Method for managing brightness in a display device and display device

Abstract

A method for managing brightness in a display device comprising a matrix of variable transmittance elements (7) and a light source (6) configured to emit a light beam (Lm) of adjustable intensity through said matrix, said matrix being capable of being subjected to possible solar radiation, the method comprising, - a step of estimating a first value of the maximum temperature reached by the matrix which does not take into account possible solar radiation, - a step of estimating a second value of the maximum temperature reached by the matrix taking into account possible solar radiation, - a step of determining a maximum admissible luminous intensity of the light beam as a function of the difference between the first estimated value and the second estimated value. A device configured to implement this method is also proposed. Fig. 1

Description

Title of the invention: Method for managing brightness in a display device and display device Technical field

[0001] The present invention relates to the technical field of automobiles, and in particular the technical field of display devices for motor vehicles.

[0002] The invention relates in particular to a method for managing brightness in a display device and a display device. Technological background

[0003] The principle of head-up displays for vehicles is to project images, including for example information useful for driving, directly into a driver's field of vision, in particular at the level of the vehicle's windshield.

[0004] To this end, the head-up displays comprise an image generation device, for example a light source coupled to a screen. The screen may be, for example, a matrix of elements with variable transmittance such as a liquid crystal display (LCD), or a diffuser whose upstream face is configured to be scanned by a laser beam and on which the image is formed (laser scan technology, according to the usual English term). The head-up displays further comprise an optical system for transmitting this image to a partially transparent blade, for example the windshield of the vehicle, so that the driver can see the images without looking away from the road.

[0005] The location of the displays under the windshield of the motor vehicle makes them likely to receive a solar flux circulating in the display by following the reverse path of the light rays coming from the light source and which converges, after passing through the optical system, at a point on the screen. The focusing of the solar rays, which is added to the rise in temperature generated by the light source itself, is likely to damage the screen.

[0006] Solutions exist to try to remedy this problem and include, for example, the use of temperature sensors placed locally at different locations on the screen. These solutions are only partially satisfactory, in particular because the addition of sensors makes the device more complex and more expensive. Other solutions reduce the intensity of the beam to a minimum value as soon as a temperature exceeds a certain threshold. These solutions are not optimal since they prevent good visibility of the information displayed by the device. Summary of the invention

[0007] In order to remedy the aforementioned drawbacks of the state of the art, a method is proposed for adapting the brightness of the display so as to limit the rise in temperature.

[0008] According to one aspect, there is provided a method for managing brightness in a display device comprising a matrix of elements with variable transmittance and a light source configured to emit a light beam of adjustable intensity through said matrix, said matrix being capable of being subjected to possible solar radiation, the method comprising, - a step of estimating a first value of the maximum temperature reached by the matrix of elements with variable transmittance as a function of parameters insensitive to temperature variations induced by possible solar radiation, - a step of estimating a second value of the maximum temperature reached by the matrix of elements with variable transmittance as a function of parameters sensitive to temperature variations induced by possible solar radiation, - a step of determining a maximum admissible luminous intensity of the light beam as a function of the difference between the first estimated value and the second estimated value.

[0009] The invention makes it possible to monitor in real time the temperature rise of the matrix of elements with variable transmittance and to permanently maintain the maximum brightness level taking into account this temperature. This avoids an excessive reduction in the light intensity which would unnecessarily harm the driver's good perception of the information displayed. In addition, the two stages of estimation and the comparison of the estimated values ​​obtained make it possible to avoid the use of too many sensors and allows greater freedom in the choice of the location of the sensors.

[0010] According to one embodiment, the step of estimating the second value comprises a measurement of a temperature at a determined point of the matrix of elements with variable transmittance.

[0011] According to one embodiment, the step of estimating the second value comprises a measurement of a temperature of the light source.

[0012] According to one embodiment, the step of estimating the first value comprises the use of an isotherm map of the light source which associates a maximum temperature value with each pair comprising an ambient temperature value outside the device and an effective intensity value of the light beam.

