EP0250284A1 - Dipped headlamp without a cap and having an offset concentration - Google Patents

Abstract

The invention relates to a dipped headlight for a motor vehicle, of the type comprising a reflector (200) comprising two sectors (201,202) in the form of paraboloids of revolution with a common axis, arranged symmetrically with respect to said axis and delimited by two axial planes, one horizontal, and the other making with the latter an angle equal to the bearing angle of the cut-off of the dipped beam; an axial filament lamp offset upward radially relative to said axis; and a distribution glass placed in front of the reflector, the zones of which homologous to the two sectors in the form of paraboloids are non-deviating or weakly deviating. According to the invention, the two sectors (201,202) in the form of paraboloids have different focal lengths, their focal points being respectively located axially on either side of the center of the filament, and the reflector also comprises reflecting surfaces (203,204,205,206), extending beyond said axial planes and carrying out without interruption the connection between the two sectors in the form of paraboloids of different foci, which bring below the said cut the images of the filament which they reflect.

Description

The present invention relates to a motor vehicle headlamp intended to form a passing beam.

A passing beam is characterized by a cut, that is to say by a generally horizontal orientation limit above which no light ray must be emitted. In Figure 1 of the accompanying drawings is shown, by a front view of a screen standardized to 25 meters, the cutout which must be specifically adopted in a number of countries, especially in Europe. This cut-off is made up, for a direction of traffic on the right, by a horizontal half-plane hʹH extending to the left from the longitudinal horizontal axis of the vehicle, and by a half-plane Hc extending to the right of this same axis while being slightly inclined upwards, typically by an angle α equal to 15 degrees. Of course, this configuration is reversed for left-hand traffic.

In addition to this cut-off, making it possible not to dazzle the drivers of oncoming vehicles, there are also a certain number of requirements concerning the light intensity at various points and regions below the cut-off. In particular, the "concentration spot", that is to say the region of the illumination field in which the light concentration must be maximum, should preferably be located slightly to the right with respect to the central vertical axis vʹ -v passing through the median longitudinal plane of the vehicle, and just below the cut-off, in order to properly illuminate the aisle. This concentration is determined in particular by measuring the luminous flux at points 75R and 50R, which flux must be greater than a minimum authorized value.

In the conventional technique of low beam headlamps comprising a filament lamp provided with a concealment cup defining the cutout mentioned above, a reflector, and a distribution glass closing the projector, the desired concentration of the beam as defined above is now easily obtained thanks to very specific optical characteristics of the reflector and the glass.

However, the applicant, by its French Patent Application ^No. 2536502 of 19 November 1982, proposed a projector without crossing blackout cup. More precisely, the "European" cutoff of the type defined above is obtained only by a special design of the reflector and the glass. This projector comprises a reflector comprising two sectors in the form of paraboloids of revolution with a common axis, arranged symmetrically with respect to said axis and delimited by two axial planes, one horizontal, and the other forming an angle equal to l with the latter. 'cut-off angle of the passing beam; an axial filament lamp offset upward in the radial direction relative to said axis; and a distribution glass placed in front of the reflector, the zones of which are homologous to the two paraboloid-shaped sectors are slightly deviating. According to this patent application, the two sectors in the form of paraboloids have the same focal point, located axially above the center of the filament, and the same focal distance.

The main advantage of such a projector is a considerable increase in the output luminous flux, due to the elimination of the obscuring cup.

However, with reference to FIG. 2 of the appended drawings, which represents the isocandela curves C _i of the illumination produced by such a projector of the prior art on a screen standardized to 25 meters, the spot of concentration obtained with this projector (hatched area T) is essentially centered on the longitudinal axis of the vehicle. Such positioning has two major drawbacks. On the one hand, such a spot of central concentration is extremely sensitive to the vertical oscillations of the vehicle. Thus, during variations in attitude of the latter, it appears in the axis of the road very marked differences in illumination, which leads to visual discomfort, generating fatigue, of the driver. On the other hand, the optimization of the visibility distance given by a low beam projector leads to superimposing the concentration spot on point 75R of the European regulations, that is to say a shift of said spot to the right and upwards. In this respect, the solution which would consist in shifting this spot of concentration to the right and upwards using deflecting prisms or the like on the lens of the projector is difficult to implement in practice, because it results in degradation. sensitive to the cut, and to a certain risk of increasing the rising radii, therefore dazzling for the vehicles coming opposite, due to the inevitable inaccuracies in the production of the closing glass by molding.

