US3413583A

US3413583A - Circuit breaker

Info

Publication number: US3413583A
Application number: US606366A
Authority: US
Inventors: Donald P Clark; Jr Theodore Brassard
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 1966-12-30
Filing date: 1966-12-30
Publication date: 1968-11-26
Anticipated expiration: 1985-11-26
Also published as: GB1200477A

Description

NOV. 1963 o. P. CLARK ETAL 3,

CIRCUIT BREAKER Filed Dec. 30, 1966 2 Sheets-Sheet 1 7 FIGI. 38

FIGZ.

27 A f 9 J; 3

United States Patent M 3,413,583 CIRCUIT BREAKER Donald P. Clark, South Attleboro, and Theodore Brassard, Jr., Berkley, Mass., assignors to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed Dec. 30, 1966, Ser. No. 606,366 9 Claims. (Cl. 33755) ABSTRACT OF THE DISCLOSURE A snap-acting thermostatic member carrying a movable contact normally bridges two electrical terminals and carries current therebetween. When the member is heated to a predetermined temperature by an overload current, it snaps out of engagement with one of the terminals and trips a latch to disengage the latch from a slider assembly, thereby releasing the assembly so that it may travel from a first circuit-closed position to a second tripped or circuit-open position wherein it indicates that the breaker has been tripped. After the thermostatic member has cooled, it snaps back to its original position. However, means carried by the slider assembly prevents completion of the circuit through the breaker until the slider assembly is returned to its first position. In one embodiment the slider assembly carries a bridging contact which must engage two contacts to complete the circuit through the breaker, and this engagement occurs only when the slider assembly is returned to its first circuit-closed position from the second tripped position. In another embodiment an insulating member slides under the movable contact of the thermostatic member to prevent it from closing until the slider is returned to its first position.

Background of the invention The invention relates generally to circuit breakers for motor protection and the like which use snap-acting thermostatic members for breaking the circuit in response to current overloads. Some prior art circuit breakers are not sensitive to small current overloads and sometimes the voltage drop across the breaker is high. Frequently, the circuit breaker is larger in size than desired and requires an excessive number of parts, thus making it uneconomical to produce. Moreover, some circuit breakers can be manually held in the reset condition so that in operation they periodically open and close the circuit as long as the fault causing the circuit to overload continues to exist. This is undesirable and may shorten the useful life of the unit which the breaker was to protect. Attempts to prevent this latter drawback by a spring biased insulated slider which slides between contacts when the breaker is first tripped proved unsatisfactory since they caused creep action and also interferred with its temperature and current sensing abilities. Moreover, arcing or burning of the insulators used, tracking of the disc material and a general deterioration of the parts may result from faults in prior designs.

Summary of the invention Among the several objects of the invention may be noted the provision of a foolproof circuit breaker which is capable of sensing small overload current with a minimum voltage drop across the circuit breaker; a circ-uit breaker which can be economically produced in small sizes with a minimum number of parts; the provision of a trip-free circuit breaker which will not re cycle the unit being protected in the event the reset member is held in the reset position; and the provision of a circuit breaker which prevents contact closure after a 3,413,583 Patented Nov. 26, 1968 circuit is broken and prior to the time the circuit breaker has been reset, without unduly loading the thermostatic member to cause creep action or retard the current and temperature sensing abilities of the circuit breaker. Other objects and features will be in part apparent and in part pointed out hereinafter.

A circuit breaker of the invention comprises a support which carries a pair of spaced terminals. A snap-acting thermostatic member is fixed to one of the terminals and the member is movable by snap action into and out of contact with the other terminal in response to changes in temperature of the thermostatic member. A latch carried by the support is moved from an engaged posi tion to a disengaged position by the thermostatic member as the latter member moves out of contact with the other terminal. Means are provided to bias the latch'toward its engaged position. A slider is used for resetting the circuit breaker. The latch is adapted to hold the slider against movement from a first to a second position when the latch is in its engaged position and the slider is released for movement to its second position when the latch is disengaged. Means are provided for biasing the slider toward its second position, such occurring when the circuit breaker is tripped to break the circuit being protected. Movement of the slider back to its first position Will result in resetting or closing of the circuit when the thermostatic member has returned to its position engaging the other terminal.

Brief description of the drawings FIG. 1 is a view, partially in section and partially in side elevation, showing a circuit breaker made according to the invention;

FIG. 2 is a plan view, partially in section, of the FIG. 1 circuit breaker;

FIG. 3 is a view similar to FIG. 1 showing the parts in a moved position;

FIG. 4 is a view similar to FIG. 1 showing a modification;

FIG. 5 is a plan view partially in section of the FIG. 4 embodiment; and

FIG. 6 is a view similar to FIG. 4 showing the parts in a moved position.

