Abstract:
An extendible rail and bumper apparatus is mountable within the base frame lower rails of an automotive frame to provide an improved crash force absorbing bumper apparatus for deployment on either the front or rear bumpers of an automobile. The extendible rail member is mounted for telescopic movement through slidable guide members. A front plate is formed with wedge members positioned next to the extendible rail member. The actuation mechanism includes an electric motor that rotates a threaded rod having a conical member mounted thereon for translational movement thereon. The conical member engages a pair of outwardly projectable tabs that are driven outwardly into engagement with the wedge members when the extendible rail is fully extended. If required to absorb impact energy, the outwardly projected tabs push the wedge members into engagement with the front plate to transfer the energy into the base frame rail apparatus of the vehicle.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates generally to a longitudinally extendible front end for an automotive vehicle and, more particularly, to a locking structure for the telescopically extendible rails to transfer impact forces to the frame of the vehicle. 
       BACKGROUND OF THE INVENTION 
       [0002]    The front end structure of an automotive vehicle is designed to provide visual appeal to the vehicle owner while functioning as an energy absorbing structure during frontal and offset crashes. The size, shape and construction of the front end structure contribute to the ability of the front end structure to attenuate the crash pulse and restrict intrusions into the operator&#39;s cabin of the vehicle. It is important to design a front end structure to absorb crash energy through the most effective structural components, which is a front rail system. To that extent, a significant amount of effort by vehicle engineers is devoted to designing the front rails to crush in a controlled manner while absorbing a maximum amount of energy. If additional energy absorption is required, adding length to the front rails is the next logical engineering consideration. Even though longer front rails are desirable for efficient energy management, this option is usually commercially unacceptable to the vehicle customer because resulting structure is considered to be visually unattractive, increases the vehicle overall length and reduces vehicle parking maneuverability. 
         [0003]    One of the goals in the design of vehicle frame structure is to provide better engagement and absorption of energy during a collision. The major components in absorbing energy in frontal as well as rear impacts are the rails. Furthermore, in a side collision if the vehicle has a softer front end it can help mitigate the injuries to occupants in both vehicles. If there is an apparatus to absorb more energy and prolong the time to crush the rails, the crash pulse and intrusion can be reduced significantly. With a longer front end structure on a vehicle, there is potential to achieve this goal. A secondary aspect to extending the front end structure is to localize less severe crash damage into a few local parts that are easily repairable or replaceable. A significant problem, however, is providing the extendible front end is to do so without changing other critical design aspects, such as styling and dimensions of a vehicle, that are critical to both the manufacturer and the customer. 
         [0004]    Alternative engineering design can provide larger bumpers, deployable bumper airbags, and rails with pyrotechnique methods etc., which can have styling and packaging issues or require sensors to activate and can lead to high repair costs in the case of a false deployment of the known prior art systems. For these reasons, such alternative systems have not met with commercial acceptance. Accordingly, attempts have been made to provide a selectively extendible bumper structure that is operable to move the bumper from an aesthetically pleasing position to an extended position that positions the bumper at a significant distance from the retracted position. Such extendible bumper structures have been associated with a speed sensor such that the bumper extends automatically in response to the attainment of a preselected speed criteria. 
         [0005]    One such extendible bumper structure can be found in U.S. Pat. No. 6,773,044, issued on Aug. 10, 2004, to John E. Schambre, et al, in which the front bumper is supported on telescopically extendible rails that move the front bumper forwardly when the vehicle reaches a predetermined speed. Drive cables and a worm gear assembly drive a ball screw cam into a locking mechanism inside the movable rail pieces. The locking links are driven outwardly by the ball screw cam to extend through slots aligned in the fixed and movable rail pieces so that crash forces can be transferred from the movable rail piece to the fixed rail piece during an impact. 
         [0006]    The extendable rails disclosed in the Schambre patent are driven by a cable mechanism and a drive motor located inside the bumper. Accordingly, this bumper beam needs to be designed to have enough package space to house these components. Providing the space to house these components is an added design requirement for the bumper. The locking mechanism is one of the most critical components to manage energy during a frontal impact. The material that is removed in the fixed and movable rails to make slots for the locking links is significant. Locking links as disclosed in the Schambre patent need to be very strong and the resulting slot area becomes considerably large. As a result, the rail pieces become locally weaker at the slots and would have a tendency to bend during collision, especially when an offset impact is incurred. 
