WO2020126352A1

WO2020126352A1 - Power mirror for a head-up display device, head-up display device comprising such a mirror and mould for manufacturing such a mirror

Info

Publication number: WO2020126352A1
Application number: PCT/EP2019/082604
Authority: WO
Inventors: Armand Divine; François GRANDCLERC; Pierre Mermillod; Pierre-Alain Tremblin
Original assignee: Valeo Comfort And Driving Assistance
Priority date: 2018-12-18
Filing date: 2019-11-26
Publication date: 2020-06-25
Also published as: FR3090141B1; FR3090141A1

Abstract

The invention relates to a power mirror (14) for a head-up display device (10) intended for being mounted in a vehicle (1) for driving on the left and in a vehicle for driving on the right, the power mirror having a reflective surface (16), a representative equation of which, in a frame of reference (Ω, Χ, Υ, Ζ) associated with the power mirror, where the Z axis corresponds to a normal to the reflecting surface at the centre Ω thereof, comprises a polynomial component of the type: ∑m,n ρm,n xm yn, where m and n are natural integers and the polynomial coefficients ρm,n of the representative equation are real numbers. According to the invention, the polynomial coefficients ρm,n in odd power of y or the polynomial coefficients ρm,n in odd power of x are substantially zero. The invention also relates to a head-up display device comprising such a mirror. The invention finally relates to a mould designed for manufacturing such a mirror.

Description

DESCRI PTION

TITLE: M A KING OF POWER FOR THE HEAD-UP DISPLAY F, DISPOSITI F

HEAD-UP DISPLAY COMPRISING SUCH A MIRROR AND MOLD FOR MANUFACTURING A

SUCH A MIRROR

TECHNICAL AREA TO WHICH THE INVENTION RELATES

The present invention relates generally to the field of driver assistance systems for vehicles.

It relates more particularly to a power mirror for a head-up display device intended to be mounted in a left-hand drive vehicle and in a right-hand drive vehicle.

It also relates to a head-up display device comprising such a power mirror.

Finally, it relates to a mold designed for the manufacture of such a power mirror.

TECHNOLOGICAL BACKGROUND

Vehicles are known which are fitted with a head-up display device comprising a power mirror which is designed to enlarge and focus a virtual image to be projected to an occupant of the vehicle.

In the present application, the expression “power mirror” will be understood to mean a mirror having a non-zero optical power. In practice, such a power mirror is a mirror which is non-planar.

Such a power mirror includes a reflecting surface whose shape (ie its geometry) is determined as a function not only of the size, of the distance of the desired virtual image, but also of the optical design internal to the head display device. -high.

In particular, head-up display devices known as “on windshields” are known in which the projection of the virtual image to the occupant of the vehicle is carried out ultimately by optical reflection on the windshield of said vehicle ( actually on its internal sheet).

In this particular case, the shape of the power mirror is therefore also determined as a function of the geometry and the inclination of the vehicle windshield to guarantee good image quality of the virtual image projected to the occupant.

We then know of freeform type power mirrors which are particularly suitable for obtaining satisfactory image quality at the right projection distance.

In known manner, such a power mirror has a reflecting surface, a representative equation of which, in a frame (W, C, U, Z) linked to said power mirror where the Z axis corresponds to a normal to said sound reflecting surface center W, includes a polynomial component of the type: åm, n pm, nx ^m y ⁿ , where m and n are natural whole numbers (0, 1, 2, 3, etc ...) and the polynomial coefficients pm, n of said representative equation are real numbers (positive or negative).

In the coordinate system (W, C, U, Z), the X and Y axes are two axes orthogonal to each other and each with the Z axis also.

The representative equation above describes the location of the points M which belong to the reflecting surface of the power mirror: the variables (x, y, z) of this equation correspond to the coordinates (x, y, z) of these points M in the frame of reference (W, C, U, Z) linked to the power mirror. These coordinates (x, y, z) therefore verify said representative equation.

The polynomial component mentioned above is for example a contribution to the expression of the z coordinate (coordinate along the Z axis). In other words, the equation representative of the reflecting surface can be written as an expression of the coordinate z as a function of the coordinates x and y, this expression comprising the polynomial component åm, n pm, nx ^m y ⁿ .

Still in the representative equation, the symbol "åm, n" corresponds to the double summation operation on the indices m and n.

In other words, the polynomial component of the equation representative of the reflecting surface of the power mirror is written (only the first few polynomial terms are reported):

po, o + pi, ox + po, iy + p2, ox ² + pu xy + po, 2 y ² + ...

p3, ox ³ + p2, ix ² y + p 1, 2 xy ² + po, 3 y ³ + p4, ox ⁴ + p3, ix ³ y + ....

In practice, the representative equation below presents finite degrees mo and no for the polynomial terms, mo and no being non-harmful natural numbers.

