Abstract:
An energy absorbing device for a collapsible steering column of a vehicle includes an M-shaped plastically deformable strap for imposing a resistance to collapse of the steering column when the steering column collapses in a vehicle collision. An anvil adjusts the resistance to collapse imposed on the steering column by the strap. A controller produces a signal of a magnitude indicative of an amount of resistance needed to be imposed on the steering column by the strap to better protect from injury a driver seated behind the steering column at the time of the collision. An actuator receives the signal and actuates the anvil to adjust the amount of resistance imposed by the strap in accordance with the magnitude of the signal.

Description:
REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/329,837 filed Oct. 16, 2001. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to steering columns and more particularly to an energy absorbing device for a collapsible steering column. 
     BACKGROUND OF THE INVENTION 
     To protect a driver from severe injury in a frontal collision, many vehicles today are equipped with collapsible steering columns having energy absorbing devices to absorb some of the impact energy exerted on the driver&#39;s body during the collision. Typically such devices are designed to protect drivers of average size and weight in a collision of average severity, without taking into account the fact that drivers are not all of average size and weight and that collisions vary considerably in severity depending upon vehicle speed at the time of impact. U.S. Pat. No. 5,788,278 discloses an M-strap energy absorbing system for a collapsible column having fixed anvils about which the strap deforms to absorb energy. The energy absorption characteristics are non-adjustable during a crash event. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, provision is made for a adjusting the amount of resistance to the collapse of the steering column depending on a number of conditions including but not limited to the weight of the driver, position of the driver&#39;s seat, and speed of the vehicle at impact. The device includes an energy absorber for imposing a resistance to collapse of the steering column when it collapses in a vehicle collision, and a load adjuster for adjusting the resistance to collapse imposed by the energy absorber. A controller is provided to produce a signal of a magnitude indicative of an amount of resistance needed to be imposed on the steering column to better protect from injury a driver seated behind the steering column at the time of the collision. The signal produced will be dependent upon the various parameters measured at the time of the collision. An actuator receives the signal and actuates the load adjuster to adjust the amount of resistance imposed in accordance with the magnitude of the signal. 
     More specifically, the energy absorbing device may comprise an elongated plastically deformable metal strap and the load adjuster may be in the form of an anvil. Preferably the strap is generally M-shaped having parallel legs and a generally V-shaped portion connecting corresponding ends of the legs. The anvil engages a concave side of the V-shaped portion and may be moved in opposite directions by the actuator to vary the amount of resistance to steering column collapse imposed by the strap. 
     Preferably the actuator is in the form of a hydraulic cylinder controlled by an electronic solenoid valve. Valves of this description have a very rapid response and can make adjustments in the position of the anvil in only a few milliseconds after impact, while the steering column is still collapsing. 
     Among the conditions that may be sensed and therefore employed to influence the position of the anvil, are the weight of the driver, the position of the driver&#39;s seat, and vehicle speed at the time of impact. 
     One object of this invention is to provide an energy absorbing device having the foregoing features and capabilities. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the invention will become more apparent as the following description proceeds, especially when considered with the accompanying drawings, wherein: 
     FIG. 1 is perspective view of a steering column of an automotive vehicle having an energy absorbing system constructed in accordance with a presently preferred embodiment of the invention; 
     FIG. 2 is a sectional view taken on the line  2 — 2  in FIG. 1; 
     FIG. 3 is a force-displacement diagram indicating the amount of resistance applied to the steering column as it collapses; and 
     FIG. 4 is a view similar to FIG. 3 but shows a force-displacement curve of much greater complexity which may be developed to optimize the controlled application of force resisting collapse of the steering column. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A responsive energy absorbing (E/A) system constructed according to a presently preferred embodiment of the invention is shown generally at  10  in FIG.  1  and comprises an energy absorber in the form of at least one variable, plastically deformable metal strap  12  that is anchored to one component  14  of two relatively movable components  14 ,  16  reacting against a load adjuster in the form of an elongated anvil  18  carried on the second component  16  and operative to engage and deform the metal strap  12  in response to relative movement of the first and second components  14 ,  16  under controlled conditions. The anvil  18  is coupled to a control system  20  which is operative to control the position of the anvil  18  relative to the strap  12  in order to change the energy absorbing characteristics of the E/A system  10  in response to various inputs, some of which are described below. 
     FIG. 1 shows the E/A system  10  incorporated into a steering column assembly  22  of a vehicle (not shown). The steering column assembly  22  includes a steering column or housing  24  surrounding a steering shaft  26  that mounts a steering wheel (not shown) at its upper end and is operably coupled at its lower end to a steering mechanism (not shown) which steers the steerable wheels of the vehicle. 
     The steering column  24  is cradled by a lower mounting bracket  28  which is fixed by a mounting flange to support structure  32  of the vehicle (not shown). The mounting bracket  28  suspends the column  24  from the support structure  32 , while enabling the column  24  to collapse or slide through the bracket  28  relative to the support structure  32  in the event of a vehicle crash under circumstances in which the driver forcibly strikes the upper end of the column  24 , forcing the column to collapse relative to the support structure  32 . The E/A system  10  manages the collapse of the column  24  in such manner as to control the dissipation of energy according to certain control parameters. 
