Patent Publication Number: US-2023145552-A1

Title: Vehicle wiring system, optical coupler, and method of constructing vehicle wiring system

Description:
TECHNICAL FIELD 
     The present disclosure relates to a vehicle wiring system, an optical coupler, and a method of constructing a vehicle wiring system. 
     This application claims priority based on Japanese Patent Application No. 2020-078326 filed on Apr. 27, 2020, and the entire contents of the Japanese patent application are incorporated herein by reference. 
     BACKGROUND ART 
     Patent Literature (PTL 1) discloses a vehicle wiring system as follows. That is, the vehicle wiring system is a vehicle wiring system mounted in a vehicle, and includes a master functional unit and a plurality of slave functional units. The plurality of slave functional units is configured to transmit an uplink communication signal to the master functional unit via at least a common optical fiber. 
     Citation List 
     Patent Literature 
     PTL 1: International Patent Publication No. WO2019/111447 
     SUMMARY OF INVENTION 
     A vehicle wiring system according to the present disclosure includes a plurality of functional units to be mounted in a vehicle, an optical transmission line that is wired between the functional units and configured to transmit an optical signal of the functional units, an electric wire harness that is provided, in a partial section of the optical transmission line, together with the optical transmission line in a state of being integrated with the optical transmission line, and an optical coupler that is disposed in a portion of the optical transmission line other than the section and constitutes the optical transmission line. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram illustrating an example of a configuration of a vehicle wiring system according to a first embodiment of the present disclosure. 
         FIG.  2    is a cross-sectional view illustrating an example of a configuration of an optical fiber cable in the vehicle wiring system according to the first embodiment of the present disclosure. 
         FIG.  3    is a front view illustrating examples of optical connectors and an optical coupler according to the first embodiment of the present disclosure. 
         FIG.  4    is a cross-sectional view taken along line IV-IV in  FIG.  3   . 
         FIG.  5    is a cross-sectional view of an optical coupler and a window of a vehicle according to a first modification of the first embodiment of the present disclosure. 
         FIG.  6    is a diagram illustrating an example of a configuration of a vehicle wiring system according to a second modification of the first embodiment of the present disclosure. 
         FIG.  7    is a diagram illustrating an example of a configuration of a vehicle wiring system according to a second embodiment of the present disclosure. 
         FIG.  8    is a diagram illustrating an example of a configuration of the vehicle wiring system according to a modification of the second embodiment of the present disclosure. 
         FIG.  9    is a diagram illustrating an example of a configuration of a vehicle wiring system according to a third embodiment of the present disclosure. 
         FIG.  10    is a cross-sectional view taken along line X-X in  FIG.  9   . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Conventionally, in order to cope with increasing data communication traffic in a vehicle, a technique using an optical fiber in a vehicle wiring system has been proposed. 
     Problems to Be Solved by Present Disclosure 
     When an optical coupler is used in a vehicle wiring system, it is desirable to have a technique that can suppress breakage of the optical coupler. 
     The present disclosure has been made to solve the above-described problem, and an object of the present disclosure is to provide a vehicle wiring system, an optical coupler, and a method of constructing a vehicle wiring system that can suppress the breakage of the optical coupler in an in-vehicle network using the optical coupler. 
     Advantageous Effects of Present Disclosure 
     According to the present disclosure, it is possible to suppress breakage of an optical coupler in an in-vehicle network using the optical coupler. 
     The present disclosure may be realized as a semiconductor integrated circuit that builds a part or all of a vehicle wiring system. 
     Description of Embodiments of Present Disclosure 
     First, the contents of embodiments according to the present disclosure will be listed and described. 
     (1) A vehicle wiring system according to an embodiment of the present disclosure includes a plurality of functional units to be mounted in a vehicle, an optical transmission line that is wired between the functional units and configured to transmit an optical signal of the functional units, an electric wire harness that is provided, in a partial section of the optical transmission line, together with the optical transmission line in a state of being integrated with the optical transmission line, and an optical coupler that is disposed in a portion of the optical transmission line other than the section and constitutes a part of the optical transmission line. 
     In General, in wiring processing in a vehicle, an electric wire harness, an optical transmission line, and the like are provided together, and these are bundled. However, since a material of the optical coupler used in the optical transmission line is soft, when the optical coupler is assembled to the electric wire harness, an external force such as bending or twisting is applied to the optical coupler, and the optical coupler is easily broken. On the other hand, a configuration in which the optical coupler is disposed in the portion of the optical transmission line other than the section where the electric wire harness and the optical transmission line are provided together eliminates a need to assemble the optical coupler to the electric wire harness. Therefore, it is possible to suppress breakage of the optical coupler in the in-vehicle network using the optical coupler. 
     (2) The vehicle wiring system may include window glass to be mounted in the vehicle. The optical coupler may be disposed on or in the window glass. 
     When the optical coupler is disposed on or in the window glass of the vehicle, the optical coupler does not need to be assembled to the electric wire harness. Further, disposing the optical coupler on or in the window glass of the vehicle eliminates a need to separately provide a space for disposing the optical coupler, and thus the vehicle wiring system can be space-saving. 
     (3) A window may be constituted by laminated glass having a plurality of layers. The optical coupler may be disposed between the layers. 
