GB2181600A

GB2181600A - PC-board mounted thermal switch

Info

Publication number: GB2181600A
Application number: GB08624046A
Authority: GB
Inventors: Donald K Merchant
Original assignee: Airpax Corp
Current assignee: Airpax Corp
Priority date: 1983-03-30
Filing date: 1986-10-07
Publication date: 1987-04-23
Also published as: GB2138634B; GB2138634A; JPH0145932B2; GB2181600B; GB8325674D0; JPS59214126A; GB8624046D0

Abstract

A PC-board mounted thermal switch that opens with a snap action includes a bimetallic element 30, connected to a load terminal 6 and resting on an insulated sawtooth surface 36 when contacts 28,38 are in the closed position. A contact blade 20 connected to a line terminal 4 is pivotably biased downward into electrical contact with the bimetallic element by the action of an overcenter spring 26. An overcurrent through the breaker heats the bimetallic element 30 directly and causes it to bend upwardly, forcing the contact blade 20 to pivot against the bias of the spring. When the contact blade has pivoted sufficiently to move the spring overcenter, the direction of spring bias reverses, pivoting the contact blade rapidly upward, and thereby opening the contacts with a snap action. The housing provides an access aperture 56 to the load terminal 6 for adjusting the position of the bimetallic element 30. <IMAGE>

Description

1 GB 2 181 600 A 1

SPECIFICATION

PC Board mounted thermal breaker Background of the invention

This invention relatesto snap action electrothermally actuated circuit breakers. More particularly, the invention relatesto improved circuit breaker mechanismsfor use in compact snap action breakers com- bining the functions of switches and circuit breakers.

A compact snap action circuit breaker is disclosed in US Pat No 2,911,503 issued November 3,1959 to HelmutGarbers. Garbers discloses a safetyswitch which, in the ON orCLOSED position, establishes a circuitthrough a bimetallic element, a pairof contacts, and a lever. When the bimetallic element is heated byan overcurrent, itdeflectsthe lever pastthe center line of an overcenter spring. Theswitchthen snaps open.

In circuit breakers such as disclosed by Garbers, however, the bimetallic elements are generally suspended in air. Reactive elements, therefore, tend to bend the bimetallic element downward, in the oppsoite direction to that required fortripping of the cir- cuit. Furthermore, breakers such as described in the Garbers patent use separate heater and heating elements to heatthe bimetal. Finally, in known circuit breakers, adjustment of the breaker is usually made via an imprecise calibration screw.

Summaryof theinvention

The present invention provides a thermal circuit breaker, comprising:

an electrically insulating housing; firstand second terminal means extending 100 through said housing for connecting the breakerto an electrical circuit; a firstcontact member, comprising a a bimetallic element located in said housing and electrically coupledto said firstterminal means; a second contact member located in said housing and electrically coupled to said second terminal means; means mounting said second contact memberfor movement into and out of contactwith said firstcontact member; and means biasing said second contact membersubstantiallythrough the center of movement of said second contact memberto alternately bias said second contact member in opposite directions between first and second positions, wherein in said first position, said second contact member is biased into electrical contactwith said first contact member, and in said second position, said second contact member is biased out of electrical contactwith said first contact member; said first contact member being deformed upon application of a sufficient overcurrent therethrough to move said second contact memberfrom said first position toward said second position againstthe action of said biasing means; and wherein said housing further includes means for providing accessto said firstterminal meansfor adjustment of the position of said firstcontact member.

The bimetallic element of the present invention is heated directly by the flow of the current being monitored. The current rating may by accurately adjusted by stepping a pin through an aperture in the circuit breaker housing.

The circuit breaker of the present invention is particularlywell suited for low current applications. Since power is a function of thickness, the present invention advantageously includes a thin bimetallic element, permitting accurate and sensitive operation of the unit at very low currents.

The thin bimetallic blade in the present invention also acts like a spring providing a flexing action againstthe starting friction; in essence, the bi- metallic blade stores mechanical energy which assists the temperature related bending forces in the bimetallic material in tripping the circuit. Once the starting friction has been overcome, the circuit opens as though a spring has been released.

The small size of circuit breakerwhich the present invention makes possible provides for better mounting on a PC board with semiconductor elements than known circuit breakers. The compact design of the present invention saves space, a critical considera- tion in choosing components for PC boards, where space is at a premium.

