Abstract:
An actively variable energy absorber including a convex anvil on a steering column housing, a flat metal strap attached to a steering column support and slidably engaging the convex anvil on an active surface area of the convex anvil, and a control apparatus for actively varying the geometric relationship between the flat metal strap and the convex anvil in response to changes in a control variable thereby to adjust the magnitude of the active surface area. Adjusting the magnitude of the active surface area changes the severity of plastic deformation of the flat metal strap and the magnitude of the friction between the flat metal strap and the convex anvil thereby to adjust the force resisting linear translation of the steering column housing. In some embodiments of the actively variable energy absorber, the flat metal strap is plastically deformed by being pulled over a single convex anvil during linear translation of the steering column housing. In other embodiments of the actively variable energy absorber, the flat metal strap is plastically deformed by being pulled across a plurality of convex anvils or by being pulled edgewise between a pair convex anvils.

Description:
This application is a continuation of application Ser. No. 09/591,977, filed Jun. 12, 2000 is now 6,322,103 B 1 . 
     REFERENCE TO RELATED APPLICATIONS 
     This patent application claims priority of U.S. Provisional Patent Application No.: 60/139,055, filed on Jun. 11, 1999 
    
    
     TECHNICAL FIELD 
     This invention relates to an energy absorber for a motor vehicle steering column. 
     BACKGROUND OF THE INVENTION 
     A typical energy absorbing steering column on a motor vehicle includes a housing or mast jacket which translates linearly through a collapse stroke during a collision of the motor vehicle with another object when a steering hand wheel on the steering column is impacted by the operator of the motor vehicle. The mast jacket translates against a resisting force produced by an energy absorber which converts into work a fraction of the kinetic energy of the operator. Commonly, the resisting force is created by plastic deformation of a metal element of the energy absorber. For example, in the energy absorber described in U.S. Pat. No. 3,392,599, steel spheres plastically deform a metal mast jacket by rolling tracks in the mast jacket. In other prior energy absorbers, a flat metal strap is plastically deformed by being pulled over a stationary anvil or vice versa. Optimal performance of such energy absorbers is achieved when the kinetic energy of the operator is completely converted into work at the completion of the maximum collapse stroke of the mast jacket. However, because these energy absorbers are not adjustable after the steering column is assembled but operators of differing weight often operate the motor vehicle, optimal energy absorbing performance may not always occur. U.S. Pat. No. 4,886,295 describes an energy absorbing motor vehicle steering column having an energy absorber which is actively variable during operation of the motor vehicle for more optimal energy absorbing performance and which includes a plurality of roll deformers in an annulus between an inner tube and a longitudinally split outer tube. An expandable bag having fluid therein is disposed around the split outer. A control system which monitors control variables characteristic of the kinetic energy of an operator of the motor vehicle controls the fluid pressure in the bag and, therefore, the interference fit of the roll deformers between the inner and outer tubes, to optimize the performance of the energy absorber. 
