Head-up display device

Abstract

To provide a technique capable of extending the life of a liquid crystal panel in a head-up display using a liquid crystal display as a display unit.SOLUTION: The HUD includes a liquid crystal display as a display device. The liquid crystal display includes a liquid crystal panel 21 and an LED backlight. The liquid-crystal panel 21 includes a polarizing plate 7p including a PVA polarizing element 782 on the light-source side. An optical filter 8 for cutting off light in a wavelength region which is not used for image display is disposed on the surface of the liquid crystal panel 21 on the light source side. Since a part of the optical energy emitted from the LEDs as light sources is blocked by the optical filter 8, the amount of optical energy received by the polarizing plate 7p can be reduced.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a head-up display device that uses a liquid crystal display with an LED backlight as a display. [Background technology]

[0002] As disclosed in Patent Document 1, there is a head-up display device (hereinafter referred to as HUD) that projects image light output from a display onto the windshield of a vehicle to display a virtual image in a position in front of the vehicle as seen from the driver. HUD is an abbreviation for Head-Up Display. Patent Document 1 discloses a configuration in which, for example, a liquid crystal display using an LED backlight is used as the display.

[0003] In addition, it is known that sunlight and its heat entering the housing of an HUD can deteriorate the liquid crystal panel that makes up the LCD display. Therefore, as a general countermeasure against sunlight, HUDs sometimes have infrared blocking films placed in any location on the viewing side of the LCD display (for example, in openings or concave mirrors). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6955019 Summary of the Invention [Problem to be solved by the invention]

[0005] A configuration in which an infrared-blocking film is placed in the viewing-side area can reduce deterioration of an LCD display due to external light such as sunlight. However, the developers of the present disclosure have investigated the effects of light from an LED backlight (i.e., light from a light source) on an LCD panel and have found that the performance (mainly transmittance) of the LCD panel's polarizer can also deteriorate if light from a light source is continuously applied to the LCD panel for a long period of time. In other words, light from an LED can also deteriorate an LCD panel, although not as much as sunlight.

[0006] This is thought to be due to the polyenation of polyvinyl alcohol (PVA) that makes up the polarizing plate. In other words, when PVA is exposed to light energy, a radical reaction occurs. The radical reaction generates peroxy radicals (so-called active oxygen), which react with hydrogen atoms to generate hydroperoxides. The hydroperoxide reaction breaks down the polyene-iodine complex, resulting in polyenation. As a result, the transmittance of the polarizing plate can deteriorate over time.

[0007] The above reaction is caused by a wide range of light energy, regardless of wavelength, so reducing the amount of light energy irradiated onto the polarizing plate from the LED backlight can help protect the polarizing plate.

[0008] An object of the present disclosure is to provide a technology capable of extending the life of a liquid crystal panel in a head-up display that uses a liquid crystal display as a display. [Means for solving the problem]

[0009] One of the head-up display devices disclosed herein is A head-up display device that displays an image in front of a driver's seat by projecting image light showing an image onto a projection member, A housing (10), a display (20) that projects image light; a mirror member (30, 40) that reflects image light projected from the display in a predetermined direction; The display is a liquid crystal display including an LED backlight (22) and a liquid crystal panel (21), The liquid crystal panel includes a polarizer (7p, 78) including a polyvinyl alcohol polarizer layer (782), An optical filter (8) that blocks light in a predetermined wavelength range is disposed between the LED backlight and the polyvinyl alcohol polarizer layer.

[0010] With this configuration, the optical filter blocks part of the light (e.g., infrared light) emitted by the LED backlight, preventing it from reaching the polarizer. This reduces the amount of light energy received by the polarizer, thereby extending the life of the liquid crystal panel.

[0011] Note that the symbols in parentheses in the claims indicate a correspondence with the specific means described in the embodiments described below as one aspect, and do not limit the technical scope of the present disclosure. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of a head-up display device. [Figure 2] FIG. 2 is a diagram showing the configuration of a liquid crystal display as a display device. [Figure 3] FIG. 1 is a diagram illustrating an example of a basic configuration of a liquid crystal panel. [Figure 4] FIG. 10 is a diagram showing a liquid crystal panel having an optical filter attached to the surface facing the light source. [Figure 5] FIG. 2 is a diagram illustrating an example of the transmission characteristics of an optical filter. [Figure 6] FIG. 10 is a diagram illustrating another example of the position of the optical filter. [Figure 7] FIG. 10 is a diagram illustrating another example of the position of the optical filter. [Figure 8] FIG. 10 is a diagram illustrating another example of the position of the optical filter. [Figure 9]FIG. 2 is a diagram illustrating the configuration of a plane mirror. [Figure 10] FIG. 2 is a block diagram showing a control unit. [Figure 11] 10A and 10B are diagrams illustrating an example of brightness control of an LED backlight by a control unit in a bright environment. [Figure 12] 10A and 10B are diagrams illustrating an example of brightness control of an LED backlight by a control unit in a dark environment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments. The configurations disclosed below may be modified in various ways without departing from the spirit of the present disclosure. Various modified examples may be appropriately combined as long as no technical contradictions arise. The present disclosure also includes configurations that are not explicitly stated and are formed by combining multiple modified examples. In the following description, components having the same function may be given the same reference numerals, and specific descriptions thereof may be omitted. Furthermore, components having the same function may be given the same or similar names, and specific descriptions thereof may be omitted. When only a portion of a configuration is mentioned, descriptions given elsewhere may apply to other parts.

[0014] Fig. 1 is a diagram showing an example of a schematic configuration of a head-up display device (hereinafter referred to as HUD) 1 in one embodiment. As shown in Fig. 1, the HUD 1 is mounted on a vehicle such as a four-wheeled automobile for use. The height and width directions of the HUD 1 are set to correspond to the posture when mounted on the vehicle.

[0015] <Overall structure> Schematically, the HUD 1 projects image light onto a predetermined illumination area P on the windshield 2 of the vehicle, thereby displaying a virtual image 3 on a forward extension of a line connecting the eyes of a passenger seated in the driver's seat and the illumination area P. The windshield 2 is the windshield on the front side of the vehicle. The windshield 2 may be realized using, for example, laminated glass formed from two pieces of glass and an intermediate film disposed between them. The windshield 2 corresponds to the projection member. The projection member may also be a member that functions as a half mirror, such as a combiner.

