Abstract:
A seatbelt retractor is disclosed. The seatbelt retractor has a frame, a spindle, a seatbelt webbing and torsion bar. The frame is attached to a structure of a road vehicle. The spindle is rotatably supported by the frame. The seatbelt webbing is wound about the spindle for retraction there to and protraction there from. The torsion bar is fixedly coupled to the spindle for rotation therewith, the torsion bar has a first torsion portion mechanically coupled or press-fitted into a second torsion portion.

Description:
TECHNICAL FIELD 
   The present invention relates to seatbelt retractors for retracting and protracting seatbelt webbing from a spindle and to retractors that have load limiting capability and to methods of making same. 
   BACKGROUND 
   Vehicle manufactures are required to provide seatbelt restraint systems in almost all road vehicles today. Typically, these restraint systems include a retractor, a seatbelt webbing, a latch plate and a seatbelt buckle. When the seatbelt system is not in use, the seatbelt webbing is retracted into the retractor and wound about a spindle disposed in the retractor. When in use, the seatbelt webbing is protracted from the retractor, wrapped around the occupant and secured by the latch plate to the seatbelt buckle. 
   In an effort to improve the safety of an occupant during a vehicle crash, retractors having torsion bars have been developed to limit the forces applied by the seatbelt on the vehicle occupant. The torsion bar is fixed to a spindle on a first end and to a tread head on a second end. As the seatbelt webbing is loaded by a vehicle occupant during a crash, the torsion bar twists allowing the spindle to rotate and pay out additional webbing to reduce the peak forces on the occupant. Depending on the occupant&#39;s size and the severity of the crash, different amounts of webbing pay out and a corresponding level of twisting of the torsion bar is appropriate. 
   To achieve different load limiting characteristics and degrees of webbing pay out during a vehicle collision, retractors have been developed having multiple torsion bar segments which may be activated independently depending on the size of the occupant and the severity of the collision. While these new and improved multi-level load limiting retractors achieve their intended purpose, many issues still exist. For example, manufacturing of torsion bars that provide multiple levels of load limiting are much more complex and, consequently, more expensive to manufacture than retractors having a single load limiting level torsion bar. Therefore, a need exists for a method of constructing multi-level load limiting retractors in a feasible and cost effective manner. 
   SUMMARY 
   In an aspect of the present invention a seatbelt retractor is provided. The seatbelt retractor has a frame, a spindle, a seatbelt webbing and a torsion member. The frame is attached to a structure of a vehicle. The spindle is rotatably supported by the frame. The seatbelt webbing is wound about the spindle for retraction there to and protraction there from. The torsion member is fixedly coupled to the spindle for rotation therewith. Moreover, the torsion member has a first torsion portion mechanically coupled to a second torsion portion. 
   In another aspect of the present invention, the first torsion portion is press-fit into the second torsion portion. 
   In yet another aspect of the present invention, the second torsion portion is coupled to a third torsion portion. 
   In yet another aspect of the present invention, the first torsion portion has a first engagement portion. 
   In yet another aspect of the present invention, the second torsion portion has a second engagement portion. 
   In yet another aspect of the present invention, the first engagement portion is a spline. 
   In yet another aspect of the present invention, the second engagement portion is a spline. 
   In yet another aspect of the present invention, the first engagement portion is a rotary pretensioner pinion. 
   In still another aspect of the present invention, the first torsion portion has a diameter that is greater than a diameter of the second torsion portion. 
   In still another aspect of the present invention, the first torsion portion has a length that is greater than a length of a second torsion portion. 
   In still another aspect of the present invention, the first torsion portion has a transition area between an end of the first torsion portion and a mid-point of the first torsion portion. 
   In still another aspect of the present invention, the first torsion portion has an end having a square cross-section. 
   In yet another aspect of the present invention, the first torsion portion has an end having a rectangular cross-section. 
   In yet another aspect of the present invention, the first torsion portion has an end having non-circular cross-section. 
   In yet another aspect of the present invention, the first torsion portion has an end having a rectangular cross-section. 
   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 
       FIG. 1  is a perspective view of a seatbelt retractor having a torsion bar rotationally coupled to a spindle, in accordance with an embodiment of the present invention; 
       FIG. 2  is a perspective view of a multi-segmented torsion bar, in accordance with an embodiment of the present invention; 
       FIG. 3  is a perspective view of a multi-segmented torsion bar having segments or portions that have different cross-sectional diameters, in accordance with an embodiment of the present invention; 
       FIG. 4  is a perspective view of a multi-segmented torsion bar having different segment lengths, in accordance with an embodiment of the present invention; 
       FIG. 5  is a perspective view of a multi-segmented torsion bar having different shaped segments, in accordance with an embodiment of the present invention; 
       FIG. 6A-6D  are perspective end views of torsion bar segments, in accordance with an embodiment of the present invention; 
       FIGS. 7A-7C  are perspective views of torsion bar segments having different shaped cross-sections, in accordance with an embodiment of the present invention; and 
       FIGS. 8A-8D  are perspective views of end profiles of a torsion bar, in accordance with an embodiment of the present invention. 
