EP0258116B1 - Dipped and main beam headlamp with two transverse filaments for a motor vehicle - Google Patents

Description

The present invention relates to a headlight for a motor vehicle making it possible to fulfill the crossing illumination function and the road illumination function.

It relates more particularly to a headlamp in which the crossing light beam is located below a cut defined by two horizontal half-planes slightly offset in height relative to each other.

This type of cut, which is described in particular in patent FR-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 cutoff profile is defined approximately, on a standardized projection screen, by two horizontal half-lines located on either side of the projector axis, 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 approximately 1.5% below the horizon. In addition, the region or the maximum illumination (spot of concentration) must be shifted to the right relative to the axis of the projector.

Regarding the light beam of the road function, it must include a spot of concentration approximately centered on the axis of the road.

In the prior art, cross-beam headlamps of this type comprise for the most part a lamp with two horizontal filaments oriented transversely with respect to the axis of the headlamp and offset from each other in two directions perpendicular to the 'axis of the projector, namely laterally and vertically.

As regards the associated reflector, the current solution consists in providing a reflector in the form of a paraboloid of revolution, the focus of which is located at vertically above the two filaments, and halfway between them A beam is thus obtained, for the crossing function, located mainly below a horizontal cut, with a spot of concentration centered approximately on the axis of the road.

However, a non-negligible residual part of the bundle is located above this cut-off and makes it necessary to provide prisms or folding streaks of large thickness, and therefore this which leads to molding difficulties, in particular when the ice is made of glass; in addition, the spoils of these prisms are capable of creating parasitic light rays directed upwards and which may dazzle the conductors coming opposite.

Furthermore, the small thickness which it is desired to give to the beam in the vertical direction, before it passes through the closing glass, again in order to avoid providing on the closing glass streaks of vertical deflection with large thickness, leads to the use a relatively large parabolic reflector. However, the increase in the focal distance, for a reflector of determined contours, results in a notable reduction in the recovery of the light flux emitted by the filaments, that is to say a decrease in the light output.

The present invention aims to overcome the drawbacks of the prior art and to propose a cross-beam headlamp in which none, or essentially no vertical deflection of the light rays has to be effected by the closing glass, and in which the beam obtained meets the photometry conditions required in particular in the United States. Another object of the present invention is to obtain light beams of relatively small thickness before their passage through the closing glass, without however significantly reducing the light output of the projector.

To this end, the invention relates to a dipped-beam headlamp for a motor vehicle, of the type comprising a lamp provided with a dipped filament and a transverse horizontal road filament, the two filaments being offset one with respect to the other in two directions perpendicular to the axis of the headlamp, a reflector, the axis of which passes between the two filaments and a closing lens comprising elements for lateral deflection of the passing and driving beams, and arranged so that the beam crossing point is located below a generally horizontal orientation cut-out, characterized in that the surface of the reflector is a surface without discontinuity which in itself forms low-level images of the crossing filament and of the route filament such that the length of the images necessarily inclined with respect to the horizontal is shorter than that of the images slightly inclined with respect to the horizontal, t ous the points of the images of the crossing filament being moreover situated below the said horizontal cut, so that the glass is slightly deviating in the vertical direction.

• _ la figure 1 est une vue en perspective schéma­tique d'un projecteur code-route à deux filaments de la technique antérieure, dont on a retiré la glace de ferme­ture ;
• _ la figure 2 illustre, par deux ensembles de courbes isocandéla à l'infini, les éclairements de croise­ment et de route fournis par le projecteur de la figure 1 sans sa glace de fermeture ;
• _ la figure 3 est une vue en coupe horizontale schématique d'un projecteur croisement-route selon la pré­sente invention ;
• _ la figure 4 est une vue en coupe verticale lon­gitudinale du projecteur de la figure 3 ;
• _ la figure 5 est une vue de face du projecteur des figures 3 et 4, dépourvu de sa glace de fermeture ; et
• _ la figure 6 illustre, par deux ensembles de courbes isocandéla à l'infini, les éclairements de croi­sement et de route fournis par le projecteur des figures 3 à 5 sans sa glace de fermeture.

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:

• _ Figure 1 is a schematic perspective view of a highway code projector with two filaments of the prior art, from which the closing glass has been removed;
• _ Figure 2 illustrates, by two sets of curves isocandéla at infinity, the crossing and driving lights provided by the projector of Figure 1 without its closing glass;
• _ Figure 3 is a schematic horizontal sectional view of a dipped-beam headlamp according to the present invention;
• _ Figure 4 is a longitudinal vertical sectional view of the projector of Figure 3;
• _ Figure 5 is a front view of the projector of Figures 3 and 4, devoid of its closing glass; and
• _ Figure 6 illustrates, by two sets of isocandela curves at infinity, the crossing and driving lights provided by the projector of Figures 3 to 5 without its closing glass.

