GB2138634A

GB2138634A - PC-Board Mounted Thermal Switch

Info

Publication number: GB2138634A
Application number: GB08325674A
Authority: GB
Inventors: Donald K Merchant
Original assignee: Airpax Corp
Current assignee: Airpax Corp
Priority date: 1983-03-30
Filing date: 1983-09-26
Publication date: 1984-10-24
Also published as: GB2138634B; JPH0145932B2; GB2181600A; 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. <IMAGE>

Description

SPECIFICATION PC-Board Mounted Thermal Breaker Background of the Invention This invention relates to snap action electrothermally actuated -circuit breakers. More particularly, the invention relates to improved circuit breaker mechanisms for use in compact snap action breakers combining the functions of switches and circuit breakers.

A compact snap action circuit breaker is disclosed in U.S. Pat. No.2,911,503 issued November 3, 1959 to Helmut Garbers. Garbers discloses a safety switch which, in the ON or CLOSED position, establishes a circuit through a bimetallic element, a pair of contacts, and a lever.

When the bimetallic element is heated by an overcurrent, it deflects the lever past the center 'line of an overcenter spring. The switch then 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 opposite direction to that required for tripping of the circuit.Furthermore, .breakers such as described in the Garbers patent use separate heater and heating elements to heat the bimetal'. Finally,.in known circuit breakers, adjustment of the breaker is usually made via an imprecise calibration screw; Summary of the Invention The present invention, described with. respect to the appended drawings and the detailed description of the preferred enibodirnents below, provides new and improved electrothermally actuated circuit breaker mechanisms. The invention comprises a thermal circuit breaker with a low mass thermal element which heats and cools quickly, thus providing a faster trip time than known breakers, without the need of an auxilliary heater.

In the present invention, the thermal element is supported by the insulated housing of the breaker.

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

The circuit breaker of the present invention is particularly well 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 against the starting friction; in essence, the bimetallic 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-the circuit breaker of the present invention 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 consideration in choosing components for PC boards, where space is at a premium.

A second embodiment ofthe invention provides a multi-pole circuit breaker which opens two or more circuits in response to an overcurrent through any one of the circuits.

A third embodiment of the invention provides a dual contact breaker mechanism.

Other features and advantages of this invention will be apparent from the following 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 sh-owing the breaker'mechanism df this invention in the contacts-closed position; Figure 2 is an end view of the line terminal in the snap action PC-board-mounted thermal breaker; Figure 3 is an end view of the load terminal in the snap action PC-board-mounted thermal breaker; Figure 4 is a cut-away side view of the snap action PC-boayd--mounte.d thermal breaker showing the breaker mechanism in the contacts open position; Figure 5 is a top view of the snap action PC board-mounted thermal breaker;; -Figure 6 is a top view of the second embodiment of the present invention as a multipole breaker 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 the Preferred 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, e.g., molded plastic. A line terminal 4 and a load terminal 6 are mounted in housing 2. In the embodiment shown, line terminal 4 is a U-shaped conductor. Terminal 4 has a short leg 8, a long leg 10, and a bridging portion 12. Leg 10 has a portion 1 Oa disposed within housing 2, and a portion 1 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 14 that extends from leg 10, across bridging section 12, to leg 8. Line terminal 4 also includes a pair of notches 1 6 located midway on the two parallel sections of Jeg portion 10a.

Load terminal 6 advantageously is a straight conductor. In the disclosed embodiment, the portion 6a of terminal 6 inside housing 2 is wider than the portion 6b extending out of the housing.

A tab 18, shown in Figure 3, is provided substantially in the middle of portion 6a of load terminal 6.

The circuit breaker of the present invention further includes a movable contact blade member 20. As shown in Figures 1 and 4, contact blade 20 has a pair of (preferably beveled) tips 22 which seat in notches 1 6 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 1 4 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 pivotally biased downward when the thermal breaker is in the contacts-closed ppsition, due to the over-center position of spring 26. A (preferably circular) electrical contact pad 28 is mounted to contact blade member 20 at the opposite end from pivot tips 22.

The circuit breaker also includes a bimetallic element 30. As shown in- Figure 1, bimetallic element 30 is L-shaped and has a first portion 32 which is mounted to load terminal 6. Bimetallic element 30 also has a second, elongated portion 34 which rests on an insulated sawtooth surface 36 on the inside of housing 2. Sawtooth surface 36 is designed to provide support for bimetallic element 30 with a minimal area of contact. This failure of the present invention prevents housing 2 from acting as a heat sink to bimetallic 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 expansion than the metal of the upper layer.

Consequently, when bimetallic element 30 is heated, it bends in an upward direction, as shown in Figure 5.

Bimetallic element 30 hasa (preferably circular) contact pad 38 mounted on the free end of its elongated portion 34. When the circuit breaker is in the contacts closed position, as shown in Figure 1, pad 38 makes electrical contact with pad 28 of blade member 20.

Optionally, the circuit breaker of the present invention also may include an additiohal contact pad 40 on contact blade 20, as well as an optional terminal 42. Optional terminal 42 has a sornewhat hook-shaped conductor portion 43 at one end, as shown in Figure 1. Terminal 42 may be connected externally to a separate circuit which may activate, for example, a warning device or alarm.

