Head-up display device capable of detecting solar radiation that could overheat its image generation device

Abstract

The invention relates to a head-up display device capable of detecting solar radiation that could heat its image generation device. The head-up display device comprises an image generation device, in the form of a light beam, and an optical device (6) including a mirror (20) reflecting said light beam. The mirror (20) is at least partially transparent to infrared radiation (48), and an electrical conductor (40) is positioned behind the mirror (20). A temperature sensor (42) is in contact with the electrical conductor (40). Figure 2

Description

Title of the invention: Head-up display device capable of detecting solar radiation likely to heat its image generation device Technical field to which the invention relates

[0001] The present invention relates to a head-up display device for a motor vehicle. Technological background

[0002] A head-up display device, more commonly known as a HUD (from the English "Head-Up Display"), is a driver assistance device that allows the driver of a motor vehicle to receive information without having to take their eyes off the road.

[0003] To achieve this, a head-up display device typically comprises an image generation device and an optical device. The image generation device includes a liquid crystal display and a light source. The light source backlights the liquid crystal display to create a pixelated light beam. The light beam is then deflected by the optical device, which includes one or more mirrors, onto a partially transparent blade.

[0004] The blade is positioned in the driver's field of vision when the driver is looking at the road, so as to allow the driver to distinguish the road while viewing the information transmitted by the image generation device, in the form of a virtual image reflected on the blade. According to a known embodiment, the windshield can act as the blade in order to save material.

[0005] In a known manner, the intensity of the light beam generated by the image generation device is adapted according to the ambient brightness, to allow sufficient perception of the virtual images by the driver.

[0006] However, at certain times of day, solar radiation follows the opposite path to the light beams emitted by the image generation device. A rapid and significant temperature rise in the image generation device is then observed. This uncontrolled heating phenomenon can lead to permanent damage to the image generation device.

[0007] To prevent this phenomenon, the use of a thermistor, placed against the liquid crystal display, has been proposed to locally evaluate the temperature on the surface of the liquid crystal display. The operation of the image generation device is then controlled by the values ​​measured by the thermistor, so as to reduce the intensity of the light source backlighting the liquid crystal display, in case of excessive heating of said display.

[0008] Depending on the time of day and the vehicle's position, the liquid crystal display may be partially exposed to solar radiation. The display's temperature can therefore rise rapidly in areas illuminated by sunlight, a heating that is then detected too late by the thermistor when the latter is not exposed to sunlight. The liquid crystal display can thus be permanently damaged locally before the thermistor detects an abnormal temperature rise.

[0009] To overcome this problem, the use of several photodiodes, positioned behind a mirror of the optical device, has been proposed. Each photodiode is oriented to detect the incidence of solar radiation illuminating a distinct area of ​​the mirror. The incidence of solar radiation on a portion of the mirror and, indirectly, on a portion of the image generation device, can then be detected earlier in order to prevent local and irreversible damage to the liquid crystal display.

[0010] However, this solution has the disadvantage of requiring a multitude of photodiodes, which are fragile and expensive components. It also necessitates complex wiring to connect each photodiode to a light source control device. Another drawback is that, for the photodiodes to function properly, they must be positioned at a certain distance from the mirror, requiring a dedicated space behind the mirror for the photodiodes. Therefore, this solution is not suitable when the goal is to minimize the size of the head-up display.

[0011] The present invention aims to solve the technical problems mentioned above, by proposing a head-up display device for motor vehicles, enabling the detection of the incidence of solar radiation on the image generation device of the head-up display device, in a safer, more economical and smaller way. Object of the invention

[0012] For this purpose, the invention proposes a head-up display device comprising an image generation device, in the form of a light beam, as well as an optical device comprising a mirror reflecting said light beam, the mirror being at least partially transparent to infrared radiation.

[0013] The invention is remarkable in that an electrical conductor is positioned behind the mirror, and in that a temperature sensor is in contact with the electrical conductor.

[0014] The expression "positioned behind the mirror" refers to the positioning of the electrical conductor opposite one face of the mirror, opposite the face of the mirror reflecting the light beam from the image generation device.

[0015] The invention thus makes it possible to detect the incidence of solar radiation on the mirror, when the temperature sensor measures a temperature rise in the electrical conductor, a temperature rise due to the absorption of part of an infrared radiation passing through the mirror.

