FR3039665B1 - PROJECTION SYSTEM FOR DISPLAY AND HIGH HEAD DISPLAY - Google Patents

Abstract

A display projection system, including a head-up display, comprising a display (14) and a backlighting device (125) for said display, said backlighting device (125) comprising a plurality of diodes ( 126a, 126b) emitting light towards the screen (14). The invention is characterized in that the backlighting device (125) further comprises a carrier (130), and a plurality of electroluminescent diodes (126a, 126b) disposed on the carrier (130) and emitting light thereagainst. direction of the screen (14), the support (130) having a first plurality of facets (128a, 128b) inclined to the plane of the screen (14) at a second plurality of inclinations.

Description

TECHNICAL FIELD OF THE INVENTION The invention relates to projection systems, in particular for head-up displays. In particular, the invention relates to a virtual image projection system and a head-up display for a motor vehicle. 2. Technological background

A head-up display allows the formation of a virtual image through projection optics. The virtual image is formed by a projection system, which includes a screen which forms on its surface a real image which is projected so as to form the virtual image visible by the user of the display, superimposed on the image. environment, for example the road in the case of automobile use.

In the context of using the display as a head-up display in a motor vehicle, the driver of the vehicle, for whom the information appearing on the head-up display is intended, has a quasi-fixed position when he is on the vehicle. driver seat while driving the vehicle. Thus, the virtual image is visible only in an area called eye box, which represents the area in which the eyes of the driver can be in normal driving conditions.

To optimize the energy performance of the projection system, the screen emits light with a strong directivity, so that most of the light output is emitted so as to be directed to the eye box.

Existing displays are generally equipped with light-emitting projection systems for illuminating at least the eye box, but these projection systems also emit light in an area around and outside the eye box. Thus, the light emitted outside the eye box is not perceived by the driver and the light power in this area is lost, which reduces the optical efficiency of the projection system. OBJECTIVES OF THE INVENTION The invention aims at overcoming at least some of the disadvantages of known projection systems.

In particular, the invention also aims to provide, in at least one embodiment of the invention, a projection system for better illumination of the eye box. The invention also aims to provide, in at least one embodiment, a projection system whose optical efficiency is improved. The invention also aims to provide, in at least one embodiment of the invention, a projection system for reducing energy consumption. The invention also aims to provide, in at least one embodiment, a projection system for the reduction of stray light. The invention also aims to provide, in at least one embodiment, a projection system for increasing the contrast of the lighting. 4. Presentation of the invention

To do this, the invention relates to a projection system for display, including head-up display, comprising: a screen, a backlight device of said screen, said backlight device comprising a plurality of light-emitting diodes emitting light in the direction of the screen, characterized in that the backlight device further comprises: a support, a plurality of light-emitting diodes arranged on the support and emitting light in the direction of the screen, the support comprising a first plurality of facets inclined relative to the plane of the screen according to a second plurality of inclinations.

A projection system according to the invention therefore allows the inclination of the light-emitting diodes to enable the illumination of the screen by the light-emitting diodes in different directions. The illumination of the screen by the light-emitting diodes allows the formation of cones or lobes of illumination, each having as a vertex a point of the screen and having as axis a line called indicator. To illuminate the eye box, the projection systems of the prior art have illumination cones all of whose indicators have the same direction, generally orthogonal to the screen. The invention thus makes it possible to obtain indicators oriented in several different directions, which allows lighting whose directions are more optimized for the application of the head-up and optimized viewfinder of the eye box. This orientation of the indicators is also carried out without the need to add an additional piece forming an optical system, such as a field lens, between the light-emitting diodes and the screen: this makes it possible to obtain a lighter, cheaper projection system. , not inducing parasitic reflection and not being sensitive to positional variations as is an optical system with respect to light emitting diodes.

Advantageously and according to the invention, the facets are flat.

According to this aspect of the invention, the facets allow better support of the light emitting diodes.

Advantageously and according to the invention, at least some facets have a different inclination of the other facets.

According to this aspect of the invention, the light-emitting diodes arranged on the facets allow the formation of illumination cones having indicators of different inclinations, in particular as a function of the distance from the top of each cone to the center of the screen.

Advantageously and according to the invention, the support comprising a center, the angle of inclination of each facet increases as the distance of each facet with the center of the support increases.

Advantageously and according to the invention, each of the facets is configured to support a single light emitting diode.

Advantageously and according to the invention, the support is formed of a heat dissipating part on which the light-emitting diodes are arranged.

According to this aspect of the invention, the heat dissipating part allows an improvement in the heat dissipation of the components of the projection system, in particular light-emitting diodes placed directly on the heat dissipating part.