     This configuration prevents an occupant or an objects from touching the optical coupler, thereby preventing damage to the optical coupler due to contact. 
     (4) The optical coupler may be disposed along an outer periphery of the window glass. 
     This configuration allows the optical coupler to be disposed along a window frame of the vehicle, thereby shortening wiring sections of optical fiber cables connected to both ends of the optical coupler. 
     (5) The vehicle wiring system may include a mirror to be mounted in the vehicle. The optical coupler may be disposed on the mirror. 
     Disposing the optical coupler on the mirror of the vehicle eliminates a need to separately provide a space for disposing the optical coupler, and thus the vehicle wiring system can be space-saving. 
     (6) The vehicle wiring system may include an interior lighting device to be mounted in the vehicle. The optical coupler may be disposed on the lighting device. 
     Disposing the optical coupler on the lighting device in the vehicle eliminates a need to separately provide a space for disposing the optical coupler. Therefore, disposing the optical coupler on the lighting device in the vehicle allows the vehicle wiring system to be space-saving. 
     (7) The lighting device may be configured to be capable of being disposed in a cockpit of the vehicle. The optical coupler may be disposed on a cover of the lighting device. 
     Disposing the optical coupler on the lighting device in the cockpit of the vehicle allows the vehicle wiring system to be space-saving more efficiently. 
     (8) The vehicle wiring system may include a roof panel and a roof lining to be mounted in the vehicle. The optical coupler may be disposed between the roof panel and the roof lining. 
     When a thick object such as an electric wire harness is disposed between the roof panel and the roof lining of the vehicle, a degree of freedom in roof design of the vehicle is reduced. On the other hand, since the optical coupler is thin, even when the optical coupler is disposed between the roof panel and the roof lining, it is possible to effectively utilize a space where the electric wire harness is not disposed while maintaining the degree of freedom in the roof design. 
     (9) An optical coupler according to an embodiment of the present disclosure is configured to relay an optical signal between functional units to be mounted in a vehicle. The optical coupler includes a transparent body portion and an optical waveguide formed in the body portion and branching in the body portion. 
     With this configuration, even when the optical coupler is disposed on or in, for example, a window or a mirror of a vehicle, since the body portion is transparent, a good field of view can be ensured. In addition, even when the optical coupler is disposed on, for example, a lighting device in a vehicle, the amount of light or the like is less likely to decrease. 
     (10) A method of constructing a vehicle wiring system according to an embodiment of the present disclosure includes preparing a plurality of functional units to be mounted in a vehicle, an optical transmission line, an electric wire harness, and an optical coupler; wiring the optical transmission line between the functional units so as to transmit an optical signal of the functional units; wiring the electric wire harness in a partial section of the optical transmission line so that the electric wire harness is provided together with the optical transmission line in a state of being integrated with the optical transmission line; and disposing the optical coupler in a portion of the optical transmission line other than the section and causing the optical coupler to constitute a part of the optical transmission line. 
     Disposing the optical coupler in the portion of the optical transmission line other than the section in which the optical transmission line is provided together with the electric wire harness eliminates a need to assemble the optical coupler to the electric wire harness. Therefore, it is possible to suppress breakage of the optical coupler in the in-vehicle network using the optical coupler. 
     Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding portions are denoted by the same reference numerals, and description thereof will not be repeated. Further, at least parts of the embodiments described below may be arbitrarily combined. 
     First Embodiment 
       FIG.  1    is a diagram illustrating an example of a configuration of a vehicle wiring system according to a first embodiment of the present disclosure. 
     Referring to  FIG.  1   , a vehicle wiring system  1  is mounted in a vehicle  2 . Vehicle  2  is, for example, a four-wheeled automobile, and includes a window  20 A for a first row of seats, a window  20 B for a second row of seats, and a window  20 C for a third row of seats or for a luggage compartment, on a side surface as structural members of vehicle  2  itself. Windows  20 A and  20 B can be opened and closed, and window  20 C is a fixed window that cannot be opened and closed. Window  20 C is disposed between a C-pillar  24  and a D-pillar  25  of vehicle  2 . Glass (window glass) used for windows  20 A to  20 C is transparent. The term “transparent” as used herein means that a total light transmittance defined in JIS K 7361-1 (1997) is 90% or more. The structural members are members serving as structural bodies that support the vehicle, and are members that constitute parts of vehicle  2  and are at least partially transparent. Hereinafter, the “window glass” is also simply referred to as a “window”. 
     Vehicle wiring system  1  includes an optical transmission line  10  and an electric wire harness  11 . 
     Optical Transmission Line 
     In an example shown in  FIG.  1   , vehicle  2  includes a master functional unit  211  and slave functional units  212  and  213  as functional units  21 . Master functional unit  211  is mounted in an engine room of vehicle  2 . Slave functional units  212  and  213  are mounted in a trunk of vehicle  2 . The master functional unit may be also referred to as a “leader functional unit”, and the slave functional units may be also referred to as “follower functional units”. Optical transmission line  10  is wired between master functional unit  211  and slave functional units  212  and  213 , and transmits an optical signal between master functional unit  211  and slave functional units  212  and  213 . 
     Master functional unit  211  and slave functional units  212  and  213  may be an ECU, a camera, a sensor, or an antenna module. The ECU includes an automatic driving electronic control unit (ECU), a navigation device, a telematics control unit (TCU), a gateway device, and the like. The sensor includes a millimeter-wave sensor, a light detection and ranging (LiDAR), and the like. 
