GB2121947A

GB2121947A - Dipped headlamp for automobiles

Info

Publication number: GB2121947A
Application number: GB08315863A
Authority: GB
Inventors: Marc Stephano; Jean-Marie Brel
Original assignee: Cibie Projecteurs SA
Current assignee: Cibie Projecteurs SA
Priority date: 1982-06-09
Filing date: 1983-06-09
Publication date: 1984-01-04
Also published as: FR2528536A1; FR2528536B1; JPS595503A; IT8321516A0; DE3320662A1; DE3320662C2; GB8315863D0; GB2121947B; IT1206491B

Abstract

A dipped headlamp for automobiles, incorporates a parabolic reflector (R) revolving about a central optical axis (A-A), with a focus (F) arranged on this axis, at least one longitudinal dipped beam filament (fc) arranged on this axis in front of the focus (F), and a transparent cover and light diffuser. The base of the reflector has an aperture (O) revolving about this axis, and a crown-like zone (Z) which is located around the aperture (O) in the region of the reflector (R) serving for the formation of the dipped beam. This zone is provided with dispersing ribs (S1 and S2), and is defined at least approximately by the condition that every elementary mirror point of the zone (Z) projects on the frontal plane of the diffuser an image enclosing a trace of the optical axis. <IMAGE>

Description

SPECIFICATION Dipped headlamps for automobiles The present invention relates to headlamps for automobiles in particular, those incorporating a reflector, at least one light source co-operating with the reflector and a light diffuser.

The headlamps described in the present application are those intended for use in automobiles driven on the right hand side of the road and it is to be understood that for automobiles to be driven on the left, similar headlamps would be used but their design would be laterally inverted.

It should be understood that the term "headlamp" as it is used here is applicable both to optical units in which the light diffuser is fixed in front of the reflector, and to more complex systems in which the reflector is accommodated in a casing which may or may not be integrated into the body of the vehicle, the light diffuser being integral with the casing. Also, the headlamps can be either specialised headlamps for producing dipped beams headlamps which can function as dipped beam headlamps (for example, a main/dipped headlamp having both a main beam filament and a dipped beam filament).

Such headlamps may have a longitudinal dipped beam light filament arranged in the axis of a parabolic reflector and slightly in front of its focus.

Such dipped headlamps are widely used. The light beam from the reflector converges quite strongly in the direction of the light diffuser, the convergence thus forming a concentration of light relatively close to the reflector. Figure 1 shows such a dipped headlamp according to the prior art in schematic horizontal axial section. The headlamp comprises a parabolic reflector R with an axis of revolution A-A, a focus F and a circular central aperture 0, a longitudinal dipped beam filament Fc located in front of the focus F, and a transparent light diffuser and closure G. In a manner which is known per se a cap C partially surrounds the filament fc in order to restrict the light rays to strike a particular region of the reflector R to produce the dipped beam.The figure shows the path of different light rays emitted by the filament fc and not masked by the cap C, which may be light rays impinging upon the base of the reflector R, that is to say the region of the reflector R in the proximity of the aperture 0, or on the periphery of the said reflector R. The light rays shown illustrate the convergence of the light rays reflected by the reflector R and forming the concentration of light designated by N.

When such a concentration of light is situated, as shown in Figure 1, in the proximity of the light diffuser G, marked heating of this diffuser results and temperatures higher than 100 and even 1 500C may be reached, particularly near the optical axis A-A. Such heating is harmful: for a light diffuser made from glass there is a risk of it causing breakage of the glass at the slightest splash of water; in the case of a light diffuser made from plastics material, heating causes softening, deformation and irreparable deterioration. This problem does not seem to have been solved satisfactorily as yet with the aid of various means for the partial masking of the light rays forming the concentration of light, placed at various points in the path of these rays.

It is an object of the present invention to provide a solution to this problem.

According to the invention there is provided a dipped beam headlamp for an automobile comprising a parabolic reflector having a central optical axis and a focus arranged on this axis, a dipped beam filament located on this axis in front of the focus, and a light diffuser forming a closure to the headlamp, the base of the reflector having an aperture revolving about this axis and a crownlike zone extending around the aperture in the region of the reflector which forms the dipped beam, the said zone being provided with dispersing ribs.

Preferably, the crown-like zone is defined at least approximately by the condition that every elementary mirror point of the zone projects on the frontal plane of the diffuser an image enclosing a trace of the optical axis.

The crown-like zone may alternatively be defined as that zone in which every elementary point of the reflector gives from the dipped beam filament fc an image which cuts the optical axis at the position of the light diffuser G. It will be understood that such definition which can be achieved in a simply approximate manner without departing from the scope of the invention is linked to the distribution of light at the centre of the diffuser G.

The ribs can be symmetrical or asymmetrical depending upon whether one chooses simply to spread the concentration of light indiscriminately or to spread it in a preferred direction.

The invention may be carried into practice in various ways and some embodiments will now be described with reference to Figures 2, 3, 4 and 4a of the accompanying drawings in which: Figure 2 is a front view of a rectangular parabolic reflector in accordance with the invention; Figure 3 is a perspective view from the front of a headlamp according to the invention; Figure 4 is a front view of the ribbed zone of the reflector illustrating the layout of the ribs; and Figure 4a is a schematic representation of the transverse section of a rib.

The headlamp to which the invention is applied is generally of the type shown in Figure 1, but with significant modifications in order to influence the concentration of light N.

