Patent Publication Number: US-RE47450-E

Title: Seat belt retractor and seat belt apparatus having the same

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to a technical field of a seat belt retractor for winding up a seat belt while allowing winding and withdrawal of the seat belt. More particularly, the present invention relates to a technical field of a seat belt retractor provided with a seat belt load limiting mechanism (hereinafter, sometimes referred to as “EA mechanism”), which, by means of an energy absorbing member such as torsional deformation of a torsion bar, limits load acting on the seat belt to absorb energy added to an occupant when the seat belt is locked in the event of an emergency such as a vehicle collision where a large deceleration acts on the vehicle under the condition that the occupant wears the seat belt, and a seat belt apparatus having the same. 
     Conventionally, a seat belt apparatus installed in a vehicle such as an automobile restrains an occupant with a seat belt thereof in the event of the emergency as mentioned above. The seat belt apparatus comprises a seat belt retractor. In the seat belt retractor, the seat belt is wound onto a spool when the seat belt apparatus is not used and is withdrawn from the spool to be worn by the occupant when the seat belt apparatus is used. A locking mechanism of the seat belt retractor is actuated in the event of an emergency as mentioned above so as to prevent the spool from rotating in a belt withdrawing direction, thereby preventing the seat belt from being withdrawn. Accordingly, the seat belt restrains the occupant in the event of the emergency. 
     In the seat belt retractor of the conventional seat belt apparatus, the occupant is forced to move forward due to large inertia because a large deceleration acts on the vehicle when the seat belt restrains the occupant in the event of the emergency such as the vehicle collision. Accordingly, a large load is applied to the seat belt and the occupant receives a significant force from the seat belt. This force does not cause a serious problem to the occupant, but it is preferable to limit this force. 
     For limiting this force, a seat belt retractor has been proposed which is provided, in addition to a torsion bar, with a second EA mechanism which can operate independently so as to further flexibly and variously set the limited load applied on the seat belt according to information in the event of the emergency (for example, see Japanese Unexamined Patent Application Publication No. JP-A-2008-114659: Patent Document 1). According to the seat belt retractor disclosed in Patent Document 1, the limited load can be flexibly and variously set according to the situation in the event of the emergency. Therefore, it is possible to effectively and suitably restrain the occupant during the vehicle collision. 
     In the seat belt retractor disclosed in Patent Document 1, it is necessary to activate a gas generator for the second EA mechanism whenever the second EA mechanism is operated. Therefore, the second EA mechanism cannot be effectively operated. 
     The present invention has been made under the aforementioned circumstances and an object of the present invention is to provide a seat belt retractor wherein, in addition to a first EA mechanism, a second EA mechanism is independently and effectively operated so as to flexibly and variously set the limited load applied to the seat belt depending on the emergency situation, and a seat belt apparatus having the same. 
     Further objects and advantages of the invention will be apparent from the following description of the invention. 
     SUMMARY OF THE INVENTION 
     To solve the aforementioned problems, a seat belt retractor according to the invention comprises: a spool onto which a seatbelt is wound; a first seat belt load limiting mechanism for limiting load applied on said seat belt when an emergency occurs; a second seat belt load limiting mechanism for limiting load applied to said seat belt when the emergency occurs and a predetermined condition based on the emergency situation is satisfied; a driving member for actuating said second seat belt load limiting mechanism; and a controller for controlling said driving member, wherein the controller actuates said second seat belt load limiting mechanism by not actuating said driving member when said predetermined condition is satisfied, and does not actuate said second seat belt load limiting mechanism by actuating said driving member when said predetermined condition is not satisfied. 
     According to the present invention, when said controller determines that the actuation of said second seat belt load limiting mechanism is required, but the entire operation of said second seat belt load limiting mechanism is not required, said controller stops the operation of said second seat belt load limiting mechanism by actuating said driving member after said second seat belt load limiting mechanism is actuated and before the entire operation of said second seat belt load limiting mechanism is completed. 
     A seat belt retractor according to the present invention further comprises a locking mechanism having a locking member which is configured to normally rotate together with said spool by transmission of rotation of said spool via the first seat belt load limiting mechanism and is prevented from rotating in the seatbelt withdrawing direction when the emergency occurs, wherein when said locking member is prevented from rotating in the seat belt withdrawing direction so that said spool rotates in the seat belt withdrawing direction relative to said locking member, load applied on said seat belt is limited by at least said first seat belt load limiting mechanism. 
     Further, said second seat belt load limiting mechanism comprises a supporting member for the energy absorbing member which is disposed coaxially with said spool and rotatable relative to said spool, and an energy absorbing member which is disposed between said locking member and said supporting member and is deformed by rotation of said spool in the seat belt withdrawing direction, wherein said controller sets said second seat belt load limiting mechanism to an inoperative state by setting said supporting member to the immovable state by actuating said driving member when the emergency occurs and said predetermined condition is not satisfied, and sets said second seat belt load limiting mechanism to the operative state by setting said supporting member to the movable state by not actuating said driving member when the emergency occurs and said predetermined condition is satisfied. 
     Further, a seat belt retractor according to the present invention is such that said energy absorbing member comprises a long band-like energy absorbing plate. 
     Furthermore, a seat belt retractor according to the present invention is such that said first seat belt load limiting mechanism comprises a torsion bar disposed between said spool and said locking member. 
     On the other hand, a seat belt apparatus according to the present invention comprises at least: a seat belt retractor which winds up a seat belt, a tongue slidably supported on the seat belt withdrawn from said seat belt retractor; and a buckle detachably latched with said tongue, wherein said seat belt is prevented from being withdrawn by said seat belt retractor so as to restrain the occupant when the emergency occurs, and said seat belt retractor is one of the seat belt retractors according to the present invention. 
     In addition, a seat belt apparatus according to the present invention further comprises a pretensioner which is actuated to directly rotate said spool in the seat belt winding direction when the emergency occurs. 
