WO2023072484A1

WO2023072484A1 - Reducing installation space in a head-up display by means of a transmitting concave mirror

Info

Publication number: WO2023072484A1
Application number: PCT/EP2022/076247
Authority: WO
Inventors: Michael Arthur Janzer
Original assignee: Bayerische Motoren Werke Aktiengesellschaft
Priority date: 2021-10-29
Filing date: 2022-09-21
Publication date: 2023-05-04
Also published as: DE102021128358A1

Abstract

The invention relates to a compact projection unit for a visual-field display device for use in a vehicle, comprising: - an imaging unit designed to generate a light beam having a desired display content; - a fold mirror arranged in the beam path of the generated light beam; and - a concave mirror which is designed and arranged in the beam path of the light beam reflected by the fold mirror in such a way that the light beam leaves the projection unit in a predetermined shape and direction in order subsequently to be reflected by a reflective pane, which is partially transparent and is arranged in the visual field of a user, to the eyebox of the user and to thus present to the user the display content in the form of a virtual image behind the reflective pane; - wherein the concave mirror is arranged in the beam path between the imaging unit and the fold mirror and at least partially transmits the light beam which emerges from the imaging unit and is incident on the rear face of the concave mirror.

Description

Reduction in installation space in the head-up display thanks to a transmitting concave mirror

The invention relates to head-up display devices for a motor vehicle or other land, air or water vehicle, which are also known under the name head-up display (HUD). Devices of this type are designed to generate a virtual image that is displayed in the user's field of vision via reflection on a partially transparent reflective pane, such as a front, rear or side window of the vehicle, or on a combiner pane specially provided for this purpose, which is arranged in the user's field of vision. The invention relates in particular to a projection unit which is designed to emit a suitable light beam with the desired display content, and a vehicle equipped therewith.

With a head-up display, for example, speed information and other useful navigation and vehicle operating instructions or entertainment content in the form of a virtual image are superimposed on the real environmental image in front of the vehicle observed by the driver or another occupant in a motor vehicle. As schematically sketched in Fig. 1, a head-up display device (HUD) 200 in a classic mirror design includes a projection unit 500 accommodated below an upper side of the instrument panel 4 of a vehicle 1. This contains an imaging unit 600, for example a display, for generating a light beam L with the desired display content. Furthermore, the projection unit 500 includes imaging and projection optics to the light beam L in a suitable form and To throw the direction of the windscreen 3 of the vehicle 1, so that the virtual image (not shown) can be seen in a desired size, distance and quality from a specific area for the user's eyes, the eyebox E, in the vehicle 1.

The installation space for a head-up display 200 and its projection unit 500 on board a vehicle 1 is very expensive. Therefore, in the known HUD constructions, an attempt is made to create a system that is as compact as possible by skillful folding of the optical beam path. For this purpose, the imaging and projection optics in the beam path of the light beam L typically includes a folding mirror 700 for a space-saving folding of the beam path and also a concave mirror 800, which is used, for example, to enlarge an image and/or to compensate for a curvature of the windshield. However, as shown in FIG. 1, any folding of the beam path must always avoid the concave mirror 800 in order to avoid cropping the image. However, this never achieves the smallest possible installation volume.

It is the object of the present invention to specify an alternative projection unit or one that is improved in terms of installation space, image quality and/or other aspects for a head-up display device, which is particularly suitable for use in a vehicle.

This object is achieved by a compact projection unit according to claim 1 and by a head-up display device containing it and a vehicle equipped therewith according to the independent claims. Further developments are specified in the dependent claims. All further features and effects mentioned in the claims and the following description for the projection unit also apply in relation to the visual field display device and the vehicle, and vice versa.

According to a first aspect, there is a compact projection unit, ie one that is optimized in terms of installation space, for a visual field display device provided, which can be used in particular in a vehicle. The head-up display device can be embodied as a head-up display (HUD), for example. The vehicle can be a motor vehicle, but also any other land, air or water vehicle.

