Head-up display device

Abstract

This invention provides a head-up display device that allows users wearing polarized sunglasses to see the display light while also offering efficient use of the display light. [Solution] The head-up display device comprises a liquid crystal display element 7 having a first polarizer 21 and a second polarizer 22 facing each other with a liquid crystal cell 10 in between, and a polarization conversion liquid crystal cell 30 having a liquid crystal layer 33 through which display light Lp emitted from the liquid crystal display element 7, which receives illumination light C, passes. The display light Lp emitted from the liquid crystal display element 7 is directed towards the polarization conversion liquid crystal cell 30 as linearly polarized light along the transmission axis of the first polarizer 21. When the liquid crystal layer 33 is in the first state, S-polarized display light L is emitted from the polarization conversion liquid crystal cell 30 to the reflective surface of the windshield, and when the liquid crystal layer 33 is in the second state, P-polarized display light L is emitted from the polarization conversion liquid crystal cell 30 to the reflective surface.

Description

Technical Field

[0001] The present disclosure relates to a head-up display device.

Background Art

[0002] Patent Document 1 describes a head-up display device that allows a user to visually recognize display light (specifically, an image represented by the display light) reflected by a vehicle windshield. The device described in Patent Document 1 includes a polarization unit that emits the display light as P-polarized light, so that a user wearing polarized sunglasses can also visually recognize the image. This is because the polarized sunglasses are configured to cut S-polarized light.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, the reflectance of S-polarized light on the windshield is higher than that of P-polarized light. However, in the configuration described in Patent Document 1, since the display light is fixed to P-polarized light, the luminance of the display light reaching the user is lower than in the case where the display light contains more S-polarized light than P-polarized light. That is, with this configuration, there is a risk that the luminance of the display light for a user not wearing polarized sunglasses will be sacrificed, and there is room for improvement in terms of the utilization efficiency of the display light.

[0005] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a head-up display device that allows a user wearing polarized sunglasses to visually recognize display light while having good utilization efficiency of the display light.

Means for Solving the Problems

[0006] To achieve the above objectives, the head-up display device relating to this disclosure is A liquid crystal cell, and a liquid crystal display element having a first polarizer and a second polarizer facing each other across the liquid crystal cell, An illumination unit that emits illumination light toward the liquid crystal display element, A liquid crystal cell for polarization conversion, having a liquid crystal layer controlled to a first state and a second state, through which display light emitted from the liquid crystal display element upon receiving illumination light passes, A head-up display device that irradiates the display light that has passed through the polarization conversion liquid crystal cell onto a windshield, The first polarizer is located between the polarization conversion liquid crystal cell and the liquid crystal cell. The display light emitted from the liquid crystal display element is directed toward the polarization conversion liquid crystal cell as linearly polarized light along the transmission axis of the first polarizer. When the liquid crystal layer is in the first state, the polarization conversion liquid crystal cell emits the S-polarized display light toward the reflective surface of the windshield. When the liquid crystal layer is in the second state, the polarity conversion liquid crystal cell emits the display light with P polarization relative to the reflective surface. [Effects of the Invention]

[0007] According to this disclosure, it is possible to provide a head-up display device that allows users wearing polarized sunglasses to see the display light while also having good utilization efficiency of the display light. [Brief explanation of the drawing]

[0008] [Figure 1] A schematic diagram of a head-up display device according to one embodiment of the present disclosure. [Figure 2] A diagram illustrating S-polarization and P-polarization according to the same embodiment. [Figure 3] A schematic diagram of the display unit according to the same embodiment. [Figure 4] A diagram illustrating the control of the polarization state of the display light according to the same embodiment. [Modes for carrying out the invention]

[0009] One embodiment of this disclosure will be described with reference to the drawings.

[0010] The head-up display device 1 (hereinafter also referred to as HUD device 1) shown in Figure 1 is installed in the vehicle's dashboard 2 and projects display light L representing an image onto the vehicle's windshield 3. The display light L reflected by the windshield 3 displays a virtual image V of the image. The user 4 (mainly the vehicle's driver) views the virtual image V through the windshield 3. Hereafter, this act of the user 4 viewing the virtual image V may be referred to as the user 4 viewing the display light L.

