Patent Publication Number: US-2020282949-A1

Title: Seat belt take-up control system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 USC 119 from Japanese Patent Application No. 2019-038898, filed on Mar. 4, 2019, the disclosure of which is incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a seat belt take-up control system. 
     Related Art 
     Japanese Patent Application Laid-Open (JP-A) No. 2007-76536 discloses a seat belt take-up control system including a pretensioner mechanism that drives an electric motor and takes-up a webbing (seat belt) when a collision of a vehicle is predicted. Further, JP-A No. 2007-76536 describes that when an Automatic Locking Retractor (ALR) mechanism is operated, the seat belt is taken-up and a child seat (that is, a Child Restraint System (CRS)) is fixed to a vehicle seat by operation of the pretensioner mechanism. 
     However, JP-A No. 2007-76536 does not take into consideration the possibility of the seat belt slackening after fixing the CRS to the vehicle seat, and there is room for improvement from the viewpoint of favorably maintaining the fixed state of the CRS. 
     SUMMARY 
     The present disclosure provides a seat belt take-up control system capable of favorably maintaining a fixed state of a CRS. 
     A seat belt take-up control system according to a first aspect of the present disclosure includes: a first belt-take-up unit mounted at a child seat, the first belt-take-up unit taking up a seat belt of a vehicle seat and applying a predetermined tension at a time of fastening the seat belt; a belt lock unit that prevents pulling out of the seat belt in a state in which the seat belt has been taken up by the first belt-take-up unit; and a second belt-take-up unit that, in a state in which pulling out of the seat belt is prevented by the belt lock unit, takes up the seat belt and applies a predetermined tension after the seat belt is fastened in at least one of a case in which pulling out of the seat belt is detected or a case in which a first predetermined period of time has elapsed. 
     In the seat belt take-up control system according to the first aspect of the present disclosure, the seat belt of the vehicle seat is taken up by the first belt-take-up unit when the child seat (i.e., a CRS) is attached, and a predetermined tension is applied to the seat belt. Further, pulling out of the seat belt is prevented by the belt lock unit. Thereby, a CRS may be efficiently fixed to the vehicle seat. 
     Further, the seat belt is taken up by the second belt-take-up unit, in a state in which pulling out of the seat belt is prevented by the belt lock unit, in at least one of a case in which pulling out of the seat belt is detected or a case in which a predetermined period of time has elapsed. Further, a predetermined tension is applied to the seat belt by the seat belt being taken up. As a result, it is possible to suppress the seat belt from slackening after fixing a CRS to the vehicle seat. 
     The seat belt take-up control system according to a second aspect of the present disclosure, in the first aspect, takes up the seat belt in a case in which a predetermined amount or more of gravitational acceleration is detected to have acted on a vehicle 
     In the seat belt take-up control system according to the second aspect of the present disclosure, slackening of the seat belt may be suppressed even in a case in which a predetermined amount of gravitational acceleration or more has acted on the vehicle due to sudden acceleration or deceleration during travel. 
     The seatbelt take-up control system according to a third aspect of the present disclosure includes, in the first aspect or the second aspect, a seating detection unit that detects that an occupant is seated in the child seat, the second belt-take-up unit being enabled in a case in which the seating detection unit detects that an occupant is seated in the child seat, and the second belt-take-up unit being disabled in a case in which the seating detection unit does not detect that an occupant is seated in the child seat. 
     In the seat belt take-up control system according to the third aspect of the present disclosure, when an occupant is not seated in the CRS, that is, when the CRS is not being used, the second belt-take-up unit is disabled such that power consumption may be reduced. 
     The seat belt take-up control system according to a fourth aspect of the present disclosure is the seat belt take-up control system according to any one of the first to third aspects, wherein the first belt-take-up unit takes up the seat belt in a case in which the seat belt has been pulled a predetermined number of times within a predetermined period of time, in a state in which a tongue plate is inserted into a buckle. 
     In the seat belt take-up control system according to the fourth aspect of the present disclosure, the seat belt is taken-up by pulling the seat belt a predetermined number of times. Thereby, compared with a configuration in which operation of an ALR mechanism is detected and the seat belt is taken up, the bother of operating the ALR mechanism may be eliminated. Moreover, since it is not necessary to operate switches, workability when the CRS is mounted may be improved. 
