Abstract:
A measuring instrument includes a light source, a dial plate with a scale design, and a light guide member. The light guide member includes a receiving portion for receiving the light from the light source, and a flat plate portion for irradiating the light transmitted from the receiving portion to the dial plate. The flat plane portion includes a thick wall section located close to the scale design, and a thin wall section extending from the thick wall section in a direction away from the light source. The thick wall section is thicker than the thick wall section. A boundary end face connected to a region of the thick wall section and a region of the thin wall section in the second face of the light guide member reflects the light transmitted in the light guide member from the light receiving portion to irradiate the image design.

Description:
TECHNICAL FIELD 
     The present invention relates to a measuring instrument. 
     BACKGROUND ART 
       FIG. 5  is an exploded perspective view showing a schematic structure of a conventional measuring instrument for a vehicle which is disclosed in Patent Literature 1,  FIG. 6  is a plan view showing a light guide member in the measuring instrument which is taken out therefrom,  FIG. 7  is a sectional view as seen in a direction of arrow marks VII-VII in  FIG. 6 , and  FIG. 8  is a sectional view as seen in a direction of arrow marks VIII-VIII in  FIG. 6 . 
     This measuring instrument for a vehicle is a combination meter in which a speed meter section, a fuel meter section, a water temperature meter section, a gear position section, etc. are integrated, and includes, as shown in  FIG. 5 , a body case  110 , a light guide member  120  which is provided at a surface side of the body case  110 , a dial plate  130  which is arranged at a surface side of this light guide member  120 , and a pointer  140  which rotates on the surface of this dial plate  130 . Moreover, this meter has a movement  150  which is arranged at a back face side of the body case  110  for rotating the pointer  140 , a circuit board  160 , a light source L which is mounted on the circuit board  160 , and so on. 
     In the speed meter section of the dial plate  130 , there are provided a scale design  131  which is formed in a circular arrangement along a rotation direction of the pointer  140 , a warning design  133 , and so on. These designs  131 ,  133  are so adapted as to be lit up with an illuminating light from the back face side. 
     The light guide member  120  mainly illuminates the scale design  131  of the dial plate  130 . As shown in detail in  FIG. 6 , the light guide member  120  has a flat plate portion  121  in a shape of a semicircular disc corresponding to the speed meter section of the dial plate  130 , a pointer shaft insertion hole  125  arranged at a center of the semicircular shape, light receiving portions  122  in a shape of conical wall arranged near the pointer shaft insertion hole  125 , which will be described below, a through hole  123  provided corresponding to the warning design  133 , three triangular holes  126  arranged between the pointer shaft insertion hole  125  and the light receiving portions  122 , and light guide paths  127  interposed between two of the three triangular holes  126  thereby to guide the light which has been reflected by the light receiving portions  122  to a reflecting face  129  around the pointer shaft insertion hole  125 . The reflecting face  129  around the pointer shaft insertion hole  125  performs a function of lighting up the pointer  140 , by introducing an incident light to a light receptive face in a base part of the pointer  140 , as its light path is shown in  FIG. 8 . 
     The light receiving portion  122  is a part for performing a function of receiving a light from a spot-like light source L (hereinafter referred to as a point light source=LED) which is arranged so as to be opposed to the light receiving face  122   a  at a back face side thereof, and radially diffusing the light toward the flat plate portion  121 . As shown in  FIG. 7 , the light receiving portion  122  includes a projected part in a truncated conical shape which is projected toward the back face side of the flat plate portion  121 , and a recess in a conical shape is concentrically formed inside the truncated conical shape to be dented from a surface side of the flat plate portion  121 . In this manner, the light receiving face  122   a  is formed on a top face of the projected part in the truncated conical shape, and reflecting faces  122   b ,  122   c ,  122   d ,  122   e  are formed on conical faces outside and inside the projected part. In this prior art, an angle θ 1  of an inside conical face and an angle θ 2  of an outside conical face are set to be stepwise varied in such a manner that inclination angles of the reflecting faces  122   b ,  122   c ,  122   d ,  122   e  may approach to that of the flat face plate  121 , as approaching to the flat plate portion  121 . 
