GB2102934A

GB2102934A - Dipped headlamp for vehicles

Info

Publication number: GB2102934A
Application number: GB00431412A
Authority: GB
Inventors: Hector Pratty
Original assignee: Cibie Projecteurs SA
Current assignee: Cibie Projecteurs SA
Priority date: 1981-07-10
Filing date: 1982-07-09
Publication date: 1983-02-09
Also published as: GB2102934B; IT8221864A0; JPS5810301A; FR2509427A1; SE438025B; FR2509427B1; ES273599Y; SE8203738L; IT1152970B; JPH038041B2; DE3225609A1; DE3225609C2; ES273599U

Abstract

A dipped headlamp comprising a parabolic reflector defining an optical axis A-A and a focus F, a light source L placed on the optical axis slightly in front of the said focus, and cut-off means C to intercept a proportion of the rays emitted by the source travelling towards the reflector, in order to define a cut-off limit on the beam reflected by the reflector. The reflector R is formed by two paraboloidal portions having the same focus and extending respectively to the left and to the right of the optical axis. The paraboloidal portion RD has a greater focal length than the paraboloidal portion RG. <IMAGE>

Description

SPECIFICATION Dipped headlamp for vehicles The present invention relates to dipped headlamps for vehicles.

Known constructions for such headlamps comprise a reflector with a parabolic reflecting surface, a light source placed in front of the focus of the parabolic surface, cut-off means which only permit certain of the rays emitted by the light source to pass in the direction of the reflector. A glass closure is arranged in front of the reflector, and is most usually applied to the aperture contour of the reflector.

The light source generally consists of the filament of a bulb, and the cut-off means are formed by a screening cap incorporated in the bulb.

In the old constructions of automobiles the headlamps were in the form of complete rotational bodies extending about a central optical axis. In more modern constructions, however, only the transverse central part of the reflectors is used and is connected to the front glass by horizontal flanges in the upper part and the lower part.

Figures 1 and la show an example of this more recent prior art. Figure 1 is a horizontal axial section of a dipped headlamp with a substantially rectangular aperture contour, whilst Figure la shows a front view of the reflector R with which this headlamp is equipped. The reflector R has an optical axis A-A and a focus F. Behind the reflector R a central aperture 0 serves to receive a bulb L the iuminous filament of which is provided in a conventional manner with a screening cap c.

The filament fis on the axis A-A, slightly in front of the focus F. The reflector R is defined at top and bottom by two horizontal flanges J and J,.

It will be seen that such a dipped headlamp, just like the older headlamps, incorporates a symmetrical optical system in the sense that the right-hand part D and the left-hand part G of the reflector (when it is viewed from the interior of the vehicle) are two halves of the same reflecting surface and are equal in surface area.

The optical roles of these different parts are well known to the expert in the art and throughout the present description a system corresponding to driving on the right will be described. The expert in the art will know what transpositions to make in the case of driving on the left.

The cut-off means for the dipped beam consist, on either side of the axis of illumination, of a horizontal or substantially horizontal half-plane cutoff on the left-hand side and, on the right, a slightly inclined half-plane cut-off, raised by 1 50 from the axis of illumination. The roadside is illuminated by the light below the inclined haifplane cut-off, caused by the right-hand part of the reflector. In that zone there is a good concentration of light, since it is important to illuminate the roadside well on the nearside as specified by the various regulations in force.

As regards the mounting of the headlamps on a vehicle, it is known that the dimensions of a headlamp reflector, particularly its depth, are critical values since it is important to the automobile manufacturer that certain overall dimensions are not exceeded.

As regards style, it is known that in certain automobiles, the glass closures of the headlamps and the corresponding aperture contours of the reflector are inclined symmetrically with reference to the central longitudinal axis of the vehicle. The left-hand headlamp has its glass slightly inclined to the left and the right-hand headlamp has its glass slightly inclined to the right. Such an arrangement, however, generally reduces the space available in terms of the depth of the reflector.

It is an object of the present invention to increase the concentration of the dipped beam below the cut-off limit on the nearside without changing the overall dimensions of the headlamp.

According to the invention, there is provided a dipped headlamp for a vehicle comprising a reflector having an optical axis and a focus, a light source located on the optical axis slightly in front of the focus, and cut-off means adapted to intercept a proportion of the rays emitted by the source travelling towards the reflector so as to define a cut-off limit to the beam of light reflected by the reflector, the reflector being formed by two paraboloidal portions having the same focus and extending respectively to the left and to the right of the optical axis, the paraboloidal portion which is on the near side has a greater focal length than the other paraboloidal portion. Thus, the concentration of the dipped beam may be improved below the cut-off on the nearside.

It may therefore be said that the invention stems from the realisation that the traditional arrangement for dipped headlamps in which the reflector is essentially symmetrical from one side to the other does not represent the optimum solution as regards utilisation of the luminous flux from the source and optimum illumination of the right-hand side of the road. Thus, the arrangement of the reflector is modified in such a way that the near side or right-hand reflecting surface may be increased to the detriment of the off-side or left-hand reflecting surface.As a result the optical axis, which is common to the two parts, may be slightly offset towards the off-side or left with reference to the aperture contour of the reflector which remains substantially unchanged by comparison with a conventional symmetrical headlamp which has the same aperture contour and has the focal length situated between that of the right-hand part and that of the left-hand part.

Preferably, the near side or right-hand portion extends over a small angular sector about the optical axis of the headlamp, and the off-side or left-hand portion extends over the complementary sector.

