US3818403A

US3818403A - Circuit breaker apparatus

Info

Publication number: US3818403A
Application number: US00302157A
Authority: US
Inventors: W Ambler
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 1972-10-30
Filing date: 1972-10-30
Publication date: 1974-06-18
Anticipated expiration: 1991-06-18

Abstract

A circuit breaker device which is particularly useful with direct current such as in an automotive application comprises a main creep-acting thermostatic strip member mounted on a second auxiliary U-shaped thermostatic member, the U-shaped member being attached to the strip with the high and low expansion layers being dissimilar or reversed in order to obtain increased contact force prior to actuation and faster contact opening and in effect, greater differential after actuation. One leg of U-shaped thermostatic member is mounted on a base plate, the other leg cantilever mounts the thermostatic strip. A contact is located on the free distal end of the thermostatic strip and is adapted to move into and out of engagement with a stationary contact supported on the base plate but electrically insulated therefrom. A special insulator pad mounts the stationary contact and is received on and locked in place on the base plate. Several embodiments are shown in which the auxiliary thermostatic member is formed from the same element as the main thermostatic member.

Description

United States Patent [191 Ambler June 18, 1974 CIRCUIT BREAKER APPARATUS Walter B. Ambler, Norwood, Mass.

[73] Assignee: Texas Instruments Incorporated,

Dallas, Tex.

221 Filed: Oct. 30, 1972 211 App]. No.: 302,157

[75] Inventor:

Primary Examiner-George Harris Assistant ExaminerFred E. Bell Attorney, Agent, or FirmJohn A. Haug; James P. McAndrews; Edward J. Connors, Jr.

[5 7] ABSTRACT A circuit breaker device which is particularly useful with direct current such as in an automotive application comprises a main creep-acting thermostatic strip member mounted on a second auxiliary U-shaped thermostatic member, the U-shaped member being attached to the strip with the high and low expansion layers being dissimilar or reversed in order to obtain increased contact force prior to actuation and faster contact opening and in effect, greater differential after actuation. One leg of U-shaped thermostatic member is mounted on a base plate, the other leg cantilever mounts the thermostatic strip. A contact is located on the free distal end of the thermostatic strip and is adapted to move into and out of engagement with a stationary contact supported on the base plate but electrically insulated therefrom. A special insulator pad mounts the stationary contact and is received on and locked in place on the base plate. Several embodiments are shown in which the auxiliary thermostatic member is formed from the same element as the main thermostatic member.

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SHEET 8 BF 8 gg a2 1 CIRCUIT BREAKER APPARATUS This invention relates to circuit breaker devices and more particularly to a circuit breaker especially useful in automotive type direct current applications. There are many automotive power applications ranging from low amperage requirements, for example, 17 to 20 amperes on windshield wipers to higher amperage requirements such as 60 amperes on a seat lift which require reliable long lived circuit protection. Circuit breaker devices employing a snap-acting element are not suitable for several reaons. It is desirable to permit operation of the motor so that its intended function can be achieved, such as operating the windshield wipers, even if a fault exists but at the same time prevent overheatin g of the motor. With a snap-acting device it is difficult to obtain the desired differential, the life of the device is inherently more limited than a creep type and in general they are sensitive to ambient temperature variations. A circuit breaker useful in such applications is the subject matter of co-assigned, co-pending application, Ser. No. 302158.

A circuit breaker built in accordance with that application employs a U-shaped auxiliary thermostatic strip having legs of approximately equal length with a straight thermostatic main strip mounted to one leg of the U-shaped member with the dissimilar coefficients of expansion adjacent one another. As the most active member, the U-shaped member, deflects, it forces the main member in a direction along its longitudinal axis causing wiping of the contacts. The stationary contact is mounted on a terminal which is received on an insulating pad, the pad in turn is mounted on the circuit breaker support plate in such a way that it is securely locked in place and has positive means to prevent turning or twisting thereof. However, such a breaker has certain limitations. Welding together of the thermostatic members results in some yield loses as well as reducing the activity of the thermostatic member in the vicinity of the weld. Further, compared to circuit breakers having only a single thermostatic element, such a device necessarily is more expensive to manufacture since more parts and handling are required.

Briefly, in accordance with this invention a circuit breaker is provided which is particularly useful with direct current, has a characteristic increased contact force with increased temperature until contact opening is effected, and accelerated contact opening motion and increased open contact distance in the same manner as the circuit breaker in the afore-mentioned copending application. This is achieved by forming an auxiliary thermostatic member integrally with a main thermostatic member by striking a tongue therefrom and bending it back upon itself. In certain of the embodiments significant contact wiping is obtained when it is particularly desirable to militate against the formation of contact welds or to break them should they occur.

