Abstract:
An energy absorbing device for a collapsible steering column of a vehicle is able to compensate for the severity of a crash and the weight of the driver to better manage the absorption of energy in a crash event. A housing has at least one fixed abutment surface, and at least one adjuster disposed in the housing for selective lateral slidable movement. At least one anvil is disposed adjacent an initial abutment surface of the adjuster in spaced relation to the fixed abutment surface of the housing in a first position of the anvil associated with high energy absorption. A plastically deformable strap is supported between the anvil and the housing. The adjuster slides out of the path of the anvil in a crash event in response to input of a control signal allowing the anvil to slide into contact with the fixed abutment surface of the housing to define a second position of the anvil associated with lower energy absorption.

Description:
TECHNICAL FIELD 
     This application relates generally to steering columns, and more particularly to adaptive energy absorbing devices for collapsible steering columns. 
     BACKGROUND OF THE INVENTION 
     Automotive steering column assemblies are often equipped with kinetic energy absorbing devices to reduce the likelihood of injury to an operator in the event of collision. One such device employs a plastically deformable metal strap which is drawn across an anvil in a crash event during the collapse of the steering column to absorb some of the energy of collapse. 
     Typically, the anvil is fixed and thus there is little control over the performance of the absorbing device. 
     SUMMARY OF THE INVENTION 
     An energy absorbing device for a collapsible steering column of a vehicle comprises a housing having at least one fixed abutment surface. At least one adjuster having an initial abutment surface is disposed in the housing for selective laterally slidable movement therein. At least one anvil is disposed in the housing between a surface of the housing and the initial abutment surface of the adjuster defining a first position of the anvil. A plastically deformable strap is supported at least in part between the anvil and the housing. The anvil has an arcuate mating surface engaging the strap restricting slidable movement therebetween. A base portion of the anvil engages the initial abutment surface of the adjuster maintaining the base portion in spaced relation from the fixed abutment surface of the housing. The adjuster is laterally slidable in response to a signal in a crash condition of the vehicle removing the adjuster from between the anvil and the housing. The base portion of the anvil can then move from the first position into mating contact with the fixed abutment surface of the housing in response to an applied force from the strap defining a second position of the anvil. The arcuate surface of the anvil has a first coefficient of friction against the strap while the anvil is in the first position and a second coefficient of friction against the strap while the anvil is in the second position. The second coefficient of friction is less than the first coefficient of friction, thereby allowing the steering column to collapse under a lighter axial load while the anvil is in the second position. 
     One object of the invention is to provide an energy absorbing device for a collapsible steering column that compensates for the severity of a vehicle crash and the size, weight and/or position of the driver. 
     The invention has the advantage of providing selectively slidable anvils which can move between different positions to vary the reaction path of the strap, and thereby control the energy absorption characteristics of the system. 
     One further advantage is that the system is of simple construction and is adaptable to many different crash conditions. 
     Other objects, features and advantages of the invention will become more apparent in view of the following description and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a motor vehicle steering column having an energy absorbing device constructed according to one embodiment of the invention; 
     FIG. 2 is an exploded perspective view of the energy absorbing device of FIG. 1; 
     FIG. 3 is a partially assembled view of the energy absorbing device of FIG. 2, but with a cover omitted; 
     FIG. 4 is an enlarged cross-sectional plan view of the energy absorbing device of FIG. 3 showing a pair of anvils in a first position; 
     FIG. 5 is a view like FIG. 4, but showing one of the anvils moved to a second position; and 
     FIG. 6 is a view like FIG. 4, but showing both of the anvils moved to a second position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An energy absorbing device constructed according to a presently preferred embodiment of the invention is shown generally at  10  in FIGS. 1-6. The energy absorbing device  10  is shown for use in FIG. 1 with a steering column assembly  12  that includes a collapsible upper steering column jacket  14  relative to a lower bracket  16  generally along a longitudinal axis  15  of the assembly  12 . In a crash condition of a motor vehicle (not shown) with another object, the vehicle body decelerates more rapidly than the operator (not shown) so that the operator is thrust against a hand wheel  18  of the motor vehicle. During impact, the energy absorbing device  10  receives a signal from a transducer or sensor  19  by way of an electrical connection to an electrical control module (ECM) or computer  21 . The sensor  19  detects the operator&#39;s size or weight, position, etc. and relays the data to the onboard computer  21 . The computer  21 , in turn, generates a load curve using the data from the sensor for directing the energy absorbing device  10  to resist linear translation of the upper steering column jacket  14  to decelerate the operator, while at the same time converting into work a fraction of the operator&#39;s kinetic energy to reduce the potential harm to the operator. 
