US3011037A - Thermostatic and magnetically actuated flasher - Google Patents

Description

THERMOSTATIC AND MAGNETICALLY ACTUATED FLASHER Filed Jan. 7, 1960 J. W. WELSH Nov. 28, 1961 2 Shets-Sheet 1 FIG.1

FIG.3

FIG.2

INVENTOR.

James W. Welsh BATTERY q 61 ATTORNEYS Nov. 28, 1961 J. w. WELSH 3,011,037

THERMOSTATIC AND MAGNETICALLY ACTUATED FLASHER Filed Jan. 7, 1960 2 Sheets-Sheet 2 F|G.5A

FIG.5F K

AX. FIG.5H

| INVENTOR.

BY James W. Welsh VFMQ AT TO RN EYS United States Patent "ice York Filed Jan. 7, 1960, Ser. No. 1,064 Claims. (Cl. 200-113) This invention relates to thermomotive circuit breakers and, more particularly, to an improved form of circuitv breaker employing a novel combination of thermal and magnetic forces to effect full pressure engagement of contacts up to the instant they are snapped apart, together with snap re-engagement of the contacts under full pressure.

In most known types of thermally operated circuit breakers, the contact pressure decreases, during the opening cycle, until actual separation of the contacts. The decreasing contact pressure increases the contact resistance and decreases the life of the contacts. Recognizing this problem, many attempts have been made to rearrange the circuit breaker parameters to improve the maintenance of contact pressure during theopening cycle.

In most such switches or circuit breakers, a wiping action is provided to improve the contact life. However, the mechanical resistance characteristic of wiping action greatly increases the power requirements of the circuit breaker. To keep power losses at a minimum, the wiping action must be sacrificed with. consequent more rapid deterioration of the contacts greatly decreasing the contact life.

The aforementioned contact deteriorating conditions can be overcome by a switch design in which full contact pressure is maintained during building of contact separating pressure to a value exceeding the holding pressure, with consequent snap action separation of the contacts, and in which the gradually increasing contact closing force is suddenly and greatly augmented by a second closing force to snap the contact closed. Under these two conditions, arcing of the contacts is substantially eliminated and the contact life indefinitely prolonged. However, providing these two conditions in a simple contact unit, such as an automotive flasher, and in a circuit breaker having an acceptably long life of its operating parts, has been a difficult problem "to solve.

- In my co-pending application Serial No. 734,471, filed May 12, 1958, and now Patent No. 2,900,474, issued August 18, 1959, there is shown and described an automotive type flasher utilizing a combination of thermal and magnetic forces to meet the foregoing conditions. More particularly, a magnetic armature is mounted to extend from a thermomotive member or bimetallic strip, and carries a contact engageable with another contact on a base of the flasher. This magnetic armature is operatively associated with a long life permanent magnet mounted in the base. By virtue of the fact that the magnetic attraction varies inversely as the square of the distance between a magnet and an armature operated thereby, a holding action can be maintained on the two contacts while the thermomotive member is heating. As the thermomotive member heats, it builds up pressure in a contact separating direction, but until such pressure exceeds the magnetic force holding the contacts engaged, there will be no separation of the contacts. When, however, the kinetic energy stored in the thermomotive member exceeds the holding force exerted by the magnet, the armature and its contact are carried rapidly away from the fixed contact on the base, the separation being accelerated due to the fact that the magnetic holding force decreases as the square of the distance of the armature 3,t1i,07 Patented Nov. 28, 1961 from the magnet. Also, in re-closing of the contacts, as the thermomotive member cools, the armature again approaches the magnet. When the armature enters the elfective field of the magnet, it is accelerated in its move ment toward the magnet, and thus the closing speed of the two contacts is accelerated. This results in a snap closing action of the contact.

Flashers of this type when operated using alternating current or pulsating direct current have very satisfactory life. However, the satisfactory life cannot be maintained under abnormal high surge direct current conditions. The reason for this is that the switch or flasher of my oo-pending application did not provide continuous high contact pressure during the opening movement of the contacts, or the break cycle.

