Abstract:
Provided is a seatbelt device which prevents an occupant from hitting his face against an airbag deploying at the time of a vehicle collision. In order to take up any seatbelt slack before a collision and prevent the occupant from being displaced forward, the seatbelt device comprises a first tension modifier for winding the seatbelt and taking up the seatbelt slack when a collision is predicted, and a second tension modifier for further enhancing the tension of the seatbelt and securing the occupant to the seat at the time of such collision, thereby ensuring that the occupant does not exist in the airbag deployment zone when the airbag is activated.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a seatbelt device for securing an occupant to a seat with a seatbelt and ensuring the safety of such occupant upon a vehicle collision.  
           [0003]    2. Related Art  
           [0004]    A known seatbelt device comprises a collision detector for detecting a vehicle collision and outputting a collision signal, an airbag deploying in response to the collision signal, and a seatbelt device having a pretensioner for retracting a seatbelt in response to the collision signal.  
           [0005]    However, according to this invention, a large amount of the seatbelt is protracted if, for example, an occupant is wearing clothes made of a thick material. Consequently, the amount of the seatbelt that needs to be wound would be large, because in order to effectively secure an occupant with a seatbelt device having a pretensioner, the seatbelt must have a tension above a prescribed value. If it takes time to effectively secure the occupant after an order for activating the pretensioner is given, the occupant is in the meantime displaced forward in the direction of the collision, entering the zone where the airbag is deploying. In other words, an occupant entering the airbag deployment zone while the airbag is deploying may contact the airbag and hit his/her head against the inflating airbag at the speed of its deployment. Furthermore, winding of the seatbelt is delayed if the detection of the vehicle collision is delayed, whereby the occupant is displaced in the direction of the collision. Here also, the occupant may be displaced to the airbag deployment zone and hit his/her head against the airbag.  
           [0006]    Furthermore, for the safety of the occupants it is preferred that any vehicle employing a seatbelt device simply in combination with an airbag has its seatbelt device exchanged to a seatbelt device comprising a pretensioner. In such case, a traditional collision detector must also be exchanged to a collsion detector capable of driving both an airbag device and a pretensioner, but this increases the number of parts which needs to be exchanged and is also costly.  
         SUMMARY OF THE INVENTION  
         [0007]    A purpose of this invention is to provide a seatbelt device preventing the existence of the occupant&#39;s body in the airbag deployment zone.  
           [0008]    Another purpose of this invention is to provide a seatbelt device preventing the existence of the occupant&#39;s body in the airbag deployment zone, easily replaced with a seatbelt device of a vehicle already equipped with an airbag device.  
           [0009]    In order to accomplish the aforementioned purpose, a seatbelt device according to the present invention comprises; a seatbelt fastening detector for detecting that a tongue plate, through which a seatbelt for securing an occupant to a seat passes, has been engaged with a buckle; a collision predictor for predicting a collision of a vehicle and outputting a prediction signal before the collision; a collision detector for detecting the collision of the vehicle and outputting a collision detection signal; an airbag device deploying in response to the output of the collision detection signal; a first tension modifier and a second tension modifier capable of changing the tension of the seatbelt; and a controller for activating the first tension modifier in response to the prediction signal and enhancing the tension of the seatbelt, and activating the second tension modifier in response to the collision detection signal and further enhancing the tension of the seatbelt.  
           [0010]    With such structure, if, for example, an occupant is wearing clothes made of a thick material, the first tension modifier is capable of winding before a vehicle collision any additional slack in the seatbelt caused by the thickness of the material, which needs to be wound by a second pretensioner serving as the second tension modifier. Therefore, a low-explosive powder pretensioner may complete the winding of the seatbelt before an inertia force displacing the occupant forward acts on the seatbelt. Thus, the occupant is prevented from being displaced in the direction of the collision further than a permitted range, and would not hit his/her head, etc. against a deploying airbag.  
           [0011]    Furthermore, a seatbelt device according to the present invention comprises: a seatbelt fastening detector for detecting that a tongue plate, through which a seatbelt for securing an occupant to a seat passes, has been engaged with a buckle; a collision predictor for predicting a collision of a vehicle and outputting a prediction signal before the collision; a collision detector for detecting the collision of the vehicle and outputting a collision detection signal; an airbag device deploying in response to the output of the collision detection; an airbag activation detector for detecting the activation of the airbag device and outputting an airbag activation signal; a first tension modifier and a second tension modifier capable of changing the tension of the seatbelt; and a controller for activating the first tension modifier in response to the prediction signal and enhancing the tension of the seatbelt, and activating the second tension modifier in response to the collision detection signal and further enhancing the tension of the seatbelt.  
           [0012]    With such structure, if a vehicle already equipped with an airbag device but its seatbelt device does not include a pretensioner has its seatbelt exchanged to a seatbelt device having a pretensioner, the traditional collision detector need not be exchanged to a collision detector capable of driving both the airbag and the pretensioner. Exchanging a traditional seatbelt device to a seatbelt device having a pretensioner is relatively easy, and can be done at a low cost.  
           [0013]    Preferably, the first tension modifier is a device for winding or protracting the seatbelt by a motor power source, and the second tension modifier is a device for instantly retracting the seatbelt by a power source of powder combustion gas.  
           [0014]    Preferably, the airbag activation detector outputs the airbag activation signal when a current supplied to an igniter for operating the airbag exceeds a prescribed current value, or when the temperature of the igniter exceeds a prescribed value.  
           [0015]    Preferably, the airbag activation detector outputs the airbag activation signal when any one of currents supplied to a plurality of igniters for operating a plurality of airbags exceeds a prescribed current value, or when any one of the temperatures of the plurality of igniters exceeds a prescribed value.  
           [0016]    Preferably, a seatbelt has a seatbelt retractor fixed to either a vehicle body or the seat for winding the seatbelt, and the first tension modifier and the second tension modifier are provided to the seatbelt retractor.  
           [0017]    Preferably, a seatbelt device has a seatbelt retractor which is fixed to either a vehicle body or the seat for winding the seatbelt, and the first tension modifier is provided to the seatbelt retractor, and the second tension modifier is provided to the buckle portion.  
           [0018]    Preferably, a seatbelt device has a seatbelt retractor which is fixed to either a vehicle body or the seat for winding the seatbelt, and the first tension modifier is provided to the buckle portion and the second tension modifier is provided to the seatbelt retractor, and the seatbelt retractor has a seatbelt locking mechanism for locking the protraction of the seatbelt when the first tension modifier is activated.  
           [0019]    Preferably, the first tension modifier is provided to the seatbelt retractor winding one end of the seatbelt, and the second tension modifier is provided to the wrap belt fixing portion fixing the other end of the seatbelt to a vehicle body or the seat.  
           [0020]    Preferably, the second tension modifier is provided to the seatbelt retractor winding one end of the seatbelt, the seatbelt retractor has a seatbelt locking mechanism for locking the protraction of the seatbelt when the first tension modifier is activated, and the first tension modifier is provided to the wrap belt fixing portion fixing the other end of the seatbelt to a vehicle body or the seat.  
           [0021]    Preferably, the first tension modifier is provided to the buckle portion, and the second tension modifier is provided to a wrap belt fixing portion fixing the other end of the seatbelt to a vehicle body or the seat.  
           [0022]    Preferably, the first tension modifier is provided to the wrap belt fixing portion fixing the other end of the seatbelt to a vehicle body or the seat, the second tension modifier is provided to a buckle portion, and the seatbelt retractor fixed to the vehicle body or the seat for winding the seatbelt has a seatbelt locking mechanism for locking the protraction of the seatbelt in response to an ordering signal.  
