Projection screen, windshield with a projection screen and field of view display device for a motor vehicle

Description

Technical area

[0001] The invention relates to a projection surface for a field-of-view display device, particularly in the form of a head-up display for a motor vehicle. Furthermore, the present invention relates to possibilities for improving the display intensity of an image projected onto the projection surface. Technical background

[0002] Head-up display devices in motor vehicles are commonly known as head-up displays (HUDs). A head-up display device typically includes a projection unit for projecting a desired display content onto a windshield projection surface. A virtual image appears on the projection surface, which, for the driver, is superimposed on the real surroundings. The projection is typically performed in such a way that the driver perceives a virtual image at some distance from the eye, specifically at a certain distance above the front of the vehicle.

[0003] Previous field-of-view display devices with the above-mentioned design are provided in combination with windshields in which at least the projection surface has certain reflective properties. A certain portion of the light incident on the windshield is reflected from the inside of the windshield into the driver's eye, while another portion is coupled into the windshield. Typically, the reflective behavior depends significantly on the polarization of the incident light. In particular, the reflected portion of the projected light predominantly comprises s-polarized light due to the oblique angle of incidence on the windshield, which in common configurations is close to the Brewster angle.

[0004] The portion of the projected light coupled into the windshield is partly reflected back by the outer surface of the windshield and partly refracted into the surroundings. This portion also consists largely of s-polarized light, which overlaps with the light reflected from the inside of the windshield. To ensure that there is no offset between the main image and secondary image, which are created by reflection of the projected light from the reflective surfaces of the windshield formed by the inner and outer surfaces, the inside and outside of the windshield can be slightly tilted to one another, at least in the area of ​​the projection surface. This allows the main image and secondary image created by reflection from the reflective surfaces to be superimposed, thus enabling a clear representation of the image to be displayed.

[0005] Due to the preferential reflection of s-polarized projected light, the projection devices of existing field-of-view displays are designed to preferentially emit s-polarized light. However, this results in the projected image being very dim when wearing p-polarized sunglasses. Polarized sunglasses are generally designed to primarily absorb s-polarized light to reduce glare from reflective surfaces, such as puddle surfaces and the like, where s-polarized light is also preferentially reflected.

[0006] The publication WO 2013 / 189958 discloses a combining optics system for a head-up display for suppressing a double image. Instead of a wedge film, a transparent pane arrangement is coupled to a first optically active film and a second optically active film. The first optically active film is designed to reduce the intensity of a polarization direction of the light rays, and the second optically active film is designed to rotate the polarization direction of the light rays by an angle between 75° and 105°. This ensures that the s-polarized light coupled into the pane arrangement, which is reflected from the outside of the pane arrangement, is attenuated by passing through the first optically active film twice, so that a double image can be largely avoided.

[0007] US 2006 / 0023315 A1 discloses a projection surface for a windshield of a motor vehicle as part of a HUD display device. A projector projects p-polarized light onto the windshield, where it is reflected and can thus be seen by a driver wearing p-polarized sunglasses. For this purpose, an arrangement is applied to the inside of the windshield. The arrangement comprises a first and a second polarization-modifying layer, between which a thin-film layer is arranged, forming a reflection interface with the two polarization-modifying layers. Such an arrangement can prevent the formation of a primary and secondary image despite the two reflection surfaces formed.

[0008] Document US2009 / 0195875 A1 discloses a windshield or the like for a head-up display, the windshield comprising a first layer of transparent or partially transparent material, a second layer of transparent or partially transparent material; and a birefringent layer disposed in the windshield, the birefringent layer being capable of causing a change in the polarization of light emerging from a projector of the head-up display.

