moving said connected end of said movable arm in a direction substantially at right angles to the direction of elongation of said heated timing membeer, said adjusting mechanism being so constructed and arranged that the movement transmitted to the free end of said arm in adjusting the position of the connected end of said arm is substantially unamplied as compared with the movement of said free end due to the elongation of said timing member.

6. A hot-wire type of electro-thermal control device having a casing and a base, comprising a fixed contact supported on said base, an elongated substantially uniplanar heated timing member having one end supported on said base, a movable operating arm having one end attached to the other end of said heated timing member, a movable contact mounted on said arm, a heater in said heated timing member, said heater including opposed ilat supports, at least one of which is movable relative to the other, a wire grid formed of a plurality of continuous loops of resistance wire wound about said spaced opposed at supports,

means connected to said at supports to maintain them continuously spaced apart, and thereby maintaining said wire grid under tension, and means for securing said flat supports and said wire grid together in a unitary assembly, said grid being operative in response to the passing of a current therethrough to expand longitudinally and cause said arm to move and effect a movement of said movable contact relative to said fixed contact.

7. A hot-wire type of electro-thermal control device having a casing and a base, comprising a lixed contact supported on said base, an elongated substantially uniplanar heated timing member having one end supported on said base. a movable operating arm having one end attached to the other end of said heated timing member, a movable contact actuated by said arm, means continuously maintaining said heated timing member under tension, a heater in said heated timing member, said heater including opposed movable flat supports, and a wire grid formed of a plurality of continuous loops of resistance wire wound about said iiat supports, and means for securing said tiat supports and said wire grid together as a unitary assembly, said grid being operative in response to the passing of a current therethrough to expand longitudinally and move said arm to eliect a relative movement of one Contact relative to the other, said irstnamed means including a compensating member having an end supported on said base and an end attached to said movable arm, a spring located between said movable arm and said compensating member adapted to bias said arm away from said compensating member and to place said heated timing member under tension, and means engaging the end of said compensating member adjacent the point where it is attached to said heated timing member for maintaining said compensating member against substantial lateral movement.

8. A hot-wire time delay electrical control device comprising a base, a fixed Contact mounted on said base, an elongated substantially uniplanar heated timing member mounted on said base, an elongated compensating member mounted on said base and coacting with said heated timing member, said timing member including an elongated wire grid formed from a plurality of continuous laterally spaced loops of resistance wire, said compensating member being substantially equal in length to the length of said grid, a movable arm resiliently connected at one end to said timing member and said compensating member, said grid being longitudinally expansiblc when a current is passed therethrough for swinging said arm towards said heated timing member, and a contact carried by said arm and movable out of engagement with said fixed Contact when said grid is heated and expands.

9. The hot-wire control device defined in claim 8 ncluding a positioning element on said compensating membcr, and adjustable means engaging said element for controlling the position of said arm before said heater grid is energized.

l0. The device deiined in claim 8 including a positioning element carried by said compensating member, an adjusting lever having an arm engaging said element, and adjustable means on said lever for controlling the extent of movement of said contact carried by said movable arm into engagement with said fixed Contact.

1l, A hot-wire time delay comprising fixed supportlng means, a fixed contact on said supporting means, an elongated expansible heated timing member mounted on said supporting means, an elongated compensating member mounted on said supporting means and coacting with said timing member, said timing member consisting of a plurality of continuous loops of resistance wire, longitudinally spaced movable supports mounting said loops of wire. means securing said loops against movement on said supports,l a movable arm having one end pivotally and resiliently connected with an end of said timing member, a hat spring carried by the other end of said arm, a

lll

contact on the free end of said Hat spring, means engaging said movable arm and said compensating member for tensioning said heated timing member to prevent buckling of said loops of wire, and means for adjusting said arm to control the extent of movement of said movable contact on said tlat spring when a current is passed through said loops of wire thereby elongating said timing member.

l2, A hot-wire thermal time delay device comprising fixed supporting means, a fixed contact mounted on said supporting means, a fiat substantially uniplanar timing member mounted on said supporting means, a compensating member mounted on said supporting means, said compensating member being substantially equal in length to the heating element of said timing member, said heating element including an elongated wire grid consisting of a plurality of laterally spaced loops of resistance wire, opposed longitudinally movable supports for said loops of wire, means securing said loops of wire on said supports, a movable arm, a spring located between and having its ends connected to said movable arm and said compensating member and tensioning said timing member, resilient pivot means connecting one end of said timing member and an end of said compensating member to an end of said movable arm, a resilient elongated member attached to said movable arm, a movable contact carried by the free end of said resilient member, said grid being operative when energized by a current passing therethrough for swinging said arm and separating said contacts, said resilient member being so biased that said movable contact is maintained in engagement with said fixed contact during a portion of the movement of said arm as a result of the elongation and contraction of said grid of said timing member.

