Patent Publication Number: US-2010127554-A1

Title: Seatbelt Retractor and Seatbelt Apparatus Having the Same

Description:
BACKGROUND ART 
     The present invention relates to a technical field of a motor-driven seatbelt retractor provided on a vehicle such as an automotive vehicle and configured to perform retraction and withdrawal of a seatbelt for constraining an occupant by a motor and a seatbelt apparatus having the same and, more specifically, to a technical field of a seatbelt retractor configured to absorb inertia energy of an occupant by an energy absorbing mechanism (hereinafter, referred to also as an EA mechanism: configured as a load limiting mechanism) to limit a load applied to the seatbelt in case of emergency in which a deceleration larger than in a normal condition is applied to the vehicle upon collision or the like of the vehicle and a seatbelt apparatus having the same. 
     A seatbelt apparatus mounted on a vehicle such as an automotive vehicle in the related art is intended to constrain an occupant by a seatbelt to prevent the occupant from jumping out from a seat in case of emergency such as a case where a large deceleration is applied to a vehicle like upon collision or the like. In the seatbelt apparatus as described above, a seatbelt retractor configured to retract the seatbelt so as to be capable of being withdrawn is provided. 
     Among the seatbelt retractors in this configuration, a seatbelt retractor configured to retract and withdraw a seatbelt with a motor is proposed in Japanese Unexamined Patent Application Publication No. 2006-264397 in the related art. The seatbelt retractor disclosed in Japanese Unexamined Patent Application Publication No. 2006-264397 includes a spool that retracts the seatbelt formed into a cylindrical shape and a motor arranged in the cylindrical portion of the spool concentrically with the spool so that the width of the seatbelt retractor (that is, the axial length of the spool) is restrained from becoming large, and is formed into a downsized compact shape as a whole. 
     The seatbelt retractor disclosed in Japanese Unexamined Patent Application Publication No. 2006-264397 is configured to absorb inertia energy of an occupant who is about to move because of inertia by the EA mechanism when blocking the withdrawal of the seatbelt in case of emergency when a large vehicle deceleration acts on a vehicle upon collision or the like in a state in which the seatbelt is fastened. In this case, a torsion bar is employed as the EA mechanism, and the torsion bar is torsionally deformed in case of the emergency described above, whereby the inertia energy of the occupant is absorbed. 
     Furthermore, in the seatbelt retractor disclosed in Japanese Unexamined Patent Application Publication No. 2006-264397, a rotor of the motor arranged in the cylindrical spool is formed into a cylindrical shape. Then, the torsion bar is disposed in the cylindrical rotor so as to penetrate through an inner hole thereof in the axial direction, so that the further downsized compact seatbelt retractor is achieved. 
     Incidentally, in the seatbelt retractor disclosed in Japanese Unexamined Patent Application Publication No. 2006-264397, the diameter of a head portion which is a torque transmitting portion formed at one end of the torsion bar is set to be larger than the inner diameter of the inner hole of the rotor in order to apply a torsional torque to the torsion bar at the time of the torsional deformation of the torsion bar, and a further effective application of the torsional torque to the torsion bar is achieved by setting the diameter of the torque transmitting portion on the other end of the torsion bar to a size larger than the inner diameter of the inner hole of the rotor as well. 
     However, when the diameters of the torque transmitting portions at the both ends of the torsion bar which project from the both ends of the rotor in the axial direction are set to be larger than the inner diameter of the inner hole of the rotor, the torsion bar cannot be penetrated through the inner hole of the cylindrical rotor in the axial direction. Therefore, the torsion bar cannot be integrated in the spool and the rotor. 
     Therefore, increasing the inner diameter of the inner hole of the rotor to a size larger than the diameter of the torque transmitting portions at the both ends of the torsion bar is conceivable, but increasing the inner diameter of the rotor results in increase in the outer diameter of the rotor. Consequently, the respective diameters of the motor and the spool are increased, and hence the seatbelt retractor is inevitably upsized. 