     SUMMARY OF THE INVENTION 
     This invention is a new and improved actively variable energy absorber including a convex anvil on one of a steering column housing and a steering column support, a flat metal strap attached to the other of the steering column housing and the steering column support and slidably engaging the convex anvil on an active surface area of the convex anvil, and a control apparatus for actively varying the geometric relationship between the flat metal strap and the convex anvil in response to changes in a control variable thereby to adjust the magnitude of the active surface area. Adjusting the magnitude of the active surface area changes the severity of plastic deformation of the flat metal strap and the magnitude of the friction between the flat metal strap and the convex anvil thereby to adjust the force resisting linear translation of the steering column housing and the corresponding performance of the energy absorber. In some embodiments of the actively variable energy absorber according to this invention, the flat metal strap is plastically deformed by being pulled over a single convex anvil during linear translation of the steering column housing. In other embodiments of the energy absorber according to this invention, the flat metal strap is plastically deformed by being pulled across a plurality of convex anvils or by being pulled edgewise between a pair convex anvils. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic elevational view of a motor vehicle steering column having thereon an actively variable energy absorber according to this invention; 
     FIG. 2 is a fragmentary perspective view of the actively variable energy absorber according to this invention; 
     FIG. 3 is a fragmentary perspective view of a modified embodiment of the actively variable energy absorber according to this invention; 
     FIG. 4 is a fragmentary perspective view of a second modified embodiment of the actively variable energy absorber according to this invention; 
     FIG. 5 is a fragmentary perspective view of a third modified embodiment of the actively variable energy absorber according to this invention; 
     FIG. 6 is fragmentary perspective view of a fourth modified embodiment of the actively variable energy absorber according to this invention; 
     FIG. 7 is a fragmentary perspective view of a portion of the fourth modified embodiment of the actively variable energy absorber according to this invention; 
     FIG. 8 is a schematic plan view of a fifth modified embodiment of the actively variable energy absorber according to this invention; 
     FIG. 9 is fragmentary, exploded perspective view of a sixth modified embodiment of the actively variable energy absorber according to this invention; and 
     FIG. 10 is fragmentary perspective view of a seventh modified embodiment of the actively variable energy absorber according to this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a motor vehicle steering column  10  includes a housing  12 , a steering shaft  14  supported on the housing for rotation about a longitudinal centerline  16  of the steering column, and a steering hand wheel  18  connected to an outboard end of the steering shaft and pivotable up and down for vertical adjustment relative to an operator, not shown, of the motor vehicle seated on a seat  20  behind the steering hand wheel in conventional fashion. A steering column support  21  includes a lower bracket  22  on a schematically represented body structure  24  of the motor vehicle and a plurality of vertical hanger bolts  26  which form a shelf on the vehicle body for a lateral rod  27  on the housing  12 . 
     In a collision of the motor vehicle with another object, the vehicle body decelerates more rapidly than the operator so that the operator is thrust against the steering hand wheel  18  with an impact represented by a schematic vector force “F”. When the operator impacts the steering hand wheel, the corresponding force on the steering column housing  12  initiates linear translation of the steering column housing  12  relative to the steering column support  21  in a collapse stroke in the direction of the centerline  16  of the steering column. An actively variable energy absorber  28  according to this invention represented schematically in FIG. 1, between the steering column housing  12  and the steering column support  21  resists linear translation of the steering column housing to decelerate the occupant while at the same time converting into work a fraction of the occupant&#39;s kinetic energy. 
     Referring to FIG. 2, the actively variable energy absorber  28  includes a reaction member  30  rigidly attached to the steering column housing  12  having a cylindrical surface thereon defining a convex anvil reaction surface  32  around a longitudinal centerline  34  of the reaction member perpendicular to the direction of the linear translation of the steering column housing during its collapse stroke. A J-shaped flat metal strap  36  of the energy absorber  28  has a first leg  38  on one side of the reaction member adapted for rigid attachment to the steering column support  21 , an unattached or free second leg  40  on the other side of the reaction member, and a concave web  42  presenting a reaction surface of the strip between the first and the second legs facing convex anvil  32 . 
     A force adjustment system or control apparatus  43  of the energy absorber  28  includes a restraint pin  44  supported on the steering column housing  12  parallel to the convex anvil  32  for translation in an arc about the centerline  34  toward and away from the second leg  40  of the flat metal strap. A schematically represented actuator  46  on the steering column housing translates the restraint pin toward and away from the second leg of the metal strap. The actuator  46  is controlled by a schematically represented electronic control module (“ECM”)  48 , FIG. 1. A transducer  50 , FIG.  1 . of the control apparatus  43  on the seat  20  provides an electronic signal to the ECM  48  corresponding to the magnitude of a control variable, e.g. the weight of the operator of the motor vehicle, characteristic of the kinetic energy of the operator. Other transducers, not shown, may provide electronic signals to the ECM  48  corresponding to the magnitudes of other control variables e.g. variables e.g. vehicle velocity. 