[0016] Here, the image light means light that forms a virtual image as the image 3. The HUD 1 allows a passenger sitting in the driver's seat (hereinafter referred to as the driver) to visually recognize the image 3 superimposed on the scene in front of the vehicle. For convenience, hereinafter, the image 3, which is a virtual image perceived by the driver, will also be referred to as the HUD image.

[0017] The type of information displayed by the HUD image 3 may be designed as appropriate. For example, the HUD image 3 may be an image showing the direction of travel at an intersection, such as a turn-by-turn display. Of course, in another embodiment, the HUD image 3 may be an icon image showing the operating status of a system that provides an advanced driving assistance function or an autonomous driving function. The HUD image 3 may also be an image showing one or more of vehicle information while the vehicle is traveling, such as the driving speed, engine RPM, engine coolant temperature, and battery voltage. The HUD image 3 may also be an icon image that warns of a system abnormality. The HUD image 3 may also be an image that highlights objects that require attention, such as pedestrians.

[0018] The HUD 1 is housed in an instrument panel 4 that extends downward from the lower end of the windshield 2 toward the seat. An opening 4a is provided on the upper surface of the instrument panel 4, allowing image light emitted by the HUD 1 to pass through. A light-transmitting dust cover is provided on the opening 4a. The dust cover may be provided with a film for blocking infrared and ultraviolet rays. In FIG. 1, the dust cover is not shown to ensure visibility.

[0019] The HUD 1 is also connected to an image signal source 5 located outside the HUD 1 via an in-vehicle network established within the vehicle or a dedicated line for video signals. The image signal source 5 is a device that outputs an image signal that is the source of the HUD image 3 (e.g., a route guidance image). The image signal here may be still image data or a video signal. The image signal source 5 may be a navigation device, an electronic control unit (ECU) that provides a driving assistance function, an ECU that provides an autonomous driving function, or the like. The image signal source 5 may include multiple devices. The image signal source 5 may also be an HMI Control Unit (HCU), which is a computer that controls the content displayed as the HUD image 3.

[0020] Additionally, the HUD 1 may also be connected to an illuminance sensor 6. The illuminance sensor 6 is a sensor that detects the brightness (i.e., illuminance) outside the vehicle. A signal indicating the detection result of the illuminance sensor 6 (hereinafter also referred to as an illuminance signal) is input to the HUD 1. Note that another device (e.g., a body ECU) may be interposed between the illuminance sensor 6 and the HUD 1. In other words, the HUD 1 may be configured to indirectly acquire illuminance information from a device other than the illuminance sensor 6.

[0021] When the driver's eyes are located at a predetermined eye box Eb, the HUD1 is configured such that the driver can visually recognize the HUD image 3. The eye box Eb is a viewing area where the HUD image 3 can be visually recognized. The eye box Eb is determined by the optical characteristics of the HUD1. The HUD1 may be configured to be able to adjust the height of the eye box Eb via a viewpoint adjustment switch, which is an input device not shown in the figure.

[0022] <Regarding the configuration of HUD1> As shown in FIG. 1, the HUD1 includes a housing 10, a display 20, a plane mirror 30, and a concave mirror 40. The housing 10 is configured to accommodate the members of the display 20, the plane mirror 30, and the concave mirror 40. The housing 10 is fixed to the vehicle, and its position and orientation with respect to the windshield 2 are constant. Also, the housing 10 has a certain shape. The housing 10 may be made of resin or metal such as aluminum. Also, the housing 10 may be configured by combining resin parts and metal parts.

[0023] The display 20 is configured to emit light (i.e., image light) for forming the HUD image 3 based on the signal input from the image signal source 5. In this embodiment, as an example, the display 20 is a liquid crystal display.

[0024] As shown in FIG. 2, the display 20 includes a liquid crystal panel 21, an LED (Light Emitting Diode) backlight 22, a control board 23, and a display case 24 that integrally houses and fixes them. The liquid crystal panel 21 may be a panel module in which a polarizing plate, a glass plate, a liquid crystal array, etc. are integrally formed. The basic configuration of the liquid crystal panel 21 will be described separately later.

[0025] The LED backlight 22 is a light source module in which LEDs are arranged in an array. The LED backlight 22 of this embodiment is configured as a full-surface direct-lit type LED backlight. In other embodiments, the LED backlight 22 may be configured as an edge type LED backlight.

[0026] The LEDs (hereinafter referred to as light source LEDs) that form the LED backlight 22 may be white LEDs. In this embodiment, the light source LED is a white LED formed by combining a blue LED with a yellow phosphor. This reduces the cost of the LED backlight 22. In another embodiment, the light source LED may be a white LED formed by combining a blue LED with red and green phosphors. This increases the light component around 500 nm, making it possible to produce light that is closer to natural white. In yet another embodiment, the LEDs that form the LED backlight 22 may be an RGB-LED formed by combining three elements: an LED that emits red (R), an LED that emits green (G), and an LED that emits blue (B).

[0027] The liquid crystal panel 21 has a viewing side and a back side. The viewing side is the direction in which light from the LED backlight 22 is transmitted and output. The viewing side may be interpreted as the direction in which image light travels. The back side is the opposite direction to the viewing side. The LED backlight 22 is disposed on the back side of the liquid crystal panel 21. From another perspective, the back side corresponds to the direction in which the LED backlight 22 is disposed when viewed from the liquid crystal panel 21. In this embodiment, the back side may be referred to as the light source side, the bottom side, etc.

[0028] The control board 23 is a circuit board on which circuits for controlling the operation of the liquid crystal panel 21 and the LED backlight 22 are mounted. The control board 23 may be disposed on the rear side of the LED backlight 22. The control board 23 is connected to the image signal source 5 and the vehicle power line via cables or the like. The position of the control board 23 within the display case 24 and the specific shape of the control board 23 may be changed as appropriate.

[0029] The display case 24 is configured to house the liquid crystal panel 21, the LED backlight 22, and the control board 23. The display case 24 may be divided into a back frame, side frames, and a front frame (so-called bezel). The display case 24 may be, for example, a flat rectangular parallelepiped with an opening on the viewing side. The display case 24 may have steps, protrusions, recesses, etc. for fixing the positions of the liquid crystal panel 21, the LED backlight 22, and the control board 23. The liquid crystal panel 21, the LED backlight 22, and the control board 23 may be fixed to the display case by any method, such as screws, snap fits, or adhesives.