     According to the seatbelt take-up control system according to the present disclosure, the fixed state of the CRS may be favorably maintained. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Exemplary embodiments will be described in detail based on the following figures, wherein: 
         FIG. 1  is a front view of a vehicle seat equipped with a seat belt take-up control system according to an embodiment, as viewed from the front side of a vehicle; 
         FIG. 2  is a block diagram illustrating a hardware configuration of the seat belt take-up control system according to the embodiment; 
         FIG. 3  is a block diagram illustrating a hardware configuration of an ECU that configures the seat belt take-up control system according to the embodiment; 
         FIG. 4  is a block diagram illustrating an example of a functional configuration of the seat belt take-up control system according to the embodiment; 
         FIG. 5  is a flowchart illustrating a flow of the process of belt take-up at the time of fastening a seat belt in the embodiment; 
         FIG. 6  is a flow chart illustrating a flow of the process of belt take-up after the seat belt is fastened in the embodiment; 
         FIG. 7  is a flowchart illustrating a flow of the process of belt take-up after the seat belt is fastened in a first modified example of the embodiment; 
         FIG. 8  is a flow chart illustrating a flow the process of belt take-up after the seat belt is fastened in a second modified example of the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following, a seat belt take-up control system  10  according to an embodiment is explained with reference to the drawings. Note that arrow UP in  FIG. 1  indicates the vehicle upper side, and arrow RH indicates the vehicle right-hand side. When description is given using front-rear, left-right, and vertical directions, these refer to the front-rear of the vehicle front-rear direction, the left and right of the vehicle width direction, and the vertical of the vehicle vertical direction, unless otherwise indicated. 
     As illustrated in  FIG. 1 , a vehicle seat  12 , to which the seat belt take-up control system  10  according to the embodiment of the present disclosure is applied, includes a seat cushion  14 , a seat back  16 , and a headrest  18 . 
     A child seat  20  (hereinafter referred to as “CRS  20 ” as appropriate) is mounted on the vehicle seat  12 . The CRS  20  includes a seat cushion portion  22  that supports the buttocks and thighs of an occupant from a seat lower side, a seat back portion  24  that supports the back of an occupant from a seat rear side, and a head rest portion  26  that supports the head of an occupant from the seat rear side. Further, in the present embodiment, as an example, the seat front side of the CRS  20  is coincident with the seat front side of the vehicle seat  12 . 
     Here, the CRS  20  is fixed to the vehicle seat  12  by a seat belt  30  (that is, a webbing). The seat belt  30  is formed in a long strip shape, and one end of the seat belt  30  is wound around a spool  28 A that configures a retractor  28 . In addition, the other end of the seat belt  30  is attached to an anchor  32  that is fixed to a floor panel  34 . 
     The seat belt  30  is passed through a tongue plate  37 , and the tongue plate  37  is provided between the retractor  28  and the anchor  32 . Further, the tongue plate  37  is inserted into a buckle  36  that is provided at the vehicle seat  12 , and extraction from the buckle  36  is locked. 
     Here, the CRS  20  includes plural belt guides that are not illustrated, and the CRS  20  is mounted on the vehicle seat  12  by the tongue plate  37  being inserted into the buckle  36  in a state in which the seat belt  30  has passed through these belt guides. 
     The retractor  28  is electrically connected to an Electronic Control Unit (ECU)  38 , which is a control unit. 
       FIG. 2  is a block diagram illustrating the hardware configuration of the seat belt take-up control system  10 . As illustrated in  FIG. 2 , the ECU  38  is electrically connected to a seating sensor  40 , an acceleration sensor  42 , a buckle sensor  44 , and the retractor  28 . 
     As illustrated in  FIG. 1 , the seating sensor  40  is provided inside the seat cushion  14  and is a sensor that detects that an occupant is seated in the vehicle seat  12 . 
     The acceleration sensor  42  illustrated in  FIG. 2  is mounted on a vehicle and detects an acceleration acting on the vehicle. For example, if sudden acceleration or deceleration occurs while the vehicle is traveling, this acceleration or deceleration is detected by the acceleration sensor. 
     The buckle sensor  44  is a sensor that is provided at the buckle  36  (see  FIG. 1 ), and detects that the tongue plate  37  is inserted in the buckle  36 . 