   

   DESCRIPTION 
   Referring now to  FIG. 1 , a perspective view of a seatbelt retractor  10  is illustrated, in accordance with an embodiment of the present invention. Retractor  10  includes, generally, a frame  12  typically mounted to a vehicle structure (not shown), a spindle  14  rotatably mounted within frame  12  and a torsion bar  16  rotatably coupled to the spindle and supporting same within frame  12 . Spindle  14  is rotated in a first direction to wind a seatbelt  17  when the retractor is in a retracting mode and rotate in a second direction to unwind the seatbelt from spindle  14  when the retractor is in a protracting mode. Torsion bar  16  includes a first end spline  18 , an intermediate spline  20  and a second end spline  22 . Torsion bar  16  further includes a first torsion bar portion  24  and a second torsion bar portion  26 . First torsion bar portion  24  extends between first end spline  18  and intermediate spline  20 . Second torsion bar portion  26  extends between intermediate spline  20  and second end spline  22 . 
   In a first retractor operating state, end spline  18  is held fixed rotationally relative to frame  12  and second end spline  22  is allowed to rotate with spindle  14 . Further, in the first retractor operating state intermediate spline  20  is rotationally fixed to spindle  14  and continues to rotate with spindle  14  after end spline  18  is held in place causing torsion bar portion  24  to twist. In a second retractor operating state, torsion bar  16  is rotationally fixed at second end spline  22  and is free to rotate at first end spline  18 . Thus, in the second retractor operating state, torsion bar portion  26  twists as spindle  14  continues to rotate under seatbelt loading by the vehicle occupant. The twisting of torsion bar portions  24 ,  26  allows seatbelt webbing  17  to protract an additional amount after splines  18 ,  22  have been rotationally fixed. The dual retractor operating states just described provide different load limiting levels to accommodate different sized occupants as well as different crash severities. 
   Referring now to  FIG. 2 , torsion bar  16  is illustrated in a deconstructed state to further illustrate the method for constructing and assembling torsion bar  16 , in accordance with an embodiment of the present invention. As previously described and illustrated, torsion bar  16  has a first torsion bar portion  24  that extends between first end spline  18  and intermediate spline  20 . As illustrated in  FIG. 2 , first torsion bar portion  24  may be configured having a profiled end portion  30 . Profiled end portion  30  is configured to mate with a corresponding aperture  32  disposed in intermediate spline  20 . Moreover, profiled end portion  30  is oversized relative to aperture  32  to create an interference fit with aperture  32 . Thus, torsion bar  16  may be constructed by press-fitting profiled end portion  30  into aperture  32 . 
   A transition area  34  is provided between profiled end portion  30  and the rest of first torsion bar portion  24  to prevent shearing at the transitional area. Generally, transition area  34  includes a surface having a radius extending from the first torsion bar portion  24  to profiled end portion  30 . Second torsion bar portion  26  has an end  36  which is configured in a similar manner to end  30 . That is, end  36  is profiled and cooperates with a mating aperture  38  disposed within second end spline  22 . Again, end  36  is oversized to create an interference fit (or press-fit) with aperture  38 . A transitional portion  40  is disposed between profiled end  36  and the rest of the second torsion bar portion  26 . Generally, transition area  40  includes a surface having a radius extending from second torsion bar portion  26  to profiled end portion  36 . Thus, as can be readily seen, this configuration allows constructions of torsion bars having multiple and disparate torsion bar portions disposed between multiple end and intermediate splines. Accordingly, this torsion bar construction and method of assembly provides a cost effective and relatively low complexity method for producing multi-load limiting torsion bars and retractors. 
   Referring now to  FIG. 3 , an alternative configuration of a torsion bar  16 ′ is illustrated, in accordance with an embodiment of the present invention. Alternate torsion bar  16 ′ illustrated in  FIG. 3 , is similarly constructed using profiled ends  30 ′ and  36 ′ that are press-fit into apertures (not shown) disposed within end splines  20 ′ and pretensioner sprocket  50 . Torsion bar  16 ′ includes transition portions  34 ′ and  40 ′ that provide a radiused transition to prevent shearing at this portion of the torsion bar area. Torsion bar  16 ′ may have different splines or end configurations connected to profiled ends  30 ′ or  36 ′. For example, as illustrated in  FIG. 3 , a pretensioner sprocket  50  is matingly connected (press-fit) to profiled end  36 ′ to interact with a pretensioner device. Further, first and second torsion bar portions  24 ′ and  26 ′ may have different cross-sectional diameters, as illustrated in  FIG. 3 . Thus, the present construction and method for producing multi-load limiting torsion bars allows for easy assembly of torsion bars having different size and shaped sprockets, splines and/or torsion bar portions. This is further illustrated in  FIGS. 4 and 5 . For example, in  FIG. 4 , a torsion bar  60  may be assembled using the configuration and method of construction assembly as previously described. Torsion bar  60  has a first torsion bar portion  62  having integrally formed first and second end splines  66  and  68  and second torsion bar  64 . Further, as illustrated, first torsion bar  62  has a first predefined diameter and a predefined length L. Second torsion bar portion  64  may have a length L′ that is different than the length of first torsion bar portion  62 . The different lengths, shapes and diameters of the various torsion bar portions dictate the degree of twisting of the torsion bar portions that will occur under different loading conditions (i.e. different sized occupants and crash severities). 
