Abstract:
A collapsible steering column assembly preferably has a collapsible steering shaft that extends rotatably along a centerline and a collapsible column that houses and co-extends with the shaft. The column preferably has inner and outer jackets that retract axially to collapse the column. An energy absorbing device has a member engaged between the inner and outer jackets and controls the collapse of the column generally via a high load stage and a low load stage of operation. The member is preferably elongated axially having a distal end that is looped over and spaced radially outward from the remainder of the member. The distal end is attached disengagably to the outer jacket via a pin received in a hole in the distal end and a fuse engaged operably to the pin and attached to the outer jacket.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority and all advantages of U.S. Provisional Patent Application Ser. No. 60/776,042 filed on Feb. 23, 2006, and is incorporated herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This application relates generally to steering columns, and more particularly to adaptive energy absorbing devices for collapsible steering columns. 
     2. Description of Related Art 
     Automotive steering columns are typically equipped with kinetic energy absorption devices to reduce injury of a vehicle operator in the event of a collision that may cause the operator to impact the steering wheel. Such impacts during vehicle collision typically cause the steering column to collapse thereby absorbing energy that may otherwise be transmitted to the operator. 
     Such energy absorbing steering columns generally include a housing that translates linearly through a collapse stroke during a collision. A force generated by the driver from an impact with the steering wheel initiates the collapse stroke. The steering wheel housing moves against a resisting or reactive force that may be produced by an energy absorber designed to convert a portion of the driver&#39;s kinetic energy into work. The resisting force may be generated utilizing systems currently known in the art, including the plastic deformation of a metal element that is a part of an energy absorbing device. 
     Such energy absorbing (E/A) devices presently have fixed energy absorption capabilities, and offer no control over their performance during the collapse stroke. Typically, the resisting force against which the column is stroked is provided by plastic deformation of a metal element which comprises a part of the E/A system. 
     Generally, traditional energy absorbing devices have a fixed energy absorbing curve which is optimized to protect a given group of drivers, in most cases represented by an average size male driver. To better protect other groups of drivers not belonging to the average male driver group, such as smaller female drivers or large drivers, an adjustable energy absorbing device is needed in the art. It is also desirable for E/A devices to have performance characteristics that can vary upon factors other than driver size, such as his or her position and the speed of vehicle. 
     It is, therefore, desirable for an energy absorbing device to be adjustable based upon a given driver size and his position, as well as include variables for the severity of the collision. It is also desirable to use an energy absorbing device that is capable of adjusting in a time frame similar to that of an airbag system. Therefore, to account for the severity of the collision, and act at the same time as an airbag, an energy absorbing device should be capable of adjustment within a few milliseconds of time such that a given load curve can be utilized by the device based on the severity of the collision and the characteristics of the driver. 
     There is, therefore, a need in the art for an active energy absorbing device that is capable of automatically adjusting performance characteristics to account for the severity of a collision, as well as the characteristics of the driver; and to do so within a workable time span (i.e. a few milliseconds) and similar to that of an airbag deployment. 
     SUMMARY OF THE INVENTION 
     A collapsible steering column assembly preferably has a collapsible steering shaft that extends rotatably along a centerline and a collapsible column that houses and co-extends with the shaft. The column preferably has inner and outer tubes that retract telescopically when the column collapses. An energy absorbing (E/A) device has a member that preferably is a strap engaged between the inner and outer tubes and controls the collapse of the column generally via a high load stage and a low load stage of operation. The member is preferably elongated axially having a distal end that is looped over and spaced radially outward from the remainder of the member. The distal end is disengagably attached to the outer tube via a pin received in a hole in the distal end and a fuse engaged operably to the pin and attached to the outer tube. 
