US3134873A

US3134873A - Thermo-responsive trip free circuit breaker

Info

Publication number: US3134873A
Application number: US61274A
Authority: US
Inventors: Homer F Malone; Eugene D Lauer
Original assignee: Mechanical Products Inc
Current assignee: Mechanical Products Inc
Priority date: 1960-10-07
Filing date: 1960-10-07
Publication date: 1964-05-26
Anticipated expiration: 1981-05-26

Description

y 26, 1954 H. F. MALONE ETAL 3,

THERMO-RESPONSIVE TRIP FREE cmcun BREAKER Filed Oct. 7, 1960 2 Sheets-Sheet 1 40 INVENTORK HM, F/VaZ re. 7,55 Z'zzyerre .P. Adele? W, y/fbvu 1964 H. F. MALONE ETAL 3, ,873

THERMO-RESPONSIVE TRIP FREE CIRCUIT BREAKER Filed Oct. 7, 1960 2 Sheets-Sheet 2 United States Patent 3,134,873 THERMO-RESPONSIVE Till? FREE CIRCUIT BREAKER Homer F. Malone and Eugene D. Lauer, Jackson, Mich, assignors, by mesne assignments, to Mechanical Products, Inc, Jackson, Mich, a corporation of Delaware Filed Oct. 7, 1960, Ser. No. 61,274 3 Claims. (Cl. 260-416) This invention relates generally to electric circuit breakens and more particularly to an improved thermo-responsive trip free circuit breaker.

Automatic electric circuit breakers are often used to protect branch electrical circuits having electric motors or other electrically operated translating devices connected therein. Such circuit breakers generally comprise a pair of separable contacts, a releasable operating mechanism for effecting separation of the contacts, manual means for efiecting release of the operating mechanism, and a trip device responsive to predetermined conditions in the branch electrical circuit and operable to effect release of the operating mechanism. Release of the operating mechanism opens the separable contacts of the circuit breaker thereby to deenergize the electrically operated device.

Generally, the trip device of such circuit breakers comprises a latch mechanism and a current responsive member operable to effect movement of the latch. The latch must be relatively strong mechanically in order to retain the operating mechanism and the separable contacts in the closed condition with sufficient contact pressure to insure the electrical integrity of the circuit breaker. However, the latch must be relatively easily movable due to a relatively small increment of movement of the current responsive member to lend sensitivity to the circuit breaker. Further, the current responsive member must be sensitive to a relatively small increment of current above a preselected maximum and have a physical response characteristic capable of moving the latch.

The criticalness of the aforementioned seemingly incompatible requirements in emphasized in circuit breakers designed for the protection of relatively low current rating circuits. Circuit breakers heretofore known and used are often impractical for use in such low current applications wherein relatively rapid and sensitive overload response is required in that they characteristically require a relatively large increment of current above a preselected maximum to effect response of the trip device. The thermal inertia of, for example, the relatively large bimetallic member often used as current responsive members, limits the sensitivity thereof sufliciently to preclude their use in circuit breakers designed to protect low current circuits. Also, because in former circuit breaker trip devices latch overlap is relatively small and the latch force relatively variable, frictional resistance to unlatching effort causes wide variations in the current required to effect operation of the trip device.

Bimetallic members having a low thermal inertia and a sensitivity sufficiently high to be tactuatable by, for example, an overload current of one ampere or less, generally do not have sufficient mechanical strength to effect release of a latching mechanism. Therefore, because many modern electrical circuits, for example, aircraft branch circuits, are designed to carry currents of, for example, 1 ampere or less, there is a present need for a circuit breaker having a trip device that will respond quickly and positively to relatively small overloads in such low current circuits.

Another requirement that preferably is satisfied by such low current rating circuit breakers is that the circuit breakers be trip free in operation, or, inother words, that the separable contacts thereof cannot be manually ice held in the closed condition by movement of a manual operator to the contacts closed position if an overload condition persists in the circuit. Further, such a circuit breaker should be capable of relatively easy calibration and should retain its initial calibration even though subjected to relatively severe operating conditions.

Accordingly, one object of the present invention is an improved circuit breaker for the protection of relatively low current electrical circuits.

Another object of this invention is to provide a circuit breaker that operates substantially instantaneously upon the occurrence of a relatively small current overload thereby to provide protection for equipment subject to damage from extremely small overload currents.

-A further object of this invention is a circuit breaker having a trip device including an extensible current carrying wire that substantially instantaneously heats and elongates upon the occurrence of a predetermined current condition to effect release of an actuating mechanism and separation of a pair of electrical contacts.

it is another object of this invention to provide an im proved circuit breaker that is trip-free in operation.

