Abstract:
An energy absorbing assembly ( 20 ) providing variable energy absorption from an energy transmitting component ( 10 ) is mounted upon a mounting bracket ( 16 ) for mounting the energy absorbing assembly ( 20 ) to the energy transmitting component ( 10 ). An elongated strap ( 22 ) immovably secured at a first end ( 24 ) absorbs energy received from the energy transmitting component ( 10 ) during a collision. Cooperating anvils ( 30 A,B) are slidably received by the mounting bracket ( 16 ) and the elongated strap ( 22 ) is interwoven between the anvils ( 30 ). The anvils ( 30 A,B) include generally parallel axes (a) along which each anvil ( 30 A,  30 B) defines stepped diameters (A,B,C,D), and are slidable along the axes (a) in response to a predetermined force to provide variable energy absorption relative to the stepped diameters (A,B,C,D).

Description:
REFERENCE TO RELATED APPLICATIONS 
     This patent application claims priority to U.S. Provisional Patent Application No. 60/379,491 filed on May 9, 2002. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to an energy absorber for a motor vehicle steering column. 
     BACKGROUND OF THE INVENTION 
     Various vehicle components are known to transmit energy from collisions to vehicle occupants. A typical component is a steering column of a steering wheel that includes a housing or mask jacket that collapses during a vehicle collision. The mask jacket translates the collision energy through an energy absorber to convert the crash energy to a fraction of the kinetic energy transferred to the vehicle operator. 
     A common energy absorber transmits force created by a plastic deformation of a metal element or strap disposed in the energy absorber. An example is disclosed in U.S. Pat. No. 6,322,103 where deformation of a flat metal strap over an anvil is disclosed to absorb crash energy. It has been discovered that a benefit is derived by adjusting the amount of energy absorbed relative to the amount of energy that may be translated to the vehicle operator based on such variables as vehicle speed, vehicle weight, and operator weight. Also, U.S. Pat. No. 6,189,929 discloses an anvil having various diameters where the anvil is adjusted to position a desired diameter in contact with the metal strap to adjust the amount of energy absorption produced by the energy absorber. 
     While these devices are capable of producing various amounts of energy absorption, they have not provided a desirable degree of variable energy absorption. Further, these devices are known to provide an imprecise amount of energy absorption relative to the desired amount of energy absorption due to mechanical failures such as, for example “bounce back” where the anvil is initially moved to a desirable position but rebounds back to an initial position. Therefore, it would be desirable to provide an energy absorber having both an increased degree of variable energy absorption along with a more accurate degree of energy absorption. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an improved energy absorbing device that provides variable energy absorption transmitted from an energy transmitting component of a motor vehicle. A mounting bracket mounts the energy absorbing device to the energy transmitting component. An elongated strap is secured at at least one end for absorbing energy received from the energy transmitting component. Cooperating anvils are slidably received by the mounting bracket and are oriented so that the elongated strap is interwoven between the anvils. The anvils include a generally parallel axis along which each anvil defines stepped diameters. Each anvil is slideable along its axis in response to a predetermined force to provide variable energy absorption relative to the stepped diameters of each anvil. 
     Further, a catch is included to secure each anvil in a desired position to prevent the anvil from moving once the desired amount of energy absorption is determined and the anvil has been positioned to produce the desired amount of energy absorption. 
     By including cooperating anvils each slideable relative to the other, a more precise variation in the amount of energy absorption is provided. Further, by providing a catch to secure the anvil in its desired position once the anvil has been moved to provide a desired amount of energy absorption, mechanical failures known to prior art assemblies have been eliminated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is a perspective view of a steering column having the inventive energy absorbing assembly attached thereto; 
         FIG. 2  is a sectional view of the energy absorbing assembly showing a single anvil configuration cooperable with an elongated strap; 
         FIG. 3  shows a perspective view of an assembly having a single anvil; 
         FIGS. 3A and 3B  show a sectional view of the anvil of  FIG. 3  prior to firing and subsequent to firing; 
         FIG. 4  shows a side sectional view of a cooperable anvil embodiment having the strap interwoven therebetween; 
         FIGS. 5A-5D  show cooperable anvils having stepped diameters in various stages of orientation. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , an energy transmitting component in the form of a steering column is generally shown at  10 . The column includes a steering shaft  12  that is disposed within a steering housing  14 . A mounting bracket ( 16 ) is fixedly attached to the steering housing  14  providing attachment locations  18  disposed upon opposing sides of the steering column  10 . An energy absorbing assembly  20  is secured at each attachment location  18  to absorb energy received from the steering column  14  upon a collision of the motor vehicle. 