     Moreover, as shown in  FIG. 5 , the body case  110  is provided with a light guide member containing part  111  for containing the light guide member  120  at a surface side thereof. Dented parts  112  for containing the light receiving portions  122 , a triangular tube part  113  to be fitted to the through hole  123  in the light guide member  120 , and a pointer shaft hole  115  for passing the pointer shaft therethrough are formed in the light guide member containing part  111 . Then, the back face of the light guide member  120  is contained in the light guide member containing part  111 , the light receiving portions  122  of the light guide member  120  are contained in the dented parts  112 , and the triangular tube part  113  to which a light of another point light source is introduced is fitted into the through hole  123  in the light guide member  120 . 
     Because the measuring instrument is constructed as described above, the light R 1  from the point light source L enters into the light guide member  120  from the light receiving face  122   a  of the light receiving portion  122 , as shown in  FIG. 8 , and then, radially guided to the flat plate portion  121  sequentially repeating reflections on the reflecting faces  122   b ,  122   c ,  122   d ,  122   e , whereby the scale design  131  of the dial plate  130  is illuminated from the back face side. 
     CITATION LIST 
     Patent Literature 
     
         
         [PTL 1] JP-A-2004-354072 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     The above described conventional light guide member  120  is provided with the light receiving portion  122  in a shape of conical wall, and the light from the point light source L is radially diffused from the light receiving portion  122  toward the flat plate portion  121 . However, there are some cases where unevenness in brightness and luminance is observed particularly in a peripheral edge part of the flat plate portion  121 , and in such cases, it has been desired to improve the light guide member. Also, it is desired that some characters at specified positions in the scale design  131  are brightly illuminated to enhance an appearance of the measuring instrument, and there has been a request to improve the light guide member so that such desire can be realized. 
     The invention has been made in view of the above described circumstances, and it is an object of the invention to provide a light guide member of a measuring instrument for a vehicle, in which brightness of a peripheral edge part of the light guide member which is particularly important in case of illuminating a scale design can be sufficiently enhanced, and at the same time, unevenness of brightness and luminance can be improved, and to provide the measuring instrument for a vehicle employing the light guide member. 
     Solution to Problem 
     In order to achieve the above object, according to the present invention, there is provided a measuring instrument, comprising 
     a light source; 
     a dial plate which has a scale design; and 
     a light guide member which is provided between the light source and the dial plate, and guides a light received from the light source to the dial plate, wherein the light guide member having a first face that faces to the dial plate and a second face that is opposite to the first face, 
     wherein the light guide member includes a light receiving portion for receiving the light from the light source, and a flat plate portion for irradiating the light transmitted from the light receiving portion to the dial plate; 
     wherein the scale design is arranged in a circular shape around the light source in view from an opposite side of the light source with respect to the dial plate; 
     Wherein the flat plane portion includes a thick wall section that is positioned at a vicinity of the scale design, and a thin wall section that is provided so as to be extended from the thick wall section in a direction away from the light source, the thick wall section is greater in thickness than the thin wall section in a direction perpendicular to the dial place; and 
     Wherein a boundary end face which is connected to a region of the thick wall section and a region of the thin wall section in the second face of the light guide member reflects the light transmitted in the light guide member from the light receiving portion to irradiate the scale design. 
     Preferably, a plane which is defined by the region of the thin wall section in the second face of the light guide member and the boundary end face has a substantially triangular shape. An apex of the substantially triangular shape is set at one position of a peripheral edge of the thick wall section, and a bottom side of the substantially triangular shape is set at a peripheral edge of the thin wail section. 
     Preferably, a hole in a substantially triangular shape is formed in vicinity of the light receiving portion. One apex of the triangular shape of the hole is positioned between a side of the triangular shape connecting two other apexes and the light source. 
     Preferably, a hole is formed in the thick wall section of the light guide member, the hole passing through from the first face to the second face of the light guide member. A side face which connects the first face and the second face for defining the hole reflects the light transmitted in the light guide member from the light receiving portion to irradiate the scale design. 
     According to the light guide member of the measuring instrument having the above structure, the light from the point light source can be radially diffused toward the flat plate portion by the light receiving portion. Moreover, a part of the light diffused in the flat plate portion can be guided to the thin wall section, and at the same time, the remaining light is reflected by the reflecting face defined by the boundary end face, whereby the light can be guided toward the designs on the dial plate which is positioned near the thick wall section. In short, it is possible to increase an amount of the light around the thick wall section by the reflecting face defined by the boundary end face, while an amount of the light in the thin wall section is reduced. As the results, according to specification of the light guide member, a position to be brilliantly illuminated can be easily and brilliantly illuminated, and sensuous unevenness of brightness and luminance can be improved. Moreover, it is possible to regulate unevenness of luminance, by changing a thickness of the thin wall section and an angle of the reflecting face defined by the boundary end face. 
