LIGHTING APPARATUS FOR VEHICLES

Abstract

A lighting apparatus for vehicles with a number of semiconductor-based light sources and a projection device for generating the specified light distribution with a cut-off line. The projection device features a correction device with at least two lenses. The surface of at least one of the lenses is designed as a diffractive lens surface for achromatization in a visible wavelength range. The two lenses are made from different lens materials. The surfaces of at least two lenses are designed as refractive lens surfaces that have their optical power calculated based on a temperature range and/or expansion coefficient of the lens material of at least two lenses such that adding the optical power of the lenses yields a predefined total optical power of the correction device.

Description

FIELD OF THE INVENTION

This invention is a lighting apparatus for vehicles with a number of semiconductor-based light sources and a projection device for generating the specified light distribution with a cut-off line.

BACKGROUND OF THE INVENTION

Patent DE 10 2010 027 322 A1 specifies a lighting apparatus for vehicles that features a number of light sources arranged in a matrix structure and a projection unit assigned to the light sources so a specified light distribution can be generated. The projection unit can feature a secondary optical component consisting of one lens and one primary optical component arranged between the secondary optical component and the light sources. Unwanted color fringes often form at a cut-off line of the light distribution generated by the projection unit. Especially in cases in which the projection unit features components made of plastic, such as PMMA, PC or LSR, the refractive index of the projection unit changes more substantially due to the temperature. Within the relatively wide temperature range of −50° C. through 150° C. in which the lighting apparatus is operated, the focal point shifts several millimeters. This causes the depiction of the cut-off line to be blurry.

U.S. Pat. No. 5,737,120 A stipulates a projection unit that consists of two lenses, wherein one of the two lenses has a diffractive lens surface. However, the resulting achromatization relates to infrared radiation in a wavelength range of 8 μm through 12 μm. The two lenses are produced from different materials. This reduces thermal influences. A disadvantage of this well-known projection unit is that it cannot be used for lighting apparatus in the automotive sector.

SUMMARY OF THE INVENTION

Therefore, the purpose of this invention is to further develop a lighting apparatus for vehicles with a number of semiconductor-based light sources and a projection device for generating the specified light distribution such that thermal and chromatic perturbations are reduced or offset.

In an effort to fulfill this purpose, this invention is included under the broader term “Patent claim 1”, wherein

• • the projection device features a correction device with at least two lenses, where the surface of at least one of the lenses is designed as a diffractive lens surface for achromatization in a visible wavelength range,
  • wherein the two lenses are made from different lens materials,
  • wherein the surfaces of at least two lenses are designed as refractive lens surfaces that have their optical power calculated based on a temperature range and/or expansion coefficient of the lens material of at least two lenses such that adding the optical power of the lenses yields a predefined total optical power of the correction device.

The main advantage of this invention is that the inventive correction device offsets top-level thermal and chromatic influences. The optical power of the optical system stabilizes. This process decouples the system from most thermal influences. Chromatic effects are reduced substantially, and this effect can be further optimized by choosing from at least two different wavelengths within the light source spectrum. Though the differences between the refractive indices are greater within the visible wavelength range (380 nm through 780 nm), achromatization within this spectral range is advantageous. The use of athermalization is not limited to glass lens material. It can also used for plastic lens materials. Athermalization occurs in a temperature range from −50° C. through 150° C. This is the typical temperature range for vehicle lighting operation.

In a preferred embodiment of this invention, the correction device features a first lens and a second lens which each have a diffractive lens surface and a refractive lens surface. The diffractive lens surface and/or refractive lens surface can have a spherical or aspherical design. An aspherical design can compensate for spherical and other aberrations. The shape of the correction device is specially designed to optimize coupling of the two lenses, minimizing Fresnel losses as well as adjustment and assembly work.

In a preferred embodiment of this invention, the sides of the first and second lenses facing one another are directly adjacent. Ideally, the contact face is level with and perpendicular to the optical axis. The surface of the first lens facing toward the light source and the surface of the second lens facing away from the light source each have a diffractive lens surface and refractive lens surface. The diffractive structure is applied to the curved area/surface, directly coupling both lenses with one another on their flat sides. Fresnel losses on both lens bounding surfaces facing toward one another can be reduced because the light does not have to travel through the air from the first lens to second lens. This reduces adjustment work because only one of the two lenses needs to be aligned with the rest of the system.

