Abstract:
A kinetic energy absorption device suitable for use with a collapsible steering column includes a first and second plastically deformable member have a traveling bight, a pusher proximate to a first part of the first member attached to a first body, a catch allowing the second member move a limited distance with respect to the pusher, and an anvil arrangement fixed to a second body. The anvil arrangement is positioned proximate the traveling bights, which have a shape corresponding with an anvil surface of thereof. The anvil arrangement forces the traveling bight of the first member to travel along a length of the first member upon initial relative movement between the first and second bodies, and then forces the traveling bight of the second member to travel along a length of the second member.

Description:
TECHNICAL FIELD 
     The present invention relates to a kinetic energy absorption mechanism having applicability to vehicular collapsible steering columns. 
     BACKGROUND 
     Kinetic energy absorption devices are known for use in vehicles to reduce the likelihood of injury in the case of an accident. Such devices come in many different forms. One form that is particularly effective at absorbing significant quantities of energy in a relatively small amount of space employs a plastically deformable member, such as a plastically deformable metal wire or strap, a pusher, and an anvil across which the plastically deformable member is drawn, dissipating energy as the member is deformed. The member is initially bent to form a traveling bight which is positioned over the anvil. As the pusher draws the member over the anvil, the traveling bight travels down the length of the strap. 
     An example of this technique is described in U.S. Pat. No. 5,788,278, issued Aug. 4, 1998 to Thomas et al., which is wholly incorporated herein by reference. In this patent, a metal strap is formed into a rough M shape with the two legs much longer than the web extending between them. Each leg of the M is positioned on opposite sides of two anvils, and a central pusher is positioned between the two anvils. The pusher is attached to the body of the vehicle, while the pair of anvils are attached to a steering column housing. Upon the instance of a forward collision, the driver is expected to impact the steering wheel which will impart a compressive force on the steering column housing, causing the anvils to move past and on either side of the pusher. The metal strap will be drawn across the anvils as the center is pushed down between them. 
     Although the use a plastically deformable member is an effective and reliable means for absorbing significant quantities of kinetic energy in a compact space, it has heretofore been impossible to use this technology to adequately vary the amount of resistance in response to various loads. Because vehicular accidents occur with varying degrees of severity, it would be desirable to provide an energy absorption device that will provide a smaller amount of resistance in the case of a less severe collision, and a greater amount of resistance in the case of a more severe collision. 
     Prior attempts at using a plastically deformable member to vary the amount of resistance with displacement of the steering column housing have been inadequate. This is because the most difficult design performance centers on the desire to begin with a low force level and transition to higher levels. U.S. Pat. No. 5,375,881, issued Dec. 27, 1994 to Lewis, shows in FIG. 2 a  a metal strap that is utilized in a manner similar to that described above with reference to U.S. Pat. No. 5,778,278 above, but in this case, there are no anvils. Instead, Lewis relies on the bending and tensile strength to keep the “free” ends from buckling under compression while the inner part is under tension, in effect, pulling the bight down. The use of an anvil is preferred, since the effect of friction between the traveling bight and the anvil is desirable, and the risk of buckling is eliminated through the use of anvils. 
     The strap in FIG. 2 a  of Lewis has a varying cross section. Specifically, the Lewis strap includes a narrower section in the middle, at the vicinity of the pusher, and wider sections toward the bottom of the opposite legs. Because of the narrower section in the middle, there is a reduced initial resistance which increases when the traveling bight reaches the wider sections. The problem with this design is that the strap may fracture if the transition to the high force exceeds the tensile strength of the narrower section. Since the narrow portions of the strap have just been significantly worked by bending, the tensile strength of the narrower sections may be significantly compromised. Because of the increased resistance due to friction between the anvils and the traveling bights, this risk is heightened if anvils are used. 
     U.S. Pat. No. 5,026,092, issued Jun. 25, 1991 to Abramczyk, describes an energy absorbing steering column having a passive restraint load limiting column support system adapted to come into play only when the primary energy absorbing system, whatever it may be, fails to provide the energy absorbing controlled collapse of the steering column assembly as designed, or one which is adapted to come into play only upon receiving impact loads of greater magnitude than those for which the system was designed. This system includes a steering column support bracket that is design to fracture under high impact, allowing the steering column to move upwardly in a second degree of freedom. The steering column will then impact the instrument panel, causing its plastic deformation and that of the instrument panel itself, thereby providing additional required energy absorption. (See column 5, lines 10-50 of Abramczyk.) This system does not provide the kind of energy absorption characteristics desired of a collapsible steering column, but rather dispenses with the utility of a collapsible steering column entirely at impact loads greater than a specified threshold. 
