Motor vehicle headlamp with a narrow outlet window

A motor vehicle headlamp comprising in combination an optical system for recovering flux having a rectilinear focal segment and an optical system for rectifying images having a focal segment coinciding with the former and able to produce a beam of rays of controlled directivity passing through a narrow light window, while preserving a high luminous efficiency. The flux recovery system is constituted by an elliptical paraboloid, an hyperbolic paraboloid or their optical equivalents. By using various combinations of optical elements, it is possible to arrange the flux recovery system both in the axis of the rays leaving the headlamp, as well as on the side of the body work or on the lower part of the latter.

The present invention relates to motor vehicle headlamps. 
Motor vehicle headlamps known hitherto, whether it is a question of 
headlamps having a main beam and dipped beam, high beam headlamps or even 
fog lamps, are most frequently constituted by a light source, a reflector, 
whereof the focus is close to said light source and a closing glass, 
provided if desired with optical reliefs ensuring the diffusion of the 
light flux emitted by the source and reflected by the reflector. 
The reflector generally comprises a parabolic reflecting surface, 
constructed as one or more sectors of a paraboloid. 
It is essential that the reflector is struck by a maximum of the light flux 
emitted by the light source and that it reflects it towards the glass with 
the suitable directivity. 
For example, for a main beam headlamp, the reflector must reflect a very 
directive beam of light rays, i.e. a beam constituted by rays which are 
all substantially parallel to the direction of emission. For a dipped 
beam, the directivity must be less, the light rays having to constitute a 
slightly convergent beam. 
During recent years, it has become extremely desirable to produce motor 
vehicle headlamps whereof the outlet window (corresponding substantially 
to the contour of the closing glass), is very narrow, i.e. of no height 
with respect to its transverse dimension or width. Headlamps of this type 
of the "strip of light" type are in great demand by motor vehicle 
manufacturers, owing to the fact that narrow outlet windows provide the 
designer with new possibilities in that they can be integrated 
particularly well in the line of certain modern cars. 
To produce headlamps of this type, the pure and simple transposition of 
traditional arrangements is not satisfactory, in particular in the field 
of optical efficiency. In fact, if a headlamp having a narrow window is 
produced with a conventional reflector of the parabolic type, of low 
height and great width, only a very small part of the flux emitted by the 
light source is recovered. On the other hand, studies carried out by the 
Applicant have shown that this situation is scarcely improved when the 
reflector is constituted by a plurality of parabolic sectors, or more 
generally, when the latter is given a relatively flattened shape diverging 
from the traditional parabolic shape. Very briefly, it can be stated that 
the two conditions for good recovery of the flux, on the one hand and good 
directivity, on the other hand, are not easily compatible, when a single 
reflector is used for cooperating with the source. 
The present invention proposes a general solution to this problem, 
concerning all types of headlamps, as well as particular solutions more 
specifically suitable for the construction of a particular type of 
headlamp. 
The basic idea of the invention resides in the dissociation of the two 
functions of recovering the light flux emanating from the light source and 
rectifying images, in order to make the beam suitably directive (i.e. 
parallel to the direction of emission in the case of main beam and 
slightly convergent in the case of dipped beam). 
In order to do this, according to the invention, two optical systems are 
used in combination, which successively treat the light rays emitted by 
the source, each of the two systems comprising a rectilinear focal 
segment, the focal segments of the two systems being substantially merged. 
More precisely, the headlamp according to the invention comprises, in 
combination: 
(a) an optical system recovering the flux generating a real or virtual line 
of foci. This line of foci--which will be referred to hereafter in the 
text by the name of "focal segment"--is transverse with respect to the 
optical axis of the flux recovery means. In the case where this focal 
segment is horizontal, its length is equal to the width of the outlet 
window of the headlamp; in the case where this focal segment is vertical, 
its length is equal to the height of the outlet window of the headlamp. A 
system of this type is thus able to create from a substantially pinhole 
light source, a beam of light rays all passing through the focal segment 
whilst all being substantially parallel to the direction of the plane 
perpendicular to the focal segment. 
(b) An optical system for rectifying images having a focal segment 
coinciding with the former and able to transform the beam leaving the 
system for recovering flux into a beam having controlled directivity. 
In this case it is important to note that optical systems comprising focal 
segments have already been proposed, in particular in the construction of 
motor vehicle headlamps. But these focal segments are most frequently 
axial and not transverse. Indeed, in the case where they are transverse, 
they never use the fundamental property of the mirror for recovering flux, 
which is to create a line of foci and to use this "line of light" as a 
special source of a second optical system capable of rectifying all the 
light rays perfectly. Thus, within the knowledge of the Applicant, it has 
never been proposed to use the combination of systems whereof the focal 
segments coincide with the above mentioned separation of the functions. 
