US3213408A - Electrical switches - Google Patents

Description

OC- 19, 1965 E. KADlsEvsKls 3,213,408

ELECTRICAL SWITCHES Original Filed Oct. 20, 1960 f 202 2 .FI 5 222 'f 204 2/0 'l'f Imperator,

United States Patent O 3,213,408 ELECTRXCAL SWITCHES Edmunds Kadisevslris, Attleboro, Mass., assigner to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Original application Get. 20, 1960, Ser. No. 63,913, now Patent No. 3,133,169, dated May 12, 1964. Divided and this application Oct. 24, 1962, Ser. No. 237,784 3 Claims. (Cl. 339-218) This application is a division of my prior co-pending application, Serial No. 63,913, filed October 20, 1960, now Patent No. 3,133,169, issued May l2, 1964, and entitled Calibration Means for a Snap-Acting Switching Mechanism.

This invention relates to electrical switches, and generally involves precision switches which employ a snapacting member to effect switching. The invention is particularly concerned with providing new and improved means for mounting threaded terminals and other threaded members on a base or housing which may be used for such switches.

It is another object of the instant invention to provide a means which reliably maintains the parts in desired calibration at elevated temperatures or under shock and vibration to which the switch may be subjected during operation.

It is another object of the instant invention to provide a novel and improved means for mounting an internally threaded member on a base, whereby relative movement between the base and the internally threaded member is inhibited to facilitate reception of a mating threaded bolt member for threaded engagement therein.

It is yet another object of the instant invention to provide a novel and improved means for mounting a threaded receiving member on a base member formed of a frangible or relatively brittle material whereby relative movement between the member and the base is prevented without incurring cracking or fracture of the base member.

It is yet a further object of the invention to provide a new and improved means for tightly and ixedly mounting a terminal on a base or housing member.

It is yet a further object of the invention to provide a new and improved means of firmly and tightly mounting members on a base member or housing member formed of frangible or brittle material.

Other objects will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which one of the various possible embodiments of the invention is illustrated:

FIG. 1 is a sectional view of a switch employing the mounting means of the instant invention;

FIG. 2 is a bottom view on a reduced scale of the switch shown in FIG. 1;

FIG. 3 is an enlarged fragmentary detail view of a part of the switch shown in FIG. 1, with parts broken away for clarity of illustration;

FIG. 4 is an exploded view taken on line 4 4 of FIG. 3;

FIG. 5 is a plan view taken on line 5 5 of FIG. 4;

FIG. 6 is an exploded View taken on line 6-6 of FIG. 4.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in variousways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Referring now to the drawings, FIG. 1 illustrates an electrical switch, generally designated by numeral 10, employing mounting means according to this invention. Switch 10 is a high precision electrical switch which is operable at elevated temperatures, :and employs a snapacting switching element for which calibrationl can be reliably maintained by the mounting means of the instant invention. Switches produced according to the instant invention will retain precise operating characteristics and calibration of the snap-acting switching element at elevated operating temperature conditions, and under shock and vibration.

Switch 10 includes a casing member 12 formed of an electrically insulating material such as, for example, a ceramic or one of the phenolic thermosetting resinous materials. Casing 12 provides a cavity 14 in which is disposed a switching mechanism subassembly generally referred to by numeral 2i).

Switching mechanism 20 includes a snap-acting element 22 which may take the form of a sine blade of the type shown and described in the Burch Patent No. 2,630,504, issued on March 3, 1953. The sine blade switching element 22 is so called because its shape resembles a sine wave. The sine blade switching element 22 is a flat, single-piece, electrically conductive spring element supported at both ends and placed under a predetermined accurately controlled amount of tension. Blade element 22 includes integrally formed spaced leg mounting portions 24 and 26, each of which are provided with suitable apertures for respectively receiving mounting studs 32 and 34. Sine blade 22 includes an integrally formed contact leg or arm 36 which mounts and carries a pair of oppositely facing electrical contacts 38 and 40 at its free end. When actuated, the sine blade provides a torsional snap action. Actuator movement, e.g. in the form of a positively applied force, in one direction, causes movement of a contact arm 36 in the opposite direction.

