EP0247936A1 - Dipped headlamp without a cap and having an offset concentration - Google Patents

Abstract

The invention relates to a projector for creating a passing beam located below a horizontal cut-off, of the type comprising an axial filament lamp (100) without a cup, a reflector (200) having a surface without discontinuity, and a lens. closure placed in front of the reflector and capable of distributing said beam in a horizontal direction. According to the invention, the reflector comprises two diametrically opposed first quadrants (201, 202), the surfaces of which approach at least approximately two portions of paraboloids whose foci are each located in the vicinity of a respective axial end of the filament ( 100), to generate images of the filament creating a light concentration located below the cut-off and laterally offset with respect to the axis of the projector, the other two quadrants (203, 204) being formed by surfaces ensuring the progressive transition and continues between the first two quadrants, creating images of the filament located mainly below the cutoff.

Description

The present invention relates to a dipped headlight for a motor vehicle, in which the light beam is located below a cut-off limit defined by two horizontal half-planes slightly offset in height relative to each other.

This type of cut, which is described in particular in French patent A-2 087 317, is very particularly suitable for a passing beam as imposed for example in the United States of America and defined by standard SAEJ 579 C.

To meet this standard, the profile of

the cutoff is defined approximately, on a standardized screen, by two horizontal half-straight lines situated on either side of the axis of the projector, the half-line on the right side being at the level of the horizon and the half-line on the left side being offset by about 1.5% below the horizontal. In addition, the region of maximum illumination imposed is shifted to the right relative to the axis of the projector.

The beams meeting these standards are most often obtained using a projector comprising a transverse filament lamp cooperating with a reflector or parabolic mirror of relatively high focal distance, so as to reduce the thickness of the beam and consequently minimize the excess thickness created by the deflecting prisms on the closing glazing.

Projectors have also been proposed comprising a lamp whose axial filament is focused in a parabolic reflector inclined downward to reduce the deviation required from the prisms of the closing glass, and consequently the extra thicknesses of the latter. French patent A-2,087,317 cited above gives examples of these two types of projectors.

But in both of the embodiments of this patent, it is necessary to use a reflector parabolic with a high focal length, of the order of 29 to 32 mm, therefore with little flow recovery.

To remedy this low light output, the Applicant has proposed, in its French patent application No. 85 06655 of June 7, 1985 for a "dipped headlight for a motor vehicle", a headlamp comprising a reflector of complex shape capable of forming images of the filament below a cut of general horizontal orientation, allowing the use of reduced focal distances, and consequently a much greater flux recovery. More specifically, such a projector comprises an axial filament lamp emitting freely all around it, a reflector having an axis extending below the axis of the filament parallel to it and comprising a surface without discontinuity, and a closing glass placed in front of the reflector and capable of distributing said beam in the horizontal direction. However, whatever the practical realization of this projector, it is necessary to tilt the mirror to the right, in order to obtain the spot of concentration shifted to the right required.

However, such an inclination to the right is generally not desirable, and in particular constitutes a significant obstacle to the production of projectors with bi-mirror reflector injected in one piece. Such a projector is shown diagrammatically, in horizontal section, in FIG. 1. It comprises a unitary reflector 10 comprising a first mirror 10a for the crossing function, the axis 12a of which is offset to the right (downwards in the figure) at an angle 6, and a second mirror 10b, integral with the first, whose axis 12b is located in the axis of the road.

The demolding of such a double mirror is hampered by the fact that the support flanges 13a and 13b of the dipped and road lamps 14a and 14b, which necessarily extend along the axes 12a and 12h above, do not demold according to the same release axis. It is therefore necessary to use, for the production of such a twin-mirror projector, a mold of particular design, in particular with drawers, more expensive and more difficult to implement.

Another disadvantage of the realization of the patent application indicated above resides in the fact that the inclination which must be given to the reflector of the dipped beam is a function of the focal distance used and the optical characteristics of the closing lens. More precisely, the reflector must be inclined laterally by an angle corresponding to the angular half-width of the images participating in the concentration; however, the width of these images depends on the size of the areas of the closing glass dedicated to concentration, as well as on the focal distance of the reflector, these parameters being a function of the dimensions allocated to the dipped headlight in the vehicle, and more generally of the specifications.