Another object is to provide an improved latch structure for an electric circuit breaker that normally retains a pair of contacts in engagement.

Another object is an improved latch structure that is responsive to effect release of an operating mechanism for the circuit breaker upon a relatively small movement of a thermally responsive member.

Another object is a circuit breaker having a manual operator that is pushed to close the circuit after it has been electrically or mechanically opened and that is pulled to mechanically open the circuit.

Another object is a circuit breaker which has its component parts so disposed, and constructed of such materials, that the environmental temperature to which it is exposed has a negligible affect upon the adjusted trip value of current.

Another object is a circuit breaker having a relatively effortless unlatching means that imposes no wearing action upon the latching mechanism and therefore does not adversely affect calibration of the circuit breaker.

Other objects and advantages of the present invention will become apparent from the following detailed description, claims and drawings wherein:

FIGURE 1 is a fragmentary perspective view of a pair of separable contacts, an operating mechanism, and trip device for a circuit breaker in accordance with an exemplary embodiment of the present invention;

FIG. 2 is a front view, partially in section, of the structure of FIGURE 1 shown in the contacts open condition and mounted in an enclosure;

FIG. 3 is a fragmentary view with the operating mechanism broken away to show the trip device of the circuit breaker;

FIG. 4 is a view similar to FIG. 2 with the contacts, operating mechanism and trip device in the contacts closed position; and

FIG. 5 is a cross sectional view taken substtantially along the line 5-5 of FIG. 4.

Referring now to the drawings, a circuit breaker 10, in accordance with an exemplary embodiment of the present invention comprises an insulating housing 12 for the enclosure and support of the separable contacts, operating mechanism, and trip device of the circuit breaker 10. The housing 12 comprises a base portion 14 and a cover portion 16 (FIG. 5) having suitable recesses 18 and barriers 24) for the support of the components of the circuit breaker 10, as will be described.

A pair of

terminals

30 and 32 extend outwardly of the housing 12 from the interior recess or cavity 18 thereof for connection to an external electrical circuit -13 (not shown). The terminal 32 is of L-shaped configuration, an upper end portion 34 thereof supporting a fixed contact 36. The fixed contact 36 is maintained in operative alignment with a movable contact 38 that is supported for movement by a contact carrier 40, in a manner to be described.

As best seen in FIGURE 5, a manual operator 50, made of insulating material, extends outwardly of and is supported by a tubular collar 52. The collar 52 has a threaded outer end portion 54 so as to be mountable in, for example, a control panel (not shown). The collar 52 has a radial flange 56 at the inner end 58 thereof, the flange 56 having a generally hexagonal cross sectional configuration to preclude rotation of the collar 52 in a complementary aperture 60 in the base 14 and cover 16 of the circuit breaker 10.

The manual operator 50 has a central cavity 61 (FIGS. 4 and for the acceptance of a folded upper end portion 62 of a contact operating slide 70. The end portion 62 of the slide 70 is normally biased against the upper end of the cavity 61 by a helical compression spring 63 that extends between the end portion 62 of the slide 70 and a folded upper end portion 64 of a manual release slide 65. The folded end portion 64 of the slide 65 extends through a rectangular aperture 66 in the slide 70 and is normally biased downwardly by the spring 63 against a transversely extending lower end portion 67 of the manual operator (FIG. 5). The slide is movable relative to the slide 70 to effect manual opening of the circuit breaker, as will be described. A lower end portion 72 of the slide 70 is supported in a pair of complementary recesses '74 and 76 in the base 14 and cover 16, respectively. V V The slide 70 has a longitudinally extending slot 80 therein for the acceptance of a transversely extending pin 32that is fixedly supported by the base 14. It is to be noted that the pin 32 also extends through a complementary slot 83 in the slide 65 (FIG. 5) to permit relative movement of the slide 65 with respect to the base 14.

An operating spring 84 extends between the fixedly mounted pin 82 and a transverse flange 86 on the slide 70 to normally bias the slide 'itland manual operator 5i) outwardly of the housing 12 or, as seen in the drawings, upwardly with respect to the housing 12 and collar 52. Because the end portion 64 is biased against the end portion 67 of the manual operator 50, the slide 65 is also normally biased upwardly with respect to the housing 12.

