Head-up display device

A head-up display device that displays a virtual image to be viewable by an occupant in a movable body includes: a light source part which emits light source light; a liquid crystal panel integrally having a pair of polarizers for liquid crystals and a liquid crystal layer disposed between the polarizers in a stacked state; and an additional polarizer arranged in an optical path between the light source part and the liquid crystal panel. The additional polarizer and the pair of polarizers for liquid crystals have properties of transmitting polarized light along a transmission axis and shielding polarized light along a shielding axis which intersects the transmission axis. The additional polarizer is arranged such that the transmission axis and the shielding axis respectively match those of a polarizer for liquid crystals adjacent to the light source part, of the pair of polarizers for liquid crystals.

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/JP2016/076884 filed on Sep. 13, 2016 and published in Japanese as WO 2017/086002 A1 on May 26, 2017. This application is based on and claims the benefit of priority from Japanese Patent Application No. 2015-226956 filed on Nov. 19, 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 device (hereafter referred to as HUD device) that displays a virtual image to be viewable by an occupant in a movable body.

BACKGROUND ART

Conventionally, a head-up display device is known, which displays a virtual image to be viewable by an occupant in a movable body. A HUD device disclosed in Patent Literature 1 includes a light source part which emits light source light, and a liquid-crystal display element which forms a picture by making a part of the light source light to pass through.

The liquid-crystal display element has a liquid crystal layer between a pair of polarizers for liquid crystals. Each of the polarizers for liquid crystals is spaced from the liquid crystal layer.

PRIOR ART LITERATURES

Patent Literature

Patent Literature 1: JP 2007-86387 A

SUMMARY OF INVENTION

When the polarizer for liquid crystals is arranged through a space relative to the liquid crystal layer, for example, even if the light source light shielded by the polarizer for liquid crystals is changed into heat, the space can restrict a rise in the temperature of the liquid crystal layer such that the durability of HUD device improves. However, the quality (for example, contrast) of the picture formed by the liquid-crystal display element may deteriorate due to the space.

It is an object of the present disclosure to provide a HUD device with high durability, while deterioration in the quality of a picture can be restricted.

According to an aspect of the present disclosure, a head-up display device that displays a virtual image by projecting a picture to a projection component to be viewable by an occupant in a movable body includes: a light source part which emits light source light; a liquid crystal panel integrally having a pair of polarizers for liquid crystals and a liquid crystal layer disposed between the polarizers in a stacked state, to form the picture by making a part of the light source light to pass through; and an additional polarizer arranged in an optical path between the light source part and the liquid crystal panel. The additional polarizer and the pair of polarizers for liquid crystals have properties of transmitting polarized light along a transmission axis and shielding polarized light along a shielding axis which intersects the transmission axis. The additional polarizer is arranged such that the transmission axis and the shielding axis are respectively aligned with those of a polarizer for liquid crystals adjacent to the light source part, of the pair of polarizers for liquid crystals.

Thus, in the liquid crystal panel, the pair of the light polarizers for liquid crystals and the liquid crystal layer between the light polarizers for liquid crystals are prepared as one-piece in the stacked state. The additional light polarizer is arranged in the optical path between the light source part and the liquid crystal panel. Due to the arrangement, among the light source light from the light source part, the polarized light along the shielding axis of the additional light polarizer is shielded by the additional light polarizer before reaching the liquid crystal panel. That is, the polarized light along the transmission axis of the additional light polarizer travels toward the liquid crystal panel, of the light source light.

Since the additional light polarizer and the light polarizer for liquid crystals adjacent to the light source part are arranged such that transmission axis and the shielding axis are made common therebetween, the light source light passing through the additional light polarizer, which is a polarized light along the transmission axis, is hardly shielded by the light polarizer for liquid crystals adjacent to the light source part, and a picture is formed. In this way, while restricting the rise in temperature of the liquid crystal panel caused by conversion of the light source light into heat in the light polarizer for liquid crystals adjacent to the light source part, a picture can be formed with the liquid crystal panel in the stacked state. Accordingly, the HUD device with high durability can be offered while restricting deterioration in the quality of a picture.