     The force required to plastically deform the flat metal strap  36  by pulling it over the convex anvil  32  manifests itself as a force resisting linear translation of the steering column housing  12  in its collapse stroke. Friction between the flat metal strap  36  and the convex anvil  32  manifests itself as an additional force resisting linear translation of the steering column housing in its collapse stroke. The magnitudes of the resisting forces attributable to metal deformation and to friction depend upon a number of variables including the yield strength of the material from which the flat metal strap  36  is made and its physical dimensions, the coefficient of friction between the flat metal strap and the convex anvil  32 , the radius of curvature of the convex anvil, and the area of mutual contact between the flat metal strap and the convex anvil referred to herein as the “active surface area” of the convex anvil. These variables are related according to the following equation:        F   =     A   ·       W   ·     t   2           (     1   -     b   ·   μ       )     ·   R                                
     Where 
     F=total force resisting linear translation of the steering column housing 
     A=a material related constant, e.g. yield strength 
     W=width of the flat metal strap 
     t=thickness of the flat metal strap 
     R=radius of the convex anvil 
     b=parameter related to the active surface area of the convex anvil 
     μ=contact friction coefficient 
     In operation, at the onset of linear translation of the steering column housing  12  initiated by the impact F on the steering hand wheel  18 , the concave web  42  of the metal strap is thrust against and the flat metal strap is pulled across the convex anvil  32  while the unrestrained second leg  40  fans outward until intercepted by the restraint pin  44  as illustrated in broken lines in FIG.  2 . As the second leg fans outward, the active surface area of the convex anvil decreases. The position of the restraint pin  44  within its range of positions thus establishes the magnitude or size of the active surface area of the convex anvil. As the active surface area increases and decreases, the severity of plastic deformation of the flat metal strap across the convex anvil and the magnitude of the friction between the flat metal strap and the convex anvil likewise increase and decrease. 
     The position of the restraint pin  44  is established by the ECM  48  through the actuator  46  in accordance with the magnitude of the control or input variable, i.e. the weight of the operator on the seat  20 , as communicated to the ECM by the transducer  50 . As the control variable changes, e.g. as operators of successively greater weight occupy the seat  20 , the actuator  46  progressively minimizes the separation between the restraint pin  44  and the second leg  40  of the metal strap and increases the active surface and thereby the mutual contact area by more completely wrappin the flat metal strap around the convex anvil during the collapse stroke of the steering column housing. The magnitude of the force resisting linear translation of the steering column housing in its collapse stroke, therefore, increases for more optimal energy absorbing performance. The same alternative terminology applies to the description of the subsequent embodiments. 
     Referring to FIG. 3, a modified actively variable energy absorber  28 A according to this invention includes a pair of reaction members  52 A, 52 B each rigidly attached to the steering column housing  12 . The reaction members have cylindrical surfaces thereon defining respective ones of a pair of convex anvils  54 A, 54 B around corresponding ones of a pair of longitudinal centerlines  56 A, 56 B perpendicular to the direction of linear translation of the steering column housing during its collapse stroke. An M-shaped flat metal strap  58  has a pair of legs  60 A, 60 B outboard of the reaction members  52 A, 52 B, a lateral web  62  facing an abutment  64  on the steering column support  21 , and a pair of concave webs  66 A, 66 B facing the convex anvils  54 A, 54 B. 
     A control apparatus  43 A of the modified energy absorber  28 A includes a pair of restraint pins  68 A, 68 B supported on the steering column housing  12  outboard of the legs  60 A, 60 B of the flat metal strap  58  for translation toward and away from the legs. A pair of schematically represented actuators  70 A, 70 B on the steering column housing translate the restraint pins toward and away from the legs. The actuators  70 A, 70 B are controlled by the ECM  48 . The transducer  50  on the seat  20  provides an electronic signal to the ECM  48  corresponding to the magnitude of the aforesaid control variable characteristic of the kinetic energy of the operator. 
