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 and a backlight. The liquid crystal panel includes a polarizing plate including a PVA polarizer on a light source side. The backlight is configured as a surface light source in which RGB-LEDs including LED elements corresponding to three colors of RGB, that is, a red LED, a green LED, and a blue LED as one set are arranged in a matrix. The LED elements for each color included in the backlight are configured such that the light emission brightness can be individually controlled in units of colors. A control unit that controls the operation of the backlight operates the light emission brightness of each color at a predetermined level (for example, 20% to 60%) lower than the maximum brightness.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to a head-up display device that uses a liquid crystal display 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 by 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 a 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 a liquid crystal display due to external light such as sunlight. However, the developers of the present disclosure have investigated the effect of light from a backlight (i.e., light from a light source) on a liquid crystal panel and have found that the performance (mainly transmittance) of the polarizer of the liquid crystal panel can also deteriorate if light from a light source is continuously applied to the liquid crystal panel for a long period of time. In other words, light from an LED can also deteriorate a liquid crystal 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, and therefore reducing the amount of light energy irradiated from the backlight onto the polarizing plate can lead to protection of 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] The head-up display device disclosed herein is a head-up display device that displays an image in front of a driver's seat by projecting image light representing an image onto a projection member, and includes a housing (10), a display (20) including a backlight (22) and a liquid crystal panel (21) and configured to project the image light, mirror members (30, 40) that reflect the image light projected from the display in a predetermined direction, and a control unit (231) that adjusts the brightness of the backlight, and the liquid crystal panel includes a polarizer having a polyvinyl alcohol polarizer layer (782). The backlight includes a light plate (7p, 78), and the backlight includes a plurality of light sources, each of which is an RGB-LED having three LED elements as a set: a red LED that is an LED element that emits red light, a green LED that is an LED element that emits green light, and a blue LED that is an LED element that emits blue light. The red LED, green LED, and blue LED are configured so that their brightness can be controlled individually, and the control unit is configured to cause each of the red LED, green LED, and blue LED to emit light at a brightness lower than the maximum brightness.

[0010] According to the above configuration, the light emission luminance of the LED elements of each color that constitute the backlight is reduced, so that the amount of light energy received by the polarizing plate can be reduced, and the life of the liquid crystal panel can be extended.

[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. 2 is a diagram for explaining the configuration of a light source LED. [Figure 4] FIG. 2 is a block diagram showing a control unit. [Figure 5] FIG. 1 is a diagram illustrating an example of a basic configuration of a liquid crystal panel. [Figure 6] FIG. 10 is a diagram illustrating an example of luminance settings for each color. [Figure 7] FIG. 10 is a diagram illustrating another example of luminance settings for each color. [Figure 8] FIG. 10 is a diagram illustrating another example of luminance settings for each color. [Figure 9] FIG. 10 is a diagram illustrating another example of luminance settings for each color. [Figure 10] FIG. 2 is a diagram illustrating the configuration of a plane mirror. [Figure 11] FIG. 10 is a diagram illustrating an example of an introduction position of an optical filter. [Figure 12] 10A and 10B are diagrams illustrating other examples of the introduction position of the optical filter. [Figure 13] 10A and 10B are diagrams illustrating other examples of the introduction position of the optical filter. [Figure 14] FIG. 10 is a diagram illustrating an example of brightness control of a backlight in a bright environment. [Figure 15] FIG. 10 is a diagram illustrating an example of brightness control of a backlight 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 in the 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 may be made of a 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 (that is, 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, a 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 backlight 22 is a light source module in which a plurality of LEDs (Light Emitting Diodes) are arranged in an array as a plurality of light source elements. The backlight 22 of this embodiment is configured as a full-surface direct-lit type backlight. In other embodiments, the backlight 22 may be configured as an edge type backlight.