Thus it is an object of the invention to provide a circuit breaker particularly suitable for automotive applications which is inexpensive, easily manufactured and has improved yield.

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

In the accompanying drawings in which several of the preferred embodiments are illustrated:

FIG. 1 is a side view of a circuit breaker which is the subject matter of application, Ser. No. 302158;

FIG. 2 is a top view of the FIG. 1 structure;

FIG. 3 is a bottom view of the FIG. 1 structure;

FIG. 4 is a view similar to FIG. 2 but with the auxiliary bimetallic member broken away;

FIG. 5 is a side view of the support plate;

FIG. 6 is a top view of the FIG. 5 support plate;

FIG. 7 is a top view of the insulating pad;

FIG. 8 is a cross section of the insulating pad taken on lines 88 of FIG. 7;

FIG. 9 is a perspective view of the stationary contact and terminal structure;

FIG. 10 is a side view of a support plate mounting the insulating pad and stationary contact and terminal structure, partly broken away and partly in cross section to show certain of the locking means employed;

FIG. 11 is a view similar to FIG. 1 showing the thermostatic members as they appear just prior to contact opening and showing the loci of the two opposite ends of the main thermostatic members;

FIG. 12 is a graph showing flexivity versus temperature for two materials which can be used for the respective thermostatic members;

FIG. 13 is a side view similar to FIG. I of a circuit breaker made in accordance with a first embodiment of the invention;

FIG. 14 is a top view of the FIG. 12 structure;

FIG. 15 is a top view of a circuit breaker made in accordance with a second embodiment of the invention;

FIGS. 16-18 are side views of circuit breakers made in accordance with other embodiments of the invention; and

FIG. 19 is a top view of a circuit breaker made in accordance with yet another embodiment of the invention.

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

The invention will be described by first describing the circuit breaker of co-pending application, Ser. No. 302158 mentioned above which operates in a similar manner to those of the invention. With particular reference to FIGS. 1-12, the circuit breaker illustrated in generally indicated by numeral 10. It comprises a bracket 12 having a base plate 14 and 21 depending mounting wall 16. Apertures l8 and 20 are provided in all 16 to facilitate mounting of the circuit breaker 10 as desired, as on a brush card. Plate 14, as best seen in FIG. 6, is provided with cut out portions 22, 26 and notches 24 and 28 for purposes to be explained infra.

Mounted on plate 14 is an insulator and stationary contact assembly 50 comprising an insulative pad 32 formed of an electrically insulated material such as a therrnoset resin, having an upper platform 34 and a lower platfomi 36 connected by stop wall 38. Platforms 34 and 36 lie in generally parallel planes. As seen in FIGS. 7 and 8 boss 40 is formed between the upper and lower platforms adjacent stop wall 38. A lip 42 depends from upper platform 34 and extends laterally from the center to one side.

Ribs

44, 46 are formed in the upper platform 34 and extend along the length thereof. Plate 14 is received between upper and lower platforms 34, 36 with boss 40 of insulating member 32 received in notch 28 and lip 42 received in notch 24 to lock the insulating member in place.

Stationary contact 50 is mounted as by welding on terminal plate 52 which has an arm 54 depending downwardly therefrom. Plate 52 is received on insulating member 32 between

ribs

44, 46 which maintain plate 52 in aligned position. Leg 54 is received in aligned apertures 56 of insulating pad 32 and 26a of plate 14 and is staked securely in place by spreading

bifurcations

58, 60. As indicated in FIG. 6, aperture 26a is sized to provide desired electrical insulation (air space) between the plate 14 and the leg 54 (in dashed lines).

Striking leg 54 from terminal strip 52 and bending it to extend downwardly therefrom

leaves arms

62, 64 which provide an elongated surface for abutment with

ribs

44, 46 to provide positive maintenance of terminal plate in its proper location. The space between

legs

62, 64 is aligned with aperture 26b of plate 14 and aperture 66 of insulating pad 32 for a purpose to be described below.

Tongue 68 extends into aperture 22 and is formed with a weld projection 70 for mounting of U-shaped thermostatic member such as member 72 which in turn cantilever mounts another thermostatic member such as bimetallic strip 74 as by welding as indicated at 75. Strip 74 mounts contact 76 on its free distal end portion aligned to move into and out of engagement with stationary contact 50.