The projection unit first has an imaging unit (Picture Generating Unit, PGU) designed to generate a light beam with the desired display content, which can be designed, for example, as a liquid crystal screen (LCD, liquid crystal display) or a different type of display or much more.

In the beam path of the light beam generated by the imaging unit, a folding mirror is arranged for its folding, which in the simplest case can be designed as a plane mirror. However, the folding mirror can also be curved, i. H. generally a free-form mirror with a convex or concave mirror surface to perform additional image correction and/or beam shaping functions.

In the beam path of the light beam reflected by the folding mirror, the projection unit also includes a concave mirror that is arranged and designed in such a way that the light beam then leaves the projection unit in a predetermined shape and direction, in order to then be reflected by an at least partially transparent reflection pane arranged in the user's field of vision to his eyebox and thereby present the display content to the user in the form of a virtual image behind the reflection screen. The reflecting pane can be formed, for example, by a section of a front pane of the vehicle or by a combiner pane arranged in front of it. It is therefore a component of the field of view display device specified below, but not necessarily also a component of the projection unit, which can also be manufactured and sold without this, for example when the vehicle windscreen is used as a reflection screen. In the case of an extra combiner disc However, this can also be integrated in the projection unit in a known manner. As usual, the eyebox of the visual field display device is understood to be a two-dimensional or three-dimensional spatial area from which the virtual image can be seen without restriction.

The concave mirror is arranged in the beam path between the imaging unit and the folding mirror and is designed to be at least partially transmissive for the light beam bundle emanating from the imaging unit and impinging on its rear side. In other words, on its way from the imaging unit to the folding mirror, the bundle of light rays passes through the rear side of the concave mirror.

One idea of the present invention is therefore to design the concave mirror to be transmissive for the light incident on the rear, which emanates from the imaging unit. This makes it possible to position the imaging unit behind the concave mirror and in this way to optimally utilize the available installation space for a folded beam path, namely twice, without cutting the cross section of the light beam bundle.

This design of the projection unit enables a significant reduction in installation space compared to the conventional mirror HUD of FIG. 1 through a more compact design of the projection unit, which allows a volume reduction of approximately 25-35%. The concave mirror also serves (in particular due to its respective coating according to the embodiments specified below) at the same time as a heat protection measure for the imaging unit (e.g. display), since in the respective embodiment 50% of the incident sunlight cannot reach the display. The integration of HUDs with larger images is thus considerably simplified overall.

There are innumerable ways of making this optical system particularly simple through a specific selection of the reflection properties on the concave mirror and/or on the folding mirror, for example by means of suitable optical coatings and/or to make it particularly efficient. Two different variants are given below, purely by way of example, of which the first is particularly simple to implement and the second is particularly efficient with regard to the power consumption of the visual field display device:

According to a first embodiment, the concave mirror has a 50%R coating on its concavely curved front side, such that it transmits about 50% of the light incident from the imaging unit on the back and reflects about 50% of the light reflected by the folding mirror on the front. After passing through the optical system, this results in an overall efficiency of about 0.5*0.5=0.25, which corresponds to 25%.

According to a second embodiment, the imaging unit is designed to generate linearly p-polarized (or s-polarized) light, while the concave mirror is provided with a coating on its concavely curved front side that has an approximately 100% reflection coefficient for s-polarized (or p-polarized) light, i. H. has a 100%Rs coating (or 100%Rp coating). It can thus be achieved that the concave mirror transmits the light incident from the imaging unit on the back with almost no loss.

In this variant, however, the folding mirror must also have an optically active coating so that the light is reflected as effectively as possible on the concave mirror. The coating of the folding mirror is accordingly a λ/4 layer, which can be designed to be as broad-band as possible, in particular both in the angle spectrum and in the wavelength spectrum. The light is thus delayed by 2*0.25A=0.5A when passing through this coating, ie linearly polarized light is rotated from p to s (or s to p). The linear polarization of the light is now set in such a way that the above-mentioned front-side coating on the concave mirror reflects it as efficiently as possible. Thus, with this embodiment, an overall efficiency of the optical system of over 80% can be achieved. This efficiency can be can be increased even further by an anti-reflection coating on the (e.g. convex) rear side of the concave mirror.

