US 2866025 A
Description (OCR text may contain errors)
Dec. 23, 1958 D. E. MORAN NON-BOUNCING SWITCHING APPARATUS Filed July 19, 1956 INVENTOR. Dav 5 H024 H l5 ATTORNEY United States Patent NON-BOUNCING SWITCHING APPARATUS Don E. Moran, Morrison, Ill., assignor to General Electric Company, a corporation of New York Application July 19, 1956, Serial No. 598,960
9 Claims. (Cl. 200--87) One problem involved in the design of such switching devices is the tendency of the contacts to weld during closure in circuits designed to pass'substantial currents. This tendency toward contact welding is aggravated when the contacts continue to bounce apart for a short interval of time after their initial closure. Reduction in contact bounce thus permits the switching device to be rated for higher load currents.
Contact welding has been also found likely to occur wherever the contacting surfaces are irregular or have become pitted. It is therefore desirable that the contact engagement be such as to provide a slight wiping action thereby to maintain clean and conforming mating surfaces. The problems of providing non-bouncing and slightly wiping contacts are particularly diflicult of solution in small electromagnetic switching devices which use contact assemblies of low mass actuated by armatures moving with relatively high velocity and energy.
Accordingly, an object of the invention is to provide a contact assembly for an electric switching device which reduces contact bounce upon closure and which provides a slight wiping or scrubbing action of the contacts after closure.
Another object is to provide an electromagnetic switching device capable of energizing circuits passing considerable electric current beyond that normally controlled by a relay of the size involved.
In general, in accord with the invention, a flexible conductive strip member has its opposite ends fastened to a suitable supporting member so that the central portion of the flexible strip member is biased in outwardly bowed spaced relation to the support. This bowed central portion of the strip carries one of the contacts and the other contact is brought into engagement with this first contact with suflicient force to move the first contact against the considerable outward biasing force of the bowed flexible strip member. The second contact is preferably also carried on a flexible strip member extending alongside the bowed strip member and the angle of contact engagement is such that a slight lateral wipe or scrubbing occurs during a further slight movement of the contacts after their initial closure. The supporting member for the bowed flexible strip member-is preferably a rigid but deformable metal strip with one end free in the form of a cantilever beam.
The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may be easily understood by referring to the following description taken in connection with the accompanying drawing in which:
Figure l is a perspective view of an electromagnetic relay embodying the invention,
Figures 2, 3, and 4 are side, top and bottom views respectively of the relay of Figure l, and
Figure 5 is a perspective view of the cantilever support and flexible conductive metal strip before the strip is bowed and mounted on the cantilever support.
Referring to the drawing, one form of the invention is shown embodied in an electromagnetic relay 5 having an insulated base 6 upon which is mounted an electromagnet assembly 7 and a contact assembly 8. Electromagnet assembly 7 comprises a generally L-shaped magnetic yoke member or frame 9 having a mounting foot 10 for riveting to base 6. One portion 11 of frame 9 supports an electromagnet 12 comprising a coil 13 wound on an insulating bobbin 14 surrounding an axial cylindrical iron core 15. Another portion of frame 9 is divided into two legs 16 and 17 which support and form a pivot bearing for an armature assembly 18 of the relay. Armature assembly 18 comprises a flat metal armature plate 19 having an end portion 20 overlying magnetic core 15 and a bifurcated base portion 21 pivoted on and against the edges 22 of frame legs 16 and 17. Armature plate 19 also has an integral portion 23 on the opposite side of its pivot extending from one of the furcations of its base portion 21 substantially at right angles thereto. This integral portion 23 has a projecting arm 24 with notch 25 therein for seating one end of a helical tension spring 26; the other end of spring 26 being attached to an arm 27 extending from frame 9. Spring 26 serves to bias the end portion 20 of armature assembly 18 away from core 15 but exerts a progressively decreasing bias as the armature end portion 20 approaches and engages core 15 when electromagnet 12 is energized. The amount of gap between armature end portion 20 and core 15 is limited by a backstop member 28 welded at one end to integral portion 23 of armature plate 19 and curving at its opposite free end 29 toward the outer surface of frame leg 17. The construction of electromagnet assembly 7 and the arrangement of spring 26 is described in detail in my copending application Serial No. 495,553, filed March 21, 1955, and forms a portion of the subject matter claimed therein.
