CA1198146A - Sealed beam lamp unit sealing surfaces - Google Patents

Abstract

SEALED BEAM LAMP UNIT SEALING SURFACES
ABSTRACT OF THE DISCLOSURE

An adhesively sealed beam lamp unit including a lens and reflector preferably having substantially rec-tangular peripheries and cooperating and opposing seal-ing surfaces located approximately about the lens and re-flector peripheries. Contact between the lens and re-flector sealing surfaces is limited to one or more por-tions along the sides thereof. Additionally reservoirs, located adjacent to the sealing surfaces restrict excess adhesive from spreading onto areas affecting lamp unit optical performance, outer dimensions, and integrity.

Description

SE~ED BEAM LAMP ~NI~ SEALING SURFACES

BACKGROUND OF THE Il~V~N~l~luN
The present invention is related to lamps, partlcu-larly sealed beam lamp llnits, having two-piece envelopes comprising a reflector and lens assembled by adhesive means~ The reflector has an internal re~lective coating for reflecting and directing light, originating from a light source located within the envelope, towards a co-operating lens through which the light is transmitted.
Such sealed beam lamps have particular utility and are commonly used as headlights for motor vehicles.
Lamp units, such as headlights, recently have been introduced with lenses and reflectors having rectangular shaped peripheries, supplanting the more familiar cir-cular units. Production of assembled rectangular glassreflectors and lenses~ however, can present numerous problems. For example, stresses created in the glass lenses and reflectors during assembly by fusion sealing ~7~ ~
t~

can cause cracking thereo~. Such stresses can be signifi-cantly reduced by using an adhesive, rather than fusion, to seal the glass reflector and lens together. However, the ambient temperature, particularly at cold temperatures, can produce additional stresses due to the differences in the coefficients of expansion between glass and adhesive resulting in cracks, especially about the reflector cor-ners. Thus, the inherent problem remains of thermally in-duced stresses experienced when dissimilar materials, such as glass and adhesive, are joined.
Additionally, adhesively bonded lamps, which are gen-erally made fxom moldable materials, and especially from glass, are very susceptible to flaws. More particularly, in the manufacture of the lamp unit, moldable materials such as, but not limited to, glass typically have 1aws on the surfaces thereof. If the adhesive, which seals the reflector and lens together, is in contact with these flaws, the adhesive at cold temperatures will contract at a dif~
ferent rate than the glass and thereby place stress on one of the weaker portions of the glassware, namely the flaws.
Thus the inherent problem o thermally induced stresses ex-perienced when dissimilar materials are joined is aggra-vated by adhesive contact with flawed areas.
Furthermore, if any portion of the adhesive flows onto the light-transmitting area of ~he lens or light-reflecting area of the reflector, or beyond ~he lamp unit periphery during assembly of the unit, undesirable and unacceptable lamp unit optical performance and/or peripheral dimensions can result. Still further, due to the prior art sealing surfaces shapes~ more adhesive than desired is required.
Prior art lamp units also require a relatively high adhesive flexibility to reduce tearing or spalling of the adhesive due to the different coefficients of expansion for glass and adhesive. Such high adhesive flexibility 35 i5 achieved through the addition of flexibilizers in the I.D 8631 adhesive. Flexibilizers, however, undesira~ly increase the permeability of the adhesive resulting in moisture penetration leading to filament and lamp degradation.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provid~ a new and improved, sub-stantially rectangular shaped, adhesively sealed beam lamp unit by reducing the stresses generated about the sealing surfaces thereof.
Another object of the present invention is to provide a new and improved, substantially rectangular shaped, ad-hesively sealed beam lamp unit having means to ensure that excess adhesive does not undesirably affect lamp unit op tical performance or dimensions.
Another object of the present invention is to provide a new and improved, substantially rectangular shaped, ad-hesively sealed beam lamp unit having means which avoid adhesive contact of lamp unit surface flaws.
Another object of the present invention is to provide a new and improved, substantially rectangular shaped ad-hesively sealed beam lamp unit requiring less adhesive than prior art lamp units.
Another object of the present invention is to provide a new and improved, substantially rectangular shaped ad-~5 hesively sealed beam lamp unit which is more resistant tomoisture penetration than prior art lamp units.
These and other objects of the present invention are achieved by providing a lamp unit comprising a reflector and lens having preferably substantially rectangular periph eries and cooperating and opposing sealing surfaces, located appxoximately about the lens and reflectox peripheries, with adhesive disposed thereon and substantially contain~d therebetween. Contact between the lens and reflector sealing surEaces i5 limited to one or more poxtions along the sides thereof. Additionally, to restrict adhesive from flowing onto optically undesirable areas o~ t~le lens and/or reflector, to maintain acceptable lamp unit outer dimensions, and to avoid adhesive contact of lamp unit surface flaws, reservoirs, located adjacent to the sealing surfaces,are provided.