[0009] US 2007 / 279755 A1 discloses a head-up display system for a vehicle that also enables the vehicle driver to view selected objects that emit visible light only within a single restricted frequency band or spaced restricted frequency bands, the system comprising: a combiner acting as a partial reflector positioned in the driver's line of sight through which the driver can view the vehicle's surroundings, including the selected objects; and a projector projecting a display onto the combiner, the projector emitting light only within a single restricted frequency band or spaced restricted frequency bands, the combiner being positioned to reflect light from the projector toward the driver, the reflective characteristics of the combiner being such that it reflects only the incident light from the projector and transmits light at other frequencies;and the / each frequency band in which light is reflected from the combiner does not substantially coincide with any frequency band in which light is emitted from the selected objects;

[0010] Document EP 2 755 074 A1 discloses a display device for a vehicle comprising a display that emits an emission display light having a polarization plane in a specific direction, an illumination light source that illuminates the display, and a phase difference plate arranged opposite to the display in a state in which a fast axis is shifted by a predetermined angle with respect to the polarization plane of the emission display light emitted from the display.

[0011] Document EP 0 420 228 A2 discloses a head-up display having a transparent optical combiner, with a head-up display image projection unit for projecting an image light beam onto the optical combiner for reflection onto a predetermined field of view; wherein the optical combiner comprises a first surface and a second surface, and wherein the surfaces are non-parallel and are arranged at first and second angles, respectively, with respect to the image beam, such that the respective images reflected from the first and second surfaces substantially overlap at the field of view, thereby providing a substantially ghost-free head-up display image at the viewbox.

[0012] It is an object of the present invention to provide a field of view display device for a motor vehicle in which the light projected onto the projection surface is selectively polarized to a lesser extent than is the case with previous field of view display devices. Disclosure of the invention

[0013] This object is achieved by the field of view display device according to claim 1.

[0014] Further embodiments are specified in the dependent claims.

[0015] According to a first aspect, a field of view display device, in particular for use in a motor vehicle, is provided, comprising: a projection screen, in particular a windshield, which is designed as a projection surface in at least one region, wherein the projection surface comprises: a first reflection surface, in particular an inner side of the projection screen, for preferentially reflecting a light component polarized in a first polarization type from a projected image and for preferentially transmitting a light component polarized in a second polarization type from a projected image, a second reflection surface, in particular an outer side of the projection screen, for reflecting a light component polarized in the first polarization type from a projected image and for preferentially transmitting a light component polarized in the second polarization type from a projected image,a polarizing means arranged between the first reflection surface and the second reflection surface for changing a polarization of light transmitted to the projection surface, so that a light component of the second polarization type transmitted to the first reflection surface is reflected at the second reflection surface, changed into a light component of the first polarization type, and when passing through the polarizing means again, is changed into a light component of the second polarization type that is transmitted to the first reflection surface.

[0016] Furthermore, the polarizing agent is designed as a λ / 4 polarizing agent that causes circular polarization.

[0017] Furthermore, a projection device is provided for projecting an image to be projected onto the first reflection surface of the projection screen in a direction parallel to a first polarization plane, wherein the projection device has a light source for providing the light required for projecting the image, wherein the light source emits unpolarized light.

[0018] One idea behind the above projection surface is to provide the projection surface with a polarizing agent to change the polarization plane of the portion of the light projected onto and coupled into the projection surface. The light modified by the polarizing agent is reflected off an outer surface of the projection surface and passes through the polarizing agent again, exiting the projection surface as p-polarized light directed toward the user.

[0019] This increases the overall reflection efficiency at the projection surface, as the total proportion of light reflected toward the user increases. Furthermore, the light reflected toward the user contains a higher proportion of p-polarized light, making the projected image more visible when the user wears polarized sunglasses.

[0020] In addition, the provision of the polarizing means can be provided with an inclination between the inside and the outside of the projection surface in order to align the main image and the sub-image perceived by the user, so that no double image is created.

[0021] It can be provided that the first and the second reflection surface are inclined to one another with the aid of an inclination element, in particular a wedge film, such that a light component transmitting the first reflection surface and reflected at the second reflection surface leaves the projection surface in the same direction as a light component reflected at the first reflection surface, so that the partial images of the projected image generated by the two light components overlap without offset.

[0022] Furthermore, the polarizing agent can be formed as a layer, coating or ply, in particular as a film.

