Abstract:
In an exemplary embodiment of the invention, an energy absorbing device for a steering column assembly is provided. The device includes a first end configured to couple to a first component of the steering column assembly, a second end configured to couple to a second component of the steering column, and an intermediate portion extending between the first and second ends. The intermediate portion includes a curved portion having a radius, and an aperture extending through the intermediate portion. The aperture is configured to shift a collapse characteristic of the energy absorbing device and to facilitate maintaining the radius constant when a force moves the first end relative to the second end and deforms the energy absorbing device.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This patent application claims priority to U.S. Provisional Patent Application Ser. No. 61/774,890, filed Mar. 8, 2013, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The following description relates to energy absorbing devices, and more particularly, to energy absorbing straps for a steering column assembly. 
     BACKGROUND OF THE INVENTION 
     Roll strap devices have been used as a means to absorb energy during the collapse of a steering column. Typically, roll straps absorb energy during the deformation of the strap in crash event. For example, a vehicle operator may contact the steering column assembly, whereby kinetic energy of the occupants may be dissipated through compression of the steering column assembly. However, it may be advantageous to improve control of the collapse characteristics of some known roll strap devices. 
     Accordingly, it is desirable to provide systems and methods for controlling or tuning the characteristics of a roll strap to provide a desired kinetic energy dissipation of vehicle occupants in the event of contact between a vehicle occupant and a steering column assembly. 
     SUMMARY OF THE INVENTION 
     In an exemplary embodiment of the invention, an energy absorbing device for a steering column assembly is provided. The device includes a first end configured to couple to a first component of the steering column assembly, a second end configured to couple to a second component of the steering column, and an intermediate portion extending between the first and second ends. The intermediate portion includes a curved portion having a radius, and an aperture extending through the intermediate portion. The aperture is configured to shift a collapse characteristic of the energy absorbing device and to facilitate maintaining the radius constant when a force moves the first end relative to the second end and deforms the energy absorbing device. 
     In another exemplary embodiment of the invention, a steering column assembly is provided. The assembly includes a mounting bracket, a first jacket coupled to the mounting bracket and having a longitudinal axis, and a second jacket slidably disposed with the first jacket for telescoping movement along the longitudinal axis relative to the first jacket. The assembly further includes an energy absorbing strap having a first end coupled to the second jacket, a second end coupled to one of the first jacket and the mounting bracket, and an intermediate portion extending between the first and second ends. The intermediate portion includes a curved portion having a radius, and an aperture extending through the intermediate portion. The aperture is configured to shift a collapse characteristic of the energy absorbing device and to facilitate maintaining the radius constant when a force moves the first end relative to the second end and deforms the energy absorbing device. 
     In yet another exemplary embodiment of the invention, a method of fabricating an energy absorbing device for a steering column assembly is provided. The method includes providing a strap having a first end configured to couple to a first component of the steering column, a second end configured to couple to a second component of the steering column, and an intermediate portion extending between the first and second ends, where the intermediate portion includes a curved portion having a radius. The method further includes forming an aperture through the intermediate portion, the aperture configured to shift an initial collapse characteristic of the energy absorbing device and to facilitate maintaining the radius constant when a force acting on the steering column first component moves the first end relative to the second end and deforms the energy absorbing device. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view of a steering column assembly having an energy absorbing roll strap in accordance with an exemplary embodiment of the invention; 
         FIG. 2  is an enlarged view of the steering column assembly and roll strap shown in  FIG. 1  and taken on section  2 ; 
         FIG. 3  is a perspective view of the roll strap shown in  FIGS. 1 and 2 ; 
         FIGS. 4 and 5  illustrate performance of exemplary embodiments of a roll strap in accordance with the invention; 
         FIG. 6  illustrates another exemplary embodiment a roll strap in accordance with the invention; and 
         FIG. 7  illustrates yet another exemplary embodiment of a roll strap in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the Figures, where the invention will be described with reference to specific embodiments, without limiting same,  FIGS. 1 and 2  show an exemplary steering column assembly  10  that includes a lower jacket  12  disposed along a longitudinal axis  14  and pivotally coupled to a mounting bracket  16 , which is coupled to a host structure of a vehicle (not shown). An upper jacket  18  is arranged co-axially with lower jacket  12  and longitudinal axis  14  and is configured to translate along axis  14  relative to lower jacket  12 , thereby facilitating telescoping and/or collapse motion of steering column assembly  10 . A rotating inner shaft  20  is disposed co-axially within jackets  12 ,  18  and includes a steering wheel end  22  configured to receive a vehicle steering wheel (not shown). 
