Circuit Breaker With Bimetallic Element

Abstract

A circuit breaker device of relatively small, compact and simple construction and which may be used as a direct replacement for typical small cartridge fuses currently used in electronic and electrical equipment. The device includes a housing having metal end caps thereon. A spring-biased plunger is coupled with a bimetal strip assembly having a contact on an end thereof, the plunger being electrically coupled with one end cap. The contact normally is coupled with another contact which is electrically connected with the second cap. Current flows through the device from one end cap to the other, and upon the occurrence of current above a predetermined value, at least a portion of the bimetal strip assembly flexes thereby releasing the top contacts. This allows the plunger to withdraw the strip assembly and break the electrical circuit. The bimetal strip assembly may include an ambient temperature compensating section.

Description

This invention relates to circuit breakers, fuses and the like, and more particularly relates to a relatively simple and compact circuit breaker or resettable fuse.

Over the years, many types of devices have been manufactured for breaking or opening an electrical circuit in the event of a current overload. Various types of fuses and circuit breakers have been devised. Each has disadvantages. The fuse must be replaced with a new fuse inasmuch as its current carrying element is destroyed upon a predetermined current overload. Typical circuit breakers are characterized by relatively costly and bulky construction.

Accordingly, it is a principal object of this invention to provide a new and compact circuit breaking device.

It is an additional object of this invention to provide a relatively simple and compact circuit breaker.

It is a further object of this invention to provide an improved and compact circuit breaker providing ambient temperature compensation.

A further object of this invention is to provide a compact circuit breaker which may be easily adjusted to set the current level of operation.

A still further object of this invention is to provide a small circuit breaker which may be mounted in standard fuse holders.

An additional object of this invention is to provide a compact circuit breaker which can serve as a direct replacement for conventional cartridge fuses, including indicating or signal fuses.

A still further object of this invention is to provide a circuit breaker which is relatively simple and which may be manufactured and sold at a relatively low cost.

These and other objects and features of the present invention will become better understood through a consideration of the following description taken with the drawing in which:

FIG. 1 is a cross-sectional view of a circuit breaker constructed in accordance with the present invention;

FIG. 2 is a cross-sectional view of the circuit breaker of FIG. 1 showing the same in a tripped condition;

FIG. 3a --3c illustrate in perspective components of the circuit breaker of FIG. 1; and

FIG. 4 shows a fuse cap which can be used with the breaker of this invention.

Turning now to the drawing, a circuit breaker constructed in accordance with the teachings of the present invention includes a body 10 which may be cylindrical as seen in FIG. 3a and which may be formed of an epoxy compound, a paper-phenolic tube, glass, or other suitable material. A contact guide 11 is mounted within the body 10, and includes a pair of metal channels 12 and 13 formed integrally with a cylindrical end 14. The end of the guide 11 may be folded as indicated at 15 in FIGS. 1 and 3b to fit over the end of the body 10.

A first end cap 16 is positioned over the end of the guide 11 and includes a cup portion 17 having an opening therein through which a plunger 18 extends. The plunger 18 has a head 19 on the first end thereof, and a spring 20 is interposed between the bottom of the cup 17 and the head 19 to normally bias the plunger 18 outwardly, or to the right as seen in FIGS. 1 and 2. The other end of the plunger 18 has a clip 21 mounted thereon to provide a stop and prevent the plunger from withdrawing completely from the cup 17 as best seen in FIG. 2 This end of the plunger also has a projecting finger 22 to which is secured a bimetal strip assembly 23 and spring contacts 24 and 25. As can be seen from FIGS. 1 and 2, the spring contacts 24 and 25 ride in the respective channels 12 and 13 of the guide 11. These spring contacts serve to provide an electrical connection between the guide 11 and the bimetal strip assembly 23, to provide an electrical connection between the guide 11 and plunger 18, to prevent rotation of the plunger and bimetal strip assembly, and to properly position and orient the plunger and bimetal strip assembly within the body 10.