[0030] Such a display 20 is fixed to the housing 10 in a position in which it emits image light in the direction in which the plane mirror 30 is located. In other words, the position and position of the display 20 relative to the housing 10 may be constant. The image light emitted by the display 20 is reflected by the plane mirror 30 and the concave mirror 40, and is irradiated onto an illumination area P set on the windshield 2.

[0031] The plane mirror 30 is configured to guide the image light emitted from the display 20 to the concave mirror 40. The plane mirror 30 is configured to reflect the image light in the direction in which the concave mirror 40 is located (i.e., a predetermined direction). The concave mirror 40 is configured to reflect the image light reflected from the plane mirror 30 toward the windshield 2 through an opening 4a provided in the instrument panel 4. In addition to guiding the image light to the windshield 2, the concave mirror 40 also plays a role in enlarging and displaying the HUD image 3 formed by the image light.

[0032] The plane mirror 30 and the concave mirror 40 are arranged so that the image light emitted from the display 20 passes through a predetermined path and is projected onto the illumination area P. The installation positions and installation postures of the display 20, the plane mirror 30, and the concave mirror 40 can be changed as appropriate. For example, the path of the image light may be folded vertically or horizontally. The plane mirror 30 corresponds to the mirror member.

[0033] As described above, the image light projected by the display device 20 is reflected successively by the plane mirror 30 and the concave mirror 40, and is directed toward the windshield 2. Specifically, the plane mirror 30 reflects the image light projected from the display device 20 toward the concave mirror 40, and the concave mirror 40 reflects the image light, which is obtained by diffusing and reflecting the image light, toward the windshield 2.

[0034] <Basic structure of LCD panel> 3, the liquid crystal panel 21 has a configuration in which an exit-side polarizing plate 71, a glass plate 72, a color filter 73, a liquid crystal layer 74, an electrode layer 75, a glass plate 76, a viewing angle compensation film 77, and an entrance-side polarizing plate 78 are stacked together. Hereinafter, when there is no need to distinguish between the exit-side polarizing plate 71 and the entrance-side polarizing plate 78, they will also be collectively referred to as polarizing plate 7p.

[0035] The exit-side polarizing plate 71 is a polarizing plate 7p arranged closer to the viewer than the liquid crystal layer 74. The exit-side polarizing plate 71 may be a plate-shaped module in which a hard coat layer 711, a TAC film 712, a PVA polarizer 713, and a TAC film 714 are laminated in this order from the viewer side toward the rear side. Here, the term "plate-shaped" may also refer to a film-shaped module. TAC included in the component names is an abbreviation for triacetyl cellulose, and PVA is an abbreviation for polyvinyl alcohol. Triacetyl cellulose (TAC) may also be called cellulose triacetate.

[0036] The hard coat layer 711 is configured to protect the surface of the liquid crystal panel 21. The hard coat layer 711 may be a resin film made of a material such as PET (polyethylene terephthalate), or may be a glass film. A TAC film 712 is laminated on the lower (inner) side of the hard coat layer 711. Here, the lower side corresponds to the light source side or the back side. The TAC films 712 and 714 are configured to protect the PVA polarizer 713, which has low strength. The PVA polarizer 713 is a film-like structure formed by uniaxially stretching a PVA film dyed with iodine. The PVA polarizer 713 has polarization properties (birefringence) that allow only light vibrating in a certain direction to pass through. The output-side polarizing plate 71 has a sandwich structure in which the PVA polarizer 713 is sandwiched between the TAC films 712 and 714.

[0037] A glass plate 72, a color filter 73, a liquid crystal layer 74, an electrode layer 75, and a glass plate 76 are laminated in this order below the output-side polarizing plate 71. The glass plates 72 and 76 are flat, colorless, and transparent glass plates for holding the liquid crystal layer 74 and other components. The color filter 73 is a filter for adding color to light from the light source. The liquid crystal layer 74 is a layer in which liquid crystal cells are arranged. Alignment films for maintaining a uniform orientation of the liquid crystals may be provided above and below (before and after) the liquid crystal layer 74. The electrode layer 75 may be a layer in which electrodes for controlling the orientation of the liquid crystal molecules are arranged, for example, in an array. A viewing angle compensation film 77 is formed below the glass plate 76. The viewing angle compensation film 77 is an optical film for reducing the anisotropy of the polarizing plate and the liquid crystal cell and expanding the viewing angle of the liquid crystal display.

[0038] The incident-side polarizing plate 78 is a polarizing plate 7p arranged closer to the light source than the liquid crystal layer 74. In this embodiment, the incident-side polarizing plate 78 is arranged below the viewing angle compensation film 77. The incident-side polarizing plate 78 may be a plate-like module in which a TAC film 781, a PVA polarizer 782, a TAC film 783, and a hard coat layer 784 are laminated in this order from the viewing side to the rear side. This may be interpreted as a configuration in which the TAC film and other components are arranged in the reverse order to that of the exit-side polarizing plate 71. In other words, the incident-side polarizing plate 78 may be configured by attaching the exit-side polarizing plate 71 in the opposite direction to the viewing angle compensation film 77 below. In other words, the incident-side polarizing plate 78 and the exit-side polarizing plate 71 as materials before assembly may be the same polarizing plate. The PVA polarizer 782 corresponds to a polyvinyl alcohol polarizer layer.

[0039] The above-described structure of the liquid crystal panel 21 is an example. Various structures can be adopted as the structure of the liquid crystal panel 21. The configuration of the liquid crystal panel 21 may be changed as appropriate.

[0040] <Introduction of optical filters> As shown in FIG. 4, an optical filter 8 is provided on the surface of the liquid crystal panel 21 on the light source side of this embodiment. The optical filter 8 may be a film that blocks light in a specific wavelength range. Here, light includes electromagnetic waves other than visible light, such as ultraviolet and infrared rays. In this disclosure, the wavelength range blocked by the optical filter 8 is also referred to as a cut wavelength range. Blocking light is not limited to complete blocking (transmittance of 1% or less). A transmittance of less than 15% may also be included in blocking. In FIG. 4, the optical filter 8 is shown with dotted hatching for emphasis.

