Patent Publication Number: US-2019171014-A1

Title: Vehicular Head-Up Display Using Holographic Element

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vehicular head-up display and, more particularly, to a vehicular head-up display using a holographic element. 
     2. Description of the Prior Art 
     Referring to  FIG. 1 , there is shown a schematic view of a conventional vehicular head-up display  1 . The vehicular head-up display  1  is disposed in a vehicle  2  and includes an image forming unit  11  and a reflection mirror  12 . The image forming unit  11  is used for generating a real image; the reflection mirror  12  is used for optically reflecting and/or amplifying the real image generated by the image forming unit  11 . The image forming unit  11  and the reflection mirror  12  employ a discrete design. Specifically, the image forming unit  11  is disposed on a roof  21  of the vehicle  2 . The reflection mirror  12  is disposed below a windshield  22  in the front of the vehicle  2 . The reflection mirror  12  has a reflection surface  121  facing backward and upward with respect to the vehicle  2 ; in the embodiment, the reflection surface  121  faces backward and upward with respect to the vehicle  2  at an angle of 30 degrees from the horizontal. Light rays emitted by the image forming unit  11  are projected onto the reflection surface  121  of the reflection mirror  12 ; light rays reflected from the reflection surface  121  of the reflection mirror  12  are projected onto the windshield  22 ; and light rays reflected from the windshield  22  are projected onto a user&#39;s eyes E 1  so that the user sees a virtual image P 1  formed in front of the windshield  22 , in which the user may be a driver or a passenger. The virtual image P 1  is formed within the driver&#39;s field of view while driving so that the driver may pay attention to road conditions and acquire driving information from the virtual image P 1  at the same time. 
     However, as shown in  FIG. 2 , because the reflection surface  121  of the reflection mirror  12  of the vehicular head-up display  1  faces backward and upward with respect to the vehicle  2 , light rays which come from ambient light such as sunlight at some specific angles in some specific directions have chance to be introduced by the reflection surface  121  of the reflection mirror  12  to enter the vehicle  2  to project onto the user&#39;s eyes E 1 , resulting in the user&#39;s discomfort or even bad effects on driving safety. 
     SUMMARY OF THE INVENTION 
     The present invention is adapted to providing a vehicular head-up display using a holographic element to solve the problem of the reflection mirror introducing ambient light to enter the vehicle to project onto the user&#39;s eyes. 
     According to an aspect of the present invention, there is provided a vehicular head-up display using a holographic element. The vehicular head-up display is disposed in a vehicle and includes an image forming unit, a reflection mirror, and a holographic mirror. The image forming unit is disposed on a roof of the vehicle and employs light sources, The reflection mirror is disposed below a windshield in the front of the vehicle. The reflection mirror has a first reflection surface facing forward and upward with respect to the vehicle. The holographic mirror is disposed between the reflection mirror and the windshield. The holographic mirror has a second reflection surface facing backward with respect to the vehicle. The holographic mirror reflects light rays of a specific wavelength band and allows light rays of not the specific wavelength band to pass through. Light rays emitted by the image forming unit are projected onto the first reflection surface of the reflection mirror; light rays reflected from the first reflection surface of the reflection mirror are projected onto the second reflection surface of the holographic mirror; and the light rays of the specific wavelength band reflected from the second reflection surface of the holographic mirror are projected onto the windshield to form a virtual image in front of the windshield. 
     According to another aspect of the present invention, the light sources include a red light source, a green light source, and a blue light source. The specific wavelength band includes a wavelength band corresponding to the green light source. 
     According to another aspect of the present invention, the first reflection surface of the reflection mirror is a flat surface or a curved surface. 
     According to another aspect of the present invention, the second reflection surface of the holographic mirror is a flat surface or a curved surface. 
     According to another aspect of the present invention, the holographic mirror includes a light transmitting substrate and a holographic film disposed on the light transmitting substrate. 
     According to an aspect of the present invention, there is further provided a vehicular head-up display using a holographic element. The vehicular head-up display is disposed in a vehicle and includes an image forming unit and a holographic mirror. The image forming unit is disposed on a roof of the vehicle and employs light sources. The holographic mirror is disposed below a windshield in the front of the vehicle. The holographic mirror reflects light rays of a specific wavelength band and allows light rays of not the specific wavelength band to pass through. Light rays emitted by the image forming unit are projected onto a reflection surface of the holographic mirror; the light rays of the specific wavelength band reflected from the holographic mirror are projected onto the windshield to form a virtual image in front of the windshield. 
     According to another aspect of the present invention, the light sources include a red light source, a green light source, and a blue light source. The specific wavelength band includes a wavelength band corresponding to the green light source. 
