Head-up display device

Abstract

The invention relates to a head-up display device (1) for vehicles comprising: - an image generation device (10) designed to generate a light beam (L); - an optical system (20) configured to project said light beam towards a partially transparent blade (70) and comprising a first mirror (21) arranged to reflect said light beam; - an optical sensor (60) designed to determine a luminous flux; and - a protection module (30) capable of controlling a reduction in the intensity of said light beam based on said luminous flux. According to the invention, a field of view (C) of said optical sensor is oriented towards said first mirror. (Shorthand figure: Fig. 1)

Description

Title of the invention: Head-up display device Technical field of the invention

[0001] The present invention relates generally to the technical field of head-up display.

[0002] It relates more particularly to a head-up display device, for example for a motor vehicle. Technological background

[0003] Head-up display (HUD) devices are known, comprising an image generation device and an optical system, generally arranged within a housing. The image generation device is designed to generate a light beam. The optical system is configured to project the light beam towards a partially transparent blade through a window formed in the housing.

[0004] After partial reflection on the partially transparent blade, the light beam reaches the driver's eyes so as to form a virtual image seen by the driver beyond the partially transparent blade, i.e., in usual applications, at the front of the vehicle.

[0005] The intensity of the light beam generated by the image generation device is usually adjusted according to the ambient brightness: the higher the ambient brightness, the higher the intensity of the light beam must also be.

[0006] However, in certain solar illumination configurations (particularly for certain relative positions of the sun, the housing window, and the optical system), the solar flux follows the opposite path of the light beam forming the virtual image. The solar flux is then concentrated on the image-generating device, causing it to heat up. Such heating is detrimental to the operation of the image-generating device and can even lead to its failure.

[0007] There are strategies for protecting the head-up display device based on temperature measurements inside the head-up display device. For example, when the temperature inside the head-up display device exceeds a threshold value, the image generation device of the head-up display device can shut down or a moving part can block the solar flux.

[0008] One of the drawbacks of this strategy is that, in order to trigger the shutdown of the head-up display device, a temperature increase in the head-up display device must necessarily occur. It can be difficult to stop this temperature increase. temperature at the most opportune moment. Indeed, switching off the head-up display does not necessarily mean an immediate reduction in temperature. Presentation of the invention

[0009] In this context, the present invention proposes a head-up display device for vehicles comprising an image generation device designed to generate a light beam; an optical system configured to project said light beam towards a partially transparent blade and comprising a first mirror arranged to reflect said light beam; an optical sensor designed to determine a luminous flux; and a protection module capable of controlling a reduction in the intensity of said light beam on the basis of said luminous flux; in which a field of view of said optical sensor is oriented towards said first mirror.

[0010] Thus, thanks to the invention, the optical sensor makes it possible to determine the solar flux that enters the head-up display device and that could damage the image generation device. Indeed, the solar flux reflected by the first mirror is responsible for heating the image generation device.

[0011] Therefore, by knowing the intrinsic properties of the image generation device, or by calibration, it is possible to anticipate the heating of the image generation device when exposed to solar radiation. It is thus possible to propose a thermal protection strategy, for example, by reducing the intensity of the virtual image, which is safe and temporally relevant, that is to say, one that can anticipate the temperature rise. In other words, this strategy makes it possible to determine an effect, here the solar radiation penetrating the head-up display device, in order to prevent the cause, which is the heating of the image generation device.

[0012] Other non-limiting and advantageous features of the head-up display device according to the invention, taken individually or in all technically possible combinations, are as follows: - said optical sensor includes at least one photoelectric cell and said field of vision is oriented towards the center of the reflection surface of said light beam on said first mirror; - said optical sensor comprises an array of several photoelectric cells and said field of vision is oriented towards the reflection surface of said light beam on said first mirror; - said optical sensor is arranged near said image generation device such that the angle formed between a path of said light beam between said image generation device and said first mirror and a principal observation axis of said optical sensor is less than 45 degrees; - said first mirror includes a first optical filter disposed on its reflective surface and having a reflection coefficient of less than 5% for radiation within a given infrared range; - said first mirror includes a second optical filter disposed on its reflective surface and having a reflection coefficient of less than 5% for a given rectilinear polarization of a light beam; -said optical sensor is capable of determining a luminous flux from radiation in the visible range; - said optical system includes a second mirror which is concave, on which said light beam is reflected and which is located between said first mirror and said blade partially transparent with respect to the path of said light beam; - said second mirror is movable and can be moved to a protective position where the path of the light beam between the optical system and the partially transparent blade is interrupted; - said protection module controls said intensity reduction further on the basis of at least one of the following parameters: an ambient temperature of said image generation device; an external brightness; and a junction temperature of a semiconductor element.