     DISCLOSURE OF INVENTION 
     It is an object of the present invention to provide a motor-driven seatbelt retractor in which a retractor is formed into a downsized compact shape as a whole and a torsional torque can be applied to a torsion bar further effectively in case of emergency upon collision or the like of the vehicle by integrating the torsion bar in the spool and the motor shaft. 
     It is another object of the present invention to provide a seatbelt apparatus which is able to constrain an occupant gently without applying a large force from the seatbelt by absorbing inertia energy of the occupant further effectively when constraining the occupant by the seatbelt in case of emergency upon collision or the like of the vehicle. 
     In order to achieve the above-described object, a seatbelt retractor according to the present invention is a seatbelt retractor including: a cylindrical spool configured to retract a seatbelt so as to allow withdrawal of the same; a motor having a motor shaft disposed in a cylinder of the spool concentrically with the spool and being configured to generate a rotating force for causing the spool to be rotated in a belt retracting direction and a belt withdrawing direction, and an energy absorbing mechanism configured to absorb inertia energy of an occupant when the spool is rotated in the belt withdrawing direction in case of emergency, the motor having the motor shaft formed into a cylindrical shape, and the energy absorbing mechanism being a torsion bar being configured to absorb the inertia energy of the occupant by torsional deformation thereof and being disposed so as to penetrate through an inner hole of the motor shaft, wherein the diameter of torsion torque transmitting portions at both ends of the torsion bar are both set to be larger than the inner diameter of the inner hole of the motor shaft, and the motor shaft is divided into a predetermined number of pieces along the axial direction. 
     The seatbelt retractor according to the present invention is characterized in that the motor shaft includes first and second motor shaft members divided into two pieces along the axial direction thereof. 
     In addition, the seatbelt retractor according to the present invention is characterized in that the first and second motor shaft members are aligned in the axial direction and the radial direction and coupled with respect to each other. 
     Furthermore, a seatbelt apparatus according to the present invention at least comprises: a seatbelt configured to constrain an occupant, a seatbelt retractor configured to retract the seatbelt so as to allow withdrawal of the same, a tongue slidably supported on the seatbelt; and a buckle which allows the tongue to disengageably engage therewith, characterized in that the seatbelt retractor is the seatbelt retractor in the present invention described above. 
     According to the seatbelt retractor in the present invention configured as described above, since the motor shaft of the electric motor is divided into a predetermined number of pieces, even though the diameter of the torque transmitting portions at the both ends of the torsion bar is set to a diameter larger than the inner diameter of the inner hole of the cylindrical motor shaft, the torsion bar can be penetrated through the inner hole of the motor shaft. In this case, the motor shaft can be assembled easily in a state in which the torsional portion of the torsion bar is penetrated through the motor shaft, so that workability of assembly of the electric motor and the torsion bar into the spool is improved. 
     Also, since both the diameters of the respective torque transmitting portions at the both ends of the torsion bar can be set to large diameters, a torsional torque of the torsion bar (torsional force) can be set to a large value. Accordingly, the torsional portion of the torsion bar can be torsionally deformed effectively at the time of activation of the EA of the torsion bar, so that the EA function by the torsion bar can be demonstrated effectively. 
     In addition, since the torsion bar is penetrated through the axial inner hole of the cylindrical motor shaft, the electric motor and the torsion bar can be disposed efficiently in the spool. Furthermore, since the diameter of the torsional portion as a portion of the torsion bar in which the motor shaft is penetrated therethrough can be reduced, so that the outer diameter of the motor shaft can also be reduced. Accordingly, sine the outer diameter of the electric motor can be reduced, and hence the outer diameter of the spool can also be reduced. Accordingly, the seatbelt retractor can be formed further compactly as a whole. 
     In particular, by forming the motor shaft into a two-piece member including two members, the reduction of the number of components is achieved and, simultaneously, alignment of the divided two members when coupling is simplified, so that the reduction of the number of steps in assembly is achieved. 
     In this manner, by integrating the torsion bar into the spool and the motor shaft, the seatbelt retractor driven by the motor is formed into a downsized compact shape as a whole and, simultaneously, the torsion torque can be applied to the torsion bar further effectively in case of emergency upon collision or the like of the vehicle. 
