Abstract:
A steering column assembly for a vehicle comprises a column jacket and an energy absorption system. The column jacket is configured to undergo a collapse event involving a translation of the column jacket along a longitudinal axis in response to application of a column compression force. The energy absorption system includes an anvil coupled to the vehicle and a strap coupled to the column jacket with the strap extending through the anvil such that the strap is drawn over the anvil in response to the collapse event. The strap is configured to cause: (a) a friction force to be created between the strap and the anvil; and (b) a deformation force to be created between the strap and the anvil. The strap is configured such that at least one of the friction force and the deformation force varies along the length of the strap.

Description:
BACKGROUND OF THE INVENTION 
     The subject invention generally relates to a steering column assembly for a vehicle, and more specifically to a collapsible steering column assembly having an energy absorption system for absorbing energy during collapse of the steering column assembly. 
     A vehicle steering column assembly may include an energy absorption system for dissipating kinetic energy during an impact between a vehicle occupant and the steering column. An energy absorption system may thereby reduce the likelihood or severity of an injury to the vehicle operator in the event of a collision involving the vehicle. For example, in a front end collision interrupting the forward progress of the vehicle, a vehicle occupant impacting the steering wheel may impose a column compression force upon the steering column. If the column compression force is of sufficient magnitude, a collapse of the steering column along its longitudinal axis may be encountered. 
     An energy absorption system may be implemented and configured so as to deliver a collapse resistance force that tends to oppose the column compression force. To overcome the collapse resistance force, an input of work (i.e., energy) is required as the steering column collapses, and the steering column is thus able to “absorb” the energy (i.e., work) in overcoming the collapse resistance force as that energy is expended throughout the collapse stroke. This release of energy over the finite period of time required to traverse the collapse stroke, as apposed to the instantaneous release of energy that would be associated with an impact with a rigid body, results in a substantial decrease in the magnitude of the impulse encountered by the vehicle occupant in the event of a vehicle collision. 
     As one skilled in the art will appreciate, a collapsible steering column assembly may include a housing configured to translate linearly through a collapse stroke. As soon as the steering column has been released from its relatively fixed position with respect to the vehicle, energy absorption during the collapse stroke becomes feasible. Accordingly, when a vehicle occupant first impacts the steering wheel and exerts a sufficient break-away force on the steering column (or as soon as a collision event has been detected and the steering column is automatically released), a force exerted by the occupant upon the steering column (i.e., column compression force) is available to perform work. One skilled in the art will appreciate that the force exerted by the occupant on the steering column is related to not only the rate at which the column mass is accelerated by the force exerted by the occupant, but also to the force that resists the collapse of the steering column. This collapse resistance force may be created and controlled by an energy absorption system, which is designed to dissipate a portion of the occupant&#39;s kinetic energy. 
     In general, the collapse resistance force may be created through a variety of means, including by causing a strap to be drawn through or over a path or surface of resistance as the housing of the collapsible steering column assembly translates through the collapse stroke. As the strap passes through the path or over the surface, the strap may be deformed, friction may be encountered between the strap and the surface, and/or other mechanisms may be employed for resisting the relative movement between the strap and the surface. 
     Typically, a collapsible steering column assembly includes a column jacket having two ends; a steering wheel end and an output end. A bracket is mounted to the column jacket for attaching the column jacket to the vehicle, and one or more release modules interconnect the bracket to the vehicle. The release modules may be configured to release the interconnection between the column jacket and the vehicle upon the occurrence of a predetermined event, such as a vehicle collision. A release module may include a bore, through which a fastener, such as a bolt, passes through to mechanically couple the release module to the vehicle. A strap may be connected to the bracket for movement with the bracket and the column jacket during the collapse stroke. The strap passes through a deformation device, such as an anvil that defines a strap channel. Thus, during the collapse stroke, the strap is deformed or otherwise caused to encounter a collapse resistance force imparted by the anvil. A deformation channel may be incorporated into the release module. 
     Accordingly, it is desirable to have a steering column assembly with an energy absorption system that can facilitate reliable, cost-effective control over the collapse resistance force. It would also be advantageous to have a steering column assembly with an energy absorption system that provides for variations in the collapse resistance force at different stages of a collapse stroke. 
