US2757256A - Current responsive devices - Google Patents

Description

J. B. CATALDO ET AL 2,757,256

CURRENT RESPONSIVE DEVICES July 31, 1956 Filed Oct. 23, 1952 United States Patent CURRENT RESPQNSIVE DEVICES John B. Cataldo, Birmingham, Mich, and Elbert De F. Tidd, Clinton, and Albert N. Cook, Eernardsville, N. J., assignors to John B. Pierce Foundation, New York, N. Y., a corporation of New York Application October 23, 1952, Serial No. 316,516

Claims. (Cl. 2t)tl-113) This invention relates to current responsive devices and more particularly to circuit breakers and components thereof.

In the copending application Serial No. 162,492 filed May 17, 1951, now U. S. Patent No. 2,622,169, dated December 16, 1952, of which this application is a continuation-in-part, there is disclosed a circuit breaker of improved design which affords trip-free operation. In accordance with that invention a bimetallic snap member is so incorporated in a circuit breaker assembly that a flow of electric current is passed directly through the bimetallic snap member, the member being adapted to snap into a reversed configuration to open or close an electrical circuit when the current reaches a preestablished value. It has now been found that improved circuit breaker action may be attained by closely controlling the paths of current flow through the bimetallic member.

It is, accordingly, one object of the present invention to provide an improved circuit breaker assembly which has extremely high sensitivity.

It is another object of the invention to provide an improved circuit breaker assembly responsive to electrical current whereby the flow paths for the electrical current may be closely controlled within the unit.

It is a further object of the invention to provide an improved bimetallic snap spring member for use in circuit breakers and the like which is highly sensitive to passage of electrical current therethrough.

These and other objects and features may be attained in accordance with the invention by arranging a bimetallic snap member within a circuit breaker housing so that electrical current may be passed directly through the snap member, thus heating it and bringing about a snapping reversal of configuration to open the circuit. The snap member, which may include a rim portion and a plurality of leg portions, is preferably so arranged in the circuit breaker assembly that current flow through the snap member will follow preestablished paths, particularly in the rim portion which is most effective in inducing snapping. To this end, at least two contact points are established in the housing assembly to be bridged by the bimetallic member in such a way as to establish both maximum current flow in the rim portion and effectively balanced flow in opposite sections or halves of the rim portion.

In the case of a three-legged snap member, for example, one contact point will be disposed on the rim portion at an effective mid-point between the junctions of adjacent leg portions and the rim portion, and the other contact point will be disposed on the rim portion at a point which is along the effective diameter of the snap spring member passing through the first point. In most cases the second point will be near the junction of the third leg and the rim portion. In a four-legged snap member the contact points will be arranged so that each is disposed at an effective midpoint in the rim portion between the junctions of adjacent leg portions and the rim and so that the two points will be disposed along the effective diameter.

The assembly is so arranged in the housing that a biasing spring urges the bimetallic snap spring member toward a given position but which will yield to permit at least one pair of contacts to be opened manually without attendant snapping of the bimetallic snap spring member. Preferably this biasing spring is in the form of a snap spring having one stable and one unstable configuration of equilibrium so that any manual control of the contacts will result in snap action.

For a better understanding of the invention reference may be had to the following specification taken in conjunction with the accompanying drawing in which:

Figure 1 is a view in horizontal section of a circuit breaker assembly taken on the line 1--1 of Figure 2 looking in the direction of the arrows and showing one form of snap member and its mounting relationship to the circuit breaker housing;

Figure 2 is a view in vertical section of the-circuit breaker assembly taken on the line 22 of Figure 1;

Figure 3 is a plan view of an alternative form of snap spring member; and

Figure 4 is a plan view of another alternative form of snap spring member.

Referring to Figures 1 and 2 of the drawing, the invention is shown as embodied in a circuit breaker assembly comprising a pair of mated housing portions 10 and 11 of insulating material. The lower housing portion 11 is formed with a cylindrical cavity 12 along the axis of which is disposed a bushing 13 adjustably threaded into a wall portion 11a. The bushing 13 slidably receives a control element, such for example, as a post 14 having a shoulder 14a near its inner end which normally rests on the bushing 13.

The upper housing portion 1%) is formed with a shallow cylindrical cavity 15 which communicates coaxially with the cavity 12 of the lower housing portion 11. Received within the cavities 12 and 15 is an electrical switch assembly comprising a bimetallic snap spring member 16 and a monometallic snap spring member 17. The snap spring member 16 is bimetallic and as such is adapted to snap between two dished configurations, shown respectively in full and broken lines in Figure 2, under the influence of heat. The snap spring member 17 is, as described in greater detail below, a biasing spring and preferably is provided with a stable configuration of equilibrium as shown .in full lines in Figure 2 and an unstable configuration as shown in broken lines.