     Optical transmission line  10  connects master functional unit  211  to slave functional units  212  and  213  so as to enable optical communication with each other. In the example shown in  FIG.  1   , an optical communication system is constructed in optical transmission line  10 . The optical communication system may be, for example, a PON (Passive Optical Network) system. The optical communication system may be a system other than the PON system. 
     Optical transmission line  10  includes optical fiber cables  101 ,  102  and  103 , optical connectors  104  and  105 , and an optical coupler  106 . 
     Optical fiber cable  101  extends rearward from master functional unit  211  along an A-pillar  22  and a roof side rail  23  of vehicle  2 . Optical fiber cable  101  is connected to optical connector  104  fixed to a vehicle interior side of C-pillar  24 . Optical fiber cable  102  extends forward from slave functional unit  212  along D-pillar  25  of vehicle  2 . Optical fiber cable  102  is connected to optical connector  105  fixed to a vehicle interior side of D-pillar  25 . Similarly, optical fiber cable  103  extends forward from slave functional unit  213  along D-pillar  25  of vehicle  2 . Optical fiber cable  103  is connected to optical connector  105 . 
     Optical connectors  104  and  105  are fixed to pillars  24  and  25 , respectively, with screwing, a glue or a pressure-sensitive adhesive, for example. Optical connectors  104  and  105  relay an optical signal between master functional unit  211  and slave functional units  212  and  213 . 
     Optical coupler  106  is disposed between optical connectors  104  and  105 , and connected to both of them. That is, optical coupler  106  is disposed in a partial section of optical transmission line  10 . Optical coupler  106  is disposed on a vehicle interior side of window  20 C of vehicle  2 . Optical coupler  106  is fixed to window  20 C with, for example, a glue or a pressure-sensitive adhesive. Optical coupler  106  is disposed in a front-rear direction of vehicle  2  so as to connect C-pillar  24  and D-pillar  25  to each other. 
     Details of Optical Fiber Cable, Optical Connector, and Optical Coupler 
     Hereinafter, optical fiber cables  101 ,  102  and  103 , optical connectors  104  and  105 , and optical coupler  106  will be described in more detail. 
       FIG.  2    is a cross-sectional view illustrating an example of a configuration of an optical fiber cable in the vehicle wiring system according to the first embodiment of the present disclosure. In  FIG.  2   , a cross-section of optical fiber cable  101  is shown. Optical fiber cables  102  and  103  have the same configuration as that of optical fiber cable  101 . 
     Referring to  FIG.  2   , optical fiber cable  101  includes a tension member  101 A, a plurality of optical fibers  101 B, a protective layer  101 C, a wrapping tape  101 D, and a sheath  101 E. 
     The plurality of optical fibers  101 B is disposed around tension member  101 A. Optical fibers  101 B are, for example, optical fiber core wires. Optical fiber cable  101  includes one or more optical fibers  101 B. The number of optical fibers  101 B in optical fiber cable  101  is not limited. Optical fiber cable  101  is not limited to a configuration in which optical fibers  101 B which are optical fiber core wires are accommodated, and may be, for example, a 0.25 mm strand, a 0.9 mm core wire, a tape core wire, or the like. 
     Protective layer  101 C covers the plurality of optical fibers  101 B. Wrapping tape  101 D covers protective layer  101 C. Sheath  101 E covers wrapping tape  101 D. 
       FIG.  3    is a front view illustrating examples of the optical connectors and the optical coupler according to the first embodiment of the present disclosure. 
     Referring to  FIG.  3   , optical connector  104  can connect the optical fibers in optical fiber cable  101 . Optical connector  105  can connect the optical fibers in optical fiber cables  102  and  103 . 
       FIG.  4    is a cross-sectional view taken along line IV-IV in  FIG.  3   . 
     Referring to  FIG.  4   , optical coupler  106  includes a body portion  106 A and an optical waveguide  106 B branching in body portion  106 A. Optical connectors  104  and  105  are connected to both ends of optical coupler  106 . 
     Body portion  106 A has, for example, a rectangular film shape in a plan view. Body portion  106 A is formed of a resin. Optical coupler  106  formed of a resin is compact and flexible. A thickness of body portion  106 A is, for example, 1 mm or less. 
     Body portion  106 A is transparent. The term “transparent” as used herein means that a total light transmittance defined in JIS K 7361-1 (1997) is 90% or more. 
     Optical waveguide  106 B is formed in body portion  106 A so as to extend between optical connector  104  and optical connector  105 . Optical waveguide  106 B has a branching portion. Optical waveguide  106 B includes, for example, a first end  106 C connected to optical connector  104 , a second end  106 D connected to optical connector  105 , and a third end  106 E connected to optical connector  105 . Optical waveguide  106 B is formed in body portion  106 A by a photolithography technique or the like. 
     Optical connector  104  receives an optical signal from optical fiber cable  101 . The optical signal received by optical connector  104  from optical fiber cable  101  is output to optical fiber cables  102  and  103  via optical waveguide  106 B in optical coupler  106  and optical connector  105 . That is, the optical signal received by optical connector  104  from optical fiber cable  101  is branched by optical coupler  106  and output to optical fiber cables  102  and  103 . 
     Optical connector  105  receives optical signals from optical fiber cables  102  and  103 . The optical signal received by optical connector  105  from optical fiber cable  102  is output to optical fiber cable  101  via optical waveguide  106 B in optical coupler  106  and optical connector  104 . Further, the optical signal received by optical connector  105  from optical fiber cable  103  is output to optical fiber cable  101  via optical waveguide  106 B in optical coupler  106  and optical connector  104 . That is, the optical signals received by optical connector  105  from optical fiber cables  102  and  103  are combined by optical coupler  106  and output to optical fiber cable  101 . 
     Electric Wire Harness 
