Abstract:
A seat belt device includes a spindle  11  for retracting a seat belt  13 , an electric actuator  55 , a pre-tensioner  14  and a power transmission mechanism  20 , wherein the power transmission mechanism  20  can reversibly switch the connection and disconnection between the electric actuator  55  and the spindle  11  before the pre-tensioner  14  is activated, while when the pre-tensioner  14  is activated, the power transmission mechanism  20  non-reversibly interrupts the connection between the electric actuator  55  and the spindle  11.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to JP 2005-146173, filed May 19, 2005 and PCT/JP2006/309960, filed May 18, 2006. 
     FIELD OF THE INVENTION 
     The present invention relates to a seat belt device, and more particularly to a seat belt device which includes an electric actuator utilizing a motor and a pyrotechnic pre-tensioner actuator (a pre-tensioner). 
     BACKGROUND OF THE INVENTION 
     Conventionally, in a seat belt device of this type, when there is a possibility of collision, a seat belt (webbing) is retracted by the electric actuator before collision, and then the possibility of collision disappears, the seat belt is put back to the state before the possible collision was sensed, and when the collision occurs, the seat belt is retracted by the pre-tensioner (for example, refer to Patent Document No. JP-A-2003-191819). 
     SUMMARY OF THE INVENTION 
     In this way, in the seat belt device which includes the electric actuator which produces power to rotate a spindle and the pre-tensioner which produces another form of power to rotate the spindle, when the pre-tensioner is activated, the spindle for retracting the seat belt is desirably disconnected from the electric actuator. 
     Consequently, a main object of the invention is to provide a seat belt device including a seat belt retracting member such as a spindle for retracting the seat belt, a primary rotation source such as an electric actuator for rotating the seat belt retracting member when it is brought into connection with the seat belt retracting member, and a secondary rotation source such as a pre-tensioner for rotating the seat belt retracting member at faster speeds than the primary rotational source, wherein when the secondary rotation source such as the pre-tensioner is activated, the connection of the seat belt retracting member such as the spindle with the first rotation source such as a motor can be interrupted. 
     According to the invention, there is provided a seat belt device including:
         a spindle for retracting a seat belt;   an electric actuator for generating power for rotating the spindle;   a pre-tensioner for generating another form of power for rotating the spindle; and   a power transmission mechanism for transmitting the power from the electric actuator to the spindle, wherein the power transmission mechanism can reversibly switch the connection and disconnection between the electric actuator and the spindle before the pre-tensioner is activated, while when the pre-tensioner is activated, the power transmission mechanism non-reversibly interrupts the connection between the electric actuator and the spindle.       

     In addition, according to the invention, there is provided a seat belt device including:
         a spindle for retracting a seat belt;   an electric actuator for generating power for rotating the spindle;   a pre-tensioner for generating another form of power for rotating the spindle; and   a power transmission mechanism for transmitting the power from the electric actuator to the spindle, wherein when the pre-tensioner is activated, the power transmission mechanism interrupts the connection between the electric actuator and the pre-tensioner by making use of the rotation of the spindle by the pre-tensioner.       

     In addition, according to the invention, there is provided a seat belt device including:
         a seat belt retracting member for retracting a seat belt;   a primary rotation source for rotating the seat belt retracting member when it is brought into connection with the seat belt retracting member;   a secondary rotation source for rotating the seat belt retracting member at faster speeds than the primary rotation source; and   a power transmission mechanism, wherein the power transmission mechanism can reversibly switch the connection and disconnection between the primary rotation source and the seat belt retracting member before the secondary rotation source is activated, while when the secondary rotation source is activated, the power transmission mechanism non-reversibly interrupts the connection between the first rotation source and the seat belt retracting member.       

     Furthermore, according to the invention, there is provided a seat belt device including:
         a spindle for retracting a seat belt;   an electric actuator for generating power for rotating the spindle; and   a power transmission mechanism for transmitting the power from the electric actuator to the spindle, wherein   the power transmission mechanism has an actuator-side gear to which the power from the electric actuator is transmitted, a spindle-side gear which is provided on the spindle&#39;s side and an elastic piece which is mounted either of the actuator-side gear and the spindle-side gear and which can be brought into engagement with the other gear and includes a torque limiter in which when a torque difference which is larger than a predetermined value is generated between the actuator-side gear and the spindle-side gear, the elastic piece cancels the engagement with the other gear so as to move relative to the other gear so that the torque difference becomes equal to or less than the predetermined value.       