[0026] The light source LEDs 221, which are LEDs forming the backlight 22, are RGB-LEDs having a set of three LED elements, a red LED that emits red (R), a green LED that emits green (G), and a blue LED that emits blue (B), as shown in FIG. 3 . In this way, the backlight 22 has a plurality of red LEDs, green LEDs, and blue LEDs. In this embodiment, the light source LEDs 221 may be common-cathode RGB-LEDs in order to individually control the brightness of each color. In other embodiments, in a configuration in which a common brightness is applied to each color, the light source LEDs 221 may be common-anode RGB-LEDs. Furthermore, the light source LEDs 221 do not necessarily need to have a common cathode or anode, and the cathodes and anodes of the LED elements of each color may be independent.

[0027] The red, green, and blue LED elements are configured so that their brightness can be controlled individually. For example, the backlight 22 may be configured so that the brightness can be adjusted for each color. Specifically, a common drive signal is input to all red LEDs included in the backlight 22, causing them to light up at a common brightness. A common drive signal is input to all green LEDs included in the backlight 22, causing them to light up at a common brightness. A common drive signal is input to all blue LEDs included in the backlight 22, causing them to light up at a common brightness. The brightness level for each color may be different, as described below.

[0028] In this embodiment, the brightness of the LED (in other words, the output or drive amount) is 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. Note that although the brightness of the LED is controlled using the duty ratio (PWM value), the brightness of the LED may also be controlled by increasing or decreasing the value of the current supplied to the LED. The drive signal may be a PWM signal or a current signal. The maximum brightness is determined according to the LED specifications, such as the rated current.

[0029] The liquid crystal panel 21 has a viewing side and a rear side. The viewing side is the direction in which light from the backlight 22 is transmitted and output. The viewing side may be interpreted as the direction in which image light travels. The rear side is the opposite direction to the viewing side. The backlight 22 is disposed on the rear side of the liquid crystal panel 21. From another perspective, the rear side corresponds to the direction in which the backlight 22 is disposed when viewed from the liquid crystal panel 21. In this embodiment, the rear side may be referred to as the light source side, the bottom side, etc.

[0030] The control board 23 is a circuit board on which circuits for controlling the operation of the liquid crystal panel 21 and the backlight 22 are mounted. The control board 23 may be disposed on the rear side of the 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.

[0031] As shown in Fig. 4, the control board 23 is formed with a control unit 231 that controls the brightness of the backlight 22. The control unit 231 may be a microcomputer, an integrated circuit (IC), a field-programmable gate array (FPGA), or a combination thereof. The control unit 231 includes a storage 232 in which brightness setting data is registered. The storage 232 may be a non-rewritable non-volatile recording medium such as a read-only memory (ROM). The storage 232 may also be a rewritable non-volatile memory such as a flash memory.

[0032] The brightness setting data stored in the storage 232 includes setting values ​​for driving the LED elements, such as a base brightness setting value. The base brightness is a target brightness for controlling the brightness of the LED elements during normal operation. For convenience, the base brightness is described here as a ratio of maximum brightness, such as 50%, 70%, or 100%. The base brightness setting value may be expressed as a duty ratio of a PWM signal, a drive current value, or a voltage value. The base brightness may be set for each of the colors red (R), green (G), and blue (B). That is, the brightness setting data includes a red base brightness, which is the base brightness for the red LED, a green base brightness, which is the base brightness for the green LED, and a blue base brightness, which is the base brightness for the blue LED. The control unit 231 controls the red LED, green LED, and blue LED to emit light in accordance with the brightness setting data registered in the storage 232. Details of the control unit 231 will be described separately below.

[0033] The display case 24 is configured to house the liquid crystal panel 21, the backlight 22, and the control board 23. The display case 24 may be divided into a rear 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 backlight 22, and the control board 23. The liquid crystal panel 21, the backlight 22, and the control board 23 may be fixed to the display case 24 by any method, such as screws, snap fits, or adhesives.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] <Basic structure of LCD panel> 5, 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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. That is, the incident-side polarizing plate 78 has 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 have a configuration in which the exit-side polarizing plate 71 is placed below the viewing angle compensation film 77 with the exit-side polarizing plate 71 facing in the opposite direction. That is, 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.

[0043] 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.