     Furthermore, according to the seatbelt apparatus having the seatbelt retractor in the present invention, by using the seatbelt retractor in the present invention, the occupant can be constrained gently without applying a large force from the seatbelt by absorbing the inertial energy of the occupant further effectively when constraining the occupant by the seatbelt in case of emergency upon collision or the like of the vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing diagrammatically showing an example of an embodiment of a seatbelt apparatus provided with a seatbelt retractor according to the present invention. 
         FIG. 2  is a vertical cross-sectional view diagrammatically showing the example of the embodiment of the seatbelt retractor according to the present invention. 
         FIG. 3  is an exploded perspective view of a rotor in an electric motor in  FIG. 2 . 
         FIG. 4  is a cross-sectional view taken along the line IV-IV in  FIG. 2 . 
     
    
    
     BEST MODES FOR CARRYING OUT THE INVENTION 
     Referring now to the drawings, best modes for carrying out the present invention will be described. 
       FIG. 1  is a drawing diagrammatically showing an example of an embodiment of a seatbelt apparatus provided with a seatbelt retractor according to the present invention. 
     As shown in  FIG. 1 , a seatbelt apparatus  1  in this example includes a seatbelt retractor  3  fixed to a B-pillar  2  or the like of a vehicle body and driven by an electric motor, a seatbelt  6  withdrawn from the seatbelt retractor  3  and fixed to a floor of the vehicle body or a vehicle seat  5  via a belt anchor  4  at a distal end thereof, a guide anchor  7  provided on the vehicle body such as a center pillar or the like, for example, and configured to guide the seatbelt  6  withdrawn from the seatbelt retractor  3  toward a shoulder of an occupant C, a tongue  8  slidably supported by the seatbelt  6  guided from the guide anchor  7 , a buckle  9  fixed to the floor of the vehicle body or the vehicle seat and allows insertion and engagement of the tongue  8 , an electronic control unit (ECU)  10  configured to control the motor of the seatbelt retractor  3 , and input means  11  configured to detect various information required for controlling the motor of the seatbelt retractor  3  such as information on collision prediction and collision occurrence of a vehicle on which the seatbelt apparatus  1  is mounted, information on driving states of the vehicle, information on sitting positions and physical structures of the occupant C seated on the vehicle seat  5 , information on traffic conditions in the periphery, information on climates or time zones, information on retracted amounts and withdrawn amounts of the seatbelt  6 , information on engagement between the tongue  8  and the buckle  9  from a buckle switch and input the same into the ECU  10  constantly or at predetermined time intervals. The belt anchor  4 , the seatbelt  6 , the guide anchor  7 , the tongue  8 , and the buckle  9  may be those known in the related art. 
       FIG. 2  is a vertical cross-sectional view diagrammatically showing the example of the embodiment of the seatbelt retractor according to the present invention,  FIG. 3  is an exploded perspective view of a rotor in an electric motor, and  FIG. 4  is a cross-sectional view taken along the line IV-IV in  FIG. 2 . In  FIG. 2 , an upper side from a centerline is the rotor shown in a cross-sectional view, and a lower side of the centerline is the rotor in front view. 
     As shown in  FIG. 2 , the seatbelt retractor  3  in this example includes a base frame  14  having a pair of left and right side walls  12 ,  13 , and the pair of side walls  12 ,  13  are provided with circular openings  15 ,  16  arranged concentrically with respect to each other. 
     A spool  17  configured to retract the seatbelt  6  so as allow withdrawal of the same is disposed between the both side walls  12 ,  13  and flanges  18 ,  19  configured to guide the seatbelt  6  to be retracted are formed at both ends of the spool  17  respectively. The spool  17  is formed into a bottomed cylindrical shape formed with an annular bottom portion  20  having an opening at a center thereof at an end on the side of the side wall  12  and opened at an end on the side of the side wall  12 . 
     An electric motor  21  configured to generate a rotating force for rotating the spool  17  in a belt retracting direction and in a belt withdrawing direction is stored in the spool  17  having the bottomed cylindrical shape by being inserted from the side of the opened side wall  13 . The electric motor  21  is an “electric motor referred to as brushless motor of an inner rotor type, and includes a cylindrical motor housing  22 , an annular stator  23  formed of a coil stored in the motor housing  22  and fixed thereto, and a rotor (rotor)  24  including a magnet penetrating through the motor housing  22  and the stator  23  in the axial direction. 