In accordance with my present invention, I have found that the life of a flasher of this type can be very substantially improved by redesigning the parameters of the flasher to take into account the bending of a bi-metallic strip into a circular are when it is heated uniformly. By proper design of the parameters, and using this bending effect, the contact pressure can be made to actually increase, during the break cycle, up to the point where the kinetic energy stored in the bi-metallic element overcomes the force exerted by the magnet so that the con- I tacts are rapidly snapped apart. correspondingly, with the arc shape of the thermal or bi-metallic member being maintained but increasing in radius during cooling of the thermal member, as during the make cycle, this assists in maintaining a high pressure during the make cycle after the contacts are snapped into engagement when the force exerted by the permanent magnet overcomes the kinetic energy stored in the bi-metallic strip.

For an understanding of the invention principles, reference is made tothe following description of typical embodiments thereof as illustrated in the accompanying drawings. In the drawings:

FIG. 1 is a plan view of an automotive type flasher embodying the invention; 7

FIG. 2 is a side elevation view thereof;

FIG. 3 is a plan view of another embodiment of the flasher incorporating the present invention;

FIG. 4 is a schematic wiring diagram of an electrical circuit using the flashers of the present invention; and

FIGS. 5A through 5H are diagrams illustrating the action of the flasher during a make and break cycle.

Referring to FIGS. 1, 2 and 3, the circuit breaker or flasher 10 comprises a dielectric base 11 on which are rivets 12, 13 electrically and mechanically connected to or integral with prongs 14, 16 engageable in a suitable receptable to connect flasher 10 in circuit. For example, and referring to FIG. 4, prong 14 (rivet 12) may be connected to the ungrounded terminal of a battery 15, and prong 16 (rivet 13) may be connected to a lamp load17, 17 which may be connected to ground through a switch 18. When switch 18 is closed, a load circuit is completed including flasher 10 in series therein.

In accordance with the invention, a relatively elongated bi-metallic strip 20 has one end brazed or welded to an adjusting arm 24 brazed or welded to rivet 12, and a magnetic armature 25 is secured to extend longitudinally from the free end of strip 20. Armature 25 may be a relatively rigid bar of cold rolled steel or may be a permanent magnet. It is preferably a bar of cold rolled steel or other suitable paramagnetic material.

A high strength permanent magnet 30 is mounted in or on base 11 as by being welded or brazed to rivet 13, and is located beneath armature 25. Magnet 30 is selected so that it retains its magnetic strength substantially unimpared due either to ageing or relatively high temperature environment, For example, permanent magnet 30 may be one of the series oi fAlnicof magents manufactured by the General Electric Company.

In the embodiment of FIGS. 1 and 2, armature 25 has a wrapping 26 of dielectric or insulating material so that it will not make electrical contact with magnet 30. 4 In the embodiment of FIG. 3, the armature and magnet 30 are plated with dielectric material so that again there is no electrical contact betjw'een these elements. I A relatively movable first contact 21 is secured to the undersurface of strip 20 at the free end thereof, and is normally engaged under pressure with a relatively fixed contact 22 on the upper surface of a spring 23 having one end welded or brazed to rivet 13. r r p The operation of the flasher will be best understood from reference toFIGS. 4 and 5A throughSH. Referring first to FIG. when switch 18 is closed current flows from battery 15 to prong rivet 12. The current then flows through arm 21, bi metallic strip 2i), contacts 21 and 22, spring arm 23, rivet 13, prong 1'6, lamps l7, and switch l8 to ground.

Referring to FIGS 5A through 5H, FIG. 5A the relative positions of strip 23, armature 25, and contacts 21 and 22 are shown at the start of the cycle. As current flows through strip 20, the latter lieats and starts to deflect as shown in FIG. 5B. This arc uately bow ed deflection of strip 2 tl continues as shown. in FIGS. 5C and 5D so that armature 25 is gradually turned upwardlyaway from magnet 30. Finally, and as shownin FIG. 5B, the kinetic energy snore din strip 20 overcomes the magnetic force attracting arm atu re25 toward magnet 30 and the contacts 21 and 22 snap apart, v r

The electric circuit is now broken so that bi-meta llic strip 20 begins to cool as shown in FIG. 5F and thus begins to re-straighten'. This moves armature toward magnet 30 and contact 21 towardcontact 22 movement is illustrated in FIGS. 5G and 5H. After a given amount of movement of armature 25 toward magnet 30, the attractive force of the magnet on the armature overcomes any residual kinetic energy in strip 20 so that armature 25 is snapped toward magnet 30.. This effects snap engagement of contacts 21 and 22 under an pressure. p I