     The E/A device preferably exerts a variable resistance along collapse stroke of the column. In one embodiment of the present invention, the E/A device variably accommodates: low load stage for use with, e.g., a smaller driver, lower speed of vehicle, and/or the driver being belted; the high load stage is preferably for use with, e.g., a heavier driver, high speed of vehicle, and/or the driver being unbelted driver. Such an embodiment may include one plastically-deformable strap with two stages. Another embodiment of the present invention provides a three stage E/A device accommodating minimum, middle and maximum loads or E/A capabilities. In either the two or three-stage embodiments, which stage to be appropriately applied will depend on selective activation of one or more of the fuses, that are preferably of a pyrotechnic type, in response to conditions determined from sensors measuring: vehicle speed, weight of driver, seat position and belt function. 
     The present invention provides the ability to match E/A to load curves of different shapes during collapse of the column. The present invention achieves this result, in either of the two abovementioned embodiemnts with a single, one piece strap that deforms without friction to ensure a stable E/A process with maximum simplicity and low cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a steering column assembly of the present invention illustrated with a two-stage E/A device and without a collapsible steering shaft of the assembly to show internal detail; 
         FIG. 2  is a cross section of the steering column assembly taken along line  2 - 2  of  FIG. 1  and with the collapsible steering shaft; 
         FIG. 3  is an enlarged partial side view of the steering column assembly; 
         FIG. 4  is a perspective view of a strap of the E/A device; 
         FIG. 5  is an enlarged partial perspective view of the steering column assembly; 
         FIG. 6  is a partial cross section of the assembly taken along line  6 - 6  of  FIG. 5 ; 
         FIG. 7  is a partial perspective view of a second embodiment of a steering column assembly and similar in perspective to  FIG. 5 ; 
         FIG. 8  is a partial cross section of a third embodiment of a steering column assembly and similar in perspective to  FIG. 2 ; 
         FIG. 9  is a partial cross section of a fourth embodiment of a steering column assembly; and 
         FIG. 10  is a partial cross section of a fifth embodiment of a steering column assembly. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated or simplified in order to better illustrate and explain the present invention. The exemplifications set out herein illustrate embodiments of the invention in several forms, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1-2 , a steering column assembly  20  exemplifying the present invention includes an outer longitudinally collapsible column  22 , a telescopically collapsible steering shaft  24  and preferably a steering wheel tilt mechanism  25  engaged to a steering wheel  27 . The column  22  and the shaft  24  extend longitudinally along a centerline  26  with the shaft  24  located radially inward from and generally concentric to the column  22 . The collapsible column  22  has a radially outer jacket  28 , and a radially inner jacket  30 . The collapsible steering shaft  24  of the assembly  20  has forward and rearward portions  32 ,  34  engaged telescopically to one-another and generally extending through the jackets  28 ,  30 . The forward portion  32  projects outward from the inner jacket  30  and in a forward direction  74 , with respect to the vehicle, and the rearward portion  34  projects in a rearward direction  75  for pivotal engagement to the tilt mechanism and thus engagement to the steering wheel  27 . 
     Preferably, the outer jacket  28  is a unitary casting that integrates an outer tube or tubular portion  36  for receipt of the shaft  24  and a bracket portion  38  for releasable engagement to a vehicle chassis and generally tilt-and-lock engagement to the tilt mechanism  25 . The bracket portion  38  of outer jacket  28  preferably secures to the vehicle structure through capsules (not shown) fitted into the bracket portion  38  and designed to break away therefrom during column collapse. The tubular portion  36  preferable carries a journal or socket  39  for substantially frictionless support of a universal joint  41  at a rearward end  43  of the shaft portion  34  that generally engages the preferably tiltable steering wheel  27 . The journal, and as known in the art, is constructed and arranged to permit substantially frictionless rotation of the shaft  24  with respect to tubular portion  36  while preferably allowing axial movement between the tubular portion  36  and the shaft portion  34  during collapse of the steering shaft  24 . One skilled in the art would now know, however, that the column  22  may collapse simultaneously with the steering shaft  24  thus axial movement between the shaft portion  34  and the tubular portion  36  may not be necessary. 