     A most part of the motor housing  22  is stored in the spool  17 . Then, a flange-shaped end portion  22   a  on the side of the side wall  13  of the motor housing  22  is attached to the side wall  13  by a cylindrical mounting member  25 . The motor housing  22  is fixed to the side wall  13  in this manner. An end of the spool  17  on the side of the side wall  13  is rotatably supported on the outer periphery of the mounting member  25 . 
     The stator  23  is positioned in the motor housing  22  and is fixed to the motor housing  22 . 
     The rotor  24  is formed into a cylindrical shape as a whole. As shown in  FIG. 3 , the rotor  24  includes a cylindrical rotating member  24   a  on the outer side, and a cylindrical rotating shaft member  24   b  provided so as to penetrate along the inner periphery of the rotating member  24   a . Then, the rotating member  24   a  and the rotating shaft member  24   b  rotate integrally in either the belt retracting direction or the belt withdrawing direction by the rotating force applied to the rotating member  24   a  by an electromagnetic force from the stator  23 . In other words, the rotor  24  is rotated by the electromagnetic force from the stator  23 . 
     The rotating member  24   a  and the rotating shaft member  24   b  are both divided into two pieces in the axial direction at a position of the diameters and include respectively two members; first and second rotating members  24   a   1 ,  24   a   2  and first and second rotating shaft members  24   b   1 ,  24   b   2 . One of the two divided end edges in the axial direction of the first rotating shaft member  24   b   1  is provided with three engaging projections  24   b   3 ,  24   b   4  (a remaining one of the engaging projections is not shown), and the other divided end edge is provided with three engaging depressions  24   b   5 ,  24   b   6 ,  24   b   7 . In the same manner, one of two divided end edges of the second rotating shaft member  24   b   2  in the axial direction, which opposes the other divided end edge of the first rotating shaft member  24   b   1  is provided with three engaging projections  24   b   8 ,  24   b   9 ,  24   b   10  which are engageable respectively with the three engaging depressions  24   b   5 ,  24   b   6 ,  24   b   7  of the first rotating shaft member  24   b   1 . Although not shown in the drawing, the divided end edge of the second rotating shaft member  24   b   2  opposing one of the divided end edges of the first rotating shaft member  24   b   1  is formed with three engaging depressions which are the same as the engaging depressions  24   b   5 ,  24   b   6 ,  24   b   7 , which are engageable respectively with the three engaging projections  24   b   3 ,  24   b   4  of the first rotating shaft member  24   b   1 . Then, the first rotating shaft member  24   b   1  and the second rotating shaft member  24   b   2  are positioned and coupled in the axial direction and the radial direction by the respective engaging projections engaged with the corresponding engaging depressions, so that the cylindrical rotating shaft member  24   b  is configured. 
     Also, the two divided end edges of the first rotating member  24   a   1  in the axial direction and the two divided end edges of the second rotating member  24   a   2  in the axial direction are attached to the rotating shaft member  24   b  in abutment with each other, so that the cylindrical rotating member  24   a  is fixed to the rotating shaft member  24   b . Although the rotating member  24   a  and the rotating shaft member  24   b  may be divided into three or more pieces, but it is preferable to divide into two pieces as in this example considering reduction in number of components and in number of steps in assembly. 
     As shown in  FIG. 2 , an end of the rotating shaft member  24   b  on the side of the side wall  13  is rotatably supported on an inner peripheral surface of the opening  16  of the side wall  13  of the frame  14  via a bearing  26 . A portion of the rotating shaft member  24   b  on the side of the side wall  12  with respect to the rotating member  24   a  is rotatably supported by the motor housing  22  via a bearing  27 . Therefore, the rotating shaft member  24   b  of the rotor  24  is configured as a motor shaft (a rotating shaft of the motor) of the motor  21 . In this manner, the electric motor  21  is disposed so as to be stored in the spool  17  with the rotor  24 , that is, the motor shaft thereof being concentrically with the spool  17 . 