Movable contact 38 is positioned for engagement with stationary contact 42, provided by terminal member 44. Terminal member 44 is mounted on casing 12 by means of a threaded bolt 50 which is received in an aperture- 52 provided by casing 12. Bolt 50 is maintained in fixed, assembled relation by means of nut S4, as best seen in FIG. 1. The relationship and nature of construction of nut 54, bolt 50 and the co-operating portions of casing 12 will be described in greater detail below.

Movable contact 40 is positioned for engagement with stationary contact 56 provided by terminal 58. Terminal 58 is mounted on casing 12 by bolt 60 in a manner similar to that described above for terminal 44. Bolt 60 is received in an aperture 62 provided by casing 12, and is maintained in fixed assembled relation by nut 64.

Mounting bolts 32 and 34 are so spaced as to tension and stress the element 22 into a deformed configuration whereby leg 36 is urged out of the plane formed by legs 24 and 26 in the unstressed condition.

Contact leg 36 can assume either of two positions on opposite sides of the plane formed by legs 24 and 26. It is to be understood that either one or both of these positions of opposite configuration may be relatively stable, depending on the restraints to movement of leg 36 which may be provided. Sine blade 22 is adapted to snap leg 36 to respectively open contacts 40 and 56, and close contacts 38 and 42, upon the application of a positive force to leg 26. Positive actuating forces are transmitted to blade 22 by an actuating button 70. Actuating button 70 includes a projection 72, formed of a ceramic or electrically insulating material, and is adapted to engage the sine blade at one end of leg 26. Projection 72 is carried lby a sleeve member 74 which, in turn, is mounted on la spring member 76. Sleeve 74 is received Within a suitable aperture 78 provided by spring member 76, and includes a flange 80 which is welded to spring member 76. Spring member 76 biases the entire actuating button :assembly upwardly (as seen in FIG. l), in a direction away from sine blade 22. Switch includes a cover member 82, as shown. Cover member 82 is provided with an -aperture 84 through which button 70 extends and is loosely received therein for reciprocal vertical motion. Spring member 76 also biases the actuator button assembly toward cover member 82 to dispose button 70 exteriorly of cover member 82. Spring member 76 is welded to cover 82 and is mounted on casing 12 by means of bolt 88 and nut 90, as shown. Bolt 86 and nut 87 also serve to mount cover member 82 on base or casing 12, as shown.

It can thus be seen that, upon the application of a predetermined actuating force to actuating pin 70, in the direction of the arrow shown in FIG. 12, sine blade 22 will snap to an opposite configuration and will snap contact-carrying arm 36 to open contacts 40 and 56, and respectively close contacts 38 and 42. Upon release of the force, contact arm 36 will snap to open contacts 38 and 42, and close contacts 40 and 56.

The movement differential (the minimum amount of actuator 70 movement necessary to operate the switch) of the switch varies with the tension on the blade which is measured in terms of blade elongation. As Will be clear, the movement differential starts at a minimum at very low sine blade 22 tension. At this minimum, contact pressures are low and as tension is increased, movement differential increases accordingly to reach a maximum. Calibration of the sine blade 22 is controlled by increasing or decreasing the blade tension, which in turn is controlled by the spacing of the mounting studs or posts 32 and 34. In accordance with the instant invention, the calibration of t-he sine blade 22 can be positively locked once the desired setting is obtained. For further details concerning the switch and the calibration means reference may be had to Patent No. 3,133,169, referred to supra.

The instant invention provides a novel and unique construction to facilitate assembly of the switch parts by means of threaded membe-rs. In assembling and mounting parts on the base, as by means of bolts 50, 60 and 172, each of which respectively is threaded into flanged nuts 54, 64 and 180, it is desirable that the nuts be received within an aperture in the base member and restrained 4against rotation therein. By mounting the nut in the base member so as to prevent relative rotation therebetween, an eXtra handling `operation is eliminated, and threaded insertion of the bolt member therein is facilitated.