In other words, we can consider that the polynomial coefficients pm, n for which m> mo or n> no are rigorously harmful (mo and no being two non-harmful natural integers). This reflects the fact that the exact geometry of the reflecting surface of the power mirror cannot be determined with unlimited precision, the instruments for measuring this surface (mechanical profilometer or optical interferometer for example) always having limited precision.

In reality, the power mirror obviously has a determined finite size, its dimensions Lx, LY respectively along the axes X and Y of the reference frame (W, C, U, Z) linked to said power mirror are therefore limited.

Consequently, the coordinates (x, y, z) in the coordinate system (W, C, U, Z) of a point M belonging to the reflecting surface of the power mirror (these coordinates (x, y, z) then checking the representative equation above) are such that (the reference (W, C, U, Z) originating from the center W of the power mirror):

-Xmax £ X £ + Xmax and -ymax— y— + ymax.

The magnitudes Xmax and ymax are linked to the dimensions Lx, LY along the axes X and Y of the power mirror by the relationships: Xmax = Lx / 2 and ymax = LY / 2.

Note, however, that even if the shape of a power mirror is generally close to a rectangle (of dimensions Lx and LY), it can sometimes be cut into a more complex shape.

The power mirrors known for display device on windshield are different for left-hand drive vehicles (vehicle driver on the left) and right-hand drive vehicles.

The areas of the windshield used for head-up display devices mounted on the left and those mounted on the right are different.

As the vehicle windshields are generally symmetrical with respect to a plane separating the left and the right (see for example plane (Cn, Zn) in FIGS. 3 and 4), a solution for obtaining good image quality at left and right is to mirror the entire display device, and in particular the power mirror.

Thus, the "right" power mirror of a head-up display device intended for a right-hand drive vehicle is the symmetrical - with respect to this plane separating the left and the right - of the "left" power mirror a head-up display device for a left-hand drive vehicle.

Like a chiral molecule in chemistry which has two enantiomers, the "left" power mirror cannot be superimposed on the "right" power mirror.

As a result, it is necessary to use two types of tools (eg: injection molds for plastic power mirrors or forming molds for glass power mirrors) which are different for manufacturing, on one side, a power mirror for a head-up display device on windshield intended to be mounted in a left-hand drive vehicle, and, on the other hand, a power mirror for a head-up display device on the windshield intended to be mounted in a left-hand drive vehicle right.

This generates a complexity of industrial implementation as well as additional manufacturing costs.

OBJECT OF THE INVENTION

In order to overcome the aforementioned drawback of the state of the art, the present invention provides a power mirror for a head-up display device which has a reflective surface of suitable shape and which is equally suitable for a driving vehicle. on the left than for a right-hand drive vehicle.

More particularly, a first alternative of the invention is proposed a power mirror as defined in the introduction, in which said polynomial coefficients pm, n in odd power of are substantially affected.

According to a second alternative of the invention, there is also provided a power mirror as defined in the introduction, in which said polynomial coefficients pm, n in odd power of x are substantially harmful.

Indeed, a power mirror in which the polynomial coefficients pm, n of the polynomial component of the equation representative of its reflecting surface in odd power of y are substantially affected can be integrated into a head-up display device on the screen. -brise for left-hand drive vehicle, or to a head-up display device on windshield for right-hand drive vehicle simply by turning it 180 ° around its Z axis (normal to the center W of the mirror) .

In other words, the "left" power mirror and the "right" power mirror perfectly overlap (i.e. they are no longer "enantiomers"). In other words, the reflecting surface of such a power mirror is symmetrical with respect to the plane (X, Z) of its linked frame (W, C, U, Z).

Thus, thanks to the power mirror of the invention, it is possible to use only one manufacturing tool (eg a mold) to make this "freeform" power mirror, which is equally suitable for a head-up display device on a windscreen for left-hand drive vehicles than for a device head-up display on windshield for right-hand drive vehicle.

In other words, the same mirror can be used in both types of vehicles to have only one mold. The reflecting surfaces of the two power mirrors ("left" and "right") are therefore defined by the same representative equation.

Consequently, the manufacture of such a power mirror is simpler to implement and the costs of manufacturing such a mirror are reduced.

Finally, it should be noted that, when designing the power mirror of the invention, it is necessary to take into account its two uses - driving on the right and on the left - so as not to degrade the image quality.

The other alternative proposed in the invention - a power mirror of which all the polynomial coefficients pm, n in odd power of x are substantially harmful - corresponds to a technical solution where the "left" power mirror and the "power mirror" right ”are the image of each other by a translation from left to right (or vice versa), that is to say parallel to the windshield or perpendicular to the plane separating the left and the right.

In other words, according to this other alternative, the reflecting surface of the power mirror is symmetrical with respect to the plane (Y, Z) of its linked frame (W, C, U, Z).