[0011] The HUD device 1 comprises a display unit 5 that emits display light L, a plane mirror 1a, and a concave mirror 1b. The display light L emitted by the display unit 5 is reflected by the plane mirror 1a and then the concave mirror 1b, before heading towards the windshield 3. In this way, the display light L emitted from the HUD device 1 enters the windshield 3 and is reflected by the reflective surface 3a of the windshield 3.

[0012] Referring to Figure 2, S-polarized and P-polarized light for the windshield 3 will be explained. Here, the incident plane P with respect to the reflective surface 3a of the windshield 3 is defined in optics as a plane perpendicular to the reflective surface 3a and containing the incident and reflected rays. Note that the indicator light L shown in Figure 2 represents a representative ray of the indicator light L. S-polarized light for the windshield 3 is polarization that vibrates perpendicular to the incident plane P (i.e., vibrates in the out-of-plane direction Dv of the incident plane P). On the other hand, P-polarized light for the windshield 3 is polarization that vibrates parallel to the incident plane P (i.e., vibrates in the in-plane direction Dp of the incident plane P). The terms S-polarized and P-polarized light used below refer to polarization as described above.

[0013] Furthermore, the direction of vibration of the light rays contained in the display light L relative to the reflective surface 3a may change slightly depending on the position where they enter the windshield 3. Therefore, the expressions S-polarization or P-polarization used below do not necessarily mean that all of the display light L is perfectly S-polarized or P-polarized, but rather that the optical component in question is adjusted to emit S-polarized or P-polarized light relative to the windshield 3. Also, the display light L that reaches the user 4 after being reflected by the windshield 3 as a result of the display unit 5 emitting S-polarized display light L only needs to mainly contain an S-polarized component. Similarly, the display light L that reaches the user 4 after being reflected by the windshield 3 as a result of the display unit 5 emitting P-polarized display light L only needs to mainly contain a P-polarized component.

[0014] As shown in Figure 3, the display unit 5 comprises an illumination unit 6, a liquid crystal display element 7 having a liquid crystal cell 10, a first polarizer 21 and a second polarizer 22, a liquid crystal cell 30 for polarization conversion, and a control unit 9.

[0015] The illumination unit 6 is configured to emit illumination light C toward the liquid crystal display element 7. The configuration of the illumination unit 6 is arbitrary, but for example, the illumination unit 6 is configured to include a plurality of LEDs (Light Emitting Diodes), a condenser lens, a lenticular lens, a light diffuser plate, etc., mounted on a light source substrate in order from furthest from the liquid crystal display element 7. Furthermore, as the illumination unit 6, known configurations such as the configuration described in Japanese Patent Application Publication No. 2020-160293 can be appropriately adopted.

[0016] The liquid crystal display element 7 receives illumination light C and displays an image toward the polarization conversion liquid crystal cell 30. The liquid crystal display element 7 emits display light Lp representing the image toward the polarization conversion liquid crystal cell 30. Hereafter, this display light Lp will be called the original display light Lp to distinguish it from the display light L emitted from the polarization conversion liquid crystal cell 30 as described later. The display light L emitted from the polarization conversion liquid crystal cell 30 is no different from the original display light Lp in that it represents the image, but it is referred to in this way to distinguish which component the light is emitted from.

[0017] The liquid crystal cell 10 is, for example, a TFT (Thin Film Transistor) liquid crystal of the active matrix drive type. The liquid crystal cell 10 is composed of a pair of substrates 11, 12 and a liquid crystal layer 13 encapsulated between the pair of substrates 11, 12. The substrate 11 is located on the side of the liquid crystal cell 30 for polarization conversion. The pair of substrates 11, 12 are each transparently formed from glass, plastic, etc. On the surface of each of the pair of substrates 11, 12 facing the liquid crystal layer 13, a transparent electrode (not shown) and an alignment film (not shown) covering the transparent electrode are formed. That is, the liquid crystal cell 10 is provided with a pair of transparent electrodes and a pair of alignment films. The pair of alignment films are subjected to a rubbing treatment according to the type of the liquid crystal cell 10.