     Advantage Of The Invention 
     According to the invention, there is provided the seat belt device including the seat belt retracting member such as the spindle for retracting the seat belt, the primary rotation source such as the electric motor which is brought into connection with the seat belt retracting member to rotate the seat belt retracting member and the secondary rotation source such as the pre-tensioner for rotating the seat belt retracting member at faster speeds than the primary rotation source, wherein when the secondary rotation source such as the pre-tensioner is activated, the connection between the seat belt retracting member such as the spindle and the primary rotation source such as the motor can be interrupted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a schematic vertical sectional view which explains a seat belt device of a first embodiment of the invention. 
         FIG. 2  is a cutaway view taken along the line A-A and viewed in a direction indicated by arrows attached to the line in  FIG. 1 . 
         FIG. 3  is a vertical sectional view taken along the line B-B in  FIG. 1 , which explains the operation of a clutch for transmitting power from a motor. 
         FIG. 4  is a vertical sectional view taken along the line B-B in  FIG. 1 , which explains the operation of the clutch for transmitting power from the motor. 
         FIG. 5  is a vertical sectional view taken along the line B-B in  FIG. 1 , which explains the operation of the clutch for transmitting power from the motor. 
         FIG. 6  is a vertical sectional view taken along the line B-B in  FIG. 1 , which explains the operation of the clutch for transmitting power from the motor. 
         FIG. 7  is a vertical sectional view taken along the line B-B in  FIG. 1 , which explains the operation of the clutch for transmitting power from the motor. 
         FIG. 8  is an exploded schematic perspective view of the clutch for transmitting the power from the motor of the seat belt device of the first embodiment of the invention. 
         FIG. 9  is a view corresponding to the vertical sectional view taken along the line B-B in  FIG. 1  which explains a clutch in an inoperative state of a seat belt device of a second embodiment of the invention. 
         FIG. 10   a  is a view corresponding to the vertical sectional view taken along the line B-B in  FIG. 1  which explains the clutch of the seat belt device of the second embodiment of the invention while a retraction by a motor is in operation. 
         FIG. 10   b  is a view corresponding to the vertical sectional view taken along the line B-B in  FIG. 1  which explains the clutch of the seat belt device of the second embodiment of the invention while the retraction by the motor is in operation. 
         FIG. 10   c  is a view corresponding to the vertical sectional view taken along the line B-B in  FIG. 1  which explains the clutch of the seat belt device of the second embodiment of the invention while the retraction by the motor is in operation. 
         FIG. 11   a  is a view corresponding to the vertical sectional view taken along the line B-B in  FIG. 1  which explains the clutch of the seat belt device of the second embodiment of the invention when the retraction by the motor is cancelled. 
         FIG. 11   b  is a view corresponding to the vertical sectional view taken along the line B-B in  FIG. 1  which explains the clutch of the seat belt device of the second embodiment of the invention when the retraction by the motor is cancelled. 
         FIG. 11   c  is a view corresponding to the vertical sectional view taken along the line B-B in  FIG. 1  which explains the clutch of the seat belt device of the second embodiment of the invention when the retraction by the motor is cancelled. 
         FIG. 12   a  is a view corresponding to the vertical sectional view taken along the line B-B in  FIG. 1  which explains the clutch of the seat belt device of the second embodiment of the invention while a pre-tensioner is in operation. 
         FIG. 12   b  is a view corresponding to the vertical sectional view taken along the line B-B in  FIG. 1  which explains the clutch of the seat belt device of the second embodiment of the invention while the pre-tensioner is in operation. 
         FIG. 12   c  is a view corresponding to the vertical sectional view taken along the line B-B in  FIG. 1  which explains the clutch of the seat belt device of the second embodiment of the invention while the pre-tensioner is in operation. 