Referring to Figure 2, the reflector R has a modified central zone Z arranged like a crown around the central aperture 0 of the reflector Rin the region of the reflector R which is responsible for the formation of the dipped beam. The zone Z is provided with ribs, and is shown in hatched lines in Figure 2. The reflector R has a rectangular aperture limited above and below by two flat sides J1 and J2 through this is merely one example. In this reflector R only an upper region 100 serves for the formation of the dipped-beam, the region 100 being defined in a conventional manner by horizontal right-hand half-plane 110 which extends from the optical axis A-A of the reflector and a left-hand cut-off half-plane 120 which is inclined downwards at an angle of approximately 1 50 from the optical axis A-A.This limitation is produced by the cap C in a manner which is known per se, the cap intercepting all the rays emitted by the filament fc and which would otherwise impinge upon the relfector R outside the zone 100.

The zone Z is a crown-like zone extending around the aperture 0 of the reflector R between the aperture 0 of radius r0 and a concentric outline 130 corresponding to the intersection of the reflector R by a cylinder having an axis A-A and a radius r1. The maximum for dimension r1 can be obtained either in an empirical manner or by calculation. The limit of the zone Z is the position on the reflector of any point M from which the image i" of the filament fc projected in the frontal plane of the light diffuser PG no longer contains a trace P of the axis A-A.

It should be noted that if the radial dimension r1 defines such a limit in the axial vertical half plane V the same applies in all radial planes passing through the axis A-A. In fact, for an inclined radial plane passing through the axis A-A of the reflector R, the elementary images vary in inclination according to the inclination of the chosen plane, which means that the images are more or less inclined according to the inclination of the plane, but one and the same radial dimension makes it possible to trace the limit 130 of the zone Z beyond which the elementary images no longer contain the trace P of the axis A-A.In effect, the optical system revolves symmetrically with reference to the axis A-A and, for a variation in the inclination of the chosen radial plane, the elementary images from the reflector turn about the point P, but, for a given radial dimension of a point on the reflector, the images are always at the same distance from the point P. This is why the limit 130 appears as a circle traced on the reflector R, this circle having a radial dimension of r,.

Thus the zone may be defined and it is clear that it is the light rays from this zone 2 which contribute predominantly to the formation of the concentration of light N.

By way of example, for a parabolic mirror having a focal distance of 26.5 mm, and an aperture 0 having a radius r0 of 23 mm; the value r1 is then 41 mm.

Having defined geometrically the zone Z of the region 100 of the reflector R it is there that the dispersing ribs are laid out. This layout is illustrated in Figures 4 and 4a. In the chosen example, the ribs S1 which affect the main part of the zone 100 are vertical ribs of part circular cross-section. The ribs S2 are also part circular in cross-section but extend slightly obliquely between the half-plane h-h located a small distance above the plane H-H passing through the axis A-A and the half-plane 1 20 defined above.

The ribs S 1 and Sz widen the spot of light corresponding to the concentration N. It should be noted that the ribs S2 are inclined by approximately 1 50 to the horizontal and arranged at right angles to the cut-off plane 1 20 in such a way that the dispersion of light which it produces remains parallel to this cut-off plane. This means that there is no risk of the ribs bringing the light in front of the cut-off in a projection on a frontal screen.

Finally, although the ribs such as S,, S2 have been defined as being symmetrical, the expert in the art will easily understand that asymmetrical ribs could equally be used (for example parabolic sections offset at an angle), which make it possible to spread the beam emitted by the zone Z and, if required, to divide the beam into two spots located on either side of the point P.

As has been seen above, the zone Z can be determined strictly, within the framework of the definition given, i.e. whether or not the images of the dipped beam filament in the general plane of the light diffuser contain a trace of the optical axis. However, in practice, less strict solutions can provide appreciable results which are in any case sufficient. For parabolic reflectors used in practice for dipped headlamps, the radial dimension of the zone Z lies preferably within the range 25 mm+10 mm.

Within these limits, any ribbed zone surrounding the aperture 0 of the reflector should be considered falling within the scope of the present invention, since it provides the essential advantages as regards the dispersion of the concentration of light with a view to avoiding heating. The ribs can be chosen in many ways provided that they produce the dispersion of the spot of light N within the limits of widening i.e.

with a coefficient of spread preferably between 2 and 10.

The ribbed reflectors according to the invention could equaliy well be metal reflectors or reflectors made from a plastics material, though reflectors made from a plastics material and produced by moulding are particularly suitable for the production of the ribs.

Claims

1. A dipped beam headlamp for an automobile comprising a parabolic reflector having a central optical axis and a focus arranged on this axis, a dipped beam filament located on this axis in front of the focus, and a light diffuser forming a closure to the headlamp, the base of the reflector having an aperture revolving about this axis and a crownlike zone extending around the aperture in the region of the reflector which forms the dipped beam, the said zone being provided with dispersing ribs.

2. A headlamp as claimed in Claim 1 in which the crown-like zone is defined at least approximately by the condition that every elementary mirror point of the zone projects on the frontal plane of the diffuser an image enclosing a trace of the optical axis.

3. A headlamp as claimed in Claim 1 or Claim 2 in which the dispersing ribs are vertical for the main part of the zone.

4. A headlamp as claimed in any preceding claim in which the dispersing ribs situated below the optical axis (A-A) are inclined by approximately 1 50 to the horizontal.

5. A headlamp as claimed in any preceding Claim in which the ribs are symmetrical ribs of part circular cross-section.

.

6. A headlamp as claimed in any of Claims 1 to 4 in which the ribs are symmetrical ribs.

7. A headlamp as claimed in any preceding Claim in which the crown-like zone has a radial dimension of 25 mm+10 mm.

8. A headlamp as claimed in Claim 5 in which the ribs have a coefficient of spread between 2 and 10.

9. A dipped beam headlamp constructed and arranged substantially as herein specifically described with reference to and as shown in Figures 2, 3, 4 and 4a of the accompanying drawings.