US3265839A

US3265839A - Thermally-operable circuit breaker

Info

Publication number: US3265839A
Application number: US299940A
Authority: US
Inventors: Robert A Johnson
Original assignee: Fasco Industries Inc
Current assignee: Fasco Controls Corp
Priority date: 1963-08-05
Filing date: 1963-08-05
Publication date: 1966-08-09
Anticipated expiration: 1983-08-09

Description

1966 R. A. JOHNSON 3,265,839

I THERMALLY-OPERABLE CIRCUIT BREAKER Filed Aug. 5, 1963 Lllllllll lll:lllllll:l I'll T INVENTOR. ROBERT A. JOHNSON BY Z United States Patent New York Filed Aug. 5, 1963, Ser. No. 299,940

2 Claims. (Cl. 2t)0122) This invention relates to circuit breakers, and, more particularly, to automatically resetting circuit breakers for automotive use, for protecting automotive electrical systems.

Automatically resetting circuit breakers are in wide use particularly in the electrical systems of automotive vehicles and the like. However, when used in automotive electrical systems, the conventional circuit breakerhas a limited life because of the arcing conditions that exist in DC. circuits with the slow make and break type of devices conventionally employed. Moreover, with conventional circuit breakers a rather high temperature is necessary to maintain an open circuit. Furthermore, ordinarily, when a circuit overload condition develops, the circuit breaker recycles continuously until either the vehicles battery runs down, or the overload condition is corrected. In the case of an overload caused by a short circuit, for example, such action not only places a relatively heavy drain upon the battery, but also constitutes a fire hazard because of the relatively heavy electrical currents in the wiring.

One important object of the present invention is to provide a novel circuit breaker including means operative after a few recycling operations-of the circuit breaker due to an overload condition in the load circuit either to hold the breaker open until the load circuit is electrically removed, or to increase the reset time on subsequent cycles of operation whereby the hereinabove noted disadvantages of prior art automatically resetting circuit breakers are avoided.

Another object of the invention is to provide a circuit breaker that 'will have an extended life as compared to conventional slow make and break circuit breakers employed in automotive circuits.

Another object of the invention is to provide a circuit breaker that will operate in a DC. circuit with a snap action movement when separating the contacts.

Another object of the invention is to provide a circuit breaker than can be adjusted to initial surge currents, or temporary overloads of short duration, without permanently disrupting the operation of circuits, by acting as a normal automatic reset breaker.

Still another object of the invention is to provide a snap-action circuit breaker with which the effective current, that is allowed to pass, is held to a minimum, thereby offering the utmost in circuit protection.

A still further object of the invention is to provide a snap-action circuit breaker that remains in open position at a lower temperature than that required to maintain an open circuit with a slow make and break circuit breaker.

Other objects and advantages of the invention will become apparent from the following detailed description of representative embodiments thereof, and from the recital of the appended claims, particularly when taken in conjunction with the drawing, wherein:

FIG. 1 is a plan view of a circuit breaker made according to a first embodiment of the present invention, the circuit breaker being shown with its cover removed;

FIG. 2 is a side elevational view of the circuit breaker of FIG. 1;

FIG. 3 is a cross-sectional view on an enlarged scale taken along the line 33 of FIG. 1;

FIG. 4 is a plan view of a circuit breaker made ac- Patented August 9, 1966 cording to a second embodiment of the invention, the circuit breaker again being shown with its cover removed; and

FIG. 5 is a schematic circuit diagram illustrating how circuit breakers made according to the present invention may be connected in circuit.

Briefly, the invention contemplates connecting a Joulcan heating element across the contacts of a conventional circuit breaker of the thermally responsive, auto matically resetting type, and mounting the heating element adjacent to the armature of the circuit breaker. The value of the heating element is chosen so that when a circuit overload condition such as a short-circuit occurs, it will, after a relatively few recycling operations of the armature, produce sufficient heat either to keep the armature open, or to delay its reclosing on each subsequent cycle so that the average power delivered to the load circuit may be readily dissipated by ambient cooling. During times when the circuit breaker contacts are open, the heating element limits the current flowing into the load circuit to a very low value.

For purposes of convenient reference herein, the type of operation in which the heating element maintains the armature in its open position until the load circuit is substantially completely disconnected from the circuit breaker will be referred to as a remote reset type of operation, and the type of operation in which the reset period of the circuit breaker is prolonged will be referred to as the delayed reset type.

Referring now to the drawing, the circuit breaker shown in FIGS. 1, 2, and 3 is of the remote resetting type, although, of course, by proper choice of the values of the heating elements, 10 and 12, it may be converted to a delayed resetting type.