U-shaped thermostatic member 72 has a high coefficient of expanion side HE located on the inside of the U-shaped bend. The high coefficient of expansion side HE of strip thermostatic member 74 faces member 72 so that dissimilar sides of the members are contiguous.

Bracket 12 is preferably formed of a weldable material such as steel which is ball peened with copper flash to minimize rust. Bimetallic strip 74, U-shaped strip 72 and bracket 12 are welded together, the insulative pad 32 is slid into position and finally terminal plate 52 is placed between

ribs

44 and 46 of pad 32 with leg 54 received in aperture 56 of pad 32 and 26 of plate 14.

The circuit breaker is calibrated by inserting a rod through aperture 66 and biasing it against strip 74 with a predetermined force casing the contacts to open. Tongue 68 is then bent until the contacts close and then the rod is withdrawn with the device calibrated to that force. It should be noted that this method of calibration that 100 percent yield can be achieved since the calibration tab can be bent in either direction. Terminal piece 52 as well as stationary contact 50 is silver plated to prevent the possibility of corrosion.

U-shaped bimetallic member 72 is chosen so that it has a higher resistivity than strip 74 so that contact pressure will increase prior to opening thereof. The U- shaped member controls mainly the on times while the strip 74 controls the no current temperature trip point. It will be noted that upon overcurrent, deflection of the more active bimetallic strip 72 causes the top blade to move to the right as viewed in FIG. 11, thus causing contact wiping. This has the advantage that even contact wear is obtained and contact welds are avoided. This is particularly important on direct current motors due to the tendency to form ionized paths between the contacts and results in better life than obtainable in the prior art.

The insulative pad is made in such a way that it snaps into place with lip 42 being received in notch 24 thus facilitating assembly of the device since the part is located in its proper position without the necessity of being separately held. Cooperating with lip 42 received in notch 24 to prevent twisting or turning of insulating pad 32 is boss 40 formed on connecting portion 38 of insulating pad 32 which is received in notch 38 of the mounting bracket. Tenninal plate 42 is then placed between

ribs

44 and 46 which prevents twisting of the terminal plate within the insulative pad and when

bifurcations

58 and 60 are spread outwardly yet another means locks the pieces together. Aperture 66 in the pad is aligned with the space between

legs

62 and 64 of terminal plate 52 and portion 26b of aperture 26 to provide access for the calibrating rod. Aperture portion 26a is formed large enough that sufficient air space is provided between plate 14 and leg 54 of terminal 52 which prevents so called high pot failures.

Holes 80 in

plate

14 and 82 in terminal plate 52 are provided to facilitate electrical attachment to circuit breaker 10. The circuit breaker is normally used with bracket 12, mounted on a brush card by placing fasteners (not shown) through

apertures

18 and 20 with terminal 82 connected to the card of the motor and terminal 80 connected to ground.

Circuit breaker 10 is not adversely affected by fluctuations in ambient temperature as would snap-acting devices since deflection in strip 74 is offset by an opposite deflection in member 72. That is, as temperature increases, strip 74 deflects in a direction which tends to cause contact opening; however, member 72 deflects such that the U-shaped member opens tending to straighten itself in a contact closing direction and offsets the deflection in strip 74. Actually the net movement of contact 76 mounted on the free distal end of strip 74 is slightly to the right as viewed in FIG. 11 causing a slight amount of contact wiping. As member 72 changes in temperature, point E moves along the locus identified by dashed lines AB in FIG. 11. Since a decrease in temperature will have just the opposite effect on strip 74 and member 72 it will be seen that there is continual contact wiping as ambient temperature fluctuates thereby keeping the contact surfaces clean and preventing the beginning formations of contact welds.

Member 72 is chosen so that its value of electrical resistivity is greater by approximately twice as much as for member 74. Member 72 also preferably is formed with a smaller cross section as can be observed by comparing the width of the members in FIG. 2. It will be understood that this could also be accomplished by making the thickness of member .72 less than that of member 74. The material for member 72 is also chosen having a flexivity v. temperature curve with a sharp knee, that is the flexivity decreases with increasing temperature above a predetermined temperature. Flexivity is a measure of how much a thermostat metal moves with a change in temperature and may be defined as the change in curvature of the longitudinal center line of the specimen per unit of temperature change for unit thickness. Reference may be had to FIG. 12 showing flexivity versus temperature curves for materials which can be used for

