Abstract:
The disclosed belt winder can comprise a belt spindle for winding a safety belt, a belt force limiting device in communication with the belt spindle for limiting a belt restraining force exerted by the seat belt in case of an accident, and a belt force increasing device for blocking further extraction of the safety belt upon reaching a predetermined belt extraction length. The belt force increasing device can be configured to automatically deactivate itself upon exceeding a preset maximum belt restraining force.

Description:
BACKGROUND  
       [0001]     The invention relates to a belt winder (or belt retractor) having features of a belt spindle for winding a safety belt on and off and a belt force limiting device in communication with the belt spindle which, in case of an accident, limits the belt restraining force exerted by the safety belt.  
         [0002]     A belt winder of this kind is disclosed in the international patent application WO 97/04996. This belt winder has a torsion bar as the belt force limiting system. In addition, the previously known belt winder has a belt extraction limiting system in the form of a restraining belt which, in case of an accident, limits the belt extraction and the twisting of the torsion bar beyond a given amount as soon as the safety belt is fully wound to the locking base of the belt winder.  
         [0003]     In European patent EP 1 149 743 B1, a belt winder is disclosed that has two belt force limiting devices. The one belt force limiting device is formed by a torsion bar which twists in case of an accident and thus limits the restraining force. Another belt force limiting device is formed by a wire which is contained in a spindle of the belt winder. In case of an accident, if the belt spindle rotates relative to the locking base of the belt winder, the wire is drawn out of the belt spindle. Thus, a friction force and a deformation force need to be overcome, which increase the belt restraining power of the belt winder. Therefore, the restraining force is the torque of the torsion bar and the friction and deformation force of the wire. A cutting device is connected with the wire, which can cut through the wire and thus end the action of any friction and deformation force of the wire. In such a case, the resultant restraining force is determined solely by the torsion bar. In all, two different restraining forces can be established by the two belt force limiting devices, namely a larger restraining force which is produced by the torsion bar and the wire, and a smaller restraining force which is determined by the torsion bar alone after the wire has been cut or drawn all the way out of the belt spindle.  
         [0004]     The invention of the present application can address the problem of providing a belt winder which can be used more universally than previous belt winders.  
         [0005]     This problem can be solved by an embodiment of the present invention in which a belt winder comprises a belt force increasing device.  
       SUMMARY  
       [0006]     It is provided according to an embodiment of the present invention that a belt force increasing device is present which, when a given belt extraction length is reached, blocks any further extraction of the safety belt. Upon reaching that preset belt extraction length, the belt force increasing device thus interrupts the belt extraction. Any exceeding of a preset maximum belt restraining force can be prevented by automatically and entirely deactivating the belt force increasing device when a preset maximum belt restraining force is reached.  
         [0007]     One advantage of the belt winder according to an embodiment of the present invention is to be seen in the fact that it can be used also on rear seats. In many countries—in the USA, for example—a so-called “loop-load” test (a belt loop load test, cf. e.g. US Standard FMVSS209) is prescribed. According to this test, no more than a given belt extraction length is to be possible on the rear seats at a standard belt extraction force. This specified belt extraction force is, however, greater than the belt force level common in belt force limiting devices, such as torsion bars for example, so that a belt winder is unable to pass the “loop-load” test with a torsion bar alone. At this point, an embodiment of the present invention comes in and provides the belt force increasing device which, upon reaching the specified belt extraction length, prevents any further extraction of the safety belt; thus passing the loop-load test. Unlike the belt winder with the belt extraction limiting device according to the international patent application WO 97/04996, the belt winder according to the invention additionally offers greater protection against injury by the safety belt because the belt force increasing device, upon exceeding the given maximum belt restraining force, becomes automatically and completely deactivated. Thus, unnecessary injuries are avoided.  
         [0008]     Preferably, before the preset belt extraction length is reached, the belt force increasing device leaves the belt extraction unaffected, or at least approximately unaffected, so that the preset belt force limiting action is determined alone or mainly by the belt force limiting device.  