The two snap spring members are normally abutted back to back, with their convex surfaces opposing each other, and each is centrally apertured to receive the inner end 18 of the control element 14. The rim portion of the monometallic snap spring 17 engages an abutment in the form of an annular shoulder 19 formed on the upper housing portion 10 and the rim portion of the bimetallic snap spring member 16 is adapted to engage abutment means in the form of stationary electrical contacts 20 and 21 mounted near the base of the cavity 12. The contacts 20 and 21 are electrically connected to external terminal means 22 and 23, respectively, by means of which the circuit breaker may be connected in an external electrical circuit. The snap spring member 16 has a pair of electrical contacts 24 and 25 attached, as by welding, soldering, riveting or the like, to its periphery at diametrically spaced points and which normally engage the contacts 20 and 21, respectively. The contacts 24 and 25 preferably overhang the margin of the snap spring member 16 to be received in vertical channels 26 and 27 formed in the Wall of the lower housing portion 11,

3 housing which would take the contacts out of alignment.

As described in the said U. S. Patent No. 2,622,169, the passage of electrical current through the snap spring member 16 will cause the latter to heat. It the current is excessive, overheating will occur which will induce the member to snap to its second configuration of equilibrium, as shown in broken lines, the monometallic snap spring member 17, however, maintaining its original configuration in which the lower surface is convex. This will open the circuit by separating the contacts 2ti234- and 21-25. Resetting may be accomplished by pressing the control member 14 inwardly against the direct spring action of the monometallic snap spring member 17 to cause the shoulder 14a of the control member 14 to press against the center of the bimetallic snap spring member 16. This causes the contacts 24 and 25, carried by the member 16, to engage the lower surface llt a of the upper housing portion so that there is set up a force couple between the center and the periphery of the snap spring member 16 to cause the latter to be snapped from the dotted configuration in which a convex surface faces downwardly to its original configuration as shown in solid lines in which a convex surface faces upwardly. At the same time the snap spring member 17 will be caused to yield at its center, reversing, for the moment, its configuration. When the control member 14 is released the snap spring assembly will snap to its original, closed circuit position by the action of the snap spring member 17, which is non-stable in the configuration as shown in broken lines and which will, therefore, reassume its original configuration as shown in full lines to drive the snap spring member 17 bodily downwardly, causing the contacts 24 and to engage the contacts 29 and 21 respectively. The control member 14 may be utilized to open the contacts independently of any snap action of the snap spring member 16. The snap spring member 17 is lifted and the contacts 24 and 25 separated from the contacts 243 and 21 by pressing inwardly on the control member 14. During this operation the configuration of the bimetallic snap spring member 16 will not reverse, whereas the monometallic snap spring member 17 will. In this case the snap action of the snap spring member 17 will be useful to establish snapping engagement and disengagement of the contacts. It should be noted, however, that a conventional coil spring or other resilient means may be substituted for the snap spring 117 if this feature is not required.

The snap spring member 16 is so arranged in the housing in accordance with the present invention that as much electrical current as possible will flow through the rim portion of that member, this being a most effective way of inducing snapping by heating. Also, the arrangement is such that current flow in the member 16 will cause substantially balanced heating on opposite sides of the chord or diameter along which the contact points may be disposed.

To these ends, the snap spring member 16 may be made, for example, in the form of a legged disc including leg portions 23, 29, and 31, and rim segments 32, 33, 34 and 35. The contact points, Which may comprise the contact elements 2 and 25, are arranged in the effective centers of the rim segments and 32, respectively i. e., between the points of intersection of consecutive leg portions with the rim portion. Assuming the current flow to be from the terminal 22 to the terminal 23 of the circuit breaker, the current flow through the snap member 16 may divide at the input contact 24 and flow in opposite directions through the rim segment 34 toward the leg portions 31 and 23, respectively.

At the junction of the rim segment 34 and the leg portion 31 the current may divide again, part continuing clockwise through the rim to the contact 25 and part flowing through the leg portion 31 toward the center. The latter current will divide between the leg portions 30 and 27 and will ultimately reach the contact 25 through the rim portion 32, part flowing clockwise and part counterclockwise.