     SUMMARY OF THE INVENTION 
     In one exemplary embodiment of the invention, a steering column assembly for a vehicle comprises a column jacket and an energy absorption system. The column jacket is configured to undergo a collapse event involving a translation of the column jacket along a longitudinal axis in response to application of a column compression force following the occurrence of a predefined event. The energy absorption system includes an anvil coupled to the vehicle and a strap coupled to the column jacket with the strap extending through the anvil such that the strap is drawn over the anvil in response to the collapse event. The strap is configured to cause: (a) a friction force to be created between the strap and the anvil so as to resist relative movement between the strap and the anvil during the collapse event; and (b) a deformation force to be created between the strap and the anvil so as to resist relative movement between the strap and the anvil during the collapse event. The strap is configured such that at least one of the friction force and the deformation force varies along the length of the strap. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  shows a top plan view of a collapsible steering column assembly; 
         FIG. 2  shows an enlarged fragmentary top plan view of the collapsible steering column assembly; 
         FIG. 3  shows a fragmentary perspective view of the steering column assembly prior to collapse; 
         FIG. 4  shows a fragmentary perspective view of the steering column assembly post collapse; 
         FIG. 5  shows a partial lower plan view of the steering column assembly showing two release modules coupled to a bracket; 
         FIG. 6  shows a side view of an exemplary strap of an energy absorption system of a collapsible steering column assembly; and 
         FIG. 7  shows a side view of an exemplary strap of an energy absorption system of a collapsible steering column assembly. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the Figures, where the invention will be described with reference to specific embodiments, without limiting same,  FIGS. 1 and 2  show a steering column assembly  20  exemplifying the present invention. The steering column assembly  20  is for a vehicle, and is collapsible in response to a collision event. The steering column assembly  20  includes a column jacket  22 . The column jacket  22  includes an input end  24  and an output end  26 . A steering shaft is supported for rotation within the column jacket  22 . A steering wheel (not shown) is connected to the steering shaft near the input end  24  of the column jacket  22 . The column jacket  22  and the steering shaft define a longitudinal axis  28 . The column jacket  22  includes an upper jacket  30  and a lower jacket  32 . 
     The steering column assembly  20  is configured to collapse along the longitudinal axis  28  (through a collapse stroke) as the input end  24  moves toward the output end  26  in response to a force applied between the input end  24  and the output end  26  (e.g., as an operator of the vehicle applies the force to the steering wheel and pushes the column jacket  22  along the longitudinal axis  28  toward the output end  26  of the column jacket  22 ).  FIGS. 1 and 3  show the steering column assembly  20  prior to such a collapse, while  FIGS. 2 and 4  show the steering column assembly  20  after an exemplary collapse of the steering column assembly  20 . It should be appreciated that a collision event may be caused by a vehicular crash and may involve transmission of a force to the steering wheel by an operator of the vehicle, the force being transmitted to the steering column assembly  20 . 
     With further reference to  FIG. 1  and  FIG. 2 , the column jacket  22  includes a bracket  34  that is fixed to the column jacket  22 . In an exemplary embodiment, the bracket  34  is attached to the upper jacket  30  and is moveable with the upper jacket  30  along the longitudinal axis  28  during the collapse stroke. The bracket  34  may include a first extension  36  and a second extension  38  extending in a radial outward direction from opposing sides of the column jacket  22 . The column jacket  22  and the bracket  34  are moveable along the longitudinal axis  28  in response to the collision event in a direction indicated by arrow  40 . The bracket  34  may be integrally formed with the column jacket  22  or may be connected to the column jacket  22  by welding or by any other suitable manner known in the art. 
     A release module  46  includes a connection point  48  for reliably connecting the release module  46  to the vehicle, and the column jacket  22  is selectively coupled to the release module  46 . In an exemplary embodiment, the release module  46  is selectively coupled to the bracket  34 , which provides the connection to structural connection to the column jacket  22 . The release module  46  is coupled to the column jacket  22  in such a manner that the release module  46  remains coupled to the column jacket  22  prior to the occurrence of a predetermined event (e.g., a vehicle collision) but is selectively released from the column jacket  22  upon the occurrence of the predetermined event. When the release module  46  is released, a longitudinal collapse of the column jacket  22  is accommodated such that the bracket  34  is permitted to move relative to the release module  46  as the column jacket  22  and the bracket  34  move through the collapse stroke. 
     In an exemplary embodiment, the release module  46  is configured to couple the bracket  34 , and thus the column jacket  22 , to the vehicle prior to a release (e.g., prior to a collision event), and to release the bracket  34  (and thus the column jacket  22 ) from the vehicle as the bracket  34  and the column jacket  22  move along the longitudinal axis  28 . For example, the release module  46  may include a number of sheer pins  54  configured to fracture under imposition of a predefined load, enabling the column jacket  22  to move along the longitudinal axis  28  relative to the release module  46 . However, it should be appreciated that the release module  46  may be coupled to the bracket  34  or the column jacket  22  in some other suitable fashion. The release module  46  may include a first release module  46 A releasably coupled to the first extension  36  and a second release module  46 B releasably coupled to the second extension  38 . 