[0044] The PVA of the polarizer 7p included in such a liquid crystal panel 21 can deteriorate due to exposure to light. Because vehicles are used for long periods (for example, five years or more), the HUD 1 also used in a vehicle must be configured to maintain consistent image visibility for a long period of time. To prevent deterioration of the polarizer 7p, it is necessary to reduce the total energy of light incident on the liquid crystal panel 21. Therefore, the control unit 231 of this embodiment adjusts the brightness of the backlight 22, as will be described below. This extends the life of the polarizer 7p.

[0045] <Brightness adjustment by control unit> The control unit 231 of this embodiment is configured to reduce the energy of light incident on the polarizing plate 7p per certain time period by adjusting the light emission brightness of the LED elements of each color based on the overall transmittance spectrum of the liquid crystal panel 21. The light here includes electromagnetic waves other than visible light, such as ultraviolet and infrared rays.

[0046] Here, the transmittance spectrum refers to the transmittance for each wavelength. The overall transmittance spectrum of the liquid crystal panel 21 refers to the transmittance spectrum taking into account the optical transmission characteristics of the liquid crystal layer 74, the color filter 73, the polarizer 7p, and the like in the liquid crystal panel 21. In the overall optical characteristics of the liquid crystal panel 21, a wavelength range in which the transmittance is less than a predetermined value (hereinafter, referred to as the reduction value) is referred to as the panel attenuation range in this disclosure. The reduction value may be any value less than 50%. In this embodiment, as an example, the panel attenuation range is a wavelength range in which the overall transmittance is less than 45%. Meanwhile, a wavelength range in the visible light range in which the transmittance of the optical filter 8 is equal to or greater than a predetermined maintenance value is also referred to as the panel transmission range. The maintenance value may be any value equal to or greater than 50%. The specific values ​​of the reduction value and the maintenance value may be changed as appropriate.

[0047] For example, the liquid crystal panel 21 may have characteristics such that the blue wavelength range (450 nm to 485 nm) and the green wavelength range (500 nm to 565 nm) are panel-transmitting ranges, while part of the red wavelength range (625 nm to 780 nm) is panel-attenuated range. In such a case, the control unit 231 may be configured to reduce the brightness of the red LED compared to the brightness of the green LED and the blue LED, as shown in Fig. 6. If the brightness settings of the green LED and the blue LED are set to 60% of maximum brightness, the brightness setting of the red LED may be set to 40% of maximum brightness.

[0048] When the luminance of the LED elements of a color corresponding to a wavelength range with a transmittance of approximately 90% in the liquid crystal panel 21 is reduced by 60%, for example, from maximum luminance to 40% of the maximum luminance, the luminance of the light of that color output to the viewer side appears to decrease by 54% (0.9 × 0.6 × 100). On the other hand, when the luminance of the LED elements of a color corresponding to a wavelength range with a transmittance of approximately 45% in the liquid crystal panel 21 is similarly reduced by 60%, the luminance of the light of that color output to the viewer side appears to decrease by only 27% (0.45 × 0.6 × 100). In other words, reducing the luminance of the LEDs of a color with a wavelength range with a low transmittance in the liquid crystal panel 21 reduces color shift more effectively than reducing the luminance of the LEDs of a color with a wavelength range with a high transmittance. Of course, reducing the luminance also reduces the amount of light energy received by the polarizer 7p.

[0049] The control unit 231 reduces not only the output of the LEDs of the color corresponding to the panel attenuation region (here, red), but also the output of the LEDs of other colors (here, green and blue) to a value that is a predetermined amount lower than their maximum brightness. For example, the brightness of the green and blue LEDs is set to 60% of their maximum brightness. This configuration can further reduce the amount of light energy received by the polarizer 7p compared to a configuration that reduces the brightness of only the red LED. Furthermore, by reducing the brightness of the LEDs of the color corresponding to the panel attenuation region more than the brightness of the LEDs of other colors, the amount of light energy received by the polarizer 7p can be further reduced while reducing the change in color tone.