         [0009]     The construction of the belt winder is especially economical and therefore advantageous if the belt force increasing device is configured such that, when the preset maximum belt restraining force is exceeded, it tears or breaks. Preferably, the belt force increasing device has a corresponding break-off point.  
         [0010]     According to a preferred embodiment of the belt winder, a provision can be made for the belt force limiting device to be formed by a torsion bar which at its one end is connected with the belt spindle and at its other end to a clutch. When no accident occurs, the belt force limiting device rotates together with the belt spindle, and in the event of an accident, it locks up, especially by means of a clutch such as a locking pawl.  
         [0011]     Preferably the belt force increasing device may be formed by a windable element, especially a belt or a cable. For example, the windable element is attached at its one end to the belt spindle and at its other end to the clutch.  
         [0012]     According to a preferred embodiment of the belt winder, an arrangement can be made for the windable element to be arranged such that, in case of extraction of the belt while the clutch is engaged, it is wound onto a winding device. The winding device can be formed, for example, by a groove in the belt spindle, by an area for receiving it on the locking device, or by the torsion bar itself.  
         [0013]     Preferably, the length of the windable element is such that, after the preset belt extraction length is reached, it is wound entirely onto the winding device and the belt restraining force is increased.  
         [0014]     With a view towards an especially compact mounting of the windable element, it can be considered advantageous if the windable element is at least partially wound when the belt winder is in the ready state, i.e., before the occurrence of an accident.  
         [0015]     It can be considered to be especially advantageous if, when the belt winder is in the ready state, the windable element is wound on such that, in case of a belt extension with the clutch locked, it is first unwound and after it is fully unwound it is rewound again but in the opposite winding direction. In other words, the windable element is therefore wound on the winding device in the “delivery state” or basic state of the belt winder, contrary to the unwinding direction of the belt winder. The result of this winding direction is that activation of the belt force increasing device does not occur until the windable element has been unwound twice, namely once unwound and then wound on again. Thus a delayed triggering (i.e., a long belt extraction) can be achieved with a relatively short windable element; thus a very short length of the windable element is sufficient.  
         [0016]     In order to start the deactivation of the belt force increasing device in an especially simple manner, the windable element can have at least one break-off point which breaks open when the preset maximum belt restraint force is exceeded.  
         [0017]     If the belt winder is to withstand the above-mentioned loop-load test of US Standard FMVSS209, the maximum belt restraining force of the belt force increasing device is preferably greater than 6672 N (150 lb.). The preset belt extraction length is then preferably less than 508 mm (20″).  
         [0018]     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     These and other features, aspects, and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below.  
         [0020]      FIG. 1  shows a belt winder according to an embodiment of the present invention with a torsion bar as the belt force limiting means and a cord as the belt force increasing device.  
         [0021]      FIG. 2  shows a diagram representing the belt restraining force as a function of the belt extraction length. 
     
    
     DETAILED DESCRIPTION  
       [0022]     An embodiment of the present invention will now be described with reference to  FIG. 1 . This figure shows a belt winder  10  with a belt spindle  20  on which a safety belt  30  can be wound and unwound. A belt force limiting device in the form of a torsion bar  40  is in communication with the belt spindle  20 . One end  50  of the torsion bar  40  is co-rotationally fastened in a secured fashion to the belt spindle  20 .  
         [0023]     Another end  60  of the torsion bar  40  is co-rotationally connected with a clutch  70  which, in an accident-free case, rotates with the belt spindle  20  and, in case of an accident, locks up. For this purpose, the clutch  70  is provided with a pawl  80  which swings outwardly in case of an excessively abrupt extraction of the belt or in case of an activation by a sensor (e.g., a belt acceleration sensor, vehicle acceleration sensor, or vehicle tilt sensor). The pawl  80  thus joins the clutch  70  with a winding frame not shown in  FIG. 1  and joins it for co-rotation with the vehicle structure so that the clutch  70  is engaged and can no longer continue to rotate.  