[0013] The invention also proposes a method for protecting a head-up display device comprising: an image generation device designed to generate a light beam; an optical system configured to project said light beam towards a partially transparent blade and comprising a first mirror arranged to reflect said light beam; an optical sensor having a field of view oriented towards said first mirror; and a protection module; said method comprising the following steps: - the determination, by said optical sensor, of a luminous flux; and - the reduction, by said protection module, of the intensity of said light beam on the basis of said luminous flux determined by said optical sensor.

[0014] Other non-limiting and advantageous features of the protection method according to the invention, taken individually or in all technically possible combinations, are as follows: - the method comprises at least one of the following steps: determining, by a temperature sensor, an ambient temperature of said head-up display device; determining, by a measuring circuit, a junction temperature of a semiconductor element; and determining, by an external light sensor, an external light level; and comprising a step of reducing, by said protection module, the intensity of said light beam based on at least one of the following parameters: said ambient temperature, said junction temperature, and said outdoor brightness; - the process includes a step of moving, controlled by said protection module on the basis of said luminous flux, a second movable mirror to a protection position where the path of the light beam between the optical system and the partially transparent blade is interrupted; - said optical sensor comprises an array of several photoelectric cells and said field of vision is oriented towards the reflection surface of said light beam on said first mirror; - said optical sensor determines a luminous flux from radiation in the visible range. Detailed description of the invention

[0015] The following description with regard to the attached drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be carried out.

[0016] Of course, the different features, variants and embodiments of the invention can be combined with each other in various ways insofar as they are not incompatible or mutually exclusive.

[0017] On the attached drawings:

[0018] [Fig-1] schematically represents in cross-section a head-up display device according to the invention;

[0019] [Fig.2] represents a reduction curve based on a temperature measurement; and

[0020] [Fig.3] represents a block diagram of a sequence of steps enabling the implementation of work of a thermal protection process.

[0021] Of course, various other modifications can be made to the invention within the scope of the annexed claims.

[0022] Here, a head-up display device 1 is described in the case where it is used within a motor vehicle.

[0023] As shown in [Fig.1], the head-up display device 1 includes an image generation device 10, an optical system 20, an optical sensor 60 and a protection module 30.

[0024] The head-up display 1 is controlled by a control unit. The control unit is programmed to control and / or connect the various elements of the head-up display 1. Here, the control unit is the vehicle's control unit. Alternatively, the head-up display could include a dedicated control unit.

[0025] The image generation device 10 is designed to generate a light beam called a modulated light beam L. For this purpose, the image generation device 10 includes a light source 12 and a modulator 11.

[0026] The modulator 11 consists of an element matrix whose transmittance varies over time. The modulator 11 receives a source light beam generated by the light source 12 and transmits the modulated light beam L. Here, the light source 12 is polychromatic to form color images. Thanks to its element matrix, the modulator 11 spatially modulates the source light beam so as to form the modulated light beam L.

[0027] Here, the modulator 11 is a TFT (thin film transistor) liquid crystal display, that is, an array of liquid crystal cells, each controlled by a thin film transistor (hence the name TFT). For each element of the array, three cells, each associated with a colored filter, for example one for blue, one for green, and one for red, allow the transmittance to be controlled by orienting the liquid crystals in a stable manner and with a short response time.

[0028] Alternatively, to form the modulated light beam L, a rear face of a diffuser is scanned by a laser beam generated by an array of laser diodes, the scanning being carried out, for example, by a movable mirror. Then, a front face of the diffuser generates the modulated light beam.

