Trip Unit Having Improved Trip Adjustment Indicator And Circuit Breaker Incorporating Same

Abstract

A trip unit for molded case circuit breakers utilizes a tubular extension of its housing to carry a trip adjustment scale which is visible through an opening in the breaker case. An adjustment knob mounted on an adjustment shaft coaxially within the tubular extension is angularly positioned relative to the scale graduations to establish the desired trip setting. The scale graduations may be labeled by indicia imprinted on the breaker case about the opening therein.

Description

BACKGROUND OF THE INVENTION

The present invention relates to electric circuit breakers, and particularly to an improved, adjustable current responsive trip unit removably incorporated therein.

Electric circuit breakers of the molded case type typically include current responsive means which are adjustable by the user through a range of magnetic trip settings by manipulation of an externally accessible knob or the like. In a number of applications, it is important that the trip point, i.e., the level of over-current at which the current responsive means or trip unit automatically operates to initiate circuit interruption by the circuit breaker, be established with some degree of precision. Trip units are calibrated by the manufacturer to establish rather precise and repeatable "high" and "low" trip points to which the adjustment knob can be set. However, problems arise when the user desires a setting at a trip point intermediate the "high" and "low" trip points. The user, in most instances, does not have the capability for determining experimentally the appropriate positioning of the adjustment knob to establish a desired intermediate trip point and must therefore rely on a trip adjustment scale typically provided on the circuit breaker case by the manufacturer. Unfortunately, this adjustment scale is typically not uniformly physically related with the adjustment knob from circuit breaker to circuit breaker. That is, alignment of the adjustment knobs of two seemingly identical circuit breakers or of different poles of a single multi-pole circuit breaker to a corresponding intermediate graduation of their respective scales will not, in all likelihood, establish the same trip point. This results largely from the fact that the adjustment scale is universally provided on the circuit breaker case arrayed about an opening therein giving access to the adjustment knob which is carried by a different component, to wit, the trip unit. Manufacturing tolerances do not permit precision positional mounting of the trip unit within the circuit breaker, thus uniformity in the relationship of the adjustment knob to the adjustment scale cannot be achieved from pole to pole or circuit breaker to circuit breaker. Moreover, manufacturing tolerances require that the opening in the circuit breaker case be made considerably larger than the adjustment knob so as to avoid interference therebetween during assembly. As a consequence, the adjustment knob is not necessarily centered in the breaker case opening upon assembly, and alignment of the knob with the scale graduations becomes difficult and imprecise.

In addition, if the stops against which the adjustment knob is positioned to establish the "high" and "low" trip setting are carried by the breaker case, as is often the case, manufacturing tolerances will also adversely affect the precision of these settings as well.

It is accordingly an object of the present invention to provide a circuit breaker having provisions accommodating precise adjustment of the trip setting to a desired trip point in a range of overcurrent trip points.

Another object of the present invention is to provide circuit breaker trip units having a trip adjustment indicator which is not significantly adversely affected by customary manufacturing tolerances utilized in circuit breaker manufacture.

Still another object is to provide a circuit breaker trip unit of the above character which is capable of accommodating precise and repeatable trip settings throughout a wide adjustment range.

A further object of the present invention is to provide a circuit breaker trip unit of the above character wherein, from circuit breaker to circuit breaker, identical magnetic trip points are established by corresponding settings of the trip adjustment.

Other objects of the invention will in part be obvious and in part appear hereinafter.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided an electric circuit breaker incorporating an adjustable trip unit, wherein the trip adjustment scale is carried by the trip unit itself, rather than by the circuit breaker case, as is the current practice. As a consequence, variations in the positioning of the trip unit within the circuit breaker case and relative dimensional variations between the trip unit and circuit breaker case, permitted by manufacturing tolerances have minimal effect on the positional relationship between the adjustment scale and the movable member which is manipulated to establish a desired trip point.

More specifically, the trip unit of the present invention includes a tubular member affixed on one of its ends to the trip unit housing about an aperture therein. The tubular member is of sufficient length to extend into an opening formed in the cover portion of the circuit breaker case. The exposed other end of the tubular member is formed having an array of adjustment scale graduations visible in the breaker case opening. An adjustment shaft rotatably mounted in the trip unit housing coaxially with the tubular member carries on one end an adjustment knob accommodated within the tubular member. The adjustment knob carries a pointer working to the scale graduations on the tubular member facilitating the establishment of a desired trip setting in a wider range of permissible settings.

