US3103563A

US3103563A - Circuit making and breaking apparatus

Info

Publication number: US3103563A
Authority: US
Publication date: 1963-09-10
Anticipated expiration: 1980-09-10

Description

Sept- 1963 A. J. GRENIER 3,103,563

CIRCUIT MAKING AND BREAKING APPARATUS. I

Filed Oct. '7, 1959 CF \r II Ill 7 I I I RA RL4 a 495 1/ M62 *1 H --cc3 III/' I 5C2- 5C, E32 SP E31 M62 H LA? E E 5 64 3 SP g RA CF RC II I I I n QMCI me I 4' 2M9 United States Patent Ofilice 3,103,563 CIRCUIT MAKING AND BREAKING APPARATUS Aim J. Grenier, North Attleboro, Mass, assignor to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed Oct. 7, H59, Ser. No. 844,978 9 Claims. (Cl. Mill-88) This invention relates to circuit making and breaking apparatus, and more particularly to electrical relays.

Among the several objects of the invention may be noted the provision of circuit making and breaking appa ratus in which any sticking or welds between engaged contacts are quickly broken; the provision of relays which have increased rupture capacity; the provision of starting circuits for A.C. motors which minimize malfunctioning and possible damage to the motors; the provision of relays which have an increased capacity without an attendant increase in relay dimensions and which are economical to manufacture; and the provision of circuit making and breaking apparatus which is inexpensive in construction and reliable in operation. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the constructions hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated,

FIG. 1 is a cross section of an electrical relay of the present invention interconnected in the starting circuit of an A.C. motor; and,

FIGS. 2-5 are fragmentary cross-section views of additional illustrative embodiments of circuit making and breaking apparatus of the present invention.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

One of the important limiting design factors in electrical circuit making and breaking apparatus is the current breaking capacity of the contacts. As the magnitude of the current to be interrupted by a given set of contacts increases there is an increased tendency for the contacts to stick or weld together. The capacity of an electrical circuit making and breaking apparatus to withstand this tendency may be conveniently defined as the rupture capacity which is usually expressed as the number of contact opening and closing cycles during which the apparatus will operate satisfactorily (at a given voltage and current under specific conditions of frequency of operation, load power factor, power supply frequency, etc.) between contact failures, such as by welding together, by

eroding, cor-roding, building up of transferred material from one contact to the other, etc. It is of course quite desirable to increase the rupture capacity of any piece of electrical circuit making and breaking apparatus. This is particularly true in regard to starting relays for electric motors. This is due to the marked and continuing trend in the reduction of the size of electrical motors relative to their horsepower ratings, which has made it increasingly difiicult to provide compact starting relays for these motors which have a sufficiently high rupture capacity and reliinstead of the relay breaking or opening the start winding circuit when the rotor reaches its running speed, the relay would fail to drop out or be deactuated and would continue to energize both run and start windings and thereby cause serious and deleterious overheating.

In accordance with the present invention, electrical circuit making and breaking apparatus (e.g., starting relays) are provided which have an increased rupture capacity without substantially increasing the over-all size of the apparatus, its contacts, or the cost of its manufacture I have found that the rupture capacity of such apparatus may be greatly increased by providing the actuating member with a thermostatic element of electrically conductive material which is not only movable with the actuating member but relative thereto, and securing a movable circuit making and breaking contact to this thermostatic element. Means are provided for biasing this thermostatic element and its associated movable contact toward a mating contact so that as current flows through said element and the engaged contacts the element tends to flex and effect relative shearing, wiping, sliding, or rocking action or movement between these contacts while still maintaining good low-resistance electrical connection therebetween. This action is highly effective in increasing the rupture capacity of a given set of contacts under the same set of electrical conditions and parameters.