     While the column jacket  22  (and/or the bracket  34 ) is configured to be selectively released from the release module  46  upon the occurrence of a predetermined event, the release module  46  remains fixed to the vehicle. In an exemplary embodiment, the release module  46  defines a bore  56  aligned with the connection point  48 , through which a release module fastener  42  extends for fixing the release module  46  to the vehicle. 
     The steering column assembly  20  also includes an energy absorption system  58 . The energy absorption system  58  interconnects the bracket  34 , and the column jacket  22 , to the release module  46  and thus to the vehicle. The energy absorption system  58  includes a strap  60 . The strap  60  is secured directly or indirectly to the column jacket  22  and includes an attachment  62  and/or a strap fastener  44  to facilitate such attachments. In an exemplary embodiment, the strap  60  is selectively coupled to the bracket  34  and to the column jacket  22  to facilitate a dual mode energy absorption system  58 , in which a first mode facilitates energy absorption during collapse of the column jacket  22 , and a second mode facilitates free collapse of the column jacket  22 . 
     In an exemplary embodiment, an actuator  64  is attached to the bracket  34  in order to selectively couple the strap  60  to the bracket  34 . A controller (not shown) signals the actuator  64  to couple the strap  60  to the bracket  34  if desired. The actuator  64 , if signaled, may move the strap fastener  44 , such as a pin, through an aperture in the strap  60  to connect the strap  60  to the bracket  34 . The actuator  64  may include a pyrotechnic device or some other suitable device. However, it should be appreciated that the strap  60  may be selectively coupled to the bracket  34  by other means known in the art. 
     As shown in  FIG. 5 , the energy absorption system  58  further includes a deformation device  66 . The deformation device  66  includes a channel  68  defining an anvil  70 . The channel  68  and the anvil  70  are disposed on the release module  46 . The strap  60  is disposed within and extends through the channel  68 . As the column jacket  22  moves along the longitudinal axis  28  (e.g., during a collapse of the column jacket  22 ), the strap  60  is drawn through and deformed by the channel  68 .  FIGS. 1 ,  3  and  5  show the strap  60  prior to being drawn through the channel  68 .  FIG. 2  and  FIG. 4  show the strap  60  after the strap  60  has been drawn through the channel  68 . 
     As described above, the channel  68  defines and includes the anvil  70 , about which the strap  60  is deformed as the strap  60  is drawn through the channel  68 . The anvil  70  is disposed on the release module  46 . The channel  68  and the anvil  70  may include any suitable shape. As shown, the channel  68  and the anvil  70  generally define a U-shape. However, it should be appreciated that the resistance provided by the energy absorption system  58  is determined by the amount of energy required to deform the strap  60  as the strap  60  is drawn through the channel  68 . Accordingly, a more complex channel  68  having more and/or smaller radius bends, increases the amount of energy required to deform the strap  60  and thereby increases the resistance provided against movement of the column jacket  22 . 
     The steering column assembly  20  may include one or more energy absorption systems  58 . If multiple energy absorption systems  58  are utilized, then one or more of the energy absorption systems  58  may be selectively coupled to the bracket  34  as described above to provide multiple stages of resistance. The steering column assembly  20  includes a first energy absorption system  58 A and a second energy absorption system  58 B with the strap  60  of the first energy absorption system  58  fixedly connected to the bracket  34  and the strap  60  of the second energy absorption system  58  selectively coupled to the bracket  34 . Accordingly, the first energy absorption system  58 A will always be available to resist movement of the column jacket  22 , while the second energy absorption system  58 B may be selectively engaged if desired. 
     It should be appreciated that control over the force that resists the collapse of a steering column along the collapse stroke (i.e., the collapse resistance force) may be provided by manipulating a number of aspects of the construction of the steering column. A particularly convenient aspect to facilitate manipulation of the collapse resistance force relates to the interaction of the strap  60  and the anvil  70 . One mechanism for dissipating energy involves the deformation of the strap  60 , which occurs as the strap  60  is pulled over the anvil  70 . Another mechanism involves friction between the strap  60  and the anvil  70 . 
     In regard to the mechanism involving deformation of the strap  60 , relevant parameters for manipulation of the collapse resistance force include, as depicted in  FIG. 6  and  FIG. 7 , the yield strength of the strap  60 , the cross-sectional dimensions (i.e., width  76 , thickness  78 ) of the strap  60 , and the curvature (e.g., radius  80 ) of the anvil  70 . In regard to the mechanism involving friction between the strap  60  and the anvil  70 , relevant parameters for manipulation of the collapse resistance force include the coefficients of friction between the surface  72  of the strap  60  and the surface  74  of the anvil  70 , the area of the strap  60  in contact with the anvil  70 , and the pressure (i.e., normal force) between the strap  60  and the anvil  70 . 