     According to the seat belt retractor of the invention having the aforementioned structure and the seat belt apparatus having the same, the limited load on the seat belt in the event of the emergency is changed by controlling the operation of the first and second seat belt load limiting mechanisms based on information of the situation of the emergency such as preliminary information (the weight of the occupant and the position of a seat in the front-rear direction, and the like), collision-predicting information indicating that a collision is going to occur, and information indicating the collision severity (the collision speed, the acceleration during the collision, and the type of collision, and the like). Therefore, the limited load of the seat belt during a collision can be set more flexibly and variously depending on the conditions under the collision and the information in the emergency situation, such as the physical size of the occupant. Accordingly, the occupant can be more effectively and suitably restrained during the collision. 
     In this case, the second seat belt load limiting mechanism is actuated by not actuating the driving member, while the second seat belt load limiting mechanism is not actuated by actuating the driving member. Accordingly, when the actuation of the second seat belt load limiting mechanism is required, there is no need to actuate the driving member to generate reaction gas. Consequently, the occupant is further effectively restrained during the collision because of the effect actuation of the second seat belt load limiting mechanism. 
     When it is determined that the actuation of the second seat belt load limiting mechanism is required, but the entire operation of the second seat belt load limiting mechanism is not required in the event of the emergency, the operation of the second seat belt load limiting mechanism is stopped by actuating the driving member after the second seat belt load limiting mechanism is actuated, but before the entire operation of the second seat belt load limiting mechanism is completed. That is, even after the second seat belt load limiting mechanism is actuated, it is possible to stop the operation of the second seat belt load limiting mechanism depending on the emergency situation. Therefore, the kinetic energy absorption (EA) for the occupant in the event of an emergency can be further finely and correctly conducted. 
     Further, since the energy absorbing member is provided between the locking member and the supporting member for the energy absorbing member, the pretensioner which must operate in the event of the emergency can be arranged to directly rotate the spool in the belt winding direction. 
     Further, since the second seat belt load limiting mechanism is disposed coaxially with the spool, the seat belt retractor is small in the vertical direction. In addition, the first seat belt load limiting mechanism is composed of the torsion bar, thereby achieving the seat belt retractor having simpler structure and smaller size. The available space of the vehicle cabin is thus increased. 
     Furthermore, since the spool is designed to be rotated in the seat belt winding direction directly by the pretensioner, the pretensioner effectively conducts the seat belt winding operation in the event of the emergency even though the first and second seat belt load limiting mechanisms are provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration schematically showing a seat belt apparatus provided with an embodiment of a seat belt retractor according to the present invention. 
         FIG. 2  is a front view of the seat belt retractor of the embodiment shown in  FIG. 1 . 
         FIG. 3  is a vertical sectional view showing the seat belt retractor of the embodiment shown in  FIG. 1 . 
         FIG. 4  is a sectional view schematically showing a second EA mechanism and a driving device of the embodiment shown in  FIG. 3 . 
         FIG. 5  is a block diagram for controlling the second EA mechanism and the driving device of the embodiment shown in  FIG. 3 . 
         FIGS. 6(a) through 6(c)  are illustrations for explaining the seat belt winding by a pretensioner when the second EA mechanism is actuated in the event of the emergency. 
         FIGS. 7(a) through 7(c)  are illustrations for explaining the operation of the second EA mechanism in the event of an emergency. 
         FIG. 8(a)  is a graph showing limited load when the second EA mechanism is actuated, and  FIG. 8  (b) is a graph showing limited load when the second EA mechanism is not actuated. 
         FIGS. 9(a) through 9(d)  are illustrations for explaining the seat belt winding by the pretensioner when the second EA mechanism is not actuated in the event of an emergency. 
         FIGS. 10(a) through 10(d)  are illustrations for explaining the non-operation of the second EA mechanism in the event of an emergency. 
         FIGS. 11(a) and 11(b)  are sectional views partially and schematically showing another embodiment of a seat belt retractor according to the present invention. 
         FIGS. 12(a) and 12(b)  show the operable state of the second EA mechanism of the seat belt retractor shown in  FIGS. 11(a) and 11(b) , wherein  FIG. 12(a)  is a partial perspective view and  FIG. 12(b)  is a partial schematic view. 
         FIGS. 13(a) and 13(b)  show the inoperable state of the second EA mechanism of the seat belt retractor shown in  FIGS. 11(a) and 11(b) , wherein  FIG. 13(a)  is a partial perspective view and  FIG. 13(b)  is a partial schematic view. 
         FIGS. 14(a) and 14(b)  are illustrations for explaining the winding and withdrawal of the seat belt during normal operation of the seat belt retractor of the embodiment shown in  FIGS. 11(a) and 11(b) . 
         FIGS. 15(a) through 15(c)  are illustrations for explaining the operation of the second EA mechanism of the seat belt retractor of the embodiment shown in  FIGS. 11(a) and 11(b) . 
         FIGS. 16(a) through 16(c)  are graphs showing limited load of the seat belt retractor of the embodiment shown in  FIGS. 11(a) and 11(b) . 
         FIGS. 17 ( 1 )(a) through  17 ( 1 )(d) and  FIGS. 17 ( 2 )(a) through  17 ( 2 )(d) are illustrations for explaining the operation and non-operation of the second EA mechanism of the seat belt retractor of the embodiment shown in  FIGS. 11(a) and 11(b) . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments for carrying out the present invention will be described with reference to the attached drawings. 
       FIG. 1  is an illustration schematically showing a seat belt apparatus employing an embodiment of a seat belt retractor according to the present invention. 
     As shown in  FIG. 1 , the seat belt apparatus  1  of this embodiment is similar to a conventionally known seat belt apparatus of a three-point type. That is, the seat belt apparatus  1  comprises a seat belt retractor  3  which is fixed to a vehicle body near the vehicle seat  2 , a seat belt  4  which is retracted by the seat belt retractor  3  in such a manner as to allow the withdrawal of the seat belt  4  and is provided at its end with a belt anchor  4 a fixed to a vehicle floor or the vehicle seat  2 , a deflection fitting  5  for guiding the seat belt  4  withdrawn from the seat belt retractor  3  toward an occupant&#39;s shoulder, a tongue  6  which is slidably supported on the seat belt  4  guided by and extending from the deflection fitting  5 , and a buckle  7  which is fixed to the vehicle floor or the vehicle seat and to which the tongue  6  can be inserted and detachably latched. 