As will be seen hereafter, the constitution of the two optical systems may 
be effected in various ways. 
For a general explanation of the invention, it is sufficient to state that 
the focal segment which is common to the two systems may be vertical, or 
equally well horizontal; similarly, it may be real or virtual for one 
and/or the other of the systems. 
In addition to the features and advantages described above, which are 
fundamental, the new structure of headlamp according to the invention, 
owing to the fact that it comprises two optical systems, is suitable for 
various topological arrangements. 
In fact, as will be seen more completely hereafter, whereas the system for 
rectifying images has its optical axis in the direction of emission, 
merging with the axis of the motor vehicle, the system for recovering flux 
may have various arrangements: it may itself be located in the axis of 
emission; it may be located laterally on the side of the body-work of the 
vehicle with its transverse optical axis; it may be located on the lower 
part of the bodywork of the vehicle with its vertical optical axis. This 
gives rise to various possibilities of implantation on the bodywork of a 
motor vehicle.

Before undertaking a systematic explanation of the invention, we shall 
firstly define the various optical elements which may be used for the 
constitution of the optical system for recovering flux and the optical 
system for rectifying images according to the invention. 
A paraboloid of revolution--symbol A--is understood to mean a mirror 
whereof the reflecting surface is obtained by the rotation of a parabola 
about its focal axis. A reflecting surface of this type comprises a real 
focus, the light rays emanating from the focus being reflected parallel to 
the axis of the paraboloid. 
An elliptical paraboloid of the first type--symbol B--is understood to mean 
a reflecting surface comprising a real horizontal focal segment (FIGS. 1a 
to 1d illustrate such a surface). In order words, the light rays, 
emanating from a substantially pinhole source, are reflected as a beam of 
rays which all converge towards the focal segment SF, whilst all being 
parallel to the direction of planes perpendicular to the focal segment. If 
one wishes to define such a surface mathematically in a trirectangular 
trihedron (XYZ, in which the axis Z is vertical, the axis Y transverse and 
the axis X longitudinal, a surface of this type is defined by the 
following equation: 
EQU [x.sup.2 +2cy+k.sup.2.sub.o -c.sup.2 ].sup.2 =4 k.sup.2.sub.o (x.sup.2 
+y.sup.2 +z.sup.2), 
k.sub.o and c being characteristic constants of the mirror. 
It can be shown easily that the vertical meridian B.sub.x of such a surface 
is an ellipse, whereas the horizontal meridian B.sub.z is a parabola. 
The term elliptical paraboloid of the second type--symbol B'--is understood 
to mean a reflecting surface identical to the former, but whereof the real 
focal segment is on this occasion vertical (the preceding surface has been 
turned through a quarter of a revolution). The term hyperbolic 
paraboloid--symbol C--is understood to mean a reflecting surface having a 
vertical and virtual focal segment (FIGS. 2a to 2d). This means that the 
light rays emitted by a substantially pinhole source and reflected by a 
surface of this type constitute a beam whereof all the rays seem to come 
from the focal segment SF, whilst being parallel to the direction of a 
plane perpendicular to the focal segment, i.e. to the horizontal plane. If 
this is to be defined as previously, in a trirectangular trihedron XYZ, a 
surface of this type is generally of the equation: 
EQU (z.sup.2 -2cy+k.sup.2.sub.o -c.sup.2).sup.2 =4 k.sup.2.sub.o (x.sup.2 
+y.sup.2 +z.sup.2) 
k.sub.o and c being characteristic constants of the mirror. 
It can be shown easily that the horizontal meridian D.sub.z of such a 
surface is a hyperbola, whereas the vertical meridian D.sub.x is a 
parabola. 
The term divergent cone--symbol D--is understood to mean a reflecting 
surface having the geometric shape of a cone of revolution and which is 
struck from the outside by the light rays. 
A convergent cone--symbol E--is understood to mean a reflecting surface 
having the geometric shape of a cone of revolution and which is struck 
from the inside by the light rays. 
A cylindrical mirror having a divergent parabolic profile--symbol F--is 
understood to mean a reflecting surface defined geometrically as a 
cylinder whereof the directrix is parabolic and whereof the convexity is 
directed towards the light source. 
A cylindrical mirror having a convergent parabolic profile--symbol G-- is 
understood to mean a reflecting surface defined geometrically as a 
cylinder, whereof the directrix is a parabola and which turns its 
concavity towards the light source. 
It is also known that a plane mirror inclined at an angle of 
45.degree.--symbol H--with respect to incident light rays, deflects them 
by a right angle. Furthermore, a man skilled in the art knows without 
hesitating what is a convergent cylindrical lens--I--, a divergent 
cylindrical lens--J--and a convergent Fresnel lens--also bearing the 
reference I--or a divergent Fresnel lens--J. Finally, the reference K will 
designate the aforesaid headlamp closing glass of known type. 
