Projection lens for use in an LED module for a motor vehicle headlamp, and an LED module and motor vehicle headlamp having a projection lens of this type

The invention relates to a projection lens for use in an LED module of a motor vehicle headlamp. The LED module has a light source in the form of an LED matrix including numerous LED chips disposed in a matrix adjacent to and/or above one another, a primary lens including numerous primary lens elements disposed in a matrix adjacent to and/or above one another for bundling light emitted from the light source, and a projection lens. The projection lens projects a light exit surface of the primary lens to generate a predefined light distribution on a surface in front of the vehicle. The projection lens is designed such that it generates at least two separate images of the light exit surface of the primary lens on its image side, which are offset to one another in the horizontal direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims priority to German Patent Application No. DE 102013217843.3 filed on Sep. 6, 2013.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates, generally, to motor vehicle headlamps and, more specifically, to a projection lens for use in an LED module of a motor vehicle headlamp

2. Description of he Related Art

Motor vehicle headlamps are well known in the related art. Conventional headlamps may include a light source in the form of an LED matrix, including numerous LED chips disposed in a matrix, adjacent to and/or above one another (also referred to as matrix headlamps). The LED matrix may include a single row or column having numerous LED chips, or of numerous rows or columns disposed above or adjacent to one another, each having numerous LED chips. Matrix headlamps generate a light distribution on a road surface in front of a motor vehicle, which has numerous sub-light distributions in the form of pixels or strips, disposed adjacent to or above one another. Each LED chip normally generates its own sub-light distribution. With a targeted activation, in particular an on/off switching or dimming of the individual LED chips of the matrix light source, it is possible to influence the shape and the intensity of the light distribution. In this way, a matrix headlamp can be used to generate an adaptive light distribution without moving parts. In particular, it is possible to generate a basic low beam light distribution having a horizontal light/dark border, a conventional low beam light distribution having an asymmetrical light/dark border, a high beam light distribution, a partial high beam light distribution in which targeted regions are removed from the light distribution where other road users have been detected, or a marker light distribution in which objects detected on the road surface in front of the vehicle are illuminated in a targeted way. Matrix headlamps are known in the prior art in different embodiments, such as in published application numbers EP2306073A2, EP2306074A2, EP2306075A2, and DE102008013603A1. Further, approaches specifically for so-called “strip-headlamps” are known in the prior art, such as in published application numbers DE102011077132A1 and DE102011077636A1, with which the generated light distribution includes numerous strip shaped sub-light distributions, disposed adjacent to one another. Approaches for designing a color-correcting projection lens for matrix headlamps are known from DE102010626B4. It is proposed in EP2280215A2 that the homogeneity and the resolution of the image be improved through the use of numerous LED modules in a headlamp. An individual projection lens (or secondary lens) is allocated to each primary lens, thereby necessitating that two light source modules, at least two primary lens modules, and at least two secondary lens modules be combined for the known headlamp. Thus, at least two light exit surfaces for each matrix headlamp are visible from the outside. A so-called “compound eye” headlamp module is obtained. The strip-shaped sub-light distributions projected onto the road surface have a relatively large angular width of at least 2° horizontally, or even significantly larger. The superimposing of wide strips of this type improves the homogeneity of the light distribution, but reduces the obtainable resolution. The known headlamp requires at least two complete light modules that are independent of one another for each headlamp, wherein each light module has an LED matrix, a primary lens and a secondary lens. Thus, a headlamp of this type includes at least two light sources, two primary lenses, and two secondary lenses. With all of the matrix headlamps known from the prior art, there is, however, the problem that there are color and intensity fluctuations in the resulting light distribution. These are caused mainly by the dispersion (a change in the refraction index for optical materials in relation to the light wavelengths) and imaging errors in the projection lens. The color fluctuations occur in particular at the edges of the individual sub-light distributions.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages in the prior art in a matrix headlamp, or components thereof, with an LED module that has a light source in the form of an LED matrix, including numerous LED chips disposed in a matrix, adjacent to and/or above one another, a primary lens including numerous primary lens elements disposed in a matrix, adjacent to and/or above one another, for bundling light emitted from the light source, and the projection lens. The projection lens projects an exit surface of the primary lens for generating a predefined light distribution on a road surface in front of a vehicle.