The bimetal strip assembly 23 includes an ambient temperature compensating bimetal strip 28 and an overload bimetal strip 29. The first end of the strip 28 and the spring contacts 24 and 25 are secured, as by soldering, spot welding, or in any other suitable manner to the finger 22 of the plunger 18. The second end of the strip 28 is coupled to the first end of the strip 29 by an insulating material 30. The material 30 may be formed of plastic and adhesively or mechanically secured to the ends of the strips 28 and 29 in any suitable manner. The remaining end of the strip 29 has a contact 31 affixed thereto which normally engages a contact 32 as shown in FIG. 1. The bimetal strip assembly also includes a coil of heater wire 33 electrically coupled with the strip 29 at 34 and electrically coupled with the strip 28 at 35. The heater wire 33 may be insulated nichrome or other high-resistance wire.

The contact 32 is affixed to a lower leg 37 of an adjustment clip 38. An insulation ramp 39 is secured to the leg 37 adjacent the contact 32. An upper leg 40 of the clip 38 may be secured in position by a second end cap 42. An adjustment screw 43 is threaded into the lower portion of the end cap 42. Adjustment of this screw causes flexing of the lower leg 37 of the clip 38 and, thus, can be used to select the angular position at which the strip 29 will cause the contact 31 to disengage the contact 32. As will be apparent, this arrangement enables adjustment of the circuit breaker as to the tripping current level.

The end caps 16 and 42 of the circuit breaker will fit within a standard cartridge fuse holder. A current path exists from the end cap 16, through the guide 11, spring contacts 24 and 25, heater wire 33, bimetal strip 29, contact 31, contact 32, adjustment clip 38 and end cap 42. When a current overload occurs, the heater wire 33 heats thereby causing the bimetal strip 29 to flex in the direction of an arrow 45 in FIG. 1. As the strip 29 flexes in this direction, the contact 31 disengages or unlatches from the contact 32. As the contacts unlatch, the spring 20 forces the plunger 18 into the position shown in FIG. 2. After a short cooling period which allows the strip 29 to flex downwardly, the circuit breaker may be simply reset by pushing the plunger 18 to the left as seen in FIGS. 1 and 2. It should be noted that an electrical connection exists between the end cap 16 and the plunger 18 when the breaker is in the tripped position as seen in FIG. 2. This allows the breaker to be used in an indicating fuse holder and to operate as a signal fuse.

As noted earlier, the bimetal strip 28 is an ambient temperature compensating element. This strip is mounted with its low expanding side 46 on the bottom; whereas the strip 29 is mounted with its low expanding side 47 on the top. Thus, these two strips operate in the opposite directions. That is, the strip 29 curves upwardly as seen by the arrow 45, and the strip 28 curves downwardly upon an increase in temperature. Since the strip 28 is electrically and thermally insulated from the strip 29, the former is free to sense and compensate for changes in ambient temperature.

It should be noted that the spring contacts 24 and 25 and channels 12 and 13 of the guide 11 serve to eliminate movement of the plunger 18 and bimetal strip assembly 23 in the vertical direction as seen in FIGS. 1 and 2. This contributes greatly to the accuracy of the breaker. Furthermore, the adjustment screw 43 allows the breaker to be calibrated after final assembly, and enables compensation for variations in manufacturing. It allows the tripping current level to be changed. For example, a three-ampere breaker can be changed up or down by an ampere or so by the setting of the screw 43.

The insulating ramp 39 may be formed of any suitable insulating material, such as a plastic. It facilitates resetting the circuit breaker by guiding the contact 31 into engagement with the contact 32. It should be noted that when two current carrying contacts are caused to slide over each other, they tend to arc and thus weld or stick together. This problem is prevented by maintaining the contacts 31 and 32 insulated from each other until these contacts are almost completely reset.