Referring now more particularly to the drawings, an electric motor which may, for example, be an A.C. induction motor is generally indicated at reference character M. A run winding WR of the motor is connected via an on-off switch SW to one side of an A.C. power source as indicated at L2. The other terminal of run winding WR is connected via an annular relay coil RC of a starting relay RLl of this invention .to the other side of the power source at L1. The starting circuit for motor M also includes a pair of stationary relay contacts SCI and 8C2! series-connected with a start winding WS of motor M. These two serially connected contacts and Winding WS are shunt-connected across winding WR and relay coil RC. The magnetic circuit of coil RC includes a relay armature RA movable axially the bore of a hollow spool-shaped coil form CF of insulating material around which coil RC is wound. Contacts 801 and SCZ are secured to the underside ot the lower flange of form CF in a spaced-apart relationship. An actuator or armature stem or extension AE projects downwardly from and is coaxial with the central axis of armature RA. Loosely mounted on extension AB is a contact carrier CCI which extends outwardly on opposite sides of RA. Carrier CO1 is constituted by a thermostatic element of electrically conductive material having two layers LAT and LA2 of material with different coefficients of thermal expansion, bonded together at their interface. CCl may be a strip of rectangular shape in plan or any other configuration such as circular, elliptical, etc. Two movable contacts MCI and M02 are mounted on the upper surface of CO1, each adjacent opposite outer edges thereof. Contact carrier CCl is provided with a central aperture H through which armature extension AE projects. The relative dimensions of hole H and extension AE are such that a loose fit is provided. A cover CV of insulating material, adapted to be detachably secured to the lower flange of form CF, is dimensioned so as to have its lower inner surface constitute a stop, as indicated at a central depression S, for limiting downward axial movement of armature RA and its extension AB. The lower edge of armature RA constitutes a stop adapted to limit axial movement of contact carrier CCl upwardly along AB. The lower end of armature extension AB is provided with a shoulder E on its lower or outer end. A compression spring SP is mounted between E and the Patented Sept. 10, 1963 l tacts MC1, SCl.

undersurface or CCl to react against E and resiliently bias'the carrier toward the lower surface of armature RA and stationary contacts SC1 and 8C2. It will be understood that any conventional means may be employed to prevent rotation of contact carrier CO1 and its associated contacts MCI and M02 relative to contacts S01 and SC2, such as making aperture H and the bore of spool CF and the cross section of AE noncircular and of generally a similar or matching geometric shape. Armature RA is gravity hiaseddownwardly. It will be noted that spring biasing of armature RA may be provided simply by inserting a compression spring in the closed pocket formed between the upper end ot RA and the inner surface of the upper flange of form CF. However, whether spring or gravity biasing is employed, RA is biased downwardly, thereby normally to disengage respective pairs of contacts SCl, MCl and SC2, MC Z.

, cuit through WS around WR and RC. The current path for start winding WS traverses the engaged contacts SC2, MC2, the thermostatic element which serves as contact carrier CO1, and the other pair of closed con- As the current passes through this thermostatic element, it will heat, the heating effect being a function of the resistance of the electrically conductive path between M01 and M02 and the magnitude of current. The heating of carrier CCl in response to the magnitude of start winding current effects differential expansion of the dissimilar thermostatic element layers LA1 and LAZ, thereby causing CCI to flex. LA1 may be either the higher or lower expansion layer. Assuming it. is the higher, carrier CO1 would bow upwardly, thus sliding and rocking MCI relative to SCI and similarly effecting a shearing lateral movement of MCZ relative to the surface of SCZ. Any sticking or welds between these engaged sets of contacts are quickly broken. -It will be noted that even if one oi the two pairs of engaged contacts tends to stick and deter the dropping oif RA, the carrier thermostatic element acts as a cantilever \and its flexing and bowing action will move the other movable contact away from its stationary contact. The action of biasing means. SP is significant in the functioning of the present invention as it main- .tainsa reasonably uniform contact pressure between the respective pairs ocf contacts despite any thermostatic flexing.

Assuming the higher expansion layer is-LAZ, then the heating of carrier CCl'causes a bowing away from contacts SCI and SCZ. A gain, however, a similar advantageous shearing, sliding, wiping, rocking action takes place at the respective engaged surfaces of SC1, M01 and SC2,,MC2, with spring SP similarly functioning to maintain generally uniform contact pressure, and low-resistance electrical contact at the pairs of mating contact faces. The choice in selecting LA1 or LA2 as the higher expansion. layer is not critical, but it may be affected to some extent by the tendency of the flexing of CO1 to somewhat increase or decrease the relay differential. This relay differential (i.e., the difierence in the current ,value necessary to pull in armature RA and that level below which it must fall to permit drop out of RA) may be decreased somewhat ifLAZ is selected to be the higher expansion layer. That is, the bowing downwardly in response toincreased current flow through WS will increase the downward bias on AE and RA and thus tend to raise the level below which the current must fall to efiect drop out or have RA and AE move from the operative to a retracted position. Conversely, selecting LA1 as the higher expansion layer may increase to some extent the relay differential.