           [0023]    Preferably, the first tension modifier and the second tension modifier are provided to a wrap belt fixing portion fixing the other end of the seatbelt to a vehicle body or the seat, and the seatbelt retractor fixed to the vehicle body or the seat for winding the seatbelt has a seatbelt locking mechanism for locking the protraction of the seatbelt in response to an ordering signal.  
           [0024]    Preferably, the seatbelt retractor is provided to the seat. The wrap belt fixing portion is preferably provided to the seat. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    [0025]FIG. 1 is a diagram explaining the structure of the seatbelt device;  
         [0026]    [0026]FIG. 2 is a diagram explaining an example of the structure of an electric seatbelt retractor;  
         [0027]    [0027]FIG. 3 is a diagram explaining a potentiometer  111 ;  
         [0028]    [0028]FIG. 4 is a functional block diagram explaining the structure of a controller  200 ;  
         [0029]    [0029]FIG. 5 is a circuit diagram explaining an example of a structure of a motor driving circuit;  
         [0030]    [0030]FIG. 6 is a flowchart explaining an example of controlling a first tension modifier by a controller;  
         [0031]    [0031]FIG. 7 is a flowchart explaining an example of controlling a second tension modifier by the controller;  
         [0032]    [0032]FIG. 8 is a flowchart explaining an example of controlling an airbag device by the controller;  
         [0033]    [0033]FIG. 9 is a flowchart explaining the compulsory locking operation of a seatbelt locking mechanism controlled by the controller;  
         [0034]    [0034]FIG. 10 is a graph showing changes in the seatbelt tension when the seatbelt device is activated;  
         [0035]    [0035]FIG. 11 is a block diagram showing another example of a structure of the controller;  
         [0036]    [0036]FIG. 12 is a flowchart explaining an example where the detection of a vehicle collision by the controller is detected by the activation of the airbag device;  
         [0037]    [0037]FIG. 13 is a perspective view explaining an example of a portion of a seatbelt retractor;  
         [0038]    [0038]FIG. 14 is a perspective view explaining another example of a portion of a seatbelt retractor;  
         [0039]    [0039]FIG. 15 is a cross section of the locking mechanism of FIG. 14, shown in the direction of the rotational axis of a ratchet wheel  18 ;  
         [0040]    [0040]FIG. 16 is a diagram explaining the operation of a locking mechanism upon a rapid seatbelt protraction (seatbelt acceleration);  
         [0041]    [0041]FIG. 17 is a diagram explaining a lock arm  26 ;  
         [0042]    [0042]FIG. 18 is a diagram explaining an inertia plate  30 ;  
         [0043]    [0043]FIG. 19 is a diagram explaining the operation of a locking mechanism by the seatbelt acceleration;  
         [0044]    [0044]FIG. 20 is a diagram explaining the operation of a locking mechanism by the seatbelt acceleration;  
         [0045]    [0045]FIG. 21 is a diagram explaining the operation of a locking mechanism by the seatbelt acceleration;  
         [0046]    [0046]FIG. 22 is a diagram explaining the operation of an electromagnetic actuator (under an unlocked state);  
         [0047]    [0047]FIG. 23 is a diagram explaining the operation of an electromagnetic actuator (under a locked state);  
         [0048]    [0048]FIG. 24 is a diagram explaining another example of an electromagnetic actuator;  
         [0049]    [0049]FIG. 25 is a diagram explaining an example where an electric winch serving as a seatbelt tension modifier is fixed to the buckle side;  
         [0050]    [0050]FIG. 26 is a diagram explaining an example where an electric winch serving as a seatbelt tension modifier fixed to the seatbelt end;  
         [0051]    [0051]FIG. 27 is a diagram explaining an example of a seat provided with a seatbelt retractor;  
         [0052]    [0052]FIG. 28 is a diagram explaining a case where a pretentioner is provided on the buckle side; and  
         [0053]    [0053]FIG. 29 is a diagram explaining a case where a pretentioner is provided at the seatbelt end. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0054]    Next, the embodiments of the present invention is explained below with reference to the relevant drawings.  
         [0055]    [0055]FIG. 1 shows an example of a seatbelt device provided in a vehicle. The seatbelt device is chiefly structured of: an electric retractor  100  for winding a seatbelt  302  which is used for securing an occupant to a seat  301 ; a through anchor  303  for folding back the seatbelt  302  in the vicinity of the occupant&#39;s shoulder; a tongue plate  305  engaged with a buckle  304  provided at the hip of the occupant, through which the seatbelt passes; an anchor  306  provided at the buckle, fixing an end of the seatbelt  302  to the vehicle; a switch  307  for detecting the fastening of the seatbelt, built in the buckle; a controller  200  (not shown) for controlling a seatbelt retractor  100 ; a collision predictor  401  (not shown) for predicting a vehicle collision; and a collision detector  402  (not shown). Furthermore, an airbag device  500  is provided at the center portion of the steering wheel. Furthermore, other airbags (not shown) are also provided in the dashboard of the passenger seat and by the doors of the vehicle.  
         [0056]    [0056]FIG. 2 is a diagram roughly explaining the structure of the seatbelt retractor  100 . In this Figure, the seatbelt retractor  100  comprises a frame  101 . Rotatably provided to the frame  101  are a reel  103  for winding the seatbelt  302 , and a reel shaft  103   a  coupled with the reel  103 , which serves as an axis upon the rotation of the reel. Provided at the right end of the reel shaft  103   a  is a seatbelt locking mechanism  102  (explained below) for locking the protraction of the seatbelt  302 . The seatbelt locking mechanism  102  comprises: a VSI locking mechanism for locking the protraction of the seatbelt when a prescribed deceleration of the vehicle acts on the vehicle; and a WSI locking mechanism for locking the protraction of the seatbelt when the seatbelt  302  is protracted by a prescribed acceleration of the vehicle. Moreover, the seatbelt locking mechanism  102  is further provided with a electromagnetic actuator  112  for performing a compulsory operation of the seatbelt locking mechanism  102  in response to an ordering signal. The operation of the electromagnetic actuator  112  is controlled by the output of the controller  200  explained below. The seatbelt locking mechanism  102  is structured such that an electric motor  110  serving as a first tension modifier may protract the seatbelt  302  even if the winding of the seatbelt  302  is “locked.” 
         [0057]    A pretensioner  104  constituting a second tension modifier is actuated by the output of the collision detector (not shown), and causes the reel shaft  103   a  to rotate in the seatbelt winding direction and thereby performs compulsory winding of the seatbelt in order to secure the occupant to the seat. The pretensioner  104  may, for example, be a powder pretensioner, and be chiefly structured of a gas generator, a cylinder for enclosing any gas generated from the gas generator, a piston moving within the cylinder by the pressure of the gas, and a transmission mechanism for converting the movement of the piston to a rotational movement of the reel shaft  103   a  via a crutch mechanism.  
         [0058]    A pulley  105  secured to the reel shaft  103   a  is connected to a pulley  106  which is fixed to the axis of DC motor  110  via a power transmission belt  107 . The pulleys  105  and  106  respectively have a prescribed number of outer teeth formed along the outer peripheries thereof, and seatbelt  107  has a prescribed number of inner teeth formed on the inner periphery thereof. The teeth of the pulley  105  used for the reel shaft and the pulley  106  used for the motor exactly match and mutually bite, and the rotation of the motor  110  is thereby communicated to the reel shaft  103   a . The motor  110  is secured at two points or more and is operated by the output of the controller  200 .  