Again, according to this solution, the “left” power mirror and the “right” power mirror can be superimposed perfectly, and therefore only one tool is necessary for their manufacture.

By “polynomial coefficients p _m , n in odd power of y”, we mean all the polynomial coefficients pm, n of the representative equation for which n is an odd natural number (n = 1, 3, 5, etc ... ), i.e. there is a natural integer I (I = 0, 1, 2, etc.) such that n = 21 + 1. In other words, these are the following polynomial coefficients: p _{m, i} , pm, 3, pm.s, etc ... (m being any natural integer, even or odd).

In the same way, by “polynomial coefficients p _m , n in odd power of x”, we mean all the polynomial coefficients pm, n of the representative equation for which m is an odd natural number (m = 1, 3, 5 , etc ...), that is to say that there exists a natural integer k (k = 0, 1, 2, etc ...) such that m = 2k + 1. In other words, these are the following polynomial coefficients: pi, _n , p3, n, ps.n, etc ... (n being any natural number, even or odd).

In practice, it will also be noted that in all the equations representative of the reflecting surface of the power mirror of the invention, the polynomial coefficient po, o is strictly zero insofar as the center W of the power mirror, of coordinates ( 0,0,0), is the origin of the coordinate system (W, C, U, Z).

The polynomial coefficients po, i and pi, o of the polynomial component of the representative equation are also harmful since they correspond to an inclination of the power mirror relative to the Z axis (normal to the reflecting surface).

By “polynomial coefficient p _{m, n} in odd power of y (respectively x) substantially zero”, it will be understood that, in the polynomial component of the equation representative of the reflecting surface of the power mirror, the contribution of the term polynomial in odd power of y (respectively x) associated with this polynomial coefficient pm, n = 2i + i (respectively pm = 2k + i, n), i.e. the polynomial term p _m , 2i + ix ^m y ^{2l + 1} (respectively the polynomial term p2k _{+ i,} nx ^{2k + 1} y ⁿ ), is negligible compared to the contributions of the polynomial terms in even power of y (respectively of x), ie the polynomial terms pm, nx ^m y ⁿ with n even (respectively the polynomial terms pm, nx ^m y ⁿ with m even).

In other words, this means that the polynomial component of the reflecting surface of the power mirror is not (or only slightly) defined by the polynomial coefficients pm, n in odd power of y (respectively of x).

Mathematically, we will consider that a polynomial coefficient pm, n in odd power of y for m any natural integer (even or odd) and n odd natural integer (ie h = 2I + 1, I natural integer) is substantially zero, if the following relation is checked (m and n being thus fixed):

natural and any even r natural integer (i.e. r = 2t, t any natural integer).

The quantities Xmax and ymax are the quantities defined above in connection with the dimensions of the power mirror. The symbol "| | "Is the absolute value.

In the same way, the mathematical relation that must be verified by a polynomial coefficient pm, n in odd power of x for m odd natural integer (ie m = 2k + 1, k natural integer) and n any natural integer (even or odd), for that it is considered to be "substantially zero" is as follows:

even natural (i.e. q = 2s, s any natural integer) and any r natural integer.

The symbol "" >> in the two previous relationships means "very less than / negligible compared to".

Thus, we could say that the polynomial coefficient pm, n in odd power of y (n = 21 + 1) is substantially zero if there is a real number e strictly positive sufficiently small, such as for any natural integer q and all r even natural number (r = 2t), the following relation is verified:

(| pm, n = 2l + l | / | p _q, r = 2t |). (| Xmax ^m_q . Ymax ^{(2l + 1) _2t} |) <£.

Similarly, we could say that the polynomial coefficient pm, n in odd power of x (m = 2k + 1) is substantially zero if there is a real number e 'strictly positive sufficiently small, such that for any natural integer q even (q = 2s) and any natural r, the following relation is verified:

In theory, the real numbers e and e 'can depend on m and n.

However, in practice, we will take real numbers e and e 'fixed (i.e. independent of m and n) and equal, for example equal to 0.01, preferably equal to 0.001, better equal to 0.0001.

In a preferred embodiment of the invention, said polynomial coefficients pm, n of the polynomial component of the equation representative of the reflecting surface of the power mirror are substantially damaged when the inequality m + n> 6 is verified (by e.g. m = n = 4, m + n = 8> 6) for the indices m and n (even or odd) of the polynomial coefficients p _m, n.

The expression "substantially harmful" here has the same meaning as before (see above).