[0013] According to one embodiment, from a determined ambient temperature threshold, the maximum admissible light intensity decreases with the increase in the second estimated value.

[0014] According to one embodiment, the maximum permissible light intensity is determined by the following equation: V (t\ — Y 4- Xmax-Xmm / A \ ^max#dmssibl(\l ) Anwrr Tseuil-Tmax \ 1 threshold) ' with Xmax the maximum luminous intensity of the beam, Xmin the minimum luminous intensity of the beam, Tmax the maximum operating temperature of the variable transmittance element matrix, and Tseuii the ambient temperature threshold.

[0015] According to one embodiment, the ambient temperature threshold decreases with the increase in the difference between the first value and the second value.

[0016] According to one embodiment, the ambient temperature threshold is given by the following equation: T threshold T threshold.raax X AT max , with X a predetermined coefficient from the thermal behavior of the device, ATmax the difference between the first value and the second value, Tseuii,max a predetermined maximum value of the threshold.

[0017] According to one embodiment, the method comprises a step of controlling the light source by a control signal determining a desired light intensity value and - an adjustment of the light intensity to the desired value if the desired value is less than or equal to the maximum admissible light intensity - setting the light intensity to the maximum permissible value if the desired value is higher than the maximum permissible light intensity.

[0018] According to one aspect, a display device is provided comprising a matrix of elements with variable transmittance, a light source configured to emit a light beam of adjustable intensity through said matrix and a control unit configured to implement the method according to the invention.

[0019] According to one embodiment, the display device is a head-up display for a motor vehicle.

[0020] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Brief description of the figures

[0021] Furthermore, various other characteristics of the invention emerge from the appended description given with reference to the drawings which illustrate non-limiting forms of embodiment of the invention and where:

[0022] [Fig-1] is a schematic representation of an image generating device according to one embodiment of the invention,

[0023] [Fig.2] is a curve illustrating the maximum light intensity values ​​ad- missibles of the device of [Fig.l], and

[0024] [Fig.3] schematically illustrates the method according to one embodiment of the invention.

[0025] It should be noted that in these figures the structural and / or functional elements common to the different variants may have the same references.

[0026] In [Fig.l], the main elements of a display device 1 according to one embodiment of the invention are shown schematically, here a head-up display, intended for example to equip a vehicle, for example a motor vehicle.

[0027] Such a device 1 is configured to create a virtual image I in the field of vision of a driver of the vehicle, so that the driver can see this virtual image I and any information it contains without having to look away.

[0028] For this purpose, the display 1 comprises a partially transparent blade 2 placed in the driver's field of vision, an image generation device 3 adapted to generate a downstream light beam Lv and an optical transmission device 4, 5 adapted to return, in the direction of said partially transparent blade 2, the light beam generated by the image generation device 3.

[0029] The partially transparent blade 2 is here merged with the windshield of the vehicle. In other words, it is the windshield of the vehicle which has the function of partially transparent blade for the head-up display 1.

[0030] According to a variant, the partially transparent blade could be a combiner, that is to say a partially transparent blade separate from the windshield and dedicated to the head-up display 1. Such a combiner would be placed between the windshield of the vehicle and the eyes YX of the driver, on the path of the downstream light beam Lv.

[0031] Furthermore, here, the optical transmission device comprises two mirrors 4, 5 arranged so as to reflect the downstream light beam Lv generated by the image generation device 3 in the direction of the partially transparent blade 2. The mirrors 4, 5 advantageously make it possible to place the image generation device 3 in a configuration in which it does not face the partially transparent blade 2 and therefore to place it in any suitable location, typically under the dashboard of the vehicle.

[0032] Here, a first mirror 4 is a plane mirror, or folding mirror, and a second mirror 5 is a mirror which has a shape optimized to produce a virtual image of a shape adapted to the shape of the partially transparent blade 2, here a curved shape, so as to display the image I in an undistorted manner.