     The ECU  38  is electrically connected to a spool tachometer  46 , a motor  48 , a lock mechanism  50 , and a pretensioner  52 , respectively, which configure the retractor  28 . The spool tachometer  46  detects rotation of the spool  28 A. In the present embodiment, as an example, N-pole and S-pole magnets are alternately attached to a rotating body that is not illustrated and that rotates integrally with the spool  28 A. Further, rotation of the spool  28 A is detected by detecting a magnetic pole that changes with rotation of the spool  28 A. Note that the present disclosure is not limited to this, and rotation of the spool  28 A may be detected by another method. 
     The motor  48  is driven by power being supplied and the spool  28 A is caused to rotate in one direction or in another direction. As a result, the seat belt  30  is taken up by the retractor  28  by driving the motor  48  and rotating the spool  28 A in one direction. Further, the seat belt  30  is pulled out from the retractor  28  by the spool  28 A being rotated in the other direction. Note that the motor  48  is configured to be able to switch between a connected state in which power may be transmitted to the spool  28 A by a clutch gear and a non-connected state in which power is not transmitted. 
     The lock mechanism  50  is a mechanism that locks pulling out of the seat belt  30  by being operated. As a result, when the seat belt  30  is in a locked state due to the lock mechanism  50 , the seat belt  30  cannot be pulled out from the retractor  28  even if the seat belt  30  is pulled. Note that the lock mechanism  50  may adopt, for example, a structure in which rotation of the spool  28 A is mechanically locked or a structure in which rotation of the spool  28 A is stopped by applying a voltage to the motor  48 . In addition, as another lock mechanism, an electric lock type lock mechanism that is provided with a permanent magnet and an electromagnet may be adopted. That is, this is a system in which the core of an electromagnet repels a permanent magnet and rotation of the spool  28 A is locked by energizing the coil of the electromagnet in one direction, and the core of the electromagnet attracts the permanent magnet and rotation of the spool  28 A is unlocked by energizing the coil in the other direction. In the electric lock type lock mechanism, rotation of the spool  28 A may be locked or unlocked at any time by energizing the coil based on a signal from each sensor. 
     Further, in the present embodiment, as an example, when a collision of the vehicle is predicted based on a signal from a collision prediction sensor or the like that is not illustrated, the ECU  38  drives the motor  48  and causes the spool  28 A to rotate in one direction. As a result, the seat belt  30  is taken-up so as to have a predetermined tension, and the occupant may be restrained at the vehicle seat  12  before the collision. 
     When actuated, the pretensioner  52  rotates the spool  28 A in one direction with a force that is stronger than that of the motor  48  and forcibly takes up the seat belt  30 . Then, when a collision of the vehicle is detected based on a signal from a collision sensor or the like that is not illustrated, the ECU  38  operates the pretensioner  52  and the occupant is restrained at the vehicle seat  12 . 
       FIG. 3  is a block diagram illustrating the hardware configuration of the ECU  38  that configures the seat belt take-up control system  10 . As illustrated in  FIG. 3 , the ECU  38  is configured to include a Central Processing Unit (CPU)  54 , a Read Only Memory (ROM)  56 , a Random Access Memory (RAM)  60 , a storage  58 , and a communication interface  62 . Further, these respective components are connected via a bus  53  so as to be able to communicate with one another. 
     The CPU  54  is a central processing unit that executes various programs and controls the respective aforementioned components. That is, the CPU  54  reads out a program from the ROM  56  or the storage  58 , and executes the program by using the RAM  60  as a work space. Further, the CPU  54  controls each of the various aforementioned configurations and performs various computation processing according to the program recorded in the ROM  56  or the storage  58 . 
     The ROM  56  holds various programs and various data. The RAM  60  temporarily stores programs or data as a work space. The storage  58  is configured by a Hard Disk Drive (HDD) or a Solid State Drive (SSD), and holds various data and various programs including an operating system. 
     The communication interface  62  is an interface for the ECU  38  to communicate with various sensors, the retractor  28 , and other devices, and utilizes standards such as Ethernet (registered trademark), FDDI, and Wi-Fi (registered trademark). 
     The seat belt take-up control system  10  of the present embodiment realizes various functions using the hardware resources illustrated in  FIGS. 2 and 3 . Functions realized by the seat belt take-up control system  10  are described below. 
       FIG. 4  is a block diagram illustrating an example of a functional configuration of the seat belt take-up control system  10 . 
