Patent Publication Number: US-2023139776-A1

Title: Light guide

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present patent application claims the priority of Japanese patent application No. 2021/179322 filed on Nov. 2, 2021, and the entire contents of Japanese patent application No. 2021/179322 are hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to a light guide and, in particular, to a light guide used in a vehicle interior lighting device. 
     BACKGROUND ART 
     A light guide is known in which two concentrically-arranged annular light guide portions are connected by an intermediate light guide position located therebetween (see Patent Literature 1). In the light guide described in Patent Literature 1, light entered from a light source into the inner annular light guide portion enters the outer annular light guide portion after passing through the intermediate light guide portion, and is then reflected at a prism and output to the outside. Thus, the light guide can be arranged in such a manner that only the outer annular light guide portion is exposed to the outside and the inner annular light guide portion and the light source are placed in a location not visible from the outside. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: EP 2584249 B1 
     SUMMARY OF INVENTION 
     The light guide in Patent Literature 1 is configured such that a thickness (a width in vertical cross section) of the intermediate light guide portion is smaller than thicknesses of the two annular light guide portions, and the prism of the outer annular light guide portion is located on the outer side in a thickness direction of the intermediate light guide portion. Therefore, a problem may arise that light entering the outer annular light guide portion after passing through the intermediate light guide portion does not easily reach the prism, resulting in low light extraction efficiency. 
     It is an object of the invention to provide a light guide that can efficiently extract light entering a light guide portion with a prism surface after passing through an intermediate light guide through which two rod-shaped light guide portions are connected. 
     An aspect of the invention provides a light guide defined in (1) to (3) below. 
     (1) A light guide, comprising:
         a rod-shaped first light guide portion comprising a prism surface comprising a prism to reflect internally propagating light and output the light to an outside along a lengthwise direction thereof;   a rod-shaped second light guide portion comprising a light intake portion to take in light from a light source; and   a rod-shaped intermediate light guide portion between the first light guide portion and the second light guide portion provided such that side surfaces thereof are connected to side surfaces of the first light guide portion and the second light guide portion,   wherein, in a direction orthogonal to a direction of alignment of the first light guide portion, the second light guide portion and the intermediate light guide portion, a thickness of the intermediate light guide portion is smaller than a thickness of the first light guide portion and a thickness of the second light guide portion, and   wherein a side surface of the intermediate light guide portion on a side of the prism surface is continuous with the prism surface in a same plane.       

     (2) The light guide according to (1), wherein a side surface of the second light guide portion on the side of the prism surface comprises a surface that is inclined relative to the side surface of the intermediate light guide portion on the side of the prism surface and is continuous with the side surface of the intermediate light guide portion on the side of the prism surface. 
     (3) The light guide according to (1) or (2), wherein the first light guide portion comprises a light intake portion to take in light from a light source, wherein the light intake portion of the first light guide portion comprises a rod-shaped light guide with a polygonal shape in cross section perpendicular to the lengthwise direction, and wherein the light intake portion of the second light guide portion comprises a rod-shaped light guide with a circular shape in cross section perpendicular to the lengthwise direction. 
     ADVANTAGEOUS EFFECTS OF INVENTION 
     According to the invention, a light guide can be provided that can efficiently extract light entering a light guide portion with a prism surface after passing through an intermediate light guide through which two rod-shaped light guide portions are connected. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic diagram illustrating a vehicle cabin around an instrument panel, which is an example of an installation location of a light guide in an embodiment of the present invention. 
         FIGS.  2 A and  2 B  are respectively side and bottom views showing the light guide in the embodiment of the invention. 
         FIGS.  3 A and  3 B  are cross-sectional views showing cross sections of the light guide in the embodiment of the invention respectively cut along lines A-A and B-B shown in  FIG.  2 A . 
         FIG.  4 A  is a diagram illustrating a light intake surface of a second light guide portion when viewed in a direction indicated by an arrow C shown in  FIG.  2 A . 
         FIG.  4 B  is a diagram illustrating a light intake surface of a first light guide portion when viewed in a direction indicated by an arrow D shown in  FIG.  2 A . 
         FIG.  5    is a diagram illustrating a state when light sources to supply light to the light guide and a housing to house the light guide are attached to the light guide in the embodiment of the invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 
     A light guide  1  in the embodiment of the invention is a light guide used in a vehicle interior lighting device. The installation location of the light guide  1  in the vehicle cabin is not specifically limited, but it is typically installed on an instrument panel. Light emitted from the light guide  1  may be used for direct lighting or may be used for indirect lighting. 