Since the basic optical elements which have been used in the systems of the 
invention have thus been defined and designated by symbols, various 
embodiments of the invention will be described in succession. 
FIG. 3 shows the basic structure according to the invention. 
It is a question of obtaining from a substantially pinhole light source 10, 
which is for example the filament of a bulb, a beam of controlled 
directivity and this is through an outlet window 300 of elongated 
rectangular shape, as illustrated. 
According to the invention, a system for recovering flux 100 comprising a 
horizontal focal segment SF is used in cooperation with the light source 
10. This system for recovering flux is an elliptical paraboloid of the 
first said type (B). Its surface envelopes the light source 10 over a 
large solid angle, so that the essential portion of the flux emanating 
from the source is recovered by the elliptical parabolic mirror B. The 
beam which it reflects is constituted by rays which all converge on the 
focal segment SF, whilst all being parallel to the direction of a plane 
perpendicular to SF. The light rays are then picked up by an optical 
system 200 for rectifying images, which gives them their desired 
directivity, by returning them to infinity if a main beam is desired and 
by returning them with a slight convergence if a less directive beam is 
desired. The system for rectifying images also has a focal segment 
coinciding with SF. 
When one wishes to obtain an exactly directive beam, for example a main 
beam, the system 300 is advantageously a convergent cone (E), whereof the 
axis of revolution coincides with the focal segment SF, the half-angle at 
the vertex of the cone being 45.degree.. 
The equation of such a cone, illustrated in FIG. 4, is of the type: 
EQU y.sup.2 +z.sup.2 -(x+k.sub.o).sup.2 =o 
small k.sub.o being a constant dependent on the geometry of the apparatus. 
From the optical point of view, it can be noted that a cone of this type is 
the equivalent of the association of a plane mirror inclined by 45.degree. 
with respect to the X-axis and perpendicular to the plane XY, with a 
cylindrical lens. 
If one now wishes to obtain a dipped beam, i.e. a slightly convergent beam, 
it is possible to preserve the preceding elements, whilst moving the light 
source 10 slightly on the axis of the elliptical paraboloid 100. A 
movement of this type will cause a vertical convergence of the beam 
reflected by the elliptical paraboloid and vertical spreading-out of the 
beam reflected by the cone. It is thus sufficient to provide the window 
300 with a closing glass K causing lateral spreading-out of the beam, in 
order to obtain the desired spreading in all directions. 
Another more rigorous solution consists of producing the system 200 in the 
form of an elliptical paraboloid of the first type (B) naturally having 
different parameters to those of the system 100. 
It is important to note that the beam which has been defined has its 
contour geometrically determined by the parameters of the first elliptical 
paraboloid 100. In fact it is a question of a pseudo-ellipse (shown in 
dotted line in FIG. 3), which is inscribed in the window 300. In all the 
previously described cases, the system 200 for recovering flux is limited 
by two horizontal parallel planes and two vertical parallel planes. 
It should be noted here that optical equivalents exist and that the 
aforesaid functions can be accomplished with other elements. Thus, an 
elliptical paraboloid of the first type (B) is equivalent to the 
association of a parabolic mirror (A) and of a convergent cylindrical lens 
(I). Similarly, the previously defined cone (respectively D or E) is 
equivalent to the association of a plane mirror inclined through 
45.degree. (H) and a cylindrical lens (respectively divergent (J) or 
convergent (I)) focussed on the focal segment SF. By virtue of these 
equivalences, it is possible to define other embodiments, always 
comprising a system for recovering flux and a system for rectifying 
images, both having a focal segment SF. 
FIG. 5 shows an equivalent solution of this type, all the optical elements 
having the same optical axis, which is the axis of the headlamp. The 
system 100 for recovering flux is constituted by the association of a 
parabolic mirror A and of a convergent cylindrical lens I, whereas the 
system 200 for rectifying images is constituted by a convergent 
cylindrical lens I. In this respect, it should be noted that a movement of 
this convergent lens I in the direction S perpendicular to the optical 
axis XX' allows an adjustment of the inclination in height of the light 
rays, i.e. an adjustment of the "masking". 
In FIG. 6, the system for recovering flux is as has been described, but the 
system for rectifying images is on this occasion constituted by a 
divergent Fresnel lens J having S-F as a virtual focus. Here too, this 
lens may serve for adjusting masking. 