The headlamp of the present invention exhibits an improved homogeneity in the resulting light distribution with a single primary lens and a single projection lens, wherein it may be visible from the outside that the light distribution exits the headlamp from a single light exit aperture, or from a single projection lens. It is proposed that the projection lens is designed such that it generates at least two separate images of the exit surface of the primary lens at its imaging side, which are offset to one another in the horizontal direction, such that a superimposing of the generated images improves homogeneity of the light distribution. In this way, it is possible to generate the desired improved and more homogenous matrix light distribution with a single visible and accessible exit aperture (so-called monocular matrix headlamp). The proposed projection lens obtains a compensation for color effects and homogeneity or intensity fluctuations up to half of a pixel width, without the need for special glass materials or plastics, and without reducing the sharpness of the image, in particular the sharpness of the edges of the pixels. Thus, because of the proposed projection lens, an improvement in the color compensation and homogeneity can be obtained in a matrix headlamp, without forfeiting the sharpness (in particular, with respect to the periodically appearing color), homogeneity, and imaging errors.

Importantly, with a single matrix-type light source having a single integral primary lens disposed upstream thereof, the emitted light distribution on the light exit surface thereof is imaged onto the road surface with a single integral projection lens such that at least two separate primary lens images occur, such that in their interaction, pixel edges and border steepnesses remain intact and the remaining periodically occurring color and homogeneity or intensity fluctuations are compensated for reciprocally. It will be appreciated that there are various possibilities for designing the projection lens of the invention such that it generates the effects described above.

In order to obtain the projection lens of the present invention, it is conceivable to vary one or more of the active optically effective surfaces of the projection lens. In particular, these surfaces can be a light entry surface, a light exit surface, and/or any other surface lying therebetween (for example, with an achromatic lens). The active optically effective surfaces of the projection lens are preferably divided and/or displaced, such that the at least two separate images of the light exit surface of the primary lens, offset to one another in the horizontal direction, are generated. Each of the generated images contributes to a portion of the joint light flow, or a portion of the intensity and the illumination level. The portion contributed by each image depends on the number of separate images generated. Thus, the portion with two images is preferably 50%, and accordingly, with three images, is 33% of the overall value of the resulting light distribution.

Advantageously, the projection lens may be designed such that the separate images of the exit surface of the primary lens are each offset to one another by a value of b/n, wherein b is a width, in particular an angular width, of a pixel formed by the imaging of a single light exit surface of a single primary lens element, and n is a number of separate images of the exit surface of the primary lens generated by the projection lens. If the projection lens is designed, by way of example, for generating two separate images of the light exit surface of the primary lens, then these two images are preferably offset to one another by half of a pixel width. Accordingly, the images of the light exit surface of the primary lens are preferably offset to one another by one third of a pixel width if the projection lens is designed for generating three separate images. In this way, a particularly homogenous light distribution can be generated.

With a single matrix-type light source having a single integral primary lens disposed upstream thereof, the exit light distribution on the light exit surface thereof is imaged onto the road surface with a single integral projection lens such that at least two separate primary lens images are obtained, such that pixel edges and border steepnesses remain intact when they interact, and the remaining periodically occurring color and homogeneity or intensity fluctuations are compensated for reciprocally. There are various possibilities for designing the projection lens in accordance with the invention, such that it generates the effect described above.

In one embodiment of the present invention, it is proposed that the projection lens have at least two separate optical axes. The separate optical axes of the projection lens preferably run in the same horizontal plane. The horizontal plane preferably includes a module axis for an LED module, which is provided by the projection lens. The module axis preferably runs from the middle of the light exit surface of the primary lens in the direction of travel. The spacing of the optical axes to one another is relatively small. It is selected such that separate images of the light exit surface of the primary lens are generated, which are offset to one another in the horizontal direction by a fraction of a pixel. The different optical axes of the projection lens cause different images of the light exit surface of the primary lens to be generated. The number of separate images generated by the projection lens corresponds to the number of separate optical axes. The images of the light exit surface of the primary lens are offset to one another so to correspond to the courses of the optical axes. Because the optical axes run in the same horizontal plane, the separate images are offset to one another only in the horizontal direction. If the optical axes were disposed in different horizontal planes, then the images would also be offset to one another vertically.

