GB2109530A

GB2109530A - Automobile headlamp

Info

Publication number: GB2109530A
Application number: GB08232233A
Authority: GB
Inventors: Pascal Rol
Original assignee: Cibie Projecteurs SA
Current assignee: Cibie Projecteurs SA
Priority date: 1981-11-12
Filing date: 1982-11-11
Publication date: 1983-06-02
Also published as: FR2516203A1; ES282728U; BR8206520A; JPS5887701A; IT8224238A0; ES282728Y; GB2109530B; SE8206127L; SE8206127D0; IT1153023B; DE3241826C2; FR2516203B1; DE3241826A1; JPS6132761B2

Abstract

A headlamp for an automobile, incorporating a light source provided with a substantially cylindrical filament f, an elliptical reflector C having two foci F1, F2, one of which is located in the proximity of the filament f and the other in front of this filament, and a converging lens L the focus of which is in the proximity of the front focus of the reflector C. The reflecting surface of the reflector is modified in a critical zone Z of the reflector, this critical zone Z being defined as that capable of projecting on a standard screen, images of the filament forming a predetermined angle a at most equal to 30 DEG with the vertical. <IMAGE>

Description

SPECIFICATION Automobile headlamp The present invention relates to automobile headlamps, in particular to the type incorporating a light source, a condenser, forming a flux regenerator and consisting of an elliptical reflector, and a converging lens. The light source is located at the rear focus and the lens focus is in the proximity of the front focus of the regenerative condenser. Thus the rays emitted from the source and reflected by the regenerative condenser are brought by the lens into the direction of the axis of emission.

Such a headlamp construction is not conventional. In conventional automobile headlamps a parabolic reflector is used, with a light at its focus and a light-distributing glass in front of this reflector. However, the aforesaid construction, which makes use of a regenerative condenser and is known in theory, would seem equally interesting in practice since it permits optimum regeneration of the luminous flux emitted by the light. This is because an elliptical regenerative condenser encloses the flux over a greater solid angle, whilst occupying a smaller volume than that taken up by a conventional parabolic reflector.

With a headlamp having an elliptical regenerative condenser of the type referred to above it would be possible to obtain cut-off beams using a mask (cover or screen) arranged in the proximity of the front focus of the condenser.

Figure 1 shows schematically in horizontal section the structure which thus serves as a basis for the present invention. This shows the condenser C, with its two internal and external foci F1 and F2, the filament of the light f arranged at the focus F1, the mask 0 arranged at the focus F2, and the lens L the focus of which is also at F2.

The optical axis of the system is designated AA.

Figure 1 also shows the path of the light rays. It will be seen that the mask intercepts and eliminates the light rays which are capable of providing rays rising to the outlet of the lens and which are indicated by double hatching.

Experiments conducted by the applicants and strengthened by theoretical considerations show, however, that this type of headlamp has a severe drawback in automobile lighting. It is a system which is symmetrical in revolution and, disregarding the mask which cuts off a part of the beam, projects circular and concentric isocandela lines on a screen at 25 metres of the type used in standardising automobile lighting. In practice, this type of lighting is not satisfactory since it takes the form of a trail of light on the road whereas the general aim is to achieve a horizontally spread area of illumination.

It is the object of the present invention to remedy this inherent drawback in the type of headlamp envisaged, and to adapt the elliptical regenerative condenser with a view to optimum lighting.

The present invention is based on the careful examination of the formulation of the images from the light filament which are projected on a screen at 25 metres.

According to the present invention, there is provided a headlamp for an automobile comprising an elliptical reflector, a light source and converging lens means; the reflector having an elliptical reflecting surface and first and second foci; the light source comprising a substantially cylindrical filament which is located in the proximity of the first focus and behind the second focus with respect to the direction of the intended beam; the lens means being so located that its focus is in the proximity of the said second focus; the reflecting surface having a critical zone defined as that portion capable of projecting, on a standard screen, images of the filament forming a predetermined angle a equal at most to 300 with the vertical; the critical zone of the reflecting surface being modified whereby the beam produced by the headlamp results in a more horizontall spread area of illumination.

The light filament, which is generally in the form of an elongate cylinder, can be oriented either in the axis of the reflector system or transversely to this axis (generally a transverse filament is horizontal).

