Abstract:
A vehicle instrument cluster lens assembly for a vehicle instruments panel includes a first layer comprised of a quarter-wave plate (λ/4). A second layer which is a polarizer, a third layer of another quarter-wave plate (λ/4); the first and a fourth layer being a polarizer light to a new orientation. The quarter-wave plates change the orientation of the light angle that it can be seen with a polarized eye glass lens. The vehicle lens assembly functions in a dual manner depending on the light source direction and orientation of the light to prevent light emitted from the instrument as well as making the display light visible to viewers wearing polarized sunglasses.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to so called “dead front” type displays for a vehicle. 
       BACKGROUND OF THE INVENTION 
       [0002]    This invention relates to vehicle displays and, more particularly, to a vehicle lens assembly having a polarizer and a light retarder for reducing vehicle occupant glare and improving visibility. 
         [0003]    Vehicle displays, such as instrument clusters having a speedometer and a tachometer instrument, typically display important information to the occupants of the vehicle. Conventional vehicle displays typically include a housing that supports a circuit board. One or more light sources are typically mounted on the circuit board to illuminate a display surface within the housing, to power the instruments, and to illuminate the instruments. A clear, transparent lens is mounted on the front of the housing between the vehicles occupants and the illuminated display surface to protect the display surface and instruments 
         [0004]    Selected vehicle displays utilize a smoked lens mounted on the front of the housing instead of clear lens. In addition to protecting the display surface and instruments, the smoked lens provides a desirable appearance (i.e. a smoked lens effect). To produce the smoked lens effect, conventional smoked lens are heavily tinted to obscure the appearance of the instruments when the vehicle is turned off such that the instruments are only minimally visible to a vehicles occupant. When the vehicle is on, the light sources illuminate the instruments and are visible to the vehicle occupant through the smoke lens. 
         [0005]    Generally to maximize the smoked lens effect it is desirable to prevent light from the surrounding environment from entering through the smoked lens and reflecting off of the display surface. Conventional smoked lenses allow the reflected light to be transmitted back through the smoked lens to the vehicle occupant. This may undesirably increase the visibility of the instruments when the vehicle is turned off, and diminish the smoked lens effect. 
         [0006]    Accordingly, there is a need for a vehicle instrument cluster lens assembly that prevents light reflected off of the display surface from being transmitted back through a lens to a vehicle occupant to provide a more desirable smokes lens effect. 
         [0007]    A common solution is to use a lens assembly with polarized sections in order to achieve the smoked lens effect to a greater degree while still allowing for a bright and visible display. Polarized lens assemblies have the unintended consequence of cutting down on the visibility of the display as well as decreasing visibility for those wearing polarized sunglasses. 
         [0008]    Thus, a vehicle instrument cluster lens assembly which achieves the smoked lens effect without deterring the visibility of both sunglass wearing and sunglass free users of the instrument panel display is needed. 
       SUMMARY OF THE INVENTION 
       [0009]    A vehicle instrument cluster lens assembly for a vehicle instrument panel according to the present invention includes a first layer comprised of a quarter-wave plate (λ/4) which functions to change the orientation of polarized light which it receives. A second layer comprised of a polarizer which shifts incident light to a first orientation corresponding to the polarizing orientation specific to the polarizer. A third layer comprised of another quarter-wave plate (λ/4) which shifts the orientation of polarized light impinging on its surface from the first orientation to a second orientation. And a fourth layer comprised of a polarizer to linearly polarize light to a new orientation. The polarizers reduce the intensity of the light that passes through them depending on the orientation of the initial light when it impinges on the surface. The quarter-wave plates change the orientation of the light for specific wavelengths. 
         [0010]    In one embodiment, the vehicle lens assembly according to the present invention can function in a dual manner depending on the light source direction and orientation of the light to prevent light emitted from the instrument as well as making the display light visible to viewers wearing polarized sunglasses. The assembly prevents darkening of the instrument panel by emitting polarized light which is initially polarized to match the polarization orientation of the first polarizer. The light having the same orientation as the polarizer orientation passes through the polarizer unchanged and enters a quarter-wave plate. The quarter-wave plate rotates the orientation of the light to the polarizing orientation the second polarizer allowing the light emitted from the display to exit the lens assembly without a reduction of brightness. The final quarter-wave plate reorients the exiting light from the display in such a way that it is oriented to the polarizing orientation of polarized sunglasses so that the instrument display panel remains visible while wearing sunglasses with polarized lenses. 
         [0011]    In a second embodiment, the vehicle lens assembly according to the present invention functions to reduce light reflected off of an instrument panel&#39;s metallic frame in order to provide a desirable look which does not produce a glare. The frame around the display area on the instrument panel is covered only by one section of quarter-wave plate in order that the glare from the reflection of the metal is further cut down. The lens assembly cuts down glare from reflecting light by initially polarizing incident light which impinges on the surface at a first orientation corresponding to the polarizing orientation. The light then hits the second polarizer and is polarized to a second orientation being orthogonal to the first orientation. After passing through the polarizers, the light reflects off of the metallic frame and back to the set of polarizers where it is again polarized in a similar fashion and exits the assembly at a severely reduced intensity resulting in a near zero percentage of reflected light as compared to the light that entered the assembly. This produces the smoked lens effect. 
