EP0206908B1 - Motor vehicle headlight with a dipped beam - Google Patents

Description

The present invention relates to automobile headlights, headlights capable of emitting either a long-range light beam, for example a driving beam, or a cut beam, for example a passing beam.

Road / dipped automobile headlamps have already been proposed comprising a simple light source (filament) cooperating with movable blackout shutters. Such a system is for example described in French patent FR-A-1 296 036. It is unreliable, too sensitive to vibrations, too slow to switch, and has not given rise to industrial achievements.

In the most common automotive technique, the headlamps / dipped headlights comprise a parabolic reflector and a double light source constituted by two tungsten filaments. For road lighting, one of the filaments cooperates with the entire reflector. For the low beam lighting, a blackout screen or a blackout cup cuts off the light rays emitted by the second filament and arriving on the reflector, which returns them in the form of a cut low beam. In such a solution, known and used for a long time, the transition from the crossing lighting state to the road lighting state takes place by switching the electrical supply of the filaments.

The evolution of automotive technology suggests that such lamps with two tungsten filaments will probably be replaced by gas discharge lamps or arc lamps, the light source thus produced being much brighter than that obtained by filaments of tungsten. This high gloss is interesting, because it will allow the use of smaller headlights, and in particular of lower height which will integrate much more easily with the aerodynamic lines of a vehicle.

However, such new light sources require for each of them a high voltage electrical supply putting in series with the source a ballast of relatively high cost. In addition, the transition from one state of illumination to another must be done as quickly as possible, and the gas discharge or arc light sources have ignition times too long to allow switching fast enough.

The production of passive liquid crystal screens of all types is known in the art in the field of digital display. See for example the review LA RECHERCHE, Volume 12, n ° 125, September 1981, pages 936 - 939.

It has also been proposed to use such screens to produce light intensity modulations in automotive headlights (patent GB-A-1,451,066).

The present invention generally proposes to produce a beam cut projector eliminating the drawbacks of previous projectors, and making it possible to reach, by static means, insensitive to vibrations, extremely rapid beam variations, under the action of a command. electric. Consequently, the invention allows a particularly advantageous implementation of the aforementioned new light sources.

More specifically, the subject of the invention is an automobile headlamp of the type comprising at least one reflector cooperating with a single light source, a screen comprising liquid crystals with variable transparency, interposed on the path of the light rays, characterized in that the screen comprises at least one occultation zone to which the liquid crystals confer either a state of transparency or a state of non-transparency, and in that this zone comprises a limit which defines a cut-off limit for the light beam emitted by the projector.

It is easy to understand that, in the state of transparency, everything takes place substantially as if no obstacle were interposed on the path of the light rays, while, in the state of non-transparency, the occultation zone achieves the desired cut-off of the light beam.

The switching of the liquid crystal zone is preferably obtained by a variation in electrical voltage, this zone being produced in the manner known per se for producing passive screens in the field of digital display.

In the simplest embodiment, the screen has a single occultation zone made of liquid crystals. It consists, in a preferred example, of two transparent glass slides between which are arranged nematic liquid crystals in a helix in correspondence with the occultation zone. On the outside of the glass slides, two crossed light polarizers are arranged. Inside each blade, on the crystal side, are arranged ultra-thin transparent metallic layers or bands forming electrodes. As is well known to the specialist in liquid crystals, the application or non-application of an electrical voltage to the electrodes results in a variation in torsion of the liquid crystals, so that the assembly may or may not be crossed by the light. The transmission factor of such a system is not 100% but it remains sufficient for automotive lighting, especially when using light sources such as gas discharge lamps or arc lamps.

According to another characteristic of the invention, there is produced, by appropriately distributing various excitation electrodes according to various regions to be obscured, a modulation of the limit of the occultation zone, constituting the beam cut-off limit. For example, by using a plurality of electrodes in juxtaposed horizontal bands, it is possible to adjust the height of the occultation zone, depending on the electrodes finally excited on each of the two aforementioned plates.