It will be noted that the conditions illustrated take full advantage of the uniform arc of bowing of strip 20 as shown in FIGS. 5A through 5H. This bowing first tilts armature 25 and eventually, due to the build up of kinetic energy in strip 20 in a contact separating direction, the cont acts are snapped apart as the kinetic energy of strip 2t overbalarices or exceeds the magnetic attraction of magnet 30 for armature 25. It will thus be noted that full contact pressure is maintained right up to the point Where the contacts are snapped apart, and also that the contacts are snapped together in the re-closing direction and maintained under full pressure. This is due to the taking advantage of the bowing action of the bi-metallicstrip 2d, plus the spring action or spring arm '23. r I r I I Arm 23 is so designed and positioned that, when the contacts 21 and 22 are engaged, the arm 23 is bent inwardly from its normal position so that it tends to follow strip 20 as the free end of the latter deflects. Howev'er, the following by spring 23 of the movement of birnetallicstrip 29 is limited to a posittion in which spring arm 23 attains its normal unstressed relation.

7 While specific embodiments of the invention have been shown and described in detail to illustrate the application of the invention principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is: i. A thermostatic circuit breaker comprising, in combination a first fixed terminal; a relatively elongated electrically conductive bi-metallic strip having one end electrically and mechanically fixed relative to said first terminal; a relatively rigid and elongated paramagnetic armature electrically and mechanically secured to and extending longitudinally in alignment from the free end of said bi-metallic stripra first contact electrically and mechanically fixed to the underside of said bimetallic strip at its free end; a permanent magnet fixed beneath said armature to attract the .latter toward said magnet; a second fixed terminal; an electrically conductive spring arm having one end electrically and mechanically fixed to said second terminal and a free end extending beneaththe free end of said bi-metallic strip; a second contact electrically and mechanically secured to the free end of said spring arm and normally engaged with said first contact, said spring arm, when said bi-metallic strip is cool and said contacts are engaged, being depressed so as to maintain pressure on said fii'st and second contacts, and said pressure engagement of said contacts being augmented bythe attractiveforee of said magnet on said arn i' 'ature; Iii-metallic strip, when heated by the passage of electric current therethrough, bowing in a uniform arc inwardly to increase the pressure on said first and second contacts by deflecting the free end of said spring arm'fu rther inwardly; said relatively rigid armature, during such bowing ot said oi-metallic strip, tending to be moved mayhem said permanent magnet; the kinetic energy biiilt up in said bi-metallic strip, and resulting bowing thereof while its free end is restrained against outward movement by attraction of the armature toward said magnet, eventually exceeding the attractive force of said magnet on s aid airmature so that said armature is snapped away from said magnet with a resultatit rapid decrease in the magnetic force acting on said armature; the contacts being thereby snapped apart mom a position of full pressure engagement to a substar'itially separated position breaking an electric circuit; said bi-metallic strip, upon cooling due to the breaking of the electriccircuit gradually reassuming its normal orientation and .thereby moving said armature toward said magnet and said first contact toward said second contact; the ina gneticat'traction between the magnet and the armature increasing rapidly during such movement andhver'coming the deflecting force present in said bimetallic strip so that said armature is snapped toward said magnet to re-engage said first and second contacts under full pressure. p

2. A thermostatic circuit breaker as claimed in claim 1 including dielectric material on said armature preventirig electric connection of said armature with said magnet.

3 A thermostatic circuit breaker as claimed in claim 2 in which said dielectric material comprises a wrapping of dielectric around said armature.

'4. A thermostatic circuit breaker as claimed in claim 2 in which said dielectric material comprises a plating of dielectric material on said armature and on said magnet.

5. thermostatic circuit breaker as claimed in claim 1 i-n which the fixed end of said bimetallic strip is electrically and mechanically secured to an adjusting arm which is, in turn, electrically and mechanically secured to said first terminal.

References Cited in the file of this patent UNITED STATES PATENTS 1,981,934 Werner Nov. 27, 1934 2,467,0l8 Eggleston Apr. 12, 1949 FOREIGN PATENTS 551,613 Canada Jan. 14, 1952;

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