Head-up display

Abstract

To provide a head-up display that achieves low power consumption and bright and excellent display visibility.SOLUTION: A head-up display comprises: a reflective display element using reflected light as display light; a front windshield having a daylighting region that transmits external light and a display region that can be irradiated with the display light; and a daylighting element that guides the external light transmitted through the daylighting region to the reflective display element. The front windshield includes a screen that blocks at least part of the external light in the display region. The reflective display element includes a display panel and an off-axis reflective member.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The following disclosure relates to head-up displays. [Background technology]

[0002] In recent years, head-up displays (HUDs) have been adopted by many automobile manufacturers as driving assistance systems. HUDs are displays that use a combiner (half mirror) or front windshield to display information such as vehicle speed, route guidance, and warning lights within the forward field of view. HUDs play an important role as driving safety systems because they can prevent drivers from looking away from the road by reducing the amount of eye movement.

[0003] The main conventional HUD method combines a display element such as a transmissive liquid crystal display (LCD), digital mirror device (DMD), or LCOS (Liquid Crystal on Silicon) with an LED light source.

[0004] HUD systems that reduce power consumption by utilizing external light are also known (see Patent Documents 1 and 2). For example, Patent Document 1 describes a method in which external light is taken in through an introduction path (beam splitter, condenser lens, etc.) opened in the dashboard, and is irradiated onto a liquid crystal panel such as a reflective liquid crystal panel or a semi-transmissive liquid crystal panel, and the reflected display light from the liquid crystal panel is reflected by a half mirror placed inside the front windshield, thereby obtaining a HUD display (display by HUD).

[0005] Furthermore, Patent Documents 3 to 7 are known as documents disclosing prior art in the fields of front windshields and optical technology. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-076633 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-121988 [Patent Document 3] Patent No. 7209461 [Patent Document 4] Patent No. 6913484 [Patent Document 5] Patent No. 6757314 [Patent Document 6] Patent No. 6345259 [Patent Document 7] Patent No. 6461600 Summary of the Invention [Problem to be solved by the invention]

[0007] As the shift to electric vehicles continues worldwide, there is a demand for reducing the power consumption of in-vehicle displays. The conventional mainstream HUD system uses LED light sources, but it is difficult to reduce power consumption because the LED light sources must be constantly on and must emit high brightness light to obtain a bright display even on sunny days.

[0008] Furthermore, the HUD system disclosed in Patent Document 1 is configured such that the optical path that takes in external light is located at the bottom of the front windshield, and the half mirror for the HUD display is located above the optical path that takes in external light, so the half mirror blocks the driver's forward field of view, which hinders safe driving.

[0009] The present invention has been made in view of the above-mentioned current situation, and has as its object to provide a head-up display that consumes less power and achieves bright and good display visibility. [Means for solving the problem]

[0010] (1) One embodiment of the present invention is a head-up display comprising a reflective display element that uses reflected light as display light, a front windshield having a light-collecting area that transmits external light and a display area onto which the display light can be irradiated, and a light-collecting element that guides the external light that has transmitted through the light-collecting area to the reflective display element, wherein the front windshield has a screen in the display area that blocks at least a portion of the external light, and the reflective display element includes a display panel and an off-axis reflective member.

[0011] (2) Furthermore, in one embodiment of the present invention, in addition to the configuration of (1) above, the display area is positioned below the center of the front windshield in the vertical direction, and the lighting area is positioned above the display area on the front windshield.

[0012] (3) Furthermore, in one embodiment of the present invention, in addition to the configuration of (2) above, the display area includes a lower end of the front windshield.

[0013] (4) Furthermore, in addition to the configuration of (1), (2), or (3) above, one embodiment of the present invention is a head-up display in which the reflective display element is projected onto the surface of the front windshield along the normal direction of the surface, the projection area of ​​the reflective display element is projected onto the surface of the front windshield along the normal direction of the surface, and the projection area of ​​the reflective display element is located below the projection area of ​​the light-gathering element.

[0014] (5) In addition to the configuration of (4), one embodiment of the present invention is a head-up display, wherein the projection area of ​​the reflective display element overlaps the display area.

[0015] (6) Furthermore, in addition to the configuration of (4) or (5), one embodiment of the present invention is a head-up display, in which the projection area of ​​the light-collecting element at least partially overlaps the display area.

[0016] (7) Furthermore, in addition to the configuration of (6), one embodiment of the present invention is a head-up display, in which the projection area of ​​the light-collecting element also overlaps with the light-collecting area.

[0017] (8) Furthermore, one embodiment of the present invention is a head-up display in which, in addition to the configuration of (1), (2), (3), (4), (5), (6), or (7) above, the light-collecting element includes a light-collecting mirror, and the light-collecting mirror is positioned so that the center of its reflective surface faces the display area.

[0018] (9) Furthermore, in addition to the configuration of (8), one embodiment of the present invention is a head-up display, wherein the collecting mirror has a parabolic or free-form surface shape.

[0019] (10) Furthermore, in addition to the configuration of (9), one embodiment of the present invention is a head-up display, wherein the collecting mirror has a region whose curvature changes from the front side of the vehicle to the rear side of the vehicle.

[0020] (11) Furthermore, in one embodiment of the present invention, in addition to the configuration of (8) or (9) above, the collecting mirror has a curved surface shape extending from one side to the other in the longitudinal direction of the vehicle, and also has a curved surface shape extending from one side to the other in the vehicle width direction perpendicular to the longitudinal direction.

