EP0454563B1 - Lens for motor vehicle headlight and its manufacturing method - Google Patents

Description

The present invention relates generally to motor vehicle headlamps, and more particularly to a new concept of a deflecting stripe provided on the lens of the headlamp to effect horizontal spreading (or more generally parallel to a cut line) of the beam.

For a number of years now, motor vehicles have had a plunging front, so that it is necessary to give the lens of each headlamp a substantial inclination, up to for example 70 °, relative to the vertical plane in which such ice was usually located.

With conventional, generally cylindrical, refractive spreading streaks, such an inclination of the glass leads to a classic phenomenon according to which, the more a light ray is deflected laterally, the more it is also folded down. This leads to a generally crescent-shaped beam, as illustrated for example in French patent FR-A-2 428 204, in the name of the applicant.

This same patent proposes frustoconical streaks which have the object of voluntarily giving a beam a degree of downward well controlled downward movement at the lateral ends of the beam, in particular to improve the illumination of the side of the road. Thus, this patent does not teach or suggest in any way a streak which, provided on an inclined lens, is capable of deflecting a horizontal light ray without imparting any downward drawdown to it.

We also know, from French patent FR-A-2,542,422, also in the name of the Applicant, a stripe for inclined glass which is capable of giving an incident ray a lateral deviation without imparting any drawdown to it. However, the streaks taught by this patent are only capable of achieving this result with a significant limitation, according to which for each streak, the angular interval of the deviations given to the spokes is extremely reduced. As a corollary, it is necessary to provide a large number of streak zones, each zone being assigned to a deviation to a given degree and comprising streaks having their own geometry, if we want to ensure good complementarity between the various light spots relatively narrow corresponding to each streak area. This results in a relatively complicated ice construction, and a final beam which may lack homogeneity.

The present invention aims to overcome these drawbacks of the prior art and to propose a streak which, provided on a lens of any inclination, is capable of providing by itself a very wide and uniform spreading of the incident beam portion, and this without inducing any reduction of the light rays with respect to the essentially horizontal plane in which they are originally contained. More specifically, the invention aims to propose a streak which, receiving a concentrated beam of rays parallel to the optical axis, is capable of forming a well horizontal and very homogeneous light strip.

To this end, the invention relates first of all to a method of manufacturing a mold punch intended to form a lens comprising a plurality of streaks for a headlight of a motor vehicle, characterized in that it comprises, for each streak , the stages consisting in:
define a set of rectilinear elementary prisms oriented parallel to a plane of the ice, the prism angle and the angle of inclination, with respect to a vertical plane perpendicular to said plane of the ice, of each elementary prism being such that all Ray luminous parallel to a given reference axis is deflected laterally without undergoing vertical deflection,
define a curve without a break in slope at a given height of the ice and in a plane perpendicular to the plane of the ice and cutting the latter along a horizontal line,
adjust the placement of each elementary prism so that its surface comes to tangent to said curve,
calculating data representative of a surface tangent to each of said surfaces of elementary prisms whose placements have been adjusted, said surface constituting the surface of the streak,
machine the imprint of the streak in the punch according to said data.

In a first implementation, said data representative of the surface of the streak consists of a set of Cartesian coordinates of tangent points passing through said surface.

In a second implementation, said data representative of the surface of the streak are constituted by a set of conic equations in a plane perpendicular to the plane of the ice and intersecting the latter along a horizontal.

Advantageously, said curve without a break in slope is chosen from the group comprising circles, parabolas, hyperbolas and ellipses.

The invention also relates to a method for manufacturing a motor vehicle headlamp lens, characterized in that said lens is molded using a mold punch produced by the method as defined above.

According to another essential aspect, the invention relates to a lens for a motor vehicle headlamp, capable of being mounted in an inclined position relative to a vertical plane and of the type comprising a plurality of streaks with a view to spreading the light emitted by the headlamp substantially in the lateral direction, characterized in that each streak of at least one given group of streaks has an adjusted streak surface without breaking the slope, the tangent planes define a set of elementary prisms whose prism angles and inclinations with respect to the vertical vary in correspondence so that an incident ray on any prism is deflected laterally by said prism in a variable measure according to the prism but without undergoing vertical deflection.

