EP0256930B1 - Fog lamp with transverse filament for motor vehicles - Google Patents

Description

The present invention relates to a headlight for a motor vehicle, making it possible to fulfill the fog light function.

The beam corresponding to such an illumination is a short-range beam, limited upwards by a substantially horizontal cutting plane, very spread out laterally and not comprising rising rays capable of giving rise to undesirable optical phenomena with the droplets of water in mist suspension.

The fog lights of the prior art mostly have an axially oriented filament, that is to say in the axis of the projector.

With regard to the associated reflector, several solutions have already been proposed. The first consists of providing a reflector in the form of a paraboloid of revolution, the focus of which is located at the front end of the filament (in the direction of emission). A slightly divergent beam is thus obtained, the spokes of the upper half of which are folded down by means of deflecting elements provided on the closing glass.

This however results in significant thicknesses of the ice, and therefore molding difficulties, especially when the ice is made of glass.

It has also been proposed to form a reflector from two axially offset half-paraboloids. The upper half-dish is focused on the rear end of the filament, to form a conventional cut beam, and the lower half-dish is focused on the front end of the filament, so that all the images of the latter are located above below the cut.

Such a projector has two major drawbacks. First, the reflector has a surface discontinuity at the point of connection between the two half-paraboloids: these, focused at different points, necessarily have either different vertices, or different focal distances, and by suite have different profiles along a connection plane; because of this characteristic, a reflector manufactured according to these teachings is, in practice, imperfect at the connection, which results in an emission of parasitic light rays above the cut.

Secondly, and above all, the beam generated by the lower half-paraboloid is spread laterally in a satisfactory manner only in the zone situated just below the cut. This non-uniform spreading of the beam goes against the aim sought in a fog beam, which is to obtain a relatively uniform lateral spreading.

Finally, in the published French patent application No. 2,536,503 in the name of the Applicant, there has been proposed a fog light in which, the filament being always oriented axially, the reflector comprises a complex surface without discontinuity capable of forming images of the filament of which practically all the points are situated below the cut. Such a solution makes it possible to obtain a completely uniform lateral spreading of the beam, as well as a good definition of the cut-off.

However, the use of an axial filament with a reflector of this type necessarily causes the appearance of filament images which are large and oriented vertically, or with a slight inclination relative to the vertical. Such images must be subject to significant lateral spreading, and this must be done on the closing glass with appropriate prisms or streaks. A second disadvantage of this type of projector is that, still due to the existence of these vertical images, the beam has a greater thickness than that which is required in practice, the lower part of it not contributing to comfort. visual, and can even be annoying by lighting the road too close to the vehicle.

Finally, there are in the prior art fog lamps comprising a horizontal filament lamp transverse to the axis of the projector, associated with a reflector in the form of a paraboloid of revolution, the focus of which is located in the center of the filament. In this way, the beam does not include large images of the filament, but in certain cases it remains necessary to effect, by prisms formed on the closing glass, a folding of the images in the vertical direction, with a risk of emission. of parasitic rays upwards at the spoils of these prisms.

• la lampe et le réflecteur sont conçus pour former un faisceau étroit de faible hauteur, qui est largement étalé horizontalement par des nervures en forte surépaisseur de la glace; la fabrication de ladite glace est ainsi compliquée comme déjà mentionné. Enfin et surtout, ce brevet n'enseigne ou ne suggère par l'utilisation du faisceau ainsi obtenu comme faisceau antibrouillard.

In other cases, as described for example in FR-A 131 910:

• the lamp and the reflector are designed to form a narrow beam of low height, which is widely spread horizontally by ribs with a large thickness of the glass; the manufacture of said glass is thus complicated as already mentioned. Last but not least, this patent does not teach or suggest the use of the beam thus obtained as an anti-fog beam.

The present invention aims to overcome the drawbacks of the prior art and to propose a fog light in which none, or essentially no vertical deflection of the light rays has to be carried out by the closing glass, and in which the beam obtained is of 'a good homogeneity in its width as in its height.

To this end, the invention relates to a fog light for a motor vehicle, of the type comprising a transverse horizontal filament lamp, a reflector whose axis passes directly above the center of the filament, and a closing glass, characterized in that that the surface of the reflector is a surface without discontinuity which by itself forms images of the filament, all the points of which are situated below a horizontal cut and in a horizontal band of great width and, of height es substantially constant located under said cut, so that the ice can be smooth or only slightly deviating.