Since the angle of incidence of the light projected onto the windscreen of motor vehicles is close to Brewster's angle in common HUD configurations, predominantly s-polarized light is reflected at the interface between air and the windscreen made of glass or plastic (i.e. linearly polarized light whose polarization direction is vertical to the typically vertical plane of incidence of the windscreen, i.e. parallel to the windscreen and usually horizontal). For this reason, the projection units of many known head-up display devices are also designed to preferably emit s-polarized light.

For the highest possible reflection efficiency on the folding mirror, the λ/4 layer is ideally designed to be as broadband as possible in a spectral range corresponding to the imaging unit, for example with a broadband light source in a broad wavelength range of about 380-780 nm. The same applies accordingly to the relevant angle of incidence range of the light beam on the folding mirror.

According to another aspect, there is provided a head-up display device for use in a vehicle. In addition to the projection unit of the type presented here, the visual field display device also includes an at least partially transparent reflection pane which is arranged in the beam path of the light beam emitted by the projection unit and which can be designed in particular as a partial surface section of a front pane of the vehicle or as a combiner pane provided separately in front of it. The reflective disk is arranged and designed in a user's field of vision in such a way that it reflects the light beam to an eyebox predetermined for the user, as a result of which the display content can be displayed in the form of a virtual image behind the reflective disk and is also displayed during operation of the visual field display device. According to a further aspect, a vehicle, in particular a motor vehicle or any other land, air or water vehicle is provided. The spatial orientation terms used herein such as "above", "below", "in front of", "sideways", "horizontal", "vertical" etc. refer to the usual Cartesian coordinate system fixed to the vehicle with longitudinal, transverse and vertical axes perpendicular to one another of the vehicle.

The vehicle is equipped with a head-up display device of the type set out here, the projection unit of which can be installed, for example, directly below an upper side of an instrument panel of the vehicle, such that the light beam from the projection unit onto a windscreen arranged above the instrument panel or in the field of vision of the driver or someone else occupants positioned combiner disc is thrown.

The above aspects of the invention and its embodiments and specific configurations are explained in more detail below with reference to examples shown in the attached drawings. The drawings are intended as purely schematic illustrations of the basic optical construction principle, i. H. not to be understood as true to scale. They show, each in a vertical longitudinal section:

FIG. 1 shows a conventional mirror HUD in a motor vehicle with a beam path folded by means of a folding mirror and a concave mirror according to the prior art;

FIG. 2 shows an exemplary embodiment of a visual field display device of the type presented here in a motor vehicle with a partially transparent concave mirror in the beam path between the imaging unit and the folding mirror;

Figure 3 shows an embodiment of the head-up display of Figure 2 having a 50%R coating on the concave curved face of the concave mirror; and Figure 4 shows an alternative embodiment to Figure 3 of the head-up display of Figure 2 having a 100% Rs coating on the concave curved face of the concave mirror.

While FIG. 1 , which was described in detail at the outset, shows a conventional head-up display device 200 in the form of a so-called mirror HUD in a vehicle 1 (in this example a motor vehicle) for comparison, FIG. 2 is analogous to FIG. 1 simplified schematic longitudinal sectional view of an embodiment of a motor vehicle with a field of view display device 2 of the type presented herein.

The motor vehicle is only indicated by its windscreen 3 in FIG. A projection unit 5 of the visual field display device 2 is arranged underneath in an instrument panel 4 that is not shown in detail. It is purely an example of a head-up display (HUD). In this example, the front pane 3 serves as a partially transparent reflection pane of the head-up display device 2 so that a virtual image (not shown) is displayed for a driver or other occupants on the vehicle outside in front of the front pane 3 .