The current flowing counterclockwise from the input contact 24 through the rim segment 34 toward the leg portion 28 will divide in similar ways before reaching the output contact 25. It will be seen, therefore, that the current will be substantially balanced on opposite sides of the diameter through the contacts 24 and 25, and that much. of the current will flow through the rim. This results in rapid and balanced heating of the rim which, as stated, is most efiective in inducing snapping. Consequently the circuit breaker device may be precisely calibrated even at its lowermost trip points.

Various modifications of the basic bimetallic snap spring member design are possible within the scope of the invention. Thus, as shown in Figure 3, a three legged disc 36 may be provided having three rim segments 37, 33 and 39, and three leg portions 40, 41 and 42. Electrical contact points may be established on the member by afiixing, for example, contact elements 43 and 44 on the rim at diametrically opposite points, the contact 43 being disposed at the junction of the rim segments 37 and 39 and the contact 44 at the effective mid-point of the rim segment 38.

In this case it will be seen that the current flow between the contacts 43 and 4-4- will be equally divided in opposite halves of the member and that the majority of the current will fiow through the rim portions. Assuming current enters the member at the contact 44, there will be an equal division in opposite directions in the segment 38. Current flow at the leg portion 42 will divide, part flowing through the rim portion 39 and part through the leg portions 42 and 40 to the output contact 43. A similar flow pattern will obtain for the current flowing toward the leg portion 41 from the input contact 4 The result will be uniform heating on 0pposite sides of the contact diameter and a relatively large flow through the rim portion.

Referring to Figure 4, another alternative design for the snap spring member is shown as comprising a substantially rectangular snap spring element 45 having rim sections 46, 47, 48 and 49, a central or hub portion 59, and a plurality of leg portions 51, 52, 53 and 54. A pair of electrical contact elements 55 and 56 are disposed a't diametrically opposed points on the rim portion.

With the snap member 45 connected in a circuit breaker so that the current flowing through the snap member is between the contacts 55 and 56, the current will divide at the contact 55 between the two rim portions 46 and 4-9. A portion of the current flowing in the rim portion 4% will continue directly to the contact 56 through the rim portion 48. The remainder of this current will divide at the junction of the leg portion 54 with the rim portion 49 and will find its way to the contact 56 through the leg portions 52 and 53 via portions of the rim portions 47 and 48, respectively. In like manner the current flowing in the rim portion 46 will divide at the junction of the leg portion Sll. Some of the current will find its way directly through the rim portions 46 and 47 to the contact 56. The remainder of the current will flow through the leg portion 51 and will then divide at the hub St) between the leg portions 52 and 53, which divided current will find its way to the contact 56 through the rim portions 47 and 48, respectively.

Thus it will be understood that the rim portions are caused to conduct most of the current flowing between the contacts 55 and 56. This current flow in the rim portion will, as disclosed above, be most effective in inducing snap action of the snap member 46 between its two configurations of equilibrium.

As in the case of the snap members 16 and 36 described above for purposes of illustrating the invention, the snap member 45 may be mounted by its hub portion 50 so that the snap member may reverse its configuration to cause snap motion of both contacts 55 and 56. However, it will be understood that this snap spring member as well as the other snap spring members 16 and 36 described above may be mounted cantilever fashion with their stationary support at one of the contact points without materially altering the flow paths for the electrical current. Moreover, such mounting will result in increased travel for the one movable contact upon snapping of the snap member between its configurations.

It will be understood that various other arrangements of contacts may be provided to achieve balanced heating of the snap spring member and to assure that as much current as possible flows in the rim portions to bring about the snap action. It is important to note that although in each of the illustrated arrangements of the invention, the snap spring members are symmetrical both electrically and geometrically, such design criteria are not in fact controlling. The heating and consequent stressing of the rim portions of the bimetallic snap members are a function of the electrical resistance values of the various portions of the snap members as well as the geometry or contours thereof.

The snap spring member 16 of Figure l, for example, is arranged in the circuit breaker with the contacts 24 and 25 diametrically spaced and precisely midway between the junctions of the adjacent leg portions with the rim portions. If the geometry and/ or the resistance value of the electrical current paths were to dilfer in the two halves of the member, it follows in accordance with the invention that it would be necessary to shift the relative positions of the contact points so that an efiective mechanical and electrical balance would obtain. Thus the contact 24 should be thought of as disposed at the effective mid-point between the junctions of the leg portions 29 and 30 with the rim portion, that is to say at the point at which the flow of electrical current will so divide as to cause balanced stressing of the member pursuant to which snapping occurs, as well as large current flow in the rim portion.

