Head-up display device capable of detecting solar radiation capable of heating its image generating device

Abstract

The present invention relates to a head-up display device capable of detecting solar radiation capable of heating an image generating device of the head-up display device. The head-up display device comprises a device for generating an image in the form of a light beam, and an optical device (6) comprising a mirror (20) reflecting the light beam. The mirror (20) is at least partially transparent to the infrared radiation (48), and the electrical conductor (40) is located behind the mirror (20). The temperature sensor (42) is in contact with the electrical conductor (40).

Description

Technical Field

[0001] The invention relates to a head-up display device for a motor vehicle. Technical Background

[0002] A head-up display (HUD) device is a driver assistance device that allows a driver of a motor vehicle to attend to information without having to take their eyes off the road.

[0003] To this end, a head-up display typically includes an image generating device and an optical arrangement. The image generating device includes a liquid crystal display (LCD) and a light source. The light source backlights the LCD to produce a pixelated light beam. This light beam is then deflected by an optical arrangement comprising one or more mirrors onto a partially transparent strip.

[0004] The strip is positioned within the driver's field of vision when he is looking at the road, so that he can distinguish the road while seeing the information transmitted by the image generating device in the form of a virtual image reflected on the strip. According to a known variant embodiment, the windshield can function as the strip in order to save material.

[0005] In a known manner, the intensity of the light beam generated by the image generating device is adapted as a function of the ambient brightness in order to enable adequate perception of the virtual image by the driver.

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

[0007] To prevent this phenomenon, it has been proposed to use a thermistor placed next to the liquid crystal display to locally assess the temperature on the surface of the liquid crystal display. The operation of the device for generating the image is then dependent on the value measured by the thermistor, so that the intensity of the light source backlighting the liquid crystal display is reduced in the event of excessive heating of the display.

[0008] Depending on the time of day and the vehicle's location, the LCD may be partially exposed to solar radiation. Consequently, the temperature of the display can increase rapidly in areas exposed to solar radiation, and the thermistor detects this heating too late when it is not exposed to solar radiation. Consequently, the LCD may be permanently and locally damaged before the thermistor detects the abnormal temperature increase.

[0009] To address this issue, it has been proposed to use a plurality of photodiodes located behind the mirror of the optical device. Each photodiode is oriented to detect the incidence of solar radiation striking a different area of the mirror. This allows for earlier detection of solar radiation incident on a portion of the mirror, and indirectly on a portion of the image-generating device, thereby preventing localized and irreversible damage to the liquid crystal display.

[0010] However, this solution has the disadvantage of relying on multiple photodiodes, which are fragile and expensive components. It also requires complex wiring to connect each photodiode to the device for controlling the light source. Another drawback is that, for proper operation of the photodiodes, they must be positioned at a certain distance from the mirror, which necessitates a dedicated volume behind the mirror for the photodiodes. Therefore, this solution is unsuitable when it is desirable to limit the size of the head-up display device.

[0011] The present invention aims to solve the above technical problem by proposing a head-up display device for a motor vehicle, which makes it possible to detect the incidence of solar radiation on an image generating device of the head-up display device in a safer, more economical and smaller manner. Summary of the Invention

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

[0013] Notably, the present invention is characterized in that the electrical conductor is located behind the mirror and the temperature sensor is in contact with the electrical conductor.

[0014] The expression "behind the mirror" refers to the positioning of the electrical conductor opposite a face of the mirror, the face facing the mirror reflecting the light beam originating from the image generating 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 increase of the electrical conductor, this temperature increase being due to the absorption of a portion of the infrared radiation passing through the mirror.

[0016] The use of an electrically conductive material advantageously enables rapid, or even very rapid, heat diffusion within the material, resulting in a uniform or substantially uniform temperature of the electrical conductor as a whole over time. Consequently, partial exposure of the electrical conductor to infrared radiation will quickly, or even instantaneously, lead to a significant increase in the temperature of the entire conductor. Consequently, the temperature sensor will be able to more quickly detect even partial exposure of the electrical conductor to infrared radiation.