The invention also provides a multipole circuit breakerwhich openstwo or more circuits in responseto an overcurrentthrough any one of the circuits, and a dual contact breaker mechanism, incorporating the features defined above.

Otherfeatures and advantages of this invention will be apparentfrom thefollowing description of the preferred embodiments.

Brief description of the drawings

Figure 1 is a cut-away side view of the snap action PC-board-mounted thermal breaker showing the breaker mechanism of this invention in the contacts- closed position; Figure2 is an end view of the lineterminal in the snap action PC-board- mounted thermal breaker; Figure3 is an end view of the load terminal in the snap action PC-board- mounted thermal breaker; Figure4is a cut-away sideview of the snap action PC-board-mounted thermal breaker showing the breaker mechanism in the contacts-open position; Figure 5is a top view of the snap action PC-boardmounted thermal breaker; Figure 6is a top view of the second embodiment of the present invention as a multipole breker mechanism; Figure 7 is an end view of the second embodiment of the invention as a multipole breaker mechanism; and Figure 8 is a cut-away view of the third embodiment of the invention as a dual contact breaker mechanism.

Description of thepreferred embodiment

Figures 1-5 show a first embodiment of the snap action thermal breaker of this invention. Referring to Figure 1, the thermal breaker includes a housing 2 of insulating material, eg molded plastic. A line ter- minal 4 and a load terminal 6 are mounted in housing 2 GB 2 181 600 A 2 2. In the embodiment shown, I ine terminal 4 is a Ushaped conductor. Terminal 4 has a short leg 8, a long leg 10, and abridging portion 12. Leg 10 has a portion 10a disposed within housing 2, and a portion l Ob which extends through housing 2 for connection to an external electrical circuit to be protected. As shown in Figure 2, terminal 4 has an elongated slotted opening 14that extends from leg 10, across bridging section 12,to leg 8. Lineterminal 4also in- cludes a pairof notches 16 located midwayonthe two parallel sectionsof leg portion 10a. Loadterminal 6 advantageously is a straight conductor. In thedisclosed embodiment,the portion 6a ofterminal 6 inside housing 2 iswiderthanthe portion 6b exten- ding outof the housing. Atab 18, shown in Figure3, is provided substantially in the middle of portion 6a of load terminal 6.

As shown in Figures 1 and 4, a contact blade member 20 has a pair of (preferably beveled) tips 22 which seat in notches 16 of line terminal 4. Contact blade 20 is positioned to pivot about its tips 22. As can be seen in Figure 4, contact blade 20 also has an opening 24 located on its longitudinal axis. One end 26a of a bias spring 26 is disposed in opening 24. the other end 26b of spring 26 is secured to leg 8 of line terminal 4. Spring 26 extends through slotted opening 14 in the longer leg 10 of line terminal 4. Spring 26 biases contact blade member 20 in opposite directions as a function of the location of spring end 26a relative to a line drawn between the point of engagement of spring end 26b with terminal leg 8 (designated A) and the point of contact of contact blade tips 22 in notches 16 (designated B). Contact blade 20 is pivotably biased downward when the thermal breaker is in the contacts-closed position, due to the overcenter position of spring 26. A (preferably circular) electrical contact pad 28 is mounted to contact blade member 20 atthe opposite end from pivottips 22.

The circuit breaker also includes a bimetallic el- ement 30. As shown in Figure 1, bimetallic element is L-shaped and has afirst portion 32 which is mounted to load terminal 6.

Bimetallic element 30 also has a second, elongated portion 34which rests on an insulated sawtooth sur face 36 on the inside of housing 2. Sawtooth surface 36 is designed to provide supportfor bimetallic el ement 30 with a minimal area of contact. This feature prevents housing 2 from acting as a heat sinkto bi metallic element 30. Bimetallic element 30 comprises an upper layer and a lower layer. The lower layer is composed of a metal with a higher coefficient of ex pansion than the metal of the upper layers. Consequ ently, when bimetallic element 30 is heated, it bends in an upward direction, as shown in Figure 5.

Bimetallic element30 has a (preferably circular) contact pad 38 mounted on the free end of its elonga ted portion 34. When the circuit breaker is in the con tacts closed position, as shown in Figure 1, pad 38 makes electrical contact with pad 28 of blade 125 member20.