BRIEF DESCRIPTION OF THE DRAWING
Figure 1 illustrates a perspective view of a rectan-gular lamp unit in accordance with the present invention.
Figure 2 illustrates a fra~mentary, cross-sectional view of prior art lens and reflector sealing surfaces.
Figure 3 illustrates a fragmentary, cross-sectional view of lens and reflector sealing surfaces along the sides thereof in accordance with the present invention.
Figure 4 illustrates a fragmentary side view of the lamp unit in accordance with the present invention.
DETAILED DESCRIPTION
Figure 1 illustrates a rectangular lamp unit such as a headlamp unit 1 having a lens ~, cooperating reflector 3 and light source 4. Both lens 2 and reflector 3 can be formed by pressing "hard" glass in a mold followed by an annealing process. The lens 2 and/or reflector 3 also can be made from other materials such as, but not limited to, quartz and plastic. Lens 2 typically ha~ a slightly convex outer face and an optical prescription provided, for example, by light refracting prisms 5 formed on the inside surface thereof. Additionally, the concave inner surface 6 of the reflector 3 has a light-reflective coat-ing typically comprised of aluminum or silver. At the outer rear of the reflector 3 are conventional electrical prongs 7, providing an electrical path through which power is sup-plied to the unit 1.
As further illustrated in Fig. 1, lens 2 and re-flector 3 have substantially rectangular peripheries and sealing surfaces 8 and 9 located approximately about these ~3~

peripheries, respectively. Lens 2 has longer sides 10, shorter sides 11, and corners 12~ Likewise, reflector 3 has corresponding longer sides 13, shorter sides 14 and corners 15.
As previously discussed, fusion s~aling induced, for example, by a flame trained on the glass reflector and lens sealing surfaces 8 and 9, can create unacceptable stress patterns, in particular, with stresses tending to concentrate about the reflector corners 15, resulting in cracks especially thereat. The stresses created by flame sealing are substantially eliminated by interposing an ad-hesive 16 between the peripheral sealing surfaces 8 and 9 to seal the lens 2 to the reflector 3. For example, a light-curable, flexibilized epoxy, such as disclosed in 15 U.S. Patent No. 4,240,131, issued December 16, 1980 to Albrecht,provides a reliable seal between the glass lens 2 and glass reflector 3. Another example of an acceptable adhesive is "UNISET 929" which is a heat-curable adhesive sold by Amicon Corp. of Lexington, MassachusettsO
Although adhesive sealing substantially eliminates stresses created by fusion sealing, an additional type of stress due to thermal affects remains. ~or example, Figure