[0029] The optical system 20 is arranged to project the modulated light beam L towards a partially transparent blade 70 along a predetermined path. The modulated light beam L is reflected by the partially transparent blade 70 towards an observation area where the driver's eyes are located. The path of the modulated light beam L between the image generation device 10 and the partially transparent blade 70 defines an optical path.

[0030] The partially transparent blade 70 is oriented so as to reflect a portion of the modulated light beam L towards an observation area in which the driver's eyes are located, thus forming a virtual image. The partially transparent blade 70 may be part of the vehicle's windshield or a combiner, i.e., a partially transparent blade dedicated to the head-up display. Such a combiner would be placed between the windshield and the driver's eyes.

[0031] The virtual image contains indications or information intended for the driver of the vehicle, for example in the form of regulatory symbols and / or a speed indicator and / or an engine speed indicator and / or a fault indicator and / or a navigation instruction.

[0032] As shown in [Fig. 1], the optical system 20 here comprises a first mirror 21 (sometimes called a "folding mirror") which is a flat mirror. The optical system 20 also comprises a second mirror 25 which is a concave mirror. The second concave mirror 25 allows, for example, the enlargement of small images generated by the image generation device 10 to form virtual images of size suitable. Here, the second mirror 25 is movable, for example by rotation, so as to adjust the position of the virtual image to the observation area, which depends on the size of the conductor. The first mirror 21 directs the modulated light beam L produced by the image generation device 10 towards the second mirror 25.

[0033] Conventionally, the head-up display device 1 is contained within a protective housing 50 or a casing. An opening 51 is provided in the housing 50 to allow the modulated light beam L to propagate towards the partially transparent blade 70. The opening 51 can be covered by a transparent material such as a glass blade.

[0034] In the following, the adjective "interior" refers to the interior of the head-up display device 1, therefore here inside the housing 50. The adjective "exterior" refers to the exterior of the head-up display device 1, therefore here outside the housing 50. The adjective "exterior" refers, for example, to the passenger compartment of the vehicle.

[0035] As shown in [Fig.1], in certain solar illumination configurations (in particular for certain relative positionings of the sun, the window of the housing and the optical system), a solar light beam LS can penetrate inside the head-up display device 1, here through the aperture 51. This occurs in particular when the sun, the partially transparent blade 70 and the second mirror 25 are substantially aligned, as shown in [Fig.1].

[0036] Figure 1 represents a particular example of propagation of the solar light beam LS. In this example, the solar light beam LS travels along the optical path in the opposite direction. This scenario corresponds to the most damaging situation for the head-up display device 1, since the second mirror 25 focuses the solar light beam LS, after reflection from the first mirror 21, onto the center of the modulator 11. In other cases, the solar light beam LS may illuminate other areas of the modulator 11 but is less focused.

[0037] The modulator 11 is relatively absorbent. Thus, when the solar light beam LS reaches the modulator 11, it rapidly heats up the modulator 11 and, more generally, the image generation device 10. Such heating is detrimental to the operation of the image generation device 10 and can even lead to its deterioration. For example, above a certain temperature, the liquid crystals of the modulator 11 can lose their polarization.

[0038] To limit the heating of the image generation device 10, the first mirror 21 includes a first optical filter 22 disposed on its reflective surface and having a reflection coefficient of less than 5% for radiation within a given infrared range. The solar light beam LS is therefore filtered during its reflection on the first mirror 21. In other words, radiation included in a given infrared range, here this given range corresponds to wavelengths below 700 nm, is reflected only very weakly, less than 5%, on the first mirror 21.

[0039] Thanks to the first optical filter 22, the infrared part of the solar light beam LS does not reach the image generation device 20. This first optical filter 22 does not disrupt the operation of the head-up display device 1 because the latter operates in the visible range.