[0050] As described above, the control unit 231 controls the brightness for each color in accordance with the brightness setting data registered in the storage 232. The example shown in Fig. 6 corresponds to a pattern in which the red basic brightness is set to 40% of the maximum brightness, the green basic brightness is set to 60% of the maximum brightness, and the blue basic brightness is set to 60% of the maximum brightness.

[0051] Of course, the brightness setting pattern for each color (R / G / B) illustrated in FIG. 6 is merely an example and is not limiting. When the liquid crystal panel 21 has the same transmission characteristics as those assumed in FIG. 6 (i.e., when the red transmittance is low), the control unit 231 may further reduce the brightness of the LEDs of each color than in FIG. 6, as shown in FIG. 7. That is, the brightness of the blue LED and the green LED may be set to 25% of the maximum brightness, and the brightness of the red LED may be set to 20% of the maximum brightness. The example shown in FIG. 7 corresponds to a pattern in which the red basic brightness is set to 20% of the maximum brightness, the green basic brightness is set to 25% of the maximum brightness, and the blue basic brightness is set to 25% of the maximum brightness.

[0052] Furthermore, if the liquid crystal panel 21 has a transmission characteristic in which the transmittance of blue light is low, the control unit 231 may adopt a brightness setting in which the brightness of the blue LED is lower than the brightness of the LEDs of other colors, as shown in Fig. 8. For example, the control unit 231 may set the brightness of the green LED and the red LED to 40% of the maximum brightness, and set the brightness of the blue LED to 20% of the maximum brightness. The example shown in Fig. 8 corresponds to a pattern in which the red basic brightness is set to 40% of the maximum brightness, the green basic brightness is set to 40% of the maximum brightness, and the blue basic brightness is set to 20% of the maximum brightness.

[0053] Furthermore, if the liquid crystal panel 21 has a transmission characteristic in which the transmittance of green light is low, the control unit 231 may adopt a brightness setting in which the brightness of the green LED is lower than the brightness of the LEDs of other colors. Furthermore, if the liquid crystal panel 21 has a transmission characteristic in which the transmittance of green light is low, the transmittance of red light is high, and the transmittance of blue light is intermediate between these, the control unit 231 may apply a brightness setting pattern in which the red LED is the brightest among the three color LEDs and the green LED is the least bright among the three color LEDs, as shown in FIG. 9 . For example, the control unit 231 may set the brightness of the red LED to 40% of the maximum brightness, the brightness of the blue LED to 30% of the maximum brightness, and the brightness of the green LED to 20% of the maximum brightness. The example shown in FIG. 9 corresponds to a pattern in which the red basic brightness is set to 40% of the maximum brightness, the green basic brightness is set to 20% of the maximum brightness, and the blue basic brightness is set to 30% of the maximum brightness.

[0054] The three colors may have different luminance levels, as shown in Fig. 9. The color that most suppresses luminance may be determined by the transmission characteristics of the liquid crystal panel 21.

[0055] <Color compensation using mirror components> Adjusting the brightness for each color can result in the loss of some color components, causing the color tone of the HUD image 3 to change from its original color tone. The original color tone here refers to the color tone when the three color LED elements are lit at the same brightness (e.g., 100%). For example, if the brightness of the red LED is made lower than the brightness of the other colors, the red component is reduced, which can change the color tone of the HUD image 3. To address this issue, for example, the plane mirror 30 or the concave mirror 40 can be configured to compensate for changes in color tone (effectively, the light spectrum) caused by the brightness setting for each color using its reflection characteristics.

[0056] Hereinafter, a color in the visible light range whose luminance is reduced compared to other colors will be referred to as a suppressed color, and the wavelength range corresponding to the suppressed color will also be referred to as a suppressed wavelength range. For example, in the example of FIG. 6, red is the suppressed color. The suppressed wavelength range corresponding to red may be 625 nm to 780 nm. In the example of FIG. 8, blue is the suppressed color. The suppressed wavelength range corresponding to blue may be 450 nm to 485 nm. In the example shown in FIG. 9, green is the suppressed color. The suppressed wavelength range corresponding to green may be 500 nm to 565 nm.