The slide 70 has a transversely extending pin 98 secured thereto, as by Welding or staking, for the support of the movable contact carrier 40 and a contact actuating spring 92. The spring 92 is supported in an annular groove 94 in the pin (FIG. 5), an end portion 95 thereof engaging the flange 86 on the slide 70 and an opposite end portion 96 thereof being engaged in a complementary cutout 98 in the contact carrier 40. The contact carrier 40 is journaled about the pin 90 for rotation with respect to the slide 7% the spring 92 normally biasing the contact carrier 40 clockwise, as seen in the drawings, with respect to the slide 70 to the contacts open position, as seen in FIG. 2.

The contact carrier 40 has a latching surface 100 at an opposite end portion 102 thereof from the movable contact 38 that is engageable under a latching flange 104 on a rotatable latch lever 106. The latch lever 106 is pivotally supported on a transversely extending pin 108 that is fixedly supported by the base 14.

As best seen in FIGURE 1, the latch lever 106 has a rearwardly extending and angularly upwardly facing cam surface 110 supported on an angularly upwardly extending cam extension 111 for engagement with a complementa ry cam 112 on a rotatable trip lever 114. The trip lever 114 is journaled about a transversely extending pin 116 that is fixedly supported by the base 14.

As best seen in FIGURE 3, the latch lever 106 is normally biased toward the trip lever 114 by a helical coil spring 120 having end portions 122 and 124 engaged in

suitable apertures

126 and 128 in the latch and

trip levers

106 and 114, respectively. It is to be noted that movement of the latch and trip levers 106 and 114 toward one another is limited by engagement of the cam 112 on the trip lever 114 with the cam surface 110 on the latch lever 106.

The trip lever 114 has an upwardly extending end portion 130 with a transverse flange 132 thereon for the support of an upper end portion 134 of an extensible thermal responsive wire 136. A lower end portion 138 of the wire 136 is affixed to a calibration plate 140 that is supported in a complementary recess 18 in the base 14. The calibration plate 140 has a threaded aperture 142 therein for the acceptance of a complementary calibration screw 144. The screw 144 is supported by suitable barriers 20 in the base 14, a continual bias thereupon being maintained by a leaf spring 146 thereby to position the calibration plate 140 positively Within the base 14.

The trip lever 114 is normally biased counterclockwise, as seen in the drawings, about the support pin 116 therefor, by a helical compression spring 150 that extends between the base 14 and the trip lever 114, being disposed about a suitable car 152 on the trip lever 114 to facilitate positioning thereof.

It is to be noted that a radius extending between the central axis of the pivot pin 116 for the trip lever 114 and the point of attachment of the end portion 134 of the Wire 136 to the trip lever 114 is generally parallel to the line of extension of the wire 136. Therefore, a relatively small increment of elongation of the wire 136 effects a.

relatively large angular movement of the trip lever 114 under the bias of the spring 150. Counterclockwise movement of the trip lever 114 effects clockwise movement of the latch lever 106 due to engagement of the cam 112 on the trip lever 114 with the cam face 110 on the latch lever 106. It is to be noted that the point of engagement of the cam 112 with the cam face 110 is at a relatively small radial distance from the pivotal axis of the latch lever 106 as compared to the radial distance to the point of engagement between the latching surface 109 on the contact carrier 40 with the latch 104 on the latch lever 106. Therefore, a relatively small increment of angular movement of the cam surface 110 under the bias of the cam 112 effects a relatively large displacementof the latch 104. In this manner, a relatively small increment of elongation of the wire 136 effects a relatively large movement of the latch 104 thereby maximizing overlap between the latch 104 and latching surface 100 to insure stability and reliability of the circuit breaker 10 in conditions wherein the circuit breaker 10 is subjected to shock and vibration tending to spuriously unlatch the contact carrier 40.

Electrical continuity through the circuit breaker 10 is effected by a flexible conductor that extends from the trip lever 114 to the movable contact carrier 40. A second flexible conductor extends between the terminal 30 and the calibration plate 140. Therefore, upon closure of the

contacts

36 and 38, an electrical circuit through the circuit breaker 10 runs from the terminal 30 through the flexible conductor 162 to the calibration plate 140 thence through the extensible wire 136 to the trip lever 114. The trip lever 114 is electrically connected through the flexible conductor 160 to the movable contact carrier 40 thence to the movable contact 38, fixed contact 36 and terminal 32. 2

Upon the occurrence of an overload in an electrical circuit containing the circuit breaker 10, the thermoresponsive wire 136 elongates, permitting the trip lever 114 to rotate counterclockwise under the bias'of the spring 150. Counterclockwise rotation of the trip lever 114 is transmitted to the latch lever 106 by engagement of the cam 112 on the trip lever 114 with the cam face 110 on the latch lever 106. Clockwise rotation of the latch lever 106 effects movement of the latch 104 away from the latching surface 100 on the contact carrier 40, thereby permitting the contact carrier 40 to rotate clockwise under the bias of the spring 92 and the slide 70 to move upwardly under the bias of the spring 84.