[0018] For example, the transparent electrode formed on the substrate 11 is configured as a common electrode, and the transparent electrode formed on the substrate 12 is configured as a pixel electrode (including sub-pixel electrodes). When the type of the liquid crystal cell 10 is IPS described later, transparent electrodes constituting the common electrode and the pixel electrode are formed on the substrate 12. Further, on the substrate 11, a color filter layer (not shown) formed by arranging color filters of each color of R (red), G (green), and B (blue) is provided.

[0019] The liquid crystal display element 7 displays an image by a combination of pixels (including sub-pixels). Specifically, under the control of the control unit 9, it is selected whether to apply an on-voltage to the portion corresponding to each pixel of the liquid crystal layer 13 through the pair of transparent electrodes, and the liquid crystal display element 7 displays an image by the combination of each pixel that becomes a transmission or non-transmission state accordingly. How the liquid crystal display element 7 displays an image varies according to the type of the liquid crystal cell 10.

[0020] Any type of liquid crystal cell 10 can be used, such as TN (Twisted Nematic), VA (Vertical Alignment), or IPS (In-Plane Switching), and the type is not limited. In any case, regardless of which liquid crystal type is used, the first polarizer 21 in this embodiment is provided such that the transmission axis of the first polarizer 21 is aligned with S polarization.

[0021] The first polarizer 21 and the second polarizer 22 face each other across the liquid crystal cell 10. The first polarizer 21 is located between the polarization conversion liquid crystal cell 30 and the liquid crystal cell 10, and is, for example, bonded to the substrate 11. The first polarizer 21 is a well-known polarizing film (also called a polarizing plate), and emits light incident from one side as linearly polarized light along a transmission axis perpendicular to the absorption axis from the other side.

[0022] The second polarizer 22 is located between the illumination unit 6 and the liquid crystal cell 10 and is, for example, bonded to the substrate 12. The second polarizer 22, like the first polarizer 21, is a well-known polarizing film and emits light incident from one side as linearly polarized light along a transmission axis perpendicular to the absorption axis from the other side. Unpolarized illumination light C emitted from the illumination unit 6 is incident on the liquid crystal cell 10 as linearly polarized light along the transmission axis of the second polarizer 22.

[0023] In this embodiment, the second polarizer 22 is arranged in a crossed nicol configuration with respect to the first polarizer 21. A crossed nicol configuration means that the transmission axes of the first polarizer 21 and the second polarizer 22 are orthogonal to each other. Note that a configuration where the transmission axes of the first polarizer 21 and the second polarizer 22 are parallel to each other is called a parallel nicol configuration. The display mode of the liquid crystal display element 7 is either NB (normally black) mode or NW (normally white) mode. In NB mode, a dark display (black display) is achieved when the applied voltage is off. On the other hand, in NW mode, a bright display (white display) is achieved when the applied voltage is off.

[0024] The liquid crystal display element 7, in which the first polarizer 21 and the second polarizer 22 are arranged in a crossed nicol relationship, displays an image in NW mode when the type of liquid crystal cell 10 is TN, displays an image in NB mode when the type of liquid crystal cell 10 is VA, and displays an image in NB mode when the type of liquid crystal cell 10 is IPS. Alternatively, the display mode of the liquid crystal display element 7 may be reversed with respect to the above display modes (i) to (iii) by arranging the first polarizer 21 and the second polarizer 22 in parallel nicols.

[0025] In this embodiment, regardless of the combination of the display mode of the liquid crystal display element 7 and the type of liquid crystal cell 10, the original display light Lp emitted from the liquid crystal display element 7 of this embodiment is directed toward the polarization conversion liquid crystal cell 30 as linearly polarized light (i.e., S-polarized light) along the transmission axis of the first polarizer 21.

