Lighting device for a motor vehicle

Abstract

A lighting device for a motor vehicle, comprising a light source (2) and a scanner (3) onto which a light beam (L) generated from the light of the light source (2) falls and which, during operation, deflects the light beam (L) based on repeating raster scans in order to repeatedly generate an image (B) on the ground in the surroundings of the motor vehicle, wherein the light beam (L) performs a scanning movement along a scanning axis (x) at a predetermined frequency in a respective raster scan and is displaced perpendicular to the scanning axis (x) at reversal positions of the scanning movement, whereby the light beam (L) is moved on a plurality of parallel lines (LI) running along the scanning axis (x) and is displaced between adjacent parallel lines (LI), wherein the lighting device (1) is designed toTo set power values (Pz) of the light source (2) within a respective raster scan based on a target power distribution (ZL) corresponding to the generated image (B), which target power distribution indicates respective power values (Pz) of the light source (2) when the respective image positions are illuminated by the light beam (L) for a plurality of image positions covering the image (B) and illuminated by the light beam (L) in a respective raster scan, characterized in that the illumination device (1) is designed such that the light beam (L) passes through one or more lines (LI) several times in succession in a respective raster scan, and the maximum power value of the light source (2) within a respective raster scan is lower according to the target power distribution (ZL) than when generating the image (B) with respective raster scans in which the light beam (L) passes through each line (LI) only once.

Description

[0001] The invention relates to a lighting device for a motor vehicle and a method for operating such a lighting device.

[0002] It is known from the prior art to install scanning lighting devices in a motor vehicle, which contain a scanner that moves a light beam at a high frequency and thereby generates an image on the ground in the surroundings of the motor vehicle.

[0003] So-called line or column scanners are often used in scanning lighting devices, in which the light beam travels along a number of parallel lines. After traveling along one line, the light beam is offset to travel along an adjacent parallel line. With such line or column scanners, different images can be created on the floor by varying the electrical power of the light source used to generate the light beam. However, this does not utilize the maximum electrical power available from the light source efficiently.

[0004] Printed prior art in the field of the present invention is known from DE 10 2012 205 437 A1 and DE 10 2013 226 652 A1.

[0005] The object of the invention is therefore to provide a scanning lighting device and a method for operating such a lighting device in which the maximum electrical power of the installed light source is used more efficiently.

[0006] This object is achieved by the lighting device according to claim 1 and the method according to claim 10. Further developments of the invention are defined in the dependent claims.

[0007] The lighting device according to the invention is intended for use in a motor vehicle, such as a car and possibly also a truck. The lighting device comprises a light source and a scanner onto which a light beam generated from the light source falls. During operation, the scanner deflects the light beam based on repeating raster scans in order to repeatedly generate an image on the ground in the vicinity of the motor vehicle. The ground refers to the earth's surface on which the motor vehicle is parked and which lies within the illumination range of the lighting device.

[0008] If interactions between the lighting device and components of the motor vehicle or the ground surrounding the motor vehicle are described below, and particularly in the patent claims, this is always to be understood as meaning that the interaction occurs when the lighting device is arranged or installed in the motor vehicle. The components of the lighting device that have the corresponding interaction with the motor vehicle or components of the motor vehicle or the ground are thus designed in such a way that the interaction occurs when the lighting device is arranged or installed in the motor vehicle.

[0009] In the illumination device according to the invention, the light beam performs a scanning movement along a scanning axis in a respective raster scan at a predetermined frequency and is displaced perpendicular to the scanning axis at reversal positions of the scanning movement. The displacement does not have to occur at every reversal position. In this way, the light beam is moved along several parallel lines running along the scanning axis and is displaced between adjacent parallel lines. The illumination device is configured to measure the power values of the light source (ieThe electrical power at which the light source is operated to generate the light beam) can be set based on a target power distribution corresponding to the generated image, which target power distribution specifies the respective power values of the light source when the respective image positions are illuminated by the light beam for a plurality of image positions covering the image and illuminated by the light beam in a respective raster scan. If necessary, the power value can also be set to zero at some image positions, which, within the meaning of the patent claims, corresponds to illuminating the corresponding image position with an illuminance of zero (i.e., the light source is switched off).