         [0007]    Another extendible bumper structure is found in U.S. Pat. No. 6,709,035, issued to Chandra Namuduri on Mar. 23, 2004. The Namuduri extendable rail pieces are assembled inside a secondary casing which is mounted inside the base frame rail defining three sheet metal parts with closed cross sections at the front of the bumper when the rails are in a retracted position. The extendable rail travels inside the middle (secondary) rail casing which is rigidly attached to the outer frame rail. The actuating mechanism works with a lead screw that connects to a drive motor and a nut. The nut is connected to the inside end of the movable rail piece through a self-locking mechanism that works with a plurality of small spheres sliding on a tapered bushing. These spheres tightly constraint the extendable rail and the secondary casing during an impact. 
         [0008]    The Namuduri bumper energy absorber for supporting the bumper structure relative to a vehicle includes an inner tube, an outer tube, a lead screw, a nut and a motor. Rotation of the lead screw by the rotor causes translation of the nut along the lead screw for driving at least a portion of the bumper structure between extended and retracted positions. When the extendable rail is moving outward and inward, respectively, a sensing and controller system is used to control the position of the two moving rail pieces. The degree of extension can be controlled by various parameters via sensors, including gear position, vehicle speed, obstacle range, approach rate and hard braking. With respect to crash energy management and efficiency of the system, having three tubes in the retracted position is not desirable and also add unnecessary weight and cost of manufacturing. The positioning of the motor mechanism installed inside the rails take up a considerable length and would not crush due to the many metal pieces in the motor, drive and the constraint mechanism. Furthermore, the movable rails need to be of a considerable size to adsorb a significant amount of energy during impact. Hence, the resulting complete mechanism becomes larger than a current front end and may not be suitable for vehicle design, especially for small vehicles. 
         [0009]    U.S. Pat. No. 5,967,573, issued on Oct. 19, 1999, and related U.S. Pat. No. 6,302,458 issued on Oct. 16, 2001, and U.S. Pat. No. 6,401,565 issued on Jun. 11, 2002, all of which are issued to Jenne-Tai Wang, et al., disclose an extendible front bumper structure that actuates upon attainment of a pre-established speed criteria through a rack and pinion mechanism. The extendible rail structure is locked against the fixed rail structure by a plurality of small spheres that slide on a tapered bushing. These spheres deform the outer tube to absorb energy upon impact. U.S. Pat. No. 6,834,898, granted on Dec. 28, 2004, to Jenne-Tai Wang, et al, discloses similar structure having increased stiffness by mounting the actuator inside the tubular frame rail member. U.S. Pat. No. 6,976,565, granted to Paul Meernik et al, on Dec. 20, 2005, discloses a spring-loaded apparatus for absorbing energy in an extendible bumper apparatus as disclosed in the above-identified Wang patents. 
         [0010]    Another configuration for an extendible bumper system can be found in U.S. Pat. No. 6,976,718, issued to Isumu Nakanishi on Dec. 20, 2005, in which an electric motor drives a threaded actuator rod to extend the front bumper from a retracted position to an extended position. The bumper apparatus incorporates an electromagnetic lock mechanism and a deformable, energy absorbing shaft to absorb impact forces encountered by the bumper apparatus. 
         [0011]    It would be desirable to provide an extendible bumper for an automotive vehicle that incorporates a locking mechanism to transfer any crash forces encountered by the extended bumper to the frame of the vehicle. Such an extendible rail system would provide a rail extension apparatus and a control for extending the rails to improve crash energy management without affecting the visual appeal of the vehicle when stopped or at low speeds. The extendible rail system would be applicable to front or rear bumpers on an automotive vehicle. 
       SUMMARY OF THE INVENTION 
       [0012]    It is an object of this invention to overcome the aforementioned disadvantages of the known prior art by providing an extendible bumper apparatus that incorporates wedge members that transfer crash forces to the frame of the vehicle. 
         [0013]    It is another object of this invention to provide a tab mechanism that projects outwardly from the actuating mechanism for extending the telescopic rails supporting the extendible bumper to engage the wedge members transferring crash forces to the frame of the vehicle. 
         [0014]    It is yet another object of this invention to provide a reliable and robust rail/bumper extension system that can work independently and does not depend on expensive sensing technology to be operable to deploy when a crash is encountered. 
         [0015]    It is a feature of this invention to provide an extendable rail mechanism that provides an increase in crushable rail length. 