Each point of the reflector, which may be considered as a small plane mirror, gives rise to the formation of an image of the filament on a screen, and it may therefore be considered that the total illumination obtained is produced by superimposing all the individual images from all the points of the mirror. A filament of elongate shape results in elongate images which on the screen take up various orientations according to the mirror point under consideration. Certain images may be horizontal (i.e. their large dimension is horizontal), others oblique, others vertical. The difference points of the mirror thus give images which are inclined to greater or lesser degree.

Figure 2 shows the projection on a standard screen at 25 metres of the elementary images produced by the system of Figure 1. If one considers This total illumination, it will be seen that a vertical image such as 1v is much less effective than a horizontal image such as 1H for the formation of the illumination below the cut-off limit indicated by two halflines Ld and Lg to the right and the left of the centre of the screen, on which the left-hand roadside Bg, the right-hand roadside 8d and the axis of the road AR are shown as usual. A large part of the vertical image 1v remains ineffective as useful illumination, which is shown by hatching and corresponds to the useful range of the light beam.Thus, in accordance with the invention, preference is given to the horizontal or less inclined images to the detriment of the vertical or very inclined images. The general means for achieving this is to eliminate and/or attenuate and/or widen and/or even displace the vertical or very inclined images, that is to say the images forming an angle of less than 30 , or even preferably 200, to the vertical. For this purpose, critical zones giving rise to the formation of such inclined images are determined on the elliptical regenerative condenser and the reflecting surface is modified at such critical zones. Action is taken in relation to the condenser because it is encountered before the masking cover. In this way the glare values which are determined on the cover are not increased.In the case of an axial filament, the critical zone may be defined by the intersection of the regenerative condenser with two inclined planes on the vertical axial plane of the regenerative condenser.

In the case of a horizontal transverse filament, the critical zone may be defined by the intersection of the reflector by two pairs of cylinders of revolution one to the left and one to the right of the reflector, each of the two pairs of cylinders passing through the transverse projection of the first focus on the reflector surface, the radius of the cylinders being equal to the smallest parameter b of the ellipsoid defining the reflector, and the axes of the cylinders being located in planes which are inclined by + with reference to the horizontal, and which pass through the projections of the first focus on the reflector surface. This is shown as Z in Figures 3 and 4 which are a front view and an axial vertical section respectively.

The modifications to the zone can affect its diffusing or reflecting power and its shape.

Irrespective of whether the filament is axial or transverse, the critical zone can be rendered nonreflecting, for example by removing the reflective coating or, more preferably, by applying a matt paint. In the same way, in both cases, the illumination derived from this zone can be attenuated by rendering it diffusive, for example by incorporating a grain into it with a finer or coarser grain. This can be achieved for example by sanding, or by forming honeycombs, before applying the reflective coating.

The critical zone could also be deformed by offsetting its second or outer focus with reference to the second or outer focus of the regenerative condenser assembly (which coincides with that of the lens). Diverging ribs can also be arranged in the critical zone in accordance with the elliptical generating lines of the zone. Finally, the critical zone can be defocused with reference to the light filament.

The invention may be carried into practice in various ways and some embodiments will now be described by way of example only with reference to the accompanying drawings.

Figure 1 shows a vertical axial section the basic system to which the invention is applied; Figure 2 shows the projection on a standard screen at 25 metres of the elementary images produced by the system according to Figure 1; Figures 3 and 4 show, in front view and in vertical axial section respectively, the critical zone of the reflector forming the regenerative condenser for an assembly using a transverse filament; Figure 5 shows in front view the determination of the critical zone of the reflector in the case where it is used with an axial filament; Figure 6 shows in front view the determination of the critical zone of the reflector in the case where it is used with a transverse filament;; Figures 7a and 7b show schematically in front view and in horizontal axial section the constitution of an elliptical reflector intended for use with an axial filament, in which the second or outer focus of the critical zone is offset; Figure 8 shows in front view an elliptical reflector intended for use with a transverse filament, in which ribbing is provided in the critical zone; Figures 9a and 9b show schematically in front view and in axial horizontal section an elliptical reflector intended for use with an axial filament and in which the critical zone is defocused with reference owt the light filament.