[0023] In particular, the first reflection surface can be designed as an interface formed by a side of an inner pane and the second reflection surface can be designed as an interface of the projection surface formed by a side of an outer pane.

[0024] Furthermore, the first polarization type can correspond to an s-polarization and the second polarization type to a p-polarization.

[0025] In particular, exactly one polarizing agent can be arranged between the first and the second reflection surface.

[0026] According to one embodiment, the projection surface can be provided with exactly one first and exactly one second reflection surface. This is achieved in particular by the fact that the layers arranged between the inside and outside of the projection screen have no or no significant differences in refractive index, so that no reflection surfaces are formed. Brief description of the drawings

[0027] Embodiments are explained in more detail below with reference to the attached drawings. They show: Fig. 1 a schematic representation of a field of view display device for a motor vehicle. Description of embodiments

[0028] Figure 1 shows a schematic representation of a field of view display device 1 in the form of a head-up display. The field of view display device 1 comprises a projection device 2, which, during operation, projects a virtual image onto a projection surface 3. The projection surface 3 can be provided as an image-displaying section of a windshield 4 in a motor vehicle or another transparent pane in another application.

[0029] The projection device 2 is provided with a light source 21, an imaging unit 22, e.g., in the form of a transparent display, and typically with an imaging optics 23. The imaging optics 23 projects the image to be displayed onto the projection surface 3.

[0030] At least in the region of the projection surface 3, the windshield 4 is provided with an inclination element 31, for example in the form of a wedge film or wedge-shaped layer, which is arranged between an outer pane layer 32 and an inner pane layer 33. The inclination element 31 has a wedge shape in order to arrange an outer side A (second reflection surface) of the windshield 4 formed by the outer pane layer 32 and an inner side I (which corresponds to a first reflection surface) of the windshield 4 formed by the inner pane layer 33 at an angle to one another, i.e. to incline them relative to one another by an angle between 0.2 and 1 mrad, in particular between 0.3 and 0.6 mrad, compared to a parallel arrangement. The inner side I corresponds to the side onto which the virtual image is projected and which is directed towards the user of the field of view display device 1.The outer side A (which corresponds to a second reflection surface) corresponds to a side opposite the inner side I with respect to the projection surface 3.

[0031] Light projected onto the projection surface 3 is reflected on the inner side I and the outer side A. The inclination element 31 and the inner and outer pane layers 33, 32 are designed such that there is no boundary surface for reflection inside the windshield 4 formed in this way; in particular, the refractive indices of the pane layers 32, 33 and the inclination element 31 are the same or almost the same. The inclination serves to superimpose a projected light component that is reflected from the inside of the windshield 4 and a light component that is transmitted on the inside I, is reflected from the outside A of the outer pane layer 32 back into the projection surface 3 and is transmitted and diffracted on the inside I, in such a way that from the user's point of view, both reflected images (main image and secondary image) are superimposed and coincide.This ensures that the user does not perceive the main image H reflected on the inner side I and the secondary image N reflected on the outer side A separately, which would disturb the representation of the image to be displayed.

[0032] Since the irradiation of the projected light onto the windshield 4 during operation occurs in a first direction, in particular in a vertical direction or in the direction of the inclination of the windshield 4, a light component of the projected light that has a polarization plane perpendicular to the plane of the angle of incidence / incident plane (to the surface normal of the inner side I) of the projected light beam on the windshield 4 is preferentially reflected on the inner side I and on the outer side A. The light component that has a polarization in this polarization plane is called an s-polarized light component. A light component whose polarization plane runs parallel to this is called a p-polarized light component.

[0033] Due to the angle of incidence of the projected light beam, which is selected close to the Brewster angle by the arrangement of the projection device 2, an s-polarized light component is preferably reflected at the interfaces of the projection surface 3, namely the inner side I and the outer side A. The reflected light components are predominantly s-polarized, and the light components transmitted at the interfaces are predominantly p-polarized.