[0033] According to other embodiments, the optical transmission device 4, 5 could comprise a different number of mirrors and / or mirrors having different shapes. different, as well as other optical elements such as a lens.

[0034] The image generation device 3 comprises a light source 6, here a backlighting module, configured to produce an upstream light beam Lm, a matrix of variable transmittance elements 7 forming a screen configured to be illuminated by the upstream light beam Lm and a reflector 8 interposed between the light source 6 and the matrix 7.

[0035] The matrix 7 is configured to selectively transmit the upstream light beam Lm so as to form the downstream light beam Lv representing an image to be projected into the driver's field of vision by means of the optical transmission device 4, 5 and the partially transparent blade 2.

[0036] The head-up display device 1 also comprises a housing 9 (generally opaque) which contains the image generation device 2 and the optical transmission system 4, 5 in order in particular to protect these elements against possible external attacks (dust, liquids, etc.).

[0037] The housing 9 comprises an opening 10 through which the downstream light beam Lv passes, here after reflection on the second mirror 5.

[0038] The opening 10 of the housing 9 is closed by a window 11 (sometimes referred to by the English term “cover window”) formed for example from a sheet of polycarbonate type plastic material with a thickness of between 0.25 mm and 0.75 mm.

[0039] The head-up display further comprises a control unit 12 configured to control the image generation device 3, in particular the light source 6 and the matrix of variable transmittance elements 7, for example as a function of setpoint signals entered by the user or originating from various sensors of the head-up display 1, as will be explained below.

[0040] A first temperature sensor 13 makes it possible to measure the ambient temperature T amb(t), i.e. the temperature outside the housing 9. Here, the first temperature sensor 13 is placed in such a way that it cannot measure a temperature variation linked solely to solar radiation on the matrix of variable transmittance elements. In other words, the first sensor is insensitive to the presence of solar radiation on the matrix of variable transmittance elements.

[0041] The head-up display is here configured to determine, during an adjustment step E0, a maximum admissible light intensity XmaXjadmissiMe(t) of the upstream beam Lm as a function of the ambient temperature Tamb(t) measured by the first temperature sensor 13. [Fig.2] is a curve representing the maximum admissible light intensity XmaXjadmissibie(t) as a function of the ambient temperature Tamb(t).

[0042] According to the adjustment step E0, if the ambient temperature Tamb(t) is strictly lower than a predetermined minimum operating temperature Tmin, then the maximum admissible luminous intensity XmaXjadmissiMe will be equal to a predetermined minimum operating luminous intensity Xmin.

[0043] If the ambient temperature Tamb(t) is greater than or equal to the minimum operating temperature Tmin and less than a temperature threshold Tseuib then the maximum admissible light intensity XmaXjadmissiMe(t) is equal to the maximum intensity Xmax of the upstream beam Lm, i.e. the maximum light intensity that the light source 6 can provide.

[0044] If the measured temperature Tamb(t) is strictly greater than the temperature threshold T Seuü, and less than or equal to the maximum operating temperature Tmax of the display 1, then the maximum admissible intensity Xmax>admissibie(t) is determined by the following equation:

[0045] X, ■ n(t] = X + .-TA ^max, admissible\'J max T sewbTmax \ amb threshold)

[0046] If the ambient temperature Tamb(t) is strictly greater than the maximum operating temperature Tmax, then the maximum admissible light intensity X max,admiSSibie(t) is equal to the minimum operating light intensity Xmin.

[0047] An effective light intensity Xeffective(t), i.e. the light intensity provided by the light source, is then obtained by comparing the value of a setpoint signal Xuser(t) representative of the brightness desired by the driver of the motor vehicle (for example provided by the driver of the vehicle via a control interface, in particular a control button or a touch screen).