[0021] (12) Furthermore, in one embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), (6), or (7) above, the light-collecting element includes a light-collecting film, and the light-collecting film is positioned so that the center of its light-collecting surface faces the light-collecting area.

[0022] (13) Furthermore, in one embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), or (12) above, the off-axis reflecting member includes a Pancharatnam Berry phase diffraction grating and a quarter-wave plate.

[0023] (14) Furthermore, in one embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), or (13) above, the display panel is a head-up display that includes a reflective liquid crystal panel or a semi-transmissive liquid crystal panel.

[0024] (15) Furthermore, in one embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13), or (14) above, the screen includes a colored interlayer or window film.

[0025] (16) Furthermore, in one embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13), (14), or (15) above, the screen includes a linear polarizer, and the direction of the transmission axis of the linear polarizer is the vertical direction of the front windshield.

[0026] (17) Furthermore, in one embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13), (14), (15), or (16) above, a head-up display further includes a viewing distance magnification element disposed between the reflective display element and the display area.

[0027] (18) Furthermore, in one embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13), (14), (15), (16), or (17) above, the reflective display element has a curved shape configured so that the display light is condensed and incident on the screen. [Effects of the Invention]

[0028] According to the present invention, it is possible to provide a head-up display that consumes less power, is bright, and provides good display visibility. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a side view schematically showing a head-up display according to a first embodiment. [Figure 2] FIG. 2 is a diagram for explaining the curved surface shape of the collector mirror in FIG. [Figure 3] FIG. 2 is a cross-sectional view schematically showing the configuration of the semi-transmissive liquid crystal panel in FIG. [Figure 4] FIG. 4 is a cross-sectional view schematically showing the configuration of the PBP diffraction grating in FIG. [Figure 5] FIG. 4 is a plan view schematically showing the configuration of the PBP diffraction grating in FIG. 3. [Figure 6] FIG. 1 is a diagram illustrating the principle of off-axis reflection characteristics. [Figure 7] FIG. 10 is a side view schematically showing a head-up display according to a second modification. [Figure 8] FIG. 10 is a side view schematically showing a head-up display according to a second embodiment. [Figure 9] FIG. 10 is a side view schematically showing a head-up display according to a third embodiment. [Figure 10] FIG. 10 is a side view schematically showing an example of a head-up display according to a fourth embodiment. [Figure 11] FIG. 10 is a side view schematically showing an example of a head-up display according to a fifth embodiment. [Figure 12] FIG. 2 is a side view schematically showing a head-up display of Comparative Example 1. [Figure 13] FIG. 10 is a side view schematically showing a head-up display of Comparative Example 2. [Figure 14] 2 is a diagram for explaining the relationship between external light and display visibility using the head-up display of the first embodiment as an example. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0030] (Summary of the Disclosure) The head-up display of the present disclosure includes a reflective display element, a front windshield, and a light-collecting element.

[0031] The reflective display element is not limited to any display element that uses reflected light as display light, and includes display panels and off-axis reflectors. Examples of the display panel include semi-transmissive liquid crystal panels and reflective liquid crystal panels. Semi-transmissive liquid crystal panels can perform both reflective display using external light (outdoor light) and transmissive display using a light source such as an LED light source. The light source used for transmissive display is typically located on the rear side of the liquid crystal panel (the opposite side of the display surface relative to the liquid crystal layer of the liquid crystal panel) (also called a "backlight"). Semi-transmissive liquid crystal panels, for example, perform reflective display using reflected light as display light in bright environments and transmissive display in dark environments such as at night. The off-axis reflector is an optical element with reflection characteristics in which the incident angle and reflection angle differ, and is preferably designed to reflect obliquely incident light in the direction normal to the panel. With a normal transflective LCD panel or reflective LCD panel that does not have an off-axis reflective component, it is necessary to design the optical path using an angle that is shifted from the specular reflection angle at which the brightest reflective display is obtained so that the light specularly reflected from the LCD panel surface does not interfere with the visibility of the reflective display on the display. On the other hand, by using an off-axis reflective component, the angle at which the brightest reflective display is obtained can be shifted from the specular reflection angle, making it possible to achieve both good visibility and a bright display for the HUD display.

[0032] The front windshield has a lighting area that transmits external light and a display area onto which display light can be irradiated. The display area is not limited to a specific type, as long as it has a screen that blocks at least a portion of the external light. The screen can be a semi-transparent layer such as a colored interlayer, window film, or polarizing plate. The presence of the screen can reduce the amount of light incident from the front of the vehicle, which reduces the visibility of the HUD display.

[0033] The light-collecting element is not limited as long as it guides external light that has passed through the light-collecting area of ​​the front windshield to the reflective display element. The light-collecting element plays a role of concentrating external light on the reflective display element. The light-collecting element can be a light-collecting mirror or a light-collecting film, or both can be used.

[0034] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the same reference numerals are used in different drawings to designate the same parts or parts having similar functions, and repeated description thereof will be omitted as appropriate.