In one embodiment of the invention, it is proposed that the separate optical axes of the projection lens run parallel and at a spacing to one another. Alternatively, it is proposed that the separate optical axes of the projection lens run at an angle to one another. In this case, the optical axes of the projection lens intersect, preferably in a plane of the light exit surface of the primary lens. The plane of the light exit surface preferably runs perpendicular to the horizontal plane, in which the optical axes are disposed. It is particularly preferred that the optical axes, which run at an angle to one another, intersect the light exit surface of the primary lens at a point of intersection for the module axis.

In one embodiment of the present invention, it is proposed that at least one active optical surface of the projection lens is provided with alternating optical regions for generating substantially identical images of the exit surface of the primary lens, which are disposed adjacent to, or above, one another, wherein a first group of the optical regions generates a first image of the exit surface of the primary lens, and at least one second group of optical regions generates at least one further image of the exit surface of the primary lens, wherein the generated images are disposed offset to one another in the horizontal direction in the resulting light distribution. In this way, at least one active optical surface of the projection lens can be provided with the alternating regions as strips or a checkerboard. An individual optical axis is allocated to each group of regions, which is separate from the optical axes of the other groups of regions.

Preferably, the alternating optical regions are formed on a light exit surface of the projection lens. It is further preferred that the alternating optical regions are designed as strips, wherein the strips extend vertically. If the projection lens generates two separate images of the light exit surface of the primary lens, the strip-shaped regions preferably alternate between two groups. Accordingly, if the projection lens generates three separate images of the light exit surface of the primary lens, then each third strip-shaped region is allocated to one of three groups.

It is further proposed that the active optical surface of the projection lens is provided with numerous prisms, extending over the entire surface, disposed adjacently to one another, the longitudinal axes of which run parallel to one another, wherein one prism surface of the prisms generates the first image of the exit surface of the primary lens, and the other prism surface of the prisms generates the second image of the exit surface of the primary lens. The prism surfaces can be designed such that they are flat or curved.

In one embodiment, an apex of the prisms is flattened off over the entire length thereof, such that a roof surface of the prism is obtained, which generates a further image of the light exit surface of the primary lens, which is offset in relation to the other two images in the horizontal direction. In this way, the projection lens can thus generate three separate images of the light exit surface of the primary lens, offset to one another in the horizontal direction. The images are preferably offset to one another by b/3, wherein b is the width, in particular an angular width, of a pixel in the resulting light distribution, thus a sub-image of a sub-light exit surface of a primary lens.

Further, it is proposed that the prism surfaces of the prisms are each divided into two sub-surfaces over their entire length, wherein a contact line of the sub-surfaces of a prism surface of a prism runs parallel to the longitudinal axis of the prism, wherein the sub-surfaces each generate a separate image of the light exit surface of the primary lens, disposed such that it is offset to the other images. In this way, the projection lens can thus generate, with a prism having apexes, four separate images of the light exit surface of the primary lens, offset to one another in the horizontal direction. With a prism having a flattened off apex and a roof surface, the projection lens can generate five separate images of the light exit surface of the primary lens, offset to one another in the horizontal direction. The images are preferably offset to one another by w′/4, or w′/5 respectively, wherein w′ is the width, in particular an angular width, of a pixel of the resulting light distribution, thus a sub-image of a sub-light exit surface of a primary lens element.

It will be appreciated that other structures suitable for generating the separate images of the light exit surface of the primary lens can also be provided. Furthermore, it is conceivable to superimpose the structures for generating the separate images with an arbitrary diffusion structure.

Further, it is proposed that the alternating optical regions formed on the at least one active optical surface of the projection lens have an amplitude of less than 0.1 mm, preferably less than a small number of micrometers.

It will be appreciated that an LED module according to the invention can be obtained through the use of a projection lens according to the invention in an LED module for a motor vehicle headlamp. Likewise, a headlamp according to the invention can be obtained through the use of a projection lens according to the invention in a motor vehicle headlamp.