       FIG.  1    is a schematic diagram illustrating a vehicle cabin around an instrument panel  20 , which is an example of an installation location of the light guide  1 . The instrument panel  20  is a vehicle interior part which is arranged on the front side of seats  25  (a driver&#39;s seat  25   a,  a front passenger seat  25   b ) and on which vehicle meters and gauges and air conditioner vents, etc., are provided. The instrument panel  20  has an upper panel  21  constituting an upper portion thereof, and a lower panel  22  constituting a lower portion. For example, a glove compartment  24 , etc., is provided on the lower panel  22  in front of the front passenger seat, and an air conditioner vent  23 , etc., is provided on the upper panel  21 . 
     In the example shown in  FIG.  1   , the light guide  1  is placed on a design surface of the instrument panel  20  and light emitted from the light guide  1  is used for direct lighting to be directly visually perceived by occupants sitting in the seats  25 . In this regard, the light guide  1  may not be exposed on the design surface of the instrument panel  20 , and may be placed behind an outer lens provided on the design surface. 
     The light guide  1  may alternatively be placed, e.g., inside a space (a gap) provided between the upper panel  21  of the instrument panel  20  and the lower panel  22  located thereunder. In this case, light emitted from the light guide  1  is used for indirect lighting and is visually perceived by the occupants sitting in the seats  25  after being reflected at an upper surface of the lower panel  22 . 
       FIGS.  2 A and  2 B  are respectively side and bottom views showing the light guide  1 . The light guide  1  has a rod-shaped first light guide portion  11  having a prism surface  113  which extends along a lengthwise direction thereof and on which a prism  114  to reflect internally propagating light and output the light to the outside is provided, a rod-shaped second light guide portion  12  having a light intake portion  122  to take in light from a light source, and a rod-shaped intermediate light guide portion  13  provided between the first light guide portion  11  and the second light guide portion  12  so that side surfaces thereof are connected to side surfaces of the first light guide portion  11  and the second light guide portion  12 . In this regard, the “side surfaces” of the first light guide portion  11 , the second light guide portion  12  and the intermediate light guide portion  13  mean side surfaces of rod-shaped objects (surfaces along the lengthwise direction). 
     The prism  114  is composed of, e.g., a group of linear grooves which are aligned on the prism surface  113  and each extends along a direction orthogonal to the lengthwise direction of the light guide  1 . The linear grooves constituting the prism  114  are, e.g., straight grooves having a V-shaped cross section. Alternatively, the prism  114  may be composed of a group of linear protrusions, in place of the group of linear grooves. The linear protrusions in this case are, e.g., straight protrusions having a triangular cross section. Arrangement and intervals (pitch) of the linear groove group, etc., constituting the prism  114  are set according to a light introduction path so that uniformity of light extracted from the first light guide portion  11  is increased. 
     Light emitted from the light source enters through a light intake surface  121  into the second light guide portion  12 , enters the first light guide portion  11  after passing through the intermediate light guide portion  13 , and is then reflected at the prism  114  and output to the outside from a surface  115  of the first light guide portion  11  located opposite to the prism surface  113 . 
     By using the second light guide portion  12  and the intermediate light guide portion  13  in this manner, it is possible to supply light from the middle portion of the first light guide portion  11 , not from lengthwise ends. This can reduce a distance between a light extraction portion of the first light guide portion  11  and the light source even when the first light guide portion  11  is long. Therefore, when, e.g., RGB lights are supplied from the light source, it is possible to suppress unevenness in color of extracted light which is caused by the fast attenuation rate of blue light. 
     The light intake portion  122  of the second light guide portion  12  is, e.g., a rod-shaped light guide extending from a lengthwise end of a main body connected to the intermediate light guide portion  13 , as shown in  FIGS.  2 A and  2 B . In this case, a lengthwise end face of the light intake portion  122  serves as the light intake surface  121 . 
       FIGS.  3 A and  3 B  are cross-sectional views of the light guide  1  cut along lines A-A and B-B, respectively, in  FIG.  2 A .  FIG.  3 A  shows a cross section not including the prism  114  of the first light guide portion  11 , and  FIG.  3 A  shows a cross section including the prism  114  of the first light guide portion  11 . 
     Here, when a width of the first light guide portion  11 , the second light guide portion  12  and the intermediate light guide portion  13  in a direction orthogonal to a direction of alignment of the first light guide portion  11 , the second light guide portion  12  and the intermediate light guide portion  13  is defined as a thickness, a thickness T 3  of the intermediate light guide portion  13  is smaller than a thickness T 1  of the first light guide portion  11  and a thickness T 2  of the second light guide portion  12 . This causes many reflections to occur inside the intermediate light guide portion  13  and allows light to quickly reach the first light guide portion  11 . 