     A rotation sensor  28  formed of, for example, a Hall element or the like, is provided on the side wall  13  of the frame  14 , and a predetermined number of projections or depressions, not shown, detected by the rotation sensor  28  are provided on the outer periphery of the rotating member  24   a  of the rotor  24  equidistantly in the circumferential direction. The rotation sensor  28  and the projections or the depressions configure input means configured to input information on the retracted amount and the withdrawn amount of the seatbelt  6  in the ECU  10  as one of the input means  11 . Then, by the cooperation of the rotation sensor  28  and the projections or the depressions, the rotational position of the rotor  24  is detected. The retracted amount and the withdrawn amount of the seatbelt  6  by the spool  17  are obtained from the rotational position detection information of the rotor  24 . In other words, in this example, the rotation sensor  28  and the projections or the depressions as position detecting means configured to detect the rotational position of the rotor  24  are used also as seatbelt retracted and withdrawn amount detecting means configured to detect the retracted amount and the withdrawn amount of the seatbelt  6 . 
     Then, the ECU  10  is configured to perform ON-OFF control of the electric motor  21 , control of the number of rotation of the electric motor  21 , control of the direction of rotation of the electric motor  21 , and control of the load of the electric motor  21 , or the like on the basis of the rotational position detection information of the rotor  24  detected by the rotation sensor  28  and the projections or the depressions, that is, the information on the retracted amount and the information on the withdrawn amount of the seatbelt  6 . In this case, the ECU  10  performs the respective controls of the electric motor  21  described above by controlling the amount of power supply supplied to the coil of the stator  23  of the electric motor  21  (more specifically, a value of current or voltage supplied to the coil) and the direction of power supply (more specifically, the direction of power distribution to the coil). 
     In this manner, by using the brushless motor as the electric motor  21 , specific sensors for detecting the rotational position, the rotational speed, the direction of rotation or the like of the rotor  24  are not necessary, and hence the configuration is simplified, so that downsizing of the electric motor  21 , improvement of the output of the electric motor  21 , and improvement of heat discharging property are all achieved effectively. 
     As shown in  FIG. 2 , a planetary gear power transmitting mechanism  29  configured to perform power transmission between the electric motor  21  and the spool  17  is provided between the rotating shaft member  24   b  of the rotor  24  and the spool  17 . The planetary gear power transmitting mechanism  29  includes two first and second planetary gear mechanisms  30 ,  31  arranged side-by-side in the axial direction. 
     As shown in  FIG. 2  and  FIG. 4 , the first and second planetary gear mechanisms  30 ,  31  include a common annular-shaped annular member  32 , and a cylindrical T-shaped member  33  of T-shape in axial cross section. The annular member  32  is fitted and fixed in the opening  15  of the side wall  12  of the frame  14 . 
     The first planetary gear mechanism  30  includes a first sun gear  34  formed on an outer peripheral surface of the rotating shaft member  24   b , an annular first internal gear  35  fixed to an inner peripheral surface of the annular member  32  at an end on the opposite side from the spool and having inner teeth  35   a , first planetary gears  36  of a predetermined number (three in the illustrated example) engaging the first sun gear  34  and the first internal gear  35  so as to be capable of moving around the gears  34 ,  35  and rotating by themselves, and a first carrier  37  configured to rotatably support the first planetary gears  36 . 
     The T-shaped member  33  rotatably supports the first planetary gears  36  and is fixed to the first carrier  37  so as to be integrally rotatably by a fixture such as a bolt. 
     The second planetary gear mechanism  31  includes a second sun gear  38  formed on an outer peripheral surface of the T-shaped member  33 , an annular second internal gear  39  fixed to an inner peripheral surface of the annular member  32  at an end on the side of the spool and having inner teeth  39   a , second planetary gears  40  of a predetermined number (three in the illustrated example) engaging the second sun gear  38  and the second internal gear  39  so as to be capable of moving around the gears  38 ,  39  and rotating by themselves, and a second carrier  41  fixed to the spool  17  so as to be rotatable integrally therewith and rotatably support the second planetary gears  40 . The second planetary gears  40  are all supported so as to be rotatable relative to the spool  17 . 
