Information display apparatus

The present invention relates to an information display apparatus for projecting an image(s) onto a windshield or combiner of an automobile, train, and aircraft, etc. (hereinafter, generally referred to as “vehicle”), and to a projection optical system in which the image is observed as a virtual image through the windshield and to an information display apparatus using the projection optical system.

Already known by Patent Document 1 as mentioned below has been a head-up-display (HUD) apparatus that projects video-image light onto a windshield or combiner of an automobile to form a virtual image(s) and to display traffic information such as route information or traffic congestion information, and vehicle information such as fuel remaining amount or coolant temperature.

Regarding this type of information display apparatus, broadening an area in which a driver can observe (view) the virtual image is desired, while the virtual image with high resolution and high visibility is also an important factor for performance.

The head-up-display apparatus uses an optical system including a concave mirror (having action of a convex lens) to magnify a video image(s) displayed on a video-image display apparatus and provides, as a virtual image(s), the magnified video image to the driver, thus always requiring the windshield or combiner as final reflection surface.

A liquid crystal display element has been often used as the video-image display apparatus utilized in the above HUD apparatus since easily obtaining a high-quality video image(s) and being inexpensive. However, newly clarified has been a problem of bringing significant deterioration (reduction) in performance under a predetermine condition(s) in daytime since sunlight passes through the windshield, is condensed by the concave mirror, and damages a liquid crystal panel and a polarizer (polarizing plate).

The present invention relates to a technical means for reducing the damages given to the liquid crystal display element and the polarizer by the sunlight as mentioned above.

Additionally, according to Patent Document 2 as mentioned below, already known has been a HUD apparatus having a structure in which, for reducing the possibility that a liquid crystal display panel will be damaged by the sunlight, a transmission/reflection member (hot mirror) for causing display light from a liquid crystal display panel to be transmitted and infrared rays to be reflected is provided on a front side of and separately from the liquid crystal display panel in a non-parallel state thereto.

Meanwhile, for example, an apparatus that attaches a main body including a combiner near a ceiling (sun visor) of an automobile has been also proposed as disclosed in Non-Patent Document 1 as mentioned below. However, still remains a safety problem such as the possibility that the driver will suffer an injury when the HUD apparatus is removed from the driver at a time of causing any collision. For this reason, a method of reflecting video-image light directly onto the windshield will conceivably become a mainstream as the HUD apparatus in the future.

Patent Document 1: Japanese Patent Application Laid-open No. 2015-194707

Patent Document 2: Japanese Patent No. 4788882

Non-Patent Document 1: PIONEER R&D (Vol. 22,2013)

An example of the HUD apparatus disclosed in Patent Document 1 as the above-mentioned conventional technique includes: a display device for displaying an image(s); and a projection optical system for projecting the image displayed on the display device. The above example further has, as the projection optical system, first and second mirrors in (on) a light path (optical path) of an observer (viewer) from the display device, thereby realizing the apparatus by satisfying a predetermined condition(s) about a relationship among: an incident angle in an image long-axial direction of the first mirror; an incident angle in an image short-axial direction of the first mirror; an interval between the an image displaying surface of the display device and the first mirror; and a horizontal width of the virtual image visually recognized by the observer). However, the conventional technique has not described any new problem of bringing the significant deterioration (reduction) in performance under the above-mentioned predetermine condition in daytime since the sunlight passes through the windshield, is condensed by the concave mirror, and damages the liquid crystal panel and the polarizer.

In the future, a method of using the windshield as a reflection surface as described in Patent Document 1 will conceivably become the mainstream. However, the following phenomenon, a so-called burning (yellowing carbonation) occurs: the polarizer or liquid crystal panel itself, which is provided on a light-emission side of a liquid crystal display apparatus, leads to having no normal function under the predetermined condition in daytime since being transformed by heat and light-ray intensity of the sunlight that passes through the windshield and is condensed by a concave mirror.

Similarly, a technique disclosed in Non-Patent Document 1 in which a final reflection surface is a combiner has not considered a new problem of bringing the significant deterioration in performance under the predetermine condition in daytime since the sunlight passes through the windshield and combiner, is condensed by the concave mirror, and damages the liquid crystal panel and the polarizer.