The heater wire 33 is only necessary with the lowest current rated circuit breakers. With high current rated breakers, the resistance of the bimetal strip 29 is sufficient to produce the necessary heat to operate and trip the breaker. With such higher current rated breakers, a copper-wire jumper is connected between points 34 and 35 to short circuit the ambient compensating strip 28.

Circuit breakers according to this invention typically have respective current ratings of 1, 2, 3, 5 and 7 amperes. As an example of some of the constructional aspects of the circuit breaker which have not been mentioned above, a typical diameter of the end caps 16 and 42, and thus the overall diameter of the breaker is one-fourth inch. The caps 16 and 42 may be formed of nickel-plated brass. These caps may be crimped or connected onto the body 10. The throw of the plunger 18, which may be formed of silver-plated brass, typically may be approximately five-sixteenths inch. The spring contacts 24 and 25 are formed of approximately seven-thousandths-inch thick silver-plated spring steel, and the guide 11 is formed of approximately five-thousandths-inch thick silver-plated brass. The contacts 31 and 32 preferably are silver cadmium contacts. A force of approximately 75 grams is suitable for the spring 20. For a 3 -ampere breaker, the length of the bimetal strip assembly from one end to the other typically is one-half inch. These strips may be Trueflex P675R with 1 to 2.4 ratio between the short and long strips, and may be nine-thousandths-inch thick and one-eighth-inch wide. The contacts 31 and 32 will break in several seconds upon a 200 percent overload.

FIG. 4 illustrates a conventional-type fuse holder cap 50 which may be used with the breaker of FIG. 1. The cap 50 however, is provided with an insulating button 51 and spring 52. The button 51 is operated by the plunger 18 when in the tripped condition. The spring 52 has very low tension which is easily overcome by the circuit breaker spring 20 when the breaker trips.

The present embodiment of the invention is to be considered in all respects as illustrative and not restrictive, the scope thereof being indicated 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 therefore are intended to be embraced therein.

Claims

What I claim is:

1. A compact circuit breaker device comprising

a body member formed of electrical insulating material and having first and second electrical conductors coupled with the ends thereof defining the ends of a current path through said device, the first of said conductors having an opening therein,

an elongated plunger member extending into the opening in said first electrical conductor and reciprocable axially within said body member for resetting the device,

bimetal strip assembly means affixed to an end of said plunger within said body member, said bimetal strip assembly means including at least a bimetal strip having an electrical contact thereon,

spring contact means coupled with said end of said plunger and providing an electrical current path from said first electrical conductor through said bimetal strip to said contact thereon, and

a clip member having a contact thereon coupled with said second electrical conductor, said contacts on said bimetal strip and said clip member being normally engaged, but being caused to disengage upon the occurrence of a predetermined current through the first and the second of said electrical conductors and through said bimetal strip.

2. A compact circuit breaker device having an external configuration and dimensions similar to a conventional cartridge-type fuse comprising

a body member formed of electrical insulating material and having metal end caps coupled therewith, one of said end caps having an opening therein,

a plunger member extending through said opening in said one cap,

a bimetal strip assembly coupled with an end of said plunger within said body member, said bimetal strip assembly including at least a bimetal strip having an electrical contact thereon,

guide means mounted within said body member and electrically coupled with said one end cap,

spring contact means coupled with said end of said plunger and engaging said guide means, and

a second electrical contact coupled with the second of said end caps and mounted within said body for engagement with said electrical contact on said bimetal strip.

3. A circuit breaker device as in claim 2 wherein

said bimetal strip assembly comprises an ambient compensating bimetal strip having a first end coupled with said first end of said plunger and having a second end coupled with said first named bimetal strip and electrically insulated therefrom, the second end of said first named bimetal strip having said first electrical contact thereon.

4. A circuit breaker device as in claim 3 including

heater means mounted about said bimetal strip for heating said bimetal strip upon the occurrence of a current through said breaker device above a predetermined value.