Further development of this invention has reduced Fresnel losses even more by inserting at least one material layer between the first and second lenses. This material has a refractive index that lies between that of the first lens and that of the second lens.

In further development of this invention, the correction device is designed as a secondary optical component assigned to the light sources arranged in a matrix structure and also to the primary optical components positioned at the front that are assigned to the same light sources. The correction device combines the features of thermal/chromatic influence compensation and projection of light beams transmitted from the light sources.

In further development of this invention, the correction device is designed as a primary optical component assigned to each of the light sources arranged in a matrix structure. Ideally, a secondary optical component is arranged in front of the light sources and primary optical components in the main direction of the beam as a lens array. Ideally, in this embodiment, the correction device is used to compensate for thermal and chromatic influences. Preferably, the stipulated light distribution is projected through the secondary lens.

In further development of the invention, the optical power of the refractive lens surfaces is calculated by determining the ratio of one type of optical power (the refractive optical power or diffractive optical power of various lenses to one other yielded from an Abbe or athermalization equation). The individual optical power values can even be determined using an equation for the total optical power.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made more particularly to the drawings, which illustrate the best presently known mode of carrying out the invention and wherein similar reference characters indicate the same parts throughout the views.

FIG. 1 is a schematic side view of a correction device (initial embodiment).

FIG. 2 is a schematic side view of this correction device (second embodiment).

FIG. 3 is a schematic side view of a lighting apparatus with light sources arranged in a matrix structure and the correction device as a secondary optical component.

FIG. 4 is a schematic side view of the lighting apparatus with light sources arranged in a matrix structure and the correction device as a primary optical component.

DETAILED DESCRIPTION OF THE DRAWINGS

A lighting apparatus for vehicles can be designed as headlamp in the front area or as a combination rear lamp. At the front of a vehicle, the lighting apparatus can be used to generate low-beam light, glare-free high-beam light or other light distribution patterns, such as highway light, city driving light, etc. The light distribution typically has a cut-off line.

To prevent formation of a color fringe at the cut-off line or to reduce thermal influences resulting from the operating temperature of the lighting apparatus lying within a specified temperature range (−50° C. through 150° C.), a correction device (1) is integrated into the lighting apparatus. This correction device has a one-piece design in accordance with the first embodiment of the invention (shown in FIG. 1). This correction device (1) is part of a projection unit that projects transmitted light from a number of semiconductor-based light sources (not shown) according to the specified light distribution. In this sample embodiment, the correction device (1) is the projection device.

The correction device (1) features a first lens (2) on the side facing toward the light source and a second lens (3) on the side facing away from the light source. The second lens (3) is arranged in front of the first lens (2) in the main direction of the beam H.

The first lens (2) features a surface that faces toward one of the light sources and consists of a refractive lens surface (4) and a diffractive lens surface (5). The refractive lens surface (4) is designed such that the corrective device (1) is athermal. The refractive lens surface (4) has a spherical design. Alternatively, it can be designed to be aspherical. The refractive lens surface (4) features an optical power of φ_ref,1 that bends the design inward. The diffractive lens surface (5) is structured such that the corrective device (1) is achromatic. The diffractive lens surface (5) is designed as a Fresnel structure and features an optical power of φ_diff,1.

The surface on the side of the second lens (3) that faces away from the light source bends outward. The surface features a refractive lens surface (6) that is designed such that the corrective device is athermal. The refractive lens surface (6) features an optical power of φ_ref,2. The surface also features a diffractive lens surface (7) that is structured such that the corrective device (1) is achromatic. The diffractive lens surface (7) features a Fresnel structure with an optical power of φ_diff,2.

The sides of the first lens (2) and second lens (3) facing one another are directly adjacent. The sides of the first lens (2) and the second lens (3) facing one another each have a flat surface (8 and 9). The two surfaces (8, 9) run perpendicular to an optical axis (10) of the correction device (1). The surface (8) of the first lens (2) and the surface (9) of the second lens (3) can be firmly bonded, particularly through adhesion. As such, the first lens (2) and second lens (3) form a hybrid lens.

The first lens (2) and second lens (3) are made from different materials (more specifically, from various plastic materials with different expansion coefficients).