     The energy absorbing device  10  includes a housing  20  having a channel  22  with a serpentine path. Within the channel  22 , at least one and preferably a pair of pockets  24 ,  26  are formed for receiving a pair of anvils  28 ,  30  respectively. Each pocket  24 ,  26  has a fixed abutment surface  32 ,  34  providing a final stop surface for the anvils,  28 ,  30  in a collapsing condition of the steering column assembly  12 . 
     The housing  20  has an adjuster pocket for each anvil, shown here as a pair of adjustable pockets  36 ,  38  for receiving a pair of adjusters  40 ,  42 , respectively. Each adjuster pocket  36 ,  38  extends generally laterally in relation to opposite sidewalls  46 ,  48  of the housing  20 . The pockets  36 ,  38  preferably have a bottom or end surface  45  with tapered sidewalls  44  extending generally laterally therefrom and tapered toward one another so that they converge toward the side walls  46 ,  48 . The tapered sidewalls  44  act to maintain the adjusters  40 ,  42  within the pockets  36 ,  38  upon lateral movement of the adjusters  40 ,  42  within the housing  20 . Preferably, a threaded opening  50  is formed in each end  52 ,  54  of the housing  20  for receiving a pair of threaded fasteners  56  to maintain the adjusters  40 ,  42  in their initial position. When in their initial position, the adjusters  40 ,  42  present an initial abutment surface  58 ,  60  respectively, to maintain the anvils  28 ,  30  in a first position. 
     The adjusters  40 ,  42  are assembled within the adjuster pockets  36 ,  38  so that a bottom or end surface  47  of the adjusters  40 ,  42  preferably seat against the bottom or end surface  45  of the adjuster pockets  36 ,  38  to position the adjusters  40 ,  42  in their initial assembled position. When the adjusters,  40 ,  42  are maintained in their initial position, the initial abutment surfaces  58 ,  60  extend into the pockets  24 ,  26  to maintain the anvils  28 ,  30  in a spaced relation from the fixed abutment surfaces  32 ,  34 , respectively. The fasteners  56  are preferably threaded within the threaded openings  50  to engage the adjusters  40 ,  42  and to inhibit the adjusters from unintentional slidable movement within the adjuster pockets  36 ,  38 . To facilitate laterally slidable movement of the adjusters  40 ,  42  within the adjuster pockets  36 ,.  38 , preferably the adjusters  40 ,  42  have an explosive charge therein. 
     The anvils  28 ,  30  are inserted into the pockets  24 ,  26  with each anvil  28 ,  30  having an arcuate mating surface  62  with a base portion  64  generally opposite thereto. When inserted into the pockets  24 ,  26 , and into their first position, the base portions  64  engage or abut the initial abutment surfaces  58 ,  60  of the adjusters,  40 ,  42  and are spaced from the fixed abutment surface  32 ,  34  of the housing  20 . With the anvils  28 ,  30  in their first position, the channel  22  extends around the arcuate mating surfaces  62 , thereby forming the serpentine path in which a plastically formable metal strap  66  is routed, such that the strap  66  takes on a generally S-shaped configuration as shown in the drawings. 
     The strap  66 , with the anvils  28 ,  30  in their first position, wraps around the arcuate mating surfaces  62  of the anvils  28 ,  30  a predetermined number of degrees to restrict the slidable movement between the strap  66  and the anvils  28 ,  30 . The strap  66  preferably has an opening  68  adjacent one of its ends for fastening the strap  66  to a fixed support  70  of the vehicle. A fastener  72  is shown fastening the strap  66  to the fixed support  70  to statically maintain the strap in its generally fixed position throughout a collapsing cycle of the steering column assembly  12 . 
