Headlight with a twin filament lamp for producing a chopped beam and an unchopped beam

A motor vehicle headlamp has a lamp with two filaments, one of which has a masking screen so as to form a chopped or dipped beam, while the other filament is unmasked so as to produce an unchopped beam. The headlight also includes a reflector and a smooth cover lens. The reflector has an upper zone extending between two radial half planes which are inclined by the same amount below the horizontal, this upper zone being larger than the part of the reflector which is exposed to the first filament; the reflector has two lateral sub-zones with base surfaces which are symmetrical with respect to the vertical, with striations being formed by projection on the base surface, the striations being configured according to the particular type of chopped beam required. The reflector also has a second zone having a surface for cooperation with the second filament only, so as to form a wide portion of the beam and extending at least partly above the cut-off of the dipped beam.

FIELD OF THE INVENTION 
The present invention relates in general terms to motor vehicle headlights. 
More particularly, the invention relates to a headlight with a light 
source having two filaments, which are typically incorporated in a single 
lamp, and in which one of the filaments is associated with means for 
restricting the field of illumination given by that filament, typically in 
the form of a masking screen. This mask restricts the field of emission of 
light from this first filament by the headlight. The beam emitted by the 
headlight from this second filament is therefore a chopped beam, which may 
typically consist of a dipped beam but which may be selected among various 
types of chopped beam. The other filament has no masking means, and 
produces an unchopped beam such as a headlight main beam. 
BACKGROUND OF THE INVENTION 
Such a light source, such as a lamp, is generally associated with a 
parabolic reflector, the focus of which is located between the two 
filaments of the lamp. The headlight further includes a cover lens which 
has sets of prisms and/or striations such as to spread the beam generally 
horizontally and along the inclined part of the cut-off of the dipped 
beam, so as to give comfortable lighting and also to satisfy the 
photometric requirements laid down in regulations. 
In addition, Valeo Vision S.A. has for a number of years been developing 
reflectors which, associated with filaments that have no masking screen, 
generates beams such as a European type dipped beam, which not only 
provide a precise V-shaped cut-off, but which also give good lateral 
spread of the light. In that case, the cover lens may be smooth or nearly 
smooth, which is of advantage, not only as regards its selling costs, but 
also from the aesthetic point of view. One headlight of that type is 
described in French patent specification No. FR 2 664 677A in particular. 
Given the foregoing, the purpose of this type of reflective surface is, as 
has been indicated above, to cooperate with a filament having no masking 
screen, and has been considered a priori as being of no interest where the 
filament does have a screen for making the cut-off. Now, twin filament 
lamps, in which one filament is associated with a screen, and more 
particularly the so-called "H4" normalised lamps, continue to be widely 
used, mainly in headlights which have both a main beam and a dipped beam 
function. 
It is also known, from French patent specification No. FR 2 720 476A in the 
name of Valeo Vision S.A., to use mathematically defined surfaces such as 
are cited above, with a lamp of the H4 type or equivalent, to obtain 
better quality beams. The headlights described in that document do however 
have certain limitations. In particular, if it is required to make, in 
accordance with the descriptions in that patent, headlights which are 
adapted for use under different regulations, and in particular a headlight 
with main and dipped beam functions in which the dipped beam is a 
normalised European beam for driving on the right, or a headlight with 
main and dipped beam functions in which the dipped beam is a normalised 
European beam for driving on the left, or again, a headlight with main and 
dipped beam functions in which the dipped beam will satisfy regulations in 
the United States of America, then all the various reflectors have to be 
made each time not only with different formers in the mould (i.e. the 
core, or male member, which cooperates with the mould cavity to produce 
the moulded reflector), but the mould cavities themselves also have to be 
different. 
This is explained by the fact that the base surfaces from which the various 
reflectors are made differ quite radically from each other, and the use of 
a common mould cavity would lead to major variations in thickness of the 
reflector, leading to high consumption of moulding material and to risks 
of mechanical instability at high temperatures. 
