US3243633A

US3243633A - Filament connection for electric lamp or similar device

Info

Publication number: US3243633A
Application number: US341859A
Authority: US
Inventors: Stanley C Ackerman
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1964-02-03
Filing date: 1964-02-03
Publication date: 1966-03-29
Anticipated expiration: 1983-03-29
Also published as: GB1022889A; ES308857A1

Description

March 29, 1966, s. c. ACKERMAN FILAMENT CONNECTION FOR ELECTRIC LAMP 0R SIMILAR DEVICE Filed Feb. 5, 1964 United States Patent York Filed Feb. 3, 1964, Ser. No. 341,859 6 Claims. (Cl. 313271) This invention relates in general to electric incandescent lamps and similar devices and more particularly to an improved joint or connection between the filament and leading-in conductors of such devices.

In the service for which certain types of incandescent lamps are intended, the lamp is normally subjected to constant or prolonged periods of severe high-frequency vibration. This is particularly true, for instance, in the case of lamps employed for aircraft service such as aircraft landing lamps. Where the filaments of such lamps are, for reasons of improved lamp efficiency, unsupported except for their points of connection to the customarily larger diameter and stiffer lead-in conductors or wires of the lamp, the resulting flexure of the filament produced by the vibration of the lamp subjects the filament connections or joints to severe stresses such as would ordinarily cause the early failure thereof if the filament strength at and adjacent the connection is insufficient. Adequate filament or mount strength against such vibration and resulting stresses therefore becomes an important factor in the construction of such type lamps.

For the purpose of strengthening the filament joints in such high-vibration service lamps, and also increasing the current-carrying capacity of the filament wire at and near the usual welded connection thereof to the lead-in conductors or wires, it has been customary to provide a wire slip-over coil on each of the end legs of the filament. However, despite the presence of such a slip-over coil, there still is a sudden change in the flexibility of the filament at the points of connection thereof to the leadin conductors or wires. As a result, when the filament is subjected to vibration, the stresses produced therein are localized at, and are greatest at the said points of abrupt flexibility change in the filament, with the result that the filamentsoon becomes broken at one or the other of such points. Accordingly, filament connections such as described are of relatively low strength and inadequate resistance to Withstand stresses such as are customarily imposed on the connections by the vibration normally encountered in aircraft service.

It is an object of my invention, therefore to provide an electric incandescent lamp or similar device with a filament joint of greatly improved strength and resistance to vibrational stresses.

Another object of my invention is to provide an electric incandescent lamp or similar device with a filament joint of a construction such as to produce a gradual decrease in the flexibility of the filament from its main body portion to its points of fixed attachment to the lead-in conductors.

Still another object of my invention is to provide an electric incandescent lamp or similar device with a fila- ,ment having either a straight wire or a coiled end leg joined to a rigid lead-in conductor by a connection producing a gradually decreasing flexibility gradient 'in the filament from its main body portion outwardly thereof to a point of rigid attachment of the filament end leg to the lead-in conductor, and in addition producing a dampening action on the vibration resonance frequency of the filament.

Briefly stated, in accordance with one aspect of the invention, the straight Wire or coiled end legs of the filament which are rigidly attached to the lead-in conductors of the lamp are provided with Wire slip-over coils of progressively and substantially uniformly increasing stiffness outwardly toward the respective lead-in conductor. To such end, the wire slip-over coils are, in accordance with a preferred form of the invention, formed of progressively and uniformly increasing coil pitch in a direction outwardly toward the respective lead-in conductor.

Further objects and advantages of the invention will appear from the following detailed description of species thereof and from the accompanying drawing.

In the drawing, FIG. 1 isan elevation, in section, of an electric incandescent lamp having a filament joint comprising my invention.

FIG. 2 is a perspective view, on an enlarged scale, of the mount structure of the lamp shown in FIG. 1.

FIG. 3 is a transverse section, on a greatly enlarged scale, of the mount structure and showing one of the filament joints thereof in section, and

FIG. 4 is an elevation, partly in section and on a greatly enlarged scale, of a modified form of filament joint comprising my invention.

Referring to the drawing, the invention is there illustrated as embodied in an electric incandescent lamp of the self-contained reflector type such as described and claimed in US. Patent 2,148,314, Wright, issued February 21, 1939, and assigned to the assignee of the present invention. The lamp comprises a 'bulb or envelope 1 consisting of a preformed pressed glass reflector section 2 sealed around its periphery to a preformed pressed glass cover section 3. The interior surface of the reflector section 2 is of suitable light-concentrating shape such as paraboloidal for instance, and it is covered with a metallic coating 4, preferably of aluminum, to constitute a reflecting surface. Mounted on the reflector section 2, exteriorly thereof and at the apexofsaid section, is a base structure 5. The base structure 5 may be of the type described and claimed in US. Patent 2,272,512, Cotman et al., dated February 10, 1942, and comprising a pair of metal lugs 6 suitably secured, as by soldering, to metallic cups or thimbles 7 having feathered edges sunk and embedded in the glass of the reflector section 2 around openings 8 therein, the cups or thimbles 7 thus hermetically closing the said openings 8. The envelope 1 is exhausted and filled with a suitable inert gas through an exhaust tube 9 attached to the reflector section 2 at its apex. After the gas filling is introduced into the lamp envelope, the exhaust tube 9 is tipped off, as indicated at 10, to hermetically seal the envelope.