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

Description of the preferred embodiments Referring to FIGS. 1-3, these show a housing of insulating material generally designated 1 comprising a support body 3 and a cover 5. A pair of

electrical terminals

7 and 9 are carried by the housing and extend from the exterior to a point inside the housing. Terminal 9 comprises a portion 11 spaced from an L-shaped conductor 13, which as will be described below, during certain conditions of operation may be considered a function as part of the terminal 9.

An elongate snap-acting bimetallic thermostatic member 15 has one end portion welded at 17 to member 13. It also carries a movable contact 19 at its end portion opposite weld 17. Member 15 is preferably a dished, electrically conductive bimetallic element having one layer of metal of a low thermal coefiicient of expansion and another layer of metal of a somewhat higher thermal coefiicient of expansion so that upon heating and cooling of the member it snaps between the positions shown in FIGS. 1 and 3. This moves contact 19 between a first position (FIG. 1) wherein it is in engagement with an inside portion of terminal 7 to complete the circuit between

parts

13 and 9 and a second position (FIG. 3) wherein the circuit between these parts is opened. The member 15 is heated by electric current passing through it and it is constructed to snap to the FIG. 3 position in response to a predetermined heating current. The member 15 can be made small so that there is a very small voltage drop across it.

A latch 21 is mounted on a pivot pin 23 projecting from member of the housing. A spring 25 looped around pin 23 has end portions connected to member 5 and the latch to bias the latch clockwise (as viewed in FIG. 1) thereby urging end 27 of the latch toward a shallow groove 29 in the housing. Latch 21 has a lug portion 31 positioned immediately above the movable end portion of the thermostat 15 and to the right of pin 23 so that when the thermostat 15 moves from its FIG. 1 to its FIG. 3 position, it engages latch portion 31 to raise its end portion 27 out of the groove 29 and swing it to the FIG. 3 position. This occurs against the biasing force of spring 25. Spring 25 is comparatively weak so that little force needs to be exerted by member 15 to trip the latch, which is very desirable since it permits a very small thermostatic member to be used. This reduces the voltage drop required across the member 15, making it highly sensitive to even small current variations.

At 33 is indicated an indicator and manual reset device. This comprises a sleeve or slider 35 and an operating plunger or button member 37. Member 37 is received in the right end of sleeve 35 (FIGS. 1 and 3). The plunger fits in and slides through a hole 38 in the housing. A compression spring 39 in the sleeve is attached to plunger 37 and to a conductive bridging contact 41 held in the end of sleeve 35. The bridging contact 41 engages

portions

11 and 13 when the parts are in the FIG. 1 position to provide a path for current therebetween. Spring 39 is compressed when the parts are in the FIG. 1 position. Plunger 37 is made from an electrically insulating material.

An arm 43 (FIG. 2) projects laterally from the sleeve 35. A compression spring 45 reacts from the casing against arm 43 for biasing the sleeve 35 to the right as viewed in the drawings. When the sleeve 35 is free to move, this biasing force also causes movement of the plunger 37 due to the connection between the plunger and the sleeve through spring 39. It should be noted that spring 39 is anchored at opposite ends to the

members

41 and 37.

Sleeve 35 is cut away along the bottom and one side to provide two spaced

shoulders

47 and 49 which are located to be engaged by the upper end 51 of latch 21. When the latch is in the FIG. 1 position it engages shoulder 47 and holds the sleeve against movement toward the right under the biasing force of spring 45. When the latch has been tripped by thermostat 15, it is engaged by the shoulder 49 (FIG. 3) to limit movement of the sleeve toward the right. The latch end 51 is biased upwardly by spring 25. Movement of plunger 37 and sleeve 35 to the left from the FIG. 3 to the FIG. 1 position in order to reset the breaker results in clockwise movement ofthe latch. At this time the latch end 51 clears the lower edge of shoulder 47. This reengages the end 51 with the shoulder 47. As this occurs, latch end 27 swings down into groove 29 and holds the parts in the latched position.

Operation of the circuit breaker of FIGS. 1-3 is as iollows:

Assume initially that the parts are in the latched or reset position shown in FIGS. 1 and 2, current then passes through the circuit breaker from terminal 7 to contact 19. Normally the parts remain in the FIG. 1 position. When an excessive current flow passes through thermostat 15 and heats it to a predetermined temperature, it snaps from the FIG. 1 position to the FIG. 3 position, thereby opening the circuit between

terminals

7 and 9. At this time the contact 41 connects

parts

11 and 13, so that the latter may be considered to be part of the terminal 9 because it is in conductive connection therewith. As this occurs the right-hand end of thermo stat 15 engages latch portion 31 and swings it counterclockwise, thereby lifting latch end 27 out of groove 29 and simultaneously disengaging the end 51 of the latch from shoulder 47. This releases sleeve 35 and it moves to the right under the biasing force of spring 45 until shoulder 49 strikes the latch end 51 (FIG. 3). This moves the contact member 41 to the right, opening the circuit between

parts

11 and 13. The plunger 37 also moves at the right at this time due to the connection by spring 39 between it and the member 41. Thus the circuit through the circuit breaker is open both between

parts

11 and 13 and between

parts

13 and 7.

