AUTOMOTIVE LIGHTING DEVICE

Abstract

The invention is related to an automotive lighting device (10) comprising a light source (1) configured to emit light in a light direction (dl), a sensor (2) and a cover (3). The sensor (2) is configured to acquire information outside the lighting device by emitting a wave in a sensor direction (d2), the wavelength of the wave being comprised between 1 mm and 1 cm. The cover (3) comprises a first portion (31) located in the light direction and a second portion (32) located in the sensor direction, the second portion (32) comprising a sensor region (33) having a refractive index and a thickness which is comprised between 0.8 and 1.2 times an ideal thickness, the ideal thickness being equal to a natural number multiplied by the wavelength and divided by two times the refractive index.

Claims

1. Automotive lighting device (10) comprising: a light source (1) configured to emit light in a light direction (d1), a sensor (2) configured to acquire information outside the lighting device by emitting a wave in a sensor direction (d2), the wavelength of the wave being comprised between 1 mm and 1 cm; a cover (3) comprising a first portion (31) located in the light direction and a second portion (32) located in the sensor direction, the second portion (32) comprising a sensor region (33) having a refractive index and a thickness which is comprised between 0.8 and 1.2 times an ideal thickness, the ideal thickness being equal to a natural number multiplied by the wavelength and divided by two times the refractive index.

2. Automotive lighting device according to claim 1, wherein the light source is a solid-state light source.

3. Automotive lighting device according to any of the preceding claims, wherein the sensor is a radar sensor and the wavelength is comprised between 3 and 5 mm.

4. Automotive lighting device according to any of the preceding claims, wherein the thickness of the sensor region is comprised between 0.8 and 1.2 times the wavelength divided by two times the refractive index.

5. Automotive lighting device according to any of the preceding claims, wherein the thickness of the second portion is equal or higher than the thickness of the sensor region.

6. Automotive lighting device according to any of the preceding claims, wherein the thickness is defined for an incidence angle (0) equal to arctan(L1/(2e4)), with e4 the distance between the sensor (2) and the cover (3) and L1 the distance between an emitting antenna (100) and receiving antennas (101) of said sensor (2).

Description

[0025] To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate an embodiment of the invention, which should not be interpreted as restricting the scope of the invention, but just as an example of how the invention can be carried out. The drawings comprise the following figures:

[0026] FIG. 1 shows a section view of a lighting device according to the invention.

[0027] FIG. 2 shows a scheme of the wave path across the sensor region of the outer lens.

[0028] In these figures, the following reference numbers have been used: [0029] 1 LED [0030] 2 Radar sensor [0031] 3 Outer lens [0032] 31 first portion of the outer lens [0033] 32 second portion of the outer lens [0034] 33 sensor region of the outer lens [0035] d1 light direction [0036] d2 sensor direction

[0037] The example embodiments are described in sufficient detail to enable those of ordinary skill in the art to embody and implement the systems and processes herein described. It is important to understand that embodiments can be provided in many alternate forms and should not be construed as limited to the examples set forth herein.

[0038] Accordingly, while embodiment can be modified in various ways and take on various alternative forms, specific embodiments thereof are shown in the drawings and described in detail below as examples. There is no intent to limit to the particular forms disclosed. On the contrary, all modifications, equivalents, and alternatives falling within the scope of the appended claims should be included.

[0039] FIG. 1 shows a section view of a lighting device 10 according to the invention. In this figure, the lighting device 10 comprises [0040] a LED 1; [0041] a radar sensor 2; and [0042] an outer lens 3.

[0043] The LED 1 is arranged to emit light in a light direction d1. This means that the distribution of the light has a maximum in the light direction d1, but obviously, the LED emits light in an angular range.

[0044] The radar sensor 2 is in turn arranged to acquire information outside the lighting device by emitting a radar wave in a sensor direction d2. The radar sensor 2 comprises at least one emitting antenna 100 and at least two receiving antennas 101 as illustrated in FIG. 2. The emitting antenna 100 is configured to emit the radar wave. The receiving antennas 101 are configured to receive the radar waves R11, R12 (illustrated in FIG. 2) retransmitted towards the radar sensor 2 after having encountered an object (such as a pedestrian in a non-limitative example). Said retransmitted radar was R11, R12 are also called reflected radar waves R11, R12. There is a phase shift between the retransmitted radar waves received by the receiving antennas 101 which makes it possible to deduce the position of the object relative to the vehicle, object which is in the external environment of the vehicle.

[0045] The wavelength of the radar wave is comprised between 1 mm and 1 cm, which corresponds to a frequency between 30 Ghz (for 1 cm) and 300 GHz (for 1 mm). Therefore the frequency is within the range of 1 GHz (300 mm) to 300 GHz (1 m), which is the micro-waves frequencies range.