     In a collision of the motor vehicle (not shown), the vehicle body decelerates more rapidly than the operator so that the operator can be thrust against the steering wheel (not shown) generating an impact force relative to the speed of the vehicle, mass of the vehicle and mass of the vehicle operator amongst other variables. When the operator impacts the steering wheel, the corresponding force on the steering column housing  14  causes the housing  14  to collapse relative to the vehicle body. In order to reduce the amount of impact force transmitted to the vehicle operator, the energy absorbing assemblies  20  absorb energy generated from the vehicle operator impacting the steering column  10 . 
     A flat metal strap  22  includes a first end  24  fixedly attached to the mounting bracket ( 16 ). A second end  26  is unattached, or floats freely relative to the assembly  20 . 
     Referring to  FIG. 2 , the strap  22  is shown interwoven through the assembly  20  forming a generally S-shaped configuration between a protuberance  28  in the assembly  20  and an anvil  30 . The anvil  30  is displaceable as will be explained further below to alter the amount of energy absorption produced by the strap  22  as is shown in phantom in FIG.  2 . 
     Referring now to  FIGS. 3 ,  3 A and  3 B, the anvil  30  is shown slidably disposed within an elongated chamber  32  defined by the assembly  20 . An actuation device  34  is disposed at a first end  36  of the elongated chamber  32 . Preferably, the actuation device  34  is an explosive charge. However, other equivalent methods of propelling the anvil  30  through the elongated chamber  32  may be used. The actuation device  34  includes electrical connectors  38  that receive an electrical charge signalled from a controller (not shown) to activate the actuation device  34 . 
     A retaining pin  40  releasably secures the anvil  30  in a first position  42  (FIG.  3 A). Upon discharging, the anvil  30  is moved from the first position  42  to a second anvil position  44  (FIG.  3 B). A catch  46  secures the anvil  30  in the second position  44  to prevent the anvil  30  from rebounding back to the first position  42 . An opening  48  disposed in a second chamber end  50  allows air to vent from the chamber  32  enabling the anvil  30  to move from the first position  42  to the second position  44 . When the anvil  30  is located in the first position  42 , a greater level of energy absorption is provided than when the anvil  30  has been moved to the second position  44  and out of engagement with the strap  22 . 
     Referring to  FIGS. 4 , and  5 A through  5 D, an alternate embodiment is shown having cooperating anvils  30 A,  30 B. Each anvil  30 A,  30 B includes stepped diameters along an anvil axis a so that each anvil  30 A,  30 B includes at least two sections having different diameters as is best represented in  FIG. 5A through D  as A, B, C, D. Preferably, the anvils  30 A,  30 B include generally parallel axes a and are slidably disposed in generally parallel elongated chambers  32 A,  32 B. Referring now to  FIG. 4 , a sectional view shows the cooperating anvils  30 A,  30 B having generally parallel axes. The strip  22  is interwoven between the cooperating anvils  30 A,  30 B taking a generally S-shaped configuration. 
     Referring again to  FIG. 5A , each anvil  30 A,  30 B is disposed in first position  42 . Therefore, a first diameter A of the first anvil  30 A is cooperable with a first diameter B of the second anvil  30 B. As should be understood, if the controller determines the appropriate amount of energy absorption is provided from the strap  22  interacting with diameters A and B of the anvils  30 A,  30 B the actuation devices  34 A,  34 B are not discharged. Therefore, the energy absorption is derived from the anvils  30 A,  30 B as provided by diameters A and B. Referring now to  FIG. 5B , the second actuation device  34 B is discharged by the controller to provide a second level of energy absorption different from the first level. In this case, diameter A of the first anvil  30 A is cooperable with the diameter D of the second anvil  30 B. A receptor  52  comprising a compressible material such as, for example, a honeycomb material, optionally receives the second anvil  30 B. when propelled by the actuation device  34 B, through the elongated chamber  32 B, A catch  46 B secures the anvil  30 B in the discharged position to prevent the anvil  30 B from rebounding once the actuation device  34 A has fired. 
     Referring now to  FIG. 5C , actuation device  34 A is shown discharged moving anvil  30 A to a discharged position. Now, diameter C of anvil  30 A is cooperable with diameter B of anvil  30 B providing yet an additional level of energy absorption. As previously described, anvil  30 A is received by a receptor  52  and secured in the discharged position by catch  46 A. 
     Referring now to  FIG. 5D , actuation devices  34 A and  34 B are shown discharged so that diameter C of anvil  30 A and diameter D of anvil  30 B are cooperable. This provides still another level of energy absorption. In this case, both anvils  30 A and  30 B are received by the receptor  52  and secured in the discharged position by catches  46 A and  46 B. It should be understood that while two cooperating anvils  30 A,  30 B are shown, more than two anvils may be used to achieve even a further level of energy absorption. Further, providing anvils  30 A,  30 B with more than two stepped diameters such as, for example, three stepped diameters achieves still further levels of energy absorption. 
     The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, wherein reference numerals are merely for convenience and are not to be in any way limiting, the invention may be practiced otherwise than as specifically described.