The present invention aims to provide an improvement to a dipped headlamp without cup, thanks to which one obtains, in addition to a completely satisfactory cut-off, a concentration of the light beam correctly shifted to the right with respect to the central longitudinal axis of the vehicle.

To this end, the invention is characterized in that:
the two sectors in the form of paraboloids have different focal distances, their foci being respectively located axially on either side of the center of the filament, and
- The reflector has reflective surfaces, extending beyond said axial planes and effecting without discontinuity the connection between the two sectors in the form of paraboloids of different foci, which bring below said cut the images of the filament that they reflect.

• - la figure 1 est une vue de face schématique du plan normalisé à 25 mètres qui dicte l'éclairement d'un projecteur de croisement,
• - la figure 2 représente, dans le plan normalisé à 25 mètres, les courbes isocandéla d'un projecteur de croisement sans coupelle de l'art antérieur,
• - la figure 3 est une vue en coupe verticale longitudinale schématique d'un projecteur de croisement conforme à la présente invention.
• - la figure 4 est une vue de dos du réflecteur du projecteur de la figure 3,
• - la figure 5 est une vue à échelle agrandie, en coupe verticale longitudinale, d'un détail du projecteur des figures 3 et 4,
• - les figures 6 à 8 sont des vues de face des images réfléchies du filament sur un écran normalisé à 25 mètres, pour trois zones différentes du réflecteur des figures 3 et 4, et
• - la figure 9 représente, par un certain nombre de courbes isocandéla, l'éclairement obtenu avec le projecteur des figures 4 et 5 sur l'écran normalisé.

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

• FIG. 1 is a schematic front view of the plan standardized at 25 meters which dictates the illumination of a dipped headlight,
• FIG. 2 represents, in the plane normalized to 25 meters, the isocandela curves of a dipped headlamp of the prior art,
• - Figure 3 is a schematic longitudinal vertical sectional view of a dipped headlight according to the present invention.
• FIG. 4 is a rear view of the reflector of the projector in FIG. 3,
• FIG. 5 is a view on an enlarged scale, in longitudinal vertical section, of a detail of the headlight of FIGS. 3 and 4,
• FIGS. 6 to 8 are front views of the reflected images of the filament on a screen standardized at 25 meters, for three different zones of the reflector of FIGS. 3 and 4, and
• - Figure 9 shows, by a number of isocandéla curves, the illumination obtained with the projector of Figures 4 and 5 on the standard screen.

Figures 1 and 2 were described during the discussion in the introduction. There is no need to come back to it.

In Figures 3 and 4 is shown a dipped headlight according to a preferred embodiment of the invention.

It includes a lamp provided with an axial filament 100, a reflector 200 and a distribution glass 300 closing the projector at the front thereof.

Unlike conventional spotlights with blackout cup, in which the filament is arranged in front of the focal point of the parabolic reflector and its axis is most often confused with the optical axis of the reflector, the filament 100, which can be schematized by a cylinder of length 2ℓ and radius r, is here shifted upwards by a distance equal to its radius r with respect to the optical axis Ox of the projector. In this way, the emissive surface of the filament is essentially tangent to said axis Ox.

The reflector or mirror 200 is subdivided into several sectors 201 to 206. These six sectors are separated by axial planes, namely the horizontal plane xOy, a plane xOs which makes with the plane xOy an angle α equal to the bearing angle to the right of the crossing beam cutoff as shown in FIG. 1, of the order of 15 degrees, and a plane xOt which makes with the vertical zβ-z an angle β = α / 2, that is to say of the order 7 ° 30 '.

The planes xOy and xOs define between them two sectors 201 and 202 which are each in the form of a paraboloid. More specifically, the focal point of the first parabolic sector 201 is indicated at F₁ in FIGS. 3 and 5, and is located near the rear axial end of the filament. The focal point F₂ of the second parabolic sector 202 is in turn located near the other end of the filament. The corresponding focal distances f₁ and f₂ are determined so that these foci F₁ and F₂ are located, on either side of the center F _O of the filament in the axial direction, equidistant from it, as will be seen in more detail far.

The images of the filament 100 reflected by these two sectors are placed on the normalized screen at 25 meters as indicated in FIG. 6. As can be observed, these images P₁₂ initiate the cut hʹHc, being located just below this, while providing a concentration of light in the region located to the right of the central vertical reference vʹv, thereby greatly promoting the obtaining of suitable luminous fluxes at the standardized points 50R and 75R of European regulations, where the illumination minimum required by regulations is the highest.