     In operation, at the onset of linear translation of the steering column housing  12  initiated by the impact F on the steering hand wheel  18 , the abutment  64  thrusts the concave webs  66 A, 66 B of the flat metal strap  58  against and pulls the flat metal strap over the convex anvils  54 A, 54 B while the legs  60 A, 60 B of the metal strap fan outward until intercepted by the restraint pins  68 A, 68 B. As the legs  60 A, 60 B fan outward, the active surface area of the each of the convex anvils  54 A, 54 B decreases. The positions of the restraint pins  68 A, 68 B within their range of positions thus establishes the magnitude or size of the active surface area of each of the convex anvils. As the active surface areas increase and decrease, the severity of plastic deformation of the M-shaped flat metal strap across the convex anvils and the magnitude of the friction between the flat metal strap and the convex anvils likewise increase and decrease. 
     The positions of the restraint pins  68 A, 68 B are established by the ECM  48  through the actuators  70 A, 70 B in accordance with the magnitude of the aforesaid control variable as communicated to the ECM by the transducer  50 . As the control-variable changes, e.g. as operators of successively greater weight occupy the seat  20 , the actuators  70 A, 70 B progressively minimize the separation between the restraint pins  68 A, 68 B and legs  60 A, 60 B of the flat metal strap thereby to increase the active surface areas of the convex anvils by more completely wrapping the flat metal strap around the convex anvils during the collapse stroke of the steering column housing. The magnitude of the force resisting linear translation of the steering column housing in its collapse stroke, therefore, increases for more optimal energy absorbing performance. 
     Referring to FIG. 4, a second modified actively variable energy absorber  28 B according to this invention includes a reaction member  72  supported on the steering column housing  12  for linear translation in the direction of a longitudinal centerline  74  of the reaction member perpendicular to the direction of the linear translation of the steering column housing during its collapse stroke. The reaction member  72  includes a plurality of cylindrical surfaces defining respective ones of a plurality of three convex anvils  76 A, 76 B, 76 C having progressively smaller radii of curvature around the centerline  74 . A J-shaped flat metal strap  78  has a first leg  80  adapted for rigid attachment to the steering column support  21  on one side of the reaction member, an unattached or free second leg  82  on the other side of the reaction member, and a concave web  84  between the first and the second legs. A restraint pin  86  is rigidly attached to the steering column housing  12  outboard of the second leg  82  of the flat metal strap. 
     A control apparatus  43 B of the second modified energy absorber  28 B includes a schematically represented actuator  88  on the steering column housing operable to linearly translate the reaction member  72  between a plurality of three positions in which respective ones of the three convex anvils  76 A, 76 B, 76 C having greater or smaller radii of curvature face the concave web  84  of the flat metal strap  78 . The actuator  88  is controlled by the ECM  48 . The transducer  50  on the seat  20  provides an electronic signal to the ECM  48  corresponding to the magnitude of the aforesaid control variable characteristic of the kinetic energy of the operator. 
     In operation, at the onset of linear translation of the steering column housing  12  initiated by the impact F on the steering hand wheel  18 , the concave web  84  of the flat metal strap is thrust against and the flat metal strap is pulled across the one of the three convex anvils  76 A, 76 B, 76 C directly facing the concave web while the unrestrained second leg  82  fans outward until intercepted by the restraint pin  86 . As the radius of curvature of the one of the convex anvils  76 A, 76 B, 76 C facing the concave web  84  increases and decreases, i.e. as the reaction member translates back and forth in the direction of its centerline  74 , the active surface area of the convex anvil increases and decreases. As the active surface area increases and decreases, the severity of plastic deformation of the flat metal strap across the convex anvil and the magnitude of the friction between the flat metal strap and the convex anvil likewise increase and decrease. 
     The position of the reaction member  72  is established by the ECM  48  through the actuator  88  in accordance with the magnitude of the aforesaid control variable as communicated to the ECM by the transducer  50 . As the control variable changes, e.g. as operators of successively greater weight occupy the seat  20 , the actuator  88  translates the reaction member  72  in a direction aligning with the concave web  84  respective ones of convex anvils  76 A, 76 B, 76 C of increasing radii of curvature thereby to increase the active surface area of the convex anvil facing the concave web during the collapse stroke of the steering column housing. The magnitude of the force resisting linear translation of the steering column housing in its collapse stroke, therefore, increases for more optimal energy absorbing performance. 
