Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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
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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
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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
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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
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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
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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
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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
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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.
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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
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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.
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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
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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.