Advantageously, a region of maximum curvature of each prism has a transverse profile defined by the equation of a conic.

In a first embodiment, there is provided in at least one zone of the ice a succession of streaks separated by vertical planes and perpendicular to the plane of the ice.

In a second embodiment, there is provided in at least one zone of the glass a succession of alternately recessed and solid streaks, connected to each other without any break in slope in planes perpendicular to the plane of the ice and inclined with respect to the vertical.

• la figure 1 est une vue de l'arrière d'une glace inclinée sur laquelle est formé un prisme élémentaire permettant de définir une strie selon l'invention,
• la figure 2 est une vue d'un écran de projection normalisé à 25 m, illustrant la déviation horizontale d'un rayon lumineux,
• la figure 3 est une vue schématique de l'arrière d'une strie conçue conformément à la présente invention,
• la figure 4 est une vue en coupe transversale d'un profil d'une strie réalisée conformément à l'invention,
• la figure 5 illustre une pluralité de profils d'une strie selon un premier exemple concret de réalisation,
• la figure 6 illustre une pluralité de profils d'une strie selon un second exemple concret de réalisation, et
• les figures 7a et 7b sont des vues schématiques en perspective illustrant deux manières possibles de juxtaposer des stries selon l'invention.

Other aspects, aims and advantages of the present invention will appear better on reading the following detailed description of a preferred embodiment thereof, given by way of non-limiting example and made with reference to the accompanying drawings, on which ones:

• FIG. 1 is a view from the rear of an inclined lens on which an elementary prism is formed making it possible to define a streak according to the invention,
• FIG. 2 is a view of a projection screen standardized at 25 m, illustrating the horizontal deviation of a light ray,
• FIG. 3 is a schematic view of the rear of a streak designed in accordance with the present invention,
• FIG. 4 is a cross-sectional view of a profile of a streak produced in accordance with the invention,
• FIG. 5 illustrates a plurality of profiles of a streak according to a first concrete example of embodiment,
• FIG. 6 illustrates a plurality of profiles of a streak according to a second concrete example of embodiment, and
• Figures 7a and 7b are schematic perspective views illustrating two possible ways of juxtaposing streaks according to the invention.

Referring firstly to FIGS. 1 and 2, a streak according to the invention, intended to ensure uniform lateral spreading, in an angular interval which can be arbitrary, of a portion of light beam received, without inducing drawdown towards below, is constructed from a plurality of elementary prisms PE designed to cover, by the deviations which they cause individually, the whole of the above-mentioned angular interval.

For each elementary prism PE, we denote by A the prism angle, by i the angle of inclination of the prism on the glass G with respect to a straight line D passing through said glass and contained in a vertical plane, by DH the lateral deviation given by the prism, measured by distance from the point of impact of the ray refracted at the origin H in the normalized screen E, and by α the inclination of the glass relative to a vertical plane.

α being known, each elementary prism is first of all characterized by its prism angle A determining the particular lateral deviation effected by this prism, and each time the angle of inclination i is calculated so that the refracted ray propagates without having been deflected vertically. This calculation of i as a function of A is repeated for a set of values A corresponding to the angular interval of deviation chosen, for example [0 °, 45 °].

These relatively complex calculations of i as a function of A will not be developed here to avoid adding to the description, but those skilled in the art will be able to pose the necessary equations. Preferably, to lighten the calculations, appropriate computer means.

Thus, for a given ice slope, a plurality of pairs (A, i) are obtained which define all the elementary prisms which can be used to obtain the desired result. We can already note that i is an increasing monotonic function of A.

Now with reference to FIG. 3, we will describe the steps in accordance with the present invention for constructing a streak S from a set of elementary prisms PE as defined above.

We first define an orthonormal coordinate system [0, x, y, z] such that 0x is horizontal and contained in the plane of the ice, 0y is perpendicular to the plane of the ice and 0z is contained in the plane of the ice and perpendicular to 0x and 0y.