         [0059]    As shown in FIG. 3, the potentiometer  111  provided at the leftmost end of the reel shaft  103   a  is chiefly structured of a resister having voltage applied to both of its ends, and a slider which moves together with the rotation of the reel shaft  103   a . Furthermore, a voltage value corresponding to the amount of the rotation from the standard position of the reel shaft  103   a  is output to the controller  200 . Thus, the amount of seatbelt protraction, etc. can be estimated. Furthermore, by comparing the voltage under the non-slack state of the seatbelt with that under the protracted state of the seatbelt, the amount of the slack in the seatbelt can be estimated.  
         [0060]    [0060]FIG. 4 is a functional block diagram explaining the schematic structure of the controller  200 . As shown in FIG. 4, the controller  200  is structured as a microcomputer system. A CPU  201  loads to the work area of the RAM  203  the controlling program and the data held in ROM  202 , and thereby controls the operation of the electromagnetic actuator (for example, a solenoid)  112  which performs the compulsory operation of the motor  110  and the seatbelt locking mechanism  102 .  
         [0061]    The collision predictor  401  shown in FIG. 4 identifies whether or not there is a possibility of a collision with a vehicle driving ahead or any other obstacles, and also whether or not such collision can be avoided. For example, a non-contacting distance sensor such as a laser radar, a supersonic sensor, etc. periodically measures the distance between another vehicle or an obstacle at predetermined moments. A relative speed is calculated by the changes in such distance and the elapsed time. The time remaining until a collision is calculated by subtracting the relevant distance according to the relative speed. If the time remaining until the collision is shorter than the preset time T1, the possibility of a collision is indicated by an output of a collision prediction signal. This signal is provided to an inputting interface  204 , and a “collision prediction flag” in a flag region (flag register) of a RAM  203  is thereby set “on.” As a consequence, the interruption processing explained below is commenced by the CPU  201 .  
         [0062]    The output by a buckle switch  307  is communicated via the input interface  204 , and a flag corresponding to the fastening/non-fastening of the seatbelt is set in the flag region of the RAM  203 .  
         [0063]    The collision detector  402  detects by the acceleration sensor the impact caused to the vehicle at the time of a collision, and processes an acceleration signal and detects a collision according to the size and the initial waveform thereof. This signal is provided to the input interface  204 , whereby a “collision detection flag” included in the flag region of the RAM  203  is set “on.” As a consequence, the interruption processing later explained is commenced by the CPU  201 .  
         [0064]    Furthermore, A/D conversions of voltages output by the aforementioned potentiometer  111  is performed by the input interface  204  at prescribed intervals, but this processing has no direct relation with the present invention and is therefore not shown in the figure. The input interface  204  internally comprises a CPU, and monitors the output voltage data after it has been converted. For example, if the value of the output voltage data obtained in the current processing differs from the output voltage data obtained in the previous processing, then the rotational status of the shaft  103   a  is identified, whereby either a “seatbelt protraction” flag or a “seatbelt winding” flag is set to the flag region of the RAM  203  depending on whether or not the difference in the output voltage is negative or positive compared with the data obtained in the previous processing. Furthermore, the output voltage data is written to the rotation amount area in the RAM  203  by a DMA operation. When the seatbelt has been wound, the change in the output voltage data in the seatbelt in the seatbelt protracting direction corresponds to the amount of the slack in the seatbelt. The amount of the slack in the seatbelt is written to the slack amount area in the RAM  203 .  
         [0065]    A current detector CT provided at a motor driving circuit  206  (explained below) detects a voltage passing through the motor  110  as a voltage corresponding to the current. The voltage is subject to A/D conversions performed by the input interface  204  at prescribed intervals, and is thereafter written to the motor current region in the RAM  203  by a DMA operation. Since the current of the motor  110  is related with a torque of the motor, the torque can be estimated by the value of the load current. The torque of the motor  110  constitutes a force (tension) for retracting the seatbelt  302 .  
         [0066]    When a prescribed condition set in the controlling program is fulfilled, the CPU  201  gives an output interface  205  a normal rotation order, a reverse rotation order, or a drive suspension order regarding the motor  110 . The output interface  205  creates gate signals G 1  and G 2  pursuant to these orders, and the signals are provided to the motor driving circuit  206 . When a normal rotation order is given, the gate signals G 1  and G 2  are respectively set at “H” and “L”. When a reverse rotation order is given, the gate signals G 1  and G 2  are respectively set at “L” and “H”. When a drive suspension order is given, the gate signals G 1  and G 2  are respectively set at “L” and “L”.  
         [0067]    [0067]FIG. 5 is a circuit diagram showing an example of a structure of a motor driving circuit. A transistor bridge circuit is formed by four transistors, i.e., PNP transistors Q 1  and Q 2 , and NPN transistors Q 3  and Q 4 . Emitters of transistors Q 1  and Q 2  are mutually connected and a power source Vc is supplied to their connection point. Furthermore, emitters of transistors Q 3  and Q 4  are mutually connected and the connection point becomes a ground level.  
         [0068]    As already mentioned, the current detector CT detects the level of the currents outputted by the emitters for each of the transistors Q 3  and Q 4 , and sends a level detection signal to the input interface  204 . The input interface  204  performs an A/D conversion of the level detection signal, and thereafter writes the obtained data to the seatbelt tension area in the RAM  203  through a DMA operation. Since the value of the load current passing through the motor is related with the torque of the motor, the seatbelt tension F can be thereby estimated.  
         [0069]    The collector of the transistor Q 1  and the collector of the transistor Q 3  are connected via a diode D 1 . The collectors of the transistor Q 2  and Q 4  are connected via a diode D 2 . The base of the transistor Q 1  and the collector of the transistor Q 4  are connected via a bias resistance R1. The base of the transistor Q 2  and the collector of the transistor Q 3  are connected via a bias resistance R2. A DC electric motor M is connected between the respective collectors of the transistors Q 1  and Q 2 .  
         [0070]    With such structure, when a normal rotation order (G 1 =“H”; G 2 =“L”) is supplied to the respective gates of the transistors Q 3  and Q 4  from the output interface  205 , the transistor Q 3  becomes conductive and the transistor Q 4  becomes non-conductive. The collector of the transistor Q 3  becomes a ground level by the conductivity, and the base of the transistor Q 2  is biased to a low level (substantially a ground level) via the resistance R2 and makes the transistor Q 2  conductive. The collector of the transistor Q 4  becomes substantially the power source Vc level, and the base of the transistor Q 2  is biased to a high level via the resistance R1 and makes the transistor Q 1  non-conductive. As a result, a current path is formed in a forward direction by a route: power source Vc, transistor Q 2 , motor M, diode D 1 , transistor Q 3 , and the ground. Thus, the motor M rotates in the seatbelt winding direction.  
         [0071]    When a reverse rotation order (G 1 =“L”; G 2 =“H”) is supplied to the respective gates of the transistors Q 3  and Q 4  from the output interface  205 , the transistor Q 3  becomes non-conductive and the transistor Q 4  becomes conductive. The collector of the transistor Q 4  becomes a ground level, and the base of the transistor Q 1  is biased to a low level via the resistance R1 and makes the transistor Q 1  conductive. The collector of the transistor Q 3  becomes substantially the power source Vc level, and the base of the transistor Q 2  is biased to a high level via the resistance R2 and makes the transistor Q 2  non-conductive. As a result, a current path is formed in a reverse direction by a route: power source Vc, transistor Q 1 , motor M, diode D 2 , transistor Q 3 , and the ground. Thus, the motor M rotates in a direction to protract the seatbelt.  