The tubular member carries an inwardly extending stop against which the adjustment knob abuts to define clockwise and counterclockwise limit positions corresponding to "high" and "low" trip settings established by calibration during circuit breaker assembly.

Various approaches are disclosed for releasably retaining the adjustment knob at a desired trip setting, and thus to prevent inadvertent shifting of its angular position due to vibration, etc. In one disclosed embodiment, an O ring is included to impart a frictional drag to the adjustment shaft and knob which can be readily overcome for intended angular positioning of the adjustment knob.

In another disclosed embodiment, the inner surface of the tubular extension is formed with an axially extending arcuate groove aligned with each scale graduation. The adjustment knob is provided with a radial extension having a single, axially extending arcuate groove aligned with the knob pointer. When the pointer is aligned with one of the scale graduations, a locking pin is accommodated in the confronting arcuate grooves to lock the adjustment knob in the desired trip setting. In a third embodiment, the knob is provided with a resilient detent which is received in the arcuate axial grooves formed in the tubular member to retain the adjustment knob in the desired trip setting.

In each of the disclosed embodiments of the invention, indicia is imprinted on the circuit breaker cover arrayed about the opening therein to label the scale graduations formed on the tubular member. It will be appreciated that the cover aperture is made somewhat larger in diameter than the tubular member so as to avoid interference therebetween during assembly. This manufacturing tolerance does not, in accordance with the present invention, affect the positional relationship of the adjustment knob and scale, thus preserving the accuracy of the various trip settings defined by the scale graduations.

The invention accordingly comprises the features of construction, combinations of elements and arrangements of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a fragmentary perspective view, partially broken away, of an electric circuit breaker embodying the present invention;

FIG. 2 is a fragmentary, exploded, perspective view of a magnetic trip unit constructed according to one embodiment of the present invention;

FIG. 3 is a fragmentary, exploded, perspective view of a portion of a magnetic trip unit constructed according to an alternative embodiment of the present invention;

FIG. 4 is a fragmentary, exploded, perspective view of a portion of a magnetic trip unit constructed according to still another embodiment of the present invention; and

FIG. 4A is a sectional view taken along line 4--4 of FIG. 4.

Like reference numerals refer to corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

The present invention is shown in FIG. 1 as being incorporated in an electric circuit breaker, generally indicated at 10, including a generally rectangular insulating casing consisting of a base 12 and a cover 14. While the present invention is shown embodied in a three-pole circuit breaker, it will be appreciated that the principles involved may be readily implemented in a two-pole or single-pole circuit breaker. A trip unit, generally indicated at 16, is removably mounted within the circuit breaker case and includes a two-part housing 20 from which circuit breaker load terminals 22 emanate. The circuit breaker contacts (not shown) are operated by a suitable operating mechanism (not shown) which may be actuated by an operating handle 24 projecting through an opening 26 in the cover 14.

Turning to FIG. 2, trip unit 16 includes an adjustment shaft 30 for each pole of circuit breaker 10. Inasmuch as the trip adjustment indicator features of the present invention are identical for each pole of the circuit breaker, only a portion of the trip unit devoted to one of the circuit breaker poles will be considered. Adjustment shaft 30 is mounted for rotation at its lower end by a footing 32 carried by the trip unit housing 20 and has its upper end extending through and journalled in an opening 34 in the upper wall of the trip unit housing. A cam 36 eccentrically mounted on adjustment shaft 30 bears against and, with shaft rotation, alters the position of an adjustment arm 38 to vary the trip point of trip unit 16. The trip unit mechanism for establishing the trip point is not material to the present invention and thus is not disclosed. Such mechanisms are well known to the art, as exemplified by the disclosures in U.S. Pat. Nos. 3,084,236 and 3,053,954. It will be understood that the adjusting arm 38 is typically linked to the armature of the magnetic trip mechanism of the trip unit 16 such that the cam serves to adjust the air gap between the armature and the magnet operating to generate armature attractive forces proportional to the current in the associated pole of the circuit protected by circuit breaker 10.