[0026] The polarization conversion liquid crystal cell 30 is not provided to display an image on its own, but rather to convert the polarization of the light passing through it.

[0027] The polarization conversion liquid crystal cell 30 is composed of a pair of substrates 31 and 32 and a liquid crystal layer 33 enclosed between the pair of substrates 31 and 32. Substrate 32 is located on the side of the liquid crystal display element 7. The pair of substrates 31 and 32 are each formed transparently from glass, plastic, or the like. A transparent electrode (not shown) and an alignment film (not shown) covering the transparent electrode are formed on the surface of each of the substrates 31 and 32 facing the liquid crystal layer 33. In other words, the polarization conversion liquid crystal cell 30 is provided with a pair of transparent electrodes and a pair of alignment films. The pair of alignment films are subjected to a rubbing treatment according to the type of polarization conversion liquid crystal cell 30.

[0028] Unlike the aforementioned liquid crystal cell 10, the polarization conversion liquid crystal cell 30 does not have a color filter layer. Furthermore, in the polarization conversion liquid crystal cell 30, it is not necessary to control the state of liquid crystal molecules in the region corresponding to each pixel in response to the on / off state of the voltage, as in the aforementioned liquid crystal cell 10. Therefore, transparent electrodes are formed to control the state of liquid crystal molecules throughout the entire liquid crystal layer 33 in response to the on / off state of the voltage. If the type of polarization conversion liquid crystal cell 30 is IPS, it is sufficient that transparent electrodes are formed on the substrate 32. In addition, the driving method of the polarization conversion liquid crystal cell 30 may be passive or active.

[0029] Here, in response to the on / off switching of the voltage controlled by the control unit 9, the liquid crystal layer 33 changes between a first state, which allows the linearly polarized light incident on the polarization conversion liquid crystal cell 30 to pass through as is, and a second state, which emits linearly polarized light whose vibration direction is tilted by 90° relative to the linearly polarized light incident on the polarization conversion liquid crystal cell 30. Hereafter, the case where the liquid crystal layer 33 is in the first state may be referred to as the polarization conversion liquid crystal cell 30 in the first state, or simply as the first state. Similarly, the case where the liquid crystal layer 33 is in the second state may be referred to as the polarization conversion liquid crystal cell 30 in the second state, or simply as the second state.

[0030] Figure 4 is a diagram illustrating the control of the polarization state of the display light L emitted from the polarization conversion liquid crystal cell 30. In this figure, a mark with a horizontally extending arrow in a circle represents S polarization, and a mark with a vertically extending arrow in a circle represents P polarization.

[0031] The left-hand diagram in Figure 4 shows the polarization conversion liquid crystal cell 30 in the first state. In this case, the original display light Lp emitted from the liquid crystal display element 7, which is S-polarized, passes through the polarization conversion liquid crystal cell 30 while retaining its S-polarization, and as a result, S-polarized display light L is emitted from the polarization conversion liquid crystal cell 30. In other words, in the first state, S-polarized display light L is emitted from the display unit 5.

[0032] The right-hand diagram in Figure 4 shows the polarization conversion liquid crystal cell 30 in the second state. In this case, the original display light Lp emitted from the liquid crystal display element 7, which is S-polarized, is converted to P-polarized by the polarization conversion liquid crystal cell 30, and as a result, P-polarized display light L is emitted from the polarization conversion liquid crystal cell 30. In other words, in the second state, P-polarized display light L is emitted from the display unit 5.

[0033] If the type of the polarizing liquid crystal cell 30 is TN, the second state occurs when the voltage applied to the transparent electrode formed on the polarizing liquid crystal cell 30 is off, and the first state occurs when the voltage is on. If the type of the polarizing liquid crystal cell 30 is VA or IPS, the first state occurs when the voltage applied to the transparent electrode formed on the polarizing liquid crystal cell 30 is off, and the second state occurs when the voltage is on.

