Abstract:
An automotive vehicle front structure includes upper and lower siderails and a structural link extending from the upper and lower siderails, with the structural link having a pivotable connection to the upper siderail and a rigid connection to the lower siderail, such that energy absorption provided by the structure may be tailored by varying the character of the joint between the structural link and the upper siderail.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to an automotive vehicle front structure having a rotatable link connecting upper and lower siderails such that the rotatable link helps to control the sequence of energy absorption during a frontal impact on the vehicle.  
       BACKGROUND  
       [0002]     Designers of automotive vehicles have devised a veritable plethora of structures intended to control both dynamic deformation and energy absorption in the event of a frontal impact upon a vehicle. Such structures have, on occasion, used upper and lower frame rails. U.S. Pat. No. 6,695,393, which is assigned to the assignee of the present invention, discloses a vehicular front end structure having upper and lower frame rails connected by a fender apron. U.S. Pat. No. 4,919,474 shows a similar construction in which upper and lower members are connected by a fender apron. The structures of the &#39;393 and &#39;474 patents tie together the upper and lower frame rails before, during, and after an impact. Accordingly, both the upper and lower rails will serve to absorb energy from the beginning of an impact event. This means that the rate of energy absorption cannot be shaped as is possible with the present invention, because the present invention decouples the upper frame rail from the lower frame rail, at least at the onset of an impact event. As a result, the present system provides the ability to, in effect, shape the rate of energy absorption and hence, axial deformation of the front of the vehicle.  
       SUMMARY  
       [0003]     An automotive vehicle front structure includes a bumper beam, a lower siderail attached to and extending rearwardly from the bumper beam, and an upper siderail extending rearwardly from a location behind the bumper beam. The structure further includes a structural link extending from the lower siderail to the upper siderail, with the structural link having a first end pivotably mounted to the upper siderail and a second end attached to the lower siderail. The second end of the structural link is rigidly attached to the lower siderail, and the first end of the structural link is mounted to the leading edge of the upper siderail. The pivotal mounting of the structural link to the upper siderail is arranged such that an impact directed against the bumper beam or the structural link itself having sufficient force to cause axial deformation of the lower siderail will initially cause the second end of the structural link to deform while the first end of the structural link pivots freely with respect to the upper siderail. Further axial deformation of the lower siderail will cause additional deformation of the second end of the structural link and further pivoting of the first end of the structural link with respect to the upper siderail until the structural link reaches a position at which pivoting of the first end of the structural link with respect to the upper siderail is inhibited.  
         [0004]     Once rotation of the structural link is inhibited, further axial deformation of the lower siderail will cause the structural link to deform the upper siderail. This means that the upper siderail will then participate in the energy absorption function of the front structure by deforming the upper siderail both in bending and in crushing. In other words, the upper siderail will be moved both by bending and translationally according to column loading mechanics.  
         [0005]     The upper and lower siderails are generally parallel and horizontal when a vehicle equipped with the present structure is sitting on a horizontal roadway. A structural link member preferably extends generally vertically from the lower siderail to the upper siderail. Another structural member included in the present invention is a front cross member extending laterally across the vehicle and being attached to the lower siderail behind the bumper. Those skilled in the art will appreciate due to this disclosure that although only a driver&#39;s side structure is shown, the present invention will, most often be employed with both the left and right sides of the vehicle.  
         [0006]     The structural link connecting the upper and lower siderails will deform at its terminus with the lower siderail and rotate rearwardly upon an upper pivotable mount as the lower siderail deforms until a rotational limiter prevents further rotation of the structural link. This rotational limiter preferably comprises an abutment interposed between the structural link and upper siderail such that further rotation of the structural link will be prevented in the event that the abutment is in contact with both the structural link and the upper siderail.  
         [0007]     According to another aspect of the present invention, a method for reacting to an axial impact load applied to a vehicle front structure having upper and lower parallel siderails connected with a semi-pivoted structural link includes the steps of axially deforming the lower siderail while simultaneously deforming a lower end of the structural link attached to the lower siderail and rotating a pivoted upper end of the structural link with respect to the upper siderail, followed by continuing to deform the lower siderail, while deforming the lower end of the structural link and rotating the upper end of the structural link until a rotational stop interposed between the structural link and the upper siderail is encountered by the structural link and, finally, deforming the upper siderail by forces applied by the structural link and the lower siderail to the upper siderail once the rotational stop has been encountered and further axial deformation of the lower siderail occurs. In this manner, the forces applied by the structural link to the upper siderail will include translational and rotational forces.  
         [0008]     It is an advantage of a system according to the present invention that the absorption of energy in the event of a frontal impact of a vehicle may be more carefully controlled because the initial energy absorption arises through the use of lower siderails, whereas the upper siderails of the structure remain decoupled from the impact event during an initial period of the impact.  
