Head-up display apparatus

A HUD apparatus is provided. The HUD apparatus is provided with: an optical source part having a light emission element; a condenser lens, which faces the optical source part, and collects light source light; a field lens, which further collects the light source light transmitted from the condenser lens side, and which projects light at a predetermined angle; and an image formation element, which forms an image when the light source light transmitted from the field lens side is inputted thereto, and which projects light of an image toward the windshield side. The field lens has a composite surface on at least one of the condenser lens side and the image formation element side, the composite surface having multiple continuous optical surfaces. The condenser lens has a diffusion part that diffuses the light source light.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase Application under 35 U.S.C. 371 of International Application No. PCT/JP2016/002292 filed on May 10, 2016 and published in Japanese as WO 2016/194305 A1 on Dec. 8, 2016. This application is based on and claims the benefit of priority from Japanese Patent Application No. 2015-114904 filed on Jun. 5, 2015. The entire disclosures of all of the above applications are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a head-up display apparatus (hereinafter referred to as a “HUD apparatus”) that is mounted to a mobile body and displays a virtual image of an image so that an occupant can visually confirm the image.

BACKGROUND ART

There is a known HUD apparatus that is mounted to a mobile body and displays a virtual image of an image so that an occupant can visually confirm the image. The HUD apparatus disclosed in Patent Literature 1 includes an optical source part, which has a light emission element emitting an optical source light, a condenser lens, which faces the optical source part and collects an optical source light, and a field lens, which further collects the optical source light from the condenser lens side and projects the optical source light at a predetermined angle. The HUD apparatus further includes an image formation element, which forms an image by the optical source light entering from the field lens side and emits the light of the image to a projection member side.

The field lens forms a single surface made of a single optical surface, as a surface on the condenser lens side and as a surface on the image formation element side. A diffusion plate is arranged between the condenser lens and the field lens, as a diffusion part that diffuses an optical source light.

PRIOR ART LITERATURE

Patent Literature

Patent Literature 1: JP 2007-108429 A

SUMMARY OF INVENTION

The HUD apparatus may generate color unevenness in a displayed virtual image. The reason for the color unevenness is that lights from the light emission element of the optical source part come to present different colors according to light emission parts or directions in some case. To deal with the difficulty, the inventor of the present application has devised a method that can suppress the occurrence of color unevenness. According to the method, a composite surface made of connecting optical surfaces is employed as at least one of a surface on the condenser lens side and a surface on the image formation element side of the field lens, so that the optical source lights presenting different colors according to directions are mixed with each other.

While the method that uses the field lens can produce the effect of suppressing the occurrence of color unevenness, the arrangement of the diffusion plate in Patent Literature 1 causes another difficulty such that an optical source light having passed through the condenser lens enters the diffusion plate, with its optical amount per unit area being smaller, and this causes reduction in the density of the diffused light, which leads to an insufficient luminance for virtual image display projected to the projection member.

It is an object of the present disclosure to provide an HUD apparatus that exhibits an excellent visibility for virtual image display by concurrently achieving suppression of color unevenness and high luminance.

According to one aspect of the present disclosure, a head-up display apparatus is mounted to a mobile body, projects an image to a projection member to display a virtual image of the image so that an occupant enables to visually confirm the image, the head-up display apparatus including: an optical source part that has a light emission element emitting an optical source light; a condenser lens that faces the optical source part and collects the optical source light; a field lens that further collects the optical source light from a side of the condenser lens and projects the optical source light at a predetermined angle; and an image formation element that forms an image by incidence of the optical source light from a side of the field lens, and emits light of the image to a side of the projection member. The field lens has a composite surface on a surface of at least one of the side of the condenser lens and a side of the image formation element, the composite surface being made of a plurality of optical surfaces connecting to each other. The condenser lens has a diffusion part that diffuses the optical source light.

In the head-up display apparatus according to the present disclosure, when the light emission element of the optical source part emits optical source lights presenting different colors according to light emission parts or directions, firstly the optical source lights enter the condenser lens that faces the optical source part. The condenser lens, which has the diffusion part, collects optical source lights with large optical amounts per unit area while diffusing the lights. The optical source lights are mixed with different colors, and the density of the lights is prevented from decreasing.

