EP0558949B1 - Dipping headlamp for vehicles - Google Patents

Description

State of the art

The invention relates to a low beam headlight for motor vehicles according to the preamble of claim 1.

Such a low beam headlight is known from EP 0 250 284 A1. This low beam headlight has a reflector, a luminous element and a light plate covering the light exit opening of the reflector. The luminous element is offset upward with respect to the optical axis of the reflector so that its lower limit lies approximately on the optical axis. The reflector is divided into several sectors below and above a horizontal axial plane with different reflection surfaces. On one side of the reflector, a first sector extends from the horizontal axial plane up to an angle α to it, and on the other side of the reflector extends from the horizontal axial plane to an angle α downwards second sector, both sectors each having reflection surfaces in the form of paraboloid of revolution. These two sectors are connected by two adjoining sectors above and below the horizontal axial plane, which have reflection surfaces in the form of general paraboloids. A general paraboloid contains parabolas in all axial longitudinal sections, but with different focal lengths.

This known low-beam headlight produces a light distribution with a light-dark boundary, which has a substantially horizontal section on the oncoming traffic side and a section that rises upwards with respect to the horizontal at an angle α to the edge of the road of one's own lane. The lens only needs to have weakly effective optical means for shaping the light distribution. A high luminous intensity is sought just below the light-dark boundary in order to obtain a long range and the sharpest possible formation of the light-dark limit. With the light distribution generated by the known reflector, however, this has not been achieved to the desired extent.

DE-A1-40 10 652 also discloses a fog lamp which has a reflector, with an upper reflector region and a lower reflector region, which each have different reflection surfaces in the form of a general paraboloid. The two reflector areas touch in an axial plane, which is the horizontal central plane of the reflector. The highest images of a luminous element reflected by the reflector areas adjoin a horizontal light-dark boundary, as is usual with fog lights. This document does not contain any information on the formation of a reflector for a low beam headlight which has to emit a light beam with a light-dark boundary having a horizontal section and an inclined section.

Advantages of the invention

The low-beam headlamp according to the invention with the characterizing features of claim 1 has the advantage that a high light intensity is present just below the light-dark boundary and thus reaches a large range of light and the light-dark limit is clearly pronounced.

Advantageous refinements and developments of the invention are characterized in the subclaims.

drawing

An embodiment of the invention is shown in the drawing and explained in more detail in the following description. 1 shows a low beam headlight in vertical longitudinal section, FIG. 2 shows the reflector of the headlight in rear view, FIG. 3 shows the upper partial surface of the reflector in a cross section perpendicular to the optical axis, FIG. 4 shows images of a luminous element reflected by the upper left partial surface of the reflector, 5 images of the luminous element reflected by the lower left partial surface of the reflector and FIG. 6 the light distribution generated by the headlight.

Description of the embodiment

A low-beam headlight for motor vehicles shown in FIG. 1 has a reflector 10, the light exit opening of which is covered by a lens 11, which can have optically effective elements. There is also a luminous element 13, which can be the filament of an incandescent lamp or the arc of a gas discharge lamp. The luminous element extends approximately parallel to the optical axis 14 of the reflector 10, but is offset upwards with respect to the latter so that its lower limit lies approximately on the optical axis 14.

The reflector 10 is divided into an upper part 19 and a lower part 20 in a plane 17 shown in FIG. 2 and inclined at an angle α / 2 to the horizontal 16, both of which have reflection surfaces in the form of general paraboloids. The two parts 19 and 20 continuously merge into one another in the contact plane 17, that is, that both parts have 17 common tangents in the plane of contact.