[0010] The illumination device according to the invention is designed such that the light beam passes through one or more lines several times in succession in a respective raster scan, and the maximum power value of the light source within a respective raster scan is lower according to the target power distribution than when generating the image with respective raster scans in which the light beam passes through each line only once. The feature just described is achieved by appropriately controlling the scanner and the light source. In other words, the illumination device according to the invention contains a control unit that carries out this control.

[0011] The invention is based on the finding that by repeatedly traversing lines, the maximum operating power of the light source of the lighting device for generating a predetermined image on the ground can be selected to be lower than if the lines are only traversed once. The detailed description explains how a target power distribution can be iteratively determined according to the above criterion of the reduced maximum power value. A target power distribution determined in this way is stored in the lighting device and is then used during operation of the lighting device to generate the image.

[0012] In a particularly preferred embodiment, the illumination device is designed such that, for the generated image, the ratio of the duration of the light beam in each line within a respective raster scan to the total duration of the respective raster scan essentially corresponds to the ratio of the luminous flux in each line within the respective raster scan to the total luminous flux of the respective raster scan required to generate the image. Corresponding values of the luminous flux in each line or of the total luminous flux are predetermined by the light distribution of the image to be generated. With this variant of the invention, a very high degree of utilization of the power available from the light source can be achieved.The criterion just described of correlating the ratio of the residence times to the ratio of the luminous fluxes can be met by performing the iteration disclosed in the detailed description with a sufficient number of iteration steps.

[0013] Depending on the design of the illumination device according to the invention, it can be configured to generate monochromatic light and, optionally, also white light. In a further preferred design, the scanner of the illumination device according to the invention comprises a mirror for deflecting the light beam. The mirror is preferably a so-called MEMS component (MEMS = Micro Electro Mechanical System). This allows compact dimensions of the illumination device to be achieved. In a further preferred variant, the illumination device is configured such that the power values of the light source for illuminating the respective image positions within a raster scan are adjusted by means of pulse width modulation.

[0014] In a preferred embodiment of the lighting device according to the invention, a laser light source comprising one or more laser diodes is used as the light source. For example, an RGB laser light source is used to generate white light. Alternatively, it is also possible for the light source of the lighting device according to the invention to be an LED light source comprising one or more LEDs. In particular, the LED light source can be an RGB LED light source for generating white light.

[0015] In a further preferred embodiment, the lighting device according to the invention is an ambient lighting device for generating an image in the surroundings of the motor vehicle. The "surroundings" here are understood to mean the immediate surroundings of the motor vehicle within a range of a few meters. The surroundings differ from the far field of the motor vehicle, in which, for example, the low-beam distribution or high-beam distribution of a headlight is generated. Nevertheless, it is also possible for the lighting device according to the invention to be a headlight or a signal light, or a component of a headlight or a signal light. The images generated by the lighting device are then in the far field of the motor vehicle.

[0016] In addition to the lighting device according to the invention, the invention relates to a method for operating a lighting device for a motor vehicle. The lighting device operated by the method comprises a light source and a scanner. A light beam generated from the light of the light source falls onto the scanner, and the scanner deflects this light beam based on repeating raster scans in order to repeatedly generate an image on the ground in the vicinity of the motor vehicle. In the method according to the invention, the light beam performs a scanning movement along a scanning axis in each raster scan at a predetermined frequency and is displaced perpendicular to the scanning axis at reversal positions of the scanning movement, whereby the light beam is moved along several parallel lines running along the scanning axis and is displaced between adjacent parallel lines.In the method according to the invention, power values of the light source are set within a respective raster scan based on a target power distribution corresponding to the generated image, wherein the target power distribution indicates, for a plurality of image positions covering the image and illuminated by the light beam in a respective raster scan, respective power values of the light source when the respective image positions are illuminated by the light beam.

[0017] The method according to the invention is characterized in that the light beam passes through one or more lines several times in succession in a respective raster scan and the maximum power value of the light source within a raster scan is lower according to the target power distribution than when generating the image with respective raster scans in which the light beam passes through each line only once.

