GB2123134A - Automobile headlamp - Google Patents

Abstract

A dipped beam headlamp for an automobile, of the type incorporating a reflector revolving around a central axis A-A, a dipped beam light filament (fc) arranged in front of the reflector and a diffuser G (not shown) forming the closure to the headlamp. The reflector has a principal peripheral parabolic surface (R) with a focus (F), and a central zone (Z) behind the dipped beam filament which consists of a parabolic surface whose focus (Fz) is closer to the filament than the focus of the principal parabolic surface. <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 thatfor automobiles to be driven on the left, similar headlamps would be used buttheir 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 itsfocus.

In headlamps ofthis type the light beam from the reflector converges quite strongly in the direction of the light diffuser, the convergence forming a concentration of light relatively close to the reflector. This results from imperfections in the actual structure of the headlamp. First of all, the images of the dipped beam filament produced by the base part of the mirror are initially convergent, and their projection on a frontal plane perpendicular to the optical axis of the headlamp (particularly on a frontal plane located 25 metres in front of the headlamp, as defined in the regulations currently in force) appears as a luminous crown having a dark centre, or "black hole".This black hole corresponds geometricallyto the central circular apertureofthe reflectorwhich is provided to serve as a passageforthe bulb. Generally, the black hole corresponds to a cone, the apex ofwhich is the headlamp, the value of the half-angle atthe apex being ofthe order of 30 This results in the disadvantage of unnecessarily intense lighting in the proximity ofthe headlamp (that is to sayinthefirstten metres in frontofthe headlamp) and relatively insufficient lighting ofthezone ofthe road which one wishes to see (that is to say from 20 to 60 metres from the headlamp).

Figure lisa schematic horizontal axial section through a known dipped headlamp. The headlamp comprises a parabolic reflector R with an axis of revolution A-A, a focus F, and a circular central aperture 0. Adipped beam filamentf,is located in front of the focus F, and a light diffuser/closure G is located in front of the reflector R. A masking cap C which only permits rays emitted by into reach the reflector R in the region used for the dipped lighting is located beneath thefiIamentf.The Figureshowsthe path of different light rays emitted by the filament fc, which may be light rays impinging upon the base of the reflector R,that isto say the region of the reflector R in the proximity ofthe aperture O, or on the periphery of the reflector R. The light rays shown illustrate the convergence ofthe first of these light rays reflected by the reflector R to form the concentration of light designated by N.

Figure la illustrates in a conventional mannerthe luminous projection ofthe dipped lighting obtained by such a headlamp on a standard screen at 25 metres.

In orderto obtain the dipped beam, the masking cap C eliminates the rays emitted by the filament which are directed towards those zones of the reflector which are not used for the dipped lighting i.e.

particularly those towards the lower part ofthe reflector. The cap has on its left and righttwo horizontal edges which are parallel to the axis A-A. On the screen these edges ofthe cap determine half-lines Bd and Bg which mark the limits to the projection ofthe dipped beam to the left and to the right respectively of the axis of illumination A-A.

Figure 1 a shows the black hole TN which, as has been said, is quite significant, the dipped lighting being arranged like a crown around it, as shown.

In anotherconnection, when the concentration of light resulting from the convergence ofthe rays reflected by the reflector is situated in the proximity of the light diffuser G, marked heating ofthe diffuser results and temperatures higherthan 100 and even 1 500C may be reached, particularly nearthe 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.

It is an object ofthe present invention to remedy these disadvantages.

According to the invention, there is provided a dipped beam headlamp for an automobile comprising a reflector, a dipped beam filament and a diffuser forming a closure to the headlamp, the reflector having a central axis A-A, a principal peripheral parabolic surface with a first focus, and a central zone behind the dipped beam filamentformed by a parabolic surface having a second focus which is closerto the filament than the firstfocus of the principal parabolic surface. The central zone is preferably defined as the zone of the reflector situated behind the dipped beam filament, such a definition being capable of interpretation in a purely approxi mate manner without departing from the scope of the invention.

The central zone may have a focal distance identical to that ofthe remainder of the reflector or a different focal distance, though it is preferably greater. The two parts ofthe reflector may or may not be stepped significantly.

The invention may be carried into practice in various ways and some embodiments will now be described by way of example with reference to Figures 2 to 5 of the accompanying drawings in which: Figure 2 is a front view of a reflector in accordance with the invention; Figures 3a, 3b, and 3cshowschematically, in horizontal axial section along the sectional plane H-H in Figure 2, three embodiments of a reflector accord ing to the invention; Figure4 is a graph showing the comparative light intensities of a conventional headlamp and a headlamp modified according to the invention; and Figure5showsthe appearance on a standard screen ofthe dipped beam produced by a reflector according to the present invention.

Referring to Figure 2, a reflector R has a modified central zone Z arranged like a crown around the aperture 0 ofthe reflector R, in the region 100 of the reflector Rwhich formsthe dipped beam. The zoneZis shown in hatched lines. The reflector R has a rectangularaperturecutoffin itsupperand lower parts represented by two flat sides J 1 and J2, though this is merely one example. As can be seen in this figure, the zone Z extends abovetwo half-planes 110 and 120 defining the cut-off plane, the half plane 110 being substantially in the horizontal plane H-H passing through the axis A-A, and the half-plane 120 being inclined by approximately 15 relative to H-H.The limits ofthe region ofthe reflector R contributing to the production ofthe dipped beam are defined by a cap Cthe edges of which parallel to the axis A-A defined the cut-off of the beam.