It is true that European patent specification No. EP 0 736 726A proposes a 
headlight capable of generating a chopped beam, in which the same mould 
cavity can be used whether the reflector is to be used for driving on the 
left or driving on the right. However, the disclosures in that European 
patent document do not enable a headlight with both main beam and dipped 
beam facilities to be made with the same advantages. In particular, 
nothing is said about the positioning of the masking screen. 
DISCUSSION OF THE INVENTION 
A first object of the present invention is to provide a headlamp capable of 
generating two types of beam, with its reflector being able to be moulded 
using the same mould cavity regardless of which side of the road a vehicle 
incorporating the headlight is to be driven on. 
A further object of the invention is to provide a headlight in which its 
reflector can be moulded using the same former or male member of the 
mould, regardless of whether the headlight is intended for a vehicle of 
right drive or left hand drive. 
Yet another object of the invention is to provide a headlight in which its 
reflector can be moulded with the same male member for producing a dipped 
beam which is compatible both with European regulations and with the 
regulations of the United States of America. 
According to the present invention, a motor vehicle headlight of the type 
including a lamp having two filaments, the first of which is arranged to 
form a chopped beam, a masking screen being associated with it for that 
purpose, so as to limit the emission of light to a given angular field, 
the second filament being arranged to form a beam which is not chopped, 
and to emit light freely around the filament, together with a reflector 
and a cover lens which is essentially smooth or with no substantial 
deflecting capability, is characterised in that the reflector comprises: 
a first zone, extending in the upper part of the mirror between two 
transition half planes passing close to the optical axis of the reflector 
and inclined by the same amount below a horizontal plane, the said first 
zone having an angular field covering the angular field of emission of the 
first filament and overlapping beyond the latter, the said first zone 
comprising two lateral sub-zones which have two respective base surfaces 
that are symmetrical with respect to a vertical plane passing through the 
optical axis of the reflector, and the reflective surfaces of the said 
lateral sub-zones being obtained by projection of striations on the said 
base surfaces, in such a way as to generate two components of the chopped 
beam, the said striations being determined according to a particular type 
of chopped beam to be generated, and 
a second zone in the remaining part of the reflector, the said second zone 
having a surface adapted to cooperate with the second filament only, and 
being adapted to generate a part of the beam which is wide and extends at 
least partly above the cut-off of the chopped beam. 
According to a preferred feature of the invention, the first zone of the 
reflector further includes a central sub-zone which is sub-divided into a 
plurality of elementary regions, each of which has a horizontal axial 
cross section which is not focussed on the second filament, the said 
elementary regions being joined to each other with break of slope along 
their intersections. In that case, preferably, the central sub-zone and 
the lateral sub-zones of the first zone are joined together with zero 
order continuity. 
According to another preferred feature of the invention, the base surfaces 
of the lateral sub-zones of the first zone are part of a common paraboloid 
of revolution, the axis of which is coincident with the optical axis of 
the reflector. In preferred embodiments of this arrangement, the said 
paraboloid of revolution is focussed on a point which is situated 
immediately in front of the first filament; and/or the striations 
projected on the base surfaces of the two lateral sub-zones include, in 
each lateral sub-zone, a first set of essentially vertical rectilinear 
striations for spreading the light horizontally, and a second set of 
striations which extend below the first striations and along circular 
trajectories which are centred in the vicinity of the optical axis of the 
reflector. 
In preferred embodiments having any or all of the features set out in the 
last paragraph, the masking screen associated with the first filament 
defines an angular emission field contained between a first cut-off half 
plane, which is inclined below the horizontal and which intersects a first 
said lateral sub-zone at the level of the striations having circular 
trajectories in the said first sub-zone, and a horizontal second cut-off 
half plane intersecting the second lateral sub-zone at the level of the 
rectilinear vertical striations of the said second sub-zone. 
Preferably then, the striations with circular trajectories in the two 
lateral sub-zones extend symmetrically with respect to a vertical plane 
passing through the optical axis of the reflector, between a horizontal 
half plane and an associated transition half plane respectively, and the 
reflector includes means for mounting the lamp in one of two possible 
orientations, such that the angular field of the first filament covers 
respectively two distinct sub-groups of optical elements in the first zone 
of the reflector, whereby selectively to generate a chopped beam for use 
in traffic driving on the left and a chopped beam for use in traffic 
driving on the right. 