2 illustrates a cross-sectional view of a prior art, ad-hesively sealed beam lamp unit 20, comprising a glass lens sealing surface 21 and a glass reflector sealing surface 22 with adheQive 23 disposed thereon and therebetween. The sealins sur~aces 21 and 22 are located about the rectangu-lar peripheries of the glass lens and reflector respective-ly. During assembly of the lamp unit 20, adhesive 23 is placed between the sealing surfaces 21 and 22. When pres-sure is applied to the sealing sur~aces 21 and 22, during the manufacturing process of the lamp unit 20 9 a signifi-cant amount of adhesive 23 between the outermost sealing surace sections 24 and 25 is pressed away thererom re-~ulting in contact therebetween and especially around the ~1~8~ ~6 corners of the lamp unit 20. Such contact can create un-acceptable stress patterns,particularly around the reflec-tor corners. Additionally, the adhesive 23 when forced from between sealing surface sections 24 and 25 can flow beyond the designed lamp unit outer dimensions resulting in an oversized and unacceptable lamp unit.
Furthermore, contact between sealing surface sec-tions 24 and 25 is aggravated by the different coeffi-cients of thermal expansion of glass and adhesive. For example, the coefficient of thermal expansion for boro-silicate glass, conventionally l-sed in sealed beam auto-motive headlamps, typically is about 40 x 10 7 cm/cm/C
whereas the coefficient of thermal expansion of a typical flexibilized epoxy, suitable for sealing l~mp glassware, typically is about 40 x 10 cm/cm/C. That is, the co-efficients of thermal expansion of glass and adhesive, in a sealed beam lamp unit can differ, by a factor of about 10. Therefore, temperature changes, in particular de-creasing temperatures, produce different rates of con traction for the glass and interposed adhesive creating more stress between the sealing surfaces and thereby aggravating the glass lens to glass reflectox contact along those outermost sealing surface sections 24 and 25 where the adhesive has been pressed away. In certain in-stances, spalling of the adhesive and glass can occur.Even worse, the glassware can crack producing unaccept-able lamp performanceO
A~hesively bonded lamps are g~nerall~ made from mold-able materials such as glass. In the making of ~he lamp units, flaws typically appear on the surfaces thereof.
More specifically,certain flaws are created due to the misalignment of the tooling pieces used in the molding of the lamp units. That is, when two or more of the tooling pieces are pres~ed together, to obtain a desired molded shape/ a misalignment therebetween or thexeamong provides L~ 8631 discontinuities or flaws on the surface of the molded ma-terial. Such flaws, referred to within the art as match-lines or parting lines, are shown in Figure 2 as lamp unit portions 26. If the adhesive 23 comes into contact with these match-lines 26 and if the ambient temperature is re-duced, the adhesive will contract at a different rate than the glass due to the differences in the coefficients of ex-pansion thereof and thereby place stress on portions of the glassware highly susceptible to stress induced failure, that is, the match-lines 26, resulting in cracks thereat and jeopardizing the glassware integrity.
In contrast thereto, the present invention signifi-cantly reduces the abo~e-mentioned stresses, especially around the reflector corners 15, by modifying such un-acceptable stress patterns. Figure 3 which is a frag-mentary, cross-sectional view of the lens and xeflector sealing surfaces 8 and 9, respectively, along the sides of the lamp unit 1, illustrates the present invention in detail. Lamp unit 1 includes on ~he edges of the lens 2 and reflector 3 external molding lobes 31 and 32, respec-tively, which aid in the molding thereof. Both lens seal-ing surface 8 and reflector sealing surface 9, which are approximately located about the periphery of the lens 2 and reflector 3, respectively, cooperate with a~d oppose each vther and are preferably substantially planar in shape and substantlally transverse to the lamp unit axis.
As shown in Figure 1, part of the lens sealing surface 8 comprises protrusions 33, referred to hereinafter as keys~ located substantially about the corners thereof with cooperating and opposing indentations 34, referred to hereinafter as key recesses, located substantially about the corners of the reflector sealing surface 9. Al-ternatively, the keys 33 can be located on the reflector sealing surface 9 and the key recesses 34 located on the lens sealing surface 8. In a preferred embodiment the - - \