         [0012]    The present invention provides an instrument cluster lens assembly having two polarizers and two quarter-wave plates which function together to allow for a smokes lens effect by preventing light from reflecting off of the surface of the panel while allowing greater clarity of viewing light emitted by the instrument display panel and allowing it to be viewed by viewers wearing polarized sunglasses. 
         [0013]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0015]      FIG. 1  Is a perspective view of a vehicle dashboard having and instrument panel according to the present invention 
           [0016]      FIG. 2  is a schematic sectional view illustrating a design for a “dead front” type display for a vehicle in which the lens assembly of the present invention may be utilized in accordance with the present invention 
           [0017]      FIG. 3  is a schematic view illustrating an instrument cluster lens assembly of the present invention showing the different parts and layers of the assembly and the display in accordance with the present invention. 
           [0018]      FIG. 4  is a sectional view taken along line  4 - 4  of  FIG. 3  the path of light emitted from the “dead front” display through the instrument cluster lens assembly and the various changes to the polarity of the light as it progresses through the assembly and through another lens in this case illustrative of sunglasses. 
           [0019]      FIG. 5  is a sectional view taken along line  5 - 5  of  FIG. 3  illustrating the path of light external to the display from the environment as it goes through the instrument cluster lens assembly and reflects off of the metal frame surrounding the display and the various changes in the polarity of the light as it progresses through the assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0021]    Referring now to  FIG. 1  the placement of the invention in a vehicle is generally shown at  10 . Typically a vehicle has a front dashboard  11  and an instrument panel  12 . The present invention would be utilized in gauges  13  and or  13  which are present in the driver side of the dashboard  11 . 
         [0022]    Referring to  FIG. 1 , the instrument panel  12  of  FIG. 1  is shown schematically and includes a housing  15  that supports a lens  14 . In this example, a light guide assembly  19  located opposite from the lens  14  includes a light source  16  for illuminating the illuminable display surface  22 . The light source  16  produces a display light that travels through a light guide  20 , internally reflecting off of surfaces  21  of the light guide  20 . A light reflector  17  within the light guide  20  receives the display light and reflects the display light out of the light guide  20  toward the lens  14 . 
         [0023]      FIG. 3  illustrates the overall schematic of the instrument cluster lens assembly and the display which it covers. The display is generally shown at  23  and has components consisting of a lit LCD display section  20  a dark LCD area section  22  and a metal frame section  24 , the lens assembly, generally shown at  25 , covers the display  23 . The lens assembly  25  includes five lenses; an AR/AG coating  38  which provides a surface to diffuse some of initial incident light immediately off of the surface without penetrating into the lens assembly; a first quarter-wave plate (λ/4)  28  which functions to rotate the orientation of polarized light; a first polarizer  30  which polarizes light to an orientation specific to the polarizing orientation of the polarizer; a second quarter-wave plate  32  which functions similarly to the first quarter-wave plate  28  in that it rotates the orientation of polarization; and, a second polarizer  34  which polarizes light impinging on its surface to a second orientation corresponding to the polarizing orientation of the polarizer. All five layers of the lens assembly  25  cover the lit display section  20  and the dark display section  22 . However, it is to be appreciated that the metal frame section  24  of the assembly is covered only by a portion of the lens assembly  25 . The metal frame section  24  is covered only by four layers of the assembly  25 , the second quarter-wave plate  32  does not cover the metal frame  24  section for reasons that are set forth in further detail below. The path of incident light  26  from the environment through the lens assembly shows the orientation of the lens assembly, specifically that the AR/AG coating  38  is the top most layer with respect to the environment. The light display section of the panel  20 , which emits light from a light source  36  that passes through the lens assembly is shown. Thus the orientation of the lens assembly, being in front of the lighted LCD display within the instrument panel is shown. 
         [0024]      FIG. 3  of the quarter-wave plates and the polarizers in the assembly. In this example the quarter-wave plates  28  and  32  shift the orientation of polarized light by 90 degrees. The first polarizer  30  has a horizontal orientation and the second polarizer  34  has a vertical orientation. It should be understood to one ordinarily skilled in the art that the orientation of the quarter-wave plates could be oriented to shift the orientation of polarized light to any degree in order to produce an angle of polarization corresponding to those of polarized lenses in order to be seen through them. 
         [0025]    Thus, The AR/AG coating  38  is the outermost layer, followed by the first quarter-wave plate  28 , then the first polarizer  30  having a first orientation, the second quarter-wave plate  32 , and the second polarizer  34  having a second orientation which differs from the first polarizer&#39;s orientation by 90 degrees. 