It may be noted here that, with respect to low beam without cup patent application ^No. 82 19382 of the applicant, is obtained thanks to two F₁ and F₂ foci arranged symmetrically about the center F _O of the filament as an offset to the right of the concentration spot while retaining the advantage of doubling the luminous flux in the concentration zone compared to a conventional low beam with concealment cup.

It can also be noted that, the images from zones 201 and 202 of the reflector being suitably positioned to create in part the desired beam, as regards both the concentration spot and the inclined cut, it is not necessary to make intervene important corrective optical elements on the closing glass 300 of the projector to deflect the light rays. The homologous ice zones of zones 201 and 202 will therefore be non-deviating or slightly deviating.

From this basic configuration, the other sectors 203 to 206 of the reflector are used according to the invention, on the one hand to reinforce the intensity of the beam, and on the other hand to better define the cut-off hʹH in the half left plan. As will be seen in detail below, these sectors are determined so that the images of the filament they form all have their highest point located on the cut hʹHc, or at least in the very close vicinity thereof.

According to the present invention, these zones 203 to 206 are constituted by deflecting surfaces which ensure with second order continuity the transition between the sectors 201 and 202 in the form of paraboloids of different foci, respectively in the upper region and in the lower region of the reflector.

It may be recalled here that the second order continuity of a surface is ensured by the fact that at any point on any line drawn on the surface, the tangent planes are the same on either side of this line. In practice this results in the absence of cracks in the surface. This arrangement makes it possible, in practice, to produce real surfaces having very good compliance with the theoretical surfaces which will be indicated below, and in which no optical anomaly is observed.

In a purely mathematical aspect, the invention can be implemented with the equations below.

The paraboloidal zones 201 and 202 of different foci have the equation:

In this equation:
- (x, y, z) are the Cartesian coordinates along the axes represented in FIGS. 3 and 4,
-f _o is an imaginary focal distance, equal to the distance along Ox between the origin O and the axial center, called F _O , of the filament 100,
-ℓ is the half length of the filament,
-r is the radius of the filament, and
-n is a positive real parameter chosen in the interval [1, + ∞].

With this equation of the paraboloid type, we understand that the area 201, which differs among other things from the area 202 by y> 0, has the focal length f₁ = f _o + ℓ / n, and that the area 202 has the focal length f₂ = f _o - ℓ / n, distances which correspond respectively to the focal points F₁ and F₂ in FIGS. 3 and 5. f _o is therefore the average of the focal lengths of the respective sectors 201 and 202.

In this way, it is understood that the images of the filament 100 will be shifted to the right by both the sector 201 and by the sector 202, to initiate the cut inclined along Hc, as shown in FIG. 6. In this regard, and such a shift being a function of the parameter n, the value of the latter will be chosen so that the concentration spot thus determined is substantially superimposed with the point "75R" of European regulations.

les constantes, paramètres et variables étant les mêmes que ci-dessus.Zones 203 and 204 are determined by the following equation:

the constants, parameters and variables being the same as above.

The images P₃₄ of the filament 100 generated by these zones, as shown in FIG. 7, predominantly determine the left horizontal cut of the beam.

les constantes, paramètres et variables étant comme ci-­dessus, et l'angleα ayant dans le présent exemple une valeur de 15°, soit l'angle du demi-plan Hc de la cou­pure à droite par rapport à l'horizontale hʹ-h.The areas 205 and 206, according to the present preferred embodiment of the invention, have the equation:

the constants, parameters and variables being as above, and the angle α having in the present example a value of 15 °, that is to say the angle of the half-plane Hc of the cut on the right with respect to the horizontal hʹ-h .

We can observe that this equation (3) is deduced from equation (2) indicated above by a change of coordinates corresponding to a rotation of the angle α around the axis Ox. This rotation makes it possible in particular to ensure second order continuity with the surfaces in the form of paraboloids 201 and 202 at the level of the half-planes xOsʹ, xOs inclined by the angle α, these two half-planes being defined by the equation z / y = tg (α), i.e. zcosα - ysinα = 0.

The images P₅₆ of the reflecting surfaces 205 and 206, as shown in FIG. 8, mainly define the inclined cutoff Hc of the straight part of the beam, by extending the cutoff already initiated at the concentration spot by the areas 201 and 202.