FIG. 3 shows a cross section through the upper part 19 of the reflector 10. The upper part 19 has a reflection surface in the form of a general paraboloid. The general paraboloid contains parabolas in all axial longitudinal sections, that is to say longitudinal sections containing the optical axis 14. However, the parabolas have different focal lengths and a common apex, so that there are different focal positions for the different parabolas. The focal point Foh, the parabola lying in the contact plane 17, lies approximately at the level of the center of the luminous element 13 on the optical axis 14. The focal point Fov, which lies in the axial plane 22, which is perpendicular to the contact plane 17, lies approximately at the level of the apex of the reflector facing end region of the luminous body 13 on the optical axis 14. When transitioning from the contact plane 17 to the vertical axial plane 22, the focal point of the parabola resulting in the respective axial longitudinal section "migrates" from the center of the luminous body 13 to its end region of the luminous body 13 facing the reflector apex. In the cross section through the upper part 19 of the reflector 10, an elliptical cutting curve 23 results. The numerical eccentricity of the cutting curve 23 can be varied from the contact plane 17 to the vertical axial plane 22. The numerical eccentricity e of the intersection curve 23 is defined as the ratio of the distance c of the focal point F of the intersection curve 23 from the optical axis 14 to the major semi-axis a of the intersection curve 23, e = c / a. The eccentricity e of the intersection curve 23 in the region of the contact plane 17 is preferably almost zero, so that the normal to the intersection curve 23 intersects the optical axis 14 and the Intersection curve 23 is approximately a circle in this area. The eccentricity e of the intersection curve 23 increases in relation to the vertical axial plane 22, that is to say with increasing angle β between a straight line OP connecting a reflector point P with the optical axis 14 and the contact plane 17. The distance between the normal 24 on the intersection curve 23 and the optical axis 14 also increases up to an angle β of approximately 45 °. From an angle β of approximately 45 ° to the vertical axial plane 22 with the angle β = 90 °, the distance between the normals 24 on the intersection curve 23 and the optical axis 14 decreases again to approximately zero. The eccentricity e of the intersection curve 23 reaches its maximum value in the vertical axial plane 22.

4 shows images of the luminous element 13 which are reflected by the upper part 19 of the reflector 10. The illustrations 25 to 27 of the luminous element 13 are reflected by different areas of the reflector part 19, the normals of the intersection curve resulting in cross section, as described above, each have different distances from the optical axis 14. Due to the above-described design of the intersection curve, the image 25 of the luminous body 13, which lies at the highest, directly borders with its upper edge on a horizontal section 28 of the light-dark boundary 30. The further illustrations 26 and 27 lie below the light-dark boundary and are relative to the position of the respective reflector region Luminous body 13 inclined with respect to the horizontal. The images 27 a to c are reflected by reflector regions, which all lie on a common parabola, but are at different distances from the optical axis 14 and therefore reflect images of different sizes. Figures 25 to 27 only come from areas seen in the direction of light emission left half of the upper reflector part 19 in order to maintain the clarity of FIG.

The lower part 20 of the reflector 10 likewise has a reflection surface in the form of a general paraboloid, the focal point Fuh, the parabola lying in the contact plane 17, as in the upper part 19 being approximately at the level of the center of the luminous element 13 on the optical axis 14. The focal point Fuv, the parabola lying in the vertical axial plane 22, lies at the level of the end region of the luminous body 13 pointing away from the reflector apex on the optical axis 14. During the transition from the parabola lying in the contact plane 17 to the parabola lying in the vertical axial plane 22, it "migrates" "the focal point from the center of the luminous element 13 to its end region pointing away from the reflector apex. Also in the lower part 20, the cross section perpendicular to the optical axis 14 results in an elliptical intersection curve, the eccentricity of which, starting from the contact plane 17, where this is approximately zero, reaches its maximum value in the vertical axial plane 22.

5 shows images of the luminous element 13 which are reflected by the lower reflector part 20. The illustrations 32 to 34 of the luminous element 13 are reflected by different areas of the reflector part 20, the normals of the intersection curve resulting in cross section, as described above, each have different distances from the optical axis 14. As a result of the above-described formation of the intersection curve, the image 32 of the luminous body 13 lying at the highest edge directly borders with its upper edge on a portion 36 of the light-dark boundary 30 that rises by an angle α with respect to the horizontal. The further illustrations 33 and 34 lie below the light-dark boundary and are inclined in relation to the horizontal according to the position of the respective reflector area relative to the luminous element 13. The figures 32 to 34 come only from areas of the left half of the reflector part 20, as seen in the light exit direction, in order to maintain the clarity of FIG. 5.

wobei $${\text{a}}^{\text{2}}{\text{= 4 · f}}_{\text{x}}\text{·z}$$

und

Dabei sind:The reflecting surfaces of the upper and lower reflector parts 19 and 20 can be calculated using the mathematical equation given below. First of all, a coordinate system with the origin O in the reflector apex and the optical axis 14 as the z axis is specified. The x-axis of the coordinate system is perpendicular to the z-axis and lies in the contact plane 17. The y-axis of the coordinate system is perpendicular to both the z-axis and the x-axis and is therefore in the vertical axial plane 22. The mathematical equation for determining the reflective surfaces is as follows: $$\frac{{\text{x}}^{\text{2nd}}}{{\text{a}}^{\text{2nd}}}\text{+}\frac{{\text{y}}^{\text{2nd}}}{{\text{b}}^{\text{2nd}}}\text{- 1 = 0}$$

in which $${\text{a}}^{\text{2nd}}{\text{= 4 · f}}_{\text{x}}\text{Z}$$

and

Here are:

x, y, z

the coordinates of a reflector point

f _x , f _y

the focal lengths of the parabolas lying in the contact plane 17 or in the vertical axial plane 22

c

a coefficient that is used to adjust the upper lighting margin to the required light / dark limit

