US2876375A - Filament shield - Google Patents

Description

Mam}! 1959 c. R. MARSH .FILAMENT SHIELD Filed Au 26, 1953 I INVENTOR. C R. M51819,

I ww 2,876,375 FILAMENT SHIELD Charles R. Marsh, Boalsburgh, r5, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application August 26, 1953 Serial No. 376,556 6 Claims. c1. 31'3-+117) I This invention relates to shields for incandescent filaments and, more particularly, to shields for automobile headlight incandescent filaments.

Heretofore, shields for automobile headlight incandescent filaments have been provided between the filament and the lamp lens to prevent direct filament light from shining into the eyes of oncoming drivers, thus creating a condition of glare. In addition, automobile headlight lenses are so designed as to receive substantially parallel light, as reflected by a paraboloidal reflector, and to refract this substantially parallel light into a carefully di rected and distributed beam. To provide such a light source, an incandescent filament is normally centered at approximately the paraboloidal focus and substantially all light from the incandescent filament which strikes the paraboloidal reflector is reflected toward the lamp lens in a substantially parallel beam. I

Since the filament shield is somewhat removed from the filament, and thus the paraboloidal focus, light which is reflected from the filament shield toward the paraboloidal reflector will appear as though it is emanating from a source which is located olf the paraboloidal focus. This light will thus be re-reflected from the paraboloidal reflector in a scattered manner. This scattered light on striking the lamp lens will often be refracted toward areas which are not intended to receive such'stray light, thus causing undesirable illumination from the automobile headlight.

To eliminate this undesirable illumination emanating from the filament shield, it has been customary to provide the filament shield with a surface and coating which will minimize any reflection while simultaneously diffusing such light as is reflected, so that the unwanted light reflected from the filament shield will be minimized. Shields of the prior art have been made non-reflecting and difiusing by various methods, some of which are sandblasting a nickel-iron shield, blue-oxide coating a nickeliron shield, or acid-etching a nickel-iron shield, which methods are well known in the art. While these methods are relatively satisfactory, the reflectivity from the generally regular surface of the filament shield is still too high, the coefficient of reflection being in the order of 0.1, which, because of the proximity of the shield to the filament, results in an undue amount of light reflected by the filament shield toward the paraboloidal reflector.

It is the general object of the invention to overcome the foregoing and other difliculties of and objections to prior art practices by the provision of a filament'shield which minimizes filament reflection toward the reflector.

Still another object of the invention is the provision of a filament shield which may utilize the present nonreflecting coatings, while having a reflectivity which is approximately one order of magnitude lower than the reflectivity for the present filament shields.

A further object of the invention is to provide a filament shield which is economical to manufacture.

The aforesaid objects of the invention and other obtes Pat 2,876,375 Patented Mar. 3, 1959 jects which will become apparent as the description proceeds, are achieved by providing a filament shield with a generally serrated or corrugated surface so that most of the incandescent filament: light will be reflected at least twice by the serrated or corrugatedportions of the filament shield before being finally reflected towardthe lamp paraboloidal reflector. For a better understanding of the invention, reference should be had to the accompanying drawings, in which:

Fig. l is a sectional plan view of an automobile head light incorporating my serrated filament shield;

Fig. 2 is an elevational view of the filament shield taken along the lines 22 of Fig. 1-, in the direction of the arrows; 1

Fig. 3 is a sectional view through Fig. 2, taken along the lines 3-3 in the direction of the arrows;

Fig. 4 is a fragmentary cross-sectional enlargement of one of the serrations of the filament shield, as shown in Fig. 3, showing howv the direct light from the filament is reflected from the individual serrated or corrugated portions of the filament shield;

Fig. 5 is a front .elevational view of an alternative embodiment of the filament shield, which view corresponds to Fig. 2;

Fig. 6 is a sectional view of the alternative embodiment of the filament shield shown in Fig. 5, taken along the lines VIVI in the direction of the arrows;

Fig. 7 is a further alternative embodiment of the filament shield shown in Figs. .2 and ,3, wherein the filament shield has a generally flat configuration.

With specific reference to the form of the invention illustrated in the drawings, the numeral 10 indicates gen erally an automobile lamp having a hollow paraboloidal reflector. 12, a lens 14 having the general configuration of a hollow spherical sector, sealed to the reflector at its periphery to' form a lamp envelope, and lead-in conductors 16 sealed through the back of the reflector 12 and supporting a tungsten or other refractory metal filament 18 substantially at the focus of the paraboloidal reflector. The lens and reflector may be fabricated of pressed glass, as is common in the art, and the inner surface of the reflector is silvered or aluminized to provide the reflecting surface, as, is also common in the art. The lead-in conductors 16 may be fabricatedof copper or other conducting material and terminateat one end at the filament l8 and at the other end at lead-in conductor ferrules 20 which are sealed through the back of the reflector 12 to facilitate making electrical contact between the lead-in conductor and a source of electrical energy (not shown).

