Abstract:
A seatbelt retractor is disclosed having a frame, a spindle, a tread head and a torsion bar. The frame is attached to a structure of a vehicle. The spindle is rotatably supported by the frame. The tread head is matingly coupled to the spindle for relative rotational movement therewith and the tread head is rotationally fixable relative to the frame. The torsion bar has a torsion bar first end fixed to a first spindle end and a torsion bar second end fixed to the tread head and the torsion bar has a protrusion that selectively engages the spindle after the tread head has been fixed and the spindle has rotated a predefined angle α relative to the fixed tread head.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to seatbelt retractors and to seatbelt retractors having load limiters that control forces exerted by the seatbelt on a vehicle occupant.  
       BACKGROUND  
       [0002]     All vehicles sold today, especially throughout the United States, must have occupant safety systems. Such systems include, for example, seatbelts and airbags. Much advancement has been made and continues to be made to improve the performance of the seatbelt and airbag systems. For example, much effort is being spent on studying the interaction of the seatbelt and airbag restraint systems on a vehicle occupant. Both systems exert restraining forces on a vehicle occupant&#39;s body during a collision. These restraining forces must be properly controlled in order to obtain the desired occupant protection. For example, with regard to the airbag system the pressure and forces exerted by the airbag on the vehicle occupant has been modified in the recent generation airbag systems to enhance occupant protection by matching the restraining force required to properly restrain the occupant during a vehicle collision to the particular occupant characteristics (size, weight, etc.) and the severity of the collision. Recent seatbelt systems have incorporated devices to further enhance the performance of the seatbelt restraint device. For example, many seatbelts today incorporate pretensioners which take up slack in a seatbelt the moment a vehicle collision is detected. The pretensioner and seatbelt retractor combination prevents unrestrained movement of the vehicle occupant during a vehicle collision. Other enhancements in seatbelts include “load limiters” which are incorporated into seatbelt retractors. The function of the load limiter is to pay out a predetermined length of seatbelt webbing in order to eliminate or reduce peak loads on a vehicle occupant. A load limiter is, for example, a torsion bar that is coupled to the spindle of the retractor and is configured to twist when a predetermined amount of torque is applied to an end of the torsion bar. As torque is applied to the torsion bar, the torsion bar twists and the spindle rotates a corresponding amount paying out the seatbelt webbing.  
         [0003]     More recent enhancements in load limiters have been directed to addressing the differences in restraining forces required to safely bring occupants of different sizes to rest. For example, higher restraining forces will be applied to a larger vehicle occupant as opposed to a smaller vehicle occupant. Thus, the load limiting characteristics of torsion bars or other load limiting devices must be configured to accommodate different sized occupants. To this end, multi-stage load limiting devices have been developed. A multi-stage torsion bar, for example, is such a device. The multi-stage torsion bar is essentially two torsion bars that are axially aligned and joined at respective ends. The appropriate stage or portion of the torsion bar may be selectively oriented to provide the appropriate load limiting characteristics necessary to address the different sized occupants.  
         [0004]     While these enhancements in safety restraints have achieved their intended purpose, further enhancements are needed to ensure appropriate occupant restraint is provided in the most cost effective and efficient manner.  
       SUMMARY  
       [0005]     In an aspect of the present invention, a seatbelt retractor is provided having a frame, a spindle, a tread head and a torsion bar. The frame is attached to a structure of a vehicle. The spindle is rotatably supported by the frame. The tread head is matingly coupled to the spindle for relative rotational movement therewith and the tread head is rotationally fixable relative to the frame. The torsion bar has a torsion bar first end fixed to a first spindle end and a torsion bar second end fixed to the tread head and the torsion bar has a protrusion that selectively engages the spindle after the tread head has been fixed and the spindle has rotated a predefined angle α relative to the fixed tread head.  
         [0006]     In another aspect of the present invention the protrusion is integrally formed in the torsion bar.  
         [0007]     In yet another aspect of the present invention the seatbelt retractor includes a slot disposed in the spindle for receiving the protrusion.  
         [0008]     In yet another aspect of the present invention the slot has a length that allows the protrusion of the torsion bar to sweep through the predefined angle α.  
         [0009]     In yet another aspect of the present invention the protrusion is disposed between the first and second ends of the torsion bar.  
         [0010]     In yet another aspect of the present invention the torsion bar includes a first and a second torsion bar portions wherein the first torsion bar portion has a cross-sectional diameter that is larger than a cross-sectional diameter of the second torsion bar portion.  
         [0011]     In yet another aspect of the present invention the spindle has a spindle stop feature that engages the protrusion of the torsion bar.  