[0048] The value of the effective luminous intensity Xeffective(t) is equal to the intensity desired by the user if the latter is less than the value of the maximum admissible luminous intensity XmaXjadmissiMe(t) or equal to the maximum admissible luminous intensity Xmaxadmissibie(t) if the value of the luminous intensity desired by the user X utiiisateur(t) is greater than or equal to the maximum admissible luminous intensity X max,admissible(t) •

[0049] The image generating device 3 may experience an increase in its temperature due to the rise in the ambient temperature of the vehicle, the heat generated by the light source 6, and the solar rays which penetrate into the housing 9 via the window 11 along the reverse path of the downstream light beam Lv. After reflection on the mirrors 4 and 5, the solar rays may focus at a point on the screen and cause an increase in its temperature.

[0050] According to an advantageous characteristic of the invention, the display device 1 is configured to implement a brightness management method which takes into account the possible presence of solar radiation on the matrix of variable transmittance elements 7. A mode of implementation of the brightness management method according to the invention is illustrated in [Fig.3].

[0051] The illustrated method makes it possible to determine a maximum admissible light intensity Xmax admissible of the upstream light beam taking into account the temperature of the matrix of variable transmittance elements 7 and the possible presence of solar radiation on the matrix of variable transmittance elements.

[0052] The method comprises two steps E1, E2 of estimating the maximum temperature of the matrix of elements with variable transmittance, each step implementing different means. The method further comprises a third step of determining the maximum admissible luminous intensity of the light beam as a function of the difference between the values ​​estimated during the two estimation steps E1, E2.

[0053] A first step E1 of the method estimates the maximum temperature of the matrix of variable transmittance elements 7 as a function of parameters insensitive to the temperature rise induced by possible solar radiation. In other words, the first step E1 makes it possible to estimate a first value Tlmat>max(t) of the maximum temperature of the matrix of variable transmittance elements without taking into account the solar radiation. The first estimated value Tlmat>max(t) will therefore be the same, mutatis mutandis, whether the estimation is carried out in the presence or absence of solar radiation on the screen.

[0054] A second step E2 of the method estimates the maximum temperature of the matrix of variable transmittance elements 7 as a function of parameters sensitive to the temperature rise induced by possible solar radiation. In other words, the second step E2 makes it possible to estimate a second value T2mat>max(t) of the maximum temperature of the matrix of variable transmittance elements 7 which takes into account possible solar radiation. Thus, in the presence of solar radiation, the second estimated value T2mat>max(t) will be closer to the effective maximum temperature (closer to reality) of the matrix than the first estimated value Tlmat max(t), the difference between these two values ​​being explained mainly by the rise in the temperature of the matrix 7 due to solar radiation. In the absence of solar radiation, the two values ​​are equal or very close (a small margin of error may remain depending on the measurement and estimation means).For the sake of simplification, it will be considered here that in the absence of solar radiation, the first estimated value Tlmat>max(t) and the second estimated value T2mat>max(t) are equal.

[0055] A third step E3 comprises a determination of the maximum admissible light intensity Tmax>admissibie(t) of the upstream light beam Lm as a function of the difference between the first estimated value Tlmat>max(t) and the second estimated value T2 mat,max(t) and, in this example, the establishment of a value of the effective light intensity Xeffective(t) for the setpoint signal.

[0056] In this example, the device 1 comprises a second temperature sensor 14 configured to measure a temperature Tmatjbord(t) at a point of the matrix of elements variable transmittance 7, here at the edge of the variable transmittance element matrix 7, and a third temperature sensor 15 configured to measure a temperature TBKL(t) of the light source 6.

[0057] In this configuration of the display device 1, the first step E1 of the method comprises a recovery, by the control means 12, of the ambient temperature Tamb(t) delivered by the first temperature sensor 13 and of the effective brightness Xeffective(t) of the upstream light beam Lm.

