US2729724A - Contact structure for rotary switches - Google Patents

Description

Jan. 3, 1956 H. E. SCHLEICHER 2,729,724

CONTACT STRUCTURE FOR ROTARY SWITCHES Filed Dec. 17, 1951 ,[TCA/ldOTf- Harold 1,501: [sicker United States Patent 2,729,724 CONTACT STRUCTURE FOR ROTARY SWITCHES Harold E. Schleicher, West Hartford, Conn., assignor to The Arrow-Hart & Hegeman Electric Company, Hartford, Conn., a corporation of Connecticut Application December 17, 1951, Serial No. 261,961

11 Claims. (Cl. 200-166) This invention relates to contact structures for rotary magnetic switches of the type which is required to be operated by a balanced operating mechanism and in which the contact structure itself is also statically and dynamically balanced.

This invention is an improvement upon the contact structure of my prior Patent 2,453,161, issued November 9, 1948, which is a division of Patent 2,540,294, issued February 6, 1951.

Modern battle conditions require electric control apparatus to withstand tremendously high impact shocks. Prior to my Patent 2,453,161, efforts to provide switch structures which would pass the high standard and rigid shock-test requirements had resulted in cumbersome, involved and unsatisfactory structures. The new approach to the problem which resulted in the invention of my prior patents has been carried forward and improved upon in the present invention. Test standards have now been raised so high that the permissible circuit interruption has been cut down to two one-hun dredths (.02) of a second opening or, in other words, the contacts must not separate for more than approximately one-half an alternating current cycle in 60 cycle systems.

Therefore, an object of my invention is to produce a contact structure which meets the elevated standard of test requirements for contacts used in rotary electromagnet switches whose operating mechanism and contact structure are both statically and dynamically balanced.

Another object of the invention is to provide a contact structure of the aforementioned type which could be made without materially increasing the size or weight of the structure and which could be interchangeable with the contact structure illustrated in my prior patent.

Another object is to provide a bridging contact structure for rotary switches which, while satisfying the foregoing objectives will maintain a firm and constant pressure against the fixed contact and concomitantly, despite possible manufacturing inaccuracies, will enable the bridging contact to adjust itself to the fixed contacts for firm engagement therewith.

Other objects and advantages of the invention will appear as it is described in connection with the accompanying drawing.

In the drawing:

Fig. 1 is a plan view of a section of a rotary switch embodying the invention;

Fig. 2 is a transverse section view along line 2-2 of Fig. 1;

Fig. 3 is an enlarged detail view partly broken away showing in plan the fixed contact and terminal;

Fig. 4 is an exploded perspective view of the movable contact assembly.

A suitable electromagnetic operating mechanism for operating the contact structure of the present invention is disclosed in my prior'Patent 2,450,294 and therefore is not described nor shown herein. As in said-patent, the

armature of a rotary electromagnet rotates a square section shaft on which is slidably mounted the movable bridging contact structure designated generally by the numeral 30.

The present invention is shown incorporated in a section which may be stacked with one or more like sections as in said prior patents. As in my prior patent, each section may be made up of a spacing disc (not shown herein) and a mounting disc 102. On the latter are mounted the fixed current-carrying parts. The discs may be of molded insulation suitably recessed and apertured for the fixed and movable contact structures and the main shaft. When the spacing disc and the mounting disc are placed face-to-face with their recesses adjacent, the movable current carrying parts are enclosed and are insulated from the parts within other similar sections.

The fixed contact structures are identical and comprise stamped sheet metal pieces 10 of irregular shape as indicated in Fig. I mounted upon themounting disc 102 by means of screw bolts. As illustrated, the pieces 10 have a flat central portion lying in a radial recess adjacent the periphery of the disc. A portion 10a of the pieces 10 extend radially inward into a circular recess molded in the face of the disc within which recess the movable contact structure may oscillate. The pieces 10 also have outwardly extending terminal portions 10b which may be supplied with any suitable securing means for wiring.

