EP0623780B1 - Converging lens for vehicle headlamp - Google Patents

Description

The invention relates to a vehicle headlight projection lens for generating a low beam pattern, in which the convex emission surface of the lens has different imaging sections, an upper section lying above the horizontal plane through the optical axis and a lower section lying below this horizontal plane being provided.

Such a projection lens is shown in DE-OS 36 02 262 for a headlight for low beam or fog light, which has an aperture covering the lower section of the reflector, the upper edge of which produces the light / dark boundary.

In contrast, the projection lens according to the invention of the type mentioned at the outset is not limited to such a headlight construction and is characterized in particular by the fact that at least two lower sections are provided, one of which has an upper boundary that rises above the horizontal plane towards the lateral lens edge, or one that differs continuously imaging surface (open area) is provided.

Further advantageous embodiments of the projection lens according to the invention, which can be implemented individually or in combination, are the following:

The rising upper boundary can preferably be arranged on one side of the vertical plane through the optical axis; it can touch the horizontal plane at a point which is the point of intersection of a horizontal beam with the emitting surface, which extends from the point of intersection of the optical axis with the incident surface of the lens facing the light source at an angle to the optical axis.

The angle between the horizontal beam and the optical axis is expediently between ± 5 °.

The curvatures of the radiation surface in the vertical section through the lens from the horizontal plane through the optical axis can be to the respective Lens edge be flatter.

The length of the lens contour in the upper lens section can be greater than in the lower lens section.

The curvatures of the radiation surface in the lower section can be a mirror image with respect to the horizontal plane through the optical axis with respect to the curvatures in the upper section.

The lower section with increasing horizontal upper boundary is formed by rotating the horizontal section through the horizontal beam by 15 °, which is defined by the intersection curve of the vertical plane running through the horizontal beam with the radiation surface, the intersection curve of the horizontal plane through the optical axis with the radiation surface and the lens edge , a transition gusset with a running curvature being provided between the twisted section and the remaining lower section.

The incident surface of the lens can be provided at right angles to the optical axis.

The incident surface can be provided, preferably as a rectangle, for coupling to an optical fiber bundle.

The lower boundary of the light irradiation surface can be arranged in the horizontal plane through the optical axis.

Furthermore, the lens body can extend essentially in the shape of a truncated pyramid or in the shape of a truncated cone from the irradiation surface to the radiation surface.

The invention is explained in more detail below on the basis of an exemplary embodiment with reference to the drawing, in which FIG. 1 shows an axonometric oblique bottom view, FIG. 2 shows a bottom view, FIG. 3 shows an end view (view of the radiation surface), FIG. 4 shows a side view, 5 a vertical section through the optical axis and FIG. 6 a vertical section through the optical axis with beam path and Represent radiation imaging on a vertical plane 25 m in front of the lens with respect to a projection lens according to the invention.

From Fig. 1 it can be seen that the convex radiation surface of the lens 1 has an upper and three lower sections. The upper section is delimited by the lens edge 2 and the lines A and B, of which A lies in the horizontal plane through the optical axis 3 and B rises to the lens edge at 7.5 ° relative to the horizontal plane. A lower section is delimited by A, the lens edge 2 and the line C; this is followed by a transition gusset which is delimited by line C, lens edge 2 and line D, and a further section which is delimited by line D, lens edge 2 and line B. The lines A-D are not to be regarded as edges in the radiation area - although such an embodiment is possible - but as lines along which the curvature changes to the transition to the neighboring section.

The lines A-D touch each other in point 4, the meaning of which will be explained below.

A rectangle 5 perpendicular to the optical axis is provided as the lens irradiation surface, which sits with its lower edge centrally (point P) on the horizontal plane through the optical axis 3 and to which an optical fiber bundle can be coupled. The light exit band 6 of the optical fiber bundle, not shown, is - as indicated - vertically displaceable for the headlight range adjustment, which can take place by relative displacement between the light source and the light entry surface of the optical fiber bundle.

In the bottom view according to FIG. 2, the line C and point 4 come about by cutting a vertical plane 7 through the point P, which is the point of intersection of the optical axis with the light entry surface 5 of the lens 1, with the emission surface of the lens. The vertical plane 7 is inclined to the vertical plane through the optical axis 3 by approximately 3 to 5 °. From Fig. 3 it can be seen that line C is a curve on the radiation surface of the lens. The imaginary section delimited by the line C, the lens edge 2 and the horizontal plane 8 by the optical axis 3 becomes the formation the so-called gusset with asymmetrical low beam is pivoted upward by 15 ° around the connecting line P4 as a pivot axis, as a result of which CD and the pivoted imaginary section, together with the upper section symmetrical with respect to the horizontal plane 8, form a surface intersection line B which is inclined by 7.5 ° to the horizontal plane . In the remaining gusset, delimited by C, the lens edge 2 and D, the surface curvatures are chosen to pass smoothly.