         [0016]    It is an advantage of this invention that the extendible rail mechanism increases the energy absorption capability of the crushable rail structure of an automotive frame. 
         [0017]    It is another advantage of this invention that the extendible rail structure retracts at low vehicle speeds for vehicle appearance and easy parking. 
         [0018]    It is another feature of this invention to provide a semi-active deployment system for an extendible rail mechanism in which the extendible rail activates and extends based on minimal input signals. 
         [0019]    It is still another advantage of this invention that the actuators added to provide an extendible rail mechanism do not adversely impact the crush capability of the vehicle frame rail system on which the extendible rail mechanism is mounted. 
         [0020]    It is yet another advantage of this invention that the crash characteristic of the bumper is not adversely affected when the extendable rail mechanism is retracted and contained within the existing vehicle frame rail. 
         [0021]    It is still another feature of this invention that the extendible rail is formed with a rectangular dog-bone shape so that the extensible rail will crush during an oblique crash in a manner similar to the base rail system. 
         [0022]    It is still another advantage of this invention that the extendable rail can absorb energy in either the fully retracted or fully extended position. 
         [0023]    It is yet another feature of this invention that the retracted extensible rail does not impose any significant restraints on the ability of the base frame rail apparatus to absorb crash energy. 
         [0024]    It is a further advantage of this invention that the additional length of the extended rail apparatus will add energy absorption capability to the base rail apparatus of the vehicle. 
         [0025]    It is a further feature of this invention that a positive interlock feature is enabled when the rail is fully extended to transfer crash energy into the base frame rail mechanism. 
         [0026]    It is still a further feature of this invention that the interlock mechanism self-releases when disengaging to allow the extended rail to return to its at rest and retracted position. 
         [0027]    It is yet a further feature of this invention that the extendible rail mechanism includes a guide and support system for minimizing sliding friction to minimize the effort needed to effect rail extension. 
         [0028]    It is another feature of this invention that an electric motor provides the energy required for moving the extension rail with the bumper attached thereto, but is not part of the self-locking feature except for being operatively connected thereto for driving the tabs into engagement with the wedge members for self-locking the extensible rail mechanism. 
         [0029]    It is yet a further advantage of this invention that the actuation motor can be used to provide both position and load feedback to confirm and continuously monitor the position of the extendible rail deployment, thereby providing a means of diagnostics to ensure the system is functional and ready to absorb energy when needed. 
         [0030]    It is still another advantage of this invention that the interaction of the projectable tabs and the engaged wedge members provides a locking mechanism for the extendible bumper apparatus to transfer crash forces to the base frame of the vehicle. 
         [0031]    It is still another feature of this invention that the tabs project through small slots formed in the extensible rail when the rail has been fully extended. 
         [0032]    It is yet another feature of this invention that the actuator includes a conical member for driving the tabs outwardly into engagement with the wedge members when the extensible rail reaches the end of its extensible movement. 
         [0033]    It is a further object of this invention to provide an extensible rail system incorporating a self-locking mechanism that is durable in construction, inexpensive of manufacture, carefree of maintenance, facile in assemblage, and simple and effective in use. 