     According to the light guide member of the measuring instrument having the above structure, it is possible to adjust the brightness around the thick wall section, by appropriately changing the shape of the boundary end face. 
     According to the light guide member of the measuring instrument for a vehicle having the above structure, it is possible to adjust the brightness around the thick wall section, by appropriately changing the shape of the boundary end face. 
     Advantageous Effects of Invention 
     According to the invention, it is possible to sufficiently enhance the brightness in the peripheral edge part of the light guide member which is important particularly in case of illuminating the scale design, and at the same time, it is possible to improve unevenness of brightness and luminance. 
     The invention has been briefly described, hereinabove. Details of the invention will be further made clear, by reading the “Description of Embodiments” section which will be described below, referring to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view showing a structure of a light guide member in an embodiment of the invention, as seen from a surface side. 
         FIG. 2A  is a sectional view as seen in a direction of arrow marks IIa-IIa in  FIG. 1 . 
         FIG. 2B  is a sectional view as seen in a direction of arrow marks IIb-IIb in  FIG. 1 . 
         FIG. 3A  is a perspective view showing the structure of the light guide member as seen from a back face side. 
         FIG. 3B  is an enlarged view of an encircled part IIIb in  FIG. 3A . 
         FIGS. 4A and 4B  are views showing an advance of a light in case where a triangular hole is not present,  FIG. 4A  showing a perspective view of the structure of the light guide member as seen from the surface side, and  FIG. 4B  showing an enlarged view of an encircled part IVb in  FIG. 4A . 
         FIG. 5  is an exploded perspective view showing a schematic structure of a conventional measuring instrument for a vehicle which is disclosed in Patent Document 1. 
         FIG. 6  is a plan view showing a light guide member in the measuring instrument which is taken out therefrom. 
         FIG. 7  is a sectional view as seen in a direction of arrow marks VII-VII in  FIG. 6 . 
         FIG. 8  is a sectional view as seen in a direction of arrow marks VIII-VIII in  FIG. 6 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Now, a preferred embodiment according to the invention will be described in detail, referring to the drawings. 
       FIG. 1  is a plan view showing a structure of a light guide member as seen from a surface side (a side where a dial plate of a measuring instrument for a vehicle, which will be described below, is positioned),  FIG. 2A  is a sectional view as seen in a direction of arrow marks IIa-IIa in  FIG. 1 ,  FIG. 2B  is a sectional view as seen in a direction of arrow marks IIb-IIb in  FIG. 1 ,  FIG. 3A  is a perspective view of the structure of the light guide member as seen from a back face side (a side where a light source of the measuring instrument for a vehicle, which will be described below, is positioned),  FIG. 3B  is an enlarged view of an encircled part IIIb in  FIG. 3A ,  FIGS. 4A and 4B  are views showing a manner how a light advances in case where a triangular hole is not present.  FIG. 4A  is a perspective view of the structure of the light guide member as seen from the surface side, and  FIG. 4B  is an enlarged view of an encircled part IVb in  FIG. 4A . 
     The measuring instrument for a vehicle to which a light guide member  20  is applied is a speed meter section of a combination meter as shown in  FIG. 5 . The measuring instrument for a vehicle includes a case (not particularly shown), a dial plate  130  (See  FIG. 2 ) provided at a surface side of the case and having a scale design  131  (See  FIG. 3 ) which is arranged in a circular shape around a light source L, a pointer which rotates around the light source L for indicating the scale design  131  in a circular arrangement at the surface side of the dial plate  130 , a light guide member which is provided between the case and the dial plate  130 , a circuit board which is arranged at a back face side of the case, and a light source L which is mounted on the circuit board for entering an illumination light to a light receiving face of the light guide member through an opening formed in the case. In this description, the light guide member  20  in the embodiment of the invention, which will be described below, is used as the light guide member, and an LED is used as the spot-like light source (a point light source). 