[0035] (Embodiment 1) The configuration of a head-up display (HUD) according to the first embodiment will be described with reference to FIGS. Fig. 1 is a side view schematically showing a head-up display of embodiment 1. Fig. 2 is a diagram for explaining the curved surface shape of the collecting mirror in Fig. 1. Fig. 3 is a cross-sectional view schematically showing the configuration of the semi-transmissive liquid crystal panel in Fig. 1. Fig. 4 is a cross-sectional view schematically showing the configuration of the PBP diffraction grating in Fig. 3, and Fig. 5 is a plan view schematically showing the configuration of the PBP diffraction grating in Fig. 3. Arrows in Fig. 1 indicate the optical path of external light used for displaying on the head-up display (HUD display).

[0036] The head-up display of the first embodiment includes a reflective display element 100, a light-collecting mirror 200 as a light-collecting element, and a front windshield (windshield) 300. The reflective display element 100 includes a semi-transmissive liquid crystal panel 110 as a display panel and a laminate of a Pancharatnam-Berry Phase (PBP) diffraction grating 150 and a quarter-wave plate 140 as an off-axis reflective member. In the present disclosure, a quarter-wave plate refers to a member that imparts a phase difference corresponding to one-quarter of the wavelength of transmitted light. For example, a member that imparts a phase difference of 117.5 nm or more and 157.5 nm or less to light with a wavelength of 550 nm can be used. The front windshield 300 includes a screen 310 between laminated glass 350. The screen 310 is a member used for HUD display and is not particularly limited as long as it blocks at least a portion of external light.

[0037] The reflective display element 100 and the collecting mirror 200 are disposed in a dashboard located in front of the seats (driver's seat and passenger seat) of the vehicle C and below the front windshield 300. External light taken in from a highly transmittance light-collecting area (external light entrance area) 300L located at the top of the front windshield 300 passes through a light-transmitting area (opening) provided in the dashboard and enters the collecting mirror 200. The external light is collected by the collecting mirror 200 onto the reflective display element 100. The external light is used as a light source for the reflective display element 100, and light reflected by a reflective member within the reflective display element 100 is used for display by the reflective display element 100. The display light emitted from the reflective display element 100 is irradiated into a display area 300D located at the bottom of the front windshield 300. It is not necessary to use the entire display area 300D to perform HUD display; as shown in FIG. 1, display light may be irradiated onto a portion of the display area 300D and the portion may be used to perform HUD display. The display light is reflected off a screen 310 provided in the display area 300D and enters the eye E of the driver of the vehicle C seated in the driver's seat. As a result, the driver recognizes the display on the reflective display element 100 as a HUD display on the screen 310. That is, as shown by the arrows in the figure, the light used for HUD display travels in the following order: the sun, the light-collecting area 300L of the front windshield, the light-collecting mirror (light-collecting element) 200, the reflective display element 100, the screen 310, and the driver's eye E. This optical path makes it possible to ensure both a safe forward field of view for the driver and a bright HUD display.

[0038] As shown in FIG. 1, display area 300D is located below the center of front windshield 300 in the up-down direction (see FIG. 1), and lighting area 300L is located above display area 300D on front windshield 300. By separating lighting area 300L and display area 300D and locating lighting area 300L above display area 300D, which is located at the bottom of front windshield 300, it is possible to ensure both a safe forward field of view for the driver and a bright HUD display. Display area 300D is preferably located so as to include the lower edge of front windshield 300. Here, the lower edge does not include a portion that is not visible to the driver (for example, the attachment portion of front windshield 300 to vehicle C).

[0039] As shown in FIG. 1, the area P1 where the reflective display element 100 is projected onto the surface of the front windshield 300 along the normal direction of the surface is called the "projection area of ​​the reflective display element 100," and the area P2 where the light-collecting element (light-collecting mirror 200) is projected onto the surface of the front windshield 300 along the normal direction is called the "projection area of ​​the light-collecting element." In this case, the projection area P1 of the reflective display element 100 is located below the projection area P2 of the light-collecting element. The projection area P1 of the reflective display element 100 preferably overlaps the display area 300D. The projection area P2 of the light-collecting element preferably at least partially overlaps the display area 300D, and more preferably also overlaps the light-collecting area 300L.

[0040] The semi-transmissive liquid crystal panel 110 is a liquid crystal display element capable of both reflective display using light reflected by a reflector provided on the TFT substrate and transmissive display using light transmitted through an opening in the reflector. Since external light taken in through the light-collecting region 300L can be used as a light source during reflective display, the power consumption of the head-up display can be reduced. The reflector has a micro-reflective structure (MRS). The shape of the MRS allows it to efficiently reflect external light, resulting in a bright reflective display. While the present embodiment employs an MRS, a similarly bright reflective display can also be obtained by, for example, using a flat, mirror-like reflector and placing a scattering film outside the liquid crystal panel.

[0041] Although reflective display is possible using a reflective liquid crystal panel instead of the semi-transmissive liquid crystal panel 110, a semi-transmissive liquid crystal panel is preferable for ensuring nighttime display performance. By arranging a light source (also called a "front light") on the front side of the reflective liquid crystal panel (the same side as the display surface relative to the liquid crystal layer of the liquid crystal panel) and reflecting the light from the light source using a reflective member within the liquid crystal panel, nighttime display performance can be ensured even when using a reflective liquid crystal panel. The front light may be configured as a front light composed of a light guide plate and LEDs arranged on its edge surface, and arranged so as to overlap the display surface of the reflective liquid crystal panel. Alternatively, a front light composed of a scattering plate, a microlens array, LEDs, etc. may be arranged on the outer periphery of the collecting mirror 200 or in an opening provided in part of the collecting mirror 200.