A headlamp constructed in accordance with the invention may be particularly advantageous in so-called "shaped" headlamps, that is to say headlamps in which the glasses are inclined obliquely to the left and to the right of the vehicle, the glass of the left-hand headlamp being inclined to the left and that of the right-hand headlamp being inclined to the right. In this case a structure according to the invention may be particularly recommended for the headlamp arranged on the offside of the vehicle (that is to say, in the case of driving on the right, the left-hand headlamp).

The invention may be carried into practice in various ways and some embodiments will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a horizontal section through a known dipped headlamp with a substantially rectangular aperture contour; Figure 1 a is a front elevation of a front glass for the headlamp of Figure 1; Figures 2 and 2a are views similar to Figures 1 and 1 a but show a headlamp according to the invention; Figure 3a is a horizontal section through a left hand shaped headlamp according to the invention; Figure 3b shows a front glass for the headlamp of Figures 3a, and Figures 4a and 4b are views similar to Figures 3a and 3b showing a right-hand shaped headlamp.

In order to simplify the description the same reference numerals have been used to designate those elements which are unchanged relative to the prior art.

The surface of the reflector (Figure 2a) is formed by a right-hand part RD and an adjacent left-hand part R,. These two parts are portions of paraboloids each having a focus F and an axis A-A.

The right-hand part RD has a greater focal length than the left-hand part RG. In the present embodiment the right-hand part RD has a focal length of 35 mm, the left-hand part RG a focal length of 21 mm, the aperture 0 has a diameter of.

23 mm, the width of the right-hand part (not including the aperture 0) is 89 mm, and the width of the left-hand part RG is 55 mm. The total size of aperture of the reflector remains unchanged and the dotted lines in Figure 2a show where the aperture contour of a conventional headlamp having the same axis would be located, with a uniform width to left and to right (excluding the aperture) of 72 mm for the same total aperture the width of aperture contour being 1 90 mm.

It will be easily understood that the relative increase in the right-hand reflecting surface RD by comparison with the left-hand reflecting surface RG is translated into a gain in concentration, as indicated above. In the present embodiment, the gain in concentration is 20% which is a considerable figure in practice.

The surface RD extends over an angular section cur about the axis A-A which is relatively small (30 to 700) while the portion Re occupies a much greater sector, making up 3600. As a result, the zone below the filament fwhich is formed as shown by the surface Ra has a relatively short focal length, that is to say a good recovery of flux, and it is therefore preferable that the zone RD is limited to a limited sector.

Figures 3a, 3b, 4a, 4b illustrate the adaptation of the structure to the case of pairs of inclined headlamps ("shaped headlamps"). As before, the headlamps have a right-hand zone R0 in the form of a sector with a long focal length, and a lefthand zone Re which is complementary and bounds the right-hand zone and has a relatively shorter focal length. The dotted lines in the drawings show the reflector of conventional construction which would have an intermediate focal length and the same aperture, and also the axis of such a reflector.

In the embodiment shown in Figures 3a, 3b, i.e. the left-hand headlamp, the right-hand part has a focal length of 40 mm, and the left-hand part enclosing it has a focal length of 26.5 mm, for a total aperture of 250 mm (large horizontal diameter). This construction gives a gain in concentration of 19% by comparison with a structure having a focal length of 30 mm and the same aperture.

In the case of the right-hand headlamp (Figures 4a and 4b) the right-hand part has a focal length of 35 mm and the left-hand part a focal length of 26.5 mm. This results in a gain a approximately 9% by comparison with a conventional headlamp having the same aperture with a focal length of 30 mm.

It will therefore be seen that the invention may make it possible to provide the optimum construction for pairs of shaped headlamps, the difference in the focal lengths of the left-hand and the right-hand portions being greater for the headlamp on the left-hand side.

Naturally, as has already been stated, it would be necessary to reverse the figures given above in the case of headlamps used for driving on the left.

The shapes of the novel reflectors are easily obtained in one piece of moulding plastics materials.

Claims

1. A dipped headlamp for a vehicle comprising a reflector having an optical axis and a focus, a light source located on the optical axis slightly in front of the focus, and cut-off means adapted to intercept a proportion of the rays emitted by the source travelling towards the reflector so as to define a cut-off limit to the beam of light reflected by the reflector, the reflector being formed by two paraboloidal portions having the same focus and extending respectively to the left and to the right of the optical axis, the paraboloidal portion which is on the near side has a greater focal length than the other paraboloidal portion.

2. A headlamp as claimed in Claim 1 in which the parapoloidal portion on the nearside has the shape of a sector with an angular aperture between 30 and 700, the other paraboloidal portion.extending over the complementary angular sector to make up 3600.

3. A headlamp as claimed in Claim 1 or Claim 2 in which the focal lengths of each of the paraboloidal portions are on either side of the focal length usually given to a reflector having an aperture of the same dimensions.

4. A headlamp as claimed in any one of Claims 1 to 3 in which the reflector is made in one piece from a plastics material.

5. A pair of headlamps as claimed in any of Claims 1 to 4 each further including a front glass which is inclined obliquely with reference to the central longitudinal axis of the vehicle.

6. A pair of headlamps as claimed in Claim 5 adapted for driving on the right in which the difference in the focal lengths of the two paraboloidal portions of the reflector of the lefthand headlamp is greater than the corresponding value for the right-hand headlamp.

7. A pair of headlamps as claimed in Claim 5 adapted for driving on the left in which the difference in the focal lengths of the two paraboloidal portions of the reflector of the righthand headlamp is greater than the corresponding value for the left-hand headlamp.

8. A dipped headlamp for a vehicle constructed and arranged substantially as herein specificially described with reference to and as shown in Figures 2 and 2a or Figures 3a and 3b, or Figures 4a and 4b of the accompanying drawings.