In the illustrated embodiment of this invention, contact assembly 8 is shown as a double pole, double-throw type having a pair of normally closed contacts 31 and 32 and a pair of normally open contacts 33, 34. Contacts 32 and 33 are carried back-to-back on opposite sides of a flexible conductive strip member such as leaf spring 30 which in turn is supported on an arm 35 extending from frame 9. Leaf spring 30 has a return bent portion 36 at its upper end which is arranged to be engaged and moved by the integral extension portion 23 of armature plate 19 when the free end portion 20 of plate 19 is attracted toward core 15 of electromagnet 12. Leaf spring 30 thus functions as the operating arm for the contact assembly 8. Stationary contact 31 is mounted upon a substantially rigid supporting strip 37 which in turn is riveted to insulating base 6. The free end of strip 37 is bent slightly away from a plane per= pendicular t0 the base such that contact 31 normally bears against contact 32 and bends operating leaf spring 30 likewise away from its unstressed plane perpendicular to the base 6. Normally-closed contacts 31 and 32 are rigid supporting member or strip 41, best seen in Figure 5. Supporting strip member 41 has a base portion 42 riveted to insulating base 6 and an upstanding supporting arm portion 43 forming a cantilever beam type sup.- port. The lower portion 44 of supporting arm 43 extends perpendicuarly to base portion 42 while the upper portion thereof is bent at a slight angle away from the plane of lower portion 44-. Flexible strip member 38 upon which contact 34 is mountedis initially a perfectly flat member, as shown in Figure 5, but during assembly 1ts lower portion 39 is welded to lower portion 44 of sup.- porting strip member 41 and its upper portion 40 is then flexed until it contacts a projection 45 on supporting arm 43 to which it is welded. Flexible strip member 38 is thus fastened securely at both ends to the substantially rigid supporting strip member 41 at points spaced apart a distance less than the length of member 38 and its central portion assumes a slightly bowed configuration in spaced relation to this supporting arm. It will be appreciated that since both ends of flexible strip member 38 are fastened down, the bowed central portion thereof is not free to move or vibrate freely at low frequency and that movement of the contact 34 against the force of this bowed spring 38 is accomplished chiefly by virtue of a flexure of the regions of the resilient strip member 38 immediately above and below contact 34, the .strip member 38 being initially stressed in compression. It will also be appreciated that the cantilever beam type construction of supporting arm 43 permits a slight give or cushioning effect to the substantially rigid mounting of the bowed strip member 38.
Electrical connection to the various operating components of the relay are made through terminals 47, 48, 49, 50 and 51 riveted to the underside of the insulating base 6. The rivet 47a for terminal 47 also fastens the foot 10 of frame 9 down to the insulating base 6 and makes electrical connection between the terminal 47 and the frame 9. Since frame 9 is connected to the operating leaf spring 30 through supporting arm 35 and to the armature as sembly 18 through pivots 22 all of these members are at the same electrical potential as terminal 47. Terminal 48 is connected through its rivet 48a to the substantially rigid supporting strip 37 which carries stationary contact 31 while terminal 49 is connected through its rivet 49a to supporting strip member 41 Which in turn carries the bowed flexible strip member 33 and contact 34. Terminals 50 and 51 respectively are connected to the leacl-in wires for coil 13.
In operation, a suitable voltage applied to terminals 50 and 51 energizes electromagnet 12 causing armature assembly 18 to pivot into contact with core 15. The pivotal movement of armature assembly 18 causes the integral extension portion 23 thereof to strike the return bent portion 36 of operating leaf spring 36 and move the operating spring laterally thereby opening normallyclosed contacts 31, 32 and closing normally-open contacts 33, 34. Since armature end portion 20 is attracted toward magnet core at high velocity and strikes core 15 with high energy, the operating leaf spring 30 is likewise propelled by armature portion 23 at high velocity to bring movable contact 33 into engagement with contact 34 under considerable force. However, the sturdy shock resistant mounting of contact 34 upon the central portion of bowed flexible strip member 38 absorbs and dissipates the energy of this impact and has been found greatly to minimize contact bounce after impact. The reduction in contact bounce is quite evident when compared with constructions where only one end of a leaf spring carrying a stationary contact is fastened down or where the stationary contact is directly mounted on a substantially rigid supporting member. For example, if the upper end of flexible member 38 is dis connected from the rigid supporting strip 41, contact 34 bounces at a much higher amplitude and for a longer period of time under the impact of moving contact 33 than with the bowed fastened-down construction of the invention. Alternatively, if contact 34 is directlymounted (it on a substantially rigid supporting member such as arm 41, the movable contact 33 upon operating leaf spring 30 rebounds at much higher amplitude and for a longer period of time than with the construction of the invention. By virture of the contact assembly of the invention, both contacts after impact vibrate at high frequency and in close synchronism such that there is relatively little bounce between them and all vibrations quickly dampen out. It has also been found that with the construction shown there is a slight lateral wiping or scrubbing between the contacts 33 and 34 after impact which tends to reduce bounce further because of the friction generated as well as to insure clean mating surfaces for good contact. In general, it has been found desirable to calibrate the contact assembly to provide considerable contact tip pressure between contacts 33 and 34 upon closure of the relay; a contact tip pressure above 100 grams being preferable. Such calibration is easily accomplished by deforming the substantially rigid cantilever beam type supporting arm 41 to vary the amount of bend between the upper and lower portions 43 and 44 thereof.
As an illustration of the improvement in performance and life resulting from the invention, it has been found that if a relay, such as described above but having contact 34 mounted directly on supporting arm 41 or on flexible strip member 38 with the upper'end 40 of strip member 38 not fastened down, is used to close or make an electrical circuit initially passing amperes, connected between terminals 47 and 49, contact welding oc curs before less than ten thousand operations and often after only a few hundred operations. However with the bowed, fastened-down contact supporting construction of the invention, the relay is capable of closing or making this same circuit carrying this same initial current for over a hundred thousand operations without welding and often up to four hundred thousand operations. This greater reliability has permitted the same size relay to be rated for much higher amperage than was formerly possible.