The current. The invention aims in particular to eliminate this demolding problem by proposing a dipped headlight which requires no tilting of its axis to the right in order to obtain the offset concentration spot. The filament, and therefore the lamp, therefore retain an orientation parallel to the axis of the track, and a twin-mirror projector incorporating such a crossing projector can be produced easily and at moderate cost, with a release of the two mirrors according to the same axis.

To this end, the dipped headlight according to the present invention is characterized in that the reflector comprises two first diametrically opposite quadrants, the surfaces of which approach at least approximately two portions of paraboloids, the foci of which are each located in the vicinity of a respective axial end of the filament, for generating images of the filament creating a light concentration situated below the cut and offset laterally with respect to the axis of the projector, the other two quadrants being constituted by surfaces ensuring the gradual transition and continues between the first two quadrants by creating images of the filament located mainly below the cut.

• - la figure 1 est une vue en coupe horizontale schématique d'un projecteur bi-miroir de la technique antérieure,
• - la figure 2 est une vue en coupe verticale longitudinale schématique d'un projecteur de croisement conforme à l'invention,
• - la figure 3 est une vue en coupe horizontale schématique du projecteur de la figure 2,
• - la figure 4 est une vue de dos schématique du projecteur des figures 2 et 3,
• - les figures 5 à 9 sont des courbes isocandéla sur écran obtenues avec le réflecteur du projecteur selon ladite première forme de réalisation, et
• - la figure 10 est une vue de face schématique d'une glace de fermeture préférée pour ce même projecteur.

The invention will be better understood on reading the following detailed description of preferred embodiments thereof, given by way of example and made with reference to the accompanying drawings, in which:

• FIG. 1 is a schematic horizontal section view of a bi-mirror projector of the prior art,
• FIG. 2 is a schematic longitudinal vertical section view of a dipped headlight according to the invention,
• FIG. 3 is a diagrammatic horizontal section view of the projector of FIG. 2,
• FIG. 4 is a schematic back view of the projector of FIGS. 2 and 3,
• FIGS. 5 to 9 are isocandela curves on screen obtained with the reflector of the projector according to said first embodiment, and
• - Figure 10 is a schematic front view of a preferred closing glass for the same projector.

The projector according to the invention, shown diagrammatically in FIGS. 2 to 4, comprises a lamp with an axial cylindrical filament 100 of length ℓ and of radius r, a reflector or mirror 200 and a distribution glass 300 closing the projector.

The axis of the filament 100 is not coincident with the axis Ox of the reflector, but is shifted upwards by a distance equal to its radius r. In this way, the lowest part of the emissive surface of the filament is tangent to said axis Ox.

The surface of the reflector is a surface without discontinuity, determined so that it forms images of the filament which are for the most part located below a horizontal plane and, as will be seen below, whose most point top is located on this horizontal plane or entirely in its vicinity. It is also determined so that the concentration spot obtained is shifted to the right (or to the left depending on the direction of traffic) relative to the axis of the road.

By "absence of discontinuity" is meant a second order continuity, that is to say that at any point on any line drawn on the surface, the tangent planes are the same on both sides of this line. The surface therefore shows no breakage. This arrangement makes it possible, in practice, to produce real surfaces having very good conformity with the theoretical surfaces, in particular avoiding the defects specific to certain mirrors of the prior art having offset paraboloids. In particular, such continuity makes the reflector perfectly stampable.

As shown in Figure 3, the reflector is divided into four zones or sectors 201 to 204, defined mathematically below, the above-mentioned continuity being ensured in particular at the interface between these sectors. The four sectors, separated from each other by the horizontal plane xOy and by the vertical plane xOz, each define a quadrant. However, in the description and the claims, the term quadrant will be used to denote any sector delimited by two planes, substantially horizontal and substantially vertical respectively.

The surfaces of quadrants 201 and 202 are designed to generate images of the filament which create a spot of concentration shifted downward and to the right with respect to the axis Ox.

The surfaces of the quadrants 203 and 204 are determined to ensure with the above-mentioned continuity the transition between the quadrants 201 and 202, and, on a functional level, to generate images of the filament all located in the vicinity of the axis of the projector, but mostly below the horizontal plane passing through its axis. In particular, the centers of all these images are located below this plane.