     As illustrated in  FIG. 4 , the seat belt take-up control system  10  has a double-pull detection unit  64 , a first belt-take-up unit  66 , a belt lock unit  68 , a seating detection unit  70 , a pull-out detection unit  72 , and a second belt-take-up unit  74 , as functional components. Further, these respective functional components are realized by the CPU  36  reading out and executing programs that are recorded in the ROM  56  or the storage  58 . 
     The double-pull detection unit  64  detects that the seat belt  30  has been pulled twice in a predetermined period of time. Note that in the present embodiment, as an example, if the spool  28 A is rotated in a pull-out direction based on a signal from the spool tachometer  46 , it is determined that the seat belt  30  has been pulled. Further, the double-pull detection unit  64  is not limited to the case in which an occupant directly pulls the seat belt  30  twice, but detects the seat belt  30  being pulled twice in a predetermined period of time even in the case in which the CRS  20  is rocked back and forth such that the seat belt  30  is pulled twice or more. 
     The first belt-take-up unit  66  takes up the seat belt  30  of the vehicle seat  12 , at which the CRS  20  is mounted, and applies a predetermined tension. Specifically, the seat belt  30  is taken up by driving the motor  48  of the retractor  28  and rotating the spool  28 A in the take-up direction. Note that the first belt-take-up unit  66  is configured to drive the motor  48  and take up the seat belt  30  until the tension of the seat belt  30  reaches a predetermined tension. 
     The belt lock unit  68  operates the lock mechanism  50  of the retractor  28  to lock pulling out of the seat belt  30 . Note that the seat belt  30  is configured to be able to be taken up by rotating the spool  28 A in the take-up direction even in a state in which pulling-out of the seat belt  30  is prevented by the lock mechanism  50 . 
     The seating detection unit  70  detects that an occupant is seated in the vehicle seat  12  based on a signal from the seating sensor  40 . Note that in the present embodiment, as an example, the seating sensor  40  is not turned on in a state in which the CRS  20  is attached to the vehicle seat  12 , and a threshold value is adjusted such that the seating sensor  40  reacts and turns on in the case in which the occupant is seated in the CRS  20 . 
     The pull-out detection unit  72  detects that the seat belt  30  is pulled out (slackened). Specifically, in a state in which pulling-out of the seat belt  30  is prevented by the belt lock unit  68 , it is determined that the seat belt  30  is pulled-out when the spool  28 A has been rotated in the pull-out direction. Note that cases in which the seat belt  30  is pulled-out in a state in which pulling-out of the seat belt  30  is prevented are cases in which centrifugal forces act on the vehicle at the time of sudden acceleration or deceleration during travel, cases in which an external force is input to the vehicle from the road surface, and the like. Further, there are cases in which slackening of the seat belt  30 , which is fixing the CRS  20 , occurs due to the seat belt  30  being pulled out. 
     The second belt-take-up unit  74  takes-up the seat belt  30  and applies a predetermined tension in a state in which the CRS  20  is mounted on the vehicle seat  12 . Specifically, a predetermined tension is applied to the seat belt  30  by driving the motor  48  of the retractor  28  and rotating the spool  28 A in the take-up direction under predetermined conditions. 
     Here, the flow of the process of belt take-up at the time of fastening the seat belt by the seat belt take-up control system  10  is described with reference to the flowchart of  FIG. 5 . The CPU  54  reads out the program from the ROM  56  or the storage  58 , outputs it to the RAM  60  and executes it, whereby the process of belt take-up at the time of fastening the seat belt is performed. 
     As illustrated in  FIG. 5 , in step S 102 , the CPU  54  determines whether or not the seat belt  30  has been pulled out. That is, when an occupant mounts the CRS  20  on the vehicle seat  12 , the occupant pulls out only the required length of the seat belt  30 , against the urging force of the spring that urges the spool  28 A in the take-up direction, after the CRS  20  is placed on the vehicle seat  12 . In step S 102 , if the seat belt  30  has been pulled out as described above, it is determined based on a signal from the spool tachometer  46  that the seat belt  30  has been pulled out. 
     If the CPU  54  determines in step S 102  that the seat belt  30  has been pulled out, the CPU  54  proceeds to the process in step S 104 . Further, if the CPU  54  determines in step S 102  that the seat belt  30  has not been pulled out, the CPU  54  terminates the process of belt take-up at the time of fastening the seat belt. 