These ferrules 20 may be fabricated of nickel-iron, if desired, and are well known in the art; Other'elect'rical contact adapters 22 may be provided, if desired, to facilitate connecting the source ofelectrical potential to the lamp lead-in conductor ferrules 20.

Supported between the filament 18 and the lamp lens M is a filament shield 24 which may have the general configuration of a hollow spherical sector, so oriented with respect to the lens 14 that the concave side of. the shield is presented to the filament and the convex sideof the shield is presented to the lens. The filament shield 24 is of such size and is located at suchdistance from the filament 18 that a straight line fromlany portion of the filament to any portion of the periphery of the reflecting surface of reflector 12 will be intersected by a portion of the shield 24. The shield may be retained in position by a shield positioning strap 26 which may be secured between one lead-in conductor 16 and the filament shield 24 (as shown) or which may be secured directly to the reflector 12. H g

As illustrated in Figs. 2 and 3, the filament shield is preferably comprised of a series of concentric valleys and ridges which constitute serrations 28. Fig. 4 represents one of the serrations in an enlarged sectional view, and, as illustrated, each serration 28 is substantially identical in configuration and essentially forms an isosceles triangle having corners' A, C and B, the corner C being formed by the two sides of the serration, and the corners A and B being formed by the jointure of the sides ofthe 'serration under consideration with the sides of the adjacent serrations. V V

The angle ACB formed at the vertex of the triangle is important, which angle is, of course, always less than 180". As is well known from geometrical principles, the smaller the angle ACB, the greater the possibility that any ray oflight striking either side AC or BC will be re-refiected to the other 7 serration side before being finally reflected toward theparaboloidal reflector 14. The size of the angle ACB' which is required to produce multiple reflections, will, of course, .depend upon the distance from the filament to the shield, the radius of curvature of the spherical sector shield 24 formed by the series of concentric serrations, and the size of the light source. Obviously, if the center of the sphere of which the spherical sector forming the shield 24 is a part, coincides with the paraboloidal focus, the angle ACB may be made considerably larger and yet provide multiple reflections than if the paraboloidal focus is between the hollow spherical sector shield 24 and the center of the sphere of which the spherical sector shield is a part. In the latter case, light would emanate from the filament 18 toward some of the serrations of shield 24 in a direction other than perpendicular to the base AB or triangle ACB. In this latter case, as is obvious from geometrical considerations, the smaller the angle ACB, the greater the chances of a multiple reflection within the individual serrations. For the same reasons, the size of the incandescent filament 18, which is an indication of the amount the filament extremes are offset from the paraboloidal focus and from the axis of the shield 24, governs the minimum angle ACB which can be utilized and still achieve multiple reflections between, the serrated sides.

I have eniperically found that for a representative automobile headlamp, ifthe angle ACB is no greater than 90, a sufiicient amount. of light from the filament which strikes the shield 24 will be reflected more than once among the individual serrations 28 of shield 24 to give satisfactory results. However, this angle does not represent a limitation, and certainly may be increased for some applications, if desired.

By way of example and not by Way of any limitation, one specific embodiment of a lamp embodying my invention isas follows: Glass lens diameter (lamp envelope evacuated) 5.750". Aluminized glass paraboloidal reflector inner -diameter 5.000. Reflector focal length 0,375", Filament length (filament horizontal and centered at the paraboloidal focus) 0.200". Distance from center of filament to center of shieldvertex of center serration 0.515". Shield diameter 0.960". Radius of sphere of which hollow spherical sector shield H is a part 1.95 Distance from center of sphere of which hollow spherical sector shield is a part to the paraboloidal focus 0.66 Angle ACB of individual ser- 0 rations Number of serrations in shield (these may be formed by preshsing, or; other well-known 7 ea n1 ues ghield flniitterial t 51 f Nl-Fe alloy on-re ecting rea en 0 Acid-etch (20 7 H2804) for 1 shield inner surface a M u Then Oxi dine with .NaOH, NaVOz, NaNOs (80-10-10) for 20 min. at 290 F.

It is obvious that angle ACB may be varied, if desired, between concentric serrations, utilizing a smaller angle toward the periphery of the shield. It is also obvious that manufacturing costs dictate the use of as large an angle ACB as practical, since the shield material is less stressed and manufacturing costs are reduced where the angle ACB approaches its maximum permissible value {for the individual lamp. I have found that where the angle ACB is less than 15, the manufacturing costs are somewhat increased without appreciable increased benefits, although for some specialized applications, it might be desirable to use angles smaller than 15.

Operation Even though it is believed the operation of the shield will be apparent from the foregoing description, a brief review thereof is made for the purpose of summary and simplification. As the direct light from the filament strikes one of the sides AC or BC of the serrations, it will usually be reflectedv toward another of the sides of the serration. Assuming the coefficient of reflection of the shield to be 10- the intensity of the beam which is finally reflected toward the paraboloidal reflector will be 10- times the intensity of the beam originally striking one of the serrated sides for the first time. x," of course, represents the number of times the beam is reflected from the serrated sides. Thus, in two reflections, assuming the coeficient of reflection to be l0- the beam will be decreased in intensity 100 times, in three reflections 1000 times, etc.