In this preferred embodiment, the polynomial component of the reflecting surface of the power mirror is a “order 6” surface and is therefore represented by an equation of the type (ro, o = ri, o = po, i = 0 , see above):

(1): p2, ox ² + po, 2 y ² + p3, ox ³ + pi, 2 xy ² + p4, ox ⁴ + p2,2 x ² y ² + po, 4 y ⁴ + p5, ox ⁵ + p3.2 x ³ y ² + pi, 4 xy ⁴

+ pe, ox ⁶ + p4.2 x ⁴ y ² + p2.4 x ² y ⁴ + po, ey ⁶ ; or

(2): p2, ox ² + po, 2 y ² + p2, ix ² y + po, 3 y ³ + p4, ox ⁴ + p2,2 x ² y ² + po, 4 y ⁴ + P4, ix ⁴ y + p2.3 x ² y ³ + po, sy ⁵ + pe, ox ⁶ + p4.2 x ⁴ y ² + p2.4 x ² y ⁴ + po, ey ⁶ .

The type (1) corresponds to a power mirror according to the invention where the polynomial coefficients pm, n in odd power of y are substantially harmful (we have therefore omitted above the corresponding polynomial terms in the equation) and the type (2) to the one where the polynomial coefficients pm, n in odd power of x are substantially harmful (corresponding polynomial terms also omitted).

The equation representative of the reflecting surface of the power mirror is written for example in a form of the type: z = a K (x, y) + åm, n pm, nx ^m y ⁿ , where K is a function of revolution around said Z axis and has a real constant

By “revolution function”, we mean that the function K depends only on the variable r ² = x ² + y ² , r being the distance from point M to the axis Z.

In the representative equation, the real constant a can be non-zero, being positive or negative.

In the two alternatives proposed above, there is no particular condition which should satisfy the function of revolution K. Indeed, this one being - by definition - of revolution, it corresponds to a surface which is as well symmetrical with respect to the plane (X, Z) than with respect to the plane (Y, Z) of the coordinate system (W, C, U, Z) linked to the power mirror.

In a particular embodiment, the revolution function K is a conical function of the form: K (x, y) = c (x ² + y ² ) / {1 + [1 - (1 + k) c ² ( x ² + y ² )] ^1/2 }, where c is a real constant, and k a real constant such that k.

In practice, the constant c corresponds to a curvature of the surface associated with the function of revolution K. This curvature is equal to the inverse of the radius of curvature of this surface of revolution around the axis Z of the power mirror.

The constant k (or "conical" constant) determines the type of conical surface of revolution around the Z axis.

In another particular embodiment, the function of revolution K can include an aspherical function (of revolution around the axis Z) of the form: K (x, y) = åi a \ (x ² + y ² ) ' , where i is a non-zero natural integer (i = 1, 2, 3, etc ...), and the aspherical coefficients a \ are real numbers (positive or negative).

In practice, for the same reasons of measurement accuracy mentioned above for the polynomial coefficients p _m, n, the aspheric coefficients a \ are such that ai 0 for i> io, io being a non-zero natural integer.

The invention also provides a head-up display device intended to be mounted in a left-hand drive vehicle and in a right-hand drive vehicle, said device comprising:

an image generation unit adapted to emit a light beam representative of a scene; and

at least one power mirror according to the invention.

In a preferred embodiment of said head-up display device, said power mirror is configured to reflect said light beam emitted towards a windshield of said vehicle, said windshield projecting said scene to an occupant of said vehicle .

In the various embodiments of the device presented above, said image generation unit may comprise either a screen module of the TFT-LCD type, or a laser module of the laser-scan type, or a projection module of the DLP type.

The invention finally proposes an injection or forming mold designed for the manufacture of such a power mirror.

As explained above, such a mold allows the manufacture of a power mirror which is suitable for both a left-hand drive vehicle and a right-hand drive vehicle.

In practice, such a mold has a particular surface, a characteristic equation of which is written in the same form as the representative equation of the reflecting surface of the power mirror to be manufactured.

In other words, when the power mirror is symmetrical with respect to the plane (X, Z) of its coordinate system, this characteristic equation is such that the odd power contributions of y are zero. When the power mirror is symmetrical with respect to its plane (Y, Z), it is the odd power contributions of x which are zero.

Advantageously, the particular surface of the mold can be adapted so as to take into account the variation in the shape of the reflecting surface after molding, for example because of its cooling.

DETAILED DESCRIPTION OF AN EXAMPLE OF IMPLEMENTATION

The description which follows with reference to the appended drawings, given by way of nonlimiting examples, will make it clear what the invention consists of and how it can be achieved.

In the accompanying drawings:

[Fig. 1] is a schematic overall view of a motor vehicle comprising a head-up display device according to the invention;

[Fig. 2] is a perspective view of a power mirror according to the invention entering into the architecture of the head-up display device of FIG. 1;

[Fig. 3] is a view showing a power mirror according to a first embodiment when the mirror is mounted in a left-hand drive vehicle and in a right-hand drive vehicle; and

[Fig. 4] is a view showing a power mirror according to a second embodiment when the mirror is mounted in a left-hand drive vehicle and in a right-hand drive vehicle.