     According to another aspect of the present invention, the reflection surface of the holographic mirror is a flat surface or a curved surface. 
     According to another aspect of the present invention, the holographic mirror includes a light transmitting substrate and a holographic film disposed on the light transmitting substrate. 
     The above and other objectives, features, and advantages of the present invention will be better understood from the following detailed description of the preferred embodiments of the present invention that are illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a conventional vehicular head-up display; 
         FIG. 2  is a schematic view of ambient light affecting the vehicular head-up display as shown in  FIG. 1 ; 
         FIG. 3  is a schematic view of a vehicular head-up display according to a first embodiment of the present invention; 
         FIG. 4  is a schematic view of ambient light affecting the vehicular head-up display as shown in  FIG. 3 ; 
         FIG. 5  is a schematic view of a vehicular head-up display according to a second embodiment of the present invention; and 
         FIG. 6  is a schematic view of a holographic mirror according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following embodiments, same or similar reference numerals are used in the drawings and the description to refer to the same or like components. Moreover, directional terms, such as up, down, left, right, front, and back are used with respect to the drawings. These and similar directional terms should not be construed to limit the scope of the present invention in any manner. 
     Referring to  FIG. 3 , there is shown a schematic view of a vehicular head-up display  3  according to a first embodiment of the present invention. The vehicular head-up display  3  is disposed in a vehicle  2  and includes an image forming unit  31 , a reflection mirror  32 , and a holographic mirror  33 . The image forming unit  31  is used for generating a real image; the reflection mirror  32  and the holographic mirror  33  are used for optically reflecting and/or amplifying the real image generated by the image forming unit  31 . The image forming unit  31 , the reflection mirror  32 , and the holographic mirror  33  employ a discrete design. Specifically, the image forming unit  31  is disposed on a roof  21  of the vehicle  2 . The reflection mirror  32  is disposed below a windshield  22  in the front of the vehicle  2 . The reflection mirror  32  has a first reflection surface  321  facing forward and upward with respect to the vehicle  2 ; in the embodiment, the first reflection surface  321  faces forward and upward with respect to the vehicle  2  at an angle of 17 degrees from the horizontal. The holographic mirror  33  is disposed between the reflection mirror  32  and the windshield  22 . The holographic mirror  33  has a second reflection surface  331  facing backward with respect to the vehicle  2 ; in the embodiment, the second reflection surface  331  faces backward with respect to the vehicle  2  at an angle of about 90 degrees from the horizontal. In an embodiment, the first reflection surface  321  and/or the second reflection surface  331  may be a curved surface capable of refocusing the real image from the image forming unit  31 , but it is not limited thereto. For example, the first reflection surface  321  and/or the second reflection surface  331  may be a flat surface. 
     Light rays emitted by the image forming unit  31  are projected onto the first reflection surface  321  of the reflection mirror  32 ; light rays reflected from the first reflection surface  321  of the reflection mirror  32  are projected onto the second reflection surface  331  of the holographic mirror  33 ; light rays reflected from the second reflection surface  331  of the holographic mirror  33  are projected onto the windshield  22 ; and light rays reflected from the windshield  22  are projected onto a user&#39;s eyes E 2  so that the user sees a virtual image P 2  formed in front of the windshield  22 , in which the user may be a driver or a passenger. The virtual image P 2  is formed within the driver&#39;s field of view while driving so that the driver may pay attention to road conditions and acquire driving information from the virtual image P 2  at the same time. 
     As shown in  FIG. 4  with omitting the holographic mirror  33 , although light rays which come from ambient light such as sunlight at some specific angles in some specific directions have chance to be introduced by the first reflection surface  321  of the reflection mirror  32  to enter the vehicle  2 , the light rays which enter the vehicle  2  are projected in front of the user&#39;s eyes E 2  because the first reflection face  321  of the reflection mirror  32  faces forward and upward with respect to the vehicle  2 . Therefore, the light rays which enter the vehicle  2  through the reflection mirror  32  are not projected onto the user&#39;s eyes E 2  so that it does not result in the user&#39;s discomfort or bad effects on driving safety. 