The projection unit 5 contains an imaging unit 6 (also called Picture Generating Unit, PGU, in this example an LCD) designed to generate a light beam L (abbreviated to simply “light”) with the desired display content. The bundle of light rays L emanating from the imaging unit 6, which transports the display content to an eyebox E of a user (here driver, not shown) located in the motor vehicle at a predetermined position opposite the windscreen 3, is indicated in simplified form by its central beam, which consists of a Center of the imaging unit 6 leads to a center of the eyebox E. Similar to FIG. 1, a folding mirror 7 is also arranged in FIG. The concavely curved front side of the concave mirror 8, which faces the folding mirror 7, is also designed here in such a way that the light beam L leaves the projection unit 5 in a suitable shape and direction by reflection thereon, and then reflects from the front pane 3 to the eyebox E to become.

In contrast to FIG. 1 , however, the concave mirror 8 in FIG. 2 is designed to be at least partially transmissive for the light L generated by the imaging unit 6 . In this way, as outlined in FIG. 2, the imaging unit 6 can be positioned behind the concave mirror 8, so that the available installation space for the beam path is used twice at this point and is therefore optimally utilized.

There are several ways of making the optical system sketched in FIG. 2 particularly simple and/or particularly efficient by specifically selecting the reflection properties on the concave mirror 8 and/or on the folding mirror 7, for example by means of suitable optical coatings. Two different examples of this are given below with reference to FIGS.

Thus, FIG. 3 shows an exemplary embodiment of the head-up display device 2 of FIG. 2 according to the first embodiment of the invention mentioned above. Here, the concave mirror 8 has a 50%R coating 9 on its concavely curved front side, such that it transmits about 50% of the light L incident from the imaging unit 6 on the back and reflects about 50% of the light L reflected by the folding mirror 7 on the front. After passing through the optical system, this results in an overall efficiency of about 0.5*0.5=0.25, which corresponds to 25%. Otherwise, to avoid repetition, reference is made to the description of FIG. 2 above. FIG. 4 shows an alternative to FIG. 3 embodiment of the head-up display device 2 of FIG. 2 according to the above-mentioned second embodiment of the invention. Here the imaging unit 6 is designed to generate p-polarized light Lp, while the concave mirror 8 is provided with a coating on its concavely curved front side which has an approximately 100% reflection coefficient for s-polarized light, ie a 100% Rs coating owns 10 The light Lp of the imaging unit 6 can therefore (apart from any Fresnel losses, which can be reduced or even eliminated, for example, by suitably selected rear geometry and/or anti-reflection coatings of the concave mirror 8) without attenuation through the concave mirror 8 and reach the folding mirror 7 .

In this variant, however, the folding mirror 7 must also receive an optically active coating so that the light beam is then also reflected as effectively as possible on the concave mirror 8 . The coating of the folding mirror 7 is accordingly a λ/4 layer 11, which can be designed with as broad a bandwidth as possible, in particular, both in the angle spectrum and in the wavelength spectrum. The light Lp is thus delayed by 2*0.25λ=0.5λ when passing through this λ/4 layer 11, i. H. linearly polarized light is rotated from p to s. The linear polarization of the light Ls is now set in such a way that the front-side 100% Rs coating 10 on the concave mirror 8 reflects it as efficiently as possible. Thus, with this embodiment, an overall efficiency of the optical system of over 80% can be achieved. This efficiency can be further increased, for example, by an above-mentioned antireflection coating on the rear side of the concave mirror 8, which is convex in FIG. 4 purely by way of example. Otherwise, to avoid repetition, reference is made to the description of FIG. 2 above.

If the angle of incidence of the light L projected onto the windshield 3 of the vehicle 1 in Figs. 2 to 4, as is also the case with conventional HUD configurations according to Fig.

1 , close to Brewster's angle, becomes at the interface of air to Front pane 3 made of glass or plastic predominantly reflects s-polarized light (ie linearly polarized light whose direction of polarization is perpendicular to the vertical plane of incidence of front pane 3 shown in the figures, i.e. parallel to front pane 3 and is usually horizontal). For this reason, it can be particularly advantageous to construct the projection unit 5, for example, according to the principle of FIG. 4 for the emission of s-polarized light Ls. With other geometric constellations in the vehicle 1, however, a different linear polarization of the light beam, ie p instead of s and s instead of p everywhere, can represent a viable or even particularly favorable solution within the scope of the present invention.