         FIG. 13  are views which explain a gear assembly of a seat belt device of a third embodiment of the invention. 
         FIG. 14  is a view which explains a gear having a torque limiter in  FIG. 13 . 
         FIG. 15  are views which explain a torque limiting operation of the gear having the torque limiter. 
     
    
    
     DETAILED DESCRIPTION 
     Next, seat belt devices of respective embodiments of the invention will be described by reference to the drawings. 
       FIG. 1  is a schematic vertical sectional view which describes a seat belt device of a first embodiment of the invention,  FIG. 2  is a cutaway view taken along the line A-A and viewed in a direction indicated by arrows attached to the line in  FIG. 1 ,  FIGS. 3 to 7  are vertical sectional views taken along the line B-B in  FIG. 1  which describe the operations of a clutch for transmitting power from a motor, and  FIG. 8  is an exploded schematic perspective view of the clutch for transmitting the power from the motor of the seat belt device of the first embodiment of the invention.
         A seat belt device  1  of this embodiment includes a spindle  11  for retracting a seat belt (webbing)  13 ,   a pyrotechnic actuator (pre-tensioner)  14  connected to the spindle  11 ,   a motor  55  as an electric actuator and   a clutch  20  as a power transmission mechanism for power from the motor  55  to the spindle  11 .       

     A torsion bar  12  functioning as an energy absorbing mechanism is provided within the spindle  11  so as to be connected to the spindle  11 . 
     The pretensioner  14  includes a pinion  15  connected to the spindle  11 , a tube  17  which accommodates balls  16  and a gas generator  18  provided at one end of the tube  17 . When explosives are set alighted, the gas generator  18  generates gas, whereby the balls  16  accommodated within the tube  17  are strongly pushed out. The balls  16  which are so pushed out then move along a groove in the pinion  15  so as to rotate the spindle  11 . 
     The motor  55  is connected to a gear assembly  50 , whereby the rotation of the motor  55  is decelerated by the gear assembly  50 . The gear assembly  50  and the clutch  20  are accommodated within a container defined by a lower cover  21  and an upper cover  29 .
         The clutch  20  includes a joint  24  connected to the spindle  11 ,   a latch plate (a ratchet wheel)  27  integrated with the joint  24  to rotate together with the spindle  11 ,   a final gear  51  of the gear assembly  50  which is gear connected to a rotational shaft of the motor  55 ,   a pawl  32  mounted on the final gear  51  so as to rotate round a shaft  38  and adapted to be brought into engagement with a tooth of the latch plate (ratchet wheel)  27 ,   a return spring  39  which is a biasing member for biasing the pawl  32  in a direction in which the pawl  32  is disconnected from the latch plate  27 ,   a guide ring  30  provided inside the final gear  51  so as to be integral with the final gear  51 ,   a clutch wheel  28  including three leg portions  42  which fit into three holes  41  in the guide ring  30  so as to rotate relatively at a required angle,   a rotor cam  34  mounted on the clutch wheel  28  so as to rotate round a shaft  36  while mounted fixedly on the clutch wheel  28  by means of a fixing pin  37 , whereby its rotation is prohibited in such a state that it is fixed to the clutch wheel  28  by the fixing pin  37 , while its rotation is allowed due to the fixing pin  37  being broken,   a friction spring  25  mounted on the lower cover  21  by an end portion  26  being caused to fit in a recessed portion  22  in the lower cover  21  and connected with the clutch wheel  28  by virtue of friction sliding, and   bushes  23 ,  31 .       

     One end of the pawl  32  moves along a cam surface  35  of the rotor cam  34 . 
     In addition, a rib  28   a  is formed on the clutch wheel  28  in a predetermined position which extends in a circumferential direction, and one end portion of this rib  28   a  is situated in the vicinity of the pawl  32  when in an inoperative state where retraction by the motor  55  is not performed. Then, when the pawl  32  rotates due to a violently vehicle vibrating with the motor  55  in the inoperative state, the rib  28   a  is brought into abutment with the pawl  32  so as to prevent an abrupt rotation of the pawl  32  in a direction in which the pawl  32  is brought into engagement with the latch plate  27 . 