[0018] In a preferred variant, the method according to the invention is used to operate one or more preferred embodiments of the lighting device according to the invention.

[0019] The invention further relates to a motor vehicle which comprises one or more lighting devices according to the invention or one or more preferred variants of the lighting device according to the invention.

[0020] An embodiment of the invention is described in detail below with reference to the attached figures.

[0021] They show: Fig. 1 is a schematic representation of a variant of the lighting device according to the invention in plan view; and Fig. 2 a schematic representation of the lighting device from Fig. 1 in side view including a distribution of illuminance of a generated image.

[0022] An embodiment of the invention is described below based on an ambient lighting device 1 that is installed in the door sill of a motor vehicle (not shown) and generates a light distribution on the ground to the right of the motor vehicle. The longitudinal direction of the motor vehicle is in Fig. 1 is indicated by the x-axis, and the transverse direction by the y-axis. The illumination device 1 is a scanning illumination device comprising a laser light source 2, which in the embodiment described here is a white light source. A white laser light beam L is generated by superimposing three partial light beams from a red, green, and blue laser diode.

[0023] The lighting device 1 further includes a scanner 3 with a movable mirror embodied as a MEMS component, the movement of which is controlled by a control unit (not shown) of the lighting device. The control unit further regulates the power generated by the laser light source 2 at a given time based on pulse width modulation. During operation of the lighting device, the scanner or mirror 3 performs the pivoting movement indicated by the double arrow P at a predetermined frequency, whereby the laser light beam L, after passing the mirror 3, is moved within the range indicated by the double arrow P'. The light beam L falls obliquely downward onto the ground next to the motor vehicle.

[0024] The movement of the light beam follows parallel straight lines LI on the ground, which Fig. 1 are only partially designated with this reference symbol. At corresponding reversal positions of the movement, the mirror is tilted about an axis parallel to the plane of the page, so that the light beam alternates between adjacent lines LI. It is permissible for a light beam to travel the same line several times in succession before switching to an adjacent line by tilting the mirror. In other words, the mirror is tilted after half a period of the frequency of its pivoting movement and, if necessary, also after an integer multiple of the time of half a period.

[0025] The scanning movement of the light beam L described above generates the image B indicated by a rectangle on the ground next to the vehicle. After the generation of each image is complete, the scanner returns to its starting position to generate the same image again, as indicated by the line LI'. The generation of an image corresponds to a raster scan of the lighting device.

[0026] The lighting device or its control unit stores which image B, i.e. which desired light distribution, is to be generated on the ground next to the motor vehicle. Depending on the design, a planar light distribution, for example with constant illuminance, or possibly also a light distribution in the form of a light pattern can be generated. In addition, symbols can also be included in the image. Preferably, a so-called light carpet is generated with the lighting device 1, such a light carpet being described in the document DE 10 2013 211 877 A1. In contrast to the lighting device used in this document, however, the light carpet is generated not via an array of projection optics, but by means of a scanning lighting device.

[0027] In order to generate the desired image B on the ground next to the vehicle, a target power distribution ZL is stored in the control unit, which provides corresponding power values P for a large number of image positions illuminated by the light beam L within a raster scan. z which the light source 2 is operated when assuming the corresponding image position. These power values P z correspond to a target luminous flux distribution ZS, which describes the luminous flux used to generate the image. The target luminous flux distribution provides luminous flux values ϕ z for the illumination of the respective image positions of image B. From these luminous flux values, the illuminance in the image at the corresponding image positions can be calculated by dividing the luminous flux value by the area of the corresponding image position. Due to the oblique illumination of the image in the embodiment of the Fig. 1, this area varies in size depending on the image position. In other words, the area becomes larger the further away from the lighting device.

[0028] The essence of the invention is that, in contrast to conventional scanning illumination devices, lines LI are traversed by the light beam several times in succession, in such a way that the maximum power value to which the light source is set within a respective raster scan is lower than when generating the image with respective raster scans in which the light beam traverses each line only once. In other words, the corresponding power values P z The target power distribution ZL is determined in advance such that the above condition for the maximum power value is met. Corresponding power values are preferably determined based on an iterative procedure, which is explained below.