members

72, 74 respectively. When circuit breaker 10 is energized, auxiliary member 72 heats at a faster rate than does member 74 due to its higher value of resistivity. Thus as seen in FIG. 11, radius r of member 72 becomes larger moving member 74 and contact 76 toward the position shown in solid lines from the dashed line position. This movement causes contact 76 to slide or wipe across stationary contact 50 as well as to rock against the stationary contact. Normal current levels conducted through the breaker will cause member 72 to deflect more than strip 74 thereby causing contact 76 to move further to the right as viewed in FIG. 11 and causing an increase in contact force. Heat is conducted away from member 72 into bracket 12 and strip 74; however, a slight differential in temperature remains with member 72 maintained at a higher temperature. Eventually the auxiliary member 72 reaches a temperature at which radius r is not increasing so rapidly, that is when the slope of flexivity versus temperature curve decreases. At the same time, member 74 is being heated with the result that radius R is decreasing. It will be seen that the rate of change in radius R of member 74 in relation to radius r of member 74 increases when the flexivity of member 72 begins to decrease. Upon overcurrent, eventually member 74 deflects enough to cause contact 76 to separate from contact 50. Since member 72 is of less mass than member 74, was heated to a higher temperature, and is mounted directly on plate 14 which acts as a heat sink, it cools more quickly and point E moves along its locus AB toward its original position (dashed line in FIG. 11) causing an increase in the speed of contact opening and the total distance of separation of the contacts. Dashed line CD identifies the locus of point F near the free distal end of member 74 as it moves from contact opening to contact closing.

FIGS. 13-19 show several embodiments in which the main and auxiliary thermostatic members are formed from the same element to provide a design which requires fewer processing steps and hence is less expensive to manufacture and inherently has a higher yield than a design using two separate pieces which have to be welded together, which welding can impart undesirable stresses in the members which eventually could effect calibration of the device. As seen in FIGS. 13 and 14 portion or tongue 172 is struck from strip 174 of circuit breaker 100 and turned back upon itself forming a generally U-shaped auxiliary member. Tongue 172 bent back upon itself leaves a generally centrally located aperture 180 two of whose sides are defined by legs 176, 178. The width of tongue 172 is chosen so that it is less than the total width of legs 176 and 178. Thus passage of electric current from support 14 through tongue 172 and the remainder of strip 174 through the

contacts

76, 50 finally to terminal piece 52 will cause tongue 172 to deflect prior to the remainder or main member 174. Since tongue 172 is bent with the higher coefficient of expansion side on the inside, deflection will cause an increase in contact pressure and will cause a wiping of the contacts in the same manner as in the FIG. 1-12 embodiment. Continued heating will finally cause strip 174 to deflect separating the contacts. Tongue 172 will start to cool first since it has less mass and is connected to a support 14 which serves as a heat sink. This will cause tongue 172 to close on itself which increases the space between the contacts. This serves to increase the differential between contact opening and contact closing.

Circuit breaker 100 is mounted on a suitable support such as a brush card (not shown) as in the FIG. 1-12 embodiment using conventional fasteners inserted through apertures 18 and 2111. Terminal leads are attached to

plates

14 and 52 by conventional means, as by employing

apertures

80, 82. Thus the current path extends from plate 14, U-shaped portion 172, the remainder of the member 174,

contacts

76, 50 and finally the terminal plate 52. It will be seen that the device is ambient compensated since a deflection in strip 174 is offset by the deflection in portion 172 so that contact pressure remains essentially constant regardless of fluctuations in ambient temperature. Normal current flow will cause a temperature differential between portion 172, 174 since more heat is generated in portion 172 than 174.. This will tend to stabilize since plate 14 as well as portion 174 will act as heat sinks so that the dif ferential will be slight. Upon an overcurrent, the heat generated in portion 172 will again be more than that generated in portion 174 so that portion 172 will deflect at a faster rate causing contact 76 to slide to the right as viewed in FIG. 13 with increased contact pressure. Finally, portion 174 will deflect sufficiently so that contact 76 separates from contact 50 thereby breaking the circuit. Portion 172, being of less mass than 174 and being connected to plate 14 which acts as a heat sink will cool first causing the contacts to separate even further so that there will be no contact chattering. Eventually, strips 172, 174 cool sufficiently so that the contacts reclose.