     Next, the operation of the seat belt device of the embodiment will be described. 
     When there is a possibility of collision, the seat belt  13  is retracted by the motor  55  before the possible collision, while when the possibility of collision disappears, the seat belt  13  is brought back to the state before the possible collision was sensed. When a collision occurs, the seat belt  13  is retracted by the pyrotechnic actuator (pre-tensioner)  14  at faster speeds than the retracting speed by the motor before collision, during which when a predetermined or more tension is applied to the seat belt  13 , the tension is limited by the torsion bar  12 . 
     Next, the operation of the clutch  20  will be described. 
     Firstly, as shown in  FIG. 3 , when no retraction is performed by the motor  55 , the latch plate  27  and the pawl  32  are out of engagement. Only the latch plate  27  integrated with the spindle  11  rotates, and normal retracting/stretching of the seat belt  13  can be performed. 
     As shown in  FIG. 4 , when the motor  55  rotates in a retracting direction, the final gear  51 , which is gear connected to the rotational shaft of the motor  55 , rotates in a counterclockwise direction (C direction). The pawl  32 , which is mounted rotatably on the final gear  51 , rotates to the latch plate  27  side along the cam surface  35  of the rotor cam  34  so as to start engagement with the latch plate  27 . 
     As shown in  FIG. 5 , when the pawl  32  is brought into engagement with the latch plate  27 , the rotation of the final gear  51  is transmitted to the spindle  11  via the latch plate  27 , whereby the seat belt  13  is started to be retracted. As this occurs, the rotor cam  34  rotates together with the clutch wheel  28  while friction sliding relative to the friction spring  25 . 
     As shown in  FIG. 6 , when the motor  55  rotates in releasing direction, in response to the rotation, the final gear  51  rotates in the releasing direction (clockwise direction: D direction). While the pawl  32  rotates together with the final gear  51 , the clutch wheel  28  and the rotor cam  34  mounted on the clutch wheel  28 , are maintained by the friction spring  25 . The pawl  32  departs from the latch plate along the cam surface  35  of the rotor cam  34  by virtue of the biasing force of the return spring  39 , whereby the pawl  32  is disengaged from the latch plate. 
     As shown in  FIG. 7 , when the pre-tensioner  14  is activated, the pawl  32  is flicked out outwardly by a tooth surface of the latch plate  27  by virtue of the fast retracting rotation of the spindle  11  and the latch plate  27  integrated therewith. At the same time, the rotor cam  34  is pushed by the pawl  32  and rotates outwardly about the shaft  36  of the clutch wheel  28 . As a result, the pawl  32  and the rotor cam  34  are held on an outer circumferential portion by virtue of the biasing force of the return spring. Thereafter the power of the motor  55  is transmitted in no case to the spindle by the clutch  20 . 
     Next, a seat belt device according to a second embodiment of the invention will be described in detail by reference to  FIGS. 9 to 12(   c ). Note that like reference numerals will be imparted to like portions to those of the first embodiment, and the description thereof will be omitted or briefly made. 
     In this embodiment, in place of the fixing pin  37  of the first embodiment, a hold spring  60  as an elastic member is provided so as to hold a rotor cam  34   a . Namely, the rotor cam  34   a  has an end portion  61  which extends to an opposite side of a shaft  36  to a side where a cam surface  35  is provided. In addition, the hold spring  60  is built on a clutch wheel  28  so as to be brought into abutment with the end portion  61  on the opposite side of the rotor cam  34   a.    
     By this configuration, the rotor cam  34   a  of this embodiment is mounted on the clutch wheel  28  so as to rotate round the shaft  36 , and is fixed to the clutch wheel  28  so as not to rotate in such a state that the rotor cam  34   a  is biased by the hold spring  60 . Furthermore, the rotor cam  34   a  is allowed to rotate when the biasing by the hold spring  60  is cancelled. 
     Next, the operation of a clutch  20   a  of this embodiment will be described. 