         [0072]    When a drive suspension order (G 1 =“L”; G 2 =“L”) is supplied to the respective gates of the transistors Q 3  and Q 4  from the output interface  205 , both of the NPN transistors Q 3  and Q 4  become non-conductive. If the transistor Q 3  becomes non-conductive from a conductive state, the collector of the transistor Q 3  is enhanced from the ground level to substantially the power source level, and the base of the transistor Q 2  is biased to a high potential and the transistor Q 2  is cut off. Similarly, if the transistor Q 4  becomes non-conductive from a conductive state, the collector of the transistor Q 4  is enhanced from the ground level to substantially the power source level, and the base of the transistor Q 1  is biased to a high potential and the transistor Q 1  is cut off. Thus, if a drive suspension order is given, the respective transistors forming the bridge become non-conductive.  
         [0073]    Returning to FIG. 4, upon fulfillment of a condition for operating the compulsory lock of the seatbelt locking mechanism  102 , the CPU  201  gives the interface  205  a lock order signal (operation of the solenoid) The activation order signal set at the flag register of the output interface  205  is amplified by a power amplifier  207  from a logic-level signal to a level capable of activating the solenoid, and the signal is then provided to the solenoid  112 . The operation of the solenoid causes the displacement of the actuator and the operation of the locking mechanism  102  of the retractor  100 . When operated, the seatbelt locking mechanism  102  prevents the protraction of the wound seatbelt so that there is no slack in the seatbelt, but allows the winding of the seatbelt.  
         [0074]    [0074]FIG. 6 is a flowchart explaining the control performed by a controller  200 . Here, the operation of a first tension modifier, namely, a seatbelt winding motor is controlled.  
         [0075]    By executing a main program, the CPU  201  periodically monitors the seatbelt fastening flag (S 12 ). When the seatbelt fastening flag is “on” (S 12 ; Yes), the CPU  12  determines the possibility of a collision according to whether or not a collision prediction flag is set (S 14 ). If the flag is set (S 14 ; Yes), the motor driving circuit  206  is operated and the motor  110  serving as a slack remover or a tension modifier is driven and made to rotate in the seatbelt winding direction for winding a webbing  302  (S 16 ). Thus, the slack in the seatbelt is removed to a certain degree. For example, winding of the seatbelt may be performed either until the tension of the seatbelt exceeds a prescribed value, or for the duration of a prescribed period of time. The tension of the seatbelt can be identified by reading the sample value written in the current value area in the RAM  203 .  
         [0076]    When the seatbelt is not fastened (S 12 ; No) or the collision prediction flag is “off” (S 14 ; No), there is no need to remove the slack in the seatbelt. Therefore, the CPU  201  orders the output interface  205  to stop driving the motor  110 , so that the motor would stop rotating to wind the seatbelt (S 18 ). Consequently, the motor driving circuit  206  stops supplying the motor  110  with a current, and the operation of the motor  110  is terminated. The routine is thus terminated, and the processing returns to the main program.  
         [0077]    If a seatbelt is not fastened, the seatbelt is housed in the seatbelt winding device  100  by the force of a seatbelt winding spring  114 . When the seatbelt is fastened, the minimum slack in the seatbelt is removed.  
         [0078]    Now, referring to FIG. 7, the operation of the pretensioner serving as the second tension modifier is explained.  
         [0079]    The CPU  201  executes this routine either periodically or pursuant to an interruption processing. If the seatbelt is fastened (S 22 ; Yes), the CPU  201  identifies whether or not any collision is detected (S 24 ). If the collision detection flag is set “on” and a collision is thereby detected (S 24 ; Yes), the CPU  201  activates the pretensioner  104 , which is activated by an explosive system, as the second tension modifier. The seatbelt is thereby quickly retracted, and the slack in the seatbelt is taken up, whereby the occupant is firmly secured. If the seatbelt is not fastened (S 22 ; No), or no collision is detected (S 24 ; No), the second tension modifier is not operated, and the routine is terminated.  
         [0080]    [0080]FIG. 8 is a flowchart explaining an example of controlling the operation of the airbag device.  
         [0081]    The CPU  201  executes this routine either periodically or by an interruption processing. If the collision detection flag is set “on” and a collision is thereby detected (S 32 ; Yes), the CPU  201  supplies the airbag device with an ignition signal for igniting the low-explosive powder, and the quick expansion of the combustion gas makes the airbag deploy (S 34 ). Thus, the occupant is saved from any secondary collision inside the vehicle. If no collision is detected (S 32 ; No), this routine is terminated.  
         [0082]    [0082]FIG. 9 is a flowchart explaining the compulsory operation of the seatbelt locking mechanism.  
         [0083]    If the first tension modifier operated by the collision detection signal from the collision detector  401  shown in FIG. 4 is, by itself, or together with the second tension modifier, operated by the collision detection signal which is output from the collision detector  402  shown in FIGS. 1 and 4 and communicated to a portion other than the seatbelt retractor (e.g., the securing portion of the buckle, or a wrap belt), then the operation of the tension modifier(s) acts in the direction for protracting the seatbelt. Accordingly, the tension of the seatbelt is ensured by performing a compulsory operation of the seatbelt locking mechanism in advance and preventing any protraction of the seatbelt.  
         [0084]    The CPU  201  executes the main program and periodically monitors the seatbelt fastening flag (S 42 ). If the seatbelt fastening flag is “on” (S 42 ; Yes), a possibility of a collision is detected depending on whether or not the collision protection flag is set (S 44 ). If the flag is “on” (S 44 ; Yes), a lock ordering signal is communicated to the output interface  205 , and the locking mechanism  102  of the retractor  100  is operated. When operated, the seatbelt locking mechanism  102  prevents the protraction of the wound seatbelt and the slack in the seatbelt, but allows the winding of the seatbelt (S 46 ). The CPU  201  operates the motor driving circuit  206  and drives the motor  110  so that it rotates in the seatbelt winding direction for winding the webbing  302  (S 48 ). Thus, the slack in the seatbelt is removed to a certain degree. For example, winding of the seatbelt may be performed either until the tension of the seatbelt exceeds a prescribed value, or for the duration of a prescribed period of time. The tension of the seatbelt can be identified by reading the sample value written in the current value area in the RAM  203 .  
         [0085]    If the seatbelt is not fastened (S 42 ; No), or the collision prediction flag is “off” (S 44 ; No), the CPU  201  is not required to operate the seatbelt locking mechanism and a command for releasing the lock is provided to the output interface  205 . As a result, the lock is released, and the seatbelt can be protracted (S 50 ). Subsequently, an order for ceasing to drive the rotation of the motor  110  is provided to the output interface  205  (S 52 ). Consequently, the motor driving circuit  206  stops supplying the motor  110  with a current, and the operation of the motor  110  is terminated. The routine is thus terminated, and the processing returns to the main program.  
         [0086]    Furthermore, if the seatbelt is not fastened, the seatbelt is stored in the retractor  100  by the force of the winding coil  114 . If the seatbelt is fastened, the minimum slack in the seatbelt is removed as explained in the case above.  
         [0087]    [0087]FIG. 10 is a graph which shows for the elapsed time the changes in the seatbelt tension when the first and second tension modifiers and the airbag device are activated by the controlling process illustrated in FIGS. 6 through 8.  