         [0034]    These and other objects, features and advantages are accomplished according to the instant invention by providing an extendible rail and bumper apparatus that is mountable within the existing base frame lower rails of an automotive frame to provide an improved crash force absorbing bumper apparatus for deployment on either the front or rear bumpers of an automobile. The extendible rail member is mounted for telescopic movement through slidable guide members. A front plate is formed with wedge members positioned next to the extendible rail member. The actuation mechanism includes an electric motor that rotates a threaded rod having a conical member mounted thereon for translational movement thereon. The conical member engages a pair of outwardly projectable tabs that are driven outwardly into engagement with the wedge members when the extendible rail is fully extended. If required to absorb impact energy, the outwardly projected tabs push the wedge members into engagement with the front plate to transfer the energy into the base frame rail apparatus of the vehicle. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    The advantages of this invention will become apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein: 
           [0036]      FIG. 1  is a perspective view of an extendible rail mechanism according to the principles of the instant invention, mounted in the base lower frame rail of an automotive vehicle, the extendible rail member being shown in a retracted position; 
           [0037]      FIG. 2  is a perspective view of an extendible rail mechanism similar to that of  FIG. 1 , but showing the extendible rail member in an extended position; 
           [0038]      FIG. 3  is a partial perspective view of the bumper mounted on the extendible rail mechanism with the extendible rail being retracted into the fixed rail member; 
           [0039]      FIG. 4  is a perspective detail view of the actuation mechanism, including the electric motor, threaded rod, base plate for the extendible rail and the outwardly projectable tabs alignable with the wedge members when the extendible rail is fully extended, as is depicted herein; 
           [0040]      FIG. 5  is a partial cross-sectional view of the extendible rail mechanism showing the base plate of the extendible rail and the front plate taken at the point the extendible rail reaches full extension but immediately before the tabs are driven outwardly into alignment with the wedge members; 
           [0041]      FIG. 6  is an elevational view of the extendible rail mechanism corresponding to the position of the base member as depicted in  FIG. 5 ; 
           [0042]      FIG. 7  is a partial cross-sectional view of the extendible rail mechanism showing the base plate of the extendible rail and the front plate taken at the point the extendible rail reaches full extension and after the tabs are driven outwardly by the conical actuator into alignment with the wedge members; and 
           [0043]      FIG. 8  is an elevational view of the extendible rail mechanism corresponding to the position of the base member as depicted in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0044]    Referring to  FIGS. 1-8 , an extendible rail and bumper apparatus incorporating the principle of the instant invention can best be seen. The extendible rail apparatus  10  is mounted in the base lower frame rails F of an automotive vehicle. The extendible rail apparatus  10  can be packaged within a typical existing front rail cavity without significant changes or obstructing packaging and attachment points to other front end components such as radiator, cross members etc. The extendible rail apparatus  10  is preferably constructed as a module that is firmly secured to the fixed front rail end by a back plate  12  and a front plate  22 . Each laterally spaced lower front rail F of the automobile will be provided with a separate module  10  with the forwardly projecting ends of the movable rail member  20  being connected to the bumper system B so that the bumper B extends and retracts with the movable rail members  20 . 
         [0045]    The modular extendible rail apparatus  10  is supported within the lower frame rail F by a back plate  12  and a forwardly positioned front plate  22  on which are mounted a pair of laterally spaced slide support members  15 . A movable rail member  20  is housed within the lower frame rail F and slidably supported on the slide support members  15  for movement in a fore-and-aft direction. The movable rail member  20  has a pair of glide members  25  that are attached to the respective lateral sides of the movable rail member  20  and slidably supported within the support members  15 . In this configuration, the movable rail member  20  is linearly movable between a retracted position, as seen in  FIG. 1  where the movable rail  20  lies between the back and front plates  12 ,  22 , and an extended position, as shown in  FIG. 2  where a substantial portion of the movable rail member  20  is located forwardly of the front plate  22 . 
         [0046]    Movement of the movable rail member  20  is powered through an electric motor  27  that is mounted behind the back plate  12  and operatively coupled to the electrical system of the automobile and operatively controlled through a control mechanism described in greater detail below. The motor  27  is connected to a threaded rod  29 , as is best seen in  FIG. 4 , through a worm gear mechanism and extends forwardly from the motor  27  through the back plate  12  into engagement with an actuator mechanism  30 . As will be described in greater detail below, the operation of the electric motor  27  drives the rotation of the threaded rod  29  to move the actuation mechanism  30  forwardly or rearwardly, depending on the direction of rotation of the threaded rod  29 . 
         [0047]    The back plate  12  and the motor  27  are placed in front of a spacer reinforcement bracket S that is part of the design of the lower frame rail F. The motor  27  is mounted generally perpendicularly to the fixed lower frame rail F and the longitudinally extending slide support rails  15  and does not hinder the crush zone of the lower frame rail F. When the movable rail  20  is moved into the extended position, the movable rail is locked into engagement with the lower frame rails F through the actuation mechanism  30 , as will be described below, and provides an additional crush zone forwardly of the lower frame rail F to provide the capability of absorbing additional energy from an impact. 