     Therefore, the rotation of the rotor  24  of the electric motor  21  is reduced by single reduction according to a first predetermined reduction gear ratio and transmitted to the first carrier  37  via the first sun gear  34  and the first planetary gears  36  of the first planetary gear mechanism  30 , then the rotation of the first carrier  37  is reduced by double reduction according to a second predetermined reduction gear ratio and transmitted to the spool  17  via the second sun gear  38  and the second planetary gears  40  and the second carrier  41  of the second planetary gear mechanism  31 , so that the spool  17  is rotated in a reduced speed by the rotation of the electric motor  21 . In this manner, the planetary gear power transmitting mechanism  29  is the planetary gear power transmitting mechanism as a speed reducer having a double reduction system in which power transmission is achieved via an input to the sun gear and an output from the carrier in the first planetary gear mechanism  30 , and power transmission is performed via the input to the sun gear and the output from the carrier also in the second planetary gear mechanism  31  in the same manner. 
     As shown in  FIG. 2  and  FIG. 3 , a torsion bar  42  is provided so as to penetrate through the cylindrical rotor  24  as the EA mechanism. The torsion bar  42  includes a torsional portion  42   a  formed to have a diameter smaller than the inner diameter (diameter) of an inner hole  24   b   11  of the rotating shaft member  24   b  and penetrated through the rotor  24 , and configured to absorb torsion energy of torsional deformation, and first and second head portions  42   b ,  42   c  as torque transmitting portions provided at both ends of the torsional portion  42   a  projecting from the torsion rotating shaft member  24   b  in the axial direction and providing a torsion torque (torsional force) to the torsional portion  42   a . The first and second head portions  42   b ,  42   c  are formed into a hexagonal shape having the same size, and the respective sides of the respective hexagonal shapes are all formed into a curved surface depressed inward. The diameter of a circle passing through the most depressed portions of the respective sides of the hexagonal shapes of the first and second head portions  42   b ,  42   c  and being concentric with the torsional portion  42   a , and the diameter of a circle passing through the respective corners of the hexagonal shapes of the first and second head portions  42   b ,  42   c  and being concentric with the torsional portion  42   a  are both set to be larger than the diameter of the inner hole  24   b   11  of the rotating shaft member  24   b . In other words, at least the largest outer diameters of the first and second head portions  42   b ,  42   c  are set to be larger than the inner diameter of the inner hole  24   b   11 . By setting the diameter of the first and second head portions  42   b ,  42   c  to be large diameter as described above, the torsional deformation of the torsional portion  42   a  is effectively achieved. 
     The first head portion  42   b  which is located on the side of the planetary gear power transmitting mechanism  29  is fitted into a hexagonal depression  37   a  formed on the first carrier  37  of the first planetary gear mechanism  30  and connected to the first carrier  37  so as not to be capable of rotating relatively with respect to the first carrier  37 . The first carrier  37  is rotatably supported at the center thereof by a supporting projection  43   a  of a cover  43  attached to the annular member  32 . 
     A third side wall  44  is attached to the side wall  13  of the frame  14  at a predetermined distance in the axial direction. Deceleration sensing means  45  activated when sensing a significant vehicle deceleration generated in case of emergency described above and a locking mechanism  46  activated by the deceleration sensing means  45  to block (lock) at least the rotation in the belt withdrawing direction of the spool  17  is provided on the third side wall  44 . The locking mechanism  46  includes a locking base  47 . The locking base  47  is formed with a hexagonal depression  47   a  and the second head portion  42   c  is fitted into the depression  47   a  and is connected to the locking base  47  so as not to rotate relatively with the locking base  47 . 
