FR3049720A1 - HEAD-UP DISPLAY - Google Patents

Abstract

A head-up display (10) includes a projection unit (20) of a light beam to a combiner (40) and a housing (30) at least partially enclosing the projection unit (20). The housing (30) has a window closed by a wall (36) at least partially transparent adapted to be traversed by the light beam projected by the projection unit (20). The wall (36) has a variable light transmission factor as a function of the wavelength.

Description

Head-up display

Technical field to which the invention relates

The present invention relates to head-up display systems used for example in motor vehicles.

It relates more particularly to a head-up display. The invention is particularly advantageous in the case where the beam generated by an image projection unit is likely to have a colorimetric defect.

Technological background

A head-up display unit is known comprising a unit for projecting a light beam to a combiner, and a housing partially enclosing at least the projection unit and having a window closed by an at least partly transparent wall. designed to be traversed by the light beam projected by the projection unit.

Object of the invention

In this context, the present invention provides such a head-up display, characterized in that the wall has a variable light transmission factor as a function of the wavelength.

This variation of the transmission factor makes it possible to correct colorimetric defects in the light beam.

According to other optional (and therefore non-limiting) characteristics: the wall has a first transmission factor for a first wavelength of the visible light spectrum and a second transmission factor for a second wavelength of the visible light, the first transmission factor being less than half the second transmission factor; the wall comprises a notch filter causing attenuation over a range of wavelengths; said gap is included in the range of wavelengths between 550 nm and 600 nm; the frequency range extends between 565 nm and 580 nm; the wall comprises an interference filter and / or a colored sheet; the projection unit comprises a screen backlit by at least one light source; the screen is a liquid crystal screen, for example made of thin-film transistors; the light source emits light over the entire spectrum of visible light; the light source is a light emitting diode; the projection unit comprises an optical return element designed to send the light beam back to the combiner.

Detailed description of an example of realization

The following description with reference to the accompanying drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be achieved.

In the accompanying drawings: - Figure 1 shows a head-up display according to the invention; and FIG. 2 is a curve representing the transmission factor of the light as a function of the wavelength of the light transmitted for a wall provided in the head-up display of FIG. 1.

FIG. 1 shows a head-up display 10 for a vehicle (here for a motor vehicle). The head-up display 10 comprises a combiner 40 and a light beam projection unit 20 towards the combiner 40 (at least when the combiner 40 is in the operating position as explained hereinafter). The projection unit 20 is mounted in a housing 30 and comprises an image forming device 22 and a reflecting optical element 24 (for example a reflecting mirror). The optical return element 24 is arranged to return the beam emitted by the image forming device 22 towards the combiner 40.

The imaging device 22 comprises a screen 26 backlit by at least one light source 28 (mounted for example on a printed circuit 29 fixedly received in the housing 30). The screen 26 is here a liquid crystal display, using for example a technology based on thin film transistors (or TFT for "Thin-Film Transistor").

The image-forming device 22 here comprises a plurality of light sources 28. For example, a light-emitting diode 28 is used, for example, as a light source, in this case white, that is to say, emitting over the entire spectrum of light. visible.

The image forming device 22 may further comprise a reflector 27 designed to send back to the screen 26 at least a portion of the luminous flux that this reflector 27 receives from the source (s) of light 28.

In the example described here, the combiner 40 is mounted on a support 50 movable in the housing 30 between at least two positions: - an operating position, in which the combiner 40 is outside the housing 30 and receives as already indicated the light beam projected by the projection unit 20 (that is to say here returned by the optical return element 24); a retracted position (shown in dotted lines), in which the combiner 40 is inside the housing 30 (the image forming device 22 then being deactivated so that the projection unit 20 emits no light beam ).

Combiner 40 is a semi-transparent slide. Thus, when the support 50 is in its operating position, the combiner 40 reflects towards the driver's eyes a part of the light beam projected by the projection unit 20, so as to form a virtual image (corresponding to the image generated by the imaging device 22) in the driver's field of view.

Alternatively, the combiner 40 could be fixed and / or tiltable to accommodate the user's position. According to another variant, the combiner could be realized by the windshield of the vehicle.

The housing 30 has an opening 32 for the passage of the combiner 40 during the movement of the support 50 between its retracted position and its operating position. The opening 32 is here formed in a substantially horizontal partition 34 which closes the upper part of the housing 30.

The housing 30 also comprises a window (formed here in the partition 34) closed by a wall 36 at least partially transparent to allow the passage of the projected light beam towards the combiner 40, here between the optical return element 24 and the combiner 40 (when the support 50 is in the operating position).