Advantageously and according to the invention, the heat dissipation piece is an aluminum piece. Aluminum has a high thermal conductivity and a low density, which allows good heat dissipation performance without much impact on the total mass of the projection system. The invention also relates to a display, in particular a head-up display, comprising a semi-reflecting plate, and comprising a projection system according to the invention, adapted to project a virtual image. The invention also relates to a projection system and a display characterized in combination by all or some of the characteristics mentioned above or below. 5. List of Figures Other objects, features and advantages of the invention will become apparent on reading the following description given solely by way of non-limiting example and which refers to the appended figures in which: FIG. 1 is a diagrammatic view of a display according to one embodiment of the invention, FIG. 2 is a schematic view of a support plate and a plurality of light-emitting diodes according to the prior art, FIG. 3 is a schematic view of a system projection device according to a first embodiment of the invention, FIG. 4a is a schematic view of the illumination of the eye box by a semi-reflective optical element of a projection system according to the prior art, the FIG. 4b is a schematic view of the illumination of the eye box by a semi-reflective optical element of a projection system according to one embodiment of the invention, FIG. 5 is a diagrammatic view of A projection system according to a second embodiment of the invention, Figure 6 is a schematic view of a projection system according to a third embodiment of the invention, 6. Detailed description of an embodiment of the invention

The following achievements are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Simple features of different embodiments may also be combined to provide other embodiments.

FIG. 1 represents a display 100 comprising a projection system 10 and a semi-reflective optical element 12, according to one embodiment of the invention. The projection system 10 comprises a screen 14, for example a liquid crystal display (or LCD screen for Liquid Crystal Display in English), allowing the emission of light towards the semi-reflective optical element 12. More specifically, the light emitted by the screen 14 on the semi-reflective optical element 12 allows the formation of a virtual image 16 in the field of view of a user of the semi-reflective optical element 12, for example the driver a vehicle equipped with the semi-reflective optical element 12. To enable the formation of the virtual image, the screen 14 illuminates the semi-reflective optical element 12 according to a plurality of illumination cones whose vertices are points on the screen, each cone of illumination being defined in particular by its axis, called indicator of the cone. The semi-reflective optical element 12 allows the formation of the virtual image 16. In the context of use in a motor vehicle, this element is for example a semi-reflective plate placed between the driver and the windshield of the vehicle, or directly the windshield of the vehicle.

The driver 18 of the vehicle is here represented by one of his eyes. The objective of the screen 14 is to allow the illumination of the semi-reflective optical element 12 and thus the display of the virtual image 16 so that it is visible to the driver 18 in a zone limited to both eyes and adjusted for possible eye movements that occur under normal driving conditions. This area in which the virtual image must be visible is called an eye box. The objective of the invention is to best illuminate this eye box, so that the virtual image 16 is clearly visible to the driver 18 and to avoid the loss of optical performance due to illumination of a too wide area exceeding the eye box. The optical efficiency is the ratio between the light power of the received light on the light power of the emitted light.

FIG. 2 represents a plurality of light-emitting diodes 20, here eight light-emitting diodes arranged on a support plate 22 according to the prior art. The support plate 22 is a flat rigid plate on which the light-emitting diodes 20 are arranged to allow them to be held in place and to supply them with electrical energy. The light-emitting diodes 20 are composed of an optical portion 20a and a base 20b, and are disposed on the support plate 22 on predefined areas 21 of the support plate. Generally, the support plate 22 is a printed circuit for connecting the light-emitting diodes 20 to a power supply and any other electronic components (not shown). The use of a flat support plate 22 is encouraged in the projection systems according to the prior art for reasons of cost of manufacture and practicality of use. Nevertheless, the use of a plane support plate 22 causes the electroluminescent diodes 20 to be all situated in the same plane, and oriented in the same direction, not allowing the direction of the illumination indicators to be adjusted and therefore leads to generally an imperfect illumination of the eye box as illustrated below with reference to Figures 4a and 4b, and a drop in energy performance.

FIG. 3 represents a projection system 124 according to a first embodiment of the invention. The projected projection system 124 comprises a backlighting device 125 comprising two electroluminescent diodes 126a, 126b disposed on two facets 128a, 128b of a support 130, each inclined with respect to the plane of the screen 14. The system 124 projection device further comprises a lens array composed of two lenses 134a, 134b, each schematically represented by a circular arc, one in front of each diode 126a, 126b, allowing the collimation of the light beams from the diodes 126a, 126b. The facets 128a, 128b are inclined to allow orientation of the illumination from the diodes 126a, 126b and collimated by the lenses 134a, 134b. This orientation of the illumination allows the orientation of illumination cones 136a, 136b (or lobes of illumination), the vertices of which are points of the screen 14 and allowing the illumination of the semi-reflective optical element , and whose axes are called indicatrices 138a, 138b. The objective of the invention is the orientation of these indicators 138a, 138b to allow illumination adapted to the eye box, by an inclination of the facets 128a, 128b on which are disposed the diodes 126a, 126b. The effect of the orientation of these indicators 138a, 138b with respect to the prior art is described later with reference to FIGS. 4a and 4b.