DETAILED DESCRIPTION OF THE INVENTION

InFIG. 1, a motor vehicle headlamp according to the invention is indicated as a whole with the reference numeral1. The headlamp1has a housing2, preferably made of plastic. The headlamp housing2has a light exit aperture4facing a light exit direction3, which is closed with a transparent cover plate5. The cover plate5may be made of glass or plastic. Optically effective profiles (for example, prisms or cylindrical lenses), at least in sections, can be disposed on the cover plate5in order to diffuse the light passing through it (so-called headlamp diffusers). It is also conceivable that the cover plate5could be designed without optically effective elements (so-called clear plates).

A light module6is disposed in the interior of the headlamp housing2. The light module6can serve to generate an arbitrary headlamp function or a portion thereof. In particular, the light module6can serve to generate a low beam light distribution, a high beam light distribution, a fog light distribution, or an arbitrary adaptive light distribution. Moreover, a further light module7can be disposed in the housing2. This serves, by way of example, for generating a further headlamp function. It is also conceivably that the light modules6,7could collectively generate a specific headlamp function. Thus, the light module7could, for example, generate a low beam basic light distribution having a relatively wide diffusion and a horizontal light/dark border. The light module6could then generate a low beam spot light distribution, which is relatively strongly concentrated in comparison with the low beam basic light distribution from the light module7, and has an asymmetrical light/dark border at the top. A superimposing of the basic light distribution and the spot light distribution results in a conventional low beam light distribution. It is also conceivable that further light modules could be disposed in the headlamp housing2in addition to the light modules6,7. Furthermore, it is possible for only one light module to be disposed in the headlamp housing2, for example, the light module6without the light module7. Further, it is also possible that one or more lamp modules, such as the illustrated lamp module8, could be disposed in the housing2. By way of non-limiting example, the lamp module8may serve to generate an arbitrary lamp function, such as a blinker light, a navigation light, daytime running lights, and the like.

The light module6is advantageously designed as an LED module according to the present invention. The LED module6is shown in detail inFIG. 2. The LED module6has a light source in the form of an LED matrix, which is indicated generally at10. The LED matrix10has numerous LED chips11disposed in a matrix, adjacent or next to one another. Furthermore, the LED module6includes a primary lens, indicated generally at12. The primary lens12has numerous primary lens elements13, disposed in a matrix, adjacent to or above one another. In the depicted example, each LED chip11is allocated its own primary lens element13. As illustrated by detail I, which shows a primary lens element13of this type together with an LED chip11allocated it, the LED chip11emits light in a main beam direction14, the majority of which is coupled through a light entry surface15in the primary lens element13. The primary lens element13itself can be designed as a conventional reflector for minor reflection, or as a so-called “attachment lens element” made of a transparent material (for example, glass or plastic) for total reflection. In the depicted example, the primary lens element13is designed as a totally reflecting attachment lens made of a transparent plastic material. The primary lens12can bundle the light emitted from the LED matrix10. Further, the LED module6includes a projection lens16designed as an optical lens. The projection lens16is also referred to as a secondary lens and projects an exit surface17of the primary lens12so as to generate a predefined light distribution on a road surface in front of a vehicle equipped with the headlamp1and the LED module6. The projection lens16can be designed as a conventional optical lens or as and achromatic lens.

The headlamp1with the LED module6is referred to as a matrix headlamp, because it generates a light distribution with numerous pixel or strip shaped sub-light distributions disposed above and/or adjacent to one another. The individual sub-light distributions generated from the light of an LED11and the associated primary lens element13are also referred to as pixels. Each of the sub-light distributions is generated by imaging a sub-light exit surface of an individual primary lens element13of the primary lens12with the projection lens16. A light distribution for a matrix headlamp1known from the prior art is shown by way of example inFIG. 3. The light distribution20is imaged on a measurement screen21, which is disposed at a defined spacing to the headlamp1, or the LED module6, respectively, in front of the motor vehicle. A horizontal axis HH and a vertical axis VV running perpendicular thereto are plotted on the measurement screen. Thus, the light distribution20shown here by way of example has numerous pixels22,23,24disposed adjacent to and above one another. In particular, the pixels22,23,24in the depicted embodiment example are disposed in three rows and in thirty columns. The pixels in the upper row are indicated with the reference symbol22, the pixels in the middle row are indicated with the reference symbol23, and the pixels in the lower row are indicated with the reference symbol24. Each pixel22,23,24in the depicted light distribution20is generated with an LED chip11interacting with the allocated primary lens element13, after projection through the secondary lens16.