As the rotational speed of rotor R increases to its normal running value, the current drawn through RC drops until the flux in the magnetic circuit of relay RLl is insufficient to maintain RA in its actuated position against the gravity bias. Armature RA and its stem AE then drop to their deactuated or retracted position, moving contact carrier CCl and movable contacts MCI and MCZ out of engagement with SCI and SC2, thus opening the start winding circuit and permitting normal running operation of rmotor M. A failure of relay RL1 by reason of the contacts continuing to stick together thereby preventing normal drop out at the proper point would result in running the motor with both windings energized. Because of the high current density in the starting winding this would cause rapid and damaging overheating. Thus, the action of the apparatus of the present invention in quickly breaking apart any welds is highly advantageous in preventing such damage to the associated motor.

As a specific example of the effectiveness of the present invention, a standard motor starting relay weighing 36 grams was connected in the starting circuit of a /3 HP. appliance motor as schematically depicted in FIG. '1. This motor had a contact load of 25 amperes. It was found that there was an average number of 79 operation cyles between malfunctions due to relay contact failure. The same standard relay modified only as indicated above in accordance with the present invention was found to undergo an average of 3830 operating cycles between malfunctions.

The embodiment of FIG. 2 difiers from that of FIG. 1 in that relay RLZ has a contact carrier CCZ'of curved or bowed shape instead of being flat. Again, as in the previously described relay, layers LAB and LA4 of the thermostatic element constituting carrier CCZ may be selected so that the higher expansion layer is on the top or the bottom.

FIG. 3 illustrates a third relay RLS of the present invention in which the carrier, as indicated at CC3, is

generally U-shaped and has ears E81 and BS2 projecting outwardly and perpendicular to the legs of the U. Relay RL4 as shown in FIG. 4, has a generally C-shaped contact carrier CO4, with ends thereof turned in and directed toward each other so that they lie in a plane generally parallel to a plane common to the two stationary contacts SCI and 5C2.

The operation of each of these illustrative embodiments is similar to that described above in regard to the FIG. 1

embodiment, the degree of flexing or contact wiping or the resultant heating first causes some lateral shearing between the engaged set of contacts followed by a sudden wiping or shearing action therebetween as the thermostatic element reverses its curvature. If LA 10 is selected as the higher expansion layer, carrier CCS would move from the solid line position to the dashed line position as shown in FIG. 5 after sufficient heating. The temperature at which this disc reverses its curvature should be within the range attained when start winding current courses through carrier CCS for a period of time. This snap'action will, of course, aid in breaking any welding at the contacts. The selection of LAN as the higher expansion layer would also tend to lower somewhat the relay differential because of the resulting increase of downward biasing force on RA after the snapping of disc CC to its dashed line position. Otherwise, the operation of this circuit making and breaking embodiment is generally the same as set forth above.

It is to be understood that although two-layer, bonded together, laminated, thermostatic element contact carriers are illustrated, more than two layer elements may be used. Also, the two layers need not both be metallic in nature as long as the element has sufficient electrical con ductivity as measured between MCI and MC2.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. i

I claim:

1. An electrical relay comprising an annular relay coil adapted to be connected to a source of electrical power, a relay armature movable axially within said coil from an actuated position when said relay coil is energized by said power source to a deactuated position when the energization of said relay coil decreases below a predetermined level, means biasing said armature toward said deactuated position, an extension for said armature, a contact carrier of electrically conductive material loosely mounted on said extension and adapted to have limited but substantial movement along a central axis of said extension and armature, said carrier extending radially outward from said extension on opposite sides thereof, a movable contact mounted on said carrier adjacent an outer edge thereof, a second movable contact mounted on said carrier adjacent an opposite outer edge thereof, a pair of stationary electrical contacts adapted to be engaged respectively by said movable contacts when said relay armature is in its actuated position whereby said movable contacts and said contact carrier bridge said stationary contacts to complete an electrical circuit, and means whereby any welds that may occur between said respective engaged pairs of contacts are broken apart, said means comprising a shoulder on the end of said extension remote from said armature, a spring mounted on said extension reacting from said shoulder against said contact carrier,rsaid contact carrier comprising a thermostatic element having layers of material of different coeflicients of thermal expansion adapted to be heated and flex in response to current flow in said electrical circuit and between said movable contacts, the center of said contact carrier being capable of axial movement on said extension within a range of movement substantially greater than the thickness of said element, said contact carrier being biased by said spring in the direction toward said fixed contacts whereby the center of said contact carrier may move axially on said extension to permit flexing of said contact carrier while the movable contacts remain in engagement with the fixed contacts thereby effecting a rocking action of the movable contacts against said fixed contacts so as to break apart any welds between the respective pairs of movable and fixed contacts.

2. An electrical relay as set forth in claim 1 wherein the movable contacts are secured to the higher expansion layer of said contact carrier.

3. An electrical relay as set forth in claim 1 wherein the movable contacts are secured tothe lower expansion layer of said contact carrier.

4. An electrical relay as set forth in claim 1 wherein the contact carrier is a substantially flat strip loosely mounted at its center on said armature extension.

5. An electrical relay as set forth in claim 1 wherein the contact carrier is curved, and the movable contacts are secured to the concave surface thereof.

6. An electrical relay as set forth in claim 1 wherein the contact carrier comprises a dished disc.

7. An electrical relay as set forth in claim 1 wherein the contact carrier is generally C-s-haped with the opposing ends thereof directed toward each other and lying generally in a plane substantially parallel to a plane common to said two stationary contacts.

8. An electrical relay as set forth in claim '1 wherein the carrier is generally U-shaped and has contact-carrying ears projecting from the ends of the legs of the U at angles substantially perpendicular thereto, said ears lying generally in a plane substantially parallel to a plane common to said two stationary contacts.

9. In an electrical relay having a relay coil, a relay armature movable from a first position to a second position upon energization of said coil, and means biasing the armature toward the first position; an extension for the armature, a contact carrier of electrically conductive material loosely mounted on said extension and adapted to have limited but substantial movement along a central axis of said extension and armature, said carrier extending radially outward from said extension on opposite sides thereof, a movable contact mounted on said carrier adjacent an outer edge thereof, a second movable contact mounted on said carrier adjacent an opposite outer edge thereof, a pair of stationary electrical contacts adapted to be engaged respectively by said movable contacts when said relay (armature is in its second position whereby said movable contacts and said contact carrier bridge said stationary contacts to complete an electrical circuit, and means whereby any welds that may occur between said respective engaged pairs of contacts are broken apart, said means comprising a shoulder on the end of said extension remote from said armature, a spring mounted on said extension reacting from said shoulder against said contact carrier, said contact carrier comprising a thermostatic element having layers of material of dilferent coefiicients of thermal expansion adapted to be heated and flex in response to current flow in said electrical circuit and between said movable contacts, the center of said contact carrier being capable of axial movement on said extension within a range of movement substantially greater than the thickness of said element, said contact carrier being biased by said spring in the direction toward said fixed contacts whereby the center of said contact carrier may move axially on said extension to permit flexing of said contact carrier while the movable contacts remain in engagement with the fixed contacts thereby effecting a rocking action of the movable contacts against said fixed contacts so as to break apart any welds between the respective pairs of movable and fixed contacts.