• - pour le quadrant 201 :
  
  soit un paraboloide de distance focale f₁ et dont le foyer F₁, comme le montre la figure 2, est situé approximativement à l'extrémité axiale arrière (la plus proche de l'origine 0 des coordonnées) du filament 100,
• - pour le quadrant 202 :
  
  soit encore un paraboloide,de distance focale f₂ et dont le foyer F₂ est situé approximativement à l'extrémité axiale avant (la plus éloignée de l'origine des coordonnées) du filament 100 ;
• - pour le quadrant 203 :
  
• - et pour le quadrant 204 :
  

The theoretical calculation shows that surfaces having the properties indicated above are, inter alia, those which answer the following equations, in the orthonormal coordinate system [o, x, y, z] as illustrated:

• - for quadrant 201:
  
  either a paraboloid with focal length f ₁ and whose focal point F ₁ , as shown in FIG. 2, is located approximately at the rear axial end (closest to the origin 0 of the coordinates) of the filament 100,
• - for quadrant 202:
  
  or again a paraboloid, of focal length f ₂ and whose focus F ₂ is located approximately at the front axial end (the furthest from the origin of the coordinates) of the filament 100;
• - for quadrant 203:
  
• - and for quadrant 204:
  

In these last two equations, Δf is equal to the difference f ₂ - f ₁ and is approximately equal to the length λ of the filament.

We can demonstrate, by a complex mathematical calculation that it seems superfluous to reproduce here, that the surfaces of quadrants 203 and 204 are supported at each of their ends on the parabolic traces of foci F ₁ and F ₂ of surfaces 201 and 202 , and they ensure the transition, with the second order continuity mentioned above, between one and the other.

Figures 5 to 8 are shown, by isocandela curves on screen C ₁ to C ₄ , the illuminations provided by the quadrants 201 to 204 of the reflector 200 of Figures 2 to 4 in the absence of closing glass. As indicated above, quadrant 201 produces a spot of concentration which is shifted downwards and to the right with respect to the reference center H of the screen (intersection of said screen with the axis Ox of the projector), in the same way as quadrant 202. This shifted concentration spot initiates, as we can observe, the right half-cut of the passing beam.

It is also observed in FIGS. 7 and 8 that the illuminations produced by the quadrants 203 and 204 prolong with good clarity the right half-cut already initiated by the zones 201 and 202.

The total light distribution, obtained by superimposing the illuminations represented in FIGS. 5 to 8, is represented in FIG. 9 by isocandela curves C _T on a projection screen.

FIG. 10 represents, in front view, a possible embodiment of a closing glass particularly well suited to the mirror 200 described above. It comprises thirteen zones 301 to 313 arranged as shown. The zones 301 and 313 are each, respectively, the homolog of a large part of the surface of the quadrants 203 and 204 of the mirror. These zones are non-deflecting, or very little deflecting, so as not to alter the formation of the right cut of the beam.

The central zones 306, 307 and 308 will be able to effect a strong horizontal deflection, in particular to give the beam the large width required.

The remaining areas of the glass 300 will be moderately deviating horizontally, in particular in order to increase the illumination on the left by initiating the corresponding half-cut and to further extend the right cut as initiated by the part of the beam crossing the areas 301 and 313.

As indicated above, the axis of the filament, and therefore of the lamp of this low beam projector, is strictly parallel to the axis of the road. It is easy in this way to associate the low beam headlamp with a headlamp in the form of a single block comprising a bi-mirror reflector. Indeed, the axis of the lamp of a road projector being preferably parallel to the axis of the road, the flanges of the two mirrors will therefore be strictly parallel, which allows the realization of the bi-mirror reflector by an operation particularly simple molding, without difficulty in demolding.

However, in an alternative embodiment not illustrated, it is possible to tilt the mirror downwards, the images thus offset being appropriately raised by prisms deviating from the closing glass. Such lifting prisms have draft surfaces which, unlike the normally used folding prisms, tend to deflect the light sharply downwards, which eliminates the drawback inherent in folding prisms, whose bodies are liable to '' generate rays of light dazzling the conductors coming opposite.

In the case where such a headlamp with an inclined axis is part of a dual-headlamp combined crossing-road, it is clear that, to maintain the advantage of demolding along two parallel axes, the axis of the road mirror must also be tilted down by the same angle. To compensate for this angular offset, which would normally result in a corresponding offset of the maximum light intensity zone of the driving beam, the filament of the driving lamp will be shifted downwards, perpendicular to the axis of its mirror, so as to note the said maximum intensity zone so that it is well located in the axis of the road. In this vertical compensation offset, the focal point / filament relationship in the axial direction remains unchanged, the center of the filament being directly above the focal point.