It will be recognized that the objects of the invention have been achieved by the provision of a light filament shield which minimizes any filament reflection from its surface and which cuts down reflected light from the filament shield at least one order of magnitude from the reflection encountered in shields of the prior art. In addition, my filament shield may be economically fabricated, by conventional die-forming techniques, as are well known.'

As a possible alternative embodiment of my invention, the concentric serrations may be replaced by a series of small individual cones, as represented in Figs. 5 and 6, which correspond in view to Figs. 2 and 3. In such an embodiment, the governing design principles are the same as those utilized in designing the preferred embodiment of my invention.

As another possible embodiment of my invention there is shown, in Fig. 7, a filament shield in sectional view corresponding to Fig. 3. Such a design has the slight cost advantage in that it may be fabricated in a substantially flat configuration, when viewed from the side. In such a design, if desired, the angle ACB of the individual serrations which are located toward the periphery of the shield maybe smaller than the corresponding angle of the serrations which are located 7 toward the center of the shield, or the angle can be maintained the same but oriented toward the filament.

For purposes of economy of manufacture, the angle ACB may be rounded off to facilitate die-forming. However, in such an embodiment, the overall light reflected from the shield toward the paraboloidal reflector will be increased, as compared to the light reflected from the preferred embodiment of my invention.

While in accordance with the patent statutes one best known embodiment of the invention has been illustrated and described in detail, it is to be particularly understood that the invention is not limited thereto or thereby.

I claim:

1. An automobile headlight comprising a hollow paraboloidal reflector having a periphery and a lens sealed tojsaid reflector at its periphery to form an envelope, lead-in conductors supporting a filament within an envelope, a filament shield supported between said filament .and said lens so that a straight line between any portion of said filament and said lens is intersected by said filament shield, said filament shield being comprised of a series of joined concentric serrations to form a composite serrated body, each of said serrations having two sides which meet to form a plurality of vertices, each of said plurality of vertices describing an angle smaller than a straight angle, and said angle being less than 90 and more than 15, and the filament shield serrations facing said filament being opaque and highly light absorbing.

2. An automobile headlight as specified in claim 1, wherein said filament shield has the substantial general configuration of a spherical sector having a convex portion and a concave portion, and said shield being so oriented within said envelope that said convex portion of said shield will be nearest said lamp lens.

3. An automobile headlight comprising a hollow parabolical reflector having a periphery and a lens sealed to said reflector at its periphery to form an envelope, lead-in conductors supporting a filament Within said envelope, a one-piece opaque and light absorbing filament shield supported between said filament and said lens so that a straight line between any portion of said filament and said lens is intersected by said filament shield, said filament shield being comprised of a series of adjacent hollow conical surfaces having vertices, and said shield being so oriented that said vertices will point substantially away from said filament.

4. An automobile headlight comprising a hollow paraboloidal reflector having a periphery and a lens sealed to said reflector at its periphery to form an envelope, lead-in conductors supporting a filament within said envelope, an oqapue and light absorbing filament shield supported between said filament and said lens so that a straight line between any portion of said filament and said lens is intersected by said filament shield, said filament shield being comprised of a series of adjacent hollow conical surfaces having vertices, said shield being so oriented that said vertices will point substantially away from said filament, and each of said vertices describing an angle which is less than and more than 15.

5. An automobile headlight as specified in claim 4, wherein said filament shield has the substantial general configuration of a spherical sector having a convex portion and a concave portion, and said shield being so oriented within said envelope that saidconvex portion of said shield Will be nearest to said lamp lens.

6. An automobile headlight comprising a hollow paraboloidal reflector having a periphery and a lens sealed to said reflector at its periphery to form an envelope, lead-in conductors sealed through said envelope, a filament electrically connecting to and supported by said lead-in conductors within said envelope, a onepiece filament shield supported between filament and said lens and so positioned that a straight line between any portion of said filament and said lens is intersected by said filament shield, said filament shield having such configuration that the filament shield cross section effected by a plane through said filament and perpendicular to and through the center of said filament shield will appear as a series of connecting lines including angles therebetween of less than 90 and more than 15, and the portions of said filament shield facing said filament being opaque and highly light absorbing.

References Cited in the file of this patent UNITED STATES PATENTS 1,323,963 Caughrean Dec. 2, 1919 1,621,360 Falge Mar. 15, 1927 1,743,793 Muros Jan. 14, 1930 1,751,070 Boots Mar. 18, 1930 2,112,411 Schafiner Mar. 29, 1938 2,199,014 Stitt Apr. 30, 1940 2,305,818 Tura Dec. 22, 1942 2,744,209 Ferguson May 1, 1956

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