     The inner jacket  30  preferably has an inner tube or tubular portion  40  and a stamped bracket portion  42  preferably welded rigidly to a distal end of the tubular portion  40 . The stamped bracket portion  42  engages rigidly, and without release, to the vehicle chassis. The tubular portion  40  preferably carries a bearing ring  45  for substantially frictionless rotation of the steering shaft  24  located therein. Unlike the journal carried by the outer jacket  28 , the bearing ring  45  carried by the inner jacket  30  does not generally permit axial movement between the inner jacket  30  and the rearward portion  32  of shaft  24  during shaft collapse. 
     Preferably, the shaft portions  32 ,  34  are configured to one another along the centerline  26  to allow limited longitudinal or axial movement there-between for adjustment of steering wheel position. Whether the steering wheel position is adjustable or not during normal operation, the shaft portions  32 ,  34  are preferably constructed and arranged to collapse telescopically during a vehicle collision. During normal operation of the vehicle the column  22  is generally rigid. However, during a collision the rearward portion  34  of steering shaft  24  moves in a substantially forward direction and telescopically into the forward portion  32 . During this movement, the shaft portion  34  also moves axially with respect to jacket  28  that may remain secured to the vehicle chassis. 
     With the steering shaft  24  collapsed, and with continued forward momentum of the vehicle operator, the outer jacket  28  generally breaks away from the vehicle chassis and an energy absorption (E/A) device  44  begins to convert the remaining kinetic energy into work. With the E/A device  44  generally activated, the column  22  collapses via telescopic or axial movement between the outer jacket  28  and the stationary inner jacket  30  that remains secured to the vehicle chassis. 
     Referring to  FIGS. 1-4 , the E/A device  44  of the assembly  20  longitudinally and steadfastly fixes the outer jacket  28  to the inner jacket  30  during normal vehicle operation. The E/A device  44  is operatively positioned radially between the tubular portion  40  of the inner jacket  30  and the tubular portion  36  of the outer jacket  28  and with respect to centerline  26 . E/A device  44  of column assembly  20  includes a member or strap  46 , preferably of a two stage type, and a bi-state pyrotechnic device or fuse  48 , respectively secured through bolts  50  and  52  to inner jacket  30  and outer jacket  28 , respectively. Pyrotechnic devices such as fuse  48 , and the sensed conditions and logic for selectively firing them, are well known in the art, and may, for example, be as generally described in U.S. Pat. No. 6,749,222, which is incorporated herein by reference in its entirety. 
     Referring to  FIG. 4 , strap  46  of the E/A device  44  is formed from a single strip of a plastically-deformable material such as steel, that is folded over upon itself forming first and second portions or material layers  54  and  56 , folded end  58  that joins layers  54  and  56 , and material free ends  60  and  62 . The width of layer  54  preferably differs along its length from the width of layer  56  for creating the two stage energy absorption capability that generally matches two different load curves during collapse of column  22 . As described further below, in one of the two energy absorption stages (the first or higher load stage), both material layers  54  and  56  are stressed and deformed; in the other of the two stages (the second or lower load stage), only one of the layers is stressed and deformed, thus the energy absorption during column collapse is varied. 
     Referring to  FIGS. 1-4 , bolt  50  extends through a hole  64  in strap  46  near the folded end  58  to secure strap  46  to portion  40  of inner jacket  30 . A second hole  66  in strap  46  is defined by continuous inner edges  68 ,  70  carried respectively by layers  54 ,  56 . The hole  66  is located near the material free ends  60 ,  62  and receives a pin  72  of the fuse  48  for generally securing the layer  54  of strap  46  to the tubular portion  36  of the outer jacket  28 . In the high load stage of the E/A device  44 , the engagement of pin  72  of the unfired pyrotechnic fuse  48  with the continuous inner edges  68 ,  70  of respective layers  54 ,  56  within hole  66  preferably causes both layers  54 ,  56  to be stressed and deformed during column collapse. That is, as outer jacket  28  breaks from the vehicle chassis and shifts axially forward (with respect to the vehicle) in the direction of arrow  74  (see  FIG. 3 ) and along the centerline  26 , jacket  28  further envelopes stationary inner jacket  30  causing plastic deformation of both layers  54 ,  56 . 