According to yet another preferred feature of the invention, the lamp is a 
normalised type "H4" type, the chopped beam is a dipped beam, and the 
unchopped beam is a main beam. 
Preferably, the central sub-zone of the first zone of the reflector 
provides a greater lateral spread of the light than that provided by the 
lateral sub-zones of the said first zone, whereby to generate a complex 
cut-off half profile in the chopped beam. 
Further features and advantages of the invention will appear more clearly 
on a reading of the following detailed description of some preferred 
embodiments of the invention, given by way of non-limiting example only 
and with reference to the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
Reference is first made to FIGS. 1 and 2, showing a headlight reflector 200 
in which a twin filament lamp is mounted. One of the filaments is a dipped 
beam filament and is provided with a masking screen. In this example, the 
lamp is an "H4" normalised lamp, in which the first, or dipped beam 
filament is denoted Fc and is associated with the masking screen C. The 
second filament is a main beam filament Fr, which is arranged behind the 
dipped beam filament and slightly offset downwardly from the latter. No 
masking screen is associated with the filament Fr. 
A lamp of this kind is normally arranged to cooperate with a reflector of 
generally parabolic form, the focus of which lies somewhere between the 
filaments. The shape of the masking screen, which extends over 
approximately 165.degree. around the dipped beam filament Fc, and below 
the latter, defines a normalised European V-shaped cut-off, with a cut-off 
elevation angle .delta., typically of 15.degree., which is in the right 
hand half of the beam where the headlight is intended to be used when 
driving on the right. 
The headlight also includes, in the usual way, a cover lens (not shown) 
which is essentially smooth or which only deflects light very slightly. 
In the reflectors shown in the drawings, in accordance with the present 
invention, the reflector is not parabolic. Instead, it comprises two main 
zones 210 and 220 which will be described below. 
The first main zone 210 is situated generally in the upper part of the 
reflector, and is delimited by two axial planes, namely a half plane P1 
which is inclined slightly downwardly by an angle denoted .alpha., below 
the horizontal axial plane X0Y and in the left hand part of the reflector, 
and a half plane P2 which is in the right hand part of the reflector and 
which is inclined downwardly by the same angle .alpha. below the 
horizontal axial plane X0Y. 
The angle .alpha. is chosen to be greater than the cut-off elevation angle 
.delta., and is preferably in the region of 25.degree.. The value of this 
angle .alpha. of inclination of the half planes P1 and P2 ensures that the 
whole of the radiation from the dipped beam filament Fc lies entirely in 
the first zone 210 of the reflector. 
The second main zone 220 is generally in the lower part of the reflector, 
and is delimited between the two half planes P1 and P2 as shown in FIG. 1. 
The zone 220 cooperates only with the main beam filament Fr. By contrast, 
it will be noted that the other main zone 210 is of course exposed to the 
light from both filaments. 
The zone 210 is sub-divided into three sub-zones, namely a central sub-zone 
211 and two lateral sub-zones, namely a left hand sub-zone 217 and a right 
hand sub-zone 218. 
The central sub-zone 211 is preferably constructed from a plurality of 
elementary regions 212 to 216. More precisely, each of these elementary 
regions has a horizontal generatrix, that is to say a horizontal axial 
cross section, which is in the form of a hyperbola, and is constructed in 
the manner of a surface which automatically generates cut-off, that is to 
say with defocalisation with respect to the light source Fc such that the 
images of that light source are essentially aligned below the cut-off. As 
to the hyperbolic horizontal generatrix, this gives control of the 
horizontal spread of the light. 
Preferably, these various elementary regions 212 to 216 give different 
amounts of spread below a common horizontal cut-off line which is situated 
at the height of the horizontal cut-off line for the required dipped beam, 
in such a way that the various respective components of the beam, produced 
in the different elements of the sub-zone 211, merge homogeneously into 
the whole beam. 