         [0009]     It is another advantage of a system according to the present invention that the amount of crush resulting from a frontal impact may be adjusted by the designer of the vehicle by changing the point at which rotation of the structural link connecting the upper and lower siderails becomes constrained.  
         [0010]     Other advantages, as well as features and objects of the present invention, will become apparent to the reader of this specification. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a side view of a vehicle having a front architecture according to the present invention.  
         [0012]      FIG. 2  shows an initial response of the present structure to a frontal impact.  
         [0013]      FIG. 3  shows a more advanced response of the present structure to a frontal impact in which the rotational link has deformed the upper siderail.  
         [0014]      FIG. 4  illustrates certain details of the connection between a structural link attaching the lower and upper siderails and the upper siderail itself.  
         [0015]      FIG. 5  is a perspective view of a front frame portion of the vehicle illustrated in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     In the following figures the same reference numerals will be used to illustrate the same components.  
         [0017]      FIG. 1  shows vehicle  10  in the state prior to any frontal impact. Lower siderail  24  is shown as having at least one crushable trigger,  29 , therein, which allows controlled axial deformation of rail  24 . Upper siderail  26 , which is generally parallel to lower siderail  24  and separated vertically from lower siderail  24 , also has a crush trigger,  28 , incorporated therein. Crush triggers  28  and  29  are conventional, stamped sections allowing axial compression to occur in a controlled manner. These triggers may be selected from any number of trigger designs known to those skilled in the art and suggested by this disclosure.  
         [0018]     Upper siderail  26  and lower siderail  24  both extend rearwardly in the direction of dash panel  32 . Although upper siderail  26  is shown as extending rearwardly from a location behind bumper beam  16 , those skilled in the art will appreciate in view of this disclosure that this offset may be minimized as it is only necessary that upper siderail  26  be positioned so to allow packaging of various components, such as the radiator support, within the vehicle.  FIG. 5  shows duplicate left and right upper and lower siderails and structural link members according to the present invention.  
         [0019]     Structural link  30  has first end  30 a, which is pivotably attached to upper control arm  26  by means of fastener  40  (shown only in  FIG. 4 ), which passes through an elliptical aperture  36  formed in first end  30 a of structural link  30 . Elliptical aperture  36  allows structural link  32  to both pivot upon fastener  40 , and to move translationally to a limited extent, with respect to fastener  40  and upper siderail  26 .  
         [0020]      FIG. 2  shows vehicle  10  as having undergone an initial amount of front end deformation after impacting barrier  14 . As shown in  FIG. 2 , structural link  30  has rotated about the axis of fastener  40  to a point at which structural link  30  is roughly perpendicular to both upper siderail  26  and lower siderail  24 . At the point shown in  FIG. 2 , upper siderail  26  has not been deformed. In other words, upper siderail  26  has had no effect on the absorption of energy or crush distance characterizing impact of vehicle  10  into barrier  14 . Note, however, that second end  30   b,  which is the lower end of structural link  30 , has been plastically deformed from the as-installed condition shown in  FIG. 1 , because structural link  30  is now perpendicular to lower siderail  24 . Also, crush trigger  29  has started to deform and collapse axially, in response to the axial load imposed upon lower siderail  24 .  
         [0021]      FIG. 4  shows a rotational limiter feature which is built in to structural link  30  and upper siderail  26 . In essence, abutment  38  is interposed between structural link  30  and upper siderail  26  such that when upper siderail  26  reaches the position shown in  FIG. 2 , further rotation of structural link  30  with respect to upper siderail  26  will be prevented. As a result, further axial deformation of lower siderail  24  will cause the situation shown in  FIG. 3 , wherein structural link  30  deforms upper siderail  26  both in bending and axially. In essence, structural link  30  will apply both rotational bending forces and axially directed crushing forces to upper siderail  26 . In this manner, the upper siderail  26  will begin to absorb energy only after a controlled amount of crushing and axial deformation of lower siderail  24  has occurred. This allows the rate of energy absorption as a function of the axial deformation of the vehicle front structure to be adjusted to accommodate the needs of any particular vehicle, as affected by the vehicle architecture, weight, type of powertrain, etc. When the vehicle has deformed to the level shown in  FIG. 3 , second end  30 b of structural link  30  has also deformed more, so that structural link  30  may now tip forward rather than rearward as shown in  FIG. 1 .  
         [0022]     It should be clear from the foregoing explanation that structural link  30  is only partially rotatable because second end  30 b of link  30  is welded to lower siderail  24  and thus, that part of link  30  cannot rotate with respect to lower siderail  24 . Moreover, first end  30 a of structural link  30  is allowed to rotate only until a rotational limiter, such as abutment  38 , prevents further rotation of the structural link.  
         [0023]     While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.