[0017] The invention thus makes it possible to identify scenes in which the image-generating device is exposed to a critical level of insolation. It also makes it possible to quantify the intensity of the solar radiation that strikes the image-generating device.

[0018] Compared to the above-mentioned prior art, the present invention makes it possible to use components that are less expensive and less fragile than photodiodes to detect solar radiation incident on the mirror.

[0019] Preferably, the electrical conductor is characterized by a conductivity value equal to or greater than 10 6 Sm -1 , preferably equal to or greater than 3 × 10 7 Sm -1 .

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

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

[0022] According to a variant 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 a variant embodiment, the electrical conductor has a surface area similar or substantially similar to that of the mirror.Preferably, the electrical conductor has a 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 exposed surface area is optimal for infrared radiation passing through the first mirror.

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

[0026] According to a variant embodiment, the electrical conductor is supported by the plate. This embodiment advantageously makes it possible to reduce the amount of electrical conductor required in order to provide a mechanically resistant pattern formed by the electrical conductor. The term "thickness" is understood to mean the measurement of the dimension of the electrical conductor in a direction perpendicular or substantially perpendicular to the plate.

[0027] According to another variant embodiment, the thermal conductivity of the plate is equal to or greater than 10 W·m -1•K -1 , preferably equal to or greater than 20W·m -1 •K -1 Thus, heat generated in the portion of the plate exposed to infrared radiation and not covered by the electrical conductor diffuses more quickly to the electrical conductor, making it possible to detect solar radiation incident on the mirror. In other words, the plate also enables detection of solar radiation incident on areas of the mirror not facing the electrical conductor. Within the aforementioned range, the plate thus makes it possible to increase the surface area available for infrared radiation detection without increasing the surface area of the electrical conductor.

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

[0029] According to another variant embodiment, the head-up display device is protected from the external environment by a housing and the plate defines a portion of said housing. This embodiment makes it possible to reduce the manufacturing costs of the invention by using the wall of the housing protecting the optical device as a support plate.

[0030] According to another variant embodiment, the plate is positioned between the mirror and the electrical conductor. This embodiment advantageously makes it possible to hide the electrical conductor behind the plate so that it cannot be seen through the mirror.

[0031] Preferably, the plate is dark 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 a support for the mirror.This embodiment makes it possible to increase the mechanical resistance of the mirror and thus reduce vibration phenomena of the mirror in operating conditions.

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

[0034] According to another variant 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 in order to reduce vibration phenomena of the mirror under operating conditions.

[0035] According to another embodiment, the light beam originating from the image generating device is polarized, and the surface of the mirror reflecting the light beam is covered with a polarizer whose polarization is parallel or substantially parallel to the polarization of the light beam. This embodiment promotes optimal reflection of the light beam and increased transmission of the sun's rays through the mirror.

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

[0037] According to a preferred embodiment, the electrical conductors form several crossing 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 the peripheral area of the mirror.

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

[0039] According to a variant embodiment, a plurality of electrical sensors may be in contact with the electrical conductor in order to make it possible to detect local heating of the electrical conductor more precisely and more quickly.This embodiment thus makes it possible to increase the detection sensitivity of the invention.

[0040] According to a variant embodiment, the temperature sensor is a thermistor.The thermistor can be adhesively bonded to the electrical conductor or pressed against the electrical conductor.

[0041] According to a variant embodiment, the one or more temperature sensors are connected to a control unit configured to cause the image generation device to operate in a degraded mode when the temperature of the electrical conductor measured by the temperature sensor exceeds a predetermined value. By way of non-limiting example, degraded mode is understood to mean a reduction in the luminous intensity of the light beam emitted by the image generation device.