DESCRIPTION OF EMBODIMENTS

First Embodiment

As shown inFIG. 1, a HUD device100according to a first embodiment is disposed in a vehicle1which is a kind of movable body, and is housed in an instrument panel2. The HUD device100projects a picture to a windshield3which is a projection component of the vehicle1. When the light of picture is reflected by the windshield3, the HUD device100displays a virtual image to be viewable by an occupant of the vehicle1. That is, the light of picture reflected by the windshield3reaches an eye of the occupant in the interior of the vehicle1, and the occupant perceives the light of picture as a virtual image VI. The occupant can recognize a variety of information according to the virtual image VI. The variety of information displayed as the virtual image include, for example, vehicle status values such as speed and fuel residual quantity, or navigation information such as road information, field-of-view supplementary information.

The windshield3of the vehicle1is formed in tabular and is made of translucent glass or synthetic resin. The internal surface of the windshield3defines a projection surface3awhere a picture is projected, and is shaped in a curved concave surface or in a flat plane. Instead of the windshield3, as a projection component, a combiner which is produced separately from the vehicle1may be installed in the vehicle1, and a picture may be projected to the combiner.

The specific configuration of the HUD device100is explained below based onFIGS. 2-6. As shown inFIG. 2, the HUD device100includes a light source part12, a condensing part20, a diffusion part30, a light polarizer40, a reflective part50, a liquid crystal panel60, and a light introducing part70, which are housed and held by a housing80. The light source part12, the condensing part20, the diffusion part30, the light polarizer40, the reflective part50, and the liquid crystal panel60are further housed in a projector case10ato define a projection machine10. The projection machine10projects a picture towards the windshield3through the light introducing part70by making a part of the light source light from the light source part12to pass through the liquid crystal panel60.

The light source part12has a circuit board14for light sources, and plural light emitting elements16. The circuit board14for light sources electrically connects a power supply to each of the light emitting elements16through a circuit pattern defined on the board14. Each of the light emitting elements16is a light emitting diode element, and emits light source light with the amount of luminescence according to the amount of current. In each of the light emitting elements16, for example, luminescence in false white is realized by covering a blue light-emitting diode with a phosphor. The light source light emitted by each of the light emitting elements16is random polarized light. A radiating fin18is disposed opposite to the light emitting element16through the circuit board14for light sources, and is exposed from the projector case10aand the housing80.

In this way, the light source light emitted by the light source part12enters the condensing part20, and is condensed by the condensing part20.

As shown inFIG. 2, the condensing part20is arranged in the optical path between the light source part12and the liquid crystal panel60, and has a condenser lens22and a field lens24.

The condenser lens22shown inFIG. 3is arranged to oppose the light source part12, in the condensing part20, and is a translucent lens made of synthetic resins such as acrylic resin. The condenser lens22is a lens array in which lens elements22aare arranged, and the number of the lens elements22ais the same as the light emitting elements16. The lens elements22aare arranged to oppose the corresponding light emitting elements16, respectively. Each of the lens elements22ahas a first refraction side22bat a side adjacent to the light source part12as a single plane common among the lens elements22a. Each of the lens elements22afurther has a second refraction side22cat a side adjacent to the liquid crystal panel60, and the second refraction side22chas an individual smooth convex shape.

The light source light condensed by the refraction action of the condenser lens22enters into the field lens24.

The field lens24is, for example, a translucent lens made of synthetic resins such as an acrylic resin, and is arranged between the condenser lens22and the liquid crystal panel60in the condensing part20. The field lens24is a composite type Fresnel lens. Specifically, the field lens24has an incidence optical surface24ashaped in a smooth single plane at a side adjacent to the condenser lens22. Moreover, the field lens24has a composite optical surface24bwhere divided optical surfaces24ccontinue at a side adjacent to the liquid crystal panel60. InFIG. 3, the reference numeral24bis given to a part of the composite optical surfaces24b, and the reference numeral24cis given to a part of the divided optical surfaces24c.