[0029] The starting point of the iteration is the target luminous flux distribution ZS described above, which provides corresponding luminous flux values ϕ for the desired image to be generated. z at the respective image positions. Furthermore, there is a maximum number of line passes that can occur in a raster scan. Lines can also be passed multiple times in succession.

[0030] At the beginning of the iteration, it is assumed that the target luminous flux distribution ZS is generated using a raster scan in which each line is traversed only once. Based on this assumption, a duty cycle value is calculated for each image position, which represents the ratio of the time the light beam spends at the respective image position to the total duration of the raster scan. The target luminous flux value at each image position is then divided by the corresponding duty cycle value, from which a corresponding power value of the light source can be determined in watts. The maximum power value is determined from all power values of the image. The number of consecutive passes along the line containing the image position with the maximum power value is then increased by one, i.e.the corresponding line is traversed twice and not once in the next iteration step, which follows the first iteration step just described.

[0031] This new scanning motion then results in new duty cycle values, as certain image positions are now occupied more frequently by the light beam and thus have a longer dwell time. These new duty cycle values are calculated, and the above steps are then repeated with the new duty cycle values. In other words, based on the new duty cycle values, a maximum power value is again determined, and the number of passes in the line with the highest power value is increased by one. The iteration continues until the above maximum number of line passes is reached.

[0032] With the iteration just described, the above criterion can be met, according to which the maximum power value of the light source within a given raster scan is lower than when generating the image with respective raster scans in which the light beam passes through each line only once. This makes it possible to install a light source with a lower maximum operating power in the illumination device without compromising the illuminance of the generated image.

[0033] Fig. 2 shows in the upper part in side view, ie seen in the longitudinal direction x of the motor vehicle, the lighting device 1 from Fig. 1, the lighting device being shown only schematically. It can be seen that the lighting device radiates obliquely onto the ground next to the motor vehicle in an area between lines L1 and L2, with the extent of a generated image being indicated by reference symbol B.

[0034] Fig.The lower part of Figure 2 shows the illuminance E as a function of the distance between the image positions along the transverse axis y of the vehicle, assuming a flatly illuminated image is generated in which the luminous flux values are constant for the respective image positions. The use of constant luminous flux values results in the illuminance decreasing with increasing distance from the lighting device, since the area of illumination becomes increasingly larger at image positions with greater distance. This leads to lower illuminance values, since illuminance is the quotient of luminous flux and area.

[0035] To avoid this effect and achieve illumination with homogeneous illuminance, the prior art merely adjusts the power values of the light source of the illumination device using pulse width modulation, whereby the scanning movement remains constant and each line is always traversed by the light beam only once. However, this procedure leads to a significant reduction in the illuminance of the image. This effect can be reduced by using an illumination device according to the invention in which lines can be traversed multiple times, thereby allowing the maximum operating power of the light source to be used more efficiently. In other words, the illumination device according to the invention can generate a homogeneous light distribution with higher illuminance compared to a conventional scanning illumination device.

[0036] The embodiments of the invention described above offer a number of advantages. In particular, a scanning lighting device for a motor vehicle is created that can generate images on the ground with high illuminance and a light source with a low maximum operating power. This makes it possible, for example, to achieve a higher illuminance for a homogeneous light distribution using the scanning movement according to the invention than is the case with a conventional scanning movement of the lighting device. List of reference symbols 1 lighting device 2 light source 3 scanners L light beam P, P' swivel ranges LI, LI' lines B generated image ZL target performance distribution P z Performance values ZS target luminous flux distribution ϕ z Luminous flux values x Longitudinal direction of the vehicle y Transverse direction of the vehicle L1, L2 lines E Illuminance