[0034] In an exemplary arrangement, for a projected image that is generated with unpolarized light, ie with a light component of 50% s-polarized and 50% p-polarized light, and that is directed onto the projection surface 3 such that the light strikes the inner side I at an angle of incidence of, for example, 64° (to the surface normal), the reflected components of the main image and the secondary image add up to 15.7% s-polarized light and 0.75% p-polarized light component with respect to the original total light intensity.

[0035] In the above arrangement, when polarized light with a light component of 100% s-polarized light is output from the projection device, the s-polarized light components of the main image and the sub-image add up to a component of 31.4% s-polarized light directed toward the user of the field-of-view display device 1.

[0036] If the user wears sunglasses that are p-polarized to filter reflected radiation, in the first case, 0.75% of the total projected light may be perceived by the user. This light intensity may be too weak to produce a perceptible image compared to the ambient light when the user is wearing sunglasses. This is particularly disturbing if the user is glared by daylight without sunglasses.

[0037] Therefore, in one embodiment, a polarizing agent 34 can be provided in the projection surface 3, which acts like a λ / 2 polarizer upon a single passage of the light beam transmitted on the inner side I through the projection surface 3. A λ / 2 polarizer rotates a polarization plane by 90°. As a result, the polarization plane of the s-polarized light component transmitted on the inner side I of the projection surface 3 becomes a p-polarized light component, and the transmitted p-polarized light component is changed to an s-polarized light component.

[0038] The light component transmitted on the inner side I strikes the interface formed by the outer side A, where it is partially reflected and partially transmitted. The light component reflected on the outer side A is in turn predominantly an s-polarized light component of the transmitted, polarization-changed light, while a p-polarized light component of the transmitted, polarization-changed light is predominantly transmitted into the environment. The s-polarized light component reflected on the outer side A again passes through the projection surface 3 towards the user. In doing so, the user passes through the polarization means 34 again, so that a further polarization change of 90° occurs. As a result, the s-polarized light component reflected on the outer side A becomes a p-polarized light component.

[0039] The p-polarized light component incident from the inner side I and reflected at the outer side A is now transmitted at the inner side I and aligned parallel to the s-polarized light component previously reflected at the inner side I of the projection surface 3. This occurs due to the diffraction at the interface of the inner side I, so that the main image formed by the s-polarized light component reflected on the inner side I of the projection surface 3 and the secondary image formed by the transmitted p-polarized light component reflected on the outer side A are superimposed.

[0040] In this way, it is possible to direct the light component previously transmitted on the inner side I into the user's eye by reflection on the outer side A. In other words, a previously weakly reflected p-polarized light component of the projected image, which is essentially not reflected on the inner side I (but is essentially transmitted), is reflected onto the user's eye by reflection on the outer side A of the projection surface 3. This is achieved by changing the polarization twice, each time by 90°, so that the polarization direction of the relevant light component arriving at the user's eye corresponds to the original polarization direction.

[0041] In this way, for example, for the above arrangement example, it is possible to achieve a light component of s-polarized light of 11.4% and a light component of p-polarized light of 7.8% for a projected image generated with unpolarized light, i.e., with a light component of 50% each of s-polarized and p-polarized light. This makes it possible to perceive the projected image even when wearing polarized sunglasses.

[0042] In a further embodiment with a projection device 2 that emits unpolarized light with a light component of 50% s-polarized and 50% p-polarized light, with an otherwise identical configuration of the field of view display device 1, a polarizing agent 34 designed as a λ / 4 polarizing agent still results in a component of 14% s-polarized light and 3.7% p-polarized light of the total light intensity emitted by the light source 21. The λ / 4 polarizing agent circularly polarizes the light passing through the projection surface 3. The light is primarily s-reflected at the outer surface A of the projection surface and circularly polarized again upon passing through the λ / 4 polarizing agent.In this way, a p-polarized light component transmitted on the inner side I can be directed to the user by reflection on the outer side A to a lesser extent than in the above-described embodiment, but the overall efficiency of reflection on the projection surface 3 is nevertheless improved compared to a conventional projection surface without a polarizing agent. Furthermore, the proportion of p-polarized light in the reflected overall image is larger, so that the projected image can still be perceived when using p-polarized sunglasses.