Figures 1 to 4 have already been discussed above. As has been seen, Figure 1 shows in diagrammatic form, a headlamp of the type incorporating a light source, an elliptical reflector forming a condenser and a converging lens.

The way in which the invention is put into operation will now be described in detail with reference to Figures 5 et seq. To simplify the explanation, the same references will be used in all the figures to designate unchanged or corresponding elements.

Figure 5 shows the determination of the critical zone Z, of an elliptical reflector forming a condenser C, the condenser being intended for use with a cylindrical filament f arranged axially on the axis AA of the condenser. In this case the critical zone Z is a central zone defined by the intersection of the condenser C with two axial planes P and pr forming an angle a with the vertical axial plane VV.This corresponds to the zone responsible for the formation of elementary images from the filament f of which the inclination to the vertical VV is at least equal, in one direction or the other, to the angle a (equal for example to 20 , or better to 30 ). On the reflecting surface of the condenser C, the zone Z is defined by the curves of intersection which are ellipsoids.

As stated above the images derived from the zone Z must be modified e.g. eliminated and/or attenuated and/or widened and/or even displaced.

It will be expiained in greater detail below how this is achieved.

Figure 6 illustrates the case where the elliptical reflector C is used with a horizontal transverse cylindrical filament f. In this case, and as shown in Figures 3 and 4, the critical zone Z is divided into two half-zones Zd and Zg arranged respectively on the right and on the left of the condenser C and symmetrically with reference to the axial vertical plane W. The half-zones Zd and Zg are defined on the ellipsoidal reflecting surface as the location of the points giving rise to images of which the inclination to the vertical is at most equal to the predetermined angle c.

To a good approximation, each of the half zones Zd and Zg can be considered to be defined by the inter-section of the elliptical condenser C by two cylinders. These cylinders are determined in the following manner: the first or inner focus F, of the condenser C (coinciding substantially with the filament f) is projected on the condenser C in a horizontal transverse direction at two points Pd and Pg which are situated respectively to the right and to the left of the condenser. From each of these two points, two planes are traced parallel to the axial direction AA and inclined by an angle a with respect to the horizontal axial plane HH.

Thus, from the point Pd two planes 20d and 21d are traced and from the point Pg two planes 20g and 21g are traced. The axes of the cylinders, parallel to the direction AA, are situated in these planes and the radius of these cylinders is equal to the parameter b of the elliptical surface of the condenser C. The parameter b constitutes the smallest parameter of this ellipsoid, in the case in point, it corresponds to the vertical radius of the ellipsoid, traced from the centre of the ellipsoid, between its foci F1 and F2. It will be seen that the zone Zd is defined by the intersection of the condenser C with the cylinders 1 0d and 1 1 d with respective axes 30d and 31 d.In the same way, the zone Zg is defined by the intersection of the condenser by the two cylinders 109 and 1 1 gut centre respectively on the axes 30g and 31 g.

Such an approximate definition of the halfzones Zd and Z is very satisfactory since it comes close, within 10%, to the optimum theoretical definition. Furthermore, such a definition makes it possible in a very simple manner to trace the limits of the zones on the condenser C, or on to the moid from which this condenser is manufactured. By rotating the various parts, tracings corresponding to the intersections by the cylinders of revolution can be effected very easily.

As has been stated above with reference to Figure 5, once the critical zones are defined it is a question of providing the means for causing the corresponding images to be modified, namely eliminated and/or attenuated and/or widened and/or displaced.

A first method in accordance with the invention consists of obscuring the zones either by masking them, notably by applying a matt paint, or by dulling them. These zones can also be rendered diffusive by incorporating in them a grain whose grain can vary from fine to course. In all cases, the undesirable images corresponding to the zone are eliminated or in any case very attenuated.

Figures 7a and 7b show a solution in which the zone Z is deformed in such a way as to offset the corresponding images to the left and to the right.

In the chosen example, the condenser C cooperates with an axial filament in the axis AA.