     Referring to FIG. 5, a third modified actively variable energy absorber  28 C according to this invention includes a reaction member  90  supported on the steering column housing  12  for pivotal movement about an axis  92  perpendicular to the direction of linear translation of the steering column housing during its collapse stroke. The reaction member  90  has a pair of longitudinally separated convex anvils  94 A, 94 B thereon. An S-shaped flat metal strap  96  has a first leg  98  adapted for rigid attachment to the steering column support  21 , an unattached or free second leg  100 , and a pair of concave webs  102 A, 102 B between the first and the second legs facing respective ones of the convex anvils  94 A, 94 B. 
     A control apparatus  43 C of the third modified energy absorber  28 C includes a restraint pin  104  supported on the steering column housing  12  for linear translation in a plane perpendicular to the axis  92  toward and away from the reaction member  90 . A schematically represented actuator  106  on the steering column housing translates the restraint pin  104  toward and away from the reaction member. The actuator  106  is controlled by the ECM  48 . The transducer  50  on the seat  20  provides an electronic signal to the ECM  48  corresponding to the magnitude of the aforesaid control variable characteristic of the kinetic energy of the operator. The restraint pin  104  increasingly limits clockwise rotation of the reaction member  90  about the axis  92  as the actuator  106  translates the restraint pin toward the reaction member. 
     In operation, at the onset of linear translation of the steering column housing  12  initiated by the impact F on the steering hand wheel  18 , the concave webs  102 A, 102 B of the flat metal strap  96  are thrust against and the flat metal strap is pulled across the convex anvils  94 A, 94 B while the reaction member  90  is induced to rotate clockwise about the axis  92  until intercepted by the restraint pin  104 . As the reaction member rotates clockwise, the flat metal strap unwraps from the convex anvils and the active surface area of the each of the convex anvils  94 A, 94 B decreases. The second leg  100  of the flat metal strap is prevented from fanning outward by a wall  108  on the steering column housing  12 . The position of the restraint pin  104  within its range of positions thus establishes the magnitude or size of the active surface area of each of the convex anvils. As the active surface areas increase and decrease, the severity of plastic deformation of the flat metal strap  96  across the convex anvils  94 A, 94 B and the magnitude of the friction between the flat metal strap and the convex anvils likewise increase and decrease. 
     The position of the restraint pin  104  is established by the ECM  48  through the actuator  106  in accordance with the magnitude of the aforesaid control variable as communicated to the ECM by the transducer  50 . As the control variable changes, e.g. as operators of successively greater weight occupy the seat  20 , the actuator  106  translates the restraint pin  104  toward the reaction member  90  thereby to increase the active surface areas of the convex anvils by more completely wrapping the flat metal strap around the convex anvils during the collapse stroke of the steering column housing. The magnitude of the force resisting linear translation of the steering column housing in its collapse stroke, therefore, increases for more optimal energy absorbing performance. 
     Referring to FIGS. 6-7, a fourth modified actively variable energy absorber  28 D according to this invention includes a first reaction member  110  rigidly supported in a box  112  fixed to the steering column housing  12 . The first reaction member has a cylindrical surface thereon defining a first convex anvil  114  around a centerline  116  perpendicular to the direction of linear translation of the steering column housing during its collapse stroke. A second reaction member  118  having a cylindrical surface thereon defining a second convex anvil  120  is supported in the box  112  parallel to the first reaction member  110  by a pivotable cage  121  for linear translation in a plane perpendicular to the centerline  116  toward and away from the first reaction member. An S-shaped flat metal strap  122  has a first leg  124  adapted for rigid attachment to the steering column support  21 , an unattached or free second leg  126 , and a pair of concave webs  128 A, 128 B between the first and the second legs facing respective ones of the convex anvils  114 , 120 . 