The condenser lens22and the field lens24have non-intentional phase difference characteristic due to the remaining stress produced when fabricating.

The light source light condensed by the refraction action of the condenser lens22and the field lens24enters the diffusion part30.

As shown inFIG. 2, the diffusion part30is located in the optical path between the light source part12and the liquid crystal panel60. In this embodiment, the diffusion part30is arranged in the optical path between the condensing part20and the light polarizer40. The diffusion part30is formed in a plate shape, and is made of synthetic resins such as polyester resin. The diffusion part30includes a translucent board and a large number of the spherical beads, which have variation in diameters of particles, fixed on the surface of the translucent board. The light source light entering the diffusion part30is diffused by the diffusion action of the beads, and enters the light polarizer40.

The light polarizer40is in the optical path between the light source part12and the liquid crystal panel60. In this embodiment, the light polarizer40is arranged in the optical path between the condensing part20and the diffusion part30, and the liquid crystal panel60. In other words, the light polarizer40is located adjacent to the liquid crystal panel60than the condensing part20and the diffusion part30. The light polarizer40has properties of transmitting polarized light along the transmission axis40aand shielding polarized light along the shielding axis40bwhich intersects the transmission axis40a(also seeFIG. 6). The light polarizer40of the first embodiment is a reflection type light polarizer which reflects polarized light along the shielding axis40b.

Specifically, the light polarizer40is a wire grid polarizer as the reflection type light polarizer. The light polarizer40is formed in the shape of a film, and plural wires made of metal such as aluminum are arranged in parallel at a predetermined pitch in a direction along the film surface. The predetermined pitch is set to be smaller than a wavelength of the light source light, for example, as about 100-200 nm. In the light polarizer40, the stretching direction of the metal wire corresponds to the transmission axis40a, and the arrangement direction of the metal wires corresponds to the shielding axis40b.

As the reflection type light polarizer, instead of the wire grid polarizer, a light polarizer which reflects polarized light along the shielding axis40bmay be adopted, in which plural optical films are stacked to produce interferential actions.

A part of the light source light along the transmission axis40apasses through the light polarizer40, and a part of the light source light along the shielding axis40bis reflected by the light polarizer40toward the light source part12.

The reflective part50is arranged adjacent to the light source part12than the light polarizer40. In the first embodiment, the reflective part50is arranged adjacent to the light source part12than the condensing part20and the diffusion part30. Specifically, the reflective part50is formed by sticking a reflective film on a part of surfaces of the circuit board14for light sources opposing the liquid crystal panel60, except the area of the light emitting element16. The reflective part50reflects the light source light reflected toward the light source part12by the light polarizer40, again toward the liquid crystal panel60.

Here, the light source light which reaches the light polarizer40again by being reflected by the reflective part50passes through the diffusion part30and the condensing part20twice, respectively by going back and forth between the light polarizer40and the reflective part50. When the light source light under the round trip passes through the diffusion part30, the light source light receives the depolarization action simultaneously as the diffusion action. When the light source light under the round trip passes through the condensing part20, the polarization state is changed variously depending on the transmission course by the influence of the above-mentioned phase difference characteristic caused by the remaining stress, and the influence of a polarized light aberration produced simultaneously as the refraction action.

Therefore, when the light source light, which was the polarized light along the shielding axis40bat a time of reflection with the light polarizer40, reaches the light polarizer40again through the reflective part50, the light source light comes to include a polarized light along the transmission axis40a. In this way, of the light source light which reached the light polarizer40again, a part of the polarized light along the transmission axis40apasses through the light polarizer40.

As shown inFIGS. 2, 4, and 5, the liquid crystal panel60is produced by using a thin film transistor (Thin Film Transistor, TFT), such as active-matrix type liquid crystal panel formed from plural liquid crystal pixels60aarranged in two dimensional direction. The liquid crystal panel60integrally includes a pair of the light polarizers61and62for liquid crystals, and a liquid crystal layer64disposed between the light polarizers61and62for liquid crystals in a stacked state.