In addition, the various elementary regions 212 to 216 consist of surfaces 
which define between them intersections that extend between the upper and 
lower edges of the reflector; and they are joined one to another along 
these intersections with a break of slope, that is to say with continuity 
of zero order only. 
The lateral sub-zones 217 and 218 are arranged to complete that part of the 
beam which is generated by the central sub-zone 211, so as to give the 
whole beam the appearance required by the regulations. In the present 
example, this is obtained by forming the sub-zones by projection of 
clearly defined striations on a base surface. 
In accordance with one feature of the invention, it is arranged that, 
regardless of the type of beam which is to be produced, this base surface 
is symmetrical with respect to the vertical axial plane Y0Z, for the left 
hand lateral sub-zone and also for the right hand lateral sub-zone. 
Preferably, the base surfaces of the two sub-zones 217 and 218 are parts 
of a common paraboloid of revolution, the focus F78 of which is preferably 
situated slightly in front of the dipped beam filament Fc. It is 
particularly preferred that the focus F78 lies about 1 mm in front of the 
filament Fc, as shown in FIG. 2. 
The striations projected on this surface are so designed as to refocus the 
dipped beam filament Fc. More precisely, given that the paraboloid 
focussed at F78 as described above produces, by itself, images of the 
filament which are able to overlap above the cut-off, it is arranged that 
the striations projected on the sub-zones 217 and 218 give controlled 
downward deflection of the light. Such deflection is obtained by 
projecting striations having a level, that is to say a degree of overlap 
measured along the axis 0Y (FIG. 2) with respect to the base surface, 
which is larger in the upper region of the striations than in their lower 
region. 
Preferably, these striations provide relatively limited spread of the 
light, this being obtained by giving them large radii of curvature. 
In the present example, which relates to a headlight capable of producing a 
normalised European dipped beam for driving on the right, a first set of 
striations S7a is arranged in the left hand lateral sub-zone 217, these 
striations extending vertically between the upper edge of the reflector 
and the plane of origin X0Y; and a second set of striations S7b of 
circular form centred on the optical axis 0Y and extending in a curve 
between the plane of origin X0Y and the half plane P1. As can be seen in 
FIG. 1, the striations S7b extend the corresponding striations S7a from 
the level at which the two sets of striations join in the plane of origin 
X0Y. 
Still considering a beam for use when driving on the right, the masking 
screen C is so arranged that the light from the dipped beam filament Fc 
meets the left hand lateral sub-zone 217 down to a cut-off plane PC1 which 
is offset by 15.degree., about the optical axis 0Y, below the horizontal 
plane X0Y, that is to say in an intermediate region of the part which 
includes the circular, or curved, striations S7b. In this case, and due in 
particular to the curvature of the striations S7b, it is of course the 
half plane PC1 produced by the masking screen C that produces the half 
cut-off, inclined upwardly by 15.degree., in the right hand half of the 
beam. This is analogous to the situation with a lamp of the "H4" type or 
similar, associated with a conventional pure paraboloid of revolution. 
As to the right hand lateral sub-zone 218, this also has projected 
striations, namely a vertical first set of striations S8a which extend 
between the upper edge of the reflector and a half plane P8, which is 
slightly inclined below the horizontal plane X0Y by an angle of 
inclination .beta. which is for example 7.5.degree.; and a second set of 
striations S8b, of circular form centred on the optical axis 0Y and 
extending between the half plane P8 and the half plane P2 defining the 
transition with the main zone 220. 
The striations in the sub-zone 218, like those in the sub-zone 217, are 
arranged to provide limited spread of the light, as will be seen in detail 
later in this description. In particular, the dipped beam filament Fc, due 
to the presence of the masking screen C, cooperates only with that part of 
the striations S8a that lies between the upper edge of the reflector and 
the horizontal plane X0Y, so as to spread the light horizontally below a 
horizontal cut-off, while all of the striations S8aand S8b cooperate with 
the main beam so as to provide spreading of the light which is mainly 
horizontal, the circular, or curved, striations S8b having a correcting 
function such as to render the main beam symmetrical while taking into 
account the deflection performed by the circular striations S7b on the 
opposite side. 