     A control apparatus  43 D of the fourth modified energy absorber  28 D includes a restraint pin  136  supported by a schematically represented actuator  138  on the steering column housing for linear translation toward and away from a tang  139  of the cage  121 . The actuator  138  is controlled by the ECM  48 . The transducer  50  on the seat  20  provides an electronic signal to the ECM  48  corresponding to the magnitude of the aforesaid control variable characteristic of the kinetic energy of the operator. The restraint pin  136  increasingly limits clockwise pivotal movement of the cage  121  as the actuator  138  translates the restraint pin toward the tang  139  on the cage. 
     In operation, at the onset of linear translation of the steering column housing  12  initiated by the impact F on the steering hand wheel  18 , the concave webs  128 A, 128 B of the flat metal strap  122  are thrust against and the flat metal strap is pulled across the convex anvils  114 , 120  while the second reaction member  118  is concurrently pulled away from the first reaction member in a direction causing the cage  121  to pivot clockwise until intercepted by the restraint pin  136 . As the cage pivots clockwise, the flat metal strap unwraps from the convex anvils and the active surface area of the each of the convex anvils  114 , 120  decreases. The second leg  126  of the flat metal strap is prevented from fanning outward by a side of the box  112 . The position of the restraint pin  136  within its range of positions thus establishes the magnitude or size of the active surface area of each of the convex anvils. As the active surface areas increase and decrease, the severity of plastic deformation of the flat metal strap  122  across the convex anvils  114 , 120  and the magnitude of the friction between the flat metal strap and the convex anvils likewise increase and decrease. 
     The position of the restraint pin  136  is established by the ECM  48  through the actuator  138  in accordance with the magnitude of the aforesaid control variable as communicated to the ECM by the transducer  50 . As the control variable changes, e.g. as operators of successively greater weight occupy the seat  20 , the actuator  138  translates the restraint pin  136  toward the tang  139  on the cage  121  thereby to increase the active surface areas of the convex anvils by more completely wrapping the flat metal strap around the convex anvils during the collapse stroke of the steering column housing. The magnitude of the force resisting linear translation of the steering column housing in its collapse stroke, therefore, increases for more optimal energy absorbing performance. 
     Referring to FIG. 8, a fifth modified actively variable energy absorber  28 E according to this invention includes a pair of reaction members  140 A, 140 B rigidly supported in a box  142  on the steering column housing  12  perpendicular to the direction of linear translation of the steering column housing during its collapse stroke. The reaction members have cylindrical surfaces thereon defining respective ones of a pair of convex anvils  144 A, 144 B. A third reaction member  146  having a third convex anvil  148  thereon is supported on the box  142  between the reaction members  140 A, 140 B in a slot  150  in the box for linear translation toward and away from the reaction members  140 A, 140 B. A flat metal strap  152  traverses the box and has a first leg  154  adapted for rigid attachment to the steering column support  21 , an unattached or free second leg  156 , and a plurality of three concave webs  158 A, 158 B, 158 C facing respective ones of the first, second and third convex anvils  144 A, 144 B, 148 . 
     A control apparatus  43 E of the fifth modified energy absorber  28 E includes a schematically represented wedge block  160  supported on the box  142  for linear translation perpendicular to the direction of linear translation of the third reaction member  146 . The wedge block  160  has a ramp  161  thereon which intersects the slot  150  and blocks linear translation of the third reaction member away from the first and second reaction members  140 A, 140 B. A schematically represented actuator  164  on the steering column housing translates the wedge block  160  perpendicular to the direction of linear translation of the third reaction member  146 . The actuator  164  is controlled by the ECM  48 . The transducer  50  on the seat  20  provides an electronic signal to the ECM  48  corresponding to the magnitude of the aforesaid control variable characteristic of the kinetic energy of the operator. The wedge block  160  increasingly limits linear translation of the third reaction member  146  away from the first and second reaction members  140 A, 140 B as the actuator  164  translates the wedge block leftward and the ramp  161  further under the third reaction member. 