13. A device of the type described comprising fixed supporting means, an elongated timing member mounted on said supporting means, said member having a fixed end and a free end, an elongated compensating member substantially equal in length to said timing member having one end mounted on said supporting means, a resiliently pivoted member linking said free end of said timing member and the other end of said compensating member, a movable arm having one end rigidly connected to said resiliently pivoted member and the other end free, a movable contact, a at spring mounting said movable contact, said spring being attached to the inner face of said movable arm, a iixed contact mounted on said supporting means, and a device in said timing member for heating and elongating said timing member, said device including a wire grid consisting of a plurality of continuous loops of resistance wire, and opposed longitudinally movable supports holding said loops of Wire, and means securing said grid and opposed supports in assembled arrangement for elongation when a current is passed through said grid, whereby said movable arm is swung `and said movable contact is brought into engagement with said fixed Contact.

14. A thermal time delay electrical control device comprising a base, a fixed contact supported on said base, a movable arm, a contact mounted on said movable arm adapted to coact with said fixed contact, an elongated compensating member supported by said base spaced from and generally parallel with said movable arm, resilient means pivotally connecting said movable arm and said compensating member, a heated timing member assembly having an end connected to said base and an end attached to said resilient pivot means, said assembly including a frame provided with a cut out portion, a plurality of continuous spaced loops of resistance wire extending longitudinally about said frame, said frame having portions adapted to be served therefrom, whereby said loops of wire remain operatively supported on two opposed residual frame elements, means engaging said compensating member and said movable arm and oper- `ative in response to the separation of said portions from said frame for biasing one of said frame elements away from the other and maintaining said loops of wire supported by said elements constantly under tension, said wire being operative when a current is passed therethrough to elongate and swing said arm and close or open said contacts.

15. The device defined in claim 14 wherein said assembly includes a plurality of leaves of electrical insulating material positioned at the ends and on opposite sides of said assembly, and wherein said frame is formed of a thin mica sheet, means for securing said leaves in xed relationship in full physical contact with substantially all of the wire forming said loops, a bracket attached to one of said securing means, and means attaching said bracket to said resilient pivot means.

16. A device of the type described comprising a base, a compensating member, means connecting one end of said compensating member to said base, a movable arm, resilient pivot means connecting the other end of said compensating member and said arm, whereby the free end of said arm can swing relative to said compensating member, spring means engaging said compensating member and said arm and tending to separate said arm from said compensating member, a timing member having one end connected to said base and the other end thereof connected to said resilient pivot means, said timing member comprising an elongated insulating material frame having a central cutout portion, an elongated wire grid formed of a plurality of loops of wire wound back and forth along the length of said frame and extending over said cutout portion, said frame overcoming the tendency of said spring means to move the free end of said movable arm away from said compensating member, portions f said frame adapted to be removed therefrom whereby the residual portions support the loops of said wire grid, said spring means then being operative to maintain said residual portions of said frame separated longitudinally and said wire of said grid continuously under tension, a fixed contact, a movable contact operatively associated with the free end of said movable arm, the ends of said wire forming said grid providing leads for connecting said grid in an electric circuit for the passage of a current therethrough, said current heating and elongating said grid to cause said free end of said arm to swing said movable contact relative to said fixed contact.

17. The method of forming a timing member for a hot-wire relay comprising forming from a heat-resistant insulating material a at elongated frame having a central cutout portion, winding resistance wire back and forth on said frame with the loops of wire passing about the ends of said frame and extending longitudinally thereof over said cutout portion, attaching the ends of said wire wound frame to two spaced supports, biasing one of said supports away from the other support, and then separating said frame into two end frame portions capable of relative longitudinal separating movement when a current is passed through said wire elongating said wire.

18. The method defined in claim 17, including applying to the opposite opposed portions of said loops of wire leaves of insulating material, and securing said leaves, wire loops and end frame portions firmly together before said frame is separated into two separate parts.