It will be noted here that the fact that the vertical striations S8a are 
extended below the horizontal plane X0Y enables the horizontal cut-off to 
be respected precisely, in spite of the inevitable instances of lack of 
precision that will occur in relation to the positioning of the masking 
screen C, and therefore that of the cut-off half plane PC2. 
The second main zone 220 of the reflector is not exposed to the light 
produced by the dipped beam filament Fc, but is exposed only to that from 
the main beam filament Fr, in such a way that the two main zones 210 and 
220 together define a main beam. 
The zone 220 consists of a surface which is designed in the same way as the 
sub-zone 211 of the first main zone 210, except that in this case the 
various elementary regions of the zone 220 are parabolas and not surfaces 
that automatically generate cut-off. In addition, the elementary regions 
situated in the centre of the zone 220 are continuous downward extensions 
of the respective elementary regions of the central sub-zone 211. 
Moreover, for the reasons explained above in connection with the sub-zone 
211, the various elementary regions in the zone 220 of the reflector are 
again joined together with continuity of zero order. However, a 
discontinuity of zero order may exist along the separating half planes P1 
and P2, although these half planes are only exposed to light in main beam 
operation, so that this discontinuity will give rise to no optical anomaly 
in the dipped beam. 
The optical behaviour of the reflector just described, either in the 
absence of a cover lens, or with a cover lens which has no optically 
active elements, is illustrated in FIGS. 3 to 6, to which reference is now 
made. The projection screen on which the appearance of the various parts 
of the beam are projected is graduated in degrees in these Figures. 
FIG. 3a shows the appearance of that part of the beam that is produced by 
the portion of the central sub-zone 211 which is exposed to the light from 
the dipped beam filament. It will be noted that there is a very wide 
lateral spread of the light, but that there is no significant spot of 
light concentration, as indicated above. Also to be noted are the 
appearance of the V-shaped cut-off, with depression nearside elevation, 
i.e. elevation on the right, as is appropriate to a European dipped beam 
for traffic driving on the right. 
FIG. 3b shows the appearance of that part of the beam which is produced by 
the part of the left hand lateral sub-zone 217 which is exposed to the 
dipped beam filament, giving an enhanced degree of concentration of light 
together with limited lateral spread. It will also be noted that the 
curved striations S7b give a good spread of light below the elevated half 
cut-off on the right. 
As to FIG. 3c, this shows the appearance of that part of the beam which is 
produced by the portion of the right hand lateral sub-zone 218 that is 
exposed to the light from the dipped beam filament. This shows limited 
horizontal spread, and positioning of the beam below the horizontal left 
hand half cut-off line. Finally, the appearance of the whole beam, in 
which the images shown in FIGS. 3a to 3c are added together, is seen in 
FIG. 4. 
Reference is now made to FIGS. 5a to 5d, which show those parts of the beam 
which are produced respectively by the central sub-zone 211, the left hand 
lateral sub-zone 21 7, the right hand lateral sub-zone 218 and the main 
zone 220, when the main beam filament is in use. In particular, it will be 
observed in FIGS. 5b and 5c that there is some degree of symmetry between 
the parts of the beam produced by the lateral sub-zones 217 and 218, due 
to the circular striations in those two sub-zones. 
If FIGS. 3a, 3b and 3c are studied in particular, it will be understood 
that it is possible, while preserving the same base surfaces for all the 
zones of the reflector, to produce dipped beams, or other chopped beams 
such as fog penetrating beams, simply by suitable choice of values for the 
parameters of the various sets of striations. 
Essentially, the preservation of the base surfaces enables the same mould 
cavity to be used (and more precisely a common mould cavity whether the 
headlight is intended for use when driving on the left or on the right) 
for making reflectors suitable for producing all of these different types 
of beams. 
In addition, in the particular example described above, FIG. 4 shows that 
the dipped beam obtained can be suitable for compliance both with European 
regulations (for driving on the right) and with American regulations. More 
precisely, attention is drawn to the right hand side of FIG. 4, which 
shows the presence of the half cut-off elevated by about 15.degree. over a 
certain width, and the presence beyond this elevated portion of an 
extension of the cut-off in the form of a plateau which is slightly offset 
in height with respect to the left hand horizontal half cut-off. 