One embodiment of the invention (not shown) also allows for a material layer to be inserted between the surface (8) of the first lens (2) and the surface (9) of the second lens (3) that has a refractive index n that lies between a refractive index n₁ of the first lens (2) and a refractive index n₂ of the second lens (3). In this case, there is also no air medium between the first lens (2) and the second lens (3).

In a second embodiment of the correction device (1) (shown in FIG. 2), a first lens (12) is arranged on a side facing toward the light source and a second lens (13) is arranged on a side facing away from the light source. In this arrangement, the second lens (13) is placed at a distance from the first lens (12). The side of the first lens (12) facing away from the light source is a refractive lens surface (14) bent inward and the side of this lens facing toward the light source is a diffractive lens surface (15). The refractive lens surface (14) features an optical power of φ_ref,1 and the diffractive lens surface (15) an optical power of φ_diff,1. The surface of the first lens (12) facing toward the light source is designed so that it is mostly level and perpendicular to the optical axis (10). The surface (Fresnel) structures shown in FIG. 1 and FIG. 2 are enlarged for easier understanding and do not correspond to the actual dimensions and design.

In accordance with the first and second embodiments, identical functions of the various lenses are assigned identical reference symbols.

A surface of the second lens (13) that is facing away from the light source is a refractive lens surface (16) that is bent outward and features an optimal power of φ_ref2. surface of the second lens (13) facing toward the light source is a diffractive lens surface (17) that features an optical power of φ_diff,2. Like the surface of the first lens (12) facing toward the light source, the surface of the second lens (13) facing toward the light source is designed and arranged so that it is mostly level and perpendicular to the optical axis (10).

The method for determining the optical power φ_ref1, φ_ref2, φ_diff1, φ_diff2 of the first lenses (2, 12) and second lenses (3, 13) is described below using an example. In this example, the diffractive structure causes achromatization.

The equations (1), (2) are the starting point for the optical power values φ_ref and φ_diff:

$\begin{array}{cc}{\varphi }_{\mathrm{ref}}=\frac{n-1}{R}& \left(1\right)\\ {\varphi }_{\mathrm{diff}}=\frac{2·\lambda }{r^2-{\lambda }^2}\underset{\_}{\propto }\frac{2·\lambda }{r^2}& \left(2\right)\end{array}$

This yields the total optical power φ of the correction device (1)

$\begin{array}{cc}\varphi =\sum _i{\varphi }_i=\sum _{i=1}^2\left({\varphi }_{\mathrm{ref},i}+{\varphi }_{\mathrm{diff},i}\right)=\left(\frac{n_1-1}{R_1}+\frac{2·{\lambda }_0}{r_1^2}\right)+\left(\frac{n_2-1}{R_2}+\frac{2·{\lambda }_0}{r_2^2}\right)\stackrel{\mathrm{def}}{=}\mathrm{const},& \left(3\right)\end{array}$

where R is the refractive index n and the curvature radius of the bent spherical surfaces and r is the zone radius of the first Fresnel zone of the diffractive surfaces

n ₁ :=n ₁(λ₀,T₀)  (4)

R ₁ :=R ₁(T₀)  (5)

n ₁ :=n(T₀)  (6).

Achromatization is caused by the diffractive lens surfaces (5, 7 or 15, 17) of the lenses (2, 3 or 12, 13). The following condition applies to both lenses to ensure that two refractive lens surfaces (4, 6; or 14, 16) and two diffractive lens surfaces (5, 7 or 15, 17) can be used to correct two wavelengths (Abbe equation):

$\begin{array}{cc}{\mathrm{\Delta \varphi }}_i\left(\lambda ,T_0\right)=\frac{n_i\left({\lambda }_1\right)-n_i\left({\lambda }_2\right)}{n_i\left({\lambda }_0\right)-1}·{\varphi }_{\mathrm{ref},i}+\frac{{\lambda }_1-{\lambda }_2}{{\lambda }_0}·{\varphi }_{\mathrm{diff},i}\stackrel{\mathrm{def}}{=}0& \left(7\right)\end{array}$

The following conditions must be met for athermalization (athermalization equation):

$\begin{array}{cc}{\mathrm{\Delta \varphi }}_i\left({\lambda }_0,T\right)=\sum _{i=1}^2\left(\left(\frac{n_i\left(T_1\right)-n_i\left(T_0\right)}{n_i\left(T_0\right)-1}-{\alpha }_i·\left(T_1-T_0\right)\right)·{\varphi }_{\mathrm{ref},i}-2·{\alpha }_i·\left(T_1-T_0\right)·{\varphi }_{\mathrm{diff},i}\right)\stackrel{\mathrm{def}}{=}0,& \left(8\right)\end{array}$

where α_i is the expansion coefficient of the respective lens material and T₁ is a temperature.