It is also possible, according to another characteristic of the invention, to produce a screening screen comprising discontinuities, if it is desired to obtain, on the cut beam, a contribution of light above the cut-off. One can thus modulate by electrical means both the cut-off limit and the cut-off intensity.

• - celles comportant un réflecteur de type parabolique, la source lumineuse étant voisine de son foyer,
• - celles comportant un réflecteur elliptique, la source lumineuse étant au voisinage de l'un des foyers de ce réflecteur elliptique, les rayons lumineux émis par la source étant renvoyés par le réflecteur elliptique à son second foyer, et repris soit par une lentillé, soit par un réflecteur parabolique.

The invention is capable of application in numerous optical structures of projectors, and in particular, but not exclusively:

• - those comprising a reflector of the parabolic type, the light source being close to its focus,
• - those comprising an elliptical reflector, the light source being in the vicinity of one of the focal points of this elliptical reflector, the light rays emitted by the source being returned by the elliptical reflector to its second focal point, and taken up either by a lens, or by a parabolic reflector.

The field of beam cut projectors using very bright sources and high light fluxes is very specific; in such projectors, significant heating is inevitable. However, the tests conducted by the Applicant have shown the "feasibility" of the new projectors according to the invention. To avoid overheating problems, the screens according to the invention can be placed judiciously in the projector by moving it away from the light source. Thus, in the extreme, the liquid crystal screen merges with the exit lens of the projector. According to another arrangement preventing overheating, the glass plates of the screen are oversized; especially in thickness (compared to usual screens), to increase its heat dissipation capacities.

• - les figures 1 et 2 représentent schématiquement en perspective et en coupe verticale la réalisation d'un projecteur route/croisement selon l'invention dans un premier mode de réalisation utilisant un réflecteur elliptique et une lentille, la figure 2a montrant le détail de l'écran utilisé;
• - les figures 3 et 4 représentent en perspective et en coupe verticale schématique un projecteur route/croisement dans un second mode de réalisation de l'invention comportant un réflecteur parabolique;
• - les figures 5 et 6 représentent en perspective et en coupe horizontale la constitution d'un projecteur route/croisement selon un troisième mode de réalisation de l'invention comportant des réflecteurs elliptiques et des réflecteurs paraboliques; la figure 6a montre un détail de réalisation d'un organe des figures 5 et 6; les figures 7 et 8 représentent les éclairages obtenus sur la route dans les deux régimes d'éclairement de ce projecteur;
• - les figures 9 et 10 représentent schématiquement en perspective et en coupe verticale un projecteur route/croisement, selon un quatrième mode de réalisation de l'invention, la figure 11 représentant une vue de face schématique de ce projecteur et la figure 12 représentant l'éclairement obtenu sur un écran.

Other characteristics and advantages of the invention will emerge from the description which follows, with reference to the accompanying drawings, giving several examples of embodiment of the invention. More specifically, in the accompanying drawings:

• - Figures 1 and 2 schematically show in perspective and in vertical section the embodiment of a headlamp / crossing according to the invention in a first embodiment using an elliptical reflector and a lens, Figure 2a showing the detail of screen used;
• - Figures 3 and 4 show in perspective and in schematic vertical section a road / crossing projector in a second embodiment of the invention comprising a parabolic reflector;
• - Figures 5 and 6 show in perspective and in horizontal section the constitution of a headlamp / crossing according to a third embodiment of the invention comprising elliptical reflectors and parabolic reflectors; Figure 6a shows a detail of an organ of Figures 5 and 6; Figures 7 and 8 show the lights obtained on the road in the two lighting regimes of this projector;
• - Figures 9 and 10 schematically show in perspective and in vertical section a road / crossing projector, according to a fourth embodiment of the invention, Figure 11 showing a schematic front view of this projector and Figure 12 showing the illuminance obtained on a screen.