[0058] The estimation of the first estimated value Tlmat>max(t) of the maximum temperature of the matrix of elements with variable transmittance is a function of the effective luminous intensity Xeffective(t) and the ambient temperature Tamb(t). Here, the method implements an isotherm map of the variable transmittance element matrix 7 which associates with each pair comprising a value of the setpoint signal Xuser(t) and an ambient temperature value Tamb(t), a maximum temperature value of the variable transmittance element matrix 7. For example, the isotherm map is specific to the head-up display 1 or to the model of the head-up display 1 and is obtained by tests carried out prior to the implementation of the method, in particular during the design of the display device 1. For example, the isotherm map has isotherms parallel to the decreasing line of the curve of [Fig.2] (portion of the curve located between Tseuii and Tmax).

[0059] The estimation of the first estimated value Tlmat>max(t) here includes - a calculation of a maximum admissible temperature Tmax>admissibie(t) for which the effective luminous intensity Teffective(t) can be provided permanently, for example by the following equation: T —T 4- ( Y ,r • ( ri - Y \ - a calculation of a deviation 1 maxxidmissible 1 threshold. \^effective\ 1} Amaxl v . xz ''■min temperature AT(t) between the maximum admissible operating temperature T max,admissibie(t) and the ambient temperature Tamb(t), - a calculation of the first temperature value Tlmatmax, for example according to the following equation: Timalpax ~ Tmax - AT ( t )

[0060] The second step E2 comprises a recovery, by the control means 12, of the temperature Tmatjbord(t) measured by the second sensor 14, of the temperature TBkl (t) supplied by the third sensor 15 and, and a recovery of the effective light intensity value Xeffective(t) of the upstream light beam.

[0061] The estimation of the maximum temperature of the matrix of variable transmittance elements 7 (the determination of the second estimated value T2mat>max(t)) here comprises a first sub-step of determining the temperature rise ATdass(t) of the matrix of variable transmittance elements 7 induced by solar radiation according to the following equation:

[0062] A TclaJt) = r„„,r)- TBKL(t)) + C2;

[0063] with C1 and C2 coefficients obtained on the basis of the thermal behavior of the head-up display, the thermal behavior being for example established previously to the implementation of the method, for example during the design of the head-up display.

[0064] A second sub-step of step E2 comprises a calculation of the maximum temperature at the center of the matrix of elements with variable transmittance, as a function of the temperature TTFT>edge(t) measured by the second sensor 14, of the temperature rise ATdass(t) of the screen induced by the solar radiation of the effective light intensity value Xeffective(t) of the light beam, according to the following equation:

[0065] = T TFT, edge( t ) + A Tclass(t)*Xe f ft^

[0066] Here, during the third step E3 of the method, the first estimated value Tlmat>max(t) and the second estimated value T2mat>max(t) are compared and the sign of their difference ATmax (t)=T2mat>max - Tlmatmax is studied in order to determine the presence or absence of solar radiation on the matrix of variable transmittance elements 7.

[0067] If the difference ATmax(t) is zero, then the matrix of elements with variable transmittance is probably not exposed to solar radiation and the effective light intensity is determined by the control step E0 previously described, in which the temperature threshold Tseuii has a maximum value Tseuii,max.

[0068] If the difference ATmax(t) is positive, then the variable transmittance element matrix 7 is probably exposed to solar radiation and the effective light intensity Xeffective(t) is determined by the adjustment step E0 previously described, in which the predetermined temperature threshold Tseuii is adjusted (step E4) so ​​as to take a reduced value Tseuii>reduced lower than the maximum value Tseuibmax, according to the following equation

[0069] ^'seu iLred uiî seiddmax - ^'ATma^

[0070] with X a predetermined parameter depending on the thermal behavior of the display 1, for example during the design stage of the display.

[0071] Finally, the light source 6 is controlled so as to provide the upstream beam having the effective light intensity Xeffective(t).

[0072] The invention is not limited to the modes of implementation and embodiment described in connection with figures 1 to 3.

[0073] Thus, although the first step E1 estimates the maximum temperature of the variable transmittance element matrix as a function of the ambient temperature, this step could be carried out on the basis of a temperature provided by other sensors, for example a sensor fixed on the electronic card of the light source or on the edge of the variable transmittance element matrix.