The wall 36 makes it possible to protect the inner elements of the housing 30 (in particular the image forming device 22, the reflecting mirror 24, as well as possibly the drive mechanism of the support 15) with various external aggressions (dust, falling object from the passenger compartment of the vehicle, etc.).

In certain possible variants, the transparent wall 36 could, however, be located between the image forming device 22 and the reflecting mirror 24.

The wall 36 is designed to let light over a portion of the visible light spectrum (in practice over a major part of this spectrum) and to attenuate the light transmitted to another part of the visible light spectrum. In other words, the wall has a variable light transmission factor as a function of the wavelength.

To obtain such a property, the wall 36 comprises, for example, in at least a portion of its thickness, a colored sheet (in English: "color foif") forming a color filter. In a variant, the aforementioned property could be obtained by depositing an interference filter on a surface of the wall 36 (for example on the lower surface of the wall 36, that is to say on the surface facing the inside of the housing 30). a wavelength-variable transmission factor makes it possible to correct colorimetric defects present in the beam generated by the projection unit 20, in particular at the level of the image-forming device 22.

For example, when using a TFT type liquid crystal display 26 as indicated above with certain types of light sources (especially with certain white light emitting diodes as indicated above), the projected beam and, therefore, the virtual image seen by the user would take a yellowish hue and the desired white balance would not be respected in the absence of the correction mentioned above.

This yellowing may for example be due to the exposure of the transparent parts to heat or UV radiation. Another reason may be that the TFT type screen causes a colorimetric displacement of the white provided by the white light-emitting diode, and according to the light-emitting diode references available, it is not necessarily possible to find the desired white.

FIG. 2 shows the transmission factor (or transmittance) of the wall 36 as a function of the wavelength of the transmitted light for the spectrum of visible light (extending from about 400 nm to 700 nm).

As clearly visible in this figure, the wall 36 comprises a notch filter (or band eliminator filter) which attenuates the transmitted light over a given wavelength interval.

The wall 36 has, for example, a first transmission factor Ti for a first wavelength λι given (in the aforementioned range and here equal to 570 nm) less than half of a second transmission factor T2 of this wall. 36 for a second wavelength K2 (located outside the aforementioned range and taken here equal to 500 nm).

This range here ranges from 565 nm to 580 nm in order to attenuate the transmission of yellow light and thereby compensate for the yellowish appearance of the beam generated by the image forming device 22 (as explained above). to restore a white balance close to the desired white balance.

In general, for example, it is provided that the notch filter is defined by a lower cut-off wavelength and a higher cut-off wavelength, the lower cut-off wavelength being, for example, greater than 550 nm. and the upper cut-off wavelength being for example less than 600 nm.

It is noted that the wall 36 may furthermore comprise a phase delay plate in order to modify the polarization of the light beam passing through it, for the purpose for example of improving the rendering of the virtual image for a user equipped with polarizing glasses. .

Claims (12)

1. Head-up display (10) comprising: - a projection unit (20) of a light beam intended for a combiner (40), - a housing (30) partially enclosing at least the projection unit (20) and having a window closed by a wall (36) at least partially transparent adapted to be traversed by the light beam projected by the projection unit (20), characterized in that the wall (36) has a factor variable light transmission depending on the wavelength. A head-up display according to claim 1, wherein the wall (36) has a first transmission factor (Ti) for a first wavelength (λι) of the visible light spectrum and a second transmission factor (T2 ) for a second wavelength (λ2) of the visible light spectrum, the first transmission factor (T1) being less than half the second transmission factor (T2). A head-up display according to claim 1 or 2, wherein the wall (36) comprises a notch filter causing attenuation over a wavelength interval, said gap being included in the wavelength range. between 550 nm and 600 nm. The head-up display according to claim 3, wherein the frequency range is between 565 nm and 580 nm. Head-high display according to one of claims 1 to 4, wherein the wall (36) comprises an interference filter. The head-up display according to one of claims 1 to 5, wherein the wall (36) comprises a colored sheet. Head-high display according to one of claims 1 to 6, wherein the projection unit (20) comprises a screen (26) backlit by at least one light source (28). The head-up display of claim 7, wherein the screen (26) is a liquid crystal display. The head-up display according to claim 8, wherein the screen (26) is made of thin-film transistors. The head-up display according to one of claims 7 to 9, wherein the light source (28) emits light over the entire spectrum of visible light. The head-up display according to one of claims 7 to 10, wherein the light source (28) is a light-emitting diode. A head-up display according to one of claims 1 to 11, wherein the projection unit (20) comprises a return optical element (24) adapted to return the light beam to the combiner (40).