[0057] The suppression wavelength range corresponding to each color may be set based on the emission intensity spectrum of the LED element. If the red LED is configured to output light mainly from 620 nm to 640 nm (peaking at 630 nm), the suppression wavelength range corresponding to red may be set to 620 nm to 640 nm. If the green LED is configured to output light mainly from 510 nm to 550 nm (peaking at 525 nm), the suppression wavelength range corresponding to green may be set to 510 nm to 550 nm. If the blue LED is configured to output light mainly from 455 nm to 480 nm (peaking at 470 nm), the suppression wavelength range corresponding to blue may be set to 455 nm to 480 nm.

[0058] The wavelength range corresponding to the color with the highest basic luminance among the three colors is referred to as the high luminance range. When two colors are set to the same luminance level as shown in Figure 6, the wavelength range corresponding to each of these two colors may be the high luminance range. The high luminance range may also be a range according to the emission intensity spectrum of the LED element.

[0059] The plane mirror 30 may be configured to have a high level of reflectance (80% or more) for light in the suppressed wavelength range and a medium or low level of reflectance for light in the high brightness range. Here, a medium level may be interpreted as 50% to 79%, and a low level as 30% to 49%. More specifically, if the wavelength range corresponding to red falls within the suppressed wavelength range and the wavelength ranges corresponding to green and blue fall within the high brightness range, the plane mirror 30 may be configured to have a reflectance of 80% or more for light corresponding to red and a reflectance of approximately 50% for light corresponding to green and blue.

[0060] Light corresponding to red may be understood as light from 620 nm to 640 nm in view of the emission intensity spectrum of a red LED, light corresponding to green may be understood as light from 510 nm to 550 nm in view of the emission intensity spectrum of a green LED, and light corresponding to blue may be understood as light from 455 nm to 480 nm in view of the emission intensity spectrum of a blue LED.

[0061] As shown in FIG. 10, 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.

[0062] As described above, the overall color balance can be adjusted by using a plane mirror 30 that has high reflectivity for wavelength ranges where brightness is significantly reduced by adjusting the brightness of the LEDs for each color, and low reflectivity for wavelength ranges where the rate of reduction in brightness is small. In other words, it is possible to reduce changes in the color tone of the HUD image 3 that result from adjusting the brightness of the LEDs for each color.

[0063] While the above describes a pattern for correcting color tone changes due to LED brightness adjustment for each color 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, adjustment of the reflection characteristics may be achieved by attaching a film with the desired reflection characteristics to the reflective surface of the mirror member, rather than adjusting the dielectric multilayer film 32.

[0064] The above configuration can reduce the total energy of light incident on the liquid crystal panel 21 while ensuring the visibility of the HUD image 3. This reduces the deterioration of the polarizing plate 7p of the liquid crystal panel 21, and ultimately extends the service life (so-called life span) of the liquid crystal panel 21.

[0065] <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 degradation 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, "total 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 reactions.

[0066] The red basic luminance, blue basic luminance, and green basic luminance may be set so as to achieve the target value of the total amount of received light energy. 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 hour may be set for the polarizing plate 7p. The red basic luminance, blue basic luminance, and green basic luminance may be set according to the target value of the amount of received light energy per hour.

[0067] For example, consider a case where the total amount of received light energy is 32,000 Wh / m^2 when the base luminance of each color LED element is set to maximum luminance, and the target value for the total amount of received light energy is 10,000 Wh / m^2. In this scenario, the difference between the target value (10,000 Wh / m^2) and the total amount of received light energy is 22,000 Wh / m^2. If the total amount of received light energy can be reduced by 400 Wh / m^2 for every 1% reduction in luminance from the maximum luminance of each color, then 22,000 Wh / m^2 corresponds to 55% of the maximum luminance. Therefore, the control unit 231 may be configured to set the base luminance to 45% of the maximum luminance, which is 55% lower than the maximum luminance (=100%). This setting enables the target value to be achieved.