With reference to FIG. 3, a basic profile P₀ is then defined, in this case an arc of a circle AC of determined radius R, which is contained in the plane x0y perpendicular to the plane of the ice and which tangents the plane of ice x0z.

Then, the placement of each elementary prism PE is adjusted in the plane of the glass so that the inclined surface of said prism comes to rest against (tangent) the arc of a circle AC, as illustrated in FIG. 3. Given that i is a monotonic function increasing from A, we obtain an arrangement of the elementary prisms PE in a sort of fan shape from the arc of a circle AC, and this will lead to a streak which in this case remains concave over its entire extent but whose profile evolves as we move away from AC, flattening. We will see in the following that it is not at all a streak of frustoconical shape.

By using, as described above, a discrete number of elementary prisms, the profiles of the groove in accordance with the present invention at different heights (z dimensions) are obtained by drawing at each dimension the curve which tangents all the inclined surfaces of the elementary prisms, as this is clearly shown in Figure 4. This curve can be characterized either by the set of coordinates of the various tangent points, accompanied by the set of derivatives of the curve (given directly by A) at these points, or again by an equation mathematics determined in such a way as to pass through these tangent points, having the corresponding derivatives at these points.

Another solution can consist in using elementary prisms in progression according to a differential prism angle dA, then in calculating for each given profile of profile the coordinates of the points of the successive inclined surfaces of the elementary prisms, by making use of dA. If then one tends dA towards zero, one can obtain a mathematical definition of the profile considered.

Knowing the basic profile in this case AC, as well as the profile of the streak in at least one dimension distance from the plane of the arc AC, we then have sufficient data to carry out the machining of the impression of the streak in a mold punch used to make the ice cream.

In the example above, we used, as the base curve on which the prisms are based elementary, a hollow arc. However, it should be noted that any other curve with no slope break, recessed or full, can be used, thereby forming a recessed or full streak, respectively. One can in particular use a conic arc such as a portion of ellipse, parabola or hyperbola. The curvature of the support arc, corresponding to the maximum curvature of the groove obtained, is also chosen to be compatible with conventional machining means.

We will now describe concretely two exemplary embodiments of ridges in accordance with the present invention.

Example 1

For a lens of inclination α = 45 ° and of refractive index n = 1.5, a set of couples (A, i) is first calculated in accordance with the indications given above. The support arc at dimension z = 0 is an arc of a circle AC with a radius of 7.5 mm (P₀ profile).

The theoretical profiles of the streak obtained have been illustrated in FIG. 5, respectively for dimensions:
z = 10 mm,
z = 20 mm and
z = 30 mm.

These profiles are designated by the references PT₁₀, PT₂₀ and PT₃₀, respectively.

les profils elliptiques réels approchants PR₁₀ à PR₃₀ ont dans cette équation pour paramètres, respectivement (avec x, y, a et b en mm):
   pour PR₁₀ : a = 15,39 ; b = 19,98
   pour PR₂₀ : a = 24,55 ; b = 37,17
   pour PR₃₀ : a = 34,53 ; b = 57,88According to another aspect of the present invention, to facilitate the production of the ice cream using computer-aided manufacturing means, and more particularly to simplify the production by digital machining of the punch of the mold which will be used to make the ice cream. large series, these theoretical profiles, known only by the pairs of coordinates of points which constitute them, are substituted for profiles defined by mathematical equations. In the present for example, the profiles PT₁₀ to PT₃₀ can be approached with an excellent superposition by real profiles which are each defined by a judiciously parameterized ellipse. More specifically, if we consider the following ellipse equation: $$\text{x² / a² + y² / b² - 2y / b = 0}$$

the real elliptical profiles approaching PR₁₀ to PR₃₀ have in this equation for parameters, respectively (with x, y, a and b in mm):
for PR₁₀: a = 15.39; b = 19.98
for PR₂₀: a = 24.55; b = 37.17
for PR₃₀: a = 34.53; b = 57.88

In the representation of FIG. 5, the profiles PR₁₀ to PR₃₀ can practically not be distinguished from the corresponding theoretical profiles.

