Patent Publication Number: US-2018039080-A1

Title: Head up display with reduced package depth and volume

Description:
CROSS-REFERENCED TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Application No. 62/370,458 filed on Aug. 3, 2016, which the disclosure of which is hereby incorporated by reference in its entirety for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The disclosure relates to a head up display (HUD) in a motor vehicle. 
     BACKGROUND OF THE INVENTION 
     A head up display emits light that reflects from the front windshield to be seen by the driver. The light appears to come from a virtual image in front of the driver and in front of the windshield. This type of head up display is currently commercially available. 
     Conventional head up displays create the virtual image by first using a display to create an image. Next, the light from the image is reflected from one or more mirrors. Next, the light from the mirrors is reflected from the windshield. The mirrors are designed and positioned relative to the display so that the light seen by the driver, which is reflected from the windshield, appears to come from a virtual image that is outside of the vehicle. The mirrors and display are typically contained in a package that occupies a volume beneath the top surface of the dashboard. 
     It is difficult for vehicle manufacturers to package a conventional head up display in a vehicle because of the volume required, and because the space under the dashboard is needed for other essential systems. In general, vehicle manufacturers need to package a head up display within the dashboard. Both the depth of the package and the volume of the package are important. 
     Automotive head up displays have traditionally had a field of view of about 5°×30 to present simple information, such as speed, below the driver&#39;s view of the road ahead. Increasingly, automakers would like to implement additional features, such as augmented reality, which require a larger field of view. 
     Current automotive head up displays primarily use a large concave mirror (aspherical) and a small flat mirror. Other current head up displays have two aspherical mirrors. Head up displays including a flat mirror oriented at about 45 degrees are also known. 
     SUMMARY 
     The present invention may include a head up display having an optical arrangement that provides reduced package depth, smaller volume and improved image sharpness than is possible with the conventional optical design for an automotive head up display. The present invention may be applied to an augmented reality head up display with a 10°×4° virtual image as seen by the driver, and with a seven-meter virtual distance from the driver to the virtual image. 
     A novel aspect of the invention is that a first concave aspherical mirror may be oriented at an angle of about 45 degrees relative to a second approximately flat aspherical mirror in an automotive head up display, to reduce package depth, decrease volume, and improve image sharpness. 
     In one embodiment, the invention comprises a head up display arrangement for a motor vehicle, including an image source emitting a light field. A first freeform mirror is positioned to provide a first reflection of the light field. A generally concave second freeform mirror is positioned to receive the first reflection and provide a second reflection of the light field. The second reflection is reflected off of a windshield of the vehicle so as to be visible to a driver of the vehicle. An arcuate section of a surface of the generally concave second freeform mirror receives the first reflection and provides the second reflection. An angle between the first freeform mirror and an imaginary line that is tangent to a midpoint of the arcuate section of the surface of the generally concave second freeform mirror is approximately between thirty degrees and sixty degrees. 
     In another embodiment, the invention comprises a head up display method for a motor vehicle, including emitting a light field, and providing a first freeform mirror positioned to provide a first reflection of the light field. A generally concave second freeform mirror is provided and positioned to receive the first reflection and produce a second reflection of the light field. The second reflection is reflected off of a windshield of the vehicle so as to be visible to a driver of the vehicle. An arcuate section of a surface of the generally concave second freeform mirror receives the first reflection and produces the second reflection. An angle between the first freeform mirror and an imaginary line that is tangent to a midpoint of the arcuate section of the surface of the generally concave second freeform mirror is approximately between thirty degrees and sixty degrees. 
     In yet another embodiment, the invention comprises a head up display arrangement for a motor vehicle, including an image source emitting a light field. A first freeform mirror is positioned to provide a first reflection of the light field. A generally concave second freeform mirror has a reflective surface with an arcuate section. The arcuate section is positioned to receive the first reflection and provide a second reflection of the light field. An angle between the first freeform mirror and an imaginary line that is tangent to a midpoint of the arcuate section of the surface of the generally concave second freeform mirror is approximately between forty degrees and fifty degrees. A windshield is positioned to receive the second reflection and provide a third reflection of the light field. The third reflection is visible to a driver of the vehicle as a virtual image disposed outside of the windshield. 
