GB2248493A

GB2248493A - Headlight for motor vehicles

Info

Publication number: GB2248493A
Application number: GB9120853A
Authority: GB
Inventors: Richard Loewe; Peter Perthus
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1990-10-04
Filing date: 1991-10-01
Publication date: 1992-04-08
Anticipated expiration: 2011-10-01
Also published as: JPH04233102A; DE4031351A1; DE4031351C2; JP3476480B2; GB9120853D0; GB2248493B

Abstract

The headlight exhibits a reflector (10), in front of which a diaphragm (13) is disposed, the edge (14) of which is imaged by means of an objective (16) to form the bright-dark boundary of the light distribution. The objective (16) exhibits, towards the reflector (10), a plane side (17) and, situated opposite, a convex side (18). The convex side (18) is subdivided into a central, round region (19) and a peripheral region (20) which surrounds the latter and which extends in a circular ring shape. The focal length of the central region (19) is shorter than that of the peripheral region (20), so that the two regions (19, 20) sharply image the edge (14) of the diaphragm (13) at different distances. As a result of this, for example at the location Q, where the edge (14) is sharply imaged by the peripheral region (20), an unsharp image of the edge (14) is additionally formed by the central region (19). <IMAGE>

Description

1 Headliqht for metor vehicles

The invention proceeds from a headlight for motor vehicles of the generic type of Claim 1.

Such a headlight is known from DE-OS 3,602,262. This headlight exhibits a reflector which generates a light beam by reflection of the rays of a light source. In the beam path of the ref lected light rays there is disposed a diaphragm with an optically effective edge which is imaged by means of an objective as a bright-dark boundary of the light distribution generated by the headlight. In this case, the objective exhibits regions with different optical properties.

However, it has proved to be disadvantageous if the edge of the diaphragm is imaged with great sharpness, since then in the event of vehicle movements the brightdark boundary follows these in a clearly perceptible manner; this is perceived by the vehicle driver as disturbing. In order to reduce the sharpness of the image of the edge of the diaphragm, in the case of this headlight a region of the objective with a grained surface is also provided. As a result of the graining of the surf ace a reduction in sharpness of the image is indeed achieved overall, but the reduction in sharpness cannot be accurately controlled with respect to intensity and progression, in consequence of the irregularity of the graining.

Advantages of the invention As compared with this, the headlight according to the invention having the characterising features of Claim 1 has the advantage that as a result Of the different focal lengths of the central and peripheral region at a predetermined distance an image of the diaphragm edge is formed with great sharpness, as well as an image superposed thereon - of the diaphragm edge with low sharpness, the intensity of the reduction in sharpness being determined by the difference of the focal lengths and by the size of the central and of the peripheral region.

Advantageous refinements and further developments of the headlight are characterised in the subclaims. By the embodiment according to Claim 2, light rays at the transition between the regions are prevented from being so greatly deflected upwards that these lead to an impermissible increase in the luminous intensity values above the bright-dark boundary. In the case of the further development according to Claim 6, the different images of the edge which are generated by the regions are perceptible only to a slight extent as separate images.

Drawing An illustrative embodiment of the invention is shown in the drawing and explained in greater detail in the description which follows. Figure 1 shows a headlight in longitudinal cross section, Figure 2 the section of the objective of the headlight of Fig-ure 1 designated in Figure 1 by II, in an enlarged representation, and Figure 3 the elevation of the objective in the direction of the arrow III in Figure 1.

Description of the illustrative embodiment

A headlight, shown in Figures 1 to 3, for antidazzle light or fog light according to the projection principle exhibits a reflector 10 into which a light source 11 is inserted, which may be an incandescent lamp or a gas discharge lamp. The reflector 10 includes, in the vertical and horizontal axial section, differing ellipses with a common first focal point Fe disposed in the reflector, but different second focal points, which are disposed at different distances from the reflector in the light exit direction. The incandescent coil or the light arc of the light source is disposed approximately at the first focal point of the ellipses and extends axially. In the light exit direction of the light rays reflected by the reflector 10, a diaphragm 13 with an optically effective upper edge 14 is disposed below the optical axis 12 of the reflector 10 approximately in the region of the second focal point of the ellipse in vertical cross section. Further in the light exit direction, an objective 16 is disposed on the optical axis 12 of the reflector, by which objective the upper edge 14 of the diaphragm 13 is imaged, as a bright-dark boundary of the light distribution generated by the headlight, onto the roadway in front of the motor vehicle.