In the preamble, it will be noted that the identical or similar elements of the different embodiments shown in the different figures will be referenced by the same reference signs and will not be described each time.

In Figure 1, there is shown a vehicle 1, here a motor vehicle, in which is mounted a head-up display device 10, hereinafter called "head-up display" or more simply "display".

As we will see in the following description, this display 10 can be mounted as well in a left-hand drive vehicle (ie with the driver and the steering wheel positioned in the left part of the passenger compartment of the vehicle 1) as in a right-hand drive vehicle (ie with the driver and the steering wheel positioned in the right-hand part of the passenger compartment of vehicle 1). Consequently, the vehicle 1 in FIG. 1 can be both a left-hand drive vehicle and a right-hand drive vehicle.

In operation, the display 10 projects information in the form of images 6 into the field of vision of an individual 4 located inside the vehicle 1 (left or right). In FIG. 1, the individual 4 is represented diagrammatically in the form of one of his eyes.

This individual 4 observes, through the windshield 3 of the vehicle 1, the images 6 which are projected in an observation direction 5, outside the vehicle 1, here at the level of the hood 2 of the vehicle 1. In practice, images 6 are formed at an image distance from the individual 4 which is generally between 1.5 and 5 meters (up to 12 meters for head-up displays of the "augmented reality" type).

It will be considered in the following description that the individual 4 is here the driver (left or right) of the vehicle 1. As a variant, this could be a front or rear passenger of the vehicle.

The projected images may include, for example, information relating to vehicle 1 (speed, engine speed, fuel level, distance from other vehicles, etc.), to its environment (presence of pedestrians, traffic signs, etc. ...), or even instructions as to the route to be followed by vehicle 1 (in combination with an on-board navigation system for example).

As shown in FIG. 1, the display 10 according to the invention comprises an image generation unit 11 and a power mirror 14.

The image generation unit 11 emits a light beam 13 (in FIG. 1, only a primary light ray is shown) in the direction of the power mirror 14 of the display 10. This light beam 13 is representative of a light scene, including the images to be displayed to occupant 4 of vehicle 1.

In the particular embodiment illustrated in FIG. 1, the image generation unit 1 1 here comprises a screen module 12 of the TFT-LCD type (hereinafter designated "screen" 12) which is a type of 'thin film transistor liquid crystal display (' TFT-LCD 'means' Thin-Film Transistors-Liquid Crystal Display' in English).

The screen 12 forms a display surface, generally substantially planar, of the image generation unit 1 1 on which said light scene is displayed, this light scene therefore corresponding to the emission of the light beam 13.

The image generation unit 1 1 is generally connected to a control module (not shown) of the screen 12, this control module receiving signals from the on-board computer (not shown) of the vehicle 1 and consequently driving the screen 12 to display the light scene thereon.

In other words, when the screen 12 is controlled by the control module, the image generation unit 11 generates a light beam 13 representing the scene to be projected in the driver's field of vision 4.

Alternatively, the image generation unit may include a laser module of the "laser-scan" type. In this case, the light scene is then produced on a diffuser whose surface is scanned by a fine laser beam which generally comes from an illumination system comprising scanning optics (including, for example, galvanometric mirrors and one or more lenses) and one or more laser diodes (e.g. red, green, blue diodes).

In another variant, the image generation unit may include a projection module of the DLP (“Digital Light Processing” in English) type.

As seen previously, the display 10 also includes a power mirror 14 having a particular shape (see below with reference to FIGS. 2 to 4) so that it can be used both in a display 10 for a vehicle driving with left than in a display 10 for right-hand drive vehicles.

This power mirror 14 is here formed of a curved blade of small thickness, typically between 2 and 5 millimeters, having a rear face 15 and a front face 16, the latter facing the screen 12 (see FIG. 1). .

In certain embodiments, the power mirror 14 can be made of transparent plastic, for example polycarbonate, polymethyl methacrylate (PMMA), or cycloolefin copolymers (COC). In this case, it can be manufactured hot using an injection molding process or else a reaction injection molding process (“Reactive Injection Molding”). This then requires the use of an injection mold having a cavity whose shape is adjusted very precisely to be complementary to that of the power mirror 14 to be manufactured.

According to the invention, such an injection mold is advantageously designed for the manufacture of the power mirror s. In particular, the cavity used for the injection of the plastic material intended to produce the power mirror 14 has a particular surface, a characteristic equation of which is written in the same form as the equation representative of the reflecting surface 16 of the reflecting mirror. power 14.

As injection molding is a process carried out at high temperature, the shape of the power mirror 14 - and therefore of its reflecting surface - changes when it cools after demolding to reach room temperature (typically between 20 ° and 25 °).

Thus, it can be expected that the particular surface of the cavity of the injection mold is slightly different from that of the power mirror 14 to precisely take account of variations in shape with temperature.

