METHOD OF PRODUCING A COATED VEHICLE WINDSHIELD FOR A HEAD-UP DISPLAY (HUD)

Abstract

A method for determining pane thicknesses and a wedge angle of a coated windshield for a projection arrangement of a head-up display. A wedge angle and a combination of glass thicknesses are determined by means of which the glass ghost image and the layer ghost image are optimally reduced. The method proceeds from a starting thickness of the two glass panes of the windshield for which that wedge angle is determined, in an iterative process, that represents an optimal compromise between the minimization of the glass ghost image and the minimization of the layer ghost image. Then, the glass thicknesses are determined varied within a specified range for each combination of the optimal wedge angles. Thus, it is possible, iteratively, to identify that combination of glass thicknesses that results in the least occurrence of ghost images, in addition to the associated optimal wedge angle.

Claims

1. Method for determining pane thicknesses and a wedge angle of a coated windshield for a projection arrangement of a head-up display, wherein the windshield comprises an outer pane and an inner pane, joined to one another via a thermoplastic intermediate layer, and has an upper edge, a lower edge, and an HUD region, wherein the thickness of the thermoplastic intermediate layer increases in the vertical course between the lower edge and the upper edge at least in the HUD region with a wedge angle, a transparent, electrically conductive coating is applied on a surface of the outer pane facing the thermoplastic intermediate layer, the projection arrangement comprises the windshield and a projector that is aimed toward the HUD region, comprising: (a) selecting a starting thickness of the outer pane and a starting thickness of the inner pane, and (i) determining a glass wedge angle that results in disappearance of a glass ghost image at a reference point within the HUD region, (ii) determining a layer wedge angle that results in disappearance of a layer ghost image at the reference point within the HUD region, (iii) iteratively determining a mean wedge angle between the glass wedge angle and the layer wedge angle, for which a difference between a maximally occurring glass ghost image and a maximally occurring layer ghost image is minimal, (b) changing the thickness of the outer pane within a range of permissible values and/or the thickness of the inner pane within a range of permissible values and determining a associated mean wedge angle using steps (i) through (iii), (c) repeating step (b), until all possible combinations of thicknesses of the outer pane and inner pane within the ranges of permissible values are covered, (d) selecting a final thickness of the outer pane and a final thickness of the inner pane, for whose associated mean final wedge angle the smallest difference between the glass ghost image and the layer ghost image was determined.

2. The method according to claim 1, wherein the starting thickness of the outer pane and the starting thickness of the inner pane are from 1.2 mm to 3 mm.

3. The method according to claim 1, wherein the reference point is arranged in a centre of the HUD region.

4. The method according to claim 1, wherein the starting thickness of the inner pane is an upper limit of the range of permissible values for the thickness of the inner pane.

5. The method according to claim 4, wherein the starting thickness of the outer pane is an upper limit of the range of permissible values for the thickness of the outer pane.

6. The method according to claim 1, wherein in steps (b) and (c), the thickness of the thermoplastic intermediate layer is also varied proceeding from a starting thickness within a range of permissible values until all possible combinations of thicknesses of the outer pane, inner pane, and thermoplastic intermediate layer within the ranges of permissible values are covered, wherein in step (d), in addition to the final thickness of the outer pane and the final thickness of the inner pane a final thickness of the thermoplastic intermediate layer is also selected, for whose associated mean final wedge angle the smallest difference between the glass ghost image and the layer ghost image was determined.

7. The method for producing a coated windshield for a projection arrangement of a head-up display, comprising: (a) providing an outer pane and an inner pane having the final thicknesses determined according to claim 1, (b) coating a surface of the outer pane with a transparent, electrically conductive coating, (c) arranging a thermoplastic intermediate layer having the final wedge angle between the outer pane and the inner pane, wherein the electrically conductive coating faces the thermoplastic intermediate layer, (d) laminating the outer pane to the inner pane via the thermoplastic intermediate layer to form the windshield.

8. The method according to claim 7, wherein the final wedge angle is introduced into the thermoplastic intermediate layer by stretching or by extrusion.