     In an exemplary embodiment, a collapse resistance force is varied along a collapse stroke by varying the width  76  of the strap  60  along the lengthwise direction  82  of the strap  60 . In another exemplary embodiment, a collapse resistance force is varied along a collapse stroke by varying the thickness  78  of the strap  60  along the lengthwise direction  82  of the strap  60 . In an exemplary embodiment, the strap  60  is deformable plastically. Thus, the strap  60  may comprise a plastically deformable material such as metal. 
     In another exemplary embodiment, a collapse resistance force is varied along a collapse stroke by varying the surface finish, i.e., smoothness, and therefore the coefficient of friction, between the surface  72  of the strap  60  and the surface  74  of the anvil  70 ) between the strap  60  along the lengthwise direction  82  of the strap  60 . 
     In another exemplary embodiment, a collapse resistance force is varied along a collapse stroke by applying a relatively lower friction material  84 , such as PTFE, or a smoothed finish, to selected regions  86  along the length of the strap  60 . For example, a first region  86  may be coated with a low friction coating  84  and may be positioned so that the first region  86  interacts with the anvil  70  near a beginning of the collapse stroke. As a result, an exemplary strap  60  may be configured so as to produce a relatively low collapse resistance force at the initiation of the collapse stroke. 
     In another exemplary embodiment, a second region  88  may be coated with a low friction coating  84  and may be positioned so that the second region  88  interacts with the anvil  70  near a desired portion of the collapse stroke such as a middle of the collapse stroke. As a result, an exemplary strap  60  may be configured so as to produce a relatively low collapse resistance force at the relevant portion of the collapse stroke such as the middle of the collapse stroke. One skilled in the art will appreciate that the selective application of low friction coatings at selected locations along the length of the strap  60  may this be used so as to configure the strap  60  to produce a desired collapse resistance force profile along the collapse stroke. Thus, the strap  60  may be configured to provide a resistance force characteristic that is tailored for absorbing lesser levels of energy as may be associated with lighter weight vehicle occupants and/or associated with lower velocity collisions. At the same time, the strap  60  may be configured to provide a collapse resistance force characteristic that is tailored for absorbing greater levels of energy as may be associated with heavier vehicle occupants and/or associated with greater velocity collisions. 
     In addition to manipulating the position of the first region  86  or the second region  88 , the dimensions of each of the first region  86  or the second region  88  may also be manipulated to suit specific needs for a particular collapse resistance force characteristic. For example, a region  86 ,  88  may be configured to provide only partial coverage of the width  76  of the strap  60 , and the size and shape of the region  86 ,  88  may be configured so as to increase or decrease gradually, providing a smooth transition toward increasing collapse resistance force or a smooth transition from greater collapse resistance force to lesser collapse resistance force. 
     In another exemplary embodiment, a third region  90  may be treated so as to provide for increased friction relative to other regions of the strap  60 . For example, the third region  90  may be coated with a relatively greater friction material  92  such as tar or rubber or may be finished with a roughened, sanded, or treaded surface. The third region  90  may be positioned so that the third region  90  interacts with the anvil  70  near a desired portion of the collapse stroke such as a middle of the collapse stroke. As a result, an exemplary strap  60  may be configured so as to produce a relatively higher collapse resistance force at the relevant portion of the collapse stroke such as the middle or later stage of the collapse stroke. 
     One skilled in the art will appreciate that the selective application of increased friction coating or surface finish at selected locations along the length of the strap  60  may this be used so as to configure the strap  60  to produce a desired collapse resistance force profile along the collapse stroke. Thus, the strap  60  may be configured to provide a collapse resistance force characteristic that is tailored for absorbing lesser levels of energy as may be associated with lighter weight vehicle occupants and/or associated with lower velocity collisions. At the same time, the strap  60  may be configured to provide a collapse resistance force characteristic that is tailored for absorbing greater levels of energy as may be associated with heavier vehicle occupants and/or associated with greater velocity collisions. 
     In addition to manipulating the position of the third region  90 , the dimensions of the third region  90  may also be manipulated to suit specific needs for a particular collapse resistance force characteristic. For example, the third region  90  may be configured to provide only partial coverage of the width  76  of the strap  60 , and the size and shape of the third region  90  may be configured so as to increase or decrease gradually, providing a smooth transition toward increasing collapse resistance force or a smooth transition from greater collapse resistance force to lesser collapse resistance force. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description.