The following substitutions are yielded from the equation (7):

$\begin{array}{cc}{v}_{\mathrm{ref},i}^{-1,\lambda }\text{:=}\frac{n_i\left({\lambda }_1\right)-n_i\left({\lambda }_2\right)}{n_i\left({\lambda }_0\right)-1}& \left(9\right)\\ v_{\mathrm{diff},i}^{-1,\lambda }\text{:=}\frac{{\lambda }_1-{\lambda }_2}{{\lambda }_0}& \left(10\right)\end{array}$

The following substitutions are yielded from the equation (8):

$\begin{array}{cc}{v}_{\mathrm{ref},i}^{-1,T}\text{:=}\frac{n_i\left({\lambda }_1\right)-n_i\left({\lambda }_2\right)}{n_i\left({\lambda }_0\right)-1}-{\alpha }_i·\left(T_1-T_0\right)& \left(11\right)\\ v_{\mathrm{diff},i}^{-1,T}\text{:=}-2·{\alpha }_i·\left(T_1-T_0\right)& \left(12\right)\end{array}$

Converting the equation (7) yields the following relationship:

$\begin{array}{cc}{\varphi }_{\mathrm{diff},i}=-\frac{v_{\mathrm{ref},1}^{-1,\lambda }}{v_{\mathrm{diff},i}^{-1,\lambda }}·{\varphi }_{\mathrm{ref},i}& \left(13\right)\end{array}$

Insertion into the athermalization equation (8) yields the following relationship between φ_ref1 of the first lens (2, 12) and φ_ref2 of the second lens (3, 13):

$\begin{array}{cc}{\varphi }_{\mathrm{ref},i}=\frac{v_{\mathrm{diff},2}^{-1,T}·\frac{v_{\mathrm{ref},2}^{-1,\lambda }}{v_{\mathrm{diff},2}^{-1,\lambda }}-v_{\mathrm{ref},2}^{-1,T}}{v_{\mathrm{ref},i}^{-1,T}-v_{\mathrm{diff},1}^{-1,T}·\frac{v_{\mathrm{ref},1}^{-1,\lambda }}{v_{\mathrm{diff},i}^{-1,\lambda }}}·{\varphi }_{\mathrm{ref},2}& \left(14\right)\end{array}$

The Abbe equation (7) also yields a ratio between φ_diff2 and φ_ref2:

$\begin{array}{cc}{\varphi }_{\mathrm{diff},2}=-\frac{v_{\mathrm{ref},2}^{-1,\lambda }}{v_{\mathrm{diff},2}^{-1,\lambda }}·{\varphi }_{\mathrm{ref},2}& \left(15\right)\end{array}$

Inserting this equation (13), (14), (15) into the equation (3) for the total optical power φ allows for a conversion of this value according to φ_ref,2:

$\begin{array}{cc}{\varphi }_{\mathrm{ref},2}={\left(1-\frac{v_{\mathrm{ref},2}^{-1,\lambda }}{v_{\mathrm{diff},2}^{-1,\lambda }}+\frac{1-\frac{v_{\mathrm{ref},1}^{-1,\lambda }}{v_{\mathrm{diff},1}^{-1,\lambda }}}{v_{\mathrm{ref},i}^{-1,T}-v_{\mathrm{diff},1}^{-1,T}·\frac{v_{\mathrm{ref},1}^{-1,\lambda }}{v_{\mathrm{diff},i}^{-1,\lambda }}}·\left(v_{\mathrm{diff},2}^{-1,T}·\frac{v_{\mathrm{ref},2}^{-1,\lambda }}{v_{\mathrm{diff},2}^{-1,\lambda }}-v_{\mathrm{ref},2}^{-1,T}\right)\right)}^{-1}·\varphi & \left(16\right)\end{array}$

The other optical power values φ_ref1, φ_diff1, φ_diff2 can be calculated accordingly.