[0042] The collector mirror 200 is fabricated by forming a thin film of a highly reflective metal, such as aluminum, silver, an aluminum alloy, or a silver alloy, by vapor deposition or sputtering on a plastic substrate that has been injection-molded using a mold. The collector mirror 200 is positioned so that the center of its reflective surface faces the display area 300D. The collector mirror 200 of this embodiment has a parabolic or free-form surface shape so that it can efficiently collect incident light from the front windshield 300 onto the semi-transmissive liquid crystal panel 110. The collector mirror 200 preferably has a region whose curvature changes from the front side of the vehicle C to the rear side of the vehicle C. In the example of FIG. 2, the collector mirror 200 has two regions A and B whose curvature changes differently from each other. As shown in FIG. 2, region B of the collector mirror 200, which is located in the front side of the vehicle C and is shaded by the screen 310, has a more limited angle of incidence of external light on the collector mirror 200 than region A, which is located further rearward of the vehicle C than region B and is not shaded by the screen 310. Therefore, it is preferable that the curvature change in region A be large in order to collect external light incident at various angles of incidence, whereas the curvature change in region B may be small. In other words, the curvature change in region A is larger than the curvature change in region B. The curvature of region B may be constant. Furthermore, it is preferable that the collecting mirror 200 has a curved surface shape from one side to the other in the longitudinal direction of the vehicle C, and also from one side to the other in the width direction of the vehicle C, which is perpendicular to the longitudinal direction. In other words, it is preferable that the collecting mirror 200 has a curved surface shape along each of two directions that are perpendicular to each other (the width direction of the vehicle C and the direction perpendicular to the width direction). This makes it possible to obtain a higher external light collecting effect.

[0043] In this embodiment, the screen 310 is formed by a colored interlayer film disposed between the laminated glass sheets constituting the front windshield, as described in, for example, Japanese Patent No. 7209461 (the above-mentioned Patent Document 3). The interlayer film is a functional film disposed between the laminated glass sheets 350 of the front windshield 300. For example, a resin film made from polyvinyl butyral or ethylene vinyl acetate can be used as the interlayer film. A colored interlayer film can be obtained by coloring the resin film with a pigment. By disposing the screen 310 on the front windshield 300, the visibility of the HUD display can be improved.

[0044] <Off-axis reflection characteristics> In this embodiment, circular polarizers 120 and 130 are attached to the front and back of the semi-transmissive liquid crystal panel 110, respectively. Here, the front of the semi-transmissive liquid crystal panel 110 refers to the surface onto which external light guided by the light-collecting element is incident, and the back of the semi-transmissive liquid crystal panel 110 refers to the surface opposite to the front of the semi-transmissive liquid crystal panel 110. The circular polarizers 120 and 130 are each composed of a linear polarizer (absorptive polarizer) 122 and 132 and a retardation plate 121 and 131. The retardation plates 121 and 131 are, for example, composed of a quarter-wave plate, a combination of a quarter-wave plate and one or two half-wave plates, or a combination of these with a negative C plate or the like. The linear polarizer 122 is disposed on the outermost layer side (the side on which external light is incident) of the front-side circular polarizer 120. The off-axis reflective member is a member that imparts off-axis reflective properties to the display panel (semi-transmissive liquid crystal panel 110). In this embodiment, the off-axis reflective member is a laminate of a quarter-wave plate 140 and a Pancharatnam Berry phase (PBP) diffraction grating 150 disposed on the front-side circular polarizer 120.

[0045] The PBP diffraction grating 150 is an optical film having a retardation layer 158 formed by applying an alignment film 154 provided on a base material 152 made of a glass substrate, a PET film, or the like to an alignment film 154 that has been subjected to an alignment treatment, coating the alignment film 154 with a polymerizable liquid crystal 156, and photo-curing the polymerizable liquid crystal 156 with ultraviolet light.

[0046] The PBP diffraction grating 150 can be fabricated by the methods described in, for example, International Publication No. 2019 / 189818 and JP-A-2008-532085.

[0047] As shown in FIG. 5, in a plan view, the alignment direction of the cured polymerizable liquid crystal 156 periodically rotates in the x-axis direction from one end of the retardation layer 158 to the other end within the plane of the retardation layer 158, but does not periodically rotate in the y-axis direction perpendicular to the x-axis direction. Here, the long axis of the cured polymerizable liquid crystal 156 is the slow axis. That is, in the retardation layer 158 provided in the PBP diffraction grating 150, the direction of the slow axis derived from the cured polymerizable liquid crystal 156 changes while continuously rotating along the x-axis direction within the plane. The direction of the slow axis can be confirmed using a polarizing microscope or Axoscan (AxoMetrics).

[0048] The PBP diffraction grating 150 can control the diffraction angle of incident light by changing the pitch of the liquid crystal orientation. The pitch of the liquid crystal orientation may be varied within the plane of the PBP diffraction grating 150. This allows multiple regions with different diffraction angles to be formed within the plane of the PBP diffraction grating 150, depending on the incidence angle distribution of the incident light.

[0049] The alignment film 154 has a patterned in-plane alignment regulating force. Specifically, the alignment film 154 has an alignment regulating force that aligns the polymerizable liquid crystal 156 so that the slow axis of the retardation layer 158 rotates periodically in-plane.