     Firstly, when no retraction by a motor  55  is performed, as shown in  FIG. 9 , a pawl  32  is disengaged from a latch plate  27  by virtue of the biasing force of a return spring  39 . Due to this, only the latch plate  27  integrated with a spindle  11  rotates, whereby the normal retracting/stretching of the seat belt  13  is enabled. 
     Next, when the motor  55  rotates in a retracting direction, as shown in  FIG. 10(   a ), a final gear  51  gear connected to a rotational shaft of the motor  55  rotates in a counterclockwise direction (C direction). When the final gear  51  rotates, a friction spring  25  idly rotates until a circumferential edge portion of a hole  22   a  in a lower cover  21 . 
     When the motor  55  rotates in the retracting direction further, as shown in  FIG. 10(   b ), the clutch wheel  28  is fixed by virtue of the frictional force of the friction spring  25 , whereby only the final gear  51  rotates. In addition, the pawl  32  rotatably supported on a guide ring  30  rotates to the latch plate  27  side along the cam surface  35  of the rotor cam  34   a  against the biasing force of the return spring  39 , so as to start engagement with the latch plate  27 . Furthermore, when the final gear  51  rotates, leg portions  42   a  of the clutch wheel  28  are brought into abutment with circumferential edge portions of holes  41   a  of the guide ring  30 , whereby the final gear  51  and the clutch wheel  28  rotate together. 
     In addition, as shown in  FIG. 10(   c ), when the pawl  32  is brought into engagement with the latch plate  27 , the rotation of the final gear  51  is transmitted to the spindle  11  via the latch plate  27 , whereby the retracting of the seat belt  13  is started. 
     In addition, as shown in  FIG. 11(   a ), when the motor  55  rotates in releasing direction, in response to the rotation, the final gear  51  rotates in the releasing direction (clockwise direction: D direction). Along with this, the webbing is stretched out by virtue of a reaction force from an occupant which is acting on the webbing, and the clutch wheel  28  and the latch plate  27  rotate together by such an extent that the friction spring rotates idly. Thereafter, as shown in  FIG. 11(   b ), the clutch wheel  28  is fixed by virtue of the biasing force of the friction spring  25 , whereby only the final gear  51  and the latch plate  27  rotate in the releasing direction. The latch plate  27  maintains a meshing state with the pawl  32  while it is rotating in association with the rotation of the final gear  51 . 
     Then, as shown in  FIG. 11(   c ), when there is no reaction force coming from the occupant and the rotation of the latch plate  27  together with the spindle  11  in the stretching direction ends, the final gear  51  rotates further. Accordingly, the engagement between the pawl  32  and the latch plate  27  is interrupted and an initial state is thereby restored. 
     In addition, as shown in  FIG. 12(   a ), when the pre-tensioner  14  is activated in such a state that the motor rotates in the retracting direction, the pawl  32  is flicked out outwardly by a tooth surface of the latch plate  27  by virtue of the fast retracting rotation of the spindle  11  and the latch plate  27  integrated therewith. 
     Then, as shown in  FIG. 12(   b ), when the pawl  32  is brought into abutment with the rotor cam  34  to thereby push the rotor cam  34  outwards, the rotor cam  34  rotates about the shaft  36 , whereby the pressure from the hold spring  60  built on the clutch wheel  28  is released (refer to  FIG. 12(   c )). Thereafter, the pawl  32  and the rotor cam  34  are held on an outer circumferential portion of the guide ring  30  by virtue of the biasing force of the return spring  39 . Therefore, the rotation of the motor  55  is transmitted in no case to the spindle  11  by the clutch  20 . 
     Consequently, also in the seat belt device of this embodiment, the power transmission from the motor  55  is cut off by the clutch  20  at the time when the pre-tensioner  14  is activated, and the webbing is retracted by the pre-tensioner  14  without being subjected to power resistance by the motor  55  and the clutch  20 . Therefore, it becomes possible to increase the retracting performance of the pre-tensioner  14 . 
     Furthermore, while an energy absorbing operation is performed by the torsion bar  12 , the power resistance of the motor  55  and the clutch  20  is added in no case to the belt stretching load, thereby making it possible to increase the restraining performance. 