         [0012]     In yet another aspect of the present invention the spindle stop feature is fixed to the spindle and selectively engages the protrusion of the torsion bar.  
         [0013]     In yet another aspect of the present invention the spindle stop feature moves relative to the spindle to engage and disengage the protrusion of the torsion bar.  
         [0014]     In yet another aspect of the present invention the first bar portion has a length that is greater than a length of a second bar portion.  
         [0015]     In still another aspect of the present invention the first bar portion as an end having a square cross-section.  
         [0016]     In still another aspect of the present invention the first bar portion has an end having a rectangular cross-section.  
         [0017]     In still another aspect of the present invention the first bar portion has a non-circular cross-section.  
         [0018]     In still another aspect of the present invention the first bar portion has rectangular cross-section.  
         [0019]     These and other aspects and advantages of the present invention will become apparent upon reading the following detailed description of the invention in combination with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a partial cutaway view of a seatbelt retractor including a torsion bar and spindle, in accordance with an embodiment of the present invention;  
         [0021]      FIG. 2  is a cross-sectional view through the spindle and torsion bar at a position referenced in  FIG. 1 , in accordance with an embodiment of the present invention;  
         [0022]      FIG. 3  is a chart illustrating retractor operation in the first load limiting stage and the force applied to the vehicle occupant by the seatbelt webbing versus time duration of the vehicle collision, in accordance with an embodiment of the present invention; and  
         [0023]      FIG. 4  is a chart illustrating retractor operation in the second load limiting stage and the force applied to the vehicle occupant by the seatbelt webbing versus time duration of the vehicle collision, in accordance with the present invention. 
     
    
     DESCRIPTION  
       [0024]     Referring now to  FIG. 1 , a cross-sectional view of a seatbelt retractor  10  is illustrated, in accordance with the present invention. Seatbelt retractor  10  may be incorporated into road vehicles for use as an active restraint device. Retractor  10  operates to restrain a vehicle occupant&#39;s movement towards the interior of the road vehicle. Seatbelt retractor  10  includes a frame  12 , a spindle  14 , a tread head  16  and a torsion bar  18 . Frame  12  supports spindle  14  and is securely fixed to a vehicle structural member such as a vehicle frame (not shown). Spindle  14  is configured, as known, to retract and protract seatbelt webbing (not shown) that is wound about the spindle. Spindle  14  freely rotates to protract and retract seatbelt webbing during normal operation, however, during a vehicle crash; the spindle is locked to prevent further protraction. In order to lock spindle  14 , a tread head  16  is provided having a profile that is engageable, as known to one of ordinary skill in the art. Once tread head  16  is locked, spindle  14  can move or rotate relative to tread head  16 . Disposed within spindle  14  and between a first end  20  of spindle  14  and a first tread head end  22 , is a torsion bar  18 .  
         [0025]     Torsion bar  18  includes first and second ends  24 ,  26  having splines formed therein. Spline end  24  cooperates with a corresponding aperture  28  within spindle  14  to rotationally fix torsion bar  18  with spindle  14 . In a similar manner, spline end  26  cooperates with a corresponding aperture  30  disposed within tread head  16  to rotationally fix torsion bar  18  relative to tread head  16 . First tread head end  22  has a profile which matingly corresponds with a profile on a second end  32  of spindle  14 . The interface (mating surfaces of first tread head end  22  and second spindle end  32 ) between tread head  16  and spindle  14  allows relative movement between the tread head and spindle. In other words, when tread head  16  is rotationally locked, spindle  14  is allowed to rotate relative to the rotationally fixed tread head.  
         [0026]     With continuing reference to  FIG. 1 , torsion bar  18  is further illustrated, in accordance with an embodiment of the present invention. Torsion bar  18  further includes an intermediate head  38  disposed between spline ends  24  and  26  of torsion bar  18 . Intermediate head  38  is configured, as will be further illustrated and described, to interact with a locking or stop feature  40  disposed within spindle  14 .  
         [0027]     Torsion bar  18  provides “a multi-stage” load limiting feature by providing two distinct torsion bar portions  42  and  44 . The two distinct torsion bar portions  42  and  44  provide different load limiting characteristics, as will be described in more detail below. Various configurations of portions  42  and  44  may be provided to achieve the desired load limiting characteristics. For example, as shown, torsion bar  42  portions  42  and  44  may be cylindrical and wherein torsion bar portion  44  has a smaller diameter than torsion bar portion  42 . Of course, the present invention contemplates other shapes and configurations of torsion bar portions  42  and  44 , for example, portions  42  and  44  may have a square or rectangular cross-section.  