We can demonstrate, by a calculation that it is not necessary to reproduce here, that the surfaces of the six zones 201 to 206 present at their transition a second order continuity, with the exception of the transition according to the half-planes xOtʹ and xOt, where a slight lack of second order continuity is found in theory, as we will demonstrate below.

With regard to the continuity of first order surfaces, it is easy to verify that the various surfaces 201 to 206 have identical traces two by two when they are cut by the planes which ensure their separation.

. Les traces de cette surface dans les demi-plans xOyʹ et xOsʹ sont donc des paraboles de même foyer f₁ = f_o-

. Par un raisonnement identique, on démontre que les traces de la surface 202 dans ses demi-plans de limite xOy et xOs sont des paraboles de focale f₂ = f_o +

.More precisely, and as we have already seen, the surface 201 is a paraboloid with a focal length f₁ = f _ο -

. The traces of this surface in the half-planes xOyʹ and xOsʹ are therefore parabolas with the same focus f₁ = f _o -

. By an identical reasoning, we demonstrate that the traces of the surface 202 in its half-planes of limit xOy and xOs are parabolas of focal length f₂ = f _o +

.

soit une parabole de focale f_o -

= f₁, ce qui vérifie la continuité avec la surface 201.Concerning the trace of the area 203 in the half-plane xOyʹ, which is defined mathematically by y <o and z = o, the equation (2) which characterizes this surface becomes:

or a parable of focal length f _o -

= f₁, which checks the continuity with the surface 201.

= f₂ ; la continuité est encore vérifiée.Likewise, we show that the trace of the surface 204 in the half-plane xOy (y> o, z = o) is a parable of focal length fo +

= f₂; continuity is still checked.

The connection between surfaces 201 and 205 takes place in the half-plane xOsʹ, with the equation zcosα-ysinα = o, with ycosα + zsinα <o. Equation (3) therefore becomes:

Finally, the connection between surfaces 202 and 206 taking place in the half-plane xOs, of equation zcosα - ysinα = o with ycosα + zsinα> o, equation (3)

In the latter two cases, continuity (at least first order) is further demonstrated.

It is now necessary to approach the characteristics of the connection between surfaces 203 and 206 and surfaces 204 and 205, in the half-planes xOt and xOtʹ, respectively.

As a first approximation, we will first determine the fictitious traces of the surfaces 203 and 204 in the vertical plane by fictitiously extending them to the said plane.

The upper vertical half-plane xOz is determined by y = o and z> o. Equation (2) becomes as follows:

The fictitious trace of the surface 203 in the upper vertical half-plane is therefore a parabola of focal length f₃ = f _o - ℓ - r, corresponding to a focal point F₃ whose position behind the filament 100 is shown in FIG. 5.

soit une parabole de focale f₆ = f_o - ℓ - r, égale à f₃. (voir figure 5).The fictitious trace of the surface 206 extended in the same way is determined beyond the separation plane xOt, up to the plane xOu perpendicular to the plane xOs. The upper half-plane xOu has the equation ycosα + zsinα = o, with zcosα - ysinα> o .. Equation (3) becomes:

or a parabola with focal length f₆ = f _o - ℓ - r, equal to f₃. (see figure 5).

Thus, and because of the symmetry which exists between the surfaces 203 and 206 with respect to the plane xOt determining the transition between them, it can be affirmed that said surfaces have the same trace in this transition plane and that this trace is relatively close of the parabolic trace of focal length f₃ = f₆ = f _o - ℓ - r existing on either side of the connection.

We note that in theory, second order continuity is not locally achieved, but that there exists in the half-plane of connection xOt a very slight bend.

However, in practice, this defect will be mitigated during the machining and polishing steps of the reflector or its mold, until it disappears and does not cause any apparent defect in the projected light.

Similarly, the fictitious trace of the surface 204, extended beyond the connection xOtʹ, when it is cut by the lower vertical half-plane xOzʹ, with equation y = o and z <o, is provided by equation (2)

, correspondant à un foyer F₄ dont la position en avant du filament est représentée sur la figure 5.We thus obtain a fictitious parabolic trace of focal length f₄ = f _o + ℓ +

, corresponding to a focus F₄ whose position in front of the filament is shown in FIG. 5.