After a time interval the disc 15 cools and snaps back to the FIG} position. This, however, does not complete the circuit through the circuit breaker since the bridging contact 41 is still separated from

parts

9 and 13. The circuit may be completed by depressing the plunger member 37. This returns slider 33 to its FIG. 1 position where bridging contact 41 engages

parts

9 and 13 to again complete the circuit through the member. When the plunger is released, the parts remain in the FIG. 1 position since the spring 25 has caused clockwise movement of latch 21 to return latch end 51 into engagement with shoulder 47 and simultaneously to lower the end 27 of the latch into the groove 29. The parts remain in this latched position until such time as another current overload heats member 15 enough to cause it to flex upwardly and release the latch.

If the plunger button 37 is depressed prior to the time that member 15 returns from the FIG. 3 to the FIG. 1 position, the circuit will not be completed even though bridging contact 41 engages

contacts

11 and 13 since it is necessary for member 15 to return to its FIG. 1 position to complete the circuit through the circuit breaker. If plunger 37 is depressed prior to cooling of member 15, the latch member 21 cannot be raised to engage shoulder 47 and thus the slider parts cannot be locked in the latched position shown in FIG. 1. If the thermostatic member has cooled and reclosed on contact 7, as in recycling, and an attempt is then made to hold the reset button 37 in the FIG. 1 position, then the disc 15 will cycle once when it is heated, strike the latch 21 to disengage it from the shoulder 47 and permit sleeve 35 to move to the right, thereby opening the circuit between

contacts

11 and 13. The unit cannot cycle or be reset again until the member 37 is released, moved to the right and then returned to the left again. Thus the attempt to avoid normal operation by manually holding in the reset button 37 is avoided.

FIGS. 4-6 show another circuit breaker of the invention which comprises a hollow casing or housing 61 being composed of

parts

63 and 65. A pair of

terminals

67 and 69 have contact portions positioned within the casing. They project through the casing for connection in a protection circuit. A snap-acting bimetallic thermostatic member 71 has an end portion welded at 73 to the contact of terminal 67. The other end portion of member -71 mounts a contact 75 which is engageable with terminal 69 when the parts are in the FIG. 1 position to close a circuit between the

terminals

67 and 69. This is the normal position when the thermostatic member 71 is cool. When this member is heated to a predetermined temperature, it flexes to the FIG. 6 position to separate contact 75 from terminal 69 and thereby open the circuit through the breaker. The member 71 is similar in construction and operation to the member 15 above described.

A pivot 77 extends across the casing in spaced relation to the member 71. The pivot mounts a latch member 79. A screw 81 adjustable in the latch is engageable by the member 71 as it snaps from the FIG. 4 cold, to the FIG. 6 hot position to cause pivotal movement of the latch, the amount of movement being determined by adjustment of screw 81. A compression spring '83 reacts from the casing against the right end of the latch for biasing it in a clockwise direction as viewed in FIGS. 4 and 6. Clockwise movement of the latch is limited by engagement between the left end of the latch and a screw 85 adjustable in the casing. Spring 83 is comparatively weak so that it does not greatly resist movement by the thermostat 71.

A flange 87 at the right end of the latch is biased downwardly by spring 83 into a groove 89 in a slider or reset member 91. The reset member 91 slides through a hole 93 in the casing and an end portion 95' thereof is positioned outside the casing. The end 95 is biased to the right or outwardly by a compression spring 97 reacting from the casing against the left end of the slider. Two fingers or ramps 99 and 101 project from the main body of the slider. Movement of the slider toward the right is limited by engagement between the finger 101 and the casing. As shown in FIG. 5, the fingers are long enough so that they can be positioned between the contact 75 and the terminal 69.

Operation of the FIGS. 4-6 embodiment is as follows:

Normally current passes through the device Sfrom terminal 67, through thermostatic member 71 to terminal 69. When an overload occurs the excessive current passing through the member 71 causes it to heat to a predetermined temperature at which time it flexes from the FIG. 4 to the FIG. 6 position, thereby opening the circuit. When this occurs, the right end portion of the member 71 strikes screw 81 which swings latch 79 about pivot 77 against the biasing force of spring 83. This lifts the end flange 87 of the latch out of the groove 89 in the slider. Spring 97 then moves the slider to the FIG. 6 position. With the slider in this position the latch end 87 cannot return to groove 89. Also, as shown in FIG. 6 the finger 99 is located between the contact 75 on the thermostatic member and the terminal 69 so that even after the thermostatic member cools and flexes back toward its FIG. 4 position contact cannot be reestablished between contact 75 and terminal 69 to complete the circuit through the circuit breaker. Thus the finger 99 prevents cycling operation of the device being protected by the circuit breaker.