[0016] The use of an electrically conductive material advantageously allows for rapid, even very rapid, heat diffusion within said material, so that the temperature of the electrical conductor is homogeneous or substantially homogeneous over time. Thus, partial exposure of the electrical conductor to infrared radiation will rapidly, even instantaneously, cause a significant rise in the temperature of the entire electrical conductor. Consequently, the temperature sensor will be able to detect even partial exposure of the electrical conductor to infrared radiation more quickly.

[0017] The invention thus makes it possible to identify exposure scenarios for the image generation device under critical sunlight conditions. It also makes it possible to quantify the intensity of solar radiation illuminating the image generation device.

[0018] In relation to the prior art mentioned above, the invention allows the detection of solar radiation incident on the mirror, from components less expensive and less fragile than photodiodes.

[0019] Preferably, the electrical conductor is characterized by an electrical conductivity value equal to or greater than 106 Sm*, preferably equal to or greater than 3 x 107 S.m1.

[0020] According to one embodiment, the electrical conductor is preferably a metallic material such as copper, silver, tin or others.

[0021] According to one embodiment, in a plane parallel to the mirror, the surface area of ​​the electrical conductor is greater than the surface area of ​​the temperature sensor; preferably, the surface area of ​​the electrical conductor is at least twice, or even ten times, greater than the surface area of ​​the temperature sensor in order to increase the detection area of ​​infrared radiation by the electrical conductor. In other words, the temperature sensor partially covers the surface area of ​​the electrical conductor. The temperature sensor covers less than 30%, preferably less than 10%, of the surface area of ​​the electrical conductor.

[0022] According to one embodiment, the electrical conductor extends in a plane parallel or substantially parallel to the mirror. This embodiment promotes better exposure of the electrical conductor to the infrared radiation passing through the mirror.

[0023] According to one embodiment, the electrical conductor has a surface area similar or substantially similar to the mirror. Preferably, the electrical conductor is of sufficient thickness to form a rigid or substantially rigid plate.

[0024] Preferably, the electrical conductor extends in a plane parallel or substantially parallel to the mirror so that its exposure surface is optimal to the infrared radiation passing through the first mirror.

[0025] According to one embodiment, the smallest distance between the electrical conductor and the mirror is between 0 and 5 mm, preferably between 0 and 1 mm.

[0026] According to one embodiment, the electrical conductor is supported by a plate. This embodiment advantageously reduces the amount of electrical conductor required, so that the pattern formed by the electrical conductor is mechanically resistant. The term "thickness" refers to a measure of the dimension of the electrical conductor along a direction perpendicular or substantially perpendicular to the plate.

[0027] According to another embodiment, the thermal conductivity of the plate is equal to or greater than 10 W-nr'-K-1, preferably equal to or greater than 20 W-nr'-K-1. Thus, the heat generated at a portion of the plate exposed to infrared radiation and not covered by the electrical conductor diffuses more rapidly to the electrical conductor, enabling the detection of solar radiation incident on the mirror. In other words, the plate can also enable the detection of solar radiation incident on an area of ​​the mirror that is not directly opposite the electrical conductor. Within the ranges of values ​​mentioned above, the plate therefore makes it possible to increase the detection area of ​​infrared radiation without increasing the surface area of ​​the electrical conductor.

[0028] According to another embodiment, the head-up display device is protected from the external environment by a housing and the plate is separate from said housing.

[0029] According to another embodiment, the head-up display device is protected from the external environment by a housing, and the plate delimits a portion of said housing. This embodiment reduces the manufacturing cost of the invention by using a wall of the housing protecting the optical device as a support plate.

[0030] According to another embodiment, the plate is positioned between the mirror and the electrical conductor. This embodiment advantageously allows the electrical conductor to be concealed behind the plate, so that it is not visible through the mirror.

[0031] Preferably, the plate is dark in color or black so that it is less visible through the mirror.

[0032] Preferably, the plate is in contact with the mirror so as to also serve as support to the mirror. This embodiment increases the mechanical resistance of the mirror and, therefore, reduces the phenomena of mirror vibration under rolling conditions.

[0033] According to another embodiment, in a plane parallel to the mirror, the surface of the plate is equal to or greater than 80% of the surface of the mirror reflecting the light beam from the image generation device, preferably equal to or substantially equal to the surface of the mirror.

