GB2115543A

GB2115543A - Headlamp diffusion lens

Info

Publication number: GB2115543A
Application number: GB08236997A
Authority: GB
Inventors: Hector Fratty
Original assignee: Cibie Projecteurs SA
Current assignee: Cibie Projecteurs SA
Priority date: 1982-02-16
Filing date: 1982-12-30
Publication date: 1983-09-07
Also published as: JPS58147901A; DE3248386C2; IT8225055A1; GB2115543B; IT8225055A0; FR2521692A1; BR8207543A; ES276312Y; ES276312U; IT1153956B; DE3248386A1; FR2521692B1

Abstract

A dipped beam headlamp comprising a moulded glass diffusion lens situated in front of the reflector and the filament. The lens has an interruption to its slope in the form of a substantially horizontal ridge (a) which is situated at a distance below the axis (A) of the reflector (R) of less than one-quarter of the maximum useful aperture radius (R1) of the reflector (R). The zone (Z), defined by the segment I-I, of the interruption to the slope near the ridge has a plurality of fine vertical-deflection ribs (s) extending parallel to said ridge. <IMAGE>

Description

SPECIFICATION Dipped beam headlamp This invention relates to motor vehicle headlamps designed to emit a dipped-beam.

More particularly, it relates to dipped beam headlamps of the type comprising a parabolic reflector having an axis and a focus disposed on the said axis, an elongate lighting filament extending along the axis of the reflector and in front of its focus, cut-off means usually comprising a shield or screen surrounding at least the bottom part of the filament, and a moulded glass diffusion lens situated in front of the reflector and the filament.

Dipped beam headlamp constructions of this kind are quite conventional and in general use.

The cut-off shield and the filament are usually both built into a dipped beak bulb although it is possible to use a cut-off screen which surrounds the bulb. For information, reference may be made to the French Highway Code which sets out examples of optical and photometric standards for dipped beams. The main point is that a dipped beam projected on a standard screen situated 25 metres from the headlamp should appear to be defined by two straight lines which are termed the cut-off limits, the cut-off limit on the same side as that on which the traffic travels (i.e., the right in the case of France) being slightly raised about 1 50 from the horizontal, while the cut-off limit on the other side is substantially horizontal.

For an understanding of the following description it should be noted that with the headlamp construction described above the dipped beam comprises a number of ways to which the form of a convergent beam is imparted by the reflector. The useful rays of light of this beam pass through the top part of the end lens and also a narrow angular sector of the bottom part of the lens, this sector extending from the centre of the lens and below the horizontal, on the opposite side of the lens to that side of the road on which traffic travels, over an angle corresponding to the rise of the cut-off limit on the other side.In other words, for traffic driving on the right, the rays of the dipped beam pass through the top part of the lens and through a narrow angular sector below the horizontal on the left of the lens (with respect to the axis of movement of the vehicle on which the headlamp and the lens are assumed to be mounted).

Motor vehicle headlamps are usually completely built into the vehicle bodywork.

Consequently, the stylistic reasons they frequently deviate from the general conventional substantially flap shape. More particularly, it is sometimes desirable to give the lens the shape of a dihedral having a substantially horizontal axis, the bottom surface of the dihedral being inclined downwardly and rearwardly and the top surface being inclined upwardly and rearwardly.

The Applicants have recently studied the construction of a dipped beam headlamp provided with a lens of this kind forming a dihedral with a horizontal ridge, which forms the line along which the lens slope is interrupted, and a portion extending to the bottom part of the lens, which is made of moulded glass. The ridge is located at a vertical distance below the axis of the reflector (headlamp axis) of between one-eighth and onehalf of the (horizontal) maximum aperture radius of the reflector.

With a moulded glass lens of this kind, the interruption to the slope results in a radius of curvature which gives the glass zone in question the effect of a lens component. It should be noted that moulding imperfections make this radius of curvature fairly irregular, so that the optical effects of the interruption to the slope of the glass are necessarily uncertain.The Applicants have in any case confirmed by experiment with a number of lenses made from moulded glass and with the dihedral ridge which forms the slope interruption situated at different levels below the optical axis within the range indicated that the slope interruption causes uncontrollable and random deflections in respect to rays of the dipped beam passing through the slope interruption zone, this effect resulting in distortion of the cut-off limit, more particularly on the side corresponding to the traffic side and hence the risk of glare or dazzle from the dipped beam headlamp.