         [0088]    In FIG. 10, the possibility of a collision is identified at time t1, and the operation of the motor  110  is commenced and the tension of the seatbelt increases from F0 by the winding coil. At time t2, a collision takes place. At time t3, the collision is detected and the pretentioner  104  and the airbag  500  are operated. Since the seatbelt is wound by the motor  110  and the pretensioner  104 , the tension of the seatbelt quickly rises from tension F1 as of t1. Due to the impact of the collision, the seatbelt locking mechanism  102  locks the protraction of the seatbelt by a VSI operation. After time t4, where the tension of the seatbelt reaches F2, the tension is further increased by the addition of a forward inertia force acting on the occupant in the direction to protract the seatbelt from the retractor  100 .  
         [0089]    Furthermore, when the impact of the collision is added to the vehicle, the protraction of the seatbelt is locked by the VSI sensor located at the seatbelt retractor  100 . Moreover, if the seatbelt  302  is quickly protracted by the WSI sensor located at the seatbelt retractor  100 , the protraction of the seatbelt  302  is locked.  
         [0090]    [0090]FIG. 11 is a block diagram explaining the second embodiment of the present invention. In this figure, components corresponding to those of FIG. 4 are shown with the same reference numerals, and explanations for such components are omitted.  
         [0091]    According to this example, an operation of the airbag  500  provided independently from the seatbelt devise and operating independently from the seatbelt device is used by the seatbelt device for detecting a collision.  
         [0092]    When a collision detection signal is communicated to the airbag device  500  from the collision detector  402  detecting the collision of the vehicle, an ignition current is conducted through an ignition squib, whereby the low-explosive powder ignites and expansion gas is generated, and the airbag deploys. Supply of the ignition current is detected by the activation detector  510 . Regarding the detection of the ignition current, activation of the airbag, for example, can be detected by mounting a clamp-type current sensor on a wire harness through which the ignition current flows, and determining whether or not the detected current exceeds a prescribed value. Otherwise, activation of the airbag may be detected by providing a temperature sensor in the vicinity of the igniter of the airbag and identifying an activation of the airbag when the temperature of the ignited portion exceeds a prescribed value.  
         [0093]    The activation detector  510  supplies the input interface  204  with an activation detection signal. Through a DMA operation, the input interface  204  sets the activation detection flag “on” in the flag region of the RAM  203 . This means that a vehicle collision has taken place, and therefore, the aforementioned collsion detection flag may be set “on”.  
         [0094]    In some cases, multiple airbag devices  500  can be provided at the center portion of the steering wheel, in the dashboard of the passenger seat, by the side doors, etc. In such cases, as shown in FIG. 11, an activation detectors  510  can be mounted on each of the airbag devices, so that the activation detection signal in each of the activation detector  510  is provided to the input interface  204 . This allows the CPU  201  to determine that a vehicle collision has taken place. Other parts of the invention have the same structure as explained above.  
         [0095]    [0095]FIG. 12 is a flowchart explaining an example of controlling the operation of the pretensioner constituting a second tension modifier, synchronizing with the operation of the airbag device.  
         [0096]    The CPU  201  executes this routine either periodically or by an interruption processing. If the seatbelt is fastened (S 62 ; Yes), the CPU  201  identifies whether or not activation of the airbag device is detected (S 64 ). If the activation detection flag is set “on” and the operation of the airbag device, i.e., a collision is detected (S 64 ; Yes), the CPU  201  operates the powder pretensioner  104  serving as the second tension modifier (S 66 ). The seatbelt is thereby quickly wound, and the slack in the seatbelt is removed, whereby the occupant is firmly secured. If the seatbelt is not fastened (S 62 ; No) or no collision is detected (S 64 ; No), the second tension modifier is not activated, and this routine is terminated.  
         [0097]    [0097]FIGS. 13 through 24 are exploded perspective views of the retractor  100  and longitudinal sectional views of the major part thereof, chiefly explaining the seatbelt locking mechanism  102  (the mechanical locking mechanism of the reel, the WSI locking mechanism which is operated when sensing the seatbelt protraction acceleration, the VSI locking mechanism which is operated when sensing the vehicle deceleration, etc.), and the electromagnetic actuator  112 . As shown in FIG. 9, when a possibility of a collision is identified, a compulsory locking of the seatbelt locking mechanism  102  takes place. Accordingly, the mechanical locking mechanism explained below is provided mainly for securing the occupant at the time of a collision if the operation of this compulsory lock is hindered for any reason. In an example shown in FIG. 13, no pretensioner is provided. If a pretensioer is required due to the property of the vehicle, the pretensioner  104  shown in FIG. 2 is provided between a retractor base  1  and a power transmission unit  15  shown in FIG. 13.  
         [0098]    In FIGS. 13 through 18, the major part of the retractor base has a substantially U-shaped cross section. The facing side plates  1   a  and  1   b  have facing winding shaft through holes provided thereon. The reel  3 , which serves as the winding shaft for winding the seatbelt  302  (not shown), passes through these winding shaft through holes and is rotatably provided thereto.  
         [0099]    The winding shaft through holes on the side plate la has inner gear teeth  2  formed along its inner periphery, and a ring  4  is provided outside of the winding shaft through hole. A drawing processing is performed on the inner periphery of the ring  4 , and when the ring  4  is fixed to the outside of the side plate  1   a  by a rivet  40 , a gap is formed in the axial direction between the inner gear teeth  2  and the inner periphery edge of the ring  4 .  
         [0100]    The retractor base  1  further comprises, on the side plate  1   a  side, an emergency locking mechanism for preventing any protraction of the seatbelt upon an emergency. Furthermore, provided to the side plate  1   b  side of the base  1  is a power transmission unit  15  which includes: a pulley  105  connected to an axis  15   c  (corresponds to the reel shaft  103   a ) driven by the electric motor  110  via a timing belt  107 ; a winding coil  114 ; and a potentiometer  111  (all not shown). The reel  3  is substantially a cylindrical winding shaft integrally formed of aluminum alloy or the like. A barrel  28  to which the seatbelt is wound has a slit opening  28   a  in the diameter direction for passing and holding the seatbelt end therein. Furthermore, on the outer periphery of the reel  3 , a flange  13  formed as a separate body is provided for preventing any winding disorder of the seatbelt. Furthermore, the seatbelt is wound along the outer periphery of the reel  3  mounted on the retractor base  1 . The seatbelt is inserted and passed through the seatbelt guide  41  fixed to the upper portion of the back plate of the retractor base  1 , and the incoming/out position of the seatbelt is thereby restricted.  
         [0101]    A protruding rotation spindle for rotatably supporting the reel  3  is provided to both ends of the reel  3 . A separately-formed spindle pin  6  is press fitted to the sensor side end face of the reel  3  and serves as a rotation spindle. The sensor side end face of the reel  3  further comprises a protruding spindle  7  which rockably supports a pole  16  serving as a lock member engagable with the inner gear teeth  2  formed on the side plate  1   a . Furthermore, when the pole  16  rocks and rotates in the direction to engage with the inner gear teeth  2 , the positions of the rocking side end of the pole  16  and the rear end  16   e thereof on the opposite side are defined, and when a large load is fastened to an area between the inner gear teeth  2  and the pole  16 , a pressure receiving face  45  for receiving the load is provided on the sensor side end face of the reel  3 .  
         [0102]    Furthermore, on the sensor side end face of the reel  3 , a stopper protrusion  8  is provided for the purpose of preventing a counterclockwise rotation of the rocking lever  20  supported in a rockable manner by a ratchet wheel  18  which serves as a latch member of the lock operator explained below. A concave part  9  constitutes a recess for preventing any interference to the reel  3  either by the extension coil spring  36  urging the rotation of the ratchet wheel  18  in the seatbelt protracting direction (direction of arrow x 2  shown in FIG. 14) or by an arm portion  26   c  of the lock arm  26  pressing the sensor spring  25  explained below.  