9. The method according to claim 7, wherein the outer pane and the inner pane are subjected to a bending process between the steps (b) and (c).

10. The method according to claim 7, wherein the transparent coating contains at least one silver layer.

11. The method according to claim 7, wherein the outer pane and the inner pane contain soda lime glass.

12. The method according to claim 7, wherein the thermoplastic intermediate layer contains at least polyvinyl butyral, ethylene vinyl acetate, polyurethane, or mixtures or copolymers or derivatives thereof, preferably PVB.

13. The method according to claim 7, wherein the thermoplastic intermediate layer is implemented as a noise-damping, multi-ply film.

14. A method comprising utilizing a windshield produced by the method according to claim 7 in a vehicle as part of a projection arrangement for a head-up display.

15. The method according to claim 14, wherein the vehicle is a motor vehicle.

16. The method according to claim 15, wherein the vehicle is a passenger car.

Description

[0056] They depict:

[0057] FIG. 1 a plan view of a generic windshield,

[0058] FIG. 2 a cross-section through the windshield of FIG. 1,

[0059] FIG. 3 a cross-section through a generic projection arrangement,

[0060] FIG. 4 a flowchart of an embodiment of the method according to the invention for determining pane thicknesses and a suitable wedge angle, and

[0061] FIG. 5 a flowchart of an embodiment of the method according to the invention for producing a windshield.

[0062] FIG. 1 and FIG. 2 depict in each case a detail of a composite pane 10 according to the invention, which comprises an outer pane 1 and an inner pane 2 that are joined to one another via a thermoplastic intermediate layer 3. The composite pane 10 is intended als a windshield of a motor vehicle that is equipped with a head-up display. In the installed position, the outer pane 1 faces the outside environment; the inner pane 2, vehicle interior. In the installed position, the upper edge O of the composite pane 10 points upward toward the vehicle roof (roof edge); the lower edge U, downward toward the engine compartment (engine edge).

[0063] The outer pane 1 has an exterior-side surface I that faces the outside environment in the installed position and an interior-side surface II that faces the interior in the installed position. Likewise, the inner pane 2 has an exterior-side surface III that faces the outside environment in the installed position and an interior-side surface IV that faces the interior in the installed position. The interior-side surface II of the outer pane 1 is joined to the exterior-side surface III of the inner pane 2 via the intermediate layer 3.

[0064] A region B, corresponding to the HUD region of the composite pane 10, is also indicated In the figure. In this region, images are to be produced by an HUD projector. The primary reflection on the interior-side surface IV of the inner pane 2 produces the desired HUD display as a virtual image. The non-reflected radiation components penetrate through the composite pane 10 and are reflected again on the exterior-side surface I of the outer pane 1 (secondary reflection). The secondary reflection creates the glass ghost image G.sub.G that is offset relative to the primary image. The centre of the HUD region B serves as reference point R for calculating wedge angles.

[0065] The thickness of the intermediate layer 3 increases steadily in the vertical course from the lower edge U to the upper edge O. For the sake of simplicity, the increase in thickness is shown as linear; however, it can also have more complex profiles. The intermediate layer 3 is formed from a single film of PVB (a so-called “wedge film” with variable thickness). The extent of the change in thickness is delineated thereby.

[0066] The composite pane 10 also has an electrically conductive coating 4 on the interior-side surface II of the outer pane 1. The coating 4 is IR reflecting and is intended to reduce the heating of the vehicle interior by the IR component of sunlight. The coating 4 is, for example, a thin-film stack containing two or three layers of silver and other dielectric layers.

[0067] The coating 4 constitutes a further reflecting boundary surface in the interior of the composite pane 10, on which the projector image is again reflected and thus results in an undesirable secondary image, the so-called layer ghost image G.sub.C.

[0068] Due to the wedge-shaped implementation of the intermediate layer 3, in principle, ghost images can be avoided or at least reduced, in that the primary image and the ghost image coincide. The secondary reflection then no longer appears offset relative to the primary reflection. In the present case, there is, however, the problem, that avoiding the glass ghost image and avoiding the layer ghost image make different demands on the wedge angle oc. In the context of a compromise, a wedge angle α must be found that satisfactorily reduces both ghost images.