         [0024]     As can be seen in  FIG. 1 , a cable  100  is wound in an annular receiving channel  120 —wound, that is, contrary to the belt winding direction W of the belt winder  10 . The annular channel  120  forms a means for winding the cable  100 .  
         [0025]     The one extremity  130  of the cable  100  is fastened in the annular channel  120  that is rotationally symmetrical with the axis of rotation M of the belt spindle  20 . The other end  140  of the cable  100  is attached to the clutch  70 .  
         [0026]     The channel  120  is arranged to be concentric with the cylindrical cavity  150  in which the torsion bar  40  lies. The channel  120  and the cylindrical cavity  150  are separated from one another only by a narrow annular separation  160 . The torsion bar  40  is also separated by this separation  160  from the cable  100  so that the torsion bar  40  cannot interfere with the winding and unwinding of the cable  100 .  
         [0027]     The belt winder  10  according to  FIG. 1  operates as follows.  
         [0028]     In case of a vehicle accident, an abrupt forward movement of a vehicle occupant protected by a safety belt  30  will occur so that coincidentally therewith the safety belt  30  is unwound abruptly from the belt spindle  20 . In this case, the pawl  80  will swing outwardly—for example because it is triggered by one of the sensors referred to above—and the clutch  70  will lock with the winding frame. The other end  60  of the torsion bar  40  is now locked so that it can no longer rotate together with the belt spindle  20 . On account of the belt extraction force F occurring due to the forward movement of the vehicle occupant, the end  50  of the torsion bar  40  will, however, continue rotating so that the torsion bar  40  is torqued. The safety belt  30  is thus further unwound, while a belt restraining force F t  determined by the mechanical torque resistance is applied to the vehicle occupant.  
         [0029]     The belt restraining force F is represented in  FIG. 2  (cf. range for S&lt;Sg). It can be seen that the belt restraining force F has a value of approximately F t , which is provided substantially only by the torsion bar  40 .  
         [0030]     During the torquing of the torsion bar  40 , the cable  100  is first unwound within the receiving channel  120 . After unwinding, the cable  100  is wound up again within the receiving channel  120  but in a winding direction opposite that of the original unwinding direction.  
         [0031]     As soon as the cable  100  is completely wound up within the receiving channel  120 , the cable  100  blocks any further extraction of the belt. This is represented in  FIG. 2 . It can be seen that in the event of a given belt extraction length S g , the belt restraining force F increases abruptly.  
         [0032]     In order to prevent injury to the vehicle&#39;s occupants, the cable  100  is to be provided with at least one breaking point  200 , which limits the restraining force F applied by the cable  100  to a given maximum value F max . If the restraining force F exceeds its maximum value F max , the cable  100  breaks and the belt restraining force F falls back to the force level F t  provided by the torsion bar  40 .  
         [0033]     Thus, the function of the cable  100  rests in the fact that, when a predetermined belt extraction length S g  is reached, the belt restraining force F abruptly and instantly increases and, when the preset maximum belt restraining force F max  is exceeded, the safety belt is again released.  
         [0034]     As  FIG. 2  shows, the preset maximum belt restraining force F max  is greater than the belt restraining force F t  which is exerted by the first belt force limiting device in the form of the torsion bar  40 .  
         [0035]     In the embodiment according to  FIGS. 1 and 2 , the cable  100  is wound on and off in the channel  120 . Alternatively, the cable  100  can also be wound on and off on the clutch  70  or directly on the torsion bar  40 .  
         [0036]     The priority application, German Application 10 2005 032 012.0, filed on Jul. 1, 2005, including the specification, drawings, claims, and abstract, is incorporated herein by reference in its entirety.  
         [0037]     Given the disclosure of the present invention, one versed in the art would appreciate that there may be other embodiments and modifications within the scope and spirit of the invention. Accordingly, all modifications attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is to be defined as set forth in the following claims.