     A variety of sensors (not shown) are responsive to certain sensed conditions relating to driver weight, seat position, whether the driver is belted, and/or vehicle speed. When a pre-specified condition is sensed, the sensor sends an electric signal to the fuse  48  of the E/A device  44  that generally initiates the low load stage of device  44  operation. Upon receipt of the electric signal coupled with a collision event, the fuse  48  fires thereby removing pin  72  from hole  66  just prior to column collapse. Referring now to  FIGS. 4-6 , strap material free end  62  has two integrally-formed tabs  76  extending in opposite lateral directions. The tabs  76  are seated in a recess  78  generally in portion  36  of outer jacket  28 . Recess  78  is partially defined by a pair of shoulders or stops  80  formed in and preferably carried by portion  36  of outer jacket  28 . Each stop  80  abuts a respective tab  76  during column collapse. During an activation of the lower load stage of E/A device  44 , where the fuse  48  has removed the pin  72 , when the outer jacket  28  is loaded and moves in the direction of arrow  74  (see  FIG. 3 ) the stops  80  push the tabs  76  of the distal end  62  of layer  56  in the axial direction  74 , thereby deforming layer  56 . The end  60  of layer  54  is generally free, does not deform, and generally stays stationary with the inner jacket  30 . This configuration places layer  56  under stress causing deformation, while layer  54  is not stressed and thus does not deform. For the first embodiment of assembly  20 , the recess  78  may be completely open towards inner jacket  30  (as best shown in  FIGS. 5 and 6 ) with strap tabs  76  merely disposed therein. At the beginning of column collapse, stops  80  preferably move freely a short axial distance before picking up the load from layer  56 . 
     Alternatively and as shown in  FIG. 7 , a second embodiment of the assembly is illustrated wherein like components have the same identifying numerals except with the addition of a single prime symbol. For E/A device  44 ′, strap tabs  76 ′ may be slidably received in slots  82  formed on opposite lateral sides of recess  78 ′. Each slot  82  is defined in part by a blind end (not shown) that forms shoulders  80 ′ against which tabs  76 ′ abut during collapse of column assembly  20 ′. 
     Referring to  FIG. 8 , a third embodiment of the assembly is illustrated wherein like components have the same identifying numerals except with the addition of a double prime symbol. For E/A device  44 ″ a hole  84  in the strap  46 ″ near a material free end  62 ″ of strap  46 ″ receives a bolt  86  for securing the free end  62 ″ to portion  36 ″ of an outer jacket  28 ″. With pin  72 ″ retracted and released from strap  46 ″ (not shown) during the lower load stage of the E/A device  44 ″, free end  60 ″ remains stationary with inner jacket  30 ″ while the end  62 ″ of layer  56 ″ moves generally with the portion  36 ″ in a direction indicated by arrow  74 ″. Only the material layer  56 ″ is stressed and deformed during the lower load stage. 
     Referring to  FIG. 9 , a fourth embodiment of the assembly is illustrated wherein like components have the same identifying numerals except with the addition of a triple prime symbol. An E/A device  44 ′″ of column assembly  20 ′″ includes a strap  46 ′″ formed from a single strip of a plastically-deformable material such as steel. The strap  46 ′″ has opposite end portions  60 ′″,  62 ′″ that are folded over a central portion  88  of the strap  46 ′″, thus forming a substantially oval-shape or loop that is partially opened upward (as illustrated in  FIG. 8  but not necessarily) between the spaced apart end portions  60 ′″,  62 ′″. A hole  64 ′″ in the central portion  88  of strap  46 ′″ aligns to a threaded hole in the inner jacket  30 ′″, for receipt of a threaded bolt  50 ′″ thus securing the central portion  88  to the inner jacket  30 ′″. A hole  66 ′″ in end portion  60 ′″ receives a pin  72 ′″ of a pyrotechnic fuse  48 ′″. A hole  84 ′″ in end portion  62 ′″ receives a bolt  86 ′″ for securing the end portion  62 ′″ of strap  46 ′″ to the portion  36 ′″ of outer jacket  28 ′″. The central portion  88  of strap  46 ′″ is connected via large-radius bends  90  and  92  to the respective end portions  60 ′″,  62 ′″ that are disposed substantially parallel with strap central portion  88 . 