FIG. 15 shows a modified switch 200 in which blade 270 is formed with U-shaped portion 272 similar to portion 172 of FIG. 13; however, in this embodiment, blade 270 has only one leg 274, the distal end of which mounts movable contact 76 which is adapted to move into and out of engagement with stationary contact 50 mounted on an arm 253 transversely extending from terminal plate 252. As in the FIGS. 13 and 14 embodiments contacts 76 wipes across contact 51) as well as having a rocking motion as members 272, 274 deflect. In this embodiment less thermostatic material is required and hence the device is even less costly to produce than device 100.

Circuit breaker 300, depicted in FIG. 16 is similar to the device of FIGS. 13 and 14 but with thermostatic member 371) situated so that the high coefficient of expansion side faces away from the support, that is the low coefiicient of expansion side faces itself in the U- shaped portion 372. Movable contact 76 is mounted on a distal portion of strip 374 and adapted to move into and out of engagement with stationary contact 50 mounted on arm 353 extending from terminal plate 352. The distal end of portion 372 extends beyond the remainder of member 374 to provide more access to the tab on which portion 372 is mounted should it be desired to bend the tab during calibration.

As in the embodiments of FIGS. 13-15 during normal operation a slight temperature differential exists between portion 372 and strip 374 since portion 372 has a higher electrical resistance, thus it deflects slightly tending to close the bight, causing contact 76 to move slightly to the left as viewed in FIG. 16 and also increases contact pressure. An overload will cause even more contact wiping and increased contact pressure until strip 374 deflects sufficiently to cause the contacts to separate. Once opening occurs, this movement is accelerated and extended due to the cooling of portion 372 which has less mass than strip 374.

In certain instances it may be desirable to mount movable contact 76 on the U-shaped portion as shown in circuit breaker 400 of FIG. 17. Thermostatic member 470 has a U-shaped portion 427 struck from member 470 and bent back upon itself with the distal end mounting contact 76. The remainder of member 470, strip 474 is mounted on terminal plate 452 as by welding on welding projection 454. Stationary contact 50 is mounted on a tab 460 formed from plate 14 and which may conveniently be used for calibrating by bending to adjust contact pressure.

Circuit breaker 500 of FIG. 18 is similar to the device of HG. 17 but with the thermostatc member 570 inverted so that the high coefficient of expansion side faces itself in the U-shaped portion 572. Arm 560 extending from support plate 14 mounts stationary contact 50. Weld projection 554 mounted on terminal plate 52 is used to mount thermostatic member 570 as by welding strip 574 thereto.

The device 600 of FIG. 19 is similar to that of FIG. 17 but is formed of a generally W-shaped strip member 670.

Legs

676, 678 are attached as by welding to a platform 653 extending laterally from terminal plate 652. Portion 672 is bent back upon itself in a U-shaped configuration and mounts movable contact 76 on its distal end adapted to move into and out of engagement with stationary contact 50 mounted on a tab formed in support plate 14.

Thus it may be seen from the above that the instant invention provides an improved circuit breaker economical to produce and having improved yield in manufacture.

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

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

I claim:

1. Apparatus comprising a thermostatic member having a high coefficient of expansion side and a low coefficient of expansion side, the member having three generally parallely extending legs, the center leg bent back upon itself in a U-shaped configuration such that the low ceofficient sides faces itself, a support, a stationary contact mounted on the support, a movable contact mounted on the the high coefficient side of the member, means to mount the member on the high coefficient side on the support electrically separated from the stationary contact with the movable contact adapted to move into and out of engagement with the stationary contact.

2. Apparatus comprising a thermostatic member having a high coefficient of expansion side and a low coefficient of expansion side, a tongue struck from a generally central portion of the member, the tongue bent back upon itself in a U-shaped configuration leaving a generally centrally positioned aperture in the member, a support, a stationary contact mounted on the support, a movable contact mounted on the member, means to mount the member on the support electrically separated from the stationary contact with the movable contact adapted to move into and out of engagement with the stationary contact.

3. Apparatus according to claim 2 in which the total electrical resistivity of the U-shaped tongue is greater than the remainder of the member.

4. Apparatus according to claim 3 in which the mass of the U-shaped tongue is less than the remainder of the member.

5. Apparatus according to claim 4 in which the side of the member having the U-shaped tongue facing the remainder of the member is the low coefficient of expansion side, both the member and the movable contact are mounted on the high coefficient of expansion side.

6. Apparatus according to claim 4 in which the side of the member having the U-shaped tongue facing the remainder of the member is the high coefficient of expansion side, the member is mounted on the support on the low coefficient of expansion side while the movable contact is mounted on the high coefficient of expansion side.