In other embodiments, the power mirror 14 can be made of mineral glass, for example a silica-based glass (“soda lime” glass) or else a borosilicate glass (N-BK7 glass from the company Schott for example). In this case, it can be manufactured by forming from a flat blade of glass (as can be the two layers of the windshield 3) which, brought to high temperature, softens and collapses on a form mold. adjusted.

This forming mold can advantageously be designed for the manufacture of the power mirror s. Such a forming mold comprises, for example, a "skeleton", a particular surface of which has an equation characteristic of the same shape as the equation representative of the reflecting surface 16 of the power mirror 14.

As for the injection mold described above, the particular surface of the skeleton can be adapted so that the reflecting surface 16 of the power mirror 14 has the desired shape after cooling to room temperature.

The front face 16 of the power mirror s is covered with a reflective coating (not visible in the figures) so as to form a reflective surface of the power mirror 14. This reflective coating here comprises a thin layer of silver or aluminum (typically a few tens of nanometers) deposited on the front face 16 (possibly by means of a primary layer) and then covered with a coating (silicon or titanium coating) to prevent its oxidation.

Advantageously, the rear face 15 is - for its part - covered with an anti-reflection treatment (AR) intended to reduce parasitic reflections on this rear face 15 (these parasitic reflections can create “ghost” images of the light scene at project).

The reflective coating of the reflecting surface 16 and the AR treatment of the rear face 15 are adapted as a function of the spectral content of the light beam 13 source emitted by the screen 12 in the direction of the mirror. power 14.

In practice, the reflective coating is such that the average reflectivity over the wavelength range of the light beam 13 is greater than 50%, preferably greater than 90%, for example equal to 95%.

In the case of a “tri-chromatic” screen 12, that is to say formed of pixels of three different colors (typically red, green and blue), the light beam 13 then having a light spectrum comprising three “peaks” More or less wide and intense around three different lengths, the reflective coating (respectively the AR treatment) is then optimized to reflect (respectively to minimize the reflection) in each band of wavelengths associated with each of these peaks.

The same is true when the image generation unit includes a laser module of the laser-scan type. In this case, the relevant wavelength bands are those of the emission of the laser diodes from the laser module.

Advantageously, and as shown in FIG. 1, the power mirror 14 is configured (ie arranged) to reflect the light beam 13 emitted towards the windshield 3 of the vehicle 1, the windshield 3 projecting the scene at occupant 4 of vehicle 1.

The light beam 13 is reflected by the power mirror 14 (more precisely by its reflecting surface 16) in a first reflected beam 17 which is then itself reflected by the windshield 3 (in fact by the internal sheet of the windshield breeze 3) in a second reflected beam 18 to the driver 4 of the vehicle 1. This second reflected beam 18 is oriented in the direction of observation 5 (direction of gaze of the individual 4), the image 6 of the projected light scene then being a virtual image generally formed above the hood 2 of the vehicle 1 .

It will be noted here that the geometry of the power mirror 14, and more particularly of its reflecting surface 16 is firstly determined so that the image 6 of the scene projected by the display 10 on the windshield of the invention:

is located at a predetermined nominal distance from the driver 4 of the vehicle 1;

have the desired dimensions (width and height) seen at this nominal distance; and

presents a satisfactory optical image quality for the individual 4.

To satisfy these different criteria, a mirror is used here. power 14 which is of the “freeform” type, that is to say having a reflecting surface 16 including a representative equation, in a frame (W, C, U, Z) linked to the power mirror s where the axis Z corresponds to a normal to the reflecting surface 16 at its center W (see Figure 2), is written in a form of the type: z = a K (x, y) + åm, n pm, nx ^m y ⁿ , where:

K is a function of revolution around the Z axis and has a real constant (positive, negative or zero);

m and n are natural whole numbers (0, 1, 2, 3, etc ...); and pm, n are polynomial coefficients of the representative equation, these polynomial coefficients pm, n being real numbers.

As shown in Figure 2, the X and Y axes of the coordinate system (W, C, U, Z) are two axes orthogonal to each other and to the Z axis.

The representative equation above describes the location of the points M which belong to the reflecting surface 16 of the power mirror s (see FIG. 2): the variables (x, y, z) of this equation correspond to the coordinates (x, y , z) of these points M in the coordinate system (W, C, U, Z) linked to the power mirror 14. These coordinates (x, y, z) therefore verify the representative equation.

Thus, as explained in the introduction, the reflecting surface 16 of the power mirror 14 has a representative equation in the coordinate system (W, C, U, Z) which is written in the following form (the coefficients ro, o, pi, o and po, i being zero, see explanation above):

z = a K (x, y) + p2, ox ² + pu xy + po, 2 y ²

+ p3, ox ³ + p2, ix ² y + pi, 2 xy ² + po, 3 y ³ + p4, ox ⁴ + p3, ix ³ y + ....