In t-he past, it has been proposed to employ square or rectangular shaped nuts which intert within and are maintained against rotation within complementary shaped recesses in a base member. Such prior proposals present diculties and problems when ceramic insulating base materials are employed, such as for the casing 12 of electrical switches according to the instant invention. Where a rectangular s-haped nut is disposed within a complementary shaped recess in the base, a relatively tight t between parts is necessary to prevent relative rotation between the parts to facilitate threading of the bolt members therein. The tight fit required by the prior constructions, in addition to problems of economy created by the required close manufacturing tolerances, also c-reates other problems. Ceramic materials are frangible and notoriously weak in tension. The switches, according to the instant invention, are generally subjected to elevated temperatures during operation, and upon thermal expansion of the nut member, forces are created against the base member which may cause fracture and cracking where there is a tight lt between parts. When sucient clearance is provided between the rectangular yaperture in the base and the rectangular nut member to avoid cracking and fracture of the base upon differential thermal expansion, such clearance will generally result in a free play or looseness of t between the parts, which is beyond permissible limits for the requirements of the precision switching device. Such free play and looseness of fit of the terminal and other parts may result in deleterious shifts or changes in calibration of the switching element. This feature of the instant invention uniquely provides for tight, secure mounting of the parts whereby undesirable free play and looseness of fit is eliminated or at least minimized, while at the same time, a clearance for the-rmal expansion to avoid cracking or fracture of the ceramic base material is provided.

The instant invention recognizes and employs to advantage the compressive strength characteristic of ceramic materials. Referring now to FIGS. 3-6, there is illustrated a subassembly generally referred to by numeral 200, which subassembly may be employed for each of the bolts and nuts 50, 54; 60, 64 and 172, 180, described above. Fragmentary portions of base 12 and bolt members are shown throughout FIGS. 3, 4 and 6. Base 12 provides a tapered aperture 202, in which is received a flanged internally threaded bushing or nut member 204.

As best seen in FIG. 3, tapered recess 202 provides adequate clearance for thermal expansion of nut 204 when disposed therein. Base 12 further provides a cylindrical aperture of lesser diameter than that of cavity or aperture 202, for the reception of the threaded shank of a bolt 208. Relative rotation between the base member 12 and -nut 204, when the latter is disposed within oversized tapered cavity 202, is uniquely prevented by means of a V-shaped notched portion 210 provided on member 204, Which as best seen in FIGS. 4, 5 and 6, mates with and receives a complementary shaped projection 212 provided by casing member 12. Notched portion 210 receives projection 212 in mating and interfitting engagement, and `co-operates therewith to prevent relative rotation between the nut 204 and casing 12. When threaded shank portion 208 is inserted into aperture 206 of casing 12, and into threaded engagement with nut 204, projection 212 and notched portion 210 co-operate to prevent nut member 204 from rotating within cavity 202 of casing 12. The forces created on the casing which resist rotation of nut 204 within the cavity 202 are shown by the arrows P1 and P2 in FIG. 3. As best seen in FIG. 3, a clearance is provided between the notched end of nut 204, other lthan the notched portion 210, and the bottom wall of aperture 202 in base member 12 so that only the forces P1 and P2 are set up in the base member. It will be noted that the forces P1 and P2 are compressive forces which can effectively be resisted by a ceramic material which is comparatively strong in compression although weak in tension.

After t-he threaded shank portion 208 is received within lthreaded engagement within nut 204 so as to tightly and securely mount the respective parts to the base, the free end of nut 204 may receive a threaded shank 220 of a terminal screw such as to mount electrical leads .such as 190, 192 or 194. Threaded shank portion 220 may correspond to the threaded shank portion of terminal screws 184, 186 and 188. After the threaded parts have been assembled, an electrically insulated sealing cement such as, for example, an epoxy material 222 may be diSpOSed .in opening 202. to rmly seal and maintain the parts in assembled relation. Epoxy material 222 should be suiciently resilient so as to permit thermal expansion of nut member 204 and lto preclude creation of undesirable tensile stresses in the adjacent portions of casing 12.