   As illustrated in  FIG. 4 , second torsion bar portion  64  has profiled ends  72  and  74 . Further, first and second torsion bar portions  63  and  64  includes radiused transition areas  75 ,  76 ,  77  and  78  to prevent shearing in these portions as previously described. Profiled end  72  is matingly received and press-fit into an aperture (not shown) disposed within a tread head  80  to rotationally fix tread head  80  to torsion bar portion  64 . In this manner, torsion bar  60  may be constructed having different end portions, splines and/or tread heads. 
   As further illustrated in  FIG. 5 , a multi-level load limiting torsion bar  90  may be constructed having different shaped torsion bar portions  92  and  94 . As shown in  FIG. 5 , torsion bar portion  92  has a curved or “S-shaped” profile and may vary in length “L”. Torsion bar portions  92 ,  94  have end portions  96  and  98  that are profiled and cooperate through an interference or press-fit with apertures (not shown) disposed within a spline  100  or other end pieces, such as a pretensioner spindle end cap for a dual mode pretensioner designated by reference number  102 . 
     FIGS. 6A-6D  illustrate the various end profiles that the ends of the torsion bar portions described above may have to transmit the torque between one torsion bar portion to the other torsion bar portion, in accordance with an embodiment of the present invention. For example,  FIG. 6A , shows a profiled end  200  of a torsion bar portion (i.e., torsion bar portions  24 ,  24 ′,  26 ,  26 ′,  62 ,  64 ,  92  and  94 ) wherein the profiled end  200  has a square cross-section.  FIG. 6B  illustrates a profiled end  202  of a torsion bar portion that has an ovular cross-section.  FIG. 6C  illustrates a profiled end  204  that has a rectangular cross-section.  FIG. 6D  has a profiled end  206  that has a star shaped cross-section. As can be readily seen from the examples described above, various profiled end shapes may be used to ensure that torque is transferred between the different torsion bar portions. 
   Referring now to  FIGS. 7A-7C , various torsion bar portions  300 ,  302 ,  304  are illustrated, in accordance with an embodiment of the present invention. As illustrated in  FIGS. 7A-7C , torsion bar portions  300 ,  302 ,  304 , which may be used in place of the previously described torsion bar portions (i.e.,  24 ,  24 ′,  26 ,  26 ′,  62 ,  64 ,  92  and  94 ) may have different cross-sectional shapes. As shown in  FIG. 7A , torsion bar portion  300  has a non-circular cross-section and an overall length l o . In another embodiment as shown in  FIG. 7B , torsion bar portion  302  is shown having a cross-sectional shape in the form of a figure eight.  FIG. 7C  shows torsion bar portion  304 , which has a square or rectangular cross-section. Of course, the present invention contemplates other shapes for the various torsion bar portions to achieve the appropriate load limiting required for different occupant sizes and vehicle collisions severities. It should be appreciated after reading the above text that load limiting capability of the retractor may be varied by an appropriate selection of the torsion bar portions having a prescribed shape and length. 
   Referring now to  FIGS. 8A-8D , various torsion bar end portions  312 ,  314 ,  316 ,  320  are illustrated, in accordance with an embodiment of the present invention. For example, in  FIGS. 8A and 8B , illustrate various end spline shapes that may be utilized and connected (press-fit) to the various torsion bar portions, in accordance with the configurations and methods previously described. Further,  FIG. 8C  illustrates a spindle  316  with retaining pins  318 ,  319  for a dual mode pretensioner, as well known in the prior art. Spindle  316  may be easily mated with and rotationally fixed to any of the torsion bar portions described above using the configurations and methods previously described. Of course, many other end configurations or splines may be constructed and utilized as shown in  FIG. 8D , where a low profile spline  320  is illustrated, low profile spline  320  may be used to prevent interference with seatbelt webbing  19  that is threaded through the spindle  14  of retractor  10 . 
   As any person skilled in the art of seatbelt retractors for retracting and protracting seatbelt webbing from a spindle and which have load limiting capability 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.