By way of example, it can be indicated that such a vertical offset will be of the order of 0.5 mm for a parabolic mirror having a focal distance of 22.5 mm.

• - pour le quadrant 201 :
  

• - pour le quadrant 202 :
  

• - pour le quadrant 203 :
  
  

According to an alternative embodiment of the invention, the mirror 200, still separated into four quadrants of roughly identical dimensions, can be defined by the following equations:

• - for quadrant 201:
  

• - for quadrant 202:
  

• - for quadrant 203:
  
  

In these equations,

^f ₁₄ and fI3 are focal distances corresponding to two distinct focal points located in the vicinity of the end of the filament closest to the origin of the coordinates, and f ₂₃ and f ₂₄ are focal distances corresponding to two distinct focal points located in the vicinity of the end of the filament furthest from the origin of the coordinates.

Each of the surfaces defined above ensures the continuous transition between the neighboring surfaces, continuity being also ensured at the interface between these surfaces two by two.

The surfaces as defined above, using four different focal lengths for the parabolic traces of interface between the four quadrants, allow a fine optimization of the position of the images of the filament between them and relative to the reference axis, this which gives greater flexibility for making the closing glass.

The general concepts of the invention can be implemented in reflectors of low height, thanks to the particularly high light output which is obtained. In particular, it will be possible thanks to the invention to produce projectors having a height not exceeding 70 mm, with the focal lengths f and f ₂ of the first embodiment, for example equal to 20 and 25 mm respectively.

Of course, the present invention is in no way limited to the embodiments described above. In particular, for left-hand traffic, a person skilled in the art will be able to carry out the necessary symmetries with respect to the indications in the description above.

Claims (6)

1. Low beam headlamp for a motor vehicle, capable of creating a low beam located below a cutout of generally horizontal orientation, of the type comprising an axial filament lamp (100) emitting freely all around it, a reflector (200) having an axis (Ox) extending below the axis of the filament (100) parallel to it and having a surface without discontinuity, and a closing glass (300) placed in front of the reflector and suitable distributing said beam in a horizontal direction, characterized in that the reflector has two diametrically opposite first quadrants (201, 202), the surfaces of which approach at least approximately two portions of paraboloids, the foci of which ( _F1 , _F2 ; F ₁₃ , F ₁₄ and F _{23 '} F) are each located in the vicinity of a respective axial end of the filament (100), to generate images of the filament creating a light concentration situated below the cut and offset laterally with respect to the axis of the projector, the other two quadrants (203, 204) being constituted by surfaces ensuring the gradual and continuous transition between the first two quadrants by creating images of the filament located mainly below the cut. 2. Projector according to claim 1, characterized in that the filament (100) is cylindrical and is shifted upwards by a distance equal to its radius (r) relative to the axis (Ox) of the reflector (200) . 3. Projector according to any one of claims 1 and 2, characterized in that the first two quadrants (201, 202) are paraboloids whose foci (F ₁ , F ₂ ) are respectively located at the two axial ends of the filament ( 100). 4. Projector according to claim 3, characterized in that the first two quadrants (201, 202) have surfaces defined respectively by the equations:

and the two second quadrants (203,204) have surfaces defined respectively by the equations:

and

where f ₁ and f ₂ are the distances between the top of the reflector and the focal points F ₁ and F ₂ , respectively, and Δ f is approximately equal to the length of the filament (100.) 5. Projector according to any one of claims 1 and 2, characterized in that the first two quadrants (201, 202) have surfaces defined respectively by the equations:

and

and the two second quadrants (203, 204) have surfaces defined by the equations:

and

where ^f ₁₄ and f ₂₃ are the distances between the top of the reflector (200) and the focal points F ₁₄ and F23, respectively, ^f ₁₃ and f ₂₄ are the distances between the top of the reflector (200) and the focal points F ₁₃ and F ₂₄ , respectively. 6. Projector according to any one of claims 1 to 5, characterized in that the closing glass (300) comprises two zones (301, 313) non-deflecting or slightly deviating which are respectively the counterparts of a large part of the surface of the two second quadrants (203, 204).

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