The values for the first lens (2, 12) and second lens (3, 13) calculated using this method enable compensation for top-level thermal and chromatic influences.

In another embodiment of this invention (shown in FIG. 3), the correction device (1) is designed as a secondary optical component (20) that is assigned to most of the light sources (22) arranged in a matrix structure on a carrier plate (21). Ideally, the light sources (22) are designed as LED light sources and a primary optical component (23) is arranged in front of each in the main direction of the beam H.

In an alternative embodiment of this invention (shown in FIG. 4), the correction device (1) can be designed as a primary optical component (24) that is assigned to each of the light sources (22). Relatively speaking, the correction device (1) in this variant of the invention is smaller than the embodiments shown in FIGS. 1 through 3. A secondary optical component (25) designed as a lens is arranged in front of the primary optical components (24) in the main direction of the beam H. This secondary optical component ensures that the stipulated light distribution is achieved.

In an alternative embodiment of this invention (not shown), the correction device (1) can have more than two lenses. Ideally, the correction device (1) has at least two refractive lens surfaces.

In an alternative embodiment (not shown), the diffractive structure of the first lens (2, 12) or the second lens (3, 13) can cause athermalization. In this embodiment, the refractive optical power causes achromatization. In the equation (13), the expression A would be replaced with T and in the equation (14), the expression T with A. Accordingly, the Abbe equation (7) and athermalization equation (8) are substituted for one another. Even top-level thermal and chromatic influences are offset in this embodiment. Nevertheless, this requires more lens material, so the embodiment mentioned above is still preferable.

LIST OF REFERENCE SYMBOLS

• 1 Correction device
• 2 First lens
• 3 Second lens
• 4 Refractive lens surface
• 5 Diffractive lens surface
• 6 Refractive lens surface
• 7 Diffractive lens surface
• 8 Flat surface
• 9 Flat surface
• 10 Optical axis
• 12 First lens
• 13 Second lens
• 14 Refractive lens surface
• 15 Diffractive lens surface
• 16 Refractive lens surface
• 17 Diffractive lens surface
• 21 Carrier plate
• 22 Light sources
• 23 Primary optical component
• 24 Primary optical component
• 25 Secondary optical component
• H Main direction of beam
• n, n₁, Refractive index
• n₂

Claims

1. A lighting apparatus for vehicles comprising: a plurality of semiconductor-based light sources;a projection device for generating a specified light distribution with a cut-off linea correction device of the projection device, said correction device having at least two lenses, wherein at least two of said at least two lenses are made from different materials from one another, where the surface of at least one of the lenses is designed as a diffractive lens surface for achromatization in a visible wavelength range,wherein the surfaces of at least two lenses are designed as refractive lens surfaces that have their optical power (φref1, φref2) calculated based on a temperature range and/or expansion coefficient of the lens material of at least two lenses such that adding the optical power (φref1, φref2, φdiff1, φdiff2) of the lenses yields a predefined total optical power (φ) of the correction device.

2. The lighting apparatus in accordance with claim 1, wherein the refractive lens surface is designed such that the correction device is athermal.

3. The lighting apparatus in accordance with claim 1, wherein the refractive lens surface is designed such that it is aspherical or spherical.

4. The lighting apparatus in accordance with claim 1, wherein the diffractive lens surface is structured such that the correction device is achromatic.

5. The lighting apparatus in accordance with claim 1, wherein the diffractive lens surface features a Fresnel structure.

6. The lighting apparatus in accordance with claim 1, wherein a first lens and a second lens each feature a diffractive lens surface and a refractive lens surface.

7. The lighting apparatus in accordance with claim 6, wherein the sides of the first lens and second lens facing toward one another are directly adjacent and the surface of the first lens facing toward the light source and the surface of the second lens facing away from the light source feature a diffractive lens surface and refractive lens surface.

8. The lighting apparatus in accordance with claim 7, wherein a material layer is inserted between the first lens and second lens that has a refractive index (n) that is between the refractive index (n1) of the first lens and the refractive index (n2) of the second lens.