         [0026]      FIG. 4  illustrates the path of light  64  being emitted from the display  52  and its path and orientation through the cluster lens assembly  25  and through the lens of a polarized surface  84  representative of polarized sunglasses. The direction of propagation of the light is in the Z-direction according the coordinate system C. The light is initially emitted from the display  20  in a vertically oriented polarization as shown at  66  and in the Y-direction according to the coordinate system C. The light enters the assembly, going through the polarizer  34 ; the polarizer  34  having a vertical orientation does not polarize the light  68  as it is already vertically polarized when emitted from the LCD display  20  when it passes through the polarizer  34 . The light then enters the second quarter-wave plate  32  and its orientation is rotated 90 degrees to a second orientation  70  now being horizontally polarized in the X-direction as indicated by the circled X symbol according to the coordinate system C but not being reduced in intensity. Being of a horizontally polarized orientation the light passes through a first polarizer  30  without being polarized as the polarizer  30  has a horizontal polarizing orientation. The light then goes through first quarter-wave plate  28  rotating its orientation by 90 degrees to a third orientation corresponding to a vertically polarized orientation  74  along the Y-direction according to the coordinate system C. The now vertically polarized light  76  passes through the AR/AG coating  38  with no effect, remaining in the same orientation  78  as it passes into open air. This vertically polarized light is visible to the naked eye and also serves to be viewable for a viewer wearing polarized sunglasses  84 . Vertically oriented light  80  upon passing through polarized lenses  84  is not effected by the polarized lenses  84  and passes through them unchanged, remaining in a vertically oriented polarization  82  thus being viewable. Without polarized lenses the view of the polarized light is the same allowing for viewing with and without polarized lenses. It should be noted to one ordinarily skilled in the art that the outgoing orientation of the light need not be vertical and could be of any angle corresponding to be viewable under polarized lenses. The construction of the quarter-wave plates would therefore not be limited to shifting the orientation of light by 90 degrees but by any angle necessary. 
         [0027]      FIG. 5  illustrates the path of external light  98  as it passes from outside the assembly  25  and reflects off of the metal frame  24  of the display  23 , passing again through the assembly  25 . Initially unpolarized incident light  100  propagating in the Z-direction according to the coordinate axis C enters the assembly  25 , first impinging upon the AR/AG coating  38  which diffuses some of the light. The light is not otherwise affected and remains unpolarized light  102  as it passes into the first quarter-wave plate  28 . The quarter-wave plate  28  does not have an effect on the light as it passes through, again remaining unpolarized light  104 . Upon entering the first polarizer  30  the light is polarized into a first orientation  106  corresponding to the polarizing orientation of the polarizer  30  in this case being horizontally oriented along the X-direction as designated by the circled X symbol and according to the coordinate system C and is cut down in intensity by 1/100 th . The light then enters an unoccupied layer  32  and remains in the same orientation  108  before entering second polarizer  34  having a second orientation corresponding to the polarizing orientation of the polarizer  34 . The light having a horizontal orientation  108  upon entering the polarizer  34  is polarized to a second orientation corresponding in this example to a vertical orientation in the Y-direction according to the coordinate system C and being cut down in intensity by ½. The light exits the assembly with a vertical orientation  112  and reflects off of the metal frame  24  remaining in an unchanged orientation  114  and reenters the assembly. The light  116  reentering the polarizer  34  having the same orientation as the polarizer  34  does not become polarized and remains at the same orientation, passing through the polarizer  34  unchanged. The light passes into the unoccupied space  32  with a vertical orientation  118  in the Y-direction. The light then enters the polarizer  30  becoming polarized to a third orientation  120  corresponding to the polarizing orientation of the polarizer in this case horizontally polarized indicated by the circled X symbol and becoming reduced in intensity by a factor of 1/100 th . The now horizontally polarized light  120  enters the quarter-wave plate  28  and is rotated 90 degrees to a fourth orientation  122  corresponding to a vertical orientation in the Y-direction. The light enters the AR/AG coating  38  with no effect, remaining in the same orientation  124  as it passes out of the cluster lens assembly with the same orientation. The light leaves the cluster lens assembly with a vertical orientation in the Y-direction and at 0.005% of its initial intensity as shown by  126 . This reduction in intensity reduces any undesirable scattering of the reflected light to imperceptible levels and reorientation provided by the quarter-wave plate  28  provides for the smoked lens effect. 
         [0028]      FIG. 5  shows the path of light  98  as it passes through the assembly  99  and is polarized and reduced in intensity as it passes through a set of polarizers  30  and  34 . It is then reflected off a metal surface  96  before passing through the set of polarizers  30  and  34  again but only being polarized once due to the corresponding orientation of the light. Any reflected light then leaves the cluster lens assembly greatly reduced in intensity allowing for barely any light being reflected off of the metal frame, such as to be un-viewable by the human eye providing a smoked lens effect. In this case the orientations of the respective polarizers and the direction of propagation of the light are orthogonal with one another according to coordinate system C. 
         [0029]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.