       FIG. 2  is a front view of the seat belt retractor of this embodiment and  FIG. 3  is a vertical sectional view of the seat belt retractor of this embodiment. 
     As shown in  FIGS. 2 and 3 , the seat belt retractor  3  of this embodiment comprises a U-like frame  8  similarly to the emergency locking-type seat belt retractor (ELR) disclosed in the aforementioned Patent Document 1. A spool  9  onto which the seat belt  4  is wound is rotatably supported by the frame  8 . On one of the side walls (the right-side wall in  FIG. 3 )  8 a of the frame  8 , a locking mechanism is disposed. The locking mechanism  10  has a locking base (corresponding to the locking member of the present invention)  11  rotatably attached to one of the ends of the spool  9  and a locking gear  12  rotatably attached to the locking base  11 . On the other end wall (the left-side wall in  FIG. 3 )  8 b of the frame  8 , a pretensioner  13  and a spring mechanism  14  are attached. Between the spool  9  and the locking base  11 , a torsion bar (a first EA mechanism; corresponding to the first seat belt load limiting mechanism of the present invention)  15  is disposed and, in addition, a second EA mechanism (corresponding to the second seat belt load limiting mechanism of the present invention)  16  is disposed. 
     The basic operation of the seat belt retractor  3  of this embodiment is the same as that of the seat belt retractor of the aforementioned Patent Document 1. That is, in the event of the emergency as mentioned above, a deceleration sensing mechanism (not shown) of a vehicle sensor (not shown) is activated to prevent the locking gear  12  of the locking mechanism  10  from rotating in the seat belt withdrawing direction. Then, a relative rotation is generated between the locking base  11  and the locking gear  12  so that a pawl (not shown) attached to the locking base  11  pivots and thus engages internal teeth  8 c (shown in  FIG. 3 ) formed in the side wall  8 a of the frame  8 . Accordingly, the rotation of the locking base  11  is stopped so as to prevent the spool  9  from rotating in the seat belt withdrawing direction. Also when the seat belt is rapidly withdrawn, the rotation of the locking gear  12  in the seat belt withdrawing direction is prevented by a webbing sensor (not shown) and, similarly, the rotation of the spool  9  in the seat belt withdrawing direction is prevented. Specific actions of the seat belt retractor  3  will be described later. 
       FIG. 4  is a sectional view schematically showing the second EA mechanism and the driving device of this embodiment. 
     As shown in  FIGS. 3 and 4 , the second EA mechanism  16  of this embodiment comprises an energy absorbing plate (EA plate)  17  as an energy absorbing member, an EA plate supporting member  18  which is formed around an outer periphery of a cylindrical portion  9 a on one end (the right end in  FIG. 3 ) of the spool  9  and has an annular disc-like shape, and an EA plate operating member  19  which is rotatably attached to the EA plate supporting member  18  to operate the energy absorbing plate  17  and has a lever-like shape. The seat belt retractor  3  of this embodiment has an EA operation controlling member  20  for controlling the operation of the second EA mechanism  16  by controlling the rotation of the EA plate supporting member  18 , and a driving member  21  for driving the EA operation controlling member  20 . 
     The energy absorbing plate  17  is composed of a long and thin band-like plate having a predetermined thickness and a predetermined width and having elasticity and is formed into an anomalous S-like shape as a whole. The energy absorbing plate  17  may be composed of a bar member. One end portion of the energy absorbing plate  17  is a first supporting portion  17 a fixed to and supported by the locking base  11  and the other end portion  17 b of the energy absorbing plate  17  can come in contact with the EA plate operating member  19  in the seat belt winding direction (counter-clockwise direction in  FIG. 4 ). The energy absorbing plate  17  has a folded U-like portion  17 c formed in the vicinity of the first supporting portion  17 a. A portion between the U-like portion  17 c and the other end of the energy absorbing plate  17  is normally in contact with the inner periphery of the cylindrical portion  9 a of the spool  9 . 
     The EA plate supporting member  18  is rotatably and coaxially fitted to the outer periphery of the cylindrical portion  9 a of the spool  9 . As shown in  FIG. 3 , normally, the EA plate supporting member  18  is connected to the spool  9  by a shear pin  22  so that the EA plate supporting member  18  rotates together with the spool  9 . Once the shear pin  22  is sheared, the spool  9  and the EA plate supporting member  18  can rotate relative to each other. The EA plate supporting member  18  is provided with a predetermined number of serration teeth  18 a formed in the outer periphery thereof. 
     The EA plate operating member  19  can move between a lying position where it is retracted in an opening  18 b of the EA plate supporting member  18  and a standing position (position shown in  FIG. 4 ) where it extends to the inner periphery of the cylindrical portion  9 a through an opening  9 b of the cylindrical portion  9 a of the spool  9 . When the EA plate operating member  19  is in the standing position as shown in  FIG. 4 , the EA plate operating member  19  is prevented from pivoting in a direction (counter-clockwise direction in  FIG. 4 ) opposite to a direction toward the lying position by a circumferential inner end wall  18 c of the opening  18 b. When the EA plate operating member  19  is in the lying position of the EA plate supporting member  18 , the EA plate operating member  19  is not in contact with the both ends of the opening  9 b formed in the cylindrical portion  9 a of the spool  9 , wherein the ends extend in a direction perpendicular to the circumferential direction. When the EA plate operating member  19  is in the standing position of the EA plate supporting member  18 , the EA plate operating member  19  can be in contact with the end walls  9 b 1 ,  9 b 2  of the opening  9 b of the spool  9 . Therefore, the second EA mechanism  16  is arranged coaxially with the spool  9 . 