After passing through the condenser lens, the optical source lights of different colors are additionally mixed by the composite lens of the field lens, which is made of optical surfaces connecting to each other. Since an image formed of the mixed optical source lights is projected to the projection member, it may be possible to provide an HUD apparatus that exhibits an excellent visibility for virtual image display by concurrently achieving suppression of the occurrence of color unevenness and high luminance.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will be described below with reference to the drawings. Corresponding components between the embodiments are denoted by the same reference numbers so that overlapping descriptions can be omitted as needed. When the configurations of one embodiment have been specified only partly in the specification, the rest of the configurations of the embodiment can be described by applying the configurations of another embodiment previously described. Further, not only a combination of the configurations specified in the descriptions of the embodiments but also a combination of different parts of the configurations of the embodiments not specified are applicable as long as the combination does not conflict with the gist of the configuration.

First Embodiment

As shown inFIG. 1, an HUD apparatus100in the first embodiment is mounted to a vehicle1, which is a mobile body, and is housed in an instrument panel2. The HUD apparatus100projects an image to a windshield3that is a projection member of the vehicle1, and displays a virtual image of the image, using reflection of a light of the image from the windshield3, so that the image can be visually confirmed by an occupant in the vehicle1. In other words, when the light of the image is reflected from the windshield3and reaches the eyes of an occupant in the cabin of the vehicle1, the occupant perceives the light of the image as a virtual image VI and can recognize various types of information from the virtual image VI. The examples of the information to be displayed in the virtual image VI include a vehicle speed, a vehicle state value such as a fuel remaining amount, and navigation information such as road information and vision assisting information.

The windshield3in the vehicle1is a plate made of translucent glass or synthetic resin, for example. In the windshield3, a surface on the vehicle room side is formed as a projection surface3aonto which the image is projected, in a curved concave surface or a flat planar surface. As the projection member, a combiner separate from the vehicle1may be set in the vehicle1instead of the windshield3to receive projection of an image.

The specific structure of the HUD apparatus100will be described based onFIG. 1andFIG. 2. The HUD apparatus100includes an optical source part10, a condenser lens20, a field lens30, an image formation element40, a plane mirror50, and a concave mirror52, which are housed and held in a housing60.

The optical source part10includes an optical source circuit board12and multiple light emission elements14. The optical source circuit board12electrically connects the power source and each light emission element14to each other through an interconnection pattern on the board12. Each light emission element14is a light emission diode element generating a small amount of heat, and generates an optical source light with a light emission amount corresponding to an electric current amount by power distribution. Each light emission element14in the first embodiment is a white light emission diode element having a blue light emission diode element14aand an yellow fluorescent material14bcovering the blue light emission diode element.

More specifically, each light emission element14is formed by sealing the blue light emission diode element14ahaving a chip shape and provided in a center area15with the yellow fluorescent material14b, as shown inFIG. 3. The yellow fluorescent material14bis obtained by mixing a yellow fluorescent agent with a translucent synthetic resin. The yellow fluorescent material14bis excited by the blue light from the blue light emission diode element14a, to emit yellow light, and the blue light and the yellow light are synthesized to realize an optical source light of a false white color.

According to a light emission distribution experiment by the inventor of the present application, however, an optical source light L1, which is emitted from the center area15of each light emission element, is a bluish white light with a small deviation from a black body locus BL where a color temperature is 6500K or higher in the chromaticity diagram ofFIG. 4. On the other hand, an optical source light L2, which is emitted from a peripheral area16of each light emission element is a yellow light with a large deviation from the black body locus BL in the chromaticity diagram ofFIG. 4. Therefore, each light emission element14emits optical source lights presenting different colors according to light emission parts or directions.

As illustrated inFIG. 2, in the optical source part10, the light emission elements14are arranged in a row in an array direction Da along the optical source circuit board12. The optical source lights from the light emission elements14enter the condenser lens20.

The condenser lens20is made of translucent synthetic resin or glass, for example, and is located between the optical source part10and the field lens30. Thus, the condenser lens20faces the optical source part10.