The inner end 10a of the fixed contact supporting piece has a reduced extension 12 passing through registering apertures in leaf springs 13 and 14 consisting of two parallel'overlapping strips of thin resilient sheet metal located in planes perpendicular to the plane of the fixed contact supporting piece. The extension 12 also passes through a flat sheet metal washer 11 and is peened over on top thereof to hold the leaf springs 13 and 14 permanently against the shoulder 15 at the junction of the extension 12 and the main body of the fixed contact supporting piece. The leaf 13 is shorter than the leaf 14 and lies against that surface of the spring 14 which faces the periphery of the mounting disc 102, for reasons which will presently be explained.

On the free end of the leaf spring 14 is mounted a sliding contact element 16 comprising a block of good electric contact metal, such as copper or silver. The contact element 16 has a substantially flat contact surface 17 inclined toward the free end of the spring 14 to facilitate sliding engagement and disengagement with a similar bridging contact surface as hereinafter mentioned. Between the contact element 16 and the leaf spring 14 is the base portion of a heavy sheet metal arcing member 18 having a horn 19 extending beyond the edges of the contact element 16 in direction of contact separation. The horn 19 extends tangentially outward toward the periphery of the mounting disc 102 from the central point of contact of the contact surface 17 with the contact surface of a similar rotary contact 16' presently to be described. The tangent is to the arc of movement of the rotary contact at said point of contact. On the opposite side of the leaf spring 14 from the arcing member is a flat metal terminal member 20, a pair of whose opposite edges 22 are folded over and pressed on the ends of a loop of stranded connector wire 23 which is also connected at its center to the fixed contact support 10 by insertion in a slot and by deforming the support to press the sides of the slot firmly against the wire. Thus the wire is firmly and frictionally held to both the fixed contact support 10 and to the terminal piece 20.

The base portion of the arcing member 18 has a central stem 24 extending through registering apertures in area-r24 the ends. of. the .leaf springs-..14, and. in the, terminal piece 20. The end of the stem is peened over on the terminal thus holding said parts together. The contact element 16 is welded or otherwise rigidly affixed on the base portion of the arcing member 18.

Contact elements like that just described, and means for mounting the same are provided on the ends of a bridging contact member 30. Similar reference numerals indicate the similar parts with a prime being added to the parts supported on the bridging contact member. The bridging contact member is stamped from heavy sheet metal with a large circular central portion 33 from which extend in opposite directions and in diametrically opposite positions arms 31 and 32. On the ends of these arms the contact elements 16 are supported in the same manner as the fixed contact elements 16. The arcing horns 19' of the movable contact assembly are flared arcuately inward was properly to engage with the horn 19 of the fixed contact assembly.

Discs 34 of molded insulating material are riveted on opposite faces of the central portion 33 and seat in circular bearing recesses in the disc 102 to guide the rotary movement of the bridging contact member.

From the foregoing, it may be observed that as the switch shaft 40 rotates it causes the bridging contact member 36 to turn from open circuit position to bring the contact elements of the bridging contact member inengagement with the contact elements of the fixed contact members, or vice-versa. Closing movement is accomplished by the arcing horns i9, 19' first coming into engagement with one another and then moving onto and sliding over the inclined contact surfaces 17, 17' of the contact elements. As the closing movement continues the inclined contact surfaces themselves come into engagement and slide upon one another until these elements are fully in register. This rubbing action tends to keep the contact surfaces clean and polished. During this closing action, the contact supporting springs 14 of both the fixed and bridging contact elements are bent and put under stress. The bending is also against the short leaves 13 which resist and are also put under stress which, with the stress of springs 14, cause a firm contact engagement between the fixed and the moving contact elements.