     The EA operation controlling member  20  is arranged to face the EA plate supporting member  18 . The EA operation controlling member  20  has an arc concave face as a face thereof facing the EA plate supporting member  18  and is provided with a predetermined number of serration teeth  20 a which are formed in the concave face. The EA operation controlling member  20  is arranged to move vertically between an inoperative position as a lower position shown in  FIG. 4  where the teeth  20 a do not mesh with the teeth  18 a of the EA plate supporting member  18  and an operative position as an upper position where the teeth  20 a mesh with the teeth  18 a of the EA plate supporting member  18 . When the EA operation controlling member  20  is in the inoperative position, the teeth  18 ,  20  do not mesh with each other so as to allow the rotation of the EA plate supporting member  18 . When the EA operation controlling member  20  is in the operative position, the teeth  18 ,  20  mesh with each other so as not to allow the rotation of the EA plate supporting member  18 . Further, the end face opposite to the face facing the EA plate supporting member  18  of the EA operation controlling member  20  is an inclined face  20 b. 
     As shown in  FIG. 3 , the driving member  21  is disposed on the side wall  8 a of the frame  8 . As shown in  FIG. 4 , the driving member  12  has a gas generator  21 a and a driving piston  21 b inside thereof. The gas generator  21 a is actuated in the event of an emergency to generate reaction gas and move the driving piston  21 b toward the EA operation controlling member  20  by means of the reaction gas. The driving piston  21 b has an inclined cam face  21 c on its upper surface and the inclination of the cam face  21 c is set to be the same or substantially the same as the inclination of the inclined face  20 b of the EA operation controlling member  20 . When the driving piston  21 b is moved by the reaction gas, the driving piston  21 b enters a space between the body  21 d of the driving member  21  and the inclined face  20 b of the EA operation controlling member  20  and moves upward the EA operation controlling member  20  because of the cam face  21 c so that the EA operation controlling member  20  is set to the operative position. The body  21 d of the driving member  21  is provided with a guide portion  21 e for guiding the EA operation controlling member  20  during the upward movement of the EA operation controlling member  20 . 
     As shown in  FIG. 5 , the gas generator  21 a of the driving member  21  for controlling the operation of the second EA mechanism  16  of this embodiment is controlled its activation corresponding to an emergency situation by a CPU (corresponding to the controller of the present invention)  29  based on signals outputted from a seat weight sensor  23  for detecting the occupant&#39;s weight; a seat slide position sensor  24 , an acceleration sensor  25  for detecting deceleration of the vehicle, a front satellite sensor  26  for detecting an obstacle in front of the vehicle, a belt withdrawal amount sensor  27 , and a buckle switch  28 . That is, the second EA mechanism  16  can operate independently from the torsion bar  15  as the first EA mechanism. 
     Then, the actions of the seat belt retractor  3  of this embodiment having the aforementioned structure will be described. Since actions of the seat belt retractor  3  of this embodiment by the same components as the conventional seat belt retractor  3  disclosed in the aforementioned Patent Document 1 are the same as those of the conventional seat belt retractor  3 , the description about those actions will be omitted and only actions by the characteristic components of the seat belt retractor  3  of this embodiment will be described. 
     As shown in  FIG. 4  and  FIG. 6(a) , when the seat belt  4  is normally used, the seat belt retractor  3  maintains the energy absorbing plate  17  in its inoperative state and maintains the EA plate operating member  19  in its standing position. When the standing position of the EA plate operating member  19  is maintained, the end walls  9 b 1  of the opening  9 b of the spool  9  is in contact with the EA plate operating member  19  and the free end, i.e. the other end portion  17 b of the energy absorbing plate  17  is in contact with the EA plate operating member  19 . Therefore, the standing position of the EA plate operating member  19  is maintained. Therefore, the opening  9 b of the spool  9  is located on the left side of the EA plate operating member  19  in  FIG. 4  and  FIG. 6  (a) The spool  9  and the EA plate supporting member  18  are connected together by the shear pin  22 . 
     The EA operation controlling member  20  is in the inoperative position so that the teeth  20 a do not mesh with the teeth  18 a of the EA plate supporting member  18 . Further, the gas generator  21 a of the driving member  21  is not actuated so that the driving piston  21 b does not enter the space below the inclined surface  20 b of the EA operation controlling member  20 . 
     As a deceleration which is significantly larger than that during the normal driving acts on the vehicle in the event of the emergency as mentioned above, the pretensioner  13  is actuated. When the CPU  29  judges the emergency situation based on the signals outputted from the respective sensors  23 ,  24 ,  25 ,  26 ,  27  and the buckle switch  28  and deter-mines that the absorption of the energy on the occupant by the second EA mechanism  16  is also required, that is, that a predetermined condition for actuating the second EA mechanism  16  is satisfied such as when the occupant has a relatively heavy weight or when a collision severe enough to actuate the pretensioner  13  and the airbag occurs, the CPU  29  does not activate the gas generator  21 a of the driving member  21 . 
     As shown in  FIG. 6(a) , the spool  9  is forced to rotate in the seat belt winding direction a directly by the actuation of the pretensioner  13  without the torsion bar  15  intervening. Since the EA operation controlling member  20  is set in its inoperative position, the EA plate supporting member  18  is free to rotate. Therefore, as shown in  FIGS. 6(a) through 6(c) , all of the spool  9 , the locking base  11 , and the EA plate supporting member  18  start to rotate in the seat belt winding direction α. Accordingly, a slack of the seat belt  4  worn by the occupant is removed so as to restrain the occupant. The energy absorbing plate  17  is maintained in its initial state. 
     As shown in  FIG. 6(c) , as the winding of the seat belt onto the spool  9  by the action of the pretensioner  13  is completed, the seat belt  4  starts to be withdrawn by inertia of the occupant. Then, as shown in  FIG. 7(a) , the spool  9  rotates in the seat belt withdrawing direction β. Therefore, the EA plate supporting member  18  connected to the spool  9  by the shear pin  22  rotates together with the spool  9  in the same direction β. On the other hand, the pawl pivots to engage the internal teeth  8 c of the frame  8 , thereby preventing the locking base  11  from rotating in the seat belt withdrawing direction β. 