[0041] The optical filter 8 may be configured to block light in a wavelength range that is not used to display the HUD image 3. In the present disclosure, the wavelength range used to display the HUD image 3 is also referred to as a display range. Wavelengths that belong to the display range are also referred to as display wavelengths. The display range may be, for example, 440 nm to 690 nm.

[0042] The display usable range may be determined in consideration of the visible light range and the transmittance spectrum of the liquid crystal layer 74 of the liquid crystal panel 21. The display usable range may be a wavelength range within the visible light range where the transmittance of the liquid crystal layer 74 is equal to or greater than a predetermined threshold (hereinafter referred to as the first threshold). The first threshold may be, for example, 35%. In other embodiments, the first threshold may be 40%, 50%, or 70%. The visible light range here refers to the wavelength range that humans can generally (on average) perceive. The lower limit (λL) of the visible light range may be any value between 360 nm and 410 nm. The upper limit (λH) of the visible light range may be any value between 760 nm and 830 nm. In the following, a case where the visible light range is assumed to be from 360 nm to 780 nm will be described as an example.

[0043] If the wavelength range in which the transmittance of the liquid crystal layer 74 is equal to or greater than the first threshold is 420 nm to 800 nm, then, taking into account the assumed upper limit of the visible light range, the display range may be interpreted as 420 nm to 780 nm. The display range may be determined by the logical product of the wavelength range in which the transmittance of the liquid crystal layer 74 is equal to or greater than the first threshold and the visible light range.

[0044] The display usable range may be determined based on the visible light region and the overall transmittance spectrum of the liquid crystal panel 21, not just the liquid crystal layer 74. The overall transmittance spectrum of the liquid crystal panel 21 refers to a transmittance spectrum that takes into account the optical transmission characteristics of the color filter 73, the liquid crystal layer 74, the polarizer 7p, etc., of the liquid crystal panel 21 in a state where the optical filter 8 is not attached. When the wavelength range in which the transmittance is equal to or greater than the first threshold value is 420 nm to 740 nm in the overall optical characteristics of the liquid crystal panel 21, the display usable range may be set to 420 nm to 740 nm.

[0045] Alternatively, if the range of colors used to display an image is predetermined, for example, from blue (equivalent to 440 nm) to red (equivalent to 650 nm), the range of wavelengths required to display the image may be set as the display range, i.e., from 440 nm to 650 nm.

[0046] The optical filter 8 is configured to transmit light in the display range set as described above, while blocking some or all of the light in other wavelength bands. Here, "transmitting light" means that the transmittance is equal to or greater than a first threshold, and "blocking light" means that the transmittance is less than a second threshold that is lower than the first threshold. The second threshold may be set to a predetermined value that can be considered as blocking, such as 15%. The second threshold may also be set to the same value as the first threshold.

[0047] In consideration of the optical characteristics of the liquid crystal panel 21 and the color tone of the image, when the display range is set to 420 nm to 700 nm, the optical filter 8 may be a filter configured to have a transmittance spectrum as shown in FIG. 5. That is, the optical filter 8 may be a filter having a transmittance of less than 15% for light with a wavelength of 400 nm or less, a transmittance of 35% or more for light from 420 nm to 700 nm, and a transmittance of 15% or less for light of 720 nm or more. The filter may have a transmittance of 80% or more for light from 440 nm to 650 nm. The vertical axis of FIG. 5 represents transmittance, and the horizontal axis represents wavelength.

[0048] 5 is merely an example and is not limiting. The optical filter 8 may be a filter that has a transmittance of less than 15% for light with a wavelength of 420 nm or less and a transmittance of 80% or more for light with a wavelength of 440 nm or more, taking into account the overall transmittance spectrum of the liquid crystal panel 21. The optical filter 8 may be a filter that has a transmittance of less than 15% for light with a wavelength of 440 nm or less, a transmittance of 80% or more for light with a wavelength of 460 nm to 660 nm, and a transmittance of less than 15% for light with a wavelength of 700 nm or more.

[0049] The optical filter 8 having the specific transmission characteristics described above may be realized using a single film formed by laminating multiple types of dielectric films, or may be realized by overlapping a first film that cuts short wavelengths (420 nm or less) with a second film that cuts long wavelengths (780 nm or more). The first film may be an ultraviolet-cutting film, and the second film may be an infrared-cutting film. The optical filter may be selected based on the display use range, and its optical characteristics (transmission characteristics) do not need to completely separate the display use range from other ranges. The display use range may be used as a reference for selecting a commercially available optical filter 8 or for designing a new optical filter 8.

[0050] Furthermore, the optical filter 8 does not necessarily need to be configured to be able to block both short and long wavelengths, and may be one that cuts only the short wavelength side. For example, the optical filter may be a filter that cuts wavelengths in the 440 nm or shorter range. Specific examples of the optical filter 8 include SCF-50S-44Y manufactured by Sigma Koki Co., Ltd. and the filter disclosed in Patent Document 1. Furthermore, the optical filter 8 may be one in which an ultraviolet absorber such as OUV-015 manufactured by Fujifilm Corporation is applied to the surface of the hard coat layer 784. The optical filter 8 may be one that cuts only the long wavelength side (i.e., infrared light). The optical filter 8 may be realized using any infrared-cutting film.

[0051] In Figure 5, λL indicates the lower limit of the visible light range, and λH indicates the upper limit of the visible light range. The lower limit λL is the wavelength range that is easily perceived as green, although this differs from person to person. "V," "B," "G," "Y," "O," and "R" in Figure 4 represent purple, blue, green, yellow, orange, and red, respectively. For example, the range indicated by "G" indicates the wavelength range that is easily perceived as green, although this differs from person to person.

[0052] <Effects> Because vehicles are used for long periods of time (e.g., five years or more), the HUD 1 used in the vehicle must also be configured to be able to display the HUD image 3 with consistent visibility for a long period of time. Because the PVA that makes up the polarizing plate 7p can deteriorate when exposed to light, it is preferable to reduce the total energy of light incident on the liquid crystal panel 21 from the perspective of extending the life of the liquid crystal panel 21. On the other hand, cutting light in the visible light range darkens the image light itself, reducing the visibility of the HUD image 3.

