CA1280151C - Compact incandescent coiled coil filament - Google Patents

Abstract

COMPACT COILED COIL INCANDESCENT FILAMENT
ABSTRACT
This invention provides an improved compact fine wire incandescent lamp filament and method for making such having a primary mandrel ratio in the range of about 1.40 to about 4.00 and a secondary mandrel ratio which is greater than or equal to the primary mandrel ratio. The improved filament design exhibits an increase in compactness and retains or increases structural rigidity while exhibiting minimal sag when the filament is incorporated into an incandescent lamp of the tungsten halogen type variety. The compact coiling method is particularly useful in designing compact filaments for high voltage applications where it is desirable to eliminate the use of rectifying means to lower the effective voltage across the filament.

Description

3015~

COMPACT INCANDESCE~T COILED COIL FILAME~T

CROSS REFERE~CE TO COPENDING APPLICATION

In Canadian Serial No. 534,317-8, filed April 9, 1987, and entitled "AN IMPROVED REFLECTOR-TYPE
LAMP HAVING REDUCED FOCUS LOSS" (Pierce Johnson) filed concurrently herewith, there is described an improved reflector-type lamp having a reduction in focus loss and an improvement in reflector collection efficiency. This Application is assigned to the same assignee as the instant invention.

TECHNICAL FI~LD

This invention relates to multiple coiled fine wire incandescent lamp filaments and lamps utilizing such filament design.

BACKGROIJND OF THE I~VE~lTION

In order to achieve improved efficiency in incandescent lamp filaments, filament design has progressed toward more compact coil configurations, skarting with filament coiling as taught by Langmuir in U.S. Patent No. 1,180,159. Coiled coil filaments as taught by Benbow in U.S. Patent No. 1,247,068 also exhibit improved efficiency. Efforts to achieve compact coiled coil designs for the finer more !~
`r'~,l '; ~

"' '~

86-1-OL6 - 2 - P~TENT

r~istiv~ wir~s ~aving a dia~eter of 4.5 ~ils or le~) ~ald b~n l~ d by the nQed to lmpart rigidiSy to the ila~nt by usinq th~ smallest possible ~andrel~ for th~ pri~ary an~ secondary coiling.

The use of coiling in filaments shortens tne fila~ent and increases its dia~eter. A wire of dia~eter D is coiled about a ~andrel having a diameter M. The resulting coil is said to be compressed and is obviously shorter than the original wire and nas a diameter of Dl ~ 2d ~ M. In order to impart r~gidity to the coil. it has been co~mon coil practice to keep the diameter of the coil s~all. ~his is accomplighed by ~eeping the ~andrel ratio ~M/d) as small as po~ble. HoweYe~ a w~re o~ d~a~et~r d cannot w~thout spec~al ~roparat~ons be co~l~d ~bout a ~andrel ~a~ing a dla~ter M wh~ch ~ les8 than-d.

In U.S. patQnt No. 4,208,609 to Berlec, tbere i8 di~cloged a lo~-powQr ~ncandescent la~p having a reduction in fila~ent ~guir~ due to the ~act that She filament has higher pitch ratios, lower ~andrel ratios and is mounted under tension between the lead wires.
The teachings in the Berlec Patent apply specifically to la~pg of low power and having fila~ent dia~eters of 1 ~il or less. Triple coils have also been proposed tO
obtain even greater efficiency by ~eans of an even ~o~e co~pact coil. Hovever, triple coil~ as saught by Grave~ et al. in U.5. PaSent Nos. 4,316,116 and 4,499.401 have been unable to achieYe suf~icient l~OlSl r~gidity to support finer, more resistant filanent wir~ unless t~e ~andrel ratios in either or both its ~co~darr an~ tertiary coiling are le88 than 1. Such co~lg ar~ dit~lcult to wind and, as acknowledged by ~he ara~es Patent ~401, following the description ln t~e araves Patent ~116 has lead to triple coil filament~
haYing a flia8y structure when arranged vithin the incande~cent la~p vhich causes sagging and causes the filament to ultimately experience a burn out.
Incandescent lamps of the tungsten halogen variety generally have superior performance characteristics over traditional Edison-type incandescent lam~s because the former can be back-filled to vely high gas pressurQs. This higher fill pre~sure retard~ the evaporation rate of ~he operating ~ila~ent thus pr~lon~ing i~ t~ ~owevec, ~ro~id~n~ la~ wlt~
long li~ and co~ct t1la~entf ~ ~t~ll a ~a~or ~roblem with ~ung~ten halogen la~s, ~pecially with fine w~rq incande~c~n~ la~p~. One way o~ Qxtenaing the operating li~e of a fila~ent and the incande~cent lamp is to reduce the ~oltag~ acros~ ~he tilam~nt by ~lacing rectifying means, such as a diode, in ~eries vit~ the filament. The tilam~nt i8 operated at a subs~antially lower temperature and also at a lower eficiency in ter~s o f lumens per watt. As an example,-U.S. Patent No. 3,869,631 by Anderson et al. teaches that an incandescent lamp having a diode in series with the tungsten f ilament will provide im~roved luminous 30~5~
8fi-1-016 - 4 - PATENT