[0068] However, the amount of light energy may differ for each wavelength. Furthermore, the absolute light emission intensity at maximum brightness may also differ for each color. Therefore, the reduction in received light energy resulting from a 1% reduction in brightness may also differ for each color. For example, the reduction in received light energy resulting from a 1% reduction in the brightness of a red LED may be greater than the reduction in received light energy resulting from a 1% reduction in the brightness of a green LED. The reduction in brightness for each color may not be uniform, but may be different. For example, the reductions in brightness for the red, green, and blue LEDs may be different, such as 60%, 55%, and 50%, respectively. The final base brightness may be determined taking into account the overall transmission characteristics of the liquid crystal panel 21 and its effect on the color tone of the HUD image 3.

[0069] 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 values ​​may be determined based on the characteristics of the polarizing plate 7p used, the test time, etc. The base luminance of each color to achieve the target value may be 70%, 50%, 30%, or 20% of the maximum luminance. For example, the base luminance of each color may be set to 18% to 23% of the maximum luminance. The base luminance of each color may be set to a value of 40% or less.

[0070] In this way, the control unit 231 may be configured to drive the backlight 22 at a basic luminance determined based on a target value of the total amount of received light energy for maintaining the transmittance of the polarizing plate 7p.

[0071] <Introduction of optical filters> As shown in FIG. 11, an optical filter 8 may be attached to the surface of the liquid crystal panel 21 of this embodiment facing the light source. The optical filter 8 may be a film that blocks light in a specific wavelength range. In the present disclosure, the wavelength range blocked by the optical filter 8 is also referred to as the cut wavelength range. Blocking light is not limited to complete blocking (transmittance of 1% or less). A state where transmittance is less than 15% may also be included in blocking. In FIG. 11, the optical filter 8 is shown with dotted hatching for emphasis.

[0072] The optical filter 8 may be configured to block light in a wavelength range that is not used for display by the HUD 1. The wavelength range used for display by the HUD 1 is also referred to as a display range in the present disclosure. Wavelengths that belong to the display range are also referred to as display wavelengths. The display range may be, for example, 430 nm to 690 nm. The cut wavelength range may be set outside the display range.

[0073] The display usable range may be determined in consideration of the visible light range and the overall transmittance spectrum of the liquid crystal panel 21. The display usable range may be a wavelength range in the visible light range in which the overall transmittance of the liquid crystal panel 21 is equal to or greater than a predetermined threshold value (hereinafter referred to as the first threshold value). The first threshold value may be, for example, 35%. In other embodiments, the first threshold value may be 40%, 50%, or 70%.

[0074] If the wavelength range of the visible light range in which the transmittance of the liquid crystal panel 21 is equal to or greater than the first threshold is 430 nm to 660 nm, then 430 nm to 660 nm may be interpreted as the display range. 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.

[0075] Alternatively, if the range of colors used to display an image is predetermined or divisible, for example, from blue (equivalent to 450 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., the display range may be set from 450 nm to 650 nm.

[0076] 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.

[0077] The filter may have a cutoff wavelength range set in consideration of the optical characteristics and image color tone of the liquid crystal panel 21. For example, the optical filter 8 may be a filter having a transmittance of less than 15% for light having a wavelength of 400 nm or less, a transmittance of 80% or more for light in the range of 440 nm to 680 nm, and a transmittance of 15% or less for light of 720 nm or more.

[0078] Of course, the above characteristics of the optical filter 8 are merely examples and are not limiting. The optical filter 8 may be a filter that has a transmittance of less than 15% for light with a wavelength of 400 nm or less and a transmittance of 80% or more for light with a wavelength of 420 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 420 nm or less, a transmittance of 80% or more for light with a wavelength of 460 nm to 650 nm, and a transmittance of less than 15% for light with a wavelength of 700 nm or more.

[0079] The optical filter 8 having the specific transmission characteristics described above may be realized using a single laminated film, 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 8 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.

[0080] 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 8 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.

[0081] 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, the relationship E=hc / λ (h is Planck's constant and c is the speed of light) holds. Therefore, the optical filter 8 may be configured to block light in the short wavelength range (i.e., ultraviolet light) with priority over blocking light in the long wavelength range. However, if the 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) with priority over blocking 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 backlight 22 so as to increase the amount of unwanted light blocked.