[0040] To limit the heating of the image generation device 10, the first mirror 21 includes a second optical filter 23 arranged on its reflective surface and having a reflection coefficient of less than 5% for a given linear polarization of a light beam. Indeed, the modulator 11 polarizes the modulated light beam L linearly in a given direction. The second optical filter 23 is arranged so as to reflect almost all of the light beam in this given direction but has a reflection coefficient of less than 5% for linear polarization perpendicular to this given direction. Thus, only a portion of the solar light beam LS, that which has the same polarity as the modulated light beam L, is reflected towards the image generation device 20, which limits its heating without disrupting its operation.

[0041] Alternatively, the first optical filter and / or the second optical filter could be located elsewhere, for example on the surface of the second mirror or on the surface of the modulator. Alternatively, the first and second optical filters could be a single optical filter.

[0042] As shown in [Fig. 1], the head-up display 1 also includes a protection module 30 capable of controlling a reduction in the intensity of the modulated light beam L. The protection module 30 can, for example, control a reduction in the intensity of the source light beam emitted by the light source 12, even to its complete shutdown if necessary. To achieve this, the protection module 30 can, for example, control a reduction in the electrical current supplied to the light source 12. The actions performed by the protection module 30 are made possible by a computer internal to the protection module 30 or via the computer of the head-up display.

[0043] To determine the amplitude of the intensity reduction, the protection module 30 can, for example, be connected to a temperature sensor 40 located near the modulator 11 or on the electronic board of the light source 12. The temperature sensor 40 is designed to measure the ambient temperature TA of the image generation device 10. The temperature sensor 40 is, for example, a thermistor with a negative temperature coefficient.

[0044] Here, the protection module 30 is designed to control the reduction in intensity of the modulated light beam L when the ambient temperature TA is above an ambient threshold. The ambient threshold is, for example, between 60°C and 100°C, preferably between 70°C and 100°C.

[0045] This ambient temperature measurement TA allows for the implementation of a reduction strategy known as "derating", characterized by a reduction in the performance of the image generation device 10. This strategy consists of defining the maximum intensity of the modulated light beam L generated by the image generation device 10, i.e. the maximum luminance of the virtual image, as a function of the ambient temperature TA.

[0046] As shown in [Fig.2], the amplitude of the intensity reduction, represented by a first coefficient Cl of intensity reduction of the modulated beam L, can be given by a reduction curve called a "derating curve" defined in three intervals: i) an interval where the ambient temperature TA is less than or equal to a threshold value TA1, the image generation device 10 can then operate at its maximum capacity, the first coefficient Cl is equal to 1; ii) an interval where the ambient temperature TA is above the threshold value TA1 and below a maximum value TA2, the protection module 30 can reduce the intensity of the modulated light beam L, the amplitude of the reduction is obtained by a projection onto a decreasing linear curve, the first coefficient Cl is between 0 and 1; iii) an interval where the ambient temperature TA is greater than the maximum value TA2, the protection module 30 can control the shutdown of the image generation device 10, the first coefficient is equal to 0.

[0047] Here, the head-up display device 1 also includes a measuring circuit designed to measure an internal temperature at the level of the image generation device 10, for example at the level of the light source 12.

[0048] Thus, when the image generation device 10 includes a semiconductor element, for example a semiconductor element of the TFT screen or a light-emitting diode of the light source 12, the measuring circuit can be designed to measure a junction temperature TJ of the semiconductor element. If the limiting temperature of the semiconductor element is reached, the protection module 30 commands the image generation device 10 to shut down.

[0049] The protection module 30 can then control a reduction in the intensity of the light beam L when the junction temperature TJ is above a junction threshold. The junction threshold is preferably between 95°C and 110°C, which typically corresponds to the thermal limits of a TFT screen. The junction threshold for example, it can be equal to 110°C.

[0050] A second reduction strategy can then be implemented, linked to the operation of the semiconductor element(s) and based on the junction temperature TJ. This means that the protection module 30 can reduce the intensity of the modulated light beam L to regulate the junction temperature. As before, the magnitude of the reduction, represented by a first intensity coefficient C2, can be given by a second reduction curve defined in intervals.