     In step S 104 , the CPU  54  determines whether or not an occupant is seated in the CRS  20 . Specifically, the CPU  54  determines, by the function of the seating detection unit  70  (see  FIG. 4 ), whether or not an occupant is seated in the CRS  20  based on a signal from the seating sensor  40 . If the CPU  54  determines that an occupant is seated in the CRS  20 , the process of belt take-up after the seat belt is fastened is terminated. On the other hand, if it is determined that an occupant is not seated in the CRS  20 , the CPU  54  proceeds to step S 106 . By this process, for example, the seat belt  30  is not taken up during general use such as the seat belt  30  being pulled out and put on after the occupant is seated in the vehicle seat  12 . 
     In step S 106 , the CPU  54  turns on the clutch. Specifically, the CPU  54  connects the spool  28 A and the motor  48  via the clutch gear by slightly rotating the motor  48  in the take-up direction. In the following description, the state in which the clutch is turned on refers to a state in which the spool  28 A and the motor  48  are connected. Further, the state in which the clutch is turned off refers to a state in which the connection state between the spool  28 A and the motor  48  is released. Then, the spool  28 A is connected to the motor  48  by the clutch gear, whereby a resistance force of the energized motor  48  is transmitted to the spool  28 A. For this reason, the seat belt  30  is not taken up by the urging force of the spring. 
     In step S 108 , the CPU  54  checks the buckle sensor  44  and determines whether or not the buckle sensor  44  is ON. That is, in step S 108 , when the passenger passes the seat belt  30  through the belt guides of the CRS  20  and inserts the tongue plate  37  into the buckle  36 , the buckle sensor  44  is turned on and it is determined that the tongue plate  37  is inserted into the buckle  36 . 
     If the CPU  54  determines in step S 108  that the buckle sensor  44  is ON, the CPU  54  proceeds to step S 110 . Further, if the CPU  54  determines in step S 108  that the buckle sensor  44  is not ON, that is, if the CPU  54  determines that the buckle sensor  44  is OFF, the CPU  54  terminates the process of belt take-up at the time of fastening the seat belt. 
     The CPU  54  determines in step S 110  whether or not the seat belt  30  has been pulled only a predetermined number of times. The CPU  54  determines that the seat belt  30  has been pulled if, by the seat belt  30  being pulled, the spool  28 A of the retractor  28  is rotated in the pull-out direction based on a signal from the spool tachometer  46 . Then, if the seat belt  30  has been pulled, the CPU  54  starts a timer and determines whether or not the seat belt  30  is pulled a predetermined number of times within a predetermined period of time. In the present embodiment, the CPU  54  determines whether or not the seat belt  30  has been pulled twice within a predetermined period of time in step S 110  by the function of the double-pull detection unit  64  (see  FIG. 4 ). 
     If the CPU  54  determines in step S 110  that the seat belt  30  has been pulled twice within a predetermined period of time, the CPU  54  proceeds to the process in step S 112 . On the other hand, if the seat belt  30  has not been pulled twice in a predetermined period of time in step S 110 , that is, if a predetermined period of time elapses without the seat belt  30  being pulled after starting the timer at step S 108 , the CPU  54  terminates the process of belt take-up at the time of fastening the seat belt. 
     The CPU  54  applies a predetermined tension to the seat belt  30  in step S 112 . Specifically, by the function of the first belt-take-up unit  66  ( FIG. 4 ), the CPU  54  drives the motor  48  of the retractor  28  and takes up the seat belt  30  until the tension of the seat belt  30  reaches a predetermined tension. At this time, slack may be removed by the passenger shaking the CRS  20 . In addition, the CRS  20  may be stably fixed to the vehicle seat  12  by the occupant leading the seat belt  30  to the retractor  28 . 
     The CPU  54  prevents the seat belt  30  in step S 114 . Specifically, by the function of the belt lock unit  68  ( FIG. 4 ), the CPU  54  operates the lock mechanism  50  of the retractor  28  and locks pulling out of the seat belt  30 . Then, the CPU  54  terminates the process of belt take-up at the time of fastening the seat belt. 
     Next, the flow of the process of belt take-up after the seat belt is fastened by the seat belt take-up control system  10  is described with reference to the flowchart of  FIG. 6 . The CPU  54  reads out the program from the ROM  56  or the storage  58 , outputs it to the RAM  60 , and executes it, whereby the process of belt take-up after the seat belt is fastened is performed. 