[0053] To address this issue, the above-described configuration uses the optical filter 8 disposed between the LED backlight 22 and the liquid crystal panel 21 to transmit light in the wavelength range used for image display (i.e., the display usable range), while blocking some or all of the light in the wavelength range not used for image display. This makes it possible to reduce the total energy of light incident on the liquid crystal panel 21 while ensuring image visibility. This reduces deterioration of the polarizing plate 7p of the liquid crystal panel 21, thereby extending the service life (so-called life span) of the liquid crystal panel 21.

[0054] As mentioned above, the optical filter 8 is configured to reduce the total amount of light energy incident on the polarizing plate 7p. Physically, the shorter the wavelength of light, the greater the energy. This is because, where E is the energy and λ is the wavelength, E=hc / λ (h is Planck's constant and c is the speed of light). Therefore, the optical filter 8 may be configured to block light in the short wavelength range (i.e., ultraviolet light) more preferentially than light in the long wavelength range. However, if the LED backlight 22 has output characteristics in which the long wavelength range component is greater than the short wavelength range component, the optical filter 8 may be configured to block light in the long wavelength range (i.e., infrared light) more preferentially than light in the short wavelength range. The optical characteristics of the optical filter 8 may be determined based on the spectrum of light output by the LED backlight 22 so as to increase the amount of unwanted light blocked.

[0055] <Modification (1): Position of introduction of optical filter> In the above embodiment, the optical filter 8 is disposed on the surface of the liquid crystal panel 21 facing the light source, but the location where the optical filter 8 is introduced is not limited to this. For example, as shown in Fig. 6, the optical filter 8 may be disposed between the liquid crystal panel 21 and the LED backlight 22 so as to be spaced a predetermined distance from the liquid crystal panel 21. Alternatively, the optical filter 8 may be attached to the surface of the LED backlight 22, as shown in Fig. 7. The control board 23 is not shown in Figs. 6 and 7.

[0056] Furthermore, the optical filter 8 may be incorporated into the incident-side polarizing plate 78. For example, the optical filter 8 may be inserted between a TAC film 783 and a hard coat layer 784 as shown in FIG. 8 . The optical filter 8 may also be formed between the TAC film 783 and a PVA polarizer 782. The optical filter 8 only needs to be located closer to the light source than the PVA polarizer 782 of the incident-side polarizing plate 78, and its specific position may be changed. In FIGS. 6, 7, and 8, the optical filter 8 is shown with dotted hatching for emphasis.

[0057] <Modification (2): Color Tone Compensation Using Mirror Members> The introduction of the optical filter 8 may result in the loss of some color components, causing the hue of the HUD image 3 to change from its original hue. The "original hue" here refers to the hue when the optical filter 8 is not provided. For example, if the optical filter 8 cuts out light around 400 nm, the purple component is reduced, which may change the hue of the displayed image. To address this issue, for example, the plane mirror 30 or the concave mirror 40 may be configured to compensate for the change in color tone (effectively the optical spectrum) caused by the optical filter 8 using its reflection characteristics.

[0058] Hereinafter, the wavelength range in the visible light range where the intensity is reduced by the optical filter 8 is also referred to as the intensity reduction range. The intensity reduction range may be a wavelength range where the transmittance of the optical filter 8 is less than a predetermined suppression threshold. The suppression threshold may be, for example, 35% or 50%. On the other hand, the wavelength range in the visible light range where the transmittance of the optical filter 8 is equal to or greater than a predetermined threshold is also referred to as the intensity maintenance range. The maintenance threshold may be any value equal to or greater than 50%. The specific values ​​of the suppression threshold and the maintenance threshold may be changed as appropriate. The intensity reduction range corresponds to the first wavelength range, and the intensity maintenance range corresponds to the second wavelength range.

[0059] The plane mirror 30 may be configured so that the reflectance for visible light in the intensity-reducing region is high (80% or more) and the reflectance for visible light in the intensity-maintaining region is medium or low. Here, medium may be interpreted as 50% to 79%, and low as 30% to 49%. More specifically, if the wavelength region up to 500 nm corresponds to the intensity-reducing region, the plane mirror 30 may be configured so that the reflectance for visible light up to 500 nm is 80% or more and the reflectance for visible light over 500 nm is about 50%.

[0060] As shown in FIG. 9, a plane mirror 30 generally has a configuration in which a dielectric multilayer film 32 is formed on one surface of a plate-shaped substrate 31. The substrate 31 may be a glass plate or the like. The surface of the substrate 31 on which the dielectric multilayer film 32 is formed corresponds to the reflective surface. The dielectric multilayer film 32 is configured by alternately stacking dielectric films with different refractive indices. The thickness of each dielectric film is set to about one-fourth the wavelength to be reflected. A person skilled in the art would be able to set the reflection characteristics of the plane mirror 30 to desired characteristics by adjusting the configuration of the dielectric multilayer film 32.

[0061] As described above, the overall color balance can be adjusted by using a plane mirror 30 that has high reflectivity for wavelength ranges where the intensity is significantly reduced by the optical filter 8 and low reflectivity for wavelength ranges where the intensity is only slightly reduced by the optical filter 8. In other words, the change in color tone of the HUD image 3 caused by the introduction of the optical filter 8 can be reduced.

[0062] Although the above describes a pattern for correcting the color tone change caused by the optical filter 8 by adjusting the reflection characteristics of the plane mirror 30, it is also possible to adjust the reflection characteristics of the concave mirror 40 instead of the plane mirror 30. The mirror member used for color tone correction may be either the plane mirror 30 or the concave mirror 40. Furthermore, the adjustment of the reflection characteristics may be achieved by attaching a film having the desired reflection characteristics to the reflective surface, rather than by adjusting the dielectric multilayer film 32.

[0063] <Modification (3): Adjusting the output of the light source> The light energy received by the polarizing plate 7p can also be reduced by reducing the output brightness of the LED backlight 22 itself. The control board 23 may be formed with a control unit 231 that controls the brightness of the LED backlight 22, as shown in Fig. 10. The control unit 231 may be a microcomputer, an integrated circuit (IC), a field-programmable gate array (FPGA), or a combination thereof. For example, the control unit 231 may be configured to control the brightness of the LED backlight 22 to 30% or less of the maximum brightness of the LED backlight 22.