     The locking base  47  is rotatably provided with a pawl  48 . The pawl  48  does not rotate in the normal state in which the deceleration sensing means  45  is not activated, and rotates freely in either the belt retracting direction and the belt withdrawing direction of the locking base  47  (that is, the spool  17 ). The pawl  48  rotates when the deceleration sensing means  45  is activated and an engaging claw  48   a  thereof engages inner teeth  44   a  of the third side wall  44 , thereby blocking (locking) the rotation of the locking base  47  in the belt withdrawing direction. The deceleration sensing means  45  and the locking mechanism  46  are publicly known in the related art as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2002-120694 and Japanese Unexamined Patent Application Publication No. 2001-122077, and the configuration and the operation of these members can be understood easily by referring to these publications and the detailed description is omitted because it does not directly relate to the present invention. 
     In the seatbelt retractor  3  in this example configured as described above, in the normal state in which the belt is not fastened, the locking mechanism  46  is not activated and hence the locking base  47  is free to rotate. Also, the electric motor  21  is not rotated. Therefore, the occupant C is able to withdraw the seatbelt  6  freely from the spool  17  of the seatbelt retractor  3 . 
     When the occupant C inserts and engages the tongue  8  into and with the buckle  9  after having sit on the vehicle seat  5  and withdrawn the seatbelt  6  by a predetermined amount, a buckle switch which is one of the input means  11  is activated and input engagement information of the tongue  8  and the buckle  9  into the ECU  10 . Then, the ECU  10  rotates the electric motor  21  in the belt retracting direction. The rotation of the electric motor  21  is reduced by double reduction by the planetary gear power transmitting mechanism  29  and is transmitted to the spool  17 , and the seatbelt  6  which is excessively withdrawn is retracted by the spool  17  by the rotation of the spool  17  in the belt retracting direction, whereby the slack of the seatbelt  6  is cancelled. 
     When the slack of the seatbelt  6  is cancelled by the belt retraction, a belt tension is generated on the seatbelt  6  by the further belt retraction and a supply current or a supply voltage to the electric motor  21  is increased. At least one of the belt tension, the supply current and the supply voltage to the electric motor  21  at this time is detected by adequate detecting means as the input means  11  and is inputted to the ECU  10 . The ECU  10  stops the rotation of the electric motor  21  when at least one of the inputted belt tension, the supply current and the supply voltage reaches a predetermined value which is set in advance. Then, this state is maintained and the vehicle starts to travel. After having stopped the rotation of the electric motor  21  in this manner, the ECU  10  rotates the electric motor  21  in the reverse direction, that is, in the belt withdrawing direction by a slight amount to cause the spool  17  to rotate in the belt withdrawing direction via the planetary gear power transmitting mechanism  29  to withdraw the seatbelt  6  by a predetermined amount to set the belt tension to 0 or substantially 0, so that the occupant C can be brought into a comfortable state. 
     While the vehicle is traveling, the ECU  10  performs various sorts of control on the electric motor  21  described above on the basis of the respective information required for the motor control inputted from the input means  11  as described above, so that the belt tension is controlled to an adequate value on the basis of the respective information. 
     When the vehicle is stopped and the occupant C releases the engagement by detaching the tongue  8  from the buckle  9  for getting off the vehicle, the buckle switch is not operated, and the non-engagement information between the tongue  8  and the buckle  9  is inputted to the ECU  10 . Then, the ECU  10  rotates the electric motor  21  in the belt retracting direction. With the rotation of the electric motor  21  in the belt retracting direction, the spool  17  retracts the seatbelt  6  until the initial retracted state is assumed, that is, by the entire amount withdrawn for fastening the same. Accordingly, the seatbelt  6  is stored in the seatbelt retractor  3 . When the entire amount of the seatbelt  6  is retracted, the ECU  10  stops the rotation of the electric motor  21  on the basis of the belt retraction complete information from the rotation sensor  28 . 
     In case of emergency in which a significantly large deceleration is applied to the vehicle by, for example, the vehicle collision or the like during the travel of the vehicle in a state in which the belt is fastened, the deceleration sensing means  45  is activated, and the rotation of the locking base  47  in the belt withdrawing direction is prevented as described above. Accordingly, the rotation of the second head portion  42   c  of the torsion bar  42  in the same direction is also blocked. 