     SUMMARY 
     The disadvantages of the prior art noted above and otherwise are overcome by a kinetic energy absorption device suitable for use with a collapsible steering column that includes a first and second plastically deformable member have a traveling bight, a pusher proximate to a first part of the first member attached to a first body, a catch allowing the second member move a limited distance with respect to the pusher, and an anvil arrangement fixed to a second body. The anvil arrangement is positioned proximate the traveling bights, which have a shape corresponding with an anvil surface of thereof. The anvil arrangement forces the traveling bight of the first member to travel along a length of the first member upon initial relative movement between the first and second bodies, and then forces the traveling bight of the second member to travel along a length of the second member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features will be appreciated by reference to the detailed description and accompanying drawings in which: 
     FIG. 1 is a schematic representation of a prior art energy absorption device using a J-strap; 
     FIG. 2 is a schematic representation of a varying-resistance energy absorption device using a J-strap configuration; 
     FIG. 3 is an exemplary implementation of the energy absorption device of FIG. 2; 
     FIG. 4 is a schematic representation of a prior art energy absorption device using an M-strap; 
     FIG. 5 is a schematic representation of a varying-resistance energy absorption device using an M-strap configuration; 
     FIG. 6 is an exemplary implementation of the energy absorption device of FIG. 5; 
     FIG. 7 is a schematic representation of a prior art energy absorption device using an S-strap; 
     FIG. 8 is a schematic representation of a varying-resistance energy absorption device using an S-strap; 
     FIG. 9 is an exemplary implementation of the energy absorption device of FIG. 8; and 
     FIG. 10 is a pair of S-straps used in the implementation of FIG.  9 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 schematically shows the operation of a known kinetic energy absorption device  5  employing a J-strap configuration. Strap  10  includes a traveling bight that is looped over anvil  15 . A first end  12  of strap  10  is pulled in the direction of arrow  14  away from anvil  15 . Free end  16  of strap  10  is then pulled towards and around anvil  15 , causing the traveling bight to travel down the length of strap  10 . 
     FIG. 2 shows a partially exploded view of a varying-resistance energy absorption device  25  employing a J-strap configuration. Pin  28  is fixed to a first support  29  and anvil  35  is mounted to a second support (not shown). Anvil  35 , in this instance, is cylindrical and may be rotatably supported so that it is free to rotate on its axis. Pin  28  is positioned in hole  34  of first strap  30  and slot  44  of second strap  40 . During an event for which energy absorption is required, pin  28  moves away from anvil  35  in the direction of arrow  37 . Initially, pin  28  pushes against first end  32  of first strap  30 , causing first strap  30  to be pulled around anvil  35  as previously described with respect to FIG.  1 . Pin  28  therefore acts as the pusher in this embodiment. During this time, pin  28  travels in slot  44  formed in second strap  40 , and so second strap  40  remains stationary with respect to anvil  35 . However, once pin  28  reaches the opposite end of slot  44 , it operates as a catch, limiting further relative motion between the second strap  40  and the pin  28 . Pin  28  then begins to pull second strap  40  from first end  42  thereof. 
     FIG. 3 shows an exemplary implementation of the multi J-strap configuration described above with respect to FIG.  2 . In this case, a collar  41  is concentrically disposed about a sleeve  45  and the steering wheel shaft (not shown). Collar  41  is fixed to a body of a vehicle (not shown) while sleeve  45  is attached to a steering column housing. Upon impact, sleeve  45  is forced to the left as shown in the drawing to pass through collar  41 , which remains stationary with the vehicle. Collar  41  includes a pair of pins  28  which extend through apertures  34  formed in respective first straps  30 , of which two are shown. Second straps  40  include respective slots  44  along which pins  28  travel during a first portion of the energy absorbing movement. As sleeve  45  moves to the left, anvils  35  formed into sleeve  45  push against a traveling bight formed in first straps  30 , causing first straps  30  to bend around anvils  35 , thereby generating a resistive force and absorbing kinetic energy. 