[0050] Materials that are common in the field of liquid crystal panels, such as polymers having polyimide in the main chain, polymers having polyamic acid in the main chain, and polymers having polysiloxane in the main chain, can be used as the material for the alignment film 154. The alignment film 154 can be formed by applying an alignment film material onto the substrate 152. The application method is not particularly limited, and for example, flexographic printing, inkjet application, etc. can be used.

[0051] The type of alignment film 154 is not particularly limited, and may be a rubbed alignment film that has been subjected to a rubbing treatment as an alignment treatment, or a photo-alignment film that has photo-functional groups and has been subjected to a photo-alignment treatment as an alignment treatment. However, from the viewpoint of patterning the in-plane alignment control force into a complex pattern, a photo-alignment film is preferable.

[0052] The retardation layer 158 is obtained by polymerizing polymerizable liquid crystal 156. The type of polymerizable liquid crystal 156 is not particularly limited, and conventionally known polymerizable liquid crystal compounds can be used, with those that polymerize and harden when irradiated with ultraviolet (UV) light being preferred. Examples of the polymerizable liquid crystal 156 include polymers having a side chain with a structure that combines a mesogen group such as a biphenyl group, a terphenyl group, a naphthalene group, a phenylbenzoate group, an azobenzene group, or a derivative thereof, with a photoreactive group such as a cinnamoyl group, a chalcone group, a cinnamylidene group, a β-(2-phenyl)acryloyl group, a cinnamic acid group, or a derivative thereof, and having a structure such as acrylate, methacrylate, maleimide, N-phenylmaleimide, or siloxane in the main chain.

[0053] The polymerizable liquid crystal 156 may be a homopolymer consisting of a single repeating unit, or a copolymer consisting of two or more repeating units with different side chain structures. The copolymer may be any of an alternating type, a random type, a graft type, etc.

[0054] The diffraction efficiency η of the PBP diffraction grating 150 is expressed as η=sin 2 The efficiency is expressed as (Δndπ / λ), and is 100% when the phase difference Δnd=λ / 2. Therefore, the phase difference layer 158 is usually designed so that Δnd=λ / 2. Since the PBP diffraction grating 150 functions as a λ / 2 plate, incident circularly polarized light is converted into counter-rotating circularly polarized light before exiting.

[0055] FIG. 6 illustrates the principle of off-axis reflection characteristics. As described above, the PBP diffraction grating 150 has the property of emitting circularly polarized light with the opposite rotation when circularly polarized light is incident on it. As shown in FIG. 6, when external light is obliquely incident on the PBP diffraction grating 150 at an incident angle θ, the left-handed circularly polarized light component is diffracted at a diffraction angle of θ / 2, converted to right-handed circularly polarized light, and emitted from the PBP diffraction grating 150. The light then passes through the quarter-wave plate 140 and is converted into linearly polarized light, which then enters the front-side circular polarizer 120 and the transflective liquid crystal panel 110. When the transflective liquid crystal panel 110 is oriented in a white display mode, the incident linearly polarized light passes through the front-side circular polarizer 120 and liquid crystal layer, is reflected by the reflector on the TFT substrate, and then passes again through the liquid crystal layer and the front-side circular polarizer 120 to be emitted as linearly polarized light. The linearly polarized light specularly reflected by the transflective liquid crystal panel 110 passes through the quarter-wave plate 140 and is converted to right-handed circularly polarized light. The right-handed circularly polarized light is then diffracted by the PBP diffraction grating 150 at a diffraction angle of θ / 2, converted into left-handed circularly polarized light, and emitted in the front direction (panel normal direction) of the semi-transmissive liquid crystal panel 110. As described above, by combining the PBP diffraction grating 150, the quarter-wave plate 140, and the semi-transmissive liquid crystal panel 110, an off-axis reflection characteristic that reflects obliquely incident light in the front direction is realized.

[0056] (Variation 1) In the first embodiment, a colored interlayer film is used as a screen that blocks at least a portion of external light, but the same effect as that of a colored interlayer film can also be obtained by applying a window film to the inside of the front windshield. There are no particular limitations on the window film, as long as it is applied to the windows of vehicles such as automobiles for purposes such as UV protection, privacy protection, shatterproofing of glass, and decoration. Examples of window films include those described in Japanese Patent No. 6913484 (the above-mentioned Patent Document 4) and Japanese Patent No. 6757314 (the above-mentioned Patent Document 5), which use a polyethylene terephthalate film (PET film / PET: Polyethylene Terephthalate) colored with a pigment or the like.

[0057] (Variation 2) A linear polarizer may be used as a screen for blocking at least a portion of external light, and an absorptive polarizer is particularly preferred. Examples of absorptive polarizers include those made of a polyvinyl alcohol (PVA) dyed stretched film polarizer and a triacetylcellulose (TAC) protective layer. Various types of linear polarizers, such as dye-based polarizers and coated polarizers, may also be used.