     The overall E/A system  10  may include, in addition to the variable E/A strap  12 , one or more passive E/A straps  34 , such that the system  10  has both passive and variable E/A components. The passive E/A straps  34  may comprise, for example, one or more J-straps as illustrated in FIG. 1 which include plastically deformable metal strips  36  each having an anchored end  38  and a free end  40 . Each anchored end  38  is connected to the support structure  32  of the vehicle and by a sheerable mount  42  to a sheer bracket  44  fixed to and movable with the column  24 . The strips  36  are bent around anvils  46  on the bracket  44 . In the event of a collision, a forward movement of the column  24  relative to the support structure  32  breaks the sheerable mount  42  free of the vehicle support structure and drives the sheer bracket  44  forward with the column  24 , causing the anvils  46  to draw across the strips  36 , and in so doing dissipate a predetermined amount of energy of the load applied to the steering column  24  from the impact of the driver of the vehicle. Accordingly, the E/A system  10  of the invention preferably has a passive component of energy absorption attributable to the passive straps  34 , and a supplemental active or adaptive component attributable to the strap  12  to provide further energy dissipation in addition to that provided by the passive straps  34 , depending upon input from the control system  20  which varies the energy absorption characteristics of the active or adaptive component, that is, the variable strap  12 . 
     As shown in FIG. 1, the active E/A strap  12  is M-shaped. Legs  52  are wrapped around a set of laterally spaced stationary side anvils  49 , presenting two outer bends or loops  51  of the strap  12 . Upper ends  48  of the legs  52  are free. The lower ends of the legs  52  of the strap  12  are connected by a looped or generally V-shaped portion  50  disposed between and forward of the outer loops  51 , giving the strap  12  the M-shape. The anvil  18  contacts the outer concave surface of the V-shaped portion  50 . Forward movement of the column  24 , and thus the anvils  49  urges the outer surface of the V-shaped portion against the anvil  18 , causing the legs  52  of the strap  12  to bend around the anvils  49 , increasing the length of the V-shaped portion  50 . 
     According to the invention, the engagement and reaction between the outer surface of the V-shaped portion  50  of the strap  12  and the anvil  18  is adjustable in such manner as to vary the energy absorption characteristics of the strap  12  during collapse of the column  24 . In the preferred embodiment, the anvil  18  is selectively movable in the axial direction, that is, parallel to the column  24 . More specifically, the anvil  18  is coupled to an actuator  54  which governs the movement and position of the anvil  18  under the control of a controller  56  which is incorporated in and is a part of the control system  20 . The actuator  54  preferably comprises a hydraulic piston  58  slidable in a cylinder  60 . The piston  58  is connected to the lower end of the anvil  18 . The cylinder  60  is fitted with a rapidly operating electronic solenoid valve  62  which controls the flow of hydraulic fluid to opposite sides of the piston  58  within the cylinder  60 . When the valve  62  is closed, the piston  58  cannot move. 
     The controller  56  has sensors (not shown) which detect certain conditions that are present immediately after, or within milliseconds after, a crash, and generate a signal of a magnitude indicative of the amount of resistance to collapse of the steering column that is needed to best protect the driver. The signal is received by the solenoid valve which, through the cylinder  60 , moves the anvil appropriately to adjust the amount of resistance imposed by the anvil upon the strap  12  in accordance with the magnitude of the signal. 
     Various parameters that can be measured by the controller  56  at the time of and during a crash includes, for example, vehicle speed, driver weight and driver seat position, steering column stroke, etc. In response to the measured value of one or more or all of these variables, the controller  56  controls the operation of the valves  62 , and thus the position of the anvil  18  relative to the strap  12  during the crash event. The electronic solenoid valve  62  is extremely fast-acting and capable of causing adjustment of the anvil  18  by the actuator  54  while the column  24  is still collapsing. 
     During a crash event, detected parameters may make it beneficial to fine-tune the adjustment of the position of the anvil  18  and thus modify the force-displacement curve to achieve optimum energy absorption under the given conditions. By controlling the movement of the anvil  18  relative to the strap  12 , a number of different force-displacement curves can be developed. This enables the designer of E/A systems to tailor a vehicle&#39;s E/A system  10  to behave at peak performance to deliver optimum protection to the occupant of a vehicle under various crash scenarios. Such a system is readily adapted to different vehicles and takes into account virtually unlimited control variables to optimize the performance of the E/A system in virtually any vehicle under virtually any crash scenario through the engineered control of the actuator  54 . 
     Referring to FIG. 3, a force-displacement diagram is shown in which reaction force imposed by the energy absorbing system  20  of this invention is plotted in Newtons along a vertical axis and steering column displacement is plotted in millimeters along a horizontal axis. In the event of a head-on collision, in which there is displacement of the steering column, the initial reaction force is shown along the section  70  of the curve and is a constant which may be approximately 4,000 Newtons. This initial reaction force is imposed on the steering column  24  by the passive straps  34  and also by the variable strap  12 . In this initial reaction stage, the anvil  18  has been pre-positioned by the actuator  54  under the control of the solenoid valve  62 , determined by such factors as weight of the driver and driver seat position. Then controller  20  senses the variables to be measured, such as vehicle speed, steering column stroke, etc., also taking into account driver weight and position, and transmits an appropriate signal to the solenoid valve  62  which thereupon opens the hydraulic circuit in the cylinder  60  to deliver hydraulic fluid to one side or the other of the piston  58 , thus to adjust the position of the anvil  18  and in this case increase the amount of resistance force imposed on the steering column  24  to approximately 6,000 Newtons as represented by the portion of the curve designated  72 . The increased resistance to force thus continues during the further collapse of the steering column. 
     By using current hydraulic valve technology in the M-strap actuator  60  and an appropriate controller  20 , a force-displacement curve can be constructed of much greater complexity as indicated in FIG. 4 in which the amount of force resistance to collapse of the steering column rises and falls as the steering column collapses. The object, of course, is to protect the driver from serious injury by a controlled resistance during the entire collapse of the steering column.