The two facets are here planar, oriented at opposite angles, and are symmetrical with respect to the center 140 of the support 130. A central axis 142 extending from the center 140 of the support and perpendicular to the screen 14 makes it possible to represent the orientation of an indicator of the prior art perpendicular to the screen 14.

To allow the improvement of the heat dissipation at the level of the electroluminescent diodes 126a, 126b, the support 130 is formed of a dissipation piece 144 on which the diodes 126a, 126b are arranged. The dissipation piece 144 further comprises a radiator 146 for better heat dissipation of the heat emitted by the diodes 126a, 126b. The dissipation piece 144 is formed of a material having good thermal conductivity, in particular a metal and for example aluminum, which furthermore has a low density making it possible to reduce the mass of the projection system 124. As needed, electrical isolation means (not shown) are disposed between the diodes and the dissipation piece 144.

Figures 4a and 4b show the effects of this orientation on the illumination of an eye box and on the optical efficiency of the projection system.

FIG. 4a shows the illumination of an eye box by a projection system according to the prior art, by means of a semi-reflective optical element 36. An indicator 37 of an illuminating cone is represented and is perpendicular to the screen of the projection system 35. The illumination cone allows the illumination of an area 38 of the semi-reflective optical element delimited by the points 40a and 40b. A driver of a vehicle equipped with the projection system and the semi-reflective optical element can see the virtual image displayed by the semi-reflective optical element from the eye box 42, i.e. area in which the driver's eyes are likely to be located, as part of a normal driving situation. The virtual image is visible in an area delimited by two straight lines, a straight line 44 of upper display, in solid lines, and a straight line 46 of lower display, in dashed lines. The upper display line 44 indicates that the illumination exactly reaches the upper part of the eye box 42, and the lower display line 46 indicates that the illumination reaches the lower part of the eye box 42 as well as an additional interval 48 outside the eye box 42.

FIG. 4b shows the illumination of the eye box 42 by a projection system 10 according to one embodiment of the invention, by means of the semi-reflecting optical element 12. Unlike the projection system 35 according to FIG. prior art described with reference to Figure 4a, the indicator 50 shown is oriented relative to a direction perpendicular to the screen 14 of the projection system at a non-zero horizontal angle. The virtual image formed by the semi-reflective optical element is visible in an area delimited by two lines, a straight line 52 of higher reflection, in continuous lines, and a straight line 54 of lower reflection, in dashed lines. The line 52 of higher reflection indicates that the illumination exactly reaches the upper part of the eye box 42, and the straight line 54 of lower reflection indicates that the illumination reaches exactly the lower part of the eye box 42. 35 projection according to the prior art shown in Figure 4a, the projection system 10 according to this embodiment allows a more appropriate illumination of the eye box 42, illuminating only the eye box 42 without loss of illumination, thus improving the optical efficiency, thanks to the adjustment of the orientation of the indicators and the angle of opening of the illuminating cones coming from the screen. Lighting only the eye box 42 further allows the reduction of stray light and increasing the effective contrast of the virtual image.

In addition the improvement of the optical efficiency is also done through the reduction of the angle at the top of the cone. In FIG. 4a, the angle 56 at the vertex is divided into two angles 56a and 56b between the indicator and the cone, called half-angles at the vertex, of equal values since the indicator is the axis of the cone. In the same way, in Figure 4b, the vertex angle 58 is divided into two half-angles at the apex 58a and 58b. The angle 58 at the top of the cone necessary to cover the entirety of the eye box 42 and made possible by the projection system 10 according to one embodiment of the invention, is less than the angle 56 at the top of the cone obtained by the projection system 35 according to the prior art. Thus, the cone obtained by the projection system 10 according to one embodiment of the invention is narrower and therefore allows a reduction in the luminous power to be emitted to obtain the same luminous power received in the eye box 42. Advantageously, the orientation of the indicators is variable according to the position of the apex of the cones and the opening angle of the cone of illumination is constant.

In practice, if the value of the half-angles 56a, 56b at the top of the cone obtained by the projection system according to the prior art is equal to 20 ° and if the value of the half-angles 58a, 58b at the top of the cone obtained by the projection system according to one embodiment of the invention is equal to 15 °, the improvement of the optical efficiency is equal to:

In general, the difference in angle between the half-angle 56a, for example, in the system 35 according to the prior art and the corresponding half-angle 58a in the system 10 according to the invention is equal to the angle at which is oriented the indicator 50 of the system 10 relative to the direction perpendicular to the screen, that is to say the angular difference between the two indicators. In the case presented above, the indicator is

oriented 20-15 = 5 ° with respect to the direction perpendicular to the screen. For an orientation of 3 °, the improvement of the optical efficiency according to the preceding formula is 1.44, ie substantially 40% of additional perceived light power in the eye box 42.

