Illumination device for vehicles with temperature-dependent element for condensation removal and/or deicing

Abstract

An illuminating device for vehicles, including a housing, in which a light source and an optical unit for generating a predefined light distribution are arranged, including a cover shield, which closes an opening of the housing and through which light passes from an interior of the housing into surroundings, including means for condensation removal and/or deicing of the cover shield, characterized in that the cover shield includes a temperature-dependent light absorber, with the aid of which light is converted into heat depending on the temperature.

Claims

1. An illuminating device for a vehicle, the illuminating device comprising: a housing, in which a light source and an optical unit to generate a predefined light distribution are arranged; a cover shield that closes an opening of the housing and through which light passes from an interior of the housing into surroundings; and a temperature-dependent light absorber for condensation removal and/or deicing of the cover shield, wherein the cover shield includes the temperature-dependent light absorber to convert the light into heat depending on a temperature of the cover shield, and wherein the temperature-dependent light absorber is designed as a thermochromic layer applied to the cover shield and/or as a thermochromic admixture which is added to a material of the cover shield.

2. The illuminating device according to claim 1, wherein the temperature-dependent light absorber is designed in such that a light absorptivity is zero or close to zero upon the temperature exceeding a limit temperature.

3. The illuminating device according to claim 2, wherein the limit temperature is in a range between −2° C. and 6° C.

4. The illuminating device according to claim 3, wherein the limit temperature is 4° C.

5. The illuminating device according to claim 1, wherein the temperature-dependent light absorber is designed such that, in the presence of HaThe temperature of the cover shield below a limit temperature, a light absorptivity increases by an absolute value at a reduced temperature.

6. The illuminating device according to claim 1, wherein the temperature-dependent light absorber is designed such that a characteristic of a light absorptivity of the temperature being below 0° C. has a negative gradient in the direction of a limit temperature.

7. The illuminating device according to claim 6, wherein the characteristic of the light absorptivity decreases linearly in the direction of the limit temperature as the temperature increases.

8. The illuminating device according to claim 1, wherein a light intensity of the light source is selected such that, when the temperature of the cover shield is below a limit temperature, a minimum luminous flux emerges through the cover shield into the surroundings.

9. The illuminating device according to claim 1, wherein the thermochromic layer is applied to a flat side of the cover shield.

10. The illuminating device according to claim 9, wherein the thermochromic layer is arranged on an inside of the cover shield.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

(2) FIG. 1 shows a schematic representation of an illuminating device at a temperature of a cover shield above a limit temperature;

(3) FIG. 2 shows a schematic representation of the illuminating device at a temperature of a cover shield below the limit temperature; and

(4) FIG. 3 shows a characteristic of the absorptivity of a light absorber over temperature.

DETAILED DESCRIPTION

(5) An illuminating device for vehicles can be, for example, a headlamp, which is arranged in a front region of the vehicle, or another light arranged on the vehicle.

(6) The illuminating device includes a housing 1, within which a light source 2 and an optical unit 3 are arranged. In the present exemplary embodiment, light source 2 is made up of a plurality of LED light sources 4, which are arranged on a circuit board 5. Optical unit 3 includes a primary optical element 6 and a secondary optical element 7 arranged upstream from primary optical unit 6 in main emission direction H, with the aid of which luminous flux 8 detected by light source 2 is conducted in the direction of a cover shield 9 covering a front opening of housing 1. Secondary optical element 7 is designed as a lens, which projects the light entering on the side facing light source 2 according to a predefined light distribution, for example a low-beam distribution.

(7) Cover shield 9 is provided with a temperature-dependent light absorber 10, so that luminous flux 8 striking cover shield 9 is partially converted into thermal energy depending on the temperature. The thermal energy heats cover shield 9, so that cover shield 9 may be deiced or condensation removed therefrom. Light absorber 10 is thus used for condensation removal and/or deicing of cover shield 9.

(8) In the present exemplary embodiment, the light absorber is designed as a thermochromic layer 10, which is applied on an inside (flat side) of cover shield 9. The inside of cover shield 9 is arranged on a flat side of cover shield 9 facing optical unit 3.