Contraction of the thermo-responsive wire 136 due to cooling thereof, upon the removal of the overload condition that effects heating and elongation thereof, effects movement of the trip lever 114 clockwise against the normal bias of the spring 150. The latch lever 106 follows the trip lever 114 due to the bias of the spring 120 therebetween. Counterclockwise rotation of the latch lever 106 brings the latch 104 thereof into a position where it is conditioned to engage the latch surface 100 of the contact carrier 40. Subsequent downward movement of the slide 70, as by manually pushing on the operator 50, carries the latch surface 100 to a position under the latch 104, the end portion 102 of the contact carrier bypassing the latch 104 due to a camming action of an angularly orientated cam face 170 on the contact carrier 40. Release of the manual operator 50 permits the slide 70 to move upwardly under the bias of the spring 84, bringing the latch surface 100 into engagement with the latch 104 and the

contacts

36 and 38 into engagement. Contact pressure is thus maintained by the spring 84.

Manual opening of the

contacts

36 and 38 is accomplished by pulling outwardly on the manual operator 50. Because the latching surface 100 and contact 38 of the contact carrier 40 are latched against the latch 104 and contact 36, respectively, the slide 70 cannot move upwardly with respect to the housing 12. However, upward movement of the manual operator 50 is transmitted to the slide 65 through engagement of the lower extension 67 and folded upper end portion 64 thereof, respectively. Outward movement of the manual operator 50 and slide 65 with respect to the slide 70 is accommodated by compression of the spring 63. A lower and angularly downwardly extending end portion 180 (FIG. 4) of the slide 65 engages a lower edge face 182 of the cam face 110 on the latch lever 106 to bias the latch lever 106 clockwise, as seen in the drawings, and disengage the latch 104 from the latching surface 100 on the contact carrier 40. Release of the contact carrier 40 permits the slide 70 to move upwardly under the bias of the spring 84, and the contact carrier 40 to rotate clockwise under the bias of the spring 92 to the position shown in FIG. 2.

Another feature of the present invention is that the circuit breaker is substantially self-compensating for changes in ambient temperature. Compensation is accomplished due to the disclosed orientation of the operating components wherein the member responsive to electrical overload extends generally parallel and is connected to the trip lever that is movable upon the occurrence of the overload condition. Thus, changes in ambient temperature effect like incremental elongations of the trip lever and thermo-responsive member that cancel each other.

From the foregoing description, it should be apparent that the circuit breaker of the present invention is responsive to a relatively small change in condition of the thermo-responsive member thereby to be well suited to the protection of low amperage branch circuits.

It is to be understood that the specific construction of the improved circuit breaker herein disclosed and described is presented for the purpose of explanation and illustration and is not intended to indicate limits of the invention, the scope of which is defined by the following claims.

What is claimed is:

1. An electric circuit breaker for interrupting an electrical circuit upon the occurrence of a predetermined condition therein comprising a pair of separable contacts, a releasable operating mechanism for effecting separation of said contacts, and a trip device for normally restraining said operating mechanism and movable to effect release of said operating mechanism upon the occurrence of said predetermined condition, said operating mechanism comprising a manual operator having a contact carrier pivotally supported thereon, said contact carrier having one of said separable contacts at one end thereof and a latching surface at the other end, said trip device comprising a rotatable trip lever, means normally biasing said trip lever in one direction, an elongated latch lever pivotally supported at one end and having a latch at the other end engageable with the latching surface on said contact carrier to retain said operating mechanism and separable contacts in the contacts closed condition, said latch lever being normally biased towards said trip lever and having a cam surface angularly related to and intermediate a radius drawn between the pivotal support and latching surface thereof, and a thermo-responsive elongatable wire having one end attached to said trip lever at a point radial- 1y spaced from the pivotal axis thereof and normally restraining said trip lever frorn rotation under the bias of said means, said wire being adjustably supported at the other end thereof to provide for calibration of said trip device and extending at a relatively small angle to a radius drawn between the pivotal axis of said trip lever and the point of attachment of said wire to said lever whereby a relatively small increment of elongation of wire permits a relatively large angular movement of said trip and latch levers about their pivotal axes under the bias of said means thereby to effect disengagement of said latch and latching surfaces, release of said operating mechanism and separation of said contacts.