         [0103]    The rocking end of the pole  16  comprises an integrally-formed gear teeth  16   c  which corresponds to and is engagable with the inner gear teeth  2  formed on the side plate  1   a . Moreover, a spindle hole  16   a , to which a spindle  7  is fitted with some recess, penetrates the center of the pole  16 . Furthermore, an engaging protrusion  16   b  located on the rocking end side and an engaging protrusion  16   d  located on the rear end  16   e side protrude from the sensor side end face of the pole  16 .  
         [0104]    In other words, since the spindle  7  is loosely fitted to the spindle hole  16   a , the pole  16  is rockably and rotatably supported by the spindle  7 , and is capable of making relative movements in a prescribed amount. Furthermore, the tip of the spindle  7  penetrating the spindle hole  16   a  of the pole  16  is fastened by the stopper hole  17   b  of a retaining plate  17 , and a through hole  17   a  of a retaining plate  17  is penetrated by a spindle  6  which is press fit to the reel  3 . The retaining plate  17  prevents the pole  16  from lifting up from the end face of the reel  3 .  
         [0105]    Furthermore, the end of the engaging protrusion  16   b  of the pole  16  is inserted into the cam hole  18   a of the ratchet wheel  18 . The ratchet wheel  18  is located at the outside of the retaining plate  17  and rotatably supported by the spindle pin  6 . When the relative rotation of the ratchet wheel  18  with respect to the reel  3  is in the seatbelt winding direction (direction of arrow X 1  in FIG.  14 ), the cam hole  18   a  moves the end of the engaging protrusion  16   b  radially outward from the rotation shaft of the reel  3 . As a consequence, the pole  16  is made to rock and rotate around the spindle  7  in the direction (direction of arrow Y 1  in FIG. 13) to engage with the inner gear teeth  2  formed on the side plate  1   a.    
         [0106]    Namely, the pole  16  rocks and rotates in the direction to engage with the inner gear teeth  2 , and the engagement of the teeth  16   c  of the pole  16  with the inner gear teeth  2  constitutes a locking device for preventing any rotation of the reel  3  in the seatbelt protracting direction. The ratchet wheel  18  is a ratchet rotatably supported by the spindle pin  6 . On the outer periphery of the ratchet wheel  18 , ratchet teeth  18   b  are provided for engagement with the sensor arm  53  of the vehicle acceleration sensor  51 . Furthermore, a flange  6   a  of the spindle pin  6  supports, as its axis, the center hole  30   a  of the inertia plate  30 , i.e., a disc inertia element serving as a sensor for sensing the seatbelt protraction acceleration. In the vicinity of the center hole of the ratchet wheel  18 , a stopper pawl portion  23  engages with the engaging hole  30   b  and thereby determines the position of the inertia plate  30  in the thrusting direction thereof. The long hole  24  formed on the ratchet wheel  18  is engaged with the engaging protrusion  31  of the inertia plate  30 , and an edge  24   a  of the long hole  24  determines the position of the rotating direction of the inertia plate  30  when the emergency locking mechanism is not operated (see FIG. 16).  
         [0107]    As shown in FIG. 16, the outer side face of the ratchet wheel  18  comprises, protruding therefrom, a shaft  22  which supports the lock arm  26  as an axis and a spring hook portion  55 . Furthermore, as shown in FIG. 20, the inertia plate  30  has an opening  56  through which the spring hook portion  55  is inserted. The opening  56  is formed as a long hole such that the inertia plate  50  is able to relatively rotate with respect to the ratchet wheel  18  while the spring hook  55  is inserted therein, and a spring hook portion  57  corresponding to the spring hook  55  is provided at one end of the opening  56 .  
         [0108]    A compression coil spring  58  is fitted and inserted between a pair of the spring hooks  55  and  57 . As shown in FIG. 19, the compression coil spring  58  is urged so that the engaging protrusion  31  on the inertia plate  30  is maintained in an unlocked state where the inertia plate  30  touches the other end  24   b  of the long hole  24  formed on the ratchet wheel  18 .  
         [0109]    Provided on the inner side face of the ratchet wheel  18  is a spring hook  21 . The extension coil spring  36 , the one end of which is hooked by the hook  17   c  of the retaining plate  17 , has its other end hooked by the coil hook  21 . The extension coil spring  36  urges the rotation of the ratchet wheel  18  with respect to the reel  3  in the seatbelt protracting direction (in the direction of arrow X 2 ). As shown in FIG. 17, the lock arm  26  includes a stopper pawl  26   b  capable of biting an inner teeth gear  34   a  of a gear case  34 , and also an arm portion  26   c  for pressing the center portion of the linear sensor spring  25  in a longitudinal direction, whose both ends are supported by a pair of hooks  18   d  formed on the outer side face of the ratchet wheel  18 .  
         [0110]    Accordingly, the lock arm  26  bites the inner teeth gear  34   a , thereby engaging with the stopper pawl  26   b  and constituting a stopper element for preventing the rotation of the ratchet wheel in the seatbelt protracting direction. By the urging force of the sensor spring  25 , the stopper pawl  26   b  is pressed and urged toward the contacting portion  32  of the inertia plate  30 . Furthermore, the ratchet wheel  18  corresponding to the rocking range of the arm portion  26   c  has an opening for the penetration of the arm portion  26   c  formed thereon, which is provided solely for ensuring the engagement of the arm portion  26   c  with the sensor spring  25 .  
         [0111]    As a cam face grinding and contacting the back  26   d  of the stopper pawl  26   b  of the lock arm  26 , the contacting portion  32  is structured of a first cam face  32   a  not affecting the lock arm  26  by the rotation of the inertia plate  30 , and a second cam face  32   b  for rocking the arm  26  in correspondence with the delay in the rotation of the inertia plate  30  from the rotation of the reel  3  and causing the stopper pawl  26   b  to bite the inner teeth  34   a.    
         [0112]    The emergency locking mechanism being unlocked, the first cam face  32   a  contacts the back  26   d  of the lock arm  26 , and the back  26   d  does not contact the second cam face  32   b  until the delay in the rotation of the inertia plate  30  from the rotation of the reel  3  exceeds a prescribed value. Regarding the length of the first cam face  32   a , i.e., the quantity of the rotation of the inertia  30  in the state of the back  26   d  slidably contacting the first cam face  32   a , if the rotation of the inertia plate  30  is delayed from the rotation of the reel  3  by the inertia force acting on the inertia plate  30  when the entire seatbelt is retracted, the first cam face  32   a  is set at a length to prevent the back  26   d  of the lock arm from reaching the second cam face  32   b  by such level of delay in the rotation.  
         [0113]    Furthermore, the lock arm  26  according to the present embodiment includes a contacting pawl  26   e at its rocking end located opposite to the stopper pawl  26   b . Corresponding to the contacting pawl  26   e , the inertia plate  30  includes a step  33  to which the contacting pawl  26   e can contact. The step  33  is provided for enabling such contact of the contacting pawl  26   e when the inertia plate  30  is at its initial position under an unlocked state, and thereby restricting the rotation and movement of the lock arm  26  in the locking direction. As shown in FIGS. 20 and 21, when the rotation of the inertia plate  30  is delayed more than a prescribed value and the back  26   d  of the lock arm  26  touches the second cam face  32   b , the lock arm  26  can rock in the looking direction by the pressing effect of the second cam face  32   b.    