Mounted within the envelope 1 and supported therein from the metal thimbles 7 is a mount structure 11 comprising an electric energy translation element or filament 12 disposed between and connected to a pair of rigid leadin wires or conductors 13 of suitable material, such as nickel or iron. The lead-in conductors 13 are rigidly secured at their outer ends to the metal thimbles 7, as by being soldered or brazed therewithin, and they extend straight through the respective openings 8 in the reflector section into the interior of, and in more or less parallel relation to one another and preferably in a plane parallel to and including the axis of the reflector section 2. The lead-in conductors 13 are held in rigid spaced relation by an insulating bridge or cross bar member comprising a glass rod 14 extending between and secured to the lead-in conductors 13 by short fastening wires 15 which may be spot-welded to the lead-in conductors.

The filament 12 is constituted of tungsten or other suitable refractory metal wire and, in the particular case illustrated, comprises a linear coiled-coil or main body portion 16 disposed coaxially of the reflector axis in a position in definite optical relation'to the" focus of the reflecting surface 4, preferably symmetrically about the Patented Mar. 29, 1966 reflector focus. Each end of the filament 12 is provided with an end section or leg portion extending laterally across and rigidly connected to the respective lead-in conductor 13. In the form of the invention shown in FIGS. 1 to 3, the filament end legs are comprised of straight or uncoiled w'iresections17 while in the modified form of the invention shown in FIG. 4 they are comprised of singly coiled wire sections 18 constituting continuations of the primary coiling of the main body portion 15 of the filament 12. A slip-over wire coil 19 of a suitable refractory metal such as tungsten or molybdenum or an alloy thereof is slipped over the respective filament

end leg portions

17 or 18. The said slip-over coil 19 is made just large enough in diameter to fit more or less snugly around the filament

end leg portions

17 or 18. The

filament end legs

17 or 18, together with the associated slipover coils 19, thus form composite end conductor portions 20 for the filament, the filament end legs serving as core members for such composite conductors.

The composite end conductor portions 20 of the filament, comprised of the

end leg sections

17 or 18 together with their associated slip-over coils 19, are suitably connected to the respective lead-in conductors 13, as by being welded directly thereto, for example. Preferably, however, they are connected to the conductors 13 in the manner disclosed and claimed in my US. Patent 2,987,643, issued June 6, 1961, and assigned to the assignee of the present invention. To this end, each end conductor portion 20 is tightly clamped against the respective lead-in conductor 13 by a thin metal strap or plate member 21 which is securely fastened to the lead-in conductor as by welding it thereto at points on either side of the filament end conductor portions 20, as indicated at 22. The tight clamping of the coil-enclosed

filament end leg

17 or 18 to the lead-in conductor 13 thus forms a rigid mechanical clamp connection therebetween which constitutes the first point of completely rigid anchorage of the filament end leg outwardly therealong from the main body portion 16 of the filament 12. The metal strap or plate members 21 may be made of any suitable material such as nickel or iron for example, and they are fastened to the lead-in conductors 13 in a manner such as to extend outwardly away from the said conductors in opposite directions therefrom and substantially in the plane of the said conductors 13 whereby the plate members 21 intercept a minimum of the radiations from the filament so as not to produce undesirable shadows or dark spots in the light beam projected by the lamp. Each filament end conductor portion 20, instead of being welded directly to the lead-in conductor 13, is extended outwardly beyond the lead-in conductor and is welded to the metal strap or plate member 21 at a point along its length spaced some distance, for example, one-eighth inch or so, outwardly thereof from its mechanical clamp connection to the leadin conductor as indicated at 23. The strap or plate members 21 are each formed with a cross corrugation 24 extending thereacross and preferably tapered down in size (i.e., both in width and depth) in a direction outwardly from the respective lead-in conductor 13 to provide a correspondingly tapered groove or channel 25 for accommodating the filament end conductor portions 20 therein. This tapering of the channel or groove 25 in the metal strap 21 serves to raise or expose the filament end conductor portions 20 above the plane of the welding faces of the metal strap, thereby assuring contacting of the welding electrode with the filament end conductor portions 20 during the welding thereof to the metal strap.

By clamping the filament end conductor portions 20 to the respective lead-in conductors 13 by means of the metal clamping plates 21 and welding the filament end conductor portions to the metal plates 21 at points out- Ward of the lead-in conductors 13 instead of directly thereto, the points of maximum flexure stress that develop in the filament on vibration thereof then occur at the mechanical pressure or clamp connection of the filament end conductor portions 20 to the lead-in conductors and are thus kept away from the recrystallized, structurally weakened section of the filament which is produced at the weld 23 thereof to the metal strap 21. As a result, a filament joint is provided of greatly increased vibration strength over that which is obtained where the filament is welded directly to the lead-in conductor so that the points of maximum fiexure stress in the filament are located at the welded and recrystallized section of the filament.