     Then, since the spool  9  rotates in the seat belt withdrawing direction β and the rotation of the locking base  11  are prevented, the torsion bar  15  is torsionally deformed similarly to the conventional one. That is, the torsion bar  15  conducts the EA action so that the inertia energy of the occupant is absorbed by the torsion bar  15 . At the same time, as shown in  FIG. 7(b) , the spool  9  and the EA plate supporting member  18  rotate together in the seat belt withdrawing direction β so that the one end wall  9 b 1  of the opening  9 b of the spool  9  presses the EA plate operating member  19  in the seat belt withdrawing direction β. 
     Then, as shown in  FIG. 7(b) , the energy absorbing plate  17  is deformed such that the U-like portion  17 c gradually moves toward the other end portion  17 b side. Accordingly, the energy applied to the occupant is also absorbed by the second EA mechanism  16 . Therefore, as shown in  FIG. 8(a) , the limited load (EA load) becomes the sum of the load by torsional deformation of the torsion bar  15  and the load by deformation of the energy absorbing plate  17 . Because of both of the deformation of the torsion bar  15  and the deformation of the energy absorbing plate  17  of the second EA mechanism  16 , the energy applied to the occupant is effectively absorbed. As the deformation of the energy absorbing plate  17  is finished, the EA load becomes the load solely by the torsional deformation of the torsion bar  15 . 
     As the energy absorbing plate  17  is completely reversed so that the energy absorption by the energy absorbing plate  17  is finished as shown in  FIG. 7(c) , the energy applied to the occupant is effectively absorbed solely by the torsion bar  17  as shown in  FIG. 8(a) . 
     As mentioned above, the second EA mechanism  16  effectively operates without actuating the gas generator  21 a of the driving member  21 , i.e. without generating reaction gas. 
     On the other hand, when the CPU  29  judges the emergency situation based on the signals outputted from the respective sensors  23 ,  24 ,  25 ,  26 ,  27  and the buckle switch  28  and determines that the absorption of the energy by the second EA mechanism  16  is not required, that is, that the aforementioned predetermined condition for actuating the second EA mechanism  16  is not satisfied such as when the occupant has a relatively light weight or when such a mild collision that the pretensioner  13  or the airbag is not actuated occurs, the CPU  29  actuates the gas generator  21 a of the driving member  21 . Therefore, the gas generator  21 a generates reaction gas to move the driving piston  21 b so that the driving piston  21 b enters the space below the EA operation controlling member  20  as shown in  FIG. 9(b) . Then, by the inclined face  21 c of the EA operation controlling member  20  and the cam face  21 c of the driving piston  21 b, the EA operation controlling member  20  is moved upward to the operative position where the teeth  20 a mesh with the teeth  18 a of the EA plate supporting member  18 . Therefore, the EA plate supporting member  18  is prevented from rotating. 
     Similarly to the aforementioned case, as shown in  FIG. 9(a) , the spool  9  starts to be rotated in the seat belt winding direction α because of the actuation of the pretensioner  13 . Since the EA plate supporting member  18  is prevented from rotating, the spool  9 , the locking base  11 , and the energy absorbing plate  17  are about to rotate in the seat belt winding direction α. Therefore, as shown in  FIG. 9(b) , the shear pin  22  is sheared so that the spool  9 , the locking base  11 , and the energy absorbing plate  17  rotate in the seat belt winding direction α relative to the EA plate supporting member  18 . Then, the end of the other end portion  17 b of the energy absorbing plate  17  moves the EA plate operating member  19  to pivot toward the lying position and, after that, the other end wall  9 b 2  of the opening  9 b of the spool  9  further moves the EA plate operating member  19  to pivot toward the lying position. In this manner; the spool  9  rotates together with the locking base  11  and the energy absorbing plate  17  in the seat belt winding direction α with moving the EA plate operating member  19  to pivot. As shown in  FIG. 9(c) , the EA plate operating member  19  is set to the lying position. 
     As shown in  FIG. 9(d) , as the seat belt winding onto the spool  9  by the action of the pretensioner  13  is terminated, the seat belt  4  starts to be withdrawn by inertia of the occupant similarly to the aforementioned case so that, as shown in  FIG. 10(a) , the spool  9  rotates in the seat belt withdrawing direction β. However, since the locking base  11  is prevented from rotating in the belt withdrawing direction β similarly to the aforementioned case and the EA plate operating member  19  is set to the lying position, the locking base  11  does not rotate and energy absorbing plate  17  keeps its initial state and is not deformed even when the spool  9  rotates. Therefore, as shown in  FIGS. 10  (b) through  10 (d), only the spool  9  rotates in the seat belt withdrawing direction β. Therefore, as shown in  FIG. 8(b) , the EA load becomes the load solely by the torsional deformation of the torsion bar  15 . Therefore, the energy absorption by the deformation of the energy absorbing plate  17  is not conducted and the energy applied to the occupant is absorbed solely by the torsion bar  15 . 
     In this manner, the limited load of the seat belt  4  is set to be small when, based on the signals outputted from the respective sensors  23 ,  24 ,  25 ,  26 , and  27 , the CPU determines that the energy absorption by the second EA mechanism  16  is not required such as when such a mild collision that the pretensioner  13  and the airbag is not actuated (for example, a mild collision of a vehicle running at a speed of 30 km/hour or less) occurs. 
     That is, the load limitation by the second EA mechanism  16  is selected such that there is a case that the load limitation is conducted in the event of an emergency and a case that the load limitation is not conducted in the event of an emergency. 
     According to the seat belt retractor  3  of this embodiment, the limited load of the seat belt in the event of an emergency is changed based on information of the situation of the emergency such as preliminary information (the weight of an occupant and the position of a seat in the front-rear direction, and the like), collision-predicting information indicating that a collision is predicted, and information indicating the collision severity (the collision speed, the acceleration during the collision, and the type of collision, and the like). Therefore, the limited load of the seat belt during a collision can be set more flexibly and variously in accordance with the information of the emergency situation, such as the conditions of the collision and the physical size of the occupant. Accordingly, the occupant can be more effectively and suitably restrained during a collision. 