FIG. 1 represents a driving beam headlamp of the prior art, intended to selectively supply a passing beam and a driving beam in accordance with the regulations currently in force, in particular in the United States of America. It comprises a lamp comprising two filaments 1a and 1b which are arranged horizontally and transversely to the axis Ox of the projector. The crossing filament 1a is offset upwards with respect to the axis Ox by a distance h / 2 and offset laterally so that its free left end is located at a distance d / 2 from the vertical plane xOz passing by the Ox axis. Each filament has a length 2ℓ and the filaments 1a and 1b have respective diameters 0̸a and 0̸b. The road filament 1b is arranged symmetrically with the filament 1a with respect to the focal point F located on the axis Ox, the two filaments both extending in the same vertical transverse plane.

In a standard lamp known under the reference HB1, the parameters described above have the following numerical values:
h = 2.3 mm; d = 2.4 mm, 2ℓ = 5.0 mm; 0̸a = 1.2 mm; 0̸b = 1.4 mm.

The projector of the prior art furthermore comprises a reflector 2 which is constituted by a paraboloid of revolution whose focal point F occupies the position shown. Finally, although it has not been shown, the projector includes a closing glass.

In FIG. 2 are illustrated, by two series of isocandela curves at infinity, respectively Ca and Cb, the illuminations provided when the crossing and driving filaments are lit individually, these illuminations being determined in the absence of the ice closing.

As we can observe, the spot of concentration Ta of the passing beam is correctly forecasted below the cut hʹHh and offset laterally to the right relative to the axis of the road (in the case of traffic with right). However, and in particular to the right of the vertical axis vʹHv, there is a significant overflow of the passing beam above the right horizontal half-cut Hh. In practice, this will lead to the provision on the closing glass of prisms or drawdowns of large thickness, which is disadvantageous because the spoils of these very thick prisms lead to light anomalies in the form of parasitic rays emanating from the projector towards high and likely to dazzle drivers of vehicles coming in front.

In addition, the main beam, located mainly above the cut, must also be "worked" by the closing glass, in particular to effect a lateral distribution. In addition, its spot of concentration is located relatively above the horizon hʹHh, which also leads to a slight downturning of the rays.

The dipped-beam headlamp of the present invention, shown diagrammatically in FIGS. 3 to 5, comprises a lamp (not shown) provided with two filaments 10a and 10b whose mutual positions are as described above, that is to say that it is the same standard lamp HB1 which is used, a reflector 20 with apex O and axis Ox and a lens 30 closing the projector.

As can be observed, the filaments 10a and 10b no longer occupy symmetrical positions with respect to the axis Ox of the reflector 20, but the lamp is shifted vertically so that the axis of the crossing filament 10a is located at a distance h _a above the axis Ox and that the axis of the filament 10b is located at a distance h _b below the Ox axis, with h _a <h _b . If, for example, the HB1 lamp is used as described above, h _a - 0.9 mm and h _b = 1.4 mm will preferably be chosen. We note that the relation h _a + h _b = h = 2.3 mm is respected. The position of the lamp in the transverse direction is unchanged.

The filaments are arranged in a vertical plane so as to be located vertically above a point F _O located on the axis Ox. The distance from the vertex O of the reflector to this point F _o is denoted f _o . Of course, the position of the filaments may vary from the indications given above, without going beyond the ambit of the invention.

The surface of the reflector 20 is a surface without discontinuity, chosen so as to form images of the crossing filament 10a, all the points of which are located below a horizontal cut passing through the axis of the projector (denoted h'Hh on Figure 6). Advantageously, all of these images have their highest point situated on the cut, or in the very close vicinity thereof.

The surface of the reflector 20 is also determined so that the photometry imposed for the driving beam is satisfied in particular in height (the lateral deflection of a centrally concentrated beam does not pose great difficulties in practice).

By "absence of discontinuity" is meant continuity guaranteed at the first order at any point on the surface of the reflector, and at the second order at any point on the surface with the exception of two localized defects as explained below, manifested by very slight breaks in the curve. We can recall here that a second order continuity means that, at any point on any line drawn on the surface, the tangent planes are the same on both sides of this line. This means in practice the absence of breaks on the surface.

Such an arrangement makes it possible to produce real surfaces having very good conformity with the theoretical surfaces, whether by stamping or by injection molding.

avec
r  = rayon du filament de croisement,
ℓ  = demi-longueur du filament de croisement,
f_o = distance horizontale entre les centres des filaments et le plan yOz (soit l'abscisse du point F_o).The theoretical calculation shows that the surface defined by the following equation, in the orthonormal coordinate system (O, x, y, z) as illustrated in FIGS. 3 to 5, exhibits the stated properties:

with
r = radius of the crossing filament,
ℓ = half-length of the crossing filament,
f _o = horizontal distance between the centers of the filaments and the plane yOz (ie the abscissa of point F _o ).

et possède également les propriétés énoncées, avec toute­fois une qualité un peu plus approximative dans le résul­tat obtenu.Furthermore, if we consider the radius r of the crossing filament as very small, the above equation becomes, as a first approximation:

and also has the stated properties, with a somewhat more approximate quality in the result obtained.

These surfaces present in the xOy plane a parabolic trace of focal distance f _o , and "work" the images of the filament as will be seen in detail below.