• - la figure 1 est une vue des images du filament projetées par un projecteur antibrouillard de la technique antérieure, à filament axial, sur un écran normalisé;
• - la figure 2 est une vue en coupe horizontale schématique d'un réalisation de base d'un projecteur antibrouillard selon l'invention;
• - la figure 3 est une vue en coupe verticale longitudinale du projecteur de la figure 2;
• - les figures 4a et 4b représentent des images du filament projetées par deux zones déterminées du réflecteur du projecteur des figures 2 et 3;
• - la figure 5 représente, par une série de courbes isocandéla de valeurs décroissantes de l'intérieur vers l'extérieur, l'éclairement fourni par le projecteur des figures 2 et 3;
• - les figures 6a et 6b illustrent, en vue de face, deux premières variantes de réalisation du projecteur de l'invention ;
• - la figure 7 représente des courbes flux lumineux/inclinaison caractérisant les variantes des figures 6a et 6b;
• - les figures 8a et 8b illustrent, en vue de face, deux autres variantes de réalisation du projecteur de l'invention; et
• - la figure 9 représente des courbes flux lumineux/inclinaison caractérisant les variantes des figures 8a et 8b.

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 view of the images of the filament projected by a fog light of the prior art, with axial filament, on a standardized screen;
• - Figure 2 is a schematic horizontal sectional view of a basic embodiment of a fog light according to the invention;
• - Figure 3 is a longitudinal vertical sectional view of the projector of Figure 2;
• - Figures 4a and 4b show images of the filament projected by two specific areas of the reflector of the projector of Figures 2 and 3;
• - Figure 5 shows, by a series of isocandela curves of decreasing values from the inside to the outside, the illumination provided by the projector of Figures 2 and 3;
• - Figures 6a and 6b illustrate, in front view, two first alternative embodiments of the projector of the invention;
• - Figure 7 shows light flow / tilt curves characterizing the variants of Figures 6a and 6b;
• - Figures 8a and 8b illustrate, in front view, two other alternative embodiments of the projector of the invention; and
• - Figure 9 shows light flow / tilt curves characterizing the variants of Figures 8a and 8b.

1 shows, on a projection screen, the filament images projected by the reflector of a headlamp according to the published patent application _No. 2,536,503 in the name of the Applicant. As indicated above, there are a number of large and orientation images approaching the vertical. The presence of these images leads to an excessive thickness of the beam in its central region, which is detrimental to visual comfort by lighting the road too close to the vehicle, and which requires on the closing glass means to effect a relatively large lateral deflection. .

The fog lamp of the invention, shown diagrammatically in FIGS. 2 and 3, comprises a lamp (not shown) provided with a filament 10, a reflector 20 and a distribution glass 30 closing the projector.

The filament is placed in a horizontal plane and oriented transversely to the axis Ox of the reflector, more precisely, in the present example, the filament, modeled in the form of a cylinder of length 2 2 and of radius r, is shifted towards the top with respect to the horizontal plane xOy by a distance equal to its radius, so that its emissive surface is tangent to said plane. It is also arranged, in the direction y'Oy, so that its center is perpendicular to a point Fo located on the axis Ox. The distance from the top of the reflector to this point F _o is denoted f _o . Of course, the position of the filament may vary slightly from the position indicated above, without departing from the scope of the invention.

The surface of the reflector is a surface without discontinuity, chosen so as to form the images of the filament, all the points of which are situated below a horizontal cut passing through the axis of the projector (denoted h ′ Hh in FIGS. 4a, 4b, and 5), and in a horizontal band of essentially constant height delimited at the top by said cut.

Advantageously, all of these images have their highest point situated on the cut, or in the very close vicinity thereof.

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 of a line drawn on the surface, the tangent planes are the same on both sides of this line.

Such an arrangement makes it possible in practice to produce real surfaces having very good conformity with the theoretical surfaces, whether by stamping or by injection molding, thereby avoiding the defects specific to the system with offset half-paraboloids discussed above.

avec

• r = rayon du filament
• £ = demi-longueur du filament,
• fo = distance du centre du filament au plan yOz (soit l'abscisse du point Fo).

The theoretical calculation shows that the surface defined by the following equation, in the orthonormal coordinate system (O, x, y, z) as illustrated in Figures 2 and 3, has the properties stated:

with

• r = radius of the filament
• £ = half length of the filament,
• fo = distance from the center of the filament to the yOz plane (i.e. the abscissa of the point Fo).

et possède également les propriétés énoncées, avec toutefois une qualité très légèrement inférieure du résultat.Furthermore, if we consider the radius r of the filament as very small, the above equation becomes a first approximation:

and also has the stated properties, but with a slightly lower quality of the result.

These surfaces present in the xOy plane a parabolic trace of focal distance fo, and define complex surfaces which "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.

Figures 4a and 4b show the images of the projected filament, on a standardized screen located 25 m from the projector, by reflection at points located on the same horizontal plane of the reflector, with dimensions z = - 40 mm respectively (Figure 4a) and z = - 20 mm (figure 4b). These two figures are to be compared with FIG. 1, which represents the distribution of the images for a reflector projector with a complex surface without discontinuity associated with an axial filament. Unlike the latter, the distribution of the images below the cut, in particular in the horizontal direction, is here of very good uniformity, more precisely, it can be observed that the images of the filament, progressively that they rotate around their center from horizontal to vertical, see their length progressively reduced. Thus, not only the highest point of each image is located in the very close vicinity of the cut h'Hh, but also the lowest point of these images only very occasionally exceeds a lower cut, denoted b'b on the Figures 4a, 4b and 5, so that a beam is obtained whose thickness is approximately constant over a large width. This especially avoids lighting the road too close to the vehicle, which contributed to making the large vertical images shown in Figure 1 and which is not desirable in practice.