Optionally, the circuit breaker also may include an additional contact pad 40 on contact blade 20, as well as an optional terminal 42. Optional terminal 42 has a somewhat hook-shaped conductor portion 43 atone end, as shown in Figure 1. Terminal 42 may be connected externallyto a separate circuitwhich may activate, for example, a warning device oralarm.

Optional terminal 42 also functions as a stop to pre- vent overtravel of contact blade 20. Hence, if an alarm orwarning circuit is not required, housing 2 may be designed to include a stop boss, orthe equivalent, to replace terminal 42.

A reset button 44 is provided in housing 2. The upper portion 46 reset button 44 extends outside the top of housing 2. The lower portion 48 of reset button 44 extends into housing 2 and includes a generally cylindrical shaft 50 and a leg 52 extending from the end of shaft 50. Shaft 50 extends through slotted op- ening 14 of line terminal 4. Leg 52 is provided with an opening 54. The circuit breaker is assembled so that spring 26 extends through opening 54, as shown in Figure 1.

An aperture 56 is located at one end of housing 2, providing access to the bending tab 18 of load terminal 6. The current rating of the circuit breaker may be adjusted by inserting a pin-type devicethrough aperture 56 and bending tab 18 inward. This action, in turn, pivots bimetallic element 30, in a counter- clockwise direction.

In the operation of the circuit breaker, currentflows between terminals 4 and 6 via contact blade 20, contact 28 and 38, and bimetallic element 30. An overcurrentthrough the breaker causes bimetallic el- ement 30 to heat and bend upwardly, causing blade 20 to pivot in the counterclockwise direction against the bias force of spring 26. When bimetallic element 30 pivots blade 20 upwardly sufficiently to move the contact point of spring end 26a and blade 20 (des- ignated C) above the line between points A and B,the direction of spring bias reverses, pivoting blade 20 rapidly in a counterclockwise direction, and thereby opening the breakerwith a snap action, as shown in Figure 5. In the optional configuration shown, contact pad 40 on blade 20then makes contactwith terminal 42 in the contactsopen position, thereby actuating an alarm circuit, orthe like.

No current flows through bimetal 30 oncethe circuit breaker istripped open. Bimetal 30thereupon cools and returnsto its original position on sawtooth surface 36. Spring 26 continuesto bias blade 20 in the counterclockwise direction; the breaker remains open until manually reset. The breaker is reset by a downward movement of reset button 44. Spring 26 is forced downwardly by leg 52 until engagement point C moves belowthe line between pointsA and B. The direction of spring biasforce again reverses and urges blade 20 downwardly into contactwith bimetal 30. The breaker isthus returned tothe contacts closed position.

The breaker may be manually opened by an upward movement of reset button 44, whereby spring 26 is forced upward overcenter.

A second embodiment of the invention, shown in Figures 6 and 7, provides a multipole breaker mechanism. This embodiment, as shown, includes two thermal breaker mechanisms substantially like the first embodiment and contained in a single housing 2'. In Figures 6 and 7, parts corresponding to those of the first embodiment are designated by"'" and C p 3 GB 2 181 600 A 3 marks, respectively. Both ofthethermal breaker poles are controlled by a single reset button 44'consisting of a single crossarm 48'and a single cylindrical shaft 50'. Crossarm 48'is provided with two cir- cular openings 54'and 54'. The circuit breaker is assembled so that springs 2Wand 26' extend through openings 54'and 54", respectively.

In the operation of this embodiment, the opening of either breaker pole (as a result of an overcurrent or by manual upward movement of reset button 44') forces crossarm 48'up, thereby opening both poles atthe same time. Similarly, downward movement of reset button 44'forces crossarm 48'down, thereby closing both mechanism and setting both poles at the sametime. ltshould be apparent that this embodiment is not limited to a two pole breaker mechanism.

Athird embodiment of the invention, shown in Figure 8, provides a dual contact breaker mech- anism. This embodiment includes a housing 58 of insulating material, wherein a line terminal 60 and two load terminals 62 and 64 are mounted. Line terminal 60 may be located in the center portion of the dual contactthermal breaker.

In the disclosed embodiment, lineterminal 60 consists of a portion inside housing 58 with an elongated slotted opening 66, as shown bythe dotted lines in Figure 6. Similartothefirst embodiment, linetermina] 60 also includes a pairof notches68 located on opposite sides of slotted opening 66.