[0069] The outer pane 1 and the inner pane 2 are made, for example, of soda lime glass. The intermediate layer 3 is formed here by a single, wedge-shaped PVB film. The minimum thickness of the intermediate layer 3 is, for example, 0.76 mm (measured at the lower edge U). However, a multilayer structure of the intermediate layer 3 is also conceivable, for example, a 0.36-mm-thick PVB film with a constant thickness, a 0.76-mm-thick PVB wedge film, and a 0.05-mm-thick PET film positioned therebetween.

[0070] For the sake of simplicity, the windshield is shown planar, but has, in reality, a three-dimensional curvature that must be taken into account in the determination of the wedge angles and ghost images.

[0071] FIG. 3 depicts the composite pane 10 of FIGS. 1 and 2 as part of a projection arrangement for an HUD. The arrangement comprises, in addition to the composite pane 10, a projector 5, which is aimed toward the HUD region B. The projector 5 can generate images in the HUD region B that are perceived by the viewer 6 (vehicle driver) as virtual images on the side of the composite pane 10 facing away from him.

[0072] The region within which the eyes of the viewer 6 must be situated in order to perceive the virtual image is referred to as the “eye box window”. The eye box window is vertically displaceable by mirrors in the projector 5, in order to adapt the HUD to viewers 6 of different body size and seat position. The entire accessible region within which the eye box window can be displaced is referred to as “eye box E”. The beam that connects the projector 5 with the centre of the eye box E (usually the mirrors of the projector 5 are in the zero position) is referred to as centre beam M. The point on the inner pane 2, where the centre beam M strikes, is a characteristic parameter in the design of HUD projection arrangements.

[0073] FIG. 4 depicts a flowchart of an exemplary embodiment of the method according to the invention for determining pane thicknesses and a wedge angle. First, the starting thicknesses d.sub.A.sup.0, d.sub.I.sup.0 of the outer pane 1 and of the inner pane 2 are selected. These values are used to calculate the glass wedge angle α.sub.G and the glass ghost image G.sub.G maximally occurring therewith and the layer wedge angle α.sub.C and the layer ghost image G.sub.C maximally occurring therewith. Then, the mean wedge angle α.sub.opt, that is numerically between the glass wedge angle α.sub.G and the layer wedge angle α.sub.C and results in a minimal quantitative difference between the maximally occurring glass ghost image G.sub.G and the maximally occurring layer ghost image G.sub.C is determined iteratively. The calculation of the maximally occurring ghost images with the original glass wedge angle and the original layer wedge angle is not essential, but later enables estimating the extent to which the occurrence of ghost images has been improved by the optimization method according to the invention.

[0074] Then, ranges Δd.sub.A, Δd.sub.I of permissible values for the pane thicknesses d.sub.A, d.sub.I are selected, which, of course, also can be done and, in practice, is done already at the beginning of the process after the selection of the starting thicknesses d.sub.A.sup.0, d.sub.I.sup.0. The pane thicknesses d.sub.A, d.sub.I within the ranges Δd.sub.A, Δd.sub.I are repeatedly changed and determined for each possible combination of pane thicknesses d.sub.A, d.sub.I of the mean wedge angle α.sub.opt. When all possible combinations of the pane thicknesses d.sub.A, d.sub.I have been considered, the combination whose associated mean wedge angle α.sub.opt yields the smallest difference between glass ghost image G.sub.G and layer ghost image G.sub.C Is selected. The pane thicknesses and this mean wedge angle constitute, as final thicknesses d.sub.A.sup.f, d.sub.I.sup.f and as mean final wedge angle α.sub.opt the results of the process.