5. A compact circuit breaker device comprising

a body member formed of electrical insulating material and having electrically conductive caps on the ends thereof, a first of said caps having an opening therein,

plunger means extending into the opening in said first cap,

bimetal strip assembly means coupled with a first end of said plunger within said body member, said bimetal strip assembly means including at least a bimetal strip having a first electrical contact thereon, electrical conductor means coupled between said first end of said plunger and said first cap,

a second electrical contact, said second electrical contact being electrically coupled with the second of said caps and positioned to allow engagement therewith of said first electrical contact, and

a clip member having said second electrical contact thereon, said clip member being electrically coupled with said second cap, said second cap including means for varying the position of said clip member for setting the current tripping level of said breaker device.

6. A compact circuit breaker device comprising

a body member formed of electrical insulating material and having electrically conductive caps on the ends thereof, a first of said caps having an opening therein,

plunger means extending into the opening in said first cap,

bimetal strip assembly means coupled with a first end of said plunger within said body member said bimetal strip assembly means including at least a bimetal strip having a first electrical contact thereon,

electrical conductor means coupled between said first end of said plunger and said first cap,

guide means coupled with said first cap and extending into said body member, said electrical conductor means comprising a pair of spring contacts mounted on said first end of said plunger and extending into engagement with said guide means, and

a second electrical contact, said second electrical contact being electrically coupled with the second of said caps and positioned to allow engagement therewith of said first electrical contact.

7. A compact circuit breaker device having an external configuration and dimensions similar to a conventional cartridge-type fuse comprising

a body member formed of electrical insulating material and having metal end caps coupled therewith, one of said end caps having an opening therein,

a plunger member extending through said opening in said one cap,

a bimetal strip assembly coupled with an end of said plunger within said body member, said bimetal strip assembly including at least a bimetal strip having an electrical contact thereon,

guide means mounted within said body member and electrically coupled with said one end cap said guide means comprising a pair of channel members extending into said body,

spring contact means comprising a pair of spring contacts respectively engaging said channel members, and

a second electrical contact coupled with the second of said end caps and mounted within said body for engagement with said electrical contact on said bimetal strip.

8. A circuit breaker as in claim 7, including

electrical heater means mounted in a series with and about said bimetallic strip for heating said bimetallic strip upon the occurrence of a current through said breaker device above a predetermined value.

9. A compact circuit breaker device comprising

an elongated body member formed of electrical insulating material and having first and second electrical conductors coupled with the ends thereof defining the ends of a current path through said device, said body member and electrical conductors having a configuration, size and appearance similar to a cartridge fuse, the first of said conductors having an opening therein,

an elongated plunger extending into the opening in said first electrical conductor and reciprocal axially within said body member for resetting the device, said plunger member being capable of movement in the direction of the axis of said body member automatically upon a current overload from a set position to an unset position and manually from the unset to the set position,

guide means physically retained within said body member and electrically connected with said first electrical conductor,

spring contact means within said body member and coupled with an internal end of said plunger member extending within said body member, said spring contact means engaging said guide means for reciprocally guiding said internal end of said plunger member within said body member and electrically coupling said internal end of said plunger member through said guide means with said first electrical conductor, said spring contact means having a pair of contact members,

first contact latch means electrically connected to the second of said electrical conductors and positioned within said body member,

second contact latch means positioned within said body member and normally engaging said first contact latch means when said device is in the set position, said second contact latch means being electrically connected through said spring contact means and said guide means to said first electrical conductor and physically connected to said internal end of said plunger member, one of said contact latch members including a bimetallic strip which flexes upon current overload to move said one contact latch member from a latched position to an unlatched position with respect to the other contact latch member for allowing said plunger member to move to said unset position, and

means normally urging said plunger member in an axial direction to said unset position whereby excessive current passing through said device causes a heating of said bimetallic strip, resulting flexing of said strip, and unlatching of said first and second contact latch means and an axial movement of said plunger from its set position to an unset position.