Specifically, the condenser lens20is a lens array formed by arranging the same number of lens elements21as the number of the light emission elements14. The lens elements21are arranged in the array direction Da as well to face the light emission elements14in one-to-one correspondence. Each lens element21has a first refraction surface22on a side of the optical source part10in a single flat shape common to all the lens elements21and the first refraction surface22is provided with a diffusion part26. More specifically, the first refraction surface22is formed to be flat in a macroscopic viewpoint, and the diffusion part26of each lens element21forms a minute, random, and concavo-convex shape as of ground glass. The diffusion part26preferably has a haze value of 30% or higher, and actually has a haze value of 50% in the present embodiment.

Further, each lens element21forms a second refraction surface24on a side of the field lens30, and the second refraction surface24is smooth and convex. The focal length of the condenser lens20by each lens element21is set larger than the distance between the condenser lens20and each light emission element14.

In the condenser lens20, an optical source light from a light emission element14enters the corresponding lens element21, and is collected by the refraction action while being diffused by the diffusion part26. After that, the optical source light enters the field lens30.

The field lens30is made of translucent synthetic resin or glass, for example, and is located between the condenser lens20and the image formation element40. Thus, the field lens30faces the image formation element40. The field lens30is a lens that further collects the optical source light from the condenser lens20and projects the light to the image formation element40at a predetermined angle.

The field lens30in the present embodiment is a composite Fresnel lens. Specifically, the field lens30forms an incident optical surface32in a smooth flat shape on a side of the condenser lens20, and forms a composite surface34made of optical surfaces35and36connecting to each other on a side of the image formation element40.

The composite surface34will be described in detail below with reference toFIG. 5. The composite surface34is formed on the entire region, which corresponds to the light emission elements14and to the lens elements21, of the field lens30. In other words, the optical source lights from the light emission elements14and the lens elements21inevitably pass through the composite surface34.

The composite surface34of the present embodiment forms an alternate arrangement structure in which a light collecting optical surface35and a deflection optical surface36are alternately connected in the array direction Da of the light emission elements14.

Each light collecting optical surface35is formed to be one of the division regions made by dividing a virtual light collecting surface Sic at predetermined widths Ws in the array direction Da. The virtual light collecting surface Sic is a virtual lens array surface where the same number of virtual lens element surfaces Sie as the number of the lens elements21or the light emission elements14is arranged. Each virtual lens element surface Sie of the virtual light collecting surface Sic is a surface being convex on a side of the image formation element40, and an array pitch Paf of the virtual lens element surfaces Sie is substantially the same as an arrangement pitch Pac of the lens elements21of the condenser lens20.

Each deflection optical surface36is formed to be one of the division regions made by dividing a virtual deflection surface Sid at predetermined widths Ws in the array direction Da of the light emission elements14. The virtual deflection surface Sid is configured by multiple inclined surfaces Sis that have inclination reversed at every half value of the array pitch Paf of the virtual lens element surfaces Sie, and the inclined surfaces Sis are flat. The inclination of each inclined surface Sis is set to be reversed to the inclination of the virtual light collecting surface Sic at the corresponding position in the array direction Da of the light emission elements14.

While the predetermined width Ws applied to the division region of the light collecting optical surface35and the deflection optical surface36are set differently, the amount of the sag between the light collecting optical surface35and the deflection optical surface36is set to be nearly constant so that the thickness of the entire field lens30is constant. Further, the predetermined width Ws is set to be smaller than the pitch Ps between the light emission elements adjacent to each other. With the alternate arrangement of the light collecting optical surface35and the deflection optical surface36, a part of the shape of the virtual light collecting surface Sic and a part of the shape of the virtual deflection surface Sid are extracted and are reproduced on the composite surface34. InFIG. 5, the size of a part of the predetermined width Ws is shown.

One of the light collecting optical surfaces35that has a surface vertex35abased on each virtual lens element surface Sie is arranged on a straight line Lt connecting the center area15of each light emission element14and a surface vertex21aof the second refraction surface24of each lens element21. In the present embodiment, the straight line Lt is substantially perpendicular to the array direction Da of the light emission elements14.