     Next, a seat belt device according to a third embodiment of the invention will be described in detail by reference to  FIGS. 13 to 15 . This embodiment differs from the first embodiment in the configuration of a gear assembly, and like reference numerals will be imparted to the other like constituent portions to those of the first embodiment, whereby the description thereof will be omitted or made briefly. 
     As shown in  FIG. 13 , a gear assembly  50   a  of this embodiment includes first to fourth gears  71 ,  72 ,  73 ,  74 , and a tooth surface of the fourth gear  74  is in mesh engagement with a final gear  51 . The first gear  71  is coupled to a motor shaft of a motor  55 , and the second gear  72  has tooth surfaces  72   a ,  72   b  which are brought into mesh engagement with the first gear  71  and the third gear  73 , respectively. As shown in  FIG. 14 , the third gear  73  is a gear assembly with a torque limiter mechanism including a large diameter side gear (an actuator-side gear)  80 , a plurality of limit springs (elastic pieces)  81  and a tubular small diameter side gear (spindle-side gear)  82 . 
     The small diameter side gear  82  has a shape in which a gear portion  82   a  meshing with the fourth gear  74 , and a spring support portion  82   c  including slits  82   b  to which a plurality of limit springs  81  are assembled are coupled together in an axial direction. 
     The large diameter side gear  80  has a tooth portion  80   a  meshing with the second gear  72  on an outer circumferential surface thereof. Further, the large diameter side gear  80  accommodates the spring support portion  82   c  and the limit springs  81  of the small diameter side gear  82  in an interior wall  80   b  and a bottom portion  80   c  thereof to which grease is applied. 
     A plurality of concave locking surfaces  80   d  are formed at predetermined intervals on the interior wall  80   b  of the large diameter side gear  80 . Projecting portions  81   a  formed on the limit springs  81  are brought into engagement with the locking surfaces  80   d . In addition, the locking surfaces  80   d  are formed an integer number of times the number of the projecting portions  81   a.    
     Next, the operation of the torque limiter mechanism will be described. 
     In the normal state, as shown in  FIG. 13(   a ), the phases of the large diameter side gear  80  and the small diameter side gear  82  of the third gear  73  are held relative to each other. The large diameter side gear  80  and the small diameter side gear  82  rotate in the same direction in the retracting direction shown by a solid line or the releasing direction shown by a broken line. Here, when retracting is performed by driving the motor  55 , in the event that a torque difference larger than a predetermined value is generated between the large diameter side gear  80  and the small diameter side gear  82  due to a light collision or braking which does not activate the pre-tensioner  14 , as shown in  FIG. 15 , the projecting portions  81   a  of the limit springs  81  are released from the engagement with the locking surfaces  80   d  and then start to slide along the interior wall  80   b  while being deformed. 
     Then, due to the projecting portions  81   a  being brought into engagement with the adjacent locking surfaces  80   d , a rotating deviation is generated between the large diameter side gear  80  and the small diameter side gear  82 , and as shown in  FIG. 13(   b ), the fourth gear  74  and the final gear  51  rotate in a belt stretching direction. As a result, the transmission of excessive torque by the motor  55  is suppressed, whereby the failure of gear teeth can be prevented and the effect on the restraining performance during energy absorption operation can be decreased. 
     In addition, the torque limiter mechanism is built in the third gear  73  of the gear assembly  50   a , whereby although it is configured small, the torque limiter mechanism can increase the limiter torque of the spindle  11 . 
     In addition, while the gear assembly  50   a  is preferably applied to the seat belt device which includes the power transmission mechanism of the first or second embodiment, the application thereof is not limited thereto. The gear assembly  50   a  may be applied to known seat belt devices. 
     Additionally, while the limit spring  81  of the embodiment is mounted on the small diameter side gear  82 , the limit spring  81  may be mounted on the large diameter side  80 , so as to be brought into engagement with or disengagement from the locking surfaces provided on the small side gear  82 . 
     Note that the invention is not limited to the embodiments that have been described above but can be modified or improved as required. 
     In addition, this patent application is based on the Japanese Patent Application (No. 2005-146173) filed on May 19, 2005, and all the contents thereof are incorporated herein by reference. 
     While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.