With a targeted activation of the individual LED chips11in the LED matrix12, it is possible to vary the resulting light distribution20in a number of different ways. As such, it is conceivable, for example, to temporarily shut off those LED chips11in the pixel region of the light distribution20in which other road users have been detected. In this way, it is possible to drive with a continuous high beam, wherein a blinding of other road users is prevented by locally removing the pixels22,23,24from the light distribution (so-called partial high beams). Likewise, it would be conceivable that the LED module6generates a low beam light distribution with an asymmetrical upper light/dark border, wherein the LED chips11for generating the upper row of pixels22are shut off, except for a few LED chips11for generating the pixels22on the side of the traffic in which the vehicle is located. Furthermore, it would be conceivable to turn on individual LED chips11in a targeted way for illuminating objects detected on a road surface in front of the motor vehicle, in order to generate one or more pixels22,23above the light/dark border of the low beam light distribution, such that the objects detected on the road surface can be illuminated in a targeted way (so-called marking light or marker light). It will be appreciated that many other adaptive light distributions20can be obtained with targeted on/off switching and/or dimming of the LEDs11.

In particular, along the edge of the individual pixels22,23,24, the resulting light distribution20may exhibit an undesired color fringe. In addition, clearly visible intensity fluctuations may occur in the light distribution20. With the present invention, the homogeneity of the light distribution20with respect to disruptive color effects and intensity fluctuations is to be improved.

The present invention proposes, in particular, a special homogenizing projection lens (or secondary lens)16as a component of a matrix headlamp1for motor vehicles, in which a light exit surface17of the primary lens12includes numerous pixel or strip shaped periodic structures, aligned in rows, which are projected with the special projection lens16onto the road surface in order to implement a dynamic low beam, partial high beam, matrix light or high beam light function. The projection lens16generates at least two separate images25,26(compareFIGS. 4 and 5) of the light exit surface17of the primary lens12located on the object side on the image side, i.e. on the road surface or on a measurement screen21. By superimposing the at least two separate images25,26, a resulting light distribution27is obtained (compare withFIG. 6), wherein the at least two images25,26are offset to one another in the horizontal direction in such a way that a significant improvement in the homogeneity of the light distribution27is obtained. In particular, undesired color effects or intensity fluctuations in the light distribution27are reduced in a targeted way, or even eliminated entirely. The separate images25,26of the light exit surface17of the primary lens12are generated with a shared projection lens16.

A first image25of the light exit surface17of the primary lens12, which can be generated with the projection lens16of the present invention, is shown by way of example inFIG. 4. The image25inFIG. 4is displaced in the depicted example approximately ¼ pixel to the left with respect to the vertical axis VV. A second image26of the light exit surface17of the primary lens12is depicted inFIG. 5. The second separate image26is displaced approximately ¼ pixel to the right with respect to the vertical axis VV. In this way, the first and the second image25,26are offset in relation to one another by approximately ½ of a pixel. Each image25,26provides one half of the joint luminous flux for the resulting overall light distribution27, or one half of the intensity and one half of the illumination for the overall value of the light distribution27. Because the edges of the pixels22,23,24and the pixel centers of the images25,26do not lie directly on one another, the color and intensity in-homogeneities are compensated for reciprocally with the superimposing of the images25,26. As a result, it is possible with the present invention to generate a substantially more homogenous light distribution27with just one LED module6having a primary lens12and a projection lens16, than was possible in the prior art under similar circumstances or conditions.

The intensity of the individual images25,26depends on the lengths of the prism surfaces, or on the proportion of the prism base surface to which the corresponding prism surface is allocated. One embodiment of the present invention includes prisms having identical prism base surface proportions.