[0042] Of course, the various features, variations and embodiments described above can be combined with one another in various combinations, as long as they are not mutually exclusive or incompatible. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0044] Figure 1 A schematic diagram showing a cross section of a head-up display device according to the present invention;

[0045] Figure 2 A schematic exploded view of a system for detecting solar radiation is shown. Figure 1 In the head-up display device shown;

[0046] Figure 3 Shown by Figure 2 Several non-limiting variations of the patterns formed by the electrical conductors on the surface of the plate of the depicted detection system;

[0047] Figure 4 shows the connection for attaching by Figure 2 A method of describing a plate detection system;

[0048] Figure 5 A schematic diagram showing a cross section of a variant embodiment of a system for detecting solar radiation according to the present invention;

[0049] Figure 6 Shown Figure 5 Schematic exploded view of the depicted detection system. DETAILED DESCRIPTION

[0050] As a reminder, the present invention proposes a head-up display device for a motor vehicle, which makes it possible to detect the incidence of solar radiation on an image generating device of the head-up display device in a safer, more economical and less bulky manner.

[0051] Figure 1 A non-limiting example of embodiment of a head-up display device according to the invention is shown.In a known manner, the head-up display device 2 comprises image generating means 4 and optical means 6, both placed in a housing 8 in order to protect them from the external environment.

[0052] The image generating means 4 comprise a light source 10 which backlights a liquid crystal display 12. The operation of the light source and the liquid crystal display is synchronised by a control unit 14 so as to enable the projection of an image in the form of a polarised light beam propagating in an optical chamber 16.

[0053] The optical device 6 of the display device makes it possible to direct the light beam to the opening 18 formed in the housing 8. For this purpose, the optical device comprises a first mirror 20, for example a folding mirror, which reflects the light beam originating from the image generating device in the direction of a second mirror 22, for example a mirror with optical power, such as a parabolic mirror.

[0054] The first mirror 20 is characterized by being at least partially transparent to infrared radiation, which constitutes the solar spectrum. As a non-limiting example, the first mirror is constructed from a transparent glass plate to which is bonded CMF (Cold Mirror Film) sold by 3M. The CMF forms the front surface of the first mirror. More specifically, the CMF is composed of several thin layers, on the order of 300, each specific to a wavelength in the solar spectrum. The CMF features up to 80% infrared transmission and up to 30% visible light transmission.

[0055] Positioned opposite or indeed against the front face 26 of the first mirror, the polarizer 24 reflects the light beam originating from the image generating device so as to promote optimal reflection of said light beam, which is itself polarized at the output of the liquid crystal display 12 .

[0056] The light beam reflected by the second mirror 22 is then projected through the opening 18 , here closed by a transparent protective cover, onto a partially transparent strip, here the windshield 28 of the motor vehicle, where it is reflected again, this time in the direction of the eyes of the driver of the motor vehicle.

[0057] The driver of the motor vehicle can thus view in front of the windshield 28 a virtual image defined by the information transmitted by the image generating device.

[0058] At certain times of the day, solar radiation 32 can follow the reverse path of the light beam emitted by the image-generating device and partially illuminate liquid crystal display 12. This can then cause image-generating device 4 to experience a localized and sudden increase in temperature. This uncontrolled heating phenomenon can lead to permanent degradation of the liquid crystal display of the display device. To avoid this irreversible phenomenon, it is necessary to be able to detect partial illumination of liquid crystal display 12 by solar radiation 32 at an early stage so that, if necessary, image-generating device 4 can be operated in a degraded mode to reduce its temperature.

[0059] For this purpose, the invention proposes positioning a system 30 for detecting solar radiation 32 behind the first mirror 20, such as Figure 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 so that the plate 34 is parallel or substantially parallel to said mirror.

[0060] The size of the plate 34 is similar or substantially similar to the first mirror 20. The plate 34 is made of a material having a thermal conductivity equal to or greater than 10 W·m -1 •K -1 , preferably equal to or greater than 20W·m -1 •K -1 made of materials.

[0061] According to this example, the plates are made of thermoplastic material, reinforced with graphite for better thermal conductivity. According to an alternative, the plates are made of aluminum.

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

[0063] like Figure 2 As shown, the 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 that is equal to or greater than 10 6 Sm -1 , preferably equal to or greater than 3 × 10 7 Sm -1 By way of non-limiting example, the electrical conductors may be made of the following metals: copper, silver, tin, etc.