Furthermore, it could be demonstrated that the surfaces defined mathematically above are continuous in second order, with the exception of two defects located in the vertical plane xOz, where continuity is only assured in first order. Thus, there remains in these regions a very slight bend, which can in practice be eliminated during the polishing steps usually included in the manufacturing processes of the reflectors. In addition, these localized faults do not generate substantially any anomaly in the beam obtained.

It could be demonstrated that the specific shape of the reflector 20 leads to a distribution of the images of the crossing filament 10a which is entirely appropriate. In particular, it appears that all the images of this filament have their highest point aligned with the half-line Hh, or located in the very close vicinity of the latter, so as to define the corresponding half-cut with high quality, and that, moreover, there is no image of the crossing filament which extends in a generally vertical direction with great height. More precisely, we could demonstrate that the images of the crossing filament, as they rotate around their center from the horizontal to the vertical (depending on the part of the reflector which returns them), see their length progressively reduced . Thus, the beam obtained, before it passes through the closing glass, advantageously has a small thickness:
not only the highest point of each image is located in the very close vicinity of the cut hhʹ, but also the lowest point of each image does not extend at great distance below this cut. This especially avoids lighting the road too close to the vehicle, which helped to make the large vertical images created by the parabolic reflector of the projector of Figure 1.

For more details concerning the formation and the arrangement of the images of the filament, reference will be made to the patent application filed by the applicant on the same day as the present application for a "transverse filament fog light for motor vehicle", under priority of French application ^No. 86 11263 of August 4, 1986 (EP-A-0256930).

FIG. 6 represents, by two series of isocandela curves Cʹ _a and Cʹ _b of decreasing values from the inside towards the outside, the illuminations provided by the reflector in cooperation with the crossing filament 10a and with the route filament 10b, respectively. In this figure, we can observe in particular the sharpness of the horizontal half-cut Hh of the passing beam as well as the reduced thickness of the latter, the slight shift to the right of the concentration spot Tʹa of the passing beam and the adequate centering of the spot of concentration Tʹb of the driving beam on the axis of the headlight (the point H designating the projection of this axis).

The closing glass will be designed to ensure a slight lateral spread of the two beams. In particular, elements (prisms or streaks) for lateral deflection of the spot of concentration of the crossing beam to the left will be provided to define the left half-cut, shifted downward, of this beam. The main beam will also be dispersed laterally to give it its wide width. But in all cases, a certain spreading being already obtained by the very nature of the reflector, there will be no need to provide prisms or streaks of great thickness on the closing glass: it will therefore be easy to mold , whether made of glass or plastic, and in addition no rising stray ray will be generated by the spoils of these prisms.

Of course, the present invention is not limited to the various embodiments described above, but those skilled in the art can make any variant or modification without departing from its scope.

Claims (7)

1. A dipped-beam and main beam headlamp for an automotive vehicle, of the type comprising a lamp having a dipped beam filament and a main beam filament arranged horizontally and transversely (10a, 10b), the two filaments being offset with respect to each other in two directions perpendicular to the axis of the headlamp, a reflector (20) the axis (Ox) of which passes between the two filaments, and a closure glass (30) which includes lateral deviation elements for the dipped beam and the main beam, and so arranged that the dipped beam is situated below a cut-off (Hh) orientated generally horizontally, characterised in that the surface of the reflector is a surface without any discontinuity which, of itself, forms shallow images of the dipped beam filament and of the main beam filament, such that the length of the images which are steeply inclined with respect to the horizontal, is shorter than that of the images when only slightly inclined with respect to the horizontal, all the points in the images of the dipped beam filament being further situated below the said horizontal cut-off (Hh), in such a way that the glass (30) has a low deflecting action in the vertical direction.

2. A headlamp according to Claim 1, characterised in that the images of the dipped beam filament (10a) formed by the reflector (20) have all of their highest points aligned with the said horizontal cut-off (Hh).

3. A headlamp according to Claim 2 characterived in that the dipped beam filament is offset upwardly by a distance (h_a) which is smaller than the distance (h_b) by which the main beam filament is offset downwardly with respect to the axis (Ox) of the reflector

4. A headlamp according to Claim 3, characterised in that the surface of the reflector (20) is defined by the equation:

where
x, y, z are cartesian coordinates, the axis Ox being the axis of the headlamp,
ℓ  = the half length of the dipped beam filament (10a),
r  = radius of the dipped beam filament (10a),
f_o = horizontal distance between the dipped beam filament and the plane yOz.

5. A headlamp according to Claim 3, characterised in that the surface of the reflector (20) is defined by the equation:

where
x, y, z are cartesian coordinates, the axis, Ox being the axis of the headlamp,
ℓ  = the half length of the dipped beam filament (10a),
f_o = horizontal distance between the dipped beam filament and the plane yOz.

6. A headlamp according to either one of Claims 4 and 5, characterised in that the light bulb of the headlamp is an HB1 normalised bulb.

7. A headlamp according to Claim 6, characterised in that the vertical distance (h_a) between the axis of the dipped beam filament (10a) and the axis (Ox) of the reflector is of the order of 0.9 mm, and in that the vertical distance (h_b) between the axis of the main beam filament (10b) and the axis (Ox) of the reflector is of the order of 1.4 mm.

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