     To complete the assembly of the energy absorbing device  10 , a cover  74  is fastened to the housing  20  preferably by way of a pair of fasteners  75  that pass through a pair of openings  77  in the upper steering column jacket  14 , through a pair of fastener openings  76  in the cover  14  and into a pair of threaded openings  78  within the housing  20 . As such, the fasteners  75  both attach the housing to the upper steering column jacket  14  and secure the cover  74  to the housing  20 . The cover  74  preferably has a pair of openings  80  allowing the emission of gas from the pockets  36 ,  38  upon ignition or detonation of the explosive within of the adjusters  40 ,  42 . 
     At the time of a crash or head-on collision in which the steering column assembly  12  collapses, conditions such as vehicle speed, driver seat position, driver weight or size, etc. are monitored by the sensor  19  and a signal is sent to the vehicle body computer  21  to generate an optimal load curve value to actuate or detonate the adjusters  40 ,  42 . Depending on the results of the load curve value, either one or both of the adjusters  40 ,  42  detonate, thereby emitting a gas such that the respective adjusters  40 ,  42  travel laterally outwardly within the adjust pockets  36 ,  38 . As such, the initial abutment surfaces  58 ,  60  are removed from between the anvils  28 ,  30  and the fixed abutment surfaces  32 ,  34 . As a result, the anvils  28 ,  30  move from the first position into mating contact with the fixed abutment surfaces  32 ,  34  in response to an applied force from the metal strap  66  defining a second position of the anvils  28 ,  30 . 
     Upon movement of the anvils  28 ,  30  from their first position to their second position, a first coefficient of friction between the arcuate mating surfaces  62  of the anvils  28 ,  30  and the strap  66  is reduced to a second coefficient of friction, thus allowing the steering column assembly  12  to collapse under a lighter axial load (i.e., with less resistance to deformation). 
     As shown in FIG. 5, when one of the anvils  28  moves from its first position to its second position, the strap  66  moves from a more severe S-shaped configuration to a less severe S-shaped configuration. As a result, the predetermined number of degrees of wrap of the strap  66  about the arcuate mating surfaces  62  is altered to a lesser predetermined number of degrees of wrap when the anvil  28  is seated against the fixed abutment surface  32  and in its second position. Further yet, as seen in FIG. 6, when both anvils  28 ,  30  move from their first positions to their second positions, the strap  66  takes on an even less severe S-shaped configuration, and thus the number of degrees of wrap of the strap  66  about the arcuate mating surfaces  62  is further reduced. As a result, the predetermined number of degrees of wrap of the strap  66  about the arcuate mating surfaces  62  while the anvils  28 ,  30  are in their first position is greater than the predetermined degrees of wrap of the strap  66  about the arcuate mating surfaces  62  while the anvils  28 ,  30  are in their second position. With fewer degrees of wrap of the strap  66  about the arcuate mating surfaces  62 , the coefficient of friction between the strap  66  and the arcuate mating surfaces  62  is reduced. This allows the housing  20  of the energy absorbing device  10  to slide relative to the plastically deformable strap  66  under a lighter applied axial load along the longitudinal axis  15  of the steering column assembly  12 . 
     It should be recognized, that the movement of one or both of the anvils  28 ,  30  from their first position to their second position is dependent upon the signal received from the ECM to the adjusters  40 ,  42 . If conditions warrant a more resistant system to collapsing of the steering column assembly  12 , then only one of the adjusters  40 ,  42  will ignite and move laterally within the respective adjuster pocket  36 ,  38 . However, if conditions warrant a more compliant system, then both adjusters  40 ,  42  will ignite to move laterally within the adjuster pockets  36 ,  38 . Either way, upon removal of one or more of the adjusters  40 ,  42  from between the anvils  28 ,  30  and the fixed abutment surfaces  32 ,  34 , the anvils  28 ,  30 , upon being forced by the strap  66  to move to their second position, move generally away from one another toward their respective fixed abutment surfaces  32 ,  34 . 
     It should be recognized that although the adjusters  40 ,  42  are represented here as having an explosive charge, the adjusters  40 ,  42  could comprise other mechanisms to facilitate lateral movement of the adjusters within the pockets  36 ,  38 , such as solenoids or the like. 
     Obviously, many modifications and variation 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, the invention may be practiced otherwise than as specifically described. The invention is defined by the claims.