[0064] The brightness of the LED (in other words, the output or drive amount) may be adjusted by PWM (Pulse Width Modulation) control. When the duty ratio of the PWM signal is 1, the LED emits light at maximum brightness, and when the duty ratio of the PWM signal is 0, the LED does not emit light. By adjusting the pulse width of the PWM signal, the ratio of the LED's light-emitting time in a certain period (so-called duty ratio) is determined, and the brightness of the LED is controlled. Here, the control unit 231 controls the brightness of the LED using PWM, but the brightness control method is not limited to this. The brightness of the LED may also be controlled by increasing or decreasing the value of the current supplied to the LED. The maximum brightness is determined according to the LED specifications, such as the rated current.

[0065] The control unit 231 may have registered therein brightness setting data including a plurality of brightness setting values. For example, the brightness setting data includes a first brightness and a second brightness as brightness for a bright environment, and a third brightness and a fourth brightness as brightness for a dark environment. Here, the bright environment refers to a situation in which the external illuminance is equal to or greater than a predetermined illuminance threshold. The dark environment refers to a situation in which the external illuminance is less than the illuminance threshold.

[0066] The first brightness is set to be lower than the second brightness by a predetermined amount. The first brightness may be set to a value between 18% and 23% of the maximum brightness. In other embodiments, the first brightness may be set to 30% or 40%. The first brightness may be at a level that makes it slightly difficult for the driver to see the HUD image 3 in a bright environment, or at a level at which the HUD image 3 is not noticeable. The first brightness may be set to a level at which the driver can faintly see the HUD image 3 in a bright environment. The level at which the HUD image 3 can be faintly recognized may be a level at which the presence of the display can be recognized, but the content cannot be recognized unless the driver pays attention to it, and the display content can be recognized if the driver pays attention to it.

[0067] The second brightness is a brightness setting value for clearly or emphasizing the HUD image 3 in a bright environment, and is set to a predetermined amount higher than the first brightness. The second brightness may be set to, for example, 80% of the maximum brightness. The second brightness may also be set to 60% or 100% of the maximum brightness. The second brightness may be set to a level that allows the driver to clearly view the HUD image 3 even in a bright environment.

[0068] The third luminance is set to a level lower than the fourth luminance by a predetermined amount. For example, the third luminance may be set to 10% or 15% of the maximum luminance. The third luminance may be set to a level that makes it slightly difficult for the driver to see the HUD image 3 in a dark environment, or a level that makes the HUD image 3 inconspicuous. The third luminance may also be set to a level that allows the driver to faintly see the HUD image 3.

[0069] The fourth luminance is a luminance setting value for clearly or emphasizing the HUD image 3 in a dark environment, and is set to a predetermined amount higher than the third luminance. The fourth luminance is set to be lower than the second luminance because it is a luminance for nighttime use. For example, the fourth luminance is set to 40% or 50% of the maximum luminance. The fourth luminance may be set to a level that allows the driver to clearly view the HUD image 3 in a dark environment. The fourth luminance may be set to a level that does not cause the driver to feel dazzled.

[0070] The setting values ​​of each luminance, such as a level at which the driver can faintly see the HUD image 3, may be determined through testing. Note that, as an example, the fourth luminance is higher than the first luminance here, but the fourth luminance may be lower than the first luminance. From another perspective, the first luminance may be higher than the fourth luminance. Note that the first luminance and the third luminance are luminances that are basically applied in a bright environment or a dark environment, as described below, and are therefore collectively referred to as basic luminance. The second luminance and the fourth luminance are luminance settings for temporarily displaying the HUD image 3 with good visibility or in an emphasized manner, and are collectively referred to as temporary luminance.

[0071] The control unit 231 adjusts the brightness output of the LED backlight 22 based on an information signal input from another in-vehicle device. The other in-vehicle device may include an illuminance sensor 6 or an image signal source 5. The other in-vehicle device serving as the image signal source 5 may include a navigation device or a driving assistance device. The navigation device provides route guidance and may input a signal indicating a planned lane change event, such as a right or left turn, to the HUD 1. The driving assistance device provides driving assistance and may present safety-related information, such as the status of traffic lights, crosswalk locations, stop line locations, and pedestrian highlighting. When the driving assistance device detects a notification target, such as a stop line, based on the recognition results of the forward camera or map data, it may input a signal indicating the presence of the notification target to the HUD 1. The other in-vehicle device may include devices other than the illuminance sensor 6 and the image signal source 5. For example, the other in-vehicle device may include a vehicle speed sensor. The other in-vehicle device may be an in-vehicle communication device connected to the driver's smartphone for communication.

[0072] For example, when the external illuminance is equal to or greater than the illuminance threshold, the control unit 231 basically sets the luminance of the LED backlight 22 to a first luminance, as shown in Fig. 11. The horizontal axis in Fig. 11 represents the passage of time, and the vertical axis represents the luminance of the LED backlight 22. In Fig. 11, "B1" represents the first luminance, "B2" represents the second luminance, and "Bmx" represents the maximum luminance.

[0073] When a specific event is detected based on an input signal from another in-vehicle device, the control unit 231 temporarily increases the brightness of the LED backlight 22 from the first brightness to the second brightness. The event may be, for example, speeding, approaching a left / right turn point, approaching a stop line, approaching a pedestrian crossing, detection of a red light, detection of a green arrow light, or detection of a pedestrian. Speeding may be when the traveling speed exceeds the speed limit by a predetermined amount (for example, 10 km / h). The control unit 231 may detect speeding based on the output of a speed sensor.

[0074] The control unit 231 may detect route guidance-related events, such as approaching a left turn point / right turn point, based on signals input from the navigation device. A left turn point may be an intersection where a left turn is planned. A right turn point may be an intersection where a right turn is planned. The control unit 231 may detect safety-related events, such as approaching a stop line / crosswalk, a red light, a green arrow light, or a pedestrian, based on input from the driving assistance device. These events may correspond to situations (specific scenes) in which visibility of the HUD image 3 should be increased.