As shown inFIG. 6, of the pair of light polarizers61and62for liquid crystals, the light polarizer61for liquid crystals adjacent to the light source part12has properties of transmitting the polarized light along the transmission axis61aand shielding the polarized light along the shielding axis61bwhich intersects the transmission axis61a. Similarly, the light polarizer62for liquid crystals adjacent to the windshield3(namely, adjacent to the light introducing part70) also has properties of transmitting the polarized light along the transmission axis62aand shielding the polarized light along the shielding axis62bwhich intersects the transmission axis62a. The pair of light polarizers61and62for liquid crystals are arranged such that the transmission axes61aand62aare substantially perpendicular to each other. Each of the light polarizers61and62for liquid crystals is an absorbing type light polarizer which absorbs polarized light along the shielding axis61b,62b.

Specifically, each of the light polarizers61and62for liquid crystals is an absorbing type light polarizer formed by adding iodine which is dichroism pigment to polyvinyl alcohol. Each of the light polarizers61and62for liquid crystals has the transmission axis61a,62aand the shielding axis61b,62bwhich are substantially perpendicular to each other, due to the iodine molecular orientation.

The light polarizer61for liquid crystals adjacent to the light source part12is arranged relative to the light polarizer40, such that the transmission axes61aand40amatch with each other, and that the shielding axes61band40bmatch with each other. In this embodiment, in case where the light polarizer61for liquid crystals and the light polarizer40are seen in a stacking direction LD which defines the thickness of the liquid crystal panel60, the arrangement is set so that the transmission axes61aand40aexactly overlap with each other.

The polarized light of the light source light passing through the light polarizer40is along the transmission axis40a, and further passes through the light polarizer61for liquid crystals with high transmissivity as it is. In other words, the polarized light along the shielding axis61bhardly enters the light polarizer61for liquid crystals. In this embodiment, as shown inFIG. 2, the light polarizer40is stuck with the liquid crystal panel60without a gap.

Moreover, as shown inFIG. 4, the liquid crystal panel60has a pair of transparent electrodes63aand63b. The transparent electrode63ais between the light polarizer61and the liquid crystal layer64, and the transparent electrode63bis between the light polarizer62and the liquid crystal layer64. The liquid crystal layer64is between the transparent electrode63aand the transparent electrode63b. The liquid crystal layer64is filled with a solution in which the main ingredient is liquid crystal molecules such as nematic liquid crystal. A voltage is applied between the pair of transparent electrodes63aand63bin each of the liquid crystal pixels60ato control the molecular orientation of liquid crystal. Thus, it is possible to change the polarization direction of the light source light passing through the liquid crystal layer64according to the applied voltage in the liquid crystal layer64.

The thickness of the liquid crystal layer64is set up so that the polarization direction of the light perpendicularly entering in the stacking direction LD of the liquid crystal panel60changes by 90 degrees after passing through the liquid crystal layer64, in case a predetermined voltage (for example, 0V) corresponding to the maximum transmissivity is applied. Since the polarization direction of light source light changes by 90 degrees between the light polarizers61and62for liquid crystals, the light source light can pass through the light polarizer62for liquid crystals adjacent to the windshield3.

Moreover, as shown inFIG. 5, each of the liquid crystal pixels60adefines a wiring part65which is a portion not forming a picture, and an opening66which can form a picture. The opening66is opened and surrounded by the wiring part65. Moreover, a color filter67for forming a color image is also stacked in the liquid crystal panel60.

The transmissivity of the incident light source light is controlled by controlling the applied voltage in each of the liquid crystal pixels60a. Therefore, the liquid crystal panel60can form a picture by making a part of the light source light to pass through.

As shown inFIG. 2, the light of the projected picture is introduced into the light introducing part70, because a portion of the liquid crystal panel60adjacent to the light introducing part70is exposed in the projector case10a. The light introducing part70is an optical system which introduces the light of the picture from the projection machine10toward the windshield3. The light introducing part70has a plane mirror72and a concave mirror74.