[0051] The intensity of the modulated light beam L at a given instant also depends on external factors such as ambient brightness LEX. Indeed, it is important to consider the ambient brightness LEX around the driver to adapt the luminance of the virtual image, for example, to adapt to entering or exiting a tunnel, or to a glare situation. Thus, a dimming strategy can be implemented to adapt the luminance of the virtual image according to the ambient brightness LEX. This dimming strategy can cause the image generation device 10 to increase or decrease the intensity of the modulated light beam L by a third factor C3. To implement the dimming strategy, the protection module 30 can, for example, be connected to an external brightness sensor located in the vehicle's passenger compartment.

[0052] Thus, during a thermal protection process represented in [Fig. 3], the corrected intensity IC of the modulated light beam at a given instant can correspond to a setpoint intensity, for example previously chosen by the driver to obtain a desired luminance of the virtual image, weighted by the first coefficient Cl and / or the second coefficient C2 and / or the third coefficient C3. This means that the luminance of the virtual image at a given instant can correspond to an original luminance weighted by the first coefficient Cl and / or the second coefficient C2 and / or the third coefficient C3, called the corrected luminance.

[0053] Thus, the protection method may include: - a step e3 in which the ambient temperature TA is determined by the temperature sensor 40 and in which the protection module 30 determines a first coefficient Cl of reduction of the intensity of the modulated light beam L on the basis of the ambient temperature TA; - a step e4 in which the junction temperature TJ is determined by the measuring circuit and in which the protection module 30 determines a second coefficient C2 of reduction of the intensity of the modulated light beam L on the basis of the junction temperature TJ; - a step e5 in which the external brightness LEX is determined by the external light sensor and in which the protection module 30 determines a third coefficient C3 for adapting the intensity of the modulated light beam L; - a step e6 in which the corrected intensity IC is determined by the protection module 30 on the basis of the first coefficient Cl and / or the second coefficient C2 and / or the third coefficient C3.

[0054] The protection module 30 can therefore be based on the following parameters to control a reduction in the intensity of the modulated light beam L: - ambient temperature TA; - the external brightness LEX; - the junction temperature TJ.

[0055] Although they may be sufficient to protect the head-up display device 1 against internal thermal stresses due to its operation, strategies based on temperature measurements, such as reduction strategies, have limitations in protecting the head-up display device 1 from the external thermal stress of solar radiation.

[0056] Indeed, the solar light beam LS is an external thermal stress that can be three to four times greater than the internal thermal stresses and can generate rapid local heating; therefore, it is necessary to anticipate this heating. Anticipating this heating means, for example, that the protection module 30 can reduce the intensity of the modulated light beam L preventively to avoid damage to the image generation device 10 and, in particular, to the modulator 11.

[0057] In addition, it can also be provided that the protection module 30 can control the closing of the opening 51 by means of a movable part so as to prevent the solar light beam LS from penetrating inside the head-up display device 1. It can also be provided that the second mirror 25, which here is movable, is moved to a protection position where the path of the modulated light beam L between the optical system 10 and the partially transparent blade 70 is interrupted, i.e. to a position where the solar light beam LS cannot reach the image generation device 10.

[0058] In this context, the head-up display device 1 includes an optical sensor 60 designed to determine a luminous flux FL. The optical sensor 60 has a field of view C that can be defined by a solid angle through which the optical sensor 60 is sensitive to electromagnetic radiation.

[0059] As shown in [Fig.1], the field of view C of the optical sensor 60 is oriented towards the first mirror 21. Thus, the optical sensor 60 can determine the luminous flux FL coming from the first mirror 21.

[0060] In the case where, as in [Fig. 1], a solar light beam LS enters the head-up display device 1, the luminous flux FL from the first mirror 21 is primarily due to the solar light beam LS. Here, more specifically, the arrangement and orientation of the optical sensor 60 mean that the luminous flux FL, determined by the optical sensor 60, from the first mirror 21 is mainly due to the solar light beam LS compared to the modulated light beam L. Indeed, the luminous flux FL determined by the optical sensor 60 is a fraction of the luminous flux incident on the image generation device 10.

[0061] Based on the luminous flux FL determined by the optical sensor 60, correction factors make it possible to determine an incident luminous flux on the image generation device 10. These correction factors, which can be determined by calibration, depend for example on the position and orientation of the optical sensor 60.