In order to reset the circuit breaker the slider 91 is pushed to the left from the FIG. 6 position past its FIG. 4 position until its right end is substantially at the position designated R in FIG. 4. At this time the finger 101 is between the contact 75 and terminal 79 and simultaneously the groove 89 is in a position beneath the latch end 87 so that spring 83 returns the latch to the FIG. 4 position. When the slider 91 is released, the spring 97 moves it back to the solid-line position in FIG. 4, such movement being limited by interengagement between the latch end 87 and the left side of groove 89.

The finger 101 prevents operation of the circuit breaker in the event the slider 91 is fully retracted to the position marked R and mechanically held there to attempt to avoid normal operation of the circuit breaker. Thus the

fingers

99 and 101 together prevent cycling operation when the latch is tripped and prior to the time the slider is reset and also prevent operation of the circuit breaker in the event the slider is fully pushed into the housing and mechanically held in this position.

Both forms of the circuit breaker are capable of sensing very small current overloads and since the thermostatic members can be very small there is a minimum voltage drop across the circuit breaker. Very few parts are required in each form and both are economical to produce and small in size. They are also essentially foolproof and trip free. Both forms also provide means to prevent completion of the circuit through the circuit breaker until it is manually reset. In the FIGS. l-3 embodiment this is prevented by the bridging contact 41 and in the FIGS. 4-6 embodiment it is prevented by the finger 99. In the case of FIGS. l-3, the part 13 may be considered as a part of terminal 9 wherein there is a separation made by spaced contact portions bridged by 41 when the switch is closed.

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.

What is claimed is:

1. A circuit breaker comprising,

a support,

a pair of spaced terminals carried by the support,

a snap-acting thermostatic member connected with one of said terminals, said member being movable into and out of contact with the other terminal in response to changes in temperature of said member,

a latch carried by the support, the latch being moved from an engaged position to a disengaged position by the thermostatic member as said member moves out of contact with said other terminal,

means biasing the latch toward its engaged position,

a slider for resetting the circuit breaker,

the latch being adapted to hold the slider against movement from a first to a second position when the latch is in the engaged position and the slider being released for movement .to its second position when the latch is disengaged,

means biasing the slider toward its second position,

and means preventing completion of the electrical circuit between the terminals when the slider is in its second position.

2. A circuit breaker according to claim 1 wherein one of the terminals has two spaced contact portions, and the means preventing completion of the electrical circuit when the slider is in its second position comprising a bridging contact carried by the slider, the bridging contact engaging both contact portions when the slider is in its first position to complete the circuit therebetween, and the bridging contact being spaced from the contact portions when the slider is in its second position, thereby opening the circuit therebetween.

3. A circuit breaker according to claim 2 wherein the slider comprises a sleeve carrying the bridging contact and a plunger slidable in the sleeve.

4. A circuit breaker according to claim 3 wherein the slider further comprises resilient means in the sleeve connecting the bridging contact and the plunger.

5. A circuit breaker according to claim 3 wherein the sleeve has spaced portions engaged by the latch to hold the slider against movement by the slider biasing means when the slider is in each of its positions.

6. A circuit breaker according to claim 3 wherein the sleeve has two spaced shoulders, the latch is pivoted to the support and has a first portion engageable with each of the shoulders to limit movement of the slider when the slider is in each of its positions, the support has a recess adapted to receive a second portion of the latch when the slider is in its first position, and the latch biasing means urges the second portion of the latch toward the recess.

7. A circuit breaker according to claim 1 wherein the slider has a recess therein adapted to receive a portion of the latch when the slider is in its first position, and the recess being out of alignment with the latch portion when the slider is in its second position.

8. Circuit breaker according to claim 1 wherein said means preventing completion of the circuit when the slider is in its second position comprises a finger of electrical insulating material on the slider which is moved to a position between said other terminal and said thermostatic member when the slider moves to its second position, the finger being moved from between said other contact and said thermostatic member when the slider moves from its second to its first position.

9. Circuit breaker according to claim 8 further comprising an elongate recess in the slider adapted to receive a portion of the latch, the recess being larger than the latch portion to permit limited movement of the slider against its biasing means from the first position of the slider to a third position, and a second finger of electrical insulating material attached to the slider and positionable between said other terminal and said thermostatic member when the slider is in its third position thereb preventing completion of the electrical circuit between the terminals when the slider is in said third position.

8 References Cited UNITED STATES PATENTS 2,743,333 4/1956 Epstein 200-413 2,745,922 5/ 1956 Roberts et a1 200122 3,141,941 7/1964 Dew 200-116 BERNARD A. GILHEANY, Primary Examiner.

R. COHRS, Assistant Examiner.