     In this case, the second EA mechanism is actuated by not actuating the driving member  21 , while the second EA mechanism  16  is not actuated by actuating the driving member  21 . Accordingly, when the actuation of the second EA mechanism  16  is required, there is no need to actuate the driving member to generate reaction gas. Consequently, the occupant is further effectively restrained during a collision because of the effect actuation of the second EA mechanism  16 . 
     Since the energy absorbing plate  17  is provided between the locking base  11  and the EA plate supporting member  18 , the pretensioner  13  which must operate in the event of an emergency can be disposed to directly rotate the spool  9  in the belt winding direction α. 
     Further, since the second EA mechanism  16  is disposed integrally and coaxially with the spool  9 , the seat belt retractor  3  which is small-sized in the vertical direction is achieved, thereby increasing the effective space of the vehicle cabin. 
     Furthermore, since the spool  9  is designed to be rotated in the seat belt winding direction α directly by the pretensioner  13  without the torsion bar  15  intervening, the pretensioner  13  effectively exhibits the seat belt winding in the event of an emergency even though the torsion bar  15  and the second EA mechanism  16  are provided. 
     The other structure and the other works and effects of the seat belt retractor  3  are the same as those of the seat belt retractor  3  disclosed in Patent Document 1, which is incorporated herein by reference. 
       FIGS. 11(a), 11(b)  through  FIG. 13(a), 13(b)  are illustrations partially and schematically showing another embodiment of the seat belt retractor according to the present invention. 
     In the aforementioned embodiment, in case of not actuating the second EA mechanism  16  in the event of an emergency, the EA plate operating member  19  is moved to the lying position by the seat belt winding action of the pretensioner  13  when the gas generator  21 a of the driving member  21  is actuated, thereby setting the second EA mechanism  16  to the inoperative state. For this, if the second EA mechanism  16  is first actuated in the event of an emergency, it is impossible to stop the operation of the second EA mechanism  16  on the way even when the gas generator  21 a is actuated in order to stop the operation of the second EA mechanism  16 . In the aforementioned embodiment, that is, once the second EA mechanism  16  is actuated, it is impossible to stop the operation of the second EA mechanism  16  until the operation of the second EA mechanism  16  is completely terminated whether or not the generator  21 a is actuated or not. 
     On the other hand, in the seat belt retractor  3  of this embodiment, it is possible to stop the operation of the second EA mechanism  16  on the way. In other words, in the seat belt retractor  3  of this embodiment, the operation of the second EA mechanism  16  is controllable selectively to be stopped or not stopped. Hereinafter, the seat belt retractor  3  of this embodiment will be described. 
     As shown in  FIGS. 11(a) and 11(b) , the seat belt retractor  3  of this embodiment comprises a casing  30  (corresponding to the supporting member for the energy absorbing member of the present invention) which is disposed in the cylindrical portion  9 a on one end side (the right side in  FIG. 11(a) ) of the spool  9 . The casing  30  is formed in a bottomed cylindrical member having a cylindrical portion  30 a and a bottom  30 b. In this case, the cylindrical portion  30 a of the casing  30  is disposed inside the cylindrical portion  9 a of the spool  9  and the shaft portion of the locking base  11  penetrates through a circular hole, which is formed in the bottom of the casing  30 , without touching the casing  30 . 
     On the inner periphery of the cylindrical portion  30 a of the casing  30 , an EA plate operating portion  31  which is a convex portion projecting radially is provided. The EA plate operating portion  31  actuates the second EA mechanism  16  similarly to the EA plate operating member  19  of the aforementioned embodiment. 
     Between the spool  9  and the casing  30 , a rod-like stopper  32  is fitted in grooves formed in the spool  9  and the casing such that the stopper  32  is slidable. Therefore, when the stopper  32  is positioned between the spool  9  and the casing  30 , the spool  9  and the casing  30  are not allowed to rotate relative to each other so that they rotate together. When the stopper  32  is not positioned between the spool  9  and the casing  30 , the spool  9  and the casing  30  are allowed to rotate relative to each other. The stopper  32  has a pair of shear pins  32 a projecting therefrom. As the shear pins  32 a are fitted into the grooves of the spool  9 , the stopper  32  is normally held between the spool  9  and the casing  30  as shown in  FIG. 11(b) . 
     As shown in  FIG. 11(a)  and  FIG. 12(a) , a stopper operating member  33  and an EA operation controlling member  34  are disposed on the outer periphery of the cylindrical portion  9 a of the spool  9 . The stopper operating member  33  is formed in an annular shape and is not allowed to rotate relative to the frame  8  and is allowed to move in the axial direction of the spool  9 . As the stopper operating member  33  moves in the axial direction of the spool  9 , the stopper  32  is pressed by the stopper operating member  33  so as to get out of the groove of the casing  30 . As the stopper  32  gets out of the groove of the casing  30 , the spool  9  and the casing  30  are allowed to rotate relative to each other. 
     The EA operation controlling member  34  has an annular portion  34 a of which diameter is the same as that of the stopper operating member  33 , and a long operating lever  34 b extending radially outwardly from the annular portion  34 a. The stopper operating member  33  and the annular portion  34 a of the EA operation controlling member  34  are opposed to each other in the axial direction of the spool  9 . On the opposed faces of the stopper operating member  33  and the EA operation controlling member  34 , a movement converting mechanism  35  for converting the rotation of the EA operation controlling member  34  to the axial movement (i.e. linear movement) of the stopper operating member  33  is provided. As shown in  FIG. 12(a)  and  FIG. 13(a) , the movement converting mechanism  35  comprises a stopper operating member side corrugated portion  33 a and an EA operation controlling member side corrugated portion  34 c which are annular and formed in the opposed faces of the stopper operation member  33  and the EA operation controlling member  34 , respectively. 