Also, the example of the HUD apparatus disclosed in Patent Document 1 as the conventional technique is established by including: the display device for displaying the image; and the projection optical system for projecting the image displayed on the display device, and by providing as the projection optical system the first and second mirrors on the light path from the display device to the observer. However, since disposing no optical element between the concave mirror and the liquid crystal panel serving as a video-image display apparatus, the above example has not considered a new problem of bringing significant deteriorate in quality of the video image visually recognized by the driver, particularly, in contrast performance and apparent resolution besides the above problem since light passing through the windshield, condensed by the concave mirror, and reflected by a surface of the optical element disposed between the liquid crystal panel and the concave mirror returns to eyes of the driver and overlaps the visual image obtained by the video-image display apparatus.

Further, according to Patent Document 2, disposing on the light path the transmission reflection member (hot mirror) for selectively reflecting infrared rays of the sunlight is proposed for reducing a possibility of damaging the liquid crystal display panel due to the sunlight. However, the entering (invading) sunlight contains not only the infrared rays but also light rays having a visible region and an ultraviolet region, so that the reduction only in the infrared rays is insufficient to reduce the damages to the liquid crystal display element and the polarizer due to the sunlight. That is, Patent Document 2 has not made any consideration about a new problem of bringing the significant deteriorate in quality of the video image visually recognized by the driver, particularly, in contrast performance and apparent resolution, the deterioration being an adverse effect (influence) due to entry of external light including visible light as described above.

Thus, the liquid crystal display element is often used as a video-image display apparatus utilized for the above HUD apparatus since being capable of easily obtaining a high-quality video image(s) and being inexpensive. However, the sunlight under the predetermined condition in daytime passes through the windshield, is condensed by the concave mirror, and brings image damages to the liquid crystal panel and the polarizer, which has consequently clarified one new problem of significantly reducing performance.

Further, surface reflection of the optical element disposed between the concave mirror and the video-image display apparatus is reduced for miniaturizing the HUD apparatus, and a part of the sunlight returns to a driver's visual point (eye) and overlaps the virtual image obtained by the video-image display apparatus, which has clarified a second problem of bringing significant deteriorate in quality of the video image visually recognized by the driver, particularly, in contrast performance and apparent resolution.

The present invention has an object of providing an information display apparatus, which resolves the significant deteriorate in quality of the video image visually recognized by the driver, particularly, in the contrast performance and the apparent resolution since the damages to the liquid crystal display element and the polarizer due to infrared components of the sunlight are mainly reduced and illumination light with high specific intensity in daytime or nighttime is reflected onto the surface of the optical element disposed between the video-image display apparatus forming the information display apparatus and the concave mirror, returns to the driver's eyes, and overlaps the virtual image obtained by the video-image display apparatus. That is, the present invention has an object of providing the information display apparatus capable of reducing an adverse effect(s) due to light having the wide-ranged wavelengths contained in external light including the sunlight.

The present invention is an invention for attaining the above-mentioned object and is, as one example, an information display apparatus. The information display apparatus, which displays video-image information on a projection surface by a virtual image, includes in a housing partly having an opening: a video-image-light generator configured to generate video-image light for displaying the video-image information; a video-image-light processor configured to perform a predetermined optical processing to a video image generated by the video-image-light generator; and a projector configured to project, onto the projection surface through the opening of the housing, the video-image light optically processed by the video-image-light processor so that a viewer is capable of virtually recognizing the video-image information as a virtual image in front of the projection surface, wherein a light path in the housing is provided with a suppressor selectively suppressing a P-polarizing component of light in a visible light region.