(9) The thermochromic layer is preferably designed as a film, which is applied to a base material 11 of cover shield 9. Base material 11 may be made from a transparent plastic material which is conventionally used for cover shields 9.

(10) In the present exemplary embodiment, thermochromic layer 10 includes leuco dyes, which result in a darkening of cover shield 9 below a limit temperature T.sub.G. The darkening of cover shield 9 effectuates a partial conversion of the light energy provided by light source 2 into thermal energy, so that cover shield 9 is heated.

(11) According to an alternative specific embodiment of the invention, base material 11 of cover shield 9 may also be provided with light absorber 10 only partially on the inside facing optical unit 3. For example, light absorber 10 may be applied in a segmented manner to the inside of cover shield 9, the light absorption segments being preferably evenly distributed over the surface of base material 11. This ensures that a uniform heating of cover shield 9 takes place over the surface thereof.

(12) The light absorption segments may be designed in the shape of strips, rectangles or ovals.

(13) According to a further alternative specific embodiment of the invention, which is not illustrated, light absorber 10 may also be designed as a thermochromic admixture within base material 11. In this specific embodiment, no subsequent application of the light absorber takes place. Instead, the light absorber is introduced into the material of cover shield 9 during the manufacturing of cover shield 9, for example as dye pigments.

(14) The temperature dependence of light absorber 10 is apparent from FIG. 3. An absorptivity A of light absorber 10 is zero or in the vicinity of zero above a limit temperature T.sub.G. Thus, no luminous flux 8 entering cover shield 9 is absorbed above this limit temperature T.sub.G. The transmittance of the light is more or less 100%, so that entering luminous flux 8 essentially corresponds to a luminous flux 8 emerging from cover shield 9. Luminous flux 8 is thus not influenced by cover shield 9; cf. FIG. 1.

(15) If a temperature T of cover shield 9 is below limit temperature T.sub.G, light absorber 10 is activated after light source 2 is switched on, a portion of luminous flux 8 entering cover shield 9 being absorbed according to an absorption characteristic K in FIG. 3 and being converted into thermal energy. Assuming a temperature T of 1° C., the absorptivity is 50%, so that cover shield 9 allows only a luminous flux 8′ to pass through, which corresponds to 50% of luminous flux 8 of entering luminous flux 8.

(16) As is apparent from FIG. 3, absorptivity A increases linearly with a reduction in temperature T, starting at limit temperature T.sub.G. The steepness of absorption characteristic K is dependent on the “doping” of light absorber 10 on cover shield 9. The greater the concentration of light absorber 10 on or in cover shield 9, the steeper is the rise in absorption characteristic K.

(17) Limit temperature T.sub.G is 4° C. in the present exemplary embodiment. According to an alternative specific embodiment, limit temperature T.sub.G may also be varied. Limit temperature T.sub.G is preferably in a range between 0° C. and 6° C. Activation range 12, in which light absorber 10 develops its effect, is thus in a range below limit temperature T.sub.G, preferably in a temperature range between −2° C. and 6° C. If temperature T is further reduced, light absorber 10 undergoes a saturation.

(18) It is understood that the light intensity of light source 2 is selected in such a way that luminous flux 8′ transmitting through cover shield 9 is so great even at low temperature T below limit temperature T.sub.G, i.e., within activation temperature range 12 of light absorber 10, so that the minimum legal requirements of a minimum luminous flux are met.

(19) According to a further specific embodiment of the invention, cover shield 9 may be provided with a temperature-dependent wavelength shifter, spectral components of the light being partially and/or completely shifted into an infrared wavelength range depending on the temperature. Instead of a light absorption, a shifting of the spectral color components of the light in the direction of the infrared wavelength range takes place, so that a portion of the luminous flux may be used for heating cover shield 9. With respect to the legal requirements of a minimum luminous flux, the same applies as in the aforementioned exemplary embodiment.

(20) Alternatively or additionally, light absorber 10 may also be arranged on an outside 13 (flat side) of base material 11 or cover shield 9.

(21) 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.