Optional terminal 42 also function as a stop to prevent overtravel of contact blade 20. Hence, if an alarm or warning circuit is not required, - housing 2 may be designed to include a stop boss, or the equivalent, to replace terminal 42.

A reset button 44 is provided in housing 2. The upper portion 46 of 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 opening 1 4 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.

In the preferred embodiment, an aperture 56 is located on one end of housing 2, providing access to the bending tab 1 8 of load terminal 6. The current rating of the circuit breaker may be adjusted by inserting a pin-type device through aperture 56 and bending tab 18 inward. This action, in turn, pivots bimetallic element 30, in a counterclockwise direction.

In the operation of the circuit breaker, current flows between terminals 4 and 6 via contact blade 20, contacts 28 and 38, and bimetallicelement 30. An overcurrent through the breaker causes bimetallic element-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 (designated 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 breaker with a snap action, as shown in Figure 5. In the optional configuration shown, contact pad 40 on blade 20 then makes contact with terminal 42 in the contacts-open position, thereby actuating an alarm circuit, or the like.

No current flows through bimetal 30 once the circuit breaker is tripped open. Bimetal 30 thereupon cools and returns to its original position on sawtooth surface 36. Spring 26 continues to 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 downward by leg 52 until engagement point C moves below the line between points A and B. The direction of spring bias force against reverses and urges blade 20 downwardly into contact with bimetal 30. The breaker is then returned to the 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 arid 7, parts corresponding to those of the first embodiment are designated by""' and """ marks, respectively.

Both of the thermal 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 circular openings 54' and 54". The circuit breaker is assembled so that spring 26' and 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 at the same time. Similarly, downward movement of reset button 44' forces crossarm 48' down, thereby closing both mechanisms and setting both poles at the same time. It should be apparent that this embodiment is not limited to a two pole breaker mechanism.

A third embodiment of the invention, shown in Figure 8, provides a dual contact breaker mechanism. 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 cqhtact thermal breaker.

In the disclosed embodiment line terminal 60 consists of a portion inside housing 58 with an elongated slotted opening 66, as shown by the dotted lines in Figure 6. Similar to the first embodiment, line terminal 60 also includes a pair of notches 68 located on opposite sides of slotted opening 66.

Load terminals 62 and 64 are straight conductors. Tabs 70 and 72, similar in shape to tab 18 of the first embodiment, are provided in load terminals 62 and 64 for adjustment of the circuit breaker.

Similar to the configuration of the first embodiment, the dual contact thermal breaker includes a movable contact blade 74. Contact blade 74 has a pair of (preferably beveled) tips 76, which seat in notches 68 of line terminal 60.

Contact blade 74 is positioned to pivot about its tips 76. Contact blade 74 also has an 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 extends through slotted opening 66 of line terminal 60. Spring biases contact blade 74 in opposite directions as a function of the location of spring end 80a relative to a line drawn between the point of engagement of spring end 80b with extension 82 (designated 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 at the opposite end from pivot tips 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. Irk 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 inner face. As shown in Figure 6, bimetallic elements 88 and 90 rest on sawtooth surfaces 104 and 106, respectively, in the absence of an overcurrent. As in the first embodiment of the invention, these surfaces provide support for their corresponding bimetallic element with a minimal area of contact.

Apertures 108 and 110 are provided through the housing adjacent to load terminals 62 and 64.

The current ratings of the two breaker mechanismsmay be adjusted by inserting a pintype device through the appropriate aperture 108 or 110 and bending the tab terminal 70 or 72.

This action, in turn, pivots corresponding bimetallic element 88 or 90 to provide the desired calibration.

In operation, contact blade 74 rests overcenter on one of the two contacts 96 or 98, thus providing a closed circuit to the corresponding load terminal. An overcurrent through the closed circuit causes the corresponding bimetallic element to deform sufficiently to pivot contact blade 74 over the center of spring 80, and snap over to the contact of the other bimetallic element.

It is apparent from the foregoing that the present invention provides an improved snap action thermal breaker mechanism. The thermal breaker of the present invention provides a faster trip time than prior thermal breakers, due to the quick heating and cooling of the bimetallic unit resulting from a unique set of notches designed in the housing of the unit. Furthermore, due to its compact size, the thermal breaker of the present invention is also better for PC-board mounting with semiconductor elements than prior devices.

A second embodiment of the invention provides a multi pole circuit breaker which opens all circuits in response to an overcurrent through any one of the circuits. A third embodiment of the present invention provides for switching between two individual circuits by using two separate bimetallic elements.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being limited by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency.of the claims are, therefore, intended to be embraced therein.

Claims

1. A thermal circuit breaker, comprising: an electrically insulating housing; first and second terminal means extending through said housing for connecting the breaker to an electrical circuit; a first contact member, comprising a bimetallic element located in said housing and electrically coupled to said first terminal; a second contact member located in said housing and electrically coupled to said second terminal; means mounting said second contact member for movement into and out of contact with said first contact member; and means biasing said second contact member substantially through the center of movement of said second contact member to 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 contact with said first contact member, and in said second position, said second contact member is biased' out of electrical contact with said first contact member; said first contact member being deformed upon application of a sufficient overcurrent therethrough to move said second contact member from said first poslticn'toward said second position against the action of said biasing means.