With reference to FIGS. 1 and 2, the first embodiment of the invention will be described.

From the point of view of its optical structure, the projector of this first embodiment comprises an elliptical reflector 10, a light source 11 disposed in the vicinity of its internal focus 12, the light rays emitted by the source returned by the elliptical reflector 10 converging in the vicinity of the external focus 13. The converging-diverging reflected rays are taken up by a lens 14 to finally constitute a useful emitted beam.

According to the invention, in order to make the cut-off, a liquid crystal screen 15 of the aforementioned type is defined in the vicinity of the external focal point 13 of the elliptical reflector 10 defining a concealment zone Z defined between two glass plates comprising liquid crystals.

In a typical example, the screen 15 comprises two parallel glass blades assembled in leaktight manner and between which are arranged "nematic helical" liquid crystals. Figure 2a shows such a glass slide 15a. On the two internal faces of the two parallel glass plates 15a are arranged electrodes 15b in very thin transparent layers (indium or tin oxide). By chemical etching, the configuration of the electrode layer located in front is given the configuration corresponding to the concealment of zone Z. For example, the electrodes are arranged in strips 15c. Between the plates a few tens of microns apart, the liquid crystal molecules are oriented in a quarter helix (twisted structure). On the two outer faces of the glass plates are arranged crossed polarizers 15d. When such a screen is illuminated 15, the light polarized by the first polarizer of the first glass plate undergoes a rotation of 90 ° between the two plates due to the helical configuration of the liquid crystals and leaves at the rear polarized perpendicularly to its direction of entry, the second polarizer of the second plate letting it exit. There is transparency.

If an electric field is applied between the electrodes 15c of the screen 15 via the terminals 15e, a deformation of the liquid crystals is caused, the molecules are oriented parallel to the direction of the field. They therefore become perpendicular to the two glass plates 15a. The polarized light at the entrance is no longer rotated 90 ° by the liquid crystals. It is stopped by the output polarizer 15d. There is opacity.

It can be seen in Figure 1 that zone Z is provided with a limit corresponding simply to the requirements of the passing light (concealment of zone 17 on a protective screen 18). Depending on the state of excitation of the electrical terminals 15e, the light rays are or are not obscured by the screen 15. The headlamp can emit either a driving beam or a passing beam.

The input electrodes can be arranged in parallel horizontal bands such as 15c which can be variably excited. Thus, the height, and more generally the configuration of the cut-off zone Z can be adjusted by varying the cut-off limit.

Likewise, completely transparent and always transparent zones can be provided between electrodes 15c, if one wishes to have light above the cut-off.

We will now describe the second embodiment of the invention with reference to FIGS. 3 and 4.

The projector of this second embodiment comprises a main parabolic reflector 20 having a focus 21 on its optical axis constituting the optical axis 22 of the protector. A light source 23, constituted for example by a filament or an electric arc, is situated slightly in front of the hearth 21, its rear part coinciding with this hearth. As can be seen in the figure, the rays emitted by the light source and returned by the reflector are therefore slightly convergent. In front of the reflector is arranged a closing glass 24 provided with beam distribution streaks, in a manner known per se.

Between the reflector and the glass is disposed a liquid crystal screen 25 according to the invention having a structure similar to that which has just been described, with two electrical control terminals 25e. When no potential difference is applied to these terminals 25e, the light rays, such as β, which pass above the horizontal, freely cross the screen and come to refract in the glass 24 thus ensuring a beam complementary to that created by rays such as a which, them, always freely cross the upper part of the glass 24.

Thus, when no voltage is applied to the terminals 25e, the headlamp emits a beam corresponding to all of the rays reflected by the reflector and refracted by all of the glass 24. A beam of beam is thus obtained.