More specifically, although detailed below, the virtual image optical system ranging from the concave mirror to the video-image display apparatus (liquid crystal panel) in the information display apparatus of the present invention:

The present invention makes it possible to: correct distortion and aberration of the virtual image observed by the driver due to external light including the sunlight along with realization of the apparatus' s miniaturization; and simultaneously reduce such a state that external light including the sunlight entering through the windshield is condensed by the concave mirror forming the virtual-image optical system, damages the liquid crystal panel serving as the video-image display apparatus or/and the polarizer, and deteriorates their performance. That is, the present invention can provide the information display apparatus that reduces the adverse effect due to the light having a wide-ranged wavelengths in the external light containing the sunlight and forms a virtual image(s) of excellent performance.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to the following description, and various changes and modifications can be made by those skilled in the art within a scope of the technical idea disclosed herein. Further, components having the same function are denoted by the same reference characters throughout the drawings for describing the embodiments, and the repetitive description thereof may be omitted.

<Outline of Information Display Apparatus>

is a schematic configuration diagram showing a peripheral equipment configuration of an information display apparatus according to an embodiment of the present invention. Here, particularly explained as an example thereof will be an information display apparatusprojecting an image(s) onto a windshield of an automobile.

As shown in, the information display apparatusis an apparatus (so-called HUD (Head up Display)) that displays, as a virtual image(s) VI, various pieces of information reflected by a projected member(an inner surface of a windshield in this embodiment) in order to form the virtual image Vin front of a driver's own vehicle and on (at) a driver's sightline (eye point detailed later). Incidentally, the projected membermay be not only the above-mentioned windshield but also a combiner so long as being a member onto which information is projected. That is, the information display apparatusaccording to the present embodiment may be a member so long as such a member forms a virtual image(s) in front of the own vehicle and on the driver's sightlineand causes the driver to visually recognize it. Of course, the information displayed as the virtual image includes, for example, vehicle information and foreground information photographed (captured) by a camera (not shown) such as a surveillance camera or an around viewer (around view camera).

Also, the information display apparatusincludes: a video-image display apparatusthat projects video-image light for displaying information; a correction lensthat corrects distortion and aberration caused in forming a virtual image(s) by a concave (free-form surface) mirrorfrom a video image(s) displayed in the video-image display apparatus; and an optical element (not shown) that is between the correction lensand the video-image display apparatusand prevents sunlight from returning to the video-image display apparatusafter the sunlight is condensed by the concave mirror.

Then, the information display apparatushas a controller, which controls the above video-image display apparatusand a backlight. Incidentally, optical components including the above video-image display apparatus, the backlight, and etc. are a virtual-image optical system described below, and include a concave mirrorfor reflecting light. Also, the light reflected by those optical components is reflected by the projected memberand is directed to the sightlineof the driver.

Incidentally, used as the above video-image display apparatusis, for example, a self-light-emitting VFD (Vacuum Fluorescent Display) or the like besides an LCD (Liquid Crystal Display) having a backlight.

Meanwhile, instead of the above video-image display apparatus, an image(s) may be displayed on a screen by a projector, formed as a virtual image(s) by the above concave mirror, and reflected by the windshieldor a combiner (not shown) serving as the projected member to be directed toward a visual pointof the driver.

Configured as such a screen may be, for example, a microlens array in which microlenses are two-dimensionally arranged.

Here, a shape of the concave mirrorin order to reduce distortion of the virtual image may have an upper portion (an area where light rays are reflected and which is below the windshieldhaving a relatively short distance from the visual pointof the driver) shown in, and a lower portion (an area where the light rays are reflected and which is above the windshieldhaving a relatively long distance from the visual point of the driver), the upper portion having a relatively small curvature radius so that an enlargement ratio increases, the lower portion having a relatively large curvature radius so that the enlargement ratio decreases. Additionally, inclination of the video-image display apparatusto an optical axis of the concave mirrormakes it possible to realize further good correction also by correcting a difference between magnifications of the above-mentioned virtual images and reducing the distortion itself to be caused.