         [0048]    The actuation mechanism  30  is best seen in  FIGS. 5-8  and is formed with a drive plate  32  that is secured to the rearward portion of the movable rail member  20 . A conical drive member  35  is threadably mounted on the threaded rod  29  for translational movement along the rod  29  when the rod  29  is rotated by the electric motor  27 . The conical drive member  35  includes a shaft portion  36  that is slidably received through an opening in the drive plate  32  and terminates in a conical cam member  37  positioned forwardly of the drive plate  32 . The conical cam member  37  is too large to move rearwardly through the opening in the drive plate  32  and forms an apex at the forwardmost point thereof. A spring  38  is mounted on the shaft portion  36  rearwardly of the drive plate  32  and is retained in position on the shaft portion  36  by a keeper nut  39  affixed to the rearward end of the shaft portion  36 . The spring  38  exerts a biasing force on the keeper nut  39  to urge the keeper nut  39  rearwardly and, thus, force the conical cam member  37  against the drive plate  32 . 
         [0049]    The drive plate  32  has mounted on a forward side thereof a pair of vertically spaced locking members  40  that are retained on the drive plate  32  by respective fasteners  42  positioned within slots  43  formed in the locking members  40  to allow vertical movement of the locking members  40  relative to the drive plate  32 . Each locking member  40  is formed with a pair of tabs  45  that correspond to openings formed in the top and bottom surfaces, respectively, of the movable rail member  20 . A biasing spring  48 , located between the tabs  45  on each respective locking member  40 , is trapped between the corresponding top or bottom surface of the movable rail member  20  and each of the locking members  40 . The biasing spring  48  urges the locking members  40  inwardly toward engagement with the conical cam member  37 . 
         [0050]    The front plate  22  has an appropriately shaped opening therethrough for the passage of the movable rail member  20  and the glide members  25 . The top and bottom portions of the opening through the front plate  22  have a gap between the front plate  22  and the movable rail member  20 , which gap is filled with a wedge member  50  positioned at the top and bottom of the front plate  22 . The corresponding surface of the front plate  22  is sloped inwardly toward the rear to mate with the correspondingly sloped surface of the wedge member  50 . Thus, when the wedge member  50  is attempted to be moved rearwardly relative to the front plate  22 , the mating sloped surfaces of the wedge member  50  and the front plate  22  prevent such movement. 
         [0051]    The translational movement of the conical drive member  35  effected by the rotating threaded rod  29  pushes the drive plate  32 , and therefore the movable rail member  20 , in the direction of movement induced into the conical drive member  35 . When the drive member  35  is moving forwardly, the spring  38  keeps the conical cam member  37  against the drive plate  32  and forces the movable rail member  20  forwardly. Similarly, when the conical drive member  35  is moving rearwardly, the cam member  37  pushes against the drive plate  32  to pull the movable rail member  20  rearwardly. The forward movement of the movable rail member  20  is limited by a stop member  26  affixed to the glide member  25  to engage limits on the slide support member  15  and halt the continued forward movement of the glide member  25 . When the forward movement of the movable rail member  20  is stopped, the continued rotation of the threaded rod  29  pushes the conical drive member  35  forwardly relative to the drive plate  32 , compressing the spring  38  between the keeper nut  39  and the back wall of the drive plate  32 , as can be seen in a comparison of  FIGS. 5 and 7 . 
         [0052]    The forward progression of the conical cam member  37  drives the respective locking members  40  outwardly due to the biased engagement of the locking members  40  with the cam member  37 , as is depicted in  FIG. 7 . This outward movement of the locking members  40  extends the tabs  45  through the corresponding slots in the movable rail member  20  and places the tabs  45  in alignment with the wedge members  50 . Thus, if the bumper B incurs an impact that pushes the movable rail member  20  rearwardly, the tabs  45  engage the wedge member and lock the extendible rail apparatus  10  in an extended position to provide an additional crush zone and an efficient transfer of the energy imparted into the movable rail member  20  into the fixed lower frame rails F through the wedge members  50  engaged with the front plate  22 . 
         [0053]    When the movable rail  20  extends forwardly and stops the locking tabs  45  are driven outward by the tapered cam  37  and extend through small slots on the movable rail member  20 . This happens when the slots on the movable rail member  20  are moved forwardly to be positioned in front of the front plate  22  and wedge members  50 . During an impact, two wedge members  50  (top and bottom) on each front plate  22  are driven between the movable rail member  20  and the front plate  22  to secure the fixed lower frame rail F and the extended rail member  20  when a load is applied to the retractable rail member  20  through the bumper B. This interengagement between the wedge members  50  and the front plate  22  allows the retractable rail member  20  to crush and transfer the load to the rest of the frame structure of the automobile before and during the collapse of the movable rail member  20 . 