Outside the central zone Z, the reflector has the characteristics ofthe reflector shown in Figure 1. Itis parabolic with an axis A-A and its focus F is behind the lightfilamentfc. However, the central zone Z departs from the geometric shape ofthe reflector R. It is a parabolic zone with an axis A-A but its focus Fz is nearer to the filament fcthan the focus F of the principal peripheral zone of the reflector R outsidethe zoneZ.Thefocal distance fz ofthe central zone Z can be equal to the focal distance ofthe reflector R or it can be different.

In the case of Figure 3a, the zone Z has the same focal distance as the principal peripheral zone. Its focus Fz is in front ofthefocus Fofthe reflector R, but is close to the front end of the filament f,. There is a step D between the two parabolic surfaces.

In the case of Figure 3b, the focal distance fz of the zone Z is greaterthan the focal distance f of the reflector R. As in the previous case, the focus Fz is closerto the front end ofthe filament fc, and is in front of the focus F of the reflector R. Again, there is a step D between the two parabolic surfaces ofthe zone Z and the principal peripheral zone ofthe reflector R.

In the case of Figure 3c, the zone Z is focused at Fz, which close to the front end of the filament fc, the focal distances f,and f being different. The two parabolic surfaces do not have any discontinuity relative to one another. Such a reflector is very easyto produce in pressed steel.

In the three cases shown in Figures 3a, 3b, and 3c, thezoneZcan be defined as regards its limits as the zone extending around the rear aperture ofthe reflector (not shown in Figures 3a, 3b, 3c) and behind thefilamentfc In practice,forallthefocal distancesfusedforthe dipped headlamps,the radial dimension ofthecrown Z is preferably between 15 and 35 mm. This dimension of the crown corresponds to the difference between the radius rl ofthe limit ofthe zone 130 and the radius r0 of the aperture 0 (Figure 2).

With the reflector R modified according to the invention, that is to say with the creation of a central zone Zthefocus of which is in the proximity ofthe front end of the dipped beam filament, the dipped lighting may be improved. Figtire4 illustratesthis improvement. It shows the luminousflux in lumens, calculated in horizontal bands of 3/4"thickness and marked bytheir angular rabatment measured in degrees with reference to the axis ofthe headlamp (which corresponds to the distance with reference to the headlamp).

The curve obtained with the unmodified reflector R is shown in solid lines. Broken lines are used to represent the curve obtained with a reflector R modified according to the present invention with a zone Z extending behind the dipped beam filament.

Figure 4 shows that compared to the lighting obtained with the reflector R alone, the reflector modified according to the invention may show two advantages.

Firstly, as regards the lighting a short distance from the headlamp, that is to say at less than 8 metres approximately, the level of lighting is reduced, and secondly, for greater distances, the level of lighting is increased.

These two results are very advantageous, since lighting in the proximity ofthe headlamp is of little interest, whilst on the other hand for greater distances it is importantto raise the level of lighting in orderto improve visual comfort.

A comparison of Figures 1 and 5 illustrates thetwo advantages referred to. Thus, comparing the case of the known reflector R of Figure 1 a with the case of the reflector modified according to the invention (Figure 5), itwill be noted thatthere is a displacement of the images effectively distancing the lightfrom the vehicle. This is represented in Figure 5 by a reduction in the dimensions of the black hole compared to Figure 1a.

It should also be pointed outthatthe presence of a central zoneZwhich is modified relativetothe geometric shape ofthe reflector R constitutes an advantage in connection with the heating effect. Thus, the modification of the zone results in a spreading of the light compared to the concentration of light N. If the diffuserG ofthe headlamp is located in the proximity of the concentration of light N created by the reflector R,the modification accordingtothe invention reduces the risk of heating the diffuser by reducing the concentration of light in the region N since the zone Z givesto the light rays emitted byfc a different convergence from that given by the reflector R.

Finally, the central zone Z could also be provided with dispersing ribs if it is wished to reduce further the harmful concentration of light on the diffuser.

Claims (7)

1. A dipped beam headlamp for an automobile comprising a reflector, a dipped beam filament and a diffuserforming a closure to the headlamp, the reflector having a central axis A-A, a principal peripheral parabolic surface with a first focus, and a central zone behind the dipped beam filament formed by a parabolic surface having a second focus which is closer to the filament than the first focus ofthe principal parabolic surface.

2. A headlamp as claimed in Claim 1 in which the second focus of the central zone ofthe reflector is close to the rear end of the dipped beam filament.

3. A headlamp as claimed in Claim 1 or Claim 2 in which the principal surface and the central zone have the same focal distance.

4. A headlamp as claimed in Claim 1 or Claim 2 in which the principal surface and the central zone have different focal distances.

5. A headlamp as claimed in any preceding claim in which the principal surface and the central zone are connected by astep (D).

6. A headlamp as claimed in any of Claims 1 to 4, in which the principal surface and the central zone are connected without discontinuity.

7. Adipped beam headlamp constructed and arranged substantially as herein specifically described with reference to and as shown in Figure 2 together with any of Figures 3a, 3b and 3cofthe accompanying drawings.