Since the fixed and moving contact elements are of exactly the same construction, their masses are equal. Hence when a shock occurs and one element tends to move; its inertia and momentum are equaled by the other element. Assuming that the shock would tend to cause a fixed contact element 16 to move radially inward, the force of the shock'would act in the same direction as the bias of leafsprings 13 and 14. 7 As the movement of the contact radially inward proceedsto the normal or unstressed condition of the leaf springs 13, 14 the stress of spring 13 gradually diminishes and disappears because of its independence of the moving masses tied tospring 14. At the same time the stress of the springs 13, 14- (and also of spring 14 as it moves past its normal unstressed position) increases taking up the energy of the shock. When the energy of the shock has been absorbed by the springs 13', 14' and 14, those springs tend to move reversely toward normal closed position. In so doing, springs 14' and 14 and contact elements 16' and 16 maymove past normal position. On this return to normal position, spring 13' diminishes to-zeroand the inertia of spring 13 and its inherent force then opposes the tendency to move beyond said normal closed position due to expenditure of the considerable energy stored up. This to and fro movement damps out the shock force while the contact elements are constantly held firmly in engagement.

lt 'should be noted that" upon a shock moving the contacts '16 and 16" (radiallyoutward, for example), con-.

tact 16 throughoutthe whole of that outward move acts againstthebias of its supporting spring 14 and the dampbias of .its supporting spring 14'v and damping spring 13 after passing through neutral or unstressed position, is restrained only by the reversed bias of its supporting spring 14'. The latter bias being less than the combined force of springs 14 and 13 acting on contact 16, and the mass of the contacts 16 and 16 being identical, the contact 16' can readily follow any movement of the contact 16. The same is true of movement in the opposite direction. I

It is important that the damping springs 13, 13' have negligible mass and beonly on the side of the contactsupporting spring 14 or 14 opposite the contact 16 or 16' and be of independent suspension from and not tied to masses 16 and 16' or, in other words, on the side of the contact-supporting spring to oppose movement of the one contact away from the other. Tests have shown that if damping springs are placed on both sides of the contactexplanation and is believed correct.

ing spring 13; but contact-16'," assisted'at first bythe supporting spring 14 or 14"that the operation of the invention is not entirely satisfactory and will often fail to meet the rigid' test requirements. This is due to the added restraint of different vibration periods and moments of inertias of the extra inside spring upon the movement of one contact toward the other when a shock occurs. The result is somewhat like striking one of two abutting balls with a mallet while restraining the struck ball. The second ball receives the energy through the struck ball which remains stationary while the second ball moves.

Because springs 13, 13 are not tied to the contact masses and have negligible mass, they are acted upon by the contact masses through the- springs 14 and 14 in a single direction only, from static equilibrium position when any force acts to pass that position. In other words, the springs 13 are added forces opposing movement of the contacts 16 radially outward only; and springs 13 are added forces opposing movement of the contacts 16 radially inward only. They act thus to dampen motion and to tend to stabilize the contacts in closed position.

Thus when the switch is subjected to shock, the shock force may be transmitted to both contacts 16 and 16. In the construction as illustrated, the force is damped out in the manner explained above while the contacts move together. But if damping springs are used on both sides of each contact-supporting spring 14, one contact is apparently restrained sufliciently for all or most of the energy to be transmitted to the other, which keeps on moving until the energy it possesses is absorbed by the damping spring. In the course of this motion, the contact elements can separate; and on reverse movement, a similar action occurs in the opposite direction.

The foregoing theory is offered as the logical physical Actual tests have proved that the-damping spring should be placed only on the side of the contact-supporting spring opposite the opposing contact; p

The structure hereinabove described permits of keeping the springs short to avoid the necessity of increasing the stiffness or increasing the number of leaves in the spring. Too great stiffness increases the rubbing friction of the contacts so that the magnet would have difficulty in closing the switch; and also a stronger spring for rotating the switch shaft in opening direction would be necessary to overcome the increased rubbing friction.