     In operation, at the onset of linear translation of the steering column housing  12  initiated by the impact F on the steering hand wheel  18 , the third concave web  158 C of the flat metal strap  152  is thrust against and the flat metal strap is pulled across the third convex anvil  148  causing the third reaction member  146  to translate linearly away from the first and second reaction members  140 A, 140 B until intercepted by the ramp  161  on the wedge block  160 . At the same time, the first and second concave webs  158 A, 158 B are thrust against and the flat metal strap is pulled across the convex anvils  144 A, 144 B. As the third reaction member translates linearly away from the first and second reaction members, the flat metal strap unwraps from the convex anvils  144 A, 144 B, 148  and the active surface area of the each of the convex anvils decreases. The second leg  156  of the flat metal strap is prevented from fanning outward by a slot in the box  142 . The position of the wedge block  160  within its range of positions thus establishes the magnitude or size of the active surface area of each of the convex anvils. As the active surface areas increase and decrease, the severity of plastic deformation of the flat metal strap  152  across the convex anvils  144 A, 144 B, 148  and the magnitude of the friction between the flat metal strap and the convex anvils likewise increase and decrease. 
     The position of the wedge block  160  is established by the ECM  48  through the actuator  164  in accordance with the magnitude of the aforesaid control variable as communicated to the ECM by the transducer  50 . As the control variable changes, e.g. as operators of successively greater weight occupy the seat  20 , the actuator  164  translates the wedge block leftward, FIG. 8, thereby to increase the active surface areas of the convex anvils  144 A, 144 B, 148  by more completely wrapping the flat metal strap around the convex anvils during the collapse stroke of the steering column housing. The magnitude of the force resisting linear translation of the steering column housing in its collapse stroke, therefore, increases for more optimal energy absorbing performance. 
     Referring to FIG. 9, a sixth modified actively variable energy absorber  28 F according to this invention includes a 2-piece box  168 A, 168 B fixed to the steering column housing  12  having an arc-shaped guide surface  170  thereon. A first reaction member  172  is rigidly supported in the box perpendicular to the direction of linear translation of the steering column housing during its collapse stroke and includes a cylindrical surface defining a first convex anvil  174 . A second reaction member  176  is supported in the box  168 A, 168 B for linear translation in a plane perpendicular to the first reaction member. An arched surface on the second reaction member  176  defines a second convex anvil  178  thereon parallel to the first convex anvil  174 . A flat metal strap  180  has a first leg  182  adapted for rigid attachment to the steering column support  21 , an unattached or free second leg  184 , an arch  186  facing the guide surface  170  on the box, and a pair of concave webs  188 A, 188 B facing respective ones of the first and second convex anvils  174 , 178 . 
     A control apparatus  43 F of the sixth modified energy absorber  28 F includes a schematically represented actuator  192  on the steering column housing operable to translate the second reaction member  176  back and forth to increase and decrease the separation between the first and the second convex anvils  174 , 178 . The actuator  192  is controlled by the ECM  48 . The transducer  50  on the seat  20  provides an electronic signal to the ECM  48  corresponding to the magnitude of the aforesaid control variable characteristic of the kinetic energy of the operator. 
     In operation, at the onset of linear translation of the steering column housing  12  initiated by the impact F on the steering hand wheel  18 , the first and the second concave webs  188 A, 188 B are thrust against and the flat metal strap is pulled across the first and second convex anvils  174 , 178  while the second reaction member  176  is held stationary by the actuator  192 . The second leg  184  of the flat metal strap is prevented from fanning outward by a side of the box  168 A, 168 B. When the actuator  192  translates the second reaction member  176  in a direction increasing the separation between the first and the second convex anvils  174 , 178 , the flat metal strap unwraps from the convex anvils and the active surface area of the each of the convex anvils decreases. The position of the second reaction member  176  within its range of positions thus establishes the magnitude or size of the active surface area of each of the convex anvils. As the active surface areas increase and decrease, the severity of plastic deformation of the flat metal strap  180  across the convex anvils  174 , 178  and the magnitude of the friction between the flat metal strap and the convex anvils likewise increase and decrease. 