Thus the zone Z is as shown in Figure 5. In the assembly of the condenser C there are two foci F, and F2, as defined in Figure 1. In to this embodiment of the invention, all the surface of the condenser remains reflective, but the surface of the condenser is deformed in the critical zone Z. More precisely, the right-hand and left-hand halves Zd and Zg of the zone Z are inclined, the inclination being divergent with reference to the axis AA in such a way that their first or inner focus remains essentially at F, whilst their second or outer focus is displaced laterally to F2d for the half-zone Zd and to F2g for the half-zone Zg.As a result of this offsetting of the outer foci, where the images of the filament f which is arranged in the proximity of the common internal focus F, are formed, the final images on the screen of Figure 2, which would be vertical images at an angle of +a with the vertical, are displaced laterally thus rendering them acceptable.

In the case of zones Zc, and Zg, traced on the condenser C for use with a transverse filament f, Figure 8 illustrates a different arrangement for diffusing the images corresponding to the critical zones. In this case the critical zones are provided with vertical diffusing ribs are shown in the drawing. Owing to these ribs the light corresponding to the vertical images is diffused in such a way that they become acceptable.

In another case where the condenser C is used with an axial filament, Figures 9a and 9b show an arrangement in which the critical left-hand and right-hand half-zones Zg and Zd are systematically defocused with reference to the filament f and the inner focus F, of the condenser C. As can be seen in Figure 9b, which is a schematic view in a horizontal plane, the axes of the zones Zd and Zg are offset so that their two foci F1g, F2g and F,d and F2d are offset laterally to the horizontal. The offsetting is for example of the order of 1 .5mm for an axial filament. With such an arrangement, the vertical images corresponding to the critical zone are widened laterally so as to contribute to the illumation of the sides of the road. This renders them acceptable and even useful.

Naturally, all the solutions which have been explained above with either arrangement to the filament (axial or transverse) are equally applicable to both arrangements.

Claims

1. A headlamp for an automobile comprising an elliptical reflector, a light source and converging lens means; the reflector having an elliptical reflecting surface and first and second foci; the light source comprising a substantially cylindrical filament which is located in the proximity of the first focus and behind the second focus with respect to the direction of the intended beam; the lens means being so located that its focus is in the proximity of the said second focus; the reflecting surface having a critical zone defined as that portion capable of projecting, on a standard screen, images of the filament forming a predetermined angle a equal at most to 30O with the vertical; the critical zone of the reflecting surface being modified whereby the beam produced by the headlamp results in a more horizontally spread area of illumination.

2. A headlamp as claimed in Claim 1 in which the filament extends axially and the critical zone is defined by the intersection of the reflector with two axial planes each inclined by the angle a to the vertical.

3. A headlamp as claimed in Claim 1, in which the filament extends transversely, and the critical zone is substantially defined by the intersection of the reflector by two pairs of cylinders of revolution one to the left and one to the right of the reflector, each of the two pairs of cylinders passing through the transverse projection of the first focus on the reflector surface, the radius of the cylinders being equal to the smallest parameter b of the ellipsoid defining the reflector, and the axes of the cylinders being located in planes which are inclined by + with reference to the horizontal, and which pass through the projections of the first focus on the reflector surface.

4. A headlamp as claimed in any one of Claims 1 to 3 in which the surface of the critical zone is rendered non-reflecting.

5. A headlamp as claimed in any one of Claims 1 to 3 in which the surface of the critical zone is provided with diffusing ribs.

6. A headlamp as claimed in any one of claims 1 to 3 in which the critical zone is deformed symmetrically in its left-hand and in its right-hand part, with reference to the theoretical form of the ellipsoid defining the reflector in such a way that the second focus is displaced towards the left for the left-hand part and towards the right for the right-hand part, whilst the first focus of the zone remains unchanged.

7. A headlamp as claimed in any one of Claims 1 to 3 in which the critical zone is deformed with reference to the theoretical shape coinciding with the elliptical surface of the reflector in such a way that the critical zone is formed, on the left hand and on the right, by two ellipsoid portions the axes of which are offset in translation to the left and to the right with reference to the central axis of the reflector.

8. A headlamp for an automobile constructed and arranged substantially as herein specifically described with reference to and as shown in Figure 5, or Figure 6, or Figures 7a and 7b, or Figure 8, or Figures 9a and 9b of the accompanying drawings.