[0034] According to another embodiment, the electrical conductor is in contact with the mirror. Thus, the electrical conductor can advantageously serve as a support or mechanical reinforcement for the mirror, in particular to reduce mirror vibration under rolling conditions.

[0035] According to another embodiment, the light beam from the image-generating device is polarized, and the surface of the mirror reflecting the light beam is covered by a polarizer whose polarization is parallel or substantially parallel to the polarization of said light beam. This embodiment promotes optimal reflection of the light beam as well as increased transmission of a solar ray through the mirror.

[0036] According to another embodiment, the electrical conductor comprises at least one straight or substantially straight part and / or at least one curved or substantially curved part.

[0037] According to a preferred embodiment, the electrical conductor forms several intersecting lines, and the ends of the lines are opposite the edges and / or corners of the mirror. This embodiment is particularly advantageous for detecting the presence of solar radiation on a peripheral area of ​​the mirror.

[0038] According to another embodiment, in a plane parallel to the mirror, the surface area of ​​the electrical conductor is equal to or greater than 30% of the surface area of ​​the mirror reflecting the light beam, preferably equal to or greater than 90%. In other words, the electrical conductor can form a plate of similar or substantially similar dimensions to the mirror, so as to be able to absorb all solar radiation passing through said mirror.

[0039] According to one embodiment, several electrical sensors can be in contact with the electrical conductor so as to allow for more precise and faster detection of local heating of the electrical conductor. This embodiment thus increases the detection sensitivity of the invention.

[0040] According to one embodiment, the temperature sensor is a thermistor. The thermistor can be glued or plated against the electrical conductor.

[0041] According to one embodiment, the temperature sensor(s) are connected to a control unit, configured to operate the generation device Images are captured in degraded mode when the temperature of the electrical conductor, as measured by the temperature sensor, exceeds a predetermined value. By way of example, degraded mode refers to a reduction in the light intensity of the beam emitted by the image generation device.

[0042] Of course, the different features, variants and embodiments mentioned above can be combined with each other in various ways, provided that they are not incompatible or mutually exclusive. Description of the figures

[0043] The invention will be better understood from the following description, which relates to preferred embodiments, given by way of non-limiting examples, and explained with reference to the accompanying schematic drawings, in which:

[0044] [Fig-1] illustrates a schematic view of a cross-section of a device head-up display according to the invention;

[0045] [Fig.2] illustrates a schematic and exploded view of a detection system solar radiation present in the head-up display device represented by [Fig.1];

[0046] [Fig.3] illustrates several non-limiting variants of patterns formed by a conductor electrical to the surface of a plate of the detection system represented by [Fig.2];

[0047] [Fig.4] illustrates a method of fixing a plate of the detection system re presented by [Fig.2];

[0048] [Fig. 5] illustrates a schematic view of a cross-section of a variant of a implementation of a solar radiation detection system according to the invention;

[0049] [Fig.6] illustrates a schematic and exploded view of the detection system represented by the [Fig.5]. Detailed description of the invention

[0050] As a reminder, the invention proposes a head-up display device for motor vehicles, allowing the detection of the incidence of solar radiation on an image generation device of the head-up display device, in a safer, more economical and less bulky way.

[0051] Figure 1 illustrates a non-limiting embodiment of a head-up display device according to the invention. In a known manner, the head-up display device 2 comprises an image generation device 4 and an optical device 6, both housed in a casing 8 to protect them from the external environment.

[0052] The image generation device 4 comprises a light source 10, backlighting a liquid crystal display 12. The operation of the light source and the liquid crystal display are synchronized by a control unit 14, of in order to allow the projection of images in the form of a polarized light beam propagating in an optical chamber 16.

[0053] The optical device 6 of the display device allows the light beam to be directed to an opening 18 provided in the housing 8. To do this, the optical device includes a first mirror 20, for example a folding mirror, reflecting the light beam from the image generation device, towards a second mirror 22, for example a mirror having optical power (such as a parabolic mirror).

[0054] The first mirror 20 is characterized by at least partial transparency to the infrared radiation that makes up the solar spectrum. By way of non-limiting example, the first mirror consists of a transparent glass plate onto which a CMF (Cold Mirror Film), marketed by the company "3M", is bonded. The CMF then forms the front face of the first mirror. More precisely, the CMF is composed of several thin layers, on the order of 300 layers, each layer being specific to a wavelength of the solar spectrum. The CMF is characterized by a transmission of up to 80% of infrared radiation and up to 30% of visible light.

