GB2162625A - Headlamp for vehicle - Google Patents

Abstract

The present invention provides a headlamp for a vehicle wherein a reflector (11) has upper portions and lower portions of a parabolic surface with different focal lengths (F1 and F2) A focal point (f2) of the lower surface portion is positioned forwardly of the focal point (f1) of the upper surface portion by a distance greater than the length ( l ) of the sub-filament. A sub-filament (13) is positioned between the two focal points to thereby efficiently utilise the light generated and obtain a light distribution pattern of high luminous intensity. A main filament (12) is longer than the sub-filament and is positioned below the sub-filament. <IMAGE>

Description

SPECIFICATION Headlamp for vehicle The present invention relates to a headlamp for a vehicle in which a main beam or a sub-beam may be selected.

An example of a filament arrangement of a conventional headlamp for a vehicle is shown in Figures 1 and 2 of the accompanying drawings. Figure 1 shows an arrangement wherein a forwardly directed main filament and a sub- filament 3 are successively arranged on the axis of revolution of a parabolic surface of a reflector 1, the main filament being positioned behind the sub-filament 3. A shield plate 4 is arranged under the sub-filament 3.

A light image of the sub-beam assumes an approximately semicircular form by the use of a semicircular portion of the reflector plus a further small sector of the reflector as shown in Figure 3(a). A light image of the main beam assumes a circular form by the use of the whole reflector as shown in Figure 3(b).

Figure 2 shows an arrangement wherein a main filament 2 is arranged centrally along a major transverse axis of the reflector 1, and a sub-filament 3 is arranged thereabove. A light image of the main beam assumes a laterally extended elliptical shape as shown in Figure 4(b), and a light image of the sub-beam assumes a shape in which an ellipse is expanded in one direction along a minor axis thereof as shown in Figure 4(a).

As will be apparent from the light images, in the filament arrangement of Figure 1 the sub-beam merely utilises light from about half of the reflector and, therefore, the rate of utilisation is bad.

On the other hand, in the filament arrangement of Figure 2 the light image of the sub-beam tends to be spread, possibly resulting in low intensity of illumination. In addition, the gap between the main filament 2 and the sub-filament 3 should be more than a given value. Therefore, if the centre of the light image is positioned much lower than the centre point of the reflector 1, correction becomes difficult to make, and lateral light is weak. If combined with a laterally extending reflector, the degree of utilisation of light is low and therefore, the selection of a reflector has to be made with care.

According to the present invention, there is provided a headlamp for a vehicle having a main filament and a sub-filament arranged parallel to an axis of revolution of a parabolic surface of a reflector, the sub-filament being positioned above the main filament, in which headlamp the reflector has upper and lower portions of the parabolic surface of different focal length, the focal point of the lower portion of the parabolic surface is positioned forwardly of the focal point of the upper portion of the parabolic surface by a distance greater than the length of the sub-filament, the sub-filament is positioned between the two focal points, and the main filament is longer than the sub-filament and is positioned thereunder.

In order that the invention may be readily understood, embodiments thereof will now, be described, by way of example, with reference to the accompanying drawings, in which: Figures 1 and 2 are respective diagramatic front views of two examples of filament arrangements in conventional headlamps for vehicles; Figures 3Fa) and (b) and Figures 4(a) and (b) show the sub-beam and main beam patterns obtained with the filament arrangements of Figures 1 and 2; Figures 5 and 6 are respective a diagrammatic longitudinal sectional view and a diagrammatic front view illustrating one embodiment of the present invention; Figures 7(a) and (b) show sub-beam and main beam patterns obtained with the embodiment of Figures 5 and 6; and Figures 8 and 9 show other beam patterns which can be realised by the present invention.

Figures 5 and 6 of the drawings show one embodiment of the present invention. Reference numeral 11 denotes a reflector, reference numeral 12 a main filament, and reference numeral 13 a subfilament.

The reflector 11 has an upper parabolic surface (upper reflecting surfaces A, B) of focal length F1, and a lower parabolic surface (lower reflecting surfaces C, D) of focal length F2. The distance between the focal points f, and f2 of the two parabolic surfaces (f2 is positioned forwardly of f,) has a value equal to the length f of the sub-filament 13 plus 01.0mm. The boundary between the two parabolic surfaces is a horizontal line intersecting the axis of revolution Z of the parabolic surfaces of the reflector.