When a potential difference is applied across the electrodes 25e, the liquid crystals orient themselves and make the screen 25 opaque. The rays such as are now stopped by the opaque zone Z of the screen, and only the convergent and therefore non-dazzling rays such as a pass freely through the upper part of the glass 24 which ensures the light distribution. This gives a passing beam.

The example of FIGS. 3 and 4 thus shows, in a very simple optical configuration, the intervention of a liquid crystal screen 25 according to the invention to achieve, depending on the state of excitation of the screen, two regimes of illumination. It will be noted that it is a static electrically controlled system using only one light source, which obviously makes it much superior both to the systems of the prior art using mobile screens and to the systems using two light sources, and in any case much less expensive than systems using two discharge sources.

We will now describe, with reference to FIGS. 5 to 8, a third embodiment of the invention.

The projector of Figures 5 and 6 comprises two substantially elliptical reflectors 30a, 30b, arranged symmetrically with respect to a central vertical plane. These two reflectors 30a, 30b have a common internal focal point 31 and each an external focal point (32a, 32b), the two external focal points (32a, 32b) of the two elliptical reflectors also being symmetrical with respect to a central plane. The light source 33 which can for example be a tungsten filament, an electric arc, a discharge lamp, is arranged at the common focus 31 of the two reflectors (30a, 30b), so that, as shown, the rays coming from the light source and returned to the left and right by the two elliptical reflectors come to converge on the focal points (32a, 32b).

Outside the two elliptical reflectors, and always symmetrically with respect to a central vertical plane, are arranged two parabolic reflectors (34a, 34b) whose respective focal points are merged with the external focal points (32a, 32b) of the elliptical reflectors (30a , 30b). The overall arrangement is such that the light rays coming from the source 33 returned by the elliptical reflectors (30a, 30b) come to converge at their external focal points (32a, 32b), meet the parabolic reflectors (34a, 34b) and are finally returned in substantially parallel beams in the emission direction E.

In the vicinity of the focal point 32b is arranged vertically an opaque screen of the conventional type 35, which obscures the rising rays and here gives a beam cut horizontally of the passing beam type obtained by reflection on the reflectors 30b and 34b giving an illumination of the type represented on the Figure 7 (the opaque screen 35 is shown from the front fig. 6b).

On the contrary, the associated reflectors 30a and 34a do not have a cut-off device. They therefore give a complete beam illuminating the entire perspective of the road and which therefore overlap the lower part of the beam given by the reflectors 30b and 34b, as seen in FIG. 8.

With the above-defined device, there are thus crossing illumination means, and route illumination means.

According to the invention, there is associated with the reflectors 30a and 34a and over the entire exit light window a screen 36 containing liquid crystals constituted as indicated above. When this screen 36 is not subjected to an activation voltage of the crystals at its terminals 36e, the rays such as Ra pass freely through said screen and the whole of the road perspective is illuminated as in FIG. 8. route function. When an electrical voltage is applied to the screen 36, it becomes opaque and obscures the rays Ra. Only the rays Rb emitted by the subassembly (30b, 34b), that is to say rays of crossing light are emitted (Fig. 7).

Here again, as previously, static switching by electrical means is carried out with a single light source. As a variant, the sub-assembly (30a, 34a) can be equipped with a permanent screen to conceal the rays of the crossing type permanently since the other sub-assembly (30b, 34b) always emits enough of them.

In a fourth embodiment, corresponding to FIGS. 9 to 12, a projector is produced comprising a parabolic upper half-reflector 40 of focus 41. The light source 42 constituted by an axial filament is slightly in front of this focus 41. This half -reflector 40 gives descending rays such as β _o . and gives on a screen (FIG. 12) a projection 43, the upper part of which is substantially horizontal, therefore not dazzling. The upper half-reflector 40 is associated with a lower parabolic half-reflector 50 whose focal point 51 is located in the middle of the source 42. This lower half-reflector therefore gives a beam of rays such as a _o whose projection on a screen ( figure 12) gives an image such as 53.