The objective 16 exhibits a plane or slightly curved side 17 facing the reflector 10 and a convex side 18 remote from the reflector 10. The convex side 18 of the objective is subdivided into a central region 19 and a peripheral region 20 which surrounds the latter. The central region 19 is designed to be round and the peripheral region 20 surrounds this in the manner of a circular ring. The surface area of the central region 19 is smaller than the surface area of the peripheral region 20. Moreover, the focal length of the central region 19 is shorter than that of the peripheral region 20.

The upper edge 14 of the diaphragm 13 is imaged by the peripheral region 20 of the objective at a distance L at the point Q with great sharpness. In the case of the design of the headlight in the laboratory, the distance L amounts to approximately 10 metres; in this case,, a measurement screen 22 is disposed at this distance. As a result of the shorter focal length of the central region 19, the upper edge 14 is sharply imaged by the latter already at a shorter distance S at the point P, i.e. the light rays 23 intersect one another at the point P at the distance S, these then forming an unsharp image of the upper edge 14 at the distance L, which - 4 unsharp image is superposed upon the sharp image of the peripheral region 20. Thus, on an overall basis, there is formed at the distance L a sharp image of the upper edge 14 with a superposed, unsharp zone with a width B, which is determined by the difference of the focal lengths of the regions 19 and 20 and by the size of the central region; in this case, the unsharp zone becomes broader with increasing difference of the focal lengths and increasing size of the central region. At a given diameter of the objective, the peripheral region becomes smaller on increasing the size of the central region.

The angle a, which a tangent 26 to the peripheral region 20, set at the transition 25 between the regions, includes with a tangent 27 to the central region 19, set at the transition 25, amounts, in the case of antidazzle light, to a maximum of 5. As a result of this, the zone B which has had its sharpness reduced is prevented from becoming too broad and thus impermissibly high luminous intensity values are prevented from arising above the bright-dark boundary. The transition between the regions 19 and 20 does not need to be provided with an edge 25, but can also be rounded, as shown by broken lines in Figure 2.

Preferably, the central region 19 is provided, on the convex side 18 of the objective 16, with a graining or orange-peel structure. The graining is formed by a multiplicity of microelevations on the surface of the central region 19. As a result of the graining, the image of the edge 14 of the diaphragm 13 is made additionally less sharp, so that, even at the distance S, the edge 14 is not sharply imaged. In consequence of the graining, two differently focused images of the edge 14 of the diaphragm 13 are no longer perceptible, but essentially only the image of the edge at the distance L with a superposed unsharp zone.

The central and the peripheral region 19, 20 are designed to be aspheric and exhibit differing asphericities. In order to increase the reduction in sharpness of the bright-dark boundary in one direction, the central and/or the peripheral region of the objective can be designed toroidally. In the case of a toroidal design, the pertinent region includes differing asphericities in various axial sections; in this case, a continuous, nonrotationally-symmetrical surface is formed.

Conversely to the above described example, the focal length of the central region 19 can also be longer than that of the peripheral region 20. Moreover, the edge 14 of the diaphragm 13 can also be sharply imaged on the screen 22 by the central region; in this case, the reduction in sharpness then arises as a result of the peripheral region. In principle, the differing focal lengths of the regions 19 and 20 give superposed images of the edge 14 and a reduction in sharpness with a specified width.

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Claims

1. Headlight for motor vehicles, especially headlight for antidazzle light or fog light, having a reflector (10) which generates a light beam by reflection of the rays of a light source (11), in the beam path of which light beam a diaphragm (13) with an optically effective edge (14) is disposed, and having an objective (16), which images the edge (14) as a bright-dark boundary of the light beam on the roadway, the objective (16) exhibiting regions with different optical properties, characterised in that the objective (16) exhibits a central region (19) with a first focal length and a peripheral region (20), surrounding the latter, with a second focal length different from the first focal length, the edge (14) being sharply imaged by the regions (19, 20) at different distances.

2. Headlight according to Claim 1, characterised in that at the transition between the regions (19, 20) the angle a between a tangent (27) set to the central region (19) and a tangent (26) set to the peripheral region (20) is at most 50.

3. Headlight according to Claim 1 or 2, characterised in that the transition between the regions (19, 20) is rounded.

4. Headlight according to one of the preceding claims, characterised in that the objective (16) exhibits a plane or slightly curved side (17) facing the reflector (10) and, situated opposite, a convex side (18), the convex side (18) being designed aspherically and the regions (19, 20) being formed by appropriate design of the convex side (18).

5. Headlight according to Claim 4, characterised in that the convex side (18) is designed toroidally in the central region (19) and/or in the peripheral region (20).

6. Headlight according to one of the preceding claims, characterised in that the surface of the central region (19) and/or that of the peripheral region (20) is provided with a graining.

7. A headlight substantially as herein described with reference to the accompanying drawing.

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