     Referring to  FIG.  1   , electric wire harness  11  includes a cable, a terminal, a connector, and the like. Electric wire harness  11  extends rearward from a battery  26  along A-pillar  22 , roof side rail  23 , and D-pillar  25  in vehicle  2 . Electric wire harness  11  connects master functional unit  211  and slave functional units  212  and  213  to battery  26 . Electric power supplied from battery  26  is supplied to master functional unit  211  and slave functional units  212  and  213  via electric wire harness  11 . 
     Since electric wire harness  11  includes a plurality of bundled cables, electric wire harness  11  is thicker than optical transmission line  10 , and is, for example, 20 mm to 100 mm in thickness. Electric wire harness  11  may be used for transmitting and receiving an electric signal in addition to supplying electric power. Electric wire harness  11  is used for at least one of supplying electric power or transmitting and receiving the electric signal. 
     Electric wire harness  11  is provided together with optical fiber cable  101  in a partial section between master functional unit  211  and optical connector  104 . Electric wire harness  11  is provided together with optical fiber cables  102  and  103  in a section from slave functional units  212  and  213  to optical connector  105 . In these sections, electric wire harness  11  is bundled with, for example, optical fiber cables  101 ,  102  and  103  by a cable tie  40 . That is, in these sections, electric wire harness  11  is provided together with optical fiber cables  101 ,  102  and  103  in a state of being integrated with optical fiber cables  101 ,  102  and  103  by cable tie  40 . 
     On the other hand, electric wire harness  11  is not provided together with optical coupler  106  in a state of being integrated with optical coupler  106 . That is, electric wire harness  11  includes a section where electric wire harness  11  is provided together with optical transmission line  10  in a state of being integrated with optical transmission line  10  in a portion of optical transmission line  10  other than a section in which optical coupler  106  is disposed. Here, the phrase “provided together in a state being integrated” includes a state in which electric wire harness  11  and optical transmission line  10  are integrated with each other by one tying member  40  and a state in which electric wire harness  11  and optical transmission line  10  are fixed by one fixing member  40 . 
     More specifically, electric wire harness  11  extends from master functional unit  211  toward a rear of vehicle  2  in a state of being bundled with optical fiber cable  101  and is separated from optical fiber cable  101  just before optical connector  104 . 
     After separating from optical fiber cable  101 , electric wire harness  11  extends to a rear end of roof side rail  23  and is directed toward slave functional units  212  and  213  along D-pillar  25 . Electric wire harness  11  is merged and bundled with optical fiber cables  102  and  103  in D-pillar  25 . 
     Communication Operation Using Vehicle Wiring System 
     Next, a communication method using vehicle wiring system  1  will be described. Hereinafter, optical communication using optical transmission line  10  will be described, and electric communication using electric wire harness  11  will not be described in detail since it is well-known. 
     Hereinafter, a direction from slave functional units  212  and  213  to master functional unit  211  is referred to as an uplink direction, and a direction from master functional unit  211  to slave functional units  212  and  213  is referred to as a downlink direction. The optical communication system using optical transmission line  10  is, for example, a TDM-PON system. Specifically, time division multiple access (TDMA) is used in the uplink direction, and time division multiplexing (TDM) is used in the downlink direction. 
     Each of slave functional units  212  and  213  can transmit an upstream optical signal including a upstream communication signal such as a frame to master functional unit  211  via a corresponding one of optical fiber cables  102  and  103 , optical coupler  106 , optical connectors  105  and  104 , and optical fiber cable  101 . In addition, master functional unit  211  can transmit a downstream optical signal including a downstream communication signal such as a frame to a corresponding one of slave functional units  212  and  213  via optical fiber cable  101 , optical coupler  106 , optical connectors  104  and  105 , and the respective optical fiber cables  102  and  103 . 
     Each of master functional unit  211  and slave functional units  212  and  213  includes an optical transceiver (not shown). The optical transceiver in master functional unit  211  is connected to optical fiber cable  101 . The optical transceiver receives, for example, an upstream optical signal in a 1280 nm band from optical fiber cable  101 , and converts the received upstream optical signal into an electric signal to output the electric signal to a processing unit (not shown). The optical transceiver in master functional unit  211  receives an electric signal from the processing unit (not shown), and converts the received electric signal into a downstream optical signal in a different wavelength band, for example, a 1570 nm band to output the downstream optical signal to optical fiber cable  101 . 
     The optical transceiver in slave functional unit  212  is connected to optical fiber cable  102 . The optical transceiver in slave functional unit  213  is connected to optical fiber cable  103 . Each of the optical transceivers receives a downstream optical signal in the 1570 nm band from optical fiber cables  102  and  103 , and converts the received downstream optical signal into an electric signal to output the electric signal to the processing unit (not shown). The optical transceivers in slave functional units  212  and  213  receive electric signals from the processing unit, and convert the received electric signals into uplink optical signals, for example, in the 1280 nm band to output the uplink optical signals to the respective optical fiber cables  102  and  103 . 
     In the optical communication using vehicle wiring system  1 , not only the TDMA but also wavelength division multiplexing (WDM) suitable for communication with a larger amount of data may be used in the uplink direction. In this case, the plurality of slave functional units  212  and  213  transmits uplink optical signals having different wavelengths from each other. 