[0075] In this way, the control unit 231 is configured to determine whether or not the scene requires increased visibility of the HUD image 3 based on input signals from other in-vehicle devices, and to control the brightness according to the determination result. The display content of the HUD image 3 may be changed in conjunction with an event. For example, when a route guidance-related event occurs, the HUD image 3 may be an image related to route guidance. When speeding is detected, the HUD image 3 may be an image showing the driving speed and the speed limit. When a safety-related event is detected, an image corresponding to the event may be displayed.

[0076] Time t1 in FIG. 11 represents the timing at which a certain event A is detected. Event A may be, for example, speeding. When the control unit 231 detects the occurrence of an event, it may maintain the second luminance for a predetermined period of time. The timing at which the maintenance of the second luminance is released and the luminance starts to be reduced toward the first luminance is also referred to as the release timing. Time t2 in FIG. 11 represents the release timing for event A. The time from when the luminance is increased to when the luminance starts to be reduced may be a fixed time. Alternatively, the release timing may be the timing at which the event that triggered the increase in luminance is completed. The control unit 231 may be configured to maintain the second luminance while the event that triggered the increase in luminance continues (for example, while speeding is occurring).

[0077] 11 illustrates an example in which the brightness is gradually reduced to the first brightness from the release timing. Of course, the control unit 231 may reduce the brightness from the second brightness to the first brightness in a stepwise manner at the release timing.

[0078] After returning the brightness from the second brightness to the first brightness, the control unit 231 maintains the first brightness until another event occurs. Time t3 in the figure indicates the timing when event B is detected. Event B may be, for example, approaching a left turn point. The display at the second brightness resulting from event B may continue until the left turn is completed. Time t4 indicates the timing when the left turn is completed. The increase in brightness for the left turn may be canceled when the steering angle reaches a predetermined value or greater. The control unit 231 may determine the completion of a left turn or a right turn based on an input signal from a steering angle sensor. The control unit 231 may also detect the completion of a left turn or a right turn based on an input signal from a navigation device. In this way, the first brightness is basically applied in a bright environment, and the second brightness is continuously increased when an event occurs.

[0079] The control unit 231 may also control the luminance in response to the detection of an event in a dark environment, as well as in a bright environment. When the external illuminance is below the illuminance threshold, the control unit 231 basically sets the luminance of the LED backlight 22 to the third luminance, as shown in FIG. 12 . Then, in response to the detection of events C and D, the control unit 231 temporarily increases the luminance from the third luminance to the fourth luminance. Event C detected at time t5 may be, for example, the detection of a pedestrian crossing 50 meters ahead of the host vehicle. The HUD image 3 displayed at this time may be an image that notifies / highlights the pedestrian crossing. The application of the fourth luminance for notifying / highlighting the pedestrian crossing may be canceled when the vehicle passes the crosswalk (t6). Event D detected at time t7 may be the approach of a right turn point. The HUD image 3 displayed at this time may be an image that provides guidance to make a right turn. The application of the fourth luminance for right turn guidance may be canceled when the right turn is completed.

[0080] According to the above configuration, the brightness output of the LED backlight 22 is basically suppressed. Therefore, the total amount of light energy (hereinafter referred to as the amount of received light energy) received by the polarizing plate 7p per certain period of time (for example, one hour) can be reduced. As a result, the life of the polarizing plate 7p can be extended. Furthermore, when a predetermined event occurs, the brightness of the HUD image 3 is temporarily increased. This makes it possible to maintain the information presentation function using the HUD image 3.

[0081] The control unit 231 may be configured to detect the occurrence of an event and temporarily increase the brightness depending on the type of image displayed as the HUD image 3. For example, the control unit 231 may automatically increase the brightness to a temporary brightness such as the second brightness or the fourth brightness when a video signal related to route guidance such as a right or left turn is input as the HUD image 3. The control unit 231 may also automatically increase the brightness from the basic brightness to the temporary brightness when a video signal for displaying an image notifying of a safety-related object such as a crosswalk, a stop line, or a pedestrian / cyclist on the roadway is input as the HUD image 3. The control unit 231 may automatically adjust the brightness depending on the type of image displayed as the HUD image 3.

[0082] When a specific type of video signal is not input, the control unit 231 may display a so-called meter-type image, such as the current vehicle speed or the shift position, as the HUD image 3. When the speed is not exceeded or an event such as a change in the shift position has not occurred and the specific type of video signal is not input, the control unit 231 may set the brightness of the LED backlight 22 to a basic brightness, such as the first brightness or the third brightness. When an event such as an exceeding of the speed limit or a change in the shift position has occurred, the control unit 231 may temporarily increase the brightness of the LED backlight 22 to a temporary brightness, even when a specific type of video signal is not input.

[0083] <Supplement: Brightness setting based on target value> The performance / specifications of the liquid crystal panel 21 may require that the transmittance after displaying an image be maintained at or above X% of the initial transmittance for a specified test time. X% may be a value corresponding to the test time, such as 60% or 70%. The test time may be set to a value such as 3,000 hours, 4,000 hours, or 5,000 hours, assuming that a vehicle equipped with the liquid crystal panel 21 will be used for more than five years. Because deterioration of the polarizing plate 7p due to polyenation reduces the transmittance of the entire liquid crystal panel 21, a specified target value may also be set for the total amount of light energy received by the polarizing plate 7p during the test time (hereinafter, the total amount of received light energy). In one aspect, polyenation here may be understood as a phenomenon related to the decomposition / disintegration of polyiodine complexes due to radical reaction.

[0084] The base luminance, which is the luminance level normally used by the control unit 231 in a bright environment, may be set to achieve a target value. For example, consider a case where the total amount of received light energy is 32,000 Wh / m^2 when the optical filter 8 is not used and maximum luminance is used as the base luminance, and the target value for the total amount of received light energy is 10,000 Wh / m^2. The base luminance here refers to the luminance that is always applied when the HUD image 3 is displayed. Under this assumption, if the introduction of the optical filter 8 can reduce light energy by 22% (≒7,000 Wh / m^2), the base luminance may be set to achieve the target value. Specifically, if the optical filter 8 can reduce light energy by 7,000 Wh / m^2, the total amount of received light energy is 32,000 - 7,000 = 25,000 Wh / m^2. The difference between this and the target value (10,000 Wh / m^2) is 15,000 Wh / m^2. If the total amount of light energy received is reduced by 250Wh / m^2 for every 1% reduction in brightness from the maximum brightness, then 15,000Wh / m^2 is equivalent to 60% of the maximum brightness. Therefore, the control unit 231 may be configured to adopt 40% of the maximum brightness, which is 60% lower than the maximum brightness (=100%), as the basic brightness. This setting makes it possible to achieve the target value.