In correspondence, the fictitious trace of the surface 205 of equation (3) extended to the lower half-plane xOuʹ, of equation ycosα + zsinα = o with zcosα - ysinα <o, is determined by:

. (foyers F₄ = F₅ sur la figure 5) caractérisant deux traces fictives des surfaces raccordées, à faible distance angulaire de part et d'autre du raccordement.By reasoning similar to that which precedes, surfaces 204 and 205 have the same trace in the half-plane of connection xOtʹ, trace which can be considered as relatively close to a parabola of focal length f₄ = f₅ = f _o + ℓ +

. (homes F₄ = F₅ in FIG. 5) characterizing two fictitious traces of the connected surfaces, at a small angular distance on either side of the connection.

We will indicate below possible numerical values for the different variables and constants of equations (1) to (3), these values being particularly well suited for use in the low beam projector of a HlA type lamp:
ℓ = 2.75 mm
r = 0.6 mm
f _o = 22.5 mm, and
n = 1.375

These values lead to the following focal distances:
- f₁ = 20.5 mm for the paraboloid 201,
- f₂ = 24.5 mm for the paraboloid 202,
- f₃ = f₆ = 19.15 mm approximately for the pseudo-parabola of transition between zones 203 and 206) and
- f₄ = f₅ = 25.55 mm approximately for the pseudo-parable of transition between zones 204 and 205).

Of course, such a reflector will be used with a lens intended to improve the distribution of the beam, and in particular to effect horizontal spreading. Preferably, the homologous ice zones of sectors 201 and 202 of the reflector, which mainly participate in the creation and well-determined positioning of the concentration spot, will be smooth or slightly deviating. But in all cases, the glass 300 closing the headlamp will be designed so as not to effect substantially any vertical deflection, so as not to degrade the satisfactory cut obtained by the specific design of the reflector, and in particular not to increase the dazzling illumination at standard point B50 (see Figure 1).

Of course, the present invention is in no way limited to the embodiment described above, but includes any variant in accordance with its spirit. In particular, it will be possible to determine surfaces other than those defined by equations (2) and (3) to ensure the continuous transition between surfaces 201 and 202 while reducing the images of the filament below the cut.

Finally, the above description refers to a right-hand traffic direction. It is understood that, for a left-hand traffic direction, the skilled person will carry out the appropriate symmetry with respect to the vertical plane.

Claims (6)

1.- Headlamp for motor vehicle, comprising:
- A reflector (200) comprising two sectors (201,102) in the form of paraboloids of revolution of common axis, arranged symmetrically with respect to said axis and delimited by two axial planes, one horizontal, and the other making with the latter a angle equal to the bearing angle (α) of the cut-off (hʹHc) of the passing beam,
- an axial filament lamp (100) offset upwards in the radial direction relative to said axis, and
- a distribution glass (300) placed in front of the reflector, the areas of which are homologous to the two sectors in the form of paraboloids are non-deflecting or slightly deviating,
characterized in that:
the two sectors (201.202) in the form of paraboloids have different focal distances (f₁, f₂), their foci being respectively located axially on either side of the center of the filament, and
- The reflector comprises reflecting surfaces (203,204,205,206), extending beyond said axial planes and effecting without discontinuity the connection between the two sectors in the form of paraboloids of different foci, which bring below said cut the images of the filament let them reflect. 2.- passing beam according to claim 1, characterized in that the foci (F₁, F₂) of the two sectors in the form of paraboloids (201,202) are arranged, in axial direction, equidistant from the center (F _O ) of the filament , on both sides of it. 3.- passing beam according to claim 2, characterized in that the foci (F₁, F₂) of two paraboloid-shaped sectors (201,202) are arranged in an axial direction, at a distance from the center (F _O ) of the filament less than half the length (2ℓ) of the filament (100). 4. Crossing headlight according to claim 3, characterized in that the sectors (201,202) in the form of paraboloids are defined by the equation:

and in that the reflecting surfaces are defined by the equations:

where f _o is an imaginary focal distance corresponding to a focal point located axially in the center of the filament,
ℓ is the half-length of the filament,
r is the radius of the filament, and
n is a constant chosen in the interval (1, + ∞). 5.- dipped beamer according to any one of claims 1 to 4, characterized in that the angle (α) which separates the two axial planes delimiting the sectors (201,202) in the form of paraboloids is approximately 15 °. 6.- passing beam according to any one of claims 1 to 5, characterized in that the filament (100) is offset upwards by a distance equal to its radius (r) relative to said axis.

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