     A restraining support  94 , which is shown as being attached to portion  36 ′″ of outer jacket  28 , but which may instead be integral therewith, maintains a substantial overhead segment of end portion  62 ′″ in parallel with strap central portion  88 . A substantial overhead segment of end portion  60 ′″ is likewise confined by a radially inward facing surface of portion  36 ′″ to maintain the parallel relationship with strap central portion  88 . 
     During column  22 ′″ collapse with E/A device  44 ′″ in a high load stage, fuse pin  72 ′″ remains in the hole  66 ′″ and the outer jacket  28 ′″ moves in direction of arrow  74 ′″ as the inner jacket  30 ′″ remains generally stationary. The strap  46 ′″ is plastically deformed such that part of the overhead segment of the strap end portion  62 ′″ is moved generally through bend  90  and relocated to lie along inner jacket  30 ′″ with central portion  88 , and part of strap central portion  88  is moved through bend  92  and relocated to lie along portion  36 ′″ of the outer jacket  28 ′″ with the overhead segment of the strap end portion  60 ′″. Responsive to certain sensed conditions relating to driver weight, seat position, whether the driver is belted, and/or vehicle speed, the low load stage of device  44 ′″ is activated and fuse  48 ′″ is fired just prior to the column collapsing, thereby removing pin  72 ′″ from hole  66 ′″. In the low load stage, only the material comprising the overhead segment of end portion  62 ′″ is deformed and the end portion  60 ′″ stays stationary with inner jacket  30 ′″ without deforming and with respect to centerline  26 ′″ and preferably sliding against the radially inward facing surface of portion  36 ′″ of outer jacket  28 ′″. 
     Referring to  FIG. 10 , a fifth embodiment of the assembly  20 ″″ is illustrated wherein like components have the same identifying numerals except with the addition of a quadruple prime symbol. An E/A device  44 ″″ of assembly  20 ″″ has three or more load stages and preferably three to four load stages. Device  44 ″″ is similar to that previously described for device  44 ″ of the third embodiment but having an additional pyrotechnic fuse  96 , associated pin  98  and associated layer  100  of a strap  46 ″″. Fuse  48 ′″ and fuse  96  of device  44 ″″ are preferably of a common type. Layer  100  of strap  46 ″″ is similar in shape, structure and function to layer  54 ″″ of strap  46 ″″ including the presence of a hole  102  near a distal end  104  for insertion of the releasable pin  98 . However, layer  100  is longer than layer  54 ″″ because both layers preferably engage an inner jacket  30 ″″ at a common axial location, with layer  56 ″″ and via bolt  50 ″″, yet layer  100  extends axially further with respect to a centerline  26 ″″ because placement of the associated fuse  96  is preferably axially rearward of fuse  48 ″″. 
     Those of ordinary skill in the art will now appreciate that the dimensions and material characteristics of strap  46 ″″ of in E/A device  44 ″″ may differ considerably from straps  46 ,  46 ′,  46 ″,  46 ′″, and is designed to match the three-stage or four-stage device&#39;s column collapse E/A characteristics to each of three or four different load curves, each stage selected based on sensed driver weight and position, whether belted, and vehicle speed. 
     For instance and during column  22 ″″ collapse, in a highest load stage of E/A device  44 ″″, neither of fuses  48 ″″ and fuse  96  are fired. For the highest load E/A stage, layers  54 ″″,  56 ″″,  100  of strap  46 ″″ are all placed under stressed and subsequently deformed. In a lowest load stage of E/A device  44 ″″ both fuses  48 ″″ and fuse  96  do fire removing respective pins  72 ″″,  98  from respective holes  66 ″″,  102  in respective layers  54 ″″,  100  of strap  46 ″″. Thus and similar to that previously described in the other embodiments, only the layer  56 ″″ is stressed and deformed. Yet further, in a third or primary intermediate load stage of E/A device  44 ″″, only one of fuses  48 ″″,  96  is fired just prior to column collapse and the other is not fired. Consequently layer  56 ″″ in addition to either layer  54 ″″ or layer  100  of strap  46 ″″ is stressed and deformed. In a fourth or secondary intermediate load stage of E/A device  44 ″″, only the other one of fuses  48 ″″,  96  is fired just prior to column collapse. 
     For example, with reference to  FIG. 10 , the following four-stage fuse firing logic could be used: 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Load, E/A Characteristic 
                 Fuse 48″″ fired 
                 Fuse 96 fired 
               