The device includes a conventional body member 14, which may be, for example, of a molded plastic material. A pair of

studs

16 and 18 extend through the body 14 for connecting the device to an external circuit. A fixed contact 20 is welded, or otherwise securely attached to one end of right hand stud 18; and a bimetallic, thermally reacting conductive anmature 22 is cantilevered on the other stud 16, with its free end extending over the fixed contact 20. The armature 22 is secured to stud 16 by welding or by a headed stud or screw 23.

The movable contact 24 is fixed on the free end of the armature or switch blade 22, and is normally held in pressure engagement with the fixed contact 20 by the armature or switch blade. The armature or switch blade 22 is preferably of the snap-action type such as the armatures or switch blades shown in US. Patents 2,533,274, Matulaitis et al., and 2,425,717, Bean. Thus, the armature or switch blade 22 shown has slots 25 therein whose adjacent sides converge toward the fixed end of the blade, and cars 27 along the distal, generally parallel sides of the slots, which protrude both into the slots and from the longitudinal sides of the blades.

The circuit breaker of FIGS. 1 to 3 inclusive is made to operate in the remote resetting mode by connecting a pair of

resistors

10 and 12 in parallel with armature blade 22 between the

studs

16 and 18 closely adjacent to the armature 22 so that when an overload condition develops in the load circuit, they will conduct current and heat the armature 22 while the armature is in its open position. For convenience in assembly and for added rigidity of construction, the body 14 is provided with side and

end walls

26 and 28, which extend from the main portion of the body upwardly and define a recess 30 for receiving the

resistors

10 and 12 and holding them snugly against the

studs

16 and 18. The

resistors

10 and 12 constitute an electrical connection between the two studs 16 and 18in parallel with the connection afforded through the armature 22 and the

contacts

20 and 24, as schematically shown in FIG. 5. A cover (not shown) may be provided, if desired, fitting over the armature and sealing upon the body 14 to protect the

contacts

20 and 22 from dust and other environmental effects.

The values of the resistors 19 and 12 are so chosen that in operation, when a short circuit develops in the load circuit, the resistors will develop sufficient heat-to prevent In an ordinary automobile the armature 22 from closing. type circuit breaker, for example, designed to operate in a 12 volt electrical system, in which the armature 22 is adapted to reset when at a temperature of between about 200 F. and 180 F., and which is provided with a sheet metal cover, it has been found that the remote reset type of operation is obtained when the resistors and 12 have values of about 40 ohms each, making a net resistance of 20 ohms. Different values will be required for use in circuit breakers having other operating characteristics and specifications.

In operation under normal conditions, the

resistors

10 and 12 have substantially no effect on the circuit breaker, or on the load circuit, because their resistance is many times higher than the resistance of the armature 22 in series with the contacts 21] and 24. In a parallel circuit current flows through the path of least resistance. The resistor value is higher than the bi-metallic blade resistance by a ratio that allows only a minute portion of current to flow through the resistors until such time that an overload condition causes the bi-metallic blade to open that part of the circuit, which then allows the resistors to heat to the point where they will keep the blade 22 open. When an overload condition such as a short circuit develops, the

resistors

10 and 12 still have no effect until after the-armature 22 opens. They do not operate to delay opening of the armature to any appreciable extent. As soon as the armature opens, the full electrical supply voltage, assuming a short circuit in the load circuit, ap-

pears across the two

resistors

10 and 12 in parallel, and they begin to produce heat. The temperature of the

resistors

10 and 12 increases relatively slowly so that the first two or three recycling operations of the armature 22 are at a rate relatively close to its normal rate of recycling, that is, relatively close to the rate at which it would recycle if the

resistors

10 and 12 were removed from the device. Thereafter, the

resistors

10 and 12 become warm enough to hold the temperature of the armature 22 above its reset temperature, thereby holding the armature open and preventing it from closing until such time as the flow of energizing current through the

resistors

10 and 12 is stopped, such as by opening the load circuit. The resistors hold the blade 22 open because they produce an ambient temperature around the blade which is in excess of the temperature that would have permitted the blade to reset had the resistors not been present. The

resistors

10 and 12 allow a relatively small current of less than 1 ampere to flow in the load circuit during the existence of the overload condition, which current is insufficient to present a fire hazard under most conditions and will not rapidly drain the vehicles battery 32 (FIG. 5).