The plane mirror72is formed, for example, by vapor-depositing aluminum as a reflective surface72aon the surface of the base material made of synthetic resin or glass. The reflective surface72ais provided on the side opposing the liquid crystal panel60and the concave mirror74, and is formed in the shape of a flat plane. The plane mirror72reflects the light of the picture from the liquid crystal panel60toward the concave mirror74.

The concave mirror74is formed, for example, by vapor-depositing aluminum as a reflective surface74aon the surface of the base material made of synthetic resin or glass. The reflective surface74ais provided on the side opposing the plane mirror72and the windshield3, and is formed in the shape of a smooth curved surface where the center of the concave mirror74is recessed. The concave mirror74reflects the light of the picture from the plane mirror72towards the windshield3through an opening80adefined in the housing80.

The action and effect of the first embodiment described above is explained below.

According to the first embodiment, the liquid crystal panel60integrally includes the pair of the light polarizers61and62for liquid crystals and the liquid crystal layer64between the light polarizers61and62for liquid crystals in the stacked state. The additional light polarizer40is arranged in the optical path between the light source part12and the liquid crystal panel60. Due to the arrangement, of the light source light from the light source part12, the polarized light along the shielding axis40bof the additional light polarizer40is shielded by the additional light polarizer40before reaching the liquid crystal panel60. That is, the polarized light along the transmission axis40aof the additional light polarizer40travels toward the liquid crystal panel60, of the light source light.

The additional light polarizer40and the light polarizer61for liquid crystals adjacent to the light source part12are arranged such that the transmission axes40aand61amatch with each other and that the shielding axes40band61bmatch with each other. Therefore, the light source light passing through the additional light polarizer40, which is a polarized light along the transmission axis40a, is hardly shielded by the light polarizer61for liquid crystals adjacent to the light source part12, and a picture is formed. In this way, a picture can be formed with the liquid crystal panel60in the stacked state while a rise in temperature of the liquid crystal panel60can be restricted, which is caused by conversion from the light source light to heat, in the light polarizer61for liquid crystals adjacent to the light source part12. By the above, the HUD device100with high durability can be offered, while controlling deterioration in the quality of a picture.

Moreover, according to the first embodiment, the additional light polarizer40is arranged in the optical path between the diffusion part30and the liquid crystal panel60. Therefore, even if the polarized light of the light source light diffused by the diffusion part30is disturbed simultaneously with the diffusion action, the polarized light passing through the additional light polarizer40becomes suitable for the light polarizer61for liquid crystals adjacent to the light source part12and enters the light polarizer61for liquid crystals. Thus, the rise in temperature of the liquid crystal panel60can be restricted, which is caused by conversion from the light source light to heat in the light polarizer61for liquid crystals. In this way, the durability of the HUD device100can be improved, while raising the quality of a picture using the diffusion.

Moreover, according to the first embodiment, the additional light polarizer40is arranged in the optical path between the condensing part20and the liquid crystal panel60. Therefore, even if a polarized light aberration etc. occurs to the light source light condensed by the condensing part20simultaneously with the condensing action, the light source light passing through the additional light polarizer40becomes a polarized light suitable for the light polarizer61for liquid crystals adjacent to the light source part12and enters the light polarizer61for liquid crystals. Thus, the rise in temperature of the liquid crystal panel60can be restricted, which is caused by conversion from the light source light to heat in the light polarizer61for liquid crystals. In this way, the durability of the HUD device100can be improved, while raising the quality of a picture using the condensing.

Moreover, according to the first embodiment, the additional light polarizer40is the reflection type light polarizer which reflects the polarized light along the shielding axis40btoward the light source part12. Therefore, the conversion from the light source light to heat around the liquid crystal panel60can be restricted by the reflection toward the light source part12.