[0034] As mentioned above, polarized sunglasses are configured to cut S-polarized light. Therefore, the second state, in which P-polarized display light L is emitted from the display unit 5 and as a result reaches the user 4, is suitable when the user 4 is wearing polarized sunglasses. On the other hand, the first state, in which S-polarized display light L is emitted from the display unit 5 and as a result reaches the user 4, is suitable when the user 4 is not wearing polarized sunglasses.

[0035] Thus, the HUD device 1 emits P-polarized display light L in the second state, allowing users wearing polarized sunglasses to see the display light L, while in the first state, it emits S-polarized display light L, which has a higher reflectivity on the windshield 3 than P-polarized light. Therefore, the HUD device 1 has good utilization efficiency of the display light L.

[0036] The control unit 9 is composed of a microcontroller, various drive circuits, etc., and controls the operation of the illumination unit 6, the liquid crystal display element 7, and the polarity conversion liquid crystal cell 30. For example, the control unit 9 communicates with the vehicle's ECU (Electronic Control Unit) and other equipment to display various vehicle-related information on the liquid crystal display element 7.

[0037] Furthermore, the control unit 9 communicates with input devices (not shown) such as a touch panel and steering wheel switches mounted on the vehicle and receives instructions from the user 4 via the input devices. In this embodiment, the control unit 9 receives a first trigger signal T1 from the input device as an instruction from the user 4 via the input device, which indicates a switch from one of the first state and the second state to the other state. In response to the first trigger signal T1, the control unit 9 switches the polarization conversion liquid crystal cell 30 from one of the first state and the second state to the other state.

[0038] Furthermore, the control unit 9 is located inside the vehicle and includes a camera that images the user 4, and communicates with a sensor (not shown) that detects whether the user 4 is wearing polarized sunglasses. The control unit 9 receives a second trigger signal T2 from the sensor, which is a detection signal indicating whether the user 4 is wearing polarized sunglasses. If the second trigger signal T2 indicates that the user 4 is not wearing polarized sunglasses, the control unit 9 controls the polarized liquid crystal cell 30 to the first state, and if the second trigger signal T2 indicates that the user is wearing polarized sunglasses, the control unit 9 controls the polarized liquid crystal cell 30 to the second state. In other words, the control unit 9 switches the polarized liquid crystal cell 30 from one of the first and second states to the other state in response to the second trigger signal T2.

[0039] Furthermore, the control unit 9 may control the brightness of the illumination light C emitted by the illumination unit 6 so that it is lower when the liquid crystal layer 33 is in the first state (i.e., a state suitable when the user 4 is not wearing polarized sunglasses) than when the liquid crystal layer 33 is in the second state (i.e., a state suitable when the user 4 is wearing polarized sunglasses). In other words, the control unit 9 may relatively increase the brightness of the illumination light C in the second state compared to the first state. Here, the reflectivity of the windshield 3 is significantly lower for P-polarized light than for S-polarized light. Therefore, if the brightness of the illumination light C is not changed between the first and second states, the image viewed by user 4 wearing polarized sunglasses in the second state will be unnecessarily darker than the image viewed by user 4 wearing polarized sunglasses in the first state. However, by controlling the brightness of the illumination light C as described above, it is possible to prevent the image viewed by user 4 wearing polarized sunglasses in the second state from becoming unnecessarily dark.

[0040] The present invention is not limited by the embodiments and drawings described above. Modifications (including the deletion of components) can be made as appropriate, without altering the essence of the invention.

[0041] The HUD device 1 may be mounted on a vehicle other than a vehicle and may be configured to emit display light L toward the windshield of the vehicle.

[0042] The liquid crystal display element 7 is not limited to an active drive system, but may also be a passive drive system. Furthermore, the liquid crystal display element 7 is not limited to one that displays an image using a matrix of pixels, but may also be a monochrome liquid crystal display element that performs segment display. In the case of a liquid crystal display element 7 that performs segment display, the image in the region where the transmission and opacity of light can be controlled in the liquid crystal display element 7 can be considered as the image represented by the original display light Lp and the display light L.