[0062] For example, for a given sensor position, the intensity of the modulated light beam L can be varied, and a first mathematical correlation model can be constructed between the intensity of the modulated light beam L and the luminous flux values ​​FL measured by the optical sensor 60. The intensity of a light beam entering the head-up display device 1 can then be varied, and a second mathematical correlation model can be constructed between the intensity of the solar light beam LS and the luminous flux values ​​FL measured by the optical sensor 60. Finally, a third mathematical correlation model can be constructed by varying both the intensity of the modulated light beam L and the intensity of a light beam entering the head-up display device 1.

[0063] According to a first possible embodiment, the optical sensor 60 can include a photoelectric cell and the field of vision C is then oriented towards a remarkable point R which is the center of the reflection surface of the modulated light beam L on the first mirror 21. Here, this remarkable point R also corresponds to the image of the center of the modulator 11 on the first mirror 21.

[0064] When the solar light beam LS enters the head-up display device 1, the solar light beam LS is concentrated towards the notable point R because it lies on the optical axis of the second concave mirror 25. The luminous flux FL from the first mirror 21, which is here mainly due to the solar light beam LS, can therefore be determined with high precision by orienting the field of view C of the optical sensor 60 towards this notable point R.

[0065] According to a second embodiment, the optical sensor 60 may comprise an array of several photoelectric cells, and the field of vision C is then oriented towards the reflection surface of the modulated light beam L on the first mirror 21. An array of photoelectric cells improves the accuracy of The determination of the solar luminous flux FL is achieved by combining measurements at several points on the surface of the first mirror 21. An array of several photoelectric cells makes it easier to detect hot spots that could form on the modulator 11 by focusing the solar light beam LS. A hot spot can be very localized, which can damage the image generation device 10 without significantly raising the ambient temperature.

[0066] Remarkably, orienting the optical sensor 60 towards the first mirror 21 rather than towards the modulator 11 allows for a better determination of the light flux incident on the image generation device 10. Indeed, since the modulator is relatively absorbent, only a small portion of the solar light beam would be reflected towards an optical sensor oriented towards the modulator, which would make determining its intensity imprecise. Furthermore, this positioning of the optical sensor 60 facilitates its integration within the head-up display device 1.

[0067] Here, the optical sensor 60 operates mainly in the visible range. Indeed, since the infrared part of the solar light beam LS is hardly reflected by the first mirror 21, only the visible part of the solar light beam LS can cause heating of the image generation device 10. The optical sensor 60 is therefore designed to measure a luminous flux FL of radiation in the visible range, for example for a wavelength range from 700 nm to 400 nm.

[0068] To best determine the incident light flux on the image generation device 10, the optical sensor 60 is here arranged close to the image generation device 10, that is to say, it is closer to the image generation device 10 than to the first mirror 21 or the second mirror 25.

[0069] For example, the optical sensor 60 can be positioned such that the angle formed between a path of the modulated light beam L between the image-generating device 10 and the first mirror 21 and a principal observation axis of the optical sensor 60 is less than 45 degrees and preferably less than 20°. The path of the modulated light beam L between the image-generating device 10 and the first mirror 21 corresponds to the cross-section of the optical path from the image-generating device 10 to the first mirror 21.

[0070] The principal observation axis P of the optical sensor 60 is defined as the direction along which the optical sensor 60 is most sensitive to radiation. Here, the principal observation axis P corresponds to the average direction of the field of view C of the optical sensor 60 passing through the center of the optical sensor 60.

[0071] As shown in [Fig.1], the principal observation axis P is here oriented towards the reflection surface of the modulated light beam L on the first mirror 21. More specifically, the principal observation axis P is oriented towards the notable point R. Here, in order for the angle formed between the optical path and the principal observation axis P of the optical sensor 60 to be less than 20 degrees, the optical sensor 60 is placed close to the modulator 11. It is nevertheless important not to obstruct the optical path to allow the formation of the virtual image.