     With further reference to  FIG. 3 , steering column assembly  10  includes an energy absorbing roll strap  30  that is coupled between lower jacket  12  and upper jacket  18 . During a collapse event (e.g., a vehicle crash), a force ‘Fx’ may move or collapse upper jacket  18  along axis  14  relative to fixed mounting bracket  16 , and energy absorbing strap  30  dissipates at least some of the kinetic energy of collapsing upper jacket  18 . 
     In the exemplary embodiment, energy absorbing strap  30  includes a first end  32 , a second end  34 , and an intermediate portion  36  extending therebetween. First end  32  is coupled to upper jacket  18  by a fastener  38 , and second end  34  is coupled to lower jacket  12  by a fastener  40 . Alternatively, first and second ends  32 ,  34  may be coupled to their respective steering column components using any suitable method that enables assembly  10  to function as described herein. For example, first and second ends  32 ,  34  may be welded to upper jacket  18  and mounting bracket  16 , respectively. 
     Strap intermediate portion  36  includes a curved portion  42  having a radius ‘R’. Curved portion  42  facilitates “rolling” of strap  30  during a collapse event as first end  32  moves in the direction of force ‘Fx’. An initial collapse or roll area  44  is located at the transition between curved portion  42  and a flat portion  46  of intermediate portion  36 . Initial collapse area  44  represents the starting roll or deformation location where the “roll” or deformation of strap  30  begins during a collapse event. 
     In the exemplary embodiment, energy absorbing strap  30  includes an inner wall  48  defining an aperture  50  that extends through intermediate portion  36 . Aperture  50  facilitates controlling or tuning initial collapse characteristics of energy absorbing strap  30 . In the embodiment shown in  FIG. 3 , aperture  50  is a slot  52  extending through curved portion  42  and includes a first end  54  and a second end  56 . Although illustrated as having a slot shape, aperture  50  may have any suitable shape or cross-section that enables strap  30  to function as described herein. For example, aperture  50  may have a round cross-section or slot  52  may be tapered from first end  54  to second end  56 . Additionally, although strap  30  is illustrated with a single aperture  50  to tune collapse characteristics, strap  30  may have any number of apertures  50  formed in strap intermediate section  36  to provide strap  30  with desired collapse characteristics. Accordingly, various increments/shapes of roll strap material can be removed from intermediate portion  36  to influence the load profile of energy absorbing strap  30 . 
     Slot first end  54  is located at or in proximity to starting roll location  44  and, as illustrated in  FIG. 3 , slot  52  extends along curved portion  42  to slot second end  56 , which is located at the transition between curved portion  42  and a flat portion  58  of intermediate portion  36 . The arrangement of slot  52  on strap intermediate portion  36  shifts or tunes the initial collapse characteristics of energy absorbing strap  30 , which includes the position of the initial collapse load peak, magnitude of the initial peak, and amount of drop in load following the peak. For example, the position and length of slot  52  may be used to reduce the starting collapse load and/or reduce the drop in load typically experienced in the early portion of the collapse curve. For example, as illustrated in  FIGS. 4 and 5 , exemplary graphs plots collapse load of energy absorbing strap  30  vs. movement of strap first end  32  in the direction of longitudinal axis  14 . 