EXAMPLE

[0075] The following starting thicknesses, which correspond to a standard windshield with a total thickness of 4.46 mm, were selected: [0076] starting thickness d.sub.A.sup.3=2.1 mm [0077] starting thickness d.sub.I.sup.0=1.6 mm [0078] thickness of the intermediate layer 3=0.76 mm

[0079] The following wedge angle and ghost images were calculated therewith: [0080] glass wedge angle α.sub.G=0.52 mrad [0081] maximally occurring glass ghost image G.sub.G=1.21 mm [0082] layer wedge angle α.sub.C=0.24 mrad [0083] maximally occurring layer ghost image G.sub.C=2.95 mm

[0084] Then, a mean wedge angle α.sub.opt of 0.38 mrad, for which the difference between G.sub.G and G.sub.C mit 0.03 mm was minimal (G.sub.G=1.70 mm; G.sub.C=1.73 mm) was determined iteratively.

[0085] The following ranges of permissible values for the pane thicknesses were defined (values in the unit mm, in each case): [0086] Δd.sub.A={2.6; 2.1; 1.8; 1.6; 1.4} [0087] Δd.sub.I={2.1; 1.8; 1.6; 1.4; 1.2; 1.0; 0.9; 0.7; 0.5}

[0088] The pane thicknesses were then varied, and for each possible combination of d.sub.A and d.sub.I, the associated mean wedge angle α.sub.opt with the associated difference between G.sub.G and G.sub.C was determined. Then, that combination was selected that yielded the smallest difference between G.sub.G and G.sub.C. The result was as follows: [0089] final thickness d.sub.I.sup.f=0.7 mm

[0090] With the unchanged thickness of the intermediate layer 3 of 0.76 mm, a total thickness of the windshield 10 of 3.06 mm was obtained. For this combination, the following wedge angles were calculated: [0091] glass wedge angle α.sub.G=0.355 mrad [0092] layer wedge angle α.sub.C=0.162 mrad [0093] mean final wedge angle α.sub.opt.sup.f=0.25 mm

[0094] With α.sub.opt.sup.f, a maximally occurring glass ghost image G.sub.G of 1.18 mm and a maximally occurring layer ghost image G.sub.C of 1.13 mm were obtained, corresponding to a difference of 0.05 mm, representing the minimally observed value.

[0095] FIG. 5 depicts in continuation of the method of FIG. 4, a flowchart of an exemplary embodiment of the method according to the invention for producing a coated windshield.

LIST OF REFERENCE CHARACTERS

[0096] (10) windshield [0097] (1) outer pane [0098] (2) inner pane [0099] (3) thermoplastic intermediate layer [0100] (4) electrically conductive coating [0101] (5) projector [0102] (6) viewer/vehicle driver [0103] (O) upper edge of the windshield 10 [0104] (U) lower edge of the windshield 10 [0105] (B) HUD region of the windshield 1 [0106] (I) exterior-side surface of the outer pane 1 [0107] (II) interior-side surface of the outer pane 1 [0108] (III) exterior-side surface of the inner pane 2 [0109] (IV) interior-side surface of the inner pane 2 [0110] (α) wedge angle of the intermediate layer 3 [0111] (E) eye box [0112] (M) centre beam (between projector 5 and center of the eye box E) [0113] (R) reference point for determining the wedge angle [0114] (d.sub.A) thickness of the outer pane 1 [0115] (d.sub.A.sup.0) starting thickness of the outer pane 1 [0116] (d.sub.A.sup.f) final thickness of the outer pane 1 [0117] (d.sub.I) thickness of the inner pane 2 [0118] (d.sub.I.sup.0) starting thickness of the inner pane 2 [0119] (d.sub.I.sup.f) final thickness of the inner pane 2 [0120] (Δd.sub.A) range of permissible values for d.sub.A [0121] (Δd.sub.I) range of permissible values for d.sub.I [0122] (α.sub.G) glass wedge angle [0123] (α.sub.C) layer wedge angle [0124] (α.sub.opt) mean wedge angle [0125] (a.sub.opt.sup.f) mean final wedge angle [0126] (G.sub.G) maximally occurring glass ghost image [0127] (G.sub.C) maximally occurring layer ghost image