     The position of the second reaction member  176  is established by the ECM  48  through the actuator  192  in accordance with the magnitude of the aforesaid control variable as communicated to the ECM by the transducer  50 . As the control variable changes, e.g. as operators of successively greater weight occupy the seat  20 , the actuator  192  translates the second reaction member  176  toward the first reaction member  172 , thereby to increase the active surface areas of the convex anvils  174 , 178  by more completely wrapping the flat metal strap around the convex anvils during the collapse stroke of the steering column housing. The magnitude of the force resisting linear translation of the steering column housing in its collapse stroke, therefore, increases for more optimal energy absorbing performance. 
     Referring to FIG. 10, a seventh modified actively variable energy absorber  28 G according to this invention includes a pair of reaction members  194 A, 194 B supported on the steering column housing  12  for rotation about respective ones of a pair of parallel axes  195 A, 195 B perpendicular to the direction of linear translation of the steering column housing. Side edges of the reaction members define respective ones of a pair of convex anvils  196 A, 196 B each of which has a radius of curvature from a corresponding one of the rotation axes  195 A, 195 B which increases along the length of the convex anvil so that the convex anvils flare radially outward from the rotation axes. A flat metal strap  198  in a plane perpendicular to the rotation axes  195 A, 195 B includes a tongue  200  between the convex anvils  196 A, 196 B, a pair of split edges  202 A, 202 B, and a pair of concave shoulders  203 A, 203 B intersecting the split edges and facing respective ones of the convex anvils  196 A, 196 B. The concave shoulders correspond to the concave webs of the embodiments of the actively variable energy absorbers according to this invention described above. The tongue  200  is adapted for rigid attachment to the steering column support  21 . 
     A control apparatus  43 G of the seventh modified energy absorber  28 G includes a pair of schematically represented actuators  206 A, 206 B on the steering column housing operable to rotate corresponding ones of the first and second reaction members  194 A, 194 B to progressively decrease the span between the convex anvils  196 A, 196 B. The actuators  206 A, 206 B are controlled by the ECM  48 . The transducer  50  on the seat  20  provides an electronic signal to the ECM  48  corresponding to the magnitude of the aforesaid control variable characteristic of the kinetic energy of the operator. 
     In operation, at the onset of linear translation of the steering column housing  12  initiated by the impact F on the steering hand wheel  18 , the first and the second concave shoulders  203 A, 203 B are thrust against and the flat metal strap is pulled between and across the first and second convex anvils  196 A, 196 B while the first and second reaction members  194 A, 194 B are held stationary by the actuators  206 A, 206 B. When the actuators  206 A, 206 B rotate the first and second reaction members in directions increasing the span between the first and second convex anvils, the active surface area of the each of the convex anvils decreases and vice versa. The angular positions of the first and second reaction members  194 A, 194 B within their range of angular positions thus establishes the magnitude or size of the active surface area of each of the convex anvils. As the active surface areas increase and decrease, the severity of plastic deformation of the flat metal strap  198  across the convex anvils  196 A, 196 B and the magnitude of the friction between the flat metal strap and the convex anvils likewise increase and decrease. 
     The angular position of each of the first and second reaction members  194 A, 194 B is established by the ECM  48  through the actuators  206 A, 206 B in accordance with the magnitude of the aforesaid control variable as communicated to the ECM by the transducer  50 . As the control variable changes, e.g. as operators of successively greater weight occupy the seat  20 , the actuators  206 A, 206 B to rotate the first and second reaction members  194 A, 194 B in directions decreasing the span between the convex anvils  196 A, 196 B, thereby to increase the active surface areas of the convex anvils during the collapse stroke of the steering column housing. The magnitude of the force resisting linear translation of the steering column housing in its collapse stroke, therefore, increases for more optimal energy absorbing performance. 
     In each of the embodiments of the actively variable energy absorber according to this invention described herein, the flat metal strap is described as being attached to the steering column support and the convex anvils and the control apparatuses are described as being supported on the steering column housing. It is, of course, within the scope of this invention to reverse the positions of the flat metal strap, the reaction members, and the control apparatuses relative to the steering column housing and the steering column support.