[0082] 11 shows a configuration in which the optical filter 8 is disposed on the surface of the liquid crystal panel 21 facing the light source, but the location of the optical filter 8 is not limited to this. The optical filter 8 may be disposed between the liquid crystal panel 21 and the backlight 22 so as to be spaced a predetermined distance from the liquid crystal panel 21. The optical filter 8 may also be attached to the surface of the backlight 22 as shown in FIG. 12. The control board 23 is not shown in FIGS. 11 and 12.

[0083] 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. 13. 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. 11 to 13, the optical filter 8 is shown with dot-pattern hatching for emphasis.

[0084] Dynamic brightness control The basic luminance for each color described above may be a basic luminance for a bright environment. A bright environment refers to a situation in which the external illuminance is equal to or greater than a predetermined illuminance threshold. A dark environment refers to a situation in which the external illuminance is less than the illuminance threshold. Possible dark environments include nighttime, the inside of a tunnel, and an underground parking lot. In addition to the basic luminance for a bright environment, the storage 232 may also store a basic luminance for a dark environment. Furthermore, in addition to the basic luminance, the storage 232 may also store a temporary luminance for displaying the HUD image 3 with good visibility or in an emphasized manner. In this way, the storage 232 may store luminance setting data including multiple luminance setting values.

[0085] For example, the storage 232 may store the following brightness setting data: a first brightness that is a basic brightness for a bright environment, a second brightness that is a temporary brightness for a bright environment, a third brightness that is a basic brightness for a dark environment, and a fourth brightness that is a temporary brightness for a dark environment. The four types of brightness settings include brightness setting values ​​for each color. That is, the brightness setting data may include first to fourth brightness values ​​for a red LED, first to fourth brightness values ​​for a green LED, and first to fourth brightness values ​​for a blue LED.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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% 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.

[0090] The setting value of each luminance, such as a level at which the driver can faintly see the HUD image 3, may be determined by 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.

[0091] The setting value of each brightness, such as a level at which the driver can faintly see the HUD image 3, may be determined by testing. Note that, as an example, the third brightness is set to be higher than the second brightness here, but the third brightness may be lower than the second brightness. From another perspective, the second brightness may be higher than the third brightness.

[0092] The control unit 231 adjusts the brightness output of the 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 location guidance, stop line location guidance, 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.

[0093] 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 backlight 22 to a first luminance, as shown in FIG. 14. Setting the luminance of the backlight 22 to the first luminance corresponds to setting the luminance of the LED elements for each color to the first luminance corresponding to that color. The horizontal axis in FIG. 14 represents the passage of time, and the vertical axis represents the luminance of the backlight 22. In FIG. 14, "B1" represents the first luminance, "B2" represents the second luminance, and "Bmx" represents the maximum luminance.

[0094] 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 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.

[0095] The control unit 231 may detect route guidance-related events, such as approaching a left turn point / right turn point, based on signals 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.

[0096] 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.

[0097] Time t1 in FIG. 14 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. 14 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).

[0098] 14 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.

[0099] 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 at which event B is detected F. 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 at which the left turn is completed. The increase in brightness associated with 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.

[0100] Furthermore, the control unit 231 may 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 less than the illuminance threshold, the control unit 231 basically sets the luminance of the backlight 22 to the third luminance as shown in FIG. 15 . 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 at the timing (t6) when the pedestrian crossing is passed. 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 turn right. The application of the fourth luminance for right turn guidance may be canceled at the timing when the right turn is completed.

[0101] According to the above configuration, the brightness output of the backlight 22 is basically suppressed. Therefore, the total amount of light energy (i.e., the amount of light energy received) 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.

[0102] The control unit 231 may also 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 temporarily 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 temporarily increase the 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.