The association of these two beams given by the same source 42 can give, after optical correction by a closing glass (not shown), a good driving beam. To make the blackout necessary for obtaining a passing beam, there are (FIGS. 9 and 11) around the source two liquid crystal screens 45 as defined above, arranged in V below the source 42.

When these screens 45 are in their state of transparency, the rays such as α¿. Emitted by the source 42 can pass through them easily to come to be reflected on the reflector 50 and to rise above the horizontal plane to form the hatched area 53 ( figure 12).

In the case where it is desired to switch to a passing beam, it suffices to apply the appropriate excitation voltage to the liquid crystal screens 45 to make them opaque. At this time, all the rays such as a _o are stopped, the hatched area on the screen is therefore no longer lit. Only area 43 remains and the lower part of area 53 located above the horizontal. The cut beam then constitutes a passing beam. It will be noted that this fourth embodiment, which has just been described, represents the transposition, in a system of liquid crystal screens of the system with movable shutters described in French patent FR-A-1 296 036 given here as for reference and further information. This reference also makes it possible to understand all the advantages of the static electrically controlled system according to the invention which has the advantage of being faster, more reliable and insensitive to vibrations.

The four embodiments given above are not limiting. They all have the advantage of allowing the realization of a projector with two lighting regimes comprising static electrically controlled systems.

They show that the invention applies to the most diverse optical structures, as to the nature of the optical elements used, in particular reflectors.

The production of a liquid crystal screen was given in a technological embodiment known to the Applicant. Of course, this embodiment is only an example, and other liquid crystal screens can be used without departing from the scope of the invention.

Finally, it should be understood that the invention applies to any switchable beam cut projector. It is possible, for example, to produce a dipped headlight whose illumination changes from "right-hand traffic" to "left-hand traffic" mode.

It is also possible to subject the cut-off limit to any leading phenomenon, for example the attitude of the vehicle.

Claims (7)

1. An automobile headlamp of the kind comprising at least one reflector (10; 20; 30a - 30b - 34a; 40 - 50) cooperating with a single light source (11; 23; 33; 42), a screen (15; 25; 36; 45) containing liquid crystals of variable transparency, interposed in the path of the light rays, characterised in that the screen comprises at least one masking zone (Z) to which the liquid crystals give either a state of transparency or a state of non-transparency, and in that the said zone (Z) has a limit which defines a cut-off limit for the light beam emitted by the headlamp.

2. A headlamp according to Claim 1, characterised in that the cut-off screen (15; 25; 36; 45) is of the kind comprising, from the outside to the inside, two polarisers, two layers of glass, two transparent thin layers constituting electrodes, at least one of which has a surface defining the configuration of the masking zone, and a central charge of liquid crystals arranged as a helix.

3. A headlamp according to one of Claims 1 and 2, characterised in that the electrode and the masking zone (Z) of the screen (15) are arranged in horizontal bands (15c).

5. A headlamp according to one of Claims 1 to 3, characterised by a parabolic reflector (20) cooperating with a light source (11) slightly in front of the focus of the reflector, and a cut-off screen (25) interposed in the path of the light rays reflected by the reflector (20).

6. A headlamp according to one of Claims 1 to 3, characterised by an elliptical reflector (10) having a light source (11) in the vicinity of its internal focus (12), and a liquid crystal screen (15) in the vicinity of its external focus (13).

6. A headlamp according to one of Claims 1 to 3, characterised by a single light source (33) cooperating with two groups of elliptical reflectors (30a, 30b) associated with two parabolic reflectors (34a, 34b), one of the said groups (30b, 34b) including a means (35) for chopping the beam, and the other (30a, 34a), a liquid crystal screen (36) disposed in the aperture through which light is emitted.

7. A headlamp according to one of Claims 1 to 3, characterised in that it includes a light source (42) cooperating with at least one reflector (40, 50), and at least one liquid crystal screen (45) interposed between the source and the reflector.

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