4 to 6 that the contour 0 of the upper half of the radiation surface is longer in vertical section than its lower contour U, i.e. the distance between the intersection of the optical axis with the radiation surface and the upper lens edge is greater than that between this intersection and the lower lens edge.

In Fig. 6, the beam path in the central vertical plane is drawn from a light entry surface with the height h, provided that the light guide bundle does not transmit parallel light, but is fed by a point light source, so that edge rays emerge at an angle to the optical axis. In the vertical section it is a condition that the upper and lower half of the radiation surface produce sharp images in the horizontal plane through the optical axis; fuzzy images below this result automatically. These images P and P 'are shown on a vertical projection wall 10 25 m in front of the lens 1.

The contour of the lower half of the radiation in FIGS. 4-6 is essentially symmetrical to the horizontal plane through the optical axis.

= 1 erfüllen müssen.Diese Bedingung gilt für Lichtstrahlen ausgehend von der der Horizontalebene durch die optische Achse zugewandten Kante des Lichtbands, die in der Horizontalebene in 25 m Abstand von der Linse (bzw. 5 m für die Tabelle) enden.The curvature of the radiation surface is calculated iteratively approximately, with the points of the curve in relation to the optical axis being the condition in the central vertical section $\frac{\text{n.sinα}}{\text{sin β}}$

This condition applies to light rays starting from the edge of the light band facing the horizontal plane through the optical axis and ending in the horizontal plane at a distance of 25 m from the lens (or 5 m for the table).

Here n is the refractive index of the lens material (here n = 1.49 assumed), the angle of incidence α and β included with the tangent normal of the respective surface point is the corresponding departure angle, taking into account that the transition from the solder to the optically denser / optically thinner, ie β> α.

The coordinates were determined on the basis of a lens length (distance between the irradiation surface and the intersection of the optical axis with the emission surface) of 90 mm and a lens height of 70 mm. The lens height results from the numerical aperture of the light guide or the maximum opening angle of the light cone in the lens material, starting from the boundary of the incident surface; here about 55 °.

In the following table, z is the coordinate of the respective point on the optical axis and y the distance of this point from the optical axis, each in mm.

In the case of projection lenses for producing low beam, the vertical cut contours are particularly important; the horizontal cut contours are not critical and can e.g. Be circular sections with flattened edge areas; this is regulated by the width of the desired light pattern and the required central illuminance.

The projection lens according to the invention does not have to be provided for irradiation via an optical fiber bundle; usual light sources / reflector combinations can also be provided. The rear irradiation surface of the lens is designed accordingly. The projection lens with a flat irradiation surface shown in Figs. 1-4 can e.g. can be used very well with a light source with an ellipsoid reflector.

As already mentioned in connection with FIG. 1, a relative displacement between the light source and the light entry surface of the optical fiber bundle enables the light exit band on the light entry surface of the lens to be shifted for the headlight range adjustment. This is particularly effective if the light guide transmits light bundled in parallel, since a sharp light band limitation can then be achieved in the optical fiber bundle. The displacement of the light band across the cross section of the optical fiber bundle is particularly easy to implement in an arrangement in which at least one light source in the form of a flash lamp is moved past the inlet openings of successive optical fiber bundles. In this case, the time of flash firing is the control factor for determining the position of the light band in the entry surface of the projection lens and thus the lighting range. The light band limitation can also depend on the light exit surface of the light entry surface of the Optical fiber bundle passed reflector (eg 5 x 10 mm) and the gap between them (eg 0.1 mm) because the edge blur of the light band also decreases with a decreasing gap.

The light band limitation can be adjusted according to static criteria (inclination of the optical axis to the horizontal due to vehicle load) and / or dynamic criteria (compensation for uneven roads), as well as depending on the light emitted by oncoming vehicles.

It is understandable that - with reference to FIGS. 1 and 6 - the further the light band 6 of the lens entrance surface 5 of the lens 1 is from the horizontal plane 8 through the optical axis 3, the smaller the light range. the further it is in the upper half of the lens.

There are various types of optical fiber bundles in terms of the cross section of the fibers that make them up. A film stack is preferred for the lens construction shown, the films of which lie on the light entry surface 5 of the lens 1 parallel to the horizontal plane 8 through the optical axis 3 and preferably have a thickness of 0.2 mm.