[0055] A polarizer 24 is positioned opposite or against a front face 26 of the first mirror, reflecting the light beam from the image generation device, so as to promote optimal reflection of said light beam, itself polarized at the output of the liquid crystal screen 12.

[0056] The light beam reflected by the second mirror 22 is then projected through the opening 18, closed here by a transparent protective cover, to a partially transparent blade (here the windscreen 28 of a motor vehicle) where the light beam is reflected again, this time towards the eyes of the driver of the motor vehicle.

[0057] Thus, the driver of the motor vehicle is able to view, at the front of the windshield 28, a virtual image defined by the information transmitted by the image generation device.

[0058] At certain times of day, solar radiation 32 can follow the opposite path of the light beam emitted by the image generation device and partially illuminate the liquid crystal display 12. The image generation device 4 can then experience a localized and abrupt temperature increase. This uncontrolled heating phenomenon can lead to permanent damage to the liquid crystal display of the display device. To avoid this irreversible phenomenon, it is necessary to be able to detect early partial illumination of the liquid crystal display 12 by solar radiation 32 in order to, if necessary, operate the image generation device 4 in a degraded mode and thus lower its temperature. pérature.

[0059] To this end, the invention proposes to position behind the first mirror 20, a solar radiation detection system 30 as illustrated by [Fig. 2]. The detection system 30 consists of a plate 34 placed between a wall 36 of the protective housing 8 and the first mirror 20, such that the plate 34 is parallel or substantially parallel to said mirror.

[0060] The dimensions of the plate 34 are similar or substantially similar to the first mirror 20. The plate 34 is made from a material whose thermal conductivity is equal to or greater than 10 W-nr'-K"1, preferably equal to or greater than 20 W-nr'-K"1.

[0061] According to the present example, the plate is made from a thermoplastic material, reinforced with graphite, for better thermal conductivity. Alternatively, the plate is made of aluminum.

[0062] The thickness of the plate, measured along a direction normal to one of its large faces, is between 1 mm and 5 mm, preferably between 1 mm and 2 ms.

[0063] As illustrated in [Fig. 2], a front face 38 of the plate, facing the first mirror 20, is partially covered by an electrical conductor 40. The electrical conductor is characterized by an electrical conductivity equal to or greater than 10⁶ Sm', preferably equal to or greater than 3 x 10⁷ Sm'. By way of non-limiting example, the electrical conductor may be made of metal: copper, silver, tin...

[0064] According to the present example, the electrical conductor 40 reproduces the shape of an "H" which is centered on the front face 38 of the plate 34.

[0065] The detection system 30 also includes a temperature sensor 42, a thermistor according to the present example, bonded to and in the middle of the central bar of the "H" formed by the electrical conductor 40. The thermistor 42 is connected to a measuring unit 44 via conducting wires 46. The measuring unit 44 is capable of emitting a control signal when the temperature sensor 42 detects a rise in the temperature of the electrical conductor 40 beyond a pre-recorded threshold value.

[0066] When solar radiation 32 partially illuminates the first mirror 20, as illustrated in [Fig. 3], some of the infrared radiation 48 that makes up the solar radiation 32 passes through the first mirror 20. The infrared radiation 48 illuminates part of the plate 34, causing the plate to heat up in the area 49 exposed to the infrared radiation. Due to the thermal conductivity properties of the plate, the heat generated in the exposed area is rapidly transferred to the electrical conductor 40. The electrical conductivity properties of the conductor are then significantly altered, with these changes detected instantaneously by the thermistor 42.

[0067] When these variations exceed a threshold value, pre-recorded by the measuring unit 44, the measuring unit transmits a control signal to the image generation device 4 so that it operates in degraded mode to lower its temperature.

[0068] The detection system 30 according to the invention therefore makes it possible to prevent local and uncontrolled heating of the image generation device due to partial exposure to solar radiation, using simple, robust and economical components compared to the use of photodiodes as proposed by the prior art.

[0069] In order to enable rapid detection of solar radiation illuminating a peripheral area of ​​the image generation device 4, the electrical conductor 40 preferably covers one or more peripheral areas of the plate 34. [Fig.3] illustrates several non-limiting variants of patterns (A, B, C, D, E, F) formed by the electrical conductor 40 on the surface 38 of the plate 34.