[0058] FIG. 7 is a side view schematically illustrating a head-up display (HUD) according to Modification 2. The arrows in FIG. 7 indicate the optical paths of external light used for HUD display. The head-up display shown in FIG. 7 is similar to the head-up display according to Embodiment 1, except that a linear polarizer 320 is provided instead of the colored interlayer. As shown in FIG. 7, the linear polarizer 320 is disposed so that the absorption axis direction is perpendicular to the paper surface and the transmission axis direction is perpendicular to the absorption axis direction (the direction indicated by the double arrow in the figure). This axial arrangement allows the linear polarizer 320 to block unnecessary reflected light from the road surface. During rainy nights, reflected light from puddles on the road surface can interfere with driving, but the linear polarizer 320 effectively ensures safe driving of the vehicle C and the display performance of the HUD. Furthermore, reflections from the road surface (such as asphalt) on clear days reduce the clarity of the HUD display. Unwanted reflected light from the road surface contains a large amount of S-waves, which vibrate horizontally to the road surface. By arranging the linear polarizer 320 inside the front windshield 300 so that the absorption axis is aligned horizontally to the road surface as seen by the driver of vehicle C, in other words so that the direction of the transmission axis of the linear polarizer 320 coincides with the vertical direction of the front windshield 300, it is possible to effectively remove the S-wave component of unnecessary reflected light.

[0059] (Variation 3) In embodiment 1, a combination of a PBP diffraction grating and a quarter-wave plate is used as the off-axis reflecting element, but similar off-axis reflection characteristics can also be obtained by placing an anisotropic scattering film, such as that described in Japanese Patent No. 6345259 (the above-mentioned Patent Document 6), in front of the semi-transmissive liquid crystal panel.

[0060] (Embodiment 2) Fig. 8 is a side view showing a schematic diagram of a head-up display according to the second embodiment. The arrows in Fig. 8 indicate the optical path of external light used for HUD display. The head-up display according to the second embodiment has the same configuration as the head-up display according to the first embodiment, except that a lighting film 210 is used as the lighting element. The lighting film 210 is arranged so that the center of its lighting surface faces the lighting area 300L. The lighting element of the head-up display is housed in an opening in the dashboard, and a protective cover made of a transparent resin substrate such as glass or acrylic is provided over the opening to prevent the intrusion of dust and debris. The lighting film 210 is preferably used in a state where it is attached to the protective cover with an adhesive. For the sake of simplicity, the protective cover is not shown in Figure 8. The daylighting film 210 is not particularly limited as long as it has a structure for efficiently capturing external light. Examples include those installed on windowpanes in homes and offices to efficiently capture external light indoors. Specifically, for example, the film described in Japanese Patent No. 6461600 (Patent Document 7) can be used. The daylighting film 210 is manufactured by forming an acrylic or epoxy-based photosensitive resist film on a substrate such as a TAC or PET film, and then forming fine, regular stripe-shaped protrusions using a photolithography process with an exposure mask. The daylighting film 210 utilizes total reflection within the protrusions to transmit external light incident at various angles from one side of the film at a constant angle from the other side. In this embodiment, the light path conversion function of the daylighting film 210, like the light-collecting mirror of Embodiment 1, can effectively guide external light to a semi-transmissive liquid crystal panel.

[0061] (Embodiment 3) Fig. 9 is a side view showing a schematic diagram of a head-up display according to embodiment 3. The arrows in Fig. 9 indicate the optical path of external light used for HUD display. The head-up display according to embodiment 3 has the same configuration as the head-up display according to embodiment 1, except that a combination of a lighting film 210 and a light-collecting mirror (free-form surface mirror) 200 is used as the lighting element. As explained in the second embodiment above, the daylighting film 210 has the function of using total reflection within the protrusions to emit external light incident at various angles from one side of the film at a fixed angle from the other side, but not all of the incident light is totally reflected; some of it passes through the daylighting film (protrusions) 210 at the same angle as the incident light. In Figure 9, the optical path of light emitted from the daylighting film 210 at a specified angle is shown by a solid line, and the optical path of light that has passed through the daylighting film 210 is shown by a dotted line. In this embodiment, the optical path of the transmitted light that is not totally reflected is changed by the collecting mirror 200, so that external light can be effectively guided to the semi-transmissive LCD panel without any waste.

[0062] (Embodiment 4) The head-up display of embodiment 4 has the same configuration as the head-up displays of embodiments 1 to 3, except that a convex lens serving as a viewing distance magnification element is additionally provided between the reflective display element and the display area. As an example of the head-up display of embodiment 4, a configuration in which a convex lens is added to the head-up display of embodiment 1 is shown in FIG. 10. FIG. 10 is a side view schematically showing an example of the head-up display of embodiment 4. The arrows in FIG. 10 indicate the optical path of external light used for HUD display. The shorter the distance the focus shifts from the vehicle's forward field of view to the HUD display while driving, the less strain the driver's eyes will have, which is preferable for safe driving. For this reason, HUD displays are generally designed to be displayed at a distance from the front windshield 300. Drivers typically look about 20 meters ahead, and displaying the HUD display about 2 meters from the driver's seat reduces the strain on the driver's eyes in adjusting the focus. Taking the above into consideration, in this embodiment, a convex lens 400 is disposed on the front windshield 300 side of the semi-transmissive liquid crystal panel. As shown in Fig. 10, display light emitted from the semi-transmissive liquid crystal panel is condensed by the convex lens 400, reflected by a screen 310 made of a colored interlayer film, and reaches the driver's eye E. Because the human brain determines that light travels in a straight line and enters the eye, the human perceives a distant virtual image at the end of the optical path of the reflected light from the screen 310 extended to the outside of the vehicle as the HUD display.