     As shown in  FIGS. 1 and 2 , the light guide member  20  is positioned between the light source L and the dial plate  130 , and guides a light received from the light source L to the back face of the dial plate  130 . The light guide member  20  includes light receiving portions  22  for receiving the light from the point light source L which is arranged so as to be opposed to a light receiving face  22   a  at a back face side of the light guide member itself, and a flat plate portion  21  in a circular shape which is arranged near a back face of the scale design  131  of the dial plate  130  in a circular arrangement. The light transmitted from the point light source L to the light receiving portions  22  is radially diffused toward the flat plate portion  21 , and further, the light traversing the flat plate portion  21  is irradiated to the back face of the dial plate  130 . A face of the flat plate portion  21  in contact with the back face of the dial plate is formed as a delustered face, for example, for enabling the light to be easily diffused. 
     The light receiving portion  22  is arranged on an inner peripheral part of the flat plate portion  21  in a circular shape. As shown in  FIG. 2 , The light receiving portion  22  has a projected part in a truncated conical shape projected toward the back face side of the flat plate portion  21 , and a recess in a conical shape concentrically formed inside the truncated conical shape from a surface side of the flat plate portion  21 . The light receiving face  22   a  is formed on a top face of the projected part in the truncated conical shape, and reflecting faces  22   b ,  22   d ,  22   e ,  22   f  are formed on conical faces outside and inside the recess. In this embodiment, the outside conical face (the reflecting face  22   b ) is at a constant angle, but an angle of the inside conical face (the reflecting faces  22   d ,  22   e ,  22   f ) is stepwise varied so as to gradually approach to an angle of the flat plate portion  21 . 
     As shown in  FIG. 1 , a plurality of the light receiving portions  22  each having the above described structure are provided on an inner periphery of the flat plate portion  21  in the circular shape, at an interval in a circumferential direction. These light receiving portions  22  are formed by cutting off those regions of the flat plate portion  21  in the circular shape which are positioned at the inner peripheral side toward the center, and planes of the regions which have been cut off serve as the reflecting faces  22   d ,  22   e ,  22   f.    
     Because the light receiving portion  22  having the above described structure is formed in the light guide member  20 , the light from the point light source L is received by the light receiving face  22   a  of the light receiving portion  22 , and radially guided to the flat plate portion  21 , while being repeatedly reflected by the reflecting faces  22   b ,  22   d ,  22   e ,  22   f . In this manner, the scale design  131  of the dial plate  130  can be illuminated from the back face side. 
     In this light guide member  20 , as shown in  FIG. 1  and  FIG. 2A , cut-outs  25  in a planar shape are formed in a peripheral edge area of the flat plate portion  21 , by cutting off the back face of the flat plate portion  21  toward the peripheral edge area. Consequently, the flat plate portion  21  has thick wall sections  25   q  which are positioned near the inner periphery of the flat plate portion  21 , and thin wall sections  25   p  having a thinner wall thickness than the thick wall sections and positioned near the outer periphery of the flat plate portion  21 . The thick wall sections  25   q  are positioned near the scale design  131  of the dial plate  130 , while the thin wall sections  25   p  are formed so as to extend from the thick wall sections  25   q  in a direction away from the point light source L. 
     Because the thin wall section  25   p  and the thick wall section  25   q  are different in thickness from each other, an inclined face is formed in a boundary which connects a back face of the thin wall section  25   p  and a back face of the thick wall section  25   q . This inclined face (sometimes referred to as a boundary end face  25   a ) serves as a reflecting face for reflecting the light which has been transmitted from the light receiving portion  22  to the thick wall section  25   q  of the flat plate portion  21 . Inclination or a shape of the boundary end face  25   a  is appropriately designed so that the light reflected by the reflecting face may be favorably irradiated to the scale design. For example, in this embodiment, a plane including the thin wall section  25   p  and the boundary end face  25   a  which are formed by the cut-out  25  in the planar shape has a substantially triangular shape, setting an apex at one position of a peripheral edge of the thick wall section  25   q , and setting a base at a peripheral edge of the thin wall section  25   p . The boundary end face  25   a  in the triangular shape serves as the reflecting face. In this embodiment, a plurality of the cut-outs  25  as described above are provided on the outer periphery of the flat plate portion  21  at an interval in the circumferential direction. 