The representative equation therefore includes a polynomial component of the type:

p2, ox ² + pu xy + po, 2 y ² + p3, ox ³ + p2, ix ² y

+ pi, 2 xy ² + po, 3 y ³ + p4, ox ⁴ + p3, ix ³ y + ....

As shown in FIG. 2, the reflecting surface 16 has, along the axes X and Y of the reference frame (W, C, U, Z) which are linked to it, of the respective dimensions Lx and LY.

We are interested below for the sake of simplification in embodiments for which the representative equation includes only the aforementioned polynomial component (which amounts to taking a = 0 in the above equation). In other embodiments, however, the constant a could be non-zero (being positive or negative).

In other words, in these embodiments, there is no contribution of the function K to the equation of the reflecting surface 16.

This does not harm the generality of the presentation insofar as this contribution is of revolution around the axis Z, and is therefore symmetrical according to the planes (X, Z) and (Y, Z) of the power mirror 14 .

In the embodiment presented in FIG. 2, the dimensions Lx and LY are such that the reflecting surface 16 typically has the size of a sheet A5 (148 mm x 210 mm), or even A4 (210 mm x 297 mm).

The coordinates (x, y, z) in the coordinate system (W, C, U, Z) of a point M belonging to the reflecting surface 16 (which therefore verify the representative equation above) are such that (the coordinate system (W, C, U, Z) originating from the center W of the power mirror 14): -Xmax <x <+ Xmax and -ymax <y <+ y _ma x.

In other words, the magnitudes Xmax and ymax are linked to the dimensions Lx, LY along the axes X and Y of the power mirror 14 by the relationships: Xmax = Lx / 2 and ymax = LY / 2.

According to a first embodiment illustrated in FIG. 3, the power mirror of the display 10 is such that the polynomial coefficients p _m, n in odd power of y are substantially affected (the meaning of the expression "substantially affected" is the one given in the introduction).

Consequently, the representative equation of the reflecting surface 16 is written in the following polynomial form:

z = p2, ox ² + po, 2 y ² + p3, ox ³ + pi, 2 xy ²

+ p4, ox ⁴ + p2.2 x ² y ² + po, 4 y ⁴ + ....

As shown in Figure 3 schematically, a power mirror of this type can be used both in a windshield display for a left-hand drive vehicle (case of the 14G "left" power mirror) as in a display on windshield for a right-hand drive vehicle (case of the 14D “right” power mirror).

The respective positions of the two power mirrors 14G, 14D are then symmetrical with respect to a separation plane 7 separating the left and the right part of the windshield 3 of the vehicle 1 (the mark (Cn, Un, Zn) corresponds to a reference linked to the vehicle 1).

Furthermore, it can be shown in this case that the power mirror 14D "Right" is obtained by 180 ° rotation of the power mirror 14G "left" around its normal Z. Thus, the two power mirrors 14G, 14D have exactly the same geometry (ie the shape of the reflecting surface is identical) and can be manufactured with a single production tool, for example a single injection mold (in the case of plastic power mirrors).

Preferably, the power mirror 14 is designed so that the polynomial coefficients pm, n of the equation representative of its reflecting surface 16 are appreciably affected if the indices m and n of said polynomial coefficients pm, n are such that m + n > 6 (ie m + n> 7). In this preferred case, the power mirror 14 _"freeform" can be described as mirror "of the ^6th order."

The representative equation of the reflecting surface 16 can then be written (approximately, considering pm, n "0 if m + n> 6 or if n is odd) in the following simplified polynomial form:

z = p2, ox ² + po, 2 y ² + p3, ox ³ + pi, 2 xy ² + p4, ox ⁴ + p2,2 x ² y ² + po, 4 y ⁴ + p5, ox ⁵ + p3, 2 x ³ y ² + ft, 4 xy ⁴

+ pe, ox ⁶ + p4.2 x ⁴ y ² + p2.4 x ² y ⁴ + po, ey ⁶ .

As an illustrative example, the polynomial coefficients pm, n (for m + n <6) of the reflecting surface 16 of a power mirror 14 (of the 6 ^th have been reported in the table below (Table 1). order) according to the first embodiment described above:

[Table 1]

We check in Table 1 above that the polynomial coefficients pm, n in odd power of y (ie the coefficients pi, i, p2, i, po, 3, etc ...) are appreciably harmful (in the sense defined above).

According to a second embodiment illustrated in FIG. 4, the power mirror of the display 10 is such that the polynomial coefficients pm, n of the equation representative of the reflecting surface 16 which are in odd power of x are substantially harmful (same meaning as before).

z = p2, ox ² + po, 2 y ² + p2, ix ² y + po, 3 y ³

+ p4, ox ⁴ + p2.2 x ² y ² + po, 4 y ⁴ + ....

