METHOD FOR OPERATING A LIGHTING APPARATUS OF A MOTOR VEHICLE

Abstract

A method for operating a lighting apparatus of a vehicle. A temperature of the light source is recorded while the first light distribution is generated, a temperature change of the light source which is expected to emerge during the transition from the first to the second light distribution is calculated. Should the calculation predict that the transition from the first to the second light distribution would rise to an excessive temperature leading to a temperature above a threshold value in at least one critical region, then the power of at least one of the semiconductor elements is reduced during the control of the semiconductor elements implemented for generating the second light distribution, such that the temperature in the at least one critical region of the light source is not expected to exceed the specified threshold value as a result of the transition from the first to the second light distribution.

Claims

1. A method for operating a lighting apparatus of a motor vehicle, in particular a high-resolution headlamp of a motor vehicle, the lighting apparatus comprising a light source with semiconductor elements arranged in a matrix for a targeted generation of pixels of a light distribution and the lighting apparatus being configured to control the semiconductor elements so that at least one first and one second light distribution are generated in succession, the method comprising: recording a temperature of the light source while the first light distribution is generated; calculating a temperature change of the light source that is expected to emerge during a transition from the first to the second light distribution; and reducing, if the calculation predicted that the transition from the first light distribution to the second light distribution would give rise to an excessive temperature leading to a temperature above a specified threshold value in at least one critical area of the light source, the power of at least one of the semiconductor elements during the control of the semiconductor elements implemented to generate the second light distribution such that the temperature in the at least one critical region of the light source is not expected to exceed the specified threshold value as a result of the transition from the first to the second light distribution.

2. The method according to claim 1, wherein the at least one critical region whose temperature should not rise above the specified threshold value is the junction region of at least one of the semiconductor elements.

3. The method according to claim 1, wherein the recorded temperature of the light source is a temperature at or in the junction region of at least one of the semiconductor elements.

4. The method according to claim 1, wherein the threshold value of the temperature in the at least one critical range of the light source is between 140? C. and 160? C., or between 145? C. and 155? C., or is about 150? C.

5. The method according to claim 1, wherein, for the purpose of calculating the temperature change at the transition from the first to the second light distribution, an algorithm is used which calculates a temperature difference between two regions of at least one semiconductor element, in particular a temperature difference between the solder joint and the junction region of the at least one semiconductor element.

6. The method according to claim 5, wherein the calculation of the temperature difference is carried out by estimating the thermal resistance of the at least one semiconductor element as a function of the light distribution to be generated.

7. The method according to claim 6, wherein the thermal resistance R.sub.th is calculated by a formula: $R_{th}=c_1.Math.p_1+c_2.Math.p_2+c_3.Math.p_3.Math.+b$ wherein c.sub.1, c.sub.2, c.sub.3, . . . and b are experimentally determined coefficients and wherein p.sub.1, p.sub.2, p.sub.3, . . . are parameters which are calculated when the lighting apparatus is operated or when the first light distribution is generated.

8. The method according to claim 7, wherein the coefficients are determined from an experimentally determined data set via a multiple linear regression.

9. The method according to claim 6, wherein, for the estimation of the thermal resistance of the at least one semiconductor element, as a function of the light distribution to be generated, a light pattern corresponding to the control of the semiconductor elements during generation of the light distribution is analyzed, or wherein pulse width modulation is used to control the semiconductor elements.

10. The method according to claim 9, wherein one of the first of the parameters corresponds to the average of the bit values or the PWM values of the light pattern of the light distribution to be generated.

11. The method according to claim 9, wherein a second of the parameters corresponds to the highest average value of the bit values or PWM values of an area of the light pattern of the light distribution to be generated, in particular a range between 5?5 pixels and 20?20 pixels, or a range of 10?10 pixels.

12. The method according to claim 9, wherein a third of the parameters corresponds to the number of pixels whose bit values or whose PWM values are equal to 0.

13. A lighting apparatus for a motor vehicle, in particular high-resolution headlamps for a motor vehicle, the lighting apparatus comprising: a light source with semiconductor elements arranged in a matrix for a targeted generation of pixels of a light distribution, the lighting apparatus being configured to control the semiconductor elements so that at least one first and one second light distribution are produced in succession, wherein the lighting apparatus is adapted to perform the method according to claim 1.

14. The lighting apparatus according to claim 13, wherein the semiconductor elements are formed as light emitting diodes or as laser diodes, or wherein the semiconductor elements are part of a solid-state LED array.

15. The lighting apparatus according to claim 13, wherein the lighting apparatus comprises at least one temperature sensor located on or in the light source and/or wherein the lighting apparatus comprises a control unit for controlling the semiconductor elements, which is configured to calculate the parameters when the lighting apparatus is operated.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0019] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawing which is given by way of illustration only, and thus, is not limitive of the present invention, and wherein the sole FIGURE shows a schematic representation of the sequence of the inventive method.