In order to illustrate the invention, reference is made to the light distributions20,27shown inFIGS. 7 and 8, having ISO lines plotted therein (isolux lines for indicating regions having identical illumination values). InFIG. 7, the light distribution20that would be generated with a conventional LED module is shown. The depicted light distribution20concerns a low beam light distribution, or a partial high beam, wherein the entire region of the traffic lane for oncoming traffic is removed from the light distribution20, in order to prevent blinding oncoming traffic. The light distribution20is imaged on a measurement screen21. As shown, the lines30with identical intensity or illumination values exhibit in-homogeneities, which is indicated by the uneven courses of the lines. In contrast thereto, the lines31having identical intensities or illumination values in the light distribution27generated with the matrix headlamp1according to the invention, or the LED module6according to the invention, respectively, exhibit significantly fewer in-homogeneities, as is indicated by the significantly more even courses of the lines.

FIGS. 7 and 8show by way of example the same low beam pattern20,27of a matrix headlamp1having an LED matrix light source10with three rows. All LED chips11of the LED matrix10that generate pixels in the upper and lower rows on the left side of the light distribution20,27, plus one pixel, respectively, on the right side of the light distribution20,27adjacent to the HV point, are switched off, in order to not blind the oncoming traffic. The ISO lines30inFIG. 7are significantly more uneven. The ISO lines31for the light distribution27inFIG. 8, in contrast, are more even and have fewer fluctuations.

An LED module6according to the invention, having a projection lens16according to the invention, is shown in detail inFIG. 9. Here, the projection lens16serves for generating two separate images25,26of the light exit surface17of the primary lens12. It will be appreciated that the projection lens16can also be designed so as to generate more than two separate images, displaced in relation to one another in the horizontal direction. The projection lens16has two parallel optical axes, indicated by the reference numerals40and41. The reference numeral42indicates a module axis of the LED module6, which runs from the middle of the primary lens12in the direction of travel3. The spacing between the optical axes40,41is small and only large enough that the projection lens16can project two separate images25,26at a ½ pixel spacing onto the road surface in front of the motor vehicle. The optical axes40,41are preferably disposed on a common horizontal plane, which may also include the module axis42. In the depicted embodiment, the projection lens16is divided into two halves16a,16balong a vertical central plane, which includes the module axis42. The one half16ais preferably allocated to the optical axis41and the other half16bis preferably allocated to the optical axis40.

It is not necessary that all of the active optical surfaces of the projection lens16are subjected to a division and/or displacement of the generated surfaces. It is sufficient if only one of these surfaces is formed in this way. This can be, for example, a light entry surface, a light exit surface, or a surface of the primary lens16disposed therebetween. At least one of the active optical surfaces of the projection lens16, however, should be modified such that the at least two images25,26of the light exit surface17of the primary lens12can be generated, which are offset to one another in the horizontal direction.

Another embodiment of an LED module6according to the invention, having two optical axes43,44running at an angle to one another, is shown inFIG. 10. Preferably, the optical axes43,44intersect in a plane of the light exit surface17of the primary lens12. The optical axes43,44are preferably also disposed on a common horizontal plane, which preferably also includes the module axis42. In the depicted embodiment, a first half16aof the projection lens16is allocated to the optical axis44and a second half16bof the projection lens16is allocated to the optical axis43.

Another preferred embodiment of the projection lens16according to the invention is based on a special structure on one of the active optical surfaces of the projection lens16. A corresponding embodiment is shown inFIG. 11, wherein alternating optical regions16c,16ddisposed adjacent to one another are formed on the light exit surface of the projection lens16. In the depicted embodiment example, the regions16c,16dare disposed in the shape of strips on the light exit surface of the projection lens16. As a matter of course, the regions can also be designed as a checkerboard, or in any other way. Moreover, it is conceivable that the optical regions16c,16dare formed, not on the light exit surface, but rather on the light entry surface or any other surface between the light entry surface and the light exit surface of the projection lens16. The optical regions16c,16dare designed for generating substantially identical images25,26of the exit surface17of the primary lens12. In doing so, all of the regions16ccollectively generate a first image of the light exit surface17, and all of the regions16dcollectively generate a second image26of the exit surface17. The first optical regions16care preferably allocated to the first optical axis40and the second optical regions16dare preferably allocated to the second optical axis41. A projection lens16can also be implemented in this way, which can generate numerous separate images25,26of the light exit surface17of the primary lens12, which are displaced in relation to one another in the horizontal direction. With the embodiment example fromFIG. 11, the first optical regions16cform a first group, which generates the first image25of the exit surface17, and the second regions16dform a second group, which generates the second image26of the exit surface17of the primary lens12.