It will be understood that although I have described my invention in connection with a contact assembly where the bowed flexible strip mounting is applied to a stationary contact, alternatively the movable contact may be so mounted and the stationary contact rigidly supported. Similarly, although I have shown the invention in connection with normally open contacts that are closed during the energization of the relay, the invention is likewise applicable to normally open contacts that are closed by the deenergization of the relay if the drop-out of the relay occurs at high velocity.
Although I have described a particular embodiment of the invention many modifications may be made, and I intend, therefore, by the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.
What I claim as new and desire to secure by Letters Patent of the United States is:
1. In an electric switching device, a substantially rigid support, a first flexible conductive strip having its opposite ends fastened to said support so that its central portion is biased in outwardly bowed spaced relation to said support, a first contact on said central portion, a second flexible conductive strip extending alongside said first strip, a second contact on said second strip and means for actuating said second flexible conductive strip to bring said second contact into engagement with said first contact at high velocity, said engagement initially stressing said first strip in compression.
2. In an electric switching device, a substantially rigid supporting arm, a first flexible conductive strip member having its opposite ends fastened to said arm so that its central portion is flexed in outwardly bowed spaced relation to said arm, a first contact on said central portion, a second flexible conductive strip member carrying a second contact, and electromagnetic means for bringing said contacts rapidly into engagement with each other and for maintaining said contact engagement under pressure, said engagement initially stressing said first strip in compression.
3. In an electric switching device, a base member, a substantially rigid supporting arm having one end fastened to said base member and the other end free, a flexible conductive strip having its opposite ends fastened to said arm so that its central portion is biased in outwardly bowed spaced relation to said arm, a first contact on said central portion, an operating member carrying a second contact, and electromagnetic means for actuating said operating member to bring said second contact rapidly into engagement with said first contact and for.
maintaining said contact engagement under pressure.
4. In an electric switching device, a base member, a substantially rigid flat supporting arm having one end fastened to said base member and the other end free, said arm having its free end portion extending in a plane at a slight angle to a plane perpendicular to said base member, a flexible conductive strip member having one end fastened to the free end of said arm and the other end fastened to the body of said arm so that the strip member is flexed in outwardly bowed spaced relation to said arm, a first contact on said bowed strip, a second flexible conductive strip member extending alongside said first strip member and carrying a second contact, and means for flexing said second strip member toward said first strip member to bring said second contact rapidly into engagement with said first contact.
5. An electromagnetic relay comprising an electromag net, an armature arranged for rapid movement under the magnetic influence of said electromagnet, a supporting member, a flexible strip member having its ends fastened to said supporting member so that its central portion is flexed in outwardly bowed spaced relation to said supporting member, a first contact on said central portion, a second contact, and means operated by the movement of said armature for bringing said contacts into engagement with each other, said engagement initially stressing said flexible strip member in compression.
6. An electromagnetic relay comprising an electromagnet, an armature arranged for rapid movement toward and into engagement with said electromagnet upon energization of said electromagnet, a substantially rigid supporting member, a flexible conductive strip member having its ends fastened to said supporting member at points spaced apart less than the length of said strip member so that the central portion of the strip member is flexed in outwardly bowed spaced relation to said supporting member, a first contact on said central portion, a second contact, and means operated by the movement of said armature toward and into engagement with said electromagnet for bringing said second contact rapidly into engagement with said first contact and for maintaining said contact engagement under pressure, said engagement initially stressing said flexible conductive strip member in compression.
7. An electromagnetic relay comprising an electromagnet, an armature arranged for rapid movement between open and closed stable positions under the magnetic influence of said electromagnet, a substantially rigid supporting member, a first flexible-conductive strip member having its ends fastened to spaced points on said supporting member so that the central portion of the strip member is flexed in outwardly bowed slightly spaced relation to said supporting member, a second flexible conductive strip member extending alongside said first strip ember and carrying a second contact, said second strip member being flexed by saidarmature during the movement of said armature to bring said second contact into engagement with said first contact and to maintain said contact engagement under pressure when said armature is in one of its stable positions, said contact engagement initially stressing said first strip member in compression.
8. An electromagnetic relay comprising a base member, a substantially rigid supporting arm having one end secured to said base member and one end free, a first flexible conductive strip member having one end fastened to the free end of said arm and the other end fastened to the body of said arm so that the central portion of said strip member is flexed in outwardly bowed slightly spaced relation to said arm, a first contact on said central portion, a second flexible-conductive strip member alongside said first strip member and having one end secured to said base member and one end free, a second contact on said second strip member, an electromagnet, and an armature member for said electromagnet operable upon said second strip member to engage said contacts when said electromagnet is energized.
9. The electromagnetic relay of claim 8 wherein the free end of the supporting arm extends at a slight angle to a plane perpendicular to said base member and the armature member operates to maintain said contact engagement under pressure above grams.
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