The invention enables this effect to be obtained by the combination of: 
firstly, the heavily striated central sub-zone 211, the portion of which 
lying between the plane X0Y and the first cut-off half plane PC1 generates 
the right hand half plateau as shown in FIG. 3a; and secondly, the lateral 
sub-zone 217, in particular at the level of the circular striations S7b, 
which generate the right hand elevated cut-off portion as shown in FIG. 
3b. 
That implies that, in order to make a headlamp with main and dipped beam 
functions for use with European traffic driving on the right, and a 
headlamp with the same functions for American traffic, it is possible to 
use for each headlight (i.e. both the left hand light and the right hand 
light of the vehicle), not only the same mould cavity but also the same 
mould former (or male member) cooperating with the mould cavity, and this 
leads to substantial economy in tooling costs. 
It is useful to recall here that, in modern methods of making reflectors, 
these are made by injection of mouldable synthetic materials into moulds 
which comprise a fixed cavity defining the posterior face of the 
reflector, and a movable former, or male mould component, which will 
define its anterior face, on which a varnish and a reflective metalisation 
coating are subsequently successively applied. 
Reference is now made to FIGS. 7a and 7b, which show a modified embodiment 
of the invention. With this version, the same mould cavity and the same 
male mould component can be used, not only for making reflectors for 
headlights having a main beam function and a dipped beam function for 
European and American traffic for driving on the right, but also for 
reflectors for headlights intended for driving on the left, in Europe or 
elsewhere. 
In this embodiment, the central sub-zone 211 and the main zone 220 of the 
reflector are made as described above. However, the lateral sub-zones 217 
and 218, which remain established on symmetrical parabolic base surfaces, 
here consist of sets of striations, S7a, S7b and S7a', S7b' respectively, 
which are fully symmetrical with respect to the vertical axial plane Y0Z. 
In particular, the curved striations S7b, of circular form, are identical 
to those described above with reference to FIG. 1, while the curved 
striations S8b' are, similarly, circular striations centred on the optical 
axis 0Y and extending between the horizontal plane X0Y and the transition 
half plane P2. 
In the case shown in FIG. 7a, the lamp, which is of the "H4" normalised 
type, is oriented in the same way as in FIG. 1, this Figure showing a 
headlight mirror for main and dipped beams for use with European traffic 
driving on the right, but being equally suitable for American traffic as 
has been seen above. 
In the case shown in FIG. 7b, the same lamp, i.e. the light source, is 
simply turned clockwise through 15.degree., so as to move the cut-off 
planes PC1 and PC2 to the new positions shown. In this case, for obvious 
reasons of symmetry it will be understood that the headlight thereby 
becomes, without any other modification, a headlight with a main beam 
function and a dipped beam function suitable for use in traffic driving on 
the left, for example under the appropriate European regulations. 
Thus in this embodiment, manufacture of the headlight reflectors calls only 
for one mould cavity and one former for the left-hand headlight of the 
vehicle, and one corresponding set of mould parts for its right-hand 
headlight. In this connection, in some very special cases, it will be 
realised that the reflectors of the left and right hand headlights of the 
vehicle may sometimes be identical, and this enables a single common set 
of mould components, to be used for both headlights of the vehicle. 
The present invention is of course not limited to the embodiments described 
above and shown in the drawings, and a person familiar with this technical 
field will be able to apply any variation or modification within the 
spirit of the invention. In particular, the invention can be applied to 
any other type of headlight which includes a lamp having two filaments, 
one of which is associated with a mask, with a view to producing, 
selectively, a chopped beam and a beam which is not chopped. 
Finally it will be observed that the reflector designed in accordance with 
the present invention may have, in some zones, optical surfaces in which 
the striations are superfluous. In that case, decorative striations may be 
provided in such zones, that is to say striations which play no part in 
the optics of the headlight, but which give the reflector a homogeneous 
appearance.