E.g. In this way, an at least one-dimensional strip order can be achieved in the light guide bundle, with different orders also being able to be provided within the individual strips. In general, the smallest possible angular resolution of the light exit angle of the light guide bundle is aimed for with a sharp light / dark edge, the angular resolution preferably not being constant over the bundle cross section. It is also preferred that the illuminance distribution over the bundle cross section is not constant.

It is known that direct coupling of optical fiber bundles with one another and with lens surfaces increases the reflection losses; it is therefore preferred to join the coupling points with a self-crosslinking resin that can be removed later. Silicone rubbers that form an elastomer are suitable for this. Couplings with large refractive index transitions are preferred.

There is also the possibility of varying the light intensity distribution in the light band 6; This is done through the targeted use of appropriately shaped reflectors that project the light from the light source into the optical fiber bundle.

While the light entry surface of the lens is shown in the figures as rectangular and at right angles to the optical axis, it can be different in shape - e.g. be adapted to the light exit surface of light guide bundles of any cross section. The projection lens according to the invention is furthermore not limited to feeding via optical fiber bundles; in particular not the solid lens of uniform cross section shown in the figures, which can also be illuminated using incandescent lamps / reflector combinations. Furthermore, the light entry surface of the lens can be at an angle to the optical axis, e.g. in the case of flat headlights in which the entire luminous flux has to be deflected by refraction and in which the light irradiation surface of the projection lens can then be up to about 25 ° to the optical axis. The light incident surface of the projection lens can also be particularly preferably a curved surface in order to achieve the greatest possible image sharpness.

The outer surfaces of the projection lens according to the invention - of course with the exception of the irradiation surface and the radiation surface - can be opaque to increase the light output, especially coated white.

Claims (11)

1. A vehicle headlight projection lens for creating a low beam pattern, wherein the convex light-emitting surface of the lens has portions of different image-forming characteristics, provision being made for an upper portion located above the horizontal plane through the optical axis and a lower portion located below this horizontal plane, characterized in that at least two lower portions are provided, one of which has an upper boundary ascending above said horizontal plane (8) towards the lateral edge of the lens, and/or that a surface with steadily varied image-forming characteristics (so-called complex surface or computer-calculated surface) is provided.
2. The projection lens according to claim 1, characterized in that the ascending upper boundary (B), preferably located on one side of the vertical plane through the optical axis, contacts the horizontal plane in a point (4), which is the intersection of a horizontal ray (7) with the light-emitting surface, said horizontal ray running from the intersection (P) of said optical axis (3) with the light-receiving surface (5) of the lens, facing towards the source of light at an angle with regard to said optical axis.
3. The projection lens according to claim 2, characterized in that the angle between horizontal ray (7) and optical axis (3) is between ± 5°.
4. The projection lens according to any of claims 1 to 3, characterized in that the curvatures of the light-emitting surface in vertical section through lens (1) become less arcuate from horizontal plane (7) through optical axis (3) towards the respective edge of the lens.
5. The projection lens according to claim 4, characterized in that the length of the lens contour is longer in the upper lens portion than in the lower lens portion.
6. The projection lens according to any of claims 4 to 5, characterized in that the curvatures of the light-emitting surface in the lower portion form a mirror image with regard to the horizontal plane (8) through the optical axis (3) of the curvatures in the upper portion.
7. The projection lens according to any of claims 2 to 6, characterized in that the lower portion having the ascending upper boundary (8) is formed by pivoting the imaginary lower portion confined by the intersection curve (C) of the vertical plane running through the horizontal beam (7) with the light-emitting surface, the intersection curve of the horizontal plane (8) through the optical axis (3) with the radiating surface, and the lens edge (2), by 15° around horizontal beam (7), a transition wedge zone of approximation curvature being provided between said pivoted portion and the remaining lower portion.
8. The projection lens according to any of claims 1 to 7, characterized in that the light-receiving surface (5) of lens (1) is plane and at right angles to the optical axis (3).
9. The projection lens according to claim 8, characterized in that the light-receiving surface (5) is provided as a rectangle for coupling to a bundle of light-transporting elements.
10. The projection lens according to claim 9, characterized in that the lower boundary of the light-receiving surface is located in the horizontal plane (8) through the optical axis (3).
11. The projection lens according to any of claims 9 or 10, characterized in that the lens body extends from the light-receiving surface (5) to the light-emitting surface substantially in the form of a truncated pyramid or of a truncated cone.

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