     Further, in the optical communication using vehicle wiring system  1 , not only the TDM but also the WDM suitable for communication with a larger amount of data may be used in the downlink direction. In this case, master functional unit  211  transmits downstream optical signals having different wavelengths to the respective slave functional units  212  and  213 . 
     In the optical communication using vehicle wiring system  1 , not only the TDMA but also code division multiplexing (CDM) suitable for communication with a larger amount of data may be used in the uplink direction. In this case, the plurality of slave functional units  212  and  213  transmits uplink optical signals including communication signals spread by different spreading codes from each other. 
     Further, in the optical communication using vehicle wiring system  1 , not only the TDM but also the CDM suitable for communication with a larger amount of data may be used in the downlink direction. In this case, master functional unit  211  transmits downstream optical signals including communication signals spread by different spreading codes from each other to the respective slave functional units  212  and  213 . 
     In addition, in the optical communication using vehicle wiring system  1 , frequency division multiplexing (FDM), space division multiplexing (SDM), time and wavelength division multiplexing (TWDM), or the like which is suitable for communication with a larger amount of data may be used. 
     When an optical coupler is used in a vehicle wiring system, it is desired to suppress breakage of the optical coupler. 
     Electric wire harness  11  is disposed inside a vehicle to transmit electricity to functional unit  21 . When optical transmission line  10  is wired from master functional unit  211  to slave functional units  212  and  213  in the vehicle, it is usually necessary to assemble optical transmission line  10  to electric wire harness  11 . However, since optical coupler  106  in optical transmission line  10  is formed of a soft material, it is easily broken during assembly. 
     On the other hand, in vehicle wiring system  1  according to the first embodiment, optical coupler  106  is not assembled to electric wire harness  11 , but is disposed on window  20 C of vehicle  2 . Therefore, even when optical coupler  106  is used in vehicle wiring system  1 , it is possible to suppress breakage of optical coupler  106 . Since the electric wire harness has a certain thickness, it is difficult to wire the electric wire harness on the window of the vehicle. 
     When electric wire harness  11  is wired along A-pillar  22 , roof side rail  23 , and D-pillar  25  in vehicle  2  as in vehicle wiring system  1  according to the first embodiment, optical coupler  106  may be disposed above ½ of a height of window  20 C in order to facilitate the wiring. Further, optical coupler  106  may be disposed above ¼ of the height of window  20 C. 
     Modification  1   
       FIG.  5    is a cross-sectional view of an optical coupler and a window of a vehicle according to a first modification of the first embodiment of the present disclosure.  FIG.  5    shows a cross section perpendicular to a front-rear direction of vehicle  2 . 
     Referring to  FIG.  5   , a window  20 C 1  is constituted by laminated glass having a plurality of layers. Specifically, window  20 C 1  includes two sheet glasses  20 C 2  and an interlayer  20 C 3 . Two sheet glasses  20 C 2  are disposed at an interval. Interlayer  20 C 3  is formed between two sheet glasses  20 C 2 . Interlayer  20 C 3  may be filled with air, argon gas, or the like, or may be in vacuum, and is not particularly limited. 
     Optical coupler  106  is disposed between the layers of the laminated glass. Specifically, optical coupler  106  is disposed in interlayer  20 C 3 , and is fixed to one of two sheet glasses  20 C 2  with a glue, a pressure-sensitive adhesive, or the like. 
     With this a configuration, optical coupler  106  is disposed inside window  20 C 1 , so that even when an occupant or an object touches window  20 C 1 , the occupant or the object does not touch optical coupler  106 . Therefore, damage to optical coupler  106  due to contact with optical coupler  106  is suppressed. 
     Modification  2   
       FIG.  6    is a diagram illustrating an example of a configuration of a vehicle wiring system according to a second modification of the first embodiment of the present disclosure. 
     Referring to  FIG.  6   , optical coupler  106  is disposed along at least a portion of a frame (outer periphery) of window  20 C of vehicle  2 . More specifically, optical coupler  106  extends rearward in the front-rear direction of vehicle  2  from optical connector  104 , and is bent just before D-pillar  25  so as to extend along D-pillar  25 . Optical coupler  106  extending along D-pillar  25  is bent in the front-rear direction of vehicle  2  just before a beltline  27  of vehicle  2  and is connected to optical connector  105 . That is, optical coupler  106  is disposed so as to pass through a portion along roof side rail  23  and a portion along D-pillar  25  in the frame of window  20 C. 
     In this case, optical connector  104  is disposed at a relatively high position, that is, in a vicinity of roof side rail  23  in C-pillar  24 . On the other hand, optical connector  105  is disposed at a relatively low position, that is, in a vicinity of beltline  27  in D-pillar  25 . As described above, in a side view of vehicle  2 , optical connector  105  is disposed below optical connector  104  and is disposed at a position closer to slave functional units  212  and  213 . 
     With this configuration, a distance between optical connector  105  and slave functional units  212  and  213  becomes short, it is possible to shorten wiring sections of optical fiber cables  102  and  103  that connect optical connector  105  and slave functional units  212  and  213  to each other, thereby saving wires. 
     In addition, it is not necessary to pass optical fiber cables  102  and  103  through the entire region of D-pillar  25  or most of the region, thereby making D-pillar  25  thinner and vehicle  2  lighter. 
     Furthermore, disposing optical coupler  106  along the frame of window  20 C allows a field of view of the central portion of window  20 C to be secured, and a decrease in the field of view of window  20 C due to optical coupler  106  to be minimized. However, optical coupler  106  may be disposed so as to pass through the central portion of window  20 C. 
     Second Embodiment 
       FIG.  7    is a diagram illustrating an example of a configuration of a vehicle wiring system according to a second embodiment of the present disclosure. The vehicle wiring system according to the second embodiment is different from that of the first embodiment in that optical coupler  106  is disposed on a mirror of vehicle  2 . The vehicle wiring system according to the second embodiment is the same as vehicle wiring system  1  according to the first embodiment except for the contents described below. 