In accordance with the present invention, a tubular member 40 is integrally formed with or fixedly secured on end to the trip unit housing 20 in a position concentrically about opening 34. The upper edge of tubular member 40 is provided with a spaced array of scale graduations 42 in the form of semi-circular, radially extending notches. The upper end of adjustment shaft 30 extending above trip unit housing 20 is splined and formed with a diametrical slot 44 to resiliently engage an adjustment knob 46 press-fitted thereon. The adjustment knob is therefore keyed to the adjustment shaft 30 such that rotational movement of the knob is communicated to the shaft pursuant to varying the trip point of the circuit breaker 10. An O-ring 48 is inserted between the knob 46 and trip unit housing 20 so as to provide sealing, as well as frictional drag to discourage unintended shifting of the angular position of adjustment shaft and knob.

Adjustment knob 46 is formed having a radial extension 50 terminating in an arcuate surface having a radius of curvature conforming to the inner surface of the tubular member 40. The tubular member is formed with a radially, inwardly extending stop 52 against which the adjustment knob extension 50 abuts to define limits of clockwise and counter-clockwise rotation. These limits correspond to calibrated "high" and "low" trip settings established at the factory. These "high" and "low" trip setting positions are factory-calibrated in a conventional manner by adjusting the armature spring tension and the angular position of cam 36 on shaft 30 prior to fixing the cam on the shaft by suitable means such as solder.

The adjustment knob further includes a pointer working to the scale graduations 42 in the form of a groove 54 extending radially outwardly into the knob extension 50. Preferably, the width of the pointer groove 54 is made to equal the width of the scale graduation grooves 42 on tubular member 40, thus facilitating accurate alignment of the pointer groove with a selected one of the scale graduation grooves using a suitable tool such as a screw driver. It is also preferable that groove 54 bisect the angle included by the knob extension 50 and the arcuate length of the terminal surface of the knob extension on either side of the pointer groove be made to correspond to the arcuate length between scale graduation 42, thus providing additional aligning marks for achieving precise trip settings.

The trip adjustment knob and scale are visible through an aperture 56 formed in the circuit breaker cover 14. This cover aperture is made somewhat larger in diameter than tubular member 40 such that the latter can extend freely into the aperture with the cover in place, manufacturing tolerances notwithstanding. Preferably, member 40 terminates flush with the outer surface of the cover. It will be appreciated that any eccentricity in the positioning of the tubular member 40 in the cover aperture 56 occasioned by manufacturing tolerances has no effect on the ability to establish precise trip settings. As seen in FIG. 2, indicia is imprinted on or molded in the circuit breaker cover 14 about cover aperture 56 to label the scale graduations 42.

In the embodiment of the invention shown in FIG. 3, the inner surface of the tubular member 40 is formed having axially extending half-round notches or grooves 60, one aligned with each scale graduation 42. The arcuate surface of the knob extension 50 is formed with a complementary, axially extending surface groove 62 aligned with pointer groove 54 in the top surface of the knob. As a consequence, when the pointer groove 54 is aligned with any one of these scale graduations 42, a pin 64 may be inserted in the circular hole formed by the confronting, half-round grooves 60 and 62, thereby positively locking the adjustment knob and shaft in the desired trip setting. Washer 66 is interposed between the adjustment knob 46 and the trip unit housing 20 to seal the interior of the trip unit 16 from dust, etc.

In the embodiment of FIG. 4, knob extension 50 is undercut, as indicated at 70 in the sectional view of FIG. 4A. A dog 72 is formed extending from the arcuate terminus of knob extension 50. The nose of this dog 72 is conformed to be received in any one of the axially extending grooves 60 aligned with scale graduations 42 in the upper end surface of tubular member 40. The undercutting 70 of the knob extension 50 imparts flexibility to the terminal portion of the knob extension carrying dog 72. As a consequence, a detenting action is achieved as the adjustment knob 46 is rotated through its range of trip settings. When the adjustment knob pointer 54 is aligned with one of the scale graduations 42, the dog 72 is received in the registered groove 60 to releasably retain the established trip setting.

It will thus be seen that the objects set forth above, including those made apparent from the preceding description, are efficiently attained and, since certain changes may 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.