[0043] In a further embodiment with a projection device 2 that emits purely s-polarized light, with an otherwise identical configuration of the field of view display device 1, a λ / 4 polarization means (polarization means 34) still results in a proportion of s-polarized light of 23.8% and p-polarized light of 4.2% of the total light intensity emitted by the light source 21. Thus, even with a projection device 2 that emits only s-polarized light, perception of the p-polarized secondary image is possible when using a λ / 4 polarization means.

[0044] The polarizing agent 34 can be applied as a coating or layer (film) on the inner or outer pane layer 33, 32. Alternatively, the polarizing agent 34 can be incorporated into or applied to the tilt element 31, which is designed as a wedge film or plate.

[0045] The outer pane layer 32, the tilt element 31, the polarizing means 34, and the inner pane layer 33 are designed such that, apart from the inner side I and the outer side A of the projection surface 3 or windshield 4 formed thereby, no optical interfaces are formed at which reflection could occur. In particular, no reflection planes are provided within the interior of the projection surface 3.

[0046] Furthermore, it can be provided that the polarizing means 34 is provided between two interfaces (in the embodiments shown between the outer side A and the inner side I of the windshield 4). In particular, the outer pane layer 32, the inclination element 31, the polarizing means 34 and the inner pane layer 33 have the same or approximately the same refractive indices. List of reference symbols

[0047] 1Viewing field display device 2Projection device 3Projection surface 4Windshield 21Light source 22Transparent display device 23Image optics 31Tilt element 32Outer pane layer 33Inner pane layer 34Polarizing agent IInside AOutside

Claims

1. Field-of-view display device (1), in particular for use in a motor vehicle, comprising: - a projection screen (4), in particular a windscreen, which is designed at least in one region as a projection surface (3), the projection surface (3) comprising: o a first reflection surface (I), which is suitable for reflecting from a projected image a light component that is polarized in a first type of polarization and transmitting from a projected image a light component that is polarized in a second type of polarization, o a second reflection surface (A), which is suitable for reflecting from the projected image a light component that is polarized in the first type of polarization and for transmitting from a projected image a light component that is polarized in the second type of polarization, o a polarization means (34), arranged between the first reflection surface (I) and the second reflection surface (A), for changing a polarization of the light transmitting through the projection surface (3) in such a way that the light component of the second type of polarization transmitting through the first reflection surface (I) is changed to a light component of the first type of polarization, is reflected at the second reflection surface (A) and, when passing again through the polarization means (34), is changed to a light component of the second type of polarization, which transmits through the first reflection surface (I), wherein the polarization means is formed as a λ / 4 polarization means, which brings about circular polarization, and - a projection device (2) for projecting an image to be projected onto the first reflection surface (I) of the projection screen (3) in a direction parallel to a first polarization plane, with the projection device (2) having a light source (21) for providing the light required for the projection of the image, with the light source (21) emitting unpolarized light.

2. Field-of-view display device (1) according to Claim 1, wherein the first and the second reflection surface (I, A) are inclined, using an inclination element (31), in particular a wedge film, relative to each other in such a way that a light component which transmits through the first reflection surface (I) and is reflected at the second reflection surface (A) leaves the projection surface (3) in the same direction as a light component reflected at the first reflection surface (I) in such a way that the partial images of the projected image which are generated by the two light components overlap without offset.

3. Field-of-view display device (1) according to Claim 1 or 2, wherein the polarization means (34) is formed as a layer, in particular as a film.

4. Field-of-view display device (1) according to any of Claims 1 to 3, wherein the first reflection surface (I) is formed as an interface formed by one side of an inner screen layer (33) and the second reflection surface (A) is formed as an interface of the projection surface (3) formed by one side of an outer screen layer (32).

5. Field-of-view display device (1) according to any of Claims 1 to 4, wherein exactly one polarization means (34) is arranged between the first and the second reflection surface (I, A).

6. Field-of-view display device (3) according to any of Claims 1 to 5, wherein only a first and only a second reflection surface (I, A) are provided.