As shown in Figure 4 schematically, a power mirror of this type can be used both in a windshield display for a left-hand drive vehicle (case of the 14G "left" power mirror) as in a display on windshield for a right-hand drive vehicle (case of the 14D “right” power mirror).

As before, the respective positions of the two power mirrors 14G, 14D are always symmetrical with respect to a separation plane 7 separating the left and the right part of the windshield 3 of the vehicle 1 (the mark (Cn, Un, Zn ) corresponds to a reference linked to the vehicle 1).

It can be shown in this particular embodiment that the “right” power mirror 14D is obtained simply by translation of the “left” power mirror 14G along the axis Yv of the vehicle (see FIG. 4).

The two power mirrors 14G, 14D therefore have the same geometry and can be manufactured with the same production tool.

Similarly as above, the mirror power s of the second embodiment may be designed to be a mirror "of the ^6th order 'polynomial coefficients am, n in the equation representative of its reflective surface 16 are then substantially harm if the indices m and n of said polynomial coefficients pm, n are such that m + n> 6. The equation representative of the reflecting surface 16 can therefore be written (approximately, considering pm, n ^" 0 if m + n> 6 or if m is odd) in the following simplified polynomial form:

z = p2, ox ² + po, 2 y ² + p2, ix ² y + po, 3 y ³ + p4, ox ⁴ + p2,2 x ² y ² + po, 4 y ⁴ + p4, ix ⁴ y ¹ + p2.3 x ² y ³ + in, sy ⁵

+ pe, ox ⁶ + p4.2 x ⁴ y ² + p2.4 x ² y ⁴ + po, ey ⁶ .

As an additional illustrative example, the polynomial coefficients pm, n (for m + n <6) of the reflecting surface 16 of a mirror of power s (from 6) have been reported in the table below (Table 2). ^th order) according to the second embodiment described below:

[Table 2]

We check once again in Table 2 above that the polynomial coefficients pm, n in odd power of x (ie the coefficients pi, o, pu, p3, o and p 1, 2) are appreciably harmful (in the sense defined above).

The present invention is not limited to the embodiment described and shown.

Claims

1. Power mirror (14) for a head-up display device (10) intended to be mounted in a left-hand drive vehicle (1) and in a right-hand drive vehicle (1), said power mirror (14 ) having a reflecting surface (16) including a representative equation, in a reference (W, C, U, Z) linked to said power mirror (14) where the axis Z corresponds to a normal to said reflecting surface (16) in its center W, includes a polynomial component of the type: åm, n pm, nx ^m y ⁿ , where m and n are natural integers and the polynomial coefficients pm, n of said representative equation are real numbers,

characterized in that said polynomial coefficients pm, n in odd power of y are substantially detrimental.

2. Power mirror (14) for a head-up display device (10) intended to be mounted in a left-hand drive vehicle (1) and in a right-hand drive vehicle (1), said power mirror (14) having a reflecting surface (16) including a representative equation, in a reference (W, C, U, Z) linked to said power mirror (14) where the Z axis corresponds to a normal to said reflecting surface (16 ) at its center W, comprises a polynomial component of the type: åm, n pm, nx ^m y ⁿ , where m and n are whole numbers and the polynomial coefficients pm, n of said representative equation are real numbers,

characterized in that said polynomial coefficients pm, n in odd power of x are substantially harmful.

3. Power mirror (14) according to claim 1 or 2, wherein said polynomial coefficients pm, n of the equation representative of the reflecting surface (16) of the power mirror (14) are substantially damaged when m + n> 6.

4. Power mirror (14) according to one of claims 1 to 3, wherein said representative equation is written in a form of the type: z = a K (x, y) + åm, n pm, nx ^m y ⁿ , where K is a function of revolution around said axis Z and has a real constant.

5. Head-up display device (10) intended to be mounted in a left-hand drive vehicle (1) and in a right-hand drive vehicle (1), said device (10) comprising:

an image generation unit (1 1) adapted to emit a beam luminous (13) representative of a scene; and

at least one power mirror (14) according to one of claims 1 to 4.

6. A head-up display device (10) according to claim s, wherein said power mirror (14) is configured to reflect said light beam (13) emitted towards a windshield (3) of said vehicle. (1), said windshield (3) projecting said scene to an occupant (4) of said vehicle (1).

7. A head-up display device (10) according to claim 5 or 6, wherein said image generation unit (1 1) comprises a screen module (12) of the TFT-LCD type.

8. A head-up display device according to claim 5 or 6, wherein said image generation unit comprises a laser module of the laser-scan type.

9. A head-up display device according to claim 5 or 6, wherein said image generation unit comprises a DLP type projection module.

10. Mold characterized in that it is designed for the manufacture of a power mirror according to one of claims 1 to 4.