Example 2

For a lens of inclination α = 70 ° and of refractive index n = 1.5, the same construction steps as in Example 1 were repeated. Here again, the profile on which the elementary prisms PE have been pressed is an arc of a circle AC having a radius of 7.5 mm and located at the dimension z = 0 (profile P₀).

The theoretical profiles PT₁₀, PT₂₀ and PT₃₀ of the streak obtained have been illustrated in FIG. 6, respectively for dimensions
z = 10 mm,
z = 20 mm and
z = 30 mm.

avec
   a = 104,71 et b = 49,14 pour le profil PR₂₀ et
   a = 99,88 et b = 55,52 pour le profil PR₃₀.In the present example, it has proved advantageous to substitute for the profile PT réel a real profile PR₁₀ constituted by a portion of a parabola with axis 0y and a focal length of 7.60 mm. On the other hand, we found that the PT₂₀ and PT₃₀ profiles were approached in a way optimal by real profiles PR₂₀ and PR₃₀ constituted by portions of hyperbolas of equation: $$\text{x² / a² - y² / b² + 2y / a = 0}$$

with
a = 104.71 and b = 49.14 for the PR₂₀ profile and
a = 99.88 and b = 55.52 for the PR₃₀ profile.

Also in the representation of FIG. 6, the profiles PR₁₀ to PR₃₀ can practically not be distinguished from the corresponding theoretical profiles.

Referring now to Figures 7a and 7b, there are illustrated two possible ways of juxtaposing on a closing glass streaks made in accordance with the present invention.
In the example of FIG. 7a, the individual streaks S are delimited laterally by two vertical planes PV parallel to the plane y0z.

In the example of FIG. 7b, particularly advantageously streaks are produced which are alternately hollow and solid and separated by transition planes which have the same inclination as the marginal elementary prisms of said streaks. The streaks here have a length L, extending downward from a dimension z = 0.

Thus in this figure, the groove S1 is produced as described above, that is to say that the support curve P₀₁ is an arc of a circle (or other curve without a break in slope) concave located in the upper part of the groove . On the other hand, the immediately adjacent streak S2 is made with the same type of construction, but taking as support curve P _L2 an arc of a circle (or other regular curve) convex located in the lower part of the streak. As a corollary, the streaks S1 and S2 are separated by an inclined transition plane PI which is perpendicular to the plane of the ice and which extends parallel to the inclination of the elementary prism border of each of the two streaks, having the maximum prism angle. It should be noted here that two ridges can be made which connect to one another without a slope break. It suffices in fact to ensure that the basic profile P _L2 of the streak S2 connects itself without a slope break with the profile P _L1 of the streak S1 at the same height. Thus there are on either side of the transition plane between the two streaks two elementary prisms having the same prism angle and the same inclination relative to the vertical, said inclination corresponding moreover to that of said transition plane.

In the foregoing description, there have been described streaks making it possible to deflect incident rays laterally without inducing vertical drawdown. But it is understood that the invention also applies to the production of streaks intended to spread a light beam for example below a rising half-cutting plane, inclined at 15 ° with respect to the horizontal, as provided in particular in European regulations on the subject. In this case, the couples (A, i) of each elementary prism PE are calculated so that said prisms provide a deviation in the appropriate direction, parallel to the inclined half-plane. Thus, in the description as in the claims, the term "horizontal" should not be taken in its literal sense.

Furthermore, an essential advantage of the present invention is that each streak, constructed from a multitude of rectilinear elementary prisms, is a ruled surface. This, combined with the fact that the profiles of the ridges can be approached with excellent precision by appropriate conic equations, considerably facilitates the production of the mold punch by a digital machining apparatus, and in particular greatly simplifies the configuration thereof.

In particular, it is possible with the present invention to perform machining by a succession of straight passes whose orientations, mutually inclined, correspond to the straight lines of the elementary prisms constituting the ridges (angular machining). This makes manufacturing extremely simple and economical.