     An advantage of the present invention is that it may reduce the required HUD volume and increase flexibility to package the HUD in the vehicle with other vehicle systems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention will be had upon reference to the following description in conjunction with the accompanying drawings. 
         FIG. 1  is a schematic bottom view of one example embodiment of a HUD optical arrangement of the present invention. 
         FIG. 2  is a schematic diagram of one example embodiment of a HUD system including the HUD optical arrangement of  FIG. 1 . 
         FIG. 3  is another schematic view of the mirrors and windshield of the HUD system of  FIG. 2 . 
         FIG. 4  is a schematic perspective view of the HUD system of  FIG. 2 . 
         FIG. 5  is a flow chart of one embodiment of a head up display method of the present invention for a motor vehicle. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates one embodiment of a HUD optical arrangement  10  of the present invention, including two reflective freeform mirrors  12  and  14 . Mirror  14  is concave and is arranged to aim rays  16  to reflect from a windshield  18 , as shown in  FIG. 2 , to be seen by a human driver  20 . Rays  16  begin at diffuser  22 , reflect from mirror  12 , pass from mirror  14  to windshield  18 , and reflect from windshield  18  to be seen by the driver. Mirror  12  is approximately flat and is oriented to reflect light rays or a light field from a display, or from an image presented on a diffuser  22 , to mirror  14 . To simplify  FIG. 2 , diffuser  22  and the ray from diffuser  22  to mirror  12  have been rotated about the ray from mirror  12  to mirror  14  so as to be in the same plane as the other objects shown in  FIG. 2 . 
     In one embodiment, diffuser  22  is a diffuser supplied by Kuraray Co., Ltd., of Tokyo, Japan. The image on the diffuser is created by a projector. The projector may be a DLP projector such as a digital imaging system including micromirrors separately controlled to create a digital image. In one embodiment, a digital light projector or a digital multi-mirror device in a kit marketed from Texas Instruments, may be used as the image source. 
     In one specific embodiment, arrangement  10  is applied to a head up display for augmented reality with a 11.4°×4.30 field of view and a package volume of about 8.5 liters. The display may be in the form of a liquid crystal display having an 80×40 mm active area. 
     Imaginary line  24  is tangent to a midpoint  26  of an arcuate section  28  of the surface of mirror  14  that receives the light field reflected off of mirror  12 . An angle θ between mirror  12  and tangent line  24  may be approximately between 30 degrees and 60 degrees. In one embodiment, angle θ may be approximately between 40 degrees and 50 degrees. In another embodiment, angle θ may be approximately 45 degrees. Tangent line  24  may alternatively be thought of as an imaginary plane that is perpendicular to the page of  FIG. 1 . 
     The concave curvature of the surface of mirror  14  may be modeled and/or designed with an extended polynomial description in a Zemax optical design software program. Other aspherical mirror types within Zemax that could be used to model and/or design mirror  14  include a Chebyshev polynomial description, a Zernike polynomial description, and a biconic Zernike description. Another optical design software program that may be used to model and/or design mirror  14  is Code V. 
       FIG. 3  illustrates the mirrors and windshield of the HUD system of  FIG. 2 .  FIG. 4  illustrates the HUD system of  FIG. 2 . Mirror A in  FIGS. 3-4  corresponds to mirror  12  in  FIGS. 1-2 , and mirror B in  FIGS. 3-4  corresponds to mirror  14  in  FIGS. 1-2 . 
     Each of mirrors  12  and  14  may be a freeform mirror. The term “freeform” may mean that the mirror is not flat, conical, or frusto-conical, wherein cylindrical is considered to be a special case of conical. Mirror  14  may be generally concave, but mirror  12  may be neither generally concave nor generally convex. Mirror  12  may be approximately flat, but is designed to direct the rays appropriately. The reflective surface of mirror  12  may be described in Zemax as an extended polynomial with twenty-seven terms, wherein the X and Y are two perpendicular axes, and the value of the polynomial is the value of a third axis Z that is perpendicular to both of axes X and Y. The first two terms (X1Y0 and X0Y1) are constrained to zero, so the polynomial has twenty-five non-zero terms. The polynomial includes all possible terms in X, X 2 , X 3 , X 4 , X 5 , X 6 , and Y, Y2, Y 3 , Y 4 , Y 5 , Y 6 . 
     In a particular embodiment, the equations for mirror  12  and mirror  14  are described in the table below: 
     