Claims

Having described our invention, what we claim as new and desire to secure by Letters Patent is:

1. An over-current trip unit for use in a molded case circuit breaker, said trip unit comprising, in combination:

A. a housing;

B. means forming an aperture in said housing;

C. a tubular member secured on one end to said housing about said aperture, the other end of said member extending into an opening in the circuit breaker case when said trip unit is operatively positioned therein;

D. means forming an array of trip adjustment scale graduations on said tubular member adjacent said other end, said graduations being visible externally of the circuit breaker case;

E. an adjustment shaft rotatably mounted in said housing and having an end portion extending coaxially within said tubular member;

F. means carried by said end portion facilitating manual rotation of said adjustment shaft; and

G. pointer means carried by said shaft and working to said adjustment scale graduations to indicate the various trip settings of said trip unit.

2. The trip defined in claim 1, wherein said manual rotation facilitating means is in the form of a knob mounted on said shaft end portion coaxially within said tubular member.

3. The trip unit defined in claim 2, wherein said tubular member carries a stop for establishing limits of clockwise and counterclockwise rotation of said knob and shaft.

4. The trip unit defined in claim 3, wherein said knob is formed with an outwardly radiating extension and said stop extends radially inwardly from said tubular member adjacent said other end thereof, whereby said knob extension abuts either side of said stop to establish said rotational limits.

5. The trip unit defined in claim 2, wherein said scale graduations are in the form of notches formed in the edge surface of said tubular member other end, and said pointer means is in the form of a radial groove formed in the exposed surface of said knob.

6. A circuit breaker comprising, in combination:

A. a case including a base and a cover;

B. means forming an opening in said cover;

C. an adjustable trip unit located in said case and operating automatically in response to a selected level of over-current to initiate circuit interrupting operation of said circuit breaker, said trip unit including

1. a housing,

2. means forming an aperture in said housing,

3. a tubular member secured on one end to said housing about said aperture, the other end of said member extending into said cover opening;

4. means forming an array of trip adjustment scale graduations on said tubular member adjacent said other end, said graduations being visible externally of said case,

5. an adjustment shaft rotatably mounted in said housing and having an end portion extending coaxially within said tubular member,

6. an adjustment knob mounted on said shaft end portion facilitating manual rotation of said adjustment shaft, and

7. means forming a pointer on said knob working to said adjustment scale graduations to indicate the various trip settings of said trip unit; and

D. indicia carried by said cover about said cover opening to label said scale graduations.

7. The circuit beaker defined in claim 6, wherein said tubular member carries a stop for establishing clockwise and counter-clockwise rotational limits for said knob and shaft.

8. The circuit breaker defined in claim 7, wherein said knob is formed with an outwardly radiating extension and said stop extends radially inwardly from said tubular member adjacent said other end thereof, whereby said knob extension abuts either side of said stop to establish said rotational limits.

9. The circuit breaker defined in claim 8, wherein said trip unit further includes means imparting frictional drag to the rotation of said knob and shaft, thereby to discourage spurious shifting of the manually established trip setting.

10. The circuit breaker defined in claim 8, wherein said trip unit further includes:

1. means forming a plurality of first axially extending grooves in the inner surface of other end portion of said tubular member, one of said grooves being aligned with each said scale graduation,

2. means forming an axially extending second groove in said knob extension aligned with said pointer, and

3. a pin insertable in the recess formed by confronting said second groove with one of said first grooves to positively lock said knob at a desired trip setng.

11. The circuit breaker defined in claim 8, wherein said trip unit further includes:

1. means forming a plurality of axially extending grooves in the inner surface of other end portion of said tubular member, one of said grooves being aligned with each said scale graduation,

2. means forming an undercut in said knob extension to impart flexibility to the terminal portion thereof, and

3. a dog extending radially from said knob extension terminal portion, said dog being resiliently biased into one of said grooves to releasably detain said knob at a desired trip setting.

12. The circuit breaker defined in 6, wherein said scale graduations are in the form of notches formed in the edge surface of said tubular member other end, and said pointer means is in the form of a radially extending groove formed in the exposed surface of said knob.

13. The circuit breaker defined in claim 12, wherein the width of said pointer groove conforms to the width of each of said scale graduation notches.

14. The circuit breaker defined in claim 13, wherein said knob is formed having an outwardly radiating extension terminating in contiguous relation to the inner surface of said tubular member, said pointer groove extending to the termination of said knob extension.