In the manner as described above, an optical source light that has passed through a light collecting optical surface35of the composite surface34is collected. More specifically, the optical source light is collected so that the travelling direction of the optical source light after passing through a light collecting optical surface35is closer to the direction of the straight line Lt than the travelling direction of the optical source light before passing through the light collecting optical surface35is.

On the other hand, an optical source light that has passed through a deflection optical surface36of the composite surface34is deflected by the prismatic effect to the side opposite to the side where an optical source light is collected by a light collecting optical surface35. The deflection to the opposite side herein means that an optical source light is farther from the nearest straight line Lt to the optical source light (in other words, the straight line Lt for the light emission element14that emits the optical source light) as the optical source light travels nearer to the image formation element40.

The image formation element40inFIG. 2is a liquid crystal panel using a thin film transistor (TFT) and more specifically is an active matrix liquid crystal panel formed of multiple liquid crystal pixels arranged in a two-dimensional direction. The image formation element40includes a laminate structure of a pair of polarizing plates and a liquid crystal layer in between, for example. The polarizing plates have properties of transmitting a light of a predetermined direction by an electric field vector and blocking a light of a direction substantially perpendicular to the predetermined direction by the electric field vector, and are arranged to be substantially perpendicular to the predetermined direction. The liquid crystal layer is capable of rotating, by applying a voltage to each liquid crystal pixel, the polarization direction of a light entering the liquid crystal layer according to the applied voltage.

Hence, the image formation element40is configured to control the transmissivity of an optical source light for each liquid crystal pixel and to form an image, by incidence of the optical source light from the field lens30. The liquid crystal pixels are each provided with a color filter and the color filters of adjacent liquid crystal pixels present different colors from each other (red, green, or blue, for example). Combinations of the filters can produce various different colors. The image formation element40emits a light of an image to the plane mirror50on a side of the windshield3in an optical path OP inFIG. 1.

The plane mirror50is formed by depositing aluminum for a reflection surface51on the surface of a base material made of synthesis resin or glass, for example. The reflection surface51is formed into a smooth flat surface. The plane mirror50reflects the light of the image from the image formation element40to the concave mirror52.

The concave mirror52is formed by depositing aluminum for a reflection surface53on the surface of a base material made of synthesis resin or glass, for example. The reflection surface53is formed into a smooth curved surface as the recessed center of the concave mirror52. The concave mirror52reflects the light of the image from the plane mirror50to the windshield3.

In that way, an optical source light emitted from each light emission element14of the optical source part10passes through the diffusion part26of the condenser lens20and the composite surface34of the field lens30and then enters the image formation element40. After that, the optical source light is reflected from the windshield3as the light of the image from the image formation element40and reaches an eye box EB. The eye box EB is set based on the eyelips of an occupant sitting in a seat4, where the eye point EP of the occupant can exist, as a region where the occupant can visually confirm a displayed virtual image of the image.

The description will be made below on how a virtual image of an image is displayed, based on an experiment by the inventor of the present application.FIG. 6andFIG. 7illustrate virtual images observed from the upper end of the eye box EB.FIG. 6specifically illustrates a comparative example which is different from the present embodiment in that the first refraction surface is a mirror surface and the condenser lens does not have the diffusion part (other configurations are the same as those of the present embodiment), andFIG. 7specifically illustrates a case of the present embodiment. The distance between each light emission element14and the first refraction surface22is set to 0.5 mm.

In the comparative example shown inFIG. 6, the upper and lower end parts of the displayed virtual image have not turned white but turned yellow (see the yellow part YP surrounded by the broken line). This indicates that the color distribution in the position of the eye box has come to reflect the light emission distribution of the light emission elements as a result of designing the device so that the light emission elements and the eye box are in a conjugate relation for increasing the usage efficiency of optical source lights. In the present embodiment inFIG. 7, on the other hand, the upper and lower end parts are prevented from turning yellow. Note that the rectangular areas inFIG. 6andFIG. 7represent reference positions in the comparison of the images inFIGS. 6 and 7.

The actions and effects obtained in the first embodiment set forth above will be described below.