~f~ficacy without reducing lamp life p~ovided the t~la~ent weight i8 ~ncreased ap~roximately 50~ over that ord~nar~ly used with the particular lamp.

It is believed, therefore, that an incandescent la~p filament which achieves a high deqree of compactness for the finer more resistive wires while retaining or increasing structural rigidity in an incandescent lamp would constitute an advancement in the art. In addition, a filament design which would pro~ote ~maller capsule design for high pressure halogen lamp~ and would p ovide for a simpler and less expens~ve mounting arrangement~ for the filament would const~tute an even further advancement in the art.
SUMMA~ OY TH~ INY~N~I0~

~ t ~ an ob~c~ of th~s inv~ntion to provlde an incandeseent lamp t~la~nt whic~ achieve~ a greater degre~ of co~pactne~s while retaining or increasing seructural rigiaity in order to elimina~e fila~ent sag .

It is a further object of this invention to provide a filament designed for a tungsten halogen la~p which has eguivalent or improved operating characteristics, including prolonged lamp life, without the need for filament supports due to the strength and co~pactness of the new improved filament design.

~X80151 86-1-016 - 5 - PAT~NT

In accordance with one aspect of the present i~vention, there i8 provided an incandescent lamp co~prlsing a herm~ically sealed llght t~ansm~ss~Ye ~rl~lope, ~eans ~or structurally and electrically ~ounting a fila~ent within the envelope, and a r~fract~ry ~etal coiled coil fila~ent electrically coupled to and supported by means for ~ounting wherein the pri~ary windiAq dia~eter, Dl and the secondary winding dia~eter, D2, of the fila~ent are:
Dl ~ d(A~2) and D2 ~ Dl(B~2) wherein d equals the fila~ent vire diameter and 1.40 ~ A <4.00 and B ~ A

such ehat the ~lament e%hib1ts an increase in co~pactn~s and rota~n~ or éxhib~ an ~ncr~a~e in ~tructural c~gla~ty.

In accoraance w~th anot~r aspect of the preseA~
invention, th-re ~8 prov~ded a ~et~od of ~aking a coiled coil fila~ent that exhibits an increase in coupactness and retains or exbib~ts an ~ncr~a~e ~n structural rigia~ty for an incandoscent la~p rated at a particular wattage, voltage and efficacy, the ~ethod comprising the steps of providing a strand of fibrous filament vire having a particular length, L, and dia~eter, d,- for a particular wattage, voltage and 1~8015~
86-1-016 - 6 - . PATENT

efficacy~ The ~ethod further including the ~tep of v1nding the fila~ent wire around a pri~ary mandrel ~Ylnq a dia~eter f ~1 determined by:

Ml . A(a~, to produce a pri~ary coil, wherein 1.40 ~ A < 4.00.

The pri~ary coil iB then wound around a secondary ~andrel having a secondary ~andrel diameter M2 deter~ined by Mz = B(~1~2d), to ~roauce a coiled coil configuration, where B > A.