     Normally, as shown in  FIG. 12(a) , the stopper operating member  33  and the EA operation controlling member  34  are set to the inoperative position where the peaks of the stopper operating member side corrugated portion  33 a and the valleys of the EA operation controlling member side corrugated portion  34 c are opposed to each other and the valleys of the stopper operating member side corrugated portion  33 a and the peaks of the EA operation controlling member side corrugated portion  34 c are opposed to each other. In the inoperative position of the stopper operating member  33  and the EA operation controlling member  34 , the respective corrugated surfaces of the stopper operating member and the EA operation controlling member  34  are wholly or substantially wholly in contact with each other. In this state, the stopper operating member  33  is placed at a position closest to the EA operation controlling member  34  in the axial direction of the spool  9 . 
     When the EA operation controlling member  34  rotates relative to the stopper operating member  33  in the event of an emergency, as shown in  FIG. 13(a) , the stopper operating member  33  and the EA operation controlling member  34  are set to the operative position where the peaks of the stopper operating member side corrugated portion  33 a and the peaks of the EA operation controlling member side corrugated portion  34 c are opposed to each other and the valleys of the stopper operating member side corrugated portion  33 a and the valleys of the EA operation controlling member side corrugated portion  34 c are opposed to each other. In the operative position of the stopper operating member  33  and the EA operation controlling member  34 , only the peaks of the respective corrugated surfaces of the stopper operating member  33  and the EA operation controlling member  34  are in contact with each other. In this case, the stopper operating member  33  moves in the axial direction of the spool  9  and is thus place at a position farthest from the EA operation controlling member  34  in the axial direction of the spool  9 . In the operative position of the stopper operating member  33  and the EA operation controlling member  34 , the stopper  32  is pressed by the stopper operating member  33  to get out of the groove of the casing  30 . 
     As shown in  FIGS. 11(a), 11(b)  and  FIG. 12(b) , an operation lever  34 b of the EA operation controlling member  34  has a tip end  34 b 1  which is formed by folding at a right angle or a substantially right angle. The tip end  34 b 1  penetrates a circular guide hole  36 , which is formed in one side wall  8 a of the frame  8  coaxially with the spool  9 . The tip end  34 b 1  of the operation lever  34 b penetrating the guide hole  36  further enters into a guide hole  21 f of the driving piston  21 b of the driving member  21 . 
     The tip end  34 b 1  of the operation lever  34 b is normally located at one end  36 a of the guide hole  36  as shown in  FIG. 11(b) . When the tip end  34 b 1  is located at this position, as shown in  FIGS. 12(a) and 12(b) , the stopper operating member  33  and the EA operation controlling member  34  are located at the inoperative position and the driving piston  21 b in the inoperative state is in contact with the tip end  34 b 1 . On the other hand, when the gas generator  21 a of the driving member  21  is actuated, the driving piston  21 b is actuated by gas generated from the gas generator  21 a to press the tip end  34 b 1  of the operation lever  34 b. Accordingly, the tip end  34 b 1  is moved to rotate the EA operation controlling member  34  so that the stopper operating member  33  is moved in the axial direction of the spool  9  by means of the movement converting mechanism  35 . As the tip end  34 b 1  arrives at the other end  36 b of the guide hole  36 , the top end  34 b 1  is stopped at this position. When the tip end  34 b 1  is located at this position, as shown in  FIGS. 13(a) and 13(b) , the stopper operating member  33  and the EA operation controlling member  34  are located at the operative position. 
     The other components of the seat belt retractor  3  of this embodiment are the same as those of the aforementioned embodiment. 
     In the seat belt retractor  3  of this embodiment structured as mentioned above, normally the stopper operating member  33  and the EA operation controlling member  34  are set at the inoperative position. In this state, the stopper  32  is located between the spool  9  and the casing  30 . In addition, the locking base  11  is allowed to rotate together with the spool  9 . Therefore, the spool  9 , the locking base  11 , and the casing  30  are allowed to rotate together. That is, as the seat belt  4  is withdrawn at a normal withdrawing speed for wearing the seat belt  4 , the spool  9 , the locking base  11 , and the casing  30  rotate together in the seat belt withdrawing direction from a position shown in  FIG. 14(a)  to a position shown in  FIG. 14(b)  so that the seat belt  4  is withdrawn. On the other hand, when the seat belt wearing is cancelled, the spool  9 , the locking base  11 , and the casing  30  rotate together in the seat belt winding direction as the opposite direction so that the seat belt  4  is wound up onto the spool  9  by the spring mechanism  14 . During this, even though the spool  9 , the locking base  11 , and the casing  30  rotate together, the stopper operating member  33  and the EA operation controlling member  34  are maintained at the inoperative position. 
     In the event of an emergency as mentioned above, the pretensioner  13  is actuated similarly to the aforementioned case. Further, similarly to the aforementioned embodiment, it is assumed that the CPU  29  determines that the operation of the second EA mechanism  16  is required. In this case, the CPU  29  does not actuate the gas generator  21 a so that the stopper operating member  33  and the EA operation controlling member  34  are maintained at the inoperative position. As the pretensioner  13  is actuated in this state, the spool  9 , the locking base  11 , and the casing  30  are rotate together in the seat belt winding direction, thereby removing a slack of the seat belt  4 . Then, the seat belt  4  is withdrawn because of inertia of the occupant. At this point, since the locking base  11  is prevented from rotating in the belt withdrawing direction by the locking mechanism  10 , only the spool  9  and the casing  30  rotate together in the seat belt withdrawing direction. 
     Then, the torsion bar  15  is torsionally deformed similarly to the aforementioned embodiment. Since the energy absorbing plate  17  is pressed by the EA plate operating portion  31  of the casing  30 , the energy absorbing plate  17  is gradually deformed as shown in  FIGS. 15(a) through 15(c) , similarly to the aforementioned embodiment. That is, the EA action by the first EA mechanism (the torsion bar  15 ) and the EA action by the second EA mechanism  16  are both conducted. Therefore, as shown in  FIG. 16(a) , the EA load becomes the sum of the load by torsional deformation of the torsion bar  15  and the load by deformation of the energy absorbing plate  17  (similarly to the case shown in  FIG. 8(a)  of the embodiment). Because of both of the deformation of the torsion bar  15  and the deformation of the energy absorbing plate  17  of the second EA mechanism  16 , the energy applied to the occupant is effectively absorbed. As the deformation of the energy absorbing plate  17  is finished, the EA load becomes the load solely by the torsional deformation of the torsion bar  15 . 