The various solutions which can be achieved with a system for recovering 
flux constituted by an elliptical paraboloid of the first type are 
illustrated in FIGS. 7 to 16 with the previously mentioned symbolism. In 
addition to the in-line arrangements (FIGS. 7, 8), it is possible to use 
arrangements in which the axis of the system for recovering flux is 
perpendicular to the axis of emission, either below (recovery of flux at 
the bottom of the bodywork, see FIGS. 13 to 16), or from the side (flux 
recovery means located laterally, see FIGS. 9 to 12). FIGS. 7a to 16a are 
equivalent solutions to those of FIGS. 7 to 16, in which the elliptical 
paraboloid (B) is replaced by the combination of a paraboloid of 
revolution (A) and a convergent lens (I). 
Hitherto, embodiments have been described using a real focal segment for a 
flux recovery system constituted by an elliptical paraboloid of the first 
type (B) i.e. with a horizontal axis. A second type of construction, which 
will now be described, uses an elliptical paraboloid of the second type 
(B'), i.e. a vertical focal segment. FIG. 17 illustrates such an 
arrangement. In this case, since the focal segment SF, defined as 
previously, is vertical, the system for rectifying images is constituted, 
as illustrated, by a convergent cylindrical lens (I) having a vertical 
axis, 250. This lens has a focal line coinciding with SF. A distribution 
glass may be used to give the beam any desired diffusion. 
By utilizing optical equivalents within the knowledge of a man skilled in 
the art, other equivalent constructions may also be provided. FIGS. 18 to 
20 illustrate different variations, the letters being used with the 
symbolism mentioned at the beginning of this description. FIGS. 18a to 20a 
are the counterparts to FIGS. 18 to 20, the elliptical paraboloid (B') for 
recovering flux being replaced by the combination of a paraboloid of 
revolution (A) and a convergent lens (I). 
Hitherto, the cooperation of a flux recovery system and of a system for 
rectifying images having the same focal segment has been explained, this 
focal segment being real for the flux recovery system. 
In a third major type of construction, it is possible to use a flux 
recovery system having a virtual focal segment, since this is constructed 
in the form of a hyperbolic paraboloid (C), or of all these optical 
equivalents. FIGS. 21 to 23 and 21a to 23a illustrate these arrangements, 
with the symbolism of letters explained previously. 
One embodiment of the invention will now be described with reference to 
FIGS. 24 (axial section) and 25 (perspective). In this case, as shown, the 
flux recovery system is a hyperbolic paraboloid mirror (C) having a 
vertical virtual focus, which has the following charcteristics: 
opening: l.sub.1 =310 mm, 
height: h.sub.1 =95 mm, 
depth: l.sub.2 =150 mm, 
diameter of the hole in the base: d.sub.1 = 40 mm, 
focus: 18 mm.sub.2, 
constant k.sub.o : 151 mm.sup.2, 
constant c: 187 mm. 
In turn, the system for rectifying images is a cylindrical Fresnel lens (I) 
located in front of the hyperbolic paraboloid mirror and having the 
following characteristics: 
opening: l.sub.3 =l.sub.1 =310 mm, 
height: h.sub.3 =h.sub.1 =95 mm, 
focus: 319 mm, 
pitch of the prisms: e.sub.1 =3 mm. 
If one wishes to reduce losses due to clearances, it is possible to 
orientate the prisms towards the outside of the mirror and not towards the 
inside as shown in FIG. 25. 
FIG. 24 shows the path of the pencils of light coming from the filaments of 
a bulb constituting the light source 10. FIG. 25 illustrates the numerical 
parameters used. 
A prototype constructed according to FIGS. 24 and 25 was completely 
satisfactory, with a very good recovery of the flux emitted by the bulb 
and excellent directivity, even when the opening window had a width more 
than three times greater than its height. 
FIGS. 26a, 26b, 26c illustrate a fourth major type of construction, in 
three diagrammatic views, in which the flux recovery system 100 is an 
elliptical paraboloid (B') of the second type defined previously, 
orientated such that its axis of symmetry is directed vertically. 
This elliptical paraboloid B' forming the flux recovery means generates a 
focal segment SF which is in its optical axis. The image rectifying means 
200 are a convergent cone (E) with a half-angle at the vertex of 
45.degree. and having its axis along SF. 
FIGS. 27 to 30 and 27a to 30a illustrate eight variations of the fourth 
type of construction. 
Naturally, the invention is not limited to the embodiments described, but 
extends to all variations in accordance with its spirit, which is the 
association of two systems having the same focal segment, one for the 
recovery of the flux, the other for rectifying images, i.e. a correction 
of the divergence of the rays of the first system in order to give the 
beam finally emitted the suitable directivity. It seems important to 
stress the fact that an association of this type appears novel, although 
mirrors comprising a focal segment, used separately as the main element of 
headlamps have already been proposed, for example in French Pat. No. 1 039 
135. 
Any group of symbolic letters appearing in a figure is there to define a 
particular combination which forms an integral part of the invention.