[0046] This wave is emitted in a frequency around 76 GHz, so its wavelength is around 4 mm. The same as in the previous case, the intensity of the radar wave has a maximum in the sensor direction d2, but there is also emission of the radar wave in an angular range. Naturally, this frequency is a non-limitative example. In a non-limitative embodiment, the wave is emitted on a frequency band between 100 MHz and 3 GHz. Thus, in a non-limitative example, if the sensor radar 2 operates at a radar frequency of 77 GHz with a frequency band of 1 GHz, the radar sensor 2 will operate on a frequency band from 76.5 GHz to 77.5 GHz.

[0047] The outer lens 3 comprises a first portion 31 and a second portion 32. The first portion 31 is located in the light direction and the second portion 32 is located in the sensor direction, so that the first direction d1 crosses the first portion 31 and the second direction d2 crosses the second portion 32. In this non-limitative example, the cover 3 is an outer lens. In other non-limitative examples, the cover 3 is a bezel, or a radome.

[0048] The second portion 32 comprises in turn a sensor region 33 which has a refractive index and a thickness.

[0049] FIG. 2 shows a scheme of the wave path across the sensor region 33 of the outer lens. This sensor region 33, due to its thickness, may be treated as a thin layer.

[0050] The wave is emitted from the radar sensor 2 and travels until the sensor region 33, which has a refractive index n and a thickness t. Reflection and refraction phenomena take place as usual. The optical path difference δ of the reflected light is calculated in order to determine the condition for interference:

δ=2.Math.n.Math.t.Math.cos(r)+λ/2

[0051] The phase shift between the two reflected waves (the one R11 which has been reflected from the face of the sensor region 33 which in regard to the radar sensor 2, and the one R12 which has been reflected inside the sensor region 33 as illustrated in FIG. 2) is equal to 2π (n×2t×tan(r)sin(θ))/Δ)+π. Since sin(θ)=n sin(r), this leads to a phase shift equal to (2π×n×(2t×cos (r)/Δ)+t. As δ equal to the phase shift multiplied by λ/2*π, one obtains δ=2.Math.nt.Math.cos(r)+λ/2.

[0052] In order to have destructive interference, the phase shift should be equal to π modulo 2π. Hence the phase shift equal to (2m+1)*π, with m a natural number. This leads to (2m+1)*π=(2π×n×(2t×cos (r)/λ)+π. This leads to t=m λ/(2n cos (r)).

[0053] Thus, based on the refractive index n and of the wavelength A used over the operating frequency range of the radar sensor 2, the thickness t can be determined so that said reflected waves R11 and R12 cancel each other.

[0054] An ideal thickness is defined when the incidence angle θ is considered as 0, an m (described hereinafter) is equal to 1. Since the incidence angle θ is considered as 0, the angle r will be 0 as well. As a consequence, for a destructive interference condition, the following equation is to be solved:

2.Math.n.Math.t+λ/2=λ/2+mλ

[0055] wherein m is a natural number. For m=1, the thickness of this sensor region 33 is t=λ/(2n), wherein λ is the wavelength of the radar wave. This thickness t is the ideal thickness. When r=0°, which means cos (r)=1, and when the phase shift is equal to π modulo 27c, this leads to (2m+1)*π=(2π×n×(2t/λ)+π. And, when one multiplies each side of the equation by λ/2π, this leads to 2.Math.nt+λ/2=λ/2+mλ and to ideal thickness t=λ/(2n).

[0056] The sensor region 33 has a thickness which is between 0.8 and 1.2 times said ideal thickness. This equation is applied whatever the value of the angle r is. This range of value takes into account the possible angles of emission of the radar sensor 2. The possible values of the incidence angle θ are defined in the technical specifications of the radar sensor 2, which means the possible values of the incidence angle θ are in the field of view of the radar sensor 2. Usually, the incidence angle θ is between 0° and +−30°. This range value of 0.8 to 1.2 enables to take into account the manufacturing tolerances of the thickness of the sensor region 33.

[0057] In non-limitative examples, when the ideal thickness equal to 1.18 (for n=1.67, m=1 and λ=3.947), t is between 0.94 mm and 1.42 mm.

[0058] It is to be noted that there is a value of the angle of incidence 8 for which the reflected waves R11, R12 cause a maximum of disturbance for the receiving antennas of the radar sensor 2. In a non limitative embodiment, this value is equal to 8=arctan(L1/(2e4)), with L1 the distance between the transmitting antenna 100 and the receiving antennas 101 of the radar sensor 2 and e4 the distance between the radar sensor 2 and the cover 3 as illustrated in FIG. 2. In a non-limitative embodiment, the value of the thickness t is defined for an incidence angle θ=arctan (L1/(2e4)). This makes it possible to be sure of suppressing the disturbances created by the reflected waves R11, R12 when they are at their maximum.

[0059] It is to be understood that the present invention is not limited to the aforementioned embodiments or applications, and variations and modifications may be made without departing from the scope of the invention. In the respect, the following remarks are made. In other non-limitative embodiments, the corresponding frequency of the wavelength of the wave may be within the so millimetre frequency range (24 GHz to 300 GHz) or the high frequency range (300 Mhz to 81 GHz). In another non-limitative embodiment, the lighting device 10 has been described for an automotive vehicle, but it may be used within any other types of vehicle, such as semi-automotive or non-automotive ones.