     At some point, pins  28  will reach a position in slots  44  opposite from that shown, and pins  28  will then hold first ends  42  of straps  40  stationary with respect to collar  41 . When this happens, further movement to the left of sleeve  45  will cause the respective free ends of straps  40  to be pulled toward and around anvils  35 , thereby significantly increasing the resistance and therefore energy absorption. 
     A second embodiment of the invention will now be described with reference to FIGS. 4-6. FIG. 4 schematically shows the operation of a known kinetic energy absorption device  55  employing an M-strap configuration. Strap  60  includes two traveling bights looped over respective anvils  68 . A central bight is placed adjacent pusher  66 . As a force is applied on pusher  66  as represented by arrow  67  free ends  62  of strap  60  are drawn around respective anvils  68 , causing the traveling bights to travel down the length of the free ends of strap  60 . Note here that anvils  68  may be rotatably supported or not, depending on whether additional friction resistance is desired. 
     FIG. 5 shows a schematic representation of a varying-resistance energy absorption device  65  employing an M-strap configuration. Pusher  66  is fixed to a first support (not shown) and anvils  68  are mounted to a second support (not shown). During an event for which energy absorption is required, pusher  66  moves in the direction of arrow  67  with respect to anvils  68 . Initially, pusher  66  pushes against first strap  70 , at central bight  74  causing the first strap  70  to deform with free ends  72  being drawn around respective anvils  68 . During this time, second strap  80  remains stationary in its position as pusher  66  has yet to contact second strap  80 . However, once pusher  66  reaches central bight  84  of second strap  80 , pusher  66  begins to pull the central portion of second strap  80  away from anvils  68 , causing free ends  82  of second strap  80  to be pulled around respective anvils  68 . In this way, pusher  66  and recessed central bight  84  of second strap  80  cooperate as a catch, the recess of central bight  84  permitting limited relative motion between said pusher and said central bight  84 . 
     FIG. 6 shows a partially exploded diagram of an exemplary implementation of a varying resistance energy absorption device employing an M-strap configuration as described above with respect to FIG.  5 . Telescopically-collapsible steering shaft  76  is positioned within a steering column housing  86  and supported at a forward end by bearing support  75  and at a second end by a bearing in an enlarged, reinforced rear end  87  of steering column housing  86 . Steering shaft  76  is connected to an upper shaft  78  by universal joint  77 ; upper shaft  78  is positioned in tilt housing  88 . 
     Bracket  85  is fixed to a body of the vehicle (not shown) while steering column housing  86  is positioned more with respect to a steering wheel (not shown). Steering column housing  86  includes a cavity  89  which houses the energy absorption device as will now be described. Cavity  89  includes a pair of anvils  68  upon which a first strap  70  and a second strap  80  are nested. A first end  81  is inserted through bracket  85  and attached to bearing support  75 . Bracket  85  includes a pusher  66  which is aligned with central bights  74  and  84  of first and second straps. 
     In the case of a frontal collision, the driver will impact the steering wheel (not shown) and the force thereof will be transferred to steering column housing  86 , which will be urged forward in the direction of arrow  91 . Anvils  68 , being attached to steering column housing  86  will push first and second straps  70  and  80  forward. Pusher  66  of stationary bracket  85  will initially contact central bight  74  of first strap  70 , causing first strap  70  to be pulled across anvils  68 . At some point thereafter, pusher  66  will reach the location of the central bight  84  in second strap  80 , then causing second strap  80  to be pulled across anvils  68 , thereby significantly increasing the resistance and therefore energy absorption. 
     A third embodiment will now be described with reference to FIGS. 7-10. FIG. 7 schematically shows the operation of a known kinetic energy absorption device  90  employing an exemplary S-strap configuration. The S-strap configuration is usually characterized by a plastically deformable strap  100  and bending configuration wherein a first end  102  and a second end  104  move together during the energy absorption process, with at least two traveling bights therebetween that travel down the length of the strap, although this is by no means a requirement of the S-strap configuration. In the configuration of FIG. 7, strap  100  includes several traveling bights arranged in an anvil arrangement  96  that includes two bending surfaces  97  formed in a block  105 , and a central roller  98 , and a stay roller  99 . A first end  102  of strap  100  is pulled in the direction of arrow  94  away from anvil arrangement  96 . Free end  104  of strap  100  is pulled towards anvil arrangement  96 , causing strap  100  in contort around the various bending surfaces, thereby dissipating a significant amount of energy. It should be noted that although three traveling bights are shown in this example, any combination or number of bends may be used. An example of a known S-strap configuration using only two bends is disclosed in U.S. Pat. No. 5,605,352, issued Feb. 25, 1997 to Riefe et al. 