     As illustrated in  FIG. 6 , the CPU  54  checks the buckle sensor  44  in step S 202 . That is, the CPU  54  checks whether the tongue plate  37  is inserted into the buckle  36 . Next, in step S 204 , the CPU  54  determines whether or not the buckle sensor  44  is ON. 
     If the CPU  54  determines in step S 204  that the buckle sensor  44  is ON, the CPU  54  proceeds to step S 206 . Further, if the CPU  54  determines in step S 204  that the buckle sensor  44  is not ON, that is, if the CPU  54  determines that the buckle sensor  44  is OFF, the CPU  54  terminates the process of belt take-up after the seat belt is fastened. 
     In step S 206 , the CPU  54  determines whether or not an occupant is seated in the CRS  20 . Specifically, by the function of the seating detection unit  70  (see  FIG. 4 ), the CPU  54  determines whether or not an occupant is seated in the CRS  20  based on a signal from the seating sensor  40 . If the CPU  54  determines that an occupant is seated in the CRS  20 , the CPU  54  proceeds to step S 208 . On the other hand, if the CPU  54  determines that an occupant is not seated in the CRS  20 , the process of belt take-up after the seat belt is fastened is terminated. 
     The CPU  54  starts a timer at step S 208 . That is, the CPU  54  starts the timer from the time when it is detected that the occupant is seated in the CRS  20  in a state in which the buckle sensor  44  is ON. 
     At step S 210 , the CPU  54  determines whether or not a predetermined period of time has elapsed. If it is determined in step S 208  that a predetermined period of time has elapsed since the timer was started, the CPU  54  proceeds to step S 212 . On the other hand, if a predetermined period of time has not elapsed since the timer was started, the CPU  54  repeats the process of step S 210  until a predetermined period of time elapses. 
     In step S 212 , the CPU  54  performs additional pulling of the seat belt  30 . Specifically, the motor  48  of the retractor  28  is driven to cause the spool  28 A to rotate in the take-up direction, thereby applying a predetermined tension to the seat belt  30  that is fixing the CRS  20 . 
     In step S 214 , the CPU  54  determines whether or not the buckle sensor  44  is ON. If the CPU  54  determines that the buckle sensor  44  is ON, the CPU  54  proceeds to the process of step S 216 . If the CPU  54  determines that the buckle sensor  44  is not ON, that is, if it is determined that the buckle sensor  44  is OFF, the process of belt take-up after the seat belt is fastened is terminated. 
     In step S 216 , the CPU  54  determines whether or not an occupant is seated in the CRS  20 . If the CPU  54  determines that an occupant is seated in the CRS  20 , the CPU  54  proceeds to step S 208 . On the other hand, if it is determined that an occupant is not seated in the CRS  20 , the process of belt take-up after the seat belt is fastened is terminated. 
     In this manner, the CPU  54  repeats the process of from step S 208  to step S 216  when the buckle sensor  44  is ON and an occupant is seated in the CRS  20 . 
     Note that when an occupant gets off the CRS  20 , it is confirmed that the occupant has left the seat based on a signal from the seating sensor  40 , and it is confirmed that the tongue plate  37  has been removed from the buckle  36  based on a signal from the buckle sensor  44 . Then, the CPU  54  turns off the clutch by slightly rotating the motor  48  in the pull-out direction. As a result, the seat belt  30  may be taken up by the spring. 
     (Operation) Next, the operation of the present embodiment will be described. 
     In the seat belt take-up control system  10  according to the present embodiment, the CRS  20  may be efficiently fixed to the vehicle seat  12  as described in the process of belt take-up at the time of fastening the seat belt in  FIG. 5 . That is, when the tongue plate  37  is inserted into the buckle  36  in a state in which the seat belt  30  has been passed through the belt guides of the CRS  20 , the buckle sensor  44  is turned on (step S 108 ). In this state, the seat belt  30  is taken up by the function of the first belt-take-up unit  66 , and a predetermined tension is applied to the seat belt  30 , whereby the CRS  20  may be fixed to the vehicle seat  12  (step S 112 ). Further, pulling out of the seat belt  30  may be prevented by the belt lock unit  68  (step S 114 ). 