9. The lighting apparatus in accordance with claim 1, wherein the correction device is designed as a secondary optical component that is assigned to the light sources arranged in a matrix structure and also to the corresponding primary optical components that are also assigned to these light sources.

10. The lighting apparatus in accordance with claim 1, wherein a ratio of the optical power (φref1) for the refractive lens surface of the first lens to the optical power (φref2) for the refractive lens surface of the second lens and/or a ratio of the optical power (φdiff1) for the diffractive lens surface of the first lens to the optical power (φdiff2) for the diffractive lens surface of the second lens is formed through substitution in an Abbe equation and an athermalization equation, wherein a ratio of the optical power (φref1) for the refractive lens surface of the first lens to the optical power (φdiff1) for the diffractive lens surface of the first lenses and a ratio of the optical power (φref2) for the refractive lens surface of the second lens to the optical power (φdiff2) of the diffractive lens surface of the second lens is formed through substitution in the Abbe equation and the athermalization equation, ensuring that an equation for the total optical power (φ) can be solved based on the individual optical power values (φref1, φref2,φdiff1,φdiff2) of the refractive lens surfaces and diffractive lens surfaces.

11. A lighting apparatus for vehicles comprising: a plurality of semiconductor-based light sources;a projection device for generating a specified light distribution with a cut-off line;a correction device of the projection device, said correction device having at least two lenses, wherein at least two of said at least two lenses are made from different materials from one another, where the surface of at least one of the lenses is designed as a diffractive lens surface for athermalization;wherein the lens surface of at least two lenses is designed as a refractive lens surface for achromatization in a visible wavelength range,wherein the optical power of the refractive lens surface is calculated based on a temperature range and/or expansion coefficient of the lens material of at least two lenses such that adding the optical power of the lenses yields a predefined total optical power of the correction device.

12. The lighting apparatus in accordance with claim 11, wherein the refractive lens surface is designed such that the correction device is athermal.

13. The lighting apparatus in accordance with claim 11, wherein the refractive lens surface is designed such that it is aspherical or spherical.

14. The lighting apparatus in accordance with claim 11, wherein the diffractive lens surface is structured such that the correction device is achromatic.

15. The lighting apparatus in accordance with claim 11, wherein the diffractive lens surface features a Fresnel structure.

16. The lighting apparatus in accordance with claim 11, wherein a first lens and a second lens each feature a diffractive lens surface and a refractive lens surface.

17. The lighting apparatus in accordance with claim 16, wherein the sides of the first lens and second lens facing toward one another are directly adjacent and the surface of the first lens facing toward the light source and the surface of the second lens facing away from the light source feature a diffractive lens surface and refractive lens surface.

18. The lighting apparatus in accordance with claim 17, wherein a material layer is inserted between the first lens and second lens that has a refractive index (n) that is between the refractive index (n1) of the first lens and the refractive index (n2) of the second lens.

19. The lighting apparatus in accordance with claim 11, wherein the correction device is designed as a secondary optical component that is assigned to the light sources arranged in a matrix structure and also to the corresponding primary optical components that are also assigned to these light sources.

20. The lighting apparatus in accordance with claim 11, wherein a ratio of the optical power for the refractive lens surface of the first lens to the optical power for the refractive lens surface of the second lens and/or a ratio of the optical power for the diffractive lens surface of the first lens to the optical power for the diffractive lens surface of the second lens is formed through substitution in an Abbe equation and an athermalization equation, wherein a ratio of the optical power for the refractive lens surface of the first lens to the optical power for the diffractive lens surface of the first lenses and a ratio of the optical power for the refractive lens surface of the second lens to the optical power of the diffractive lens surface of the second lens is formed through substitution in the Abbe equation and the athermalization equation, ensuring that an equation for the total optical power can be solved based on the individual optical power values of the refractive lens surfaces and diffractive lens surfaces.

21. The lighting apparatus in accordance with claim 1 wherein the correction device is assigned each of the light sources arranged in a matrix structure as a primary optical component, where a secondary optical component assigned to the same light sources is arranged in front of the primary optical components in the main direction of the beam.

22. The lighting apparatus in accordance with claim 11 wherein the correction device is assigned each of the light sources arranged in a matrix structure as a primary optical component, where a secondary optical component assigned to the same light sources is arranged in front of the primary optical components in the main direction of the beam.