An exhaustive study of the available literature on dipped beam headlamps has not revealed any publication relating to this problem.

The present invention proposes a solution to this problem which goes beyond the obvious remedy which would lie in simpiy eliminating from from the beam those rays which impinge on the slope interruption zone forming the ridge of the dihedral of the lens. A remedy of this kind which could, for example, comprise rendering opaque the zone in question, is unsatisfactory because it produces a loss of luminous flux and, of course, it is very difficult to render a lens portion opaque without additional operations.

According to the invention, there is provided a dipped beam headlamp comprising a parabolic reflector, an elongate lighting filament extending along the axis of the reflector and in front of its focus, cut-off means surrounding at least the bottom part of the filament and a diffusion lens situated in front of the reflector and the filament, in which the lens has an interruption to its slope in the form of a substantially horizontal ridge situated at a distance below the axis of the reflector of less than one-quarter of the maximum useful aperture radius of the reflector and in which the zone of the interruption to the slope near the said ridge has a plurality of vertically extending deflection ribs extending parallel to the ridge. The ribs are preferably disposed solely on the side corresponding to the side of the road on which the traffic travels.

The ribs may have, for example, an undulating profile in section and a total amplitude variation of the order of 1 to 3-tenths of a millimetre, the rib height zone being, for example, between 2 and 10 millimetres.

With an arrangement of this kind, the optimum cut-off conditions for the dipped beam can be restored and in addition low-level ambient illumination may be produced on the traffic side of the road above the cut-off limit and this may advantageously facilitate the vehicle driver's reading of road signs on the side on which the traffic drives. The reason for this is that the ribs may significantly raise a fraction of the luminous flux emitted thus bringing it to a useful height corresponding to the road sign.

The invention may be carried into practice in various ways and some embodiments will now be described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic vertical axial section of a dipped beam/main beam headlamp comprising a lens in the form of a dihedral whose ridge forms an interruption to the slope; Figure 2 is a front view of a headlamp of this kind showing the construction of its lens; Figure 3 is a diagrammatic section on the line Ill-Ill in Figure 2 showing the profile of the ribs; Figure 4 shows the photometric characteristics of a dipped beam produced, on a standard screen at a distance of 25 metres, by the headlamp shown in Figure 1 in the absence of the ribs which characterise the invention; and Figure 5 is a view similar to Figure 4 but in respect to a headlamp whose lens is provided with ribs according to the invention.

The headlamp shown in Figures 1 and 2 is of the dipped/beam type with a rectangular front opening.

It consists essentially of a parabolic reflector R having the axis A-A, a lamp L disposed inside the reflector R, and an end lens G disposed in front of the reflector R at the lamp L. The lens G is in the form of a dihedral having a substantially horizontal ridge a defined by a substantially flap top wall P, which is inclined upwardly and rearwardly, and a bottom re-entrant wall P2 i.e., it is inclined downwardly and rearwardly, the intersection of the walls P1 and P2 defining the ridge a.

The ridge a is disposed below the axis A-A at a vertical distance h therefrom, this distance being less than one-quarter of the maximum aperture radius of the reflector R, i.e., the dimension R, shown in Figure 2.

The lamp L comprises a main beam filament fr and a dipped beam filament fc disposed on the axis A-A. The focus F of the reflector R is also situated on the axis A-A near the main beam filament fr; the dipped beam filament fc is in turn disposed in front of the focus F. The bottom part of the filament fc is surrounded in a manner known per se, by a shield C which in known manner selects the rays emitted by fc to form the dipped beam.

Figure 2 shows the structure of the lens which comprises various zones etc, provided with ribs having an optical effect and which, in manner known per se, play their part on either the main or dipped beam to give it the optimum configuration.

The effect of each of these zones is in accordance with conventional practice and will not be described in detail since it does form part of the invention. For an understanding of the invention all that is required is to know that the zones of the lens through which the dipped beam rays pass are those situated above the line X A-X in Figure 2.

The problem with which the invention is concerned arises out of the fact that the dihedral shape of the lens causes the ridge a to intersect that zone of the lens which results in the formation of the dipped beam. This intersection occurs along the segment I-I of the ridge a. With a headlamp structure of this kind, the exact dimensions and parameters of which need not be given here, the presence of an interruption to the slope of the lens at the ridge a would result in an unacceptable dipped beam in the absence of any specific arrangements to the contrary.

Figure 4 illustrates this theory. It shows the photometric curves obtained by projection on a standard screen at a distance of 25 metres, using a glass lens of the structure shown in Figure 2 with a headlamp of the kind described above.