According to the first embodiment, when the light emission elements14of the optical source part10emit optical source lights presenting different colors according to light emission parts or directions, for example, firstly the optical source lights enter the condenser lens20that faces the optical source part10. The condenser lens20receives the optical source lights, and collects optical source lights having large optical amounts per unit area, while diffusing the optical source lights in the diffusion part26. The optical source lights thus diffused are mixed with different colors and the density of the lights is suppressed from decreasing.

After passing through the condenser lens20, the optical source lights of different colors are additionally mixed with one another by the composite surface34of the field lens30, which is made of the optical surfaces35and36connecting to each other. The image formed by such optical source lights is projected to the windshield3as a projection member, it may be possible to provide an HUD apparatus100that concurrently attains suppression of the occurrence of color unevenness and high luminance, and offer an excellent visibility for virtual image display.

Further, according to the first embodiment, the condenser lens20has the first refraction surface22, which is provided with the diffusion part26, on a side of the optical source part10, and has the second refraction surface24, which is convex, on a side of the field lens30. With the condenser lens20thus configured, optical source lights having large optical amounts per unit area are diffused by the diffusion part26, as well as the enlargement effect of the diffusion part26are obtained using the field lens30and the second refraction surface24. Consequently, it may be possible to suppress the occurrence of color unevenness and to enhance the luminance for virtual image display.

Moreover, according to the first embodiment, when the light emission elements14of the optical source part10emit optical source lights presenting different colors according to light emission parts or directions, for example, the optical source lights enter the lens elements21that face the light emission elements14. Since the diffusion part26is formed for each lens element21, the lens elements21collect optical source lights from the corresponding light emission elements14having large optical amounts per unit area, while diffusing the optical source lights. The optical source lights thus diffused are mixed with different colors, and the density of the lights is suppressed from decreasing.

In addition, by forming the composite surface34of the field lens30, made of the optical surfaces35and36connecting to each other, on all over the lens elements21, not only the different colors of the optical source lights in one light emission element14but also the different colors of optical source lights among the light emission elements14are mixed with one another. The optical source lights form an image and the image is projected to the windshield3, it may be possible to surely suppress the occurrence of color unevenness even when more than one light emission element14are used, and to enhance the luminance for virtual image display.

Furthermore, according to the first embodiment, the composite surface34is made of the optical surfaces35and36connecting at least in the array direction Da of the light emission elements14, and the width Ws of the optical surfaces35and36is smaller than the pitch Ps between the light emission elements14adjacent to each other in the array direction Da. With that setting, the optical source lights between the light emission elements14arranged in the array direction Da are surely mixed by the composite surface34and the effect of suppressing the occurrence of color unevenness is further enhanced accordingly.

Moreover, according to the first embodiment, the optical source lights having entered the field lens30are partly collected by the light collecting optical surfaces35, and are partly deflected by the deflection optical surfaces36to the opposite side to the side where the lights are collected by the light collecting optical surfaces35, so that the optical source lights of different colors are mixed with one another. Hence, the effect of suppressing the occurrence of color unevenness is further enhanced.

Furthermore, according to the first embodiment, each light emission element14has the blue light emission diode element14aand the yellow fluorescent material14bthat surrounds the blue light emission diode element14a. While the light emission elements14each emit a white optical source light in the center area15and emit a yellowish optical source light in the peripheral area16, it may be possible to suppress the occurrence of color unevenness by the diffusion part26and the composite surface34. Since the light emission elements14do not generate a large amount of heat, it may be possible to make the diffusion part26is closer to the light emission elements14, and it may be possible that the diffusion part26diffuses optical source lights having large optical amounts per unit area. Hence, it may be possible to enhance the luminance for virtual image display.

The diffusion part26in the first embodiment has a haze value of 30% or higher, and the haze value of that level can ensure a sufficient effect of suppressing the occurrence of color unevenness by the diffusion.

Second Embodiment

As shown inFIG. 8, a second embodiment is a modified example of the first embodiment. The differences of the second embodiment from the first embodiment will be mainly described.