2. Appára'tus 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 first contact member rests when said first contact member is not in a deformed state.

3. Apparatus according to claim 1, wherein said circuit breaker further comprises an 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 claim 1, wherein said circuit breaker further comprises reset means operable to return said second contact member to said first position from said second position.

5. Apparatus according to claim 1, wherein said housing further includes means for providing access to said first terminal for adjustment of the position of said first contact member.

6. Apparatus according to claim 5, wherein said first terminal includes a bendable tab on the housed portion thereof.

7. Apparatus according to claim 6, wherein said first contact member is L-shaped, comprising a first portion and a second portion, and wherein said first portion abuts on said bendable tab of said first terminal.

8. Apparatus according to claim 1, wherein said mounting means comprises a blade member with an opening located along the longitudinal axis thereof.

9. Apparatus according to-claim. 3y,-whernin 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.

10. Apparatus according to claim 9, \wherein said circuit breaker further comprises reset means operable to return said second contact member to said first position from said second position, and reset means including a reset member extending into said housing and being movable therein, said reset member and'said biasing means engaging each other to move said second contact member between said first and second positions.

11. Apparatus according to claim 10, wherein said reset member hasan opening therein through which said biasing means passes.

12. Apparatus according to claim 1 wherein said circuit breaker further comprises reset means operable to return said second contact member to said first position when said second contact member is in said second position; and wherein: said electrically insulated housing of said circuit breaker includes a sawtooth surface in-the lower portion of said housing; upon - which sa'id first contact member rests when saidfirst contact members not in a deforsned state; said housing further includes means for - providing access to said first terminal for adjustment af the position of said first contact member;.

said first terminal includes a bendahle tab on the housed portion thereof adjacent said access means.

said first contact member comprises a first portion and second portion, said first portion abutting on said bendable tab of said first terminal; said mounting means comprises a blade with an opening located along the longitudinal axis thereof; and 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.

13. Apparatus according to claim 12, wherein said reset means includes a reset member extending into said housing and being movable therein, said reset member having an opening therein through which said biasing means passes, said reset member and said biasing means engaging each other to move said second contact member between said first and second positions.

14. A thermal circuit breaker, comprising: an electrically insulated housing; first, second, and third terminal means extending through said housing, wherein said first terminal is connected to a first electrical circuit and said second terminal is connected to a second electrical circuit; a first contact member, comprising a first bimetallic element located in said housing and electrically coupled to said first terminal; a second contact member, comprising a second bimetallic element located in said housing and electrically coupled to said second terminal; a third contact member located in said housing and electrically coupled to said third terminal; means mounting said third contact member for movement alternatively into and out of contact with said first and second contact members, respectively; and means biasing said third contact member substantially through the center of movement of said third contact member to alternatively bias said third contact member in opposite pivotal directions between first and second positions, wherein in said first position, said third contact member is biased into electrical contact with said first contact member, and in said second position, said third contact member is biased into electrical contact with said second contact member; said first contact member being deformed upon application of a sufficient overcurrent therethrough against the action of said biasing means to move said third contact member from said first position toward said second position; and said second contact member being deformed upon application of a sufficient overcurrent therethrough against the action of said biasing means to move said third contact member from said second position toward said first position.

1 5. Apparatus according to claim 14, 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.

1 6. Apparatus according to claim 14, wherein said housing further includes means for providing access to said first and second terminals for adjustment of the positions of said first and second contact members, respectively.

1 7. A multiple thermal circuit breaker, comprising: an electrically insulated housing; a plurality of pole units in said housing, each pole unit having substantially the same breaker mechanism, and each breaker mechanism comprising: first and second terminal means extending through said housing for connecting the breaker to an electrical circuit; a first contact member, comprising a bimetallic element located in said housing and electrically coupled to saTa first terminal; a second contact member located in said housing and electrically coupled to said second terminal; means mounting said second contact member for movement into and out of contact with said first contact member; and means biasing said second contact member substantially through the center of .

movement of said second contact member to 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 contact with said first contact member, and in said second position, said second contact member is biased out of electrical contact with said first contact member; said first contact member being deformed upon application of a sufficient overcurrent therethrough to move said second contact member from said first position toward said second position against the action of said biasing means; said multipole breaker further comprising:: a common reset means coupled to each of said plurality of breaker mechanism and operable to return all of said second contact members to said first position when said second contact members are in said second position.

18. Apparatus according to claim 17, further comprising means coupling 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 overcurrent through any of said breaker mechanisms.

19. Apparatus according to claim 17, 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 plurality of openings therein through which each of said biasing means passes, said reset member and said biasing means engaging each other to move each of said second contact members between said first and second positions substantially concurrently.

20. A thermal circuit breaker substantially as hereinbefore described with reference to the accompanying drawings.