length of each key or key recess comprises approxi-mately 3.5% of the total lamp unit perimeter as mea-sured at the junction of the sealing surfaces. Alterna tively, the length of each key and key recess pair can vary from pair to pair which advantageously can be used to assure proper orientation of the lens 2 to the re-flector 3.
Lamp unit 1 can be assembled by disposing the ad-hesive 16, such as a heat curing adhesive, on and be-tween the sealing surfaces 8 and 9. The lens 2 andreflector 3 are then pressed together,such that opposing sides and corners are mated with each other to thereby cooperate with and oppose each other. The lens-reflector assembly is then placed in an oven and brought to and kept at a requisite curing temperature until the adhesive is cured. As sealing surfaces 8 and 5 are pressed to-gether and/or during curing of the adhesive, adhesive 16 substantially covers and is substantially contained therebetween.
As shown in Figure 3, reservoirs 35 located adjacent to the sealing surfaces 8 and 9 retain any excess ad-hesive, which oozes ~rom therebetween and ~hereby prevent the adhesive 16 from spreading onto undesirable portions of the lamp unit 1. That is, the reservoirs 35 enable application of suf~icie~t adhesive to ensure an acceptable peripheral seal without such adhesive oozing onto the lens light-transmitting portions, such as the lens prisms 5, and/or beyond the desiyned lamp unit outer periphery.
Furthermore, the reservoirs serve to keep the adhesive 16 away from the match-lines 36 of the lamp unit lo Thus the adhesive 16 avoids contacting portions of the glassware which are less able tv successfully withstand stresses exerted by the adhesive.
The reservoir on each side of the sealin~ surfaces is 35 ~ormed by joining curved surfaces 37-38 and 39-40 together.

_ g _ As illustrated in Fig. 3, curved surfaces 37 and 38 need not have the same curvature as 39 and 40. Additionally, that portion of each reservoir ad~acent to each sealing surface need not form a substantially continuous curved surface with that portion of the reservoir which coop-erates and opposes it. For example, curved surface 37 does not form a substantially continuous surface with curved surface 38.
During assembly of the lamp uni~ 1, keys 33 and key recesses 34 serve several functions. First by pairing together, the keys 33 and key recesses 34 aid in the alignment of lens 2 to reflector 3. Additionally, by fitting together, the keys 33 and key recesses 34 pre-vent the lens 2 from slipping off the reflector 3 and thereby restrict lateral movement of lens 2 relative to reflector 3. Most importantly, and as will be discussed below, the keys 33 and key recesses 34 serve to alter the stress pattern experienced in prior art, adhesively sealed beam lamp units and thereby substantially reduce the num ber of cracks that can occur, especially about the lamp unit corners.
Of particular note,and as shown in a cross sec-tion view of the lamp unit sides, Figure 3 illustrates that between the sealing surfaces 8 and 9 a thin layer of ad-hesive 16 exists. The adhesive layer, however, càn be so~hin that pockets, void of adhesive, can form therein re-sulting in lens-reflector contact thereat. Such pockets are due to adhesive 16 having been pressed away from between the sealing surfaces sides during assembly of the lamp unit l. It is to be emphasized, however, that such lens-reflector contact is limited specifically to one or more portions along cooperating sides lO 13 ~nd 11-14.
Furthermore, and as shown in Figure 4, once lamp unit 1 is assembledr cooperating and opposing keys 33 and key recesses 34 are unable to come into contact with each other due to a space 41 formed therebetween. That is, the keys 33 rise to a height that is less than the depth of the key recesses 34. In a preferred embodiment, ~he height of the keys 33 is approximately 0.8 millimeters and the depth of the key recesses 34 is appro~imately 1.0 millimeter re-sulting in a gap between the sealing surfaces of approxi-mately 0.2 millimeters at and around the corners 12 and 15 of the lens 2 and reflector 3, respectively.
The present invention therefore limits contact to one or more portions o~ the sealing surface sides exclusively.
In particular, the present invention eliminates the prior art practice of the lens and reflector outermost sealing surface sections contacting each other about the lamp unit corners where stresses tend to concentrate. By the pres2nt invention isolating lens-reflector contact to one or more portions along the sealing surface sides, stresses genera ted in the present invention are substantially reduced, as compared to the prior art, and thereby substantially eliminate cracks about the sealing surfaces and especially a~out the xeflector corners. Theoretical explanation ac-countiny for this significant change in the stress pat-tern is not fully understood, however, test results dem onstrate a substantial elimination of cracks, in parti-cular, during decreasing ambient temperatures.
Additionally and as commonly experienced in the art, the lens can waxp along its sides resulting in the lens having a much more convex outer face. Such warpage, however, does not affect the present invention inasmuch as a sufici~nt space is provided ~etween the keys and key recesses to ensure that only the sides of the sealing surfaces can come into contact with each other. That is, even when such warp~ge occurs, the corners 12 of the lens sealing surfaces are unable to come into contact with the corresponding and opposing reflector sealing surface coxners 15.