2. An electric circuit breaker for interrupting an electrical circuit upon the occurrence of a predetermined condition therein comprising a pair of separable contacts, a releasable operating mechanism for effecting separation of said contacts, a trip device for normally restraining said operating mechanism and movable to effect release of said operating mechanism upon the occurrence of said predetermined condition, said trip device comprising a rotatable trip lever, means normally biasing said trip lever in one direction, a latch lever normally biased towards said trip lever and movable with and with respect to said trip lever, a thermo-responsive elongatable wire attached to said trip lever at a point radially spaced from the pivotal axis thereof and normally restraining said trip lever from rotation under the bias of said means, said wire extending generally normally to the direction of the movement of the point of attachment thereof to said trip lever whereby a relatively small increment of elongation of wire permits a relatively large angular movement of said trip lever about its pivotal axis under the bias of said means, and manually operable means comprising a first slide normally biased towards the contacts open position and a second slide movable with respect to said firs-t slide towards the contacts open position to effect movement of said latch lever with respect to'said trip lever thereby to release said operating mechanism and separate said contacts.

3. An electric circuit breaker for interrupting an electrical circuit upon the occurrence of a predetermined condition therein comprising a pair of separable contacts, a releasable operating mechanism for effecting separation of said contacts, a trip device for normally restraining said operating mechanism and movable to effect release of said operating mechanism upon the occurrence of said predetermined condition, said trip device comprising a rotatable trip lever, means normally biasing said trip lever in one direction, a latch lever normally biased towards said trip lever and movable with and with respect to said trip lever, a thermo-responsive elongatable wire attached to said trip lever at a point radially spaced from the pivotal axis thereof and normally restraining said trip lever from rotation under the bias of said means, said wire extending generally normally to the direction of movement of the point of attachment thereof to said trip lever whereby a relatively small increment of elongation of wire permits a relatively large angular movement of said trip lever about its pivotal axis underthe biasof said means, a first slide having a contact carrier pivotally supported thereon with one of said contacts at one end thereof and a latch surface at the other end thereof en- 'gagable with said latch lever, said slide being normally 5 biased towards the contacts open position, and a second slide movable with respect to said first slide towards the contacts open position to effect movement of said latch lever with respect to the latch surface on said contact carrier thereby to release said operating mechanism and 1 separate said contacts.

References Cited in the file of this patent UNITED STATES PATENTS Greenway et 'al. May 3, 1927 Combi Oct. 19, 1937 Ingwersen June 28, 1960 FOREIGN PATENTS Germany Dec. 6, 1956

Claims

2. AN ELECTRIC CIRCUIT BREAKER FOR INTERRUPTING AN ELECTRICAL CIRCUIT UPON THE OCCURRENCE OF A PERDETERMINED CONDITION THEREIN COMPRISING A PAIR OF SEPARABLE CONTACTS, A RELEASABLE OPERATING MECHANISM FOR EFFECTING SEPARATION OF SAID CONTACTS, A TRIP DEVICE FOR NORMALLY RESTRAINING SAID OPERATING MECHANISM AND MOVABLE TO EFFECT RELEASE OF SAID OPERATING MECHANISM UPON THE OCCURRENCE OF SAID PREDETERMINED CONDITION, SAID TRIP DEVICE COMPRISING A ROTATABLE TRIP LEVER, MEANS NORMALLY BIASING SAID TRIP LEVER IN ONE DIRECTION, A LATCH LEVER NORMALLY BIASED TOWARDS SAID TRIP LEVER AND MOVABLE WITH AND WITH RESPECT TO SAID TRIP LEVER, A THERMO-RESPONSIVE ELONGATABLE WIRE ATTACHED TO SAID TRIP LEVER AT A POINT RADIALLY SPACED FROM THE PIVOTAL AXIS THEREOF AND NORMALLY RESTRAINING SAID TRIP LEVER FROM ROTATION UNDER THE BIAS OF SAID MEANS, SAID WIRE EXTENDING GENERALLY NORMALLY TO THE DIRECTION OF THE MOVEMENT OF THE POINT OF ATTACHMENT THEREOF TO SAID TRIP LEVER WHEREBY A RELATIVELY SMALL INCREMENT OF ELONGATION OF WIRE PERMITS A RELATIVELY LARGE ANGULAR MOVEMENT OF SAID TRIP LEVER ABOUT ITS PIVOTAL AXIS UNDER THE BIAS OF SAID MEANS, AND MANUALLY OPERABLE MEANS COMPRISING A FIRST SLIDE NORMALLY BIASED