     In addition, the holographic mirror  33  may reflect light rays of a specific wavelength band and allow light rays of not the specific wavelength band to pass through. Therefore, the holographic mirror  33  may be designed to let light rays of unwanted wavelength bands to pass through so that the light rays of unwanted wavelength bands are not projected onto the windshield  22  thereby increasing the display quality of the virtual image P 2 . For example, if the image forming unit  31  employs a red light source with a wavelength band of 630-650 nm, a green light source with a wavelength band of 510-530 nm, and a blue light source with a wavelength band of 440-460 nm to combine color images, the holographic mirror  33  may be designed to reflect light rays of a wavelength band of 510-530 nm (corresponding the green light source) and let light rays of other wavelength bands to pass through. It is noted that the wavelength band of 510-530 nm corresponding to the green light source is the specific wavelength band. Moreover, the holographic mirror  33  may be designed with the angle of incidence unequal to the angle of reflection whereby the disposition positions and angles of the image forming unit  31 , the reflection mirror  32 , and the holographic mirror  33  have more flexible designs. But it is not limited the present invention, for example, the holographic mirror  33  may be designed with the angle of incidence equal to the angle of reflection. 
     Referring to  FIG. 5 , there is shown a schematic view of a vehicular head-up display  5  according to a second embodiment of the present invention. The vehicular head-up display  5  is disposed in a vehicle  2  and includes an image forming unit  51  and a holographic mirror  53 . The image forming unit  51  is used for generating a real image; the holographic mirror  53  is used for optically reflecting and/or amplifying the real image generated by the image forming unit  51 . The image forming unit  51  and the holographic mirror  53  employ a discrete design. Specifically, the image forming unit  51  is disposed on a roof  21  of the vehicle  2 . The holographic mirror  53  is disposed below a windshield  22  in the front of the vehicle  2 ; in the embodiment, the holographic mirror  53  has a reflection surface  531  facing backward and upward with respect to the vehicle  2  at an angle of 50 degrees from the horizontal. In an embodiment, the reflection surface  531  may be a flat surface or a curved surface. Light rays emitted by the image forming unit  51  are projected onto the reflection surface  531  of the holographic mirror  53 ; light rays reflected from the reflection surface  531  of the holographic mirror  53  are projected onto the windshield  22 ; and light rays reflected from the windshield  22  are projected onto a user&#39;s eyes E 3  so that the user sees a virtual image P 3  formed in front of the windshield  22 , in which the user may be a driver or a passenger. The virtual image P 3  is formed within the driver&#39;s field of view while driving so that the driver may pay attention to road conditions and acquire driving information from the virtual image P 3  at the same time. 
     The holographic mirror  53  may reflect light rays of a specific wavelength band and allow light rays of not the specific wavelength band to pass through. Therefore, the holographic mirror  53  may be designed to let light rays of unwanted wavelength bands to pass through so that the light rays of unwanted wavelength bands are not projected onto the windshield  22  thereby increasing the display quality of the virtual image P 3 . For example, if the image forming unit  51  employs a red light source with a wavelength band of 630-650 nm, a green light source with a wavelength band of 510-530 nm, and a blue light source with a wavelength band of 440-460 nm to combine color images, the holographic mirror  53  may be designed to reflect light rays of a wavelength band of 510-530 nm (corresponding the green light source) and let light rays of other wavelength bands to pass through. It is noted that the wavelength band of 510-530 nm corresponding to the green light source is the specific wavelength band. Light rays of not the specific wavelength band which come from ambient light such as sunlight pass through the holographic mirror  53  so that most of the light rays which come from ambient light do not enter the vehicle  2  through the holographic mirror  53  to project onto the user&#39;s eyes E 3  so that it does not result in the user&#39;s discomfort or bad effects on driving safety. Moreover, the holographic mirror  53  may be designed with the angle of incidence unequal to the angle of reflection whereby the disposition positions and angles of the image forming unit  51  and the holographic mirror  53  have more flexible designs. Even the reflection surface  531  of the holographic mirror  53  may be horizontal. Compared to the holographic mirror  33  in the first embodiment, the holographic mirror  53  have more flexible disposition. But it is not limited to the present invention; for example, the holographic mirror  53  may be designed with the angle of incidence equal to the angle of reflection. 
     Referring to  FIG. 6 , there is shown a schematic view of a holographic mirror  63  according to an embodiment of the present invention. The holographic mirror  63  includes a light transmitting substrate  632  and a holographic film  633  with microstructures. The holographic film  633  is disposed on the light transmitting substrate  632 , and a surface of the holographic film  633  away from the light transmitting substrate  632  is taken as a reflection surface  631  of the holographic mirror  63 . In an embodiment, the light transmitting substrate  632  may be made of glass, plastic or other material. Alternatively, the holographic mirror may be implemented by directly forming optical structures on a surface of the light transmitting substrate without using the holographic film. The holographic mirror  63  may be applied to the holographic mirror  33  or  53  as shown in  FIG. 3  to  FIG. 5 . 
     Although the present invention has been described in terms of the preferred embodiments, it is not limited thereto. It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the present invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.