Overall, a significant reduction in installation space can be achieved in FIGS. 2-4 through a more compact design of the projection unit 5 (approx. 25-35% volume reduction) compared to the conventional HUD design according to FIG. The concave mirror 8, with its coating 9 or 10, serves at the same time as a thermal protection measure for the imaging unit 6, in that about 50% of the incident sunlight cannot reach the display of the imaging unit 6 as a result. This simplifies the integration of HUDs with larger images.

Reference List

1 vehicle

2 head-up display device

3 windscreen

4 instrument panel

5 projection unit

6 imaging unit

7 folding mirrors

8 concave mirrors

9 50%R coating

10 100%Rs coating

11 A/4-layer L light beam, also called “light” for short Lp light beam with p-polarized light

Ls light beam with s-polarized light E Eyebox

Claims

Claims Compact projection unit (5) for a visual field display device (2) for use in a vehicle (1), comprising: an imaging unit (6) designed to generate a light beam (L; Lp) with the desired display content; a folding mirror (7) arranged in the beam path of the generated light beam (L; Lp); and a concave mirror (8) arranged and designed in the beam path of the light beam (L; Ls) reflected by the folding mirror (7) in such a way that the light beam (L; Ls) leaves the projection unit (5) in a predetermined shape and direction in order to then be a partially transparent reflection disc arranged in the field of vision of a user to be reflected to his eyebox (E) and thereby to show the user the display content in the form of a virtual image behind the reflection disc; wherein the concave mirror (8) is arranged in the beam path between the imaging unit (6) and the folding mirror (7) and at least partially transmits the light beam (L; Lp) emanating from the imaging unit (6) and incident on its rear side. Projection unit (5) according to claim 1, wherein the concave mirror (8) has a 50% R coating (9) on its front side facing the folding mirror (7) such that it has about 50% on the rear side. of the light (L) incident on the imaging unit (6) is transmitted and about 50% of the light (L) reflected by the folding mirror (7) is reflected at the front. unit (5) according to claim 1, wherein the imaging unit (6) is designed to generate p-polarized light (Lp); the concave mirror (8) has a coating (10) with an approximately 100% reflection coefficient for s-polarized light on its concavely curved front side facing the folding mirror (7), such that it reflects the light ( Lp) transmitted with almost no loss; and the folding mirror (7) has a λ/4 layer (11) on its mirror side facing the concave mirror (8), so that the concave mirror (8) reflects the light (Ls) incident from the folding mirror (7) almost without loss. unit (5) according to claim 1, wherein the imaging unit (6) is designed to generate s-polarized light; the concave mirror (8) has a coating with an approximately 100% reflection coefficient for p-polarized light on its concavely curved front side facing the folding mirror (7), such that it transmits the light incident from the imaging unit (6) almost loss-free on the back; and the folding mirror (7) has an λ/4 layer (11), so that the concave mirror (8) reflects the light incident from the folding mirror (7) almost without loss at the front. 15 projection unit (5) according to any one of the preceding claims, wherein the concave mirror (8) on its the imaging unit (6) facing back has an anti-reflective coating. Head-up display device (2) for use in a vehicle (1), comprising: a projection unit (5) according to any one of the preceding claims; and an at least partially transparent reflection disk arranged in the beam path of the light beam (L; Ls) emitted by the projection unit (5); wherein the reflection disc is arranged and designed in a user's field of vision in such a way that it reflects the light beam (L; Ls) to an eyebox (E) predetermined for the user, whereby the display content in the form of a virtual image in a virtual image plane behind the reflection disc is shown to him is representable. Vehicle (1), in particular a motor vehicle, with mutually perpendicular longitudinal, transverse and vertical axes of an on-board Cartesian coordinate system, comprising: a windscreen (3) and a dashboard (4) arranged underneath; and a head-up display device (2) according to claim 6, the projection unit (5) of which is arranged inside the instrument panel (4) or on the upper side thereof and the reflecting plate arranged as a portion of the windshield (3) or as one arranged in front of it on the inside of the vehicle

Combiner disc is formed.