The position of the first contact 24 relative to the leg portions 29 and 30 is important in the initial division of the current. Further, the relative position of the two contacts 24 and 25 on the rim portion is important in achieving the desired balance of stresses and current flow in the overall snap member. For purposes of definition, therefore, the locations of the contact points on a bimetallic snap spring member are characterized, for example, as being at the eflective mid-point between leg portions or as being disposed along the effective diameter of the snap spring member.

The particular forms of the invention described above and illustrated in the accompanying drawings are presented merely as examples of how the invention may be applied. Other forms, embodiments and applications of the invention coming within the scope of the following claims will readily suggest themselves to those skilled in the art.

We claim:

1. In a current responsive device, a housing, terminal means carried by the housing for connecting the device in an electrical circuit, a bimetallic snap spring member adapted to snap between at least two configurations under the influence of heat, said member comprising a rim portion and a plurality of leg portions, contact means on said housing adapted to be separably engaged by said rim portion to complete an electrical circuit across said terminal means through said bimetallic snap spring member, and means for mounting said member in the housing to partake of snap movement therein and with said rim portion in separable engagement with said contact means when the member is in one of its said configurations, said rim portion having contact means thereon engaging said contact means at the efiective mid-point 6 between the points of intersection of two consecutive leg portions with said rim portion.

2. In a current responsive device, a housing, terminal means carried by the housing for connecting the device in an electrical circuit, a bimetallic snap spring member adapted to snap between at least two configurations under the influence of heat, said member comprising a rim portion, a center portion and a plurality of equi-angularly spaced leg portions, first and second spaced apart contact means on said housing adapted to be separably engaged by said rim portion to complete an electrical circuit across said terminal means, through said bimetallic snap spring member, and means for mounting said member by its center in the housing to enable its rim portion to partake of snap movement therein and with said rim portion in engagement with said first and second contact means when the member is in one of its said configurations, said rim portion having contact means thereon engaging said first contact means at the point on the rim portion which is the efiective mid-point between the points of intersection of two consecutive leg portions with said rim portion.

3. In a current responsive device as set forth in claim 2, said bimetallic snap spring member and said second contact means being respectively disposed in said housing so that the contact means of the rim portion of the snap spring member which engages the second contact means is disposed along the effective diameter of the member passing through the point of the rim portion which engages said first contact means.

4. A bimetallic snap spring member adapted to snap between two configurations under the influence of heat, comprising a rim portion, a plurality of leg portions intersecting said rim portion, and an electrical contact member disposed on the rim portion at the eitective midpoint between the points of intersection of two consecutive leg portions with the rim portion.

5. A bimetallic snap spring member as set forth in claim 4, including a second electrical contact member on said rim portion at a point which is along the effective diameter of the member passing through the point on the rim portion at which the first contact member is mounted.

6. A bimetallic member having two configurations of equilibrium and adapted to snap therebetween under the influence of heat, said member having a rim portion and a center portion, an even number of leg portions extending inwardly from the rim portion to the center portion, and a pair of electrical contacts disposed respectively at points spaced apart along the rim portion, said first and second contacts being disposed respectively at the effective mid-point between the points of intersection of two consecutive leg portions with the rim portion.

7. A bimetallic member having two configurations of equilibrium and adapted to snap therebetween under the influence of heat, an annular rim portion, a center portion, a plurality of equi-angularly spaced leg portions joining the center and rim portions, a plurality of electrical contacts on the rim portion at spaced-apart points, at least one of said contacts being disposed at a point which is the effective mid-point between the points of intersection of the rim portion by two consecutive leg portions.

8. A bimetallic snap spring disc comprising an annular rim portion, a central hub portion and a plurality of leg portions joining the hub and rim portions, said leg portions being equi-angularly spaced, a pair of electrical contacts carried by said rim portion at diametrically spaced points, at least one of said contacts being spaced at a point equi-distant between the points of intersection of a pair of adjacent leg portions with the rim portion.

9. A bimetallic snap spring disc as set forth in claim 7, said snap spring disc comprising at least four leg portions, said first and second contacts being disposed respectively at points equi-distant between the points of intersection of adjacent leg portions with the rim portion.

10. A snap spring disc as set forth in claim 7, said disc having three leg portions, one of said contacts being mounted on the rim portion at the point of engagement With the leg portion and the rim portion, and the other contact being disposed equi-distant between the point of intersection of the second and third leg portions with the rim portion.

References Cited in the file of this patent UNITED STATES PATENTS 1,654,320 Colby Dec. 27, 1927 StilWell Dec. 7, 1943 Cataldo et a]. May 13, 1947 Stilwell Dec. 6, 1949 Moorhead et al. July 25, 1950 Mertler Feb. 27, 1951

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