Claims

[1] Lighting device for a motor vehicle, comprising a light source (2) and a scanner (3) onto which a light beam (L) generated from the light of the light source (2) falls and which, in operation, deflects the light beam (L) based on repeating raster scans in order to repeatedly generate an image (B) on the ground in the surroundings of the motor vehicle, wherein the light beam (L) performs a scanning movement along a scanning axis (x) in a respective raster scan at a predetermined frequency and is displaced perpendicular to the scanning axis (x) at reversal positions of the scanning movement, whereby the light beam (L) is moved on a plurality of parallel lines (LI) running along the scanning axis (x) and is displaced between adjacent parallel lines (LI), wherein the lighting device (1) is designed to measure power values (P z) of the light source (2) within a respective raster scan based on a target power distribution (ZL) corresponding to the generated image (B), which target power distribution (ZL) for a plurality of image positions covering the image (B) and illuminated by the light beam (L) in a respective raster scan, respective power values (P z ) of the light source (2) when the respective image positions are illuminated by the light beam (L), characterized by that the illumination device (1) is designed such that the light beam (L) passes through one or more lines (LI) several times in succession in a respective raster scan and the maximum power value of the light source (2) within a respective raster scan according to the target power distribution (ZL) is lower than when generating the image (B) with respective raster scans in which the light beam (L) passes through each line (LI) only once. [2] Lighting device according to claim 1, characterized by that the illumination device (1) is designed such that, for the generated image (B), the ratio of the residence time of the light beam (L) in each line (LI) within a respective raster scan to the total duration of the respective raster scan substantially corresponds to the ratio of the luminous flux in each line (LI) within the respective raster scan to the total luminous flux of the respective raster scan required for generating the image (B). [3] Lighting device according to claim 1 or 2, characterized by that the lighting device (1) is designed to generate monochromatic light or white light. [4] Lighting device according to one of the preceding claims, characterized by that the scanner (3) comprises a mirror for deflecting the light beam (L), wherein the mirror (3) is preferably a MEMS component. [5] Lighting device according to one of the preceding claims, characterized bythat the lighting device (1) is designed such that the power values (P z ) of the light source (2) for illuminating the respective image positions within a raster scan by means of pulse width modulation. [6] Lighting device according to one of the preceding claims, characterized by that the light source (2) is a laser light source comprising one or more laser diodes, in particular an RGB laser light source. [7] Lighting device according to one of claims 1 to 5, characterized by that the light source (2) is an LED light source comprising one or more LEDs, in particular an RGB LED light source. [8] Lighting device according to one of the preceding claims, characterized by that the lighting device (1) is an ambient lighting device for generating an image (B) in the surroundings of the motor vehicle. [9] Lighting device according to one of claims 1 to 7, characterized bythat the lighting device (1) is a headlight or a signal light or a component of a headlight or a signal light. [10] Method for operating a lighting device for a motor vehicle, which comprises a light source (2) and a scanner (3), wherein a light beam (L) generated from the light of the light source (2) falls onto the scanner (3) and the scanner (3) deflects the light beam (L) based on repeating raster scans in order to repeatedly generate an image (B) on the ground in the surroundings of the motor vehicle, wherein the light beam (L) performs a scanning movement along a scanning axis (x) in a respective raster scan at a predetermined frequency and is displaced perpendicular to the scanning axis (x) at reversal positions of the scanning movement, whereby the light beam (L) is moved on a plurality of parallel lines (LI) running along the scanning axis (x) and is displaced between adjacent parallel lines (LI), wherein power values (P z) of the light source (2) within a respective raster scan based on a target power distribution (ZL) corresponding to the generated image (B), which target power distribution (ZL) for a plurality of image positions covering the image (B) and illuminated by the light beam (L) in a respective raster scan, respective power values (P z ) of the light source (2) when the respective image positions are illuminated by the light beam (L), characterized by that the light beam (L) in a respective raster scan passes through one or more lines (LI) several times in succession and the maximum power value of the light source (2) within a respective raster scan according to the target power distribution (ZL) is lower than when generating the image (B) with respective raster scans in which the light beam (L) passes through each line (LI) only once. [11] Method according to claim 10, characterized bythat the method operates a lighting device according to one of claims 2 to 9. [12] Motor vehicle, wherein the motor vehicle comprises one or more lighting devices (1) according to one of claims 1 to 9.

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