Finally, it will be noted that, compared to the known prior art, the groove surface according to the present invention is the only one which is both a regulated surface and a surface capable of giving a uniform deviation in any angular interval, in practically imparting no vertical drawdown, to a portion of light beam emitted towards the streak parallel to the optical axis of the projector.

Of course, the present invention is in no way limited to the embodiment described above and shown in the drawings, but those skilled in the art will know how to make any variant or modification within the scope of the claims.

In particular, it will be able to provide on an inclined lens streaks in accordance with the present invention, with appropriate optical characteristics and in appropriate zones of the lens, as a function of both the characteristics of the beam formed by the lamp and the reflector upstream of the lens and the photometric characteristics sought for the beam leaving the lens.

In addition, the present invention advantageously applies to windows which can be inclined not only with respect to the vertical, but also with respect to a horizontal transverse to the direction of movement of the vehicle, in correspondence with the receding edges of the front of the vehicle.

It should also be noted that the invention is easily applicable to non-flat glass, including the inclination relative to the vertical varies as one moves laterally on the ice. It suffices in this case, when defining the set of elementary prisms, to define a new set of elementary prisms for each new value of the angle of inclination α. In this case, "ice plane" means the plane tangent to the ice at the level of the streak considered.

Claims (9)

1. A method of making a mold die for manufacturing a motor vehicle headlight glass having a plurality of stripes, the method being characterized in that it comprises, for each stripe, the following steps:
      defining a set of rectilinear unit prisms (PE) oriented parallel to a plane of the glass, with the prism angle (A) and the angle of inclination (i) relative to a vertical plane perpendicular to said plane of the glass being such in each unit prism that any light ray parallel to a given reference axis is deflected laterally without being subjected to vertical deflection;
      defining a curve (P0) having a slope without discontinuity, the curve being defined at a given height on the glass and lying in a plane (xOy) perpendicular to the plane of the glass and intersecting the glass on a horizontal line;
      adjusting the positioning of each unit prism (PE) in such a manner that its surface is tangential to said curve;
      calculating data representative of a surface which is tangential to the surfaces of each of said unit prisms whose positions have been adjusted, said surface constituting the surface of the stripe (S); and
      machining the imprint of the stripe in the die as a function of said data.
2. A method according to claim 1, characterized in that said data representative of the surface of the stripe is constituted by a set of Cartesian coordinates for tangency points on said surface.
3. A method according to claim 1, characterized in that said data representative of the surface of the stripe is constituted by a set of equations of conics in planes perpendicular to the plane of the glass and intersecting the plane of the glass horizontally.
4. A method according to any one of claims 1 to 3, characterized in that said curve (P0) without slope discontinuity is selected from the group constituted by: circles, parabolas, hyperbolas, and ellipses.
5. A method of manufacturing a motor vehicle headlight glass characterized in that said glass (G) is molded using a mold die made by the method according to any one of claims 1 to 4.
6. A motor vehicle headlight glass suitable for mounting in a sloping position relative to a vertical plane and of the type comprising a plurality of stripes (S) for spreading the light emitted by the headlight substantially in a lateral direction, the glass being characterized in that each stripe in at least a given group of stripes has a stripe surface which is ruled and without slope discontinuity, having tangency planes defining a set of unit prisms (PE) whose prism angles (A) and whose slopes (i) relative to the vertical vary together in such a manner that an incident ray on any one of the prisms is deflected laterally by said prism by an amount that varies depending on the prism but without being subjected to vertical deflection.
7. A glass according to claim 6, characterized in that a region of maximum curvature of each stripe has a transverse profile (P0) defined by the equation of a conic.
8. A glass according to claim 6 or 7, characterized in that it includes a succession of stripes (S) in at least one zone that are separated by planes (PV) that are vertical and perpendicular to the plane of the glass.
9. A glass according to claim 6 or 7, characterized in that it includes a succession of stripes (S1, S2) in at least one zone that alternate between constituting ridges and furrows, adjacent stripes meeting without slope discontinuity in planes (PI) that are perpendicular to the plane of the glass and that slope relative to the vertical.

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