19. The method of forming a heated timing member comprising forming an elongated thin frame from a sheet of insulating material, providing an elongated cutout portion in said frame and centrally thereof, winding a continuous length of resistance wire back and forth on said frame over the ends of said frame with portions of said loops ot wire extending longitudinally of said frame and over said cutout portion, placing on opposite sides of said wire wound frame and adjacent the ends thereof, elongated leaves of mica having free end portions overlapping substantially centrally of the length of said frame, securing said overlapping portions of said leaves loosely together for endwise movement one relative to the other, securing said frame and said loops of wire and the other ends of said leaves firmly together whereby to prevent lateral movement of said loops of wire on said frame, mounting said wire wound frame on spaced relatively tensioned members, and then cutting said frame into two longitudinally movable parts held apart under tension.

20. A heated timing member assembly for a hot-wire relay comprising an elongated mica frame having a central opening, and an ear at each end, a plurality of continuous loops of resistance wire wound back and forth about said frame with longitudinal portions of said loops extending over said opening, a leaf of insulating material extending lengthwise of said wire wound frame from a point adjacent an ear of said frame to a point beyond the central point of said frame, one of said leaves being positioned on each side and at each end of said frame, means attaching said leaves to said frame, a centrally located element loosely holding the free ends of said leaves logether, said frame having portions adapted to be removed therefrom, whereby upon removal of said portions said assembly comprises two end frame parts supporting said loops of wire and said leaves, and means for holding said end frame parts against longitudinally inward movement towards each other.

21. The invention defined in claim 20 including a xed support for one of said end frame parts, a resiliently pivoted support mounting the other of said end frame parts, and means for placing said resilient pivoted support under continuous longitudinal tension to maintain said wire on said frame parts continuously tensioned.

22. A thermal relay having a fixed and a movable contact comprising a heatable expanding member, said member including a plurality of elongated lengths of a continuous resistance wire arranged substantially in a single plane, means for maintaining said lengths of wire continuously under tension, said wire when a current is passed therethrough being adapted to expand longitudinally and effect a relative movement between said contacts, and strips of insulating material forming a permanent part of said expanding member supported in substantially full physical contact with all of said lengths of wire over a substantial portion of their length without interfering with the thermal elongation or contraction thereof, thereby increasing the thermal capacity of said elongated lengths of said resistance wire, the number and positioning of said strips being operative to control the rate of temperature change of said lengths.

23. A thermal relay having a fixed and a movable con` tact, comprising a heatable expanding member, said member including a plurality of elongated lengths of a continuous resistance wire arranged substantially in a single plane, means for maintaining said lengths of wire continuously under tension, said wire when a current is passed therethrough being adapted to expand longitudinally and effect a relative movement between said contacts, and one or more strips of insulating material arranged in substantially full slidable physical contact with all of said lengths of wire over a substantial portion of their length without interfering with the thermal elongation or contraction thereof, thereby increasing the thermal capacity of said elongated lengths of said resistance wire, the number and positioning of said strips being operative to control the rate of temperature change of said lengths.

24. A hot-wire type of electro-thermal control device comprising a base, a fixed contact supported on said base, an elongated substantially uniplanar heated timing member having one end supported on said base, a movable operating arm having one end attached to the other end of said heated timing member, a movable contact actuated by said arm, a heater in said heated timing member, said heater including opposed relatively movable flat supports and a wire grid formed of a plurality of continuous loops of resistance wire wound about said at supports, means maintaining said ilat supports continuously spaced apart and thereby maintaining said wire grid under tension, and means clamping said loops of wire and said at supports together and securing said loops of wire mechanically in parallel and electrically in series, whereby if the electrical continuity of said grid is broken the mechanical integrity of said grid is unaffected, said grid being operative in response to the passing of a current therethrough to expand longitudinally and cause said arm to move and eect the movement of said movable contact relative to said xed Contact.

25. The device defined in claim 24, including at least one strip of an insulating material attached to opposite sides of said flat opposed relatively movable supports and in slidable physical contact with said loops of resistance wire, whereby to increase the thermal capacity of said resistance wire, the number and thickness of said strips being operative to control the rate of temperature change in said loops.

References Cited in the le of this patent UNITED STATES PATENTS Oakes Feb. 28, Rozumek Aug. 22, Brogger Feb. 13, White May 10, Simmons Jan. 13, Montague Nov. 1, Gustafsson May 23, Aske June 20, Ingram Aug. 1, Sitzer May 19,

FOREIGN PATENTS France Oct. 2,

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