[0072] Thus, thanks to the optical sensor 60, the protection module 30 can control the reduction of the intensity of the modulated light beam L, i.e. a reduction of the performance of the image generation device 10, on the basis of a luminous flux FL coming from the first mirror 21. If the luminous flux FL is high, for example because of an intense solar light beam LS, the protection module 30 can control the reduction of the intensity of the modulated light beam L.

[0073] As shown in [Fig. 3], the method for protecting the head-up display device 1 comprises: - a step e1 of determination by the optical sensor 60 of a luminous flux FL; and - a step e2 of reduction, controlled by the protection module 30, of the intensity of the modulated luminous beam L on the basis of the luminous flux FL.

[0074] Thus, thanks to the optical sensor 60, the protection module 30 can control a solar protection strategy, consisting of the steps of determining a luminous flux el and reducing intensity e2, in order to anticipate heating of the head-up display device 1 and in particular of the image generation device 10. Here, the solar protection strategy represents an additional level of safety compared to the reduction strategies.

[0075] The corrected intensity IC of the modulated light beam L therefore depends on the intensity reduction controlled on the basis of the luminous flux FL determined by the optical sensor 60. Here, the corrected intensity IC corresponds to the weighted setpoint intensity, among other things, by a fourth coefficient C4 determined on the basis of the luminous flux FL.

[0076] If the intensity of the solar light beam LS is such that the stopping of the head-up display device 1 is not sufficient to protect it, the protection module can control the closing of the housing 50 or the movement of the second mirror 25. The movement of the second mirror 25 can therefore be controlled by the protection module 30 on the basis of the luminous flux FL.

[0077] Furthermore, it can be anticipated that the solar protection strategy will take into account the ambient temperature TA. Thus, here, the protection module 30 uses a lookup table indicating the maximum intensity of the modulated light beam L as a function of the luminous flux FL and for a given ambient temperature TA. This lookup table can be obtained by calibrations by subjecting the image generation device 10 to determined luminous fluxes and measuring its heating. The lookup table can be based on the ma- correlations themes presented previously.

[0078] Here, the lookup table provided to the protection module 30 gives the fourth coefficient C4 for controlling the reduction in intensity of the light beam L. The fourth coefficient C4 depends on the luminous flux FL. Here, the fourth coefficient C4 also depends on the ambient temperature TA. The shutdown of the head-up display device 1 can correspond to a fourth coefficient C4 equal to 0.

[0079] Alternatively, it could be provided that to determine the fourth coefficient, the protection module uses a protection curve based on the luminous flux determined by the optical sensor and characterized by two limit values ​​of luminous flux.

[0080] Alternatively, it could be provided that the heating of the image generation device is estimated by simulation on the basis of the light flux incident on the image generation device and its intrinsic properties such as its absorbance and its thermal capacity.

[0081] As shown in [Fig. 3], the solar protection strategy can also take into account the corrected intensity IC of the modulated light beam L. Indeed, when the optical sensor 60 determines the luminous flux FL from the first mirror 21, the proportion of this luminous flux FL attributable to the modulated light beam L can be estimated, since the corrected intensity IC of the modulated light beam L at a given instant is known. Since the relative positions of the image-generating device 10, the first mirror 21, and the optical sensor 60 are fixed, it is easy, by calibration, to determine the luminous flux due to the modulated light beam L at a given instant. Consequently, the proportion of the luminous flux FL attributable to the solar light beam LS can be precisely determined.

[0082] In other words, the protection module 30 can take into account the corrected intensity IC to control the intensity reduction at step e2, consequently forming a feedback loop.

[0083] Thus, the different strategies (reduction, attenuation and solar protection) interact optimally in order to maximize the luminance of the virtual image while protecting the head-up display device 1 from heating that could damage it.

Claims

Demands

1. Head-up display device (1) for vehicle comprising: - an image generation device (10) designed to generate a light beam (L); - an optical system (20) configured to project said light beam (L) towards a partially transparent blade (70) and comprising a first mirror (21) arranged to reflect said light beam (L); - an optical sensor (60) designed to determine a luminous flux (FL); and - a protection module (30) capable of controlling a reduction in the intensity of said light beam (L) on the basis of said luminous flux (FL); characterized in that a field of view (C) of said optical sensor (60) is oriented towards a reflective surface of said first mirror (21).