~RIeP D~CaIPTION OP TH~ D~AWlNGg PIGUR~ 1 ~llu~trate~ one ~bod~ment of an incandescent la~. ~articularly of t~ tung~t~n halogen variety, ~ado in accordance with the teachings of the pr~ent invention:

~IGURE.2 illu~trates a ~ilamént wire wh~ch was wound to for~ a coiléd fila~ent:

FIGUR~ 3 illu~trates a filament ~ire which was wound to form a coiled coil fila~ent:

~01~

~ GURE 4 illustrates a filament wire wound around a pr~acy aandr~l to form a pri~ary coil PIaUR~ 5 illustrates a primacy coil which i8 wound 5 around a secondary ~andrel to form the coiled coil filamen~: and ~ IGURE 6 illustrates the various parameters related to determining the outer dia~eter of a coiled coil fila~ent of the p{esent invention.

B~ST MOD~ POR CARRYING OUT THE INVEUTION

Por a be~ter understanding o~ the present invention tog~ther ffith other and furth~r o~3ec~ dvan~aq~ and capa~ t~e~ thereo~, r~erence i~ made ~o the ~olloving disclo~ure and ~p~ended clai~s in con~unction vith the above de~cr~bed drawing~.
~ eferring now to the drawings w~th greater particularity, PIGU~ 1 illu~rate~ an exa~ple of an incandescent lam~ 10, in this particular e~bodi~ent being of the tungsten halogen variety, made in accordance wit~ the teachings of the present invention. As used herein, a fine wire filament ifi defined to be a filament having a dia~eter of about 4.5 mils or less and low wattage i~ defined to be about 150 vatts or less. The present invention provide~ for a coiled coil filament for incande~cen~ lamps having ~'~801~;~
86-1-016 - ~ - PATENT

i~proved aesign flexibility which ig readily adaptable ~o a nua~er of di~ferent enYolope and la~p-type con~iguration~. It i8 r~ad~ly apparent that the co11ed coil filamQnt of the present invention oay be used in c~bina~ion with a variety of different lamp bases and envelope configurations including those of ~iniature and subminiaturQ lamps.

In one e~bodiment of the pre6ent invention, lamp 10 has a tubulac envelope 12 made of a suitable light transmissive material such as aluminosilicate glass. A
pair of lead in wires 14 and 16, portions of which serve as ~ounting means, are press sealed in envelope 12 at press seal 18. Lead in wires 14 and 16 can be for~od from molybdenum, wh~ch will tor~ a rsldtively strain ~ree her~tic ssal with glas~ onvelo~ 12. A
r~ractory ~tal ~uch as tungsten) coiled co~l fila~ent 20, with legs 21~ ~ade in accordance with the teaching~ o~ the present ~nvention, i~ di~po~ed within envelope 12 and i8 attached to th~ internal ends of lead in wires 14 and 16. In thi~ particu$ar o~bodiment, envolope 12 i8 ~ d wit~ a fill ga~
comprising an inert gas and a halogen or halide.
Suitable examples of such an inert gas include argon or krypton or xenon and nitrogen. The ~alogen oc halide additive, ~hich is in thé gaseous state under the heat of lamp operation or may be incorporated as part of the gaseous compound, functions to reduce the coloration o~
the lamp envelope.

lX~30~
8fi-1-016 - 9 - PATENT

~GUR~S 2 and 3 illustrate enlarged views of tllngsten filam*nt 20 and it8 coiled and coiled coiled ~aq~E~ respectivQly. Each ~age has a pitch or ~l~rcent pitch, which i8 ~gual to S, the center ~o c~nter spacang of the turns, divided by d, the diameter o~ the ~ire or coil, multiplied by 100. Specifically, PIGUR~ 2 illu~trates the primary pitch of filament 20A
having a center to center spacing of Sl, wire diameter dl and outer diameter of Dl. In the present invention, the primary pitch P1 i8 equal to Sl/dl and the ~econdary pitch P2 i8 equal to S2/d2 (Note: d2 ~ Dl~ have values that do not exceed about 1.70 ~or 170%). In ~IGUR~ 3, S2 i8 the center to center spacing of the coiled coil filament, dz tNote: d2 ~ Dl) i8 the primary coil diameter and BL i8 the body length o~ the coiled co~l ~or seconaary) f~la~ent. I~ t~e pre~srrQd ~bodlm~nt, ~he ~econaary pitch o~ the ~alament i8 ~h the range o~
about 1~40 ~o about 1.60.
I ha~e di~covered, surprisingly, a ~ethod of ma~ing a coiled coil filament that e%hibits an increase in coapactnes~ and retain~ or exhibits an incrQase in structural rigidity for an incandescQnt lamp rated at a particular wattage, voltage and efficacy. ~ith reference to FIGURES 4-6, the ~ethod comprises the ~tep~ of providing a strand of fibrous filament wire lg having a particular length L and diameter d f~r a particular ~attage, voltage and e~ficacy and w~nding filament wire 19 around a primary ~andrel 30 having a 1~80151 dia~et~r f ~1 determined by: ~1 s A(d), to ~roduc~ a jr~aary coil 20A as ~llustrated in FlGURe 4, wh~r~in th~ Yalu~s oP A are exprQssed by the ~ollow~ng:

1.40 ~ A ~ 4.00.

Referring to FIGURE 5, tbe method further includes the step of ~inding primary coil 20A around a secondary ~andrel 40 having a secondary mandrel diameter f ~2 determined by: ~2 = Bt~l + 2d), to produce a coiled coil configuration, where B ~ A. As illustrated in FIGURES 4 and 5, respectively, the pr~ary wind~ng diameter is egual to Dl and the ~econdary winding diameter i8 egual to D2. T~e ~ethod further includes the ~tep o~ removing sub~tant~ally all of the cor~ o~ cs~led co~l ~lla~ent 20 ~xcept ~or re~o~ing t~e core ~n leg~ 21 of flla~ent 20. The cor- in leg~ 21 i~ pr~ferably le~t intact in order to pro~erve the structural integrity of fila~ent 20 ~hen t~e fila~ent i~ mount~d within ~he enYelope and crim~ed or attached by the legs to the ~ounting means.

~ ith referencQ to rIGU~ 6, PIGURE 6 illustratQ~
outer diameter D2 f the ila~en~ winding illustrated in FrGu~E 5, wherein the primary mandrel diameter ~1 is greater than the diameter of filament wire ~9 and the ~econdary mandrel diameter M2 i8 greater Shan the diameter of primary coil 20A. PIGU~E 6 ~hould ~erve to illustrate that both the pr~ary mandrel ratio, A, and secondary mandrel ratio, B, are greater t~an 1 and that ~80~5~

the s~condary ~andrel ratio (i.e. B=M2/D2) i~
~r~ater than the pri~ary mandrel ratlo (i.e. A~Ml~d), ~here~n:
1.40 < A ~ 4.00 and B ~ A.
To ~llustrate the improvement in coil or filament compactness through the use o larger mandrel ratios, particularly where the secondary mandrel ratio i~
greater than the primary mandrel ratio, tvo la~ps having a visible difference in value and wattage and voltage will be used: a 105 watt lamp operated at 245 volts and a 35 watt lamp operated at 84 volts. Each exa~ple will illustrate first a filament which i8 wound using low ~andrel ratios, which was thought to be the pre~erréd method o developing a filament which ex~b~t~ a h~gh d~gree Or structural r~g~d~ty but ~nstead ~he r~g~dlty ~ onl~ betw~n ~u~orted portions of the tila~ent~ When sub~ected to shock, the long ~ilaments tend to vibrate excessively. This i~ due in part to their length and to the fact that these fila~eQts are heated less unifor~ly due to the closer or s~aller inner pitch that re~ult~ rom small ~andrel ratios. Another e%ample will then ~ollow o~ the improved method of winding the filament with the use of larger values of mandrel ratios in order to achieve a high degree of compactness, while retaining or increasing structural~rigidity, and ~ubstantially eliminating, in most cases, the need for additional filament supports in an incandescent lamp.