Referring to Figure 4 references 1g and 1d denote the theoretically desirable cut-off limits as defined by the left-hand and right-hand standards for a vehicle driven on the right. The numerical values given in Figure 4 are expressed in candelas. It will readily be seen that there are appreciable luminous fluxes above the optimum cut-off limit 1g, 1d.

Those versed in the art will readily appreciate that a dipped beam of this kind is unsatisfactory because it is likely to cause dazzie, and does not have the clean cut-off limit desirable and recommended by the standards.

This drawback is obviated by providing in that zone of the lens which surrounds the segment I I of the ridge a, plurality of vertical-deflection ribs s disposed parallel to the ridge a. Such ribs extend, for example, on either side of the axis I-I over a height of 3-10 mm, the rib pitch being of the order of one to some tenths of a millimetre.

The ribbed zone Z is shown in section in Figure 3 which shows the rib profile as an undulating or sinusoidal profile though it may have any other sectional shape adapted to give the rays of light and most widely varying upward or downward vertical deflections.

Such ribs disposed parallel to the lens ridge a are easy to make during the moulding of the lens.

The die used to form the lens may be given a ridge corresponding to the ridge a and, on the other hand, ribs parallel to such ridge, without any difficulty.

Figure 5 shows the effect of the ribs s in the zone Z. This is an identical illustration to Figure 4, all the characteristics of the headlamp being assumed to be unchanged except for the presence of the ribs s.

Referring to Figure 5 it will be seen (a) that the useful luminous flux is generally brought below the cut-off limit 1 g1 d; and (b) that the ribs s result in an ambient illumination peak E immediatley to the right of the illumination axis above the cut-off limit 1 dug This illumination peak E is of low intensity since it does not exceed a few hundred candelas. It does not destroy the clean cut-off impression. However, this ambient illumination is sufficiently strong to illuminate satisfactorily road signs appearing on the right of the road.

Thus the invention successfully solves the new problem arising out of the need to interrupt the inclination of the lens of a headlamp, a factor whih may have an adverse effect on optimum formation of the dipped beam. Aiso, with the solution according to the invention, the dipped beam incorporates a new function, i.e. an ambient illumination peak above the cut-off in the direction of travel, and this facilitates the vehicle driver's view of road signs.

The solution is applicable not only to headlamps having a rectangular opening, but all headlamps if their lens has an interruption to the slope which is likely to interfere with the dipped beam. As already stated, for the solution according to the invention to be significantly applicable the ridge a of the dihedral must be situated beneath the horizontal axis and spaced from the optical axis by a distance less than onequarter of the maximum aperture radius of the reflector.

It should also be noted that the application of the solution according to the invention is all the more effective the farther the dipped beam filament fc is away from the focus F of the reflector R. In practice the best results are obtained with a distances of 2-3 mm between focus F and the nearest end of the dipped beam filamentf. The amplitude variation in respect of the rib height ranges from 1 to a few tenths of a millimetre, like their pitch.

As will be appreciated, while the embodiment described has been in relation to headlamps for automobiles driving on the right, the invention is equally applicable to headlamps for automobiles driving on the left. In such cases, the shield C would be such as to produce a beam which is laterally inverted, i.e. the cut-off limit is raised by about 1 50 from the horizontal on the left.

Claims

1. A dipped beam headlamp comprising a parabolic reflector, an elongate lighting filament extending along the axis of the reflector and in front of its focus, cut-off means surrounding at least the bottom part of the filament, and a diffusion lens situated in front of the reflector and the filament, in which the lens has an interruption to its slope, in the form of a substantially horizontal ridge situated at a distance below the axis of the reflector of less than one-quarter of the maximum useful aperture radius of the reflector and in which the zone of the interruption to the slope near the said ridge has a plurality of vertically extending deflection ribs extending parallel to the ridge.

2. A dipped beam headlamp as claimed in Claim 1, in which the ribs have an undulating profile in section with a total amplitude variation of the order from one to some tenths of a millimetre, the height of the zone to the ribs being between 3 and 10 mm.

3. A dipped beam headlamp as claimed in Claim 1 or Claim 2 in which the ribs extend in the zone of the interruption to the slope over a segment limited to that part of the lens through which the rays of the dipped beam pass.

4. A dipped beam headlamp constructed and arranged substantially as herein specifically described with reference to and as shown in the accompanying drawings.