The sub-filament 13 is arranged between the focal points f, and f2 on the axis Z of the parabolic surfaces of the reflector 11, and the main filament 12 is arranged thereunder at a spacing S (1.0-3.0 mm) and parallel to the sub-filament 13. In this case, the main filament 12 has a length which is greater than that of the sub-filament 13 by 4" or " (0.5-1.5 mm), projecting rearwardly (reflector side) by 4"-{" + L/2 or forwardly (lens side) by 4'-4' + L/ 2 (where L:length of the main filament).

It will be noted that both the filaments are manufactured as a bulb with the aforesaid positional relation.

With the above-described construction, light from the sub-filament 13 will be light externally of the focal point f, with respect to the reflecting surfaces A, B of focal length F, and focal point f,.

When light from the filament 13 is incident on the reflecting surfaces A, B, a light image is therefore formed under the horizontal boundary or centre line intersecting the axis Z as shown in Figure 7(a).

The aforesaid light will be light within the focal point with respect to the reflecting surfaces C, D of focal length F2 and focal point f2, and a light image is formed at the same position as the reflecting surfaces A, B.

The main filament 12 is arranged parallel to the sub-filament 13 at a spacing S (1.0-3.0 mm), and a light image (contour m, of Figure 7(b)) is accordingly formed in a portion of the same length as the sub-filament 13 according to the same principle as the sub-beam. However, light generated from the portion of dimension t" constitutes light within the focal point with respect to the reflecting surfaces A, B of the focal length F1, and a light image Icontour m2 of Figure 7(b) is thus formed above the centre line. Light in the portion of dimension i" will be light within the focal point with respect to the reflecting surfaces C, D of the focal length F2 and has the same directivity as the portion of dimension and therefore, a light image of contour m3 of Figure 7(b) is obtained.

In case of the main beam, even if the main filament is arranged so as to project forwardly by an amount {', the directivity of light is merely changed in the reflecting surfaces A, B and C, D, and the combined light image is the same as the portion of dimension r". Also, the axis of reflection of any of the reflecting surfaces A, B, C and D may be varied to vary the light image stepwise as shown in Figure 8. This stepwise light image will be a light image convenient for finding a central axis of the lamp when the lamp is mounted on the vehicle. Moreover, by varying the spacing S of Figure 6 or by varying the displacement T of the subfilament 13 to right or left, it is possible to provide dipping of the headlamp and selectively to brighten the illumination provided by the lamp to the right or left.

As described above, in the present invention the sub-beam is formed by improving the construction of the reflecting surface of the reflector and by positioning the filaments in accordance with optical considerations, so that light is effectively utilised and a pattern of sufficient light intensity is obtained. Moreover, the minimum light of the main beam is used to illuminate the sky, and the remaining light is used to illuminate the road surface. Therefore, the road surface can be illuminated brightly, contributing safety driving.In the known arrangement shown in Figure 2 wherein the filaments are arranged one above the other there is a limitation on the reduction of the switching width between the main beam and the subbeam in terms of the arrangement of filaments, and the sub-beam has a disadvantage in that is illuminates a short depth of field as compared with the sub-beam of the type shown in Figure 1 which employs an arrangement of longitudinally extending filaments. However, even if both filaments are likewise arranged one above the other, illumination of an adequate range with high light intensity can be achieved using an arrangement embodying the invention. Moreover, various light images may be realised by adjustment of the axis of the reflecting mirror, and the sub-beam may illuminate a remotely located area without dazzling an on coming vehicle. Furthermore, by effective utilisaton of the emitted light there is provided the advantage in that the vertical dimension employed in the type in which filaments are longitudinally arranged may be reduced.

Claims (5)

1. A headlamp for a vehicle having a main filament and a sub-filament arranged parallel to an axis of revolution of a parabolic surface of a reflector, the sub-filament being positioned above the main filament, in which headlamp the reflector has upper and lower portions of the parabolic surface of different focal length, the focal point of the lower portion of the parabolic surface is positioned forwardly of the focal point of the upper portion of the parabolic surface by a distance greater than the length of the sub-filament, the sub-filament is positioned between the two focal points, and the main filament is longer than the sub-filament and is positioned thereunder.

2. A headlamp according to Claim 1, wherein the main filament extends rearwardly beyond the focal point of the upper portion of the parabolic surface.

3. A headlamp according to Claim 1, wherein the main filament extends forwardly beyond the focal point of the lower portion of the parabolic surface.

4. A headlamp substantially as hereinbefore described with reference to, and as illustrated by, Figures 5 to 9 of the accompanying drawings.

5. Any novel feature or combination of features disclosed herein.