Moreover, according to the first embodiment, the reflective part50is arranged adjacent to the light source part12than the additional light polarizer40, to reflect the light source light reflected by the additional light polarizer40, again toward the liquid crystal panel60. A part of the light source light reflected by the reflective part50can be reused by passing through the additional light polarizer40, and the luminosity of a picture can be raised. In this way, the quality of a picture can be raised.

Moreover, according to the first embodiment, the additional light polarizer40is stuck with the liquid crystal panel60. Therefore, increase in the number of components held at the HUD device100can be restricted even if adding the light polarizer40.

Second Embodiment

As shown inFIG. 7, a second embodiment is a modification of the first embodiment. The second embodiment is described focusing on a point different from the first embodiment.

In the second embodiment, a light polarizer240corresponding to the light polarizer40is arranged in the optical path between the condensing part20and the diffusion part230, and the liquid crystal panel260, similarly to the first embodiment. In other words, the light polarizer240is arranged adjacent to the liquid crystal panel260than the condensing part20and the diffusion part230. However, the light polarizer240is stuck on the diffusion part230, and is arranged through the space SP relative to the liquid crystal panel260.

Moreover, the light polarizer240is the absorbing type light polarizer which absorbs polarized light along the shielding axis40b. Specifically, the light polarizer240is the absorbing type light polarizer formed by adding iodine which is dichroism pigment to polyvinyl alcohol, similarly to the pair of light polarizers61and62for liquid crystals. The light polarizer240has the transmission axis40aand the shielding axis40bapproximately perpendicular to each other due to the iodine molecular orientation.

Further, the reflective part50is not formed in the HUD device200of the second embodiment.

According to the second embodiment, the light polarizer240is arranged to the light polarizer61for liquid crystals adjacent to the light source part12, of the pair of light polarizers61and62for liquid crystals, such that the transmission axes40aand61amatch with each other, and that the shielding axes40band61bmatch with each other. Therefore, it becomes possible to obtain the action and effect similar to the first embodiment.

Moreover, according to the second embodiment, the additional light polarizer240is the absorbing type light polarizer which absorbs polarized light along the shielding axis40b, and is arranged through the space SP relative to the liquid crystal panel260. Since the space SP can make the heat of the light source light absorbed by the additional light polarizer240hard to get across to the liquid crystal panel260, the durability of the HUD device200can be improved.

Other Embodiment

The present disclosure is not limited to the embodiments mentioned above, and can be applied to various embodiments and its combinations within the range of the disclosure not deviated from the scope.

Specifically, as a first modification, as shown inFIG. 8, the light introducing part70may have only the concave mirror74, without having the plane mirror72.

As a second modification, various optical elements such as a reflecting mirror, a lens, a prism, a polarizing plate, a retardation film, and an optical filter may be added to the light introducing part70.

As a third modification, the additional light polarizer240of the second embodiment may be a reflection type light polarizer instead of the absorbing type light polarizer. Even when the additional light polarizer240is a reflection type light polarizer, the additional light polarizer240is stuck with the diffusion part230, and is arranged to the liquid crystal panel260through the space SP. Even when the additional light polarizer240is a reflection type light polarizer, it is not always necessary to form the reflective part50.

As a fourth modification, the additional light polarizer40may be formed in the shape of a board not stuck with the other components, and may be independently held at the projector case10a.

As a fifth modification, the reflective part50may reflect the light source light reflected by the light polarizer40again toward the liquid crystal panel60, by making a solder resist on the surface of the circuit board14for light sources to have bright color (for example, white).

As a sixth modification, the condensing part20that condenses the light source light from the light source part12may be one lens and may be a lens group including more than three lenses.

As a seventh modification, the HUD device100may not have at least one of the condensing part20and the diffusion part30.

As an eighth modification, other drive systems other than the TN (Twisted Nematic) system, such as VA (Vertical Alignment) system, an IPS (In-Place-Switching) system, etc. are employable for the liquid crystal panel. Moreover, a passive-matrix type panel may be adopted as the liquid crystal panel.

As a ninth modification, the present disclosure may be applied to various movable bodies (transport machines) such as vessel or airplane other than the vehicle1.