[0063] (Embodiment 5) The head-up display of embodiment 5 has the same configuration as the head-up displays of embodiments 1 to 3, except that a reflective display element employing a curved semi-transmissive liquid crystal panel is used as the display panel. The laminate of the Pancharatnam-Berry phase grating and the quarter-wave plate serving as the off-axis reflector also has a curved shape that conforms to the curved shape of the curved semi-transmissive liquid crystal panel. As an example of the head-up display of embodiment 5, FIG. 11 shows a configuration in which a curved semi-transmissive liquid crystal panel is applied to the head-up display of embodiment 1. FIG. 11 is a side view schematically illustrating an example of the head-up display of embodiment 5. The arrows in FIG. 11 indicate the optical path of external light used for HUD display. The reflective display element 180, which employs a curved semi-transmissive liquid crystal panel as the display panel, is composed of a thinned semi-transmissive liquid crystal panel, a curved backlight unit with a curved surface of a certain curvature, and a curved housing that secures them. The curved housing is composed of a top chassis, a molded frame, a bottom chassis, etc. In this embodiment, since the semi-transmissive liquid crystal panel itself has a curved surface, display light is incident on the screen 310 on the front windshield 300 in a concentrated state. As a result, the HUD display is displayed as a virtual image in the distance, similar to the fourth embodiment.

[0064] The effects of the present invention will be explained below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0065] Example 1 The head-up display of the first embodiment has the following configuration. Reflective display elements: PBP diffraction grating, 1 / 4 wavelength plate and semi-transmissive LCD panel Light collecting element: Free-form mirror Screen: Colored interlayer (transmittance 20%)

[0066] Example 2 The head-up display of the first embodiment has the following configuration. Reflective display elements: PBP diffraction grating, 1 / 4 wavelength plate and semi-transmissive LCD panel Light collecting element: Free-form mirror Screen: Colored interlayer (transmittance 5%)

[0067] Example 3 The head-up display of the first embodiment has the following configuration. Reflective display elements: PBP diffraction grating, 1 / 4 wavelength plate and semi-transmissive LCD panel Light collecting element: Free-form mirror Screen: Colored interlayer (transmittance approximately 0% (infinitely small))

[0068] Example 4 The head-up display of the first embodiment has the following configuration. Reflective display elements: PBP diffraction grating, 1 / 4 wavelength plate and semi-transmissive LCD panel Light collecting element: Free-form mirror Screen: Linear polarizer (single transmittance 45%)

[0069] Example 5 A head-up display according to a second embodiment has the following configuration. Reflective display elements: PBP diffraction grating, 1 / 4 wavelength plate and semi-transmissive LCD panel Lighting element: Lighting film Screen: Colored interlayer (transmittance 20%)

[0070] Example 6 A head-up display according to a third embodiment has the following configuration. Reflective display elements: PBP diffraction grating, 1 / 4 wavelength plate and semi-transmissive LCD panel Light-collecting elements: Light-collecting film and free-form mirror Screen: Colored interlayer (transmittance 20%)

[0071] Example 7 A head-up display according to a fourth embodiment has the following configuration. Reflective display elements: PBP diffraction grating, 1 / 4 wavelength plate and semi-transmissive LCD panel Viewing distance expansion element: Convex lens Light collecting element: Free-form mirror Screen: Colored interlayer (transmittance 20%)

[0072] Example 8 A head-up display according to a fifth embodiment has the following configuration. Reflective display elements: PBP diffraction grating, 1 / 4 wave plate and curved transflective LCD panel Light collecting element: Free-form mirror Screen: Colored interlayer (transmittance 20%)

[0073] (Comparative Example 1) 12 is a side view schematically illustrating a head-up display of Comparative Example 1. The arrows in the figure indicate the optical path of external light used for HUD display. As shown in the figure, the head-up display of Comparative Example 1 has the following configuration. Reflective display element 100: PBP diffraction grating, 1 / 4 wavelength plate and semi-transmissive liquid crystal panel Light collecting element: None Screen: None

[0074] (Comparative Example 2) 13 is a side view schematically illustrating a head-up display of Comparative Example 2. The arrows in the figure indicate the optical path of external light used for HUD display. As shown in the figure, the head-up display of Comparative Example 2 has the following configuration. Reflective display element 100: PBP diffraction grating, 1 / 4 wavelength plate and semi-transmissive liquid crystal panel Light collecting element: None Screen 310: Colored interlayer (transmittance 20%)

[0075] (Evaluation of Examples and Comparative Examples) In this embodiment, a PBP diffraction grating and a quarter-wave plate are placed on the front surface of the transflective LCD panel to impart off-axis reflectivity to the panel. Conventional transflective LCD panels without an off-axis reflector require an optical path design that uses an angle shifted from the specular reflection angle at which the brightest reflective display is obtained, so that the light specularly reflected from the LCD panel surface does not interfere with the visibility of the reflective display on the display. By using an off-axis reflector, however, the angle at which the brightest reflective display is obtained can be shifted from the specular reflection angle, thereby achieving both good visibility and a bright display for the HUD display.