Many modifications within the scope of the invention will occur to those skilled in the art as they study and comprehend the principle and disclosure of my invention. Therefore I do not limit the invention to the precise form illustrated. I

What I claim is:

l. Contact structure for rotary shock-proof electric switches, comprising a balanced rotary conductive bridging member having oppositely extending arms, a resilient leaf-spring,contact-support on the end of each arm lying in planes parallelto'the axis of rotation of said bridging member, a contact: element on one end of each support facing-ina'direction for engagement with a fixed contact,

a damping spring lying against that face of said leaf-spring support which is opposite the contact element, in combination with fixed terminal members, a leaf-spring contactsupport mounted on each terminal member, a contact element mounted on one end of said terminal-mounted contact-support slidably engageable with one of said bridging contact elements, a damping spring lying against that face of said terminal-mounted support which is opposite its contact element.

2. Contact structure as claimed in claim 1 wherein said contact elements have their engaging surfaces inclined to increase the pressure as they move into fully engaged position and to maintain contact during the first few degrees of angular rotation of said rotary bridging member.

3. Contact structure as claimed in claim 2 wherein the damping springs are shorter than the contact-supporting leaf-springs.

4, Contact structure as claimed in claim 1 wherein the damping springs are shorter than the contact-supporting leaf-springs.

5. Contact structure as claimed in claim 1 wherein the contact elements and contact-supports of the fixed and movable contacts are of equal mass and balance.

6. Contact structure as claimed in claim 1 having arc horns with oppositely flared ends connected with the fixed and movable contact elements, said horns engaging and disengaging before and after the contact elements.

7. In a switch, a pair of contact carriers which are relatively movable to cause sliding engagement of contact elements, a cantilever spring member mounted on each carrier, a contact element mounted on one side of each said spring member, said elements slidably engaging and disengaging upon relative movement of said carriers, a cantilever leaf-spring damping member lying against that face of each contact-carrying spring which is opposite the face on which its contact element is mounted, said damping members being shorter than said contact-carrying spring members and mounted at the same points on the carriers as their respective contact-carrying spring members, said contact elements being wedge shaped and having their engaging surfaces inclined to increase the pressure as they move into finally engaged position and to maintain con tact from the inception of contact engagement.

8. A construction as claimed in claim 1 having means anchoring said damping springs at one point to said bridg- 6 ing members and said terminal members respectively and leaving said damping springs with a free end not tied to said leaf spring contact supports and contact elements but resisting movements of said contact elements and their supports from static equilibrium position only.

9. A construction as claimed in claim 7 having an arcing horn connected with each contact element and flaring from the thinnest portion of its associated contact away from the opposite contact, the horns engaging and disengaging respectively, before and after said contact elements.

10. Contact structure for rotary shock-proof electric switches, comprising a balanced rotary conductive bridging member having oppositely extending arms, a resilient leaf-spring contact-support on the end of each arm lying in planes parallel to the axis of rotation of said bridging member, a contact element on one end of each support facing in a direction for engagement with a fixed contact, a damping spring lying against that face of said leaf-spring support which is opposite the contact element, in combination with fixed terminal members, a contact element mounted on one end of said terminal members slidably engageable laterally with said bridging contact elements as said bridging contact rotates, said contact elements having their engaging surfaces inclined to increase pressure as they move into fully engaged position and to maintain contact during the first few degrees of angular rotation of said bridging member.

11. Contact structure as claimed in claim 10 having arc horns with oppositely flared ends connected with the fixed and movable contact elements and extending in opposite directions, said horns engaging and disengaging before and after said contact elements.

References Cited in thefile of this patent UNITED STATES PATENTS 680,981 Johnson Aug. 20, 1901 881,306 Cutter Mar. 10, 1908 1,293,309 Benjamin Feb. 4, 1919 1,601,205 Fisher et al Sept. 28, 1926 1,804,748 Derrick May 12, 1931 1,879,303 Kempton Sept. 27, 1932 2,199,357 Dilhnan et al Apr. 30, 1940 2,453,161 Schleicher Nov. 9, 1948

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