     Further, by the function of the double-pull detection unit  64 , the first belt-take-up unit  66  of the present embodiment takes up the seat belt  30  if the seat belt  30  is pulled twice within a predetermined period of time in a state in which the tongue plate  37  is inserted into the buckle  36  (step S 110 ). Thereby, compared with a configuration in which operation of an ALR mechanism is detected and the seat belt  30  is taken up, the bother of operating the ALR mechanism may be eliminated. That is, due to a standard ALR function being activated by pulling out the entirety of the seat belt  30 , the bother of an occupant pulling out the entirety of the seat belt  30  in order to fix the CRS  20  to the vehicle seat  12  occurs. In contrast, in the present embodiment, since the CRS  20  may be fixed to the vehicle seat  12  by merely pulling the seat belt  30  twice, it does not take time and effort. In addition, since it is not necessary to operate switches in order to take up the seat belt  30 , workability when mounting the CRS  20  may be improved. 
     Further, in the present embodiment, as described in the process of belt take-up after the seat belt is fastened in  FIG. 6 , if an occupant is not seated in the CRS  20 , that is, if the CRS  20  is not being used, the process of belt take-up after the seat belt is fastened is terminated (step S 206 ). That is, when an occupant is not seated in the CRS  20 , the second belt-take-up unit is disabled, such that power consumption may be reduced. 
     Furthermore, if a predetermined period of time elapses in a state in which pulling-out of the seat belt  30  is prevented by the belt lock unit  68 , a predetermined tension is applied to the seat belt  30  by the seat belt  30  being taken up by the second belt-take-up unit  74 . Thereby, it is possible to suppress the seat belt  30  from slackening after the CRS  20  is fixed to the vehicle seat  12 . As a result, the fixed state of the CRS  20  may be maintained satisfactorily. 
     Further, in the present embodiment, since the CRS  20  may be mounted without requiring a complicated configuration such as an ALR mechanism, the retractor  28  may be downsized as compared with a retractor including an ALR mechanism. As a result, the retractor  28  may be attached to the vehicle seat  12 , and the degree of freedom of the seat layout may be improved as compared with a configuration in which a retractor is attached to the vehicle body side. 
     Note that in the present embodiment, the seat belt  30  is additionally pulled if a predetermined period of time has elapsed; however, the present disclosure is not limited to this. For example, the present disclosure may also be a configuration provided with the process of belt take-up after the seat belt is fastened illustrated by the flowcharts of  FIG. 7  and  FIG. 8 . 
     First Modified Example 
       FIG. 7  is a flowchart illustrating the flow of the process of belt take-up after the seat belt is fastened in a first modified example. The CPU  54  reads out the program from the ROM  56  or the storage  58 , outputs it to the RAM  60 , and executes it, whereby the process of belt take-up after the seat belt is fastened is performed. 
     As illustrated in  FIG. 7 , the processes in steps S 202  to S 208  and steps S 212  to S 216  in the present modified example are the same as the processes in  FIG. 6 . Further, in this modified example, the process of step S 211  is performed in place of step S 210  of  FIG. 6 . 
     In step S 211 , the CPU  54  determines whether or not a predetermined period of time has elapsed, and whether or not a predetermined amount of gravitational acceleration or more has acted. If it is determined that a predetermined period of time has elapsed since the timer was started in step S 208 , the CPU  54  proceeds to step S 212 . Further, if predetermined amount of gravitational acceleration or more is detected based on a signal from the acceleration sensor  42  (see  FIG. 2 ) before a predetermined period of time elapses, the CPU  54  proceeds to step S 212 . 
     On the other hand, the CPU  54  repeats the process of step S 211  if a predetermined period of time has not elapsed without a predetermined amount of gravitational acceleration or more in step S 211  being detected. 
     In step S 212 , the CPU  54  performs additional pulling of the seat belt  30 . Specifically, the motor  48  of the retractor  28  is driven to rotate the spool  28 A in the take-up direction, thereby applying a predetermined tension to the seat belt  30  that is fixing the CRS  20 . 
     As described above, in this modified example, it is possible to suppress the seat belt  30  from slacking even if a predetermined amount of gravitational acceleration or more acts on a traveling vehicle due to sudden acceleration or deceleration. 
     Second Modified Example 
       FIG. 8  is a flowchart illustrating the flow of the process of belt take-up after the seat belt is fastened in a second modified example. The CPU  54  reads out the program from the ROM  56  or the storage  58 , outputs it to the RAM  60 , and executes it, whereby the process of belt take-up after the seat belt is fastened is performed. 
     As illustrated in  FIG. 8 , the processes in steps S 202  to S 206  and steps S 212  to S 216  in the present modified example are the same as the processes in  FIG. 6 . In the present modified example, the process of step S 207  is performed in place of the processes of step S 208  and step S 210  of  FIG. 6 . 