[0074] Various other modifications may be made to the invention within the scope of the appended claims.

Claims

Claims

1. Method for managing brightness in a display device comprising a matrix of variable transmittance elements (7) and a light source (6) configured to emit a light beam (Lm) of adjustable intensity (Xeffective(t)) through said matrix (7), said matrix (7) being capable of being subjected to possible solar radiation, the method comprising, - a step (El) of estimating a first value (Tlmat>max(t)) of the maximum temperature reached by the matrix of variable transmittance elements (7) as a function of parameters insensitive to temperature variations induced by possible solar radiation, - a step (E2) of estimating a second value (T2mat>max(t)) of the maximum temperature reached by the matrix of variable transmittance elements (7) as a function of parameters sensitive to temperature variations induced by possible solar radiation,- a step of determining a maximum admissible luminous intensity (Xmax admissible(t)) of the light beam as a function of the difference (ATmax(t)) between the first estimated value (Tlmat>max(t)) and the second estimated value (T2mat>max(t)).,

2. Method according to claim 1, in which the step of estimating (E2) the second value (Tlmat>max(t)) comprises a measurement of a temperature (Tmat>edge(t)) at a determined point of the matrix of variable transmittance elements (7).

3. Method according to claim 2, in which the step of estimating (E2) the second value (T2mat>max(t)) comprises a measurement of a temperature ((Tbkl(1))) of the light source (6).

4. Method according to any one of claims 1 to 3, in which the step of estimating (El) the first value (Tlmat,max(t)) comprises the use of an isotherm map of the light source (6) which associates a maximum temperature value (Tlmat,max(t)) with each pair comprising an ambient temperature value (Tamb(t)) outside the device and an effective intensity value (Xeffective(t)) of the light beam (Lm).

5. Method according to claim 4, in which, from a determined threshold (Tseud(t)) of ambient temperature (1^(1)), the maximum admissible luminous intensity (XmaXjadmissiMe(t)) decreases with the increase of the second estimated value (T2mat>max(t)).

6. The method of claim 5, wherein the maximum permissible light intensity (Xmax>admissibie(t) is determined by the following equation: y {À_ y ■ Xmax-Xmin Wy (t\ T 1 AtnaxMlmissibl^1) — Amax Tseuil-Tmax V aml\')~ 1 seuil) ' with Xmax the maximum light intensity of the beam, Xmin the minimum light intensity of the beam, Tmax the maximum operating temperature of the matrix of variable transmittance elements, and TseuU the ambient temperature threshold (Tamb(t)).

7. Method according to claim 5 or 6, wherein the ambient temperature threshold (Tamb(t)) decreases with the increase in the difference (ATmax(t)) between the first value (Tlmat>max(t)) and the second value (T2mat>max(t)).

8. Method according to any one of claims 5 to 7, in which the estimated ambient temperature threshold (Tamb(t)) is given by the following equation: Tseuil Tseuil,max X ATmax , with X a predetermined coefficient from the thermal behavior of the device, ATmax the difference between the first value (Tlmat>max(t)) and the second value (T2mat>max(t)), Tseuibmax a predetermined maximum value of the threshold.

9. Method according to any one of claims 1 to 8, comprising a step of controlling the light source (6) by a control signal determining a desired value of light intensity (Xuser(t)) ^t - an adjustment of the light intensity to the desired value (Xuser(t)) if the desired value (Xuser(t)) is less than or equal to the maximum admissible light intensity (XmaXjadmissiMe(t)), - an adjustment of the light intensity to the maximum admissible value if the desired value (Xuser(t)) is greater than the maximum admissible light intensity (Xmax>admissibie(t)).

10. Display device comprising a matrix of variable transmittance elements (7), a light source (6) configured to emit a light beam (Lm) of adjustable intensity through said matrix (7) and a control unit (12) configured to implement the method according to any one of claims 1 to 9.

11. A display device according to claim 10, the display device (1) being a head-up display for a motor vehicle.

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