[0070] According to an embodiment not shown, the detection system is arranged in the head-up display such that the front face of the plate is opposite a wall of the protective housing. In other words, the large face of the plate not covered by the electrical conductor is facing the mirror. This embodiment advantageously ensures that the pattern formed by the electrical conductor is not visible through the first mirror. This embodiment ensures that the shape of the electrical conductor is not perceptible in the images viewed by the driver of the motor vehicle.

[0071] For the same reasons, according to another embodiment, the large face of the plate opposite the mirror is dark in color, preferably black. Optionally, both the large face and the electrical conductor may be coated with a black layer.

[0072] According to an alternative embodiment, illustrated by [Fig.4], the plate can be screwed into a wall 36 of the protective housing in order to ensure that it does not generate vibrations when the vehicle is in a driving situation.

[0073] According to another embodiment, illustrated in Figures 5 and 6, the electrical conductor 40 can form a plate with dimensions similar to the mirror, so that an additional plate to support the electrical conductor is not necessary. The plate formed by the electrical conductor 40 can have several indentations 50, intended to keep the electrical conductor away from a wall 36 of the protective housing. The electrical conductor 40 can also serve as a support for the first mirror 20, in order to hold the mirror securely to the protective housing 8. This embodiment advantageously prevents vibration of both the mirror and the electrical conductor. two held firmly to the casing, when the vehicle is moving.

Claims

Demands

1. Head-up display device (2) comprising an image generation device (4), in the form of a light beam, and an optical device (6) comprising a mirror (20) reflecting said light beam, the mirror (20) being at least partially transparent to infrared radiation (48), characterized in that an electrical conductor (40) is positioned behind the mirror (20) and in that a temperature sensor (42) is in contact with the electrical conductor (40) so as to allow detection of the incidence of solar radiation on the mirror, when the temperature sensor (42) measures a temperature rise in the electrical conductor (40), a temperature rise due to the absorption of part of an infrared radiation passing through the mirror (20).

2. Head-up display device (2) according to claim 1, characterized in that the electrical conductor (40) is characterized by an electrical conductivity value equal to or greater than 106 Sm*.

3. Head-up display device (2) according to claim 1 or 2, characterized in that in a plane parallel to the mirror (20), the surface of the electrical conductor (40) is greater than the surface of the temperature sensor (42).

4. Head-up display device (2) according to any one of claims 1 to 3, characterized in that the electrical conductor (40) extends in a plane parallel or substantially parallel to the mirror (20).

5. Head-up display device (2) according to claim 4, characterized in that the electrical conductor (40) has a surface similar or substantially similar to the mirror (20).

6. Head-up display device (2) according to any one of claims 1 to 5, characterized in that the electrical conductor (40) is supported by a plate (34).

7. Head-up display device (2) according to claim 6, characterized in that the thermal conductivity of the plate (34) is equal to or greater than 10 W-nr'-K"1.

8. Head-up display device (2) according to claim 6 or 7, characterized in that the display device is protected from the external environment by a housing (8) and the plate (34) is separate from said housing.

9. Head-up display device (2) according to claim 6 or 7, ca- characterized in that the display device is protected from the external environment by a housing (8) and the plate (34) delimits a part of said housing.

10. Head-up display device (2) according to any one of claims 6 to 8, characterized in that the plate (34) is positioned between the mirror (20) and the electrical conductor (40).

11. Head-up display device (2) according to claim 6 to 10, characterized in that in a plane parallel to the mirror (20), the surface of the plate (34) is equal to or greater than 80% of the surface of the mirror (20) reflecting the light beam.

12. Head-up display device (2) according to any one of claims 1 to 11, characterized in that the electrical conductor (40) is in contact with the mirror (20).

13. Head-up display device (2) according to any one of claims 1 to 12, characterized in that the light beam from the image generation device is polarized, and in that the surface of the mirror (20) reflecting the light beam is covered by a polarizer (24) whose polarization is parallel or substantially parallel to the polarization of said light beam.

14. Head-up display device (2) according to any one of claims 1 to 13, characterized in that the electrical conductor (40) comprises at least one straight or substantially straight portion and / or at least one curved or substantially curved portion.

15. Head-up display device (2) according to any one of claims 1 to 14, characterized in that in a plane parallel to the mirror (20), the surface area of ​​the electrical conductor (40) is equal to or greater than 30% of the surface area of ​​the mirror (20) reflecting the light beam.

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