References Cited in the file of this patent UNITED STATES PATENTS 1,766,965 Thomas June 24, 1930 1,996,496 Wertz et al. Apr. 2, 1935 2,299,669 Werner Oct. 20, 1942 2,307,776 Grant et al. Jan. 12, 1943 2,320,252 Vaughan May 25, 1943 2,335,888 StilWell Dec. 7, 1943 2,434,186 Wilson Jan. 6, 1948 2,482,955 Wilson Sept. 27, 1949 2,490,103 Stillwell Dec. 6, 1949 2,650,328 James Aug. 25, 1953 2,673,909 Bonanno Mar. 30, 1954 2,711,503 Elliott June 211, 1955 2,786,171 Clark Mar. 19, 1957 FOREIGN PATENTS 69,390 France July 15, 1958

Claims

1. AN ELECTRICAL RELAY COMPRISING AN ANNULAR RELAY COIL ADAPTED TO BE CONNECTED TO A SOURCE OF ELECTRICAL POWER, A RELAY ARMATURE MOVABLE AXIALLY WITHIN SAID COIL FROM AN ACTUATED POSITION WHEN SAID RELAY COIL IS ENERGIZED BY SAID POWER SOURCE TO A DEACTUATED POSITION WHEN THE ENERGIZATION OF SAID RELAY COIL DECREASES BELOW A PREDETERMINED LEVEL, MEANS BIASING SAID ARMATURE TOWARD SAID DEACTUATED POSITION, AN EXTENSION FOR SAID ARMATURE, A CONTACT CARRIER OF ELECTRICALLY CONDUCTIVE MATERIAL LOOSELY MOUNTED ON SAID EXTENSION AND ADAPTED TO HAVE LIMITED BUT SUBSTANTIAL MOVEMENT ALONG A CENTRAL AXIS OF SAID EXTENSION AND ARMATURE, SAID CARRIER EXTENDING RADIALLY OUTWARD FROM SAID EXTENSION ON OPPOSITE SIDES THEREOF, A MOVABLE CONTACT MOUNTED ON SAID CARRIER ADJACENT AN OUTER EDGE THEREOF, A SECOND MOVABLE CONTACT MOUNTED ON SAID CARRIER ADJACENT AN OPPOSITE OUTER EDGE THEREOF, A PAIR OF STATIONARY ELECTRICAL CONTACTS ADAPTED TO BE ENGAGED RESPECTIVELY BY SAID MOVABLE CONTACTS WHEN SAID RELAY ARMATURE IS IN ITS ACTUATED POSITION WHEREBY SAID MOVABLE CONTACTS AND SAID CONTACT CARRIER BRIDGE SAID STATIONARY CONTACTS TO COMPLETE AN ELECTRICAL CIRCUIT, AND MEANS WHEREBY ANY WELDS THAT MAY OCCUR BETWEEN SAID RESPECTIVE ENGAGED PAIRS OF CONTACTS ARE BROKEN APART, SAID MEANS COMPRISING A SHOULDER ON THE END OF SAID EXTENSION REMOTE FROM SAID ARMATURE, A SPRING MOUNTED ON SAID EXTENSION REACTING FROM SAID SHOULDER AGAINST SAID CONTACT CARRIER, SAID CONTACT CARRIER COMPRISING A THERMOSTATIC ELEMENT HAVING LAYERS OF MATERIAL OF DIFFERENT COEFFICIENTS OF THERMAL EXPANSION ADAPTED TO BE HEATED AND FLEX IN RESPONSE TO CURRENT FLOW IN SAID ELECTRICAL CIRCUIT AND BETWEEN SAID MOVABLE CONTACTS, THE CENTER OF SAID CONTACT CARRIER BEING CAPABLE OF AXIAL MOVEMENT ON SAID EXTENSION WITHIN A RANGE OF MOVEMENT SUBSTANTIALLY GREATER THAN THE THICKNESS OF SAID ELEMENT, SAID CONTACT CARRIER BEING BIASED BY SAID SPRING IN THE DIRECTION TOWARD SAID FIXED CONTACTS WHEREBY THE CENTER OF SAID CONTACT CARRIER MAY MOVE AXIALLY ON SAID EXTENSION TO PERMIT FLEXING OF SAID CONTACT CARRIER WHILE THE MOVABLE CONTACTS REMAIN IN ENGAGEMENT WITH THE FIXED CONTACTS THEREBY EFFECTING A ROCKING ACTION OF THE MOVABLE CONTACTS AGAINST SAID FIXED CONTACTS SO AS TO BREAK APART ANY WELDS BETWEEN THE RESPECTIVE PAIRS OF MOVABLE AND FIXED CONTACTS.