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

[0065] The detection system 30 also includes a temperature sensor 42, which in this example is a thermistor, adhesively bonded to and located in the middle of the center bar of the "H" formed by the electrical conductor 40. The thermistor 42 is connected to a measurement unit 44 via a wire 46. When the temperature sensor 42 detects that the temperature of the electrical conductor 40 has increased beyond a pre-stored threshold value, the measurement unit 44 can issue a control signal.

[0066] When solar radiation 32 partially illuminates the first mirror 20, as shown Figure 2 As shown, a portion of the infrared radiation 48 constituting the solar radiation 32 passes through the first mirror 20. The infrared radiation 48 strikes a portion of the plate 34, resulting in heating of the plate in the area 49 exposed to the infrared radiation. Due to the thermal conductivity of the plate, the heat generated in the exposed area is quickly transferred to the electrical conductor 40. The electrical conductivity of the electrical conductor is then significantly altered by the change, which is instantaneously detected by the thermistor 42.

[0067] When these variations exceed threshold values pre-stored by the measuring unit 44 , the measuring unit sends a control signal to the image generating device 4 in order to cause it to operate in a degraded mode in order to reduce its temperature.

[0068] The detection system 30 according to the invention thus makes it possible to prevent localized and uncontrolled heating of the image-generating device due to partial exposure to solar radiation using simple, robust and economical components compared to the use of photodiodes proposed in the prior art.

[0069] In order to enable rapid detection of solar radiation that strikes the peripheral area of the image generating device 4 , the electrical conductors 40 preferably cover one or more peripheral areas of the plate 34 . Figure 3 Several non-limiting variations (A, B, C, D, E, F) of the pattern formed by the electrical conductors 40 on the surface 38 of the plate 34 are shown.

[0070] According to a variant embodiment (not shown), the detection system is arranged in the head-up display device so that the front face of the panel faces the wall of the protective housing. In other words, the large face of the panel not covered by the electrical conductor faces the mirror. This embodiment advantageously makes it possible to prevent the pattern formed by the electrical conductor from being visible through the first mirror. This embodiment ensures that the shape of the electrical conductor is not perceptible in the image viewed by the driver of the motor vehicle.

[0071] For the same reasons, according to another variant, the large face of the plate opposite the mirror is dark, preferably black. Alternatively, the large face as well as the electrical conductors can be covered by a black layer.

[0072] according to Figure 4 In a variant embodiment shown, the plate can be screwed into the wall 36 of the protective casing to ensure that it does not vibrate when the vehicle is in motion.

[0073] according to Figure 5 and Figure 6 In another variant embodiment shown, the electrical conductor 40 can be formed into a plate having similar dimensions to the mirror, eliminating the need for an additional plate to support the electrical conductor. The plate formed by the electrical conductor 40 can include a plurality of recesses 50 designed to keep the electrical conductor at a distance from the wall 36 of the protective housing. The electrical conductor 40 can also serve as a support for the first mirror 20, thereby firmly holding the mirror in the protective housing 8. This embodiment advantageously prevents the mirror and the electrical conductor, both firmly held in the housing, from vibrating when the vehicle is moving.

Claims

1. A head-up display device (2) comprising a device (4) for generating an image in the form of a light beam, and an optical device (6) comprising a mirror (20) for reflecting the light beam, the mirror (20) being at least partially transparent for infrared radiation (48), characterized in that An electrical conductor (40) is located behind the mirror (20), and a temperature sensor (42) is in contact with the electrical conductor (40).

2. The head-up display device (2) according to claim 1, characterized in that The electrical conductor (40) is characterized by being equal to or greater than 10 6 Sm -1 conductivity value.

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

4. The 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 that is parallel or substantially parallel to the mirror (20).

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

6. The head-up display device (2) according to any one of claims 1 to 5, characterized in that The electrical conductors (40) are supported by the plate (34).

7. The 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·m -1 K -1 .

8. The head-up display device (2) according to claim 6 or 7, characterized in that: The display device is protected from external environmental influences by a housing (8), and the board (34) is distinct from the housing.

9. The 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 board (34) defines a part of the housing.

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

12. The 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. The head-up display device (2) according to any one of claims 1 to 12, characterized in that The light beam originating from the image generating device is polarized, and 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 the light beam.

14. The 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. The 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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