InFIG. 11, the first regions16care indicated by a cross-hatching. This serves, primarily, to identify and better distinguish the two regions16c,16dfrom one another. This does not necessarily mean that an optically effective structure, such as a diffusion structure, is formed on the light exit surface of the projection lens16in the regions16c, while in contrast no such structure is formed in the regions16d. This would be entirely possible, however. Likewise, it would be conceivable to provide a diffusion structure on the entire light exit surface of the projection lens16.

Another embodiment example of an LED module6according to the invention, or a projection lens16, respectively, is shown inFIG. 12. In this case, an active optical surface of the projection lens16, the light exit surface in the depicted embodiment example, is provided with numerous prisms, extending over the entire surface, disposed adjacent to one another, the longitudinal axes of which run parallel to one another in the vertical direction. A first prism surface16eof the prisms generates a first image25of the exit surface17of the primary lens12. Another prism surface16fof the prisms generates a second image26of the exit surface17of the primary lens12. Thus, a respective first prism surface16e, together with a second prism surface16f, forms one of the prisms on the light exit surface of the projection lens16. Preferably the first prism surfaces16eare allocated to the first optical axis41, and the other prism surfaces16fare allocated to the second optical axis42. In this way, separate images25,26of the exit surface17of the primary lens12are generated, which are offset to one another in the horizontal direction.

The amplitudes of the prism structure on the light exit surface of the projection lens16inFIG. 12are relatively small, such that they are difficult to detect with the naked eye. In particular, the amplitudes are conceived on a scale of a few micrometers to a few tens of micrometers. The structures are thus at best perceived by an observer seeing the headlamp1through the cover plate5from the outside as lightly indicated strips, or alternatively, as a relatively inconspicuous checkerboard pattern on the projection lens16.

Different design possibilities for the prism structure on the optically active surface of the projection lens16are proposed inFIGS. 13A-13C, wherein each Figure shows a cross-section cut through one of the prisms, in each case, at the top, and beneath this, the images of the light exit surface17of the primary lens12that can be obtained with the illustrated prism structure, are depicted.

The prism structure inFIG. 13Acorresponds to the prism structure that is used in the embodiment example of the projection lens16fromFIG. 12. The images25and26that can be obtained thereby are offset to one another by ½ of a pixel width w′. With the embodiment example inFIG. 13B, an apex of the prisms16e,16fis flattened off over the entire length, such that a roof surface16gof the prisms is obtained, which generates a further image28of the light exit surface17of the primary lens12, which is offset in the horizontal direction in relation to the other two images25,26, which are generated by the prism surfaces16e,16f. The three images25,26,28are preferably offset in relation to one another in the horizontal direction by ⅓ of a pixel width w′. In order to obtain the desired distribution at ⅓ of the pixel or strip width w′, the prism angle α should be adapted accordingly. The surface16ggenerates an image28in the center of the light distribution. With the embodiment inFIG. 13C, the prism surfaces16e,16fof the prisms are each divided into two sub-surfaces16e1,16e2;16f1,16f2over their entire lengths. In doing so, a contact line of the sub-surfaces16e1,16e2;16f1,16f2of a prism surface16e;16fof a prism runs parallel to a longitudinal axis of the prism. The sub-surfaces16e1,16e2;16f1,16f2of a prism surface16e;16fgenerate two separate images25,28;26,29, disposed offset to one another, which are also offset in relation to the other images26,29;25,28. In particular, it is proposed that the four images25,26,28,29of the light exit surface17of the primary lens12are each offset in relation to one another by ¼ of a pixel width w′.

It is conceivable to generate more than four images of the light exit surface17of the primary lens12with other designs for the prism structure. As such, it is conceivable, for example, that with the prism structure fromFIG. 13C, the apexes of the prisms are flattened off over their entire lengths, such that a roof surface, similar to the roof surface16cof the prism structure fromFIG. 13Bis obtained, which generates a further image of the light exit surface17of the primary lens12.