         [0054]    To retract the movable rail member  20 , the motor  27  drives the screw rod  29  in the opposite direction, which first pulls the conical cam member  37  rearwardly into the drive plate  32 . This movement of the cam member  37  allows the locking members  40  to retract inwardly due to the biasing force imparted by the springs  48  keeping the locking members  40  in engagement with the conical cam member  37 . As a result, the tabs  45  are retracted through the slots in the movable rail member  20  to allow the movable rail member  20  to retract into the fixed lower frame rail F. The extended rail member  20  is now free to retract rearwardly inside into the fixed rail F. 
         [0055]    The extendible rail apparatus  10  incorporating the principles of the instant invention is much simpler and easy to implement than is known in the art. The extendible rail apparatus  10  does not demand any significant structural changes to the existing current automotive frame design for packaging. Also, the locking members  40  do not require large openings in the extendable rails for implementation. The actuation mechanism  30  provides an effective constraint mechanism since the locking members  40  do not depend on the strength of locking forks that come out through the slots on the moving rails. The operation of the instant invention depends on friction based wedge members  50  that are driven by small tabs  45  through small slots. These tabs  45  do not transfer the impact load but instead drive the wedge members to constraint the already extended movable rail member to the stationary lower rail frames and transfer loads thereto. 
         [0056]    The actuation mechanism  30  also does not adversely use up the valuable crush zone already available in the front rail for the mounting and packaging of the drive motor  27  and the actuation mechanism. The extendible rail apparatus  10  also does not have three layers of sheet metal parts in the retracted mode which compromises the capability of the lower frame rails to dissipate impact energy. The drive motor  27  is mounted perpendicular to the axis of the lower frame rail F and can be disengaged during the collapse of the lower frame rail F. The modular extendible rail apparatus  10  incorporating the instant invention provides a pre-assembled module that can be inserted into a slightly modified lower front rail F and does not obstruct the collapse of existing crush zones during a frontal crash. The internal parts of the actuation mechanism  30  can be designed to crush using low cost plastics and mild steel components. 
         [0057]    In operation, the retracted movable rail member  20  can be extended when the vehicle reaches a threshold criteria, such as a preset speed of operation. A speed sensor, which is already available in vehicles, signals the control mechanism that the threshold criteria has been reached and the electric motor  27  is activated to cause rotation of the threaded rod  29  operatively connected thereto. As the rod  29  rotates the conical drive member  35  moves along the rod  29  pushing the drive plate  32  and the movable rail  20  to which the drive plate  32  is connected forwardly through the spring  38 . When the forward movement of the movable rail member  20  is halted through the stop member  26 , the drive member  35  moves forwardly relative to the drive plate  32 , compressing the spring  38  and sliding the cam member  37  forwardly to drive the engaged locking members  40  vertically. The cam member  37  causes the locking tabs  45  to project through aligned slots in the movable rail member  20  to become aligned with the wedge members  50  located between the movable rail member  20  and the front plate  22  connected to the fixed lower frame rail F. 
         [0058]    Since the extendible rail apparatus  10  activates when the vehicle reaches a threshold speed, no pre-crash sensors are needed. The extended movable rail member  20  increases the front impact crush zone and, thereby mitigates the adverse effects on the occupants of the vehicle, as long as one or both rails are engaged during a collision. The collisions that engage one or both rails include full, offset, and angular in both frontal and rear crashes. The movable rail member can also provide a softer impact on a target vehicle in a side impact collision and, hence, leads to a more compatible vehicle for the real world crashes. 
         [0059]    Assuming that no impact has occurred, the lowering of the operating speed of the vehicle again activates the electric motor  27  to rotate the threaded rod  29  in the opposing direction than that use to extend the movable rail member  20 . The rearward movement of the cam member allows the springs  48  to retract the locking tabs  45  back through the slots in the movable rail member  20 , while the drive member  35  continues to move rearwardly along the threaded rod  29  with the cam member  37  pulling the drive plate  32  and the attached movable rail member  20  rearwardly to the retracted position. 
         [0060]    It will be understood that changes in the details, materials, steps and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention. 
         [0061]    For example, although the description of the preferred embodiment above relates to a front bumper configuration, the instant invention can be equally applied to rear bumper structures on automotive vehicles, thus providing a front or back or front and back telescopic bumper assemblies  10 . Furthermore, the instant invention can be retrofitted to an existing automotive frame structure or incorporated into new automotive frame design.