     In addition, a side surface  131  of the intermediate light guide portion  13  on the prism surface  113  side is continuous with the prism surface  113  in the same plane, as shown in  FIGS.  3 A and  3 B . Light entered from the intermediate light guide portion  13  into the first light guide portion  11  thereby easily reaches the prism  114 , which increases light extraction efficiency. In addition, since light easily reaches the prism  114 , uniformity of brightness of light extracted from the first light guide portion  11  is enhanced. 
     In addition, a side surface  123  of the second light guide portion  12  on the prism surface  113  side has a flat surface  124  that is inclined relative to the side surface  131  of the intermediate light guide portion  13  on the prism surface 113  side and is continuous with the side surface  131 , as shown in  FIGS.  3 A and  3 B . In this case, the intermediate light guide portion  13  has a shape which is narrowed with respect to the second light guide portion  12  on the prism surface  113  side. This allows light propagating in the second light guide portion pipe  12  to efficiently advance into the intermediate light guide portion  13 . 
     In the light guide described in Patent Literature 1 (European Patent No. 2584249, Specification) mentioned above, the light guide portion corresponding to the second light guide portion  12  is a light guide having a circular cross section and is configured such that its side surface continuous with a side surface of the intermediate light guide portion is a curved surface. In the light guide  1 , having the flat surface  124  allows light to advance from the second light guide portion  12  into the intermediate light guide portion  13  more efficiently as compared to when having a curved surface as provided on the light guide described in Patent Literature 1 instead of having the flat surface  124 . 
     An angle of the flat surface  124  of the second light guide portion  12  relative to the side surface  131  of the intermediate light guide portion  13  is in a range of, e.g., more than 0° and less than 90°, preferably in a range of not less than 30° and not more than 60°. End portions of the flat surface  124  (a boundary with a non-inclined portion of the side surface  123  and a boundary with the side surface  131 ) may be curved, i.e., may have an R-shape. 
     In the example shown in  FIGS.  3 A and  3 B , the first light guide portion  11  and the intermediate light guide portion  13  have rectangular shapes in cross section perpendicular to the lengthwise direction, and the second light guide portion  12  having the flat surface  124  inclined relative to the side surface  131  of the intermediate light guide portion  13  has a pentagonal shape in cross section perpendicular to the lengthwise direction. 
     The first light guide portion  11 , the second light guide portion  12  and the intermediate light guide portion  13  are formed of a material which can transmit visible light emitted from the light source, such as clear acrylic. The light guide  1  is usually formed by injection molding, etc., and first light guide portion  11 , the second light guide portion  12  and the intermediate light guide portion  13  are formed in one piece. 
     In addition, in  FIGS.  3 A and  3 B , a side surface  125  of the second light guide portion  12  located on the light extraction side and a side surface  132  of the intermediate light guide portion  13  located on the light extraction side are continuous in the same plane. However, the side surface  125  may have a flat surface that is inclined relative to the side surface  132  and is continuous with the side surface  132  in the same manner as the flat surface  124  on the side surface  123  side. That is, the intermediate light guide portion  13  may have a shape which is narrowed with respect to the second light guide portion  12  on both sides. 
     The first light guide portion  11  preferably has a light intake portion  112  at its longitudinal end to take in light from the light source, as shown in  FIGS.  2 A and  2 B . As a result, light from the light source can be taken in from both the light intake portion  112  and the light intake portion  122  of the second light guide portion  12 , hence, brightness of light extracted from the first light guide portion  11  and uniformity of the brightness can be improved. 
     The light intake portion  112  of the first light guide portion  11  is, e.g., a rod-shaped light guide extending from a lengthwise end of a main body having the prism  114  of the first light guide portion  11 , as shown in  FIGS.  2 A and  2 B . In this case, a lengthwise end face of the light intake portion  112  serves as a light intake surface  111 . 
     The light guide  1  preferably includes plural second light guide portions  12  to improve brightness of light extracted from the first light guide portion  11  and uniformity of the brightness. In the example shown in  FIGS.  2 A and  2 B , the light guide  1  includes two second light guide portions  12 . 
       FIG.  4 A  is a diagram illustrating the light intake surface  121  of the second light guide portion  12  when viewed in a direction indicated by the arrow C shown in  FIG.  2 A , and  FIG.  4 B  is a diagram illustrating the light intake surface  111  of the first light guide portion  11  when viewed in a direction indicated by the arrow D shown in  FIG.  2 A . 