A delayed reset type of circuit breaker according to an alternative modification of the invention is shown in FIG. 4, and is generally similar to the circuit breaker shown in FIGS. 1 to 3, except that it includes only one resistor 10 connected between the terminal studs (not shown in FIG. 4). The armature or switch blade 42 is here also bimetallic and of the snap action type but its longitudinal sides are parallel as are the adjacent sides of the slots 45 formed therein. The distal sides of the slots have, however, lobes 47 formed thereon extending toward one another.

In the delayed reset type of device shown in FIG. 4, when an overload condition first arises in the load circuit, the armature 42 recycles three or four times at a rate close to its normal recycling rate, but thereafter its resetting time becomes greatly extended due to the rise in temperasuch that the average power delivered to the load circuit a may be'dissipatedwithout fire hazard and is insufficient to cause a rapid exhaustion of the battery 32 (FIG. 5).

The inclusion of the resistors, or

heating elements

10 and 12 according to the invention has substantially no effect on the initial opening characteristics of the circuit breakers, and therefore permits the utilization of the advantageous snap-action type of armature. Because the circuit breakers can open and reset several times on overload, before the heating elements become warm enough to have a significant effect, the circuit breakers may be subjected to initial surge currents or temporary overloads of short duration, acting otherwise as conventional, automatically resetting circuit breakers. However, when the circuit overload condition persists, the circuit breakers of the invention will then function in either the delayed reset or remote reset mode.

The remote reset device requires that the circuit be disconnected electrically, external to the circuit breaker,

by means of a switch or some device which limits or stops the flow of current through the resistors. The delayed reset type of device extends the reset time beyond that which would normally be inherent to the breaker; the result is a reduction in the effective value of currentthat the circuit breaker will allow to pass over an extended period of time. The remote reset type will completely stop the overloaded value ofcurrent from flowing. Moreover, because a'circuit breaker made according to the invention will trip and recycle far fewer times during the existence of an overload condition than a conventional circuit breaker, the life of the circuit breaker and its contacts is greatly extended relative to circuit breakers of previously known types.

be lower than the temperature that is necessary to main tain an open circuit on a slow make and break circuit breaker. This is an added advantage in a circuit breaker made according to the present invention.

While the remote reset type circuit breaker shown uses two resistors, and this type of circuit breaker may be converted to a delayed reset type by removing one resistor, it will be obvious that it is possible to build the delayed reset type with any resistor or with a pair of resistors, selected to generate the desired resistance. Obviously it is also possible to build the remote reset type circuit breaker by using only a single resistor whose resistance is low enough to cause the bi-metallic armature to remain open as long as voltage is applied.

While the invention has been described in connection with a specific embodiment thereof, then, it will be under- In both the remote reset and the delayed reset type of operation, the effective current Having thus described my invention, what I claim is:

1. A circuit breaker comprising (a) a pair of contacts adapted to be connected to an external electric circuit,

(b) a bimetallic, electrically-conducting snap-action blade cantilevered at one end on one of said contacts and having its free end positioned to engage the other contact, said blade being responsive to current flowing therethrough to heat and to snap out of engagement with said other contact when heated beyond a predetermined degree and said blade being constructed to reengage said other contact when said blade cools below said predetermined degree, and

(c) a resistance connected continuously at opposite ends to said contacts in parallelism with and spaced from said blade when said blade is in its engaged, closed position,

(d) the value of the resistance being many times higher I than that of said blade, whereby said blade will make and break the circuit through said blade under normal circuit loads, said resistance being adapted to heat up when an overload occurs in the circuit and being disposed close enough to said blade to heat said blade and to maintain said blade in its open position when an overload persists.

2. An automatically resetting, electric circuit breaker having a pair of contacts, a snap-action bimetallic armature electrically connected in series with the contacts for alternately opening and closing them in accordance with the heat produced in the armature by current flowing through it, a Joulean heating element continuously connected across the contacts in parallelism with said armature and mounted adjacent to but spaced from the armature for heating it during times when the contacts are held in their open position by the armature, whereby the reset time of the circuit breaker is lengthened, the value of said heating element being chosen in view of the supply voltage of the system in which it is intended for use and in view of the operating characteristics of the armature so that in service when a short circuit occurs in the load circuit said heating element will heat the armature sufficiently to prevent its reclosing once thermal equilibrium is established.

References Cited by the Examiner UNITED STATES PATENTS 1,701,757 2/1929 Lea 200-122 2,403,803 7/1946 Kearsley 200-138.6 2,884,501 4/1959 Dorian 200l 38.6 2,914,637 11/1959 Wuerth 200-122 3,141,080 7/1964 Ege 200113.7

FOREIGN PATENTS 677,161 8/1952 Great Britain.

BERNARD A. GILHEANY, Primary Examienr. L. A. WRIGHT, Assistant Examiner.