In FIG. 5, which represents, by a series of isocandela curves C of decreasing values from the inside towards the outside, the illumination provided by the whole of the reflector, one can observe the sharpness of the upper horizontal cut h ' Hh, the large beam width with a practically constant thickness, and the concentration point P located below the cut h 'Hh and centered on the vertical v' Hv.

The closing glass can optionally provide additional lateral spreading of the beam. However, such spreading is already obtained by the very nature of the reflector, and there will be no need to provide significant extra thicknesses on the closing glass: it will therefore be easy to mold, whether made of glass or made of plastic.

Furthermore, when the reflector is truncated at the top and bottom by two horizontal flat cheeks 21 and 22 (FIG. 3), it may be advantageous to give these cheeks a non-reflecting character, so as to avoid a significant amount of light is not diffused above the cut-off.

One can imagine giving the reflector different shapes. Thus, Figure 6a shows, in schematic front view without closing glass, a projector whose reflector has a width yi approximately equal to twice its height zi. In FIG. 6b, these proportions have been reversed, the height z ₂ being approximately equal to twice the width y ₂ . These values are determined so that the surfaces ef the total reflectance of the two reflectors are approximately identical. One can determine the influence of the shape of the contour of the reflector on the characteristics of the beam obtained. In particular, for these two projectors, in the longitudinal vertical plane xOz, the luminous flux (in lumens) obtained was measured as a function of the inclination (in degrees) at which one places oneself below the cut-off. FIG. 7 represents the curves $ ₁ and ϕ ₂ obtained respectively with the projectors of FIGS. 6a and 6b.

As can be observed, with the headlamp of FIG. 6b, a greater luminous flux is obtained between about 0 and 2 _° below the cut; the yield in this region is slightly increased. On the other hand, with this configuration, a residual luminous flux of very low value is created above the cut-off. In practice, it will not degrade visual comfort.

By keeping the contour of the reflector of FIG. 6b, it was also determined whether the fact of varying the position of the filament in the vertical direction relative to this contour (and not relative to the surface of the reflector, which is always determined relative to filament position) led to changes in the beam illumination characteristics. In FIG. 8a, the filament is located at a distance z ₃ below the upper edge of the reflector, a distance which is approximately one tenth of the total height z ₂ of the reflector, and in FIG. 8b, the filament is a distance _Z4 , substantially equal to z ₃ , above the lower edge of the reflector. Here again, the surfaces of the two reflectors are equal.

The variations in the luminous flux (in lumens) as a function of the inclination (in degrees) relative to the cut-off for these two projectors are represented by the curves φ ₃ and <)) 4 in FIG. 9. As can be observe, we obtain when the lamp is shifted up not only a greater luminous flux between about 0.4 and 2 ° below the horizontal, but also a much clearer cut at this horizontal, sharpness illustrated by the steep slope of the curve.

Thus, although the invention can be implemented with any contours of reflectors and any filament / reflector positions in a given contour, the height of the headlamp can advantageously be increased as far as possible, to the detriment of its width, and shift the lamp upwards.

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 fog light for an automotive vehicle, of the type including a lamp having a horizontal, transverse filament (10). a reflector (20) the axis (Ox) of which is vertically aligned with the centre of the filament, and a closure glass (30), characterised in that the surface of the reflector is a surface without discontinuity, which by itself forms images of the filament, all points of which are situated below a horizontal cut-off line (h'Hh) and in a horizontal band, which is of large width and has an essentially constant height situated below the said cut-off line, in such a way that the glass (30) can be smooth or only slightly deflecting.

2. A light according to Claim 1, characterised in that the images of the filament which are formed by the reflector (20) have all of their most elevated points aligned with the said horizontal cut-off line (h'Hh).

3. A light according to Claim 2, characterised in that the filament is offset upwardly by a distance such that its surface is essentially tangential to the horizontal plane (xOy) intersecting the axis of the reflector (Ox).

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

where:

x, y, z = cartesian coordinates, the axis Ox being the axis of the fog light,

r = radius of the filament (10),

£ = half length of the filament,

fo = distance from the axis of the filament to the plane yOz.

5. A light according to Claim 1, characterised in that the surface of the reflector (20) is defined by the equation:
where:

where:

x, y, z = cartesian coordinates, with the axis Ox being the axis of the fog light,

I = half length of the filament (10),

fo = distance from the axis of the filament to the plane yOz.

6. A light according to any one of Claims 1 to 5, characterised in that the lamp is offset upwardly with respect to the centre of the reflector opening.

7. A light according to any one of the preceding Claims, in which the reflector is truncated on at least two of its four sides by flat portions (21, 22), characterised in that the surface of these portions is a nonreflective surface.

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