[0076] Because a head-up display projects the display panel's content onto a translucent screen, the brightness of external light from behind the screen (outside the vehicle) affects the visibility of the head-up display's content (HUD display). The contrast ratio, expressed by the following formula, is used as an index to evaluate the visibility of a head-up display. Generally, when the external light is bright, a contrast ratio of 1.2 or higher is desirable. Contrast ratio = (background luminance + display luminance) / background luminance

[0077] FIG. 14 is a diagram illustrating the relationship between external light and display visibility using the head-up display of the first embodiment as an example. The arrows in the diagram indicate the optical path of external light used for HUD display. The luminance (external light luminance) of external light L1 incident from the upper part of the front windshield 300 affects the luminance of the display light (display luminance). Furthermore, the luminance of reflected light L2 from the road surface (asphalt) incident on the screen 310 arranged at the lower part of the front windshield 300 corresponds to the background luminance.

[0078] The visibility of the HUD display was compared between Examples 1 to 4 and Comparative Examples 1 and 2. Specifically, the brightness of external light L1 (external light brightness) in a 50,000 lx environment on a fine day with thin clouds was 6,500 cd / m 2 The luminance (background luminance) due to reflected light L2 from the road surface (asphalt) is 2000 cd / m 2 The contrast ratio of the HUD display was calculated when the following conditions were met. The results are shown in Table 1 below.

[0079] [Table 1]

[0080] Due to differences in the configuration of the lighting area 300L and the display area (screen 310), the transmittance varies, resulting in different values ​​of background luminance and display luminance for each example and comparative example, and thus differences in contrast ratio. The contrast ratios of comparative examples 1 and 2 were below 1.2, which is a benchmark for visibility of head-up display information, while the contrast ratios of examples 1 to 4 exceeded 1.2. In example 3, the transmittance of screen 310 was infinitesimal, resulting in an infinite contrast ratio and extremely high visibility of the head-up display information. From the above results, it was found that the examples provided HUD display with good visibility. [Explanation of symbols]

[0081] 10, 100, 180: Reflective display element 30, 300: Front windshield 110: Semi-transmissive LCD panel 120, 130: Circular polarizer 121, 131: Retardation plate 122, 132: Linear polarizer 140:1 / 4 wavelength plate 150: Pancharatnam Berry Phase (PBP) diffraction grating 152: Base material 154: Alignment film 156: Polymerizable liquid crystal 158: Retardation layer 200: Condenser mirror 210: Lighting film 300D:Display area 300L: Daylighting area 310: Screen 320: Linear polarizer 350: Laminated glass 400: convex lens C: Vehicle E: Eyes L1: External light L2: Reflected light from the road surface P1: Area where reflective display element is projected P2: Area projected onto the focusing mirror VI: Virtual Image

Claims

1. a reflective display element that uses reflected light as display light; a front windshield having a lighting area that transmits external light and a display area onto which the display light can be irradiated; a light-collecting element that guides the external light that has passed through the light-collecting area to the reflective display element, the front windshield has a screen in the display area that blocks at least a portion of external light, The reflective display element includes a display panel and an off-axis reflective member. Head-up display.

2. the display area is disposed below the center of the front windshield in the up-down direction, The head-up display according to claim 1 , wherein the light-collecting area is disposed above the display area on the front windshield.

3. The head-up display according to claim 2 , wherein the display area includes a lower edge of the front windshield.

4. 2. A head-up display as described in claim 1, wherein the projection area of ​​the reflective display element, which is an area where the reflective display element is projected onto the surface of the front windshield along a normal direction of the surface, is located below the projection area of ​​the light-collecting element, which is an area where the light-collecting element is projected onto the surface of the front windshield along the normal direction of the surface.

5. The head-up display according to claim 4 , wherein the projection area of ​​the reflective display element overlaps the display area.

6. The head-up display according to claim 4 , wherein a projection area of ​​the light-collecting element at least partially overlaps the display area.

7. The head-up display according to claim 6 , wherein the projection area of ​​the light-collecting element overlaps with the light-collecting area.

8. the light collecting element includes a light collecting mirror, 8. The head-up display according to claim 1, wherein the light-collecting mirror is disposed so that a center portion of the reflective surface thereof faces the display area.

9. The head-up display according to claim 8 , wherein the light-collecting mirror has a parabolic or free-form surface shape.

10. 10. The head-up display according to claim 9, wherein the light-collecting mirror has a region whose curvature changes from the front side of the vehicle to the rear side of the vehicle.

11. 9. The head-up display according to claim 8, wherein the collecting mirror has a curved surface shape extending from one side to the other in a longitudinal direction of the vehicle and from one side to the other in a vehicle width direction perpendicular to the longitudinal direction.

12. the light-collecting element includes a light-collecting film, 8. The head-up display according to claim 1, wherein the light-collecting film is disposed so that a center portion of the light-collecting surface faces the light-collecting area.

13. The head-up display according to any one of claims 1 to 7, wherein the off-axis reflecting member includes a Pancharatnam Berry phase grating and a quarter-wave plate.

14. 8. The head-up display according to claim 1, wherein the display panel includes a reflective liquid crystal panel or a semi-transmissive liquid crystal panel.

15. The head-up display according to any one of claims 1 to 7, wherein the screen includes a colored interlayer or a window film.

16. the screen includes a linear polarizer; 8. The head-up display according to claim 1, wherein the direction of the transmission axis of the linear polarizer is the vertical direction of the front windshield.

17. 8. The head-up display according to claim 1, further comprising a viewing distance magnifying element disposed between the reflective display element and the display area.

18. 8. The head-up display according to claim 1, wherein the reflective display element has a curved surface configured so that the display light is condensed and incident on the screen.

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