         [0114]    Furthermore, on the spindle  19  protruding from the inner side face of the ratchet wheel  18 , a rocking lever  20  supported by an shaft hole  20   a  is rockably provided. A counterclockwise rotation of the rocking lever  20  is suitably restricted by the stopper protrusion  8  protruding from the sensor side end face of the reel  3 . Furthermore, the rocking lever  20  is assembled between the reel  3  and the ratchet wheel  18 , so that when the pressing protrusion  16   d  protruding from the sensor side face contacts an area between the spindle  19  and the stopper protrusion  8 , the clockwise rotation of the rocking lever  20  is suitably restricted.  
         [0115]    At the center portion of the gear case  34  provided outside the inertia plate  30 , a shaft supportor  34   b  is provided via the spindle  6  to rotatably support the reel  3 . A collar  6   a  of the spindle  6  contacts the bottom face of the shaft supporter  34   b , which constitutes a surface for defining the axial direction of the reel  3 . Furthermore, provided at the lower portion of the gear case  34  is a box-shaped housing  50  which houses the vehicle acceleration sensor  51  for sensing the acceleration of the vehicle.  
         [0116]    The sensor cover  35  is provided outside the side plate  1   a  covering the gear case  34 .  
         [0117]    Next, the operation of the aforementioned seatbelt retractor is explained below. Foremost, as shown in, FIG. 19, in a normal state, the ratchet wheel  18  is urged with respect to the reel in the seatbelt protracting direction by the urging force of the extension coil spring  36  hanging from a hook  17   c  of a plate  17 , and the pole  16  having an engaging protrusion  16   b  which engages with a cam hole  18   a  is thereby urged in a direction to disengage from the inner gear teeth  2 . Consequently, the reel  3  can rotate, and the seatbelt is freely protracted.  
         [0118]    Thus, if the seatbelt acceleration sensor or the vehicle acceleration sensor  51  including the inertia plate  30  is activated upon an emergency such as a vehicle collision, a rotation of the ratchet wheel  18  in the seatbelt protracting direction is prevented either by the lock arm  26  or the sensor arm  53  which serve as stopper elements for preventing the rotation of the ratchet wheel  18  in the seatbelt protracting direction, and the locking element of the retractor is activated.  
         [0119]    After the vehicle acceleration sensor  51  or the seatbelt acceleration sensor is activated and the seatbelt is protracted from the retractor, the rotation of the ratchet wheel  18  is delayed compared with the rotation of the reel  3 , and the ratchet wheel  18  performs a relative rotation in the seatbelt winding direction (direction of arrow X 1 ). Thus, the cam hole  18   a  of the ratchet wheel  18  displaces the engaging protrusion  16   b  on the pole  16  radially outward from the central axis of rotation. The pole  16  thereby rockably rotates around the spindle  7  in a direction (direction of arrow Y 1  in FIG. 13) to engage with the inner gear teeth  2 .  
         [0120]    Furthermore, when the seatbelt is protracted from the retractor, the gear teeth  16   c  bites the inner engaging  2  and the operation is thereby completed. Under this condition, there is a gap between the rear end  16   e of the pole  16  and the pressure receiving face  45  of the reel  3 , while the rotation of the rocking lever  20  is restricted by both the stopper protrusion  8  of the pole  3  and the pressing protrusion  16   d  of the pole  16  with almost no recess.  
         [0121]    The spindle  7  of the reel  3  loosely fits into the spindle hole  16   a  of the pole  16 , such that the spindle hole  16   a  is rockably and rotatably supported, capable of making relative movements toward the reel  3  in a prescribed value. Therefore, if the seatbelt is protracted from the retractor, the pole  16  performs relative rotations with respect to the reel  3  around the rotational axis of the reel  3  until the rear end  16   e contacts the pressure receiving face  45 .  
         [0122]    In such case, although the pressing protrusion  16   d  of the pole  16  is in an immobile position with respect to the side plate  1   a , the stopper protrusion  8  of the reel  3  rotates in the seatbelt protracting direction (direction of arrow X 2 ). As a result of this movement, the rocking lever  20  rockably rotates in the clockwise direction shown in FIG. 14 as the rocking end is pressed by the stopper protrusion  8 , and is made to rockably rotate around the pressing protrusion  16   d  being the fulcrum of its rotation. When the rocking lever  20  rockably rotates in the clockwise direction in FIG. 14 around a contact point of the rocking lever  20  and the pressing protrusion  16   d , the shaft hole  20   a  rotatably supported by the spindle  19  of the ratchet wheel  18  rotates in the seatbelt winding direction (direction of arrow X 1 ) with respect to the central rotational axis of the reel  3 . As a result, the ratchet wheel  18  rotates in the reverse direction with respect to the reel  3  in the seatbelt winding direction (in the direction of arrow X 1 ).  
         [0123]    Accordingly, even if the vehicle acceleration sensor  51  or the seatbelt acceleration sensor is activated and the locking element of the retractor is “locked” for preventing the rotation of the reel  3  in the seatbelt protracting direction, the ratchet wheel  18  which is prevented from rotating in the seatbelt protracting direction can be set “free” in order to disengage from the inner gear teeth  34   a  of the gear case  34  either the sensor arm  53  of the car acceleration sensor  51  or the lock arm  26  of the seatbelt acceleration sensor.  
         [0124]    When the pole  16  is locked, any larger tension acting on the seatbelt causes deformation of the supporting axis  34   b  of the gear case  34  and the portion supporting the axis  15   c  of the power transmission unit  15 , and the reel  3  attempts to move upward. This can be avoided by the contacting face  3   a  and a groove  3   b  formed on the reel respectively contacting the inner gear teeth  2  and the gear teeth  62  formed on the side board  1   b  (see FIG. 13), and the tension acting on the seatbelt is received by these surfaces.  
         [0125]    By the time the vehicle stops and the tension acting on the seatbelt is released, the engagement between the ratchet wheel  18  and the inner teeth gear  34   a  formed on the gear case  34  of the sensor arm  53  or the lock arm  26  has been released, and the urging force of the extension coil spring  36  makes the ratchet wheel  18  rotate with respect to the reel  3  in the direction of arrow X 2 , such that the cam hole  18   a  of the ratchet wheel  18  displaces the engaging protrusion  16   b  of the pole  16  to the rotational axis side of the reel  3 . At this time, the tension acting on the seatbelt in the seatbelt protracting direction is released in the manner described above and the reel  3  is permitted to rotate in the seatbelt winding direction (direction of arrow X 1 ) Accordingly, if the reel  3  rotates in the direction of arrow X 1  without the tip of the gear teeth  16   c  of the pole  16  involving with the tip of the inner gear teeth  2 , then the pole  16  rockably rotates around the spindle  7  in a direction to disengage from the inner gear teeth  2 , and the reel  3  is thereby unlocked and the seatbelt can be freely protracted.  
         [0126]    Subsequently, under the seatbelt protracting state, the electric motor  110  winds the seatbelt, and if the full length of the seatbelt is rapidly wound in accordance with the torque of the power transmission device  15 , the inertia plate  30  serving as an inertia element of the seatbelt acceleration sensor continues to rotate in the winding direction with respect to the reel  3  which has suddenly stopped rotating, such that the rotation of the inertia plate  30  proceeds in the winding direction with respect to the reel  3  and the rotation of the inertia plate  30  is delayed in respect to the protracting direction of the reel  3 . However, the contacting portion  32  of the inertia plate  30 , which makes the stopper pawl  26   b  of the lock arm  26  rock in a direction to engage with the inner gear teeth  34   a  of the gear case  34 , is structured of two cam faces  32   a  and  32   b  for making the stopper pawl  26   b  rock toward the inner teeth gear  34   a  only after the delay in the rotation of the inertia plate  30  (in comparison with the rotation of the reel  3 ) has reached a prescribed values Therefore, the stopper pawl  26   b  does not rock in a direction to engage with the inner teeth gear  34   a  until the delay in the rotation of the inertia plate  30  (in comparison with the rotation of the reel  3 ) has reached a prescribed value.  