In accordance with the invention, the fiexure stresses which are developed in the filament

end leg sections

17 or 18 at their clamped connections to the lead-in conductors 13 by the metal clamping plates 21 are materially minimized and distributed instead more or less uniformly throughout substantially the entire effective length of such filament end leg sections by forming the slip-over coils 19 of progressively and substantially uniformly increasing stiffness, or decreasing lateral flexibility, outwardly thereof toward the respective lead-in conductor 13. To such end, the wire slip-over coils 19 are, in accordance with a preferred form of the invention, wound with a varying coil pitch which progressively and uniformly increases, in a direction outwardly toward the respective conductors 13, from a closely-coiled inner end section 26 adjacent the coiled-coil body portion 16 of the filament 12 to a widely open-coiled outer end section 27 at the clamped connection of the filament end conductor portions 20 to the lead-in conductors 13. In this connection, it should be noted that the lateral flexibility of a wire coil decreases, and its resistance to lateral deformation (i.e., its stiffness) increases in direct proportion to its coil pitch. Consequently, the use of a slip-over coil 19 having a coil pitch which gradually increases in a direction outwardly thereof toward the respective lead-in conductor 13 provides a more or less gradually decreasing flexibility gradient in the filament between the points where the filament

end leg sections

17 or 18 begin at the filament proper 16 and the points where they are clamped by plates 21 to the lead-in conductors 13. Thus, there is no abrupt change in the flexibility gradient of the filament 12 toward its respective points of rigid attachment or clamping to the lead-in conductors 13, and vibrational stresses imparted to the filament are therefore effectively distributed more or less uniformly throughout the entire effective length of the

filament end legs

17 or 18 instead of being localized at one point along their length (i.e., at their points of rigid or clamped connection to the lead-in conductors 13) where they would then cause early rupture of the filament wire. The slip-over Wire coils 19 also act to dampen filament vibration so as to reduce the amplitude thereof and thereby still further decrease the filament ruptureproducing effect of such vibrations. The sum result, therefore, of the use of the particular graduated coil pitch wire slip-over coil construction according to the invention is a filament joint of greatly increased strength and resistance to vibrational stresses, as contrasted to that of prior type filament connections employing slip-over coils of uniform coil pitch throughout.

In the modified form of filament joint shown in FIG. 4 wherein the filament end legs are comprised of singlycoiled wire sections 18 formed as continuations of the primary coiling of the filament proper 16, the slip-over coils 19 are in such case wound or coiled in a reverse direction to the coiled filament end legs 18. This assures that the individual coil turns of the slip-over coils 19 will cross over the individual wire turns of the coiled filament end legs 18 instead of entering and becoming locked therebetween such as would otherwise occur if the two

coils

18 and 19 were wound in the same instead of opposite directions.

Although preferred embodiments of my invention have been disclosed, it will be understood that the invention is not to be limited to the specific construction and arrangement of parts shown, but they may be widely modified within the spirit and scope of my invention as defined by the appended claims.

What I claim as new and desired to secure by Letters Patent of the United States is:

1. In an electric lamp, the combination of a lead-in conductor, and a filament having a linearly extending end leg with a wire slip-over coil snugly fitted thereover, said end leg and slip-over coil extending across said lead-in conductor and being rigidly connected thereto, said slipover coil progressively and uniformly decreasing in lateral flexibility in a direction outwardly toward said conductor.

2. In an electric lamp, the combination of a lead-in conductor, and a filament having a linearly extending end leg with a wire slip-over coil snugly fitted thereover, said end leg and slip-over coil extending across said lead-in conductor and being rigidly connected thereto, said slipover coil progressively and uniformly increasing in coil pitch in a direction outwardly toward said conductor.

3. An electric lamp as specified in claim 2 wherein the said lead-in conductor and slip-over coil are mechanically clamped to the said lead-in conductor.

4. An electric lamp as specified in claim 2 wherein the said lead-in conductor and slip-over coil are welded to the saidlead-in conductor.

5. An electric lamp as specified in claim 2 wherein the said linearly extending filament end leg portion is in the form of a substantially straight wire section.

6. An electric lamp as specified in claim 2 wherein the said linearly extending filament end leg portion is in the form of a wire coil wound in a reverse direction to that of the said slip-over coil.

References Cited by the Examiner UNITED STATES PATENTS 2,273,762 2/ 1942 Reerink et a1 313-3461 2,848,642. 8/1958 Wisco et al 313344 X 2,987,643 6/1961 Ackerman 313-269 X JAMES D. KALLAM, Acting Primary Examiner.

JOHN W. HUCKERT, Examiner.

A. I. JAMES, Assistant Examiner.

Claims

1. IN AN ELECTRIC LAMP, THE COMBINATION OF A LEAD-IN CONDUCTOR, AND A FILAMENT HAVING A LINEARLY EXTENDING END LEG WITH A WIRE SLIP-OVER COIL SNUGLY FITTED THEREOVER, SAID END LEG AND SLIP-OVER COIL EXTENDING ACROSS SAID LEAD-IN