[0085] The target value for the total amount of received light energy is determined based on the deterioration characteristics of the polarizing plate 7p and the test time. The above figures are one assumption. The actual target value, etc. may be determined based on the characteristics of the polarizing plate 7p used, the test time, etc. The basic brightness to achieve the target value may be 70%, 50%, 30%, or 20% of the maximum brightness. The basic brightness may be set to a value of 40% or less.

[0086] In this way, the control unit 231 may be configured to drive the LED backlight 22 at a basic luminance determined based on a target value for the total amount of received light energy required to maintain the transmittance of the polarizing plate 7p. The basic luminance described here may be used as the first luminance described above. In addition to the first luminance as the basic luminance, the control unit 231 may temporarily apply a second luminance in response to the occurrence of an event.

[0087] The value obtained by dividing the total amount of received light energy by the test time corresponds to the target value of the amount of received light energy per hour. Instead of or in addition to the target value of the total amount of received light energy, a target value of the amount of received light energy per fixed time may be set for the polarizing plate 7p. The basic brightness may be set according to the target value of the amount of received light energy per fixed time. [Explanation of symbols]

[0088] 1 HUD (head-up display device), 5 image signal source, 6 illuminance sensor, 8 optical filter, 20 display, 21 liquid crystal panel, 22 LED backlight, 23 control board, 30 plane mirror, 40 concave mirror, 71 exit side polarizer, 77 entrance side polarizer, 7p polarizer, 782 PVA polarizer (polyvinyl alcohol polarizer layer), 784 hard coat layer, 231 control unit

Claims

1. A head-up display device that displays an image in front of a driver's seat by projecting image light showing the image onto a projection member, A housing (10); a display (20) that projects the image light; a mirror member (30, 40) that reflects the image light projected from the display in a predetermined direction; The display is a liquid crystal display including an LED backlight (22) and a liquid crystal panel (21), The liquid crystal panel includes a polarizer (7p, 78) including a polyvinyl alcohol polarizer layer (782), A head-up display device in which an optical filter (8) that blocks light in a predetermined wavelength range is disposed between the LED backlight and the polyvinyl alcohol polarizer layer.

2. 2. The head-up display device according to claim 1, wherein the optical filter has a transmittance of less than 15% for light having a wavelength of 400 nm or less and a transmittance of 80% or more for light having a wavelength of 440 nm or more.

3. 2. The head-up display device according to claim 1, wherein the optical filter has a transmittance of less than 15% for light having a wavelength of 400 nm or less, a transmittance of 80% or more for light having a wavelength of 440 nm to 650 nm, and a transmittance of less than 15% for light having a wavelength of 720 nm or more.

4. the optical filter has a transmittance for light in a first wavelength range that is less than a predetermined suppression threshold, and a transmittance for light in a second wavelength range that is equal to or greater than a predetermined maintenance threshold that is greater than the suppression threshold, 2. The head-up display device according to claim 1, wherein a dielectric film having a reflectance for light in the first wavelength range higher than a reflectance for light in the second wavelength range is formed on a reflective surface of the mirror member.

5. The head-up display device according to claim 1 , wherein the optical filter is attached to a surface of the liquid crystal panel on the light source side.

6. the polarizing plate has a hard coat layer (784) on the light source side of the polyvinyl alcohol polarizer layer, The head-up display device according to claim 1 , wherein the optical filter is provided between the polyvinyl alcohol polarizer layer and the hard coat layer in the polarizing plate.

7. a target value for the amount of light energy received per unit time is set for the polarizing plate; A control unit (231) that adjusts the brightness of the LED backlight, The control unit The head-up display device according to claim 1 , wherein the brightness of the LED backlight is controlled in accordance with a basic brightness determined according to the target value.

8. The head-up display device according to claim 7 , wherein the basic brightness is set to a level equal to or lower than 40% of the maximum brightness.

9. A control unit (231) that adjusts the brightness of the LED backlight, a first luminance and a second luminance are set in the control unit as luminances for a bright environment in which external illuminance is equal to or greater than a predetermined threshold; The first luminance is set lower than the second luminance, The control unit determining whether the external illuminance is equal to or greater than the threshold based on the detection result of the illuminance sensor; determining whether the image is a specific scene that should have its brightness increased based on a signal input from a predetermined other in-vehicle device or the type of the image; When the external illuminance is equal to or greater than the threshold value and the scene is not determined to be the specific scene, the luminance of the LED backlight is set to the first luminance; 2. The head-up display device according to claim 1, wherein when the external illuminance is equal to or greater than the threshold and it is determined that the specific scene is occurring, the brightness of the LED backlight is temporarily increased from the first brightness to the second brightness.

10. A control unit (231) that adjusts the brightness of the LED backlight, The control unit is configured to set a first luminance and a second luminance as luminances for a bright environment in which the external illuminance is equal to or greater than a predetermined threshold, and to set a third luminance and a fourth luminance as luminances for a dark environment in which the external illuminance is less than the threshold. The first luminance is set lower than the second luminance, the third luminance is set lower than the fourth luminance, the fourth luminance is set lower than the second luminance, The control unit determining whether the external illuminance is equal to or greater than the threshold based on the detection result of the illuminance sensor; determining whether the image is a specific scene that should have its brightness increased based on a signal input from a predetermined other in-vehicle device or the type of the image; When the external illuminance is equal to or greater than the threshold value and the scene is not determined to be the specific scene, the luminance of the LED backlight is set to the first luminance; When the external illuminance is equal to or greater than the threshold value and the specific scene is determined, the luminance of the LED backlight is temporarily increased from the first luminance to the second luminance; When the external illuminance is less than the threshold value and it is determined that the scene is not the specific scene, the luminance of the LED backlight is set to the third luminance; 2. The head-up display device according to claim 1, wherein when the external illuminance is less than the threshold and it is determined that the specific scene is occurring, the brightness of the LED backlight is temporarily increased from the third brightness to the fourth brightness.

Images