Loadterminals 62 and 64are straight conductors. Tabs70and 72, similar in shapeto tab 18 of thefirst embodiment, are provided in loadterminals62 and 64 for adjustment of the circuit breaker.

Similarto the configuration of thefirstembodiment,the dual contactthermal breaker includes a movablecontact blade 74. Contact blade74 has a pair of (preferably beveled) tips76,which seat in notches 68 of lineterminal 60. Contact blade74 is positioned to pivot about its tips 76. Contact blade 74also hasan opening 78 located on its longitudinal axis. One end 80a of a bias spring 80 is disposed in opening 78. The other end 80b of spring 80 is secured to an extension 82 of housing 58, as shown in Figure 8. Spring 80 ex- tendsthrough slotted opening 66 of line terminal 60. Spring 80 biases contact blade 74 in opposite directions as a function of the location of spring end 80a relative to a line drawn betwen the point of engagement of spring end 80b with extension 82 (designa- ted A) and the point of contact of tips 76 in notches 68 (designated B). Two contact pads 84 and 86 are mounted on opposite sides of contact blade 74 atthe opposite end from pivottips 76.

The disclosed embodiment also includes a pair of bimetallic elements 88 and 90 which are contoured to the shape of housing 58, as shown in Figure 8. In a similar manner to the first embodiment, bimetallic elements 88 and 90 have first portions 92 and 94 mounted to respective load terminals 62 and 64.

Additionally contacts 96 and 98 are mounted on the ends of the elongated portions 100 and 102 of bimetallic elements 88 and 90.

Housing 58 includes a pair of sawtooth surfaces 104 and 106 on its innerface. As shown in Figure 6, bimetallic elements 88 and 90 rest on sawtooth sur- faces 104 and 106, respectively, in the absence of an overcurrent. As in the first embodiment of the invention, these surfaces provide supportfortheir corresponding bimetallic elementwith a minimal area of contact.

Apertures 108 and 110 are provided through the housing adjacentto load terminals 62 and 64. The current ratings of the two breaker mechanisms may be adjusted by inserting a pin-type devicethrough the appropriate aperture 108 or 110 and bending the tabterminal 70 or72. This action, in turn, pivots corresponding bimetallic element 88 or90 to providethe desired calibration.

In operation, contact blade 74 rests overcenter on one of thetwo contacts 96 or 98, thus providing a closed circuitto the corresponding load terminal. An overcurrentthrough the closed circuit causesthe corresponding bimetallic elementto deform sufficientlyto pivot contact blade 74 overthe center of spr- ing 80, and snap over to the contact of the other bimetallic element.

Claims

1. Athermal circuit breaker, comprising:

an electrically insulating housing; first and second terminal means extending through said housing for connecting the breakerto an electrical circuit; a first contact member, comprising a bimetallic element located in said housing and electrically coupled to said firstterminal means; a second contact member located in said housing and electrically coupled to said second terminal means; means mounting said second contact memberfor movement into and out of contactwith said firstcontact member; and means biasing said second contact membersub- stantial ly through the centerof movement of said second contact memberto alternately bias said second contact member in opposite directions between first and second positions wherein in said first position, said second contact member is biased into electrical contactwith said first contact member, and in said second position, said second contact member is biased out of electrical contactwith said first contact member; said first contact member being deformed upon application of a sufficient overcurrenttherethrough to move said second contact memberfrom said first position towards said second position againstthe action of said biasing means; and wherein said housing further includes means for providing access to said firstterminal meansfor adjustment of the position of said firstcontact member.

2. Apparatus according to claim 1, wherein said electrically insulated housing of said circuit breaker includes a sawtooth surface in the lower portion of said housing, upon which said firstcontact member restswhen said first contact member is not in a deformed state.

3. Apparatus according to claim 1 or claim 2, wherein said circuit breaker further comprises an 4 GB 2 181 600 A 4 additional terminal wherein said second contact member is biased into electrical contact with said additional terminal when said circuit breaker is in said second position.

4. Apparatus according to any preceding claim, wherein said circuit breaker further comprises reset means operable to return said second contact memberto said first position from said second posi tion.

5. Apparatus according to any preceding claim, 75 wherein said firstterminal includes a bendable tab on the housed portion thereof.

6. Apparatus according to claim 5, wherein said first contact member is L-shaped, comprising a first portion and a second portion, and wherein said first portion abuts on said bendabletab of said firstter minal.