               
                   
                   
               
             
             
               
                   
                 Highest 
                 No 
                 No 
               
               
                   
                 Primary Intermediate 
                 No 
                 Yes 
               
               
                   
                 Secondary Intermediate 
                 Yes 
                 No 
               
               
                   
                 Lowest 
                 Yes 
                 Yes 
               
               
                   
                   
               
             
          
         
       
     
     Alternatively, the following four-stage fuse firing logic could be used: 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Load, E/A Characteristic 
                 Fuse 48 fired 
                 Fuse 96 fired 
               
               
                   
                   
               
             
             
               
                   
                 Highest 
                 No 
                 No 
               
               
                   
                 Primary Intermediate 
                 Yes 
                 No 
               
               
                   
                 Secondary Intermediate 
                 No 
                 Yes 
               
               
                   
                 Lowest 
                 Yes 
                 Yes 
               
               
                   
                   
               
             
          
         
       
     
     It is envisioned that a simpler firing logic could be employed with E/A device  44 ″″ to accommodate a three-stage load instead of a four-stage load as described above. Such an arrangement would include the above-identified highest and lowest load selections, and only one intermediate selection. For example, the highest load stage, neither of pyrotechnic fuses  48 ″″,  96  are fired, and all layers  54 ″″,  56 ″″,  100  of strap  46 ″″ are stressed and deformed. In a lowest load stage, both of pyrotechnic fuses  48 ″″,  96  are fired, and only layer  56 ″″ of strap  46 ″″ is stressed and deformed. In the single intermediate or middle load stage, second fuse  96  is fired just prior to column collapse and first fuse  48 ″″ is not fired, and layers  54 ″″ and  56 ″″ are stressed and deformed, but not layer  100 , which may freely slide along a channel formed in portion  36 ″″ of outer jacket  28 ″″. 
     For example, with reference to  FIG. 10 , the following three-stage fuse firing logic may be used: 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Load, E/A 
                   
                   
               
               
                   
                 Characteristic 
                 Fuse 48″″ fired 
                 Fuse 96 fired 
               
               
                   
                   
               
             
             
               
                   
                 Highest 
                 No 
                 No 
               
               
                   
                 Middle 
                 No 
                 Yes 
               
               
                   
                 Lowest 
                 Yes 
                 Yes 
               
               
                   
                   
               
             
          
         
       
     
     Alternatively, the following three-stage fuse firing logic could be used: 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Load, E/A 
                   
                   
               
               
                   
                 Characteristic 
                 Fuse 48″″ fired 
                 Fuse 96 fired 
               
               
                   
                   
               
             
             
               
                   
                 Highest 
                 No 
                 No 
               
               
                   
                 Middle 
                 Yes 
                 No 
               
               
                   
                 Lowest 
                 Yes 
                 Yes 
               
               
                   
                   
               
             
          
         
       
     
     Although the preferred embodiments of the present invention have been disclosed, various changes and modifications may be made thereto by one skilled in the art without departing from the scope and spirit of the invention as set forth in the appended claims. It is also understood that the terms used herein are merely descriptive, rather than limiting, and that various changes in terminology may be made without departing from the scope and spirit of the invention.