Meanwhile, as shown in, the windshieldof the automobile differs in a curvature radius Rv in a vertical direction of a main body and a curvature radius Rh in a horizontal direction thereof, and generally has a relation of Rh>Rv. This makes the windshielda toroidal surface of the concave mirrorif the windshield is considered as a reflection surface. Therefore, the shape of the concave mirrorin the information display apparatusof the present embodiment may have an average curvature radius different from them in the horizontal and vertical directions so as to correct the magnificent of the virtual image due to the shape of the windshield, that is, so as to correct a difference between the vertical and horizontal curvature radii of the windshield. At this time, if being a spherical surface or aspherical surface (indicated by [Equation 2] described below) symmetrical to the optical axis, the shape of the concave mirrorhas a function of a distance r from the optical axis. However, vertical and horizontal cross-sectional shapes at positions distant from each other in the concave mirror cannot be controlled individually, so that those shapes are preferably corrected as a function of coordinates (x, y) on a surface from an optical axis of a mirror surface serving as a free-form surface indicated by [Equation 1] described below.

Referring back toagain, for example, a lens elementis further disposed as a transmission type optical component between the video-image display apparatusand the concave mirror, thereby controlling an emission direction of light rays toward the concave mirrorto correct the distortion and aberration along with the shape of the concave mirrorand simultaneously realize the aberration correction of the virtual image including astigmatism caused by the difference between the curvature radii in the horizontal and vertical directions of the above-mentioned windshield.

Also, in order to further enhance aberration correction capability, the above-mentioned lens elementmay be composed of a plurality of lenses. Alternatively, control of a turning position on the light path and simultaneously an incident position of light onto the concave mirrorby disposing a curved (free-form) mirror instead of the lens elementalso make it possible to reduce the distortion and aberration. As described above, even if an optical element optimally designed to improve the aberration correction capability is further provided between the concave mirrorand the video-image display apparatus, it is needless to say that such an optical element does not depart from a technical idea or scope of the present invention. Further, changing a thickness of the above-mentioned lens elementin a direction of the optical axis brings varying an optical distance between the concave mirrorand the video-image display apparatusadditionally to original aberration correction, thereby also making it possible to continuously change a display position of the virtual image from a distant position to a close position.

Additionally, a difference in the magnification of the virtual image in upper and lower directions may be corrected by aslant disposing the video-image display apparatuswith respect to an optical-axis normal of the concave mirror.

Further, an optical element (not shown), which reflects or absorbs the sunlight passing through the windshield and condensed by the concave mirror, is provided between the concave mirrorand the video-image display apparatus, thereby reducing an amount of light returning to the video-image display apparatus.

Meanwhile, a factor of deteriorating image quality of the information display apparatusis that video-image light rays emitted from the video-image display apparatustoward the concave mirrorare reflected on the surface of the lens elementdisposed halfway therebetween, return to the video-image display apparatus, and are again reflected to be superimposed (overlapped) with the original video-image light. That is, the deterioration in the image quality has been known as such a factor. Consequently, the present embodiment is preferably designed as follows: an antireflection film is formed on the surface of the lens elementto suppress the reflection and, simultaneously therewith, either or both of video-image-light incidence and emission surfaces of the lens elementhas a limitation of such a shape that reflected light as mentioned above is not condensed by a part of the video-image display apparatus(for example, a shape having a concave surface that faces the video-image display apparatus).

Further, the inventors have considered characteristics of the antireflection film provided on the surface of the lens element. As a result, the following has been found through an experiment(s): reflectance in a green wavelength region having the highest visibility is kept (suppressed at) 0.2% or less, that in a red wavelength region is kept 0.6% or less, and that in a blue wavelength region is kept 1.0% or less, which has no influence on the image quality of the virtual image even if the sunlight is reflected on the surface of the optical element.

Meanwhile, if first and second polarizers are disposed as the video-image display apparatus, that is, if the first polarizer is disposed close to the liquid crystal panel and the second polarizer is disposed separately from the liquid crystal panel additionally to the first polarizer in order to absorb the reflected light from the above-mentioned lens element, the first and second polarizers can reduce the deterioration in the image quality. Simultaneously therewith, the sunlight passing through the windshield absorbs or reflects light condensed by the concave mirrorand incident on the liquid crystal panel, and reduces the light amount, thereby being capable of improving reliability of the liquid crystal panel.