FIGS. 5 and 6 show projection systems according to a second and a third embodiment of a projection system according to the invention, comprising respectively four and eight light-emitting diodes, each of the diodes being arranged on one facet. These embodiments are derived from the first embodiment described with reference to FIG. 3, and the elements already described with reference to FIG. 3 are designated by the same references. The illumination from the screen 14 is represented in these figures by lobes 144 of illumination having as an axis the illumination indicatrices. The set of facets makes it possible to obtain a support equivalent to an approximation of a sphere portion, on the surface of which the light-emitting diodes are arranged. The accuracy of the sphere portion approximation to a real sphere portion increases with increasing number of facets. The use of planar facets allows for better support of light-emitting diodes, which generally have a flat base.

The angles of inclination of the facets is the combination of two angles, called angle Θ horizontal and angle φ vertical, corresponding to the inclination of the indicators obtained thanks to the facets with respect to the central axis 142 respectively in the plane defined by the central axis 142 and a horizontal axis 146, and in the plane defined by the central axis and a vertical axis 148. The horizontal axis 146, the vertical axis 148 and the central axis 142 form an orthogonal reference. The inclination of the facets is thus represented by the pair (θ, φ).

The projection system according to the second embodiment of the invention shown in FIG. 5 comprises a backlighting device 149 comprising four electroluminescent diodes 150a, 150b, 150c, 150d disposed respectively on four inclined facets 152a, 152b, 152c, and 152d. In this embodiment, the facets 152a, 152b, 152c, 152d are inclined respectively by (-1 °, -1 °), (1 °, -r), (-i °, Γ), (Γ, Γ).

The projection system according to the third embodiment of the invention shown in FIG. 6 comprises a backlighting device 153 comprising eight light-emitting diodes 154a, 154b, 154c, 154d, 154e, 154f, 154g, 154h arranged on eight facets 156a. 156b, 156c, 156d, 156e, 156f, 156g, 156h inclined. In this embodiment, the facets 156a, 156b, 156c, 156d, 156e, 156f, 156g, 156h are, for example, respectively inclined by (-3 °, -1.5 °), (-1 °, -1.5 °, (1 °, -1.5 °), (1 °, 3 °), (-3 °, 1.5 °), (-1 °, 1.5 °), (1 °, 1, 5 °), (3 °, 1.5 °). This third embodiment advantageously replaces the plurality of diodes and the support plate according to the prior art described above with reference to FIG. 2. In this embodiment, the inclination of the facets 156a to 156h is all the more important. that the facet is far from the center of the support. Thus, at the level of the screen, the illumination indicatrices of the electroluminescent diodes 154a to 154h are all the more inclined that they are distant from the center of the screen. The invention is not limited to the embodiments described. In particular, the invention adapts to the number of electroluminescent diodes of the projection system, which may be odd, greater than eight, and so on. The number of electroluminescent diodes of the projection system depends on the complexity of the desired illumination and the necessary light output. The facets can be flat, curved or curved, totally or partially.

Claims (7)

A display projection system, including a head-up display, comprising: a display (14), a backlighting device (125,149,153) of said display, said backlighting device (125,149,153) comprising a plurality of light-emitting diodes (126, 150, 154) emitting light towards the screen (14), characterized in that the backlighting device (125, 149, 153) further comprises: a carrier (130), a plurality of electroluminescent diodes (126, 150, 154) disposed on the support (130) and emitting light toward the screen (14), the carrier (130) having a first plurality of facets (128, 152, 156) inclined relative to at the plane of the screen (14) at a second plurality of inclinations and in that the support (130) is formed of a heat-dissipating part (144) on which the light-emitting diodes (126, 150, 154) are disposed. 2. Projection system according to claim 1, characterized in that the facets (128, 152, 156) are planar. 3. projection system according to one of claims 1 or 2, characterized in that at least some facets (128, 152, 156) have a different inclination of the other facets (128,152,156). 4. projection system according to one of claims 1 to 3, characterized in that, the support (130) comprising a center (140), the inclination angle of each facet (128,152, 156) increases as the distance of each facet (128, 152, 156) with the center (140) of the support increases. Projection system according to one of claims 1 to 4, characterized in that each of the facets (128, 152, 156) is configured to support a single light emitting diode (126, 150, 154). 6. projection system according to one of claims 1 to 5, characterized in that the piece (144) of heat dissipation is aluminum. 7. Display, in particular head-up display, comprising a semi-reflective optical element (12), characterized in that it comprises a projection system (10) according to one of claims 1 to 6, adapted to allow the formation of a virtual image (16).