       
         
           
               
               
               
             
               
                   
               
               
                  Term 
                 Mirror 12 
                 Mirror 14 
               
               
                   
               
             
            
               
                 X1Y0 
                 0 
                 0 
               
               
                 X0Y1 
                 0 
                 0 
               
               
                 X2Y0 
                 3.758216827681000E+000 
                 4.806211017163000E−001 
               
               
                 X1Y1 
                 1.900693923567000E+000 
                 9.257022901890000E−002 
               
               
                 X0Y1 
                 −4.409111247532000E+000  
                 2.405827111339000E+000 
               
               
                 X3Y0 
                 5.162006391704000E+000 
                 1.639612087429000E−001 
               
               
                 X2Y1 
                 −3.061562001959000E+000  
                 −5.730690852151000E−001  
               
               
                 X1Y2 
                 −2.703129586368000E+000  
                 1.432248526776000E−002 
               
               
                 X0Y3 
                 1.596962055934000E+001 
                 2.497339025215000E−001 
               
               
                 X4Y0 
                 4.071721011694000E+000 
                 3.430056338954000E−002 
               
               
                 X3Y1 
                 −2.815160693536000E+000  
                 1.160820515645000E−001 
               
               
                 X2Y2 
                 4.792150469313000E+000 
                 2.051634427595000E−001 
               
               
                 X1Y3 
                 1.471810878826000E+001 
                 −3.298219769185000E−001  
               
               
                 X0Y4 
                 1.990887321837000E+001 
                 6.728363234852000E−001 
               
               
                 X5Y0 
                 1.512055949803000E+000 
                 −3.326563715569000E−002  
               
               
                 X4Y1 
                 −9.012755498883001E−001  
                 3.903153809891000E−002 
               
               
                 X3Y2 
                 4.234905523124000E+000 
                 −4.852380090258000E−002  
               
               
                 X2Y3 
                 1.160242638340000E+001 
                 1.987094538427000E−001 
               
               
                 X1Y4 
                 1.578156095382000E+001 
                 −3.890998607212000E−001  
               
               
                 X0Y5 
                 −7.852204663376000E+000  
                 4.018131700378000E−001 
               
               
                 X6Y0 
                 2.134147672800000E−001 
                 1.276349826294000E−002 
               
               
                 X5Y1 
                 −1.073218449779000E−001  
                 −4.083118180811000E−002  
               
               
                 X4Y2 
                 9.179753579871000E−001 
                 −9.180506284074999E−003  
               
               
                 X3Y3 
                 2.865078393453000E+000 
                 −7.129285790582000E−002  
               
               
                 X2Y4 
                 4.869942297781000E+000 
                 9.702818820677001E−002 
               
               
                 X1Y5 
                 −3.573718398775000E−001  
                 −1.072724576979000E−001  
               
               
                 X0Y6 
                 −9.147369578713001E+000  
                 1.125279474755000E−001 
               
               
                   
               
            
           
         
       
     
     For this embodiment, Z, the sum of all the terms, is vertical distance in mm. The variables X and Y are the respective horizontal distances in the X and Y direction, each divided by 100 mm (normalized to 100 mm). Accordingly, X and Y are dimensionless. 
       FIG. 5  illustrates one embodiment of a head up display method  500  of the present invention for a motor vehicle. In a first step  502 , a light field is emitted. For example, diffuser  22  may emit a light field, as shown in  FIGS. 1 = 2 . 
     Next, in step  504 , a first freeform mirror positioned to provide a first reflection of the light field is provided. For example, reflective freeform mirror  12  may be positioned to provide a first reflection of the light field emitted by diffuser  22 . 
     In a final step  506 , a generally concave second freeform mirror positioned to receive the first reflection and produce a second reflection of the light field is provided. The second reflection is reflected off of a windshield of the vehicle so as to be visible to a driver of the vehicle. An arcuate section of a surface of the generally concave second freeform mirror receives the first reflection and produces the second reflection. An angle between the first freeform mirror and an imaginary line that is tangent to a midpoint of the arcuate section of the surface of the generally concave second freeform mirror is approximately between thirty degrees and sixty degrees. For example, a generally concave second freeform mirror  14  may be positioned to receive the first reflection and produce a second reflection of the light field such that the second reflection is reflected off of windshield  18  of a vehicle so as to be visible to a driver  20  of the vehicle. An arcuate section  28  of the surface of mirror  14  receives the light field reflected off of mirror  12  and produces the second reflection. An angle θ between first freeform mirror  12  and an imaginary line  24  that is tangent to a midpoint  26  of arcuate section  28  of the surface of generally concave second freeform mirror  14  is approximately between thirty degrees and sixty degrees. The foregoing description may refer to “motor vehicle”, “automobile”, “automotive”, or similar expressions. It is to be understood that these terms are not intended to limit the invention to any particular type of transportation vehicle. Rather, the invention may be applied to any type of transportation vehicle whether traveling by air, water, or ground, such as airplanes, boats, etc. 
     The foregoing detailed description is given primarily for clearness of understanding and no unnecessary limitations are to be understood therefrom for modifications can be made by those skilled in the art upon reading this disclosure and may be made without departing from the spirit of the invention.