~280~

105 WATTS/245 VOL~S

~'rARTINa WIaE~a~e~er (L/d) 22,379 SAMPLE WINDIUG IMPROVED WINDING
PRIMARY MANDR~L RATIO ~A) 1.40 2.00 S~CONDARY MANDR~L RATIO (B~ 1.40 3.00 BL/D2 65:1 37:1 35 WATT$/84VOLTS
STARTING WI~ ~ r ~L/d) . 8342 ~AMPL~ WI~DING IMæ~OY~D WINDING
A 1.40 2.00 B 1.40 3.00 BL/D2 24:1 14:1 where: ~L , ~L~dl~ L~d~
1~ 3U ~A~Z ) ~ ) ~FJ' BL , Body Length D2 - Outer D~ameter 1~8015~

Referring to the 105 watt~245 volt lamp, it i8 ~ot0d, fir~ o all, that such a lamp will utilize an ~xtr~ely long wire ot th~n diame~e~, as exhib~ted by ~he high value obta~ned from the ratio of length to wire diameter (Ltd~, therefore, optimum winding of such a wire will be extremely important in such a lamp. In t~e sa~ple winding where the mandrel ratios are low, the resulting body length (BL) to outer diameter (D2) ratio is about 65:1; this results in a long flimsy fila~ent which vill ultimately require at least one or more additional filament supports to support such a filament within a s~all incandescent lamp envelope.
The improved winding, on the other hand, utilizes larger ~andrel ratios, particularly a secondary mandrel ratio that i~ larger than a pri~ary ~andrel ratio, ~hic~ re~ult~ i~ a body l~ng~h to ou~e~ dia~eter r~tlo of about 37:1. Illu~tratively, the ~m~roYed filament de~ign i~ ~uch ~ore compact and, dep~nding o~ the type ot ~ounting sche~e, ptobably would reguire no ext~a filament supports or at least l e88 supports than in the ~ample winding. Referring to the 35 watt~84 volt fila~ent example, similar results are ex~ibited in that in the improved vinding there is a reduction in ~he body length to outer diameter ratio which creates a more compact fila~ent design. In each of the above examples, compacting is achieved by greater mandrel ratios and the upper limit in the mandrel ratio values is determined by the body length (BL) of the ultimate filament design being greater than or egual to the outer diameter tD2) of the resulting filament.

~ '~80151 An incandescent lamp utilizing a filament that has a priaary winding diameter Dl and a secondary winding diameter D2 where Dl ~ d(A + 2) and D2 ~ Dl~B ~ 2) wherein d i8 egual to the filament wire dia~eter and 1.40 ~ A ~ 4.00 and B ~ A such that the filament exhibits an increase in compactness and retains or exhibits an increase in structural rigidity. The geometry of coiled coil filament 20 is limited by the expression BL > D2 wherein BL is egual to the body length of the filament. Such a limitation is utilized since having an outer diameter greater than the body length of the filament will create a filament which is although very compact will be dificult to mount properiy and rigidly within a small incandescent lamp such as a tungsten halogen capsule.

With respect to variations of the pcesent invention, the lamp in pIGuRe 1 may include further an outer envelope about envelope 12. The lamp of FIGURE 1 may also include rectifying means electrically coupled to one of the lead-in wires, in series with the filament, and coupled to a voltage source thereby reducing the voltage across the filament. The envelope of FIGURE 1 also may include an infrared reflective coating such that the infrared light emitted by filament 20 is reflected bac~ to the filament in order to increase its efficiency.

~'~8()~

~ ith respect to lamps operating at high voltage~, especially for overseas operation at 225 and 245 volt~, such lamps typica}ly require starting off with extremely long filament wires (as illu6trated earlier in the specification). Similarly, filaments de6igned to operate at line voltage such as 120 or 130 volts also require a long filament. The improved method for winding a filament results in a compact coil which is especially useful for these applications and can lead to enhanced operation at high voltages since typical winding technigues have lead to extremely long filaments requiring larger envelopes and more complex mounting arrangements. Furthermore, the aforementioned filament design can also lead to operation without voltage reducing or rectifying means ~e.g. a diode~
thereby el~minating the modulation o~ the lig~t and pover tluctuation~ that result from th~ use of such rectifying me?ns. Elimination of the rectifying means i8 particularly important in the 225 to 245 volt range Z0 since the small filament mass leads tO greater thermal fluctuations.