2. Head-up display device (1) according to claim 1, wherein said optical sensor (60) comprises at least one photoelectric cell and said field of view (C) is oriented towards the center (R) of the reflecting surface of said light beam (L) on said first mirror (21).

3. Head-up display device (1) according to any one of claims 1 to 2, wherein said optical sensor (60) comprises an array of several photoelectric cells and said field of view (C) is oriented towards the reflection surface of said light beam (L) on said first mirror (21).

4. Head-up display device (1) according to any one of claims 1 to 3, wherein said optical sensor (60) is disposed near said image generation device (10) such that the angle formed between a path of said light beam (L) between said image generation device (10) and said first mirror (21) and a principal observation axis (P) of said optical sensor (60) is less than 45 degrees.

5. Head-up display device (1) according to any one of claims 1 to 4, wherein said first mirror (21) comprises a first optical filter (22) disposed on its reflective surface and having a reflection coefficient of less than 5% for radiation within a given infrared range.

6. Head-up display device (1) according to any one of claims 1 to 5, wherein said first mirror (21) comprises a second optical filter (23) disposed on its reflective surface and having a reflection coefficient of less than 5% for a given rectilinear polarization of a light beam.

7. Head-up display device (1) according to any one of claims 1 to 6, wherein said optical sensor (60) is capable of determining a luminous flux (FL) from radiation in the visible range.

8. Head-up display device (1) according to any one of claims 1 to 7, wherein said optical system (20) comprises a second mirror (25) which is concave, on which said light beam (L) is reflected and which is located between said first mirror (21) and said partially transparent blade (70) with respect to the path of said light beam (L).

9. Head-up display device (1) according to claim 8, wherein said second mirror (25) is movable and can be moved to a protective position where the path of the light beam (L) between the optical system (20) and the partially transparent blade (70) is interrupted.

10. Head-up display device (1) according to any one of claims 1 to 9, in said protection module (30) controls said intensity reduction further on the basis of at least one of the following parameters: - an ambient temperature (TA) of said head-up display device (1); - an external brightness (LEX); and - a junction temperature (TJ) of a semiconductor element.

11. A method for protecting a head-up display device (1) comprising: - an image-generating device (10) designed to generate a light beam (L); - an optical system (20) configured to project said light beam (L) towards a partially transparent blade (70) and comprising a first mirror (21) arranged to reflect said light beam (L); - an optical sensor (60) having a field of view (C) oriented towards a reflective surface of said first mirror (21); and - a protection module (30); said method comprising the following steps: - the determination (e1), by said optical sensor (60), of a luminous flux (FL); and - the reduction (e2), by said protection module (30), of the intensity of said luminous beam (L) on the basis of said luminous flux (FL) determined by said optical sensor (60).

12. A protection method according to claim 11, comprising at least one of the following steps: - the determination (e3), by a temperature sensor (40), of an ambient temperature (TA) of said head-up display device (1); - the determination (e4), by a measuring circuit, of a junction temperature (TJ) of a semiconductor element; and - the determination (e5), by an external light sensor, of an external light level (LEX); and comprising a step of reducing (e6), by said protection module (30), the intensity of said light beam (L) on the basis of at least one of the following parameters: said ambient temperature (TA), said junction temperature (TJ) and said external light level (LEX).

13. A protection method according to claim 11 or 12, comprising a displacement step, controlled by said protection module (30) on the basis of said luminous flux (FL), of a second movable mirror (25) to a protection position where the path of the light beam (L) between the optical system (20) and the partially transparent blade (70) is interrupted.

14. A protection method according to any one of claims 11 to 13, wherein said optical sensor (60) comprises an array of several photoelectric cells and said field of vision (C) is oriented towards the reflection surface of said light beam (L) on said first mirror (21).

15. A protection method according to any one of claims 11 to 14, wherein said optical sensor (60) determines a luminous flux (FL) from radiation in the visible range.

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