     In step S 207 , the CPU  54  determines whether or not pulling out of the seat belt  30  is detected. Specifically, by the function of the pull-out detection unit  72  ( FIG. 4 ), the CPU  54  determines whether or not the seat belt  30  has been pulled out (slackened). If the CPU  54  determines in step S 207  that the seat belt  30  has been pulled out, the CPU  54  proceeds to the process in step S 212  and performs additional pulling of the seat belt  30 . 
     On the other hand, if the CPU  54  determines in step S 207  that the seat belt  30  has not been pulled out, the CPU  54  proceeds to step S 214  without going through the process of step S 212 . That is, in this case, the seat belt  30  is not additionally pulled. 
     As described above, in the present modified example, the seat belt  30  is additionally pulled only if the seat belt  30  is slackened, such that it is not necessary to frequently drive the motor  48  of the retractor  28 . 
     Although explanation has been given regarding a seat belt take-up control system according to the present embodiment and modified examples, obviously various embodiments are possible within a range not departing from the gist of the present disclosure. For example, the above-described present embodiment and modified examples may be combined, and the process of belt take-up after the seat belt is fastened illustrated in  FIG. 6  and the process of belt take-up after the seat belt is fastened illustrated in  FIG. 8  may be combined. In this case, the second belt-take-up unit  74  takes up the seat belt  30  and applies a predetermined tension in at least one of the case in which pulling out of the seat belt  30  is detected or the case in which a predetermined period of time has elapsed. 
     Further, in addition to the process of belt take-up at the time of fastening the seat belt described in the above present embodiment and the modified example, the seat belt  30  may be additionally pulled when the ignition (or power) of the vehicle is switched from OFF to ON. Thus, even when the ignition (or power) of the vehicle is OFF and the fixed state of the CRS  20  is in an unstable state, tension may be applied to the seat belt  30  and the fixed state of the CRS  20  made stable when the ignition (or power) is turned on. 
     In the above-described embodiment and modified examples, if the seat belt  30  is detecting as having been pulled twice within a predetermined period of time by the double-pull detection unit  64 , the seat belt  30  is taken up by the first belt-take-up unit  66  and tension is applied; however, the present disclosure is not limited to this. For example, a triple-pull detection unit may be provided in place of the double-pull detection unit  64 . In this case, if the seat belt  30  is pulled three times within a predetermined period of time, the seat belt  30  is taken up by the first belt-take-up unit  66  and a predetermined tension is applied. Conversely, in place of the double-pull detection unit  64 , it may be configured such that the seat belt  30  is taken up and a predetermined tension applied if the seat belt  30  is pulled once. 
     Furthermore, in the above-described embodiment and modified examples, the seating detection unit  70  detects that an occupant is seated in the CRS  20  based on a signal from the seating sensor  40 ; however, that an occupant is seated in the CRS  20  may be detected by another method. For example, an optical camera or the like that may capture an image of the vehicle interior may be installed, and the seating detection unit  70  may determine whether or not an occupant is seated in the CRS  20  based on an image captured by the optical camera. 
     Moreover, each process that is executed by the CPU  54  reading software (programs) in the above-described embodiment may be executed by various processors other than a CPU. Examples of such processors include Programmable Logic Devices (PLD) with circuit configurations that are reconfigurable after manufacture, such as Field-Programmable Gate Arrays (FPGA), and dedicated electronic circuits that are processors including circuit configurations custom designed to execute specific processing, such as Application Specific Integrated Circuits (ASIC) or the like. Moreover, the various processing may be executed by one type of these processors, or may be executed by a combination of two or more these processors that are of the same type or different types (for example, plural FPGAs, a combination of a CPU and an FPGA, etc.). More specific examples of hardware structures of such processors include electric circuits configured by combining circuit elements such as semiconductor devices. 
     In the above-described embodiment, each program is described as being stored (installed) in a computer-readable non-transitory recording medium in advance. However, the present disclosure is not limited to this, and each program may be provided in a format of being recorded in a non-temporary recording medium such as Compact Disc Read Only Memory (CD-ROM), a Digital Versatile Disc Read Only Memory (DVD-ROM), and a Universal Serial Bus (USB) memory. Moreover, each program may be provided in a format to be downloaded from an external device over a network.