     In an example shown in  FIG.  7   , optical coupler  106  is disposed on a room mirror  281 . Optical coupler  106  is disposed on a left side of the center of room mirror  281  in a left-right direction. Further, optical coupler  106  may be disposed near a left end of room mirror  281 . However, optical coupler  106  may be disposed on a right side of the center of room mirror  281  in the left-right direction. Optical coupler  106  is disposed so as to connect an upper portion and a lower portion of a frame  282  of room mirror  281 . Since an electric wire harness has a certain thickness, it is difficult to wire the electric wire harness on the mirror of the vehicle. 
     Optical connector  104  is disposed in the upper portion of frame  282 . Optical connector  105  is disposed in the lower portion of frame  282 . Optical connectors  104  and  105  are fixed to each position of frame  282  with, for example, a glue, a pressure-sensitive adhesive or the like. 
     In  FIG.  7   , the master functional unit and the slave functional units are not shown. The master functional unit is disposed on the floor of the vehicle, for example, and the two slave functional units are each disposed in a bonnet and a roof  29  of the vehicle. 
     The master functional unit may be, for example, an ECU for advanced driver assistance systems (ADAS), and the two slave functional units may be a sensor and a roof antenna module. 
     Optical fiber cable  101  passes from the master functional unit through the A-pillar (not shown), roof  29 , a room mirror stay  283 , and the upper portion of frame  282  to be connected to optical connector  104 . Optical fiber cable  102  passes from the slave functional unit disposed in the bonnet through the A-pillar, roof  29 , room mirror stay  283 , and the upper, right, and lower portions of frame  282  to be connected to optical connector  105 . Optical fiber cable  103  passes through the slave functional unit disposed in roof  29 , room mirror stay  283 , and the upper, right, and lower portions of frame  282  to be connected to optical connector  105 . 
     Electric wire harness  11  connects a battery to the slave functional unit disposed in roof  29 . Electric wire harness  11  extends from the battery along the A-pillar and is wired to roof  29 . 
     Electric wire harness  11  is provided, in roof  29 , together with optical fiber cables  101 ,  102  and  103  in a state of being integrated with optical fiber cables  101 ,  102  and  103 . On the other hand, electric wire harness  11  is not provided together with optical coupler  106  in a state of being integrated with optical coupler  106 . 
     More specifically, electric wire harness  11  is wired from the A-pillar to roof  29  in a state of being bundled with optical fiber cable  101 . Electric wire harness  11  is separated from optical fiber cable  101  just before room mirror stay  283 . Electric wire harness  11  is merged and bundled with optical fiber cables  102  and  103  wired from room mirror stay  283  to roof  29 . That is, in room mirror stay  283  and frame  282 , electric wire harness  11  is not wired, and only an optical transmission line is wired. 
     With this configuration, optical coupler  106  can be disposed on room mirror  281  which is a component of vehicle  2 . This configuration eliminates a need to separately provide a space for disposing optical coupler  106 , thereby making the vehicle wiring system space-saving. 
     Modification 
       FIG.  8    is a diagram illustrating an example of a configuration of a vehicle wiring system according to a modification of the second embodiment of the present disclosure. 
     Referring to  FIG.  8   , optical coupler  106  is disposed, for example, on a lighting device  30  in a cockpit of vehicle  2 . In an example shown in  FIG.  8   , optical coupler  106  is disposed on an interior lamp  301  as lighting device  30 . Optical coupler  106  is disposed so as to cross interior lamp  301  in a left-right direction of vehicle  2 . Optical coupler  106  is fixed to a cover (lamp cover), which is not shown, of interior lamp  301  with a glue, a pressure-sensitive adhesive, or the like. Since an electric wire harness has a certain thickness, it is difficult to wire the electric wire harness to the lighting device of the vehicle. 
     Optical connectors  104  and  105  are fixed to, for example, a housing to which interior lamp  301  is attached with a glue, a pressure-sensitive adhesive, or the like. 
     Electric wire harness  11  is provided together with optical fiber cables  101 ,  102  and  103  in roof  29 . On the other hand, electric wire harness  11  is not provided together with optical coupler  106 . 
     More specifically, electric wire harness  11  is wired from an A-pillar to roof  29  in a state of being bundled with optical fiber cable  101 . Electric wire harness  11  is separated from optical fiber cable  101  just before interior lamp  301 . Electric wire harness  11  is wired so as to bypass interior lamp  301 . Electric wire harness  11  is merged and bundled with optical fiber cables  102  and  103  wired from interior lamp  301  to roof  29 . That is, in interior lamp  301 , electric wire harness  11  is not wired, and only an optical transmission line is wired. 
     With this configuration, optical coupler  106  can be disposed on interior lamp  301  which is a component of vehicle  2 . This configuration eliminates a need to separately provide a space for disposing optical coupler  106 , thereby making the vehicle wiring system space-saving. Further, when the optical coupler is disposed on the lighting device provided in the cockpit of the vehicle, the vehicle wiring system can be space-saving more efficiently. Optical coupler  106  is not limited to the configuration in which optical coupler  106  is disposed on lighting device  30  in the cockpit of vehicle  2 . For example, electric wire harness  11  may be disposed inside a body of vehicle  2 , such as inside roof  29  in a section where electric wire harness  11  is not provided together with optical fiber cables  101 ,  102  and  103 . 
     Third Embodiment 
       FIG.  9    is a diagram illustrating an example of a configuration of a vehicle wiring system according to a third embodiment of the present disclosure. The vehicle wiring system according to the third embodiment is different from that of the first embodiment in that optical coupler  106  is disposed in a roof of vehicle  2 . The vehicle wiring system according to the third embodiment is the same as vehicle wiring system  1  according to the first embodiment except for the contents described below. 