     It is assumed that, in the event of an emergency during normal operation of the seat belt retractor  3  as shown in  FIGS. 17 ( 1 ) (a) and  17 ( 2 ) (a), the CPU  29  determines that the operation of the second EA mechanism  16  is not required similarly to the aforementioned embodiment. At this point, as shown in  FIGS. 17 ( 1 ) (c) and  17 ( 2 ) (c), the CPU  29  actuates the gas generator  21 a so that the gas generator  21 a generates gas. With the gas generated, the driving piston  21 b presses the tip end  34 b 1  of the operation lever  34 b so that the tip end  34 b 1  moves to the left in  FIG. 12(b)  and the annular portion  34 a of the EA operation controlling member  34  rotates in the clockwise direction in  FIG. 12(b)  by the operation lever  34 b. Then, as shown in  FIGS. 17 ( 1 ) (d) and  17 ( 2 ) (d) the tip end  34 b 1  comes at the other end  36 b of the guide hole  36 , thereby stopping the rotation of the annular portion  34 a. 
     As the annular portion  34 a rotates, the stopper operating member  33  is forced by the movement converting mechanism  35  in a direction γ so as to press the stopper  32 , thereby shearing the shear pins  32 a. Accordingly, the stopper operating member  33  moves in the direction γ and the stopper  32  also moves in the direction γ to get out of the groove of the casing  30 . As a result of this, the spool  9  and the casing  30  are allowed to rotate relative to each other. Therefore, the spool  9  rotated in the seat belt withdrawing direction β because the seat belt  4  is forced to be withdrawn due to the inertia of the occupant. 
     Since the casing  30  does not rotate even though the spool  9  rotates, the energy absorbing plate  17  keeps its initial state and is not deformed. Therefore, only the spool  9  rotates in the seat belt withdrawing direction β similarly to the aforementioned embodiment. Accordingly, the EA load becomes the load solely by the torsional deformation of the torsion bar  15  as shown in  FIG. 16(b) . In this manner, the energy absorption by deformation of the energy absorbing plate  17  is not conducted so that the energy applied to the occupant is absorbed solely by the torsional deformation of the torsion bar  15 . 
     Further, it is assumed that, in the event of an emergency during normal operation of the seat belt retractor  3  as shown in  FIGS. 17 ( 1 ) (a) and  17 ( 2 ) (a), the CPU  29  determines that the operation of the second EA mechanism  16  is required similarly to the aforementioned embodiment, but the entire operation of the second EA mechanism is not required. In this case, as shown in  FIGS. 17 ( 1 ) (b) and  17 ( 2 ) (b), the EA action by the first EA mechanism (the torsion bar  15 ) and the EA action by the second EA mechanism  16  are both conducted. Therefore, as shown in  FIG. 16(c) , the EA load becomes the sum of the load by torsional deformation of the torsion bar  15  and the load by deformation of the energy absorbing plate  17 . However, if the CPU  29  determines that the operation of the second EA mechanism  16  is not required on the way of deformation of the energy absorbing plate  17 , the CPU  29  actuates the gas generator  21 a as shown in  FIGS. 17 ( 1 ) (c) and  17 ( 2 ) (c). Then, the operation of the second EA mechanism  16  is stopped so that the energy absorbing plate  17  no more deforms before the entire deformation of the energy absorbing plate  17  is completed. Accordingly, the EA load becomes the load solely by the torsional deformation of the torsion bar  15  because of no load by the deformation of the energy absorbing plate  17  shown by a two-dot chain line in  FIG. 16(c)  before the entire deformation of the energy absorbing plate  17  is completed. 
     The timing of stopping the deformation of the energy absorbing plate  17  on the way of deformation of the energy absorbing plate  17  is determined and set by the CPU  29  according to the emergency situation. In the aforementioned embodiment, the CPU  29  determines whether or not the operation of the second EA mechanism  16  is required to be stopped during the operation of the second EA mechanism. However, immediately after the emergency, the CPU  29  may determine whether or not the operation of the second EA mechanism  16  is required to be stopped after actuation of the second EA mechanism  16 . 
     According to the seat belt retractor  3  of this embodiment, when the CPU  29  determines that the operation of the second EA mechanism  16  is required, but the entire operation of the second EA mechanism  16  is not required, the gas generator  21 a is actuated after the second EA mechanism  16  is actuated but before the entire operation of the second EA mechanism  16  is completed. That is, even after the second EA mechanism  16  is actuated, it is possible to stop the operation of the second EA mechanism  16  depending on the emergency situation. Therefore, the kinetic energy absorption (EA) for the occupant in the event of an emergency can be further finely and correctly conducted. The other works and effects of the seat belt retractor  3  of this embodiment are the same as those of the aforementioned embodiment. 
     Though the pretensioner  13  is actuated after the gas generator  21 a of the driving member  21  is actuated in case of not actuating the second EA mechanism  16  in the aforementioned embodiments, the present invention is not limited thereto. That is, in case of not actuating the second EA mechanism  16 , the driving member  21  and the pretensioner  13  may be actuated at the same time. 
     Though the gas generator  21 a is used as the driving member  21  in the aforementioned embodiments, the present invention is not limited thereto. That is, the driving piston  21 b may be actuated by driving force of another means using electromagnetic force such as an electromagnetic solenoid. In this case, the electromagnetic solenoid is controlled by the CPU  29  similarly to the aforementioned case. Briefly, various design changes may be made within a scope of the claims of the present invention. 
     The seat belt retractor of the present invention is suitably used as a seat belt retractor which is used in a seat belt apparatus installed in a vehicle such as an automobile and which prevents a seat belt from being withdrawn with absorbing energy on the occupant by limiting load applied on a seat belt in the event of an emergency. 
     The disclosures of Japanese Patent Applications No. 2008-293396 filed on Nov. 17, 2008, and No. 2009-027179 filed on Feb. 9, 2009, are incorporated by references. 
     While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.