[0103] 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 when a specific type of video signal is not input, the control unit 231 may set the brightness of the 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 backlight 22 to a temporary brightness, even when a specific type of video signal is not input. [Explanation of symbols]

[0104] 1 HUD (head-up display device), 5 image signal source, 6 illuminance sensor, 8 optical filter, 20 display, 21 liquid crystal panel, 22 backlight, 23 control board, 30 plane mirror, 40 concave mirror, 71 exit side polarizer, 77 entrance side polarizer, 7p polarizer, 713-782 PVA polarizer, 231 control unit, 232 storage

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) including a backlight (22) and a liquid crystal panel (21) and configured to project the image light; a mirror member (30, 40) that reflects the image light projected from the display in a predetermined direction; a control unit (231) that adjusts the brightness of the backlight, The liquid crystal panel includes a polarizer (7p, 78) having a polyvinyl alcohol polarizer layer (782), the backlight includes a plurality of light sources; each of the plurality of light sources is an RGB-LED having three LED elements as a set, that is, a red LED which is an LED element that emits red light, a green LED which is an LED element that emits green light, and a blue LED which is an LED element that emits blue light; the red LED, the green LED, and the blue LED are configured so that their brightness can be individually controlled; The control unit is configured to cause each of the red LED, the green LED, and the blue LED to emit light at a luminance lower than a maximum luminance.

2. a target value for the amount of light energy received per unit time is set for the polarizing plate; The control unit The head-up display device according to claim 1 , wherein the red LED, the green LED, and the blue LED are controlled in accordance with a basic brightness determined according to the target value.

3. a target value for the amount of light energy received per unit time is set for the polarizing plate; The control unit a recording medium (232) in which a red basic luminance, which is a basic luminance for the red LED, a green basic luminance, which is a basic luminance for the green LED, and a blue basic luminance, which is a basic luminance for the blue LED, which are determined according to the target value, are registered; 2. The head-up display device according to claim 1, wherein the red LED, the green LED, and the blue LED are turned on in accordance with the basic brightness for each color registered in the recording medium.

4. The control unit The head-up display device according to claim 3 , wherein at least one of the red basic luminance, the green basic luminance, and the blue basic luminance is set to a value lower than the basic luminance of the other colors.

5. 5. The head-up display device according to claim 4, wherein a dielectric film is formed on the reflective surface of the mirror member, the dielectric film having a higher reflectance for light of a suppression color, which is the color of red, green, and blue having the lowest basic luminance, than for light of other colors.

6. The control unit the red basic luminance is set to a value lower than the green basic luminance and the blue basic luminance, 4. The head-up display device according to claim 3, wherein a dielectric film having a higher reflectance for red light than for green light and blue light is formed on the reflective surface of the mirror member.

7. 4. The head-up display device according to claim 3, wherein the basic luminance of each color is set to 40% or less of the maximum luminance.

8. the liquid crystal panel has an optical characteristic in which the transmittance for light in a predetermined wavelength range is less than a predetermined value; 2. The head-up display device according to claim 1, wherein the control unit is configured to make the brightness of an LED element of a color corresponding to the wavelength range among the red LED, the green LED, and the blue LED lower than the brightness of LED elements of other colors.

9. 9. The head-up display device according to claim 8, wherein a dielectric film having a reflectance for light in the wavelength range higher than a reflectance for light in other wavelength ranges is formed on the reflective surface of the mirror member.

10. 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 it is determined that the scene is not the specific scene, the luminance of the backlight is set to the first luminance; 2. The head-up display device according to claim 1, wherein the head-up display device is configured to temporarily increase the brightness of the backlight from the first brightness to the second brightness when the external illuminance is equal to or greater than the threshold and the specific scene is determined.

11. 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 it is determined that the scene is not the specific scene, the luminance of the backlight is set to the second luminance; When the external illuminance is equal to or greater than the threshold value and the specific scene is determined, the luminance of the backlight is temporarily increased from the second luminance to the first 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 backlight is set to the fourth luminance; 2. The head-up display device according to claim 1, wherein the head-up display device is configured to temporarily increase the brightness of the backlight from the fourth brightness to the third brightness when the external illuminance is less than the threshold and the specific scene is determined.

Images