     The collapse characteristics of strap  30  are further influenced or tuned by the position of slot first end  54  in relation to starting roll location  44 . With further reference to  FIG. 3 , slot first end  54  extends to a first location ‘A’ to provide a first desired load profile or curve  102  compared to a load curve  100  of a baseline strap without a slot (see  FIGS. 4 and 5 ). Extending slot first end  54  towards strap first end  32  to a second location ‘B’ results in a second load curve  104 , extending slot first end  54  to a third location ‘C’ results in a third load curve  106 , and extending slot first end  54  to a fourth location ‘D’ results in a fourth load curve  108 . 
     Additionally, the collapse characteristics of strap  30  can be tuned or adjusted by varying other attributes of aperture  50  and strap  30 . For example, a slot width ‘w’  52  may be increased or decreased to respectively drop or raise the load required to initiate collapse, a thickness ‘t’ of strap  30  may be increased or decreased to respectively raise or drop the load required to initiate collapse, and/or radius ‘R’ may be increased or decreased to respectively drop or raise the load required to initiate collapse. 
     Accordingly, the load profile of strap  30  is influenced by direct variation of parameters of strap  30 , and the amount of roll radius expansion is influenced after the start of collapse movement at least in part by the rigidity between applied force ‘Fx’ and the position of roll radius ‘R’ (i.e., how the strap is secured to jackets  12 ,  18 ). 
     In the exemplary embodiment, when a force acts upon steering column assembly  10  (e.g., an occupant impacting the steering wheel), particularly along longitudinal axis  14 , upper jacket  18  is pushed toward lower jacket  12 . Because strap second end  56  is coupled to a fixed component of assembly  10  or the vehicle (e.g., lower jacket  12 ), as upper jacket  18  is forced toward lower jacket  12 , strap second end  56  is held in place while energy absorbing strap  30  is rolled in the direction of force ‘Fx’. As energy absorbing strap  30  rolls, roll radius ‘R’ is repositioned along strap  30  and energy is absorbed by the deformation of energy absorbing strap  30 . As such, upper jacket  18  at least partially collapses onto lower jacket  12 , thereby dissipating the kinetic energy of an occupant or object colliding with steering column assembly  10 . 
       FIG. 3  illustrates roll strap  30  as generally S-shaped such that strap first end  32  and flat portion  46  are coplanar, and flat portion  58  is substantially parallel to flat portion  46  and strap second end  34 . However, the shape of roll strap  30  may be modified to fit various applications. For example,  FIG. 6  illustrates another exemplary energy absorbing strap  130  that is similar to strap  30 , but is designed for use in a rake and telescope steering column assembly (not shown). In this embodiment, strap first end  32  may be coupled to jacket  18  movable in a collapse event and strap second end  34  may be coupled to stationary, lower jacket  12  via a suitable engagement mechanism (not shown). Strap first and second ends  32 ,  34  may be oriented substantially parallel to each other.  FIG. 7  illustrates another exemplary energy absorbing strap  230  that is similar to strap  30 , but is designed for use in both a rake and a rake and telescope steering column assembly (not shown), depending on the column architecture. In this embodiment, strap first end  32  may be coupled to a break-away mounting bracket (not shown) and strap second end  34  may be coupled to a vehicle stationary structure (not shown). 
     While energy absorbing straps  30 ,  130 , and  230  are described coupled to specific components of a steering column assembly, it should be noted that an energy absorbing strap according to the present invention can have various configurations and will function as described herein when one strap end is coupled to a fixed portion of a vehicle/column (e.g., a vehicle cross-car beam) and the other strap end is coupled to a steering column component that moves during a collapse event (e.g., an upper jacket). 
     Systems and methods to control and tune collapse characteristics of energy absorbing straps are described herein. By removing strap material to form an aperture in proximity of the starting roll position, the strap energy absorbing load profile can be purposefully influenced. Various aperture cross-sectional geometries and strap attachment configurations can be implemented between the applied force ‘Fx’ and the roll radius ‘R’. Benefits of these exemplary embodiments of the invention include increased flexibility in the energy absorbing load curve control for roll strap designs, and simplicity of production tooling. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description.