US3534313A - Self-cancelling switches - Google Patents

Description

Oct. 13,1970 w, H 3,534,313

- SELF-CANGELLING SWITCHES Filed Nov. 27, 1967 3 Sheets-Sheet 1 BM a......,.\..1..1.h ATTORNEYS W. D.HOLT

I SELF-CANCELLING SWITCHES Oct; 13, 1970 3 Sheets-Sheet 2 Filed Nov. 27, 1 967 a/MWiM ATTORNEYS Oct. 13, 1970 w. D. HOLT 3,534,313

SELF-CANCELLING SWITCHES Filed Nov. 27, 1967 5 Sheets-Sheet 8 Y 261A 26 2 i 55 57 Z 5@ L 52 Z66 I A 3 ATTORNEYS United States Patent 3,534,313 SELF-CANCELLING SWITCHES William David Holt, Colne, England, assignor to Joseph Lucas (Industries) Limited, Birmingham, England, a British company Filed Nov. 27, 1967, Ser. No. 685,802 Claims priority, application Great Britain, Dec. 13, 1966, 55,692/ 66 Int. Cl. H01h 61/00, 71/16 US. Cl. 337-39 4 Claims ABSTRACT OF THE DISCLOSURE A thermally operable, self cancelling switch including a body and an operating member mounted on the body for movement between an off position and first and second on positions. The second on position being between the first or position and the off position. Resilient means urge the operator member towards the off position. First and second bimetallic elements are carried by the operating member. Catch means are provided for each bimetallic element for maintaining the operating member in its first and second on positions. When the switch is in the first on position current flows through the first bimetallic element which upon suflicient heating flexes out of the path of its catch means. Upon release from the first on position the operating member and first and second bimetallic elements are urged by the resilient means to the second on position wherein the second bimetallic element engages its respective catch means. Upon deflection of the second bimetal the operating means is urged to the 011? position. The direction of deflection of the bimetallic elements is perpendicular to their path of movement from the first on position to the oil? position.

This invention relates to thermally operable self-cancelling switches.

A switch according to the invention includes a plurality of bimetallic elements, and means whereby the elements are heated sequentially to determine the overall operating period of the switch.

One example of the invention is illustrated in the accompanying drawings wherein FIG. 1 is a sectional view of a self-cancelling switch in its off position, FIG. 2 is a view similar to FIG. 1 but showing the switch in its operative positions, FIG. 3 is a sectional view on the line 3-3 in FIG. 2, FIG. 4 is a horizontal, sectional view of the switch of FIG. 1, but also showing in dotted lines, the parts of the switch in their operative positions and deleting certain parts for illustrative convenience, and FIGS. 5, 6 and 7 are views similar to FIGS. 1, 2 and 3 respectively of a modification.

Referring to the drawings, the switch includes a moulded synthetic resin body 11 of open rectangular box like construction having side walls 12, end walls 13 and a base 14, the open end of the body 11 being closed in use by a moulded operating member 15. The member 15 is for-med centrally, with a pair of short integral posts 16 which engage elongated vertical slots 17 in the side walls 12 of the body 11. The posts 1 6 are urged to the upper ends of the slots 17 by springs 18 housed in the slots 17. Thus, the member 15 is capable of rocking movement with respect to the body 11 in addition to vertical movement as allowed by compression of the springs 18.

The base 14 of the body 11 supports a pair of conductive terminals 19, 21. The terminal 19 is of strip like form and includes a portion 19a which extends upwardly from the base within the body 11 in contact with an end wall of the body 11 and a portion 19b which extends lownwardly from the base 14 for engagement with a lead.

3,534,313 Patented Oct. 13, 1970 The terminal 21 includes a portion 21a which extends upwardly from the base 14 and a portion 21b similiar to the portion 19b which extends downwardly from the base 14 for engagement with a second lead. The portion 21a of the terminal 21 is bifurcated and the bifurcations are bent in opposite directions towards the side walls respectively of the body 11. The bifurcations are shaped to define a spaced pair of catches 22, 23 which are parallel with, but vertically spaced from the base 14.

The member 15 is formed with a pair of downwardly extending spaced parallel lugs 24 which define between them a channel 25, within which is engaged the central portion of a spring 26. The spring 26 includes a limb 26a which engages the underside of the operating member 15 at one side of the pivotal axis of the member 15 and a second limb 26b which extends within the body 11 and engages the portion 19a of terminal 19 on the other side of the pivotal axis of the member 15. The spring 26 is secured in the channel 25 by a conductive rivet 27 which passes through the lugs 24. The rivet 27 further serves to secure a pair of bimetal strips 28, 29 to the lugs 24 respectively. The strips 28, 29 extend parallel with the walls 12 towards the base 14 of the body 11 and are electrically interconnected with the spring 26 and consequently the terminal 19, by the rivet 27. The strips 28, 29 are formed at their free ends with inwardly turned latch portions 31, 32 and the springs are so arranged that when heated they will move towards the walls 12, away from each other.