     The shape of the light intake portion  112  of the first light guide portion  11  in cross section perpendicular to the lengthwise direction is preferably polygonal such as hexagon, rectangular or triable, as is the shape of the light intake surface  111  shown in  FIG.  4 B . 
     When lights with different colors, such as red, green and blue (RGB), are taken in from the light source through the light intake surface  111 , the lights may not be mixed sufficiently in the light intake portion  112 , resulting in unevenness in color of light that is extracted from the main body having the prism  114  of the first light guide portion  11  in a region close to the light intake portion  112 . Thus, the light intake portion  112  is formed to have a polygonal shape in cross section perpendicular to the lengthwise direction so that the lights are diffusely reflected and easily mixed in the light intake portion  112 , thereby suppressing unevenness in color as compared to when the light intake portion  112  has a circular shape in cross section perpendicular to the lengthwise direction. 
     On the other hand, the shape of the light intake portion  122  of the second light guide portion  12  in cross section perpendicular to the lengthwise direction is preferably circular (including ellipse) as is the shape of the light intake surface  121  shown in  FIG.  4 A . 
     When the light intake portion  122  of the second light guide portion  12  has a circular shape in cross section perpendicular to the lengthwise direction, light loss in the second light guide portion  12  is lower than when the light intake portion  122  has a polygonal shape. In addition, light taken in from the light source through the light intake surface  121  reaches the first light guide portion  11  after passing through the second light guide portion  12  and the intermediate light guide portion  13 . Therefore, even when lights with different colors are taken in from the light source through the light intake surface  121 , the lights are mixed sufficiently before reaching the first light guide portion  11 . Therefore, unevenness in color of the extracted light does not occur even though light intake portion  122  of the second light guide portion  12  has a circular shape in cross section perpendicular to the lengthwise direction. 
       FIG.  5    is a diagram illustrating a state when light sources  31 ,  32  to supply light to the light guide  1  and a housing  40  to house the light guide  1  are attached to the light guide  1 . Here, the light source  31  supplies light to the light intake portion  112  of the light guide  1  and the light sources  32  supply light to the light intake portions  122  of the light guide  1  For example, the light guide  1  and the light sources  31 ,  32  are each fixed to the housing  40 , and the light guide  1  and the light sources  31 ,  32  and the housing  40  constitute a lighting device used in vehicle interior, etc. 
     The light source to supply light to the light guide  1  is typically a light-emitting device that includes a light-emitting element such as LED. The light-emitting element included in the light-emitting device is, e.g., an LED called a full-color LED having three LEDs of red, green and blue colors in one package, and in this case, light of a desired color can be emitted by, e.g., PWM control from an in-vehicle ECU (Electronic Control Unit) through an in-vehicle network. 
     Protrusions  116  provided on the light intake portion  112  of the first light guide portion  11  and protrusions  126  provided on the light intake portion  122  of the second light guide portion  12  are used to fix the light guide  1  to the housing  40  and are fitted to, e.g., grooves provided on the housing  40 . 
     (Effects of the Embodiment) 
     In the light guide  1  in the embodiment of the invention described above, the side surface  131  of the intermediate light guide portion  13  on the prism surface  113  side is continuous with the prism surface  113  in the same plane. Therefore, light entered from the intermediate light guide portion  13  into the first light guide portion  11  easily reaches the prism  114  and light can thus be extracted efficiently. In addition, since light easily reaches the prism  114 , uniformity of brightness of light extracted from the first light guide portion  11  is enhanced. 
     Although the embodiment of the invention has been described, the invention is not limited to the embodiment described above and the various kinds of modifications can be implemented without departing from the gist of the invention. In addition, the constituent elements in the embodiment can be arbitrarily combined without departing from the gist of the invention. 
     In addition, the embodiment described above does not limit the invention according to claims. Further, please note that not all combinations of the features described in the embodiment are necessary to solve the problem of the invention. 
     REFERENCE SIGNS LIST 
       1  LIGHT GUIDE 
       11  FIRST LIGHT GUIDE PORTION 
       112  LIGHT INTAKE PORTION 
       113  PRISM SURFACE 
       114  PRISM 
       12  SECOND LIGHT GUIDE PORTION 
       122  LIGHT INTAKE PORTION 
       124  FLAT SURFACE 
       13  INTERMEDIATE LIGHT GUIDE PORTION 
       131  SIDE SURFACE