     In  FIG.  9   , a master functional unit and slave functional units are not shown.  FIG.  9    illustrates an example in which the master functional unit is mounted in a trunk of vehicle  2 , and the two slave functional units are mounted in an engine room of vehicle  2 . 
     Referring to  FIG.  9   , optical fiber cable  101  passes from the master functional unit through D-pillar  25 , a rear roof cross member  31 A, roof side rail  23 , and a center roof cross member  31 B to be connected to optical connector  104 . Optical fiber cable  102  passes from the slave functional unit through A-pillar  22 , a front roof cross member  31 C, and roof side rail  23  to be connected to optical connector  105 . Optical fiber cable  103  passes from the slave functional unit through A-pillar  22  and roof side rail  23  to be connected to optical connector  105 . 
     Optical coupler  106  is disposed so as to connect roof side rail  23  and center roof cross member  31 B to each other in vehicle  2 . Optical coupler  106  passes through an opening  32  formed by roof side rail  23 , front roof cross member  31 C, and center roof cross member  31 B. 
       FIG.  10    is a cross-sectional view taken along line X-X in  FIG.  9   . Referring to  FIG.  10   , optical coupler  106  is disposed between a roof panel  33  and a roof lining  34  in vehicle  2 . Roof panel  33  is an exterior component that is formed of, for example, a steel plate and constitutes a ceiling portion of vehicle  2 . Roof lining  34  is a sheet-like interior component made of, for example, cloth, leather, chemical fiber or the like. The roof lining is attached to a surface on the vehicle interior side of roof panel  33 , and forms the ceiling portion in a cabin of vehicle  2 . Optical coupler  106  may be fixed to roof panel  33  with a glue, a pressure-sensitive adhesive, or the like, or may be fixed to roof lining  34 . 
     Referring to  FIG.  9   , optical connector  104  is disposed on center roof cross member  31 B. Optical connector  105  is disposed on roof side rail  23 . Optical connectors  104  and  105  are fixed to center roof cross member  31 B and roof side rail  23 , respectively, with a glue, a pressure-sensitive adhesive, or the like, for example. 
     Electric wire harness  11  connects a battery to slave functional units disposed in the engine room. Electric wire harness  11  connects the battery to the master functional unit disposed in the trunk. Electric wire harness  11  extends from the battery along A-pillar  22 , roof side rail  23 , rear roof cross member  31 A, and D-pillar  25 . 
     Electric wire harness  11  is provided together with optical fiber cable  102  in A-pillar  22 . Electric wire harness  11  is provided together with optical fiber cable  101  in a partial section of roof side rail  23 , rear roof cross member  31 A, and D-pillar  25 . On the other hand, electric wire harness  11  does not pass through opening  32 , and is not provided together with optical coupler  106 . 
     When a thick object such as electric wire harness  11  is disposed between roof panel  33  and roof lining  34 , it is necessary to design a thickness, shape, and the like of a roof component such as roof panel  33  in consideration of electric wire harness  11 . However, since optical coupler  106  is as thin as 1 mm or less, even when optical coupler  106  is inserted between roof panel  33  and roof lining  34 , it is difficult to affect the design of the roof component. Therefore, it is possible to effectively utilize a space in which the electric wire harness is not disposed while maintaining a degree of freedom in the roof design. 
     In the above embodiment, a case where optical coupler  106  is disposed on or in window  20 C, room mirror  281 , interior lamp  301 , and roof  29  of vehicle  2  in the vehicle wiring system has been described. However, the vehicle wiring system of the present disclosure is not limited thereto. Optical coupler  106  may be disposed in a portion of vehicle  2  where electric wire harness  11  is not wired. 
     The vehicle wiring system according to the above embodiment may be constructed by a method that includes preparing a plurality of functional units  21  to be mounted in vehicle  2 , optical transmission line  10 , electric wire harness  11 , and optical coupler  106 ; wiring optical transmission line  10  between functional units  21  so as to transmit an optical signal of functional units  21 ; wiring electric wire harness  11  in a partial section of optical transmission line  10  so that electric wire harness  11  is provided together with optical transmission line  10  in a state of being integrated with optical transmission line  10 ; and disposing optical coupler  106  in a portion of optical transmission line  10  other than the partial section and causing optical coupler  106  to constitute a part of optical transmission line  10 . 
     The above-described embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined not by the above description but by the claims, and is intended to embrace all the modifications within the meaning and scope of equivalency of the claims. 
     The above description includes features that are appended below. 
     Supplementary Note 1 
     A vehicle wiring system includes an optical transmission line that is configured to transmit an optical signal between functional units to be mounted in a vehicle and an electric wire harness that is provided, in a partial section of the optical transmission line, together with the optical transmission line. The optical transmission line has an optical coupler that is disposed in a portion of the optical transmission line where the electric wire harness and the optical transmission line are not provided together. The optical coupler includes a body portion formed of a resin and an optical waveguide formed in the body portion and having a branching portion. 
     Supplementary Note 2 
     A vehicle wiring system includes an optical transmission line that is configured to transmit an optical signal between functional units to be mounted in a vehicle and an electric wire harness that is provided, in a partial section of the optical transmission line, together with the optical transmission line. The optical transmission line has an optical coupler that is disposed in a portion of the optical transmission line where the electric wire harness and the optical transmission line are not provided together. The functional units are at least one of an ECU, a sensor, or an antenna module. 
     