In one exemplary embodiment, the center of the luminous element 13 is arranged at a distance of approximately 24 mm from the reflector apex. The values of the parameters for the upper reflector part 19 are:
f _x = 23.8 mm, f _y = 21.2 mm and c = 1.37

The values for the lower reflector part 20 are:
f _x = 23.8 mm, f _y = 27.6 mm and c = 0

A reflector 10 generates a light distribution shown in FIG. 6 by superimposing all the images of the luminous element 13, which distributes the legally prescribed light-dark limit 30 with the horizontal section 28 on the oncoming traffic side and the horizontal section 28 on the other side of the carriageway and rising towards the edge of the road under the angle α inclined portion 36. The light distribution is shown by means of several Isolux lines 38, which are lines of the same illuminance.

Claims (5)

1. Dipped-beam headlamp for motor vehicles, having a reflector (10), a luminous element (13) and a lens (11) covering the light exit opening of the reflector (10), the reflector (10) having in its upper region (19) and in its lower region (20) different reflection surfaces which are at least partially part of an approximately general paraboloid and by means of which images of the luminous element (13) are reflected for the purpose of forming a light distribution with a light/dark boundary (30) having an approximately horizontal portion (28) and a portion (36) inclined at an angle α to the horizontal, there being produced in sections through the reflector (10) perpendicular to its optical axis (14) intersection curves (23) whose numerical eccentricity is variable over their extent, characterized in that the upper reflector region (19) and the lower reflector region (20) touch in an axial plane (17) which is arranged inclined with respect to the horizontal (16) by half the angle α of inclination of the inclined portion (36) of the light/dark boundary (30) and in the same sense as the latter, in that the entire upper reflector region (19) and lower reflector region (20) has a reflection surface in the form of a general paraboloid, and in that the numerical eccentricity of the intersection curves (23), produced in sections through the reflector (10) perpendicular to its optical axis (14), is variable over the extent of said intersection curves in such a way that the highest image (25), reflected from the upper reflector region (19), of the luminous element (13) adjoins the horizontal portion (28) of the light/dark boundary (30) with its upper edge, and that the highest image (32), reflected from the lower reflector region (20), of the luminous element (13) adjoins the inclined portion (36) of the light/dark boundary (30) with its upper edge.
2. Dipped-beam headlamp according to Claim 1, characterized in that starting from the tangent plane (17) the eccentricity of the intersection curves (23) increases from approximately zero up to the axial plane (22) perpendicular to the tangent plane (17).
3. Dipped-beam headlamp according to Claim 1 or 2, characterized in that the upper reflector region (19) and the lower reflector region (20) have an identical intersection curve lying in their tangent plane (17), the focal point of which intersection curve is situated approximately at the level of the middle of the luminous element (13).
4. Dipped-beam headlamp according to Claim 3, characterized in that the focal point Fov of the intersection curve, lying in the perpendicular axial plane (22), of the upper reflector region (19) is situated approximately at the level of the end region, pointing towards the reflector vertex, of the luminous element (13) and in that the focal point Fov of the intersection curve, lying in the perpendicular axial plane (22), of the lower reflector region (20) is situated approximately at the level of the end region, pointing away from the reflector vertex, of the luminous element (13).
5. Dipped-beam headlamp according to one of the preceding claims, characterized in that the reflection surface of the upper reflector region (19) and/or of the lower reflector region (20) is defined by the following equation in a Cartesian coordinate system: $$\frac{{\text{x}}^{\text{2}}}{{\text{a}}^{\text{2}}}\text{+}\frac{{\text{y}}^{\text{2}}}{{\text{b}}^{\text{2}}}\text{-1=0}$$

   

   where $${\text{a}}^{\text{2}}{\text{= 4 · f}}_{\text{x}}\text{· z}$$

   

   and

   

   where:

   the z-axis is the optical axis,

   the x-axis lies in the tangent plane (17),

   the y-axis is perpendicular both to the x-axis and to the z-axis,

   x, y, z are the coordinates of a reflector point,

   f_x, f_Y are the focal lengths of the intersection curve lying in the tangent plane (17) or in the axial plane (22) perpendicular thereto, and

   c is a coefficient which serves to fit the upper edge of illumination to the required light/dark boundary.

Images