It should also be understood that while a substantially V-shaped notched portion has been illustrated and described, that other projection and notched shapes can be employed within the practice of the instant invention as long as the contacting surfaces have equal and oppositely sloped walls. Such other shapes might, for example, include a U-shape or W-shape.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

Dimensions of certain of the parts as shown in the drawings have been modified for the purposes of clarity of illustration.

As many changes could be made in the above constructions 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, and it is also intended that the appended claims shall cover all such equivalent variations as come within the true spirit and scope of the invention.

Iclaim:

1. An electrical switch including a base member formed of a frangible electrically insulating material; terminal means mounted on said base member, said terminal means including :a cylindrical member having an internal cylindrical threaded cavity, said member being received within an aperture provided in said base member having a bottom wall, said aperture being oversized and providing clearance for expansion of said member; means on said base member and cylindrical member for inhibiting relative rotation between said members, said means comprising a notched portion providing equal but yoppositely sloped walls at one end of said cylindrical member and a complementary shaped projection provided by said base member for intertitting and mating engagement with said notched portion of said cylindrical member and providing clearance between the remainder of the notched end of the cylindrical member and the bottom wall whereby only compression forces are set up in the frangible base member when pressure is applied to the base member by the notched portion of the cylindrical member.

2. The electrical switch as set forth in claim 1 and wherein said notched portion of said cylindrical member is substantially V-shaped.

3. The electrical switch as set forth in claim 1 and wherein said notched portion o f said cylindrical member is substantially U-s-haped.

References Cited by the Examiner UNITED STATES PATENTS 1,291,217 1/19 Sonneborn 174-196 X 1,344,721 6/20 Samson 174-452 1,754,718 4/30 Johnson 174-152 2,185,814 1/40 Kuhn.

FOREIGN PATENTS 462,724 1/50 Canada. 1,032,117 3/53 France. 1,138,161 1/57 France.

406,881 8/ 44 Italy.

106,640 9/ 24 Switzerland.

JOSEPH D. SEERS, Primary Examiner.

PATRICK A. CVLIFFQRD, Examinar,

Claims (1)

1. AN ELECTRICLA SWITCH INCLUDING A BASE MEMBER FORMED OF A FRANGIBLE ELECTRICALLY INSULATING MATERIAL; TERMINAL MEANS MOUNTED ON SAID BASE MEMBER, SAID TERMINAL MEANS INCLUDING A CYLINDRICAL MEMBER HAVING AN INTERNAL CYLINDRICAL THREADED CAVITY, SAID MEMBER BEING RECEIVED WITHIN AN APERTURE PROVIDED IN SAID BASE MEMBER HAVING A BOTTOM WALL, SAID APERTURE BEING OVERSIZED AND PROVIDING CLEARANCE FOR EXPANSION OF SAID MEMBER; MEANS ON SAID BASE MEMBER AND CYLINDRICAL MEMBER FOR INHIBITING RELATIVE ROTATION BETWEEN SAID MEMBERS, SAID MEANS COMPRISING A NOTCHED PORTION PROVIDING EQUAL BUT OPPOSITELY SLOPED WALLS AT ONE END OF SAID CYLINDRICAL MEMBER AND A COMPLEMENTARY SHAPED PROJECTION PROVIDED BY SAID BASE MEMBER FOR INTERFITTING AND MATING ENGAGEMENT WITH SAID NOTCHED PORTION OF SAID CYLINDRICAL MEMBER AND PROVIDING CLEARANCE BETWEEN THE REMAINDER OF THE NOTCHED END OF THE CYLINDRICAL MEMBER AND THE BOTTOM WALL WHEREBY ONLY COMPRESSION FORCES ARE SET UP IN THE FRANGIBLE BASE MEMBER WHEN PRESSURE IS APPLIED TO THE BASE MEMBER BY THE NOTCHED PORTION OF THE CYLINDRICAL MEMBER.

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