         [0028]     Referring now to  FIG. 2 , a cross-sectional view of retractor  10 , as indicated in  FIG. 1 , is illustrated in accordance with an embodiment of the present invention. Moreover,  FIG. 2  illustrates the cooperation of intermediate head  38  with the stop feature  40  disposed in spindle  14 . Intermediate head  38  includes a spline or protrusion  46 . Spline  46  is disposed within stop feature  40  which may be in the form of a slot. Alternatively, the present invention contemplates stop feature  40  being an active stop feature (rather than a fixed stop feature i.e. a slot) that may be actuated to engage torsion bar  18  after a prescribed angular rotation (or twisting) of torsion bar  18 . Thus, multiple stop features may be provided as well as stop features that allow different angular rotations of torsion bar  18 .  
         [0029]     During normal retractor  10  operation where torsion bar  18  is in a relatively untwisted state, spline  46  would be proximate to a first end  50  of stop feature  40 . However, during a vehicle collision, spline  46  will be allowed to rotate through a maximum angle α until spine  46  reaches a second end  52  of feature  40 . Retractor  10  and torsion bar  18  will operate in a first “load limiting” mode or stage until the angle α is fully traversed by spline  46  and contacts second end  52  of feature  40 . While in the first “load limiting” mode, torsion bar portion  44  will twist and the belt load is transferred over the length, L 1 , of the torsion bar  18 . Once spline  46  contacts the second end  52  of feature  40 , retractor  10  and torsion bar  18  will enter a second “load limiting” mode or stage of load limiting operation. During the second “load limiting” mode, torsion bar  18  will twist only along a portion of its length L 2 . In this manner, retractor  10  provides a “multi-stage load limiting” characteristic as will be further described and illustrated below. As further illustrated in  FIG. 2 , a transverse slot  56  is provided through spindle  14  to allow the seatbelt webbing (not shown) to pass through the spindle in order to secure the seatbelt webbing to spindle  14 .  
         [0030]     Referring now to  FIGS. 3 and 4 , charts  70 ,  72  illustrate loading of the seatbelt webbing versus time duration of a vehicle crash are provided, in accordance with the present invention. More specifically,  FIG. 3  illustrates the result of retractor  10  and torsion bar  18  load limiting characteristics during the “first mode or stage” of load limiting operation. On a vertical axis  80 , seatbelt webbing loading is plotted against time duration of the vehicle collision on a horizontal axis  82 . As illustrated during a vehicle impact, the loading of the webbing by a vehicle occupant will increase from zero to a predefined level, as indicated by segment  84 , to a predetermined maximum loading, as defined by segment  86 , and then decreased back to zero, as represented by segment  88 , when the vehicle occupant comes to rest.  
         [0031]     The predetermined maximum loading (as illustrated by segment  86 ) is defined and controlled by the load limiting characteristics of the torsion bar  18 . More specifically, during a vehicle collision the seatbelt webbing will be loaded by the vehicle occupant and start to pay-out as torsion bar  18  starts to twist. As torsion bar  18  continues to twist spline  46  will move through feature  40  towards second end  52  of feature  40 . If the vehicle collision is a low severity collision or the vehicle occupant is a small sized occupant, then loading on the seatbelt webbing will return to zero and torsion bar  18  will stop twisting before spline  46  reaches second end  52  of stop feature  40 , as represented by dashed line  89 .  
         [0032]     With now specific reference to  FIG. 4 , chart  72  is provided illustrating seatbelt webbing pay out during a second “mode or stage” of load limiting operation, in accordance with the present invention. As with  FIG. 3 , seatbelt webbing loading is plotted on a graph or chart having a vertical axis  80  corresponding to the force applied to the seatbelt webbing and on a horizontal axis  82  corresponding to time duration of a vehicle collision. Depending on the severity of the crash and the occupant size, torsion bar  18  and intermediate head  38  will continue to rotate until spline  46  contacts second end  52  of stop feature  40 . Once angle α is traversed by spline  46 , retractor  10  enters the second “mode or stage” of load limiting operation. This second stage of operation is designated by reference line  90  in  FIG. 4 . The additional energy present due to the severity of the crash and/or the occupant size will be absorbed by additional twisting of portion  42  of torsion bar  18  along its length L 2 . This twisting of portion  42  is designated by segments  92  and  94  in chart  72  of  FIG. 4 . The twisting of torsion bar  18  will continue providing a constant loading of the seatbelt webbing, as represented by segment  94  of  FIG. 4 . After the energy has been absorbed, loading of the seatbelt will rapidly decrease to zero as designated by segment  96 .  
         [0033]     As any person skilled in the art of seatbelt retractors will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention defined in the following claims.