;3 Furthermore although the present invention has for purposes of description shown all of the keys on one lamp unit sealing surface and the key recesses on the other lamp unit sealing surface, it is to be understood that both keys and key recesses can be on the same sealing surface while remaining within the scope of the present invention. For example, the bottom corners of the lens sealing surface can comprise keys while the top corners thereof can comprise key recesses. Conversely, the bottom corners of the reflector sealing surface would comprise key recesses and the top corners thereof would comprise keys. Such a configuration could be used to ensure that the lens is not placed on the reflector upside down.
By the present invention providing substantially planar sealing surfaces along the sides thereof t ~ thin ribbon of adhesive can be used thereon and therebetween, providing a substantially uniform spacing between the sealing surfaces, and reducing the amount of adhesive required to seal the envelope together as compared to the prior art. A further advantage of the present invention is in the reduced need for flexibility in the adhesive. That is, at cold tempera-tures adhesive flexibility is required to reduce the ad-hesive rigidity and resulting adhesive spalling due to incre~sed stress levels. The present invention by pro-viding preferably planar ~ealing surface shapes and a uniformly thin ribbon of adhesive can more easily and evenly distribute adhesive stresses created at cold tem-peratures without requiring as pliable and flexible an ad-hesive as in the prior art. ~hus a lower proportion offlexibilizer can be used as compared to prior art practice.
Another advantage provided by the present invention results directly from the decreased cross-sectional area of adhesive and/or the decreased proportion of flexi-bilizer required. ~ore particularly, the smaller adhesive cross-sectional area exposed to the surrounding external environment and especially the less flexibilizer required, the less permeable the adhesive is to moisture and other contaminants. That is, the present invention improves the resistance of the lamp unit to moisture and other contamin-ant penetration and thereby reduces possible filament and lamp degradation therefrom.
Therefore, while pre:Eerred embodiments of the invention have been shown and/or described, various other embodiments and modifications thereof will become apparent to persons skilled in the art and fall within the spirit and scope of the invention as defined in the following claims.

Claims (9)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A sealed beam lamp unit comprising a lens and reflector having substantially polygonal peripheries and cooperating and opposing planar sealing surfaces characterized by sides and corners, located approximately about said peripheries and with said planar sealing surfaces being in physical contact along the sides but spaced apart at the corners, with adhesive disposed on and between said planar sealing surfaces wherein a first of said planar sealing surfaces has corners protruding from a plane defined by the sides thereof and cooperating and opposing corners of a second of said planar sealing surfaces, said second planar sealing surface corners indented from a plane defined by the sides thereof, and with each side of said planar sealing surfaces further including reservoirs to contain excess adhesive.

2. A sealed beam lamp unit as defined in claim 1 wherein said peripheries are substantially rectangular.

3. A sealed beam lamp unit as defined in claim 1 wherein each of said sealing surfaces has at least one corner which protrudes and at least one corner which indents from a plane defined by the sides thereof.

4. A sealed beam lamp unit as defined in claim 3 wherein the heights of said protruding corners as measured from a plane defined by the sides thereof are less than the depths of said indenting corners as measured from a plane defined by the sides thereof.

5. A sealed beam lamp unit as defined in claim 4 wherein the heights of said protruding corners are approx-imately 0.8 millimeters and the depths of said indenting corners are approximately 1.0 millimeter.

6. A sealed beam lamp unit as defined in claim 1 wherein the distance between said sealing surfaces along said sides is substantially constant.

7. A sealed lamp unit as defined in claim 1 wherein the length of each corner comprises approximately 3.5% of the total lamp unit perimeter as measured at the junction of said sealing surfaces.

8. A sealed beam lamp unit as defined in claim 1 wherein said sealing surfaces are substantially transverse to the lamp unit axis.

9. A sealed beam lamp unit as defined in claim 1, said lens and reflector each formed in a molding operation from two or more tooling pieces, wherein said adhesive avoids contacting portions of said lens and reflector where said tooling pieces have come together during said molding operation.