DETAILED DESCRIPTION

[0020] The example describes a method for a lighting apparatus designed as a headlamp which comprises a solid-state LED array or an SSL HD LED as the light source. In particular, this light source can comprise 16,000 or more semiconductor elements. The lighting apparatus also includes at least one temperature sensor located on or in the light source, in particular in the area of the junction of at least one of the semiconductor elements. The lighting apparatus also includes a control unit for controlling the semiconductor elements.

[0021] The lighting apparatus is also configured to control the semiconductor elements so as to produce different light distributions, in particular a first and a second light distribution, wherein the light distributions are produced in succession. Transitions between the light distributions can be, for example, the transition from a low beam to a high beam or the elimination of a blanked out area in the light distribution or the intensification of the illumination of the vehicle's own lane.

[0022] The method shown schematically in the FIGURE assumes a state in which the semiconductor elements are controlled so that a first light distribution is generated. The control of the semiconductor elements to generate the first light distribution corresponds to a first light pattern. Pulse width modulation can be used to control the semiconductor elements. Based on the state in which the first light distribution is generated, the aim is to estimate how the temperature of the light source changes when changing from the first to a second light distribution.

[0023] To calculate the temperature change in the transition from the first to the second light distribution, an algorithm is used to calculate a temperature difference between the solder joint and the junction region of at least one semiconductor element. The calculation of the temperature difference is carried out by estimating the thermal resistance of the at least one semiconductor element as a function of the light distribution to be generated. The thermal resistance is given by a formula of the type:

[00002]$R_{th}=c_1.Math.p_1+c_2.Math.p_2+c_3.Math.p_3.Math.+b$

[0024] wherein c.sub.1, c.sub.2, c.sub.3, . . . and b are experimentally determined coefficients and wherein p.sub.1, p.sub.2, p.sub.3, . . . are parameters that are calculated when the first light distribution is generated in the control unit of the lighting apparatus.

[0025] The coefficients are determined from an experimentally determined data set by means of multiple linear regression. For example, the solder joint temperature and the junction temperature may be measured for different light patterns before the light source is installed in the lighting apparatus.

[0026] A first parameter p.sub.1 corresponds to the average of the bit values or the PWM values of the light pattern of the light distribution to be generated. A second parameter p.sub.2 corresponds to the highest average value of the bit values or PWM values of an area of 10?10 pixels of the light pattern of the light distribution to be generated. A third parameter p.sub.3 corresponds to the number of pixels whose bit values or PWM values are equal to 0.

[0027] It may well be provided to use more or different parameters for estimating the thermal resistance of the at least one semiconductor element as a function of the light distribution to be generated.

[0028] A second light pattern corresponds to the control of the semiconductor elements for generating the second light distribution, which is the starting point in a first step 1 of the schematically presented method. This light pattern is analyzed in a second step 2 of the method in order to calculate the parameters p.sub.1, p.sub.2, p.sub.3, . . . for this second light pattern.

[0029] In a further step 3, the coefficients c.sub.1, c.sub.2, c.sub.3, . . . and b corresponding to the parameters p.sub.1, p.sub.2, p.sub.3, . . . for this second light pattern are read out, so that in a further step 4 the thermal resistance, and therefrom the temperature difference ?T.sub.2, can be calculated for the second light pattern on the basis of the parameters and the coefficients.

[0030] The calculated temperature difference ?T.sub.2 is stored in a further step 5. In a further step 6, the previously calculated temperature difference ?T.sub.1 is read out for the first light pattern, wherein in a subsequent step 7 the temperature change in the transition from the first to the second light pattern or in the transition from the first to the second light distribution is calculated by subtracting the first temperature difference ?T.sub.1 from the second temperature difference ?T.sub.2.

[0031] In a further step 8, the current temperature of the light source is determined by reading out the at least one temperature sensor. In a further step 9, the calculated temperature change and the current temperature are used to calculate the temperature to be expected after the transition from the first to the second light pattern or after the transition from the first to the second light distribution. In a next step 10, the expected temperature is compared with the threshold value of the temperature, which is, for example, 150? C.

[0032] If the expected temperature is equal to or below the threshold value, the next step 11 is to decide that there is no need to change the control corresponding to the second light pattern. The semiconductor elements are controlled accordingly in step 12.

[0033] If the expected temperature is above the threshold value, the next step 13 is to calculate what power is permissible for the semiconductor elements without the temperature exceeding the threshold value. In a subsequent step 14, the power for the control is limited to the permissible value for the second light pattern, so that the semiconductor elements are controlled accordingly in step 1.

[0034] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.