[0043] In the liquid crystal display element 7, the first polarizer 21 may be provided such that its transmission axis aligns with the P-polarization. In this way, when the liquid crystal display element 7 emits the original P-polarized display light Lp, the polarization conversion liquid crystal cell 30 may, in the first state, convert the original P-polarized display light Lp to S-polarized display light L and emit it, and in the second state, emit the original P-polarized display light Lp as is, as P-polarized display light L. In this case, the relationship between the first and second states and the voltage on / off for each type of polarization conversion liquid crystal cell 30 will be the opposite of that in the above embodiment.

[0044] The liquid crystal display element 7 may be a reflective liquid crystal display element used in LCOS (Liquid Crystal On Silicon) (also called a reflective liquid crystal projector). In this case, three liquid crystal display elements 7 are provided, corresponding to each of the R, G, and B colors, and the illumination unit 6 emits illumination light C of each of the R, G, and B colors toward each liquid crystal display element 7 (a well-known configuration having a light source, a mirror, and a dichroic mirror). The polarization conversion liquid crystal cell 30 should be provided at a position through which the combined display light L emitted from each liquid crystal display element 7 passes.

[0045] In the above explanation, explanations of publicly known technical matters have been omitted where appropriate to facilitate understanding of this disclosure.

[0046] This invention allows for various embodiments and modifications without departing from the broad spirit and scope of the invention. Furthermore, the embodiments described above are for illustrative purposes only and do not limit the scope of the invention. In other words, the scope of this invention is indicated not by the embodiments, but by the claims. Various modifications made within the scope of the claims and the equivalent scope of the meaning of the invention are considered to be within the scope of this invention. [Explanation of Symbols]

[0047] 1. Head-up display device (HUD device) 1a...Plane mirror, 1b...Concave mirror 2… Dashboard 3...windshield, 3a...reflective surface 4…User 5…Display unit 6…Lighting Department 7… LCD display element 9... Control Unit 10...Liquid crystal cell, 11,12...Substrate, 13...Liquid crystal layer 21…First polarizer 22…Second polarizer 30...Liquid crystal cell for polarization conversion, 31,32...Substrate, 33...Liquid crystal layer C…Illumination light Lp…Display light (original display light) L...display light, V...virtual image P...Incidence plane, Dv...Out-of-plane direction, Dp...In-plane direction T1…First trigger signal, T2…Second trigger signal

Claims

1. A liquid crystal cell, and a liquid crystal display element having a first polarizer and a second polarizer facing each other across the liquid crystal cell, An illumination unit that emits illumination light toward the liquid crystal display element, A liquid crystal cell for polarization conversion, having a liquid crystal layer controlled to a first state and a second state, through which display light emitted from the liquid crystal display element upon receiving illumination light passes, A head-up display device that irradiates the display light that has passed through the polarization conversion liquid crystal cell onto a windshield, The first polarizer is located between the polarization conversion liquid crystal cell and the liquid crystal cell. The display light emitted from the liquid crystal display element is directed toward the polarization conversion liquid crystal cell as linearly polarized light along the transmission axis of the first polarizer. When the liquid crystal layer is in the first state, the polarization conversion liquid crystal cell emits the S-polarized display light toward the reflective surface of the windshield. When the liquid crystal layer is in the second state, the polarity conversion liquid crystal cell emits the display light with P polarization relative to the reflective surface. Head-up display device.

2. The brightness of the illumination light emitted by the illumination unit is lower when the liquid crystal layer is in the first state than when it is in the second state. The head-up display device according to claim 1.

3. The system further includes a control unit that controls the operation of the aforementioned liquid crystal cell for polarization conversion, The control unit switches the liquid crystal layer from one of the first state and the second state to the other state in response to at least one of the user's instructions via the input device and a detection signal from a sensor that detects whether the user is wearing polarized sunglasses. The head-up display device according to claim 1 or 2.

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