Next, if the first and second polarizers are disposed as the video-image display apparatus, that is, if the first polarizer is disposed close to the liquid crystal panel and the second polarizer is disposed separately from the liquid crystal panel additionally to the first polarizer in order to absorb the reflected light from the above-mentioned lens element, the first and second polarizers can reduce the deterioration in the image quality. Further, backlight of the liquid crystal panel is controlled so that an incident direction of light incident on the liquid crystal panel is efficiently directed in a direction incident on an entrance pupil of the concave mirror. At this time, if a divergence angle of a beam (light flux) incident on the liquid crystal panel is made small in value, the video-image light is efficiently directed to the eye point of the driver and, simultaneously therewith, a video image with high contrast and high (good) visibility can be obtained. Contrast performance with respect to the divergence angle of the video image is remarkably changed in its horizontal direction, and if the divergence angle is within ±20 degrees, excellent characteristics thereof can be obtained. In order to further improve the contrast performance, a beam under the divergence angle within a range of ±10 degrees may be used.

Meanwhile, as the light source apparatus, a solid light source having a long product life is preferably adopted and, further, polarization conversion is preferably performed by using a PBS (polarizing beam splitter) as an LED (light emitting diode) whose light output change lessens with respect to a change in ambient temperature, the PBS being provided with an optical means for reducing a divergence angle of light.

Polarizers are arranged on a backlight side (light incidence surface) of the liquid crystal panel and on a lens elementside (light emission surface), thereby enhancing a contrast ratio of the video-image light. If an iodine-based polarizer having a high polarization degree is adopted as the polarizer provided on the backlight side (light incidence surface), a high contrast ratio can be obtained. Meanwhile, using a dye-based polarizer on the lens elementside (light emission surface) makes it possible to obtain high reliability even when external light is incident or when environmental temperature is high.

When the liquid crystal panel is used as the video-image display apparatus, particularly, when the driver wears polarized sunglasses, a specific polarized wave is blocked, which brings occurrence of a problem of the driver being unable to see the video image. In order to prevent this, a λ/4 plate is disposed on an optical element side of the polarizer disposed on the lens element side of the liquid crystal panel, thereby converting the video-image light aligned in a specific polarization direction into circularly polarized light preferably.

The controlleracquires, as foreground information (i.e., information to be displayed in front of the own vehicle by the above-mentioned virtual image) from a navigation system., various pieces of information of: a speed limit and the number of lanes of a road corresponding to a current position where the own vehicle is traveling; a scheduled travel route of the own vehicle set in the navigation system; and the like.

A driving support ECUis a controller for realizing driving support control by controlling a drive system and a control system in accordance with an obstacle (s) detected as a monitoring result (s) obtained from a periphery monitor. Included as the driving support control are, for example, well-known technologies such as cruise control, adaptive cruise control, pre-crash safety, and lane keeping assist.

The periphery monitoris an apparatus for monitoring a situation around the own vehicle and includes, as an example, a camera for detecting an object(s) present around the own vehicle based on an image(s) obtained by photographing a periphery of the own vehicle; a surveying apparatus for detecting an object(s) present around the own vehicle based on a result(s) obtained from transmission and reception of a survey wave(s); or the like.

The controlleracquires, as foreground information, such information obtained from the driving support ECU(for example, a distance to a preceding vehicle, a direction of the preceding vehicle, a position where an obstacle or sign is present, and the like). Further, inputted in the controllerare an ignition (IG) signal(s) and own-vehicle state information. The own-vehicle state information among these pieces of information is information acquired as vehicle information, for example, a remaining amount of fuel in an internal combustion engine or/and temperature of cooling water therein, or the like, and includes warning information indicating that the above information is an abnormal state previously defined. Additionally, the own-vehicle state information also includes an operation result(s) of a direction indicator, a traveling speed of the own vehicle, shift position information, and/or the like. The controllerdescribed above is activated when an ignition signal is inputted. The foregoing is explanation about the overall system of the information display apparatus according to the present embodiment.

<Entry of Sunlight into Apparatus and Principle of its Suppression>