7. Apparatus according to any preceding claim, wherein said mounting means comprises a blade memberwith an opening located along the long itudinal axis thereof.

8. Apparatus according to claim 7, wherein said bias means comprises an overcenter spring, wherein one end of said overcenter spring is coupled to said second terminal, and the other end of said overcenter spring is coupled to said mounting means through said opening.

9. Apparatus according to claim 8, wherein said circuit breaker further co m prises reset means o per able to return said second contact member to said first position from said second position, said reset means including a reset member extending into said housing and being movable therein, said reset member and said biasing means engaging each otherto move said second contact member between said first and second positions.

10. Apparatus according to claim 9, wherein said reset member has an opening therein through which said biasing means passes.

11. Athermal circuit breaker, comprising; 105 an electrically insulated housing; first, second, and third terminal means extending through said housing, wherein said firstterminal means is connected to a first electrical circuit and said second terminal means is connected to a second 110 electrical circuit; afirstcontact member, comprising a first bi metallic element located in said housing and electric ally coupled to said firstterminal means; a second contact member, comprising a second bimetallic element located in said housing and electrically coupled to said second terminal means; a third contact member located in said housing and electrically coupled to said third terminal means; means mounting said third contact memberfor movement alternatively into and out of contactwith said first and second contact members respectively means biasing saidthird contact membersubstantiallythrough the center of movementof said third contactmemberto alternatively bias said third contact member in opposite pivotal directions between first and second positions, wherein in said f irst position, said third contact member is biased into electrical contactwith said first contact member, and in said second position, said third contact member is biased into electrical contactwith said second contact member; said first contact member being deformed upon application of a sufficient overcurrenttherethrough againstthe action of said biasing meansto move said third contact memberfrom saidfirst position toward said second position; said second contact member being deformed upon application of a sufficient overcu rrent therethrough againstthe action of said biasing meansto move said third contact memberfrom said second position toward said first position; and wherein said housing further includes means for providing access to said first and second terminal means for adjust- ment of the positions of said first and second contact members, respectively.

12. Apparatus according to claim 11, wherein said electrically insulated housing of said circuit breaker includes a sawtooth surface around its inner perimeter, upon which said first and second contact members alternatively rest when said circuit breaker is in said first and second positions, respectively.

13. A multiple thermal circuit breaker, comprising:

an electrically insulated housing; a plurality of pole units in said housing, each pole unit having substantiallythe same breaker mechanism, and each breaker mechanism comprising; first and second terminal means extending through said housing for connecting the breakerto an electrical circuit; a first contact member, comprising a bimetallic element located in said housing and electrically coupled to said firstterminal means; a second contact member located in said housing and electrically coupled to said second terminal means; means mounting said second contact memberfor movement into and out of contactwith said firstcontact member; and means biasing said second contact member substantially through the center of movement of said second contact memberto alterately bias said second contact member in opposite directions between first and second positions, wherein in said first position, said second contact member is biased into electrical contactwith said first contact member, and in said second position, said second contact member is biased out of electrical contactwith said firstcon- tactmember; said first contact member being deformed upon application of a sufficient overcurrenttherethrough to move said second contact memberfrom said first position toward said second position againstthe ac- tion of said biasing means; said multipole breakerfurther comprising:

a common reset means coupled to each of said plurality of breaker mechanism and operableto return all of said second contact membersto said first position when said second contact members are in said second position; and means in said housing providing accessto said firstterminal meansof each pole unitfor adjusting the positions thereof.

14. Apparatus according to claim 13, further corn- J_ GB 2 181 600 A 5 prising means cou p] ing said reset means in common to all of said breaker mechanisms to move all of said second contact members from said first position to said second position upon application of a sufficient overcurrentthrough any of said breaker mechanisms.

15. Apparatus according to claim 13, wherein said circuit breaker further comprises reset means operable to return said second contact member to said first position from said second position, said reset means including a reset member extending into said housing and being movable therein, said reset member having a pluarlity of openings therein through which each of said biasing means passes, said reset member and said biasing means engaging each otherto move each of said second contact members between said first and second positions substantially concurrently.

Printed for Her Majesty's Stationery Office by Croydon Printing Company (UK) Ltd,3187, D8991685. Published by The Patent Office, 25 Southampton Buildings, London, WC2A l AY, from which copies maybe obtained.