A condenser lens220in the second embodiment is made of translucent synthesis resin or glass, for example, as in the first embodiment and is located between the optical source part10and the field lens30. Thus, the condenser lens220faces the optical source part10. The condenser lens220is a lens array formed by arranging the same number of lens elements221as the number of the light emission elements14.

Each lens element221in the second embodiment has a first refraction surface222on a side of the optical source part10, and the first refraction surface is a single flat surface common to all the lens elements221. The lens element221has a second refraction surface224on a side of the field lens30, and the second refraction surface224is convex and is provided with a diffusion part226. Specifically, the second refraction surface224is formed to be convex in a macroscopic viewpoint, and the diffusion part226for each lens element221forms a minute, random, and concavo-convex shape as of ground glass. The diffusion part226preferably has a haze value of 30% or higher, and has a haze value of 30% in the present embodiment.

The description will be made below on how a virtual image of an image is displayed, based on simulations by the inventor of the present application.FIG. 9andFIG. 10are simulation images under the condition that the displayed virtual image is observed from the right end of the eye box EB.FIG. 9illustrates a comparative example which is different from the present embodiment in that the second refraction surface is smooth and convex (other configurations are the same as those of the present embodiment), andFIG. 10illustrates a case of the present embodiment. The distance between each light emission element14and the first refraction surface22is set to 0.5 mm.

In the comparative example shown inFIG. 9, the center area of the displayed virtual image has not turned white partially and turned yellow (see the yellow part YP surrounded by the broken line). This indicates that the color distribution in the position of the eye box has come to reflect the light emission distribution of the light emission elements as a result of designing the device so that the light emission elements and the eye box are in a conjugate relation for increasing the usage efficiency of optical source lights. In the embodiment inFIG. 10, on the other hand, the entire region of the virtual image is prevented from turning yellow.

In the second embodiment, the condenser lens220has the first refraction surface222on a side of the optical source part10, and has the second refraction surface224on a side of the field lens30. The second refraction surface224is convex and is provided with the diffusion part226. With the condenser lens220thus configured, the diffusion part226can diffuse optical source lights having large optical amounts per unit area. In that way, the occurrence of color unevenness can be suppressed and the luminance for virtual image display can be enhanced.

Other Embodiments

Although some embodiments have been described, the present disclosure is not limited to those embodiments.

For example, a first modified example of the first embodiment may be configured so that the diffusion part26of the first refraction surface22is formed of a diffusion plate or a diffusion film attached to the condenser lens20on a side of the optical source part10.

A second modified example may be configured so that the diffusion part26is provided to both the first refraction surface22and the second refraction surface24.

A third modified example may be configured so that each deflection optical surface36of the composite surface34may form the inclined surface Sis to be convex or concave, not flat.FIG. 11shows a case where the surface Sis is convex.

A fourth modified example may be configured so that the field lens30is a Fresnel lens. In the example shown inFIG. 12, a composite surface934is made of light collecting optical surfaces935and division surfaces936alternately connecting to each other. Each light collecting optical surface935is formed to be one of the division regions made by dividing single virtual light collecting surface Sic at predetermined widths Ws in the arrangement array direction Da. A division surface936is formed to be a flat surface that complements the divided part of the virtual light collecting surface Sic, and is slightly inclined inversely to the inclination of the light collecting optical surface935adjacent to the division surface936, in consideration of die cutting of molding.

A fifth modified example may be configured so that the composite surface34is formed on the surface on a side of the condenser lens20alone or both on the surface on a side of the condenser lens20and the surface on a side of the image formation element40as long as the composite surface34is formed on the surface of at least one of the condenser lens or the image formation element40.

A sixth modified embodiment may be configured so that the light emission elements14are two-dimensionally arranged in the array direction Da.

A seventh modified embodiment may be configured so that the number of the light emission elements14is one. In that case, the field lens30is desirably the Fresnel lens used in the fourth modified example.

An eighth modified example may be configured so that the head-up display apparatus is applied to various types of mobile bodies (transportation systems) other than the vehicle1, including a ship and an airplane.

Note that inFIG. 11andFIG. 12, the size of a part of the predetermined width Ws is shown, as inFIG. 5.