         [0127]    The embodiment of the present invention has a structure explained above. The activated locking mechanism is further provided with an electric magnetic actuator  112  as shown in the lower part of FIG. 14. This actuator is required for the processing illustrated in FIG. 9 mentioned above. As shown in FIGS. 22 and 23, the electric magnetic actuator  112  is structured of a solenoid (excitation coil)  112   a , a coil spring (elastic element)  112   b , a collar plunger (magnetic core)  112   c , etc. and is provided at the lower part of the vehicle acceleration sensor  51 .  
         [0128]    In a normal state, the solenoid  112   a  is excited. Under this condition, as shown in the Figures, the plunger  112   c  does not contact a ball weight  54  and therefore does not affect the locking mechanism  51 . When a controller  200  releases the excitation of the solenoid  112   a  in order to lock the seatbelt (S 30 , etc.), the plunger  112   c  is raised by the urging force of the spring  112   b . Through an opening formed on the bottom face of sensor cover  52 , the tip of the plunger  112   c  pushes up the ball weight  54 . When the ball weight is lifted up, the sensor arm moves upward in FIG. 22 and the engaging protrusion  53   a  engages with the ratchet teeth  18   b  of the ratchet wheel  18 . Thus, the rotation of the ratchet wheel in the seatbelt protracting direction (direction of arrow X 2  in FIG. 14) is prevented. When the seatbelt is protracted and the reel  3  is rotated in the seatbelt protracting direction, due to the difference in the rotation of the locked ratchet wheel  18  and the rotation of the reel  3 , the pole  16  is displaced radially outward and engages with the inner gear teeth  2  of the frame  1   a . The rotation of the reel  3  in the seatbelt protracting direction is thereby prevented.  
         [0129]    According to this example, the locking operation is not conducted when the solenoid  112   a  is supplied with an excitation current. The locking operation takes place when the excitation current is cut off. In other words, the locking mechanism can be activated by supplying low-level activation signals. Therefore, the seatbelt can be locked when the power source of the seatbelt device is cut off.  
         [0130]    [0130]FIG. 24 is a diagram showing another example of a structure of an electromagnetic actuator  112 . According to this example, the electromagnetic actuator is structured of: the solenoid  112   a ; the plunger  112   c ; a lever  112   d  substantially in L-shape, engaged with the plunger  112   c  at one end and having its center portion rotatabaly supported; and a coil spring urging the lever  112   d  in the clockwise direction in FIG. 24. When the pawl of the lever  112   d  is displaced and touches a tooth face  18   b  of the ratchet wheel  18 , the rotation of the ratchet wheel  18  is prevented and the locking mechanism is operated by the pole  16  and the frame of the inner teeth  2 .  
         [0131]    In a normal state where the solenoid  112   a  is supplied with an excitation current from the controller  200 , the solenoid  112   a  resists to the coil spring  112   b  and draws the plunger  112   c , whereby the other end of the pawl of the lever  112   d  is separated from the ratchet wheel  18 . Accordingly, the locking mechanism is not activated.  
         [0132]    Furthermore, in order to lock the seatbelt, the supply of the excitation current from the controller  200  is cut (at S 46 , etc.) The coil spring  112   b  pulls out the plunger  112   c  downward in the Figure by its urging force, thereby rotating the lever  112   d . As a consequence, the pawl at the other end of the lever  112   d  engages with the teeth  18   b  of the ratchet wheel  18  and the rotation of the ratchet wheel in the seatbelt protracting direction is prevented. When the seatbelt is protracted and the reel  3  rotates in the direction of the protraction, the difference in the rotations of the engaged ratchet wheel  18  and the reel  3  displaces the pole  16  radially outward and the pole  16  engages with the inner teeth  2  formed on the frame  1   a . Thus, the rotation of the reel  3  in the seatbelt protracting direction is prevented, and the locking is completed.  
         [0133]    [0133]FIGS. 25 through 29 show examples of structures of other seatbelt devices employing the present invention. In each drawing, components corresponding to those of FIG. 1 are shown with the same reference numerals.  
         [0134]    [0134]FIG. 25 shows another example of a seatbelt device employing the present invention. In this example, an electric winch  310  comprising a motor  311  and a reel  312  for winding the wire  313  connected to the buckle  304  is provided as a tension modifier for winding or protracting the seatbelt on the buckle  304  side. The wire is protracted or wound by a normal or a reverse rotation of the motor  311 . Instead of driving the motor  110 , the controller  200  drives the motor  311  of the winch  310  so that the slack in the seatbelt  302  is removed. Here also, the tension of the seatbelt can be estimated by detecting the current value of the motor  311 . With this structure, it is preferred that the seatbelt retractor  100  has a compulsory locking mechanism and a pretensioner, but the seatbelt retractor need not be electric. The anchor  306  for securing one end of the seatbelt  302  can be fixed to the seat  301 . By doing so, the protracted length of the seatbelt  302  is made shorter and the slack in the seatbelt can be removed faster.  
         [0135]    [0135]FIG. 26 shows an example of another seatbelt device employing the present invention. According to this example, the tension modifier for removing any slack in the seatbelt is provided on the side of the anchor  306  (wrap belt fixing portion) for securing one end of the seatbelt  302 . Similar to the example above, a tension modifier may be structured of a motor  311  and an electric winch  310  having a reel  312  for winding the wire  313  connected to the buckle. As a possible variant, a tension modifier may be structured of a screw shaft which is rotated and driven by the motor and the nut which performs reciprocating motion along the screw shaft.  
         [0136]    According to the example shown in FIG. 27, the seatbelt retractor  100  is fixed not to the bottom of the center pillar of the vehicle but to the seat  301 . The present invention can also have such structure.  
         [0137]    The example shown in FIG. 28 is structured of an electric retractor and a pretensioner  104   a  provided on the buckle side.  
         [0138]    The example shown in FIG. 29 is structured of an electric retractor and a pretensioner  104   b  provided on the side of the anchor  306  for securing one end of the seatbelt  302 .  
         [0139]    Furthermore, a pretensioner can be incorporated in the electric winch  310  shown in FIGS. 25 and 26.  
         [0140]    Although the seatbelt device according to the above-described embodiment has an electric motor as a first tension modifier and a powder pretensioner, which is activated by an explosive system, as a second tension modifier, both tension modifiers may have electric motors. Furthermore, a spring may be used as a power source. Either or both of the first and second tension modifiers may be mounted on the seatbelt retractor, and either or both of the first and second tension modifiers may be mounted on a component other than the seatbelt retractor. In such case, the tension modifier(s) may be mounted on the buckle side or on the wrap belt securing portion side.  
         [0141]    Furthermore, since the vehicle collision detector activating the pretensioner is operated when the output of the deployment (operation) of the airbag is detected, the cost of the device is further reduced.  
         [0142]    As explained above, according to the seatbelt device of the present invention, the slack in the seatbelt is removed by the first tension modifier prior to a collision, and the occupant is secured to the seat by the second tension modifier at a higher tension concurrently with the deployment of the airbag. Therefore, it is possible to save the occupant from being hit by the airbag.