In the past, filament sag was reduced and compactness achieved by iowering the voltage requirement of the lamp so that a shorter, larger diameter filament wire could be used. The shorter, thic~er wire has allowed for an increase in t~e mandrel ratios in order to achieve compactness, however transformers were now necessary to lower the line voltage. The teachings of the present invention ~as ~ X801~1 provided the ability to design compact high vo}tage filaaents that lead to a simplification in fixture design and ultimately lower costs due to the e:limination of a transformer (or voltage reducing means) in the fixture. The more compact filament de~ign of the present invention w$11 lead to an increase in structural rigidity and allows for smaller capsule design for high pressure tungsten halogen lamp~
of various wattage and voltage values that lead to lower capsule energy and improved containment due to possible lamp failures during lamp arc out. This leads to lower material cost& for glass, fill gas, and outer jac~et parts. The filament design, and method for making such, of the present invention i8 applicable to lo~er wattage lamps utilizing a hardglass envelope and may be appl~ed to high wattage lamps ut~l~zlng high temperature materials for the envelope ~uch as quartz.
Incandescent lamp capsules resulting from the use of the ~ore compact filaments may also be utilized with a reflector to improve collection efficiency and reduce focu8 1088 in a reflector-type lamp.

~ hile there have been shown what are at present considered to be preferred embodiments of t~e invention. it will be apparent to those skilled in the art t~at various changes and modifications can be made without departing from the scope of the invention as defined by the appended Claims.

Claims (14)

1. An incandescent lamp comprising:
a hermetically sealed light transmissive envelope;
means for structurally and electrically mounting a filament within said envelope; and a refractory metal coiled coil filament electrically coupled to and supported by said means for mounting having a primary winding and a secondary winding wherein the primary winding diameter D1 and the secondary winding diameter D2 Of said filament are:
D1 = d(A+2) and D2 = D1 (B+2) wherein:
d = the filament wire diameter 1.40 < A < 4.00 B > A
such that said filament exhibits an increase in compactness and retains or exhibits an increase in structural rigidity.

2. The lamp according to claim 1 wherein the geometry of said coiled coil filament is limited by:
BL > D2 wherein:
BL = body length of the secondary filament

3. The lamp according to Claim 1 wherein said filament has a primary pitch ratio and a secondary pitch ratio not exceeding about 1.70.

4. The lamp according to Claim 3 wherein said secondary pitch of said filament is in the range of about 1.40 to about 1.60.

5. The lamp according to Claim 3 wherein said means for mounting said filament is comprised of at least two lead in wires.

6. The lamp according to Claim 1 wherein the wire diameter of said coiled coil filament is about 4.5 mils or less.

7. The lamp according to Claim 1 wherein said lamp is a tungsten halogen lamp having a halogen or halide as part of the fill gas.

8. The lamp according to Claim 7 wherein said means for mounting said filament includes a pair of lead-in wires press sealed in said envelope and extending therefrom.

9. The lamp according to Claim 8 wherein said lamp further includes rectifying means electrically coupled to one of said lead-in wires, in series with said filament. and coupled to a voltage source thereby reducing the voltage across said filament.

10. The lamp according to claim 7 wherein said envelope includes an infrared reflective coating such that infrared light is reflected back to said filament.

11. The lamp according to claim 1 wherein said envelope includes an infrared reflective coating such that infrared light is reflected back to said filament.

12. The lamp according to claim 1 wherein said filament has legs and is substantially coreless except for the legs of said filament.

13. A method of making a coiled coil filament that exhibits an increase in compactness and retains or exhibits an increase in structural rigidity for an incandescent lamp rated at a particular wattage, voltage and efficacy, said method comprising the steps of:
providing a strand of fibrous filament wire having a particular length L and diameter d for a particular wattage, voltage and efficacy;
winding said filament wire around a primary mandrel having a diameter Ml determined by M1 = A(d), to produce a primary coil, wherein 1.40 c A < 4.00; and winding said primary coil around a secondary mandrel having a secondary mandrel diameter M2 determined by M2 = B(M1 + 2d), to produce a coiled coil configuration, where B > A.

14. The method according to claim 13 wherein said filament has legs and wherein said method further includes the step of removing substantially all of the core of said coiled coil filament, except for the legs of said filament.