       
         
           
               
               
             
               
                 REFERENCE SIGNS LIST 
               
             
            
               
                 
                   1 
                 
                 vehicle wiring system 
               
               
                 
                   10 
                 
                 optical transmission line 
               
               
                   101 ,  102 ,  103   
                 optical fiber cable 
               
               
                   101 A 
                 tension member 
               
               
                   101 B 
                 optical fiber 
               
               
                   101 C 
                 protective layer 
               
               
                   101 D 
                 wrapping tape 
               
               
                   101 E 
                 sheath 
               
               
                   104 ,  105   
                 optical connector 
               
               
                 
                   106 
                 
                 optical coupler 
               
               
                   106 A 
                 body portion 
               
               
                   106 B 
                 optical waveguide 
               
               
                   106 C 
                 first end 
               
               
                   106 D 
                 second end 
               
               
                   106 E 
                 third end 
               
               
                 
                   11 
                 
                 electric wire harness 
               
               
                 
                   2 
                 
                 vehicle 
               
               
                   20 A,  20 B,  20 C,  20 C 1   
                 window 
               
               
                   20 C 2   
                 sheet glass 
               
               
                   20 C 3   
                 interlayer 
               
               
                 
                   21 
                 
                 functional unit 
               
               
                 
                   211 
                 
                 master functional unit 
               
               
                   212 ,  213   
                 slave functional unit 
               
               
                 
                   22 
                 
                 A-pillar 
               
               
                 
                   23 
                 
                 roof side rail 
               
               
                 
                   24 
                 
                 C-pillar 
               
               
                 
                   25 
                 
                 D-pillar 
               
               
                 
                   26 
                 
                 battery 
               
               
                 
                   27 
                 
                 beltline 
               
               
                 
                   28 
                 
                 mirror 
               
               
                 
                   281 
                 
                 room mirror 
               
               
                 
                   282 
                 
                 frame 
               
               
                 
                   283 
                 
                 room mirror stay 
               
               
                 
                   29 
                 
                 roof 
               
               
                 
                   30 
                 
                 lighting device 
               
               
                 
                   301 
                 
                 interior lamp 
               
               
                   31 A 
                 rear roof cross member 
               
               
                   31 B 
                 center roof cross member 
               
               
                   31 C 
                 front roof cross member 
               
               
                 
                   32 
                 
                 opening 
               
               
                 
                   33 
                 
                 roof panel 
               
               
                 
                   34 
                 
                 roof lining 
               
               
                 
                   40 
                 
                 cable tie (tying member, fixing member)