     FIG. 8 shows a schematic representation of a partially exploded varying-resistance energy absorption device  115  employing an S-strap configuration. Pin  28  is fixed to a first support  29  and anvil arrangement  96  is fixed to a second support (not shown). Anvil arrangement  96 , in this instance, includes a plurality of rollers  97 ,  98 , and  99 . During an event for which energy absorption is required, pin  28  moves away from anvil arrangement  96  in the direction of arrow  37 . Initially, pin  28  pushes against first end  112  of first strap  110 , causing first strap  110  to be pulled through anvil arrangement  96  as previously described with respect to FIG.  7 . Pin  28  therefore acts as a pusher in this embodiment. During this time, pin  28  travels in slot  124  formed in second strap  120 , and so second strap  120  remains stationary with respect to anvil arrangement  96 . However, once pin  28  reaches the opposite end of slot  124 , it begins to pull second strap  120  from first end  122  thereof. In this way, pin  28  and slot  124  operate as a catch allowing only limited movement between second strap  120  and anvil arrangement  96 . Although first strap  110  is shown as being somewhat shorter than second strap  120 , this does not have to be the case. Thus, the work of the force pulling pin  28  and anvil arrangement  96  apart can be absorbed by first the first strap  110  and then the second strap  120 , or by first the first strap  110  and then both the first and second straps  110 ,  120 . 
     FIG. 9 shows a diagram of an exemplary assembled collapsible steering column  130  implementing the varying resistance energy absorption device employing an S-strap configuration as described above with reference to FIG.  8 . Steering column  130  includes an upper steering column housing  137  that is coaxially received in a lower steering column housing  135 . Coaxially received within upper and lower steering column housings  137 ,  135  are upper and lower steering shafts  127 ,  125 , which are telescopically collapsible within the respective housings. Upper and lower steering column housings  137 ,  135  are attached at a mid-point by a frangible connection (not shown) so that upon impact of a compressive force of sufficient strength, the frangible connection will shear, and allowing the compressive force to be absorbed by first and second straps  110 ,  120 , shown in FIG.  10 . Although only the free end  126  of second strap  120  is visible extending from anvil arrangement  96 , it will be understood that the opposite end of the straps will be pulled as described above with reference to FIG. 8, thereby causing at first a first amount of resistance, and then a second amount of resistance as the upper and lower steering column housings are collapsed. 
     While the invention has been shown and described with respect to several embodiments, it is to be appreciated that these embodiments are exemplary only of the invention, and are not limiting. For example, although the first strap in each embodiment is shown as being somewhat shorter than second strap, this does not have to be the case. Thus, the work of the pusher and anvil can be initially absorbed by the first strap and then the second strap, or initially by the first strap, and then both the first and second straps. If the second strap has a greater bending strength than first strap, a significantly increased resistance will be realized upon the pusher reaching the central bight of the second strap, even if the free end of the first strap has completely passed across the anvil arrangement. 
     Furthermore, the plastically deforming members do not have to take the form of flat metal straps as shown. Various other cross section shapes may be utilized, such as round, square, oval, etc. Moreover, the cross sectional areas do not need to be uniform throughout the operative length of the member as shown. For example, FIG. 7 of U.S. Pat. No. 5,788,278 (fully incorporated herein) shows a modified metal strap having a gradually reduced cross section towards the free end, thereby customizing the energy-absorbing characteristic of the plastically deformable member. 
     Furthermore, while only two straps are shown nested together, it is contemplated that any number of straps may be nested together or placed adjacent to one-another employing the same principle wherein additional straps are called into play as the displacement from an initial condition increases. In addition, while a catch comprising a pin and slot arrangement is shown for the first and third embodiments, any type of catch arrangement could be substituted therefore. 
     Furthermore, while all the embodiments shown employ an anvil arrangement for bending the traveling bight, an anvil arrangement, while preferred, is not absolutely necessary as described in the background portion of this document. One of ordinary skill could conceive of modifications to the described embodiments sans the anvil arrangement. 
     Therefore, as will be appreciated by one skilled in the art, these and many other variations are possible without departing from the spirit and scope of the invention.