Further possible designs for the prism structure on the optically active surface of the projection lens16are depicted inFIGS. 14A-14C. The actual prisms inFIGS. 14A, 14B, 14Ccorrespond substantially to the prisms inFIGS. 13A, 13B13C. With the embodiment example fromFIGS. 14A-14C, however, straight sections16hare provided between the individual prisms16e,16f. Thus, it is possible, with the prism structure fromFIG. 14A, to generate a total of two, plus one, thus three, separate images of the light exit surface17of the primary lens12. Likewise, with the prism structure according toFIG. 14Bit is possible to generate a total of two, plus two, thus four, separate images. The strips16gand16hcan generate identical images, because the optical axes are not angled toward one another, and as a result, the images coincide. In a corresponding way, with the prism structure inFIG. 14C, four plus one, thus five, images of the light exit surface17of the primary lens12can be generated.

Based on theFIGS. 15 and 16, as explained below, the height of the prism structure for a projection lens16according to the invention can be calculated. To that end, inFIG. 15, the prism structure according toFIGS. 12 and 13Awill serve as a basis. InFIG. 15:h: height of the prisms in millimetersw: wavelength (one period) of the prism structure (or a base width of a prism) in millimetersε: light incidence angle in relation to a surface norm for the prism surface16fω: light decoupling angle in relation to the surface norm for the prism surface16fδ: ω−ε=the difference in angles between incident light beams and decoupled light beamsα: prism angle in relation to a vertical, or an angle of a prism surface16e,16fin relation to a vertical surfaceφ: pixel width in angular degrees

The following relationship applies to the prism structure inFIG. 15:

From which, according to the conversion, and with nL=1 for air, the following is obtained:
sin ω=nPMMA·sin ε  (2′)

And furthermore:

The angular difference thus needs to be ±¼ of a pixel width for two separate images25,26of the light exit surface17of the primary lens12, in order that the two images25,26are offset to one another by ½ of a pixel width. Thus, from equation (4):

and after conversion:

from which the following is obtained

for α=ε:

From the equations (10) and (11):

Thus, for ½ pixel offsetting, the necessary prism height h is:

With a ½ pixel offsetting, the images25,26are shifted in relation to one another by φ/2 (±φ/4). This relates to a so-called compensation of the first order. For a compensation of the second order, two double imaging groups need to be offset in relation to one another. In the following, it is explained how one can determine the height h of the prism for a compensation of the second order:

Thus, for the pixel height h:

With very small angles, the following applies:

Thus, for the compensation of the second order, the prism height h is:

Thus, for small angles, the compensation of the first order, second order, etc. needs to occur with triangular structures, which overlap, which have doubled, quadrupled, etc. wavelengths and the same amplitudes. A detail of a surface structure for an optically active surface of a projection lens16according to the invention is depicted inFIG. 16, by way of example. The structure of the first order is indicated thereby with a solid line50, a structure of the second order is indicated by a broken line51, and a sum of the two structures50,51is indicated by the reference numeral52.

The structure of the first order50generates two separate images25,26of the light exit surface17of the primary lens12, which are shifted by ½ of a pixel width in relation to one another. The prism structure of the second order51has a frequency of ½ (doubled period) and is frequently tilted at two of its flanks (prism surfaces) toward two adjacent flanks (one whole period) of the structure of the first order50, and thus results in a shifting of the images in relation to one another by ¼ of a pixel width.

The prism structure52is the sum (resulting) from the prism structure of the first order50and the prism structure of the second order51.

The amplitude h of the structure of the first order50relates to the necessary deflection angle of ±0.3°. With a period (wavelength w) of 2 mm and a refraction index nPMMA=1.49, and nLuft=1.0 [Luft: air], the prism height h is:

The calculated prism height h=10.7 μm is relatively large. For this reason, the wavelength2, originally 2 mm, reduced by half to 1 mm. Thus, for the amplitude h of the prism structure:

The prism structure51is superimposed on the prism structure of the first order50, but should only attain one half of the deflection (½*½ pixel→±0.15° H). Thus, from the equation (14):

Thus, the results from the equation (15) are confirmed. The prism structure of the second order51has the same amplitude h as the prism structure of the first order50. In this way, it is also fundamentally possible to generate adaptations of higher orders.