     In contrast, since the seatbelt  6  is about to be withdrawn by the inertial movement of the occupant C and hence the spool  17  is about to be rotated in the belt withdrawing direction, the first head portion  42   b  of the torsion bar  42  is urged to rotate in the same direction via the second carrier  41 , the second planetary gears  40 , the second sun gear  38 , and the first carrier  37 . 
     Then, the torsional portion  42   a  of the torsion bar  42  is torsionally deformed, and the torsional deformation of the torsional portion  42   a  absorbs the inertia energy of the occupant C, so that the load acting on the seatbelt  6  is limited so as to be increased. At this time, since the diameters of the first and second head portions  42   b ,  42   c  are set to large diameters, the torsional force of the torsional portion  42   a  is set to a large value so that the torsional portion  42   a  is torsionally deformed effectively. Accordingly, when the significantly large deceleration is generated in the vehicle, the occupant C is constrained by the seatbelt  6  of the seatbelt apparatus  1  without being exerted with a large force from the seatbelt  6 . 
     According to the seatbelt retractor  3  in this example, since the rotating member  24   a  and the rotating shaft member  24   b  are divided into two pieces, that is, since the rotor  24  is formed into a two-piece member, even though the diameters of the first and second head portions  42   b ,  42   c  of the torsion bar  42  are set to be larger than the inner hole  24   b   11  of the rotating shaft member  24   b , the torsional portion  42   a  of the torsion bar  42  can be penetrated through the inner hole  24   b   11  of the rotating shaft member  24   b . Then, the rotor  24  can be assembled easily in a state in which the torsional portion  42   a  is penetrated through the inner hole  24   b   11  of the rotating shaft member  24   b , so that the assembleability of the electric motor  21  into the spool  17  is improved. 
     Then, since the diameters of the first and second head portions  42   b ,  42   c  are set to large diameters, the torsional force of the torsional portion  42   a  is set to a large value. Accordingly, the torsional portion  42   a  can be torsionally deformed effectively when the EA of the torsion bar  42  is activated. Therefore, the EA function by the torsion bar  42  can be demonstrated sufficiently. 
     In addition, since the torsion bar  42  is penetrated through the axial inner hole of the cylindrical rotor  24 , the electric motor  21  and the torsion bar  42  can be disposed efficiently in the spool  17 . In addition, since the diameter of the torsional portion  42   a  of the torsion bar  42  can be reduced, the outer diameter of the rotor  24  can also be reduced. Accordingly, sine the outer diameter of the electric motor  21  can be reduced, and hence the diameter of the spool  17  can also be reduced. Accordingly, the seatbelt retractor  3  can be formed further compactly as a whole. 
     In particular, in the seatbelt retractor  3  in this example, since the rotating member  24   a  is formed into a two-piece member including the first and second rotating members  24   a   1 ,  24   a   2 , and the rotating shaft member  24  is formed into a two-piece member including the first and second rotating shaft members  24   b   1 ,  24   b   2 , that is, since the rotor  24  is formed into the two-piece member having two members in the axial direction (two members of the first rotating member  24   a   1  and the first rotating shaft member  24   b   1 , and the second rotating member  24   a   2  and the second rotating shaft member  24   b   2 ), the number of components can be reduced, and the alignment of the divided two members when being coupled is simplified, so that the reduction of the number of steps in assembly is achieved. 
     In this manner, by integrating the torsion bar  42  into the spool  17  and the rotor  24 , the seatbelt retractor  3  driven by the motor is formed into a downsized compact shape as a whole and, simultaneously, the torsion torque can be applied to the torsion bar  42  further effectively in case of emergency upon collision or the like of the vehicle. 
     Also, by using the seatbelt retractor  3 , the seatbelt apparatus  1  in this example is able to constrain the occupant C gently without applying a large force from the seatbelt  6  by absorbing the inertial energy of the occupant C further effectively when constraining the occupant C by the seatbelt  6  in case of emergency upon collision or the like of the vehicle. 
     INDUSTRIAL APPLICABILITY 
     The seatbelt retractor and the seatbelt apparatus having the same in the present invention can be used for the seatbelt retractor mounted on a vehicle such as an automotive vehicle and configured to retract and withdraw the seatbelt for constraining the occupant by the motor and the seatbelt apparatus having the same.