The operation of the switch is as follows: the terminals 19, 21 are connected in a circuit which it is required to energise for a predetermined time. In the off position of the switch the member 15 is urged by the spring 26 to a position in which the strips 28, 29 are urged against insulating stops 33 carried by the body 11 (FIG. 4) and so the circuit between the terminals 19, 21 is not completed. In order to energize the circuit the member 15 is pivoted against the action of the spring 26 and in so doing, the strips 28, 29 are flexed to allow their portions 31, 32 to pass the respective catches 22, 23. At the limit of the pivotal movement of the member 15, the portion 32 of the strip 29 engages behind the catch 22 and makes an electrical contact therewith; thereby completing the circuit from the terminal 19 through the spring 26, the rivet 27 and the strip 29 itself to the terminal 21. As current flows through the strip 29, it becomes heated and so bends towards the wall 12 thereby disengaging the portion 32 from the catch 22. When the catch 22 and the portion 32 disengage, the spring 26 urges the member 15 towards its off position, but movement of the member 15 to its 01f position is arrested by engagement of the portion 31 of the strip 28 with the catch 23. Thus the circuit between the terminal 19, 21 is now made through the strip 28 which in turn becomes heated to allow the switch to return to its off position. The switch therefore cancels itself after a predetermined time, dependent on the sum of the operating times of the two strips 28, 29.

If it is required to cancel the switch manually, the member 15 is pressed downwardly against the action of the springs 18 so that the portions 31, 32 of the strips 28, 29 ride under the catches 22, 23 and the switch is returned to its off position.

In the modification shown in FIGS. 5, 6 and 7, the springs 18 are omitted and the diameter of the posts 16 on the member 15 and the width of the slots 17 in the side walls 12 of the body 11 are increased and a slotted plate 34 is interposed between the member 15 and the base 14 of the body 11. The plate 34 is hinged at one end 35 to one end wall 13 of the body 11 while the other end of the plate 34 is urged towards the member 15 by a spring 36. The plate 34 includes a pair of laterally spaced depressions 37 which engage the posts 16, the strips 28, 29 extending through the slot in the plate 34. Thus when it is required to manually cancel the switch, the member 15 is depressed to pivot the plate 34 against the action of the spring 36 so that the portions 31, 32 of the strips 28, 29 can ride under the catches 22, 23 as the switch is returned to its off position by the spring 26.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. A thermally operable, self-cancelling switch including a body, an operating member mounted on said body for movement between an oif position and first and second on positions, resilient means urging said operating member towards its ofi position, first and second terminal members carried by said body, first and second bi-metallic elements carried by said operating member, and first and second catch means associated with said first and second bi-metallic elements respectively for maintaining said operating member in its first and second on positions respectively, the arrangement being such that when said operating member is moved to its first on position, the circuit between said terminal members is completed and the heating circuit of said first bi-metallic element is also completed, said first catch means sewing to maintain said operating member in said on position until said first bimetallic element heats suificiently to release said first catch means whereupon said operating member is moved by said resilient means towards its off position, movement of sa d operating member into its off position being prevented by said second catch means which arrests said operating member in its second on position wherein the circuit between said first and second terminal members is again completed and the heating circuit of said second bi-metallic element is also completed, the switch being maintained in its second on position until said second bimetallic element heats sufliciently to releasesaid second catch means, so that said bi-metallic elements together determine the overall operating period of the switch.

2. A switch as claimed in claim 1 wherein in the on positions of the switch the circuit between said terminal members is completed through the respective bi-metallic element.

3. A switch as claimed in claim 1 wherein said bi-rnetallic elements are carried by said operating member and are electrically connected to one of said terminal members, the other of said terminal members defining said clutch means and being engageable by said bi-metallic elements respectively in the respective on position of the switch.

4. A switch as claimed in claim 1 including means whereby the switch can be cancelled manually before the end of said operating period.

References Cited UNITED STATES PATENTS 2,639,095 5/1953 Cubberley 337-340 FOREIGN PATENTS 1,191,018 4/1965 Germany.

BERNARD A. GILHEANY, Primary Examiner B. M. MORGAN, Assistant Examiner US. Cl. X.R. 337-40, 78, 336

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