     Moreover, triangular holes  26 ,  27  are formed in the flat plate portion  21 . Inner faces which define the holes  26 ,  27  serve as reflecting faces for changing a direction of the light which is transmitted through the flat plate portion  21  to other directions. In this case, the hole  26  is formed in a shape of a substantially triangular pyramid in the flat plate portion  21  in such a manner that one apex of a bottom face of the hole  26  in a triangular shape which is formed on the same plane as the back face of the thick wall section  25   q  so as to be positioned between a bottom side connecting the remaining two apexes of the bottom face of the hole  26  and the point light source L. Moreover, the hole  27  in a substantially triangular shape is formed near the light receiving portion  22  in such a manner that one apex of the triangular shape of the hole  27  is positioned between a side connecting the remaining two apexes and the light source L corresponding to the light receiving portion  22 . 
     According to the light guide member  20  having the above described structure, the light R from the point light source L can be radially diffused to the flat plate portion  21  by the light receiving portion  22 . Particularly, because a plurality of the light receiving portions  22  are provided at an interval in the circumferential direction of the flat plate portion  21  in the circular shape, the light can be evenly supplied to an entirety of the flat plate portion  21  in the circular shape. In addition, because those areas of the light receiving portions  22  positioned at the inner peripheral side of the flat plate portion  21  are cut out, the light receiving portions  22  are formed in such a shape that only a part of an angular range in the circumferential direction is left, and the planes which have been cut serve as the reflecting faces. Therefore, most of the light which is reflected toward the inner peripheral side of the flat plate portion  21  can be reflected again to the peripheral edge area of the flat plate portion  21 , and hence, it is possible to increase brightness of an object part to be illuminated, while useless light is decreased. 
     Moreover, a part of the light which is diffused in the flat plate portion  21  can be guided to the thin wall sections  25   p , as shown in  FIG. 2A , and the remaining light is reflected by the reflecting face defined by the boundary end face  25   a , as shown in  FIGS. 3A and 3B , whereby the light can be guided toward the design  131 . 
     It is possible to increase an amount of the light in the thick wall section  25   q  by the reflecting face defined by the boundary end face  25   a , while an amount of the light to be transmitted to the thin wall section  25   p  is reduced. As the results, according to specification (shape, quality of material) of the light guide member  20 , a position to be brilliantly illuminated (for example, the position where the design is provided) can be effectively brightly lit up, and sensuous unevenness of brightness and luminance can be improved. Moreover, it is possible to regulate unevenness of luminance, by changing a thickness of the thin wall section  25   p  and an angle of the reflecting face defined by the boundary end face  25   a.    
     Further, according to this light guide member  20 , it is possible to adjust the brightness at a desired position of the dial plate, by appropriately designing a shape of the planar cut-out  25  (a triangular shape in this embodiment), and by adjusting the amount of the light which is reflected by the reflecting face, according to the shape of the cut-out  25 . 
     Still further, according to this light guide member  20 , it is possible to convert the light which is advancing in a radial direction inside the light guide member  20  to other directions, due to presence of the holes  26 ,  27 . For example, in case where the holes are not present, as shown in  FIG. 4 , the light from the light receiving portion  22  advances only to the peripheral edge area of the flat plate portion  21 . On the other hand, in case where the hole  26  is present as shown in  FIG. 3 , the light can be converted to other directions, because the inner face of the hole  26  serves as the reflecting face, and hence, the required scale design can be brightly illuminated. 
     Particularly, because the holes  26 ,  27  are formed in a substantially triangular shape in section, the light can be reflected in a plurality of directions, and hence, the required design can be brightly illuminated. 
     Therefore, by incorporating this light guide member  20  into the measuring instrument, it is possible to brightly illuminate specified portions of the dial plate  130  which are likely to be dark, and hence, it is possible to improve unevenness of the brightness and luminance, and to enhance an appearance. 
     It is to be noted that the invention is not limited to the above described embodiment, but various modifications, improvements and so on can be appropriately made. Further, material, shape, size, number, positions to be arranged and so on of the respective constituent elements in the above described embodiment are not limited, but can be optionally selected, provided that the invention can be achieved. 
     The present application is based on Japanese Patent Application No. 2008-295911 filed on Nov. 19, 2008, the contents of which are incorporated herein for reference. 
     REFERENCE SIGNS LIST 
     
         
           20  Light guide member 
           21  Flat plate portion 
           22  Light receiving portion 
           22   a  Light receiving face 
           22   b ,  22   d ,  22   e ,  22   f  Reflecting face 
           25   a  Boundary end face 
           25   p  Thin wall section 
           25   q  Thick wall section 
           26 ,  27  Hole 
           130  Dial plate 
           131  Scale design